Abstract:
The present invention isolates the fluid streams flowing into and out of a fuel cell stack from the terminal plates so that the fluid streams and terminal plates do not come into contact with one another. The prevention of the fluid streams from contacting the terminal plate eliminates corrosion concerns associated with the terminal plate. The present invention accomplishes this isolation through the use of headers having fluid passageways therein that route the fluid streams in and/or out of the fuel cell stack while preventing contact between the fluid streams and the terminal plate.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to fuel cell stacks and, more particularly, to inlet/outlet manifold headers within a fuel cell stack.  
       BACKGROUND OF THE INVENTION  
       [0002]     Fuel cells have been and are proposed for use as a power source in many applications. A typical fuel cell assembly includes a plurality of individual fuel cells stacked one upon another to form a fuel cell stack which is held in compression. Typically, each fuel cell comprises an anode layer, a cathode layer, and an electrolyte interposed between the anode layer and the cathode layer. The fuel cell stack requires a significant amount of compressive force to squeeze the fuel cells of the stack together. The need for the compressive force comes about from the internal gas pressure of the reactants within the fuel cells plus the need to maintain good electrical contact between the internal components of the fuel cells.  
         [0003]     To apply the compressive force, the fuel cell stack is positioned between a pair of rigid endplates that apply a compressive force on the fuel cell stack. Electrically conductive terminal plates are disposed between the endplates and the fuel cell stack and are used to conduct electrical current between the fuel cell stack and the system in which the fuel cell assembly is employed. The fuel cell stack requires gaseous reactants (anode reactant and cathode reactant) to be supplied to and removed from the fuel cell stack to produce electricity. A coolant flow is also provided to and removed from the fuel cell stack to keep the stack at a desired operating temperature. These gaseous reactants and coolant can be humid flows and are supplied to the fuel cell stack by manifold headers. The headers pass through one or both of the endplates and are sealed against the terminal plate. The gaseous reactants and coolant are supplied to the fuel cell stack via the headers. With the header seal being against the terminal plate, the humid fluids (gaseous reactants and/or coolant) are in contact with the terminal plate. Ambient conditions and the voltage (electrical potential), which is applied to the terminal plates, can create electrolysis and cause corrosion of the terminal plate. Corrosion of the terminal plate is undesirable because it could decrease the lifespan of the fuel cell assembly and also contaminate the streams flowing through the headers.  
         [0004]     The terminal plates are made from a good conductor, (e.g., aluminum or copper) to facilitate the current flow between the fuel cell stack and the system in which the fuel cell assembly is employed. To protect the terminal plates against corrosion, various coatings have been used on the terminal plate. The coatings, however, can be expensive and cost prohibitive (e.g., made of gold). Additionally, the coatings can have a limited lifespan such that the life of the fuel cell assembly is reduced even with the use of the coatings. Furthermore, the coatings can be sensitive to minor damage, such as scratches, and result in poor performance or allowing the corrosion process to occur. Thus, an inexpensive way to inhibit and/or prevent corrosion of a terminal plate is desirable.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention isolates the fluid streams flowing into and out of a fuel cell stack from the terminal plates so that the fluid streams and terminal plates do not come into contact with one another. The prevention of the fluid streams from contact in the terminal plate eliminates corrosion concerns associated with the terminal plate. By eliminating these corrosion concerns, expensive protective coatings are not needed on the terminal plate. The present invention accomplishes this isolation through the use of headers having fluid passageways therein that route the fluid streams in and/or out of the fuel cell stack while preventing contact between the fluid streams and the terminal plate.  
         [0006]     In one aspect of the present invention, a fuel cell assembly is disclosed. The fuel cell assembly includes a plurality of fuel cells arranged adjacent one another to form a fuel cell stack. There is a terminal plate in electrically conductive contact with the fuel cell stack. The terminal plate is operable to conduct electrical current from the fuel cell stack. The terminal plate has an opening for transporting a fluid stream to or from the fuel cell stack. There is also an electrically non-conductive header that is sealingly engaged with the fuel cell stack. The header passes through the opening in the terminal plate. The header has a fluid transport passageway that allows the fluid stream to flow to or from the fuel cell stack through the opening in the terminal plate. The header prevents the fluid stream from contacting the terminal plate.  
         [0007]     In another aspect of the present invention, a method of preventing a fluid stream flowing into a fuel cell stack through a terminal plate from contacting the terminal plate with the use of an electrically non-conductive header having a fluid passageway is disclosed. The method includes: (1) positioning the header in a through opening in the terminal plate with the header passageway passing through the opening in the terminal plate; (2) sealingly engaging the header passageway with the fuel cell stack; (3) routing a fluid stream from or to the fuel cell stack through the header passageway; and (4) isolating the fluid stream from the terminal plate with the header thereby preventing the fluid stream from contacting the terminal plate.  
