METHOD FOR MANUFACTURING A MEMBRANE ELECTRODE ASSEMBLY (MEA) FOR A FUEL CELL WITH CATALYST-FREE EDGE TO THE FRAME; MEA AND FUEL CELL WITH MEA

Abstract

The invention relates to a method for manufacturing a membrane electrode assembly for a fuel cell, which membrane electrode assembly comprises a membrane (2) with a catalyst layer (3) and a frame (6) arranged on the same side of the membrane (2) and a gap (5) between the catalyst layer (3) and the frame (6). To allow an easy and cost-effective way for manufacturing such a membrane assembly, the manufacturing method comprises the following steps: • - Positioning a first decal layer (10, 13), which is made of the same material as the first catalyst layer (3), on the first side of the membrane (2) in a way that the first decal layer (10, 13) overlaps the frame (6), • - positioning a second decal layer (10, 14), which is made of the same material as the second catalyst layer (4), on the second side of the membrane (2), • - pressing the first decal layer (10, 13) and the second decal layer (10, 14) against each other with the membrane (2) and the frame (6) positioned in-between.

Claims

1. A method for manufacturing a membrane assembly for a fuel cell, which membrane assembly comprises: a membrane with a first side and a second side, a first catalyst layer arranged on the first side of the membrane and a second catalyst layer arranged on the second side of the membrane, a frame arranged at least on the first side of the membrane, wherein the frame encircles the first catalyst layer in a plane of the main extension direction of the first catalyst layer, and a gap between the first catalyst layer and the frame, characterized by the following steps: positioning a first decal layer, which is made of the same material as the first catalyst layer, on the first side of the membrane relative to the frame, which is positioned on the first side of the membrane, in a way that the first decal layer overlaps the frame, positioning a second decal layer, which is made of the same material as the second catalyst layer, on the second side of the membrane, pressing the first decal layer and the second decal layer against each other with the membrane and the frame positioned in-between.

2. The method according to claim 1, wherein the positioning of the second decal layer is carried out in a way that the second decal layer overlaps a projection of the frame into a plane of the second decal layer.

3. The method according to claim 1, wherein the pressing is carried out with two pressing surfaces both overlapping the frame.

4. The method according to claim 1, wherein prior to the positioning of the first decal layer and the second decal layer the frame is arranged on the membrane by a separate pressing procedure.

5. The method according to claim 1, wherein prior to the positioning of the first decal layer and the second decal layer the frame is positioned on the membrane to be fixed to the membrane in the following step of pressing the first decal layer and the second decal layer against each other.

6. The method according to claim 1, wherein a thickness of the frame is varied for adjusting the width of the gap.

7. A membrane assembly for a fuel cell, comprising a membrane with a first side and a second side, a first catalyst layer arranged on the first side of the membrane and a second catalyst layer arranged on the second side of the membrane, a frame arranged on least to the first side of the membrane, wherein the frame encircles the first catalyst layer in the plane of the main extension direction of the catalyst layer, and a gap between the first catalyst layer and the frame, wherein the first catalyst layer is formed from a first decal layer made of the same material as the first catalyst layer by decal transfer and the second catalyst layer is formed from a second decal layer made of the same material as the second catalyst layer by decal transfer, and the gap between the first catalyst layer and the frame is formed by the decal transfer by pressing the first decal layer overlapping the frame and the second decal layer against each other with the membrane and the frame in-between.

8. The membrane assembly according to claim 7, wherein the first catalyst layer and the second catalyst layer form an electrode each.

9. The membrane assembly according to claim 7, wherein the first catalyst layer and the second catalyst are at least substantially fully overlapping with respect to their extension parallel to the membrane.

10. A fuel cell with at least one membrane assembly according to claim 7.

11. The method according to claim 2, wherein the pressing is carried out with two pressing surfaces both overlapping the frame.

12. The method according to claim 2, wherein prior to the positioning of the first decal layer and the second decal layer the frame is positioned on the membrane to be fixed to the membrane in the following step of pressing the first decal layer and the second decal layer against each other.

