Abstract:
A flow plate gasket that is usable with a first fuel cell plate and a second fuel cell plate includes a material that is adapted to form a seal between the first and second fuel cell plates. The material includes at least two spaced ridges to contact the first fuel cell plate when the gasket is compressed between the first and second fuel cell plates.

Description:
BACKGROUND 
     The invention relates to a profiled fuel cell flow plate gasket. 
     A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a proton exchange membrane (PEM), a membrane that may permit only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is oxidized to produce hydrogen protons that pass through the PEM. The electrons produced by this oxidation travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions may be described by the following equations: 
     
       
         H 2 →2 H + +2e − at the anode of the cell, and 
       
     
     
       
         O 2 +4 H + +4e − →2H 2 O at the cathode of the cell. 
       
     
     Because a single fuel cell typically produces a relatively small voltage (around 1 volt, for example), several serially connected fuel cells may be formed out of an arrangement called a fuel cell stack to produce a higher voltage. The fuel cell stack may include different flow plates that are stacked one on top of the other in the appropriate order, and each plate may be associated with more than one fuel cell of the stack. The plates may be made from a graphite composite or metal material and may include various flow channels and orifices to, as examples, route the above-described reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. The anode and the cathode may each be made out of an electrically conductive gas diffusion material, such as a carbon cloth or paper material, for example. 
     Referring to FIG. 1, as an example, a fuel cell stack  10  may be formed out of repeating units called plate modules  12 . In this manner, each plate module  12  includes a set of composite plates that may form several fuel cells. For example, for the arrangement depicted in FIG. 1, an exemplary plate module  12 a may be formed from a cathode cooler plate  14 , a bipolar plate  16 , an anode cooler plate  18 , a cathode cooler plate  20 , a bipolar plate  22  and an anode cooler plate  24  that are stacked from bottom to top in the listed order. The cooler plate functions as a heat exchanger by communicating a coolant through flow channels in either the upper or lower surface of the cooler plate to remove heat from the stack  10 . The surface of the cooler plate that is not used to communicate the coolant includes flow channels to communicate either hydrogen (for the anode cooler plates  18  and  24 ) or oxygen (for the cathode cooler plates  14  and  20 ) to an associated fuel cell. The bipolar plates  16  and  22  include flow channels on one surface to communicate hydrogen to the membrane of an associated fuel cell and flow channels on the opposing surface to communicate oxygen to the membrane of another associated fuel cell. Due to this arrangement, each fuel cell may be formed in part from one bipolar plate and one cooler plate, as an example. 
     For example, one fuel cell of the plate module  12   a  may include an anode-membrane-cathode sandwich, called a membrane-electrode-assembly (MEA), that is located between the anode cooler plate  24  and the bipolar plate  22 . In this manner, the upper surface of the bipolar plate  22  includes flow channels to route oxygen near the cathode of the MEA, and the lower surface of the anode cooler plate  24  includes flow channels to route hydrogen near the anode of the MEA. 
     As another example, another fuel cell of the plate module  12 a may be formed from another MEA that is located between the bipolar plate  22  and the cathode cooler plate  20 . The lower surface of the bipolar plate  22  includes flow channels to route hydrogen near the anode of the MEA, and the upper surface of the cathode cooler plate  24  includes flow channels to route oxygen near the cathode of the MEA. The other fuel cells of the plate module  12   a  may be formed in a similar manner. 
     To communicate the hydrogen, oxygen and coolant throughout the stack, each plate includes several openings that align with corresponding openings in the other plates to form passageways of a manifold. The fuel cell stack typically includes flow plate gaskets that reside between the plates to seal off the various manifold passageways and flow channels. For example, such a flow plate gasket may be located between the anode cooler  24  and the bipolar plate  22  and reside in a gasket groove of the bipolar plate  22 , for example. The flow plate gasket may be an O-ring gasket that has a disk-shaped cross-section when uncompressed. 
     The seals that are provided by the flow plate gaskets may govern the lifetime of the fuel cell stack. For example, a coolant may be used that is incompatible with the membrane and thus, may damage the membrane on contact. Therefore, if a particular flow plate gasket is not compatible with the coolant, the coolant may permit the coolant to enter one of the reactant manifold passageways and contact the membrane, an event that may cause the corresponding fuel cell to fail. Unfortunately, the failure of a fuel cell may prompt a shut down of the entire fuel cell stack until repairs may be made. 
