Double Potential Step Chronoamperometry Research Articles

Chronoamperometric Curves Obtained from Optical Absorption Signals

A novel method of obtaining double potential-step chronoamperometric (DSAmp) curves from optical absorption signals was developed. For this purpose, the double potential-step chronoamperometry was used to investigate the first redox processes of genistein on a graphite-wax electrode in a long optical-path thin-layer spectroelectrochemical cell. Double potential-step chronoabsorptometric (DSAbs) data were recorded at the characteristic absorption wavelengths of this system, 259 and 286 nm, respectively. According to the DSAbs data, two DSAmp curves were derived using a self-developed computer program, which represented the transient reaction currents of genistein and its oxidation product in free solution, respectively. Compared with the measured DSAmp curve, the reconstructed DSAmp curves excluded not only the contribution from the species pre-adsorbed on the electrode surface but also the charging current. Accordingly, the contributions of the species in free solution and in adsorbed state to the total redox currents during the potential perturbations can be distinguished.

Three State Redox-Active Molecular Shuttle That Switches in Solution and on a Surface

Although the desirability of developing synthetic molecular machine systems that can function on surfaces is widely recognized, to date the only well-characterized examples of electrochemically switchable rotaxane-based molecular shuttles which can do so are based on the tetracationic viologen macrocycle pioneered by Stoddart. Here, we report on a [2]rotaxane which features succinamide and naphthalene diimide hydrogen-bonding stations for a benzylic amide macrocycle that can shuttle and switch its net position both in solution and in a monolayer. Three oxidation states of the naphthalene diimide unit can be accessed electrochemically in solution, each one with a different binding affinity for the macrocycle and, hence, corresponding to a different distribution of the rings between the two stations in the molecular shuttle. Cyclic voltammetry experiments show the switching to be both reversible and cyclable and allow quantification of the translational isomer ratios (thermodynamics) and shuttling dynamics (kinetics) for their interconversion in each state. Overall, the binding affinity of the naphthalene diimide station can be changed by 6 orders of magnitude over the three states. Unlike previous electrochemically active amide-based molecular shuttles, the reduction potential of the naphthalene diimide unit is sufficiently positive (-0.68 V) for the process to be compatible with operation in self-assembled monolayers on gold. Incorporating pyridine units into the macrocycle allowed attachment of the shuttles to an acid-terminated self-assembled monolayer of alkane thiols on gold. The molecular shuttle monolayers were characterized by X-ray photoelectron spectroscopy and their electrochemical behavior probed by electrochemical impedance spectroscopy and double-potential step chronoamperometry, which demonstrated that the redox-switched shuttling was maintained in this environment, occurring on the millisecond time scale.

Voltammetric Characterization of the Ferrocene|Ferrocenium and Cobaltocenium|Cobaltocene Redox Couples in RTILs

Ferrocene, Fc, and cobaltocenium hexafluorophosphate, CcPF6, have been recommended for use as internal reference redox couples in room-temperature ionic liquids (RTILs), as well as in more conventional aprotic solvents. In this study, the electrochemical behavior of Fc and CcPF6 is reported in eight commonly used RTILs; [C2mim][NTf2], [C4mim][NTf2], [C4mim][BF4], [C4mim][PF6], [C4mim][OTf], [C4mim][NO3], [C4mpyrr][NTf2], and [P14,6,6,6][FAP], where [Cnmim]+ = 1-butyl-3-methylimidazolium, [NTf2]- = bis(trifluoromethylsulfonyl)imide, [BF4]- = tetrafluoroborate, [PF6]- = hexafluorophosphate, [OTf]- = trifluoromethylsulfonate, [NO3]- = nitrate, [C4mpyrr]+ = N-butyl-N-methylpyrrolidinium, [P14,6,6,6 ]+ = tris(n-hexyl)-tetradecylphosphonium and [FAP]- = trifluorotris(pentafluoroethyl)phosphate, over a range of concentrations and temperatures. Solubilities and diffusion coefficients, D, of both the charged and neutral species were determined using double potential-step chronoamperometry, and CcPF6 (36.5−450.0 mM...

