Abstract:
An electrolyte membrane-electrode structure with a resin frame is provided with: an electrolyte membrane-electrode structure that is provided with an anode-side electrode and a cathode-side electrode, with a solid polymer electrolyte membrane being held therebetween; and a resin frame member that is arranged around the outer periphery of the solid polymer electrolyte membrane. An intermediate layer is continuously arranged: between an outer peripheral end portion of the cathode-side electrode and a first inner peripheral end portion of the resin frame member; on an outer peripheral end portion of the solid polymer electrolyte membrane, said outer peripheral end portion being exposed outside the outer peripheral end portion of the cathode-side electrode; and between an outer peripheral end portion of the anode-side electrode and a second inner peripheral end portion of the resin frame member.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fuel cell resin frame equipped membrane electrode assembly (electrolyte membrane-electrode structure with resin frame for fuel cells) including a membrane electrode assembly and a resin frame member. The membrane electrode assembly includes a first electrode, a second electrode, and a solid polymer electrolyte membrane interposed between the first electrode and the second electrode. The first electrode and the second electrode include electrode catalyst layers and gas diffusion layers, respectively. The first electrode has an outer size smaller than that of the second electrode. The resin frame member is provided around an outer end of the solid polymer electrolyte membrane. 
       BACKGROUND ART 
       [0002]    In general, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a polymer ion exchange membrane. The fuel cell includes a membrane electrode assembly (MEA) where an anode and a cathode are provided on both sides of the solid polymer electrolyte membrane. Each of the anode and the cathode includes a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon). In the fuel cell, the membrane electrode assembly is sandwiched between separators (bipolar plates). A predetermined number of the fuel cells are stacked together to form a fuel cell stack. In use, for example, the fuel cell stack is mounted in a vehicle as an in-vehicle fuel cell stack. 
         [0003]    In some cases, the membrane electrode assembly has structure where components of the MEA (stepped MEA) have different sizes, i.e., the surface area of one of gas diffusion layers is smaller than the surface area of the solid polymer electrolyte membrane, and the surface area of the other of the gas diffusion layers is the same as the surface area of the solid polymer electrolyte membrane. 
         [0004]    Normally, in the fuel cell stack, a large number of membrane electrode assemblies are stacked together. In order to reduce the cost, there is a demand to produce the membrane electrode assembly at low cost. Therefore, in particular, for the purpose of reducing the amount of expensive material used for the solid polymer electrolyte membrane, and simplify the structure of the solid polymer electrolyte membrane, various proposals have been made. 
         [0005]    For example, as shown in  FIG. 18 , a membrane electrode assembly disclosed in Japanese Laid-Open Patent Publication No. 2007-066766 includes an electrolyte membrane  1 , a cathode catalyst layer  2   a  provided on one side of the electrolyte membrane  1 , an anode catalyst layer  2   b  provided on the other surface of the electrolyte membrane  1 , and gas diffusion layers  3   a ,  3   b  provided on both sides of the electrolyte membrane  1 . 
         [0006]    The surface area of the gas diffusion layer  3   b  of the anode is equal to the surface area of the electrolyte membrane  1 , and larger than the surface area of the gas diffusion layer  3   a  of the cathode. A gasket structure body  4  is provided in an edge area of the membrane electrode assembly (MEA), and the outer end of the electrolyte membrane  1  adjacent to the gas diffusion layer  3   a  is joined to the gasket structure body  4  through an adhesive layer  5 . 
       SUMMARY OF INVENTION 
       [0007]    However, in Japanese Laid-Open Patent Publication No. 2007-066766, the MEA and the gasket structure body  4  are fixed to the outer marginal portion of the electrolyte membrane  1  exposed to the outside from the gas diffusion layer  3   a , through the adhesive layer  5  only. Therefore, the strength of joining the MEA and the gasket structure body  4  is low, and the desired strength cannot be obtained. 
         [0008]    Further, it is considerably difficult to produce the membrane electrode assembly such that the outer ends of the gas diffusion layers  3   a ,  3   b  and the inner end of the gasket structure body  4  are tightly joined together in an air tight manner. Therefore, a gap tends to be formed between the outer ends of the gas diffusion layers  3   a ,  3   b  and the inner end of the gasket structure body  4 . The sealing performance for preventing gas leakage is low, and the fuel gas and the oxygen-containing gas are mixed disadvantageously. 
         [0009]    The present invention has been made to solve the problems of this type, and an object of the present invention is to provide a fuel cell resin frame equipped membrane electrode assembly in which a resin frame member is joined firmly and easily around an outer end of a solid polymer electrolyte membrane, and desired sealing performance for preventing gas leakage is maintained reliably. 
