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 (AgNPs) confined within carbon nitride nanotubes (Ag1+NPs-CN) for enhanced photocatalytic hydrogen evolution. Mechanistic investigations reveal that H2O adsorption/dissociation predominantly occurs at Ag1 sites, while AgNPs sites notably facilitate H2 release, indicating the synergistic effect between Ag1 and AgNPs 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 AgNPs 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.