Electrochemical and structural characterisation of dip-coated Fe/Ti oxide films prepared by the sol-gel route

Thin solid films of mixed Fe/Ti oxide composition (Fe/Ti molar ratios: 0.5 : 1, 1 : 1, 1.5 : 1) have been made from Fe(NO3)(3) alcoholic solution to which Ti(OiPr)(4) was added. Films have been deposited by the dip-coating technique and heat-treated at 300 degrees C and 500 degrees C. Powders of Fe/Ti oxide heat-treated at 300 degrees C are amorphous, while powders annealed at 500 degrees C for 40 hours transformed to mixed rutile, pseudobrookite and hematite phases. The structure of the XRD amorphous films was identified with the help of near-normal reflection absorption (6 degrees) (IRRA) and near-grazing incidence angle (NGIA) spectroscopy. NGLA FT-LR spectra of films are characterised with a single phonon mode appearing in the spectral range 600-950 cm(-1) which shifts with increasing Ti concentration from 675 cm(-1) (Fe2O3) to 904 cm(-1) (TiO2) thus exhibiting one-mode behavior. Electrochemical investigations made with the help of cyclic voltammetry (CV) and chronocoulometry (CPC) performed in 0.01M LiOH and in 1M LiClO4/propylene carbonate electrolytes revealed that films are able to uptake reversibly Li+ ions with a charge capacity (Q) per film thickness (d) in the range 0.1-0.26 mC/cm(2)nm and 0.06 mC/cm(2) nm, respectively. The temperature at which the films were prepared alters the rate of Li+ insertion which is faster for less compact films obtained at 300 degrees C. In situ UV-VIS spectroelectrochemical measurements revealed that Fe/Ti oxide films bleached in the UV spectral region (300 nm < lambda < 450 nm) and colored in the VIS spectral region (450 nm < lambda < 800 nm), thus exhibiting mixed anodic and cathodic electrochromism.