Photoinduced Hydration Boosts O2 Evolution on Co-Chelating Covalent Organic Framework

The achievement of artificial photosynthesis relies on successful water oxidation and a detailed mechanistic understanding. Here, we demonstrate a photoinduced hydration pathway for O-2 evolution from water oxidation over an imine-linked covalent organic framework (COF) comprising electron-rich benzotrithiophene and electron-deficient benzothiadiazole units with atomically chelated Co sites. The experimental and theoretical results suggest that the water oxidation starts with the photoinduced hydration of imine groups. The subsequent oxidative deprotonation and intramolecular hydroxyl attack lead to O-O bond formation. The hydration path significantly averages the energy barriers of water oxidation, thus promoting O-2 evolution. Inspired by this fact, we fabricate a COF-based heterostructure, which realizes overall water splitting with H-2 and O-2 evolution rates of 450 and 212 mu mol center dot g(-1) h(-1), respectively.