SOL-GEL DERIVED HYDRATED NICKEL-OXIDE ELECTROCHROMIC FILMS - OPTICAL,SPECTROELECTROCHEMICAL AND STRUCTURAL-PROPERTIES

Electrochromic hydrated Ni-oxide films were prepared using a dip-coati ng technique from a nickel sulphate heptahydrate precursor in combinat ion with glycerol, formamide and polyvinyalcohol. In-situ monochromati c (lambda = 400 nm) spectroelectrochemical measurements using a potent ial of -0.4 V to 0.8 V in 0.1M LiOH electrolyte revealed that the elec trochromic efficiency was 23.5 cm(2)/C. The observed colouring/bleachi ng transmittance of a 100 nm thick film changed during potential cycli ng (20 cycles) by 45%. Ex-situ FT-IR absorption/reflection measurement s performed at near-grazing incidence angle conditions (80 degrees) co nfirmed transformation of as-deposited alpha-Ni(OH)(2) phase to beta-N i(OH)(2) at cathodic (bleached state) and beta-NiOOH at anodic (colour ed state) potentials during extended cycling (200 cycles). Clear evide nce of the OH- ions insertion and release of SO42- ions from the as-de posited films when soaked (0.5 hour) in 0.1M LiOH are given. These pro cesses are accompanied by the transformation of the residual COO- grou ps originating from the peptisation with glacial acetic acid into CO32 - species residing in the films during extensive potential cycling.