Asymmetric Vacancies Efficiently Couple O 2 Activation With Reactive Oxygen Species Evolution for Enhanced Photocatalytic Methane Conversion

Photocatalytic oxidation mediated by reactive oxygen species (ROS) provides an effective platform for a wide range of important chemical transformations. However, conventional oxygen-vacancy engineering strategy, while enhancing O₂ activation, often hampers subsequent ROS evolution due to overly strong adsorption, thereby limiting oxidation kinetics. Here, we demonstrate that asymmetric vacancies in ZnGa₂O₄, characterized by a Zn_Td-O_v-Ga_Oh configuration, can overcome this intrinsic limitation by synergistically coupling O₂ activation with efficient ROS evolution. Specifically, the dynamic Ga_Oh site preferentially promotes O₂ adsorption and activation, whereas the Zn_Td site interacts weakly with oxygen-derived species, facilitating ROS release and vacancy replenishment, thereby achieving an optimal balance between these critical steps. Consequently, Ag/ZnGa₂O₄ delivers the highest turnover number (TON) reported to date among Ag-based catalysts for the photocatalytic oxidative coupling of methane via a ROS-mediated pathway. The general effectiveness of this asymmetric-vacancy strategy is further validated in other representative photocatalytic reactions, including hydrogen peroxide production and the oxidative coupling of benzyl alcohol.