Low platinum fuel cells, catalysts, and method for preparing the same

• US 20060172179A1
• Filed: 12/15/2005
• Published: 08/03/2006
• Est. Priority Date: 09/08/2003
• Status: Active Grant

• Current Assignee: Intematix Corporation
• Original Assignee: Intematix Corporation
• Inventors: Gu, Tao, Dong, Yi, Li, Yi-Qun, Wang, Ning, Omstead, Thomas R.
• Granted Patent: US 8,211,593 B2
• Time in Patent Office: Days
• US Class Current: 429/482
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: H01B 1/04 mainly consisting of carbon-silicon compounds, carbon or silicon
• CPC Class Codes: H01B 1/122 Ionic conductors
• CPC Class Codes: H01M 2008/1095 Fuel cells with polymeric electrolytes
• CPC Class Codes: H01M 4/8825 Methods for deposition of the catalytic active composition
• CPC Class Codes: H01M 4/8892 Impregnation or coating of the catalyst layer, e.g. by an ionomer
• CPC Class Codes: H01M 4/90 Selection of catalytic material
• CPC Class Codes: H01M 4/9083 on carbon or graphite
• CPC Class Codes: H01M 4/921 Alloys or mixtures with metallic elements
• CPC Class Codes: H01M 4/926 on carbon or graphite
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

This invention provides novel fuel cell electrodes and catalysts comprising a series of catalytically active thin-film metal alloys with low platinum concentration supported on nanostructured materials (nanoparticles). Processing of the electrodes and catalysts can include electrodeposition methods, and high-pressure coating techniques. In certain embodiments, an integrated gas-diffusion/electrode/catalyst layer can be prepared by processing catalyst thin films and nanoparticles into gas-diffusion media such as Toray or SGL carbon fiber papers. The catalysts can be placed in contact with an electrolyte membrane for PEM fuel cell applications.

Claims

1. A composition comprising a substrate bearing nanoparticles, wherein the nanoparticles are coated with an ionomer.

2. The composition of claim 1, wherein the substrate comprises a plurality of conductive fibers.

3. The composition of claim 1, wherein the ionomer comprises a perfluorocarbonsulfonic acid ionomer.

4. The composition of claim 2, wherein the conductive fibers comprise carbon fibers.

5. The composition of claim 1, wherein the nanoparticles are selected from the group consisting of:

nanotubes, nanofibers, nanohorns, nanopowders, nanospheres, and quantum dots.

6. The composition of claim 1, wherein the nanoparticles comprise carbon nanotubes.

7. The composition of claim 2, wherein the plurality of conductive fibers comprise a porous electrode.

8. The composition of claim 4, wherein the carbon fibers comprise a porous electrode.

9. The composition of claim 4, wherein the carbon fibers comprise a carbon paper, a carbon cloth or a carbon-impregnated polymer.

10. The composition of claim 2, wherein the plurality of conductive fibers comprise a porous metal sheet.

11. The composition of claim 6, wherein the carbon nanotubes are seeded with one or more catalysts comprising one or more materials selected from the group consisting of Co, Ni, V, Cr, Pt, Ru, Mo, W, Ta, and Zr.

12. The composition of claim 6, wherein the carbon nanotubes are seeded with one or more catalysts selected from the group consisting of Fe_xNi_yCo_1-x-y where 0≦

x≦

1 and 0≦

y≦

1, Co_1-xMo_x where 0≦

x≦

0.3, Co_1-x-yNi_xMo_y where 0.1≦

x≦

0.7 and 0≦

y≦

0.3, Co_1-x-y-zNi_xV_yCr_z where 0≦

x≦

0.7, 0≦

y≦

0.2 and 0≦

z≦

0.2, Ni_1-x-yMo_xAl_y where 0≦

x≦

0.2 and 0≦

y≦

0.2, and Co_1-x-yNi_xAl_y where 0≦

x≦

0.7 and 0≦

y≦

0.2.

13. The composition of claim 6, wherein the carbon nanotubes are seeded with one or more catalysts selected from the group consisting of:

Co_8.8Mo_1.2, Co_2.2Ni_5.6Mo_2.2, Co_5.7Ni_2.1V_1.1Cr_1.1, Ni_8.0Mo_1.0Al_1.0, and CO_6.4Ni_2.4Al_1.2.

