update

Reviewed-on: http://git.djledda.de/Ledda/MA_Platteau/pulls/1

Content/Introduction.tex

@@ -3,44 +3,44 @@
 
 \section{Motivation}
 
-As stated in the special report from the Intergovernmental Panel on Climate Change (IPPC) human activities have caused a increase in global temperatures of approximately 1.0 °C when comparing it to pre-industrial levels. Furthermore, this rise could reach 1.5 °C in the overall temperature by the years 2030 and 2052 \citep{01_ipcc_sr15_2018}. The Paris Agreement aims to restrict the rise in global average warming to below 2 °C. To clarify the risk global average warming can be divided into three categorys reaching from >1,5°C which is classified as dangerous , >3°C deemed catastrophic and Warming exceeding 5°C is classified as unknown which suggests it is beyond that and could represent an existential threat by the year 2050 \citep{01_xu_ramanathan_2017}.
+As stated in the special report from the Intergovernmental Panel on Climate Change (IPPC), human activities have caused a increase in global temperatures of approximately 1.0 °C when compared to pre-industrial levels. Furthermore, this increase could reach up to 1.5 °C overall by the years 2030 or 2052 \citep{01_ipcc_sr15_2018}. The Paris Agreement aims to restrict the rise in global average warming to below 2 °C. To clarify the varying degrees of risk, global average warming can be divided into three categories: >1,5°C, classified as dangerous, >3°C, deemed catastrophic, and warming exceeding 5°C, classified as "unknown", suggesting that it is beyond this rise in temperature that an existential threat by the year 2050 is possible \citep{01_xu_ramanathan_2017}.
 
-The new climate protection program released by the German government on the 17 of July 2024 has set the goal of cutting greenhouse gas emissions (GHG) by 65\% relative to 1990 levels by the year 2030. Additionally, it sets a target for Germany of achieving greenhouse gas neutrality by 2045 \citep{01_E_klimaschutzgesetz}.
+The new climate protection program released by the German government on the 17 of July, 2024 has set the goal of cutting greenhouse gas emissions (GHG) by 65\% relative to 1990 levels by the year 2030. Additionally, it sets a target for Germany to achieving greenhouse gas neutrality by 2045 \citep{01_E_klimaschutzgesetz}.
 
-When looking into the different GHG emissions it is noticeable that 80,6\% are attributed to CO$_2$. Meanwhile methane (CH$_4$) as well as nitrous oxide (N$_2$O) are responsible for 12,1\% and 5,3\% \citep{01_umweltbundesamt_treibhausgas_eu}.
+When looking into different GHG emissions, it is of note that 80,6\% may be attributed to CO$_2$. Meanwhile, methane (CH$_4$), as well as nitrous oxide (N$_2$O), are responsible for 12,1\% and 5,3\% \citep{01_umweltbundesamt_treibhausgas_eu}. 
-It is estimated that the anthropogenic GHG emissions have contributed in the rise of global average temperature by 0,8 to 1,3 °C from the years 1850-1900 until 2010-2019. For the estimated of 1,3°C, CO$_2$ alone accounts for 0,85°C \citep{01_ipcc_ar6_wg1_2021}.
+It is estimated that anthropogenic GHG emissions have contributed to the rise of global average temperature by 0,8 to 1,3 °C from 1850-1900 to 2010-2019. For the estimate of 1,3°C, CO$_2$ alone accounts for 0,85 °C \citep{01_ipcc_ar6_wg1_2021}.
 
-Since the effect of CO$_2$ on global warming is undeniable it is worth looking at this aspect of the GHG more closely. In the year 2024 traffic in Germany amounted to 19,8\% of the total GHG emissions. \citep{01_umweltbundesamt_verkehr_emissionen}. This percentage in the EU can be broken down by vehicle type: passenger cars and motorcycles were responsible for the largest portion, contributing 60\% of the emissions, while buses and trucks accounted for 27\%. Light commercial vehicles contributed the smallest share at 13\%. Furthermore,  traffic emissions have been increasing not only in germany but also across the EU, with an estimated 24\% CO$_2$ rise since 1990 \citep{01_destatis_co2_strassenverkehr}. 
+Since the effect of CO$_2$ on global warming is undeniable, it is worth looking at this aspect of GHG more closely. In 2024, traffic in Germany amounted to 19,8\% of total GHG emissions. \citep{01_umweltbundesamt_verkehr_emissionen}. This percentage in the EU can be broken down by vehicle type: passenger cars and motorcycles were responsible for the largest proportion, contributing 60\% of the emissions, while buses and trucks accounted for 27\%. Light commercial vehicles contributed the smallest share at 13\%. Furthermore, traffic emissions have not only been increasing in Germany but also EU-wide, with an estimated 24\% rise in CO$_2$ since 1990 \citep{01_destatis_co2_strassenverkehr}. 
 
-Since fossil fuels account for almost 90\% of all CO$_2$  emissions the importance of transitioning to renewable energy sources cannot be overstated \citep{01_un_climatechange_causes_2023}. Viable alternatives to internal combustion engines (ICEs) are on the rise, such as battery electric vehicles (BEVs) and also hydrogen fuel cell vehicles (FCEVs). By adopting these greener alternatives GHG emissions of the transportation sector could be significantly reduced, contributing to a more sustainable future \citep{01_wilberforce_advances_2016}.
+Since fossil fuels account for almost 90\% of all CO$_2$  emissions the importance of transitioning to renewable energy sources cannot be overstated \citep{01_un_climatechange_causes_2023}. Viable alternatives to internal combustion engines (ICEs) are on the rise, such as battery electric vehicles (BEVs) as well as hydrogen fuel cell vehicles (FCEVs). By adopting these greener alternatives, GHG emissions by the transportation sector could be significantly reduced, contributing to a more sustainable future \citep{01_wilberforce_advances_2016}.
 
-When compared to the other alternatives fuel cells do require less mantainance than ICEs and its operating temperature can be as low as 80°C not unlike ICEs operating temperatures which can reach over 2000 °C. They can also be recharged  almost instantly unlike BEVs \citep{01_wilberforce_advances_2016}.
+When compared to the other alternatives, fuel cells require less mantainance than ICEs, and their operating temperature can be as low as 80 °C, not unlike ICEs' operating temperatures, which can reach over 2000 °C. They may also be recharged almost instantly, unlike BEVs \citep{01_wilberforce_advances_2016}. 
-Although fuel cell technology is very promising and its development is advancing at a fast pace, there are still a few challenges which make commercialization difficult. One factor in particular is the material and component costs
+Although fuel cell technology is very promising and its development is advancing at a fast pace, there are still some challenges that make commercialisation difficult. One factor in particular is the cost of materials and components 
 \citep{01_wilberforce_developments_2017}. 
-The bipolar plate (BP) of a proton-exchange membrane fuel cell (PEMFC) amounts for 45\% of the stack manufacturing cost\citep{wang_preparation_2018}. 
+The bipolar plate (BP) of a proton-exchange membrane fuel cell (PEMFC) accounts for 45\% of the stack manufacturing cost \citep{wang_preparation_2018}. 
 
-Metals such as SS316L have been under investigation for some time to reduce material and production costs of the bipolar plates and therefore of the PEMFC
+Metals such as SS316L have been under investigation for some time to reduce material and production costs of bipolar plates and as such of a PEMFC \citep{wang_preparation_2018}. 
-\citep{wang_preparation_2018}. While Stainless Steel has some promising attributes like a good mechanical strength and high power density it also has its downside like the corrosion of the metallic BPs. Another problem is the membrane degradation which could also be coupled to the corrosion of the BPs as the Fe$^{2+}$ ions are released from the plate move to the membrane and intensify the degradation \citep{elferjani_coupling_2021}.
+While stainless steel has some promising attributes such as good mechanical strength and high power density, it also has its downsides as they corrode metallic BPs. Another problem is membrane degradation, which could also be coupled with corrosion of BPs as the Fe$^{2+}$ ions released from the plate move to the membrane and intensify the degradation \citep{elferjani_coupling_2021}.
 
 
 
 
 \section{Problem Statement}
-
+E
-In the past bipolar plates for PEMFCs were made out of Titanium or Ti-C Coated materials. 
+In the past, bipolar plates for PEMFCs have been made out of titanium or Ti-C Coated materials. 
 %Toyota quelle titan platten.
-Since bipolar plates contribute to 45\% of the stack costs, there has been a constant search for new materials that could also fullfill the requirements needed but at a lower cost \citep{wang_preparation_2018}. Even though the production of stainless steel plates would cost a fraction of titanium plates and its mechanical strength and conductivity would also meet the requirements it is not as corrosion resistant as Titanium. Therefore stainless steels have been under investigation for some time. Methods used until now to evaluate the corrosion resistance and corrosion damage of PEMFCs focus on ex-situ analysis of the materials and rarely on in-situ methods as well as analyzing the actual bipolar plates with ex-situ methods. \\
+Since bipolar plates contribute to 45\% of stack costs, there has been a constant search for new materials that could also fulfill requirements at a lower cost \citep{wang_preparation_2018}. Even though the production of stainless steel plates would both cost just a fraction of titanium plates and have mechanical strength and conductivity meeting requirements, they are not as corrosion-resistant as titanium. As a result, stainless steel plates have been under investigation for some time. Methods employed thus far to evaluate the corrosion resistance and damage of PEMFCs have primarily focused on ex-situ analysis of materials, and rarely on in-situ methods, or even analysis of the actual bipolar plates with ex-situ methods. \\
 %no good insitu methods...
 \\The purpose of this master's thesis is presented as followed:
 \begin{enumerate}
-	\item Deepen the understanding of corrosion on stainless steel bipolar plates by analyzing SS316L plates and defining the main corrosion mechanism.
+	\item To deepen the understanding of corrosion on stainless steel bipolar plates by analyzing SS316L plates and defining the main corrosion mechanism.
-	\item Understanding which operating conditions will reinforce corrosion. 
+	\item To understanding which operating conditions will reinforce corrosion. 
-	\item Develop a endurance run with reinforcing conditions for corrosion.
+	\item To develop a endurance run with reinforcing conditions for corrosion.
-	\item Further developing of ex-situ Analytical methods to characterize, detect and evaluate corrosion damage on bipolar plates.
+	\item To further development of ex-situ analytical methods to characterise, detect and evaluate corrosion damage on bipolar plates.
 \end{enumerate}
 
 
 
 
 \section{Outline of the Thesis}
-In the last part of the introduction, the outline of your report should be defined. You should include the approach and applied strategy to solve your assignments as well.
+In the last part of the introduction, the outline of your report should be defined. You should include the approach and applied strategy to solve your assignments as well.

Content/Method.tex

@@ -1,58 +1,58 @@
 \chapter{Method}
 \label{chap:Methode}
 
-This chapter will provide a comprehensive overview of the methods used in this thesis. Starting with the in-situ methods in chapter \ref{sec: M_Setup}, where the hardware will be explained in more detail, as well as the characterisation method used to analyse the cells. Section \ref{sec: M_Preliminary} will dive into the methods used to determine the optimal conditions for an endurance run that accelerates corrosion. In section \ref{sec: M_Endurance run_d}, the planned endurance run will be explained. An overview as well as an detailed explanation of the analytical ex-situ methods used to evaluate corrosion in the cell will be presented in the second chapter \ref{sec: Ex-Situ}.
+This chapter will provide a comprehensive overview of the methods used in this Thesis. Starting with the In-Situ methods in chapter \ref{sec: M_Setup} where the hardware will be explained in a more detail way as well as the characterization method used to Analyze the cells. Section \ref{sec: M_Preliminary} will dive into the methods used to determine the optimal conditions for an endurance run which accelerates corrosion. In section \ref{sec: M_Endurance run_d} the planned endurance run will be explained. An overview as well as an detailed explanation of the analytical Ex-Situ methods used to evaluate corrosion in the cell will be presented in the second chapter \ref{sec: Ex-Situ}.
 
 \section{Experimental Setup}
 \label{sec: M_Setup}
 
 
-In order to gain a better understanding of the in-situ methods used to develop and analyse the endurance, this section will focus on the hardware, such as the PEMFC cells and stacks as well as the different test bench setups. 
+In order to have a better understanding of the In-Situ methods used to develop and analyse the endurance this section will focus on the hardware such as the PEMFC cells and Stacks as well as the different test bench setups. 
 
 \subsection{Stack}
 
-First of all, the components of the test specimen of a PEMFC stack that was used will be explained. Figure \ref{fig:Stack} shows a schematic representation of the different layers which compose the test specimen \citep{99_sabawa2021temperature}.
+First of all the components of the used test specimen of a PEMFC stack will be explained. Figure \ref{fig:Stack} shows a schematic representation of the different layers which compose the test specimen \citep{99_sabawa2021temperature}.
 
 %Skizze von der Zelle?
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.7\textwidth]{Figures/Method/Stack.pdf}
-	\caption{Schematic of the structure in the test specimen used with its different components and position. Retrieved from Sabawa. page 43 [99].}
+	\caption{Schematic of the structure in the used test specimen with its different components and position. Retrieved from Sabawa. page 43 [99].}
 	\label{fig:Stack}
 \end{figure}
 
-In the following, each numbered component will be named and briefly explained:
+In the following each numbered component will be named and explained shortly:
 \begin{enumerate}
-	\item \textbf{Screw-in units}: These units provide a point of connection between the test specimen and the test bench for the gases and cooling water. 
+	\item \textbf{Screw-in units}: This units provide a point of connection between the test specimen and the test bench for the gases and cooling water. 
-	\item \textbf{Compression plate}: This plate is made of aluminium and ensures the stability of the structure and that the PEMFC stays sealed.
+	\item \textbf{Compression plate}: This plate is made out of aluminium and ensures the stability of the structure and that the PEMFC stays sealed.
-	\item \textbf{O-ring}: This ring sealing ensures that the gas cannot escape through other parts of the plate and that it follows the predetermined channels.
+	\item \textbf{O-ring}: This ring sealing ensures, that the gas cannot escape through other parts of the plate and that it follows the predetermined channels.
-	\item \textbf{Clamping rods}: Ensure that the components of the MEA stay together and under pressure, even when the cell is being transported. 
+	\item \textbf{Clamping rods}: Ensure that the components of the MEA stay together and under pressure even when the cell is being transported. 
-	\item \textbf{Insulation plate}: The insulation plate is made of Ultem$^{TM}$ Resin 1000 and secures the thermal and electrical insulation from the end plate on both anode and cathode sides.
+	\item \textbf{Insulation plate}: The insulation plate is made out of Ultem$^{TM}$ Resin 1000 and secures the thermal and electrical insulation from the end plate on both anode and cathode sides.
-	\item  \textbf{Current collector}: Enables the connection of the load cable to the cell in the test bench. The current collector is made of gold-plated copper. 
+	\item  \textbf{Current collector}: It enables the connection of the load cable to the cell in the test bench. The current collector is made out of gold-plated copper. 
-	\item  \textbf{Stacked BPs and MEA}: The "sandwich structure" of the cells will be explained in the next part in more detail. 
+	\item  \textbf{Stacked BPs and MEA}: The "sandwich structure" of the cells will be explained in the next part in a more detailed way. 
 	\item  \textbf{Current collector}: Current collector at the cathode side.
 	\item  \textbf{Insulation plate}: This is the insulation plate at the cathode side.
-	\item  \textbf{Compression plate}: The compression plate on the other side with integrated pneumatic pressure pads.
+	\item  \textbf{Compression plate}: The compression plate on the other side with integraded pneumatic pressure pads.
-	\item \textbf{Pressure gauge and gas connection}: Before the cell can be used, it is brought up to the correct pressure to ensure that it is airtight and that gas will not leak during the experiments.
+	\item \textbf{Pressure gauge and gas connection}: Before the cell can be used it will be brought up to the right pressure to ensure it is air tight and gas will not leak during the experiments.
-	\item \textbf{Feet}: Since the test specimen is placed laterally in the test bench, it is supported by the feet.
+	\item \textbf{Feet}: Since the test specimen is placed lateral in the test bench it will be supported by the feet.
 \end{enumerate}
 
-Now that all the components of the PEMFC test specimen have been explained, the actual structure of the cell and its sandwich structure will be explained. Figure \ref{fig:Stack_1} shows a detailed schematic of a cell.
+Now that all the components of the PEMFC test specimen have been explained the actual structure of the cell and its sandwich structure will be explained. Figure \ref{fig:Stack_1} shows a detailed schematic of a cell.
 
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.7\textwidth]{Figures/Method/Stack_1.pdf}
-    \caption{Schematic of the sandwich structure of the BPs and the MEA within the cell stack. In (a) and (c) the BPs plates and their active area in a darker grey colour are shown. (b) shows the MEA placed between the BPs. Retrieved from Sabawa page 46 [99].}
+	\caption{Schematic of the sandwich structure of the BPs and the MEA within the cell stack. In (a) and (c) the BPs plates and its active area in a darker grey are shown. (b) shows the MEA placed between the BPs. Retrieved from Sabawa page 46 [99].}
 	\label{fig:Stack_1}
 \end{figure}
 
-As seen in the schematic, the MEA (b) is placed between two BPs (a, c). Each BP has an anodic and a cathodic side. The cells can be stacked by following this sandwich structure (BP, MEA, BP, MEA, BP) to generate more power. The darker grey part of the BPs represent the active area. Channels within the BPs ensure the distribution of the coolant flow while hydrogen flows through the flow fields in the active area of the cell, as can be seen in the figure \ref{fig:PEMFC}. On both sides, manifolds ensure that the hydrogen, air, water and coolant can be distributed from the first cell to the last cell, and afterwards the coolant used and produced water can be transported away from the cell again through the manifolds and into the outlets. The GDL is sealed by adjusting the pressure on the pneumatic pads which can be found in the compression plate at the end of the stack. 
+As seen in the schematic the MEA (b) is placed between two BPs (a, c). Each BP has an anodic and a cathodic side. The cells can be stacked by following this sandwich structure (BP, MEA, BP, MEA, BP) to generate more power. The darker grey part of the BPs represent the active area. Channels within the BPs ensure the distribution of the coolant flow while hydrogen flows through the flow fields in the active area of the cell, as can be seen in the figure \ref{fig:PEMFC}. On both sides manifolds ensure that the Hydrogen, air, water and coolant can be distributed from the first cell to the las cell and afterwards the used coolant as well as produced water can be transported away from the cell again through the manifolds and into the outlets. The GDL is sealed by adjusting the pressure on the pneumatic pads which can be found in the compression plate at the end of the stack. 
 
-Two types of cells were used in the experiment. Type one is made of titanium with a carbon coating (Ti-C) to enhance the electrical conductivity of the cell and has an active area of 273 cm$^2$. The second type is made out of stainless steel 316L, as referred to in chapter \ref{subsec: BP Corrosion}, and an active area of 285 cm$^2$.
+Two types of cells where used in the experiment. Type one is made out of titanium with a carbon coating (Ti-C) to enhance the electrical conductivity of the cell and has an active area of 273 cm$^2$. The second type is made out of stainless steel 316L like refereed to in the chapter \ref{subsec: BP Corrosion} and an active area of 285 cm$^2$.
 
 \subsection{Testbench}
 
- Two different test bench setups were used in this thesis in order to develop an endurance run with reinforced corrosion conditions and then perform the endurance run. The development of the corrosion endurance run was performed on a \textit{Horiba Fuel Con Shortstack S005} test bench as shown in the figure \ref{fig:Setup_Preliminary} \citep{horiba_fuelcon_2024}. The PEMFC 4-cell stack was placed in the middle of the test chamber and connected to the different supply lines as well as safety devices. 
+ Two different test bench setups where used in this Thesis to be able to develop an endurance run with reinforced corrosion conditions and then perform the endurance run. The development of the corrosion endurance run was performed on a \textit{Horiba Fuel Con Shortstack S005} test bench as shown in the figure \ref{fig:Setup_Preliminary} \citep{horiba_fuelcon_2024}. The PEMFC 4-cell stack was placed in the middel of the test chamber and connected to the different supply lines as well as safety and devices. 
 
 \begin{figure}[htbp]
 	\centering
@@ -61,9 +61,9 @@ Two types of cells were used in the experiment. Type one is made of titanium wit
 	\label{fig:Setup_Preliminary}
 \end{figure}
 
-In this particular case, the test bench was modified so that the product water from the cathode and anode could be collected separately. The two condenser bottles were placed under the test bench to ensure that the product water would flow away from the cell and would not accumulate in the cell after a shutdown. This minimised the corrosion at the outlet caused by standing product water and also enabled separate analysis of the product water on the cathode and anode after a test. Since the test bench was designed for a 4-cell specimen, it allowed a maximum gas supply of 200 Nl/min and a minimum of 21,4 Nl/min. Consequently, the gas stoichiometry for tests performed with a 10-cell stack at high current densities were lower than the planned $\lambda_{air}$ = 2 at the cathode and $\lambda_{H_2}$ = 1,5 at the anode.
+In this particular case the test bench was modified, so that the produced water from the cathode and anode could be collected separately. The two condenser bottles where placed under the test bench to ensure, that the produced water flows away from the cell and does not accumulate in the cell after a shutdown. Therefore minimizing the corrosion at the outlet caused by standing product water and also enabling the separate analysis of the product water on the cathode and anode after a test. Since the Test Bench was designed for a 4-cell specimen it allows a maximum gas supply of 200 Nl/min and a minimum of 21,4 Nl/min. Consequently the gas stoichiometry for tests performed with a 10-cell stack at high current densities where lower than the planed $\lambda_{air}$ = 2 at the cathode and $\lambda_{H_2}$ = 1,5 at the anode.
 
-The endurance run was performed on a \textit{Horiba Fuel Con C1000} test bench. This specific test bench allowed for a maximum gas supply of 100 Nl/min and up to 1000A \citep{horiba_fuelcon_2024}. Despite having a different maximum gas supply and despite the modifications made to the first \textit{Horiba Fuel Con Shortstack S005} test bench to be able to gather and extract the product water, the two test benches had a very similar setup. Figure \ref{fig:P&ID} presents a simplified piping \& instrumentation diagram to give a better overview of the components used to modify operating parameters.
+The endurance run was performed on a \textit{Horiba Fuel Con C1000} test bench. This specific test Bench allows a maximum gas supply of 100 Nl/min and up to 1000A \citep{horiba_fuelcon_2024}. Despite having a different maximum gas supply and the modifications made to the first \textit{Horiba Fuel Con Shortstack S005} test bench to be able to gather and extract the product water the two test benches have a very similar setup. Figure \ref{fig:P&ID} presents a simplified piping \& instrumentation Diagram in order to give a better overview of the components used to change the operating parameters.
 
 \begin{figure}[htbp]
 	\centering
@@ -72,35 +72,35 @@ The endurance run was performed on a \textit{Horiba Fuel Con C1000} test bench.
 	\label{fig:P&ID}
 \end{figure}
 
-The gases have a purity of 99,999\% and can be dosed by the mass flow controllers (MFC) as seen in the figure \ref{fig:P&ID} with the number 2. After the MFC the dew point of the gases can be adjusted with the help of the bubbler-humidifiers (4) at the anode and the cathode. The water in the bubbler can only be heated and not actively cooled, which limits the process of ramping down the dew point temperature. Number 5 is the dry gas bypass; this allows for a dew point temperature range from 10-90 °C. Furthermore, the gases can be heated up to a temperature ranging from 40 to 180 °C in step 6, with the heating hoses on the inlet of the PEMFC. Part 9 of the chart is the PEMFC, which for the endurance run consisted of a 4-cell stack of the type two cells made out of stainless steel 316L. Number 11 shows the temperature control of the cooling circuit. The cell can be cooled or heated from a temperature of 35 °C to 105 °C. It is also possible to change the pressure to be able to reach water temperatures above the boiling point. Number 13 shows the safety sensors which can shut down the cell and the test bench in case of failure. 15 allows the control of the membrane pressure. The current collectors are connected with a potentiostat to set a predefined voltage or current in the FC (18). To monitor the cell voltage, the cell is connected to the test bench with a cell voltage monitoring connector (CVM) so that each individual cell voltage can be measured (19).
+The gases have a purity of 99,999\% and can be dosed by the mass flow controllers (MFC) as seen in the figure \ref{fig:P&ID} with the number 2. After the MFC the dew point of the gases can be adjusted with the help of the bubbler-humidifiers (4) at the anode and the cathode.  The water in the bubbler can only be heated and not actively cooled which limits the process of ramping down the dew point temperature. Number 5 is the dry gas bypass, this allows for a dew point temperature range from 10-90°C. Furthermore the gases can be heated up to a temperature ranging from 40-180°C in step 6 with the heating hoses on the inlet of the PEMFC. Part 9 of the chart is the PEMFC which for the endurance run consisted of a 4-cell stack of the type two cells made out of stainless steel 316L. Number 11 shows the temperature control of the cooling circuit. The cell can be cooled or heated from a temperature of 35°C to 105°C. It is also possible to change the pressure to be able to reach water temperatures above the boiling point. Number 13 shows the safety sensors which can shut down the cell and the test bench in case of a failure. 15 allows the control of the membrane pressure. The current collectors are connected with a potentiostat to set a defined voltage or current in the FC (18). To monitor the cell voltage the cell is connected to the test bench with a cell voltage monitoring connector (CVM), so that each individual cell voltage can be measured (19).
 
