Patent Publication Number: US-2009239129-A1

Title: Metal separator for fuel cell

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a metal separator for a fuel cell, and particularly relates to the metal separator for the fuel cell capable of improving a sealing performance in peripheral parts of manifold holes. 
     2. Description of the Related Art 
     A metal separator which is thinner and stronger than a graphite separator (having thickness of 2 mm or more) is under development, as a separator for a fuel cell. A metal plate having thickness of 0.1 to 0.2 mm is normally used as the metal separator. In a polymer electrolyte fuel cell, a separator and a membrane electrode assembly (MEA), being a power generation layer (power generator, single cell) of the fuel cell are alternatively laminated to form a stack (cell stack). 
     If compared with the graphite separator, the metal separator has a thin body in a stacking direction of the separator, and such a thin separator has an advantage that it contributes to realizing a compact stack. In addition, if compared with the graphite separator, the metal separator has characteristics such as toughness in spite of its thin body and ductility, having practically sufficient strength, and capable of surely blocking gas because metal does not allow the gas to pass through. 
     However, when aiming to make the metal separator compact in a stacking direction of the fuel cell, it is difficult to form a gas flow passage to MEA from manifold holes (through holes penetrating the separator, which are the holes for forming a gas communication path common to the stacked fuel cell, for supplying the gas to each cell in the stacking direction), due to the elasticity of the thin metal separator. This invites an unstable gas sealing of this gas flow passage forming part. As a result, there is a possibility that gas leak occurs and power generation characteristics of the fuel cell are unstable. 
     Namely, a part between the metal separator and the power generation layer of the fuel cell is normally sealed by providing a soft seal member such as rubber. However, dimension accuracy of the soft member such as rubber is low and its strength is also low, and accordingly the strength of a sealing part in the periphery of the manifold holes is insufficient, thus involving a problem of insufficient seal to thereby cause the gas leak to occur by this insufficient seal. 
     For example, patent documents 1 to 4 are known as conventional techniques regarding the seal of this kind of separator. 
       FIG. 9A  and  FIG. 9B  show graphite separators disclosed in patent document 1.  FIG. 9A  is a plan view of the separator, and  FIG. 9B  is an expanded sectional view of an essential part of a periphery of the manifold holes of the fuel cell stacked by using the separator. As shown in  FIG. 9   a  and  FIG. 9B , in a gas flow structure from manifold holes  101  to a single cell (MEA)  102 , communication parts between a flow passage  103  of the separator  100  and the manifold holes  101  are communicatingly connected by a through hole  108  that penetrates to the other surface of the separator  100  from a surface of the separator  100  on which the flow passage  103  is formed, and by a groove  107  for communicating the through hole  108  and the manifold hole  101 . In addition, seal materials  105  are provided between a separator  100  and a single cell  102 , between a separator  104  and the single cell  102 , and between the separator  100  and a separator  106 , in the periphery of the manifold hole  101 . 
       FIG. 10  shows a graphite separator disclosed in patent document 2. As shown in  FIG. 10 , manifold holes  115  and flow passage grooves  111  are formed on a separator  110 . The manifold holes  115  and the flow passage grooves  111  are connected to each other by through holes  113  that penetrate to the surface of the opposite side from the surface on which the flow passage grooves  111  of the separator  110  are formed; grooves  114  formed on the surface of the opposite side, for communicating the manifold holes  115  and the through holes  113 ; and grooves  112  formed on the surface on which the flow passage grooves  111  are formed, for communicating the through holes  113  and the flow passage grooves  111 . 
       FIG. 11  shows the separator using the metal separator having a surface conductive treatment clad layer disclosed in patent document 3. As shown in  FIG. 11 , the separator is constituted of a metal separator  120  and a resin frame  123 . Manifold holes  121  and a plurality of pressed flow passage grooves  122  are formed on the metal separator  120 . In addition, manifold holes  121 , an opening  124  formed at a position corresponding to a power generator, and inlet grooves  125  formed on the gas flow passage to a plurality of flow passage grooves  122  from the manifold holes  121 , are provided on the resin frame  123 . 
     Patent document 4 provides an improved technique of the separator of the patent document 3, and basically sealing performance is increased by forming the resin frame  123  of the patent document 3 into a seal frame. Then, the seal frame is formed by screen-printing a seal material composed of an elastic body such as rubber, on the resin frame  123 . 
     When techniques of the patent document 3 and the patent document 4 are used, a compact separator for a fuel cell can be formed, and cell characteristic of the fuel cell is also stable. 
