Electron Diffraction in Surface Chemistry

May, John W.

doi:10.1021/ie50667a005

Cited by 71 publications

(10 citation statements)

References 55 publications

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“…In this case, a decrease in the surface heterogeneity is observed as it is reflected through the sharpening of the main H-adatom electroadsorption/electrodesorption current peaks and the disappearance of the anodic intermediate current peak in the voltammogram at 0.1 V/s. As was pointed out in previous work (5,15), the effect of fast periodic potential perturbations on the surface modification resembles those induced in single crystals by either bombardment with high energy particles (21,29) or thermal treatment (21,30,31) or O-adsorption from the gas-phase (30,32) yielding restructuring and eventually faceting. In these cases, the stabilization process of the perturbed surface implies an energy dissipation effect involving short and large range atom rearrangements.…”

Section: Discussionsupporting

confidence: 59%

A Study of the Optimal Conditions for the Development of Preferred Oriented Platinum Surfaces by Means of Fast Square Wave Potential Perturbations

Triaca

Kessler

Canullo

et al. 1987

J. Electrochem. Soc.

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Changes in the voltammetric response of polycrystalline platinum in the direction expected for preferred oriented surface electrodes are achieved after applying a fast repetitive square wave potential signal covering the potential range of H-and O-electroadsorption/electrodesorption. The influence of the characteristics of the square wave potential signal on the voltammetric response of the modified platinum surfaces is systematically studied to establish the optimal conditions for obtaining surface structures with determined preferred orientations.Recently, it was found that changes in the voltammetric response of polycrystalline platinum electrodes in the direction expected for preferred oriented surface electrodes can be achieved by using a fast repetitive square wave potential signal (RSWPS) within the potential range of H-and O-electroadsorption/electrodesorption in acid solution (1). Similar results were earlier obtained by applying a fast triangular potential signal to a polycrystalline platinum electrode in acid electrolyte at room temperature (2, 3). After applying the fast potential perturbation the electroae surface modifications were voltammetrically followed at a low potential sweep rate in the H-and O-electroadsorption/electrodesorption potential range by using an acid electrolyte. These changes in the electrode surface can also be seen through SEM for a relatively low magnification factor (4). The change from the initial polycrystalline platinum surface to the preferred oriented surface is independent of the shape of the periodic potential perturbation, but it is extremely sensitive to its frequency and potential limits (1, 2, 5). Thus, depending on the preset parameters of the potential perturbation either the platinum (100) preferred oriented surface or the platinum (111) preferred oriented surface are obtained (1-5).In the present work the influence of the RSWPS characteristics on the voltammetric response at low potential sweep rate of the resulting platinum surfaces is systematically studied to establish the optimal conditions for obtaining surface structures with a determined preferred orientation. ExperimentalRuns were made in 1M H2SO4 at 25~ with commercially available polycrystalline platinum wire shaped working electrodes of ca. 0.10 cm 2 geometric area. Previous to each experiment the working electrode was electropolished with ac (50 Hz; 10-15V) in a slightly acid (HC1) saturated CaC12 solution. Later, the electrode was repeatedly rinsed with triply distilled water and kept in water for lh before use. The potential of the working electrode was measured against a RHE in the acid electrolyte. A large area platinum counterelectrode (ca. 50 cm 2) concentrically surrounding the working electrode was used. The electrochemical cell and the instrumentation have been described elsewhere (1, 5). The distortion of the RSWPS, which was due to the proper risetime of the electrochemical setup, was less than 5% at frequencies lower than 6 kHz.After the pretreatment, the working electrode was subjected ...

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Section: Discussionsupporting

confidence: 59%

A Study of the Optimal Conditions for the Development of Preferred Oriented Platinum Surfaces by Means of Fast Square Wave Potential Perturbations

Triaca

Kessler

Canullo

et al. 1987

J. Electrochem. Soc.

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“…atoms which can give rise to a rearrangement of the surface metal atoms and even to the formation of a different symmetry in comparison to the situation on the metal surface before adsorption. The existence of such an effect had already been noted in the 1960s (Germer and Macrea 1962;May 1965) as well as later in the studies of Ertl and Küppers (1985) and Somorjai (1994). As a consequence, the layer of metal atoms and chemisorbed atoms X is now generally treated as a binary surface "phase".…”

Section: ∆Hmentioning

confidence: 88%

Binding Energy and the Heat of Chemisorption on Metallic Catalysts — A Thermodynamic Aspect

