Method for stabilizing polyelectrolyte membrane films used in fuel cells
View Patent ↗A novel method of altering extruded membrane films for PEM (polymer electrolyte membrane) fuel cells in such a manner that the membrane films swell substantially uniformly in both the in-plane x and y directions when immersed in water or ionomer solution is disclosed. The invention includes cutting a membrane film from an extruded membrane sheet in a diagonal orientation with respect to the membrane process direction of the membrane sheet. The membrane film exhibits reduced internal stress as compared to conventionally-prepared membrane films and allows a more even distribution of pressure in a fuel cell stack, thereby reducing the incidence of swollen membrane-induced failure mechanisms in the fuel cell stack.
1. A method of stabilizing a polyelectrolyte membrane film, comprising:
providing an extruded polyelectrolyte membrane sheet having an extrusion machine process direction axis and a transverse axis, the extruded polyelectrolyte membrane sheet being stronger in the process direction axis than in the transverse axis; and
cutting a membrane film from said membrane sheet in generally diagonal relationship with respect to said machine process direction axis.
2. The method of claim 1 wherein said membrane sheet comprises perfluorosulfonic acid.
3. The method of claim 1 wherein said cutting a membrane film from said membrane sheet comprises cutting a membrane film from said membrane sheet with each of two side edges and two transverse edges of said membrane film disposed at substantially a 45 degree angle with respect to said machine process direction axis.
4. The method of claim 1 wherein said membrane sheet comprises perfluorosulfonic acid and said cutting a membrane film from said membrane sheet comprises cutting a membrane film from said membrane sheet with each of two side edges and two transverse edges of said membrane film disposed at substantially a 45 degree angle with respect to said machine process direction axis matching the vectors of expansion with the cut of the membrane.
5. The method of claim 1 further comprising providing a liquid and immersing said membrane film in said liquid, whereby said membrane film undergoes substantially uniform planar expansion.
6. The method of claim 5 wherein said membrane film has a substantially square-shaped configuration.
7. The method of claim 5 wherein said liquid comprises water.
8. The method of claim 5 wherein said liquid comprises ionomer solution.
9. A method of stabilizing a polyelectrolyte membrane film, comprising:
extending an extruded polyelectrolyte membrane sheet from a roll along an extension machine process direction axis, the membrane sheet being stronger in the process direction axis than in a traverse direction axis;
cutting a membrane film from said membrane sheet in generally diagonal relationship with respect to said machine process direction axis;
providing a liquid; and
immersing said membrane film in said liquid, whereby said membrane film undergoes substantially uniform planar expansion.
10. The method of claim 9 wherein said membrane sheet comprises perfluorosulfonic acid.
11. The method of claim 9 wherein said cutting a membrane film from said membrane sheet comprises cutting a membrane film from said membrane sheet with each of two side edges and two transverse edges of said membrane film disposed at substantially a 45 degree angle with respect to said machine process direction axis.
12. The method of claim 9 wherein said membrane sheet comprises perfluorosulfonic acid and said cutting a membrane film from said membrane sheet comprises cutting a membrane film from said membrane sheet with each of two side edges and two transverse edges of said membrane film disposed at substantially a 45 degree angle with respect to said machine process direction axis.
13. The method of claim 9 wherein said liquid comprises water.
14. The method of claim 9 wherein said liquid comprises ionomer solution.
15. The method of claim 9 further comprising cutting a functional polymer electrolyte membrane from said membrane film after said immersing said membrane film in said liquid.
16. The method of claim 15 wherein said cutting a membrane film from said membrane sheet comprises cutting a membrane film from said membrane sheet with each of two side edges and two transverse edges of said membrane film disposed at substantially a 45 degree angle with respect to said machine process direction axis.
17. A method as set forth in claim 1 wherein the providing a membrane sheet comprises extruding a membrane material.
18. A method as set forth in claim 8 further comprising drying the membrane sheet under tension.
19. A method as set forth in claim 9 further comprising extruding a membrane material to provide the membrane sheet.
20. A method as set forth in claim 14 further comprising drying the membrane sheet under tension.
21. A method of stabilizing a polyelectrolyte membrane film, comprising:
providing an extruded polyelectrolyte membrane sheet having an extrusion machine processing direction axis and a transverse axis, the extruded polyelectrolyte membrane sheet being stronger in the process direction axis than in the transverse axis; and cutting a membrane film from said membrane sheet with each of two side edges and two transverse edges oriented in a generally diagonal relationship with respect to said machine process direction axis;
providing a liquid;
immersing said membrane film in said liquid so that the membrane film undergoes substantially uniform planar expansion.
22. A method as set forth in claim 21 wherein each of the two side edges and the two transverse edges of said membrane film are disposed at substantially a 45° angle with respect to said membrane process direction axis.
23. A method as set forth in claim 22 wherein the membrane film has a substantially square-shaped configuration.
24. A method as set forth in claim 21 wherein the liquid comprises water.
25. A method as set forth in claim 21 wherein the liquid comprises an ionomer solution.