WO2022268256A1

WO2022268256A1 - Bipolar plate and method for operating a bipolar plate

Info

Publication number: WO2022268256A1
Application number: PCT/DE2022/100434
Authority: WO
Inventors: Sebastian Zwahr; Van Hau Nguyen; Roman Stierhof; Andreas Nendel
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2021-06-22
Filing date: 2022-06-09
Publication date: 2022-12-29
Also published as: CN117121241A; DE102021116095A1; EP4360149A1

Abstract

A bipolar plate (1) is made of two half-plates (2, 3) which lie against each other, comprising a plurality of media ports (6, 7, 8), a distributor field (9) which is designed to distribute media flowing through the ports (6, 7, 8), an active field (11), and a transition region (10) which is arranged between the distributor field (9) and the active field (11) and describes a strip-shaped channel structure (14) in plan view of the half-plates (2, 3). Each half-plate (2, 3) is equipped with recesses (12) with a normal embossing depth (h0), recesses (13) with a reduced embossing depth (h1), and recesses (20) with an increased embossing depth (h2), wherein the two half-plates (2, 3) lie against each other such that the different recesses (12, 13, 20) and non-recessed regions (16) of the half-plates (2, 3) between the recesses form a channel structure (14) within which a non-recessed region (16) of one half-plate (2, 3) constantly lies over a non-recessed region (16) of the other half-plate (2, 3) such that a strip pattern of the non-recessed regions (16) is produced. Different recessed regions (17, 18, 19) are arranged between the strips formed by the non-recessed regions (16) in an alternating manner, namely a recessed region (17) which is embossed in a normal manner and in which the two half-plates (2, 3) have the normal embossing depth (h0), a modified recessed region (18) of a first type in which the first half-plate (2) has the increased embossing depth (h2) and the second half-plate (3) has a reduced embossing depth (h1), another completely embossed recessed region (17), and a modified recessed region (19) of a second type in which the first half-plate (2) has the reduced embossing depth (h1) and the second half-plate (3) has the increased embossing depth (h2).

Description

Bipolar plate and method of making a bipolar plate

The invention relates to a bipolar plate made up of two half sheets according to the preamble of claim 1 . The invention also relates to a method for producing such a bipolar plate.

A generic bipolar plate for an electrochemical system is known, for example, from DE 20 2016 107 302 U1. The well-known bipolar plate is made up of half sheets, which are referred to as separator plates. The separator plates have through-openings for passing a medium through. A dividing or collecting area of the separator plates is provided with a plurality of lands forming channels which are in fluid communication with the through-opening. Furthermore, a flow field is formed by the separator plates, which is in fluid connection with the passage opening via the distribution or collection area and has conducting structures for conducting a medium through the flow field. In addition, there is a coherent, sunken transition area that is arranged between the distribution or collection area and the flow field. In the device according to DE 202016 107 302 U1, flow-guiding structures within the transition region have a height that is less than the height of structures in the flow field, with the height being measured perpendicular to the planar surface plane of the separator plate.

Other possible configurations of separator plates for electrochemical systems, in particular fuel cells, are described in the documents DE 10 2019 217 053 A1, DE 102021 000 629 A1, EP 3 331 076 B1, and WO 2019/22 91 38 A1.

EP 3 529 842 B1 discloses a method for producing a separator plate for a fuel cell. As part of this process, a mixture of materials is applies, which contains carbon powder as a main component and also contains various plastic components.

The invention is based on the object of further developing bipolar plates for fuel cells compared to the stated prior art, in particular from a manufacturing perspective, with a high degree of process reliability and a compact structure of the end product, i.e. a fuel cell stack having a large number of bipolar plates, being aimed for.

This object is achieved according to the invention by a bipolar plate having the features of claim 1 . The object is also achieved by a method for producing a bipolar plate according to claim 7. Embodiments and advantages of the invention explained below in connection with the production method also apply analogously to the devices, i.e. the bipolar plate and a plurality of such bipolar plates fuel cell stack.

The bipolar plate is made up of two half-sheets lying one on top of the other and has a plurality of media ports, a distribution panel, which is provided for distributing the media flowing through the ports, an active panel, and one arranged between the distribution panel and the active panel, in plan view the half-plates have a transition region that describes a strip-shaped channel structure.

In each half sheet there are indentations with a normal embossing depth, indentations with a reduced embossing depth and indentations with an increased embossing depth, with the two half sheets being placed one on top of the other in such a way that a channel structure is formed by the various indentations and non-indented areas of the half sheets in between which is always a non-recessed area of one half-sheet over a likewise non-recessed area of the other half-sheet, so that a stripe pattern of the non-recessed areas is given. Different depression areas are arranged alternately between the strips formed by the non-depressed areas, namely a normally pronounced depression area in which both half-sheets have the normal embossing depth, a modified depression area of the first type in which the first half-metal sheet has the increased embossing depth and the second half-metal sheet has the reduced embossing depth, a further normally pronounced indentation area, and a modified indentation area of the second type, in which the first half sheet has the reduced embossing depth and the second half sheet has the increased embossing depth.

