Boosting Solar-Driven CO 2 Conversion to Ethanol via Single-Atom Catalyst with Defected Low-Coordination Cu-N 2 Motif.

Cu-based catalysts have been shown to selectively catalyze CO 2 photoreduction to C 2+ 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-N 2 motif (Cu-N 2 -V). Lead many recently reported photocatalysts and its Cu-N 3 and Cu-N 4 counterparts, Cu-N 2 -V exhibits superior photocatalytic activity for CO 2 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-N 3 and Cu-N 4 . Revealed by the extensive experimental investigation combined with DFT calculations, the superior photoactivity of Cu-N 2 -V stems from its defected Cu-N 2 configuration, in which the Cu sites are electron enriched and enhance electron delocalization. Importantly, Cu in Cu-N 2 -V exist in both Cu + and Cu 2+ valence states, although predominantly as Cu + . The Cu + sites support the CO 2 activation, while the co-existence of Cu + /Cu 2+ 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-N 2 -V an effective and high-performance catalyst for the solar-driven CO 2 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 Cu 2+ in Cu-N 2 -V during CO 2 photoreduction reaction.