Stokłosa

Kurek

Laskowska

2005

Adsorption Science & Technology

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ABSTRACT:The thermodynamic conditions necessary for the adsorption of gaseous molecules onto metals are discussed in this work. The differences and similarities between chemisorption and the formation of a solid oxidation product on metals are indicated. It was pointed out that the changes in the interactions between the surface metal atoms before and after adsorption must be followed by an energetic effect that would affect the value of the heat of chemisorption and its dependence on the surface coverage. The dependence of the heat of adsorption on the surface structures being formed and their concentration is discussed.It was shown that the relationships discussed in various published works between the values of the initial heat of adsorption and the formation enthalpies of the compounds are only experimental and not based on thermodynamic principles. The initial heats of adsorption, binding energies in gaseous molecules and cohesive energies for the oxidation products of metals are discussed for O 2 and H 2 chemisorption.

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“…A few instances only can be quoted here. 77 On the cleavage face of sodium chloride, steps analogous to those of Fig. 12 could be detected in distances of, say, 0.05 micron from each other.…”

Section: Solid Surfacesmentioning

confidence: 88%

Solid Surfaces

1970

Physical Chemistry

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SURFACE ROUGHNESS §98.It was pointed out in §65 that liquid surfaces are in a state of permanent agitation and, consequently, are not absolutely smooth. Analogous vibra tions, although with much smaller amplitudes, take place on solid surfaces also. Reflextion of low-energy electrons (of, for instance, 100 electron volts) from metals shows 1 (see also Reference 2) that the amplitude of vibrations, normal to the surface, of the exterior atoms of palladium is about 0.14 A while the corresponding amplitude in the bulk is near 0.07 A. The results for platinum, lead and so on are similar.However, the roughness caused by molecular motion is negligibly small compared with the mechanical rugosity of all solids, which does not vanish when a time-average is taken. Because of the high viscosity or the high yield stress of solids, their profile usually remains almost unaltered for months or years and, as a rule, demonstrates no tendency to become a straight line. Roughness is perhaps the most striking property of solid surfaces. Several books 3 " 6 have ably reviewed it. In this section, the main geometrical para meters of rugosity are listed; the following seven sections deal with the main methods of measuring these and related parameters, and some typical numeri cal data are presented in §106.Let A A in Fig. 1 be the profile of a solid surface magnified perhaps, 1000 times. If all hills on it were rased and employed to fill in the valleys, the new, perfectly smooth boundary would have been BB. This is known as the main plane or the mean surface of the sample. If it really is a plane, the actual surface (that is AA) has rugosity but no waviness; and if BB itself has (macroscopically) concave and convex segments, as a file has, both waviness and roughness are present. Both can be measured together, but only the latter is considered in the following. METHODS FOR DETERMINING SURFACE ROUGHNESS 171Bearing-area curves 8 can be computed from surface profiles, if the mag nification is much greater than in Fig. 1; see Fig. 2. The line y = 0, identical y FIG. 2. Determination of the bearing area curve from the surface profile (shown by the irregular curve passing through a and b). Abscissa: distance from a point along the plane which is parallel to the mean surface and includes the bottom of the deepest indentation. Ordinate: height above this plane. Only p% of the dotted line (and its continuation) is within the solid. Values of ρ plotted against y form the bearing area curve. After Bikerman. 78with the abscissa, lies wholly within the solid. All other straight lines, parallel to it and situated above it, pass partly within the solid and partly outside it; thus, only ρ % of the line determined by y = y t is in the solid body. When y is plotted as a function of /?, a bearing-area curve results, see Fig. 3. FIG. 3. Bearing area curves. 1: Johansson block. 2: lapped metal. 3: ground metal. After Abbott and Firestone. 8METHODS FOR DETERMINING SURFACE ROUGHNESS §99. As the effects of surface tension are so pervading in liquids, the metho...

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Electron Diffraction in Surface Chemistry

Cited by 71 publications

References 55 publications

A Study of the Optimal Conditions for the Development of Preferred Oriented Platinum Surfaces by Means of Fast Square Wave Potential Perturbations

A Study of the Optimal Conditions for the Development of Preferred Oriented Platinum Surfaces by Means of Fast Square Wave Potential Perturbations

Binding Energy and the Heat of Chemisorption on Metallic Catalysts — A Thermodynamic Aspect

Solid Surfaces

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