DE102016121954A1 - Bipolar plate, fuel cell stack and a motor vehicle - Google Patents

Abstract

A bipolar plate (10) for a fuel cell with an anode plate (12) and a cathode plate (10), each having an active region (AA) and two inactive regions (IA), wherein in the inactive regions (IA) in each case a supply region ( SA), each with two main gas ports (24, 26) and one main coolant port (28) and one distribution area (DA) for connecting the main gas ports (24, 26) and the main coolant port (28) to the active area (AA), It is proposed that the distribution regions (DA) for each operating medium have a distribution structure (30, 34, 38) which permits longitudinal and transverse flow of the respective operating medium, with a maximum of two distribution structures ( 30, 34, 38) are arranged completely or partially above one another. Furthermore, a fuel cell stack and a motor vehicle are disclosed.

Description

The invention relates to a bipolar plate for a fuel cell with an anode plate and a cathode plate, each having an active area and two inactive areas, wherein in the inactive areas each have a supply area with two main gas ports for supply and removal of reaction gases and a respective coolant main port to - And discharge of coolant and each a distribution region for connection of the main gas ports and the coolant main port are arranged on the active region, wherein the anode plate and the cathode plate are formed and arranged one above the other, that on the opposite sides of the reaction gases and between the facing sides the coolant is feasible, a fuel cell stack 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 ⁺ + 2 e ^- ). Via the membrane, which separates the reaction spaces gas-tight from each other and electrically isolated, takes place (water-bound or anhydrous) transport of the protons H ⁺ from the anode compartment into 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 (½ O ₂ + 2 e ^- → O ^2- ). At the same time, these oxygen anions in the cathode compartment react with the protons transported through the membrane to form water (2 H ⁺ + 0 ^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 of the process gases. These are first the main channels or fluid ports through 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 described above take place.

In the area of the distribution structure, usually all operating media are routed one above the other, with the resulting basic form representing, for example, a triangle. In this triangular shape, the media are directed through directional channels to provide the flow field with the operating media across its entire width.

But there are also other distribution structures known in the WO2015150524A1 discloses a bipolar plate for a fuel cell, wherein in the distribution regions of the plates recesses, forming a distribution structure, are arranged. The recesses of the two plates partially overlap so that a coolant flow area is formed between the two plates, while flow areas for anode and cathode gas are provided on the two outer sides. The distribution structures allow longitudinal and transverse flow of the operating media in the bipolar plate.

The invention is based on the object of providing a bipolar plate which offers an improved constant pressure of the operating media.

This object is achieved by a bipolar plate according to claim 1, a fuel cell stack according to claim 9 or a motor vehicle according to claim 10. Preferred embodiments of the invention are the subject of the dependent claims.

There is provided a bipolar plate for a fuel cell having an anode plate and a cathode plate, each having an active region and two inactive regions, wherein in the Inactive areas each have a supply area each with two main gas ports for supply and removal of reaction gases and a main coolant port for supplying and discharging coolant and each a distribution area for connecting the main gas ports and the coolant main port are arranged on the active area. The anode plate and the cathode plate are formed and arranged one above the other so that on the opposite sides of the reaction gases and between the facing sides, the coolant is feasible or in each case a corresponding flow region is provided. According to the invention, the distribution areas for each operating medium have a distribution structure, wherein a maximum of two distribution structures are arranged completely or partially above one another.

The invention therefore relates essentially to the configuration of the distribution structures, that is to their shape and position relative to one another, and optionally to feed channels from the main channels to the respective distribution structure and bridge channels, which connect the corresponding distribution structure to the flow field via two other distribution structures arranged one above the other ,

The dimensions of the three distribution structures and the position of the distribution structures to each other are advantageously almost freely selectable, so that the usually given conflict of objectives of minimum cell length or volume and sufficient uniform distribution of the operating media can be solved efficiently.

Depending on the dimensions of the distribution structures, the dimensioning of the feed and bridge channels takes place. Optionally, an offset may be provided in the feed channels to compensate for differences in height to the distribution structure. In the area of the bridge channels, one or both of the distribution structures located underneath or above can have a reduced height in order to obtain a uniform overall height of the bipolar plate.

