| AVS 60th International Symposium and Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | R.P. Galhenage, University of South Carolina |
| Authors: | R.P. Galhenage, University of South Carolina K. Xie, University of South Carolina J.M.M. Tengco, University of South Carolina J.R. Monnier, University of South Carolina D.A. Chen, University of South Carolina |
| Correspondent: | Click to Email |
Bimetallic Pt-Ru clusters on highly oriented pyrolytic graphite (HOPG) have been studied as model systems for direct methanol fuel cell catalysts. Metal clusters deposited via vapor-deposition in ultrahigh vacuum have been compared with clusters prepared via electroless deposition (ED) of Ru onto existing Pt seed clusters. Cluster sizes and distributions are characterized by scanning tunneling microscopy (STM), while surface compositions are examined by low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). For the growth of 0.25 ML of pure Pt on HOPG, STM images show that large Pt clusters (average height 33 Å) are formed, and these clusters are located almost exclusively at the step edges. Ar ion sputtering was used to introduce defects and create nucleation sites for Pt clusters on the terraces; this treatment resulted in smaller cluster sizes (12 Å ) and higher cluster densities (0.12 x 1012 cm-2 vs. 2.25 x 1012 cm-2 ) compared to growth on the unmodified HOPG surface. When 0.5 ML of Ru was vapor-deposited onto 0.5 ML Pt clusters, the number of clusters did not increase, indicating that bimetallic clusters are formed by incorporation of Ru into the Pt seed clusters. Electroless deposition of Ru onto 0.5 ML Pt clusters on HOPG was carried out in solution using Ru(NH3)6Cl3 with formic acid as a reducing agent at pH 3. LEIS experiments confirmed that Ru was deposited onto the Pt seed clusters, whereas no Ru was deposited on HOPG in the absence of the Pt seed clusters. STM images of the Pt-Ru clusters grown by ED indicate that the cluster densities and sizes are comparable to that of the vapor-deposited clusters. Methanol oxidation experiments will be carried out to study the activity of the Pt-Ru/HOPG surfaces in a recirculating loop reactor coupled to the vacuum chamber.