Abstract:
An object is to provide a technique that improves the power generation performance, while enhancing the strength of a reinforced electrolyte membrane. There is provided a method of manufacturing a reinforced electrolyte membrane that comprises a first reinforcing film on one surface of an electrolyte membrane and a second reinforcing film on the other surface of the electrolyte membrane. The method of manufacturing the reinforced electrolyte membrane comprises (a) process of thermally compressing the first reinforcing film and the second reinforcing film to the electrolyte membrane. In the process (a), a number of times of thermally compressing the second reinforcing film to the electrolyte membrane is less than a number of times of thermally compressing the first reinforcing film to the electrolyte membrane.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national phase application of International Application No. PCT/JP2015/001242, filed Mar. 6, 2015, and claims the priority of Japanese Application Nos. 2014-051214, filed Mar. 14, 2014 and 2015-040961, filed Mar. 3, 2015, the content of all of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a reinforced electrolyte membrane and a membrane electrode assembly. 
       BACKGROUND ART 
       [0003]    A known configuration of a reinforced electrolyte membrane includes reinforcing films provided on respective surfaces of an electrolyte. The reinforced electrolyte membrane may be manufactured by, for example, pressure bonding under application of heat (thermally compressing) a heated and molten electrolyte resin with porous reinforcing films supplied from the respective sides of the electrolyte resin (for example, JP 2008-004344A). 
       CITATION LIST 
     Patent Literature 
       [0004]    [PTL 1] JP2008-004344A 
         [0005]    [PTL 2] JP2008-277288A 
         [0006]    [PTL 3] JP2011-146256A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    In general, in order to enhance the strength of the reinforced electrolyte membrane, it is preferable to increase the elastic modulus on the surface of the reinforced electrolyte membrane. In the process of manufacturing a membrane electrode assembly using the reinforced electrolyte membrane, however, there has been no specific consideration on the elastic modulus of a surface placed on the cathode side and the elastic modulus of a surface placed on the anode side. There is accordingly a need for a technique that improves the power generation performance while enhancing the strength of the reinforced electrolyte membrane. With regard to the prior art reinforced electrolyte membrane and the prior art membrane electrode assembly, other needs include simplification of the manufacturing process and reduction of cost. 
       Solution to Problem 
       [0008]    In order to solve at least part of the above problems, the invention may be implemented by any of the following aspects. 
         [0009]    (1) According to one aspect of the invention, there is provided a method of manufacturing a reinforced electrolyte membrane that comprises a first reinforcing film on one surface of an electrolyte membrane and a second reinforcing film on the other surface of the electrolyte membrane. The method of manufacturing the reinforced electrolyte membrane comprises (a) process of thermally compressing the first reinforcing film and the second reinforcing film to the electrolyte membrane. In the process (a), number of times of thermally compressing the second reinforcing film to the electrolyte membrane is less than number of times of thermally compressing the first reinforcing film to the electrolyte membrane. In the method of manufacturing the reinforced electrolyte membrane according to this aspect, the number of times of thermally compressing the first reinforcing film to the electrolyte membrane is set to two or more number of times. This enhances the strength of the reinforced electrolyte membrane, compared with single thermal compression. According to this aspect, the number of times of thermally compressing the second reinforcing film to the electrolyte membrane is less than the number of times of thermally compressing the first reinforcing film to the electrolyte membrane. The surface elastic modulus of the second reinforcing film side is thus lower than the surface elastic modulus of the first reinforcing film side. This enables a catalyst layer to be better bonded to the second reinforcing film side having the lower surface elastic modulus, compared with the first reinforcing film side. Especially a cathode catalyst layer often has a less content of an ionomer than an anode catalyst layer, in order to suppress flooding and improve the power generation performance. The less content of the ionomer leads to the higher elastic modulus of the catalyst layer, so that the cathode catalyst layer has the lower bondability to the electrolyte membrane than the anode catalyst layer. The configuration of this aspect, however, enables the cathode catalyst layer to be placed on the second reinforcing film side having the lower surface elastic modulus than the first reinforcing film side and thereby to be well bonded to the electrolyte membrane. This aspect accordingly manufactures the reinforced electrolyte membrane to which the cathode catalyst layer having significant contribution to the power generation performance is well bondable. This improves the power generation performance of a membrane electrode assembly that includes this reinforced electrolyte membrane. 
