Theoretical aspects of some prototypical fuel cell reactions

Leiva, E.P.M.; Sánchez, Cristián G.

doi:10.1002/9780470974001.f202012

Cited by 2 publications

(3 citation statements)

References 60 publications

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“…Alcohol electrooxidations may also generate homogeneous species under similar conditions. 60 Although these are far more complex mechanisms than the reactions in this work, some electrocatalytic systems such as the oxidation of formic acid, 61 hydrogen 62 or hydrogen peroxide 63 may be treatable by the SI-SECM mode.…”

Section: Comparison Of Chemical and Electrochemical Routesmentioning

confidence: 92%

“…This includes complex reaction mechanisms, such as the oxygen reduction reaction, where oxidizable species, e.g., hydrogen peroxide, , might be released at potentials where submonolayers of oxide are present. Alcohol electrooxidations may also generate homogeneous species under similar conditions . Although these are far more complex mechanisms than the reactions in this work, some electrocatalytic systems such as the oxidation of formic acid, hydrogen or hydrogen peroxide may be treatable by the SI-SECM mode.…”

Section: Comparison Of Chemical and Electrochemical Routesmentioning

confidence: 93%

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Reaction of Various Reductants with Oxide Films on Pt Electrodes As Studied by the Surface Interrogation Mode of Scanning Electrochemical Microscopy (SI-SECM): Possible Validity of a Marcus Relationship

2010

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The surface interrogation mode of scanning electrochemical microscopy (SI-SECM), an in situ method for the quantification of adsorbed intermediates at electrodes at open circuit, was used to evaluate the rate of reaction of four redox mediators of different reducing power (methyl viologen+ > Ru(NH3)6 2+ > Fe(II)[EDTA]2− > Fe(CN)6 4−) with electrogenerated platinum oxides (PtO x ) at different pHs. The rate constant determined by SI-SECM was sensitive to the nature of the Pt oxide formed at different potentials. A simplified model with finite element method simulation was used to fit the SI-SECM experimental response. The extraction of kinetic constants and their comparison to the potential (reducing power) of the mediator yielded a Marcus-theory type relationship. Although these are clearly not outer sphere reactions, if subjected to the Marcus theory treatment, one can extract an estimated value of λ = 1.3 ± 0.3 eV for the reduction of “place exchanged” oxide, which forms with oxide coverage values larger than 0.5 (as PtO). Steady state feedback experiments were also conducted in which the reduced form of the mediators was oxidized at Pt with different oxide coverage, i.e., over a wide range of potentials. A comparison of SI-SECM kinetic analysis with the Pt substrate at open circuit to the case where an electrode bias is applied indicates that for Fe(II)[EDTA]2−, the feedback current follows the oxide coverage at the Pt substrate. We suggest that thin layers of oxide provide a chemical route in which the oxide mediates oxidation of the reduced electrogenerated species; this route is governed by the reactivity of the different species of oxide formed at the electrode and not necessarily by other effects, such as direct electron tunneling through the oxide layer.

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Section: Comparison Of Chemical and Electrochemical Routesmentioning

confidence: 92%

Section: Comparison Of Chemical and Electrochemical Routesmentioning

confidence: 93%

Reaction of Various Reductants with Oxide Films on Pt Electrodes As Studied by the Surface Interrogation Mode of Scanning Electrochemical Microscopy (SI-SECM): Possible Validity of a Marcus Relationship

2010

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“…For CO electrooxidation, similar ideas apply, but with some differences. At lower potentials, the barrier for CO 2 formation rather than surface blocking by CO ad is rate limiting [121,123,138]. At higher potentials, the surface is covered by a OH ad /O ad adlayer rather than being essentially adsorbate free as for CO oxidation in the highrate branch in gas phase (see also the simulations for CO electrooxidation on a Pt (111) electrode [54,139,140]).…”

Section: Co Oxidation On Bimetallic Ptru Electrodesgeneral Aspectsmentioning

confidence: 99%

The Effect of Structurally Well‐Defined Pt Modification on the Electrochemical and Electrocatalytic Properties of Ru(0001) Electrodes

Hoster

Behm

2008

Fuel Cell Catalysis

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The effects of structurally well defined Pt modifications of Ru(0001) single crystal electrodes on their electrochemical behavior and their CO oxidation properties are identified and quantitatively related to the structural characteristics. Pure Ru(0001) and the bimetallic surfaces, including Ru(0001) surfaces covered by Pt monolayer islands, by a complete Pt monolayer or by monolayer PtRu surface alloys of varying composition, were prepared under ultrahigh vacuum (UHV) conditions and characterized quantitatively by high resolution scanning tunneling microscopy (STM). The electrochemical/-catalytic properties were determined under defined electrolyte flow conditions in an electrochemical flow cell attached to the UHV system. While on pure Ru(0001) the overlapping stability ranges of underpotential deposited hydrogen (H upd ) or CO ad on the one hand and OH ad /O ad on the other hand hinder the adsorption of the respective adsorbates, Pt promotes and catalyzes the potential dependent formation and removal of adlayers. Monolayer Pt islands and pure Pt or mixed Pt x Ru 1-x (x = 1,2) adsorption ensembles provide additional channels for the adsorption (H upd  OH ad exchange, CO ad  OH ad exchange) and reaction (CO oxidation) of the respective second adsorbate on the adsorbate covered Ru(0001) areas. Quantitative correlation between the surface atom distribution and the electrochemical characteristics shows that the uptake/desorption of H upd is correlated with the abundance of threefold coordinated Ru sites, while on mixed Ru n Pt 3-n sites, H upd and OH ad adsorption is much weaker and shifted to lower and higher potentials, respectively. For both types of model surfaces, the availability of Pt sites leads to a substantially higher activity for the electrooxidation of CO as compared to bare Ru(0001), with significant differences between the behavior of surface alloys and Pt island modified Ru(0001). The different effects contributing to the modified adsorption/reaction behavior and the relative contributions are identified and discussed comparing with results obtained on Ru and PtRu electrodes reported previously and on bimetallic PtRu surfaces under UHV conditions.

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Theoretical aspects of some prototypical fuel cell reactions

Cited by 2 publications

References 60 publications

Reaction of Various Reductants with Oxide Films on Pt Electrodes As Studied by the Surface Interrogation Mode of Scanning Electrochemical Microscopy (SI-SECM): Possible Validity of a Marcus Relationship

Reaction of Various Reductants with Oxide Films on Pt Electrodes As Studied by the Surface Interrogation Mode of Scanning Electrochemical Microscopy (SI-SECM): Possible Validity of a Marcus Relationship

The Effect of Structurally Well‐Defined Pt Modification on the Electrochemical and Electrocatalytic Properties of Ru(0001) Electrodes

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