Applications of solid state galvanic cells

In this section we shall discuss some typical applications of solid state galvanic cells in the study of solid state reactions. The use of these cells to obtain thermodynamic data has already been discussed. For example, the emf of the galvanic cell [24] 

The two following examples will show how galvanic cells can be used in the direct study of diffusion-controlled solid state reactions and phase boundary reactions. These examples are illustrative of a large number of possible applications in the field of solid state reaction kinetics. Emphasis here will be placed upon the principles of the methodology. Further examples can be found in the literature cited above. 

The first example is concerned with the study of tarnishing processes [32]. By applying an external voltage U between the Pt leads of the galvanic cell  

The Ag ions will then be removed through the Agl electrolyte in order to maintain the sulphur activity at its potentiostatically fixed value. At the same time, a corresponding electric current flows through the external circuit. This current can easily be measured. In this way, a very precise determination of the tarnishing rate can be made (1 mA 1 sec corresponds to 1/2 10 moles ). The situation is schematically illustrated in Fig. 9-7. 

The activity gradient (chemical potential gradient) in the NiS can be determined by a measurement of the voltage U. Thus, by combining equations (8-8 a) and (9-20), the average component diffusion coefficient 5 of Ni in NiS can also be calculated. If the activity gradient in the NiS is not too large, then  

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Before discussing further interesting applications of solid state galvanic cells, let us first examine the thermodynamic and electrical processes which occur in these cells in the light of the general transport theory of solids. We shall then be better able to understand the applications. 

These few examples of the application of solid state galvanic cells in the field of solid state reactions can only present a very limited view of this important area of solid state science. The examples were chosen primarily in order to demonstrate the principles according to which solid state research in thermodynamics and kinetics should be conducted with the use of electrochemical tools and methods. Such measurements are only possible because of the existence of suitable solid electrolytes. The most important of these are Zr02(-f CaO) and Th02(+Y2 03) for oxygen, silver halides and Ag4Rbl5 for silver, copper halides for copper, some glasses in which certain ions are dissolved, and p — Al2 03(-hNaO) for sodium. 

Hotzel G. and Weppner W., Application of fast ionic conductors in solid state galvanic cells for gas sensors. Solid State Ionics, 18/19, 1223-1227, 1986. 

Application of the general transport theory to solid state galvanic cells Let us once again consider, as a specific example, the cell Pt/FeO, Fe3 04/Zr02(-1-Me0)/Fe304, Fe203/Pt... 

With the advent of solid electrolytes, such as the stabilized forms of zirconia, the field of solid-state electrochemistry has grown. Galvanic cells utilizing this material as an electrolyte for anionic (0 ) conduction have been used in conjunction with the Nernst equation to measure within various ceramic systems (1) the Gibbs free energy of formation, (2) the activity of, and (3) the kinetics of solid-state reactions. Electrolytic cells can be used to drive reactions in the non-equilibrium direction by the application of an electrical current. The reader is again referred to Schmalzried. ... 

As far as electrochemical cells relevant for applications or electrochemical measurements are concerned, we must distinguish between polarization cells, galvanic cells and open-circuit cells, depending on whether an outer current flows and, if so, in which direction this occurs. Table 1.1 provides examples of the purposes for which such cells may be used. In terms of application, we can distinguish between electrochemical sensors, electrochemical actors and galvanic elements such as batteries and fuel cells. These applications offer a major driving force for dealing with solid-state electrochemistry. 

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