14. The composition of claim 6, wherein the nanoparticles are nanotubes having a length less than 50 μ

m and a diameter less than about 500 nm.

15. The composition of claim 6, wherein the nanoparticles are nanotubes having a diameter in the range from about 1 nm to about 100 nm.

16. The composition of claims 1 or 6, wherein the nanoparticles are coated with a substantially continuous thin film comprising a platinum alloy.

17. The composition of claim 16, wherein the thin film partially covers the nanoparticles.

18. The composition of claim 16, wherein the nanoparticles are fully coated with the thin film.

19. The composition of claim 16, wherein the thin film ranges in thickness from about 1 to about 1000 angstroms.

20. The composition of claim 19, wherein the thin film ranges in thickness from about 5 to about 500 angstroms.

21. The composition of claims 1 or 6, wherein the nanoparticles are coated with a non-continuous thin film comprising a platinum alloy.

22. The composition of claim 21, wherein the thin film comprises islands ranging in thickness from about 5 to about 100 angstroms and ranging in area from about 1 to 10⁴ nm².

23. The composition of claim 19, wherein the thin film ranges in thickness from about 5 to about 100 angstroms.

24. The composition of claim 23, wherein the thin film comprises an alloy comprising platinum (Pt), vanadium (V), and one or more metals selected from the group consisting of Co, Ni, Mo, Ta, W, and Zr.

25. The composition of claim 24, wherein the thin film comprises an alloy comprising platinum (Pt), vanadium (V), and one or more metals selected from the group consisting of Co, and Ni.

26. The composition of claim 24, wherein platinum comprises from about 12% up to about 99% mole ratio or atomic percentage of the alloy.

27. The composition of claim 24, wherein platinum comprises up to about 50% mole ratio or atomic percentage of the alloy.

28. The composition of claim 24, wherein the alloy contains platinum, vanadium, nickel, and cobalt.

29. The composition of claim 24, wherein the thin film comprises an alloy having the formula:

Pt_xV_yCo_zNi_w

wherein;

x is greater than 0.06 and less than 1;

y, z, and w are independently greater than zero and less than 1;

x+y+z+w=1.

30. The composition of claim 29, wherein x is 0.12.

31. The composition of claim 29, wherein x is 0.12, y is 0.07, z is 0.56, and w is 0.25.

32. A composition comprising a substrate substantially coated with a polytetrafluoroethylene and bearing a plurality of nanoparticles, the nanoparticles substantially coated with an ionomer.

33. The composition of claim 32, wherein the substrate comprises conductive fibers.

34. The composition of claim 33, wherein the ionomer comprises a perfluorocarbonsulfonic acid ionomer.

35. The composition of claim 32, wherein the nanoparticles are selected from the group consisting of nanotubes, nanofibers, nanohorns, nanopowders, nanospheres, and quantum dots.

36. The composition of claim 35, wherein the nanoparticles comprise carbon nanotubes.

37. The composition of claim 36, wherein the carbon nanotubes are seeded with one or more catalysts comprising one or more materials selected from the group consisting of Co, Ni, V, Cr, Pt, Ru, Mo, W, Ta, and Zr.

38. The composition of claim 36, wherein the carbon nanotubes are seeded with one or more catalysts selected from the group consisting of Fe_xNi_yCo_1-x-y where 0≦

x≦

1 and 0≦

y≦

1, Co_1-xMo_x where 0≦

x≦

0.3, Co_1-x-yNi_xMo_y where 0.1≦

x≦

0.7 and 0≦

y≦

0.3, Co_1-x-y-zNi_xV_yCr_z where 0≦

x≦

0.7, 0≦

y≦

0.2 and 0≦

z≦

0.2, Ni_1-x-yMo_xAl_y where 0≦

x≦

0.2 and 0≦

y≦

0.2, and Co_1-x-yNi_xAl_y where 0≦

x≦

0.7 and 0≦

y≦

0.2.

39. The composition of claim 36, wherein the carbon nanotubes are seeded with one or more catalysts selected from the group consisting of Co_8.8Mo_1.2, Co_2.2Ni_5.6Mo_2.2, Co_5.7Ni_2.1V_1.1Cr_1.1, Ni_8.0Mo_1.0Al_1.0, and Co_6.4Ni_2.4AI_1.2.

