Abstract:
An electrolyte membrane-electrode assembly is provided with: a solid polymer electrolyte membrane; and an anode-side electrode and a cathode-side electrode that sandwich the solid polymer electrolyte membrane. The cathode-side electrode has smaller planar dimensions than the anode-side electrode. In the electrolyte membrane-electrode assembly, a resin frame member is provided around the outer periphery of the solid polymer electrolyte membrane. The resin frame member is bonded to the cathode-side electrode by having only the outer peripheral portion of the cathode-side electrode being impregnated with the inner peripheral portion of the resin frame member.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fuel cell membrane electrode assembly (electrolyte membrane-electrode assembly for fuel cells), and a method of producing the fuel cell membrane electrode assembly. The fuel cell membrane electrode assembly includes a solid polymer electrolyte membrane and a first electrode and a second electrode provided on both sides of the solid polymer electrolyte membrane. Each of the first electrode and the second electrode includes an electrode catalyst layer and a gas diffusion layer. The outer size of the first electrode is smaller than the outer size of the second electrode. 
       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. For example, the fuel cell stack is mounted in a fuel cell electric vehicle as an in-vehicle fuel cell stack. 
         [0003]    In certain cases, the membrane electrode assembly has structure where components of the MEA have different sizes, i.e., the surface size (surface area) of one of diffusion layers is smaller than the surface size (surface area) of the solid polymer electrolyte membrane, and the surface size of the other of the gas diffusion layers is the same as the surface size of the solid polymer electrolyte membrane (a stepped-type MEA). 
         [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. 19 , a membrane electrode assembly disclosed in Japanese Laid-Open Patent Publication No. 2007-066766 (hereinafter referred to as conventional technique) 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 the conventional technique, 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]    The present invention has been made to solve the problem of this type, and an object of the present invention is to provide a fuel cell membrane electrode assembly and a method of producing the fuel cell membrane electrode assembly in which it is possible to firmly and easily join a resin frame member around a solid polymer electrolyte membrane, and suitably suppress deformation of the resin frame member. 
         [0009]    The present invention relates to a fuel cell membrane electrode assembly, and a method of producing the fuel cell membrane electrode assembly. The fuel cell membrane electrode assembly includes a solid polymer electrolyte membrane and a first electrode and a second electrode provided on both sides of the solid polymer electrolyte membrane. Each of the first electrode and the second electrode includes an electrode catalyst layer and a gas diffusion layer. An outer size of the first electrode is smaller than an outer size of the second electrode. 
         [0010]    The membrane electrode assembly includes a resin frame member provided around the solid polymer electrolyte membrane and an impregnation portion for joining the resin frame member and at least one of an outer marginal portion of the first electrode and an outer marginal portion of the second electrode together. 
         [0011]    Further, the production method includes the steps of forming the first electrode and the second electrode on both sides of the solid polymer electrolyte membrane, forming a resin frame member, and overlapping an outer marginal portion of the first electrode and an inner marginal portion of the resin frame member with each other and heating the overlapped portions of the first electrode and the resin frame member to impregnate only the outer marginal portion of the first electrode with the inner marginal portion of the resin frame member and join the resin frame member around the solid polymer electrolyte membrane. 
         [0012]    Further, the production method includes the steps of overlapping an outer marginal portion of the gas diffusion layer of the first electrode and an inner marginal portion of the resin frame member with each other and heating the overlapped portions of the first electrode and the resin frame member to impregnate only the outer marginal portion of the first electrode with the inner marginal portion of the resin frame member and join the resin frame member to the first electrode, forming the electrode catalyst layers on both surfaces of the solid polymer electrolyte membrane, and combining the gas diffusion layer of the first electrode joined to the resin frame member and the gas diffusion layer of the second electrode on both sides of the solid polymer electrolyte membrane into one piece. 
         [0013]    Further, the production method includes the steps of overlapping an outer marginal portion of the gas diffusion layer of the first electrode and an inner marginal portion of the resin frame member with each other and heating the overlapped portions of the first electrode and the resin frame member to impregnate only the outer marginal portion of the first electrode with the inner marginal portion of the resin frame member and join the resin frame member to the first electrode, forming the electrode catalyst layer on the gas diffusion layer of the second electrode and forming the electrode catalyst layer of the first electrode on one side of the solid polymer electrolyte membrane, and combining the first electrode joined to the resin frame member and the second electrode on both sides of the solid polymer electrolyte membrane into one piece. 
