High-performance membrane electrode unit and the use thereof in fuel cells

Abstract

The present invention relates to a membrane electrode unit comprising a polymer membrane doped with a mineral acid as well as two electrodes, characterized in that the polymer membrane comprises at least one polymer with at least one nitrogen atom and at least one electrode comprises a catalyst which is formed from at least one precious metal and at least one metal less precious according to the electrochemical series.

1 - 31 . (canceled) 
     
     
         32 . A membrane electrode unit consisting essentially of
 A) at least one polymer membrane which consists essentially of at least one alkaline polyazole polymer with at least one nitrogen atom, the polymer membrane including at least one mineral acid which is phosphoric acid,   B) at least two electrodes one which is a cathode and one is an anode, wherein   i) the cathode side consists of a Pt/Ni catalyst the Pt/Ni catalyst being on a carbon support and   ii) the catalyst on the anode side consists of a Pt catalyst on a carbon support,   iii) the alkaline polyazole polymer is a polybenzimidazole,   iv) said catalyst on the anode side is loaded with 0.3 to 3 g/m 2  Pt based on the surface area of the polymer membrane,   v) said polymer membrane has proton conductivity of at least 0.1S/cm @ 120° C. and   vi) the membrane electrode unit providing for a current density of at least 0.3 A/cm 3 (cell voltage of 0.6) when air is used on the cathode side.   
     
     
         33 . The membrane electrode unit according to  claim 32 , wherein a mixture of one or more polybenzimidazole polymers with another polymer is employed. 
     
     
         34 . The membrane electrode unit according to  claim 32 , wherein the polymer membrane comprises para-polybenzimidazoles. 
     
     
         35 . The membrane electrode unit according to  claim 32 , wherein the polymer membrane can be obtained by a process comprising the steps of
 i) preparing a mixture comprising   polyphosphoric acid,   at least one polybenzimidazole polymer and/or at least one or more compounds which are suitable for the formation of the alkaline polyazole polymer with action of heat in accordance with step ii),   ii) heating the mixture obtainable in accordance with step i) under inert gas to temperatures of up to 400° C.,   iii) applying a layer using the mixture in accordance with step i) and/or ii) to a carbon support, and   iv) treating the membrane formed in step iii).   
     
     
         36 . The membrane electrode unit according to  claim 35 , wherein the mixture produced in step i) comprises one or more aromatic and/or heteroaromatic tetraamino compounds and one or more aromatic and/or heteroaromatic carboxylic acids or their derivatives, which comprise at least two acid groups per carboxylic acid monomer, and/or one or more aromatic and/or heteroaromatic diaminocarboxylic acids which are suitable for the formation of the alkaline polyazole polymer with action of heat in accordance with step ii). 
     
     
         37 . The membrane electrode unit according to  claim 35 , wherein the mixture produced in step i) comprises compounds which are obtainable by reaction of one or more aromatic and/or heteroaromatic tetraamino compounds with one or more aromatic and/or heteroaromatic carboxylic acids or their derivatives, which contain at least two acid groups per carboxylic acid monomer, or of one or more aromatic and/or heteroaromatic diaminocarboxylic acids in the melt at temperatures of up to 400° C., which are suitable for the formation of the alkaline polyazole polymer with action of heat in accordance with step ii). 
     
     
         38 . The membrane electrode unit according to  claim 36 , wherein the compounds suitable for the formation of the alkaline polyazole polymer as aromatic and/or heteroaromatic tetraamino compound comprise compounds which are selected from the group consisting of 3,3′,4,4′-tetraaminobiphenyl, 2,3,5,6-tetraaminopyridine and/or 1,2,4,5-tetraaminobenzene. 
     
     
         39 . The membrane electrode unit according to  claim 36 , wherein the compounds suitable for the formation of the alkaline polyazole polymer as aromatic and/or heteroaromatic carboxylic acids or their derivatives, which contain at least two acid groups per carboxylic acid monomer, comprise compounds which are selected from the group consisting of isophthalic acid, terephthalic acid, phthalic acid, 5-hydroxyisophthalic acid, 4-hydroxyisophthalic acid, 2-hydroxyterephthalic acid, 5-aminoisophthalic acid, 5-N,N-dimethylaminoisophthalic acid, 5-N,N-diethylaminoisophthalic acid, 2,5-dihydroxyterephthalic acid, 2,5-dihydroxyisophthalic acid, 2,3-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid, 2,4-dihydroxyphthalic acid, 3,4-dihydroxyphthalic acid, 3-fluorophthalic acid, 5-fluoroisophthalic acid, 2-fluoroterephthalic acid, tetrafluorophthalic acid, tetrafluoroisophthalic acid, tetrafluoroterephthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, diphenic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid, diphenyl ether-4,4′-dicarboxylic acid, benzophenone-4,4′-dicarboxylic acid, diphenylsulphone-4,4′-dicarboxylic acid, biphenyl-4,4′-dicarboxylic acid, 4-trifluoromethylphthalic acid, 2,2-bis-(4-carboxyphenyl)hexafluoropropane, 4,4′-stilbenedicarboxylic acid, 4-carboxycinnamic acid or their C1-C20 alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid chlorides. 
     
