Abstract:
A fuel cell endplate to be combined with a membrane/electrode assembly comprising a high-polymer electrolytic membrane and electrodes sandwiching the membrane; which comprises a resin substrate, a collector plate and a gasket; the collector plate being in contact with the surface of the resin substrate and the membrane/electrode assembly; the gasket being provided so as to surround the periphery of the collector plate; a terminal connector connected to the collector plate and being disposed at a position where it does not contact with the membrane/electrode assembly.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority from Japanese application serial no. 2004-343451, filed Nov. 29, 2004, the content of which is hereby incorporated by reference into this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to fuel cell endplate and fuel cell, and particularly to a fuel cell endplate for use in a solid polymer type fuel cell or a direct methanol fuel cell that comprises a membrane/electrode assembly of a high-polymer electrolytic membrane and electrodes.  
         [0004]     2. Related Art  
         [0005]     A fuel cell has advantages that it has high-energy efficiency because electric energy is electro-chemically outputted directly from fuel and easily harmonizes with the environment because discharge from it is mostly water. Accordingly, attempts have been made to apply fuel cells to automobiles, distributed power supplies and electronic information processing devices. One of the major problems related to the fuel cell is how to prevent fuel leakage. The Patent Document 1 describes a gasket used as a seal for the fuel cell.  
         [0000]     [Patent Document 1] WO 02/001659 (Summary)  
         [0006]     The present inventors have acquired knowledge through our study that, in the case of a stacked type fuel cell comprising stacked unit cells, a main cause of the fuel leakage lies in the vicinity of manifolds. In the case of the stacked type fuel cell, for example, the fuel must be supplied evenly to all separators of the stacked fuel cell units and a lot of fuel is supplied into the manifold at a time; a pressure is applied not only in the direction of grooves of the separator but also in other directions, resulting in the breakage of the seal. On the other hand, in the case of a flat type fuel cell having multiple generators in a plane, the cause of the fuel leakage has not been revealed as yet. Recently, however, we have found out through our study that gaps are easily formed among the gasket, collector plates and a resin substrate bonded to the collector plates. The gaps are one of the main causes of the fuel leakage.  
       SUMMARY OF THE INVENTION  
       [0007]     An object of the present invention is to offer a fuel cell endplate with high sealing performance and a fuel cell provided with the endplate, and particularly to offer an endplate suitable for the flat type fuel cell.  
         [0008]     The present invention relates to a fuel cell endplate which comprises a resin substrate, a collector plate and a gasket, wherein a terminal connector of the collector plate is located at a place where as the terminal connector does not contact the membrane/electrode assembly. For example, the terminal connector is exposed to the side face of the resin substrate. The endplate of this construction can be manufactured, for example, by forming the collector plate and terminal connecter in a united form, bending the terminal connector and exposing it to the side face of the resin substrate through the resin substrate.  
         [0009]     In addition, the present invention is concerned with a fuel cell having a membrane/electrode assembly with endplates having collector function on both sides thereof, the membrane/electrode assembly being constituted by a high-polymer electrolytic membrane and a pair of electrodes, wherein the endplates each comprises a resin substrate, a collector plate and a gasket, and wherein the terminal connectors of the collector plates are disposed at positions where the terminal connectors do not contact the membrane/electrode assembly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     FIGS.  1  ( a ), ( b ) and ( c ) are plan views and a cross-sectional perspective view of the fuel cell endplate of an embodiment of the present invention.  
         [0011]      FIG. 2  ( a ) is a developed view of a unit cell and ( b ) is a perspective view of the unit cell according to an embodiment of the present invention  
         [0012]      FIG. 3  is a diagrammatic view of the test equipment built for checking the sealing performance of the unit cell.  
         [0013]      FIG. 4  is a plan view showing the fuel cell endplate of a comparative sample.  
         [0014]      FIG. 5  is a perspective view of an embodiment of the collector plate used in the fuel cell endplate of the present invention.  
         [0015]      FIG. 6  is a perspective view of another embodiment of the collector plate.  
         [0016]     FIGS.  7  ( a ) and ( b ) are plan views showing the fuel cell endplate having multiple collector plates.  
         [0017]      FIG. 8  is a perspective view showing another embodiment of the collector cell.  
