Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1995-11-24
1998-03-31
Skapars, Anthony
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 33, 429 35, H01M 2810
Patent
active
057336784
DESCRIPTION:
BRIEF SUMMARY
The invention relates to fuel cells the individual components of which are current collectors, solid electrolytes in the form of membranes, gas distributor ring and current distributors made from one and the same basic polymer, individual components being combined by a bonding process.
Fuel cells are constructed either as separate individual cells or as a so-called fuel cell stack. In the stack construction, a certain number of individual cells are incorporated one after the other, in order to provide a correspondingly higher output voltage. The fuel cell most frequently used, a hydrogen/oxygen fuel cell, is predominantly constructed from the following individual components: a current collector, a hydrogen gas distributor ring, an ion-exchange membrane, current distributor structures and hydrogen gas distributor rings. In the case of individual cells, there are used as current collectors positive or negative plates, and in the case of fuel cell stacks, there are used as current collectors bipolar plates, which are built up into a corresponding fuel cell stack. In prior art, until now the individual components have been connected together via seal rings.
This procedure however has considerable disadvantages. The use of seal materials is in general not an uncritical factor as, in addition to the required sealing properties, the material must withstand pure and moist oxygen and hydrogen at an increased temperature (approximately 80.degree. C.) as a permanent load, without the occurrence of embrittlement or degradation. The use of materials with additives or plasticisers as proposed for this purpose then has the result that these materials diffuse out in the process of time, are deposited elsewhere or contaminate the catalyst, which can lead to breakdown of the system. Materials without additives frequently require a high contact pressure in order to ensure the sealing effect. This in turn requires membranes which are mechanically extremely stable, in order to withstand these stresses. Thin membranes, whose use is desirable because of their extremely good ion conductivity, cannot be produced by the previous techniques known to prior art.
In particular, in the case of fuel cell stacks, the use of seal materials gives rise to further problems. Due to the mechanical deformability of the seal material an alteration occurs in the geometric position relative to one another of the individual components. In particular, in the case of ion exchanger membranes clamped between two seal rings, the formation of creases in the membrane material is possible, which represent potential breakage points during operation. Such material failure can then lead to a direct contact between hydrogen and oxygen, which will involve failure of a cell.
Proceeding from this prior art, the purpose of the present invention is to propose a fuel cell or a fuel cell stack in which the use of seal material between the individual components is minimised or entirely avoided.
This purpose is fulfilled by the characterising features of claim 1. The secondary claims 2 to 14 show advantageous further developments.
Due to the solution according to the invention, i.e. the production of all components from one and the same basic polymer, or from a modified form thereof for the individual components, a situation is achieved in which the individual components may be connected together by a bonding process and thus sealing material may be minimised or entirely avoided.
In this respect the thermoplastic polymer provided for the production of the individual components is of critical importance.
Only those thermoplastic polymers are suitable in this case which satisfy the specific mechanical and chemical requirements arising in a hydrogen/oxygen fuel cell.
The thermoplastic polymer provided must be suitable as a constructional material for supporting parts of the fuel cell structure, i.e. must have dimensional stability under pressure and at increased temperatures. In addition, the material must not be attacked chemically by dry and moist hydrogen or oxygen, and
REFERENCES:
patent: 5176966 (1993-01-01), Epp et al.
Extended Abstracts, vol. 87, No. 2, pp. 250-251, Oct. 18, 1987, of Hertwig, New Approach to a Low Temperature Solid State Fuel Cell".
Ledjeff Konstantin
Nolte Roland
Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung
Skapars Anthony
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