A Comprehensive Review on the Boosted Effects of Anion Vacancy in the Photocatalytic Solar Water Splitting: Focus on Sulfur Vacancy

In recent decades, a great interest in photocatalytic water splitting has been due to the importance of sunlight water splitting hydrogen production as a renewable energy source to reduce global warming effects. The photocatalytic water splitting applications of metal sulfide semiconductors photocatalysts, as chalcogenide compounds, with advantages of the wide range for light harvesting and tunable bandgap, may be restricted by the limited active sites, poor conductivity, photo corrosion, and charge recombination. The sulfur vacancy (SV) effectively addresses these issues and generates H2 and O2 by attaining adequate water-splitting because of the improved optoelectronic features. This review article aims to comprehensively highlight the synergistic roles of SV in metal sulfides for amended overall water-splitting activity. The SV-modulated metal sulfides' photocatalytic features are deliberated, followed by different advanced synthetic techniques for effectual vacancy defect generation. The specific SV aspects in refining the optical harvesting range, dynamics of charge carrier, and photoinduced surface chemical reactions are deeply described for overall water splitting applications. Finally, summarized vouchsafing outlooks and opportunities confronting the S-vacancy engineered metal sulfides-based photocatalysts are elucidated. It would be expected and hoped that this review will help researchers design/fabricate better metal sulfide-based photocatalytic systems.