DE102017202048A1 - Bipolar plate and fuel cell stack - Google Patents

Abstract

The invention relates to a bipolar plate for forming fuel cell stack fuel cells stacked along a stack axis, comprising media ports for supplying media, namely, fuel, oxidant and coolant, an active surface having a plurality of media channels for distributing the media over the active surface, wherein the media channels are connected to the respective media ports, an anode plate with media channels of the fuel, a cathode plate with media channels of the oxidant, voids between the anode plate and the cathode plate to form the media channels of the coolant, at least one cohesive master seam for connecting the anode plate and cathode plate the main seam extends at least in sections through the active area.

Description

The technology disclosed herein relates to a bipolar plate and a fuel cell stack having a plurality of bipolar plates.

The fuel cell is an electrochemical energy converter that converts fuel and oxidant into reaction products, producing electricity and heat. The fuel cell comprises an anode and a cathode which are separated by an ion-selective or ion-permeable separator (membrane).

The fuel cells contemplated herein include a cathode plate and an anode plate. The cathode plate of a fuel cell and the anode plate of an adjacent fuel cell together form a bipolar plate. Between the bipolar plates are each membrane electrode units.

The bipolar plates have media openings for supplying or discharging the media (fuel, oxidant and coolant). As a rule, at least six media openings are provided for this purpose. In the stacked state, corresponding media openings are aligned, thereby forming respective media channels which extend parallel to the stack axis. In or on the bipolar plates run media channels that distribute the media over the active surface of the bipolar plate or the fuel cell.

It is a preferred object of the technology disclosed herein to reduce or eliminate at least one disadvantage of a previously known solution or to suggest an alternative solution. Other preferred objects may result from the beneficial effects of the technology disclosed herein. The object (s) is / are solved by the subject matter of the independent claims. The dependent claims are preferred embodiments.

The object is achieved by a bipolar plate, which are used for the production of fuel cells of a fuel cell stack. In the fuel cell stack, the bipolar plates are stacked along a stacking axis. Membrane layers with membrane electrode assemblies are placed between the bipolar plates.

The single bipolar plate is composed of an anode plate and a cathode plate. The two plates are superimposed and connected. In the bipolar plate and thus both in the anode plate and in the cathode plate, there are several media openings. These media openings are through holes. In the stacked state of a plurality of bipolar plates, associated media openings are aligned, thereby forming media lines that extend parallel to the stack axis across a plurality of bipolar plates. The media openings are also referred to as "media ports". Specifically, the bipolar plate has a media port for supplying the fuel, a media port for discharging the fuel, a media port for supplying the oxidant, a media port for discharging the oxidant, a media port for supplying the coolant, and a media port for discharging the coolant.

A fuel cell has an active area. The active surface extends perpendicular to the stack axis. In the active area, the fuel and the oxidant react with each other. At the bipolar plates, the active area is defined by the area over which a plurality of media channels extend. In the finished state of the fuel cell overlaps the active surface of the bipolar plate with the active surface of the membrane electrode assembly. The media channels serve to distribute the media, in particular fuel and oxidant, over the active area. Accordingly, the media channels extend perpendicular to the stack axis and are connected to the associated media openings. Preferably, the media channels for the coolant also extend over the entire active area to cool it.

On the anode plate of the bipolar plate, the media channels of the fuel are formed. These media channels are open and are covered in the finished state of the fuel cell by the membrane electrode assembly. The fuel thus diffuses from the media channels into the membrane electrode assembly.

On the cathode plate of the bipolar plate, the media channels of the oxidizing agent are formed. These media channels are also open and are covered in the finished state of the fuel cell by the membrane electrode assembly. The oxidant thus diffuses from the media channels into the membrane electrode assembly.

Cavities are provided between the anode plate and the cathode plate. These cavities form the media channels of the coolant. For example, the anode plate and the cathode plate are formed sheets. By appropriate depressions and elevations in the sheets, the media channels for the three media are formed.

For connecting the anode plate and the cathode plate at least one cohesive main seam is provided. This main seam preferably extends around all media openings of the coolant, ie at least one Media port for feeding and the one media port for discharging the coolant, and / or a large part of the active area. By the main seam, the anode plate and the cathode plate are materially connected to each other, preferably by welding and / or soldering and / or gluing.

