Vertically aligned NiS nano-flakes derived from hydrothermally prepared Ni(OH)2 for high performance supercapacitor

Abstract

In present work, the vertically aligned NiS nano-flakes composed thin film is prepared by anionic exchange process in which hydrothermally prepared Ni(OH)2 is used as a parent thin film and Na2S as a sulfide ion source. This synthesis process produced fully transformed and shape-controlled nano-flakes of NiS from nano-flowers of Ni(OH)2. The electrochemical supercapacitor properties of NiS electrode are studied with cyclic voltammetry (CV), galvonostatic charge discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. Highly porous surface area (85 m2/g) of NiS nano-flakes makes large material contribution in electrochemical reaction stretching specific capacitance (Cs) of 880 F/g at scan rate of 5 mV/s and 90% electrochemical stability up to 4000 CV cycles in 2 M KOH electrolyte. Further, the flexible solid-state symmetric supercapacitor device (NiS/PVA–LiClO4/NiS) has been fabricated using NiS electrodes with polyvinyl alcohol (PVA)–lithium perchlorate (LiClO4) gel electrolyte. The NiS/PVA–LiClO4/NiS device exhibits specific capacitance of 56 F/g with specific energy of 14.98 Wh/kg and excellent cycling stability after 2000 cycles. In addition, the NiS/PVA–LiClO4/NiS device demonstrates illumination of red light emitting diode (LED) for 60 s, which confirms the practical applicability of NiS/PVA–LiClO4/NiS device in energy storage.