SEALING LAYER, SEPARATOR PLATE AND ELECTROLYZER

[0001]The present invention relates to a sealing layer for use in an electrolyzer, a separator plate therefor and an electrolyzer. Electrolyzers produce, for example, hydrogen and oxygen from water by applying a potential and may at the same time compress at least one of the gases produced.

[0002]Conventional electrolyzers consist of a stack of individual cells, each of which has a sequence of layers with a separator plate, also referred to as bipolar plates in the following as representative of the various designs of individual cells, two gas diffusion layers (GDL) and a membrane electrode assembly (MEA). This stack of electrochemical cells must be sealed off with respect to the external environment since the media are guided within the cells at an overpressure relative to the external pressure.

[0003]For this purpose, electrolyzers typically have a cell frame running around the outer edge of the electrochemical cell for each of the individual electrochemical cells, which are stacked on top of each other to form an electrolyzer. The individual cells in the stack are compressed together, for example by means of screws, between two end plates.

[0004]The stack of electrochemical cells now has sealing elements between the individual cell frames, that is between the cell frames and the separator plates or the membrane electrode assemblies that are arranged between the cell frames along the outer circumference but spaced inwards from the outer circumference. Traditionally, elastomer seals are used for this purpose, for example as ring seals inserted into a groove. Alternatively, injection-molded elastomer seals can also be used. It is also known to use flat, soft material gaskets as seals, which run as frame seals along the outer circumferential edge of the respective cell frame.

[0005]In an electrolyzer, the pressure of the media used, e.g. water, and the pressure of the gases produced, e.g. hydrogen and oxygen, changes during operation. Therefore, in the following, the assembled ready-to-operate state refers to the state in which the cell stack of the electrolyzer is assembled under nominal compression, but no media has yet been introduced into the cell stack. This state is a well-defined state for each cell stack, which is determined during the development of the stack components for a given cell stack.

[0006]Only after the cell stack has been filled with the reaction gases and/or cooling fluid does a state arise that is referred to below as the ready-to-operate state, but in which the forces acting on a component of the cell stack are different from the forces under nominal compression in the ready-to-operate state and can also vary during operation of the cell stack.

[0007]However, a change in pressure (“breathing stacks”) during operation must not lead to leakage of the seal around the outside of the respective electrochemical cell. It must therefore be ensured that the force of compression on the stack of electrochemical cells remains sufficiently constant even under changing conditions. For this purpose, in addition to the elastomer seals at the respective ends of the stack, a spring assembly is conventionally used, which is arranged between the stack and the screws used to fix it together. These spring assemblies lead to a uniform compression pressure of the stack even if the length of the stack changes due to pressure and temperature changes within the stack.

[0008]Furthermore, metallic frame seals are known in the state of the art, which have circumferential beads as sealing elements. To ensure the required constant compression force, the beads of such bead seals are designed in such a way that their compression remains within the elastic range of the compression characteristic curve of the beads. This allows the beads to ensure an clastic seal over a wide region. However, such bead seals have proven to be unsuitable for ensuring a reliable seal in electrolyzers whose pressure conditions change considerably during the operation of the electrolyzer.

[0009]Based on this state of the art, the present invention therefore sets itself the object of providing a seal for electrolyzers, which also enables a reliable sealing effect with respect to the scaled region during operation of the electrolyzer.

[0010]This object is solved by a sealing layer according to claim 1, a separator plate according to claim 10 and an electrolyzer according to claim 15. Advantageous further embodiments of the sealing layer according to the invention, the separator plate according to the invention and the electrolyzer according to the invention are provided by the respective dependent claims.

[0011]Electrolyzers usually have at least one cell stack of electrochemical cells. The scaling layer according to the invention for use in an electrolyzer of this type has at least one sealing bead that runs in a self-contained manner around the region to be sealed, which here for example is the flow field of a separator plate of the electrolyzer. According to the invention, the sealing bead has an initial bead height H₀ before the first compression in the electrolyzer, i.e. before the stack of electrochemical cells of the electrolyzer is assembled. The stiffness of the bead is designed in such a way that after an initial one-time compression of the sealing layer under nominal compression in the assembled, ready-to-use state of the stack and subsequent disassembly of the stack, the sealing bead is compressed to a bead height H that is ≤0.3 H₀, advantageously ≤0.2 H₀, advantageously ≤0.1 H₀. In other words, the sealing layer has a sealing bead that is plastically compressed when the sealing layer is compressed during assembly in the electrolyzer and is therefore no longer operated in the elastic range.

