Electrode ionic

Iodjn6 Solid Silver electrode Ag-ionic electrode conductor... 

Finally, it should be realized that modem electroanalysis is most fruitfully stimulated by the harmonious combination of ionics, electrodics and electronics (terms first proposed by Bockris), representing knowledge and experience of the phenomena and processes that occur in ionic solutions, at electrodic surfaces and in electronic circuits, respectively. 

Electrodes may be classified into the following two categories as shown in Fig. 4-3 one is the electronic electrode at which the transfer of electrons takes place, and the other is the ionic electrode at which the transfer of ions takes place. The electronic electrode corresponds, for instance, to the case in which the transfer of redox electrons in reduction-oxidation reactions, such as Fe = Fe + e,occurs and the ionic electrode corresponds to the case in which the transfer of ions, such as Fe , , = Fe, occiirs across the electrode interface. Usually, the former is found with insoluble electrodes such as platinum electrodes in aqueous solution containing redox particles and the latter is found with soluble metal electrodes such as iron and nickel. In practice, both electron transfer and ion transfer can take place simultaneously across the electrode interface. 

Fig. 4-3. (a) electronic electrode and (b) ionic electrode OX = oxidant particle RED s reductant particle M = ion transferring across the electrode interface... 

Fig. 4-16. Energy levels of metal ion and electron in an ionic electrode of metal ion transfer 4Cjn i = sublimation energy of solid metal /m" = ionization energy of gaseous metal atoms > >s = outer potential of electrolyte solution E s electrode potential (absolute electrode potential).

The electrode potential can be defined not only by the energy level of electrons (the real potential ofelectrons)butalsoby theener gy/eue/oftons (the real potential of ions) in the electrode. The former maybe called the electronic electrode potenticd and the latter may be called the ionic electrode potential [Sato, 1995]. For instance, the electrode potential of a metal electrode can be defined in terms of the metal ion level (the real potential of metal ions), aM-ai/s/v), in the electrode as... 

For electrodes which have no electron energy levels in the energy range of general interest, such as ionic crystalline sohd electrodes and membrane electrodes, only the concept of ionic electrode potential can be of practical significance. 

Fig, 4-19. Ionic electrode in equilibrium of metal ion transfer M = metal ion to transfer Pm" = electrochemical potential of metal ions. 

Fig. 4-21. Electron energy levels of an ionic electrode of silver-silver chloride in ion transfer equilibrium cfia ) = Fermi level of electron in silver part of electrode snvAfCici-) = equivalent Fermi level to transfer equilibriiun of silver ions and chloride ions in silver-silver chloride electrode.

Gas electrodes may also be regarded as electronic-and-ionic electrodes covered with a gaseous film. The electron transfer occurs between the electrode and the gaseous film (2 + 2 eoii H2( >) and the ion transfer occurs between the... 

In Chapter 4 the physical basis for the electrode potential is presented based on the electron and ion levels in the electrodes, and discussion is made on tiie electronic and ionic electrode potentials. Chapter 5 deals with the structure of... 

J. Vesel and J. Jindra, Ionic electrodes on single crystal basis and with solid... 

We will see that in the steady state of the blocking cells, we can extract partial conductivities, and from the transients chemical diffusion coefficients (and/or interfacial rate constants). Cell 7 combines electronic with ionic electrodes here a steady state does not occur but the cell can be used to titrate the sample, i.e., to precisely tune stoichiometry. Cell 1 is an equilibrium cell which allows the determination of total conductivity, dielectric constant or boundary parameters as a function of state parameters. In contrast to cell 1, cell 2 exhibits a chemical gradient, and can be used to e.g., derive partial conductivities. If these oxygen potentials are made of phase mixtures212 (e.g., AO, A or AB03, B203, A) and if MO is a solid electrolyte, thermodynamic formation data can be extracted for the electrode phases. 

With the initial condition c (t= 0,x) = c °, and the boundary conditions / n = 0 (for an electronic electrode), fam = 0 for an ionic electrode or, dc Idt =0 for a reversible electrode one obtains with the flux equations and the continuity equation the following as solution for the concentration profile ... 

An electrode is called an electronic electrode when the transfer of electrons occurs, while it is called an ionic electrode when the transfer of ions occurs at the electrode interface. Although electrons and ions are in the same category of charged particles, they are different in electrochemical behavior due to a difference in the type of statistics that governs them. Electrons are Fermi particles which obey the Fermi statistics, whereas ions are Boltzmann particles which obey the Boltzmann statistics. 

The second and third terms on the right hands side of Eq. 9.8 remain constant for a given electrode-electrolyte system, and hence the electrode potential is a linear function of the interfacial potential A MIS of the electrode. This definition of the electrode potential holds valid for all electronic and ionic electrodes, whether the electrode reaction is in equilibrium or non-equilibrium. The potential defined by Eq. 9.8 is called the absolute electrode potential. 

In the case of an ionic electrode at which the transfer of ions, such as metal ions shown in Eq. 9.12, is in equilibrium across the electrode interface ... 

The electrode potential of an ionic electrode can also be defined by the ionic level rather than by the electronic level in the electrode. For instance, the electrode potential of a metallic electrode may be given by the real potential Om cm/s/v) of metallic ion in the electrode as shown in Eq. 9.15 ... 

We may call the electrode potential defined by the ionic energy level the ionic electrode potential, and the electrode potential defined by the electronic energy level may be called the electronic electrode potential. In the case in which the electrode has no electronic level in the energy range of our interest such as certain membrane electrodes, it is convenient to describe the system in terms of the ionic electrode potential rather than the electronic electrode potential [Refs. 4 and 5.]. 

Table 9.2 shows the numerical values of the standard equilibrium potentials for a few reactions of ion transfer at ionic electrodes. Electrochemical handbooks provide us with the standard equilibrium potential for a number of ionic transfer reactions. 

Table 9.2. Standard equilibrium potential of ionic electrode reactions PZn is referred to the standard hydrogen electrode potential and e is the equilibrium electron in the ion transfer reactions.

IONICS ELECTRODICS Concerns ions in solution and in Concerns the region between an the liquids arising from melting electronic end an ionic conductor snlida nomonsad of ions. and the transfer of electric charoea ... 

Figure 7.31 reproduces Yokota s classical polarization and depolarization curves for Ag2Te , in which, on the one hand, ionic electrodes (above), and, on the other hand, electronic electrodes (below) have been employed (corresponding to cells E2, 12). The independent results for diffusion coefficients and partial conductivities are consistent [324]. 

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