Chelated Linkage and Framework Isomerism Effect Toward Robust Zn-Salen MCOFs for Dual-Channel Overall H₂O₂ Photosynthesis

It remains challenging to synthesize effective and photocorrosion-tolerated organic photocatalysts for two-electron oxygen reduction reaction (2e⁻ ORR) and water oxidation reaction (2e⁻ WOR). Herein, two isomeric Zn-Salen metal covalent organic frameworks (Zn-Salen-MCOFs) with kgd-v or hcb topology are designed as robust and efficient photocatalysts for dual-channel H₂O₂ photosynthesis. Zn-Salen-MCOF with kgd-v topology shows a higher H₂O₂ photocatalytic production rate of 6617/3438 µmol gcat.⁻¹ h⁻¹ in pure water with/without additional O₂ or air saturation, together with long-time continuous H₂O₂ photosynthesis performance (100 h). The framework isomerism effect and the chelated linkages contribute to the improved H₂O₂ photosynthesis efficiency and stability of it. A three-step 2e⁻ WOR with the initial H₂O adsorption over the ZnO₂N₂ unit and a four-step 2e⁻ ORR reaction mechanism with the key H_ad adsorption at the pyrazinic N site are proposed. This study paves the way for developing robust MCOF-based photocatalysts for dual-channel H₂O₂ production based on chelated linkage and framework isomerism effect.