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

Abstract

Abstract We studied the water splitting into H2 and O2 using two different semiconductor photocatalysts and a redox mediator, mimicking the Z-scheme mechanism of the photosynthesis. It was found that the H2 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 O2 evolution using an IO3− electron acceptor under visible light. Both H2 and O2 gases evolved in the stoichiometric ratio (H2/O2=2) for more than 250 h 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.