 \subsection{Dew Point Calculation}
 
-As previously explained, the dew point can be varied by changing the temperature of the bubbler-humidifier to adjust the humidity of the cathode and anode separately. Since the experiment aims for a specific level of humidity on the anode and the cathode of about 30 \% and 50 \%, the correct dew point temperatures have to be calculated. The Sonntag formula for saturation pressure of water was used to calculate the relative humidity at both anode and cathode based on the pressure, temperature of the cell and molecular weight as stated in the British Standard 1339:1 \citep{sonntag1990important}.
+As explained before the dew point can be varied by changing the temperature of the bubbler-humidifier to adjust the humidity of the cathode and anode separately. Since the experiment aims for a specific level of humidity on the anode and the cathode of about 30 \% and 50\% the right dew point temperatures have to be calculated. The Sonntag formula for saturation pressure of water was used to calculate the relative humidity at both anode and cathode based on the pressure, temperature of the cell, molecular weight as stated in the British Standard 1339:1 \citep{sonntag1990important}.
 
-\subsection{Stochiometry Calculation}
+\subsection{Calculation of the Stochiometrie}
 
-Since the stoichiometry of the reactants at the anode and cathode and therefore of the dosed gas both play a very important role to avoid phenomena like hydrogen starvation (which could be fatal for the cell), it is important to understand how the gas flow was calculated. To avoid hydrogen starvation, the tests were conducted with a stoichiometry of $\lambda_{air}$ = 2 at the cathode and $\lambda_{H_2}$ = 1,5 at the anode.
+Since the stoichiometry of the reactants at the anode and cathode and therefore of the gas dosed plays a very important role to avoid phenomena like hydrogen starvation (which could be fatal for the cell) it is important to understand how the gas flow was calculated. To avoid hydrogen starvation the test where conducted with a stoichiometry of $\lambda_{air}$ = 2 at the cathode and $\lambda_{H_2}$ = 1,5 at the anode.
 
-Since the tests where carried out at both different stoichiometries and via setting the current density, the flow rate had to be adjusted and calculated. The first step of this calculation is to multiply the current density with the active area of one BP to determine the electrical current $I$ in A. In the second step, with the help of Faradays law and Faraday's constant $F$ 96485,3 As/mol, the flow rate can be calculated using the following equation \citep{Fundamentals_scherer2012fuel}.
+Since the tests where carried out at different stoichiometries and by setting the current density the flow rate had to be adjusted and calculated. The first step of this calculation is to multiply the current density with the active area of one BP to determine the electrical current $I$ in A. In the second step the with the help of Faradays law and Faraday's constant $F$ 96485,3 As/mol the flow rate can be calculated using the following equation \citep{Fundamentals_scherer2012fuel}.
 
 \begin{equation}
 	\varphi=\frac{1}{z \cdot F} \cdot V_{\mathrm{mol}} \cdot \frac{60 \mathrm{~s}}{\mathrm{~min}}
 \end{equation}
 
-In this equation z is equal to 2 for H$_2$ (anode) and equal to 4 for O$_2$ (cathode). Furthermore, $V_{mol}$ = 22,414 l/mol, and indicates the molar volume of an ideal gas. Then, $\varphi$ can be multiplied with the electrical current and the result can be multiplied with the stochiometry factor. The last step is to multiply this with the number of cells to get the final gas flow in Nl/min for each new current density at the selected stoichiometry. 
+In this equation z is equal to 2 for H$_2$ (anode) and equal to 4 for O$_2$ (cathode). Furthermore, $V_{mol}$ = 22,414 l/mol and indicates the molar volume of an ideal gas. Then $\varphi$ can be multiplied with the electrical current and the result can be multiplied with the stochiometry factor. The last step is to multiply this with the number of cells to get the final gas flow in Nl/min for each new current density at the selected stoichiometry. 
 
 \subsection{Measurement of pH and Electrical Conductivity}
 
-In order to determine which set of operating parameters of the PEMFC have a reinforcing impact on the corrosion of the BPs the pH and the conductivity of the product water was measured. The measurement was made by using the seven excellence pH meter from the company \textit{Mettler Toledo} \citep{mettler_toledo_ph_meters_2024}. To avoid sudden changes of pressure in the cell, which could cause an alteration of the results as well as hard shutdown by the security sensors, the product water was extracted after the normal shutdown and then brought back to the laboratory to be measured.
+In order to determine which set of operating parameters of the PEMFC have a reinforcing impact on the corrosion of the BPs the pH and the conductivity of the product water was measured. The measurement was made by using the seven excellence pH meter from the company \textit{Mettler Toledo} \citep{mettler_toledo_ph_meters_2024}. To avoid sudden changes of pressure in the cell which could cause an alteration of the results as well as hard shut down caused by the security sensors, the product water was extracted after the normal shut down and then brought back to the laboratory to be measured.
 
-\subsection{Characterisation of Cells}
+\subsection{Characterization of Cells}
 
-The method used for the in-situ characterisation of the cell in this thesis is the polarisation curve. as mentioned in the second chapter in section \ref{subsec: Polarizaiton}. To monitor the state of health of the cell and therefore also the degradation of the cell, the polarisation curves will be performed at the start of life of the cell and then periodically repeated after the test and in the end of life characterisation.
+The method used for the In-Situ characterization of the cell in this thesis is the polarization curve as mentioned in the second chapter in the section \ref{subsec: Polarizaiton}. To monitor the state of health of the cell and therefore also the degradation of the cell the polarization curves will be performed at the start of life of the cell and then periodically repeated after the test and in the end of life characterization.
 
-\subsubsection{Polarisation Curves}
+\subsubsection{Polarization Curves}
 
-As a standard procedure, three different polarisation curves will be tested. Between them the temperature of the cell, which should be very similar to the coolant temperature ($T_{coolant,in}$), the gas temperature at the anode and cathode ($T_{gas,A}$, $T_{gas,C}$) and the dew point temperature will be increased while the cell is at a safe point before performing the next curve. The exact parameters for the three polarisation curves can be found in the following table \ref{tab:PolKurve}.
+As a standard procedure three different polarization curves will be tested. Between them the temperature of the cell which should be very similar to the coolant temperature ($T_{coolant,in}$), the gas temperature at the anode and cathode ($T_{gas,A}$, $T_{gas,C}$) and the dew point temperature will be increased while the cell is at a safe point before performing the next curve. The exact parameters for the three polarization curves can be found in the following table \ref{tab:PolKurve}.
 
 \begin{table}[h]
 	\centering
@@ -113,23 +113,23 @@ As a standard procedure, three different polarisation curves will be tested. Bet
 		90& 105 & 62& 2&105& 62& 2\\
 		
 	\end{tabular}
-	\caption{Operating parameters of the polarisation curves at 60, 80 and 90 °C and 2 bar pressure to characterise the cell performance. Temperatures in [°C] and pressure in [bar].}
+	\caption{Operating parameters of the polarization curves at 60, 80 and 90 °C  and 2 bar pressure to characterize the cell performance.Temperatures in [°C] and pressure in [bar].}
 	\label{tab:PolKurve}
 \end{table}
 
-Since the bubblers can not be cooled actively, the characterisation starts with the 60 °C polarisation curve to avoid long waiting periods. In each polarisation curve, the current density is increased gradually from 0 A/cm$^2$ to 2,2 A/cm$^2$ and then back down to 0 A/cm$^2$. Each step is maintained for 120s. With each change, the volume flow of the gases on cathode and anode is also adjusted to avoid H$_2$ starvation.
+Since the bubblers can not be cooled actively the characterization starts with the 60°C polarization curve to avoid long waiting periods. In each polarization curve the current density is increased gradually from 0 A/cm$^2$ to 2,2 A/cm$^2$ and then back down to 0 A/cm$^2$. Each step is maintained for 120s. With each change the Volume flow of the gases on cathode and anode is adjusted as well to avoid H$_2$ starvation.
 
 \newpage
 \section{Preliminary Investigation}
 \label{sec: M_Preliminary}
 
-It is essential to look into how different parameters affect the cell when designing an endurance run, as it takes place under conditions that reinforce the corrosion mechanism within the cell and must avoid inducing total failure of the cell before corrosion becomes visible. Therefore, before starting an endurance run, various parameters such as the temperature of the coolant at the inlet ($T_{coolant,in}$), gas temperature at the anode and cathode ($T_{gas,A}$, $T_{gas,C}$ ) and the dew point temperature at the anode and cathode ($T_{dp,A}$) were tested to measure their effects on the cell.
+In order to design an endurance run in which the conditions will reinforce corrosion mechanism within the cell without inducing a total failure of the cell before corrosion becomes visible, It is essential to look into how different parameters affect the cell. Therefore, before starting an endurance run various parameters like the temperature of the coolant at the inlet ($T_{coolant,in}$), gas temperature at the anode and cathode ($T_{gas,A}$ , $T_{gas,C}$ ) as well as the dew point temperature at the anode and cathode ($T_{dp,A}$) where tested to measure the effects they have on the cell.
 
-High humidity along with a low pH in the product water were identified as conditions that could intensify the  corrosion of the BPs. Therefore, the following experiment was designed to be able to measure the pH and the electrical conductivity of the product water and trace metal ions dissolving from the BP which could potentially lead to an increased electrical conductivity. The pH could also be theoretically lowered by the Nafion degradation and a potential release of F$^-$.
+High humidity as well as a low pH in the product water where identified as conditions which could intensify the  corrosion of the BPs. Therefore the following experiment was designed to be able to measure the pH and the electrical conductivity of the product water and trace metal ions dissolving from the BP which could potentially lead to an increased electrical conductivity. The pH could also be theoretically lowered by the Nafion degradation and a potential release of F$^-$.
 
 \subsection{Experimental Setup}
 
-The test specimen used for the preliminary investigations was a 4-cell stack of the type one cell made of titanium and a carbon coating (Ti-C) and an active area of 273 cm$^2$. As previously stated, this test was performed on the \textit{Horiba Fuel Con Shortstack S005} test bench, modified as seen in the figure \ref{fig:Setup_Preliminary} in order to be able to extract the product water of the anode and cathode separately.
+The test specimen used for the preliminary investigations was a 4-cell stack of the type one cell made out of titanium and a carbon coating (Ti-C) and an active area of 273 cm$^2$. As stated before this test was performed on the \textit{Horiba Fuel Con Shortstack S005} test bench which was modified as seen in the figure \ref{fig:Setup_Preliminary} to be able to extract the product water of the anode and cathode separately.
 
 \subsection{Experimental Execution}
 
@@ -137,25 +137,25 @@ The preliminary investigation can be divided into the following 4 steps:
 
 \begin{enumerate}
 	\item Startup and activation of the cell.
-	\item Begin of life characterisation with polarisation curves.
+	\item Begin of life characterization with polarization curves.
-	\item Parameter variation tests with voltage cycling.
+	\item  Parameter variation tests with voltage cycling.
-	\item End of life characterisation of the cells.
+	\item  End of life characterization of the cells.
 \end{enumerate}
 
-These steps will be explained in a more detail in the following. Starting with the activation of the cell after the startup.
+This Steps will be explained in a more detailed way in the following. Starting with the activation of the cell after the startup.
 
 \subsubsection{Activation of the Cell}
 
-After startup, the cell is not completely ready to perform. Even though the materials were carefully stored in a clean room to avoid having the membrane dry out, which could cause mechanical stress and damage to it. To avoid any damage to the MEA, the cell must be carefully activated to ensure that the membrane has the right humidity in order to perform. 
+After the startup the cell it is not completely ready to perform. Even though the materials where carefully stored in a clean room to avoid the drying out of the membrane which could cause mechanical stress and damage it. To avoid any damage to the MEA the cell has to be carefully activated to ensure that the membrane has the right humidity in order to perform. 
-After startup, the cell is at a temperature of 60 °C, the gas temperature at 85 °C and the dew points at 46 °C. Therefore, to activate the cell the 60 °C polarisation curve is performed three times in a row and then the 80 °C polarisation curve is performed. After this process, the cell should have reached an optimal performance and the polarisation curves should look stable.
+After the start up the cell is at a temperature of 60°C, the gas temperature at 85°C and the dew points at 46°C. Therefore, to activate the cell the 60°C polarization curve is performed 3 times in a row and afterwards the 80°C polarization curve is performed. After this process the cell should have reached an optimal performance and the polarization curves should look stable.
 
-\subsubsection{Begin of Life Characterisation}
+\subsubsection{Begin of Life Characterization}
 
-For the begin of life characterisation, the three polarisation curves at 60, 80 and 90 °C are performed to set a benchmark which can then be analysed and compared with the following characterisations so that the drop in performance due to the degradation can be seen.
+For the begin of life characterization the three polarization curves at 60,80 and 90 °C are performed to set a benchmark which can then be analyzed and compared to the following characterizations to be able to see the drop in the performance due to the degradation.
 
 \subsubsection{Parameter Variation} 
 
-Three different operating parameters were tested to see how the cell and gas temperature could affect the pH and electrical conductivity of the product water. The cell was tested at 60 °C, 75 °C and 90 °C. The exact parameters for the gas temperatures and pressures can be found in table \ref{tab:3_pH_T}.
+Three different operating parameters where tested to see how the cell and gas temperature could affect the pH and electrical conductivity of the product water. The cell was tested at 60°C, 75°C and 90°C. The exact parameters for the gas temperatures and pressures can be found in table \ref{tab:3_pH_T}.
 
 \begin{table}[h]
 	\centering
@@ -172,25 +172,21 @@ Three different operating parameters were tested to see how the cell and gas tem
 	\label{tab:3_pH_T}
 \end{table}
 
-The dew point temperatures were adjusted so that the cell could have a relative humidity of about 30 \% at the anode and 50 \% at the cathode. Furthermore, since the first test with a low temperature and high humidity at 60 °C should have a dew point temperature of 37 °C at the anode, and normal startup raises the dew point temperature to 46°C, the startup script had to be adjusted. Consequently, the temperature of the dew point at the anode were simply elevated to 37°C.
+The dew point temperatures where adjusted so that the cell could have a relative humidity of about 30\% at the anode and 50\% at the cathode. Furthermore, since the first test with a low temperature and high humidity at 60°C should have a dew point temperature of 37°C at the anode and the normal start up rises the dew point temperature to 46°C the startup script had to be adjusted. Consequently the temperature of the dew point at the anode would just be elevated to 37°C.
 
-After the start up in all three tests the desired temperatures found in table \ref{tab:3_pH_T} were set in a specific order:
+After the start up in all three test the desired temperatures found in table \ref{tab:3_pH_T} where set in a specific order:
 \begin{enumerate}
 	\item Increase anode pressure to 2,4 bar.
 	\item Decrease cathode pressure to 1,5 bar.
 	\item Increase cell temperature by increasing the coolant temperature $T_{coolant,in}$.
 	\item Increase the gas temperatures $T_{gas,A}$ and $T_{gas,C}$ to the desired temperature.
-	\item Increase the dew point temperatures $T_{dp,A}$ and $T_{dp,C}$ to reach the desired relative humidity.
+	\item  Increase the dew point temperatures $T_{dp,A}$ and $T_{dp,C}$ to reach the desired relative humidity.
-	\item Ramp up current density and volume flow of the gases until 2 A/cm$^2$.
+	\item Ramp up current density and Volume flow of the gases until 2 A/cm$^2$.
-	\item Start voltage cycling for 2h.
+	\item Start Voltage cycling for 2h.
     \item Shut down.
 \end{enumerate} 
 
-After reaching the set parameters the voltage cycling of the cell was
+After reaching the set parameters the cell Voltage cycling of the cell was manually started. In this process the cell switched between 15s at 0,85V and 10s at 0,6V. This can be clarified by the following figure. After the two hours the cell could be shut down and after the shot down the product water was collected at the cathode and anode to be measured at the laboratory.
-manually started. In this process, the cell switched between 15s at 0,85V and
-10s at 0,6V. This can be clarified by the following figure. After the two hours
-the cell could be shut down and after shutdown the product water was
-collected at the cathode and anode to be measured at the laboratory.
 
 \begin{figure}[htbp]
 	\centering
@@ -202,19 +198,19 @@ collected at the cathode and anode to be measured at the laboratory.
 \section{Developement of Endurance Run}
 \label{sec: M_Endurance run_d}
 
-The endurance run was developed after the preliminary investigations with the three different settings and voltage cycling. Some changes were made to the methods which will be explained in this section. In order to compare the temperature effects on the corrosion and other degradation mechanisms like Pt dissolution and agglomeration, two different endurance runs were performed. First, the low temperature high humidity endurance run, in order to trigger the corrosion mechanisms, and second, a high temperature endurance run, in order to trigger other degradation mechanisms such as Pt dissolution, agglomeration and membrane degradation. The changes to the mehtod will be explained in the following sections.
+The endurance run was developed after the preliminary investigations with the three different settings and voltage cycling. Some changes where made to the methods which will be explained in this section. In order to compare the temperature effects on the corrosion and other degradation mechanisms like Pt dissolution and agglomeration two different endurance runs where performed. The low temperature high humidity endurance run to trigger the corrosion mechanisms and a high temperature endurance run to trigger other degradation mechanisms like Pt dissolution, agglomeration and membrane degradation. The changes to the mehtod will be explained in the next sections.
 
 \subsection{Experimental Setup}
 
-Both endurance runs were performed at simultaneously on two identical \textit{Horiba Fuel Con C1000} test benches \citep{horiba_fuelcon_2024}. The cells used for both 4-cell stacks were the type two cells made of stainless steel 316L and an active area of 285 cm$^2$. This time, no product water was extracted from the cell because of the space limitations of the two test benches. 
+Both endurance runs where performed at the same time on two identical \textit{Horiba Fuel Con C1000} test benches \citep{horiba_fuelcon_2024}. The cells used for both 4-cell stacks  where the type two cells made out of stainless steel 316L and an active area of 285 cm$^2$. This time no product water was extracted from the cell because of the space limitations of the two test benches. 
 
 \subsection{Experimental Execution}
 
-First, the experimental execution of the low temperature corrosion endurance run will be explained, and next the high temperature endurance run. It is worth mentioning that the two endurance runs had the same activation procedure and characterisation procedure between each cycle. Since both differed from that used in the preliminary investigations, they will be explained prior to outlining the plan and parameters for both endurance runs.
+First the experimental execution of the low temperature corrosion endurance run will be explained and afterwards the high temperature endurance run. It is worth mentioning that the two endurance runs had the same activation procedure and characterization procedure between each cycle. Since both differed from the one used in the preliminary investigations they will be explained prior to outlining the plan and parameters for both endurance runs.
 
 \subsubsection{Activation of the Cell}
 
-Since the 60 °C polarisation curve presents a higher humidity than the 80 °C polarisation curve, the latter is better equipped for the activation of the type two cells. Therefore, for the activation of the endurance run cells the 80 °C polarisation curve was repeated four times as an activation. After the third, the difference between the curves was minimal so that the hydration of the membrane as well as the performance of the cell could be optimal. The results can be seen in chapter \ref{chap:Ergebnisse und Diskussion}.
+Since the 60°C polarization curve presents a higher humidity than the 80°C polarization curve the last is better equipped for the activation of the type two cells. Therefore, for the activation of the endurance run cells the 80°C polarization curve was repeated four times as an activation. After the third the difference between the curves was minimal so that the hydration of the membrane was optimal as well as the performance of the cell. The results can be seen in chapter \ref{chap:Ergebnisse und Diskussion}.
 
 \subsubsection{Endurance Runs}
 
@@ -222,24 +218,24 @@ Since the 60 °C polarisation curve presents a higher humidity than the 80 °C p
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.8\textwidth]{Figures/Method/In-Situ.pdf}
-	\caption{Structure for the corrosion endurance run and high temperature endurance run with the three steps of 12500, 25000 and 43500 voltage cycles. The in-situ characterisation is performed between each step.}
+	\caption{Structure for the corrosion endurance run and high temperature endurance run with the three steps of 12500, 25000 and 43500 voltage cycles. Between each step the in-situ characterization is performed.}
 	\label{fig:In-Situ}
 \end{figure}
 
-Figure \ref{fig:In-Situ} shows the structure of both the corrosion endurance run and the high temperature endurance run, since they have the same number of voltage cycling cycles. For the in-situ characterisation of the cells after the activation and in between each set of voltage cycles, two polarisation curves are planned. This time, only the 60 °C and the 80 °C polarisation curves will be used to characterise the cell and its performance loss. Due to the high temperature and volume flow of the 90°C polarisation curve, this could intensify the degradation before the next cycle, as well as trigger a hard shutdown on the test bench. To avoid any damage to the cell caused by the hard shutdown, the decision was made to only work with the other two curves for these tests.
+Figure \ref{fig:In-Situ} shows the structure of both the corrosion endurance run and the high temperature endurance run since they have the same amount of voltage cycling cycles. For the in-situ characterization of the cells after the activation and in-between each set of voltage cycles two polarization curves are planned. This time only the 60°C and the 80°C polarization curves will be used to characterize the cell and its performance loss. Due to the high temperature and volume flow of the 90°C polarization curve that could intensify the degradation before the next cycle as well as trigger a hard shut down on the test bench. To avoid any damage to the cell caused because of the hard shut down the decision was made to only work with the other two curves for this tests.
 
-The voltage cycling in the two endurance runs is also differs from that used in the preliminary study. Since the endurance run would be much longer than the first tests. each cycle was modified and now consists of a 10-second hold time at 0,88 V and then another 10 seconds at 0,6 V. This modified cycle is illustrated in figure \ref{fig:ECU}.
+The voltage cycling in the two endurance runs is also different from the one used in the preliminary study. Since the endurance run would be a lot longer than the first tests each cycle was modified and now consists of 10s hold time at 0,88V and then another 10s at 0,6V. This modified cycle is illustrated in figure \ref{fig:ECU}.
 
