Tailoring cyano-functionalized covalent organic frameworks with highly ordered charge network structure for efficient hydrogen peroxide photosynthesis

Abstract

As a vital industrial oxidant, H₂O₂ suffers from energy-intensive conventional production methods. Covalent organic frameworks (COFs) have emerged as promising photocatalysts for producing H₂O₂. Conventional imine-linked COFs suffer from inefficient charge separation due to electron localization at nitrogen atoms, which disrupts π-conjugation and promotes charge recombination. To overcome these limitations, we propose cyano-vinylene-linked COFs with precisely designed highly ordered charge networks as an alternative to conventional imine-linked frameworks. The vinyl bridges establish continuous π-conjugation pathways for charge separation, while the cyano groups guide directional electron transfer, collectively forming an efficient charge transport network. Density functional theory (DFT) calculations reveal that synergy between the π-conjugated backbone and cyano groups enhances electron mobility and facilitates electron injection into O₂, accelerating *OOH formation and oxygen reduction. Using benzotrithiophene-2,5,8-tricarboxaldehyde (BTT) as a key building block, we synthesized three distinct COF architectures: an imine-linked framework (Mph-2NH₂-COF) and two cyano-vinylene-linked variants (Bph-2CN-COF and Mph-2CN-COF). Experimentally, the optimized Mph-2CN-COF achieves a record H₂O₂ production rate of 9423.2 μmol g⁻¹ h⁻¹ under alkaline conditions, with stable performance over 8 h in a flow reactor, and completes benzylamine coupling in 90 min. These findings demonstrate that constructing highly ordered charge networks is an effective strategy for high-performance photocatalysis, enabling sustainable H₂O₂ production and organic synthesis.