Critical risks with the permeability dimension to describe the hydrogen crossover phenomenon

Abstract

Hydrogen crossover in water electrolyzer systems equipped with ion exchange membranes (IEM) poses significant safety risks and reduces overall process efficiency. This communication identifies and addresses two critical errors in current hydrogen crossover literature: inaccurate measurement methods and the inappropriate use of permeability (e.g., barrer) to quantify hydrogen crossover. Accurate evaluation of hydrogen crossover through an IEM can be challenging because it is a two-phase material fully hydrated in liquid water. We propose a standardized protocol for accurately measuring hydrogen crossover in fully hydrated IEMs and emphasize the necessity of using flux (e.g., mole∙m−2∙s−1) instead of permeability (e.g., barrer) dimension. The obtained data reveal that normalizing hydrogen crossover by transmembrane pressure and membrane thickness can result in significant errors, with relative errors reaching up to 25%. When applied to the actual electrolysis operation, using the permeability data to predict hydrogen crossover at a current density of 0.4 A cm−2 results in 47% error, with the actual system reaching the lower explosion limit (LEL) while the predicted value does not. Additionally, hydrogen crossover data provides insights into the internal ion channel morphology of IEMs. This communication article intends to convey the current existing safety hazards to the hydrogen research community with a detailed transport models and validation.