Use of Raman spectroscopy and rotating split ring disc electrode for identification fo surface layers on iron in 1M NaOH

A. Hugot-Le Goff, J. Flis, N. Boucherit, S. Joiret, J. Wilinski

Journal of the Electrochemical Society 137, 1990, 2684

In situ Raman spectroscopy and rotating split-ring disk electrode were used to identify products formed on iron in 1M NaOH at 22°C at various peaks of cyclic voltammograms. The peak at the most active potential of the cathodic reverse sweep has been ascribed to the reduction of Fe3O4 to Fe2+ species; this peak suggested that Fe3O4 started to form at the first peak of anodic sweep and that it built up at nobler potentials. The Raman spectroscopy has revealed the formation of F3O4 in the wide range of potentials, of d-FeOOH and/or Fe3O4, at peak III of anodic sweep, and of g-Fe2O3 after prolonged polarization at a potential of 0,27 V (SCE). Rapid cycling or long exposure resulted in the formation of Fe3O4 and a-FeOOH. It is suggested that the passivating film on iron in 1M NaOH is composed of an inner Fe3O4 layer and of an outer layer containing products.