Gas/ion species selective membrane supported by multi-stage nano-hole array metal structure

• US 20050242022A1
• Filed: 03/25/2005
• Published: 11/03/2005
• Est. Priority Date: 03/30/2004
• Status: Active Grant

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company), Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Prinz, Friedrich B., Kang, Sangkyun, Saito, Yuji, Cha, Suk-Won, Park, Yong-Il, Su, Pei-Chen, Farvid, Ali
• Granted Patent: US 7,108,813 B2
• Time in Patent Office: Days
• US Class Current: 210/500.250
• CPC Class Codes: B01D 2325/02 Details relating to pores or porosity of the membranes
• CPC Class Codes: B01D 2325/02833 more than 10 and up to 100 nm
• CPC Class Codes: B01D 2325/04 Characteristic thickness
• CPC Class Codes: B01D 53/228 characterised by specific membranes
• CPC Class Codes: B01D 67/0062 by micromachining techniques, e.g. using masking and etching steps, photolithography
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 69/10 Supported membranes; Membrane supports
• CPC Class Codes: B01D 69/108 Inorganic support material
• CPC Class Codes: B01D 71/022 Metals
• CPC Class Codes: B01D 71/02231 Palladium
• CPC Class Codes: B01D 71/02232 Nickel
• CPC Class Codes: B01D 71/024 Oxides
• CPC Class Codes: H01M 4/861 with a gradient in the porosity
• CPC Class Codes: H01M 4/8657 layered
• CPC Class Codes: H01M 4/92 Metals of platinum group H01M4/94 , H01M4/9058 take precedence
• CPC Class Codes: H01M 8/1226 characterised by the supporting layer
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y10T 428/12028 Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, etc.]
• CPC Class Codes: Y10T 428/2944 Free metal in coating
• CPC Class Codes: Y10T 428/31678 Of metal

Abstract

An improved two-step replication process for fabrication of porous metallic membranes is provided. A negative of a porous non-metallic template is made by infiltration of a liquid precursor into the template, curing the precursor to form a solid negative, and removing the template to expose the negative. Metal is deposited to surround the exposed negative. Removal of the negative provides a porous metallic membrane having pores which replicate the pores of the original template membrane. The negative is kept immersed in a liquid at all times between removing the template and depositing the metal. This immersion eliminates damage to the negative that would be incurred in drying the negative out between these processing steps. Another aspect of the invention is metallic membranes prepared according to the preceding method. For example, metallic membranes having pores smaller on one side than on the other side of the membrane are provided.

Claims

1. Apparatus comprising:

a porous metallic membrane having opposite first and second surfaces;

wherein the membrane has a first pore size at the first surface and has a second pore size at the second surface;

wherein the second pore size is greater than the first pore size.

2. The apparatus of claim 1, wherein said first pore size is about 20 nm to about 30 nm and said second pore size is about 200 nm to about 300 nm.

3. The apparatus of claim 1, wherein said metallic membrane has a diameter greater than 1 cm.

4. The apparatus of claim 1, wherein said membrane includes two or more different metallic compositions.

5. The apparatus of claim 1, wherein said metallic membrane comprises nickel, platinum, palladium, gold, copper or an alloy or mixture thereof.

6. A supported membrane assembly comprising:

a) a porous metallic support membrane having opposite first and second surfaces;

wherein the support membrane has a first pore size at the first surface and has a second pore size at the second surface;

wherein the second pore size is greater than the first pore size; and

b) a gas or ion species selective membrane assembly in contact with the first surface.

7. The supported membrane assembly of claim 6, wherein said selective membrane assembly has a thickness less than 1 μ

m and comprises a material selected from the group consisting of;

yttrium-stabilized zirconia, gadolinium doped ceria, palladium, and barium zirconate.

8. The supported membrane assembly of claim 6, wherein said selective membrane assembly comprises a catalyst layer having a pore size of about 20 nm to about 40 nm and including a material selected from the group consisting of:

platinum, nickel, palladium, gold, and alloys or mixtures thereof.

9. The supported membrane assembly of claim 6, wherein said support membrane includes a first region including said first surface and a second region including said second surface, wherein the first region and the second region are adjacent to each other at an interface.

10. The supported membrane assembly of claim 9, wherein said first region has a thickness of about 70 nm and said first pore size is about 20 nm to about 40 nm, and wherein a pore size of said first region at said interface is about 70 nm to about 100 nm.

11. The supported membrane assembly of claim 9, wherein said second region has a thickness of about 20 μ

m to about 40 μ

m and said second pore size is about 200 nm to about 300 nm.

12. A method of fabricating a metallic membrane, the method comprising:

a) providing a porous non-metallic template membrane having opposing first and second surfaces;

b) first depositing a first metal layer on the first surface such that pores on the first surface are not blocked by the first metal layer;

c) providing a polymer negative of the template membrane and affixed to the first metal layer;

d) removing the non-metallic template membrane to expose pore-filling parts of the polymer negative;

e) second depositing a second metal onto the first metal layer such that the second metal makes contact with the pore-filling parts of the polymer negative, wherein the polymer negative is kept immersed in a liquid at all times between the removing the non-metallic template membrane and the depositing a second metal; and

f) removing the polymer negative.

13. The method of claim 12:

wherein the non-metallic template membrane comprises a first region including the first surface and a second region including the second surface;

wherein the first region has a first pore size and the second region has a second pore size;

wherein the second pore size is greater than the first pore size.

14. The method of claim 12, wherein said non-metallic template membrane comprises alumina or silicon.

15. The method of claim 12, wherein said first depositing comprises depositing two or more different metallic compositions.

16. The method of claim 12, wherein said first depositing comprises depositing about 30 nm to about 40 nm of Pt.

17. The method of claim 12, wherein said first depositing comprises RF sputtering of Pt for about 30 to 40 seconds at a deposition rate of about 1 nm/s.

18. The method of claim 12, wherein said providing a polymer negative comprises:

filling space in said template membrane with a liquid polymer precursor; and

curing the polymer precursor to provide said polymer negative.

19. The method of claim 18, wherein said polymer precursor is selected from the group consisting of methyl-methacrylate (MMA), and mixtures of MMA and poly-MMA.

20. The method of claim 18, wherein said curing comprises thermal curing or exposing said polymer precursor to ultraviolet radiation in a nitrogen ambient.

21. The method of claim 12, wherein said removing the non-metallic template membrane comprises dissolving the template membrane in an etchant, wherein said etchant is a basic solution.

22. The method of claim 12, wherein said second depositing comprises electroplating.

23. The method of claim 12, wherein said second depositing comprises depositing two or more different metallic compositions.

24. The method of claim 12, wherein said removing the polymer negative comprises dissolving the polymer negative in a solvent selected from the group consisting of acetone, toluene, methyl ethyl ketone, formaldehyde, and mixtures thereof.

25. The method of claim 12, further comprising third depositing a gas or ion species selective membrane on said first surface.

26. The method of claim 25, wherein said third depositing comprises a method selected from the group consisting of:

atomic layer deposition;

pulsed laser deposition;

sputtering of a metal followed by oxidizing the sputtered metal;

RF sputtering of a metal oxide; and

sputtering of a metal.