Electrochemistry of Hydrous Oxide Films

Burke, L.D.; Lyons, Michael E. G.

doi:10.1007/978-1-4613-1791-3_4

Cited by 65 publications

(33 citation statements)

References 195 publications

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“…This is why further modelling was based on the assumption that three different forms of adsorbed oxygen can coexist on platinum: hydroxyl, oxygen adatoms and subsurface oxygen. Three different types of surface oxygen were indeed reported by Vishnevskii and Savchenko (1990) and Kislyuk et al (1981) for platinum in contact with gas and by Burke and Lyons (1986) for platinum in contact with oxygen dissolved in water. In this final model the dissolved oxygen is considered to adsorb on the surface in the hydroxyl form as is generally accepted in electrochemistry.…”

Section: Model Constructionmentioning

confidence: 60%

Kinetic modelling of multiple steady-states for the oxidation of aqueous ethanol with oxygen on a carbon supported platinum catalyst

Jelemenský

Kuster

Marin

1996

Chemical Engineering Science

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-Multiple steady-states data were used for the construction of a kinetic model for the oxidation of aqueous ethanol with oxygen on a carbon supported platinum catalyst. A model, incorporating reversible creation of oxygen adatoms on the catalyst surface from surface hydroxyl as well as reversible formation of subsurface oxygen from oxygen adatoms, couid describe quantitatively all the observations. It was essential that the reaction rate coefficients for the formation of atomic and subsurface oxygen strongly depend on the corresponding degrees of coverage introducing positive and negative feedback features. INTRODUCTIONThe selective catalytic oxidation of alcohols and carbohydrates with dioxygen has received considerable attention in the recent past ( Mallat and Balker, 1994). Supported noble metals are the favourite catalysts. The reaction can be performed selectively at relatively mild conditions i.e. in aqueous media at a pH around 7 and at temperatures around 300 K.The major bottleneck for the commercial application consists in so-called catalyst deactivation. Several causes have been put forward for the latter ( Schuurman et al., 1992b;Mallat and Baiker, 1994;Vleeming et al., 1994). There is evidence for well known deactivation mechanisms such as metal dissolution and/or sintering (Schuurman et al., 1992b) and coverage of active sites by side or intermediate products of the desired reaction ( Mallat and Baiker, 1994). A phenomenon more specific to the considered type of reactions has also been suggested. It is referred to as overoxidation of the metal surface. The term stems from the observation that the loss in activity occurs in parallel with an increase of the catalyst potential (Vleeming et al., 1994).Recently steady-state multiplicity of the selective oxidation rate of aqueous ethanol over a platinum on carbon catalyst has been reported (Jelemensky et al., 1995). Up to three stable steady-state rates could be established over a feed ethanol concentration range from 300 to 400 mol m 3 in a continuous flow stirred tank reactor. The upper steady-state was reached by a reductive start-up procedure while the two lower steady-states required an oxidative start-up. The existence of steady-state multiplicity is believed to be rather common for selective oxidations and hydrogenations by noble metals in the liquid phase.Bifurcation phenomena, such as multiple steady-states (R~zon and Schmitz,1987;Zhdanov and Kasemo, 1994), autonomous oscillations ( Gray and Scott, 1990) or chaos ( Scott, 1991) are well documented for heterogeneous catalytic reactions. In the absence of heat and/or mass transport limitations such phenomena have to be caused by purely chemical feedback features such as autocatalysis. The observations of Jelemensky et al. (1995) were free of transport limitations.The present paper concerns the development of an intrinsic kinetic model for the platinum catalyzed selective oxidation of ethanol which allows a quantitative description of the complete set of data reported by Jelemensky et al. (...

