Patent Publication Number: US-2003221311-A1

Title: Fuel cell assembly and sealing

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] This clams the benefit of U.S. provisional patent application identified as Application No. 60/365,928, filed Mar. 20, 2002. 
    
    
     
       BACKGROUND OF INVENTION  
       [0002] This invention relates in general to methods of assembly static seals to mating parts, and more particularly to a method for assembling gaskets and other components employed in a fuel cell.  
       [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.  
       [0005] Moreover, in order to assure a good seal and a properly operable fuel cell, the seals and other components in the MEA need to be formed accurately as well as aligned properly with each other. Also, it is desirable that the seal is formed and assembled to the other components with minimal waste material and contaminants that might interfere with the operation of the cell.  
       [0006] Unfortunately, the current methods of assembling the components involves cutting all of the components to final size before any assembly takes place. Then, all of the individual components must be very carefully aligned and stacked. All of the layers of the MEA are very thin and difficult to handle, some layers are relatively easily damaged when handled, and some produce loose fibers while being handled that can end up contaminating a finished assembly, so it is desirable to handle them less than this assembly method requires. Further, this type of method, by employing stacks of pre-cut components, can allow the components to possibly wrinkle, warp, bend, or twist, thus making proper alignment during assembly more difficult. In addition, because full coverage of the active area of the cell by both gas diffusion layers is important, and alignment is difficult, the gas diffusion layers are being cut larger than is actually needed, and the active area may be made smaller than otherwise necessary, in order to assure this full coverage. But the material for the gas diffusion layers is very expensive, so the extra material increases the cost of each cell. And, a reduced active area reduces the fuel cell output.  
       [0007] Thus, it is desirable to be able to assemble a membrane electrode sealed assembly, for an individual cell of a fuel cell, that is relatively easy to accurately align, with minimal handling of the components, and while assuring the proper sealing and operation of the finished assembly.  
       SUMMARY OF INVENTION  
       [0008] In its embodiments, the present invention contemplates a method for assembling a membrane electrode sealed assembly, the method comprising the steps of: unrolling a first cell section from a first gasket roll; aligning a first cell section of a first gas diffusion layer with the first cell section of the first gasket roll; aligning a first cell section of a membrane layer with the first cell section of the first gas diffusion layer; aligning a first cell section of a second gas diffusion layer with the first cell section of the membrane layer; locating a first catalyst layer on one of the membrane layer and the first gas diffusion layer prior to the first cell section of the membrane layer being aligned with the first cell section of the first gas diffusion layer; locating a second catalyst layer on one of the second gas diffusion layer and the membrane layer prior to the first cell section of the second gas diffusion layer being aligned with the first cell section of the membrane layer; unrolling a first cell section from a second gasket roll; and aligning the first cell section from the second gasket roll with the first cell section of the second gas diffusion layer.  
       [0009] The present invention further contemplates a method for assembling a membrane electrode sealed assembly, the method comprising the steps of: orienting a first cell section from a first gasket layer; unrolling a first cell section of a first gas diffusion layer from a first gas diffusion layer roll; aligning the first cell section of the first gas diffusion layer with the first cell section of the first gasket layer; aligning a first cell section of a membrane layer with the first cell section of the first gas diffusion layer; unrolling a first cell section of a second gas diffusion,layer from a first gas diffusion layer roll; aligning the first cell section of the second gas diffusion layer with the first cell section of the membrane layer; locating a first catalyst layer on one of the membrane layer and the first gas diffusion layer prior to the first cell section of the membrane layer being aligned with the first cell section of the first gas diffusion layer; locating a second catalyst layer on one of the second gas diffusion layer and the membrane layer prior to the first cell section of the second gas diffusion layer being aligned with the first cell section of the membrane layer; and aligning a first cell section from a second gasket layer with the first cell section of the second gas diffusion layer.  
       [0010] The present invention additionally contemplates a method for assembling a membrane electrode sealed assembly, the method comprising the steps of: orienting a first cell section from a first gasket layer; aligning a first cell section of a first gas diffusion layer with the first cell section of the first gasket layer; unrolling a first cell section of a membrane layer from a membrane layer roll; aligning the first cell section of the membrane layer with the first cell section of the first gas diffusion layer; aligning a first cell section of a second gas diffusion layer with the first cell section of the membrane layer; locating a first catalyst layer on one of the membrane layer and the first gas diffusion layer prior to the first cell section of the membrane layer being aligned with the first cell section of the first gas diffusion layer; locating a second catalyst layer on one of the second gas diffusion layer and the membrane layer prior to the first cell section of the second gas diffusion layer being aligned with the first cell section of the membrane layer; and aligning a first cell section from a second gasket layer with the first cell section of the second gas diffusion layer.  
