Sealed membrane electrode assembly

Abstract

The invention relates to a membrane electrode assembly (MEA) comprising a membrane (4) arranged between two electrodes and made of a polymer ion-conducting material, and a flat sealing element (5) surrounding an outer peripheral edge and 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 an integral bond. Furthermore, a method for manufacturing such an MEA (10) is described.

Description

[0001] Sealed membrane electrode assembly

[0002] Description

[0003] Technical area

[0004] 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 extending around the outer peripheral edge and embedded in the membrane at least in one edge region. The invention further relates to a method for producing such an MEA.

[0005] State of the art

[0006] Membrane electrode assemblies (MEAs), hereinafter referred to as MEAs, are the core components in polymer electrolyte membrane (PEM) fuel cells. The electrochemical reactions of a fuel cell and other electrochemical reactors (e.g., electrolysis) take place in the MEA. Therefore, the MEA consists of various functional active materials.

[0007] 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.

[0008] GDLs coated with a catalyst layer are also known as gas diffusion electrodes (GDEs). The GDL is typically coated with a microporous layer (MPL) on the catalyst side.

[0009] The electrodes typically comprise (supported) catalysts combined with a so-called ionomer. The anodic hydrogen oxidation reaction and the cathodic oxygen reduction reaction take place on the catalyst surface. These reactions generate the subsequently 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.

[0010] The membrane separates the electrodes from each other. It not only prevents the flow of electrons but also prevents gas exchange between the two electrodes. In addition to its separating function, the membrane also allows the diffusion of protons (products of the anodic hydrogen oxidation reaction) from the anode to the cathode. These protons react at the cathode to form water.

[0011] The GDL and the MPL applied to it have the function of transporting 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.

[0012] To operate the MEA, the two electrodes must also be separated gas-tight at the interface to the periphery. This is ensured by the so-called gasket (sometimes also called an internal seal). The gasket separates the anode and cathode media at the interface of the active materials (electrodes, membrane, GDL / MPL).

[0013] From EP 3 807 946 A1, which constitutes the generic prior art, a method for producing an 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 such that the membrane layer(s) are enclosed by both GDEs. From EP 3 807 946 A1 it is also known to provide the MEA produced in this way with a circumferential sealing frame. In this case, an additional sealing element can be provided which extends parallel to the plane of the MEA and engages in an edge region in the joint between the two membrane layers of the MEA.

[0014] For further processing of the MEA, the roll-to-roll processes commonly used in fuel cell manufacturing are generally used. When the MEA is clamped onto the roll and the material web is transported at high speed, mechanical stresses can occur in the material web, which the joint between the sealing element and the layers in particular must withstand. However, reliable media sealing must be ensured in the MEA. An improvement in the mechanical stability of the material web would therefore be desirable.

[0015] Description of the invention

[0016] The object of the invention is therefore to further develop a membrane electrode assembly of the type mentioned above so that it can withstand high mechanical loads and can thus be easily processed in a roll-to-roll manufacturing process without the seal becoming detached. A further object is to provide a method for producing such an MEA.

[0017] This object is achieved with a membrane electrode assembly (MEA) according to claim 1. Claim 14 describes a method for producing such an MEA. Advantageous embodiments of the invention are described in the subclaims.

[0018] 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 running around the outer peripheral edge and embedded in the membrane at least in one edge region, it is provided that the sealing element is designed such that it is anchored in the membrane by means of a positive fit.

[0019] Surprisingly, it has been shown that mechanical anchoring of a sealing element in the membrane does not impair the functioning 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 further processed in the roll-to-roll process in fuel cell production.

[0020] According to a preferred embodiment of the invention, the sealing element is flat and the positive connection is produced by through-openings in the flat sealing element, which are at least partially penetrated by the membrane material.

[0021] The through-holes can be easily created by perforating the flat sealing element. The perforation can be introduced into the flat sealing element, for example, by laser treatment or punching. The perforation can have a regular or irregular hole pattern.

[0022] Advantageously, the diameter of the through-openings should be greater than or equal to 5 μm. At diameters smaller than 5 μm, the ionomer can no longer fully join the seal and therefore the gas-tight property of the interface between MEA and gasket is no longer present. 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 mean that the advantageous mechanical anchoring is no longer guaranteed. The increased mechanical stability of the interface between MEA and gasket is therefore no longer present. Very good mechanical stability is achieved with diameters less than or equal to 5 cm, and even better with diameters less than or equal to 3 cm.

