Switching CO₂ Electroreduction toward Ethanol by Delocalization State-Tuned Bond Cleavage

The electrochemical CO₂ reduction reaction by copper-based catalysts features a promising approach to generate value-added multicarbon (C₂₊) products. However, due to the unfavored formation of oxygenate intermediates on the catalyst surface, the selectivity of C₂₊ alcohols like ethanol remains unsatisfactory compared to that of ethylene. The bifurcation point (i.e., the CH₂═CHO* intermediate adsorbed on Cu via a Cu-O-C linkage) is critical to the C₂₊ product selectivity, whereas the subsequent cleavage of the Cu-O or the O-C bond determines the ethanol or ethylene pathway. Inspired by the hard-soft acid-base theory, in this work, we demonstrate an electron delocalization tuning strategy of the Cu catalyst by a nitrene surface functionalization approach, which allows weakening and cleaving of the Cu-O bond of the adsorbed CH₂═CHO*, as well as accelerating hydrogenation of the C═C bond along the ethanol pathway. As a result, the nitrene-functionalized Cu catalyst exhibited a much-enhanced ethanol Faradaic efficiency of 45% with a peak partial current density of 406 mA·cm^-2, substantially exceeding that of unmodified Cu or amide-functionalized Cu. When assembled in a membrane electrode assembly electrolyzer, the catalyst presented a stable CO₂-to-ethanol conversion for >300 h at an industrial current density of 400 mA·cm^-2.