N-Doped carbon nanospheres with nanocavities to encapsulate manganese oxides as ORR electrocatalysts

Abstract

Herein we report a facile strategy to embed manganese oxide (MnO_X) nanoparticles into nanocavities of N-doped carbon nanospheres (N-CNs). N-CNs were first synthesized through polymerization of pyrrole and self-assembly of polypyrrole with silica nanospheres as a template, followed by pyrolysis treatment and silica template removal. The addition of KMnO₄ to N-CNs resulted in the formation of N-CNs@MnO₂ hybrids. After calcination of the N-CN@MnO₂ hybrids at temperatures of 100 °C, 300 °C and 500 °C, the crystalline phase of manganese oxides can be transformed from MnO₂ into Mn₃O₄ and MnO. The N-CN@MnO_X hybrids were characterized by SEM, TEM, HRTEM, XRD, Raman, XPS and nitrogen adsorption–desorption techniques. Finally, N-CN@MnO_X hybrids were used as electrocatalysts toward the oxygen reduction reaction (ORR). The results indicated that N-CN@Mn₃O₄ hybrids exhibited the best ORR performance and superior electrocatalytic stability.