The main seam does not necessarily represent a continuous cohesive connection, but it can also be formed several cohesive connection points along the main seam. However, it is particularly preferred that the main seam represents a continuous cohesive connection and thus also represents a seal between the anode plate and the cathode plate.

It has been recognized in the present technology that, depending on the positioning of the main seam, respective cavities (also referred to as voids) between the anode plate and the cathode plate outside the active area are flooded with coolant. For efficient cooling of the fuel cells, however, the coolant should essentially be distributed only in the area of the active area.

Therefore, according to the present technology, the main seam runs at least in sections through the active area. It has been found that the very narrow area between the outer seal and the active area is partly not suitable for setting the main seam. Therefore, the main seam is partially set in the active area.

It is preferably provided that the anode plate has first recesses. These first depressions form the media channels of the fuel. The cathode plate has second recesses. The second wells form the media channels of the oxidant. The wells of the anode plate or cathode plate are thus part of the active surface. In these recesses, the fuel and the oxidant are distributed over the active area. From these recesses, the two media diffuse into the membrane electrode assembly and react with each other within the membrane electrode assembly.

Preferably, the main seam runs in sections in one of the recesses. In particular, a first bottom is defined at the first recesses. At the second wells, a second bottom is defined. When the anode plate and the cathode plate are adjacent to each other, the two bottoms are also adjacent to each other. Preferably, the main seam connects the two floors cohesively. The main seam thus runs through the bottoms of the two wells and thus through the active surface.

Looking at the bipolar plate in the plane perpendicular to the stacking axis, it is, for example, the active area in the middle and on both sides of the active area three of the media openings are formed. The outer seal extends on two opposite sides outside the active area. It is preferably provided that the main seam extends through the active surface on these two opposite sides.

Preferably, the bipolar plate has at least one outer surface surrounding the active area. Usually, two outer seals are provided: one on the outside of the cathode plate and one on the outside of the anode plate. The outer seals seal the individual bipolar plates to one another in the stacked state of a plurality of bipolar plates. In the finished state of the fuel cell, in particular the frame (sub-frame), which accommodates the membrane electrode unit, is located between the outer seals of two adjacent bipolar plates.

The main seam for cohesive connection of the anode plate and the cathode plate extends in conventional bipolar plates outside of the outer seals, since there is sufficient space available. The term "outside or inside" in the context of the present technology refers to a viewing plane perpendicular to the stack axis. If one thus considers the bipolar plate in the plane perpendicular to the stacking axis, the main seam for the material-locking connection outside the outer seal, which surrounds at least the active surface, is located in conventional bipolar plates.

In the present technology, it has been recognized that in positioning the main seam outside the outer seal, relatively many voids (also referred to as voids) between the anode plate and the cathode plate outside the active area are flooded with coolant.

The outer seals are for example on elevations of the cathode plate and the anode plate. The corresponding elevations on the two plates face each other in the assembled state and thus form a cavity or space between the anode plate and the cathode plate along the outer seal. If the main seam is outside the outer seal, then this entire cavity is flooded with coolant. In the context of available technology it was found out that with usual fuel cell stacks approx. 1 kg of coolant are in these cavities, in which no cooling makes sense.

The bipolar plate presented here provides that the main seam preferably within the Outer seal is located. The description "within" again refers to the viewing plane perpendicular to the stacking axis. By positioning the main seam within the outer gasket, the entire area outside the main seam, and thus the entire area in which the outer gasket is located, is flooded with no or little coolant.

As already described, the main seam does not necessarily represent a continuous cohesive connection, but it can also be formed several material connection points along the main seam. In this case, although coolant can also flow into unwanted cavities between the connection points, at least the circulation of the coolant in these unwanted cavities is greatly reduced. However, it is particularly preferred that the main seam represents a continuous cohesive connection and thus also represents a seal between the anode plate and the cathode plate.

In the following, the term "ring" is not used for a circular shape, but generally for a self-contained shape or curve.

Preferably, the outer seal is a closed ring which encloses the active surface and at least all media openings of the coolant. Furthermore, the complete main seam lies within this outer seal. Particularly preferably, the outer seal encloses not only the active surface and all media openings of the coolant as a closed ring but also all media openings of the fuel and the oxidizing agent. The outer seal thus encloses all functional components of the bipolar plate. The main seam is inside this outer seal.

Particularly preferably, the main seam also forms a closed ring. As already described, it is provided in particular that this ring represents a continuous cohesive connection and thus acts as a seal. The annular main seam preferably encloses at least all media openings of the coolant.

