Showing papers on "Supporting electrolyte published in 1988"

Electrodeposition of silicon from a nonaqueous solvent

Abstract: Electroplating of silicon from solutions of , , , , , , and in tetrahydrofuran, using , TBAP, or TBAB as supporting electrolyte has been studied Si‒C, Si‒O, and Si‒N bonds are not reduced. Cyclic voltammetry shows a reduction peak, followed by passivation, for the halogenosilanes. Potentiostatic and galvanostatic deposition on Pt, Au, Ni, Cu glassy carbon, or ITO glass yields smooth layers up to 0.25 μm. Thicker layers have cracks. Auger spectroscopy shows C (∼8), O (∼8), and Cl (∼1.5) as impurities (atomic percent).

Potentiometric determination of the molal formation constants of ferrous acetate complexes in aqueous solutions to high temperatures

Abstract: The formation quotients of ferrous acetate complexes were determined in aqueous solutions from 50 to 295/degrees/C at ionic strengths of 0.03, 0.1, 0.3, and 1.0 m using sodium trifluoromethanesulfonate as the supporting electrolyte. The potentiometric titrations were carried out in a Teflon-lined concentration cell fitted with hydrogen electrodes. Three complexes, namely, Fe(CH/sub 3/COO)/sub n//sup 2-n/, where n = 1, 2, and 3, were identified by regressional analysis of the data. The relevant thermodynamic quantities were calculated for the first two species.

Effects of supporting electrolyte and pH on charge transport within electropolymerized poly(o-phenylenediamine) films deposited on graphite electrodes

Abstract: The homogeneous charge-transport process within electropolymerized electroactive poly(o-phenylenediamine) (PPD) films on graphite electrodes in various supporting electrolytic solutions (i.e., NaCl, NaClO4, Na2SO4, LiCl, CF3COONa, tetraethylammonium chloride (TEACl) and sodium p-toluenesulfonate (NaPTS)) at various pH’s was examined by potential-step chronoamperometry and chronocoulometry. The overall charge-transport process was found to obey Fick’s diffusion laws and thus the apparent diffusion coefficients (Dapp) for the diffusion-like charge-transport process were estimated. The Dapp values for the oxidation and reduction processes (i.e., Dappa and Dappc) were almost the same at pH 1.0 irrespective of the thickness of PPD films and were actually independent of the supporting electrolytes except for NaPTS. As pH was increased from 1 to 7, the Dappa values decreased slightly from ca. 5.6×10−8 to 1.6×10−8 cm2 s−1 and the Dappc values did more largely from ca. 5.6×10−8 to 2.2×10−9 cm2 s−1. This behavior w...

Application of Nafion/Platinum Electrodes (Solid Polymer Electrolyte Structures) to Voltammetric Investigations of Highly Resistive Solutions

Abstract: Platinum electrodes on Nation~ 115 membranes, designated Pt/Naf and prepared by an electroless plating method (PtC162- with hydrazine), were used for voltammetric investigations. Scanning electron microscopy (SEM) of these electrodes showed the Pt electrode surface to have the continuous, yet porous, structure necessary for both electronic conduction to the Pt particles and ionic conduction through the membrane/electrode/solution interface. These electrodes were used in the configuration S/Pt/Naf/H20 + electrolyte, where the counter and reference electrodes were in the aqueous electrolyte solution and the substance of interest was dissolved in solvent, S. Cyclic voltammetry was used to characterize the behavior of several substrates in H20, MeCN, THF, and toluene. Tetracyanoquinod imethane (TCNQ) in acetonitrile (MeCN), tetrahydrofuran (THF), and toluene and benzoquinone (BQ) in THF and toluene could be reduced to anion radicals in the absence of added supporting electrolyte. In THF and toluene, the formation of the radical anion of BQ and TCNQ often involved ion pair formation with alkali metal ion and precipitation. The reduction of TCNQ in toluene in the presence of Na § ions resulted in the formation of the electronically conducting salts, Na+TCNQ -. This paper describes the construction of Pt electrodes, based on solid polymer electrolyte (SPE) technology, that can be employed for voltammetric measurements and their application to studies with several solvent systems, including some very resistive ones that contain no or low amounts of added supporting electrolyte. SPE techniques involve the use of an ion exchange membrane (usually Nation 1) with porous contacting electrodes for the construction of electrochemical devices in which ionic migration to maintain charge neutrality occurs within the membrane. SPE technology was first applied to fuel cells (1) and later to water electrolyzers (2) and electrochemical oxygen separators (3). Our goal was to utilize these SPE electrodes in a voltammetric mode to help establish appropriate conditions for bulk electrolysis and for analysis. In this way such SPE electrodes could be used to complement ultramicroelectrodes (4, 5) in the electrochemical characterization of systems in resistive media. We also were interested in obtaining a better understanding of the operation and structure of the voltammetric SPE electrode.

