Highly accessible atomically dispersed FeN_x 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 MN_x 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 FeN_x sites by Fe₃C@C core-shell nanoparticles, Fe-Phen-800 exhibits exceptional onset (E_onset = 0.994 V) and half-wave (E_1/2 = 0.878 V) potentials for ORR and a very low overpotential of 285 mV @ 10 mA cm⁻² (E_j=10) for OER, indicating excellent bifunctional activity (ΔE = E_j=10 - E_1/2 = 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.