DE102007025828B4 - Process for producing bipolar or electrode plates for fuel cell or electrolyzer stacks, and method for producing a stack of bipolar or electrode plates and bipolar or electrode plate - Google Patents

Abstract

Process for the production of bipolar or electrode plates for fuel cell or electrolyser stacks with a flow field in which the bipolar or electrode plate (1) has a middle field in the area of the flow field (3) on the parallel wire - Conductor tracks (2, 15, 16) are arranged, which consist of a conductive and corrosion-resistant metal, and in which the wire conductor tracks (2, 15, 16) are then partially coated with plastic, characterized in that the wire conductor tracks (2, 15, 16) according to the arrangement on the middle field on both sides of the bipolar plate (1) in the area of the flow field (3) are fixed in a pre-molded half-shell and that the wire conductor tracks (2, 15, 16) of Endlessly wound side to side.

Description

The invention relates to a method for the production of bipolar or electrode plates for fuel cell or electrolyzer stack and a bipolar or electrode plate.

Fuel cell bipolar or electrode plates are used to generate power and heat, or electrolyzer stacks to produce hydrogen and oxygen. Because of the basically same structure will be in the following only talk of a fuel cell. However, it equally means an electrolyzer stack.

A major impediment to the increased use of fuel cells (membrane fuel cell (PEM - Proton Exchange Membrane) or direct methanol fuel cell (DMFC - Direct Methanol Fuel Cell)) is the complex and complicated production of bipolar plates constructed fuel cell stack.

According to the state of the art bipolar plates made of metal or graphite are currently used. The openings and channels for the introduction and distribution of the reactants and the coolant are prepared by costly processes.

The state of the art also includes pressing methods for producing structured bipolar plates with subsequent post-processing.

For injection molding, there are mixtures of graphite and plastic (composite). The channel structure and the openings for the gas supply are completely injected.

The injection molding with these graphite-plastic mixtures (composite) has the disadvantage that these mixtures are relatively viscous and thus small structures can hardly or not be injected.

The prior art also includes bipolar plates, which are made only of sheet metal. The sealing is done with gaskets or molded gaskets.

The prior art ( US 6,071,635 A ) includes a separator plate containing a conductive metal plate. According to this prior art, the conductor track, seen in cross section, is brought into a wave-shaped form to form channel sections. This prior art separator plate has the disadvantage that in a first process step, the conductor must be reshaped and in a second process step, the reshaped circuit board must be arranged in an injection mold such that it can be encapsulated precisely with a plastic. This separator plate belonging to the prior art has the disadvantage that no small structures can be produced. The production is also expensive.

Furthermore belongs to the state of the art ( US 6,096,450 A ) a bipolar plate with an iron foil as a barrier layer and a gas distribution structure sprayed on both sides. Also, these prior art bipolar plate can not be made with very small structures. In addition, the production is relatively expensive.

Furthermore belongs to the state of the art ( FR 2 810 795 A1 ) a bipolar plate for a fuel cell having two metal plates. These bipolar plate is by training with metal plates only in a certain minimum size and consuming to produce.

The prior art ( US 6,511,766 B1 ) also includes a bipolar or unipolar plate for a fuel cell, which, however, also can not be made with very small structures.

The prior art ( EP 1 517 388 A1 ) also includes a process for the production of bipolar plates for fuel cell or electrolyzer stack, in which a punching tape and / or a board are punched and encapsulated in plastic. In this belonging to the prior art method, the punching and injection process are coupled together, since the strip material is cut in strips and pushed out of a central position. Subsequently, the injection process is carried out. This method can only be used with band-shaped materials.

All of the prior art bipolar plates have the disadvantage that they are very complex and expensive to manufacture. In addition, especially small structures for small-scale fuel cells can not or can not be easily manufactured.

The technical problem underlying the invention is to provide a method for the production of small bipolar plates for fuel cell or electrolyzer stack, which are extremely inexpensive to manufacture and beyond in spatially small dimensions to produce specify.

The inventive method for the production of bipolar or electrode plates for fuel cell or electrolyzer stack with a flow field, wherein the bipolar or electrode plate in the flow field a middle Field on which are arranged on the parallel wire conductor tracks, which consist of a conductive and corrosion-resistant metal, and in which then the wire traces are partially encapsulated in plastic, characterized in that the wire traces after arrangement on the middle field on both sides of the bipolar plate in the area of the flow field are fixed in a pre-molded half-shell and that the wire traces are wound from side to side endlessly.

During the manufacturing process, the wire tracks are advantageously fixed in their final position in a half-shell, so that they in the previously molded plastic part from a more than 200 ° C resistant plastic, in the same time the channels for the reactants (hydrogen (H ₂ ) and Oxygen (O ₂ )) are formed, a fixed position.

