DE102008005502A1 - Fuel cell, in particular for arrangement in a fuel cell stack and fuel cell stack - Google Patents

Abstract

The invention relates to a fuel cell (1), in particular for arrangement in a fuel cell stack, with a first bipolar plate (2) and a second bipolar plate (3) and with a membrane-electrode arrangement (4) between the two bipolar plates arranged plane-parallel to one another (2, 3), wherein between the first bipolar plate (2) and the membrane electrode assembly (4) an anode flow field (F1) and between the second bipolar plate (3) and the membrane electrode assembly (4) Cathode flow field (F1) by in the first bipolar plate (2) and in the second bipolar plate (3) introduced channel structures with anode channels (K1) and cathode channels (K2) is formed, and wherein the membrane-electrode assembly (4) at least one Opening (8), the flow-side of the anode flow field (F1) from this part of the anode exhaust gas on the inlet side introduces into the cathode flow field (F2) in a cathode gas. According to the invention, at least one connection element (9) is arranged in the region of the opening (8), which controls the discharge of the part of the anode exhaust gas into the cathode gas.

Description

The The invention relates to a fuel cell, in particular for the arrangement in a fuel cell stack according to the preamble of claim 1 and a fuel cell stack according to the The preamble of claim 13.

One Fuel cell stack (also called stack for short) consists of several, electrically connected in series, plane-parallel one above the other Stacked arranged fuel cells. Each fuel cell points an anode, a cathode and an electrolyte therebetween on, for example in the form of a polymer electrolyte membrane (short PEM), which together form a membrane-electrode assembly (MEA short) form. Between those in the fuel cell stack adjacent membrane electrode assemblies are each a bipolar plate (also called bipolar separator plate unit) arranged. The bipolar plate serves the spacing of adjacent membrane electrode assemblies, distributing reactants for the fuel cell such as fuel and oxidizer via the adjacent membrane-electrode assemblies and the removal of the reactants in this provided, respectively to the membrane-electrode assemblies out open channels, the removal of the heat of reaction via a guided in separate coolant channels Coolant and the production of an electrical connection between the anode and the cathode of adjacent membrane-electrode assemblies.

When Reactants are a fuel and an oxidant used. Most gaseous reactants (in short: reaction gases) are used, z. B. hydrogen or a hydrogen-containing gas (eg, reformate gas) as fuel and oxygen or an oxygen-containing gas (eg. As air) as an oxidizing agent. Under Reactants are all understood substances involved in the electrochemical reaction, including the reaction products, such as. B. water.

The respective bipolar plate consists for example of two plane-parallel interconnected moldings, in particular plates - one first plate for connection to the anode of a membrane-electrode assembly and a second plate for connection to the cathode of another The membrane electrode assembly. At the one membrane electrode assembly facing surface of the first plate are anode channels for distributing a fuel along the membrane-electrode assembly arranged on the other of the membrane electrode assembly facing surface of the second plate cathode channels for distributing the oxidizer via this membrane-electrode assembly are arranged. The cathode channels and the anode channels have no connection with each other.

The Cathode and anode channels are thereby by surveys mutually separate recesses on each of the membrane-electrode assemblies facing surfaces of the first and second plates formed. The first and second plates are preferably shaped, in particular hollow embossed. The surveys and depressions, for example discontinuous by forming, deep drawing, extrusion or the like, or produced continuously by rolling or drawing. Depending on the design of the two plates, these can the side facing away from the membrane-electrode assembly side again Cathode or anode channels of an adjacent another Have fuel cell. In this case, the respective bipolar plate from a molded part with channel structures introduced on both sides and thus executed as a plate. Also can the plates coolant channels for passage of coolant.

Certain Fuel cells also need a certain water content, to ensure adequate ionic conductivity exhibit. This is especially true for polymer electrolyte membrane fuel cells to, fluorinated sulfonic acid based materials exist, such. Nafion.

Further it is especially under certain operating conditions, such as during a cold start or during operation at low temperatures or low power or partial moistening of the cathode gas required to heat the fuel cell. This is It is known, excess anode exhaust gas which for example due to the non-homogeneous distribution of the hydrogen contained on the membrane in the anode exhaust gas to supply the cathode gas, to burn either in the anode channels or in provide the cathode channels.

From the DE 10 2005 045 319 A1 For example, a fuel cell system is known that provides a flow of anode exhaust gas into the cathode side of the fuel cell without allowing the anode exhaust gas flow and the cathode input flow to mix in a large volume. For this purpose, openings are provided as a grouping of small holes in the membrane electrode assembly. The fuel cell system disclosed therein provides for controlling the anode stoichiometry and correspondingly limiting the apertures to control how much anode exhaust gas flows into the cathode gas.