13. The method according to claim 3, wherein prior to the positioning of the first decal layer and the second decal layer the frame is positioned on the membrane to be fixed to the membrane in the following step of pressing the first decal layer and the second decal layer against each other.

14. The membrane assembly according to claim 8, wherein the first catalyst layer and the second catalyst are at least substantially fully overlapping with respect to their extension parallel to the membrane.

15. A fuel cell with at least one membrane assembly according to claim 8.

16. A fuel cell with at least one membrane assembly according to claim 9.

17. The method according to claim 2, wherein a thickness of the frame is varied for adjusting the width of the gap.

18. The method according to claim 3, wherein a thickness of the frame is varied for adjusting the width of the gap.

19. The method according to claim 4, wherein a thickness of the frame is varied for adjusting the width of the gap.

20. The method according to claim 5, wherein a thickness of the frame is varied for adjusting the width of the gap.

Description

[0040] The drawings show in:

[0041] FIG. 1 a schematic cross-section of an excerpt of a membrane assembly with additional gas diffusion layers;

[0042] FIG. 2 exemplary steps for manufacturing the membrane assembly with one pressing procedure;

[0043] FIG. 3 a method for manufacturing the membrane assembly with two separate pressing procedures;

[0044] FIG. 4 a technical apparatus for performing the manufacturing method with two pressing steps; and

[0045] FIG. 5 a schematic representation of a prototype of the membrane assembly in a cross section.

[0046] In the figures the same elements or elements having the same function are indicated by the same reference signs.

[0047] FIG. 1 shows a membrane assembly 1 comprising a membrane 2, a frame 6 arranged on the membrane 2 and catalyst layers 3, 4 on both sides of the membrane too. On both sides the membrane assembly 1 is coated is with a gas diffusion layer 8, 9. The respective gas diffusion layers 8, 9 can be either considered a part of the membrane assembly 1 or not part of the membrane assembly 1.

[0048] The membrane 2, which can also referred to as electrolyte, has a first side 18 and a second side 19. The membrane 2 can permeable or semi-permeable to enable an exchange of ions and/or molecules between the first side 18 and the second side 19. A first catalyst layer 3 is arranged on the first side 18 of the membrane 2. A second catalyst layer 4 is arranged on the second side 19 of the membrane 2. The frame 6 is arranged on the first side 18 of the membrane 2. The first catalyst layer 3 and the second catalyst layer 4 can be formed as electrodes. In other words, the catalyst layers 3, 4 can be configured to conduct an electrical current. The catalyst layers 3, 4 can be made of different or the same material. Both catalyst layers 3, 4 can be configured to catalyze a conversion from a fuel into electrical energy. For example, fuel and ambient air or oxygen can be converted to energy and exhaust gases by the catalyst layers 3, 4. When arranged in a fuel cell, the membrane assembly 1 can be arranged to carry out the conversion. The fuel cell can comprise one or more membrane assemblies 1 and a housing (not shown in the figures).

[0049] Catalytic reactions in and around the first catalyst layer 3 can lead to degradation processes at the frame 6. This may happen especially when the first catalyst layer 3 and the frame 6 face each other directly. In other words, the degradation especially occurs where the first catalyst layer 3 and the frame 6 touch each other or are at least very close to each other. The degradation can be a chemical degradation which is caused by a local open circuit voltage type condition in this area. The open circuit voltage type degradation occurs when hydrogen peroxide and associated radicals are formed by either hydrogen diffusing the membrane 2 and reacting with oxygen at the cathode or oxygen diffusing through the membrane 2 and reacting with hydrogen at the anode. This degradation pathway is turned off when there is no catalyst layer 3, 4 present in this area. Hence, there is a gap 5 between the frame 6 and the first catalyst layer 3. In other embodiments not shown in the figures, the frame 6 may be arranged on both sides 18, 19 of the membrane 2. For example, the frame 6 may consist of at least two parts, where a first part is arranged on the first side 18 and a second part is arranged on the second side 19. It is also possible that the frame 6 unfolds a match of the membrane 2 and therefore touches both sides 18, 19 of the membrane 2. If this is the case, the above-mentioned is also valid for the second catalyst layer 4 and the frame 6. Anyway, there is an additional gap 12 between the second catalyst layer 4 and a projection of the frame 6 into a plane of the second catalyst layer 4. In the present case, there is an additional catalyst layer 11 in the area of the projection of the frame 6 into the plane of the second catalyst layer 4.

