Atomic-Level Synergy of Dual Single-Atom Catalysts for Photocatalytic Hydrogen Evolution Reaction

Dual-atom catalysts (DACs) have emerged as promising candidates for various chemical transformations with excellent atom utilization and synergistic effects between adjacent metal sites. However, their controlled synthesis and detailed understanding of cooperative effects remain challenging. Here, we design Ag-Cu dual sites embedded in a g-C₃N₄ matrix (AgCu-CN) through a supramolecular self-assembly approach followed by thermal polymerization by pyrolysis. The atomically engineered catalyst exhibits a hydrogen evolution rate of 2126 µmol g^-1 h^-1, and an apparent quantum yield (AQY) of 20% at 400 nm, surpassing the other reported metal-N coordinated photocatalysts. X-ray absorption spectroscopy (XAS) confirms the atomic-level dispersion and coordination with the g-C₃N₄ framework of the Ag and Cu single atomic sites. Comprehensive characterizations including transient absorption (TA) spectroscopy and theoretical calculations based on density functional theory demonstrate that the presence of the two metal centers broadens the photoabsorption range, enhances density of states close to the Fermi level. Thus we posit that it promotes excited state electron transfer and charge separation, and facilitate H₂O activation by directing electron migration toward the protonation site, thereby stabilizing the H^* intermediate, a crucial step in hydrogen evolution reaction. The catalysts developed in this study exhibit excellent activity, stability, and cost-effectiveness, highlighting their strong potential for practical clean hydrogen production.