Shape Of Cyclic Voltammograms Research Articles

Electrochemical and electron paramagnetic resonance study of the mechanism of oxidation of 2,3,5,6-tetra-Me-pyrazine-di-N-oxide as a mediator of electrocatalytic oxidation of isopropyl alcohol at glassy carbon and single-walled carbon nanotube electrodes

The mechanism of oxidation of 2,3,5,6-tetra-Me-pyrazine-di-N-oxide (Pyr2) as a mediator of electrooxidation of isopropyl alcohol was studied by cyclic voltammetry at glassy carbon (GC) and single-walled carbon nanotubes (SWCNT) electrodes in 0.1M LiClO4 solutions in acetonitrile. The adsorption of Pyr2 at SWCNT electrode in 0.1M LiClO4 solution in acetonitrile was investigated by measurement of the dependence of the differential double layer capacitance of the electrode C on potential E. The effect of isopropyl alcohol on the shape of cyclic voltammograms (CVs) of Pyr2 and the intensity of EPR signal of its radical cation was investigated. The catalytic currents were recorded at the oxidation of Pyr2 at SWCNT and GC electrodes in the presence of isopropyl alcohol. The effect of acid and water (as a base) on the catalytic process was studied. The results were explained in terms of the E1C1E2C2 mechanism of two-stage electrode process characterized by catalytic current recorded at the second electrode stage. The overall two-electron catalytic oxidation of isopropyl alcohol in complex with the Pyr2 radical cation was assumed to occur. It was found that the use of SWCNT electrode instead of GC one increases the catalytic efficiency of i-PrOH oxidation by 17 times.

Role of vanadium ions on structural, optical and electrochemical properties of the vanadate-lead glasses

New different series of xV2O3∙(100−x)[4PbO2·Pb] glasses were prepared by melt-quenching method in a wide range of compositions defined by the parameter x=0–30mol% V2O5. InfraRed (IR) data reveal that by increasing the V2O5 content, the glass network was transformed into a mixture of modified [VO4] structural units, namely pyrovanadate and orthovanadate ones. The UltraViolet–Visible (UV–VIS) spectra show that addition of V2O5 produces a gradual shift of the absorption edge towards the higher wavelength side (indicating the increase in concentration of vanadyl species) and a decrease of the gap energy.The shape of the Electron Spin Resonance (ESR) spectra changes with increasing the V2O5 content suggesting that the interactions between vanadium centers strongly depend on x parameter which plays an important role. A hyperfine structure becomes visible in the glass with x=20mol% V2O5 suggesting modifications of the glass structure caused by the network modifier. If the network is moderately disrupted the formation of Pb+2–V+4 pairs was coupled through the oxygen atom or the interactions within V+4–O–V+5 chains mask hyperfine structure.The shape of cyclic voltammograms, redox waves and good reversibility of the x=20mol% V2O5 glassy electrode depends on the electrolyte acidity and electrochemically active species present in the glass network.

Electrochemical and Electron Paramagnetic Resonance Study of the Mechanism of Oxidation of Phenazine-di-N-oxide in the Presence of Isopropyl alcohol at Glassy Carbon and Single-Walled Carbon Nanotube Electrodes

The mechanism of oxidation of phenazine-di-N-oxide in the presence of isopropyl alcohol was studied by cyclic voltammetry at glassy carbon (GC) and single-walled carbon nanotubes (SWCNT) electrodes in 0.1M LiClO4 solutions in acetonitrile. The adsorption of phenazine-di-N-oxide at SWCNT electrode in 0.1M LiClO4 solution in acetonitrile was investigated by measurement of the dependence of the differential double layer capacitance of the electrode C on potential E. The effect of isopropyl alcohol on the shape of cyclic voltammograms (CVs) of phenazine-di-N-oxide and the intensity of Electron Paramagnetic Resonance (EPR) signal of its radical cation was investigated. The catalytic currents were recorded at the oxidation of phenazine-di-N-oxide at SWCNT and GC electrodes in the presence of isopropyl alcohol. The results were explained in terms of the E1C1E2C2 mechanism of two-stage electrode process characterized by catalytic current recorded at the second electrode stage. The overall two-electron catalytic oxidation of isopropyl alcohol in complex with the phenazine-di-N-oxide radical cation was assumed to occur. It was shown that SWCNT electrodes can be used in the electrocatalytic oxidation of organic compounds in the presence of electrochemically generated phenazine-di-N-oxide radical cation.

