Nitrogen-stabilized oxygen vacancies in TiO₂ for site-selective loading of Pt and CoO_x cocatalysts toward enhanced photoreduction of CO₂ to CH₄

Photocatalysis provides an attractive approach to convert CO₂ into valuable fuels, which yet highly relies on a well-designed photocatalyst with good selectivity and high CO₂ reduction ability. Herein, we report a mild synthesis of mesoporous spherical N-doped TiO₂ photocatalyst with site-selective deposition of redox cocatalysts. Theoretical calculations prove that nitrogen doping favors the formation of oxygen vacancies (V_O) in TiO₂ and stabilizes them as well. The combination of ESR characterization, theoretical calculation and photocatalytic tests confirms V_O-induced site-selective loading of the redox cocatalysts (Pt, CoO_x). The designed composite shows a maximal CH₄-yielding rate of 409.17 μmol g⁻¹, which is 180 times higher than that of pure TiO₂. Photoelectrochemical and optical measurements indicate that Pt is the key active center for CO₂ adsorption and activation, while CoO_x is responsible for H₂O oxidization and proton transfer. The separation of reaction site and accelerated mass transfer on the catalyst surface largely enhance the conversion efficiency of CO₂. This work provides a strategy to selectively deposit dual cocatalysts on semiconductor surface through introduction of oxygen vacancies for substantially improved photocatalytic reduction of CO₂.