Cyclic Voltammetric Behavior Research Articles

Silver-exchanged zeolite Y-modified electrodes: size selectivity for anions

The cyclic voltammetric (CV) behavior of silver ions encapsulated into zeolite Y (NaY) has been investigated in aqueous solution containing different anions. It was found that the electroactivity of silver ions relied on the solvated anionic radii. Cl − and Br − anions suppressed the electroactivity of silver ions. PMT − (1-phenyl-5-mercaptotetrazole) and SO 3 2− anions, however, had little influence on this, which implies that silver-exchanged zeolite Y-modified electrodes have a high selectivity for Cl − and Br − anions.

Cyclic voltammetric studies on nitro radical anion formation from megazol and some related nitroimidazole derivatives

Megazol (2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazol, CAS 19622-55-0) and related nitroimidazole compounds are being tested as antichagasic drugs. Little is known on the mode of action of megazol. However, there is evidence that one-electron reduction of megazol to the corresponding nitro radical anion is a key step in the reaction mechanism. Consequently, this paper is focused on the cyclic voltammetric behaviour of megazol and related nitroimidazole derivatives with the aim of revealing the formation and stability of the corresponding nitro radical anions. All the compounds studied produce a well resolved nitro/nitro radical anion couple. The resolution of the couple was improved with the addition of tetrabutylammonium ions which hinders the protonation of the nitro radical anion at the electrode surface, thus enhancing the stability of the nitro radical anion. Only megazol produced a cyclic voltammogram distorted by the presence of a pre-peak due to strong adsorption of the corresponding nitro radical anion. The pre-peak occurs at potentials more positive than the diffusion controlled peak because the Gibbs energy of adsorption of the nitro radical anion makes the reduction of megazol to the adsorbed nitro radical anion easier than to the radical anion in solution. The sulphur atom in the thiadiazole ring plays a crucial role in the adsorption phenomena. Using the cyclic voltammetry theory for the disproportionation reaction, we have calculated the second-order decay rate constant, k 2, and the half-life time, t 1/2, for all the nitro radical anions of the studied nitroimidazole derivatives. The values obtained were compared with those of the corresponding nitro radical anions obtained from nifurtimox and benznidazole, the classic antichagasic drugs. Also, our results show that cyclic voltammetry is a good alternative to the classic pulse radiolysis method to obtain reliable values of the E 1 7 parameter for nitro radical anions.

Voltammetric studies of the interaction of nogalamycin antitumor drug with DNA

The interaction of nogalamycin (NOM), an anthracycline antitumor drug, with calf thymus DNA has been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The variations in the cyclic voltammetric behaviour of NOM on addition of DNA have been carried out. The experimental results reveal that the reduced form (H 2NOM) red, of NOM is bound more strongly to DNA than the oxidised form (NOM) ox. The calibration graph for the determination of DNA was obtained by the decrease in the DPV peak current of NOM in the presence of DNA. Furthermore, the results are compared with the similar type of interaction behaviours of daunomycin (DAM), adriamycin (ADM) and 4′-deoxyadriamycin (DADM), mainly from the viewpoint of the influence of chemical structure. Binding constants were determined from voltammetric data, i.e. changes in limiting current with addition of DNA. In comparison with DAM, ADM and DADM, nogalamycin displayed high binding affinity to DNA ( K=4.44×10 5 M −1), and the binding affinity increases in the sequence: DAM<DADM<ADM<NOM. The results show also that, a slight change in chemical structure causes significant changes in the binding affinity to DNA and consequently in clinical properties.

