Yttrium electrolyte

Another application is in tire oxidation of vapour mixtures in a chemical vapour transport reaction, the attempt being to coat materials with a tlrin layer of solid electrolyte. For example, a gas phase mixture consisting of the iodides of zirconium and yttrium is oxidized to form a thin layer of ytnia-stabilized zirconia on the surface of an electrode such as one of the lanthanum-snontium doped transition metal perovskites Lai j.Srj.M03 7, which can transmit oxygen as ions and electrons from an isolated volume of oxygen gas. 

Solid oxide fuel cells consist of solid electrolytes held between metallic or oxide elecU odes. The most successful fuel cell utilizing an oxide electrolyte to date employs Zr02 containing a few mole per cent of yttrium oxide, which operates in tire temperature range 1100-1300 K. Other electrolytes based... 

Conceptually elegant, the SOFC nonetheless contains inherently expensive materials, such as an electrolyte made from zirconium dioxide stabilized with yttrium oxide, a strontium-doped lanthanum man-gaiiite cathode, and a nickel-doped stabilized zirconia anode. Moreover, no low-cost fabrication methods have yet been devised. 

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... 

Self-Test 12.12A Calculate the molar concentration of Y1H in a saturated solution of YF3 by using a cell constructed with two yttrium electrodes. The electrolyte in one compartment is 1.0 M Y(NO ),(aq). In the other compartment you have prepared a saturated solution of YF3. The measured cell potential is +0.34 V at 298 K. 

High-temperature solid-oxide fuel cells (SOFCs). The working electrolyte is a solid electrolyte based on zirconium dioxide doped with oxides of yttrium and other metals the working temperatures are 800 to 1000°C. Experimental plants with a power of up to lOOkW have been built with such systems in the United States and Japan. 

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. 

Solid oxide fuel cells use zirconium oxide stabilized with yttrium as an electrolyte and have an OT of 850 to 1000°C. 

Liu J and Barnett SA. Thin yttrium-stabilized zirconia electrolyte solid oxide fuel cells by centrifugal casting. J Am Ceram Soc 2002 85 3096-3098. 

In the electrolytic process, a fused bath of yttrium fluoride and lithium fluoride is heated to nearly 1,700°C and electrolyzed. The electrolysis is done in a graphite crucible using molybdenum cathodes at which yttrium is produced as molten metal. 

Yttrium oxide has become increasingly inportant in the stabilization of Zr02 in the cubic phase. This Zr02 is used as a high temperature material. Because at hi tanperatures it becomes conductive, the Y20-3-stabilized Zr02 serves also as an electrode, for exairple in" tne high tenperature electrolysis of water, where in addition yttrium-lanthanum oxide serves as the solid electrolyte. has a similar function as an... 

Oxygen sensors, in low volume use as part of a closed loop emission control system for automotive applications since 1977, have seen wide-spread use starting with the 1981 model year. At the present time, a partially stabilized zirconia electrolyte using yttrium oxide as the stabilizer appears to be the most common choice for this application. 

Yttrium stabilized zirconia (Zr02-Y203) as an electrolyte for reduction of molecular oxygen at elevated temperatures (400-800°C) has been already discussed in Section 6.23.4. In fact, both the reduction of oxygen and the oxidation of the oxide ion at the Pt/zirconia interface is reversible and the transport of both species in zirconia is so rapid it is possible to construct an electrochemical oxygen pump, which is the heart of the limiting current oxygen sensor described in this chapter (Saji, 1987). The overall electrochemical reaction that takes place at the porous Pt electrode is... 

The fuel cell analyzed in the present section is a disk-shaped anode-supported SOFC, currently produced by H.C. Starck/InDEC B.V As illustrated in Figure 4.1 [1], the anode material is a cermet of nickel oxide doped with yttrium stablilized zir-conia (NiO/8YSZ). The cathode is composed of two layers one made of 8YSZ with strontium-doped LaMnC>3 (8YSZ/LSM) and one of LSM. The electrolyte consists of a dense 8YSZ material. 

