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

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.