         [0014]    In the present invention, the impregnation portion joining the resin frame member and the at least one of the outer marginal portion of the first electrode and the outer marginal portion of the second electrode together is provided. In the structure, in comparison with the case where the resin frame member is joined to the first electrode or the second electrode by adhesion, the joining strength for joining the resin frame member to at least one of 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. 
         [0015]    In the production method of the present invention, the resin frame member is joined only to the first electrode. Therefore, the portion of the resin frame member where heat contraction occurs is reduced, and it becomes possible to suppress occurrence of warpage or the like of the resin frame member. Thus, it is possible to firmly and easily join the resin frame member around the solid polymer electrolyte membrane, and suitably suppress deformation of the resin frame member. 
         [0016]    Further, in the present invention, the outer ends of the gas diffusion layers of the first electrode and the second electrode and the resin frame member are impregnated with resin to form the resin impregnation portion integrally. 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. 
         [0017]    Further, in the present invention, the outer end of the gas diffusion of the second electrode and the resin frame member are impregnated with resin to form the resin impregnation portion integrally. Therefore, the portion of the resin frame member where heat contraction occurs is reduced, and it becomes possible to suppress occurrence of warpage or the like of the resin frame member. Further, since the resin impregnation portion is provided only at the second electrode having the large size, as the resin member, resin mixed with a glass filler is adopted, and it becomes possible to use resin having high melting temperature. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  is an exploded perspective view showing main components of a solid polymer electrolyte fuel cell including a 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 membrane electrode assembly; 
           [0021]      FIG. 4  is a partial cross sectional view showing an MEA having different sizes of components in a production method according to the first embodiment of the present invention; 
           [0022]      FIG. 5  is a view showing a resin frame member; 
           [0023]      FIG. 6  is a view showing a process of joining the MEA and the resin frame member; 
           [0024]      FIG. 7  is a diagram showing steps of a production method according to a second embodiment of the present invention; 
           [0025]      FIG. 8  is a diagram showing steps of a production method according to a third embodiment of the present invention; 
           [0026]      FIG. 9  is a cross sectional view showing a solid polymer electrolyte fuel cell including a membrane electrode assembly according to a fourth embodiment of the present invention; 
           [0027]      FIG. 10  is a front view showing a cathode of the membrane electrode assembly; 
           [0028]      FIG. 11  is a front view showing an anode of the membrane electrode assembly; 
           [0029]      FIG. 12  is a view showing a method of producing the membrane electrode assembly; 
           [0030]      FIG. 13  is a view showing a comparative example of the membrane electrode assembly; 
           [0031]      FIG. 14  is a cross sectional view showing main components of a membrane electrode assembly according to a fifth embodiment of the present invention; 
           [0032]      FIG. 15  is a cross sectional view showing main components of a membrane electrode assembly according to a sixth embodiment of the present invention; 
           [0033]      FIG. 16  is a cross sectional view showing main components of a membrane electrode assembly according to a seventh embodiment of the present invention; 
           [0034]      FIG. 17  is a cross sectional view showing a solid polymer electrolyte fuel cell including a membrane electrode assembly according to an eighth embodiment of the present invention; 
           [0035]      FIG. 18  is a view showing a method of producing the membrane electrode assembly; and 
           [0036]      FIG. 19  is a view showing a membrane electrode assembly disclosed in Japanese Laid-Open Patent Publication No. 2007-066766. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0037]    As shown in  FIGS. 1 and 2 , a solid polymer electrolyte fuel cell  12  including a membrane electrode assembly  10  according to a first embodiment of the present invention is formed by sandwiching the 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 . 
         [0038]    As shown in  FIG. 2 , the membrane electrode assembly  10  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 . 
