Merge pull request 'Method' (#3) from method into master

Reviewed-on: http://git.djledda.de/Ledda/MA_Platteau/pulls/3

Content/Introduction.tex

@@ -3,40 +3,40 @@
 
 \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}.
-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}.
+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 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}.
-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
+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 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
-\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}.
+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}. 
+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}
-
-In the past bipolar plates for PEMFCs were made out of Titanium or Ti-C Coated materials. 
+E
+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 Understanding which operating conditions will reinforce corrosion. 
-	\item 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 deepen the understanding of corrosion on stainless steel bipolar plates by analyzing SS316L plates and defining the main corrosion mechanism.
+	\item To understanding which operating conditions will reinforce corrosion. 
+	\item To develop a endurance run with reinforcing conditions for corrosion.
+	\item To further development of ex-situ analytical methods to characterise, detect and evaluate corrosion damage on bipolar plates.
 \end{enumerate}
 
 

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 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}.
+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}.
 
 \section{Experimental Setup}
 \label{sec: M_Setup}
 
 
-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. 
+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. 
 
 \subsection{Stack}
 
-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}.
+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}.
 
 %Skizze von der Zelle?
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.7\textwidth]{Figures/Method/Stack.pdf}
-	\caption{Schematic of the structure in the used test specimen with its different components and position. Retrieved from Sabawa. page 43 [99].}
+	\caption{Schematic of the structure in the test specimen used 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 explained shortly:
+In the following, each numbered component will be named and briefly explained:
 \begin{enumerate}
-	\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 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{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 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}: 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 a more detailed way. 
+	\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{Compression plate}: This plate is made 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{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{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{Stacked BPs and MEA}: The "sandwich structure" of the cells will be explained in the next part in more detail. 
 	\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 integraded pneumatic pressure pads.
-	\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 lateral in the test bench it will be supported by the feet.
+	\item  \textbf{Compression plate}: The compression plate on the other side with integrated 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{Feet}: Since the test specimen is placed laterally in the test bench, it is 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 its active area in a darker grey 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 their active area in a darker grey colour 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 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. 
+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. 
 
-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$^2$.
+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$^2$.
 
 \subsection{Testbench}
 
- 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. 
+ 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. 
 
 \begin{figure}[htbp]
 	\centering
@@ -61,9 +61,9 @@ Two types of cells where used in the experiment. Type one is made out of titaniu
 	\label{fig:Setup_Preliminary}
 \end{figure}
 
-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.
+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.
 
-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.
+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.
 
 \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 40-180°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).
+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).
 
 \subsection{Dew Point Calculation}
 
-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}.
+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}.
 
-\subsection{Calculation of the Stochiometrie}
+\subsection{Stochiometry Calculation}
 
-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 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 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}.
+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}.
 
 \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 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.
+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.
 
-\subsection{Characterization of Cells}
+\subsection{Characterisation of Cells}
 
-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.
+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.
 
-\subsubsection{Polarization Curves}
+\subsubsection{Polarisation Curves}
 
-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}.
+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}.
 
 \begin{table}[h]
 	\centering
@@ -113,23 +113,23 @@ As a standard procedure three different polarization curves will be tested. Betw
 		90& 105 & 62& 2&105& 62& 2\\
 		
 	\end{tabular}
-	\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].}
+	\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].}
 	\label{tab:PolKurve}
 \end{table}
 
-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.
+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.
 
 \newpage
 \section{Preliminary Investigation}
 \label{sec: M_Preliminary}
 
-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.
+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.
 
-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$^-$.
+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$^-$.
 
 \subsection{Experimental Setup}
 
-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.
+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.
 
 \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 characterization with polarization curves.
+	\item Begin of life characterisation with polarisation curves.
 	\item Parameter variation tests with voltage cycling.
-	\item  End of life characterization of the cells.
+	\item End of life characterisation of the cells.
 \end{enumerate}
 
-This Steps will be explained in a more detailed way in the following. Starting with the activation of the cell after the startup.
+These steps will be explained in a more detail in the following. Starting with the activation of the cell after the startup.
 
 \subsubsection{Activation of the Cell}
 
-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 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.
+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 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.
 
-\subsubsection{Begin of Life Characterization}
+\subsubsection{Begin of Life Characterisation}
 
-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.
+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.
 
