Yolk–shell structured iron carbide/N-doped carbon composite as highly efficient and stable oxygen reduction reaction electrocatalyst

We report a simple route to synthesize iron carbide/carbon yolk–shell composite via a facile two-step process including polymerization of pyrrole using Fe3O4 as a sacrificial template to form a Fe3O4/polypyrrole composite, followed by annealing at high temperature in N2 atmosphere. The yolk–shell composite, with iron carbide (Fe2.5C) embedded in nitrogen-doped carbon layers, shows impressively high catalytic activity and stability for oxygen reduction reaction in alkaline solution. Both the pyridinic-N and graphic-N in the shell of Fe3O4–PPy-700, together with the Fe2.5C confined in carbon layers are believed to be the active sites for the ORR.