125 research outputs found
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Characterization of ceria-based SOFCs
Solid Oxide Fuel Cells (SOFCs) operating at low temperatures (500-700 C) offer many advantages over conventional zirconia-based fuel cells operating at higher temperatures. Cathode performance is being improved by using better materials and/or microstructures. Fabrication of thin dense electrolytes is also necessary to achieve high cell performances
The low-temperature partial-oxidation reforming of fuels for transportation fuel cell systems
Argonne`s partial-oxidation reformer (APOR) is a compact, lightweight, rapid-start, and dynamically responsive device to convert liquid fuels to H{sub 2} for use in automotive fuel cells. An APOR catalyst for methanol has been developed and tested; catalysts for other fuels are being evaluated. Simple in design, operation, and control, the APOR can help develop efficient fuel cell propulsion systems
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Partial oxidation reforming of methanol
Methanol is an attractive fuel for fuel cell-powered vehicles because it has a fairly high energy density, can be pumped into the tank of a vehicle mush like gasoline, and is relatively easy to reform. For on-board reforming, the reformer must be compact and lightweight, and have rapid start-up and good dynamic response. Steam reforming reactors with the tube-and-shell geometry that was used on the prototype fuel cell-powered buses are heat transfer limited. To reach their normal operating temperature, these types of reactors need 45 minutes from ambient temperature start-up. The dynamic response is poor due to temperature control problems. To overcome the limitations of steam reforming, ANL explored the partial oxidation concept used in the petroleum industry to process crude oils. In contrast to the endothermic steam reforming reaction, partial oxidations is exothermic. Fuel and air are passed together over a catalyst or reacted thermally, yielding a hydrogen-rich gas. Since the operating temperature of such a reactor can be controlled by the oxygen-to- methanol ratio, the rates of reaction are not heat transfer limited. Start-up and transient response should be rapid, and the mass and volume are expected to be small by comparison
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Microengineered cathode interface studies
The overpotential at the cathode/electrolyte interface has been recognized as an important limitation on the performance of solid oxide fuel cells (SOFCs). This project is an effort to gain a scientific understanding of which interface features and conditions contribute to cathode polarization in SOFCs. The paper discusses three possible rate-limiting factors in the cathode reaction. The paper studies the electronic conductivity in the electrolyte, the ionic conductivity in the cathode, cathode geometry near the interface, and cathode surface area
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The low-temperature partial oxidation reforming of fuels for transportation fuel cell systems
Argonne`s partial-oxidation reformer (APOR) is a compact, lightweight, rapid-start, and dynamically responsive device to convert liquid fuels to H{sub 2} for use in automotive fuel cells. An APOR catalyst for methanol has been developed and tested; catalysts for other fuels are being evaluated. Simple in design, operation, and control, the APOR can help develop efficient fuel cell propulsion systems
Characterization of ceria-based SOFCs
Solid Oxide Fuel Cells (SOFCs) operating at low temperatures (500-700 C) offer many advantages over conventional zirconia-based fuel cells operating at higher temperatures. Cathode performance is being improved by using better materials and/or microstructures. Fabrication of thin dense electrolytes is also necessary to achieve high cell performances
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Cathodes for ceria-based fuel cells
Work is underway to develop a solid oxide fuel cell that has a ceria-based electrolyte and operates at lower temperatures (500-600{degrees}C) than conventional zirconia-based cells. At present the performance of this ceria-based solid oxide fuel cell is limited by the polarization of conventional cathode materials. The performance of alternative cathodes was measured by impedance spectroscopy and dc polarization. The performance was found to improve by using a thin dense interface layer and by using two-phase cathodes with an electrolyte and an electronic phase. The cathode performance was also found to increase with increasing ionic conductivity for single phase cathodes
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Non-segregating electrolytes for molten carbonate fuel cells
Current MCFCs use a Li/K carbonate mixture; the segregation increases the K concentration near the cathode, leading to increase cathode solubility and performance decline. ANL is developing molten carbonates that have minimal segregation; the approach is using Li-Na carbonates. In screening tests, fully developed potential distributions were obtained for 4 Li/Na compositions, and performance data were used to compare these
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Micro-engineered cathode interface studies
The aim of this work is to increase the performance of the cathode in solid oxide fuel cells (SOFCs) operating at 1,000 C by decreasing the polarization resistance from 0.2 {Omega}-cm{sup 2} at 300 mA/cm{sup 2}. Decreased polarization resistance will allow operation at higher current densities. This work is in support of the Westinghouse tubular SOFC technology using YSZ electrolyte and strontium doped lanthanum manganite (LSM) cathode. As a result of work performed last year at Argonne National Laboratory and information derived from the literature, the limitations at the cathode/electrolyte interface can be classified into two main areas. First, the ionic conductivity of the LSM cathode material is low which limits the reaction zone to an area very close to the interface, while the rest of the cathode thickness acts essentially as current collector with channels for gas access. Second, the electronic conductivity in YSZ is very low which limits the reaction zone to areas that are the boundaries between LSM and YSZ rather than the YSZ surface away from LSM at the interface. Possible solutions to this problem being pursued are: (1) introducing an ionic conducting YSZ phase in LSM to form a porous two-phase mixture of LSM and YSZ; (2) applying a thin interlayer between the electrolyte and the cathode where the interlayer has high ionic and electronic conductivity and high catalytic activity for reduction of O{sub 2}; (3) increasing the ionic conductivity in the LSM by suitable doping; and (4) increasing the electronic conductivity in the electrolyte by doping or by depositing an appropriate mixed conducting layer on the YSZ before applying the cathode
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Sealant materials for solid oxide fuel cells
The objective of this work is to complete the development of soft glass-ceramic sealants for the solid oxide fuel cell (SOFC). Among other requirements, the materials must soften at the operation temperature of the fuel cell (600--1,000 C) to relieve stresses between stack components, and their thermal expansions must be tailored to match those of the stack materials. Specific objectives included addressing the needs of industrial fuel cell developers, based on their evaluation of samples the authors supply, as well as working with commercial glass producers to achieve scaled-up production of the materials without changing their properties. Results from long-term stability testing, stability in voltage gradients, thermal expansion and softening, and scaled-up production methods are presented
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