The photoelectrolysis of water has been investigated in a photoelectrochemical cell with the single-crystal photoanodes Nb: Sr Ti O3 (0mol%, 0.07mol%, and 0.69mol%) and the electrolyte Na2SO4s0.1M, pH=5.92d. The Nb: Sr Ti O3 anodes (0.07 mol% and 0.69 mol%) show much higher photocurrent density than the pure Sr Ti O3 anode in several orders of magnitude. The incident photon to current conversion efficiencies at 298.2 nm and an applied potential 1.5V (versus the saturated calomel electrode) for three Nb: Sr Ti O3 (0mol%, 0.07mol%, and 0.69mol%) anodes are 0.92%, 15.67%, and 4.32%, respectively. The transmittance spectra of the Nb: Sr Ti O3 show an obvious optical absorption around 516 nm (～2.4eVd). It is interpreted that two-photon process takes part in the charge transfer from the valence band to the conduction band through the intermediate states induced by Nb doping.

The research on a new series of solid photocatalysts with different crystal structures was reviewed. The first system is A2B2O7 pyrochlore-crystal type: Bi2 MNb O7 (M=Al, Ga, In and Y, rare earth, and Fe), which is cubic system and space group Fd3m. The second system is ABO4 stibotantalite-crystal type: BiMO4 (M =Nb5+, Ta5+), in which both the triclinic system with space group P1 in the case of M=Ta and the orthorhombic system with space group Pnna in the case of M=Nb. The third system is ABO4 wolframite-crystal type: InMO4 (M=Nb5+, Ta5+), which is monoclinic system and space group P2/a. Although these photocatalysts crystallize in the different crystal structure, they contain the same octahedral TaO6 and/or NbO6 in the different photocatalysts. The band structure of the photocatalysts is defined by Ta/Nb d-level for a conduction band and O2p-level for a valence band. The band gaps of the photocatalysts were estimated to be between 2.7 and 2.4eV. Metal doped InTaO4 photocatalysts were also investigated. Under visible light (λ>420nm) or ultra-violet irradiation, the H2 and/or O2 evolutions were observed from pure water as well as aqueous CH3OH/H2O and AgNO3 solutions. The photocatalytic activity increases significantly by loading co-catalysts such as Pt, RuO2 and NiOx on the surface of the photocatalysts. Finally, direct water splitting into H2 and O2 under visible light irradiation was firstly established using newly synthesized NiOx (partly oxidized nickel) promoted In0.9 Ni0.1TaO4 photocatalyst.

A photocatalyst, Ag In W2O8, with a layered structure was synthesized. The physical and photophysical properties of the photocatalyst were characterized by XRD, BET measurement, UV-visible diffuse reflectance, and photoluminescence, respectively. The photocatalytic properties of the photocatalyst for H2 evolution with Pt cocatalyst from CH3OH/H2O solution and O2 evolution from Ag NO3 solution were observed under UV and visible light irradiation. The Ag In W2O8 photocatalyst presented not only the activity of O2 evolution but also the activity of H2 evolution. Also the photocatalyst showed the ability to evolve H2 from pure water under full arc irradiation. On the basis of all the results, the band structure of the photocatalyst was discussed.

The highly crystalline nanoparticles of In0.9Ni0.1TaO4, with a wolframite-type structure, were prepared by a solid-state reaction method. The band gap Eg of In0.9 Ni0.1 TaO4 is about 2.3eV, and particles with sizes in the range of 300-500 nm were observed by TEM measurements. We loaded 1.0 wt % partially oxidized nickel as electron-trapping and hydrogen-evolution sites onto the In0.9 Ni0.1 TaO4 surface from an aqueous Ni (NO3) 2 solution. The TEM measurements show that nearly spherical nano NiOx particles with a size of about 15nm are distributed on the surface of In0.9Ni0.1TaO4. Stoichiometric amounts of oxygen and hydrogen were evolved under visible-light irradiation using NiOx/In0.9 Ni0.1 TaO4 with a quantum yield of about 0.66%. This system behaves as a short-circuited microphotoelectrochemical cell. The surface of NiOx is the cathode, and the surface of In0.9 Ni0.1 TaO4 is the anode.