| Abstract
| - We used in situ Se K-edge X-ray spectroscopy to characterize Ru nanoparticles chemically modified withsubmonolayers of selenium (Se/Ru) [Cao et al. J. Electrochem. Soc.2006, 153, A869]. X-ray powder diffractionverified that the Se/Ru catalyst had metallic Ru cores. The in situ X-ray absorption near edge structure takenat the open circuit potential showed that there were both elemental and oxidized selenium on the as-preparedSe/Ru samples. All selenium oxide was reduced to the elemental form of selenium by applying negativepotentials. By applying positive potentials, selenium was subsequently reoxidized. The analysis of the extendedX-ray absorption fine structure shows the appearance of selenium hydration (Se−OH2) in a deaerated solution,which was not observed during the oxygen reduction reaction. We present evidence that Se-free Ru atomsplay an important role in the ORR activity of the Se/Ru catalyst studied in this paper.
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