Anodic Voltammograms Research Articles

Stripping voltammetry of thallium at a film mercury electrode

The electrochemical dissolution of thallium from the surface of a mercury film electrode was studied in different supporting electrolytes. The effects of the concentration of thallium(I), electrolysis potential and time, and the potential sweep rate on anodic voltammograms were studied. The electrode process in solutions containing EDTA, HCl, and ascorbic acid at a potential sweep rate of 0.020 V/s is reversible. A stripping voltammetric procedure was developed for determining thallium(I) in the concentration range 1 × 10–9 to 5 × 10–7 M. The detection limit (3σ, n = 3) is 5 × 10–10 M.

Temperature Dependence of Inward Diffusion of Underpotentially-Deposited Cd into a Au (100) Bulk Phase under Electrochemical Environment

We investigated the inward diffusion of underpotentially-deposited (UPD) Cd into a Au (100) substrate in 50 mol m -3 sulfuric acid solution under potential control by anodic voltammetry at the temperature range from 295 to 333 K, as well as by the electrochemical quartz crystal microbalance (EQCM) analysis and X-ray diffractmetry (XRD). The anodic voltammograms show that inward diffusion of the Cd adatoms into a Au (100) bulk phase is classified into two types of steps. One is a very fast step, which is the diffusion of UPD Cd into a Au (100) electrode at the surface layer; the activation energy of this step is ≅ 70 kJ mol -1 . The other is a much slower step; the activation energy of this step (110kJ mol -1 ) agrees well with that of Cd bulk diffusion into a Au-Cd compound. The amount of UPD Cd is calculated from EQCM analysis, and it nearly agrees with that obtained from anodic voltammetry. We found that the amount of UPD Cd increases with temperature. We confirmed the formation of β Au-Cd layer on the sample by XRD after maintained at the UPD region of -1100mV vs. Hg/Hg 2 SO 4 for 1 h at 333 K.

Overestimation of heterogeneous rate constants of hexacyanoferrate at nanometer-sized ultramicroelectrodes

Standard rate constants of hexacyanoferrate (Fe(III)/Fe(II)) at nanometer-scaled ultramicroelectrodes were evaluated from a plot of half-wave potentials of the steady-state voltammograms against logarithms of radii of ultramicroelectrodes. The smaller is the radius, the more positively shifts the anodic voltammogram and the more negatively does the cathodic wave. The shift is ascribed to the increase in the current density, which alters the diffusion-control into the charge-transfer control. However, the amount of the shift was smaller than that predicted from the conventional theory for the kinetic mass transport at ultramicroelectrodes. Consequently, the standard rate constant was overestimated by three times. A possible reason of the smaller shift is a non-negligible length of the mean free path of the diffusing redox particle in comparison with the electrode size. A stochastic diffusion model is proposed, in which a particle walks by random distances of which average is of the order of the electrode diameter. Monte Carlo simulation for this model showed that the concentration profiles were more uniform than the conventional profile, and hence the overpotential is observed to be apparently smaller.

Properties of Microlayers of Ionic Liquids Generated at Microelectrode Surface in Undiluted Redox Liquids. Part II

For several simple alcohols such as methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol, physical properties of the microlayers of the new-type ionic liquids generated during the electrode processes of these undiluted redox liquids were studied. In all cases, well-reproducible, transport-controlled, anodic voltammograms were obtained at Pt microelectrodes. It has been found that the transport properties of the undiluted alcohols, such as activation energy of diffusion and diffusion coefficients, are strongly affected by the enormously large concentration of ions in the region adjacent to the electrode surface. The results obtained for alcohols were compared to those of diluted 1,1‘-ferrocenedimethanol, which compound may be treated as a model redox system. This comparison revealed, in contrast to the Stokes−Einstein relation, that the molecules of each alcohol, while having much smaller size than the molecules of 1,1‘-ferrocenedimethanol, diffuse to the microelectrode surface at a similar rate (metha...

Differential pulse stripping voltammetry of mercury(II) ions at a cylindrical carbon-fiber microelectrode in the presence of au(III)ions

The determination of Hg(II) ions in aqueous solutions containing Au(III) ions was studied using differential pulse stripping voltammetry at a cylindrical carbon-fiber (d= 30 μm) microelectrode fabricated from a pitch at 2800°C. At the [Au(III)]/[Hg(II)] ratio higher than 25, the anodic voltammogram of mercury accumulated in the potential range from 0.2 to –0.2 V for 40–200 s exhibited a current peak at 0.62–0.72 V. The peak height and area were directly proportional to the concentration of Hg(II) in the range (1–1000) × 10–10M. The results of determining Hg(II) in waters of different origin are reported.

