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.