Localized Asymmetric Electron Distribution in Covalent Organic Frameworks Promotes Efficient Photocatalytic H2O2 Production
Covalent organic frameworks (COFs) with highly symmetric skeletons exhibit limited O2 adsorption and weak thermodynamic driving force for the two-electron oxygen reduction reaction (2e− ORR), constraining photocatalytic H2O2 production. Here, we modulate the local arrangement of fluorine atoms in COFs, creating para- and ortho-fluorinated variants (Fp-COFs and Fo-COFs) to induce an asymmetric electronic distribution. This asymmetry provides effective O2-adsorption sites and strengthens the driving force for 2e− ORR. Theoretical analysis reveals that asymmetric fluorination delocalizes lone-pair electrons of F atoms to adjacent carbons, producing a discretized electron distribution that enhances 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, Fo-COFs achieve a quantum yield of 8.8% for H2O2 photosynthesis in pure water. This work provides a new approach for tuning local electron distribution in COFs, offering guidance for rational design of efficient photocatalytic materials and broadening the application prospects of asymmetric electronic structures.