Dynamic modeling of chemical membrane degradation in polymer electrolyte fuel cells: Effect of pinhole formation

The continuous chemical degradation of the polymer membrane in polymer electrolyte fuel cells causes membrane pinhole formation, therefore substantial increase in the gas cross-over flux. In this paper, a numerical method to simulate the pinhole formation process during chemical degradation is proposed. The method assumes that a membrane pinhole is formed by connected local micro-pores, which are generated owing to the mass loss during chemical membrane degradation. In addition, pinhole formation is combined with reduction of the membrane thickness to account for the membrane structure changes. A dynamic chemical degradation model that incorporates the effects of membrane structure changes is validated against the experimental results of the accelerated stress test. Results confirm the proposed method increases the accuracy of the chemical degradation model in predicting the macroscopic properties, including cumulative mass loss, hydrogen cross-over and open circuit voltage. Formation of pinhole starts from the anode, where degradation is more severe, and propagates to the cathode. The model also systemically studies the effects of temperature, pressure, and relative humidity on chemical degradation. The degradation rate increases with elevated temperatures and pressures. The degradation is shown to be more severe at moderate relative humidity, and the comparison with experimental findings are discussed.