WO2017215872A1

WO2017215872A1 - Method for manufacturing a flow field plate for a fuel cell, and fuel cell

Info

Publication number: WO2017215872A1
Application number: PCT/EP2017/061864
Authority: WO
Inventors: Harald Bauer; Silvan Hippchen
Original assignee: Robert Bosch Gmbh
Priority date: 2016-06-14
Filing date: 2017-05-17
Publication date: 2017-12-21
Also published as: DE102016210513A1

Abstract

The invention relates to a method for manufacturing a flow field plate (40) for a fuel cell (2), wherein expanded graphite is compressed to obtain a plate-shaped workpiece, and a media distribution structure (45) is created in the plate-shaped workpiece. The invention also relates to a fuel cell (2) comprising at least one flow field plate (40) manufactured according to the disclosed method.

Description

Method for producing a bipolar plate for a fuel cell and

fuel cell

The invention relates to a method for producing a bipolar plate for a fuel cell, wherein a plate-shaped workpiece is produced, and wherein a media distribution structure is introduced into the plate-shaped workpiece.

The invention also relates to a fuel cell, which comprises at least one

Bipolar plate, which is prepared by the process according to the invention. State of the art

A fuel cell is a galvanic cell, which is the chemical

Reaction energy of a continuously supplied fuel and an oxidizing agent converts into electrical energy. A fuel cell is therefore an electrochemical energy converter. In known fuel cells in particular hydrogen (H2) and oxygen (02) in water (H20), electrical energy and heat are converted. But there are also known fuel cells, which work with methanol or methane. Among other things, proton exchange membrane (proton exchange membrane =

PEM) fuel cells known. Proton exchange membrane fuel cells have a centrally arranged membrane, which is permeable only to protons, so only for hydrogen ions. The oxidizing agent,

in particular atmospheric oxygen, is spatially separated from the fuel, in particular hydrogen.

Proton exchange membrane fuel cells further include an anode and a cathode. The fuel is supplied to the anode of the fuel cell and catalytically oxidized to protons with release of electrons. The protons pass through the membrane to the cathode. The emitted electrons are derived from the fuel cell and flow through an external circuit to the cathode.

The oxidant is supplied to the cathode of the fuel cell and reduced to anions by receiving the electrons from the external circuit. The anions react with the protons which have passed through the membrane to the cathode to water. The resulting water is discharged from the fuel cell.

In this case, a voltage is applied between the anode and the cathode of the fuel cell. To increase the voltage, a plurality of fuel cells can be arranged mechanically one behind the other to form a fuel cell stack and electrically connected in series.

For uniform distribution of the fuel at the anode and for uniform distribution of the oxidant at the cathode are

Distributor plates provided, which are also referred to as bipolar plates. The bipolar plates have, for example, channel-like structures for distributing the fuel and the oxidizing agent. The bipolar plates may further include structures for passing a cooling liquid through the fuel cell to dissipate heat.

From DE 10 2012 221 730 Al a fuel cell with a bipolar plate is known, which is composed of two plate halves. In this case, each of the two plate halves has a distributor structure, which are provided for distributing the reaction gases and a cooling liquid. Between the two plate halves a coolant space is provided.

From DE 10 2014 207 594 Al a bipolar plate for a fuel cell is known. The bipolar plate in this case has a meandering channel, which is formed for example as a groove. The meandering channel serves to introduce hydrogen or oxygen into the fuel cell. Further, a plurality of heat pipes are provided, through which a cooling medium is passed through the bipolar plate. Disclosure of the invention

A method for producing a bipolar plate for a fuel cell is proposed. According to the invention, expanded graphite, in particular in a suitable press, is pressed into a plate-shaped workpiece, and at least one media distributor structure is introduced into the plate-shaped workpiece.

The said media distribution structure can be introduced in the same operation in the plate-shaped workpiece, in which the compression takes place. But it is also conceivable that initially the plate-shaped

Workpiece is produced, and that in a subsequent, separate operation, the at least one media distribution structure is introduced into the plate-shaped workpiece.

The media distribution structure is used, for example, to distribute

Reaction gases, in particular hydrogen and oxygen or air in the fuel cell. The media distribution structure can also be provided for the passage of a cooling liquid through the fuel cell to dissipate heat.

