Proton-conducting membrane and use thereof

Abstract

A membrane obtainable by A) mixing: (vii) aromatic tetraamino compounds and (viii) aromatic carboxylic acids or esters thereof which contain at least two acid groups per carboxylic acid monomer, or (ix) 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) adding polyazole polymers, D) heating the mixture from step C), E) applying a membrane layer using the mixture according to step D) on a carrier or an electrode, F) treating the membrane formed in the presence of water and/or moisture, G) removing the membrane from the carrier;
wherein the content of all polyazole polymers in the membrane is between 5% to 25% by weight and wherein the membrane has a Young Modulus is at least 2.0 MPa.

Claims

1. A proton-conducting polymer membrane based on polyazoles, obtainable by a process comprising steps of A) providing a monomer solution and/or dispersion including (i) one or more aromatic tetraamino compounds and either (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 monomer solution and/or dispersion from step A), and polymerizing until a formed polyazole polymer having an intrinsic viscosity of at least 0.8 dl/g is obtained, C) adding of one or more polyazole polymer to the polyphosphoric acid and the formed polyazole polymer of step B), the added one or more polyazole polymer being different from the formed polyazole polymer of step B), D) heating the mixture from step C), E) applying a membrane layer using the mixture heated according to step D) on a carrier, G) treating the membrane layer formed in the presence of water and/or moisture to provide a membrane including at least a formed polyazole and an added polyazole being different from the formed polyazole, and H) removing the membrane from the carrier; wherein a total content of all polyazole polymers in the membrane is at least 10% 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 and wherein the membrane has a Young Modulus of at least 4.5 MPa, and wherein the monomers in the monomer solution and/or dispersion of step A accounts for less than 10% by weight of the total solid content of all polyazole polymers in the membrane.

2. The membrane as claimed in claim 1, wherein the aromatic and heteroaromatic tetraamino compounds are selected from 2,3,5,6-tetraaminopyridine, 3,3′,4,4′-tetraaminodiphenylsulfone, 3,3′,4,4′-tetraaminodiphenyl ether, 3,3′,4,4′-tetraaminobiphenyl, 1,2,4,5-tetraaminobenzene, 3,3′,4,4′-tetraaminobenzophenone, 3,3′,4,4′-tetraaminodiphenylmethane, 3,3′,4,4′-tetraaminodiphenyldimethyl-methane, or the salts of the aforementioned compounds.

3. The membrane as claimed in claim 1, wherein the diaminocarboxylic acids are selected from diaminobenzoic acid and the mono and dihydrochloride derivatives of said acid, or 1,2-diamino-3′-carboxy acid 4,4′-diphenyl ether.

4. The membrane as claimed in claim 1, wherein the one or more aromatic carboxylic acids or esters thereof includes an aromatic tricarboxylic acid selected from 1,3,5-benzenetricarboxylic acid (trimesic acid), 1,2,4-benzenetricarboxylic acid (trimellitic acid), (2-carboxyphenyl)iminodiacetic acid, 3,5,3′-biphenyltricarboxylic acid, 3,5,4′-biphenyltricarboxylic acid, or any one mixture thereof.

5. The membrane as claimed in claim 1, wherein the one or more, aromatic carboxylic acids or esters thereof includes an aromatic tetracarboxylic acid selected from 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, 1,4,5,8-naphthalenetetracarboxylic acid, or any one mixture thereof.

6. The membrane as claimed in claim 1, wherein the aromatic carboxylic acids include heteroaromatic carboxylic acids, including their respective esters, or the acid anhydrides of said heteroaromatic acids, or the acid chlorides of said heteroaromatic acids, wherein the heteroaromatic carboxylic acids include at least one nitrogen in the aromatic moiety.

7. The membrane as claimed in claim 6, wherein,the heteroaromatic carboxylic acids are selected from 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, each of their C1-C20-alkyl esters, their C5-C12-aryl esters, their acid anhydrides or their acid chlorides, or any one mixture thereof.

8. The membrane as claimed in claim 1, wherein the polyphosphoric acid are concentrated grades of phosphoric acid (H.sub.3PO.sub.4) above 95% in which the individual PO.sub.4 units are polymerized and the polyphosphoric acids can be expressed by the formula H.sub.n+2P.sub.nO.sub.3n+1(n>1).

9. The membrane as claimed in claim 8, wherein the polyphosphoric acid [H.sub.n+2P.sub.nO.sub.3n+1(n>1)] have a content, calculated as P.sub.2O.sub.5 (by acidimetry), of at least 70% by weight and not more than 86% by weight.

