Gas diffusion units, membrane electrode units, and components for fuel cells

Abstract

The present invention relates to a gas diffusion unit (1), a membrane electrode assembly (11), and an assembly (15) for a fuel cell. The gas diffusion unit includes a planar gas diffusion layer (3) disposed on a carrier substrate (4), wherein a sealing assembly (7) is provided on at least one main side (5, 6) of the carrier substrate (4), a connecting section (8) of the sealing assembly (7) corresponds to the surrounding edge (9) of the gas diffusion layer (3), the connecting section (8) forms a sealing protrusion, and the connecting section (8) fixes the gas diffusion layer (3) to the carrier substrate (4) in a material-fitting manner.

Description

Field of the invention

[0001] The invention relates to a gas diffusion unit for a fuel cell, comprising a gas diffusion layer arranged in a planar manner on a carrier substrate, wherein a sealing assembly is arranged on at least one main side of the carrier substrate, a connection section of the sealing assembly corresponding to a circumferential edge of the gas diffusion unit, the connection section forming a sealing ridge. Gas diffusion units of the type mentioned at the outset are not only used in fuel cells, but also in similar applications, for example in electrolysis cells or redox flow cells. BACKGROUND

[0002] Fuel cells generate electrical energy by oxidation of a fuel and are mostly composed of several electrically conductive electrodes arranged in a stack-like overlap, which are gas-permeable and separated from one another by ion-conducting membranes. The reaction media are supplied by means of bipolar plates provided with fluid channels, wherein a cooling medium can also be guided through the bipolar plates, which leads the reaction heat out. In this case, in order to divert the reaction media and the cooling medium purposefully, a distribution structure and channels need to be sealed.

[0003] EP 1 320 142 B1 proposes, for example, the use of a sealing element arranged between two bipolar plates, which seals the bipolar plates and the gas diffusion layers comprising membranes arranged between the bipolar plates, so that the reaction media contact one another through the membranes and the cooling medium flows in a dedicated channel.

[0004] A stack element of a fuel cell usually comprises two bipolar plates between which a membrane electrode assembly is arranged. The membrane electrode assembly in turn comprises two gas diffusion layers between which a catalyst-coated membrane is arranged, or two gas diffusion electrodes between which a membrane is arranged. One fuel cell stack can comprise more than 200 assemblies, each comprising two bipolar plates and one membrane electrode assembly. In this case, in order to achieve high performance, the components of the assemblies need to be mounted in a positionally correct manner relative to one another, wherein leakage of the reaction media should be avoided. The reaction media should only react with one another in the region of the gas diffusion layers and in the region of the catalyst-coated membrane.

[0005] The object of the invention is to further develop the assembly in order to simplify the mounting.

[0006] The solution according to the invention to achieve the above object is characterized in claims 1, 7 and 9. The claims back-referenced to the above claims relate to preferred embodiments.

[0007] The gas diffusion unit for a fuel cell according to the invention comprises a gas diffusion layer arranged in planar fashion on a carrier substrate, wherein a sealing assembly is arranged on at least one main side of the carrier substrate, a connection section of the sealing assembly corresponding to a circumferential edge of the gas diffusion layer, the connection section forming a sealing ridge, the connection section fixing the gas diffusion layer on the carrier substrate in a material-fit manner.

[0008] The carrier substrate is provided with a sealing assembly which is arranged on one or, preferably, both main sides of the carrier substrate. In this case, the sealing assembly enables sealing with respect to the bipolar plate. By arranging the sealing assembly on the carrier substrate, it is particularly easy to position the sealing assembly between the bipolar plates. In this case, for example, it is not necessary to apply a separately constructed sealing element to the bipolar plates by hand, which has hitherto been associated with a particularly high level of manual manufacturing effort. By arranging the sealing assembly on the carrier substrate, the sealing assembly is brought into correspondence with the bipolar plates in a form-stable and particularly easy-to-achieve positionally correct manner.

