ELECTROCHEMICAL REDUCTION OF DIOXYGEN AT PYRITE

Cyclic voltammetry, the rotating disk and ring-disk electrode, and X-ray photoelectron spectroscopy were used to study the influence of surface condition (standard, oxidized, and reduced) on the electrochemical reduction of O2 at natural pyrite samples with different crystallographic orientations in aqueous solutions (pH 7-13). The FeS2 surface was shown to be covered with iron oxides and sulfoxides [sic] regardless of the surface treatment; the amount of these compounds on oxidized surfaces is twice that found on the standard surface and on the reduced surfaces. Pyrite behaves like a typical metal electrode in O2 electroreduction; the reaction rate decreases drastically after surface oxidation, but increases after surface reduction. The O2 electroreduction at FeS2 is a four-electron process occurring with the intermediate formation of hydrogen peroxide.