Patent Publication Number: US-2022231310-A1

Title: Seal structure for fuel cell separator

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/JP2020/031811, filed on Aug. 24, 2020, which claims priority to Japanese Patent Application No. 2019-163737, filed on Sep. 9, 2019. The entire disclosures of the above applications are expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     Technical Field 
     The disclosure relates to a seal structure for a fuel cell separator. 
     Related Art 
     Fuel cells which generate electric power by electrochemical reaction of reaction gas are rapidly becoming widespread. The fuel cells have been attracting attention as a preferable energy source because they are high in power generation efficiency and have little impact on the environment. 
     Among the fuel cells, the solid polymer type has a stack structure in which a plurality of fuel battery cells are stacked. Each individual fuel battery cell has a membrane electrode assembly (MEA) sandwiched between a pair of separators. The membrane electrode assembly is of a structure in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode. Each electrode has a stacked structure of a catalyst layer and a gas diffusion layer (GDL). The separator is in close contact with the gas diffusion layer and forms a flow path for hydrogen and oxygen between the separator and the gas diffusion layer. 
     Such a fuel battery cell uses the flow path formed in the separator to supply hydrogen to the anode electrode and oxygen to the cathode electrode. Consequently, power is generated by the electrochemical reaction opposite to the electrolysis of water. 
     As shown in the respective figures of Japanese Patent Application Laid-Open No. 2016-143479, the electrolyte membrane (reference numeral 55 in JP 2016-143479) of the membrane electrode assembly is sealed at the end thereof. As the seal, for example, such gaskets (gasket bodies  21 ,  31 ) as described in JP 2016-143479 are used. The gasket elastically deforms in a direction orthogonal to the surface of the separator and seals the electrolyte membrane of the membrane electrode assembly between the pair of separators. Since a seal structure using such gaskets generates a certain degree of tightening force, it is suitable for use in separators made of metal. 
     As another configuration example of sealing the electrolyte membrane of the membrane electrode assembly, an adhesive seal or a sticking seal may be used. Since these seals do not require a large tightening force, they can also be applied to brittle separators such as those made of carbon. 
     Since the fuel cell is raised in temperature by power generation, a gap between the pair of separators that sandwich the membrane electrode assembly therebetween is easy to fluctuate. Therefore, a seal relatively high in hardness such as an adhesive seal or a sticking seal cannot follow the fluctuation in the gap, and has the possibility of causing peeling off from the separator or breakage or the like in the case of a brittle separator. 
     On the other hand, in the case of a gasket using a rubber-like elastic material relatively low in hardness, as mentioned above, it is strong in tightening force and is not suitable for application to the brittle separator. 
     A seal structure that can follow fluctuations in a gap between a pair of fuel cell separators without generating a large tightening force is required. 
     SUMMARY 
     One aspect of a seal structure for a fuel cell separator includes a pair of separators facing each other with a mating member interposed therebetween and having beads forming a flow path for fluid between the separator and the mating member in close contact with the mating member, and a seal provided with a seal material having elasticity between side walls of the beads of the pair of separators, which are overlapped in a nested manner and facing each other. 
     Effect 
     It is possible to realize a seal structure which can follow fluctuations in a gap between a pair of separators without generating a large tightening force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view conceptually showing a stack structure in which a plurality of fuel battery cells are stacked. 
         FIG. 2  is a vertical cross-sectional view of a seal structure that seals a gap between a pair of separators. 
         FIG. 3  is a vertical cross-sectional view showing a state of a seal structure of a comparative example when a gap between beads of a pair of separators fluctuates from a specified state in a direction of its expansion. 
         FIG. 4  is a vertical cross-sectional view showing a state of a seal structure of the present embodiment when a gap between beads of a pair of separators fluctuates from a specified state in a direction of its expansion. 
         FIG. 5  is a vertical cross-sectional view showing another example of separators for a fuel cell. 
         FIG. 6  is a vertical cross-sectional view showing a further example of separators for a fuel cell. 
         FIG. 7  is a vertical cross-sectional view showing yet another example of separators for a fuel cell. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of a seal structure for a fuel cell separator will be introduced. 
     First Embodiment 
     A first embodiment will be described based on  FIGS. 1 to 4 . 
     As shown in  FIG. 1 , a fuel cell  1  has a stacked structure in which a plurality of fuel battery cells  2  are stacked. In the fuel battery cell  2 , an electrolyte membrane  102  provided with a membrane electrode assembly  101  called a MEA is interposed between a pair of separators  11  for the fuel cell. Such fuel battery cells  2  are stacked through a cooling surface seal  201  as a seal. In  FIG. 1 , only two sets of fuel battery cells  2  are drawn, but in reality, hundreds of sets of fuel battery cells  2  are stacked to constitute the fuel cell  1 . 
