Showing papers on "Supporting electrolyte published in 1992"

Electrochemistry and Langmuir Trough Studies of C60 and C70 Films

Abstract: Thin films of the fullerenes C{sub 60} and C{sub 70}, formed by solution casting, were studied by cyclic voltammetry (CV) in MeCN solutions containing quaternary ammonium or alkali-metal salts as supporting electrolytes. The film shows four CV reduction waves and one oxidation wave. The CV behavior for the first reduction, coulometrically equivalent to a one-electron reduction, indicates a large structural reorganization of the film with intercalation of the supporting electrolyte cation and a small amount of dissolution. Upon oxidation of the reduced form, the structure rearranges to form the parent. Similar effects occur for the second reduction/reoxidation process. The size of the cations affects the nature of these CV waves. Scanning electrochemical microscopy (SECM) of the C{sub 60} films indicates that neither the C{sub 60} film nor the completely reduced, C{sub 60}{sup -}, form is a good electronic conductor, while a partially reduced film displays enhanced conductivity. Langmuir trough studies of C{sub 60} and C{sub 70} show the preparation of highly incompressible monolayer and multilayer films at the air/water interface. Mixed films of the fullerenes with the surfactant arachidic acid can also be prepared. 42 refs., 18 figs., 1 tab.

Electroreduction of Buckminsterfullerene, C60, in aprotic solvents. Solvent, supporting electrolyte, and temperature effects

Abstract: The electroreductions of Buckminsterfullerene (C{sub 60}) in aprotic solvents were examined as a function of solvent, supporting electrolyte, and temperature. Altogether, 11 different solvents and 17 different supporting electrolytes were utilized in measurements made between 223 and 348 K. The cations of the supporting electrolytes were Li{sup +} and Na{sup +} as well as quaternary ammonium and quaternary phosphonium cations. The anions of the supporting electrolytes were ClO{sub 4}{sup {minus}}, BF{sub 4}{sup {minus}}, PF{sub 6}{sup {minus}}, and Br{sup {minus}}. Cyclic voltammograms, rotating disk electrode voltammograms, and controlled potential coulometry revealed up to five reversible one-electron reductions. A qualitative approach is used to elucidate the effects of solvent, supporting electrolyte and temperature on the half-wave potentials, E{sub 1/2}, of the reductions of C{sub 60}. A qualitative approach is used to elucidate the effects of solvent, supporting electrolyte, and temperature on the half-wave potentials, E{sub 1/2}, of the reductions of C{sub 60}. 38 refs., 5 figs., 7 tabs.

Transport of inorganic colloids through natural aquifer material : implications for contaminant transport

Abstract: The stability and transport of radiolabeled Fe2O3 particles were studied using laboratory batch and column techniques. Core material collected from a shallow sand and gravel aquifer was used as the immobile column matrix material. Variables in the study included flow rate, pH, ionic strength, electrolyte composition, particle concentration, and particle size. Transport was highly dependent upon colloidal stability. Iron oxide colloids were not only mobile to a significant extent, but under some hydrogeochemical conditions were transported faster than tritiated water, a conservative tracer. The extent of colloid breakthrough was dependent upon a variety of parameters; however, the highest statistical correlation was observed with particle size and anionic composition of the supporting electrolyte. Arsenate was utilized for assessment of colloid-contaminant and contaminant-aquifer interactions and comparison of dissolved and colloidally associated transport in dynamic model systems. The rate of colloid-associated arsenate transport was over 21 times that of the dissolved arsenate. (Copyright (c) 1992 American Chemical Society.)

Steady-state voltammetry of strong and weak acids with and without supporting electrolyte

Abstract: Voltammetric reduction of perchloric, phosphoric, acetic, and ascorbic acid was investigated under steady-state conditions at platinum- and gold-disk microelectrodes. The dependence of the wave height of proton in perchloric acid on the concentration of supporting electrolyte (lithium perchlorate) was compared with the theory for currents limited by migration and diffusion. The wave height depends linearly on hydrogen ion concentration without and with supporting electrolyte up to 0.04 and 0.08 M, respectively

Electrochemical reduction of nitrogen oxyanions in 1 M sodium hydroxide solutions at silver, copper and CuInSe2 electrodes

Abstract: The reduction of nitrate and nitrite ions was studied in 1m NaOH supporting electrolyte. Voltammetric investigations show that, on silver cathodes, nitrate reduction begins at potentials about 500 mV more positive than nitrite reduction, the latter being superimposed on hydrogen evolution. Electrolyses of nitrate solutions at −1.4V/sce give nitrite with good selectivity. On copper cathodes, nitrate and nitrite reductions occur in the same region of potentials and show similar voltammetric profiles. The dominant product of nitrite reduction is ammonia, whereas nitrate may be reduced to nitrite at −1.1 V/sce and to ammonia with high yields at −1.4 V/sce. Reduction of nitrogen oxyanions may also be performed on CuInSe2 (photo)cathodes. Photoassisted reductions of nitrate performed on p-CuInSe2 at −1.4 V/sce gave mixtures of ammonia, nitrite and hydrogen.

