Patent Publication Number: US-2012034543-A1

Title: Fuel cell separator, and fuel cell stack and fuel cell system using same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fuel cell separator, and a fuel cell stack and a fuel cell system using the fuel cell separator. More particularly, the present invention relates to a passage structure at a cathode side of a separator. 
     2. Background Art 
     Recently, with the rapid widespread of portable and cordless electronic devices, as driving power sources for such electronic devices, secondary batteries having a small size, light weight and large energy density have been increasingly demanded. Furthermore, technology development has been accelerated in not only secondary batteries used for small consumer goods but also large secondary batteries for electric power storages and electric vehicles, which require durability and safety over a long period. In addition, more attention has been paid to fuel cells that can be continuously used for a long time with fuel supplied rather than secondary batteries that need charging. 
     A fuel cell system is provided with a fuel cell stack including a cell stack, a fuel supply section for supplying fuel to the cell stack, and an oxidizing agent supply section for supplying gas containing an oxidizing agent. The cell stack is formed by laminating membrane electrode assemblies and separators to each other, and disposing an endplate on each of the both end sides in the laminating direction. Each membrane electrode assembly is composed of an anode electrode, a cathode electrode, and an electrolyte membrane interposed between the anode and cathode electrodes. 
     Each of a surface of the anode-side end plate and a surface of the separator facing the anode electrode is provided with a serpentine groove in order to supply fuel to the entire surface of the anode electrode. Likewise, each of a surface of the cathode-side end plate facing the cathode electrode and a surface of the separator facing the cathode electrode is provided with a serpentine groove in order to supply gas containing an oxidizing agent to the entire surface of the cathode electrode. In general, both these grooves are formed such that they extend in the direction perpendicular to each other and they are folded back and forth (to right and left) in a meander form. 
     However, when liquid such as water is generated as a product at a cathode side depending on operation conditions, a passage formed by the serpentine grooves may be closed with this liquid product. Furthermore, in a case of such a passage shape, as an area of the cathode electrode becomes larger and the length of the passage becomes longer, a pressure loss in the passage is increased. Therefore, in order to supply gas containing an oxidizing agent to the downstream side, it is necessary to increase a discharging pressure of a pump as an oxidizing agent supply section. This makes it difficult to miniaturize a fuel cell system and this increases the power consumption of the pump. As a result, energy conversation efficiency of the fuel cell system is reduced. 
     SUMMARY OF THE INVENTION 
     A fuel cell separator according to the present invention includes a first surface configured to face a cathode electrode, and a second surface provided on a rear side of the first surface and configured to face an anode electrode. The separator includes a first edge, a second edge that is adjacent to the first edge, a third edge that faces the first edge and is adjacent to the second edge, and a fourth edge that faces the second edge. The first surface includes an inlet (gas inlet) provided on the first edge side, an inlet chamber linked to the inlet, a first outlet provided on the second edge side, a second outlet provided on the fourth edge side, an outlet chamber linked to the first and second outlets, a plurality of linear partition walls, and a center partition wall. The linear partition walls are provided in parallel to each other in the direction from the first edge to the third edge, and the center partition wall is provided in parallel to the linear partition walls at a center position, in the direction from the first edge to the third edge. The partition walls have the same length. Each two of the partition walls, and the center partition wall and two of the partition walls neighboring the center partition wall form a plurality of linear passages having the same width therebetween, which are linked between the inlet chamber and the outlet chamber along the direction from the first edge to the third edge. A space is provided between the center partition wall and an inner wall surface of the third edge, and the first outlet and the second outlet communicate with each other via the space. 
     In addition, a fuel cell stack of the present invention includes a cathode-side end plate, a membrane electrode assembly, and an anode-side end plate. The membrane electrode assembly is formed by laminating a cathode electrode that faces the cathode-side end plate, an anode electrode provided on a rear side of the cathode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode to each other. The anode-side end plate faces the anode electrode. The cathode-side end plate has a similar structure to that of the first surface of the separator mentioned above on a cathode-facing surface that faces the cathode electrode. 
     Furthermore, a fuel cell system of the present invention includes the above-mentioned fuel cell stack, a fuel supply section, and a gas supply section. A fuel passage is provided on a surface of the anode-side end plate, which faces an anode electrode, and a fuel inlet linked to the fuel passage on the edge corresponding to the third edge of cathode-side end plate. The fuel supply section is disposed on a surface side including the third edge of the cathode-side end plate of the fuel cell stack, and supplies a fuel to the fuel inlet of the anode-side end plate. The gas supply section supplies gas containing an oxidizing agent to the gas inlet of the cathode-side end plate. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a fuel cell system in accordance with an embodiment of the present invention. 
         FIGS. 2A and 2B  are perspective views of a fuel cell stack in accordance with the embodiment of the present invention. 
         FIG. 3  is a plan view of a surface, which faces a cathode electrode, of a separator of the fuel cell stack shown in  FIGS. 2A and 2B . 
         FIG. 4  is a plan view of a surface, which faces an anode electrode, of the separator of the fuel cell stack shown in  FIGS. 2A and 2B . 
         FIG. 5  is a conceptual sectional view showing an outline configuration of a principal part of the fuel cell stack shown in  FIGS. 2A  and  2 B. 
         FIG. 6  is a perspective view for illustrating a connection between the fuel cell stack shown in  FIGS. 2A and 2B  and a fuel pump shown in  FIG. 1 . 
         FIG. 7  is a perspective view for illustrating a connection between the fuel cell stack shown in  FIGS. 2A and 2B  and an air pump shown in  FIG. 1 . 
