Abstract:
A fuel cell gasket employed to seal around an individual cell of a fuel cell assembly. The gaskets include sealing beads that are compressed against separator plates. Adhesive layers located between the gaskets and separator plates hold the gaskets against the separator plates and maintain a desired pre-load on the sealing beads. These structural seals provide good seals along the surfaces of the separator plates, thus reducing or eliminating the need for bolts to maintain the pre-load on the sealing beads of the gaskets.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This clams the benefit of United States provisional patent application identified as Application Number 60/344,323, filed Dec. 20, 2001. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    This invention relates in general to fluid seals, and more particularly to static gaskets for various encapsulating covers and especially fuel cells.  
           [0003]    A fuel cell is an electrochemical energy converter that includes two electrodes placed on opposite surfaces of an electrolyte. In one form, an ion-conducting polymer electrolyte membrane is disposed between two electrode layers to form a membrane electrode assembly (MEA). The MEA is used to promote a desired electrochemical reaction from two reactants. One reactant, oxygen or air, passes over one electrode while hydrogen, the other reactant, passes over the other electrode. The oxygen and hydrogen combine to produce water, and in the process generate electricity and heat.  
           [0004]    An individual cell within a fuel cell assembly includes a MEA placed between a pair of separator plates. The separator plates are typically fluid impermeable and electrically conductive. Fluid flow passages or channels are formed adjacent to each plate surface at an electrode layer to facilitate access of the reactants to the electrodes and the removal of the products of the chemical reaction. In such fuel cells, resilient gaskets or seals are typically provided between the faces of the MEA and the perimeter of each separator plate to prevent leakage of the fluid reactant and product streams. Since the fuel cell operates with oxygen and hydrogen, it is important to provide a seal that not only seals well against hydrogen, oxygen and water, but that will seal well as the temperature changes due to the heat that is given off during fuel cell operation. To assure a good seal, bolts or other clamping mechanisms are used to maintain a compression load between the separator plates. This adds to the number of components in the assembly as well as making the assembly process more time consuming.  
           [0005]    Thus, it is desirable to have a fuel cell with components that are relatively easy to assemble, while assuring the proper sealing for the finished assembly. And, in particular, it is desirable to have a fuel cell where the individual cells employ a minimum number of parts to assemble, while maintaining the proper compression load on the seal to assure the desired sealing characteristics for each individual cell.  
         SUMMARY OF INVENTION  
         [0006]    In its embodiments, the present invention contemplates an apparatus for use in a fuel cell. The apparatus includes a membrane electrode assembly, and a first gasket, formed of an elastomeric material, having a first surface and a second surface, with the first surface secured to the membrane electrode assembly, and with the first gasket including a first sealing bead protruding from the second surface. A first separator plate is mounted to the first gasket in compressing engagement with the first sealing bead, and a first layer of adhesive is located between the first gasket and the first separator plate such that the first separator plate is maintained in compressing engagement with the first sealing bead.  
           [0007]    The present invention further contemplates a method of forming an individual cell adapted for use in a fuel cell, the method comprising the steps of: assembling a membrane electrode assembly having a first gas diffusion layer and a second gas diffusion layer; securing a first gasket to the first gas diffusion layer on a first surface of the first gasket; providing a first sealing bead protruding from a second surface of the first gasket; coating the second surface of the first gasket with a first layer of adhesive; mounting a first separator plate against the first sealing bead; applying a pressure against the first separator plate to thereby compress the first sealing bead; and maintaining the pressure against the first separator plate until the first layer of adhesive has cured.  
           [0008]    An advantage of the present invention is that it reduces the number of potential leak paths.  
           [0009]    Another advantage of the present invention is that it reduces or eliminates the need for forming bolt holes to hold the assembly together, and further eliminates concerns of bolts relaxing over time, causing a reduction in the seal loading.  
           [0010]    A further advantage of the present invention is that the individual cell is less complex and allows for a less expensive assembly. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]    [0011]FIG. 1 is a schematic plan view of an individual cell according to this invention;  
         [0012]    [0012]FIG. 2 is a section cut, on an enlarged scale, taken along line  2 - 2  in FIG. 1;  
         [0013]    [0013]FIG. 3 is an enlarged, partial, sectional view of the gasket of FIG. 2 after an adhesive has been applied but before assembly to a MEA or separator plates, according to this invention; and  
         [0014]    [0014]FIG. 4 is an enlarged, partial, sectional view of a MEA assembled to a pair of gaskets, according to this invention. 