 \subsubsection{Parameter Variation} 
 
-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}.
+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}.
 
 \begin{table}[h]
 	\centering
@@ -172,21 +172,25 @@ Three different operating parameters where tested to see how the cell and gas te
 	\label{tab:3_pH_T}
 \end{table}
 
-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.
+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.
 
-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:
+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:
 \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 Ramp up current density and Volume flow of the gases until 2 A/cm$^2$.
-	\item Start Voltage cycling for 2h.
+	\item Ramp up current density and volume flow of the gases until 2 A/cm$^2$.
+	\item Start voltage cycling for 2h.
     \item Shut down.
 \end{enumerate} 
 
-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.
+After reaching the set parameters the 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 shutdown the product water was
+collected at the cathode and anode to be measured at the laboratory.
 
 \begin{figure}[htbp]
 	\centering
@@ -198,19 +202,19 @@ After reaching the set parameters the cell Voltage cycling of the cell was manua
 \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 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.
+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.
 
 \subsection{Experimental Setup}
 
-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. 
+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. 
 
 \subsection{Experimental Execution}
 
-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.
+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.
 
 \subsubsection{Activation of the Cell}
 
-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}.
+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}.
 
 \subsubsection{Endurance Runs}
 
@@ -218,24 +222,24 @@ Since the 60°C polarization curve presents a higher humidity than the 80°C pol
 \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. Between each step the in-situ characterization is performed.}
+	\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.}
 	\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 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.
+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.
 
-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}.
+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}.
 
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.6\textwidth]{Figures/Method/ECU.pdf}
-	\caption{Voltage cycling of the cell between 10s at 0,88V and 10s at 0,6V.}
+	\caption{Voltage cycling of the cell between 10 seconds at 0,88 V and 10 seconds at 0,6 V.}
 	\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 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}.
+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}.
 
 \begin{table}[h]
 	\centering
@@ -245,15 +249,15 @@ 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 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.
+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.
 
 \subsubsection{High Temperature Endurance Run}
 
-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}.
+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}.
 
 \begin{table}[h]
 	\centering
@@ -267,19 +271,19 @@ For the high temperature endurance run the parameters are different. Starting wi
 	\label{tab:3_ER_HT}
 \end{table}
 
-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.
+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.
 
 \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 optically 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 visually analysed.
 
 \begin{figure}[htbp]
 	\centering
 	\includegraphics[width=0.8\textwidth]{Figures/Method/FlowField.pdf}
-	\caption{Matrix of the active area of the cell for to clarify the exact positions analysed.}
+	\caption{Matrix of the active area of the cell to clarify the exact positions analysed.}
 	\label{fig:Matrix}
 \end{figure}
 
@@ -287,16 +291,16 @@ 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 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}.
+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}.
 
 \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 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. 
+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. 
 
 
 \subsection{SEM/EDX Analysis}
 
-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}.
+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}.
 
 
 

Content/Results and Discussion.tex

@@ -1,34 +1,546 @@
 \chapter{Results and Discussion}
 \label{chap:Ergebnisse und Diskussion}
 
+The following chapter will present the findings of both in-situ and ex-situ investigations, along with a 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}, will present and discuss the results of the in-situ methods.
 
 
-\section{Material Characterization of  SS316L}
+\section{Preliminary Investigation}
+\label{subsec:4_Prelim}
 
