Method for producing a laminate having at least two sub-layers for a membrane electrode unit

Abstract

The invention relates to a method for producing a laminate having at least two sub-layers for a membrane electrode unit (MEA) of a fuel cell (1), comprising the following steps: - providing a membrane material made of a proton-conducting electrolyte, - providing an electrode material comprising at least one catalyst, - applying a liquid adhesive onto a surface of the membrane material and / or onto a surface of the electrode material, and - contacting the surfaces of the membrane material and the electrode material to form a material connection by the liquid adhesive, wherein in addition a production aid is introduced or applied into or onto the composite formed from the electrode material, the membrane material and the liquid adhesive which has not yet solidified, wherein the production aid is arranged to stabilize the not yet solidified composite.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for producing a laminate having at least two sub-layers for a membrane electrode unit (MEA) of a fuel cell. BACKGROUND

[0002] Fuel cell devices are used to chemically react fuel with oxygen to form water in order to generate electrical energy. For this purpose, a fuel cell comprises a proton-conducting (electrolyte) membrane as a core component, to which electrodes are assigned, thereby forming a common membrane electrode unit (MEA stands for "membrane electrode assembly"). During operation of a fuel cell device having a plurality of fuel cell assemblies to form a fuel cell stack, fuel, in particular hydrogen (H2) or a hydrogen-containing gas mixture, is supplied to the anode. In the case of a hydrogen-containing mixture, this is first reformed, thereby providing hydrogen. At the anode, H2 occurs electrochemically oxidized to form H + , wherein electrons are released. The electrons provided at the anode are guided to the cathode by an electrical conductor. Oxygen or an oxygen-containing gas mixture is supplied to the cathode, whereby O2 occurs reduced to form O 2- , wherein electrons are received.

[0003] It is known to connect the individual components of a membrane electrode unit into a composite in separate, i.e. individual steps, wherein the elements connecting the components are formed by adhesives in the form of liquid adhesives, which simultaneously seal off the anode side from the cathode side in a gas-tight manner upon curing. Such liquid adhesives require a certain time in the production process until they are cured and thus have the necessary stability, in particular when handling the composite of the membrane electrode unit.

[0004] WO 2006 / 047 950 A1 describes the production of a membrane electrode unit together with gas diffusion sub-layers, which are connected in a hot press to form a composite. In the hot press, a hot-melt adhesive strip is melted here until it is cross-linked and cured. WO 2013 / 178987 A1 describes a method for assembling a fuel cell stack, wherein a prefabricated membrane electrode unit (so-called MEA having four sub-layers) with a gas diffusion sub-layer is materially connected by an adhesive strip to a further gas diffusion sub-layer and a bipolar plate. EP 1 772 922 A1 describes the composition of an electrode layer of a membrane electrode unit for a fuel cell, wherein the electrode layer comprises a polymer binder, which is combined with catalyst particles by means of plasma, UV radiation or gamma radiation.

[0005] DE 10 2016 006 225 A1 shows a method for producing a product from at least two components which are connected to one another by at least one adhesive, wherein a first adhesive quantity is applied to the first component. US 2013 / 0306237 A1 describes a clamping device for fixing a laminate and a method for producing a laminate, for example for producing a membrane electrode assembly. Here, a proton-conducting electrolyte and two electrodes comprising a catalyst layer are clamped into the clamping device and hot-pressed therein, wherein elements for stabilizing the uncured layers can be introduced between the layers. SUMMARY

[0006] The object of the present application is to provide a method for producing a laminate having at least two sub-layers of a membrane electrode unit, which can be operated reliably in mass production of fuel cells, wherein the higher forces due to the shortened cycle times for producing the individual components are withstood during operation.

[0007] The object is achieved by a method having the features according to the application. Advantageous configurations having advantageous extensions of the application are explained in the further description.

[0008] The method according to the application for producing a laminate having at least two sub-layers of a membrane electrode unit (MEA) for a fuel cell comprises in particular the following steps:

[0009] - providing a membrane material made of a proton-conducting electrolyte,

[0010] - providing an electrode material comprising at least one catalyst,

[0011] - applying a liquid adhesive to a surface of the membrane material and / or to a surface of the electrode material, and

[0012] - contacting the surfaces of the membrane material and the electrode material to form a material connection by the liquid adhesive, wherein in addition a production aid is introduced or applied into or onto the composite made of the electrode material, the membrane material and the liquid adhesive which has not yet solidified, wherein the production aid is arranged to stabilize the uncured composite.

