Oxygen ion electrolytes

The basic zirconia oxygen sensor design is illustrated in Fig. 13.52, which shows the principle of the zirconia solid oxygen-ion electrolyte. The sensor consists of a closed-end tube of ceramic zirconia ZrO )). The zirconia ceramic... 

Figure 23. Proton conductivities of Y-doped BaZrtV65 and BaCeCV66 in comparison with the ion conductivity of the relevant solid oxygen ion electrolytes. Reprinted from K.D. Kreuer, St. Adams, W. Munch, A. Fuchs, U. Klock, and J. Maier, Solid State Ionics, 155 (2001) 295-306. Copyright 2001 with permission from Elsevier.

The development of electrolytes that exhibit a higher conductivity at low temperature. Three candidates have emerged, namely doped ceria, doped lanthanum gallate, and doped barium zirconate. The first two of these are oxygen ion electrolytes, and the latter is a proton conductor. 

The initial powder of the solid oxygen ion electrolyte of the formula Ceo.8Gdo,20i,9 was synthesized by laser evaporation of a target at the Institute of Electrophysics, Ural Branch RAS [1], The average size of particles was dg = 9.4 nm. More than 95% particles were 3-20 nm in size. The X-ray diffraction analysis confirmed that the powder structure had a cubic... 

Figure 7 Schematic representation of the range of application of various experimental methods to the investigation of the Gibbs energies of dissociation of metal oxides at 1273 K. (1) Direct dissociation (2) equilibria with CO + CO2 or Hg + HgO mixtures (3) e.m.f methods employing solid oxygen-ion electrolytes (4) equilibration method after Komarek and Kubaschewski...

Different from the MBE technique, the PLD is becoming a very generally used growth technique to study the properties of thin films of complex oxides in the field of nanoionics. Most studies have been focused on the oxygen ion electrolyte... 

H. S, Spadl, Solid oxygen-ion electrolyte cell for the dissociation of steam. US Patent 3,635.812, filedjuly 5,1968. 

H. S. Spadl and D. W. White, Internally short-circuited solid oxygen-ion electrolyte cell, USPatent 3,630,979, filed January 2.1969. 

In low temperature fuel ceUs, ie, AEG, PAEC, PEEC, protons or hydroxyl ions are the principal charge carriers in the electrolyte, whereas in the high temperature fuel ceUs, ie, MCEC, SOEC, carbonate and oxide ions ate the charge carriers in the molten carbonate and soHd oxide electrolytes, respectively. Euel ceUs that use zitconia-based soHd oxide electrolytes must operate at about 1000°C because the transport rate of oxygen ions in the soHd oxide is adequate for practical appHcations only at such high temperatures. Another option is to use extremely thin soHd oxide electrolytes to minimize the ohmic losses. 

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). 

In the ceramics field many of the new advanced ceramic oxides have a specially prepared mixture of cations which determines the crystal structure, through the relative sizes of the cations and oxygen ions, and the physical properties through the choice of cations and tlreh oxidation states. These include, for example, solid electrolytes and electrodes for sensors and fuel cells, fenites and garnets for magnetic systems, zirconates and titanates for piezoelectric materials, as well as ceramic superconductors and a number of other substances... 

Unlike the PEM, the ionic conduction occurs for the oxygen ion instead of the hydrogen ion. SOFCs are made of ceramic materials like zirconium (Z = 40) stabilized by yttrium (Z = 39). High-temperature oxygen conductivity is achieved by creating oxygen vacancies in the lattice structure of the electrolyte material. The halfcell reactions in this case are... 

E.C. Subbarao, and H.S. Maiti, Solid electrolytes with oxygen ion conduction, Solid State Ionics 11, 317-338 (1984). 

This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

In general Zr02 oxygen sensors consist of a tube-like solid-state Zr02 electrolyte where the electronic conductivity is based on oxygen ion charge carrier transport. The inner and outer surface of the yttrium-doped and stabilized zirconia tube is covered by porous platinum electrodes. 

The transport numbers of the ions can be determined by using a solid-state electrolyte. The cell voltage across an oxygen-conducting electrolyte subjected to an oxygen pressure gradient is given by the Nemst equation (Section 6.8.3) ... 

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