Infrared characterization of electrochromic nickel hydroxide prepared by homogeneous chemical precipitation

Abstract

Two different methods for preparing electrochromic nickel hydroxide films are tested: thermal hydrolysis of [Ni(NH 3) 6] 2+ complex and thermal decomposition of a mixture of urea and NiSO 4. Both methods lead to adherent and homogeneous films presenting good electrochromic properties. Thermogravimetric analysis shows that Ni(OH) 2 prepared from urea decomposition has intercalated water molecules, while hydroxides prepared from ammonia complexes present ß-like structure without hydration. Ex-situ infrared spectroscopy was used to characterize virgin, bleached and colored states of the films under different experimental conditions. 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 the physicochemical nature of alkaline cations incorporated in the oxide matrix during the coloration process.