Solids supporting mass transfer for fuel cells and other applications and solutions and methods for forming

• US 20040045816A1
• Filed: 09/11/2002
• Published: 03/11/2004
• Est. Priority Date: 09/11/2002
• Status: Active Grant

• Current Assignee: Board of Trustees of The University of Illinois
• Original Assignee: Board of Trustees of The University of Illinois
• Inventors: Masel, Richard I., Rice, Cynthia A.
• Granted Patent: US 7,108,773 B2
• Time in Patent Office: Days
• US Class Current: 204/290.14
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: H01M 4/8605 Porous electrodes
• CPC Class Codes: H01M 4/8652 as mixture
• CPC Class Codes: H01M 4/8828 Coating with slurry or ink
• CPC Class Codes: H01M 4/8882 Heat treatment, e.g. drying, baking
• CPC Class Codes: H01M 4/90 Selection of catalytic material
• CPC Class Codes: H01M 4/92 Metals of platinum group H01M4/94 , H01M4/9058 take precedence
• CPC Class Codes: H01M 4/926 on carbon or graphite
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A solution useful for forming a solid that supports mass transfer includes carbon nanotubes and a solvent. Solids formed using the solution thereby have carbon nanotubes dispersed therein that are useful for communicating gas and/or electric charges within the solid. Catalyst layers of the invention that include carbon nanotubes can provide high levels of efficiency while requiring low catalyst concentrations.

Claims

1. A catalyst ink comprising:

at least one solvent;

carbon nanotubes dispersed in said solvent; and

,

catalyst particles dispersed in said solvent, at least about 1% by weight of said particles being independent from said carbon nanotubes.

2. The catalyst ink as defined by claim 1 wherein said catalyst particles comprise one or more of Pt, Pd, Ir, Ru, Os, Rh, Ni, Co, Mn, Mo, W, V, Ce, and Ti.

3. The catalyst ink as defined by claim 1 wherein said catalyst particles have a diameter of between about 6 and about 20 nm.

4. The catalyst ink as defined by claim 1 wherein said catalyst particles are supported on one of carbon particles or conducting polymer particles.

5. The catalyst ink as defined by claim 4 wherein said carbon nanotubes have an inside diameter, and wherein said one of said carbon particles or conducting polymer particles have a diameter larger than said inside diameter.

6. The catalyst ink as defined by claim 1 wherein said carbon nanotubes have an inside diameter, and wherein said catalyst particles have a diameter larger than said smaller than said inside diameter.

7. The catalyst ink as defined by claim 1 wherein said carbon nanotubes are present in the ink at a weight ratio of between about 1:

100 and about 500;

1 to said catalyst particles.

8. The catalyst ink as defined by claim 1 wherein said carbon nanotubes are present in the ink at a weight ratio of between about 1:

100 and about 100;

1 to said catalyst particles.

9. The catalyst ink as defined by claim 1 wherein said carbon nanotubes are present in the ink at a weight ratio of between about 1:

10 and about 10;

1 to said catalyst particles.

10. The catalyst ink as defined by claim 1 wherein said carbon nanotubes are present in the ink at a weight ratio of between about 1:

3 and about 3;

1 to said catalyst particles.

11. The catalyst ink as defined by claim 1 and further comprising a proton-conducting material dissolved in said at least one solvent.

12. The catalyst ink as defined by claim 11 wherein said proton-conducting material comprises a perfluorosulfonic acid polymer or copolymer, and wherein at least one of said at least one solvent comprises an alcohol or a ketone.

13. The catalyst ink as defined by claim 11 wherein said proton-conducting material is present in the ink at a weight ratio of between about 1:

20 and about 1;

2 to said catalyst particles.

14. The catalyst ink as defined by claim 1 further comprising a binder.

15. A catalyst ink as defined by claim 1 wherein said at least one solvent comprises one or more solvents selected from the group of solvents consisting of water, alcohols, aldehydes, ethers, amines, esters, and ketones.

16. A catalyst ink as defined by claim 1 wherein said at least one solvent is protic.

17. A catalyst ink as defined by claim 1 wherein at least about 5% by weight of said catalyst particles are independent from said carbon nanotubes.

18. A catalyst ink as defined by claim 1 wherein at least about 75% by weight of said catalyst particles are independent from said carbon nanotubes.

