Electrochemical synthesis of electrochromic Ce–V oxide films in NH4HSO4 melts

Cerium oxide and cerium (Ce)–vanadium (V) oxide films were synthesized on an ITO electrode by electrolysis in NH4HSO4–Ce2O3 and NH4HSO4–Ce2O3–NH4VO3 melts at a temperature of about 300 °C. The films obtained were characterized by X-ray diffraction, spectroscopic measurements and electrochemical measurement. In addition, the electrochromic (EC) reactions of the oxide films in a solution of propylene carbonate were investigated. The absorption spectra of Ce–V mixed oxide films obtained by electrodeposition in the NH4HSO4–Ce2O3–NH4VO3 melt showed peaks at 680 and 451 nm, due to a mixed valence of V4+ and V5+ in the orthovanadates (CeVO4), and these absorption peaks increased with Li+ insertion and disappeared with Li+ extraction in EC reactions. The Ce–V mixed oxide films showed a lower absorbance than vanadium oxide and cerium oxide films, respectively in the visible region.