WO2020007677A1

WO2020007677A1 - Method and device for producing a bipolar plate half for a fuel cell

Info

Publication number: WO2020007677A1
Application number: PCT/EP2019/066985
Authority: WO
Inventors: Martin Schoepf; Arne Stephen FISCHER
Original assignee: Robert Bosch Gmbh
Priority date: 2018-07-06
Filing date: 2019-06-26
Publication date: 2020-01-09
Also published as: DE102018211187A1

Abstract

The invention relates to a method and a device for producing a bipolar plate half (14) for a fuel cell. The method comprises the steps of synchronously passing an endlessly circulating screen (40) past a moving substrate (48), applying a media distribution material (62) onto the substrate (48) by means of a screen printing step for forming a media distribution structure (44), and lifting the screen (40) from the substrate (48).

Description

description

Title:

Method and device for producing a bipolar plate half for a

fuel cell

The present invention relates to a method and an apparatus for

Manufacture of a bipolar plate half for a fuel cell. The invention also relates to a fuel cell which comprises at least one bipolar plate half which is produced by the method according to the invention.

Fuel cells are electrochemical energy converters in which, for example.

Hydrogen and oxygen are converted into water, electrical energy and heat. Generic fuel cells or

Fuel cell stacks are constructed from membrane electrode units and bipolar plates which are arranged alternately one above the other. Here, the bipolar plates, which can be formed from two adjacent bipolar plate halves, serve to supply the electrodes with starting materials and to cool the fuel cell stack. For this purpose, the bipolar plates have a distributor structure which guides fluids containing starting material along the electrodes. In addition, the distributor structures serve to guide a cooling fluid along the further distributor structures. These distributor structures are designed as channels, as a result of which the different fluids can be conducted.

State of the art

WO 2017/215872 A1 discloses a method for producing a bipolar plate for a fuel cell, a plate-shaped workpiece being produced in this method, and a media distribution structure being introduced into the plate-shaped workpiece. The background of the invention lies in the fact that the gas diffusion layer (GDL) which is in contact with the bipolar plate half and pressurized penetrates into the channel structure, so that the effective channel cross section available for media distribution is reduced.

In addition, there is the problem that the

Bipolar plate half accumulates water on the cathode side. This water is typically formed between the GDL and the membrane and has to leave the GDL in the direction of the air channels in the half of the bipolar plate, where it is removed by the air flow. However, this process is hindered by the webs on the bipolar plate half resting on the GDL, so that there is water accumulation there.

However, these problems could be solved if the web width and the channel width were reduced. To the rough distribution of

A conventional bipolar plate half is typically produced by embossing a channel structure in an approximately 0.1 mm thick sheet metal to ensure operating media with a low pressure drop and without major costs. With regard to the channel dimensions, in particular the channel width, limits are thereby specified which result from the sheet thickness and the stamping process.

The object of the present invention is therefore a method

to provide, with which the aforementioned problems can be solved economically. In addition, it is an object of the invention to provide a device for performing such a method.

Disclosure of the invention

The object is achieved by a method for producing a bipolar plate half for a fuel cell. This method comprises the steps of synchronously passing an endlessly rotating screen past a moving substrate, applying a media distribution material onto the substrate by means of a screen printing step to form a

Media distribution structure, and the lifting of the screen from the substrate. A screen in the sense of the invention is understood to be a mask which has a negative shape of the structure to be created. This mask may also be around support structures for stabilizing the

Media distribution structure added. A synchronized passing in the sense of the invention is understood to mean that the speed of the screen and the substrate are matched to one another. As a result, there is no relative speed between the screen and the substrate. As

Media distribution structure or media distribution material is understood to be the channel structure provided for guiding and distributing the media or the material from which the channel structure is produced. An electrically conductive paste, in which carbon black is embedded in a binder, is preferably used as the media distribution material. The use of soot in one

Media distribution material has the advantage that the coated sheets used in the prior art have a higher corrosion resistance. In a preferred embodiment, the substrate is sheet metal or foil.

