METHOD FOR ATTACHING A GASKET TO A BIPOLAR PLATE

Description

[0001] The present invention relates to a method for attaching a gasket to a bipolar plate and to a fuel cell manufactured according to such a method. State of the art

[0002] Fuel cells are electrochemical energy converters that convert, for example, hydrogen and oxygen into water, electrical energy, and heat. Fuel cells, or fuel cell stacks, are composed of multi-part cells that alternately feature membrane electrode units and bipolar plates. The bipolar plates supply the electrodes with reactants and cool the fuel cell stack. For this purpose, the bipolar plates have a distribution structure that guides reactant-containing fluids along the electrodes. Furthermore, the distribution structures also guide a cooling fluid along other distribution structures. These distribution structures are designed as channels, allowing the different fluids to flow freely.

[0003] From DE 10 2005 058 370 A1, a fuel cell is known which has two bipolar plates, wherein a membrane electrode assembly is arranged between the bipolar plates and a gas diffusion layer is arranged between the membrane electrode assembly and the bipolar plates. The membrane electrode assembly is arranged on a support frame. An ultrasonic weld connection is formed between the membrane electrode assembly and the support frame, via which the membrane electrode assembly is connected to the support frame.

[0004] It is also known from the prior art that the support frame is directly connected to the bipolar plate via an ultrasonic weld. Alternatively, a laser-welded connection can be used instead of ultrasonic welding. While these methods have the advantage of requiring no additional material, a rough surface is still necessary.

[0005] From DE 10 2017 101 958 A1 a method for attaching a separator to a sealing element of a fuel cell is further known, wherein the sealing element has an adhesive layer on both sides, and features arranged on the separator are joined to the adhesive layer during hot pressing.

[0006] The object of the present invention is to provide a method for attaching a gasket to a bipolar plate, in which the gasket can be connected to the bipolar plate in a simple and economical manner with little additional material.

[0007] To solve the problem, the method for attaching a gasket to a bipolar plate with the features of claim 1, as well as a fuel cell manufactured according to such a method, are specified. Advantageous embodiments of the invention can be found in the respective dependent claims. Disclosure of the invention

[0008] A method for attaching a gasket to a bipolar plate is proposed, comprising the steps of applying and aligning a first gasket film onto a second gasket film having connection recesses, joining the first gasket film to the second gasket film to form the gasket, and placing the gasket onto the bipolar plate so that the second gasket film with the connection recesses rests against the bipolar plate. In a further process step, an embossing step is carried out in which an embossing tool is used to apply an embossing force in the area of ​​the connection recesses, so that an embossed adhesive point is formed and the first gasket film is bonded to the bipolar plate via an adhesive placed in the connection recess on the first gasket film.

[0009] A connection recess, as defined in the present invention, is a breakthrough through the second gasket film that enables a connection. The adhesive point is the area where the first gasket film is connected to the bipolar plate. The embossing process connects the gasket to the bipolar plate only in the area of ​​the connection recesses. This connection is achieved through a simple embossing step. Additionally, an adhesive is only required in the area of ​​the connection recesses. Therefore, very little adhesive is needed to attach the gasket to the bipolar plate. Consequently, only a small amount of additional material is required. Furthermore, this method is simple and economical.

[0010] In a preferred embodiment of the invention, an adhesive is applied to at least the first gasket film before the first gasket film is joined to the second gasket film. The first and second gasket films are thus joined to each other via an adhesive bond. Adhesive is also present in the area of ​​the joining recess. The gasket is bonded to the bipolar plate via this adhesive. Therefore, no additional step is required to apply the adhesive. Since this adhesive is applied to join the first and second gasket films, no additional material is needed to bond the gasket to the bipolar plate. This makes such a process simple and economical.

[0011] In a further preferred embodiment of the invention, the adhesive is a UV adhesive, which is cured by means of a UV source. Preferably, at least the first gasket film is permeable to UV light, so that the adhesive can be cured with a UV source. This process step allows the gasket to be bonded to the bipolar plate at a specific time, thus still enabling positional correction. Furthermore, curing via UV light enables simple and controlled attachment.

[0012] Preferably, the adhesive is a hot-melt adhesive, allowing the gasket films to be bonded together via a lamination process. A hot-melt adhesive is an adhesive that becomes adhesive when exposed to heat. This process step makes it possible to easily bond the two gasket films together by heating. In the lamination process, the two gasket films are preferably bonded at a temperature of 100–200°C and a pressure of 0.5–5 MPa.

[0013] In a preferred further development, the embossing force is applied to the first gasket film. Alternatively, it is of course also possible to apply the embossing force to the bipolar plate. However, since the first gasket film is more flexible than the bipolar plate, this facilitates a bond between the bipolar plate and the first gasket film. Furthermore, it prevents damage to the distribution structure of the bipolar plate. Preferably, an embossing force in the range of 0.5–5 MPa is applied.