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.6\textwidth]{Figures/Method/ECU.pdf}
-	\caption{Voltage cycling of the cell between 10 seconds at 0,88 V and 10 seconds at 0,6 V.}
+	\caption{Voltage cycling of the cell between 10s at 0,88V and 10s at 0,6V.}
 	\label{fig:ECU}
 \end{figure}
 
 \subsubsection{Corrosion Reinforcing Endurance Run}
 
-Before starting each cycle of voltage cycling as seen in figure \ref{fig:In-Situ}, the cell first must reach the desired operating parameters. For this corrosion reinforcing endurance run, the specific parameters can be found in the table \ref{tab:3_ER_S}.
+Before starting each cycle of voltage cycling as seen in figure \ref{fig:In-Situ} the cell first hast to get to the desired operating parameters. For this corrosion reinforcing endurance run the specific parameters can be found in the table \ref{tab:3_ER_S}.
 
 \begin{table}[h]
 	\centering
@@ -249,15 +245,15 @@ Before starting each cycle of voltage cycling as seen in figure \ref{fig:In-Situ
 		\hline
 		65&	85 & 45& 2,3&85 &53& 1,4\\
 	\end{tabular}
-	\caption{Temperature and pressure parameters of the corrosion reinforcing endurance run. Temperatures in [°C] and pressure in [bar].}
+	\caption{Temperature and pressure parameters of the corrosion reinforcing endurance run.Temperatures in [°C] and pressure in [bar].}
 	\label{tab:3_ER_S}
 \end{table}
 
-This time, the relative humidity of both cathode and anode is increased compared to the preliminary study. The cathode is run at a relative humidity of about 54,66 \% and the anode at 36,65 \% to further increase corrosion. The volume flow of the gases is increased to cope with a current density of 1,5 A/cm$^2$ before starting the voltage cycling. The stoichiometry stays at $\lambda_{air}$ = 2 at the cathode and $\lambda_{H_2}$ = 1,5 at the anode to increase the performance at the cell and avoid H$_2$ starvation at the anode.
+This time the relative humidity of both cathode and anode is increased compared to the preliminary study. The cathode is run at a relative humidity of about 54,66\% and the anode at 36,65\% to increase corrosion even more. The volume flow of the gases is increased to cope with an current density of 1,5 A/cm$^2$ before starting the voltage cycling. The stoichiometry stays at $\lambda_{air}$ = 2 at the cathode and $\lambda_{H_2}$ = 1,5 at the anode to increase the performance at the cell and avoid H$_2$ starvation at the anode.
 
 \subsubsection{High Temperature Endurance Run}
 
-For the high temperature endurance run, the parameters are different. To start with, a much higher cell temperature is used due to the cooling temperature of the cell, which is at 103 °C compared to the 65 °C of the corrosion endurance run. The temperature and pressure parameters of the high temperature endurance run can be seen in table \ref{tab:3_ER_HT}.
+For the high temperature endurance run the parameters are different. Starting with a much higher cell temperature due to the cooling temperature of the cell which is at 103°C compared to the 65°C of the corrosion endurance run. The temperature and pressure parameters of the high temperature endurance run can be seen in table \ref{tab:3_ER_HT}.
 
 \begin{table}[h]
 	\centering
@@ -271,19 +267,19 @@ For the high temperature endurance run, the parameters are different. To start w
 	\label{tab:3_ER_HT}
 \end{table}
 
-Since the high temperature already accounts for a higher product water production in the cell, the pressure in the anode is not lowered to 1,4 bar, but only to 1,8 bar in order to avoid an accumulation of water at the cathode exit. The relative humidity is also lower than in the corrosion endurance run with a relative humidity of about 30,1 \% at the anode and 51 \% at the cathode. As previously explained, the two setups, characterisation methods and number of cycles in the endurance run are the same as in the corrosion run, only the parameters have been changed.
+Since the hight temperature already accounts for a higher product water production in the cell the pressure in the anode is not lowered to 1,4 bar but only to 1,8 bar to avoid an accumulation of water at the cathode exit. The relative humidity is also lower than in the corrosion endurance run with a relative humidity of about 30,1\% at the anode and 51\% at the cathode. As explained before the two setups, characterization methods and number of cycles in the endurance run are the same as in the corrosion run, just the parameters have changed.
 
 \newpage
 
 \section{Ex-Situ analysis}
 \label{sec: Ex-Situ}
 
-After the endurance runs, the components of the PEMFC test specimen are analysed to detect and evaluate the corrosion damage caused by the operating conditions. Therefore, the cell is brought to the laboratories and into a clean room to avoid any contaminations of the BPs and the MEA while opening. The stacked cells are then dismounted to be visually analysed.
+After the endurance runs the components of the PEMFC test specimen are analysed to detect and evaluate the corrosion damage caused by the operating conditions. Therefore, the cell is brought to the laboratories and into a clean room to avoid any contaminations of the BPs and the MEA while opening. The stacked cells are then dismounted to be optically analysed.
 
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.8\textwidth]{Figures/Method/FlowField.pdf}
-	\caption{Matrix of the active area of the cell to clarify the exact positions analysed.}
+	\caption{Matrix of the active area of the cell for to clarify the exact positions analysed.}
 	\label{fig:Matrix}
 \end{figure}
 
@@ -291,16 +287,16 @@ Figure \ref{fig:Matrix} provides a matrix of the BP to enable a clearer understa
 
 \subsection{Microscopy}
 
-The first step after the cells have been removed from the stack is to search for abnormalities or discolorations in the stainless steel 316L that could be caused by the operating conditions and could also include corrosion damages. In this step, the whole cathode side of the BP is analysed, including the cathode inlet and outlet. Since the humidity is higher at the cathode, the positions M1 and A6 as well as the cathode outlet will be analysed in greater detail. For this analysis, a microscope from the company \textit{Keyence} model VHX 7000 is used as well as a VHX 6000 \citep{keyence_digital_microscope_2024}.
+The first step after the cells have been removed from the stack is to look for abnormalities or discolorations in the stainless steel 316L which could be caused by the operating conditions and could include corrosion damages. In this step the whole cathode side of the BP is analysed including the cathode inlet and outlet. Since the humidity is higher at the cathode the positions M1 and A6 will be analysed in greater detail as well as the cathode outlet. For this analysis a microscope from the company \textit{Keyence} model VHX 7000 is used as well as a VHX 6000 \citep{keyence_digital_microscope_2024}.
 
 \subsection{LIBS Analysis}
 
-After the microscopical analysis, the positions M1, A6, cathode outlet and the selected points of interest will be further investigated using laser induced breakdown spectroscopy (LIBS). LIBS will be performed by an EA-300 from the company \textit{Keyence} \citep{keyence_ea_300_2024}. This atomic-emission spectroscopy method enables a quick material analysis. A high energy laser converts the material into a plasma plume which cools and breaks down very quickly, breaking down into excited ionic atomic species. Thanks to the quick cooldown, the visual breakdown of the plasma can be analysed with the spectrometer. This could give more insights into the material composition of the selected sites and help understand the changes in the surface composition related to corrosion. 
+After the microscopical analysis the positions M1, A6, cathode outlet and the selected points of interest will be further investigated using laser induced breakdown spectroscopy (LIBS). LIBS will be performed by an EA-300 from the company \textit{Keyence} \citep{keyence_ea_300_2024}. This atomic-emission spectroscopy method enables for a quick material analysis. A high energy laser converts the material into a plasma plume which cools down and breaks down really fast and breaks down into ionic atomic species which are excited. Thanks to the quick cool down the optical breakdown of the plasma can be analysed with the spectrometer. This could give more insights into the material composition of the selected sites and help understand the changes in the surface composition related to corrosion. 
 
 
 \subsection{SEM/EDX Analysis}
 
-The corrosion mechanism can cause severe damage to the metal structure and dissolution of the metal. As stated in the theoretical part of this thesis, the metal ions can move from the BPs to the MEA and catalyse the Fenton mechanism, degrading the membrane \citep{ruvinskiy2011using, Corr_mele2010localised}. Therefore, scanning electron spectroscopy (SEM), as well as energy dispersive x-ray spectroscopy (EDX), will both be used to evaluate the BP and attempt to find cases of metal dissolution or formation of an oxide layer due to corrosion. Furthermore, the MEA will be analysed to attempt to find metal contaminations of Ni, Fe and Cr on the GDL and CCM and prove the movement from the metal ions from the BPs into the MEA are a result of the corrosion \citep{105_novalin2022concepts}. Both SEM and EDX will be performed on a Zeiss EVO 10 with smart EDX \citep{zeiss_evo_sem_2024}.
+The corrosion mechanism can cause severe damage of the metal structure and cause the dissolution of the metal. As stated in the theoretical part of this thesis the metal ions can move from the BPs to the MEA and catalyse the Fenton mechanism which degrades the Membrane \citep{ruvinskiy2011using, Corr_mele2010localised}. Therefore, scanning electron spectroscopy (SEM) as well as energy dispersive x-ray spectroscopy (EDX) will be used evaluate the BP and try to find cases of metal dissolution or formation of an oxide layer as a result of the corrosion. Furthermore, the MEA will be analysed to try to find metal contaminations of Ni, Fe and Cr on the  GDL and CCM and prove the movement from the metal ions from the BPs into the MEA as a result from the corrosion \citep{105_novalin2022concepts}. Both SEM and EDX will be performed on a Zeiss EVO 10 with smart EDX \citep{zeiss_evo_sem_2024}.
 
 
 

Content/Results and Discussion.tex

@@ -1,34 +1,547 @@
 \chapter{Results and Discussion}
 \label{chap:Ergebnisse und Diskussion}
 
+Chapter \ref{chap:Ergebnisse und Diskussion} will present the findings of both in-situ and ex-situ investigations, along with the discussion of the results. First the in-situ results will be presented starting with the preliminary investigations in section \ref{subsec:4_Prelim} which helped develop the corrosion endurance run. The results from the corrosion endurance run as well as the high temperature endurance run will be presented in \ref{sec:4_Corrosion} and \ref{sec:4_High Temp}. The final section, \ref{sec: Ex-Situ}, provides the results of the in-situ methods will be presented and discussed.
 
 
-\section{Material Characterization of  SS316L}
+\section{Preliminary Investigation}
+\label{subsec:4_Prelim}
 
-\subsubsection{Corrosion Parameters}
+Before starting the endurance run first a preliminary investigation was conducted in order to find the optimal operating conditions for the corrosion endurance run. The table \ref{tab:versuche} found in the appendix \ref{sec:A_1} provides a chronological overview of the testing activities conducted. Although this investigations were planed on a 10 cell stack made out of type 2 cells (stainless steel 316L BP) the plan was changed due to the limited stock of these cells after the first stack broke down due to several hard shut downs and problems with the test bench. Therefore a 4 cell stack of the type 1 cells (Ti-C) was used to conduct the preliminary investigations and afterwards test the other test bench before changing to the type 2 cells again and starting the endurance run.
+ 
+\subsection{pH and Electrical Conductivity Measurement}
+
+As explained in the chapter \ref{sec: M_Preliminary} the measured product water was extracted from the condensator bottles located at the cathode and anode outlets. The results from the extracted product water are presented in the following table \ref{tab:3_ER}.
+
+\begin{table}[h]
+	\centering
+	\begin{tabular}{cccc} 
+		\hline
+		Position & Temperature [°C]&pH &   Electrical Conductivity [$\mu \mathrm{S} / \mathrm{cm}$]\\
+		\hline
+		Cathode &90 &	6 & 1,36\\
+		Anode &90 &	5,73 & 2,07\\
+		Cathode &75 &	5,83 & 2,29\\
+		Anode &75 &	5,94 & 2,93\\
+		Cathode& 60 &	5,51 & 12,75\\
+		Anode &60 & 5,69 & 6,99\\
+	\end{tabular}
+	\caption{Measurement of the pH and electrical conductivity of the product water in the preliminary investigations.}
+	\label{tab:3_ER}
+\end{table}
+
+The high temperature and high humidity test (HTHH) conducted at 90°C differed from the other two tests since the water production was higher than expected and the test stopped after 45 minutes of voltage cycling between 15s at 0,85V and 10s at 0,6V while the other two tests cycled for 2 hours before shutting down. The measured electrical conductivity of the test was lower than the one of the other two test with a the lowest measurement at the cathode with 1,36 $\mu \mathrm{S} / \mathrm{cm}$. On the other hand the pH measured in the product water of the cathode was the highest with a value of 6. In all the other tests the measured pH at the cathode was lower than in the anode.
+
+At a medium temperature of 75°C and high humidity (MTHH) the ph of the cathode was lower than in the HTHH. The electrical conductivity was higher at the anode and cathode at 75°C than at 90°C. The lowest pH of the preliminary investigations was achieved in the test with low temperature and high humidity (LTHH). The cathode side presented a pH of 5,51 and also the highest electrical conductivity with a value of 12,75 $\mu \mathrm{S} / \mathrm{cm}$ after two hours of voltage cycling at a cell and cooling temperature of 60°C.
+
+The results measured at a high pH is in accordance with the study performed by Abdullah et al. since an increase of the pH with an increase of the temperature. Although the increase of the temperature from 50°C to 90°C at a relative humidity of 35\% showed a pH increase from 2 to 5 \citep{107_abdullah2008effect}. The increase of the pH from 5,51 to 6 at the cathode by raising the cell temperature from 60°C to 90°C although noticeable is still much smaller than the one found in the study performed by Abdullah et al.
+
+The difference in the pH measured in the preliminary investigations to the one found in literature could be attributed to two main factors. The first one being the duration of the test. Since the conducted tests had a relative short operating time with a 2 hours of voltage cycling compared to the minimum of 30 hours of Abdullah et al. the membrane had little to no degradation resulting in a much lower amount of H$_2$O$_2$ produced as a result of membrane degradation \citep{wallnofer2024main, 107_abdullah2008effect}. The second reason for the higher pH could be the use of the type 1 cell made out of Ti-C. The corrosion resistance of Ti is much higher than the one of stainless steel, consequently less particles will leave the BP because of corrosion \citep{Corr_Mat_wang2010electrochemical}. Since the fenton mechanism is catalysed by metal ions such as Fe$^{2+}$ the membrane degradation caused by this reaction will be less when using Ti BPs \citep{elferjani_coupling_2021}.
+
+\section{Corrosion Endurance Run}
+\label{sec:4_Corrosion}
+
+Following the results of the preliminary investigation the decision was made to lower the temperature from the endurance run from 90 to 66°C in order to produce a more acid product water and therefore reinforce the corrosion mechanism. For both endurance runs cells type 2 were used since the type 1 cells made out of Ti-C have a higher corrosion resistance. After the test Bench was successfully tested with a 4 cell stack made out of type 1 cells to avoid any damage to the 4 cell stack made out of type 2 (that could have been caused by a malfunction of a test bench) the corrosion endurance run could be started. The results of the in in-situ characterization of the cells will be presented in a more detailed way in the following section.
+
+\subsection{Polarization Curves at 60°C}
+\label{subsec: 60_PolCurve}
+
+After the test specimen was activated by repeating the 80°C polarization curve four times in a row until the performance of the cell was optimal for the endurance run to start. Before beginning the endurance run the cell underwent a beginning-of-life (BoL) characterization which included the polarization curves at 60°C and 80°C. The results of the BoL characterization as well as those after 12500 , 37500 and 81000 cycles are shown in figure\ref{fig:60_Pol}. It is also worth mentioning, that the stoichiometry of cathode and anode was constant at $\lambda_{air}$ = 2  and $\lambda_{H_2}$ = 1,5 throughout the 60°C and 80°C polarization curves after the current density was increased above 0,3 A/cm$^2$ and therefore the minimum volume flow of the test bench was also surpassed (see appendix \ref{sec:A_Sto}). 
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/60_PolCurve_Korrosion.pdf}
+	\caption{60°C polarization curve at BoL after 12500 VC, 37500 VC and 81000 VC.}
+	\label{fig:60_Pol}
+\end{figure}
+
+At low current densities the BoL curve shows the highest Voltage and therefore the lowest activation polarization. The second best curve at low current densities is the polarization curve after 81000 VC at the end of the endurance run. When the current density is increased to over 0,6 A/cm$^2$ the the curve after 81000 VC shows a higher loss compared to the other ones. At high current dentities the curve after 81000 VC presents higher losses than the other curves. The degradation of the test specimen over the period of the 81000 VC is made clear since the voltage of the curves decreases after each characterization with the BoL curve being the one with the least losses followed by the  12500 VC as well as the 37500 VC and the highest loss at high current densities after the last characterization at 81000 VC.
+
+
+\subsubsection{High-Frequency Resistance (HFR)}
+
+The high-frequency resistance (HFR) was also measured during the polarization curves since it gives an insight on the performance of the cell. A lower HFR can indicate a higher performance as well as better hydration of the membrane \citep{108_lin2021prediction}. The results of the measurements during the 60°C polarization curves can be found in the following figure \ref{fig:60_HFR}.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/60_HFR.pdf}
+	\caption{HFR during the 60°C polarization curve at the BoL, after 12500 VC, 37500 VC and 81000 VC.}
+	\label{fig:60_HFR}
+\end{figure}
+
+The curves of the BoL and after 12500 cycles show a peak in the HFR at the beginning of the test and at very low current densities (under 0,2 A/cm$^2$). Moreover, the after 37500 cycles the HFR is still low at very low current densities when compared to the curve after 81000 VC. When current densities are increased in the polarization curves the HFR of the curves after 12500 VC and after 37500 VC decreases while the curve after 81000 VC shows an very stable and low value of around 50,5 $m\Omega\cdot\text{cm}^2$ per cell.
+
+The peaks at the beginning are likely to be caused by the high cathode and anode stoichiometry at low current densities until the volume flow can be increased from the minimum (5,6 Nl/min at anode and 11,36 Nl/min cathode until 0,3 A/cm$^2$) with the increasing current densities. The initial increase in HFR was also detected by Ma et al. until the cell reaches a final stable HFR \citep{109_ma2022effect}. This can also be seen in the last polarization curve after 81000 VC when a stable HFR value of around 50,5 is reached and maintained throughout the curve.
+
+
+\subsubsection{60°C Polarization Curves of the Cells after 81000 VC}
+
+Since the voltage decrease was the highest in the EoL polarization curve after 81000 VC the voltage and polarization curves was also analysed to be able to get a better overview of the degradation in the cells. The results of the 60°C polarization curve of each of the 4 cells in the stack is presented in Figure \ref{fig:60_Cells}.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/60_Cells.pdf}
+	\caption{60°C polarization curves of the 4 cells after 81000 VC.}
+	\label{fig:60_Cells}
+\end{figure}
+
+At very low current densities cells 1-4 have roughly the same voltage loss. As current density increases the voltage loss of the cells increases as well with the first cell showing the highest voltage at 0,6V and the others decreasing in numerical order until the lowest voltage detected in the cell 4 with 0,53V. Due to the significant difference between the voltage in cell 1 and the cell 4 at high current densities both cells will be analysed in greater detail in the ex-situ investigations in section \ref{sec: Ex-Situ}.
+
+The higher RH of the 60°C polarization curve could have caused a high concentration polarization at high current densities. Since the RH is at 50,6 \% the higher water content could have limited the transport of the reactants to the reaction site in the cell 4. Another reason could have been the corrosion of the plates. If the MEA at the cell 4 was degraded due to the Fe$^{2+}$ catalysing the fenton reaction when set free due to the corrosion of the BP leading the cell 4 to a lower performance than the other cells \citep{elferjani_coupling_2021, frensch2019impact}.
+
+\subsection{Polarization Curves at 80°C}
+\label{subsec: 80_PolCurve}
+
+After the 60° polarization curve the temperature of the cell was increased to 80°C by increasing the coolant temperature ($T_{coolant,in}$), then the dew point temperatures ($T_{dp,A}$, $T_{dp,C}$) were increased to 53°C which results in a RH of 30,1\% for cathode and anode. The results from the 80°C polarization curves can be seen in Figure \ref{fig:80_Pol}.
+
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/80_PolCurve_Korrosion.pdf}
+	\caption{80°C polarization curve at BoL after 12500 VC, 37500 VC and 81000 VC.}
+	\label{fig:80_Pol}
+\end{figure}
+
+
+The 80°C polarization curve show almost no signs of degradation of the cells. The voltage at high current densities of 2,2 A/cm$^2$ are almost identical for all the curves at 0,59V which is the same as the value for the BoL voltage for the 60°C curve. At a low current density of 0,1 A/cm$^2$ the BoL curve is slightly better than the other ones. It is also noticeable, that the 81000VC curve is better than the 37500 VC and the 12500 VC curve has the lowest value at this current density. At a higher current density of 1,4 - 1,6 A/cm$^2$ the the BoL curve has a slightly higher average voltage than the other curves.
+
+Overall the 80°C polarization curves present much lower degradation than the 60°C polarization curve. One reason for this could be the lower RH value of 30,1\% of this polarization curve when compared to the RH 50,6\% which can be found in the 60°C curve. The higher humidity of the 60°C curve could lead to a much higher activation polarization which is heavily influenced by the hydration of the membrane \citep{jouin2016}. The ohmic loss at higher current densities is very similar for all the curves since they are almost parallel to each other until the end. 
+
+In addition, the effects of the mass transport losses that could have made a great difference at very high current densities cannot be significantly detected in the figures. A reason for this could be the high stoichiometry used in both cathode and anode. Since there is more reactant than needed at the active sites even the a high reaction rate at high current densities will not consume all the reactants and limit the reaction like it would at a lower stoichiometry
+\citep{Loss_mazzeo2024assessing}.
+
+
+
+\subsubsection{High-Frequency Resistance (HFR)}
+
+The HFR measured during the 80° polarization curves is presented in Figure \ref{fig:80_HFR}. At very low current densities (under 0,2 A/cm$^2$) the BoL, 12500 and 37500 curves show a peak of 160 $m\Omega\cdot\text{cm}^2$ per cell. For the 81000 VC curve the peak is not as high with a start value of around 62 $m\Omega\cdot\text{cm}^2$ per cell. 
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/80_HFR.pdf}
+	\caption{HFR during the 80°C polarization curve at the BoL, after 12500 VC, 37500 VC and 81000 VC.}
+	\label{fig:80_HFR}
+\end{figure}
+
+The 81000 VC curve is the first one to reach a stable HFR at 51 $m\Omega\cdot\text{cm}^2$ per cell. The 37500 VC and the 12500 VC curves reach a stable HFR at a current density of 0,3 A/cm$^2$. At a current density of 2,2 A/cm$^2$ the BoL curve has the highest HFR followed by the 37500 VC and the 12500 VC curves.
+
+Just like in the 60°C polarization curve the lowest HFR was measured in the 81000 VC curve. A reason for this could be that the membrane has reached an optimal level of humidity to reach a lower HFR at 51. In the investigations by Ma et al. the peak at the beginning was also measured and then quickly reached its stable HFR \citep{109_ma2022effect}.
+
+\subsubsection{80°C Polarization Curves of the Cells after 81000 VC}
+
+Figure \ref{fig:80_Cells} displays the 80°C polarization curve after 81000 VC of each cell separately. Cell 1 is again the best performing cell just like in the 60°C curve. Cells 2, 3 and 4 show a very similar voltage at high current densities of 2,2 A/cm$^2$ with the highest voltage after cell 1 belonging to cell 4 although the voltages of cells 2, 3 and 4 are very similar and do not show a significant decrease in the performance compared to each other.
+ 
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/80_Cells.pdf}
+	\caption{80°C polarization curves of the 4 cells after 81000 VC.}
+	\label{fig:80_Cells}
+\end{figure}
+
+%Discussion Overall performance at 80°C better than at 60°C discuss??
+
+\section{High Temperature Endurance Run}
+\label{sec:4_High Temp}
+
+The high temperature endurance run was conducted on the same model of test bench as the corrosion endurance run and also at the same time. The same activation sequence with four 80°C polarization curves was performed for the activation of the 4 cell stack. The cell temperature was ramped up to 103°C with a dew point temperature at 72°C at the anode and 85°C at the cathode. This leads to a RH of 30,1\% at the anode and 51,3\% at the cathode and consequently lower than the 36,65\% at the anode and 54,66\% of the cathode of the corrosion endurance run. The high temperature endurance run could not be completed due to the formation of pinholes in the cell which created a leak between anode anode cathode. However, the BoL and the characterization after 12500 VC was completed and its findings will be explained in the following. 
+
+\subsection{Polarization Curves at 60°C}
+\label{subsec: 60_PolCurve_HT}
+
+The results of the BoL characterization and the characterization of the cell after 12500 VC can be found in the Figure \ref{fig:60_Pol_HT}. The BoL curve has a  slightly higher average cell voltage at current densities ranging from 0,1 to 1 A/cm$^2$ as well as from 1,6 to 2,2 A/cm$^2$.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/60_PolCurve_HT.pdf}
+	\caption{60°C polarization curve at BoL and after 12500 VC.}
+	\label{fig:60_Pol_HT}
+\end{figure}
+
+Between 1 and 1,6 A/cm$^2$ the 60° polarization curve after 12500 VC has a slightly better performance as the BoL curve. This could be attributed to a better humidity level of the membrane leading to a lower ohmic voltage loss and a better performance in that section \citep{108_lin2021prediction}
+
+
+\subsubsection{High-Frequency Resistance (HFR)}
+
+Figure \ref{fig:60_HFR_HT} illustrates the measured HFR during the two 60°C polarization curves. Both curves show a peak in the HFR of 64,4 $m\Omega\cdot\text{cm}^2$ per cell at the lowest current densities (<0,1 A/cm$^2$). After the initial peak the HFR of the 12500 VC curve stays lower than then HFR of the BoL curve.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/60_HFR_HT.pdf}
+	\caption{HFR during the 60°C polarization curve at the BoL.}
+	\label{fig:60_HFR_HT}
+\end{figure}
+
+The 12500 VC curve has the lowest HFR between the current densities of 1 and 1,6 A/cm$^2$ and reaches the lowest point at an HFR of around 50,7 $m\Omega\cdot\text{cm}^2$ per cell. At a current density of 2,2 A/cm$^2$ the BoL curve has a  HFR of 56,7 while the 12500 VC curve has a HFR of 51,8 $m\Omega\cdot\text{cm}^2$ per cell.
+
+The sudden drop of the HFR of the 12500 VC curve to the lowest points at the current densities between 1 and 1,6 A/cm$^2$ could explain the performance boost as the activation losses are compensated at this point due to a lower ohmic loss in this section \citep{108_lin2021prediction}. 
+
+\subsubsection{60°C Polarization Curves of the Cells after 12500 VC}
+
+Figure \ref{fig:60_Cells_HT} shows the voltage of the 4 cells at the different current densities during the 60°C polarization curve. Cell 4 presents the lowest voltage with a value of  0,57V while cell 1 has the highest voltage of the cells with a value of 0,6V at a current density of 2,2 A/cm$^2$ after 12500 VC. 
+
+Meanwhile the cell 4 of the corrosion endurance run after the 12500 VC at 2,2 A/cm$^2$ had a voltage of 0,58V. Therefore, a higher degradation of the cell can already be seen at this early stage after just 12500 VC.
+
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/60_Cells_HT.pdf}
+	\caption{60°C polarization curves of the 4 cells after 12500 VC.}
+	\label{fig:60_Cells_HT}
+\end{figure}
+
+This increased degradation of the cell 4 compared to the corrosion endurance run after the same number of cycles could be caused by the Pt dissolution and redeposition resulting in a loss of the electrochemical surface area (ECSA). This mechanism is influenced by high temperatures as well as high water content in the ionomer which are the exact conditions in after the first cycle of the high temperature endurance run as well as in the 60°C polarization curve with the high RH \citep{wallnofer2024main}.
+
+
+\subsection{Polarization Curves at 80°C}
+\label{subsec: 80_PolCurve_HT}
+
+The results of the in-situ characterization with the 80°C polarization curve of the high temperature are presented in the following Figure \ref{fig:80_Pol_HT}. With a decrease in the RH due to the 80°C characterization method both curves show almost the same voltage at the highest tested current density of 2,2 A/cm$^2$.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/80_PolCurve_HT.pdf}
+	\caption{80°C polarization curves at BoL after 12500 VC.}
+	\label{fig:80_Pol_HT}
+\end{figure}
+
+At very low current densities the BoL curve has a slightly higher voltage than the 12500 VC curve. The higher activation loss at the beginning could be caused by a degradation of the Pt catalyst when compared to the BoL \citep{jouin2016}.
+
+At higher current densities the 12500 VC curve shows a lower ohmic resistance and is therefore able to compensate the first losses until at the highest current desensitise it has the same voltage as the BoL curve. The HFR which will be shown in the following could explain this behaviour.
+
+
+\subsubsection{High-Frequency Resistance (HFR)}
+
+The HFR of the cells during the 80°C polarization curve of the high temperature endurance run are depicted in the following Figure \ref{fig:80_HFR_HT}. At low current densities the HFR of both curves peaks at a maximum value of 168 $m\Omega\cdot\text{cm}^2$ per cell and then quickly stabilizes at a lower HFR value of around 57 $m\Omega\cdot\text{cm}^2$ per cell.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/80_HFR_HT.pdf}
+	\caption{HFR during the 80°C polarization curve at the BoL, after 12500 VC.}
+	\label{fig:80_HFR_HT}
+\end{figure}
+
+The phenomena seen in the 80°C polarization curve at high current densities (above 1,6 until 2,2 A/cm$^2$) could be attributed to the lower HFR presented by the 12500 VC curve at this current densities. During the 12500 VC curve the membrane has a slightly better humidification an therefore is able to be more efficient and produce a better power output due to a lower ohmic voltage loss \citep{108_lin2021prediction}. 
+
+
+\subsubsection{80°C Polarization Curves of the Cells after 12500 VC}
+
+Figure \ref{fig:80_Cells_HT} shows the voltage of the 4 cells at the different current densities during the 80°C polarization curve after 12500 VC. Cell 1 has the highest voltage of the cells at high current densities (2,2 A/cm$^2$) while the other cells (2, 3, 4) have almost the same voltage at 0,58V.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/80_Cells_HT.pdf}
+	\caption{80°C polarization curves of the 4 cells after 12500 VC.}
+	\label{fig:80_Cells_HT}
+\end{figure}
+
+Although the activation losses of all the cells are almost the same, ohmic and polarization losses of the cells differ from each other. Therefore the voltage of cells 2,3 and 4 is under 0,6V.
+
+
+Ma et. al. suggests that higher the initial HFR peak and the temperature of the cell are more time will be needed to reach a stable HFR \citep{109_ma2022effect}. This was validated with the results of the HFR on the high temperature endurance run and corrosion endurance run. The HFR of the high temperature endurance run had a higher peak at 168 $m\Omega\cdot\text{cm}^2$ per cell on the 80°C polarization curve and reached a stable HFR after a current density of 0,3 A/cm$^2$. Meanwhile the corrosion endurance run and its 60°C polarization curve reached a lower HFR much faster since the peak was only at 64,4  $m\Omega\cdot\text{cm}^2$ per cell and the 81000 VC did not have a peak at all.
+
+Furthermore the significant decrease in the voltage at high current densities of the cell 4 from the corrosion endurance run at the 60°C polarization curve after 81000 VC will be further investigated using the ex situ-methods in the next section.
+
+\newpage
 
