WO2015150524A1

WO2015150524A1 - Bipolar plate, fuel cell, and motor vehicle

Info

Publication number: WO2015150524A1
Application number: PCT/EP2015/057325
Authority: WO
Inventors: Benno Andreas-Schott; Markus Ritter; Christian Martin ZILLICH
Original assignee: Volkswagen Ag
Priority date: 2014-04-02
Filing date: 2015-04-02
Publication date: 2015-10-08
Also published as: DE102014206336A1

Abstract

The invention relates to a bipolar plate (10) for a fuel cell, comprising a structure consisting of two plates (32, 34) joined to each other, wherein each of the two plates (32, 34) has, in the cross-section, a periodic structure having cavities (24), wherein recesses of the cavities (24) of the two plates (32, 34) are arranged pointing away from each other such that a coolant flow region (36) is formed. According to the invention the cavities (24) are formed exclusively in a distribution structure (18) of the bipolar plate (10) arranged before a flow field (20) in a main flow direction (X) and the cavities (24) of the two plates (32, 34) overlap with each other partially such that a coolant flow region (36) allowing a longitudinal and transverse flow is provided. The invention further relates to a fuel cell having such a bipolar plate (10).

Description

description

Bipolar plate, fuel cell and a motor vehicle

The invention relates to a bipolar plate for a fuel cell, a fuel cell and a motor vehicle.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as a core component the so-called membrane-electrode assembly (MEA for membrane electrode assembly), which is a composite of a proton-conducting membrane and in each case an electrode disposed on both sides of the membrane (anode and cathode). During operation of the fuel cell, the fuel, in particular hydrogen H ₂ or a hydrogen-containing gas mixture, is fed to the anode, where an electrochemical oxidation takes place with emission of electrons

Via the membrane, which separates the reaction spaces gas-tight from each other and electrically isolated, takes place (water-bound or anhydrous) transport of protons H ⁺ from the anode compartment in the cathode compartment. The electrons provided at the anode are supplied to the cathode via an electrical line. The cathode is supplied with oxygen or an oxygen-containing gas mixture, so that a reduction of the oxygen takes place with absorption of the electrons

At the same time, in the cathode compartment, these oxygen anions react with the protons transported through the membrane to form water. Through the direct conversion of chemical into electrical

Energy fuel cells achieve compared to other electricity generators due to the circumvention of the Carnot factor improved efficiency. The cathode reaction represents u. a. due to the lower compared to hydrogen diffusion rate of oxygen is the rate-limiting element of the fuel cell reaction.

As a rule, the fuel cell is formed by a multiplicity of stacked membrane-electrode arrangements whose electrical powers add up.

Between two membrane electrode assemblies of a fuel cell stack, a respective bipolar plate is arranged, which has channels for supplying the process gases to the anode or cathode of the adjacent membrane-electrode assemblies and cooling channels for dissipating heat. Bipolar plates are made of an electrically conductive material to make the electrical connection. They thus have the triple function of Process gas supply to the membrane electrode assemblies, the cooling and the electrical connection.

Bipolar plates have different areas in a main flow direction

arranged one behind the other. These are first the main channels or fluid ports, via which the reactants and / or the coolant are supplied. This is followed by an inflow region, which leads to a distribution structure. The distribution structure distributes the fluids, which are then fed to a flow field where the chemical reactions take place.

WO 2008024400 A1 discloses a metallic bipolar plate which, however, has a considerable pressure loss in the distribution structure. Although the flow field is already experiencing a high pressure drop, here the distribution structure accounts for about 80% of the bipolar plate pressure drop.

DE10 2005 057 045 A1 discloses a bipolar plate in which the overall height of the

Inflow is reduced. This is achieved by a regular arrangement of support points and similar free spaces,

DE 101 63 631 A1 discloses a bipolar plate for a fuel cell with a

Distribution structure of several adjacent rows in a row arranged elongated webs.

The invention is based on the object to reduce the pressure loss of a bipolar plate.

