Formation of thin walled ceramic solid oxide fuel cells

• US 4,883,497 A
• Filed: 03/28/1988
• Issued: 11/28/1989
• Est. Priority Date: 03/28/1988
• Status: Expired due to Fees

• Current Assignee: ARCH Development Corporation (University of Chicago)
• Original Assignee: ARCH Development Corporation (University of Chicago)
• Inventors: Claar, Terry D., Picciolo, John J., Busch, Donald E.
• Primary Examiner(s): Skapars, Anthony
• Application Number:
  US07/174,146
• Time in Patent Office: 610 Days
• Field of Search: 429/32, 429/33, 429/34, 429/12, 429/193, 29/623.1, 29/623.5, 264/23, 264/44, 264/105, 264/241, 264/297.4
• US Class Current: 29/623.5
• CPC Class Codes: H01M 8/2404 Processes or apparatus for grouping fuel cells
• CPC Class Codes: H01M 8/2435 with monolithic core structure, e.g. honeycombs
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y10T 29/49115 including coating or impregnating

Abstract

To reduce thermal stress and improve bonding in a high temperature monolithic solid oxide fuel cell (SOFC), intermediate layers are provided between the SOFC'"'"'s electrodes and electrolyte which are of different compositions. The intermediate layers are comprised of a blend of some of the materials used in the electrode and electrolyte compositions. Particle size is controlled to reduce problems involving differential shrinkage rates of the various layers when the entire structure is fired at a single temperature, while pore formers are provided in the electrolyte layers to be removed during firing for the formation of desired pores in the electrode layers. Each layer includes a binder in the form of a thermosetting acrylic which during initial processing is cured to provide a self-supporting structure with the ceramic components in the green state. A self-supporting corrugated structure is thus formed prior to firing, which the organic components of the binder and plasticizer removed during firing to provide a high strength, high temperature resistant ceramic structure of low weight and density.

Claims

1. A method for forming an SOFC comprising the steps of:

dispersing each of four ceramic powders into respective ones of a plurality of liquid media to form four slips of an anode, a cathode, an electrolyte and an interconnect;

milling a binder and a plasticizer into each of said four slips;

casting the four slips into thin layers or tapes;

forming a plurality of said tapes into a stacked array including the step of depositing an intermediate bonding layer between adjacent tapes, wherein said intermediate layers are comprised of portions of each of the adjacent layers between which the intermediate layer is disposed;

forming a plurality of corrugations in the stacked array of tapes, wherein said corrugated stacked array is self-supporting; and

heating the stacked array of tapes at an elevated temperature so as to increase the density of electrolyte and interconnect tapes, form bonds between adjacent tapes, and rigidify and increase the strength of the stacked array of tapes.

2. The method of claim 1 wherein the anode is selected from one of the class consisting of the combination Ni and yttria stabilized zirconia, and the combination Co and yttria stabilized zirconia.

3. The method of claim 2 wherein the cathode is comprised of strontium doped LaMnO₃.

4. The method of claim 3 wherein the electrolyte is comprised of yttria stabilized zirconia.

5. The method of claim 4 wherein the interconnect is comprised of magnesium doped LaCrO₃.

6. The method of claim 1 wherein the binder is selected from one of the class consisting of acrylics, vinyls, cellulosics, and other film-forming binders.

7. The method of claim 1 wherein the plasticizer is selected from one of the class consisting of phthalates, polyethylene glycol, and glycerol.

8. The method of claim 1 wherein the liquid medium is selected from one of the class consisting of organic solvents, a mixture of organic solvents, and water.

9. The method of claim 8 wherein said organic solvent is selected from one of the class consisting of alcohols, ketones, hydrocarbons, and chlorinated hydrocarbons.

10. The method of claim 1 further comprising the step of milling each slip to a paint-like consistency to break up powder agglomerates, to disperse the ceramic particles uniformly within the slip, and to homogenize the binder, the plasticizer and the dispersant.

11. The method of claim 10 further comprising the step of de-airing each of the slips prior to deposit onto a substrate.

12. The method of claim 11 wherein the step of de-airing each of the slips includes the step of ultrasonic agitating the slip in a partial vacuum.

13. The method of claim 1 wherein the step of forming the layers of anode, electrolyte, cathode, and interconnect includes tape casting with a doctor blade each of the slips into which a respective ceramic powder has been dispersed.

14. The method of claim 1 wherein the step of forming the layers includes spraying onto a substrate the slips into which a ceramic powder has been dispersed.

15. The method of claim 1 further comprising the step of adding a pore forming material to the cathode and anode slips.

16. The method of claim 15 wherein the pore forming material is selected from one of the class consisting of graphite, carbon black, rice starch, cornstarch, or other cellulosic derivative, wherein the pore forming material is removed during subsequent heating of the stacked array of tapes.

17. The method of claim 1 wherein the anode is comprised of Ni and yttria stabilized zirconia and the electrolyte is comprised of yttria stabilized zirconia, and wherein the intermediate layer disposed between the anode and electrolyte is comprised of 30 vol % Ni/70 vol % yttria stabilized zirconia in contact with the yttria stabilized zirconia electrolyte and a 50 vol % Ni/50 vol % yttria stabilized zirconia in contact with the anode.

18. The method of claim 1 wherein the anode is comprised of Co and yttria stabilized zirconia and the electrolyte is comprised of yttria stabilized zirconia, and wherein the intermediate layer disposed between the anode and electrolyte is comprised of 30 vol % Co/70 vol % yttria stabilized zirconia in contact with the yttria stabilized zirconia electrolyte and a 50 vol % Co/50 vol % yttria stabilized zirconia in contact with the anode.

19. The method of claim 1 wherein the cathode is comprised of strontium doped LaMnO₃ and the electrolyte is comprised of yttria stabilized zirconia, and wherein the intermediate layer disposed between the cathode and electrolyte is comprised of 50 vol % LaMnO₃ /50 vol % yttria stabilized zirconia.

20. The method of claim 19 further comprising the step of spraying the intermediate layer on the interface between the cathode and electrolyte and on the interface between the anode and electrolyte.

21. The method of claim 1 wherein the anode is comprised of Ni and yttria stabilized zirconia and the interconnection is comprised of LaCrO₃, and wherein the intermediate layer between the anode and interconnection is comprised of 50 vol % LaCrO₃ /50 vol % yttria stabilized zirconia.

22. The method of claim 1 wherein the anode is comprised of Co and yttria stabilized zirconia and the interconnection is comprised of LaCrO₃, and wherein the intermediate layer between the anode and interconnection is comprised of 50 vol % LaCrO₃ /50 vol % yttria stabilized zirconia.