Size-dependent electrochemical kinetics of nano-granular WO3 thin films

Abstract

Electrochromic devices are mainly investigated for energy harvesting and saving applications. Electrochromic supercapacitors (ECSC) attract smart electronics device applications by integrating electrochromic materials into energy storage devices. WO3 has been predominantly investigated materials for this application. Amorphous, transparent WO3 thin films owing to diffusive charge storage kinetics with improved active sites promote the better intercalation of Li+ ions in the porous surface area, which yields electrochromic supercapacitive performance. In the present study, WO3 thin films were prepared by electrodeposition and studied for their physicochemical, electrochemical, and electrochromic properties. Electronic properties of WO3 thin films were measured by using electrochemical impedance spectroscopy (EIS) in terms of density of states [D(Ef)] at the Fermi level. Charge storage kinetics of WO3 thin films studied by EIS corroborated with the voltammetry studies. The WO3 electrode exhibits wide optical modulation (∼90%) with the highest coloration efficiency (η) of 132.89 cm2/C, including higher areal capacitance of 39.81 mF/cm2 and volumetric capacitance of 180.91 mF/cm3 at 20 mV/s scan rate with the capacitance retention up to 83% after 1000 CV cycles.