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Section: Model Constructionmentioning

confidence: 60%

Kinetic modelling of multiple steady-states for the oxidation of aqueous ethanol with oxygen on a carbon supported platinum catalyst

Jelemenský

Kuster

Marin

1996

Chemical Engineering Science

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“…• C. Furthermore, Burke and Lyons 24 have discussed super-Nernstian shifts that have been observed for various hydrous oxide systems -in these cases the potential/pH shift differs from the expected 0.059V/pH unit at 25…”

Section: Resultsmentioning

confidence: 98%

“…The next stage of the film thickening process, the hydration reaction, is generally very slow, because as in phase transformation reactions, it involves rupture of primary coordination metal-oxygen bonds. We have shown 24 that the extent of hydrous oxide growth depends strongly on the value chosen for the upper and lower limit of the potential sweep as well as on the cycling frequency adopted, the solution temperature and the solution pH.…”

Section: Resultsmentioning

confidence: 99%

Hydrous Nickel Oxide: Redox Switching and the Oxygen Evolution Reaction in Aqueous Alkaline Solution

Lyons

Doyle

Godwin

et al. 2012

J. Electrochem. Soc.

118

137

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The redox switching reaction and the oxygen evolution reaction at multi-cycled nickel oxy-hydroxide films in aqueous alkaline solution are discussed. The hydrous oxide is considered as a porous assembly of interlinked octahedrally coordinated anionic metal oxyhydroxide surfaquo complexes which form an open network structure. The latter contains considerable quantities of water molecules which facilitate hydroxide ion discharge at the metal site during active oxygen evolution. The dynamics of redox switching has been quantified in terms of a diffusive frequency using the Laviron-Aoki diffusion model. Steady state Tafel plot analysis has been used to elucidate the kinetics and mechanism of oxygen evolution with slopes of ca. 60 mVdec −1 and ca. 120 mVdec −1 at low and high overpotentials respectively, whereas the reaction order with respect to hydroxide ion activity remains invariant at ca. 1.0 as the potential is increased. These observations are rationalized in terms of a kinetic scheme involving surfaquo groups.

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“…59 mV per unit change in pH at 25ºC. Furthermore, Burke and Lyons (27) have discussed super-Nernstian shifts that have been observed for various hydrous oxide systems -in these cases the potential/pH shift differs from the expected 0.059V/pH unit at 25 0 C. The mathematical treatment of this situation is beyond the scope of the present paper, but suffice to say, the phenomena have recently been qualitatively summarized (33). Thus, a zero potential shift (with respect to a pH dependent reference electrode) implies that both the reactants and the product possess the same net charge.…”

Section: Resultsmentioning

confidence: 93%

“…We have previously noted (27) that even though it is directly produced in the initial electrochemical oxidation process, the anhydrous film is probably not the most stable metal oxidation product in the aqueous medium but it may be regarded as an intermediate or metastable product in the formation of a hydrous oxide layer. In the anhydrous film ions are held in a rigid manner in an extended network of polar covalent bonds which drastically reduce ion transport through (and consequently extension of) the surface layer.…”

Section: Resultsmentioning

confidence: 99%

Redox Switching and Oxygen Evolution at Hydrous Nickel Oxide Films in Aqueous Alkaline Solution

et al. 2013

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The redox switching reaction and the oxygen evolution reaction at multi-cycled nickel oxy-hydroxide films in aqueous alkaline solution are discussed. The hydrous oxide is considered as a porous assembly of interlinked octahedrally coordinated anionic metal oxyhydroxide surfaquo complexes which form an open network structure. The latter contains considerable quantities of water molecules which facilitate hydroxide ion discharge at the metal site during active oxygen evolution. The dynamics of redox switching has been quantified in terms of a diffusive frequency using the Laviron-Aoki diffusion model. Steady state Tafel plot analysis has been used to elucidate the kinetics and mechanism of oxygen evolution with slopes of ca. 60 mVdec -1 and ca. 120 mVdec -1 at low and high overpotentials respectively, whereas the reaction order with respect to hydroxide ion activity remains invariant at ca. 1.0 as the potential is increased. These observations are rationalized in terms of a kinetic scheme involving surfaquo groups.

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Electrochemistry of Hydrous Oxide Films

Cited by 65 publications

References 195 publications

Kinetic modelling of multiple steady-states for the oxidation of aqueous ethanol with oxygen on a carbon supported platinum catalyst

Kinetic modelling of multiple steady-states for the oxidation of aqueous ethanol with oxygen on a carbon supported platinum catalyst

Hydrous Nickel Oxide: Redox Switching and the Oxygen Evolution Reaction in Aqueous Alkaline Solution

Redox Switching and Oxygen Evolution at Hydrous Nickel Oxide Films in Aqueous Alkaline Solution

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