Kinetic Parameters Of Electrode Reaction Research Articles

Electrochemical behaviour of antioxidants: Part 2. Electrochemical oxidation mechanism of quercetin at glassy carbon electrode modified with multi-wall carbon nanotubes

Electrochemical oxidation mechanism of quercetin was investigated at glassy carbon electrode modified with multi-wall carbon nanotubes in aqueous 0.2M phosphate solutions with different pHs. The investigation was carried out using cyclic voltammetry, double potential step chronoamperometric and chronocoulometric techniques. It was found that the oxidation mechanism proceeds in sequential steps, related with the five-hydroxyl groups in the three aromatic rings. The mechanism was proposed to be an ECEC, first-order kinetics. The proposed mechanism was confirmed on comparing the digital simulated cyclic voltammetric responses with the experimental ones. The electrode homogeneous and heterogeneous kinetic parameters of electrode reaction are estimated from the simulated data. Moreover, quercetin molecules adsorb on the electrode surface.

The Dynamic Micropolarization Method: I . Application to Aluminum

A new approach is proposed for the study of the rate of corrosion and its decay with time after a protective surface layer is removed by abrasion in situ. The method, termed the dynamic micropolarization (DMP) method, was tested for aluminum electrodes in neutral and mildly acid solutions. The corrosion rate of the in situ‐abraded surface is determined as a function of time (from milliseconds to days). A short current pulse is applied at a given time from the end of each abrasion, and the overpotential is measured in the linear region. The total charge passed during measurement is not enough to form more than a few percent of a monolayer and has a negligible effect on the rate of growth of the oxide. Tafel slopes are determined from macropolarization measurements. They are found to be independent of time after abrasion. The corrosion currents are derived from the measured faradaic resistance using these values of the Tafel slopes. The rate of corrosion varies by an order of magnitude over a period of 18h, the first measurement taken 0.5s after termination of abrasion. Depending on the kinetic parameters of the system, a double pulse method may have to be used, to allow rapid charging of the double layer, before any secondary effects could influence the overpotential. The on‐line computerized system used, with averaging of repeated experiments, yields highly reproducible data, not commonly obtained in electrochemical measurements on solid electrodes. Thus, the experimental system developed here may also have future applications for the accurate determination of kinetic parameters of electrode reactions on solid electrodes.

Electrochemical Kinetic Parameters of Geometric Isomers of Singly Charged Cobalt(III) Complexes

Abstract The kinetic parameters of electrode reactions of several geometric isomers of singly charged cobalt(III) complexes have been determined by means of Tast polarography. The complexes studied are trans-[Co(NCS)(NO2)(en)2]Cl·H2O, cis-[Co(NCS)(NO2)(en)2]Cl·2H2O, trans-[Co(NO2)2(en)2]NO3, cis-[Co(NO2)2(en)2]NO3, trans-[Co(NO2)2(NH3)4]NO3·0.5H2O, cis-[Co(NO2)2(NH3)4]NO3, trans-[CoCl(NO2)(en)2]NO3, and cis-[CoCl(NO2)(en)2]NO3. These complexes showed two irreversible reduction waves; the first corresponds to CoIII→CoII, and the second, to CoII→Co0. The electrochemical kinetic parameters for the one-electron reduction wave were obtained in 0.1 and 1.0 M acetate buffer solutions. The half-wave potentials for the first wave of the complexes were more positive for the cis isomers than for the corresponding trans isomers. The cathodic rate constants at E=0 for the cis isomers were also larger than those for the corresponding trans isomers. A slight increase in the rate constant with the decrease in ionic strength was observed.

