DE102014208445A1 - Bipolar plate, fuel cell and method for producing the bipolar plate - Google Patents

Abstract

The invention relates to a bipolar plate (10) for a fuel cell (100), wherein the bipolar plate (10) has a base body (12) and a sealing material (16) on the base body (12). It is characteristically provided that the base body (12) forms at least one edge elevation (20) in an outer edge area (18), and the bipolar plate (10) at the maximum (15) of the at least one edge elevation (20) forms an electrically insulating material (24 ) having. Furthermore, the invention relates to a fuel cell (100) with a bipolar plate (10) according to the invention and to a method for producing the bipolar plate (10).

Description

The invention relates to a bipolar plate for a fuel cell, wherein the bipolar plate has a base body and a sealing material on the base body. Furthermore, the invention relates to a fuel cell with a bipolar plate according to the invention and a method for producing the bipolar plate.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as core component the so-called membrane electrode assembly (MEA for membrane electrode assembly), which is a composite of a proton-conducting membrane and one, both sides of the membrane disposed electrode (anode and cathode). In addition, gas diffusion layers (GDL) can be arranged on both sides of the membrane-electrode assembly on the sides of the electrodes facing away from the membrane. As a rule, the fuel cell is formed by a multiplicity of MEAs arranged in the stack, the electrical powers of which accumulate. During operation of the fuel cell, the fuel, in particular hydrogen H ₂ or a hydrogen-containing gas mixture, is supplied to the anode, where an electrochemical oxidation of H ₂ to H ⁺ takes place with emission of electrons. Via the electrolyte or 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 O ₂ to O ^2- taking place of the electrons takes place. At the same time, these oxygen anions in the cathode compartment react with the protons transported via the membrane to form water. 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.

Currently the most advanced fuel cell technology is based on polymer electrolyte membranes (PEMs), where the membrane itself consists of a polymer electrolyte. In this case, acid-modified polymers, in particular perfluorinated polymers, are often used. The most common representative of this class of polymer electrolytes is a membrane of a sulfonated polytetrafluoroethylene copolymer (trade name: Nafion; copolymer of tetrafluoroethylene and a sulfonyl fluoride derivative of a perfluoroalkyl vinyl ether). The electrolytic conduction takes place via hydrated protons, which is why the presence of water is a prerequisite for the proton conductivity and moistening of the operating gases is required during operation of the PEM fuel cell. Due to the necessity of the water, the maximum operating temperature of these fuel cells is limited to below 100 ° C at standard pressure. In contrast to high-temperature polymer electrolyte membrane fuel cells (HT-PEM fuel cells) whose electrolytic conductivity is based on an electrostatic complex bound to a polymer backbone of the polymer electrolyte membrane electrolyte (for example, phosphoric acid-doped polybenzimidazole (PBI) membranes) and at temperatures of 160 ° C, this type of fuel cell is also referred to as a low-temperature polymer electrolyte membrane fuel cell (NT-PEM fuel cell).

The membrane-electrode assemblies are stacked alternately with electrically conductive bipolar plates of the fuel cell and thus connected in series. During operation of the fuel cell, it must be ensured that neighboring bipolar plates do not come into electrically conductive contact.

The WO 2011/002823 discloses a bipolar plate whose outer edge is enclosed by a seal. The bipolar plate and the seal form an assembly. The seal can be molded onto the bipolar plate.

Furthermore, bipolar plates are known, whose outer edge within a fuel cell stack has an air gap to adjacent membrane electrode assemblies and / or adjacent bipolar plates. Otherwise, possible creepage currents are prevented or at least reduced by the air gap. This results in a larger air gap in a larger creepage distance. If it is appropriate to increase the creepage distance and thus the air gap, thereby also a cell distance of single cells of the fuel cell is increased, which usually leads to a reduced volumetric power density. If deformations of the bipolar plates occur during assembly or operation of the fuel cell, the air gap can be reduced.

Furthermore, it is known to provide a large projection of arranged between the bipolar plates membrane assemblies. However, an orientation of the bipolar plates and the membrane assemblies over their outer edge is no longer readily possible.

An alternative is insulation rings as part of a Bipolarplattenbaugruppe. However, for their preparation, an additional Manufacturing step needed. In addition, the insulation rings are not rigidly attached.

The invention is an object of the invention to provide a bipolar plate and a fuel cell available, which is characterized by increased reliability and reliability while cost-effective production. Furthermore, a manufacturing method for cost-effective production of the bipolar plate is to be made available.

