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.

Key words: Ion exchange membranes, CO₂ electrolysis, Electrochemical CO₂ reduction, Membrane-based CO₂ electrolyzer, Carbon capture and utilization