ELECTROCHROMIC BEHAVIOR OF NICKEL-OXIDE ELECTRODES .2. IDENTIFICATION OF THE BLEACHED STATE BY RAMAN-SPECTROSCOPY AND NUCLEAR-REACTIONS

Three different types of nickel oxide electrochromic films are colored and bleached in 1M KOH solution: porous NiO prepared by anodic oxidation of nickel, NiO(OH)x obtained by reactive evaporation, and Ni(OH)2 cathodically deposited. Their crystallographic and chemical identification in the colored and bleached states after one cycle and after long time performance testing is obtained by Raman spectroscopy. Nuclear reaction analysis is also performed. If the elementary oxidation reaction is the same in the three cases (transport by OH-), the global phenomenon depends extensively on the crystallographic nature of the material; the coloration reaction in the oxides is, contrary to the case of hydroxide, a local one, and it is proved here that the bleached state can never be, in the oxides, assimilated to Ni(OH)2.