[0023] According to a preferred embodiment of the invention, the distance between the through-holes is between 1 μm and 5 cm. At distances between the through-holes of less than 1 μm, the web between the through-holes becomes mechanically unstable and can no longer ensure the advantageous mechanical anchoring. If a distance of 5 cm between the through-holes is exceeded, 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.

[0024] 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 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.

[0025] Surprisingly, it has been shown that the flat sealing element with through-holes can also be used as a planar reinforcement layer for the MEA. For this purpose, the flat sealing element can extend either partially or completely over the entire surface of the membrane. Planar reinforcement layers are well known. They are usually 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.

[0026] Typically, porous materials, often ePTFE, are used as planar reinforcement layers in membranes. For this purpose, the porous materials must be impregnated with the material in which they are embedded. Due to the small pore size (usually < 0.2 μm) of the commonly used materials, this process step can be very complex. When using the planar sealing element, which has a relatively large through-hole, as a planar reinforcement layer, the impregnation step is eliminated. The through-hole of the planar sealing element is simply filled with the ion-conducting polymer material of the membrane during compression.

[0027] The MEA can be equipped with a sealing frame around the outer perimeter, which extends essentially perpendicular to the planar extent of the layers and covers and seals the edges of the individual layers. A particularly good sealing effect can be achieved if the planar sealing element is connected to the sealing frame at its outer perimeter.

[0028] 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.

[0029] A preferred method for producing a membrane electrode assembly according to the invention with a sealing element comprises the following steps: i) providing two gas diffusion layers (GDL), optionally 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 provided with through-openings, v) cutting two ionomer-coated GDEs or one ionomer-coated GDE and one uncoated GDE, 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 one another, and vii) joining by hot pressing, wherein the flat sealing element is introduced into the joining gap before joining.

[0030] In case a sealing frame is provided, step vi) also includes the positioning of the sealing frame.

[0031] Since according to the present invention the electrodes are not pressed with a separately manufactured membrane, as is usually the case, but an ionomer layer is applied, it is necessary to build up the GDE gradually.

[0032] GDLs are well known. They typically consist of a planar, porous, gas-permeable material, such as carbon fibers with a PTFE hydrophobic coating.

[0033] 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.

[0034] According to the invention, the GDL / MPL layers are coated with a catalyst layer, initially with a first, industry-standard catalyst layer and optionally with a second, highly efficient catalyst / ionomer layer, which subsequently prevents the penetration of the ionomer solution in step iii) "application of the ionomer paste to the GDL." Direct coating, decal transfer, or comparable processes can be used as coating methods.

[0035] The catalyst layers are preferably produced using standard pastes containing the catalyst components. After the pastes are applied, the layers are dried.

[0036] To produce the ionomer layer on at least one GDE, a paste containing ionomer is also applied and then dried according to the invention. Suitable ionomer paste components are commercially available ionomers (e.g., Nation®), solvents such as methanol, ethanol, propanol, acetone, DMAc, DMF, butanol, etc., and water.

[0037] In the next step, the two ionomer-coated GDEs, or the one ionomer-coated GDE and the uncoated one, are cut and positioned so that the ionomer layers, or the ionomer and catalyst layers, are in contact with 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 together with the sealing element provided with through-holes, the ionomer / membrane material penetrates the through-holes, thus creating the anchoring.

[0038] The method according to the invention not only has the advantage of easily anchoring a seal firmly in the membrane, but this secure connection is also achieved purely mechanically. No adhesives or adhesion promoters, which can have negative effects on the MEA, are used.

[0039] The invention is described in more detail below with reference to the figures:

[0040] Brief description of the drawings

[0041] They show:

[0042] Fig. 1 shows a schematic side sectional view of a symmetrically constructed MEA according to a preferred embodiment of the invention, Fig. 2 shows a schematic side sectional view of an asymmetrically constructed MEA according to a further preferred embodiment of the invention,

[0043] Fig. 3 is an electron micrograph of a longitudinal section through an MEA with anchored sealing element (rotated by 90° compared to Figs. 1, 2 and 4).

