Well-dispersed iron oxide stabilized Fe-N4 active sites in porous N-doped carbon spheres as alternative superior catalyst for oxygen reduction

The fabrication of highly active oxygen reduction reaction (ORR) catalysts with strong anti poisoning and durability at low cost is extremely desirable but still remains a great challenge. Herein, a novel hierarchically structured material of N-doped porous carbon spheres embedded with monodispersed Fe2O3 clusters (Fe2O3/NPCS) is constructed. The composition and microstructure of Fe2O3/NPCS are carefully characterized, and the existed Fe2O3-stabilized Fe N-4 active sites for ORR are verified. The Fe2O3/NPCS catalyst exhibits a superior ORR activity with a positive half-wave potential of 0.95 V, showing an obvious around 90 mV positive-shift over commercial Pt/C (20 wt%). Additionally, the high ORR catalytic activity is also accompanied by a smaller Tafel slope of 45.3 mV decade(-1) than Pt/C, implying a fast kinetics at high potentials. Furthermore, the high-active catalyst also demonstrates an outstanding anti-poisoning capacity and long-term durability. The excellent ORR activites are attributed to the synergistic effect between the rich Fe N-4 active sites protected by Fe2O3 clusters, the porous structures facilitating electron transport as well as the electrolyte and oxygen diffusion. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.