Method for manufacturing a membrane electrode unit for an electrochemical cell

Abstract

The invention relates to a method for producing a membrane electrode unit (1) for an electrochemical cell (100), having the following method steps: - providing a membrane (2) coated with electrodes (3, 4), - providing a first film (11) and a second film (12), wherein at least one of the two films (11, 12) is provided with an adhesive (13), - laminating the membrane (2) coated with the electrodes (3, 4) between the two films (11, 12), wherein in a bonding region (23) the two films (11, 12) are bonded directly to one another by means of the adhesive (13), such that the two films (11, 12) form a frame structure (10) for the membrane electrode unit (1), - punching at least one media interface (30) out of the frame structure (10) and simultaneously fusing the two films (11, 12) on at least a partial periphery (33) of the media interface (30) in a connection region (15).

Description

Background Technology

[0001] A fuel cell is an electrochemical cell with two electrodes separated from each other by an electrolyte that conducts ions. Fuel cells directly convert the energy from the chemical reaction between fuel and oxidant into electrical energy. Different types of fuel cells exist.

[0002] One particular type of fuel cell is the polymer electrolyte membrane fuel cell (PEM-FC). In the active region of a PEM-FC, two porous electrodes with catalyst layers are adjacent to the polymer electrolyte membrane (PEM). Furthermore, the PEM-FC includes a gas diffusion layer (GDL) in the active region, which confines the polymer electrolyte membrane (PEM) and the two porous electrodes with catalyst layers on both sides. The PEM, the two electrodes with catalyst layers, and optionally two GDLs can form a so-called membrane electrode assembly (MEA) in the active region of the PEM-FC. Two opposing bipolar plates (half-sections) further confine the MEA on both sides. The fuel cell stack consists of alternating stacked MEAs and bipolar plates. Fuel, particularly hydrogen, is distributed through the anode plate of the bipolar plates, and oxidant, particularly air / oxygen, is distributed through the cathode plate of the bipolar plates. For electrical insulation between adjacent bipolar plates, for shape stability of the MEA, and to prevent unwanted leakage of fuel or oxidant, the MEA can be embedded in a frame-like opening between two adjacent membranes. Typically, the two films in this framework structure are made of the same material, such as polyethylene naphthalate (PEN). The two films made of the same material can have redundant properties that can be omitted, such as the electrical insulation capability (electrical insulation) and / or hydrogen tightness of each of the two films.

[0003] DE 101 40 684 A1 discloses a membrane electrode unit for a fuel cell, comprising a layer assembly consisting of an anode electrode, a cathode electrode and a membrane disposed therebetween, wherein a polymer material is applied to the upper and lower sides of the layer assembly.

[0004] DE 10 2018 131 092 A1 describes a membrane electrode unit with a frame structure. As known from DE 10 2020 213132 A1, the two films of the frame structure can be fused together at the connection region, thereby preventing the outward leakage of adhesive. Summary of the Invention

[0005] The objective of this invention is to manufacture membrane electrode units efficiently or at low cost.

[0006] The method for manufacturing a membrane electrode unit for an electrochemical cell includes the following steps: - Provides a film coated with electrodes, - Provide a first film and a second film, wherein at least one of the films is provided with an adhesive. - An electrode-coated film is laminated between two thin films, wherein the two thin films are directly bonded to each other in the bonding area by means of an adhesive, such that the two thin films constitute a frame structure for a membrane electrode unit. - At least one medium interface is stamped out from the frame structure, and the two films are simultaneously fused in the connection area on at least a portion of the periphery of the medium interface.

[0007] Therefore, the first and second films are simultaneously fused in the connection region, and the subsequent media interface is stamped out from the two films. This optimizes the manufacturing method; cycle time is reduced, and the number of tools is also reduced. Consequently, the manufacturing method becomes less costly and therefore more efficient. In an advantageous further extension, the two films are fused over the entire periphery of the media interface.

[0008] Preferably, a hot punch is used to fuse the two films, and this hot punch particularly preferably has a stamping edge for stamping out the media interface. The functions of fusion and stamping are thus integrated into a single tool.

