DE102018203132A1 - Bipolar plate for fuel cell stack - Google Patents

Abstract

A bipolar plate (50) for a fuel cell stack (9), comprising at least one first distribution structure formed as a metallic fabric (1) for a first operating medium (1a) of the fuel cell stack (9), a second formed as a metallic fabric distribution structure (2) for a second Operating medium (2a) of the fuel cell stack (9) and a first gas-tight partition wall (4) between the first manifold structure (1) and the second manifold structure (2), wherein a plurality of connecting elements (6) are provided, the first gas-tight partition (4 ) and are intertwined and / or soldered to both distributor structures (1, 2) .A method (100) for producing a bipolar plate (50) according to any one of claims 1 to 8, wherein metallic filaments are used as connecting elements (6, 7) different distributor structures (1, 2, 2, 3), designed in each case as metallic fabric, for operating media (1a, 2a, 3a) of the fuel cell stack (9 ) (110).

Description

The present invention relates to bipolar plates for connecting fuel cells in a fuel cell stack with each other.

State of the art

A fuel cell comprises an anode space in which a fuel is introduced, a cathode space in which an oxidant is introduced, and an electrolyte or a semi-permeable membrane as a separation between the anode space and the cathode space. The fuel is oxidized at the anode to ions that pass through the electrolyte, or through the membrane, in the cathode space and react there with the oxidizing agent. In this case, electrons are released, which can flow via an external load from the anode to the cathode to close the circuit.

A single fuel cell only supplies voltages typically less than 1.5V. To achieve higher voltages, a plurality of fuel cells in a fuel cell stack are connected in series. The individual fuel cells are electrically interconnected by bipolar plates. A bipolar plate typically includes on one side an oxidant media distribution structure associated with the cathode space of a first fuel cell and on the other side a fuel media manifold structure associated with the anode space of a second fuel cell. It is important to minimize the electrical resistance in the transition from one fuel cell to the next, as this resistance is multiplied by the number of fuel cells in the stack. Bipolar plates are for example in the DE 10 2016 213 057 A1 disclosed.

Disclosure of the invention

In the context of the invention, a bipolar plate for a fuel cell stack has been developed. This bipolar plate comprises at least a first distribution structure formed as a metallic tissue for a first operating medium of the fuel cell stack, a second formed as a metallic fabric distribution structure for a second operating medium of the fuel cell stack and a first gas-tight partition between the first distribution structure and the second distribution structure.

There is provided a plurality of connecting elements which traverse the first gas-tight partition wall and are intertwined and / or soldered to both distributor structures.

It has been found that the coupling of the connecting elements to the two distribution structures by braiding and / or soldering provides such good electrical and thermal conductivity that these connecting elements, although they traverse the gas-tight partition only on a small part of their total area, the thermal and electrical Conductivity for traversing the bipolar plate from one fuel cell to the adjacent fuel cell dominate. This means in particular that a contact resistance between the distributor structures and the gas-tight partition wall no longer plays a role. The fuel cell stack therefore benefits from the controllable and reproducibly continuous porosity of a distributor structure formed from a fabric, without this being associated with an increase in the resistance during the transition from one fuel cell to the next.

This in turn means that it no longer depends on the electrical or thermal conductivity of the gas-tight partition. So there is complete freedom to select a material for the gas-tight partition on the basis of other requirements for the fuel cell stack. For example, a plastic can be used for the mobile use for weight saving.

Furthermore, the production of the bipolar plate is significantly simplified. The gas-tight partition can be produced and at the same time coupled to the distributor structures by introducing a material in the liquid state into the intermediate space between the distributor structures and then solidifying it. The gas-tightness is then directly produced without the need for a separate sealing element. Also, it is not necessary to observe close manufacturing tolerances when assembling the distributor structures with the gas-tight partition.

In a particularly advantageous embodiment, at least one connecting element is both part of the fabric of the first distributor structure and part of the fabric of the second distributor structure. This means that this connection element is woven into both fabrics. Since the contact resistance between the individual threads of the fabric is negligible within each tissue, the connecting element is then optimally coupled to both distributor structures.

Thus, the tissues of both distribution structures eventually merge into a single "two-story tissue" extended into the third dimension. The position and density (frequency) of the connecting elements can then be advantageously selected so that the connecting elements not only provide optimum conductivity, but also stability and strength according to the framework principle.

The first distributor structure for distributing a fuel as the operating medium of the fuel cell stack and the second distributor structure for distributing an oxidizing agent as the operating medium of the fuel cell stack are advantageously formed. In the finished assembled fuel cell stack, the first distributor structure is then located in the anode compartment of a fuel cell, and the second distributor structure is located in the cathode compartment of an adjacent fuel cell.

