Spectroscopic studies of the corrosion of model iron electrodes in carbonate and phosphate buffer solutions

Abstract We have extended our unenhanced (non‐SERS) Raman spectroscopic investigations to include a study of the corrosion of an iron electrode in carbonate and phosphate buffer solutions. The measurements have been supported by electrochemical investigations (via cyclic voltammetry), enabling oxidation and reduction reactions to be systematically followed at variable applied potentials. In a carbonate buffer (pH = 9.4) the surface oxidation led to the formation of a ‘green rust’ (a hydrated hydroxy‐carbonate), followed by the α‐ and β‐forms of FeOOH and an underlying magnetite layer formed on the cathodic (reduction) cycle. In a phosphate buffer (pH = 7.7) the surface was passivated by hydrated phosphates of iron [identified as FePO 4 · x H 2 O and Fe 3 (PO 4 ) 2 ·8H 2 O]. The formation of oxides (Fe 2 O 3 and Fe 3 O 4 ) were inferred from voltammetry, but spectral identification was more difficult because of broad, ill‐defined spectra. Despite the challenges of using unenhanced Raman spectroscopy, we believe that the effort was worthwhile, the reactions identified being more likely to be relevant to real electrochemical environments. Copyright © 2008 John Wiley & Sons, Ltd.