Iron and nitrogen co-doped carbon derived from soybeans as efficient electro-catalysts for the oxygen reduction reaction

Iron and nitrogen co-doped carbon (Fe-N/C) materials were fabricated by one-step pyrolysis of the mixture of FeCl3 and the low-cost biomass soybeans in N2 atmosphere at different temperatures. The physical properties of the prepared Fe-N/C catalysts were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) et al., the catalytic activity and stability of the Fe-N/C catalysts toward the oxygen reduction reaction (ORR) in alkaline solution were investigated by the electrochemical techniques. The results show that Fe is mainly in the form of Fe3O4 with the particle size of about 10 nm and encapsulated by thin graphite layers, and the content of Fe decreases from 1.19 to 0.24 wt.% with the increase of pyrolysis temperature from 600 to 900 °C. The ORR activity on the sample prepared at 700 °C (Fe-N/C-700) is preferable among the series of Fe-N/C catalysts, with the half-wave potential of the ORR shifting negatively only about 0.020 V as compared to that on the commercial Pt/C (40 wt.%, JM). The superior electro-catalytic performance of the Fe-N/C-700 catalyst would be due to the higher degree of the graphitization, the higher total contents of the pyridinic-N, quaternary-N/graphitic-N, as well as the relatively higher Fe3O4 content and surface area. The electron transfer number of the ORR on the Fe-N/C-700 catalyst approaches four indicating the 4-electron transfer pathway. Besides, the methanol tolerance and durability are superior to those on the Pt/C.