Multi-layers coating for protecting metallic substrates

• US 20030099847A1
• Filed: 05/20/2002
• Published: 05/29/2003
• Est. Priority Date: 05/18/2001
• Status: Active Grant

• Current Assignee: Institut national de la recherche scientifique, McGill University
• Original Assignee: Institut national de la recherche scientifique
• Inventors: Hay, Allan S., Dodelet, Jean-Pol, Cunningham, Nicolas, Meng, Yuezhong
• Granted Patent: US 6,828,040 B2
• Time in Patent Office: Days
• US Class Current: 428/469
• CPC Class Codes: H01M 8/021 Alloys based on iron
• CPC Class Codes: H01M 8/0213 Gas-impermeable carbon-containing materials
• CPC Class Codes: H01M 8/0228 in the form of layered or coated products
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y10T 428/12625 Free carbon containing component
• CPC Class Codes: Y10T 428/12951 Fe-base component
• CPC Class Codes: Y10T 428/12972 Containing 0.01-1.7% carbon [i.e., steel]
• CPC Class Codes: Y10T 428/12979 Containing more than 10% nonferrous elements [e.g., high alloy, stainless]
• CPC Class Codes: Y10T 428/263 Coating layer not in excess of 5 mils thick or equivalent
• CPC Class Codes: Y10T 428/265 1 mil or less
• CPC Class Codes: Y10T 428/30 Self-sustaining carbon mass or layer with impregnant or other layer

Abstract

The invention relates to an improved composite used as a bipolar separator plate in fuel cells. The composite of the invention comprises a steel substrate having a carbon coating thereon, the carbon coating comprises a carbon layer derived by pyrolysis of an acetylenic polymer having a content of carbon of at least 90%, the carbon layer protects the substrate against corrosion and improves long term contact resistivity, the polymer is soluble at a temperature below 110° C. in an organic solvent, and the carbon layer contacts said steel substrate. A process for preparing the composite according to the invention is also disclosed.

Claims

1. A composite comprising a steel substrate having a carbon coating thereon, said carbon coating comprising a carbon layer derived by pyrolysis of an acetylenic polymer having a content of carbon of at least 90% said carbon layer protecting said substrate against corrosion and improving long term contact resistivity, said polymer being soluble at a temperature below 110°

C. in an organic solvent, and said carbon layer contacting said steel substrate.

2. The composite of claim 1 wherein, said steel substrate comprises a steel comprising at least 50 weight % of iron.

3. The composite of claim 2 wherein, said steel is selected from the group consisting of 304, 316 and 316L stainless steels

4. The composite of claim 3 wherein, said stainless steel 316L.

5. The composite of claim 1 wherein, the acetylenic polymer comprises up to 85 mole % of m-diethynylbenzene.

14. The composite of claim 1 wherein, the acetylenic polymer comprises up to 85 mole % of a mixture of p-diethynylbenzene and m-diethynylbenzene.

15. The composite of claim 14 wherein, said mixture comprises from 0 to 35 mole % of p-diethynylbenzene.

16. The composite of claim 15 wherein, said mixture comprises from 5 to 10 mole % of p-diethynylbenzene.

17. The composite of claim 14 wherein, the acetylenic polymer is a terpolymer comprising m-diethynylbenzene, p-diethynylbenzene and a flexibilizing agent effective to enhance solubility of said polymer in said solvent, below 110°

C.

18. The composite of claim 17 wherein, the acetylenic polymer comprises from 15 to 30 mole % of the flexibilizing agent.

19. The composite of claim 18 wherein, the acetylenic polymer comprises about 20 mole % of the flexibilizing agent.

20. The composite of claim 17 wherein, the flexibilizing agent is a monomer of formula:

21. The composite of claim 20 wherein, the C₆-C₁₂ aryl is

22. The composite of claim 20 wherein, the C₆-C₁₂ arylene is selected from the group consisting of:

23. The composite of claim 20 wherein, the monomer is selected from the group consisting of.

24. The composite of claim 23 wherein, said monomer is

25. The composite of claim 1 wherein, the electrical resistivity of the carbon coating is below 0.25 Ω

-cm.

26. The composite of claim 1 wherein, said solvent is selected from the group consisting of 1,1,2,2-tetrachloroethane, chlorobenzene, o-dichlorobenzene and mixtures thereof.

27. The composite of claim 1 wherein, said acetylenic polymer is soluble at a temperature below 80°

C.

28. The composite of claim 27 wherein, said solvent is 1,1,2,2-tetrachloroethane.

29. The composite of claim 28 wherein, said acetylenic polymer is soluble in a temperature ranging from 50 to 60°

C.

30. The composite of claim 1 wherein, the acetylenic polymer has a content of carbon from 92 to 97%

31. The composite of claim 1 wherein, the carbon coating further comprises an intermediate layer on said carbon layer and an outer layer on said intermediate layer.

32. The composite of claim 31 wherein, the combination of said carbon layer and said intermediate layer provides a non-porous coating;

and said outer layer is effective to protect the intermediate layer.

