Gasochromic effect of palladium doped peroxopolytungstic acid films prepared by the sol-gel route

Gasochromic palladium doped peroxopolytungstic acid (Pd:P-PTA) films have been prepared using dip-coating deposition from peroxopolytungstic acid (P-PTA) sols into which PdCl2 was added in molar ratios Pd:W = 1:125, 1:100, 1:53, and 1:40. These films exhibit reversible colouring/bleaching changes when exposed to hydrogen or hydrogen/argon mixture (4%) and air, alternatively. Gasochromically coloured and bleached films were characterised using in-situ Fourier transform infrared (FT-IR) spectroscopy. The vibrational modes of as-deposited, coloured and bleached films were assigned and the polaron absorption, which characterises the IR spectra of coloured films, was detected. Colouring/bleaching kinetics of films exposed to H-2 and H-2/Ar mixture as a function of the concentration of the catalyst and temperature of heat-treatment is reported. Proton (sigma(pr)) and electronic (sigma(el)) conductivities determined from impedance spectra revealed an increase in sigma(el) from 10(-5) S cm(-1) in bleached state, to 10(-3) S cm(-1) in coloured state, while sigma(pr) remained constant (10(-2) S cm(-1)). (C) 1998 Elsevier Science S.A. All rights reserved.