Electrode degradation during a chemical/mechanical accelerated stress test of membranes in polymer electrolyte membrane fuel cells

Abstract Improving the durability of polymer electrolyte membrane fuel cells requires a comprehensive understanding of membrane and electrode degradation. Although the U.S. Department of Energy introduced the OCV-Wet/Dry Cycle as a protocol for evaluating membrane durability, the voltage fluctuations occurring during this process also induce electrode degradation. This study investigated electrode degradation and its effects on membrane durability during 6,000 OCV-Wet/Dry cycles. The electrochemically active surface area (ECSA) decreased by approximately 50%, and the short-circuit resistance decreased to 0.5 kΩ·cm2, at which point the test was terminated. Up to 5,000 cycles, the open-circuit voltage (OCV) exhibited reversible fluctuations, and the hydrogen crossover current density (HCCD) remained nearly constant. Beyond 5,000 cycles, irreversible OCV fluctuations emerged, accompanied by an approximately fivefold increase in the ECSA degradation rate and a sharp rise in HCCD. Transmission electron microscopy and X-ray diffraction revealed a 1.7–1.8-fold increase in Pt catalyst particle size. Electrochemical impedance spectroscopy and distribution of relaxation times analysis, together with thermal imaging, indicated that catalyst degradation was associated with shorting and accelerated membrane degradation. These results indicate that the OCV-Wet/Dry Cycle is more appropriately regarded as a protocol that induces coupled degradation of both the electrodes and the membrane in the MEA.