N-Doped carbon nanospheres with nanocavities to encapsulate manganese oxides as ORR electrocatalysts†
Abstract
Herein we report a facile strategy to embed manganese oxide (MnOX) 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@MnOX hybrids were characterized by SEM, TEM, HRTEM, XRD, Raman, XPS and nitrogen adsorption–desorption techniques. Finally, N-CN@MnOX 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.