         [0008]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention will become more fully understood from the detailed description and the accompanying drawings,. wherein:  
         [0010]      FIG. 1  is a simplified perspective view of a fuel cell assembly according to the principles of the present invention;  
         [0011]      FIG. 2  is a simplified perspective view of the wet end assembly according to the principles of the present invention utilized in the fuel cell assembly of  FIG. 1 ;  
         [0012]      FIG. 3  is a simplified exploded perspective view of the wet end assembly of  FIG. 2 ;  
         [0013]      FIGS. 4A  and B are perspective views of opposite sides of an isolated header according to the principles of the present invention and used in the wet end assembly of  FIGS. 2 and 3 ; and  
         [0014]      FIG. 5  is a partial cross-sectional view of the fuel cell assembly of  FIG. 1 , taken along line  5 - 5 , showing the preferred embodiment of a fuel cell assembly according to the principles of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]     The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0016]     Referring to  FIG. 1 , there is shown a fuel cell assembly  20  according to the principles of the present invention. Fuel cell assembly  20  includes a plurality of fuel cells  22  ( FIG. 5 ) arranged in a stacked configuration to form a fuel cell stack  24 . The fuel cell stack  24  is interposed between upper and lower end assemblies  26 ,  28 . Upper end assembly  26  is referred to as a wet end assembly because the fluid streams (cathode and anode reactants, cathode and anode effluents, and coolant) flow to or from fuel cell stack  24  through upper end assembly  26 . In contrast, lower end assembly  28  is referred to as a dry end assembly because the fluid streams do not flow therethrough. End assemblies  26 ,  28  are discussed in more detail below. End assemblies  26 ,  28  are held in a fixed space relation by one or more side plates  30 . Side plates  30  hold the upper and lower end assemblies  26 ,  28  in a spaced relation so that a compressive force is imparted on fuel cell stack  24 . Other methods of imparting a compressive force, however, can be employed without departing from the scope of the present invention. Fuel cell assembly  20  is typically a part of a fuel cell system (not shown) that includes appropriate supply plumbing (not shown) for supplying cathode reactant (such as O 2  or air), anode reactant (such as hydrogen), and coolant that connect to wet end assembly  26  and flow therethrough to fuel cell stack  24  within fuel cell assembly  20 . Similarly, the fuel cell system includes appropriate return plumbing (not shown) that connect to wet end assembly  26  and allow the cathode effluent, anode effluent and return coolant fluid streams to flow from fuel cell stack  24  to other components within the fuel cell system.  
         [0017]     Referring now to  FIGS. 2 and 3 , wet end assembly  26  is shown. Wet end assembly  26  includes an end plate  32 , an insulator plate  34 , a terminal plate  36 , a pair of headers  38 ,  40  and a pair of gaskets or seals  42 . Terminal plate  36  is positioned between insulator plate  34  and an end of fuel cell stack  24 , as shown in  FIG. 5 . Terminal plate  36  conducts electrical current to/from fuel cell stack  24 . Accordingly, terminal plate  36  is made from a highly conductive material capable of handling the current densities that will be encountered in the production of electricity by fuel cell assembly  20 . For example, terminal plate  36  can be made from aluminum and be capable of handling a current density of about 8 A/mm 2  or greater depending upon the specific configuration and power output of fuel cell assembly  20 . Terminal plate  36  has an extension  36   a  that extends through side plates  30  to facilitate the electrical connection of fuel cell assembly  20  to other components. Insulator plate  34  serves to isolate end plate  32  from terminal plate  36  so that electrical current flowing to/from fuel cell stack  24  does not flow through end plate  32 . Accordingly, insulator plate  34  is made from an electrically non-conductive material.  
         [0018]     Headers  38 ,  40  are non-conductive and operable to direct the fluid streams between fuel cell stack  24  and the supply/return plumbing (not shown) external to fuel cell assembly  20 . To facilitate the routing of the fluid streams between fuel cell stack  24  and the plumbing, each header  38 ,  40  has a base  44  and a plurality of fluid transport passageways  46  that extend generally orthogonally from base  44 . Each passageway  46  passes through wet end assembly . 26  and is configured to direct a fluid stream between fuel cell stack  24  and the appropriate return or supply plumbing. Passageways  46  are sealingly engaged with fuel cell stack  24  and the appropriate plumbing so that fluid tight seals are formed therebetween. To facilitate this sealing engagement, each passageway  46  has a recessed channel  48  that is configured to accept a gasket or seal, such as an O-ring, to sealingly engage with the appropriate plumbing. Similarly, the opposite sides of each passageway  46  on the bottom of base  44  also have recessed channels  50  within which seals  42  are positioned to allow headers  38 ,  40  to be sealingly engaged with fuel cell stack  24 .  
