Membrane electrode assembly comprising a planar reinforcement component

Abstract

The invention relates to a membrane electrode assembly (MEA) comprising: a membrane (4) that is made of a polymeric ion-conducting material and is arranged between two electrodes; and at least one planar reinforcement component in the layered structure, wherein, according to the invention, the at least one planar reinforcement component comprises a perforated layer (5) made of a reinforcement material. The invention also relates to a method for manufacturing such an MEA.

Description

[0001] Membrane electrode assembly with planar reinforcement component

[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 at least one planar reinforcement component in the layered composite. 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] EP 3 807 946 A1, which represents the prior art, discloses a method for producing an MEA, 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. EP 3 807 946 A1 also discloses providing membranes with a porous reinforcement layer to increase their mechanical stability.

[0014] Planar reinforcement layers are well known. 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.

[0015] Typically, porous materials, often ePTFE, are used as planar reinforcement layers. This requires the porous materials to be impregnated with the material in which they are embedded.

[0016] For example, US 9034134 B2 describes a process for the layer-by-layer construction of an MEA by applying the individual components, such as a catalyst layer, ionomer layer, etc., one on top of the other in liquid form. This process also involves incorporating a reinforcement layer of ePTFE (expanded polytetrafluoroethylene) into an ionomer layer. The layered composite must be kept moist until the ePTFE has absorbed the ionomer component. The layered composite must then be dried. Due to the small channel cross-sections of the pores in ePTFE (typically < 0.2 pm), this process is very complex.

[0017] Description of the invention

[0018] 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 be easily processed in a roll-to-roll manufacturing process, while being simple and cost-effective to manufacture. A further object is to provide a method for producing such an MEA.

[0019] This object is achieved with a membrane electrode assembly (MEA) according to claim 1. Claim 9 describes a method for producing such an MEA. Advantageous embodiments of the invention are described in the subclaims.

[0020] 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 at least one planar reinforcing component in the layer composite, it is provided that the at least one planar reinforcing component comprises a perforated layer made of a reinforcing material.

[0021] Perforation, in the context of the invention, refers to the piercing or puncturing of a material, e.g., a planar layer. This can be done, without limitation, by means of laser processing or punching. This inevitably results in hole diameters that are significantly larger than the diameters of porous materials, e.g., ePTFE, which are typically used to reinforce an MEA. It is not necessary for the perforated layer of a reinforcing material to have a regular hole pattern and / or uniform hole diameters across its entire surface. The hole pattern can be adapted to individual requirements.

[0022] Surprisingly, it has been shown that perforated layers of a reinforcing material with comparatively large hole diameters can be used as reinforcing layers instead of the porous materials impregnated with the membrane material without compromising the function of the MEA.

[0023] The perforated reinforcing layer can be placed in individual layers of the composite layer or between two adjacent layers. The holes are at least partially penetrated by the material of the respective layer. This not only ensures good mechanical anchoring of the perforated reinforcing layer in the layer, but also ensures that the perforated reinforcing layer does not impair the function of the layer.

[0024] Several perforated layers of a reinforcing material can also be provided in the layer composite of the MEA.

[0025] According to a preferred embodiment of the invention, the perforated layer of a reinforcing material is embedded in the membrane. This has the further advantage that it can also be used to seal the membrane. In this case, it can advantageously extend beyond the edge of the MEA. In this case, the material should also be suitable as a sealing material. It can also be connected to an external sealing frame on the outer circumference.

[0026] Advantageously, the hole diameters of the perforated layer made of a reinforcement material should be greater than or equal to 5 μm. With diameters smaller than 5 μm, especially when the reinforcement layer is embedded in the membrane, the ionomer may no longer fully penetrate the reinforcement layer, which can disrupt proton diffusion and thus impair the function of the fuel cell.

[0027] According to a further preferred embodiment of the invention, the diameter should be less than or equal to 10 cm, particularly preferably less than 5 cm, and even more preferably less than 3 cm. Depending on the material of the reinforcement layer, hole diameters greater than 10 cm may result in the MEA's higher mechanical load-bearing capacity being lost compared to a structure without a reinforcement layer. 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.

[0028] According to a preferred embodiment of the invention, the distance between the holes in the perforated reinforcement layer is between 1 μm and 2 cm. At distances between the holes of less than 1 μm, the bridge between the holes becomes mechanically unstable and can no longer ensure the advantageous mechanical reinforcement of the MEA. If a distance between the holes exceeds 2 cm, the diffusion of protons from the anode to the cathode (through the membrane) is disrupted, impairing the functionality of the fuel cell.

