An All-Ceramic Interconnect for Use in Solid-Oxide Fuel Cell Stacks
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An All-Ceramic
Interconnect for Use in Solid-Oxide Fuel Cell Stacks
Thomas A. Morris, Eric A. Barringer, Steven C. Kung, and Rodger W. McKain Abstract This article summarizes a unique approach in which all-ceramic interconnects are used in place of metal interconnects in solid-oxide fuel cell (SOFC) stacks. The approach combines advanced SOFC materials with the manufacturing technology and infrastructure established for multilayer ceramic (MLC) packaging for the microelectronics industry. The MLC interconnect is fabricated using multiple layers of yttria-stabilized zirconia (YSZ) tape, with each layer containing conductive vias to provide for electrical current flow through the interconnect. The all-ceramic interconnect design facilitates uniform distribution of air and fuel gas to the respective electrodes of adjacent cells. The multilayer interconnects are fabricated using traditional MLC manufacturing processes. A detailed description of the processes for fabricating the all-ceramic interconnect is presented. To aid in moving from prototype fabrication to commercialization of these fuel cell systems, a detailed cost model has been used as a roadmap for commercial stack development. Cost model projections are presented for three different interconnect footprint sizes. These projections show an SOFC stack cost of less than $150 per kilowatt for the optimized SOFC stack design produced at high volume. Keywords: ceramics, layered structure, solid-oxide fuel cells, zirconia, interconnects.
Introduction Fuel cells are electrochemical devices that directly convert chemical energy into electricity. Because fuel cells operate at low voltages (less than one volt per cell), cells are stacked in series to produce usable power. In a fuel cell stack, adjacent cells are separated by interconnects. The interconnects in a stack serve three important purposes. First, they distribute the air and fuel gas to the respective electrodes. Second, they must be hermetic so that the air and fuel are not permitted to physically mix in the stack. Third, they provide an electrical path for electrons from one cell to be transported to the adjacent cell in a stack. Solid-oxide fuel cell (SOFC) stacks employ one of three approaches for the interconnects: metal interconnects, electrically conductive ceramic perovskites, or
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nonconducting ceramic structures containing vias for electrical conduction. Vias are electrical conduits in a planar structure that are processed by punching or drilling holes, then filling them with an electrically conductive paste. This material is then cosintered with the main body of the laminated structure. Of the three interconnect types, clearly metal interconnects are the most widely used. However, the metal interconnects are not without technical issues, which are currently being addressed by fuel cell developers and groups performing materials research. New materials have shown a good coefficient of thermal expansion (CTE) match with the cell and reduced electrical resistance of oxide scales, but the long-te
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