Polymer electrolyte membrane having high durability and method for producing the same

Abstract

A polymer electrolyte membrane comprising: (a) a fluorinated polymer electrolyte having an ion exchange group, and (b) a basic polymer, wherein, optionally, at least a part of component (a) and at least a part of component (b) are chemically bonded to each other. A method for producing the above-mentioned polymer electrolyte membrane. A membrane/electrode assembly comprising the above-mentioned polymer electrolyte membrane which is securely sandwiched between an anode and a cathode. A polymer electrolyte fuel cell comprising the membrane/electrode assembly.

1 . A fuel cell component comprising:
 (a) 50.000 to 99.999% by weight, based on the total weight of components (a) and (b), of a fluorinated polymer electrolyte having an ion exchange group; and   (b) 0.001 to 50.000% by weight, based on the total weight of components (a) and (b), of a basic polymer which can form an acid-base ion complex   wherein a uniform microdispersion polymer mixture of components (a) and (b) forms a polymer electrolyte membrane,   wherein at least a part of component (a) and at least a part of component (b) are chemically bonded to each other.   
     
     
         2 . A fuel cell component comprising:
 (a) 95.000 to 99.990% by weight, based on the total weight of components (a) and (b), of a fluorinated polymer electrolyte having an ion exchange group; and   (b) 0.100 to 5.000% by weight, based on the total weight of components (a) and (b), of a basic polymer, wherein   a uniform microdispersion polymer mixture of components (a) and (b) forms a polymer electrolyte membrane.   
     
     
         3 . A fuel cell component comprising:
 (a) 90.000 to 99.990% by weight, based on the total weight of components (a) and (b), of a fluorinated polymer electrolyte having an ion exchange group; and   (b) 0.001 to 50.000% by weight, based on the total weight of components (a) and (b), of a basic polymer, wherein   a uniform microdispersion polymer mixture of components (a) and (b) forms a polymer electrolyte membrane, and   the polymer electrolyte membrane has an ion exchange capacity of from 1.0 to 1.5 milliequivalents per gram of said membrane.   
     
     
         4 . The fuel cell component according to any one of  claims 1  and  3 , wherein the amount of said basic polymer (b) is from 0.100 to 5.000% by weight, based on the total weight of components (a) and (b). 
     
     
         5 . The fuel cell component according to any one of  claims 1  and  2 , which has an ion exchange capacity of from 1.0 to 1.5 milliequivalents per gram of said membrane. 
     
     
         6 . The fuel cell component according to any one of  claims 1 - 3 , wherein said basic polymer (b) is a nitrogen-containing aliphatic basic polymer. 
     
     
         7 . The fuel cell component according to any one of  claims 1 - 3 , wherein said basic polymer (b) is a nitrogen-containing aromatic basic polymer. 
     
     
         8 . The fuel cell component according to  claim 7 , wherein the nitrogen-containing aromatic basic polymer is a polyaniline or a heterocyclic compound. 
     
     
         9 . The fuel cell component according to  claim 7 , wherein said nitrogen-containing aromatic basic polymer is poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole]. 
     
     
         10 . The fuel cell component according to any one of  claims 1 - 3 , wherein said basic polymer (b) is selected from the group consisting of polyethylene imines, polyanilines, polybenzimidazoles, polypyridines, polypyrimidines, polyvinylpyridines, polyimidazoles, polypyrrolidines and polyvinylimidazoles. 
     
     
         11 . The fuel cell component according to any one of  claims 1 - 3 , wherein said basic polymer (b) is elected from the group consisting of a polybenzimidazole represented by formula (4) below, a polybenzimidazole represented by formula (5) below, and a poly(2,5-benzimidazole) represented by formula (6) below: 
       
         
           
           
               
               
           
         
         wherein:
 each R independently represents a divalent group, which is an alkane chain, a fluoroalkane chain or any one of the following structures: 
 
       
       
         
           
           
               
               
           
         
         
           each R 1  independently represents a hydrogen atom, an alkyl group, a phenyl group or a pyridyl group; and 
           x is a number in the range of from 10 to 1.0×10 7 ; 
         
       
       
         
           
           
               
               
           
         
         wherein R and R 1  are as defined for formula (4), and l is a number in the range of from 10 to 1.0×10 7 ; 
       
       
         
           
           
               
               
           
         
         wherein R 1  is as defined for formula (4), and m is a number in the range of from 10 to 1.0×10 7 . 
       
