HYDROGEN TRANSPORT THROUGH PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITED TIO2 FILM-PALLADIUM BILAYER BY AC-IMPEDANCE SPECTROSCOPY

Abstract

Hydrogen adsorption-absorption reaction and transport through TiO2 film were investigated by using ac-impedance spectroscopy and modulation method as a function of applied cathodic potential and applied anodic potential. The hydrogen diffusivity in the oxide film and kinetic parameters related to hydrogen adsorption and absorption reactions were evaluated by using complex non-linear least squares (CNLS) fitting method. The diffusivity of hydrogen in the oxide film and the concentration of hydrogen in the each layer were determined from the measured phase shift between the input hydrogen concentration and the hydrogen flux at the hydrogen exit side of the membrane specimen and from the measured steady-state hydrogen flux, respectively. The kinetic parameters were discussed in terms of hydrogen adsorption and absorption reaction on/into the oxide surface. Also, variation in hydrogen diffusivity in the oxide film was explained in terms of the hydrogen content in the oxide film.