Trilayer Polymer Electrolytes Enable Carbon-Efficient CO 2 to Multicarbon Product Conversion in Alkaline Electrolyzers.

The electrochemical CO 2 reduction reaction (CO 2 RR) is an appealing method for carbon utilization. Alkaline CO 2 electrolyzers exhibit high CO 2 RR activity, low full-cell voltages, and cost-effectiveness. However, the issue of CO 2 loss caused by (bi)carbonate formation leads to excessive energy consumption, rendering the process economically impractical. In this study, we propose a trilayer polymer electrolyte (TPE) comprising a perforated anion exchange membrane (PAEM) and a bipolar membrane (BPM) to facilitate alkaline CO 2 RR. This TPE enables the coexistence of high alkalinity near the catalyst surface and the H + flux at the interface between the PAEM and the cation exchange layer (CEL) of the BPM, conditions favoring both CO 2 reduction to multicarbon products and (bi)carbonate removal in KOH-fed membrane electrode assembly (MEA) reactors. As a result, we achieve a Faradaic efficiency (FE) of approximately 46 % for C 2 H 4 , corresponding to a C 2+ FE of 64 % at 260 mA cm -2 , with a CO 2 -to-C 2 H 4 single-pass conversion (SPC) of approximately 32 % at 140 mA cm -2 -nearly 1.3 times the limiting SPC in conventional AEM-MEA electrolyzers. Furthermore, coupling CO 2 reduction with formaldehyde oxidation reaction (FOR) in the TPE-MEA electrolyzer reduces the full-cell voltage to 2.3 V at 100 mA cm -2 without compromising the C 2 H 4 FE.