Electrochemical Redox of Benzoquinone in Ionic Liquids

The reduction of 1,4-benzoquinone(BQ) on Pt electrode was investigated in various ionic liquids by cyclic voltammetry(CV). Over a wide range of scan rates,two couples of redox peaks were clearly observed in cyclic voltammogram,showing a quasi reversible diffusion process of BQ with the two-step electrochemical reduction. Diffusion coefficient and activation energy were obtained from cyclic voltammogram, which displayed the increase of diffusion coefficient accompanying temperature rise from 298. 15 K to 343. 15 K. The techniques of cyclic voltammetry,in situ FTIR spectroelectrochemistry(FTIR),cyclic voltabsorptometry(CVA) and derivative cyclic voltabsorptometry(DCVA) were used to investigate the electrochemical behavior of BQ in ionic liquids,BMIMBF4and BMIMPF6. The results support that BQ undergoes two successive one-electron reductions,corresponding to the formation of a radical anion intermediate and then the dianion,in ionic liquids,while presenting a different shape of cyclic voltammogram compared to anhydrous acetonitrile solvent.

Hydrothermal process synthesized electrocatalytic multi-walled carbon nanotubes-inserted gold composite microparticles toward ethanol oxidation reaction

Composite microparticles consisting of large gold (Au) particles embedded with multi-walled carbon nanotubes (MWCNTs), denoted as MWCNTs-Au, have been successfully prepared by a facile hydrothermal process of gold(III) chloride (AuCl3) in a MWCNT aqueous solution. X-ray diffraction and scanning electron microscopy reveal that the obtained Au particles have an average diameter of about 500 nm and some MWCNTs are inserted into the Au particles. The MWCNTs-Au composites in the ethanol oxidation reaction (EOR) show quite different shape of cyclic voltammograms (CVs) toward EOR when compared to the previous CV reports on the pure Au substrate.

The electrochemical behavior of PtRu- and Pt-modified zeolite X in alkaline solution

Zeolite NaX was modified by Pt and Pt/Ru nanodispersed metallic clusters. The procedure of impregnation with acetylacetonate salt/acetone solution was applied. Scanning electron microscope analysis confirmed partial zeolite framework destruction. According to energy dispersive X-ray analysis, Pt/Ru ratio in sample was about 1. Electrochemical behavior of PtRu- and Pt-modified zeolites was investigated in alkaline solutions, 5 mM NaOH + 1 M Na2SO4 and 0.1 M NaOH. The shape of cyclic voltammograms of 13XPtRu electrode, recorded in slightly alkaline solution, was greatly affected by the presence of hydrogen that remained in the sample after synthetic procedure. Oxygen reduction reaction (ORR) was investigated in an O2-saturated aqueous 0.1-M NaOH solution. The obtained Tafel slopes indicated ORR mechanism that involves one-electron discharge-determining step. According to Koutecky–Levich slope, the oxygen reduction reaction followed 4e− mechanism on both 13XPtRu and 13XPt electrode. The onset of ORR on 13XPtRu electrode was shifted toward more positive potentials in comparison to 13XPt electrode.

Self-assembling ensembles of silicomolybdic acid-diamines

Modification of the surface of the conductive glass [conductive layer is indium-tin oxide (ITO)] by diamines (1,8-diaminooctane and piperazine) and organic polycations [poly(diallyldimethylammonium chloride) and poly(allylamine) hydrochloride] followed by the formation of electroactive composites with silicomolybdic acid H4SiMo12O40 was carried out. The two-layer ITO/cationic/anionic coatings were shown to differ by the shape of cyclic voltammograms depending on the cationic component.

Electrochemical Assessment of Cu-PIII Treated Titanium Samples for Antimicrobial Surfaces

Titanium implant surfaces should ideally be designed to promote the attachment of target tissue cells. At the same time they should prevent bacterial adhesion, achievable through specific modification strategies. Copper could be well-suited as an antimicrobial finish, since it combines good antimicrobial properties with a certain bio-tolerance with regard to eukaryotic cells. In the present contribution, we evaluate electrochemical results of antimicrobial titanium surfaces generated by the insertion of copper. The surface was prepared via copper implantation into the titanium subsurface by means of plasma-immersion ion implantation (Cu-PIII) until a depth of about 30 nm. The amount and profile of copper ion implantation was changed by variation of the pulse length which was equivalent to the duty cycles of 0.2 % up to 90 %. Specimens containing 3 – 12 % copper (XPS) were used for electrochemical investigations with the help of the mini cell system in 0.9 % NaCl solution. The change in the shape of cyclic voltammograms demonstrated an alteration of the electrochemical behaviour. Copper oxidation peaks appeared in copper-implanted samples and their height was proportional to the copper concentration. These peaks are related to an electrochemical activity and not suppressed by the superficial titanium oxidation.

