In-Situ Raman Spectroscopy of α- and γ-FeOOH during Cathodic Load

Abstract

Water reduction on corroded iron surfaces is technologically and fundamentally important. Here, the technological interest originatesfrom the chlorate process where water reduction is the main cathodic process. Fundamentally, water reduction on oxide surfaces raisesquestions on the stability of the oxide and the nature of electrocatalytic surface sites. Two iron oxyhydroxides,α-andγ-FeOOH,were electrodeposited on titanium substrate and their reduction processes were followed in detail with in-situ Raman spectroscopy,using low incident laser power to avoid sample damaging. Polarization to negative potentials show two reduction peaks forγ-FeOOHand one peak forα-FeOOH prior to hydrogen evolution. The characteristic Raman peaks gradually disappear as the potential ismade more negative but no new peaks can be observed.δ-FeOOH was detected as an intermediate phase upon oxidation of thereduced surface layer. This indicates that Fe(OH)2is formed during cathodic polarization and initially re-oxidized to the isostructuralδ-FeOOH. Characteristic Raman signals of the original phases appear upon further oxidation in air