The invention is therefore based on the object to provide a fuel cell, the one multiple anode exhaust gas removal allows. In addition, an improved fuel cell stack is to be specified.

The The object is achieved by in the claim 1 and the features specified in claim 13.

advantageous Further developments of the invention are the subject of the dependent claims.

The Fuel cell comprises a first bipolar plate and a second Bipolar plate and a membrane electrode assembly between arranged the two plane-parallel arranged bipolar plates is. It is between the first bipolar plate and the membrane-electrode assembly an anode flow field and between the second bipolar plate and the membrane-electrode assembly, a cathode flow field through into the first bipolar plate or into the second bipolar plate introduced channel structures with anode channels or cathode channels educated. To use the unreacted in the anode exhaust gas Hydrogen includes the membrane-electrode assembly at least an opening, the flow exit side of the Anodenströmungsfelds of this part of an anode exhaust gas flow side into the cathode flow field into a cathode gas. According to the invention at least one switching element is arranged in the region of the opening, this is the removal of the anode exhaust gas into the cathode gas controls.

By the integration of a Zuschaltelements in the region of the opening for discharging the anode exhaust gas into the cathode gas a targeted control of the supply of hydrogen in the cathode gas, In particular, air allows for a resulting to limit catalytic combustion. In particular, it is possible over such targeted metered discharge of the anode exhaust gas to control the temperature of the fuel cell and thus a for a cold start or similar heat requiring Set operating processes required temperature. About that It is also through the control of anode exhaust gas removal ensures that no uncontrolled combustion takes place. Consequently are damage to the membrane-electrode assembly, in particular their gas diffusion layers safely avoided. Furthermore is by the Zuschaltelement an uncontrolled feed from anode exhaust gas into the cathode gas via the opening safely avoided. For temperature-dependent control of anode exhaust gas removal In particular, the already existing monitoring of Cell or stack operating temperature and used in the controller the anode exhaust gas removal are integrated.

Around an accumulation of the mixture of anode exhaust gas and cathode gas to avoid and damage gas diffusion layers the membrane electrode assembly by the targeted triggered and to safely avoid controlled combustion is the opening expediently in a catalyst-free region arranged the membrane-electrode assembly. Furthermore is the opening, especially its size, adjusted accordingly. For example, the opening at least one or more through holes or one or more slots. Here are the openings a particularly small diameter in the μm or mm range on.

In One possible embodiment is the opening in a support frame of the membrane-electrode assembly arranged on which expediently an anode outlet (also called anode port) of the anode flow field and a cathode input (also called cathode port) of the cathode flow field adjoin.

For a compact construction of the fuel cell is possible the switching element in whole or in part in the region of the anode output or the cathode input on or in the first bipolar plate or second bipolar plate arranged.

Preferably the Zuschaltelement is very compact and automatic effective. This allows a simple structure and a compact design of the fuel cell or the fuel cell stack.

In a possible embodiment is the Zuschaltelement designed as a pressure switch valve. The pressure switch valve locks in analogy to a pressure relief valve the opening until a pressure set at the pressure switch valve decreases is reached. When the set pressure is reached, opens the pressure switch valve and a part of the anode exhaust gas is in the Cathode gas introduced. Conveniently, is the pressure switch valve on one side of the opening arranged either on the cathode or on the anode side. As Druckzuschaltventil is for example an automatic Spring flap valve provided. It is set according to the set Spring tension of the spring flap valve at a correspondingly high overpressure in the anode flow field at the anode outlet, the spring flap opened and thus a discharge of the anode exhaust gas in the cathode gas allows. Here is both the size the opening as well as the set spring tension the type, size and pressure conditions adapted to the fuel cell.

Since the membrane electrode assembly consists largely of soft and very flexible materials, a spring tension of the spring flap valve can be difficult to adjust. For this Basically, the invention provides alternatively to support the spring tension to be adjusted by internals in at least one of the bipolar plates. In one possible embodiment, this is an elastic compressible material, in particular a plastic, for. As an elastomer, such as silicone, or polypropylene, provided, which is arranged for example as a molded part between the opening and designed as a spring flap valve switching element.

alternative to the use of a spring flapper valve and / or an elastic Compressible material, the pressure switch valve as a electrically, pneumatically, hydraulically or electropneumatically driven Control valve to be formed. For example, the pressure switch valve as be a movably driven cylinder valve executed that is essentially at least over the length the opening extends. By turning or longitudinal displacement of the cylinder valve arranged in the opening is the Removal of a portion of the anode exhaust gas in the cathode gas controllable.

