Membrane-electrode assembly for an electrolysis cell, membrane structure, method for producing a membrane-electrode assembly, method for producing a membrane structure and method for operating an electrolysis cell with a membrane-electrode assembly

Abstract

The present invention relates to a membrane structure (40) for a membrane-electrode assembly (10) for an electrolysis cell. The membrane structure (40) has a membrane (41) with an anode-side catalyst membrane coating (42) and a cathode-side catalyst membrane coating (43). The membrane structure (40) comprises a reinforcement element (50) for locally increasing the stability of the membrane structure (40).

Description

[0001] Description

[0002] title

[0003] Membrane electrode for a Membrane structure.

[0004] Method for producing a membrane electrode Method for

[0005] Manufacturing a membrane structure and method for operating a membrane electrode structure

[0006] The present invention relates to a membrane electrode assembly for an electrolysis cell, a membrane structure for a membrane electrode assembly, a method for producing a membrane electrode assembly, a method for producing a membrane structure and a method for operating an electrolysis cell with a membrane electrode assembly.

[0007] State of the art

[0008] Electrochemical energy converters such as fuel cell systems or electrolyzers are known in numerous different designs. The core component of these systems is usually a stacked structure comprising several electrolysis cells. More precisely, such a stacked structure usually comprises alternating bipolar plates (BPPs) and membrane electrode assemblies (MEAs). Similar to the PEM fuel cell, the membrane in the PEM electrolyzer is designed to allow only cations, typically H+ ions, to pass through to the cathode. In the case of an alkaline AEM electrolyzer, which is operated with an alkaline solution on the anode and / or cathode side, such as a KOH solution, only anions, typically OH- ions, pass through to the anode. For the sake of simplicity, the PEM electrolyzer is explained below as an example.Generic membrane electrode assemblies can be configured for PEM electrolyzers, AEM electrolyzers, and other system structures for electrochemical energy conversion. Such a PEM electrolyzer is known, for example, from WO2212812.

[0009] Depending on the system structure and operating mode, membrane-electrode assemblies are subject to high thermal and mechanical stresses. In the case of a PEM electrolyzer, water is added to the anode-side chamber, and water and oxygen are removed. The cathode-side chamber preferably contains the majority of the hydrogen produced. The hydrogen chamber on the cathode side preferably has a higher pressure, for example, on the order of 30 bar, which is higher than the pressure acting on the anode-side chamber, which is on the order of 1 bar to 5 bar. The aforementioned chambers must be sealed from one another in the stack, usually by a frame structure and the membrane.

[0010] Particularly in a transition region or in the region of a gap between the frame structure (subgasket) and a transport layer to the catalyst-coated membrane (CCM) of the membrane-electrode assembly, high forces can act in a stacking direction, which can cause damaging stress to the catalyst-coated membrane, especially in an electrolyzer which is operated with greatly different pressures on the anode and cathode sides.

[0011] Disclosure of the invention

[0012] Within the scope of the present invention, systems and methods for improving the stability of membrane structures and membrane-electrode assemblies are proposed. Features described in connection with the membrane-electrode assembly naturally also apply in connection with the membrane structure according to the invention and the methods according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always refers to each other. The membrane structure is suitable for electrochemical cells, in particular electrolysis cells, and is preferably used for PEM and AEM electrolyzers.

[0013] The membrane structure comprises a membrane with a catalyst membrane coating on the anode side and a catalyst membrane coating on the cathode side. The membrane structure includes a reinforcing element for locally increasing the stability of the membrane structure. This increases the mechanical stability of the membrane structure. Such a membrane structure is therefore particularly suitable for electrochemical cells that operate with a large differential pressure between the anode and cathode.

[0014] The reinforcing element is preferably made of PPS (polyphenylene sulfide), PEN (polyethylene naphthalate), a pressure-sensitive adhesive (PSA), and / or FEP (fluoroethylene propylene). These materials are chemically resistant and therefore suitable for use in electrochemical cells. Furthermore, they exhibit strengths that can reinforce the membrane structure of the electrochemical cells. The reinforcing element particularly preferably has a modulus of elasticity of at least 4000 N / mm². 2 on.

[0015] In alternative designs, the reinforcement element is also a membrane. It is made of the same material as the membrane and is essentially a kind of membrane adhesive bead.

