Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-04-05
2001-03-06
Osele, Mark A. (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S281000, C156S324000, C429S047000
Reexamination Certificate
active
06197147
ABSTRACT:
Fuel cells are electrochemical systems which can convert chemical energy into electrical energy. Thus, a hydrogen/oxygen fuel cell converts these gases into water with a release of electrical energy.
Fuel cells are composed of an array of a plurality of membrane/electrode assemblies, separated by bipolar plates, a so-called stack, the membrane/electrode assemblies (MEA) in turn being constructed from two catalytically active electrodes for the electrochemical conversion of the chemical substances and an ion-conductive electrolyte between the electrodes for the charge transport. The bipolar plates serve to separate the gas spaces and to connect the individual cells electrically. Modern fuel cell designs operating at low temperatures do not contain any liquid electrolytes but conductive polymeric ion exchanger membranes (polymeric solid electrolytes).
The currently most promising production processes for membrane/electrode assemblies are an impregnation process and a casting process, each of which is followed by hot-pressing of the components.
In the impregnation process, a dissolved solid electrolyte is spread on the electrode surface, or it is sprayed on as an emulsion by means of a pressurized gas; it is capable of penetrating for a few micrometers into the pore system. The prepared electrodes are then pressed with heating until the electrode membrane fuses with them. Such a process for producing membrane/electrode assemblies is described, for example, in U.S. Pat. No. 5,211,984, where a cation exchanger membrane is coated with a cation exchanger solution in which a platinum catalyst is suspended. This process is also known under the term “ink process”.
In casting, the dissolved solid electrolyte is mixed with the catalyst material and, if appropriate, a waterproofing agent, for example polytetrafluoroethylene (PTFE), to give a paste. This is either applied first to a carrier or spread directly on the membrane and then hot-pressed together with the latter, in order to minimize the contact resistances at the transitions between the membrane and the solid electrolyte layers located in the paste or on the electrode.
A further process for producing electrode/membrane composites from an ion exchanger material forming a core region and fuel cell electrodes contacted with both faces thereof is described in DE-C-4,241,150. The ion exchanger material is here formed from homopolymers or copolymers soluble in a solvent and having at least one radical which can dissociate into ions.
All preparation processes for gas diffusion electrodes with polymer membranes require a large number of in most cases manual working steps which are difficult to automate. Methods which are acceptable for experiments on laboratory scale frequently lead in industrial manufacture to insuperable obstacles, above all because of the high costs.
Even though fuel cells are already in use in the space travel industry, a general commercial use in the automobile industry, for example, is not foreseeable in the near future, since the production costs, in particular for membrane/electrode assemblies and the fuel cells resulting from them, are several orders of magnitude above the costs for conventional internal combustion engines. Also for use in the decentralized energy supply, the now available fuel cells are too expensive, for example as compared with oil heating and gas heating or diesel generators.
For the use in a car, however, fuel cells in conjunction with an electric drive represent a new drive concept which has some advantages. Thus, in the case of a fuel cell operated, for example, with hydrogen and oxygen, there is no pollutant emission at the vehicle, and the emission of the entire energy conversion chain is lower than in other vehicle drive systems. Moreover, the overall efficiency relative to the primary energy is significantly higher. The use of fuel cells in the automobile industry would make a noticeable contribution to the reduction of traffic-related pollutant emissions and the consumption of energy resources.
It is therefore the object to provide a process for producing laminates, in particular membrane/electrode assemblies suitable for use in fuel cells, which process allows the manufacture thereof in such a way that the production costs and the performance satisfy the requirements of the users.
The present invention achieves this object by providing a process for producing laminates, i.e. composites obtainable by bonding at least two components, in particular membrane/electrode assemblies, which contain at least one centrally arranged, ion-conductive membrane which is, at least over a substantial part (>50%) of its two mutually opposite flat faces, bonded to at least one catalytically active substance and to at least one two-dimensional, gas-permeable, electron-conductive contacting material, the bonding of at least two of the said components having been effected by lamination. The process comprises carrying out the bonding of the ion-conductive membrane, of the catalytically active substance and of the electron-conductive contacting material continuously.
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Bönsel Harald
Clauss Joachim
Deckers Gregor
Frank Georg
Heine Michael
Frommer & Lawrence & Haug LLP
Hoescht Research & Technology Deutschland GmbH & Co. KG
Osele Mark A.
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