Highly accessible atomically dispersed FeNx sites coupled with Fe3C@C core-shell nanoparticles boost the oxygen catalysis for ultra-stable rechargeable Zn-air batteries

It is significant but challenging to develop a cost-effective, high-efficiency, and stable bifunctional electrocatalyst of oxygen reduction and evolution reactions (ORR and OER) for rechargeable Zn-air batteries. Herein, we present a novel bifunctional catalyst constructed by highly accessible atomically dispersed MNx sites coupled with core-shell nanoparticles (M-Phen-800; M = Fe, Co, and Ni) from easily accessible M-Phenanthroline (M-Phen) complexes. Due to the synergistically induced symmetric charge distribution around FeNx sites by Fe3C@C core-shell nanoparticles, Fe-Phen-800 exhibits exceptional onset (Eonset = 0.994 V) and half-wave (E1/2 = 0.878 V) potentials for ORR and a very low overpotential of 285 mV @ 10 mA cm−2 (Ej=10) for OER, indicating excellent bifunctional activity (ΔE = Ej=10 - E1/2 = 0.637 V) over the state-of-the-art Pt/C-RuO2 (0.702 V) combination. Moreover, the Fe-Phen-800-based Zn-air battery demonstrates a remarkable energy density of 1022 Wh kg−1 and greater cycling stability (>800 cycles) than the commercial Pt/C-RuO2 battery.