10. The membrane as claimed in claim 1, wherein the monomers in the monomer soltution and/or dispersion of step A accounts for less than 10% by weight, of the of the total content of all polyazole polymers in the membrane.

11. 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) ##STR00008## ##STR00009## ##STR00010## in which Ar are the same or different and are each a tetravalent aromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.1 are the same or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.2 are the same or different and are each a di- or trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.3 are the same or different and are each a trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.4 are the same or different and are each a trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.5 are the same or different and are each a tetravalent aromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.6 are the same or different and are each a divalentaromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.7 are the same or different and are each a divalent aromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.8 are the same or different and are each a trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.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.sup.10 are the same or different and are each a di- or trivalent aromatic or heteroaromatic group which may be mono- or polycyclic, Ar.sup.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, preferably a branched or unbranched alkyl or alkoxy group, or an aryl group as further radical, 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.

12. 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 ##STR00011## ##STR00012## where n and m are each an integer greater than or equal to 10.

13. 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.

14. 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.

15. 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.

16. The membrane as claimed in claim 1, wherein a membrane having a thickness of 20 and 4000 μm is obtained in step C).

17. The membrane as claimed in claim 1, wherein the membrane formed by step E) has a thickness between 15 and 3000 μm.

18. 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.

19. A membrane-electrode unit comprising at least two electrodes and at least one membrane as claimed in claim 1.

20. A fuel cell comprising one or more membrane-electrode units as claimed in claim 19.

21. The membrane as claimed in claim 1, wherein the aromatic and heteroaromatic tetraamino compounds of step A) are selected from 2,3,5,6-tetraaminopyridine, 3,3′,4,4′-tetraaminodiphenylsulfone, 3,3′,4,4′-tetraaminodiphenyl ether, 3,3′,4,4′-tetraaminobiphenyl, 1,2,4,5-tetraaminobenzene, 3,3′,4,4′-tetraaminobenzophenone, 3,3′,4,4′′-tetraaminodiphenylmethane or 3,3′,4,4′-tetraaminodiphenyldimethyl-methane or the salts of the aforementioned compounds, and the heteroaromatic carboxylic acids are selected from 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, or their C.sub.1-C.sub.20-alkyl esters or their C.sub.5-C.sub.12-aryl esters, or their acid anhydrides or their acid chlorides.

22. An electrode having a proton-conducting polymer membrane coating based on polyazoles, obtainable by a process comprising the steps of A) providing a monomer solution and/or dispersion including (i) one or more aromatic tetraamino compounds and either (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, B) heating the monomer solution and/or dispersion from step A), preferably under inert gas, and polymerizing until a formed polyazole polymer having an intrinsic viscosity of at least 0.8 dl/g is obtained, C) adding one or more polyazole polymer to the polyphosphoric acid and the polymer formed in step B, the added one or more polyazole polymer being different from the formed polyazole polymer of step B), D) heating the mixture from step C), E) applying a membrane layer using the mixture heated according to step D) on an electrode, F) optionally heating the membrane layer on the electrode obtained from step E), and G) treating the membrane layer formed in step E) or optionally step F) in the presence of water and/or moisture to provide on the electrode a membrane including at least a formed polyazole and an added polyazole being different from the formed polyazole, wherein a total solid content of all polyazole polymers in the membrane is at least 10% by weight and up to about 25% by weight and said total content includes any acids and water being present, said total content excluding any optional additives, and wherein the membrane has a Young Modulus of at least 4.5 MPa, and wherein the monomers in the monomer solution and/or dispersion of step A accounts for less than 10% by weight of the total solid content of all polyazole polymers in the membrane.

23. The electrode as claimed in claim 22, the membrane having a thickness between 2 and 3000 μm.

24. A membrane-electrode unit comprising at least one electrode as claimed in claim 22.

Description

EXAMPLES

Example 1

(1) 95 g para-PBI/PPA solution (BASF Fuel cell, 1.6 wt % of para-PBI) was pre-heated at 160° C. under dry nitrogen. 5 g meta-PBI powder (IV=0.5 dL/g measured a 0.2 g/dL in concentrated sulfuric acid, 100 mesh) was added to the above pre-heated para-PBI/PPA solution and mixed with overhead stirrer at 50 rpm for 4 hours. 5 ml of 85% phosphoric acid was added dropwise to reduce the solution viscosity. Slight vacuum was applied to remove the bubbles from the system. The temperature was increased to 200° C. for 30 minutes, and then was cast using a 25 mil gap casting blade onto clear glass plates. The cast membrane was hydrolyzed at 25° C., 55% relative humidity (RH) for 24 hours.

