Membrane electrode assembly manufacturing process
A method of making a component of a membrane electrode assembly comprising the steps of forming an electrode on an air-permeable backer comprising ePTFE, depositing a mixture comprising ionomer and a water-insoluble alcohol onto said electrode, drying said mixture to form a protective ionomer layer, and depositing an ePTFE-reinforced ionomer layer onto said protective ionomer layer.
1. A method of making a component for a membrane electrode assembly comprising the steps of:
(a) providing an air-permeable backer;
(b) depositing an electrode onto said backer;
(c) depositing an aqueous wet layer comprising a fluoroionomer mixture comprising a water-insoluble alcohol and an ionomer onto said electrode;
(d) substantially drying said wet layer to form a protective ionomer layer; and
(e) depositing, after substantially drying said wet layer, a proton conducting composite wet layer onto said protective ionomer layer, wherein the proton conducting composite wet layer has an occlusive interior volume.
2. A method as defined in claim 1 wherein the air-permeable backer comprises an expanded polymer having release characteristics.
3. A method as defined in claim 2 wherein the expanded polymer is ePTFE.
4. A method as defined in claim 3 wherein said expanded polymer has a mass per area of less than about 16 g/m 2 of ePTFE.
5. A method as defined in claim 3 wherein said expanded polymer has a bubble point of greater than about 70 psi.
6. A method as defined in claim 3 wherein said air-permeable backer has a Z-strength sufficient to prevent cohesive failure of said ePTFE when said electrode is peeled off of said air-permeable backer.
7. A method as defined in claim 1 wherein the air-permeable backer is a gas diffusion layer.
8. A method as defined in claim 1 further comprising coupling a fabric to said backer.
9. A method as defined in claim 8 wherein said air-permeable backer is dimensionally stable within +/−4% throughout the manufacturing process.
10. A method as defined in claim 8 wherein said fabric comprises polyester.
11. A method as defined in claim 8 wherein said fabric has a thickness of less than about 0.006 inches.
12. A method as defined in claim 8 wherein said fabric has a mass/area of less than about 64 g/yd 2 .
13. A method as defined in claim 8 further comprising the step of bonding said fabric to said backer with an adhesive in a discontinuous pattern.
14. A method as defined in claim 13 wherein said fabric is dot-laminated to said backer with a urethane adhesive.
15. A method as defined in claim 13 wherein said adhesive is a solvent-resistant adhesive.
16. A method as defined in claim 1 wherein said ionomer is perfluorosulfonic acid (PFSA) ionomer.
17. A method as defined in claim 1 wherein said wet layer is aqueous and comprises greater than about 60 wt % water.
18. A method as defined in claim 1 wherein said wet layer is aqueous and comprises greater than about 90 wt % water.
19. A method as defined in claim 1 wherein said wet layer is aqueous and comprises less than about 3 wt % of said water-insoluble alcohol.
20. A method as defined in claim 1 wherein said wet layer is aqueous and comprises less than about 5 wt % of said water-insoluble alcohol.
21. A method as defined in claim 1 wherein said water-insoluble alcohol comprises hexanol.
22. A method as defined in claim 1 wherein said wet layer further comprises a water-soluble alcohol.
23. A method as defined in claim 22 wherein said wet layer comprises less than about 10 wt % of said water-soluble alcohol.
24. A method as defined in claim 22 wherein said water-soluble alcohol comprises glycol ether present in an amount of less than about 5 wt %.
25. A method as defined in claim 1 wherein said proton conducting composite wet layer comprises an ionomer.
26. A method as defined in claim 1 wherein said proton conducting composite wet layer comprises a reinforcement.
27. A method as defined in claim 26 wherein said reinforcement comprises an ePTFE membrane.
28. A method as defined in claim 1 further comprising the step of depositing an ionomer layer onto said proton conducting composite wet layer.
29. A method as defined in claim 28 further comprising the step of depositing another electrode onto said ionomer layer.
30. A method as defined in claim 1 further comprising the step of depositing another electrode onto said proton conducting layer.
31. A method as defined in claim 1 wherein said protective ionomer layer has a thickness of about 0.1 to about 25 microns.
32. A method as defined in claim 1 wherein said protective ionomer layer has a thickness of about 0.1 to about 10 microns.
33. A method as defined in claim 1 wherein said protective ionomer layer has a thickness of about 0.1 to about 3 microns.