Elaboration and characterization of ZnO/CuO nano-composites produced by sol-gel route for supercapacitor application

Abstract

In the present work, CuO with concentration of 0.15 mol/L, ZnO with a concentration of 0.25 mol/L, and ZnO/CuO Nano composites with following ratios (50% ZnO & 50% CuO and 70% ZnO & 30% CuO) were prepared and deposited on glass substrates by the sol-gel spin coating process. Physical techniques such as X-ray diffraction analysis (XRD), atomic force microscopy, and UV-Vis spectroscopy were used for the characterization of the crystal structure, surface topography, and optical properties. The XRD analysis showed that CuO and ZnO crystallize respectively in monoclinic and hexagonal symmetries. Crystallite size decreased while dislocation density and microstress increased upon addition of CuO. These increases are responsible for the reduction in crystallite size. The AFM microscopy demonstrates alteration in the surface morphology, with inclusion of CuO leading to decrease in the average roughness (Ra) of ZnO. The UV-Vis spectrophotometry indicate that the band edge absorption is red-shifted whereas 50%ZnO/50%CuO is highly red-shift in spectra. The gap energies (Eg) of 1.73, 3.25, 3.19, and 2.88 eV are found respectively for CuO, ZnO, 70%ZnO/30%CuO and 50%ZnO/50%CuO. The films exhibit high super-capacitor properties, the electrochemical study showed that the electrode 50% ZnO/50%CuO has high specific capacitance of 217.81 F/g at 1 mV/s and excellent cyclic stability with nearly 96% capacity retention after 5000 cycles at 0.1 mA/cm².

Graphical Abstract