         [0039]    The surface size (surface area) of the cathode  22  is smaller than the surface sizes (surface areas) of the solid polymer electrolyte membrane  18  and the anode  20 . It should be noted that the surface size of the cathode  22  may be equal to or larger than the surface size of the anode  20 . 
         [0040]    The anode  20  is provided on one surface  18   a  of the solid polymer electrolyte membrane  18  and the cathode  22  is provided on the other surface  18   b  of the solid polymer electrolyte membrane  18  such that a frame shaped outer portion of the solid polymer electrolyte membrane  18  is exposed. 
         [0041]    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   c  stacked on the electrode catalyst layer  20   a  through an intermediate layer (underlying layer)  20   b . 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   c  stacked on the electrode catalyst layer  22   a  through an intermediate layer (underlying layer)  22   b.    
         [0042]    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  18   a ,  18   b  of the solid polymer electrolyte membrane  18  to form the electrode catalyst layers  20   a ,  22   a.    
         [0043]    Carbon black and FEP (fluorinated ethylene-propylene copolymer) particles and carbon nanotube are prepared in a form of paste, and coated on the gas diffusion layer  20   c ,  22   c  to form the intermediate layers  20   b ,  22   b . The gas diffusion layers  20   c ,  22   c  are made of carbon papers or the like, and the surface size of the gas diffusion layer  20   c  is larger that the surface size of the gas diffusion layer  22   c.    
         [0044]    As shown in  FIGS. 2 and 3 , the membrane electrode assembly  10  includes a resin frame member  24  formed around the solid polymer electrolyte membrane  18 , and joined only to the cathode  22  of the solid polymer electrolyte membrane  18 . For example, the resin frame member  24  is made of PPS (poly phenylene sulfide), PPA (polyphthalamide), etc., and includes an impregnation portion  26  for impregnation of only the outer marginal portion of the cathode  22  with the inner marginal portion of the resin frame member  24 . 
         [0045]    As shown in  FIG. 1 , at one end 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. 
         [0046]    At the other end 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. 
         [0047]    The second separator  16  has an oxygen-containing gas flow field  36  on its surface  16   a  facing the 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.    
         [0048]    The first separator  14  has a fuel gas flow field  38  on its surface  14   a  facing the 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.    
         [0049]    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 . 
         [0050]    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 membrane electrode assembly  10 , and a second ridge seal  42   b  interposed between the first separator  14  and 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). 
         [0051]    Each of the first seal member  42  and the second seal members  44  is made of 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. 
         [0052]    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.    
         [0053]    In this fuel cell  12 , a method of producing the membrane electrode assembly  10  according to a first embodiment of the present invention will be described below. 
         [0054]    Firstly, as shown in  FIG. 4 , an MEA  50  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 , and the intermediate layers  20   b ,  22   b  each comprising a mixture of water-repellent agent and carbon particles are coated on the gas diffusion layers  20   c ,  22   c.    
         [0055]    Then, the gas diffusion layer  20   c  is placed on a side adjacent to the surface  18   a  of the solid polymer electrolyte membrane  18 , i.e., the gas diffusion layer  20   c  is placed such that the intermediate layer  20   b  faces the electrode catalyst layer  20   a . Further, the gas diffusion layer  22   c  is placed on a side adjacent to the surface  18   b  of the solid polymer electrolyte membrane  18 , i.e., the gas diffusion layer  22   c  is placed such that the intermediate layer  22   b  faces the electrode catalyst layer  22   a . These components are stacked together, and subjected to hot pressing treatment to produce the MEA  50 . 
         [0056]    As shown in  FIG. 5 , the resin frame member  24  is formed by an injection molding machine (not shown) beforehand. The dimension (width) H 1  of the resin frame member  24  and the dimension (thickness) H 1  of the MEA  50  are the same. The resin frame member  24  has an inner extension  24   a  at its inner marginal portion. The thickness H 2  of the inner extension  24   a  and the thickness H 2  of the cathode  22  of the MEA  50  are the same. The extension length L of the inner extension  24   a  is the sum of the distance from the front end of the solid polymer electrolyte membrane  18  of the MEA  50  to the front end of the cathode  22  and the length of the impregnation portion  26 . 