[0029] According to another preferred embodiment of the invention, the thickness of the reinforcement layer is between 1 μm and 1000 μm. If the thickness of the reinforcement layer falls below 1 μm, the reinforcement layer itself becomes mechanically and chemically unstable, making it impossible to further process under typical fuel cell manufacturing conditions or meet the required service life of a fuel cell. If the reinforcement layer is thicker than 1000 μm, the subsequent function of the MEA will be negatively affected.

[0030] According to the invention, the material of the reinforcement layer can be selected from the group 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 or other cellulose-based polymers), thermoplastic elastomers and / or coated metal foils.

[0031] Preferably, the electrodes are designed as gas diffusion electrodes (GDE), with a catalyst coating on the gas diffusion layers (GDL).

[0032] Particularly preferably, the gas diffusion layer is provided with a microporous layer (MPL) in a known manner.

[0033] 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 perforated layer made of a reinforcing material, v) cutting two ionomer-coated GDEs or one ionomer-coated GDE and one uncoated one, 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 perforated layer made of a reinforcing material is introduced into the joining gap before joining.

[0034] In case a sealing frame is provided, step vi) also includes the positioning of the sealing frame.

[0035] 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.

[0036] GDLs are well known. They typically consist of a planar, porous, gas-permeable material, such as carbon fibers with a PTFE hydrophobic coating.

[0037] 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.

[0038] 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. The catalyst layers are preferably produced using industry-standard pastes containing the catalyst components. After application of the pastes, the layers are dried.

[0039] 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.

[0040] In the next step, the two ionomer-coated GDEs, or the one ionomer-coated GDE and the uncoated GDE, 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 planar, perforated reinforcement layer by hot pressing. When the ionomer-coated electrodes are pressed together with the perforated reinforcement layer, the ionomer / membrane material penetrates the holes, thus creating a membrane with a reinforcement layer that provides a mechanically stable separation between the anode and cathode while still allowing proton diffusion from the anode to the cathode.

[0041] In the process for manufacturing an MEA described above, the reinforcement layer is placed within the membrane. However, it can also be incorporated into any other layer. Additional reinforcement layers can also be incorporated within the layers.

[0042] The invention is described in more detail below with reference to the figures: Brief description of the drawings

[0043] It shows:

[0044] Fig. 1 shows a schematic side sectional view of an MEA according to the invention with a perforated layer of reinforcing material.

[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 perforated layer (5) made of a reinforcing material, which is embedded, without restriction of generality, into the membrane (4). The membrane material penetrates the holes in the perforated layer (5). This is easily achieved by hot-pressing the layers. In this process, the membrane material is also pressed into the holes.

Claims

Patent claims 1. Membrane electrode assembly (MEA), comprising a membrane (4) made of a polymeric ion-conducting material arranged between two electrodes, and at least one planar reinforcing component in the layer composite, characterized in that the at least one planar reinforcing component comprises a perforated layer (5) made of a reinforcing material.

2. Membrane electrode unit according to claim 1, characterized in that the hole diameter of the holes (6) of the perforated layer of a reinforcing material is between 5 pm and 10 cm.

3. Membrane electrode unit according to claim 1 or 2, characterized in that the distance between the holes (6) of the perforated layer of a reinforcing material (5) is between 1 pm and 2 cm.

4. Membrane electrode unit according to at least one of claims 1 to 3, characterized in that the thickness of the perforated layer of a reinforcing material (5) is between 1 pm and 1000 pm.

5. Membrane electrode unit according to at least one of claims 1 to 4, characterized in that the layer of a perforated reinforcing material (5) is embedded in the membrane (4).

6. Membrane-electrode unit according to at least one of claims 1 to 5, characterized in that the reinforcing material is selected from the group 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 or other Cellulose-based polymers), thermoplastic elastomers and / or coated metal foils.

7. Membrane electrode assembly according to one of claims 1 to 6, characterized in that the electrodes are designed as gas diffusion electrodes.

8. Membrane electrode unit according to one of claims 1 to 7, characterized in that the gas diffusion layer (1) is provided with a microporous layer (2).

9. A method for producing a membrane electrode assembly according to any one of claims 1 to 8, 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 perforated layer of a reinforcing material, v) cutting two ionomer-coated GDEs or one ionomer-coated GDE and one uncoated GDE, vi) positioning the two GDEs from step v) such that the ionomer layers or ionomer and catalyst layer come into contact with one another, and vii) joining by hot pressing, wherein the perforated layer of a reinforcing material is introduced into the joining gap before joining.

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