Electrochemical cell comprising a membrane-electrode unit, a diffusion layer and a distributor plate, and a method for manufacturing the electrochemical cell

Abstract

The present invention relates to an electrochemical cell (100) comprising a membrane-electrode unit (1), a diffusion layer (5) and a distributor plate (7, 20). The membrane-electrode unit (1) comprises a frame structure (16) which comprises a film (161) which is attached to a membrane (2) by means of an adhesive means (163). The diffusion layer (5) and the distributor plate (7, 20) are partially in contact with the film (161). The film (161) comprises at least one first cavity (161a) and at least one second cavity (161b). The adhesive means (163) is disposed in both cavities (161a, 161b) so as to form a bond through the first cavity (161a) with the diffusion layer (5, 6) located thereon, and through the second cavity (161b) with the distributor plate (7, 8, 20) located thereon.

Description

[Technical Field]

[0001] The present invention relates to an electrochemical cell, in particular a fuel cell, comprising a membrane-electrode unit, a diffusion layer and a distributor plate, and further to a method for producing such an electrochemical cell. [Background technology]

[0002] Fuel cells are electrochemical energy converters in which hydrogen and oxygen, for example, are converted into water, electrical energy, and heat. A fuel cell or fuel cell stack is made up of cells consisting of multiple parts, each of which has a membrane-electrode unit and a bipolar plate arranged one on top of the other. The bipolar plates are used to supply reactants to the electrodes and to cool the fuel cell stack. For this purpose, the bipolar plates have a distributor structure that guides the reactant-containing fluid along the electrodes. Typically, a bipolar plate in this case consists of two distributor plates. Furthermore, a distributor structure is used to guide the cooling fluid along another distributor structure or within the bipolar plate. The distributor structure is usually formed as a plurality of channels, which allow different fluids to be guided.

[0003] One particular type of fuel cell is the polymer electrolyte membrane fuel cell (PEM-FC). In the active area of a PEM-FC, two porous electrodes with catalyst layers are bounded by a polymer electrolyte membrane (PEM). The PEM-FC also comprises gas diffusion layers (GDLs) in the active area, which define the polymer electrolyte membrane (PEM) and the two porous electrodes with catalyst layers on either side. The PEM, the electrodes with catalyst layers, and optionally both GDLs may form a so-called membrane-electrode-unit (MEA) in the active area of the PEM-FC. Two opposing bipolar plates (bipolar plate halves), on the other hand, define the MEA on either side. A fuel cell stack is made up of alternating MEAs and bipolar plates. The anode plate of the bipolar plate distributes the fuel, particularly hydrogen, and the cathode plate of the bipolar plate distributes the oxidant, particularly air / oxygen. To electrically insulate adjacent bipolar plates, to stabilize the MEA, and to prevent unintentional leakage of fuel or oxidant, the MEA can be enclosed in a frame-like opening of two films placed in contact with each other. Typically, both films of this frame structure are made of the same material, for example, polyethylene naphthalate (PEN). Both films made of the same material may have redundant or optional properties, such as their respective electrical insulating capabilities (electrical insulation) and / or oxygen sealing properties.

[0004] Patent document 1 discloses a fuel cell having two bipolar plates, between which a membrane-electrode unit is arranged, and between the membrane-electrode unit and the bipolar plates, a diffusion layer is arranged in each case. The membrane-electrode unit is arranged on a carrier frame or frame structure. An ultrasonic welded connection is formed between the membrane-electrode unit and the frame structure, and the membrane-electrode unit is connected to the frame structure via the ultrasonic welded connection.

[0005] It is also known in the prior art that the frame structure is directly connected to the bipolar plate via an ultrasonic welding joint. Similarly, instead of an ultrasonic welding joint, a laser-generated welding joint can also be used. This method certainly has the advantage that no additional material is required, but it does require a roughened surface.

