Abstract:
A fuel cell component includes a sub-gasket including a structural component and a thermally conductive layer. The sub-gasket defines a central opening while the structural component includes a first side and a second side. The sub-gasket also has an inner portion proximate to the central opening and an outer portion. The inner portion is positioned between the cathode layer outer edge and the ion-conducting membrane outer edge or between the anode layer outer edge and the ion-conducting membrane outer edge. Finally, the thermally conductive layer contacts the second side of the structural component. Advantageously, the thermally conductive layer dissipates locally generated heat caused by unintended particles falling on the sub-gasket.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Fuel cells are used as an electrical power source in many applications. In particular, fuel cells are proposed for use in automobiles to replace internal combustion engines. A commonly used fuel cell design uses a solid polymer electrolyte (“SPE”) membrane or proton exchange membrane (“PEM”), to provide ion transport between the anode and cathode. 
         [0002]    In proton exchange membrane type fuel cells, hydrogen is supplied to the anode as fuel, and oxygen is supplied to the cathode as the oxidant. The oxygen can either be in pure form (O 2 ) or air (a mixture of O 2  and N 2 ). PEM fuel cells typically have a membrane electrode assembly (“MEA”) in which a solid polymer membrane (i.e., ion conducting membrane) has an anode catalyst on one face, and a cathode catalyst on the opposite face. The anode and cathode layers of a typical PEM fuel cell are formed of porous conductive materials, such as woven graphite, graphitized sheets, or carbon paper to enable the fuel to disperse over the surface of the membrane facing the fuel supply electrode. Each electrode has finely divided catalyst particles (for example, platinum particles) supported on carbon particles to promote oxidation of hydrogen at the anode, and reduction of oxygen at the cathode. Protons flow from the anode through the ionically conductive polymer membrane to the cathode where they combine with oxygen to form water, which is discharged from the cell. The MEA is sandwiched between a pair of porous gas diffusion layers (“GDL”) which in turn are sandwiched between a pair of non-porous, electrically conductive elements or plates. The plates function as current collectors for the anode and the cathode, and contain appropriate channels and openings formed therein for distributing the fuel cell&#39;s gaseous reactants over the surface of respective anode and cathode catalysts. In order to produce electricity efficiently, the polymer electrolyte membrane of a PEM fuel cell must be thin, chemically stable, proton transmissive, non-electrically conductive and gas impermeable. In typical applications, fuel cells are provided in arrays of many individual fuel cell stacks in order to provide high levels of electrical power. 
         [0003]    Some prior art fuel cells include sub-gaskets between the catalyst electrodes and ion conducting membrane. During manufacture and operation of a fuel cell, it is possible that one or more catalyst containing particles can become attached to the sub-gasket, and these unintended particles are capable of generating levels of thermal energy that have the ability to elevate temperatures of polymer based sub-gasket material to their melt temperatures when exposed to combustible mixtures of hydrogen and oxygen. The fuel cell stack is regularly exposed to such combustible mixtures as a method to start the fuel cell from freeze conditions or during anode bleed to the cathode to purge nitrogen. In many cases, the sub-gasket material becomes the primary thermal conduction media for the energy generated. Although the prior art subgasket designs work reasonably well during normal operation, these particles represent a manufacturing defect that can overwhelm the thermal properties of these sub-gaskets. 
         [0004]    Accordingly, the present invention provides improved designs for dissipating the thermal energy generated by unintended particles resulting in localized heating in a fuel cell. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention solves one or more problems of the prior art by providing in at least one embodiment a fuel cell component for dissipating heat. The fuel cell component includes a sub-gasket including a structural component and a thermally conductive layer. The sub-gasket defines a central opening while the structural component includes a first side and a second side. The sub-gasket also has an inner portion proximate to the central opening and an outer portion. The inner portion is positioned between the cathode layer outer edge and the ion-conducting membrane outer edge or between the anode layer outer edge and the ion-conducting membrane outer edge. Finally, the thermally conductive layer contacts the second side of the structural component. Advantageously, the thermally conductive layer is tailored to dissipate heat energy. Based on thickness of layer the thermal energy can be dissipated before the sub-gasket is exposed to thermal energy (or melt temp) that will cause premature failure (i.e., melting of polymer sub-gasket layer which results in anode and cathode streams mixing). 