[0009] In the solution according to the invention, the gas diffusion layer is fixed on the carrier substrate in a material-fit manner. This is effected by the region of the sealing assembly which constitutes the connection section. The connection section forms a sealing ridge on the one hand, which can be used to achieve sealing with respect to an adjoining component, and on the other hand, the gas diffusion layer is connected to the carrier substrate by means of the connection section. In this way, the gas diffusion layer is connected to the carrier substrate in a loss-free and material-fit manner. In this case, it is particularly preferred that the gas diffusion layer is fixed on the carrier substrate in a positionally correct manner, so that it is particularly easy to install a membrane, for example a catalyst-coated polymer electrolyte membrane (CCM), in the assembly.

[0010] In order to manufacture the gas diffusion unit, a carrier substrate can be provided on which the gas diffusion layer is arranged. Subsequently, the sealing assembly is applied to the carrier substrate, wherein the sealing material forms a connection section in the edge region of the gas diffusion layer, by means of which the gas diffusion layer is joined to the carrier substrate in a material-fit manner. In this case, the sealing material is preferably shaped in such a way that at least one sealing ridge is formed.

[0011] The carrier substrate is preferably constructed as a thin film, wherein through-holes are provided in the thin film. Due to the construction as a thin film, the carrier substrate is particularly thin. By means of the through-holes, it is possible to transport reaction media and cooling media unhindered through the carrier substrate. In particular, the through-holes are provided in the region of the carrier substrate in which the gas diffusion layer is arranged. In this way, it is possible to transport reaction media unhindered towards the membrane.

[0012] Preferably, a sealing assembly is arranged on both main sides of the carrier substrate. In this technical solution, only a single carrier substrate is required between two bipolar plates. On both main sides of the carrier substrate, a sealing assembly is provided, which sealing assembly is respectively applied against an adjoining bipolar plate.

[0013] The sealing assembly can have a sealing ridge, which surrounds the through-hole and / or corresponds to the edge of the carrier substrate. The reaction medium is guided through the first through-hole and the cooling medium is guided through the second through-hole. Due to the sealing ridge, which surrounds the through-hole, a leakage can be avoided. The sealing assembly, which corresponds to the edge of the carrier substrate, seals the assembly comprising the two bipolar plates in the edge region.

[0014] The carrier substrate can consist of a thermoplastic. A material which is advantageous for the carrier substrate is polyethylene naphthalate (PEN). PEN is a thermoplastic from the polyester series, which is prepared by polycondensation. PEN has a high gas tightness, a high resistance to heat deformation, a high chemical resistance and a resistance to hydrolysis. Accordingly, PEN is particularly suitable for use in fuel cells.

[0015] The sealing assembly preferably consists of an injection-moldable elastomer material. In this technical solution, the sealing assembly can be applied, for example, in an injection-molding process. In particular, the sealing material can be selected from the group consisting of polyolefin elastomers, fluoroelastomers and silicone elastomers.

[0016] The membrane electrode unit for a fuel cell according to the application comprises a gas diffusion unit according to the application, a further gas diffusion layer and a catalyst-coated membrane, which is arranged between the gas diffusion unit and the further gas diffusion layer, wherein the further gas diffusion layer is provided with a further sealing ridge along the circumferential edge, the catalyst-coated membrane is arranged between the gas diffusion unit and the further gas diffusion layer, and the sealing ridge of the connection section and the further sealing ridge of the gas diffusion layer are sealingly applied against the membrane.

[0017] For the production of the membrane electrode unit, a gas diffusion unit comprising a carrier substrate and a gas diffusion layer is provided, wherein the gas diffusion layer is joined to the carrier substrate in a material-fit manner. The catalyst-coated membrane is arranged on the gas diffusion layer such that the connecting section adhesively seals against the edge of the catalyst-coated membrane. A further gas diffusion layer covers the catalyst-coated membrane, wherein the further gas diffusion layer has a further sealing ridge which likewise adhesively seals against the catalyst-coated membrane and seals the membrane in the region of the edge on the side opposite the gas diffusion unit. Due to the gas diffusion layer of the gas diffusion unit being fixed on the carrier substrate, the production of the membrane electrode unit is particularly simple. In particular, it is not necessary to fix the catalyst-coated membrane in the membrane electrode unit. By means of the sealing ridges of the two gas diffusion layers, the membrane is fixed in the region of the edge in a sealed and positionally correct manner. In this regard, it is also not necessary to join the catalyst-coated membrane to one or both gas diffusion layers in a material-fit manner. It is possible to merely place the catalyst-coated membrane loosely between the gas diffusion layers.

