Sealed membrane electrode assembly

Abstract

Membrane electrode assembly (MEA) comprising a membrane (4) made of a polymeric ion-conducting material arranged between two electrodes, and a planar sealing element (5) circumferentially around the outer circumferential edge, which is embedded in the membrane (4) at least in an edge region, wherein the sealing element (5) is designed such that it is anchored in the membrane (4) by means of a positive locking, wherein the positive locking is formed by through openings (6) in the planar sealing element (5) which are at least partially penetrated by the membrane material, characterized in that the through openings (6) are formed by a perforation.

Description

Technical field

[0001] The invention relates to a membrane electrode assembly (MEA) comprising a membrane made of a polymeric ion-conducting material arranged between two electrodes, and a sealing element circumferentially surrounding the outer edge, which is embedded in the membrane at least in an edge region. The invention further relates to a method for manufacturing such an MEA. State of the art

[0002] Membrane electrode assemblies (MEAs), hereinafter referred to as MEAs, are the core component in polymer electrolyte membrane (PEM) fuel cells. The electrochemical reactions of a fuel cell and other electrochemical reactors (e.g., electrolysis) take place within the MEA. Therefore, the MEA consists of various functional active materials.

[0003] In the simplest case, the MEA comprises a composite of two electrodes (anode and cathode), each consisting of a porous, air-permeable layer (GDL) coated with a catalyst on the membrane side, and a membrane made of a polymeric ion-conducting material arranged between the electrodes.

[0004] The GDLs coated with the catalyst layer are also known as gas diffusion electrodes (GDEs). The GDL is typically also coated with a microporous layer (MPL) on the catalyst side.

[0005] The electrodes typically comprise (supported) catalysts combined with the so-called ionomer. The anodic hydrogen oxidation reaction and the cathodic oxygen reduction reaction take place on the catalyst surface. These reactions generate the usable electricity from the chemical energy of the fuels. The ionomer performs the electrolytic conduction function, while the catalyst support or the catalyst itself performs the electrical conduction.

[0006] The membrane separates the electrodes from each other. It prevents not only the flow of electrons but also the exchange of gases between the two electrodes. In addition to its separating function, the membrane also allows the diffusion of protons (product of the anodic hydrogen oxidation reaction) from the anode to the cathode. These protons react at the cathode to form water.

[0007] The GDL and the MPL applied to it have the function of supplying the reactants of the electrochemical partial reactions (hydrogen and atmospheric oxygen) as well as the water produced during the reactions to and from the electrodes.

[0008] In order to operate the MEA, the two electrodes must also be gas-tightly separated at the interface with the periphery; this is ensured by the so-called gasket (sometimes also called internal seal). The gasket separates the media of the anode and cathode at the interface of the active materials (electrodes, membrane, GDL / MPL).

[0009] From EP 3 807 946 A1, which constitutes the prior art, a method for manufacturing a MEA is known in which two GDLs are each provided with a catalyst coating to produce two GDEs. A thin membrane is then applied to at least one of the GDEs. Finally, both GDEs are arranged and pressed together so that the membrane layer(s) are enclosed by both GDEs. From EP 3 807 946 A1, it is also known to provide the MEA manufactured in this way with a circumferential sealing frame. A further sealing element may be provided that extends parallel to the plane of the MEA and engages in the joint between the two membrane layers of the MEA at an edge.

[0010] A lower seal that engages laterally in the layered composite is also known from DE 10 2009 004 054 A1. The lower seal can be formed directly on the proton exchange membrane layer or cast, molded, or applied as a film with cutouts to provide the electrochemically active area of ​​the membrane electrode assembly. A similar arrangement is also known from US 11 600 827 B2. Here, too, a partial seal is provided that additionally seals the chemically active area to the outside. In US 11 600 827 B2, the outermost lower seal can be made of a rigid or elastic material.

[0011] The further processing of the MEA typically employs roll-to-roll processes common in fuel cell manufacturing. When the MEA is mounted onto the roll and the material web is transported at high speed, mechanical stresses can occur within the web, which the joint between the sealing element and the layers, in particular, must withstand. However, reliable media sealing must be ensured for the MEA. Therefore, improving the mechanical stability of the material web would be desirable. Description of the invention

[0012] The object of the invention is therefore to further develop a membrane electrode assembly of the type mentioned above in such a way that it can withstand high mechanical loads and can thus, in particular, be easily processed in a roll-to-roll manufacturing process without the seal detaching. A further object is to provide a method for manufacturing such a membrane electrode assembly.