     (Documents of Conventional Techniques) 
     (Patent Document 1) 
     Japanese Patent Laid Open Publication No. 2002-83614 
     (Patent document 2) 
     Japanese Patent Laid Open Publication No. 2002-298872 
     (Patent document 3) 
     Japanese Patent Publication No. 3723515 
     (Patent document 4) 
     Japanese Patent Laid Open Publication No. 2006-172845 
     The graphite separator of the patent document 1 and the patent document 2 has a structure in which through holes  108 ,  113  and grooves  107 ,  114  are provided on the separator, as a gas flow structure to a power generation layer from the manifold holes. These through holes  108 ,  113 , and the grooves  107 ,  114  are face-sealed by being covered with the separator  106 , etc, for inter-layer sealing. This seal is stable owing to face-sealing. However, in order to perform face-sealing, the separator  106 , etc, must be separately added, and when the techniques of the patent document 1 and the patent document 2 are applied to the metal separator, thinness and compactness, which are the characteristics of the metal separator, is halved and cost is increased. 
     Meanwhile, in the separator disclosed in the patent document 3 and the patent document 4, the resin frame  123  or a seal frame is used, thus involving a problem of incurring a high cost as a result. In addition, projection parts for forming inlet grooves  125  on fringe parts of the manifold holes are provided in the resin frame  123  or the seal frame, to form the flow passage. Therefore, stable sealing performance is not ensured. 
     Thus, when aiming to make the metal separator compact in the stacking direction of the fuel cell, it is difficult to form the gas flow passage to the power generation layer from the manifold holes, thus making the gas seal unstable in this gas flow passage forming part, because the metal separator is thin and has elasticity. This poses a problem of inviting gas leak and unstable power generation characteristics of the fuel cell. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a compact metal separator for the fuel cell capable of increasing the sealing performance in the peripheral parts of the manifold holes. 
     An aspect of the present invention provides a metal separator for a fuel cell, including: 
     a plurality of flow passage grooves for flowing a fluid for operating the fuel cell; 
     manifold holes provided on each side of an upper stream and a lower stream of the plurality of flow passage grooves and formed so as to penetrate a separator made of metal for the fuel cell; 
     communication grooves formed on a separator surface of the separator, for connecting inlets/outlets of the plurality of flow passage grooves and the manifold holes to flow the fluid; 
     a fluid flowing structure part made of metal, in which a through hole is formed on the separator surface that forms the communication grooves, formed in the vicinity of the manifold hole so as to traverse the communication groove; and 
     a flat seal surface formed on the fluid flowing structure part, for sealing a surface of a member that shields an opening of the communication grooves in a state of a face contact. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view of a metal separator for a fuel cell according to a first embodiment of the present invention. 
         FIG. 1B  is a perspective view of a gasket provided on the separator of  FIG. 1A . 
         FIG. 1C  is a perspective view of a gasket provided on the separator of  FIG. 1A . 
         FIG. 2  is an exploded perspective view showing a stack of the fuel cell made by using the metal separator for the fuel cell according to the first embodiment. 
         FIG. 3  is a sectional view of the stack of  FIG. 2  cut at a part corresponding to the line A-A of  FIG. 1 . 
         FIG. 4A  is an expanded plan view of peripheral parts of manifold holes of  FIG. 1A , showing an essential part of the separator of  FIG. 1A . 
         FIG. 4B  is an expanded sectional view taken along the line R-R of  FIG. 4A . 
         FIG. 4C  is an expanded sectional view of  FIG. 4A  and  FIG. 4B  taken along the line U 1 -U 1 . 
         FIG. 4D  is an expanded sectional view of  FIG. 4A  and  FIG. 4B  taken along the line U 2 -U 2 . 
         FIG. 5  is a perspective view showing an expanded periphery of a fluid flowing structure part in the separator of  FIG. 1 . 
         FIG. 6  is an arrangement view showing a positional relation in which each part of the stack of  FIG. 2  is arranged, with its sectional stacking position aligned. 
         FIG. 7  is a step view showing the step of making the fluid flowing structure part in the metal separator for the fuel cell according to a second embodiment of the present invention. 
         FIG. 8  is a perspective view showing the fluid flowing structure part formed by a manufacturing step of  FIG. 7  and a part of the separator in its periphery. 
         FIG. 9A  is a plan view of a conventional graphite separator. 
         FIG. 9B  is an expanded sectional view of the periphery of the manifold holes of the fuel cell stacked by using the separator of  FIG. 9A . 
         FIG. 10  is a perspective view showing the conventional graphite separator. 