Computer-aided measurement of kinetic parameters of electrode reactions of cobalt(III)—ammine complexes at mercury electrodes

A computer-aided technique based on Tast polarography is examined for the determination of kinetic parameters of electrode reactions. It is particularly useful for the investigation of unstable species because of the simple and rapid processing of data. Kinetic parameters of cobalt(III)—ammine complexes at mercury electrodes are given for [Co(NH 3) 6]Cl 3, [Co(H 2O)(NH 3) 5](ClO 4) 3, [Co(NO 3)(NH 3) 5](NO 3) 2 [CoF(NH 3) 5](Cl0 4) 2, [Co(C0 3)(NH 3) 5] NO 3 , cis-[Co(H 2O) 2(NH 3) 4] (Cl0 4) 3 [Co(CO 3)(NH 3) 4] NO 3 · 0.5H 20, [Co(ox)(NH 3) 4]Cl · H 20, and NH 4[Co(ox) 2(NH 3) 2] · H 2O, which are obtained in solutions containing 0.1 M acetate buffer and 0.005% gelatin at 25°C.

An Alternative Display of Potentiostatic Measurements. I. Instrumental Design and Verification of Modified Pulse Polarograph

Abstract A modified instrument for the potentiostatic method (modified pulse polarograph) has been developed, which uses techniques of the time-to-voltage converter. The modified pulse mode and the modified differential pulse mode have been tested as tools for quantitative analysis. The determination of kinetic parameters of electrode reactions is presented, together with the characteristics of the modified pulse polarograph.

A Contribution to the Theory of Pulse Polarography. I. Theory of Current-Potential Curves

Abstract A general theory of pulse polarographic current-potential curves is developed for a simple electrode reaction proceeding at the expanding plane electrode. It is shown that when the ratio of the sampling time to the pre-electrolysis time is smaller than 1/30, this condition being satisfied in usual pulse polarographic practice, the equation of current-potential curves can be greatly simplified. The theory developed is applied to the three modes of pulse polarography nowadays practically employed, i.e., normal pulse, scan-reversal pulse and differential pulse polarography. For each mode, the dependence of current-potential curves on the kinetic parameters of electrode reaction as well as on the experimental variables is discussed.

A polarographic cell system with a novel temperature-controlled reference electrode for the determination of kinetic parameters of electrode reactions

An improved experimental arrangement for the determination of kinetic data relating to polarographic reductions is described. The significant feature is the constant-temperature reference electrode; its construction and use in this context are described. A comparison is made of the more realistic results obtained by these means, with those obtained with a more conventional cell where the temperature of the reference electrode is varied with that of the working solution.

The Effect of Adsorption Conformation of Intermediates on Kinetic Parameters of Electrode Reactions. Mechanism of the Electroreduction of Dihalopyridines on the DME

AbstractThe mechanism of reduction of 2,6‐dichloropyridine, 2,5‐dibromopyridine and 2,3‐dichloropyridine in ethanol‐water media was investigated at the DME. The electrode processes were studied by measurements of Tafel slopes, reaction orders and pH effects. The proposed mechanism involves: (i) first protonation and electronation in a quasi‐equilibrium step resulting in an adsorbed pyridinyl radical (intermediate I) parallel to the electrode surface, (ii) Cleavage of the C–X bond in the rate‐determining step, resulting in an adsorbed cation radical (intermediate II), perpendicular to the electrode. The Tafel slope computed via the combined‐adsorption isotherm are in agreement with the experimental values.

Kinetic Parameters of Electrode Reactions of Metallic Compounds by R. Tamamushi, IUPAC Additional Publication, Butterworths, London, 1975

Kinetic Parameters of Electrode Reactions of Metallic Compounds by R. Tamamushi, IUPAC Additional Publication, Butterworths, London, 1975

Temperatur- und konzentrationsabhängigkeit der stromausbeute bei der transpassiven auflösung des eisens unter stationären bedingungen

It is possible, to write an expression for the current efficiency of transpassive metal-dissolution reactions, connected with an oxygen evolution, as a function of reaction cd. It can be shown, which parameter of this function is affected by temperature and the concentration of the reactants. The variation of this parameter allows the calculation of the order of the reactions and the activation energies. This introduces a new method for the estimation of kinetic parameters of electrode reactions at high cd, avoiding potential measurements. With respect to the practical importance of a mathematical expression for the current efficiency as a function of cd, concentration of electrolyte and temperature, for instance for the electrochemical machining, the validity of the deduced equations is demonstrated by experimental investigations concerned with the dissolution of steels in nitrate solutions.