         [0057]    Next, as shown in  FIG. 6 , the MEA  50  is placed on a base table  52  such that the anode  20  is positioned on the lower side. The front end of the inner extension  24   a  of the resin frame member  24  is overlapped with the outer marginal portion of the cathode  22  of the MEA  50 . A glass plate  54  is placed on the resin frame member  24 . A load F is applied to the resin frame member  24  through the glass plate  54 , toward the base table  52 , and a laser beam Lb is radiated from a laser machine  56  through the glass plate  54  to the overlapped portions (an area where the outer marginal portion of the cathode  22  and the inner marginal portion of the resin frame member  24  are overlapped with each other). 
         [0058]    Thus, the inner extension  24   a  of the resin frame member  24  as the inner marginal portion is locally heated in a concentrated manner, and melted. The gas diffusion layer  22   c  of the cathode  22  is impregnated with the melted resin of the inner extension  24   a  of the resin frame member  24 . Therefore, as shown in  FIG. 2 , the resin frame member  24  is joined to the cathode  22  by the impregnation portion  26  where only the outer marginal portion of the cathode  22  is impregnated with the melted resin of the inner marginal portion of the resin frame member  24 . In this manner, the membrane electrode assembly  10  is produced. 
         [0059]    In the first embodiment, after the MEA  50  and the resin frame member  24  are produced separately, only the outer marginal portion of the cathode  22  is impregnated with the melted resin of the inner marginal portion of the resin frame member  24  to join the resin frame member  24  to the cathode  22 . Thus, in comparison with the case where the resin frame member  24  is joined to the cathode  22  by adhesion, the joining strength for joining the resin frame member  24  to the cathode  22  is improved suitably, and it is possible to suppress occurrence of peeling or the like as much as possible. 
         [0060]    Further, since the resin frame member  24  is joined only to the cathode  22 , the portion of the resin frame member  24  where heat contraction occurs is reduced, and it becomes possible to suppress occurrence of warpage or the like of the resin frame member  24 . 
         [0061]    In particular, the heating treatment is applied only to the overlapped portions in a concentrated manner by laser heating using the laser machine  56 . Therefore, since the resin frame member  24  is heated only locally, the time required for melting is reduced. Accordingly, cost reduction is achieved, and deformation is reduced as much as possible. It should be noted that infrared welding, impulse welding or the like may be adopted instead of laser welding using the laser machine  56 . 
         [0062]    Operation of the fuel cell  12  will be described. 
         [0063]    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, coolant such as pure water, ethylene glycol, or oil is supplied to the coolant supply passage  32   a.    
         [0064]    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 . 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 . 
         [0065]    Thus, in each of the membrane electrode assemblies  10 , 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. 
         [0066]    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. 
         [0067]    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 , the coolant is discharged into the coolant discharge passage  32   b.    
         [0068]      FIG. 7  is a diagram showing steps of a method of producing the membrane electrode assembly  10  according to a second embodiment of the present invention. 
         [0069]    In the second embodiment, the intermediate layer  20   b  is coated on the gas diffusion layer of the anode (S 1 ), and the intermediate layer  22   b  is coated on the gas diffusion layer  22   c  of the cathode (S 2 ). The resin frame member  24  formed by injection molding beforehand is joined to the gas diffusion layer  22   c  (S 3 ). The process of joining the gas diffusion layer  22   c  of the cathode  22  to the resin frame member  24  is substantially the same as in the case of the first embodiment. For example, the gas diffusion layer  22   c  and the resin frame member  24  are joined together by placing the gas diffusion layer  22   c  on the base table  52  shown in  FIG. 6 . In this manner, the resin frame member  24  and the gas diffusion layer  22   c  of the cathode  22  are combined into one piece by the impregnation portion  26 . 
         [0070]    The electrode catalyst layers  20   a ,  22   a  are coated on both surfaces  18   a ,  18   b  of the solid polymer electrolyte membrane  18  (S 4 ). Further, the gas diffusion layer  20   c  of the anode and the gas diffusion layer  22   c  joined to the resin frame member  24  are placed on both surfaces  18   a ,  18   b  of the solid polymer electrolyte membrane  18 , respectively. These components are subjected to hot pressing treatment to produce the membrane electrode assembly  10  (S 5 ). 
