Cobalt nanoparticles encapsulated in iron and nitrogen co-doped urchin-like porous carbons as an efficient bifunctional oxygen reversible catalyst for Zn-air batteries

Design of the cheap and high-efficiency catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is imperative for rechargeable Zn-batteries (r-ZABs). Herein, the cobalt nanoparticles encapsulated in iron and nitrogen co-doped urchin-like porous carbons (Co@Fe-Nx/C) as a bifunctional electrocatalyst for ORR and OER is fabricated via a facile pyrolysis treatment. The Co@Fe-Nx/C catalyst displays a typical urchin-like morphology anchored with numerous CNTs and many monodispersed cobalt nanoparticles are encapsulated in the carbon matrices, which not only enable effective and fast electron transfer, but also can prevent Co nanoparticles from surface oxidation and agglomeration-induced activity degradation, thus improving the electrocatalytic activities and durability. The Co@Fe-Nx/C catalyst exhibits a superb ORR/OER catalytic activities with a low reversible oxygen potential gap (0.67 V), surpassing the commercial Pt/C and RuO2 catalysts (0.69 V). Liquid r-ZAB constructed with Co@Fe-Nx/C as the air cathode manifest outstanding energy density (802 mAh g(-1)), superb charge/discharge performance and excellent reversibility and durability compared to the precious metal couple catalysts. The remarkable bifunctional catalytic activities are due to the synergistic effect of Co nanoparticles and Fe-Nx/C substrates.