     The membrane electrode assembly  101  is a structure in which electrodes not shown in the drawing are provided at the central portions of both surfaces of the electrolyte membrane  102 . The electrode has a stacked structure having a catalyst layer formed on the electrolyte membrane  102  and a gas diffusion layer (GDL) formed on the catalyst layer (neither is shown). In such an electrode, one surface of the electrolyte membrane  102  is used as an anode electrode, and the surface opposite thereto is used as a cathode electrode. 
     The separator  11  for the fuel cell is a flat plate-shaped member formed of a resin such as carbon as an example. However, the separator is not limited to the brittle member like such a carbon-made one. As another example, a flat plate-like member that can be pressed, such as a thin stainless steel plate, may be used as the separator  11 . 
     The separator  11  has a rectangular planar shape and is provided with an arrangement region  12  for arranging the membrane electrode assembly  101 . Openings provided three by three at positions of both ends out of the arrangement region  12  are manifolds  13  for circulating fluid used for power generation or generated by power generation. The fluid caused to flow through the manifolds  13  is a fuel gas (hydrogen), an oxidizing gas (oxygen), water generated by electrochemical reaction during power generation, an excess oxidizing gas, a refrigerant, or the like. 
     The manifolds  103  are provided even on the electrolyte membrane  102  in alignment with the manifolds  13  provided on the separator  11 . These manifolds  103  are openings which are respectively provided three at positions of both ends away from the membrane electrode assembly  101 . 
     The fuel cell  1  uses the manifolds  13  and  103  to introduce the fuel gas (hydrogen) between the electrolyte membrane  102  provided with the membrane electrode assembly  101  and the separator  11 A facing one surface of the electrolyte membrane  102 , and to introduce the oxidizing gas (oxygen) between the electrolyte membrane  102  and the separator  11 B facing the surface opposite to one surface of the electrolyte membrane  102 . Cooling water used as the refrigerant is introduced between the two sets of fuel battery cells  2  sealed by the cooling surface seal  201 . At this time, the fuel gas, the oxidizing gas, and the cooling water flow through respective flow paths formed by the pair of separators  11  ( 11 A,  11 B) that assemble the fuel battery cell  2 . 
     The pair of separators  11  face each other with the electrolyte membrane  102  as a mating member interposed therebetween to form the fuel battery cells  2 . The separator  11  includes a bead  14  that forms a fluid flow path between the separator and the electrolyte membrane  102  in close contact with the electrolyte membrane  102 . A space between the electrolyte membrane  102  and the bead  14 A of the separator  11 A forms a flow path for the fuel gas. A space between the electrolyte membrane  102  and the bead  14 B of the separator  11 B forms a flow path for the oxidizing gas. A space between the beads  14 A and  14 B provided between the separator  11 A of one set of fuel battery cells  2  and the separator  11 B of the set of fuel battery cells  2  overlapping the separator  11 A forms a flow path for the cooling water. 
     The fuel battery cell  2  has a seal structure at the outer peripheral edges of the separator  11  and the membrane electrode assembly  101 , and at the peripheral edges of the manifolds  13  and  103 . The seal structure includes a cooling surface seal  201  interposed between the two sets of fuel battery cells  2  and a reaction surface seal  202  as a seal provided between the separator  11  and the membrane electrode assembly  101 . In such a seal structure, the flow path for the fuel gas and the surplus fuel gas, the flow path for the oxidizing gas and the water generated by the electrochemical reaction at the power generation, and the flow path for the cooling water as the refrigerant are made independent of each other to prevent mixing of different types of fluids. 
     As shown in  FIG. 2 , in a portion where the cooling surface seal  201  and the reaction surface seal  202  are provided, the beads  14  of the separators  11  are overlapped in a nested manner. As an example, the bead  14 B of the separator  11 B facing the surface opposite to one surface of the electrolyte membrane  102  is formed larger than the bead  14 A of the separator  11 A facing one surface of the electrolyte membrane  102  provided with the membrane electrode assembly  101 . The bead  14 A has entered the bead  14 B in a non-contact state. 
     A seal material  203  having elasticity forms the cooling surface seal  201  and the reaction surface seal  202 . As an example, as the seal material  203 , a gasket formed of a rubber-like elastic material like low-hardness vulcanized rubber is used. Such a seal material  203  is arranged and fixed between side walls  15  of the beads  14  ( 14 A,  14 B) facing each other by overlapping in the nested manner. 
     Various embodiments are allowed to fix the seal material  203 . 
