Modification of Visible-Light-Responsive Pb 2 Ti 2 O 5.4 F 1.2 with Metal Oxide Cocatalysts to Improve Photocatalytic O 2 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, Pb 2 Ti 2 O 5.4 F 1.2 , to improve the water oxidation activity. Among the metal oxides examined as cocatalysts, RuO 2 was found to be the most suitable, and the O 2 evolution activity depended on the preparation conditions for Ru/Pb 2 Ti 2 O 5.4 F 1.2 . The highest activity was obtained with RuCl 3 -impregnated Pb 2 Ti 2 O 5.4 F 1.2 heated under a flow of H 2 at 523 K. The H 2 -treated Ru/Pb 2 Ti 2 O 5.4 F 1.2 showed an O 2 evolution rate an order of magnitude higher than those for the analogues without the H 2 treatment (e. g., RuO 2 /Pb 2 Ti 2 O 5.4 F 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 RuO 2 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 O 2 . The optimized Ru/Pb 2 Ti 2 O 5.4 F 1.2 could function as an O 2 -evolving photocatalyst in Z-scheme overall water splitting, in combination with an Ru-loaded, Rh-doped SrTiO 3 photocatalyst.