Long Side Chain PEGMA in Ion Exchange Membranes toward Reducing CO ₂ Reduction Product Crossover

The CO2 reduction process typically utilizes two half-cells separated by an ion exchange membrane (IEM) and occurs with the help of a suitable cathode catalyst. Being a highly complicated reaction process, this produces a mixture of valuable products. One limitation of these devices is the crossover of these products through the IEM to the anode from the cathode. Here, a significant role is played by the IEMs, requiring selectivity toward the important ion transport for the reactions to proceed and simultaneously impeding the crossover of products. This work investigates the role of the side chain comonomer poly(ethylene glycol methyl acrylate) (PEGMA) in IEMs of various chemistries for reducing the transport of select CO2 reduction products. Here, PEGDA-AMPS (AMPS: 2-acrylamide-2-methylpropanesulfonic acid) membranes are fabricated, and the membrane physicochemical, transport, and cotransport behavior are characterized for methanol, ethanol, sodium formate, and sodium acetate. Three series of membranes are synthesized with varied prepolymerization water content, PEGMA content, and AMPS content. Overall, PEGMA has a minimal impact on pure water volume fraction or ionic conductivity. However, it reduces membrane permeability to carboxylates in cotransport with alcohols compared to PEGMA-free membranes. Leveraging this emergent behavior is thereby a potential design strategy for improving IEMs for electrochemical CO2 reduction devices.