According to the invention, the wire traces are wound endlessly from side to side. In this way, one obtains a very simple production process, so that the bipolar or electrode plate can be produced inexpensively.

By forming the bipolar or electrode plate with wire conductor tracks, the bipolar and electrode plate according to the invention can be made very small in their structures. The structures may be made smaller than the prior art bipolar and electrode plates made by, for example, etching.

In the method, the contact surfaces to the anodes or cathodes are advantageously fixed alternately offset on both sides with half the circumference of the wire in the bipolar plate. This achieves a sufficient fixation with minimal use of material.

Advantageously, the wire tracks are arranged such that the wire tracks of opposite sides of the flow field are offset from one another. This offset allows for a simple way a continuous winding technique. On the other hand, it is possible by the offset to make the intermediate layer of plastic thinner. With the thickness of the plastic layer, care must be taken that the required gas tightness is ensured. Due to the offset of the wire tracks to each other, the plastic layer can be made thinner overall.

The wire conductor tracks are advantageously fixed only in the region of the channels (flow field) in a molded trough. This is preferably done in such a way that, when the bipolar or electrode plate is arranged in direct contact with a gas diffusion layer of a membrane, the wire conductor tracks make the current transition possible.

The particular advantage of the method according to the invention is that it is very easy to arrange very thin corrosion-protected wires (preferably smaller than 0.5 mm (millimeters) in diameter) at very short intervals. As a result, very small channels can be produced very economically.

It is also advantageous that the wires are already protected against corrosion when they are wound around the middle field. This eliminates post-processing of the metal during the manufacture of the bipolar and electrode plate.

According to a further advantageous embodiment of the invention, the channels for guiding the reactants are finished sprayed between the wire tracks in the injection process. By this manufacturing process to obtain a simple and thus inexpensive bipolar or electrode plate.

From the bipolar or electrode plates according to the invention can be a stack (stack) produced in a simple manner. At least one membrane carrying at least one gas diffusion layer is arranged between the plates. The course of the channels in a flow field is advantageously arranged in parallel between the opposing plate planes, so that in each case two mutually opposite wire conductor tracks are fixed with plastic and are arranged adjacent to pressure on both sides of the membrane carrying the gas diffusion layer. Preferably, the gas diffusion layer should be compressed by about 40%.

This contact pressure must be maintained relatively accurately. If the pressure is too low, the contact resistance is too high. But if it is too high, no gases can penetrate through the gas diffusion layer, so that an insufficient gas supply arises.

The attachment of the wire tracks outside of the flow field on a conductive sheet metal frame is advantageously carried out so that the wire tracks are wrapped endlessly in the area of the flow field from side to side and applied to a flap raised from the sheet metal frame. This contact between wire and sheet metal frame is soldered in accordance with a preferred embodiment of the invention. This achieves good current and heat transfer from the wire track to the sheet metal frame.

At this soldered contact point advantageously a plastic frame made of temperature-resistant plastic and a seal made of thermoplastic elastomer (TPE) are sprayed in 2-component technology. This causes the fuel cell to be gastight in the area of the flow field.

If the outer surface of the sheet metal frame protrudes beyond the plastic frame with gasket, this "cooling surface" can be used to release excess heat to the environment.

Advantageously, a stack is built up by juxtaposing the same sections. In this case, the first portion of a bipolar plate on distribution channels and connections for the reactants and a membrane electrode assembly (MEA). The membrane-electrode assembly of this first section forms the gas-tight and electrically insulating, but proton-conductive boundary of the second section. The membrane-electrode unit of the second section forms the gas-tight and electrically insulating, but proton-conductive boundary of the third section and so on.

According to a further advantageous embodiment of the invention, a plurality of juxtaposed cells are arranged as a series or parallel circuit in the bipolar or electrode plate according to the invention in the same plane.

According to a further advantageous embodiment of the invention, the membrane-electrode unit is formed with a division, such that the conductive diffusion layer is adapted to the size of the flow field.

At both ends of the electrode stack usually end plates are arranged, between which the individual juxtaposed sections are clamped with their seals. The end plates advantageously have connections for the supply and removal of the reactants.

The bipolar or electrode plate according to the invention is characterized in that the bipolar or electrode plate in the region of the flow field has a central field, are arranged on the parallel wire conductor tracks, which consist of a conductive and corrosion-resistant metal, and that the Wire interconnects are partially molded with plastic. As a result, the bipolar or electrode plate according to the invention has the advantage that it can be manufactured in very small dimensions in an automated process from corrosion-protected wire conductor tracks in the area of the flow field and is connected to a current and heat-conductive sheet metal frame.

