Showing papers on "Supporting electrolyte published in 2002"

Influence of electronic and structural effects on the oxidative behavior of nickel porphyrins.

Abstract: With the aim of better understanding the electronic and structural factors which govern electron-transfer processes in porphyrins, the electrochemistry of 29 nickel(II) porphyrins has been examined in dichloromethane containing either 0.1 M tetra-n-butylammonium perchlorate (TBAP) or tetra-n-butylammonium hexafluorophosphate (TBAPF6) as supporting electrolyte. Half-wave potentials for the first oxidation and first reduction are only weakly dependent on the supporting electrolyte, but E1/2 for the second oxidation varies considerably with the type of supporting electrolyte. E1/2 values for the first reduction to give a porphyrin π-anion radical are effected in large part by the electronic properties of the porphyrin macrocycle substituents, while half-wave potentials for the first oxidation to give a π-cation radical are affected by the substituents as well as by nonplanar deformations of the porphyrin macrocycle. The potential difference between the first and second oxidations (Δ|Ox2 − Ox1|) is highly var...

Superoxide Electrochemistry in an Ionic Liquid

Abstract: The superoxide ion (O2•-) has been generated electrochemically from oxygen dissolved in two different solvent systems: (1) acetonitrile with tetraethylammonium perchlorate (TEAP) as the supporting electrolyte at elevated pressure and (2) in a room-temperature ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][HFP]), at atmospheric pressure. A high-pressure electrochemical cell with a quasi reference electrode was developed for elevated pressure tests. Increasing the partial pressure of oxygen in the first system increased the rate of superoxide generation because of the increased solubility of oxygen according to Henry's law. The subsequent addition of gaseous carbon dioxide enhances the rate of oxygen reduction in both systems but inhibits the reverse (oxidation) reaction of O2•- to O2. This later observation is consistent with the irreversible formation of a peroxydicarbonate ion, as has been postulated by others.

The Voltammetric Response of Nanometer-Sized Carbon Electrodes

Abstract: in both the presence and absence of supporting electrolyte has been investigated. In the presence of supporting electrolyte, well-defined steady-state voltammograms of sigmoidal shape have been obtained on electrodes with effective radii as small as 1 nm. In the absence of supporting electrolyte, however, the voltammetric behavior varies with the redox system. Deviation from the expected migration-diffusion response is observed when the electrode is smaller than 20 nm for the reduction of the multicharged cationic species hexammineruthenium(III) (Ru(NH3)6 3+ ). Deviation from the ideal behavior of migration-coupled diffusion is exhibited at electrodes even of micrometer size during the reduction of the multicharged hexacyanoferrate(III) anion (Fe(CN)6 3- ), which has a median reduction potential and relatively low k 0 . Such an effect is also observed for the oxidation of the hexacyanoferrate(II) anion (Fe(CN) 6 4- ). In comparison, the hexachloroiridate(IV) anion (IrCl6 2- ), with a higher k 0 and more positive reduction potential, shows deviations similar to those seen for hexaammineruthenium(III); i.e., no deviation from expected behavior is seen until the electrode size is less than ca. 20 nm. It is argued that the dynamic diffuse double-layer effect rather than the Frumkin effect is the major source of the observed nonideal behavior. The results indicate that the dynamic diffuse doublelayer effect can function even when the electrode reaction is reversible or quasi-reversible and becomes more pronounced at very small electrodes. The nature of size effects on the voltammetric response at nanometer size electrodes are discussed.

Anodic oxidation of 4-chlorophenoxyacetic acid on synthetic boron-doped diamond electrodes

Abstract: The anodic oxidn. of 4-chlorophenoxyacetic acid (CPA) on synthetic B-doped diamond thin film electrodes in acid media was studied, using cyclic voltammetry and bulk electrolysis. The results showed that in the potential region where the supporting electrolyte is stable, reactions occur, resulting in the loss of activity due to electrode fouling. Electrolysis at high anodic potentials in the region of electrolyte decompn. causes complex oxidn. reactions that lead to the complete incineration of CPA. There is no indication of electrode fouling under these conditions. The exptl. were compared with a theor. model. This model is based on the assumption that the electrochem. oxidn. of CPA by electrogenerated hydroxyl radicals is a fast reaction and that the process is diffusion-controlled. [on SciFinder (R)]

Electrochemistry of Metalloporphyrins in Nonaqueous Media

Abstract: The sections in this article are Introduction Porphyrin Electrochemistry in the Early 1960s and the 1970s Porphyrin Electrochemistry in the 1980s and the 1990s Selection of Appropriate Solvent and Supporting Electrolyte Selection of Appropriate Supporting Electrolyte Effect of Macrocycle Structure on Potentials Effect of Axial Ligation Periodic Table of Metalloporphyrins Groups 1–4 Groups 5 and 6 Group 7 Group 8 Ruthenium Osmium Iron Group 9 Group 10 Group 11 Group 12 Group 13 Group 14 Group 15 Concluding Statement Acknowledgments

