Platinum electrodes modified with

Figure 2. Normalized EXAFS spectra for (A) bulk [Ru (v-bpy)3]+, (B) platinum electrode modified with 5...

D KIEs proved439 that in the oxidation of formaldehyde on a polycrystalline platinum electrode modified with Pb atoms and on pure platinum electrode, the cleavage of both OH and CH bonds and the abstraction of the hydrogen atom from an OH bond in hydrated formaldehyde are rate-determining on the Pt/Pb and on the Pt electrode, respectively. The ku/ku for the oxidation of formaldehyde at copper electrode (at pH 13, at 25 °C) depends on the electrode potential and reaches the highest value of 7 at low potentials and drops to about 2.5 at higher positive potentials440. 

Figure 5.11 Voltammetric response for a 5 pm platinum electrode modified with a monolayer of [(pOp)Os(bpy)2(4-tet)Os(bpy)2Cl]3+, measured at a scan rate of 10 V s 1. The supporting electrolyte is 1.0 M LiCICh in acetonitrile, and the monolayer surface coverage is 9.8 x 10 n mol cm-2. The cathodic currents are shown as up, while the cathodic currents are shown as down. Reprinted with permission from R. J. Forster and T. E. Keyes, /. Phys. Chem., B, 105, 8829 (2001). Copyright (2001) American Chemical Society...

Figure 5.72 Typical Koutecky-Levich plots for the reduction of a 0.2 mM [Fe(H20)6]3+ solution in 0.1 M H2S04 at platinum electrodes modified with layers of different surface coverages of [Os(bpy)2(PVP)ioCl]+. From top to bottom, the surface coverages (in mol cm-2) are 1.7 x 10-1°, 1.8 x 10 9, 2.7 x 10-9, 5.0 x 10 9,1.1 x 10 8, and bare platinum. From R. J. Forster and J. G. Vos, /. Chem. Soc., Faraday Trans., 87,1863-1867 (1991). Reproduced by permission of The Royal Society of Chemistry...

The same polarization characteristics exhibit the platinum electrode modified with copper dendrites formed by the use of the PO regime described in caption of Fig. 26a. It can be seen from Fig. 27 that the process on the electrode with increased surface roughness takes place at considerably lower overpotential than on the smoother one. 

Iwuoha, E., D. de Villaverde, N. Garcia, M.R. Smyth, and J. Pingarron. 1997. Reactivities of organic phase biosensors. 2. The amperometric behavior of horseradish peroxidase immobilised on a platinum electrode modified with an electrosynthetic polyaniline film. Biosens Bioelectron 12 749. 

Devadoss etal. (18) have developed a cholesterol oxidase modified electrode that has been used to detect cholesterol in the plasma membranes of Xenopus oocytes. A platinum electrode modified with a lipid bilayer containing cholesterol oxidase (50) is operated in the amperometric mode and placed adjacent to an oocyte (Figure 17.1.3A-B). 

Li et al. (2006) reported a procedure for a-tocopherol determination in vegetable oil by differential pulse voltammetry in the medium of 1,2-dichloroethane/ethanol on a platinum electrode modified with a polypyrrole coating. The use of the coated electrode allowed the attainment of better analytical parameters of determination. The calibration graph was linear in the range 5.0-300 pmol/L, with a limit of detection 1.5 pmol/L. 

Figure 3. A Calibration curve for the determination of copper using a 75pm diameter platinum electrode modified with an electropolymerized film of [Ru(v-bpy)3] + with Xylenol Orange incorporated by ion exchange B Differential pulse voltammogram for the determination of copper from a 5x10" M solution. Figure adapted from reference 32.

Keeping these requirements and restrictions in mind, we have employed a platinum electrode modified with Nafion and cellulose acetate (hydrolyzed or unhydrolyzed) for the duect determination of NO based on its oxidation at -K).90V. 

Figure 6. Current vs. time trace for a platinum electrode modified with Nafion and in contact with a pH 7.5 phosphate buffer containing 10 mM so um nitrite and after bubbling the solution with either N2 or NO.

Jia,., Fujitani, Mv Yae, S., and Nakato, Y., Hole diffusion length and temperature dependence of photovoltages for n-Si electrodes modified with LB layers of ultrafine platinum particles, Electrochim. Acta, 42, 431,1997. 

Figure 6. Cyclic voltammograms of a platinum disk-electrode modified with a film of the octanuclear dendrimer 2, measured in 0.1 M Bu NPFj/CHjClj. The surface coverage of electroactive ferrocenyl sites in the film is determined to be T = 2.01 x 10" mol cm . inset, scan rate dependence of the anodic peak current.