For the production of expanded graphite, natural graphite is treated with at least one acid. In particular, hydrochloric acid, sulfuric acid and hydrofluoric acid are used for this purpose, in some cases individually or else as a mixture in the form of concentrated acids. The natural graphite is for example in the form of

Dandruff or flakes. The treated natural graphite is heated to a temperature of at least 1000 ° C. This leads to an enlargement of the particles of natural graphite by a factor of 200-400. This results in graphite dwarfs, which are referred to as expanded graphite.

When pressing the expanded graphite thus prepared takes place

Interlocking, or entanglement of the said graphitwürmchen with each other. By this interlocking of the graphiteworm with each other receives the plate-shaped workpiece produced by the compression a relatively high mechanical strength. The expanded graphite is preferably pressed in a mold provided for this purpose with a surface pressure of at least 10 ⁴ N / m ² . Particularly preferably, the expanded graphite is pressed with a surface pressure of 10 ⁶ N / m ² . By the embossing mold, the geometric contour of the plate-shaped workpiece and the bipolar plate is specified. In the case of said surface pressure, the bipolar plate obtains a sufficiently high mechanical strength.

As already mentioned, the IVI distribution structure in the same

Operation are introduced into the plate-shaped workpiece in which the compression takes place. For this purpose, a surface of the embossing mold advantageously has a structuring. The structuring of the surface of the embossing mold corresponds to a negative contour of the IVIedienverteilerstruktur to be created in the bipolar plate.

According to a possible embodiment of the invention, the structuring of the surface of the embossing mold is designed to be homogeneous.

According to another possible embodiment of the invention is the

Structuring the surface of the embossing mold designed inhomogeneous.

In particular, the structuring of the surface of the embossing mold according to another possible embodiment of the invention may have a graduation.

According to a preferred embodiment of the invention, an IVIedienverteilerstruktur is introduced into the plate-shaped workpiece on both sides for producing the bipolar plate. For example, the IV distribution manifold structure on one side of the bipolar plate serves to distribute hydrogen, and the

IVial distributor structure on the other side of the bipolar plate serves to distribute oxygen or air in the fuel cell.

It is also conceivable that the IVIedienstverteilerstruktur on one side of the

Bipolar plate for distributing a reaction gas, for example hydrogen or oxygen, or air, is used in the fuel cell, and that the media distribution structure on the other side of the bipolar plate for the passage of a cooling liquid through the fuel cell for dissipating heat is provided.

It is also proposed a fuel cell, which comprises at least one bipolar plate, which is produced by the process according to the invention. A fuel cell according to the invention advantageously finds use in one

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

Advantages of the invention

The inventive method bipolar plates for fuel cells can be produced, which are relatively thin, but still have a relatively high mechanical strength. As a result, fuel cells and fuel cell stacks are more compact executable. By the method according to the invention, the production of bipolar plates is also relatively

cost, especially because graphite is available as a raw material cost. Furthermore, the bipolar plates produced by the process according to the invention are electrically conductive and corrosion-resistant, in particular against the chemically pure water which is formed during the reaction in the fuel cell. The bipolar plates are also corrosion resistant to sulfonic acid groups that may be formed in the reaction in the fuel cell. Advantageously, the media distribution structure can be constructed such that reaction gases and cooling liquid can be passed through the bipolar plate optimally, in particular with low pressure loss.

Brief description of the drawings

Embodiments of the invention will be explained in more detail with reference to the drawings and the description below. Show it:

FIG. 1 shows a schematic representation of a fuel cell,

Figure 2 is a schematic process flow of the production and

Pressing of expanded graphite,

FIG. 3 shows a stamping mold,

4 shows a surface of a stamping mold with homogeneous structuring and Figure 5 shows a surface of a stamping mold with inhomogeneous structuring. Embodiments of the invention

In the following description of the embodiments of the invention, the same or similar elements are denoted by the same reference numerals, wherein a repeated description of these elements is dispensed with in individual cases. The figures illustrate the subject matter of the invention only schematically.

