Efficient photocatalytic H2 evolution over NiMoO4/twinned-Cd0.5Zn0.5S double S-scheme homo-heterojunctions

Abstract

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 Cd0.5Zn0.5S (T-CZS) homojunctions comprising of wurtzite Cd0.5Zn0.5S (WZ-CZS) and zinc blende Cd0.5Zn0.5S (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.