Oxidation on Platinum Electrode

Angelucci CA, Herrero E, Feliu JM. 2007b. Bulk CO oxidation on platinum electrodes vicinal to the Pt(lll) surface. J Solid State Electrochem 11 1532-1539. 

Watanabe M, Shibata M, Motoo S. 1985. Electrocatalysis hy ad-atoms. PartXn. Enhancement of carbon monoxide oxidation on platinum electrodes by oxygen adsorbing ad-atoms (Ge, Sn, Pb, As, Sb and Bi). J Electroanal Chem 187 161-174. 

The glow electrolysis technique (electrolysis with an anode immersed in the solution and the cathode above the surface) at 600-800 V dc and 300-500 mA converts a solution of starch into ethylene, methane, hydrogen, and both carbon mono- and dioxides.323 Electrochemical methods for converting polysaccharides and other biomass-derived materials have been reviewed briefly by Baizer.324 These methods are mainly oxidations along a potential gradient, which decreases the activation energy of the reactants. Starch in 5 M NaOH solution is oxidized on platinum electrodes to carboxylic acids with an activation energy of about 10 kcal/mol. In acidic media oxidation takes place at C-l followed by decarboxylation and oxidation at the C-2 and C-6 atoms.325... 

Studies In our laboratories (43-51) have concentrated on the effects of quaternary salts on electrochemical oxidations on platinum electrodes In emulsion and micelle systems. In addition studies have been made of the effect of these surfactants on a noncatalytlc process occurring at the platinum solution Interface. The quaternary salt used for most of the experiments was Hyamlne 2389 (predominantly methyldodecylbenzyl trlmethylammonlum chloride) and the aqueous solution was strongly basic. Under these conditions It was concluded (49) that the anode was covered... 

Seland F, Tunold R, Harrington DA (2008) Impedance study of formic acid oxidation on platinum electrodes. Electrochim Acta 53 6851-6864... 

Colmati E, Tremiliosi G, Gonzalez ER, Bema A, Herrero E, Feliu JM (2009) The role of the steps in the cleavage of the C-C bond during ethanol oxidation on platinum electrodes. Phys Chem Chem Phys 11 9114-9123... 

On the other hand, an increase in polymerization rate is observed when the electrolyte concentration rises [75-77], This effect has been explained in different ways the increase in the conductivity of the electrolyte solution, the stabilization of the growing radical cations by the anions of the electrolyte, their coupling being favored over secondary reactions, and the effect of electrolyte concentration on the formation of oxides on platinum electrodes, which catalyze the monomer oxidation [78], Finally, some authors have suggested that the polymerization process can be initiated by the oxidation of the anion [40],... 

F. Seland, R. Tunold, D. A. Harrington, Impedance study of methanol oxidation on platinum electrodes, Electrochim. Acta, 2006,51, pp. 3827-3840. 

This Is also consistent with mechanistic studies on platinum electrodes. Although there are cases, such as In the oxidation of As(III) by platinum oxides (30), the predominating observation Is... 

Pakalapati SNR, BN Popov, RE White (1996) Anodic oxidation of ethylenediaminetetraacetic acid on platinum electrode in alkaline medium. J Electrochem Soc 143 1636-1643. 

On the surface of metal electrodes, one also hnds almost always some kind or other of adsorbed oxygen or phase oxide layer produced by interaction with the surrounding air (air-oxidized electrodes). The adsorption of foreign matter on an electrode surface as a rule leads to a lower catalytic activity. In some cases this effect may be very pronounced. For instance, the adsorption of mercury ions, arsenic compounds, or carbon monoxide on platinum electrodes leads to a strong decrease (and sometimes total suppression) of their catalytic activity toward many reactions. These substances then are spoken of as catalyst poisons. The reasons for retardation of a reaction by such poisons most often reside in an adsorptive displacement of the reaction components from the electrode surface by adsorption of the foreign species. 

Nakabayashi, S., Yagi, 1., Sugiyama, N., Tamura, K. and Uosaki, K. (1997) Reaction pathway of four-electron oxidation of formaldehyde on platinum electrode as observed by in situ optical spectroscopy. Surf. Sci., 386, 82-88. 

Damjanovic A, Bmsic V. 1967. Electrode kinetics of oxygen reduction on oxide-free platinum electrodes. Electrochim Acta 12 615-628. 