     Thus, there is a continuing need for fuel cell flow plate gaskets that have improved sealing capabilities. 
     SUMMARY 
     In one embodiment of the invention, a flow plate gasket that is usable with a first fuel cell plate and a second fuel cell plate includes a material that is adapted to form a seal between the first and second fuel cell plates. The material includes at least two spaced ridges to contact the first fuel cell plate when the gasket is compressed between the first and second fuel cell plates. 
     In another embodiment of the invention, an assembly includes a first fuel cell plate, a second fuel cell plate and a gasket. The gasket is adapted to form a seal between the first and second fuel cell plates. The gasket includes at least two spaced ridges to contact the first fuel cell plate when the gasket is compressed between the first and second fuel cell plates. In general, advantageous features of embodiments of the present invention may include: seals having higher void volume for improved compression than traditional o-ring seals that are placed in rectangular grooves; seals having an increased number of sealing surfaces than o-ring configurations; seals that can more accurately and reliably be placed into position during fuel cell stack assembly; and seals that provide less movement during compression, such as the twisting and other movement of o-rings that may occur during compression. 
     Advantages and other features of the invention will become apparent from the following description, from the drawing and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic diagram illustrating a fuel cell stack according to the prior art. 
     FIG. 2 is a side view of a fuel cell stack according to an embodiment of the invention. 
     FIGS. 3A and 3B illustrate two halves of a bottom perspective view of an anode cooler plate and a gasket that forms a seal against the anode cooler plate according to an embodiment of the invention. 
     FIG. 4 is a cross-sectional of a bipolar plate and a flow plate gasket according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 2, an embodiment  50  of a fuel cell stack in accordance with the invention includes flow plate gaskets that include profiled features to seal off the various manifold passageway openings and flow channels that are established by flow plates of the stack  50 . 
     More specifically, the fuel cell stack  50  may be formed from repeating units called plate modules  51 . An exemplary plate module  51   a  (having a design similar to the other plate modules  51 ) is depicted in FIG.  2 . As shown, the plate module  51   a  includes flow plates (graphite composite or metal plates, for example) that include flow channels to communicate reactants and coolants to fuel cells of the stack  50 . As an example, the plate module  51  a may include the following flow plates: bipolar plates  54  and  60 ; cathode cooler plates  52  and  58 ; and anode cooler plates  56  and  62 . 
     FIGS. 3A and 3B illustrate a bottom up perspective view of the anode cooler plate  62  that is joined in FIGS. 3A and 3B at line A—A. Similar to the other flow plates, the anode cooler plate  62  includes openings that form a manifold for communicating reactants (oxygen and hydrogen) for the fuel cells and a coolant (Therminol D-12 made by Solutia Inc., for example) to and from the various surface flow channels of the plates. In this manner, the anode cooler plate  62  may include an opening  170  (see FIG. 3A) to form part of a vertical inlet passageway of the manifold for delivering hydrogen to the fuel cells. The anode cooler plate  62  may also include an opening  168  (see FIG. 3B) to form part of a vertical outlet passageway of the manifold for removing unconsumed hydrogen from the stack  50 . Similarly, openings  174  (see FIG. 3A) and  164  (see FIG. 3B) of the anode cooler plate  62  may form partial vertical inlet and outlet passageways, respectively, of the manifold for communicating an air flow (that furnishes oxygen) to the fuel cells; and openings  172  (see FIG. 3A) and  166  (see FIG. 3B) in the anode cooler plate  62  may form part of vertical inlet and outlet passageways, respectively, of the manifold for communicating the coolant. 
     As an example of the fluid flows through the plate module  51   a , the anode cooler plate  62  may include horizontal flow channels (not shown) on its upper surface through which the coolant flows to remove heat from the stack  50 . For purposes of communicating hydrogen to an associated membrane (a proton exchange membrane (PEM), for example), the lower surface of the anode cooler plate  62  includes horizontal surface flow channels  84  (see FIGS.  3 A and  3 B). In this manner, the hydrogen may flow in a serpentine path through the flow channels  84  between the openings  170  and  168 . While flowing through the flow channels  84 , some of the hydrogen diffuses through a gas diffusion layer (located between the anode cooler plate  62  and the lower adjacent bipolar plate  60 ) and reaches the membrane of the associated fuel cell. Thus, coolant flows through the upper surface flow channels of the anode cooler plate  62 , and hydrogen flows through the lower surface flow channels  84  of the anode cooler plate  62 . 
