Showing papers on "Cyclic voltammetry published in 1989"

Effect of Coprecipitated Metal Ions on the Electrochemistry of Nickel Hydroxide Thin Films: Cyclic Voltammetry in 1M KOH

Abstract: Binary 9:1 composite hydroxides of nickel with 13 other metals were prepared by cathodic electrocoprecipitation from metal nitrate solutions and characterized by cyclic voltammetry in . Under these conditions, coprecipitated Ce, Fe, and La strongly catalyzed the oxygen evolution reaction. Conversely, Cd, Pb, and Zn poisoned this reaction. The hydrogen evolution reaction was less affected by the coprecipitated metals; Ag and Pb had a catalytic effect on this reaction. Co and Mn shifted the nickel hydroxide redox potentials to more cathodic values. In contrast, Cd, Ce, Cr, Fe, La, Y, and Zn each shifted these redox potentials anodically. The coulombic efficiency of the oxidation‐reduction process was substantially lowered by Ce, Fe, and La.

Activation of highly ordered pyrolytic graphite for heterogeneous electron transfer: relationship between electrochemical performance and carbon microstructure

Abstract: The electrochemical and vibrational spectroscopic properties of highly ordered pyrolytic graphite (HOPG) were determined before and after modification by anodization or pulsed laser irradiation. Both treatments greatly accelerated the heterogeneous electron-transfer-rate constants for the Fe(CN)6(3-/4-) and dopamine redox systems on HOPG by approximately six orders of magnitude. At intermediate electrochemical pretreatment (ECP) potentials, a spatially heterogeneous surface resulted, with surface regions exhibiting the 1360/cm band being separated by tens of microns. The results clearly indicate that graphitic edge plane is necessary for fast electron transfer, and that the pretreatment procedures accelerate k0 by generating edge-plane defects in the HOPG lattice. The mechanisms of defect generation for the two procedures appear very different, with ECP appearing to follow a nucleation process leading to a spatially heterogeneous surface, while the laser pulse appears to shatter the HOPG lattice, leading to a more uniform distribution of active sites. The results provide important conclusions about the relationship between carbon electrode microstructure and heterogeneous electron transfer activity. Of particular interest is the heterogeneous electron transfer rate between carbon electrodes and various well-known redox systems such as ascorbic acid, ferri/ferrocyanide, and the catecholamines. Not only are these systems of significant analytical interest, but they serve asmore » benchmarks for comparisons of electrode performance.« less

Synthesis and characterization of poly(alkylanilines)

Abstract: Synthese par polymerisation chimique (persulfate d'ammonium) et electrolytique de methyl-2(methyl-3, ethyl-2, ethyl-3 et propyl-2) aniline

Electrochemical and Spectroscopic Evidence on the Participation of Quadrivalent Nickel in the Nickel Hydroxide Redox Reaction

Abstract: Electrochemical and iodometric measurements on anodically charged thin film nickel hydroxide electrodes indicated an average nickel valence of . In situ visible spectroscopy of nickel hydroxide deposited on optically transparent electrodes featured one strong and broad absorption band with an intensity proportional to the state of charge. The results are not consistent with the presence of separate trivalent and quadrivalent phases or the participation of peroxide radicals in the nickel hydroxide redox reaction, but are best explained by the formation of a single mixed valence phase such as which has a 3.67 average nickel valence. Full utilization of the proposed oxidized phase could increase the discharge capacity of nickel battery electrodes by 67% beyond the previously assumed one‐electron theoretical capacity. That the discharge is generally incomplete may be due to electronic isolation of portions of the oxidized material by a high resistivity layer of divalent nickel hydroxide produced at the surface during discharge.

Electrochemical Properties of Organic Disulfide/Thiolate Redox Couples

Abstract: The redox behavior, kinetic reversibility, chemical reversibility, and stability, and the specific adsorption or chemisorption at electrode surfaces of a diverse group of organodisulfide cathode materials have been studied by potential-sweep and potential-step methods. The number of electrons involved in the redox reaction and the diffusion coefficients of the organodisulfide species in electrolyte solutions were determined with a rotating disk electrode in conjunction with chronocoulometry/chronoamperometry. Observations indicate that the overall, stoichiometric reaction of those redox couples is RSSR + {r reversible} where R represents an organic moiety. These reactions are chemically reversible, yet kinetically hindered, especially at ambient temperatures. The microscopic reversibility of the redox couples promises the possibility of constructing secondary energy conversion systems based on these materials. The slow electrode kinetics, however, indicates that the introduction of electrocatalysts to assist the electrode reaction may be effective in improving battery performance. The negligible adsorption of these materials at platinum electrodes, in addition, implies that the electrode kinetics can be formulated by simple electrodic equations without consideration of surface coverage.