According to the invention, a bipolar plate is provided for a fuel cell. The bipolar plate has a base body and a sealing material on the base body. Characteristically, it is provided that the base body forms at least one edge elevation in an outer edge region, and the bipolar plate has an electrically insulating material at a maximum of the at least one edge elevation.

By the bipolar plate according to the invention an increased short-circuit safety is ensured during operation of the fuel cell, since edges of the bipolar plates (with electrically conductive bodies) to each other by the arranged on the edge elevations, electrically insulating material are isolated. Furthermore, the bipolar plate according to the invention can be produced particularly inexpensively, since a known from the prior art, material-consuming encapsulation of the edge region of the bipolar plate is no longer necessary, yet within the fuel cell, a contact of the electrically insulating material with adjacent components, for. B. produce a membrane electrode assembly. Among other things, the contact improves the stability of the fuel cell. Rather, application of the electrically insulating material can preferably take place by rolling up or printing. This is possible because in the outer edge region, a surface of the base body is raised by means of at least one Randerhöhung, and thus now a less large distance to adjacent components by means of the electrically insulating material must be bridged.

It is preferably provided that the base body forms at least one seal increase and the bipolar plate has the sealing material at a maximum of at least one seal elevation, the maximum of the seal elevation and the maximum of the elevation are komplanar (ie in the same plane) are arranged. This embodiment of the bipolar plate makes it particularly easy and inexpensive to manufacture, since both the electrically insulating material and the sealing material can be applied by means of a tool with an angle-conforming surface in one and the same manufacturing step.

In the context of the invention, the term "maximum" (with the plurality of "maxima") designates the highest point, that is to say the head end, the summit or the top of the seal elevation and the elevation of the rim. The seal increase and the Randerhöhung forms the body with a material of the body, z. As a metal.

The elevations, in particular the at least one seal elevation, may be elevations extending along a major surface of the bipolar plate. In particular, the maxima of the elevations over their (entire) course are coplanar. In this case, a bipolar plate typically has two main surfaces, which are those surfaces of greatest extent, that is to say the planar surfaces of the bipolar plate. The elevations can also be called elevations.

It is preferably provided that the at least one edge elevation has the maximum at an outer edge of the edge region. Thus, the outer edge of the ridge elevation not only forms the outer edge of the bipolar plate but also has the maximum height of the ridge elevation there. This ensures that within a fuel cell, the outer edge of the edge enhancement rests against an adjacent component (with the intermediate electrically insulating material). Thus, vibrations of the edges of the bipolar plates are prevented during operation and the short circuit safety further increased.

Preferably, the sealing material and the electrically insulating material are the same material. It is the sealing material and the electrically insulating material that is the same, electrically insulating sealing material. By this configuration, not two different materials must be handled in the production, but only a single material having the properties of both materials. The electrically insulating sealing material is preferably an elastomer, in particular a fluororubber (FKM).

It is preferably provided that the base body forms edge margins arranged opposite one another in a cross section. Thus, within the fuel cell, a bilateral support by the bipolar plate, whereby a particularly robust fuel cell is achieved. The cross-section is typically a cross-section perpendicular to a major surface of the bipolar plate.

It is preferably provided that the base body is open in the cross section at its outer edge. The main body therefore has a divergent (expanding) cross-section towards its outer edge. The open one Cross section typically extends within the edge region. Thus, the main body forms a fanning out in its cross section to its outer edge out. As a result, the two edge enhancements are realized by means of the fanning of the base body. Thus, the edge enhancements can be realized without additional material costs.

According to a preferred embodiment of the invention, it is provided that at least two of the seal elevations and / or at least two of the edge elevations are symmetrical to a center plane of the bipolar plate. Thus, within the fuel cell, a rectilinear force transmission perpendicular to the center plane, whereby the stability of the fuel cell is further increased.

It is preferably provided that the base body in a cross section has a step shape towards its outer edge, wherein the step shape forms the at least one edge elevation. Thus, the at least one edge enhancement is realized by means of a step of the base body. As a result, the base body has a closed, stepped cross section within the edge region. It follows that the base body in the edge region typically only on one side has at least one edge elevation. The other side of the main body is within the fuel cell in the edge region by the step shape so far away from an adjacent component that can be dispensed with an additional insulation in the edge region on this page. The step shape can be described as a shape which, in the cross section towards its outer edge, initially follows a course in the direction of a major surface of the bipolar plate, then in a direction away from the bipolar plate and then in the direction of the edge enhancement in the direction parallel to the main surface ,

According to a preferred embodiment of the invention it is provided that the seal increases a higher compressive stiffness (ie perpendicular to the main surface) than the edge elevations. If the two elevations are compressed by the same amount within a fuel cell, this will have greater pressure forces on the seal elevations than on the edge elevations, thereby preventing an excessive loss of sealing force (due to the edge elevations).