         [0010]    The present invention relates to a fuel cell resin frame equipped membrane electrode assembly including a membrane electrode assembly and a resin frame member. The membrane electrode assembly includes a first electrode, a second electrode, and a solid polymer electrolyte membrane interposed between the first electrode and the second electrode. Each of the first electrode and the second electrode includes an electrode catalyst layer and a gas diffusion layer. The first electrode has an outer size smaller than that of the second electrode. The resin frame member is provided around an outer end of the solid polymer electrolyte membrane. 
         [0011]    In the fuel cell resin frame equipped membrane electrode assembly, an intermediate layer is provided between an outer end of the first electrode and an inner end of the resin frame member, at an outer marginal portion of the solid polymer electrolyte membrane exposed from the outer end of the first electrode to outside, and between an outer end of the second electrode and an inner end of the resin frame member, in a contiguous manner. 
         [0012]    Further, in the fuel cell resin frame equipped membrane electrode assembly, preferably, the intermediate layer is made of material different from that of the resin frame member. 
         [0013]    Further, in the fuel cell resin frame equipped membrane electrode assembly, preferably, an outer marginal portion of at least one of the gas diffusion layers is impregnated with same material composition as that of the intermediate layer to form an impregnation layer. 
         [0014]    Further, in the fuel cell resin frame equipped membrane electrode assembly, preferably, the gas diffusion layer is impregnated with the impregnation layer at a pore filling rate of 85% or more. 
         [0015]    Further, in the fuel cell resin frame equipped membrane electrode assembly, preferably, a first gap is formed between one end of the intermediate layer, the outer end of the first electrode, and the inner end of the resin frame member; a second gap is formed between another end of the intermediate layer, the outer end of the second electrode, and the inner end of the resin frame member; a first projection provided integrally with or separately from the resin frame member is melted to form a first resin impregnation portion in the first gap; and a second projection provided integrally with or separately from the resin frame member is melted to form a second resin impregnation portion in the second gap. 
         [0016]    In the present invention, the intermediate layer is provided at the outer marginal portion of the solid polymer electrolyte membrane exposed from the outer end of the first electrode to the outside. Additionally, the intermediate layer is provided between the outer end of the first electrode and the inner end of the resin frame member, and between the outer end of the second electrode and the inner end of the resin frame member in a contiguous manner. 
         [0017]    In the structure, in comparison with the case where the resin frame member is joined to the first electrode and the second electrode by adhesion, the joining strength for joining the resin frame member to the first electrode and the second electrode is improved suitably, and it is possible to suppress occurrence of peeling or the like as much as possible. Further, no gap is formed between the outer end of the first electrode and the inner end of the resin frame member, and no gap is formed between the outer end of the second electrode and the inner end of the resin frame member. Therefore, it becomes possible to maintain the desired sealing performance for preventing the gas leakage. With the simple and economical structure, mixture of the fuel gas and the oxygen-containing gas can be suppressed as much as possible. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  is an exploded perspective view showing main components of a solid polymer electrolyte fuel cell including a resin frame equipped membrane electrode assembly according to a first embodiment of the present invention; 
           [0019]      FIG. 2  is a cross sectional view showing the fuel cell, taken along a line II-II in  FIG. 1 ; 
           [0020]      FIG. 3  is a front view showing a cathode of the resin frame equipped membrane electrode assembly; 
           [0021]      FIG. 4  is a front view showing an anode of the resin frame equipped membrane electrode assembly; 
           [0022]      FIG. 5  is a view showing a method of producing the resin frame equipped membrane electrode assembly; 
           [0023]      FIG. 6  is a view showing the method of producing the resin frame equipped membrane electrode assembly; 
           [0024]      FIG. 7  is a view showing the method of producing the resin frame equipped membrane electrode assembly; 
           [0025]      FIG. 8  is a graph showing the relationship between the pore filling rate and the gas flow rate; 
           [0026]      FIG. 9  is a view showing another method of producing the resin frame equipped membrane electrode assembly; 
           [0027]      FIG. 10  is a view showing another method of producing the resin frame equipped membrane electrode assembly; 
           [0028]      FIG. 11  is an exploded perspective view showing main components of a solid polymer electrolyte fuel cell including a resin frame equipped membrane electrode assembly according to a second embodiment of the present invention; 
           [0029]      FIG. 12  is a cross sectional view showing a solid polymer electrolyte fuel cell including a resin frame equipped membrane electrode assembly according to a third embodiment of the present invention; 
           [0030]      FIG. 13  is a cross sectional view showing a solid polymer electrolyte fuel cell including a resin frame equipped membrane electrode assembly according to a fourth embodiment of the present invention; 
           [0031]      FIG. 14  is a cross sectional view showing a solid polymer electrolyte fuel cell including a resin frame equipped membrane electrode assembly according to a fifth embodiment of the present invention; 
           [0032]      FIG. 15  is a view showing a method of producing the resin frame equipped membrane electrode assembly; 
           [0033]      FIG. 16  is a view showing the method of producing the resin frame equipped membrane electrode assembly; 
           [0034]      FIG. 17  is a view showing the method of producing the resin frame equipped membrane electrode assembly; and 
           [0035]      FIG. 18  is a view showing a membrane electrode assembly disclosed in Japanese Laid-Open Patent Publication No. 2007-066766. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0036]    As shown in  FIGS. 1 and 2 , a solid polymer electrolyte fuel cell  12  including a resin frame equipped membrane electrode assembly  10  according to a first embodiment of the present invention is formed by sandwiching the resin frame equipped membrane electrode assembly  10  between a first separator  14  and a second separator  16 . For example, the first separator  14  and the second separator  16  are made of metal plates such as steel plates, stainless steel plates, aluminum plates, plated steel sheets, or metal plates having anti-corrosive surfaces by surface treatment. Alternatively, carbon members may be used as the first separator  14  and the second separator  16 . 
