Efficient photocatalytic H₂ evolution over NiMoO₄/Twinned-Cd_0.5Zn_0.5S double S-scheme homo-heterojunctions

The effectiveness of charge transfer and separation between bulk phase and the interface is crucial for evaluating the performance of photocatalysts. In this study, NiMoO₄ was employed to enhance the photocatalytic activity for hydrogen (H₂) evolution in twinned Cd_0.5Zn_0.5S (T-CZS) homojunctions comprising of wurtzite Cd_0.5Zn_0.5S (WZ-CZS) and zinc blende Cd_0.5Zn_0.5S (ZB-CZS) with alternating arrangements. The investigation reveals that the introduction of NiMoO₄ can lead to an increase of active sites for H₂ evolution, a prolongation of charge carrier lifetime, and a decrease of H₂ evolution overpotential. The H₂ production rate of 8 wt% NiMoO₄/T-CZS reaches up to 71.2 mmol h⁻¹ g⁻¹, while its apparent quantum efficiency (AQY) is 8.23% at 400 nm. The enhanced activity can be attributed to the synergistic effects of homojunctions and heterojunctions in NiMoO₄/T-CZS. According to the density functional theory (DFT), photoelectric response, and radical trapping experimental analysis, the charge transfer between WZ-CZS and ZB-CZS in T-CZS, as well as NiMoO₄ and T-CZS, both follow the S-scheme pathway under the influence of band bending, Coulombic force, and built-in electric field. This leads to an effective internal and interfacial charge separation in NiMoO₄/T-CZS homo-heterojunctions, while maintaining their high reactivity. Additionally, the H₂ evolution activity of T-CZS can also be increased in different degrees by various metal molybdates (MMoO₄) including CoMoO₄, Ag₂MoO₄, Bi₂(MoO₄)₃, BaMoO₄, ZnMoO₄, and CdMoO₄. The bulk and interfacial synergistic double S-scheme homo-heterojunctions in this study provide new insights for targeted solar driven H₂ evolution engineering.