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

Abstract

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 (CoO_x-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 (CoO_x-loaded TaON photoanode), enabling Z-scheme water splitting.