Energy Efficiency Limit in CO‐to‐Ethylene Electroreduction and the Method to Advance Toward

Abstract The electrified synthesis of high‐demand feedstocks (C 2 H 4 ) from CO and H 2 O through a CO electroreduction (COR) protocol is attractive for large‐scale applications; however, a high reaction potential and modest Faradaic efficiencies (FEs) limit its practical energy efficiency (EE). In this study, a quantitative reaction–transport model was constructed to analyze the root causes of low performance in COR, which revealed low volumetric exchange current density and limited intermediate surface reaction as key factors, constraining CO‐to‐C 2+ and CO‐to‐C 2 H 4 conversion energetics and selectivities. Consequently, a robust, high active‐site density electrode, featuring nanometer‐scale interspacing between the active, Nafion‐wrapped Cu + –Cu nanosheet catalysts, was designed. This design increases volumetric COR activity with an efficient intermediate surface reaction mechanism for C 2 H 4 production, substantially lowering the full‐cell COR potential to 1.87 V at 4 A in a 25 cm 2 membrane electrode assembly, thereby achieving a record >50% C 2+ EE with a 90 ± 1% FE along with a >40% C 2 H 4 EE with a 71 ± 1% FE throughout stable >100 h operation. Similarly designed high‐volumetric‐activity Bi and Ag nanosheet catalysts enabled >60% and >55% EEs for the CO 2 ‐to‐formate and CO 2 ‐to‐CO electroreduction, demonstrating the broader applicability of our electrochemical activity and EE enhancement concept on a three‐phase interface.