Coverage enhancement accelerates acidic CO2 electrolysis at ampere-level current with high energy and carbon efficiencies

Abstract Acidic CO 2 electroreduction (CO 2 R) using renewable electricity holds promise for high-efficiency generation of storable liquid chemicals with up to 100% CO 2 utilization. However, the strong parasitic hydrogen evolution reaction (HER) limits its selectivity and energy efficiency (EE), especially at ampere-level current densities. Here we present that enhancing CO 2 R intermediate coverage on catalysts promotes CO 2 R and concurrently suppresses HER. We identified and engineered robust Cu 6 Sn 5 catalysts with strong * OCHO affinity and weak * H binding, achieving 91% Faradaic efficiency (FE) for formic acid (FA) production at 1.2 A cm −2 and pH 1. Notably, the single-pass carbon efficiency reaches a new benchmark of 77.4% at 0.5 A cm −2 over 300 hours. In situ electrochemical Fourier-transform infrared spectroscopy revealed Cu 6 Sn 5 enhances * OCHO coverage ~2.8× compared to Sn at pH 1. Using a cation-free, solid-state-electrolyte-based membrane-electrode-assembly, we produce 0.36 M pure FA at 88% FE over 130 hours with a marked full-cell EE of 37%.