Synergistic catalytic effect of N-doped carbon embedded with CoFe-rich CoFe2O4 clusters as highly efficient catalyst towards oxygen reduction

Abstract

Spinel cobalt ferrite is one of the promising electrocatalysts for the ORR, but the poor electrical conductivity limits its application. Herein, we report a simple and efficient method to synthesize the N-doped carbon-shielding CoFe-rich CoFe2O4 catalyst which exhibits superior ORR catalytic activity under alkaline conditions due to the improved conductivity and high electrochemically active surface area. The NC@CoFe–CoFe2O4 catalyst shows a positive onset potential (1.0 V), half-wave potential (0.89 V) and maximum limiting current density (−5.0 mA cm−2), which are similar to commercial Pt/C, while significantly higher than those of all other controls and most of the previously reported catalysts. The Koutecky-Levich equation and rotating ring-disk electrode test prove a direct four-electron reduction process. Moreover, the NC@CoFe–CoFe2O4 catalyst also demonstrates superior methanol tolerance and long-term stability compared to Pt/C. The proposed catalytic mechanism analysis illustrates that the excellent ORR electrocatalytic activities and durability are the combined effect of highly conductive CoFe alloy, abundant Co–N/Fe–N sites along with the hydrophilic nature of CoFe2O4 clusters.