Electrode Reaction Rate Research Articles

Determination of Rutin on the Poly(p-aminobenzene sulfonic acid) Modified Glassy Carbon Electrode

The electrochemical behaviors of rutin at a poly(p-aminobenzene sulfonic acid) modified glassy carbon electrode (PABSA/GC) have been investigated. Rutin can generate a pair of well-defined redox peaks at the PABSA/GC located at 0.440 V (E(pa)) and 0.396 V (E(pc)) (vs. saturated calomel electrode (SCE)), respectively. The results indicate that the reaction involves two electrons transfer, accompanied by two protons and the electrochemical process is controlled by adsorption. The electrochemical parameters of rutin on the modified electrode were calculated with the results of the charge transfer coefficient (alpha), the number of electron transfer (n) and the electrode reaction rate constant (k(s)) as 0.61, 2.08 and 2.18 s(-1), respectively. Under the selected conditions, the oxidation peak current was linear to the rutin concentration over the range of 2.5x10(-7)-1.0x10(-5) M with a detection limit of 1.0x10(-7) M. The proposed method has been successfully applied to the determination of compound rutin tablets with no interference from the coexisting ascorbic acid.

Exploiting Binding-Induced Changes in Probe Flexibility for the Optimization of Electrochemical Biosensors

Electrochemical sensors employing redox-tagged, electrode-bound oligonucleotides have emerged as a promising new platform for the reagentless detection of molecular analytes. Signal generation in these sensors is linked to specific, binding-induced changes in the efficiency with which an attached redox tag approaches and exchanges electrons with the interrogating electrode. We present here a straightforward means of optimizing the signal gain of these sensors that exploits this mechanism. Specifically, using square-wave voltammetry, which is exquisitely sensitive to electrode reaction rates, we can tune the frequency of the voltammetric measurements to preferentially enhance the signal associated with either the unbound or target-bound conformations of the probe. This allows us to control not only the magnitude of the signal gain associated with target binding but also the sign of the signal change, generating "signal-on" or "signal-off" sensors. This optimization parameter appears to be quite general: we show here that tuning the square-wave frequency can significantly enhance the gain of the sensors directed against specific oligonucleotide sequences, small molecules, proteins, and protein-small molecule interactions.

Effect of the composition of water-acetone solvent and benzhydrazine structure on their efficiency during cadmium electrodeposition from perchlorate media

The feasibility of controlling the degree of retardation of a cathodic process by changing the ratio of the components in the liquid phase and nature of electron shifts in additive molecule (benzhydrazine) is discussed. The minimum electrode reaction rate is observed in a range of water structure stabilization under conditions of the predominant adsorption of organic molecules. The highest efficiency are achieved using an additive with an electron-donating substituent in the molecule. The highest rate of the electroreduction of Cd2+ and the lowest efficiency of the additives are registered in the region of the loosening of the structure of the mixed solvent, causing selective ion solvation to become possible, which results in an abrupt increase in the adsorption activity of ClO4− anions on the cathode and is the main reason for the ψ’ effect during the electroreduction of metal ions.

Voltammetric determination of sericin based on its interaction with carmine

A simple yet sensitive method is developed for the determination of sericin using voltammetry based on the interaction between sericin and carmine for the first time. In the absence of sericin, carmine has a pair of well-defined redox peaks in a pH 1.81 Britton–Robinson buffer solution. Although no new redox peaks appear upon the addition of sericin into a carmine solution, the peak currents of the old peaks reduce while the peak potentials shift positively. This observation is attributed to the decrease in the diffusion coefficient and electrode reaction rate constant of carmine in the presence of sericin. A binding mechanism is proposed and discussed, and the binding constant and binding ratio are calculated as 2.32 × 10 6 L mol −1 and 1:1, respectively. Furthermore, the decrease in the peak currents is found proportional to the sericin concentration in the range of 32.0–800.0 μg mL −1 with a detection limit of 13.52 μg mL −1. The method is further applied to the determination of sericin in degumming wastewater with satisfied average recoveries from 96.7 to 103.3%. The results are in good agreement with those obtained by the conventional Coomassie brilliant blue G-250 spectrophotometric method.

