Modulation of Sulfur Vacancies in ZnIn₂S₄/MXene Schottky Heterojunction Photocatalyst Promotes Hydrogen Evolution

The sustainable production of hydrogen utilizing solar energy is a pivotal strategy for reducing reliance on fossil fuels. ZnIn₂S₄ (ZIS), as a typical metal sulfide semiconductor, has received extensive attention in photocatalysis. Although the introduction of sulfur (S) vacancies in ZIS to enhance photocatalytic hydrogen production by creating defect energy levels has been explored, detailed studies on the control and modulation of S-vacancies in ZIS are sparce. This study demonstrates that while moderate levels of S-vacancies can enhance hydrogen evolution, excessive vacancies may hinder the process, underscoring the importance of S-vacancy modulation. Guided by theoretical calculations, We have designed and synthesized ZIS with modulated S-vacancies to realize favorable hydrogen adsorption-free energy and integrated in a Schottky-heterojunction with MXene co-catalysts for enhanced hydrogen evolution. The optimized hydrogen evolution performance of ZnIn₂S₄/MXene (ZMX) reaches 14.82 mmol g⁻¹ h⁻¹ under visible light irradiation, surpassing many reported ZnIn₂S₄-based photocatalysts. The enhanced performance is ascribed to widened light absorption and enhanced carrier transportation realized by S-vacancy modulation and the co-catalytic effect. Femtosecond ultrafast absorption (fs-TA) spectra and other in-situ/ex-situ characterizations further prove an efficient separation and transfer in an as-prepared ZMX catalyst. These findings open up new perspectives for designing catalysts with vacancy modulation. © 2024 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH.