Synthesis and electrochemical properties of nanostructured nickel-cobalt oxides as supercapacitor electrodes in aqueous media

Co-precipitation method was adopted in the preparation of nickel-cobalt oxides for potential application in supercapacitors. The formation of spinel nickel-cobalt oxide, NiCo2O4 started below 400 degrees C as confirmed by X-ray diffraction analysis. Pure phase nickel cobaltite with cation ratio of 1:2 (Ni:Co) was obtained at calcination temperature of 400 degrees C. The spinel phase decomposed gradually until 700 degrees C. The calcination time for the formation of NiCo2O4 was found to be between 2 to 4h. The particle size of the prepared sample studied by transmission electron microscopy showed a value of 9.47nm. The electrochemical properties of the metal oxide were measured in various acidic, neutral and alkaline electrolyte systems (1.0M HCl, 1.0M KCl and 1.0M KOH) by employment of cyclic voltammetry, galvanostatic charge-discharge test and electrochemical impedance spectroscopy. Ideal capacitor behaviour with the largest operating voltage of 1.0V and good electrochemical stability were observed in NiCo2O4 using neutral KCl aqueous electrolyte. Meanwhile, the prepared sample displayed the highest surface redox activity in 1.0M KOH alkaline electrolyte but showed the lowest electrochemical performance in acidic electrolyte. At the current density of 0.5Ag(-1), 1.0M HCl, 1.0M KCl and 1.0M KOH gave specific capacitance values of 3.8, 41.9 and 249.8Fg(-1) respectively. Copyright (c) 2015 John Wiley & Sons, Ltd.