Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1997-09-24
1999-07-20
Bell, Bruce F.
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 30, 429 34, 429 38, 429 39, 429 18, 429 40, 429 41, H01M 810
Patent
active
059254777
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an assembly of single cells to form a diaphragm electrode unit, with which the single cells, by stepwise superposition of the electrode areas, are series-connected and to the use of same in a polymer electrolyte diaphragm fuel cell.
Electrochemical cells, e.g. with solid polymeric electrolytes (PEM), comprise, to put it simply, two electrodes on which the electrochemical reactions proceed as well as an electrolyte situated therebetween, carrying out the task of transporting the ions between the electrodes, and being made of an ion-conductive polymer.
When electrochemical reactions voluntarily proceed on both electrodes (oxidation on the anode, reduction on the cathode), the electrochemical cell will deliver a voltage. A single cell will deliver but a relatively low voltage within the range of some millivolts up to some volts. For many practical applications, such as e.g. application of battery fuel cells within traction range, substantially higher voltages are, however, needed.
That is why, up to now, a plurality of such cells have been separately assembled, arranged the one behind the other, and electrically connected in series with one another so that the voltages of the single cells will be added (bipolar stack-type construction). This way of bringing about a series connection certainly enables a realisation of higher voltages; nevertheless, it gives rise to considerable drawbacks. For instance, the constructional efforts of such a series connection are very great since, for one hydrogen/oxygen fuel cell stack, a bipolar plate, a hydrogen gas distributing ring, an ion exchange diaphragm coated with a catalyser, an oxygen gas distributing ring, sealing rings for sealing those components as well as the current distributing structures are generally needed for each single cell. This is a total of 10 components for each single cell. Now if, e.g., a stack output voltage of 70 V is to be realised, then, in case of a single cell voltage of 0.7 V, 100 single cells are required after all, i.e. 1,000 components must be assembled, in which case 400 sealing rings must be fixed.
Another drawback due to series connection is that, in case of failure of only one single cell in the fuel cell stack, the entire stack will break down. A redundant type of construction for the above example, i.e. a parallel connection of several stacks of 70 V, would, however, render the constructional efforts absolutely intolerable. Therefore, the decisive factor for an efficient operation of a PEM fuel cell accordingly is the structure of the diaphragm electrode unit.
Departing from these facts, it, thus, is the object of the present invention to specify a diaphragm electrode unit which is primarily suited for use in PEM fuel cells and which shall possess a high output voltage as well as a simple and low-cost structure.
SUMMARY OF THE INVENTION
In accordance with the invention, it, thus, is suggested to assemble a diaphragm electrode unit such that an assembly of several single cells will be provided, assembly being effected in such a manner that the electrode areas will overlap stepwise and shunt conductive structures being incorporated in the region of overlap.
The diaphragm electrode unit according to the invention comprises ionically conductive diaphragm districts that are bonded with electrode material on both sides. In case of a hydrogen/oxygen fuel cell, each diaphragm district will then be bonded with a hydrogen electrode on the one side and with an oxygen electrode on the opposed side. This being so, all hydrogen electrodes are situated on one side of the diaphragm and all oxygen electrodes on the other side of the diaphragm. Together with the bonded two electrodes, each diaphragm district constitutes a fuel cell unit and, thus, delivers an output voltage. Now, the characteristic feature for the diaphragm electrode unit according to the invention is that each single cell within the diaphragm is series-connected. In accordance with the invention, this is brought about by realising, with a stepwise overlap
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patent: 5171646 (1992-12-01), Rohr
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Ledjeff Konstantin
Nolte Roland
Bell Bruce F.
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
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