Electrochromic properties of TiO2 nanotubes coated with electrodeposited MoO3

Abstract

Despite a favourable morphology, anodized and ordered TiO₂ nanotubes are incapable of showing electrochromic properties in comparison to many other metal oxide counterparts. To tackle this issue, MoO₃ of ∼5 to 15 nm thickness was electrodeposited onto TiO₂ nanotube arrays. A homogenous MoO₃ coating was obtained and the crystal phase of the electrodeposited coating was determined to be α-MoO₃. The electronic and optical augmentations of the MoO₃ coated TiO₂ platforms were evaluated through electrochromic measurements. The MoO₃/TiO₂ system showed a 4-fold increase in optical density over bare TiO₂ when the thickness of the MoO₃ coating was optimised. The enhancement was ascribed to (a) the α-MoO₃ coating reducing the bandgap of the composite material, which shifted the band edge of the TiO₂ platform, and subsequently increased the charge carrier transfer of the overall system and (b) the layered morphology of α-MoO₃ that increased the intercalation probability and also provided direct pathways for charge carrier transfer.