DE2402156A1 - BIFUNCTIONAL ELEMENT FOR FUEL CELL WITH FILTER PRESS DESIGN - Google Patents

Description

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PBO / F / RCH
F 8702

SOCIETE GENERALE DE CONSTRUCTIONS ELECTRIQUES ET MECANIQUES

ALSTHOM & Cie 38 Avenue Kleber, 75784 PARIS CEDEX l6 (France)

BIFUNCTIONAL ELMENT FOR FUEL CELL WITH FILTER PRESS CONSTRUCTION

The invention relates to a bifunctional element or a porous electrode for fuel cells, in particular for a cell that contains a liquid fuel such as methanol and a gaseous oxygen carrier such as air or ■ Oxygen used seibat.

It also relates to a manufacturing method for such an electrode.

Eb electrodes are known which mainly consist of a catalysis layer applied to a support, wherein one of the sides of the carrier is in contact with an electrolyte, which forms the fuel in a dissolved state or as an emulsion.

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2402136

holds while the other side of the carrier is in contact with the oxygen carrier. Current collectors are in a conductive connection with these sides and ensure the transport of the electrons that graze freely during the electrochemical process.

However, such electrodes have certain disadvantages.

In particular, they usually have insufficient porosity, which results in the need to use high Use pressurized oxygen carriers.

In addition, such electrodes have low potentials and conductivities, the fourth of which is very far from the optimal Deviate from values that correspond to the maximum performance of the electrochemical generator for a given electrolyte.

In addition, certain types of electrodes are used Finely ground nickel mesh or stainless steel mesh used, which is embedded in the catalysis layer - whereby the manufacturing price increases significantly.

The invention is intended to remedy such disadvantages. It concerns a bifunctional element or a porous electrode, which has optimal properties in terms of conductivity and potential, but simple and can be manufactured at low cost.

The invention relates to a bifunctional element or a porous electrode for fuel cells with

- A catalytic layer composed of a mixture of a catalyst and a polymer, especially polytetrafluoroethylene,

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ORIGINAL

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- a so-called barrier layer, which is applied to the catalytic layer and whose main component is the named polymer,

- a cathode current collector, which has electrical contact with the barrier layer and is made of an electron-conducting and chemically inert metal,

- a mambran on which the catalytic layer is applied, wherein the barrier layer is made electrically conductive by adding a conductive substance to the polymer, characterized in that that the cathode current collector is preferably glued to the barrier layer with the aid of a conductive lacquer.

The manufacturing process of such an electrode is characterized in that one after the other

- The catalysis layer is applied to the membrane by distributing a mixture of a catalyst with 80 to 40% by weight and of polytetrafluoroethylene with 20 to 60% by weight, which are preferably dispersed beforehand in dibutyl phthalate,

- this arrangement is dried,

- The conductive barrier layer is applied to it by a mixture of polytetrafluoroethylene with 80 to 30% by weight and carbon of $ 20 to $ 70 by weight, previously preferred are dispersed in dibutyl phthalate, are spread,

- the whole thing is dried,

- then by heating in a neutral or reducing atmosphere

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ORIGINAL! NSPECTED

at a temperature of 350 to 420 ° for 5 to 50 minutes is sintered,

- · this cathode current collector on the barrier layer with the help a conductive varnish is glued.

Further characteristics and advantages of the invention are given in the following description on the basis of an exemplary embodiment clarified with reference to the accompanying figure. The layers in this figure have been intentionally greatly enlarged drawn.

The figure shows a porous electrode according to the invention with a porous catalytic layer 1, which consists of a mixture of activated carbon and polytetrafluorethylene (PTFE) with practically 70 or 30% by weight is formed. On this layer 1 a layer 2. the so-called conductive barrier layer is applied, which consists of a mixture of PTFE and graphite with about 40 or 60% By weight. It is also shown a cathodic current collector 3, the electrical connection with the Adjacent electrode (not shown) produces, of course, the described electrode to an electrode assembly that forms the fuel cell; such a whole corresponds to the filter press construction.

The current collector 3 is attached to the barrier layer 2 with the aid of a conductive lacquer which is sufficiently rigid to prevent changes in resistance not to let occur, glued to the barrier layer 2. Such a paint is mixed with graphite dust Epoxy resin.

