Reaction Model for Iron Dissolution Studied by Electrode Impedance: Part. I. Experimental results and reaction model. Part. II . Determination of the Reaction Model
Résumé
The electrode impedance determined experimentally shows a certain number of time constants as capacitive or inductive features. These impedances arise from various processes occurring at or near the electrode interface, such as charge transfer, adsorption‐desorption of reaction intermediate species, changes of the roughness factor, changes of the number of active sites or of volume concentration in the vicinity of the electrode, etc. The origins of impedances are examined on the basis of experimental results given in Part I . Then, hypotheses describing reaction rates, such as the Tafel law, reaction reversibility, and the adsorption isotherm law, are analyzed in order to translate reasonably the reaction models into mathematical expressions. With hypotheses retained, it is concluded that the experimental results should be interpreted by a model including three adsorbed reaction intermediate species. Forty possible reaction schemes, as the complete set of prospective models, were written and examined according to both steady‐state polarization curves and electrode impedances. The appearance of two current maxima implies at least two dissolution paths in the reaction models and allowed us to eliminate 10 of the 40 reaction schemes. On the other hand, the appearance of inductive impedance was found to constitute a very selective criterion. Only one model, given in Part I , was found to simulate suitably the whole set of experimental results.