Electrode kinetics by analysis of polarographic current-time curves

The method, which enables the evaluation of the kinetic parameters of electrode reactions by analysing the polarographic current-time curve, is presented. As examples of the application of this method, the electrode reactions of the simple zinc ions and of the zinc-acetate complex ions were experimentally examined. For the former case the current-time curves were measured as a function of the electrode potential and the perchlorate concentration. It was found that the standard rate constant, corrected both for the increase of the activity coefficient of the zinc ion and for the Frumkin double-layer effect, has a constant value over the concentration range of perchlorate 0.6–4.0 M. For the latter case the current-time curves in the solution with constant ionic strength (4 M) are measured as a function of the electrode potential and of the acetate concentration. It was concluded that the potential-determining reaction of zinc-acetate complexes is referred only to the species Zn(Ac)2 over a range of acetate concentrations larger than 0.5 M.

Electrode kinetics by analysis of polarographic current-time curves

The method, which enables the evaluation of the kinetic parameters of electrode reactions by analysing the polarographic current-time curve, is presented. As examples of the application of this method, the electrode reactions of the simple zinc ions and of the zinc-acetate complex ions were experimentally examined. For the former case the current-time curves were measured as a function of the electrode potential and the perchlorate concentration. It was found that the standard rate constant, corrected both for the increase of the activity coefficient of the zinc ion and for the Frumkin double-layer effect, has a constant value over the concentration range of perchlorate 0.6–4.0 M. For the latter case the current-time curves in the solution with constant ionic strength (4 M) are measured as a function of the electrode potential and of the acetate concentration. It was concluded that the potential-determining reaction of zinc-acetate complexes is referred only to the species Zn(Ac)2 over a range of acetate concentrations larger than 0.5 M.

Theory of stationary current—voltage curves of redox-electrode reactions in hydrodynamic voltammetry IX. Double electrodes in channel flow

A theoretical treatment is given for simple redox-electrode reactions (Ox+neRed) proceeding at the double electrode in a laminar channel flow. The general equation of the stationary current-voltage curves at the detector electrode (which is located in the down stream) is derived for the redox-couple, whose components are Ox in the bulk of the solution and Red produced at the generator electrode (which is located in the upper stream). A simple approximate expression is also presented, which represents with reasonable accuracy the dependence of the current-voltage curves on the geometry of double electrode, the kinetic parameters of electrode reaction and the flow rate; this equation has the same form as that previously derived for the rotating ring-disk electrode.

Theory of stationary current-voltage curves of redox-electrode reactions in hydrodynamic voltammetry: IX. Double electrodes in channel flow

Summary A theoretical treatment is given for simple redox-electrode reactions (Ox+n e Red) proceeding at the double electrode in a laminar channel flow. The general equation of the stationary current-voltage curves at the detector electrode (which is located in the down stream) is derived for the redox-couple, whose components are Ox in the bulk of the solution and Red produced at the generator electrode (which is located in the upper stream). A simple approximate expression is also presented, which represents with reasonable accuracy the dependence of the current-voltage curves on the geometry of double electrode, the kinetic parameters of electrode reaction and the flow rate; this equation has the same form as that previously derived for the rotating ring-disk electrode.

Galvanostatic pulse followed by coulostatic impulse with reversed sign. A new double-pulse method for the determination of the kinetic parameters of electrode reactions II. Experimental verification

Galvanostatic pulse followed by coulostatic impulse with reversed sign. A new double-pulse method for the determination of the kinetic parameters of electrode reactions II. Experimental verification

Galvanostatic pulse followed by coulostatic impulse with reversed sign. A new double-pulse method for the determination of the kinetic parameters of electrode reactions: II. Experimental verification

Galvanostatic pulse followed by coulostatic impulse with reversed sign. A new double-pulse method for the determination of the kinetic parameters of electrode reactions: II. Experimental verification

Galvanostatic pulse followed by coulostatic impulse with reversed sign: A new double-pulse method for the determination of the kinetic parameters of electrode reactions I. Theory and classification

Summary A new double pulse method is presented in which a galvanostatic pre-pulse is followed by a coulostatic impulse with reversed sign. The coulostatic charge density selected is such that the overvoltage-time curve starts with a horizontal tangent after the impulse has ceased. As both the net current through the cell and the charging current through the double layer capacity are zero, the faradaic current must also be zero. This allows the elimination of both concentration polarization and ohmic drop so that the charge transfer overvoltage is obtained directly. The method, denoted as GRC, is mainly distinguished by very simple analysis of experimental data and good potentialities. In addition it seems to be especially promising for the study of electrode processes where determination of double layer capacity in situ is vital.