[0013] This problem is solved with a membrane electrode assembly (MEA) according to claim 1. Claim 12 describes a method for manufacturing such an MEA. Advantageous embodiments of the invention are described in the dependent claims.

[0014] According to the invention, in a membrane electrode assembly (MEA) comprising a membrane made of a polymeric ion-conducting material arranged between two electrodes and a sealing element circumferentially around the outer circumferential edge, which is embedded in the membrane at least in an edge region, the sealing element is designed in such a way that it is anchored in the membrane by means of a positive locking mechanism.

[0015] Surprisingly, it has been shown that mechanically anchoring a sealing element in the membrane does not impair the functionality of the membrane, but on the other hand, the mechanical stability of the joint between the seal and the layers can be increased to such an extent that the material web can be easily processed further in the roll-to-roll process in fuel cell manufacturing.

[0016] According to the invention, the sealing element is designed as a flat surface and the positive locking is achieved through through openings in the flat sealing element, which are at least partially penetrated by the membrane material.

[0017] According to the invention, the through-openings are produced in a simple manner by perforating the flat sealing element. The perforation can be introduced into the flat sealing element, for example, by means of laser treatment or punching. The perforation can have a regular or irregular hole pattern.

[0018] Advantageously, the diameter of the through-holes should be greater than or equal to 5 µm. With diameters smaller than 5 µm, the ionomer can no longer fully fuse the seal, and therefore the gas-tight property of the interface between the MEA and the gasket is no longer guaranteed. According to a further preferred embodiment of the invention, the diameter should be less than or equal to 15 cm, particularly preferably less than 5 cm, and even more preferably less than 3 cm. Diameters greater than 15 cm result in the advantageous mechanical anchoring no longer being ensured. The increased mechanical stability of the interface between the MEA and the gasket is therefore no longer present. Very good mechanical stability is achieved with diameters less than or equal to 5 cm, and even better stability with diameters less than or equal to 3 cm.

[0019] According to a preferred embodiment of the invention, the distance between the through-holes is between 1 µm and 5 cm. If the distance between the through-holes is less than 1 µm, the web between the through-holes becomes mechanically unstable and can no longer guarantee the advantageous mechanical anchoring. If the distance between the through-holes exceeds 5 cm, the advantageous mechanical anchoring is also no longer guaranteed. The increased mechanical stability of the interface between the MEA and the gasket is therefore no longer present.

[0020] According to a further preferred embodiment of the invention, the thickness of the planar sealing element is between 1 µm and 1000 µm. If the thickness of the sealing element (or gasket) falls below 1 µm, the sealing element itself becomes too mechanically and chemically unstable, so that it can neither be further processed under typical fuel cell manufacturing conditions nor meet the required service life of a fuel cell. If the sealing element (or gasket) is thicker than 1000 µm, the subsequent function of the MEA is negatively affected.

[0021] Surprisingly, it has been shown that the planar sealing element with through-holes can also be used as a planar reinforcement layer for the MEA. For this purpose, the planar sealing element can extend either partially or completely across the surface of the membrane. Planar reinforcement layers are a known technique. They are typically incorporated into the layered composite of an MEA to impart mechanical strength to the composite. This is particularly important if the material is subjected to mechanical stress during further processing, for example, using a roll-to-roll process.

[0022] Porous materials, often ePTFE, are typically used as planar reinforcement layers in membranes. This requires impregnating the porous materials with the material in which they are embedded. Due to the small pore size (generally < 0.2 µm) of commonly used materials, this process step can be very complex. When using the flat sealing element with its relatively large openings as a planar reinforcement layer, the impregnation step is eliminated. The openings of the flat sealing element simply fill with the ion-conducting polymer material of the membrane during compression.

[0023] The MEA can be provided with a circumferential sealing frame that extends essentially perpendicular to the planar extent of the layers and covers and seals the edges of the individual layers on the outer circumference.

[0024] A particularly good sealing effect can be achieved if the flat sealing element is connected to the sealing frame on its outer circumference.

[0025] The following materials can be used for the flat sealing element and the sealing frame: thermoplastics (PET, PEN, LDPE, MDPE, HDPE, LLDPE, PP, polyester, nylon, PTFE, PEEK, PEEKK etc.), fiber-reinforced thermoplastics (e.g. glass fiber), bioplastics (cellulose hydrate and / or other cellulose-based polymers), thermoplastic elastomers and / or coated metal foils.

