Shallow-Trap Relay and Type-II Band Alignment Synergy in Vs-ZnS/In2S3 for Accelerated Photoelectrochemical Water Splittin

In conventional photoelectrochemical (PEC) water-splitting systems, the high recombination rate of photogenerated charge carriers and sluggish interfacial charge transfer kinetics serve as the core bottlenecks restricting energy conversion efficiency. In this study, a sulfur-vacancy-engineered Vs-ZnS/In 2 S 3 heterojunction was constructed to demonstrate the “electron relay” function of sulfur vacancies within a Type-II heterojunction. Specifically, sulfur vacancies create a localized shallow trap level below the conduction band of In 2 S 3 , amplifying the potential driving force for interfacial electron transfer. Concurrently, these defect states effectively capture photogenerated electrons transitioning across the interface and serve as highly active sites directly participating in surface reactions, thereby significantly suppressing both the bulk and surface recombination of charge carriers. Benefiting from this synergistic mechanism, the as-prepared Vs-ZnS/In 2 S 3 photoelectrode exhibits exceptional PEC performance, achieving a maximum photocurrent density of 1.26 mA·cm –2 and an applied bias photon-to-current efficiency of approximately 0.26%. This is substantially superior to pristine ZnS and conventional ZnS/In 2 S 3 electrodes. Kinetic and separation efficiency characterizations indicate that the bulk and surface charge separation efficiencies are drastically improved to 68.4% and 38.1%, respectively. This exceptional performance stems from the synergistic interplay between the heterojunction and the sulfur vacancies: the localized electronic structure modulated by defect states facilitates the directional transfer of interfacial electrons and accelerates the hydrogen evolution reaction kinetics. This work provides a novel design paradigm for regulating charge transport pathways within heterojunctions via defect engineering to realize highly efficient energy conversion.