Method for producing a membrane made of bridged polymer and a fuel cell
View Patent ↗Method for producing a membrane made of bridged polymer and a fuel cell. The present invention relates to a membrane comprising a bridged polymer which is produced by a selected process. The membrane of the invention displays a significantly improved fracture toughness (elongation at break/tensile strength) with virtually unchanged swelling behavior. The membranes of the invention are suitable for producing membrane-electrode units for fuel cells.
1. A membrane comprising a bridged polymer obtained by a process comprising the following steps:
A. preparing a solution comprising a basic polymer having at least one amino group in a repeating unit and at least one bridging reagent in a suitable solvent,
B. casting a film using the solution obtained from step A),
C. removing the solvent from step A),
D. carrying out a bridging reaction in the film obtained in step C),
E. doping the film obtained in step D) with a strong acid,
wherein a basic catalyst is additionally added in step A) and said basic catalyst is a basic oxide of elements of main groups I, II and III of the Periodic Table, a basic hydroxide of elements of main groups I, II and III of the Periodic Table, a hydride of elements of main group I of the Periodic Table or an organolithium compound.
2. A membrane as claimed in claim 1 , wherein the bridging reagent has at least two epoxide groups or isocyanate groups per molecule.
3. A membrane as claimed in claim 1 , wherein the bridging reagent is at least one compound of the formula (II) and/or (III)
where R 1 is a hydrocarbon group having from 1 to 30 carbon atoms.
4. A membrane as claimed in claim 3 , wherein R 1 is
where m, k and l are identical or different and are each an integer from 1 to 6.
5. A membrane as claimed in claim 1 , wherein the bridging reagent contains at least three epoxide groups per molecule.
6. A membrane as claimed in claim 5 , wherein the bridging reagent is the compound
7. A membrane as claimed in claim 1 , wherein the bridging reagent is bisphenol A glycidyl ether [BPAGDE] and/or 1,4-butanediol diglycidyl ether.
8. A membrane as claimed in claim 1 , wherein the solution obtained in step A) contains from 0.1 to 7 mol% of the bridging reagent per unit of the basic polymer.
9. A membrane as claimed in claim 1 , wherein the basic polymer used is polybenzimidazole, polyimidazole, polyvinylimidazole or polybenzobisimidazole.
10. A membrane as claimed in claim 9 , wherein the polybenzimidazole used is a polymer of the formula;
where R is alkylene, perfluoroalkylene or a substituent having one of the following formulae:
where each alkylene and perfluoroalkylene group R has from 1 to 10 carbon atoms.
11. A membrane as claimed in claim 10 , wherein R is an alkylene or perfluoroalkylene group that has from 1 to 6 carbon atoms.
12. A membrane as claimed in claim 9 , wherein the polybenzobisimidazole used is a polymer of the formula
where R is as defined in claim 10 .
13. A membrane as claimed in claim 1 , wherein bridging in step D) is effected by heating so that bridging (step D) and drying (step C) are carried out at the same time in one step.
14. A membrane as claimed in claim 1 , wherein drying of the film is carried out at a temperature below the reaction temperature of the bridging reagent and the film is subsequently heated further to effect bridging.
15. A membrane as claimed in claim 1 , wherein bridging in step D) is effected by irradiation with electromagnetic waves (photochemical reaction).
16. A membrane as claimed in claim 1 , wherein the strong acid used in step E) is phosphoric acid or sulfuric acid.
17. A membrane as claimed in claim 1 , wherein basic catalysts used are KOH, LiOH, NaOH, RbOH, CsOH, Ca(OH) 2 , Mg(OH) 2 , Ba(OH) 2 , LiH, NaH, KH, methyllithium and/or butyllithium.
18. A membrane as claimed in claim 1 , wherein the basic catalyst is added in amounts of from 0.01 to 5 mol %, based on the bridging reagent used, to the solution obtained in step A).
19. A membrane as claimed in claim 1 which has a fracture toughness which is more than 100% above that of a membrane containing no bridges.
20. A membrane as claimed in claim 1 which has an elongation at break of at least 60% and an ultimate tensile strength of at least 1.5 MPa.
21. A membrane-electrode unit comprising at least one electrode and at least one membrane as claimed in claim 1 .
22. A fuel cell comprising at least one membrane-electrode unit as claimed in claim 21 .