Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1996-03-22
1999-01-19
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 33, 429158, 429162, H01M 810, H01M 824
Patent
active
058612211
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
The present invention claims the priority under 35 U.S.C. .sctn. 119 of German Patent Applications Nos. P43 25 353.9 filed on Jul. 28, 1993 and P43 29 819.2 filed on Sep. 3, 1993.
The invention relates to the structure of an electrochemical cell with a core region comprising a plurality of individual cells, which are designed in the form of a strip membrane.
Discussion of Background Information
Electrochemical cells, e.g. with polymeric solid electrolytes, consist basically of two electrodes, at which the electrochemical reactions occur, and with an interposed electrolyte, which fulfils the purpose of ion transportation between the electrodes, and which consists of an ion conductive polymer.
If, at both electrodes, electrochemical reactions occur freely (oxidation at the anode, reduction at the cathode), the electrochemical cell provides a voltage. One individual cell provides only a relatively small voltage in the region from a few milivolts up to a few volts. For many practical applications, such for example as the use of battery fuel cells in the field of traction, however, considerably higher voltages are required.
Until the present, therefore, a plurality of such cells was built up separately, located one behind the other and incorporated in series, so that the voltages of the individual cells are added to one another. This type of series incorporation does in fact enable larger voltages to be produced, but involves considerable disadvantages. Technically and constructively, such series incorporation is extremely complex. For example, for a hydrogen/oxygen fuel cell stack there is generally required for each individual cell a bipolar plate, a hydrogen gas distributor ring, an ion exchange membrane coated with catalyst, an oxygen gas distributor ring, seal rings in order to seal these components, and current distributor structures. This comes in all to 10 components per individual cell. If for example a stack output of 70 volts is to be produced, with an individual cell voltage of 0.7 volts, 100 individual cells are required, i.e. 1000 components must be combined, with the necessity to fix 400 seal rings.
A further disadvantage arises from series incorporation in that, when a single cell in the fuel cell stack fails, the entire stack breaks down. A redundant method of construction for the above example, i.e. incorporation in parallel of a plurality of 70 volt stacks, would however drive the construction costs to levels which can no longer be justified.
SUMMARY OF THE INVENTION
Proceeding from this, therefore, the object of the present invention is to propose an electrochemical cell which, compared to prior art, has a simpler and more cost-effective construction, and permits a reliable method of operation.
Firstly the invention proposes that the core region of an electrochemical cell should be formed by so-called strip membranes. By the term `core region of the electrochemical cell` is meant the unit at which the electrochemical reactions take place. According to the invention, the core region comprises at least one sheet-like strip membrane which has at least 2 and a maximum of 10,000 individual cells incorporated in series.
Incorporation of the individual cells may be effected either by electronically conductive regions or by a step-like configuration of the individual cells.
The preferred embodiment proposes that incorporation be undertaken via sheet-like electronically conductive regions.
The strip membrane itself in this case consists of regions located in sheet form next to one another, which have different conductivities.
A region is formed by the individual cell itself. In order to ensure ion conductivity, the individual cell is made of an ion conductive material. For this purpose polymeric solid electrolytes in the form of membranes are used. As either cations or anions must be transported, the membrane must be permeable either to cations or anions. Ion conductivity in an aqueous environment for cation conductive polymers is generally provided when
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Ledjeff Konstantin
Nolte Roland
Fraunhofer -Gesellschaft Zur Forderung der Angewandten Forschung
Kalafut Stephen
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