Metallic Covalent Organic Frameworks as Dual-Function Electrocatalysts for Oxygen Reduction and Evolution Reactions

Designing high-performance, bifunctional electrocatalysts that can facilitate both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is crucial for the widespread application of rechargeable zinc-air batteries, yet it remains challenging. One effective strategy is to design active sites for the ORR and the OER in a targeted manner, integrate them into a structure, and exercise precise control over their electronic structure. Here, we present the design of bifunctional covalent organic frameworks (COFs), which use iron phthalocyanine (FePc) and cobalt phthalocyanine (CoPc) as building blocks. In these COFs, Fe and Co act as active sites for the ORR and the OER, respectively. The electronic structure of the active sites can be well regulated by fluorine (F) atoms in the framework’s structure. An increased number of F atoms enhances the adsorption strength of the oxygen intermediate by regulating the d-band center of the metal site, thereby lowering the reaction energy barrier. FePcF8-CoPcF8–COF exhibited superior activity for both reactions, with an overpotential of 0.71 V and a power density of 222 mW cm–2. This research paves the way for developing bifunctional electrocatalysts for energy conversion devices.