Electrooxidation of CO on Pt

1997

Effect of molecular mobility on kinetics of an electrochemical Langmuir-Hinshelwood reaction

Author: A.V. Petukhov

Journal: Chemical Physics Letters 277 (1997) 539-544

Abstract:

A simple model to study the kinetics of a Langmuir-Hinshelwood surface reaction is developed and applied to the oxidation of a complete monolayer of CO molecules at a metal/electrolyte interface in a potential-step experiment. A dramatic influence of the molecular mobility on the reaction kinetics is found. The present model is able to connect the simple Langmuir-Hinshelwood kinetics to that predicted by Kolmogoroff-Avrami theory since it includes them as the two limiting cases of high and low mobility, respectively.

1998

Kinetics of electrooxidation of a CO monolayer at the platinum/electrolyte interface

Author: A.V. Petukhov, W. Akemann, K.A. Friedrich b, U. Stimming

Journal: Surface Science 402–404 (1998) 182–186

Abstract:

The kinetics of electrooxidation of a complete monolayer of carbon monoxide (CO) at the Pt/electrolyte interface is studied both theoretically and experimentally. Recent studies indicate that CO diﬀusion is an important process aﬀecting considerably the CO oxidation reaction. By comparing experimental and theoretical results, it is argued that the reaction kinetics is signiﬁcantly aﬀected by CO diﬀusion over the electrode surface. On the other hand, the diﬀusion is found not to be fast enough in order to reach the simple Langmuir–Hinshelwood kinetics since the transient width depends very sensitively on the density of surface defects.

Monte Carlo simulations of a simple model for the electrocatalytic CO oxidation on platinum

Author: M. T. M. Koper, A. P. J. Jansen, and R. A. van Santen, J. J. Lukkien and P. A. J. Hilbers

Journal: J. Chem. Phys. 109, 6051 (1998); https://doi.org/10.1063/1.477230

Abstract:

A simple lattice-gas model for the electrocatalytic carbon monoxide oxidation on a platinum
electrode is studied by dynamic Monte Carlo simulations. The CO oxidation takes place through a Langmuir–Hinshelwood reaction between adsorbed CO and an adsorbed OH radical resulting from the dissociative adsorption of water. The model enables the investigation of the role of CO surface mobility on the macroscopic electrochemical response such as linear sweep voltammetry and potential step chronoamperometry. Our results show that the mean-ﬁeld approximation, the traditional but often tacitly made assumption in electrochemistry, breaks down severely in the limit of vanishing CO surface mobility. Comparison of the simulated and experimental voltammetry suggests that on platinum CO oxidation is the intrinsically fastest reaction on the surface and that CO has a high surface mobility. However, under the same conditions, the model predicts some interesting deviations from the potential step current transients derived from the classical nucleation and growth theories. Such deviations have not been reported experimentally. Furthermore, it is shown that our simple model predicts different Tafel slopes at low and high potential, the qualitative features of which are not strongly inﬂuenced by the CO mobility. The comparison of our simulation results to the experimental literature is discussed in some detail.

1999

2000

2001

2002

Mechanism and kinetics of the electrochemical CO adlayer oxidation on Pt(111)

Author: N.P. Lebedeva, M.T.M. Koper, J.M. Feliu, R.A. van Santen

Journal: Journal of Electroanalytical Chemistry 524–525 (2002) 242–251

Abstract:

The electrochemical oxidation of saturated and sub-saturated CO adlayers on Pt(111) in 0.5 M $H_2SO_4$ has been studied using chronoamperometry. For the saturated CO coverage the oxidation is initiated by an apparently zeroth-order process of removing 2–3% of the adlayer, followed by the main oxidation process, which is shown to be of the Langmuir–Hinshelwood type with a competitive adsorption of the two reactants, CO and OH. The Langmuir–Hinshelwood kinetics can be modeled using the mean-ﬁeld approximation, which implies fast diffusion of adsorbed CO on the Pt(111) surface under electrochemical conditions. The apparent rate constant for the electrochemical CO oxidation and its potential dependence are determined by a ﬁtting of the experimental data with the mean-ﬁeld model. For sub-saturated CO coverages the overall picture is shown to be more complicated and remains to be understood.

