Activation energy, solid electrolytes

Solid electrolytes are frequently used in studies of solid compounds and solid solutions. The establishment of cell equilibrium ideally requires that the electrolyte is a pure ionic conductor of only one particular type of cation or anion. If such an ideal electrolyte is available, the activity of that species can be determined and the Gibbs energy of formation of a compound may, if an appropriate cell is constructed, be derived. A simple example is a cell for the determination of the Gibbs energy of formation of NiO ... 

The activation energy represents the ease of ion hopping, as already indicated above and shown in Fig. 2.5. It is related directly to the crystal structure and in particular, to the openness of the conduction pathways. Most ionic solids have densely packed crystal structures with narrow bottlenecks and without obvious well-defined conduction pathways. Consequently, the activation energies for ion hopping are large, usually 1 eV ( 96 kJ mole ) or greater and conductivity values are low. In solid electrolytes, by contrast, open conduction pathways exist and activation energies may be much lower, as low as 0.03 eV in Agl, 0.15 eV in /S-alumina and 0.90 eV in yttria-stabilised zirconia. 

In activated ion hopping processes such as occur in solid electrolytes, there is an inverse correlation between the magnitude of the activation energy and the frequency of successful ion hops this leads us to the concept of ion hopping rates. 

Solid electrolyte Mobile ion Conductivity/S cm temperature/°C Activation energy/e-y Reference... 

Activation energy for 0 conduction in solid electrolyte, J/mole... 

Research in the area of fast-ion transport in solids has been extremely active in recent years, partly because of the many potential technological applications of solid electrolytes. These applications include high-energy-density... 

Surfaces of crystals and the grain boundaries may have disordered regions where proton transport is facilitated. Adsorbed water or electrolyte solution trapped between the grains will also increase the conductivity and give rise to false conclusions concerning the solid-state nature of conductivity. Surface or liquidlike conductivity has a low activation energy ( a 0.1-0.4eV), approaching the of aqueous acidic... 

The exchange current and cathodic transfer coefficient for the PEVD system can be extracted from standard Tafel plots (Figure 40) as described in detail previously, and provide a measure of the nonpolarizability of the solid electrolyte/electrode interface. The values of Ig and at various temperatures are shown in Table 3. The activation energy of the exchange current can then be obtained from an Arrhenius... 

Figure 4. The activation energy of ferrocenium-ferrocene (Cp2Pe+/°) self-exchange in acetone (e = 20.70) as the function of electrolyte concentration, (a and ) - experimental values for tetraethylammoniym perchlorate and tetraethylammoniym hexafluorophosphate correspondingly [42], (solid and dashed line)-theoretical prediction from the AMS A theory with parameters Rd = Rb. = L = 8 A, Ri = 6 A, and ft, = 8 A, respectively [41],...

This is because the apparent activation energies for the interfacial processes are, in general, higher than those for oxygen ionic transport in solid electrolytes (Yamamoto, 2000). The reduction of the working temperature results in a lower oxygen vacancy concentration with concomitant increase of the role of ionic conductivity of electrode material. 

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