         [0010]    (2) In the above aspect, the process (a) may comprise (a1) process of thermally compressing the first reinforcing film to one surface of the electrolyte membrane; and (a2) after the process (a1), process of placing the second reinforcing film on the other surface of the electrolyte membrane to which the first reinforcing film is thermally compressed and thermally compressing a stacked body including the first reinforcing film, the electrolyte membrane and the second reinforcing film. The method of manufacturing the reinforced electrolyte membrane of this aspect efficiently makes the number of times of thermal compression of the second reinforcing film less than the number of times of thermal compression of the first reinforcing film 
         [0011]    (3) According to another aspect of the invention, there is provided a method of manufacturing a membrane electrode assembly that comprises a reinforced electrolyte membrane manufactured by the method of manufacturing according to either the aspect (1) or the aspect (2) described above, an anode catalyst layer and a cathode catalyst layer. The method of manufacturing the membrane electrode assembly of this aspect comprises (b) process of forming the anode catalyst layer on a side of the reinforced electrolyte membrane to which the first reinforcing film is thermally compressed and forming the cathode catalyst layer on a side of the reinforced electrolyte membrane to which the second reinforcing film is thermally compressed. The method of manufacturing the membrane electrode assembly according to this aspect enables the cathode catalyst layer having significant contribution to the power generation performance to be well bonded to the reinforced electrolyte membrane, thus improving the power generation performance of the membrane electrode assembly. 
         [0012]    (4) According to another aspect of the invention, there is provided a membrane electrode assembly. The membrane electrode assembly comprises a reinforced electrolyte membrane that comprises an electrolyte membrane, a first reinforcing film placed on one surface of the electrolyte membrane and a second reinforcing film placed on the other surface of the electrolyte membrane; an anode catalyst layer that is placed on a surface of a side of the reinforced electrolyte membrane on which the first reinforcing film is placed; and a cathode catalyst layer that is placed on a surface of a side of the reinforced electrolyte membrane on which the second reinforcing film is placed. The second reinforcing film has a lower surface elastic modulus than a surface elastic modulus of the first reinforcing film In the membrane electrode assembly of this aspect, the surface elastic modulus of the second reinforcing film placed on the cathode side is lower than the surface elastic modulus of the first reinforcing film placed on the anode side. This enhances the adhesiveness of the reinforced electrolyte membrane with the cathode catalyst layer having the higher contribution to the power generation performance. This results in improving the power generation performance of the membrane electrode assembly. The surface elastic modulus of the anode-side reinforcing film is higher than the surface electric modulus of the cathode-side reinforcing film. This configuration ensures the sufficient strength of the membrane electrode assembly as a whole, while improving the power generation performance of the membrane electrode assembly. 
         [0013]    The invention may be implemented by various aspects other than the aspects of the method of manufacturing the reinforced electrolyte membrane, the method of manufacturing the membrane electrode assembly and the membrane electrode assembly described above. For example, the invention may be implemented by aspects such as a fuel cell including the reinforced electrolyte membrane or the membrane electrode assembly and an apparatus for manufacturing the reinforced electrolyte membrane or the membrane electrode assembly. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a diagram illustrating a membrane electrode assembly according to one embodiment of the invention; 
           [0015]      FIG. 2  is a flowchart showing a method of manufacturing a reinforced electrolyte membrane; 
           [0016]      FIG. 3  is a diagram schematically illustrating the processes of steps S 100  to S 104  in  FIG. 2 ; 
           [0017]      FIG. 4  is a diagram schematically illustrating the processes of steps S 106  to S 108  in  FIG. 2 ; 
           [0018]      FIG. 5  is a diagram schematically illustrating the processes of steps S 110  to S 112  in  FIG. 2 ; 
           [0019]      FIG. 6  is a diagram schematically illustrating the processes of steps S 114  to S 116  in  FIG. 2 ; 
           [0020]      FIG. 7  is a diagram schematically illustrating the process of step S 118  in  FIG. 2 ; 
           [0021]      FIG. 8  is a flowchart showing a method of manufacturing a membrane electrode assembly; 
           [0022]      FIG. 9  is a diagram schematically illustrating the method of manufacturing the membrane electrode assembly of  FIG. 8 ; 
           [0023]      FIG. 10  is a table showing the results of measurement of surface elastic modulus; 
           [0024]      FIG. 11  is a graph showing relationship between the current density and the average cell voltage; and 
           [0025]      FIG. 12  is a table showing the results of measurement of surface elastic modulus after evaluation of power generation performance. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     A. First Embodiment 
     A1. Configuration of Membrane Electrode Assembly 
       [0026]      FIG. 1  is a diagram illustrating a membrane electrode assembly (MEA)  50  according to one embodiment of the invention. The MEA  50  includes a reinforced electrolyte membrane  10   c,  an anode catalyst layer  20  and a cathode catalyst layer  30 . The reinforced electrolyte membrane  10   c  is a membrane formed by integrating an electrolyte membrane  10 , a first reinforcing film  11  placed on one surface of the electrolyte membrane  10  and a second reinforcing film  12  placed on the other surface of the electrolyte membrane  10 . The first reinforcing film  11  and the second reinforcing film  12  are porous films having pores. The pores of the first reinforcing film  11  and the second reinforcing film  12  are filled with part of the electrolyte of the electrolyte membrane  10 . According to this embodiment, the reinforced electrolyte membrane  10   c  is formed such that a second reinforcing film  12 -side surface has a lower elastic modulus than the elastic modulus of a first reinforcing film  11 -side surface. 