         [0006]    In another embodiment, a fuel cell component is provided. The fuel cell component includes a cathode catalyst layer having a cathode layer outer edge, an anode catalyst layer having an anode layer outer edge, an ion-conducting membrane, a sub-gasket, and a shim. The ion-conducting membrane has an ion-conducting membrane outer edge interposed between the cathode catalyst layer and the anode catalyst layer. The sub-gasket includes a structural component and a thermally conductive layer and defines a central opening. The structural component has a first side and a second side while the sub-gasket having an inner portion proximate to the central opening and an outer portion. The inner portion is positioned between the cathode catalyst layer outer edge and the ion-conducting membrane outer edge or between the anode catalyst layer outer edge and the ion-conducting membrane outer edge. The thermally conductive layer contacts the second side of the structural component. Finally, the shim contacts the thermally conductive layer. 
         [0007]    In yet another embodiment, a fuel cell component for providing thermal dissipation within a polymer layer is provided. The fuel cell component includes a sub-gasket having a first side, a second side, and a peripheral section that defines a central opening. The peripheral section has an inner portion proximate to the central opening and an outer portion. The proximate section is positionable between a fuel cell cathode layer outer edge and a fuel cell ion-conducting membrane outer edge or between a fuel cell anode layer outer edge and a fuel cell ion-conducting membrane outer edge. The central opening is aligned in a fuel cell such that a fuel cell active region is positioned therein. The fuel cell component also includes a thermally conductive layer adhered to the outer region of the sub-gasket and a shim contacting the second side of the sub-gasket. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Exemplary embodiments of the present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0009]      FIG. 1  provides a schematic illustration of a fuel cell incorporating a separator; 
           [0010]      FIG. 2  is a schematic cross section of a fuel cell incorporating the sub-gasket; 
           [0011]      FIG. 3  is a perspective view of the sub-gasket. 
           [0012]      FIG. 4  is a partial exploded view of a fuel cell incorporating a sub-gasket; 
           [0013]      FIG. 5  is an exploded view of the fuel cell incorporating a sub-gasket; 
           [0014]      FIG. 6  provides a perspective view of a section of a sub-gasket having a thermally conductive adhesive; and 
           [0015]      FIG. 7  provides a perspective view of a sub-gasket having a thermally conductive metal layer. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0016]    Reference will now be made in detail to presently preferred compositions, embodiments and methods of the present invention, which constitute the best modes of practicing the invention presently known to the inventors. The Figures are not necessarily to scale. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the invention and/or as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0017]    Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: percent, “parts of,” and ratio values are by weight; the term “polymer” includes “oligomer,” “copolymer,” “terpolymer,” and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; molecular weights provided for any polymers refers to number average molecular weight; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; the first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation; and, unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property. 
         [0018]    It is also to be understood that this invention is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present invention and is not intended to be limiting in any way. 
         [0019]    It must also be noted that, as used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components. 
         [0020]    Throughout this application, where publications are referenced, the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains. 
         [0021]    With reference to  FIG. 1 , a schematic cross section of a fuel cell that incorporates an embodiment that incorporates a sub-gasket is provided. Fuel cell  10  includes the membrane electrode assembly  12  which includes anode catalyst layer  14 , cathode catalyst layer  16 , and ion conducting membrane (i.e., proton exchange membrane, ionomer, etc.)  20 . Ion conducting membrane  20  is interposed between anode catalyst layer  14  and cathode catalyst layer  16  with anode catalyst layer  14  disposed over the first side of ion conducting membrane  20 , and cathode catalyst layer  16  disposed over the second side of ion conducting membrane  20 . A portion of sub-gasket  21  is interposed between anode catalyst layer  14  and ion conducting membrane  20 . The details of sub-gasket  21  are set forth below. In a variation, fuel cell  10  also includes porous gas diffusion layers  22  and  24 . Gas diffusion layer  22  is disposed over anode catalyst layer  14  while gas diffusion layer  24  is disposed over cathode catalyst layer  16 . The fuel cell  10  includes anode flow field plate  26  disposed over gas diffusion layer  22 , and cathode flow field plate  28  disposed over gas diffusion layer  24 . 
