Engineering Interfacial Band Bending over ZnIn₂S₄/SnS₂ by Interface Chemical Bond for Efficient Solar‐Driven Photoelectrochemical Water Splitting

Abstract Developing a simple and effective strategy to modulate the energy band bending of heterojunction photoelectrodes is pivotal in terms of photoelectrochemical (PEC) water splitting. Herein, it is demonstrated that the introduction of the interfacial InOSn chemical bonds at the ZnIn₂S₄/SnS₂ interface regulates the band bending of ZnIn₂S₄/SnS₂ heterojunction photoanodes, reverses the charge transport direction, and reduces the oxygen evolution reaction (OER) overpotential. Detailed analysis indicates that the interfacial InOSn bond makes band adaptation to promote carrier separation and transfer through ultraviolet photoelectron spectrometry, hydroxyl radical production tests, and surface photovoltage measurements. Due to the special nanosheet morphology with exposed edges of the heterojunction interface, the InOSn bonds are partially exposed, which can reduce the OER overpotential and boost the surface injection efficiency according to the PEC impedance spectroscopy and density functional theory calculations. The synergistic modulation of InOSn bond yields a photocurrent of 4.57 mA cm⁻² at 1.23 V (vs reversible hydrogen electrode, AM 1.5 G) and a low onset potential of −0.14 V_RHE. This work provides a new solution for energy band regulation to improve the performance of heterojunction photoelectrodes for PEC water splitting.