title: Overall water splitting under visible light through a two-step photoexcitation between TaON and WO3 in the presence of an iodate-iodide shuttle redox mediator.
abstract: A two-step, photocatalytic water splitting system consisting of Pt-loaded TaON (a H(2) evolution photocatalyst), Pt-loaded WO(3) (an O(2) evolution photocatalyst), and an iodate-iodide (IO(3)(-)/I(-)) shuttle redox mediator is investigated under visible light irradiation. Photocatalytic oxidation of water to O(2) and reduction of IO(3)(-) to I(-) proceeded with good selectivity over the Pt-WO(3) photocatalyst, even in the presence of a considerable amount of I(-) anions in the solution. The key difference between the adsorption properties of IO(3)(-) and I(-) anions on WO(3) strongly suggested that the photoexcited electrons could react efficiently with IO(3)(-) adsorbed on WO(3), whereas the photogenerated holes selectively reacted with water molecules owing to the low adsorptivity of I(-) on WO(3). Photocatalytic H(2) evolution on Pt-TaON proceeded efficiently, accompanied by I(-) oxidation to IO(3)(-) due to a substantial amount of adsorption of I(-) anions on the surface, whereas H(2) evolution was significantly inhibited by the competitive adsorption of IO(3)(-), which consumes photoexcited electrons. It was also found that WO(3) photocatalysts loaded with platinum oxide (PtO) showed a much higher activity for O(2) evolution in the presence of the electron acceptor IO(3)(-), compared to those loaded with Pt metal. Overall water splitting at a steady rate was demonstrated using a combination of Pt-TaON and Pt(PtO)-WO(3) in an aqueous NaI solution with neutral or weakly acidic pH values, where the concentration of NaI significantly affected the efficiency.
authors.affiliation: Catalysis Research Center, Hokkaido University, North 21, West 10, Sapporo 001-0021, Japan. ryu-abe@cat.hokudai.ac.jp
authors.forename: Ryu
authors.initials: R
authors.lastname: Abe
authors.forename: Masanobu
authors.initials: M
authors.lastname: Higashi
authors.forename: Kazunari
authors.initials: K
authors.lastname: Domen
mesh_terms: D000327:Adsorption; D002384:Catalysis; D006863:Hydrogen-Ion Concentration; D007452:Iodates / Q000737:chemistry; D007454:Iodides / Q000737:chemistry; D007455:Iodine / Q000737:chemistry*; D007700:Kinetics; D008027:Light; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D010777:Photochemistry / Q000379:methods*; D010984:Platinum / Q000737:chemistry; D013635:Tantalum / Q000737:chemistry*; D014414:Tungsten / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D007452:Iodates; D007454:Iodides; D010087:Oxides; C514637:platinum oxide; D014867:Water; D010984:Platinum; D013635:Tantalum; C511604:tungsten oxide; D007455:Iodine; D014414:Tungsten