Benchmarking Anion Exchange Membranes and Ionomers for Electrochemical CO ₂ Reduction

Anion exchange membranes and ionomers are critical components of membrane electrode assemblies for electrochemical CO2 reduction, strongly influencing electrolyzer performance and stability through properties such as ionic conductivity and water management. While numerous studies have investigated various commercial materials, the comparability of results across different laboratories is often limited by variations in preparation and experimental conditions. In this study, we systematically compare four frequently used commercially available anion exchange membranes and their corresponding ionomers. Silver gas diffusion electrodes are prepared using a consistent protocol, varying only the ionomer type. The resulting cathodes are combined with the respective membranes and a commercial anode, and subsequently tested in a zero-gap electrochemical cell under identical conditions using a concentrated bicarbonate anolyte. We observe substantial differences in short-term performance at high current densities up to 600 mA cm–2, with CO Faradaic efficiency deviations of up to 60% and cell potential differences exceeding 2.5 V. The reproducibility of results for the different ionomer/membrane combinations is shown to be highly variable. Long-term measurements at 200 mA cm–2 reveal that stability strongly depends on the choice of ionomer/membrane, with operating times ranging from only a few hours up to 180 h. For certain systems, oscillating behavior in cell potential and product selectivity is observed. By applying nanocomputed tomography to cathodes extracted at different operational stages, these oscillations are linked to transient salt precipitation and dissolution within the gas diffusion electrode. Practical handling aspects are also discussed to provide guidance for selecting suitable ionomer/membrane combinations for CO2 electrolyzers.