WO2015169543A1

WO2015169543A1 - Bipolar plate, fuel cell and method for producing the bipolar plate

Info

Publication number: WO2015169543A1
Application number: PCT/EP2015/057948
Authority: WO
Inventors: Ian Stewart
Original assignee: Volkswagen Ag
Priority date: 2014-05-06
Filing date: 2015-04-13
Publication date: 2015-11-12
Also published as: DE102014208445A1

Abstract

The invention relates to a bipolar plate (10) for a fuel cell (100), said bipolar plate (10) having a main body (12) and a sealing material (16) on the main body (12). The invention is characterised in that the main body (12) has at least one raised edge (20) formed in an outer edge region (18) and the bipolar plate (10) has an electrically insulating material (24) on the maximum point (15) of the at least one raised edge (20). The invention also relates to a fuel cell (100) comprising a bipolar plate (10) according to the invention and to a method for producing the bipolar plate (10).

Description

description

Bipolar plate, fuel cell and method for producing the bipolar plate

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 large number of stacked MEAs whose electrical powers are added together. 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 becomes oxygen or an oxygen-containing one

Gas mixture is fed, so that a reduction of 0 ₂ to O ^{2 "takes} place under receiving the electrons. At the same time react in the cathode chamber, this oxygen anions with the transported across the membrane protons to form water. Due to the direct conversion of chemical to electrical energy achieve fuel cell 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 a sulfonated polytetrafluoroethylene copolymer (trade name: Nation; 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 electrode bound by electrostatic complexation 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.

WO 201 1/002823 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. Does it come to the assembly or operation of the fuel cell to deformations of the

Bipolar plates, so 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 to use insulating rings as part of a bipolar plate assembly. However, their manufacture requires an additional manufacturing step. In addition, the

Insulation rings 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 in a particularly cost-effective manner, since one 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 forms the sealing material at a maximum of at least one

Has seal increase, wherein the maximum of the seal increase and the maximum of the edge elevation komplanar (ie in one and the same plane) are arranged. Due to this configuration of the bipolar plate, this can be made particularly simple and inexpensive be there by means of a tool with angled surface in one and the same

Manufacturing step, both the electrically insulating material and the sealing material can be applied.

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 forms

Edge enhancement not only the outer edge of the bipolar plate, but there also has the maximum amount of edge enhancement. This ensures that within a

Fuel cell, the outer edge of the edge enhancement on an adjacent component (with the intervening electrically insulating material) is applied. 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 cross-section extends

typically within the border area. Thus, the main body forms in his

Cross-section a fanning 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 increases and / or at least two of the edge elevations to a

Center plane of the bipolar plate are designed symmetrically. Thus, within the

Fuel cell 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 heights. If the two elevations are compressed by the same amount within a fuel cell, the larger the seal increases Compressive forces 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 by means of the

Sealing material sealed a closed area. 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. But it can also be several single or interrupted all around

Randerhöhungen be provided per 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) and 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, this is easily recognizable from outside the fuel cell, as exiting reactants or reaction products not from the electrically insulating material

held back 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 may be outwardly facing beads in the sheet. A cavity within the seal elevation, ie within the body, is preferably as a

Operating medium channel formed. 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

Seal material komplanare outer surfaces have. 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.

In addition, a method for producing a bipolar plate according to the invention for

Provided, the method comprising the steps of:

- 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 at least one seal increase and the maxima of the increases Komplanar are, as a tool for applying the materials may have an angled 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 is described below in embodiments with reference to the associated

Drawings explained. Show it:

1 shows a bipolar plate according to the prior art,

2 shows a bipolar plate with two, by means of a fanning out of the main body

realized edge enhancements, and

FIG. 3 shows a bipolar plate with one realized by means of a step of the basic body

Marginal increase.

FIG. 1 shows a partial region of a fuel cell 100 according to the prior art.

Within the illustrated subregion, two bipolar plates 10 according to the prior art are shown with a membrane arrangement 11 arranged therebetween. The visible in the figures part of the membrane assembly 1 1 z. B. an edge reinforcing film or the membrane of the membrane assembly 1 1 be. The membrane assembly 1 1 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 base bodies 12 of the bipolar plates 10 each have two seal elevations 14. These are at their maxima 15 with a

Sealant 16 provided. To isolate the bipolar plates 10 from each other 10 air gaps between the bipolar plates

19 (free spaces) provided. In order to be able to ensure the air gaps 19, the edges 17 (ie narrow sides of the main body 12) of the bipolar plate 10 are typically cut by laser. Nevertheless, such insulation is susceptible to deformation which the

Reduce air gap 19.

