Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1998-10-21
2001-05-01
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C029S623100
Reexamination Certificate
active
06224993
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed in general to electrolytes of solid oxide fuel cells, and more particularly, to an improved electrolyte structure and associated method of manufacturing same.
2. Background Art
Solid oxide fuel cells (SOFCs) are well known in the art. Indeed, SOFCs are recognized as having the potential to mitigate environmental problems while meeting the power generation and cogeneration needs of tomorrow. Thus, much emphasis has been concentrated on the lowering of the SOFC operating temperatures while increasing SOFC stack performance.
In particular, one such development has been the use of the electrode supported thin film electrolytes for high performance SOFC systems. Processes for manufacturing thin electrolyte films include Allied Signal roll calandering, Lawrence Berkeley Labs and University of Missouri (Rolla) spin coated sol-jel, University of Utah dip coated, Dow tape laminate, and Westinghouse electrochemical vapor deposition (EVD) processes. Each of these processes are capable of producing 5-50 &mgr;m electrolyte layers on an electrode substrate. In particular, calendering and tape lamination processes appear to be the most promising and have demonstrated some levels of commercial viability in electronic chip packaging.
While these types of structures have been demonstrated to be quite successful in small area single cells, these structures have not been applicable with success to stackable large area cells. In particular, thin film electrolyte relies on the substrate electrode material for mechanical support. The mechanical, chemical and micro structural requirements of the electrode function are incompatible with the mechanical support functions of the electrode. In addition, due to the porous microstructure required by the electrode, the mechanical strength of the electrode is quite poor. With both the anode and the cathode materials, volume and composition changes accompany oxygen potential changes, and, these changes all greatly affect the mechanical integrity of the cell.
In addition, the exposure to the oxygen potential gradients are unavoidable in the prior art inasmuch as the supporting electrodes extend to cell edges so as to fully support the thin film electrolyte, exposing cathodes to fuel and anodes to air. In addition, the use of nickel cermet anode substrates which are fired in air as oxide, is likewise detrimental to the mechanical integrity of the cell. In particular, as the NiO is reduced to nickel as the cell begins operation, the cell is detrimentally affected relative to its mechanical strength.
One solution has been disclosed in Ishida, U.S. Pat. No. 5,312,700. This reference contemplates the use of intersecting support ribs on a single plane, on one or both sides of a thin plate for increased support and rigidity of the electrolyte. While this disclosure addresses certain of the shortcomings relative to strength, the intersecting support structure is difficult, time consuming and costly to manufacture.
SUMMARY OF THE INVENTION
The present invention is directed to an electrolyte for a solid oxide fuel cell. The electrolyte comprises an electrolyte plate and means for supporting the electrolyte plate. The electrolyte plate includes an upper surface and a lower surface. The support means includes a plurality of non-intersecting support members. The support members are positioned on at least one of the upper and lower surfaces of the electrolyte plate.
In a preferred embodiment, the non-intersecting support members may be positioned on both of the upper and lower surfaces of the electrolyte plate. Moreover, in such an embodiment, the non-intersecting support members on the upper surface of the electrolyte plate are substantially perpendicular to the non-intersecting support members on the lower surface of the electrolyte plate.
In another preferred embodiment, the non-intersecting support members are substantially identical in geometric configuration. In such an embodiment, the non-intersecting support members may be substantially rectangular or sinusoidal.
In a preferred embodiment, the non-intersecting support members are of a thickness greater than the electrolyte plate.
Preferably, the non-intersecting support members extend across the entirety of the electrolyte plate.
In yet another preferred embodiment, the electrolyte plate and the non-intersecting support members comprise a yttria stabilized zirconia.
The invention further includes a method of manufacturing the electrolyte of a solid oxide fuel cell. The method includes the steps of providing an electrolyte plate, having an upper surface and a lower surface, and a second plate; forming an opening through the second plate; and positioning the second plate on one of the upper and lower surfaces of the electrolyte plate, in a desired orientation. Once positioned, the method further includes the steps of associating the electrolyte plate with the second plate; and trimming the associated electrolyte plate and second plate, so as to render a plurality of non-intersecting support members on the electrolyte plate.
In a preferred embodiment, the method further comprises the steps of providing a third plate; forming at least one opening through the third plate; positioning the third plate on the opposite side of the electrolyte plate from which the second plate is positioned; and associating the third plate with the electrolyte plate. In such an embodiment, the step of trimming further renders a plurality of non-intersecting support members on both surfaces of the electrolyte plate. Moreover, in such a preferred embodiment, the third plate may be positioned such that the at least one opening of the second plate is perpendicular to the at least one opening of the third plate.
In another preferred embodiment, the step of forming openings in the second and/or third plates comprises the forming of a plurality of substantially identical openings in each plate which are substantially parallel to each other. Subsequently, the step of positioning further comprises the positioning of the second and third plates so that the openings in the second plate are substantially perpendicular to the openings of the third plate.
In another preferred embodiment, the method may further comprise the step of forming registering openings on each of the electrolyte plate and the second plate. In such an embodiment, the step of positioning further comprises the step of aligning the registering openings of each of the electrolyte plate and the second plate, to, in turn, properly orientate the plates relative to each other.
REFERENCES:
patent: 4396480 (1983-08-01), Hegedus et al.
patent: 4857420 (1989-08-01), Maricle et al.
patent: 4910100 (1990-03-01), Nakanishi et al.
patent: 4950562 (1990-08-01), Yoshida et al.
patent: 5145754 (1992-09-01), Misawa et al.
patent: 5162167 (1992-11-01), Minh et al.
patent: 5270131 (1993-12-01), Diethelm et al.
patent: 5312700 (1994-05-01), Ishida
patent: 5547777 (1996-08-01), Richards
patent: 1-128359 (1989-05-01), None
Elangovan Singaravelu
Hartvigsen Joseph Jay
Khandkar Ashok Chandrashekhar
Merrill Robert Phillip
Factor & Partners
Kalafut Stephen
Mercado Julian A.
Sofco
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