Asymmetric Ion Regulation for Stabilising Acidic CO2 Electrolysis and Chlorine Evolution in Zero-Gap Electrolysers

While CO2 reduction reaction (CO2RR) coupled with chlorine evolution reaction (CER) can enhance the energy efficiency and economic viability of CO2 electrolysis, its implementation in zero-gap membrane-electrode-assembly (MEA) electrolysers remains challenging as CER-compatible systems require acidic chloride-rich anolytes and chlorine-tolerant cation exchange membranes that induce detrimental cation crossover. The resulting disruption of the cathodic microenvironment causes (bi)carbonate precipitation, hydrogen evolution, and operational instability. Here we report an asymmetric ion-regulation strategy using chloride-bearing, water-miscible poly(diallyldimethylammonium chloride) in the anolyte to maintain high chloride availability for CER while reducing K+ crossover and modifying proton transport through the membrane. Optimised MEA electrolysers achieve about 90% Faradaic efficiencies for both CO and Cl2 and more than 200 h of cumulative operation under replenishment/maintenance protocols, advancing CO2RR-CER beyond laboratory flow-cell demonstrations toward zero-gap MEA operation. Techno-economic and life-cycle analyses indicate that Cl2 co-production can improve process economics under the stated assumptions and reduce the greenhouse-gas intensity of CO production by 75% relative to conventional CO2RR coupled with oxygen evolution benchmarks.