An investigation of the electrochemically capacitive performances of mesoporous nickel cobaltite hollow spheres

Mesoporous NiCo2O4 hollow spheres are prepared by a soft template method utilizing a hydrothermal route. Three kinds of NiCo2O4 morphologies can be obtained, including solid sphere, hollow sphere and collapsed hollow sphere with the adjustment of the concentration of hexamethylenetetramine (HMT). Compared with solid spheres and collapsed hollow spheres, the as-prepared NiCo2O4 hollow spheres show enhanced electrochemical properties, manifesting a high specific capacitance (204.4 mAh g(-1) at 2 A g(-1)), exceptional rate capability (62.8% capacity retention at 50 A g(-1)) and good cycling stability (93.2% capacity retention after 1000 cycles). Such remarkable electrochemical properties of the NiCo2O4 hollow spheres can be primarily ascribed to the high specific surface area and uniform mesoporous hollow structure that can increase the exposure of active sites available for reaction on the surface, shorten transport pathways for both electrons and ions, and alleviate the volume change during charge-discharge process. This work is significant because the unique mesoporous NiCo2O4 hollow spheres demonstrate the great potential in the development of high-performance electrode materials for supercapacitors. Additionally, this soft template method can be extended to the fabrication of other binary or even ternary metal oxides hollow micro-/nanostructure materials. (C) 2015 Elsevier Ltd. All rights reserved.