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

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 KMnO(4)to N-CNs resulted in the formation of N-CNs@MnO(2)hybrids. After calcination of the N-CN@MnO(2)hybrids at temperatures of 100 degrees C, 300 degrees C and 500 degrees C, the crystalline phase of manganese oxides can be transformed from MnO(2)into Mn(3)O(4)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@Mn(3)O(4)hybrids exhibited the best ORR performance and superior electrocatalytic stability.