Modification of Visible-Light-Responsive Pb2Ti2O5.4F1.2 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, Pb2Ti2O5.4F1.2, 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/Pb2Ti2O5.4F1.2. The highest activity was obtained with RuCl3-impregnated Pb2Ti2O5.4F1.2 heated under a flow of H2 at 523 K. The H2-treated Ru/Pb2Ti2O5.4F1.2 showed an O2 evolution rate an order of magnitude higher than those for the analogues without the H2 treatment (e. g., RuO2/Pb2Ti2O5.4F1.2). 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/Pb2Ti2O5.4F1.2 could function as an O2-evolving photocatalyst in Z-scheme overall water splitting, in combination with an Ru-loaded, Rh-doped SrTiO3 photocatalyst.

Improvement of Visible-Light H2 Evolution Activity of Pb2 Ti2 O5.4 F1.2 Photocatalyst by Coloading of Rh and Pd Cocatalysts.

Pb2 Ti2 O5.4 F1.2 modified with various metal cocatalysts was studied as a photocatalyst for visible-light H2 evolution. Although unmodified Pb2 Ti2 O5.4 F1.2 showed negligible activity, modification of its surface with Rh led to the best observed promotional effect among the Pb2 Ti2 O5.4 F1.2 samples modified with a single metal cocatalyst. The H2 evolution activity was further enhanced by coloading with Pd; the Rh-Pd/Pb2 Ti2 O5.4 F1.2 photocatalyst showed 3.2 times greater activity than the previously reported Pt/Pb2 Ti2 O5.4 F1.2 . X-ray absorption fine-structure spectroscopy, photoelectrochemical, and transient absorption spectroscopy measurements indicated that the coloaded Rh and Pd species, which were partially alloyed on the Pb2 Ti2 O5.4 F1.2 surface, improved the electron-capturing ability, thereby explaining the high activity of the coloaded Rh-Pd/Pb2 Ti2 O5.4 F1.2 catalyst toward H2 evolution.