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

Ryu Abe, Masanobu Higashi, Kazunari Domen

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Abstract

A two-step, photocatalytic water splitting system consisting of Pt-loaded TaON (a H2 evolution photocatalyst), Pt-loaded WO3 (an O2 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 IO3- to I- proceeded with good selectivity over the Pt-WO3 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 WO3 strongly suggested that the photoexcited electrons could react efficiently with IO 3- adsorbed on WO3, whereas the photogenerated holes selectively reacted with water molecules owing to the low adsorptivity of I- on WO3. Photocatalytic H2 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 H2 evolution was significantly inhibited by the competitive adsorption of IO3 -, which consumes photoexcited electrons. It was also found that WO3 photocatalysts loaded with platinum oxide (PtO) showed a much higher activity for O2 evolution in the presence of the electron acceptor IO3-, 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)-WO3 in an aqueous NaI solution with neutral or weakly acidic pH values, where the concentration of NaI significantly affected the efficiency.

Original languageEnglish
Pages (from-to)228-237
Number of pages10
JournalChemSusChem
Volume4
Issue number2
DOIs
Publication statusPublished - 18 Feb 2011
Externally publishedYes

Keywords

  • hydrogen
  • photocatalysis
  • redox mediator
  • visible light
  • water splitting

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