Decoration of TiO2 nanotube layers with WO3 nanocrystals for high-electrochromic activity

We report a simple approach to decorate ordered TiO2 nanotube (TiNT) layers with tungsten trioxide nanocrystallites by the controlled hydrolysis of a WCl6 precursor. These WO3 nanocrystallites, when formed, are amorphous, but can be annealed to a monoclinic crystal structure. The WO3 crystallites on the TiO2 nanotube skeleton are electrochemically active, and hence ion insertion reactions are possible. As a result, the decorated nanotube layers show remarkable enhancement of the electrochromic properties. In particular, a significantly lower threshold voltage and an increased electrochromic contrast can be achieved compared with unloaded (neat) TiO2 nanotube layers.