Single Pass CO ₂ Conversion Exceeding 85% in the Electrosynthesis of Multicarbon Products via Local CO ₂ Regeneration

The carbon dioxide reduction reaction (CO 2 RR) presents the opportunity to consume CO 2 and produce desirable products. However, the alkaline conditions required for productive CO 2 RR result in the bulk of input CO 2 being lost to bicarbonate and carbonate. This loss imposes a 25% limit on the conversion of CO 2 to multicarbon (C 2+ ) products for systems that use anions as the charge carrier—and overcoming this limit is a challenge of singular importance to the field. Here, we find that cation exchange membranes (CEMs) do not provide the required locally alkaline conditions, and bipolar membranes (BPMs) are unstable, delaminating at the membrane–membrane interface. We develop a permeable CO 2 regeneration layer (PCRL) that provides an alkaline environment at the CO 2 RR catalyst surface and enables local CO 2 regeneration. With the PCRL strategy, CO 2 crossover is limited to 15% of the amount of CO 2 converted into products, in all cases. Low crossover and low flow rate combine to enable a single pass CO 2 conversion of 85% (at 100 mA/cm 2 ), with a C 2+ faradaic efficiency and full cell voltage comparable to the anion-conducting membrane electrode assembly.