         [0027]    The anode catalyst layer  20  is formed on the first reinforcing film  11 -side of the reinforced electrolyte membrane  10   c.  The cathode catalyst layer  30  is formed on the second reinforcing film  12 -side of the reinforced electrolyte membrane  10   c.  Each of the anode catalyst layer  20  and the cathode catalyst layer  30  includes a catalyst that accelerates the chemical reaction of hydrogen and oxygen, carbon particles that have the catalyst supported thereon, and an ionomer that is identical with or analogous to the constituent of the electrolyte membrane  10 . According to this embodiment, in order to suppress flooding, the cathode catalyst layer  30  is configured as a catalyst layer having a less content of the ionomer than that of the anode catalyst layer  20 . In general, the less content of the ionomer leads to the higher elastic modulus of the resulting catalyst layer. According to this embodiment, the cathode catalyst layer  30  is thus configured to have a higher elastic modulus than the elastic modulus of the anode catalyst layer  20 . 
       A2. Method of Manufacturing Reinforced Electrolyte Membrane 
       [0028]      FIG. 2  is a flowchart showing a method of manufacturing the reinforced electrolyte membrane  10   c.    FIG. 3  is a diagram schematically illustrating the processes of steps S 100  to S 104 .  FIG. 4  is a diagram schematically illustrating the processes of steps S 106  to S 108 .  FIG. 5  is a diagram schematically illustrating the processes of steps S 110  to S 112 .  FIG. 6  is a diagram schematically illustrating the processes of steps S 114  to S 116 . The following describes the method of manufacturing the reinforced electrolyte membrane  10   c  with reference to  FIGS. 2 to 6 . 
         [0029]    The procedure of manufacturing the reinforced electrolyte membrane  10   c  first bonds the electrolyte membrane  10  and a first back sheet lb together (step S 100  in  FIGS. 2 and 3 ). According to this embodiment, the first back sheet lb is a polytetrafluoroethylene (PTFE) film of approximately 50 μm in thickness. The electrolyte membrane  10  is a synthetic resin having —SO 2 F as a side-chain end group. The electrolyte membrane  10  has the thickness of approximately 10 μm. At step S 100 , the synthetic resin having —SO 2 F as the side-chain end group is extruded onto the first back sheet  1   b  by a molding machine, so that the electrolyte membrane  10  and the first back sheet  1   b  are bonded together. 
         [0030]    The procedure subsequently bonds the first reinforcing film  11  on the electrolyte membrane  10  bonded with the first back sheet  1   b  (step S 102  in  FIGS. 2 and 3 ). The first reinforcing film  11  is a film made porous by stretching polytetrafluoroethylene (PTFE) which is a fluorine-based synthetic resin. 
         [0031]    After bonding the first reinforcing film  11  on the electrolyte membrane  10 , the procedure bonds a second back sheet  2   b  on the first reinforcing film  11  (step S 104  in  FIGS. 2 and 3 ). The second back sheet  2   b  is a perfluoroalkoxy fluororesin (PFA) film of approximately 50 μm in thickness. 
