Carbon doped cobalt nanoparticles encapsulated in graphitic carbon shells: Efficient bifunctional oxygen electrocatalysts for ultrastable Zn-air batteries.

Rational design of low-cost, highly active and robust bifunctional oxygen electrocatalysts is essential for advancing the performance of rechargeable Zn-air batteries (ZABs). Herein, a facile one-step pyrolysis approach is reported to synthesize cobalt nanoparticles encapsulated in N-doped graphitic carbon with a core-shell structure. The temperature-dependent interdiffusion of C and Co atoms at the interface was observed. The catalyst prepared at an optimized temperature of 800 °C (Co@NC-800) exhibited a half-wave potential of 0.82 V for oxygen reduction reaction and an overpotential of 350 mV at 10 mA cm for oxygen evolution reaction. Density functional theory calculations demonstrated the electron redistribution of the metallic active sites and provided insights into the origin of bifunctional activity. The rechargeable ZAB assembled using Co@NC-800 demonstrated superior performance compared to precious metal based electrocatalysts, achieving a peak power density up to 213.6 mW cm, a specific capacity of 774.1 mAh g, and notable durability. This work provides a strategy for rational design of highly efficient and durable non-noble metal catalysts for rechargeable ZAB technologies.