-\subsubsection{Corrosion Parameters}
+Before starting the endurance run, a preliminary investigation was first 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 that were conducted. Although these investigations were planed on a 10 cell stack made of type 2 cells (stainless steel 316L BP), the plan was changed due to limited stock of these cells after the first stack broke down. This was due to several hard shutdowns 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 then changing to 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 in that the water production was higher than expected, as well as the fact that the test stopped after 45 minutes of voltage cycling between 15s at 0,85 V and 10s at 0,6 V. The other two tests instead cycled for 2 hours before shutting down. The measured electrical conductivity of the test was lower than that of the other two test with 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 each of the other tests the pH measured at the cathode was lower than at 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 in pH coincided with an increase in temperature. Although the increase in temperature from 50 °C to 90 °C at a relative humidity of 35\% showed a pH increase from 2 to 5 \citep{107_abdullah2008effect}. There was an increase in pH from 5,51 to 6 at the cathode achieved by raising the cell temperature from 60 °C to 90 °C. Although noticeable, this increase is still much smaller than that found in the study performed by Abdullah et al.
+
+The difference in the pH measured in the preliminary investigations to that found in the literature could be attributed to two main factors, the first being the duration of the test. Since the tests conducted had a relatively short operating time, with two hours of voltage cycling (compared to the minimum of 30 hours of Abdullah et al.), the membrane had little to no degradation. This resulted 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 composed of Ti-C. The corrosion resistance of Ti is much higher than that of stainless steel; as such, fewer particles will leave the BP due to 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 more acidic product water and hence reinforce the corrosion mechanism. For both endurance runs, cells type 2 were used, as the type 1 cells made out of Ti-C have a higher corrosion resistance. The test bench was successfully tested with a 4 cell stack composed of type 1 cells. These were used to avoid any damage to the 4 cell stack composed of type 2 (that could have been caused by a malfunction of a test bench). After this test bench, the corrosion endurance run could be started. The results of the in in-situ characterisation of the cells will be presented in more detail in the following section.
+
+\subsection{Polarisation Curves at 60 °C}
+\label{subsec: 60_PolCurve}
+
+The test specimen was activated by repeating the 80 °C polarisation 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) characterisation which included the polarisation curves at 60 °C and 80 °C. The results of the BoL characterisation 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 polarisation curves after the current density was increased to above 0,3 A/cm$^2$. 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 polarisation 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 polarisation. The second best curve at low current densities is the polarisation 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 others. At high current densities, the curve after 81000 VC presents higher losses than the others. The degradation of the test specimen over the period of the 81000 VC is clear, as the voltage of the curves decreases after each characterisation, with the BoL curve being that with the fewest losses followed by the 12500 VC along with the 37500 VC. The highest loss was at high current densities after the last characterisation at 81000 VC.
+
+
+\subsubsection{High-Frequency Resistance (HFR)}
+
+The high-frequency resistance (HFR) was also measured during the polarisation curves since it gives insight into the performance of the cell. A lower HFR may indicate a higher performance, as well as improved hydration of the membrane \citep{108_lin2021prediction}. The results of the measurements during the 60 °C polarisation 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 polarisation 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 polarisation curves, the HFR of the curves after 12500 VC and after 37500 VC decreases, while the curve after 81000 VC shows a very stable and low value of around 50,5 $m\Omega\cdot\text{cm}^2$ per cell.
+
+The peaks at the beginning are likely 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 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 polarisation curve after 81000 VC when a stable HFR value of around 50,5 is reached and maintained throughout the curve.
+
+
+\subsubsection{60°C Polarisation Curves of the Cells after 81000 VC}
+
+Since the voltage decrease was the highest in the EoL polarisation curve after 81000 VC, the voltage and polarisation curves were also analysed in order to obtain a better overview of the degradation in the cells. The results of the 60 °C polarisation 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 polarisation 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 too, with the first cell showing the highest voltage at 0,6V and the others decreasing in numerical order up 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 polarisation curve could have caused a high concentration polarisation 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 via corrosion of the BP, it may have led to a lower performance in the cell 4 than the others \citep{elferjani_coupling_2021, frensch2019impact}.
+
+\subsection{Polarisation Curves at 80 °C}
+\label{subsec: 80_PolCurve}
+
+After the 60° C polarisation 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, resulting in a RH of 30,1\% for cathode and anode. The results from the 80 °C polarisation 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 polarisation curve at BoL after 12500 VC, 37500 VC and 81000 VC.}
+	\label{fig:80_Pol}
+\end{figure}
+
+
+The 80 °C polarisation curve shows almost no signs of degradation of the cells. The voltage at high current densities of 2,2 A/cm$^2$ is almost identical for all curves at 0,59V, 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 superior to the others. 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 others.
+
+Overall, the 80 °C polarisation curves present much lower degradation than the 60 °C polarisation curve. One reason for this could be the lower RH value of 30,1\% of this polarisation 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 polarisation, 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 very 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. One factor could be the high stoichiometry used in both cathode and anode. Since there is more reactant than needed at the active sites, even a high reaction rate at high current densities will not consume all the reactants and limit the reaction as it would at a lower stoichiometry
+\citep{Loss_mazzeo2024assessing}.
+
+
+
+\subsubsection{High-Frequency Resistance (HFR)}
+
+The HFR measured during the 80° C polarisation curves is presented in Figure \ref{fig:80_HFR}. At very low current densities (below 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 polarisation 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 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 as for the 60 °C polarisation curve, the lowest HFR was measured in the 81000 VC curve. One reason for this could be that the membrane 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 Polarisation Curves of the Cells after 81000 VC}
