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 O-2/H2O 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 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 O-2 during O-2/H2O redox, synergistically promoting 2e(-) O-2 reduction and 2e(-) H2O oxidation for ultrahigh H2O2 productivity. The optimal catalyst displays a H2O2 productivity of 1706.4 mu mol g(-1) h(-1) under visible-light irradiation without a sacrificial agent, which is similar to 29 times higher than that of pristine ZIS (59.4 mu mol 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 similar to 0.81%, significantly higher than the value for natural synthetic plants (similar to 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.