Nanowire-based membrane electrode assemblies for fuel cells

• US 20060188774A1
• Filed: 12/06/2005
• Published: 08/24/2006
• Est. Priority Date: 12/09/2004
• Status: Active Grant

• Current Assignee: ONED Material Incorporated
• Original Assignee: Nanosys Incorporated (Shoei Electronic Materials, Inc.)
• Inventors: Niu, Chunming, Parce, J. Wallace, Empedocles, Stephen A., Chow, Calvin Y.H.
• Granted Patent: US 7,179,561 B2
• Time in Patent Office: Days
• US Class Current: N/A
• 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 4/881 Electrolytic membranes
• CPC Class Codes: H01M 4/8846 Impregnation
• CPC Class Codes: H01M 4/8853 Electrodeposition
• CPC Class Codes: H01M 4/8867 Vapour deposition
• CPC Class Codes: H01M 4/90 Selection of catalytic material
• CPC Class Codes: H01M 4/9075 Catalytic material supported on carriers, e.g. powder carriers H01M4/8807, H01M4/881, H01M4/8814, H01M4/925 take precedence
• CPC Class Codes: H01M 4/921 Alloys or mixtures with metallic elements
• CPC Class Codes: H01M 4/925 supported on carriers, e.g. powder carriers
• CPC Class Codes: H01M 4/926 on carbon or graphite
• CPC Class Codes: H01M 8/023 Porous and characterised by the material
• CPC Class Codes: H01M 8/0232 Metals or alloys
• CPC Class Codes: H01M 8/0234 Carbonaceous material
• CPC Class Codes: H01M 8/0236 Glass; Ceramics; Cermets
• CPC Class Codes: H01M 8/0241 Composites
• CPC Class Codes: H01M 8/1004 characterised by membrane-electrode assemblies [MEA] H01M8/12 takes precedence
• CPC Class Codes: H01M 8/1007 with both reactants being gaseous or vaporised H01M8/12 takes precedence
• CPC Class Codes: H01M 8/1011 Direct alcohol fuel cells [DAFC], e.g. direct methanol fuel cells [DMFC]
• CPC Class Codes: H01M 8/1086 After-treatment of the membrane other than by polymerisation
• CPC Class Codes: Y02E 60/50 : Fuel cells
• CPC Class Codes: Y02P 70/50 : Manufacturing or production processes characterised by the final manufactured product
• CPC Class Codes: Y10S 977/762 : Nanowire or quantum wire, i.e. axially elongated structure having two dimensions of 100 nm or less
• CPC Class Codes: Y10S 977/948 : Energy storage/generating using nanostructure, e.g. fuel cell, battery

Abstract

The present invention discloses nanowires for use in a fuel cell comprising a metal catalyst deposited on a surface of the nanowires. A membrane electrode assembly for a fuel cell is disclosed which generally comprises a proton exchange membrane, an anode electrode, and a cathode electrode, wherein at least one or more of the anode electrode and cathode electrode comprise an interconnected network of the catalyst supported nanowires. Methods are also disclosed for preparing a membrane electrode assembly and fuel cell based upon an interconnected network of nanowires.

Claims

17. A nanostructured catalyst support for a membrane electrode assembly of a fuel cell comprising a network of inorganic nanowires each having a metal catalyst deposited thereon.

18. The nanostructured catalyst support of claim 17, wherein the catalyst metal comprises platinum.

19. The nanostructured catalyst support of claim 17, wherein the catalyst metal comprises platinum and ruthenium.

20. The nanostructured catalyst support of claim 17, wherein the catalyst metal is selected from the group comprising one or more of Pt, Au, Pd, Ru, Re, Rh, Os, Ir, Fe, Co, Ni, Cu, Ag, V, Cr, Mo, W and alloys or mixtures thereof.

21. The nanostructured catalyst support of claim 17, wherein the catalyst metal comprises nanoparticles having a diameter less than about 10 nm.