Oxidative Electropolymerization of Metal Schiff-Base Complexes

Abstract: New electropolymerizable metal Schiff-base complexes (M = Ni, Co, or Mn) were prepared for use in polymer modified electrodes by incorporating two N,N-dimethylaniline-like moieties onto the periphery of the salen (salen = ethylenebis(salicyldiminato)) ligand Oxidative electropolymerzation appears to occur by the tail-to-tail coupling of aromatic amine cation radicals on adjacent molecules near the electrode surface The electrochemistry of the resulting redox-conductive polymer film in solvent and supporting electrolyte with no monomer present resembles that for the respective monomer in solution The voltammetric response for the manganese complex polymer is generally poor but can be enhanced by the addition of a redox mediator tetracyanoquinodimethane (TCNQ) to the solution in which the electrode is immersed Utilizing the mediation reaction approach, approximately twenty five percent of the available manganese in the polymer film was electrochemically active

Electrogenerated Chemiluminescence. 50. Electrochemistry and Electrogenerated Chemiluminescence of Micelle Solubilized Os(bpy)32

Abstract: The oxidative electrochemistry and electrogenerated chemiluminescence (ECL) of Os(bpy)32+ were studied in the presence of sodium dodecyl sulfate (SDS), Triton X-100, and cetyltrimethylammonium bromide (CTAB) in aqueous solutions. Variation of supporting electrolyte (NaCl) concentration affected the interaction between Os(bpy)32+ and the surfactants. The measurement of oxidation peak current (ipa) and ECL intensity at different NaCl concentrations suggested a strong interaction of Os(bpy)32+ with SDS. Above the critical micelle concentration (cmc) the strong hydrophobic interaction of Os(bpy)32+ and the SDS micelle core greatly suppresses both ipa and the ECL intensity. The interaction of Os(bpy)32+ with CTAB micelle is much weaker because of electrostatic effects. Triton X-100 micelles do not interact with Os(bpy)32+.

Passivation of Iron in Sulfate, Perchlorate, and Borate Solutions: Role of Borate in the Passivation Process

Abstract: The anodic passivation of Fe has been investigated in borate buffer, sulfate, and perchlorate solutions. In sulfate and perchlorate solutions of either pH 3.0 or 8.4, the passivation process is highly inefficient with very large amounts of anodic charge passing before a substantial decrease in current is observed. In these solutions, passivation appears to be associated with precipitation of a salt film and/or changes in the solution pH near the surface which permits the formation of a passive oxide. The efficiency for potential‐step passivation cannot be significantly increased by changing the concentration of the supporting electrolyte, the pH of the solution from 3.0 to 8.4, or the potential of anodization. However, the addition of <5% pH 8.4 borate buffer to the neutral sulfate or perchlorate solutions results in a dramatic increase in the efficiency, with the anodic passiyation charge decreasing by as much as two orders of magnitude. Similar trends are observed in pH 8.4 solutions with previously passivated Fe electrodes which were cathodically reduced to different extents prior to anodization. The more of the prior film that remains on the surface before the anodic potential step in sulfate, the more efficient is the passivation process. The marked similarity of these results suggests that the beneficial action of borate towards Fe passivation is due to its ability to assist in the formation of the surface oxide film. While the pH buffering capacity of the borate can be playing a role, it is possible that borate buffer contains strongly interacting anions which give it an inhibiting capability. The interaction of these anions with the Fe surface is believed to stimulate formation of a surface oxide film, and this could explain the results in the present work. Passivation of Fe in sulfate and perchlorate solutions would be inefficient because these anions, unlike those derived from borate, do not have inhibitive abilities, nor do their solutions have buffering capacity. The results indicate the important role played by prior oxide films, and the need for well‐defined starting surface conditions in passivation experiments.

Voltammetric behaviour of all-trans-retinol (vitamin A1) at a glassy carbon electrode and its determination in human serum using high-performance liquid chromatography with electrochemical detection

Abstract: Cyclic voltammetry has been used to investigate the oxidation of all-trans-retinol (vitamin A1) at a planar glassy carbon electrode. The electrode reaction was found to be dependent on the percentage of methanol, pH and ionic strength of the acetate buffer. The maximum electrochemical signal was obtained with a supporting electrolyte containing 95% methanol-0.075 M acetate buffer (pH 5.0). The oxidation was found to occur in two steps and to be irreversible; the reactant was found to undergo adsorption at the glassy carbon surface. The final product may also be adsorbed; this did not affect the signal obtained with a glassy carbon electrode in the wall-jet configuration, but did affect seriously that obtained with a thin-layer cell. Liquid chromatography with electrochemical detection (LCEC) was performed with the optimum supporting electrolyte as the mobile phase; the calibration graph was linear in the range 0.05–22.0 ng injected. The LCEC method was shown to be about four times more sensitive than liquid chromatography with UV detection; the former was applied successfully to the determination of normal and depressed circulating levels of the vitamin in human serum samples.

