Abstract-The oxidation of submonolayers of Ru and Sn on Pt in sulfuric acid was monitored with ellipsometry.In the presence of methanol the oxides on Ru and Sn disappear but the Pt-oxide is not affected by methanol.This signifies that Ru and Sn are present in their zero valent state during the methanol oxidation.DEMS measurements showed that both metals enhance methanol oxidation. The promoting role of these metals is explained with the bifunctional mechanism.

Abstract-The adsorption behaviour of Pt was investigated with the electrochemical quartz microbalance during potential scanning in acid electrolytes. From the mass increase with potential it is concluded that in the potential range of hydrogen desorption and double layer both water and anions are adsorbed in H2SO4 and H3PO4, whereas in HClO4 there is only adsorption of water molecules. The mass changes in the oxygen region indicate that anions are included in the oxide layer. The Pt/COads system was studied in H2SO4, HClO4 and H3PO4. The presence of adsorbed CO is observed as a mass increase with respect to the CO-free system. The results show that water is adsorbed on top of the adsorbed CO layer at low potentials. Moreover, it can be concluded from the mass-balance data that water molecules are attached to the hydrogen monolayer at 0.03 V vs R.H.E. in sulfuric and perchloric acid, but not in phosphoric acid. 7 1997

The growth of an oxide layer on Pt, Ru and codeposited Pt‐Ru was monitored ellipsometrically during the electrooxidation of CH3OH, HCOOH and adsorbed CO. In the potential region where these molecules or their intermediates are oxidized at the Pt‐Ru surface, the Ru‐oxide is no longer observed. This supports the bifunctional mechanism that has been proposed for the promoting role of Ru on Pt. PtO is not involved in the HCOOH and COads oxidation. The adsorbed CO layer on Pt and on Pt‐Ru could also be observed with ellipsometry.

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