Synergy\nof Copper\nDoping and Carbon Defect Engineering\nin Promoting C–C Coupling for Enhanced CO<sub>2</sub> Photoreduction\nto Ethanol Activity

Photocatalytic conversion of carbon\ndioxide (CO<sub>2</sub>) to\nfuel provides an ideal pathway to achieving carbon neutrality. One\nsignificant hindrance in achieving the reduction of CO<sub>2</sub> to higher energy density multicarbon products (C<sub>2+</sub>) was\nthe difficulty in coupling C–C bonds efficiently. Copper (Cu)\nis considered the most suitable metal catalyst for C–C coupling\nto form C<sub>2+</sub> products in the CO<sub>2</sub> reduction reaction\n(CO<sub>2</sub>RR), but it encounters challenges such as low product\nselectivity and slow catalytic efficiency. Herein, we constructed\na carbon defect on Cu-doped carbon nitride (Cu–C<sub>v</sub>N), as an efficient catalyst for photocatalytic CO<sub>2</sub>RR.\nThe optimized catalyst (Cu–C<sub>v</sub>N-550) with a carbon\ndefect shows high photocatalytic activity for CO<sub>2</sub> reduction\nto ethanol, with an ethanol production rate of 122.6 μmol g<sup>–1</sup> h<sup>–1</sup> and a selectivity of 93.7%.\nThe yield was 4.5 times higher than that of the Cu–CN-550 without\ncarbon defect. The ratio of Cu<sup>+</sup>/Cu<sup>0</sup> in Cu species\nchanges regularly with calcination temperature, which was linearly\ncorrelated with the selectivity of the liquid product of CO<sub>2</sub>RR. DFT calculations combined with experimental results revealed\nthat Cu doping promoted CO<sub>2</sub> activation, followed by enhanced\n*CO adsorption and weakened hydrogenation and desorption. Carbon defects\nlower the free energy and greatly accelerate the *CO transfer process\nby promoting the formation of a six-membered ring intermediate state,\nserving as an intramolecular catalyst for *CO dimerization. Synergistic\nthermodynamic and kinetic interactions were realized through Cu doping\nand the introduction of carbon defects, thereby enhancing the catalytic\nperformance of photocatalytic reduction of CO<sub>2</sub> for ethanol\nproduction.