Electrode with reduced mud cracking via mixed equivalent weight ionomers

1. An ink composition for forming a fuel cell electrode, the ink composition comprising:

a first protogenic group-containing ionomer having an equivalent weight less than 800;

an optional second protogenic group-containing ionomer having an equivalent weight greater than 800; and

a catalyst composition.

2. The ink composition of claim 1 wherein the first protogenic group-containing ionomer and the second protogenic group-containing ionomer each independently include a component selected from the group consisting of —SO 2 X, —PO 3 H 2 , and —COX; and X is an —OH, a halogen, an ester, or

3. The ink composition of claim 1 wherein the first protogenic group-containing ionomer and the second protogenic group-containing ionomer each independently include a sulfonic acid group (—SO 3 H).

4. The ink composition of claim 1 wherein the first protogenic group-containing ionomer has an equivalent weight less than 750 and the second protogenic group-containing ionomer has an equivalent weight greater than 850.

5. The ink composition of claim 1 wherein the first protogenic group-containing ionomer is present in an amount from about 5% to about 95% of the combined weight of the first protogenic group-containing ionomer and the second protogenic group-containing ionomer, and the second protogenic group-containing ionomer is present in an amount from about 5% to about 95% of the combined weight of the first protogenic group-containing ionomer and the second protogenic group-containing ionomer.

6. The ink composition of claim 1 wherein the first protogenic group-containing ionomer is present in an amount from about 10% to about 75% of the combined weight of the first protogenic group-containing ionomer and the second protogenic group-containing ionomer, and the second protogenic group-containing ionomer is present in an amount from about 25% to about 90% of the combined weight of the first protogenic group-containing ionomer and the second protogenic group-containing ionomer.

7. The ink composition of claim 1 wherein the first protogenic group-containing ionomer and the second protogenic group-containing ionomer are each independently a perfluorosulfonic acid (PFSA) polymer.

8. The ink composition of claim 1 wherein the first protogenic group-containing ionomer and the second protogenic group-containing ionomer each independently include a polymer having perfluorocyclobutyl moieties, wherein the perfluorocyclobutyl moieties are:

9. The ink composition of claim 8 wherein the first protogenic group-containing ionomer and the second protogenic group-containing ionomer each independently include a polymer segment comprising polymer segment 1:

E 0 -P 1 -Q 1 -P 2   1

wherein:

E 0 is a moiety that has a protogenic group;

P 1 , P 2 are each independently absent, —O—, —S—, —SO—, —CO—, —SO 2 —, —NH—, NR 2 —, or —R 3 —;

R 2 is C 1-25 alkyl, C 1-25 aryl or C 1-25 arylene;

R 3 is C 1-25 alkylene, C 1-25 perfluoroalkylene, perfluoroalkyl ether, alkylether, or C 1-25 arylene;

X is an —OH, a halogen, an ester, or

R 4 is trifluoromethyl, C 1-25 alkyl, C 1-25 perfluoroalkylene, C 1-25 aryl, or E 1 (see below); and

Q 1 is a fluorinated cyclobutyl moiety.

10. The ink composition of claim 8 wherein the first protogenic group-containing ionomer and the second protogenic group-containing ionomer each independently include polymer segments 2 and 3:

[E 1 (Z 1 ) d ]—P 1 -Q 1 -P 2   2

E 2 -P 3 -Q 2 -P 4   3

wherein:

Z 1 is absent or a protogenic group such as —SO 2 X, —PO 3 H 2 , —COX, and the like;

E 1 is an aromatic containing moiety;

E 2 is an unsulfonated aromatic-containing and/or aliphatic-containing moiety;

X is an —OH, a halogen, an ester, or

d is the number of Z 1 attached to E 1 ;

P 1 , P 2 , P 3 , P 4 are each independently absent, —O—, —S—, —SO—, —CO—, —SO 2 —, —NH—, NR 2 —, or —R 3 —;

R 2 is C 1-25 alkyl, C 1-25 aryl, or C 1-25 arylene;

R 3 is C 1-25 alkylene, C 1-25 perfluoroalkylene, perfluoroalkyl ether, alkylether, or C 1-25 arylene;

R 4 is trifluoromethyl, C 1-25 alkyl, C 1-25 perfluoroalkylene, C 1-25 aryl, or another E 1 group; and

Q 1 , Q 2 are each independently a fluorinated cyclobutyl moiety.

11. The ink composition of claim 8 wherein the first protogenic group-containing ionomer and the second protogenic group-containing ionomer each independently include polymer segments 4 and 5:

wherein:

Z 1 is absent or a protogenic group such as —SO 2 X, —PO 3 H 2 , —COX, and the like;

E 1 , E 2 are each independently an aromatic-containing and/or aliphatic-containing moiety;

X is an —OH, a halogen, an ester, or

d is the number of Z 1 attached to R 8 ;

P 1 , P 2 , P 3 , P 4 are each independently absent, —O—, —S—, —SO—, —CO—, —SO 2 —, —NH—, NR 2 —, or —R 3 —;

R 2 is C 1-25 alkyl, C 1-25 aryl, or C 1-25 arylene;

R 3 is C 1-25 alkylene, C 1-25 perfluoroalkylene, perfluoroalkyl ether, alkylether, or C 1-25 arylene;

R 4 is trifluoromethyl, C 1-25 alkyl, C 1-25 perfluoroalkylene, C 1-25 aryl, or another E 1 group;

R 8 (Z 1 ) d is a moiety having d number of protogenic groups;

R 8 is C 1-25 alkylene, C 1-25 perfluoroalkylene, perfluoroalkyl ether, alkylether, or C 1-25 arylene; and

Q 1 , Q 2 are each independently a fluorinated cyclobutyl moiety.

12. The ink composition of claim 8 wherein the first protogenic group-containing ionomer and the second protogenic group-containing ionomer each independently include polymer segments 6 and 7:

E 1 (SO 2 X) d —P 1 -Q 1 -P 2   6

E 2 -P 3 -Q 2 -P 4   7.

13. The ink composition of claim 1 wherein the catalyst composition includes a precious metal and an optional catalyst support.

14. The ink composition of claim 1 further comprising solvent.

15. The ink composition of claim 10 wherein:

R 2 is C 1-25 alkyl;

R 3 is C 1-25 alkylene or C 1-25 perfluoroalkylene;

R 4 is trifluoromethyl or C 1-25 alkyl; and

R 8 is C 1-25 alkylene or C 1-25 perfluoroalkylene.

16. The ink composition of claim 15 wherein d is 1 to 4.

17. The ink composition of claim 11 wherein:

R 2 is C 1-25 alkyl;

R 3 is C 1-25 alkylene or C 1-25 perfluoroalkylene;

R 4 is trifluoromethyl or C 1-25 alkyl; and

R 8 is C 1-25 alkylene or C 1-25 perfluoroalkylene.

18. The ink composition of claim 17 wherein d is 1 to 4.