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

Abstract

H₂O₂ photosynthesis has attracted\ngreat interest\nin harvesting and converting solar energy to chemical energy. Nevertheless,\nthe high-efficiency process of H₂O₂ photosynthesis\nis driven by the low H₂O₂ productivity due to\nthe recombination of photogenerated electron–hole pairs, especially\nin the absence of a sacrificial agent. In this work, we demonstrate\nthat ultrathin ZnIn₂S₄ nanosheets with S vacancies\n(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\nextend the lifetimes of photogenerated carriers and suppress their\nrecombination, which triggers the O₂ reduction and H₂O oxidation to H₂O₂ through radical\ninitiation. Theoretical calculations suggest that the formation of\nS_v can strongly change the coordination structure of ZIS,\nmodulating the adsorption abilities to intermediates and avoiding\nthe overoxidation of H₂O to O₂ during O₂/H₂O redox, synergistically promoting 2e^– O₂ reduction and 2e^– H₂O\noxidation for ultrahigh H₂O₂ productivity. The\noptimal catalyst displays a H₂O₂ productivity\nof 1706.4 μmol g^–1 h^–1 under\nvisible-light irradiation without a sacrificial agent, which is ∼29\ntimes higher than that of pristine ZIS (59.4 μmol g^–1 h^–1) and even much higher than those of reported\nphotocatalysts. Impressively, the apparent quantum efficiency is up\nto 9.9% at 420 nm, and the solar-to-chemical conversion efficiency\nreaches ∼0.81%, significantly higher than the value for natural\nsynthetic plants (∼0.10%). This work provides a facile strategy\nto separate the photogenerated electron–hole pairs of ZIS for\nH₂O₂ photosynthesis, which may promote fundamental\nresearch on solar energy harvest and conversion.