Axial Ligand Engineering of Silver Single-Atom Catalysts with N -Heterocyclic Carbenes Unlocks Efficient Photocatalytic H 2 O 2 Production

Photocatalytic H2O2 production from H2O and O2 is an energy-efficient and environmentally friendly process. While single-atom catalysts (SACs) offer superior selectivity over nanoparticle-based systems, their H2O2 production efficiency is often limited by the electron deficiency of isolated metal sites. Herein, N-heterocyclic carbene (NHC) ligands are used to tailor the electronic structure of single Ag atoms on TiO2, leading to a significant enhancement in photocatalytic performance through axial coordination engineering. The optimized IPr0.5@Ag1/TiO2 catalyst achieves a 5-fold increase in the H2O2 production rate (15.06 mmol g–1 h–1) compared to pristine Ag1/TiO2 (2.64 mmol g–1 h–1), outperforming most semiconductor-based photocatalysts. In situ and time-resolved characterizations, along with theoretical calculations, reveal that the electron transfer from NHC ligands to single Ag atoms promotes efficient charge separation and facilitates O2 activation to selectively generate key O2– intermediates, thus accelerating overall reaction kinetics. This work establishes axial NHC coordination as an effective strategy for modulating the electronic structure of SACs, offering a promising approach for the development of high-performance photocatalytic systems for sustainable chemical synthesis.