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

Abstract

The electrified synthesis of high-demand feedstocks (C₂H₄) from CO and H₂O 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-C₂₊ and CO-to-C₂H₄ 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 C₂H₄ production, substantially lowering the full-cell COR potential to 1.87 V at 4 A in a 25 cm² membrane electrode assembly, thereby achieving a record >50% C₂₊ EE with a 90 ± 1% FE along with a >40% C₂H₄ 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 CO₂-to-formate and CO₂-to-CO electroreduction, demonstrating the broader applicability of our electrochemical activity and EE enhancement concept on a three-phase interface.