         [0071]    Accordingly, in the second embodiment, the same advantages as in the case of the first embodiment are obtained. 
         [0072]      FIG. 8  is a diagram showing steps of a method of producing a membrane electrode assembly  10  according to a third embodiment of the present invention. 
         [0073]    In the third embodiment, after the intermediate layer  20   b  is coated on the gas diffusion layer  20   c  of the anode (S 11 ), the electrode catalyst layer  20   a  is coated on the intermediate layer  20   b  of the gas diffusion layer  20   c  (S 12 ). Further, after the intermediate layer  22   b  is coated on the gas diffusion layer  22   c  of the cathode (S 13 ), the resin frame member  24  is joined to the gas diffusion layer  22   c  (S 14 ). The process of joining the gas diffusion layer  22   c  to the resin frame member  24  is the same as in the cases of the first and second embodiments. 
         [0074]    Further, the electrode catalyst layer  22   a  of the cathode is coated on the surface  18   b  of the solid polymer electrolyte membrane  18  (S 15 ). Then, the gas diffusion layer  20   c  of the anode and the gas diffusion layer  22   c  of the cathode joined to the resin frame member  24  are placed on both surfaces  18   a ,  18   b  of the solid polymer electrolyte membrane  18 , respectively. These components are subjected to hot pressing treatment to produce the membrane electrode assembly  10  (S 16 ). 
         [0075]    Accordingly, in the third embodiment, the same advantages as in the cases of the first and second embodiments are obtained. 
         [0076]      FIG. 9  is a cross sectional view showing a solid polymer electrolyte fuel cell  62  including a membrane electrode assembly  60  according to a fourth embodiment of the present invention. The constituent elements of the solid polymer electrolyte fuel cell  62  that are identical to those of the solid polymer electrolyte fuel cell  12  including the 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 fifth and subsequent embodiments described later, the constituent elements that are identical to those of the solid polymer electrolyte fuel cell  12  including the membrane electrode assembly  10  according to the first embodiment are labeled with the same reference numerals, and descriptions thereof will be omitted. 
         [0077]    In the membrane electrode assembly  60 , 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   c  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   c  stacked on the electrode catalyst layer  22   a . Though not shown, the electrode catalyst layer  20   a  and the gas diffusion layer  20   c  may be provided through an intermediate layer (underlying layer). Likewise, the electrode catalyst layer  22   a  and the gas diffusion layer  22   c  may be provided through an intermediate layer (underlying layer). 
         [0078]    The resin frame member  24  and the gas diffusion layer  22   c  of the cathode  22  are combined into one piece by a first resin impregnation portion  26   a , and the resin frame member  24  and the gas diffusion layer  20   c  of the anode  20  are combined into one piece by a second resin impregnation portion  26   b.    
         [0079]    As shown in  FIG. 10 , the first resin impregnation portion  26   a  is formed over the entire circumference of the gas diffusion layer  22   c  of the cathode  22 . The width L 1  on the long side of the first resin impregnation portion  26   a  (side extending in the direction indicated by the arrow B) is larger than the width L 2  on the short side of the first resin impregnation portion  26   a  (side extending in the direction indicated by the arrow C) (L 1 &gt;L 2 ). 
         [0080]    As shown in  FIG. 11 , the second resin impregnation portion  26   b  is formed over the entire circumference of the gas diffusion layer  20   c  of the anode  20 . The width L 3  on the long side of the second resin impregnation portion  26   b  (side extending in the direction indicated by the arrow B) is larger than the width L 4  on the short side of the second resin impregnation portion  26   b  (side extending in the direction indicated by the arrow C) (L 3 &gt;L 4 ). 
         [0081]    As shown in  FIG. 9 , the second resin impregnation portion  26   b  is terminated at a position spaced outward of a first inner circumferential portion  24   c  of the resin frame member  24  adjacent to the cathode  22  by the distance H. That is, the second resin impregnation portion  26   b  is not provided at a position overlapped with the cathode  22  in the stacking direction. 
         [0082]    Next, a method of producing the membrane electrode assembly  60  will be described below. 
