Fuel cell interconnect device

Details Fuel cell interconnect device Fuel cell interconnect device

1997-11-25

1999-08-24

Bell, Bruce F.

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

429 30, 429 38, 429 39, 427115, 4271263, 4271266, 4274192, 4274193, H01M 200

Patent

active

059423498

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to fuel cells and is particularly concerned with an interconnect device for planar solid oxide fuel cells and with a method for preparing such an interconnect device.


BACKGROUND ART

Fuel cells convert gaseous fuels (such as hydrogen, natural gas, and gasified coal) via an electrochemical process directly into electricity. A fuel cell operates like a battery, but does not need to be recharged and continuously produces power when supplied with fuel and oxidant, normally air. A typical fuel cell consists of an electrolyte (ionic conductor, H.sup.+, O.sup.2-, CO.sub.3.sup.2- etc.) in contact with two electrodes (mainly electronic conductors). On shorting the cell through an external load, fuel oxidises at the anode resulting in the release of electrons which flow through the external load and reduce oxygen at the cathode. The charge flow in the external circuit is balanced by ionic current flows within the electrolyte. Thus, at the cathode oxygen from the air or other oxidant is dissociated and converted to oxygen ions which migrate through the electrolyte membrane and react with the fuel at the anode/electrolyte interface. The voltage from a single cell under load conditions is in the vicinity of 0.6 to 1.0 V DC and current densities in the range 100 to 500 MAcm.sup.-2 can be achieved.
Several different types of fuel cells are under development. Amongst these, the solid oxide fuel cell (SOFC) is regarded as the most efficient and versatile power generation system, in particular for dispersed power generation, with low pollution, high efficiency, high power density and fuel flexibility.
Single fuel cells are connected via interconnects to form multi-cell units, termed fuel cell stacks. Gas flow paths are provided between the interconnects and respective electrodes. Numerous SOFC configurations are under development, including the tubular, the monolithic and the planar design. The planar or flat plate design is the most widely investigated. In this concept the components--electrolyte/electrode laminates and interconnect plates, which may have gas channels formed therein--are fabricated individually and then stacked together and sealed with a high temperature sealing material to form either a fixed or sliding seal. With this arrangement, external and internal co-flow, counter-flow and cross-flow manifolding options are possible for the gaseous fuel and oxidant.
Apart from good electrical, electrochemical, mechanical and thermal properties, the individual cell components must be stable in demanding fuel cell operating environments. SOFCs operate in the vicinity of 950-1000.degree. C. although substantial efforts are under way to reduce the operating temperatures to 800-900.degree. C. For fuel cells to be economical, typical life times of 5-6 years of continuous operation are desired. Thus long term stability of the various cell components is essential. Only a few materials are likely to fulfil all the requirements. In general, the high operating temperature of SOFCs, the multi-component nature of the fuel cell and the required life expectancy of several years severely restricts the choice of materials for cells and manifold components.
A typical solid oxide electrolyte material used in an SOFC is Y.sub.2 O.sub.3 -doped ZrO.sub.2 which is an oxygen ion conductor. However, many other materials have been proposed, and the invention is applicable to all of these. A variety of different anode materials have been proposed for use at the fuel side of SOFCs, but the particular anode material is not relevant to the present invention. However, nickel-containing anodes are preferred. Such anodes have included nickel plating layers and nickel alloys, but the presently most preferred material is a Ni/ZrO.sub.2 cermet. Likewise, a variety of different cathode materials have been proposed for the air side of SOFCs, but the particular cathode material is not relevant to the present invention. However, the presently preferred cathode material is strontium doped lanthanum manganite

REFERENCES:
patent: 4950562 (1990-08-01), Yoshida et al.

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