Controlled Photocatalytic Reduction of CO ₂ by Precise Atomic‐Level Interface Modification and Engineering of Silver Nanoclusters

The emission of carbon dioxide (CO₂) and other greenhouse gases has raised serious environmental concerns, and artificial photosynthesis is a promising approach to reducing the carbon footprint. The primary challenge for photocatalytic systems is how to optimally separate interfacial charges, while the hydrogen evolution reaction limits the selectivity of products in the photocatalytic reduction of CO₂. Herein, highly stable Ag₄₄ nanoclusters (Ag₄₄ NCs) protected by thiol salt ligands are prepared with atomic-level precision. The ultra-small Ag₄₄ NCs shorten the distance for electrons to migrate from the bulk phase to the surface and accelerate interfacial charge transfer. Furthermore, the molecule-like properties of Ag₄₄ NCs broaden the light absorption range of the semiconducting substrate, and quantum confinement rendered by Ag₄₄ NCs produces a potential well, which promotes electron aggregation and generates a long-range ordered electric field to transfer electrons directionally. Since the electrostatic repulsion of positively charged Ag₄₄ NCs hinders electron transfer and proton coupling, the hydrogen evolution reaction is inhibited.