Electrochromism of rutilenanowires, vertically aligned along the [001] direction, due to alkali metal ion intercalation

Abstract

Rutile nanowires were grown along the [001] direction and perpendicular to the fluorine doped tin oxide coated glass substrate (R_⊥) by a solvothermal process using titanium isopropoxide as the precursor in acidic solution. The edge length of the nanowires obtained in isopropyl alcohol is ten times less than that of the nanowires obtained in water. Due to the high ionic diffusion rate along the rutile [001] direction and good optical transmittance, R_⊥ was used as an electrochromism electrode. When −2 V was applied, the color of the electrode became blue with a 60% change in the transmittance for 30 s due to the cathodic polarization potential in LiClO₄/PC electrolyte (where PC is propylene carbonate). The lithium ion intercalated/extracted densities of R_⊥, P25-coated and rutile nanowires-coated electrodes are 138.6/129.1 mC cm⁻², 93.6/83.2 mC cm⁻² and 31.7/15.9 mC cm⁻² respectively. After 50 cycles, the R_⊥electrode still performs very well. Furthermore, a large amount of sodium cation intercalation into TiO₂ was observed for the first time at −1.0 V. According to these results, the R_⊥electrode is a promising candidate to be a multi-function device.