This application claims priority to German Application No. 10 2005 061 585.6, filed Dec. 22, 2005, the entire disclosure of which is hereby incorporated in its entirety.
The invention relates to a solid oxide fuel cell stack having individual cells arranged above one another, which are each arranged, if required, with contact layers between a top shell and a bottom shell gas-tightly connected with the top shell in the edge region, as well as having a gas distributor structure in each case between the top shell of a first individual cell and of the bottom shell of the adjacent individual cell. Concerning the known state of the art, reference is made, in addition to German Patent Document DE 102 38 859 A1, particularly to International Patent Document WO 01/45186 A2.
Solid oxide fuel cells or so-called stacks of individual solid oxide fuel cells (“individual cells”) are to be economically and reliably producible in large-scale production in the near future and, particularly, should also operate reliably without the occurrence of the slightest leakiness or the like in the stack during the operation. The latter problems are often caused by different thermal coefficients of expansion of the individual elements or components of the fuel cell stack. A considerable improvement of these problems can be achieved by means of the last-mentioned known state of the art, specifically in that a voltage-equalizing layer provided with openings (specifically for a gas supply to the anode layer through the gas-permeable substrate) is applied quasi to the underside of a substrate which, on its top side, carries an individual fuel cell in the form of an anode layer, a solid electrolyte layer applied thereto, and a cathode layer applied to the latter, which stress equalizing layer has a thermally caused expansion and shrinkage behavior in the temperature range required for the production and for the operation of the electrode-electrolyte unit, which expansion and shrinkage behavior is essentially identical with that of the solid electrolyte layer.
However, this state of the art known from International Patent Document WO 01/45186 does not meet the first mentioned requirements with respect to an economical and reliable producibilty. Therefore, there remains a need for a solid oxide fuel cell stack that is economically and reliably producible in large-scale production that operates reliably without the occurrence of the slightest leakiness or the like in the stack during the operation.
By means of the characteristics according to the invention, first—as basically known—so-called “symmetrical” individual cells are used (as anode-electrolyte-cathode units), which are optimized such that they have essentially no or, at the most, only a minimal change of curvature in the complete operating temperature range (starting at the ambient temperature and ranging to the continuous operation). As it is known, this is achieved such by a “partially symmetrical” construction with respect to the substrate carrying the anode-electrolyte-cathode layers that a so-called voltage-equalizing layer with a comparable thermal expansion behavior is applied to the underside of the substrate (compare, the above-mentioned International Patent Document WO 01/45186), which may be formed, for example, by the material of the solid electrolyte layer. Each so-called “symmetrical” individual cell is furthermore quasi enclosed between a top shell and a bottom shell, so that a self-sufficient so-called individual cell unit is thereby created. In the edge region, the top shell and the bottom shell are connected with one another in a gas-tight manner, so that that a transfer of process gases to the cathode or to the anode of the individual cell from the outside can only still take place through openings which are provided in the top shell and the bottom shell within the edge region. Each such individual cell unit closed off, with the exception of the openings, can therefore be produced separately and can advantageously also be checked separately with respect to its working capability.
A solid oxide fuel cell stack can then be constructed of several individual-cell units already checked first. In this case, suitable so-called gas distributor structures only still have to be inserted between the individual units, by means of which gas distributor structures, the process gases (for example, hydrogen as the fuel gas for the anode and ambient air with oxygen as the oxidant for the cathode) are guided separately from one another to the respective electrode layers or to the openings in the respective plate (top shell or bottom shell) from the lateral direction, and the reaction products are also discharged again. For this purpose, these gas distributor structures may be constructed, for example, in the fashion of a corrugated sheet. With respect to a use of identical parts, it is particularly advantageous for not only the gas distributor structures but also the top shell and the bottom shell to be constructed such that all gas distributor structures and all plates respectively are identical parts. The top shell and the bottom shell are disposed in a manner rotated by 180° with respect to one another in an individual-cell unit; and also mutually adjacent gas distributor structures constructed, for example, in the form of corrugated sheets, may be arranged in the fuel cell stack in a manner rotated by 180° with respect to one another and are therefore not congruent, in order to obtain a sufficiently stiff structure because then, relative to an individual cell, one wave crest and one wave trough respectively are situated opposite one another and thereby quasi clamp this individual cell between one another.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings for example.
a shows a first step for forming a fuel cell stack of one embodiment of the present invention wherein a substrate is provided having a fuel cell formed thereon.
b shows another step for forming a fuel cell stack of one embodiment of the present invention wherein a stress equalizing layer is formed on the underside of the substrate.