Synthesis and structural characterization of {μ 3-H(Ph)CC}FeCo 2(CO) 7dppm (dppm=Ph 2PCH 2PPh 2) and {μ 3-H(Ph)CC}FeCo 2(CO) 9− nL n [L=PPh 3 ( n=1, 2), AsPh 3 ( n=1)

The new mixed-metal clusters {μ 3-H(Ph)CC}FeCo 2(CO) 7dppm (dppm=Ph 2PCH 2PPh 2) ( 1) and {μ 3-H(Ph)CC}FeCo 2(CO) 9− n L n [L=PPh 3, n=1 ( 2), n=2 ( 3); AsPh 3, n=1 ( 4)] have been synthesized by facile substitution reactions. The molecular structures of 1, 2 and 4 have been determined by single-crystal X-ray analysis; dppm replaces two equatorial carbonyls from two Co(CO) 3 groups, and PPh 3 and AsPh 3 replace one equatorial carbonyl from a Co(CO) 3 group, respectively. The new compounds were characterized by IR, 1H-, 31P- (for 1– 3) NMR and MS. Cyclic voltammetric behavior for 1, 2 and 4 was investigated, and the results show the order of σ-donator ability is CO<PPh 3<AsPh 3<dppm.

Comparison Between the Electrochemical Behavior of Disordered Carbons and Graphite Electrodes in Connection with Their Structure

This work relates to a rigorous study of the surface chemistry (Fourier transform infrared, X-ray photoelectron spectroscopy), crystal structure (X-ray diffraction), galvanostatic, cyclic voltammetric, and impedance behavior of lithiated carbon electrodes in commonly used liquid electrolyte solutions. Two different types of disordered carbons and graphite, as a reference system, were explored in a single study. All three types of carbons develop a similar surface chemistry in alkyl carbonate solutions, which are dominated by reduction of solvent molecules and anions from the electrolyte. The differences in the crystal structure of these carbons lead to pronounced differences in the mechanisms of Li insertion into them. Whereas Li-ion intercalation into graphite is a staged process, Li-ion insertion into the disordered carbons occurs in the form of adsorption on both sides of the elementary graphene flakes and on their edges. The electroanalytical behavior of the disordered carbons was found to correlate well with their unique structure described in terms of the butterfly model. Both types of the disordered carbons reveal exceptionally good cyclability in coin-type cells (vs. Li counter electrodes), with only moderate capacity fading. Highly resolved plots of the chemical diffusion coefficient of Li-ions, D vs. potential E, for the disordered carbon electrodes were obtained. Surprisingly, a maximum in D appears on these plots at intermediate levels of Li-ion insertion corresponding to ca. 0.4-0.5 V (vs. We propose that these maxima may originate from a combination of two effects, (i) repulsive interactions between the inserted species, and (ii) pronounced heterogeneity of Li insertion sites in terms of carbon-Li interactions and Li-ion mobility. © 2001 The Electrochemical Society. All rights reserved.

On the electrochemically driven formation of bilayered systems of solid Prussian-blue-type metal hexacyanoferrates: a model for Prussian blue ∣ cadmium hexacyanoferrate supported by finite difference simulations

The solid-state electrochemical formation of bilayered electrode structures of different metal hexacyanoferrates was studied. This formation occurs as a result of an insertion/substitution reaction during prolonged voltammetric cycling of microparticles immobilized on the surface of a graphite electrode in an electrolyte solution of the respective metal ions. A theoretical model is proposed for the cyclic voltammetric behavior for the case of the transformation of Prussian blue into cadmium hexacyanoferrate, using the finite difference simulation method. The simulated voltammetric curves and the assumed model are in good agreement with new experimental results which give clear evidence that the exchange reaction of this model reaction, i.e. the intramolecular substitution of high-spin iron by cadmium ions, takes place simultaneously with the electrochemical oxidation of Prussian blue (KFe IIIFe II(CN) 6) to Berlin green (Fe IIIFe III(CN) 6). The bilayered structures obtained with immobilized microparticles are discussed in comparison to those prepared by subsequent deposition as thin films.

Cyclic voltammetric behaviour of – brass in alkaline media

AbstractThe electrochemical behaviour of a brasses was studied in NaOH solutions using the cyclic voltammetric technique to establish the effect of such variables as alloy composition, reversal anodic potential, scan rate, NaOH concentration, and temperature. Compounds that formed on the surface during the anodic sweep were analysed using X-ray diffraction analysis (XRD). The data show that the voltammetric behaviour of – brass consists of two potential regions. The first or subcritical potential region was indicated by two anodic peaks designated A1 and A2. Within this potential region, selective dissolution of the less noble component, zinc, occurs (i.e. dezincification). The second potential region consists of three anodic peaks, designated A3, A4, and A5, where the two components of the alloy, namely copper and zinc, dissolve simultaneously. Alloying zinc with copper resulted in a decrease in the dissolution of zinc from the alloy. This behaviour could be explained on the basis that the dissolution is...