+
+Figure \ref{fig:80_Cells} displays the 80 °C polarisation curve after 81000 VC of each cell separately. Cell 1 is once again the best performing cell, just as 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 performance compared to one another.
+ 
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/80_Cells.pdf}
+	\caption{80 °C polarisation 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 simultaneously on the same model of test bench as the corrosion endurance run. The same activation sequence with four 80 °C polarisation 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 and cathode. However, the BoL and the characterisation after 12500 VC was completed and its findings will be explained in the following. 
+
+\subsection{Polarisation Curves at 60 °C}
+\label{subsec: 60_PolCurve_HT}
+
+The results of the BoL characterisation and the characterisation 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 polarisation curve at BoL and after 12500 VC.}
+	\label{fig:60_Pol_HT}
+\end{figure}
+
+Between 1 and 1,6 A/cm$^2$ the 60° C polarisation curve after 12500 VC has a slightly better performance than the BoL curve. This could be attributed to an improved humidity level of the membrane leading to a lower ohmic voltage loss and better performance in this section \citep{108_lin2021prediction}
+
+
+\subsubsection{High-Frequency Resistance (HFR)}
+
+Figure \ref{fig:60_HFR_HT} illustrates the HFR measured during the two 60°C polarisation 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 polarisation 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 be one explanation for the performance boost, as the activation losses are compensated at this point by a lower ohmic loss in this section \citep{108_lin2021prediction}. 
+
+\subsubsection{60 °C Polarisation 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 polarisation curve. Cell 4 presents the lowest voltage with a value of  0,57 V, 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 polarisation 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 from after the first cycle of the high temperature endurance run as well as in the 60 °C polarisation curve with the high RH \citep{wallnofer2024main}.
+
+
+\subsection{Polarisation Curves at 80 °C}
+\label{subsec: 80_PolCurve_HT}
+
+The results of the in-situ characterisation with the 80 °C polarisation 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 characterisation 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 polarisation 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 desensities, it results in  the same voltage as the BoL curve. The HFR, to be shown in the following, could explain this behaviour.
+
+
+\subsubsection{High-Frequency Resistance (HFR)}
+
+The HFR of the cells during the 80 °C polarisation 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 stabilises 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 polarisation curve at the BoL, after 12500 VC.}
+	\label{fig:80_HFR_HT}
+\end{figure}
+
+The phenomena seen in the 80 °C polarisation 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 these current densities. During the 12500 VC curve, the membrane has a slightly superior humidification and is therefore able to be more efficient and produce a higher power output due to lower ohmic voltage loss \citep{108_lin2021prediction}. 
+
+
+\subsubsection{80 °C Polarisation 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 polarisation curve after 12500 VC. Cell 1 has the highest voltage of all the cells at high current densities (2,2 A/cm$^2$) while the other cells (2, 3, 4) have almost the same voltage at 0,58 V.
+
+\begin{figure}[htbp]
+	\centering
+	\includegraphics[width=0.9\textwidth]{Figures/Results/PolCurves/80_Cells_HT.pdf}
+	\caption{80 °C polarisation curves of the 4 cells after 12500 VC.}
+	\label{fig:80_Cells_HT}
+\end{figure}
+
+Although the activation losses of all the cells are very similar, the ohmic and polarisation losses of the cells differ from each other. The voltage of cells 2, 3 and 4 is under 0,6 V.
+
+
+Ma et. al. suggest that the higher the initial HFR peak and the temperature of the cell are, the 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 polarisation 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 polarisation curve reached a lower HFR considerably 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 polarisation 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 into 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 polarisation curve after 81000 VC of the corrosion endurance run, these two cells will be compared to a reference cell. The results of this analysis will be presented in the following section, beginning 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 position A6 can be seen in part (a) of the figure and for M1 in part (c) of the figure. In the overview, almost no discolorations were found, except for in the welding seams. These presented a slight red and brown discoloration 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 was conducted. On the other hand, the discoloration 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 exhibits 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 polarisation 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 discoloration, whereas the outlet in the BP 1 (\ref{fig:4_Micro_SP} (b)) remains without discolorations. 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 discolorations and corrosion in the reference plate without having conducted an endurance run, these positions were reanalysed in the BP 4 to inspect for damages. Figure \ref{fig:4_Micro_SP} (e) shows the welding seam in 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 begun to take place.
+
+Welding seams are known to be a weak point for corrosion, as the temperatures of the process causes a decomposition of the austenitic matrix. Cr and Mo are consumed by the formation of precipitates such as carbides, and cause Cr-depleted areas that are more vulnerable to corrosion \citep{yan2019effect}. 
+
+
+\newpage
+\subsubsection{Analysis of the CCM}
+
+Furthermore, the CCM will also be inspected for corrosion or Pt agglomeration, dissolution or any other damage. Since the CCM showed no increased damage at positions A6 and M1 when compared to the other positions in the cell matrix, the positions M6 and A1 will be analysed this time 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 that can be seen in this position are cracks in the CCM. Furthermore, wave structures are also visible across all positions. When inspecting position A1 of the CCM shown in \ref{fig:4_Micro_CCM} (b), the Pt agglomeration is even more prevalent 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 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 presents 4 darker spots that could be part of the MPL that 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, consequently leading to more water in the cell, and in some cases its flooding. This could also result in a limited amount of oxygen reaching the active sites and a decrease in 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 discolorations found in the BP4 and additionally provide better insight into the conditions of the stainless steel 316L plate and its possible corrosion and performance, an additional LIBS analysis was conducted. First the relative atomic concentrations of the positions M1 and A6 of the BP4 were compared to those of the reference BP. The results of this analysis can be found in 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 position M1 of BP4 with the reference plate.}
+	\label{fig:LIBS_M1}
+\end{figure}
 
