Academician A. N. Frumkin
and Modern Advances in Electrochemistry

1995 marks the centenary of the birth of Academician Aleksandr Naumovich Frumkin, one of the founders of present day, XX century electrochemistry. His contribution to the development of this branch of science has long been widely acknowledged. A.N. Frumkin became a classic in his lifetime, and his foreign colleagues called him "the father of modern electrochemistry". His high authority as a scientist of encyclopedic erudition made him the world's acknowledged expert on quite a variety of controversial problems of electrochemistry and physical chemistry. Even today, almost 20 years after his death, the role of Aleksandr Frumkin in the development of electrochemistry remains equally high.
Having decided to devote a special issue of the journal Elektrokhimiya to this significant anniversary, the Editorial Board received additional confirmation that the memory of Aleksandr Frumkin remains alive among scientists: the response was so strong that the papers received will fill not only the present issue, but also at least two subsequent ones. In some of the papers readers will find high appraisal of the contribution made by Frumkin to modern electrochemistry, while other papers deal with the further development of his ideas.
Aleksandr Frumkin used to say that modern electrochemistry rests on three "whales": the theory of interfaces, diffusion kinetics, and the theory of the charge transfer across interfaces. He made a major contribution to the development of each of these directions of modern electrochemistry, but the greatest credit is due to him for the development of the general theory of the kinetics and mechanism of electrode processes, linking them with the concepts of surface phenomena and the structure of the electrical double layer.
Originating at the turn of the XVIII to the XIX century, electrochemistry in the XIX century mostly dealt with thermodynamic problems, i.e., the investigation of equilibrium systems. By the end of the XIX and the beginning of the XX centuries, the creation of "classical" electrochemistry, which was based on the works of W. Ostwald, S. Arrhenius, and W. Nernst, was completed. In the XX century, a new era began in natural sciences, and the attention of electrochemists was focused chiefly on the problems of the kinetics of electrode processes. Although at the beginning of the XX century, numerous kinetic studies were carried out and the main empirical equation of electrochemical kinetics - the Tafel equation - was obtained, electrochemical kinetics was not yet a science in the full sense of the word. Fortunately, Frumkin started his studies at precisely this moment.
The active scientific work of Frumkin lasted for more than half a century, and the list of his published scientific works numbers 755. However, we can single out several fundamental key works that had a profound effect on the entire development of electrochemistry. The first of these works was, undeniably, his dissertation "Electrocapillary Phenomena and Electrode Potentials," which was published in 1919 [1]. Soon afterwards, the author published a short version of this work in English [2], German [3], and Russian [4].
In this work, impressive by the maturity, wide erudition, and deep penetration into the heart of phenomena, which were amazing for a young man at the age when other students had usually just graduated from a university, Frumkin carried out a complete analysis of the electrocapillarity theory and derived general relationships between the surface tension, surface charge, and potential, which are valid for solutions of any composition and include the well-known Lippman equation as a special case. In this work, he also obtained experimental confirmation of the derived relationships.
In this work, he had already found and explained the result that completely changed the views on the nature of electrode potentials, the concepts that had ruled European science since the works of Nernst - the dependence of the potential of the electrocapillary curve maximum on the solution composition. This led later [5] to formulating the concept of the zero charge point as the most important characteristic of metals and the solution of Volta's problem, which had challenged scientists for almost a century and a half. The role of zero charge potentials in electrochemistry, their relation to the adsorption of ions and organic substances, their dependence on electrolyte nature, and their influence on electrochemical kinetics were the focus of Frumkin's attention throughout his long scientific career. His last major work, to which he devoted several years, was a monograph entitled "Potentials of Zero Charge" [6], published posthumously.
Studies of the adsorption effect of organic substances on the electrocapillary curve of a mercury electrode led Frumkin to experimentally check the Gibbs adsorption equation [7] and to the discovery of the famous isotherm that became known as the Frumkin isotherm [8, 9]. While in the Langmuir model it was assumed that all the surface sites are identical in their properties, and the adsorbed particles do not interact with each other, Frumkin showed that such interaction can be sufficiently strong and can manifest itself both as interparticle attraction and their mutual repulsion. The Frumkin isotherm combined with the model of two parallel capacitors, also put forward by him, has played an important role in the study of the adsorption processes on electrodes. Of great importance also were his studies on the adsorption drop of the potential across the solution/air interface, specifically across the boundary of organic solutions with air [10].
