Abstract:
According to an example embodiment, a method of making a fuel cell component includes permeating at least a portion of a component layer with a polymer. The portion of the component layer is adjacent an edge of the component layer. Some of the polymer is allowed to extend beyond the edge to thereby establish a flap beyond the edge of the component layer. A fuel cell component includes a component layer having a portion adjacent an edge of the layer that is impregnated with a polymer material and a flap of the polymer material extending beyond the edge.

Description:
BACKGROUND 
       [0001]    Fuel cells are useful for generating electricity based on an electrochemical reaction. Several components of the fuel cell are designed to facilitate the electrochemical reaction. One of the challenges associated with operating a fuel cell is maintaining an adequate seal at various locations within the cell stack assembly. For example, it is desirable to maintain the reactants in the chemically active portion of the fuel cell to realize the electrochemical reaction. In the case of a phosphoric acid fuel cell, it also is desirable to maintain the phosphoric acid in appropriate locations within the cell stack assembly. Various proposals have been made to address such concerns, however, some of them may not provide adequate sealing performance while others introduce undesired additional expense into the cost of a fuel cell system. 
       SUMMARY 
       [0002]    According to an example embodiment, a method of making a fuel cell component includes permeating at least a portion of a component layer with a polymer. The portion of the component layer is adjacent an edge of the component layer. Some of the polymer is allowed to extend beyond the edge to thereby establish a flap beyond the edge of the component layer. 
         [0003]    A fuel cell component includes a component layer having a portion adjacent an edge of the layer that is impregnated with a polymer material and a flap of the polymer material extending beyond the edge. 
         [0004]    The various features and advantages of at least one disclosed example embodiment will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  diagrammatically illustrates a fuel cell component designed according to an embodiment of this invention. 
           [0006]      FIGS. 2A-2C  schematically illustrate an arrangement and method for making a fuel cell component according to an embodiment of this invention. 
           [0007]      FIG. 3  illustrates features of an example flap configuration. 
           [0008]      FIG. 4  illustrates another example arrangement for making a fuel cell component according to an embodiment of this invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]      FIG. 1  schematically shows a fuel cell component  20 . In this example, the component  20  comprises a porous, graphitized substrate  22  with a polymer impregnated region  24 . In the illustrated example, the polymer impregnated region  24  is situated around a periphery of the component  20 . In embodiments that are configured for use in a phosphoric acid fuel cell assembly, the polymer impregnated into the region  24  is chemically resistant to phosphoric acid and provides a seal against phosphoric acid movement through or across the region  24 . The seal provided by the impregnated region  24  is also useful for controlling outboard reactant leaks (e.g., in-plane movement out of the substrate). The impregnated region  24  in the illustrated example is a seal to prevents reactant leaks and phosphoric acid leaks. In some embodiments less than the entire periphery includes an impregnated region. For example, some components have a two-sided or three-sided seal. In such embodiments, at least the side or portion of the component that includes the region  24  is a sealed side or portion of the component. 
         [0010]    The example component  20  may be used as an electrode in a phosphoric acid fuel cell. In some examples, the component  20  comprises a gas diffusion layer. 
         [0011]    The example component  20  includes a flap  26  of the polymer material protruding from or extending beyond an edge  28  of the substrate  22 . In this example a flap  26  is provided on each of the edges  28  around the periphery of the substrate  22 . Other embodiments include a flap  26  on less than all of the edges  28  (e.g., a rectangular substrate  22  may have a flap  26  at two oppositely facing edges but no flap  26  on the other two edges). Other embodiments include more than one flap  26  on at least one of the edges  28 . 
         [0012]    The flap  26  provides a barrier for preventing fluid movement along an outer surface (i.e., the edge  28 ) of the substrate  22  when the component  20  is situated within a fuel cell assembly. For example, the flap  26  is configured to prevent phosphoric acid migration or movement along the outer edge of the cell stack assembly. 