[0009] In an alternative embodiment, a heated rotary die is used. The rotary die is particularly advantageous when the two thin films and / or membrane electrode units are processed as a roll.

[0010] The frame structure is used in the assembly of electrochemical cells to seal the electrochemical cell relative to the medium interface, so that only the medium within the medium interface is connected to the corresponding channel of the electrochemical cell; mixing of different media is prevented.

[0011] The fusion of the two films prevents the adhesive from penetrating the dielectric interface and thus prevents the electrochemical cell from being blocked by the adhesive. The fusion of the two films thus creates a barrier relative to the adhesive, preventing it from being extruded from the frame structure, especially during the stacking and compression of the electrochemical cells. The adhesive is approximately trapped within the frame structure. Furthermore, the limited volume of the relatively incompressible adhesive also regulates the defined uniform height of the membrane electrode units. Accordingly, the cell stack can be clamped with a more uniform contact pressure distribution, and the tolerance of the stack height can be limited to a narrower boundary.

[0012] In an advantageous embodiment, the two films are made of the same material, particularly preferably of a thermoplastic polymer such as PEN. Therefore, the two films can be fused together in a very simple manner, especially by means of a hot stamping tool.

[0013] The membrane electrode unit includes a membrane, particularly a polymer electrolyte membrane (PEM). The membrane electrode unit also includes two porous electrodes, each having an embedded catalyst, wherein these electrodes are arranged on the PEM and confined to it on both sides. This may be specifically referred to as MEA-3. Additionally, the membrane electrode unit may include two diffusion layers. These diffusion layers may confine MEA-3, particularly on both sides. This may be specifically referred to as MEA-5. If MEA-5 is laminated with two thin films, it may be referred to as MEA-7.

[0014] Electrochemical cells can be, for example, fuel cells, electrolyzers, or storage batteries. Fuel cells are particularly PEM-FC (polymer electrolyte membrane fuel cells). Battery stacks especially consist of multiple electrochemical cells arranged on top of each other.

[0015] The frame structure, in particular, has a frame shape. The frame structure is preferably implemented as a surrounding structure. Therefore, the membrane and two electrodes—and in some embodiments, additionally two diffusion layers—can be advantageously enclosed within the frame structure. Furthermore, the frame structure is particularly configured in a U-shape or Y-shape in cross-section to accommodate the membrane and two electrodes between the U-shaped or Y-shaped supports.

[0016] The adhesive preferably seals the membrane electrode unit outwards, the two films are bonded to each other and the films and two electrodes are fixed in the frame structure.

[0017] In a preferred further extension, the two films are fused together around the periphery of the active region of the membrane electrode unit. Thus, the adhesive seals the edges of the active region. The sealing function is significantly better guaranteed when the extrusion of the adhesive is prevented. Attached Figure Description

[0018] The attached diagram schematically illustrates: Figure 1 : Existing membrane electrode units, in which only the main areas are shown.

[0019] Figure 2 The membrane electrode unit of DE 10 2020 213 132 A1, where only the main area is shown.

[0020] Figure 3 : A schematic perspective view of a membrane electrode unit, where only the main areas are shown.

[0021] Figure 4 The illustration schematically shows the manufacturing steps for manufacturing a membrane electrode unit according to the present invention, wherein only the main areas are shown. Detailed Implementation

[0022] Figure 1The membrane electrode assembly 1 of the electrochemical cell 100, particularly a fuel cell, is shown in a vertical cross-section in the edge region, with only the main area shown. The membrane electrode assembly 1 has a planar membrane 2, exemplarily a polymer electrolyte membrane (PEM), and two porous electrode layers 3 or 4, wherein the electrode layers 3 or 4 are respectively disposed on one side or one face of the membrane 2. Furthermore, the electrochemical cell 100 has two diffusion layers 5 or 6, which may also be part of the membrane electrode assembly 1 according to embodiments.

[0023] The membrane electrode assembly 1 is surrounded by a frame structure 10, also referred to herein as an auxiliary gasket. The frame structure 10 contributes to the rigidity and sealing of the membrane electrode assembly 1 and is a non-active area of ​​the electrochemical cell 100.