Nature of a Positive Anodic Peak in the Stripping Voltammogram of Binary Platinum–Metal Systems

The effect of platinum on the electrodeposition of cadmium, lead, copper, and mercury at the surface of a solid electrode was studied by stripping voltammetry. It was shown that an additional current peak in the anodic voltammogram corresponded to the metal ionization to support electrolytic platinum.

The Surface Morphology of Mercury Plated Glassy-Carbon Electrodes and Stripping Voltammetry of Heavy Metals

This article deals with the investigation into the correlation between the surface morphology of the glassy carbon electrodes modified with mercury and the characteristics of voltammograms of copper, lead, cadmium and mercury. The methods of voltammetry and in-situ microscopy were used. It is shown that nucleation is the slow step of the mercury evolution on glassy carbon electrode. Overvoltage of the process is reduced after nuclei form. The factors, which determine the distribution of mercury on the electrode surface, are the degree of polishing of glassy carbon and exposure of the electrode to the air. Two types of insoluble compounds are formed on the electrode in solutions containing chloride-ions. One type of the compounds, a calomel, forms a reversible redox pair and is reduced to metallic mercury during cathodic polarization of the electrode. Well-defined voltammograms of the metals are observed in this case. The other type of the compounds appears during anodic polarization of the mercury-coated electrode in solutions containing chloride-ions when the mole ratio HCl/Hg2+ of the solution is less than 104. The formation of these compounds, which possess anomalous properties, is followed by appearance of a cathodic peak in the anodic voltammogram (‘reverse’ peak). A special electrochemical ‘conditioning’ of the electrode is needed to remove the precipitate of insoluble compounds. Otherwise, unusual ‘reverse’ peaks complicate the voltammograms of the elements to be determined.

New Procedure for Linear Sweep Voltammetric Determination of Catalytic Reaction Rate Constant. Oxidation of Some Aliphatic Alcohols with Electrolytically Generated Os(VIII)

Oxidation rate of methanol, ethanol and 2-propanol by Os(VIII) in 1 M KOH was determined by evaluating anodic voltammograms of Os(VI) in the presence of the aliphatic alcohols. The proposed method is based on the evaluation of the change of voltammogram shape by catalytic process and on the assumption of its approximation by fractionally integrated voltammograms. This assumption has been confirmed empirically for k'f /a in the interval of <0.04,1>. The rate constants from this interval could be determined with sufficient accuracy. The method is suitable for evaluation of reaction rates slow and moderately fast catalytic reactions. It was compared with other evaluation methods from the literature.

Voltammetric study of the extractant 4-methyl-N-quinolin-8-ylbenzenesulfonamide at a carbon paste electrode

An electroanalytical study of 4-methyl-N-quinolin-8-ylbenzenesulfonamide, a model compound of similar structure to that of the active component in the commercial extractant LIX 34, at a carbon paste electrode, has been carried out using different voltammetric techniques. The compound was oxidized in methanolic medium (methanol– H2O, 20 + 80), with Britton–Robinson buffers as supporting electrolytes and KCl solution (ionic strength 1 mol l–1), giving rise to a voltammetric peak in the pH range 1.2–12.0. The effect of pH on the anodic voltammograms has been studied and the graph of Epversus pH shows two straight lines intercepting at a pH value of 9.6. The oxidation process for the compound is irreversible (text-decoration:overlineαn= 0.63) and predominantly diffusion controlled, although with an important adsorptive component. The electrode process can be attributed to the oxidation of the sulfonamide group. A voltammetric method for the determination of the compound has been developed and has been applied to samples of LIX 34.

Mechanism of anodic dissolution and passivation of iron—II. Comparison of the behavior in neutral benzoate and acetate buffer solutions

The kinetics of the dissolution and passivation of Fe has been studied in neutral benzoic acid/sodium benzoate buffer solution as a function of the total benzoate buffer concentration and pH. The results have been obtained from potential sweep experiments at 5 mV s−1, which corresponds to quasi steady-state conditions. Two anodic peaks were found in the active dissolution region of the anodic voltammogram. A reaction order of about −1 with respect to benzoate concentration and of about 2 with respect to pH has been found for the Tafel region of the first peak. The corresponding reaction orders were −1 and 0.7 for the second peak. Galvanostatic cathodic reduction experiments were used to characterize the surface film formed during the anodic sweep. Anodic sweep experiments were also performed using mixtures of benzoate and acetate buffers. The behavior of Fe in benzoate and acetate buffer solutions has been compared and contrasted. Benzoate buffer is found to be a much better inhibitor than acetate buffer, and the results can be understood in terms of a strong interaction between the Fe surface and benzoate-containing adsorbates.

