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New Thin Film Electrolyte for Fuel Cells
New Ceramic Process Doubles Performance
and Lowers Operating Temperature
Steven Visco and Lutgard DeJonghe
MSD researchers Selmar de Souza, Steven Visco, and Lutgard DeJonghe have made an important breakthrough in the effort to build an affordable commercial fuel cell. The MSD team has developed a new "thin-film electrolyte" that doubles the performance of solid oxide fuel cells (SOFCs) whose commercial viability to date has been limited by cost and performance problems.
Fuel cells "burn" hydrogen or hydrocarbons to produce electricity. They are highly fuel-efficient and almost non-polluting. Some solid oxide fuel cells burn hydrocarbons by first converting them to hydrogen, while others burn them directly. The latter are the leading candidates for commercial applications. Until now, SOFC's have been most efficient when operated at 1000 C. This high temperature operation, however, requires the use of expensive materials, decreases the lifetime of the cell, and thus has been the major barrier to widespread commercialization. Researchers have worked for years without success to reduce the operating temperature while maintaining performance.
The MSD team was able to reduce the operating temperature of their SOFC to 800 C by reducing by ten-fold (to 10 microns) the thickness of the electrolyte film which provides ion transport in the cell. To do this, the MSD team developed an inexpensive and simple ceramic process in which yttria-stabilized zirconia powder is suspended in solution. Much like latex paint, the suspension is painted onto the porous ceramic substrate (anode) of the cell and then fired (sintered) to form the thin electrolyte layer. A similar process is used to form the air electrode to complete the fuel cell (see figure). Over a three year period, the team developed the correct combination of powders and processing that allow the "paint" to cover the anode pores without clogging them and to survive the sintering without cracking or developing pinholes. Due to its simplicity, the new process lends itself easily to assembly line operation.
Prototype cells fabricated with the new electrodes operate at 800 C with twice the power output (2 W cm-2) of the previous best SOFC's operating at 1000 C (see figure). In preliminary endurance testing, the cells have operated for over 700 hours with no loss of performance. While this is far short of the 5 to 10 years of operation required for commercial power generation, the test results are extremely promising.
Selmar de Souza, Steven Visco, and Lutgard De Jonghe (510.486-6138), Materials Sciences Division (510.486-4755).
de Souza, Selmar, Steven J. Visco, and Lutgard C. De Jonghe, "High Performance Low-Temperature Solid Oxide Fuel Cell," Mat. Res. Soc. Symp. Proc., 369 (1995).
Research funding from Division of Materials Sciences (DMS), U.S. Department of Energy (DOE).
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