     
         40 . The membrane electrode unit according to  claim 36 , wherein the compounds suitable for the formation of the alkaline polyazole polymer comprise aromatic tricarboxylic acids, their C1-C20 alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid halides, or tetracarboxylic acids, their C1-C20 alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid halides. 
     
     
         41 . The membrane electrode unit according to  claim 40 , wherein the aromatic tricarboxylic acids comprise compounds of 1,3,5-benzenetricarboxylic acid (trimesic acid); 2,4,5-benzenetricarboxylic acid (trimellitic acid); (2-carboxyphenyl)iminodiacetic acid, 3,5,3′-biphenyltricarboxylic acid; 3,5,4′-biphenyltricarboxylic acid; 2,4,6-pyridinetricarboxylic acid, benzene-1,2,4,5-tetracarboxylic acids; naphthalene-1,4,5,8-tetracarboxylic acids, 3,5,3′,5′-biphenyltetracarboxylic acids, 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. 
     
     
         42 . The membrane electrode unit according to  claim 40 , wherein the content of tricarboxylic acid and/or tetracarboxylic acids is between 0 and 300 mol-%, based on dicarboxylic acid used. 
     
     
         43 . The membrane electrode unit according to  claim 36 , wherein the compounds suitable for the formation of the alkaline polyazole polymer comprise heteroaromatic dicarboxylic acids, tricarboxylic acids and/or tetracarboxylic acids, which contain at least one nitrogen, or oxygen, atom in the aromatic group. 
     
     
         44 . The membrane electrode unit according to  claim 43 , wherein 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 their C1-C20 alkyl esters or C5-C12 aryl esters or their acid anhydrides or their acid chlorides are employed. 
     
     
         45 . The membrane electrode unit according to  claim 36 , wherein the compounds suitable for the formation of the alkaline polyazole polymer comprise diaminobenzoic acid and/or its monohydrochloride and dihydrochloride derivatives. 
     
     
         46 . The membrane electrode unit according to  claim 36 , wherein at least one para-dicarboxylic acid is employed. 
     
     
         47 . The membrane electrode unit according to  claim 36 , wherein the heating in accordance with step ii) is performed after the formation of a flat structure in accordance with step iii). 
     
     
         48 . The membrane electrode unit according to  claim 32 , wherein the catalyst is applied to the polymer membrane. 
     
     
         49 . The membrane electrode unit according to  claim 32 , wherein the catalyst layer has a thickness in the range of from 0.1 to 50 μm. 
     
     
         50 . The membrane electrode unit according to  claim 32 , wherein the catalyst comprises catalytically active particles on a carbon support, the size of the catalyst particles being in the range of from 1 to 20 nm. 
     
     
         51 . A fuel cell containing one or more membrane electrode units according to  claim 32 . 
     
     
         52 . The membrane electrode unit according to  claim 40 , wherein the content of tricarboxylic acid and/or tetracarboxylic acids is between 0.5 and 10 mol-%, based on dicarboxylic acid used. 
     
     
         53 . The membrane electrode unit according to  claim 32 , wherein the ratio of Pt to Ni is 1:100 to 100:1. 
     
     
         54 . The membrane electrode unit according to  claim 32 , wherein said polymer membrane has proton conductivity of at least 0.12 S/cm @ 120° C. 
     
     
         55 . The membrane electrode unit according to  claim 32 , wherein the catalyst is on a carbon black support, graphite support or graphitized carbon black support. 
     
     
         56 . The membrane electrode unit according to  claim 32 , wherein the ratio of Pt to Ni is 1:100 to 100:1. 
     
     
         57 . The membrane electrode unit according to  claim 32 , wherein the ratio of Pt to Ni is 1:1. 
     
     
         58 . The membrane electrode unit according to  claim 32 , wherein the Pt/Ni is on the carbon catalyst and the Pt/Ni has a particle size of 1 to 20 nm and the carbon particles have a particle size of 20 to 100 nm. 
     
     
         59 . The membrane electrode unit according to  claim 32 , wherein the Pt/Ni is on the carbon catalyst and the Pt/Ni has a particle size of 2 to 6 nm and the carbon particles have a particle size of 30 to 60 nm. 
     
     
         60 . The membrane electrode unit according to  claim 32 , wherein the alkaline polymer is a polybenzimidazole. 
     
     
         61 . The membrane electrode unit according to  claim 32 , wherein the polymer membrane has a thickness from 20 to 1500 m and the membrane is doped with phosphoric acid and the degree of doping expressed as mole per acid per repeat unit is from 15 to 80. 
     
     
         62 . The membrane electrode unit according to  claim 32 , wherein hydrogen gas is fed on the anode side. 
     
     
         63 . The membrane electrode unit according to  claim 32 , wherein the membrane electrode unit providing for a current density of at least 0.4 A/cm 3  (cell voltage of 0.6) when air is used on the cathode side.