Framework-Porphyrin-Derived Single-Atom Bifunctional Oxygen Electrocatalysts and their Applications in Zn-Air Batteries.

High-performance bifunctional oxygen electrocatalysis constitutes the key technique for the widespread application of clean and sustainable energy through electrochemical devices such as rechargeable Zn-air batteries. Single-atom electrocatalysts with maximum atom efficiency are highly considered as an alternative of the present noble-metal-based electrocatalysts. However, the fabrication of transition metal single-atoms is very challenging, requiring extensive attempts of precursors with novel design principles. Herein, an all-covalently constructed cobalt-coordinated framework porphyrin with graphene hybridization is innovatively designed and prepared as the pyrolysis precursor to fabricate single-atom Co-Nx -C electrocatalysts. Excellent electrochemical performances are realized for both bifunctional oxygen electrocatalysis and rechargeable Zn-air batteries with regard to reduced overpotentials, improved kinetics, and prolonged cycling stability comparable with noble-metal-based electrocatalysts. Design principles from multiple scales are proposed and rationalized with detailed mechanism investigation. This work not only provides a novel precursor for the fabrication of high-performance single-atom electrocatalysts, but also inspires further attempts to develop advanced materials and emerging applications.