Instead of a uniformly designed modified depression area of the first type and a modified depression area of the second type that is also designed the same in all cases, subtypes of depression areas can also be formed, which can be assigned to the modified depression area of the first type or second type. For example, there are two subtypes that fall under the collective term modified depression area of the first type and two further subtypes that are subsumed under the modified depression area of the second type, so that together with the normally pronounced depression area there are a total of five different expressions of depressions. An even number of different areas of specialization is also possible.

The targeted variation of the embossing depth has proven to be suitable for positively influencing the equal distribution of media, in particular a cooling medium, over the entire width of the active field of the bipolar plate. The fact that an indentation with a reduced embossing depth is not opposite an indentation with an equally reduced embossing depth, but an indentation with an increased embossing depth is of importance here. In the direction transverse to the strips, which are formed by the depressions, strip-shaped sections with a reduced embossing depth are thus arranged alternately on both sides of the central plane of the bipolar plate. In particular, the distance between a depression in the first half-sheet and a depression in the second half-sheet lying opposite it is uniform in all three different depression areas. According to various possible configurations, the reduced embossing depth is at least 75% and at most 95% of the full embossing depth, while the increased embossing depth is at least 105% and at most 125% of the normal embossing depth. In particular, the amount of the normal embossing depth can correspond to the mean value between the reduced and the increased embossing depth. The relations mentioned apply to both half-sheets of the bipolar plate. Due to the different arrangement of the areas with a reduced or increased embossing depth, the two half-sheets are not completely mirror-symmetrical to one another.

As far as the cross-sections of the flow channels delimited by the half-plates are concerned, there are various design options. For example, a structuring with a trapezoidal cross section can be provided. Rounded cross sections of channels are also possible.

Various variants can be distinguished from one another with regard to contact points between the half-sheets on the one hand and a membrane-electrode arrangement arranged between the half-sheets. On the one hand, a fuel cell stack, which includes numerous bipolar plates and membrane-electrode assemblies, can be constructed in such a way that only the more pronounced depression areas of the half-sheets make contact with the membrane-electrode assemblies. Variants can also be implemented in which all recessed areas contact the relevant MEA if there is a membrane electrode assembly (MEA) between them.

In any case, significantly different flow conditions are produced in the various sections due to the less pronounced depressions, that is to say having a smaller embossing depth, the sections with normal embossing depth and the sections with increased embossing depth. Coolant, in particular cooling water, generally flows on one side of each half-plate, whereas a gaseous fluid within a fuel cell flows on the opposite side of the half-plate flows. A reduction in size of one flow space is therefore inevitably accompanied by an increase in the other flow space.

If the two half-sheets are brought into contact with the membrane-electrode assembly before they are permanently connected to one another, the indentations of increased embossing depth initially touch surface sections of the membrane-electrode assembly if geometrically ideal conditions are present. If increasing pressure is exerted on the half-sheets, as the distance between the half-sheets becomes smaller, contacts can also be produced between the depressions of normal or reduced embossing depth and the membrane electrode arrangement. This can lead to a targeted displacement between adjacent channels, in particular a displacement of at least 10 gm and at most 150 gm. This is associated with a targeted stretching effect, which ultimately reduces channel penetration due to surface pressure, with no major deformations of the membrane-electrode assembly occurring.

Forming processes known per se, in particular deep-drawing, are suitable for producing the depressions in the half-sheets. Forming in a continuous process is also possible, i.e. using rotating structured rollers.

The half sheets are made of sheet steel, for example, and optionally provided with a coating.

An exemplary embodiment of the invention as well as a comparative example serving only for explanation purposes is explained in more detail with reference to a drawing. Show in it:

1 a detail of a bipolar plate in plan view,

2 a sectional view of a non-claimed comparative example, 3 shows a section through the bipolar plate according to FIG. 1 in an analogous view

2

Unless otherwise stated, the following explanations relate both to the exemplary embodiment illustrated in FIGS. 1 and 3 and to the comparative example sketched in FIG. 2, which is not claimed. Parts and contours that correspond to one another or have the same effect in principle are identified by the same reference symbols in all figures.

A fuel cell stack, shown only in part, comprises a multiplicity of bipolar plates 1 which are each formed from a first flap plate 2 and a second flap plate 3 . The Flalbbleche 2, 3 of a bipolar plate 1 example, be firmly connected to each other by soldering or welding. The bipolar plates 1 are components of a fuel cell system provided for mobile or stationary use, with regard to the basic function of which reference is made to the prior art cited at the outset.

