MIXED PHOSPHOTUNGSTIC ACID TITANIUM OXIDE GELS AND THIN SOLID XEROGELFILMS WITH ELECTROCHROMIC-IONIC CONDUCTIVE PROPERTIES/

Electrochromic-ion conductive gels (sigma = 1.7 X 10(-4) S/cm) and thi n solid films composed of phosphotungstic acid (PWA) incorporated in t itanium oxide xerogel (PWA:Ti= 0.07) were made via the sol-gel route b y the dip-coating technique. The electrochromism of the as-deposited f ilms was studied with the help of cyclic voltammetric (CV) measurement s in HClO4 electrolyte, in situ ultraviolet-visible spectroelectrochem ical measurements and ex situ near-grazing incidence angle (NGIA) refl ection spectroscopy. It was demonstrated that the colour change from t ransparent to blue is about 40% efficient and is accompanied by effect ive inserted charges up to 35 mC/ cm(2), giving rise to (HxPW12O403-)- O-y+ species with x = 4.7 and y = 5.6. Ex situ NGIA Fourier transform infrared reflection measurements revealed that proton injection decrea ses the intensity of the longitudinal optical (LO) modes corresponding to the intra nu W-O-c-W and inter nu W-O-b-W vibrations of the Keggin 's ions, while the nu W-O-d modes remain unaffected. An intensity decr ease of the LO modes of Ti-O vibrations was also detected in the ex si tu NGIA reflection spectra of cathodically coloured pure Ti xerogel fi lms. It was found that the proton insertion process is accompanied by the hydroxylation of titanate ions, while no such effect was noted for PWA/Ti and Ti xerogel films aged in water and the corresponding elect rolytes without the applied potential. The electrochromic-ionic conduc tive properties of mixed PWA/Ti gels were demonstrated in a semi-liqui d electrochromic cell.