Uniform Fe₃O₄/Nitrogen-Doped Mesoporous Carbon Spheres Derived from Ferric Citrate-Bonded Melamine Resin as an Efficient Synergistic Catalyst for Oxygen Reduction

Abstract

Developing a facile strategy to synthesize an efficient and inexpensive catalyst for the oxygen reduction reaction (ORR) is critical to the commercialization of many sustainable energy storage and conversion techniques. Herein, a novel and convenient strategy was presented to prepare Fe₃O₄ embedded into nitrogen-doped mesoporous carbon spheres (Fe₃O₄/N-MCS) by the polycondensation between methylolmelamines and ammonium ferric citrate (AFC) and subsequent pyrolysis process. In particular, the polycondensation reaction was completely finished within a very short time (6.5 min), and the iron contents can be adjusted and had a great influence on the microstructure. Moreover, the Fe₃O₄/N-MCS can be used as a robust catalyst for the ORR in alkaline media, and the catalyst with the iron content of 3.35 wt % exhibited excellent electrochemical performance in terms of more positive onset potential (E₀ = 1.036 V vs RHE) and half-wave potential (E_1/2 = 0.861 V) and much better methanol tolerance and long-term durability, in comparison with that of 20% Pt/C. The remarkable performance was ascribed to the characteristics of large specific surface area, mesoporous structure, high contents of pyridinic N and graphitic N, as well as strong electronic interaction between Fe₃O₄ and protective N-doped graphitic layers.