-\subsubsection{Department of Energy Target}
 
-\section{pH Measurement}
 
-\section{Endurance Run}
 
-Betriebsbedingungnen  soll ist vergleich 
 
-\subsubsection{Polarization Curves}
 
-\subsubsection{Effects of Relative Humidity in the Air}
 
-\subsection{Product Water Analysis}
 
 
 \section{Ex-Situ Analysis}
 
+After the corrosion endurance run the cells were brought to the laboratory for further investigation. To avoid contamination the cells were opened in a clean room and then underwent a microscopical, LIBS and REM/EDX analysis. Since the cell 4 presented a significantly higher voltage loss than the cell 1 in the 60°C polarization curve after 81000 VC of the corrosion endurance run this two cells will be compared to a reference cell. The results of this analysis will be presented in the following section starting with the microscopical analysis in Section \ref{subsec:4_Microscope}. 
+
+
+\subsection{Microscopical Analysis}
+\label{subsec:4_Microscope}
+
+The microscopical analysis focuses its attention on the positions A6 and M1 of the BPs 1 and 4 as well as the cathode outlet. A6 refers to the position in the matrix shown in Figure \ref{fig:Matrix} at the cathode outlet while M1 is located at the cathode inlet. 
+
+\subsubsection{Analysis of the BPs}
+	% Vergleich von Referenz zu BP1
+\begin{figure}[htbp]
+	\centering
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_A6_1.pdf}
+		\caption{Reference BP position A6.}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_A6_2.pdf}
+		\caption{Reference BP position A6 x 100 ($\mu m$).}
+	\end{subfigure}
+	
+	\vspace{0.2cm}
+	
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_M1_1.pdf}
+		\caption{Reference BP position M1.}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_M1_2.pdf}
+		\caption{Reference BP position M1 x 100 ($\mu m$).}
+	\end{subfigure}
+		\caption{Microscopy Analysis of the BP: Stainless Steel 316L Reference BP.}
+	\label{fig:4_Micro_ref}
+\end{figure}
+
+Figure \ref{fig:4_Micro_ref} shows the results of the microscopy of the reference BP. An overview of the position A6 can be seen in the part (a) of the figure and for M1 in the part (c) of the figure. In the overview almost no discolourations were found except for the welding seams which presented a slight red and brown discolouration in the reference plate. A close-up of the channels between the C coated ribs in positions A6 and M1 did not show any particular defects in the metal.  
+
+Figure \ref{fig:4_Micro_BP1} shows the microscopy of the BP1 of the cell from the corrosion endurance run. The channels show no clear defects or signs of degradation after the 81000 VC conducted. On the other hand the discolouration at the welding seams is now more visible than in the reference plate. Over the flow field in the upper right corner of position M1 (\ref{fig:4_Micro_BP1} (c))  the BP also presents some scratches in the surface.
+
+
+\begin{figure}[htbp]
+	\centering	
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP1_A6_1.pdf}
+		\caption{BP1 position A6.}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP1_A6_2.pdf}
+		\caption{BP1 position A6 x 100 ($\mu m$).}
+	\end{subfigure}
+
+		\vspace{0.2cm}
+	
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP1_M1_1.pdf}
+		\caption{BP1 position M1}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP1_M1_2.pdf}
+		\caption{BP1 position M1 x 100($\mu m$)}
+	\end{subfigure}
+	\caption{Microscopic Analysis of the BP: Stainless Steel 316L BP1.}
+	\label{fig:4_Micro_BP1}
+\end{figure}
+
+The cell 4 of the stack had the highest voltage drop at high current densities through the 60°C polarization curve. Therefore the BP 4 was analysed under the microscope as well and the results can be seen in the following Figure \ref{fig:4_Micro_BP4}. The red and brown discolourations at the welding seam on the positions M1 and A6 are more visible than in the reference BP. The close-up of the channel in \ref{fig:4_Micro_BP4} (d) also shows defects in the material on the side of the channels. The top right corner of the BP 4 position M1 ( Figure 4.15 (c)) also shows scratches in the metal.
+
+\begin{figure}[h]
+	\centering	
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP4_A6_1.pdf}
+		\caption{BP4 position A6.}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP4_A6_2.pdf}
+		\caption{BP4 position A6 x 100 ($\mu m$).}
+	\end{subfigure}
+	
+	\vspace{0.2cm}
+	
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP4_M1_1.pdf}
+		\caption{BP4 position M1.}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP4_M1_2.pdf}
+		\caption{BP4 position M1 x 100 ($\mu m$).}
+	\end{subfigure}
+	\caption{Microscopic Analysis of the BP: Stainless Steel 316L BP4.}
+	\label{fig:4_Micro_BP4}
+\end{figure}
+
+However, the most significant difference between the BPs 1 and 4 can be seen at the cathode outlet in Figure \ref{fig:4_Micro_SP}. The BP 4 (\ref{fig:4_Micro_SP}(d)) has a severe red and brown discolouration whereas the outlet in the BP 1 (\ref{fig:4_Micro_SP} (b)) remains without discolourations. The edges of the cathode outlet in BP 4 also show signs of metal dissolution due to corrosion. 
+
+\begin{figure}[htbp]
+	\centering
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP1_Co_1.pdf}
+		\caption{BP1 Cathode Outlet.}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP1_Co_2.pdf}
+		\caption{BP1 Cathode Outlet x 100 ($\mu m$).}
+	\end{subfigure}
+	
+	\vspace{0.2cm}
+	
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP4_Co_1.pdf}
+		\caption{BP4 Cathode Outlet.}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP4_Co_2.pdf}
+		\caption{BP4 Cathode Outlet x 100 ($\mu m$).}
+	\end{subfigure}
+	
+	\vspace{0.2cm}
+	
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP4_A6_S.pdf}
+		\caption{BP4 A6 Welding Seam x 10 ($\mu m$).}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/M_BP4_M1_S.pdf}
+		\caption{BP4 M1 Welding Seam x 100 ($\mu m$).}
+	\end{subfigure}
+	
+	\caption{Microscopic Analysis of the BP: Stainless Steel 316L at the Cathode Outlet and Welding Seam.}
+	\label{fig:4_Micro_SP}
+\end{figure}
+
+Since the welding seam already showed signs of discolourations and corrosion in the reference plate without having conducted an endurance run this positions were analysed again in the BP 4 to look for damages. Figure \ref{fig:4_Micro_SP} (e) shows the welding seam in the position A6 of the BP 4. Across the lower part of this image three light coloured points stand out in the brown discoloured part, this could indicate three sites where pitting corrosion has already started.
+
+Welding seams are known to be a weak point for corrosion. Since the temperatures of the process causes a decomposition of the austenitic matrix. Cr and Mo are consumed by the formation of precipitates like carbides and cause Cr-depleted areas which are more vulnerable to corrosion \citep{yan2019effect}. 
+
+
+\newpage
+\subsubsection{Analysis of the CCM}
+
+Furthermore, the CCM will also be analysed to look for corrosion or Pt agglomeration, dissolution or any other damages. Since the CCM showed no increased damage at the positions A6 and M1 when compared to the other positions in the cell matrix this time the positions M6 and A1 will be analysed in greater detail. Figure \ref{fig:4_Micro_CCM} depicts the microscopical analysis of the CCMs from the cathode side of BPs 1 and 4.
+
+\begin{figure}[h]
+	\centering	
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/CCM_M_1_M6.pdf}
+		\caption{CCM cathode BP1 M6 x 200 ($\mu m$).}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/CCM_M_1_A1.pdf}
+		\caption{CCM cathode BP1 A1 x 200($\mu m$).}
+	\end{subfigure}
+	
+	\vspace{0.2cm}
+	
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/CCM_M_4_M6.pdf}
+		\caption{CCM cathode BP4 M6 x 200($\mu m$).}
+	\end{subfigure}
+	\begin{subfigure}{0.45\textwidth}
+		\centering
+		\includegraphics[width=\linewidth]{Figures/Results/CCM_M_4_A1.pdf}
+		\caption{CCM cathode BP 4 A1 x 200 ($\mu m$).}
+	\end{subfigure}
+	\caption{Microscopic Analysis of the CCM: Sx 200 ($\mu m$).}
+	\label{fig:4_Micro_CCM}
+\end{figure}
+
+Position M6 of the CCM from the BP 1 shows signs of Pt-agglomeration. The three small darker lines in that can be seen in this position are cracks in the CCM. Furthermore wave structures are also visible across all the positions. When looking at the position A1 of the CCM shown in \ref{fig:4_Micro_CCM} (b)
+the Pt agglomeration is even more visible in the bright spots. 
+
+The CCM from the cathode in BP 4 shown in  \ref{fig:4_Micro_CCM} (c) and (d) also shows signs of Pt agglomeration. Especially the bright parts in the position A1. Both position M6 and A4 show the same wave structures previously observed in the CCM of the cathode from the BP 1. Unlike BP 1 the image \ref{fig:4_Micro_CCM} (c) also present 4 darker spots which could be a part of the MPL which adhered to the CCM.
+
+The ORR reaction relies heavily on the Pt catalyst of the CCM which highlights the important role of Pt in the performance of the cell \citep{PEM_MEA_parekh2022recent}. The agglomeration process can increase the hydrophilicity of the carbon support which consequently can lead to to more water in the cell and in some cases flooding of the cell. This could also lead to a limited amount of oxygen reaching the active sites and a decrease of the cell performance \citep{okonkwo2021platinum}. The Pt agglomeration will be further investigated using the REM and EDX.
+
+
+
 \subsection{LIBS Measurement}
+\label{subsec:4_LIBS}
 
-\subsection{EDX Measurement}
+In order to further evaluate the discolourations found in the BP4 and to provide a better insight into the conditions of the stainless steel 316L plate and its possible corrosion and loss in performance, an additional LIBS analysis was conducted. First the positions M1 and A6 of the BP4, where the relative atomic concentrations of its components were compared to those of the reference BP. The results of this analysis can be found in the Figures \ref{fig:LIBS_M1} and \ref{fig:LIBS_A6}.
 
-\subsection{SEM Measurement}
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.7\textwidth]{Figures/Results/LIBS_M1.pdf}
+	\caption{LIBS: Comparison of the position M1 of BP4 with the reference plate.}
+	\label{fig:LIBS_M1}
+\end{figure}
 
-\subsection{ICP Measurement}
+When comparing the position M1 of the BP4 with the reference plate the BP4 shows a light increase of the oxygen concentration as well as a decrease in carbon. Although the increase in oxygen is clear, the standard deviation of the 16 points measured on the carbon is to high on as to be able to draw any conclusions. The standard deviation of Fe, Ni and Cr is as large as the difference measured from the reference plate to the BP making it imposable to draw a conclusion from this change. Since the position M1 did not present any discolourations it could be possible that only a light oxide layer started to appear on it.
+
+Figure \ref{fig:LIBS_A6} compares the position A6 from the BP 4 to the reference plate. Since the microscopy of position A6 did not present any discolourations or alterations of the BP this result is also reflected in the LIBS measurement.
+
+\begin{figure}[H]
+	\centering
+	\includegraphics[width=0.7\textwidth]{Figures/Results/LIBS_A6.pdf}
+	\caption{LIBS: Comparison of the position A6 of BP4 with the reference plate.}
+	\label{fig:LIBS_A6}
+\end{figure}
+
+The increase on oxygen is even less noticeable than in the comparison of M1 to the reference plate. The other elements stay have the same concentrations as in the reference plate which does not indicate corrosion in this part of the cell.
+
+However, the cathode outlet showed a significant difference when analysed with the microscope. Therefore the cathode outlet of the BP 1 and BP 4 were compared with the one of the reference plate. The result of this comparison can be found in the following Figure \ref{fig:LIBS_Cathode}.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.7\textwidth]{Figures/Results/LIBS_Cathode Outlet.pdf}
+	\caption{LIBS: Comparison of the cathode outlet of the BP 1, BP 4 and the reference BP.}
+	\label{fig:LIBS_Cathode}
+\end{figure}
+
+BP 4 shows a significant decrease in carbon of almost 23\% compared to the reference plate as well as the BP 1. In addition, a decrease in Cr and Ni of the BP 4 is also detected by the LIBS. BP 4 also shows an increase of 12\% in the oxygen concentration compared to the BP 1. This increase shows clear signs of the formation from an oxide layer which could explain the discolouration found in Figure  \ref{fig:4_Micro_SP}. This oxide layer is also a clear sign for corrosion in the cell since the corrosion reaction causes the formation of a passive oxide layer.
+
+Since the welding seam also showed a clear discolouration across the reference plate and was even more visible on the BP 1 and BP 4 after the corrosion endurance run it was also analysed using LIBS. The results of the comparison from the welding seam in position A6 of the BP 4 with the reference plate can be seen in the following Figure \ref{fig:LIBS_Sonderpositionen}.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.7\textwidth]{Figures/Results/LIBS_Sonderposition.pdf}
+	\caption{LIBS: Comparison of the welding seam in position A6 of the BP 4 with the reference plate.}
+	\label{fig:LIBS_Sonderpositionen}
+\end{figure}
+
+When comparing the welding seam to the reference plate it is visible, that the oxygen percentage increases around 8\% showing sings of the formation of an oxide layer \citep{laedre2017materials}. Furthermore the decrease in carbon can also be detected at the welding seam. The high standard deviation of Fe makes it impossible to evaluate the decrease in the concentration. Since the concentration change in Cr, Ni and Mo was barely noticeable, it is also not possible to make a final conclusion about this metals.
+
+ Due to the fact, that welding seams are more susceptible to corrosion as mentioned before the discolouration seen at in this spots as well as the increased oxygen percentage measured by the LIBS the corrosion can be confirmed \citep{yan2019effect}. The protective oxide layer created by the metal could also lead to a higher ohmic resistance due to a less reactive oxide layer formed to protect the metal from corrosion \citep{105_novalin2022concepts}.
+
+
+\subsection{SEM/EDX Measurement}
+\label{subsec:4_SEM/EDX}
+
+The final section of this chapter will present the results of the SEM and EDX measurements of the CCM. The Fenton mechanism mentioned in the theoretical background \ref{subsec:membrane degradation} is responsible for the membrane degradation and can be catalysed with Fe$^{2+}$ as well as other metal ions from the BP. Therefore, the CCM of the cathode was analysed using SEM and EDX in order to find traces of metal which could have come from the BP and travelled from there to the MPL, GDL or CCM and into the membrane during the corrosion process of the BP and whit its dissolution from the BP.
+
+\subsubsection{CCM BP 1}
+
+The results of the SEM and EDX analysis of the cathode CCM from BP 1 is presented in the following Figure \ref{fig:REM_4_A1}. Since the microscopical analysis performed in \ref{subsec:4_Microscope} showed a Pt agglomeration it was further analysed with SEM and EDX.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.8\textwidth]{Figures/Results/CCM_REM_BP1_A1.pdf}
+	\caption{REM/EDX of the CCM at the position A1.}
+	\label{fig:REM_1_A6}
+\end{figure}
+
+As seen in Figure  \ref{fig:REM_4_A1} no traces of Fe, Ni or Cr could be found in the CCM of the BP 1. The Pt agglomeration could be proved with the spectrum since the Pt peak was found in the position A1 of the CCM. The results of the position M6 did not confirm any traces of Fe, Ni or Cr and can be found in the appendix \ref{sec: A_REM/EDX}.
+
+
+\subsubsection{CCM BP 4}
+
+Since the BP 4 showed clear signs of corrosion in the microscopy and in the LIBS analysis as well as a Pt-agglomeration in the CCM this was also furher analysed with SEM and EDX. The results of both SEM and EDX analysis of the cathode CCM from the BP 4 at the position A1 are presented in the following Figure \ref{fig:REM_4_A1}.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.8\textwidth]{Figures/Results/CCM_REM_BP4_A1.pdf}
+	\caption{REM/EDX of the CCM 4 at the position A1.}
+	\label{fig:REM_4_A1}
+\end{figure}
+
+Even though the BP 4 corroded, still no traces of Fe, Ni or Cr could be found in the CCM and therefore the EDX showed no peak of any of the aforementioned elements. However, the Pt- agglomeration was also visible with a peak in Pt shown in the EDX analysis.
+
+A reason for this could be the duration of the endurance run. The corrosion endurance run only lasted 400 hours which compared to the 8000 hours the lifetime could have resulted in a much lower degradation of the BP due to corrosion and consequently a much lower concentration of metal ions being released from the BP to the membrane through the CCM.
+
+As mentioned by Low et al. the the MEA is very vulnerable to metallic poisoning. When the oxidation process starts the metallic cations migrate from the BP through the cell and cause a greater membrane degradation and also cause a higher ohmic resistance due to the reduced ionic conductivity \citep{low2024understanding}.
+
+A study performed by Novalin et al. analysed also analysed the metal ion dissolution from the BPs as a result of cycling measurement. They were able to find traces of Fe, Ni and Cr in the GDL and MEA after 700 cycles and a RH of 66\% and a stoichiometry of 2 at the anode and 2,5 at the cathode (higher than in the corrosion run). Novalin concluded, that dryer conditions enhance repassivation mechanisms of the metal BP which makes the transport of the metal ions to the MEA  less probably \citep{105_novalin2022concepts}.
+
+Lastly, since the Pt agglomeration was identified by the microscopy and the EDX analysis it is also worth discussing. Pt agglomeration could also be a factor influencing the activation losses due to the possible loss of ECSA produced by the voltage cycling
+\citep{Pol_thiele2024realistic}.
+
+%\subsection{SEM Measurement}
+
+%\subsection{ICP Measurement}
 

Content/Theoretical Background.tex

@@ -2,26 +2,27 @@
 \label{cap: Theorie}
 
 
-In this chapter, the fundamental concepts and components of fuel cells are explored to provide a comprehensive understanding of Proton Exchange Membrane Fuel Cells (PEMFCs). Section 2.1 covers the basic principles of fuel cells, followed by Section 2.2, which delves into the electrochemical fundamentals, including the thermodynamics of the cell (2.2.1). Section 2.3 focuses specifically on PEMFCs, discussing their operation (2.3.1), overpotential (2.3.2), and methods of characterization (2.3.4). Finally, Section 2.4 examines degradation mechanisms in PEMFCs, detailing the degradation of the platinum catalyst (2.4.1), membrane degradation (2.4.2), electrochemical carbon corrosion (2.4.3), and overall corrosion processes (2.4.4). This structure lays the groundwork for understanding the challenges and performance factors of PEMFCs in practical applications.
+In this chapter, the fundamental concepts and components of fuel cells are explored to provide a comprehensive understanding of Proton Exchange Membrane Fuel Cells (PEMFCs). Section 2.1 covers the basic principles of fuel cells, followed by Section 2.2, which explores electrochemical fundamentals, including the thermodynamics of the cell (2.2.1). Section 2.3 focuses specifically on PEMFCs, discussing their operation (2.3.1), overpotential (2.3.2), and methods of characterisation (2.3.4). Finally, Section 2.4 examines degradation mechanisms in PEMFCs, detailing the degradation of the platinum catalyst (2.4.1), membrane degradation (2.4.2), electrochemical carbon corrosion (2.4.3), and general corrosion processes (2.4.4). This structure lays the groundwork for understanding the challenges and performance factors of PEMFCs in practical applications.
 
