Photoinduced Generation of Metastable Sulfur Vacancies Enhancing the Intrinsic Hydrogen Evolution Behavior of Semiconductors

Hydrogen evolution over pristine semiconductors is desirable but seldom realized in powdered photocatalysis. It requires the catalyst surface simultaneously possessing efficient electron transfer and rapid H 2 production properties. The current semiconductor photocatalysts have to depend on additional cocatalysts to achieve the H 2 evolution process. Herein, theoretical and experimental results demonstrate that metastable sulfur vacancy could significantly enhance the intrinsic H 2 evolution behavior of semiconductors. The hydrogen adsorption free energy (Δ G H ) of CdS could be optimized to Δ G H = 0.01 eV, much lower than that over thermodynamically stable vacancies (Δ G H = 0.31 eV). The experiment is conducted based on kinds of supported CdS nanoparticles prepared with the anion‐exchange method. A series of in situ characterizations disclose that a metastable sulfur vacancy forms under photoexcitation and is stable during the reaction. These metastable sulfur vacancies cause the formation of intermediate states between the valence band and the conduction band that increase transportation and utilization of photogenerated electrons. The conceptual finding of the critical role of the metastable vacancy in enhancing H 2 evolution would bring new thinking on the design of semiconductor photocatalysts to be less dependent on cocatalysts.