March 2004 Low-Temperature Fabrication of Oxide Composites for Solid-Oxide Fuel Cells 1673K 1523K 1373K 1073K 20(deg.) Fig 10. XRD patterns of the LSM-YSZ composite, prepared by impregnation, as a function of sintering temperature((+)LSM (A)La2Zr, O and ()YSZ bases) that reasonable electronic properties could be obtained with very Regarding composition, the work in this article demonstrates low processing temperatures LSC below 1073 K. This temperature is low enough that solid- state reactions should not present problems, Because this temper- IV. Discussion ature is similar to the operating temperature of an SOFC. it may Recent interest in decreasing the operating temperature of not be necessary to have a separate sintering step to form the SOFCs has led to renewed investigations into alternative cathode composite. Furthermore, the LSM and LSC phases are formed materials. For example, Sr-doped LaFeO,(LSF) and Sr-doped below 1073 K without the use of special precursors to promote a Coo, ( LSCo) exhibit superior performance as SOFC cathodes mixing of the metal cations that make up the perovskite struc ompared with LSM. -However, because these materials reac ures: the salts used in this study have been chosen simply for with YSZ at temperatures lower than that necessary for synthesis their solubility and price. Finally, it is likely that the doped LaFeO3 of the cell. it is usually necessary to avoid contact between YSZ and LacoO, phases can be formed by similar procedures nd either LSF or LSCo by incorporating an additional material in Regarding microstructure, the synthesis of the second oxide the cathode as a barrier. Even without changing the material, phase within the preexisting YSZ matrix has several potential the performance of LSM-YSZ composites can be significantl dvantages. First. various sintering temperatures can be used in the enhanced by tailoring the microstructure. The formation of oxide preparation of the two oxide phases. With YSZ, high temperatures composites by impregnation of the components of one oxide into are advantageous for preparing an interconnected network in a porous matrix of the second oxide presents interesting opportu which ions can pass freely from the electrolyte to the YSZ within nities for the optimization of composition and microstructure in the electrode. Obviously, this porous structure can be forme oxide composites and clearly deserves additional investigation along with the dense electrolyte through the use of bilayers, so that very good connectivity can be established between the electrolyte and electrode layers. Second, a wide range of pore sizes and porosities can be established in the YSZ through the use of various pore formers and YSZ particle sizes.22. 5.6 Therefore, it is elatively easy to control the microstructure of the YSZ phase Our results demonstrate that the materials made by impregna ion cannot be modeled as random distributions of the oxide phases. Because the second phase tends to coat the walls of the YSZ matrix, high conductivities can be obtained at low volume fractions of the conductive oxide. Again, for applications in which it is necessary to limit the amount of conductive oxide that is used this property can be advantageous Finally, the LSC-YSZ composite results demonstrate that it ay be possible to form novel, composite oxides for anodes as well as cathodes Ceramic anodes show great promise for SOFCs hydrocarbons to syngas; 4-2737uy, without first reforming those hat convert hydrocarbons dire however these oxides are often LSM(vol%) used in their pure form on electrolyte-supported cells. By impreg Fig. Il. Electrical conductivities at 973 K for LSM-YSZ composites a nating conducting oxides into a porous matrix, it should be a function of co oJ'pregnation followed e s prepared from the possible to make anode-supported cells with thin electrolytes,with a are U)mixed powders ar sintering to()1523 enhanced three-phase boundaries caused by good connection or(●)1073K between the electrolyte and electrode phases