Effect of nanoparticle composition on oxygen reduction reaction activity of Fe/N–C catalysts: a comparative study

Abstract

The Fe/N–C catalyst is a type of promising catalyst to replace costly Pt/C for oxygen reduction reaction (ORR). The Fe agglomerates in the Fe/N–C catalyst are capable of enhancing the ORR activity, but the effect of the agglomerate composition has not received prior investigation. In this paper, three Fe/N–C catalysts composed of different Fe-based nanoparticles including metal/oxide, carbide, and nitride on nitrogen-doped graphene sheets (denoted as Fe/Fe₃O₄@N-G, Fe₃C@N-G and Fe_xN@N-G, respectively) are synthesized and their oxygen reduction reaction activities are compared. Electrochemical evaluation reveals an order of Fe/Fe₃O₄@N-G > Fe_xN@N-G > Fe₃C@N-G in ORR activity, and the best Fe/Fe₃O₄@N-G catalyst is even superior to the commercial Pt/C catalyst. Detailed structure and composition analyses suggest that the excellent catalytic performance is tightly associated with the high N (particularly pyridinic-N) dopants and the chemical composition of metal agglomerates in the catalyst. Our work explores a highly active ORR electrocatalyst and also reveals the effect of agglomerate composition on the activity, which may provide valuable insights into the rational design and controllable synthesis of sustainable high-performance ORR electrocatalysts.