This object is achieved by a bipolar plate according to claim 1, a fuel cell according to claim 8 or a motor vehicle according to claim 10. Preferred embodiments of the invention are the subject of the dependent claims.

The bipolar plate according to the invention, designed for use in fuel cells, comprises a structure of two plates arranged with one another. In this case, each of the two plates in the

Cross-section depending on a periodic structure with recesses, wherein recesses of the recesses of both plates forming a coolant flow area are arranged facing away from one another, characterized in that the recesses

are formed exclusively in a arranged in the main flow direction before and / or after a flow field distribution structure of the bipolar plate and that the recesses the two plates partially overlap, so that a longitudinal and transverse flow allowing coolant flow area is provided. The distributor structure, which may also be referred to as a collector downstream of the flow field, is preferably arranged directly on or next to the flow field.

In the distribution area or in the distribution structure, the pressure loss is significantly reduced by improving the hydraulic diameter of the flow cross sections. The length and width ratio of the formed channel cross sections can now tend to the ideal ratio of 1: 1. The uniform distribution in the flow field is significantly improved, since now the flow field and not the distribution area causes the largest part of the pressure loss. The invention also ensures a support or clamping of the membrane electrode assembly with the bipolar plate in the distribution area.

According to the invention plates are thus used for the construction of the bipolar plate, which have no channel-like, continuous recesses as in the prior art, but partially overlapping, periodic structures with recesses. The term recess is understood to mean a bulge or embossing of an otherwise flat plate which has a continuous circumferential contour with respect to the flat background of the plate. The recesses allow not only the longitudinal main flow but also a transversely or perpendicularly extending transverse or secondary flow, which the

Flow properties further improved. By the transverse and longitudinal flow creates a connected flow volume, the recesses or stampings the

Control or adjust pressure loss.

The recesses are preferably rounded cross or rhombic structures. Rounded or rounded cross or rhombic structures are particularly suitable for generating the coordinated longitudinal and transverse flow of the coolant. The pressure loss of the coolant and the reactants in the longitudinal and transverse directions can be influenced by the length, width and the intersection of the recesses or stampings. The discharge of water, critical for a frost start, is favored by the rounded structures. The more strongly the structures or recesses are rounded or rounded, the larger channel cross sections are formed. The rounding consists of rounding sharp corners and / or forming straight side regions of the structures concave, that is, inwards into the structure. Also, an oval shape or ellipse is suitable, wherein an oval or round shape represents a maximum rounded structure or contour. Finally, such forms can become a recess or structure be combined. This can be realized for example by two orthogonal and penetrating ellipse shapes.

In a preferred embodiment of the invention, it is provided that the recesses of the two plates are in edge regions and / or in corner regions of the recesses

overlap. For this purpose, the recesses can be made identical on both plates. The recesses of the two plates can be arranged offset by half a recess, for example, a half width or length. A smaller offset is also possible, which is then unbalanced.

The recesses may have a height between half the height and the total height of the structure. This optimizes flow and minimizes pressure loss as the height of the channel is maximized. In this consideration, the wall thicknesses or thicknesses of the plates of the plates or the plates can be disregarded. In other words, a recess may have half the height or the full height of the total flow volume. The full height will be in the area

overlapping recesses, while half of the height is in the range of individual recesses.

For the production of the plates is advantageously provided that the recesses are embossed in the plates. Alternatively, a deep drawing process can also be used. The provision of the two plates to a bipolar plate is preferably carried out by welding the two plates. This is preferably done in the form of continuous welds, whereby a seal of the coolant channels formed by the recesses is obtained. A particularly suitable welding process is the laser welding.

In a preferred embodiment of the invention, it is provided that the recesses partially overlap along the main flow direction and along a transverse flow direction. The Oberschneidung in two preferably mutually perpendicular directions simultaneously optimizes the longitudinal and transverse flow.

The invention further relates to a fuel cell comprising a stack of a plurality of previously described bipolar plates and a plurality of membrane-electrode assemblies, the bipolar plates and the membrane-electrode assemblies

are stacked alternately. The advantages and modifications described above apply. In this arrangement, the membrane electrode units rest on the recesses. The recesses thus act - as well as their function for coolant channel formation - as

Spacer between the membrane-electrode assembly and the bipolar plate, whereby spaces for the resource supply are formed in the form of Betriebsfuss fields.