[0006] Patent document 2 discloses a membrane-electrode unit for a fuel cell, which includes a layer assembly consisting of an anode electrode, a cathode electrode, and a membrane disposed therebetween, and in which a polymer material is deposited on the upper and lower surfaces of the layer assembly. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] German Patent Application Publication No. 102005058370 [Patent Document 2] DE 10140684 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a method for attaching a frame structure to a diffusion layer and a distributor plate or a bipolar plate, which method allows the frame structure to be attached to the diffusion layer and the distributor plate in a simple and economical manner while saving materials. The present invention also encompasses a corresponding electrochemical cell. [Means for solving the problem]

[0009] For this purpose, the electrochemical cell comprises a membrane-electrode unit, a diffusion layer, and a distributor plate. The membrane-electrode unit has a frame structure, which has a film attached to the membrane by an adhesive means. The diffusion layer and the distributor plate are partially in contact with the film. The film has at least one first cavity and at least one second cavity. The adhesive means is arranged in both cavities, so that the film forms a bond with the diffusion layer located thereon via the first cavity and a bond with the distributor plate located thereon via the second cavity.

[0010] The membrane-electrode unit preferably comprises a planar membrane, in particular a polymer electrolyte membrane (PEM). The membrane-electrode unit further comprises two preferably porous electrode layers, each with a catalyst paste, which are arranged on the membrane and define it on both sides. This may be referred to as MEA-3. Additionally, the membrane-electrode unit may comprise two diffusion layers, which may define MEA-3 on both sides. This may be referred to as MEA-5.

[0011] The invention also encompasses a method for manufacturing an electrochemical cell of this kind, which in this case comprises the following method steps: a method step of placing a diffusion layer on a frame structure so that the film having the first voids abuts the diffusion layer; - a method step of bonding the frame structure to the diffusion layer by melting the adhesive means in the area of the first cavity by hot stamping and forcing it into the first cavity; a method step of placing the frame structure on a distributor plate, so that the film with the second cavities abuts the distributor plate; a method step of joining the frame structure to the distributor plate by melting the adhesive means in the area of the second cavity by hot stamping and forcing it into the second cavity; It is equipped with:

[0012] For these method steps, one or more hot stamping processes can be used. In the sense of the present invention, a cavity is understood to mean, in particular, a penetration through the film that allows the adhesive means to be bonded to the distributor plate or the diffusion layer. This bonding is preferably achieved by a simple hot stamping process. The adhesive means only needs to be provided in the region of the cavity. This reduces the adhesive means required to attach the frame structure to the diffusion layer and the bipolar plate. Accordingly, only a small amount of additional material is required. In addition, this method can be easily and economically implemented. The resulting assembly of electrochemical cells is ideally suited for stacking several electrochemical cells into a cell stack.

[0013] In one advantageous configuration of the electrochemical cell, the frame structure of the electrochemical cell has a further film, which is connected to the further film by adhesive means, whereby the adhesive means is also used to connect the two films, i.e., is already present, so that no additional step for applying the adhesive means is required; the existing adhesive means only needs to be melted, so that the diffusion layer and distributor plate can then also be connected to the frame structure.

[0014] The other film advantageously has at least one third cavity, and the adhesive means is arranged in the third cavity, so as to form a bond with the other diffusion layer located thereon via the third cavity.

[0015] The two films are thus bonded to each other by adhesive means. The same adhesive means is arranged in this area through the gap. The frame structure is bonded to the two diffusion layers and the distributor plate via this adhesive means. Since the adhesive means is applied anyway to bond the two films, no additional material is required to bond the frame structure to the diffusion layer and the distributor plate. This makes the method simple and economical to implement.

[0016] In an advantageous development, the first cavity has a lateral offset relative to the third cavity in the stacking direction, so that the adhesive in the first and third cavities does not have to be hot-stamped on top of each other. Furthermore, sufficient adhesive is therefore present for both the first and third cavities, since the cavities are thus filled with adhesive from different regions.

[0017] Preferably, the second cavity is formed in the remaining area, in which the distributor plate protrudes beyond the diffusion layer, so that the diffusion layer and the distributor plate can be attached to the frame structure side by side.