         FIG. 11  is an exploded perspective view showing a conventional separator. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     Preferred embodiments of the present invention will be described hereunder, based on the drawings. 
     First Embodiment 
       FIG. 1A  is a plan view of a metal separator for a fuel cell according to a first embodiment of the present invention.  FIG. 1B  and  FIG. 1C  are perspective views of a gasket provided on the separator of  FIG. 1A . 
     As shown in  FIG. 1A , a metal separator  2  for the fuel cell is made by using a rectangular metal plate. The metal plate having thickness of, for example, 0.1 to 0.2 mm is used. As a material of the separator  2  made of metal, for example, it is preferable to use a Ti clad material clad with Ti (titanium) on the surface of a metal base material and further subjected to surface conductive treatment. 
     A plurality of flow passage grooves  6 , being fluid supply/discharge passages for supplying/discharging a fluid for operating the fuel cell, are formed in a center part of the rectangular separator  2 . The plurality of fluid passages grooves  6  are linearly formed in parallel to each other along a direction of a long line of the rectangular separator  2 .  FIG. 5  is an expanded view of a part of the plurality of flow passage grooves  6 , wherein flow passage grooves have a waveform structure with a cross-sectional face formed into a trapezoidal shape, and is molded by press working. A rib  16  is provided between flow passage grooves  6 ,  6 , and a side face of the flow passage groove  6  is formed by the rib  16 . Note that when the separator  2  is viewed from a backside, with a separator face  2   a  of the separator  2  shown in  FIG. 5  set as a surface (front surface), the flow passage grooves  6  shown in  FIG. 5  constitute ribs, and the ribs  16  constitute the flow passage grooves. A fluid for operating the fuel cell different from that of the front side is flown through the flow passage grooves of the backside. 
     Rectangular manifold holes  7   a ,  9   a ,  8   b  are formed on the separator  2  of one of the inlet/outlet sides of the plurality of flow passage grooves  6 , so as to penetrate the separator  2 . Also, rectangular manifold holes  8   a ,  9   b ,  7   b  are formed on the separator  2  of the other inlet/outlet side of the plurality of flow passage grooves  6 . The manifold holes are the holes for forming the gas communication passage common to the fuel cell, for supplying/discharging the gas to each power generation layer in the stacking direction of the fuel cell in which the separator  2 , etc, is stacked (see  FIG. 2 ). 
     The manifold holes  7   a  and  7   b  arranged at diagonal positions of four corner parts of the rectangular separator  2  are the holes for supplying/discharging a fuel gas (such as hydrogen gas). A manifold hole  7   a  is provided for supplying the fuel gas, and a manifold  7   b  is provided for discharging the fuel gas. Similarly, the manifold holes  8   a  and  8   b  arranged at the diagonal positions are the holes for supplying/discharging an oxidant gas (such as air and oxygen gas). The manifold hole  8   a  is provided for supplying the oxidant gas, and the manifold hole  8   b  is provided for discharging the fuel gas. A manifold hole  9   a  positioned between the manifold holes  7   a  and  8   b , and a manifold hole  9   b  positioned between the manifold holes  8   a  and  7   b  are the manifold holes for supplying/discharging a cooling fluid (such as cooling water). The manifold hole  9   a  is provided for supplying the cooling fluid, and the manifold hole  9   b  is provided for discharging the cooling fluid. The fluid for operating the fuel cell is the fuel gas, the oxidant gas, and the cooling fluid. 
     Communication grooves  10  for flowing the fluid for operating the fuel cell are respectively formed between the inlet/outlet of the plurality of flow passage grooves  6  and the manifold holes  7   a ,  7   b ,  8   a ,  8   b ,  9   a ,  9   b . The communication grooves  10  shown in solid line in  FIG. 1A  are formed into the flow passages (diffuser parts) with gradually larger groove width toward the inlet/outlet of the plurality of flow passage grooves  6  from the manifold holes  7   a  and  7   b  side. In addition, as shown by chain line in  FIG. 1A , the communication grooves  10  for communicatingly connecting the manifold holes  8   a ,  8   b ,  9   a ,  9   b  and the inlet/outlet of the plurality of flow passage grooves  6 , are also formed into a similar expanded flow passages (diffuser parts). 
     For example, the fuel gas such as the hydrogen gas supplied to the communication grooves  10  from the manifold hole  7   a  is expandingly flown through the communication grooves  10 , then distributed and flown into the plurality of flow passage grooves  6 . The fuel gas such as the hydrogen gas flown out from the plurality of the flow passage grooves  6  is merged at the communication groove  10  on the manifold hole  7   b  side, and flown so as to gradually gather in the communication groove  10 , and is discharged from the manifold hole  7   b.    