Electrochemical behaviour of solid lithium cobaltate (LiCoO2) and lithium manganate (LiMn2O4) in an aqueous electrolyte system

Lithium cobaltate (LiCoO2) and lithium manganate (LiMn2O4) were synthesized by self-propagating high-temperature combustion and their phase purity and composition were characterized by X-ray diffraction and inductively coupled plasma spectroscopy. These transition metal oxides were mechanically immobilized on the surface of paraffin-impregnated graphite electrodes and their cyclic voltammetric behaviour in aqueous alkali electrolytes was examined. It was shown that both the oxides undergo proton insertion upon the reduction of Co3+ to Co2+ in LiCoO2 and Mn4+ to Mn3+ in LiMn2O4, while they deintercalate protons on the reverse oxidation. Scanning electron microscopy reveals spherical LiCoO2 particles with a very narrow size distribution. Energy dispersive X-ray detection proved the absence of metal cation intercalation.

Carbon Nanotube Anodes for Lithium Ion Batteries

AbstractHighly purified single-wall carbon nanotubes (SWCNT) were investigated for use as an anode material for thin film lithium ion batteries. The high purity nanotubes were obtained through chemical refinement of soot generated by pulsed laser ablation. The purity of the nanotubes was determined via thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. The specific surface area and lithium capacity of the SWCNT's was compared to that of other conventional anode materials (i.e., carbon black, graphite, and multi-walled carbon nanotubes). The Brunauer, Emmett, and Teller (BET) technique based on nitrogen adsorption was used to measure the specific surface area of the various anode materials. The SWCNT's exhibited a specific surface area on the order of 915 m2/g, much higher than the other carbonaceous materials. Cyclic voltammetric behavior and the lithium-ion capacity of the materials were measured using a standard 3-electrode electrochemical cell. The cyclic voltammetry showed evidence of “staging” that was similar to other carbonaceous materials. The electrochemical discharge capacity of the purified single walled carbon nanotubes was in excess of 1300 mAh/g after 30 charge/discharge cycles when tested using a current density of 20μA/cm2.

Cyclic voltammetric studies of alumina supported monometallic Pt and bimetallic PtSn catalysts using carbon paste electrodes

Abstract The present work relates to the cyclic voltammetric studies of alumina supported monometallic Pt and bimetallic PtSn catalysts using solid carbon paste electrodes. The cyclic voltammetric data of the solid catalysts, which were reproducible, were in agreement with those of electro-deposited Pt and PtSn electrode systems. The reversibility of the H-adsorption–desorption system in representative 0.3 Pt–Al2O3 monometallic catalyst was confirmed by the difference between the anodic and cathodic peak potentials. The unit ratio of the cathodic to anodic peak currents observed, indicated the equality of the transfer coefficient in the kinetics for the respective processes. The O2-adsorption–desorption reaction was found to be irreversible as expected. The lower area of the curve for H-adsorption–desorption in the case of bimetallic catalysts gives an indication for the formation of alloys. The use of a carbon paste electrode in studying the cyclic voltammetric behavior of heterogenous catalysts yielded qualitative information about the activity of the catalysts. Good correlations were found between cyclic voltammetric parameters and activity results in both monometallic and bimetallic catalysts.