[0013] In this way, an additional production aid is used for this, which provides the overall composite which is still not solidified with increased stability and thus improved handling. The production aid is applied here to the uncured composite or introduced or embedded between the individual sub-layers of the composite. In this way, a membrane electrode unit can be produced in a continuous process, for example in "roll-to-roll" production, which is known, for example, from newspaper printing.

[0014] In this case, it is also possible to provide a further electrode material comprising at least one catalyst, which is applied to the opposite surface of the membrane or membrane material and is fixed by means of a liquid adhesive, so that in this case a cathode material is also applied on both sides of the membrane material. It is also possible to introduce an additional production aid on one side of the further cathode material, wherein this production aid can also be integrated between the individual layers of the not yet cured membrane electrode unit.

[0015] It has proven advantageous to apply the production aid for stabilizing the not yet cured composite in the edge region, which is remote from the active area of the membrane electrode device. In this way, the active area, i.e. the area in which the actual fuel cell reactions take place, can be kept free of production aids, so that the production aids do not negatively influence the flow of process gas. In contrast, the production aid, due to its placement in the edge region, can additionally also be used to make the membrane electrode unit more tightly sealed against the media, as it can also at least partially serve as an edge seal.

[0016] The production aid for stabilizing the not yet cured composite can be applied in a dot-like manner. In this way, only a small amount of material for the production aid is required, but this at the same time results in a reliable and stable composite by means of the not yet cured liquid adhesive. Alternatively or additionally, the production aid for stabilizing the not yet cured composite can also be applied in a surface-like manner, wherein the entire edge region, i.e. that region of the membrane electrode device which is remote from the active area, can also be covered with the production aid in a surface-like manner. This results in additional stabilization and additional sealing, for example to prevent the liquid adhesive from running out even when the not yet cured composite is handled. Alternatively or additionally, the production aid can also be applied in a line-like manner, so that here too additional tightness can be obtained.

[0017] The production aid can be attached to the not yet cured composite, for example by a mechanical connection, for example by clamping or stapling.

[0018] It has proven advantageous according to the application that the production aid is formed as a connector for a material connection with the membrane material and / or the electrode material, which has a shorter curing time than the liquid adhesive. Thus, in addition to the liquid adhesive, another connector is provided by the production aid, but this connector cures more quickly and thus provides a stabilizing function for the composite which has not yet been cured by the liquid adhesive more quickly.

[0019] It is advantageous in this case that the connector is a UV-curable adhesive and that the connector is cured under UV radiation even before the liquid adhesive is cured. When using a UV-curable adhesive, it is also possible to achieve a particularly simple mass production of the membrane electrode unit, since it is thereby possible to pass through a drying chamber in a simple manner and thus to coat the strip-shaped membrane material with a strip-shaped catalyst electrode material.

[0020] The connecting means can also be a pressure-sensitive adhesive in the form of a tape, which is applied to one or both surfaces away from the liquid adhesive. The advantage of using a tape is that it is already dry, wherein in particular it can also be formed as a double-sided adhesive tape to provide additional connection of the membrane material and the electrode material.

[0021] Furthermore, the connecting means can be a hot-melt adhesive, which liquefies under the action of heat and solidifies again even before the liquid adhesive has cured. In this way, the hot-melt adhesive crosslinks and solidifies with the surfaces of the membrane material and the electrode material, wherein due to this "pre-curing" of the liquid adhesive, it is harmless that it cures only at a later point in time, so that the prefabricated membrane electrode unit can be supplied to further process steps at an early stage.

[0022] Cyanoacrylate adhesives are particularly fast-drying and advantageous material choices for the individual components of the MEA. They usually cure very much faster than liquid adhesives.

[0023] The connecting means can also form a laminated connection, which solidifies even before the liquid adhesive.

[0024] Alternatively or additionally, it is advantageous if the production aid comprises a frame, which is placed on the unsolidified composite or integrated into the unsolidified composite, and the frame is melted, in particular using a laser, and solidifies again even before the liquid adhesive has cured, in a dot-like and / or surface-like and / or line-like manner. In this way, the frame ("frame") can thus be melted, so that it crosslinks with one or the other surface of the membrane material or the electrode material and material connects after curing. By the use of the frame, additional stability is provided, which makes handling of the prefabricated membrane electrode unit by the liquid adhesive, which is still liquid or unsolidified, easier.

[0025] In order that the production steps can be carried out as quickly as possible, it has proven advantageous if the production aid remains in the composite of the membrane electrode unit after the liquid adhesive has cured. However, it is also possible to remove the production aid from the composite again before or during the assembly of a plurality of membrane electrode units to form a fuel cell stack ("stack").