     A gasket  11 , being a seal surface part of the separator  2 , is attached to the surface of the separator  2  by adhesive agent, etc. Preferably, the gasket  11  is made by using a material such as resin or rubber, so that no adverse influence is added on the cell characteristics. 
     The gasket  11  installed on the upper surface of the separator  2  shown in  FIG. 1A  is constituted of a rectangular annular gasket  11   b  surrounding an outer peripheral part of the manifold hole ( FIG. 1B ), and a gasket  11   a  provided on both sides of the plurality of flow passage grooves  6  ( FIG. 1C ). The gasket  11   b  is respectively installed on outer peripheral parts of the manifold holes  8   a ,  8   b ,  9   a ,  9   b , on the upper surface of the separator  2  shown in  FIG. 1A . The gasket  11   a  is also a member for separately forming the communication grooves  10 , etc, being the flow passages of the fuel gas flowing over the separator  2  of  FIG. 1A . The gaskets  11   a ,  11   a  are installed so as to surround both sides of the communication grooves  10 ,  10 , both sides of the plurality of flow passage grooves  6 , and the outer peripheral part excluding the side of the communication grooves  10 ,  10  of the manifold holes  7   a ,  7   b . Also, the gasket is similarly provided on the surface of the separator  2  on which the oxidant gas and the cooling fluid is flown. 
     The upper surface of the separator  2  shown in  FIG. 1A  is a surface on which the flow passage for flowing the fuel gas such as hydrogen is formed, and fluid flowing structure parts  15 ,  15  made of metal are provided on the communication grooves  10 ,  10  positioned on the outer peripheral parts of the manifold holes  7   a ,  7   b  for supplying/discharging the fuel gas, so as to traverse the communication grooves  10 ,  10 . 
     Similarly, the fluid flowing structure parts  15 , are provided on the communication grooves  10  positioned on the outer peripheral parts of the manifold holes  8   a ,  8   b , so as to traverse the communication grooves  10 ,  10 , on the surface of the separator  2  on which the flow passage for flowing the oxidant gas such as air is formed. Also, similarly the fluid flowing structure parts  15 ,  15  are provided on the communication grooves  10 ,  10  positioned on the outer peripheral parts of the manifold holes  9   a ,  9   b , so as to traverse the communication grooves  10 ,  10 , on the surface of the separator  2  on which the flow passage for flowing the cooling fluid such as cooling water is formed. 
     The fluid flowing structure parts  15 ,  15  will be further specifically described. A fluid flowing structure part  15  provided facing the fringe part of the manifold hole  7   a  will be described hereunder, by using the drawings. However, the fluid flowing structure part  15  installed on the other communication groove  10  has also the same structure. 
       FIG. 4A  is an expanded plan view of the peripheral part of the manifold hole  7   a  of  FIG. 1A ,  FIG. 4B  is an expanded sectional view of  FIG. 4A  taken along the line R-R,  FIG. 4C  is an expanded sectional view of  FIG. 4A  and  FIG. 4B  taken along the line U 1 -U 1 , and  FIG. 4D  is an expanded sectional view of  FIG. 4A  and  FIG. 4B  taken along the line U 2 -U 2 . Also,  FIG. 5  is a perspective view of the fluid flowing structure part  15  viewed from the manifold hole  7   a  side. 
     As shown in  FIG. 4A  to  FIG. 4D , and  FIG. 5 , the fluid flowing structure part  15  has a seal member  12  of a flat plate shape positioned apart from the separator surface  2   a , in parallel to the separator surface  2   a  of the separator  2  that forms the communication groove  10 . Minute gap (flow passage with slit-like cross sections) formed between the seal member  12  and the separator surface  2   a  is the through hole (flowing hole)  14  through which the fuel gas flowing through the manifold hole  7   a  passes. The surface of the seal member  12  of the opposite side to the separator surface  2   a  side is a flat seal surface  12   a . The seal surface  12   a  of the seal member  12  seals a surface of a member for shielding the opening of the communication groove  10  (such as a support frame  1   a  as will be described later) in a state of a face contact. Attachment parts  12   b  for attaching the seal member  12  to the separator surface  2   a  are provided at both ends and in the center of the seal member  12 . The seal member  12  is supported by the attachment parts  12   b , so as to be apart from the separator surface  2   a , and can be formed, for example by folding a plate material for manufacturing the seal member  12  in a step form. The attachment parts  12   b  are fixed to the separator surface  2   a  of an outer fringe part of the manifold hole  7   a  by adhesion or welding. 
