Hierarchical (CdZnCuCoFe)S_1.25/ZnIn₂S₄ Heterojunction for Photocatalytic CO₂ Reduction: Insights into S-Scheme Charge Transfer Pathways in Type-I Band Alignment

Photocatalytic CO 2 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 /ZnIn 2 S 4 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) ZnIn 2 S 4 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 CO 2 photoreduction process. As an outcome, the optimized S-scheme heterojunction (HES/ZIS-10) unveils a higher CO 2 -to-CO photoreduction rate (2.43 μmol g –1 h – 1), which is 5.3 times higher than that of pristine ZnIn 2 S 4 .