(Invited) Solid-State Z-Scheme Photocatalysts for Overall Water-Splitting Under Visible Light

We fabricated an Ag-inserted hetero-junction photocatalyst for water-splitting under visible light, similar to a Z-scheme system but is not required for a redox mediator. In this system, Ag acts as a solid electron mediator for water-splitting. We selected ZnRh₂O₄ (Eg=1.2 eV) and AgSbO₃ (Eg=2.5 eV) as H₂- and O₂-photocatalysts, respectively. Ag could be inserted between these photocatalysts using a thermal-decomposition reaction of Ag₂O and following melt reaction of Ag. In short, commercially available powder of Ag₂O and prepared powders of ZnRh₂O₄ and AgSbO₃ were thoroughly mixed and heat-treated at 900^oC, which is slightly lower than the melting temperature of Ag. Then, the obtained powder was washed with HNO₃ aqueous solution to remove excess Ag, forming the solid-state photocatalyst, ZnRh₂O₄/Ag/Ag_1-xSbO_3-y. The Ag_1-xSbO_3-y and ZnRh₂O₄ particles were connected to each other with their particle sizes of ~1000 and ~200 nm. In this system, Ag acted as the solid-state electron mediator for the transfer of electrons from the conduction band of Ag_1-xSbO_3-y to the valence band of ZnRh₂O₄. Utilizing the constructed photocatalyst, the simultaneous liberation of H₂ and O₂ from pure water at a molar ratio of ~ 2:1 was achieved under irradiation with visible light at ~ 545 nm. Utilizing the same strategy by changing the O₂-evolution photocatalyst, we recently succeeded in pure water-splitting under visible light up to 600 nm. Detailed investigations will be discussed at the conference.