Orthogonal relay system for efficient CO-to-ethanol electrosynthesis.

The electrosynthesis of ethanol from carbon monoxide (CO) can potentially provide low-carbon-intensity fuels and platform chemicals. However, the process performance is compromised by low selectivity, due to the predominant generation of competing products, especially ethylene. Here, we show an orthogonal relay catalysis mechanism that lowers the hydrogenation energy barrier while suppressing carbon-oxygen (C-O) cleavage. Atomic doping with lead electronically tunes the copper (Cu) catalyst to lower the hydrogenation barrier of the key intermediate *CH2COH, making ethanol formation feasible. An interfacial ionomer-catalyst heterojunction (IICH) creates partially desolvated cesium (Cs⁺) cations that selectively stabilize the C-O bond in *CH2COH, making ethanol formation selective. This mechanistic enhancement enables a 71.5% CO-to-ethanol Faradaic efficiency in flow cell. We demonstrate a membrane electrode assembly (MEA) electrolyzer achieving competitive ethanol production: 28.1% energy efficiency and 300 hours of stable operation. Scaled operation at 100 cm2 delivers a total current of 15 A with 39.8 mmol h-1 ethanol productivity, suggesting its potential for practical applications.