Hydrogen transport through alpha-iron studies using a current modulation method

A new transfer function for electrochemical hydrogen permeation through met allic membranes is defined, and its analytical expression is obtained throu gh a theoretical model including surface processes and bulk diffusion. By m eans of the EIS technique combined with electrochemical hydrogen permeation , this transfer function was experimentally measured for iron membranes, co vered with a thin layer of electrodeposited Pd at the exit side, immersed i n alkaline media at the input cell. By fitting of the model to the experime ntal results a hydrogen diffusion coefficient in iron of 9.6 (+/- 0.6) 10(- 9) m(2) s(-1) was obtained independently of the membrane thickness in agree ment with the values obtained by other authors with different techniques. I t has been demonstrated that the thin Pd layer avoids formation of an oxide film without introducing new significant delays. The determination of the permeation transfer function allows to obtain relevant information about th e electrochemical mechanisms of hydrogen discharge on the metallic surface. (C) 1999 International Association for Hydrogen Energy. Published by Elsev ier Science Ltd. All rights reserved.