Neighboring Effect of Adjacent Nitrogen Sites on Vinylene Linkage in Covalent Organic Frameworks for Regulating Oxygen Reduction Reaction

Vinylene-linked covalent organic frameworks (COFs) are attractive electrocatalysts owing to their corresponding high chemical stability and excellent conjugated frameworks. In this study, for the first time, the methyl group of the pyrimidine ring was used to synthesize conjugated COFs (TB-TFT-COF and TB-TFC-COF) with vinylene linkages, which were employed as catalysts for the oxygen reduction reaction (ORR). In addition, local electronic structures of the vinylene linkages could be regulated by the adjacent nitrogen atomic sites of various functional moieties (triazine, pyridine, and pyrimidine), resulting in tunable electrocatalytic activity and selectivity of the COFs. Notably, the TB-TFT-COF attained a half-wave potential of 0.74 V relative to RHE alongside superior electrochemical stability, matching the performance of metal-free COF-based catalysts for ORR. Furthermore, as evidenced by density functional theory (DFT) calculations, the adjacent nitrogen sites of the pyrimidine unit around the vinylene linkage are crucial for enhancing the utilization of electrocatalytic active sites. This work establishes that the precise modulation of electronic coupling between neighboring active sites enables the development of efficient oxygen reduction reaction catalysts.