According to a preferred embodiment, the media openings of the fuel and the oxidizing agent are outside the annular main seam. It is then particularly preferred for additional seams to enclose the media openings of the fuel and oxidizing agent. The two ends of each additional seam are connected to the main seam. The additional seam thus branches off the main seam and opens again into the main seam. The single peripheral seam together with a small portion of the main seam encloses the single media port of the fuel or oxidant in closed ring form. The additional seam is a cohesive connection between the cathode plate and the anode plate, in particular formed by welding and / or soldering and / or gluing.

It is preferably provided that the anode plate and / or the cathode plate between the corresponding media opening and the active surface comprise a Vorverteilstruktur, designed for distributing the fuel or oxidizing agent to the media channels. According to this embodiment, the anode plate has a pre-distribution structure which distributes the fuel from the media opening for supplying the fuel to the corresponding media channels of the active area. Accordingly, the cathode plate has a pre-distribution structure that distributes the oxidant from the media port for supplying the oxidant to the corresponding media channels of the active area. The pre-distribution structures are in particular no components of the active surface.

It is preferably provided that the anode plate and / or the cathode plate between the active surface and the corresponding media opening comprise a collecting structure, designed to guide the fuel or oxidant from the media channels to the corresponding media opening. According to this embodiment, the anode plate has a collecting structure that leads the fuel from the media channels of the active surface to the media port for discharging the fuel. Accordingly, the cathode plate has a collection structure that guides the oxidant from the media channels of the active area to the media port for removal of the oxidant. The collecting structures are in particular no components of the active surface.

Among other things, the technology disclosed herein relates to a fuel cell stack having a plurality of the described bipolar plates stacked along the stack axis. In each case between two bipolar plates is a membrane layer.

The membrane layer in particular comprises a membrane electrode unit. In the membrane electrode assembly, the fuel from one side and the oxidizer from the other side can diffuse. Within the membrane electrode unit, the two media react with each other. Preferably, the membrane layer also includes a frame (sub-frame) that holds at least parts of the membrane electrode assembly.

In particular, the membrane electrode assembly comprises a membrane and a gas diffusion layer on at least one side of the membrane. Preferably, at least the membrane is clamped in the frame. The gas diffusion layer can also be positioned independently of the frame between the membrane and the bipolar plate.

It is preferably provided that the entire active area of the bipolar plate is aligned with the active area of the membrane electrode unit so that the reaction between the fuel and the oxidant can take place over the entire active area of the bipolar plate. Thus, here only the area of the bipolar plate is regarded as an "active area", which is also aligned with the active area of the membrane electrode unit. It should be noted that parts of the membrane electrode assembly, in particular the membrane, can be clamped in the frame and thus do not act actively.

Preferred fuels for the fuel cell stack are: hydrogen, low molecular weight alcohol, biofuels, or liquefied natural gas. The cathode is preferably supplied with air, oxygen or peroxide. The membrane (ion-selective separator) may be formed, for example, as a proton exchange membrane (PEM). Preferably, a cation-selective polymer electrolyte membrane is used. Materials for such a membrane include: Nation®, Flemion® and Aciplex®.

The fuel cell stack is in particular part of a fuel cell system. The fuel cell system is intended in particular for mobile applications such as motor vehicles, in particular for providing the energy for at least one drive machine for locomotion of the motor vehicle.

• 1 eine schematische Ansicht eines hier offenbarten Brennstoffzellenstapels mit den hier offenbarten Bipolarplatten,
• 2 eine schematische Ansicht der Bipolarplatte, und
• 3 eine schematische Schnittansicht eines Details der Bipolarplatte.

The technology disclosed herein will now be explained with reference to the figures. Show it:

• 1 a schematic view of a fuel cell stack disclosed herein with the bipolar plates disclosed herein,
• 2 a schematic view of the bipolar plate, and
• 3 a schematic sectional view of a detail of the bipolar plate.

1 shows purely schematically a fuel cell stack 2 , The fuel cell stack 2 includes a variety of fuel cells 3 , stacked along a stacking axis 7 , At the front ends of the fuel cell stack 1 there are end plates 4 , These endplates 4 can also be designed as media plates or printing plates. Between the end plates 4 and the respective adjacent fuel cell 3 there are pantograph plates 6 , Between the pantograph plates 6 and the endplates 4 are insulator plates 5 arranged.