[0018] In another preferred embodiment of the present invention, the adhesive is a UV adhesive, which is cured by a UV light source. Preferably, in this case, at least the film is UV-transparent, so that the adhesive can be cured by a UV light source. This method step allows the frame structure to be bonded to the diffusion layer or the distributor plate at a specific time, so that subsequent positional adjustments are possible. In addition, curing via UV light allows for easy and controlled installation.

[0019] Preferably, the adhesive is a hot-melt adhesive, so that the films are bonded to each other by a lamination process. Hot-melt adhesives are adhesives that turn tacky when heated. This method step allows the films to be bonded to each other simply by heating, for example, by hot stamping. In the lamination process, the films are preferably bonded at a temperature of 100-200°C and a pressure of 0.5-5 MPa. The same applies to the bonding of the frame structure to the diffusion layer and distributor plate.

[0020] The electrochemical cell may be, for example, a fuel cell, an electrolysis cell or a battery cell. The fuel cell is in particular a PEM-FC (Polymer Electrolyte Membrane Fuel Cell). The cell stack in particular comprises a number of electrochemical cells arranged one on top of the other.

[0021] An embodiment of the invention is illustrated in the drawings and explained in more detail in the following description. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a cross-sectional view of a schematic electrochemical cell showing only the main regions. [Figure 2] FIG. 1 is a vertical cross-section of a membrane-electrode assembly showing only the main areas. [Figure 3] FIG. 2 is a vertical cross-sectional view of another membrane-electrode assembly showing only the main areas. [Figure 4] 1 is a vertical cross-section of a membrane-electrode assembly according to the invention, showing only the main areas; FIG. [Figure 5] FIG. 1 is a perspective exploded view of a schematic process flow for the manufacture of an electrochemical cell. [Figure 6] 10A-10C illustrate exemplary method steps for attaching a frame structure onto a bipolar plate by hot stamping. DETAILED DESCRIPTION OF THE INVENTION

[0023] 1 shows, in a schematic manner, an electrochemical cell 100 in the form of a fuel cell, as known in the prior art, of which only the main regions are shown. The fuel cell 100 comprises a membrane 2, in particular a polymer electrolyte membrane, on one side of which a cathode compartment 100a is formed, and on the other side an anode compartment 100b is formed.

[0024] Arranged in the cathode chamber 100a from the membrane 2 outward, i.e., in the normal direction or stacking direction z, are an electrode layer 3, a diffusion layer 5, and a distributor plate 7. Similarly, arranged in the anode chamber 100b from the membrane 2 outward, are an electrode layer 4, a diffusion layer 6, and a distributor plate 8. The membrane 2 and the two electrode layers 3 and 4 form the membrane-electrode assembly 1. The two diffusion layers 5 and 6 are also part of the membrane-electrode assembly 1.

[0025] The distributor plates 7, 8 have channels 11 for supplying gas, e.g., air in the cathode chamber 100a and hydrogen in the anode chamber 100b, to the diffusion layers 5, 6. The diffusion layers 5, 6 typically consist of a nonwoven carbon fiber fabric on the channel side, i.e., toward the distributor plates 7, 8, and a microporous particle layer on the electrode side, i.e., toward the electrode layers 3, 4.

[0026] The distributor plates 7, 8 have channels 11 and, by implication, also have banks 12 bounding the channels 11. The lower surfaces of these banks 12 therefore form the contact surface 13 of the respective distributor plate 7, 8 with the underlying diffusion layer 5, 6.

[0027] Typically, the cathode distributor plate 7 and the anode distributor plate 8 are distinct from one another. Advantageously, the cathode distributor plate 7 of one electrochemical cell 100 and the anode distributor plate 8 of the electrochemical cell adjacent to this electrochemical cell 100 are firmly connected, for example by welding, and thus form a single bipolar plate.

[0028] 2 shows a vertical cross section in the edge region of an electrochemical cell 100, in particular a membrane-electrode assembly 1 of a fuel cell, of which only the main area is shown. The membrane-electrode assembly 1 comprises an areal membrane 2, for example a polymer electrolyte membrane (PEM), and two porous electrode layers 3 and 4, each with a catalyst layer, arranged on one side or face of the membrane 2. The electrochemical cell 100 further comprises two diffusion layers 5 and 6, which may, depending on the configuration, belong to the membrane-electrode assembly 1.

