Active dissolution mechanisms of iron using EIS with channel flow double electrode. Influences of chloride and fluoride ions

The active dissolution mechanism of iron in acidic solutions containing halide ions was investigated by electrochemical impedance spectroscopy (EIS) with channel how double electrode (CFDE). CFDE is a hydrodynamic technique similar in principle to the rotating ring disc electrode (RRDE); A dissolution efficiency Phi(diss) of the iron electrode in the frequency domain was obtained using the dynamic collection efficiency N(omega). By the addition of NaCl and NaF in sulfuric acid solution (pH 1), Nyquist plot of the electrochemical impedance Z showed a capacitive semicircle and apparently two inductive semicircles, and that of Phi(diss) showed two semicircles. These experimental results indicate that ferrous ions dissolve through two dissolution paths in the presence of chloride ions, ie, reaction paths through a FeOH adsorbed intermediate and through a FeCl adsorbed intermediate. In order to investigate the role of chloride ions, numerical simulations for EIS responses and polarization curves were performed on the basis of the above reaction model, assuming the two dissolution paths, and simulated results were in good agreement with the experimental results.