         [0018]      FIG. 9  ( a ) is a developed view of a unit fuel cell and ( b ) is a sectional view of the unit fuel cell of another embodiment of the present invention.  
         [0019]      FIG. 10  ( a ) is a plan view of a fuel cell module and ( b ) is a cross sectional view of the fuel cell module.  
         [0020]     FIGS.  11  ( a ) and ( b ) show a method for the connection the unit cells.  
         [0021]     FIGS.  12  ( a ) and ( b ) show another method for the connection the unit cells. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Preferred embodiments are described hereunder but the present invention is not limited thereto.  
       Embodiment 1  
       [0023]     FIGS.  1 ( a ), ( b ) and ( c ) show the fuel cell endplate of the present invention. The fuel cell endplate  4 , comprising a collector plate  1 , gasket  2  and resin substrate  3 , is formed into one piece for example by injection molding. The collector plate  1  has a surface  5   a  contacting a membrane/electrode assembly and another surface  5   b  having a terminal connector  6 . Grooves  7  are formed on the surface  5   a , where fuel is supplied and carbon dioxide is discharged through these grooves  7  when the endplate is used as anode, and air is supplied and water is discharged when used as cathode. Generated electricity can be outputted when terminal is connected with this terminal connector  6 .  
         [0024]     The fuel cell endplate is formed in two steps. The collector plate  1  and resin substrate  3  are formed together in the first step, and then the gasket  2  and resign substrate  3  are formed together in the second step. Preferable material for the collector plate  1  is one that is stable in a reaction place and also capable of collecting electricity. It can be not only be carbon but also metals including gold, platinum, stainless steel and titanium. Titanium is employed in the Embodiment 1.  
         [0025]     However, since bare titanium causes high electric resistance due to the effect of oxide film generated on the surface, the titanium is plated with gold in about several-micrometer thickon the surface. Preferable materials for the gasket  2  are ones that are chemically stable in a reaction site and also easy to mold as the gasket  2  is formed by one-piece molding in this embodiment. It can be EPDM (ethylene-propylene-diene three-way copolymer), PET (polyethylene-telephthalate) or silicone resin, for example. EPDM was employed in the Embodiment 1. Preferable materials for the resin substrate  3  are ones that are chemically stable in a reaction site, hard enough to fasten the fuel cells as the substrate for the fuel cell endplate  4 , and also easy to be molded as the resin substrate  3  is formed into one-piece molding in this embodiment. It can be, for example, AS (acrylonitrile-styrene copolymer), PEEK (polyether etherketone), PC (polycarbonate), VC (vinyl chloride) or PBT (poly buthylene telephthalate). PBT was employed in the Embodiment 1.  
         [0026]     Although the collector plate  1  and resin substrate  3  are formed together in this embodiment, it is anticipated that a gap is caused between the collector plate  1  and resin substrate  3  in case of poor molding precision and consequently liquid may leak through it because the collector plate  1  and resin substrate  3  are not chemically bonded. If liquid leakage occurs, it is preferred to add silicone resin to fill up the gap.  
         [0027]      FIG. 1 ( a ) shows the fuel cell endplate viewing from the side where the gasket is visible, and  FIG. 1 ( b ) shows the fuel cell endplate viewing from the other side where the gasket is not visible. As understood from the FIGS.  1 ( a ) and ( b ), it is so constructed that the surface  5   a  contacting the membrane/electrode assembly is not exposed on the side where the gasket  2  is not visible.  FIG. 1 ( c ) is an oblique view of the section A-A in  FIG. 1 ( a ). As shown in  FIG. 1 ( c ), the collector plate  1  is a bent piece made from a single plate, and the portion exposed on the surface of the resin substrate  3  is the surface  5   a  contacting the membrane/electrode assembly. The portion extended inside the resin substrate and exposed outside is the other surface  5   b  having the terminal connector  6 . The gasket  2  is formed around the periphery of the surface  5   a  on the resin substrate  3  so as not to contact the collector plate  1 .  
