Ammonia Defective Etching and Nitrogen-Doping of Porous Carbon toward High Exposure of Heme-Derived Fe–Nx Site for Efficient Oxygen Reduction

The utilization of metal and nitrogen doped carbon as a Pt-free oxygen reduction electrocatalyst depends largely on the homogeneous composition of the metal–nitrogen sites with limited content. Herein a simple and feasible ammonia defective activation strategy is explored on ordered mesoporous carbon (APC) to confine hematin precursor and suppress the formation of inorganic Fe-based derivatives during pyrolysis. Thus, a hierarchically nanoporous Fe/N/APC catalyst with high numbers of exposed iron–nitrogen sites exhibits an impressive performance for oxygen reduction reaction in alkaline media, with large diffusion-limited current density and positive half-wave potential with respect to commercial Pt/C catalyst. The enhanced ORR properties can be majorly ascribed to synergistic contributions of high numbers of exposed catalytic sites completion from high contents of Fe–N and pyridinic N along with the fast mass-transport properties arising from the etched high permeable porous structure. When applied as cathodic catalyst in Zn-air battery, it demonstrates a power density of 200 mW cm–2 and a specific capacity of 605 mA h g–1Zn higher than those of Pt/C catalyst.