Ion-conductors

Electrochemical Microsensors. The most successful chemical microsensor in use as of the mid-1990s is the oxygen sensor found in the exhaust system of almost all modem automobiles (see Exhaust control, automotive). It is an electrochemical sensor that uses a soHd electrolyte, often doped Zr02, as an oxygen ion conductor. The sensor exemplifies many of the properties considered desirable for all chemical microsensors. It works in a process-control situation and has very fast (- 100 ms) response time for feedback control. It is relatively inexpensive because it is designed specifically for one task and is mass-produced. It is relatively immune to other chemical species found in exhaust that could act as interferants. It performs in a very hostile environment and is reHable over a long period of time (36). 

Solid Oxide Fuel Cell In SOF(7s the electrolyte is a ceramic oxide ion conductor, such as vttriurn-doped zirconium oxide. The conduetKity of this material is 0.1 S/ern at 1273 K (1832°F) it decreases to 0.01 S/ern at 1073 K (1472°F), and by another order of magnitude at 773 K (932°F). Because the resistive losses need to be kept below about 50 rn, the operating temperature of the... 

We developed a sensor for determination of content of phosphorars in metallurgical melts. In quality of ion conductor used orthophosphate of calcium which pressed in tablets 010 mm. Tablets (mass 1-2 g) annealed at a temperature 400°C during 7-10 h. Tablets melts then in a quartz tube and placed the alloy of iron containing 1 mass % P. Control of sensor lead on Fe - P melts. Information on activities (effective concentration) of phosphorars in Fe - P melts was received. It is set that the isotherm of activity of phosphorars shows negative deviations from the Raouls law. Comparison them with reliable literary inforiuation showed that they agree between itself. Thus, reliable data on activities (effective concentration) of phosphorars in metallic melts it is possible to received by created electrochemical sensor for express determination. 

The silver ions are almost randomly distributed on these sites, thus accounting for their high mobility. Many other fast ion conductors have subsequently been developed on this principle, e.g. 

The lead-acid battery has a peculiarity the electrolyte sulfuric acid not only serves as ion conductor (as charge-transport medium), but it actively participates in the electrochemical reaction ... 

Chemists prefer to use the term electrolyte for the salt itself, in contrast to the above definition of the term. According to their use, the liquid ion-conductor is called an electrolyte solution. 

Figure 3. Schematic representation of the lithium-ion conductor LiAICl4. The A1C14 may be considered as tetrahedral anions, as indicated by green. The lithium ions are located between them.

The structure of the perovskite-type lithium ion conductor Li0 29La0 57Ti03 is represented in Fig. 6. The small gray circles depict the lithium ions, the big gray circles the lanthanum ions. These are randomly distributed over the A sites 14 per-... 

Figure 6. Structure of the perovskite-type lithium-ion conductor Li 2yLa057TiO3. The lithium ions (small, gray) and the lanthanum ions (large, gray) are randomly distributed over the A sites, of which 14 percent are vacancies, enabling the lithium ions to be mobile. Titanium forms TiOh octahedra, as shown in yellow. The unit cell is indicated.

Figure 8. Arrhenius diagram for various fast ion conductors. For each indicated monovalent mobile ion, the given ionic conductors are the fastest ones known (Na Na 1 - / "-Al203 Cu+, CulflRb4I7Cll3 K+, K+-/T-A120, H H3Moi2P04(, -30H2O Ag, Ag Rbls F, La0 95Sr005F295 Li, ...

Quite a large variety of interesting fast lithium-ion solid conductors is now known, as compiled in Fig. 9 and Table 1. In the case of sodium- and potassium-ion conductors only the / / / " -alumina fam-... 

Figure 10. Practically useful solid sodium-and potassium-ion conductors [4, 20).

In spite of the extraordinarily high ionic conductivity of silver- and copper-ion conductors, these materials suffer from their low capacity and energy density. In addition, only a few positive electrode materials have been found until now. 

Some fluorine-ion conductors exhibit high ionic conductivities, even at room temperature [4], which are not equaled by other halide-ion conductors. However, there is a lack of known electrode materials. Further research on this topic is very worthwhile. 

Apart from applications in sensors [21, 22], divalent-ion conductors, e.g., for Mg2+ ions, are of great interest for thin film batteries which may be incorporated into microelectronics as memory backups and into other applications. For these batteries high volumetric specific energy densities rather than high current densities are required, and thin films offer in addition a major decrease in the total ionic resistance. 

In the case of potassium, a large number of very fast ion conductors [4] and very fast insertion/extraction materials, such as the potassium hexacyanoferrates, are... 

The third aspect, the stability range of solid electrolytes, is of special concern for alkaline-ion conductors since only a few compounds show thermodynamic stability with, e.g., elemental lithium. Designing solid electrolytes by considering thermodynamic stability did lead to very interesting compounds and the discovery of promising new solid electrolytes such as the lithium nitride halides [27]. However, since solid-state reactions may proceed very slowly at low temperature, metasta-... 

In practice, for a ternary system, the decomposition voltage of the solid electrolyte may be readily measured with the help of a galvanic cell which makes use of the solid electrolyte under investigation and the adjacent equilibrium phase in the phase diagram as an electrode. A convenient technique is the formation of these phases electrochemically by decomposition of the electrolyte. The sample is polarized between a reversible electrode and an inert electrode such as Pt or Mo in the case of a lithium ion conductor, in the same direction as in polarization experiments. The... 

Acknowledgment. The authors thank S. Scharner for his support in preparing Figs. 1-6, showing the crystal structures of fast ion conductors. 

Since the realization in the early 1980s that poly (ethylene oxide) could serve as a lithium-ion conductor in lithium batteries, there has been continued interest in polymer electrolyte batteries. Conceptually, the electrolyte layer could be made very thin (5im ) and so provide higher energy density. Fauteux et al. [31] have recently reviewed the present state of polymer elec-... 

This cell reaction necessitates a so-dium-ion-conductive electrolyte. At present, the best and most stable sodium ion conductor is / "-alumina. This electrolyte has sufficient high sodium ion conductivity at temperatures of about 300 °C. The ft"-alumina electrolyte is normally designed as a tube closed at one end with a negative... 

In the Na/S system the sulfur can react with sodium yielding various reaction products, i.e. sodium polysulfides with a composition ranging from Na2S to Na2S5. Because of the violent chemical reaction between sodium and sulfur, the two reactants have to be separated by a solid electrolyte which must be a sodium-ion conductor. / " -Alumina is used at present as the electrolyte material because of its high sodium-ion conductivity. 

Reactions involving the catalytic reduction of nitrogen oxides are of major environmental importance for the removal of toxic emissions from both stationary and automotive sources. As shown in this section electrochemical promotion can affect dramatically the performance of Rh, Pd and Pt catalysts (commonly used as exhaust catalysts) interfaced with YSZ, an O2 ion conductor. The main feature is strong electrophilic behaviour, i.e. enhanced rate and N2 selectivity behaviour with decreasing Uwr and , due to enhanced NO dissociation. 

This can be considered to be the case when using alkali ion conductors. But classical promotion by species like O2 or H+ does not appear to be experimentally feasible, due to the experimental difficulty of introducing them under controlled conditions from the gas phase. Also their short lifetime under reaction conditions essentially limits their usefulness only to situations where they can be continuously replenished on the catalyst surface, i.e. only to electrochemical promotion. 

Nasicon solid electrolyte electrochemical promotion with, 440 sodium ion conductor, 440 NEMCA, see electrochemical promotion NEMCA coefficient, 152,319... 

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