\chapter{Introduction}
\label{cap:Introduction}

\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}.

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}.

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}.

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 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}.

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
\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}. 

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}.




\section{Problem Statement}

In the past bipolar plates for PEMFCs were 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. \\
%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.
\end{enumerate}




\section{Outline of the Thesis}
In the last part of the introduction, the outline of your report should be defined. You should include the approach and applied strategy to solve your assignments as well.