According to one embodiment, the distribution structures can also be applied directly to the main supply channels (ports).

The distribution structures may be designed as a directed structure, for example in the form of channels or open structures, which may be a longitudinal and transverse flow, for example in the form of knobs or the like, or as a combination thereof, whereby it must of course be taken into account whether they are distribution structures for the reaction gases or the coolant.

Distribution structures that allow longitudinal and transverse flow and do not have the aforementioned triangular structure in which all media are superimposed, are known in the art, such as from WO2015150524A1 , which was honored above.

The distribution structures of all operating media preferably have a rectangular basic shape, since this is particularly advantageous for manufacturing reasons and with regard to a particularly simple optimizability.

Rectangular basic form of the distribution structures means that this is the space provided for the distribution of the respective operating medium, which, however, does not necessarily have to be fully utilized. Thus, it is also possible according to the invention for the distribution structures to have other geometric shapes in order to be able to control the supply of the operating media as required in the case of corresponding fuel cell concepts.

For demand-controlled control of the supply of the operating media, it is also important that the distribution structures have different flow cross sections and / or heights.

This applies in comparison of the distribution structures with each other and also for the individual distribution structure, which may have different flow cross sections and / or heights depending on the arrangement in relation to the other distribution structures. A corresponding height adjustment in the area of the bridge channels has already been described above.

Preferably, the distribution structures of all operating media each extend over the entire width of the active area in order to ensure a uniform supply without pressure differences of the active area.

The arrangement of the respective distribution structures may preferably have a different distance to the supply area and to the distribution area in order to advantageously design the distribution structures as needed. Thus, in a preferred embodiment, the anode gas distribution structure is closer to the active region than the cathode gas and coolant distribution structures because the anode requires the lowest mass flow. This results in the smallest width of the corresponding feed channels and the smallest width of the height restriction of the coolant distribution structure compared to the configurations for the other operating media.

Thus, the constant space height is used in a first section for uniform distribution of air and coolant. In a second section, the height is used for equal distribution of anode gas and supply of air / coolant to the active area.

The connection from the main ports of one or two media to the respective distribution structure is formed by relatively long feed channels. As a result, as already described, a height restriction of the distribution structure of another medium may become necessary. This constriction leads to low flow through the active area on the corresponding width. If the restricted medium is the cooling medium, this effect can be advantageous since it allows a second temperature zone in the edge region of the active region or counteracts the cooling of this region adjacent to the environment. This can also be provided on both sides of the active area.

An inventive embodiment of a bipolar plate offers a number of advantages:

A significant advantage of the bipolar plate according to the invention is the suitability for computer-aided optimization (virtual engineering) of the individual structures, regardless of the configuration of the structures of the other operating media. Thus, the greatest possible optimization potentials are already raised in earlier phases of the development process of a bipolar plate which is designed according to the invention (front loading).

The development of a fuel cell for a fuel cell stack requires the consideration of many requirements simultaneously. In particular, an ideal media supply of the active area faces the package, material and manufacturing restrictions. Therefore, a suitable cell concept is always a compromise of the various development goals. Due to the configuration of a bipolar plate according to the invention, the development process can advantageously be subdivided into sequences more intensively than hitherto according to the prior art in order to be able to optimize individual requirements one after the other.

Due to the parametric structure and the use of rectangular basic shapes: for the distribution structures can advantageously be a variant generation within short periods of time, which can be easily further optimized.

The process for the design of the fuel cell starts first from the design of the active area and then from the required distribution structures and ultimately from the dimensioning of the main supply channels (ports).

For optimization, five domains for the computation of the three fluid spaces of anode and cathode plates are generated and investigated by CFD (Computational Fluid Dynamics) and FEM (Finite Element Method).

The rectangular basic shape of the fuel cell is advantageously retained when using the invention. In addition, it is achieved that the blank of the cost-intensive semi-finished products CCM (catalyst coated membrane) and GDL (gas diffusion layer) can also be made rectangular, which advantageously significantly reduces the waste and thus the production costs.

