Abstract:
A method for forming variable section thicknesses from a uniformly thick resinous sheet in a PEM fuel cell. A method for forming a seal in a fuel cell includes a step of providing a sheet including a layer of resinous material. A first fold is formed in the sheet. The first fold extends from a substantially planar section of the sheet having a first side section and a second side section opposing the first side section and connected by a top section. A gasket is formed by folding the first fold over towards the planar section to form a compound fold. The compound fold is placed between a first fuel cell component and a second fuel cell component to form the seal therein. A fuel cell incorporating the gasket is also provided.

Description:
TECHNICAL FIELD 
       [0001]    In at least one aspect, the present invention is related to catalyst layers used in fuel cell applications. 
       BACKGROUND 
       [0002]    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. 
         [0003]    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. 
         [0004]    Some prior art fuel cells include gaskets between the catalyst electrodes and ion conducting membrane. Different areas of the repeating cell designs have different functional requirements which are satisfied by utilizing varying cross sectional thicknesses of materials. For example, the fuel cell section depicted in  FIG. 1  illustrates a prior art sealing configuration. Fuel cell stack  10  includes a sealing gasket  12  interposed between gas diffusion layers  14  and  16  as well as between bipolar plates  20  and  22 . In this example, gasket  12  should be thin when between the gas diffusion layers and thicker between the bipolar plates. Some prior art gaskets use beads  24  in conjunction with a sealing sheet  26  in order to achieve the desired thickness variation. 
         [0005]    Accordingly, the present invention provides improved designs for fuel cell gasket components. 
       SUMMARY 
       [0006]    The present invention solves one or more problems of the prior art by providing in at least one embodiment a method for forming a gasket for fuel cell applications. The method includes a step of providing a substantially planar sheet including a layer of resinous material. A first folded sheet is formed from the substantially planar sheet. The first folded sheet has a first fold that extends from a substantially planar section of the substantially planar sheet having a first side section and a second side section opposing the first side section and connected by a top section. A gasket is formed by folding the first fold over towards the planar section to form a compound fold. The compound fold is placed between a first fuel cell component and a second fuel cell component. Advantageously, the gasket forms an electrically insulation, sealing, spacing functionality, or combinations thereof. 
         [0007]    In another embodiment, a fuel cell formed by the method set forth above is provided. The fuel cell includes a membrane electrode assembly having an anode side and a cathode side. A first flow field is disposed over the anode side and a second flow field is disposed over the cathode side. A first gas diffusion medium is interposed between the anode side and the first flow field and a second gas diffusion medium is interposed between the cathode side and the second flow field. A gasket is interposed between the first flow field and the second flow field, the gasket defining a central opening. The gasket optionally includes a peripheral sealing region including a resinous material with a compound fold therein. The compound fold includes a first fold in a sheet extending from a substantially planar region of the sheet. The first fold has a first side section and a second side section opposing the first side section such that the first side section and the second side section are connected by a top section. The compound fold includes a second fold formed by folding the first fold over towards a planar section of the sheet. 
     
    
     
       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  is a perspective view of a fuel seal stack using a prior art gasket system; 
           [0010]      FIG. 2A  is a cross section of an embodiment of a fuel cell using a gasket having folded regions; 
           [0011]      FIG. 2B  is a cross section of an embodiment of a fuel cell using a gasket having folded regions; 
           [0012]      FIG. 3  is a perspective view of an embodiment of a fuel cell using a gasket having folded regions; 
           [0013]      FIG. 4  is a top view of a fuel cell gasket; 
           [0014]      FIG. 5  is a cross sectional view of a fuel cell gasket; and 
           [0015]      FIGS. 6A and 6B  provide a schematic flow chart of a method for forming a gasket for fuel cell applications. 
       
    
    