Example 2

(2) 3.214 g tetraaminobiphenyl (TAB, 15 mmol) and 2.492 g terephthalic acid (TPA, 15 mmol) was added to 137 g polyphosphoric acid [PPA concentration 116%], mixed with overhead stirrer, purged with dry nitrogen. The mixture was heated at 150° C. for 3 hours, 170° C. for 3 hours, and then 195° C. for 12 hours.

(3) 5 ml of 85% phosphoric acid was added dropwise to reduce the solution viscosity. Temperature increased to 220° C. for half an hour before the casting.

(4) The polymer solution (having a total solids content of FBI of 3.26 wt %) was casted onto clear glass plates. The cast membrane was hydrolyzed in 65% phosphoric acid bath for 24 hours. This example corresponds to the membranes known from International patent application WO 02/081547.

(5) The mechanical properties of the membranes were measured by cutting dumb bell specimens (ASTM D683 Type V) from the bulk membrane using a cutting press. Tensile properties were measured using an Instron Tensile Tester (5543A) with a 10N load cell. All measurements were made at room temperature on samples preloaded to 0.1N with a crosshead speed of 5 mm per minute.

(6) TABLE-US-00001 Strain at Thickness Max. Load Young's Modulus Modulus sample (mm) (mm/mm) (MPa) (MPa) Example 1 0.43 2.334 4.904 1.562 Example 2 0.36 4.908 1.863 0.865

(7) The higher modulus means that higher resistance to flow/creep of the membranes is obtained.

(8) Examples of polymer addition process:

Example 3

(9) 95 g para-PBI/PPA solution (1.6 wt % of para-PBI solids) was pre-heated at 160° C. under dry nitrogen. 5 g meta-PBI powder (IV=0.5 dL/g measured at 0.2 g/dL in concentrated sulfuric acid, 100 mesh) was added to the above pre-heated para-PBI/PPA solution and mixed with overhead stirrer at 50 rpm for 4 hours. 5 ml of 85% phosphoric acid was added dropwise to reduce the solution viscosity. Slight vacuum was applied to remove the bubbles from the system. The temperature was increased to 200° C. for 30 minutes, and then was cast using a 25 mil gap casting blade onto clear glass plates. The cast solution was hydrolyzed at 25° C., 55% relative humidity (RH) for 24 hours to produce a membrane with the properties listed below.

Example 4

(10) 95 g para-PBI/PPA solution (1.6 wt % of para-PBI solids) was pre-heated at 160° C. under dry nitrogen. 5 g meta-PBI powder (IV=0.5 dL/g measured at 0.2 g/dL in concentrated sulfuric acid, 100 mesh) was mixed with 15 g polyphosphoric acid, then added to the above para-PBI/PPA solution, and mixed with an overhead stirrer at 50 rpm for 4 hours. Slight vacuum was applied to remove the bubbles from the system. The temperature was increased to 200° C. for 30 minutes before casting. The polymer solution was cast onto clear glass plates and hydrolyzed at 25° C., 55% RH for 24 hours to produce a membrane with the properties listed below.

Example 5

(11) 95 g para-PBI/PPA solution (1.6 wt % of para-PBI solids) was pre-heated at 160° C. under dry nitrogen. 5 g para-PBI powder (IV=2.3 dL/g measured at 0.2 g/dL in concentrated sulfuric acid, 100 mesh) was added to the above para-PBI/PPA solution and mixed with an overhead stirrer at 50 rpm for 4 hours. 5 ml of 85% phosphoric acid was added dropwise to reduce the solution viscosity. Slight vacuum was applied to remove the bubbles from the system. The temperature was increased to 200° C. for 30 minutes before casting. The polymer solution was cast onto clear glass plates and hydrolyzed at 25° C., 55% RH for 24 hours to produce a membrane with the properties listed below.

(12) TABLE-US-00002 Polymer Proton Tensile Strain at Young's content Conductivity Strength Max. Load Modulus sample (%) (S/cm) (MPa) (mm/mm) (MPa) Example 3 13.3 0.272 1.51 2.33 4.90 Example 4 9.7 0.275 1.36 3.08 2.72 Example 5 13.1 0.270 1.30 1.73 1.84