Boosting Membrane Hydration for High Current Densities in Membrane Electrode Assembly CO₂ Electrolysis

Despite the advantages of CO₂ electrolyzers, efficiency losses due to mass and ionic transport across the membrane electrode assembly (MEA) are critical bottlenecks for commercial-scale implementation. In this study, more efficient electrolysis of CO₂ was achieved by increasing cation exchange membrane (CEM) hydration via the humidification of the CO₂ reactant inlet stream. A high current density of 755 mA/cm² was reached by humidifying the reactant CO₂ in a MEA electrolyzer cell featuring a CEM. The power density was reduced by up to 30% when the fully humidified reactant CO₂ was introduced while operating at a current density of 575 mA/cm². We reduced the ohmic losses of the electrolyzer by fourfold at 575 mA/cm² by fully humidifying the reactant CO₂. A semiempirical CEM water uptake model was developed and used to attribute the improved performance to 11% increases in membrane water uptake and ionic conductivity. Our CEM water uptake model showed that the increase in ohmic losses and the limitation of ionic transport were the result of significant dehydration at the central region of the CEM and the anode gas diffusion electrode-CEM interface region, which exhibited a 2.5% drop in water uptake.