Spectroelectrochemical studies of V/Ti-, V/Ti/Zr- and V/Ti/Ce-oxide counter-electrode films

V/Ti-, V/Ti/Zr- and V/Ti/Ce-oxide films were prepared using the sol-gel route and deposited by dip-coating. After heating at 300 and 400 degrees C the films showed mixed anodic-cathodic electrochromism similar to V2O5 films. In situ W-VIS spectroelectrochemical measurements revealed a small optical modulation in the films and evaluated their appropriateness for counter electrodes in electrochromic devices. Additionally, a thorough analysis of the IR vibrational spectra (4000-400 cm(-1)) of amorphous (300 degrees C) and crystalline (400 degrees C) V/Ti-oxide films was made. We investigated the initial, charged and discharged states of films with a molar ratio V:Ti in alkoxide precursors 3:1 and 1:1. We found that Ti formed a solid solution with V when the films were annealed at 300 degrees C. The characteristic V-O-Ti stretching appeared at 790 cm(-1). This mode showed a modulation of intensity with charging/discharging indicating the contribution of V and Ti species to the insertion processes. Alternatively, annealing at 400 degrees C leads to a segregation of phases into V2O5 and TiO2 and a decrease in cycling stability. (C) 1999 Elsevier Science Ltd. All rights reserved.