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

Abstract 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 Fe 2 O 3 clusters (Fe 2 O 3 /NPCS) is constructed. The composition and microstructure of Fe 2 O 3 /NPCS are carefully characterized, and the existed Fe 2 O 3 -stabilized Fe N 4 active sites for ORR are verified. The Fe 2 O 3 /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 Fe 2 O 3 clusters, the porous structures facilitating electron transport as well as the electrolyte and oxygen diffusion.