Diffusion of CO on Pt(111) studied by an optical diffraction method

Ma, Junwu; Xiao, Xudong; DiNardo, N. J.; Loy, M. M. T.

doi:10.1103/physrevb.58.4977

Cited by 59 publications

(60 citation statements)

References 27 publications

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“…3), it was concluded that CO must be very mobile on the (111) terraces of all Pt[n(111) · (111)] surfaces. This is in agreement with the fast diffusion of CO on platinum (111) terraces under UHV conditions with a typical hopping rate in the order of 10 5 s -1 at 195 K and low CO coverage [19][20][21] and 10 7 s -1 at 300 K and CO coverage of 0.67 M [22]. From reviewing over 500 systems Seebauer et al concluded an apparent insensitivity of diffusional parameters to the presence of an aqueous ambient [23], which suggests that a high hopping rate of CO should be expected under electrochemical conditions as well.…”

Section: Co Electrooxidation On Ptsupporting

confidence: 70%

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

et al. 2007

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The electrochemical oxidation of carbon monoxide and methanol on single-crystal noble metal electrodes has been studied using cyclic voltammetry, chronoamperometry, in situ FTIR spectroscopy, online electrochemical mass spectrometry, and theoretical methods. The oxidation of CO was found to be enhanced by steps and defects. Furthermore, the surface diffusion rate was found to have a significant influence on the kinetics of the oxidation process: for high diffusion rates, such as the oxidation of CO on platinum, the kinetics can be described by a mean field model, while for low diffusion rates, such as CO oxidation on rhodium in sulfuric acid, a nucleationand-growth model was found to be more suitable. Voltammetric and mass spectrometric measurements on the oxidation of methanol on platinum indicate that steps enhance the overall reaction rate. In general, the selectivity towards the direct oxidation pathway through soluble intermediates was found to be higher in the absence of strongly adsorbing anions. In both perchloric and sulfuric acid, this selectivity was also found to increase with increasing step density. In sulfuric acid, Pt(111) shows the highest relative contribution for the direct pathway of all surfaces studied in that electrolyte. Based on these results, a detailed reaction scheme for the electrochemical oxidation of methanol is presented.

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Section: Co Electrooxidation On Ptsupporting

confidence: 70%

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

et al. 2007

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“…It will be important to see whether future QHAS experiments with improved resolution 57 give the same higher value of D and lower value of E d for the present H on Pt͑111͒ system, and in many other cases when comparisons from other techniques are available. 36,[58][59][60][61][62][63][64][65] We also note the different temperature range used in the two experiments. As shown by TDS of H / Pt͑111͒, 12 the take-up desorption temperature of H is about 170 K at high coverage and 200 K at low coverage, thus, the H atoms will partially desorb from the Pt͑111͒ over the QHAS measurement temperature range from 140 to 250 K. The partial desorption of H will not only affect the coverage of H, but also the H-H lateral interaction.…”

Section: Comparison With Previous Resultsmentioning

confidence: 99%

“…34,35 Thus, experiment on well characterized stepped Pt͑111͒ surfaces for H diffusion should be performed to quantitatively understand the influence of steps, and to experimentally test the tentative conclusion of Graham et al 1 In this paper, we present results of surface diffusion of H on stepped Pt͑111͒ surfaces, using linear optical diffraction (LOD), on vicinal Pt͑111͒ surface with specified miscuts. As shown for CO/ Pt͑111͒, 32,33,36,37 the linear optical diffraction technique [38][39][40] can be employed to study the step effects in both step-parallel and perpendicular directions. A number of advantages make the LOD technique particularly suited to study the step effects.…”

Section: Introductionmentioning

confidence: 99%

Step effects and coverage dependence of hydrogen atom diffusion onPt(111)surfaces

2004

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Step effects on surface diffusion of hydrogen on stepped Pt͑111͒ have been studied by linear optical diffraction technique over a temperature range from 90 to 150 K. Diffusion anisotropy on stepped Pt͑111͒ surfaces has been observed: the unexpected enhanced diffusion perpendicular to steps cannot be explained within the lattice gas model on stepped substrates, indicating a nonlocal and directional step effect. The coverage-dependent diffusion coefficient on flat Pt͑111͒ surface was also measured over a wide coverage range from 0.1 to 0.8 ML. They were analyzed within the framework of the lattice gas model using quasichemical approximation, indicating that H-H repulsive interaction can significantly affect the energy of saddle point as well as that at the adsorption sites.

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“…It is important to note for diffusion of more massive molecules such as CO on this surface, we have previously firmly established [37][38][39] that there is only one single thermally activated process within comparable diffusivity range.…”

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confidence: 99%

Quantum Diffusion of H on Pt(111): Step Effects

2006

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Using a linear optical diffraction technique, we have systematically investigated the defect effects on quantum surface diffusion of hydrogen on Pt(111) surfaces. The quantum tunneling effect was clearly observed for hydrogen diffusion at low temperatures as manifested by a leveling off of the diffusion coefficient on flat surfaces. The strong influence of surface defects on the quantum diffusion is in good agreement with the creation of an inhomogeneous surface with adsorption sites of different binding energies. DOI: 10.1103/PhysRevLett.97.166101 PACS numbers: 68.35.Fx, 68.35.Dv, 68.43.Jk, 82.20.Xr Because of the small mass of the hydrogen atom and the weakly corrugated potential energy surface, diffusion of hydrogen on metal surfaces may take both classical overbarrier hopping and quantum mechanical under-barrier tunneling. Quantum effects in surface diffusion are of broad interest and have been intensively studied both experimentally [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and theoretically [16 -26]. The first observation of a nearly temperature independent surface (chemical) diffusivity of H on W(110) in the low temperature regime by Gomer and coworkers [1] using field emission microscopy (FEM) has stimulated a great theoretical effort [16 -26] because of the observed unexpected different behavior from the light atom diffusion in bulk metals, for which a much stronger temperature dependence was found [27]. Experimentally, while similar behaviors were observed by the same group using the same technique for H on a number of other metal surfaces [2 -7], only one report using a different technique, scanning tunneling microscopy (STM), has confirmed the weak temperature dependence of surface (tracer) diffusivity for H on Cu(100) [13], but at a diffusion rate about 6 -9 orders of magnitude slower (10 ÿ19 cm 2 = sec vs 10 ÿ10 -10 ÿ13 cm 2 = sec). Using a linear optical diffraction (LOD) technique that probes diffusion over a length scale of microns, Zhu and his coworkers found an activated quantum diffusion with a strong temperature dependence for H on Ni(111) [11,12] and Ni(100) [8], drastically different from what has been observed by Gomer and his coworkers on the same systems [7]. These differing and apparently contradictory observations, using different techniques, need to be resolved in order to remove any doubts on the experimental observation of quantum surface diffusion.Recognizing that different techniques detect different physical properties of a system, and that such properties might be influenced by different processes, we studied the quantum effects in surface diffusion using one of the above techniques, the linear optical diffraction technique [28][29][30]. The system we have chosen is H on Pt(111), because there is a theoretical prediction for this system [26], and we have extensively studied the over-barrier diffusion of this system [31]. Compared to FEM and STM, which detect the H diffusion only within a single well-ordered terrace, the linear optical diffraction technique probes...

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Diffusion of CO on Pt(111) studied by an optical diffraction method

Cited by 59 publications

References 27 publications

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

Step effects and coverage dependence of hydrogen atom diffusion onPt(111)surfaces

Quantum Diffusion of H on Pt(111): Step Effects

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