Transport of Hydrogen Through Anion Exchange Membranes in Water Electrolysis

Abstract

The transport of hydrogen through an anion-exchange membrane (AEM) is analyzed by in-line product gas analysis in a large dynamic range (0.1–2 Acm⁻²) at ambient pressure and correlated to ex situ membrane properties, including volumetric electrolyte uptake, dimensional swelling and diffusivities. A commercial AF3-HWK9-75-X membrane from Ionomr Innovations Inc. is characterized and employed in a 25 cm² electrolyzer cell, which is operated for 56 h at 60 °C in 1 M KOH solution. A model of the membrane is developed, based on a combination of existing theoretical knowledge regarding liquid electrolytes and measured properties of the membrane. The model is employed to quantify the transport parameters through the membrane and the porous electrode. The hydrogen transport through the membrane is 770 times slower than through the electrode. The anion-exchange membrane permits a low degree of gas crossover, with a hydrogen-in-oxygen concentration of $0.37\%$ at 2 Acm⁻². The model indicates that modifying the membrane's microstructure has a more pronounced effect on the gas crossover than altering the swollen thickness. A correlation is derived to estimate the polymer diffusivity from the derived effective diffusivity through the membrane, which allows the determination of preferred membrane properties to lower hydrogen crossover.