The electrochemical synthesis of ferrate(VI) was studied in a eutectic NaOH-KOH molten salt environment and in a highly alkaline mixed NaOH-KOH aqueous solution. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the processes taking place on the stationary iron electrode. Cyclic voltammetric curves show similar characteristics in both environments in the potential region of the active iron dissolution. The anodic current peak corresponding to the ferrate(VI) production was identified for both systems in a similar position close to the potential region denoting the start of the oxygen evolution. A well-defined cathodic current peak corresponding to the ferrate(VI) reduction appearing during the reverse potential scan is shifted to the significantly less cathodic potential in the molten salt when compared to the aqueous environment. This indicates significant differences in the properties of surface film developing in the transpassive potential region. This finding was confirmed by means of electrochemical impedance spectroscopy. (C) 2008 The Electrochemical Society.