METHOD FOR PRODUCING A MEMBRANE-ELECTRODE ASSEMBLY AND MEMBRANE-ELECTRODE ASSEMBLY

Abstract

The invention relates to a method for producing a membrane electrode assembly (10) for a fuel cell, comprising the following steps in the order given: provide two gas diffusion layers (13) that each have a catalytically coated surface; apply an ionomer dispersion (15a) onto the coated surface of at least one of the gas diffusion electrodes (13), arrange the gas diffusion layers (13) on each other such that the coated surfaces face each other, and a layer stack (18) comprising a gas diffusion layer (13)-catalytic coating (14)-ionomer coating (15)-catalytic coating (14)-gas diffusion layer (13) arises, and arrange a peripheral seal (17) around the layer stack (18), wherein the seal (17) has a height that at least corresponds to the height of the layer stack (18).

Furthermore, the invention relates to a membrane electrode assembly (10) that is or can be produced by means of the method according to the invention.

Claims

1. A method for producing a membrane electrode assembly for a fuel cell, comprising: providing two gas diffusion layers that each have a catalytically coated surface; forming an ionomer coating by applying an ionomer dispersion onto the catalytically coated surface of at least one of the gas diffusion layers; arranging the gas diffusion layers adjacent to each other such that the catalytically coated surfaces of the gas diffusion layers face each other to produce a layer stack comprising the gas diffusion layers, catalytic coatings on the gas diffusion layers, and the ionomer coating; and arranging a peripheral seal around the layer stack, wherein the seal has a height that at least corresponds to the height of the layer stack.

2. The method according to claim 1, wherein the peripheral seal is an injection-molded seal.

3. The method according to claim 1, wherein the ionomer dispersion is applied by an inkjet method onto the gas diffusion layer.

4. The method according to claim 1, wherein a respective ionomer dispersion is applied onto the catalytically coated surfaces of both gas diffusion layers.

5. The method according to claim 1, wherein an ionomer layer is formed between the catalytic coatings and is in contact with the catalytic coatings of both gas diffusion layers, and wherein the ionomer layer comprises the ionomer coating of one of the gas diffusion layers, or ionomer coatings on both gas diffusion layers.

6. The method according to claim 5, wherein the ionomer layer is in contact with the catalytic coatings of both gas diffusion layers over the entire surfaces of the catalytic coatings.

7. The method according to claim 1, wherein the ionomer dispersion comprises a polymer electrolyte.

8. A membrane electrode assembly produced or producible by a method comprising: providing two gas diffusion layers that each have a catalytically coated surface; applying an ionomer dispersion onto the catalytically coated surface of at least one of the gas diffusion layers to produce an ionomer coating; arranging the gas diffusion layers adjacent to each other such that the catalytically coated surfaces of the gas diffusion layers face each other to produce a layer stack comprising the gas diffusion layers, catalytic coatings on the gas diffusion layers, and the ionomer coating; and arranging a peripheral seal around the layer stack, wherein the seal has a height that at least corresponds to the height of the layer stack.

9. A membrane electrode assembly comprising: two gas diffusion layers, wherein each of the two gas diffusion layers has a surface coated with a catalytic material to form a catalytic coating, and an ionomer coating on the catalytic coating of at least one of the gas diffusion layers to form an ionomer layer, wherein the two gas diffusion layers with the catalytically coated surfaces are arranged to face each other and are separated from each other by the ionomer layer, the ionomer layer being in contact with the catalytic coatings of both gas diffusion layers.

10. A fuel cell having a membrane electrode assembly, the membrane electrode assembly comprising: a layer stack including: two gas diffusion layers that each have a catalytically coated surface; an ionomer coating on at least one of the catalytic coated surfaces of the gas diffusion layers, wherein the gas diffusion layers are positioned adjacent to each other such that the catalytic coated surfaces of the gas diffusion layer face each other; and a peripheral seal around the layer stack, wherein the seal has a height that at least corresponds to the height of the layer stack.

11. The membrane electrode assembly according to claim 8, comprising forming an ionomer layer between the catalytic coatings which is in contact with the catalytic coatings of both gas diffusion layers.

12. The membrane electrode assembly according to claim 9, wherein the ionomer layer is in contact with the catalytic coatings of both gas diffusion layers over entire surfaces of the catalytic coatings.

