Solid oxide fuel cell devices

Nagata A and Okayama H. Characterization of solid oxide fuel cell device having a three-layer film structure grown by RF magnetron sputtering. Vacuum 2002 66 523-529. 

O.K. Davtyan of the Soviet Union did many experiments to increase the conductivity and mechanical strength of the electrolyte in the 1940s. Many of the designs did not yield the desired results, but Davtyan s and Baur s work contributed to the necessary preliminary research for today s current molten carbonate and solid oxide fuel cell devices [11,13, 35]. 

The tape-casting method makes possible the fabrication of films in the region of several hundred micrometers thick. The mechanical strength allows the use of such a solid electrolyte as the structural element for devices such as the high-temperature solid oxide fuel cell in which zirconia-based solid electrolytes are employed both as electrolyte and as mechanical separator of the electrodes. 

Oxide ion conductors have found widespread apphcations in our modem society. The devices based on oxide ion conductors include oxygen sensors, solid oxide fuel cells (SOFCs), and oxygen pump. 

A solid oxide fuel cell is an electrochemical device which converts the Gibbs free enthalpy of the combustion reaction of a fuel and an oxidant gas (air) as far as possible directly into electricity. Hydrogen and oxygen are used to illustrate the simplest case. This allows the calculation of the reversible work for the reversible reaction. Heat must be transferred reversibly as well to the surrounding environment in this instance. 

Solid oxide fuel cell — Solid oxide fuel cell (SOFC) is a device that converts the energy of combustion reactions (e.g., H2 + I/2O2, CO + I/2O2, CH4 + 2O2) into electrical energy. It is therefore called a fuel cell. It comprises two -> porous electrodes that sandwich -> solid... 

Refs. [i] http /lwww.seca.doe.gov [ii] http //www.spice.or.jp/ fisher/ sofc.html descript [iii] http //www.pg.siemens.com/en/fuelcells/sofc/ tubular/index.cfm [iv] Weissbart J, Ruka R (1962) J Electrochem Soc 109 723 [v] Park S, Vohs JM, Gorte RJ (2000) Nature 404 265 [vi] Liou J, Liou P, Sheu T (1999) Physical properties and crystal chemistry of bismuth oxide solid solution. In Processing and characterization of electrochemical materials and devices. Proc Symp Ceram Trans 109, Indianapolis, pp 3-10 [vii] Singhal SC (2000) MRS Bull 25 16 [viii] Matsuzaki Y, Yasuda I (2001) J Electrochem Soc 148 A126 [ix] Ralph JM, Kilner JA, Steele BCH (1999) Improving Gd-doped ceria electrolytes for low temperature solid oxide fuel cells. In New Materials for batteries and fuel cells. Proc Symp San Francisco, pp 309-314... 

PEVD has been applied to deposit auxiliary phases (Na COj, NaNOj and Na SO ) for solid potenfiometric gaseous oxide (CO, NO, and SO ) sensors, as well as a yttria stabilized zirconia (YSZ) ceramic phase to form composite anodes for solid oxide fuel cells. In both cases, the theoretically ideal interfacial microstructures were realized. The performances of these solid state ionic devices improved significantly. Eurthermore, in order to set the foundation for future PEVD applications, a well-defined PEVD system has been studied both thermodynamically and kinetically, indicating that PEVD shows promise for a wide range of technological applications. 

The present availabihty of numerous types of solid electrolytes permits transport control of various kinds of mobile ionic species through those solid electrolytes in solid electrochemical cells, and permits electrochemical reactions to be carried out with the surrounding vapor phase to form products of interest. This interfacing of modem vapor deposition technology and solid state ionic technology has led to the recent development of polarized electrochemical vapor deposition (PEVD). PEVD has been applied to fabricate two types of solid state ionic devices, i.e., solid state potenfiometric sensors and solid oxide fuel cells. Investigations show that PEVD is the most suitable technique to improve the solid electrolyte/electrode contact and subsequently, the performance of these solid state ionic devices. 

Solid oxide fuel cells (SOFCs) are solid-state energy conversion devices with the potential advantages of high efficiency, silent operation and low emissions. However, the high operating temperature (1000°C) of SOFCs... 

Using fossil fuels in solid oxide fuel cells, it is possible in cars to reform the fuels to hydrogen within the device. CO2 will be a side product, unlikely to be collectable as in stationary installations. What are the implications for greenhouse gas emissions For natural gas as fuels, what is the global gas re-... 

The low ionic resistivities of these materials (reported to be under 10 Q cm at 1000°C in some compositions) make them very attractive candidates for use in electrochemical devices such as the solid oxide fuel cell. Their proton conductivity is highly dependent on the partial pressure of water in the atmosphere. Whether these materials exhibit longterm stability in highly oxidizing and/or highly reducing atmospheres remains to be seen. Many of the preparation techniques discussed for the oxygen ion conductors should be applicable to this relatively new class of ionic conductors. 

Sprayed Electrodes for Solid Oxide Fuel Cells (SOFCs) Sprayed Alternating Layers fer Thermeelectric Devices... 

Development of planar solid oxide fuel cells (SOFCs) and other electrochemical devices, such as oxygen generators and sensors, makes it necessary to elaborate sealant materials for hermetization in high-temperature zone. The sealants should satisfy numerous requirements, including chemical stability, good adhesion and thermal expansion. 

Zirconia (Zr02) stabilized in its high temperature, cubic form by addition of 8 to 12 mol.% yttria or scandia is currently the materials of choice in devices utilizing a solid-state oxide ion conducting electrolyte, eg oxygen sensors, oxygen pumps and solid oxide fuel cells (SOFCs), because of its good oxide ion conductivity and redox resistance [1-4]. Improvements in conductivity, however, are necessary to enhance theirs performance and efficiency. 

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