Polymer electrolyte membrane, membrane electrode assembly, water electrolyzer, and method for producing polymer electrolyte membrane

Abstract

To provide a polymer electrolyte membrane which is excellent in the strength and the surface property, and which can achieve a low membrane resistance when applied to a water electrolyzer, a membrane electrode assembly, a water electrolyzer, and a method for producing the polymer electrolyte membrane. A polymer electrolyte membrane comprising a fluorinated polymer having ion exchange groups and a nonwoven fabric, wherein the nonwoven fabric contains polyphenylene sulfide fibers; in a fiber diameter distribution histogram of fibers constituting the nonwoven fabric, the maximum frequency peak appears in a range of 100 to 900 nm; and the polymer electrolyte membrane has a thickness of 30 to 90 μm.

What is claimed is: 
     
         1 . A polymer electrolyte membrane comprising a fluorinated polymer having ion exchange groups and a nonwoven fabric, wherein
 the nonwoven fabric contains polyphenylene sulfide fibers,   in a fiber diameter distribution histogram of fibers constituting the nonwoven fabric, the maximum frequency peak appears in a range of 100 to 900 nm, and   the polymer electrolyte membrane has a thickness of 30 to 90 μm.   
     
     
         2 . The polymer electrolyte membrane according to  claim 1 , wherein the ion exchange groups of the fluorinated polymer are sulfonic acid functional groups. 
     
     
         3 . The polymer electrolyte membrane according to  claim 1 , wherein the fluorinated polymer comprises at least one type selected from the group consisting of units represented by the formula (1-1), units represented by the formula (1-2), units represented by the formula (1-3) and units represented by the formula (1-4): 
       
         
           
           
               
               
           
         
         wherein R f1  is a perfluoroalkylene group which may have an oxygen atom between carbon atoms; R f2  is a single bond or a perfluoroalkylene group which may have an oxygen atom between carbon atoms; R f3  is a single bond or a perfluoroalkylene group which may have an oxygen atom between carbon atoms; r is 0 or 1; m is 0 or 1; and M is a hydrogen atom, an alkali metal or a quaternary ammonium cation. 
       
     
     
         4 . The polymer electrolyte membrane according to  claim 1 , which contains at least one element selected from the group consisting of platinum, palladium, cerium and manganese. 
     
     
         5 . The polymer electrolyte membrane according to  claim 1 , wherein the content of the nonwoven fabric is 5 mass % or more and 40 mass % or less to the total mass of the polymer electrolyte membrane. 
     
     
         6 . The polymer electrolyte membrane according to  claim 1 , which is for water electrolysis. 
     
     
         7 . A membrane electrode assembly comprising:
 the polymer electrolyte membrane as defined in  claim 1 ;   a cathode catalyst layer provided on one surface of the polymer electrolyte membrane; and   an anode catalyst layer provided on the other surface of the polymer electrolyte membrane.   
     
     
         8 . A water electrolyzer comprising:
 the membrane electrode assembly as defined in claim  7 ;   a power supply unit connected to the cathode catalyst layer side and the anode catalyst layer side of the membrane electrode assembly; and   a water supply unit to supply water to the anode catalyst layer side.   
     
     
         9 . A method for producing the polymer electrolyte membrane as defined in  claim 1 , which comprises:
 step 1 of converting, in a precursor membrane containing the polymer having groups convertible to ion exchange groups and the nonwoven fabric, the groups convertible to ion exchange groups to ion exchange groups, and   step 2 of drying the membrane obtained in step 1 while its edges are kept fixed to obtain the polymer electrolyte membrane.   
     
     
         10 . The polymer electrolyte membrane production method according to  claim 9 , which further has, before step 1, step 3 of sandwiching the nonwoven fabric between a plurality of polymer membranes containing a polymer having groups convertible to ion exchange groups, to obtain the precursor membrane. 
     
     
         11 . The polymer electrolyte membrane production method according to  claim 10 , which further has, before step 3, step 4 of kneading a compound containing at least one element selected from the group consisting of platinum, palladium, cerium and manganese and the polymer having groups convertible to ion exchange groups, and extruding the kneaded product to obtain the precursor membrane.