Modeling Gas Crossover and Recombination in Proton-Exchange Membrane Water Electrolysis

Proton-exchange membrane water electrolysis (PEMWE) is promising method for generation of hydrogen fuels from clean electricity, and is most economical when operating at variable current densities, with thin membranes, and under high differential pressures. However, crossover of evolved hydrogen and oxygen gases through the membrane creates safety, durability, and efficiency concerns under these conditions. In this talk, we will discuss our two-dimensional multiphysics PEMWE model and use it to study gas-crossover mechanisms including the contribution of side reactions due to the crossover species and the effect of adding a gas-recombination catalyst layer within the membrane. The model is parametrized using new experiments at industrially relevant differential pressures and current densities, which will also be presented. The results demonstrate how convective gas transport is strongly coupled to current density through electroosmotic water transport, leading to mitigated hydrogen crossover at high current densities (i.e., a current dependent crossover rate). Furthermore, we will discuss how the efficacy of the recombination catalyst layer is highly dependent on its location within the membrane and performs best in the vicinity of the anode. Finally, we will compare the 2-D model results with a simplified analytic one-dimensional diffusive crossover model to identify discrepancies and operational range of the simplified model that can be used for upscaling. Overall, the model and associated insights help guide design of effective and efficient recombination catalyst layers for safe and durable PEMWE operation.