Metal working – Method of mechanical manufacture – Electrical device making
Patent
1995-09-20
1996-12-10
Skapars, Anthony
Metal working
Method of mechanical manufacture
Electrical device making
296235, 429 16, 429 41, H01M 488, H01M 814
Patent
active
055826245
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for producing a molten-carbonate fuel cell according to the preamble of claim 1.
Molten carbonate fuel cells (MCFC) of this type are known. By means of a direct electrochemical approach, they permit the obtaining of electric energy with an efficiency of more than 50% from the reaction of a high-hydrogen burnable gas with oxygen. The electric collectible energy may be obtained between the anode layer and the cathode layer as direct current or direct voltage. A molten mixture of lithium carbonate and potassium carbonate or sodium carbonate and other admixtures is used as the electrolyte. The molten electrolyte is held in the fine-pored matrix layer which usually consists of lithium aluminate and separates the gas chambers of the anode (burnable gas) and of the cathode (air) from one another. The molten carbonate fuel cell operates at temperatures of between 550.degree. and 750.degree. C. It may be operated atmospherically but also by means of several hundred kPa above the atmospheric pressure.
A gas mixture, which contains oxygen and carbon dioxide, is fed to the cathode layer. The oxygen is reduced on the cathode layer and, together with the carbon dioxide, forms carbonations which are absorbed by the electrolyte. On the anode layer, the hydrogen from the burnable gas with the carbonations of the electrolyte melting are oxidized to form carbon dioxide and water. The carbon dioxide formed on the anode layer may be returned to the cathode gas. Hydrogen-rich gases, such as natural gas, may also be used as the burnable gas in the molten-carbonate fuel cell. By means of a catalyst and with the addition of heat--in which case the heat is utilized which is released in the fuel cell operation--, the gases are reformed to form a hydrogen-rich burnable gas which is converted on the anode layer of the fuel cell.
Currently, molten-carbonate fuel cells are usually produced in that at first a layer arrangement consisting of a porous nickel anode layer, a porous lithium aluminate matrix layer and a porous nickel cathode layer is deposited between the current collector plates of the cell and is adjusted. Generally, a metallic current transmission plate, as a bipolar plate, is also applied to each of the two current collector plates of the fuel cell. Several of such fuel cells are arranged in a stack in a cell holder. The matrix layer protrudes over the electrode layers, thus over the cathode and the anode layer. The protruding edge of the matrix layer is pressed in between the edges of the bipolar plates of the fuel cell stack, whereby the sealing of the electrode spaces and the electric series connection of the cells is caused in the interior of a fuel cell stack. In the case of the burnable gas and the supplying of air with an external distribution on the electrode spaces between the bipolar plate and the adjacent electrode layer--so-called external gas distribution ("manifolding")--the porous electrode layers will contain the molten electrolyte in their pores during the start, while, in the case of the internal gas distribution, the molten electrolyte is placed as a lithium potassium carbonate foil on the electrode layers into the layer arrangement so that the molten electrolyte is not taken in by the matrix layer before the starting procedure of the fuel cell.
In the case of a molten-carbonate fuel cell, the external and internal gas distribution basically differ from one another in that, in the case of the external gas distribution, no shrinkage of the cell stack can be accepted when the heating is started because otherwise the external gas sealing of the gas distributor case to the cells would be non-existent.
For producing the porous electrode layers, a suspension or a slip is prepared from nickel powder with the addition of binding agents, softeners and other auxiliary agents and is drawn out to form a foil. The foil is shaped to form the usable electrode layers in that it is heated, in which case, all organic constituents are expelled up to maximally 450.degree. C. Then sintering
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Jantsch Uwe
Koch Hermann
Rohland Bernd
Weilberg Frank U.
Wendt Hartmut
MTU Motoren-und Turbine-Union Friedrichshafen GmbH
Skapars Anthony
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