Molecular Space-Charge Layering in Ionic Covalent Organic Frameworks for Unidirectional Charge Transfer toward Efficient H2O2 Photosynthesis

Abstract

Solar-driven hydrogen peroxide (H₂O₂) production over covalent organic frameworks (COFs) represents a promising sustainable paradigm, yet its efficiency is severely restricted by formidable exciton recombination. Herein, we employed a solvent-free melt polymerization method to synthesize a highly crystalline sp² carbon-linked ionic COF, designated as TMB-COF-Br. Incorporating N⁺-functionalized pyridine units constructed as electron-withdrawing centers, a robust molecular space-charge layer was successfully engineered within the pristine skeleton. The tailored electrostatic environment functioned as an intramolecular charge-rectifying valve along the sp² carbon-linked conjugation, which significantly promoted electron/hole dissociation and enabled directional charge transport, thereby markedly boosting photocatalytic H₂O₂ production. Furthermore, the localized electropositive microenvironment effectively stabilized the crucial *OOH intermediate via electrostatic interactions. Consequently, TMB-COF-Br achieved a remarkable H₂O₂ photosynthesis rate of 5770 μmol·g^–1·h^–1 at pH = 3 without any sacrificial agents, markedly outperforming the nonionized COF. This work unveils the fundamental role of molecular space-charge layers in gating charge transfer in supramolecular systems, providing a powerful paradigm for designing high-efficiency photocatalysts.