Effects of additives and temperature on iron electrode behavior in KOH electrolytes

The effect of temperature, electrolyte additives, and KOH concentration on the electrochemical behavior of iron electrodes in KOH electrolytes was studied by the cyclic voltammetric method. It is indicated that the charging efficiency of the iron electrode will be decreased at lower temperatures. To achieve the same state of charge as that obtained at higher temperatures, a higher charging voltage is required at lower temperatures. The higher charging voltage will increase hydrogen evolution, which will cause the charging efficiency of the iron electrode to decrease. The addition of K2S to the KOH electrolyte can effectively suppress the H2 evolution on the iron electrode during charging. The addition of LiOH to the electrolyte will be beneficial to the stability of the iron electrode, particularly at the transitions from lower to higher oxidation states. The saturation of the KOH electrolyte with FeO causes significant changes in the mechanisms and reaction rates of the electrode reduction-oxidation processes because of the competing reactions of Fe(II) species which become more available at the iron electrode surface. The decrease in reaction rates in more concentrated electrolytes was probably caused by the increased formation of solid film products of higher oxidation states at the electrode surface.