[0044] Fig. 4 shows a schematic side sectional view of an MEA in which the sealing element is designed as a reinforcing layer.

[0045] Implementation of the invention

[0046] Figure 1 shows 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 thereon and a catalyst layer 3 deposited thereon.

[0047] Also visible is a sealing element 5 embedded in the membrane 4 in the edge region. According to the invention, the sealing element 5 is anchored in the membrane 4. For this purpose, it has through-openings 6 through which the membrane material penetrates, thus creating a positive connection.

[0048] In Fig. 1, the sealing element 5 is arranged centrally in the membrane 4.

[0049] Fig. 2 shows an MEA analogous to that shown in Fig. 1, in which, however, the seal 5 is arranged according to a further preferred embodiment of the invention at the edge of the membrane, adjacent to the catalyst layer 3.

[0050] Fig. 3 shows an electron micrograph of a longitudinal section through an MEA according to the invention. The gas diffusion layers are designated by reference numeral 1, while 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 protrudes into the membrane 4 in an edge region (from right to left) and is embedded therein. The section passes through a through-opening 6 in the sealing element 5. The through-opening 6 is filled with membrane material. This creates a positive fit, and the sealing element 5 is anchored in the membrane 4.

[0051] Fig. 4 shows a schematic longitudinal section of another embodiment of an MEA according to the invention, in which a perforated sealing element 5 extends over the entire surface area of ​​the membrane in the manner of a reinforcement layer. A further reinforcement layer is therefore not required. The through-openings 6 of the perforated sealing element are simply filled with the membrane material during hot-pressing of the layers. The anchoring is thus formed by the sealing element 5.

Claims

Patent claims 1 . Membrane electrode assembly (MEA), comprising a membrane (4) arranged between two electrodes and made of a polymeric ion-conducting material, and a flat sealing element (5) running around the outer peripheral edge and embedded in the membrane (4) at least in one edge region, characterized in that the sealing element (5) is designed such that it is anchored in the membrane (4) by means of a positive fit.

2. Membrane electrode unit according to claim 1, characterized in that the positive connection is formed by through openings (6) in the flat sealing element (5), which are at least partially penetrated by the membrane material.

3. Membrane electrode unit according to claim 1 or 2, characterized in that the through openings (6) are formed by a perforation.

4. Membrane electrode unit according to at least one of claims 1 to 3, characterized in that the diameter of the through openings (6) is between 5 pm and 15 cm.

5. Membrane electrode unit according to at least one of claims 1 to 4, characterized in that the distance between the through openings (6) is between 1 pm and 5 cm.

6. Membrane electrode unit according to at least one of claims 1 to 5, characterized in that the thickness of the flat sealing element (5) is between 1 pm and 1000 pm.

7. Membrane electrode unit according to at least one of claims 1 to 6, characterized in that the flat sealing element (5) extends in the manner of a reinforcing layer over the entire flat extent of the membrane (4).

8. Membrane electrode assembly according to at least one of claims 1 to 7, characterized in that a sealing frame extending substantially perpendicular to the layers is provided on the outer peripheral side of the MEA (10) to seal the edges of the layers.

9. Membrane electrode unit according to claim 8, characterized in that the flat sealing element (5) is connected to the sealing frame at its outer circumference.

10. Membrane electrode unit according to at least one of claims 1 to 9, characterized in that the flat 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.

11. Membrane electrode assembly according to at least one of claims 1 to 10, characterized in 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.

12. Membrane electrode assembly according to one of claims 1 to 8, characterized in that the electrodes are designed as gas diffusion electrodes.

13. Membrane electrode assembly according to one of claims 1 to 9, characterized in that the gas diffusion layer (1) is provided with a microporous layer (2).

14. A method for producing a membrane electrode assembly according to any one of claims 1 to 13, comprising the following steps: i) providing two gas diffusion layers (GDL), optionally 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 provided with through-openings, v) cutting two ionomer-coated GDEs or one ionomer-coated GDE and one uncoated GDE, 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 one another, and vii) joining by hot pressing, wherein the flat sealing element is introduced into the joining gap before joining.

15. The method according to claim 14, characterized in that step vi) includes positioning the sealing frame.

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