         FIG. 8  is a front view of the first side surface of the fuel cell stack shown in  FIGS. 2A and 2B . 
         FIG. 9  is a sectional view of an integrated member to be attached onto the first side surface of the fuel cell stack shown in  FIGS. 2A and 2B . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of the present invention is described with reference to drawings in which a direct methanol fuel cell (DMFC) is taken as an example. Note here that the present invention is not limited to the contents described below as long as it is based on the basic features described in the present specification. 
       FIG. 1  is a block diagram showing a configuration of a fuel cell system in accordance with the embodiment of the present invention.  FIGS. 2A and 2B  are perspective views of a fuel cell stack in accordance with the embodiment of the present invention.  FIG. 2A  is a perspective view seen from a first side surface side, and  FIG. 2B  is a perspective view seen from a third side surface side that is the opposite side to the first surface.  FIG. 3  is a plan view of a surface (first surface), which faces a cathode electrode, of a separator used in the fuel cell stack shown in  FIGS. 2A and 2B .  FIG. 4  is a plan view of a surface (second surface), which faces an anode electrode, of the separator used in the fuel cell stack.  FIG. 5  is a conceptual sectional view showing an outline configuration of a principal part of the fuel cell stack. 
     As shown in  FIG. 1 , the fuel cell system includes fuel cell stack  1 , fuel tank  4 , fuel pump  5 , air pump  6 , controller  7 , storage section  8 , and DC/DC converter  9 . Fuel cell stack  1  has an electricity generation section, and generated electric power is output from positive electrode terminal  2  and negative electrode terminal  3 . The output electric power is input into DC/DC converter  9 . Fuel pump  5  supplies fuel in fuel tank  4  to anode electrode  31  of fuel cell stack  1 . Air pump  6  supplies air as an oxidizing agent to cathode electrode  32  of fuel cell stack  1 . Controller  7  controls the driving of fuel pump  5  and air pump  6  and controls DC/DC converter  9  so as to control the output to the outside and the charge and discharge with respect to storage section  8 . Fuel tank  4 , fuel pump  5  and controller  7  constitute a fuel supply section for supplying fuel to anode electrode  31  in fuel cell stack  1 . On the other hand, air pump  6  and controller  7  constitute a gas supply section for supplying gas containing an oxidizing agent to cathode electrode  32  in fuel cell stack  1 . Note here that the fuel supply section and the gas supply section are not necessarily limited to this configuration. 
     As shown in  FIGS. 2A and 2B , fuel cell stack  1  includes cell stack  16 , backing plates  14  and  15 , first plate spring  11  and second plate spring  12 . Cell stack  16  includes membrane electrode assemblies (hereinafter, referred to as “MEAs”)  35  as the electricity generation sections shown in  FIG. 5 , separators  34  disposed so as to sandwich each MEA  35 , anode-side end plate  17  and cathode-side end plate  18  (hereinafter, both are referred to as an “end plate”). End plates  17  and  18  sandwich MEAs  35  and separators  34  from both sides in the direction in which MEA  35  are made by laminating, that is, from both sides in the direction in which MEAs  35  and separators  34  are laminated. 
     As shown in  FIG. 5 , MEA  35  is formed by laminating anode electrode  31 , cathode electrode  32 , and electrolyte membrane  33  interposed between anode electrode  31  and cathode electrode  32 . Anode electrode  31  is supplied with a methanol aqueous solution as fuel, and cathode electrode  32  is supplied with air. 
     Anode electrode  31  includes diffusion layer  31 A, microporous layer (hereinafter, referred to as “MPL”)  31 B and catalyst layer  31 C, which are laminated sequentially from the separator  34  side. Cathode electrode  32  also includes diffusion layer  32 A, microporous layer (hereinafter, referred to as “MPL”)  32 B and catalyst layer  32 C, which are laminated sequentially from the separator  34  side. Positive electrode terminal  2  is electrically connected to cathode electrode  32 , and negative electrode terminal  3  is electrically connected to anode electrode  31 , respectively. Diffusion layers  31 A and  32 A are made of, for example, carbon paper, carbon felt, carbon cloth, or the like. MPLs  31 B and  32 B are made of, for example, polytetrafluoroethylene or a tetrafluoroethylene-hexafluoropropylene copolymer, and carbon. Catalyst layers  31 C and  32 C are formed by highly diffusing a catalyst such as platinum and ruthenium suitable for each electrode reaction onto a carbon surface and by binding this catalyst with a binder. Electrolyte membrane  33  is formed of an ion-exchange membrane for allowing a hydrogen ion to permeate, for example, a perfluorosulfonic acid—tetrafluoroethylene copolymer. 
     End plates  17  and  18  and separator  34  are made of a carbon material or stainless steel. As shown in  FIG. 5 , separator  34  has a surface (first surface) that faces cathode electrode  32 , and a surface (second surface) that faces anode electrode  31  at the rear side of the first surface. Furthermore, as shown in  FIGS. 3 and 4 , separator  34  has a rectangular shape, and includes first edge  134 , second edge  234  that is adjacent to first edge  134 , third edge  334  that faces first edge  134  and is adjacent to second edge  234 , and fourth edge  434  that faces second edge  234 . 