[0026] A preferred method for manufacturing a membrane electrode assembly according to the invention with a sealing element comprises the following steps: i) Provision of two gas diffusion layers (GDL), possibly with microporous layers (MPL), ii) Coating the GDL / MPL on the MPL side with a catalyst paste and drying the paste to produce a gas diffusion electrode (GDE), iii) Coating at least one of the GDEs on the catalyst surface with an ionomer paste, iv) Providing a flat sealing element with through-openings, v) Cutting of two ionomer-coated GDEs or one ionomer-coated GDE and one uncoated, vi) Positioning the two GDEs from step v) in such a way that the ionomer layers or ionomer and catalyst layer come into contact with each other and vii) Joining by hot pressing, wherein the flat sealing element is inserted into the joining gap before joining.

[0027] In the event that a sealing frame is provided, step vi) also includes the positioning of the sealing frame.

[0028] Since, according to the present invention, the electrodes are not pressed with a separately produced membrane as is usually the case, but rather an ionomer layer is applied, it is necessary to build up the GDE gradually.

[0029] GDLs are known. They typically consist of a planar, porous, gas-permeable material, e.g., carbon fibers with a PTFE hydrophobic coating.

[0030] MPLs are also known per se. According to the invention, MPLs made of carbon (graphite, carbon black) and a binder (e.g. PTFE) are preferred.

[0031] According to the invention, the GDL / MPL layers are provided with a catalyst layer, first with a standard industrial catalyst layer and optionally additionally with a second, highly precipitated catalyst / ionomer layer, which later prevents the penetration of the ionomer solution in step iii) "application of the ionomer paste to the GDE". Direct coating, decal transfer, or comparable methods can be used as coating processes.

[0032] The catalyst layers are preferably produced using industrially available pastes containing the catalyst components.

[0033] After the pastes are applied, the layers are dried.

[0034] To produce the ionomer layer on at least one GDE, a paste containing an ionomer is applied and then dried, according to the invention. Suitable ionomer paste components are commercially available ionomers (e.g., Nafion®), solvents such as methanol, ethanol, propanol, acetone, DMAc, DMF, butanol, etc., and water.

[0035] In the next step, the two ionomer-coated GDEs, or the one ionomer-coated GDE and the uncoated one, are cut to size and positioned so that the ionomer layers, or the ionomer and catalyst layers, are adjacent to each other. The layers are then joined to the flat sealing element by hot pressing. This is a standard hot pressing process known in the art. When the ionomer-coated electrodes are pressed against the sealing element, which has through-holes, the ionomer / membrane material penetrates the through-holes, thus creating the bond.

[0036] The inventive method not only has the advantage of easily anchoring a seal firmly in the membrane, but this firm connection is also achieved purely mechanically. No adhesives or bonding agents, with their potentially negative effects on the MEA, are used.

[0037] The invention is described in more detail below using the figures: Brief description of the drawings

[0038] They show: Fig. 1 in a schematic lateral sectional view a symmetrically constructed MEA according to a preferred embodiment of the invention, Fig. 2 in a schematic lateral sectional view an asymmetrically constructed MEA according to a further preferred embodiment of the invention, Fig. 3 an electron micrograph of a longitudinal section through an MEA with an anchored sealing element (opposite the Fig. 1, Fig. 2 and Fig. 4 rotated by 90°). Fig. 4 in a schematic lateral sectional view an MEA in which the sealing element is designed as a reinforcement layer. Implementation of the invention

[0039] One can recognize in Fig. 1 A membrane electrode assembly (MEA) 10 comprising a membrane 4 made of a polymeric ion-conducting material arranged between two electrodes. The electrodes are each formed by a gas diffusion layer 1 with a microporous layer 2 arranged on it and a catalyst layer 3 deposited thereon.

[0040] A sealing element 5 is also visible, which is embedded in the membrane 4 at its edge. According to the invention, the sealing element 5 is anchored in the membrane 4. For this purpose, it has through-openings 6 which are penetrated by the membrane material and thus create a positive fit.

[0041] In Fig. 1 The sealing element 5 is arranged centrally in the membrane 4.

[0042] Fig. 2 shows an MEA analogous to the one in Fig. 1 shown, in which, however, according to a further preferred embodiment of the invention, the seal 5 is arranged at the edge of the membrane, adjacent to the catalyst layer 3.