[0012]However, it is not absolutely necessary to produce a complete electrolyzer in order to determine the properties of the sealing bead; it is sufficient to press the scaling layer according to the invention under nominal pressure or nominal/nominal compression force of the electrolyzer stack. Ideally, to determine the properties of the sealing bead, the stack of electrochemical cells containing the sealing layer according to the invention is completely assembled, compressed under nominal compression force without filling with gas, and then dismantled. The bead heights are preferably determined using an uncoated blank sheet of the sealing layer, i.e. a sheet on which no coating, in particular no coating with an elastomer, has yet been applied. Alternatively, the bead heights H and H₀ can also be determined on a fully coated sealing layer or a sealing layer having a uniform coating over the entire surface. It has also been found that the duration of the initial compression has practically no influence on the ratio of the bead heights before compression and after compression.

[0013]The bead of the sealing layer according to the invention is therefore permanently plastically compressed and can no longer spring out over a large region, as is the case with conventional sealing beads. Nevertheless, it has been found that conventional electrolyzer seals can advantageously be replaced with such plastically compressed sealing beads.

[0014]Such plastically compressed sealing beads have, for example, a residual bead height in the uncompressed state of less than 10% of the material thickness of the sealing layer. Typical sealing layers have, for example, thicknesses in the range of 200 to 300 μm, so that the residual bead height is only up to 20 to 30 μm.

[0015]According to the invention, this is not a conventional sealing principle based on an clastic effect, as is the case with conventional elastomer seals or conventional bead seals.

[0016]Advantageously, the height of the sealing bead in the uncompressed state is designed so that its height is lower than embossings that are used, for example, in a flow region of a separator plate of an electrolyzer. As a result, the main force of the compressing of the cell stack of an electrolyzer is introduced into the sealing bead of the sealing layer, for example via a cell frame. The sealing bead according to the invention is therefore located in the main force path, while the flow region of the separator plate is located in the force shunt of the compressing of the electrolyzer.

[0017]The sealing layer according to the invention can be, for example, the separator plate of an electrolyzer or the cell frame of an electrochemical cell of an electrolyzer. It is also possible to provide a separate scaling layer that has the sealing bead according to the invention. For example, this can also simply run around the outer circumference of the electrolyzer along the cell frame. It is essential that the sealing between the individual electrochemical cells and the outside space is achieved by means of the sealing bead according to the invention in a layer of the electrolyzer that acts as a sealing layer.

[0018]The plastically deformed sealing bead according to the invention can additionally be combined with a sealing bead operated in the elastic range in an adjacent layer, arranged one above the other, so that the acting compressing forces act on the plastically deformed sealing bead according to the invention and the elastic bead.

[0019]The sealing bead according to the invention can be introduced into the sealing layer by embossing processes, for example, whereby embossing processes such as stroke embossing, roll embossing, flat embossing, impulse embossing or hydraulic forming are suitable for this purpose.

[0020]Particularly advantageously, the scaling layer according to the invention consists of a metallic material, for example a metal sheet. Steels, for example spring steels and/or soft steels such as stainless steel and the like, are particularly suitable for this.

[0021]In contrast to conventional sealants, the sealing bead according to the invention advantageously has a height of only 2 μm to 60 μm, advantageously 3 μm to 20 μm, advantageously 5 μm to 10 μm, excluding or including the value range limits, after an initial one-time plastic compression under nominal compression force of the electrolyzer. A height between 100 μm and 500 μm, preferably 200 μm and 300 μm, is advantageously used as the initial bead height H₀, in each case also including or excluding the range limits.

[0022]The choice of these advantageous height ranges for H₀ and H also provides that the scaling bead according to the invention is plastically compressed in the scaling layer according to the invention under nominal operating conditions of the electrolyzer and only has a small spring deflection. In fact, the sealing bead is typically compressed to a height of 0 or almost 0 when the sealing layer is installed in the electrolyzer. The small spring deflections, which were shown as an example for the advantageous bead height H, nevertheless enable the stack of electrochemical cells to be securely sealed from the external environment.