It is preferably provided that the at least one seal increase is executed closed around the circumference. Thus, within a fuel cell, a closed area is sealed by means of the sealing material. The closed area may be, for example, a chemically active area or a resource opening within the fuel cell. The at least one edge elevation (and on it the electrically insulating material) may be designed to be closed around the circumference, whereby a uniform load distribution of the fuel cell, ie within a fuel cell stack. However, it is also possible to provide a plurality of individual or discontinuously circumferential edge elevations per base body.

Preferably, the edge elevation and / or the electrically insulating material is formed (shaped) such that the electrically insulating material does not assume a sealing function on the edge elevation. This results in a clear functional separation of the sealing material (and the preferred seal increase) as well as the arranged on the base body outside the sealing material, electrically insulating material and the edge elevation. With a loss of sealing force of the arranged on the seal increase sealing material from the outside of the fuel cell, this is easier to see because leaving reactants or reaction products are not retained by the electrically insulating material and a defect is thus not obscured.

Preferably, at least one of the maxima is designed as a particular coplanar plateau. Thus, the at least one seal elevation and / or the at least one edge elevation has a plateau with the height of the respective maximum, which is coplanar with the at least one further maximum. This results in a larger contact surface for the electrically insulating material and / or the sealing material.

According to a preferred embodiment of the invention, it is provided that the base body comprises at least one metallic sheet, wherein the at least one seal elevation and / or the at least one edge elevation are bends of the sheet. As a result, the base body and also its seal increase and / or edge increase can be produced particularly inexpensively. Preferably, the base body has two metallic sheets, whereby the main body as a whole, including extending within the body channels, can be realized by means of the two sheets. In particular, the seal increases can be outwardly facing beads in the sheet. A cavity within the seal elevation, that is to say within the main body, is preferably designed as a resource channel. As a result, the seal elevation can be used as a channel for a resource (eg, a coolant).

It is preferably provided that a narrow side of the bipolar plate (ie the end face) is covered by the electrically insulating material. Thus, leakage currents can be prevented even better.

It is preferably provided that the electrically insulating material and the sealing material have coplanar outer surfaces. Thus, the outer surfaces are angled to each other. Such outer surfaces can preferably be produced by means of a tool with an angle-conforming surface.

Furthermore, a fuel cell with at least one bipolar plate according to the invention is provided. The fuel cell is characterized by increased reliability and simplified assembly. Until now, special care had to be taken during assembly not to bend edge regions of the bipolar plates, in order not to reduce a required air gap. As a result of the at least one edge increase provided with the electrically insulating material, the assembly is thus simplified.

• – Bereitstellen des Grundkörpers der Bipolarplatte;
• – Gleichzeitiges Aufbringen des Dichtungsmaterials auf den Grundkörper und des elektrisch isolierenden Materials auf das Maximum der wenigstens einen Randerhöhung mittels eines Werkzeugs.

In addition, a method for producing a bipolar plate according to the invention is provided, the method comprising the following steps:

• - Providing the body of the bipolar plate;
• - Simultaneous application of the sealing material to the base body and the electrically insulating material to the maximum of at least one Randerhöhung means of a tool.

The simultaneous application of the materials saves time and money during production. This is especially true when the sealing material and the electrically insulating material are the same electrically insulating sealing material. In particular, one and the same tool is used for applying both materials, in particular the electrically insulating sealing material.

Furthermore, the production is simplified if the sealing material is applied to a maximum of the at least one seal increase and the maxima of the elevations are coplanar, since thereby a tool for applying the materials can have an angle-faithful surface.

It is preferably provided that the application comprises a rolling up or an imprinting. By means of these methods, the sealing material can be applied particularly effectively.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

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

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

1 a bipolar plate according to the prior art,

2 a bipolar plate with two, by means of a fanning of the body realized edge elevations, and

3 a bipolar plate with a, realized by means of a step of the body Randerhöhung.

1 shows a portion of a fuel cell 100 according to the prior art. Within the illustrated subregion are two bipolar plates 10 according to the prior art with a membrane arrangement arranged therebetween 11 shown. The visible in the figures part of the membrane assembly 11 can z. B. an edge reinforcement film or the membrane of the membrane assembly 11 be. The membrane arrangement 11 may also be formed as a membrane electrode assembly.

