Fluoride solid electrolytes

Calcium fluoride, solid electrolyte, 92, 420 Capacitance charging current, 2... 

Since the discovery of the MAg4I5 compounds, very many more solid electrolytes have been reported. Sodium, lithium, copper, proton, oxide and fluoride solid electrolytes are now well known. An important example is sodium /3-alumina which was discussed in Chapter 8. The conductance... 

Fluoride solid electrolytes with fluorite- 7.2.5. Sensors for lean-bum combustion 170... 

Fluoride solid electrolytes with fluorite-type structure... 

For the galvanic cells with fluoride solid electrolytes, electrodes with either gaseous oxygen, oxide mixtures, or fluoride components can be employed. As an example, emf of the cell [116]... 

In Figure 14.3 the conductivity of various fluoride-ion solid electrolytes with tysonite-and fluorite-like structures is presented as a function of the ionic transfer activation energy (Ea). It can be seen that a suitable fluoride solid electrolyte with optimal properties for any applications could be chosen or its targeted search could be carried out. 

Metal-metal fluoride electrodes can be connected by calcium fluoride crystal discs which function as solid electrolytes by fluoride ion transport without any electronic conduction (224) (see Table VII). The... 

Applications to complex fluorides should be possible using the more conducting solid electrolytes now available. 

To reduce the working temperature for solid electrolyte oxygen sensors, fluoride electrolytes have been proposed. Such sensors are composed of the following cell (Sibert, Fouletier and Vilminot, 1983),... 

Similar types of electric double layer may also be formed at the phase boundary between a solid electrolyte and an aqueous electrolyte solution [7]. They are formed because one electrically-charged component of the solid electrolyte is more readily dissolved, for example the fluoride ion in solid LaFs, leading to excess charge in the solid phase, which, as a result of movement of the holes formed, diffuses into the soUd electrolyte. Another possible way a double layer may be formed is by adsorption of electrically-charged components from solution on the phase boundary, or by reactions of such components with some component of the solid electrolyte. For LaFa this could be the reaction of hydroxyl ions with the trivalent lanthanum ion. Characteristically, for the phase boundary between two immiscible electrolyte solutions, where neither solution contains an amphiphilic ion, the electric double layer consists of two diffuse electric double layers, with no compact double layer at the actual phase boundary, in contrast to the metal electrode/ electrolyte solution boundary [4,8, 35] (see fig. 2.1). Then, for the potential... 

Fluoride conducting solid electrolyte -> solid electrolyte... 

For PEMFCs, the solid electrolytes are polymer membranes polymers modified to include ions, usually sulfonic groups. One of the most widely used membranes today is the polymer Nafion , created by the DuPont company. These membranes have aliphatic perfluorinated backbones with ether-linked side chains ending in sulfonate cation exchange groups [6, 7], Nafion is a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether [8] and has a semi-crystalline structure [9], This structure (which resembles Teflon ) gives Nafion long-term stability in oxidative or reductive conditions. The sulfonic groups of the polymers facilitate the transport of protons. The polymers consist of hydrophilic and hydrophobic domains that allow the transport of protons from the anode to the cathode [10, 11],... 

The electrical conductivity of rare-earth oxide fluorides was first investigated for the development of a binary anion conductive solid electrolyte. As a result, it was found that the binary rare-earth oxide fluorides exhibited oxide ion conductivity. Among them, the conductivity of neodymium europium oxide fluoride, Nd2Eu203F6, was reported to be much higher than that of yttria-stabilized zirconia, YSZ, practically used as an oxygen sensor [34]. The electrical conductivities of the binary rare-earth oxide fluorides vary not only with the combination of Ln203 with Ln F3... 

Solid oxides and fluorides satisfy the same conditions, and when used as electrolyte for forming solid state galvanic cells they are referred to as Solid Electrolytes. ... 

The fluorides of calcium, magnesium, lead and a few other metal fluorides, being strongly ionic compounds, have served as solid electrolytes for the purpose of activity measurements. 

What makes the sodium-sulfur cell possible is a remarkable property of a compound called beta-alumina, which has the composition NaAlnOiy. Beta-alumina allows sodium ions to migrate through its structure very easily, but it blocks the passage of polysulfide ions. Therefore, it can function as a semipermeable medium like the membranes used in osmosis (see Section 11.5). Such an ion-conducting solid electrolyte is essential to prevent direct chemical reaction between sulfur and sodium. The lithium-sulfur battery operates on similar principles, and other solid electrolytes such as calcium fluoride, which permits ionic transport of fluoride ion, may find use in cells based on those elements. 

CHA/KAR] Chattopadhyay, G., Karkhanavala, M. D., Chandrasekharaiah, M. S., Standard free energies of formation of metal fluorides by solid electrolytic galvanic cell method. I. Metal difluorides, J. Electrochem. Soc., 122, (1975), 325-327. Cited on page 120. 

Some examples of solid electrolytes are presented in Table 1. In the limited scope of this article, only a few examples of some of the most important (i.e. for potentiai commercial applications) monovaient cation (Li+, Na+, and H+) and anion (oxide and fluoride) conductors wiii be discussed. Amorphous materials, glasses, and polymers are treated in Section 4. However, it shouid be noted thatreiativeiy good ionic conductors are known with many other monovaient ions including K+, Rb+, Cu+, Ti+, and Ag+, divaient ions, for example, Pb +, Ca +, Ba +, Zn +, Sn + in jS -aiumina, and even trivalent cations, and tetravaient cations. In Section 5, the application of some of these materiais in electrochemical devices inciuding batteries, sensors, smart windows and fuels cells are discussed. 

There have been cases wherein a fluoride ion solid electrolyte, in particular CaF2r has been placed between two different metal oxide electrodes and behaved as if it were an oxide solid electrolyte. That is, the emf was found to be equal to that measured previous with caloia- or yttria-stabilized zirconial No very suitable explanation has been offered yet, but I think that these findings have been published or soon will be. But if my conjectures above are correct, the following explanation could be offered. 

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