         [0019]     Each passageway  46  extends from base  44  to an opposite side of wet end assembly  26 . End plate  32  has a plurality of openings  52  through which passageways  46  extend. Passageways  46  of header  38  also extend through openings  54  in insulator plate  34  and through openings  56  in terminal plate  36 . This is necessitated by the fact that extension  36   a  of terminal plate  36  extends out of fuel cell assembly  20  in that direction thus making terminal plate  36  and insulator plate  34  extend over the flow channels within fuel cell stack  24 .  
         [0020]     Headers  38 ,  40  operate to isolate terminal plate  36 , insulator plate  34  and base plate  32  from the fluid streams flowing to and from fuel cell stack  26  through passageways  46 . Passageways  46  prevent the fluid streams flowing therethrough from contacting terminal plate  36 , insulator plate  34  and end plate  32 . By preventing the fluid streams from contacting these plates, the problem of corrosion occurring on these plates as a result of contact with the fluid streams is avoided. By avoiding this fluid contact, terminal plate  36  does not need a protective coating, as done in the prior art, to protect against the contact with the fluid streams. Additionally, terminal plate  36  can now be coated with more desirable coatings, such as tin, to facilitate current collection and transport. Furthermore, the use of headers  38 ,  40  also facilitates the manufacture of the plates. Specifically, the openings  52 ,  54 ,  56  in the respective end plate  32 , insulator plate  34  and terminal plate  36  can be generic openings that are easily machined in the plates. Headers  38 ,  40  can then have passageways  46  that have an external configuration that matches the openings and an internal configuration that corresponds to the shape of the flow headers within fuel cell stack  24  and the configuration of the supply/return plumbing.  
         [0021]     Headers  38 ,  40  are electrically non-conductive and can be easily produced by molding or casting headers  38 ,  40  into desired shapes. For example, headers  38 ,  40  can be injection molded from a polymeric material that is capable of withstanding the acidic environments of the fluid streams. Headers  38 ,  40  can also be injection molded with a glass filled polypheny sulfide or a polysulfone. If desired, headers  38 ,  40  can be compression molded. These methods of producing headers  38 ,  40  facilitates the forming of passageways  46  into a desired orientation/configuration that provides a requisite transition between the supply/return plumbing and the flow headers within fuel cell stack  24 . The use of a polymer for headers  38 ,  40  also minimizes concerns associated with thermal expansion of the various components of fuel cell assembly  20 . The thermal expansion rates of end plate  32 , insulator plate  34  and terminal plate  36  may vary and cause relative movement therebetween. However, headers  38 ,  40  pass through all of these plates to provide fluid tight communication paths between fuel cell stack  24  and the supply/return plumbing so that thermal expansion of these plates does not effect the sealing engagement of headers  38 ,  40 .  
         [0022]     The dry end  28  (not shown in detail) is very similar to wet end assembly  26  and includes a terminal plate that is positioned adjacent an opposite end of fuel cell stack  24  and conducts electrical current to/from fuel cell stack  24 . There is also an insulator plate that is sandwiched between an end plate and the terminal plate to electrically insulate the end plate from the terminal plate. The main difference in dry end assembly  28  is that the fluid streams flowing to/from fuel cell stack  24  do not pass through dry end assembly  28 . Accordingly, dry end assembly  28  does not utilize headers  38 ,  40  nor openings within the terminal plate, insulator plate, and end plate. However, it should be appreciated, if desired, such as when cascading two or more fuel cell assemblies together, the fuel cell assembly  20  can have two end assemblies that are both wet and allow fluid streams to flow therethrough. In this case, headers  38 ,  40  according to the principles of the present invention can also be utilized to isolate and protect the end plates, insulator plates and terminal plates from contact with the fluid streams.  
         [0023]     It should be appreciated that the embodiments shown and the specific configurations therein are for illustrative purposes and are merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. For example, headers  38 ,  40  are shown with each having three passageways and being formed as a single integral unit. However, the headers  38 ,  40  can be separate components each having one or more passageways that direct the fluid streams and protect the plates from contact with these fluid streams. Additionally, the openings within the various plates are shown as being three discrete openings. However, the openings can be combined into larger openings and the passageways in the headers combined into multiple passageways that correspond to the configuration of the openings in these plates. Additionally, header  40  can be configured to have its passageways  46  flow through openings in insulator plate  54  and terminal plate  56  if those plates were to extend over top of the flow headers within fuel cell stack  24 . Furthermore, it should be appreciated that extensions  36   a  of terminal plates  36  can extend outwardly from fuel cell assembly  20  from other locations that may or may not be adjacent to the locations of headers  38 ,  40 . Moreover, headers according to the present invention can also be used to provide pathways through the end assemblies for instrumentation or the like, if desired, although all of the benefits of the present invention may not be realized. Accordingly, such variations are not to be regarded as a departure from the spirit and scope of the invention.