Electrocatalytic Reduction of CO 2 to Ethanol at Close to Theoretical Potential via Engineering Abundant Electron-Donating Cu δ+ Species.

Electrochemical CO 2 reduction to liquid multi-carbon alcohols provides a promising way for intermittent renewable energy reservation and greenhouse effect mitigation. Cu δ+ (0<δ<1) species on Cu-based electrocatalysts can produce ethanol, but the in situ formed Cu δ+ is insufficient and easily reduced to Cu 0 . Here a Cu 2 S 1-x catalyst with abundant Cu δ+ (0<δ<1) species is designedly synthesized and exhibited an ultralow overpotential of 0.19 V for ethanol production. The catalyst not only delivers an outstanding ethanol selectivity of 86.9 % and a Faradaic efficiency of 73.3 % but also provides a long-term stability of Cu δ+ , gaining an economic profit based on techno-economic analysis. The calculation and in situ spectroscopic results reveal that the abundant Cu δ+ sites display electron-donating ability, leading to the decrease of the reaction barrier in the potential-determining C-C coupling step and eventually making the applied potential close to the theoretical value.