This work presents formic acid oxidation on Pt deposits on Au nanoparticles dispersed on Vulcan XC-72R. The Pt deposits were produced using spontaneous deposition method contacting the Au nanoparticles with solutions containing Pt complex ions in various concentrations. The Pt deposits were characterized using CO stripping coulometry, X-ray photoelectron spectroscopy, and inductively coupled plasma atomic emission spectroscopy. When the Pt concentration is 10(-5)-10(-4) M, the Pt deposits are nanoislands of monatomic height. In the concentration range of 10(-4)-10(-3) M, the Pt deposits are most likely two-layer-thick nanofeatures. As Pt concentration increases further, the deposits become wider and thicker. Voltammetric behavior of Pt deposits reveals that on Pt deposits, dehydrogenation path is activated at the expense of poison-forming dehydration path. Furthermore, chronoamperometric measurement of the catalytic activity of Pt deposits supports that the two-layer-thick Pt deposits are most efficient in formic acid oxidation among the studied Pt deposits on Au nanoparticles. The enhancement factor of the particular Pt deposits is 2 in terms of turnover frequency, compared with a commercial Pt catalyst. Details are discussed in conjunction with Pt deposits on Au(111).

This work presents formation of single-layered Pt islands on Au electrodes using CO route and the electrochemical behavior of CO, hydrogen, and ethanol as investigated with scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. Conventional route, consisting of irreversible adsorption of Pt precursor ions (10 -3 M PtCl 4 2-in 0.05 M H 2 SO 4 ) and subsequent electrochemical reduction, resulted in multiple-layered Pt islands; CO route, utilizing CO adsorption to protect pre-existing Pt islands from irreversible adsorption of Pt, exclusively produced single-layered Pt islands.Furthermore, STM results implied that single-layered Pt islands on Au (111) were islands of alloyed Pt in a (√3×√3)R30° arrangement, while multiple-layered islands were stacked layers of Pt in an (1×1) array. The coverages of deposited Pt estimated from STM and XPS measurements were quantitatively consistent with each other to confirm existence of the single-layered Pt islands. Coulometric analyses of adsorbed CO and hydrogen indicated lower adsorption stoichiometry of hydrogen on Pt islands prepared by the two deposition routes, especially when the deposited amount of Pt was small. Comparison of the coulometric coverages of CO and hydrogen with electrochemically active Pt coverages estimated with STM results supported that the adsorption stoichiometries of CO and hydrogen were higher on single-layered Pt islands than on multiple-layered ones, roughly by factor of ~1.8. Also, ethanol oxidation was enhanced on single-layered Pt islands approximately ~4 times in average referring to Pt(poly), while the enhancement factor on multiple-layered ones was ~1.5. Thus, this work demonstrated that CO route exclusively produced single-layered Pt islands on Au, contrasting with multiple-layered islands in various electrochemical aspects.

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Dimethylglyoxime (DMG) adsorbed on Au(111) was investigated using electrochemical scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM experiments revealed three different structures of adsorbed DMG at open circuit potential (~0.07 V versus Ag/AgCl): (2√3×2√3)R30°-α, (2√3×4√3)R30°-β, and (2√3×4√3)R30°-γ. The coverage of adsorbed DMG obtained using XPS was 0.33. A combination of structural and quantitative information identified the adsorbed DMG as an anionic tetramer, held together by intermolecular hydrogen bonding and arrayed in three ordered patterns. Domains of adsorbed DMG underwent phase transitions between the observed structures, most likely due to the influence of the STM tip. However, a significant correlation between the observed structures and the imaging conditions was not found. The ordered layers existed only at open circuit potential as evidenced by their disappearance when the potential was shifted to 0.2 or -0.15 V. The ordered layers were also removed by immersion in a solution of Ni(2+), implying that the adsorbed DMG was converted to a soluble dimer complex with the Ni(2+) ion. This particular observation is discussed in terms of the rigidity of the organic network.

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