No abstract

No abstract

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.

No abstract

No abstract

As the catalytic cycle for electrochemical hydrogen generation includes cobalt(I, II, and III)-containing clathrochelate species, we performed a detailed study of their electronic structure. The Co K-edge spectra demonstrated a lowering of the Co 1s ionization potentials from cobalt(III) complexes to their cobalt(II)-containing analogs and then to the cobalt(I) clathrochelates. The absence of pre-edge structure and specific peculiarities suggested a high symmetry of the N6-coordination polyhedra of an encapsulated cobalt(I) ion. The Co 2p core-level spectra contained very weak shakeup satellites, suggesting a hybridization of the cobalt-localized 3d orbitals and the valent orbitals of their encapsulating ligands, while the binding energy Co 2p3/2 increased with a formal oxidation state of an encapsulated cobalt ion(I, II, or III) from 780.5–780.8 eV and 780.9–781.2 eV to 781.8–782.2 eV. The Cl 2p, C 1s, N 1s, O 1s, B 1s, and Co 2p core-level spectra and data of X-ray absorption near edge structure (XANES) proved that both the electronic and spatial structures of the highly conjugated polyene macrobicyclic ligands are affected by the metal-localized redox processes. The nature of these encapsulating ligands influenced the redox characteristics of the caged metallocenters, allowing them to adopt unusual catalytically active oxidation state.

No abstract

No abstract