[0014] Advantageously, the embossing tool is heated during the embossing step, causing a hot-melt adhesive located in the connection recess to bond with the bipolar plate. This allows an adhesive bond between the bipolar plate and the first gasket film to be achieved simultaneously with the embossing step. This reduces the number of process steps. Preferably, the embossing tool is heated to a temperature of 100–200°C. A temperature of 130–170°C is particularly preferred.

[0015] Preferably, the hot melt adhesive is the adhesive that was applied to join the first gasket film to the second gasket film, so that no additional process step for applying the hot melt adhesive or additional hot melt adhesive is necessary.

[0016] Furthermore, a fuel cell for a fuel cell stack is proposed. The fuel cell comprises at least one bipolar plate and a gasket, the gasket comprising a first and second gasket film, the second gasket film having connection recesses and bearing against the bipolar plate, and the gasket being connected to the bipolar plate via embossed adhesive points formed in the area of ​​the connection recesses by means of an adhesive arranged in the connection recesses. The fuel cell is preferably manufactured according to the aforementioned method. Such a fuel cell exhibits essentially the advantages described in the method. In particular, such fuel cells exhibit a higher efficiency due to the precise positioning of the gasket and bipolar plate.

[0017] In a further advantageous embodiment, the adhesive points have a geometric shape in which one side of the adhesive point runs parallel to and is aligned with a transverse central axis of the bipolar plate. The geometric shape is understood to be the two-dimensional geometric form that results from the adhesive point when viewed from above on the bipolar plate. The adhesive point side is a side of the geometric shape that runs as a line. The transverse central axis is an axis that runs perpendicular to the bipolar plate and is located centrally to it. In addition to being parallel, this adhesive point side is positioned closer to the transverse central axis than the other sides of the adhesive point.

[0018] A peeling force directed longitudinally acts orthogonally across the entire adhesive side, thus distributing the peeling force more effectively across that side. This significantly improves the durability of the adhesive point.

[0019] In a practical embodiment, the adhesive points additionally feature an adhesive side that runs parallel to and is aligned with a longitudinal center axis. This longitudinal center axis runs parallel to the transverse center axis along the length of the bipolar plate and is located at its center. Since a peel force also occurs in the transverse direction, although it is less than the peel force in the longitudinal direction, the adhesive point's durability with respect to this transverse peel force is improved by having an additional adhesive side aligned parallel to the longitudinal center axis. This adhesive side is oriented towards a center point in the transverse direction of the bipolar plate.

[0020] Furthermore, a fuel cell stack comprising multiple fuel cells is proposed. Such a fuel cell stack offers the aforementioned advantages.

[0021] Exemplary embodiments of the invention are shown in the drawing and explained in more detail in the following description. It shows: Figure 1 Perspective view of the structure of a fuel cell according to the invention, Figure 2 Method steps for attaching the gasket to the bipolar plate, and Figure 3 Fuel cell with various embodiments of an adhesive point.

[0022] In Figure 1Figure 1 shows a perspective view of the structure of a fuel cell 1 according to the invention. The fuel cell 1 comprises at least one first gasket film 4a and one second gasket film 4b. The first gasket film 4a and the second gasket film 4b together form the gasket 4 of the fuel cell 1. These are stacked directly on top of each other, as shown in the figure. In contrast to the first gasket film 4a, the second gasket film 4b has four connecting recesses 8, which are arranged symmetrically on the second gasket film 4b. In this embodiment, these connecting recesses 8 are designed as round holes. The fuel cell 1 also has a bipolar plate 12 on which the gasket 4 rests. The bipolar plate 12 has a distribution structure, as is known, to guide the reactants along an electrode (not shown).

[0023] Figure 2Figure 2a shows the process steps for attaching the gasket 4 to the bipolar plate 12. This figure shows a section through a region of a connection recess 8. Partial Figure 2a shows that an adhesive 16 is arranged between the first and second gasket films 4a, 4b, by means of which the two gasket films 4a, 4b are joined together. In this embodiment, the adhesive 16 is a hot-melt adhesive, by means of which the two gasket films 4a, 4b are joined together by a lamination process. Due to the connection recess 8, the two gasket films 4a, 4b are not joined in this region. Partial Figure 2a shows the step before the gasket 4 is placed onto the bipolar plate 12.

[0024] Figure 2b shows the step in which an embossing step is performed using an embossing tool 20. In this step, the second gasket film 4b is in direct contact with the bipolar plate 12. The embossing tool 20 is positioned in the area of ​​the connection recess 8 and applies an embossing force to the first gasket film 4a. This brings the adhesive 16, which is arranged on the first gasket film 4a, into contact with the bipolar plate 12. In this embodiment, the embossing tool 20 is heated so that the first gasket film 4a bonds to the bipolar plate 12 via the adhesive 16, which is designed as a hot-melt adhesive.

