Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-02-11
2001-11-13
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06316136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an interconnector for high temperature fuel cells and to a fuel cell battery.
2. Description of the Prior Art
The fuel cells of a fuel cell battery in accordance with the invention comprise (see EP-A 0 714 147) in each case a so-called PEN and an interconnector which connects the cells adjacent to the PEN in an electrically conducting manner and at the same time separates a combustion gas (in particular a mixture of carbon monoxide and hydrogen) from a gaseous oxygen carrier (in particular air). The PEN has a planar three-layer construction consisting namely of a solid electrolyte (E), a positive electrode (P) and a negative electrode (N). Electrochemical reactions at the PEN with the fuel and the oxygen of the oxygen carrier take place at about 900° C.
Due to the high operating temperatures, a material must be used for the interconnectors of which the coefficient of thermal expansion is largely equal to that of the solid electrolyte. A powder-metallurgically manufactured alloy is known which is suitable for the manufacture of interconnectors. This material, which consists mainly of chromium (about 95% by weight) and which is manufactured through sintering at high pressure and high temperature, is expensive. The alloy is manufactured in plate form and must therefore be further processed in a form suited to the function of the interconnectors, with complicated and expensive work steps being required and material being lost.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an interconnector which permits substantial cost savings.
The interconnector for high temperature fuel cells is arranged between a first and a second planar electrochemically active element, a so-called PEN. In this it separates a chamber containing a combustion gas from a chamber containing oxygen. A porous sinter body of the interconnector has pores which are at least partly sealed by a medium. Through the sealing, a passage of gases between the named chambers is prevented.
The interconnector in accordance with the present invention comprises a sinter body which prevents a mixing of the reactants and which is porous, with its pores being filled with an additional medium for the sealing off. The porosity permits more economical manufacturing methods. Other powder mixtures can also be used, for example those which consist to a large part of ceramic material with a low coefficient of thermal expansion and for which the manufacture of a tight, pore-free solid body would not be possible. In particular the powder mixture can also largely be brought into the form of the finished part though a form compression procedure.
Chromium is an important constituent in known interconnectors because this metal has a low coefficient of thermal expansion and its oxide is electrically conducting. At the operating temperature of the fuel cells, however, a material transport of sublimated chromium oxide takes place via the gas phase to the electrodes, through which their activity is impaired. For this reason it is necessary to coat the surfaces of the interconnector with a material which acts as a chromium oxide barrier (for this, cf. EP-A 0 714 147=P.6651).
For coating layers which act as chromium oxide barriers, ceramic materials (in particular Perovskite) or enamel come into consideration. An enamel, for example with the composition (in percentage by weight): MgO (5-15), Al
2
O
3
(15-30), B
2
O
3
(10-15), SiO
2
(35-55), MnO (15-30), has a softening point of about 1000° C., a coefficient of thermal expansion which coincides approximately with that of the solid electrolyte (about 8 10
−6
K
−1
at 800° C.) and the property of wetting an alloy well which is rich in chromium. This enamel is suitable not only as a chromium oxide barrier but also as a medium by means of which the pores of the sinter body can be sealed.
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Chemical Abstracts, vol. 126, No. 6, Feb. 10, 1997, Columbus, Ohio, US; abstract No. 77495, Fujimoto, Tetsuo Et Al: “Planar ceramic interconnectors for solid electolyte fuel cells and their manufacture”, XP002071911, Abstract, & JP 08 287 929 A (Mitsubishi Heavy Ind) Nov. 1, 1996.
Patent Astracts of Japan, vol. 97, No. 3, Mar. 31, 1997 & JP 08 287929 A (Mitsubishi Heavy Ind), Nov. 1, 1996, Abstract.
Patent Abstracts of Japan, vol. 096, No. 011, Nov. 29, 1996 & JP 08 185870 A (Tonen Corp; Sekiyu Sangyo Kasseika Center) Jul. 16, 1996, Abstract.
Patent Abstracts of Japan, vol. 096, No. 011, Nov. 29, 1996 & JP 08 171924 A (Tonen Corp; Sekiyu Sangyo Kasseika Center), Jul. 2, 1996, Abstract.
Brouillette Gabrielle
Sulzer Hexis AG
Townsend and Townsend / and Crew LLP
Tsang Susy
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