[0016] The invention also includes a membrane electrode assembly for an electrochemical cell, in particular for an electrolysis cell.

[0017] The membrane electrode assembly includes:

[0018] - an anode side with an anode-side transport layer and an anode-side frame structure, which is at least partially designed in a frame-like manner around the anode-side transport layer,

[0019] - a cathode side with a cathode-side transport layer and a cathode-side frame structure, which is at least partially designed in a frame-like manner around the cathode-side transport layer, - an anode-side gap between the anode-side transport layer and the anode-side frame structure,

[0020] - a cathode-side gap between the cathode-side transport layer and the cathode-side frame structure,

[0021] - a membrane structure according to one of the above embodiments, positioned in a layered manner between the anode side and the cathode side, wherein the membrane has at least one bridge section which extends in a bridge-like manner over the anode-side gap and / or over the cathode-side gap, and wherein the reinforcing element is arranged on the at least one bridge section for locally increasing the stability of the membrane structure.

[0022] The reinforcement element is therefore arranged in the gap area between the transport layer and the frame structure. This prevents the membrane structure from being pushed into the gap and thus damaged during operation of the electrochemical cell. The membrane structure is reinforced particularly in the gap area so that it cannot be pushed into one of the gaps, or is only slightly pushed into one of the gaps, thus preventing mechanical failure of the membrane structure or even cracks in the membrane structure.

[0023] Within the scope of the present invention, it was initially recognized that the gap between the respective transport layer and the respective frame structure can lead to the membrane, including the catalyst coating, being mechanically overstressed in this area under high relative pressures between the anode side and the cathode side. This can lead to the membrane being damaged or destroyed in this area. To take this problem into account, the invention proposes providing a local reinforcing element in the area of ​​the respective gap to stabilize the respective bridge section. The reinforcing element can be specifically designed at the point where there is the greatest risk of mechanical overstressing of the membrane or membrane structure. In this way, the reinforcing element can be integrated into the membrane structure orinto the membrane electrode assembly. The basic structure of the membrane electrode assembly does not need to be modified for this purpose. This allows established processes and systems for manufacturing membrane electrode assemblies to continue to be used virtually unchanged.

[0024] The reinforcing element can be configured as a single piece or in multiple pieces. This means that the reinforcing element can comprise a plurality of reinforcing elements positioned at a distance from one another. The reinforcing element can be configured in the form of a reinforcing layer, i.e., in a layered configuration, in the bridge section. The position in the bridge section can be understood as a positioning and / or configuration of the reinforcing element in and / or on the bridge section. The reinforcing element can be configured on the anode-side catalyst membrane coating, on the membrane, and / or on the cathode-side catalyst membrane coating. This means that the reinforcing element does not have to be positioned directly on the membrane in order to increase the stability of the membrane in at least one bridge section.

[0025] Increasing stability in the region of at least one bridge section can be understood as meaning that the positioning and / or configuration of the reinforcing element according to the invention stabilizes the membrane or membrane structure locally in the region of the bridge section, in particular mechanically stabilizes it, so that there is greater mechanical resistance to the high relative pressures compared to adjacent areas. The reinforcing element therefore does not have to influence the material properties of the membrane itself. Rather, the reinforcing element can be understood as an auxiliary structure for locally increasing mechanical stability and / or strength.

[0026] The transport layer can comprise at least one media diffusion layer, in particular a gas diffusion layer (GDL), and thus, in principle, several different media diffusion layers. The transport layer can be configured at least partially as a porous transport layer.

[0027] In advantageous further developments, the reinforcement element extends in a frame-like or partially frame-like manner around the anode-side transport layer and / or the cathode-side transport layer. The reinforcement element thus serves as a positioning aid and / or a storage aid for the transport layer.

[0028] In preferred embodiments, the anode-side frame structure and / or the cathode-side frame structure has a recess for partially accommodating the reinforcing element. This allows the function of the positioning aid and / or storage aid to be better implemented. In particular, the lack of planarity of the surface of the membrane structure caused by the reinforcing element can be compensated for; as a result, the reinforcing element does not act as a bead, which would result in a concentration of stress on the electrochemical cells precisely in the area of ​​the gap, which in turn would be counterproductive to the intended goal, namely relieving the load on the membrane structure precisely in this area.

