Hydrogen diffusion in α-iron studied using an electrochemical permeation transfer function

A new transfer function for electrochemical hydrogen permeation through metallic membranes is defined, and its analytical expression is obtained through a theoretical model including surface processes and bulk diffusion. By means of the EIS technique combined with electrochemical hydrogen permeation, this transfer function was experimentally measured for iron membranes, covered with a thin layer of electrodeposited Pd at the exit side, immersed both in acid and alkaline media at the input cell. By fitting of the model to the experimental results a hydrogen diffusion coefficient in iron of 9.6 (+/-0.6) 10(-9) m(2) s(-1) was obtained independently of both the membrane thickness and the input side solution pH in agreement with the values obtained by other authors with different techniques. It has been demonstrated that the oxide film formed on iron at the output side of the membrane delays hydrogen transport and that the thin Pd layer avoids the formation of this film without introducing new significant delays. The determination of the permeation transfer function allows to obtain relevant information about the electrochemical mechanisms of hydrogen discharge on the metallic surface. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.