Claims
- 1. A method of fabricating a molten carbonate fuel cell cathode comprising:
- (a) prefiring a composition comprising oxides of nickel and lithium salts in an oxidizing atmosphere at temperatures of about 600.degree. C. to about 1000.degree. C.;
- (b) mixing barium salts with said prefired composition;
- (c) forming said prefired composition into an electrode; and
- (d) sintering said electrode in an oxidizing atmosphere at about 850.degree. C. to about 1250.degree. C.;
- wherein said electrode has improved strength.
- 2. The method of fabricating a molten carbonate fuel cell cathode of claim 1 wherein said prefired composition is leached with an organic acid prior to sintering said electrode.
DISCLOSURE OF INVENTION
This is a division of application Ser. No. 812,218, filed on Dec. 23, 1986, now U.S. Pat. No. 4,708,917.
1. Technical Field
This disclosure relates to electrodes and methods for fabricating electrodes, particularly molten carbonate fuel cell cathodes.
2. Background Art
Molten carbonate fuel cells generally comprise two electrodes, a cathode and an anode, their current collectors, and an electrolyte matrix making contact with both electrodes. A cell housing is used to physically retain the cell components. Air and carbon dioxide are fed to the cathode where CO.sub.2 is oxidized to form a carbonate ion.
To maintain a high level of stable performance, both the electrolyte matrix and electrode structures must be engineered to optimize the gas-electrolyte-electrode interface. Electrode structures must be fabricated with controlled pore spectra since electrolyte fill of the electrodes is controlled by capillary forces. High porosities are desired to maximize electrode surface area and electrochemical activity; the maximum porosity is limited by the resulting strength of the structure. Pores must also be of the proper size. Large pores will limit the extent of electrolyte fill, reducing the amount of three phase interface and resulting in poor performance. Small pores will cause electrolyte flooding, resulting in high losses due to necessary diffusion of gaseous reactants through the electrolyte.
Conventional molten carbonate cathodes have been formed by the in-situ oxidation and lithiation of porous nickel structures. Porous nickel structures of this type can be produced by a variety of powder metallurgical techniques to form a green compact with voids between the particles forming interconnected pore channels throughout the compact. The green compact is then sintered by heating at temperatures of greater than about 70 percent of the melting point temperatures. This produces cathodes with interconnected particles and pore channels throughout the structure. When the fuel cell is heated to operating temperatures of 500.degree. C. to 700.degree. C., the carbonate electrolyte melts and wets the cathode structure. The nickel cathode is violently oxidized and lithiated. This in-situ oxidation disrupts the sintered structure, resulting in a weak structure with an uncontrolled pore spectra.
There has been an extensive search for methods of making pre-oxidized nickel cathodes with a known and controlled pore spectra and improved strength. E. Gorin et al (U.S. Pat. No. 2,914,596) teaches a method for fabricating lithiated nickel oxide air electrodes for use in high temperature fuel cells. U.S. Pat. No. 4,247,604 teaches molten carbonate anodes having stabilizing agents such as lithium salts. Although there are a variety of electrodes and methods of making them in the prior art, it is important to have electrodes that perform well and have the high strength which helps provide a fuel cell with a long life.
Accordingly, there is a constant search in this art for electrodes and methods of making them that result in electrodes having high strength so that the long life fuel cell necessary for successful commercial operation can be achieved.
This disclosure is directed to molten carbonate fuel cell cathodes that have improved strength. The molten carbonate fuel cell cathode is formed from a composition comprising oxides of nickel, lithium salts and barium salts.
Another aspect of this disclosure is methods for fabricating molten carbonate fuel cell cathodes that have improved strength. Oxides of nickel are prefired in an oxidizing atmosphere at temperatures of about 600.degree. C. to about 1000.degree. C. The prefired nickel oxides is formed into an electrode and sintered in an oxidizing atmosphere at about 850.degree. C. to about 1250.degree. C.
This invention makes a significant contribution to the molten carbonate fuel cell field by providing electrodes having higher strength. As a result, it advances the industry's quest for a long life fuel cell.
The foregoing and other features and advantages of the present invention will become more apparent from the following description and accompanying drawings.
US Referenced Citations (9)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 55-19043 |
May 1980 |
JPX |
Non-Patent Literature Citations (4)
| Entry |
| "Time Dependence of NiO-Li.sub.2 O Solid Solution Formation", by Yoshio Iida-Journal of the Ceramic Society Discussion & Notes, Jan. 1960. |
| "Fuel Cells With Molten-Carbonate Electrolytes", by Liebhafsky et al., J. Wiley, Chapter 12, Fuel Cells and Fuel Batteries, 1968, pp. 524-553. |
| Argonne National Laboratory Paper ANL-79-55, "Critical Survey on Electrode Aging in Molten Carbonate Fuel Cells", by K. Kinoshita-Dec. 1979. |
| CA Selects-Batteries & Fuel Cells, Issue 26, 1983, p. 6, Abstract 99:21587e, Molten-Carbonate Fuel Cell Cathode. |
Divisions (1)
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Number |
Date |
Country |
| Parent |
812218 |
Dec 1986 |
|
Patent Grant
4800052