[0018] Preferably, the gas diffusion layer and the further gas diffusion layer have a matrix composed of a fiber-containing material. The fiber-containing material is, for example, a fabric, paper and a nonwoven fabric. The use of a nonwoven fabric is preferred here, since it is inexpensive to produce and has a high permeability for the reaction medium. In addition, the nonwoven fabric can be electrically conductive.

[0019] The assembly for a fuel cell according to the application comprises the membrane electrode unit according to the application, which is arranged between two bipolar plates, wherein the bipolar plates have a distribution structure in the region corresponding to the gas diffusion layers and channels for the transport of the medium are provided in the bipolar plates.

[0020] Preferably, a sealing assembly is arranged on both main sides of the carrier substrate, which adhesively seals against the bipolar plates in order to seal the channels. In this regard, the carrier substrate is sealed between the bipolar plates by means of the sealing assemblies arranged on both main sides and leakage of the reaction medium or the cooling medium is prevented. BRIEF DESCRIPTION OF DRAWINGS

[0021] Some technical solutions of the gas diffusion unit, the membrane electrode unit and the assembly according to the application will be explained in detail below with reference to the drawings. In this regard:

[0022] Figure 1 schematic top view of a gas diffusion unit comprising a carrier substrate;

[0023] Figure 2 schematic view of a further gas diffusion layer;

[0024] Figure 3 schematic sectional view of a membrane electrode unit;

[0025] Figure 4 is a schematic exploded view of an assembly comprising a bipolar plate and a membrane electrode unit. DETAILED DESCRIPTION

[0026] Figure 1 is a top view of a gas diffusion unit 1 for a fuel cell. The gas diffusion unit 1 comprises a gas diffusion layer 3 in the form of a flat sheet which is made of an electrically conductive nonwoven fabric. The gas diffusion layer 3 is arranged on a carrier substrate 4. The carrier substrate 4 is constructed as a thin film and in the present technical solution is made of polyethylene naphthalate (PEN). Through-holes 10 are provided in the thin film.

[0027] On both main sides 5, 6 of the carrier substrate 4, a sealing assembly 7 is respectively arranged. In this case, the sealing assembly 7 constitutes a connection section 8 on one main side 5, wherein the connection section corresponds to a circumferential edge 9 of the gas diffusion layer 3. In this way, the connection section 8 constitutes a sealing bead and fixes the gas diffusion layer 3 on the carrier substrate 4 in a material-fit manner.

[0028] The carrier substrate 4 has through-holes 10 which correspond to the gas diffusion layer 3 and serve for the transport of a transport medium through the gas diffusion layer 3. The carrier substrate 4 has further through-holes 10 which serve for the transport of a cooling medium through the carrier substrate 4. The sealing assembly 7 has a sealing bead which surrounds the through-holes 10. A further sealing bead corresponds to an edge of the carrier substrate 4. The sealing assembly 7 is made of an injection-moldable elastomer material. In this technical solution, the sealing assembly 7 is made of a polyolefin elastomer.

[0029] Figure 2 A further gas diffusion layer 12 is shown. The further gas diffusion layer 12 is made of an electrically conductive nonwoven fabric in the form of a flat sheet and is provided with a further sealing bead 14 along the circumferential edge 9.

