Electrode processes kinetics

Q. X. Zha, Introduction of Electrode Process Kinetics, 2nd ed., Science Press, Beijing, 1987. 

The most extensive research results concern the hydride electrolyte system 2 [13-16, 68, 78, 82, 92, 93, 102, 209]. With the help of Raman spectroscopic measurements, the chemical constituents of the electrolyte were determined and the electrode reactions examined with chronoamperometric methods [82]. The catalytic role of hydride and the role of neutral and ionic aluminum components were thus detected. The dependence of the polarization parameters on the electrolyte composition shows a marked maximum from which the bath composition with the highest current distribution can be determined. The influence of the temperature and the composition on the electrode process kinetics was studied by Badawy et al. [13-16]. The results of Eckert et al. [68] show a dependence of the activation energy on the electrolyte composition of the hydride baths. The first electrochemical investigation results with respect to type 3 aluminum alkyl electrolyte were obtained by Kautek et al. [100, 101] and Tabataba-Vakili [186, 187, 133]. 

Figure 2. Working diagram showing how the linear free-energy relationship, common in electrode process kinetics, arises from changes in electrode potential. is a symmetry factor. An extreme case of an anharmonic oscillator energy profile is shown in schematic form (cf. Ref. 25). This representation assumes changes in V affect only the energy of electrons in the initial state at the Fermi level.

Cha Q. An introduction to electrode process kinetics. Beijing Chinese Science Press 2002. 

Organic Electrode Processes. Kinetics, Mechanisms, and Prospects for Commercial Development... 

Fourier Transform Faradic Admittance Measurements On the Use of High-Precision Data for Characterization of Very Rapid Electrode Process Kinetic Parameters, J. Electroanal. Chem. 47, 9. 

This investigation base shown that linear sweep voltammetry is not only an effective method for study the electrode process kinetics, but an express and simple method for determining a number of thermodynamic parameters as well. 

Electrode processes are a class of heterogeneous chemical reaction that involves the transfer of charge across the interface between a solid and an adjacent solution phase, either in equilibrium or under partial or total kinetic control. A simple type of electrode reaction involves electron transfer between an inert metal electrode and an ion or molecule in solution. Oxidation of an electroactive species corresponds to the transfer of electrons from the solution phase to the electrode (anodic), whereas electron transfer in the opposite direction results in the reduction of the species (cathodic). Electron transfer is only possible when the electroactive material is within molecular distances of the electrode surface thus for a simple electrode reaction involving solution species of the fonn... 

Similarly to the response at hydrodynamic electrodes, linear and cyclic potential sweeps for simple electrode reactions will yield steady-state voltammograms with forward and reverse scans retracing one another, provided the scan rate is slow enough to maintain the steady state [28, 35, 36, 37 and 38]. The limiting current will be detemiined by the slowest step in the overall process, but if the kinetics are fast, then the current will be under diffusion control and hence obey the above equation for a disc. The slope of the wave in the absence of IR drop will, once again, depend on the degree of reversibility of the electrode process. 

T. Erdey-Gm2, Kinetics of Electrode Processes, Wiley-Interscience, New York, 1972. 

It is not appropriate here to consider the kinetics of the various electrode reactions, which in the case of the oxygenated NaCl solution will depend upon the potentials of the electrodes, the pH of the solution, activity of chloride ions, etc. The significant points to note are that (a) an anode or cathode can support more than one electrode process and b) the sum of the rates of the partial cathodic reactions must equal the sum of the rates of the partial anodic reactions. Since there are four exchange processes (equations 1.39-1.42) there will be eight partial reactions, but if the reverse reactions are regarded as occurring at an insignificant rate then... 

Although Table 2.16 shows which metal of a couple will be the anode and will thus corrode more rapidly, little information regarding the corrosion current, and hence the corrosion rate, can be obtained from the e.m.f. of the cell. The kinetics of the corrosion reaction will be determined by the rates of the electrode processes and the corrosion rates of the anode of the couple will depend on the rate of reduction of hydrogen ions or dissolved oxygen at the cathode metal (Section 1.4). 

This chapter attempts to give an overview of electrode processes, together with discussion of electron transfer kinetics, mass transport, and the electrode-solution interface. 