     Reinforcing members  13  for reinforcing the seal member  12  are provided in the through holes  14  between the attachment parts  12   b ,  12   b . The reinforcing members  13  receive a surface pressure such as 10 kg/cm 2  added to the seal member  12  in the stacking direction (plate thickness direction of the separator  2 ) at the time of stacking the separator  2 , and the seal member  12  is supported thereby in parallel to the separator surface  2   a , so as to withstand this seal surface pressure. As shown in  FIG. 5  and  FIG. 4B , the reinforcing members  13  are sectional arch-like members, with its longitudinal direction provided along the communication groove  10 . A plurality of reinforcing members  13  are provided at predetermined intervals in the longitudinal direction of the seal member  12  (groove width direction of the communication groove  10 ). A convex surface of each reinforcing member  13  is attached and fixed to the seal member  12  by spot welding or adhesion. 
     Since the reinforcing members  13  are provided in the through holes  14 , as shown in  FIG. 4B ,  FIG. 4C , and  FIG. 4D , each through hole  14  is constituted of a through hole  14   a  formed between the reinforcing members  13 ,  13 , and a tunnel-shaped through hole  14   b  formed between the reinforcing members  13  and the separator  2 . 
     Since a plurality of reinforcing members  13  are provided along the communication groove  10  at predetermined intervals in a groove width direction of the communication groove  10 , the gas can be uniformly flown into the communication groove  10  in the groove width direction of the communication groove  10 . Further, since the communication groove  10  is a flow passage, with its groove width gradually increasing toward the inlet/outlet side of the flow passage grooves  6 , uniformity of a gas pressure in the communication groove  10  is achieved, and the gas, with uniform flow rate, is flown into each flow passage groove  6 . 
     The fluid flowing structure part  15  is a structure having a predetermined rigidity, by providing the attachment part  12   b  and the reinforcing member  13 , on the plate-shaped seal member  12 . As a result, deformation of the seal member  12  is restrained, and the sealing performance in the peripheral part of the manifold holes, into which the fluid is supplied/discharged, is considerably improved. 
     For example, as shown in  FIG. 1A , the outer peripheral part of the manifold hole  9   a  is surrounded by the rectangular annular gasket  11   b , and the strength and the sealing performance of the outer peripheral part of the manifold hole  9   a  is thereby ensured. Meanwhile, although three sides of the outer peripheral part of the manifold hole  7   a  excluding the communication groove  10  side is surrounded by the gasket  11   a , one side of the outer peripheral part of the communication groove  10  side of the manifold hole  7   a  is opened. However, by providing the fluid flowing structure part  15 , being the structure having rigidity, on one side of the outer peripheral part of the communication groove  10  side where no gasket  11   a  exists, it is possible to create a state such as surrounding four sides of the outer peripheral part of the manifold hole  7   a  by a gasket, with the through holes  14  opened, and the strength and the sealing performance of the outer peripheral part of the manifold hole  7   a  is ensured. 
     Accordingly, sealing failure of the peripheral part of the manifold hole and gas leak can be prevented, and consequently the fuel cell characteristics can be stabilized, by the separator  2  made of metal according to this embodiment. 
     Note that although the reinforcing member may not be a member with arch-like cross-section, preferably the reinforcing member and the attachment part have a slightly deformable elastic structure, while uniformly supporting the pressure in the surface added to the seal member  12 . 
     The fluid flowing structure part  15  is formed of a metal plate of the same kind or similar kind as that of the separator  2  made of metal, from a viewpoint of strength and chemical stability. Although not surface conductivity is necessary like the separator  2  made of metal, for example Ti (titanium) clad material or Ti plate material is preferably used, and a plate material having a thickness of 0.2 mm or less and 50 μm or more is preferably used. Although smaller thickness is favorable for the plate material for use, provided that the flow passage can be ensured, in a case of an excessively small thickness, the strength is decreased. Therefore the thickness is preferably set at 0.2 mm or less and 50 μm or more. 
     The fluid flowing structure part  15  of this embodiment is formed separately from the separator  2  and installed on the separator  2 . Therefore, a thinner plate material than that of the separator  2  can be used. This makes it possible to optimize a flow passage sectional area of the through hole  14 , and also optimize the sealing performance/sealing surface pressure, by appropriately selecting dimension/number of the seal member  12  and the reinforcing member  13 . In addition, an attachment position of the fluid flowing structure part  15  on the communication groove  10  can be freely adjusted. 