The distributor structures may be provided with respective coatings adapted to the respective media in order to improve the durability of the metallic threads of the fabric. For example, the channels of the hydrogen distribution structure may be provided with an embrittlement-inhibiting coating as fuel. The channels of the distributor structure for air as the oxidizing agent can be provided, for example, with a product water (DI-water) resistant to coating during operation of the fuel cell stack.

For example, the coating can already be applied to the metallic threads before they are interwoven into the respective distributor structures. This is much easier to manufacture than coating the distribution structures from the inside out. In particular, it is then ensured that the respective coating material does not displace the continuous pores in the distributor structures.

In the finished assembled fuel cell stack, the distributor structures are in contact with gas diffusion layers of catalysts on both sides of the electrolyte, or the semipermeable membrane. These contact points should be corrosion resistant, but also be electrically and thermally conductive. A coating for this purpose can likewise be applied to the threads already before the interweaving of the metallic threads into the distributor structures, but also, for example, can only be subsequently applied to the finished distributor structures.

In a further particularly advantageous embodiment, a third distribution structure formed as a metallic fabric and a second gas-tight partition wall between the second distribution structure and the third distribution structure are additionally provided. It is then further provided a plurality of further connecting elements which traverse the second gas-tight partition and are intertwined and / or soldered to the second and the third distributor structure, respectively.

The electrical and thermal connection between the second and the third distributor structure works completely analogously to the connection between the first and the second distributor structure. In this way, on the way from the first to the third distributor structure results in a particularly low total resistance compared to a structure in which a plurality of contact resistances is to be overcome in each case between a distributor structure and an adjacent gas-tight partition.

Analogously to the connection between the first and second distributor structure, in a particularly advantageous embodiment at least one of the further connecting elements is both part of the fabric of the second distributor structure and part of the fabric of the third distributor structure. The "two-storey tissue" is therefore extended to a "three-storey tissue".

In a particularly advantageous embodiment, the first distribution structure for distributing a fuel as the operating medium of the fuel cell stack, the second distribution structure for distributing a coolant as the operating medium of the fuel cell stack and the third distribution structure for distributing an oxidizing agent as the operating medium of the fuel cell stack. Thus, by inserting "intermediate floors" for the cooling in the fuel cell stack, the cooling can be spatially distributed over the entire fuel cell stack. This avoids large temperature differences within the fuel cell stack, which due to thermal expansion effects lead to mechanical stresses. Furthermore, a total of a larger amount of heat can be dissipated from the fuel cell stack and thus its power density can be further increased.

At least one of the distributor structures advantageously comprises threads made of steel and / or aluminum. These metals are comparatively inexpensive and at the same time well interleaved. The connecting elements need not necessarily be made of the same metal as the threads which run only within one of the distributor structures. Only shared metals need to be compatible in terms of contact corrosion.

In a particularly advantageous embodiment, the first gas-tight partition, and / or the second gas-tight partition, aluminum, a plastic and / or a resin.

Aluminum has the advantage here that it is particularly light and also has a comparatively low melting point. Furthermore, contact corrosion can be ruled out if the distributor structures adjoining the gas-tight partition also consist of aluminum.

A plastic and a resin are even lighter than aluminum and even at temperatures even lower than aluminum liquid. Furthermore, irrespective of which metals the adjacent distributor structures consist of, no contact corrosion of these distributor structures is effected.

The solidification of the plastic or the resin does not necessarily take place by cooling below a melting point. For example, the plastic or resin may be a mixture of two or more components that react with one another to effect solidification. It is also possible, for example, to use a plastic or a resin whose solidification is activated by irradiation with UV light. The plastic, or the resin, can then have a higher melting point, so that the fuel cell stack can be operated at higher temperatures.

The invention also relates to the method described above for producing the bipolar plate. In this method, metallic threads are intertwined as connecting elements with different, each formed as a metallic fabric, distribution structures for operating media of the fuel cell stack.

In this case, for example, finished fabric mats can be used as distributor structures and the connecting elements can be subsequently interwoven with these fabric mats.

In order to form each distributor structure, metallic filaments are particularly advantageously interlaced, wherein some of the filaments are guided as connecting elements from one distributor structure into another distributor structure, or through all distributor structures. Then, on the one hand, the electrical and thermal resistance in the transition from a distribution structure to the connecting element and vice versa minimal. On the other hand, the connecting elements then maximally contribute to the stability and strength of the bipolar plate.

Advantageously, the material of the gas-tight partition, or partitions, each inserted in the liquid state in intermediate spaces between adjacent distributor structures and solidified there. In this way, it adapts to the exact dimensions of the distributor structures, so that when assembling the partitions with the distributor structures no close tolerances are to be observed.