22. The nanostructured catalyst support of claim 17, wherein the catalyst metal comprises nanoparticles having a diameter between about 1 nm and 5 nm.

23. The nanostructured catalyst support of claim 17, wherein each nanowire in the network of nanowires is contacted by at least one or more other nanowires in the nanowire network.

24. The nanostructured catalyst support of claim 17, wherein each nanowire in the network of nanowires is physically connected to at least one or more other nanowires in the nanowire network.

25. The nanostructured catalyst support of claim 17, wherein two or more nanowires in the network of nanowires are in electrical contact with each other.

26. The nanostructured catalyst support of claim 17, wherein two or more nanowires in the network of nanowires are in electrical contact with at least one or more of each other or a bipolar plate.

27. The nanostructured catalyst support of claim 17, wherein the nanowires are made from conducting or semiconducting carbides, nitrides and oxides.

28. The nanostructured catalyst support of claim 17, wherein the nanowires are selected from the group comprising RuO₂, SiC, GaN, TiO₂, SnO₂, WC_x, MoC_x, ZrC, WN_x, and MoN_x nanowires.

29. The nanostructured catalyst support of claim 17, wherein the nanowires in the network of nanowires are each functionalized with at least a first chemical binding moiety.

30. The nanostructured catalyst support of claim 17, wherein the nanowires in the network of nanowires are cross-linked together at points where such nanowires contact or are proximal to others of said nanowires.

31. The nanostructured catalyst support of claim 17, further comprising a proton conducting polymer in contact with the nanowires.

32. The nanostructured catalyst support of claim 17, wherein the membrane electrode assembly is a component in a direct methanol fuel cell (DFMC).

33. The nanostructured catalyst support of claim 17, wherein the nanowire network defines a plurality of pores between the nanowires in the network, wherein the plurality of pores have an effective pore size of less than 1 μ

m.

34. The nanostructured catalyst support of claim 17, wherein the nanowire network defines a plurality of pores between the nanowires in the network, wherein the plurality of pores have an effective pore size of less than 0.05 μ

m.

35. The nanostructured catalyst support of claim 17, wherein the nanowire network defines a plurality of pores between the nanowires in the network, wherein the plurality of pores have an effective pore size of between about 0.002 to 0.05 μ

m.

36. The nanostructured catalyst support of claim 17, wherein the nanowires in the nanowire network are oriented in a parallel array substantially perpendicular to a surface of one or more bipolar plate or proton exchange membrane of the membrane electrode assembly.

37. The nanostructured catalyst support of claim 17, wherein the amount of deposited catalyst metal is about 10% to 85% by weight based on the total amount of catalyst metal and nanowire material.

38. The nanostructured catalyst support of claim 17, wherein the amount of deposited catalyst metal is about 20% to 40% by weight based on the total amount of catalyst metal and nanowire material.

39. The nanostructured catalyst support of claim 17, wherein the plurality of nanowires comprise a semiconductor material selected from group IV, group II-VI, group III-V semiconductors and alloys and mixtures thereof.

40. A membrane electrode assembly, comprising a proton exchange membrane, an anode electrode, and a cathode electrode, wherein at least one or more of the anode electrode and cathode electrode comprise an interconnected network of nanowires.

1. Inorganic nanowires for use in a fuel cell comprising a metal catalyst deposited on a surface of the nanowires.

2. The inorganic nanowires of claim 1, wherein the metal catalyst is selected from the group comprising one or more of Pt, Au, Pd, Ru, Re, Rh, Os, Ir, Fe, Co, Ni, Cu, Ag, V, Cr, Mo, W and alloys or mixtures thereof.

3. The inorganic nanowires of claim 1, wherein the nanowires are branched structures.

4. The inorganic nanowires of claim 1, wherein the metal catalyst comprises nanometer-sized catalyst particles having a diameter between about 1 and 10 nm.

