Redox electrode kinetics

The effects of complexation of redox particles on the redox reaction kinetics are frequently more evident with semiconductor electrodes than with metal electrodes, since the transfer of electrons takes place at the band edge levels rather than at the Fermi level of electrodes. For example, the anodic transfer of... 

To summarize, one can say that the electrochemical performance of CNT electrodes is correlated to the DOS of the CNT electrode with energies close to the redox formal potential of the solution species. The electron transfer and adsorption reactivity of CNT electrodes is remarkably dependent on the density of edge sites/defects that are the more reactive sites for that process, increasing considerably the electron-transfer rate. Additionally, surface oxygen functionalities can exert a big influence on the electrode kinetics. However, not all redox systems respond in the same way to the surface characteristics or can have electrocatalytical activity. This is very dependent on their own redox mechanism. Moreover, the high surface area and the nanometer size are the key factors in the electrochemical performance of the carbon nanotubes. 

In some cases, the kinetics of the redox charge— discharge reactions can proceed almost as quickly and reversibly as EDL charging. Thin film redox electrodes, based on the lithium intercalation/inser-tion principle such as Li4Ti50i2, exhibit high reversibility and fast kinetics. The Ru02 materials deposited on carbon show pseudo-capacitive charge—... 

Tafel s law is the primary law of electrode kinetics, in the sense that Arrhenius law is the basic law of thermal reaction. It applies universally to all processes that are controlled in rate by the interfacial transfer of electrons or by a rate-determining surface reaction that may be coupled to the interfacial electron [Fig. 9.25(a)]. Redox reactions without surface intermediates demonstrate Tafel s law well [Fig. 9.25(b)]. 

S. U. M. Khan, P. Wright, and J. O M. Bockris, Elektrokhimya 13 914 (1977). The first application of time-dependent perturbation theory to quantum electrode kinetics redox reactions. 

It is possible to find a range in which the electrode potential is changed and no steady state net current flows. An electrode is called ideally polarized when no charge flows accross the interface, regardless of the interfacial potential gradient. In real systems, this situation is observed only in a restricted potential range, either because electronic aceptors or donors in the electrolyte (redox systems) are absent or, even in their presence, when the electrode kinetics are far too slow in that potential range. This represents a non-equilibrium situation since the electrochemical potential of electrons is different in both phases. 

As in the homogeneous case, heterogeneous redox electrode reactions involve the chemical reorganization of the coordination spheres of the participating ions, which determines the kinetics of the overall electron transfer process because the electronic transition is a very fast event. 

The effect of upd on outer sphere redox electrode reaction kinetics has been studied [129], but no clear picture emerges because of mass transport limitations for those very fast kinetics. 

Carbon electrodes exhibit a wide range of electron transfer rates for benchmark redox systems, depending on carbon material and surface history. Two examples are shown in Figure 10.2, which compares two carbon surfaces with very different k° for Fe(CN) /4. In some cases, the variations in electrode kinetics have been particularly important to analytical applications. For example, carbon paste and carbon fiber electrodes have been used to monitor neurotransmitters in living animal brains [5,6]. The determination of catechol transmitters in the presence of relatively large amounts of interferents (e.g., ascorbate) de-... 

McCreery and co-workers have investigated the redox reactions for several redox analytes at glassy carbon electrodes, and have summarized the categorization of redox systems according to the effects of surface modification on electrode kinetics [1-3]. These redox analytes in the present study are known to be sensitive or insensitive to the electronic properties, surface microstructure, and surface termination of the carbon electrodes. 

Peiffer, S., O. Klemm, K. Pecher, and R. Hollerung. 1992. Redox measurements in aqueous solutions—A theoretical approach to data interpretation based on electrode kinetics. J. Contam. Hydrol. 10, 1-18. 

He had a productive stay in die Department of Inorganic Chemistry at die University of Oxford carrying out bioelectrochemical work with H. A. O. Hill, hi fact, some think that he introduced electrode kinetics to Hill s department (see the latter s contribution to die redox behavior of proteins at metal/solution interfaces, Chapter 14). 

The possibility of reversible electron transfer within the modified DNA film was tested by carrying out an electrochemical study [85] of the redox couple Fe(lll)/Fe(Il) which has reasonably fast electrode kinetics, and which are dependent on electrode material. The oxidation of Fe(CN)g in 0.4 M K2S04 aqueous solution contacting the DNA-modified glassy carbon electrode showed virtually the same reaction rate as when using the bare glassy carbon electrode, Fig. 3.10, and the results were comparable to... 

July 13,1916 in Berlin, Germany - Dec. 12,1974 in Berlin, Germany) Study of chemistry and physics in Gottingen and Berlin from 1955 professor of physical chemistry at the Free University of Berlin. Cooperation with K. F. Bonhoeffer, - Gerischer, and J. W. Schultze, almost 100 publications (fundamentals of electrode kinetics, overpotential, redox reactions, ion transfer, passivity and corrosion, especially of iron), most important is his book [i] ... 

The same equation had previously been derived by Fronaeus and Ostman [249]. These workers made two further important contributions to the theory. Taking it for granted that the catalysed exchange proceeded by an electron transfer mechanism, they related ucat to the concentrations of Ox and Red by the theory of electrode kinetics. For simple redox couples whose electrochemical reaction orders are unity, this leads to... 

Volumes 26 and 27 are both concerned with reactions occurring at electrodes arising through the passage of current. They provide an introduction to the study of electrode kinetics. The basic ideas and experimental methodology are presented in Volume 26, whilst Volume 27 deals with reactions at particular types of electrode. Thus, Chapter 1 of the present volume deals with redox reactions at metal electrodes, Chapter 2 with semiconducting electrodes and Chapter 3 with reactions at metal oxide electrodes. Both theoretical aspects and experimental results are covered. 

Phelps et al. [180] have studied the influence of seven solvents on the rate constants for three sesquibicyclic hydrazine-radical cation redox systems. The authors have found that the electrode kinetics of these systems depends on the overdamped solvent dynamics, though the activation barrier due to reactant vibrational rearrangements is substantial. 

Note that from an electrode kinetic point of view, the Nemst equation does not give any information as to the actual species that establishes the electrode potential. In the case of a fluoride-containing solution, it is very possible that one of the fluoro-iron(III) complexes rather than the Fe " ion participates in the electron-exchange reaction at the electrode. Complexation usually stabilizes a system against reduction. In the example just considered, because complexation is stronger with Fe(III) than with Fe(II), the tendency for reduction of Fe(III) to Fe(II) is decreased. It is apparent that coordination with a donor group, in general, decreases the redox potential. In the relatively rare instances where the lower oxidation state is favored (e.g., complexation of aqueous iron with phenanthroline), the redox potential is increased as a result of coordination. 

A mathematical model was designed to extract electrode kinetic data for the deposition of Ag+ from solution and the stripping of silver from silver on the electrode from experimental data [159], The results suggested that the TMPD TMPD+ (TMPD = A,A,iV, iV -tetramethyl-p-phenylenediamine) system is more suitable than the Ag Ag+ system as a redox couple for use in reference electrodes for ILs [159],... 

---