The wire conductor tracks are advantageously formed from a current and heat conductive and corrosion-protected metal. This has the advantage that the heat is dissipated well. Because the wire conductor tracks are formed from a corrosion-protected metal from the outset, the bipolar or electrode plate according to the invention no longer has to undergo electroplating during the manufacturing process, for example.

According to a further advantageous embodiment of the invention, the contact surfaces of the anodes and cathodes have a low contact resistance, so that the least possible power losses occur.

According to an advantageous embodiment of the invention, good contact between the membrane-electrode assembly (MEA) and the anode or cathode is achieved by a surface coating, for example gold.

The sheet metal frame is punched according to a particularly preferred embodiment of the invention in the endless belt, soldered with wound wire conductor tracks in the flow field and sprayed with plastic and gasket. Several rows can be placed side by side and thereby a multiple arrangement, for example a group of four can be made. As a result, the interconnection of series and / or parallel connection in the same plane with corresponding connecting webs between the individual flow fields or with an assembly on top of each other in several levels to a stack (stack) can be achieved.

For example, a particularly low profile elastic fuel cell can be fabricated from only one plane by using thin sheet metal for the outer frame and thermoplastic elastomer for the plastic frame and the gasket. This construction should preferably be carried out with an open cathode, because then the pump for the oxygen supply and the fan for the cooling can be omitted.

The wire used for the wire conductor tracks is advantageously coated, for example gold-plated. It is also possible to form the wire from solid material such as gold or palladium. It is necessary in this case for the wire conductor tracks to have the required conductivity and for another to be cost-effective.

According to a particularly preferred embodiment of the invention, a high-temperature plastic is provided in the bipolar or electrode plate according to the invention, the durable endures temperatures of 180 ° C to 260 ° C. As a result, the longevity of the bipolar or electrode plate according to the invention is ensured.

Be particularly advantageous, the use of the plastic polyphenylene sulfide has been found.

According to a further advantageous embodiment of the invention, the plastic for the flow field and the plastic frame on a seal made of an elastic thermoplastic elastomer (TPE).

The material PTS-Thermoflex V50 · 710 has proved particularly advantageous for the gasket.

Further features and advantages of the invention will become apparent from the accompanying drawings, in which an embodiment of a bipolar plate according to the invention is shown only by way of example. In the drawing show:

1 a longitudinal section through a bipolar plate;

2 a cross section through a stack of bipolar plates;

3 a detail of 1 ;

4 a representation of the connection for supplying the reactants in plan view.

The 1 and 3 show a bipolar plate 1 with a conductor track 2 , which is designed as a wire conductor. The wire trace 2 is about a flow field 3 wound. The winding is designed as a continuous winding.

After wrapping the flow field 3 becomes the wire trace 2 on rags 4a . 4b a sheet metal frame 5 created. Subsequently, the sheet metal frame 5 , the rag 4a . 4b and the end of the wire tracks 2 with a plastic frame 6 molded. This plastic frame is also a seal 7 molded.

As in 3 is represented by the flow field 3 which also. is formed as an injection molded plastic part, and the wire conductor 2 channels 8th . 9 formed in which hydrogen H ₂ (channel 8th ) and oxygen O ₂ (channel 9 ) to be led.

In 2 is a stack 10 shown, made of bipolar plates 1 . 11 . 12 consists. The wire tracks 2 are in the flow field 3 arranged up to half, that is half-coated with plastic. Between the wire tracks 2 are the channels 8th . 9 educated. Between the bipolar plates 1 . 11 . 12 are membranes carrying gas diffusion layers 13 arranged. The channels 9 . 14 in a flow field are arranged in parallel between the opposite plate planes, so that in each case two mutually opposite wire conductor tracks 15 . 16 plastic encapsulated or fixed and with pressure on both sides of the gas diffusion layer bearing membrane 13 are arranged adjacent. On the opposite sides of the flow field 3 are the wire tracks 2 . 15 staggered to each other. As a result, the plastic layer can be made thinner than when the wire tracks 2 . 15 are arranged opposite, since the thickness of the plastic of the flow field 3 must have a certain thickness to ensure the required gas tightness.

4 shows the bipolar plate 1 with the wire tracks 2 and the flow field 3 , The bipolar plate 1 has the sheet metal frame 5 as well as the molded seal 7 on. The channels 8th . 9 lead to an opening 17 , The opening 17 represents an access for the hydrogen (H ₂ ) or the oxygen (O ₂ ).