Mechanistic aspects and synthetic applications of the electrochemical and iodobenzene bistrifluoroacetate oxidative 1,3-cycloadditions of phenols and electron-rich styrene derivatives

Abstract: Anodic oxidation of p-methoxy-substituted phenols and electron-rich styrene or propenylbenzene derivatives affords in good yield trans-dihydrobenzofurans derived from a formal 1,3-oxidative cycloaddition of the phenol to the styrene derivative. The yield of product in the electrochemical oxidation depends upon the ratio of phenol to styrene derivative, current density, and to a lesser extent the amount of supporting electrolyte

Effects of supporting electrolyte and zeolite co-cations on the electrochemical response of zeolite-modified electrodes

Abstract: The interpretation of cyclic voltammograms observed for ion-exchanged zeolite-modified electrodes is discussed in this paper. The conditions under which intrazeolite moieties are electrochemically silent are described with emphasis on the zeolite size exclusion of electrolyte cations. The influence of zeolite co-cation on electrochemical response is addressed using silver-ion-exchanged zeolite Y containing exclusively small-channel silver ions. Furthermore, the effects of electrolyte anions and solvent on the electrode response are utilized to establish the location of the electron-transfer process making use of the anion and molecule exclusion properties of zeolites.

Electrochemistry of rhodium and cobalt corroles. Characterization of (OMC)Rh(PPh3) and (OMC)Co(PPh3) where OMC is the trianion of 2,3,7,8,12,13,17,18-octamethylcorrole

Abstract: The first oxidative electrochemistry of rhodium(III) and cobalt(III) corroles is reported in tetrahydrofuran, N,N-dimethylformamide, benzonitrile, and dichloromethane containing tetrabutylammonium perchlorate as supporting electrolyte. The investigated compounds are represented as (OMC)Rh(PPh3) and (OMC)Co(PPh3) where OMC is the trianion of 2,3,7,8,12,13,17,18-octamethylcorrole. Each complex undergoes up to three oxidations and two reductions depending upon solvent. The oxidations occur at the corrole I€-ring system while the reductions occur at the rhodium or cobalt metal center. The three one-electron oxidations are electrochemically reversible by cyclic voltammetry at fast potential scan rates, but several chemical reactions occur at lower scan rates or in the presence of added triphenylphosphine. An overall oxidation reduction mechanism is proposed for each complex and comparisons are made with the well-characterized reactions of cobalt and rhodium tetraphenylporphyrins under the same experimental conditions. © 1992 American Chemical Society.

Ethylene carbonate-based organic electrolytes for electric double layer capacitors

Abstract: A new electrolytic solution based on a mixed solvent of ethylene carbonate (EC) with sulfolane (SL) or γ-butyrolactone (γ-BL) has been examined as an electric double layer capacitor. Fundamental properties, such as electrolytic conductivity, viscosity, and thermal stability, were measured for solutions containing quaternary alkylammonium salts as the supporting electrolyte. Maximum conductivities were obtained for the solutions with mixed solvent of 20–40 mol % EC in the EC+γ-BL system: 1.2–1.3×10−2S cm−1 for EC+γ-BL dissolving 0.5 M Et4 NBF4 (Et=C2H5). The electrochemical and the thermal stabilities of the solution were dependent on the electrolytic salt as well as the solvent composition. A stable discharge capacitance and a high coulombic efficiency were obtained in a model capacitor using carbon fibre electrodes and the organic electrolyte of EC+γ-BL/Et4NBF4 (or EC+γ-BL/Et4NPF6).

The electrocatalytic hydrogenation of soybean oil

Abstract: Soybean oil has been hydrogenated electrocatalytically at a moderate temperature, without an external supply of pressurized H2 gas. In the electrocatalytic reaction scheme, atomic hydrogen is produced on an active Raney nickel powder cathode surface by the electrochemical reduction of water molecules from the electrolytic solution. Adsorbed hydrogen then reacts with an oil’s triglycerides to form a hydrogenated product. Experiments were carried out at 70°C with a flow-through electrochemical reactor operating in a batch recycle mode. The reaction medium was a two-phase mixture of soybean oil in a water/t-butanol solvent containing tetraethylammoniump-toluenesulfonate as the supporting electrolyte. In all experiments the reaction was allowed to continue for sufficient time to synthesize a brush hydrogenation product. The effects of oil content, applied current, solvent composition, and supporting electrolyte concentration on the efficiency of hydrogen addition to the oil and on the chemical properties of the hydrogenated oil product were determined. The electrohydrogenated oil is characterized by a high stearic acid content and a low percentage of totaltrans isomers, as compared to that produced in a traditional hydrogenation process.

Voltammetric behaviour of vitamins D2 and D3 at a glassy carbon electrode and their determination in pharmaceutical products by using liquid chromatography with amperometric detection

Abstract: Cyclic voltammetry was used to study the oxidation of vitamin D2(ergocalciferol) and vitamin D3(cholecalciferol) at a planar glassy carbon electrode. The electrode reaction for cholecalciferol was found to be dependent on the apparent pH between 4.95 and 6.10, and pH independent between pH 6.10 and 8.65 when the solutions contained 90% methanol; this suggested a pKa value of 6.10 for vitamin D3. Similar behaviour was exhibited by ergocalciferol, and a pKa value of 6.35 was found. The peak currents for both vitamins were found to be dependent on the methanol concentration of the supporting electrolyte. The peak currents were also found to be dependent on the ionic strength of the acetate buffer (pH 6.0) over the range 0.1–1.0 mol dm–3. Both substances were oxidized in one step, which was found to be an irreversible reaction; the final product for vitamin D2 can undergo absorption at the electrode surface. The parent compounds could be undergoing oxidation at the triene moieties. The optimum mobile phase for liquid chromatography with amperometric detection was found to be 95% methanol–0.05 mol dm–3 acetate buffer (pH 6.0); the detector was operated at a potential of + 1.3 V (versus Ag—AgCl), and a linear response was obtained for vitamin D3 over the range from 10 to 100 ng injected; for vitamin D2 the response was linear from 20 to 200 ng injected. Extracts of pharmaceutical products were separated on reversed-phase columns prior to amperometric detection of the vitamins. Cholecalciferol was successfully determined in a multivitamin table, and ergocalciferol in a multivitamin liquid preparation.