Galvanostatic pulse followed by coulostatic impulse with reversed sign: A new double-pulse method for the determination of the kinetic parameters of electrode reactions I. Theory and classification

A new double pulse method is presented in which a galvanostatic pre-pulse is followed by a coulostatic impulse with reversed sign. The coulostatic charge density selected is such that the overvoltage-time curve starts with a horizontal tangent after the impulse has ceased. As both the net current through the cell and the charging current through the double layer capacity are zero, the faradaic current must also be zero. This allows the elimination of both concentration polarization and ohmic drop so that the charge transfer overvoltage is obtained directly. The method, denoted as GRC, is mainly distinguished by very simple analysis of experimental data and good potentialities. In addition it seems to be especially promising for the study of electrode processes where determination of double layer capacity in situ is vital.

Electrode kinetics and double layer structure

Several electrochemical methods have been developed in recent years for the study of the kinetic parameters of electrode reactions. These methods have been used for obtaining an abundance of experimental data for the standard heterogeneous rate constant, k sh, of electrode reactions, mostly limited to reactions at a mercury electrode. As early as 1933, Frumkin recognized the essential correlation between the double layer structure at the electrode interface and electrode kinetics. As enough data for the kinetic parameters are yet available, interest is growing in this correlation, because it may result in a better understanding of heterogeneous reaction rates. According to Frumkin the potential difference existing in the double layer, influences the kinetic parameters for two reasons: (a) It influences the effective potential difference which favours or hinders the reaction, (b) The effective concentration of reacting species is different from the “bulk” concentration. The Frumkin effect with its limitations is discussed. Adsorption of electroinactive species, e.g. organic adsorbates, may have two effects: variation of the potential difference in the double layer and hence of the Frumkin correction and secondly a blocking effect. Some examples, illustrating these effects, are presented. If the anions of the supporting electrolyte were specifically adsorbed at the interface, it appeared that the Frumkin correction did not suffice. For some reactions, e.g. the zinc system in mixed halide solutions, we found a linear relation between log k sh and the amount of specifically adsorbed anions q− 1, from which it is inferred that the energy of activation for the electrode reaction decreases linearly with q− 1. Quite frequently, the electroactive species themselves are adsorbed at the interface. In that case the adsorption complicates matters considerably, e.g. the mass transport equations change, so that the electrochemical methods, as normally used, are inapplicable. Recently Delahay has presented expressions based on the concept of the coupling between faradaic and double layer charging processes. These expressions can be used successfully for systems with adsorption of the electroactive species. Such systems have been investigated with sine wave methods and some results are presented. Almost all systems with adsorption of the reacting species were found to be mass transfer controlled, so that no influence of the double layer structure on the kinetic parameters could be investigated for these cases.

The galvanostatic single-pulse and the coulostatic impulse methods for the determination of the rate constants of electrode reactions

The information on kinetic parameters of electrode reactions obtained with the galvanostatic single-step, the coulostatic impulse and the faradaic impedance methods is examined as a function of the applied electrolysis time and the ac frequency. A time and a frequency condition is given for which the information on kinetics obtainable with these methods is maximal. In the usual approach to the single-step and the coulostatic impulse methods these optimal conditions cannot be met. We present here a new procedure with which the experimental data measured with both methods can be interpreted exactly over the whole region of the η/ t curve by means of numerical tables. The application of these tables enhances the limit of the applicability of the single-step method by a factor of 3 and that of the coulostatic impulse method by a factor of 100. The methods are applied to the Cd 2+/Cd (Hg)-electrode in 1 M NaClO 4 and the Hg 2 2+/ Hg electrode in 1 M HClO 4.