The outlet (not shown) is located diagonally to the entrance, and the change from H ₂ to O ₂ is made by rotating the bipolar plate in the stack.

LIST OF REFERENCE NUMBERS

1

bipolar

2

Wire conductor track

3

Flow Field

4a

cloth

4b

cloth

5

sheet metal frame

6

Plastic frame

7

poetry

8th

channel

9

channel

10

Stack

11

bipolar

12

bipolar

13

Gas diffusion layer bearing membrane

14

channel

15

Wire conductor track

16

Wire conductor track

17

Access for H ₂ and O ₂

Claims (17)

Method for producing bipolar or electrode plates for fuel cell or electrolyzer stacks with a flow field, in which the bipolar or electrode plate ( 1 ) in the area of the flow field ( 3 ) has a middle field, on the parallel wire conductor tracks ( 2 . 15 . 16 ) are arranged, which consist of a conductive and corrosion-resistant metal, and then the wire traces ( 2 . 15 . 16 ) are partially encapsulated with plastic, characterized in that the wire tracks ( 2 . 15 . 16 ) after placement in the middle field on both sides of the bipolar plate ( 1 ) in the area of the flow field ( 3 ) are fixed in a pre-sprayed half shell and that the wire traces ( 2 . 15 . 16 ) are wound endlessly from side to side. Method according to claim 1, characterized in that the wire tracks ( 2 . 15 . 16 ) are arranged such that the wire tracks ( 2 . 15 . 16 ) of opposing sides of the flow field ( 3 ) are offset from each other Method according to one of the preceding claims, characterized in that between the wire tracks ( 2 . 15 . 16 ) in the injection process channels ( 8th . 9 ) are sprayed finished to guide the reactants. Method according to one of the preceding claims, characterized in that the wire conductor tracks ( 2 . 15 . 16 ) in an outer frame ( 5 ) are mounted from sheet metal and soldered. A method according to claim 4, characterized in that at the soldered connection point a plastic frame ( 6 ) with seal ( 7 ) on both sides of the flow field ( 3 ) is injected. Method according to claim 5, characterized in that the wire tracks ( 2 . 15 . 16 ) on at least one of the sheet metal frame ( 5 ) raised lobe ( 4a . 4b ). Method for producing a stack of bipolar or electrode plates, produced according to one of the preceding claims, characterized in that between the opposing wire conductor tracks ( 2 . 15 . 16 ) at least one membrane carrying at least one gas diffusion layer ( 13 ) is arranged. A method according to claim 7, characterized in that the course of the cannula ( 8th . 9 ) in the flow field ( 3 ) is arranged in parallel between opposite wire track planes, so that the wire tracks ( 2 . 15 . 16 ) each on both sides with pressure on the at least one gas diffusion layer-bearing membrane ( 13 ) issue. Method according to claim 7, characterized in that the stack ( 10 ) is constructed by juxtaposing similar sections, wherein a portion of an electrode plate ( 1 ) Distribution channels and connections for the reactants and a membrane-electrode assembly (MEA). Method according to one of claims 7 to 9, characterized in that a plurality of adjacent cells are arranged as a series or parallel circuit in the same plane. Method according to claim 10, characterized in that the membrane-electrode unit has a division for adaptation of the conductive diffusion layer to the size of the flow field ( 3 ) such that the conductive diffusion layer is the size of the flow field ( 3 ) adapted adapted. Method according to one of claims 7 to 11, characterized in that at both ends of the electrode stack ( 10 ) End plates are arranged, between which individual juxtaposed sections are clamped with seals, and that the end plates have connections for the supply and removal of the reactants. Bipolar or electrode plate produced by the method according to claim 1, characterized in that the bipolar or electrode plate ( 1 ) in the area of the flow field ( 3 ) has a middle field, on the parallel wire conductor tracks ( 2 . 15 . 16 ) are arranged, which consist of a conductive and corrosion-resistant metal, and that the wire tracks ( 2 . 15 . 16 ) formed partially encapsulated in plastic and fixed in a pre-injection half-shell. Bipolar or electrode plate according to claim 13, characterized in that the wire conductor tracks ( 2 . 15 . 16 ) are formed from a current and heat conductive and corrosion-protected metal. Bipolar or electrode plate according to claim 13 or 14, characterized in that between the membrane-electrode assembly (MEA) and the anode or cathode, a surface coating is provided. Bipolar or electrode plate according to one of claims 13 to 15, characterized in that a high-temperature plastic is provided as a plastic, which can withstand temperatures of 180 ° C to 260 ° C permanently. Bipolar or electrode plate according to claim 13, characterized in that as a plastic polyphenylene sulfide is provided.

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