         [0037]    As shown in  FIG. 2 , the resin frame equipped membrane electrode assembly  10  includes a membrane electrode assembly  10   a , and the membrane electrode assembly  10   a  includes a solid polymer electrolyte membrane  18 , and an anode (second electrode)  20  and a cathode (first electrode)  22  sandwiching the solid polymer electrolyte membrane  18 . The solid polymer electrolyte membrane  18  is formed by impregnating a thin membrane of perfluorosulfonic acid with water, for example. A fluorine based electrolyte may be used as the solid polymer electrolyte membrane  18 . Alternatively, an HC (hydrocarbon) based electrolyte may be used as the solid polymer electrolyte membrane  18 . 
         [0038]    The surface area of the cathode  22  is smaller than the surface areas of the solid polymer electrolyte membrane  18  and the anode  20 . Alternatively, the surface area of the cathode  22  may be larger than the surface area of the anode  20 . As long as the outer marginal portion of the solid polymer electrolyte membrane  18  protrudes beyond the outer end of the smaller electrode, e.g., the outer end of the cathode  22 , the outer marginal portion of the solid polymer electrolyte membrane  18  may not be aligned with the end of the larger electrode, e.g., the end of the anode  20 . 
         [0039]    The anode  20  is provided on one surface  18   a  of the solid polymer electrolyte membrane  18  and the cathode  22  is provided on another surface  18   b  of the solid polymer electrolyte membrane  18  such that a frame shaped outer end  18   be  of the solid polymer electrolyte membrane  18  is exposed. 
         [0040]    The anode  20  includes an electrode catalyst layer  20   a  joined to the surface  18   a  of the solid polymer electrolyte membrane  18  and a gas diffusion layer  20   b  stacked on the electrode catalyst layer  20   a . The cathode  22  includes an electrode catalyst layer  22   a  joined to the surface  18   b  of the solid polymer electrolyte membrane  18  and a gas diffusion layer  22   b  stacked on the electrode catalyst layer  22   a.    
         [0041]    Each of the electrode catalyst layers  20   a ,  22   a  is formed by carbon black supporting platinum particles as catalyst particles. As an ion conductive binder, polymer electrolyte is used. Catalyst paste formed by mixing the catalyst particles uniformly in the solution of this polymer electrolyte is printed, applied (coated) or transferred on both surfaces of the solid polymer electrolyte membrane  18  to form the electrode catalyst layers  20   a ,  22   a . The gas diffusion layers  20   b ,  22   b  are made of carbon paper or the like, and the surface size of the gas diffusion layer  20   b  is larger that the surface size of the gas diffusion layer  22   b.    
         [0042]    As shown in  FIGS. 2 through 4 , the resin frame equipped membrane electrode assembly  10  includes a resin frame member  24  provided around the outer end of the solid polymer electrolyte membrane  18 , and joined to the cathode  22  and the anode  20 . For example, the resin frame member  24  is made of PPS (polyphenylene sulfide), PPA (polyphthalamide), etc. Alternatively, the resin frame member  24  may be made of polymer material having elasticity. 
         [0043]    A stepped opening is formed inside the resin frame member  24 , and includes a first inner end  24   a  positioned on the inner side, and a second inner end  24   b  positioned outside the first inner end  24   a . An intermediate layer  26  is provided between the resin frame member  24  and the membrane electrode assembly  10   a.    