         [0032]    The procedure subsequently applies heat and pressure from the respective surfaces of the first back sheet  1   b  and the second back sheet  2   b,  so as to thermally compress the electrolyte membrane  10  with the first reinforcing film  11  (step S 106  in  FIGS. 2 and 4 ). The process of thermal compression uses a roll heated to a temperature of  260 ° C. and applies a pressure of 1.2 ton from the respective surfaces of the first back sheet  1   b  and the second back sheet  2   b  to a stacked body  40  in which the first back sheet  1   b,  the electrolyte membrane  10 , the first reinforcing film  11  and the second back sheet  2   b  are sequentially stacked. The conveying speed of the stacked body  40  is 0.5 m/min The contact time of the roll with the stacked body  40  is approximately 3 minutes. The process of thermal compression forms a molten impregnated membrane  10   r  in which the first reinforcing film  11  is impregnated with part of the electrolyte of the electrolyte membrane  10 . 
         [0033]    The procedure subsequently peels off the first back sheet  1   b  bonded to the electrolyte membrane  10 -side of the molten impregnated membrane  10   r,  from the molten impregnated membrane  10   r  (step S 108  in  FIGS. 2 and 4 ). The first back sheet  1   b  has the lower adhesive force than the second back sheet  2   b,  so that the first back sheet  1   b  is readily peeled off from the molten impregnated membrane  10   r.    
         [0034]    The procedure subsequently bonds the second reinforcing film  12  on the side of the molten impregnated membrane  10   r  from which the first back sheet  1   b  is peeled off, i.e., on the electrolyte membrane  10  (step S 110  in  FIGS. 2 and 5 ). The second reinforcing film  12  is a film made porous by stretching PTFE. The procedure then bonds a third back sheet  3   b  on the second reinforcing film  12  (step S 112  in  FIGS. 2 and 5 ). According to this embodiment, the third back sheet  3   b  is a PFA film of approximately 50 μm in thickness, like the second back sheet  2   b.    
         [0035]    After bonding the third back sheet  3   b,  the procedure thermally compresses the electrolyte membrane  10  with the first reinforcing film  11  and the electrolyte membrane  10  with the second reinforcing film  12  from the respective surfaces of the second back sheet  2   b  and the third back sheet  3   b  (step S 114  in  FIGS. 2 and 6 ). The process of thermal compression uses a roll heated to a temperature of 260° C. and applies a pressure of 1.2 ton from the respective surfaces of the second back sheet  2   b  and the third back sheet  3   b  to a stacked body  41  in which the second back sheet  2   b,  the molten impregnated membrane  10   r,  the second reinforcing film  12  and the third back sheet  3   b  are sequentially stacked. The conveying speed of the stacked body  41  is 0.5 m/min The contact time of the roll with the stacked body  41  is approximately  3  minutes. The process of thermal compression causes the second reinforcing film  12  to be impregnated with part of the electrolyte of the electrolyte membrane  10 . This process also causes the first reinforcing film  11  to be impregnated with part of the electrolyte of the electrolyte membrane  10 . This forms a reinforced electrolyte membrane  10   rr.    
         [0036]    The procedure subsequently peels off the third back sheet  3   b  bonded to the second reinforcing film  12 -side of the reinforced electrolyte membrane  10   rr,  from the reinforced electrolyte membrane  10   rr  (step S 116  in  FIGS. 2 and 6 ). The third back sheet  3   b  is thermally compressed to the second reinforcing film  12  only once (step S 108 ). The second back sheet  2   b  is, on the other hand, thermally compressed to the first reinforcing film  11  twice (steps S 106  and S 108 ). According to this embodiment, the third back sheet  3   b  and the second back sheet  2   b  are formed from the same PFA films The less number of times of thermal compression, however, causes the third back sheet  3   b  to be more weakly bonded to the stacked body  41 , compared with the second back sheet  2   b.  The third back sheet  3   b  is thus readily peeled off from the reinforced electrolyte membrane  10   rr.    
         [0037]    After peeling off the third back sheet  3   b,  the procedure makes the reinforced electrolyte membrane  10   rr  subject to hydrolysis (step S 118  in  FIGS. 2 and 7 ). The process of hydrolysis provides the reinforced electrolyte membrane  10   rr  with the proton conductivity, so as to manufacture the reinforced electrolyte membrane  10   c  having —SO 3 H as the side-chain end group. According to this embodiment, the thickness of the final reinforced electrolyte membrane  10   c  is approximately 8 μm. The manufacturing method described above efficiently makes the number of times of thermal compression of the second reinforcing film  12  less than the number of times of thermal compression of the first reinforcing film  11 . 
