The influence of an oxide layer on hydrogen permeation through steel

Most experiments studying hydrogen permeation use a Devanathan cell with a membrane covered on the exit side by a palladium layer. To examine the results of dispensing with the palladium layer, the effect of hydrogen permeation through an oxide layer on the exit side of an iron membrane was studied. The results show that an iron membrane without a palladium layer on the hydrogen exit side can be used, if the aim of the experiments is to detect the variation of the steady state hydrogen permeation current as a function of the experiments carried out in the input cell, running comparative experiments. The passive layer formed on the exit side, from de-aerated NaOH solution, was perfectly stable even for long periods of hydrogen permeation. This result shows that the charge transfer takes place at the iron-iron oxide interface. The effect of hydrogen evolution on an oxide layer built on the input side of the membrane a was also studied. Preliminary work on bulk iron showed the electrochemical formation and reduction of a passive layer on iron. During hydrogen evolution, the iron oxide layer on the input side was rapidly reduced in two steps, according to the study on bulk iron. The two step reduction was displayed by modifications of the permeation currents which depend on the efficiency of the barrier effect of the oxides.