[0029] In further embodiments, the anode-side transport layer and / or the cathode-side transport layer also have a further recess for partially accommodating the reinforcement element. Here, too, the recess compensates for any non-planarity, allowing for a homogeneous surface pressure in the overall composite of the membrane-electrode assembly in the pressed or stacked state.

[0030] The recess and the further recess thus serve to ensure a homogeneous distribution of the surface pressure, thus avoiding harmful stress peaks, particularly in the area of ​​the gap between the transport layer and the frame structure; this applies to the arrangement of the reinforcing element on both the anode and cathode sides.

[0031] The reinforcement element can be integrally integrated with the membrane or designed as a separate part. If it is designed as a separate part, it can be attached, for example, by adhesive bonding. This allows for shear loading of the bonded area, resulting in a reduction of the membrane structure's load at the bonded area; a favorable uniaxial stress state is achieved. In advantageous embodiments, the anode-side transport layer, the anode-side frame structure, the cathode-side transport layer, and the cathode-side frame structure are designed such that the anode-side gap and the cathode-side gap are offset from one another in a transverse direction from the respective transport layer to the associated frame structure.As a result, the two critical gaps in the membrane structure are not arranged directly opposite each other, but are supported or supported on the opposite side by a frame structure or a transport layer. This design increases the stability of the overall membrane-electrode assembly.

[0032] In other words, the cathode window (or the cathode-side active area) can be designed smaller than the anode window (or the anode-side active area) (or vice versa), so that the coated membrane in the region of the respective gap is supported on its side facing away from the gap either by the frame structure or by the transport layer. In this way, stability can be further increased in a simple manner. The offset gaps mean that, in a plan view of the membrane-electrode assembly, one gap is formed closer to an outer edge region of the membrane-electrode assembly to the surroundings of the membrane-electrode assembly than the other gap. In this exemplary embodiment, one gap is therefore not located directly above the other gap.In particular, it is preferred that the anode-side gap and the cathode-side gap are formed offset from one another in the transverse direction such that they have no overlapping region in a stacking direction orthogonal to the transverse direction or are designed offset from one another accordingly without overlap. In this case, the bridge sections of the membrane are also correspondingly offset from one another. This means that in this case, the membrane or the membrane structure can have two bridge sections arranged next to one another, with one bridge section being designed within the other bridge section in the transverse direction. In other words, one bridge section can be designed in a frame-like manner or at least partially in a frame-like manner around the other bridge section in a plan view or in a projection in the stacking direction.In preferred developments, the offset between the anode-side gap and the cathode-side gap is designed such that the active area on the anode side is larger than the active area on the cathode side. The anode-side gap is therefore positioned closer to the outer region of the electrochemical cell, while the cathode-side gap is positioned closer to the active area of ​​the electrochemical cell. As a result, the more critical gap, namely the anode-side gap, is not subjected to the pressure of the cathode side on its opposite side, namely the cathode side; the cathode-side frame structure is therefore opposite the anode-side gap. If the cathode side is operated with overpressure compared to the anode side, then in this embodiment the anode-side gap is no longer in the overpressure region; on the contrary, the anode-side gap on the cathode side is underpinned by the frame structure or even supported by it.

[0033] In advantageous further developments, the reinforcing element is arranged only on the cathode side. A type of underlining of the catalyst-coated membrane only on the cathode side in the manner according to the invention may already be sufficient to achieve the desired stability with respect to the relative pressure conditions. Configuring the reinforcing element only on the cathode side may be sufficient, in particular, if further stabilization measures are implemented, such as the configuration with offset gaps described above.

[0034] The membrane electrode assembly can be configured for use in an electrolyzer and / or in a fuel cell, in particular in an electrolyzer and / or a fuel cell for a PEM fuel cell system, for a PEM electrolyzer, for an AEM fuel cell system, and / or for an AEM electrolyzer. The membrane electrode assembly can further be configured and designed for use in a mobile electrochemical energy converter, for example for use in a road vehicle. The membrane electrode assembly can be designed as an electrolysis cell or as part of an electrolysis cell. The invention also relates to a method for operating an electrolysis cell. The electrolysis cell has a membrane electrode assembly according to one of the above embodiments. The cathode side is operated with an overpressure of at least 20 bar, preferably at least 30 bar, relative to the anode side.During such operation, the membrane structure is subjected to particularly high mechanical stress; the reinforcement element attached to it is therefore particularly effective.

