Amplification Effect of Side Groups Regulation via Imidazolate linkages of Covalent Organic Frameworks for Efficient Oxygen Reduction

Abstract

Metal-free covalent organic framework material is a kind of promising catalyst of oxygen reduction reduction (ORR). However, it is difficult to markedly modulate catalytic performance via only changing side groups, because their partial conjugated linkages weaken the influences of electronic and charge transferring properties along the frameworks. Here, we demonstrated amplification effect of micro-changes of side units of COFs via constructing imidazole-linkages for ORR, and four different electron effect groups (H, F, OMe and OH) have been introduced. Due to the conjugated linkages, the electronic effects can be transmitted to the active site 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, which were 180 mV more positive and 11 times of those from H-COF, indicating the high catalytic activty of OH-COF. The theoretical calculation revealed that different side groups influenced the binding ability of intermediates, and thus contributed to modulated catalytic properties. This work demonstrated that a small change in the pore surface will lead to big differences in electrocatalytic performance, which provides significant insight in the relationship between structural design and performance for COF as electrocatalysts.