     As shown in  FIG. 3 , the first surface of separator  34  has gas inlets (hereinafter, referred to as “inlets”)  343 A and  343 B, inlet chamber  345 , first outlet  344 A, second outlet  344 B, outlet chamber  346 , a plurality of linear partition walls  34 E, and center partition wall  34 H. Inlets  343 A and  343 B configured to take in air that is oxygen-containing gas as an oxidizing agent are provided on first edge  134 . Inlet chamber  345  is linked to inlets  343 A and  343 B. First outlet  344 A is provided on second edge  234 , and second outlet  344 B is provided on fourth edge  434 . Outlet chamber  346  is linked to first outlet  344 A and second outlet  344 B. 
     Partition walls  34 E are provided in parallel to each other in the direction from first edge  134  to third edge  334 , and center partition wall  34 H is provided in parallel to partition walls  34 E at the center position, in the direction from first edge  134  to third edge  334 . Partition walls  34 E have substantially the same length. Each two of partition walls  34 E, or center partition wall  34 H and two partition walls  34 E neighboring center partition wall  34 H form a plurality of linear passages  34 D having the same width, which are linked between inlet chamber  345  and outlet chamber  346  along the direction from first edge  134  to third edge  334 . 
     A space is provided between center partition wall  34 H and an inner wall surface of third edge  334 , and first outlet  344 A and second outlet  344 B communicate with each other via the space. If center partition wall  34 H is linked to third edge  334  to divide outlet chamber  346  into two portions, produced water does not easily flow out from one of the divided portions of outlet chamber  346  when fuel cell stack  1  is inclined. However, thanks to the structure in which a space is provided between center partition wall  34 H and third edge  334 , produced water can be exhausted from any of first outlet  344 A and second outlet  344 B. Therefore, the produced water does not remain in outlet chamber  346  and does not close the passage. Thus, even when fuel cell stack  1  is disposed in such a manner that second edge  234  is positioned higher than fourth edge  434  or second edge  234  is positioned lower than fourth edge  434  positioned, water is not accumulated in a corner portion formed by center partition wall  34 H and third edge  334 . The water flows in the direction of the gravity through the space between center partition wall  34 H and third edge  334 . In this way, water is exhausted from any one of first outlet  344 A provided on second edge  234  and second outlet  344 B provided on fourth edge  434 . Therefore, even when fuel cell stack  1  is placed on an inclined place, stable electric generation can be maintained. 
     It is preferable that the plurality of partition walls  34 E are disposed to be displaced with respect to each other in the direction from first edge  134  to third edge  334  such that outlet chamber  346  is the smallest (narrowest) at the center portion of third edge  334  and gradually becomes larger toward first outlet  344 A and second outlet  344 B, respectively. That is to say, the plurality of partition walls  34 E are formed so as to sandwich center partition wall  34 H in substantially an equal interval and in substantially the same length, and form a plurality of linear passages  34 D together with center partition wall  34 H. It is preferable that outlet chamber  346  is formed at the end side of partition walls  34 E and center partition wall  34 H, and that outlet chamber  346  is widened in the direction toward first outlet  344 A and second outlet  344 B. 
     Similarly, a cathode-facing surface of cathode-side end plate  18  has gas inlets (hereinafter, referred to as “inlet”)  183 A and  183 B, inlet chamber  185 , first outlet  184 A, second outlet  184 B, outlet chamber  186 , a plurality of linear partition walls  18 E, and center partition wall  18 H. Inlets  183 A and  183 B are provided on first edge  118 , and inlet chamber  185  is linked to inlets  183 A and  183 B. First outlet  184 A is provided on second edge  218 , and second outlet  184 B is provided on fourth edge  418 . Outlet chamber  186  is linked to first outlet  184 A and second outlet  184 B. 
     Partition walls  18 E are provided in parallel to each other in the direction from first edge  118  to third edge  318 , and center partition wall  18 H is provided in parallel to partition walls  18 E at the center position, in the direction from first edge  118  to third edge  318 . Partition walls  18 E have substantially the same length. Each two of partition walls  18 , and center partition wall  18 H and two partition walls  18 E neighboring center partition wall  18 H form a plurality of linear passages  18 D having the same width, which are linked between inlet chamber  185  and outlet chamber  186  along the direction from first edge  118  to third edge  318 . A space is provided between center partition wall  18 H and an inner wall surface of third edge  318 , and first outlet  184 A and second outlet  184 B communicate with each other via the space. 
     It is preferable that the plurality of partition walls  18 E are disposed to be displaced with respect to each other in the direction from first edge  118  to third edge  318  such that outlet chamber  186  is the smallest at the center portion of third edge  318  and gradually becomes larger toward first outlet  184 A and second outlet  184 B. That is to say, the plurality of partition walls  18 E are formed so as to sandwich center partition wall  18 H in substantially an equal interval and in substantially the same length, and form a plurality of linear passages  18 D together with center partition wall  18 H. It is preferable that outlet chamber  186  is formed at the end side of partition walls  18 E and center partition wall  18 H, and that outlet chamber  186  is widened in the direction toward first outlet  184 A and second outlet  184 B. 
     As shown in  FIGS. 2A and 2B , inlet  343 A and inlet  183 A, inlet  343 B and inlet  183 B, first outlet  344 A and first outlet  184 A, as well as second outlet  344 B and second outlet  184 B are formed in corresponding positions, respectively. That is to say, first edge  134  and first edge  118 , second edge  234  and second edge  218 , third edge  334  and third edge  318 , as well as fourth edge  434  and fourth edge  418  are disposed in the positions corresponding to each other. 