[0026] The features mentioned in the description above and the features of the figures described below and / or shown in the figures alone or in combination can be used not only in the specified combination, but also in other combinations or alone without departing from the scope of the present application. Therefore, embodiments not explicitly shown or explained in the figures, but resulting and producible from the individual feature combinations of the explained embodiments, are also regarded as included and disclosed in the present application. Brief Description of the Drawings

[0028] Further advantages, features and details of the present application result from the following description of preferred embodiments and with reference to the drawings, in which:

[0029] Figure 1 Structure diagram of a fuel cell with a three-piece laminate of a membrane electrode unit (MEA). DETAILED DESCRIPTION

[0030] Figure 1 A fuel cell 1 is shown in Fig. 1. Here, a semi-permeable electrolyte membrane 2 is covered on a first side 3 with a first electrode 4 (in this case an anode) and on a second side 5 with a second electrode 6 (in this case a cathode) and is materially connected therewith. The electrodes 4, 6 and the membrane 2 form a composite of a so-called membrane electrode unit (short: MEA). The first electrode 4 and the second electrode 6 comprise carrier particles on which catalyst particles made of a noble metal or a mixture containing a noble metal such as platinum, palladium, ruthenium, etc. are arranged or loaded. These catalyst particles serve as reaction accelerators in the electrochemical reactions of the fuel cell 1. The carrier particles can be carbon-containing. However, carrier particles formed from metal oxides or carbon with a corresponding coating are also conceivable. The electrodes 4, 6 are preferably formed from a large number of catalyst particles which can be formed as nanoparticles, for example core-shell nanoparticles ("core-shell-nanoparticles"). They have the advantage of a large surface area, wherein the noble metal or noble metal alloy is only arranged on the surface, while a less valuable metal, for example nickel or copper, forms the core of the nanoparticles. In such a polymer electrolyte membrane fuel cell (PEM fuel cell), a fuel or fuel molecules, in particular hydrogen gas, are split into protons and electrons at the first electrode 5 (anode). The electrolyte membrane 2 lets the protons (for example H + ) through, but is impermeable to the electrons (e - ). In this embodiment, the electrolyte membrane 2 is formed from an ionomer, preferably a sulfonated tetrafluoroethylene polymer (PTFE) or a perfluorosulfonic acid (PFSA) polymer. At the anode, the following reaction takes place here: 2H2→ 4H + + 4e - (Oxidation / electron release). When the protons pass through the electrolyte membrane 2 to the second electrode 6 (cathode), the electrons are conducted to the cathode or an energy store via an external circuit. At the cathode, a cathode gas, in particular oxygen or air containing oxygen, is provided, so that the following reaction takes place here: O2+ 4H + + 4e -→ 2 H2O (reduction / electron acceptance). In the present case, the electrodes 4, 6 are assigned gas diffusion sub-layers 7, 8, one of which 7 is assigned to the anode and the other 8 to the cathode. In addition, the gas diffusion sub-layer 7 on the anode side is assigned a flow field plate designed as bipolar plate 9 and used for the supply of fuel gas, which has a fuel flow field 11. Through the fuel flow field 11, fuel is supplied to the electrode 4 through the gas diffusion sub-layer 7. On the cathode side, the gas diffusion sub-layer 8 is assigned a flow field plate which comprises a cathode gas flow field 12 and is also designed as bipolar plate 10 and used for the supply of cathode gas to the electrode 6.

[0031] The membrane electrode unit (MEA) of the present application does not have to be produced in separate steps nor does it have to wait for the individual components to be firmly connected to each other by means of the liquid adhesive before further processing of the membrane electrode unit. The present application focuses on the fact that the liquid adhesive requires a certain time during the production process until it has reached the required strength, so that it has proven difficult to operate with the liquid adhesive alone, in particular in a continuous production process.

[0032] It is therefore advantageous to unwind the strip-shaped proton-conducting membrane material provided on a reel and to transport it in a suitable device to a first application tool with which the liquid adhesive is applied to the surface of the membrane material. However, in addition or alternatively, the liquid adhesive can also be applied to the surface of the electrode material, which can also be provided on a reel or as a single piece, for example. After the application of the liquid adhesive, the surfaces of the membrane material and the electrode material are superimposed and thereby brought into contact to form a material connection by means of the liquid adhesive. In addition, a production aid is introduced or applied into or onto the composite formed by the electrode material, the membrane material and the still uncured liquid adhesive, wherein the production aid is provided for stabilizing the uncured composite.