Prefers the fuel cell is part of a fuel cell stack. at The fuel cell is in particular a so-called Polymer electrolyte membrane fuel cell (called PEMFC for short). These is commonly referred to as a fuel cell stack of a Variety of plane-parallel stacked fuel cells formed with a variety of bipolar plates, between each one a membrane-electrode assembly with an anode flow field on the one hand and a cathode flow field on the other is arranged, wherein the flow-side of the anode flow field from this part of the anode exhaust gas flow input side into the cathode flow field in a cathode gas insertable is. According to the invention, a collection anode channel arranged in end plates and a collection cathode channel fluidly with each other over connected at least one opening, wherein in the region of the opening at least one switching element is arranged, which is the discharge a portion of the anode exhaust gas controls in the cathode gas.

In One possible embodiment is the opening in the form of a through hole or a channel in the end plate between those in a single end plate parallel to each other arranged collecting anode channel and collection cathode channel arranged wherein the Zuschaltelement laterally on the collecting anode channel or the collecting cathode channel in or at the opening in the relevant End plate is arranged.

In an alternative embodiment is the opening between parallel stacked collecting anode channel and collecting cathode channel in the form of recesses in two adjacent end plates introduced, wherein the Zuschaltelement head or front side of the fuel cell stack extends over at least two end plates.

embodiments The invention will be explained in more detail with reference to drawings.

there demonstrate:

1 1 schematically shows a sectional view of a fuel cell with a first bipolar plate and a second bipolar plate, between which a membrane electrode arrangement is arranged which comprises at least one opening for the fluidic connection of an anode flow field to a cathode flow field, wherein a connection element is arranged in the region of the opening,

2 1 is a schematic sectional view of a fuel cell with an alternative embodiment for a connection element;

3 1 is a schematic sectional view of a fuel cell with a further alternative embodiment for a connection element;

4 schematically a sectional view of a fuel cell with a further alternative embodiment for a Zuschaltelement, and

5 2 schematically shows a sectional view of a fuel cell stack formed from a plurality of fuel cells with an opening through an end plate for the fluidic connection of anode and cathode flow field and a connection element for controlling the opening cross section,

6 schematically a sectional view of a multi-fuel cell fuel cell stack with an alternative arrangement of an opening through an end plate for fluidic connection of anode and cathode flow field and a connection element for controlling the opening cross-section.

each other corresponding parts are in all figures with the same reference numerals Mistake.

1 shows schematically in section a fuel cell 1 with a first bipolar plate 2 and a second bipolar plate 3 and a membrane electrode assembly disposed therebetween 4 ,

It is between the one side, in particular the underside of the first bipolar plate 2 and the membrane electrode assembly 4 an anode flow field F1 and between the one side, in particular the top of the second bipolar plate 3 and the membrane electrode assembly 4 a ka thodenströmungsfeld F1 arranged. The anode flow field F1 and the cathode flow field F2 are respectively through the first bipolar plate 2 or in the second bipolar plate 3 introduced channel structures formed with anode channels K1 and cathode channels K2. The other sides of the bipolar plates 2 and 3 also have channel structures that form the cathode or anode side of adjacent fuel cells. Depending on the type and training, the respective bipolar plate 2 and 3 in a manner not shown with coolant channels for temperature control of the fuel cell 1 be provided.

The membrane electrode assembly 4 includes in detail a membrane, on both sides of each a corresponding catalyst and gas diffusion layers 5 respectively. 6 are applied and positioned in a known manner.

On the frame side, to avoid a fluidic connection of the anode flow field F1 and the cathode flow field F2, the membrane-electrode arrangement is on both sides 4 a seal 7 arranged.

To achieve a controlled combustion, inter alia for controlling the temperature of the fuel cell 1 is in the membrane electrode assembly 4 According to the invention in the catalyst-free area an opening 8th which fluidly connects the anode flow field F1 with the cathode flow field F2. For targeted control of combustion is in the area of the opening 8th at least one connection element 9 arranged, which controls the discharge of a portion of the anode exhaust gas in the cathode gas. The opening is preferred 8th in the support frame of the membrane-electrode assembly in the region adjacent to which an anode output Ka of the anode flow field F1 and a cathode input Ke of the cathode flow field are adjacent.