[0024] The frame structure 10 is constructed in a U-shape or Y-shape in cross-section, wherein the first leg of the U-shaped frame segment is formed by a first film 11 made of a first material W1, and the second leg of the U-shaped frame segment is formed by a second film 12 made of a second material W2. Additionally, the first film 11 and the second film 12 are bonded together by means of an adhesive 13 made of a third material W3. Typically, the first material W1 and the second material W2 are identical and made of a thermoplastic polymer, such as PEN (polyethylene naphthalate).

[0025] Two diffusion layers 5 or 6 overlap the frame structure 16 in the overlap region 22. In the overlap region 22, electrode layers 3 and 4 are covered by the frame structure 10, which relates to the inactive region of the electrochemical cell 100. Alternatively, the frame structure 10 may also enclose both diffusion layers 5 and 6.

[0026] In the active region 21, diffusion layers 5 and 6 each contact an electrode layer 3 and 4, allowing for electrochemical reactions characteristic of the electrochemical cell 100 to occur; the two thin films 11 and 12 have grooves of considerable area for the active region 21. Electrode layers 3 and 4 typically contain catalyst particles.

[0027] In the inactive overlap region 22, no reactive fluid reaches the catalyst embedded in the electrode layers 3 and 4; therefore, no chemical reaction occurs in the overlap region 22, and the current density of the electrochemical cell 100 drops very sharply or even to zero relative to the active area 21.

[0028] In the inactive overlap region 22, the following components of the membrane electrode assembly 1 are arranged from the inside out: -membrane 2, -Electrode layers 3, 4, - Adhesive 13, - First film 11 or second film 12, - Diffusion layers 5 and 6.

[0029] Furthermore, there is an adhesive region 23 in which the two films 11, 12 are directly connected to each other by means of adhesive 13. In this case, it is preferable to use films 11, 12 pre-coated with adhesive 13. The compound is "adhesive," meaning that films 11, 12 are fixed to each other after the first contact and cannot be repositioned or shifted.

[0030] There is a risk when clamping multiple electrochemical cells 100 into a battery stack: the adhesive 13 may be extruded from the frame structure 10. This could lead to incomplete sealing of the membrane electrode unit 1 and cause complete failure of the entire battery stack. Furthermore, the extruded adhesive may block the medium flow path and thus severely impair the efficiency of the electrochemical cells 100.

[0031] It is now known from DE 10 2020 213 132 A1 that the two films 11, 12 can be fused together at the connection area 15, thereby preventing the outward leakage of the adhesive 13.

[0032] In response, Figure 2 The membrane electrode unit 1 of DE 10 2020 213 132 A1 is shown in cross-section, in which a first thin film 11 and a second thin film 12 are fused together at a connection region 15, such that an adhesive 13 is sealed. Even when the two films 11 and 12 are pressed together, it is no longer possible for the adhesive 13 to remain sealed. Figure 2 It leaks to the left in the diagram.

[0033] The enclosed volume of adhesive 13 also ensures the defined height of the adhesive 13 layer and thus the entire membrane electrode unit 1 in the stacking direction of the electrochemical cell 100, as the defined spacing between the two films 11, 12 is maintained.

[0034] exist Figure 2The diagram also illustrates the manufacturing method for the membrane electrode unit 1. The fusion or material-locking connection of the two films 11, 12 is preferably achieved using a hot punch 40. In the illustrated embodiment, the hot punch 40 includes a first punch 41 and a second punch 42. The two punches 41, 42 are heated during the manufacturing process and brought close together in the connection region 15, such that the first punch 41 acts on the first film 11 and the second punch 42 acts on the second film 12. The two punches 41, 42 move toward each other to such an extent that the first film 11 contacts the second film 12 in the connection region 15. The high temperature of the two punches 41, 42 melts the two films 11, 12 at least in the connection region 15, allowing the associated polymer chains to connect with each other; thus, after the two films 11, 12 cool, a material-locking connection is formed between the two films 11, 12 in the connection region 15.

