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

摘要

Hydrogen evolution over pristine semiconductors is desirable but seldom realizedin powdered photocatalysis. It requires the catalyst surface simultaneouslypossessing efficient electron transfer and rapid H_2 production properties. Thecurrent semiconductor photocatalysts have to depend on additional cocatalyststo achieve the H_2 evolution process. Herein, theoretical and experimental resultsdemonstrate that metastable sulfur vacancy could significantly enhance theintrinsic H_2 evolution behavior of semiconductors. The hydrogen adsorption freeenergy (ΔG_H) of CdS could be optimized to ΔG_H = 0.01 eV, much lower than thatover thermodynamically stable vacancies (ΔG_H = 0.31 eV). The experiment isconducted based on kinds of supported CdS nanoparticles prepared with theanion-exchange method. A series of in situ characterizations disclose that ametastable sulfur vacancy forms under photoexcitation and is stable during thereaction. These metastable sulfur vacancies cause the formation of intermediatestates between the valence band and the conduction band that increase transportationand utilization of photogenerated electrons. The conceptual finding ofthe critical role of the metastable vacancy in enhancing H_2 evolution would bringnew thinking on the design of semiconductor photocatalysts to be less dependenton cocatalysts.