ZnIn2S4 nanosheets with tunable dual vacancies for efficient sacrificial-agent-free H2O2 photosynthesis†

ZnIn₂S₄ nanosheets with tunable concentration of dual vacancies (i.e. Zn vacancy and S vacancy) were prepared and used for photocatalytic H₂O₂ production. Introducing dual vacancies effectively promotes exciton dissociation, facilitates O₂ adsorption, and reduces the free energy of subsequent activation and protonation of adsorbed O₂. These intriguing properties endow ZnIn₂S₄ with excellent performance for sacrificial agent-free H₂O₂ photosynthesis via a two-step single-electron oxygen reduction reaction pathway under AM 1.5 and visible-light irradiation. Almost double amounts of H₂O₂ can be produced over ZnIn₂S₄ with dual vacancies compared to pristine ZnIn₂S₄ without vacancies. Corresponding SCC efficiency and AQY at 420 ± 20 nm reached ∼0.031% and 0.34%, respectively. In addition, the abundant dual vacancies inhibit H₂O₂ decomposition because of enhanced hydrophilicity. This work provides a new strategy to improve the photocatalytic performance of ZnIn₂S₄ through defect engineering and brings new mechanistic insights into the role of these defects.