Ion exchange membranes for valorizing CO2 Electroreduction: A deep dive into their pivotal role, challenges, and innovations

Abstract

The escalating atmospheric levels of carbon dioxide (CO₂) demand urgent breakthroughs in electrochemical CO₂ reduction (e-CO₂R) to convert CO₂ to value-added chemicals and fuels. Ion exchange membranes (IEMs) are crucial to optimizing e-CO₂R operations through ion conduction, charge balance, and reaction selectivity. This review provides an extensive comparison of the role, challenges, and recent advances in IEMs in the case of anion exchange membranes (AEMs), cation exchange membranes (CEMs), and bipolar membranes (BPMs) with a comparative analysis of the variations within each membrane. For AEMs, the comparison involves polymers like polysulfones, poly (arylene ether), and functional groups like quaternary ammonium to imidazolium to assess their contribution to hydroxide conductivity and alkaline stability. The comparison of fluorinated (e.g., Nafion) to non-fluorinated (e.g., sulfonated polyether ether ketone) materials follows the case of CEMs to determine proton conduction efficiency and cost. BPMs are considered through the aspect of layer composition (e.g., sulfonic acid to carboxylate interfaces) and how it affects water dissociation kinetics. The important performance characteristics like ion conductance, permselectivity, chemical stability, and mechanical durability are carefully considered within the various classes of materials. Methods like polymer backbone engineering, chemical crosslinking, nanostructured composites, and low-cost fabrication are reviewed within the frame of optimizations specific to the materials. The identification of research gaps like the lack of standardizing the comparison of the variations within the materials lays the emphasis on the need to create high-performance low-cost IEMs specific to the case of e-CO₂R to move the pursuit towards a zero‑carbon economy.