The electro-oxidation of carbon monoxide on ruthenium modified Pt()

Davies, Julie Olivia; Hayden, Brian E.; Pegg, D. J.; Rendall, Michael E.

doi:10.1016/s0039-6028(01)01562-x

Cited by 114 publications

(133 citation statements)

References 29 publications

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“…Instead there must be different rates for the formation of OH ads on the active sites, such that the formation of OH ads at the active sites is faster than on the plateaux. The reaction can then best be explained by the OH ads 105 spill over mechanism suggested by Hayden et al for PtRu 63 forming a hydrogen bonded water-OH ads network. This can also explain the current decay seen before the main CO ads oxidation peak.…”

Section: Co Reorganisation Compared To Oh Ads Redistributionmentioning

confidence: 99%

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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Section: Co Reorganisation Compared To Oh Ads Redistributionmentioning

confidence: 99%

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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“…also at "lower potentials" on Ru domains, the overall reaction is: 23 Ru∝-(CO) + Ruγ-(H2O) → CO2 + (∝ + γ)Ru + 2H + + 2e - (2) On the other hand, no matter if CO is adsorbed on step or terrace sites, the oxidation of COads on Pt sites far from Ruγ-(H2O) has been conceived to occur only at "higher" electrode potentials, 23,24 which in such case would be the oxidation of CO on {111}…”

Section: Introductionmentioning

confidence: 99%

“…Under this condition, the overall reaction should be formally written as: 23,24 PtT-(CO) + PtT-(H2O) → CO2 + 2PtT + 2H + + 2e -…”

Section: Introductionmentioning

confidence: 99%

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Disentangling Catalytic Activity at Terrace and Step Sites on Selectively Ru-Modified Well-Ordered Pt Surfaces Probed by CO Electro-oxidation

et al. 2016

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In heterogeneous (electro)catalysis, the overall catalytic output results from responses of surface sites with different catalytic activities, and their discrimination in terms of what specific site is responsible for a given activity is not an easy task. Here, we use the electrooxidation of CO as a probe reaction to access the catalytic activity of different sites on high Miller index stepped Pt surfaces with their {110} steps selectively modified by Ru at different coverage. Data from in situ FTIR spectroscopy and cyclic voltammetry evidence that Ru deposited on {110} steps modifies the surface in a non-trivial way, only favoring the electrocatalytic oxidation of CO over {111} terraces. Moreover, these {111} terraces become catalytically active throughout a large potential window. On the other hand, after the deposition of Ru on {110} steps, the partial oxidation of a CO adlayer (by stripping voltammetry and in situ FTIR potential steps) show that those {110} steps that remain free of Ru seem to be not influenced by the presence of this metal. As a result, the remaining CO adlayer is oxidized on these Ru-free {110} steps at potentials identical to those observed in steps of pure stepped Pt surfaces (in absence of Ru). Firstly, these This is a previous version of the article published in ACS Catalysis. 2016, 6(5): 2997-3007. doi:10.1021/acscatal.6b00439 2 findings suggest that COads behaves as a motionless species during its oxidation. Secondly, they evidence that the impact caused by the presence of Ru in the catalytic activity of Pt(s)-[(n-1)(111)×(110)] stepped surfaces depends on the crystallographic orientation of Pt sites. These results help us to shed new light about the role of Ru in the mechanism of oxidation of CO and allow a deeper understanding regarding the CO tolerance in Pt-Ru catalysts.

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“…22 The properties of the mixed H 2 O -OH phase on Ru͑0001͒ could affect possible OH spillover from Ru to neighboring Pt sites. 23 In this paper, we describe the results of a study using core-level spectroscopies, x-ray photoelectron spectroscopy ͑XPS͒, and x-ray absorption spectroscopy ͑XAS͒ to identify the species present on the surface and their orientation, and scanning tunneling microscopy ͑STM͒ to determine the structures formed by water adsorption on Ru͑0001͒ after heating above 140 K. We found that as predicted, H 2 O and OH are produced and that they form elongated stripes with an internal honeycomb structure. Geometrical models based on STM images were used as starting points and optimized by density functional theory ͑DFT͒ calculations.…”

Section: Introductionmentioning

confidence: 99%

The structure of mixed H2O–OH monolayer films on Ru(0001)

Tatarkhanov

Фомин

Salmerón

et al. 2008

The Journal of Chemical Physics

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Scanning tunneling microscopy ͑STM͒ and x-ray absorption spectroscopy ͑XAS͒ have been used to study the structures produced by water on Ru͑0001͒ at temperatures above 140 K. It was found that while undissociated water layers are metastable below 140 K, heating above this temperature produces drastic transformations, whereby a fraction of the water molecules partially dissociate and form mixed H 2 O -OH structures. X-ray photoelectron spectroscopy and XAS revealed the presence of hydroxyl groups with their O-H bond essentially parallel to the surface. STM images show that the mixed H 2 O -OH structures consist of long narrow stripes aligned with the three crystallographic directions perpendicular to the close-packed atomic rows of the Ru͑0001͒ substrate. The internal structure of the stripes is a honeycomb network of H-bonded water and hydroxyl species. We found that the metastable low temperature molecular phase can also be converted to a mixed H 2 O-OH phase through excitation by the tunneling electrons when their energy is 0.5 eV or higher above the Fermi level. Structural models based on the STM images were used for density functional theory optimizations of the stripe geometry. The optimized geometry was then utilized to calculate STM images for comparison with the experiment.

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The electro-oxidation of carbon monoxide on ruthenium modified Pt()

Cited by 114 publications

References 29 publications

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

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

Disentangling Catalytic Activity at Terrace and Step Sites on Selectively Ru-Modified Well-Ordered Pt Surfaces Probed by CO Electro-oxidation

The structure of mixed H2O–OH monolayer films on Ru(0001)

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