Proton conducting electrolytes with cross-linked copolymer additives for use in fuel cells

1. A method of making a proton conducting polymer electrolyte comprising a proton conducting ionomer and a polymetaloxane copolymer additive, the method comprising:

(a) copolymerizing

a plurality of metal oxide monomers with cross-linking functional groups and

a plurality of metal oxide monomers with other functional groups, in random or block sequence to form the metaloxane copolymer exhibiting the cross-linking functional groups and the other functional groups, wherein:

the metal oxide monomers with the cross-linking functional groups comprise:

a first metal bonded to at least two oxygen atoms and selected from the group consisting of Si, Ti, Zr, Ce, Ta, and Cr; and

the cross-linking functional groups bonded to the first metal and comprising a functional end group containing nitrogen or oxygen and characterized by a chemical structure selected from the group consisting of —NH 2 , ═NH, -(aliphatic)-OH, -(aryl)-OH,

wherein R is a hydrocarbon group; and

wherein the metal oxide monomers with the other functional groups comprise:

a second metal bonded to at least two oxygen atoms and selected from the group consisting of Si, Ti, Zr, Ce, Ta, and Cr; and

the other functional groups bonded to the second metal are selected from the group consisting of:

i) proton carrier functional groups comprising a functional end group selected from the group consisting of —PO 3 H 2 , —COOH, —SO 3 H, and —SO 2 NHSO 2 CF 3 ,

ii) metal chelating functional groups comprising a functional end group selected from the group consisting of phosphonic acid, bipyridine, phenanthroline, and derivatives thereof, and

iii) free radical scavenger functional groups comprising a functional end group selected from the group consisting of aminophenyl, hydroxyphenyl and derivatives thereof,

(b) mixing an amount of (i) the polymetaloxane copolymer following copolymerization, or (ii) a mixture of the metal oxide monomers prior to copolymerization, with an amount of the proton conducting ionomer; and

(c) heating the mixture such that a polymetaloxane copolymer is formed and the polymetaloxane copolymer and the proton conducting ionomer are covalently bonded or acid-base complexed together at the cross-linking functional groups of the polymetaloxane copolymer.

2. The method of claim 1 , comprising:

preparing the polymetaloxane copolymer;

adding the polymetaloxane copolymer to a dispersion comprising the proton conducting ionomer;

removing solvent from the dispersion thereby providing a solid mixture of the polymetaloxane copolymer and the proton conducting ionomer; and

heating the mixture.

3. The method of claim 1 , comprising:

adding the metal oxide monomers with cross-linking functional groups and the metal oxide monomers with other functional groups to a dispersion comprising the proton conducting ionomer and thereby making the polymetaloxane copolymer in situ in the dispersion; and

removing solvent from the dispersion thereby providing a solid mixture of the polymetaloxane copolymer and the proton conducting ionomer; and heating the mixture.

4. The method of claim 1 , comprising:

preparing the polymetaloxane copolymer;

adding the polymetaloxane copolymer to a dispersion comprising a precursor for the proton conducting ionomer;

removing solvent from the dispersion thereby providing a solid mixture of the polymetaloxane copolymer and the precursor;

heating the mixture; and

converting the precursor to the proton conducting ionomer.

5. The method of claim 1 , wherein the polymetaloxane copolymer is prepared by:

preparing a solution comprising the metal oxide monomers with cross-linking functional groups and the metal oxide monomers with other functional groups; and

heating the solution to a reaction temperature for a period of time thereby forming the polymetaloxane copolymer in solution.

6. The method of claim 5 , comprising preparing the metal oxide monomers with cross-linking functional groups by hydrolyzing unhydrolyzed metal oxide monomers with cross-linking functional groups.

7. The method of claim 6 , wherein the unhydrolyzed metal oxide monomers with cross-linking functional groups are 3-aminopropyl-trimethoxysilane, aminophenyltrimethoxysilane, or 3 -(1H-benzimidazol-2-yl)propyl-trimethoxysilane.

8. The method of claim 5 , comprising preparing the metal oxide monomers with other functional groups by hydrolyzing unhydrolyzed metal oxide monomers with other functional groups.

9. The method of claim 8 , wherein the unhydrolyzed metal oxide monomers with other functional groups are (2-diethylphosphatoethyl)triethoxysilane.

10. The method of claim 6 , wherein the hydrolyzing and the making of the polymetaloxane copolymer are performed in the same solution.

11. The method of claim 8 , wherein the hydrolyzing and the making of the polymetaloxane copolymer are performed in the same solution.

12. The method of claim 1 , wherein the solution comprises at least two different metal oxide monomers with other functional groups.

13. The method of claim 12 , wherein the solution comprises metal oxide monomers with free radical scavenger functional groups and the free radical scavenger functional groups are hydrolyzed 3-amino-4-nitrophenyl-triethoxysilane.