Modification of Visible‐Light‐Responsive Pb₂Ti₂O_5.4F_1.2 with Metal Oxide Cocatalysts to Improve Photocatalytic O₂ Evolution toward Z‐Scheme Overall Water Splitting

The development of a highly active photocatalyst for visible-light water splitting requires a high-quality semiconductor material and a cocatalyst, which promote both the migration of photogenerated charge carriers and surface redox reactions. In this work, a cocatalyst was loaded onto an oxyfluoride photocatalyst, Pb₂Ti₂O_5.4F_1.2, to improve the water oxidation activity. Among the metal oxides examined as cocatalysts, RuO₂ was found to be the most suitable, and the O₂ evolution activity depended on the preparation conditions for Ru/Pb₂Ti₂O_5.4F_1.2. The highest activity was obtained with RuCl₃-impregnated Pb₂Ti₂O_5.4F_1.2 heated under a flow of H₂ at 523 K. The H₂-treated Ru/Pb₂Ti₂O_5.4F_1.2 showed an O₂ evolution rate an order of magnitude higher than those for the analogues without the H₂ treatment (e. g., RuO₂/Pb₂Ti₂O_5.4F_1.2). Physicochemical analyses by X-ray absorption fine-structure spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and time-resolved microwave conductivity measurements indicated that the optimized photocatalyst contained partially reduced RuO₂ species with a particle size of ~5 nm. These partially reduced species effectively trapped the photogenerated charge carriers and promoted the oxidation of water into O₂. The optimized Ru/Pb₂Ti₂O_5.4F_1.2 could function as an O₂-evolving photocatalyst in Z-scheme overall water splitting, in combination with an Ru-loaded, Rh-doped SrTiO₃ photocatalyst.