| Platinum and gold single crystal electrodes were decorated by noble metal islands (Ru, Os or Pt) by the spontaneous deposition procedure. These surfaces were characterized by scanning tunneling microscopy (STM) and electrochemical methods to develop fundamental structure-activity relationships relevant to direct methanol fuel cell research. The structures of the admetal deposits (Ru or Os) on Pt(111) and Au(111) were also compared to better understand the spontaneous deposition process. X-ray photoelectron spectroscopy (XPS) was used to provide supporting information for Pt(111)/Os. Repeating the spontaneous deposition process for low-index Pt(hkl)/Ru increases the Ru coverage and results in more active Pt(hkl)/Ru surfaces, with Pt(111)/Ru being the most active after 3--5 spontaneous depositions (ca. 30-40% Ru coverage). Pt(111)/Os is less active than Pt(111)/Ru at fuel cell relevant potentials, and a higher Os coverage (60-70%) is required for effective methanol electrooxidation. These differences are related to the greater oxygen-affinity of Ru under these conditions. Osmium deposition proceeds at a faster rate than ruthenium on both Pt(111) and Au(111) surfaces. The Au(111) surface exhibits preferential deposition of Ru or Os islands near steps in contrast to Pt(111), which shows homogeneous deposition across the surface. The structure of admetal deposits can be further manipulated by electrochemical treatments, as demonstrated for Pt(111)/Ru and Au(111)/Os. The size of the islands can be reduced and the island-island distance increased. For Pt(111)/Ru prepared by two spontaneous depositions, this resulted in a less active surface for methanol electrooxidation. Finally, ternary Au(111)/Ru/Pt and Pt(111)/Ru/Os surfaces were prepared as part of an ongoing study. The presence of the Au(111) substrate appears deactivating for the Pt-Ru deposit for both CO and methanol electrooxidation. The Pt(111)/Ru/Os surface compares favorably with optimized Pt(111)/Ru surfaces, and further optimization of Pt(111)/Ru/Os may result in increased activity. |
