Electrochemical Supercapacitive Performance of Spray-Deposited NiO Electrodes

Transition-metal oxides with porous structure are considered for use as promising electrodes for high-performance supercapacitors. Nanocrystalline nickel oxide (NiO) thin films have been prepared as active material for supercapacitors by spray pyrolysis. In this study, the effects of the film thickness on its structural, morphological, optical, electrical, and electrochemical properties were studied. X-ray diffraction analysis revealed cubic structure with average crystalline size of around 21 nm. Scanning electron microscopy showed porous morphology. The optical bandgap decreased from 3.04 eV to 2.97 eV with increase in the film thickness. Electrical resistivity measurements indicated semiconducting behavior. Cyclic voltammetry and galvanostatic charge/discharge study revealed good pseudocapacitive behavior. Specific capacitance of 564 F g−1 at scan rate of 5 mV s−1 and 553 F g−1 at current density of 1 A g−1 was observed. An NiO-based supercapacitor delivered specific energy of 22.8 W h kg−1 at specific power of 2.16 kW kg−1, and retained 93.01% specific capacitance at current density of 1 A g−1 after 1000 cycles. Therefore, taking advantage of the porous morphology that exists in the nanostructure, such NiO materials can be considered for use as promising electrodes for high-performance supercapacitors.