Efficient oxygen reduction through metal-free 3D covalent organic frameworks: a novel approach

Covalent organic framework (COF) materials have gained significant applications in electrocatalytic systems due to their structural diversity and tunable functionalities. Moreover, three-dimensional (3D) COFs exhibit multistage pore structures, exposing numerous open sites, which facilitate the oxygen reduction reaction (ORR) process. However, the advancement of 3D COFs for ORR has been hindered by challenges, including limited topologies, the scarcity of building blocks with the required reactivity and symmetries, and difficulties in determining crystalline structures. In this work, we utilized an 8-connectivity building unit and successfully constructed two isoreticular 3D COF materials, which exhibited exceptionally high catalytic activity for 2e⁻ oxygen reduction reaction without the addition of any metal or conductive support materials, nor the pyrolyzed process. The electrochemically active surface areas (ECSAs) of the two 3D COFs were found to be 17.19 and 12.18 mF/cm², respectively, which were significantly higher than those reported from other framework materials.