     
     
         12 . The fuel cell component according to any one of  claims 1 - 3 , wherein said uniform microdispersion is a uniform (b)-in-(a) microdispersion comprising a continuous phase and, contained therein, a dispersed phase which are, respectively, composed mainly of said fluorinated polymer electrolyte (a) and said basic polymer (b). 
     
     
         13 . The fuel cell component according to any one of  claims 1 - 3 , wherein:
 when said polymer electrolyte membrane has a thickness of 50 μm, said membrane exhibits a haze value of 25% or less as measured in accordance with JIS K 7136, and   when said polymer electrolyte membrane has a thickness other than 50 μm, said membrane exhibits a calculated haze value (H 50 ) of 25% or less, wherein said calculated haze value (H 50 ) is defined as a haze value calculated on the assumption that the polymer electrolyte membrane has a thickness of 50 μm,   said calculated haze value (H 50 ) being obtained by the following formula:   
       
         
           
             
               
                 H 
                 50 
               
               = 
               
                 100 
                 · 
                 
                   { 
                   
                     1 
                     - 
                     
                       
                         ( 
                         
                           
                             100 
                             - 
                             
                               H 
                               t 
                             
                           
                           100 
                         
                         ) 
                       
                       
                         50 
                         t 
                       
                     
                   
                   } 
                 
               
             
           
         
         wherein t represents the thickness (μm) of the polymer electrolyte membrane, and H t  represents the haze value of the polymer electrolyte membrane, as measured in accordance with JIS K 7136. 
       
     
     
         14 . The fuel cell component according to any one of  claims 1 - 3 , wherein said fluorinated polymer electrolyte (a) is represented by the following formula:
   [CF 2 CF 2 ] a —[CF 2 —CF(—O—(CF 2 —CF(CF 3 )) b —O—(CF 2 ) f —X 4 )] g  
   wherein 0≦a<1, 0<g≦1, a+g=1, 1≦b≦3, 1≦f≦8, and X 4  represents —COOH, —SO 3 H, —PO 3 H 2      
       or
 —PO 3 H. 
 
     
     
         15 . The fuel cell component according to any one of  claims 1 - 3 , wherein said fluorinated polymer electrolyte (a) is represented by the following formula:
   [CF 2 CF 2 ] a —[CF 2 —CF(—O—(CF 2 ) f —X 4 )] g  
   wherein 0≦a<1, 0<g≦1, a+g=1, 1≦f≦8, and X 4  represents —COOH, —SO 3 H, —PO 3 H 2  or —PO 3 H.   
     
     
         16 . The fuel cell component according to any one of  claims 1 - 3 , wherein the polymer electrolyte membrane has a thickness of from 2 to 150 μm. 
     
     
         17 . The fuel cell component according to any one of  claims 1 - 3 , wherein the polymer electrolyte membrane is supported by has at least one reinforcement selected from the group consisting of a reinforcement contained in said membrane and a reinforcement secured to a surface of said membrane. 
     
     
         18 . A membrane/electrode assembly comprising the fuel cell component of any one of  claims 1 - 3 , which is securely sandwiched between an anode and a cathode, wherein said anode comprises an anodic catalyst layer and is proton-conductive, and said cathode comprises a cathodic catalyst layer and is proton-conductive. 
     
     
         19 . A polymer electrolyte fuel cell comprising the membrane/electrode assembly of  claim 18 , wherein said anode and said cathode are connected to each other through an electron conductive material which is positioned in the outside of said polymer electrolyte membrane. 
     
     
         20 . A method for producing a polymer electrolyte membrane, comprising:
 providing a casting liquid in which a liquid medium comprising a protic solvent is mixed with a polymer mixture of:   (a) 50.000 to 99.999% by weight, based on the total weight of components (a) and (b), of a fluorinated polymer electrolyte having an ion exchange group, and   (b) 0.001 to 50.000% by weight, based on the total weight of components (a) and (b), of a basic polymer which can form an acid-base ion complex,   casting said casting liquid onto a substrate to thereby form a liquid coating on said substrate, and   removing said liquid medium from said liquid coating to thereby form a solid polymer electrolyte membrane.   
     
     
         21 . The method according to  claim 20 , which further comprises subjecting the formed polymer electrolyte membrane to heat treatment. 
     
     
         22 . The method according to  claim 20 , wherein said liquid medium further comprises an aprotic solvent, and the amount of said protic solvent is 0.5 to 99.5% by weight, and the amount of said aprotic solvent is 99.5 to 0.5% by weight, each based on the total weight of said protic solvent and said aprotic solvent. 
     
     
         23 . The method according to  claim 20 , wherein said protic solvent is water.