 
 \section{Fundamentals of the Fuel Cell}
 \label{sec: Revox}
 
-As said in the introduction, the clear impact of the GHG emissions and specially of the CO$_2$ emissions on climate change and the environment is undeniable. Therefore, new technologies such as fuel cells with almost no emissions and also no noise pollution are becoming a promising alternative to conventional Internal combustion engines (ICEs). This engines continue to depend on fossil fuels to function, whereas fuel cells run on hydrogen and air which undergo an electrochemical reaction within the fuel cell to generate electrical power, this reaction results in water as a byproduct\citep{01_wilberforce_advances_2016,02_baroutaji2015materials}.
+As mentioned in the introduction, the clear impact of GHG and especially CO$_2$ emissions on climate change and the environment is undeniable. Therefore, new technologies such as fuel cells with practically zero emissions as well as no noise pollution are becoming a promising alternative to conventional internal combustion engines (ICEs). These engines continue to depend on fossil fuels to function, whereas fuel cells run on hydrogen and air undergoing electrochemical reactions within the fuel cell to generate electrical power. This reaction results in water as a byproduct \citep{01_wilberforce_advances_2016,02_baroutaji2015materials}.
-Battery electric vehicles (BEVs) are another alternative to ICEs which could also lower GHG as well as CO$_2$ emissions but only if the electric energy is also produced by renewable sources. However, when comparing fuel cells with BEVs there are some advantages that are worth mentioning. Fuel cells can be recharged almost instantly like ICEs and unlike BEVs. Besides that fuel cells can also run on other fuels and not only on pure Hydrogen depending on the fuel cell type. Fuel cells do not need to be disposed like Batteries and have a much longer operation time. Last but not least fuel cells have a wider range of temperatures in which they can be operated \citep{01_wilberforce_advances_2016, 02_lucia2014overview}.
+Battery electric vehicles (BEVs) are another alternative to ICEs that could lower GHG and CO$_2$ emissions, but only if the electric energy is also produced via renewable sources. However, when comparing fuel cells with BEVs there are some advantages worth mentioning. Fuel cells, like ICEs, can be
+recharged almost instantly; a feature that BEVs do not share. Besides this, fuel cells may also run on other fuels and not just on pure hydrogen. This does however depend on fuel cell type. Fuel cells do not need to be disposed of like batteries and have a much longer operation time. Finally, fuel cells have a wider range of temperatures in which they may be operated \citep{01_wilberforce_advances_2016, 02_lucia2014overview}.
 
-Before continuing into the way of operation and the electrochemistry behind the fuel cell, it is essential to briefly explain the different types of fuel cells. These can be categorized based on the type of electrolyte membrane they use into solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MFCSs), alkaline fuel cells (AFCs) and the most important one for this Thesis: polymer electrolyte membrane fuel cells (PEMFCs)\citep{02_wang2020fundamentals}. Also depending on the fuel cell type, operating temperatures may vary between -40 to almost 1000°C which will be explained in the following\citep{02_Abderezzak2018}.
+Before continuing into the mode of operation and electrochemistry behind the fuel cell, it is essential to briefly explain the various types of fuel cells. These may be categorised based on the type of electrolyte membrane they use: solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MFCSs), alkaline fuel cells (AFCs) and the most important for this thesis: polymer electrolyte membrane fuel cells (PEMFCs)\citep{02_wang2020fundamentals}. Also depending on the fuel cell type, operating temperatures may vary between -40 to almost 1000 °C. This phenomenon will be explained in the following\citep{02_Abderezzak2018}.
 
 \subsubsection{Solid Oxide Fuel Cells (SOFCs)}
 
-The operating temperatures of SOFCs is higher than in the other types of fuel cells ranging from 500 to 1000 °C \citep{SOFC_hauser2021effects}. This high operating temperature allows the fuel cell to run not only on pure hydrogen but with gases which also contain methane (CH$_4$), carbon dioxide (CO$_2$) as well as carbon monoxide (CO), water vapour (H$_2$O) and hydrogen H$_2$ \citep{SOFC_lin_analysis_2024}. If the anode fuel has CH$_4$ and water vapour in it, the methane (CH$_4$) can be reformed in the fuel cell by the process of steam reforming shown in the equation \ref{eq:Steam reforming} which will produce hydrogen (H$_2$)and carbon monoxide (CO) \citep{SOFC_Haberman2004}.
+The operating temperatures of SOFCs is higher than in the other types of fuel cells. They range from 500 to 1000 °C \citep{SOFC_hauser2021effects}. This high operating temperature allows the fuel cell to run not only on pure hydrogen but also with gases which also contain methane (CH$_4$), carbon dioxide (CO$_2$) as well as carbon monoxide (CO), water vapour (H$_2$O) and hydrogen H$_2$ \citep{SOFC_lin_analysis_2024}. If the anode fuel has CH$_4$ and water vapour in it, the methane (CH$_4$) may be reformed in the fuel cell by the process of steam reforming as shown in the equation \ref{eq:Steam reforming}, producing hydrogen (H$_2$)and carbon monoxide (CO) \citep{SOFC_Haberman2004}.
 \begin{equation}
 	\mathrm{CH}_4+\mathrm{H}_2 \mathrm{O} \leftrightarrow \mathrm{CO}+3 \mathrm{H}_2, \Delta H_{298}=2.06 \times 10^5 \mathrm{KJ} / \mathrm{Kmol}
 	\label{eq:Steam reforming}
 \end{equation}
 
-Another internal reaction is the water-gas-shift reaction which can turn carbon monoxide and water vapour into carbon dioxide and hydrogen in the SOFC as shown in the following equation \ref{eq:WGS} \citep{SOFC_lin_analysis_2024,SOFC_WGS_Buttler2016}.
+Another internal reaction is the water-gas-shift reaction, which can turn carbon monoxide and water vapour into carbon dioxide and hydrogen in the SOFC as shown in the following equation \ref{eq:WGS} \citep{SOFC_lin_analysis_2024,SOFC_WGS_Buttler2016}.
 
 \begin{equation}
 	\mathrm{CO}+\mathrm{H}_2 \mathrm{O} \leftrightarrow \mathrm{CO}_2+\mathrm{H}_2, \Delta H_{298}=-4.1 \times 10^4 \mathrm{KJ} / \mathrm{Kmol}
@@ -31,16 +32,16 @@ Another internal reaction is the water-gas-shift reaction which can turn carbon
 
 \subsubsection{Molten Carbonate Fuel Cells (MCFCs)}
 
-MCFCs are also high temperature cells with an operating temperature of about 600 to 700 °C and a Electrolyte made out of molten carbonate (CO$_3$$^{2-}$). Like SOFCs they can also be operated not only with pure hydrogen (H$_2$) but also with biogas which could also contain CH$_4$ as well as CO$_2$ and CO \citep{02_lucia2014overview, 02_wang2020fundamentals}.
+MCFCs are also high temperature cells with an operating temperature of about 600 to 700 °C and a electrolyte made out of molten carbonate (CO$_3$$^{2-}$). Like SOFCs, they can also be operated with both pure hydrogen (H$_2$) and biogas, which could also contain CH$_4$ as well as CO$_2$ and CO \citep{02_lucia2014overview, 02_wang2020fundamentals}.
-Therefore, SOFCs and MCFCs do not any external reformer to convert other fuel types into H$_2$ as they use the same reforming reactions from the equations \ref{eq:Steam reforming} and \ref{eq:WGS}
+As such, SOFCs and MCFCs do not require any external reformers to convert other fuel types into H$_2$ as they use the same reforming reactions from the equations \ref{eq:Steam reforming} and \ref{eq:WGS}
 \citep{MCFScontreras2021molten}.
-It is also possible to combine SOFC and MCFC with working temperatures of 550-700°C which are slighlty higher than a normal MCFC at 650
+It is also possible to combine SOFC and MCFC with working temperatures of 550-700 °C which are slighlty higher than a normal MCFC at 650 °C
-\citep{MCFS_cui2021review}. Furthermor, the electrical efficiency of the MCFCs can reach up to 60\% \citep{wang_preparation_2018}.
+\citep{MCFS_cui2021review}. Furthermore, the electrical efficiency of the MCFCs can reach up to 60\% \citep{wang_preparation_2018}.
 
 
 \subsubsection{Alkaline Fuel Cells (AFCs)}
 
-For AFCs the operating temperature is about 50-200 °C which is much lower than those of the SOFC and MCFC but a lot closer to the temperature in which PEMFCs are operated \citep{02_wang2020fundamentals}. Another main difference between AFCs and SOFCs is, that the electrolyte in a AFC is liquid unlike the solid state of the ceramics used in SOFCs. AFCs uses a potassium hydroxide solution (KOH) as an electrolyte which is embedded in the matrix \citep{02_Abderezzak2018,02_wang2020fundamentals}. Unlike SOFCs and MCFC and due to the lower temperature, AFCs can be poisoned by carbon dioxide (CO$_2$). In that case, the alkaline electrolyte could  react directly with the CO$_2$ which could lead to the the following reaction equations \ref{eq:AFC_Poisoning} \citep{AFC_mclean2002assessment}:
+For AFCs, the operating temperature is about 50-200 °C, much lower than that of the SOFC and MCFC, but much closer to the temperature in which PEMFCs are operated \citep{02_wang2020fundamentals}. Another important difference between AFCs and SOFCs is that the electrolyte in a AFC is liquid, unlike the solid state of the ceramics used in SOFCs. AFCs use a potassium hydroxide solution (KOH) as an electrolyte embedded in the matrix \citep{02_Abderezzak2018,02_wang2020fundamentals}. Unlike SOFCs and MCFC and due to the lower temperature, AFCs can be poisoned by carbon dioxide (CO$_2$). In this case, the alkaline electrolyte could react directly with the CO$_2$ leading to the following reaction equations \ref{eq:AFC_Poisoning} \citep{AFC_mclean2002assessment}:
 
 \begin{equation}
 	\begin{aligned}
@@ -50,22 +51,22 @@ For AFCs the operating temperature is about 50-200 °C which is much lower than
 \label{eq:AFC_Poisoning}
 \end{equation}
 
-This reaction could reduce the ionic conductivity of the electrolyte as well as block the pores in the electrode. The carbonate shown in the equation \ref{eq:AFC_Poisoning} could also block the pores of the catalyst resulting in the aforementioned reduction of ionic conductivity in the electrolyte
+This reaction could reduce the ionic conductivity of the electrolyte and block the pores in the electrode. The carbonate shown in the equation \ref{eq:AFC_Poisoning} could also block the pores of the catalyst, resulting in the aforementioned reduction of ionic conductivity in the electrolyte
 \citep{AFC_mclean2002assessment, AFC_AlSaleh1994_CO2, AFC_AlSaleh1994_Ni}.
 
 \subsubsection{Polymer Electrolyte Membrane Fuel Cells (PEMFCs)}
 
-For Polymer electrolyte membrane fuel cells the operating temperature can be lower than those from the other fuel cell types including the AFCs, PEMFCs can be operated at 40 to 80 °C \citep{02_lucia2014overview}. For high temperature PEMFCs the operating temperature can even go as high as 150-180 °C \citep{02_wang2020fundamentals}. Because of its low operating temperature and its high output power density it is highly suited for mobile applications like the automotive industry. PEMFCs run on pure hydrogen as fuel and cannot use Biogas containing methane (CH$_4$), carbon dioxide (CO$_2$) or carbon monoxide CO as they cannot reform it internally to pure hydrogen H$_2$ \citep{PEM_Atuomotive_arrigoni2022greenhouse}. 
+For polymer electrolyte membrane fuel cells, the operating temperature may be lower than that of the other fuel cell types including the AFCs. PEMFCs can be operated at 40 to 80 °C \citep{02_lucia2014overview}. For high temperature PEMFCs, the operating temperature may even reach up top 150-180 °C \citep{02_wang2020fundamentals}. Because of its low operating temperature and high output power density, it is highly suited to mobile applications like the automotive industry. PEMFCs run on pure hydrogen as fuel and cannot use biogas containing methane (CH$_4$), carbon dioxide (CO$_2$) or carbon monoxide (CO) as they cannot reform it internally to pure hydrogen H$_2$ \citep{PEM_Atuomotive_arrigoni2022greenhouse}. 
 
-Its mobile applications have turned the PEMFCs into one of the biggest research fields in the search for greener alternatives to conventional ICEs. It typically features a solid polymer electrolyte membrane and porous carbon electrodes with platinum functioning as catalyst \citep{01_wilberforce_developments_2017}.
+Its mobile applications have turned the PEMFCs into one of the biggest research fields in the search for greener alternatives to conventional ICEs. They typically features a solid polymer electrolyte membrane and porous carbon electrodes with platinum functioning as catalyst \citep{01_wilberforce_developments_2017}.
 
-Since this thesis focuses its attention on automobile applications, the following sections will provide a detailed explanation of the relevant fuel cell. However, before looking into the way of function the subsequent section will first cover the electrochemical fundamentals. 
+Since this thesis focuses its attention on automotive applications, the following sections will provide a detailed explanation of the relevant fuel cell. However, before looking into their mode of operation, the subsequent section will first cover the relevant electrochemical fundamentals. 
 
 
 
-\section{Electrochemical  Fundamentals}
+\section{Electrochemical Fundamentals}
 
-The function of a fuel cell is to transform the chemical energy stored in the fuel (hydrogen H$_2$) in electrical energy. During this electrochemical reaction the fuel is transformed but the fuel cell is not consumed by the energy production unlike in a battery. In a fuel cell the electrochemical redox reaction is split in two between the cathode and the anode which are separated by an electrolyte \citep{Fundamentals_o2016fuel}.
+The function of a fuel cell is to transform the chemical energy stored in the fuel (hydrogen H$_2$) into electrical energy. During this electrochemical reaction, the fuel is transformed, but the fuel cell is not consumed by the energy production as in a battery. In a fuel cell, the electrochemical redox reaction is split in two between the cathode and the anode separated by an electrolyte \citep{Fundamentals_o2016fuel}.
 
 \begin{align}
 	\text{Anode:} \quad & \text{H}_2 \rightarrow 2\text{H}^+ + 2e^- \\
@@ -74,17 +75,17 @@ The function of a fuel cell is to transform the chemical energy stored in the fu
 	\label{eq:PEM}
 \end{align}
 
-In the anode the oxidation part of the reaction takes place. Electrons are removed from the Hydrogen H$_2$ as shown in the equation (2.4). In the Cathode those liberated electrons are consumed by the reduction reaction and oxygen (O$_2$) and 2H$^+$ form water (H$_2$O) as a product. This is summed up in the overall reaction from te equation (2.6) \citep*{Fundamentals_o2016fuel}. Moreover, the anodic reaction can also be called hydrogen oxidation reaction (HOR) and the cathodic reaction is called oxygen reduction reaction (ORR) \citep{Fundamentals_scherer2012fuel}.
+In the anode, the oxidation part of the reaction takes place. Electrons are removed from the hydrogen H$_2$ as shown in the equation (2.4). In the cathode, these liberated electrons are consumed by the reduction reaction, and oxygen (O$_2$) and 2H$^+$ form water (H$_2$O) as a product. This is summarised in the overall reaction from the equation (2.6) \citep*{Fundamentals_o2016fuel}. The anodic reaction may be called a hydrogen oxidation reaction (HOR) and the cathodic reaction a oxygen reduction reaction (ORR) \citep{Fundamentals_scherer2012fuel}.
 
 \subsection{Thermodynamics of the Cell}
 
-In addition, the reaction produces heat (or enthalpy H) since there is a difference $\Delta$H between the enthalpy of the products and the enthalpy of the reactants \citep{Fund_barbir2008fuel}.
+In addition, the reaction produces heat (or enthalpy H), since there is a difference $\Delta$H between the enthalpy of the products and the enthalpy of the reactants \citep{Fund_barbir2008fuel}.
 \begin{equation}
 	\Delta H=\Delta H_{product}- \Delta H_{reactant}
 	\label{eq:Enthalpy}
 \end{equation}
 
-The Gibbs free energy corresponds to the enthalpy in the reaction that can be converted to electricity. It is defined by the following equation (\ref{eq:Gibbs}). $\Delta$H is the difference of the enthalpy and T$\Delta$S expresses the losses of entropy ($\Delta$S) which are dependent on the temperature
+The Gibbs free energy corresponds to the enthalpy in the reaction that can be converted to electricity. It is defined by the following equation (\ref{eq:Gibbs}). $\Delta$H is the difference of the enthalpy and T$\Delta$S expresses the losses in entropy ($\Delta$S) which are dependent on temperature
 \citep{Fund_barbir2008fuel}.
 
 \begin{equation}
@@ -92,7 +93,7 @@ The Gibbs free energy corresponds to the enthalpy in the reaction that can be co
 	\label{eq:Gibbs}
 \end{equation}
 
-Furthermore, with the help of the Faraday constant F (96,487 C/mol) and n for the number of electrons transferred in the reaction as well as a value for $\Delta$G for the Gibbs free energy the reversible theoretical potential E$_{rev}$ of a cell and in standard conditions can be calculated with the following equation
+Furthermore, using the Faraday constant F (96,487 C/mol) and n for the number of electrons transferred in the reaction as well as a value for $\Delta$G for the Gibbs free energy, the reversible theoretical potential E$_{rev}$ of a cell and in standard conditions may be calculated via following equation
 \citep{Fundamentals_scherer2012fuel}:
 
 \begin{equation}
@@ -100,7 +101,7 @@ Furthermore, with the help of the Faraday constant F (96,487 C/mol) and n for th
 	\label{eq:E}
 \end{equation}
 
-E$_{rev}$ can also be referred to as E$^0$ which is the open circuit voltage (OCV) in standard conditions (1 atm and 25°C or 298K)\citep{Fundamentals_scherer2012fuel, F_omran2021mathematical}. Since this equation (\ref{eq:E}) can be used only in standard conditions the reversible potential of a cell in non-standard conditions cannot by calculated by it. In a non-standard case where the temperature or the pressure is another, the Nernst equation can be used
+E$_{rev}$ can also be referred to as E$^0$, the open circuit voltage (OCV) in standard conditions (1 atm and 25°C or 298K)\citep{Fundamentals_scherer2012fuel, F_omran2021mathematical}. Since this equation (\ref{eq:E}) can be used only in standard conditions, it cannot be used to calculate the reversible potential of a cell in non-standard conditions. In a non-standard case where the temperature or the pressure is different, the Nernst equation can be used
 \citep*{Fundamentals_o2016fuel,Nernst_sahu2014performance}.
 
 \begin{equation}
@@ -108,41 +109,42 @@ E$_{rev}$ can also be referred to as E$^0$ which is the open circuit voltage (OC
 	\label{eq:nernst}
 \end{equation}
 
-To be able to understand the Nernst equation first the concept of chemical potential $\mu$ has to be explained \citep{Nernst_mardle2021examination}. The chemical potential describes how the number of molecules or atoms $n_i$ of a species $i$ afects the thermodynamic potentials. In this case $a$ is the activity of the species. which for an ideal gas is $a_i$ = $p_i$/$p^0$. If the gas is non ideal it has to be multiplied with $\gamma$ wich describes how far away the gas is from an ideal one $(0<\gamma<1)$ with $\gamma=1$ as an ideal gas \citep{Fundamentals_o2016fuel}. In the Nernst equation $v_i$ refers to the stoichiometric coefficient of the products or of the reactants. R is the gas constant (R = 8,314 J/molK)
+To be able to understand the Nernst equation, the concept of chemical potential $\mu$ must first be explained \citep{Nernst_mardle2021examination}. The chemical potential describes how the number of molecules or atoms $n_i$ of a species $i$ affects thermodynamic potentials. In this case, $a$ is the activity of the species, which for an ideal gas is $a_i$ = $p_i$/$p^0$. If the gas is non-ideal, it must be multiplied with $\gamma$, which describes how far away the gas is from an ideal one $(0<\gamma<1)$ with $\gamma=1$ as an ideal gas \citep{Fundamentals_o2016fuel}. In the Nernst equation, $v_i$ refers to the stoichiometric coefficient of the products or of the reactants. R is the gas constant (R = 8,314 J/molK).
 
 \begin{equation}
 	\mu=\mu^0+R \operatorname{Tln}(a)
 	\label{eq:mu}
 \end{equation}
 
-The following equation can also be rewritten to describe how the chemical potential relates to the Gibbs free energy.
+The following equation may also be rewritten to describe how the chemical potential relates to the Gibbs free energy.
 
 \begin{equation}
 	\mu_i^\alpha=\left(\frac{\partial G}{\partial n_i}\right)_{T, p, n_{j \neq i}}
 	\label{eq:chem1}
 \end{equation}
 
-Using the equations (\ref{eq:chem1}) and (\ref{eq:mu}) it is possible to calculate how the Gibbs free energy changes with the $i$ different chemical species resulting in the following equation (\ref{eq:gibbs_2}):
+Using the equations (\ref{eq:chem1}) and (\ref{eq:mu}), it is possible to calculate how the Gibbs free energy changes with the $i$ different chemical species, resulting in the following equation (\ref{eq:gibbs_2}):
 
 \begin{equation}
 	d G=\sum_i \mu_i d n_i=\sum_i\left(\mu_i^0+R T \ln a_i\right) d n_i
 	\label{eq:gibbs_2}
 \end{equation}
 
-Finally this equation (\ref{eq:gibbs_2}) can be inserted into the equation (\ref{eq:E}) to form the Nernst equation (\ref{eq:nernst}) in its general form\citep{Fundamentals_o2016fuel}.
+Finally, this equation (\ref{eq:gibbs_2}) can be inserted into the equation (\ref{eq:E}) to form the Nernst equation (\ref{eq:nernst}) in its general form\citep{Fundamentals_o2016fuel}.
 
 \newpage
 
 \section{PEMFC}
 \label{sec: PEMFC}
 
-Since this Thesis focuses on the automotive applications of fuel cells the focus of the following sections will shift to the Polymer Electrolyte Membrane Fuel Cell (PEMFC) which are the most widely used in automotive contexts due to their low operating temperature as well as its high output power density \citep{PEM_Atuomotive_arrigoni2022greenhouse}.
+Since this thesis focuses on the automotive applications of fuel cells, the focus of the following sections will shift to the Polymer Electrolyte Membrane Fuel Cell (PEMFC), which is the most widely used in automotive contexts due to its low operating temperature as well as its high output power density \citep{PEM_Atuomotive_arrigoni2022greenhouse}.
-In the following section \ref{subsec:2_wayoffunct} the PEMFC will be described in more detailed way starting with its main components and its way of function.
+In the following section \ref{subsec:2_wayoffunct}, the PEMFC will be described in more detail, starting with its main
+components and its mode of operation.
 
-\subsection{Way of Function PEMFCs}
+\subsection{Mode of Operation PEMFCs}
 \label{subsec:2_wayoffunct}
 
-To be able to produce more energy PEMFCs use not only one cell but a stack formed by hundreds of cells stacked on top of each other in between two monopolar plates at the ends as shown in the left side of the following figure \ref{fig:PEMFC} \citep{PEMSchem_xu2020towards}.
+To be able to produce more energy, PEMFCs not only use a single cell but a stack formed by hundreds of cells stacked on top of each other between two monopolar plates at each end, as shown in the left side of the following figure \ref{fig:PEMFC} \citep{PEMSchem_xu2020towards}.
 
