Ion Exchange Membranes in Electrochemical CO2 Reduction Processes

Abstract The low-temperature electrolysis of CO2 in membrane-based flow reactors is a promising technology for converting captured CO2 into valuable chemicals and fuels. In recent years, substantial improvements in reactor design have significantly improved the economic viability of this technology; thus, the field has experienced a rapid increase in research interest. Among the factors related to reactor design, the ion exchange membrane (IEM) plays a prominent role in the energetic efficiency of CO2 conversion into useful products. Reactors utilizing cation exchange, anion exchange and bipolar membranes have all been developed, each providing unique benefits and challenges that must be overcome before large-scale commercialization is feasible. Therefore, to direct advances in IEM technology specific to electrochemical CO2 reduction reactions (CO2RRs), this review serves to first provide polymer scientists with a general understanding of membrane-based CO2RR reactors and membrane-related shortcomings and to encourage systematic synthetic approaches to develop membranes that meet the specific requirements of CO2RRs. Second, this review provides researchers in the fields of electrocatalysis and CO2RRs with more detailed insight into the often-overlooked membrane roles and requirements; thus, new methodologies for membrane evaluation during CO2RR may be developed. By using CO2-to-CO/HCOO− methodologies as practical baseline systems, a clear conceptualization of the merits and challenges of different systems and reasonable objectives for future research and development are presented. Graphical Abstract