Physical properties of Ni: Co3O4 thin films and their electrochemical performance

Abstract

In this research work, we have deposited cobalt oxide as pure and Ni-doped thin films using spray pyrolysis. The concentration of Ni has been changed from 0 to 6 wt% in all films while other deposition parameters are fixed. The characterization of deposited films has been c using X-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), x-ray photoelectron microscope (XPS), scanning electron microscope (SEM), and optical spectroscopy. The XRD results confirm the formation of Co3O4 as the low-temperature stable phase of cobalt oxide and the successful doping with nickel. The XRD also shows the preferred orientation of growth of film is along the (111) plane and the crystallite size was found to decrease with increasing Ni content. The SEM micrograph of the deposited film surfaces revealed that the samples are porous and in some parts of the sample, the particles are agglomerated due to doping. The Ni doping was confirmed by both EDX and XPS. The Ni concentration was found to increase according to dopant concentration. The XPS data of the 4 wt% film has been recorded which confirms the existence of Ni+2 in the deposited films. Both optical transmission and reflection spectra have been recorded using a spectrophotometer. The band gap values have been found to decrease upon Ni-doping. The electrochemical properties of the pure and nickel-doped cobalt oxide films were measured by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in 0.3 M KOH electrolyte. The specific capacitance of 4 wt% Ni doped Co3o4 was found to be 804 Fg-1 at a 2 mVs−1 scan rate which is 90% higher than pure films. The important property of this material is that it shows excellent retention of 96% and remains almost constant for 10000 cycles. The impedance analysis reveals that 4 wt% Ni doped cobalt oxide film has the lowest RS value of 0.2 Ω cm−2 and lowest RCT value of 0.05 Ω cm−2 in comparison to other films which have excellent super-capacitive nature. These outstanding electrochemical properties of 4 wt % Ni-doped Co3O4 thin film have made it a potential candidate for anode material in supercapacitor devices.