Influence of pH and annealing on the optical and electrochemical properties of cobalt (III) oxide (Co₃O₄) thin films

Cobalt (III) oxide (Co₃O₄) thin films were deposited on glass and FTO substrates using chemical bath deposition method at a temperature of 80 °C in the alkaline bath maintaining the pH values of 10 and 12. X-ray diffraction result reveals that the crystallinity increased with increasing pH and annealing. Scanning electron microscopy (SEM) revealed features of flower-like particles, which transformed into a needle and rod-like structures after annealing. The optical studies showed a higher absorption in the visible region, which decreases as the wavelength increases, energy band gap range of 1.3 eV–1.85 eV and a remarkable refractive index of 1.40–1.75. The electrochemical testing of the electrodes obtained the highest specific capacitance of 1567F/g, the energy density of 245.98 (Wh/Kg) and power density of 2.08 (W/Kg) for pH 12 annealed. Specific capacitances, power densities and energy densities values obtained from electrochemical studies suggest that the films are suitable for use as supercapacitors electrodes materials.