[0035] Figure 3 A perspective view of the membrane electrode unit 1 is shown schematically. At the center of the membrane electrode unit 1 is a preferably rectangular active region 21 with a coated membrane. The coated membrane is surrounded by a frame structure 10. Figure 3 In this embodiment, the frame structure 10 has three media interfaces 30 on its narrow end side for inputting and outputting media fuel, oxidant, and coolant. A so-called distribution region 31 is constructed between the media interfaces 30 and the active region 21, which is used to distribute the media from the narrower media interfaces 30 (input side) to the wider active region 21, or to collect it (output side).

[0036] In an embodiment of the invention, the two films 11, 12 of the frame structure 10 are now fused together on at least a portion of the periphery 33 of at least one media interface in the media interface 30.

[0037] In a preferred embodiment of the invention, the two films 11, 12 are also fused together on the periphery 36 of the active region 21 and / or on the periphery 32 of the distribution region 31. Therefore, the volume of adhesive 13 is defined in the respective regions 21, 31, preventing further overflow of adhesive 13. The uniform thickness of the membrane electrode unit 1 is thus stably set, and the respective regions 21, 31 are very well sealed.

[0038] In the method according to the invention, it is preferably carried out in one working step by means of a hot punch 40 on which stamping edges are constructed: fusing on the periphery 33 of at least one of the media interfaces 30 and just stamping the media interface 30 out of the frame 10.

[0039] In response, Figure 4 Schematic illustration of the use of the invention Figure 2In the case of a further extension of the hot punch 40, it is used in the manufacturing steps of manufacturing the membrane electrode unit 1. The hot punch 40 now has at least one stamped edge 43, which stamped edge in Figure 4 In the embodiment, the stamping edge 43 is constructed on the first punch 41. Alternatively, the stamping edge 43 can also be constructed on the second punch 42, or each of the two punches 41 and 42 can have a stamping edge 43.

[0040] When the two heated punches 41, 42—or at least one heated punch—come together, the two films 11, 12 fuse together in the connection area 15, where the adhesive 13 is pressed outward. At the same time, the stamping edge 43 cuts the two films 11, 12 and thus forms the periphery 33 of the medium interface 30.

[0041] The stamped scrap 50, consisting of portions of the two films 11, 12 and adhesive 13, typically corresponds to the geometry of the periphery 33 of the media interface 30.

[0042] The two films 11 and 12 are fused together to form a frame 10 and a medium interface 30 is stamped out, thus advantageously being carried out in a single manufacturing step.

[0043] In alternative manufacturing methods, the fusion and stamping of the two films 11, 12 can be carried out using a heated rotary die. This is particularly advantageous when processing roll materials.

Claims

1. A method for manufacturing a membrane electrode unit (1) for an electrochemical cell (100), comprising the following method steps: - Provide a membrane (2) coated with electrodes (3, 4). - Provide a first film (11) and a second film (12), wherein, At least one of the two films (11, 12) is provided with an adhesive (13). - The membrane (2) coated with electrodes (3, 4) is laminated between two thin films (11, 12), wherein the two thin films (11, 12) are directly bonded to each other in the bonding area (23) by means of the adhesive (13), such that the two thin films (11, 12) constitute a frame structure (10) for the membrane electrode unit (1). - At least one medium interface (30) is stamped out from the frame structure (10), and the two films (11, 12) are fused in the connection area (15) on at least a portion of the periphery (33) of the medium interface (30).

2. The method according to claim 1, characterized in that, The two films (11, 12) are made of thermoplastic polymers, preferably PEN.

3. The method according to claim 1 or 2, characterized in that, The two films (11, 12) are fused together on the periphery (36) of the active region (21).

4. The method according to any one of the preceding claims, characterized in that, Each of the two films (11, 12) has a portion of the active region (21) for the electrochemical cell (100).

5. The method according to any one of the preceding claims, characterized in that, The stamping and fusion are performed using a hot punch (40).

6. The method according to claim 5, characterized in that, The hot punch (40) has a stamping edge (43) for stamping out the medium interface (30).

7. The method according to any one of claims 1 to 4, characterized in that, The stamping and fusion are carried out using a heated rotating die.

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