In 1926, Frumkin began wide research into ionic and atomic adsorption on adsorbents with highly developed surfaces - on platinum black and activated carbon. When studying these complex systems, he singled out as the key problem the interrelation between the adsorption of hydrogen and oxygen atoms and the adsorption of solution ions [11, 12]. Methods of charging and adsorption curves were developed for studying platinized platinum and other electrodes with highly developed surfaces [13]. The obtained hydrogen adsorption isotherms on platinum substantially differed both from the Langmuir isotherm and the Frumkin isotherm. It was M.I. Temkin, prompted by Frumkin, who developed the theory of this phenomenon and introduced the concept of particle adsorption on a uniformly heterogeneous surface. The Temkin logarithmic isotherm derived for solving purely electrochemical problems later found very wide application in the adsorption theory and heterogeneous catalysis.
At the beginning of the 1960s, Frumkin turned again to the problem of the thermodynamics of surface phenomena on electrodes at the simultaneous adsorption of hydrogen (or oxygen) atoms and solution ions [14, 15]. It was shown that an electrocapillary curve can be transformed into an electrocapillary surface in a space of three of more dimensions. The development of the thermodynamic theory of reversible electrodes led to the more precise formulation of one of the fundamental problems of electrochemistry - the concept of the electrode charge. It was proposed to distinguish between the concepts of the total charge (a thermodynamical quantity that enters into the Lippman equation) and the free charge (which can be determined only within the framework of concrete double-layer models) [16].
In the works of Frumkin and his school, for the first time, correct values were obtained for the capacitance of the electrical double layer by using a.c. measurements [17]. It was shown that, when microquantities of organic substances that adsorb on the electrode are found in the electrolyte, underestimated differential capacitance values are obtained, and this was the reason for the failure of numerous attempts to use this method. It was after this work that solution purity became a factor of primary importance in electrochemical investigations - the foundation was laid for the electrochemical experiments of high standards inherent in Frumkin's school. In [17], the characteristic adsorption-desorption peaks of organic substances were also obtained for the first time in the dependences of the differential capacitance on the potential. Subsequently, the theory of these phenomena was developed.
The a.c. method of differential capacitance measurements was first used by Frumkin for determining potentials of zero-charge in diluted solutions that exhibit capacitance vs. potential curves with a clearly pronounced deep minimum [18].
A.N. Frumkin turned to electrochemical kinetic studies in 1932 [19], soon after T. Erdey-Gruz and M. Volmer had formulated their theory of the slow discharge. In this small (about 2 pages) work, he established that the dependence of the hydrogen overpotential on the current density (i.e., the empirical Tafel equation and the theoretical conclusion of Erdey-Gruz and Volmer) as well as the relationship between the homogeneous catalytic activity and the affinity of weak acids and bases (the Bronsted relatioship) have a common (probably, a fundamental) basis. The work [19], in fact, initiated a phenomenological approach to the description of the charge-transfer elementary act and also gave impetus to J. Horiuti and M. Polanyi who built the first molecular model of this process.
Using the method of impedance measurements on a platinum hydrogen electrode, A.N. Frumkin, B.V. Ershler, and P.I. Dolin found for the first time a direct experimental proof of the assumption that the electron transfer stage can be slow [20].
Paper [21] is undeniably the most significant work of Frumkin in the field of electrochemical kinetics. In this paper, the author substantiated for the first time the necessity of taking into account the effect of the double-layer structure on the electrode kinetics. The concepts formulated on the role of the y₁ potential in the charge transfer stage were later called the "Frumkin correction" and made it possible to explain the data concerning the effect of foreign electrolyte additives on the hydrogen evolution rate at mercury, which did not fall into the framework of the Erdey-Gruz-Volmer model.
Soon after this, Frumkin noted that, although it is essential to take into account the double layer structure effect on the hydrogen evolution kinetics, the most significant effects should be expected in the cathodic reduction of anions, because in this case, the charge transfer proceeds from a negatively charged electrode to a like-charged ion [22]. The first experimental confirmation of this prediction was obtained only 13 years later. Subsequently, anion electroreduction kinetics was thoroughly studied by scientists of Frumkin's school.
