Investigation of hydrogen insertion in palladium using permeation transfer function techniques

Transfer functions between the input and output currents and potentials at a hydrogen permeable palladium membrane were measured in potentiostatic and galvanostatic modes at the exit side. The current density transfer function in the potentiostatic input mode and, probably, the potential transfer function in the galvanostatic output mode, are insensitive to surface processes and only the entry impedance is influenced by the charge transfer at the input interface. By using simultaneous measurements of the entry side impedance and the transfer functions, hydrogen insertion (surface process) and diffusion can be characterized by means of permeation transfer function techniques. Neither trapping processes nor influence of stress due to hydrogen insertion were observed. The kinetic parameters obtained by means of the permeation transfer function technique are in good agreement with those determined through classical electrochemical impedance measurements. However, no extra information can be expected as compared with data obtained by impedance measured at electrodes in reflective conditions. Only at extremely thin membranes, which are difficult to prepare experimentally, would surface effects be observed.