In situ spectroelectrochemical study of the passivation of iron in alkaline solutions

Abstract

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 Fe^II species (HFeO^–₂ or FeO^2–₂). 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 Fe^II species on the passive film has been also investigated by u.v.–vis. reflection spectroscopy using 2,2′-bipyridine as specific reactant for Fe^II.