Mechanism of anodic dissolution and passivation of iron—I. Behavior in neutral acetate buffer solutions

The kinetics of the anodic dissolution and passivation of Fe have been studied in neutral and slightly acidic acetic acid/sodium acetate buffer solution as a function of the total acetate buffer concentration and pH. The results have been obtained from potential sweep experiments at 4 mV s−1, which corresponds to quasi-steady state conditions. Two anodic peaks were found in the active dissolution region of the voltammogram. A reaction order of −0.7 ± 0.2 with respect to acetate concentration and of 1.4 ± 0.2 with respect to pH has been found for the Tafel region of the first peak; more complicated behavior was found for the remainder of the voltammogram. Galvanostatic cathodic reduction experiments were used to characterize the surface film formed during the anodic sweep. A mechanism is proposed which accounts for the observed reaction orders, and simulates the observed anodic voltammograms in a semi-quantitative fashion. The mechanism provided a simple, physical expalantion for the observed negative reaction order with respect to acetate concentration.

Monte Carlo simulation of two-dimensional growth of conductive zones in interconversion of conducting polymer films involving random morphology

Morphological effects of the interconversion of conductive polymers on anodic voltammograms were estimated by Monte Carlo simulation when the film had a random distribution of electroactive and electroinactive sites. The simulation was based on the propagation theory of the conductive zone under charge-transfer control. The electroactive site was assigned either to a conductive (oxidation) or to a non-conductive (reduction) state. The non-conductive site contact with the conductive site was converted electrochemically into a conductive state in linear sweep voltammetry. When the composition ratio, p, of the electroactive sites ranged from 0.5 to 0.7, various patterns of the conductive zone were observed and appeared visually to be fractal. The current density at p = 0.59 had maximum fluctuation, depending on the initial distribution of the electroactive sites. Then the growing length of the conductive front was ten times longer than the film thickness, indicating that the front wandered in the film. The conversion ratio changed dramatically at p ranging from 0.56 to 0.62. Electric percolation from the film surface to the electrode occurred at p > 0.56. From variations of the variance of the current, the peak current and the conversion ratio with p, the voltammogram was classified into the following three controlled processes: Nernstian boundary condition control for 0 < p < 0.56; morphological control for 0.56 < p < 0.62; and charge-transfer control at the interface between the conductive and non-conductive sites for p > 0.62.

On Propagation Mechanism of the Electrochemically Doped Conductive Layer in Polypyrrole Films by Means of the Analysis of Linear Sweep Anodic Voltammograms

On Propagation Mechanism of the Electrochemically Doped Conductive Layer in Polypyrrole Films by Means of the Analysis of Linear Sweep Anodic Voltammograms

Investigation of the pH response of single carbon fibre electrodes

The potentiometric response of single carbon electrodes was examined in the titration of hydrochloric acid with potassium hydroxide. The electrodes were prepared either from two types of commercially available carbon fibre samples or from samples that were surface treated in the laboratory. Each carbon fibre electrode was examined by anodic voltammetry. This method was capable of showing that the presence of oxidisable surface groups could be altered by the prior surface treatment. Although the anodic voltammograms were different for each kind of surface treatment, the effect on the shape of the potentiometric curves was slight. It is suggested that there is an instability of the surface groups on carbon fibre.

導電性固体材料とガラス融液との反応に関する研究 Ｖ 金属とケイ酸塩ガラス融液との分極下における反応について Ｗ，Ｃｒ，Ｆｅ，ＳＵＳ３０４およびＩｎｃｏｎｅｌ ６００

In the previous paper, the electrochemical phenomena of Ni and Mo in a molten silicate glass of the composition 16 Na2O·12 CaO·72 SiO2 in wt% were investigated. In this paper, W, Cr, Fe, SUS 304 and Inconel 600 were chosen as the objects to be measured. Anodic dissolution, passivation and cathodic deposition for these metals were investigated by linear potential sweep voltammetry at various potential sweep rates (5-0.05V/sec) with platinum reference and auxiliary electrodes in Ar gas atmosphere or in air. Moreover, the metal-glass interface after polarization was analysed by EPMA.On cathodic potential sweep of every metal investigated here, silicate anions were easily reduced to silicon element and a kind of silicide layer covered the electrode surface. Since the silicide has high electrical resistance, its formation made the measurement of voltammogram difficult at slower sweep rates.The anodic voltammogram of W at 3V/sec showed a large current peak around 1.7V (relative to Pt reference). The peak potential shifted to more cathodic direction with decreasing sweep rate. The current peak was attributed to the formation of a passsive layer on the W electrode. The occurrence of tungsten oxide layer with 30μm thick on the W electrode was confirmed by EPMA. The oxide layer seemed to be made up by WO3. The broad current peak was observed on anodic voltammogram of Cr due to the formation of chromium oxide Cr2O3. There was no peak on the anodic current-potential curve for the Fe electrode and Fe dissolved rapidly and easily. Both SUS 304 and Inconel 600 were subject to passivation by oxide film formation of Cr2O3 and NiO on anodic polarization.