-\subsection{ICP Measurement}
+When comparing position M1 of the BP4 with the reference plate, the BP4 shows a mild increase in 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 too high 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 impossible to draw a conclusion from this change. Since the position M1 did not present any discolorations it could be possible that only a light oxide layer had started to appear on it.
+
+Figure \ref{fig:LIBS_A6} compares position A6 from the BP 4 to the reference plate. Since the microscopy of position A6 did not present any discolorations 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 in oxygen is even less noticeable than in the comparison of M1 to the reference plate. The other elements 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 from 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 and 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 of an oxide layer, which could explain the discoloration found in Figure  \ref{fig:4_Micro_SP}. This oxide layer is also a clear sign of corrosion in the cell since the corrosion reaction causes formation of a passive oxide layer.
+
+Since the welding seam also showed a clear discoloration 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 apparent that the oxygen percentage increases around 8\% showing signs 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 concentration. Since the concentration change in Cr, Ni and Mo was barely noticeable, it is also not possible to make a final conclusion regarding these metals.
+
+ Due to the fact that welding seams are more susceptible to corrosion, the discoloration seen in these spots and 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 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.
+
+\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}
+
+Despite the fact that the BP 4 corroded, no traces of Fe, Ni or Cr could be found in the CCM, and the EDX therefore 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.
+
+One 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 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 as well as a higher ohmic resistance due to reduced ionic conductivity \citep{low2024understanding}.
+
+A study performed by Novalin et al. also analysed the metal ion dissolution from the BPs due to cycling measurement. They were able to find traces of Fe, Ni and Cr in the GDL and MEA after 700 cycles. They also found 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 drier conditions enhance repassivation mechanisms of the metal BP, making the transport of the metal ions to the MEA less probable \citep{105_novalin2022concepts}.
+
+Lastly, it is also worth discussing the Pt agglomeration, as it was identified by the microscopy and the EDX analysis. Pt agglomeration could be an additional 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/SummaryAndOutlook.tex

