Hierarchical (CdZnCuCoFe)S_1.25/ZnIn₂S₄ Heterojunction for PhotocatalyticCO₂ Reduction: Insights into S‑Scheme Charge TransferPathwaysin Type‑I Band Alignment

Abstract

Photocatalytic CO₂ reduction has emerged as a promising technology to cope with the need for greenhouse gas emission reduction and renewable energy sources. Herein, a novel hierarchical (CdZnCuCoFe)­S_1.25/ZnIn₂S₄ photocatalyst was synthesized by in situ growth of high-entropy sulfide (i.e., (CdZnCuCoFe)­S_1.25) nanoparticles (HES) on the surface of three-dimensional (3D) ZnIn₂S₄ hierarchical nanosheets (ZIS). Density functional theory calculations and experimental evaluation demonstrated the electron transfer from ZIS to HES, resulting in an internal electric field directed from ZIS to HES. Although the composite exhibited a type-I band alignment, the intimate interfacial contact and an internal electric field still triggered an S-scheme charge transfer process. The interplay of the internal electric field, band bending, and electrostatic repulsion between homogeneous charges guided electrons in the conduction band of HES to recombine with holes in the valence band of ZIS, thus promoting the separation of electron–hole pairs to boost the CO₂ photoreduction process. As an outcome, the optimized S-scheme heterojunction (HES/ZIS-10) unveils a higher CO₂-to-CO photoreduction rate (2.43 μmol g^–1 h^–1), which is 5.3 times higher than that of pristine ZnIn₂S₄.