Monitoring of the electrochemical degradation of PEDOT films on gold using the bending beam method

Electrochemical and mechanical properties of thin poly(3,4-ethylenedioxythiophene) films deposited on gold have been investigated in aqueous sulfuric acid and sodium-sulfate solutions. It has been shown that at sufficiently positive electrode potentials, overoxidation of the polymer takes place. In some cases, only small changes could be observed in the shape of cyclic voltammograms taken in the “stability region” before and after overoxidation. In contrast to this, the impedance spectra recorded after overoxidation differed considerably from the impedance spectra of a freshly made electrode. Morphological changes of the polymer caused by overoxidation (degradation) could be detected by using the bending beam method.

Mixed solutions of silver cation and chloride anion in acetonitrile: Voltammetric and EQCM study

Electrochemical behavior of Pt and Au electrodes in acetonitrile solutions at different concentration ratios of Cl(-) and Ag(+) ions was studied by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The composition of the mixed silver chloride solutions, i.e. the amount of each component of the system (solid AgCl and solute species: Ag(+), Cl(-), AgCl(2)(-)), is governed by the solubility product of AgCl and the stability constant of AgCl(2)(-)complex and depends strongly on the ratio of the total concentrations of chloride and silver ions. In this work we analyze in detail the influence of the Cl(-)/Ag(+) concentration ratio on the value of equilibrium electrode potential and the shape of cyclic voltammograms. We explain the complicated shapes of the experimental curves observed at different concentration ranges, propose the mechanisms of the processes occurring at the electrode and substantiate them by EQCM data.

Cyclic voltammograms at coplanar and shallow recessed microdisk electrode arrays: guidelines for design and experiment.

Although microdisk electrode arrays (MEAs) have been extensively used for more than three decades, the existing rules do not provide an unambiguous formula for the calculation of the minimum interelectrode distance (d) necessary for steady-state current response. With the aim of formulating generally applicable guidelines for design and experiment with MEAs, cyclic voltammograms were simulated for coplanar and shallow recessed microdisk electrode arrays with various interelectrode distances and dimensionless scan rates (V). The dimensionless scan rate (V) is a function of the radius (a) of the individual electrodes in the array, the diffusion coefficient (D) of the analyte, and the potential scan rate (v). The cyclic voltammograms at microdisk electrode arrays are grouped into five categories corresponding to the contributions of linear and radial diffusion to the overall responses. These categories are illustrated in a zone diagram based on the effect of V and d on the shape of cyclic voltammograms. The zone diagram reveals the minimum d and a cluster of linked d and V values that are incident to sigmoidal wave responses. For shallow recessed microdisk electrode arrays, the zones representing hemispherical diffusion are larger than that for coplanar arrays. The minimum d necessary for hemispherical diffusion becomes smaller as recess depth increases. With the zone diagram, one can predict the type of the cyclic voltammograms that can be expected for different microelectrode array geometries and experimental conditions. The fitting between simulation and experimental data validates our conclusions.

Influence of Electrode Roughness on Cyclic Voltammetry

Electrodes with rough surfaces are of great practical importance from both applied and fundamental points of view. The diffusion domain approach is used to model cyclic voltammetry at such electrodes. Electrode roughness only has a significant effect on the shape of cyclic voltammograms and peak currents at relatively high values of electrode roughness. To verify the theory two experimental systems were used: TMPD in acetonitrile and Ru(NH3)6Cl3 in aqueous solution. In both cases cyclic voltammograms on the flat and roughened glassy carbon electrodes were in agreement with theory. Even significant surface roughness produced by deliberate polishing or scratching is not sufficient to be distinguished in cyclic voltammetry experiments conducted under the usual conditions.

Nickel–poly(o-aminophenol)-modified carbon paste electrode; an electrocatalyst for methanol oxidation

In this work, a modified carbon paste electrode consisting of Nickel dispersed in poly(ortho-aminophenol) was used for electrocatalytic oxidation of methanol in alkaline solution. A carbon paste electrode bulk modified with o-aminophenol was used for polymer preparation by cyclic voltammetry method; then, Ni(II) ions were incorporated by immersion of the modified electrode in 1 M Ni(II) ion solution at open circuit. The electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)–Ni(II) couple. Electrocatalytic oxidation of methanol on the surface of modified electrode was investigated with cyclic voltammetry and chronoamperometry methods, and the dependence of the oxidation current and shape of cyclic voltammograms on methanol concentration and scan rate were discussed. Also, long-term stability of modified electrode for electrocatalytic oxidation of methanol was investigated.

