Superior Electrochemical Properties of Nanofibers Composed of Hollow CoFe2O4 Nanospheres Covered with Onion-Like Graphitic Carbon

Abstract

Nanofibers composed of hollow CoFe2O4 nanospheres covered with onion-like carbon are prepared by applying nanoscale Kirkendall diffusion to the electrospinning process. Amorphous carbon nanofibers embedded with CoFe2@onion-like carbon nanospheres are prepared by reduction of the electrospun nanofibers. Oxidation of the CoFe2-C nanofibers at 300 degrees C under a normal atmosphere produces porous nanofibers composed of hollow CoFe2O4 nanospheres covered with onion-like carbon. CoFe2 nanocrystals are transformed into the hollow CoFe2O4 nanospheres during oxidation through a well-known nanoscale Kirkendall diffusion process. The discharge capacities of the carbon-free CoFe2O4 nanofibers composed of hollow nanospheres and the nanofibers composed of hollow CoFe2O4 nanospheres covered with onion-like carbon are 340 and 930 mA h g(-1), respectively, for the 1000th cycle at a current density of 1 Ag-1. The nanofibers composed of hollow CoFe2O4 nanospheres covered with onion-like carbon exhibit an excellent rate performance even in the absence of conductive materials.