Influence of palladium films on hydrogen gas entry into iron: a study by electrochemical impedance spectroscopy

Covering the bare surface of a hydride forming metallic material with a thin film of Pd is a method to accelerate hydriding, through avoiding the formation of a passive oxide film and allowing hydrogen to diffuse easily through the Pd film. In this work we performed permeation experiments to study the hydrogen ingress rate into Pd-plated iron membranes. The experimental conditions are such that the Pd deposit and their interfaces (rather than the bulk iron substrate) determine the permeation results. Thus, it is possible to characterize the Pd film behavior with respect to the passage of hydrogen. We used the electrochemical impedance spectroscopy technique, where the excitation signal was a modulated hydrogen pressure, and the response signal was the modulated hydrogen flux, measured by an electrochemical method at the exit side of the permeation membrane.