Iron containing CeVO4 films were prepared using the sol-gel method. The crystalline structure of powders and films with Fe/Ce/V ratios of 0.1:1:1, 0.3:1:1 and 0.5:1:1 were investigated by X-ray diffraction (XRD) and infrared (IR) spectroscopy. XRD revealed the predominance of a CeVO4-W (wakefieldite) crystalline phase with a small amount of monoclinic CeVO4, CeO2 and Fe2O3. Ex situ IR absorbance spectra of charged and discharged films show the changes in intensity of the V-O stretching mode at 770 cm(-1).Cyclic voltammetry showed that Li+ intercalation occurs in three steps with total capacities of 22 mC cm(-2) (Fe/Ce = 0.1), 32 mC cm(-2) (Fe/Ce = 0.3) and 37 mC cm (-2) (Fe/Ce = 0.5). The increase in the overall charge capacity with increasing Fe content is accompanied by a loss of capacity with cycling. The lithium diffusion coefficient: calculated by the galvanostatic intermittent titration method (GITT), the potentiostatic intermittent titration method (PITT) and electrochemical impedance spectroscopy (EIS), ranges from 10(-12) to 10(-14) cm(2) s(-1). UV-vis in situ transmittance spectra showed that these films are highly transparent with a photopic transmittance T-Vis similar to 0.85 for intercalated and deintercalated states. This suggests that Fe/Ce/V oxide films are good candidates for optically passive counter-electrodes in electrochromic (EC) devices. (C) 2001 Elsevier Science Ltd. All rights reserved.

Various mixed Fe/V-oxides can be used as anodes in Li+ rocking chair batteries, however, their small optical modulation during the insertion/extraction of Li+ ions makes them candidates for the counter electrodes in electrochromic (EC) devices. The sol–gel route in combination with dip-coating deposition was used for the preparation of Fe/V-oxide films with molar ratios Fe:V=0.1:1, 1:2, 1:1 and 2:1. X-ray diffraction combined with Fourier transform infrared (FT-IR) spectroscopy studies of films and powders reveal that heating of xerogel films at 400°C produces films with nanosized FeVO4 (Fe:V=1:1) and Fe2V4O13 (Fe:V=1:2) grains, while the corresponding crystalline powders were obtained at 500°C (8 h). Charge capacities (Q) of Fe/V-oxide films (300 and 400°C) were determined using cyclic voltammetry (CV) from 1.5 to −1.5 V vs. Ag/AgCl (4.8 to 1.8 V vs. Li) in 1 M LiClO4/propylene carbonate (PC) electrolyte. Our results revealed that Q values of Fe/V-oxide films are up to 20 mC cm−2 depending on the thickness (40–100 nm), temperature of heating and the Fe:V molar ratio (1:2, 1:1). During the first 300 cycles the cycling stability of the Fe-containing films is better than that of V2O5 crystalline films. UV-visible spectra of charged/discharged films revealed that these films, similar to V2O5 films, exhibit a mixed anodic/cathodic electrochromism. It was established that with regard to the colouring/bleaching changes of V2O5 crystalline films, the Fe/V-oxide films exhibit smaller cathodic colouring at wavelengths λ>600 nm and higher visible transmittance. IR spectroscopy of charged/discharged Fe/V-oxide films confirmed that the reduction of Fe3+ prevents the overreduction of V5+ to V3+, which takes place in V2O5 films cycled in the same potential range.