Recent advances in paired electrolysis coupling CO2 reduction with alternative oxidation reactions

The latest advances in paired systems for simultaneous CO 2 reduction and anode valorization that circumvent the “energy waste” issue of traditional oxygen-producing CO 2 electrolyzers are reviewed in this paper. Electrocatalytic CO 2 reduction reaction (CO 2 RR) holds great promise in green energy conversion and storage. However, for current CO 2 electrolyzers that rely on the oxygen evolution reaction, a large portion of the input energy is “wasted” at the anode due to the high overpotential requirement and the recovery of low-value oxygen. To make efficient use of the electricity during electrolysis, coupling CO 2 RR with anodic alternatives that have low energy demands and/or profitable returns with high-value products is then promising. Herein, we review the latest advances in paired systems for simultaneous CO 2 reduction and anode valorization. We start with the cases integrating CO 2 RR with concurrent alternative oxidation, such as inorganic oxidation using chloride, sulfide, ammonia and urea, and organic oxidation using alcohols, aldehydes and primary amines. The paired systems that couple CO 2 RR with on-site oxidative upgrading of CO 2 -reduced chemicals are also introduced. The coupling mechanism, electrochemical performance and economic viability of these co-electrolysis systems are discussed. Thereby, we then point out the mismatch issues between the cathodic and anodic reactions regrading catalyst ability, electrolyte solution and reactant supply that will challenge the applications of these paired electrolysis systems. Opportunities to address these issues are further proposed, providing some guidance for future research.