Localized asymmetric electron distribution in COFs promotes efficient photocatalytic H 2 O 2

Abstract In covalent organic frameworks (COFs), the highly symmetric skeleton limits O2 adsorption and weakens the thermodynamic driving force of the two-electron oxygen reduction reaction (2e− ORR), thus restricting photocatalytic efficiency. In this study, we modulated the local arrangement of fluorine atoms in COFs (para- and ortho-fluorinated, named Fp-COFs and Fo-COFs) to create an asymmetric electronic distribution, which supplies effective O2-adsorption sites, strengthens the driving force for 2e− ORR and ultimately elevates the photocatalytic activity. Theoretical analysis shows that asymmetric fluorination delocalizes the lone-pair electrons of F atoms to adjacent carbons, producing a discretized electron distribution that improves O2 adsorption at imine bonds. The increased electron density on these carbons facilitates electron transfer into the π* orbital of adsorbed O2, accelerating ·OOH* intermediate formation and lowering the Gibbs free energy barrier of the 2e− pathway. Consequently, a quantum yield of 8.8% for H2O2 photosynthesis in pure water is achieved. This work provides a new approach for tuning local electron distribution in COFs, offering guidance for the rational design of efficient photocatalytic materials and broadening the application prospects of asymmetric electronic structures.