 %vielleicht eine selber machen? Was ist hier los mit der quelle? Bug
 \begin{figure}[htbp]
@@ -152,72 +154,70 @@ To be able to produce more energy PEMFCs use not only one cell but a stack forme
 	\label{fig:PEMFC}
 \end{figure}
 
-Every cell is composed by two bipolar plates (BPs) each with its anode and cathode side. Between each BP there is the membrane electrode assembly layer (MEA). The MEA consists of a proton exchange membrane in the middle of two catalyst layers (CL) and two gas diffusion layers (GDL) one on the cathode side and one on the anode side. Since the redox reaction in the fuel cell (equation \ref{eq:PEM}) is an exothermic reaction which generates heat the cell needs cooling, therefore the coolant can flow inside specific flow channels of the BP as illustrated in the figure \ref{fig:PEMFC} to prevent the system from overheating \citep{PEMSchem_xu2020towards}. The key components of the PEMFC and its functions will be explained in the following starting with the BPs. Since the focus of this Thesis is the BP corrosion this key component will be presented in a more detailed form.
+Every cell is composed by two bipolar plates (BPs), each with its anode and cathode side. Between each BP is the membrane electrode assembly layer (MEA). The MEA consists of a proton exchange membrane in the middle of two catalyst layers (CL) and two gas diffusion layers (GDL), one on the cathode side and one on the anode side. Since the redox reaction in the fuel cell (equation \ref{eq:PEM}) is an exothermic reaction generating heat, the cell needs cooling. As such, the coolant can flow inside specific flow channels of the BP, as illustrated in the figure \ref{fig:PEMFC}, in order to prevent the system from overheating \citep{PEMSchem_xu2020towards}. The key components of the PEMFC and its functions will be explained in the following, starting with the BPs. Since the focus of this thesis is BP corrosion, this key component will be presented in more detail.
 
 \newpage
 \subsubsection{Bipolar Plate (BP)}
 
-The main functions of the BPs is to distribute fuel on the anode side and oxidant on the cathode side to the reactive sites in the catalyst layer (CL). It also collects the generated current and removes the byproducts from the reaction. Heat management is also a very important function, therefore special channels (flow channels) transport the coolant and remove the heat from the cell \citep{PEM_baroutaji2015materials}. 
+BPs have various functions. One important function is to distribute fuel on the anode side and oxidant on the cathode side to the reactive sites in the catalyst layer (CL). It also collects the current generated and removes byproducts from the reaction. Heat management is also a very important; special channels (flow channels) transport the coolant and remove the heat from the cell \citep{PEM_baroutaji2015materials}. 
 
-Since the BPs are responsible for 60-80 \% of the weight of as well as 20-30\% of the total cost of the fuel stack the materials used for it have been under investigation for some time and the Department of Energy (DOE) has set up Targets for the components of the fuel cell \citep{doe_pemfc_targets}. This targets evaluate not only the cost of the materials but also durability and performance \citep{doe_pemfc_targets}. Due to their durability, excellent mechanical strength, high power density and electric conductivity, the investigations of new BP materials has been primarily focused on stainless steels, titanium alloys and aluminium alloys \citep{antunes2010}. In the past BPs were made out of graphite. Graphite is highly corrosion resistant, unfortunately it has some drawbacks like its high permeability for gases and production costs \citep{PEM_baroutaji2015materials}. 
+Since BPs are responsible for 60-80 \% of the weight and 20-30 \% of the total cost of the fuel stack, the materials used have been under investigation for some time, and the Department of Energy (DOE) has set up targets for the components of the fuel cell \citep{doe_pemfc_targets}. These targets evaluate not only the cost of the materials but also durability and performance \citep{doe_pemfc_targets}. Due to their durability, excellent mechanical strength, high power density and electric conductivity, investigations into new BP materials have been primarily focused on stainless steels, titanium alloys and aluminium alloys \citep{antunes2010}. In the past, BPs have been made out of graphite. Graphite is highly corrosion resistant, but it unfortunately has drawbacks like high gas permeability and high production costs \citep{PEM_baroutaji2015materials}. 
 
-Stainless steels on the other hand are more cost effective and versatile, its high mechanical strength and malleability results in the possibility of producing thinner BPs which can lead up to a weight reduction of 40\% of the fuell cell stack
+Stainless steels, on the other hand, are more cost effective and versatile; their high mechanical strength and malleability makes possible the production of thinner BPs, leading to a weight reduction of up to 40 \% of the fuel cell stack 
-\citep{SSweight_li2005review}. This optimal characteristics have attracted the automotive sector and companies like Hyundai, GM and Honda which have produced fuel cell vehicles (FCV) with this stainless steels \citep{Automotive_leng2020}. Toyota on the other hand
+\citep{SSweight_li2005review}. These optimal characteristics have attracted the automotive sector and companies such as Hyundai, GM and Honda, which have all produced fuel cell vehicles (FCV) with these stainless steels \citep{Automotive_leng2020}. Toyota, however,
-uses a titanium bipolar plate nano composite (NC) as a surface treatment for the BPs used in the Mirai stack. This ensured a reduction in the thickness of the Titanium (Ti) plates so that the Platinum (Pt) used in the stack could be reduced by 58\% from its 2008 model to the second-generation Mirai \citep{toyota_technical_review_2021}. Since the collaboration between BMW and Toyota was announced in September 2024, BMW will also be using BPs manufactured by the Toyota Motor Corporation for its BMW iX5 Hydrogen planned for series production in 2028 \citep{bmw_hydrogen_2024}.
+uses a titanium bipolar plate nano composite (NC) as a surface treatment for the BPs used in the Mirai stack. This has, for example, ensured a reduction in the thickness of the Titanium (Ti) plates so that the Platinum (Pt) used in the stack could be reduced by 58 \% from its 2008 model to the second-generation Mirai \citep{toyota_technical_review_2021}. Since the collaboration between BMW and Toyota was announced in September 2024, BMW will also be using BPs manufactured by the Toyota Motor Corporation for its BMW iX5 Hydrogen, planned for series production in 2028 \citep{bmw_hydrogen_2024}.
 
-Stainles Steels BPs have a lower cost than Ti plates but its durability has been questioned since its corrosion resistance is lower than Ti plates and Aluminium plates. When Stainless steel plates corrode they release metal ions like Fe$^{2+}$ which lead to a accelerated chemical degradation of the membrane by contaminating the MEA. \citep{eom2012}. Even though Aluminium has a higher corrosion restistance than stainless steels it would release Al$^{3+}$ ions during the corrosion process which have an even bigger effect than Fe$^{2+}$ on the fuel cell catalyst \citep{sulek2011}. This form of degradation will be explained in the Section \ref{sec:Degradation}. Although SS316L has proven to have a higher corrosion resistance and is therefore used as reference material for Bipolar plates other more cost effective options have also been studied like stainless steels 310L, 304 and 904L\citep{papadias2015degradation,feng2011}.
+Stainless steel BPs have a lower cost than Ti plates, but their durability has been questioned, since their corrosion resistance is lower than Ti and aluminium plates. When stainless steel plates corrode, they release metal ions like Fe$^{2+}$ which lead to an accelerated chemical degradation of the membrane by contaminating the MEA. \citep{eom2012}. Even though aluminium has a higher corrosion restistance than stainless steel, it would release Al$^{3+}$ ions during the corrosion process which have an even larger effect than Fe$^{2+}$ on the fuel cell catalyst \citep{sulek2011}. This form of degradation will be explained in Section \ref{sec:Degradation}. Although SS316L has been proven to have a higher corrosion resistance and is therefore used as reference material for bipolar plates, other, more cost effective options have also been studied such as stainless steels 310L, 304 and 904L\citep{papadias2015degradation,feng2011}.
 
-\subsubsection{Membrane Electrode Assembly (MEA)}
+\subsubsection{Membrane Electrode Assembly (MEA)} 
 
-As mentioned before the Membrane Electrode Assembly (MEA) is conformed by the Gas Diffusion layer (GDL) on the cathode side as well as the GDL on the anode side followed by the two catalyst layers (CL) which contain platinum (Pt) and Nafion and in the middle the proton exchange membrane (PEM) \citep{PEMSchem_xu2020towards}.
+As previously mentioned, the Membrane Electrode Assembly (MEA) is conformed by the Gas Diffusion layer (GDL) on the cathode side, as well as the GDL on the anode side, followed by the two catalyst layers (CL) which contain platinum (Pt) and Nafion. In the middle is the proton exchange membrane (PEM) \citep{PEMSchem_xu2020towards}.
-The MEA could be looked at as the most important component of a PEMFC as it is responsible for the chemical reactions and consequently for the performance of the fuel cell \citep{MEA_lim2021comparison}. 
+The MEA could be considered as the most important component of a PEMFC, as it is responsible for the chemical reactions, and consequently for the fuel cell's performance \citep{MEA_lim2021comparison}. 
 
-Three fabrication methods of MEA stand out because of its perfomance, the first one catalyst-coated membranes (CCMs) and catalyst-coated substrates (CCSs) and catalyst-coated electrode(CCE) \citep{MEA_lapicque2012,MEA_bhosale2020}. 
+Three methods of fabricatoin of MEA stand out due to their perfomance. They are catalyst-coated membranes (CCMs), catalyst-coated substrates (CCSs) and catalyst-coated electrodes (CCE) \citep{MEA_lapicque2012,MEA_bhosale2020}. 
- A comparative study by Bhosale et al. \citep{MEA_bhosale2020} showed that the most effective method is CCE. Nevertheless, CCM shows high performance and many studies suggest that MEA produced with a CCM method can have many advantages over CCS and CCE, therefore it is the most used method \citep{PEM_MEA_parekh2022recent}. 
+ A comparative study by Bhosale et al. \citep{MEA_bhosale2020} showed that the most effective method is CCE. Nevertheless, CCM shows high performance and many studies suggest that MEA produced with a CCM method can have many advantages over CCS and CCE. Consequently it is the method most frequently used \citep{PEM_MEA_parekh2022recent}. 
  
- CCM can lead to an increase of the total reactions in the MEA as well as reducing the Pt amount in the catalyst \citep{MEA_lim2021comparison}.
+ CCM can lead to an increase in total reactions in the MEA, as well as reduce the amount of Pt in the catalyst \citep{MEA_lim2021comparison}. Since Pt can be very expensive, methods to reduce the weight-loading percentage of the catalyst have also been under investigation, and even Pt-free catalysts have been investigated \citep{Pt_liew2014}. Moreover, Pt catalysts can be lost during dynamic operation of the cell (voltage cycling) either by Pt agglomeration or Pt dissolution, also leading to further degradation of the cell and higher mass transport losses and activation losses \citep{thiele2024realistic}. In order to better understand the MEA, its components will now also be explained.
-Since Pt can be very expensive methods to reduce the weight-loading percentage of the catalyst have also been under investigation and even Pt-free catalysts \citep{Pt_liew2014}. Moreover, Pt catalyst can be lost during dynamic operation of the cell (voltage cycling) either by Pt agglomeration or Pt dissolution which also leads to further degradation of the cell and  higher mass transport losses as well as activation losses \citep{thiele2024realistic}. To be able to understand the MEA better now its components will be explained as well.
 
 
 \subsubsection{Gas Diffusion Layer (GDL)}
 
-Starting with the first layer of the MEA right between the BPs and the catalyst layers (CL) on both sides is the gas diffusion Layers (GDL) and also the microporous layer (MPL)\citep{PEMSchem_xu2020towards}. Their primary function is to offer mechanical support to the MEAs, ensure the flow of the reactants and also the removal of products. Furthermore, they have to enable the electron conduction between the CLs and the BPs on both sides. 
+Starting with the first layer of the MEA, right between the BPs and the catalyst layers (CL) on each side are the gas diffusion layer (GDL), as well as the microporous layer (MPL) \citep{PEMSchem_xu2020towards}. Their primary functions are to offer mechanical support to the MEAs, ensure the flow of the reactants and also remove products. Furthermore, they must enable electron conduction between the CLs and the BPs on each side. 
 
-Since its main functions are related to diffusion the GDL is made out of porous materials, typically it is made out of carbon paper\citep{02_wang2020fundamentals}.
+Since its main functions are related to diffusion, the GDL is made out of porous materials. Typically, it is made out of carbon paper \citep{02_wang2020fundamentals}.
-To enhance water management and prevent flooding in the electrode the carbon paper GDL hast to be hydrophobic. For that reason Polytetrafluorethylene (PTFE) is often added to it as treatment to achieve this hydrophobicity
+To enhance water management and prevent flooding in the electrode, the carbon paper GDL has to be hydrophobic. For this reason, Polytetrafluorethylene (PTFE) is often added as treatment to achieve this hydrophobicity
-\citep{02_wang2020fundamentals,GDL_zamel2011}. Since a high PTFE load can cause an obstruction in the pores of the GDL and consequently cause mass transport limitations it is crucial to add the right amount. Studys have shown that 20 wt.\% is an optimal load percentage for PTFE to turn the carbon paper hydrophobic without blocking the pores \citep{GDL_zamel2011}. Also important are the capillary effects of the MPL, since the MPL is also hydrophobic it provides a great drainage as well as stable gas and electron channels \citep{ijaodola2019}. This helps the overall performance of the cell by reducing the flooding of the cell since this layer is in-between of the GDL and CL \citep{majlan2018}.
+\citep{02_wang2020fundamentals,GDL_zamel2011}. Since a high PTFE load can cause an obstruction in the pores of the GDL, and consequently cause mass transport limitations, it is crucial to add the right amount. Studies have shown that 20 wt. \% is an optimal load percentage for PTFE to turn the carbon paper hydrophobic without blocking the pores \citep{GDL_zamel2011}. Also important are the capillary effects of the MPL. Since the MPL is also hydrophobic, it provides great drainage as well as stable gas and electron channels \citep{ijaodola2019}. This helps the overall performance of the cell by reducing flooding, since this layer sits between the GDL and CL \citep{majlan2018}.
 
 \subsubsection{Catalyst Layer (CT)}
 
-The catalyst layers (CTs) are positioned between the PEM and the MPL on both sides. Electrochemical reactions take place here in the CL therefore it has to provide continuous pathways for the different reactants. More specific it has to provide a route for proton transport, its porous structure has to supply the gaseous reactants to the site as well as remove the water while also being able to form a conductive pathway for electrons between the CL and the current collector \citep{02_wang2020fundamentals}.
+The catalyst layers (CTs) are positioned between the PEM and the MPL on both sides. Electrochemical reactions take place here in the CL and, therefore, it must provide continuous pathways for the different reactants. More specifically, it must provide a route for proton transport; its porous structure must supply the gaseous reactants to the site whilst removing water, while also being able to form a conductive pathway for electrons between the CL and the current collector \citep{02_wang2020fundamentals}.
 
-The oxygen reduction reaction (ORR) takes place at the CL and is the most critical process for a PEMFC at the anode \citep{PEM_baroutaji2015materials}. This reaction heavily relies on platinum (Pt) catalyst, by increasing the platinum load  the ORR rate can be enhanced which leads to a higher power output in the cell \citep{PEM_MEA_parekh2022recent}. Contrary to the GDL and MPL platinum particles are not hydrophobic since they present hydrophilic capabilities \citep{CT_malek2011}. 
+The oxygen reduction reaction (ORR) takes place at the CL and is the most critical process for a PEMFC at the anode \citep{PEM_baroutaji2015materials}. This reaction heavily relies on the platinum (Pt) catalyst. By increasing the platinum load, the ORR rate can be enhanced leading to a higher power output in the cell \citep{PEM_MEA_parekh2022recent}. In contrast to the GDL and MPL, platinum particles are not hydrophobic, since they present hydrophilic capabilities \citep{CT_malek2011}. 
 
-As stated before, the CCM method is currently the most used in the production of the MEA. Since Pt is the most expensive part of the production and CCM production already has a better electrochemical performance than the CCS method and it showcases a lower Pt load\citep{hnat2019}. In this method the catalyst layer is produced by applying catalyst ink on a PEM \citep{MEA_lim2021comparison}. But a big challenge continues to be the search for a more cost effect alternative to Pt catalyst with the same electrochemical performance \citep{PEM_MEA_parekh2022recent}.
+As previously before, the CCM method is currently the most frequently used in the production of the MEA. This is because Pt is the most expensive part of the production, and CCM production already has a better electrochemical performance than the CCS method and exhibits a lower Pt load\citep{hnat2019}. In this method, the catalyst layer is produced by applying catalyst ink onto a PEM \citep{MEA_lim2021comparison}. However, the search for a more cost effect alternative to Pt catalyst with the same electrochemical performance continues to be a challenge \citep{PEM_MEA_parekh2022recent}.
 
-The Catalyst layer consists of a catalyst (Pt), carbon support, ionomer and a void space. PTFE was subsituted with recast Nafion ionomer as a binder allowing for a significant reduction in Pt loadings. Additionally Pt supported on carbon (Pt/C) also helps to decreases the metal content\citep{ink_zamel2016catalyst}. The ionomer serves a dual purpose as a binder for Pt/C particles and as a proton conductor. An imbalance in ionomer loading can lead to transport or ohmic losses which will be discussed in the subchapter \ref{subsec:losses}. Insufficient ionomer diminishes proton conductivity and an excessive amount can increase a resistance of  gaseous reactant transport \citep{02_wang2020fundamentals}.
+The catalyst layer consists of a catalyst (Pt), carbon hsupport, ionomer and a void space. PTFE was substituted with recast Nafion ionomer as a binder, allowing for a significant reduction in Pt loadings. Additionally, Pt supported on carbon (Pt/C) also helps to decrease the metal content \citep{ink_zamel2016catalyst}. The ionomer serves a dual purpose as a binder for Pt/C particles and as a proton conductor. An imbalance in ionomer loading can lead to transport or ohmic losses, which will be discussed in subchapter \ref{subsec:losses}. Insufficient ionomer diminishes proton conductivity, and an excessive amount can increase resistance of gaseous reactant transport \citep{02_wang2020fundamentals}.
 
 
 
 
 \subsubsection{Proton Exchange Membrane (PEM)}
 
-The proton exchange membrane is the heart of the PEMFC, it is in the middle between cathode and anode followed by CL, MLP and then GDL in that order from the inside to the outside. The PEM has to primary functions. The first one is serving as a barrier, it prevents the mixing of reactant gases and electrons between the anode and cathode. The second one is to facilitate proton conduction from the CL on the anode to the CL on the cathode side. Furthermore, the PEM is impermeable for gas, it stops the oxygen and hydrogen crossover and it has to be electrically insulating. Another requirement for the membrane is a exceptional chemical and mechanical stability to be able to endure the harsh operating conditions of the PEM fuel cells \citep{ghassemzadeh2010chemical}.
+The proton exchange membrane is the heart of the PEMFC. It is right in the middle of the cathode and anode, followed by CL, MLP and then GDL, in that order from inside to outside. The PEM has two primary functions. The first is to server as a barrier. It prevents the mixing of reactant gases and electrons between anode and cathode. The second is to facilitate proton conduction from the CL on the anode to the CL on the cathode side. Furthermore, the PEM is impermeable to gas. It stops oxygen and hydrogen crossover and must be electrically insulating. Another requirement for the membrane is exceptional chemical and mechanical stability in order to endure the harsh operating conditions of the PEM fuel cells \citep{ghassemzadeh2010chemical}.
 
-The most widely used material for the membrane in a PEMFC is perfluorosulfonic acid (PFSA) also referred to as Nafion which was developed by DuPont
+The most widely used material for the membrane in a PEMFC is perfluorosulfonic acid (PFSA), also referred to as \textit{Nafion}, developed by DuPont \citep{PEM_MEA_parekh2022recent}. Figure \ref{fig:Nafion} shows the chemical structure of Nafion \citep{okonkwo2021nafion}.
-\citep{PEM_MEA_parekh2022recent}. Figure \ref{fig:Nafion} shows the chemical structure of Nafion \citep{okonkwo2021nafion}.
 
 
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.5\textwidth]{Figures/Theorie/Nafion.pdf}
-	\caption{Chemical structure of PFSA also called Nafion. Retrieved from Chen et al., page 1436 (1) [59]}
+	\caption{Chemical structure of PFSA, also called Nafion. Retrieved from Chen et al., page 1436 (1) [59]}
 	\label{fig:Nafion}
 \end{figure}
 
- Since the main chain is Teflon-like it has an hydrophobic side and the sulfonic acid groups on the side chains are hydrophilic. This is a great advantage because it facilitates water adsorption and consequently proton conduction. To maintain an effective proton transport proper hydration of the membrane is vital while avoiding excessive moisture that could lead to flooding in the CL and GDL \citep{zaidi2009polymer}.
+ Since the main chain is Teflon-like, one side is hydrophobic and the sulfonic acid groups on the side chains are hydrophilic. This is a great advantage because it facilitates water adsorption and consequently proton conduction. To maintain an effective proton transport, proper hydration of the membrane is vital, while simultaneously avoiding excessive moisture that could lead to flooding in the CL and GDL \citep{zaidi2009polymer}.
  
-  However the membrane can degrade when it is exposed to low humidity and high temperatures. While degrading Nafion can release F$^-$, CO$_2$, SO$_4^{2-}$, SO$_2$ as well as fluorocarbons \citep{teranishi2006}. Besides this form of degradation the electrochemical reaction in a PEMFC can also produce hydrogen peroxide (H$_2$O$_2$) when the entry of oxygen in the PEM reacts with the hydrogen in the anode as shown in the following equation (\ref{eq:h2o2}) \citep{ren2020degradation}:
+  However the membrane can degrade when it is exposed to low humidity and high temperatures, while degrading Nafion can release F$^-$, CO$_2$, SO$_4^{2-}$, SO$_2$ as well as fluorocarbons \citep{teranishi2006}. Besides this form of degradation, the electrochemical reaction in a PEMFC can also produce hydrogen peroxide (H$_2$O$_2$) when the entry of oxygen in the PEM reacts with the hydrogen in the anode, as shown in the following equation (\ref{eq:h2o2}) \citep{ren2020degradation}:
   
 \begin{equation}
  	\mathrm{O}_2+2 \mathrm{H}^{+}+2 e^{-} \rightarrow \mathrm{H}_2 \mathrm{O}_2, \mathrm{E}_{\mathrm{O}}=0.695 \mathrm{~V} \text { vs. } \mathrm{SHE}\left(75^{\circ} \mathrm{C}\right)
@@ -225,16 +225,17 @@ The most widely used material for the membrane in a PEMFC is perfluorosulfonic a
  \end{equation}
  
  
- Furthermore, H$_2$O$_2$ in the presence of ferrous ions like Fe$^{2+}$ which are released by the BP when corroding can trigger the formation of hydroxyl radicals which attack the membrane as well. It is thought that an incomplete reduction of the oxygen by the Pt catalyst can trigger the production of H$_2$O$_2$ as well \citep{elferjani_coupling_2021}.
+ Furthermore, H$_2$O$_2$ in the presence of ferrous ions like Fe$^{2+}$, which are released by the BP when corroding, can trigger the formation of hydroxyl radicals that also attack the membrane. It is thought that an incomplete reduction of the oxygen by the Pt catalyst can also trigger the production of H$_2$O$_2$ \citep{elferjani_coupling_2021}.
 
 
 
 \subsection{Department of Energy Targets}
+\label{subsec:2_DOE}
 
-The Deparment of Energy (DOE) of the United States(U.S.) with the help from the U.S. DRIVE partnership has set targets for the components of PEMFC to help FC developers develop them without the need to test the full system
+The Deparment of Energy (DOE) of the United States(U.S.) with the help from the U.S. DRIVE partnership has set targets for the components of PEMFC to help FC developers develop them without needing to test the full system
-\citep{doe_pemfc_targets}. U.S DRIVE FC team aims to develop a PEMFC system for transportation able to resist 8000 hours and with a mass production cost of 35\$ per Kilowatt (kW) by 2025 \citep{trabia2016}.
+\citep{doe_pemfc_targets}. The U.S DRIVE FC team aims to develop a PEMFC system for transportation that is able to resist 8000 hours and with a mass production cost of 35\$ per Kilowatt (kW) by 2025 \citep{trabia2016}.
 