19. A catalyst ink as defined by claim 1 wherein at least about 1% by weight of said carbon nanotubes have a substantially open inner passage.

20. A catalyst ink as defined by claim 1 wherein at least 10% by weight of said carbon nanotubes have a substantially open inner passage.

21. A catalyst ink as defined by claim 1 wherein at least 50% by weight of said carbon nanotubes have a substantially open inner passage.

22. A catalyst ink as defined by claim 1 wherein substantially all of said carbon nanotubes have a substantially open inner passage.

23. A catalyst ink as defined by claim 1 wherein said carbon nanotubes have an inside diameter of between about 6 and about 20 nm.

24. A solution useful for forming a-solid, the solution comprising:

a solid dissolved in at least one solvent; and

,

carbon nanotubes dispersed in said solvent, at least about 1% by weight of said nanotubes having unobstructed inner passages.

25. A solution as defined by claim 24 wherein at least about 10% by weight of said nanotubes have unobstructed inner passages.

26. A solution as defined by claim 24 wherein at least about 50% by weight of said nanotubes have unobstructed inner passages.

27. A solution as defined by claim 24 wherein said solid dissolved in said at least one solvent comprises a polymer.

28. A solution as defined by claim 24 wherein said at least a solvent is protic.

29. A solution as defined by claim 24 wherein said solution is a catalyst ink, the solution further comprising catalyst particles dispersed in said solvent.

30. A solid that supports mass transfer comprising:

a solid material; and

,

carbon nanotubes distributed in said solid material, at least about 1% by weight of said nanotubes having unobstructed inner passages and thereby operative to communicate gas within said solid material.

31. A solid that supports mass transfer as defined by claim 30 wherein said solid material comprises a polymer.

32. A solid that supports mass transfer as defined by claim 30 wherein at least about 5% by weight of said nanotubes have unobstructed inner passages.

33. A solid that supports mass transfer as defined by claim 30 wherein at least about 50% by weight of said nanotubes have unobstructed inner passages.

34. A solid that supports mass transfer as defined by claim 30 wherein substantially all of said nanotubes have unobstructed inner passages.

35. A solid that supports mass transfer as defined by claim 30 wherein said nanotubes have a multiplicity of holes along their walls operable to communicate gas.

36. A solid that supports mass transfer as defined by claim 30 wherein said nanotubes have an inside diameter of between about 6 and about 20 nm.

37. A solid that supports mass transfer as defined by claim 30 wherein said solid material is formed in the shape of a layer having a thickness, and wherein said nanotubes have a length that is at least as large as said layer thickness.

38. A solid that supports mass transfer as defined by claim 30 wherein said carbon nanotubes are operative to conduct electrical charge in said solid material.

39. A solid that supports mass transfer as defined by claim 30 wherein at least a portion of said nanotubes are exposed to a surface of said solid material.

40. A solid that supports mass transfer as defined by claim 30 wherein the solid is a catalyst layer, wherein said solid material is a proton conducting layer, and further comprising catalyst particles dispersed in said proton-conducting layer.

41. A catalyst layer as defined by claim 40 wherein at least about 1% by weight of said catalyst particles are independent from said carbon nanotubes.

42. A catalyst layer as defined by claim 40 wherein at least about 5% by weight of said catalyst particles are independent from said carbon nanotubes, and wherein at least about 10% by weight of said carbon nanotubes have unobstructed inner passages.

43. A catalyst layer as defined by claim 40 wherein at least about 75% by weight of said catalyst particles are independent from said carbon nanotubes, and wherein at least about 50% by weight of said nanotubes have unobstructed inner passages.

44. A catalyst layer as defined by claim 40 wherein said catalyst particles have a diameter, and wherein said carbon nanotubes have an inside diameter equal to or smaller than said catalyst particle diameter.

45. A catalyst layer as defined by claim 40 wherein substantially all of said catalyst particles are located within a distance of about 50 nm from at least one of said carbon nanotubes.

46. A catalyst layer as defined by claim 40 wherein the catalyst layer is part of a fuel cell that includes a current collector, and wherein said proton conducting layer has a surface adjacent to said fuel cell current collector.

47. A catalyst layer as defined by claim 40 wherein said carbon nanotubes are present in a weight ratio to said catalyst particles of between about 3:

1 and about 1;

3.