The bipolar plates 10 comprise an electrically conductive base body 12 , which in the example of two adjoining and z. B. welded together (metal) sheets 13 is formed. In the illustrated subregion, the main body 12 the bipolar plates 10 two seals each 14 on. These are at their maxima 15 with a sealing material 16 Mistake.

For isolation of bipolar plates 10 each other are between the bipolar plates 10 air gaps 19 (Free spaces) provided. Around the air gaps 19 To be sure, the edges become 17 (ie narrow sides of the main body 12 ) of the bipolar plate 10 typically laser cut. Nevertheless, such insulation is susceptible to deformations affecting the air gaps 19 reduce.

2 shows a portion of a fuel cell 100 according to a preferred embodiment of the invention. Within the illustrated subregion are two bipolar plates 10 provided according to a preferred embodiment of the invention. In turn, it is an interposed membrane assembly 11 shown.

In contrast to the prior art according to 1 has the bipolar plate 10 now in addition to the seal raisings 14 (Which may also be omitted depending on the design) in a peripheral area 18 bifurcated margins on both sides 20 on. The margins increases 20 are in relation to the seal heights 14 on the bipolar plate 10 further outside. Per main area 21 have the seal increase 14 and the edge enhancement 20 mutually coplanar maxima 15 on. The maxima 15 So are per major area 21 each in a common plane 23 , Furthermore, the levels can 23 also parallel to one another and in particular also parallel to a center plane 25 be, which is a contact plane of the two sheets 13 represents. Thus, the maxima point 15 the raises 14 . 20 per main area 21 same heights 22 above the middle level 25 on.

The raises 14 . 20 are realized in the example as outwardly directed beads.

On the maxima 15 the seal increases 14 have the bipolar plates 10 a sealing material 16 and on the maxima 15 marginal increases 20 an electrically insulating material 24 on. Instead of two different materials 16 . 24 to use, a single material may be provided. This is thus an electrically insulating sealing material.

The maxima 15 are as plateaus (also by the reference numeral 15 characterized), which per main surface 21 to each other coplanar, ie in the same plane 23 are arranged.

The margins increases 20 have their maxima on an outer edge 17 of the border area 18 (ie on an outer edge 17 the main surface 21 ) on. Thus, the bipolar plate ends to its edge 17 with the plateaus of the margins 20 , In the cross section shown by the bipolar plate 10 are the margins increases 20 arranged opposite.

In the cross section shown is also a fanning 26 the main body 12 to the outer edges 17 towards. The fan-out 26 are realized by the two sheets 13 each bipolar plate 10 to the edge 17 the respective bipolar plate 10 are bent apart. The main body 12 is at its outer edge 17 open formed.

The main body of the bipolar plates 10 can also on their narrow sides 27 (End faces) the electrically insulating material 24 have (not shown).

During operation of the fuel cell 100 seal the seals 14 with the sealing material 16 enclosed areas, e.g. As an active area or resource channels from, so that no resources from the fuel cell 100 can escape.

Inside the fuel cell 100 support the edge elevations 20 attached to them membrane arrangements 11 on both sides of the bipolar plates 10 from. By the electrically insulating sealing material 16 is an insulation between the bipolar plates 10 even with an offset between them (eg due to tolerances) ensured. Furthermore, through the narrow sides 27 which may also comprise the electrically insulating sealing material, also an insulation to components outside the fuel cell 100 be ensured.

The edges 17 are subject to further tolerances than the air gap insulation and are therefore less expensive to manufacture and easier to handle. Even if an edge 17 a sheet 13 is damaged, is by the edge 17 of the second sheet 13 ensures alignment. In addition, there is a short distance between adjacent plate surfaces.

3 also shows a fuel cell 100 and a bipolar plate 10 according to a preferred embodiment of the invention. The bipolar plate 10 is different from the bipolar plate 10 according to 2 in that the main body 12 in cross section a step shape 28 in the edge region 18 so to its outer edge 17 hin, wherein the step shape 28 the at least one edge enhancement 20 formed. Thus, both sheets are 13 of the basic body 12 at the edge 18 bent in a common direction and thereby realize an edge enhancement 20 on a major surface of the bipolar plate 10 ,

Inside the fuel cell 100 support the edge elevations 20 the bipolar plates 10 attached to them membrane arrangements 11 (in contrast to the embodiment according to 2 ) on one side of the bipolar plate 10 from. On the opposite, the edge elevations 20 opposite side of the bipolar plate 10 is located through the step shape 28 now an enlarged in comparison to the prior art air gap 19 ,

Because of the edge 17 and the border area 18 of the basic body 12 at the same height as the maximum of the seal increase 14 is also a coating of centering features with the (electrically insulating) sealing material 16 respectively. To a nesting of the two sheets 13 To allow extra marginal tolerances 18 be provided.

