CN117121241A

CN117121241A - Bipolar plate and method for producing a bipolar plate

Info

Publication number: CN117121241A
Application number: CN202280028104.6A
Authority: CN
Inventors: 塞巴斯蒂安·茨瓦尔; 阮文浩; 罗曼·施蒂尔霍夫; 安德烈亚斯·内德尔
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2021-06-22
Filing date: 2022-06-09
Publication date: 2023-11-24
Also published as: WO2022268256A1; DE102021116095A1

Abstract

A bipolar plate (1) constructed from two half-plates (2, 3) stacked on top of each other, having: a plurality of media ports (6, 7, 8); -a distribution zone (9) designed for distributing the medium flowing through said ports (6, 7, 8); a reaction zone (11); and a transition region (10) arranged between the distribution region (9) and the reaction region (11), which transition region describes a strip-shaped channel structure (14) in a top view of the half-plates (2, 3). In each half plate (2, 3) there is a recess (12) of normal embossing depth (h 0), a recess (13) of reduced embossing depth (h 1) and a recess (20) of increased embossing depth (h 2), wherein the two half plates (2, 3) are stacked on top of each other such that a channel structure (14) is formed by different recesses (12, 13, 20) of the half plates (2, 3) and non-recessed areas (16) located therebetween, in which channel structure the non-recessed areas (16) of one half plate (2, 3) are always located above the non-recessed areas (16) of the other half plate (2, 3) such that a stripe pattern of the non-recessed areas (16) is provided, wherein between stripes formed by the non-recessed areas (16) different recessed areas (17, 18, 19) are alternately arranged, i.e. a normally formed recessed area (17), a modified recessed area (17) of a first type, a second completely formed recessed area (17) and a second type of recess (19) are formed, the non-recessed areas (16) of the first half plate (2, 3) having the normal embossing depth (h) and the second half plate (2, 3) having the modified recessed depth (2, 3) in the normal embossing depth (h) of the second half plate (2), in the second type of modified recessed region, the first half-plate (2) has the reduced embossing depth (h 1) and the second half-plate (3) has the increased embossing depth (h 2).

Description

Bipolar plate and method for producing a bipolar plate

Technical Field

The present invention relates to a bipolar plate constructed from two half-plates according to the preamble of claim 1. The invention further relates to a method for producing such a bipolar plate.

Background

Such bipolar plates for electrochemical systems are known, for example, from DE 20 2016 107 302 U1. Known bipolar plates are constructed from half plates called separator plates. The partition plate has a through hole for passing a medium. The distribution or collection area of the separator plate is provided with a plurality of tabs through which channels are formed that are in fluid connection with the through holes. Furthermore, a flow field is formed by the separator plate, which flow field is in fluid connection with the through-holes via the distribution or collection area and has guiding structures for guiding the medium through the flow field. Furthermore, there is a continuous, reduced transition region which is arranged between the distribution or collection region and the flow field. In the device according to DE 20 2016 107 302 U1, the height of the flow guiding structures in the transition region is lower than the height of the structures in the flow field, wherein the heights can each be measured perpendicular to the flat plane of the separator plate.

Other possible designs of separator plates for electrochemical systems, in particular for fuel cells, are described in DE 10 2019 217 053 A1, DE 10 2021 000 629 A1, EP 3 331 076 B1 and WO 2019/229138 A1.

EP 3 529 842 B1 discloses a method for producing a separator plate for a fuel cell. Within the scope of the method, a material mixture is used which contains carbon powder as a main component and additionally contains different plastic components.

Disclosure of Invention

The object of the present invention is to develop bipolar plates for fuel cells further than the prior art described above, in particular in terms of manufacturing technology, wherein a high process reliability and a compact structure of the end product, i.e. a fuel cell stack with a large number of bipolar plates, are sought.

According to the invention, this object is achieved by a bipolar plate having the features of claim 1. Also, the object is achieved by a method for manufacturing a bipolar plate according to claim 7. The embodiments and advantages of the invention described below in connection with the production method are also applicable in terms of meaning to devices, namely bipolar plates, and to fuel cell stacks comprising a plurality of such bipolar plates.

