Parameters Influencing Pinhole Formation in PEMFC Membranes

The degradation mechanisms of PFSA-membranes are in the focus of research efforts over the last years. It is assumed, that membrane degradation is accelerated by hydrogen peroxide and its radicals, which are formed mainly at the anode by hydrogen and oxygen. Idle operation at open circuit voltage is the most damaging operation condition for the membrane with the highest potential for hydrogen peroxide formation. Under this condition, peroxide is not reduced to hydrogen due to the low potentials at the anode.

The membrane degradation at OCV performance has been analysed in many studies in the past. In most of the studies the operating conditions of idealised test cells are not comparable to real fuel cell operating conditions.

The results to be presented focus on commercial Membrane-Electrode-Assemblies. Every test series consists of five parallel operated test cells with an active area of 25 cm2. The operation conditions like gas humidity, cell temperature, gas pressure and current density are varied. The test cells are operated continuously up to 1200 hours. Cell voltage, current density, hydrogen diffusion, membrane resistance (EIS), fluoride emissions and the change of membrane thickness (SEM) are monitored during the test series with the aim, to develop a model which evaluates the influence of varying operation parameters on the lifetime. The end of lifetime is defined by the formation of pinholes in the membrane.