High efficient charges separation-type photo-electrode with controlled energy band-bending

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An energy band-bending induced by homo-and hetero-junctions of semiconductors must be a key factor for attainment of efficient hydrogen production via photo-electrode water splitting. In the present study, composites of TiO_2 with donor-doped titanate, Sr(Ti_<1x>Nb_x)O_<3+5> in states of powder, single crystal and thin film, were prepared, and various pysico-chemical phenomena, i.e., photo-bleaching of dyes, water splitting photo-reaction, dye-sensitized photo-current, and ions adsorption, were investigated. (1) Photobleaching of methylene blue aqueous solution sensitized with Sr(Ti_<1-x>Nb_x)O_<3+δ>/ TiO_2 composite powders proceeded several time faster than that with TiO_2 alone. Strong adsorption of MB on the powder was observed. This revealed spatial separation of photo-excited charges near the junction. (2) When Sr(Ti_<0.98>Nb_<0.02>)O_<3+δ> single crystal plate covered by TiO_2 thin film was used as a photo-electrode, the photo-current was larger 1.5 or 2 times than that for glass plate with FTO thin film covered by TiO_2 thin film. The TiO_2 thin film was prepared by sol-gel method. (When mono-light was irradiated, on-set wavelength for Sr(Ti_<0.98>Nb_<0.02>)O_<3+δ> single crystal / TiO_2 was shifted toward shorter wavelength 20 nm (0.1 eV) than that for FTO glass plate / TiO_2. (3)This proved the existence of spike in the heterojunction, end therefore this confirms the appearance of band-bending due to heterjunction. (4)The preparation of Sr(Ti_<i-x>Nb_5)O_<3+5>/ TiO_2 junction on the Ti-based alloy plates and controlling of ion adsorption on the composite powder were examined. (5) The controlling of the ion species adsorbed on the electrode must become important for photo-electrochemical reaction. The findings described above should be applied for highly efficient photo-electrochemical water splitting