Effect of Hydrogen Reduction on Photo-Anodic Polarization of TiO<SUB>2</SUB> Films Formed by High Temperature Oxidation

The effect of hydrogen reduction on photo-anodic polarization behavior for TiO2 films formed by high temperature oxidation was investigated in Na2SO4 solution. The hydrogen reduction was conducted at 773∼1173 K for 1.8 ks in 2.9 vol.%H2-Ar atmosphere. The rate of increase in anodic photocurrent with an increase in polarization potential grew as reduction temperature increased. In order to explain this increase of photo-anodic reaction rate for the TiO2 films, the changes in limiting wavelength for the generation of photocurrent, surface morphology, crystal structure, and chemical composition of the films were examined as a function of reduction temperature. The limiting wavelength for the generation of photocurrent was almost independent of the reduction temperature. The rutile structure of the TiO2 films was not changed by the hydrogen reduction. On the contrary, the concentration of titanium in the films increased consistently with the reduction temperature. Therefore, it was thought that the increase in photo-anodic reaction rate for the TiO2 films with rising reduction temperature was attributable to an increase in concentration of excessive titanium ions, which may become the sites for the formation of the surface state on the oxide film.