Dynamics of CO at the solid/liquid interface studied by modeling and simulation of CO electro-oxidation on Pt and PtRu electrode

Author: M. T. M. Koper, N. P. Lebedeva and C. G. M. Hermse

Journal: Faraday Discuss., 2002, 121, 301–311

Abstract:

We consider theoretical models for CO monolayer oxidation on stepped Pt single-crystal electrodes and Ru-modiﬁed Pt(111) electrodes. For both systems, our aim is to assess the importance of CO surface diﬀusion in reproducing the experimental chronoamperometry or voltammetry. By comparing the simulations with the experimental chronoamperometric transients for CO oxidation on a series of stepped Pt surfaces, it was concluded that mixing of CO on the Pt(111) terrace is good, implying rapid diﬀusion (N. P. Lebedeva, M. T. M. Koper, J. M. Feliu and R. A. van Santen, J. Phys. Chem. B, submitted). We discuss here a more detailed model in which the CO adsorbed on steps is converted into CO adsorbed on terraces as the oxygen-containing species occupy the steps (as observed experimentally on stepped Pt in UHV), followed by a subsequent oxidation of the latter, to reproduce the observed chronoamperometry on stepped surfaces with a higher step density. On Ru- modiﬁed Pt(111), the experimentally observed splitting of the CO stripping voltammetry into two stripping peaks, may suggest a slow diﬀusion of CO on Pt(111). This apparent contradiction with the conclusions of the experiments on stepped surfaces, is resolved by assuming a weaker CO binding to a Pt atom which has Ru neighbors than to ‘‘bulk’’ Pt(111), in agreement with recent quantum-chemical calculations. This makes the eﬀective diﬀusion from the uncovered Pt(111) surface to the perimeter of the Ru islands, which are considered to be the active sites in CO oxidation electrocatalysis on PtRu surfaces, very slow. Diﬀerent models for the reaction are considered, and discussed in terms of their ability to explain experimental observations.

Role of Crystalline Defects in Electrocatalysis: Mechanism and Kinetics of CO Adlayer Oxidation on Stepped Platinum Electrodes

Author: N. P. Lebedeva, M. T. M. Koper, J. M. Feliu, and R. A. van Santen

Journal: J. Phys. Chem. B 2002, 106, 12938 - 12947

Abstract:

The kinetics of the electrochemical oxidation of a CO adlayer on Pt[n(111) $\times$ (111)] electrodes in 0.5 M $H_2SO_4$ has been studied using chronoamperometry. The objective is to elucidate the effect of the crystalline defects on the rate of the reaction by using a series of stepped surfaces. The reaction kinetics of the main oxidative process can be modeled using the mean-field approximation for the Langmuir - Hinshelwood mechanism, implying fast diffusion of adsorbed CO on the Pt[n(111)$\times$ (111)] surfaces under electrochemical conditions. The apparent rate constant for the electrochemical CO oxidation, determined by a fitting of the experimental data with the mean-field model, is found to be proportional to the step fraction (1/n) for the surfaces with n5, proving steps to be the active sites for the CO adlayer oxidation. An apparent intrinsic rate constant is determined. The potential dependence of the apparent rate constants is found to be structure insensitive with a Tafel slope of ca. 80 mV/dec, suggesting the presence of a slow chemical step in an ECE reaction mechanism.

2003

Simulation of CO electrooxidation on nm-sized supported Pt particles: stripping voltammetry

Author: Vladimir P. Zhdanov, Bengt Kasemo

Journal: Chemical Physics Letters 376 (2003) 220–225

Abstract:

We analyze the kinetics of CO electrooxidation on nm-sized supported Pt crystallites exhibiting (111) and (100) facets. Speciﬁcally, we show how the CO-diﬀusion-mediated communication between these facets may modify voltammograms observed by using CO stripping voltammetry. The results obtained demonstrate that the reaction kinetics for nm-sized particles can be remarkably diﬀerent compared to those expected on the basis of simple superposition of the kinetics corresponding to the inﬁnite faces. These ﬁndings have implications for interpretation of experimental data and for the design of real catalysts and also have important consequences for the eﬀorts to bridge the so-called structure gaps in electrocatalysis.

CO monolayer oxidation at Pt nanoparticles supported on glassy carbon electrodes

Author: O.V. Cherstiouk, P.A. Simonov, V.I. Zaikovskii, E.R. Savinova*

Journal: Journal of Electroanalytical Chemistry 554-555 (2003) 241-251

Abstract:

CO monolayer oxidation on glassy carbon supported 1 / 2 nm Pt nanoparticles is studied using potential sweep and potential step methods. The CO stripping peak on the nanoparticles is significantly shifted to positive potentials vs. the corresponding feature at bulk polycrystalline Pt. Current transients at nanoparticulate electrodes are highly asymmetric with a steep rise, maximum at $\theta_{ CO } \approx$ 0.8- 0.9, and a slow decay following $t^{-1/2}$. The experimental results are compared to the theoretical models of adsorbed CO oxidation described in the literature. A tentative model is suggested to account for the experimental observations, which comprises spatially confined formation of oxygen containing species at active sites, and slow diffusion of CO molecules to the active sites, where they are oxidized. The upper limit of the CO surface diffusion coefficient at Pt nanoparticles is estimated as approximately $4\times 10^{-15} cm^2 s^{-1}$

