Nitrogen-Doped Carbon Flowers with Fe and Ni Dual Metal Centers for Effective Electroreduction of Oxygen

Carbon-based nanocomposites have been attracting extensive attention as high-performance catalysts in alkaline media towards the electrochemical reduction of oxygen. Herein, polyacrylonitrile nanoflowers are synthesized via a free-radical polymerization route and used as a structural scaffold and precursor, whereby controlled pyrolysis leads to the ready preparation of carbon nanocomposites (FeNi-NCF) doped with both metal (Fe and Ni) and nonmetal (N) elements. Transmission electron microscopy studies show that the FeNi-NCF composites retain the flower-like morphology, with the metal species atomically dispersed into the flaky carbon petals. Remarkably, despite a similar structure, elemental composition, and total metal content, the FeNi-NCF sample with a high Fe:Ni ratio exhibits an electrocatalytic performance towards oxygen reduction reaction (ORR) in alkaline media that is similar to that by commercial Pt/C, likely due to the Ni to Fe electron transfer that promotes the adsorption and eventual reduction of oxygen, as evidenced in X-ray photoelectron spectroscopic measurements. Results from this study underline the importance of the electronic properties of metal dopants in the manipulation of the ORR activity of carbon nanocomposites.