[0029] The membrane-electrode assembly 1 is surrounded by a frame structure 16 (also referred to herein as a subgasket) around the membrane-electrode assembly 1. The frame structure 16 contributes to the rigidity and sealing of the membrane-electrode assembly 1 and is the inactive area of the electrochemical cell 100.

[0030] The frame structure 16 is formed in particular with a U-shaped or Y-shaped cross section, with a first leg of the U-shaped frame section being formed by a film 161 made of a first material W1 and a second leg of the U-shaped frame section being formed by another film 162 made of a second material W2. Additionally, the film 161 and the other film 162 are attached together by an adhesive means 163 made of a third material W3. In most cases, the first material W1 and the second material W2 are the same and consist of a thermoplastic polymer, for example PEN (polyethylene naphthalate).

[0031] Both diffusion layers 5 and 6 are accommodated, so to speak, in a framework 16, typically in such a way that they are in contact with one electrode layer 3 or 4, respectively, via the active surface 21 of the membrane-electrode assembly 1. The electrode layers 3 and 4 each have one catalyst paste 31 or 41, in which a catalyst, typically catalyst particles, are embedded.

[0032] When the electrode layers 3, 4 are covered by the framework 16, they form an inactive edge region 22 of the membrane-electrode assembly 1. In this inactive edge region 22, the reactant fluids do not reach the electrode layers 3, 4 or the catalysts embedded in the catalyst pastes 31, 41. As a result, no chemical reactions take place in the edge region 22, and the current density of the electrochemical cell 100 drops very strongly here, i.e., relative to the active surface 21, or even becomes zero.

[0033] 3 shows a vertical cross section of another membrane-electrode assembly 1 of an electrochemical cell 100, in which only the main areas are shown. The configuration of FIG. 3 is similar to that of FIG. 2, but this time both diffusion layers 5, 6 overlap the frame structure 16. This causes the diffusion layers 5, 6 to extend into the edge area 22, thus defining an overlap area 23. In the overlap area 23, from the inside to the outside, the following components of the membrane-electrode assembly 1 are arranged: - membrane 2, electrode layers 3, 4 with catalyst pastes 31, 41, - adhesive means 163, - film 161 or another film 162, - Diffusion layers 5,6.

[0034] Figure 4 shows a vertical cross section of a membrane-electrode unit 1 according to the invention, showing only the main areas. As in the embodiment of Figure 3, in the embodiment of Figure 4 too the diffusion layers 5, 6 overlap the framework 16, resulting in an overlap area 23.

[0035] In the overlap region 23, now, the film 161 has a first gap 161a and the other film 162 has a third gap 162a, and the adhesive means 163 passes through the first gap 161a and the third gap 162a, thus forming an adhesive bond with the diffusion layers 5, 6 located thereon.

[0036] In the edge regions 23, the distributor plates 7, 8 protrude beyond the underlying diffusion layers 5, 6, respectively. The distributor plates 7, 8 therefore protrude beyond the overlap region 23. In the resulting remaining region 24, the distributor plates 7, 8 can come into contact with the underlying frame structure 16, at least under the clamping force of the assembled cell stack. In the remaining region 24, the film 161 now has a second cavity 161b, and the further film 162 has a fourth cavity 162b, and the adhesive means 163 passes through the second cavity 161b and the fourth cavity 162b, thus establishing an adhesive bond with the distributor plates 7, 8 located above.

[0037] Preferably, the distributor plate 7 on the cathode side and the distributor plate 8 on the anode side of the adjacent electrochemical cell 100 are joined, particularly preferably by a welded joint, to form one bipolar plate.

[0038] The adhesive means 163 thus not only connects the membrane 2 and both electrode layers 3, 4 to the framework 16, but also connects the resulting membrane-electrode unit 1 to the diffusion layers 5, 6 and the distributor plates 7, 8 or to one or two bipolar plates 20.