Influence of Charge Distribution on the Properties of Keggin- and Dawson-Type Heteropolyanions

The cyclic voltammetric behavior of selected Keggin- and Dawson-type heteropolyanions has been studied as a function of electrolyte composition. The buffer capacity of the electrolyte is shown to be an important parameter that can be used to reveal the symmetry or dissymetry in charge distribution within each oxometalate. A fully symmetrical heteropolyanion like [P2W18O62]6− exhibits a uniform protonability, while its α1 and α2 lacunary derivatives present a donor set of hard oxide ions with stepwise acid-base equilibria. The behavior of these sites is revealed readily in unbuffered or poorly buffered media at pH = 3, and is ascribed to the change in symmetry of charge distribution in the molecules. It is shown that cations other than the proton, even in very high excess, fail to give rise to the classical voltammograms of lacunary heteropolyanions. The same behavior also appears in α2[Mo2P2W15O61]10−, α[PW11O39]7−, α[SiW11O39]8−, [H2P2W12O48]12−, and, to a lesser extent, in α2[Ni(H2O)P2W17O61]8− and α2[Zn(H2O)P2W17O61]8−. The analogy in the cyclic voltammograms of most dication-substituted heteropolyanions with those of the precursor lacunary species could thus be explained.

Blend-based polymer electrolytes of poly(ethylene oxide) and hyperbranched poly[bis(triethylene glycol)benzoate] with terminal acetyl groups

Blend-based polymer electrolytes, with favorable mechanical strength, consisting of a linear poly(ethylene oxide) (PEO), a hyperbranched polymer (poly[bis(triethylene glycol)benzoate] with terminal acetyl groups), and LiN(CF 3SO 2) 2 salt, were prepared by the solvent casting technique. Thermal properties, ionic conductivity, electrochemical stability window, lithium ion transference number, and cyclic voltammetric behavior of the blend-based polymer electrolytes were all evaluated and discussed. In comparison with polymer electrolytes based on PEO, the blend-based polymer electrolytes exhibited improved lithium ionic conductivity and lithium/electrolyte interfacial performance. Blend-based polymer electrolyte with a hyperbranched polymer/PEO ratio of 20/80 in wt% and [LiN(CF 3SO 2) 2] 0.125 exhibited ionic conductivities as high as 8.1×10 −4 S cm −1 at 80°C and 3.8×10 −5 S cm −1 at room temperature. The electrochemical stability window was about 4.9 V. It was also demonstrated that crystallinity of the blend-based polymer electrolytes depends significantly on the hyperbranched polymer/PEO weight ratio as well as the lithium salt content.

Optimization of the Preparation Conditions of Sol‐Gel Derived Ni‐Co Oxide Films

In this work, sol‐gel (SG) oxide films were formed by dip‐coating Pt substrates from Ni, Co, and mixed Ni‐Co sols. After withdrawing the substrate at a constant rate, the films were dried between 100 and 400°C for various periods of time (15 min to 1 h). Based primarily on the cyclic voltammetric behavior of the SG‐formed Ni‐Co films after drying at high temperatures, it is suggested that both the Ni and Co sites undergo redox reactions in 1 M NaOH solutions. This also explains the high charge efficiency and charge density of SG‐derived, Co‐containing Ni oxide films. Careful optimization of the experimental variables in the SG film preparation route indicated that the use of 50:50 Ni‐Co sols, a withdrawal rate of 6 cm/min, and drying at 250°C for 1 h yields films which display the highest charge density, the most rapid redox kinetics, and good stability to prolonged potential cycling. In addition, the charge capacity of the optimized 50:50 Ni‐Co SG oxide films can be increased further by the deposition of multilayers. The redox kinetics of the optimized coatings in 1 M NaOH solution were superior to those for Ni‐Co oxide films of comparable charges, but formed in other ways. Diminished reaction rates resulted when higher film drying temperatures were used (denser films) and when thicker, multilayered films were formed. © 2000 The Electrochemical Society. All rights reserved.