     DETAILED DESCRIPTION 
       [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  FIGS. 2A ,  2 B, and  3 , schematics illustrating the incorporation of a gasket into a fuel cell is provided.  FIG. 2  is a schematic cross section of a fuel cell that incorporates an embodiment of a gasket while  FIG. 3  is a perspective view of a portion of a fuel cell stack using the gasket. Fuel cell  30  includes a membrane electrode assembly which includes anode catalyst layer  34 , cathode catalyst layer  36 , and ion conducting membrane (i.e., proton exchange membrane, ionomer, etc.)  38 . Ion conducting membrane  38  is interposed between anode catalyst layer  34  and cathode catalyst layer  36  with anode catalyst layer  34  disposed over the first side of ion conducting membrane  38 , and cathode catalyst layer  36  disposed over the second side of ion conducting membrane  38 . Fuel cell  30  also includes porous gas diffusion layers  42  and  44 . Gas diffusion layer  42  is disposed over anode catalyst layer  34  while gas diffusion layer  44  is disposed over cathode catalyst layer  36 . Fuel cell  30  includes anode flow field plate  46  disposed over gas diffusion layer  42 , and cathode flow field plate  48  disposed over gas diffusion layer  44 . Fuel cell  30  utilizes gasket  50  in order to provide an edge seal. 
         [0022]    With reference to  FIGS. 2A ,  2 B,  3 ,  4 , and  5 , schematics illustrating the design of gasket  50  are provided.  FIG. 4  is a top view of gasket  50  while  FIG. 5  is a cross sectional view of gasket  50 . In general, gasket  50  includes peripheral sealing region  52  which defines central opening  54 . Gasket  50  includes compound fold  56  in region  58  in order to provide sealing between anode flow field plate  46  and cathode flow field plate  48 . In another refinement, the gasket also provides a seal for reactant and coolant header apertures depicted generally by item  59 . Examples of such apertures are set forth in U.S. Pat. No. 8,524,414; the entire disclosure of which is hereby incorporated by reference. The term “compound fold” as used herein means a region that is folded at least twice. For example, compound fold  56  includes first fold  60  and second fold  62 . Near the edge  64  of the gas diffusion layers, gasket  50  includes thinner (i.e., unfolded) region  66  in order to provide sealing therein. In a refinement, gasket  50  includes two compound folds—compound fold  56  and compound fold  68 . In one variation, a portion of gasket  50  is interposed between a catalyst layer (anode or cathode catalyst layer) and ion-conducting membrane  38 .  FIG. 2A  depicts the gasket interposed between the anode catalyst layer and the ion-conducting membrane.  FIG. 2B  depicts an example with gasket  50  interposed between and contacting gas diffusion layer  42  and gas diffusion layer  44 . 
         [0023]    In one variation, gasket  50  is formed from a sheet of resinous material. In a refinement, the sheet of resinous material includes a thermoplastic polymer. Examples of suitable thermoplastic polymers include, but are not limited to, polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polyphenylene ether, polyphenylene oxide, and combinations thereof. The sheet of resinous material may include a single layer or a laminate structure. Typically, the laminate structure is a multilayer thermoplastic or a thermoplastic with a non-thermoplastic elastomer layer (e.g., silicon, ethylene propylene diene monomer rubber, etc.). In a refinement as set forth in  FIG. 5 , the laminate structure includes a first solid layer  70  and a first foamed layer  72 , and an optional second solid layer  74 . First foamed layer  72  is interposed between the first solid layer  70  and the second solid layer  74 . In another refinement, the first solid layer, the second solid layer, and the first foamed layer each independently include a thermoplastic polymer as set forth above. 
         [0024]    With reference to  FIGS. 6A and 6B , a method for forming a seal in a fuel cell is provided. 
         [0025]    The method includes a step of providing substantially planar sheet  80  which includes a layer of resinous material. In a refinement, the layer of resinous material includes a thermoplastic polymer as set forth above. In another refinement, substantially planar sheet  80  has a thickness from about 0.050 mm to about 1 mm. First folded sheet  82  is formed from substantially planar sheet  80 . First folded sheet  82  includes first fold  60  which typically includes protrusion section  84  that extends substantially planar section  88 . First fold  60  includes first side section  90  and second side section  92  which opposes first side section  90 . First side section  90  and second side section  92  are connected by top section  94 . First folded sheet  82  also includes intermediate folds  96  and  98 . 
         [0026]    Typically, first fold  60  is formed by drawing substantially planar sheet  80  over mandrel  100  as depicted by step a). In this step, uniformed thinning can be maintained. In a refinement, substantially planar sheet  80  is heated to assist in forming first fold  60 . In this regard, sheet  80  is typically heated to a temperature from about 90 to 300 degrees C. In step b), a vacuum is applied (i.e., vacuum forming) to impart a mandrel form onto the sheet thereby forming the first fold  60 . After such forming, first folded sheet  82  with the first fold therein is removed from the mandrel in step c). In step d), gasket  50  is formed by folding the first fold, and in particular, protrusion section  84  over towards the planar section to form compound fold  56 . Gasket  50  and, therefore, compound  56  are placed between first fuel cell component  102  and second fuel cell component  104  to form a seal. In a refinement, gasket  50 , and in particular, the compound fold is allowed to cool after being placed between first fuel cell component  102  and second fuel cell component  104 . In a refinement as set forth above, the first fuel cell component and the second fuel cell component are each independently flow fields. In one refinement, gasket  50  is used to form a seal between such component and/or in apertures in such components. In another refinement, gasket  50  is used to form an insulating layer between the fuel cell components and in particular electrically conductive fuel cell components such as the flow field plates. In another refinement, gasket  50  is used to provide thicker insulation or spacing material in desired areas between electrically conductive components of serially adjacent fuel cells. Additional placement of gasket  50  are set forth above with respect to the description of  FIGS. 2A and 2B . 
         [0027]    In a refinement, sheet  80  has a laminate structure. Typically, the laminate structure is a multilayer thermoplastic or a thermoplastic with a non-thermoplastic elastomer layer. In a refinement, the laminate structure includes a first solid layer and a first foamed layer, and an optional second solid layer, the first foamed layer being interposed between the first solid layer and the second solid layer. In another refinement, the first solid layer, the second solid layer, and the first foamed layer each independently include a thermoplastic polymer. 
         [0028]    While exemplary embodiments are described above, it is not intended that these embodiments 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. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.