According to the 2 and 3 show the individual fuel cells 3 each bipolar plates 1 and an intermediate membrane layer 28 on. The two sides of the bipolar plate 1 are each a fuel cell 3 assigned.

The bipolar plates 1 each have six media openings 9 - 11 on. In the fuel cell stack 2 the corresponding media openings are aligned 9 - 11 and thereby form six media lines 8th (S. 1 ) for distributing the media across the multiple bipolar plates 1 ,

In detail, the bipolar plate 1 two media openings 9 for supplying and discharging the oxidant, two media ports 10 for supplying and discharging the fuel and two media ports 11 for supplying and discharging the coolant.

In particular, the sectional view in 3 illustrates that the single bipolar plate 1 from an anode plate 17 and a cathode plate 20 is composed. On the anode plate 17 are media channels 13 formed of the fuel. On the cathode plate 20 are media channels 12 formed of the oxidizing agent. Between the anode plate 17 and the cathode plate 20 form corresponding cavities media channels 14 of the coolant.

As 2 shows form the media channels 13 fuel and media channels 12 of the oxidizing agent an active surface 33 the bipolar plate 1 , The view in 2 shows the anode plate 17 and thus on the surface of the anode plate 17 trained media channels 13 of the fuel in the active area 33 , For the sake of clarity, here is only one media channel 13 shown. In fact, however, extend over the active area 33 a variety of media channels 12 - 14 ,

Outside the active area 33 each is a pre-distribution structure 15 , at least for the fuel and the oxidant, on the anode plate 17 and the cathode plate 20 intended. The pre-distribution structures 15 distribute the appropriate medium to the media channels 12 . 13 , Corresponding collection structures 16 lead the media from the media channels 12 . 13 back together on the appropriate media openings 9 . 10 ,

2 shows the course of an annular closed outer seal 25 , As 3 clarified, located on both sides of the bipolar plate 1 each one of these outer seals 25 , The single outer seal 25 encloses both the active area 33 as well as all media openings 9 - 11 ,

Further shows 2 the course of a ring-shaped main seam 23 , The main seam 23 encloses both media openings 11 of the coolant and passes through the active surface on two opposite sides 33 , Here is the main seam 23 inside the outer seal 25 arranged.

3 shows that the media channels 13 of the fuel through first depressions 18 in the anode plate 17 are formed. The first wells 18 have a first floor 19 on. The media channels 12 of the oxidizing agent are through second depressions 21 in the cathode plate 20 educated. The second wells 21 have a second floor 22 on. The two floors 19 . 22 lie together. The main seam 23 passes through the two recesses 18 , 21 and connects the two floors 19 . 22 cohesively with each other. In the example shown, it is the main seam 23 a continuous cohesive connection to form a welded sealing seam. In the wells 18 . 21 and thus in the media channels 12 . 13 the main seam runs 23 through the active area 33 ,

Further shows 3 that the outer seals 25 on elevations of the anode plate 17 or cathode plate 20 are located. Between the two outer seals 25 a cavity or empty space remains 24 , The white space 24 forms an unnecessary space in which no or as little as possible coolant should flow. Without the main seam 23 which are inside the outer seals 25 The coolant would be out of the media channels 14 unhindered in this white space 24 flow.

3 further shows the arrangement of a membrane layer 28 on both sides of the bipolar plate 1 , The membrane layer 28 includes a frame 29 and a membrane electrode assembly 30 , The membrane electrode unit 30 in turn comprises a membrane 31 and a gas diffusion layer 32 , At least the membrane 31 is in the frame 29 clamped. In that not from the frame 29 hidden area (active area of the membrane electrode unit 30 ) of the membrane 31 For example, the two reactants, fuel and oxidant, can react with each other. The here as active area 33 the bipolar plate 1 defined area completely overlaps with the active area of the membrane electrode assembly 30 ,

Further shows 3 that is between the outer seals 25 two adjacent bipolar plates 1 the frame 29 the membrane layer 28 located.

In 2 are in the plane perpendicular to the stack axis 7 a width 34 and a height 35 the active area 33 located. The main seam 23 extends to the two opposite sides of the active area 33 over the entire width 34 through the active area 33 ,

Further shows 2 four additional seams 27 , One additional seam each 27 branches from the main seam 23 and flows back into the main seam 23 so that the single additional seam 27 along with a small section of the main seam 23 one of the media openings 9 . 10 closed ring surrounds.

