Electrode kinetics Frumkin

Finally, it must be taken into account that the use of large concentrations of supporting electrolyte minimizes the Frumkin effects. This is important in that we can now realize that high concentrations of supporting electrolyte not only minimize either migration or the capacitive currents, but also allow us to adopt the simple electrode kinetics discussed in Section 4. 

CI2 evolution reaction, 38 56 electrochemical desorption, 38 53-54 electrode kinetics, 38 55-56 factors that determine, 38 55 ketone reduction, 38 56-57 Langmuir adsorption isotherm, 38 52 recombination desorption, 38 53 surface reaction-order factor, 38 52 Temkin and Frumkin isotherm, 38 53 real-area factor, 38 57-58 regular heterogeneous catalysis, 38 10-16 anodic oxidation of ammonia, 38 13 binding energy quantification, 38 15-16 Haber-Bosch atrunonia synthesis, 38 12-13... 

Irreversible reaction, 1251, 1419 Isoconic, definition, 933, 978, 982 Isotherm, 932, 964, 1197 applicability, 941 and charge transfer, 954, 955 Conway and Angersein-Kozlowska, 943 definition, 933 in electrode kinetics, 1197 Flory—Huggins type, 941,942, 944, 965 Frumkin, 938, 942, 965 Frumkin-Temkin, 1197, 1198 Habib-Bockris, 943... 

A discussion of the effects of the structure of the interface on electrode kinetic rates is the right moment to introduce a seminal figure in electrochemistry, a person who played a part later than—but hardly less than—that of Butler and of Volmer and Erdey-Gmz, in establishing the basis of the modem subject. It was A. N. Frumkin who first introduced interfacial structure considerations into electrode kinetics, in 1932. However, to leave a mention of Frumkin at that would sadly underdescribe a great leader whose influence in creating physical electrochemistry was outstanding.16... 

For many years, the study of the electrode—electrolyte interface and electrode kinetics was confined to the very reproducible mercury-aqueous system because of the availability of the dropping mercury electrode (DME) and development of polarography. Extensive leading work in this field was carried out by Heyrovsky, Frumkin, Grahame, and Randles. 

The importance of double layer structure on electrode kinetics was first shown by Frumkin for the hydrogen evolution reaction on mercury [44]. As a result of the structure of the electrochemical interface, the pre-electrode plane, i.e. the plane where the reactant undergoes electron transfer to become product, is such that the concentration of the reactant ion is different from that in the bulk solution and the corresponding potential difference with respect to the solution, (less than the applied electrode—solution potential difference ([Pg.34]

When reactants or intermediates are adsorbed, the rate of the reaction may no longer be related to the concentration by a simple law. This situation is best understood where a reactant is nonspecifically adsorbed in the outer -> Helmholtz plane. The effect of such adsorption on the electrode kinetics is usually termed the -> Frumkin effect. Physical and chemical adsorption on the electrode surface is usually described by means of an -> adsorption isotherm and kinetic equations compatible with various isotherms such as the - Langmuir, -> Temkin, -> Frumkin isotherms are known. 

Frumkin s slow discharge theory — had been first proposed in 1933 [i] for taking into account the role of reaction layer structure in electrode kinetics. The theory is based on the potential dependence of the - activation energy AG ... 

Refs. [i] Frumkin A (1933) Z phys Chem A 164 121 [ii] Frumkin AN (1961) Hydrogen overvoltage and adsorption phenomena, part 1, mercury. In Delahay P (ed) Advances in electrochemistry and electrochemical engineering, vol 1. Interscience, New York [iii] Frumkin AN, Petrii OA, Nikolaeva-Ferdorovich NV (1963) Electrochim Acta 8 177 [iv] Frumkin AN, Nikolaeva-Fedorovich NV, Berezina NP, Keis KhE (1975) J Electroanal Chem 58 189 [v] Fawcett WR (1998) Double layer effects in the electrode kinetics of electron and ion transfer reactions. In Lipkowski J, RossPN (eds) Electrocatalysis. Wiley-VCH, New York, p 323... 

Although the author believes that the generalized concept was originally responsible for the electrochemical treatment of corrosion processes by the early workers, it appears that Hammett and Lorch (23) and Frumkin (24) were among the first to specifically describe metallic dissolution according to this concept. Wagner and Traud (16) showed that the electrode kinetics for hydrogen evolution are not affected by the simultaneous dissolution of the metallic ions. 

Perhaps the most striking example of the effect of the diffuse double layer on electrode kinetics was demonstrated by Frumkin in 1955,... 

Disregarding for a moment the electrochemical aspect of this isotherm, we note that 0 is proportional to logC, (as opposed to the Langmuir isotherm, where it is proportional to a linear function of the concentration.) A simitar "logarithmic isotherm" was developed by Temkin. His derivation is much more complex, but in the final analysis it is based on the same physical assumptions. It has, therefore, become common to refer to Eq. 141 as the Temkin isotherm, although Temkin has never used it in this form. It is this approximate form of the Frumkin isotherm which is applied to electrode kinetics, as we shall see below. 

