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 CsPbI ₃ quantum dots (QDs) within a hydrophobic chlorine-functionalized covalent organic framework (COF-Cl) through multisite atomic-chlorine passivation, forming dual Cl–Pb coordination and Cl–I halogen bonding at the interface. This suppresses ionic migration while creating a gas–liquid–solid triphase interface for enhanced O ₂ diffusion. The resulting S-scheme heterojunction spatially separates carriers to concurrently drive two-electron oxygen reduction and water oxidation for H ₂ O ₂ synthesis without sacrificial agents. The system achieves record production rates of 25.29 mmol h ^-1 g ^-1 in pure water and 20.37 mmol h ^-1 g ^-1 in seawater under visible light, with a solar-to-chemical conversion efficiency of 1.38%. Crucially, it operates stably for 20 h in seawater and produces 11.7 mmol L ^-1 H ₂ O ₂ in 10 h under natural sunlight. Mechanistic studies confirm synergistic interfacial charge transfer and dual-reaction pathways via both oxygen reduction and water oxidation. This work establishes a paradigm for robust perovskite-based photocatalysts toward scalable solar-driven chemical synthesis from seawater.