[0025] The embossing process creates an embossed adhesive point 24, which is essentially determined by the shape of the connection recess 8 and the shape of the embossing tool 20. Partial figure 2c shows the corresponding part of the fuel cell 1 after the embossing tool 20 has been removed. It can be seen that the embossing tool 20 has formed a recess 28 in the first gasket sheet 4a. This recess 28 extends into the connection recess 8 of the second gasket sheet 4b. This further improves the mechanical connection between the two gasket sheets 4a and 4b.

[0026] Figure 3 shows a top view of a fuel cell manufactured in this way 1. In this figure, apart from the ones in Figure 1In addition to the round connecting recesses 8 shown, four further embodiments of connecting recesses 8 are depicted, shown with dashed lines. The connecting recesses 8 produced in this way create corresponding geometric shapes of adhesive points 24.

[0027] The adhesive point 24, depicted as a triangle in the upper right corner, has an adhesive side q that is parallel to a transverse central axis 32 of the fuel cell 1. This adhesive side q also points towards the transverse central axis 32. This applies a peeling force directed longitudinally towards the edges 36 of the fuel cell 1 to the adhesive side q, thus improving the durability of the adhesive point 24. The lower right and left adhesive points 24 show further possible geometric configurations that also offer these advantages.

[0028] In the upper left corner, an adhesive point 24 shaped like a rectangle is shown. In addition to the aforementioned adhesive point side q, this point has a further adhesive point side l, which is arranged parallel to and in addition to a longitudinal center axis 40. This further improves the durability of the adhesive point 24 with respect to a peeling force acting in the transverse direction. Reference symbol list

[0029] 1 Fuel cell 4 Gasket 4 First gasket sheet 4 Second gasket sheet 8 Connection recess 12 Bipolar plate 16 Adhesive 20 Embossing tool 24 Adhesive dot 28 Recess 32 Transverse center axis 36 Edge 40 Longitudinal center axis q Adhesive dot side l Adhesive dot side

Claims

1. Method for securing a gasket (4) to a bipolar plate (12), comprising the steps of: - applying and aligning a first gasket film (4a) to / with a second gasket film (4b) having connecting cutouts (8), - connecting the first gasket film (4a) to the second gasket film (4b), so that the gasket (4) is formed, - placing the gasket (4) onto the bipolar plate (12), so that the second gasket film (4b) with the connecting cutouts (8) bears against the bipolar plate (12), - carrying out an embossing step, in which an embossing force is applied in the region of the connecting cutouts (8) by an embossing tool (20), so that an embossed adhesive point (24) is formed and the first gasket film (4a) is connected to the bipolar plate (12) via an adhesive (16) arranged in the connecting cutout (8) on the first gasket film (4a).

2. Method according to Claim 1, characterized in that an adhesive (16) is applied to at least the first gasket film (4a) before the first gasket film (4a) is connected to the second gasket film (4b).

3. Method according to Claim 1 or 2, characterized in that the adhesive (16) is a UV adhesive, so that the UV adhesive is cured by means of a UV source.

4. Method according to Claim 2, characterized in that the adhesive (16) is a hot-melt adhesive, so that the gasket films (4a, 4b) are connected to each other by means of a laminating process.

5. Method according to any of the preceding claims, characterized in that the embossing force is applied to the first gasket film (4a).

6. Method according to any of the preceding claims, characterized in that the embossing tool (20) is heated up with the embossing step, so that a hot-melt adhesive arranged in the connecting cutout (8) is connected to the bipolar plate (12).

7. Fuel cell (1) for a fuel cell stack, wherein the fuel cell (1) has at least one bipolar plate (12) and a gasket (4), in which the gasket (4) comprises a first and a second gasket film (4a, 4b), wherein the second gasket film (4b) has connecting cutouts (8) and bears against the bipolar plate (12), and the gasket (4) is connected to the bipolar plate (12) via embossed adhesive points (24), which are formed in the region of the connecting cutouts (8), by means of adhesive (16) arranged in the connecting cutouts (8).

8. Fuel cell (1) according to Claim 7, characterized in that the adhesive points (24) have a geometric shape in which an adhesive point side (q) of the geometric shape runs parallel to a transverse centre axis (32) of the bipolar plate (1) and is aligned with this transverse centre axis (32).

9. Fuel cell (1) according to Claim 8, characterized in that the adhesive points (24) additionally have an adhesive point side (I), which runs parallel to a longitudinal centre axis (40) and is aligned with this longitudinal centre axis (40).

10. Fuel cell stack, which has a plurality of fuel cells (1) according to any of Claims 7 to 9.