Achieving Ordered-Cationic-Vacancy-Mediated Photohole Transfer Dynamics via Phase and Facet Engineering toward Highly Efficient Photoelectrochemical Water Splitting

Defect engineering is promising to solve the photocarrier dynamics mismatch between rapid bulk recombination and sluggish surface oxygen evolution reaction (OER) in PEC water splitting but is limited by forming random or bulk defects. Herein, we adopt a phase and facet modulation strategy to construct a 2D defective spinel β-In2S3 photoanode with highly exposed, well-ordered indium vacancies (VIn). These VIn introduce a shallow acceptor level near the valence band (VB), which induces selective photohole capture to VIn shallow traps. The efficient and fast (∼0.13 ps) photohole transfer from the VB to the VIn state and the sharply elongated lifetime for photoholes accumulated at VIn, by facilitating band-edge exciton dissociation, induce separation efficiency nearly 100% even at low bias. Meanwhile, surface VIn lowers the OER barrier by boosting the conversion of *OH to *O and promotes surface reaction kinetics, enabling the photohole transfer efficiency to reach 95%. Thus, VIn simultaneously acts as photohole-capture centers and surface-active sites to optimize photohole separation and interfacial transfer dynamics. Through introducing and exposing ordered VIn to reaction interfaces, the β-In2S3-2D photoanode achieves a record-high photocurrent density of 9.7 mA cm–2 at 1.23 VRHE and an IPCE reaching 80% without hole scavengers. Such a regulation mechanism can guide reverse design of defective semiconductor photoanodes for efficient PEC conversion.