Oxygen-Bridged Cu Binuclear Sites for Efficient Electrocatalytic CO₂ Reduction to Ethanol at Ultralow Overpotential

Electrocatalytic CO₂ reduction (CO₂RR) to alcohols offers a promising strategy for converting waste CO₂ into valuable fuels/chemicals but usually requires large overpotentials. Herein, we report a catalyst comprising unique oxygen-bridged Cu binuclear sites (CuOCu-N₄) with a Cu···Cu distance of 3.0-3.1 Å and concomitant conventional Cu-N₄ mononuclear sites on hierarchical nitrogen-doped carbon nanocages (hNCNCs). The catalyst exhibits a state-of-the-art low overpotential of 0.19 V (versus reversible hydrogen electrode) for ethanol and an outstanding ethanol Faradaic efficiency of 56.3% at an ultralow potential of -0.30 V, with high-stable Cu active-site structures during the CO₂RR as confirmed by operando X-ray adsorption fine structure characterization. Theoretical simulations reveal that CuOCu-N₄ binuclear sites greatly enhance the C-C coupling at low potentials, while Cu-N₄ mononuclear sites and the hNCNC support increase the local CO concentration and ethanol production on CuOCu-N₄. This study provides a convenient approach to advanced Cu binuclear site catalysts for CO₂RR to ethanol with a deep understanding of the mechanism.