Hemin: A Highly Effective Electrocatalyst Mediating the Oxygen Reduction Reaction

Abstract

Carbon-supported hemin (hemin/C) was investigated as a nonprecious metal electrocatalyst mediating the oxygen reduction reaction (ORR). The effect of the heat treatment and metal content on the electrocatalytic activity was extensively studied. We found that the electrocatalytic activity was significantly improved after the heat treatment, and the best performance was achieved at the treatment temperature of 600 °C. Physico-chemical characterizations indicated that the heat treatment temperature yielded a coincident effect on the composition and microstructure of the catalyst. X-ray photoelectron spectroscopy (XPS) revealed that the atomic ratio of Fe to N was 1:4.7 for pristine hemin/C, which amounted to the highest value of 1:1.9 for hemin/C heat-treated at 600 °C. Nitrogen ad/desorption analysis showed that the pyrolysis at 600 °C resulted in the largest microporous surface area. On the basis of the above findings, we suggest that FeN2 be the active center in hemin/C and the micropore play an important role in catalyzing the ORR. Furthermore, we also found that the electrocatalytic activity of hemin/C was improved with increasing the metal content. More inspiringly, we report that the optimized hemin/C electrocatalyst could yield a comparable electrochemical performance with the commercial Pt catalyst in alkaline media.