文摘
Oxidation states of ruthenium on a Pt(111)/Ru electrode were investigated by X-ray photoelectron spectroscopy. Ruthenium was added to platinum by electrochemical deposition methods: spontaneous deposition and electrolysis. Depending on the electrode potential, deposition conditions, and presence/absence of methanol in solution, metallic ruthenium (3d5/2 core-level binding 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 oxidation reactivity, we concluded that the presence of a Ru metallic phase – covered by a weakly bonded Ru oxidation precursor – was a prerequisite for effective 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.