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Novel cluster Ru chalcogenide materials Mo x Ru y Se z and Ru x Te y were studied in situ using EXAFS in the transmission mode during the oxygen reduction reaction. Reversible changes in the structure of the active center were revealed for the electrochemical reaction as a function of the applied electrode potential. The shift of the potential in the anodic direction from 0.08 to 0.78 V versus rhe (reference hydrogen electrode) in the presence of oxygen resulted in an increase of the Ru-O and simultaneous decrease of the Ru-Ru coordination numbers in the first coordination shell of Ru. Along with the variation of the coordination numbers, we observed reversible changes of the coordination distances: a decrease of the Ru-O and an increase of the Ru-Ru distance with the positive polarization. These changes witness the distortion of the catalytic center upon oxygen adsorption. A tentative mechanism of oxygen activation on Ru x X y cluster materials is proposed on the basis of the in situ EXAFS data.

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