40. The composition of claim 36, wherein the nanoparticles are nanotubes having a length less than 50 μ

m and a diameter less than about 100 nm.

41. The composition of claim 36, wherein the nanoparticles are nanotubes having a diameter in the range from about 1 nm to about 100 nm.

42. The composition of claim 36, wherein the nanoparticles are coated with a substantially continuous thin film comprising a platinum alloy.

43. A method of coating a plurality of nanoparticles with an ionomer, the method comprising:

contacting the nanoparticles with the ionomer;

placing the nanoparticles in the pressure vessel; and

,

pressurizing the pressure vessel, whereby said pressurizing enhances coating of the nanoparticles with the ionomer.

44. The method of claim 43, wherein the nanoparticles are selected from the group consisting of nanotubes, nanofibers, nanohorns, nanopowders, nanospheres, and quantum dots.

45. The method of claim 44, wherein the nanoparticles are carbon nanotubes.

46. The method of claim 45, wherein the carbon nanotubes are seeded with one or more catalysts comprising one or more materials selected from the group consisting of Co, Ni, V, Cr, Pt, Ru, Mo, W, Ta, and Zr.

47. The method of claim 45, wherein the carbon nanotubes are seeded with one or more catalysts selected from the group consisting of Fe_xNi_yCo_1-x-y where 0≦

x≦

1 and 0≦

y≦

1, Co_1-xMo_x where 0≦

x≦

0.3, Co_1-x-yNi_xMo_y where 0.1≦

x≦

0.7 and 0≦

y≦

0.3, Co_1-x-y-zNi_xV_yCr_z where 0≦

x≦

0.7 and 0≦

y≦

0.2, 0≦

z≦

0.2, Ni_1-x-yMo_xAl_y where 0≦

x≦

0.2 and 0≦

y≦

0.2, and Co_1-x-yNi_xAl_y where 0≦

x≦

0.7 and 0≦

y≦

0.2.

48. The method of claim 45, wherein the carbon nanotubes are seeded with one or more catalysts selected from the group consisting of Co_8.8Mo_1.2, Co_2.2Ni_5.6Mo_2.2, Co_5.7Ni_2.1V_1.1Cr_1.1, Ni_8.0Mo_1.0Al_1.0, and Co_6.4Ni_2.4Al_1.2.

49. The method of claim 43, further comprising contacting the nanoparticles with additional ionomer and pressurizing the nanoparticles again to increase the thickness or weight percentage of the ionomer coating the nanoparticles.

50. The method of claim 43, further comprising drying the nanoparticles.

51. The method of claim 43, further comprising pretreating the nanoparticles by exposure to a vacuum or by sonication.

52. The method of claim 43, further comprising pretreating the nanoparticles by etching in an argon plasma.

53. The method of claim 52, further comprising controlling the depth of ionomer coating by adjusting the extent of said etching.

54. The method of claim 43, wherein said contacting comprises spraying or brushing the ionomer onto the nanoparticles.

55. The method of claim 43, wherein said pressurizing comprises pressurizing the vessel to a pressure of at least about 100 psi.

56. The method of claim 54, wherein said pressurizing comprises contacting the nanoparticles with isopropyl alcohol.

57. The method of claim 43, wherein the pressure vessel is pressurized by introducing a pressurized gas, or by applying force to a liquid with a mechanically driven piston.

58. The method of claim 43, wherein the pressure vessel is pressurized using an impact or an explosive.

59. The method of claim 43, wherein said contacting the nanoparticles with the ionomer precedes said placing the nanoparticles in the pressure vessel.

60. The method of claim 43, wherein the ionomer comprises a polymer or copolymer.

61. The method of claim 43, wherein the ionomer comprises a perfluorocarbonsulfonic acid ionomer.

62. The method of claim 43, wherein the nanoparticles are attached to a substrate.

63. The method of claim 62, wherein the substrate comprises a plurality of conductive fibers.

64. The method of claim 63, wherein the conductive fibers comprise carbon fibers.

65. The method of claim 63, wherein the plurality of conductive fibers comprise a porous electrode.

66. The method of claim 63, wherein the plurality of conductive fibers comprise a carbon paper, or a carbon cloth, or a carbon-impregnated polymer.

