Selective applications solid electrolytes

A solid electrolyte is an ionic conductor and an electronic insulator. Ideally, it conducts only one ionic species. Aside from a few specialty applications in the electronics industry, solid electrolytes are used almost exclusively in electrochemical cells. They are particularly useful where the reactants of the electrochemical cell are either gaseous or liquid however, they may be used as separators where one or both of the reactants are solids. Used as a separator, a solid electrolyte permits selection of two liquid or elastomer electrolytes each of which is matched to only the solid reactant with which it makes contact. 

Both SnOz and ZrOz are important catalysts and catalyst supports. SnOz is widely used in the selective catalytic reduction of NO because of its good hydrothermal stability as well as its fine oxidative selectivity [1,2] and SnOz-based composite oxides are very active catalysts for CH4 deep oxidation [3,4], ZrOz as a catalyst or catalyst support is used in many catalytic processes [5]. Besides their wide applications in catalysis, SnOz and ZrOz are useful materials as sensors, ceramics and solid electrolytes. 

The first volume of this Handbook contains brief reviews dealing with the general methodology of solid-state electrochemistry, with the major groups of solid electrolytes and mixed ionic-electronic conductors, and with selected applications for electrochemical cells. Attention is drawn in particular to the nanostructured solids, superionics, polymer and hybrid materials, insertion electrodes, electroanalysis and sensors. Further applications, and the variety of interfacial processes in solid-state electrochemical cells, will be examined in the second volume. 

Electrochemical gas sensors detect gases based on the electromotive force(EMF) or the current of an electrochemical cell due to the electrochemical reaction of a particular gas. Solid electrolyte which a specific ion can selectively permeate is used as a diaphragm. Potentiometric type gas sensors have been most widely adopted. Among them potentiometric oxygen sensors composed of partial stabilized zirconia have already had practical application and heen extensively used for the feedback control of the air-fuel ratio of automobile engines. The oxygen sensor elements are composed of the following electrochemical cell. 

Electrochemical promotion (EP) denotes electrically controlled modification of heterogeneous catalytic activity and/or selectivity. This recently discovered phenomenon has made a strong impact on modem electrochemistry/ catalysis/ and surface science. Although it manifests itself also using aqueous electrolytes/ the phenomenon has mainly been investigated in gas-phase reactions over metal and metal oxide catalysts. In the latter case, the catalyst, which is an electron conductor, is deposited in the form of a porous thin film on a solid electrolyte support, which is an ion conductor at the temperature of the catalytic reaction. Application of an electric potential on the catalyst/support interface or, which is equivalent, passing an electric current between catalyst and support, causes a concomitant change also in the properties of the adjacent catalyst/gas interface, where the catalytic reaction takes place. This results in an alteration of the catalytic behaviour, controllable with the applied potential or current. 

Thus, a short survey of technologies suitable for gas sensor fabrication shows that we do not have ideal technology and we cannot name the best method of sensing-layer deposition. The selection of the method optimal for each specific engineering application should take into account the properties of the deposited material, the construction of the sensor design, and the possible consequences for the sensor s parameters during the application of the method selected. Will et al. (2000) considered and analyzed current methods and their possibilities for forming thin-fihn solid electrolytes. The results of that comparison are presented in Table 28.9. 

This "teaching paper sets out to survey broadly the application of solid electrolytes and ionic cathodes to battery systems and to highlight recent developments. References to the literature are selective and the paper is by no means a comprehensive review of the subject. 

Combining IL properties with macromolecular architectures opens manifold potential applications. Tailored PILs have been designed for use as solid electrolytes in electrochemical devices such as lithium-ion batteries. By mixing with low-molecular-weight ILs and lithium salts, the ionic conductivity can be drastically increased without a loss in mechanical stability. Apart from ion conducting materials, additional proposed and already tested PIL applications include selective CO2 adsorption, their use as sorbent coatings in chromatography, catalysis, and the fabrication of optoelectronic devices. ... 

PEM fuel cells have emerged as the most common type of fuel cell under development today. As stated above, they also are commonly referred to as proton exchange membrane fuel cells based on the key characteristic of the solid electrolyte membrane to transfer protons from the anode to the cathode. The solid electrolyte avoids problems caused by liquid electrolytes used in other systems, and the temperature range of <100°C enables rapid start-up under low temperature operation, with operation possible down to subfreezing temperatures. The lower temperature also allows a wider range of materials to be used and enables relatively easy stack design in terms of sealing issues and material selection. This type of fuel cell is the most feasible for use under transportation applications. 

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