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Published: 2001

Total Pages: 91

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Solid oxide fuel cells (SOFCs) are the future of energy production in America. They offer great promise as a clean and efficient process for directly converting chemical energy to electricity while providing significant environmental benefits (they produce negligible hydrocarbons, CO, or NO(subscript x) and, as a result of their high efficiency, produce about one-third less CO2 per kilowatt hour than internal combustion engines). Unfortunately, the current SOFC technology, based on a stabilized zirconia electrolyte, must operate in the region of 1000 C to avoid unacceptably high ohmic losses. These high temperatures demand (a) specialized (expensive) materials for the fuel cell interconnects and insulation, (b) time to heat up to the operating temperature and (c) energy input to arrive at the operating temperature. Therefore, if fuel cells could be designed to give a reasonable power output at low to intermediate1 temperatures tremendous benefits may be accrued. At low temperatures, in particular, it becomes feasible to use ferritic steel for interconnects instead of expensive and brittle ceramic materials such as those based on LaCrO3. In addition, sealing the fuel cell becomes easier and more reliable; rapid start-up is facilitated; thermal stresses (e.g., those caused by thermal expansion mismatches) are reduced; radiative losses ((almost equal to)T4) become minimal; electrode sintering becomes negligible and (due to a smaller thermodynamic penalty) the SOFC operating cycle (heating from ambient) would be more efficient. Combined, all these improvements further result in reduced initial and operating costs. The problem is, at lower temperatures the conductivity of the conventional stabilized zirconia electrolyte decreases to the point where it cannot supply electrical current efficiently to an external load. The primary objectives of the proposed research are to develop a stable high conductivity (> 0.05 S cm−1 at (less-than or equal to) 550 C) electrolyte for lower temperature SOFCs. This objective is specifically directed toward meeting the lowest (and most difficult) temperature criteria for the 21st Century Fuel Cell Program. Meeting this objective provides a potential for future transportation applications of SOFCs, where their ability to directly use hydrocarbon fuels could permit refueling within the existing transportation infrastructure. In order to meet this objective we are developing a functionally gradient bilayer electrolyte comprised of bismuth oxide on the air side and ceria on the fuel side. Bismuth oxide and doped ceria are among the highest ionic conducting electrolytes and in fact bismuth oxide based electrolytes are the only known solid oxide electrolytes to have an ionic conductivity that meets the program conductivity goal.

Download or read book STABLE HIGH CONDUCTIVITY BILAYERED ELECTROLYTES FOR LOW TEMPERATURE SOLID OXIDE FUEL CELLS. written by and published by . This book was released on 2001 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: Solid oxide fuel cells (SOFCs) are the future of energy production in America. They offer great promise as a clean and efficient process for directly converting chemical energy to electricity while providing significant environmental benefits (they produce negligible hydrocarbons, CO, or NO(subscript x) and, as a result of their high efficiency, produce about one-third less CO2 per kilowatt hour than internal combustion engines). Unfortunately, the current SOFC technology, based on a stabilized zirconia electrolyte, must operate in the region of 1000 C to avoid unacceptably high ohmic losses. These high temperatures demand (a) specialized (expensive) materials for the fuel cell interconnects and insulation, (b) time to heat up to the operating temperature and (c) energy input to arrive at the operating temperature. Therefore, if fuel cells could be designed to give a reasonable power output at low to intermediate1 temperatures tremendous benefits may be accrued. At low temperatures, in particular, it becomes feasible to use ferritic steel for interconnects instead of expensive and brittle ceramic materials such as those based on LaCrO3. In addition, sealing the fuel cell becomes easier and more reliable; rapid start-up is facilitated; thermal stresses (e.g., those caused by thermal expansion mismatches) are reduced; radiative losses ((almost equal to)T4) become minimal; electrode sintering becomes negligible and (due to a smaller thermodynamic penalty) the SOFC operating cycle (heating from ambient) would be more efficient. Combined, all these improvements further result in reduced initial and operating costs. The problem is, at lower temperatures the conductivity of the conventional stabilized zirconia electrolyte decreases to the point where it cannot supply electrical current efficiently to an external load. The primary objectives of the proposed research are to develop a stable high conductivity (> 0.05 S cm−1 at (less-than or equal to) 550 C) electrolyte for lower temperature SOFCs. This objective is specifically directed toward meeting the lowest (and most difficult) temperature criteria for the 21st Century Fuel Cell Program. Meeting this objective provides a potential for future transportation applications of SOFCs, where their ability to directly use hydrocarbon fuels could permit refueling within the existing transportation infrastructure. In order to meet this objective we are developing a functionally gradient bilayer electrolyte comprised of bismuth oxide on the air side and ceria on the fuel side. Bismuth oxide and doped ceria are among the highest ionic conducting electrolytes and in fact bismuth oxide based electrolytes are the only known solid oxide electrolytes to have an ionic conductivity that meets the program conductivity goal.