     One allowable embodiment is a form to cause the seal material  203  to have stickiness that it is stuck to the side wall  15  of the bead  14 . As a method for that purpose, in the seal structure of the present embodiment, the seal material  203  is molded by a rubber molded product having stickiness, and the seal material  203  itself is caused to have stickiness. 
     As rubber having stickiness, for example, a rubber-based sticking agent using, as base polymer, butyl rubber, polyisobutylene rubber, styrene-butadiene rubber, ethylenepropylene diene rubber, natural rubber, or the like can be used. 
     It is also possible to blend rubber that becomes a material for the seal material  203  with additives. The additives that can be blended include, for example, cross-linking agents, tackifiers, fillers, anti-aging agents, and the like. 
     As another embodiment in which the seal material  203  is caused to have stickiness that it sticks to the side wall  15  of the bead  14 , for example, it is also possible to cause the seal material  203  to have a multi-layer structure of a low-hardness vulcanized rubber and a sticking layer (refer to a fourth embodiment). In this case as well, the above-mentioned butyl rubber or the like can be used as rubber having stickiness, and various additives can also be blended. 
     Another embodiment allowed to fix the seal material  203  is a form to give adhesiveness or tackiness to the separator  11  and fix the seal material  203 . 
     For example, there may be mentioned an aspect in which a sticking agent is formed on a side wall  15 A inside the bead  14 A of the separator  11 A to fix the seal material  203 , and the seal material  203  is brought into close contact with a side wall  15 B outside the bead  14 B of the separator  11 B. There may also be mentioned an aspect in which a sticking agent is formed on a side wall  15 B outside the bead  14 B of the separator  11 B to fix the seal material  203 , and the seal material  203  is brought into close contact with the side wall  15 A inside the bead  14 A of the separator  11 A. Alternatively, there may also be mentioned an aspect in which a sticking agent is formed on the side walls  15 A and  15 B inside the beads  14 A and  14 B of the separators  11 A and  11 B to fix the seal material  203 . 
     Thus, when the sticking agent is formed on the bead  14 , for example, a rubber-based sticking agent using, as the base polymer, butyl rubber, polyisobutylene rubber, styrene-butadiene rubber, ethylenepropylene diene rubber, natural rubber, or the like can be used as the sticking agent. Further, various additives such as cross-linking agents, tackifiers, fillers, anti-aging agents, and the like can also be blended. 
     The shaping of the sticking agent on the bead  14  can be realized by, for example, a method such as application by a dispenser, integral molding by injection molding or transfer molding, post-pasting of a sticking agent shaped by compression molding or the like, or the like. 
     A further embodiment allowed to fix the seal material  203  is a form to adhere the seal material  203  to the separator  11 . 
     There may be mentioned an aspect in which the seal material  203  is adhered and fixed to the side wall  15 A inside the bead  14 A of the separator  11 A with an adhesive, and the seal material  203  is brought into close contact with the side wall  15 B outside the bead  14 B of the separator  11 B. There may also be mentioned an aspect in which the seal material  203  is adhered and fixed to the side wall  15 B outside the bead  14 B of the separator  11 B with an adhesive, and the seal material  203  is brought into close contact with the side wall  15 A inside the bead  14 A of the separator  11 A. Alternatively, there may also be mentioned an aspect in which the seal material  203  is adhered and fixed to the side walls  15 A and  15 B inside the beads  14 A and  14 B of the separators  11 A and  11 B with an adhesive. 
     In such a configuration, the seal structure of the present embodiment realizes a fluid seal by the seal material  203  interposed between the side walls  15  of the beads  14  of the separators  11  which are overlapped with each other in the nested manner. Therefore, the seal material  203  can be made to follow a fluctuation in a gap between the pair of separators  11  ( 11 A,  11 B) due to factors such as a temperature rise by power generation without generating a large tightening force. Hereinafter, description will be made while comparing with a comparative example. 
       FIG. 3  shows a state of a seal structure of a comparative example when a gap between beads B of a pair of separators S fluctuates from a specified state in its expanding direction. In the seal structure of this comparative example, the beads B of the pair of separators S have the mutual tops brought into close contact with each other through a seal material SM. Therefore, when the gap between the beads B is expanded to a dimension t 2  where a specified gap dimension between the beads B is assumed to be t 1 , the seal material SM is elongated correspondingly. Although not shown in the drawing, when the gap between the beads B is narrowed, the seal material SM is crushed correspondingly. 
     The seal structure of the comparative example described above causes sealing action by compressive deformation of the seal material SM. Due to such a structure, a large tightening force is generated between the beads B of the pair of separators S, and the tightening force also fluctuates greatly when the gap between the beads B fluctuates. Therefore, when a brittle material made of a resin such as carbon is used as the separators S, the separators S may be destroyed. 
