A. Surca et al., OPTICAL, SPECTROELECTROCHEMICAL AND STRUCTURAL-PROPERTIES OF SOL-GEL DERIVED NI-OXIDE ELECTROCHROMIC FILM, Journal of electroanalytical chemistry [1992], 408(1-2), 1996, pp. 83-100
Ni-oxide films prepared using the sol-gel route and dip-coating method
have been investigated by X-ray diffraction, scanning electron micros
copy, FT-IR spectroscopy, cyclic voltammetry and in situ UV-VIS spectr
oelectrochemical methods. The sols were prepared from a nickel sulphat
e hexahydrate precursor with formamide and polyvinylalcohol added to i
mprove the abrasive resistance of films and to increase the yield from
dip-coating deposition method (100-120 mu m per dipping cycle). The f
ilms consisted of 40% NiO crystalline phase with an average grain size
of 10 to 30 Angstrom. The crystallites were incorporated into the amo
rphous phase which was found to resemble the alpha(II)-Ni(OH)(2) phase
. A pronounced electrochromic effect (Delta T approximate to 60%) was
found by cycling the films in a 0.1 M LiOH electrolyte. This produced
a maximum colouration efficiency (lambda = 450 nm) of 35-40 cm(2) C-1.
Longitudinal optical (LO) mode of films potentially cycled up to 200
times have been detected by near-grazing incidence angle (NGIA) FT-IR
reflection-absorption spectroscopy. The results revealed that the as-d
eposited films are progressively transformed to the beta(II)-Ni(OH)(2)
phase which is then converted to the beta(III)-NiOOH phase during fur
ther potential cycling. The influence of foreign ions (SO42-, CO32-, O
H-) on the development of persistent electrochromism and stability of
films was established and discussed in detail.