Investigation of the Temperature Dependence of the Transpassive Dissolution of Iron Using Dual Dynamic Voltammetry

During the experiments presented in this work, the electrochemical synthesis of ferrate ions was performed from high-purity iron electrode in a 45% (m/m) aqueous NaOH solution at different temperatures. The synthesis process was investigated using dual dynamic voltammetry (DDV), which involves applying independent potential–time waveforms (dynamic potential programs) simultaneously to the disk and ring electrodes of a rotating ring–disk electrode (RRDE, Pt-ring—Fe-disk) setup. This innovative technique facilitates the instantaneous measurement of the concentration of ferrate ions generated at the disk electrode. The effect of temperature on ferrate ion formation was examined, and the optimal potential range and applied current density at various temperatures were determined to maximize ferrate ion production and current efficiency. The results indicate that the rate of both ferrate ion production and oxygen evolution increases with temperature within the investigated temperature range (15–45 °C). It was found that there is an optimal potential range at each temperature where ferrate ion formation occurs at the highest rate (limited by other factors). The maximum current efficiency was determined at each temperature, with the highest value obtained at approximately 35 °C.