       [0011] An advantage of the present invention is that the assembly method for the membrane electrode sealed assembly, by employing components taken from rolls, allows for more accurate alignment. Being on rolls allows for a slight tension in the component materials, thus reducing concerns with wrinkling, warp, bend or twisting. Moreover, since accurate alignment is more repeatably obtained, the need for gas diffusion layer overlap is avoided, thus reducing the cost and/or increasing the active area of the cell.  
       [0012] Another advantage of the present invention is that assembling from the material rolls also, reduces the amount of handling for individual components prior to being assembled. This reduces the chances for damage of components during assembly, and reduces the amount of contaminants produced during assembly. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0013]FIG. 1 is a schematic, plan view of an individual cell of a fuel cell assembly, assembled in accordance with a method of the present invention.  
     [0014]FIG. 2 is a section cut, on an enlarged scale, taken along line  2 - 2  in FIG. 1.  
     [0015]FIG. 3 is a section cut, similar to FIG. 2, but illustrating a different embodiment of an individual cell of a fuel cell assembly, prior to compressing separator plates onto a membrane electrode sealed assembly, assembled in accordance with a method of the present invention.  
     [0016]FIG. 4 is a schematic, plan view of a portion of a gasket roll, as is employed in an assembly method of the present invention.  
     [0017]FIG. 5 is a schematic view of a series of rolls from which the membrane electrode sealed assembly components are cut and aligned in order to form a membrane electrode sealed assembly, as assembled in accordance with a method of the present invention.  
     [0018]FIGS. 6 a  and  6   b  are portions of a flow chart illustrating an embodiment of an assembly method of the present invention.  
     [0019]FIG. 7 is a view similar to FIG. 5, but illustrating a first alternate set of rolls from which membrane electrode sealed assembly components are cut and aligned.  
     [0020]FIGS. 8 a  and  8   b  are portions of a flow chart illustrating a first alternate embodiment of the assembly method of FIGS. 6 a  and  6   b.   
    
    
     DETAILED DESCRIPTION  
     [0021] 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)  21 , that is formed as part of a membrane electrode sealed assembly  22 . The MEA  21  is made up of a membrane  24 , with a layer of catalyst material  26  on both sides of the membrane  24 . The MEA  21  also includes a first gas diffusion layer (GDL)  30  and second GDL  32  on either side of the layers of catalyst material  26 . With a first gasket  34  and a second gasket  36  secured around the perimeters  41 ,  42  of the first GDL  30  and the second GDL  32 —preferably, the gaskets  34 ,  36  are secured to the GDLs  30 ,  32  by adhesive  31 —a membrane electrode sealed assembly  22  is formed. Each gasket  34 ,  36  includes an inner perimeter  29 , which defines an active area  35 . Preferably, the adhesive  31  extends around and seals the entire edge of the MEA  21 . A first separator plate  38  mounts against the first gasket  34 , and against the first GDL  30  in the active area  35 . A second separator plate  40  mounts against the second gasket  36 , and against the second GDL  32  in the active area  35 . The separator plates  38 ,  40  assembled to the membrane electrode sealed assembly  22  essentially form the individual cell  20 .  
     [0022] Since the thicknesses of the various components are very thin, they are only depicted schematically in the figures in order to aid in describing the invention. The actual thicknesses of each of the components will vary according to the particular application of the fuel cell and are known to those skilled in the art.  
     [0023] The membrane  24  is preferably an ion-conducting, polymer, electrolyte membrane, as generally employed in this type of fuel cell application. The catalyst material  26  is 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, or a combination of the two, 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 order to make up a completed fuel cell assembly. The adhesive is preferably one that is activated by some external source, such as pressure, heat, or ultraviolet light—although, other types of adhesive may be employed instead, if so desired.  
