Why Wet–Dry Cycling Matters for Polymeric Membrane Durability in Water Electrolysis: The Role of Membrane–Electrode Interface Design

For green hydrogen production, proton exchange membrane water electrolysis (PEMWE) systems are inevitably subjected to dynamic loads due to the intermittency of renewable energy sources. Under such load fluctuations, the cathode-side relative humidity undergoes wet–dry cycling as a result of current density-dependent water crossover from the continuously hydrated anode. This wet–dry cycling induces repeated swelling and deswelling of the proton exchange membrane (PEM), accelerating mechanical degradation and compromising durability. To mitigate hydration-induced stress, a pre-swollen PEM was employed using a catalyst-coated substrate (CCS) membrane–electrode assembly (MEA) design. For comparison, a conventional catalyst-coated membrane (CCM) and a CCS MEA with a dry PEM were also fabricated. The CCS MEA with a pre-swollen PEM exhibited a significantly reduced degradation rate of 158 μV/h at 1.5 A/cm 2, compared to 196 μV/h for the CCS MEA with a dry PEM and 1770 μV/h for the CCM. Furthermore, the molecular weight of the hydrocarbon-based PEM was least degraded in the pre-swollen CCS MEA, indicating suppressed polymer chain scission. This study experimentally demonstrates that wet–dry cycling is a critical factor in PEM durability under fluctuating power, underscoring the importance of MEA interface design and membrane preconditioning strategies to improve the long-term reliability of PEMWE systems powered by renewable energy sources.