         [0083]    Firstly, as shown in  FIG. 12 , an MEA  64  having different sizes of components (stepped-type MEA) of the membrane electrode assembly  60  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 . The gas diffusion layer  20   c  is placed adjacent to the surface  18   a  of the solid polymer electrolyte membrane  18 , i.e., on the electrode catalyst layer  20   a , and the gas diffusion layer  22   c  is placed adjacent to the surface  18   b  of the solid polymer electrolyte membrane  18 , i.e., on the electrode catalyst layer  22   a . These components are stacked together, and subjected to hot pressing treatment to produce the MEA  64 . 
         [0084]    In the meanwhile, the resin frame member  24  is formed beforehand by an injection molding machine (not shown). The resin frame member  24  is positioned in alignment with the MEA  64 . The resin frame member  24  has the first inner circumferential portion  24   c  and a second inner circumferential portion  24   d . The end of the cathode  22  is positioned at the first inner circumferential portion  24   c , and the end of the anode  20  is positioned at the second inner circumferential portion  24   d.    
         [0085]    A first resin member  26   aa  forming the first resin impregnation portion  26   a  is prepared at the cathode  22 , and a second resin member  26   bb  forming the second resin impregnation portion  26   b  is prepared at the anode  20 . Each of the first resin member  26   aa  and the second resin member  26   bb  has a frame shape, and is made of the same material as the resin frame member  24 , for example. 
         [0086]    The resin frame member  24  uses resin material enforced by mixing a filler with the resin material. The first resin member  26   aa  and the second resin member  26   bb  may be made of resin material which is not mixed with any filler. In the structure, using the robust resin frame member  24 , the MEA  64  and the resin frame member  24  can be joined together. 
         [0087]    Then, in the state where the first resin member  26   aa  and the second resin member  26   bb  are placed over the MEA  64  and the resin frame member  24  and a load is applied to the MEA  64  and the resin frame member  24  through the first resin member  26   aa  and the second resin member  26   bb , the first resin member  26   aa  and the second resin member  26   bb  are heated. As a heating method, any of laser welding, infrared welding, and impulse welding, etc. is adopted. 
         [0088]    Thus, the first resin member  26   aa  and the second resin member  26   bb  are melted by heating. Both of the gas diffusion layer  22   c  of the cathode  22  and the resin frame member  24  are impregnated with the melted resin of the first resin member  26   aa , and both of the gas diffusion layer  20   c  of the anode  20  and the resin frame member  24  are impregnated with the melted resin of the second resin member  26   bb.    
         [0089]    Thus, as shown in  FIG. 9 , the first resin impregnation portion  26   a  is formed over the gas diffusion layer  22   c  of the cathode  22  and the resin frame member  24 , and the second resin impregnation portion  26   b  is formed over the gas diffusion layer  20   c  of the anode  20  and the resin frame member  24  to produce the membrane electrode assembly  60 . 
         [0090]    In the fourth embodiment, the outer ends of the gas diffusion layers  22   c ,  20   c  of the cathode  22  and the anode  20  and the resin frame member  24  are impregnated with resin, respectively, and formed integrally with the first resin impregnation portion  26   a  and the second resin impregnation portion  26   b.    
         [0091]    In the structure, 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. 
         [0092]    Further, the width L 1  on the long side of the first resin impregnation portion  26   a  is larger than the width L 2  on the short side of the first resin impregnation portion  26   a  (L 1 &gt;L 2 ) (see  FIG. 10 ). Moreover, the width L 3  on the long side of the second resin impregnation portion  26   b  is larger than the width L 4  on the short side of the second resin impregnation portion  26   b  (L 3 &gt;L 4 ) (see  FIG. 11 ). Thus, further improvement in the joining strength for joining the resin frame member  24  to the cathode  22  and the anode  20  is achieved suitably, 
         [0093]    Further, as shown in  FIG. 9 , the second resin impregnation portion  26   b  is terminated at a position spaced outward of the first inner circumferential portion  24   c  of the resin frame member  24  adjacent to the cathode  22 , by the distance H. In the range of the distance H, since the electrode catalyst layer  22   a  of the cathode  22  facing the anode  20  is not present, abnormal reaction does not occur. 