Advantageously, such a ratio is chosen between the pore size in the distributor structures and the viscosity and / or surface tension of the liquid material that the liquid material does not penetrate into the pores of the distributor structures. In this way it is ensured that the pores of the distributor structures are not displaced by the liquid material.

Advantageously, a material is selected which has a lower melting point than the metallic filaments. Then, the metallic threads are not thermally attacked on contact with the liquid material.

However, it is also possible to choose a material which has an equal or higher melting point than the metallic threads. The metallic filaments may then be protected by a coating at least for the time to solidification of the material prior to melting. It is advantageous if the liquid material does not have to cool down too quickly. The liquid material can then adapt to the connecting elements during cooling, in particular in the areas in which it is traversed by the connecting elements. There are then no paths along the connecting elements, along which the gas-tightness is weakened.

In a further advantageous embodiment, the distributor structures are connected by heat conduction with a heat sink, while they are in contact with the liquid material of the gas-tight partition, or partitions. By this cooling, on the one hand, the solidification of the material can be accelerated. On the other hand, the cooling, in contrast to a coating, leaves no permanent residues on the distributor structures. Further measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

list of figures

• 1 Prinzipieller Aufbau eines Brennstoffzellenstapels 9;
• 2 Ausführungsbeispiel der bipolaren Platte 50;
• 3 Ausführungsbeispiel des Verfahrens 100.

It shows:

• 1 Basic structure of a fuel cell stack 9 ;
• 2 Embodiment of the bipolar plate 50 ;
• 3 Embodiment of the method 100 ,

To 1 includes the fuel cell stack 9 a plurality of fuel cells connected in series, of which only two are fuel cells 91 and 92 drawn by way of example. In the fuel cell stack 9 are alternating bipolar plates 50 and membrane-electrode assemblies 8th stacked. Every fuel cell 91 . 92 includes a first distribution structure 1 for a first operating medium 1a that from a first bipolar plate 50 is provided, a membrane electrode assembly 8th and a second distribution structure 2 for a second operating medium 2a that from the next bipolar plate 50 provided. It can now, for example, the first operating medium 1a a fuel and the second operating medium 2a be an oxidizing agent.

Each membrane-electrode unit 8th consists of catalyst layers 81 and 83 , which also comprise gas diffusion layers, respectively. Between the catalyst layers 81 and 83 is the membrane 82 ,

2 shows an embodiment of the bipolar plate 50 in the extended version, in which they are of three operating media 1a . 2a and 3a can be flowed through. It can now, for example, the first operating medium 1a a fuel, the second operating medium 2a a coolant and the third operating medium 3a be an oxidizing agent.

For the management of each operating medium 1a . 2a . 3a Each is its own distribution structure 1 . 2 . 3 intended. The first distribution structure 1 is from the second distribution structure 2 through a first gas-tight partition 4 separated. The second distribution structure 2 is from the third distribution structure 3 through a second gas-tight partition 5 separated. Each distribution structure 1 . 2 . 3 is formed by a metallic fabric of a multiplicity of threads, of which in 2 only a few are shown schematically.

Some threads are initially part of the first distribution structure 1 However, in their further course, they pass through the first gas-tight partition 4 and enter the second distribution structure 2 in order to be intertwined in the fabric with the other threads. These threads are the fasteners 6 between the first distribution structure 1 and the second distribution structure 2 , In 2 For the sake of clarity, only such a connecting element 6 located.

Similarly, some threads are initially part of the second distribution structure 2 , however, pass through the second gas-tight partition wall in their further course 5 and enter the third distribution structure 3 in order to be intertwined in the fabric with the other threads. These threads are the fasteners 7 between the second distribution structure 2 and the third distribution structure 3 , In 2 For the sake of clarity, only such a connecting element 7 located.

The gas-tight partitions 4 and 5 were not present in the prior art.

3 shows an embodiment of the manufacturing process 100 , According to step 110 become metallic threads as connecting elements 6 . 7 each with adjacent distribution structures 1 and 2 , or. 2 and 3 , intertwined. These fasteners can 6 . 7 in particular according to block 112 initially in a distribution structure 1 . 2 intertwined in the tissue and then in another distribution structure 2 . 3 be guided. In this way, the in 2 shown configuration of the threads emerged.

According to step 120 becomes the material of the gas-tight partition 4 . 5 in the liquid state of matter in interspaces between adjacent distributor structures 1 and 2 , or. 2 and 3 , brought in. According to step 130 the material is then solidified.

Within step 120 can according to block 121 such a ratio between the pore size in the manifold structures 1 . 2 . 3 on the one hand and the viscosity and / or surface tension of the liquid material on the other hand be chosen so that the liquid material does not penetrate into the pores of the distributor structures 1 . 2 . 3 penetrates.