Given the results obtained on platinum electrodes discussed in some detail in the previous section, it is clearly of fundamental interest to study the mechanism of CO oxidation on other transition metal electrodes, and to compare the results with platinum. Rhodium has been the electrode material that has been studied in greatest detail after platinum, and results obtained with rhodium have provided some very significant insights into some of the general issues about the CO oxidation mechanism. 

Capon A, Parsons R. 1973b. Oxidation of formic acid at noble metal electrodes. III. Intermediates and mechanism on platinum electrodes. J Electroanal Chem 45 215-231. 

Miki A, Ye S, Sensaki T, Osawa M. 2004. Surface-enhanced infrared study of catal)4ic electio-oxidation of formaldehyde, methyl formate, and dimethoxymethane on platinum electrodes in acidic solution. J Flectroanal Chem 563 23-31. 

Love B, Lipkowski J. 1988. Effect of surface crystallography on electrocatalytic oxidation of carbon-monoxide on platinum-electrodes. ACS Symp Ser 378 484-496. 

Effect of Surface Crystallography on Electrocatalytic Oxidation of Carbon Monoxide on Platinum Electrodes... 

Although CO is the simplest Ci component, its electrochemical oxidation mechanism is yet to be fully understood even on platinum electrodes. One of the most important issues on this topic is the sovurce of oxygen since CO needs one oa en atom to be folly oxidized to CO2. 

In this chapter, oxidation characteristics of COad on platinum electrode were investigated focusing on this issue using various types of platinum electrodes such as single cnrstals, smooth and high area... 

The oxidation of toluene to benzaldehyde (max. yield 98.8%) can be performed in a Ce(Cl04)3-HCl04-(Pt/Ti-Cu) system by using the in-cell method in an undivided cell [28]. Indirect electrooxidations of organic compounds with Ce(IV) are listed in Table 12 [221-230]. For the electrogeneration of Ce(IV), platinized titanium or platinum oxide-on-titanium electrodes are known to be suitable for continuous oxidation of Ce(III) in perchloric acid. 

The presence of a metal surface can catalyze redox reactions which also constitute mixed electrode reactions. For example, the oxidation of hydrogen molecules (2H2, , + 02, , - > 2H2O ) does not occur in aqueous solutions but this oxidation catalyticaUy proceeds on platinum electrodes as a coupled process of the anodic and the cathodic reactions shown in Eqn. 11—2 and in Fig. 11—3 ... 

In the presence of Pb(II) ions in sulfuric acid, potential oscillations have been observed for galvanostatic oxidation of hydrogen on platinum electrode [129]. This behavior has been attributed to ad-sorption/oxidation/desorption processes of lead on the platinum surface. Lead at high values of coverage is oxidized to insoluble PbS04, which blocks the Pt surface. 

Metallic NPs are most widely used in catalytic applications due to their inherent properties. Several examples of platinum and gold NPs are apparent in the literature. For example, electrodeposited platinum NPs on porous carbon substrates exhibit electrocatalytic activity for the oxidation of methanol.60 In another example, gold NPs catalyze the electrochemical oxidation of nitric oxide on modified electrodes.61 In general, catalytic NPs provide two distinct functions enhancing an electrochemical reaction and/or increasing electron transfer to an electrode. 

The conclusion here is therefore that activity in methanol oxidation on platinum is limited to the 111 plane. The other planes are blocked with a radical, probably adsorbed CO or -C-OH. It is not known at present what fraction of the electrode corresponds to each plane, but it is clear that greatly improved electrocatalysis of CH3, OH to C02 would be observed if electrodes containing only the 111 plane were available. 

Takahashi and co-workers (69,70,71) reported both cathodic and anodic photocurrents in addition to corresponding positive and negative photovoltages at solvent-evaporated films of a Chl-oxidant mixture and a Chl-reductant mixture, respectively, on platinum electrodes. Various redox species were examined, respectively, as a donor or acceptor added in an aqueous electrolyte (69). In a typical experiment (71), NAD and Fe(CN)g, each dissolved in a neutral electrolyte solution, were employed as an acceptor for a photocathode and a donor for a photoanode, respectively, and the photoreduction of NAD at a Chl-naphthoquinone-coated cathode and the photooxidation of Fe(CN)J at a Chl-anthrahydroquinone-coated anode were performed under either short circuit conditions or potentiostatic conditions. The reduction of NAD at the photocathode was demonstrated as a model for the photosynthetic system I. In their studies, the photoactive species was attributed to the composite of Chl-oxidant or -reductant (70). A p-type semiconductor model was proposed as the mechanism for photocurrent generation at the Chi photocathode (71). 

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