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Charge across the interface

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... [Pg.1922]

The present Section, which provides an outline of selected relevant topics in electrochemistry, is intended primarily as an introduction to aqueous corrosion for those readers whose basic training has not involved a study of electrochemistry. The scope of electrochemistry is enormous and cannot be treated adequately here, but there are now a number of excellent books on the subject, and it is hoped that this outline will serve to stimulate further study. The topics selected are as follows a) the nature of the electrified interface between the metal and the solution, (b) adsorption, (c) transfer of charge across the interface under equilibrium and non-equilibrium conditions, d) overpotential and the rate of an electrode reaction and (e) the hydrogen evolution reaction and hydrogen absorption by ferrous alloys. For reasons of space a number of important topics, such as the electrochemistry of electrolyte solutions, have been omitted. [Pg.1165]

As mentioned above, the distribution of the various species in the two adjacent phases changes during a potential sweep which induces the transfer of an ion I across the interface when the potential approaches its standard transfer potential. This flux of charges across the interface leads to a measurable current which is recorded as a function of the applied potential. Such curves are called voltammograms and a typical example for the transfer of pilocarpine [229] is shown in Fig. 6, illustrating that cyclic voltammograms produced by reversible ion transfer reactions are similar to those obtained for electron transfer reactions at a metal-electrolyte solution interface. [Pg.740]

Fig. 3.9 Energy diagram of the semiconductor-electrolyte interface under equilibrium, (a) The Fermi level Ep is equal to redox potential energy, Ep, redox (b) The Fermi level, Ep is equal to reference electrode energy, Ereference- (c) Potential disMbution. (d) Charge across the interface. Fig. 3.9 Energy diagram of the semiconductor-electrolyte interface under equilibrium, (a) The Fermi level Ep is equal to redox potential energy, Ep, redox (b) The Fermi level, Ep is equal to reference electrode energy, Ereference- (c) Potential disMbution. (d) Charge across the interface.
When j is the species that is exchanged across the nonpolarizable interface (i.e., the species involved in the charge-transfer reaction leading to the leakage of charge across the interface), it is customary to say that the interface, or the electrode, is reversible with respect to the species j. [Pg.117]

In Section 6.3.3 the polarizability of an interface was discussed. To revise what was said earlier, the ideal polarizable interface is one in which, when the potential on the metal side is forced to move in the positive or negative direction, there is a change of potential across the interpliasial region, but no consequent passage of charge across the interface. [Pg.338]

To take into account all the above-mentioned effects, it is convenient to introduce into formulas (31) and (34) an empirical factor M, called the photocurrent multiplication coefficient. It reflects the fact that a single lightgenerated carrier can, by virtue of secondary reactions, initiate the transition of several elementary charges across the interface. [Pg.282]

In this discussion the mercury-solution interface is assumed to be completely polarizable that is, there is no transfer of charge across the interface. Therefore each of the charged species (including electrons) occurs in only one of the phases. The requirement of complete polarizability means that the surface excess may be divided between that in the aqueous phase (W) and that in the mercury (Hg). In view of Equations (85) and (86), we write... [Pg.346]

Since electrode reactions are heterogeneous chemical processes with transference of charge across the interface, for a net reaction to take place at commensurable rate reactants and products must be transported to and from the electrode surface to sustain a net flux and thus an electrical current across the electrode—electrolyte interface. [Pg.18]

Galvani potential difference — A

electrostatic component of the work term corresponding to the transfer of charge across the - interface between the phases a and f whose - inner electric potentials are (/>" and R, respectively, i.e., the Galvani potential difference is the difference of inner electric potentials of the contacting phases. The electrical potential drop can be measured only between the points which find themselves in the phases of one and the same chem-ical composition [i,ii]. Indeed, in this case p ( = p and... [Pg.534]

The essential idea here is that, because of the slow rate of interband transitions, there is more than one way of transferring charge across the interface. This may be symbolized... [Pg.212]

The phenomenon of flyaway is a result of charge repulsion between hair fibers, which makes hair hard to comb or to keep in place. This problem occurs when hair is combed or brushed, particularly at low humidity. The generation of static charges is due to an unequal transfer of charges across the interface between materials in contact. [Pg.433]

The key feature of electrochemical surface reactions is the transfer of charge across the interface between the electrode and species in the electrolyte phase. This charge may be in the form of electrons as, for example, with the redox couple ... [Pg.143]

Although the first reaction does not pass electric charge across the interface directly, each time it occurs the second reaction must pass two electrons across the interface. Consequently, we can write the rate of reaction (1) in terms of an equivalent current density,... [Pg.882]

Corrosion is an electrochemical process. Therefore, some understanding of the fundamentals of electrochemistry is necessary [11-13]. Electrochemistry is the study of reactions that occur at the interface of an electrode, which is a metallic or semiconducting solid or liquid, and an electrolyte, which is a liquid or solid ionic conductor. These reactions typically involve the transfer of charge across the interface. There are two types of charge transfer reactions. Ion transfer reactions involve the transfer of ions from the electrode to the electrolyte, or vice versa. Electron transfer reactions involve the transfer of charge between ions in the electrolyte (or adsorbed on the surface), and typically occur heterogeneously at an electrode surface. Redox reactions are pure electron transfer reactions that occur at inert electrode surfaces. A more detailed discussion of electrochemical concepts can be found in the other volumes of this encyclopedia. A simplified view of certain aspects relevant to corrosion will be presented in this section. [Pg.5]

The Butler-Volmer equation describes the kinetics for electrochemical reactions that are controlled by the transfer of charge across the interface. It has been derived here in a simpKfied way. For a more complete discussion of charge transfer reactions and of electron tunneling, the reader is referred to the volume of this series dealing with electrode kinetics. [Pg.30]

In order to set the scene for some of the chapters that follow, it is useful to provide a brief overview of some of the terminology and basic concepts needed to understand electroanalytical techniques. Electrochemistry is a broad field, encompassing those processes that involve the passage of charge across the interface between two... [Pg.2]

While following the general pattern of heterogeneous chemical reactions, electrode reactions are additionally characterized by being associated with the transfer of electric charge across the interface between two conductive phases. This is why the energetics, hence, the rate of charge transfer from one phase to the other, depends on the electric potential difference between these phases. Thus, in addition to the variables commonly involved in chemical... [Pg.93]

Any chemical transformation that implies the transfer of charge across the interface between an electronic conductor (the electrode) and an ionic conductor (the electrolyte) is referred to as an electrochemical reaction. An electrochemical reaction can include one or several electrode reactions. For example the reaction (1.3) is an electrochemical reaction each atom of iron that passes into solution implies the exchange of two electrons between the metal and the protons. Two electrode reactions are involved the oxidation of the iron and the reduction of the proton. According to the definition given above, all corrosion reactions that involve metal oxidation are electrochemical reactions. In order to understand and control corrosion phenomena it is essential to study the thermodynamics and kinetics of electrochemical reactions. [Pg.6]

When a d.c. voltage is applied across an electrochemical cell, the response of its electrodes can be considered in terms of two possible modes of idealized behavior. These are illustrated in Fig. 1. The left-side electrode is composed of the parent metal M(s) of an electrolyte for the conduction of a cation species MT ". Because of the presence of M(s) and at the electrode interface, an equilibrium M(s)= M + e is assumed to obtain. If establishment and maintenance of the equilibrium is ideally rapid, then the response of the interface to a nonequilibrium field is to drive the equilibrium predominantly in one of its component directions and result in a basically nonresistive transfer of charge across the interface. This is the well-known behavior of the ideally reversible electrode. [Pg.119]


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