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Hydrogen chemisorption on Pt single crystal surfaces in acidic solutions

1981; Elsevier BV; Volume: 102; Issue: 2-3 Linguagem: Inglês

10.1016/0039-6028(81)90040-6

1879-2758

Philip N. Ross,

Molecular Junctions and Nanostructures

Hydrogen chemisorption from dilute acidic solution onto Pt single crystal surfaces was examined using an electrochemical cell directly coupled to LEED/Auger analytical system. No pre-anodization was used prior to observing hydrogen adsorption by cyclic voltammetry so that clean surfaces having the ordered structures indicated by LEED were studied. The problem of contributions from non-ordered parts of the electrode like support wires and edges was solved by using a gold evaporation masking technique. The specific contribution of atomic imperfections to the voltammetry curve was deduced from the ordered and countable imperfections occurring on high Miller index single crystal surfaces that have a stepped structure. The H-Pt bond energy was found to be structure sensitive, and sensitive both to local site geometry and long range order in the surface. The bond strength was found to vary systematically: n(111) × (100) > (100) >n(111) × (111) > (110) > (111). Distinct states for hydrogen at steps versus hydrogen on terraces could be distinguished. The (110) surface is shown to be a (111) vicinal, probably the [3(111) × 2(111)] microfacetted surface. The zero coverage heat of adsorption on the well-ordered (111) surface (48 kJmol) in solutions is the same as the value reported by Ertl and co-workers for adsorption on a (111) surface in vacuum. Adsorption isotherms for hydrogen on the (111) and (100) surfaces are adequately fit by the classical model for immobile adsorption at single sites with nearest neighbor repulsive interaction.