Showing papers on "Cyclic voltammetry published in 1982"

Enhanced Stability of Photoelectrodes with Electrogenerated Polyaniline Films

Abstract: Polyaniline was electrodeposited on platinum and semiconducting (Cd-chalcogenides, Si, GaAs, GaP) electrodes from aqueous solution (pH = 1) containing aniline. The electrochemical behavior of such films was examined in aqueous and nonaqueous solutions by cyclic voltammetry. Results show that the polyaniline film is conducting in both cathodic and anodic regions at pH < 3 as evidenced by the electrochemical redox reactions of various redox couples on polyanilinecoated electrodes. In general, all polyaniline-coated semiconductor electrodes examined in this work exhibited enhanced stability of the photocurrent when compared to that of the naked electrodes.

Reversible electrochemical reduction and oxidation of cytochrome c at a bis(4-pyridyl) disulphide-modified gold electrode

Abstract: At a gold electrode on which bis(4-pyridyl) disulphide had been pre-adsorbed, horse heart ferricytochrome c exhibited a well developed quasi-reversible redox wave by cyclic voltammetry in the absence of any promoter in the solution.

Structure and properties of cation-radical salts of arenes. II. Crystal structure, phase transitions and analysis of the electrochemical crystallization process of fluoranthenyl cation-radical salts

Abstract: Crystal structures and phase transitions in fluoranthenyl radical cation salts, a new family of organic conductors are reported. The metal to semiconductor transition which is observed seems to be related to a distortion of the stacks of aromatic molecules perpendicular to the stacking direction. Cyclic voltammetry and chronoamperometry were employed to study the electrochemical production of these cation radical crystals of the type (A2)⊚⊕X⊖, where A was either fluoranthene or perylene and X is PF6. It appears that following the initial oxidation of A at the electrode a dimer radical cation is formed. This species then complexes with the anion to give the species of the proper stoichiometry from which the crystals grow. The crystals growing on the anode function directly as electrodes.

Anodic dissolution of n-type and p-type chalcopyrite

Abstract: The anodic dissolution of n- and p-type chalcopyrite (CuFeS2) was studied in both acidic sulphate and acidic chloride media under conditions relevant to chemical leaching, i.e., at temperatures >70° C and over the potential region 0.2–0.6 V versus SCE. Double potential pulse chronoamperometry was used to probe the surface of the chalcopyrite anodes to determine the activation currents at various applied overpotentials. Analysis of the data obtained in both systems indicated the formation of a surface layer, a solid electrolyte interphase (SEI), which slows the rate of electron transfer. The electron transfer between various redox couples, including Cu2+/Cu2+, Fe2+/Fe2+ and I3−/I− on n- and p-type chalcopyrite and on Pt, was compared using cyclic voltammetry. In the potential region of interest, the Fe2+/Fe2+ couple is much less reversible on chalcopyrite than are the Cu2+/Cu2+ and I3−/I− redox couples. Chemical leaching of chalcopyrite in the presence of various oxidants was also carried out, and the results of the chemical experiments were discussed in terms of the electrochemical properties of the systems.

Electrochemistry of (CH)x: Lightweight rechargeable batteries using (CH)x as the Cathode- and anode-active materials

Abstract: Polyacetylene, (CH)x, can be controllably doped p-type (oxidized) or n-type (reduced) by simple electrochemical procedures. Cyclic voltammetry studies on freestanding films of cis-(CH)x show that (CH)x can be reversibly oxidized at ~+3.6V vs. Li and reversibly reduced at ~+1.4V vs. Li. The spontaneous electrochemical “undoping” of p- and/or n-doped (CH)x, which occurs when appropriate combinations and configurations of (CH)x are employed, permits (CH)x to be used in the fabrication of lightweight rechargeable batteries having large energy and large power densities. Cis-(CH)x can be readily isomerized to the trans-isomer by electrochemical p-doping followed by electrochemical reduction to (CH)x.

Interaction of Methylated Adenine Derivatives with the Mercury Electrode.

Abstract: : Adenine and its methylated derivatives, 1-methyl-6-aminopurine, 3-methyl-6 aminopurine, N-methyl-6-aminopurine, and N,N-dimethyl-6-aminopurine, were studied in alkaline solution by DC, normal pulse and differential pulse polarography and by cyclic voltammetry and cathodic stripping voltammetry at hanging mercury drop electrodes. All save N, N-dimethyl-6-aminopurine gave polarographic mercury drop electrodes. All save N, N-dimethyl-6-aminopurine gave polarographic currents anc cathodic stripping peaks due to the formation of slightly soluble compounds with mercury. It was concluded that the 6-amino group of adenine is the mercury binding site in these cases. Cathodic stripping behavior suggests that 1-methyl-6-aminopurine, 3-methyl-6-aminopurine, and N-methyl-6-aminopurine can be determined by cathodic stripping voltammetry, and that detection limits for N-methyl-6-aminopurine are comparable to those for adenine (10 to the minus 9th power M). (Author)

Electrostatic binding of electroactive and nonelectroactive anions in a surface-confined, electroactive polymer: selectivity of binding measured by Auger spectroscopy and cyclic voltammetry

