An Ultrastable Bifunctional Electrocatalyst Derived from a Co 2+ -Anchored Covalent-Organic Framework for High-Efficiency ORR/OER and Rechargeable Zinc-Air Battery.

It remains a great challenge to develop alternative electrocatalysts with high stability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a bifunctional electrocatalyst composed of hollow CoO x (Co 3 O 4 /CoO) nanoparticles embedded in lamellar carbon nanofibers is derived from a Co 2+ -anchored covalent-organic framework. The as-fabricated electrocatalyst (CoO x @NC-800) exhibits a half-wave potential ( E 1/2 ) of 0.89 V with ultrahigh long-term stability (100% current retention after 3000 CV cycles). Together with promising OER performance, the CoO x @NC-800 based reversible Zn-air battery displays a small potential gap (0.70 V), superior to that of the commercial 20% Pt/C + RuO 2 . The density functional theory (DFT) calculations reveal that the remarkable electrocatalytic performance and stability of CoO x @NC-800 are attributed to the optimized adsorption of the *OOH intermediate and reduced free energy of the potential-limiting step. This study establishes the functionalization of COF structure for fabrication of high-performance carbon-based electrocatalysts.