Enhanced Catalytic Performance of FeCoNi/N-Doped Carbon Nanospheres as Bifunctional Oxygen Catalysts

Iron, cobalt, nickel, and nitrogen doped-carbon nanospheres (FeCoNi/N-C) are synthesized by the pyrolysis of globular Fe/Co/Ni-polypyrrole formed through a microemulsion method. The content and ratio of Fe/Co/Ni in N-C can be adjusted by adding different quantities of metal ions in microemulsion. Compared to Fe/N-C, FeCoNi/N-C demonstrates high conductivity, fast mass transport, superior catalytic properties of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The results showed multi-doping can facilitate the combination of metal and nitrogen and sustain their contents in pyrolysis process to improve conductivity and enhance bifunctional activities. According to the density functional theory calculations, co-doping of Co or/and Ni with Fe element on N-C material can help the desorption of *OH into water in ORR and accelerate the transformation of *O to *OOH in OER. Besides, FeCoNiN 4 is a dominant contributor to bifunctional activities.