33. The composite of claim 31 wherein, the carbon layer and the outer layer are derived by the pyrolysis of the acetylenic polymer.

34. The composite of claim 31 wherein, the intermediate layer comprises pyrolyzed carbon derived by contacting a suspension of particulate carbon in an organic solvent or an aqueous media with said carbon layer.

35. The composite of claim 34 wherein, said suspension comprises particulate carbons selected from the group consisting of carbon black, graphite, acetylene black, Ketjen black and mixtures thereof.

36. The composite of claim 31 wherein, the carbon coating is from 70 to 100 μ

m thick

37. The composite of claim 1 wherein, the carbon coating improves the contact resistance to carbon paper of said substrate.

38. The composite of claim 1 wherein, said substrate is in the form of a plate.

63. In a fuel cell having electrodes, membranes and a bipolar separation plate the improvement wherein, said bipolar separation plate comprises the composite of claim 1.

6. The composite of wherein, the acetylenic polymer is a copolymer comprising m-diethynylbenzene and a flexibilizing agent effective to enhance solubility of said polymer in said solvent, below 110°

C.

7. The composite of claim 6 wherein, the acetylenic polymer comprises from 15 to 30 mole % of the flexibilizing agent.

8. The composite of claim 7 wherein, the acetylenic polymer comprises about 20 mole % of the flexibilizing agent.

9. The composite of claim 6 wherein, the flexibilizing agent is a monomer of formula:

10. The composite of claim 9 wherein, the C₆-C₁₂ aryl is

11. The composite of claim 9 wherein, the C₆-C₁₂ arylene is selected from the group consisting of:

12. The composite of claim 9 wherein, the monomer is selected from the group consisting of:

13. The composite of claim 12 wherein, said monomer is

39. A process for the preparation of a composite comprising a steel substrate having a carbon coating, comprising the steps of:

a) contacting a solution with a steel substrate and coating a film of the solution on a surface of said steel substrate, said solution comprising an acetylenic polymer and a solvent; and

b) pyrolyzing said film at a temperature ranging from 600 to 1000°

C. to form said carbon coating comprising a carbon layer.

40. The process of claim 39 wherein, in step (a) said solution is sprayed on the surface of said steel substrate to form said film;

and said process further comprises after step (a) and prior to step (b);

a′

) contacting a suspension of particulate carbon in an organic or aqueous solvent with said film to form an intermediate film on said film;

a″

) contacting said solution with said intermediate film to form an outer film on said intermediate film; and

in step (b), said films are pyrolyzed to form said carbon coating comprising the carbon layer, an intermediate layer and an outer layer.

41. The process of claim 40 wherein, in step (a′

), said suspension is sprayed on said film to form said intermediate film, and in step (a″

), said solution is sprayed on said intermediate film to form said outer film.

42. The process of claim 40 wherein, in step (a), said solution is sprayed from 10 to 50 times.

43. The process of claim 42 wherein, the solution is sprayed from 15 to 25 times.

44. The process of claim 41 wherein, in step (a′

), said suspension is sprayed 1 to 5 times.

45. The process of claim 44 wherein, the suspension is sprayed 2 times.

46. The process of claim 41 wherein, in step (a″

), said solution is sprayed from 1 to 5 times.

47. The process of claim 46 wherein, the solution is sprayed 3 times.

48. The process of claim 41 wherein, steps (a) and/or (a″

), further comprise a spin coating film of said acetylenic polymer prior to a first spray of said solution.

49. The process claim 41 wherein, steps (a) and/or (a″

) further comprise cross-linking said acetylenic polymer using an UV light.

50. The process claim 41 wherein, steps (a) and/or (a″

) further comprise cross-linking said acetylenic polymer between each spray of said solution using an UV light.

51. The process of claim 41 wherein, steps (a) and/or (a″

) further comprise pyrolyzing said film(s) after a last spray of said solution.

52. The process of claim 41 wherein, steps (a) and/or (a″

) further comprise pyrolyzing said film(s) after each spray of said solution.

53. The process of claim 41 wherein, step (a′

) further comprises pyrolyzing said film after a last spray of said suspension.

54. The process of claim 41 wherein, step (a′

) further comprises pyrolyzing said film after each spray of said suspension.

55. The process of claim 41 wherein, said solution has a concentration of acetylenic polymer ranging from 20 to 200 mg/mL.

56. The process of claim 41 wherein, said solution has a concentration of acetylenic polymer ranging from 10 to 20 mg/mL.

57. The process of claim 41 wherein, the temperature when pyrolyzing is ranging from 600 to 800°

C.

58. The process of claim 57 wherein, the temperature when pyrolyzing is ranging from 700 to 780°

C.

59. The process of claim 41 wherein, pyrolyzing occurs under an inert gas atmosphere.

60. The process of claim 41 wherein, the inert gas is argon.

61. The process of claim 41 wherein, said acetylenic polymer is soluble at a temperature below 110°

C.

62. The process of claim 41 wherein, said solution further comprises graphite powder or fiber.