[0035] Furthermore, the invention relates to a method for producing a membrane structure as described above, comprising:

[0036] - Providing the membrane

[0037] - applying the anode-side catalyst membrane coating and the cathode-side catalyst membrane coating to the membrane, and

[0038] - Locally applying the reinforcing element to at least one catalyst membrane coating.

[0039] A further aspect of the invention relates to a method for producing a membrane electrode assembly as described above, comprising:

[0040] - Providing the membrane structure according to one of the above embodiments,

[0041] - Positioning the anode-side frame structure on the anode-side catalyst membrane coating and / or the cathode-side frame structure on the cathode-side catalyst membrane coating,

[0042] - applying the reinforcing element to the anode-side catalyst membrane coating and / or the cathode-side catalyst membrane coating, and

[0043] - Positioning the anode-side transport layer on the anode-side catalyst membrane coating and / or the cathode-side transport layer on the cathode-side catalyst membrane coating.

[0044] In this way, the membrane-electrode assembly can be manufactured particularly quickly and easily. Preferably, the reinforcing element can be introduced, in particular injected, into a transition region between the respective catalyst membrane coating and a respective edge structure, so that the reinforcing element can act not only as a reinforcing element, but also as a sealant for the fluids of the membrane-electrode assembly towards the environment of the membrane-electrode assembly. The sequence of process steps described above is nevertheless to be considered optional. In this case, the reinforcing element can, for example, be injection-molded as a bead during the manufacturing process if at least one frame structure is already positioned on the catalyst-coated membrane, but the associated transport layer has not yet been inserted or positioned.

[0045] Preferably, the anode-side frame structure and / or the cathode-side frame structure has a recess that interacts with the reinforcing element, for example, for positioning during the manufacturing process. The manufacturing process thus comprises the further method step:

[0046] - Positioning the anode-side frame structure and / or the cathode-side frame structure so that the recess interacts with the reinforcing element.

[0047] Further measures improving the invention will become apparent from the following description of various exemplary embodiments of the invention, which are schematically illustrated in the figures. All features and / or advantages apparent from the claims, the description, or the figures, including structural details and spatial arrangements, may be essential to the invention both individually and in various combinations.

[0048] They show schematically:

[0049] Figure 1 shows a membrane electrode assembly according to a first embodiment of the present invention, with only the essential areas being shown.

[0050] Figure 2 shows a membrane electrode assembly according to a second embodiment of the present invention, with only the essential regions shown. Figure 3 shows a membrane electrode assembly according to a third embodiment of the present invention, with only the essential regions shown.

[0051] Elements with the same function and mode of operation are provided with the same reference symbols in the figures.

[0052] Fig. 1 shows a cross-section of a membrane electrode assembly 10 for an electrolysis cell according to a first embodiment. As shown in Fig. 1, the membrane electrode assembly 10 has an anode side 20 with an anode-side transport layer 21 and an anode-side frame structure 22. The anode-side frame structure 22 is configured in a frame shape around the anode-side transport layer 21. Furthermore, the membrane electrode assembly 10 has a cathode side 30 with a cathode-side transport layer 31 and a cathode-side frame structure 32, wherein the cathode-side frame structure is configured in a frame shape around the cathode-side transport layer 31. The transport layers 21, 31 are also called PTL (Porous Transport Layer).

[0053] An anode-side gap 23 is formed between the anode-side transport layer 21 and the anode-side frame structure 22. A cathode-side gap 33 is formed between the cathode-side transport layer 31 and the cathode-side frame structure 32. Furthermore, the membrane-electrode assembly 10 comprises a membrane 41 positioned in a layered manner between the anode side 20 and the cathode side 30, with an anode-side catalyst membrane coating 42 and a cathode-side catalyst membrane coating 43. The catalyst-coated membrane 41, 42, 43 is also called CCM (catalyst coated membrane) or can be referred to as membrane structure 40. The membrane 41 or the membrane structure 40 has a bridge section 44 which extends in a bridge-like manner over the anode-side gap 23 and over the cathode-side gap 33.In addition, the membrane structure 40 has a reinforcing element 50 for locally increasing the stability of the membrane structure 40 in the bridge section 44 with respect to the differential or relative pressures prevailing there. The differential pressures of an electrolysis cell or electrolyzer between the cathode and anode can easily reach 30 bar, for example, to generate hydrogen at the corresponding pressure on the cathode side.