Based on
b shows the underside of an individual fuel cell 1 according to the invention, to which or to whose substrate a so-called stress equalizing layer 3 provided with openings 2 is applied to the side facing away from the anode layer. This stress equalizing layer 3 is formed of a material which, in the possible operating temperature range of the fuel cell (preferably starting in the range of the minimal cold-start temperature and ranging to the maximal operating temperature), has a thermal expansion behavior which is essentially equal to that of the electrolyte layer of the individual cell. Thereby, as a result of corresponding shaping of the here grid-shaped stress equalizing layer 3, that is, as a result of the shape, size and position of the openings 2 as well as the layer thickness, it can be ensured that the individual cell 1 (with the stress equalizing layer 3) experiences no significant curving at temperature changes; that is, the so-called thermo-bimetal effect does not occur. The material of the stress equalizing layer 3 may, for example, be the solid electrolyte material. In addition, the openings 2 in the stress equalizing layer 3 are required in order to permit—in
Since the stress equalizing layer 3 has a layer structure which is dense in itself, it is advantageously suitable for a mechanical or material-locking connection with a shell 4 enveloping the individual cell 1, which shell 4 is essentially composed of two half-shells, specifically a so-called bottom shell 4a and a so-called top shell 4b, with respect to which reference is made to
First, the individual cell 1 is now prepared for a soldering by way of its stress equalizing layer 3, which preferably operates additionally as a connection layer for fixing the individual cell 1 in a or the above-mentioned enveloping shell 4. For this purpose, a metal solder 5 is applied to the stress equalizing layer 3—starting from the condition according to
A so-called bottom shell 4a of the enveloping shell 4, which is formed by this bottom shell 4a as well as a so-called top shell 4b corresponding therewith, is illustrated separately in
Returning to the above-mentioned gas-tight sealing by means of the insulation element 6, this can again take place by means of a metal solder, as illustrated in
Before the top shell 4b and the bottom shell 4a are combined to form the “enveloping” shell, a metallic, electrically conductive, so-called cathode contact element 11 is applied, for example, by means of capacitor discharge welding to the interior side of the top shell 4 facing the individual cell 1, which cathode contact element 11 is or will be provided with a chrome blocking contact layer in the direction of the top side (
For a gas-tight joining operation of the bottom shell 4a and the top shell 4b in the surrounding edge region (edge strips 16 and transverse strips 17 connecting the latter), suitable metallic solders can be used. Since, however, the top shell 4b and the bottom shell 4a have to be electrically insulated with respect to one another, either the mutually facing surfaces in the edge region (edge strips 16 and transverse strips 17) of the preferably metallic top shell 4b and bottom shell 4a may the ceramized in an electrically non-conductive manner, or a ceramic foil or an electrically non-conductively coated metal element can be placed in-between as an above-mentioned electrical insulation element 6. During the soldering-together of the top shell 4b and the bottom shell 4a, the individual cell 1 is simultaneously connected with the bottom shell 4a by way of the above-mentioned metal solder 5, and the insulation element 6 is connected by way of the above-mentioned metal solder 7 also with the bottom shell 4a and the top shell 4b. By way of the mentioned cathode contact element 11 and the chrome blocking contact layer situated thereon, the individual cell 1 is electrically contacted with the top shell 4a. To this extent, an individual-cell unit 10 is therefore created by means of the individual cell 1 enveloped in this manner, in which individual-cell unit 10,—if the top shell 4b and the bottom shell 4a had no openings 2′—the individual cell 1 would be hermetically enclosed, in which case the so-called anode space—where the anode of the individual cell 1 is situated—within this composite, cannot interact with the so-called cathode space of this composite.
Several such individual-cell units 10 are then combined to form a fuel cell stack while being stacked upon one another. However, it is required in this case that the above-mentioned so-called gas distributor structure 9 be provided between the top shell 4b of a “lower” individual cell unit 10 and the bottom shell 4a of the individual cell unit 10 situated over it, which gas distributor structure 9 permits the required process gas supply and removal. Such a gas distributor structure 9 can optionally still before the soldering-together of the top shell 4b and the bottom shell 4a, be welded, for example, by means of cathode discharge welding, upon the exterior side of the top shell 4b or of the bottom shell 4a. This gas distributor structure 9 is preferably also welded to the shell 4a and 4b respectively (preferably by means of a laser) in the edge regions (edge strips 16 and transverse strips 17), in order to increase the stiffness of the individual-cell unit 10. Preferably, an identical or a comparable material is selected for the shells 4a, 4b as well as for the gas distributor structure 9, so that no thermomechanically caused curvature effects occur during temperature changes.
The suggested laser-welding of the gas distributor structure 9 to the individual-cell unit 10 in its edge region makes a separate joining for the soldering-together of the individual cells 1 by operating the fuel cell stack at a raised temperature superfluous—which had taken place so far and is known to a person skilled in the art, because this joining process takes place together with the suggested laser welding.
As illustrated in
Another, so far not described component inside individual-cell unit 10 is also visible in the fuel cell stack according to
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
Number | Date | Country | Kind |
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10 2005 061 585.6 | Dec 2005 | DE | national |