Here is the opening 8th formed in particular from a plurality of through-holes, not shown, or from one or more slots whose size is adapted to the amount of anode exhaust gas to be discharged.

Preferably, the Zuschaltelement 9 wholly or partially in the region of the cathode input Ke the opening 8th completely overlapping on or in the second bipolar plate 3 arranged. Alternatively, the connection element 9 also completely or partially in the region of the anode output Ka of the first bipolar plate 2 be arranged.

1 shows as a possible embodiment for the Zuschaltelement 9 a pressure switch valve, in particular an automatic spring flap valve 9.1 , which automatically opens and closes depending on the set spring tension under appropriate pressure conditions. Thus, especially at a high pressure in the anode flow field F1 automatically the spring flap valve 9.1 opened, so that anode exhaust gas is introduced into the cathode gas.

To adjust the spring tension can also between spring flap valve 9.1 and opening 8th a flexible compressible material M, z. As an elastomer, such as silicone, or another suitable material may be arranged as a molded part. Also, the spring tension by a in the respective bipolar plate 2 or 3 (In the embodiment in the second bipolar plate 3 ) arranged mechanical spring element can be adjusted.

Also, the Zuschaltelement 9 only be formed from the flexible compressible material M, as exemplified in 2 is shown. To adjust the compressibility, the material M with gas inclusions, z. As air, as in foamed plastic or elastomer containing be provided.

3 and 4 show a further alternative embodiment of the Zuschaltelement 9 , It shows the 3 a control valve driven as an electropneumatic 9.2 trained Zuschaltelement 9 , Alternatively, the control valve 9.2 also be operated electrically, pneumatically or hydraulically.

The for controlling the control valve 9.2 required energy can directly from the fuel cell 1 be removed. Alternatively, the supply of the control valve 9.2 also via an external voltage source. By means of the control valve 9.2 can the control of the discharged portion of the anode exhaust more targeted and better than the self-operated spring flap valve 9.1 or another suitable pressure relief valve.

4 shows as an alternative Zuschaltelement 9 a cylinder valve rotatable about a rotation axis D and longitudinally displaceable along a translation axis T. 9.3 , Under a cylinder valve 9.4 In particular, a cylindrical and movably arranged control valve is understood. In this case, the amount of anode exhaust gas to be discharged by changing the position of the cylinder valve 9.3 set. For this purpose, the cylinder valve extends 9.3 at least over the entire length of the opening 8th ,

5 and 6 show several superimposed fuel cells 1 as part of a fuel cell stack 10 ,

For the fluidic connection of the anode stream tion field F1 with the cathode flow field F2 is an opening 14 provided, one in end plates 11 arranged collecting anode channel 12 and a collection cathode channel 13 fluidly interconnected. The opening can be 14 in the area of one of the end plates 11 be arranged, in which the collecting cathode channel 13 and the collecting anode channel 12 parallel to each other in the relevant end plate 11 are arranged as in 5 shown. In this case, one of the types of switching elements described above is 9 laterally on the collecting anode channel 12 or the collection cathode channel 13 in the relevant end plate 11 arranged.

In an alternative embodiment, the opening 14 in that area of the end plates 11 arranged in which the collecting cathode channel 13 and the collecting anode channel 12 are each formed by depressions in two adjacent end plates, wherein the two channels are parallel to each other in the adjacent end plates 11 are arranged as in 6 shown. In this case, the connection element 9 head or end face over at least two end plates 11 arranged extending.

In particular, in the embodiments according to 5 and 6 with in the end plates 11 arranged openings 14 in the form of slots or through holes or channels in the end plates 11 as switching elements 9 electrically, pneumatically, hydraulically and / or electro-pneumatically operated control valves 9.2 , in particular electrically operated solenoid valves or electropneumatic piezo valves, used. These are partially or completely in the end plate / s 11 installed and integrated, so that additional supply lines are avoided. This is a very compact structure of the fuel cell stack 10 allows.