@@ -1,10 +1,32 @@
 \chapter{Summary and Outlook}
 \label{cap:SummaryAndOutlook}
 
-\section{Summary}
-Sum up the most important concepts and results of your work in a clear and straightforward way. What was again the main reason for your wok? How did you proceed? Where did you find the biggest problems? Which results did you get?
+The final chapter of this thesis will present a brief summary of the work as well as its motivation in the first section \ref{sec:5_Summary}. The second and last part of this chapter \ref{sec:5_Outlook} will offer an outlook on potential directions for future research.
+
+
+\section{Summary}
+\label{sec:5_Summary}
+
+Since global temperature is on the rise with projections of an increase of 1,5 °C by 2030, it is of utmost importance to implement effective measures to mitigate climate change. GHG and especially CO$_2$ emissions have been identified as the main contributor to global climate, accounting for 80,6\% of emissions. The transportation sector in Germany is responsible for 19,8\% of emissions in the country. It is therefore crucial to transition from ICEs to more sustainable alternatives such as BEVs and FCEVs. While FC technology is on the rise, manufacturing costs continue to be a limiting factor as the BPs constitute 45\% of manufacturing costs. The search for more cost effective alternatives has suggested a change from Ti BPs to stainless steel plates. Although the plates are more cost effective, the corrosion of BP plates raises questions about their durability and how it may affect PEMFC performance. Therefore, this thesis aims to deepen the understanding of the corrosion in stainless steel plates by developing a corrosion reinforcing endurance run and studying the effect of corrosion on the performance of PEMFCs, as well as analysing corrosion damage in cells.
+
+Chapter \ref{cap: Theorie} lays the theoretical background of this thesis. The fundamentals of the fuel cell are explained as well as the components of a PEMFC (PEM, GDL, CL and BP). The membrane is composed of Nafion (PFSA) and the CL has Pt as catalyst for the electrochemical reactions. Before explaining the degradation mechanisms, the overpotentials are first explained using the polarisation curve. At low current densities, the activation losses dominate the polarisation curve. At medium current densities, the ohmic losses dominate the form of the curve and at high current densities the form of the polarisation curve is determined by the concentration polarisation or mass transport losses related to the diffusion limitations of the cell. Afterwards, the main degradation mechanisms are explained, starting with Pt catalyst dissolution and agglomeration, moving on to electrochemical carbon corrosion, membrane degradation and finally corrosion. In the membrane degradation, the fenton reaction is of utmost importance, and this reaction is catalysed by metal ions such as Fe$^{2+}$, which react with H$_2$O$_2$ to form hydroxyl radicals that attack the membrane. In this process, F$^-$ from the membrane is released. F$^-$ decreases the pH of the product water which can then attack the BPs or reinforce corrosion. Pitting corrosion and crevice corrosion as well as galvanic corrosion can lead to structural damages to the cell, cause pinholes or even gas crossover, which will all dramatically shorten the lifespan of the cell.
+
+Chapter \ref{chap:Methode} explains the methods used to analyse the operating conditions that reinforce corrosion and afterwards design a corrosion reinforcing endurance run. In the preliminary investigations, the pH and the electrical conductivity of the product water at three different operating points is tested. The effect of the operating temperature is then measured by searching for the lowest pH due to membrane degradation and release of F$^-$, and subsequently the highest electrical conductivity as a sign from the metal ions released by the BP during a corrosion mechanism. Afterwards, two endurance runs are performed: one with corrosion reinforcing operating parameters, and a second high temperature endurance run for compariso. The cell components of the 4 cell stack are then analysed in the ex-situ investigations using microscopy, LIBS as well as REM and EDX.
+
+The results along with their discussion are then presented in Chapter \ref{chap:Ergebnisse und Diskussion}. Two types of cells were used in this thesis: type 1 made of Ti-C with an active area of 273 cm$^2$ (used for the preliminary investigation) and type 2 cells, made of stainless steel 316L and an active area of 285 cm$^2$ (used in the endurance runs). The preliminary investigations concluded that the lowest pH as well as the highest electrical conductivity was found at a lower temperature (60 °C) at the cathode and the highest pH and lowest electrical conductivity at a temperature of 90 °C after 2 hours of voltage cycling between 10s at 0,6 V and 15s at 0,85 V. The pH found in the literature of 2 was not reached; this could have been caused by the higher corrosion resistance of Ti-C compared to 316L. As such, fewer metal ions moved from the BP to the membrane to catalyse the fenton reaction and the degradation was less than it would have been with a stainless steel plate. The corrosion endurance run was performed at a cell temperature of 66 °C with a 4 cell stack made of type 2 cells (316L). After the activation of the cells using four 80 °C polarisation curves, the BoL characterisation was performed with a 60° C polarisation curve and a 80° C polarisation curve as in-situ characterisation. Then, the cell was set up for 12500 VC of 10s at 0,6 V and 10s at 0,88 V, followed by the in-situ characterisation. Next, the 25000 VC was followed by the in-situ characterisation and finally 42500 VC followed by the last in-situ characterisation. The 60 °C polarisation curve showed a higher degradation than the 80 °C polarisation curve. A significant difference in the cell voltages at high current densities was measured in the 60°C polarisation curve between cells 1 and 4. Cell 1 presented a voltage of 0,6 V while cell 4 had a voltage of 0,53V. Due to this difference, the two cells were further analysed in the ex-situ section. The 80 °C polarisation curve showed almost no signs of degradation after 81000 VC, which can be attributed to the high stoichiometry of 1,5 at the anode and 2 at the cathode, as well as to the low HFR measured. The low HFR after 81000 VC indicates an optimal humidity level of the cell and therefore a lower ohmic polarisation. This results in improved cell performance.
+
+The ex-situ analysis of cells 1 and 4 of the corrosion endurance run showed signs of corrosion in the welding seams of both cells as well as corrosion in the cathode outlet of the cell 4. The CCM of both BP 1 and 4 showed Pt agglomeration as well as cracks and a wave structure. The LIBS analysis performed on the welding seam and the cathode outlet showed an increased oxide layer and decreased carbon percentage in the measurement. The Fe, Ni and Cr percentages could not be analysed correctly due to their high standard deviations. The oxide layer and the Pt agglomerations could have caused increased losses in performance of the cell, although the losses could also be attributed to membrane degradation and carbon corrosion (i.e. decrease in carbon percentage of the material). A REM and EDX analysis of the cathode CCM in BP 1 and 4 showed no traces of metals from the BP (Fe, Ni, Cr), and thus no signs of the migration from the BP to the CCM. This could be attributed to the duration of the endurance run of 400h. Finally, the next section will present an outlook on the topic of this thesis.
 