         [0022]    With reference to  FIGS. 2 and 3 , a sub-gasket for fuel cell applications is provided.  FIG. 2  is a schematic cross section of a fuel cell incorporating the sub-gasket.  FIG. 3  is a perspective view of the sub-gasket. Fuel cell  10  includes anode catalyst layer  14  having an anode layer outer edge  30  and cathode catalyst layer  16  which has cathode layer outer edge  32 . Ion-conducting membrane  20  has ion-conducting membrane outer edge  34 . As set forth above, ion-conducting membrane  20  is interposed between anode catalyst layer  14  and cathode catalyst layer  16 . Sub-gasket  40  includes structural component  42  which has first side  44  and second side  46 . Typically, structural component  42  is a polymeric component able to withstand temperatures from 0° C. to 150° C. without substantial degradation (e.g., melt temperature 250° C. to 260° C.). In a refinement, structural component  42  comprises an ester such as polyethylene naphthalate and polyethylene terephthalate (PET). Additional polymers that can be used for structural component  42  include, but are not limited to, polyimides (e.g., KAPTON™), thermoplastics (e.g., poly(p-phenylene sulfide)) and other types of polymers that can operate effectively with respect to temperature, hydrogen and oxygen permeation, and modulus. In another variation, structural component  42  has a thickness from about 1 to 3 mil. Structural component  42  defines central opening  48 . Structural component  42  includes inner portion  50  proximate to central opening  48  and an outer portion  52 . The inner portion  50  is positioned between cathode layer edge  32  and ion-conducting membrane outer edge  34  or between anode layer outer edge  30  and ion-conducting membrane outer edge  34 . Sub-gasket  40  includes thermally conductive layer  56  that is adhered to the second side of sub-gasket  40 . In a refinement, thermally conductive layer  56  has a thickness from about 5 microns to about 50 microns. In particular, when thermally conductive layer  56  includes a metal layer and an adhesive, the metal layer can be about  5  microns while the adhesive layer is about  25  microns. Shim  58  contacts thermally conductive layer  56 . Typically, shim  58  includes a polymer such as an ester (polyethylene naphthalate). In yet another refinement, shim  58  has a thickness from about 2 to 6 mil. Shim  58  provides structural support, limits plate flexing due to pressure differentials in feed region, and provides hard stop to control plate to plate spacing. 
         [0023]      FIGS. 4 and 5  provide exploded views showing integration of sub-gasket  40  into a fuel cell. Fuel cell  10  includes active area  60  which includes anode catalyst layer/gas diffusion medium combination  62 , cathode catalyst layer/gas diffusion medium  64 , and ion conducting membrane  20 . Anode catalyst layer/gas diffusion medium combination  62  is disposed over ion conducting membrane  20  with sub-gasket  40  interposed between the edge regions of anode catalyst layer/gas diffusion medium combination  62  and ion conducting membrane  20 . Ion conducting membrane  20  is disposed over cathode catalyst layer/gas diffusion medium  64 . Cathode flow field plate  28  includes cathode plate half  66  and cathode plate half  68 . It should be appreciated that a plurality of the fuel cell units depicted in  FIGS. 4 and 5  are typically stacked to form a fuel cell stack.  FIG. 4  also depicts shim  58 . Seal  70  is used to effect sealing between fuel cell units in such stacks. 
         [0024]    With reference to  FIGS. 6 and 7 , variations of the sub-gasket are provided.  FIG. 6  provides a perspective view of a section of a sub-gasket having a thermally conductive adhesive. In this variation, adhesive layer  74  (layer  56  of  FIG. 2 ) is adhered to structural component  42 . Adhesive layer  74  is formed from an adhesive with conductive particles dispersed therein. In a refinement, the thermally conductive particles include a component selected from the group consisting of carbon, silver, copper, nickel, steel, other metals, metal alloys, and combinations thereof. In another refinement, the adhesive is a thermally activated adhesive such as polyesters, thermoplastics, polyurethanes, polyalcohol polymers, polyamine polymers, ethylene copolymers, epoxies, urethanes, polyimides, and combinations thereof. More specific examples of the adhesive include, but are not limited to, ethylene acrylic copolymers, ethylene-vinyl acetate, and combinations thereof. Typically, the adhesive melts or solidifies at a temperature from about 50° C. to about 125° C. In another refinement, the adhesive melts or solidifies at a temperature from about 50° C. to about 95° C. 
         [0025]      FIG. 7  provides a perspective view of a sub-gasket having a thermally conductive metal layer. In this variation, metal layer  76  (between layer  56  and  42  of  FIG. 2 ) is disposed over and contacts structural component  42 . In a refinement, metal layer  76  is a metallic film deposited on the sub-gasket or a metal foil contacting the sub-gasket. Such metal layers may be deposited by sputtering, evaporation, chemical vapor deposition, and the like. In another refinement, adhesive layer  78  is disposed over metal layer  76  to provided adhesion to shim  58  ( FIG. 2 ). 
         [0026]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.