Multisite atomic-chlorine-passivation stabilizes perovskite interfaces for efficient H2O2 photosynthesis from seawater

Lead halide perovskites are promising for artificial photosynthesis but suffer from aqueous instability. Here, we stabilize CsPbI₃ quantum dots within a hydrophobic chlorine-functionalized covalent organic framework through multisite atomic-chlorine passivation, forms dual Cl-Pb coordination and Cl-I halogen bonding at the interface. This suppresses ionic migration while creating a gas-solid-liquid triphase interface for enhanced O₂ diffusion. The resulting S-scheme heterojunction spatially separates carriers to concurrently drive two-electron oxygen reduction and water oxidation for H₂O₂ synthesis without sacrificial agents. The system achieves production rates of 20.37 mmol h^-1 g^-1 in seawater, with a solar-to-chemical conversion efficiency of 1.38%, and operates stably for 20 h. Importantly, natural sunlight tests yield 11.7 mmol L^-1 H₂O₂ in 10 h. Mechanistic studies confirm synergistic interfacial charge transfer and dual-reaction pathways via both oxygen reduction and water oxidation. This work demonstrates an approach for robust perovskite-based photocatalysts toward solar-driven chemical synthesis from seawater.