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

Highlights: • Mesoporous NiCo₂O₄ hollow spheres are prepared via a soft template method. • Mesoporous NiCo₂O₄ hollow spheres manifest enhanced electrochemical performances. • Large BET surface area and unique hollow structure give the excellent electrochemical properties. - Abstract: 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.