Each half sheet 2, 3 delimits a half cell 4, 5 of a fuel cell. Various media flow into the fuel cells, namely cooling water, hydrogen and air, through a coolant port 6 , a hydrogen port 7 and an air port 8 . The media flow from the ports 6, 7, 8 via a distributor field 9 and a transition area 10 to the active field, designated 11, of the bipolar plate 1.

The entire bipolar plate 1 shown only partially in FIG. 1 has a long stretched te rectangular shape, with the ports 6, 7, 8 are on a narrow side and further, not shown, ports on the opposite narrow side to flow from the media are provided. The width of each individual port 6, 7, 8, to be measured in the transverse direction of the bipolar plate 1, is significantly less than the width of the active field 11, which has a rectangular basic shape. The patch panel 9 provides ensure that the various media flows are fanned out over the full width of the active field 11. In relation to the arrangement according to FIG. 1, the partly gaseous, partly liquid media flow essentially in the horizontal direction from right to left. In fact, in the finished state of the fuel cell stack, which comprises a multiplicity of bipolar plates 1, the media mainly flow in the vertical direction.

In relation to the arrangement according to FIG. 1, the transition area 10 describes a narrow strip in total, which is directed transversely to the direction of flow of the media. Within this strip, a channel structure denoted by 14 can be seen, which is aligned essentially in the direction of flow of the media, ie in the longitudinal direction of the bipolar plate 1 .

In the arrangement according to FIG. 3, a half-plate 2 of a first bipolar plate 1 and a half-plate 3 of a further, similar bipolar plate 1 can be seen. The same applies to the arrangement according to FIG. 2. A membrane-electrode arrangement 15, which includes a proton-permeable membrane, catalyst layers and gas diffusion layers, is located between the various half-sheets 2, 3 that can be attributed to stacked bipolar plates 1. The membrane is held in position by a frame, which is also referred to as a subgasket and is also part of the membrane-electrode assembly 15 . The frame surrounds the membrane in such a way that the various gaseous fluids, which are on the cathode side and the anode side of the fuel cell, remain separate from one another.

Through the channel structure 14 are within each bipolar plate 1 channels for coolant, ie cooling water or other cooling liquid given. The coolant channels are located above the first half-plate 2 and below the second half-plate 3. In the simplified, non-claimed design according to FIG. The non-recessed areas of each half-sheet 2, 3 are labeled 16. The indentations of normal embossing depth present in the areas 17 are denoted by 12 .

In the embodiment according to FIGS. 1 and 3, depressions 12 of normal embossing depth are to be distinguished from depressions 13 of reduced embossing depth and depressions 20 of increased embossing depth. At points at which the membrane-electrode assembly 15 is contacted by two indentations 12 of normal embossing depth, a fully-embossed indentation region 17 is also spoken of in FIG. 3 . In addition, as shown in FIG. 3, there are various modified depression areas 18, 19. In a modified depression area 18 of the first type, the flap plate 2 has a depression 20 with an increased embossing depth, whereas the flap plate 3 has a depression 13 with a reduced embossing depth. Conversely, in the case of a modified depression region 19 of the second type, there is a depression 13 of reduced embossing depth in the flat sheet 2, whereas the opposite depression 20 of the half-sheet 3 of the next bipolar plate 1 is designed as a depression 20 of increased embossing depth.

The normal embossing depth of the depressions 12 is given with h0, the reduced embossing depth of the depressions 13 with h1 and the increased embossing depth of the depressions 20 with h2. A uniform distance h is given between two opposite depressions 13, 20 of modified embossing depth h1, h2 and between two opposite depressions 12 of normal embossing depth h0.

As can also be seen from FIG. 3, a fully developed depression region 17 and a modified depression region 18, 19 always alternate in the transverse direction of the transition region 10. FIG. Every second modified depression area is a modified depression area 18 of the first type and every second modified depression area is a modified depression area 19 of the second type. Fig. 3 shows an idealized state within a fully assembled fuel cell stack. Here, the half-sheets 2, 3 lie on the membrane-electrode assembly 15 with pressure. Contact between all the depressions 12, 13, 20 and the membrane-electrode assembly 15 is produced by slight deformation of the membrane-electrode assembly 15 shown in simplified form in FIG. 3 with a rectangular cross-section. The difference between the embossing depths h0, h1, h2 is exaggerated in FIG. All non-recessed areas 16 of the various half-sheets 2, 3 are net angeord in mutually parallel planes. Here are within one and the same fuel cell 1, the non-depressed areas 16 of the different half-plates 2, 3 on each other.

