Calculating the coverage of saturated and sub-saturated layers of carbon monoxide adsorbed onto platinum

Offer, Gregory J.; Kucernak, Anthony

doi:10.1016/j.jelechem.2007.10.028

Cited by 10 publications

(15 citation statements)

References 31 publications

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“…It is likely that CO itself acts as an inhibitor of the COOR, as it is highly adsorbed on the metallic surface, meanwhile, the coverage of OH ad is almost negligible. It should be noticed that the value obtained for Pt (q e CO =0.64) is near the saturation coverage (θ CO = 0.68) found for Pt(111) [43]. The corresponding value for ruthenium was q e CO ≅0.25, indicating a lower CO adsorption capability than platinum.…”

Section: Evaluation Of the Kinetic Parametersmentioning

confidence: 61%

Resolution of the mechanism of CO electrooxidation on steady state and evaluation of the kinetic parameters for Pt and Ru electrodes

Rau

Chialvo

2011

J Solid State Electrochem

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The carbon monoxide oxidation reaction (COOR) was studied on steady-state conditions by chronoamperometry on polycrystalline smooth platinum and ruthenium rotating disc electrodes in CO-saturated acid solution. The chronoamperometric response did not show current oscillations and therefore the current density (j) vs. overpotential (η) curves on steady state could be obtained. In order to interpret these results, kinetic expressions were derived starting from the mechanism proposed by S. Gilman, which considers two adsorbed reaction intermediates, carbon monoxide (CO ad ) and hydroxyl (OH ad ). Analytical expressions as a function of overpotential for the current density, the surface coverage of the adsorbed species (θ CO and θ OH ) and the CO and CO 2 pressures at the electrode surface on steady state were obtained. This set of equations was used for the correlation of the experimental polarization curves and the evaluation of the corresponding kinetic parameters. From these values, the dependences of the surface coverage of the adsorbed intermediates on overpotential were simulated, as well as those of the partial pressure of CO and CO 2 . Thus, it was demonstrated that the Gilman's mechanism accurately describes the experimental results on steady state of the COOR on these metals.

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Section: Evaluation Of the Kinetic Parametersmentioning

confidence: 61%

Resolution of the mechanism of CO electrooxidation on steady state and evaluation of the kinetic parameters for Pt and Ru electrodes

Rau

Chialvo

2011

J Solid State Electrochem

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“…These were positioned in an impinging jet flow cell configuration 57 as described previously 58,59 with 25 modifications to ensure uniform access similar to those described by Melville et al 60 . With this setup it is possible to change the electrolyte bathing the electrode (e.g.…”

Section: Methodsmentioning

confidence: 99%

“…Partial adlayers were produced either by exposing the electrode to CO for a much shorter time, 0.1-2s (partial 40 admission), or by taking a CO saturated electrode and pulsing the potential to 800 mV for a defined period (<1s) before returning it to the admission potential. In both cases, the coverage was calculated by measuring the charge required to remove the remaining CO ads in N 2 saturated electrolyte whilst 45 at the same time correcting for double layer and anion adsorption effects 59 . Coverages are reported as a fraction of the saturated CO ads adlayer produced under identical conditions.…”

Section: Methodsmentioning

confidence: 99%

“…This is in good agreement with similar experiments in the literature for Pt(111) electrodes, for which the maximum coverage in CO-free 0.1 mol dm -3 H 2 SO 4 was 55 shown to be 0.68 42 . During CO ads oxidation experiments it is also important to correct for any residual oxygen reduction 59 . We therefore took stringent measures to exclude oxygen from these experiments, and measured a background oxygen 65 concentration in the electrolyte of 4.5x10 -8 mol dm -3 .…”

Section: Methodsmentioning

confidence: 99%

“…We have developed this approach in order to assess the CO coverage as a function of time during the CO oxidation reaction. In this approach, we make 5 corrections for changes in double layer capacitance and anion absorption to produce a more accurate measure of CO coverage 59 . Provided in Figure 4 is a plot of the CO oxidation transient seen at 0.70 V along with the measured CO coverage as a function of time.…”

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The role of adsorbed hydroxyl species in the electrocatalytic carbon monoxide oxidation reaction on platinum

Kucernak

Offer

2008

Phys. Chem. Chem. Phys.

