Defective ZnIn₂S₄ Nanosheets for Visible-Light and Sacrificial-Agent-Free H₂O₂ Photosynthesis via O₂/H₂O Redox

H₂O₂ photosynthesis has attracted great interest in harvesting and converting solar energy to chemical energy. Nevertheless, the high-efficiency process of H₂O₂ photosynthesis is driven by the low H₂O₂ productivity due to the recombination of photogenerated electron–hole pairs, especially in the absence of a sacrificial agent. In this work, we demonstrate that ultrathin ZnIn₂S₄ nanosheets with S vacancies (S_v-ZIS) can serve as highly efficient catalysts for H₂O₂ photosynthesis via O₂/H₂O redox. Mechanism studies confirm that S_v in ZIS can extend the lifetimes of photogenerated carriers and suppress their recombination, which triggers the O₂ reduction and H₂O oxidation to H₂O₂ through radical initiation. Theoretical calculations suggest that the formation of S_v can strongly change the coordination structure of ZIS, modulating the adsorption abilities to intermediates and avoiding the overoxidation of H₂O to O₂ during O₂/H₂O redox, synergistically promoting 2e^– O₂ reduction and 2e^– H₂O oxidation for ultrahigh H₂O₂ productivity. The optimal catalyst displays a H₂O₂ productivity of 1706.4 μmol g^–1 h^–1 under visible-light irradiation without a sacrificial agent, which is ∼29 times higher than that of pristine ZIS (59.4 μmol g^–1 h^–1) and even much higher than those of reported photocatalysts. Impressively, the apparent quantum efficiency is up to 9.9% at 420 nm, and the solar-to-chemical conversion efficiency reaches ∼0.81%, significantly higher than the value for natural synthetic plants (∼0.10%). This work provides a facile strategy to separate the photogenerated electron–hole pairs of ZIS for H₂O₂ photosynthesis, which may promote fundamental research on solar energy harvest and conversion.