Electrode Impedance Measurements Research Articles

Electrode processes at mercury in the far cathodic potential region: III. The reduction of K + from KOH solution

The reduction of K + , in 0.88 M concentration, from KOH solution has been studied at the dropping mercury electrode using d.c. polarography and electrode impedance measurements as a function of frequency and electrode potential. The K + reduction is reversible within the limitations of the measuring technique. The K + reduction process was accompanied by a secondary irreversible process as had already been found in neutral aqueous solutions. From the similarity between the results in neutral and alkaline media, it was concluded that water and not the proton is the primary species reduced during the amalgam dissolution process.

Electrode processes at mercury in the far cathodic potential region: II. The reduction of Li + and m M Na + from aqueous 1 M LiCl solution

The reduction of Li + ions in 1 M concentration and the reduction of Na + ions in m M concentration in aqueous solution, has been studied at the dropping mercury electrode, using d.c. polarography and electrode impedance measurements, as a function of frequency and electrode potential. The reduction of Li + was found to be quasireversible ( k f sh =0.08±0.04 cm s −1 ). The reduction process was accompanied by an irreversible secondary process as was found previously for K + and Na + reductions. This is attributed to the reaction of the alkali metal amalgam with water. The error in potentiometric measurements of the standard potential of the lithium/lithium ion couple has been calculated (21 mV). The reversibility of the Na + reaction was confirmed by the measurements in m M concentration. The presence of the irreversible reaction due to water reduction was detected over the entire polarographic reduction range of the Na + ion. This irreversible reaction was found to be in agreement with the theory developed for the process in the presence of 1 M alkali metal ions.

Electrode processes at mercury in the far cathodic potential region: I. The reduction of K + and Na + in neutral aqueous media

The reduction of K + and Na + ions at the dropping mercury electrode in 1 M aqueous solutions of halide salts has been studied using d.c. polarography and electrode impedance measurements as a function of frequency and electrode potential. The results confirm that the reductions are reversible but that the primary reduction process is accompanied by an irreversible secondary process which seems likely to be reduction of water. The influence of this process on the analysis of the K + wave is discussed. The implications of the observation of a coupled process are more generally discussed. In particular, it is concluded that potentiometric measurements of the standard potentials of alkali-amalgam/alkali ion redox couples are always in error because a mixed potential is observed instead of the Nernst potential. Two principally different correction procedures are suggested.

Electrode kinetics of nickel hydroxide in alkaline solution

The electrode kinetics of a nickel hydroxide electrode and effects of Li + ions and rare-earth compounds were studied by the means of observation of decay and growth of polarization and measurement of electrode impedance. From the experimental results, the rate-determining step of the charge and discharge reaction is considered to be the diffusion process of protons and/or defects in the hydroxide layer. The values of ∐ D/φ or ∐ D. L in the hydroxide layer can be obtained from theoretical treatment of the observed data. These values may be used as the measured of activity of the nickel-hydroxide electrode. By addition of Li + ions in the electrolyte, the values of ∐ D. L were increased for charge, but slightly decreased for the discharge. Such phenomena may be explained as the effect of the Li + ion, which has lower valency than the nickel ion in nickel hydroxide, an n-type semiconductor during charge and p-type semiconductor during discharge. And then, by addition of rare-earth compounds to the electrolyte solution, the values of ∐ D. L were slightly increased for charge and discharge, probably due to the increase of active centres on the electrode surface.

Application of the method of time-domain reflectometry to the study of electrode processes

Summary o 1. A technique has been developed for the application of the methods of time-domian reflectometry to measurements of electrode impedance in electrochemical systems. 2. The impedance has been measured at a platinum electrode in aqueous HClO 4 and H 2 SO 4 solutions. The capacitance is normally independent of time in the range 1–100 nsec except at the reversible hydrogen potential where the effect of the electrode reaction results in a time-dependent decrease of the electrode impedance at times >30 nsec. No detectable relaxation of the double layer occurs within the time range of the experiments.

Application of the method of time-domain reflectometry to the study of electrode processes

Summary o 1. A technique has been developed for the application of the methods of time-domian reflectometry to measurements of electrode impedance in electrochemical systems. 2. The impedance has been measured at a platinum electrode in aqueous HClO 4 and H 2 SO 4 solutions. The capacitance is normally independent of time in the range 1–100 nsec except at the reversible hydrogen potential where the effect of the electrode reaction results in a time-dependent decrease of the electrode impedance at times >30 nsec. No detectable relaxation of the double layer occurs within the time range of the experiments.

A device for the measurement of electrode impedance

A device for the measurement of electrode impedance

A device for the measurement of electrode impedance

A device for the measurement of electrode impedance

The redox system Fe(III)/Fe(II) oxalate at platinum and mercury electrodes

The dissociation equilibria of the complex ions present in a solution of Fe(III) and/or Fe(II) oxalate systems depend upon the pH, since H2C2O4 is a weak acid. Equilibrium diagrams have been drawn from the best information available about stability constants of these systems. Absorption spectra suggest that the octahedral configuration of the complexes is preserved and the dissociation is concerned with a process of aquation in the first co-ordination sphere. A study of the polarographic behaviour shows that both electron exchange at the electrode surface and setting of the dissociation equilibria are very fast. Impedance measurements of platinum and mercury electrodes immersed in solutions of Fe(III)/Fe(II) oxalate systems have been carried out. The results confirm the fast exchange of electrons at the electrode interface and the important role played by adsorption in the mechanism of this electrode reaction.

