| Résumé | In this work, unsupported Pt/Ru catalysts are used to address the issue of Ru oxide involvement during the methanol oxidation reaction, from the point of view of both Ru “oxidation state” (metal vs oxide) and amount of Ru oxide. It is shown that a simple electrochemical method is useful as in situ probe for the Ru oxidation state. The method also yields insight into the Pt to Ru site distribution of the catalyst surface. The results indicate that the electrochemical formation of reversibly reducible Ru oxides is effectively suppressed in CH₃OH solutions, most probably because of its involvement in the anodic oxidation reaction to CO₂. In the case of PtRu alloys that consist of surfaces of well-distributed Pt to Ru sites, Ru oxides are not detected on this surface for CH₃OH concentrations greater than 0.1 M. It is also shown that the electrochemical formation of Ru oxides at the potential of interest prior to the CH₃OH oxidation reaction deenhances the catalyst activity for CH₃OH oxidation. However, the experiments suggest the deenhancement is low (<5% at 0.6 and <15% at 0.8 V vs the reversible hydrogen electrode) and only observed at potentials equal to or more positive than 0.6 V. |
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