     Next, an example of a polymer electrolyte fuel cell using the aforementioned separator  2  will be described.  FIG. 2  is an exploded perspective view of the stack of the fuel cell having a lamination structure using the separator  2 , etc, of  FIG. 1A . 
     As shown in  FIG. 2 , a power generation layer (power generation part, cell)  1  of the fuel cell is provided between separators  2 ,  2 . The power generation layer  1  is constituted of a MEA (membrane/electrode assembly)  1   a  and a support frame  1   b  for supporting the outer peripheral part of the MEA  1   a . The MEA  1   a  has a sandwich structure, with a polymer electrolyte membrane placed between two electrodes. The polymer electrolyte membrane of the MEA  1   a  is made of a water-permeable resin, and the support frame  1   b  is made of a water-impermeable resin. 
     The support frame  1   b  is a seal part in a face contact with the gaskets  11   a ,  11   b  of the separator  2 , and is also a member for forming a power generation flow passage part including a plurality of flow passage grooves  6 , and an expanded flow passage including the communication groove  10 . Three manifold holes  1   c  communicating with the manifold holes  7   a ,  7   b ,  8   a ,  8   b ,  9   a ,  9   b  of the separator  2  at the time of laminating the stack, are formed on both sides of the support frame  1   b . A diffusion layer  3  of a reaction gas (common designation of the fuel gas and oxidant gas) is provided between the power generation flow passage part of the separator  2  on which a plurality of flow passage grooves  6  are formed, and the MEA  1   a . Also, a diffusion layer  4  of a cooling fluid is provided on the opposite side to the diffusion layer  3  side of the separator  2 . The diffusion layer  3  and the diffusion layer  4  are manufactured by using a carbon cross and carbon paper, etc. Note that the material of the diffusion layer  4  is not limited to the carbon cross and the carbon paper, and may be a material having conductivity, cushioning property, and not contaminating water. 
     In  FIG. 2 , when a laminating direction, in which the separators  2 , etc, are laminated, is set as a vertical direction, a unit from the diffusion layer  4  of the cooling fluid to the separator  2  of the lower side as shown in the figure is set as a unit U. Then, by repeatedly vertically laminating this unit U, a stack (cell stack) S of the fuel cell is constituted. The MEA  1   a  is sandwiched between power generation flow passage parts of the vertical separators  2 , and is fastened thereto under a fixed pressure. 
       FIG. 3  is a sectional view of the stack of  FIG. 2  cut at a part corresponding to the line A-A of  FIG. 1 . As shown in the figure, seal members  12  are provided on a layer for flowing H 2  gas as a fuel gas, via a plurality of reinforcing members  13  on the separators  2 , and the through holes  14  are formed between the separators  2  and the seal members  12 , and the H 2  gas is flown into these through holes  14  from the manifold hole. The seal members  12  supported by a plurality of reinforcing members  13  are air-tightly pressed against support frames  1   b  of the power generation layer at a uniform surface pressure. Layers not allowing the H 2  gas to flow are shielded by the gaskets  11   b.    
       FIG. 6  is an arrangement view showing a positional relation of each sectional part of the stack of  FIG. 2 , with sectional laminating positions aligned.  FIG. 6(   a ) is a sectional view of a part corresponding to the line A-A of  FIG. 1A ,  FIG. 6(   b ) is a sectional view of a part corresponding to the line C-C of  FIG. 1A ,  FIG. 6(   c ) is a sectional view of a part corresponding to the line B-B of  FIG. 1A , and  FIG. 6(   d ) is a sectional view of a part corresponding to the line X-X of  FIG. 1A . 
     As shown in (a), (b), (c) of  FIG. 6 , layers for flowing the H 2  gas, layers for flowing air, and layers for flowing water are respectively formed in the manifold holes  7   a ,  8   b ,  9   a . Also, as shown in (d) of  FIG. 6 , the flow passage grooves  6  of the separators  2  for flowing air, and the flow passage grooves  6  of the separators  2  for flowing the H 2  gas are respectively arranged in an upper part and a lower part of the MEA 1   a , via the diffusion layers  3 . The air and H 2  gas are supplied to the MEA 1   a . Then a cooling layer part having the diffusion layer  4  for flowing cooling water is arranged between the power generation layers sandwiched by upper and lower separators  2 . 
     Next, the flow of the fluid in one unit U shown in  FIG. 2  will be described. In this description, the laminating direction, in which the separators  2 , etc, of  FIG. 2  are laminated, is set as the vertical direction. 
