Study of hydrogen permeation through passive films on iron using electrochemical impedance spectroscopy

The influence exerted by a passive film, grown at the detection side of an iron membrane, on the transport of hydrogen was studied using the classic electrochemical permeation tests combined with the electrochemical impedance spectroscopy technique. A theoretical model, considering the presence of traps to proton flux inside the passive film, fitted well the experimental results. It was found that protons move through the oxide at a mean velocity of 10(-6) cm s(-1) and that their concentration inside the film is three orders of magnitude higher than the concentration of hydrogen atoms inside the metal phase.