Low-Coordination Triangular Cu₃ Motif Steers CO₂ Photoreduction to Ethanol

Photoreduction of CO₂ using copper-based multi-atom catalysts (MACs) offers a potential approach to achieve value-added C₂₊ products. However, achieving MACs with high metal contents and suppressing the thermodynamically favored competing ethylene production pathway remain challenging, thus leading to unsatisfactory performance in ethanol production. Herein, we developed a "pre-locking and nanoconfined polymerization" strategy for synthesis of an ultra-high-density Cu MAC with low-coordination triangular Cu₃ motifs (Cu₃ MAC) on polymeric carbon nitride mesoporous nanofibers. The Cu₃ MAC with Cu contents of 36 wt% achieves a high reactivity of 117 µmol g^-1 h^-1 for ethanol production from CO₂ and H₂O, with a remarkable selectivity of 98% under simulated sunlight irradiation, representing one of the highest performances in ambient conditions without sacrificial reagents. The superior catalytic efficiency is attributed to the triangular Cu₃ configuration, in which both Cu(I) and Cu(II) coexist, predominantly as Cu(I). Such Cu₃ motifs act as strong alkaline sites that effectively chemisorb and activate CO₂, extend visible-light absorption range, while accumulating high-density electrons and favoring 12-electron-transfer products. An accelerated asymmetric C─C coupling with adsorption configuration of the bridge-adsorbed *CO at paired Cu sites and atop-adsorbed *CO at adjacent single Cu atom was observed, enabling preferential formation of *CHCHOH intermediates to produce ethanol.