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

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.