         [0028]     FIGS.  2 ( a ) and ( b ) shows a fuel cell provided with the endplate of the invention. The membrane/electrode assembly  11  (hereinafter called the MEA) is sandwiched between an anode endplate  9  and cathode endplate  10 , bolts  12  are put into though holes  8 , and a fuel tank frame  13 , gas-liquid separation membrane  14  and tank cover  15  are installed outside the anode endplate  9 , all of which are fastened together with nuts  16  to form a unit cell  17 .  
         [0029]     The MEA  11  of this embodiment is so constructed that the electrolytic membrane  11   a  is provided with an anode catalyst layer (not shown) on one side and a cathode catalyst layer  11   c  on the other side and is further sandwiched between a cathode dispersion layer  11   d  and anode dispersion layer  11   e . When a tube (not shown) is connected with the tube coupling  18  provided on the fuel tank frame  13  and fuel is supplied from the outside to the tube by a fuel supply device such as micro tube pump, the unit cell  17  becomes ready for generation. The gas-vapor separation membrane  14 , which is a special membrane through which gas can pass but liquid cannot, plays a role of exhausting carbon dioxide generated in the tank quickly from inside the tank.  
         [0030]     In order to verify the sealing performance, which is the effect of the present invention, we made a piece of test equipment built as in  FIG. 3  and measured the fuel leakage versus the inside pressure of the tank. In this description, tank means a space formed by the anode endplate  9 , fuel tank frame  13  and gas-vapor separation membrane  14 .  
         [0031]     The test equipment is so constructed that two tubes  19  are connected with the two tube couplings of the unit cell  17  and that one of the tubes  19  is connected with a pressure gauge  20  and the other is connected with a pressurizing unit  21 . The pressurizing unit  21  consists of a liquid reservoir (not shown) and external piping (not shown) of the liquid reservoir. By adjusting the flow rate of the liquid using a flow meter (not shown), the internal pressure of the tank can be freely controlled. For a comparison purpose in this test, we also made a fuel cell endplate  25  comprising a collector plate  22 , of which terminal connector was provided on the surface of the resin substrate, i.e. the surface contacting the MEA, gasket  23  and resin substrate  24  and assembled a unit cell in the same manner as in the present invention.  
         [0032]     Table 1 shows the verification result of the sealing performance improvement, which is the effect of the present invention. The test was carried out as follows: the flow rate of the gas incoming into the pressurizing unit  21  was controlled and, when a set pressure was reached, the incoming gas was stopped to maintain a constant pressure; after this condition was kept for two minutes, leakage from the tank was checked. In Table 1, “◯” means no leakage from the tank was observed and “X” means leakage was observed. The comparative samples 1 to 3 in Table 1 employ the unit cell  25  in  FIG. 4  using different gaskets. On the comparative sample 1, one each silicone rubber gasket of 300 μm thick is put on both sides of the electrolytic membrane. On the comparative sample 2, one each three-layer gasket (hardness 60 degree) of 220 μm thick (EPDM 95 μm/PET 50 μm/EPDM 75 μm) was put on each of the sides of the electrolytic membrane. In the comparative sample 3, one each three-layer gasket (hardness 70 degree) of 220 μm thick (EPDM 95 μm/PET 50 μm/EPDM 75 μm) was put on each of the sides of the electrolytic membrane. As clearly shown in Table 1, the sealing performance has improved on the unit cell that employs the fuel endplate of the present invention.  
                                                                                                 TABLE 1                                       Test pressure: kPa            Test Cell   0   20   40   60   80   100   120   140   160   180   200   220   240   260   280   300   320               Present   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘       invention       Comparative   ∘   ∘   ∘   x   x   x   x   x   x   x   x   x   x   x   x   x   x       sample 1       Comparative   ∘   ∘   x   x   x   x   x   x   x   x   x   x   x   x   x   x   x       sample 2       Comparative   ∘   ∘   x   x   x   x   x   x   x   x   x   x   x   x   x   x   x       sample 3                  
 
       Embodiment 2  
       [0033]      FIG. 5  shows another embodiment of the fuel cell endplate of the present invention. In this embodiment, the collector plate  26  consists of curved surfaces  26   a  and  26   b . The curved surface  26   a  contacts the MEA directly and, through the grooves  27  formed on the surface  26   a , fuel is supplied and carbon dioxide is discharged when the endplate is used as anode, and air is supplied and water is discharged when used as cathode. A terminal connector  28  is provided on the curved surface  26   b  and generated electricity can be outputted when terminal is connected with this terminal connector  28 . The endplate of this construction produces an effect that the MEA can be fastened positively.  