[0050] A first gas diffusion layer 8 covers the first catalyst layer 3, the gap 5 and the frame 6. The region of a thought triangle above the gap 5 is also referred to as triangle region 7. In other words, all arrangements on the first side 18 are fully covered with the gas diffusion layer 8. In case there would be no gap 5, the triangle region would be located between the first catalyst layer 3, the first gas diffusion layer 8 and the frame 6. A second gas diffusion layer 9 is arranged on the second catalyst layer 4 and the additional catalyst layer 11. The second catalyst layer 9 also covers the additional gap 12. Analogously, the gap 5 is covered by the first gas diffusion layer 8.

[0051] Now referring to FIG. 2, a first possibility for manufacturing the membrane assembly 1 is shown. In a first step S1.1 of the exemplary method, the membrane 2, the frame 6, a first decal layer 13 and a second decal layer 14 are positioned relative to each other. More precisely, the second decal layer 14 is positioned on the second side 19 of the membrane 2. The frame 6 is positioned on the first side 18 of the membrane 2. The first decal layer 13 is also positioned on the first side 18 of the membrane 2. The position of the first decal layer 13 is carried out in a way that it overlaps the frame 6. In other words, the frame 6 is positioned between the membrane 2 and the first decal layer 13. Hence, the frame 6 touches the first side 18 of the membrane 2 with its first side and the frame 6 touches the first decal layer 13 with its second side. The first side and the second side of the frame 6 can be at least substantially parallel to each other. Both decal layers 13, 14 are arranged on a respective backer 10. The backer 10 or substrate makes a handling of the respective decals 13, 14 easier. In other words, the backer 10 facilitates the handling of the decal layers 13, 14. In a following step S1.2, the whole arrangement of decal layers 13, 14, membrane 2 and frame 6 is pressed in a pressing procedure 20. By the pressing procedure 20 the frame 6 gets firmly connected to the membrane 2. Also parts of the decal layers 13, 14 are getting firmly connected to the membrane 2. In particular, the first decal layer 13 gets partly attached to the first side 18 of the membrane 2. The part of the first decal layer 13 which gets attached to the membrane 2 forms the first catalyst layer 3. In particular, the second decal layer 14 gets partly attached to the second side 19 of the membrane 2. The part of the second decal layer 14 which gets attached to the membrane 2 forms the second catalyst layer 4. This can be seen in step 1.3.

[0052] Therefore, the first decal layer 13 is made of the same material as the first catalyst layer 3. Analogously, the second decal layer 14 is made of the same material as the second catalyst layer 4. If both catalyst layers 3, 4 consist of the same material, both decal layers 13, 14 may be equal.

[0053] In the step S1.2 due to the presence of the frame 6 in the triangle region 7, less pressure is applied compared to the region where the respective catalyst layers 3, 4 are formed. Of course, a relatively high pressure is also applied where the frame 6 is. Because there the first decal layer 13 does not connect properly to the frame 6, the decal layer remains on the backer 10, where the frame 6 and the first decal layer 13 face without. On the second side 19 of the membrane 2 the decal layer also gets attached to the membrane 2 opposite the frame 6. This leads to the formation of the additional catalyst layer 11. This additional catalyst layer 11 is not necessary for the function but does not any harm to the fuel cell or the membrane assembly 1. Due to the lower pressure during the pressing procedure 20, neither the first decal layer 13 nor the second decal layer 14 are getting attached to the membrane 2 in the area of the gap 5 and the additional gap 12. This is the desired effect of the present manufacturing method.

