Assessing the Long-Term Stability of Anion Exchange Membranes for Electrochemical CO2 Reduction

Materials and cell components used in CO2 electrolysis have largely been adapted from technologies initially developed for water electrolysis and fuel cells. However, electrochemical CO2 reduction introduces distinct material challenges due to the unique chemical environment in this process. In this study, we conducted ex-situ 1000 h stability tests on commonly used anion exchange membranes, exposing them exclusively to electrolytes and organic molecules used or produced during CO2 electrolysis, at concentrations relevant to and compatible with postseparation processes. Notably, 15% w/w n-propanol and 5 M acetic acid caused complete dissolution or partial disintegration of the membranes unless cross-linking was present and remained stable throughout the test. When the membranes stayed physically intact, most of them exhibited excellent chemical stability in alkaline medium containing alcohols or formic acid, which was confirmed by vibrational spectroscopy and ion exchange capacity measurements. However, exposure to alcohol-and acid-containing solutions led to a substantial increase in swelling and water uptake, with potential implications for mechanical stability, ion/product crossover, and compression management of adjacent components. The potential effects of CO2 electroreduction products on membrane stability, their subsequent impact on electrolyzer performance, and mitigation strategies are discussed.