Electrochromic Properties of WO3 Nanorod Films Prepared by Hydrothermal Method

This paper adopted the hydrothermal method to prepare tungsten oxide (WO 3 ) nanorod films and studied the effects of precursor solution concentration (0.02, 0.03, 0.06 mol/L peroxytungstic acid) and annealing temperature (200, 300, 400 °C) on their electrochromic properties. The microstructure characterization of WO 3 films were performed using scanning electron microscope (SEM), X-ray diffraction (XRD), and transmission electron microscope (TEM), and their electrochromic properties were tested by combining an electrochemical workstation with an ultraviolet-visible spectrophotometer. The results showed that the precursor solution concentration directly affected the thickness (290, 560, 990 nm) and microstructure of WO 3 films, significantly impacting their electrochromic properties. However, the annealing temperature had a negligible effect. As the precursor solution concentration increased, the optical modulation of WO 3 films gradually decreased, reaching 51.1%, 43.8%, and 35.1%, respectively. The switching time first increased and then stabilized, with coloring times of 7.3, 7.7, and 7.7 s, respectively, and bleaching times of 3.8, 6.5, and 6.5 s, respectively. The coloration efficiency gradually increased but the increase was relatively small, reaching 41.8, 44.4, and 44.8 cm 2 /C, respectively. Moreover, the cycling stability of WO 3 films was poor, with the ratios of the final value of optical modulation to the initial value 0.33, 0.26, and 0.34, respectively. Additionally, there were bigger differences in the bleached state transmittance, while the colored state transmittance showed smaller variations. However, the former has better cycling stability than the latter. In summary, to obtain better electrochromic properties, the thickness of WO 3 films should not exceed 290 nm.