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

The electrochemical CO reduction reaction (CORR) is an appealing method for carbon utilization. Alkaline CO electrolyzers exhibit high CORR activity, low full-cell voltages, and cost-effectiveness. However, the issue of CO 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 CORR. 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 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 CH, corresponding to a C FE of 64 % at 260 mA cm, with a CO-to-CH single-pass conversion (SPC) of approximately 32 % at 140 mA cm-nearly 1.3 times the limiting SPC in conventional AEM-MEA electrolyzers. Furthermore, coupling CO reduction with formaldehyde oxidation reaction (FOR) in the TPE-MEA electrolyzer reduces the full-cell voltage to 2.3 V at 100 mA cm without compromising the CH FE.