The effects of high-performance Al3+ electrolyte and driving voltage on the electrochromic properties of WO3 films

Tungsten oxide (WO 3 ) films were prepared by the hydrothermal method, and their micro-properties were characterized by microscopic testing techniques. Combining an electrochemical workstation with an ultraviolet–visible (UV–Vis) spectrophotometer, the effects of electrolyte type (1 mol/L AlCl 3 •6H 2 O/H 2 O and LiClO 4 /C 4 H 6 O 3 ) and driving voltage (0.4, 0.6, 0.8 V for Al 3+ electrolyte, 0.8, 1.0, 1.2 V for Li + electrolyte) on their electrochromic properties were systematically investigated. The results indicated that WO 3 films exhibited a nanorod cluster morphology with a hexagonal phase crystal structure. Al 3+ electrolyte demonstrated superior electrochromic properties compared to Li +  electrolyte. At the same driving voltage of 0.8 V, the peak current density and area of the cyclic voltammetry curve for Al 3+ electrolyte were 4.19 times and 5.20 times those of Li +  electrolyte. Additionally, the charge transfer resistance was lower, the static optical modulation curve was higher, and the dynamic optical modulation and coloration efficiency were 1.88 times and 1.46 times those of Li + electrolyte. Notably, the colored time for Al 3+ electrolyte was shorter than that of Li +  electrolyte, while its bleached time was longer. Furthermore, increasing the driving voltage enhanced optical modulation but decayed cycling stability. The decay evolution model of cycling stability comprised three stages: stable decay, rapid decay, and residual decay. At lower driving voltages, only the stable decay stage occurred. With driving voltage increasing, all three stages emerged, accompanied by accelerated decay rates and shortened decay cycles. Besides, the driving voltage threshold for Al 3+ electrolyte was lower than that for Li +  electrolyte, while its optical modulation and cycling stability were superior. The decay mechanism of cycling stability could be attributed to four factors: ion trapping, lattice distortion, electrostatic attraction, and interfacial reaction. This study can provide theoretical references for the development and application of high-performance electrochromic smart windows.