[0023]Known layer thicknesses D are used as the layer thickness for the sealing layer, with D advantageously being between 100 μm and 500 μm, advantageously between 200 μm and 300 μm, in each case including or excluding the range limits.

[0024]The sealing layer can be coated over the entire surface or only in certain regions, for example only in the region of the sealing beads according to the invention. Micro-sealing can be improved by means of such a coating. However, it is also possible to coat a mating component to the sealing layer according to the invention, for example with an elastomer, over the entire surface or in certain regions, in particular in the region opposite the sealing bead according to the invention.

[0025]The sealing layer according to the invention can be part of a separator plate according to the invention or can form the separator plate itself.

[0026]Typical separator plates are single-layered, so that this layer can also be configured as a sealing layer according to the invention. Furthermore, typical separator plates may also be configured with two layers, in which case the sealing layer according to the invention can be added, or one or both of the layers of a two-layer separator plate can be configured as a sealing layer according to the invention.

[0027]Typical separator plates have a flow region in which flow channels, which serve to guide the media, for example the hydrogen and oxygen produced, are embossed into the separator plates. According to the invention, this flow region is enclosed in a sealing manner by the scaling bead according to the invention.

[0028]The present invention also relates to an electrolyzer having a sealing layer according to the invention as described above, wherein one, several or each of the electrochemical cells of the electrolyzer may have such a sealing layer. The sealing layer can be configured here to be provided in addition to a separator plate as described above, or as a separator plate itself. The sealing layer can also be configured as a cell frame that runs around the separator plates of the electrolyzer on the outer periphery of the separator plates.

[0029]According to the invention, the electrolyzer can also have a further metallic layer that is not the sealing layer according to the invention. When viewed from above in the stacking direction of the electrolyzer, the further metallic layer can have a further sealing bead, for example a sealing bead that is not plastically compressed but is operated in the elastic range. This further scaling bead can be arranged above the sealing bead according to the invention in the sealing layer according to the invention, for example in such a way that the bead roofs of the additional bead and the sealing bead according to the invention come to lie on top of each other. Alternatively, the feet of these beads can be positioned to face towards each other and the bead roofs of the two layers can face away from each other, i.e. the beads can have an essentially opposite course.

[0030]Examples of sealing layers and electrochemical cells according to the invention as well as electrolyzers according to the invention are given below. Identical and similar reference signs will be used for identical and similar elements and therefore these may not be repeatedly described. In addition to the essential features of the present invention, the following examples each contain a large number of optional features which, individually or in combination, can further form the present invention. Optional features from different examples can also be combined.

[0031]In the figures:

[0032]FIG. 1 shows a compression diagram of different sealing systems;

[0033]FIG. 2 shows a compression diagram for a metallic sealing bead;

[0034]FIG. 3 shows, in sub-figures A and B, two different combinations of a sealing layer according to the invention with a cell frame;

[0035]FIG. 4 shows, in sub-figures A and B, structural elements of an electrochemical cell having a sealing layer according to the invention;

[0036]FIG. 5 shows a sealing layer with a cell frame according to the invention;

[0037]FIG. 6 shows, in sub-figures A and B, two scaling layers with cell frames according to the invention;

[0038]FIG. 7 shows a sealing layer with a cell frame according to the invention;

[0039]FIG. 8 shows a sectional view of a sequence of electrochemical cells of an electrolyzer according to the invention in the uncompressed state;

[0040]FIG. 9 shows a further view of a section of the sequence of electrochemical cells of the electrolyzer according to the invention in the uncompressed state

[0041]FIG. 10 shows the sequence from FIG. 8 in the compressed state;

[0042]FIG. 11 shows an enlarged view of a section from FIG. 10;

[0043]FIG. 12 shows a sequence of electrochemical cells of an electrolyzer according to the invention in the uncompressed state;

[0044]FIG. 13 shows another view of the sequence of electrochemical cells of the electrolyzer according to the invention in the uncompressed state;

[0045]FIG. 14 shows the sequence of electrochemical cells in FIG. 12 in the compressed state; and

[0046]FIG. 15 shows the sequence of electrochemical cells in FIG. 13 in the compressed state.

[0047]FIGS. 1 to 7 illustrate the invention, in each case using still uncompressed arrangements of cell frames, sealing layers, separator plates etc.

