Showing papers on "Cyclic voltammetry published in 1985"

Resistance of Polyaniline Films as a Function of Electrochemical Potential and the Fabrication of Polyaniline-Based Microelectronic Devices.

Abstract: : Anodic growth of polyaniline films on a Au microelectrode array has been carried out to add to the characterization of polyaniline and to fabricate polyaniline-based microelectronic devices, diodes and transistors, that function when the polyaniline-functionalized microelectrode array is immersed in an electrolyte solution. The microelectrode array is a set of eight Au electrodes, 0.1 micrometer thick, 4.4 micrometers wide and 50 micrometers long, each individually addressable and separated from each other by 1.7 micrometers. Polyaniline can be deposited in controlled amounts by electrochemical oxidation of aniline. When the polyaniline is deposited in sufficient amounts, two or more of the eight Au microelectrodes can be connected in the electrical sense. Current can pass between two connected microelectrodes when there is an applied potential between them. The magnitude of the current at a given applied potential depends on the electrochemical potential of the polyaniline. In 0.5 M NaHsSO4/H20 the current (at a fixed applied potential) is maximum at an electrochemical potential of approx. +0.4 V vs. SCE and declines by a factor of greater than 1,000,000 upon reduction to +0.1 or oxidation to +0,7 V vs. SCE. Owing to the large change in resistance upon change in electrochemical potential, the functionalized microelectrodes is crucial to device function, owing to the limited conductivity of the polyaniline. The switching time of a transistor-like device is faster than 0.1 s.

“Polyaniline”: Interconversion of Metallic and Insulating Forms

Abstract: “Polyaniline” has been synthesized in various forms both chemically and electrochemically in aqueous media. The qulnoid-benzenoid-diimine form, an insulator, is doped by dilute aqueous protonic acids to the metallic regime ([sgrave] = 5 ohm−1cm−1; compressed pellet) to give the corresponding iminium salt. This represents a new type of p-doping phenomenon in a conducting polymer. Both these forms are stable in the presence of air and/or water. The doping process is reversed by treatment with aqueous alkali. Cyclic voltammetry studies in an aqueous electrolyte show excellent reversibility between selected reduced and oxidized forms of polyaniline.

Electron-Transfer Reactions Associated with Host-Guest Complexation. Oxidation of Ferrocenecarboxylic Acid in the Presence of β-Cyclodextrin

Abstract: L'etude est faite par voltammetrie cyclique en solution aqueuse a pH 9,2 dans laquelle le ferrocene est present sous forme d'anion ferrocenecarboxylate

The electronic and electrochemical properties of poly(isothianaphthene)

Abstract: The physical and electronic properties of poly(isothianaphthene) PITN, are reported, including initial characterization, electrochemical cyclic voltammetry, spectroscopy, and transport properties. PITN has the smallest energy gap of any known conjugated organic polymer, Eg≂1 eV. This novel conjugated polymer exhibits reversible chemical and electrochemical p‐type doping with an associated high contrast color change. After doping, thin films of PITN have very low optical density in the visible portion of the spectrum. Thus, PITN is the first example of a transparent highly conducting polymer (σ∼50 Ω−1 cm−1).

Poly(3-methylthiophene)-coated electrodes: optical and electrical properties as a function of redox potential and amplification of electrical and chemical signals using poly(3-methylthiophene)-based microelectrochemical transistors

Abstract: : Optical and electrical properties of anodically grown poly-3-methythiophene are reported as a function of redox potential in CH3CN/0.1M (n-Bu4N)ClO4. Poly-3-methylthiophene can be grown by the oxidation of 3-methylthiophene and deposited onto Au or Pt electrode surfaces. A pair of poly-3-methylthiophene-connected microelectrodes can function as a transistor where one of the electrodes is regarded as 'source' and the other as 'drain' with the source being referenced to the solution as a gate. The poly-3-methylthiophene is the analogue of the channel of a solid state field effect transistor, since its conductivity changes by 100,000,000 depending on the potential. Large optical (300-800 nm) and electrical changes for the poly-3-methylthiophene occur between approx. +0.3 V and approx. +0.8 V vs. SCE. The reduced material has an absorption maximum at 490 nm and the oxidized material has an absorption maximum at 750 nm. The optical density changes parallel the resistant changes that occur as the potential of the polymer changes between approx. +0.3 and approx. +0.8 V vs. SCE. The charging of a 1.5 micrometer thick film of poly-3-methylthiophene involves approx. 10,000 time more charge per unit of projected area then a smooth Pt electrode, consistent with a large effective internal surface area for the conducting polymer.

Vacuum heat-treatment for activation of glassy carbon electrodes

Abstract: Le traitement thermique d'une electrode de carbone vitreux, a 725°C sous vide pousse (<2.10 −6 Torr) permet d'obtenir une electrode active vis-a-vis de l'oxydoreduction du ferro-ferricyanure et pour l'oxydation d'acide ascorbique

Cyclic voltammetry and anodic stripping voltammetry with mercury ultramicroelectrodes