No sheet is thus embossed in the method according to the invention. When the bipolar plate half is formed, the usual limits set by the stamping process of the sheet are therefore not present. With the

The method according to the invention makes it possible to provide significantly smaller web widths, channel widths and channel heights. Likewise, more flexible

Structures are made. The method according to the invention thus forms flexible structures on the order of magnitude of preferably 100 pm to 500 pm. Structures in one are particularly preferred

Order of magnitude from 100pm to 200pm.

Due to the smaller channel width, the GDL is better supported, so that the GDL hardly penetrates into the channel structure and thus the cross section is not reduced. Due to the smaller width of the webs, the water drainage is hardly hindered, so that there is hardly any

Water accumulation in the area of the piers comes. This will create a

trouble-free and efficient operation of the fuel cell ensured.

The invention has the additional advantage that a minimum stack height is achieved due to the lower channel height of the bipolar plate half. This results in a smaller space requirement for the fuel cell. Thanks to the endlessly circulating sieve and the screen printing step, this has

The method according to the invention additionally has the advantage that a bipolar plate half produced using this method can nevertheless be produced economically.

In a preferred development of the invention, a heating step of the media distribution material applied to the substrate is carried out after the screen has been lifted off the substrate. This has the advantage that the

Drying process ends faster after the sieve is lifted off and the bipolar plate half can thus be used more quickly.

In a preferred embodiment of the invention, a heating step is carried out between applying the media distribution material and lifting off the screen. In this heating step, the media distribution structures are pre-consolidated before the sieve is lifted off. This improves the detachability of the screen from the media distribution structures and reduces the proportion of media distribution material residues in the screen. This has the advantage that the shape accuracy of the media distribution structures is improved.

In a further preferred embodiment of the invention, the method comprises the step of cleaning the screen after it has been lifted off

Substrate. The step of cleaning will leave any remaining in the sieve

Media distribution material remnants removed. With a subsequent one

Coating process, these residues do not interfere with the formation of the

Media distribution structures. This ensures high quality in the formation of the media distribution structures.

The method advantageously comprises the step of checking the screen after it has been lifted off the substrate. In this step, it is checked in particular whether the screen has defects which affect the formation of the media distribution structure or could lead to failure of the screen. In addition, it can preferably be checked whether a previous cleaning step has been successful. This ensures a high and consistent quality of the media distribution structures. The method preferably comprises the step of applying a separating agent to the screen before applying the media distribution material. In the context of the invention, a separating agent is understood to mean an agent which enables the sieve to be simply lifted off the substrate. This is to prevent parts of the media distribution structure from getting caught in the sieve during lifting. This ensures a high quality of the media distribution structure. Also one after the take off

This simplifies the cleaning process. Alternatively, a means provided as a permanent release agent can also be applied to the screen before first use. In this case, a constant application step during the process could be omitted.

According to a possible embodiment of the invention,

Media distribution material uses a material which comprises graphite particles and binders, or metal particles and binders. These graphite particles and binders are preferably applied as a paste. The use of such a material has the advantage of being used in the prior art

coated sheets have a higher corrosion resistance. As a result, the service life of a fuel cell produced in this way can be extended. The metal particles made of stainless steel are particularly preferred. A later sintering step is necessary here.

The object of the invention is additionally achieved by a device for

Implemented the method according to the invention. The device comprises an endlessly circulating sieve, by means of which a media distribution structure can be formed on a substrate, a drive unit which is set up to drive and deflect the sieve so that the sieve can be circulated endlessly, a coating unit, by means of which a media distribution material is screen-printed can be applied to the substrate, and a heating unit for heating and drying the media distribution material, the heating unit being arranged in the direction of movement of the substrate after a region of the endlessly rotating sieve.

