DE102014206336A1 - Bipolar plate, fuel cell and a motor vehicle - Google Patents

Abstract

The invention relates to a bipolar plate (10) for a fuel cell comprising a structure of two mutually connected plates (32, 34), wherein each of the two plates (32, 34) in cross section each having a periodic structure with recesses (24), wherein depressions the recesses (24) of both plates (32, 34) forming a coolant flow region (36) are facing away from each other. It is provided that the recesses (24) are formed exclusively in a distributor structure (18) of the bipolar plate (10) arranged in front of a flow field (20) in the main flow direction (X) and in that the recesses (24) of the two plates (32, 34 ) partially overlap so as to provide a longitudinal and transverse flow allowing coolant flow area (36). The invention further relates to a fuel cell with such a bipolar plate (10).

Description

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 release of electrons (H ₂ - 2H ⁺ + 2e ^- ). 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 (½O ₂ + 2e ^- → O ^2- ). At the same time, these oxygen anions in the cathode compartment react with the protons transported through the membrane to form water (2H ⁺ + O ^2- → H ₂ O). The direct conversion of chemical to electrical energy fuel cells achieve over other electricity generators due to the circumvention of the Carnot factor improved efficiency. The cathode reaction is, inter alia, due to the lower compared to hydrogen diffusion rate of oxygen, 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 threefold function of the process gas supply of the membrane-electrode assemblies, the cooling and the electrical connection.

Bipolar plates have different regions arranged one behind the other in a main flow direction. 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 significant 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 height of the inflow area is reduced. This is achieved by a regular arrangement of support points and similar open spaces.

DE 101 63 631 A1 discloses a bipolar plate for a fuel cell having a manifold structure of a plurality of elongate ridges arranged in succession in adjacent rows.

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 has a periodic structure with recesses in cross-section, recesses of the recesses of both plates forming a coolant flow area forming away from one another, characterized in that the recesses exclusively in a arranged in the main flow direction before and / or after a flow field distribution structure the bipolar plate are formed and that the recesses of the two plates partially overlap, so that a longitudinal and transverse flow permitting 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 by improving the hydraulic diameter of the Flow cross sections significantly reduced. 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 in addition to the longitudinal main flow and a transverse or perpendicular thereto extending transverse or secondary flow, which further improves the flow characteristics. By the transverse and longitudinal flow creates a connected flow volume, wherein the recesses or stampings control or adjust the 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 shapes can be combined into a recess or structure. 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 overlap in edge regions and / or in corner regions of the recesses. 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 is achieved in the area of overlapping recesses, while half of the height is in the area 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 intersection 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, wherein the bipolar plates and the membrane-electrode assemblies are alternately stacked on each other. The advantages and modifications described above apply.

In this arrangement, the membrane electrode units rest on the recesses. The recesses thus act - in addition to their function for coolant channel formation - as spacers between the membrane-electrode assembly and the bipolar plate, whereby spaces for the resource supply are designed in the form of Betriebsmittelflussfeldern.

In a preferred embodiment, the passage of the anode and / or the Kathodenbetriebsmittelstoms parallel to the flow of coolant 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 resource streams, and the coolant stream are conducted in parallel cocurrent.

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:

1 a top view of a schematic bipolar plate according to the invention,

2 a schematic representation of a detail of the distribution structure,

3 a schematic representation of a detail of the distribution structure with hidden edges of the underlying plate,

4 a sectional view according to section AA according to 1 .

5 a sectional view according to section BB according to 1 .

6 a schematic representation of a detail of a rounded distribution structure,

7 a schematic representation of a detail of the rounded distribution structure with hidden edges of the underlying plate,

8th a perspective view of the bipolar plate according to the invention and

9 a perspective view of a section of the bipolar plate 8th ,

1 schematically shows a plan view of a bipolar plate 10 , The bipolar plate 10 has usually a rectangular extension, wherein the longitudinal direction in a main flow direction X and the transverse side is parallel to a direction Y of the transverse flow. 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 passage 16 are located. About the channels 12 . 14 and 16 become the respective fluids of the bipolar plate 10 fed. Farther downstream is the distribution area or distribution structure 18 , which will be described in more detail below. Next in the main flow direction X is followed by the distributor structure 18 the river field 20 the bipolar plate 10 at. Between the channels 12 . 14 and 16 and the distribution structure 18 are one or more inflow areas 22 provided, via which the respective fluid passes from the corresponding channel into the distributor structure. The distribution structure 18 The task is to move the fluids from the width of the associated channel in the Y direction to the entire width of the flow field 20 to distribute throughout the country to allow chemical reactions or cooling. These are in the distribution structure 18 a variety of recesses 24 arranged.