         [0094]    For example, in a comparative example shown in  FIG. 13 , the gas diffusion layer  22   c  of the cathode  22  and the resin frame member  24  are combined into one piece by a first resin impregnation portion  27   a . Further, the gas diffusion layer  20   c  of the anode  20  and the resin frame member  24  are combined into one piece by a second resin impregnation portion  27   b . The second resin impregnation portion  27   b  extends inward of the end of the first resin impregnation portion  27   a  by the distance Ha. 
         [0095]    In the comparative example, the electrode catalyst layer  22   a  of the cathode  22  is present in the range of the distance Ha where the second resin impregnation portion  27   b  is provided. In the structure, shortage of hydrogen occurs at the anode  20  in the range of the distance Ha, and abnormal reaction tends to occur at the cathode  22 . 
         [0096]    Specifically, by reactions of H 2 O→1/2O 2 +2H + +2e − , C+2H 2 O→CO 2 +4H + +4e − , and Pt→PT 2+ +2e − , dissolution of corrosive Pt of the supporting carbon occurs, and consequently, the performance is lowered undesirably. 
         [0097]      FIG. 14  is a cross sectional view showing main components of a membrane electrode assembly  70  according to a fifth embodiment of the present invention. 
         [0098]    The membrane electrode assembly  70  includes a resin frame member  72  joined to the cathode  22  and the anode  20 . A first resin protrusion  74   a  and a second resin protrusion  74   b  are formed integrally with the resin frame member  72  for combining the resin frame member  72  and the gas diffusion layer  22   c  of the cathode  22  into one piece, and combining the resin frame member  72  and the gas diffusion layer  20   c  of the anode  20  into one piece. 
         [0099]    The first resin protrusion  74   a  is formed in a frame shape around the first inner circumferential portion  24   c , and the second resin protrusion  74   b  is formed in a frame shape around the second inner circumferential portion  24   d . Preferably, the first resin protrusion  74   a  has an inclined surface  74   as  as an end surface opposite to the first inner circumferential portion  24   c , and the inclined surface  74   as  is inclined in a direction spaced from the resin frame member  72 . 
         [0100]    Likewise, preferably, the second resin protrusion  74   b  has an inclined surface  74   bs  as an end surface opposite to the second inner circumferential portion  24   d , and the inclined surface  74   bs  is inclined in a direction spaced from the resin frame member  72 . 
         [0101]    The first resin protrusion  74   a  and the second resin protrusion  74   b  are heated by a heating machine (not shown), and melted. By applying a load to the first resin protrusion  74   a  and the second resin protrusion  74   b , the gas diffusion layers  22   c ,  20   c  are impregnated with the melted resin of the first resin protrusion  74   a  and the second resin protrusion  74   b . In this manner, the first resin impregnation portion  26   a  and the second resin impregnation portion  26   b  are formed. Thus, in the fifth embodiment, the same advantages as in the case of the fourth embodiment are obtained. 
         [0102]      FIG. 15  is a cross sectional view showing main components of a membrane electrode assembly  80  according to a sixth embodiment of the present invention. 
         [0103]    The membrane electrode assembly  80  includes a resin frame member  82  joined to the cathode  22  and the anode  20 . The resin frame member  82  includes a first resin member  84   a  and a second resin member  84   b  for combining the resin frame member  82  and the gas diffusion layer  22   c  of the cathode  22  into one piece, and combining the resin frame member  82  and the gas diffusion layer  20   c  of the anode  20  into one piece. The first resin member  84   a  and the second resin member  84   b  are formed integrally with the resin frame member  82  by insert molding beforehand. 
         [0104]    The first resin member  84   a  and the second resin member  84   b  are heated by a heating machine (not shown), and melted. By applying a load to the first resin member  84   a  and the second resin member  84   b , the gas diffusion layers  22   c ,  20   c  are impregnated with the melted resin of the first resin member  84   a  and the second resin member  84   b . In this manner, the first resin impregnation portion  26   a  and the second resin impregnation portion  26   b  are formed. Thus, in the sixth embodiment, the same advantages as in the case of the fourth and fifth embodiments are obtained. 