2004

Size eﬀects on reactivity of Pt nanoparticles in CO monolayer

oxidation: The role of surface mobility

Author: F. Maillard, M. Eikerling, O. V. Cherstiouk, S. Schreier, E. Savinova* and U. Stimming

Journal: Faraday Discuss., 2004, 125, 357–377

Abstract:

In the present paper we study the reactivity of model Pt nanoparticles supported on glassy carbon. The particle size eﬀect is rationalized for CO monolayer oxidation exploring electrochemical methods (stripping voltammetry and chronoamperometry) and modelling. Signiﬁcant size eﬀects are observed in the particle size interval from ca. 1 to 4 nm, including the positive shift of the CO stripping peak with decreasing particle size and a pronounced asymmetry of the current transients at constant potential. The latter go through a maximum at low CO ads conversion and exhibit tailing, which is the longer the smaller the particle size. Neither mean ﬁeld nor nucleation & growth models give a coherent explanation of these experimental ﬁndings. We, therefore, suggest a basic model employing the active site concept. With a number of reasonable simpliﬁcations a full analytical solution is obtained, which allows a straightforward comparison of the theory with the experimental data. A good correspondence between experiment and theory is demonstrated. The model suggests restricted CO ads mobility at Pt nanoparticles below ca. 2 nm size, with the diﬀusion coeﬃcient strongly dependent on the particle size, and indicates a transition towards fast diﬀusion when the particle size exceeds ca. 3 nm. Estimates of relevant kinetic parameters, including diﬀusion coeﬃcient, reaction constant etc. are
obtained and compared to the literature data for extended Pt surfaces.

2005

An NMR Determination of CO Diffusion on Platinum Electrocatalysts

Author: Takeshi Kobayashi, Panakkattu K. Babu, Lajos Gancs, Jong Ho Chung, Eric Oldfield, and Andrzej Wieckowski

Journal: J. AM. CHEM. SOC. 2005,127, 14164 - 14165

Abstract:

Study of the diffusion of small molecules on catalyst surfaces is of broad general interest, and there have been numerous investigations of surface CO diffusion on Pt under ultrahigh vacuum (UHV)
or gas phase conditions. Both diffusion coefficients ($D_{CO}$) as well as activation energies ($E_d $) for diffusion have been measured and are of importance in the context of, among other topics, CO
hydrogenation in fuel synthesis 8 and CO oxidation in heterogeneous catalysis. The latter topic is also of interest in the context of fuel cell catalysis, but there has been no direct experimental determination of $D_{CO}$in an electrochemical environment due to problems associated with the presence of the electrolyte. Fortunately, however, NMR methods are not plagued by these problems, and in this paper, we report the first direct determination of the diffusion constants of CO on Pt in a liquid electrochemical environment, together with the activation energy for diffusion, using the techniques of electrochemical NMR (EC-NMR) and selective spin inversion NMR.

2006

Kinetic Modeling of CO ad Monolayer Oxidation on Carbon-Supported Platinum

Nanoparticles

Author: Bernhard Andreaus, Frederic Maillard, Joanna Kocylo, Elena R. Savinova, and
Michael Eikerling

Journal: J. Phys. Chem. B 2006, 110, 21028 - 21040

Abstract:

We present a theoretical study of CO ad electrooxidation on Pt nanoparticles. Effects of size and surface texture of nanoparticles on the interplay of relevant kinetic processes are investigated. Thereby, strong impacts of particle size on electrocatalytic activities, observed in experiments, are rationalized. Our theoretical approach employs the active site concept to account for the heterogeneous surface of nanoparticles. It, moreover, incorporates finite rates of surface mobility of adsorbed CO. As demonstrated, the model generalizes established mean field or nucleation and growth models. We find very good agreement of our model with chronoamperometric current transients at various particle sizes and electrode potentials (Maillard, F.; Savinova, E. R.; Stimming, U. J. Electroanal. Chem., in press, doi:10.1016/j.jelechem.2006.02.024). The full interplay of on- site reactivity at active sites and low surface mobility of CO ad unfolds on the smallest nanoparticles ( ~2 nm).
In this case, the solution of the model requires kinetic Monte Carlo simulations specifically developed for this problem. For larger nanoparticles ( > 4 nm) the surface mobility of CO ad is high compared to the reaction rate constants, and the kinetic equations can be solved in the limiting case of infinite surface mobility. The analysis provides an insight into the prevailing reaction mechanisms and allows for the estimation of relevant kinetic parameters.