     For purposes of sealing the various flow channels and manifold passageways, the fuel cell stack  50  (and plate module  51   a ) includes flow plate gaskets, such as a flow plate gasket  100  (shown in relation to the anode cooler plate  62  in FIGS. 3A and 3B) that resides in a gasket groove  112  of the bipolar plate  60  (see FIGS.  2  and  4 ). In this manner, when the flow plates of the stack  50  are compressed, the flow plate gasket  100  forms a seal between the anode cooler plate  62  and the bipolar plate  60 . This seal, in turn, seals off regions (between the plates  60  and  62 ) that are associated with the coolant and reactant flows. 
     A cross-sectional view of the flow plate gasket  100  in a gasket groove  102  of the bipolar plate  60  is depicted in FIG.  4 . As described below, in some embodiments, the profiled features of the gasket  100  may cause the gasket  100  to outperform conventional O-ring gaskets. 
     In particular, the gasket  100  may include spaced ridges  102  (ridges  102   a ,  102   b ,  102   c ,  102   d ,  102   e  and  102   f ) that form sealing surfaces for sealing the gasket  100  between the anode cooler plate  62  and the bipolar plate  60 . In this manner, the ridges  102   a ,  102   b  and  102   c  are formed on an upper surface  108  of the flow plate gasket  100  and are designed to form sealing surfaces between the gasket  100  and the lower surface of the anode cooler plate  62 . In some embodiments, the ridges  102   a ,  102   b  and  102   c  may be uniformly spaced apart. 
     In some embodiments, when the gasket  100  is uncompressed, the ridge  102   b  in the middle is shorter than the other two outer ridges  102   a  and  102   c . In this manner, when the plates of the fuel cell stack  50  are compressed, the gasket  100  is compressed so that the middle ridge  102   b  seals against the anode cooler plate  62 . Due to this design, the middle ridge  102   b  is less deformed and the ridges  102   a  and  102   c  are more deformed when the flow plate gasket  100  is compressed. 
     Similar to the ridges  102   a ,  102   b  and  102   c , ridges  102   d ,  102   e  and  102   f  may also be formed on a lower surface  110  of the flow plate gasket  100 . In this manner, the ridges  102   d ,  102   e  and  102   f  form sealing surfaces for sealing the flow plate gasket  100  to the upper surface of the bipolar plate  60  (i.e., for sealing the flow plate gasket  100  to a bottom surface  103  of the gasket groove  102 ). In some embodiments, the ridges  102   d ,  102   e  and  102   f  may be uniformly spaced apart, and the middle ridge  102   e  may be shorter than the outer edges  102   d  and  102   f  when the flow plate gasket  100  is uncompressed. 
     In some embodiments, channels  104  may separate the ridges  102 . In this manner, each ridge  102  may be generally concave to the associated flow plate (to which the ridge  102  seals), and each channel  104  (that spaces a particular ridge  102  from an adjacent ridge  102 ) may be generally convex with respect to the associated flow plate surface. The channel  104 , in some embodiments, may have a generally arcuate cross-section, and in some embodiments, the ridge  102  may have a generally arcuate cross-section. 
     Among the other features of the gasket  100 , the sides of the gasket  100  may form generally outwardly bowed edges  107  when the gasket  100  is uncompressed. Therefore, when the gasket  100  is compressed, the bowed edges  107  laterally expand to seal against side walls  103  of the gasket groove  102 . 
     Profiled flow plate gaskets, such as the flow plate gasket  100 , may be used between other flow plates of the stack  50 . 
     As a more specific example, in some embodiments, the gasket  100  may be made out of an elastomer, such as a silicone, flourosilicone, viton, or nitrile material, as just a few examples. In some embodiments, each ridge  102  may have a radius of curvature between approximately 0.005 inches (in.) to 0.010 in., such as approximately 0.08 in., for example. In some embodiments, the channel  104  may have a generally arcuate cross-section that may have a radius of curvature between approximately 0.020 in. to 0.025 in., such as approximately 0.023 in., for example. The bowed edge  107 , in some embodiments, may have a radius of curvature between approximately 0.02 in. to 0.04 in., such as approximately 0.03 in., for example. In some embodiments, the uncompressed thickness of the gasket  100  may be between approximately 0.03 in. to 0.10 in., such as approximately 0.06 in., for example. 
     In the preceding description, directional terms, such as “upper,” “lower,”“vertical,”“horizontal,” etc. may have been used for reasons of convenience to describe the fuel cell stack and its associated components. However, such orientations are not needed to practice the invention, and thus, other orientations are possible in other embodiments of the invention. For example, the fuel cell stack  50  and its associated components, in some embodiments, may be tilted by approximately 90°. 
     While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.