Temperature dependence of the electrochemical corrosion characteristics of carbon steel in a salty soil

The electrochemical corrosion characteristics of carbon steel in a salty soil at different temperatures were studied by measurements and analyses of potentiodynamic polarization curves, linear polarization resistance and electrochemical impedance spectroscopy. The results showed that the mass-transfer of dissolved oxygen plays an essential role in carbon steel corrosion, and the whole corrosion process is mix-controlled by both activation and mass-transfer steps. Passivity can be developed on carbon steel in the soil at low temperatures. With the increase of temperature, the passive current density increases and the passive potential range decreases. When temperature is elevated to a certain value, 50 °C in this system, passivity cannot be maintained and the steel is dominated by an active dissolution status. Anodic Tafel slope decreases continuously with the increase in temperature, which is mainly due to the enhanced electrode reaction rate at an elevated temperature. Simultaneously, cathodic Tafel slope increases with temperature continuously due to the decrease of the solubility of dissolved oxygen in soil. Since the diffusion activation energy is generally much smaller than the reaction activation energy, the effect of temperature on diffusion is far less than that on electrode reaction rate.

Electrochemical behavior and determination of rutin on a pyridinium-based ionic liquid modified carbon paste electrode

In this paper the electrochemical behavior of rutin on a pyridinium-typed ionic liquid modified carbon paste electrode (IL-CPE) was investigated and further used for rutin sample determination. The IL-CPE showed strong electrocatalytic effects to the oxidation of rutin. In phosphate buffer solution (PBS, pH 2.5; 0.1 M) a pair of well-defined cyclic voltammetric redox peaks of rutin appeared with the redox peak located at 512 mV (Epa) and 448 mV (Epc) ( vs. SCE), respectively. The redox peak current was increased about 27.5 times more than that on traditional carbon paste electrode (CPE). The electrochemical parameters of rutin on the IL-CPE were calculated with the results of the charge transfer coefficient ( α), the number of electron transfer ( n) and the electrode reaction rate constant ( k s ) as 0.53, 1.80 and 2.39 s −1, respectively. The cathodic peak currents increased linearly with the concentration of rutin in the range from 5.0 × 10 −7 to 1.0 × 10 −4 M with the detection limit as 3.58 × 10 −7 M (3 σ). The relative standard deviation (RSD) of 10 successive detection of 5.0 × 10 −5 M rutin was 4.2%. The method was successfully applied to the determination of rutin content in tablets samples with good recovery. The modified electrode showed good stability and reproducibility without the influence of the coexisting substances.

Electrochemical behaviors of metol on ionic-liquid-modified carbon paste electrode and its analytical application

The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (k s) as 4.02 × 10−3 s−1, and the diffusion coefficient (D) as 6.35 × 10−5 cm2/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10−6 ∼ 1.0 × 10−3 mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10−6 mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions.

PEM fuel cell relative humidity (RH) and its effect on performance at high temperatures

The water balance inside a fuel cell was analysed and several equations were introduced as functions of fuel cell gas-stream inlet and outlet pressures, inlet relative humidities (RHs), temperature, pressure drops across flow channels, and reactant partial pressures. The effect of RH on PEM fuel cell performance was studied at elevated temperatures under ambient backpressure using Nafion ®-based MEAs. The results showed that fuel cell performance could be depressed significantly by decreasing RH from 100 to 25%. AC impedance and cyclic voltammetry techniques were employed to diagnose the RH effect on fuel cell reaction kinetics. Reducing RH can result in slower electrode kinetics, including electrode reaction and mass diffusion rates, and higher membrane resistance.

Electrochemical oxidation of nitrite on nanodiamond powder electrode

Nanodiamond (ND) powder electrodes were fabricated and the electrochemical properties were investigated in the solution containing nitrite in this article. This electrode exhibits substantial catalytic ability toward the oxidation of nitrite anions. The electrochemical oxidation mechanism of nitrite on the ND powder electrode is discussed. The oxidation of NaNO 2 is a two-electron transfer process. The electrode reaction rate constant k is estimated to be 2.013 × 10 −4 cm/s and (1 − α) n α is 0.1643. The peak current increases linearly with the rising of the concentration of NaNO 2.

