Polyelectrolyte membranes and methods for making
A polymer electrolyte membrane includes a porous base membrane and electrolytes dispersed within the pores of the base membrane. The electrolytes include metal oxide compounds having acid functionality. A process for making the membrane is also provided. The membrane is compatible, durable, highly conductive, mechanically strong and dimensionally stable.
1. A polymer electrolyte membrane comprising a porous base membrane and electrolytes disposed within pores of the porous base membrane, said electrolytes comprising metal oxide compounds having acid functionality, wherein the metal oxide compound having acid functionality comprises at least one structural unit selected from the group consisting of formula I and formula II:
wherein M is independently at each occurrence a metal or metalloid selected from the group consisting of Si, Al, Ti, Zr, Sn and Ge; R is independently at each occurrence an aliphatic or aromatic diradical or bond; and Z is independently at each occurrence an acid functional group.
2. The membrane of claim 1 comprising a continuous pore structure with numerous interconnecting pores that extend completely through the membrane.
3. The membrane of claim 2 wherein the porous base membrane has a porosity of greater than about 20 percent by volume.
4. The membrane of claim 2 wherein the porous base membrane comprises expanded polytetrafluoroethylene (ePTFE).
5. The membrane of claim 1 wherein the electrolytes at least partially fill the pores of the porous base membrane.
6. The membrane of claim 5 wherein the electrolytes fill 90% or more of the pores in the porous base membrane.
7. The membrane of claim 1 wherein the base membrane comprises polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride co-hexafluoropropylene, polytetrafluoroethylene oxide-co-difluoromethylene oxide, polytetrafluoroethylene-co-perfluoropropylvinyl ether, polyolefin,polyamide, polyester, polysulfone, polyether, acrylic-based polymers, polystyrene, polyurethane, polypropylene, polyethylene, polyphenylene sulfone, nylon, polyphenylene oxide, cellulosic polymer or combinations of the foregoing.
8. The membrane of claim 1 , wherein the metal oxide compound having acid functionality comprises acid functional groups or latent acid functional groups selected from the group consisting of sulfonic acid, peifluorinated sulfonic acid, partially perfluorinated sulfonic acid, sulfonyl halide, perfluorinated sulfonyl halide, partially perfluorinated sulfonyl halide, dialkyiphosphonate, phosphonic acid, carboxylic acid, carbonyl halide and the alkaline salt forms of the foregoing.
9. The membrane of claim 1 wherein M is silicon.
10. The membrane of claim 1 wherein the electrolyte further comprises a nonconductive metal oxide compound.
11. The membrane of claim 10 , wherein the nonconductive metal oxide compound comprises at least one structural unit selected from the group consisting of formula VI and formula VII:
wherein M is independently at each occurrence a metal or metalloid selected from the group consisting of Si, Al, Ti, Zr, Sn and Ge; and R″ is independently at each occurrence a hydrogen, an aliphatic group, a cylcoaliphatic group or an aromatic group.
12. The membrane of claim 10 wherein the nonconductive metal oxide compound is selected from the group consisting of halosilanes, alkoxysilanes, trihalodisilanes, trialkoxydisilanes and disilazanes.
13. The membrane of claim 10 wherein the ratio of the nonconductive metal oxide compound to the acid functionalized metal oxide compound is from about 0:1 to about 12:1.
14. The membrane of claim 10 wherein the electrolyte further comprises an inorganic filler.
15. The membrane of claim 14 , wherein the inorganic filler may be silica, titania, zirconia, heteropolyacids, zeolites and clays.
16. The membrane of claim 1 wherein the electrolyte further comprises an inorganic filler.
17. The membrane of claim 16 , wherein the inorganic filler may be silica, titania, zirconia, heteropolyacids, zeolites and clays.
18. The membrane of claim 16 , wherein the amount of inorganic filler ranges from about 0.1 percent by weight to about 50 percent by weight, based on the weight of the electrolyte.