         [0044]    The intermediate layer  26  includes a first plate portion  26   a , a second plate portion  26   b , and a third plate portion  26   c  that are contiguous to one another. The first plate portion  26   a  is provided between an outer end  22   be  of the gas diffusion layer  22   b  of the cathode  22  and the first inner end  24   a  of the resin frame member  24 . The second plate portion  26   b  is provided at the outer end  18   be  of the solid polymer electrolyte membrane  18  exposed from the outer end  22   be  to the outside. The third plate portion  26   c  is provided between an outer end  20   be  of the gas diffusion layer  20   b  of the anode  20  and the second inner end  24   b  of the resin frame member  24 . 
         [0045]    The intermediate layer  26  has a substantially Z shape in cross section, and made of material different from that of the resin frame member  24 . Specifically, a silicone based rubber (elastomer) a fluoro rubber (elastomer), epoxy based resin (elastomer), urethane based resin (elastomer), modified PET (polyethylene terephthalate) resin (elastomer), PVDF (polyvinylidene fluoride) resin (elastomer), orefin based resin (elastomer), or hot melt material may be used for the intermediate layer  26 . 
         [0046]    An outer marginal portion of the gas diffusion layer  22   b  of the cathode  22  is impregnated with the same material composition as that of the intermediate layer  26  to form a first impregnation layer  28   a . The first impregnation layer  28   a  has a predetermined area inside of the outer end position. An outer marginal portion of the gas diffusion layer  20   b  of the anode  20  is impregnated with the same material composition as that of the intermediate layer  26  to form a second impregnation layer  28   b . The second impregnation layer  28   b  has a predetermined area inside of the outer end position. The gas diffusion layer  22   b  and the gas diffusion layer  20   b  are impregnated with the first impregnation layer  28   a  and the second impregnation layer  28   b  at a pore filling rate of 85% or more, respectively. 
         [0047]    As shown in  FIG. 3 , the first impregnation layer  28   a  is formed over the entire periphery of the gas diffusion layer  22   b  of the cathode  22 . As shown in  FIG. 4 , the second impregnation layer  28   b  is formed over the entire periphery of the gas diffusion layer  20   b  of the anode  20 . 
         [0048]    As shown in  FIG. 1 , at one end marginal portion of the fuel cell  12  in a direction indicated by an arrow B (horizontal direction in  FIG. 1 ), an oxygen-containing gas supply passage  30   a  for supplying an oxygen-containing gas, a coolant supply passage  32   a  for supplying a coolant, and a fuel gas discharge passage  34   b  for discharging a fuel gas such as a hydrogen-containing gas are arranged in a vertical direction indicated by an arrow C. The oxygen-containing gas supply passage  30   a , the coolant supply passage  32   a , and the fuel gas discharge passage  34   b  extend through the fuel cell  12  in a stacking direction indicated by an arrow A. 
         [0049]    At the other end marginal portion of the fuel cell  12  in the direction indicated by the arrow B, a fuel gas supply passage  34   a  for supplying the fuel gas, a coolant discharge passage  32   b  for discharging the coolant, and an oxygen-containing gas discharge passage  30   b  for discharging the oxygen-containing gas are arranged in the direction indicated by the arrow C. The fuel gas supply passage  34   a , the coolant discharge passage  32   b , and the oxygen-containing gas discharge passage  30   b  extend through the fuel cell  12  in the direction indicated by the arrow A. 
         [0050]    The second separator  16  has an oxygen-containing gas flow field  36  on its surface  16   a  facing the resin frame equipped membrane electrode assembly  10 . The oxygen-containing gas flow field  36  is connected to the oxygen-containing gas supply passage  30   a  and the oxygen-containing gas discharge passage  30   b.    
         [0051]    The first separator  14  has a fuel gas flow field  38  on its surface  14   a  facing the resin frame equipped membrane electrode assembly  10 . The fuel gas flow field  38  is connected to the fuel gas supply passage  34   a  and the fuel gas discharge passage  34   b . A coolant flow field  40  is formed between a surface  14   b  of the first separator  14  and a surface  16   b  of the second separator  16 . The coolant flow field  40  is connected to the coolant supply passage  32   a  and the coolant discharge passage  32   b.    
         [0052]    As shown in  FIGS. 1 and 2 , a first seal member  42  is formed integrally with the surfaces  14   a ,  14   b  of the first separator  14 , around the outer end of the first separator  14 . A second seal member  44  is formed integrally with the surfaces  16   a ,  16   b  of the second separator  16 , around the outer end of the second separator  16 . 
