Method for producing bipolar plates for fuel cells

Abstract

A method for producing bipolar plates for fuel cells, one metal strip or two metal strips is/are guided through a second or third device. The second device is designed to carry out fine cleaning and/or nitriding of the metal strip, and the third device carries out surface coating on one side of a surface with a metal layer that improves adhesion. Applying a carbon layer in a fourth device. The metal strips are then shaped, during which process channels are formed. The shaped metal strips are moved and positioned such that surface regions come into contact with one another. Joining is performed with a laser beam, which is directed into a gap between the shaped metal strips moved towards one another. The individual steps in the devices, like shaping and joining, are carried out in a continuous process.

Claims

1. A method for producing bipolar plates for fuel cells, arranging a bipolar plate on at least one side of at least one of two electrodes of fuel cells which can be electrically conductively connected to a membrane-electrode arrangement, wherein the membrane-electrode which form an electrolyte is a polymer membrane, wherein guiding one metal strip or two metal strips through a second device or a third device, wherein the second device is designed to carry out fine cleaning or nitriding of the metal strip and the third device is designed to carry out surface coating on one side of a surface with a metal layer that improves adhesion, and applying a carbon layer to the surface thus treated in a fourth device, and subsequently shaping the metal strips is carried out, in which channels are formed for the supply of fuel and oxidant and the removal of reaction products of the electrochemical reactions, wherein the then shaped metal strips are moved towards one another and positioned in such a way that surface regions in which a joining with material continuity is to be performed come into direct contact with one another, and a joint is formed with at least one laser beam which is directed into a gap between the shaped metal strips moved towards one another and a welded joint is formed only there, and during this process the individual steps of shaping and joining in the devices are carried out one after the other in a continuous process.

2. The method according to claim 1, wherein the second device, third device and fourth device are operated under reduced internal pressure relative to the environment and are separated from the environment or from one another by sluices.

3. The method according to claim 1, wherein the one metal strip or the two metal strips are guided in a conveying direction upstream of the second device or third device through a first device which is designed for precleaning the metal strip or the one or two metal strips.

4. The method according to claim 1, wherein during the feed movement of one of the metal strips thus pretreated, after formation of the carbon layer, a preferably central division in the feed axis direction and rotation of one of the divided metal strips by 180° or a 180° rotation of one of the two metal strips thus pretreated is carried out.

5. The method according to claim 1, forming the carbon layer with sp2 hybridized carbon on a surface of the one metal strip or the two metal strips by the fourth device by means of non-pulsed ion implantation at high ion energies, wherein ion energies greater than 100 eV are maintained.

6. The method according to claim 1, wherein pre-cleaning is carried out wet-chemically or by means of a heat treatment in which hydrocarbon compounds are oxidized and then the oxidation products are removed.

7. The method according to claim 1, wherein the fine cleaning or the nitriding is carried out with a plasma, wherein the metal strip(s) has/have been heated to a temperature in the range 320° C. to 450° C.

8. The method according to claim 1, wherein an adhesive layer is formed in which metal ions, are placed onto the surface to be coated by means of an electric arc process.

9. The method according to claim 1, wherein at least two shaping tools of at least one tool pair, through which the pretreated metal strips are moved and the surfaces of the tool pair facing each other are formed for shaping the pretreated metal strips, are used for shaping the pretreated metal strips.

10. The method according to claim 1, wherein the shaping of the metal strips is carried out in such a way that regions of the metal strips to be joined with material continuity with laser radiation are either not shaped or are shaped in such a way that, following the shaping, these surface regions are positioned with respect to one another during the joining in such a way that they come into direct contact with one another and, before the joining, a gap is formed between the shaped metal strips to be joined, into which gap the at least one laser beam can be directed onto the surface regions to be joined.

11. The method according to claim 10, wherein the metal strips are circumferentially joined with the at least one laser beam from the direction of one of the two metal strips and at least in the edge region of the bipolar plates and a media supply.

12. The method according to claim 1, wherein a nitration is carried out at temperatures below 450° C. in a nitrogen atmosphere in the second device for a period of time of at the most 5 minutes.

13. The method according to claim 1, wherein the one metal strip or the two metal strips made of a steel or titanium is/are used.

14. The method according to claim 1, wherein the two metal strips are moved in parallel alignment to each other and at the same speed through the devices and an apparatus for joining the metal strips, maintaining this speed also during shaping and, if necessary, during a strip turn or rotation.

