Thermodynamic Analysis of the Temperature Dependence of OH Adsorption on Pt(111) and Pt(100) Electrodes in Acidic Media in the Absence of Specific Anion Adsorption

Climent, Vı́ctor; Gómez, Roberto; Orts, J.M.; Feliu, Juan M.

doi:10.1021/jp054948x

Cited by 146 publications

(185 citation statements)

References 37 publications

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“…In detail, the contributions in the range between 0.3-0.5 V can be clearly related to the presence of (100) sites due to OH adsorption on the (100) well-ordered domains as proposed for the single crystal electrodes with this orientation. 37,38 Thus, the voltammograms of the PtNP cubic , and also that of the PtNP trunc , although that in a lesser extent, Similar behavior has been observed in the voltammetry of Pt(110) single crystal electrodes and its vicinal surfaces in perchloric acid and points out the complexity of this adsorption state, which is the least studied among the platinum single crystal basal planes. [39][40][41] Finally, in this solution, the (111) bidimensional states cannot be identified, as they are shifted towards high potentials and overlap with oxygenated species adsorption at (100) and (110) .…”

Section: Voltammetric Characterization Of the Nanoparticlessupporting

confidence: 67%

Electrochemical Characterization of Shape-Controlled Pt Nanoparticles in Different Supporting Electrolytes

et al. 2012

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ABSTRACT.The voltammetric profile of preferentially shaped platinum nanoparticles has been used to analyze of the different sites present on the surface. This analysis has been made, for the first time, in NaOH solutions and revisited in sulfuric and perchloric acid media. The comparison with the voltammetric profiles of the model surfaces, i.e., single crystal electrodes, allows assigning the different signals appearing in the voltammograms of the nanoparticle to specific sites on the surface. A good correlation between the shape of the nanoparticle determined by TEM and the voltammetric profile is obtained. For the nanoparticles characterized in alkaline media, the adsorbed species on the surface has been characterized and three major regions can be identified. Below 0.2 V, the major contribution is due to hydrogen adsorption whereas above 0.6 V, adsorbed OH is the main species on the surface. In between both values, the signals are due to competitive adsorption/desorption process of OH/H. New criteria for determining the active area in NaOH solutions has been proposed. In this medium, the total charge density measured between 0.06 and 0.90V stands for 390 µC cm 2 have been characterized, the behavior of the nanoparticles towards CO oxidation has been analyzed.It has been found that the nanoparticle edges are key sites in the oxidation of CO.

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Section: Voltammetric Characterization Of the Nanoparticlessupporting

confidence: 67%

Electrochemical Characterization of Shape-Controlled Pt Nanoparticles in Different Supporting Electrolytes

et al. 2012

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“…In recent years, it has become well-established that platinum electrodes immersed in acidic or basic aqueous electrolytes react with water when the potential is increased from the edge of the hydrogen under potential deposition potential region,~0.35 V on the reversible hydrogen electrode scale, which will be used in this paper, to around 0.6 V. At 0.6 V, water begins to be oxidized to OH(ads), and at around 0.8 V OH(ads), it begins to be oxidized to O(ads) [1][2][3]. Even before the careful work in these recent references, it was well-known that water oxidizes on platinum cathodes in acid or base as the potential is increased out of the double-layer region, beginning around 0.6 V. It has been long assumed that these adsorbates control the kinetics and current densities of oxygen cathodes by blocking active adsorption sites for O 2 .…”

Section: Volcano Plots and Electrode Surface Site Blockingmentioning

confidence: 99%

Volcano Plots and Effective Reversible Potentials for Oxygen Electroreduction

Anderson

2012

Electrocatalysis

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It has recently been found that there are ideal values for O, OH, and OOH Gibbs adsorption bond strengths to a catalyst that will allow each electron transfer step to have 1.23 V for its reversible potential. In the case of Pt(111), the bond strengths are too high by~0.9 eV for O and~0.7 eV for OH and too small by~0.4 eV for OOH. These discrepancies result in OOH(ads) dissociation to O (ads)+OH(ads) being~1.2 eV exergonic. The lost Gibbs energy causes the reversible potential for the four-electron reduction on Pt(111) to have a value of~0.9 V, which is called the effective reversible potential. Volcano plots of activity measured at around 0.9 V depend on the adsorption energies scaling, that is, if one increases they all increase, or if one decreases they all decrease. Volcano plots have been drawn for several transition metal catalysts and platinum and platinum alloy catalysts in the pioneering work of Appleby, Mukerjee, and Adzic and have been seen by many other workers. Although they allow grading the active catalysts in the high overpotential region where reduction current flows, they do not point the direction to better catalysts that will operate at potentials approaching 1.23 V. The search should be for new catalysts which with the right balance of OOH, O, and OH adsorption energies.

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“…In contrast, a number of studies of the formation of oxides on 30 platinum assume that the onset of formation of oxygen containing species on polycrystalline or nanostructured Pt does not occur until above 700 mV [18][19][20][21][22][23] and some have even claimed that it has been 'unambiguously proven' 21 that the initial oxide growth on Pt leads directly to the formation of 35 PtO 20,21,23 , contrary to others who suggest it is via the formation of OH ads 22 . This is despite the fact that it is known that the formation of OH ads on Pt(111) and Pt(100) takes place in wide potential regions positive to the potential of zero charge of these surfaces but significantly less positive than the 40 threshold for the formation of the surface oxide phases 24 . Therefore, there seems to be a problem in rationalising between the need for oxygen containing species on polycrystalline or nanostructured Pt at low potentials (otherwise known reactions could not proceed), and the belief 45 that the oxide formation region on these Pt surfaces only begins at 700mV, and even the belief that OH ads is never present.…”

Section: Introductionmentioning

confidence: 95%

“…However the mean field approximation is misleading as it assumes that OH ads will be formed spontaneously upon the adsorption of water, which is unlikely except at very high potentials (>800 mV). In addition the role of the adsorption of 30 water and anions cannot be overlooked 71 , and their role in forming or suppressing the formation of a hydrogen bonded water-OH ads network appears to be crucial in understanding the CO ads oxidation process 24,[65][66][67][68][69][70][71] . Both Bergelin et al 80 and Koper et al 53 invoked a 35 reorganisation mechanism to explain the initial current plateau that they observed, where the initial oxidation of CO ads is accompanied by a reorganisation or redistribution of the adlayer such that there is no effective freeing of sites, and as the oxidation proceeds the ability of this reorganisation 40 mechanism to compensate for the removal of CO ads decreases due to the CO ads adlayer becoming more stable.…”

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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Thermodynamic Analysis of the Temperature Dependence of OH Adsorption on Pt(111) and Pt(100) Electrodes in Acidic Media in the Absence of Specific Anion Adsorption

Cited by 146 publications

References 37 publications

Electrochemical Characterization of Shape-Controlled Pt Nanoparticles in Different Supporting Electrolytes

Electrochemical Characterization of Shape-Controlled Pt Nanoparticles in Different Supporting Electrolytes

Volcano Plots and Effective Reversible Potentials for Oxygen Electroreduction

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

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