Radical-Driven Photosynthesis of Hydrogen Peroxide From Only Water Promoted by Porous Aromatic Frameworks

Direct water oxidation to hydrogen peroxide (H₂O₂) solely from water and sunlight represents a highly economical solar-to-chemical pathway, but suffers from the competition of thermodynamically-favored oxygen evolution reaction (OER). Herein, we report a radical-driven strategy for H₂O₂ photosynthesis through water oxidation reaction (WOR), enabled by rationally engineered porous aromatic frameworks (PAFs). PAF-261N, -262, and -263 with donor-π-acceptor architectures were targeted synthesized using the thiol-alkyne click reaction, and thiyl radicals can be in situ generated from pendant thiol groups in these customized PAFs under visible light irradiation. These highly reactive thiyl radicals enables to bypass the competitive OER pathway and overcoming WOR redox-potential limitations via a hydrogen atom transfer mechanism. This unique pathway was unequivocally confirmed through comprehensive isotopic labeling, radical trapping and verification, and density functional theory calculations. Notably, the free thiol group densities within PAF-263 can be easily tuned, and we achieved a high H₂O₂ production rate of 13.68 mmol g^-1 h^-1, significantly outperforming existing benchmarks in photocatalytic systems. Being completely metal-free and independent of sacrificial reductants, this work establishes a robust photosynthetic process for H₂O₂ production and opens a door for effective and scalable photocatalyst design for many challenging chemical transformations.