15. The method according to claim 1, wherein in the second device or in a further device which is arranged upstream of the fourth device in a feed movement direction of the one metal strip or of the two metal strips, an additional carburizing is carried out by adding carbon.

16. The method according to claim 1, wherein the metal strips of different thickness are used.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention is intended to be explained subsequently in more detail, by way of example.

(2) In the drawings:

(3) FIG. 1 schematically shows an example of the implementation of the method according to the invention and

(4) FIG. 2 shows one way of joining two pretreated metal strips.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) In the example shown in FIG. 1, a metal strip 1 is unwound from a roller 8 and fed via a deflecting roller 9 into a first device 2 for carrying out a preliminary cleaning.

(6) From there, the metal strip 1 is conveyed further into a second device 3, in which fine cleaning and nitriding is carried out by means of plasma. The metal strip 1 thus treated is then further conveyed to the third device 4, in which a chromium layer is formed to improve adhesion and provide corrosion protection on surfaces of the metal strip 1.

(7) A carbon layer is then formed in the fourth device 5.

(8) At least the second to fourth devices 3 to 5 should have an internal pressure that is lower than the ambient pressure and is suitable for carrying out the respective process in the respective device.

(9) A sluice is provided between each of the devices 2 to 5, wherein the sluice 6.2 provides the transition from the first device 2 to the second device 3 in this example, with an internal pressure below ambient pressure, wherein the sluices 6.3 provide transitions between the third device 4 with reduced internal pressure and sluice 6.4 provides the transition from a fourth device 5 with reduced internal pressure in relation to the ambient atmosphere. A sluice 6.1 is also provided in front of the first device 2.

(10) A device 10 is arranged downstream of the fourth device 5 in the feed movement direction of the metal strip 1, with which a separation of the metal strip 1 into two pretreated metal strips 1.1 and 1.2 is achieved. In this case, the metal strip 1 can be separated preferably centrally parallel to the axis of feed movement of the metal strip 1.

(11) One of the two pretreated metal strips 1.2 thus obtained is fed to a device 11 by which it is rotated by 180°. Since usually only one surface of the metal strip is pretreated, the rotation is carried out in such a way that the pretreated surfaces of the metal strips 1.1 and 1.2 do not face each other.

(12) In this example, each of the metal strips 1.1 and 1.2 is fed to at least one shaping device 7 and conveyed further. After shaping, the strip is no longer planar but has a wavy, typically three-dimensional surface with depressions or elevations.

(13) The forming device can, for example, comprise embossing rollers which are structured in such a way that the metal strips 1.1 and 1.2 are deformed in such a way that depressions and, if required, also elevations, in the form of channels or mounds, can be formed for the supply and removal of operating materials and reaction products and their distribution within fuel cells. In this case, the rollers consist of pairs, one of which forms the female and one the male die.

(14) The metal strips 1.1 and 1.2 thus shaped are fed to a device 12 for joining with material continuity, which can preferably be carried out with laser radiation.

(15) Subsequently, a separation and further production of fuel cells can be carried out as explained in the general part of the description.

(16) FIG. 2 shows how two metal strips 1.1 and 1.2, one of which has the anode-side channel structure and one of which has the cathode-side channel structure, which have been shaped and rotated in a suitable shape relative to each other, are moved together into the gap between the two rollers 7.1 and 7.2. When the rollers 7.1 and 7.2 rotate, they also continue to move.

(17) If, by means of the rollers 7.1 and 7.2, surface regions of the shaped metal strips 1.1 and 1.2 are brought into direct contact with one another, at which an integral bond is to be produced, a laser beam 13 is directed into the gap between the rollers 7.1 and 7.2 onto surfaces of the pre-treated and shaped metal strips 1.1 and 1.2 which are to be directed towards one another, so that an integral welded joint is made at these positions. At these positions, surface regions of the metal strips 1.1 and 1.2 come into contact with each other. The channel structure formed between the metal strips 1.1 and 1.2 may form the cooling channels.

(18) The laser beam 13 can be directed to the respective positions for forming the integral joints by means of two reflecting elements 14.1 and 14.2, which form a scanner or galvo scanner, and by means of which it can be deflected to the respective positions at which integral joints with material continuity are to be made. By means off-theta optics 15, the focal length and thus the position of the focal plane of the laser beam 13 can be influenced in a defined manner.