     Two kinds of reaction gas are used as the fluid for power generation. Here, the H 2  gas is used as the fuel gas, and air is used as the oxidant gas. Also, water is used as the cooling fluid. 
     The H 2  gas of the fuel gas is flown through the upper surface of the separator  2  positioned on the lower side of the unit U. Namely, the H 2  gas flowing through the manifold hole  7   a  passes through the fluid flowing structure part  15 , then passes through the communication groove  10  on the upper stream side, a plurality of flow passage grooves  6 , and the communication groove  10  on the lower stream side, and flows into the manifold hole  7   b , and is discharged to outside through the manifold hole  7   b . The H 2  gas is supplied to the electrode on the lower side of the MEA 1   a  via the diffusion layer  3 , while flowing through a plurality of flow passage grooves  6 . 
     The air of the oxidant gas flows through a lower surface of the separator  2  which is positioned on the upper side of the unit U (air flows through a plurality of flow passage grooves  6  reversely to the H 2  gas). Namely, the air flowing through the manifold hole  8   a  passes through the fluid flowing structure part  15 , then passes through the upper stream side communication groove  10 , a plurality of flow passage grooves  6 , the lower stream side communication groove  10 , and flows into the manifold hole  8   b , and is discharged to the outside through the manifold hole  8   b . The air is supplied to the electrode on the upper side of the MEA 1   a  via the diffusion layer  3 , while flowing through the plurality of flow passage grooves  6 . 
     Water for cooling the fluid flows through an upper surface of the separator  2  positioned on the upper side of the unit U. Namely, the water flowing through the manifold hole  9   a  flows through the fluid flowing structure part  15 , then passes through the communication groove  10  on the upper stream side, the plurality of flow passage grooves  6 , and the communication groove  10  on the lower stream side, and flows into the manifold hole  9   b  on the lower stream side, and is discharged to the outside through the manifold hole  9   b . The water is supplied to the diffusion layer  4  while flowing through the plurality of flow passage grooves  6 . Also, similarly the water of the cooling fluid flows through the lower surface of the separator  2  positioned on the lower side of the unit U. 
     A function of the separator is to press the polymer electrolyte membrane of MEA at a constant pressure, then make electric conductivity, and separate the fuel gas flown to the cathode side from the oxidant gas flown to the anode side of the MEA, so as not to be directly mixed with each other. Sealing between the outer peripheral part of the MEA and the separator is relatively easy. However, it is difficult to seal the gas inlet/outlet of the manifold hole, because the layer for the gas to go in and out and a layer for sealing the gas are alternately present in the laminating direction. Therefore, power generation characteristics are greatly influenced, if inlet/outlet of the gas and sealing are not surely performed. 
     As a specific example of this embodiment, a Ti layer is cladded on the surface of a thin-plate shaped stainless steel (SUS), and further an Au (gold) layer is formed on the Ti layer by nano-level coating using a sputtering method, to thereby form a metal material (clad material M-TST by HITACHI CABLE, having thickness of 0.2 mm). Then, by using this metal material, the separator  2  is formed and the fluid flowing structure part  15 , which is formed by using the Ti plate material having thickness of 80 μm, is spot-welded to the separator  2 . The stack in which 30 units are laminated, is manufactured by using this separator, and it is found that even under a constant surface pressure (about 10 kg/cm 2 ) during power generation, excellent power generation characteristics without seal leakage can be exhibited. 
     Second Embodiment 
     Next, the metal separator for the fuel cell according to a second embodiment of the present invention will be described. 
     In the aforementioned first embodiment, the fluid flowing structure part  15  formed separately from the separator  2  is attached to the separator  2 . However, in this second embodiment, a fluid flowing structure part  20  is formed by folding, etc, a part of the separator  2 . The other structure of the separator  2  is the same as that of the separator  2  according to the first embodiment. 
       FIG. 7  is a step view showing the step of forming the fluid flowing structure part  20  in the separator of the second embodiment, and  FIG. 8  is a perspective view showing the fluid flowing structure part  20  formed by the step of  FIG. 7  and its periphery. 
     Each step will be specifically described by using  FIG. 7 . Note that  FIG. 7  shows a case that the fluid flowing structure part  20  is formed on the fringe part of the manifold hole  7   a . However, the fluid flowing structure part  20  is also formed on the fringe parts of other manifold holes  7   b ,  8   a ,  8   b ,  9   a , and  9   b , in the same step. 
