A new photocatalytic water splitting system under visible light irradiation mimicking a Z-scheme mechanism in photosynthesis

We studied the water splitting into H, and 02 using two different semiconductor photocatalysts and a redox mediator, mimicking the Z-scheme mechanism of the photosynthesis. It was found that the H-2 evolution took place on a Pt-SrTiO3 (Cr-Ta-doped) photocatalyst using an I- electron donor under the visible light irradiation. The Pt-WO3 photocatalyst showed an excellent activity of the O-2 evolution using an IO3- electron acceptor under visible light. Both H, and O-2 gases evolved in the stoichiometric ratio H-2/O-2 = 2) for more than 250h under visible light using a mixture of the Pt-WO3 and the Pt-SrTiO3 (Cr-Ta-doped) powders suspended in NaI aqueous solution. It is for the first time that the stoichiometric water splitting occurred over oxide semiconductor photocatalysts under the visible light irradiation. We proposed a two-step photo-excitation mechanism using a pair of I-/IO3- redox mediators. The quantum efficiency of the stoichiometric water splitting was ca. 0.1% at 420,7 nm. (C) 2002 Elsevier Science B.V. All rights reserved.