-Targets of the DOE include specifications for the MEA, PEM, electrocatalysis and bipolar plates. The goal for BPs is to reduce the plate cost from 5,4\$ to 2\$ per kW until 2025. Some other goals include the weight reduction of the BPs and increased corrosion resistance as well as a higher electric conductivity\citep{PEM_MEA_parekh2022recent}. Overall the DOE wants to increase cell performance and at the same time reduce production costs to allow PEMFCs in FCV and fuel cell electrical vehicles (FCEV) becoming an cost effective and green alternative to ICE in the series production.
+Targets of the DOE include specifications for the MEA, PEM, electrocatalysis and bipolar plates. The goal for BPs is to reduce the plate cost from 5,4\$ to 2\$ per kW by 2025. Some other goals include the weight reduction of the BPs and increased corrosion resistance, as well as higher electric conductivity \citep{PEM_MEA_parekh2022recent}. Overall, the DOE intends to increase cell performance and simultaneously reduce production costs to allow PEMFCs in FCV and fuel cell electrical vehicles (FCEV) to become a cost effective and green alternative to ICE in the series production.
 
 
 \subsection{Overpotentials of the PEMFC}
@@ -244,49 +245,49 @@ Targets of the DOE include specifications for the MEA, PEM, electrocatalysis and
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.8\textwidth]{Figures/Theorie/Polarization.pdf}
-	\caption{Polarization curve of a fuel cell including the different losses. Retrieved from Jung et al., page 741 (4) [64].}
+	\caption{Polarisation curve of a fuel cell including the different losses. Retrieved from Jung et al., page 741 (4) [64].}
 	\label{fig:losses}
 \end{figure}
 
-The Nernst equation \ref{eq:E} calculates the reversible cell potential which is the current that should be drawn by the PEMFC. However the actual measured open-circuit voltage (OCV) is lower than the theoretical one calculated by the equation \citep{Loss_mardle2021examination}. 
+The Nernst equation \ref{eq:E} calculates the reversible cell potential, which is the current that should be drawn by the PEMFC. However the actual open-circuit voltage (OCV) measured is lower than the theoretical one calculated by the equation \citep{Loss_mardle2021examination}. 
-This deviation can be observed in the figure \ref{fig:losses} \citep{Loss_jung2010dynamic}. This first deviation is caused by the hydrogen (H$_2$) crossover. This occurs when H$_2$ diffuses through the membrane, leading to a mixed potential that lowers the overall open-current potential (OCP). Internal short circuits also lead to OCV losses in this stage as well \citep{Loss_mazzeo2024assessing}.
+This deviation can be observed in the figure \ref{fig:losses} \citep{Loss_jung2010dynamic}. This first deviation is caused by the hydrogen (H$_2$) crossover. This occurs when H$_2$ diffuses through the membrane, leading to a mixed potential that lowers the overall open-current potential (OCP). Internal short circuits also lead to OCV losses in this stage \citep{Loss_mazzeo2024assessing}.
 
-In addition to the first loss the polarization curve experiences other deviations as the current density starts to grow. Starting with the activation losses then the Ohmic losses and at high current densities the mass transport losses which will all be explained in the following \citep{02_lucia2014overview}.
+In addition to the first loss, the polarisation curve experiences other deviations as the current density begins growing, starting with the activation losses, then the Ohmic losses and at high current densities the mass transport losses. These will all be explained in the following \citep{02_lucia2014overview}.
 
 
-\subsubsection{Activation Polarization}
+\subsubsection{Activation Polarisation}
 
-The activation loss also called activation polarization loss is driven by the voltage loss caused by the activation energy required for the electrochemical reaction to start as the protons move through the reaction interface. Therefore it is a loss related to the kinetic of the cathode and anode electrodes \citep{Loss_li2022new}. As shown in the image \ref{fig:losses} it takes place at a region with low current densities. It$\eta_{act}$ can be calculated using the following equation (\ref{eq:Loss_N}) \citep{ren2020degradation}.
+The activation loss, also called activation polarisation loss, is driven by the voltage loss caused by the activation energy required for the electrochemical reaction to start as the protons move through the reaction interface. Therefore, it is a loss related to the kinetic of the cathode and anode electrodes \citep{Loss_li2022new}. As shown in the image \ref{fig:losses}, it takes place at a region with low current densities. It$\eta_{act}$ can be calculated using the following equation (\ref{eq:Loss_N}) \citep{ren2020degradation}.
 
 \begin{equation}
 	\eta_{\text {act }}=\frac{R T}{\alpha n F} \ln \left(\frac{i_{\text {loss }}}{i_0}\right)
 	\label{eq:Loss_N}
 \end{equation}
 
-In this equation the following parameters are taken into account: F for the Faraday constant, $i_0$ as the exchange current density for the active area of the FC, $\alpha$ as charge transfer coefficient, R is the gas constant and n the number of molecules or atoms. Furthermore, $i_{loss}$ is formed as the addition of $i_{short}$ for the current density of short-circuits and $i_{crossover}$ which is the gas-crossover current density \citep{ren2020degradation,jouin2016}.
+In this equation the following parameters are taken into account: F for the Faraday constant, $i_0$ as the exchange current density for the active area of the FC, $\alpha$ as charge transfer coefficient, R is the gas constant and n, the number of molecules or atoms. Furthermore, $i_{loss}$ is formed as the addition of $i_{short}$ for the current density of short-circuits and $i_{crossover}$, the gas-crossover current density \citep{ren2020degradation,jouin2016}.
 
 \begin{equation}
 	i_{\text {loss }}=i_{\text {crossover }}+i_{\text {short }}
 \end{equation}
 
-It is worth mentioning that the exchange current density of the oxygen reduction reaction (ORR) can be perceived as a limiting factor in low temperature PEMFC like the ones used for the automotive sector \citep{Loss_mazzeo2024assessing}. 
+It is worth mentioning that the exchange current density of the oxygen reduction reaction (ORR) can be perceived as a limiting factor in low temperature PEMFC such as the ones used for the automotive sector \citep{Loss_mazzeo2024assessing}. 
 
 
-\subsubsection{Ohmic Polarization}
+\subsubsection{Ohmic Polarisation}
 
-As the current density increases, ohmic polarization loss becomes the dominant factor in the polarization curve. Voltage decreases in an almost linear way with increasing current density \citep{Loss_li2022new}. Ohmic losses are associated with the resistance encountered by the flow of the electrons through various components of the FC \citep{Loss_mazzeo2024assessing}. The resistance of the hydrogen ion flow into the electrolyte is a significant factor. This resistance is heavily influenced by membrane's hydration level as well as operating temperatures and current density \citep{springer1991}. Mathematically it can be described with the following equation (\ref{eq:Loss_ohm})\citep{ren2020degradation}.
+As the current density increases, ohmic polarisation loss becomes the dominant factor in the polarisation curve. Voltage decreases in an almost linear way with increasing current density \citep{Loss_li2022new}. Ohmic losses are associated with the resistance encountered by the flow of the electrons through various components of the FC \citep{Loss_mazzeo2024assessing}. The resistance of the hydrogen ion flow into the electrolyte is a significant factor. This resistance is heavily influenced by membrane's hydration level as well as operating temperatures and current density \citep{springer1991}. Mathematically it can be described with the following equation (\ref{eq:Loss_ohm})\citep{ren2020degradation}.
 
 \begin{equation}
 	\eta_{\mathrm{ohm}}=\left(R_{\mathrm{ion}}+R_{\mathrm{ele}}+R_{\mathrm{con}}\right) \cdot i
 	\label{eq:Loss_ohm}
 \end{equation}
 
-In this equation R$_{ion}$ represents the ionic resistance, R$_{con}$ the contact resistance and R$_{ele}$ the electronic resistance. For this section the polarization behaves linearly since it is multiplied with the current density ($i$) \citep{ren2020degradation}.
+In this equation R$_{ion}$ represents the ionic resistance, R$_{con}$ the contact resistance and R$_{ele}$ the electronic resistance. For this section, the polarisation behaves linearly since it is multiplied with the current density ($i$) \citep{ren2020degradation}.
 
-\subsubsection{Concentration Polarization}
+\subsubsection{Concentration Polarisation}
 
-At high current densities the concentration polarization or concentration loss occurs. The reactants are consumed very quick during the electrochemical reactions at a high current density. Because of transport and diffusion resistance the availability in of the reactants at the reaction sites decrease which limits the the reactions and thereby the efficiency of the PEMFC \citep{Loss_li2022new}.
+At high current densities, concentration polarisation or concentration loss occurs. The reactants are consumed very quickly during the electrochemical reactions at a high current density. Because of transport and diffusion resistance, the availability of the reactants at the reaction sites decreases, limiting the reactions and thereby the efficiency of the PEMFC \citep{Loss_li2022new}.
-The ohmic polarization can be calculated using the  following equation (\ref{eq:Loss_con}) 
+The ohmic polarisation can be calculated using the following equation (\ref{eq:Loss_con}) 
 \citep{ren2020degradation}:
 
 \begin{equation}
@@ -294,30 +295,31 @@ The ohmic polarization can be calculated using the  following equation (\ref{eq:
 	\label{eq:Loss_con}
 \end{equation}
 
-The parameters of the equation (\ref{eq:Loss_con}) are the same as in the others before that with the only new one being $i_L$ which stands for the limiting current density.
+The parameters of the equation (\ref{eq:Loss_con}) are the same as in those previously discussed, the only new one being $i_L$, which stands for the limiting current density.
 
-At such high operating it is important to avoid undersupply of the anode which could damage the PEMFC. Therefore, changing the hydrogen-oxygen stoichiometric ratio from 1:1 to 1.5:2.2 can improve the performance of the PEMFC as well as reduce damage caused by the operation on high current densities \citep{liu2024study}.
+At such high current densities it is important to avoid undersupply of the anode, which could damage the PEMFC. Therefore, changing the hydrogen-oxygen stoichiometric ratio from 1:1 to 1.5:2.2 can improve the performance of the PEMFC, as well as reduce damage caused by the operation on high current densities \citep{liu2024study}.
 
 
-\subsection{Characterization of PEMFC}
+\subsection{Characterisation of PEMFC}
+\label{subsec: Polarizaiton}
 
-As this thesis includes an endurance run and preliminary investigations to better understand the operating conditions of the PEMFC and identify the optimal point for triggering cell corrosion, this section will detail the in-situ methods employed to characterize the cells. Parameters like the cell potential and the current density can give an insight into the state of health of the cell. By using predefined characterisation curves in-between a specific number of voltage cycles the cell degradation can be tracked. Figure \ref{fig:PolCurve} shows an example of a the polarization curves after a specific number of voltage cycles \citep{mohsin2020electrochemical}.
+As this thesis includes an endurance run and preliminary investigations to better understand the operating conditions of the PEMFC and identify the optimal point for triggering cell corrosion, this section will detail the in-situ methods employed to characterise the cells. Parameters such as cell potential and current density can provide insight into the state of the cell's health. By using predefined characterisation curves between a specific number of voltage cycles, the cell degradation may be tracked. Figure \ref{fig:PolCurve} shows an example of the polarisation curves after a specific number of voltage cycles \citep{mohsin2020electrochemical}.
 
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.7\textwidth]{Figures/Theorie/PolCurve.pdf}
-	\caption{Example of a polarization curve of a PEMFC after different numbers of voltage cycles (VC)  . Retrieved from Mohsin et al., page 24096 (4) [69].}
+	\caption{Example of a polarisation curve of a PEMFC after different numbers of voltage cycles (VC)  . Retrieved from Mohsin et al., page 24096 (4) [69].}
 	\label{fig:PolCurve}
 \end{figure}
 
 
-In this polarization curves the potential of the cell is plotted over the current densities. Degradation of the membrane, corrosion, carbon corrosion or as a consequence of it platinum catalyst dissolution causes the polarization curve to have a higher drop in the potential at much lower current densities after more cycles as shown in the aforementioned figure \ref{fig:PolCurve} \citep{Pol_thiele2024realistic}. This mechanisms will be explained in the following section \ref{sec:Degradation}. After a larger number of voltage cycles the higher current densities can no longer be reached as a consequence of the degradation as well as bigger activation, ohmic and concentration losses in the cell \citep{mohsin2020electrochemical}.
+In these polarisation curves, the potential of the cell is plotted over the current densities. Degradation of the membrane, corrosion, carbon corrosion or, as a consequence thereof, platinum catalyst dissolution, all cause the polarisation curve to have a higher drop in the potential at much lower current densities after more cycles, as shown in the aforementioned figure \ref{fig:PolCurve} \citep{Pol_thiele2024realistic}. These mechanisms will be explained in the following section \ref{sec:Degradation}. After a larger number of voltage cycles the higher current densities can no longer be reached as a consequence of the degradation as well as larger activation, ohmic and concentration losses in the cell \citep{mohsin2020electrochemical}.
 
 
 \section{Degradation Mechanisms}
 \label{sec:Degradation}
 
-Automotive conditions can be very stressful for the PEMFC. Start-stop procedures, idling conditions, operation at maximum power as well as quick changes from full power to stop can speed up the degradation progress of the cell and therefore shorten its lifetime \citep{pei2008}. Accelerated stress tests (AST) are a way of testing the components of a PEMFC in a controlled environment without them being in the actual vehicle. It can shorten the test duration by accelerating the degradation processes and simulating different conditions and automotive scenarios \citep{Pol_thiele2024realistic}. This section will provide information on a few of the most important degradation mechanisms that can be found in a PEMFC like platinum catalyst dissolution, membrane degradation, carbon corrosion and finally corrosion. It is also important to mention that there are a lot more mechanisms which can contribute to the degradation of the fuel cell and that these mechanism impact one another\citep{Pol_thiele2024realistic}.
+Automotive conditions can be very stressful for the PEMFC. Start-stop procedures, idling conditions, operation at maximum power, as well as quick changes from full power to stopping can all speed up the degradation progress of the cell and consequently shorten its lifespan \citep{pei2008}. Accelerated stress tests (AST) are one way components of a PEMFC may be tested in a controlled environment without them needing to be in the actual vehicle. It can shorten the test duration by accelerating the degradation processes and simulating different conditions and automotive scenarios \citep{Pol_thiele2024realistic}. This section will provide information on a few of the most important degradation mechanisms that can be found in a PEMFC, such as platinum catalyst dissolution, membrane degradation, carbon corrosion and finally corrosion in general . It is also important to mention that there are many more mechanisms that may contribute to the degradation of the fuel cell, and that these mechanisms all impact one another\citep{Pol_thiele2024realistic}.
 
 \newpage
 
@@ -325,10 +327,10 @@ Automotive conditions can be very stressful for the PEMFC. Start-stop procedures
 \subsection{Platinum Catalyst Dissolution and Agglomeration}
 \label{subsec: Pt}
 
-Carbon-supported platinum nanoparticles in the CL of the PEMFC increase the oxygen reduction reaction (ORR) at the cathode making the cell more efficient. With such an important task it is of utmost importance to understand the degradation mechanism. Studys  have shown, that corrosive acidic environments in the PEMFC under a positive potential can lead to platinum dissolving which consequently causes a reduction in the catalyst performance \citep{cherevko2015}.
+Carbon-supported platinum nanoparticles in the CL of the PEMFC increase the oxygen reduction reaction (ORR) at the cathode making the cell more efficient. With such a crucial task it is of utmost importance to understand the degradation mechanism. Studies have shown that corrosive acidic environments in the PEMFC under a positive potential can lead to the dissolution of platinum, causing a reduction in the catalyst performance \citep{cherevko2015}.
-Pt loss during PEMFC operation is a major contributor to the degradation of the CL. This is driven by processes such as platinum dissolution, Pt-detachment, Pt-migration and Pt-agglomeration. In a study by Luo et al. a 10 cell stack was operated for 200 hours at a temperature of 60 °C. When analysed, the stack showed a reduction from an initial Pt content of 20\% to 13,5\% \citep{luo2010}.
+Pt loss during PEMFC operation is a major contributor to the degradation of the CL. This is driven by processes such as platinum dissolution, Pt-detachment, Pt-migration and Pt-agglomeration. In a study by Luo et al., a 10 cell stack was operated for 200 hours at a temperature of 60 °C. When analysed, the stack showed a reduction from an initial Pt content of 20 \% to 13,5 \% \citep{luo2010}.
 
- While Pt can remain stable at potentials below 1,188 V at high cell voltages and OCV direct electrochemical dissolution may occur at the cathode. At normal operation conditions or during load cycling the dissolution of Pt is more likely to occur \citep{wallnofer2024main}. Lower electrode potentials as well as the voltage cycling can cause Pt oxide dissolution which can be described by the following equations \citep{takei2016}:
+ While Pt can remain stable at potentials below 1,188 V, at high cell voltages and OCV direct electrochemical dissolution may occur at the cathode. During normal operation conditions or load cycling, the dissolution of Pt is more likely to occur \citep{wallnofer2024main}. Lower electrode potentials as well as voltage cycling can cause Pt oxide dissolution which can be described by the following equations \citep{takei2016}:
 
 
 \begin{equation}
@@ -341,21 +343,21 @@ Pt loss during PEMFC operation is a major contributor to the degradation of the
 	\mathrm{PtO}+2 \mathrm{H}^{+} \rightarrow \mathrm{Pt}^{2+}+\mathrm{H}_2 \mathrm{O}
 \end{equation}
 
-Since water is produced in the reaction (2.21)  the higher water content in the ionomer leads to a greater mobilty of the dissolved Pt ions which can facilitate the Ostwald ripening of the particles beneath it \citep{takei2016}.
+Since water is produced in the reaction (2.21) the higher water content in the ionomer leads to a greater mobilty of the dissolved Pt ions, which can facilitate the Ostwald ripening of the particles beneath it \citep{takei2016}.
 
-Platinum migration is another Problem which can degrade the PEMFC by loss of CL performance. The Pt particles may diffuse into the ionomer phase and then precipitate within the membrane (PEM). Furthermore, hydrogen migrating from the anode to the cathode can reduce the Pt ions forming Pt$^{2+}$ and Pt$^{4+}$. This can again cause the oxidation of Pt to PtO as shown in the previous reactions and consequently decrease the cell performance due to the lingering oxygen \citep{pavlivsivc2018platinum,okonkwo2021platinum}. Agglomeration process can facilitate the formation of oxygenated functional groups on the carbon surface which then lead to an increased hydrophilicity of the carbon support. This altered hydrophilicity can influence the displacement of oxygen towards the Pt by controlling the flooding in the CL. Flooding can limit oxygen access to the active reaction sites within the CL and hence decrease the efficiency of the PEMFC \citep{okonkwo2021platinum}.
+Platinum migration is another problem that can degrade the PEMFC by loss of CL performance. The Pt particles may diffuse into the ionomer phase and then precipitate within the membrane (PEM). Furthermore, hydrogen migrating from the anode to the cathode can reduce the Pt ions, forming Pt$^{2+}$ and Pt$^{4+}$. This can again cause the oxidation of Pt to PtO as shown in the previous reactions, and subsequently decrease the cell performance due to the lingering oxygen \citep{pavlivsivc2018platinum,okonkwo2021platinum}. The agglomeration process can facilitate the formation of oxygenated functional groups on the carbon surface which then lead to an increased hydrophilicity of the carbon support. This altered hydrophilicity can influence the displacement of oxygen towards the Pt by controlling the flooding in the CL. Flooding can limit oxygen access to the active reaction sites within the CL and hence decrease the efficiency of the PEMFC \citep{okonkwo2021platinum}.
 
-Losses of activity in the reaction sites can be categorized into two groups. The first one being the unrecoverable losses and the second one are the re-coverable losses. Pt-dettachment as well as agglomeration, dissolution, carbon corrosion and Pt re-deposition are associated with the first group, the unrecoverable losses. Start/ End scenarios expose the cell to very rapid changes in the parameters. Also operating under extreme conditions can accelerate the degradation of the cell and favor the aforementioned mechanisms. 
+Losses of activity in the reaction sites can be categorised into two groups. The first being the unrecoverable losses and the second being those that are recoverable. Pt detachment as well as agglomeration, dissolution, carbon corrosion and Pt redeposition are all associated with the first group, the unrecoverable losses. Start and end scenarios expose the cell to very rapid changes in these parameters. Additionally, operating under extreme conditions can accelerate the degradation of the cell and favour the aforementioned mechanisms. 
- \citep{okonkwo2021platinum}. The recovery loss was linked either to the reduction of platinum oxide or the removal of carbon monoxide which is produced because of the carbon corrosion \citep{okonkwo2021platinum} .
+ \citep{okonkwo2021platinum}. The recovery loss was linked either to the reduction of platinum oxide or the removal of carbon monoxide produced via carbon corrosion \citep{okonkwo2021platinum} .
 
-There is also a second way of classifying the degradation mechanisms. Since one degradation mechanism can trigger or favour another mechanism they can also be classified as primary or secondary depending on their ability to start or intensify another mechanism. For example carbon corrosion is a primary mechanism since it can be responsible for Pt agglomeration and detachment leading to an increased degradation \citep{okonkwo2021platinum}.
+There is also a second way of classifying the degradation mechanisms. Since one degradation mechanism can trigger or favour another, they may also be classified as primary or secondary, depending on their ability to start or intensify another mechanism. For example, carbon corrosion is a primary mechanism, since it can be responsible for Pt agglomeration and detachment, leading to an increase in degradation \citep{okonkwo2021platinum}.
 
 \subsection{Electrochemical Carbon Corrosion}
 \label{subsec: Carbon corrosion}
 
-Since carbon corrosion is a primary degradation mechanism for PEMFCs it is essential to examine this process in greater detail. A deeper understanding of electrochemical carbon corrosion can provide insights into its impact on other mechanisms and especially on the performance and durability of the fuel cell.
+Since carbon corrosion is a primary degradation mechanism for PEMFCs, it is essential to examine this process in greater detail. A deeper understanding of electrochemical carbon corrosion can provide insights into its impact on other mechanisms, and especially on the performance and durability of the fuel cell.
 
-Studys have shown, that start-stop cycles of fuel cells primarily initiate surface corrosion of the carbon support in the CL. Repeated cycles of start-stop conditions can modify the crystalline carbon which will be transformed into a more corrosion-prone amorphous carbon \citep{park2016effects}. Due to the carbon corrosion the CL experiences a loss of thickness which results in detachment of the Pt particles especially at the cathode. This mechanism is not only intensified by start-stop cycles but also by square wave cycles and triangular wave cycles. The first one triggering the corrosion on its surface and internally while the second one targets surface defects \citep{zhao2021carbon}. It is also worth mentioning, that results of an AST in which the cell was exposed to various conditions like load change cycles and start-stop cycles the decreasing perfomance could be attributed by one third to the shutdown and startup cycles proving how demanding this step can be for a cell and how it can increase the degradation \citep{zhao2021carbon,lin2015investigating}. Dependening on the cell conditions either one of the following three reactions can lead to carbon corrosion \citep{wallnofer2024main}.
+Studies have shown that start-stop cycles of fuel cells primarily initiate surface corrosion of the carbon support in the CL. Repeated cycles of start-stop conditions can modify the crystalline carbon which will be transformed into a more corrosion-prone amorphous carbon \citep{park2016effects}. Due to the carbon corrosion, the CL experiences a loss of thickness, resulting in detachment of the Pt particles, especially at the cathode. This mechanism is not only intensified by start-stop cycles, but also by square wave cycles and triangular wave cycles. The former triggering the corrosion on its surface and internally, while the latter targets surface defects \citep{zhao2021carbon}. It is also worth mentioning that in the results of an AST in which the cell was exposed to various conditions, like load change cycles and start-stop cycles, the decreasing perfomance could be attributed by one third to the shutdown and startup cycles, proving how demanding this step can be for a cell and how it can increase the degradation \citep{zhao2021carbon,lin2015investigating}. Dependening on the cell conditions, either one of the following three reactions can lead to carbon corrosion \citep{wallnofer2024main}.
 
 \begin{equation}
 	\mathrm{C}+2 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{CO}_2+4 \mathrm{H}^{+}+4 e^{-} \mathrm{E}_0=0.207 \mathrm{~V}
@@ -367,101 +369,101 @@ Studys have shown, that start-stop cycles of fuel cells primarily initiate surfa
 	\mathrm{CO}+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{CO}_2+2 \mathrm{H}^{+}+2 e^{-} \mathrm{E}_0=-0.103 \mathrm{~V}
 \end{equation}
 
-Another effect of carbon corrosion is the reduction in the hydrophobicity of the GDL which could be attributed to the loss of PTFE and its hydrophobic properties if the cell is flooded while operating at a high current \citep{pei2008}. As mentioned before carbon corrosion can be increased not only by start-stop conditions but also by high potentials. This can then be observed in the polarization curve causing a bigger activation loss at low current densities \citep{Pol_thiele2024realistic}. 
+Another effect of carbon corrosion is the reduction in the hydrophobicity of the GDL, which could be attributed to the loss of PTFE and its hydrophobic properties if the cell is flooded while operating at a high current \citep{pei2008}. As mentioned previously, carbon corrosion may be increased not only by start-stop conditions but also by high potentials. This can then be observed in the polarisation curve, causing a larger activation loss at low current densities \citep{Pol_thiele2024realistic}. 
 