     (Punching Step, FIG.  7 ( 1 )) 
     In the punching step, an opening part  21   i  is punched, so that reinforcing parts  21   m , being reinforcing members, are arranged in a comb-teeth shape at equal intervals along the groove width direction of the communication groove  10 . Simultaneously, slits  21   j  connected to an opening part  21   i  are formed on both sides of the communication groove  10  in the groove width direction. The slits  21   j  are cut into approximately the same dimension as that of the manifold hole  7   b  formed after a folding step as will be described later. Also, simultaneously with forming the slits  21   j , a plurality of holes  21   k  are formed between end portions of the slits  21   j ,  21   j , along the groove width direction of the communication groove  10 . The holes  21   k  are formed so as to be positioned between the adjacent reinforcing parts  21   m  at the same intervals as those of the reinforcing parts  21   m.    
     (Pressing Step, FIG.  7 ( 2 )) 
     In the next pressing step, the reinforcing parts  21   m  are press-molded, and center line parts of the thin and long reinforcing parts  21   m  are molded into an arch-shape in a state of being sagged downwards of a paper surface of  FIG. 7 . In this case, root parts of the reinforcing parts  21   m  are not molded. 
     (Folding Step, FIGS.  7 ( 3 ),( 4 )) 
     Folding operation is performed twice in the next folding step. 
     In the first folding step, the reinforcing parts  21   m  are folded to the communication groove  10  side at about 180° via the upper part of the paper surface of  FIG. 7 . Each folded reinforcing part  21   m  is positioned between adjacent holes  21   k . In addition, a part of the separator  2  between the slits  21   j ,  21   j  in a region where the folded reinforcing parts  21   m  are present, becomes a seal part  21   n  for forming a seal surface of the fluid flowing structure part  20  by the next second folding. 
     In the second folding step, the part of the separator  2  between the slits  21   j ,  21   j  where the folded reinforcing parts  21   m  are present, is folded at about 180° to the communication groove  10  side, with the center line of a plurality of holes  21   k  set as a folding line q. Thus, a seal part  21   n , being the seal member parallel to the separator surface  2   a , is formed. The reinforcing parts  21   m  having arch-like sectional faces, being reinforcing members, are provided between the seal part  21   n  and the separator surface  2   a , and the seal part  21   n  is supported by the reinforcing parts  21   m . In addition, the opening part  21   i  is expanded by second folding, and the manifold hole  7   a  is thereby formed. 
     (Fixing Step) 
     This step is performed as needed, in a viewpoint of strength. In the fixing step, a contact point, etc, between each reinforcing part  21   m  formed by press-molding and the seal part  21   n  is fixed by spot welding, etc. Note that this fixing step may be performed after the first folding step. 
     By the above-described step, as shown in  FIG. 8 , the fluid flowing structure part  20  of this embodiment is formed on the fringe part of the communication groove  10  side of the manifold hole  7   a . The gas flowing through the manifold hole  7   a  passes through holes  21   k  arranged on the communication groove  10 , at equal intervals in a groove width direction, then further passes through through holes  21   h  connected to the holes  21   k , formed between the seal part  21   n  and the separator surface  2   a , and between the adjacent reinforcing parts  21   m , and flows into the communication groove  10 . 
     As a specific example of this embodiment, the Ti layer is cladded on the surface of a thin-plate shaped stainless steel (SUS), and further an Au (gold) layer is formed on the Ti layer by nano-level coating using a sputtering method, to thereby form a metal material (clad material M-TST by HITACHI CABLE, having thickness of 0.1 mm). Then, by using this metal material, the separator  2  is formed and the fluid flowing structure part  20  is formed on the Ti layer by punching, pressing, folding, and fixing. The stack, in which 10 units are laminated, is manufactured by using this separator  2 , and when a power generation test is performed, excellent power generation characteristics can be obtained. 
     Note that when the fluid flowing structure parts  15 ,  20  are installed or formed, after press-molding a plurality of flow passage grooves  6  on the separator  2 , or after fitting the gaskets  11   a ,  11   b  to the separator  2 , the sealing performance is ensured, mass productivity can be realized, and decrease of cost can be expected. 
     In addition, irrespective of the above-described embodiments, the inventors of the present invention study on a structure that a plurality of projection parts for forming the inlet/outlet grooves or openings are formed on the separator surface of the peripheral parts of the manifold holes, and the upper surface, etc, of these projection parts are sealed. However, the sealing performance in this case is not ensured, and a lot of trouble is taken to perform sealing. Meanwhile, in the structure of the above-described embodiment, assembly of the stack can be efficiently performed, and the sealing performance is ensured.