Unveiling the Effect of Solution Concentration on the Optical and Supercapacitive Performance of CoWO4 Nanoparticles Prepared via the Solvothermal Method

Abstract

This study explores the influence of solution concentration, specifically that of water and ethylene glycol mixtures, on the optical and supercapacitive properties of cobalt tungstate (CoWO4) nanoparticles. CoWO4 nanoparticles were synthesized using varying ratios of water to ethylene glycol to ascertain the optimal conditions for enhanced performance. Detailed characterization was conducted using UV–Vis spectroscopy, photoluminescence (PL) spectroscopy, cyclic voltammetry (CV), and galvanostatic charge–discharge (GCD) to evaluate the optical properties and electrochemical behavior, respectively. The results revealed that the solution concentration significantly impacted the bandgap, absorbance, and emission properties of the CoWO4 nanoparticles. Effective bandgap tuning was achieved by altering the solution concentration. When using only water, the nanoparticles displayed the lowest bandgap of 2.57 eV. In contrast, a solution with equal water and ethylene glycol concentrations resulted in the highest bandgap of 2.65 eV. Additionally, the electrochemical studies demonstrated that the water/ethylene glycol ratio markedly influenced the charge storage capacity and cyclic stability of the nanoparticles. The results indicated that the solvent concentration significantly influenced the crystallinity, particle size, and surface morphology of the CoWO4 nanoparticle nanoparticles, which affected their optical properties and electrochemical performance. Notably, nanoparticles synthesized with a 1.25:0.75 proportion of water to ethylene glycol exhibited superior supercapacitive performance, with a specific capacitance of 661.82 F g−1 at a current density of 7 mA cm−2 and 106% capacitance retention after 8000 charge–discharge cycles. These findings underscore the critical role of solvent composition in tailoring the functional properties of CoWO4 nanoparticles, providing insights for their application in optoelectronic devices and energy storage systems.