The bipolar plate according to the invention offers a high space efficiency, since the distribution structures are arranged one behind the other between the supply area and the active area, so that the individual distribution structure each has a greater height at constant pressure across the width of the bipolar plate than distribution structures according to the prior art.

By varying the height of the distribution structures for the coolant can advantageously be a second temperature range (lower flow) at the edge (also on both sides) of the active area, which prevents excessive cooling of the edge and also reduces in this area a tendency to condensation of water.

There is a particularly effective distribution of the cathode gas by a large coverage of the distribution structure.

The embodiment of a bipolar plate according to the invention is advantageously suitable for various basic forms of a bipolar plate and a fuel cell or a fuel cell stack based thereon. So it is not relevant, whether they are rather "long and narrow" for an arrangement in the underfloor area of a vehicle or for a double stack or rather "short and wide" for an arrangement in the front area of a vehicle.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

• 1 in vier Draufsichten beide Seiten einer Kathodenplatte und einer Anodenplatte einer erfindungsgemäßen Bipolarplatte,
• 2 in zwei schematischen Ansichten von entgegengesetzten Seiten die Fluidräume der Betriebsmedien der erfindungsgemäßen Bipolarplatte
• 3 in drei schematischen Ansichten jeweils ein Fluidraum für ein Betriebsmedium,
• 4 in zwei schematischen, perspektivischen Detailansichten die Fluidräume für die drei Betriebsmedien der erfindungsgemäßen Bipolarplatte, und
• 5 in zwei schematischen, perspektivischen Detailansichten die Fluidräume für drei Betriebsmedien der erfindungsgemäßen Bipolarplatte nach 4, wobei diese für das Anodengas nur teilweise wiedergegeben sind.

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

• 1 in both plan views both sides of a cathode plate and an anode plate of a bipolar plate according to the invention,
• 2 in two schematic views from opposite sides of the fluid spaces of the operating media of the bipolar plate according to the invention
• 3 in three schematic views in each case a fluid space for a working medium,
• 4 in two schematic, perspective detailed views of the fluid spaces for the three operating media of the bipolar plate according to the invention, and
• 5 in two schematic, perspective detailed views of the fluid spaces for three operating media of the bipolar plate according to the invention 4 , which are only partially reproduced for the anode gas.

In 1 are a cathode plate 10 and an anode plate 12 an otherwise not shown bipolar plate shown from the cathode plate 10 and the anode plate 12 is usually joined, with each side facing away from each other 14a . 16a the cathode plate 10 or the anode plate 12 and the sides facing each other 14b . 16b the cathode plate 10 or the anode plate 12 are shown. To clarify the spatial orientation of the views of cathode plate 10 and anode plate 12 are given in x and y direction.

On the other hand shows 2 instead of the cathode plate 10 and the anode plate 12 the fluid spaces of the operating media therein, namely anode gas, cathode gas and coolant. The fluid spaces are shown from opposite sides, the spatial orientation of which is illustrated by specifying the x and y directions. The reference numerals correspond to those in FIG 1 with the difference that the reference numeral 1 is preceded by a distinction. This also applies to the following 3 to 5 , in which also the corresponding fluid spaces of the operating media are shown.

The fluid spaces for the cathode gas are on the anode plate 12 opposite side 14a the cathode plate 10 arranged and for the anode gas on the cathode plate 10 opposite side 16a the anode plate 12 , Between the cathode plate 10 and the anode plate 12 otherwise the fluid spaces are arranged for the coolant. The fluid spaces for the cathode gas and the anode gas are formed as open channel structures, while the fluid spaces for the coolant are closed channel structures. Open and closed refers only to the nature of the cathode plate 10 and the anode plate 12 in the form of an assembled bipolar plate. In a fuel cell or a fuel cell stack, all channel structures are closed.

The fluid spaces are configured differently according to the requirements in the different areas, as described below.

