Oxysulfide semiconductors have narrow bandgaps — a property that makes them suitable photocatalysts for water splitting under irradiation with visible light (640 nm wavelength). That’s because the electronegative sulfide ions negatively shift the valence band edges of the corresponding oxides. However, the instability of sulfide ions during the water oxidation is a critical obstacle to simultaneous evolution of hydrogen and oxygen.

Now, a Japanese collaboration of industry, academia and government has demonstrated the activation and stabilization of Y2Ti2O5S2 (1.9 eV bandgap), as a photocatalyst for overall water splitting. On loading of IrO2 and Rh/Cr2O3 as O2 and H2evolution co-catalysts, respectively, and fine-tuning of the reaction conditions, simultaneous production of stoichiometric amounts of H2 and O2 was achieved on Y2Ti2O5S2 during a 20-h reaction. The fine particles of the photocatalyst could be handled by a simple spray-coating procedure to produce a photocatalyst sheet with a large surface-area. The discovery of the overall water-splitting capabilities of Y2Ti2O5S2 is expected to be applied for the inexpensive production of H2, while extending the range of promising materials for solar-H2 production.

The consortium is made up of researchers from the New Energy and Industrial Technology Development Org. (NEDO, Kawasaki City, www.nedo.go.jp) and the Japan Technological Research Association of Artificial Photosynthetic Chemical Process (ARPChem), which six industrial companies have joined, in collaboration with the University of Tokyo, Shinshu University and more.

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