Hydrothermally synthesized WO3 nanowire arrays with highly improved electrochromic performance

Abstract

A hexagonal WO₃ nanowire array film is obtained using a template-free hydrothermal method by adding ammonium sulfate as a capping agent. The WO₃ nanowires grown vertically on a FTO-coated glass substrate are woven together at the surface of the film, forming well-aligned arrays at the bottom part and a porous surface morphology. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that each nanowire is a hexagonal single crystal and their long axes are oriented toward the [0001] direction. Due to the highly porous surface, good contact with the conductive substrate and large tunnels of the hexagonal-structured WO₃, a fast switching speed of 7.6 and 4.2 s for coloration and bleaching, respectively, and a high coloration efficiency of 102.8 cm²C⁻¹ are achieved for the WO₃ nanowire array film.