Zinc Assisted Thermal Etching for Rich Edge-Located Fe-N Active Sites in Defective Carbon Nanofiber for Activity Enhancement of Oxygen Electroreduction.

Single-atom catalysts (SACs) with edge-located metal active sites exhibit superior oxygen reduction reaction (ORR) performance due to their narrower energy gap and higher electron density. However, controllably designing such active sites to fully reveal their advantages remains challenging. Herein, rich edge-located Fe-N active sites anchored in hierarchically porous carbon nanofibers (denoted as e-Fe-N-C) are fabricated via an in situ zinc-assisted thermal etching strategy. The e-Fe-N-C catalyst demonstrates superior alkaline ORR activity compared to counterparts with fewer edge-located Fe-N sites and commercial Pt/C. Density functional theory calculations show that the accumulation of more negative charges near the Fe-N and the formation of partially reduced Fe state in the edge-located Fe-N sites reduce the energy barrier for the ORR process. Additionally, the unique hierarchically porous structures with mesopores and macropores facilitate full utilization of the active sites and enhance long-range mass transfer. The zinc-air battery (ZAB) assembled with e-Fe-N-C has a peak power density of 198.9 mW cm, superior to commercial Pt/C (152.3 mW cm). The present strategy by facile controlling the amount of the zinc acetate template systematically demonstrates the superiority of edge-located Fe-N sites, providing a new design avenue for rational defect engineering to achieve high-performance ORR.