Growth-controlled NiCo2S4 nanosheet arrays with self-decorated nanoneedles for high-performance pseudocapacitors

Abstract

We report a synthesis of NiCo₂S₄ nanosheet arrays with self-decorated nanoneedles on nickel foams by a facile and efficient two-step hydrothermal approach. We demonstrate that the morphologies of various three-dimensional nanostructures such as nanoneedle arrays, nanosheet arrays, and nanoneedle-decorated nanosheet arrays can be manipulated by tuning the amount of additive ammonium fluoride alone in the reaction. The unusual nanostructure of nanoneedles grown on the surface of NiCo₂S₄ nanosheet arrays shows a large electroactive surface area and superior electrochemical properties. The electrode made of the NiCo₂S₄ nanosheet arrays with self-decorated nanoneedles shows greatly improved electrochemical performances with an ultrahigh specific capacitance of 2617.6 F g⁻¹ at a current density of 15 mA cm⁻² and of 2051.0 F g⁻¹ even at a current density of 30 mA cm⁻². The electrode also exhibits an excellent cycling stability by retaining 93.2% of its original state after 5000 cycles, rendering the NiCo₂S₄ nanosheet arrays with self-decorated nanoneedles a potential electrode material for high-performance supercapacitors.