Proton-conducting membrane, method for their production and their use in electrochemical cells

Abstract

The present invention relates to a novel proton-conducting polymer membrane based on polyazole polymers which, owing to their outstanding chemical and thermal properties, can be used widely and are suitable in particular as polymer electrolyte membrane (PEM) for producing membrane electrode assemblies or so-called PEM fuel cells.

1 . A proton-conducting polymer membrane based on polyazoles, obtainable by a process comprising the steps of
 A) mixing:
 (i) one or more aromatic tetramino compounds and 
 (ii) one or more aromatic carboxylic acids or esters thereof which contain at least two acid groups per carboxylic acid monomer, 
 or 
 (iii) one or more aromatic and/or heteroaromatic diaminocarboxylic acids, in polyphosphoric acid to form a solution and/or dispersion 
   B) heating the mixture from step A), and polymerizing until an intrinsic viscosity of at least 0.8 dl/g, is obtained for the polymer being formed,   C) applying a membrane using the mixture according to step B) on a carrier or on an electrode,   D) optionally heating the membrane on the carrier or electrode obtained from step C),   E) treating the membrane formed in step C) or D) in the presence of water and/or moisture,   F) removal of the membrane from the carrier,   characterized in that the total content of all polyazole polymers in the membrane is at least 5% by weight and up to about 25% by weight and said total content includes any acids, and water being present, said total content excluding however any optional additives.   
     
     
         2 . The membrane as claimed in  claim 1 , wherein the aromatic and heteroaromatic tetramino compounds are 2,3,5,6-tetraminopyridine, 3,3′,4,4′-tetraminodiphenylsulfone, 3,3′,4,4′-tetraminodiphenyl ether, 3,3′,4,4′-tetraminobiphenyl, 1,2,4,5-tetraminobenzene, 3,3′,4,4′-tetraminobenzophenone, 3,3′,4,4′-tetraminodiphenylmethane and 3,3′,4,4′-tetraminodiphenyldimethyl-methane and the salts of the aforementioned compounds. 
     
     
         3 . The membrane as claimed in  claim 1 , wherein the aromatic carboxylic acids are dicarboxylic acids, either alone or in combination with tricarboxylic acids and/or tetracarboxylic acids, the esters of the aforementioned dicarboxylic acids, tricarboxylic acids or tetracarboxylic acids, or the anhydrides of the aforementioned dicarboxylic acids, tricarboxylic acids or tetracarboxylic acids, or the acid chlorides of the aforementioned dicarboxylic acids, tricarboxylic acids or tetracarboxylic acids. 
     
     
         4 . The membrane as claimed in  claim 1 , wherein the aromatic carboxylic acids are dicarboxylic acids. 
     
     
         5 . The membrane as claimed in  claim 1 , wherein the diaminocarboxylic acids are diaminobenzoic acid and the mono and dihydrochloride derivatives of said acid, and 1,2-diamino-3′-carboxy acid 4,4′-diphenyl ether. 
     
     
         6 . The membrane as claimed in  claim 1 , characterized in that the aromatic tricarboxylic acid is 1,3,5-benzenetricarboxylic acid (trimesic acid), 1,2,4-benzenetricarboxylic acid (trimellitic acid); (2-carboxyphenyl)iminodiacetic acid, 3,5,3′-biphenyltricarboxylic acid, and/or 3,5,4′-biphenyltricarboxylic acid. 
     
     
         7 . The membrane as claimed in  claim 1 , characterized in that the aromatic tetracarboxylic acids is 3,5,3′,5′-biphenyltetracarboxylic acid, benzene-1,2,4,5-tetracarboxylic acid, benzophenonetetracarboxylic acid, 3,3′,4,4′-biphenyltetracarboxylic acid, 2,2′,3,3′-biphenyltetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid and/or 1,4,5,8-naphthalenetetracarboxylic acid. 
     
     
         8 . The membrane as claimed in  claim 1 , wherein the aromatic carboxylic acids include heteroaromatic carboxylic acids, or the acid anhydrides of said heteroaromatic acids, or the acid chlorides of said heteroaromatic acids. 
     
     
         9 . The membrane as claimed in  claim 8 , characterized in that the heteroaromatic carboxylic acids are aromatic systems which contain at least one nitrogen, oxygen, sulfur or phosphorus atom in the aromatic moiety. 
     
     
         10 . The membrane as claimed in  claim 9 , characterized in that the heteroaromatic carboxylic acids are pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3,5-pyrazoledicarboxylic acid, 2,6-pyrimidinedicarboxylic acid, 2,5-pyrazinedicarboxylic acid, 2,4,6-pyridinetricarboxylic acid, benzimidazole-5,6-dicarboxylic acid, and also their C1-C20-alkyl esters or their C5-C12-aryl esters, or their acid anhydrides or their acid chlorides. 
     
     
         11 . The membrane as claimed in  claim 1 , characterized in that the content of tricarboxylic acid or tetracarboxylic acids (based on dicarboxylic acid used) is between 0.1 and 30 mol %. 
     
     
         12 . The membrane as claimed in  claim 1 , characterized in that the polyphosphoric acid are concentrated grades of phosphoric acid (H 3 PO 4 ) above 95% in which the individual PO 4  units are polymerized and the polyphosphoric acids can be expressed by the formula H n+2 P n O 3n+1  (n>1). 
     