Optoelectrochemical properties of the copolymer of 2,5-di(4-methylthiophen-2-yl)-1-(4-nitrophenyl)-1H-pyrrole monomer with 3,4-ethylenedioxythiophene

Copolymer of 2,5-di(4-methylthiophen-2-yl)-1-(4-nitrophenyl)-1H-pyrrole (MTNP) with 3,4-ethylene dioxythiophene (EDOT) was electrochemically synthesized and characterized via cyclic voltammetry, Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy, conductivity measurements. Spectroelectrochemical investigations showed that resulting copolymer film has distinct electrochromic properties. It has five different colors (dark purple, red, light grey, green, blue). At the neutral state λ max due to the π-π ⁎ transition was found to be 500 nm and E g was calculated as 1.71 eV. Double potential step chronoamperometry experiment shows that copolymer film has good stability, fast switching time (1.1 s) and high optical contrast (30%). Electrochromic device based on P(MTNP-co-EDOT) and PEDOT was constructed and characterized. Oxidized state of the device shows dark purple color with a blue color reduced state. At interval potentials device has good transparency and colors of the device are yellow and grey. Maximum contrast and switching time of the device were measured as 23% and 1.1 s at 650 nm.

Double potential step chronoamperometry at spherical electrodes and microelectrodes

A general and explicit analytical easy solution for double potential step chronoamperometry applicable to microelectrodes is presented. This solution considers that both electroactive species are initially present. The solution indicates that the smaller the electrode radius, the more notorious the influence of the diffusion coefficient ratio, so the use of microelectrodes is of great utility for determining the diffusion coefficients of the electroactive couple. The analytical solutions given until now can only be considered as partial solutions for this problem, since they lead to absurd results for electrode radii <10 −2 cm. This equation has also been applied to the study of amalgamation processes and it could also be applicable to the study of the ionic transfer at hanging and microspherical electrolyte drop electrodes (i.e., liquid–liquid interfaces). In these last cases, the use of this equation is limited by the validity of Koutecký’s approximation, which neglects the electrode finite volume.

Electrochemical Analysis of D‐Penicillamine Using a Carbon Paste Electrode Modified with Ferrocene Carboxylic Acid

AbstractThe electrochemical behavior of D‐penicillamine (D‐PA) studied at the surface of ferrocene carboxylic acid modified carbon paste electrode (FCAMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00), the oxidation of D‐PA at surface of such an electrode is occurred about 420 mV less positive than that an unmodified carbon paste electrode (CPE). The catalytic oxidation peak current was linearly dependent on the D‐PA concentration and a linear calibration curve was obtained in the ranges 7.5×10−5 M – 1.0×10−3 M and 6.5×10−6 M−1.0×10−4 M of D‐PA with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 6.04×10−5 M and 6.15×10−6 M. This method was also used for the determination of D‐PA in pharmaceutical preparation (capsules) by standard addition method.

Diffusion Coefficients of Tris(β-diketonato)ruthenium Complexes of Different Charge Numbers in Acetonitrile Solutions, Measured by Chronoamperometry

The diffusion coefficients of several tris(β-diketonato) ruthenium complexes in acetonitrile solutions containing a supporting electrolyte were determined by chronoamperometry. The diffusion coefficients of the charged complexes, which were produced by electrochemical oxidation or reduction, were also determined by double potential step chronoamperometry. Two kinds of radii of the complexes were evaluated. One was the Van der Waals radius and the other was the geometric distance from the center of the complex to the outer surface of the farthest atom. The latter quantity was determined from X-ray diffractometric data. The diffusion coefficients of the neutral complexes were discussed on the basis of the Stokes-Einstein equation. Those of charged complexes could not be explained by the theoretical equation presented by Hubbard and Onsager.

L‐Cysteine Voltammetry at a Carbon Paste Electrode Bulk‐Modified with Ferrocenedicarboxylic Acid

AbstractThe electrochemical behavior of L‐cysteine studied at the surface of ferrocenedicarboxylic acid modified carbon paste electrode (FDCMCPE) in aqueous media using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry. It has been found that under optimum condition (pH 8.00) in cyclic voltammetry, the oxidation of L‐cysteine occurs at a potential about 200 mV less positive than that of an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, kh were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L‐cysteine showed a linear dependent on the L‐cysteine concentration and linear analytical curves were obtained in the ranges of 3.0×10−5 M–2.2×10−3 M and 1.5×10−5 M–3.2×10−3 M of L‐cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 2.6×10−5 M and 1.4×10−6 M by CV and DPV methods.

Intra vs Intermolecular Association Processes in the Radical Anions of b-Hydroxyquinones. Influence on the Structural Properties of the Radical Anion of Julgone.

