Study of lepidocrocite γ-FeOOH electrochemical reduction in neutral and slightly alkaline solutions at 25 °C

The electrochemical reduction of lepidocrocite γ-FeOOH was investigated at 25 °C in neutral or slightly alkaline solutions containing chloride, sulphate or bicarbonate anions by means of thin lepidocrocite film electrodeposited on inert gold substrate or graphite/lepidocrocite powder composite electrode. Electrochemical measurements were coupled to in situ electrochemical quartz crystal microbalance (EQCM) and ex situ SEM and FTIR analysis. The reduction of lepidocrocite occurs in all the electrolytes considered here. The initial reduction product is adsorbed ferrous ion, Feads2+. The desorption of Feads2+ is promoted as pH increases, leading to an increase of reduction depth. This promotion is related to the formation of secondary FeII-containing species, as revealed by SEM and FTIR. The comparison of γ-FeOOH reduction potentials and iron corrosion potentials let us state that the galvanic coupling is possible.