Well-defined Fe, Fe3C, and Fe2O3 heterostructures on carbon black: a synergistic catalyst for oxygen reduction reaction

Abstract

Constructing non-precious metal-based catalysts with a smart heterostructure, by using 3d transition metals and carbon as building blocks, has drawn increasing attention due to these construction materials having high abundance, affordable prices, and promising catalytic activity for the oxygen reduction reaction (ORR) in alkaline solutions. Herein, we report synthesizing well-defined Fe₃C/Fe₂O₃/Fe heterostructures via a simple partial chemical conversion of Fe₂O₃ into Fe₃C and metallic Fe, using 1,2-diaminobenzene as a reductive additive at an elevated temperature. These epitaxially grown heterostructures are uniformly dispersed on a carbon black surface with an average particle size of about 10.8 nm. Compared with pure Fe₃C/C or Fe₂O₃/C, the Fe₃C/Fe₂O₃/Fe/C composite exhibits a remarkably improved activity and durability toward the ORR, which is also superior to the state-of-the-art Pt/C catalyst in an alkaline environment. The origin of this enhanced electrocatalytic performance is associated with a synergy among Fe, Fe₂O₃, and Fe₃C components, raised by a chemical interaction between them. The electron-accepting Fe₂O₃ can promote electron transfer from the carbon support to active Fe₃C through O–Fe–C–Fe–C bonds formed in the heterostructured composite, which improves ORR kinetics. Therefore, developing a Fe-based composite with a smart heterostructure may open the door to rationally designing highly active and low-cost 3d transition metal-based catalysts for ORR.