All these findings may point to limitations of the classical Frumkin model for correction of the double-layer influence on electrode kinetics in nonaqueous solvents, although it works well in aqueous solution. In the present author s opinion these rather surprising results may follow from some kind of compensation effects. For instance, ion-pair formation in these solutions by decreasing the effective charge of the reactant could reduce the double-layer effect. 

The current situation in electrode kinetics is thoroughly presented in Vetter s book. Useful but rather specialized reviews are the recent ones by Parsons and Frumkin. Gierst s 1958 thesis and his many valuable later publications show how far an essentially nonthermodynamic point of view can penetrate into the intricacies of electrode kinetics Hurwitz s 1963 thesis adds to that of Gierst a certain amount of correlation with a thermodynamic leading thread which, however, retains the arbitrary separation of chemical and electric terms in the electrochemical potentials and the a priori introduction of transfer coefficients. 

An interesting conflict arises between the implications of MD electrode kinetics and the derivation of what has become to be known as Frumkin s double-layer correction. Frumkin s derivation has remained essentially unchanged over the years between its first presentation in 1933 and, for instance, that of 1961 in Advances in Electrochemistry and Electrochemical Engineering. It can be summarized as follows, for the case of hydrogen overtension and assuming ideality ... 

In the past, the majority of the basic laws and concepts in electrode kinetics were developed and verified by Tafel [11], Volmer [12], and Frumkin [13] using the hydrogen electrode. Two important reaction mechanisms are well recognized and experimentally validated. The first is the Volmer-Tafel mechanism, shown in Equations 3.11-3.13. The other, which is more important for the hydrogen electrode, is the Hyrovsky-Volmer mechanism, expressed in Equations 3.14-3.17. 

In 1933, Fmmkin [14] became the first person to relate the rate of an electrode process to the stmcture of the double layer, by taking into account an effect which he called the psi-prime (i/rj) effect (now universally referred to as the Frumkin correction ). Thus, a close relationship was established between the two great divisions of electrochemistry, namely the double layer and electrode kinetics. 

We know that thermodynamics is a very powerful tool for the study of systems at equilibrium, but electrode processes are systems not at equilibrium when at equilibrium there is no net flow of current and no net reaction. Therefore electrode reactions should be studied using the concepts and formalities of kinetics. Indeed, the same period that saw the flourishing of solution electrochemistry, also saw the formulation of the fundamental theoretical concepts of electrode kinetics the work of Tafel on the relationship of current and potential was published in 1905 those of Butler and Volmer and Erdey Gruz, which formulated the basic equation for electrode kinetics, were published in 1924 and 1930 respectively. Frumkin in 1933 showed the correlation between the structure of the double layer and the kinetics of the electrode process. The first quantum mechanical approach to electrode kinetics was published by Gurney in 1931. 

The effect of the structure of the double layer on the kinetics of electrode reactions, which was first reported by Frumkin, is well known, and is usually taken into account in electrode kinetics (for a discussion see standard textbooks of electrochemistry, for example. Ref. 84-87). In electrode kinetic measurements, this effect... 

Figure 9.7 Electrocapillary curves for solutions of TINO3 in 1.0 M KNO3, and 0.01 M HNO3. Data from A.N. Frumkin, Transactions of the Symposium on Electrode Kinetics, Yeager, Ed. Wiley, pp. 1-12, (1961).

Transient measnrements (relaxation measurements) are made before transitory processes have ended, hence the current in the system consists of faradaic and non-faradaic components. Such measurements are made to determine the kinetic parameters of fast electrochemical reactions (by measuring the kinetic currents under conditions when the contribution of concentration polarization still is small) and also to determine the properties of electrode surfaces, in particular the EDL capacitance (by measuring the nonfaradaic current). In 1940, A. N. Frumkin, B. V. Ershler, and P. I. Dolin were the first to use a relaxation method for the study of fast kinetics when they used impedance measurements to study the kinetics of the hydrogen discharge on a platinum electrode. 

Reactant concentrations Cyj in the bulk solution, as well as the Galvani potential between the electrode and the bulk solution (which is a constituent term in electrode potential E), appear in kinetic equations such as (6.8). However, the reacting particles are not those in the bulk solution but those close to the electrode surface, near the outer Helmholtz plane when there is no specific adsorption, and near the inner Helmholtz plane when there is specific adsorption. Both the particle concentrations and the potential differ between these regions and the bulk solution. It was first pointed out by Afexander N. Frumkin in 1933 that for this reason, the kinetics of electrochemical reactions should strongly depend on EDL structure at the electrode surface. 

Frumkin, A. N., V. S. Bagotsky, Z. A. lofa, and B. N. Kabanov. Kinetics of Electrode Reactions [in Russian], Moscow University PubUshers, Moscow, 1952. 

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