       A3. Method of Manufacturing Membrane Electrode Assembly 
       [0038]      FIG. 8  is a flowchart showing a method of manufacturing the MEA  50 .  FIG. 9  is a diagram schematically illustrating the method of manufacturing the MEA  50 . The procedure of manufacturing the MEA  50  first provides the reinforced electrolyte membrane  10   c  manufactured by the method of manufacturing the reinforced electrolyte membrane ( FIG. 2 ) described above (step S 200  in  FIGS. 8 and 9 ). 
         [0039]    The procedure subsequently forms the anode catalyst layer  20  on the side of the reinforced electrolyte membrane  10   c  which the first reinforcing film  11  is thermally compressed to, and forms the cathode catalyst layer  30  on the side of the reinforced electrolyte membrane  10   c  which the second reinforcing film  12  is thermally compressed to (step S 202  in  FIGS. 8 and 9 ). In other words, the process of step S 202  forms the anode catalyst layer  20  on the surface of the reinforced electrolyte membrane  10   c  subjected to the more frequent thermal compression, while forming the cathode catalyst layer  30  on the surface of the reinforced electrolyte membrane  10   c  subjected to the less frequent thermal compression. The anode catalyst layer  20  and the cathode catalyst layer  30  are formed by hot pressing. The temperature of hot pressing is 160° C. This manufactures the MEA  50 . According to this embodiment, hot pressing at the temperature of 160° C. does not reduce the membrane thickness of the reinforced electrolyte membrane  10   c  or does not cause deformation on the surface of the reinforced electrolyte membrane  10   c.    
         [0040]    In the method of manufacturing the reinforced electrolyte membrane  10   c  and the method of manufacturing the MEA  50  according to the embodiment described above, the number of times of thermal compression of the second reinforcing film  12  to the electrolyte membrane  10  is less than the number of times of thermal compression of the first reinforcing film  11  to the electrolyte membrane  10 . This causes the surface elastic modulus on the second reinforcing film  12 -side to be lower than the surface elastic modulus on the first reinforcing film  11 -side. This enables a catalyst layer to be better bonded to the second reinforcing film  12 -side having the lower surface elastic modulus, compared with the first reinforcing film  11 -side. Especially this embodiment employs a catalyst layer that has a less content of the ionomer than that of the anode catalyst layer, for the cathode catalyst layer  30 , in order to suppress flooding and improve the power generation performance. The less content of the ionomer leads to the higher elastic modulus of the catalyst layer, so that the cathode catalyst layer  30  has the lower bondability to the electrolyte membrane  10  than the anode catalyst layer  20 . According to this embodiment, the cathode catalyst layer  30  is placed on the second reinforcing film  12 -side having the lower surface elastic modulus. This configuration enables the cathode catalyst layer  30  to be better bonded to the electrolyte membrane  10 , compared with a configuration that the cathode catalyst layer  30  is placed on the first reinforcing film  11 -side. In other words, the procedure of this embodiment manufactures the reinforced electrolyte membrane  10   c  to which the cathode catalyst layer  30  having significant contribution to the power generation performance is well bondable, thus improving the power generation performance of the MEA  50 . The surface elastic modulus of the anode-side reinforcing film (first reinforcing film  11 ) is higher than the surface elastic modulus of the cathode-side reinforcing film (second reinforcing film  12 ). This configuration ensures the sufficient strength of the MEA  50  as a whole, while improving the power generation performance of the MEA  50 . 
         [0041]    Additionally, according to this embodiment, the first reinforcing film  11  of the reinforced electrolyte membrane  10   c  is thermally compressed to the electrolyte membrane  10  twice. This enhances the strength of the reinforced electrolyte membrane  10   c,  compared with a method of manufacturing a reinforced electrolyte membrane by single thermal compression. The process of thermal compression employs a relatively high temperature of 260° C. This causes the first reinforcing film  11  and the second reinforcing film  12  to be impregnated with the electrolyte of the electrolyte membrane  10  more homogeneously in a shorter time period, compared with a process of thermal compression employing a lower temperature. The method of manufacturing the reinforced electrolyte membrane  10   c  according to the embodiment thus shortens the time period required for manufacturing the reinforced electrolyte membrane  10   c.    
