Polymeric electrolyte membrane (PEM) fuel cells are in contrast to SOFCs based on a polymeric electrolyte which is proton conducting. Conventional PEMs usually employ water containing polymers as electrolyte, which is responsible for the proton conduction. Due to the physical properties of water they cannot be used above a temperature of 80 °C. High temperature PEMs (HTPEM) are based on polymers doped with phosphoric acid. Thus, HTPEMS can operate at temperatures up to 200° C. This leads to faster chemical reactions, higher efficiencies and most importantly better tolerance to fuel impurities. Since HTPEMs can be started and shutdown relatively quickly and also have good fuel tolerance, they are most promising for mobile applications (e.g. electric cars, caravans or boats). The material challenges encountered in HTPEMs are mainly related to the phosphoric acid which migrates under operation. This leads to decreasing performance and severe corrosion problems.