         [0053]    As shown in  FIG. 2 , the first seal member  42  includes a first ridge seal  42   a  which contacts the resin frame member  24  of the resin frame equipped membrane electrode assembly  10 , and a second ridge seal  42   b  which contacts the second seal member  44  of the second separator  16 . The second seal member  44  is a flat surface seal. Instead of providing the second ridge seal  42   b , the second seal member  44  may have a ridge seal (not shown). 
         [0054]    Each of the first seal member  42  and the second seal members  44  is made of an elastic seal member, e.g., seal material, cushion material, or packing material such as an EPDM (ethylene propylene diene monomer) rubber, an NBR (nitrile butadiene rubber), a fluoro rubber, a silicone rubber, a fluorosilicone rubber, a butyl rubber, a natural rubber, a styrene rubber, a chloroprene rubber, or an acrylic rubber. 
         [0055]    As shown in  FIG. 1 , the first separator  14  has supply holes  46  connecting the fuel gas supply passage  34   a  to the fuel gas flow field  38 , and discharge holes  48  connecting the fuel gas flow field  38  to the fuel gas discharge passage  34   b.    
         [0056]    Next, a method of producing the resin frame equipped membrane electrode assembly  10  will be described below. 
         [0057]    Firstly, as shown in  FIG. 5 , the membrane electrode assembly  10   a  as an MEA having different sizes of components is produced. Specifically, the electrode catalyst layers  20   a ,  22   a  are coated on both surfaces  18   a ,  18   b  of the solid polymer electrolyte membrane  18 . Then, the gas diffusion layer  20   b  is placed on a side of a surface  18   a  of the solid polymer electrolyte membrane  18 , i.e., the gas diffusion layer  20   b  is placed on the electrode catalyst layer  20   a . The gas diffusion layer  22   b  is placed on a surface  18   b  of the solid polymer electrolyte membrane  18 , i.e., the gas diffusion layer  22   b  is placed on the electrode catalyst layer  22   a . These components are stacked together, and subjected to hot pressing treatment to produce the membrane electrode assembly  10   a.    
         [0058]    The resin frame member  24  is formed by an injection molding machine (not shown) beforehand. The resin frame member  24  is aligned with the membrane electrode assembly  10   a . The resin frame member  24  includes the first inner end  24   a  and the second inner end  24   b . In the membrane electrode assembly  10   a , the frame shaped outer end  18   be  of the solid polymer electrolyte membrane  18  is exposed, and the second plate portion  26   b  of the intermediate layer  26  is provided in correspondence with the outer end  18   be.    
         [0059]    Then, as shown in  FIG. 6 , the cathode  22  of the membrane electrode assembly  10   a  is placed at the first inner end  24   a  of the resin frame member  24 , and the solid polymer electrolyte membrane  18  and the anode  20  are placed at the second inner end  24   b . Thus, the resin frame member  24  and the membrane electrode assembly  10   a  are joined together through the second plate portion  26   b . Further, a gap S 1  is formed between the first inner end  24   a  and the outer end  22   be  of the gas diffusion layer  22   b  of the cathode  22 , and a gap S 2  is formed between the second inner end  24   b  and the outer end  20   be  of the gas diffusion layer  20   b  of the anode  20 . 
         [0060]    Then, as shown in  FIG. 7 , material of the intermediate layer  26  which is the same as the second plate portion  26   b  is injected into each of the gaps S 1 , S 2 . Therefore, the material filled in the gaps S 1 , S 2  is hardened to form the first plate portion  26   a  and the third plate portion  26   c , and these components are joined to the second plate portion  26   b  to form the intermediate layer  26 . As long as the first plate portion  26   a , the second plate portion  26   b , and the third plate portion  26   c  can be joined together suitably, the first plate portion  26   a , the second plate portion  26   b , and the third plate portion  26   c  may have different material compositions. 
         [0061]    The gas diffusion layers  22   b ,  20   b  are impregnated with the injected material. Therefore, the first impregnation layer  28   a  is provided at the outer marginal portion of the gas diffusion layer  22   b , in a predetermined area inside the outer end position. The second impregnation layer  28   b  is provided at the outer marginal portion of the gas diffusion layer  20   b , in a predetermined area inside the outer end position. 
         [0062]    At this time, the gas diffusion layer  22   b  and the gas diffusion layer  20   b  are impregnated with the first impregnation layer  28   a  and the second impregnation layer  28   b , respectively, at the pore filling rate of 85% or more. As a result of evaluation, e.g., by a perm-porometer, it has been proven that the pore filling rate and the gas flow rate at the gas diffusion layer have a relationship as shown in  FIG. 8 . As can be seen from  FIG. 8 , at the pore filling rate of 85% or more, the gas leakage can be prevented reliably. 