Frumkin's studies made a substantial contribution to the corrosion theory as well. In an appendix to the above-mentioned work [19], Frumkin analyzed the effect of the sodium amalgam concentration on the rate of its destruction by water and came to the conclusion that even on a metal with a physically and chemically uniform surface, the conjugated processes of the anodic dissolution of metals and the cathodic evolution of hydrogen can simultaneously take place at the same potential. It was exactly this idea that K. Wagner and W. Traud turned into a principle of establishing steady-state (mixed) potentials - the main principle of the modern corrosion theory. Some time later, the electrochemical theory of corrosion was also confirmed experimentally for solid metals [23].
Dealing with mercury electrodes, Frumkin came up against the well-known difficulties associated with the so-called polarographic maxima. The detailed study of these phenomena led to the creation of the theory of the polarographic maxima of the Ist kind [24, 25], the II kind [26], and the III kind [27].
Speaking of Frumkin's works in the field of macrokinetics, one should also mention the development of the theory and practice of the rotating ring-disk electrode [28], and Frumkin's contribution to the theory of processes in the systems with distributed parameters [29].
The most significant event, which had a great effect on the development of electrochemical kinetics and modern electrochemistry as a whole, was the appearance in 1952 of his book "Kinetics of Electrode Processes" [30]. It was the first book ever on electrochemical kinetics, whose appearance marked the emergence of electrochemical kinetics as an independent scientific branch. For almost 10 years, until the appearance of Vetter's book, the "Kinetics of Electrode Processes" remained the only book in the world on the subject.
We have not yet mentioned Frumkin's studies on the practical application of electrochemistry. It is well known that his activity had a considerable effect on the development of new chemical power sources, including the problem of fuel cells, which was posed by him in the Soviet Union, on the development of chemotronics, the progress in the studies on the organic semiconductors, the works on radiation chemistry, etc.
To Frumkin's pen also belong quite a number of reviews as well as articles for popular publications (the newspapers Izvestiya, Vechernyaya Moskva, Pravda, Sovetskaya Kul'tura, etc., and also the journals Priroda, Nauka i Zhizn', Khimiya i Zhizn', Tekhnika Molodezhi, etc.).
Mention must be made of the special role played by A.N. Frumkin in the electrochemical community, in the establishment and development of scientific East-West contacts. He always followed the principle that the achievements of Soviet scientists should be brought to attention of the world scientific community as quickly and fully as possible. He ably combined this principle with his firm position in defending Soviet scientific priorities. Probably that is why to this day the school created by A.N. Frumkin is better known in the West than any other Russian electrochemical school.
Despite extreme hardships, the Frumkin school maintains a high level of studies in traditional Frumkin fields and also has a sufficiently strong potential for intergrating into new directions of modern electrochemistry. The publications of Russian authors in the jubilee issues of Elektrokhimiya provide convincing proof of the justice of this thesis.

REFERENCES

1. Frumkin, A.N., Electrocapillary Phenomena and Electrode Potentials, Dissertation, Odessa, 1919.
2. Frumkin, A., On the Theory of Electrocapillarity, I and II, Philos. Mag., 1920, vol. 40, no. 237, pp. 363, 375.
3. Frumkin, A., On the Theory of Electrocapillarity, I and II, Z Phys. Chem., 1923, vol. 103, no. 1/2, pp. 43, 55.
4. Frumkin, A.N., Electrocapillary Phenomena and Electrode Potentials; Abstract, Usp. Fiz. Nauk, 1923, vol. 3, p. 286.
5. Frumkin, A. and Gorodetzkaja, A., Electrocapillarity Phenomena on Amalgams. I. Thallium Amalgam, Z Phys. Chem., 1928, vol. 136, p. 451.
6. Frumkin, A.N., Potentsialy Nulevogo Zaryada (Potentials of Zero Charge), Moscow: Nauka, 1979.
7. Frumkin, A., On a Simple Method of Testing the Gibbs Concepts, Z Phys. Chem., 1925, vol. 116, p. 498.
8. Frumkin, A., Electrocapillary Curve of Higher Aliphatic Acids and the State Equation of the Surface Layer, Z Phys. Chem., 1925, vol. 116, p. 466.
9. Frumkin, A., The Influence of the Electric Field on the Adsorption of Neutral Molecules, Z Phys., 1926, vol. 35, p. 792.
10. Frumkin, A.N., The Surface Layer Structure. Part II. Potential Difference on the Interface between Air and Solutions of Aliphatic-Series Compounds, Sbornik Rabot po Chistoi i Prikladnoi Khimii (Collection of Articles on Pure and Applied Chemistry), Bakh, A.N., Ed., Moscow: NTO VSNKh, 1924, p. 3 (Trudy Khim. Inst. im. L.Ya. Karpova, no. 3).
