ON THE ROLE OF RU AND SN AS PROMOTERS OF METHANOL ELECTRO-OXIDATION OVER PT

摘要

The role of Ru and Sn on the methanol oxidation over Pt was investigated for three different systems viz. Pt covered with adatom layers of Ru and Sn, electro-codeposited Pt-Ru and carbon supported Pt-Ru. By following the oxide growth on the Pt-promoter metal electrodes with ellipsometry it was found that in the presence of methanol the surface oxides of the promotor metal are no longer present on the surface. This supports the bifunctional model of the promotor action. DEMS measurements at Pt with submonolayer coverage of Ru or Sn revealed that the current efficiency of the methanol oxidation to CO2 is increased in the presence of Ru or Sn and that the onset potential of the oxidation keeps lowering with increasing amounts of the promoting metal. On electrodeposited Pt-Ru systems the adsorption of methanol already takes place at potentials in the hydrogen range. These results seem to point to an electronic (ligand) effect. This is further corroborated by activity measurements at carbon supported Pt-Ru with very small particles, which show a tenfold higher activity compared with the Ru-free system. It is concluded that the promoting action of Ru and Sn may involve both a bifunctional and an electronic (ligand) effect. References: 26