Abstract: A method for the preparation of mercury microvoltammetric electrodes of hemispherical geometry with radii of 2.3-7.3 ..mu..m has been developed. Mercury is electrodeposited from solutions of Hg(I) onto a microvoltammetric platinum disk electrode at a constant potential sufficient to ensure diffusion limited conditions. The radius of the deposited mercury electrode is a function of the square root of the deposition time and was experimentally evaluated by applying the equation for steady-state limiting current at a hemispherical electrode to the reduction of Ru(NH/sub 3/)/sub 6//sup 3 +/ at the mercury electrode. The mercury microvoltammetric electrode has been employed in several unique applications. Anodic stripping voltammetry with these electrodes can be performed with a quiescent solution during deposition due to the enhanced mass transfer resulting from nonlinear diffusion. The stripping peaks are as narrow as those expected for thin films, and the peak current for the stripping of lead was found to be linear over the concentration range of 7 x 10/sup -10/ M to 1 x 10/sup -7/ M (5-min preconcentration interval) and to have higher precision than conventional stripping techniques. Mercury microvoltammetric electrodes also are demonstrated to be of value in fast scan cyclic voltammetry in aqueous solution. A well-definedmore » wave can be obtained for the oxidized form of ascorbic acid at pH 7.0 at a scan rate greater than 1 kV s/sup -1/. 26 references, 3 figures, 2 tables.« less

Micellar effects on the reductive electrochemistry of methylviologen

Abstract: Etudes de la reduction du methylviologene en presence de micelles de laurylsulfate de sodium, de Triton X100 et de bromure de cetyltrimethylammonium

Analysis of Passive Films on Stainless Steel by Cyclic Voltammetry and Auger Spectroscopy

Abstract: Anodic passivation of Type 316L stainless steel in a borate-boric acid buffer solution was studied using cyclic voltammetry and Auger spectroscopy. Based on a comparison with the results obtained on the metals (iron, chromium, and nickel), the reduction peaks appearing in the voltammograms for the steel were attributed to the reductive dissolution of a ferric oxide and to valence transitions associated with chromium and nickel in the oxide. It is shown that cyclic voltammetry in the buffer solution provides a qualitative and semiquantitative analysis of the passive film growth. Okamoto's model of formation of two types of films, determined by the anodization potential, is found to be applicable; the mechanism of oxide growth is related to selective enrichment of iron or chromium, which is based on solubility relationships predicted by thermodynamic considerations. 12 references, 8 figures.

Electrocatalytic reduction of CO2 at a chemically modified electrode

Abstract: When electropolymerized, the complex Re(vbpy)(CO)3Cl (vbpy = 4-vinlyl-4′-methyl-2,2′-bipyridine), as a polymeric film on a Pt electrode, electrocatalytically reduces CO2 to CO with turnover numbers greatly exceeding those observed for the analogous electrocatalytic reduction of CO2 by Re(bpy)(CO)3Cl in homogeneous solution (bpy = 2,2′-bipyridine).

Trace determination of chromium in various water types by adsorption differential pulse voltammetry

Abstract: A new sensitive voltammetric method is presented for the determination of trace amounts of total chromium [Cr(III) and Cr(VI)] in natural waters. The method is based on the preconcentration of the Cr(III)-DTPA complex by adsorption at the HMDE at the potential of −1.0 V. The adsorbed complex is then reduced producing a response with a peak potential of −1.22 V and the peak height of the Cr(III) reduction is measured. The catalytic action of nitrate and bromate ions on the Cr(III)-DTPA reduction has been elucidated using cyclic voltammetry. The adsorption of chromium complexes at the HMDE was investigated using out-of-phase a. c. voltammetry and the potential range of adsorption was determined. Based on these investigations optimal conditions for the determination of the total chromium concentration in the range 20–2,000 ng/l have been established. The determination limit is 20 ng/l and the RSD is 5% for chromium concentrations ⩾200 ng/l.

Temperature and electrolyte effects on the electron-transfer reactions of cytochrome c

Abstract: On decrit les effets de la temperature sur a la fois le potentiel standard et la vitesse de transfert d'electron heterogene pour le cytochrome c a des electrodes d'oxyde d'indium dopees a l'etain

Electrochemistry on Liquid/Liquid Interfaces

Abstract: I Introduction- II Theory- Equilibrium Conditions- The Nernst Potential- Single Ion Gibbs Energy of Transfer- Ideally Polarizable L/L Interface- Redox System Equilibrium- III Experimental Arrangements- Electrode Configuration- Quasi-Reference Electrodes- Reference Electrodes- Four Electrode Potentiostat- Convention of Signs- Experimental Arrangements- Electrolyte Dropping Electrode- Stationary Interface- Chronopotentiometry- Cyclic Voltammetry- IV Double Layers at L/L Interfaces- V Current Flow Across the Interface- VI Mediated Properties- VII Impedance Measurements- AC Bridges- Lissajous Figures- Phase Sensitive Detection- VIII Phase Transfer Catalysis- References

Electrochemically polymerized N,N-dimethylaniline film with ion-exchange properties as an electrode modifier

Abstract: Poly(N,N-dimethylaniline) (PDMA) was prepared by electrochemical polymerization of the corresponding monomer and was found to have the structure of an ionene polymer with positively charged sites as quaternary ammonium groups in the polymeric backbone. It is demonstrated that the PDMA film has an anion-exchange character irrespective of the pH of a solution, and coating electrodes with PDMA produces surface which strongly bind multiply charged negative ions. 65 references, 7 figures, 1 table.

Copper Hexacyanoferrate-Modified Glassy Carbon: A Novel Type of Potassium-Selective Electrode

Abstract: Chemically modified electrodes are prepared by deposition of copper hexacyanoferrate (CuHCF) on glassy carbon. These electrodes are characterized by voltammetric and potentiometric measurements. After suitable conditioning they exhibit nearly Nernstian response to changes in activity of potassium or ammonium ions as well as good selectivity with respect to sodium ions. The kinetics of potassium ion exchange between the CuHCF film and aqueous solutions is studied and the diffusion coefficient of potassium ion in CuHCF is determined.