Boosting Solar-Driven CO₂ Conversion to Ethanol via Single-Atom Catalyst with Defected Low-Coordination Cu-N₂ Motif

Cu-based catalysts have been shown to selectively catalyze CO₂ photoreduction to C₂₊ solar fuels. However, they still suffer from poor activity and low selectivity. Herein, we report a high-performance carbon nitride supported Cu single-atom catalyst featuring defected low-coordination Cu-N₂ motif (Cu-N₂-V). Lead many recently reported photocatalysts and its Cu-N₃ and Cu-N₄ counterparts, Cu-N₂-V exhibits superior photocatalytic activity for CO₂ reduction to ethanol and delivers 69.8 μmol g^-1 h^-1 ethanol production rate, 97.8 % electron-based ethanol selectivity, and a yield of ~10 times higher than Cu-N₃ and Cu-N₄. Revealed by the extensive experimental investigation combined with DFT calculations, the superior photoactivity of Cu-N₂-V stems from its defected Cu-N₂ configuration, in which the Cu sites are electron enriched and enhance electron delocalization. Importantly, Cu in Cu-N₂-V exist in both Cu⁺ and Cu²⁺ valence states, although predominantly as Cu⁺. The Cu⁺ sites support the CO₂ activation, while the co-existence of Cu⁺/Cu²⁺ sites are highly conducive for strong *CO adsorption and subsequent *CO-*CO dimerization enabling C-C coupling. Furthermore, the hollow microstructure of the catalyst also promotes light adsorption and charge separation efficiency. Collectively, these make Cu-N₂-V an effective and high-performance catalyst for the solar-driven CO₂ conversion to ethanol. This study also elucidates the C-C coupling reaction path via *CO-*CO to *COCOH and rate-determining step, and reveals the valence state change of partial Cu species from Cu⁺ to Cu²⁺ in Cu-N₂-V during CO₂ photoreduction reaction.