Measurement of Critical Micelle Concentration (CMC) by Cyclic Voltammetry: CMCs for Sodium Dodecyl Sulfate Solution with Compounds Having Pyridine

Electrochemical behavior of CMC in sodium dodecyl sulfate (SDS)-tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3 ) solution is reported using a cyclic voltammetry (CV). Discussion of SDS-Ru(bpy)3 2+ solution is restricted to the regions slightly below and above the CMC. Kaifer and Bard suggested that detection of the CMC of SDS for methyl viologen is possible through the changes observed in the shape of cyclic voltammograms. This work was originated from doing experiment for enhancement of electrogenerated chemiluminescence intensity in the Ru(bpy)3 2+ solution with surfactants. Until recently, most applications of aqueous micelles were restricted to regions extending slightly below and above the CMC. Because, the interesting effects are being discovered at surfactant concentrations much below and above the critical point. Although various techniques of electrical conductance, turbidity, osmotic pressure, magnetic resonance, solubilization, light scattering intensity, surface tension, and fluorescence quenching to measure the CMC have been utilized, a determination of the CMC by the CV has been received little attention. And so, in this work the method of determining the CMC for compounds having pyridine is explained, and a variation of the microenvironments of SDSRu(bpy)3 2+ interactions in the vicinity of the CMC is discussed by using the model proposed by Brajter-Toth et al.

Effect of diffusion in underpotential deposition: Simulated and experimental results

Diffusion limitation can play a role in shaping the CVs during upd formation, in spite of the fact that the amount of metal deposited is very small, of the order of 1–2 nmol/cm 2. In this paper, the shapes of cyclic voltammograms are evaluated quantitatively by digital simulation. The Frumkin adsorption isotherm and reversibility are assumed. A dimensionless parameter P is defined, which is proportional to the ratio between the diffusion-limited and the surface-controlled peak current densities. A domain in which diffusion can be neglected is presented by a series of lines of constant P in plots of log c bulk vs. log | v | . This will allow one to choose the combinations of concentrations and sweep rates where experiments can be conducted without significant interference by diffusion limitation. The results of simulation were compared for the case of upd formation of lead on a polycrystalline silver substrate. Very narrow CV peaks are observed for this system, and the value of the interaction parameter in the Frumkin isotherm is found to be f = −2.5 ± 0.1. Good agreement between experiment and the results of simulation was found when this value was employed.

Radical Cation of Pyrazine-di-N-oxide as a Mediator in Electrocatalytic Oxidation of Organic Compounds

The mechanism of oxidation of cyclohexanol, methanol, diethyl ether, triethyl orthoformate, and cyclohexane in the presence of a mediator—electrochemically generated radical cation of pyrazine-di-N-oxide (PyrDNO)—is studied on glassy carbon and platinum in a 0.1 M LiClO4 solution in acetonitrile employing cyclic voltammetry, ESR electrolysis, and gas chromatography. Effect of temperature, additives of acid and water, oxygen, and the nature of the substrate and solvent on the shape of cyclic voltammograms and intensity of ESR signal of PyrDNO is examined. ESR spectra for radical cations and anions of PyrDNO with g factors equal to, respectively, 2.0090 and 2.0031 are recorded. A mechanism for the overall two-electron catalytic oxidation of an organic substance, which involves a stage in which it complexes with the radical cation of PyrDNO, is suggested.

A model of cyclic voltammetry for a thin organic layer sandwiched between an electrode and an aqueous solution.: Convolutive modelling in the absence of supporting electrolyte

We address experiments in which an electroactive substrate is dissolved in an organic solvent which is then placed on a voltammetric working electrode (WE) and overlain by an aqueous electrolyte solution. Such ‘layered’ systems combine some of the attributes of ITIES experiments with those of more standard voltammetric techniques. In this paper, we use the powerful tool of convolutive modelling to predict how the shapes of cyclic voltammograms from layered systems depend on the experimental parameters for the reaction N−e −→P + occurring reversibly at the electrode ∣ organic interface, electroneutrality being maintained by entry of anions from the aqueous phase. Transport, both diffusive and migratory, occurs partly in a finite domain and partly semiinfinitely. Among the factors that affect the cyclic voltammetry, and whose influence is revealed in this study, are: the concentrations of the substrate and electrolyte, the rest potential, the scan rate, the reversal potential and the thickness of the organic layer. Values of the various diffusion coefficients are also important parameters. Because five distinct polarizations, all of which are time-dependent, are involved, the results are far from simple. Though they hold promise of providing information which is inaccessible conventionally, the analysis of cyclic voltammograms from layered systems will be a major challenge.

Voltammetric studies of the Au|YSZ interface at temperatures between 300 and 600°C

Abstract Electrochemical processes occurring at the gold|yttria stabilised zirconia interface were studied by cyclic voltammetry and steady-state current potential curves in different mixtures of oxygen and nitrogen at temperatures between 300 and 600°C. Point and paste electrodes were employed. The equilibrium of the oxygen electrode is not established at temperatures below 450°C any more. Contrary to Pt electrodes, the electrochemical formation and reduction of an oxide are reflected by the shape of cyclic voltammograms. However, gold oxide is not formed from O 2 in the gas phase.