67. The method of claim 63, wherein the plurality of conductive fibers comprise a porous metal sheet.

73. The fuel cell electrode of claim 72, wherein the nanoparticles are coated with the ionomer according to the method of claim 43.

68. A method of forming a nanoparticle composite material, the method comprising:

combining a collection of nanoparticles with a liquefied polymer to form a mixture; and

,

pressurizing the mixture to form a composite of the polymer and nanoparticle material.

69. The method of claim 68, wherein said pressurizing comprises pressurizing the mixture to a pressure of at least about 100 psi.

70. The method of claim 68, wherein the nanoparticles comprise carbon nanotubes.

71. The method of claim 68, wherein the liquefied polymer comprises an ionomer or a perfluorocarbonsulfonic acid ionomer.

72. A fuel cell electrode comprising:

a porous conductive substrate, the substrate bearing a plurality of nanoparticles, the nanoparticles comprising an ionomer coat.

74. The fuel cell electrode of claim 72, wherein the nanoparticles are selected from the group consisting of:

nanotubes, nanofibers, nanohoms, nanopowders, nanospheres, and quantum dots.

75. The fuel cell electrode of claim 72, wherein the nanoparticles are carbon nanotubes.

76. The fuel cell electrode of claim 72, wherein the electrode comprises a porous electrode.

77. The fuel cell electrode of claim 72, wherein the porous conductive substrate comprises a plurality of carbon fibers.

78. The fuel cell electrode of claim 77, wherein the plurality of carbon fibers comprise a carbon paper, a carbon cloth or a carbon-impregnated polymer.

79. The fuel cell electrode of claim 72, wherein the porous conductive substrate comprises a coating of a polytetrafluoroethylene.

80. The fuel cell electrode of claim 72, wherein the porous conductive substrate comprises a coating of aluminum oxide treated with perfluoroalkylsilane or similar compounds.

81. The fuel cell electrode of claim 72, wherein the porous conductive substrate comprises a porous metal sheet.

82. The fuel cell electrode of claim 72, wherein the nanoparticles comprise a substantially continuous thin film coat comprising platinum or a platinum alloy.

83. The fuel cell electrode of claim 72, wherein the ionomer comprises a perfluorocarbonsulfonic acid ionomer.

84. The fuel cell electrode of claim 72, further comprising Pt or a Pt alloy substantially coating the nanoparticles.

85. A vapor deposition system comprising:

a plurality of substrates;

a plurality of chambers comprising two or more vapor deposition chambers; and

,

a drive mechanism capable of transporting one or more of the substrates between two or more of the vapor deposition chambers;

wherein one or more materials can be deposited on the one or more substrates in each of two or more of the deposition chambers.

86. The system of claim 85, wherein the plurality of substrates comprises from 2 to about 20 substrates.

87. The system of claim 85, wherein the substrates comprise a porous material selected from the group consisting of:

carbon fiber papers, carbon fiber cloths, and porous electrodes.

88. The system of claim 85, wherein the system comprises three or more vapor deposition chambers.

89. The system of claim 85, wherein the plurality of chambers comprise one or more chemical vapor deposition (CVD) chambers, one or more physical vapor deposition (PVD) chambers or a plasma etching chamber.

90. The system of claim 85, wherein the plurality of chambers comprise a PVD chamber comprising a Ni electrode, a CVD chamber configured to grow carbon nanotubes, and a PVD chamber comprising a Pt electrode.

91. The system of claim 90, wherein the chamber comprising the Ni electrode further comprises a heater capable of heating the substrate to a temperature ranging from about 500°

C. to about 1500°

C.

92. The system of claim 90, wherein the CVD chamber comprises a radiant heater or an ohmic heater that provides electric current to the one or more substrates.

93. The system of claim 85, wherein the drive mechanism comprises a conveyor belt.

94. The system of claim 85, further comprising one or more substrate loadlock stations.

95. The system of claim 94, wherein the system comprises two or more multi-pallet loadlock stations.

96. The system of claim 85, further comprising one or more slit valves between two or more chambers and capable of hermetically sealing the two or more deposition chambers from each other.

