Amplification effect of side group regulation via imidazolate linkages of covalent organic frameworks for efficient oxygen reduction

Abstract

Metal-free covalent organic framework (COF) materials are promising catalysts for the oxygen reduction reaction (ORR). However, it is difficult to markedly modulate their catalytic performance by only changing the side groups because their partially conjugated linkages weaken the influence of the electronic and charge transfer properties along the frameworks. Here, we demonstrated the amplification effect of micro-changes in the side units of COFs by constructing imidazole linkages for the ORR, and four different electron effect groups (H, F, OMe, and OH) were introduced. Owing to the conjugated linkages, electronic effects can be transmitted to the active sites through the skeleton. Notably, the half-wave potential (E_1/2) and mass activity of OH-COF were 0.80 V vs. RHE and 12.43 A g⁻¹, respectively, which were 180 mV more positive and 11 times more than those of H-COF, indicating the superior catalytic activity of OH-COF. Theoretical calculations revealed that different side groups influenced the binding ability of the intermediates and thus contributed to the modulated catalytic properties. This work demonstrates that a small change in the pore surface leads to substantial variations in the electrocatalytic performance, offering valuable insights into the relationship between the structural design and performance of COFs as electrocatalysts.