Sulfur Vacancies in ZnIn2S4 Boost Photocatalytic H2O2 Production: Unveiling the Role of Sulfur Vacancies in the Superoxide Radical Pathway for H2O2 Photosynthesis

Hydrogen peroxide (H2O2) is widely regarded as a clean and high-value chemical; however, its conventional industrial production remains both energy-intensive and environmentally unsustainable. In this study, sulfur-deficient ZnIn2S4 (denoted SDZIS) was developed as an efficient photocatalyst for H2O2 generation through oxygen reduction under visible-light irradiation. SDZIS photocatalysts with controllable sulfur-vacancy concentrations were synthesized via a one-step citric-acid-assisted hydrothermal process combined with NaOH etching. The results of transient photocurrent response and electrochemical impedance spectroscopy show that the separation efficiency of charge carriers has been improved. Compared with pristine ZnIn2S4, the optimized SDZIS catalyst achieved a nine-fold enhancement in the H2O2 production rate, reaching 2711.81 μmol g−1 h−1. Results of experimental and density functional theory calculations suggest that sulfur vacancies can modulate the catalyst work function and the adsorption energy of O2. Comparative experiments indicate that an appropriate concentration of sulfur vacancies can lead to a high H2O2 yield. Combined with scavenger tests, DMPO-EPR, and rotating ring disk electrode measurements, these results support a sulfur-vacancy-associated enhancement in charge separation and a tendency toward a superoxide-involved 2e− ORR pathway for H2O2 production.