Permselectivity and ion-exchange properties of Eastman-AQ polymers on glassy carbon electrodes.

Abstract: Eastman-AQ55D is a new poly(ester sulfonic acid) cation exchanger available in a commercial dissolved form. Films of this polymer were coated onto glassy carbon surfaces, and the resulting electrodes exhibit attractive permselectivity, ion-exchange, and antifouling properties. Substantial improvement in the selectivity is observed as a result of excluding anionic species from the surface. The charge-selective behavior is demonstrated in the presence of a variety of compounds of neurological significance. A rapid response to dynamic changes in the concentration of cationic and neutral species is observed. The polymer strongly binds multiply charged counterions. Cyclic voltammetry is used to determine the quantity of incorporated ions as a function of time, concentration, and other variables. The oxidation of hydrogen peroxide is catalyzed when Ru(bpy)3(2+) is incorporated in the coating. The film can also protect the substrate electrode from foulants present in the contacting solution. These features, as well as the low cost, simple coating procedure, strong adherence to surfaces, and versatility, make the Eastman-AQ55D polymer well-suited for a variety of electro-analytical applications.

Electrocatalysis and detection of amino sugars, alditols, and acidic sugars at a copper-containing chemically modified electrode

Abstract: Etude par voltammetrie cyclique et microscopie electronique a balayage, de l'oxydation des composes polyhydroxyles sur une electrode de carbone modifiee par CuCl 2

Electrochemistry of cytochrome c, plastocyanin, and ferredoxin at edge- and basal-plane graphite electrodes interpreted via a model based on electron transfer at electroactive sites of microscopic dimensions in size

Abstract: The electrochemistry of a range of electron-transfer proteins at edge- and basal-plane graphite electrodes has been reconsidered using a microscopic model, which involves fast electron transfer at very small oxygen-containing electroactive surface sites. This model assumes that mass transport to the electrode occurs by radial diffusion when the density of the surface active sites is low (as is generally true in the case of the basal-plane graphite electrode) and by linear diffusion when the density of the active sites is increased sufficiently to cause overlap of the diffusion layers. With this model it is now proposed that the electrochemistry of cytochrome c, plastocyanin, and ferredoxin occurs with a very fast rate of charge transfer (≥1 cm s-1) at both edge- and basal-plane graphite electrodes. Critical factors, such as the mode of surface preparation (including covalent derivatization), the pH, and the presence in the electrolyte of cations such as Mg2+ or Cr(NH3)63+, control the density of surface sites, which result in the electrochemistry of a specific protein. This contrasts with the conclusion that has been reached previously based upon a conventional macroscopic model, which supposes that the rate of electron transfer is subject to enhancement or depression through these factors. The proposal that the electron-transfer process at the protein-graphite electrode interface is very fast over a wide range of conditions is now consistent with homogeneous kinetic studies where electron-transfer reactions of proteins, particularly amongst physiological partners, are also known to be fast. © 1989 American Chemical Society.

Development and ageing of the rat nigrostriatal dopamine system studied with fast cyclic voltammetry.

Abstract: Fast cyclic voltammetry at carbon fibre microelectrodes was used to measure electrically stimulated dopamine release in the striatum of anaesthetised young, adult, and senescent Wistar rats. By alteration of stimulus parameters and by use of nomifensine, investigation of dopamine release, uptake, and compartmentalisation within the striatum was possible. The rate of dopamine release was highest in adult rats. No difference was observed between young and old animals. The size of the releasable (newly synthesised) dopamine pool was also largest in the adult group, again with no significant difference occurring between young and aged rats. The rate of dopamine uptake was highest in adult rats, although, when expressed as a function of dopamine release, young and aged rats showed proportionally greater uptake. Nomifensine (10 mg/kg i.p.) increased dopamine release by mobilising the inert storage pool to a greater extent in young than in adult rats, whereas the effect of the drug on uptake was similar in all age groups. The functional significance and possible explanation of these results are discussed.