Preparation of a Novel NH2 + Ion Implantation Modified Electrode and Its Study of the Electrochemical Behavior of Hemoglobin

A novel functional electrode was obtained by implanting NH2 + into ITO film (NH2/ITO) for the first time. The NH2/ITO surface showed a better affinity to gold nanoparticles than bare ITO. Gold nanoparticles were deposited on the surface of NH2/ITO electrode (Au/NH2/ITO). The Au/NH2/ITO and NH2/ITO electrodes were used to observe the electrochemical behavior of Hemoglobin (Hb) immobilized on the electrodes surfaces. The peak current value of Hb immobilized on NH2/ITO increased compared with on bare ITO while peak current value of Hb immobilized on Au/NH2/ITO increased compared with on Au/ITO. Linkage between the ‐NH2 implanted into the ITO film and the ‐COOH of Hb was thought to be the reason for the increase of active Hb coverage on NH2/ITO compared with bare ITO. Increase of active Hb coverage on Au/NH2/ITO compare with Au/ITO was attributed to the different amount of gold nanoparticles deposited. Results showed the novel NH2/ITO and Au/NH2/ITO electrodes exhibited good stability, reproducibility besides selectivity and sensitivity. The electrode process of Hb immobilized on Au/NH2/ITO was quasi‐reversible with adsorption. The electrode reaction rate constant ks and other related constants were determined. X‐ray photoelectron spectroscopy (XPS), field‐emission scanning electron microscopy (FE‐SEM), and impedance spectra were used to characterize the different surfaces.

Electrochemical Determination of Ascorbic Acid in Room Temperature Ionic Liquid BPPF6 Modified Carbon Paste Electrode

AbstractA room temperature ionic liquid N‐butylpyridinium hexafluorophosphate (BPPF6) was used as a binder to make an ionic liquid modified carbon paste electrode (IL‐CPE), which showed good characteristics such as simple preparation procedure, fast electrochemical response and good conductivity. The electrochemical oxidation of ascorbic acid (AA) on the new IL‐CPE was carefully studied. The oxidation peak potential of AA on the IL‐CPE appeared at 109 mV (vs. SCE), which was about 338 mV decrease of the overpotential compared to that obtained on the traditional carbon paste electrode (CPE) and the oxidation peak current was increased for about four times. The electrochemical parameters of AA on the IL‐CPE were calculated with the charge transfer coefficient (α) and the electrode reaction rate constant (ks) as 0.87 and 0.800 s−1, respectively. Based on the relationship of the oxidation peak current and the concentration of AA a sensitive analytical method was established with cyclic voltammetry. The linear range for AA determination was in the range from 1.0×10−5 to 3.0×10−3 mol/L with the linear regression equation as Ip (μA)=−2.52–0.064C (μmol/L) (n=13, γ=0.9942) and the detection limit was calculated as 8.0×10−6 mol/L (3σ). The proposed method was free of the interferences of coexisting substances such as dopamine (DA) and amino acids etc., and successfully applied to the vitamin C tablets determination.

Cadmium electrodeposition from water-acetone perchlorate baths

It is the composition of the bath that determines a) the nature of species adsorbed and reduced at the cathode (such as molecules of a nonaqueous solvent, perchlorate anions, metal ions, or their complexes with organic ligands) and b) the electrode reaction rate. The process is best inhibited in a range of water structure stabilization under conditions of the predominant adsorption of acetone molecules, when the discharge of electroactive species is preceded by their “constrained” dissociation during the penetration through the layer adsorbed at the cathode. The highest reduction rate was observed in the acetone structuration range, when the adsorption of perchlorate anions reaches a maximum because of the desalting effect of the mixed solvent and the selective solvation (Ψ’-effect).