[0043] In Fig. Figure 3 shows an electron micrograph of a longitudinal section through a MEA according to the invention. The gas diffusion layers are designated by reference numeral 1, and the microporous layers and catalyst layers, which are indistinguishable from one another in this image, are designated by 2 and 3. The image shows the membrane 4 and the sealing element 5, which projects into and is embedded in the membrane 4 at an edge (from right to left). The section passes through a through-opening 6 in the sealing element 5. The through-opening 6 is filled with membrane material. In this way, a positive fit is created, and the sealing element 5 is anchored in the membrane 4.

[0044] Fig.Figure 4 shows a schematic longitudinal section depicting a further embodiment of a MEA according to the invention, in which a perforated sealing element 5 extends over the entire surface area of ​​the membrane, acting like a reinforcing layer. A further reinforcing layer is therefore not required. The through-holes 6 of the perforated sealing element are simply filled with the membrane material during the hot pressing of the layers. The anchoring is thus formed by the sealing element 5.

Claims

[1] Membrane electrode assembly (MEA) comprising a membrane (4) made of a polymeric ion-conducting material arranged between two electrodes, and a planar sealing element (5) circumferentially surrounding the outer circumferential edge, which is embedded in the membrane (4) at least in an edge region, wherein the sealing element (5) is designed such that it is anchored in the membrane (4) by means of a positive fit, wherein the positive fit is formed by through openings (6) in the planar sealing element (5) which are at least partially penetrated by the membrane material, characterized by , that the through-openings (6) are formed by a perforation. [2] Membrane electrode assembly according to claim 1, characterized by , that the diameter of the through-holes (6) is between 5 µm and 15 cm. [3] Membrane electrode assembly according to claim 1 or 2, characterized by , that the distance between the through-holes (6) is between 1 µm and 5 cm. [4] Membrane electrode assembly according to at least one of claims 1 to 3, characterized by that the thickness of the planar sealing element (5) is between 1 µm and 1000 µm. [5] Membrane electrode assembly according to at least one of claims 1 to 4, characterized by , that the planar sealing element (5) extends over the entire planar extent of the membrane (4) in the manner of a reinforcement layer. [6] Membrane electrode assembly according to at least one of claims 1 to 5, characterized by , that a sealing frame extending substantially perpendicular to the layers is provided for sealing the edges of the layers on the outer circumference of the MEA (10). [7] Membrane electrode assembly according to claim 6, characterized by , that the flat sealing element (5) is connected to the sealing frame at its outer circumference. [8] Membrane electrode assembly according to at least one of claims 1 to 7, characterized by, that the planar sealing element (5) consists of thermoplastics (PET, PEN, LDPE, MDPE, HDPE, LLDPE, PP, polyester, nylon, PTFE, PEEK, PEEKK etc.), fiber-reinforced thermoplastics (e.g. glass fiber), bioplastics (cellulose hydrate and / or other cellulose-based polymers), thermoplastic elastomers and / or coated metal foils. [9] Membrane electrode assembly according to at least one of claims 1 to 8, characterized by , that the sealing frame consists of thermoplastics (PET, PEN, LDPE, MDPE, HDPE, LLDPE, PP, polyester, nylon, PTFE, PEEK, PEEKK etc.), fiber-reinforced thermoplastics (e.g. glass fiber), bioplastics (cellulose hydrate and / or other cellulose-based polymers), thermoplastic elastomers and / or coated metal foils. [10] Membrane electrode assembly according to any one of claims 1 to 9, characterized by that the electrodes are designed as gas diffusion electrodes. [11] Membrane electrode assembly according to any one of claims 1 to 10, characterized by , that the gas diffusion layer (1) is provided with a microporous layer (2). [12] Method for manufacturing a membrane electrode assembly according to any one of claims 1 to 11, comprising the following steps: i) Provision of two gas diffusion layers (GDL), possibly with microporous layers (MPL), ii) Coating the GDL / MPL on the MPL side with a catalyst paste and drying the paste to produce a gas diffusion electrode (GDE), iii) Coating at least one of the GDEs on the catalyst surface with an ionomer paste, iv) Providing a flat sealing element with through-openings, v) Cutting of two ionomer-coated GDEs or one ionomer-coated GDE and one uncoated, vi) Positioning the two GDEs from step v) in such a way that the ionomer layers or ionomer and catalyst layer come into contact with each other and vii) Joining by hot pressing, wherein the flat sealing element is inserted into the joining gap before joining. [13] Method according to claim 12, characterized by , that step vi) includes the positioning of the sealing frame.

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