Enhanced electrochemical performance of facilely synthesized cobalt doped cubic NiO nanoflakes for supercapacitor application

Being inexpensive, nontoxic and environmental friendly, NiO has caught special attention as a promising electrode material for supercapacitors. We recently reported facile synthesis of porous NiO nanocrystallites for energy storage application. A sophisticated strategy to improve the electrochemical properties of NiO which is a ptype semiconductor is the incorporation of 3d metal ions into it. In this article, we present successful fabrication of highly porous cobalt doped NiO nanostructures through a facile, low cost, one step solution combustion method without a post calcination treatment and demonstrate the influence of cobalt content on structural properties and electrochemical behavior. The thus prepared Co doped NiO samples were systematically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, BrunauerEmmett-Teller measurements, cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. It was found that the phase structure of pristine NiO remains unaffected by the process of doping. But doping obviously influences the textural and morphological properties, more importantly, enhances the electrochemical properties of pristine NiO. A maximum specific capacity of 746 C/g (specific capacitance of 1244 F/ g) was obtained for an optimum cobalt dopant ratio, which is superior to undoped NiO (295 C/g). Moreover, cobalt doped NiO nanostructures exhibited a good rate capability (71 % capacity retention from 1 to 15 A/g) and long term cycling stability (83.7 % after 5000 cycles at 100 mV/s). An asymmetric device fabricated using Co doped NiO electrode as the positive electrode and activated carbon as the negative electrode delivered an energy density of 32.7 Wh/kg at a power density of 261 W/kg.