Observation of L-cysteine enhanced zinc dissolution during cathodic polarization and its consequences for corrosion rate measurements
The corrosion inhibiting and accelerating effect of L-cysteine on Zn were correlated with the formation of Zn oxides by means of a novel coupling of impedance spectroscopy (EIS) with atomic emission spectroelectrochemistry (AESEC). A plateau of anodic Zn dissolution was discovered in the cathodic branch of the polarization curve, hidden by the large cathodic current. The effect of L-cysteine at all pH values and all concentrations was to increase the plateau current. The effect was most pronounced at high pH suggesting a synergy between hydroxide and L-cysteine. Due to the presence of Zn plateau current, Tafel extrapolation resulted in wrong estimation of corrosion currents. The contribution of the anodic Zn oxidation in plateau region to the total current was inversely proportional to the frequency of AC perturbation.