In a preferred embodiment, the passage of the anode and / or the cathode operating medium flow takes place parallel to the coolant flow within the channels formed by the recesses. In other words, the main flow directions or the longitudinal flows are parallel or substantially parallel. This can be done in cocurrent or countercurrent. Preferably, all of the three streams, anode and

Cathode fluid streams and the coolant flow passed in parallel in the DC.

The fuel cell can be used for mobile or stationary applications. In particular, it serves to supply power to an electric motor for driving a vehicle. Thus, another aspect of the invention relates to a vehicle having a fuel cell as described above. The advantages and modifications described above apply.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

FIG. 1 shows a plan view of a schematized bipolar plate according to the invention,

Figure 2 is a schematic representation of a detail of the distribution structure _»

Figure 3 is a schematic representation of a detail of the distribution structure with hidden

Edges of the underlying plate,

FIG. 4 shows a sectional view along section A-A according to FIG. 1

5 shows a sectional view along section B-B according to FIG. 1, FIG.

FIG. 6 shows a schematic illustration of a detail of a rounded distribution structure, 7 shows a schematic representation of a detail of the rounded distribution structure with hidden edges of the underlying plate, FIG.

FIG. 8 shows a perspective view of the bipolar plate according to the invention and FIG

9 shows a perspective view of a section of the bipolar plate from FIG. 8, FIG.

1 shows schematically a plan view of a bipolar plate 10. The bipolar plate 10 usually has a rectangular extent, wherein the longitudinal direction in a

Main flow direction X runs and the transverse side parallel to a direction Y of

Cross flow runs. In the course of the main flow X upstream of an inlet or channel region is arranged, in which an anode main gas channel 12, a

Cathode main gas channel 14 and a coolant main gas channel 16 are located. Above the channels 12, 14 and 16, the respective fluids of the bipolar plate 10 are supplied. Further downstream is the distribution area or manifold structure 18, which will be described in more detail below. Next in the main flow direction X, the flow field 20 of the bipolar plate 10 adjoins the distributor structure 18. Between the channels 12, 14 and 16 and the distributor structure 18, one or more inflow regions 22 are provided, via which the respective fluid passes from the corresponding channel into the distributor structure. The distributor structure 18 has the task of distributing the fluids from the width of the associated channel in the Y direction to the entire width of the flow field 20, in order to enable surface-wide chemical reactions or cooling. For this purpose, a plurality of recesses 24 are arranged in the distributor structure 18.

As shown in FIG. 2, the recesses 24 are formed in a periodic structure 26. As shown here, the recesses 24 have a diamond-shaped structure, with the diamonds being arranged with their longitudinal axis parallel to the main flow direction X. The recesses 24 are arranged relatively close to each other, so that a plurality of recesses 24 are provided in the distributor structure 18. Thus, the distance between two recesses 24 corresponds approximately to 3 to 7 times, preferably 5 times, an outer edge or side of the recess 24. The recesses 24 are also offset such that the distances between the recesses 24 are approximately equal are. For this purpose, the recesses 24 may be arranged in rows, wherein the rows are each offset by the dimension of half a recess 24 to each other. The rows may be formed in the longitudinal flow direction X and / or in the transverse flow direction Y. In FIG. 3, the periodic structure 26 of FIG. 2 is extended by a further periodic structure 26, which is arranged below the periodic structure 26 shown in FIG.

Correspondingly, recesses 24a of a first plate corresponding to the recesses 24 of FIG. 2 are shown in full. Recesses 24b of an underlying second plate are shown hatched. As can be seen, the two plates are offset from each other so that the recesses 24a of the first plate and the recesses 24b of the second plate partially overlap. Since the recesses 24a and 24b are formed symmetrically, a symmetrical overlapping structure results.