The combination of photocurrent measurements with photoinduced microwave conductivity measurements yields, as we have seen [Eqs. (11), (12), and (13)], the interfacial rate constants for minority carrier reactions (kn sr) as well as the surface concentration of photoinduced minority carriers (Aps) (and a series of solid-state parameters of the electrode material). Since light intensity modulation spectroscopy measurements give information on kinetic constants of electrode processes, a combination of this technique with light intensity-modulated microwave measurements should lead to information on kinetic mechanisms, especially very fast ones, which would not be accessible with conventional electrochemical techniques owing to RC restraints. Also, more specific kinetic information may become accessible for example, a distinction between different recombination processes. Potential-modulation MC techniques may, in parallel with potential-modulation electrochemical impedance measurements, provide more detailed information relevant for the interpretation and measurement of interfacial capacitance (see later discus-... 

In the majority of examples in the Uterature, the desired product is obtained by applying a single fixed potential. It is also possible, however, to programme the electrode potential to change in a pre-determined manner, and this is commonly done in studies of reaction intermediates and the kinetics of electrode processes. Thus, cyclic voltammetry (Adams,... 

Kinetics of electrode processes at an electrode in contact with an electrolyte solution )... 

Parry have described procedures to determine the kinetic parameters of totally irreversible electrode processes using various polarographic techniques [6801d]. (Data obtained with these methods are collectively labelled POL.)... 

As this volume attests, a wide range of chemistry occurs at interfacial boundaries. Examples range from biological and medicinal interfacial problems, such as the chemistry of anesthesia, to solar energy conversion and electrode processes in batteries, to industrial-scale separations of metal ores across interfaces, to investigations into self-assembled monolayers and Langmuir-Blodgett films for nanoelectronics and nonlinear optical materials. These problems are based not only on structure and composition of the interface but also on kinetic processes that occur at interfaces. As such, there is considerable motivation to explore chemical dynamics at interfaces. 

Before treating specific faradaic electroanalytical techniques in detail, we shall consider the theory of electrolysis more generally and along two different lines, viz., (a) a pragmatic, quasi-static treatment, based on the establishment of reversible electrode processes, which thermodynamically find expression in the Nernst equation, and (b) a kinetic, more dynamic treatment, starting from passage of a current, so that both reversible and non-reversible processes are taken into account. 

Processes involving transport of a substance and charge in a streaming electrolyte are very important in electrochemistry, particularly in the study of the kinetics of electrode processes and in technology. If no concentration gradient is formed, transport is controlled by migration alone convection... 

Electrochemical kinetics is part of general chemical kinetics and has a similar purpose to determine the mechanism of the electrode process and quantitatively describe its time dependence. Mostly the study involves several stages. Firstly it is necessary to determine the reaction path, i.e. to determine the mechanism of the actual electrode reaction (for more detail, see Section 5.3.1), and the partial steps forming the overall electrode... 

The basic relationships of electrochemical kinetics are identical with those of chemical kinetics. Electrochemical kinetics involves an additional parameter, the electrode potential, on which the rate of the electrode reaction depends. The rate of the electrode process is proportional to the current density at the studied electrode. As it is assumed that electrode reactions are, in general, reversible, i.e. that both the anodic and the opposite cathodic processes occur simultaneously at a given electrode, the current density depends on the rate of the oxidation (anodic) process, ua, and of the reduction (cathodic) process, vc, according to the relationship... 

This is the Tafel equation (5.2.32) or (5.2.36) for the rate of an irreversible electrode reaction in the absence of transport processes. Clearly, transport to and from the electrode has no effect on the rate of the overall process and on the current density. Under these conditions, the current density is termed the kinetic current density as it is controlled by the kinetics of the electrode process alone. 

The classification of methods for studying electrode kinetics is based on the criterion of whether the electrical potential or the current density is controlled. The other variable, which is then a function of time, is determined by the electrode process. Obviously, for a steady-state process, these two quantities are interdependent and further classification is unnecessary. Techniques employing a small periodic perturbation of the system by current or potential oscillations with a small amplitude will be classified separately. 

Sonovoltametric measurement of the rates of electrode processes with fast coupled homogeneous kinetics making macroelectrodes behave like microelectrodes Compton RG, Marken F, Rebbitt TO (1996) Chem Commun 1017-1018... 

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