Membrane-electrode assembly, polymer membranes for a membrane-electrode assembly, polymer electrolyte fuel cells, and methods for the production thereof
A membrane-electrode assembly and polymer electrolyte fuel cells and methods of production thereof, in which a polymer membrane, containing at least one basic polymer membrane, is sandwiched between two flat gas diffusion electrodes each of which is loaded with a dopant, whereby after reaching a mass transport equilibrium for the exchange of the dopant between the gas diffusion electrodes and the polymer membrane, the polymer membrane has a conductivity of at least 0.1 S/m at a temperature of no less than 25° C.
1. A membrane-electrode assembly comprising
two flat gas diffusion electrodes each loaded with a dopant, and
a polymer membrane comprising at least one basic polymer, the polymer membrane sandwiched between said electrodes,
wherein the gas diffusion electrodes are loaded with a content of dopant of 60 to 120% of the weight of the basic polymer in the polymer membrane, and wherein after reaching a mass transport equilibrium for the exchange of the dopant between the gas diffusion electrodes and the polymer membrane, the polymer membrane has a conductivity of at least 0.1 S/m at a temperature of no less than 25° C.
2. The membrane-electrode assembly as claimed in claim 1 , wherein at least one basic polymer is selected from the group consisting of polybenzimidazoles, polypyridines, polypyrimidines, polyimidazoles, polybenzthiazoles, polybenzoxazoles, polyoxadizoles, polyquinoxalines, polythiadiazoles, poly(tetraazapyrenes) and a copolymer.
3. The membrane-electrode assembly as claimed in claim 2 , wherein at least one basic polymer is polybenzimidazole.
4. The membrane-electrode assembly as claimed in claim 1 , wherein the polymer membrane is a dry undoped polymer membrane produced by industrial machine drawing.
5. The membrane-electrode assembly as claimed in claim 4 , wherein the polymer membrane is crosslinked by reaction with polyfunctional crosslinking agents.
6. The membrane-electrode assembly as claimed in claim 5 , wherein the crosslinking agent comprises one or more of epoxy groups and isocyanate groups.
7. The membrane-electrode assembly as claimed in claim 1 , wherein the polymer membrane is a plasticized polymer membrane comprising no more than 40 wt % plasticizer.
8. The membrane-electrode assembly as claimed in claim 7 , wherein the plasticizer is a reaction product of at least a dibasic acid and an organic compound.
9. The membrane-electrode assembly as claimed in claim 7 , wherein the organic compound is phosphoric acid diester.
10. The membrane-electrode assembly as claimed in claim 8 , wherein the organic compound is phosphoric acid diester.
11. The membrane-electrode assembly as claimed in claim 8 , wherein the phosphoric acid diester is one or more of di-(2-ethylhexyl)phosphoric acid ester and diphenyl phosphoric acid ester.
12. The membrane-electrode assembly as claimed in claim 1 , wherein the dopant content in the gas diffusion electrodes is 60% to 120% of the weight of the basic polymer in the polymer membrane.
13. The membrane-electrode assembly as claimed in claim 12 , wherein the dopant is a polybasic inorganic acid.
14. The membrane-electrode assembly as claimed in claim 13 , wherein the acid is phosphoric acid.
15. The membrane-electrode assembly as claimed in claim 1 , wherein at least one basic polymer of the polymer membrane comprises a stress at failure of more than 110 N/mm 2 at room temperature and an elongation of more than 6%.
16. The membrane-electrode assembly as claimed in claim 15 , wherein the polymer membrane is crosslinked with a bifunctional crosslinking agent.
17. The membrane-electrode assembly as claimed in claim 16 , wherein the polymer membrane is plasticized with a plasticizer, wherein the plasticizer is a reaction product of at least a dibasic acid and an organic compound.
18. The membrane-electrode assembly as claimed in claim 17 , wherein the polymer membrane consists of polybenzimidazole and 1,4-butanediol diglycidyl ether and wherein the plasticizer is di-(2-ethylhexyl)phosphate.
19. A polymer electrolyte fuel cell comprising a membrane-electrode assembly arranged between bipolar plates, the membrane electrode assembly comprising:
two flat gas diffusion electrodes each loaded with a dopant, and
a polymer membrane comprising at least one basic polymer, the polymer membrane sandwiched between said electrodes,
wherein the gas diffusion electrodes are loaded with a content of dopant of 60 to 120% of the weight of the basic polymer in the polymer membrane, and wherein after reaching a mass transport equilibrium for the exchange of the dopant between the gas diffusion electrodes and the polymer membrane, the polymer membrane has a conductivity of at least 0.1 S/m at a temperature of no less than 25° C.