Method for regenerating an electrolysis cell having a membrane-electrode assembly
Patent Information
- Application Number
- EP2024703785
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-02-21
- Filing Date
- 2024-02-07
- Publication Date
- 2025-12-31
AI Technical Summary
Electrolysis cells with membrane-electrode arrangements face mechanical stress and potential damage due to high relative pressures between the anode and cathode sides, leading to deformation and possible failure of the membrane structure.
A regeneration method is introduced where the anode side is operated at a higher pressure than the cathode side during a regeneration period, reversing the deformation and replastifying the membrane structure, which can be done during normal operation or shutdown, and preferably at temperatures above 100°C to enhance stress reduction and recrystallization of ionomers.
This method effectively compensates for and reverses the plastic deformations of the membrane structure, reducing the risk of damage and increasing the stability of the membrane-electrode arrangement by managing pressure differences and temperature, thereby extending the lifespan of the electrolysis cell.
Smart Images
Figure EP2024052996_29082024_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] title
[0003] Procedure for one with a membrane
[0004] Electrode Anc
[0005] The present invention relates to a method for regenerating an electrolysis cell with a membrane electrode assembly.
[0006] State of the art
[0007] Electrochemical energy converters such as 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 (BPP) and membrane electrode assemblies (MEA). Similar to the PEM fuel cell, the membrane in the PEM electrolyzer should only allow cations, usually H+ ions, to pass through to the cathode. In the case of an alkaline AEM electrolyzer, which is operated with an alkaline solution, e.g. a KOH solution, on the anode side and / or the cathode side, only anions, usually OH- ions, pass through towards 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. A PEM electrolyzer, for example, is known from WO2212812.
[0008] Depending on the system structure and operating mode, membrane electrode assemblies are subject to high thermal and mechanical stresses. Particularly in the transition region or gap between a frame structure (subgasket) and a transport layer to a catalyst-coated membrane (CCM) of the membrane electrode assembly, high forces can act in a stacking direction, which can deform the catalyst-coated membrane, especially in an electrolyzer that operates at significantly different pressures on the anode and cathode sides.
[0009] Disclosure of the invention
[0010] Within the scope of the present invention, methods for at least partially regenerating such deformations are proposed. The electrolysis cell thus comprises a membrane-electrode assembly with the following features:
[0011] - 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,
[0012] - 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,
[0013] - an anode-side gap between the anode-side transport layer and the anode-side frame structure,
[0014] - a cathode-side gap between the cathode-side transport layer and the cathode-side frame structure,
[0015] - a membrane structure positioned in a layered manner between the anode side and the cathode side, comprising a membrane with an anode-side catalyst membrane coating and a cathode-side catalyst membrane coating.
[0016] During a regeneration period, the anode side is operated at a higher pressure than during normal operation.
[0017] Deformation of the membrane structure during normal operation is thus at least partially compensated by an opposite deformation during the regeneration period. The regeneration period can range from several seconds to several days. The membrane-electrode assembly is suitable for electrolysis cells and is preferably used for PEM and AEM electrolyzers.
[0018] Within the scope of the present invention, it was recognized that the gap between the respective transport layer and the respective frame structure can lead to mechanical overloading of the membrane, including the catalyst coating, in the area under high relative pressures between the anode and cathode sides. This can lead to damage or destruction of the membrane or membrane structure in this area.
[0019] 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.
[0020] The invention relates to a method for regenerating an electrolysis cell which, during normal operation, is operated on the cathode side with an overpressure relative to the anode side. The cathode side is preferably operated with an overpressure of at least 20 bar, particularly preferably at least 30 bar, relative to the anode side. During such operation, the membrane structure is subjected to particularly high mechanical stress; however, this does not lead to failure of the membrane structure but is at least partially compensated by the regeneration process. During the regeneration process, an opposing relative pressure is generated, and during a regeneration period, the anode side is operated with an overpressure relative to the cathode side.
