Tailoring the electric, dielectric and optical properties of template-free hydrothermally synthesized CuO nanostructures via Co doping

Facile template-free hydrothermal method was utilized for preparing CuO nanostructures (NSs) doped with Co
element (Cu1-xCoxO (x = 0.0, 0.02, 0.04, 0.06 and 0.08)). A single-phase monoclinic crystal with changing in
morphology from rod-to sphere-like nanoparticles was observed. The temperature dependency of DC electrical
conductivity revealed that the shallow and deep donor levels are responsible for the DC conduction in low and
high temperature ranges, respectively. The Ac electrical conductivity, dielectric constant and dielectric loss were
also measured as functions in frequency and temperature. The frequency dependence of the AC conductivity was
well represented by the Jonscher’s universal power law. The AC conduction was governed by the Correlated
Barrier Hopping model where the inter-well and intra-well hopping mechanisms contribute to the electrical
conduction in the low and high frequency ranges, respectively. The activation energies and the barrier height
decreased while the dielectric constant and dielectric loss increased with increasing the Co content. The relaxation
and deformational polarizations predominate and the overall behavior of dielectric constant fits well with
the Koops’ model. The Cole-Cole plots indicated a decrease in the sample resistance with increasing temperatures
and Co concentrations. UV–vis absorption spectra exhibited two peaks at wavelengths 252 and 323 nm. The
optical energy gap was calculated using Tauc’s equation and decrease from 2.24 to 2.1 eV with increasing the Co
concentrations. The effect of Co-doping on CuO was explored for oxygen evolution reaction (OER) and found a
decrease in the overvoltage (μ) about 50 mV at 0.08 ratios, which declares that the doping of Co element enhances
the electrical conductivity and feasibility for further electrocatalytic improvement.