[0054] As a result of a pressure difference between the anode side 20 and the cathode side 30, the membrane structure 40 is slightly deformed, but this deformation is greatly reduced due to the reinforcing element 50. As a result, fatigue fracture, violent fracture and mechanical cracks in the membrane structure 40 are prevented.

[0055] The reinforcing element 50 is preferably made of PPS (polyphenylene sulfide), PEN (polyethylene naphthalate), a pressure-sensitive adhesive (PSA), and / or FEP (fluoroethylene propylene). These materials are particularly well suited to the conditions in electrochemical cells. They are characterized by appropriate chemical resistance and mechanical stability.

[0056] The reinforcing element 50 shown in Fig.1 is designed in a projection-like manner on the anode side 20 and on the cathode side 30 and projects there into the anode-side gap 23 and into the cathode-side gap 33. Furthermore, the reinforcing element 50 extends in a frame-like manner around the anode-side transport layer 21 on the anode side 20 and in a frame-like manner around the cathode-side transport layer 31 on the cathode side 30.

[0057] The embodiment shown in Fig. 2 essentially corresponds to the embodiment shown in Fig. 1, wherein the anode-side transport layer 21, the anode-side frame structure 22, the cathode-side transport layer 31, and the cathode-side frame structure 32 are configured such that the anode-side gap 23 and the cathode-side gap 33 are formed offset from one another in a transverse direction 60 from the respective transport layer 21, 31 to the associated frame structure 22, 32. The membrane 41 or membrane structure 40 shown in Fig. 2 has two bridge sections 44, 45 that extend over the gaps 23, 33 formed offset from one another in the transverse direction 60. More precisely, a first bridge section 44 extends over the cathode-side gap 33, and a further bridge section 45 extends over the anode-side gap 23.

[0058] Preferably, the gaps 23, 33 are arranged offset such that a larger anode-side active area 29 results than a cathode-side active area 39. The overpressure of the compressed hydrogen on the cathode side 30 thus no longer acts vertically (i.e., in the stacking direction) above the anode-side gap 23. The combination of the reinforcing element 50 with such an offset thus particularly effectively prevents the membrane 41 or membrane structure 40 from being pressed into the anode-side gap 23.

[0059] In preferred developments of the invention, a corresponding recess 35 is formed in the frame structure 22, 32 in order to accommodate that part of the reinforcing element 50 which projects beyond the planarity of the membrane structure 40 below the respective frame structure 22, 32. In the embodiment of Fig. 3, the cathode-side frame structure 32 has such a recess 35. Analogously, such a recess can also be formed on the anode side 20 in the anode-side frame structure 22. The cathode-side transport layer 31 is usually soft enough so that it does not require such a recess; however, a further recess 65 can also be formed here in order to provide height compensation for the reinforcing element 50 below the transport layer 31.

[0060] In addition to the illustrated embodiments, the invention permits further design principles. This means that the invention should not be considered limited to the exemplary embodiments explained with reference to the figures. As can be seen from the figures, numerous further combination variants of the illustrated embodiments are possible, not all of which have been described in detail. The same applies analogously to different variants for implementing the method. These variants should, of course, not be considered excluded from the scope of protection of the claimed invention.

Claims

Claims 1 . Membrane structure (40) for a membrane electrode assembly (10) for an electrolysis cell, comprising a membrane (41) with an anode-side catalyst membrane coating (42) and a cathode-side catalyst membrane coating (43), characterized in that the membrane structure (40) has a reinforcing element (50) for locally increasing the stability of the membrane structure (40).

2. Membrane structure (40) according to claim 1, characterized in that the reinforcing element (50) consists of PPS (polyphenylene sulfide), PEN (polyethylene naphthalate), a pressure-sensitive adhesive (PSA) and / or FEP (fluoroethylene propylene).