         [0063]    In the first embodiment, the intermediate layer  26  is provided between the resin frame member  24  and the membrane electrode assembly  10   a . The intermediate layer  26  includes the first plate portion  26   a , the second plate portion  26   b , and the third plate portion  26   c  that are contiguous to one another. The first plate portion  26   a  is provided between the outer end  22   be  of the gas diffusion layer  22   b  of the cathode  22  and the first inner end  24   a  of the resin frame member  24  without any gap. The second plate portion  26   b  is provided at the outer end  18   be  of the solid polymer electrolyte membrane  18  exposed from the outer end  22   be  to the outside. The third plate portion  26   c  is provided between the outer end  20   be  of the gas diffusion layer  20   b  of the anode  20  and the second inner end  24   b  of the resin frame member  24  without any gap. 
         [0064]    Moreover, the first impregnation layer  28   a  and the second impregnation layer  28   b  are provided at the gas diffusion layer  22   b  and the gas diffusion layer  20   b . It should be noted that only the first impregnation layer  28   a  or the second impregnation layer  28   b  may be provided. 
         [0065]    Thus, in comparison with the case where the resin frame member  24  is joined to the cathode  22  and the anode  20  by adhesion, the joining strength for joining the resin frame member  24  to the cathode  22  and the anode  20  is improved suitably, and it is possible to suppress occurrence of peeling or the like as much as possible. 
         [0066]    Further, no gap is formed between the first inner end  24   a  and the outer end  22   be  of the gas diffusion layer  22   b  of the cathode  22 , and no gap is formed between the second inner end  24   b  and the outer end  20   be  of the gas diffusion layer  20   b  of the anode  20 . Therefore, it becomes possible to maintain the desired sealing performance for preventing the gas leakage. With the simple and economical structure, mixture of the fuel gas and the oxygen-containing gas can be suppressed as much as possible advantageously. 
         [0067]    Operation of the fuel cell  12  having the above structure will be described. 
         [0068]    Firstly, as shown in  FIG. 1 , an oxygen-containing gas is supplied to the oxygen-containing gas supply passage  30   a , and a fuel gas such as a hydrogen-containing gas is supplied to the fuel gas supply passage  34   a . Further, a coolant such as pure water, ethylene glycol, or oil is supplied to the coolant supply passage  32   a.    
         [0069]    Thus, the oxygen-containing gas flows from the oxygen-containing gas supply passage  30   a  to the oxygen-containing gas flow field  36  of the second separator  16 . The oxygen-containing gas moves in the direction indicated by the arrow B, and the oxygen-containing gas is supplied to the cathode  22  of the membrane electrode assembly  10   a . In the meanwhile, the fuel gas flows from the fuel gas supply passage  34   a  through the supply holes  46  into the fuel gas flow field  38  of the first separator  14 . The fuel gas flows along the fuel gas flow field  38  in the direction indicated by the arrow B, and the fuel gas is supplied to the anode  20  of the membrane electrode assembly  10   a.    
         [0070]    Thus, in each of the membrane electrode assemblies  10   a , the oxygen-containing gas supplied to the cathode  22  and the fuel gas supplied to the anode  20  are partially consumed in the electrochemical reactions in the electrode catalyst layers for generating electricity. 
         [0071]    Then, the oxygen-containing gas partially consumed at the cathode  22  flows along the oxygen-containing gas discharge passage  30   b , and the oxygen-containing gas is discharged in the direction indicated by the arrow A. Likewise, the fuel gas partially consumed at the anode  20  flows through the discharge holes  48 . Then, the fuel gas flow along the fuel gas discharge passage  34   b , and the fuel gas is discharged in the direction indicated by the arrow A. 
         [0072]    Further, the coolant supplied to the coolant supply passage  32   a  flows into the coolant flow field  40  between the first separator  14  and the second separator  16 . Then, the coolant flows in the direction indicated by the arrow B. After the coolant cools the membrane electrode assembly  10   a , the coolant is discharged into the coolant discharge passage  32   b.    
         [0073]    Next, another method of producing the resin frame equipped membrane electrode assembly  10  will be described below. 
         [0074]    Firstly, as shown in  FIG. 9 , the membrane electrode assembly  10   a  is produced in the same manner as described above. Thereafter, a liquid seal LS made of the same material as the intermediate layer  26  is formed integrally with the outer end of the membrane electrode assembly  10   a . The liquid seal LS covers the outer end  22   be  of the gas diffusion layer  22   b  of the cathode  22 , the outer end  18   be  of the solid polymer electrolyte membrane  18 , and the outer end  20   be  of the gas diffusion layer  20   b  of the anode  20 . The first impregnation layer  28   a  and the second impregnation layer  28   b  are joined together by the liquid seal LS. 
