Hydrogen Crossover in AEM Water Electrolysis: Influence of Cell Architecture and Catalyst Layer Supersaturation

Abstract Hydrogen gas crossover limits part-load flexibility and pressurized operation of anion exchange membrane water electrolysis. This phenomenon is often attributed to the membrane properties, while the influence of cell architecture remains poorly quantified. In this work, two zero-gap cells (a commercial Baltic flow cell and a 3D printed diagnostic cell) with identical membrane electrode assembly (MEA) were tested in 1M KOH at 25°C and 60°C to isolate the effect of cell topology. A 1D transport model was further developed to isolate the contributions of membrane and dissolved hydrogen supersaturation at the catalyst layer to the measured crossover flux. The two cells showed a 2.9 fold difference in crossover, which was attributed to differences in catalyst-layer supersaturation. Comparison with independently reported data for the same commercial platform operated with a hydrophobic carbon gas diffusion electrode at the cathode, shows a further reduction of crossover by more than an order of magnitude. Across the published PEM and alkaline studies the catalyst-layer supersaturation varies by at least two orders of magnitude. A Pt/C recombination layer reduced crossover by 40%, but with the voltage penalty of 230 mV. Cathode redesign can therefore substantially reduce crossover using existing membranes, without adding any significant efficiency penalty.