Self-Assembly and Photovoltaic Property of Covalent-Attached Multilayer Film Based on Highly Sulfonated Polyaniline and Diazoresin

Abstract: A novel multilayer film is assembled from highly sulfonated polyaniline (SPAN) and diazoresin (DR) in aqueous solution via electrostatic attraction. Under UV irradiation, following the decomposition of diazonium group between the adjacent interfaces of the multilayer, the ionic bonds of the self-assembled film convert to covalent bonds and the film becomes very stable toward polar solvent or electrolyte solutions. Thus the photoelectric conversion property of highly sulfonated polyaniline containing film can be measured in conventional three-electrode photoelectrochemical cell, and a 0.5 mol/L KCl solution is used as the supporting electrolyte. The photocurrent spectroscopy responses coincide with the absorption spectrum of the self-assembly film, which means that the SPAN/DR film is responsible for the photocurrent generation, and the effects of bias voltage and photo intensity to the self-assembly film were also investigated in this article.

Homoepitaxial Single-Crystal Boron-Doped Diamond Electrodes for Electroanalysis

Abstract: In order to study the properties of single-crystal boron-doped diamond electrodes for electroanalysis, (100) and (111) boron-doped homoepitaxial single-crystal and polycrystalline diamond thin films were deposited by means of microwave plasma-assisted chemical vapor deposition. Features in the cyclic voltammograms (CVs) for aqueous H 2 SO 4 supporting electrolyte and Fe(CN) 3-/4- 6 in aqueous Na 2 SO 4 for polycrystalline electrodes were dominated by behavior typical of (111) single-crystal facets, rather than (100) facets. Apparent heterogeneous electron-transfer rate constants (k 0 ) for various redox systems were estimated with CV simulation at polycrystalline, (111) and (100, off-axis. 4°). Based on comparison with the Marcus model, the behavior of the k° values, except for that of Fe(CN) 3-/4- 6 , indicates apparent outer-sphere electron-transfer, but with a lower density of states compared to glassy carbon or typical metal electrodes. The (111) homoepitaxial film performed better than a polycrystalline film in the cyclic voltammetric detection of serotonin, with signal-to-background ratios of 5 and 2, respectively. Single-crystal diamond may thus be an even more optimal electrode material for electroanalysis than polycrystalline diamond, which has been shown to have superior characteristics as an electrode material.

Direct determination of diffusion coefficients of substrate and product by chronoamperometric techniques at microelectrodes for any level of ionic support.

Abstract: A new method for the determination of the diffusion coefficients of both the substrate, D s , and the product, Dp, of an electrode process has been developed. The method proposed is based on the analysis of the transient currents and can be applied to some reactions of the type S z s = P z p + ne and, in contrast to the concept based on the steady-state current, to any ratio of the concentrations of supporting electrolyte and substrate. The diffusion coefficients can be evaluated sequentially from the two parts of the double-potential step chronoamperogram, since the magnitude of the normalized chronoamperometric current of the first step depends on the D s value, while that of the second step is controlled by both D s and Dp values. The corresponding, easy-to-use equations and procedures are given in the paper. The equations were derived on the basis of the numerical simulation data. The proposed methods of determination of diffusion coefficients for the substrates and products have been examined experimentally with the charged and uncharged ferrocene derivatives under diffusional and mixed diffusion-migration conditions. Only the chronoamperometric D s values obtained for the substrates could be compared to those determined from the steady-state diffusional current. It was found that for the systems investigated the agreement between these two methods was good. In this limited comparison, the standard deviations for the transient techniques were slightly larger than those obtained for the excess supporting electrolyte steady-state voltammetry.

Electrochemical Comparative Study of Riboflavin, FMN and FAD Immobilized on the Silica Gel Modified with Zirconium Oxide

Abstract: Modified carbon paste electrodes were prepared by the adsorption of flavin on a silica gel modified with zirconium oxide (Si:Zr:flavin). The electrochemical behavior of immobilized riboflavin, FMN and FAD was investigated. The formal potentials, Eo´, for the flavins in these electrodes were found to be -0.46 V vs. SCE, this being similar to their values obtained in solution. Their Eo´ values remained pH dependent with certain invariance for riboflavin between 4 and 5. The composition of the supporting electrolyte did not affect the Eo´ with exception of Ca2+, but in buffer systems and especially in phosphate a good rate of electron transfer was observed. The differences verified in the electrochemical behavior and UV-visible absorption spectra among the immobilized flavins are discussed in terms of different kinds of interaction.