     [0024] Each gasket  34 ,  36  preferably has a gasket carrier  50 , with an elastomeric seal  52  molded to a first side  54 . The carrier  50  is preferably a thin, flexible member, and may be made of a polymeric material, such as, for example, polyester, polyimid, or nylon. The elastomeric seal  52  is preferably made of an elastomeric material with good sealing properties, such as, for example, rubber. The seal  52  may include a sealing bead  56  protruding therefrom, if so desired, as is known in the art. An advantage of having multi-component gaskets  34 ,  36  is that it is easy for the carriers  50  to have the adhesive  31  pre-applied to a second side  58  prior to assembly of the membrane electrode sealed assembly  22 .  
     [0025]FIG. 3 illustrates a second embodiment of an individual cell  120  assembled with an assembly method of the present invention. In this figure, elements that are the same as FIG. 2 will retain the same element number, while changed or added elements will have a 100-series number. FIG. 3 illustrates the components of an individual cell  120 , but just prior to compressing the separator plates  38 ,  40  against the membrane electrode sealed assembly  122 . In this embodiment, the MEA  121  is different in that the perimeters  141  of the gas diffusion layers  130 ,  132  are adjacent to but do not overlap with the gaskets  134 ,  136 , while the membrane  124  and catalyst layers  126  still overlap with the gaskets  134 ,  136 . Also the elastomeric seals  152 , mounted on the carriers  150 , are shaped differently, providing a different sealing bead  156 . Still, this embodiment of an individual cell  120 , as with other similar types of embodiments of individual cells, can be assembled with the improved methods of assembly of the present invention.  
     [0026]FIG. 4 illustrates a portion of a first gasket roll  200 , with a series of cell sections  202  that can be cut to form gaskets  204 . An interior phantom line  206  shown in each cell section  202  indicates a cut line which, after removal, will create the boundaries for active areas  208  in each cell section. Exterior phantom lines  201  shown around each cell section  202  indicate cut lines for forming the exterior perimeter of each gasket, preferably being cut after assembly. Preferably, an elastomeric seal  212  is already molded onto a carrier  214  prior to creating the gasket roll  200 . Also, preferably, an adhesive  216  is already coated on the opposite side of the carrier  214  prior to creating the gasket roll  200 . Alternatively, the adhesive layer can be added during the process of assembling the various layers, but that may complicate the stacking and alignment process.  
     [0027]FIG. 5 illustrates rolls of the various components that can be assembled using the assembly method shown in FIGS. 6 a  and  6   b.  A first gasket roll  300  preferably comes off in a single sheet that includes a carrier layer  302 , with elastomeric seals  304  molded onto a first side  306  and an adhesive layer  308  applied to the second side  310 . The gasket roll  300 , when the time in the assembly step is reached, will then be cut during the formation of a first cell section  312  for a first membrane electrode sealed assembly  314 , then for the formation of a second cell section  316  for a second membrane electrode sealed assembly  318 , etc. Active areas  317  will also be cut from the first cell section  312 , second cell section  316 , etc. A first GDL roll  320  includes a single layer  322  that is unrolled, and can be cut prior to assembly with the first gasket roll  300  (or after if preferred) in order to form a first cell section  324 , a second cell section  326 , etc.  
     [0028] A membrane roll  328  preferably comes off in a single sheet that includes a membrane layer  330 , with a catalyst layer  332 ,  334  on either side. The membrane roll  328  can then be cut to form a first cell section  336 , a second cell section  338 , etc. As an alternative, the catalyst layers  332 ,  334  can be pre-applied to the GDL layers, rather than to the membrane layer  330 , if so desired. A second GDL roll  340  is similar to the first and includes a single layer  342  that is unrolled and cut to form a first cell section  344 , a second cell section  346 , etc. A second gasket roll  348  includes a carrier layer  350 , with elastomeric seals  352  molded onto a first side and an adhesive layer  354  applied to a second side. It is also cut at some step in the assembly process to form a first cell section  356 , a second cell section  358 ;an active area  351 , etc.  
     [0029] While the all of the rolls of component material are shown oriented in the same direction, they can, of course be oriented however one wishes in order to best utilize the factory space where the assembly is taking place. Different types of rollers and other tools (not shown) can then be employed to assure the desired tension in the various layers as they are being oriented, aligned, cut, etc.  
     [0030] The various component layers shown in FIG. 5 can be assembled employing an assembly process of the present invention, such as that illustrated in FIGS. 6 a  and  6   b.    
