Study of the input-side subsurface reorganization vs. the outside current density in hydrogen permeation under constant cell voltage through iron membrane according to RHC concept

In this work, hydrogen permeation tests were performed on pure iron membrane in 1 M sodium hydroxide at 298 K, subjected to hydrogen charging under “quasi-potentiostatic” polarization conditions, i.e. constant cell voltage applied between the cathode (membrane entry side) and the anode (counter electrode), which is a typical situation during metal electrodeposition or cathodic degreasing on steel in metal finishing industry. Two consecutive charging–discharging runs were carried out. Prolonged hydrogen charging under quasi-potentiostatic polarization was investigated and the change of cathodic current density image and electrode potential image as well as permeation current density image were analysed. Three singularities were underlined for each experiment: (i) the curve image = f(image), illustrating the inverse of hydrogen charge resistance image evolution which was negative, equal to zero and then became positive; (ii) quasi-periodic instabilities during the image zero period, probably induced by atomic reorganizing due to subsurface hydrogen insertion in the input-side; (iii) the same ratio image = −6 × 10−5. During discharge runs, both sides of the membrane were polarized at the same potential image = image = −0.285 V/Hg/HgO/NaOH 1 M and the current densities, image and image which corresponded to the desorption rates of hydrogen, were measured. The following correlation image vs. image = −6 × 10−5 was confirmed leading us to introduce the image mirror concept to observe the input-side subsurface reorganization by the survey of its potential vs. outside current density during the hydrogen charge. Thus, this image mirror concept showed: (i) a non-stop and irreversible progress in the subsurface reorganization during the two permeations; (ii) a probable structural evolution to a stable subsurface structure, the only condition of a real steady-state charge when image and image were stable together, either under potentiostatic or galvanostatic conditions.