According to block 122 For example, a material may be chosen that has a lower melting point than the metallic filaments in the manifold structures 1 . 2 . 3 , Alternatively, according to block 123 a material having an equal to or higher melting point than the metallic filaments, wherein then according to block 124 the metallic threads through a coating at least for the time to solidify 130 the material is protected from melting.

The distribution structures 1 . 2 . 3 can according to block 125 be connected by heat conduction with a heat sink while in contact with the liquid material of a gas-tight partition 4 . 5 stand.

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

• DE 102016213057 A1 [0003]

Claims (15)

A bipolar plate (50) for a fuel cell stack (9), comprising at least one first distribution structure formed as a metallic fabric (1) for a first operating medium (1a) of the fuel cell stack (9), a second formed as a metallic fabric distribution structure (2) for a second Operating medium (2a) of the fuel cell stack (9) and a first gas-tight partition (4) between the first distributor structure (1) and the second distributor structure (2), characterized in that a plurality of connecting elements (6) are provided, the first gas-tight Pass through the partition wall (4) and in each case intertwined and / or soldered to both distributor structures (1, 2). Bipolar plate (50) after Claim 1 , characterized in that at least one connecting element (6) is both part of the fabric of the first distributor structure (1) and part of the fabric of the second distributor structure (2). Bipolar plate (50) after one of the Claims 1 to 2 , characterized in that the first distributor structure (1) for distributing a fuel as the operating medium (1a) of the fuel cell stack (9) and the second distributor structure (2) for distributing an oxidizing agent as operating medium (2a) of the fuel cell stack (9) are formed. Bipolar plate (50) after one of the Claims 1 to 2 , characterized in that in addition a third designed as a metallic fabric distributor structure (3) and a second gas-tight partition (5) between the second distributor structure (2) and the third distributor structure (3) are provided, wherein a plurality of further connecting elements (7) are provided are passing through the second gas-tight partition wall (5) and are intertwined and / or soldered to the second (2) and the third (3) distribution structure, respectively. Bipolar plate (50) after Claim 4 , characterized in that at least one of the further connecting elements (7) is both part of the fabric of the second distributor structure (2) and part of the fabric of the third distributor structure (3). Bipolar plate (50) after one of the Claims 4 to 5 , characterized in that the first distributor structure (1) for distributing a fuel as operating medium (1a) of the fuel cell stack (9), the second distribution structure (2) for distributing a coolant as the operating medium (2a) of the fuel cell stack (9) and the third distribution structure (3) for distributing an oxidizing agent as the operating medium (3a) of the fuel cell stack (9) are formed. Bipolar plate (50) after one of the Claims 1 to 6 , characterized in that at least one of the distributor structures (1, 2, 3) comprises threads of steel and / or aluminum. Bipolar plate (50) after one of the Claims 1 to 7 , characterized in that the first gas-tight partition (4), and / or the second gas-tight partition (5), aluminum, a plastic and / or a resin. Method (100) for producing a bipolar plate (50) according to one of the Claims 1 to 8th , characterized in that metallic threads are intertwined as connecting elements (6, 7) with different distributor structures (1, 2, 2, 3) for operating media (1a, 2a, 3a) of the fuel cell stack (9), each designed as metallic fabric ( 110). Method (100) according to Claim 9 characterized in that metallic threads are interlaced (112) to form each distributor structure (1, 2, 3), some of the threads being used as connecting elements from one distributor structure (1, 2) to another distributor structure (2, 3), or through all distribution structures (1, 2, 3), (114). Method (100) according to one of Claims 9 to 10 , characterized in that the material of the gas-tight partition (4, 5), or partitions, respectively in the liquid state state in intermediate spaces between adjacent distributor structures (1, 2, 2, 3) introduced (120) and solidified there (130). Method (100) according to Claim 11 , characterized in that such a ratio between the pore size in the distributor structures and the viscosity and / or surface tension of the liquid material is selected (121) that the liquid material does not penetrate into the pores of the distributor structures (1, 2, 3). Method (100) according to one of Claims 11 to 12 , characterized in that a material is chosen (122), which has a lower melting point than the metallic threads. Method (100) according to one of Claims 11 to 12 characterized in that a material is selected (123) having an equal or higher melting point than the metallic filaments, the metallic filaments being protected by a coating at least for the time to solidification (130) of the material prior to melting (124). Method (100) according to one of Claims 11 to 14 , characterized in that the Distributor structures (1, 2, 3) are connected by heat conduction with a heat sink, while they are in contact with the liquid material of the gas-tight partition (4, 5), or partitions.

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