Zwitterionic Ionenes toward Processable, Low Water-Containing Anion Exchange Membranes: Synthesis, Characterization, and Application in Electrochemical CO2 Reduction

Anion exchange membranes (AEMs) have gained significant attention in the past two decades for their potential use in electrochemical energy conversion devices. Achieving a balance between facile anion transport and chemical/mechanical stability remains a challenge due to the correlated nature of key membrane properties, such as water uptake, ion exchange capacity, dimensional swelling, and susceptibility to nucleophilic hydroxide ion attack. We present the preparation and characterization of novel zwitterionic functionalized AEMs based on hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI). By introducing sulfobetaine side chains to induce ionic cross-linking within the polymeric membrane, properties such as transport, stability, and hydration behavior were modulated. The zwitterionic functionalization of HMT-PMBI reduced excessive swelling while maintaining high conductivity and alkaline stability as well as mechanical robustness, demonstrating the potential of this approach for improving membrane properties for facilitating their implementation in electrochemical devices. The utility of these membranes in CO2 electrolyzer cells is demonstrated, where they are found to limit carbonate crossover and increase K2CO3 retention at the cathode.