[0030] Figure 3 A membrane electrode unit 11 for a fuel cell is shown which comprises a gas diffusion unit 1 as shown in Figure 1 and a further gas diffusion layer 12 as shown in Figure 2 Between the gas diffusion unit 1 and the further gas diffusion layer 12, a catalyst-coated membrane 13 is arranged. The sealing bead of the connection section 8 of the sealing assembly 7 of the gas diffusion unit 1 and the further sealing bead 14 of the further gas diffusion layer 12 sealingly abut on the catalyst-coated membrane 13. In this case, the catalyst-coated membrane 13 is held only in a force-fit manner between the gas diffusion unit 1 and the gas diffusion layer 12.

[0031] Figure 4 An assembly 15 for a fuel cell is shown. The assembly 15 comprises a gas diffusion unit 1 as shown in Figure 3The membrane electrode unit 11 shown is arranged between two bipolar plates 16, 17. The bipolar plates 16, 17 are made of a graphite-containing material in planar form. As an alternative, the bipolar plates 16, 17 can also be made of a metallic material. The bipolar plates 16, 17 have distribution structures for distributing the reaction medium in the regions corresponding to the gas diffusion layers 3, 12. Furthermore, channels 18 for the transport of reaction medium and cooling medium are provided in the bipolar plates 16, 17.

[0032] The sealing assemblies 7 arranged on the two main sides 5, 6 of the carrier substrate 4 are applied against the bipolar plates 16, 17 in order to seal the channels 18.

Claims

1. A membrane electrode unit (11) for a fuel cell, comprising a gas diffusion unit (1) comprising a gas diffusion layer (3) in the form of a plane arranged on a carrier substrate (4), wherein On at least one main side (5, 6) of the carrier substrate (4) there is provided a sealing assembly (7), a connecting section (8) of the sealing assembly (7) corresponding to a circumferential edge (9) of the gas diffusion layer (3), the connecting section (8) forming a sealing ridge, the connecting section (8) fixing the gas diffusion layer (3) on the carrier substrate (4) in a material-fit manner; and a further gas diffusion layer (12) and a catalyst-coated membrane (13) arranged between the gas diffusion unit (1) and the further gas diffusion layer (12), wherein the further gas diffusion layer (12) is provided with a further sealing ridge (14) along the circumferential edge (9), characterized in that the sealing ridge of the connecting section (8) and the further sealing ridge (14) sealingly abut on the catalyst-coated membrane (13).

2. The membrane electrode unit according to claim 1, characterized in that The carrier substrate (4) is constructed as a thin film, wherein through-holes (10) are provided in the thin film.

3. The membrane electrode unit of claim 1, wherein, On both main sides (5, 6) of the carrier substrate (4) there is arranged a sealing assembly (7).

4. The membrane electrode unit of claim 2, wherein, On both main sides (5, 6) of the carrier substrate (4) there is arranged a sealing assembly (7).

5. The membrane electrode unit of claim 3, wherein, The sealing assembly (7) has a sealing ridge, which surrounds the through-holes (10) and / or corresponds to the edge of the carrier substrate (4).

6. The membrane electrode unit according to any one of claims 1 to 5, characterized in that, The carrier substrate (4) is made of a thermoplastic material.

7. The membrane electrode unit according to any one of claims 1 to 5, characterized in that, The sealing assembly (7) is made of an injection-moldable elastomer material.

8. The membrane electrode unit according to any one of claims 1 to 5, characterized in that, The gas diffusion layer (3, 12) has a matrix made of a fiber-containing material.

9. An assembly (15) for a fuel cell, the assembly comprising a membrane electrode unit (11) as claimed in any one of claims 1 to 8, the membrane electrode unit being arranged between two bipolar plates (16, 17), wherein, The bipolar plate (16, 17) has a distribution structure in the region corresponding to the gas diffusion layer (3, 12), and channels (18) for transport are provided in the bipolar plate (16, 17).

10. The assembly of claim 9, wherein, On both main sides (5, 6) of the carrier substrate (4) there is arranged a sealing assembly (7), which abuts on the bipolar plate (16, 17) in order to seal the channels (18). On both main sides (5, 6) of the carrier substrate (4) there is arranged a sealing assembly (7), which abuts on the bipolar plate (16, 17) in order to seal the channels (18).

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