[0039] In a preferred configuration, the first cavity 161a and the third cavity 162a have an offset a in the stacking direction z. This is particularly advantageous if the bonding is performed by hot stamping, since in this way sufficient adhesive medium 163 is present in the individual cavities 161a, 162a so that the adhesive medium 163 can flow in a liquefied state through the cavities 161a, 162a and bond with the diffusion layers 5, 6 located thereon.

[0040] FIG. 5 shows, in a perspective exploded view, a schematic process flow for manufacturing one electrochemical cell 100 comprising one membrane-electrode-unit 1 and one bipolar plate 20.

[0041] 5a shows the structure of a membrane-electrode unit 1 with a membrane 2, both electrode layers 3, 4 and a frame structure 16, which in turn has a film 161, a further film 162 and adhesive means 163 arranged therebetween. The adhesive means 163 can in this case, for example, first be applied to both films 161, 162 in an initial state.

[0042] In the configuration of Fig. 5a, the film 161 has four first voids 161a and four second voids 161b. The other film 162 has only four third voids 162a, since one electrochemical cell 100 with one membrane-electrode assembly 1 and one bipolar plate 20 is to be manufactured.

[0043] 5b shows the bonding of this membrane-electrode assembly 1 to the two diffusion layers 5, 6. This bonding is preferably performed in this case by hot stamping, in which the adhesive means 163 is melted in the area of the first void 161a and the third void 162a, flows or is forced through these voids 161a, 162a and is then bonded to the diffusion layers 5, 6 located thereon.

[0044] 5c shows the joining of an electrochemical cell 100 consisting of this membrane-electrode assembly 1 with a bipolar plate 20. For this purpose, the membrane-electrode assembly 1 has one diffusion layer 5, 6 on each side of the membrane 2. The joining of this bipolar plate 20 to the membrane-electrode assembly 1 is preferably carried out in this case by hot stamping, in which the adhesive means 163 is melted in the region of the second cavities 161b, flows or is pressed through these cavities 161b and is then bonded to the bipolar plate 20 or distributor plate located above it.

[0045] 6 exemplarily shows a method step for attaching the frame structure 16 to the bipolar plate 20 by hot stamping 30. In this configuration, the frame structure 16 is bonded to the bipolar plate 20 in the areas where the membrane 2 and the electrode layers 3, 4 are no longer present. A cross section through the area of the fourth cavity 162b is shown in this figure. Preferably, adhesive means 163 bond the membrane-electrode unit 1 to the bipolar plate 20, i.e. at the second film 162. This is essentially the same as bonding the membrane-electrode unit 1 to the bipolar plate 20 at the first film 161.

[0046] Partial view 6a shows that in this case, adhesive means 163 are arranged between the first and second films 161, 162, and the two films 161, 162 are bonded to each other via the adhesive means 163. In this embodiment, the adhesive means 163 is a hot melt adhesive, and the two films 161, 162 are bonded to each other via the hot melt adhesive by a lamination process. Due to the void 162b, no bonding of the two films 161, 162 occurs in this area. Partial view 6a shows a step before the membrane-electrode unit 1 is placed on the bipolar plate 20.

[0047] Partial view 6b shows the step in which the stamping step is carried out by the hot stamp 30. In this step, the further film 162 is placed directly against the bipolar plate 20. The hot stamp 30 is then positioned in the area of the cavity 162b and applies a stamping force to the film 161, introducing thermal energy into the adhesive means 163 in this area. The heated adhesive means 163 is thus brought into contact with the bipolar plate 20. The hot stamp 30 is thus heated, so that the film 161 is bonded to the bipolar plate 20 via the adhesive means 163, which is formed as a hot-melt adhesive.

