H2-production and electron-transfer mechanism of a noble-metal-free WO3@ZnIn2S4 S-scheme heterojunction photocatalyst

Abstract

Solar-driven hydrogen production can alleviate the ever-growing energy crisis, but developing affordable and efficient photocatalysts is challenging. We here report a noble-metal-free WO₃@ZnIn₂S₄ S-scheme heterojunction photocatalyst with ZnIn₂S₄ nanosheets vertically growing out of WO₃ nanofibers. Due to the difference in work function, ZnIn₂S₄ donates electrons to WO₃ upon their combination and thereby creates an internal electric field (IEF) at their interfaces. Driven by the IEF and bent energy bands, the photogenerated charge carriers of WO₃@ZnIn₂S₄ follow an S-scheme transfer and separation pathway and maintain strong redox ability, as unveiled by in situ X-ray photoelectron spectroscopy (XPS) and time-resolved photoluminescence spectroscopy. Benefiting from the S-scheme electron/hole separation and lower H₂-evolution barrier (ΔG_H* = −0.36 eV at S sites), the optimized WO₃@ZnIn₂S₄ heterojunction affords a remarkable H₂-evolution activity of 8500 μmol h⁻¹ g⁻¹ with an apparent quantum yield of 3.61% at 420 nm, outperforming most photocatalysts with deposition of noble metals.