The Influence of Fluoride Media and CH3CN on the Voltammetric Behavior of Ferrocene, Quinhydrone, and Methyl Phenyl Sulfide on Pt and Carbon Electrodes

Cyclic voltammetric behavior of ferrocene, quinhydrone, and methyl phenyl sulfide on Pt, glassy carbon (GC) and polypropylene composite graphite (CPP) electrodes are compared in TBAP/CH3CN, triethylamine (TEA).3HF/CH3CN and TEA.3HF media. In medium containing CH3CN, the voltammetric behavior of title compounds are quite similar in the absence and presence of fluoride ions. The voltammetric features vary only slightly, due to some adsorption effects and catalytic hydrogen evolution on Pt. In TEA.3HF medium, all three electrodes show significantly higher background currents in the middle potential region itself. The peak potential and the charge transfer rate constant of these compounds are also found to be significantly different in TEA.3HF room temperature melt. The analytical implications of these medium effects are also discussed.

Effect of oxygen on the electrochromism of RF reactive magnetron sputter deposited tungsten oxide

High coloration efficient WO 3, deposited by reactive sputtering, is influenced by the oxygen concentrations in a sputtering system. In this study, a survey on the effect of oxygen concentration in the rf sputtering atmosphere and the subsequent deposited film was studied to reveal the microstructural changes in relation to the electrochromic properties. The electrochromic properties determined include cyclic voltammetric behavior, coloring and bleaching response time, x(Li x WO 3), optical density changes and coloration efficiency. Experimental results show that the maximum current, as well as the x(Li x WO 3) value, occurred in the O 2/Ar flow ratio at 0.3–0.4. This may be compromised by the low valence tungsten ions that play a role in expelling cations in the films deposited at a low O 2/Ar flow ratio and hypothetically due to the limitation of electron conduction for high oxidation films deposited at high O 2/Ar flow ratios. The response time, decreased with the increasing O 2/Ar flow ratio, can be considered separately by the ion diffusion difficulty already established elsewhere. As a whole, the optimized O 2/Ar flow ratio would be in the range of 0.3–0.4 for transmittance control applications.

Multiple square wave voltammetry of nanomolar and subnanomolar concentrations of europium (III) at polymer-coated electrodes

The ion-exchange voltammetric determination of europium(III) at polymer-coated electrodes is examined. The comparison between the ion-exchange cyclic voltammetric behaviour at glassy carbon electrodes, modified with the poly(estersulfonate) Kodak AQ55 and Nafion, indicates a better suitability of the latter. The use of multiple square wave voltammetry (MSWV) results in a dramatic improvement of the signal-to-noise ratios of the voltammograms recorded at the modified electrodes. Eu (III) determinations by MSWV at Nafion-coated electrodes are characterised by detection limits 2–3 orders of magnitude lower than those obtained with differential pulse voltammetry and the rare earth cation can be analysed at nano- and subnanomolar levels, depending on the experimental conditions adopted.

Study of the Correlation of the Cyclic Voltammetric Responses of a Nonionic Surfactant Containing an Anthraquinone Group with the Dissolved States

Cyclic voltammetric behavior of a nonionic surfactant, α-(anthraquinonyloxyhexyl)-ω-hydroxy-oligo(ethylene oxide), ACPEG, has been studied in detail in aqueous media with NaCl as the supporting electrolyte. Attempts have been made to correlate the electrochemical responses with the dissolved states of the surfactant. The shapes of the cyclic voltammograms at a glassy carbon electrode have proved to be fairly dependent on the concentration of ACPEG and on the redox state of the anthraquinone group. Below the critical micelle concentration (cmc), the cyclic voltammogram (v = 10 mV/s) corresponds to the surfactant molecules adsorbed onto the electrode surface. The adsorption of ACPEG molecules at the electrode surface is very weak in nature owing to its low surface activity. A high cmc value and weak adsorption allow diffusion of the monomeric species prior to the reduction to contribute to the total current even below the cmc. At concentrations higher than the cmc, the diffusion-controlled waves are superim...