     Inlets  343 A,  343 B,  183 A, and  183 B are provided on the first side surface of cell stack  16  on which first plate spring  11  and second plate spring  12  are not placed. The first side surface is parallel to the laminate direction. The first side surface includes first edges  134  and  118 . On the other hand, first outlets  344 A and  184 A are provided on the second side surface on which first plate springs  11  are applied. The second side surface includes second edges  234  and  218 . Furthermore, second outlets  344 B and  184 B are provided on the fourth side surface on which second plate springs  12  dare applied. The fourth side surface includes fourth edges  434  and  418 . 
     On the other hand, as shown in  FIG. 4 , on a second surface of separator  34 , fuel passage  34 B for supplying fuel to anode electrode  31  is formed in a groove shape. Fuel passage  34 B at a first end is linked to fuel inlet  341  formed on plane portion  34 A via through hole  34 C as shown in  FIG. 2B . On the other hand, fuel passage  34 B at a second end is linked to fuel outlet  342  on first edge  134 . At least one of a reaction product of fuel and a reaction residue of fuel is exhausted from fuel outlet  342 . 
     Also on an anode-facing surface of anode-side end plate  17 , similar to  FIG. 4 , fuel passage  17 B for supplying fuel to anode electrode  31  is formed in a groove shape. Fuel passage  17 B at a first end is linked to fuel inlet  171  formed on plane portion  17 A via through hole  17 C. On the other hand, fuel passage  17 B at a second end is linked to fuel outlet  172  on first edge  134 . At least one of a reaction product of fuel and a reaction residue of fuel is exhausted from fuel outlet  172 . 
     As shown in  FIG. 2B , plane portions  17 A and  34 A are parallel to the laminate direction and are provided on a third side surface on which first plate spring  11  and second plate spring  12  are not placed and which is opposite to the first side surface provided with inlets  343 A,  343 B,  183 A, and  183 B. The third side surface includes third edges  334  and  318 . 
     The dimension of plane portions  34 A and  17 A in the laminating direction is larger than the thickness of a portion of separator  34  where separators  34  sandwich MEA  35  separator  34  and anode-side end plate  17  sandwich MEA  35 . 
     Backing plate  14  is disposed at the anode electrode  31  side in cell stack  16 , and backing plate  15  is disposed at the cathode electrode  32  side. Backing plates  14  and  15  are made of electrically-insulating resin, ceramic, or resin containing a glass fiber, a metal plate coated with an electrically-insulating membrane, or the like. 
     First plate spring  11  and second plate spring  12  fasten cell stack  16  with the spring elastic force thereof via backing plates  14  and  15 . Second plate spring  12  is disposed so as to face first plate spring  11 . First plate spring  11  and second plate spring  12  are made of, for example, a spring steel material. 
     Next, an operation in fuel cell stack  1  is briefly described. As shown in  FIGS. 1 and 5 , anode electrode  31  is supplied with an aqueous solution containing methanol by fuel pump  5 . On the other hand, cathode electrode  32  is supplied with air pressurized by air pump  6 . A methanol aqueous solution as a fuel supplied to anode electrode  31 , and methanol and water vapor derived therefrom are diffused through diffusion layer  31 A to the entire surface of MPL  31 B. These further pass through MPL  31 B and reach catalyst layer  31 C. 
     On the other hand, oxygen contained in the air supplied to cathode electrode  32  is diffused through diffusion layer  32 A to the entire surface of MPL  32 B. The oxygen further passes through MPL  32 B and reaches catalyst layer  32 C. Methanol that reaches catalyst layer  31 C reacts as in formula (1), and oxygen that reaches catalyst layer  32 C reacts as in formula (2). 
       CH 3 OH+H 2 O→CO 2 +6H + +6 e   −   (1)
 
       3/2O 2 +6H + +6 e   − →3H 2 O  (2)
 
     As a result, electric power is generated, as well as carbon dioxide is generated at the anode electrode  31  side, and water is generated at the cathode electrode  32  side as reaction products, respectively. Carbon dioxide is exhausted from fuel outlets  172  and  342  to the outside of fuel cell stack  1 . Gases such as nitrogen that do not react in cathode electrode  32  and unreacted oxygen are also exhausted to the outside of fuel cell stack  1 . Note here that since not all methanol in the aqueous solution react at the anode electrode  31  side, the exhausted aqueous solution is generally allowed to return to fuel pump  5  as shown in  FIG. 1 . Furthermore, since water is consumed in the reaction in anode electrode  31 , water generated in cathode electrode  32  may be allowed to return to the anode electrode  31  side as shown in  FIG. 1 . 
     In the embodiment, cell stack  16  is fastened by first plate spring  11  and second plate spring  12  via backing plates  14  and  15 . First plate spring  11  and second plate spring  12  fasten cell stack  16  extremely compactly along the outer shape of cell stack  16  as shown in  FIGS. 2A and 2B . That is to say, dead space is extremely reduced in size on the side surfaces of cell stack  16 , and fuel cell stack  1  can be reduced in size as compared with the case in which fastening is carried out by using bolts and nuts as in a conventional case. 
     Furthermore, in a case in which bolts and nuts are used for fastening, a pressing point is provided at the outside of cell stack  16 . However, first plate spring  11  and second plate spring  12  have a pressing point in a relatively central portion in cell stack  16 . Therefore, pressing power works in cell stack  16  uniformly in the planar direction of backing plates  14  and  15 . With such a pressing power, entire cell stack  16  can be fastened uniformly. Thus, the electrochemical reactions expressed by the formulae (1) and (2) proceed uniformly in the planar direction of MEA  35 . As a result, current-voltage characteristics of fuel cell stack  1  are improved. 