       Embodiment 3  
       [0034]      FIG. 6  shows another embodiment of the collector on the fuel cell endplate of the present invention. In this embodiment, the collector plate  29  consists of two flat surfaces. Positions of the two flat surfaces are so correlated with each other that one flat surface  29   b  is connected perpendicularly with the other flat surface  29   a . The flat surface  29   a  contacts the MEA directly and, through the grooves  30  formed on the flat surface  29   a , fuel is supplied and carbon dioxide is discharged when the endplate is used as anode, and air is supplied and water is discharged when used as cathode. The flat surface  29   b  is connected perpendicularly with the other side of the flat surface  29   a  opposed to the side contacting the MEA directly, on which a terminal connector  31  is provided and generated electricity can be outputted when terminal is connected with this terminal connector  31 .  
       Embodiment 4  
       [0035]     Another embodiment of the fuel cell endplate and a fuel cell using the fuel cell endplate are described hereunder. FIGS.  7 ( a ) and ( b ) shows the fuel cell endplate. The fuel cell endplate  36  comprises a collector plate  32 , gasket  33  and resin substrate  34 , and an external terminal connector  35  is provided on part of the collector plate  32 . The external terminal connector  35  is exposed on the side of the fuel cell endplate  36 .  FIG. 7 ( a ) shows the fuel cell endplate  36  viewing from the side where the gasket  33  is visible, and  FIG. 7 ( b ) shows the same viewing from the other side.  
         [0036]     As understood from the FIGS.  7 ( a ) and ( b ), it is so constructed that the collector plate  32  is not exposed on the side where the gasket  33  is not visible.  
         [0037]     For easier understanding, portions of the collector plate  32  and terminal connector  35  embedded in the resin substrate  34  are shown in dotted line. Six collector plates  32  and six gaskets  33  are installed on one fuel cell endplate  36 , which forms six unit cells in series when assembled into a fuel cell. The fuel cell endplate  36  is formed into one-piece molding. It is formed in two steps. The collector plate  32 , resin substrate  34  and external terminal connector  35  are formed together in the first step, and then the gasket  33  and resign substrate  34  are formed together in the second step. As shown in  FIG. 8 , the collector plate  32  is a bent piece made from a single plate, containing the surfaces  32   a ,  32   b  and  32   c.    
         [0038]     The surface  32   a  contacts the MEA and the surface  32   b  is provided with the terminal connector  37 . The surface  32   c  is provided so that the collector plate  32  and resin substrate  34  are tightly fastened with each other when molded into one piece. Grooves  38  are formed on the surface  32   a , where fuel is supplied and carbon dioxide is discharged through these grooves  38  when the endplate is used as anode, and air is supplied and water is discharged when used as cathode. The gasket  33  is formed around the periphery of the surface  32   a  on the resin substrate  34  so as not to contact the collector plate  32 . Symbol  39  represents through hole.  
         [0039]     As understood from FIGS.  7 ( a ) and ( b ), the area of the fuel cell endplate  36  depends upon the size of the collector plate  32 . In this embodiment, reduction of size has been considered in view of future application to mobile devices. The size of the surface  32   a  of the collector plate  32  has not been reduced as it affects the output, but the surface  32   b  is made as small as possible. While the external terminal connector  35  has been provided so as to be connected with external terminal for outputting the power after the endplate is assembled into a fuel cell, it is not always necessary because the terminal connector  37  is already provided. In this embodiment, however, an external terminal connector has been provided because connection with external terminal becomes easier in assembling a fuel cell if a portion for connecting with external terminal is provided on the side of the fuel cell endplate.  
         [0040]     Materials for the collector plate  32  and external terminal connector  35  of this embodiment are titanium, of which surface is gold plated by several μm thick. The gasket  33  is EPDM, and the resin substrate is PBT. As shown in FIGS.  9 ( a ) and ( b ), the MEA  42  is sandwiched between an anode endplate  40  and cathode endplate  41 , bolts  43  are put into though holes  39 , and a fuel tank frame  44 , gas-liquid separation membrane  45  and tank cover  46  are installed outside the anode endplate  40 , all of which are fastened together with nuts  47  and washers  48  to form a fuel cell module  49  shown in FIGS.  10 ( a ) and ( b ). In  FIG. 9 ( a ), however, the bolts  43 , nuts  47  and washers  48  are not shown.  
