Characterization of FeS2-Based Thin Films as Model Catalysts for the Oxygen Reduction Reaction

FeS 2 and (Fe,Co)S 2 thin films prepared by magnetron sputtering have been investigated as model catalysts for the oxygen reduction reaction (ORR), and their activities were compared against that of a sputtered thin film of Pt. Scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and micro-Raman spectroscopy have been used, in parallel with electrochemical activity measurements using the thin film as a rotating disk electrode (RDE), to assess how the electrochemical performances of the sulfide films relate to chemical composition and structure. Comparisons were also made against a mineral FeS 2 pyrite whose open circuit potential (OCP) was 0.62 V and much less than the values of 0.78 and 0.80 V found for the FeS 2 and (Fe,Co)S 2 thin films, respectively (all potentials are given vs the reversible hydrogen electrode). There are indications that the ORR activities for these films may be associated with the presence of some polysulfides in addition to the expected S 2 2- bulk and surface sites.