-Due to an more hydrophilic behaviour because of the carbon corrosion and loss of PTFE the membrane responds slow to quick changes from high to low load which results in water accumulating on the anode side and therefore a reduced hydrogen supply, furthermore the pressure difference between inlet and outlet on the anode hinders the water from being removed. As a consequence of this when the load is increased again quickly the anode can suffer from partial hydrogen starvation which again intensifies the carbon corrosion because of the high electrode potential forming on the cathode side \citep{Pol_thiele2024realistic}.
+Due to more hydrophilic behaviour due to carbon corrosion and loss of PTFE, the membrane responds slowly to quick changes from high to low load, resulting in water accumulating on the anode side and therefore a reduced hydrogen supply. Furthermore, the pressure difference between inlet and outlet on the anode prevents the water from being removed. As a consequence of this, when the load is increased again quickly, the anode can suffer from partial hydrogen starvation, again intensifying the carbon corrosion due to the high electrode potential forming on the cathode side \citep{Pol_thiele2024realistic}.
 
-Lastly not only the activation polarization is affected by the carbon corrosion but also the ohmic loss is increased. This increase in the ohmic loss results from the decrease activity of the Pt catalyst since the loss in thickness from the CL and its consequent detachment of Pt particles at the cathode weaken its activity \citep{ren2020degradation}. To be more precise the degradation of the porous structure in the CL causes extended pathways for electrons which increase the contact resistance of the PEMFC \citep{wallnofer2024main}.
+Lastly, the activation polarisation is affected by the carbon corrosion and the ohmic loss is increased. This increase in the ohmic loss results from the decrease in activity of the Pt catalyst, since the loss in thickness from the CL and its consequent detachment of Pt particles at the cathode weaken its activity \citep{ren2020degradation}. To be more precise, the degradation of the porous structure in the CL causes extended pathways for electrons, increasing the contact resistance of the PEMFC \citep{wallnofer2024main}.
 
 \subsection{Membrane Degradation}
 \label{subsec:membrane degradation}
 
-As membrane degradation plays a huge roll in the performance of the cell it is important to understand how it works and how the PEMFC can be affected by this mechanisms. Since the polyelectrolyte membrane (PEM) is formed by perfluorsulfonic acid (PFSA) also known as Nafion it is important to look at the degradation mechanism of it \citep{okonkwo2021nafion}.
+As membrane degradation plays a significant role in the performance of the cell, it is important to understand how it works and how the PEMFC can be affected by these mechanisms. Since the polyelectrolyte membrane (PEM) is formed by perfluorsulfonic acid (PFSA), also known as Nafion, it is important to look at its degradation mechanism \citep{okonkwo2021nafion}.
 
- The chemical degradation of the PFSA ionomer is linked to the membrane decay and can lead to pinhole formations. It is driven by hydrogen peroxide radicals which are known to be formed at potentials below 0,682V and in acid environment \citep{wallnofer2024main}. Since the membrane transports water (H$_2$O), protons (H$^+$) as well as oxygen (O$_2$) form the anode to the cathode it is possible that the Pt in the CL catalyses the reaction of the oxygen with the protons from the hydrogen (H$^+$) forming hydrogen peroxide (H$_2$O$_2$) as an intermediate product \citep{frensch2019impact}. This can be described using the following reaction equation (\ref{eq: h2o2}) \citep{ruvinskiy2011using} .
+ The chemical degradation of the PFSA ionomer is linked to the membrane decay and can lead to pinhole formations. It is driven by hydrogen peroxide radicals, which are known to be formed at potentials below 0,682V and in acidic environments \citep{wallnofer2024main}. Since the membrane transports water (H$_2$O), protons (H$^+$) and oxygen (O$_2$) from the anode to the cathode, it is possible that the Pt in the CL catalyses the reaction of the oxygen with the protons from the hydrogen (H$^+$), forming hydrogen peroxide (H$_2$O$_2$) as an intermediate product \citep{frensch2019impact}. This can be described using the following reaction equation (\ref{eq: h2o2}) \citep{ruvinskiy2011using} .
  
  \begin{equation}
  	\mathrm{O}_2+2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_2 \mathrm{O}_2
  	\label{eq: h2o2}
  \end{equation}
 
-The PFSA membrane can also be suffer from the chemical degradation caused by an attack of free radicals. Hydroxyl radicals (OH), hydroperoxyl radicals (OOH) and hydrogen radicals (H) can be the species responsible for this attack to the membrane which can again lead to the formation of pinholes in the membrane and therefore cause its failure \citep{ren2020degradation}. With the presence of metal ions like Fe$^{2+}$ or Cu$^{2+}$ the formations of radicals from hydrogen peroxide can be catalysed. This mechanism is called the Fenton reaction and can be seen in the following equation
+The PFSA membrane can also suffer from chemical degradation caused by an attack of free radicals. Hydroxyl radicals (OH), hydroperoxyl radicals (OOH) and hydrogen radicals (H) can be the species responsible for this attack to the membrane, again possibly leading to the formation of pinholes in the membrane, therefore causing its failure \citep{ren2020degradation}. With the presence of metal ions like Fe$^{2+}$ or Cu$^{2+}$, the formation of radicals from hydrogen peroxide can be catalysed. This mechanism is called the Fenton reaction and can be seen in the following equation
 \citep{frensch2019impact, ruvinskiy2011using}.
 
 \begin{equation}
 	\mathrm{H}_2 \mathrm{O}_2+\mathrm{Fe}^{2+} \rightarrow \mathrm{Fe}^{3+}+\mathrm{HO}^{+}+\mathrm{HO}^{-}
 \end{equation}
 
-It is believed, that metal components like the BPs made out of Stainless Steels can release metal ions which can then travel to the membrane and either stay in it or transported out by one of the outlets \citep{elferjani_coupling_2021}.
+It is believed that metal components like the BPs made out of stainless steels can release metal ions which can then travel to the membrane and either stay in it or be transported out by one of the outlets \citep{elferjani_coupling_2021}.
-Hydrogen peroxide radicals released by the Fenton reaction cause degradation at the weaker points in the ionomer. This could be for example the functional end groups or C-H bonds in the PTFE chain which sometimes arise from the manufacturing process as well as substituted C-F bonds. The  attack leads to either breakdown of the ionomers main or side chain or to elimination of the end groups consequently accelerating the degradation process of the membrane and the PEMFC \citep{wallnofer2024main}.
+Hydrogen peroxide radicals released by the Fenton reaction cause degradation at the weaker points in the ionomer. This could be, for example, the functional end groups or C-H bonds in the PTFE chain which sometimes arise from the manufacturing process as well as substituted C-F bonds. The attack leads to either breakdown of the ionomers main or side chain or to elimination of the end groups, subsequently accelerating the degradation process of the membrane and the PEMFC \citep{wallnofer2024main}.
 
-Pt dissolution as mentioned before can also have a huge impact on the membrane degradation. Studys have shown, that Pt band formation although it is minimal during open circuit conditions can also degrade the membrane. However, Pt particles which infiltrate in the membrane may also act as a catalyst for direct generation of OH free radicals bypassing the intermediate formation of H$_2$O$_2$ \citep{ohma2008}.
+Pt dissolution, as mentioned before, can also have a huge impact on the membrane degradation. Studies have shown that Pt band formation, although minimal during open circuit conditions, can also degrade the membrane. However, Pt particles which infiltrate into the membrane may also act as a catalyst for direct generation of OH free radicals bypassing the intermediate formation of H$_2$O$_2$ \citep{ohma2008}.
 
-Membrane degradation can have a series of devastating consequences in the PEMFC like the formation of pinholes which lead to a high gas crossover rate and consequently to high voltage losses or even the reversal of the current in specific cells \citep{Weber_2008}. The loss of functional end groups in the ionomer is also known to increase the membrane resistance and to change water management properties of the membrane \citep{wallnofer2024main}.
+Membrane degradation can have a series of devastating consequences in the PEMFC, such as the formation of pinholes, which lead to a high gas crossover rate and as such to high voltage losses. or even reversal of current in specific cells \citep{Weber_2008}. The loss of functional end groups in the ionomer is also known to increase the membrane resistance and to change water management properties of the membrane \citep{wallnofer2024main}.
 
 \subsection{Corrosion}
 \label{subsec: BP Corrosion}
 
-The use of stainless steel in metallic bipolar plates (BPs) has become increasingly common in PEMFCs due to its low cost and excellent mechanical and electrical properties. However the implementation of stainless steels as a BP material has raised some questions about how its corrosion may affect the durability of FCs since automotive conditions have been known to accelerate the corrosion rate and surface destruction \citep{Corr_ren2022corrosion}. There different types of corrosion like uniform corrosion, galvanic corrosion, interangular corrosion, crevice corrosion and pitting corrosion \citep{jones1996principles}.
+The use of stainless steel in metallic bipolar plates (BPs) has become increasingly common in PEMFCs due to its low cost and excellent mechanical and electrical properties. However, the implementation of stainless steels as a BP material has raised some questions as to how its corrosion may affect the durability of FCs, as automotive conditions have been known to accelerate the corrosion rate and surface destruction \citep{Corr_ren2022corrosion}. The many different types of corrosion include uniform corrosion, galvanic corrosion, interangular corrosion, crevice corrosion and pitting corrosion \citep{jones1996principles}.
 
-Although before getting into the types of corrosion that may occur on the metallic BPs, it is important to first explore the various metals used for their construction. Understanding this materials provides can provide insights into how specific corrosion mechanisms can impact them and consequently damage the PEMFC. Because of its higher corrosion resistance and great properties stainless steels like 304L, 316L and 904L have been under investigation. The composition of these three stainless steels is very similar since they are made out of iron (Fe), chromium (Cr), and nickel (Ni) which could contaminate the MEA \citep{novalin2023demonstrating}. Furthermore, the iron in the   aforementioned stainless steels can catalyse the Fenton reaction seen in equation (\ref{eq: h2o2}) which leads to chemical degradation and the formation of pinholes in the membrane \citep{ruvinskiy2011using,novalin2023demonstrating}.
+Before discussing the types of corrosion that may occur on metallic BPs, it is important to first explore the various metals used for their construction. Understanding these materials can provide insight into how specific corrosion mechanisms can impact them and in turn damage the PEMFC. Because of their higher corrosion resistance and great properties, stainless steels like 304L, 316L and 904L have been under investigation. The composition of these three stainless steels is very similar since they are made of iron (Fe), chromium (Cr) and nickel (Ni) which could all contaminate the MEA \citep{novalin2023demonstrating}. Furthermore, the iron in the aforementioned stainless steels can catalyse the Fenton reaction seen in equation (\ref{eq: h2o2}) leading to chemical degradation and the formation of pinholes in the membrane \citep{ruvinskiy2011using,novalin2023demonstrating}.
 
 \subsubsection{Stainless Steel 316L}
 
- Stainless steel 316 differentiates itself from 304 because of the added molybdenum (Mo) which reinforces its corrosion resistance and offers a higher protection against mechanisms like pitting and crevice corrosion \citep{novalin2023demonstrating}.
+ Stainless steel 316 differentiates itself from 304 because of the added molybdenum (Mo), which reinforces its corrosion resistance and offers a higher protection against mechanisms like pitting and crevice corrosion \citep{novalin2023demonstrating}.
 
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.6\textwidth]{Figures/Theorie/SS316L.pdf}
-	\caption{Comparison of polarization curves at 70 °C and ambient temperature for stainless steel 316L. Retrieved from Wang et al. page 60 [89].}
+	\caption{Comparison of polarisation curves at 70 °C and ambient temperature for stainless steel 316L. Retrieved from Wang et al. page 60 [89].}
 	\label{fig:SS316L}
 \end{figure}
 
-In a study performed by Wang et al the electrochemical behaviour of stainless steel 316L was tested in a potentiodynamic test in 0,5M H$_2$SO$_4$ with a a potential reaching from -0,1V to 1,2V with a scanning rate of 1mV/s at room temperature and 70 °C as shown in figure \ref{fig:SS316L}
+In a study performed by Wang et al., the electrochemical behaviour of stainless steel 316L was tested in a potentiodynamic test in 0,5M H$_2$SO$_4$ with a potential reaching from -0,1V to 1,2V with a scanning rate of 1mV/s at room temperature and 70 °C, as shown in figure \ref{fig:SS316L}
-\citep{Corr_Mat_wang2010electrochemical}. This polarization curve can be divided into three different parts\citep{Corr_Mat_wang2010electrochemical}:
+\citep{Corr_Mat_wang2010electrochemical}. This polarisation curve can be divided into three different parts\citep{Corr_Mat_wang2010electrochemical}:
 \begin{enumerate}
 	\item Active region: OCP to -0,15V.
 	\item Passive region: -0,15V to 0,9V.
 	\item Transpassive region: 0,9V to 1,2V
 \end{enumerate}
 
-Since the curve at high temperatures shows a higher current density a higher operation temperature of a PEMFC can also be associated to a higher corrosion rate. Furthermore the formation of the passive region shows that the Cr in 316L is able to produce a passive film that inhibits further corrosion until the transpassivation is reached with a higher potential \citep{Corr_Mat_wang2010electrochemical}. Although the corrosion is enhanced at the passive region with the formation of an oxide layer, since this layer is less reactive it can also contribute to the performance degradation of the PEMFC
+Since the curve at high temperatures shows a higher current density, a higher operation temperature of a PEMFC can also be associated to a higher corrosion rate. Furthermore, the formation of the passive region shows that the Cr in 316L is able to produce a passive film that inhibits further corrosion until the transpassivation is reached with a higher potential \citep{Corr_Mat_wang2010electrochemical}. Although the corrosion is enhanced at the passive region with the formation of an oxide layer, since this layer is less reactive it can also contribute to the performance degradation of the PEMFC
 \citep{laedre2017materials}.
 
-Startup and shutdown conditions in the PEMFC can lead to an increase in the cathode potential which leads to the potential being at the transpassivation region \citep{Corr_ren2022corrosion}. Cycling between the transpassivation region and the passive or passivation region causes the dissolution of Cr species as well as Fe species leading to an extensive structural damage also causing nonuniformity scratches and defects in the surface of the BP\citep{Corr_ren2022corrosion}. The cathode environment because of the contant with oxygen as well as the produced water at the outlet hosts an environment which can lead to the accumulation of metallic elements \citep{Corr_kumagai2012high}.
+Startup and shutdown conditions in the PEMFC can lead to an increase in the cathode potential, which results in the potential being at the transpassivation region \citep{Corr_ren2022corrosion}. Cycling between the transpassivation region and the passive or passivation region causes the dissolution of Cr species as well as Fe species leading to extensive structural damage, also causing nonuniformity scratches and defects in the surface of the BP\citep{Corr_ren2022corrosion}. The cathode environment, because of the contact with oxygen as well as the water produced at the outlet, hosts an environment that is favourable to the accumulation of metallic elements \citep{Corr_kumagai2012high}.
 
 
 \subsubsection{Pitting Corrosion}
 
-Pitting corrosion is a mechanism which causes localized depassivation, this usually happens at vulnerable surface sites like defects, grain boundaries or impurities \citep{novalin2023demonstrating}. Additionally, changes in the pH can alter the composition of the passivation layer. In the presence of fluoride (F$^-$) this process is intensified leading more severe pitting corrosion which causes the corrosion current density to increase which can be detected by the density of pits formed on the surface \citep{Corr_ren2022corrosion}. Once one or more pits are initiated, the material undergoes rapid dissolution further compromising the integrity of the material \citep{elferjani_coupling_2021}.
+Pitting corrosion is a mechanism which causes localised depassivation. This usually happens at vulnerable surface sites like defects, grain boundaries or impurities \citep{novalin2023demonstrating}. Additionally, changes in the pH can alter the composition of the passivation layer. In the presence of fluoride (F$^-$), this process is intensified, leading to more severe pitting corrosion which causes the corrosion current density to increase. This can be detected by the density of pits formed on the surface \citep{Corr_ren2022corrosion}. Once one or more pits are initiated, the material undergoes rapid dissolution, further compromising the integrity of the material \citep{elferjani_coupling_2021}.
 
-The F$^-$ is most commonly encountered in the FC environment due to the membrane degradation (or PFSA). High concentrations of F$^-$  may come from localized evaporations of water droplets which consequently increase the corrosiveness of the run-off water and all in all lead to a more severe degradation of the PEMFC \citep{talbot2018corrosion}. Stainless steel plates are sensible to changes in temperature, humidity and pH therefore a change of any of these parameters can have a big influence on its corrosion resistance. Furthermore 316L has a known depassivation at pH levels ranging from 1,5 to 2 \citep{elferjani_coupling_2021}. Consequently conditions in a PEMFCs creates an environment that may promote pitting corrosion \citep{novalin2023demonstrating}.
+The F$^-$ is most commonly encountered in the FC environment due to the membrane degradation (or PFSA). High concentrations of F$^-$  may come from localised evaporations of water droplets, which consequently increase the corrosiveness of the run-off water and overall lead to a more severe degradation of the PEMFC \citep{talbot2018corrosion}. Stainless steel plates are sensitive to changes in temperature, humidity and pH. Therefore, a change of any of these parameters can have a big influence on its corrosion resistance. Furthermore, 316L has a known depassivation at pH levels ranging from 1,5 to 2 \citep{elferjani_coupling_2021}. Consequently, conditions in PEMFCs create an environment that may promote pitting corrosion \citep{novalin2023demonstrating}.
 
 
 
 \subsubsection{Crevice Corrosion}
 
-Crevice corrosion has a similar effect than pitting corrosion but unlike pitting corrosion it is driven by geometric features of the components which lead to the creation of highly corrosive micro-environments \citep{talbot2018corrosion}. This type of corrosion may be found in the flow field of the BPs depending on its design. As mentioned before, the molybden in stainless steel 316L provides a higher resistance against crevice corrosion \citep{novalin2023demonstrating}.
+Crevice corrosion has a similar effect to pitting corrosion but, unlike pitting corrosion, it is driven by the geometric features of the components that lead to the creation of highly corrosive micro-environments \citep{talbot2018corrosion}. This type of corrosion may be found in the flow field of the BPs depending on its design. As mentioned before, the molybdenum in stainless steel 316L provides a higher resistance against crevice corrosion \citep{novalin2023demonstrating}.
 
 
 \subsubsection{Interangular Corrosion}
 
-Intergranular corrosion typically occurs along the boundaries of the grains of the stainless steel alloys therefore it is often associated with the welding process  \citep{talbot2018corrosion}. In this mechanism the boundary acts as the anode , while the surrounding metal serves as the cathode. Due to the big size difference from this anode to the cathode a rapid and concentrated attack to the metal takes place \citep{pe2009fundamentals}. This process leads to significant localized degradation of the material \citep{pe2009fundamentals}.
+Intergranular corrosion typically occurs along the boundaries of the grains of the stainless steel alloys and it therefore is often associated with the welding process \citep{talbot2018corrosion}. In this mechanism, the boundary acts as the anode, while the surrounding metal serves as the cathode. Due to the big size difference from this anode to the cathode, a rapid and concentrated attack on the metal takes place \citep{pe2009fundamentals}. This process leads to significant localised degradation of the material \citep{pe2009fundamentals}.
 
 \subsubsection{Galvanic Corrosion}
 
-Galvanic corrosion can occur when two different metals are in electrical contact in a conductive corrosive environment \citep{al2016modeling}. In this case the driving force is the potential difference between the two metals and the more active metal will act as the anode and corrode. Meanwhile, the more noble metal will function as cathode and be protected from the degradation \citep{al2016modeling}. Since galvanic corrosion leads to the degradation from the anodic metal it will also trigger pitting corrosion \citep{saeed2013effect}.
+Galvanic corrosion can occur when two different metals are in electrical contact in a conductive corrosive environment \citep{al2016modeling}. In this case the driving force is the potential difference between the two metals, and the more active metal will act as the anode and corrode. Meanwhile, the more noble metal will function as the cathode and be protected from degradation \citep{al2016modeling}. Since galvanic corrosion leads to degradation from the anodic metal it will also trigger pitting corrosion \citep{saeed2013effect}.
 
 \subsubsection{Uniform Corrosion}
 
-In the uniform corrosion the material occurs consistently across the entire metal surface and leads to the gradual thinning of the material over time weakening its structure \citep{pe2009fundamentals}. The material has be in contact with the corrosive environment with an equal access to the entire area for it to be degraded evenly \citep{pe2009fundamentals}.
+In uniform corrosion, the material corrodes consistently across the entire metal surface and leads to the gradual thinning of the material over time, weakening its structure \citep{pe2009fundamentals}. The material must be in contact with the corrosive environment with equal access to the entire area for it to be degraded evenly \citep{pe2009fundamentals}.
 
 \subsubsection{Effects of Corrosion}
 
-In addition to the degradation of the BP, it is important to consider that the corrosion reaction releases metal ions into the cell which can lead to the contamination of other FC components in the PEMFC. For example metal ions from Fe or Cr can migrate throughout the cell and potentially poison the MEA which can further contribute to the performance loss and degradation of the cell \citep{low2024understanding}. In a study performed by Mele et al. a high accumulation of Fe was found in the MEA and especially in the GDL \citep{Corr_mele2010localised}.
+In addition to the degradation of the BP, it is important to consider that the corrosion reaction releases metal ions into the cell which may lead to the contamination of other FC components in the PEMFC. For example, metal ions from Fe or Cr can migrate throughout the cell and potentially poison the MEA, potentially further contributing to loss in performance and degradation of the cell \citep{low2024understanding}. In a study performed by Mele et al., a high accumulation of Fe was found in the MEA and especially in the GDL \citep{Corr_mele2010localised}.
 
-Structural changes in the BPs, such as variations in shape and thickness caused by corrosion can affect the gas flow  and disrupt the water management of the cell leading to cell flooding or air starvation which will dramatically shorten the lifespan of the PEMFC \citep{low2024understanding}. Pinholes or cracks in the BPs due to corrosion can also lead to gas crossover as well as liquid leakage which can destroy the cell  \citep{low2024understanding}. 
+Structural changes in the BPs, such as variations in shape and thickness caused by corrosion, can affect the gas flow and disrupt the water management of the cell, leading to cell flooding or air starvation, dramatically shortening the lifespan of the PEMFC \citep{low2024understanding}. Pinholes or cracks in the BPs due to corrosion can also lead to gas crossover as well as liquid leakage, possibly destroying the cell \citep{low2024understanding}. 
 
-The cathode CL is susceptible to corrosion as a consequence of Pt disintegration or dissolution which is particularly pronounced during fatigue because of voltage cycling or due to high potentials applied to the anode electrode \citep{matsutani2010}.
+The cathode CL is susceptible to corrosion as a consequence of Pt disintegration or dissolution, which is particularly pronounced during fatigue because of voltage cycling or even high potentials applied to the anode electrode \citep{matsutani2010}.