As in 2 the recesses are shown 24 in a periodic structure 26 educated. As shown here, the recesses have 24 a diamond-shaped structure, wherein the diamonds are 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 in the distribution structure 18 are provided. So corresponds the distance between two recesses 24 about 3 to 7 times, preferably 5 times, an outer edge or side of the recess 24 , The recesses 24 are also arranged offset so that the distances between the recesses 24 are approximately the same. These can be the recesses 24 be arranged in rows, wherein the rows each by the dimension of half a recess 24 offset from one another. The rows may be formed in the longitudinal flow direction X and / or in the transverse flow direction Y.

In 3 is the periodic structure 26 out 2 around another periodic structure 26 that under the in 2 illustrated periodic structure 26 is arranged, expanded. Corresponding recesses 24a a first plate, the recesses 24 out 2 correspond, fully illustrated. recesses 24b an underlying second plate are shown hatched. As can be seen, the two plates are offset from one another so that the recesses 24a the first plate and the recesses 24b partially overlap the second plate. Because the recesses 24a and 24b are formed symmetrically, results in a symmetrical overlap structure.

As in 3 shown, the recesses overlap 24a and 24b in corner areas of the recesses 24 , Thus, each diamond-shaped recess has here 24 four overlapping areas 28 of which one is exemplified by the reference numeral 28 is provided. In the overlapping areas 28 lie the two recesses 24a and 24b one above the other, so that a relatively high flow cross section is formed here. Accordingly, there are also contact or support areas 30 in which the two plates lie directly on top of each other, ie neither a recess 24a the first plate still a recess 24b the second plate are present.

4 shows the sectional view of the bipolar plate 10 according to the line AA in 1 , The first plate 32 and the second plate 34 form a cooling channel or coolant flow area 36 in which exemplifies the coolant flow 38 in the main flow direction X is shown. As you can see, the two plates are 32 and 34 arranged such that the recesses 24a and 24b are arranged pointing away from each other. In other words, the two plates are 32 and 34 with their main faces touching each other, which is left in 4 is shown, wherein the recesses 24 then each outwardly formed. This results in inner sides or inner surfaces of the two plates 32 and 34 a continuous flow area, here as the coolant flow area 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 inside of the plate to an outside of the plate in the areas of the recess 24 is h, wherein the height of the recess h is equal to half the height H of the structure. Thus, the distribution structure has 18 a high height h for the coolant flow area 36 , which leads to a favorable hydraulic cross section and thus low pressure loss.

Also, the flow volumes or channels for the reactants have a height which corresponds to half the total height H. These flow areas are on the outsides of the two plates 32 and 34 each between the recesses 24 educated. There is then in a stack of a complete fuel cell, a membrane-electrode assembly on the recesses 24 on.

In 5 is a cross section along the line BB in 1 the bipolar plate 10 shown. Analogous to 4 are also the first record here 32 and the second plate 34 shown, which with their respective recesses 24a and 24b a coolant flow area located between the two plates 36 form. The coolant flow 38 of the coolant in the coolant flow area 36 is also shown. While in 4 the flow pattern in the longitudinal direction X is shown here 5 the flow path in the transverse direction Y or the transverse component of the coolant flow is shown. The coolant flow 38 thus has a longitudinal component as well as a transverse component in a continuous flow space of the support areas 30 is interrupted. The flow area or coolant channel 36 due to the high height h and the formation and arrangement of the recesses 24 a favorable hydraulic diameter.