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The assumption that "OH ads " or other oxygen containing species is formed on polycrystalline or nanoparticulate platinum through a fast and reversible process at relatively low potentials is often made. In this paper we discuss the implications of this assumption and the difficulty in reconciling it with experimental phenomena. We show how presenting chrono-amperometric transients as log-10 log plots for potentials steps in the presence and absence of an adlayer of carbon monoxide o n polycrystalline platinum is particularly useful in understanding the time evolution of the CO oxidation reaction. When using log-log plots a clear power law decay can be observed in the transients both in the presence and absence of an adlayer of carbon monoxide. We explain this as an extension of current theory, such that the rate determining step in both cases is the formation of 15 a hydrogen bonded water-OH ads network, strongly influenced by anions, and that CO ads oxidation occurs, at least in part by the diffusion of OH ads through this network. We hypothesize that, at low potentials the formation of OH ads at active sites is fast and reversible but that transport of OH ads away from those sites may be rate limiting. The assumption that overall OH ads formation on platinum is fast and reversible is therefore highly dependent upon the platinum surface and th e 20 experimental conditions and it may not be appropriate for polycrystalline surfaces in sulphuric acid. Therefore, although the formation of OH ads on platinum in the absence of strongly adsorbing anions on 'ideal' surfaces is almost certainly fast and reversible, on realistic fuel cell relevant surfaces under non-ideal conditions this assumption cannot be made, and instead the formation of an OH ads adlayer may be somewhat slow and is associated with the formation of hydrogen bonded 25 water-OH ads networks on the surface. We expect this to be a more realistic description for what occurs during CO ads oxidation on fuel cell relevant catalysts which are highly heterogeneous and which have a highly defective surface. IntroductionThe formation of oxides on platinum surfaces at high potentials is relatively well studied yet contentious. The role of the species typically called "OH ads " in the surface catalysis of platinum catalysts is crucial in understanding a large 5 number of reactions, of which the most common example is the carbon monoxide oxidation reaction (COOR). The nature of this species is somewhat controversial, although Anderson has recently shown through theoretical ab initio charge selfconsistent methods that OH ads should form on a Pt surface at a 10 potential of about 0.6 V. Several investigators claim that OH ads is the species responsible for reacting with adsorbed CO ads , and that this is a chemical Langmuir-Hinshelwood (L-H) reaction [1][2][3][4][5][6][7] . The lowest potentials at which the COOR has been reported is 150 mV for carbon supported platinum 8 , 200 15 mV for a porous platinum electrode 9 and for polycrystalline platinum 10 , and ...

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Formic Acid Electrooxidation on Platinum, Resolution of the Kinetic Mechanism in Steady State and Evaluation of the Kinetic Constants

2018

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A kinetic mechanism recently proposed for the formic acid oxidation (FAO) on platinum in acid solutions was analytically solved in order to verify its capability to correlate experimental measurements in steady state conditions. It involves three adsorbed reaction intermediates (COad, HCOOad, OHad) and two reaction pathways. The derived kinetic equations enabled the fitting of the experimental current‐potential curves at three different formic acid concentrations, as well as the evaluation of the corresponding kinetic constants of the elementary steps involved in the mechanism. An expression for the variation of the COad surface coverage on potential was included in the calculations, obtained from measurements of the oxidation charges by voltammetric stripping. Finally, the dependences of the surface coverages of OHad and HCOOad on potential could be simulated, which are consistent with results obtained by other authors through spectroscopic techniques.

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Calculating the coverage of saturated and sub-saturated layers of carbon monoxide adsorbed onto platinum

Cited by 10 publications

References 31 publications

Resolution of the mechanism of CO electrooxidation on steady state and evaluation of the kinetic parameters for Pt and Ru electrodes

Resolution of the mechanism of CO electrooxidation on steady state and evaluation of the kinetic parameters for Pt and Ru electrodes

The role of adsorbed hydroxyl species in the electrocatalytic carbon monoxide oxidation reaction on platinum

Formic Acid Electrooxidation on Platinum, Resolution of the Kinetic Mechanism in Steady State and Evaluation of the Kinetic Constants

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