       FIG. 4  shows a state of the seal structure of the present embodiment when the gap between the beads  14  of the pair of separators  11  fluctuates from the specified state in its expanding direction. Even if the gap dimension between the pair of separators  11  changes from t 1  to t 2  as in the case of the comparative example, the dimension between the side walls  15  of the beads  14  between which the seal material  203  is interposed does not change. The initial dimension t 3  between the side walls  15  and the dimension t 4  between the side walls  15  when the distance between the two separators  11  fluctuates remain in agreement. At this time, a shearing force is generated in the seal material  203 , and a larger force than the compressive force is unlikely to act on the bead  14  of the separator  11 . Therefore, it is possible to obtain the seal structure that can follow the fluctuation in the gap between the pair of separators  11  without generating the large tightening force, and it is also possible to use the brittle separator  11  made of the resin such as carbon. 
     Second Embodiment 
     A second embodiment will be described based on  FIG. 5 . The same parts as those in the first embodiment are designated by the same reference numerals, and a description thereof will also be omitted. 
     As shown in  FIG. 4 , the present embodiment relates to a rising angle θ from the separator  11  of the side wall  15  of each of the beads  14  facing each other of the pair of separators  11 . The rising angle θ from the separator  11  of the side wall  15  in the first embodiment is a right angle, i.e., 90°. It is desirable that the rising angle θ of the side wall  15  is in the range of 5 to 90°. The rising angle θ of the side wall  15  in the present embodiment is around 70°. That is, the side walls  15  of the beads  14  facing each other of the pair of separators  11  are inclined with respect to the separators  11 . 
     The seal material  203  is a parallelogram in cross section, which is in contact with the surface of the separator  11  communicating with the side wall  15 . Such a seal material  203  is stuck or adhered not only to the side wall  15  of the bead  14  but also to the surface of the separator  11  communicating with the side wall  15 . 
     In such a configuration, since the side wall  15  of each of the beads  14  is inclined with respect to the separator  11 , the seal material  203  can be interposed between these beads  14  only by moving the mutual beads  14  in the proximity direction to each other upon stacking the pair of separators  11  to assemble the fuel battery cell  2 . Thus, it is possible to facilitate the assembly of the fuel battery cells  2  and the fuel cell  1 . 
     Third Embodiment 
     A third embodiment will be described based on  FIG. 6 . The same parts as those in the first and second embodiments are designated by the same reference numerals, and a description thereof will also be omitted. 
     In the seal structure of the present embodiment, the length of the seal material  203  which is stuck or adhered to the surface of the bead  14  of the separator  11  is made shorter than the length between the side walls  15  of the beads  14 . Consequently, when the gap between the pair of separators  11  fluctuates, the seal material  203  becomes easy to deform in the shearing direction, and the stress applied to the separator  11  can be made smaller. 
     Fourth Embodiment 
     A fourth embodiment will be described based on  FIG. 7 . The same parts as those in the first and second embodiments are identified by the same reference numerals, and a description thereof will also be omitted. 
     In the present embodiment, as a structure of fixing the seal material  203  to the separator  11 , sticking layers  204  are each provided on the seal material  203  instead of forming the sticking agent on the side wall  15  of the bead  14 . The seal material  203  is a low-hardness vulcanized rubber, and the sticking layer  204  is provided on the surface of the seal material  203  to be joined to the side wall  15  of the bead  14 . 
     In such a configuration, the seal material  203  is adhered to the side wall  15 B of the separator  11 B by the sticking layer  204  on one side. By superimposing the separator  11 A on the separator  11 B in this state, the side wall  15 A of the separator  11 A is adhered to the sticking layer  204  on the opposite side. Thus, the seal material  203  is provided between the side walls  15 A and  15 B of the pair of stacked separators  11 A and  11 B. 
     In the present embodiment, since the sticking layer  204  is provided on the seal material  203  itself, it is not necessary to perform working for adhering and fixing the seal material  203  on the separator  11 , and it is possible to facilitate manufacturing. 
     Modification Example 
     Various modifications and changes are allowed upon implementation. 
     For example, the angle of the bead  14  with respect to the separator  11  is not limited to 90° (first embodiment) and around 70° (second to fourth embodiments). It is possible to set it to various angles in the range of 5 to 90°. Further, in the pair of separators  11 A and  11 B constituting the fuel battery cell  2 , the rising angles of the individual beads  14 A and  14 B do not have to match each other, and they may be raised at different angles. 
     Upon other implementations, any deformation or change is allowed.