Defective ZnIn 2 S 4 Nanosheets for Visible-Light and Sacrificial-Agent-Free H 2 O 2 Photosynthesis via O 2 /H 2 O Redox.

H 2 O 2 photosynthesis has attracted great interest in harvesting and converting solar energy to chemical energy. Nevertheless, the high-efficiency process of H 2 O 2 photosynthesis is driven by the low H 2 O 2 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 ZnIn 2 S 4 nanosheets with S vacancies (S v -ZIS) can serve as highly efficient catalysts for H 2 O 2 photosynthesis via O 2 /H 2 O redox. Mechanism studies confirm that S v in ZIS can extend the lifetimes of photogenerated carriers and suppress their recombination, which triggers the O 2 reduction and H 2 O oxidation to H 2 O 2 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 H 2 O to O 2 during O 2 /H 2 O redox, synergistically promoting 2e - O 2 reduction and 2e - H 2 O oxidation for ultrahigh H 2 O 2 productivity. The optimal catalyst displays a H 2 O 2 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 H 2 O 2 photosynthesis, which may promote fundamental research on solar energy harvest and conversion.