Neutral Ni(II) and Cu(II) complexes of tetraazatetraenemacrocyles

A series of electron donors [neutral Ni(II) and Cu(II) complexes of tetraazatetraenemacrocyclic ligands] differing in metal ion, size of the macrocyclic ligand, and the length of the aliphatic bridges linking the macrocyclic units in dimeric species were synthesized and their redox, structural and spectroscopic properties were studied. The x-ray results for the donors under study show a nearly planar geometry of the monomeric tetraazamacrocyclic complexes and interesting ‘organic-zeolite-like’ structures of the dimers. The dimeric Ni complexes have flexible cavities between the two single ligands linked with aliphatic chains suitable for accommodating some small-sized guests. For the dimeric compounds the metal oxidation [M(II)/M(III)] takes place independently on each centre except one binuclear Ni complex, where the cooperativity of the metal centres was observed. Methyl substituents give rise to irreversibility of the oxidation process of the complexes studied. In the absence of these substituents neither reorganization nor ligand addition/elimination kinetics affect the electrode process. A common scale for the donors under study and some important acceptor compounds (p-benzoquinone, chloranil, tetracyanoethylene and tetracyanoquinodimethane, etc.) was proposed on the basis of their cyclic voltammetric behaviour in the same physicochemical conditions. Copyright © 2000 John Wiley & Sons, Ltd.

Synthesis, characterisation, and molecular and electronic structure of CpMoCl2(R1CCR2) (R1, R2 = Ph, Et, Me): a new class of half-sandwich 17-electron molybdenum(III) organometallics

Addition of alkyne to [CpMoCl2]2 affords compounds CpMoCl2(η2-alkyne) (alkyne = EtCCMe, 1; EtCCEt, 2; PhCCMe, 3; PhCCPh, 4) in good yields. The compounds have been characterised by C,H analyses, IR, EPR and mass spectroscopies, magnetic susceptibility, and cyclic voltammetry. In addition, a single crystal X-ray diffraction analysis has been carried out for compound 4. The alkyne ligand adopts an almost parallel conformation relative to the Cp ring, essentially identical with that of previously reported Nb, Ta, and W analogues. Geometry optimisations on the CpMCl2(HCCH) (M = Nb, Mo) model compounds show that the total energy is nearly independent of the alkyne orientation. The SOMO for M = Mo is an essentially metal-based orbital with a slight Mo-Cl π* component, in agreement with the observed trends in M–Cl bond lengths on going from Group 5 to Group 6. The cyclic voltammetric behaviour of 1–4 is similar to the analogous diene complexes CpMoCl2(η4-diene). A reaction between 1–4 and excess alkyne takes place only for the dialkylsubstituted alkyne complexes under forcing conditions. Compound CpMoCl2(η4-C4Et4H), 5, has been isolated from the reaction between 2 and excess EtCCEt and crystallographically characterized.

Proton addition and hydrogen-bond formation in reactions of the dicyano-complex [NBu4][trans-Re(CN)2(dppe)2] with protic reagents

[NBu4][trans-Re(CN)2(dppe)2] (1, dppe = Ph2PCH2CH2PPh2) reacted with protic acids (HA = HBF4, CH3CO2H or [Et3NH][BPh4], added in stoichiometric amounts) to give, on protonation of one of the cyano-ligands, the isocyanide complex trans-[Re(CN)(CNH)(dppe)2] 3a, whereas the hydrogen-bonded cyano-adducts trans-[Re(CN·HO2CCF3)2(dppe)2] 4, trans-[Re(CN·HOMe)2(dppe)2] 5 and trans-[Re(CN·HNEt3)2(dppe)2][BPh4] 6 were obtained on treatment of 3a with an excess of CF3CO2H or of 1 with an excess of MeOH or [Et3NH][BPh4], respectively. However, solvent or other molecules can be trapped in the crystal lattice without hydrogen-bond interaction and trans-[Re(CN)2(dppe)2]·2L (L = MeOH 2a or Me2CO 2b) or trans-[Re(CN)2(dppe)2]·NEt37 are formed on attempted recrystallization of 1 from MeOH or Me2CO, or as a side product in the reaction of 1 with [Et3NH][BPh4], respectively. The crystal structures of 2b, 4, 5 and partially that of 2a were also determined and the anodic cyclic voltammetric behaviour (which is shown to distinguish between the CN–H and the hydrogen-bond CN⋯H formations) of the above complexes is described as well as an interpretative theoretical study (by extended Huckel and ab initio methods) of the CN and CNH complexes.