       A4. Results of Experiments 
       [0042]    The following describes the grounds on which the reinforced electrolyte membrane  10   c  and the MEA  50  are manufactured by the manufacturing methods described above, with reference to experimental examples. 
       A4-1. Measurement of Surface Elastic Modulus 
       [0043]      FIG. 10  is a table showing the results of measurement of the surface elastic modulus of the reinforced electrolyte membrane  10   c.    FIG. 10  shows the results of measurement of the surface elastic modulus of the first reinforcing film  11 -side and the second reinforcing film  12 -side with regard to the reinforced electrolyte membrane  10   c  manufactured by the manufacturing method described above (hereinafter referred to as sample 1) and a reinforced electrolyte membrane manufactured by changing the temperature of the roll to 230° C. in the process of thermal compression (steps S 106  and S 114 ) in the above manufacturing method (hereinafter referred to as sample 2). The measurement of surface elastic modulus used Nano Indenter G200 (manufactured by Agilent Technologies Inc.) to measure the elastic modulus at the depth of approximately 800 nm from the surface with regard to the sample 1 and the sample 2. The measurement temperature was 120° C. 
         [0044]    As shown in  FIG. 10 , with regard to the sample 1, the surface elastic modulus of the second reinforcing film  12 -side was 24 MPa, and the surface elastic modulus of the first reinforcing film  11 -side was 39 MPa. With regard to the sample 1, the first reinforcing film  11 -side had the higher surface elastic modulus than the second reinforcing film  12 -side. The difference between the surface elastic modulus of the first reinforcing film  11 -side and the surface elastic modulus of the second reinforcing film  12 -side was 15 MPa. The number of times of thermal compression was twice on the first reinforcing film  11 -side (steps S 106  and S 114  in  FIG. 2 ), while being only once on the second reinforcing film  12 -side (step S 114  in  FIG. 2 ). The first reinforcing film  11  was thus subjected to more frequent thermal compression to the electrolyte membrane  10 , compared with the second reinforcing film  12 . This causes the first reinforcing film  11  to be impregnated with a larger amount of the electrolyte of the electrolyte membrane  10 , compared with the second reinforcing film  12 . This appears to make the surface elastic modulus of the first reinforcing film  11 -side higher than the surface elastic modulus of the second reinforcing film  12 -side. 
         [0045]    With regard to the sample 2 manufactured at the temperature of the roll set to 230° C. in the process of thermal compression, the surface elastic modulus of the second reinforcing film  12 -side was 22 MPa, and the surface elastic modulus of the first reinforcing film  11 -side was 25 MPa. With regard to the sample 2, the first reinforcing film  11 -side had the slightly higher surface elastic modulus than the second reinforcing film  12 -side. The difference between the surface elastic modulus of the first reinforcing film  11 -side and the surface elastic modulus of the second reinforcing film  12 -side was 3 MPa. 
         [0046]    These results show that the first reinforcing film  11  subjected to the more frequent thermal compression to the electrolyte membrane  10  has the higher surface elastic modulus, out of the reinforcing films of the reinforced electrolyte membrane  10   c.  These results also show that the higher temperature of the roll leads to the higher surface elastic modulus. Additionally, these results show that the higher temperature of the roll leads to the greater difference between the surface elastic modulus of the first reinforcing film  11 -side and the surface elastic modulus of the second reinforcing film  12 -side. 
       A4-2. Evaluation of Power Generation Performance 
       [0047]      FIG. 11  is a graph showing relationship between the current density and the average cell voltage.  FIG. 11  shows the results of evaluation of power generation performance with regard to a fuel cell including the MEA  50  in which the anode catalyst layer  20  is formed on the first reinforcing film  11 -side of the reinforced electrolyte membrane  10   c  manufactured by the above manufacturing method and the cathode catalyst layer  30  is formed on the second reinforcing film  12 -side (hereinafter referred to as fuel cell 1) and a fuel cell including an MEA in which the cathode catalyst layer  30  is formed on the first reinforcing film  11 -side of the reinforced electrolyte membrane  10   c  and the anode catalyst layer  20  is formed on the second reinforcing film  12 -side (hereinafter referred to as fuel cell 2). 
