Fuel cell electrolyte membrane with basic polymer
The present invention is an electrolyte membrane comprising an acid and a basic polymer, where the acid is a low-volatile acid that is fluorinated and is either oligomeric or non-polymeric, and where the basic polymer is protonated by the acid and is stable to hydrolysis.
1. An electrolyte membrane comprising:
a fluorinated acid that contains 20 acid-functional groups or less per molecule and has a molecular weight of less than 10,000, wherein, after being heated from 1° C. to 200° C. at a ramp rate of 10° C./minute, and then cooled to 120° C. within 5 minutes, the fluorinated acid exhibits a cumulative mass loss of about 6% or less, based on an initial weight of the fluorinated acid, while being maintained at 120° C. for a 24 hour period, the cumulative mass loss being measured during the 24 hour period, and wherein the electrolyte membrane contains less than about 60% by weight phosphoric acid; and
a basic polymer protonated by the fluorinated acid, wherein the basic polymer retains at least about 90% of original functional groups of the basic polymer and at least about 90% of an original molecular weight of the basic polymer when the electrolyte membrane is subjected to an environmental temperature of 85° C. and an environmental relative humidity of 95% for 100 hours.
2. The electrolyte membrane of claim 1 , wherein the basic polymer has a backbone chain comprising aromatic groups.
3. The electrolyte membrane of claim 1 , wherein the basic polymer comprises polyimidazole.
4. The electrolyte membrane of claim 3 , wherein the polyimidazole is selected from the group consisting of poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole], poly(2,5-benzimidazole), a polymer comprising
and combinations thereof.
5. The electrolyte membrane of claim 1 , wherein the fluorinated acid comprises a bis-acid.
6. The electrolyte membrane of claim 1 , wherein the fluorinated acid is selected from the group consisting of HO 3 S(CF 2 ) n SO 3 H, C m F 2m+1 SO 2 NHSO 2 (CF 2 ) n SO 2 NHSO 2 C m F 2m+1 , compounds thereof where the (CF 2 ) n group comprises a first heteroatom, compounds thereof where the C m F 2m+1 group comprises a second heteroatom, and combinations thereof, wherein n ranges from 1-10 and m ranges from 1-8, and wherein the first heteroatom and the second heteroatom are each selected from the group consisting of oxygen and nitrogen.
7. The electrolyte membrane of claim 1 , wherein the electrolyte membrane contains less than about 25% by weight phosphoric acid.
8. The electrolyte membrane of claim 7 , wherein the electrolyte membrane is substantially free of phosphoric acid.
9. The electrolyte membrane of claim 1 , further comprising inorganic additives.
10. The electrolyte membrane of claim 1 , further comprising a reinforcement matrix.