Electrochemical study of hydrogen permeation through tungsten near room temperature

We used an electrochemical double cell to study permeation of hydrogen through a 3.5 mu m thick sputter-deposited tungsten layer on a 25 mu m thick palladium support. The temperature dependence of the steady-state permeation current was studied in the range from 266 to 333 K for a constant charging potential on the entry side and zero hydrogen concentration on the exit side of the sample foil. We found that the data is best described by a sum of two Arrhenius terms. We postulate that the higher activation energy of 0.86 +/- 0.07 eV corresponds to permeation through bulk grains and may approach the literature value of 1.43 +/- 0.26 eV for even higher temperature. For the second, lower activation energy of 0.39 +/- 0.03 eV, we currently consider fast diffusion along grain boundaries the most likely explanation. (C) 2014 Elsevier B.V. All rights reserved.