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-C_vN), as an efficient catalyst for photocatalytic CO₂RR. The optimized catalyst (Cu-C_vN-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.