Spatially Coupled Pd SA -Ovs Dual Sites on TiO ₂ for Synergistic Regulation of CO ₂ Photoreduction to CH ₄

Efficient photocatalytic reduction of carbon dioxide (CO2) to methane (CH4) relies on a continuous proton-coupled electron transfer process, which places high demands on the spatial arrangement and functional synergy of catalytic active sites. Herein, we propose a vacancy-directed oxygen-bridge scission and coordination coupling (VD-OSCC) strategy, successfully establishing spatially coupled (adjacent and functionally complementary) dual-active sites composed of palladium single atoms and oxygen vacancies (PdSA-Ovs) on the surface of TiO2. These dual sites collaboratively regulate directional charge transfer and ensure efficient proton transport, thereby creating a favorable microenvironment for the multi-step proton-electron coupling process. Ovs sites primarily facilitate the adsorption and activation of CO2, while the adjacent PdSA sites act as efficient hole-trapping centers for accelerating water dissociation to continuously supply protons in CO2 hydrogenation. Furthermore, the adjacent configuration of PdSA and Ovs provides protons with the shortest migration path, effectively facilitating the proton-coupled electron transfer process. The designed PdSA-Ovs exhibit selectivity of 91.8% for CO2 reduction to CH4 with a corresponding production rate of 46.57 μmol g−1 h−1 in pure water. This work provides insights into the design of synergistic neighboring adjacent active sites photocatalysts to achieve highly efficient and selective photocatalytic reduction of CO2 to CH4.