Preparation and storage of membrane and electrode assemblies
View Patent ↗Protecting a membrane and electrode assembly in an electrochemical cell having one or more electrocatalysts in intimate contact with the membrane during storage or shipment of the cell. The membrane may be provided in either the non-proton form of a dry or hydrated cation exchange membrane, such as an alkali metal cation form or an ammonium cation form; the wet or dry precursor form of a cation exchange membrane, such as the non-ionically conducting sulfonyl-fluoride polymer membrane; or the dry proton form of a cation exchange membrane. These membrane surfaces are not acidic under open circuit conditions experienced during storage or shipment of the cell. Since some electrocatalysts are degraded during contact with the acidic surface of a hydrated membrane, the non-acidic surface of the membrane protects these electrocatalysts. The method may be used on newly assembled electrochemical cells, on cells being taken out of service, and on membrane and electrode assemblies.
1. A method, comprising:
providing a membrane and electrode assembly having one or more electrocatalysts in intimate contact with a cation exchange membrane in an alkali metal cation form during a period without an electrical current passing through the membrane and electrode assembly.
2. The method of claim 1 , wherein at least one of the one or more electrocatalysts has an electrocatalytic activity that diminishes when placed in contact with a hydrated proton form of the cation exchange membrane in the absence of an electrical current flowing through the cell.
3. The method of claim 2 , wherein the electrocatalytic activity diminishes by a process selected from degradation, dissolution, corrosion, or a combination thereof.
4. The method of claim 1 , wherein the one or more electrocatalysts includes lead dioxide.
5. The method of claim 1 , further comprising:
placing the membrane and electrode assembly into an electrochemical cell or an electrochemical cell stack.
6. The method of claim 5 , wherein the electrochemical cell or electrochemical cell stack includes a fuel cell or an electrolytic cell.
7. The method of claim 1 , wherein the cation exchange membrane is hydrated.
8. The method of claim 1 , wherein the cation exchange membrane is dry.
9. The method of claim 1 , further comprising:
supplying the membrane and electrode assembly with reactants; and
providing an electrical current through the membrane and electrode assembly to liberate protons and convert the cation exchange membrane from the alkali metal cation form to an acidic proton form.
10. The method of claim 1 , further comprising:
placing the membrane and electrode assembly into an electrochemical cell or an electrochemical cell stack.
11. The method of claim 10 , wherein the cation exchange membrane is wet during the placing of the membrane and electrode assembly into the electrochemical cell or the electrochemical cell stack.
12. The method of claim 10 , wherein the cation exchange membrane is dry during the placing of the membrane and electrode assembly into the electrochemical cell or the electrochemical cell stack.
13. A method, comprising:
providing a membrane and electrode assembly having one or more electrocatalysts in intimate contact with a sulfonyl fluoride form of a precursor to a cation exchange membrane during a period without an electrical current passing through the membrane and electrode assembly.
14. The method of claim 13 , wherein at least one of the one or more electrocatalysts has an electrocatalytic activity that diminishes when placed in contact with a hydrated proton form of the cation exchange membrane in the absence of an electrical current flowing through the cell.
15. The method of claim 14 , wherein the electrocatalytic activity diminishes by a process selected from degradation, dissolution, corrosion, or a combination thereof.
16. The method of claim 13 , wherein the one or more electrocatalysts includes lead dioxide.
17. The method of claim 13 , further comprising:
placing the membrane and electrode assembly into an electrochemical cell or an electrochemical cell stack.
18. The method of claim 17 , wherein the electrochemical cell or electrochemical cell stack includes a fuel cell or an electrolytic cell.
19. The method of claim 13 , further comprising:
converting the cation exchange membrane from the sulfonyl-fluoride form to an alkali metal cation form.
20. The method of claim 19 , wherein the step of converting includes contacting the cation exchange membrane with an alkali metal hydroxide solution.
21. The method of claim 20 , wherein the alkali metal hydroxide is selected from NaOH, KOH, LiOH, RbOH, CsOH, FrOH, and combinations thereof.
22. The method of claim 20 , wherein the alkali metal hydroxide solution has a concentration of between about 0.1M and about 10M.
23. The method of claim 20 , wherein the alkali metal hydroxide solution has a concentration of between about 0.5M and about 5M.
24. The method of claim 20 , wherein the alkali metal hydroxide solution has a concentration of between about 0.75M and about 3M.
25. The method of claim 20 , wherein the alkali metal hydroxide solution contacts the proton exchange membrane for between about 0.25 hours and about 24 hours.
26. The method of claim 20 , wherein the alkali metal hydroxide solution contacts the proton exchange membrane for between about 0.5 hours and about 12 hours.
27. The method of claim 20 , wherein the alkali metal hydroxide solution contacts the proton exchange membrane for between about 1 hour and about 6 hours.
28. The method of claim 19 , further comprising:
providing the cation exchange membrane in a wet state.
29. The method of claim 19 , further comprising:
providing the cation exchange membrane in a dry state.
30. The method of claim 19 , further comprising:
assembling the membrane and electrode assembly into an electrochemical cell or an electrochemical cell stack.
31. The method of claim 30 , wherein the cation exchange membrane is wet during the assembling of the membrane and electrode assembly into the electrochemical cell or the electrochemical cell stack.
32. The method of claim 30 , wherein the cation exchange membrane is dry during the assembling of the membrane and electrode assembly into the electrochemical cell or the electrochemical cell stack.
33. The method of claim 19 , further comprising:
supplying the membrane and electrode assembly with reactants; and
providing an electrical current through the membrane and electrode assembly to liberate protons and convert the cation exchange membrane from the alkali metal cation form to an acidic proton form.
34. The method of claim 33 , wherein the steps of supplying reactants and providing an electrical current are performed simultaneously or nearly simultaneously.
35. A method, comprising:
passing electrical current through a membrane and electrode assembly having one or more electrocatalysts in intimate contact with a cation exchange membrane in a hydrated proton form; and then
supplying an alkali metal hydroxide solution to a membrane and electrode assembly under an electrical potential; and then
removing an electrical potential from across the membrane and electrode assembly, wherein the proton exchange membrane is converted from the hydrated proton form to the alkali metal cation form.
36. The method of claim 35 , further comprising:
removing the alkali metal hydroxide solution from the electrochemical cell.
37. The method of claim 35 , further comprising:
supplying the electrochemical cell with reactants; and
restoring the electrical potential across the electrochemical cell to liberate protons and convert the proton exchange membrane from the alkali metal cation form back to the acidic form.
38. The method of claim 35 , wherein the alkali metal hydroxide is selected from NaOH, KOH, LiOH, RbOH, CsOH, FrOH and combinations thereof.
39. The method of claim 38 , wherein the alkali metal hydroxide solution has a concentration of between about 0.1M and about 10M.
40. The method of claim 38 , wherein the alkali metal hydroxide solution has a concentration of between about 0.5M and about 5M.
41. The method of claim 38 , wherein the alkali metal hydroxide solution has a concentration of between about 0.75M and about 3M.
42. The method of claim 34 , wherein the step of converting the proton exchange membrane further comprises:
contacting the proton exchange membrane with the alkali metal hydroxide solution for a period between about 0.25 hour and about 24 hours.
43. The method of claim 42 , wherein the period is between about 0.5 hours and about 12 hours.
44. The method of claim 42 , wherein the period is between about 1 hour and about 6 hours.