         [0105]      FIG. 16  is a cross sectional view showing a membrane electrode assembly  90  according to a seventh embodiment of the present invention. 
         [0106]    The membrane electrode assembly  90  includes a resin frame member  92  joined to the cathode  22  and the anode  20 . A first resin protrusion  94   a  and a second resin protrusion  94   b  are provided integrally with the resin frame member  92  for combining the resin frame member  92  and the gas diffusion layer  22   c  of the cathode  22  into one piece, and combining the resin frame member  92  and the gas diffusion layer  20   c  of the anode  20  into one piece. 
         [0107]    The first resin protrusion  94   a  is formed in a frame shape around the first inner circumferential portion  24   c , and the second resin protrusion  94   b  is formed in a frame shape around the second inner circumferential portion  24   d.    
         [0108]    Each of the first resin protrusion  94   a  and the second resin protrusion  94   b  has a rectangular shape in cross section. In effect, the first resin protrusion  94   a  and the second resin protrusion  94   b  are formed by eliminating the inclined surfaces  74   as ,  74   bs  of the first resin protrusion  74   a  and the second resin protrusion  74   b  in the membrane electrode assembly  70  according to the fifth embodiment. 
         [0109]    In the seventh embodiment, the first resin protrusion  94   a  and the second resin protrusion  94   b  are heated by a heating machine (not shown), and melted. By applying a load to the first resin protrusion  94   a  and the second resin protrusion  94   b , the gas diffusion layers  22   c ,  20   c  are impregnated with the melted resin of the first resin protrusion  94   a  and the second resin protrusion  94   b . In this manner, the first resin impregnation portion  26   a  and the second resin impregnation portion  26   b  are formed. 
         [0110]    Thus, in the seventh embodiment, the same advantage as in the case of the fourth to sixth embodiments are obtained. Further, in particular, operation of producing the first resin protrusion  94   a  and the second resin protrusion  94   b  can be carried out simply. 
         [0111]      FIG. 17  is a cross sectional view showing a solid polymer electrolyte fuel cell  102  including a membrane electrode assembly  100  according to an eighth embodiment of the present invention. 
         [0112]    In the membrane electrode assembly  100 , the resin frame member  24  and the gas diffusion layer  20   c  of the anode  20  are combined into one piece by a resin impregnation portion  104 . That is, the resin frame member  24  is joined only to the anode  20  which is larger than the cathode  22 . 
         [0113]    At the time of producing the membrane electrode assembly  100 , as shown in  FIG. 18 , an MEA  106  having different sizes of components (stepped-type MEA) of the membrane electrode assembly  100  is produced. In the state where the resin frame member  24  and the MEA  106  are positioned with respect to each other, a resin member  104   a  for forming the resin impregnation portion  104  is prepared. The resin member  104   a  has a frame shape, and uses resin material enforced by mixing a glass filler with the resin material. 
         [0114]    Then, in the state where the resin member  104   a  is placed, and a load is applied to the MEA  106  and the resin frame member  24 , the resin member  104   a  is heated. Thus, the heated resin member  104   a  is melted to form the resin impregnation portion  104  over the gas diffusion layer  20   c  of the anode  20  and the resin frame member  24 . In this manner, the membrane electrode assembly  100  is produced. 
         [0115]    In the eighth embodiment, when the resin member  104   a  is heated, and melted, the glass filler does not enter the gas diffusion layer  20   c . Therefore, the resin member  104   a  does not directly contact the solid polymer electrolyte membrane  18 . 
         [0116]    Further, when the resin member  104   a  is melted at high temperature, the gas diffusion layer  20   c  and the electrode catalyst layer  20   a , and in certain cases, an intermediate layer  20   b  are present between the solid polymer electrolyte membrane  18  and the resin member  104   a . Thus, thermal effect on the solid polymer electrolyte membrane  18  is reduced. 
         [0117]    Accordingly, as the resin member  104   a , it become possible to adopt resin mixed with a glass filler, and use resin having high melting temperature. Thus, the resin used for the resin member  104   a  can be adopted from a wide variety of selection advantageously.