Enhanced electrocatalytic oxygen reduction reaction for Fe–N4–C by the incorporation of Co nanoparticles

Abstract

Oxygen reduction reaction (ORR) catalytic activity can be improved by means of enhancing the synergy between transition metals. In this work, a novel porous Fe–N₄–C nanostructure containing uniformly dispersed Co nanoparticles (CoNPs) is prepared by an assisted thermal loading method. The as-prepared Co@Fe–N–C catalyst shows enhanced ORR activity with a half-wave potential (E_1/2) of 0.92 V vs. RHE, which is much higher than those of the direct pyrolysis CoNP-free sample Fe–N–C (E_1/2 = 0.85 V) and Pt/C (E_1/2 = 0.90 V) in alkaline media. It exhibits remarkable stability with only a 10 mV decrease in E_1/2 after 10 000 cycles and an outstanding long-term durability with 85% current remaining after 60 000 s. In acidic media, this catalyst exhibits catalytic activity with an E_1/2 of 0.79 V, comparable to Pt/C (E_1/2 = 0.82 V). X-ray absorption fine spectroscopy analysis revealed the presence of active centres of Fe–N₄. Density functional theory calculations confirmed the strong synergy between CoNPs and Fe–N₄ sites, providing a lower overpotential and beneficial electronic structure and a local coordination environment for the ORR. The incorporation of CoNPs on the surface of Fe–N₄–C nanomaterials plays a key role in enhancing the ORR catalytic activity and stability, providing a new route to prepare efficient Pt-free ORR catalysts.