FIG. 2 shows a partial region of a fuel cell 100 according to a preferred embodiment

Embodiment of the invention. Within the illustrated subregion, two bipolar plates 10 are provided according to a preferred embodiment of the invention. It is also shown in turn a membrane arrangement 1 1 arranged therebetween.

In contrast to the prior art according to FIG. 1, the bipolar plate 10 now has edge elevations 20 arranged on both sides in an edge region 18 in addition to the seal elevations 14 (which may also be omitted depending on the configuration). The margins increases

20 are located farther outward relative to the seal risers 14 on the bipolar plate 10. For each major surface 21, the seal elevation 14 and the elevation 20 have mutually coplanar maxima 15. The maxima 15 thus lie per main surface 21 in each case in a common plane 23. Furthermore, the planes 23 can also be parallel to one another and in particular also parallel to a center plane 25, which represents a contact plane of the two plates 13. Thus, the maxima 15 of the elevations 14, 20 per main area 21 have equal heights 22 above the center plane 25.

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

On the maxima 15 of the seal increases 14, the bipolar plates 10 a

Seal material 16 and on the maxima 15 edge elevations 20 an electrically insulating material 24. Instead of using two different materials 16, 24, a single material may also be provided. This is thus an electrically insulating

Sealing material.

The maxima 15 are in the form of plateaus (also identified by the reference numeral 15), which are arranged to be coplanar with one another per main surface 21, that is to say in the same plane 23.

The edge elevations 20 have their maxima on an outer edge 17 of the edge region 18 (ie on an outer edge 17 of the main surface 21). Thus, the bipolar plate ends too its edge 17 with the plateaus of the Randerhöhungen 20. In the cross section shown by the bipolar plate 10, the edge elevations 20 are arranged opposite one another.

In the cross section shown, a fanning out 26 of the base body 12 to the outer edges 17 is also apparent. The fanning 26 are realized by the two sheets 13 per bipolar plate 10 to the edge 17 of the respective bipolar plate 10 back

are bent apart. The main body 12 is thus formed open at its outer edge 17.

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

During operation of the fuel cell 100, the seal risers 14 seal with the

Sealing material 16 enclosed areas, z. B. an active area or

Resource channels, from, so that no resources can flow out of the fuel cell 100.

Within the fuel cell 100, the edge elevations 20 support adjacent ones

Membrane assemblies 1 1 on both sides of the bipolar plates 10 from. Insulation between the bipolar plates 10 is ensured by the electrically insulating sealing material 16 even when they are offset between them (eg due to tolerances). Furthermore, by the narrow sides 27, which may also have the electrically insulating sealing material, insulation to components outside the fuel cell 100 can 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 of a sheet 13 is damaged, by the edge 17 of the second sheet 13 is an orientation

guaranteed. In addition, there is a short distance between adjacent

Plate surfaces.

FIG. 3 likewise shows a fuel cell 100 and a bipolar plate 10 according to a preferred embodiment of the invention. The bipolar plate 10 differs from the bipolar plate 10 according to FIG. 2 in that the base body 12 has a step shape in cross-section 28 in the edge region 18, ie towards its outer edge 17, wherein the step shape 28 forms the at least one edge elevation 20. Thus, both plates 13 of the body 12 bent in the edge region 18 in a common direction, thereby realizing a Randerhöhung 20 on a major surface of the bipolar plate 10th

Within the fuel cell 100, the edge elevations 20 of the bipolar plates 10 support membrane assemblies 1 1 (as opposed to the embodiment according to FIG. 2) on one side of the bipolar plate 10. On the opposite side of the bipolar plate 10 facing away from the edge elevations 20, the stepped mold 28 now has an enlarged air gap 19 in comparison with the prior art.

The fact that the edge 17 and the edge region 18 of the base body 12 is at the same height as the maximum of the seal increase 14, a coating of

Centering with the (electrically insulating) sealing material 16 done. In order to enable a nesting of the two sheets 13, additional tolerances may be provided in the edge region 18.