As shown in Figure 3, the recesses 24a and 24b overlap in corner regions of the recesses 24. Thus, each diamond-shaped recess 24 has four

Overlapping areas 28, one of which is exemplified by the reference numeral 28. In the overlap regions 28, the two recesses 24a and 24b lie one above the other, so that here a relatively high flow cross-section is formed.

Correspondingly, there are also contact or support regions 30 in which the two plates lie directly on one another, ie neither a recess 24a of the first plate nor a recess 24b of the second plate are present.

Figure 4 shows the sectional view of the bipolar plate 10 along the line AA in Figure 1. The first plate 32 and the second plate 34 form a cooling channel or

Coolant flow region 36, in the example of the coolant flow 38 in

Main flow direction X is shown. As can be seen, the two plates 32 and 34 are arranged to each other such that the recesses 24a and 24b are arranged facing away from each other. In other words, the two plates 32 and 34 are with their

Main surfaces to each other, which is shown on the left in Figure 4, wherein the recesses 24 are then formed in each case to the outside. This results in inner sides or inner surfaces of the two plates 32 and 34, a continuous flow area, here as

Coolant flow region 36 is designated.

The structure of the first plate 32 and the associated second plate 34 has a total height H. The height of a recess 24, calculated from an inner side of the plate to an outer side of the plate in the areas of the recess 24 is h, wherein the height of the recess h corresponds to half the height H of the structure. Thus, the

Manifold 18 a high height h for the coolant flow area 36, which leads to a favorable hydraulic cross section and thus low pressure drop. Also, the flow volumes or channels for the reactants have a height that corresponds to half the total height H. These flow areas are formed on the outer sides of the two plates 32 and 34 between the recesses 24, respectively. There is then in a stack of a complete Brennstoffelleelle a membrane-electrode assembly on the recesses 24.

FIG. 5 shows a cross section according to the line BB in FIG. 1 of the bipolar plate 10. Analogous to FIG. 4, here too the first plate 32 and the second plate 34 are shown, which with their respective recesses 24a and 24b one between the two plates

form arranged coolant flow region 36. The coolant path 38 of the

Coolant in the coolant flow area 36 is also shown. While the flow profile in the longitudinal direction X is shown in FIG. 4, the flow profile in the transverse direction Y or the transverse component of the coolant flow is shown here in FIG. The coolant path 38 thus has a longitudinal component as well as a transverse component in a continuous flow space which is interrupted by the support regions 30. Of the

Flow region or coolant channel 36 has due to the large height h and the formation and the arrangement of the recesses 24 has a favorable hydraulic diameter.

In FIGS. 6 and 7, a periodic structure 26 of the recesses 24 is shown analogously to FIGS. 2 and 3. While in Figures 2 and 3, the recesses 24 have the shape or contour of a rhombus, the recesses 24 are formed in Figure 6 and 7 as a rounded cross pattern. This embodiment can also be used as a rounded cross or

Diamond structure are called. As shown in Figure 8, the side surfaces of the recesses 24 are now concave, so curved inward. As a result, the cathode and / or anode course takes a wave-shaped or meandering course, which is the

Flow behavior positively influenced. In Figure 7, the recesses 24a of the first plate are fully shown, while the recesses 24b of the second plate are hatched or only partially shown. Here again, the overlapping areas 28 between the two recesses 24a and 24b are located in corner regions of the recesses 24. Support areas 30 are arranged where neither a recess 24a nor a recess

Recess 24b is formed.

Figure 9 shows a perspective view of the bipolar plate 10. In comparison to Figure 1, the top of Figure 1 is shown below. Thus, in the illustration in FIG. 8, the first one Plate 32 arranged below, while the second plate 34 is arranged at the top. Corresponding to FIG. 1, a plurality of recesses 24 are arranged in the distributor structure 18

FIG. 9 shows a detail according to section C of FIG. 8. In this illustration, it can be seen how the recesses 24b are formed outwardly in the second plate 34, so that the outer walls of the recesses 24b project as protrusions from the plane of the second plate 34. Similarly, the recesses 24a of the first plate 32 are formed. Thus, the staggered recesses 24a and 24b form the

Coolant flow region 36, in which the coolant flows controlled by the shape and arrangement of the recesses 24 in a favorable hydraulic diameter or cross-section in the longitudinal and transverse directions. This causes the pressure loss across the manifold structure 18 to be low. To form a fuel cell or a fuel cell stack, a plurality of the bipolar plates 10 are stacked alternately with a membrane-electrode assembly. That is, each membrane-electrode assembly is sandwiched by two bipolar plates 10. Likewise, each bipolar plate 10 is sandwiched by two membrane-electrode assemblies.

