Synergistic effect of Urea and Potassium Sulphate during hydrothermal synthesis of NiO nanospheres with reduced crystallite size and enhanced electrical conductivity

Nickel oxide (NiO) nanoparticles (NPs) have been synthesized using a high-yield, efficient hydrothermal technique. Investigations have been done to study the effect of the alkaline environment provided by Urea and Potassium Sulphate on the structural, optical and electrochromic properties of NiO nanoparticles. Hydrolysis of Urea provides an alkaline environment that controls the formation of NiO precipitate. SO42- ions in Potassium Sulphate create active sites on the surface of Ni(OH)2 leading to better absorption of Ni2+ and OH– ions. Present study shows that Urea and Potassium Sulphate act synergistically as structure directing/ complexing agents in the formation of NiO nanoparticles. FESEM studies of the NiO particles depict a spherical morphology with an average crystallite size of 7 to 11 nm as calculated using XRD. The process of charge transfer in electrodes, diffusion of molecules and ions within the electrolyte and adsorption of ions on an electrode surface has been explored using Cyclic Voltammetry and Electrochemical Impedance Spectroscopy. The carrier lifetime has been observed as 5–7 μs, upon fitting the exponential decay curve of TRPL. So, lower charge transfer resistance, higher carrier lifetime and uniformly distributed nanoparticles are indicative of the material to offer better electrical conductivity for enhanced performance in solar cells and electrochromic applications.