Investigation of hydrogen adsorption and absorption in palladium thin films - III. Impedance spectroscopy

The electrochemical impedance of palladium films of various thicknesses, deposited on a gold electrode, was measured in the potential range where hydrogen absorbs in palladium. The kinetic and diffusion parameters of the whole electrochemical process were determined. One of the main results was the observation of a maximum on the curves of charge-transfer resistance vs. electrode potential. At this maximum the charge-transfer resistance decreased with the increase of film thickness. This finding is in agreement with the model proposed in Part I, where such a behavior is found to be related to the trapping of the hydrogen atoms in a sublayer just under the electrode surface and a direct exchange of the trapped hydrogen with the electrolyte. (C) 2004 The Electrochemical Society.