5. The inorganic nanowires of claim 1, wherein the metal catalyst is deposited on the nanowires by using a process selected from the group comprising chemical vapor deposition, electrochemical deposition, electroless chemical plating, physical vapor deposition, solution impregnation and precipitation, colloid particle absorption and desorption, binding through a chemical linker, atomic layer deposition, and combinations thereof.

6. The inorganic nanowires of claim 1, wherein the nanowires are resistant to degradation in a weak acid.

7. A fuel cell using the inorganic nanowires of claim 1 in which the nanowire are deposited on the surface of a proton exchange membrane.

8. A fuel cell using the inorganic nanowires of claim 1 in which the nanowires are deposited on the surface of one or more bipolar plates of the fuel cell.

9. A fuel cell using the inorganic nanowires of claim 1 in which the nanowires are directly grown on one or more bipolar plates of the fuel cell.

10. The fuel cell according to claim 9 wherein the nanowires are oriented substantially perpendicular to a surface of the one or more bipolar plates.

11. A fuel cell using the inorganic nanowires of claim 1 in which the nanowires are directly grown on a proton exchange membrane of the fuel cell.

12. The fuel cell according to claim 11 wherein the nanowires are oriented substantially perpendicular to a surface of the proton exchange membrane.

13. The fuel cell according to claims 7, 8, 9, or 11 wherein the nanowires are interconnected with a polymer electrolyte network.

14. The fuel cell according to claim 13, wherein the nanowires are in electrical contact with one or more bipolar plates and the polymer electrolyte is in contact with the proton exchange membrane.

15. The fuel cell according to claims 7, 8, 9, or 11 wherein the nanowires are derivatized with at least a first functional group which binds to the metal catalyst.

16. The fuel cell according to claim 15, wherein the nanowires are derivatized with at least a second functional group which interacts with the polymer electrolyte to promote substantially uniform wetting of the electrolyte on the surface of the nanowires.

41. The membrane electrode assembly of claim 40, wherein the plurality of nanowires are attached to a portion of the overall surface area of one or more of an anode and cathode bipolar plate by having been grown on the portion of the surface area.

42. The membrane electrode assembly of claim 41, wherein the plurality of nanowires are electrically coupled to one or more of the anode and cathode bipolar plates and the proton exchange membrane.

43. The membrane electrode assembly of claim 40, wherein each of the nanowires has a metal catalyst deposited thereon.

44. The membrane electrode assembly of claim 43, wherein the catalyst metal comprises platinum.

45. The membrane electrode assembly of claim 43, wherein the catalyst metal comprises platinum and ruthenium.

46. The membrane electrode assembly of claim 43, wherein the catalyst metal is selected from the group comprising one or more of Pt, Au, Pd, Ru, Re, Rh, Os, Ir, Fe, Co, Ni, Cu, Ag, V, Cr, Mo, W and alloys or mixtures thereof.

47. The membrane electrode assembly of claim 43, wherein the catalyst metal comprises nanoparticles having a diameter between about 1 and 10 nm.

48. The membrane electrode assembly of claim 40, wherein each nanowire in the network of nanowires is contacted by at least one other nanowire in the nanowire network.

49. The membrane electrode assembly of claim 40, wherein each nanowire in the network of nanowires is electrically connected to one or more other nanowires in the nanowire network.

50. The membrane electrode assembly of claim 40, wherein at least one or more nanowires in the network of nanowires has a branched structure.

51. The membrane electrode assembly of claim 47, wherein the nanowires in the network of nanowires are each functionalized with a first chemical binding moiety which binds the catalyst nanoparticles.

52. The membrane electrode assembly of claim 40, wherein the nanowires in the network of nanowires are each functionalized with a chemical binding moiety which binds a proton conducting polymer coating to the nanowires.

53. The membrane electrode assembly of claim 52, wherein the proton conducting polymer coating comprises Nafion®

and its derivatives.

54. (canceled)

55. The membrane electrode assembly of claim 40, wherein the membrane electrode assembly is a component in a hydrogen fuel cell.