     Next, an effect of a passage structure provided on a first surface of separator  34  and a cathode facing surface of cathode-side end plate  18  is described. Herein, as a representative example, separator  34  is described. As mentioned above, partition walls  34 E and center partition wall  34 H form a plurality of linear passages  34 D having substantially the same width, which are linked between inlet chamber  345  and outlet chamber  346  along the direction from first edge  134  to third edge  334 . Therefore, the main direction in which air flows is linear one direction. That is to say, bending portions are reduced so as to increase the total cross-sectional area, and thus to reduce a pressure loss as compared with a serpentine-shaped passage. Moreover, even when water as a reaction product is generated inside linear passages  34 D, it easily moves toward outlet chamber  346  by the air supplied from inlet chamber  345 . 
     Furthermore, a plurality of partition walls  34 E have substantially the same length. Therefore, linear passages  34 D other than those neighboring center partition wall  34 H have substantially the same length, and the air resistance is also substantially the same. Therefore, substantially the same amount of air flows in each linear passage  34 D. As a result, in the direction parallel to first edge  134 , air can be supplied uniformly. 
     Moreover, the plurality of partition walls  34 E are disposed to be displaced with respect to each other in the direction from first edge  134  to third edge  334  such that outlet chamber  346  becomes larger gradually toward first outlet  344 A and second outlet  344 B. Therefore, in outlet chamber  346 , since the air resistance is reduced from the center portion of third edge  334  toward first outlet  344 A and second outlet  344 B, and the direction toward first outlet  344 A or second outlet  344 B is the same direction in each linear passage  34 D, smooth air flow can be formed. Therefore, produced water can be allowed to flow to first outlet  344 A or second outlet  344 B with a small air flow pressure. 
     It is preferable that the distance by which two of neighboring partition walls  34 E in the plurality of partition walls  34 E are displaced from each other in the direction from first edge  134  to third edge  334  is constant. Thus, the end portions of partition walls  34 E at the outlet chamber  346  side are linearly aligned. Therefore, a cross-sectional area of outlet chamber  346  is in proportion to the moving distance from the center portion of third edge  334  to first outlet  344 A or second outlet  344 B. As mentioned above, air flows in each linear passage  34 D in substantially the same air volume. Therefore, outlet chamber  346  can receive such exhausted gas smoothly. 
     As shown in  FIG. 3 , inlet  343 A and inlet  343 B are separately provided at first edge  134 . Therefore, fuel outlet  342  and inlets  343 A and  343 B are not overlapped with each other, so that introduction of air into cell stack  16  and outflow of exhausted gas at the fuel side from cell stack  16  can be easily separated from each other. Moreover, by dividing inlets  343 A and  343 B further separately, a pressure loss at inlet chamber  345  can be reduced. However, when the size of fuel cell stack  1  is small, one each of inlets  343 A and  343 B may be provided. 
     Furthermore, as shown in  FIG. 3 , center partition wall  34 H is linked to the inner wall surface of first edge  134  such that inlet chamber  345  is divided into a first inlet chamber and a second inlet chamber at the center part of first edge  134 . First inlet  343 A and second inlet  343 B are linked to the first inlet chamber and the second inlet chamber, respectively. In this configuration, even when first edge  134  is long, air can be supplied uniformly to the entire of inlet chamber  345 . However, when the size of fuel cell stack  1  is small, center partition wall  34 H may not be linked to the inner wall surface of first edge  134 , and the number of gas inlet may be one. 
     Furthermore, protrusions  34 F are provided in inlet chamber  345 . Protrusion  34 F promotes diffusion of air entering from inlets  343 A and  343 B inside inlet chamber  345 . Therefore, substantially the same amount of air can be allowed to flow in each linear passage  34 D reliably. 
     Furthermore, protrusions  34 G are provided in outlet chamber  346 . Protrusion  34 G promotes flow of water generated in linear passages  34 D and pushed out from linear passages  34 D toward first outlet  344 A or second outlet  344 B in outlet chamber  346 . That is to say, when a water droplet attached to one protrusion  34 G expands (extends) toward a downstream side (outlet side) by an air flow pressure, it is brought into contact with next protrusion  34 G and moves easily between protrusions  34 G. 
     Furthermore, similar to partition walls  34 E, when protrusions  34 F and  34 G are formed at such a height that they are brought into contact with cathode electrode  32 , a conducting area between MEAs  35  is increased, which is advantageous in terms of current collection. 
     Also in cathode-side end plate  18 , similarly, protrusions  18 F are provided in inlet chamber  185 , and protrusions  18 G are provided in outlet chamber  186 . 
     Furthermore, it is preferable that the surfaces of protrusions  34 G,  18 G and partition walls  34 E are treated to have a hydrophilic property. Thus, the produced water is not easily formed into a spherical water droplet, and the produced water can be easily exhausted. 
     Next, connection between fuel cell stack  1  and fuel pump  5  is described with reference to  FIGS. 2B and 6 .  FIG. 6  is a perspective view illustrating connection between fuel cell stack  1  shown in  FIG. 2  and fuel pump  5  shown in  FIG. 1 . 
