Examination of Pt(111)/Ru and Pt(111)/Os surfaces: STM imaging and methanol oxidation activity

Ruthenium and osmium were deposited in submonolayer amounts on Pt(111) sing le crystal surfaces using the previously reported 'spontaneous deposition' procedure [Chrzanowski et al., Langmuir, 13 (1997) 5974]. Such surfaces wer e first explored using ex situ scanning tunneling microscopy (STM) to image the deposition characteristics of ruthenium and osmium islands on Pt(111). It was found that, using the spontaneous deposition procedure, a maximum c overage of 0.20 ML ruthenium is formed on the surface after 120 s of exposu re to a RuCl3 solution in 0.1 M HClO4. A homogeneous deposition on the Pt(1 11) surface was found, with no observed preferential deposition on step edg es or surface defect sites. In contrast, in the spontaneous deposition of o smium, osmium clusters form preferentially at, though not limited to, surfa ce defect sites and step edges. Osmium island deposition occurs at a greate r rate than ruthenium on Pt(111), and possible explanations are presented. Methanol activity on the Pt(111)/Ru and Pt(111)/Os surfaces is also studied , using the coverage values determined to yield the highest activity for me thanol electro-oxidation (0.20 ML coverage for Ru and 0.15 ML for Os). At p otentials more negative than 0.40 V vs. RHE, the Pt(111)/Ru surface yields a higher surface activity than Pt(111)/Os. However, at potentials more posi tive than 0.04 V, Pt(111)/Os exhibits demonstrably higher surface activity. The relevance of this data is discussed and future avenues of interest are indicated. (C) 2001 Elsevier Science B.V. All rights reserved.