Asymmetric supercapacitors based on β-Ni(OH)2 nanosheets and activated carbon with high energy density

Ni(OH)(2) nanosheets are directly grown on nickel foam by a simple template-free growth process. Their microstructure and surface morphology are studied by X-ray diffraction spectroscopy and scanning electron microscopy. The XRD and SEM results show that Ni(OH)(2) has a beta-phase structure and covers the nickel foam skeleton with nanosheets. This beta-Ni(OH)(2)/Ni-foam electrode exhibits a high specific electric quantity of 790.3 C g(-1), approaching the theoretical value (1040.6 C g(-1)) and high electrochemical activity. Asymmetric supercapacitor has been fabricated successfully using beta-Ni(OH)(2)/Ni-foam nanosheets as positive electrode and activated carbon as negative electrode in a KOH aqueous electrolyte. The electrochemical capacitances of this supercapacitor are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. An asymmetric supercapacitor AC/6 mol L-1 KOH/beta-Ni(OH)(2)/Ni-foam could be cycled reversibly in the high-voltage region of 0-1.6 V and displays intriguing performances with a specific capacitance of 105.8 F g(-1) and high energy density of 36.2 W h kg(-1). Importantly, this asymmetric supercapacitor device exhibits an excellent long cycle life along with 92% specific capacitance retained after 1000 cycles. (C) 2013 Elsevier B.V. All rights reserved.