Other seals 26 each enclosed annular surround a single media port 9 - 11 , so that the appropriate media opening 9 - 11 close to the associated media opening of the adjacent bipolar plate 1 followed.

LIST OF REFERENCE NUMBERS

1

bipolar

2

fuel cell stack

3

fuel cells

4

endplates

5

insulator plates

6

Current collector plates

7

stacking axis

8th

media lines

9

Media openings of the oxidizing agent

10

Media openings of the fuel

11

Media openings of the coolant

12

Media channels of the oxidant

13

Media channels of the fuel

14

Media channels of the coolant

15

Vorverteilstruktur

16

collecting structure

17

anode plate

18

first recess

19

first floor

20

cathode plate

21

second recess

22

second floor

23

main seam

24

whitespace

25

outer seal

26

further seals

27

additional seams

28

membrane layer

29

Frame (sub-frame)

30

Membrane electrode assembly

31

membrane

32

Gas diffusion layer

33

active area

34

Width of the active area

35

Height of the active area

Claims (14)

Bipolar plate (1) for forming along a stacking axis (7) stacked fuel cells (3) of a fuel cell stack (2) comprising Media openings (9-11) for supplying or discharging media, namely fuel, oxidant and coolant, An active surface (33) having a plurality of media channels (12-14) for distributing the media across the active surface (33), the media channels (12-14) being connected to the respective media ports (9-11), An anode plate (17) with the media channels (13) of the fuel, A cathode plate (20) with the media channels (12) of the oxidant, Cavities between the anode plate (17) and the cathode plate (20) to form the media channels (14) of the coolant, and At least one cohesive main seam (23) for connecting anode plate (17) and cathode plate (20), • wherein the main seam (23) extends at least in sections through the active surface (33). Bipolar plate after Claim 1 • wherein the anode plate (17) has first recesses (18) and the first recesses (18) form the fuel media channels (13), and • the cathode plate (20) has second recesses (21) and the second recesses (21 ) form the media channels (12) of the oxidizing agent. Bipolar plate after Claim 2 wherein the first recess (18) has a first bottom (19), wherein the second recess (21) has a second bottom (22), wherein the two bottoms (19, 22) abut each other and through the main seam (23) materially are connected. A bipolar plate according to any one of the preceding claims, wherein the main seam (23) extends through the active surface (33) on two opposite sides. A bipolar plate according to any one of the preceding claims, comprising an outer seal (25) surrounding the active surface (33) on the cathode plate (20) and / or anode plate (17), the main weld (23) being radially inward of the outer seal (25) ) runs. Bipolar plate after Claim 5 in that the outer seal (25) encloses, as a closed ring, the active surface (33) and at least all media openings (11) of the coolant, the complete main seam (23) extending radially inwardly of the outer seal (25) with respect to the stacking axis. Bipolar plate after Claim 6 , wherein the outer seal (25) as a closed ring all media openings (9-11) of all media and encloses. Bipolar plate according to one of the preceding claims, wherein the main seam (23), in particular as a closed ring, encloses at least all the media openings (11) of the coolant. Bipolar plate after Claim 8 , wherein the media openings (9, 10) of the fuel and the oxidizing agent are outside the annular main seam (23). Bipolar plate after Claim 9 comprising at least one cohesive additional seam (27) whose two ends are connected to the main seam (23), wherein the single additional seam (27) encloses a medium opening (9, 10) of the fuel or the oxidant closed annular together with the main seam (23) , Bipolar plate according to one of the preceding claims, wherein the main seam (23) is formed as a sealing seam. Bipolar plate according to one of the preceding claims, wherein the main seam (23) is welded and / or glued and / or soldered. Fuel cell stack (2) comprising a plurality of bipolar plates (1) stacked along the stack axis (7) according to one of the preceding claims and in each case a membrane layer (28) between two bipolar plates (1). Fuel cell stack after Claim 13 wherein the membrane layer (28) comprises a membrane electrode assembly (30) into which fuel and oxidant can diffuse and react with each other, the full active surface (33) of the bipolar plate (1) being aligned with the membrane electrode assembly (30), such that the reaction between the fuel and the oxidant can take place over the complete active area (33) of the bipolar plate (1).

Images