Size dependent electrochemical properties of green synthesized NiO nanoparticles as a supercapacitor electrode

Abstract

The nickel oxide nanoparticles (NiO NPs) are synthesized by a green method using the leaf extract of Ocimum sanctum (OS) as a reducing agent. The NiO NPs of different sizes are synthesized using various concentrations of leaf extract of OS. The average crystallite size and particle size of the NiO NPs is measured using XRD and Transmission electron microscope (TEM) respectively. The size of NiO NPs is observed to decrease from ∼ 17 nm to ∼ 13 nm with increase in concentrations of leaf extract of OS. The morphology and elemental analysis of the NiO NPs is carried out using Field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray (EDX) analysis respectively. The cyclic voltammetric (CV) studies on electrode of NiO NPs showed a pseudocapacitive behavior with a specific capacitance of 100 Fg−1 at a scan rate of 100 mV/sec for the particles with the size of ∼ 13 nm. The Galvonostatic charge–discharge studies showed a prolonged discharge time for the electrode of NiO NPs with size of ∼ 13 nm for a current density of 5 A/g. The electrochemical impedance spectroscopy (EIS) studies of electrodes of NiO NPs indicate the electric double layer capacitance (EDLC) and diffusion controlled pseudo capacitance behavior. The synthesized electrode shows capacitance retention of 84 % for 2500 cycles, is chosen for designing a supercapacitor device for glowing 10 red light emitting diodes (LEDs). Therefore, the use of leaf extract of OS is an ecofriendly alternative for synthesis of NiO NPs of different sizes that has applications in energy storage devices.