Boosting Hydrogen Evolution Performance of a CdS-Based Photocatalyst: In Situ Transition from Type I to Type II Heterojunction during Photocatalysis

The heterojunction in photocatalysis establishes an internal electric field between the semiconductors, which is one of the effective methods for enhancing the separation of photogenerated carriers of semiconductors. Herein, a strategy is rationally proposed, which is performed in situ to transform the hybrid photocatalyst composed of the Ni–Co Prussian blue analogue (PBA) and CdS (CP) into another more active hybrid photocatalyst consisting of NiS and CdS (CN) during photocatalysis in the sulfur sacrificial reagent. The coupled component on the n-type CdS is converted from an n-type Ni–Co PBA to another p-type NiS during the process, thus constructing a p–n heterojunction and achieving a good photocatalytic hydrogen evolution reaction (HER) performance. Moreover, the carrier transfer mechanism is also an in situ transition from type I in CP to type II in CN during the HER process, which is supported by surface photovoltage and transient absorption spectroscopy. The CP-2 photocatalyst in the sulfur sacrificial reagent has a high photocatalytic hydrogen evolution amount of 176.6 μmol, which is 13.9 times higher than that of pure CdS. Overall, this work develops an in situ carrier transfer mechanism conversion strategy for expanding the HER photocatalysts and enhancing their photocatalytic HER performance.