The seal elevations 14 may be made stiffer than the edge heights 20. This can be realized (as in Figure 2) by the maxima 15 of

Seal elevations 14 are supported on both sides by flanks of the seal elevation 14, while the maxima 15 of the edge elevations 20 are supported only on one side by a respective edge of the edge elevations 20. The flanks extend between the

This ensures, on the one hand, a sufficiently high contact pressure on the seal elevations 14, while an unnecessarily high contact pressure on the edge elevations 20 is avoided.

The bipolar plates 10 according to the invention can be produced in accordance with a preferred method by firstly providing the main body 14 of the bipolar plate 10, in particular by producing it (for example by pressing it). This is followed by a simultaneous

Applying the electrically insulating material 24 to the maxima 15 of the edge elevations and the sealing material 16 to the base body 12, in particular to the maxima 15 of the seal increases 14th

For example, the materials 16, 24 may be applied by being rolled up or printed. Due to the coplanar maxima, a tool for applying the sealing material 16 and the electrically insulating material 24 an angle-faithful (ie level) and the

Seal material 16 have directed surface.

Thus, for the application of the materials 16, 24 only one common

Manufacturing step required. Further, the fuel cell 100 is more tolerant to deformation than conventional air gap insulations.

The invention can be used both to drive a motor vehicle and within

Electrolyzers are used. In addition, it is suitable both for low-temperature polymer electrolyte membrane fuel cells (NT-PEM fuel cells) according to the fuel cell 100, solid oxide fuel cells (SOFC) shown in the figures,

Phosphoric acid fuel cells (PAFC), as well as for alkaline fuel cells (AFC).

LIST OF REFERENCE NUMBERS

bipolar

Membrane assembly

body

sheet

seal increase

maximum

sealing material

edge

border area

air gap

marginal increase

main area

height

level

electrically insulating material

midplane

fanning

narrow side

step shape

fuel cell

Claims

claims

1 . Bipolar plate (10) for a fuel cell (100), wherein the bipolar plate (10) has a

Base body (12) and on the base body (12) has a sealing material (16), characterized in that the base body (12) in an outer edge region (18) at least one edge elevation (20) is formed, and the bipolar plate (10) on a Maximum (15) of the at least one edge elevation (20) has an electrically insulating material (24).

2. bipolar plate (10) according to claim 1, characterized in that the base body (12) at least one seal elevation (14) and the bipolar plate (10) forms the

Sealing material (16) on a maximum (15) of the at least one seal elevation (14), wherein the maximum (15) of the at least one seal elevation (14) and the maximum (15) of the at least one edge elevation (20) are coplanar.

3. Bipolar plate (10) according to one of the preceding claims, characterized in that the at least one edge elevation (20) has the maximum (15) on an outer edge (17) of the edge region (18).

4. bipolar plate (10) according to any one of the preceding claims, characterized in that the sealing material (16) and the electrically insulating material (24) are the same material.

5. bipolar plate (10) according to any one of the preceding claims, characterized in that the base body (12) arranged in a cross section opposite

Edge enhancements (20) trains.

6. bipolar plate (10) according to claim 5, characterized in that the base body (12) in the cross section at its outer edge (17) is formed open.

7. bipolar plate (10) according to one of claims 1 to 4, characterized in that the base body (12) in a cross-section a step shape (28) to its outer edge (17) out, wherein the step shape (28) the at least one Randerhöhung (20) trains.

8. bipolar plate (10) according to any one of the preceding claims, characterized in that the base body (12) seal increases (14) and forms the bipolar plate (10) the sealing material (16) has maxima (15) of the seal elevations (14), wherein the maxima (15) of the seal elevations (14) are formed on both sides by flanks of the

Seal increase (14) are supported, while the maxima (15) of the edge elevations (20) are supported only on one side by a respective edge of the edge elevations (20).

9. fuel cell (10) with at least one bipolar plate (10) according to one of

previous claims.

10. A method for producing a bipolar plate (10) according to any one of claims 1 to 8, wherein the method comprises the steps of:

- Providing the main body (12) of the bipolar plate (10);

- Simultaneous application of the sealing material (16) on the base body (12) and the electrically insulating material (24) to the maximum (15) of the at least one edge elevation (20).

1 1. A method according to claim 10, characterized in that the application comprises a rolling or printing.