Ionic conduction of solid electrolytes

This relationship makes it possible to calculate the maximum ionic conductivity of solid electrolytes. Assuming that the mobile ions are moving with thermal velocity v without resting and oscillating at any lattice site, this results in a jump frequency... 

Another way of looking at high ionic conductivities of solid electrolytes is to consider the activation enthalpy as illustrated in Fig. 8. Generally, the activation enthalpy is strongly correlated with the room-temperature ionic conductivity the higher the room-temperature ionic conductivity, the lower the activation enthalpy. The straight lines in the Arrhenius... 

As the ionic conductivity of solid electrolytes is generally much lower than the electronic conductivity of electrode materials, the ionic conductivity of the solid electrolytes may determine the lowest possible operational temperature of SOFCs. Apart from high ionic conductivity, the following properties are required ... 

Detailed information about the conductivity of solid electrolytes can be found elsewhere.2,3,6 8,10,11 As shown in Fig. 3.1, the temperature dependence of the ionic conductivity o can, in general, be described by the semiempirical equation ... 

For a battery to give a reasonable power output, the ionic conductivity of the electrolyte must be substantial. Historically, this was achieved by the use of liquid electrolytes. However, over the last quarter of a century there has been increasing emphasis on the production of batteries and related devices employing solid electrolytes. These are sturdy and ideal for applications where liquid electrolytes pose problems. The primary technical problem to overcome is that of achieving high ionic conductivity across the solid. 

SOE cells utilize solid ceramic electrolytes (e.g. yttria stabilized zirconia) that are good oxygen ion (0 ) conductors at very high temperatures in the range of 1000°C [8]. The operating temperature is decided by the ionic conductivity of the electrolyte. The feed gas, steam mixed with hydrogen, is passed through the cathode compartment. At the cathode side, the reaction is... 

BIMEVOX — Figure. Oxygen ionic conductivity of solid oxide electrolytes at atmospheric oxygen pressure. See Ref. [ii] for details... 

Of course an appropriate ionic conductivity in the active layer is important as well. Organic solid polymer electrolytes (SPEs) provide only k = 0.1-1 mS/cm, and liquid organic electrolytes k — 1-lOmS/cm. But aqueous electrolytes have much better values in the order of lO-lOOmS/cm. One of the consequences of the low ionic conductivities of organic electrolytes is a minimization of transport length L (cf. Vetter s model [64]), or the capillary gap cell in organic electrosynthesis [4]. 

Pornprasertsuk, R., Ramanarayanan, P., Musgrave, C.B., Prinz, F.B. Predicting ionic conductivity of solid oxide fuel cell electrolyte from first principles. J. Appl. Phys. 2005, 98,103513. 

Uchida, H., Yoshida, M., Watanabe, M. Effect of ionic conductivity of zirconia electrolytes on the polarization behavior of various cathodes in solid oxide fuel cells. J. Electrochem. Soc. 1999,146, 1-7. 

Kang et al. also prepared poly-31-33 [79]. The heterocycle units of poly-31 can form doubly hydrogen bonded homodimer, while the heterocycle units of poly-32 and poly-33 form triply hydrogen bonded heterodimer. In the solid state, these hydrogen bonding motifs would drive the ditopic molecules to form polymeric strucmres, both of which were utilized to increase the energy conversion efficiency of solid state DSSC up to 4.6 and 4.5 %, respectively, at 1 sun condition. Their better performance than the poly-30 electrolyte was attributed to the slower electron recombination rates and the faster ionic conductivity of the electrolytes formed from them. 

From these considerations it can be seen that there is a natural upper limit for the value of the ionic conductivity of solid compounds. This upper limit is between 1 and 10 cm corresponding to a component diffusion coefficient of about 2 to 20 x 10 cm s. These values correspond to those in liquid electrolytes. Good... 

Having discussed in Sections II and III concentration and mobility, which influence the conductivity of solid electrolytes, a compilation of solid ionic conductors will be given in this section. This compilation does not presume to be complete because new solid electrolytes are discovered and developed continuously. In Fig. 4, the conductivities of some of the most important ones are shown as a function of temperaure and reciprocal temperature. The conductivity of liquid sulfuric acid is included for comparison. In the following, several important solid electrolytes will be treated according to the type of mobile ions that cause the ionic conductivity. 

Masuda Y, Seki M, Nakayama M, Wakihara M, Mita H (2(X)6) Study on ionic conductivity of polymer electrolyte plasticized with PEG-aluminate ester for rechargeable lithium ion battery. Solid State Ion 117(9-10) 843-846... 

Zhou, J. and Fedkiw, PS. 2004. Ionic conductivity of composite electrolytes based on oligo(ethylene oxide) and fumed oxides. Solid State Ionics 166 275-293. 

Figure 7.33 Temperature dependence of the ionic conductivity of ceramic electrolytes relevant for application in solid oxide fuel cells. Modified after Haering (2001).

Figure 5.3 Water content of (a) Nafion 117, (b) Flemion F-1.44 and (c) Flemion F-1.8 membranes of various ionic forms. Abbreviations used for alkyl ammonium ions are TMA, TEA, TPrA, TBA for tetramethyl, tetraethyl, tetrapropyl and tetrabutyl ammonium ions, respectively (Reprinted with permission from Asaka, K., Fujiwara, N., Oguro, K. et al. State of water and ionic conductivity of solid polymer electrolyte membranes in relation to polymer actuators, J. Electroanalytical Chem., 505 (1 2), 24-32. Copyright (2001) Elsevier).

Asaka, K., Fujiwara, N., Oguro, K., et al. (2001) State of water and ionic conductivity of solid polymer electrolyte membranes in relation to polymer actuators. J. Electroanal. Chem., 505, 24-32. 

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