Voltammetric determination of traces of silver in some metals after dissolution of the sample in mercury

The general possibility of analysing metals and alloys by dissolution of the sample in mercury and recording the anodic voltammogram is examined for the determination of silver in some metals. In order to obtain good separation of the silver peak from the anodic limit, acetonitrile is used in the supporting electrolyte. If the main component of the sample is more noble than mercury, analysis is simple and takes ⩽ 20 min. Significant amounts of base metals in samples must be removed from the amalgam prior to the anodic stripping; optimum conditions for the removal are given. The detection limits found for the determination of silver in gold and lead and in indium amalgam are 4 × 10 −3, 4 × 10 −4 and 4 × 10 −6 % respectively. Dissolution of the lead button in mercury seems to be a successful alternative to the cupellation procedure. Silver in mercury does not form intermetallic compounds with gold.

Electrochemical oxidation of arsenious acid at a platinum electrode

At a clean Pt electrode, the As(III) oxidation wave in a cyclic voltammogram exhibited a large overpotential with respect to the thermodynamic reversible potential, and the cathodic wave of the reverse process was not present before onset of hydrogen evolution. The potential for the oxidation was found to be dependent on the electrode pretreatment, and deactivation was evident as the oxidation proceeded beyond the peak potential of the anodic As(III) voltammogram. The electrode could be reactivated by stepping to potentials less positive than the potential region at which platinum oxide was reduced. Although the cyclic voltammogram did not exhibit a reverse cathodic wave for As(V) reduction, the shape and peak height of the anodic voltammogram for an “active” electrode appeared if as a reversible two electron electrode reaction occurred. A mechanism based on the idea that lower valent forms of platinum oxide catalyze As(III) oxidation was postulated from evaluation of the potential and time dependences for actvation. The relationship between platinum oxides and arsenic ad-atoms to the As(III) oxidation is discussed. The conclusions drawn from the electrochemical results were supported by X-ray photoelectron spectroscopic analysis of the Pt surface prior to and after various pretreatments, with and without arsenic present.

Direct determination of traces of silver in mercury by voltammetry at the hanging mercury drop electrode in acetonitrile medium

A direct method for the determination of silver in mercury is described. The sample of mercury is introduced into the container of the hanging mercury drop electrode and the anodic voltammograms are recorded in a 0.1 M lithium perchlorate solution in acetonitrile. The anodic peak of silver obtained under these conditions is well separated from the mercury dissolution current. The peak height is proportional to silver concentration over the wide range 2 × 10 −6 mol dm −3 (1.6 × 10 −6%) to at least 2.0 × 10 −2 mol dm −3. No prior separation is needed; the procedure requires less than 20 min. The diffusion coefficient of silver in mercury was determined at several temperatures. It was found that silver in mercury does not form intermetallic compounds with copper, lead, thallium, cadmium, tin and bismuth.

Electrochemical oxidation of organic fluorosulfuric acid Part VII. comparison of voltammetric potentials in HSO3F and acetonitrile

The anodic voltammograms of 32 aromatic compounds with different functional groups were measured both in 0.1 M CH3COOH/HSO3F at −76°C vs. a Hg/Hg2SO4 electrode in this electrolyte and in 0.1 M tetraethylammonium perchlorate/acetonitrile at room temperature vs. the saturated aqueous calomel electrode. Because of a minimal specific solvent effect in HSO3F the oxidation of the acridizinium ion 1 and of the N-methylacridium ion 2 to their dication radicals are chosen as reference redox systems for a comparison between both solvents. Specific interactions with HSO3F, e.g. protonation of functional groups, formation of arenium ions, acylium ions or benzyl cations as well as a fluorosulfonation, are indicated by a characteristic positive shift of the anodic half-peak potential with respect to the acetonitrile scale.

Electrochemical oxidation of organic compounds in fluorosulfuric acid: Part VII. Comparison of voltammetric oxidation potentials in HSO 3F and acetonitrile

The anodic voltammograms of 32 aromatic compounds with different functional groups were measured both in 0.1 M CH 3COOH/HSO 3F at −76°C vs. a Hg/Hg 2SO 4 electrode in this electrolyte and in 0.1 M tetraethylammonium perchlorate/acetonitrile at room temperature vs. the saturated aqueous calomel electrode. Because of a minimal specific solvent effect in HSO 3F the oxidation of the acridizinium ion 1 and of the N-methylacridium ion 2 to their dication radicals are chosen as reference redox systems for a comparison between both solvents. Specific interactions with HSO 3F, e.g. protonation of functional groups, formation of arenium ions, acylium ions or benzyl cations as well as a fluorosulfonation, are indicated by a characteristic positive shift of the anodic half-peak potential with respect to the acetonitrile scale.