These electrodes modified with metal complexes could have been substitutes for expensive platinum if they had been usable under conditions compatible with requirements for efficient fuel cells. However, they are not stable, particularly in contact with acidic media, which results from demetallation. This is known since the early works with N4 macrocycles and heat treatment has been proposed to enhance the durability of the carbon... 

Bond and coworkers [521] have described Au(III) electroreduction and Au(0) oxidation stripping processes in dilute aqua regia utilizing platinum, rhodium, iridium, gold, and glassy carbon electrodes. Sorption of tetrachloroaureate ions on carbon paste electrode modified with montmorillonite has been performed as a preconcentration step in the determination of gold in pharmaceutical preparation [522]. 

An electrocatalytic reaction is an electrode reaction sensitive to the properties of the electrode surface. An electrocatalyst participates in promoting or suppressing an electrode reaction or reaction path without itself being transformed. For example, oxygen reduction electrode kinetics are enhanced by some five orders of magnitude from iron to platinum in alkaline solutions or from bare carbon to carbon electrodes modified with Fe phthalocyanines or phenylporphyrins. For a comprehensive discussion of the subject, the reader is referred to refs. (76, 95, and 132-136). 

Some papers have appeared that deal with the use of electrodes whose surfaces are modified with materials suitable for the catalytic reduction of halogenated organic compounds. Kerr and coworkers [408] employed a platinum electrode coated with poly-/7-nitrostyrene for the catalytic reduction of l,2-dibromo-l,2-diphenylethane. Catalytic reduction of 1,2-dibromo-l,2-diphenylethane, 1,2-dibromophenylethane, and 1,2-dibromopropane has been achieved with an electrode coated with covalently immobilized cobalt(II) or copper(II) tetraphenylporphyrin [409]. Carbon electrodes modified with /nc50-tetra(/7-aminophenyl)porphyrinatoiron(III) can be used for the catalytic reduction of benzyl bromide, triphenylmethyl bromide, and hexachloroethane when the surface-bound porphyrin is in the Fe(T) state [410]. Metal phthalocyanine-containing films on pyrolytic graphite have been utilized for the catalytic reduction of P anj -1,2-dibromocyclohexane and trichloroacetic acid [411], and copper and nickel phthalocyanines adsorbed onto carbon promote the catalytic reduction of 1,2-dibromobutane, n-<7/ 5-l,2-dibromocyclohexane, and trichloroacetic acid in bicontinuous microemulsions [412]. When carbon electrodes coated with anodically polymerized films of nickel(Il) salen are cathodically polarized to generate nickel(I) sites, it is possible to carry out the catalytic reduction of iodoethane and 2-iodopropane [29] and the reductive intramolecular cyclizations of 1,3-dibromopropane and of 1,4-dibromo- and 1,4-diiodobutane [413]. A volume edited by Murray [414] contains a valuable set of review chapters by experts in the field of chemically modified electrodes. 

Modified electrodes for this analytical purpose have mostly been formed by electrode adsorption of the mediator systems on the electrode surface or by electropolymerization [24,116]. Recently, for example, NAD(P)H oxidations have been performed on platinum or gold electrodes modified with a monolayer of pyrroloquinoline quinone (PQQ) [117] or on poly(methylene blue)-modified electrodes with different dehydrogenases entrapped in a Nafion film for the amperometric detection of glucose, lactate, malate, or ethanol [118]. In another approach, carbon paste electrodes doped with methylene green or meldola blue together with diaphorase were used for the NADH oxidation [119]. A poly(3-methylthio-phene) conducting polymer electrode was efficient for the oxidation of NADH [120]. By electropolymerization of poly(aniline) in the presence of poly(vinylsulfonate) counterions. 

Fig. 3.3 Surface modification with Pd thin films by UHV vapor deposition (Left) Gold surface modified with Pd thin film (a) Rotating disc electrode (RDE) polarization curves for electrochemical hydrogen oxidation reaction on pure Au(lll), Au(lll)-Pd (for different rpm ) and Pt(lll) surfaces [51] (b) and (c) LEIS spectra of Au(lll)-Pd surfaces after vapor deposition of Pd in the amount that corresponds to four atomic monolayers. (Right) Platinum surface modified with Pd thin film (d) LEIS spectra of the Pt(l 11)-Pd surface with 65% of Pd and (e) LEIS spectra of Pd monolayer on Pt(lll) (red line) and pure Pt(lll) (dashed line), (a) Reprinted with permission from [51], copyright 2002 Elsevier...

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