56. A fuel cell comprising the membrane electrode assembly of claim 40.

57. A direct methanol fuel cell comprising the membrane electrode assembly of claim 40.

58. A hydrogen fuel cell comprising the membrane electrode assembly of claim 40.

97. A fuel cell using the inorganic nanowires of claim 1 in which one or more of an anode electrode and a cathode electrode of the fuel cell comprises a conductive grid or mesh having the inorganic nanowires deposited thereon.

98. The fuel cell according to claim 97, wherein the conductive grid or mesh is made from one or more of a metal, a semiconductor, or a conductive polymer material.

99. A membrane electrode assembly using the inorganic nanowires of claim 1 in which an anode electrode of the membrane electrode assembly comprises the inorganic nanowires arranged in an interconnecting network of wires in which each wire is physically and/or electrically connected to at least one other wire in the network.

100. A fuel cell using the membrane electrode assembly of claim 40, wherein the fuel cell comprises first and second bipolar plates disposed on either side of the membrane electrode assembly and does not include a gas diffusion layer located between the membrane electrode assembly and either the first or second bipolate.

54-1. The membrane electrode assembly of claim 40, wherein the membrane electrode assembly is a component in a direct methanol fuel cell (DFMC).

59. A method for preparing a fuel cell membrane electrode assembly, comprising (a) associating a catalyst metal selected from the group comprising one or more of chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), tin (Sn), aluminum (Al), and combinations thereof, with a plurality of inorganic nanowires to form a plurality of inorganic nanowires with associated catalyst metal, and (b) forming a membrane electrode assembly comprising the plurality of inorganic nanowires with associated catalyst metal.

60. The method of claim 59, further comprising annealing the nanowires with associated catalyst metal prior to forming the membrane electrode.

61. The method of claim 59, wherein the plurality of inorganic nanowires are derivatized with at least a first functional group which binds the catalyst metal.

62. The method of claim 61, wherein the first functional group includes a group selected from a nitric acid, a carboxylic acid group, a hydroxyl group, an amine group, and a sulfonic acid group.

63. The method of claim 61, wherein the first functional group is coupled to the nanowires via a linking group.

64. The method of claim 63, wherein the nanowires with associated catalyst metal are treated with heat, vacuum, chemical agents or a combination thereof to remove the linking group to improve electrical contact between the metal catalyst and nanowires.

65. The method of claim 64, wherein the nanowires with associated catalyst metal are annealed to remove the linking group to improve electrical contact between the metal catalyst and nanowires.

66. The method of claim 59, wherein associating is done by a method selected from the group comprising chemical vapor deposition, electrochemical deposition, physical vapor deposition, solution impregnation and precipitation, atomic layer deposition, colloid absorption and desorption, and combinations thereof.

67. The method of claim 59, wherein the catalyst metal comprises platinum.

68. The method of claim 59, wherein the catalyst metal comprises platinum and ruthenium.

69. The method of claim 59, wherein the plurality of nanowires are formed into an interconnected network of nanowires in which two or more nanowires in the network are physically and/or electrically coupled to each other.

70. The method of claim 59, wherein the associating is done by chemical deposition of a catalyst metal precursor.

71. The method of claim 69, further comprising cross-linking the plurality of nanowires together at points where such nanowires contact or are proximal to others of said nanowires.

72. The method of claim 59, wherein the catalyst metal is in the form of metal nanoparticles on the inorganic nanowires.

73. The method of claim 59, wherein the catalyst metal is deposited on the nanowires in the form of one or more of islands, stripes or rings on the surface of the nanowires.

74. The method of claim 59, wherein the forming is done on a proton exchange membrane by a method selected from the group comprising spray/brush painting, solution coating, casting, electrolytic deposition, filtering a fluid suspension of the nanowires, and combinations thereof.

75. The method of claim 69, wherein the nanowires are formed into an interconnected network of nanowires by filtering a fluid suspension of the nanowires.

76. The method of claim 59, further comprising mixing an ionomeric resin with the plurality of inorganic nanowires with associated catalyst metal.

