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 originates from the chlorate process where water reduction is the main cathodic process. Fundamentally, water reduction on oxide surfaces raises questions on the stability of the oxide and the nature of electrocatalytic surface sites. Two iron oxyhydroxides, α- and γ-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 for γ-FeOOH and one peak for α-FeOOH prior to hydrogen evolution. The characteristic Raman peaks gradually disappear as the potential is made more negative but no new peaks can be observed. δ-FeOOH was detected as an intermediate phase upon oxidation of the reduced surface layer. This indicates that Fe(OH)2 is formed during cathodic polarization and initially re-oxidized to the isostructural δ-FeOOH. Characteristic Raman signals of the original phases appear upon further oxidation in air.