Construction of dangling and staggered stacking aldehyde in covalent organic frameworks for 2e− oxygen reduction reaction

Abstract

Covalent organic frameworks (COFs) have been utilized as the ideal candidates to preciously construct electrocatalysts. However, the highly ordered degree of COFs renders the catalytic centers closely stacked, which limits the utilization efficiency of catalytic sites. Herein, we have first constructed dangling and staggered-stacking aldehyde (–CHO) from [4 + 3] COFs as catalytic centers for 2e⁻ oxygen reduction reaction (ORR). The new catalytic COFs have unreacted dangling -CHO out of the COFs' planes, which are more easily exposed in electrolytes than the sites in the frameworks. More importantly, these –CHO adopt staggered stacking models, and thus provide larger space for mass transport than those with eclipsed stacking models. In addition, by tuning the triratopic linkers in the COFs, the catalytic properties are well modulated. The optimized COF shows high selectivity and activity for 2e⁻ ORR, with H₂O₂ selectivity of 91%, and mass activity of 12.2 A g⁻¹, respectively. The theoretical calculation further reveals the higher activity for the pyridine-contained B18C6-PTTA-COF due to the promoted binding ability of the intermediate OOH* at the carbon in dangling –CHO. This work provides us with a new insight into designing electrocatalysts based on COFs.