Iron–nitrogen co-doped hollow carbon sphere with mesoporous structure for enhanced oxygen reduction reaction

Abstract

An iron–nitrogen co-doped hollow carbon sphere (FeN-HCS) with a mesoporous structure is designed and prepared via simple pyrolysis of melamine on the surface of Fe₃O₄ nanospheres. In the reaction, Fe₃O₄ nanospheres are used both as templates for catalyzing the growth of carbon shells and iron sources to form ORR active sites. The FeN-HCS catalyst obtained exhibits extremely high oxygen reduction activity in an alkaline medium with a half-wave potential of 0.834 V (vs. RHE), which is 5 mV more positive than a Pt/C catalyst, and shifts negatively by only 6 mV after accelerated degradation tests (ADT). Moreover, the FeN-HCS catalyst shows a clear 4-electron reduction pathway and a high methanol tolerance. The outstanding performance of FeN-HCS can be attributed to its unique hierarchical porous hollow shell structure, which maximizes exposure of active sites and enhances mass transfer. Such a synthetic strategy offers a novel route to prepare functional hollow carbon spheres for energy storage and conversion applications.