Synergy of Copper Doping and Carbon Defect Engineering in Promoting C–C Coupling for Enhanced CO2 Photoreduction to Ethanol Activity

Photocatalytic conversion of carbon dioxide (CO2) to fuel provides an ideal pathway to achieving carbon neutrality. One significant hindrance in achieving the reduction of CO2 to higher energy density multicarbon products (C2+) was the difficulty in coupling C–C bonds efficiently. Copper (Cu) is considered the most suitable metal catalyst for C–C coupling to form C2+ products in the CO2 reduction reaction (CO2RR), but it encounters challenges such as low product selectivity and slow catalytic efficiency. Herein, we constructed a carbon defect on Cu-doped carbon nitride (Cu–CvN), as an efficient catalyst for photocatalytic CO2RR. The optimized catalyst (Cu–CvN-550) with a carbon defect shows high photocatalytic activity for CO2 reduction to ethanol, with an ethanol production rate of 122.6 μmol g–1 h–1 and a selectivity of 93.7%. The yield was 4.5 times higher than that of the Cu–CN-550 without carbon defect. The ratio of Cu+/Cu0 in Cu species changes regularly with calcination temperature, which was linearly correlated with the selectivity of the liquid product of CO2RR. DFT calculations combined with experimental results revealed that Cu doping promoted CO2 activation, followed by enhanced *CO adsorption and weakened hydrogenation and desorption. Carbon defects lower the free energy and greatly accelerate the *CO transfer process by promoting the formation of a six-membered ring intermediate state, serving as an intramolecular catalyst for *CO dimerization. Synergistic thermodynamic and kinetic interactions were realized through Cu doping and the introduction of carbon defects, thereby enhancing the catalytic performance of photocatalytic reduction of CO2 for ethanol production.