Chemical state of ruthenium submonolayers on a Pt(111) electrode

Oxidation states of ruthenium on a Pt(1 1 1)Ru electrode were investigated by X-ray photoelectron spectroscopy, Ruthenium was added to platinum by ele ctrochemical deposition methods: spontaneous deposition and electrolysis. D epending on the electrode potential, deposition conditions, and presence/ab sence of methanol in solution, metallic ruthenium (3d(5/2) core-level bindi ng energy of 280.3 eV), RuO2 (280.9 eV), and RuO3 (282.8 eV) were found on the surface. After correlating ruthenium valence states to methanol oxidati on reactivity, we concluded that the presence of a Ru metallic phase - cove red by a weakly bonded Ru oxidation precursor - was a prerequisite for effe ctive methanol oxidation electrocatalysis. This precursor was most likely " activated" water supplying the oxygen needed for transformation of surface CO to CO2 at the edge of ruthenium islands on the Pt substrate. (C) 2001 Pu blished by Elsevier Science B.V. All rights reserved.