The bipolar plate is formed from two half-plates lying on top of each other and has a plurality of medium ports, a distribution region for distributing the medium flowing through the ports, a reaction region and a transition region arranged between the distribution region and the reaction region, which describes a strip-shaped channel structure in a top view of the half-plates.

In each half plate there is a recess of normal embossing depth, a recess of reduced embossing depth and a recess of increased embossing depth in comparison with this, wherein the two half plates are stacked on top of each other such that a channel structure is formed by the different recesses of the half plates and the non-recessed areas located between them, within which channel structure the non-recessed areas of one half plate are always located above the same non-recessed areas of the other half plate such that a stripe pattern of non-recessed areas is provided.

Different recessed areas, i.e. a normally formed recessed area in which the first half plate has a normal embossing depth, a first type of modified recessed area in which the first half plate has an increased embossing depth and the second half plate has a reduced embossing depth, another normally formed recessed area in which the second half plate has a reduced embossing depth, and a second type of modified recessed area are alternately arranged between the strips formed by the non-recessed areas.

Instead of a uniformly designed first type of modified recess region and a likewise in each case identically designed second type of modified recess region, it is also possible to form a subtype of recess region which belongs to the first type of modified recess region and to the second type of modified recess region. For example, there are two sub-types belonging to the aggregate concept "changed recessed area of the first type" and two other sub-types belonging to the "changed recessed area of the second type" such that a total of five different forms of recesses are provided in connection with the normally formed recessed area. An even number of different recessed areas is also possible.

The targeted variation of the embossing depth has proved to be suitable for positively influencing the uniform distribution of the medium, in particular of the cooling medium, over the entire width of the reaction zone of the bipolar plate. In this case, it is important that the recess with the reduced embossing depth is not opposite the recess with the same reduced embossing depth, but opposite the recess with the increased embossing depth. Thus, the strip-shaped sections with reduced embossing depth are alternately arranged on both sides of the central plane of the bipolar plate in the transverse direction with respect to the strips formed by the recesses. In particular, the spacing between the recess of the first half plate and the recess of the second half plate opposite it is uniform in all three different recess areas.

According to different possible designs, the reduced imprint depth is at least 75% and at most 95% of the entire imprint depth, while the increased imprint depth is at least 105% and at most 125% of the normal imprint depth. In particular, the amount of normal imprint depth can correspond to an average between a reduced imprint depth and an increased imprint depth. The above relationship applies to both halves of the bipolar plate. By a different arrangement of areas with reduced or increased embossing depth, the two half-plates are not perfectly mirror-symmetrical.

The cross section of the flow channel defined by the half plates is related to the different design possibilities that exist. For example, a trapezoid-shaped structuring in cross section can be provided. Also circular cross sections of the channels are possible.

In relation to the contact points between the half plates and the membrane electrode assemblies arranged between the half plates, on the one hand, different variants can be distinguished from one another. In one aspect, a fuel cell stack comprising a number of bipolar plates and a membrane electrode assembly can be configured such that only the increasingly formed recessed areas of the half plates are in contact with the membrane electrode assembly. A variant is also possible in which all of the recessed areas are in contact with the associated Membrane Electrode Assembly (MEA) as long as there is a MEA between them.

In any case, the sections with normal embossing depth and the sections with increased embossing depth create significantly different flow conditions in the different sections due to the dimpled recesses, i.e. recesses with smaller embossing depth. In general, within a fuel cell, a cooling fluid, particularly cooling water, flows on one side of each half-plate, while a gaseous fluid flows on the opposite side of the half-plate. Thus, the reduction of one flow space is necessarily accompanied by an increase of the other flow space.

