Vulcanizing time controlled synthesis of NiS microflowers and its application in asymmetric supercapacitors

Hierarchical NiS was synthesized under different vulcanizing time via a facial sacrificial template method with Ni(OH)(2) microflowers as precursors. The as-prepared samples were characterized by XRD, BET, XPS, SEM and TEM. The results show that the NiS microstructure changes from microflower to microspheres gradually with the increase of vulcanizing time. Impressively, with the reaction time extending to 18 h, the NiS-18 microflowers have the largest surface areas (20.5 m(2.)g(-1)) and the roughest surface. Electrochemical measurements showed that NiS-18 possessed the highest specific capacitance (1315.4 F.g(-1) at current density of 1 A.g(-1)) and excellent cycling stability (89.2% of the C-m retained after 5000 GCD cycles at current density of 10 A.g(-1)). More importantly, an asymmetric supercapacitor (SC), consisting of NiS-18 as positive electrode and active carbon (AC) as negative electrode (NiS//AC), achieves a high potential window of 1.6 V. The NiS//AC displays a high energy density of 33.4 Wh.kg(-1) at power density of 0.8 kW.kg(-1). Additionally, NiS//AC SC exhibits excellent cycling performance (87.3%C-m retained after 5000 GCD cycles at current density of 5 A.g(-1)) and nearly 100% Coulombic efficiency. (C) 2017 Elsevier Ltd. All rights reserved.