Reactivity and activation parameters in methanol oxidation on platinum single crystal electrodes 'decorated' by ruthenium adlayers

Using spontaneous deposition of ruthenium or electrolysis from ruthenium co ntaining media, ruthenium-covered platinum single crystal electrodes were p repared, and were employed as catalysts for electrooxidation of methanol. T he experiments were carried out using electrochemical techniques and electr on spectroscopies of surface science. As before, structure/function measure ments indicate that the Pt(111)/Ru electrode is the most effective catalyst . We show that at a typical potential of interest to methanol fuel cell tec hnology (ca. 0.3 V vs. RHE), methanol oxidation reaction occurs at the surf ace which is covered by the chemisorbed CO at high coverage. In order to in vestigate temperature effects, we have constructed several Arrhenius plots for all Pt(hkl)/Ru surfaces investigated, and tabulated the apparent activa tion energies from the plots. The data indicate that the electrode surface structure is the controlling factor in these activation energies, as well a s in the Tafel slopes (see also: W. Chrzanowski, A. Wieckowski, Langmuir, 1 4 (1998) 1967). Mechanisms involved in the studied heterogeneous reactions on the complex, bimetallic surfaces are discussed in extenso, albeit still on the qualitative level, while a more quantitative treatment is under deve lopment. With further efforts, this project may contribute to the design of small particle, fuel cell catalysts having activity superior to those that are considered presently for utilization in the direct oxidation methanol fuel cell. (C) 1999 Elsevier Science S.A. All rights reserved.