         [0075]    After the liquid seal LS is semi-hardened, as shown in  FIG. 10 , the resin frame member  24  and the membrane electrode assembly  10   a  are joined together. Therefore, the semi-hardened liquid seal LS flows into and is hardened in the gaps S 1 , S 2  formed between the membrane electrode assembly  10   a  and the resin frame member  24 . Thus, by removing burr (not shown) which is present outside the resin frame member  24 , the resin frame equipped membrane electrode assembly  10  is obtained. 
         [0076]      FIG. 11  is an exploded perspective view showing main components of a solid polymer electrolyte fuel cell  62  including a resin frame equipped membrane electrode assembly  60  according to a second embodiment of the present invention. 
         [0077]    The constituent elements that are identical to those of the fuel cell  12  including the resin frame equipped membrane electrode assembly  10  according to the first embodiment are labeled with the same reference numerals, and descriptions thereof will be omitted. Likewise, also in third and subsequent embodiments described later, the constituent elements that are identical to those of the fuel cell  12  including the resin frame equipped membrane electrode assembly  10  according to the first embodiment are labeled with the same reference numerals, and descriptions thereof will be omitted. 
         [0078]    The resin frame equipped membrane electrode assembly  60  includes a membrane electrode assembly  10   a  and a resin frame member  64 . The resin frame member  64  is provided around the outer end of the solid polymer electrolyte membrane  18 , and joined to the cathode  22  and the anode  20 . The outer size of the resin frame member  64  is the same as the outer sizes of the first separator  14  and the second separator  16 . The oxygen-containing gas supply passage  30   a , the coolant supply passage  32   a , the fuel gas discharge passage  34   b , the fuel gas supply passage  34   a , the coolant discharge passage  32   b , and the oxygen-containing gas discharge passage  30   b  are formed in the outer marginal portion of the resin frame member  64 . 
         [0079]    In the second embodiment having the above structure, the intermediate layer  26  is provided between the resin frame member  64  and the membrane electrode assembly  10   a , and the first impregnation layer  28   a  and the second impregnation layer  28   b  are provided for the gas diffusion layer  22   b  and the gas diffusion layer  20   b , respectively. 
         [0080]    Thus, in comparison with the case where the resin frame member  64  is joined to the cathode  22  and the anode  20  by adhesion, the joining strength for joining the resin frame member  64  to the cathode  22  and the anode  20  is improved suitably, and it is possible to suppress occurrence of peeling or the like as much as possible. Further, the same advantages as in the case of the first embodiment are obtained. For example, with the simple and economical structure, mixture of the fuel gas and the oxygen-containing gas can be suppressed as much as possible. 
         [0081]      FIG. 12  is a cross sectional view showing a solid polymer electrolyte fuel cell  72  including a resin frame equipped membrane electrode assembly  70  according to a third embodiment of the present invention. 
         [0082]    The resin frame equipped membrane electrode assembly  70  includes a membrane electrode assembly  10   a  and a resin frame member  74 . The resin frame member  74  is provided around the outer end of the solid polymer electrolyte membrane  18 , and joined to the cathode  22  and the anode  20 . The outer size of the resin frame member  74  is the same as the outer sizes of the first separator  14  and the second separator  16 . A seal member  76   a  is provided between the resin frame member  74  and the first separator  14 , and a seal member  76   b  is provided between the resin frame member  74  and the second separator  16 . 
         [0083]      FIG. 13  is a cross sectional view showing a solid polymer electrolyte fuel cell  82  including a resin frame equipped membrane electrode assembly  80  according to a fourth embodiment of the present invention. 
         [0084]    The resin frame equipped membrane electrode assembly  80  includes a membrane electrode assembly  10   a  and a resin frame member  84 . The resin frame member  84  is provided around the outer end of the solid polymer electrolyte membrane  18 , and joined to the cathode  22  and the anode  20 . The outer size of the resin frame member  84  is larger than the outer sizes of the first separator  14  and the second separator  16 . A seal member  86   a  is provided between the resin frame member  84  and the first separator  14 , and a seal member  86   b  is provided between the adjacent resin frame members  84  outside the first separator  14  and the second separator  16 . 
         [0085]    In third and fourth embodiment having the above structure, the same advantages as in the cases of the first and second embodiments are obtained. 
         [0086]      FIG. 14  is a cross sectional view showing a solid polymer electrolyte fuel cell  92  including a resin frame equipped membrane electrode assembly  90  according to a fifth embodiment of the present invention. 
