Enhanced Hydrogen Entry in Iron at Low Anodic and Low Cathodic Polarizations in Neutral and Alkaline Solutions

Electrochemical permeation technique was used with voltammetric cycling to examine hydrogen entry in iron during anodic and cathodic polarizations. Measurements were performed at 25°C on a 40-μm thick membrane. On curves of hydrogen-permeation rate (HPR) vs potential, peaks appeared at potentials of low anodic polarization during potential sweeps in the noble direction and at more negative potentials during the reverse sweeps. The peaks were most distinct in slightly alkaline (carbonate/bicarbonate) and in neutral (phosphate, acetate) solutions. However, they did not appear in an acidic solution (0.1 M H2SO4). It has been suggested that the HPR peaks form mainly as a result of an activation of the metal surface during anodic dissolution, due to a partial removal of surface layers (iron hydroxides and oxides), which constitute a barrier for the hydrogen entry into iron. Other possible reasons have also been discussed.