Thin Membranes for PEM Water Electrolysis and the Challenge to Reduce Hydrogen Permeation

In order to reach the system efficiency targets for PEM water electrolysis of more than 70% LHV at current densities of up to 3 A/cm², thin membranes are indispensable. It is known that the use of thin membranes leads to the disadvantage that they additionally have to be stabilized mechanically and chemically for cell operation. Furthermore, it is known that during pressure operation, a large amount of gas permeates through the thin membrane. This can result in forming explosive gas mixtures of oxygen and hydrogen at the anode, especially at low current densities, which prevents a safe electrolysis operation. However, little research has been done so far that, when using thin membranes, additional effects can arise which significantly increase the gas permeation. These effects lead to safety-relevant hydrogen concentrations at the anode, not only for small but also for larger current densities of a few amperes per square centimeter. It is demonstrated that, without an intensive comparison of material and cell operating parameters, a comparison of different investigations with respect to the measured permeation values in PEM water electrolysis can hardly be made. Important parameters are discussed which have to be taken into account in cell assemblies when thin membranes are used. The presented experimental results show a correlation in the PEM water electrolysis MEA which can significantly increase the hydrogen permeation through a 50 μm thin N212 membrane under ambient pressure. At the same time, it is demonstrated how the hydrogen content in the anode gas can be reduced to very low levels using the identified correlation.