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 (CO 2 ) to fuel provides an ideal pathway to achieving carbon neutrality. One significant hindrance in achieving the reduction of CO 2 to higher energy density multicarbon products (C 2+ ) was the difficulty in coupling C–C bonds efficiently. Copper (Cu) is considered the most suitable metal catalyst for C–C coupling to form C 2+ products in the CO 2 reduction reaction (CO 2 RR), 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–C v N), as an efficient catalyst for photocatalytic CO 2 RR. The optimized catalyst (Cu–C v N-550) with a carbon defect shows high photocatalytic activity for CO 2 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 + /Cu 0 in Cu species changes regularly with calcination temperature, which was linearly correlated with the selectivity of the liquid product of CO 2 RR. DFT calculations combined with experimental results revealed that Cu doping promoted CO 2 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 CO 2 for ethanol production.