[0054] In another possible manufacturing method two pressing procedures 21, 24 are envisaged in opposite to the single pressing procedure 20. A step by step diagram is shown in FIG. 3. In a first step S2.1, the frame 6 gets positioned on the membrane 2 and pressed in a first separate pressing procedure 21. During the first separate pressing procedure 21, the frame 6 gets attached to the first side 18 of the membrane 2. During the first pressing procedure 21, the membrane 2 can be attached to a backer 30 or substrate. Analogously to the backer 10 of the decal layers 13, 14, the backer 30 can facilitate the handling of the membrane 2. After the first pressing procedure 21, the backer 30 gets removed from the membrane 2. This can happen in a step S2.2. In a following step S2.3, both decal layers 13, 14 are positioned on the membrane 2. This step can be understood analogously to step S1.1, as the decal layers 13, 14 have to be positioned relative to the membrane 2 and the frame 6 the same way. In particular, the first decal layer 13 is positioned on the first side 18 of the membrane 2 in a way that the first decal layer 13 overlaps the frame 6. In particular, the second decal layer 14 is positioned on the second side 19 of the membrane 2. Advantageously, the second decal layer 14 is positioned in a way that the decal layer 14 overlaps the projection of the frame 6 into a plane of the second decal layer 14.

[0055] In a step S2.4, a second pressing procedure 24 is carried out. By that pressing procedure 24, the first catalyst layer 3 and the second catalyst layer 4 are formed. In a step S2.5, the pressure is removed and the backers 10 are removed. The result is literally the same as described above according to the steps S1.2 and S1.3. Pressing surfaces 22 and 23 used for the respective pressing procedures 21 and 24 can be the same or different. The pressing surfaces 22 and/or 23 may be part of a hot press or a respective hot press. Hence, the pressing procedures 21 and 24 can be hot pressing procedures. Analogously, the pressing procedure 20 can be a hot pressing procedure.

[0056] FIG. 4 shows an example for an apparatus to perform the manufacturing method according to FIG. 3. The pressing surfaces 22 can be provided by rollers 25, each. Analogously, the pressing surfaces 23 can be provided by respective rollers 26. The apparatus should briefly be described in the following:

[0057] The membrane 2 and its backer 30 and together with the frame 6 get into the rollers 25. The rollers 25 are performing the first pressing procedure 21. Due to the continuous process in which the membrane 2 moves to the right according to FIG. 1, the rollers 25 provide a singular effect like the plane pressing surfaces 22. After the first pressing procedures 21 in-between the two rollers 25, the backer 30 is removed from the membrane 2. The result is a framed membrane 16 as an intermediate product. For the second pressing procedure 24 realized by the rollers 26, both decal layers 13, 14 are provided on their respective backer on the respective side of the membrane or the framed membrane 16, respectively. So just before the rollers 26, the step S2.3 is carried out. In-between the rollers 26, the step S2.4 or the second pressing procedure 24 is carried out. When leaving the rollers 26, both backers 10 are removed. That equals the step S2.5. The result is the endless role of membrane assemblies 17.

[0058] Finally, FIG. 5 shows a cross section of an excerpt of the membrane assembly 1. FIG. 5 is a drawing of a prototype manufactured with the present manufacturing method according to FIG. 2 or FIG. 3. In FIG. 5 can be seen that both catalyst layers 3 and 4 are aligned to each other very well. The difference of size and/or alignment d1 was approximately 10 .Math.m. In other words, bot catalyst layers 3, 4 are positioned opposite to each other within the neglectable tolerance of 10 .Math.m. A width d2 of the gap 5 equals 500 .Math.m in the prototypes. It should be mentioned that the give measures for d1 and the width d2 are only exemplary. Nevertheless, both measures have proven to be useful in practical examples.

TABLE-US-00001 Reference signs 1 membrane assembly 2 membrane 3 first catalyst layer 4 second catalyst layer 5 gap 6 frame 7 triangle region 8 first diffusion layer 9 second diffusion layer 10 backer 11 additional catalyst layer 12 additional gap 13 first decal layer 14 second decal layer 16 framed membrane 17 membrane assemblies 18 first side 19 second side 20 pressing procedure 21 pressing procedure 22 pressing surfaces 23 pressing surfaces 24 pressing procedure 25 rollers 26 rollers 30 backer S1.1...S1.3 steps S2.1...S2.5 steps