Crossover as Determinant for Safety and Performance Tradeoffs in Proton Exchange Membrane Water Electrolyzers

Abstract Hydrogen (H2) crossover constrains the safe and efficient operation of proton exchange membrane water electrolyzers (PEMWEs), as thinner membranes and elevated cathode pressures are pursued to improve overall energy efficiency. We develop a microstructure-aware, multicomponent reactive-transport framework that resolves dissolved-phase and gaseous H2-transport pathways and mechanistically links electrode architecture to crossover-driven safety and performance. We show that operability is cogoverned by the cathode catalyst layer (CCL) and the anode porous transport layer (APTL), which regulate the fraction of generated-H2 lost to crossover and anode-side H2 egress, respectively. Within the investigated design window, increasing Pt/C in the CCL suppresses crossover flux by up to 23%, while higher APTL porosity lowers H2-in-O2 by 0.6 vol % in the anode effluent. We integrate these responses into cathode pressure−current density maps overlaid with safety and efficiency thresholds and define two unified metrics to gauge the size and quality of the operating window. This work guides safer, high-yield elevated-pressure operation at deep turndowns.