Each membrane-electrode assembly may comprise a polymer electrolyte membrane sandwiched between two electrodes, namely an anode and a cathode. The polymer electrolyte membrane may be a per se conductive polymer, for example, the polymer known under the trade name Nafion, or a polymer by

Doping with an electrolyte receives its proton conductivity. An example of the latter embodiment is phosphoric acid doped polybenzimidazole (PBI). The electrodes typically comprise a particulate supported catalytically active noble metal. Externally to the electrodes each includes a diffusion layer, which is a porous, gas-permeable and electrically conductive medium. The catalytic layers of the electrodes may either be applied directly to the polymer electrolyte membrane or to the gas diffusion layer.

The plate 10 is made of an electrically conductive material, for example a metal or a carbon-based material or a composite material of such. LIST OF REFERENCE NUMBERS

10 bipolar plate

12 anode main gas channel

14 Cathodert main gas channel

16 coolant main gas channel

18 distribution structure

20 river field

22 inflow area

24 recess

24a recess first plate

24b recess second plate

26 periodic structure

28 overlap area

30 support area

32 first plate

34 second plate

36 coolant flow area

38 coolant flow h height recess

H total height

X main flow direction

Y transverse flow direction

Claims

claims

A bipolar plate (10) for a fuel cell comprising a structure of two plates (32, 34) disposed one on the other, each of the two plates (32, 34) each having a periodic structure with recesses (24) in cross section, with depressions of the

Recesses (24) of both plates (32, 34) a coolant flow region (36) are arranged facing away from each other, characterized dadyrch that the

Recesses (24) exclusively in a main flow direction (X) before and / or after a flow field (20) arranged distributor structure (18) of the bipolar plate (10) are formed and that the recesses (24) of the two plates (32, 34) itself partially overlap, allowing a longitudinal and cross flow permitting

Coolant flow region (36) is provided,

2. bipolar plate according to claim 1, characterized in that the recesses (24) are rounded cross or rhombic structures.

3. bipolar plate according to claim 1 or 2, characterized in that the recesses (24) of the two plates (32, 34) overlap in edge regions of the recesses (24).

4. bipolar plate according to one of the preceding claims, characterized in that the recesses (24) of the two plates (32, 34) in corner regions of

Recesses (24) overlap.

5. bipolar plate according to one of the preceding claims, dadyrch in that the recesses (24) have a height (h) between half the height (H) and the entire height (H) of the structure.

6. bipolar plate according to one of the preceding claims, characterized in that the recesses (24) in the plates (32, 34) are embossed.

7. Bipolar plate according to one of the preceding claims, characterized in that the recesses (24) along the main flow direction (X) and along a transverse flow direction (Y) partially overlap.

8. Bipolar plate according to one of the preceding claims, characterized in that the recesses (24) have concave side surfaces.

9. A fuel cell comprising a stack of a plurality of bipolar plates (10) according to any one of the preceding claims and a plurality of membrane electrode assemblies, characterized in that the bipolar plates (10) and the membrane electrode assemblies are stacked alternately.

10. Fuel cell according to claim 9, characterized in that in a Verteiierstruktur (18) of the bipolar plate (10) an anode-side flow region and a cathode-side flow region through gaps between the bipolar plates (10) and the membrane-electrode assemblies is formed and that a main flow direction an anode and / or a cathode resource flow parallel to the

Main flow direction (X) of the coolant extends.

11. Motor vehicle with a fuel cell according to claim 9 or 10.