Contrasting Electrochemical Behavior of CO, Hydrogen, and Ethanol on Single-Layered and Multiple-Layered Pt Islands on Au Surfaces

This work presents formation of single-layered Pt islands on Au electrodes using the CO route, and the electrochemical behavior of CO, hydrogen, and ethanol was investigated with scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry. The conventional route, consisting of irreversible adsorption of Pt precursor ions (10^–3 M PtCl₄^2– in 0.05 M H₂SO₄) and subsequent electrochemical reduction, resulted in multiple-layered Pt islands; the 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)<i>R</i>30° 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 a factor of ∼1.8. Also, ethanol oxidation was enhanced on single-layered Pt islands approximately ∼4 times on average referring to Pt­(poly), while the enhancement factor on multiple-layered ones was ∼1.5. Thus, this work demonstrated that the CO route exclusively produced single-layered Pt islands on Au, contrasting with multiple-layered islands in various electrochemical aspects