If the two half-plates are brought into contact with the membrane electrode assembly before they are permanently connected to one another, the recesses of increased embossing depth initially come into contact with the surface sections of the membrane electrode assembly, assuming the desired geometry. If the pressure applied to the half-plates is greater and greater, as the spacing between the half-plates decreases, contact is also established between the recesses of normal or reduced imprint depth and the membrane electrode assembly. This can cause a targeted displacement between adjacent channels, in particular a displacement of at least 10 μm and at most 150 μm. This is associated with a targeted stretching effect which ultimately reduces the passage penetration due to the pressure per unit area without major deformation of the membrane electrode assembly taking place.

The molding methods known per se, in particular deep drawing, are suitable for producing the recesses of the half-plates. A continuous forming process, i.e. using rotating structured rollers, can also be used. The half-plates are for example made of steel plate and are optionally also provided with a coating.

Drawings

Hereinafter, embodiments of the present invention and comparative examples for illustration only will be described in more detail with reference to the accompanying drawings. Here, it is shown that:

figure 1 shows a partial top view of a bipolar plate,

figure 2 shows a cross-section of an unprotected comparative example,

fig. 3 shows a cross-section of the bipolar plate according to fig. 1 from a similar view to fig. 2.

Unless otherwise indicated, the following description refers to the embodiments illustrated in fig. 1 and 3 and the non-claimed comparative example sketched in fig. 2. In all the figures, components and contours which correspond to each other or which act in principle identically are denoted by the same reference numerals.

Detailed Description

The fuel cell stack, which is only partially shown, comprises a plurality of bipolar plates 1, which are formed from a first half-plate 2 and a second half-plate 3, respectively. The half plates 2,3 of the bipolar plate 1 can be firmly connected to each other, for example by soldering or welding. The bipolar plate 1 is a component of a fuel cell system designed for mobile or stationary use, see the prior art cited at the outset for its basic function.

Each half-plate 2,3 defines a half-cell 4, 5 of the fuel cell. Different media, namely cooling water, hydrogen and air, flow into the fuel cell through coolant port 6, hydrogen port 7 and air port 8. From the ports 6, 7, 8, the medium flows via the distribution region 9 and the transition region 10 to the reaction region indicated by 11 of the bipolar plate 1.

The entire bipolar plate 1, which is only partially shown in fig. 1, has an elongated rectangular shape, with the ports 6, 7, 8 on the narrow sides, while further, not shown, ports are provided on the opposite narrow sides for the outflow of the medium. The width of each individual port 6, 7, 8, measured in the transverse direction of the bipolar plate 1, is significantly smaller than the width of the reaction zone 11, which has a rectangular basic shape. The distribution zone 9 ensures that the different media streams fan out over the entire width of the reaction zone 11. With reference to the arrangement according to fig. 1, the partially gaseous, partially liquid medium flows substantially in a horizontal direction from right to left. In fact, in the finished state of the fuel cell stack comprising a large number of bipolar plates 1, the flow of the medium takes place mainly in the vertical direction.

With reference to the arrangement according to fig. 1, the transition region 10 is overall a narrow strip oriented transversely to the flow direction of the medium. Within this bar, a channel structure, indicated at 14, can be seen, which is oriented substantially in the flow direction of the medium, i.e. in the longitudinal direction of the bipolar plate 1.

In the arrangement according to fig. 3, the half-plate 2 of the first bipolar plate 1 and the half-plate 3 of another bipolar plate 1 of the same kind can be seen. The corresponding applies to the arrangement according to fig. 2. The membrane electrode assembly 15 comprising proton permeable membrane, catalyst layer and gas diffusion layer is located between the different half plates 2,3 which are attributed to the bipolar plates 1 arranged in a stack. The membrane is held in place by a frame, also called a sub-gasket, and is likewise assigned to the membrane electrode assembly 15. The frame surrounds the membrane such that the different gaseous fluids on the cathode side and the anode side of the fuel cell remain separate from each other.

