Electron Source in Photoinduced Hydrogen Production on Pt-supported TiO₂ Particles

Photoinduced reaction in relations to water photolysis was studied on Pt- or other catalysts-supported TiO 2 (P-25) particles. It was found that stoichiometric H 2 and O 2 formation does not take place with the photocatalyst, and only H 2 production was observed. A long-term water photolysis was carried out by Pt-supported TiO 2 (TiO 2 /Pt) to produce H 2, in which H 2 formation stopped almost after 600 h irradiation. After recovering the TiO 2 /Pt particles used in the long-term reaction, they were reused in a photocatalytic H + reduction by adding methanol as an electron donor, but no H 2 production was observed showing that the TiO 2 /Pt particles have lost their photocatalytic activity after the long-term reaction. These results suggest that TiO 2 itself works as an electron donor to produce H 2 . Structural change of the TiO 2 /Pt have been studied by both X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) before and after the photoreaction. In both the XRD and XPS, the structure of the original TiO 2 almost disappeared after the photoreaction and new structures appeared, showing that Ti 4+ changed irreversibly to a higher valance state (Ti 5+ ) after producing H 2 .