     
         13 . The membrane as claimed in  claim 12 , wherein the polyphosphoric acid [H n+2 P n O 3n+1  (n>1)] have a content, calculated as P 2 O 5  (by acidimetry), of at least 70% by weight. 
     
     
         14 . The membrane as claimed in  claim 13 , characterized in that the polyphosphoric acid [H n+2 P n O 3n+1  (n>1)] have a content of not more than 86% by weight, calculated as P 2 O 5  (by acidimetry).1 
     
     
         15 . The membrane as claimed in  claim 1 , wherein the total content of monomers in step A) is at least 5% by weight and up to about 25% by weight, of the total mixture including the polyphosphoric acid. 
     
     
         16 . The membrane as claimed in  claim 1 , wherein the polymers based on polyazole being formed in step B) comprise repeat units of the general formula (I) and/or (II) and/or (III) and/or (IV) and/or (V) and/or (VI) and/or (VII) and/or (VIII) and/or (IX) and/or (X) and/or (XI) and/or (XII) and/or (XIII) and/or (XIV) and/or (XV) and/or (XVI) and/or (XVII) and/or (XVIII) and/or (XIX) and/or (XX) and/or (XXI) and/or (XXII) 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         in which
 Ar are the same or different and are each a tetravalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
 
         Ar 1  are the same or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 2  are the same or different and are each a di- or trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 3  are the same or different and are each a trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 4  are the same or different and are each a trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 5  are the same or different and are each a tetravalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 6  are the same or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 7  are the same or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 8  are the same or different and are each a trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 9  are the same or different and are each a di- or tri- or tetravalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 10  are the same or different and are each a di- or trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         Ar 11  are the same or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polycyclic, 
         X are the same or different and are each oxygen, sulfur or an amino group which bears a hydrogen atom, a group having 1-20 carbon atoms, 
         R is the same or different and is hydrogen, an alkyl group or an aromatic group, with the proviso that R in formula (XX) is not hydrogen, and 
         n, m are each an integer greater than or equal to 10. 
       
     
     
         17 . The membrane as claimed in  claim 1 , wherein the polymers based on polyazole being formed in step B) comprise repeat benzimidazole units of the formula 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         where n and m are each an integer greater than or equal to 10. 
       
     
     
         18 . The membrane as claimed in  claim 1 , characterized in that the polyazole polymer being formed in step B) is meta-polybenzimidazole and/or para-polybenzimidazole. 
     
     
         19 . The membrane as claimed in  claim 1 , characterized in that the membrane obtained in step C) or D) is treated in the presence of moisture at temperatures and for a period until the membrane is self-supporting and can be removed from the carrier without damage. 
     
     
         20 . The membrane as claimed in  claim 1 , wherein the treatment in step E) is performed at temperatures above 0° C. and 150° C., in the presence of moisture or water or liquids containing water and/or steam. 
     
     
         21 . The membrane as claimed in  claim 1 , wherein the treatment of the membrane in step E) is between 10 seconds and 300 hours. 
     
     
         22 . The membrane as claimed in  claim 1 , characterized in that the carrier selected in step C) is an electrode and the treatment in step E) is such that the membrane formed is no longer self-supporting. 
     
     
         23 . The membrane as claimed in  claim 1 , wherein a membrane having a thickness of 20 and 4000 μm, is obtained in step C). 
     
     
         24 . The membrane as claimed in  claim 1 , wherein the membrane formed by step E) has a thickness between 15 and 3000 μm. 
     
     
         25 . The membrane as claimed in  claim 1 , wherein the total solid content of the polyazole polymer in the membrane is at least 8% by weight and up to about 25% by weight, of the total weight of the membrane including acids and water and excluding any other optionally additives. 
     
     
         26 . The membrane as claimed in  claim 1 , wherein the membranes have a Young's modulus of at least 2.0 Mpa. 
     
     
         27 . An electrode which having a proton-conducting polymer coating based on polyazoles, obtainable by a process comprising the steps of
 A) mixing:
 (i) one or more aromatic tetramino compounds and 
 (ii) one or more aromatic carboxylic acids or esters thereof which contain at least two acid groups per carboxylic acid monomer, 
 or 
 (iii) one or more aromatic and/or heteroaromatic diaminocarboxylic acids, in polyphosphoric acid to form a solution and/or dispersion 
   B) heating the mixture from step A), and polymerizing until an intrinsic viscosity of at least 0.8 dl/g, is obtained for the polymer being formed,   C) applying a layer using the mixture according to step B) on an electrode,   D) optionally heating the layer on the electrode obtained from step C),   E) treating the membrane formed in step C) or D) in the presence of water and/or moisture,   wherein the total content of all polyazole polymers in the membrane is at least 5% by weight and up to about 25% by weight and said total content includes any acids, and water being present, said total content excluding however any optional additives.   
     
     
         28 . The electrode as claimed in  claim 27 , the membrane after Step E) having a thickness between 2 and 3000 μm. 
     
     
         29 . A membrane-electrode unit comprising at least two electrodes and at least one membrane as claimed in  claim 1 . 
     
     
         30 . A membrane-electrode unit comprising at least one electrode as claimed in  claim 27 . 
     
     
         31 . A fuel cell comprising one or more membrane-electrode units as claimed in  claim 29 .