3. Membrane structure (40) according to claim 1, characterized in that the reinforcing element (50) is also a membrane (40) 4. Membrane structure (40) according to one of the preceding claims, characterized in that the reinforcing element (50) has a modulus of elasticity of at least 4000 N / mm 2 has.

5. Membrane electrode assembly (10) for an electrolysis cell, comprising: - an anode side (20) with an anode-side transport layer (21) and an anode-side frame structure (22) which is at least partially designed in a frame shape around the anode-side transport layer (21), - a cathode side (30) with a cathode-side transport layer (31) and a cathode-side frame structure (32), which is at least partially designed in a frame-like manner around the cathode-side transport layer (31), - an anode-side gap (23) between the anode-side transport layer (21) and the anode-side frame structure (22), - a cathode-side gap (33) between the cathode-side transport layer (31) and the cathode-side frame structure (32), - a membrane structure (40) according to one of claims 1 to 3, positioned in a layered manner between the anode side (20) and the cathode side (30), wherein the membrane (41) has at least one bridge section (44, 45) which extends in a bridge-like manner over the anode-side gap (23) and / or over the cathode-side gap (33), and wherein the reinforcing element (50) is arranged on the at least one bridge section (44, 45) for locally increasing the stability of the membrane structure (40).

6. Membrane electrode assembly (10) according to claim 5, characterized in that the reinforcing element (50) extends in a frame-like or partially frame-like manner around the anode-side transport layer (21) and / or around the cathode-side transport layer (31).

7. Membrane electrode assembly (10) according to one of claims 5 or 6, characterized in that the anode-side frame structure (22) and / or the cathode-side frame structure (32) has a recess (35) for partially receiving the reinforcing element (50).

8. Membrane electrode assembly (10) according to claim 7, characterized in that the anode-side transport layer (21) and / or the cathode-side transport layer (31) has a further recess (65) for partially receiving the reinforcing element (50).

9. Membrane electrode assembly (10) according to one of claims 5 to 8, characterized in that the anode-side transport layer (21), the anode-side frame structure (22), the cathode-side transport layer (31) and the cathode-side frame structure (32) are designed such that the anode-side gap (23) and the cathode-side gap (33) are offset from one another in a transverse direction (60) from the respective transport layer (21, 31) to the associated frame structure (22, 32).

10. Membrane electrode assembly (10) according to claim 9, characterized in that the offset between the anode-side gap (23) and the cathode-side gap (33) is designed such that a larger anode-side active area (29) results than a cathode-side active area (39).

11. Membrane electrode assembly (10) according to one of claims 5 to 10, characterized in that the reinforcing element (50) is arranged only on the cathode side (30).

12. A method for producing a membrane structure (40) according to one of claims 1 to 4, comprising the following method steps: - Providing the membrane (41) - applying the anode-side catalyst membrane coating (42) and the cathode-side catalyst membrane coating (43) to the membrane (41), and - Locally applying the reinforcing element (50) to at least one catalyst membrane coating (42, 43).

13. A method for producing a membrane electrode assembly (10) according to one of claims 5 to 11, comprising the following method steps: - Providing the membrane structure (40) according to one of claims 1 to 3, - positioning the anode-side frame structure (22) on the anode-side catalyst membrane coating (42) and / or the cathode-side frame structure (22) on the cathode-side catalyst membrane coating (42), - applying the reinforcing element (50) to the anode-side catalyst membrane coating (42) and / or the cathode-side catalyst membrane coating (43), and - Positioning the anode-side transport layer (21) on the anode-side catalyst membrane coating (42) and / or the cathode-side transport layer (31) on the cathode-side catalyst membrane coating (43).

14. The method according to claim 13, wherein the anode-side frame structure (22) and / or the cathode-side frame structure (32) has a recess (35), characterized by the following method step: - Positioning the anode-side frame structure (22) and / or the cathode-side frame structure (22) so that the recess (35) interacts with the reinforcing element (50).

15. A method for operating an electrolysis cell with a membrane electrode arrangement (10) according to one of claims 5 to 11, characterized in that the cathode side (30) is operated with an overpressure of at least 20 bar, preferably of at least 30 bar, relative to the anode side (20).

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