Unraveling the Multifunctional Sites of Ag Single-Atom and Nanoparticles Confined Within Carbon Nitride Nanotubes for Synergistic Photocatalytic Hydrogen Evolution.

The development of novel nano-single-atom-site catalysts with optimized electron configurations and active water adsorption (^*H₂O) to release hydrogen protons (^*H) is paramount for photocatalytic hydrogen evolution (PHE), a multi-step reaction process involving two electrons. In this study, an atom-confinement and thermal reduction strategy is introduced to achieve synergistic Ag single-atoms (Ag₁) and nanoparticles (Ag_NPs) confined within carbon nitride nanotubes (Ag_1+NPs-CN) for enhanced photocatalytic hydrogen evolution. Mechanistic investigations reveal that H₂O adsorption/dissociation predominantly occurs at Ag₁ sites, while Ag_NPs sites notably facilitate H₂ release, indicating the synergistic effect between Ag₁ and Ag_NPs in the H₂ evolution reaction. Furthermore, the effective confining of Ag species is beneficial for trapping electrons in highly active reaction regions, while the "electronic metal-support interactions" (EMSIs) of Ag_NPs and Ag₁-C₂N sites regulate the d-band centers and effectively optimize the adsorption/desorption of intermediates in photocatalytic hydrogen evolution, leading to enhanced H₂ production performance. This work demonstrates the potential of the construction of synergistic photocatalysts for efficient energy conversion and storage; Hydrogen production; Nanoparticles; Photocatalysis; Single atom; and Synergistic effect.