In situ spectroelectrochemical study of the passivation of iron in alkaline solutions
Enhanced Raman spectra of silver-coated iron electrodes passivated in 0.1 mol dm–3 and 1 mol dm–3 KOH solutions are presented. The results have been interpreted in terms of the logarithmic activity-ratio diagrams for iron in alkaline solutions. The observed Raman signals have been assigned to the following species : Fe(OH)2, δ-FeOOH, Fe(OH)3, Fe3O4 and some soluble FeII species (HFeO–2 or FeO2–2). The Raman intensity of each species depends on the applied potential and on the history of the preparation of the passive film. The formation of FeII species on the passive film has been also investigated by u.v.–vis. reflection spectroscopy using 2,2′-bipyridine as specific reactant for FeII.