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

Abstract

Gasochromic palladium doped peroxopolytungstic acid (Pd:P-PTA) films have been prepared using dip-coating deposition from peroxopolytungstic acid (P-PTA) sols into which PdCl 2 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 ( σ pr) and electronic ( σ el) conductivities determined from impedance spectra revealed an increase in σ el from 10 −5 S cm −1 in bleached state, to 10 −3 S cm −1 in coloured state, while σ pr remained constant (10 −2 S cm −1).