19. A method for making a polymer electrolyte membrane by impregnating the pores of a porous base membrane with metal oxide precursors having acid functionality and reacting the metal oxide precursors to form metal oxide compounds having acid functionality, wherein the acid functionalized metal oxide precursor has formula V:
A a MX 4-a V
wherein A is —R—Z; R is independently at each occurrence an aliphatic or aromatic diradical or bond; Z is independently at each occurrence an acid functional group; X is a halogen or a C 1 -C 10 alkoxy radical; M is a metal or metalloid selected from the group consisting of Si, Al, Ti, Sn, Zr and Ge; and a is a number from about 1 to about 3.
20. The method of claim 19 wherein the metal oxide precursors are impregnated into the pores of the base membrane by an infiltration method selected from the group consisting of solution deposition, high pressure solution deposition, vacuum filtration, painting, gravure coating, dipping, spin-coating, spraying and air brushing.
21. The method of claim 19 wherein the base membrane comprises polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride co-hexafluoropropylene, polytetrafluoroethylene oxide-co-difluoromethylene oxide, polytetrafluoroethylene-co-perfluoropropylvinyl ether, polyolefin, polyamide, polyester, polysulfone, polyether, acrylic-based polymers, polystyrene, polyurethane, polypropylene, polyethylene,polyphenylene sulfone, nylon, polyphenylene oxide, cellulosic polymer or combinations of the foregoing.
22. The method of claim 19 , wherein the metal oxide precursors having acid functionality groups or latent acid functional groups comprise acid functional groups selected from the group consisting of sulfonic acid, perfluorinated sulfonic acid, partially perfluorinated sulfonic acid, sulfonyl halide, perfluorinated sulfonyl halide, partially perfluorinated sulfonyl halide, dialkylphosphate, phosphonic acid, carboxylic acid, carbonyl halide and the alkaline salt forms of the foregoing.
23. The method of claim 19 wherein the method further comprises impregnating a nonconductive metal oxide precursor.
24. The method of claim 23 , wherein the nonconductive metal oxide precursor has the structure:
R″ a MX 4-a
wherein M is a metal or metalloid selected from the group consisting of Si, Al, Ti, Zr, Sn and Ge; X is a halogen or C 1 -C 10 alkoxy radical; a is an integer from 1 to 3; and R″ is independently at each occurrence a hydrogen, an aliphatic group, a cycloaliphatic group or an aromatic group.
25. The method of claim 19 wherein the method further comprises impregnating the base membrane with an inorganic filler.
26. The method of claim 25 , wherein the inorganic filler may be silica, titanic, zirconia, heteropolyacids, zeolites and clays.
27. The method of claim 19 , wherein the metal oxide precursors are reacted at a temperature from about 24 ° C. to about 250 ° C.
28. A fuel cell comprising a proton exchange membrane comprising a porous base membrane and electrolytes disposed within pores of the porous base membrane, said electrolytes comprising metal oxide compounds having acid functionality, wherein the metal oxide compound having acid functionality comprises at least one structural unit selected from the group consisting of formula I and formula II:
wherein M is independently at each occurrence a metal or metalloid selected from the group consisting of Si, Al, Ti, Zr, Sn and Ge; R is independently at each occurrence an aliphatic or aromatic diradical or bond; and Z is independently at each occurrence an acid functional group.
29. A fuel cell comprising a proton exchange membrane comprising a porous base membrane and electrolytes disposed within pores of the porous base membrane, said electrolytes comprising metal oxide compounds having acid functionality, wherein the metal oxide compound having acid functionality comprises at least one structural unit selected from the group consisting of wherein the acid functionalized metal oxide precursor has formula V:
A a MX 4-a V
wherein A is —R—Z; R is independently at each occurrence an aliphatic or aromatic diradical or bond; Z is independently at each occurrence an acid functional group; X is a halogen or a C 1 -C 10 alkoxy radical; M is a metal or metalloid selected from the group consisting of Si, Al, Ti, Sn, Zr and Ge; and a is a number from about 1 to about 3.