77. The method of claim 76, wherein the ionomeric resin comprises a perfluorosulfonic acid/PTFE copolymer.

78. The method of claim 76, wherein the plurality of inorganic nanowires are derivatized with at least a first chemical binding moiety which binds the ionomeric resin.

79. The method of claim 59, wherein the nanowires are in contact with at least one or more of a proton exchange membrane or a bipolar plate after said forming.

80. A method of making a membrane electrode assembly for a fuel cell, comprising:

forming nanowires on a growth substrate;

transferring the nanowires from the growth substrate into a fluid suspension;

depositing one or more catalyst metals on the nanowires to form a nanowire supported catalyst;

filtering the fluid suspension of nanowires to create a porous sheet of interconnected nanowires;

infiltrating the sheet of interconnected nanowires with an ionomer; and

combining the sheet of interconnected nanowires with a polymer membrane to form the membrane electrode assembly.

81. The method of claim 80, wherein said depositing one or more catalyst metal particles comprises depositing a metal selected from the group comprising Pt, Au, Pd, Ru, Re, Rh, Os, Ir, Fe, Co, Ni, Cu, Ag, V, Cr, Mo, W and alloys or mixtures thereof.

82. The method of claim 80, wherein said depositing comprises an electrodeposition process.

83. The method of claim 80, wherein said infiltrating comprises depositing a solubilized perfluorosulfonate ionomer into the spare space between nanowires.

84. The method of claim 80, further comprising forming a proton exchange membrane fuel cell utilizing the formed electrode, comprising:

adding first and second bipolar plates on either side of the polymer membrane; and

sealing the bipolar plates to form the proton exchange membrane fuel cell.

85. The method of claim 80, wherein the porous sheet of interconnected nanowires has a porosity of from about 30% to 95%.

86. The method of claim 80, wherein the porous sheet of interconnected nanowires has a porosity of from about 40% to 60%.

87. The method of claim 80, further comprising derivatizing the nanowires with a first functional group prior to said depositing the metal catalyst on the nanowires.

88. The method of claim 87, wherein the first functional group comprises one or more of a nitric acid group, a carboxylic acid group, a hydroxyl group, an amine group, and a sulfonic acid group.

89. The method of claim 80, further comprising derivatizing the nanowires with a functional group which binds the ionomer to the nanowires.

90. The method of claim 89, wherein the functional group is selected from the group comprising a short hydrocarbon, fluorocarbon, and branched hydrocarbon chain.

91. The method of claim 80, wherein the nanowires comprise semiconducting, conducting, carbide, nitride, or oxide nanowires.

92. The method of claim 80, wherein the nanowires are selected from the group comprising RuO₂, SiC, GaN, TiO₂, SnO₂, WC_x, MoC_x, ZrC, WN_x, and MoN_x nanowires.

93. The method of claim 80, wherein said filtering comprises vacuum filtration of the nanowire fluid suspension over a polyvinylidene fluoride (PVDF) membrane.

94. The method of claim 80, wherein said depositing is performed prior to said filtering.

95. The method of claim 80, wherein said depositing is performed after said filtering.

96. The method of claim 80, wherein the nanowires are derivatized with a first functional group and the catalyst is derivatized with a second functional group and the first and second functional groups are the same or different and wherein one of the first and second functional groups binds the ionomer and/or promotes wetting of the ionomer on the surface to which the functional group is attached.

101. A bipolar plate for a fuel cell comprising a plurality of inorganic nanowires deposited thereon.

102. A nanowire for use in a fuel cell comprising a carbon nanotube or silicon nanowire core and one or more shell layers disposed about the core, wherein the outermost shell layer comprises silicon carbide (SiC) having a catalyst metal deposited thereon.

103. The nanowire of claim 102, wherein the SiC shell layer is functionalized with a proton conducting coating.

104. The nanowire of claim 103, wherein the proton conducting coating comprises a perfluorinated sulfonated hydrocarbon molecule.