INFRARED CHARACTERIZATION OF ELECTROCHROMIC NICKEL-HYDROXIDE PREPAREDBY HOMOGENEOUS CHEMICAL PRECIPITATION

Two different methods for preparing electrochromic nickel hydroxide fi lms are tested: thermal hydrolysis of [Ni(NH3)6]2+ complex and thermal decomposition of a mixture of urea and NiSO4. Both methods lead to ad herent and homogeneous films presenting good electrochromic properties . Thermogravimetric analysis shows that Ni(OH)2 prepared from urea dec omposition has intercalated water molecules, while hydroxides prepared from ammonia complexes present beta-like structure without hydration. Ex-situ infrared spectroscopy was used to characterize virgin, bleach ed and colored states of the films under different experimental condit ions. IR spectra of the colored state show the diminution of the 3650 cm-1 band related to free OH- stretching vibrations. The disappearance of this band is associated with the oxidation process and also with t he physicochemical nature of alkaline cations incorporated in the oxid e matrix during the coloration process.