Electrode-Supported Solid State Electrochemical Cell

• US 20080308975A1
• Filed: 08/26/2008
• Published: 12/18/2008
• Est. Priority Date: 05/22/2000
• Status: Active Grant

• Current Assignee: Acumentrics SOFC Corporation (Acumentrics, Inc.)
• Original Assignee: Acumentrics Corporation (Acumentrics, Inc.)
• Inventors: Brown, Michael, Murray, Tracy, Sammes, Nigel, Ziegler, Warren
• Granted Patent: US 7,659,025 B2
• Time in Patent Office: Days
• US Class Current: 264/563
• CPC Class Codes: G01N 27/419 Measuring voltages or currents with a combination of oxygen pumping cells and oxygen concentration cells
• CPC Class Codes: H01M 2004/8684 Negative electrodes
• CPC Class Codes: H01M 2008/1293 Fuel cells with solid oxide electrolytes
• CPC Class Codes: H01M 2300/0077 based on zirconium oxide
• CPC Class Codes: H01M 4/8605 Porous electrodes
• CPC Class Codes: H01M 4/8626 characterised by the form
• CPC Class Codes: H01M 4/8642 Gradient in composition
• CPC Class Codes: H01M 4/8652 as mixture
• CPC Class Codes: H01M 4/8657 layered
• CPC Class Codes: H01M 4/8864 Extrusion
• CPC Class Codes: H01M 4/8875 Methods for shaping the electrode into free-standing bodies, like sheets, films or grids, e.g. moulding, hot-pressing, casting without support, extrusion without support
• CPC Class Codes: H01M 4/8885 Sintering or firing
• CPC Class Codes: H01M 4/9016 Oxides, hydroxides or oxygenated metallic salts
• CPC Class Codes: H01M 4/9025 Oxides specially used in fuel cell operating at high temperature, e.g. SOFC
• CPC Class Codes: H01M 4/9033 Complex oxides, optionally doped, of the type M1MeO3, M1 being an alkaline earth metal or a rare earth, Me being a metal, e.g. perovskites
• CPC Class Codes: H01M 4/9041 Metals or alloys H01M4/92 takes precedence
• CPC Class Codes: H01M 4/9066 of metal-ceramic composites or mixtures, e.g. cermets
• CPC Class Codes: H01M 8/1231 with both reactants being gaseous or vaporised
• CPC Class Codes: H01M 8/1246 the electrolyte consisting of oxides
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02P 70/50 : Manufacturing or production processes characterised by the final manufactured product

Abstract

A process for manufacturing a solid oxide fuel cell involves forming a tubular anode comprising an electrolyte substance and an oxide of an electrochemically active metallic substance without a distinct pore forming substance, sintering the tubular anode, forming an electrolyte onto the sintered anode, forming a cathode onto the electrolyte, and after forming the electrolyte and the cathode, reducing the oxide of the electrochemically active substance in the sintered anode to form pores in the anode.

Claims

1. A method for manufacturing a solid oxide fuel cell, the method comprising:

forming a tubular anode comprising an electrolyte substance and an oxide of an electrochemically active metallic substance without a distinct pore forming substance;

sintering the tubular anode;

forming an electrolyte onto the sintered anode;

forming a cathode onto the electrolyte; and

after forming the electrolyte and the cathode, reducing the oxide of the electrochemically active metallic substance in the sintered anode to form pores in the anode.

2. A method according to claim 1, wherein sintering the tubular anode comprises:

drying the tubular anode; and

sintering the tubular anode in air in a furnace having a furnace temperature ramp rate of approximately 0.5°

C. per minute, up to approximately 500°

C., followed by a ramp rate of approximately 3°

C. per minute up to approximately 1300°

C., and a dwell time of approximately 2 hours for sintering.

3. A method according to claim 1, wherein the electrolyte substance of the anode includes stabilized zirconia and wherein the oxide of the electrochemically active metallic substance includes at least one of a nickel oxide, a platinum oxide, a palladium oxide, and a cobalt oxide.

4. A method according to claim 1, wherein forming and sintering the tubular anode comprises:

forming a plastic mass comprising a mixture of the electrolyte substance and the oxide of the electrochemically active metallic substance;

extruding the plastic mass through a die to form an extruded tube; and

sintering the extruded tube.

5. A method according to claim 1, wherein the anode comprises more than one anode layer, each layer having a different composition.

6. A method according to claim 5, wherein there are two anode layers.

7. A method according to claim 5, wherein there are more than two anode layers.

8. A method according to claim 5, wherein each of the anode layers comprises a ratio of electrochemically active metallic substance to electrolyte substance, and wherein such ratios are higher for layers that are layered further from a surface of the anode that contacts a fuel gas than for layers that are layered closer to the fuel gas.