Channels for coolant, i.e. cooling water or other cooling liquid, are provided in each bipolar plate 1 by means of the channel structure 14. The coolant channels are located above the first half-plate 2 and below the second half-plate 3. In the simplified, not-claimed embodiment according to fig. 2, the channel structure 14 is formed by a recess region 17 of uniform depth, which is strip-shaped in plan view. The non-recessed area of each half-plate 2,3 is indicated with 16. The recesses of normal imprint depth present in region 17 are indicated at 12.

In the embodiment according to fig. 1 and 3, the recesses 12 of normal embossing depth are different from the recesses 13 of reduced embossing depth and the recesses 20 of increased embossing depth. In the case of fig. 3, the completely formed recess region 17 is also involved at the point where the membrane electrode assembly 15 is in contact with the two recesses 12 of normal embossing depth. As can be seen from fig. 3, there are additionally different modified recess regions 18, 19. In the modified recess region 18 of the first type, the half plate 2 has recesses 20 of increased embossing depth, whereas in the half plate 3 there are recesses 13 of reduced embossing depth. In contrast, in the case of the modified recess region 19 of the second type, a recess 13 of reduced embossing depth is present in the half-plate 2, while the opposite recess 20 of the half-plate 3 of the next bipolar plate 1 is formed as a recess 20 of increased embossing depth.

The normal imprint depth of recess 12 is denoted by h0, the reduced imprint depth of recess 13 is denoted by h1, and the increased imprint depth of recess 20 is denoted by h 2. A uniform distance h is provided between two opposing recesses 13, 20 of the varying embossing depth h1, h2 and between two opposing recesses 12 of the normal embossing depth h 0.

It can also be seen from fig. 3 that in the transverse direction of the transition region 10, the completely formed recess regions 17 and the modified recess regions 18, 19 always alternate. In this case, each second modified recessed region is a modified recessed region 18 of the first type, and each second modified recessed region is a modified recessed region 19 of the second type.

Fig. 3 desirably shows a state in the completed fuel cell stack. In this case, the half-plates 2,3 are placed on the membrane electrode assembly 15 by means of pressure. By a slight deformation of the membrane electrode assembly 15, which is shown simplified in fig. 3 by means of a rectangular cross section, contact is established between all recesses 12, 13, 20 and the membrane electrode assembly 15. The differences between the embossing depths h0, h1, h2 are shown exaggerated in fig. 3. All non-recessed areas 16 of the different half-plates 2,3 are arranged in planes parallel to each other. In this case, in the same fuel cell 1, the non-recessed areas 16 of the different half-plates 2,3 are stacked on top of each other.

Description of the reference numerals

1. Bipolar plate

2. Half plate

3. Half plate

4. Half-cell

5. Half-cell

6. Coolant port

7. Hydrogen port

8. Air port

9. Distribution area

10. Transition region

11. Reaction zone

12. Recesses of normal imprint depth

13. Recesses of reduced imprint depth

14. Channel structure

15. Membrane electrode device

16. Non-recessed areas

17. Normally formed recessed areas

18. A modified recessed region of a first type

19. A second type of modified recessed region

20. Recesses of increased imprint depth

h spacing between recesses

h0 Normal impression depth

h1 Reduced imprint depth

h2 Increased imprint depth

Spacing between p non-recessed regions

Claims

1. A bipolar plate (1) constructed from two half-plates (2, 3) stacked on top of each other, having: a plurality of media ports (6, 7, 8); -a distribution zone (9) designed for distributing the medium flowing through said ports (6, 7, 8); a reaction zone (11); and a transition region (10) arranged between the distribution region (9) and the reaction region (11), which transition region describes a strip-shaped channel structure (14) in a top view of the half-plates (2, 3), characterized in that in each half-plate (2, 3) there is a recess (12) of normal embossing depth (h 0), a recess (13) of reduced embossing depth (h 1) and a recess (20) of increased embossing depth (h 2), and that the two half-plates (2, 3) are stacked on top of each other such that a channel structure (14) is formed by different recesses (12, 13, 20) of the half-plates (2, 3) and non-recessed regions (16) located therebetween, in which channel structure the non-recessed regions (16) of one half-plate (2, 3) are always located above the same non-recessed regions (16) of the other half-plate (2, 3) such that a pattern of the non-recessed regions (16) is provided, wherein at least one of the different types of recesses (17), the normal regions (17) are formed by alternating between the different recesses (12, 13, 20) of the other ones of the non-recessed regions (17), the normal regions (17) are formed, the two half-plates (2, 3) have said normal embossing depth (h 0), in said first type of modified recessed area the first half-plate (2) has said increased embossing depth (h 2) and the second half-plate (3) has said reduced embossing depth (h 1), in the second type of modified recessed area the first half-plate (2) has said reduced embossing depth (h 1) and the second half-plate (3) has said increased embossing depth (h 2).