[0021] The overpressure on the anode side relative to the cathode side during the regeneration period is preferably more than 10 bar, particularly preferably at least as much as the overpressure during normal operation, for example, 20 bar or 30 bar, but in the opposite direction. This results in re-plasticization of the membrane structure on the order of the plasticization during normal operation. In advantageous developments, the regeneration period runs either during a shutdown of the electrolysis cell or during normal operation. During shutdown, normal operation is not disrupted; the pressure on the cathode side can be significantly reduced during the regeneration period, while the pressure on the anode side can be significantly increased simultaneously.During normal operation, the pressure on the cathode side may not be able to be reduced arbitrarily; however, this depends on the topology of the electrolyzer and possibly also on various storage volumes at the cathode outlet.
[0022] In advantageous developments of the process, regeneration is carried out at a temperature of the membrane structure that is higher than 100°C, particularly preferably higher than 130°C. The temperature during the regeneration period is therefore higher than the temperature during normal operation. Due to the temperature-dependent stress-strain curve of the membrane structure, greater replasticization occurs than at low temperatures during normal operation (e.g., around 80°C). At higher temperatures (e.g., 100°C-160°C), stress peaks can be better dissipated due to the flow of the material. In the case of ionomers, such as the membrane or the membrane structure, recrystallization can also occur at these temperatures, which also results in slight flow and dissipation of stress peaks.
[0023] 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 on the membrane structure are not arranged directly opposite one another, but are supported or lined on the other side by a frame structure or a transport layer. This design increases the stability of the overall composite of the membrane-electrode assembly or the electrochemical cell. In other words, the cathode window (or the cathode-side active area) can be smaller than the anode window (orThe coated membrane can be designed in a different way (e.g., the anode-side active area) (or vice versa), so that the coated membrane is supported in the region of the respective gap on its side facing away from the gap either by the frame structure or by the transport layer. In this way, the stability of the membrane structure can be further increased in a simple manner. The term “gaps formed offset from one another” means 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 in such a way that they do not have an overlap region in a stacking direction orthogonal to the transverse direction.are designed to be offset from one another without overlap. In this case, the bridge sections of the membrane are also correspondingly offset from one another. This means that the membrane or the membrane structure can in this case have two bridge sections arranged next to one another, with one bridge section being designed transversely within the other bridge section. In other words, one bridge section can be designed frame-shaped or at least partially frame-shaped around the other bridge section in a plan view or in a projection in the stacking direction.
[0024] 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.
[0025] The membrane electrode assembly is configured for use in an electrolyzer, in particular in a PEM electrolyzer or in an AEM electrolyzer. The membrane electrode assembly is thus designed as part of an electrolysis cell.
[0026] 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.
[0027] They show schematically:
[0028] Figure 1 shows a membrane electrode assembly according to a first embodiment of the present invention, with only the essential areas being shown.
[0029] Figure 2 shows a membrane electrode assembly according to a second embodiment of the present invention, with only the essential areas being shown.
[0030] Elements with the same function and mode of operation are provided with the same reference symbols in the figures.
[0031] 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 32 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) or GDL (Gas Diffusion Layer).
[0032] 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.
[0033] The differential pressures of an electrolysis cell or electrolyzer between cathode and anode can easily reach 30 bar, for example, to produce 30 hydrogen at the corresponding pressure on the cathode side.
[0034] As a result of a pressure difference between the anode side 20 and the cathode side 30, the membrane structure 40 can be deformed and pressed into the gap 23, 33; if there is excess pressure on the cathode side 30, the membrane structure 40 is pressed into the anode-side gap 23. As a result, fatigue fractures, forced fractures, and / or mechanical cracks can occur in the membrane structure 40.
[0035] According to the invention, a regeneration process is now introduced which counteracts such deformations of the membrane structure 40. For this purpose, the anode side 20 is pressurized and / or the pressure on the cathode side 30 is reduced, so that during a regeneration time T an anode pressure pA,Re gwhich is greater than an anode pressure pA,Norm during normal operation of the electrolysis cell. The anode pressure pA,Re is preferably g at least temporarily during the regeneration process even greater than the cathode pressure pc, particularly preferably by more than 10 bar. This advantageously results in a pressure difference ApR during the regeneration process. eg 60, which acts in a direction 60 orthogonal to the membrane structure 40 from the anode side 20 to the cathode side 30, and thus opposite to a pressure difference of normal operation ApNorm 65. Preferably, the amount of the pressure difference ApR eg 60 is approximately equal to the amount of pressure difference during normal operation ApNorm 65 or even greater than this in order to carry out the recovery of the membrane structure 40 as efficiently as possible.