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The catalysis layer 1 - is applied to a membrane 4, which consists, for example, of asbestos paper impregnated with epoxy resin. Advantageously, this membrane can consist of one Gewehe made with intertwined and calcined in a neutral atmosphere Viscose cellulose fibers are made.

The figure also shows an anodic current collector 5, which establishes the electrical connection with the neighboring electrode (not drawn) and the membrane 4 opposite Side carries an anodic catalysis layer.

One of the sides of the electrode shown in this way is fed along the arrow F with methanol and an electrolyte formed from a potassium buffer solution or an alkaline carbonate solution, while the other side along the arrow ΐ ^1? is supplied with air.

The manufacturing process for such a porous electrode is as follows:

The catalysis layer 1 is applied to the membrane L , which is made of either epoxy resin-soaked asbestos paper or a fabric of cellulose previously formed in a neutral atmosphere with about 400 ° C., using a known screen printing process, and a predetermined thickness is maintained. For this purpose, the activated carbon and the PTFE are previously dispersed in dibutyl phthalate or water, so that an oily ink is obtained. After drying, a porous layer 1 results, on which the barrier layer 2 is placed using an analogous technique *

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Then the whole thing becomes neutral or reducing Atmosphere at a temperature of about 340 ° to 400 ° C for 30 to 60 minutes.

Then only the current collector 3 needs to be used up the barrier layer 2, as previously indicated, glued.

/ Ulf this way one obtains an electrode whose thickness is about 200 to 350 microns total and has a porosity of 50 ^.

The electrodes produced in this way can, as shown above, be combined to form a battery cell in accordance with the filter press design. Of course, especially the anodic separators 5 taken into account.

It should also be noted that such a soft and porous electrode allows the fuel cell to supply air with only a slight overpressure of a few grams per ci7i2, which can be done easily with the help of a normal fan can be achieved.

In addition, in the case that the membrane consists of a fabric made of calcined cellulose, the electrode can be used in any chemical medium, and especially in an acidic medium.

Finally, it is also noteworthy that the barrier layer 2 prevents the methanol from passing through the electrode and evaporates, since the temperature of the whole is around 75 ° C.

- Claims 409831/0772

Claims (6)

24,9156 PATSTT APPROPRIATIONS (ϊ.) Bifuiictionales element or a porous electrode for Fuel cells, with - A catalytic layer composed of a mixture of a catalyst and a polymer, especially polytetrafluoroethylene, - a so-called barrier layer, which is applied to the catalytic layer and whose main component is the named polymer, - a cathode current collector, which makes electrical contact with the Has a barrier layer and is made of an electron-conducting and chemically inert metal, - a membrane on which the catalytic layer is applied, the barrier layer being rendered electrically conductive by adding a conductive substance to the polymer, thereby characterized in that the cathode current collector (3) is preferably applied to the barrier layer with the aid of a conductive lacquer (2) is glued. 2. Element according to claim 1, characterized characterized in that the membrane (4) consists of a consists of asbestos film impregnated with an epoxy resin. 3. Element according to claim 1, characterized characterized in that the membrane consists of a woven fabric made of intertwined and under an inert or reducing atmosphere cellulose fibers calcined at a temperature of 340 to 400 ° C is formed. 4 0 9 8 3 1/0772 4. Element according to any one of claims 1 to 3, characterized in that the conductive Lacquer contains graphite. 5. Manufacturing method for an element according to claims 1 to 4, characterized in that - The catalytic layer (1) is applied to the membrane (4) by a mixture of a catalyst with 80 to 40 percent by weight and made of polytetrafluoroethylene weighing $ 20 to $ 60 s fraction, which are preferably dispersed beforehand in dibutyl phthalate, is distributed, - this arrangement is dried, - On top of it the conductive barrier layer (2) is applied by adding a mixture of polytetrafluoroethylene with 80 to 30 $ by weight and carbon with 20 to 70 $ by weight, the previously are preferably dispersed in dibutyl phthalate, is spread, - the whole thing is dried, - then by heating in a neutral or reducing atmosphere is sintered at a temperature of 350 to 420 ° for 5 to 60 minutes, - this cathode current collector (3) is glued to the barrier layer with the aid of a conductive lacquer. 6. Electrochemical generator, in particular of the filter press design, with at least one element according to FIG one of the preceding claims. 409831/0772