97. The system of claim 85, wherein at least one of the deposition chambers comprises two or more electrodes.

98. The system of claim 97, wherein the chamber comprising two or more electrodes further comprises a transfer belt that moves the one or more substrates for sequential exposure to plasma from the two or more electrodes in turn.

99. A method of depositing layers on a substrate using the system of claim 85.

100. The method of claim 99, wherein two or more materials are separately deposited in two or more chambers onto each of two or more substrates while the chambers remain under a vacuum pressure.

101. A method of preparing an electrode, the method comprising:

forming a plurality of nanotubes on a porous substrate; and

electrodepositing a metal onto the nanotubes.

102. The method of claim 101, wherein the nanotubes comprise carbon nanotubes.

103. The method of claim 101, wherein the substrate comprises a plurality of conductive fibers.

104. The method of claim 101, wherein the plurality of conductive fibers comprise carbon fibers.

105. The method of claim 104, wherein the carbon fibers comprise a porous electrode.

106. The method of claim 101, wherein the metal is selected from the group consisting of:

platinum (Pt), vanadium (V), Co, Ni, Mo, Ta, W, Zr, and alloys thereof.

107. The method of claim 101, wherein said electrodeposition comprises exposure of the nanotubes to a pulsed voltage or pulsed current in a solution of the metal.

108. The method of claim 101, further comprising coating the electrode with a hydrophobic material and plasma etching the hydrophobic material from the nanotubes.

109. The method of claim 101, further comprising forming a seed layer on the nanotubes before said electrodeposition.

110. The method of claim 109, wherein said forming comprises sputtering or vapor deposition of the seed layer onto the nanotubes.

111. The method of claim 109, wherein the seed layer comprises a thickness of about 25 Å

or less.

112. The method of claim 101, wherein said elecrtodeposition comprises:

exposing the nanotubes to a current in a lower conductivity solution of the metal to obtain a shallower deposition of the metal onto the nanotubes or exposing the nanotubes to a current in a higher conductivity solution of the metal to obtain a deeper deposition of the metal onto the nanotubes.

113. The method of claim 112, wherein the conductivity is controlled by adjusting a pH of the solution or a concentration of supporting electrolyte.

114. The method of claim 101, further comprising controlling the depth of said electrodeposition by saturating the nanotubes with a low ionic strength solution before placing the nanotubes in an electrolyte comprising the metal;

wherein said controlling comprises adjusting a delay time between said placing and initiating said electrodepositing.

115. The method of claim 101, wherein said electrodepositing takes place in a plating solution comprising isopropanol, thereby improving wettability of the nanotubes in the solution.

116. The method of claim 101, further comprising heating the nanotubes at a temperature 300°

C. or more until the nanotubes are converted to a more hydrophilic form.

117. The method of claim 101, wherein the electrode comprises a fuel cell electrode.

118. A method of preparing an electrode, the method comprising:

providing an electrode comprising a substrate layer bearing nanostructures;

contacting the nanostructures with a hydrophobic material, whereby all or part of the nanostructures are coated with the hydrophobic material; and

,

removing all or part of the hydrophobic material coating from the nanostructures by plasma etching.

119. The method of claim 118, wherein the electrode comprises a fuel cell electrode.

120. The method of claim 118, wherein the substrate layer comprises a porous layer of conductive fibers.

121. The method of claim 120, wherein the fibers comprise carbon fibers.

122. The method of claim 118, wherein the nanostructures are selected from the group consisting of:

nanotubes, nanofibers, nanohorns, nanopowders, nanospheres, carbon nanotubes and quantum dots.

123. The method of claim 118, wherein said hydrophobic material comprises a polytetrafluoroethylene or an aluminum oxide.

124. The method of claim 118, wherein the plasma etching comprises argon plasma etching.

125. The method of claim 118, further comprising controlling a depth of etching by adjusting a time of said etching or by adjusting a plasma current.

126. The method of claim 118, further comprising:

contacting the nanostructures with an ionomer; and

,

exposing the nanostructures to a high pressure.

127. The method of claim 118, further comprising:

electrodepositing a metal onto the nanostructures.