     
    
     DETAILED DESCRIPTION  
       [0015]    FIGS.  1 - 2  illustrate an individual cell  20  for use in a fuel cell assembly. The individual cell  20  includes a membrane electrode assembly (MEA)  22 . The MEA  22  is made up of a membrane  24 , with a first layer of catalyst material  26  a second layer of catalyst material  28  on either side of the membrane  24 , and a first gas diffusion layer (GDL)  30  and second GDL  32  on either side of the layers of catalyst material  26 ,  28 , respectively. The individual cell  20  also includes a first gasket  34  and a second gasket  36 , secured around the perimeter of the first GDL  30  and the second GDL  32 , respectively. Preferably, the gaskets  34 ,  36  are secured to the GDLs  30 ,  32  by layers of adhesive  44 ,  46 , although other means of securing may be used if so desired. A first separator plate  38  mounts against the first gasket  34  and the first GDL  30 , and a second separator plate  40  mounts against the second gasket  36  and the second GDL  32 , in order to form a cell  20 .  
         [0016]    The membrane  24  is preferably an ion-conducting, polymer, electrolyte membrane, as generally employed in this type of fuel cell application. The first and second layers of catalyst material  26 ,  28  are preferably platinum or other suitable catalyst material for a typical polymer electrode membrane type of fuel cell application. The first and second GDLs  30 ,  32  are preferably a carbonized fiber, or may be another suitable gas permeable material for use as an electrode in a fuel cell. The MEA  22  can include a catalyzed membrane with GDLs assembled thereto, or a membrane assembled between two catalyzed GDLs, each of which is known to those skilled in the art. The first and second separator plates  38 ,  40  are generally rectangular in shape, although other shapes can also be employed if so desired. The plates  38 ,  40  have outer surfaces that are made to mate with adjoining individual cells in making up a completed fuel cell assembly. These fuel cell components are generally known to those skilled in the art.  
         [0017]    FIGS.  1 - 4  illustrate the individual cell  20 , as well as portions of the cell  20  as it is being assembled. The gaskets  34 ,  36  are preferably an elastomeric material, such as, for example, rubber. Each gasket  34 ,  36  includes a sealing bead  48 ,  50 , which extends around substantially the entire perimeter of the cell  20  in order to accomplish its sealing function. A first set of channels  52 ,  54  are formed adjacent the first bead  48  and a second set of channels  56 ,  58  are formed adjacent the second bead  50 . Each bead  48 ,  50  in its uncompressed state, as shown in FIGS. 3 and 4, is generally triangular in cross section—although other suitable shapes as are typically employed for sealing beads in gaskets can be employed instead. In the initial uncompressed state, the height of the sealing beads  48 ,  50  is selected so that they project beyond the outer surfaces  60 ,  62  of the gaskets  34 ,  36  and adhesive layers  64 ,  66 .  
         [0018]    In a method of assembly, the layer of adhesive  44  is applied to an inner surface  70  of the first gasket  34 , as is illustrated in FIG. 3. Then, the first gasket  34  is assembled to the MEA  22 , which has already been assembled by means known to those skilled in the art, and the layer of adhesive  64  is applied to the outer surface  60 , as is illustrated in FIG. 4. The same process is also accomplished for the second gasket  36 , with layers of adhesive  46 ,  66  placed on the inner surface  72  and outer surface  62 , respectively—thus forming a cell subassembly  76 . As mentioned above, the adhesive is preferably a pressure sensitive adhesive that is screen printed onto the gaskets  34 ,  36 , although other suitable types of adhesive may also be employed. The first separator plate  38  and second separator plate  40  are then assembled to the cell subassembly  76 , and compressed with a predetermined amount of pressure until the adhesive has cured—thus forming the individual cell  20 , as shown in FIGS. 1 and 2. Of course, as an alternative, the adhesive layers  44 ,  46  may be instead first applied to the GDLs  30 ,  32 , and/or the adhesive layers  64 ,  66  first applied to the separator plates  38 ,  40  during the assembly of the various components.  
         [0019]    Each bead  48 ,  50  extends beyond where the adjacent adhesive layer is so that it will be compressed during the assembly to its respective separator plate  38 ,  40  and remain in a compressed state after assembly is completed along a bead contact line  80 , thus forming a structural seal. The compression of the beads is controlled by the adhesive layers  64 ,  66 . This assures an appropriate pre-load on the seal beads  48 ,  50  will be maintained along the contact line  80  in order to have a good seal. The sealing beads  48 ,  50  prevent gases from leaking out along the surfaces of the separator plates  38 ,  40 .  
         [0020]    These adhesive layers  64 ,  66  reduce or eliminate the need for mechanical fasteners or other clamping devices to retain the plates  38 ,  40  to their respective gaskets  34 ,  36 , while also maintaining the appropriate compression of the beads  48 ,  50  needed to assure a good seal. Consequently, the assembly process is less complex and the individual cell less expensive to manufacture.  
         [0021]    While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.