In the 6 and 7 is analogous to the 2 and 3 a periodic structure 26 the recesses 24 shown. While in 2 and 3 the recesses 24 have the shape or contour of a rhombus, are the recesses 24 in 6 and 7 formed as a rounded cross pattern. This embodiment can also be referred to as a rounded cross or rhombic structure. As in 6 is shown, are now the side surfaces of the recesses 24 concave, so curved inward. As a result, the cathode and / or anode course takes a wave-shaped or meandering course, which positively influences the flow behavior. In 7 are the recesses 24a the first plate fully illustrated, while the recesses 24b the second plate hatched or only partially shown. Again, there are the overlapping areas 28 between the two recesses 24a and 24b in corner areas of the recesses 24 , support areas 30 are arranged there, where neither a recess 24a another recess 24b is trained.

9 shows a perspective view of the bipolar plate 10 , Compared to 1 here's the top off 1 shown below. Thus, in the illustration in FIG 8th the first record 32 arranged below while the second plate 34 is arranged above. Correspondingly too 1 is in the distribution structure 18 a variety of recesses 24 arranged.

In 9 is a detail according to section C off 8th shown. In this representation, it can be seen how the recesses 24b to the outside in the second plate 34 are formed so that the outer walls of the recesses 24b as elevations from the level of the second plate 34 protrude. The recesses are analogous 24a the first plate 32 educated. Thus, the staggered recesses form 24a and 24b the coolant flow area 36 in which the coolant is controlled by the shape and arrangement of the recesses 24 in a favorable hydraulic Diameter or cross section flows in the longitudinal and transverse directions. This causes the pressure drop across the manifold structure 18 is low. To form a fuel cell or a fuel cell stack, a plurality of bipolar plates 10 alternately stacked with a membrane-electrode assembly. That is, each membrane-electrode assembly of two bipolar plates 10 sandwiched. Likewise, each bipolar plate 10 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 which obtains its proton conductivity by doping with an electrolyte. 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

12

Anode main gas passage

14

Cathode main gas passage

16

Coolant main gas passage

18

distribution structure

20

flow field

22

inflow

24

recess

24a

Recess first plate

24b

Recess second plate

26

periodic structure

28

overlapping area

30

support area

32

first plate

34

second plate

36

Coolant flow area

38

Coolant course

H

Height recess

H

total height

X

Main flow direction

Y

Cross-flow direction

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2008024400 A1 [0005]
• DE 102005057045 A1 [0006]
• DE 10163631 A1 [0007]

Claims (10)

Bipolar plate ( 10 ) for a fuel cell comprising a structure of two plates ( 32 . 34 ), each of the two plates ( 32 . 34 ) in cross-section each have a periodic structure with recesses ( 24 ), wherein depressions of the recesses ( 24 ) of both plates ( 32 . 34 ) a coolant flow area ( 36 ) are arranged facing away from one another, characterized in 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 ) partially overlap so that a longitudinal and transverse flow allowing coolant flow area (FIG. 36 ) is provided. Bipolar plate according to claim 1, characterized in that the recesses ( 24 ) are rounded cross or rhombic structures. Bipolar plate according to claim 1 or 2, characterized in that the recesses ( 24 ) of the two plates ( 32 . 34 ) in peripheral areas of the recesses ( 24 ) overlap. Bipolar plate according to one of the preceding claims, characterized in that the recesses ( 24 ) of the two plates ( 32 . 34 ) in corner areas of the recesses ( 24 ) overlap. Bipolar plate according to one of the preceding claims, characterized in that the recesses ( 24 ) have a height (h) between half the height (H) and the total height (H) of the structure. Bipolar plate according to one of the preceding claims, characterized in that the recesses ( 24 ) in the plates ( 32 . 34 ) are coined. Bipolar plate according to one of the preceding claims, characterized in that the recesses ( 24 ) partially overlap along the main flow direction (X) and along a cross flow direction (Y). Fuel cell comprising a stack of a plurality of bipolar plates ( 10 ) according to 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. Fuel cell according to claim 8, characterized in that in a distributor structure ( 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, and that a main flow direction of an anode and / or a cathode fluid flow is parallel to the main flow direction (X) of the coolant. Motor vehicle with a fuel cell according to claim 8 or 9.

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