The cathode plate 10 and the anode plate 12 and thus also the fluid spaces are subdivided into an active area AA and inactive areas IA , The active area AA is characterized by the fact that fuel cell reactions take place in this area. This active area AA is also called river field 18 . 118 designated. The inactive areas IA , each can be divided into service areas SA and distribution areas THERE divide. For clearer optical demarcation of active area AA and inactive area IA are dashed lines in the figures 20 and 22 provided the transition from the active area AA to the inactive area IA symbolize.

Within the service areas SA are each an anode gas main port 24 . 124 a cathode gas main port 26 . 126 and a main coolant port 28 . 128 to the supply to the river field 18 . 118 or for the discharge of the operating media after overflow of the flow field 18 . 118 arranged in a fuel cell stack, not shown here, substantially aligned with each other and form main supply channels within the fuel cell stack.

The following statements always refer to both inactive areas IA even if the description is in the singular.

Each operating medium has a specific distribution structure 30 . 130 . 34 . 134 . 38 . 138 on. The distribution structure 30 . 130 for the cathode gas is in the distribution area THERE adjacent to the utility area SA arranged and is via feed channels 32 . 132 with the cathode gas main port 26 . 126 , the center between the anode gas main port 24 . 124 and the main coolant port 28 . 128 is arranged, connected. The distribution structure 30 . 130 for the cathode gas is rectangular and is spaced from the active area AA arranged. By not shown channels or other directed structures is the distribution structure 30 . 130 for the cathode gas to the active area AA or the river field 18 . 118 tethered. These channels may also be extended channels or structures of the active area AA act, which are also not shown in detail in the figures. This free area of the distribution area THERE is on the corresponding side of the anode plate 12 from the distribution structure 34 . 134 for the Anodengas taken, so that the distribution structures 30 . 130 . 34 . 134 for the cathode and anode gas are not superimposed in a bipolar plate, not shown here. The distribution structure 34 . 134 for the anode gas is at the anode gas main port 24 . 124 via connection channels 36 . 136 with the distribution structure 34 . 134 tethered directly into the corresponding structures of the active area AA or the river field 18 . 118 passes. The connection channels 36 . 136 for the anode gas are going through the distribution structure 30 . 130 for the cathode gas and distribution structure 38 . 138 led for the coolant. The distribution structure 38 . 138 for the coolant extends in the region of the distribution structure 30 . 130 for the cathode gas, however, is additional from the supply area SA spaced. The connection to the coolant main port 28 . 128 via connection channels 40 . 140 , As can be seen, all distribution structures 30 . 130 . 34 . 134 . 38 . 138 rectangular designed. There are also other embodiments possible, however, the variant shown in the production proves to be advantageous. As in 5 and 6 shown in more detail, has the distribution structure 38 . 138 for the coolant in the area where the connection channels 36 . 136 are arranged for the anode gas, a lower height.

In 3 are the fluid spaces for the operating media according to the 1 and 2 shown separately. In addition, were still dashed lines 20a . 20b . 22a . 22b introduced the extension of the distribution areas 30 . 130 . 34 . 134 . 38 . 138 to represent more clearly. The description therefore corresponds to the description of the fluid spaces in the 1 and 2 , The lines 20a indicates the extent of the distribution structure 38 . 138 for the anode gas towards the service area SA and the extent of the distribution structure 30 . 130 for the cathode gas and distribution structure 38 . 138 of the coolant toward the active area AA , By line 20b becomes the extension of the distribution structure 30 . 130 for the cathode gas towards the service area SA shown. By contrast, the supply area extends 38 . 138 for the coolant not to the line 20b and is therefore not congruent with the coverage area 30 . 130 for the cathode gas.

As can be seen, the sizing of the distribution structures 30 . 130 . 34 . 134 . 38 . 138 , the width and / or number of connection channels 32 . 132 . 36 . 136 . 40 . 140 and the sizing of anode gas main port 24 . 124 , Cathode gas main port 26 . 126 as well as coolant main port 28 . 128 Specified specifically for the respective operating medium.