With the device according to the invention, the method

stated advantages can be achieved. Preferred embodiments of the device are specified in the dependent claims. With the embodiments of the device claimed in the dependent claims, the advantages mentioned for the method according to the invention can be achieved.

According to a possible embodiment of the invention, the screen has a mask for forming media distribution structures in the form of columns, channels and / or curved webs. This allows one to get to the one you want

Application area of the bipolar plate half desired media distribution structure can be produced.

A fuel cell is also proposed which comprises at least one bipolar plate half which is produced by the method according to the invention. This enables the advantages mentioned for the method to be achieved.

A fuel cell according to the invention is advantageously used in an electric vehicle (EV), in a hybrid vehicle (HEV) or in a plug-in hybrid vehicle (PHEV). As a result, the advantages mentioned for the fuel cell can be achieved.

Embodiments of the invention are shown in the drawing and explained in more detail in the following description. It shows:

FIG. 1 a shows a bipolar plate half according to the prior art with a channel cross section reduced by the GDL,

FIG. 1b shows a bipolar plate half according to the prior art with water accumulation between the bipolar plate half and the GDL or in the GDL,

Figure 2 shows an embodiment of the invention

Device for carrying out the method according to the invention,

FIG. 3 shows an enlarged representation of the essential process steps according to an embodiment of the invention, Figure 4 embodiments of the media distribution structures, and

Figure 5 shows an embodiment of an inventive

Bipolarplattenhälfte.

FIG. 1 a shows a bipolar plate half 14 according to the prior art with a gas diffusion layer (GDL) 18 lying against the bipolar plate half 14. The bipolar plate half 14, which consists of an embossing process

machined sheet 24 is formed with an initial thickness of about 0.1 mm, forms webs 28 which have an average web width d and abut the GDL 18. A sum of web width d and an average channel width b for an air channel 32 is usually not less than approximately 1.5 to 2 mm for production reasons. With a corresponding duct height h, which is typically around 0.5 mm, a duct cross section Q is available for the air duct 32. FIG. 1 a additionally shows the deformation (see dashed lines) of the GDL 18 'under pressure. This reduces the available channel cross-section Q.

A further bipolar plate half 14 according to the prior art is shown in FIG. 1b. With this bipolar plate half 14, water 18 “is formed on the webs 28. This water 18 “comes from the fact that it turns out to be

Water forming reaction product at the webs 28 can be poorly removed by the GDL 18. This results in one in GDL 18

Water accumulation, which leads to a blockage of gas transport.

FIG. 2 is an illustration of an embodiment of the device 36 according to the invention for carrying out the method according to the invention. The device 36 comprises a sieve 40, by means of which a media distribution structure (see FIG. 4) 44 can be applied to a moving substrate 48. The

Device 36 additionally comprises a drive unit 52, which has driven deflection rollers 56, via which the sieve 40 is deflected and is provided in an endlessly rotating manner along a sieve movement direction 58. The

Drive unit 52 synchronizes the speed of the screen 40 with the speed of the moving substrate 48. The device 36 comprises a coating unit 60 which is activated by means of a screen printing step

Media distribution material 62 applies to the substrate 48. In the field of endless circulating sieve 40 in the direction of movement 64 of the substrate 48 after the coating unit 60 is a preheating unit 68, for heating and

Drying the applied media distribution material 62 arranged. When leaving the area of the endlessly rotating sieve 40, the sieve 40 is lifted off the substrate 48, so that a media distribution structure 44 remains on the substrate 48. A heating unit 72 is arranged in the direction of movement 64 of the substrate 48 after a region of the endlessly circulating sieve 40, which heats and dries or hardens or sinters the media distribution structure 44 - depending on the material and binder used. After the screen 40 has been lifted off the substrate 48 and before the screen 40 has been applied again to the substrate 48, a cleaning unit 76 and a checking unit 80 are arranged. In these units 76, 80, the sieve 40 is cleaned and checked for errors.