         [0087]    An intermediate layer  94  is provided between a resin frame member  93  and the membrane electrode assembly  10   a  of the resin frame equipped membrane electrode assembly  90 . The intermediate layer  94  is made of the same material as the intermediate layer  26 , and has a Z shape in cross section. A first gap  96   a  is formed between one end of the intermediate layer  94 , the outer end  22   be  of the gas diffusion layer  22   b  of the cathode  22 , and a first inner end  93   a  of the resin frame member  93 . A second gap  96   b  is formed between the other end of the intermediate layer  94 , the outer end  20   be  of the gas diffusion layer  20   b  of the anode  20 , and a second inner end  93   b  of the resin frame member  93 . 
         [0088]    As described later, a first resin impregnation portion  100   a  is formed in the first gap  96   a  by melting a first projection  98   a  provided integrally with, or separately from the resin frame member  93 . As described later, a second resin impregnation portion  100   b  is formed in the second gap  96   b  by melting a second projection  98   b  provided integrally with, or separately from the resin frame member  93 . 
         [0089]    The first resin impregnation portion  100   a  is partially overlapped with one end of the intermediate layer  94  by impregnation inside the gas diffusion layer  22   b . The second resin impregnation portion  100   b  is partially overlapped with the other end of the intermediate layer  94  by impregnation inside the gas diffusion layer  20   b . Adhesion layers  102   a ,  102   b  are provided at the gas diffusion layers  22   b ,  20   b . The gas diffusion layers  22   b ,  20   b  are impregnated with the intermediate layer  94  partially to form the adhesive layers  102   a ,  102   b.    
         [0090]    Next, a method of producing the resin frame equipped membrane electrode assembly  90  will be described below. 
         [0091]    Firstly, as shown in  FIG. 15 , the resin frame member  93  is formed by an injection molding machine (not shown) beforehand. The frame shaped first projection  98   a  is formed integrally with one outer surface of the resin frame member  93  (outer surface adjacent to the first inner end  93   a ), around the first inner end  93   a . The frame shaped second projection  98   b  is formed integrally with the other outer surface of the resin frame member  93  (outer surface adjacent to the second inner end  93   b ), around the second inner end  93   b . Alternatively, the first projection  98   a  and the second projection  98   b  may be provided as frame members separate from the resin frame member  93 , and overlapped with the resin frame member  93 . 
         [0092]    The resin frame member  93  is aligned with the membrane electrode assembly  10   a , and a plate member  94   a  of the intermediate layer  94  is provided in correspondence with the outer end  18   be  of the solid polymer electrolyte membrane  18 . 
         [0093]    Then, as shown in  FIG. 16 , the resin frame member  93  and the membrane electrode assembly  10   a  are joined together through the plate member  94   a  such that the cathode  22  is provided at the first inner end  93   a , and the solid polymer electrolyte membrane  18  and the anode  20  are provided at the second inner end  93   b.    
         [0094]    At this time, the plate member  94   a  is sandwiched between the resin frame member  93  and the membrane electrode assembly  10   a . Thus, the plate member  94   a  enters between the first inner end  93   a  and the outer end  22   be  of the gas diffusion layer  22   b  of the cathode  22 , and between the second inner end  93   b  and the outer end  20   be  of the gas diffusion layer  20   b  of the anode  20 . As a result, the intermediate layer  94  formed in a substantially Z shape in cross section is obtained. 
         [0095]    The first gap  96   a  is formed between one end of the intermediate layer  94 , the outer end  22   be  of the gas diffusion layer  22   b  of the cathode  22 , and the first inner end  93   a  of the resin frame member  93 . Further, the second gap  96   b  is formed between the other end of the intermediate layer  94 , the outer end  20   be  of the gas diffusion layer  20   b  of the anode  20 , and the second inner end  93   b  of the resin frame member  93 . 
         [0096]    Then, as shown in  FIG. 17 , the first projection  98   a  and the second projection  98   b  of the resin frame member  93  are heated. As a heating method, any of laser welding, infrared welding, and impulse welding, etc. is adopted. 
         [0097]    Thus, the first projection  98   a  is melted by heating to cover the first gap  96   a . The gas diffusion layer  22   b  of the cathode  22  is impregnated with the first projection  98   a . The second projection  98   b  is melted by heating to cover the second gap  96   b . The gas diffusion layer  20   b  of the anode  20  is impregnated with the second projection  98   b . In this manner, the resin frame equipped membrane electrode assembly  90  is produced. 
         [0098]    In the resin frame equipped membrane electrode assembly  90  according to the fifth embodiment produced as described above, the same advantages as in the cases of the first to fourth embodiments are obtained.