     As shown in  FIG. 2B , plane portions  17 A and  34 A are formed on the third side surface to be connected to fuel pump  5 . In fuel pump  5 , fuel discharging section  51 A is provided on a position corresponding to plane portion  17 A, and each of fuel discharging sections  51 B is provided on a position corresponding to respective one of plane portions  34 A. On fuel discharging section  51 A, seal member  52 A is disposed. Similarly, on each of fuel discharging sections  51 B, seal member  52 B is disposed. Seal members  52 A and  52 B are formed smaller in size than plane portions  17 A and  34 A, respectively. Fuel inlet  171  and fuel discharging section  51 A are allowed to face each other, and each of fuel inlets  341  and respective one of fuel discharging sections  51 B are allowed to face each other. Furthermore, fuel pump  5  and fuel cell stack  1  are fastened by, for example, a bolt so that seal members  52 A and  52 B are compressed by plane portions  17 A and  34 A. Thereby, a fuel passage is sealed. 
     With this structure, even if thin anode-side end plate  17  and separator  34  are used, by securely carrying out sealing with the use of plane portions  17 A and  34 A, the fuel cell stack can be connected to fuel pump  5 . This makes it possible to prevent fuel from leaking at the connection portions. 
     As shown in  FIG. 2B , it is preferable that plane portion  17 A and plane portion  34 A or plane portions  34 A are displaced from each other in the direction perpendicular to the laminating direction.  FIG. 2B  shows that plane portions  17 A and  34 A are provided alternately in the laminating order. With such a position relation, plane portion  17 A and plane portion  34 A, or plane portions  34 A are not brought into contact with each other. Consequently, it is possible to prevent short circuit in cell stack  16 . Furthermore, the degree of freedom in disposing of fuel discharging sections  51 A and  51 B is obtained. 
     Furthermore, it is further preferable that plane portion  17 A and plane portion  34 A or plane portions  34 A are provided on the same plane. By providing plane portion  17 A and plane portion  34 A on the same plane in which they are displaced from each other in the direction perpendicular to the laminating direction, fuel discharging sections  51 A and  51 B may be provided on the same plane. Thus, fuel discharging sections  51 A and  51 B can be sealed, reliably. 
     Furthermore, it is preferable that fuel pump  5  is capable of individually controlling the flow rates of fuel discharged from fuel discharging sections  51 A and  51 B, respectively. By using such a fuel pump  5 , it is possible to supply fuel to each unit cell at an optimum flow rate. Since there is a variation in the electromotive force and/or a pressure loss of a flow passage among unit cells, it is preferable that the flow rate of the fuel is controlled for each unit cell. 
     Thus, fuel pump  5  forming a fuel supply section is attached to the third side surface including third edge  318  of cathode-side end plate  18  and third edge  334  of separator  34 . Accordingly, a fuel cell system can be reduced in size. In the above description, an example is described in which fuel inlets  341  and  171  are provided in plane portions  34 A and  17 A. However, a fuel pump may be connected to a fuel passage by any other configurations. For example, a through hole is provided in the thickness direction of separator  34  from through hole  34 C connected to fuel passage  34 B, and these through-holes are allowed to communicate with each other in the laminating direction of cell stack  16 . Then, fuel may be supplied from a fuel pump to the thus formed communicating tube. Such a configuration is possible because neither gas inlet nor gas outlet is provided on the third edge  334  side. In any case, when a fuel inlet is provided on the third side surface side and fuel pump  5  is disposed on the third side surface side, a fuel cell system can be reduced in size. 
     Next, the connection between fuel cell stack  1  and air pump  6  is described with reference to  FIGS. 2A and 7  to  9 .  FIG. 7  is a perspective view illustrating the connection between fuel cell stack  1  shown in  FIG. 2  and air pump  6  shown in  FIG. 1 .  FIG. 8  is a front view showing a first side surface of fuel cell stack  1 .  FIG. 9  is a sectional view showing integrated member  61  to be attached to the first side surface. 
     Air pump  6  forming a gas supply section has gas discharging section  6 A as shown in  FIG. 9  and is attached to integrated member  61  by bolt  66  as shown in  FIG. 7 . Integrated member  61  includes gas discharging sections  73 A and  73 B and receiver section  74 . Gas discharging section  6 A communicates with gas discharging section  73 A of integrated member  61 , and gas discharging section  73 A communicates with gas discharging section  73 B. Receiver section  74  is configured to receive exhausted gas from fuel outlets  172  and  342 . Receiver section  74  is a hollow structure, and communicates with an exhaust pipe (not shown) provided in the lower part. In this way, integrated member  61  is formed by integrating gas discharging sections  73 A and  73 B configured to supply air sent from air pump  6  to inlets  183 A,  183 B,  343 A, and  343 B and receiver section  74  configured to receive exhausted gas from fuel outlets  172  and  342 . 
     On the other hand, seal member  62  is attached to the first side surface of cell stack  16  as shown in  FIGS. 7 and 8 . The first side surface is provided with inlets  183 A,  183 B,  343 A, and  343 B as well as fuel outlets  172  and  342 . Seal member  62  is provided with opening  63 A at the position corresponding to inlets  183 A and  343 A, and opening  63 B at the position corresponding to fuel inlets  183 B and  343 B. On the other hand, seal member  62  is provided with opening  64  at the position corresponding to fuel outlets  172  and  342 . 
     Integrated member  61  is attached to fuel cell stack  1  with seal member  62  sandwiched therebetween by screwing screws  65  into screw holes  67  provided on backing plates  14  and  15 . In this state, seal member  62  separates inlets  183 A,  183 B,  343 A, and  343 B from fuel outlets  172  and  342 . Furthermore, seal member  62  connects gas discharging section  73 A to inlets  183 A and  343 A, gas discharging section  73 B and inlets  183 B and  343 B, respectively. Therefore, air sent from air pump  6  is supplied to inlets  183 A,  183 B,  343 A, and  343 B. Furthermore, seal member  62  binds receiver section  74  to fuel outlets  172  and  342 . 