9. A method according to claim 5, wherein forming and sintering the tubular anode comprises:

forming first and second plastic masses, each plastic mass comprising a mixture of the electrolyte substance and the oxide of the electrochemically active metallic substance, the first plastic mass having a higher relative content ratio of oxide to electrolyte substance, and the second plastic mass having a lower relative content ratio of oxide to electrolyte substance;

extruding the first plastic mass through a die to form a first extruded tube;

extruding the second plastic mass through a die to form a second extruded tube;

fitting the first extruded tube inside the second extruded tube to form a combined tube; and

sintering the combined tube.

10. A method according to claim 9, wherein each plastic mass comprises a mixture of stabilized zirconia and nickel oxide, the first plastic mass having a higher relative content ratio of nickel oxide to stabilized zirconia, and the second plastic mass having a lower relative content ratio of nickel oxide to stabilized zirconia.

11. A method according to claim 5, wherein forming and sintering the tubular anode comprises:

co-extruding more than one anode layer to form a co-extruded tube; and

sintering the co-extruded tube.

12. A method according to claim 5, wherein the more than one anode layers comprise a thicker support layer for contact with a fuel gas and a thinner active layer.

13. A method according to claim 12, wherein the support layer comprises a higher ratio of stabilized zirconia to nickel, and wherein the active layer comprises a lower such ratio.

14. A method according to claim 12, wherein the support layer comprises from 0% to 50% nickel by volume.

15. A method according to claim 12, wherein the active layer comprises from 40% to 45% nickel by volume.

16. A method according to claim 12, wherein the active layer comprises an embedded current-collecting wire.

17. A method according to claim 16, wherein the active layer is extruded around the current-collecting wire.

18. A method according to claim 12, wherein the support layer comprises aluminum oxide.

19. A method according to claim 1, wherein the anode further includes a catalyst material.

20. A method according to claim 19, wherein the catalyst material includes at least one of:

CeO₂, ruthenium, rhodium, rhenium, palladium, scandia, titania, vanadia, chromium, manganese, iron, cobalt, nickel, zinc, and copper.

21. A method according to claim 19, wherein the catalyst material includes CeO₂ in a proportion of between 1% and 3% by weight.

22. A method according to claim 19, wherein forming the anode comprises milling the catalyst with the oxide of the electrochemically active substance.

23. A method according to claim 1, wherein reducing the oxide of the electrochemically active metallic substance in the sintered anode to form pores comprises flowing a reducing gas over a surface of the sintered anode.

24. A method according to claim 1, wherein reducing the oxide of the electrochemically active metallic substance in the sintered anode to form pores comprises flowing hydrogen gas over a surface of the sintered anode at a temperature between approximately 800°

C. and 1000°

C.

25. A method according to claim 1, wherein the anode comprises a substantially uniform ratio of electrochemically active metallic substance to electrolyte substance.

26. A method according to claim 1, wherein the anode comprises a volume percentage of nickel of between 40% and 50%.

27. A method according to claim 1, wherein a thickness of the anode comprises over 50% of a total thickness of the anode, the electrolyte, and the cathode.

28. A method according to claim 1, wherein the anode has a thickness of at least 300 μ

m.

29. A method according to claim 1, wherein the anode has a circular cross-section.

30. A method according to claim 1, wherein the anode has a non-circular cross-section.

31. A method according to claim 1, wherein the electrolyte formed onto the sintered anode comprises stabilized zirconia.

32. A method according to claim 1, wherein forming the electrolyte onto the sintered anode comprises at least one of:

spraying the electrolyte onto the sintered anode; and

dip-coating the electrolyte onto the sintered anode.

33. A method according to claim 1, wherein the cathode comprises a strontia-doped lanthanum manganite.

34. A method according to claim 1, wherein the cathode comprises at least one of:

gadolinium manganate; and

a cobaltate.

35. A method according to claim 1, wherein the cathode comprises more than one cathode layer, each cathode layer having a different composition.

36. A method according to claim 35, wherein there are two cathode layers.

37. A method according to claim 36, wherein the two cathode layers comprise:

an inner cathode layer comprising a mixture, 50/50 wt % of La_0.80Sr_0.20MnO₃ (Rhodia, 99.9% pure) with 8 mol % YSZ (Tosoh); and

an outer cathode layer comprising substantially only La_0.80Sr_0.20MnO₃ (Rhodia, 99.9% pure).

38. A method according to claim 35, wherein there are more than two cathode layers.

39. A method according to claim 1, wherein forming the cathode onto the electrolyte comprises spraying at least one cathode layer onto the electrolyte.