Although the preheating unit 68 is shown in the above exemplary embodiment, exemplary embodiments are also conceivable in which only the heating unit 72 is used alone. In the same way, a checking unit 80 and a cleaning unit 76 are only optionally provided.

In Figure 3 in an enlarged view of the essential process steps according to an embodiment of the invention shown. It can be seen here that the coating unit 60 applies the media distribution material 62 to the substrate 48 in channels 84 of the screen 40. Subsequent to the coating process, the media distribution material 62 is heated by means of the preheating unit 68 in order to dry and solidify the media distribution material 62. Subsequently, the screen 40 is lifted off the substrate 48, so that only the media distribution structure 44 remains on the substrate 48.

FIG. 4 shows two different examples of media distribution structures 44. Columns 88 and channels 92 are shown here as possible media distribution structures 44.

In Figure 5 is an embodiment of an inventive

Bipolar plate half 14 shown. This figure shows the significantly smaller web width d, channel width b and web height h in relation to the bipolar plate half shown in FIG. 1 a according to the prior art.

Claims

Expectations

1. A method for producing a bipolar plate half (14) for a

Fuel cell, the method comprising the steps of:

Synchronized feeding of an endlessly rotating sieve (40) past a moving substrate (48),

Applying a media distribution material (62) to the substrate (48) by means of a screen printing step to form a

Media distribution structure (44), and

Lifting the screen (40) from the substrate (48).

2. The method according to claim 1, characterized in that a

Heating step of the applied to the substrate (48)

Media distribution material (62) after lifting the screen (40) from the substrate (48) is performed.

3. The method according to claim 1 or 2, characterized in that a heating step between applying the media distribution material (62) and lifting the screen (40) is carried out.

4. The method according to any one of the preceding claims, characterized

characterized in that the method comprises the step of cleaning the screen (40) after lifting it off the substrate (48).

5. The method according to any one of the preceding claims, characterized

characterized in that the method comprises the step of checking the screen (40) after it has been lifted off the substrate (48).

6. The method according to any one of the preceding claims, characterized

characterized in that the method includes the step of applying a release agent to the screen (40) before applying the

Media distribution material (62) comprises.

7. The method according to any one of the preceding claims, characterized in that a material is used as the media distribution material (62), which comprises graphite particles and binders, or metal particles and binders.

8. Device (36) for performing a method according to one of the

The previous claims, wherein the device (36) comprises:

an endlessly circulating sieve (40), by means of which a

Media distribution structure (44) can be formed on a substrate (48), a drive unit (52) which is set up to drive and deflect the sieve (40) so that the sieve (40) can circulate endlessly, and a coating unit (60), by means of which one

Screen printing step a media distribution material (62) can be applied to the substrate (48).

9. The device (36) according to claim 8, characterized by, a heating unit (72) for heating and drying the media distribution material (62), wherein the heating unit (72) in the direction of movement (64) of the substrate (48) according to a region of the endless revolving sieve (40) is arranged.

10. The device (36) according to claim 8 or 9, characterized by a

Cleaning unit (76) with which the sieve (40) can be cleaned.

1 1. Device (36) according to one of claims 8 to 10, characterized

through, a checking unit (80), with which an error-free and / or cleanliness of the sieve (40) can be checked.

12. The device (36) according to any one of claims 8 to 1 1, characterized

through, a preheating unit (68), for heating and drying the

Media distribution material (62), the preheating unit (68) being arranged in the region of the endlessly rotating sieve (40) in the direction of movement (64) of the substrate (48) after the coating unit (60).

13. The device (36) according to any one of claims 8 to 12, characterized

characterized in that the screen (40) has a mask for molding media distribution structures (44) in the form of columns (88), channels (92) and / or curved webs.

14. A fuel cell comprising at least one bipolar plate half (14), which is produced by the method according to any one of claims 1 to 7.

15. Use of a fuel cell, according to claim 14 in one

Electric vehicle (EV), in a hybrid vehicle (HEV) or in a plug-in hybrid vehicle (PHEV).