         [0048]    As shown in  FIG. 11 , at an identical cell voltage, the current density of the fuel cell 1 is higher than the current density of the fuel cell 2. For example, at an average cell voltage of 0.6 V, the current density of the fuel cell 1 was about 2.25 (A/cm 2 ), while the current density of the fuel cell 2 was about 2.05 (A/cm 2 ). These results of evaluation show that the fuel cell 1 including the MEA  50  manufactured by the method of this embodiment, i.e., the MEA  50  in which the cathode catalyst layer  30  is formed on the second reinforcing film  12 -side having the lower surface elastic modulus, has the better power generation performance than the fuel cell 2 including the MEA in which the anode catalyst layer  20  is formed on the second reinforcing film  12 -side. 
       A4-3. Measurement of Surface Elastic Modulus after Evaluation of Power Generation Performance 
       [0049]      FIG. 12  is a table showing the results of measurement of the surface elastic modulus after evaluation of the power generation performance. This measurement experiment manufactured MEAs respectively using the reinforced electrolyte membrane of the sample 1 and the reinforced electrolyte membrane of the sample 2 and provided fuel cells including such MEAs. These fuel cells were evaluated by the above evaluation of power generation performance. The MEAs were then taken out of the respective fuel cells, and only the reinforced electrolyte membrane was left by peeling off the cathode catalyst layer and the anode catalyst layer from each of the MEAs. The surface elastic modulus was then measured on the first reinforcing film  11 -side and the second reinforcing film  12 -side.  FIG. 12  shows the results of measurement. The surface elastic modulus was measured by the same measurement method as that described above. 
         [0050]    As shown in  FIG. 12 , after evaluation of the power generation performance, with regard to both the sample 1 and the sample 2, the values of the surface elastic modulus of the first reinforcing film  11 -side and the second reinforcing film  12 -side of the reinforced electrolyte membrane  10   c  are increased from the values shown in  FIG. 10 . These results may be attributed to that the surface elastic modulus is increased by the heat history at the time of manufacturing the MEA and at the time of evaluation of the power generation performance. According to these results of measurement, with regard to the reinforced electrolyte membrane  10   c  of the sample 1, the surface elastic modulus of the first reinforcing film  11 -side is higher than the surface elastic modulus of the second reinforcing film  12 -side by at least 15 MPa even after evaluation of the power generation. These results of measurement further prove that the configuration of placing the cathode catalyst layer  30  having significant contribution to power generation on the second reinforcing film  12 -side having the lower surface elastic modulus and placing the anode catalyst layer  20  on the first reinforcing film  11 -side having the higher surface elastic modulus is advantageous for the strength of the MEA  50 . 
       B. Modifications 
     B1. First Modification 
       [0051]    The procedure of the above embodiment thermally compresses the first reinforcing film  11  to the electrolyte membrane  10  twice, while thermally compressing the second reinforcing film  12  to the electrolyte membrane  10  only once. The number of times of thermal compression of the first reinforcing film  11  to the electrolyte membrane  10  may be three or more number of times. The number of times of thermal compression of the second reinforcing film  12  may be two or more number of times as long as the number of times of thermal compression of the second reinforcing film  12  is less than the number of times of thermal compression of the first reinforcing film  11 . 
       B2. Second Modification 
       [0052]    The procedure of the above embodiment bonds the reinforcing films  11  and  12  on the electrolyte membrane  10  (steps S 102  and S 110  in  FIG. 10 ) and additionally bonds the back sheets  2   b  and  3   b  on the reinforcing films  11  and  12  (steps S 104  and S 112  in  FIG. 2 ). A modified procedure may bond reinforcing films  11  and  12  that are respectively bonded in advance with back sheets  2   b  and  3   b,  on the electrolyte membrane  10 . 
       B3. Third Modification 
       [0053]    In the embodiment described above, the first reinforcing film  11  and the second reinforcing film  12  are made of PTFE. The first reinforcing film  11  and the second reinforcing film  12  may be made of another porous polymer resin, such as PE (polyethylene), PP (polypropylene) or polyimide. 
       Reference Signs List 
       [0000]    
       
           1   b  first back sheet 
           2   b  second back sheet 
           3   b  third back sheet 
           10  electrolyte membrane 
           10   c,    10   rr  reinforced electrolyte membrane 
           10   r  molten impregnated membrane 
           11  first reinforcing film 
           12  second reinforcing film 
           20  anode catalyst layer 
           30  cathode catalyst layer 
           40 ,  41  stacked body 
           50  MEA