Single-crystal β-NiS nanorod arrays with a hollow-structured Ni₃S₂ framework for supercapacitor applications

In this work, single-crystal β-NiS nanorod arrays have been in situ grown on a hollow structured Ni₃S₂ porous framework, and finally the Ni₃S₂ @ β-NiS materials with a pine twig-like structure and a novel three-dimensional (3D) architecture are constructed for high-performance electrode materials by using a facile one-step solvothermal approach. The as-prepared Ni₃S₂ @ β-NiS materials show a core-shell structure with the single-crystal β-NiS nanorods as the external shell and the hollow-structured Ni₃S₂ porous framework as the internal core. The electrochemical tests demonstrate that the Ni₃S₂ @ β-NiS materials achieved a high capacitance of 1158 F g^-1 at a current density of 2 A g^-1 in a three-electrode cell, and the capacitance still remained at 57.8% (i.e.; 670 F g^-1) when the current density is increased up to 50 A g^-1. The retained capacitance of the as-prepared Ni₃S₂ @ β-NiS electrode materials with a pine twig-like structure is up to 961.6 F g^-1 (that is, 97.4% retention as compared to the initial capacitance of 987 F g^-1) at a current density of 15 A g^-1 after 2000 cycles, which shows their excellent electrochemical cycling stability. Furthermore, the asymmetric device of Ni₃S₂ @ β-NiS//Activated Carbon (AC) shows a high energy density of 55.1 W h kg^-1 at a power density of 925.9 W kg^-1 and a high power density of 28.1 kW kg^-1 at an energy density of 22.2 W h kg^-1. All these results demonstrate that the Ni₃S₂ @ β-NiS is a promising electrode material for supercapacitors. This work also paves the way for fabricating a 3D hierarchical architecture of nickel sulfides for energy storage applications, and it may serve as a generic way for materials fabrication in the fields of photocatalysis (including water-splitting), electrocatalysis, and so on.