Polymer membrane, method for the production and use thereof

Abstract

The present invention relates to an acid-doped polymer membrane based on polyazoles. The acid-doped polymer membrane can be used in a variety of applications because of its excellent mechanical properties and is useful as polymer electrolyte membrane (PEM) in PEM fuel cells. A doped polymer membrane based on polyazoles is obtained by a process comprising the steps of: A) casting a film using a solution of polymers based on polyazoles in a polar, aprotic organic solvent; B) drying the film formed in step A) until it is self-supporting; C) treating the film obtained in step B) with a treatment liquid at a temperature in the range from room temperature to the boiling point of the treatment liquid; D) drying and/or dabbing the film treated according to step C) to remove the treatment liquid from step C); and E) doping the film treated according to step D) with a doping agent.

1 . A doped polymer-membrane based on polyazoles, obtained by a process comprising the steps
 A) casting a film using a solution of polymers based on polyazoles in a polar, aprotic organic solvent,   B) drying the film formed in step A) until it is self-supporting to form a dried film, said dried film having a residual content of said polar, aprotic organic solvent in a range of 10 to 23%,   C) treating the film obtained in step B) with a treatment liquid at a temperature in the range from 20° C. to the boiling point of the treatment liquid,   D) drying and/or dabbing the film treated according to step C) to remove the treatment liquid from step C),   E) doping the film treated according to step D) with a doping agent, where said doping agent is selected from the group consisting of: Lewis acids and BrØnsted acids, and where doping is of a degree from 3 to 15 mol of acid per mol of recurring unit of polymer.   
   
   
       2 . A polymer membrane as claimed in  claim 1  having a degree of doping from 6 to 12 mols of acid per mol of recurring units of said polymer. 
   
   
       3 . A polymer membrane as claimed in  claim 1 , wherein the polymer based on polyazoles comprises recurring azole units of the formula (I) and/or (II) 
     
       
         
         
             
             
         
       
     
     where
 Ar are identical or different and are each a tetravalent aromatic or heteroaromatic group which may have one or more rings, 
 Ar 1  are identical or different and are each a divalent aromatic or heteroaromatic group which may have one or more rings, 
 Ar 2  are identical or different and are each a trivalent aromatic or heteroaromatic group which may have one or more rings, 
 X are identical or different and are each oxygen, sulfur or an amino group which bears a hydrogen atom and a group having 1-20 carbon atoms, preferably a branched or unbranched alkyl or alkoxy group, or an aryl group as other radical. 
 
   
   
       4 . A polymer membrane as claimed in  claim 3 , wherein the polymer comprising recurring azole units is a copolymer comprising at least two units of the formula (I) and/or (II) which differ from one another. 
   
   
       5 . A polymer membrane as claimed in  claim 4 , wherein the polyazole consists only of units of the formula (I) and/or (II). 
   
   
       6 . A polymer membrane as claimed in  claim 1 , wherein the polyazole is a polymer comprising recurring benzimidazole units of the formula (III) 
     
       
         
         
             
             
         
       
     
     where n is an integer greater than or equal to 10, preferably greater than or equal to 100. 
   
   
       7 . A polymer membrane as claimed in  claim 1 , wherein doping is performed for 1 to 96 hours at a temperature ranging from 20° C. to 100° C. 
   
   
       8 . A membrane-electrode unit comprising at least one polymer membrane as claimed in  claim 1  and at least one electrode. 
   
   
       9 . A polymer electrolyte fuel cell comprising at least one membrane-electrode unit as claimed in  claim 8 . 
   
   
       10 . A polymer membrane as claimed in  claim 1  where said doping agent is selected from the group consisting of: inorganic Lewis acids and inorganic BrØnsted acids. 
   
   
       11 . A polymer membrane as claimed in  claim 7  where said doping agent is selected from the group consisting of: sulfuric acid and phosphoric acid. 
   
   
       12 . A polymer membrane as claimed in  claim 7  where said doping agent phosphoric acid. 
   
   
       13 . A polymer membrane as claimed in  claim 12  where said phosphoric acid has a concentration of 85%. 
   
   
       14 . A doped polymer membrane based on polyazoles, obtained by a process comprising the steps
 A) casting a film using a solution of polymers based on polyazoles in a polar, aprotic organic solvent,   B) drying the film formed in step A) until it is self-supporting to form a dried film, said dried film having a residual content of said polar, aprotic organic solvent in a range of 10 to 23%,   C) treating the film obtained in step B) with a treatment liquid at a temperature in the range from 20° C. to the boiling point of the treatment liquid, where said treatment liquid is selected from the group consisting of: water, acetone and methanol,   D) drying and/or dabbing the film treated according to step C) to remove the treatment liquid from step C),   E) doping the film treated according to step D) with a doping agent, where said doping agent is selected from the group consisting of: sulfuric acid and phosphoric acid,   
     where said doping is performed for 1 to 96 hours at a temperature ranging from 20° C. to 100° C. and said doping agent has a concentration of 85%, and 
     where doping is of a degree from 3 to 15 mol of acid per mol of recurring unit of polymer.