1 shows a fuel cell 2 is shown schematically. The fuel cell 2 comprises a negative terminal 11 and a positive terminal 12. A voltage supplied by the fuel cell 2 can be tapped off via the terminals 11, 12. During operation of the fuel cell 2, an electric current flows between the two terminals 11, 12 via an external circuit.

The fuel cell 2 has a first connection point 31, which serves to supply a fuel, in the present case hydrogen. The fuel cell 2 also has a second connection point 32, which serves to supply an oxidizing agent, in the present case atmospheric oxygen. The fuel cell 2 also has a third connection point 33, which serves for the derivation of originated water. Furthermore, the fuel cell 2 has an anode 21, a cathode 22 and a membrane 18. The membrane 18 is arranged between the anode 21 and the cathode 22. The anode 21, the cathode 22 and the membrane 18 together form a membrane electrode assembly 10, which is arranged centrally within the fuel cell 2.

On the side of the anode 21, a first bipolar plate 40 is arranged, which is connected to the first connection point 31. The first bipolar plate 40 has a media distributor structure 45, via which the fuel, which is supplied via the first connection point 31 of the fuel cell 2, to the anode 21 on. The first bipolar plate 40 is electrically conductive and made of graphite.

On the side of the cathode 22, a second bipolar plate 40 is arranged, which is connected to the second connection point 32. The second bipolar plate 40 has a media distribution structure 45, via which the oxidizing agent, which is supplied via the second connection point 32 of the fuel cell 2, to the cathode 22 on. The second bipolar plate 40 is also electrically conductive and made of graphite.

Furthermore, the second bipolar plate 40 arranged on the side of the cathode 22 is connected to the third connection point 33. Via the media distributor structure 45 of the second bipolar plate 40, the water produced during operation of the fuel cell 2 is also discharged from the fuel cell 2 via the third connection point 33.

The bipolar plates 40 furthermore have structures (not illustrated here) for the passage of a coolant through the fuel cell 2. Thus, a discharge of the resulting during operation of the fuel cell 2 heat and thus cooling of the fuel cell 2 is possible.

Between the anode 21 and the first bipolar plate 40 is a first

Gas diffusion layer 30 is provided. The first gas diffusion layer 30 is electrically conductive and made, for example, of a porous foam. The first gas diffusion layer 30 ensures a uniform distribution over the Media distribution structure 45 of the first bipolar plate 40 supplied fuel to the anode 21st

Between the cathode 22 and the second bipolar plate 40, a second gas diffusion layer 30 is provided. The second gas diffusion layer 30 is electrically conductive and made, for example, of a porous foam. The second gas diffusion layer 30 ensures uniform distribution of the material supplied via the Medienverteilstruktur 45 of the second bipolar plate 40

Oxidizing agent to the cathode 22nd

The anode 21, the first bipolar plate 40, and the first gas diffusion layer 30 interposed therebetween are electrically connected to the negative terminal 11 of FIG

Fuel cell 2 connected. The cathode 22, the second bipolar plate 40, and the second gas diffusion layer 30 interposed therebetween are electrically connected to the positive terminal 12 of the fuel cell 2.

FIG. 2 shows a schematic process sequence of the production and

Compression of expanded graphite 62. Starting material is natural graphite 60, which is shown in part a). The natural graphite 60 is present, for example, in the form of flakes or flakes.

First, the natural graphite 60 is treated with an acid, and the natural graphite 60 thus treated is heated to a temperature of at least 1000 ° C. This leads to an enlargement of the particles of the

Natural graphite 60 by a factor of 200-400. This gives rise to the

Natural graphite 60 Graphite worms 63, which are referred to as expanded graphite 62. These graphite worms 63, designated as expanded graphite 62, are shown in subfigure b). The expanded graphite 62 thus produced, or the graphite worms

63, is then pressed in a designated embossing mold 65 with a surface pressure of about 10 ⁵ N / m ² . A compression with 10 ⁴ N / m ² is already conceivable, but it is also a compression with 10 ⁶ N / m ² conceivable. The design of the embossing mold 65, the geometric contour of the plate-shaped workpiece and thus the produced bipolar plate 40th specified. This process of pressing the expanded graphite 62, or the graphite worm 63, is shown in subfigure c).

