Abstract
The goal of the research reported herein was to accomplish a quantitative mechanistic analysis of iron dissolution in strong acid in a potential range in the proximity of its open circuit potential (OCP), leading to articulation of a revised narrative of BDD† mechanism for iron dissolution; additional mechanistic pathways were postulated in addition to the hypothesized mechanisms of BDD and Heusler. Thirty-eight different pathways were investigated here and theoretical Butler-Volmer equations were written for each. The kinetic consequences of each pathway and the corresponding theoretical values of the main kinetic parameters were determined, and the theoretical outcomes were compared to the experimental observations. It was found that in strong acids (pH ⩽ 4) in the potential range of ±50 mV vs. OCP, the mechanism of iron dissolution agrees well with three pathways, and all three were explainable within the same framework of BDD mechanism, where the reaction of OH− with iron produces the adsorbed intermediate FeOHads. One single dissolution pathway which corresponds to the conversion of FeOHads to Fe(II)sol is dominant in the potential range adjacent to the OCP. Near OCP the effect of hydrogen reduction was taken into account using the linearity of the cathodic potentiodynamic branch to approximately extract the pure anodic data points from both anodic and cathodic sweeps.
