TiO2 nanotubes: H+insertion and strong electrochromic effects

The present work studies H+ intercalation and electrochromic effects on anodic TiO2 nanotube layers. The nanotube layers were fabricated by anodization of titanium in 1 M (H3PO4) + 1 M (NaOH) + 0.5 wt% HF electrolyte at 20 V, this results in nanotubular layers with a thickness of 1 ± 0.1 μm with individual tube diameter of 100 ± 10 nm and a tube wall thickness of 10 ± 2 nm.The cathodic behavior of the nanotube layers in the “as formed” (amorphous) structure as well as in the annealed (anatase) structure were studied in 0.1 M (HClO4) solution.Cyclic voltammograms and potential step experiments combined with reflectance measurements show a high storage capacity for H+ for the nanotubes structures and a very high specific optical contrast when switching the layers from the H-loaded to the H-unloaded state.