         [0041]     Individual unit cells are connected with each other by a collection bolt  50 . FIGS.  11 ( a ) and ( b ) is a cross-sectional view for better understanding the connection between each unit cell. It is a B-B cross-section of  FIG. 10 ( a ). In order to highlight the connection between unit cells, the bolts  43 , fuel tank frame  44 , gas-vapor separation membrane  45 , tank cover  46 , nuts  47  and washers  48  are not shown in the figure.  FIG. 11 ( a ) shows a module before assembly and  FIG. 11 ( b ) shows an assembled module. FIGS.  12 ( a ) and ( b ) shows another method for the connection between unit cells. Also in this figure, the bolts  43 , fuel tank frame  44 , gas-vapor separation membrane  45 , tank cover  46 , nuts  47  and washers  48  are not shown in order to highlight the connection between the unit cells.  FIG. 12 ( a ) shows a module before assembly and  FIG. 12 ( b ) shows an assembled module. A collection bolt  50  is inserted from both sides of the two fuel cell endplates  36  and connected with each other by a collection nut  51 .  
         [0042]     Comparing the connection of the unit cells shown in FIGS.  11 ( a ) and ( b ) with the connection of the unit cells shown in FIGS.  12 ( a ) and ( b ), the method in  FIG. 12  can connect more tightly but results in lower productivity because more number of parts are needed. Accordingly, in this embodiment, the method in  FIG. 11  is employed. The MEA of this embodiment is so constructed that the electrolytic membrane  42   a  is provided with an anode catalyst layer on one side and a cathode catalyst layer  42   c  on the other side and is further sandwiched between a cathode dispersion layer  42   d  and anode dispersion layer  42   e . When a tube (not shown) is connected with the tube coupling  52  provided on the fuel tank frame  44  and fuel is supplied from the outside to the tube by a fuel supply device such as micro tube pump (not shown), the unit cell module  49  becomes ready for generation.  
         [0043]     In order to verify the sealing performance, which is the effect of the present invention, we built a piece of same test equipment as in  FIG. 3  and measured the fuel leakage versus the inside pressure of the tank.  
         [0044]     Table 2 shows the verification result of the sealing performance. The test was carried out as follows in the same procedure as in the Embodiment 1: the flow rate of the gas incoming into the pressurizing unit was controlled and, when a set pressure was reached, the incoming gas was stopped to maintain a constant pressure; after this condition was kept for two minutes, leakage from the tank was checked. “◯” in the table means no leakage from the tank was observed at the test pressure and “X” means leakage was observed. “Present invention” in Table 2 represents the fuel cell module  49  and “Comparative samples 1 to 3” represent the fuel cell modules employing the fuel cell endplate constructed as shown in  FIG. 4 , using different gaskets as explained in the Embodiment 1. The risk of fuel leakage normally increases as the number of cells employed increases. As shown in Table 2, however, tremendously higher sealing performance has been verified on the fuel cell module  49  that employs the fuel cell endplate of the present invention than on the comparative sample.  
                                                                                                 TABLE 2                                       Test pressure: kPa            Test cell   0   20   40   60   80   100   120   140   160   180   200   220   240   260   280   300   320               Present   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘   ∘       invention       Comparative   ∘   x   x   x   x   x   x   x   x   x   x   x   x   x   x   x   x       sample 1       Comparative   ∘   x   x   x   x   x   x   x   x   x   x   x   x   x   x   x   x       sample 2       Comparative   ∘   x   x   x   x   x   x   x   x   x   x   x   x   x   x   x   x       sample 3                  
 
         [0045]     The present invention enables to obtain a fuel cell endplate having excellent sealing performance and has solved the fuel leakage problem involved in sold high-polymer fuel cell containing membrane/electrode assembly.  
         [0046]     According to the present invention, a fuel cell endplate with high sealing performance can be offered.