48. A catalyst layer as defined by claim 40 wherein said carbon nanotubes are present in a weight ratio to said catalyst particles of between about 10:

1 and about 1;

10.

49. A catalyst layer as defined by claim 40 wherein said proton-conducting layer comprises one or more of a perfluorosulfonic acid polymer or copolymer, sulfuric acid, sulfonated and phosphated polymers, metal oxides, metal phosphates, metal sulfates, metal hydrates, and wherein said catalyst particles comprise one or more of Pt, Pd, Ir, Ru, Os, Rh, Ni, Co, Mn, Mo, W, V, Ce, and Ti.

50. A catalyst layer as defined by claim 40 wherein said proton-conducting, material is present in a weight ratio to said catalyst particles of between about 1:

20 and about 1;

2.

51. A catalyst layer as defined by claim 40 wherein substantially all of said catalyst particles are active.

52. A catalyst layer as defined by claim 40 wherein the catalyst layer has a thickness of not more than about 10 microns.

53. A catalyst layer as defined by claim 40 wherein said catalyst layer is sandwiched between an electrolyte layer and a current collector.

54. A catalyst layer as defined by claim 40 wherein said catalyst particles comprise one or more of Pt, Pd, Ir, Ru, Os, Rh, Ni, Co, Mn, Mo, and W, and wherein said catalyst particles are dispersed in the layer at a concentration of greater than about 12 mg/cm².

55. A catalyst layer as defined by claim 40 wherein said catalyst particles comprise one or more of Pt, Pd, Ir, Ru, Os, Rh, Ni, Co, Mn, Mo, and W, and wherein said catalyst particles are dispersed in the layer at a concentration of greater than about 20 mg/cm².

56. A catalyst layer as defined by claim 40 wherein said catalyst particles, comprise one or more of Pt, Pd, Ir, Ru, Os, Rh, Ni, Co, Mn, Mo, and W, and wherein said catalyst particles are dispersed in the layer at a concentration of less than about 10 mg/cm².

57. A catalyst layer as defined by claim 40 wherein the layer is porous.

58. A membrane electrode assembly comprising:

a solid electrolyte having two opposing surfaces; and

,

a catalyst layer on each of said two opposing surfaces of said solid electrolyte, each of said catalyst layers having a thickness of not more than about 500 μ

m and comprising a proton-conducting material, precious metal catalyst particles dispersed in said proton-conducting material and carbon nanotubes dispersed in said proton-conducting material, at least about 10% by weight, of said carbon nanotubes having unobstructed inner passages with a diameter of between about 6 and about 20 nm.

59. A membrane electrode assembly as defined by claim 58, wherein said membrane electrode assembly is part of a solid polymer electrolyte fuel cell, and further comprising:

an anode layer on one of said catalyst layers; and

a cathode layer on the other of said catalyst layers.

60. A method for preparing a solution useful to form a solid for supporting mass transfer, the method comprising the steps of:

dissolving a solid material into at least one solvent; and

dispersing carbon nanotubes into said at least one solvent to form the solution, at least about 1% of said carbon nanotubes having an unobstructed inner passage.

61. A method for preparing a solution as defined by claim 60 wherein at least about 10% by weight of said carbon nanotubes have an unobstructed inner passage.

62. A method for preparing a solution as defined by claim 60 wherein at least about 50% by weight of said carbon nanotubes have an unobstructed inner passage.

63. A method for preparing a solution as defined by claim 60 wherein the solution comprises a catalyst ink, wherein said solid material comprises a proton conducting material, and further comprising catalyst particles dispersed in said at least one solvent, at least about 1% by weight of said carbon nanotubes being independent of said catalyst particles in said at least one solvent.

64. A method for preparing a catalyst ink as defined by claim 63 wherein at least a portion of said catalyst particles comprise one or more of Pt, Pd, Ir, Ru, Os, Rh, Ni, Co, Mn, Mo, and W, and wherein the step of dispersing said carbon nanotubes into said at least one solvent comprises mixing between about 0.1 and about 10 parts by weight of said carbon nanotubes per part of said metal catalyst particles.

65. The method for preparing a catalyst ink as defined by claim 63 wherein said at least one solvent is protic.

66. The method for preparing a catalyst ink as defined by claim 63 wherein at least about 75% of said carbon nanotubes being independent of said catalyst particles, and wherein at least about 50% by weight of said carbon nanotubes have an unobstructed inner passage.