Sealant materials for solid oxide fuels and other high-temperature ceramics

Glass-ceramic sealing materials have been developed with mechanical and chemical properties suitable for a variety of high-temperature applications. We have demonstrated the ability to tailor the thermal expansion coefficient between 8 and 12 x 10{sup -6}/{degrees}C, and the softening temperature can be adjusted such that the materials have suitable viscosities for a soft, compliant seal at temperatures ranging from 650 to 1000{degrees}C. These materials form excellent bonds to a variety of ceramics and metals during heating to the target operation temperature. They have limited reactivity with the fuel cell materials tested and are stable in both air and reducing environments

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

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

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

Imaging and quantification of spreading and trapping of carbon dioxide in saline aquifers using meter-scale laboratory experiments

The role of capillary forces during buoyant migrati on of CO2 is critical towards plume immobilization within the post-injection phase of a geological carbon sequestration operation. However, the inherent heterogeneity of the subsurface makes it very challenging to evaluate the effects of capillary forces on the storage capacity of these formations and to assess in-situ plume evolution. To overcome the lack of accurate and continuous observations at the field scale and to mimic vertical migration and entrapment of realistic CO2 plumes in the presence of a background hydraulic gradient, we conducted two unique long-te rm experiments in a 2.44 m × 0.5 m tank. X-ray attenuation allowed measuring the evolution of a CO2-surrogate fluid saturation, thus providing direct insight into capillarity- and buoyancy-domin ated flow processes occurring under successive drainage and imbibition conditions. The comparison of saturation distributions between two experimental campaigns suggests that layered-type h eterogeneity plays an important role on non- wetting phase (NWP) migration and trapping, because it leads to (i) longer displacement times (3.6 months vs. 24 days) to reach stable trapping c onditions, (ii) limited vertical migration of the plume (with center of mass at 39% vs. 55% of aquife r thickness), and (iii) immobilization of a larger fraction of injected NWP mass (67.2% vs. 51. 5% of injected volume) as compared to the homogenous scenario. While these observations confirm once more the role of geological heterogeneity in controlling buoyant flows in the s ubsurface, they also highlight the importance of characterizing it at scales that are below seismic resolution (1-10 m)

Advances in research for solid oxide fuel cells

Solid oxide fuel cells are attracting considerable interest among industrial organizations wanting to position themselves in a potentially important technology of the future. More than a dozen new organizations worldwide have begun SOFC development in the last few years. Most of this R and D activity is in the planar technology, because it represents a good compromise between the proven but IR-limited tubular configuration and the high-performance but difficult-to-fabricate monolithic structure. The challenges of developing the planar cell configurations are finding high-temperature edge and manifold seal materials that will make very flat ceramic trilayers of sufficiently large area, and minimize contact resistances in stacks of cells. Also, decreasing the operating temperature requires development of reliable thin-film fabrication methods for the electrolyte, and finding a metal with good oxidation resistance and a thermal expansion coefficient well matched with the different cell components. Finally, toughness and a thermal stress tolerance of stacks need to be improved

Sealants for Solid Oxide Fuel Cells

Basic requirements for a sealant are good bonding to the materials of interest, chemical stability in the operating environment, and low gas permeability. For high-temperature operation as in Solid Oxide Fuel Cells (SOFCs), the sealant must also have a thermal expansion which is reasonably close to that of the other materials involved and must have some compliance, or softness, to allow for some mismatch between the components to be joined. In this paper, we discuss a family of glass-ceramic materials with mechanical, chemical, and electrical properties that are suitable for these demanding high-temperature applications