2007

CO monolayer oxidation on Pt nanoparticles: Further insights into the particle size eﬀects

Author: Frederic Maillard, Elena R. Savinova, Ulrich Stimming

Journal: Journal of Electroanalytical Chemistry 599 (2007) 221–232

Abstract:

This paper provides further insights into the particle size eﬀects in CO monolayer oxidation. Strong particle size eﬀects are conﬁrmed in the size range from 1.8 to 5 nm. The discrepancies in the literature concerned with the particle size eﬀects in CO monolayer oxidation are reconciled by exploring the inﬂuence of the experimental conditions on the stripping voltammograms and chronoamperograms. Evidence supporting the contribution of slow non-electrochemical step to the overall mechanism of CO oxidation is presented. The particle size eﬀects in CO monolayer oxidation are attributed to the size-dependent CO ads + OH ads interaction as well as to the size-dependent CO ads surface diﬀusion coeﬃcient.

Coverage Dependence of CO Surface Diffusion on Pt Nanoparticles: An EC-NMR Study

Author: Takeshi Kobayashi, Panakkattu K. Babu, Jong Ho Chung, Eric Oldfield, and Andrzej Wieckowski

Journal: J. Phys. Chem. C 2007, 111, 7078 - 7083

Abstract:

We have studied the effects of CO surface coverage on the diffusion rates of CO adsorbed on commercial Pt-black in sulfuric acid media by using $^{13}C$ electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy in the temperature range 253 - 293 K. The temperature range chosen for these measurements was such that the electrolyte is in a liquid-like and liquid environment. For CO coverage between $\theta$ = 1.0 and 0.36, the CO diffusion coefficients ($D_{CO}$ ) follow a typical Arrhenius behavior and both the activation energies (E d ) as well as the pre-exponential factors ($D^0_{CO}$ ) show CO coverage dependence. For partially CO covered samples, E d decreases linearly with increasing CO coverage, indicating that the repulsive CO - CO interactions exert a stronger influence on the coverage dependence of the activation energy than does the nature of the CO adlayer structure. On the other hand, DCO0shows an exponential decrease with increasing CO coverage, consistent with the free site hopping model [Gomer, R. Rep. Prog. Phys. 1990, 53, 917] as the major mechanism for surface diffusion of CO at partial coverages, unlike the situation found with a fully CO covered surface [Kobayashi et al., J. Am. Chem. Soc., 2005, 127, 14164]. Overall, these results are of interest
since they improve our understanding of the surface dynamics of molecules at electrochemical interfaces, and may help facilitate better control of fuel cell reactions in which the presence of surface CO plays a crucial role in controlling electrocatalytic reaction rates.

Active site model for CO adlayer electrooxidation on nanoparticle catalysts

Author: Bernhard Andreaus, Michael Eikerling *

Journal: Journal of Electroanalytical Chemistry 607 (2007) 121–132

Abstract:

We present a two-state model for CO electrooxidation on catalyst nanoparticles. It exploits the active site concepts in order to describe the eﬀects of the heterogeneous surface structure on the catalytic activity of nanoparticle systems. In this approach, the apparent reactivity results from the interplay between kinetic processes that occur on active sites and surface transport of adsorbed reactants from inactive towards active sites. It is demonstrated that this model is a generalization of well-known mean ﬁeld (MF) and nucleation and growth models. Kinetic Monte Carlo (kMC) simulations speciﬁcally developed for this problem were employed for establishing the relevance of the diﬀerent model parameters for the shape of chronoamperometric and linear sweep current transients. In the limit of fast CO ad surface mobility, the corresponding MF approximation with active sites and its analytical solutions for limiting cases are presented. The comparison of the general kMC solution with the MF approximation reveals major applicability limits of the MF approach for heterogeneous surface models. Although the current work concentrates on the speciﬁc case of CO ad adlayer electrooxidation, the model is readily applicable for other reactions where surface heterogeneity is likely to play an important role.

