Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1992-08-03
1994-07-12
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 37, 429 40, H01M 812
Patent
active
053287797
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of The Invention
The invention relates to a fuel-cell element which comprises a combination of two porous and metallic electrodes with a gastight and oxidic electrolyte layer, and a process for its manufacture.
2. Description of The Related Art
Fuel cells are interesting devices for converting chemical energy directly into electrical energy. Theoretically, substantially higher conversion rates are achievable than via the Carnot cycle process. A very simple hydrogen/oxygen cell was put forward as long as 150 years ago by R. Grove. Since that time the problem has been to react fuel (for example CH.sub.4) electrochemically with oxygen (air) in such a way that the energy of oxidation of carbon monoxide to CO.sub.2 and of the hydrogen component to H.sub.2 O is directly converted into electrical energy. In this connection, the following reactions occur at the cell electrodes: ##STR1##
This requires a gastight separation of the coreactants by means of a barrier, the electrolyte layer, which is permeable only to oxygen ions but is electrically insulating. Electrical connection has in turn to be made with both sides of said barrier in such a way that the supply and removal of the electron currents is ensured in as loss-free a manner as possible. At the same time, good accessibility of the electrolyte surfaces for the gaseous coreactants (CO and H.sub.2 on the anode side, O.sub.2 on the cathode side) and removal of the reaction products (H.sub.2 O vapor and CO.sub.2) are required.
For most fuels, carbon monoxide and hydrogen have first to be produced via preliminary thermal reactions (reforming), for example for CH.sub.4 via the reactions: ##STR2## For the invention described below, it is irrelevant whether the starting gases for the electrochemical reaction are produced simultaneously inside the fuel cell or outside and upstream of it, or whether pure hydrogen is directly converted into electrical energy.
At this point it should also be stated that the process can also be reversed with the fuel cell element according to the invention. This relates, in particular, to the electrochemical decomposition of H.sub.2 O vapor into H.sub.2 and O.sub.2, or of other gaseous oxides, for the purpose of fuel synthesis accompanied by power consumption.
Many types of fuel cell have already been proposed. In various versions, an attempt has been made to overcome the discrepancy between the theoretical conversion rates and the values achieved in practice. Real electrochemical reaction rates are limited by mass transport, by electron conduction, by the physical properties of the cell element materials used and by geometrical effects. A key role is played by the two porous electrodes, whose structural and material long-term stability has a very critical effect on the performance of the cell element.
Among the many proposed cells, high-temperature fuel cells with solid electrolyte are of particular interest. The application temperatures of this cell type are between 700.degree. and 1100.degree. C. They can therefore be fed directly with air and natural gas or other gaseous hydrocarbons. A cell temperature which is adequate for an internal reforming process for CO is desirable. In addition to electricity, usable heat can also be generated simultaneously by a chemical combustion, a very important factor for the total energy balance. An adjustable proportion of the fuel is burnt, and the entire cell is thereby simultaneously kept at a temperature level which is favorable for the electrochemical conversion.
The solid electrolyte preferably used for this type of cell is cubic stabilized ZrO.sub.2, a material which conducts oxygen ions at fairly high temperatures with very good electrical resistance for electron conduction.
Since an individual element only generates a low electrical voltage, many individual elements are assembled to form batteries. The individual cells have to be electrically connected in series with one another, using a material which conducts electrons very well and has as low a contac
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Gruner Heiko
Tannenberger Helmut
Kalafut Stephen
Medicoat AG
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