Electrochemistry phenomenological

Electrochemistry plays an increasingly important role in biology and medicine and the electrochemical treatment of tumors (ECT) is receiving considerable attention as a viable alternative to the more classical tumor treating approaches of surgery and chemotherapy. Dr. A. Vijh, a specialist in this area, describes both the phenomenology and the proposed physicochemical mechanisms of ECT in a comprehensive chapter. 

Electrons and ions are the principal particles that play the main role in electrochemistry. This text, hence, emphasizes the energy level concepts of electrons and ions rather than the phenomenological thermodynamic and kinetic concepts on which most of the classical electrochemistry texts are based. This rationalization of the phenomenological concepts in terms of the physics of semiconductors should enable readers to develop more atomistic and quantitative insights into processes that occur at electrodes. 

Erdey-Gruz and Volmer contribution in 1930 form the basis of phenomenological kinetic electrochemistry. 

Volmer turned his attention to processes at - nonpo-larizable electrodes [iv], and in 1930 followed the famous publication (together with - Erdey-Gruz) on the theory of hydrogen - overpotential [v], which today forms the background of phenomenological kinetics of electrochemistry, and which resulted in the famous - Butler-Volmer equation that describes the dependence of the electrochemical rate constant on applied overpotential. His major work, Kinetics of Phase Formation , was published in 1939 [v]. See also the Volmer reaction (- hydrogen), and the Volmer biography with selected papers [vi]. 

Because of the inadequacies of QED a fundamental theory of electrode processes is still lacking. The working theories are exclusively phenomenological and formulated entirely in terms of ionic distributions in the vicinity of electrode interfaces. An early, incomplete attempt [54] to develop a quantum mechanical theory of electrolysis based on electron tunnelling, is still invoked and extensively misunderstood as the basis of charge-transfer. It is clear from too many superficial statements about the nature of electrons that the symbol e is considered sufficient to summarize their important function. The size, spin and mass of the electron never feature in the dynamics of electrochemistry. 

Several famous equations (Einstein, Stokes-Einstein, Nemst-Einstein, Nernst-Planck) are presented in this chapter. They derive from the heyday of phenomenological physical chemistry, when physical chemists were moving from the predominantly thermodynamic approach current at the end of the nineteenth century to the molecular approach that has characterized electrochemistry in this century. The equations were originated by Stokes and Nernst but the names of Einstein and Planck have been added, presumably because these scientists had examined and discussed the equations first suggested by the other men. 

For example, see (a) P. Delahay, Double Layer and Electrode Kinetics. Interscience, New York, 1965, Ch. 7 A rigorous description of the phenomenology of electrochemical kinetics, (b) J. O M. Bockris, A. K. N. Reddy. Modern Electrochemistry, Vol. 2, Plenum Press, New York, 1970, Ch. 8 An explanative description of fundamental concepts. 

This novel effect has been termed non-Faradaic electrochemical modification of catalytic activity (NEMCA effect [5-15]) or electrochemical promotion [16] or in situ controlled promotion [20]. Its importance in catalysis and electrochemistry has been discussed by Haber [18], Pritchard [16] and Bockris [17], respectively. In addition to the group which first reported this new phenomenon [5-7], the groups of Lambert [12], Haller [10], Sobyanin [8], Comninellis [13], Pacchioni [21] and Stoukides [11] have also made important contributions in this area, which has been reviewed recently [14,15]. In this review the main phenomenological features of NEMCA for oxidation reactions are briefly surveyed and the origin of the effect is discussed in the light of recent kinetic, surface spectroscopic and quantum mechanical investigations. 

R. Wuthrich, E.A. Baranova, H. Bleuler, Ch. Comninellis A phenomenological model for macroscopic deactivation of surface processes. Electrochemistry Communications 6 (2004), pp. 1199-1205. 

Stress corrosion cracking is a complicated subject. Unless that is emphasized at the beginning, then the fine details of phenomenological and mechanistic factors will not be appreciated. In order to gain some understanding of stress corrosion cracking, it is necessary to realize that three different disciplines are at work in any stress corrosion situation. These are physical metallurgy, electrochemistry and fracture mechanics. 

Electrochemistry is one of the oldest defined areas in physical science, and there was a time, less than 50 years ago, when one saw Institute of Electrochemistry and Physical Chemistry in the chemistry buildings of European universities. But after early brilliant developments in electrode processes at the beginning of the twentieth century and in solution chemistry during the 1930s, electrochemistry fell into a period of decline which lasted for several decades. Electrochemical systems were too complex for the theoretical concepts of the quantum theory. They were too little understood at a phenomenological level to allow the ubiquity in application in so many fields to be comprehended. 

These ideas, which come from electrochemistry of aqueous solutions, have been further developed and applied to the processes in molten salts media [24,25]. It was found that the properties of the intermediate film could be represented in terms of the concept of a polyfunctional conductor (PFC), which was invented and described by Velikanov [26]. This phenomenological concept is based on the theory of amorphous [27] and liquid [28-30] semiconductors. Since it is important for our purposes, it will be discussed in more detail below in Chap. 4. Here we should only emphasise a few main features of the object... 

There are two approaches to modeling the SOFC electrochemistry at the mesoscale an elementary kinetics-based model and a modified Butler-Volmer model. In the elementary kinetics-based model, the electrochemical reactions of the SOFC are modeled exactly, whereas in the modified Butler-Volmer model, the phenomenological Butler-Volmer equation is solved based on the local Faradaic current density. 

It must first be pointed out that the idea and phenomenology of electric charge originated in the 18th century work on the physics of electrostatics, well before any of the principal developments of electrochemistry historically associated with the names of Luigi Galvani, Alessandro Volta, Sir Humphry Davy and Michael Faraday. 

Bockris JOM, Khan SUM. Phenomenological electrode kinetics. In Surface electrochemistry a molecular level approach. New York Plenum Press, 1993 211-406. 

Figure 10. Typical impedance spectra, obtained from the fresh (open circle) and the aged cell (open square) at the cell potential of 4.2 V (vs. Li/Li. The inset is the phenomenological equivalent circuit to model the overall process. Solid lines were determined from the CNLS fittings of the impedance spectra to the equivalent circuits. Figure 2 in D.-K. Kang and H.-C. Shin, Investigation on cell impedance for high-power lithium-ion batteries . Journal of Solid State Electrochemistry 11 (2007) 1405-1410, Copyright (2007), with kind permission of Springer Science and Business.

The German chemist Max Vohner rrtade irrrportant contributiorrs in electrochemistry, particularly in electrode kinetics He co-developed the Butler-Volmer eqrration, which formed the basis of phenomenological kinetic electrochemistry, and discovered the migration of adsorbed molecules, known as Volmer diffusion. 

---