Efficient Proton Transfer and Charge Separation within Covalent Organic Frameworks via Hydrogen-Bonding Network to Boost H₂O₂ Photosynthesis.

Abstract

Photocatalytic synthesis based on the oxygen reduction reaction (ORR) has shown great promise for H₂O₂ production. However, the low activity and selectivity of 2e^- ORR result in a fairly low efficiency of H₂O₂ production. Herein, we propose a strategy to enhance the proton-coupled electron transfer (PCET) process in covalent organic frameworks (COFs), thereby significantly boosting H₂O₂ photosynthesis. We demonstrated that the construction of a hydrogen-bonding network, achieved by anchoring the H₃PO₄ molecular network on COF nanochannels, can greatly improve both proton conductivity and photogenerated charge separation efficiency of COFs. Thus, COF@H₃PO₄ exhibited superior photocatalytic performance in generating H₂O₂ without sacrificial agents, with a solar-to-chemical conversion efficiency as high as 0.69%. Results indicated that a much more localized spatial distribution of energy band charge density on COF@H₃PO₄ led to efficient charge separation, and the small energy barrier of the rate-limiting step from *OOH to H₂O₂ endowed COF@H₃PO₄ with higher 2e^- ORR selectivity.