Hydrogen crossover in PEM water electrolyzers at high current density: Impact of temperature rise

Hydrogen crossover critically affects the safety and efficiency of proton exchange membrane (PEM) water electrolyzers. This study fabricated a composite membrane embedded with temperature sensors to enable in situ monitoring of the membrane electrode assembly temperature. The results show that rising current density elevates membrane temperature beyond equilibrium, thereby intensifying hydrogen crossover. Lower inlet flow rates further aggravate crossover owing to reduced heat dissipation. Mechanistic analysis reveals that temperature elevation enlarges the membrane permeability and raises dissolved hydrogen concentration in the catalyst layer, both of which promote hydrogen crossover. Importantly, the H2 diffusion coefficient in PEM exhibits a linear dependence on temperature in the range of 50–90 °C. Increasing inlet water flow rate partially mitigates this effect, while Pd-doped composite membranes achieve a significant reduction through combined physical and chemical mechanisms. These findings highlight the importance of thermal management and hydrogen removal strategies for ensuring the safe operation of PEM electrolyzers under high current density.