Multistage coloring electrochromic device based on TiO₂ nanotube arrays modified with WO₃ nanoparticles

WO₃ nanoparticles loaded in TiO₂ nanotube arrays, fabricated by a chemical bath deposition (CBD) technique in combination with a pyrolysis process, is uniform and the diameter can be easily adjusted by the deposition times. The resultant hybrid nanotubes array shows a multistage coloring electrochromic response at different potential bias. The formation of a 3-dimensional WO₃/TiO₂ junction promotes unidirectional charge transport due to the one-dimensional features of the tubes, which leads to the significant positive-shift onset potential of the cathodic reaction (ion insertion) and the highly increased proton storage capacity. Compared to non-decorated nanotube arrays, the enhanced electrochromic properties of longer lifetime, higher contrast ratio (bleaching time/coloration time), and improved tailored electrochromic behavior could be achieved using the composite films.