The seal raisings 14 can be made stiffer than the edge elevations 20 , This can (as well as in 2 ) be realized thereby by the maxima 15 the seal increases 14 on both sides by flanks of the seal increase 14 are supported while the maxima 15 the margins increases 20 only on one side by a respective edge of the edge enhancements 20 are supported. The flanks extend between the middle plane 25 and the maxima 15 , As a result, on the one hand, a sufficiently high contact pressure on the seal increases for the seal 14 ensured while an unnecessarily high contact pressure on the edge elevations 20 is avoided.

The bipolar plates according to the invention 10 can be prepared according to a preferred method, by first the main body 14 the bipolar plate 10 provided, in particular produced (eg pressed). Subsequently, a simultaneous application of the electrically insulating material takes place 24 to the maxima 15 the edge elevations and the sealing material 16 on the main body 12, in particular on the maxima 15 the seal increases 14 ,

For example, the materials 16 . 24 be applied by being rolled up or printed.

Due to the coplanar maxima can be a tool for applying the sealing material 16 and the electrically insulating material 24 an angle (ie level) and the sealing material 16 have directional surface.

Thus, for the application of the materials 16 . 24 only a common manufacturing step required. Further, the fuel cell 100 Compared to conventional air-gap insulation more tolerant to deformation.

The invention can be used both to drive a motor vehicle and within electrolyzers. In addition, it is suitable both for low-temperature polymer electrolyte membrane fuel cells (NT-PEM fuel cells) according to the fuel cell shown in the figures 100 Solid oxide fuel cells (SOFC), phosphoric acid fuel cells (PAFC) as well as alkaline fuel cells (AFC).

LIST OF REFERENCE NUMBERS

10

bipolar

11

Membrane assembly

12

body

13

sheet

14

seal increase

15

maximum

16

sealing material

17

edge

18

border area

19

air gap

20

marginal increase

21

main area

22

height

23

level

24

electrically insulating material

25

midplane

26

fanning

27

narrow side

28

step shape

100

fuel cell

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 2011/002823 [0005]

Claims (10)

Bipolar plate ( 10 ) for a fuel cell ( 100 ), wherein the bipolar plate ( 10 ) a basic body ( 12 ) and on the base body ( 12 ) a sealing material ( 16 ), characterized in that the basic body ( 12 ) in an outer edge region ( 18 ) at least one edge enhancement ( 20 ), and the bipolar plate ( 10 ) at a maximum ( 15 ) of at least one edge enhancement ( 20 ) an electrically insulating material ( 24 ) having. Bipolar plate ( 10 ) according to claim 1, characterized in that the basic body ( 12 ) at least one seal increase ( 14 ) and the bipolar plate ( 10 ) the sealing material ( 16 ) at a maximum ( 15 ) the at least one seal increase ( 14 ), where the maximum ( 15 ) the at least one seal increase ( 14 ) and the maximum ( 15 ) of at least one edge enhancement ( 20 ) are coplanar. Bipolar plate ( 10 ) according to one of the preceding claims, characterized in that the at least one edge increase ( 20 ) the maximum ( 15 ) on an outer edge ( 17 ) of the edge area ( 18 ) having. Bipolar plate ( 10 ) according to one of the preceding claims, characterized in that the sealing material ( 16 ) and the electrically insulating material ( 24 ) are the same material. Bipolar plate ( 10 ) according to one of the preceding claims, characterized in that the basic body ( 12 ) in a cross-section oppositely disposed edge elevations ( 20 ) trains. Bipolar plate ( 10 ) according to claim 5, characterized in that the basic body ( 12 ) in the cross-section at its outer edge ( 17 ) is open. Bipolar plate ( 10 ) according to one of claims 1 to 4, characterized in that the basic body ( 12 ) in a cross section a step shape ( 28 ) to its outer edge ( 17 ), wherein the step shape ( 28 ) the at least one edge increase ( 20 ) trains. Fuel cell ( 10 ) with at least one bipolar plate ( 10 ) according to any one of the preceding claims. Method for producing a bipolar plate ( 10 ) according to one of claims 1 to 7, wherein the method comprises the following steps: - providing the basic body ( 12 ) of the bipolar plate ( 10 ); Simultaneous application of the sealing material ( 16 ) on the basic body ( 12 ) and the electrically insulating material ( 24 ) to the maximum ( 15 ) of at least one edge enhancement ( 20 ). A method according to claim 9, characterized in that the application comprises a rolling or a printing.

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