Double-Layer Impedance of Electrodes with Charge-Transfer Reaction

Abstract : Equations for the electrode impedance are derived for metal-ion amalgam electrodes and other electrode reactions without a priori separation of faradaic and double layer charging processes. Experimental conditions for electrode impedance measurements are re-examined with some emphasis on Sluyters's method for separation of the double layer capacity. Results are derived for metal-ion amalgam electrodes, and other types of electrode reactions are discussed.

Elektrochemische untersuchungen an kohleelektroden—IV. Die Überspannung des Sauerstoffs

Investigations of the oxygen overvoltage on carbon electrodes are described: 1. cd/ potential plots; 2. determination of the exchange current density by applying the double-pulse method; 3. electrode-impedance measurements; 4. application of the potentiodynamic triangular-sweep method.In accordance with the electrode-impedance measurements, the exchange-current densities are high. Therefore the oxygen overvoltage is mainly concentration overvoltage. At low cd an adsorption overvoltage is predominating, changing to a predominating diffusion overvoltage, which is followed by a reaction overvoltage involving diffusion. At high cd and high overvoltage there is evidence of another effect, caused by the heavy destruction of the graphite lattice, which inhibits electron transport.

Elektrochemische Untersuchungen an Kohleelektroden—III. Die Überspannung des Chlors

Investigation of the chlorine overvoltage on carbon electrodes is described: 1. Current- density/potential plots; 2. electrode-impedance measurements; 3. determination of the exchange cd; 4. measurements by application of the potentiodynamic triangular-sweep method. Exchange current densities are found to be high. Chlorine overvoltage is mainly diffusion overvoltage. At low cd, diffusion of Cl atoms is predominating; diffusion of Cl− ions in the pores is predominating at high cd's. Peaks from the potentiodynamic triangular-sweep method can be explained quantitatively by the diffusion process.

Studies on the Electroreduction of Uranyl (VI) in Molten Equimolar KCl ‐ NaCl by Chronopotentiometric and Electrode Impedance Measurements

The reduction of to in molten salt at 716°C has been shown by chronopotentiometry to be diffusion controlled at a platinum electrode. Furthermore, the potential‐time curves indicated that the reaction occurred in two steps at nearly the same potential. This observation was verified by measuring the pseudo capacity of the polarized cathode as a function of its potential for which a plot of the data shows two peaks in capacity. The first was found to be symmetric with a concentration‐independent potential, which is indicative of an electrode reaction producing a soluble product. The second peak was asymmetric with a concentration‐dependent potential, which is indicative of an electrode reaction producing an insoluble product. These observations suggested that the electrode reaction proceeds by a reduction of to followed by the reduction of the to Additional verification of this mechanism was provided by the reduction of by to yield a stable solution of . The heterogeneous rate constant for the reduction of to was estimated to be 2 cm sec−1, but a value for the reduction of could not be determined because of the solid deposit. The diffusion coefficient was estimated from the chronopotentiometric data to be .

Study of the impedance of a platinum electrode in the system Cl 2/Cl − (HClO 4aq)

A Randles circuit has been used as a first approximation to explain the a.c. impedance of a platinum electrode in the system Cl 2/Cl − (HClO 4aq). However, in all cases the coefficient of the Warburg impedance is much higher than the theoretical value. This fact is interpreted in terms of the surface oxidation of the electrode. The adjustment of an equivalent circuit may be improved by considering the admittance due to electrode reactions at the oxidized part of the surface. The values of the exchange current j 0, obtained from electrode impedance measurements, show that system Cl 2/Cl − is more irreversible than system Br 2/Br − for the same experimental conditions.

On the impedance of galvanic cells: IV. Determination of rate constants of rapid electrode reactions from electrode impedance measurements

AbstractIf, at one particular frequency, the electrode impedance is plotted in the complex impedance plane at varying bulk concentrations C*ox and C*RED, keeping C*ox = C*RED, a circle is obtained. Moreover, through one of the points measured a semicircle can be drawn with its centre on the real axis.From the coordinates of the centres of these circles information can be gained on the rate constant of the electrode reaction. The ohmic resistance, the double layer capacity, diffusion polarization and activation polarization may contribute to the impedance of the electrode.The upper limit of the rate constant ksh that can be measured by this method is valued at 0.65 cm sec−1.

Electrode Impedance Measurements on the Cerium(IV) - Cerium(III) Couple in Perchloric Acid Solutions.

Electrode Impedance Measurements on the Cerium(IV) - Cerium(III) Couple in Perchloric Acid Solutions.