     By using integrated member  61  and seal member  62  in this way, an air introducing passage and a fuel side exhaust passage can be formed on the first side surface in compact in size. As a result, a fuel cell system can be reduced in size. 
     In the above description, a configuration is described in which a plurality of MEAs  35  are used and separator  34  is interposed between MEAs  35 , end plates  17  and  18  are disposed on both ends in the laminating direction so as to form cell stack  16 , and backing plates  14  and  15  are further disposed on the outside end plates  17  and  18 . However, the present invention is not limited to this configuration. A single MEA  35  may be sandwiched by end plates  17  and  18  from the both sides in the laminating direction, and MEA  35  and end plates  17  and  18  may be fastened in the laminating direction in MEA  35  by only first plate spring  11 . In this case, it is preferable that first plate spring  11  is formed so as to press the vicinity of the center part of end plates  17  and  18 . Needless to say, in this configuration, second plate spring  12  may further be used. Furthermore, in  FIGS. 2A and 2B , a plurality of first plate springs  11  and second plate springs  12  are used. However, one first plate spring  11  and one second plate spring  12  may be used depending upon the size of cell stack  16 . Thus, the subject to be pressed may be a single cell or a cell stack. One plate spring may be used and a plurality of or a pair of or a plurality of pairs of plate springs may be used. 
     Furthermore, without using backing plates  14  and  15 , end plates  17  and  18  may be directly sandwiched by first plate spring  11  and second plate spring  12 . In this case, an insulating film is formed inside the C-shaped cross section of each of first plate spring  11  and second plate spring  12  so that first plate spring  11  does not cause short circuit. Furthermore, fastening sections (for example, screw hole  67 ) between fuel pump  5  and integrated member  61  are provided on end plates  17  and  18 . That is to say, backing plates  14  and  15  are not essential. 
     However, it is preferable that backing plates  14  and  15  are provided and that backing plates  14  and  15  are formed of different materials from those of end plates  17  and  18 . Thus, it is possible to optimize backing plates  14  and  15  that directly receive a pressing force of first plate spring  11 , and end plates  17  and  18  that also function as flow passages of fuels and air. For example, by forming backing plates  14  and  15  with materials harder than end plates  17  and  18 , it is possible to suppress the deformation of backing plates  14  and  15  due to the pressing force of first plate spring  11 . As a result, a unit cell of fuel cell or a cell stack can be fastened more uniformly in the planner direction of MEA  35 . Furthermore, by forming backing plates  14  and  15  with an insulating material, it is not necessary to consider short circuit due to arm sections of first plate spring  11 . 
     In this embodiment, cell stack  16  is fastened by using first plate spring  11  and second plate spring  12 , and fuel and air are supplied from facing side surfaces that are not fastened by first plate spring  11  and second plate spring  12 . However, the present invention is not limited to this configuration. When second plate spring  12  is not used, a side surface, which is covered with second plate spring  12  in this embodiment, may be used for supplying fuel and air. Furthermore, when a pair of backing plates are fastened by, for example, a bolt, without using first plate spring  11  and second plate spring  12 , any side surfaces may be used for supplying fuel and air. 
     In the embodiment, DMFC is described as an example. However, the configuration of the present invention can be applied to any fuel cells using a power generation element that is the same as cell stack  16 . For example, the configuration of the present invention may be applied to a so-called polymer solid electrolyte fuel cell and a methanol modified fuel cell, which use hydrogen as fuel. However, DMFC is operated at a relatively low temperature and produced water is easily aggregated in the passage. Therefore, the present invention is particularly effective in DMFC. 
     In the above description, inlets  183 A and  183 B are formed on first edge  118  of end plate  17 , first outlet  184 A is formed on second edge  218 , and second outlet  184 B is formed on fourth edge  418 . Similarly, inlets  343 A and  343 B are formed on first edge  134  of separator  34 , first outlet  344 A is formed on second edge  234 , and second outlet  344 B is formed on fourth edge  434 . These inlet and outlets faces out sides of cell stack  16  on the respective edges. However, the present invention is not limited to this structure. In other words, it is not necessary to provide the gas inlets on the first edge, the first outlet on the second edge, and the second outlet on the fourth edge. For example, a gas inlet can be formed as a through hole extending along a thickness direction of end plate  18  and separator  34  at a vicinity of each of the first edges. In this case, a tube is inserted in the through holes so that the cathode-facing surface of end plate  18  and the first surface of each of separator  34  communicate to each other, the tube is extended to the underside of cell stack  16  and gas including oxidant can be supplied from the extended portion. The first and second outlets can be formed in the same manner. Thus, it is acceptable that the gas inlets are provided at the first edge sides, the second outlets are provided at the second edge sides, and the second outlets are provided at the fourth edge sides. 
     As mentioned above, separator  34  includes a first surface configured to face cathode electrode  32  and a second surface provided on a rear side of the first surface and configured to face anode electrode  31 . Furthermore, separator  34  includes first edge  134 , second edge  234  that is adjacent to first edge  134 , third edge  334  that faces first edge  134  and is adjacent to second edge  234 , and fourth edge  434  that faces second edge  234  so that separator  34  is defined of a first edge side along first edge  134 , a second edge side along second edge  234 , a third edge side along third edge  334 , and a fourth edge side along fourth edge  434 . The first surface includes inlets  343 A and  343 B provided at the first edge  134  side, inlet chamber  345 , first outlet  344 A provided at the second edge  234  side, second outlet  344 B provided at the fourth edge  434  side, outlet chamber  346 , a plurality of linear partition walls  34 E, and center partition wall  34 H. Inlet chamber  345  is linked to inlets  343 A and  343 B, and outlet chamber  346  is linked to first outlet  344 A and second outlet  344 B. 