Abstract: : Electrodes derivatized with electroactive polymers or with charged, nonelectroactive polymers can be significantly influenced by the nature of the electrolyte and other ions present in a solution contacted by the derivatized electrode. It has been shown that charged, nonelectroactive polymers can persistently bind significant quantities of charged, electroactive species such as Fe(CN)(6)(4-) by surface polyvinylpyridinium or Ru(bipyridine)(3)(2+) by Nafion. Theses examples illustrate how electrostatic binding may be exploited for anlaysis, preparation of a variety of modified electrodes, and study of electrocatalysis. Electroactive polymers are charged in at least one of their accessible redox states and both selectivity of counterion binding and the movement of ions in and out of the surface polymer associated with change of redox state may affect electrochemical behavior. Electrodes coated with electroactive polymers may have a number of uses, including desalting of H20, that depend on the behavior of solution ions.

Catalysis of Oxygen Cathodic Reduction by Adsorbed Iron(111)‐Tetra (N,N,N‐Trimethylanilinium) Porphyrin on Glassy Carbon Electrodes

Abstract: The adsorption of iron(111)‐tetra (N,N,N‐trimethylanilinium) porphyrin on glassy carbon was studied in aqueous solutions using cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and the RRDE technique. The porphyrin was found to catalyze oxygen electroreduction; the overpotential is reduced by about 400 mV and the hydrogen peroxide yield is 5% compared to 25% in the absence of catalyst.

Electrochemical behaviour of complexes of copper(II) with 14-membered saturated tetra-aza macrocycles

Abstract: The electrochemistry of copper(II) with three 14-membered saturated tetra-aza macrocyclic ligands (L) is reported. Both anodic and cathodic electrode processes involve complicated mechanisms; nevertheless cyclic voltammetry at high potential scan rates allowed evaluation of the E½ values for the couples [CuL]3+–[CuL]2+ and [CuL]2+–[CuL]+. Reduction and oxidation mechanisms have been studied and the half-life of the species [CuL]3+ anodically electrogenerated has been evaluated. The thermodynamic data are discussed.

Electron Exchange Phenomena of Polymers Containing Nitroxyl Radicals

Abstract: The influence of electron exchange on the physical properties of polymers containing nitroxyl radical in their side chains has been studied by ESR, magnetic susceptibility measurement and cyclic voltammetry. ESR study shows that the electron exchange interaction between free radicals bound to a polymer chain is more effective than that between the corresponding monomeric radicals. Magnetic susceptibility (XM) was measured at temperatures between 4K and 273 K. The values of XM for the polymers obey the Curie-Weise Law (XM=c/(T−θ)), where magnetic moments obtained from XM show the presence of antiferromagnetic interaction between the nitroxyls of a polymer chain, although the interaction is not large enough to bring about long range ordering in the spin orientation of the nitroxyls. In the corresponding monomers, no antiferromagnetic interaction was observed. Cyclic voltammetry in DMF shows that the electrode process in polymer system is a reversible multiple-electron transfer reaction, where the number of the transfer (np) is 60% of the total free radicals per molecule. A comparison of the shape of the voltammetric response curve in the polymers with that in the corresponding monomers suggests that the interaction between nitroxyl radicals in the polymer is too weak to be reflected in electrochemical behavior.

Electron transfer in authentic triangular copper(II) trimers with Cu3X (X = oxygen or hydroxy) core. The CuII2CuIII-CuII3 and CuII3-CuCuICuII2 couples

Abstract: Trinuclear triangular copper(II) complexes of pyridine•2-carbaldoxime (HPL) and isonitrosoketimine ligands of type RNC(R(R')C(R')NOH (R = Et, n-Pr, n-Bu, Ph; R'=Me. Ph) have been examined electrochemically. These strongly antiferromagnetic complexes are of types (Cu30(ligand)3)+ and [Cu3OH(ligand)2+, having Cu30 and Cu30H cores, respectively. The known structure of [Cu3OH(PL)3]2+ provides an authentic reference point for data analysts. Cyclic voltammetry and constant-potential electrolysis (platinum working electrode) show that complexes with a Cu30 ooze uniformly display a one-electron-transfer process characterized by the oxidation-state description CuIIICuII+e-⇌ CuII3 with E°298 in the range 0.3-0.6 V vs. SCE in acetonitrile and dimethylformamide. The species with a Cu3OH core do not have this electrochemical response. On the other hand, such species show a novel one-electron-transfer process of the type CuII3+e-⇌ CuII2CuI with E°298 in the range -0.3 to -0.45 V vs. SCE at a hanging-mercury-drop electrode in acetonitrile. The Cu30 core does not display this process. In effect the electrochemical behaviors of the two cores are complementary: the Cu3O core undergoes oxidation while the Cu3OH core undergoes reduction. Thus the core proton acts in a va/velike fashion in controlling the direction of electron transfer Addition of an acid (HCl04) converts the Cu3O species to the Cu3OH species. Conversely, addition of a base (NEt3) converts Cu3OH to Cu30. The electrochemical responses change accordingly with addition of acid or base The interconversion reactions are also useful at preparative levels.