Simultaneous Measurements of Polarization Resistance and Hydrogen Permeation Current of Iron in an Aqueous NaCl Droplet

In this study, a Kelvin probe (KP) technique combined with the Devanathan-Stachurski electrochemical hydrogen permeation method was applied for simultaneous measurements of polarization resistance and hydrogen permeation current for iron to clarify the hydrogen uptake mechanism during drying of an NaCl droplet. The reciprocal of the polarization resistance, which is an index of the corrosion rate, the hydrogen permeation current, and the corrosion potential under the droplet were successfully measured. The corrosion potential decreased, and the hydrogen permeation current increased, after the NaCl droplet had been applied to the iron surface. The reciprocal of the corrosion resistance increased gradually during the drying of the droplet with increasing the corroded areas on the iron. The hydrogen permeation current decayed with the shift in the corrosion potential toward the noble side during the drying stage, before the droplet dried up completely. The hydrogen permeation current mainly followed the change in the corrosion potential. The hydrogen uptake mechanism of iron during corrosion is discussed in detail based on the corrosion potential, corrosion rate and hydrogen permeation behavior.