When pressing the expanded graphite 62, or the

Graphitwürmchen 63, there is a toothing, or entanglement of the said graphite worms 63 together. As a result of this toothing of the graphitic worms 63, the plate-shaped workpiece produced by the compression obtains a comparatively high mechanical strength. This process of entanglement, or Verzahnens, the

Graphitwürmchen 63 is shown in part d).

FIG. 3 shows a perspective view of a stamping mold 65 which is provided for pressing expanded graphite 62. The embossing mold 65 has a surface 67 on which the expanded graphite 62 to be pressed is placed. The surface 67 of the embossing mold 65 is presently not smooth but has a structuring.

The structuring of the surface 67 of the embossing mold 65 corresponds to a negative contour of the IVIedienverteilerstruktur 45 in the bipolar plate 40 to be produced. When pressing the expanded graphite 62, as shown in Figure 2, thus the IVIedienverteilerstruktur 45 is simultaneously introduced into the bipolar plate 40 with.

As shown in Figure 2, the expanded graphite 62 is between two

Embossing forms 65 added. In this case, each of the two embossing forms 65 each have a surface 67 with a structuring. As a result, each time an IVIedienverteilerstruktur 45 is introduced into the plate-shaped workpiece, or in the bipolar plate 40 during pressing.

In this case, the IV distributor structure 45 serves on one side of the bipolar plate 40, for example for distributing hydrogen in a fuel cell 2, and the IV distributor structure 45 on the other side of the bipolar plate 40 serves to distribute oxygen or air in an adjacently arranged fuel cell 2 in a fuel cell stack. It is also conceivable that the media distribution structure 45 on one side of the bipolar plate 40 for distribution of hydrogen or air, or oxygen, and the media distribution structure 45 on the other side of the bipolar plate 40 for the passage of a cooling liquid through the fuel cell 2 is used.

FIG. 4 shows a surface 67 of a stamping mold 65 with a homogeneous structuring. Under a homogeneous structuring is in this

Context to understand that surveys and recesses of the

Structuring at least approximately uniform over the complete

Surface 67 of the embossing mold 65 are distributed.

FIG. 5 shows a surface 67 of a stamping mold 65 with an inhomogeneous structuring. Under an inhomogeneous structuring is in this

Context to understand that surveys and recesses of the

Structuring unevenly over the entire surface 67 of the embossing mold 65 are distributed.

In the present case, the structuring of the surface 67 of the embossing mold 65 has a graduation. In this context, graduation is to be understood as meaning that elevations are formed more strongly than depressions in a partial area of the surface 67 of the embossing mold 65, and that recesses are formed more strongly in a different partial area of the surface 67 of the embossing mold than elevations.

The invention is not limited to the embodiments described herein and the aspects highlighted therein. Rather, within the scope given by the claims a variety of modifications are possible, which are within the scope of expert action.

Claims

Expectations

1. Method for producing a bipolar plate (40) for a

Fuel cell (2), where

expanded graphite (62) is pressed into a plate-shaped workpiece, and

a media distribution structure (45) is introduced into the plate-shaped workpiece.

2. The method according to claim 1, wherein

for the production of expanded graphite (62)

Natural graphite (60) treated with at least one acid and

is heated to a temperature of at least 1000°C.

3. The method according to any one of the preceding claims, wherein

the expanded graphite (62) in an embossing mold (65) with a

Surface pressure of at least 10 ⁴ N/m ² is pressed.

4. The method according to claim 3, wherein

a surface (67) of the embossing mold (65) has a structuring.

5. The method according to claim 4, wherein

the structuring of the surface (67) is designed to be homogeneous.

6. The method according to claim 4, wherein

the structuring of the surface (67) is inhomogeneous.

7. The method according to claim 6, wherein

the structuring of the surface (67) has a graduation.

8. The method according to any one of the preceding claims, wherein

An IVIediendistribution structure (45) is introduced into the plate-shaped workpiece on both sides. Fuel cell (2), comprising at least one bipolar plate (40), which is produced by the method according to one of the preceding claims.

Use of a fuel cell (2) according to claim 9 in an electric vehicle (EV), in a hybrid vehicle (H EV) or in a plug-in hybrid vehicle (PHEV).