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  • Electronic Resource  (29)
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  • 1
    Electronic Resource
    Electronic Resource
    Oscillatory instabilities during formic acid oxidation on Pt(100), Pt(110) and Pt(111) under potentiostatic control. II. Model calculations (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 991-1003 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A kinetic model is developed for the electrocatalytic oxidation of formic acid on Pt under potentiostatic control. The model development proceeds stepwise via a simple model of the electrocatalytic CO oxidation. The full model consists of four coupled, nonlinear ordinary differential equations. The scanned and stationary current/outer potential (I/U) behavior, stationary current oscillations, two-parameter bifurcation diagrams and stirring effects are simulated using realistic model parameters. The numerical findings are found to be consistent with the experimental results given by Strasser et al. The model reproduces period-1 as well as mixed-mode oscillations. Furthermore, a mechanistic analysis of the model was performed: two suboscillators are identified whose characteristics allow a plausible interpretation of the observed dynamics. After a classification of the suboscillators into previously described categories, an attempt is made to identify the minimal mechanistic requirements for electrochemical current oscillations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474451
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  • 2
    Electronic Resource
    Electronic Resource
    Oscillatory instabilities during formic acid oxidation on Pt(100), Pt(110) and Pt(111) under potentiostatic control. I. Experimental (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 979-990 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The experimental characterization of the current/outer potential (I/U) behavior during the electrochemical CO oxidation on Pt(100), Pt(110) and Pt(111) is used as the first step towards a thorough investigation of the processes occurring during the electrochemical formic acid oxidation. The CO study is followed by new cyclovoltammetric results during the electrochemical formic acid oxidation on the corresponding Pt single crystals. At high concentrations of formic acid, the cyclovoltammograms revealed a splitting of the large current peak observed on the cathodic sweep into two peaks whose dependence on scan rate and reverse potential was investigated. It turned out that the presence of a sufficiently large ohmic resistance R was crucial for oscillatory instabilities. Given an appropriate resistance, all three Pt surfaces were found to exhibit current oscillations at both low and high formic acid concentrations. On Pt(100) stable mixed-mode oscillations were observed. In addition, the sensitivity of the oscillations to stirring was investigated. Whereas the period-1 oscillations were found to be independent of stirring, the mixed-mode oscillations transformed into simple oscillations with stirring. The mechanism giving rise to instability and oscillations is described. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474450
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetic oscillations in the catalytic CO oxidation on Pt(100): Computer simulations (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5328-5336 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The previously observed phenomena of temporal and spatial self-organization during the catalytic oxidation of CO on a Pt(100) surface were computer simulated by use of the cellular automaton technique. The underlying model is footed on the knowledge about the individual reaction steps (adsorption, desorption, surface structural transformation, etc.), which in turn formed the basis of a previous theoretical treatment in terms of the formulation and solution of a set of coupled differential equations. The present result nicely show the formation and propagation of two-dimensional patterns, and they reproduce qualitatively well all the experimental observations. The development of macroscopic patterns even with an a priori perfectly homogeneous surface is a particularly interesting effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451676
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetic oscillations in the catalytic CO oxidation on Pt(100): Periodic perturbations (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 742-749 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Periodic modulations of oxygen pressure or temperature were applied in the catalytic oxidation of CO on a Pt(100) surface under isothermal, low pressure conditions. Transitions from aperiodic autonomous oscillations to regular phase-locked behavior could be observed. Computer simulations using a stochastic cellular automaton model yielded qualitatively similar results. The spatial distribution in both experiment and simulation varies essentially in phase over the whole surface area under the influence of the periodic perturbation, while wave propagation in the autonomous system causes more irregular overall behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453572
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  • 5
    Electronic Resource
    Electronic Resource
    Chemical turbulence and standing waves in a surface reaction model: The influence of global coupling and wave instabilities (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 4 (1994), S. 499-508 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Among heterogeneously catalyzed chemical reactions, the CO oxidation on the Pt(110) surface under vacuum conditions offers probably the greatest wealth of spontaneous formation of spatial patterns. Spirals, fronts, and solitary pulses were detected at low surface temperatures (T〈500 K), in line with the standard phenomenology of bistable, excitable, and oscillatory reaction-diffusion systems. At high temperatures (T(approximately-greater-than)540 K), more surprising features like chemical turbulence and standing waves appeared in the experiments. Herein, we study a realistic reaction-diffusion model of this system, with respect to the latter phenomena. In particular, we deal both with the influence of global coupling through the gas phase on the oscillatory reaction and the possibility of wave instabilities under excitable conditions. Gas-phase coupling is shown to either synchronize the oscillations or to yield turbulence and standing structures. The latter findings are closely related to clustering in networks of coupled oscillators and indicate a dominance of the global gas-phase coupling over local coupling via surface diffusion. In the excitable regime wave instabilities in one and two dimensions have been discovered. In one dimension, pulses become unstable due to a vanishing of the refractory zone. In two dimensions, turbulence can also emerge due to spiral breakup, which results from a violation of the dispersion relation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166028