Reference character list

1 bipolar plate

2 half sheet

3 half sheet

4 half cell

5 half cell

6 coolant port

7 hydrogen port

8 air port

9 patch panel

10 transition area

11 active field

12 indentation normal embossing depth

13 Deepening reduced embossing depth

14 channel structure

15 membrane electrode assembly

16 non-recessed area

17 normal deepening area

18 modified depression area of the first type

19 modified depression area of the second type

20 Depression increased embossing depth h distance between the depressions hO normal embossing depth h1 reduced embossing depth h2 increased embossing depth p distance between the non-depressed areas

Claims

patent claims

1. Bipolar plate (1), constructed from two half-sheets (2, 3) lying one on top of the other, with a plurality of media ports (6, 7, 8), a distribution panel (9), which is used to distribute the through the ports (6, 7, 8) flowing media is provided, an active field (11), and between the distributor field (9) and the active field (11) arranged, in the plan view of the half-plates (2, 3) a strip-shaped channel structure (14) descriptive transition area (10), characterized in that in each half sheet (2, 3) depressions (12) normal embossing depth (hO), depressions (13) reduced embossing depth (h1) and depressions (20) increased embossing depth (h2) exist and the two half-sheets (2, 3) are placed one on top of the other in such a way that a channel structure (14) is formed by the various depressions (12, 13, 20) and non-depressed areas (16) of the half-sheets (2, 3) lying between them, within which there is always a non-recessed area (16) of one half-plate (2, 3) above e inem area (16) of the other sheet metal (2, 3) that is also not recessed, so that a stripe pattern of the non-recessed areas (16) is given, with alternating different strips between the non-recessed areas (16). Depression areas (17, 18, 19) are arranged, namely a normally pronounced depression area (17) in which both half-sheets (2, 3) have the normal embossing depth (hO), at least one modified depression area (18) of the first type in which the first half sheet (2) has the increased embossing depth (h2) and the second half sheet (3) has the reduced embossing depth (h1), a further normally pronounced depression area (17), and at least one modified depression area (19) of the second type, in which the first half sheet (2) has the reduced embossing depth (h1) and the second half sheet (3) has the increased embossing depth (h2).

2. Bipolar plate (1) according to claim 1, characterized in that the reduced embossing depth (h1) is at least 75% and at most 95% of the normal embossing depth (hO) and the increased embossing depth (h2) is at least 105% and at most 125% of the normal embossing depth (hO).

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

4. Bipolar plate (1) according to one of claims 1 to 3, characterized in that a trapezoidal cross-section structuring is formed by the depressions (12, 13, 20).

5. bipolar plate (1) according to any one of claims 1 to 4, characterized in that between the half-sheets (2, 3) lying membrane-electrode assembly (15) both the depressions (12) normal embossing depth (hO) and the Depressions (13) reduced embossing depth (h1) and the depressions (20) he increased embossing depth (h2) contacted.

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

7. A method for producing a bipolar plate (1), wherein two half-sheets (2, 3) are structured by forming such that in each half-sheet (2, 3) depressions (12) normal embossing depth (hO), depressions (13) reduced pre depressions (h1) and depressions (20) of increased embossing depth (h2) are created, and the two half-sheets (2, 3) are placed one on top of the other in such a way that the various depressions (12, 13, 20) and non-depressed areas ( 16) of the half-sheets (2, 3) a channel structure (14) is created, within which there is always a non-recessed area (16) of one half-sheet (2, 3) over a non-recessed area (16) of the other half-sheet (3, 2) lies, so that a stripe pattern of the non-recessed areas (16) is formed, with different recess areas (17, 18, 19) being arranged in alternation between the strips formed by the non-recessed areas (16), namely a normally pronounced recess area ( 17), in w elchem both half-sheets (2, 3) have the normal embossing depth (hO), at least one modified depression region (18) of the first type, in which the first half-sheet (2) has the increased embossing depth (h2) and the second half-sheet (3) has the has a reduced embossing depth (h1), another normal deepening area (17), and at least one modified depression area (19) of the second type, in which the first half sheet (2) has the reduced embossing depth (h1) and the second half sheet (3) has the increased embossing depth (h2), and wherein the two half sheets (2, 3) in be firmly connected to each other in this position.

8. The method according to claim 7, characterized in that between two

Half sheets (2, 3), which are to be attributed to mutually parallel bipolar plates (1), a membrane electrode assembly (15) is inserted in such a way that it is first contacted by the depressions (12) of increased embossing depth (h2).

9. The method according to claim 8, characterized in that the two half-plates (2, 3) after the indentations (20) of increased embossing depth (h2) have contacted the membrane-electrode assembly (15) with increasing force on each other are pressed so that all depressions (12) with normal embossing depth (h0) and depressions (13) with reduced embossing depth (h1) also contact the membrane-electrode assembly (15).

10. The method as claimed in claim 9, characterized in that the contacts between the depressions (12, 13, 20) which are pronounced to different extents and the membrane-electrode arrangement (15) in a distribution field (9) and an active field ( 11) of the bipolar plate (1) arranged transition area (10) can be produced.