     [0031]FIGS. 6 a  and  6   b  illustrate an assembly method for assembling a membrane electrode sealed assembly. A cell section  312  is unrolled from a first gasket roll  300 , block  410 . The active area  317  for this first cell section  312  is punched out, block  412 . A cell section  324  from the first GDL roll  320  is aligned with the cell section  312 , block  414 . The perimeter of the GDL cell section  324  is then cut to its final size, block  416 . A cell section  336  from the catalyst coated membrane roll  328  is aligned with the cell section  324 , block  418 . A cell section  344  of the second GDL roll  340  is aligned with the cell section  336 , block  420 . The perimeter of the cell section  344  is then cut to its final size, block  422 . A cell section  356  is unrolled from a second gasket roll  348 , block  424 , and the active area portion  351  is punched out from the cell section  356 , block  426 . The cell section  356  is aligned with the cell section  344  from the second GDL roll  340 , block  428 . Now that the component layers are stacked and aligned properly, the adhesive is activated in order to allow it to flow and cure, block  430 . As discussed above, the adhesive can then act to hold the layers of the membrane electrode sealed assembly together and seal about the perimeter. The perimeter of the cell sections is then cut to final size, block  432 . The membrane electrode sealed assembly is now ready for assembly between separator plates (not shown in these figures), block  434 , in order to form an individual cell of a fuel cell assembly.  
     [0032] Where tension is desired during the alignment process in order to minimize wrinkles and twisting, the particular component layer may be left uncut from the roll. The roll can then be used to maintain the desired tension until the proper alignment is secured, after which, the particular cell section is cut from the particular roll.  
     [0033]FIG. 7 illustrates an alternative embodiment of the component rolls shown in FIG. 5, which can be assembled using the assembly method shown in FIGS. 8 a  and  8   b.  In this embodiment, elements that are similar to those in FIG. 5 will have the same general reference number, except they will be 600-series numbers. The first gasket roll  600 , with its cell section  608 , the second GDL roll  640 , with its cell section  644 , and the second gasket roll  648 , with its cell section  656 , are essentially the same as in the embodiment of FIG. 5. In this embodiment, however, the first catalyst layer  632  is applied to the GDL roll  620  as it comes off of the roll, thus forming a different cell section  624 , which is catalyst coated. This coating is preferably rolled-on, but other methods of application may also be employed if so desired. Also, the membrane roll  628  does not include any catalyst material when pulled from the roll. Rather a second layer of catalyst material  634  is applied as the membrane comes off of the roll. This forms a different cell section  636  than the one in FIG. 5. As an alternative, the catalyst layer  634  can be applied to the second GDL roll  640  rather than the membrane  628 , if so desired.  
     [0034]FIGS. 8 a  and  8   b  illustrate an alternative embodiment of the assembly method illustrated in FIGS. 6 a  and  6   b.  This method includes the steps of perforating an active area portion for each gasket cell section on both rolls prior to rolling, block  510 , and unrolling a cell section!from the first gasket roll, block  512 . A cell section from the first GDL roll is unrolled and the perimeter is cut to final size, block  514 , before aligning the cell section of the first GDL with the cell section of the first gasket roll, block  516 . A first layer of catalyst material is applied to the cell section of the first GDL roll, block  518 , and a cell section from a membrane roll is unrolled in alignment with the GDL, block  520 . A second layer of catalyst is applied to the membrane cell section, block  522 , and the perimeter of the membrane is cut to its final size, block  524 . A cell section from the second GDL is unrolled and the perimeter of this cell section is cut to its final size, block  526 , before aligning with the membrane, block  528 , and the cell section from the second gasket is unrolled, block  530 , and aligned with the cell section from the second GDL roll, block  532 . The active area portion is then removed from both gaskets, along the perforations, block  534 , and then the adhesive is activated and cures, block  536 . The perimeter of the gasket cell sections are cut to final size, block  538  and the membrane electrode sealed assembly is ready to be assembled between separator plates, block  540 .  
     [0035] Of course, since several of the steps of FIGS. 8 a  and  8   b  are different than the steps of  6   a  and  6   b,  many of the different steps can be applied in different combinations between the two illustrated embodiments in order to achieve the final assembled membrane electrode sealed assembly.  
     [0036] 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.