         [0013]      FIGS. 2A-2C  schematically illustrate an arrangement and method for making a fuel cell component such as the component  20  shown in  FIG. 1 . In this example, a heated press includes plates  30 , which may comprise graphite for example. The porous substrate  22  is situated between the plates  30  with at least one polymer film layer situated against the substrate  22 . In the example of  FIG. 2A , four separate polymer film layers are situated between the plates  30 . Polymer film layers  32 A and  32 B are situated directly against the substrate  22  on opposite sides of the substrate  22 . Additional polymer film layers  34 A and  34 B are included in this example. In some situations, a desired thickness of the polymer film layers may be achieved by using a single polymer film layer on each side of the substrate  22 . Depending on commercially available film thicknesses, some examples include providing multiple polymer film layers to achieve a desired thickness. 
         [0014]    In some embodiments, an exterior perimeter of the film layer  32 A corresponds to the exterior of the substrate  22 . An interior perimeter is situated to establish a surface area of the polymer film  32 A. The total surface area of the polymer film  32 A is less than the total surface area of the substrate  22 . The interior perimeter may be selected to correspond to the outside border of the chemically active region of the substrate  22  so that the polymer impregnated into the substrate  22  does not hinder or interfere with the electrochemical reaction that is desired within a fuel cell incorporating the component  20 . 
         [0015]    Example materials useful as a polymer film are commercially available, such as PEEK™ and Teflon™ (e.g. PFA). The polymer material in the illustrated example is a high melt flow, thermally stable, non-wetting material that is chemically resistant to phosphoric acid. The high melt flow characteristics of the material correspond to a minimum of 0.25 g/10 mins per ASTM D2116. The example polymer material is thermally stable below 220° C. 
         [0016]    In other examples, a polymer powder is used instead of a polymer film. Given the particular substrate characteristics of a particular fuel cell arrangement, those skilled in the art who have the benefit of this description will be able to select an appropriate polymer film, powder or other material composition to meet their particular needs. 
         [0017]    As can be appreciated from  FIG. 2A , the polymer film layers  32 A and  32 B have a first thickness T 1 . The polymer film layers  34 A and  34 B have a second, smaller thickness T 2 . The substrate  22  has a third thickness T 3 . The desired total thickness of all the polymer films involved in the manufacturing process corresponds to a porosity of the substrate  22  multiplied by the thickness T 3  of the substrate  22 . The minimum thickness of the polymer films (collectively if there are multiple layers) is approximately equal to the product of the porosity and the third thickness T 3 . In some examples, the porosity of the substrate  22  is not entirely consistent across the entire substrate. One example embodiment includes using the maximum porosity of the substrate to determine the desired polymer film thickness. Using the maximum porosity assists in establishing an adequate seal in the region  24 . 
         [0018]    In the illustrated example, T 1 +T 2  is approximately equal to one-half of the porosity of the substrate  22  multiplied by the thickness of the substrate  22 . Providing the film layers  32  and  34  on each side of the substrate  22  yields a total thickness of the polymer films that correspond to the porosity of the substrate  22  multiplied by the thickness T 3  of the substrate  22 . 
         [0019]    One feature of the example of  FIG. 2A  is that a thicker polymer film layer is placed closer to the substrate  22  than another polymer film layer that is thinner. The layers  32 A and  32 B are thicker than the layers  34 A and  34 B and, therefore, the layers  32 A and  32 B are placed against the substrate  22 . Situating thinner films further from the substrate  22  facilitates more uniform melting and distribution of the polymer used to impregnate the region  24  in some examples. 
         [0020]    For purposes of facilitating an easy release of the impregnated substrate from between the plates  30 , release films  40  are included between the most exterior polymer film layers and the plates  30 . An example release film  40  includes at least one opening within the film to facilitate allowing gases to escape from between the release films  40  included in the example of  FIGS. 2A and 2B . Allowing gases to escape in this way avoids any undesired variations or defects along the substrate  22  and, in particular, the polymer impregnated region  24 . 