2008

2009

2010

CO electrooxidation on carbon supported platinum nanoparticles: Effect of aggregation

Author: Ana López-Cudero, José Solla-Gullón, Enrique Herrero * , Antonio Aldaz, Juan M. Feliu

Journal: Journal of Electroanalytical Chemistry 644 (2010) 117–126

Abstract:

CO oxidation on 2.2 ± 0.5 nm platinum nanoparticles deposited on carbon with different platinum loadings (from 10% to 50%) has been studied and compared to the behavior of unsupported platinum nanoparticles. The different samples contain always nanoparticles of the same size and surface structure, and therefore the only characterization parameter that changes is the loading. TEM images and the voltammetric behavior in the supporting electrolyte demonstrate that the increasing loading leads to nanoparticle agglomeration, but the nanoparticles retain most of their individual physical identity and significant loss of active surface area does not take place. For the CO oxidation, the voltammograms show a single peak at ca. 0.8 V for the samples with low loading. As the loading increases, a second peak at lower potentials starts to develop and for the 50% loading sample and the unsupported nanoparticles, the peak is well resolved. Chronoamperometric transients also show the same behavior. The analysis of the results suggests that the peak at lower potentials (at shorter times in the transients) is associated to CO inter-particle oxidation, that is, OH and CO species that participate in the process are adsorbed in two different but close nanoparticles. The kinetic analysis of the two processes show different Tafel slopes, which indicates that the adsorption behavior of the OH species involved in the two peaks are different.

2011

2012

New Insights into the Mechanism and Kinetics of Adsorbed CO Electrooxidation on Platinum: Online Mass Spectrometry and Kinetic Monte Carlo Simulation Studies

Author: Hongsen Wang, Zenonas Jusys, R. Jürgen Behm, and Héctor D. Abruña* ,

Journal: J. Phys. Chem. C 2012, 116, 11040 − 11053

Abstract:

The electrooxidation of saturated CO adlayers on Pt/Vulcan and polycrystalline Pt has been studied by potential step techniques combined with diﬀerential electrochemical mass spectrometry (DEMS) and kinetic Monte Carlo (KMC) simulations. DEMS was used to selectively monitor the CO ad electrooxidation, via the CO2 formation rate, without interference from the pseudocapacitive double-layer charging and electrode surface oxidation, while the KMC simulations were employed to understand the mechanism and kinetics of CO ad electrooxidation at the molecular level. Our DEMS data show that the current transients of CO ad electrooxidation on polycrystalline Pt and Pt/Vulcan exhibit an initial spike immediately after the potential step, followed by a slow current decay and ﬁnally a broad main peak. The temporal evolution of the transients depends strongly on the oxidation potential applied, resulting in the overlap of the initial spike and the main peak for high potentials. A model is proposed to account for the observed phenomena. On the basis of this model, we developed a kinetic Monte Carlo simulation code speciﬁc to the electrooxidation of adsorbed CO on Pt. The simulations reproduce the experimental data very well, conﬁrming the robustness of our model.

Studies Diffusion of adsorbed CO on platinum (100) and (111) oriented nanosurfaces

Author: C. Coutanceau , P. Urchaga, S. Baranton

Journal: Electrochemistry Communications 22 (2012) 109–112

Abstract:

Platinum nanocubes exhibiting oriented surface domains were used to study the electrooxidation of chemisorbed CO (COchem. ). The amount of oriented surface nanodomains was characterized by hydrogen underpotential deposition (Hupd ), bismuth and germanium spontaneous adsorption/oxidation. The surface diffusion of CO chem toward low coordination sites, where oxidation is expected to take place, is more rapid on (111) than on (100) nanodomains and no diffusion of CO from (100) domains toward (111) nanodomains seems to occur.

2013

Changes in COchem oxidative stripping activity induced by reconstruction of Pt (111) and (100) surface nanodomains

Author: P. Urchaga, S.Baranton, C. Coutanceau*

Journal: Electrochimica Acta 92 (2013) 438–445

Abstract:

The H-upd and COchem oxidative stripping on preferentially oriented Pt nanoparticles exhibiting clean surfaces and different ratios of (1 0 0) and (1 1 1) surface domains are investigated in 0.5 M H-2 SO4 aqueous electrolyte. Shorter range order (1 0 0) and (1 1 1) surface domains can be created in the early stage of the progressive surface reconstruction of the nanoparticles by cycling the electrode to an upper potential E-up = 1.2V vs. RHE. By increasing the number of cycles, the reconstruction of the Pt nanoparticle surface leads to the disappearance of (1 00) and (1 1 1) ordered surface domains. Changes in the related oxidative stripping voltammograms (OSV) recorded on the reconstructed nanoparticle surfaces as a function of the number of potential cycles at 1.2V confirm that the COchem oxidative feature from 0.3 to 0.8V is composed of different contributions which are related to different surface microstructures and different COchem oxidation mechanisms. Detailed analysis of the charge difference between the signal recorded on reconstructed nanoparticles and that recorded on fresh catalysts allows moreover evidencing a surface domain size effect.

2014

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