13. The fuel cell according to claim 10, wherein the ionomer coating forms an ionomer layer which is in contact with the catalytic coatings of both gas diffusion layers over entire surfaces of the catalytic coatings.

Description

[0022] The invention is explained below in exemplary embodiments in reference to the associated drawings. The following is shown:

[0023] FIG. 1 a schematic representation of the cross-section of a fuel cell according to the prior art,

[0024] FIG. 2 a schematic representation of a cross-section of a fuel cell according to a preferred embodiment of the invention, and

[0025] FIG. 3 a schematic flow chart of a method for producing a membrane electrode assembly according to a preferred embodiment of the invention.

[0026] FIG. 1 shows a schematic representation of a cross-section of a fuel cell 1 according to the prior art. The fuel cell 1 according to the prior art comprises two bipolar plates 11 that have reactant flow channels 12 to conduct oxidant, or rather fuel. A membrane electrode assembly 10 according to the prior art is arranged between the two bipolar plates. The membrane electrode assembly 10 comprises two gas diffusion layers 13 that have a catalytic coating 14 on one of their surfaces. In the membrane electrode assembly 10 according to the prior art, the two catalytically coated gas diffusion layers 13 are arranged so that the coated surfaces face each other. An ionomer is arranged between the coated surfaces that separates the two gas diffusion electrodes from each other gas-tight. The ionomer is either designed as an ionomer coating 14 as shown in FIG. 1 that is applied to each catalytic coating of the two gas diffusion layers 13. To separate the gas compartments, a subgasket 16 is then provided that separates the two gas compartments from each other. Alternatively (not shown here), the ionomer is designed as an ionomer film that is arranged between the gas diffusion electrodes 19. In this version, the ionomer film is either designed significantly larger than the surface of the gas diffusion electrode 19, so that it projects beyond the two gas diffusion electrodes 19 in a layer stack consisting of a gas diffusion electrode 19 ionomer and gas diffusion electrode 19, or the ionomer film is encompassed in a support frame that then for its part projects beyond the gas diffusion electrodes 19. Depending on the embodiment, the protrusion serves to separate the gas compartments of the two gas diffusion electrodes 19.

[0027] The ionomer coating 14 of the two gas diffusion electrodes 19 of the fuel cell 1 shown in FIG. 1 does not contact each other in the membrane electrode assembly 10 according to the prior art, but is rather separated by the subgasket 16. A gap is created.

[0028] In contrast, FIG. 2 shows a cross-section of a fuel cell 1 according to the invention. The fuel cell 1 comprises two bipolar plates 11 that in turn have flow channels 12 to supply a membrane electrode assembly 10 with operating gases. The membrane electrode assembly 10 is arranged between the two bipolar plates 11 and comprises two gas diffusion electrodes 19 between which an ionomer layer 20 is arranged. The gas diffusion electrodes 19 each comprise a gas diffusion layer 13 as well as a catalytic coating 14 deposited on their surface. The ionomer layer 20 comprises at least one ionomer coating 15 that is deposited on a catalytic coating 14 of one of the gas diffusion electrodes 19. In the shown embodiment, the ionomer layer 20 comprises two ionomer coatings 15, wherein one is deposited on each of the gas diffusion electrodes 19. Deposition can occur for example by means of the method according to the invention, for example, which will be described in greater detail with reference to FIG. 3.

[0029] It can be seen in FIG. 2 that a fuel cell according to the invention does not have a gap between the gas diffusion electrodes 19. In particular, no macroscopic cavities or gaps arise between the layers of the layer stack 18 of a first gas diffusion electrode 13 with catalytic coating 14, an ionomer layer 20, and a second catalytic coating 14 that in turn is arranged on a second gas diffusion electrode 13. A material bond arises instead of a friction bond. This is in particular realized in that the fuel cell 1 according to the invention does not have a separating layer between the gas diffusion electrodes in the form of a subgasket, a membrane film or a membrane frame. Instead, a sealing material, 17 for example in the form of an injection-molded seal, is arranged between the bipolar plates 11, peripherally around the layer stack 18. This sealing material extends beyond the total height of the layer stack 18. The sealing material layer is arranged in an integrally bonded manner on the side edges of the layer stack 18 so that no operating gases can escape from the gas diffusion layers, and in particular cannot mix. This means that the peripheral seal 18 prevents an exchange of substances between the gas diffusion layers, in which it enables essentially no fluid-conducting connections between the gas diffusion layers. The sealing material 17 is a polymer seal, for example, in particular an elastomer or a thermoplastic elastomer. As further shown in FIG. 2 in comparison to the prior art the peripheral seal 17 according to the invention combines two seals, that each are arranged between a bipolar plate and the separating layer 16, with the separating layer into a single seal 17.

