Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1997-03-24
1998-09-08
Nuzzolillo, M.
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 31, 429 34, H01M 802
Patent
active
058043284
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a current collecting device for a fuel cell stack comprising a number of stack-forming fuel cell plates between opposite end plates, each end plate being connected to a current collector.
In order to be able to make use of the electricity generated in a fuel cell stack in the best possible manner, it is necessary to have a current collector wherein the voltage loss is low when current is tapped. One must then have a good electrical contact between the end plates and the current collector of the fuel cell stack, at the same time as the ohmic voltage loss through the current conductor to the terminals is low.
2. Description of Related Art
A current collecting device of the introductorily stated type is known from U.S. Pat. No. 4,719,157. In this known device, the end plates are insulated from the current collector by means of a heat resisting insulator arranged therebetween, each of the current collectors comprising a plurality of independent current collecting sections which are spaced from each other and of which each is provided with a single terminal extending therefrom through the insulator and the end plate. An object of the known device is to provide a device having a high current collecting efficiency even if it is applied to a fuel cell assembly with a large electrode area.
Even if it is not stated in the patent specification, it is supposed that the device has appeared in connection with phosphorous acid fuel cells or melting carbonate fuel cells having an operating temperature of 200.degree. C. and 600.degree. C., respectively. Both of these fuel cell types have metallic connection elements and large electrode areas (1000-3000 cm.sup.2). For solid-state oxide fuel cells (SOFC), having an operating temperature of approximately 1000.degree. C., the posing of the problem is quite another one. In these fuel cell stacks, the connection elements are ceramics, and the electrode area is relatively large (100-500 cm.sup.2). Current conductors for output of current from the stack can hardly be welded to the ceramic end plates. One therefore has to establish contact with the current conductor in another manner.
Several metals and metal alloys have a high electrical conductivity at 1000.degree. C. However, in the oxidizing atmosphere there is formed a thin, non-conducting oxide layer on the surface. This oxide layer protects the metal or the metal alloy against further corrosion, but prevents an efficient current collection since it is electrically insulating. Consequently, it is no solution to use a high-temperature metal alloy directly against ceramic end plates in a fuel cell stack. Noble metals are resistant materials where there is not formed any oxide layer in air. However, the price of noble metals entails that it is not of current interest to use noble metals alone as current collectors. In addition, noble metals are ductile materials and therefore do not have the mechanical strength which is desirable for the total current collecting device.
BRIEF DESCRIPTION OF THE INVENTION
It is therefore an object of the invention to provide a current collecting device, especially for high temperature fuel cells with ceramic end plates, by which there is established and maintained a good electrical contact, and therewith a high electrical conductivity, between the fuel cell stack and the current collector at the operating temperature.
Another object of the invention is to provide such a current collecting device which is chemically stable in a given atmosphere at the operating temperature.
An additional object of the invention is to provide a current collecting device of the topical type which is arranged for possible adjustable compression of the fuel cell stack with associated end plates, in order to avoid high mechanical loads and secure optimum electrical contact conditions at the operating temperature.
For the achievement of the above-mentioned objects there is provided a device of the introductorily stated type which, accordi
REFERENCES:
patent: 4719157 (1988-01-01), Tsutsumi et al.
patent: 4791035 (1988-12-01), Reichner
patent: 5387476 (1995-02-01), Koch et al.
Patent Abstracts of Japan, vol. 14, NO. 192, (C-711), abstract of JP, A, 2-37669, Feb. 7, 1990.
Odegard Rolf
Ravnanger Roald
Sundal Per
Den norske stats ol jeselskap a.s
Nuzzolillo M.
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