Under pressure: Hydrogen crossover in anion exchange membrane water electrolysis – experimental and modeling study

Anion exchange membrane water electrolysis (AEMWE) offers a promising route for efficient hydrogen production, yet data on hydrogen crossover under elevated differential pressures remain scarce. This study investigates hydrogen crossover through seven state-of-the-art AEMs under non-operando conditions, replicating realistic temperature, pressure, mass flow, and contact pressure. A dedicated setup enables quantification of hydrogen transport through fully hydrated membranes without applying current or potential, thereby isolating diffusion and convection from electro-osmotic drag, supersaturation, and recombination effects. Measurements between 10 and 70 bar are complemented by a physical model describing diffusion and convective transport in the water-filled channels and within the polymer matrix. Results show a significant polymer-phase contribution to overall crossover and a clear trade-off between hydrogen permeability and area-specific resistance of the membrane. The presented data and model represent a lower limit for hydrogen crossover in current AEMs, providing essential guidance for membrane design and safe operation of pressurized AEM electrolyzers. • Non-operando high-pressure (10–70 bar) hydrogen crossover in seven AEMs. • Model combines diffusion in water channels, polymer matrix and convection. • Thickness and temperature variation show good agreement with model. • ASR–permeability trade-off defines a limit for pressurized AEMWE. • Guidelines for safe, efficient high-pressure AEMWE and Faradaic efficiency.