[0033] In this process, the production aid for stabilizing the uncured composite is applied in the edge region away from the active area of the membrane electrode unit. Thus, the production aid is applied away from the active area in which the fuel cell reactions take place. In other words, there is no production aid for stabilizing the uncured composite in the active area. The production aid can be applied in a point-like and / or in a planar and / or in a line-like manner and is preferably present as a further connector for material connection to the membrane material and / or to the electrode material, but which has a shorter curing time than the liquid adhesive.

[0034] The connecting material can be, for example, an adhesive which can be cured by UV light, wherein the connecting material is cured under UV radiation even before the liquid adhesive is cured. Alternatively or additionally, the connecting material can be a pressure-sensitive adhesive in the form of a tape which is applied to one or both surfaces of the membrane material or the electrode material away from the liquid adhesive. The connecting material can also be a hot-melt adhesive which is liquefied under the action of heat and solidifies again even before the liquid adhesive is cured. The connecting material preferably forms a laminated connection which itself is cured even before the liquid adhesive.

[0035] Alternatively or additionally, the production aid can also comprise a frame which is placed on the uncured composite or integrated therein, wherein the frame is melted, in particular using a laser, in a dot-like and / or surface-like and / or line-like manner and solidifies again even before the liquid adhesive is cured.

[0036] After the liquid adhesive is cured, the production aid can remain in the now dried composite, i.e. in the finished membrane-electrode unit. However, in the case of the production aid, it is not necessary here to meet the product requirements which are required for a fuel cell, it only needs to provide the strength required for handling, thus ensuring the stability of the membrane-electde unit required during production. The production aid can optionally be removed after the production of the membrane-electrode unit, in particular after the curing of the liquid adhesive, in particular after the membrane material is connected to the first electrode material on one of its sides and to the second electrode material on its second side, wherein it can also remain in the composite as long as it does not impair the product properties of the finished (actual) membrane-electrode unit.

[0037] Overall, the advantage of the present application is that the production aid can be applied before, during or after the liquid adhesive for producing the membrane-electrode unit is applied and ensures the strength of the membrane-electrode unit after the shortest time until the actual liquid adhesive itself is cured, thus all individual components of the membrane-electrode unit are connected together.

[0038] List of reference signs:

[0039] 1 fuel cell

[0040] 2 electrolyte membrane

[0041] 3 first side of the membrane

[0042] 4 electrode / anode

[0043] 5 second side of the membrane

[0044] 6 electrode / cathode

[0045] 7 gas diffusion sublayer on the anode side

[0046] 8 gas diffusion sublayer on the cathode side

[0047] 9 fuel gas bipolar plate

[0048] 10 cathode gas bipolar plate

[0049] 11 fuel gas flow field

[0050] 12 cathode gas flow field

Claims

1. A method for producing a laminate having at least two sublayers for a membrane electrode unit (MEA) for a fuel cell (1), comprising the following steps: - providing membrane materials made of proton-conducting electrolytes, - providing an electrode material comprising at least one catalyst, - applying a liquid adhesive to the surface of the membrane material and / or the surface of the electrode material, and - Bringing the surfaces of the membrane material and the electrode material into contact to form a material connection via a liquid adhesive, wherein a production aid is additionally introduced into or applied to an uncured composite formed by the electrode material, the membrane material and the not yet cured liquid adhesive, wherein the production aid is configured to stabilize the uncured composite, characterized in that the production aid is formed as a connector for material connection to the membrane material and / or the electrode material, which connector has a shorter curing time than the liquid adhesive.

2. The method according to claim 1, characterized in that Production aids for stabilizing the uncured composite are applied in edge regions remote from the active region of the membrane electrode unit (MEA).

3. The method according to claim 1 or 2, characterized in that The production aids for stabilizing the uncured composite are applied in the form of points and / or areas and / or lines.

4. The method according to any one of claims 1 to 2, characterized in that The connector is an adhesive that is curable by UV light, and the connector is cured under UV radiation even before the liquid adhesive cures.

5. The method according to any one of claims 1 to 2, characterized in that The connector is a pressure sensitive adhesive in the form of a tape that is applied to one or both surfaces remote from the liquid adhesive.

6. The method according to any one of claims 1 to 2, characterized in that The connecting substance is a hot melt glue, which liquefies under the action of heat and solidifies again even before the liquid adhesive solidifies.

7. The method according to any one of claims 1 to 2, characterized in that The joint forms a laminate connection that cures even before the liquid adhesive.

8. The method according to any one of claims 1 to 2, characterized in that The production aid comprises a frame which is placed on or integrated into the uncured composite part and which is melted in a point-shaped and / or area-shaped and / or line-shaped manner and solidifies again even before the liquid adhesive solidifies.

9. The method according to any one of claims 1 to 2, characterized in that The production aid remains in the composite component after the liquid adhesive has cured.

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