-You can include here a commented and reviewed analysis of your procedure. Comments and opinions must not necessarily be negative. Try to mention both positive and negative sides.
 
 \section{Outlook}
-Try to mention what could be done in the future. This section is of major importance for future works dealing with similar problems. Let people working on these future works take advantage from the experience you gained. The outlook is very important for a scientific report. Mention also possible future work that can be carried out from your results.
+\label{sec:5_Outlook}
+
+Due to time constraints and problems with the first test bench in which the preliminary investigations were conducted, some of the experiments will have to be repeated. After a promising result in the pH and electrical conductivity measurements, the next step would have been to repeat these analyses with a stack made of the type 2 stainless steel cell. This could lead to lower pH and a higher electrical conductivity as a sign of corrosion, which was not the case with the type 1 plates made of Ti-C. Furthermore, an online pH and electrical conductivity measurement of the endurance runs could lead to a better understanding of the operating conditions and the condition of the cell in the different states of the endurance run. Moreover, a more detailed analysis of the product water, including Fe, Cr, Ni, Si, Mo, magnesium (Mg) and fluoride could provide a better overview of the corrosion mechanism and consequently the dissolution of the metal ions, enabling them to be traced in the product water. It would also be helpful to create a correlation between the fluoride content and the metal ions that cause the membrane degradation (or degradation of Nafion) catalysed by the metal ions in the Fenton reaction.
+
+The use of other analytical methods such as X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS) could also produce a much better result when analysing components of the PEMFC. Metal traces of Fe, Ni or Cr could be detected on the CCM, GDL and MPL. XPS could provide deeper insights into the oxide layer on the BP, therefore offering a more detailed understanding of BP corrosion.
+
+Potentiostatic and potentiodynamic measurements of the stainless steel could also be performed to evaluate the BP material and compare it to the targets set by the DOE for 2025 as stated in the theoretical background in section \ref{subsec:2_DOE}. Lastly, the research could also focus on other types of stainless steels. Potential candidates might be 304, 904L, 321 or even other coatings for the different BP materials to improve corrosion resistance.
+
+
+
+

Content/Theoretical Background.tex

@@ -1,8 +1,3 @@
-- electric vs. electrical ?
-- do not "require" (???) any external reformer
--
-
-
 \chapter{Theoretical Background}
 \label{cap: Theorie}
 
@@ -38,7 +33,7 @@ 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-}$). Like SOFCs, they can also be operated with both pure hydrogen (H$_2$) and biogas, which could also contain CH$_4$ as well as CO$_2$ and CO \citep{02_lucia2014overview, 02_wang2020fundamentals}.
-As such, SOFCs and MCFCs do not require 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 °C
 \citep{MCFS_cui2021review}. Furthermore, the electrical efficiency of the MCFCs can reach up to 60\% \citep{wang_preparation_2018}.