1

fuel cell

2

First bipolar

3

Second bipolar

4

Membrane-electrode assembly

5

anode side Gas diffusion layer

6

cathode side Gas diffusion layer

7

poetry

8th

opening

9

Zuschaltelement

10

fuel cell stack

11

endplates

12

Collecting cathode channel

13

Collection anode channel

14

opening

D

axis of rotation

F1

Anode flow field

F2

Cathode flow field

K1

anode channel

K2

cathode channel

ka

anode output

Ke

cathode input

T

translation axis

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 102005045319 A1 [0008]

Claims (16)

Fuel cell ( 1 ), in particular for arrangement in a fuel cell stack, with a first bipolar plate ( 2 ) and a second bipolar plate ( 3 ) and with a membrane electrode assembly ( 4 ), which between the two plane-parallel arranged bipolar plates ( 2 . 3 ), wherein between the first bipolar plate ( 2 ) and the membrane-electrode assembly ( 4 ) an anode flow field (F1) and between the second bipolar plate ( 3 ) and the membrane-electrode assembly ( 4 ) a cathode flow field (F1) into the first bipolar plate ( 2 ) or in the second bipolar plate ( 3 ) channel structures having anode channels (K1) and cathode channels (K2) is formed, and wherein the membrane electrode assembly ( 4 ) at least one opening ( 8th ), which introduces, from the flow outlet side of the anode flow field (F1), a part of the anode exhaust gas into the cathode flow field (F2) into a cathode gas, characterized in that in the area of the opening (FIG. 8th ) at least one connection element ( 9 ) is arranged, which controls the discharge of the anode exhaust gas into the cathode gas. Fuel cell according to claim 1, characterized in that the opening in a catalyst-free region of the membrane electrode assembly ( 4 ) is arranged. Fuel cell according to claim 1 or 2, characterized in that the opening ( 8th ) is formed from at least one or more through-holes or from one or more slots. Fuel cell according to one of claims 1 to 3, characterized in that the opening ( 8th ) in a support frame of the membrane electrode assembly ( 4 ) to which an anode output (Ka) of the anode flow field (F1) and a cathode input (Ke) of the cathode flow field (F2) adjoin. Fuel cell according to claim 4, characterized in that the switching element ( 9 ) wholly or partially in the region of the anode output (Ka) or the cathode input (Ke) on or in the first bipolar plate ( 2 ) or second bipolar plate ( 3 ) is arranged. Fuel cell according to claim 5, characterized in that the connection element ( 9 ) is formed of an elastically compressible material, in particular an elastomer or plastic. Fuel cell according to one of claims 1 to 6, characterized in that the switching element ( 9 ) is designed as a pressure switching valve. Fuel cell according to claim 7, characterized in that the pressure switching valve is an automatic spring flap valve ( 9.1 ). Fuel cell according to claim 7, characterized in that the pressure switching valve is an electrically, pneumatically, hydraulically or electro-pneumatically driven control valve ( 9.2 ). Fuel cell according to one of claims 1 to 9, characterized in that the switching element ( 9 ) a movably driven cylinder valve ( 9.3 ). Fuel cell according to claim 10, characterized in that the cylinder valve ( 9.3 ) rotatable and / or longitudinally displaceable in the region of the opening ( 8th ) is arranged. Fuel cell according to one of claims 1 to 11, characterized in that the fuel cell part of a fuel cell stack ( 10 ). Fuel cell stack ( 10 ) with a plurality of fuel cells ( 1 ) with a plurality of bipolar plates ( 2 . 3 ) and between each of which a membrane electrode assembly ( 4 ) is arranged with an anode flow field (F1) on the one hand and a cathode flow field (F2) on the other hand, wherein the flow output side of the anode flow field (F1) from this part of an anode exhaust gas flow input side into the cathode flow field (F2) is inserted into a cathode gas, characterized in that a End plates ( 11 ) arranged collecting anode channel ( 12 ) and a collection cathode channel ( 13 ) fluidly with each other via an opening ( 14 ), wherein in the region of the opening ( 14 ) at least one connection element ( 9 ), which controls the discharge of a part of the anode exhaust gas into the cathode gas. Fuel cell stack according to claim 13, characterized in that the opening ( 14 ) between the in one of the end plates ( 11 ) parallel juxtaposed collecting anode channel ( 12 ) and collection cathode channel ( 13 ) is arranged, wherein the Zuschaltelement ( 9 ) laterally on the collecting anode channel ( 12 ) or the collection cathode channel ( 13 ) in the relevant end plate ( 11 ) is arranged. Fuel cell stack according to claim 13 or 14, characterized in that the opening ( 14 ) between the parallel stacked collecting anode channel ( 12 ) and collection cathode channel ( 13 ) of two adjacent end plates ( 11 ) is arranged, wherein the Zuschaltelement ( 9 ) head or front side of the fuel cell stack ( 10 ) over the two end plates ( 11 ) extending is orders. Fuel cell stack according to claim 14, characterized in that the opening ( 14 ) as a through hole and / or slot in walls of the collecting anode channel ( 12 ) or the collecting cathode channel ( 13 ) is introduced.