11. Frumkin, A. and Obrutschewa, A., Adsorption of Electrolytes on Platinum Black, Z Anorg. Allg. Chem., 1926, vol. 158, p. 84.
12. Frumkin, A. and Donde,A., Adsoption of Electrolytes on Platinum Black and Carbon, Ber. Dt. Chem. Ges. A, 1927, vol. 2, p. 1816.
13. Frumkin, A.N. and Shlygin, A.I., On Platinum Electrode, Dokl Akad. Nauk SSSR, 1934, vol. 2, p. 173.
14. Frumkin, A.N., Dependence of the Hydrogen Electrode Potential on the Solution pH under Isoelectric Conditions, Elektrokhimiya, 1966, vol. 2, p. 387.
15. Frumkin, A., Petry, O., and Marvet, R., The Dependence of the Double Layer Charge on the Platinum Hydrogen Electrode Surface upon the Potential, J. Electroanal. Chem., 1966, vol. 12, p. 504.
16. Frumkin, A., Petry, O., and Damaskin, B., The Notion of the Electrode Charge and the Lippman Equation, J. Electroanal. Chem., 1970, vol. 27, p. 81.
17. Proskurnin, M. and Frumkin, A., A New Determination of the Capacity of the Electrical Double Layer, Trans. Faraday Soc., 1935, vol. 31, p. 110.
18. Vorsina, M.A. and Frumkin, A.N., Double Layer Capacitance of a Mercury Electrode in Dilute Solutions of Hydrochloric Acid and Potassium Chloride, Dokl. Akad. Nauk SSSR, 1939, vol. 24, p. 918.
19. Frumkin, A., Comments to the Theory of Hydrogen Overpotential, Z Phys. Chem., 1932, vol. 160, p. 116.
20. Dolin, P.I. and Ershler, B.V., Zh. Fiz. Khim., 1940, vol. 14, p. 886; Dolin, P.I., Ershler, B.V., and Frumkin, A.N., Comparison of the H+ Ion Discharge Rate with the Rate of the Overall Process of Hydrogen Evolution on Pt. II, Zh. Fiz. Khim., 1940, vol. 14, p. 907.
21. Frumkin, A., Hydrogen Overpotential and the Double Layer Structure, Z. Phys. Chem., 1933, vol. 164, p. 121.
22. Frumkin, A., Couche Double. Electrocapillarite. Surten-sion., Paris: Herman et Cie, 1936 (Actual Sci. et Industr., no. 373).
23. Frumkin, A. and Kolotyrkin, J., Hydrogen Overpotential and Dissolution of Metals. I. Dissolution of Lead in Acids, Acta Physicochim. URSS, 1941, vol. 14, p. 469.
24. Frumkin, A. and Bruns, B., On the Maxima of Polarization Curves of a Mercury Cathode, Acta Physicochim. URSS, 1934, vol. l,p.232.
25. Frumkin, A. and Levich, B., The Motion of Solid and Liquid Metallic Bodies in Solutions of Electrolytes. I, Acta Physicochim. URSS, 1945, vol. 20, p. 769.
26. Frumkin, A. and Levich, B., The Motion of Solid and Liquid Metallic Bodies in Solutions of Electrolytes. II, Acta Physicochim. URSS, 1946, vol. 21, p. 193.
27. Frumkin, A.N., Stenina, E.V., and Fedorovich, N.V., Polarographic Maxima of the Third Kind. I, Elektrokhimiya, 1970, vol. 6, p. 1572.
28. Frumkin, A.N. and Nekrasov, L.N., On the Ring-Disk Electrode, Dokl Akad. Nauk SSSR, 1959, vol. 126, p. 115.
29. Frumkin, A.N., Distribution of the Corrosion Process Along the Tube Length, Zh. Fiz. Khim., 1949, vol. 23, p. 1477.
30. Frumkin, A.N., Bagotzky, V.S., Iofa, Z.A., and Kabanov, B.N., Kinetika Elektrodnykh Protsessov (Kinetics of Electrode Processes), Moscow: Izd. Mosk. Univ., 1952.

From: Ya. M. Kolotyrkin, O. A. Petrii, and A. M. Skundin,
Russ. J. Electrochem., 1995, v.31, p.709-712

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