During the operation of a PEMFC, the polymer membrane is degraded by electrochemical reactions and mechanical stresses. We investigated the effects of repeated electrochemical and mechanical degradations in a membrane. For mechanical degradation, the membrane and MEA were repeatedly subjected to wet/dry cycles; for electrochemical degradation, the cell was operated under open-circuit voltage (OCV)/low-humidity conditions. The repeated wet/dry cycles led to a decrease in the mechanical strength of the membrane. When the MEA was degraded electrochemically, repeated wet/dry cycling resulted in the formation of pinholes in the membrane. In the case of different MEAs that were first degraded electrochemically, the extents of their hydrogen crossover currents increased due to repeated wet/dry cycling being different. Therefore, these results indicated that the membrane durability could be evaluated by these methods of repeated electrochemical degradation and wet/dry cycles.

An accelerated single cell test and single electrode cell test were carried out to investigate membrane degradation by Pt dissolved/deposited on the membrane. For a cell operating under accelerated conditions (OCV, 90 o C, anode RH 0%, cathode O 2 supply), MEA analyses revealed that Pt particles were deposited in the membrane at the anode side, with a decrease in F, O, and C content near the anode side of the membrane. Dissolved Pt from the cathode showed that Pt existed mainly in the form of Pt 2+ ionic species. Oxygen and hydrogen helped Pt dissolution from the cathode and Pt deposition in the membrane, respectively. Radical formation on deposited Pt in the membrane was detected by electron spin resonance (ESR). Fluoride emission rate (FER, an indicator of membrane degradation rate) increased with an increase in the amount of Pt in the membrane.

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In this study, the electrochemical and mechanical durabilities of two types of cast membranes and a reinforced composite membrane based on sulfonated poly(arylene ether sulfone) were evaluated by OCV test and wet–dry cycle test. The composite membrane with electrospun microporous polyimide substrates showed higher mechanical stability than the cast membranes. Also, the higher the molecular weight of polymer membrane, the greater the electrochemical stability.