Large-scale production of tungsten trioxide nanoparticles for electrochromic application

Abstract

Large-scale, high yield production of tungsten trioxide (WO₃) particles was successfully realized by using a facile, high-temperature, catalyst-free, solid evaporation route with ammonium paratungstate tetrahydrate as raw material. The crystalline structure, size, and morphology of the as-synthesized WO₃ particles were systematically investigated by combined techniques of X-ray diffraction and electron microscopy, as a function of reaction temperature, deposition temperature, carrier gas flow rate, and size of the quartz tube. With low carrier gas flow rate (1–2 L min⁻¹), the WO₃ products collected from different deposition regions were found to exhibit a diversity of forms, such as thick rods, irregular, polyhedral, and octahedral particles, depending on the reaction temperature. At a reaction temperature of 1350 °C, increasing the carrier gas flow rate led to the formation of semi-spherical or quasi-spherical WO₃ particles with decreased size and improved size distribution. A reaction temperature of 1350 °C and an Ar flow rate of 6 L min⁻¹ yielded optimized quasi-spherical WO₃ nanoparticles with high size uniformity, which have been found to exhibit stable electrochromic performance with high colour contrast and H⁺ insertion ability. The WO₃ nanoparticles that can be effectively produced in high quantity are promising electrochromic candidates for potential applications in large-area smart windows.