Mechanisms and applications of cell electrochemical technique to prepare luminescent SrMoO4 thin films

Abstract Cell electrochemical technique is a novel film deposition method. With the improved cell device, the rate determining step, utilization ratio of molybdenum, and applications to deposit SrMoO 4 thin films have been investigated. Researches on the relation between the overpotentials of electrodes and the currents in the circuit reveal that the rate determining step is the reduction of water during the deposition of SrMoO 4 thin films. The rates of electrode reactions can be tailored by controlling the electrolyte temperature. The utilization ratio of molybdenum is up to 90%, while it is nearly 60% for constant current method. In addition, X-ray diffraction analyses show that the as-grown SrMoO 4 thin films are well crystalline and have a scheelite structure; scanning electron microscopy examinations reveal that SrMoO 4 crystals grow well in tetragonal tapers. These thin films show a broad emission band centered at 520 nm using an excitation wave of 230 nm at room temperature.

Electrochemistry and Homogeneous Self‐Exchange Kinetics of the Aqueous 12‐Tungstoaluminate(5‐/6‐) Couple.

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Electrochemistry and Homogeneous Self-Exchange Kinetics of the Aqueous 12-Tungstoaluminate(5−/6−) Couple

The effect of alkali metal (M) chloride or triflate supporting electrolytes (0.1-1.0 mol L(-1)) on the midpoint potential E(m) of the aqueous AlW12O40(5-/6-) couple in cyclic voltammetry, after correction (E(corr)) for liquid junction potentials, can be represented in terms of ionic strength according to the extended Debye-Hückel equation. However, unrealistically short AlW12O40(5-/6-)-cation closest-approach distances are required to accommodate the specific effects of M+, and the infinite-dilution potential E(corr)(0) values are not quite consistent from one M+ to another. The pressure dependence of Em is qualitatively consistent with expectations based on the Born-Drude-Nernst theory. The strong accelerating effects of supporting electrolytes on the standard electrode reaction rate constant k(el) at pH 3 as measured by alternating current voltammetry (ACV), and on the homogeneous self-exchange rate constant k(ex) at pH 3-7 as measured by 27Al line broadening, depend specifically on the identity and concentration of M+ (Li+ < Na+ < K+ < Rb+) rather than on the ionic strength, whereas the effect of the nature of the supporting anion (Cl- or CF3SO3-) is negligible. Extrapolation of k(el) and k(ex) to zero [M+] indicates that the uncatalyzed electron transfer rate is negligibly small relative to the M+ catalyzed rates. The kinetic effects of M+ show no evidence of the saturation expected had they been due primarily to ion pairing with AlW12O40(5-/6-). The catalytic effect of M+ operates primarily through lowering the enthalpy of activation, which is partially offset by a strongly negative entropy of activation and, for the homogeneous exchange catalyzed by K+ or Rb+, becomes mildly negative; thus, the catalytic effect of M(+) is enthalpy-driven but entropy-limited. For the electrode reaction, the volume of activation averages +4.5 +/- 0.2 cm(3) mol(-1) for all M+ and [M+], in contrast to the negative value predicted theoretically for the uncatalyzed reaction. These results are consistent with a reaction mechanism, previously proposed for other anion-anion electron-transfer reactions, in which anion-anion electron transfer is facilitated by partially dehydrated M+.

Synthetic semiconductor diamond electrodes: Electrochemical behaviour of homoepitaxial boron-doped films orientated as (111), (110), and (100) faces

Electrode behavior of homoepitaxial (single-crystal) boron-doped diamond films deposited onto differently orientated faces of dielectric diamond single crystals is studied by the electrochemical impedance and potentiodynamic curves methods. For the films grown under constant concentration of the volatile boron compound in the feeding gas, the rate of electrode reactions in the [Fe(CN)6]3−/4− and [Ru(NH3)6]2+/3+ redox systems decreases in the series: (1 1 1) → (1 1 0) → (1 0 0)-face. It is shown that the acceptor concentration (estimated from the slope of Mott–Schottky plots) also decreases in the above-given series. This is explained by the different intensity of boron incorporation into differently orientated faces of the diamond crystals during their growth. Thus, the apparent dependence of the electrochemical reaction rate on the crystal face orientation can be reduced to the earlier found interrelationship between the electrochemical kinetics at diamond electrodes and their doping level. By contrast, for the films grown under different boron concentration in the feeding gas, chosen in such a way that the acceptor concentration in the differently orientated diamond films is nearly the same, no significant difference in the kinetic behavior was found between the (equally doped) (1 1 1)- and (1 0 0)-faces.

