Structural and Electronic Modulations of Imidazolium Covalent Organic Framework-Derived Electrocatalysts for Oxygen Redox Reactions in Rechargeable Zn-Air Batteries.

Covalent organic frameworks (COFs) are promising candidates for the controllable design of electrocatalysts. However, bifunctional electrocatalytic activities for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remain challenging in COFs. In this study, imidazolium-rich COFs (IMCOFs) with well-defined active sites and characteristic three-dimensional assembly structures were readily prepared, and their electronic structures were tuned by Co incorporation to elicit bifunctional electrocatalytic activities for the ORR and OER. The Co nanoparticle-incorporated spherical IMCOF-derived electrocatalyst (CoNP--IMCOF) exhibited lower overpotentials for the ORR and OER compared with the atomic Co-incorporated planar IMCOF-derived electrocatalyst (Co--IMCOF). Computational simulations revealed that the imidazole carbon sites of CoNP--IMCOF rather than the triazine carbons were the active sites for the ORR and OER, and its -band center downshifted via charge transfer, facilitating the chemisorption of oxygen intermediates during the reactions. A Zn-air battery with CoNP--IMCOF exhibited a small voltage gap of 1.3 V with excellent durability for 935 cycles. This approach for control over the three-dimensional assembly and electronic structures of IMCOFs can be extended to the development of diverse catalytic nanomaterials for applications of interest.