2. Bipolar plate (1) according to claim 1, characterized in that the reduced embossing depth (h 1) is at least 75% and at most 95% of the normal embossing depth (h 0) and the increased embossing depth (h 2) is at least 105% and at most 125% of the normal embossing depth (h 0).

3. Bipolar plate (1) according to claim 1 or 2, characterized in that the spacing (h) between the recesses (12, 13, 20) of the first half plate (2) and the recesses (12, 13, 20) of the second half plate (3) is uniform in all three recess areas (17, 18, 19).

4. A bipolar plate (1) according to one of claims 1 to 3, characterized in that a trapezoid-shaped structuring is formed in cross section by the recesses (12, 13, 20).

5. Bipolar plate (1) according to one of claims 1 to 4, characterized in that a membrane electrode assembly (15) located between the half plates (2, 3) is in contact not only with the recess (12) of the normal embossing depth (h 0) but also with the recess (13) of the reduced embossing depth (h 1) and the recess (20) of the increased embossing depth (h 2).

6. A fuel cell stack comprising a plurality of bipolar plates (1) according to claim 1.

7. A method for manufacturing a bipolar plate (1), wherein two half-plates (2, 3) are structured by molding such that recesses (12) of normal embossing depth (h 0), recesses (13) of reduced embossing depth (h 1) and recesses (20) of increased embossing depth (h 2) are produced in each half-plate (2, 3), and the two half-plates (2, 3) are stacked on top of each other such that channel structures (14) are produced by different recesses (12, 13, 20) of the half-plates (2, 3) and non-recessed areas (16) located therebetween, within which channel structures non-recessed areas (16) of one half-plate (2, 3) are always located above non-recessed areas (16) of the other half-plate (3, 2) such that a stripe pattern of the non-recessed areas (16) is formed, wherein different areas (17, 18, 19) are alternately provided between stripes formed by the non-recessed areas (16), i.e. forming at least one of the normal areas (17), the second type of recess (17), the normal areas (17) of the first half-plate (17) and the normal areas (19) are formed, the normal areas (17) are changed in the normal type of recess type (17) of the second half-plate (3), the first half-plate (2) has said increased embossing depth (h 2) and the second half-plate (3) has said reduced embossing depth (h 1), the first half-plate (2) having said reduced embossing depth (h 1) and the second half-plate (3) having said increased embossing depth (h 2) in the second type of modified recessed area, and wherein the two half-plates (2, 3) are firmly connected to each other in this positioning.

8. Method according to claim 7, characterized in that a membrane electrode device (15) is inserted between the two half plates (2, 3) belonging to the bipolar plates (1) parallel to each other, such that the membrane electrode device is first contacted by the recess (12) of the increased embossing depth (h 2).

9. Method according to claim 8, characterized in that after the recesses (20) of the increased embossing depth (h 2) have been brought into contact with the membrane electrode assembly (15), the two half plates (2, 3) are pressed against each other with increasing force, so that the recesses (12) of all normal embossing depths (h 0) as well as the recesses (13) of the reduced embossing depth (h 1) are also brought into contact with the membrane electrode assembly (15).

10. Method according to claim 9, characterized in that contact between recesses (12, 13, 20) formed in different sizes and the membrane electrode assembly (15) is established in a transition region (10) provided between the distribution zone (9) and the reaction zone (11) of the bipolar plate (1).