The Electrochemistry of Iridium Oxide Films in Some Nonaqueous Solvents

Abstract: Ir oxide films, grown in aqueous LIClO/sub 4/ solutions (rhoH -- 9), have been found to exhibit excellent charge capacities, charging and discharging kinetics, and stability in acetonitrile and propylene carbonate with LiClO/sub 4/ as the supporting electrolyte, while the results in THF also appear to be quite promising. The oxide is electrochromic in all of these media. In order to obtain the optimum response of Ir oxide in nonaqueous solutions, it is important to prevent the drying out of the oxide when transferring it from the aqueous to nonaqueous media. Discharging and charging of the oxide appears to involve Li/sup +/ insertion and expulsion from the oxide, respectively. Oxides formed in neutral aqueous LiClO/sub 4/ solutions have been found to be mechanically more stable than those grown in aqueous 0.5M H/sub 2/SO/sub 4/ or in 50% aqueous acetonitrile/LiClO/sub 4/. This is supported by SEM evidence of a less cracked and more adherent Ir oxide film when grown in neutral aqueous LiClO/sub 4/ solutions, as compared to the case in the latter solutions.

Reaction of Triphenylphosphine Radical Cation with 1, 3-Dicarbonyl Compounds : Electrochemical One-Step Preparation of Dioxomethylenetriphenylphosphoranes

Abstract: Electrochemical oxidation of Ph3P (1) in MeCN in the presence of 1, 3-dicarbonyl compounds, R1COCH2COR2 (3), with HCIO4 as the supporting electrolyte resulted in the formation of the phosphonium salts, Ph3P+-CH(COR1)COR2 ClO4- (4), provieded that R1 and/or R2 is a phenyl group. On the other hand, electrolysis in CH2Cl2 with 2, 6-lutidinium perhlorate gave the phosphoranes, Ph3P=C(COR1)COR2 (5), directly from 1 and 3 in fair to excellent yields : in this case, R1 or R2 need not necessarily be a phenyl group. Thus, the electrolysis is shown to be a convenient method to perpare 5 in a single step. Plausible processes for the formation of 4 and 5 are proposed, involving the reaction of electrochemically generated Ph3P+·with the enol form of 3 as the keystep.

Preparation of High Quality Polypyrrole Films

Abstract: Influences of the polymerization condition on properties of electrochemically synthesized polypyrrole film were studied with the aim of preparing high quality films for device application. Polymerization condition parameters such as the content of dissolved oxygen in the electrolytic solution, the polymerization temperature, the concentrations of monomer and supporting electrolyte, and others were varied, and the conductivity, the surface morphology, and adhesion to substrate of resulting films were examined. High quality films were synthesized as double-layered films consisting of a thin well adherent sublayer and a highly conductive thick overlayer. Optimizing various parameters, we could obtain high quality films with a satisfactorily flat surface, good adhesion to substrate, and a high conductivity (more than 300 S/cm).

Determination of thiram in water and soils by cathodic stripping voltammetry based on adsorptive accumulation

Abstract: A very sensitive electrochemical stripping procedure for thiram is reported Accumulation is achieved by adsorption of the compound on the hanging mercury drop electrode Optimal experimental parameters include an accumulation potential of −02 V vs Ag/AgCl, a 0075 mol/l ammonia solution as supporting electrolyte and a differential pulse stripping mode The detection limit is 03 ng ml−1 after 120 s accumulation and 003 ng ml−1 after 600 s accumulation Results are reported for water and soil samples

Electroanalytical studies of ferrocene and substituted ferrocene in non-aqueous solvents by rotating disc voltammetry

Abstract: Ferrocene, ferrocene carboxyaldehyde, acetylferrocene and benzoylferrocene were investigated by anodic rotating disc voltammetry at platinum, gold and glassy carbon electrodes in dimethyl sulphoxide and acetonitrile. All displayed a single wave and obeyed the Levich plots. The limiting current is linearly proportional to concentration, affording an excellent and rapid determination of these compounds in the presence of tetraethylammonium perchlorate (0.1 M) as supporting electrolyte. The electrode kinetic parameters were determined and mechanisms are suggested.

A thermodynamic analysis of common intersection points in potentiometric titration studies of solid surfaces

Abstract: Potentiometric titration curves for solid/solution interfaces often exhibit common intersection points (CIP) at different levels of supporting electrolyte and, for a fixed electrolyte level, at different concentrations of cosolvents. Both situations are discussed. For the first, explicit expressions are derived which summarise the conditions for a CIP to occur in the presence of specific adsorption and which allow formally for solution non-ideality. Attention is focussed primarily on plots of amount adsorbed vs. activity of the potential determining species rather than concentration. However, the latter case is also discussed briefly. The treatment is extended to cases where several ionic species are strongly specifically adsorbed and leads to a useful test for the occurrence of specific adsorption which is applicable in non-ideal systems. The situation where the bulk concentrations of such species are not negligible is also considered. For mixed solvents a simple expression is derived which describes the effect of solvent composition on the concentration of potential determining ions at the zero point of charge (z.p.c.). In this case CIP may arise from competition between medium effects associated with the adsorption of potential determining ions and electric fields in the diffuse double layer. The treatment is applicable to ionic crystals and to surfaces with fixed dissociable groups.