Optimizing the semiconductor–metal-single-atom interaction for photocatalytic reactivity

Metal single-atom (MSA) catalysts with 100% metal atom utilization and unique electronic properties are attractive cocatalysts for efficient photocatalysis when coupled with semiconductors. Owing to the absence of a metal–metal bond, MSA sites are exclusively coordinated with the semiconductor photocatalyst, featuring a chemical-bond-driven tunable interaction between the semiconductor and the metal single atom. This semiconductor–MSA interaction is a platform that can facilitate the separation/transfer of photogenerated charge carriers and promote the subsequent catalytic reactions. In this Review, we first introduce the fundamental physicochemistry related to the semiconductor–MSA interaction. We highlight the ligand effect on the electronic structures, catalytic properties and functional mechanisms of the MSA cocatalyst through the semiconductor–MSA interaction. Then, we categorize the state-of-the-art experimental and theoretical strategies for the construction of the efficient semiconductor–MSA interaction at the atomic scale for a wide range of photocatalytic reactions. The examples described include photocatalytic water splitting, CO2 reduction and organic synthesis. We end by outlining strategies on how to further advance the semiconductor–MSA interaction for complex photocatalytic reactions involving multiple elementary steps. We provide atomic and electronic-scale insights into the working mechanisms of the semiconductor–MSA interaction and guidance for the design of high-performance semiconductor–MSA interface photocatalytic systems.