Boosting the photocatalytic H2O2 production of covalent organic frameworks with a heteroatom-locked acceptor and gas diffusion system

Abstract

Simultaneously improving charge carrier separation and surface reaction efficiency is crucial for enhancing the photocatalytic H₂O₂ production efficiency of covalent organic frameworks (COFs). Here, a heteroatom-lock strategy is introduced into the acceptor structure of COFs, with the “lock” effect to enhance the coplanarity and conjugation, and the “heteroatom” effect to improve the O₂ adsorption. It turns out that the photocatalytic H₂O₂ production yield of the N-heteroatom locked COF (2.08 mmol g⁻¹ h⁻¹ under pure water and air conditions) is 2.1 times that of the S-heteroatom locked COF and 4.7 times that of the original COF. Experimental results and theoretical calculations reveal that the heteroatom-lock-induced H₂O₂ production enhancement of COFs is attributed to their lower exciton binding energy (E_b) and smaller charge transfer resistance, together with the bigger O₂ adsorption energy and lower transition state energy of the intermediates. Additionally, a novel gas diffusion reaction system is developed to further improve the O₂ diffusion efficiency, which not only enhances the photocatalytic H₂O₂ production yield to 4.06 mmol g⁻¹ h⁻¹, but also realizes the immobilization and efficient recycling of the COF catalyst. This study provides new insights into the rational design of COF-based photocatalysts, and offers a novel approach for the reaction system of photocatalytic H₂O₂ production.