Theory of irreversible electrode reactions coupled to ion transfer across the liquid/liquid interface

Kinetically controlled electro-oxidation of a redox probe dissolved in the organic solvent, which is interposed between an electrode surface and an aqueous solution as a thin layer, is analyzed theoretically. It is demonstrated that the electrode reaction rate constant can be measured by the variation of scan rate in linear scan voltammetry both in the absence and in the superfluity of the supporting electrolyte dissolved in the film.

Electrochemical properties of nanodiamond powder electrodes

Detonation-synthesized nanocrystalline diamond is a novel carbon material. Its increased electrical conductivity, due to the features of giant specific surface area and large numbers of surface defects as well as the cluster structure, makes it possible to be used as an electrode material. Nanodiamond powder electrodes were fabricated and the electrochemistry was investigated by cyclic voltammetry and AC impedance measurement. The results show that nanodiamond powder electrode is electrochemically stable in KCl electrolytes over a wide potential range (− 1.2–2.0 V). The electrode reaction is quasi-reversible in 0.1 M KCl containing the ferricyanide–ferrocyanide redox couple. The electrode reaction rate constant k is estimated to be 2.87 × 10 − 3 cm/s. The peak current increases linearly with the rising of the concentration of [Fe(CN) 6] 3−/4−. The AC impedance spectra have been analyzed and an equivalent circuit proposed.

Redox kinetics of adriamycin adsorbed on the surface of graphite and mercury electrodes

Kinetics of the surface redox reactions of adriamycin (doxorubicin hydrochloride) adsorbed on paraffin-impregnated graphite electrode (PIGE) and on mercury electrode is measured by square-wave voltammetry. In 0.9 mol/L KNO 3 buffered to pH 4.65, the standard electrode reaction rate constants of the first quinone/hydroquinone redox couple (see Scheme 2) on PIGE and mercury are k s1 = 49 ± 12 s − 1 and k s1 = 147 ± 36 s − 1 , respectively. Under the same conditions, the standard rate constant of the second redox couple on the PIGE is smaller than 4 s − 1 and the electron transfer coefficient of the reduction is α 2 = 0.35.

Estimation of Coupling Rate Constant ofL-Cysteine Radical Studied by Concentration-Step Coulometry Using Porous Carbon Felt Electrode Impregnated with an Electrolyte

Controlled potential coulometry using carbon felt electrode impregnated with electrolytic solution realizes very rapid complete electrolysis and can be used to measure the faster reaction rate constant than that using conventional electrolytic cell. In this research, concentration step method was adopted to investigate coupling reaction rate of L-cysteine radical. The coupling reaction rate of L-cysteine radical becomes much larger than further electrode reaction rate of L-cysteine radical at high L-cysteine concentration, because the coupling reaction rate is proportional to the second order of L-cysteine radical concentration although the further electrode reaction rate is proportional to the first order of L-cysteine radical concentration. At a low constant potential value, apparent number of electrons (napp) increased from 1 (L-cystine is produced) to 2 (L-cysteine sulfenic acid, RSOH, may be produced) according to decrease in concentration of L-cysteine to be electrolyzed. The second order rate constant of coupling reaction was estimated to be about 1200 dm3 mol−1 s−1 at 20 °C by curve fitting method for napp vs. logarithm of L-cysteine concentration. Apparent number of electrons (napp) consumed in the electrode oxidation of L-cysteine gradually increased as an applied potential increases, because the consecutive electrode reaction steps with different electrode reaction rates were involved in the electrode oxidation of L-cysteine. In the present method, the constant limited electrolytic current was observed at high electrode potential range, which suggests that electrode oxidation rate of L-cysteine is kinetically controlled.