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

Abstract Atomically precise Cu clusters are highly desirable as catalysts for CO 2 reduction reaction (CO 2 RR), and they provide an appropriate model platform for elaborating their structure–activity relationship. However, an efficient overall photocatalytic CO 2 RR with H 2 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 Cu 6 −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 CO 2 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 Cu 6 −NH cluster act as a proton relay station, providing a local proton during the photocatalytic CO 2 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.