Experimental Study on Reversible Degradation and Recovery of PEMFC under High Current Density

Reversible degradation frequently occurs in proton exchange membrane fuel cells (PEMFC) operating under high current density conditions. Single-factor experiments combined with an equivalent circuit model were employed to systematically investigate the effects of operating parameters, including current density, backpressure, cathode stoichiometric ratio, cathode inlet humidity, and stack temperature, on voltage behavior and impedance characteristics of PEMFC. In addition, performance recovery behavior under different intervention strategies was analyzed. The results indicate that increasing current density significantly aggravated voltage loss and led to simultaneous increase in charge transfer resistance and mass transport resistance. Elevating backpressure and cathode stoichiometric ratio effectively reduced mass transport resistance; however, under high current density conditions, a high stoichiometric ratio accelerated platinum oxidation, resulting in an increase in charge transfer resistance. Under conditions of high current density, low backpressure, and low stoichiometric ratio, reversible degradation was mainly governed by ionomer structural changes and platinum oxidation, whereas under high-humidity or low-temperature conditions, the dominant degradation mechanism shifted to flooding. Effective recovery of both impedance and performance could be achieved through humidification or temperature-reduction interventions, with the recovery extent increasing with prolonged cooling duration and higher cathode inlet humidity. These findings provide a theoretical basis for impedance-based identification of reversible degradation mechanisms and operational parameter regulation in PEMFC.