Bor‐organische Redoxsysteme

Abstract: Die Verbindungen BPh3−nMesn, n = 0–3 (1 –4), AlPh3 (5), AlMes3 (6), 1,4-Mes2BC6H4NMe2 (7), 1,4-Mes2BC6H4BMes2 (8) und 4,4′-Mes2BC6H4C6H4BMes2 (9) wurden UV/VIS-spektroskopisch sowie durch cyclischen Voltammetrie untersucht. Bereits eine Mesityl-Gruppe (Mes) am Bor reicht aus, um die reduzierten Formen, d. h. die Radikalanionen von Triarylboranen durch Erschwerung einer Aufweitung der Koordinationszahl kinetisch zu stabilisieren und um eine reversible Elektronenubertragung an der Elektrodenoberflache zu ermoglichen. Dieser Effekt konnte fur die Aluminium-Analogen nicht festgestellt werden. Der kinetischen Stabilisierung steht eine geringe thermodynamische Destabilisierung der Triarylboran-Radikalanionen aufgrund des Donor-Effekts der Mesityl-Gruppe gegenuber. Die disubstituierten Aromaten 8 und 9 zeigen zweistufig reversibles Redoxverhalten. Spektroskopische und elektrochemische Ergebnisse lassen den Dimesitylboryl-Substituenten als einen starken, der Nitril-Gruppe vergleichbaren π-Akzeptor erkennen. Organoboron Redox Systems The compounds BPh3−nMesn, n = 0–3 (1–4), Alph3 (5), AlMes3 (6), 1,4-Mes2BC6H4NMe2 (7), 1,4-Mes2BC6H4BMes2 (8), and 4,4′-Mes2BC6H4C6H4BMes2 (9) were studied by UV/VIS spectroscopy and cyclic voltammetry. A single mesityl substituent (Mes) is sufficient to permit reversible electron transfer at the electrode surface and to stabilize the singly reduced, i.e. radical anionic form of trialrylboranes by preventing an increase of the coordination number at boron. This electrochemical effect is not observed for the aluminum analogues. In contrast to the kinetic stabilization of triarylborane anion radicals by mesityl substituents stands the slight thermodynamic destabilization by this electron donor group. Disubstituted aromatics such as 8 and 9 show two-step reversible redox behaviour. Spectroscopic and electrochemical results reveal that the dimesitylboryl substituent is a strong π acceptor, comparable to the nitrile group.

Measurement of nanomolar dopamine diffusion using low-noise perfluorinated ionomer coated carbon fiber microelectrodes and high-speed cyclic voltammetry.

Abstract: Several improvements in the fabrication and use of carbon fiber voltammetric microelectrodes (CFVMs) are described. These procedures did not involve oxidative treatment, but resulted in sensitivities and selectivities approaching those of treated CFVMs, without the inherent slow response times associated with the latter electrodes. To accomplish this we reduced CFVM noise by (1) improving the adhesive seal between the 8 microns o.d. carbon fiber and the glass insulation using vacuum, (2) snapping rather than cutting or beveling the fiber to be flush with the glass, and (3) using a concentrated electrolyte solution to make electrical contact with the fiber. System noise was reduced by digital smoothing and signal averaging. Selectivity of the CFVMs for dopamine over ascorbate was enhanced to better than 2000:1 by coating with Naflon, a perfluorinated cation exchange polymer, using a low (+0.5 V vs Ag/AgCl) electroplating potential. This low voltage also prevented electrode surface oxidation. To demonstrate the performance of our CFVMs, we used them in conjunction with high-speed cyclic voltammetry to accurately measure the diffusion coefficient of iontophoretically released dopamine at concentrations as low as 35 nM over distances of less than 200 microns in agarose gel.

Electrochemical Polymerization of Electroactive Polyaniline in Nonaqueous Solution and Its Application in Rechargeable Lithium Batteries

Abstract: An electroactive polyaniline (PAn) was successfully prepared from nonaqueous propylene carbonate (PC) solution containing acid and electrolyte . PAn deposition and the doping‐undoping process of deposited PAn film were investigated by consecutive cyclic voltammetry in various electropolymerization solutions. It is confirmed by infrared spectral measurement that there is no essential difference in the manner of bonding between the electroactive PAn films deposited from aqueous and PC solutions. Inspection by scanning electron microscope revealed that PAn films deposited from aqueous solution had a fibrous structure, whereas the PAn film deposited from PC solution had a porous surface which resembled polypyrrole films. The shape of the electro‐oxidation curve is found to be essentially different, depending on the solvent or the value of acid in an electropolymerization solution. An electroactive PAn film deposited from PC solution was applied to an effective cathode material of a rechargeable lithium battery . The (deposited from PC solution) battery showed a high coulombic efficiency and high‐energy density in charging‐discharging behavior. The electroactivity of PAn film deposited from PC solution was found to be as high as, or higher than, that of PAn film deposited from aqueous solution.