Interrelation between Kinetics of the Hydrogen Ion Reduction on Iron and the Hydrogen Diffusion Flux into Carbon Steel in Acidic Solutions

Kinetic parameters of discharge of hydrogen ions, which depend on the nature of the slow stage in the Volmer–Tafel and Volmer–Heyrovský mechanisms, are obtained theoretically for commensurate rates of successive reactions on energetically-uniform and evenly-nonuniform surfaces. The results are compared with similar experimental parameters for the Armco iron in the system C₂H₄(OH)₂–H₂O + HCl. Upon adding 2–10 wt % H₂O into C₂H₄(OH)₂, the slow discharge stage gives way to the Tafel reaction if the hydrogen ion adsorption obeys the Temkin isotherm. Upon going to purely aqueous solutions, the discharge process becomes the limiting stage again. A change in the hydrogen diffusion flux through a steel membrane from these mixed solvents does not correlate with the nature of the stage that controls the cathodic reduction of hydrogen ions.