Fe-Nx active sites embedded into metal-organic-framework-derived mesoporous carbon for highly efficient oxygen reduction

Fe-Nx/C materials have proven to be one of the most promising electrocatalysts. However, it is impractical to increase the loading of Fe-Nx only by increasing the Fe content in the catalyst. Too much Fe content will lead to its aggregation into Fe nanoparticles during the pyrolysis process. In contrast to Fe-Nx, the formed Fe-nanoparticles result in many metal atoms inside the catalyst that cannot directly act as active sites, thus losing some of the electrocatalytic activity. Herein, we synthesized Fe-Nx/mesoporous carbon materials (FeTA- Nx/NC-900) by stepwise pyrolysis using MIL-101 with larger porosity as the structural substrate and iron tet-raaminophthalocyanine (FeTAPc) as the Fe dopant source. The composite has high porosity with rod structure that can effectively stabilize Fe-Nx sites, large specific surface area, and higher atom utilization for high dispersed Fe-Nx active sites. Especially, FeTA-Nx/NC-900 exhibits ORR half-wave potentials of 0.82 V and 0.65 V in alkaline/acidic media, respectively. Moreover, FeTA-Nx/NC-900 exhibits a peak power density of 74.3 mW cm-2 and excellent stability of more than 55 h when it is used as the cathodic electrocatalyst in Zn-air battery.