[0030] The membrane electrode assembly 10 according to the invention is designed as shown in FIG. 2, for example, such that the layer stack 18 in the membrane electrode assembly 10 has no or as few as possible macroscopic cavities, however in any case no gaps, that would reduce the proton conductivity or the current conductivity across the membrane electrode assembly.

[0031] Moreover, the combination of three sealing elements as used in the prior art into a single peripheral seal 17 as provided according to the invention is associated with fewer interfaces, and is accordingly not only easier to produce but also displays better sealing results.

[0032] FIG. 3 shows a schematic flow chart of a method according to the invention for producing a membrane electrode assembly 10 in a preferred embodiment. In a first step I in the flowchart, a gas diffusion electrode 19 is provided that comprises a gas diffusion layer 13 which has a catalytic coating 14 on one of its surfaces. A liquid ionomer dispersion 15a is applied thereupon. For example, this can be done by means of an inkjet printing method, spraying, brushing, rolling, doctoring or the like.

[0033] The dispersion comprises a polymer electrolyte, in particular Nafion, such as Nafion D2020. A mixture comprising water, alcohol, and ether can be used as the dispersant. For example a mixture comprising water, propanol, ethanol, and an ether mixture has proven to be advantageous. Positive results were able to be be generated with a dispersion that comprises approximately one part polymer electrolyte and two parts dispersant. Such a mixture is, for example, obtainable as DuPont's Nafion) D2020 dispersion from Ion Power, that comprises 21% by weight Nafion, 34% by weight water, 44% by weight 1-propanol, 1% by weight ethanol, and an ether mixture.

[0034] The application of an ion ionomer mixture 15a onto a gas diffusion electrode 19 is known from a review article in the Journal of Material Chemistry A, von Klingele et al., to which reference is hereby made or that is referenced.

[0035] In a second step II, a second gas diffusion electrode 19 also comprising a gas diffusion layer 13 and a catalytic coating 14, is arranged on the ionomer coating of the gas diffusion electrode 19.

[0036] The gas diffusion electrodes 19 are aligned relative to each other such that the catalytic surfaces face each other. The layer stack 18 shown in the third step III arises which comprises gas diffusion layer 13, catalytic coating 14, ionomer coating 15 or rather ionomer layer 20, another catalytic coating 14 arranged therein which is arranged on another gas diffusion layer 13. Optionally, an ionomer coating 15 can also be applied onto the second gas diffusion electrode 19 and is connected to the ionomer coating 15 of the first gas diffusion electrode 19, preferably over its entire surface, when forming the layer stack 18.

[0037] According to the invention, a sealing material 17a is arranged peripherally along a side edge of the layer stack 18, beyond the total height of said side edge. For example, the sealing material 17a is preferably a polymer, in particular an elastomer or a thermoplastic elastomer. The sealing material 17a is, for example, applied by means of injection molding to the layer stack. After the sealing material 17a cures, the membrane electrode assembly according to the invention as shown in step IV arises with a peripheral seal 17. The seal 17 has a height that at least corresponds to the height of the layer stack 18.

LIST OF REFERENCE SYMBOLS

[0038] 1 fuel cell [0039] 1 fuel cell according to the prior art [0040] 10 membrane electrode assembly [0041] 10 membrane electrode assembly according to the prior art [0042] 11 bipolar plate [0043] 12 reactant flow channel [0044] 13 gas diffusion layer [0045] 14 catalytic coating [0046] 15 ionomer coating [0047] 16 subgasket [0048] 17 seal [0049] 17a sealing material [0050] 18 layer stack [0051] 19 gas diffusion electrode (GDE) [0052] 20 ionomer layer