The electrochemical study of the β-hydroxyquinone Juglone by cyclic voltammetry and double step potential chronoamperometry is presented in this work. The results show that the electroreduction of Juglone at the first electron transfer process in DMSO is determined by the extent of the reduction of the self-associated quinone as a homoconjugate, which changes the reduction pathway for this compound at high concentrations. This set of reactions is associated to the presence of a selfprotonation process mediated by the formation of the homoconjugate. The changes in structure of the semiquinone analyzed by Electron Spin Resonance spectroelectrochemical experiments confirms the change in the structural properties of the corresponding semiquinones.

Electrochromic properties of a novel low band gap conductive copolymer

Abstract A copolymer of 2,5-di(thiophen-2-yl)-1- p -tolyl-1 H -pyrrole (DTTP) with 3,4-ethylene dioxythiophene (EDOT) was electrochemically synthesized. The resultant copolymer P(DTTP- co -EDOT) was characterized via cyclic voltammetry, FTIR, SEM, conductivity measurements and spectroelectrochemistry. Copolymer film has distinct electrochromic properties. It has four different colors (chestnut, khaki, camouflage green, and blue). At the neutral state λ max due to the π–π * transition was found to be 487 nm and E g was calculated as 1.65 eV. Double potential step chronoamperometry experiment shows that copolymer film has good stability, fast switching time (less than 1 s) and good optical contrast (20%). An electrochromic device based on P(DTTP- co -EDOT) and poly(3,4-ethylenedioxythiophene) (PEDOT) was constructed and characterized. The device showed reddish brown color at −0.6 V when the P(DTTP- co -EDOT) layer was in its reduced state; whereas blue color at 2.0 V when PEDOT was in its reduced state and P(DTTP- co -EDOT) layer was in its oxidized state. At 0.2 V intermediate green state was observed. Maximum contrast (%Δ T ) and switching time of the device were measured as 18% and 1 s at 615 nm. ECD has good environmental and redox stability.

Kinetics of Homogeneous Reactions using Double Potential Step Chronoamperometry in Room Temperature Ionic Liquids

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A novel multielectrochromic copolymer based on 1-(4-nitrophenyl)-2,5-di(2-thienyl)-1H-pyrrole and EDOT

Abstract Copolymer of 1-(4-nitrophenyl)-2,5-di(2-thienyl)-1H-pyrrole (NTP) with 3,4-ethylene dioxythiophene (EDOT) was electrochemically synthesized and characterized. Resulting copolymer film has distinct electrochromic properties. It has five different colors (light red, red, light grey, green, and blue). At the neutral state λ max value due to the π–π ∗ transition was found to be 550 nm and E g was calculated as 1.6 eV. Double potential step chronoamperometry experiment shows that copolymer film has good stability, fast switching time (1.2 s) and high optical contrast (42%). Electrochromic device based on P(NTP-co-EDOT) and poly(3,4-ethylenedioxythiophene) was constructed and characterized. Oxidized state of the device shows light red color whereas reduced state blue color. At interval potentials device has good transparency and colors of the device are yellow and grey. Maximum contrast ( T %) and switching time of the device were measured as 23% and 1.1 s at 650 nm. Electrochromic devices has good environmental and redox stability.

Platinum-macrocycle co-catalyst for electro-oxidation of formic acid

In this work, a new promoter, tetrasulfophthalocyanine (FeTSPc), one kind of environmental friendly material, was found to be very effective in both inhibiting self-poisoning and improving the intrinsic catalysis activity, consequently enhancing the electro-oxidation current during the electro-oxidation of formic acid. The cyclic voltammograms test showed that the formic acid oxidation peak current density has been increased about 10 times compared with that of the Pt electrode without FeTSPc. The electrochemical double potential step chronoamperometry measurements revealed that the apparent activity energy decreases from 20.64 kJ mol −1 to 17.38 kJ mol −1 after Pt electrode promoted by FeTSPc. The promoting effect of FeTSPc may be owed to the specific structure and abundant electrons of FeTSPc resulting in both the steric hindrance of the formation of poisoning species (CO) and intrinsic kinetic enhancement. In the single cell test, the performance of DFAFC increased from 80 mW cm −2 mg −1 (Pt) to 130 mW cm −2 mg −1 after the anode electrode adsorbed FeTSPc.

