Copper-Sulfur-Nitrogen Cluster Providing a Local Proton for Efficient Carbon Dioxide Photoreduction

Atomically precise Cu clusters are highly desirable as catalysts for CO₂ reduction reaction (CO₂ RR), and they provide an appropriate model platform for elaborating their structure-activity relationship. However, an efficient overall photocatalytic CO₂ RR with H₂ O using assembled Cu-cluster aggregates as single component photocatalyst has not been reported. Herein, we report a stable crystalline Cu-S-N cluster photocatalyst with local protonated N-H groups (denoted as Cu₆ -NH). The catalyst exhibits suitable photocatalytic redox potentials, high structural stability, active catalytic species, and a narrow band gap, which account for its outstanding photocatalytic CO₂ RR performance under visible light, with ≈100 % selectivity for CO evolution. Remarkably, systematic isostructural Cu-cluster control experiments, in situ infrared spectroscopy, and density functional theory calculations revealed that the protonated pyrimidine N atoms in the Cu₆ -NH cluster act as a proton relay station, providing a local proton during the photocatalytic CO₂ RR. This efficiently lowers the energy barrier for the formation of the *COOH intermediate, which is the rate-limiting step, efficiently enhancing the photocatalytic performance. This work lays the foundation for the development of atomically precise metal-cluster-based photocatalysts.