[0036] The deformations of the membrane structure 40 during operation of the electrolysis cell are thus at least partially compensated or reversed by opposing deformations of the membrane structure 40 during the regeneration process. The regeneration process is preferably carried out by increasing the water pressure on the anode side 20. In this process, the membrane structure 40 is replasticized in the region of the gaps 23, 33, i.e., plasticized back in the direction opposite to normal operation, so that, ideally, the plastic deformations from the operation of the electrolysis cell are reversed. Ideally, the membrane structure 40 is returned to the structural state at the end of the manufacturing process and before the start of operation. This replasticization also mitigates any degradation of the membrane structure 40, provided it is also reversible.
[0037] The regeneration process is preferably carried out at comparatively high temperatures, for example, up to 160°C. This results in greater deformation of the membrane structure 40 and thus also greater replasticization. The regeneration process is advantageously carried out at temperatures of the membrane structure 40 above 100°C, preferably above 130°C, particularly in the presence of steam.
[0038] The regeneration process can preferably be carried out either during the
[0039] During normal operation of the electrolysis cell or during shutdown or stopping of the electrolysis cell, it is easier to reduce the pressure on the cathode side 30 to atmospheric pressure and thereby achieve the largest possible pressure difference ApR eg60. During normal operation of the electrolysis cell, the regeneration process is preferably supported by increasing the anode pressure pA,Norm. In both cases, the pressure on the anode side 20 can be increased during the regeneration process, for example, by means of a water pump, preferably to such an extent that the pressure on the anode side 20 becomes greater than that on the cathode side 30.
[0040] 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 offset from one another in a transverse direction 50 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 50. 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.
[0041] 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 ApNorm 65 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 regeneration process with such an offset thus particularly effectively prevents permanent indentation of the membrane 41 or membrane structure 40 into the anode-side gap 23, in particular in the case of an overpressure ApNorm 65 of the cathode side 30 relative to the anode side 20.
[0042] In addition to the embodiments shown, the invention allows further
[0043] Design principles apply. 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 disclosure as a whole, numerous other combination variants of the illustrated embodiments are possible, not all of which have been described in detail. These variants should, of course, not be considered excluded from the scope of the claimed invention.
Claims
Claims 1 . A method for regenerating an electrolysis cell with a membrane electrode assembly (10), wherein the membrane electrode assembly (10) - 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) positioned in a layered manner between the anode side (20) and the cathode side (30), comprising a membrane (41) with an anode-side catalyst membrane coating (42) and a cathode-side catalyst membrane coating (43), characterized in that during a regeneration time (T) the anode side (20) is operated at a higher pressure than during normal operation.
2. Method according to claim 1, characterized in that during the regeneration time (T) the anode side (20) is at least temporarily pressurized with an overpressure (ApR eg ) opposite the cathode side (30).
3. Method according to claim 2, characterized in that the overpressure is at least 10 bar.
4. Method according to one of claims 1 to 3, characterized in that the regeneration time (T) elapses during a shutdown of the electrolysis cell.
5. Method according to one of claims 1 to 3, characterized in that the regeneration time (T) elapses during normal operation of the electrolysis cell.
6. Method according to one of the preceding claims, wherein in normal operation of the electrolysis cell the cathode side (30) is operated with an overpressure (ApNorm) compared to the anode side (20).
7. The method according to claim 6, wherein in normal operation the cathode side (30) is operated with an overpressure of at least 20 bar, preferably at least 30 bar, relative to the anode side (20).
8. The method according to claim 6 or 7, wherein during the regeneration time (T) the anode side (20) is at least temporarily pressurized with an overpressure (ApR eg ) opposite the cathode side (30), characterized in that the amount of ApR eg (60) is at least as large as the magnitude of ApNorm (65).
9. Method according to one of the preceding claims, characterized in that the method is carried out at a temperature of the membrane structure (40) which is higher than 100°C, preferably higher than 130°C.
10. Method according to one of the preceding claims, 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 designed such that The anode-side gap (23) and the cathode-side gap (33) are offset from one another in a transverse direction (50) from the respective transport layer (21, 31) to the associated frame structure (22, 32).
11. The method according to claim 10, wherein 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).