Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Patent
1995-07-12
1998-03-03
Gorgos, Kathryn L.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
204282, 204283, 204296, 429 30, 429 33, 429 41, 521 27, 156 60, C25B 1300, C25B 1100, H01M 810, B31B 160
Patent
active
057230862
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of PCT/DE93/01162 filed Dec. 2, 1993.
FIELD OF THE INVENTION
The invention relates to an electrode membrane comprising an ion exchange material forming a core zone and electrodes bonded on either side thereof, for fuel cells or electrolyser, and to a method of manufacturing these electrode membranes.
BACKGROUND OF THE INVENTION
Electrolysers and fuel cells are electrochemical systems which can convert electrical energy into chemical energy (principle of electrolysis) or chemical energy into electrical energy (fuel cell principle). Thus a water electrolyzer with the aid of electrical energy produces hydrogen and oxygen, and conversely a hydrogen/oxygen fuel cell converts these gases into water, releasing electrical energy. In order to operate, these systems among other things require two catalytically active electrodes for electrochemical conversion of the chemical substances, and an ion-conducting electrolyte between the electrodes for charge transfer.
Examples of modern electrolyzer and fuel cell constructions are systems which do not use any liquid electrolyte, but rather highly-conductive polymeric ion exchange membranes (polymeric solid electrolytes).
The central purpose of these systems is the production of the membrane electrode unit with the smallest possible resistance, in order to minimize the excess voltages occurring. This initially means the realization of minimum electrical losses during the transition between electrode and ion-conductive membrane. In this case an intensive bonding is necessary of the polymeric membrane to the catalyst, in order to ensure problem-free supply or derivation of the protons migrating through the membrane towards or from the catalyst, and the transfer of electrons between electrode and reactant. When there is poor bonding, no direct contact exists, at least at many points, between the materials, which leads to an excess voltage. In addition, porous membrane and catalyst surfaces are desirable, in order to make a large area available, because of their roughness, for the three-phase contact of membrane/catalyst/liquid or gas. A low resistance of the electrode-membrane-electrode unit in addition means realization of a low resistance of the ion exchange membrane itself, in which case minimal thickness and high ion exchange capacity play an important part.
In the prior art, insoluble and infusible ion exchange membranes are proposed for the polymeric solid electrolyte. These prefabricated membranes are subsequently brought into contact with the electrodes by means of wet chemical or hot pressing methods.
In the wet chemical method the membrane is for example incorporated in a coating cell, so that the cell is divided by the membrane into two spaces separate from one another. One side contains hexachloroplatinic acid, the other for example hydrazine as a reduction agent, which diffuses through the membrane and precipitates platinum in the surface area of the membrane. Such a method is described by H. Takenaka and E. Torikai (JP 80-38934, Application 78/110, 267 of 7 Sep. 1978).
Alternatively, the catalyst may be bonded by means of application of pressure. In this case the outset material is the catalytically active powder, which is pressed on to the membrane. A general description of the pressing method appears in Appleby, Yeager, Energy (Oxford), 11 (1986), 137.
Although operative membrane electrode units can be produced by this method, they have disadvantages. Both methods use the polymeric ion conductor in a solid, i.e. dimensionally stable phase. A certain degree of bonding is in fact provided between catalyst and polymer, but it is scarcely possible to achieve the desired intensive, adhesive-like bonding of both materials. It is only possible with difficulty to provide an additional surface porosity of the dense membrane used. In addition, both methods are critical precisely for coating extremely thin membranes, i.e. membranes with low resistance. In the case of a wet chemical process, there is the risk that the metal preci
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Bauer Michael
Ledjeff Konstantin
Mahlendorf Falko
Nolte Roland
Peinecke Volker
Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung
Gorgos Kathryn L.
Wong Edna
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