     Partition walls  34 E are provided in parallel to each other in the direction from first edge  134  to third edge  334 , and center partition wall  34 H is provided in parallel to partition walls  34 E at the center position, in the direction from first edge  134  to third edge  334 . A plurality of partition walls  34 E have substantially the same length. Each two of partition walls  34 E, or center partition wall  34 H and two partition walls  34 E neighboring center partition wall  34 H form a plurality of linear passages  34 D having the same width and being linked between inlet chamber  345  and outlet chamber  346  along the direction from first edge  134  to third edge  334 . A space is provided between center partition wall  34 H and an inner wall surface of third edge  334 , and first outlet  344 A and second outlet  344 B communicate with each other via the space. Thus, regardless of the inclined direction of fuel cell stack  1 , water produced from the entire first surface can be exhausted from at least one of first outlet  344 A and second outlet  344 B. 
     Furthermore, it is preferable that partition walls  34 E are disposed to be displaced with respect to each other in the direction from first edge  134  to third edge  334  such that outlet chamber  346  is the smallest at the center portion of third edge  334  and it gradually becomes larger toward first outlet  344 A and second outlet  344 B. 
     With this passage configuration, even with a small air flow pressure, produced water can be smoothly exhausted from linear passage  34 D by the flow of air. Accordingly, the reduction of output due to closing of the passage by the produced water can be suppressed. Alternatively, an operation can be carried out with a small flowing pressure. 
     It is preferable that the distance by which two neighboring partition walls  34 E in the plurality of partition walls  34 E are displaced in the direction from first edge  134  toward third edge  334  is constant. Thus, the flow of air becomes smoother. 
     Furthermore, it is preferable that a plurality of inlets  343 A and  343 B are provided at first edge  134  and are linked to inlet chamber  345 . Thus, air can be easily blown to each linear passage  34 D more uniformly. 
     Furthermore, it is preferable that center partition wall  34 H is linked to the inner wall surface of first edge  134  so that inlet chamber  345  is divided into a first inlet chamber and a second inlet chamber at the center portion of first edge  134 , and inlets  343 A and  343 B are linked to the first inlet chamber and the second inlet chamber, respectively. Thus, air can be easily blown to each linear passage  34 D more uniformly. 
     Furthermore, the fuel cell stack includes cathode-side end plate  18 , membrane electrode assembly  35 , and anode-side end plate  17 . Membrane electrode assembly  35  is formed by laminating cathode electrode  32 , electrolyte membrane  33  and anode electrode  31  to each other. Cathode electrode  32  faces cathode-side end plate  18 , and anode electrode  31  is provided at the rear side with respect to cathode electrode  32 . Electrolyte membrane  33  is interposed between cathode electrode  32  and anode electrode  31 . Cathode-side end plate  18  has a passage configuration similar to that of the first surface of the above-mentioned separator  34  on a cathode-facing surface that faces cathode electrode  32 . With this configuration, produced water can be exhausted smoothly by an air flow passage structure formed in cathode-side end plate  18 . 
     Furthermore, the fuel cell system according to this embodiment includes the above-mentioned fuel cell stack, a fuel supply section including fuel pump  5 , and a gas supply section including air pump  6 . Fuel passage  17 B is provided on a surface of anode-side end plate  17 , which faces anode electrode  31 , and fuel inlet  171  linked to fuel passage  17 B is provided on the edge side corresponding to the third edge  318  side of cathode-side end plate  18 . The fuel supply section is disposed on the surface side including third edge  318  of cathode-side end plate  18  of the fuel cell stack and supplies fuel to fuel inlet  171  of anode-side end plate  17 . The gas supply section supplies gas that contains an oxidizing agent to inlets  343 A and  343 B of cathode-side end plate  18 . With this configuration, in addition to the effect of the above-mentioned fuel cell stack, a fuel cell system can be reduced in size. 
     Alternatively, fuel cell stack  1  includes, in addition to the above-mentioned configuration, first and second membrane electrode assemblies  35 , and separator  34  inserted between first and second membrane electrode assemblies  35 . The configuration of separator  34  is the same as mentioned above. That is to say, separator  34  includes first edge  134 , second edge  234  and third edge  334  in positions corresponding to first edge  118 , second edge  218  and third edge  318  of cathode-side end plate  18 , respectively. In this configuration, with an air passage structure formed on separator  34  or cathode-side end plate  18 , produced water can be exhausted smoothly. 
     Furthermore, also in a fuel cell system using fuel cell stack  1 , in addition to the above-mentioned effect of fuel cell stack  1 , the fuel cell system can be reduced in size. 
     As mentioned above, in the fuel cell stack and the fuel cell system using the fuel cell separator of the present invention, a liquid product at the cathode electrode side can be exhausted from at least one of the first outlet and the second outlet regardless of the inclined direction of the fuel cell stack. Therefore, the reduction of output due to closing of the passage by the produced water can be suppressed. Alternatively, an operation can be carried out with a small flowing pressure. Such a fuel cell stack and a fuel cell system using the same are useful as power sources for small electronic devices.