Abstract: Vacancy engineering in metal sulfides has garnered enormous attention from researchers because of their outstanding ability to modulate the optical and physiochemical properties of photocatalysts. Typically, in the case of sulfides, the catalytic activity is drastically hindered by the quick reassembly of excitons and the photocorrosion effect. Hence designing and generating S-vacancies in metal sulfides has emerged as a potential strategy for attaining adequate water splitting to generate H₂ and O₂ because of the simultaneous improvement in the optoelectronic features. However, developing efficient catalysts that manifest optimal photo(electro)catalytic performance for large-scale applicability remains challenging. Therefore, it is of utmost interest to explore the insightful features of creating S-vacancy and study their impact on catalytic performance. This review article aims to comprehensively highlight the roles of S-vacancy in sulfides for amended overall water-splitting activity. The photocatalytic features of S-vacancies modulated metal sulfides are deliberated, followed by various advanced synthetic and characterization techniques for effectual generation and identification of vacancy defects. The specific aspects of S-vacancies in refining the optical absorption range charge carrier dynamics, and photoinduced surface chemical reactions are critically examined for overall water splitting applications. Finally, the vouchsafing outlooks and opportunities confronting the defect-engineered (S-vacancy) metal sulfides-based photocatalysts have been summarized.

Key words: S-vacancy, Photo(electro)catalysis, Metal sulfides, Water splitting, Engineering, Identification of S-vacancies