A faradaic impedance study of the electrochemical reduction of Cd(II) ions from aqueous 1 M (KF+KCl) mixed electrolyte solutions at the dropping mercury electrode
TL;DR: In this article, it was shown that in the whole range of the composition of this base electrolyte the Cd(II) reduction can be explained on the assumption of a reaction mechanism that consists of a chemical step followed by two one-electron transfers, the transfer coefficients appearing to be 0.5.
About: This article is published in Journal of Electroanalytical Chemistry.The article was published on 1980-08-25 and is currently open access. It has received 23 citations till now. The article focuses on the topics: Dropping mercury electrode & Faradaic impedance.
Summary (1 min read)
(III) RESULTS
- The details of this analysis and also a critical discussion on its reliability have been published elsewhere [5, 6] .
- From the potential dependence of a the reversible half-wave potential E~t 2 and the diffusion coefficient of the Cd(II) species were obtained in each base electrolyte.
- (2 Do) -in (1) where p' is the experimentally obtained irreversibility quotient, Do is the diffusion coefficient and j = (nF/RT)(E --Er~12); k~ can be considered as the poten- tial dependent forward rate constant occurring in the overall rate equation.
- Fairly straight lines, from which 1~ks2 and 1/(kslK~ 1) were derived as the slope and the intercept at exp[l¢] = 0 respectively.
20[ kc
- Firstly it should be mentioned that the fit of the experimental data to eqn.
- If fluoro complexes are involved in the chemical step in 1 M KF, then the increase of k¢ with increasing KC1 concentration could mean that the chemical step is catalysed by chloride anions, or that another chemical reaction proceeds in parallel to the original one.
- Finally, it should be realized that as yet no Frumkin corrections have been applied to the electrochemical rate constants.
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TL;DR: In this paper, the reduction of Zn(II) has been studied by means of the faradaic impedance method in wide potential and frequency ranges and at varied water activity, and the results obtained could be quantitatively explained on the assumption of a mechanism including at least the following consecutive steps: 1 (1) fast partial dehydration of the electroactive species; 2 (2) fast transport from the solution into the double layer; 3 (3) slow transfer of the first electron; 4 (4) a fast second partial dehydration step; 5 (5) slow transferred of the second
86 citations
TL;DR: In this paper, it was shown that by the presence of thiourea the rate constant k t f is increased in such a way that the effect is mathematically expressed by K t f = k t,0 f (1 + B Γ TU, where B is a proportionality constant and TU stands for the surface excess of thourea.
45 citations
TL;DR: It is shown that in perchlorate base electrolyte solution the same mechanism applies and that the rate constant of the chemical step is quite close to the value in fluoride solution.
40 citations
TL;DR: In this article, the reduction of CdII to Cd(Hg) has been studied by means of demodulation voltammetry in a wide potential range and at various water activities using NaClO 4 as the base electrolyte, and it is concluded that the reduction proceeds according to: (i) fast loss of 125 water molecules in a preceding equilibrium; (ii) a slow “chemical” step, which is not a desolvation; (iii) slow transfer of the first electron; (iv) four water molecules; (v) slow
34 citations
TL;DR: In this paper, the potential dependence of the resulting adsorption parameters can be mathematically described by a Langmuir isotherm for Cd(II) with the energy being at least a quadratic function of potential.
27 citations
References
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TL;DR: In this article, a review of electron transfer reactions is presented, focusing on the absence of bond rupture in the reaction step, which is a unique feature of purely electron-transfer reactions.
Abstract: One of the active areas in reaction kinetics during the post-war years has
been that of electron-transfer reactions. These reactions constitute one type
of oxidation-reduction process and include both chemical and electrochemical
systems. Many rate constants have now been measured (1-8) and
they have stimulated a variety of theoretical studies (9-37). The field has
been characterized by a strong interplay of theory and experiment, which
now includes the testing of theoretically predicted quantitative correlations
(34). Because of a certain unique feature of the purely electron-transfer
reactions--the absence of bond rupture in the reaction step--these correlations
are unusual. They do not have the arbitrary parameters that occur
in theoretical studies of most other reactions in chemical kinetics. This review
will be limited to purely electron transfer reactions.
3,738 citations
TL;DR: A unified theory of homogeneous and electrochemical electron transfer rates using statistical mechanics is developed in this article, where the atomic motions inside the inner coordination shell of each reactant are treated as vibrations and the motions outside are treated by the particle description.
Abstract: A unified theory of homogeneous and electrochemical electron‐transfer rates is developed using statistical mechanics. The treatment is a generalization of earlier papers of this series and is concerned with seeking a fairly broad basis for the quantitative correlations among chemical and electrochemical rate constants predicted in these earlier papers. The atomic motions inside the inner coordination shell of each reactant are treated as vibrations. The motions outside are treated by the "particle description," which emphasizes the functional dependence of potential energy and free energy on molecular properties and which avoids, thereby, some unnecessary assumptions about the molecular interactions.
2,401 citations
TL;DR: In this paper, the capacity of the double-layer capacity as a function of the amount of adsorbed was investigated and shown to be a one-constant virial form of isotherm with a non-linear charge dependence of the standard free energy.
Abstract: The adsorption of chloride ions on mercury from aqueous solutions of KCl + KF at constant ionic strength has been investigated by measurements of the double-layer capacity as a function of concentration. The adsorption can be represented by a one-constant virial form of isotherm with a non-linear charge dependence of the standard free energy of adsorption in contrast to the adsorption of the same ion from KCl solutions. The hump on the anodic branch of the capacity-potential curve arises partially from the effect of a decrease in the capacity at constant amount adsorbed superimposed on an increasing adsorption capacity, and partially from an inflexion in the charge dependence of the amount adsorbed; this in turn arises from the non-linear charge dependence of the standard free energy of adsorption. The constant charge isotherms for Cl– ion adsorption from KCl and from KCl + KF solutions cannot be superimposed irrespective of the choice of salt activity or mean ionic activity as the concentration variable.
119 citations
TL;DR: In this paper, the theory of faradaic rectification polarography is extended to systems of higher order stoichiometry, and the couples Zn 2+ /Zn(Hg) in 0.5 M MgSO 4 and Cd 2+ + /Cd(Cd) in 1 M KCl are studied with the aid of this technique in a wide potential range.
63 citations
TL;DR: In this paper, a faradaic impedance study has been made of the reduction of Cd(II) ions from a 1 M KF base electrolyte at the DME.
63 citations