In the 4 and 5 are detailed views shown to the inventive arrangement of the distribution structures 30 . 130 . 34 . 134 . 38 . 138 to show more clearly. The description of the preceding figures also applies to the 4 and 5 , 4 shows the fluid spaces for all operating media while in 5 on the connection channels 136 was dispensed for the anode gas, so that the different height design of the distribution structure 38 . 138 for the coolant is visible. The connection channels 132 . 136 . 140 each have an offset 144 . 146 . 148 to differences in height in the connection of the corresponding distribution structures 30 . 130 . 34 . 134 . 38 . 138 compensate

The distribution structure 38 . 138 for the coolant points in the area in which the connecting channels 136 for the anode gas over it, a lower height on, so a paragraph 142 given is.

In the embodiment shown in the figures, the operating media can also be reversed, so that, for example, the dimensioning and arrangement of the structures for the cathode gas of the dimensioning and arrangement of the structures for the anode gas corresponds and vice versa.

LIST OF REFERENCE NUMBERS

10

cathode plate

12

anode plate

14a

from the anode plate side facing away from the cathode plate

14b

from the cathode plate side facing away from the anode plate

16a

the anode plate facing side of the cathode plate

16b

the cathode plate facing side of the anode plate

18, 118

flow field

20, 20a, 20b

dashed line

22, 22a, 22b

dashed line

24, 124

Anode gas main port

26, 126

Cathode gas main port

28, 128

Coolant main port

30, 130

Distribution structure for cathode gas

32, 132

supply channels

34, 134

Distribution structure for anode

36, 136

connecting channels

38, 138

Distribution structure for coolant

40, 140

connecting channels

142

paragraph

144

offset

146

offset

148

offset

X, Y

spatial direction

AA

Active area (reaction area, active area)

IA

Inactive area

SA

Supply area

THERE

Distribution area

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 2015150524 A1 [0006, 0015]

Claims (10)

Bipolar plate for a fuel cell with an anode plate (12) and a cathode plate (10), each having an active region (AA) and two inactive regions (IA), wherein in the inactive regions (IA) each having a supply region (SA) with two Main gas ports (24, 26) for the supply and removal of reaction gases and a main coolant port (28) for supply and removal of coolant and in each case a distribution area (DA) for connecting the main gas ports (24, 26) and the main coolant port (28) the active region (AA) are arranged, wherein the anode plate (12) and the cathode plate (10) are formed and arranged one above the other, that on the opposite sides (14a, 14b), the reaction gases and between the mutually facing sides (16a, 16b) the coolant can be guided, characterized in that the distribution regions (DA) for each operating medium have a distribution structure (30, 34, 38), wherein a maximum of two Ver partial structures (30, 34, 38) are arranged completely or partially above one another. Bipolar plate after Claim 1 , characterized in that the distribution structures (30, 34, 38) allow a longitudinal and transverse flow of the respective operating medium and / or a directed flow. Bipolar plate after Claim 1 or 2 , characterized in that the distribution structures (30, 34, 38,) of all operating media each extend over the entire width of the active region (AA). Bipolar plate after one of the Claims 1 to 3 , characterized in that the distribution structures (30, 34, 38) of all operating media have a rectangular basic shape. Bipolar plate after one of the Claims 1 to 3 , characterized in that the distribution structures (30, 34, 38) of all operating media is each formed in a rectangular space, the respective space is only partially used for the corresponding distribution structure (30, 34, 38). Bipolar plate after one of the Claims 1 to 5 , characterized in that the distribution structures (30, 34, 38) have different flow cross sections and / or heights. Bipolar plate after one of the Claims 1 to 6 , characterized in that for connection between the distribution structures (30, 34, 38) and the active area (AA) bridge channels are arranged and / or for connection between the main ports (24, 26, 28) and the distribution structures (30, 34, 38) connecting channels (32, 36, 40) are arranged. Bipolar plate after one of the Claims 1 to 7 , characterized in that the distribution structures (30, 34, 38) have a different distance to the supply area (SA) and / or the distribution area (DA). Fuel cell stack comprising a plurality of bipolar plates (10) according to one of Claims 1 to 8th , Motor vehicle after a fuel cell Claim 9 having.

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