Electrocatalytic Oxidation and Highly Selective Voltammetric Determination of l-Cysteine at the Surface of a 1-[4-(Ferrocenyl ethynyl)phenyl]-1-ethanone Modified Carbon Paste Electrode

A carbon paste electrode (CPE) chemically modified with 1-[4-(ferrocenyl ethynyl)phenyl]-1-ethanone (4-FEPEMCPE) was employed to study the electrocatalytic oxidation of L-cysteine using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry as diagnostic techniques. The diffusion coefficient (D = 7.863 x 10(-6) cm2 s(-1)) of L-cysteine was also estimated using chronoamperometry. The electron-transfer coefficient, alpha (= 0.40), for L-cysteine at the surface of 4-FEPEMCPE was determined using cyclic voltammetry technique. It was found that under an optimum pH (= 7.00), the oxidation of L-cysteine at the surface of such an electrode occurred at a potential of about 350 mV less positive than that of an unmodified CPE. The catalytic oxidation peak currents represented a linear dependence on the L-cysteine concentration. Linear analytical curves were obtained in the ranges of 9.0 x 10(-5) - 4.9 x 10(-3) M and 2.0 x 10(-5) - 2.8 x 10(-3) M of L-cysteine with correlation coefficients of 0.9981 and 0.9982 in cyclic voltammetry and differential pulse voltammetry, respectively. The detection limits (2 sigma) were determined to be 9.9 x 10(-6) M and 5 x 10(-6) M with cyclic voltammetry and differential pulse voltammetry, respectively. The influences of twenty other amino acids, such as glutamine, L-glutamic acid, L-glysine, L-histidine, L-isoleucine, L-leucine, L-arginine hydrochloride, L-aspargine, L-aspartic acid, S-carboxy methyl-L-cysteine, L-methionine, L-phenyl alanine, L-proline, L-serine, L-threonine, L-cystine, cysteamine and gluthathione, on the current response of the sensor were examined. The obtained results did not show any influence on the analytical signal of L-cysteine by these amino acids (except for cysteamine). The method was also used for the selective determination of L-cysteine in patient-blood plasma and some pharmaceutical preparations by using standard addition method.

Electrocatalytic Oxidation and Voltammetric Determination of L‐Cysteic Acid at the Surface of p‐Bromanil Modified Carbon Paste Electrode

AbstractThe electrochemical properties of L‐cysteic acid studied at the surface of p‐bromanil (tetrabromo‐p‐benzoquinone) modified carbon paste electrode (BMCPE) in aqueous media by cyclic voltammetry (CV) and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of L‐cysteic acid at the surface of BMCPE occurs at a half‐wave potential of p‐bromanil redox system (e.g., 100 mV vs. Ag|AgCl|KClsat), whereas, L‐cysteic acid was electroinactive in the testing potential ranges at the surface of bare carbon paste electrode. The apparent diffusion coefficient of spiked p‐bromanil in paraffin oil was also determined by using the Cottrell equation. The electrocatalytic oxidation peak current of L‐cysteic acid exhibits a linear dependency to its concentration in the ranges of 8.00×10−6 M–6.00×10−3 M and 5.2×10−7 M–1.0×10−5 M using CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (2σ) were determined as 5.00×10−6 M and 4.00×10−7 M by CV and DPV methods. This method was used as a new, selective, rapid, simple, precise and suitable voltammetric method for determination of L‐cysteic acid in serum of patient's blood with migraine disease.

Study of hydrogen nanobubbles in solution in the vicinity of a platinum wire electrode using double-potential step chronoamperometry

A solution supersaturated with hydrogen around a platinum wire electrode was studied by double-potential step chronoamperometry. The time–current curve at the hydrogen oxidation potential obtained with double-potential step increased with a shift of the hydrogen evolution potential to the cathodic potential. The initial slope of the chronoamperogram at the oxidation potential increased to zero with the shift from the hydrogen evolution potential to the cathodic potential. The increase was observed with increasing ionic strength and increasing cathodic current density. These phenomena were analyzed with numerical method using a number of assumptions.

Diffusion Coefficients of C60 and C60– in Benzonitrile and Dichloromethane Solutions Containing Tetrabutylammonium Perchlorate, Measured by Potential-step Chronoamperometry

The diffusion coefficients of C(60) in dichloromethane and benzonitrile solutions containing 0.1 M tetrabutylammonium perchlorate were determined by single potential-step chronoamperometry at small disk electrodes. The diffusion coefficients of C(60) were obtained by curve fitting of the chronoamperograms to a theoretical equation by Shoup and Szabo. The values were (1.4 +/- 0.3) x 10(-9) and (4.1 +/- 0.3) x 10(-10) m(2) s(-1), respectively (the errors are 95% confidence limits). The diffusion coefficients of C(60)(-) in these solutions were measured by double potential-step chronoamperometry. The ratios of the diffusion coefficients of C(60) to those of C(60)(-) were obtained from theoretical curves of the ratios of the current at the second potential step to the current at the first one. The values of the ratios were 1.2 +/- 0.2 and 1.0 +/- 0.3, respectively.