[0048] The stamping step results in the formation of stamped bonding points 164, which are essentially determined by the shape of the voids 162b and the shape of the hot stamp 30. Partial view 6c shows the corresponding part of the membrane-electrode assembly 1 after the hot stamp 30 has been removed. It can be seen here that the stamping hot stamp 30 has created recesses 28 in the first film 161, which reach into the voids 162b of the second film 162. This further improves the mechanical bond between the two films 161, 162. [Explanation of symbols]

[0049] 1. Membrane-electrode assembly, membrane-electrode unit 2 membrane 3 electrode layer 4 electrode layer 5 Diffusion layer 6 Diffusion layer 7. Distributor plate 8 distributor plate 11 Flow path 12 Bank 13 Contact surface 16 Frame structure, subgasket 20 Bipolar Plates 21 Active Surface 22 Inactive Edge Regions 23 Overlap Area 24 Residual area 28 Recess 30 Hot stamping 31 Catalyst paste 41 Catalyst Paste 100 electrochemical cells 100a cathode chamber 100b Anode chamber 161 Film 161a First Vacancy 161b Second Vacancy 162 Another Film 162a Third Vacancy 162b Fourth Void 163 Adhesion means 164 Glue point a offset W1 First Material W2 Second Material W3 The Third Material z normal direction, stacking direction

Claims

1. An electrochemical cell (100) comprising a membrane-electrode unit (1), a diffusion layer (5) and a distributor plate (7, 20), wherein the membrane-electrode unit (1) has a frame structure (16), the frame structure (16) has a film (161), the film (161) is adhered to a membrane (2) by an adhesive means (163), and the diffusion layer (5) and the distributor plate (7, 20) are partially in contact with the film (161). In the electrochemical cell (100), The film (161) has at least one first cavity (161a) and at least one second cavity (161b), and the adhesive means (163) is arranged in both of the cavities (161a, 161b) so as to form a bond with the diffusion layer (5, 6) located thereon via the first cavity (161a) and a bond with the distributor plate (7, 8, 20) located thereon via the second cavity (161b). An electrochemical cell (100) comprising a membrane-electrode unit (1), a diffusion layer (5) and a distributor plate (7, 20), characterized in that:

2. 2. The electrochemical cell (100) of claim 1, wherein the frame structure (16) comprises another film, and the film (161) is bonded to the other film (162) by the adhesive means (163).

3. 2. The electrochemical cell (100) according to claim 1, wherein the frame structure (16) comprises another film (161), the film (161) being bonded to the other film (162) by the adhesive means (163), the other film (162) having at least one third cavity (162a), the adhesive means (163) being disposed in the third cavity (162a), and thereby forming a bond with another diffusion layer (6) located thereon via the third cavity (162a).

4. 4. The electrochemical cell (100) of claim 3, characterized in that, viewed in the stacking direction (z), the first cavity (161a) has a lateral offset (a) relative to the third cavity (162a).

5. 4. The electrochemical cell (100) according to claim 1, wherein the second cavity (161b) is formed in a remaining region (24) in which the distributor plate (7, 8, 20) protrudes beyond the diffusion layer (5, 6).

6. A method for manufacturing an electrochemical cell (100), the electrochemical cell (100) comprising a membrane-electrode assembly (1), a diffusion layer (5), and a distributor plate (7, 20), the membrane-electrode unit (1) comprising a frame structure (16), the frame structure (16) comprising a film (161), the film (161) being attached to a membrane (2) by an adhesive means (163), the film (161) comprising at least one first cavity (161a) and at least one second cavity (161b), The method includes the steps of: placing the diffusion layer (5) on the frame structure (16) so that the film (161) having the first cavity (161a) abuts the diffusion layer (5); - bonding the framework (16) to the diffusion layer (5) by melting the adhesive means (163) in the area of the first cavity (161a) with a hot stamp (30) and forcing it into the first cavity (161a); placing the frame structure (16) on the distributor plate (7, 20) so that the film (161) having the second cavity (161b) abuts the distributor plate (7, 20); - bonding the framework (16) to the distributor plate (7, 20) by melting the adhesive means (163) in the area of the second cavity (161b) with a hot stamp (30) and forcing it into the second cavity (161b); A method of manufacturing an electrochemical cell (100), comprising:

7. 7. The method of claim 6, wherein said adhesive means (163) is a UV adhesive, whereby said UV adhesive is cured by a UV source.

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