Surface-modified metal sulfides as stable H2-evolving photocatalysts in Z-scheme water splitting with a [Fe(CN)6]3−/4− redox mediator under visible-light irradiation

Z-scheme splitting of water into H2 and O2 was achieved using K2[CdFe(CN)6]-modified metal sulfides as H2-evolving photocatalysts combined with an appropriate O2-evolution system (CoOx-loaded TaON photoanode) in the presence of [Fe(CN)6]3−/4− as an electron mediator. Pt/CdS showed high activity (67.7 μmol h−1) for H2 evolution in borate buffer solution containing [Fe(CN)6]4− as an electron donor under visible-light irradiation. A cyano complex containing [Fe(CN)6]4− and Cd2+, which efficiently scavenged photogenerated holes and effectively facilitated the oxidation of [Fe(CN)6]4− to [Fe(CN)6]3−, was formed on the CdS surface in the reaction. Modification of other metal sulfides, such as ZnIn2S4 and CdIn2S4, with the cyano complex K2[CdFe(CN)6] significantly improved their rates of H2 evolution (ZnIn2S4: 4.8 → 15 μmol h−1; CdIn2S4: 0.8 → 6 μmol h−1) in the presence of [Fe(CN)6]4− and an appropriate O2-evolution system (CoOx-loaded TaON photoanode), enabling Z-scheme water splitting.