Abstract: Polarization curve, electrolysis curve, and electrochemical impedance spectroscopy (EIS) were adopted to study the polarization of iron electrode in the concentrated NaOH solution. The results showed that passivation of the iron anode occured more easily at higher temperature, lower alkaline concentration, and greater current density. However, the passivation phenomenon of the iron electrode might become too weak to see under some conditions. The conditions were as follows: temperature 25-35 ℃, current density ≤ 4.7 mA·cm-2, alkaline concentration ≥ 14.5mol·L-1. EIS was used to investigate the impedance change of the electrode surface during the above polarization process. Next, the step characteristic of the iron anode polarization during its super-passivation range in theconcentrated NaOH solution was described.

Key words: Iron anode, Passivation, Ferrate(Ⅵ), Electrolysis curve, EIS, Current efficiency