Effect of Chloride Ions on Adsorption and Permeation of Hydrogen in Iron

Effects of chloride ions (Cl–) on hydrogen absorption into iron and on the hydrogen evolution reaction (HER) on an iron surface were studied in acid and alkaline solutions at 23°C using the permeation method of Devanathan and Stachurski. Cl– ions reduced the overpotential (h) for HER and, in turn, reduced hydrogen coverage and permeation. Effects on hydrogen permeation were more pronounced in alkaline than in acid solutions. Permeation transients at constant electrode potential of the charging surface and subsequent surface analyses of the uppermost atom layers of the hydrogen-charged iron surface indicated a reversible or low coverage with Cl– ions, a low hydrogen coverage that was not influenced significantly by Cl– ion concentration at low h, and a marked effect of Cl– ions in reducing hydrogen coverage of the surface and permeability in alkaline solutions at high cathodic polarizations.