Exploring water transport in membrane electrode assemblies for CO2 electrolyzers via multiphysics modeling

The long-term operation of CO 2 electrolyzers using membrane electrode assemblies (MEAs) is limited by challenges related to water management. However, water balance in CO 2 electrolyzer cells still has not been fully understood, and conflicting observations have been reported in the literature. In this study, a one-dimensional non-isothermal multiphysics model of an exchange MEA CO 2 electrolyzer with a Tokuyama A201 anion exchange membrane is developed to investigate the role of different physical and chemical phenomena on the water balance. The relative contributions of these processes vary with current density and membrane transport properties, which shift the dominant water transport mechanism in the cell. Our results highlight the significant contribution of homogeneous reactions, particularly OH − , to the water balance across the membrane. At low currents ( i 130 mA cm −2 ), the flux is governed by electro-osmotic drag and a temperature gradient over the cathode gas diffusion electrode (GDE) with their relative contributions depending on membrane properties. Homogeneous buffering can re-emerge as the dominant mechanism at high currents if the hydroxide ion concentration in the membrane increases, for example under CO 2 -limited cathode conditions, allowing hydroxide ions to react with depleted bicarbonate near the anode. • Heat, electro-osmosis, and buffer reactions can govern water flux. • Net water consumption depends on hydroxide concentration. • For current densities <130 mAcm −2 , buffer reactions govern water flux. • Above 130 mA cm −2 , water balance depends on membrane properties and hydroxide concentration. • Results provide guidelines for water management in CO 2 electrolyzers.