Interfacial Chemical Bond‐Modulated Z‐Scheme Charge Transfer for Efficient Photoelectrochemical Water Splitting

Abstract The Z‐scheme heterojunction has great potential in photoelectrochemical (PEC) water splitting due to its unique charge‐carrier migration pathway, superior carrier separation efficiency, and high redox capacity, but how to regulate the Z‐scheme charge transfer at the nanometric interface of heterostructures still remains a big challenge. Herein, InOCd bond is rationally introduced at the interface between ZnIn₂S₄ nanosheets and CdS nanoparticles through a facile cation exchange reaction, which successfully converts the previously reported type II band structure to a direct Z‐scheme heterojunction (ZnIn₂S₄/CdS) as confirmed by various characterizations. Density functional theory calculation reveals that the InOCd interfacial chemical bond significantly uplifts the Fermi level of ZnIn₂S₄ and CdS, inverts the interfacial band bending direction, thus resulting in the formation of Z‐scheme heterojunction. Moreover, an amorphous ZnO overlayer is deposited to eliminate the surface defects and accelerate the surface reaction kinetics. Benefiting from the superior charge separation efficiency and high redox ability originating from the Z‐scheme structure, the optimum ZnIn₂S₄/CdS/ZnO photoanode exhibits a dramatically enhanced PEC performance with low onset potential (−0.03 V vs reversible hydrogen electrode, V_RHE) and large photocurrent of 3.48 mA cm⁻² at 1.23 V_RHE, which is about 21.75 times that of pristine ZnIn₂S₄.