A controlled modification of the rate and selectivity of surface reactions on heterogeneous metal or metal oxide catalysts is a well-studied topic. Dopants and metal-support interactions have frequently been applied to improve catalytic performance. Studies on the electric control of catalytic activity, in which reactants were fed over a catalyst interfaced with O2--, Na+-, or H+-conducting solid electrolytes like yttrium-stabilized zirconia (or electronic-ionic conducting supports like Ti02 and Ce02), have led to the discovery of non-Faradaic electrochemical modification of catalytic activity (NEMCA, Stoukides and Vayenas, 1981), in which catalytic activity and selectivity were both found to depend strongly on the electric potential of the catalyst potential, with an increase in catalytic rate exceeding the rate expected on the basis of Faradaic ion flux by up to five orders of... 

For the HTE process, the electrochemical cell consists of a tri-layer ceramic, well known for its brittleness, which limits applied loads. In addition, the relatively low ionic conduction properties of the electrolyte materials (3% yttrium-stabilised zirconia) requires an operating temperature above 700°C to reduce ohmic losses. This creates difficulties for the involved metallic materials, including bipolar plates and seals. 

The Lambda probe consists of a solid-state electrolyte (yttrium-stabilized zirconia) that is covered with porous platinum - electrodes on the inside (1) and outside (2) (see Fig.). 

Sensor. The control of the exhaust composition was essential to maintain the air-to-fuel ratio close to stoichiometric for simultaneous conversion of all three pollutants. This control came about with the invention of the 02 sensor.21,22 The sensor head of this device was installed in the exhaust immediately at the inlet to the catalyst and was able to measure the 02 content instantly and precisely. It generates a voltage consistent with the Nemst equation in which the partial pressure of 02 (P02)exhaust in the exhaust develops a voltage (E) relative to a reference. The exhaust electrode was Pt deposited on a solid oxygen ion conductor of yttrium-stabilized zirconia (Zr02). The reference electrode, also Pt, was deposited on the opposite side of the electrolyte but was physically mounted outside the exhaust and sensed the partial pressure (P02)ref in the atmosphere. E0 is the standard state or thermodynamic voltage. R is the universal gas constant, T the absolute temperature, n the number of electrons transferred in the process, and F the Faraday constant. 

The beginnings of the SOFC are recorded in an early East German University patent (Mobius and Roland, 1968) which shows awareness of many of the variables still being worked upon today. The oxides of lanthanum, zirconium, yttrium, samarium, europium, terbium, ytterbium, cerium and calcium are mentioned as candidate electrolyte materials. The proposed monolithic planar arrangement has, however, been abandoned by many companies, on the example of Allied Signal. One notable exception is a reversion to a circular planar concept by Ceramic Fuel Cells of Australia, UK (Section 4.7). The Rolls-Royce all-ceramic fuel cell (Section 4.3), which is monolithic and has one compliant feature, namely a gap, is a major exception. One modern trend is towards lower SOFC temperatures, with the intermediate-temperature IT/SOFC allowing the use of cell and stack arrangements with some flexibility and manoeuvrability based on new electrolytes, metallic flow plates, electrodes and interconnects. 

Solid Oxide Fuel Cell In SOFCs the electrolyte is a ceramic oxide ion conductor, such as yttrium-doped zirconium oxide. The conductivity of this material is 0.1 S/cm at 1273 K (1832°F) it decreases to 0.01 S/cm 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 mV, the operating temperature of the... 

Among the various electrolytes, yttrium stabilized zirconia (YSZ) has been developed, for use in high-temperature fuel cells and oxygen sensors similarly, various S( S")-alumina materials are in development for sodium sulfur batteries. 

The basic elements of a SOFC are (1) a cathode, typically a rare earth transition metal perovskite oxide, where oxygen from air is reduced to oxide ions, which then migrate through a solid electrolyte (2) into the anode, (3) where they combine electrochemically with to produce water if hydrogen is the fuel or water and carbon dioxide if methane is used. Carbon monoxide may also be used as a fuel. The solid electrolyte is typically a yttrium or calcium stabilized zirconia fast oxide ion conductor. However, in order to achieve acceptable anion mobility, the cell must be operated at about 1000 °C. This requirement is the main drawback to SOFCs. The standard anode is a Nickel-Zirconia cermet. 

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