Sites solid oxide fuel cells

Solid mixed ionic-electronic conductors (MIECs) exhibit both ionic and electronic (electron-hole) conductivity. Naturally, in any material there are in principle nonzero electronic and ionic conductivities (a i, a,). It is customary to limit the use of the term MIEC to those materials in which a, and 0, 1 do not differ by more than two orders of magnitude. It is also customary to use the term MIEC if a, and Ogi are not too low (o, a i 10 S/cm). Obviously, there are no strict rules. There are processes where the minority carriers play an important role despite the fact that 0,70 1 exceeds those limits and a, aj,i< 10 S/cm. In MIECs, ion transport normally occurs via interstitial sites or by hopping into a vacant site or a more complex combination based on interstitial and vacant sites, and electronic (electron/hole) conductivity occurs via delocalized states in the conduction/valence band or via localized states by a thermally assisted hopping mechanism. With respect to their properties, MIECs have found wide applications in solid oxide fuel cells, batteries, smart windows, selective membranes, sensors, catalysis, and so on. 

CH4 can be oxidized directly using a solid oxide fuel cell however, high concentrations of CH4 lead to severe coking problems. Only cells containing dilute concentrations of CH4 can be oxidized directly in current SOFCs. In addition, the oxidation of CH4, like that of CO, may not actually occur at active electrochemical sites within an SOFC. Rather, CH4 is probably reformed within the cell through steam reforming. 

Siemens-Westinghouse Power Corporation of Pittsburgh, PA developed and fabricated the first advanced power plant to combine a solid oxide fuel cell and a gas turbine. The microturbine generator was manufactured by Northern Research and Engineering Corporation of Woburn, Mass. The factory acceptance test was completed in April 2000. Southern California Edison will operate the new hybrid plant at The National Fuel Cell Research Center at the University of California-Irvine. A year of testing in a commercial setting will be performed at this site. The system cycle is expected to generate electric power at 55 % efficiency. 

While natural gas reforming is the primary process for the industrial production of H2, the reforming of other gaseous hydrocarbons such as ethane, propane, and n-butane have been explored for the production of H2 for fuel cells.52,97 The reforming of propane and n-butane received particular attention in recent years, because they are the primary constituents of liquefied petroleum gas (LPG), which is available commercially and can be easily transported and stored on-site. LPG could be an attractive fuel for solid oxide fuel cells (SOFCs) and PEMFCs for mobile applications.98 01 The chemistry, thermodynamics, catalysts, kinetics, and reaction mechanism involved in the reforming of C2-C4 hydrocarbons are briefly discussed in this section. 

Lanthanoid manganites, such as LaMnOj, NdMnOj and GdMnOj, are of potential value in solid oxide fuel cell cathodes. However, many of these phase show thermal contraction because of the diminishing Jahn-Teller distortion of the Mtf " cations as the temperature is increased. Such effects tend to rule out these materials for real cell applications, although A- and B-site substitution, as demonstrated for PbTiOj earlier, can ameliorate the problem. 

The formed hydrogen by the water gas shift reaction can be electrochenticaUy oxidized in the fuel cell to water, electrical energy and heat. In solid oxide fuel cells the product water of the electrochemical oxidation of hydrogen is formed oti the anode site. This product water is available for the water gas shift reactimi on the anode side. At 650 to 850 °C reaction kinetics allows the water gas shift reaction without any catalyst or promoter. So carbon monoxide can be converted directly rai the anode side of the SOFC without any extra catalyst for promoting the water gas shift reaction. No extra converter is needed for the water gas shift reaction in SOFC fuel-cell heating appliances, which reduces the system effort. 

Zhao H, Gao F, Li X, Zhang C, Zhao Y (2009) Electrical properties of yttrium doped strontium titanate with A-site deficiency as potential anode materials for solid oxide fuel cells. Solid State Ionics 180 193... 

Oxides form the most common and interesting compounds with perovskite structure. Almost all the metallic natural elements in the periodic table are found in stable perovskites. Also, materials with this structure can be obtained by partial substitution of one or more metallic elements in the A site and/or in the B site. The wide range of properties shown by perovskite-type oxides find applications in catalysis, magnetism, solid oxide fuel cells, and superconductivity. Proper combination or partial substitution of the A site and/or B site atoms introduces abnormal valences or lattice defects, which in turn gives rise to interesting changes in their properties. 

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