Design and synthesis of hierarchical NiCo2S4@NiMoO4 core/shell nanospheres for high-performance supercapacitors

Abstract

A novel electrode material of three-dimensional (3D) hierarchical NiCo₂S₄@NiMoO₄ core/shell nanospheres for high-performance supercapacitors was successfully synthesized by a two-step method. First, ball-like NiCo₂S₄ was obtained by controlling the morphology through a hydrothermal method using diethanol amine as a new precipitant; second, the interconnected uniform NiMoO₄ nanosheets were allowed to efficiently grow on the NiCo₂S₄ backbone by the hydrothermal method to form NiCo₂S₄@NiMoO₄ core/shell nanospheres. The resultant hierarchical NiCo₂S₄@NiMoO₄ core/shell nanospheres were characterized by X-ray diffraction, energy dispersive spectrometry, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy and N₂ adsorption and desorption. The electrochemical properties of the samples were evaluated though cyclic voltammetry, charge–discharge and electrochemical impedance spectroscopy in 6.0 M KOH electrolytic solution. The results showed that the hierarchical NiCo₂S₄@NiMoO₄ core/shell nanospheres exhibited a very large specific capacitance of 1714 F g⁻¹ at 1 A g⁻¹, an outstanding cyclic stability with a capacitance retention of 96% after 5000 cycles of charge–discharge and a low resistance.