Superior performance characteristics for the poly(2,5-dimethoxyaniline)–poly(styrene sulfonic acid)-based electrochromic device

We have fabricated an electrochromic (EC) device with poly(2,5-dimethoxyaniline), PDMA, entrapped in poly(styrene sulfonic acid) (PSS) as an electrochromic layer. The device showed improved performances like stability, optical contrast, etc., over the device with a PDMA layer doped by H 2SO 4. In the process of fabrication of the EC device with a sandwich configuration, indium tin oxide (ITO)/PDMA–PSS||poly(ethyleneimine) (PEI)/orthophosphoric acid (H 3PO 4)/WO 3/ITO, electrochemical polymerization of 2,5-dimethoxyaniline (DMA) was performed with PSS as electrolyte and ITO coated glass as working electrode. The performance characteristics of EC device, like optical contrast, stability, switching time, etc., were followed by cyclic voltammetry, double potential step chronoamperometry and in-situ spectroelectrochemistry. The device was operated in between − 1 V and + 1 V, and absorption characteristics were followed by in-situ UV–visible spectroscopy. A visible contrast in color upon switching the potential from − 1 V to + 1 V was noticed for the device. The device was pale yellow at − 1 V and dark green at + 1 V. Incorporation of PSS into PDMA resulted enhancement in the performance of the complementary electrochromic device. The optical contrast of the device was improved by incorporating PSS into PDMA matrix. The device retained nearly 50% of their optical contrast after 10,000 double steps informing the superior performance of PDMA–PSS in the EC device.

Osmium Redox Polymer Film Electrode and Its Electrocatalytic Properties towards the Oxidation of Epinephrine: Electrochemical Quartz-Crystal Microbalance and Voltametric Characterization

An osmium redox polymer PVI-PAA-dmeOs is electrodeposited onto a gold electrode by using repetitive double potential step chronoamperometry. The resulting film is permeable to the substrates and products of the catalyzed reaction, and permits fast electron transfer. The frequency variation during the potential step process is recorded using electrochemical quartz-crystal microbalance (EQCM). A reaction mechanism for electrochemical deposition of the osmium redox polymer is proposed. The characteristics of the PVI-PAA-dmeOs film are investigated by EQCM and cyclic voltametry. The results show the hydrated osmium PVI-PAA-dmeOs film to exhibit excellent electrocatalytic activity towards the oxidation of epinephrine. At a bare gold electrode, the epinephrine oxidation current increases greatly and the oxidation peak potential negatively shifts to about 0.16 V (Ag/AgCl) at the film-modified electrode. Under optimal conditions, amperometric measurements are performed at 0.18 V and the current response of epinephrine changes linearly with its concentration from 5 × 10−7 to 1 × 10−4 mol l−1. A detection limit of 1.5 × 10−7 mol l−1 (S/N = 3) is obtained.

Electrochemical Behavior of Chloranil Chemically Modified Carbon Paste Electrode. Application to the Electrocatalytic Determination of Ascorbic Acid

AbstractA p‐chloranil modified carbon paste electrode was constructed and the electrochemical behavior of this electrode was studied in the aqueous solution with different pH. From the E1/2–pH diagram for this compound the values of formal potential E0' and pKa of some different redox and acid‐base couples depending on the solution pH were estimated. The diffusion coefficient, D, value for p‐chloranil was estimated 1.5×10−7 cm2 s−1. It has been shown by direct current cyclic voltammetry and double potential step chronoamperometry, that this p‐chloranil incorporated carbon paste electrode, can catalyze the oxidation of ascorbic acid in the aqueous buffered solution. Under the optimum condition (pH 7.00), the oxidation of ascorbic acid at the surface of such an electrode occurs at a potential about 325 mV less positive than that at an unmodified carbon past electrode. The catalytic oxidation peak currents was linearly dependent on the ascorbic acid concentration and a linear calibration curve was obtained in the range of 7×10−5 M–4×10−3 M of ascorbic acid with a correlation coefficient of 0.9998. The limit of detection (3σ) was determined as 3.5×10 −5 M. This method was used as simple, selective and precise voltammetric method for determination of ascorbic acid in pharmaceutical preparations.