         [0021]    During the manufacturing process, the substrate  22 , polymer film layers  32  and  34  and release films  40  are compressed between the plates  30  as shown in  FIG. 2A . A first pressure is applied to the layers between the plates  30  while the layers are heated up until at least the polymer film layers  32  and  34  reach a melting temperature of the polymer. In one example, the first pressure is less than 100 psi. After the melting temperature has been reached at a coldest portion of the polymer film layers, the pressure is increased while temperature increases to a second temperature that exceeds the melting temperature of the polymer. In one example, 100 psi pressure is used while increasing the temperature of at least the polymer material until that temperature is approximately 20° C. higher than the melting temperature of the polymer. A ten percent tolerance is acceptable in some examples (e.g., the temperature reached while applying the second, higher pressure may be between 18° and 22° above the melting temperature of the polymer). In some examples, the higher pressure and higher temperature is applied for a time on the order of one minute. Those skilled in the art that have the benefit of this disclosure will be able to choose an appropriate temperature and time to meet their particular needs for their selected polymer and component configuration. 
         [0022]    The second pressure and increased pressure causes the plates  30  to move closer together as shown in  FIG. 2B . As a result of the high temperature and the pressure applied, the polymer material of the polymer films melts and impregnates the region  24  along the portions of the substrate  22  where the polymer films were applied including the edges  28 . 
         [0023]    As can be appreciated from  FIG. 2B , some of the polymer has moved through the substrate  22  passed the edges  28  so that there is some polymer material shown at  26 ′ extending beyond each edge  28 . The polymer shown at  26 ′ may have a desired geometry as a result of some molding processes. In the illustrated example, the polymer material at  26 ′ does not have a shape or profile corresponding to a desired geometry of the flap  26 .  FIG. 2C  schematically shows a machining device  50  that machines away (e.g., trims off) some of the polymer material  26 ′ to establish a selected geometry of the flaps  26 . 
         [0024]      FIG. 3  shows one example flap geometry. In this example, the flap  26  has a flap length L extending in a direction away from the edge  28  and a flap thickness T 4  extending in a direction transverse to the direction of the length. The flap thickness T 4  is less than the thickness T 3  of the substrate  22  in the illustrated embodiment. The flap thickness T 4  may be as large as the substrate thickness T 3  in some examples. 
         [0025]    The length L is at least twice the flap thickness T 4  in some embodiments. In one example, the length L is approximately 10 mil and the thickness T 4  is approximately 5 mil. Such a flap configuration provides a 25 mil distance that a fluid, such as phosphoric acid, must travel if the fluid were moving in an undesired manner along the edge  28  of the substrate  22 . This distance and the hydrophobic barrier nature of the polymer are sufficient to prevent undesired fluid movement along the edge  28 , which facilitates better fluid management and control within a fuel cell assembly. 
         [0026]    The flap geometry in this example includes a generally rectangular cross-section. Other profiles or cross-sections, such as semi-circular, triangular or another polygon, may be useful for some situations. 
         [0027]      FIG. 4  illustrates an alternative configuration of at least one of the plates  30 . In this example, the plate  30  includes a channel  60  situated near a shoulder  62  against which the edge  28  of the substrate  22  is received. When the polymer melts and impregnates the substrate  22  some of the polymer flows into the channel  60 . The configuration of the channel  60  establishes the selected geometry or shape of the flap  26 . With such a plate  30  it may be possible to avoid machining away or trimming off excess polymer material. 
         [0028]    Manufacturing a fuel cell component utilizing the principles of this description may provide significant cost savings associated with the otherwise labor-intensive approach to providing a fluid barrier within a fuel cell assembly. For example, the flap  26  is integrated into the component  20 , such as an electrode, instead of having to be provided as a separate component. This reduces labor and expenses associated with assembly a cell stack assembly. 
         [0029]    While various features and aspects are described above in connection with one or more particular embodiments, those features and aspects are not necessarily exclusive to the corresponding embodiment. The disclosed features and aspects may be combined in other ways than those specifically mentioned above. In other words, any feature of one embodiment may be included with or substituted for a feature of another embodiment. 
         [0030]    The preceding description is illustrative rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of the contribution to the art provided by the disclosed examples. The scope of legal protection provided to the invention can only be determined by studying the following claims.