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  • 6
    Electronic Resource
    Electronic Resource
    Theory of electrochemical pattern formation (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 12 (2002), S. 215-230 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spatial coupling in electrochemical systems is mediated by ion migration under the influence of the electric field. Since field effects spread very rapidly, every point of an electrode can communicate with every other one practically instantaneously through migration coupling. Based on mathematical potential theory we present the derivation of a generally applicable reaction–migration equation, which describes the coupling via an integral over the whole electrode area. The corresponding coupling function depends only on the geometry of the electrode setup and has been computed for commonly used electrode shapes (such as ring, disk, ribbon or rectangle). The pattern formation observed in electrochemical systems in the bistable, excitable and oscillatory regime can be reproduced in computer simulations, and the types of patterns occurring under different geometries can be rationalized. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1449956
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  • 7
    Electronic Resource
    Electronic Resource
    Oscillatory CO oxidation on Pt(110): Modeling of temporal self-organization (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 9161-9172 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The parameters entering the kinetics for the mechanism of catalytic CO oxidation have been adapted for a Pt(110) surface, giving rise to a two-variable model correctly predicting bistability. Oscillations are obtained when, in addition, the adsorbate-driven 1×2–1×1 structural phase transition of Pt(110) is taken into account. Mixed-mode oscillations can be qualitatively explained by including the faceting of the surface as a fourth variable. The limitations of the model essentially stem from the fact that only ordinary differential equations have been analyzed so far neglecting spatial pattern formation. It is discussed which dynamic phenomena observed experimentally in the CO oxidation on Pt(110) will probably not be adequately describable without taking spatial effects into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462226
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  • 8
    Electronic Resource
    Electronic Resource
    Mechanisms of spatial self-organization in isothermal kinetic oscillations during the catalytic CO oxidation on Pt single crystal surfaces (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 510-521 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rate of catalytic CO oxidation on Pt(100) and (110) surfaces at low pressures (≤10−4 Torr) and under isothermal conditions may exhibit sustained temporal oscillations which are coupled with periodic transformations of the surface structures between reconstructed and nonreconstructed phases, the latter exhibiting higher oxygen sticking coefficients and hence higher reactivity. With Pt(100) the two surface phases exhibit a much larger difference in reactivity (=oxygen sticking coefficient) than with Pt(110), which effect accounts for the qualitative differences in the oscillatory behavior: if two of the control parameters (say pO2, T) are kept fixed, the third (pCO) may be varied with Pt(100) over a fairly wide range without leaving the oscillatory region. Minor (〈1%) fluctuations of the partial pressures associated with the varying reaction rate are hence without any noticeable effect. Coupling between surface reaction and diffusion causes wave propagation of the surface phase transformations and therefore spatial self-organization, as demonstrated by scanning LEED experiments. With Pt(110), on the other hand, the oscillatory region is very narrow. In this case mass transport through the gas phase as caused by the small pressure variations associated with the reaction lead to synchronization between different parts of the surface. Computer simulations with the cellular automaton technique confirm qualitatively the experimental findings and support the conclusions reached.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456501
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  • 9
    Electronic Resource
    Electronic Resource
    Traveling waves in the CO oxidation on Pt(110): Theory (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4555-4563 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A dynamic model designed to describe bistability and kinetic oscillations of the reaction rate during the oxidation of CO on a Pt(110) single crystal surface is extended by incorporating surface diffusion of adsorbed CO in order to analyze the properties of traveling waves propagating on the catalytically active surface. In the range of control parameters (partial pressure of oxygen and carbon monoxide and temperature) which corresponds to excitable dynamics, solitary pulses and periodic wave trains can be triggered. Using both asymptotic and numerical methods, the velocity and shape of the pulses as well as the dispersion relation for periodic wave trains are determined and compared to experimental data where available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463900
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  • 10
    Electronic Resource
    Electronic Resource
    Theoretical modeling of spatiotemporal self-organization in a surface catalyzed reaction exhibiting bistable kinetics (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8595-8604 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A two-variable Langmuir–Hinshelwood mechanism for isothermal CO oxidation on a catalytically active surface is presented. It shows bistability stemming from 2 cusp bifurcations, which can be obtained analytically for low pressure. Inclusion of CO diffusion on the surface leads to a system of partial differential equations, which exhibits nucleation and front propagation phenomena in the bistable region. While the line of equistability could with good accuracy be solved for analytically, the front velocities and critical radii for nucleation had to be determined numerically (using the method of heteroclinic orbits). Throughout the calculations the kinetics and rate constants for the CO oxidation on Pt(111) are used. Here the model can be reduced by adiabatic elimination of one variable (namely oxygen coverage) allowing a comparison to the exactly solved one-variable Schlögl model. Possible implications for future experimental work are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462312
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