[0048]FIG. 1 shows a compression diagram for three sealing systems according to the state of the art. The solid line shows a gasket having a metallic bead that is coated, the dotted line shows a flat gasket made of elastomer and the dashed line shows a profile gasket made of elastomer. FIG. 1 shows how the thickness of the bead decreases as a function of the pressing force with which the respective seal is compressed.

[0049]FIG. 2 shows a compression diagram of a bead in a metallic layer. The bead height, that is its compression, is plotted on the x-axis and the applied compression force is plotted on the y-axis. As the compression force increases, the height of the bead is reduced (right-hand side of the diagram). If the compression is carried out with a low force, the bead is compressed as in the region marked A. When the load is removed, the bead returns to a predetermined height or its height changes within a predetermined range. A denotes the region in which the bead springs in and out elastically.

[0050]With very strong compression, so-called plastic compression with very high pressing force, the bead is compressed to a very low height. Even when the load is removed, the bead does not return to anywhere near its original height, but instead its height only changes slightly. The region labeled B in the diagram shows such a plastic, permanently deformed compression of a bead with high pressing force. In particular, FIG. 2 shows that, with sufficient pressing force, the sealing bead is compressed to a height of 0. A sealing bead compressed in this way only springs back slightly when the load is removed.

[0051]The present invention now deviates from the state of the art, in which sealing beads with a compression in the elastic region A are usually used for sealing, by using a sealing bead that has been compressed plastically, i.e. as shown in region B.

[0052]FIG. 3 shows two examples of sealing layers 1 according to the invention, in sub-figures A and B.

[0053]Sealing layer 1 in FIG. 3A has a metallic first layer 20, which is also configured as a separator plate or as a layer of a multi-layer separator plate in an electrolyzer. A cell frame 3 is arranged adjacent to the sealing layer 1, 20, which is formed around the flow region 13 of the separator plate 20 along its outer circumference. The cell frame 3 includes a region 9 which, among other things, has a flow region 13 with flow channels 14 in the form of channel beads 15 and flow channels 14′ in the form of channel beads 15′. Educts or products of the electrolyzer, such as water, oxygen or hydrogen, can be fed into these flow channels 14 and 14′.

[0054]A sealing bead 10 according to the invention is arranged in the separator layer 20 adjacent to the cell frame 3 when viewed from above the plane of the separator layer 20. This sealing bead 10 has bead feet 17, bead flanks 18 and a bead roof 19. The bead roof 19 is arranged directly adjacent to the cell frame 3.

[0055]To form an electrolyzer, a large number of combinations of separator plate/scaling layer 1 and cell frame 3 can now be arranged on top of each other, with gas diffusion layers and membrane electrode arrangements (not shown in FIG. 3) being added.

[0056]A height between 200 μm and 300 μm is advantageously used as the initial bead height H₀.

[0057]FIG. 3B shows a separator plate 20 similar to FIG. 3A. In this case, however, the sealing bead 10 is arranged in the region of a bead groove 6 of the cell frame 3. The depth of the groove 6 is not shown to scale in FIG. 3B. It is only deep enough to achieve plastic compression of the bead 10 in accordance with the invention.

[0058]The bead roof 19, which is shown here, as in FIG. 3A, together with the separator layer 20 and the cell frame in the uncompressed state, lies against the bottom of the groove 6 in the compressed state. To form an electrolyzer, a large number of combinations of sealing layer 1 and cell frame 3 can be arranged on top of each other.

[0059]FIG. 4 shows another example of a sealing layer 1 according to the invention in sub-FIG. 4A, which is similar to the example in FIG. 3A. In contrast to FIG. 3A, in FIG. 4A not just one cell frame 3 is provided for the sealing layer 1, but two cell frames 3, 3′, which are arranged on both sides of the sealing layer 1. The channel beads 15 and 15′ have a height such that the respective bead roofs run at largely the same height or at the same height as the outer sides of the cell frames 3, 3′ facing away from the sealing layer 1. A large number of combinations of scaling layer 1 and cell frame 3, 3′ can now be arranged on top of each other to form an electrolyzer. As described, two gas diffusion layers and a membrane electrode arrangement are still required to form a functional electrochemical cell for each unit consisting of separator layer 1, 20 and adjacent cell frames 3, 3′.

[0060]This is shown in FIG. 4B, where a gas diffusion layer 5a, 5b and a membrane electrode arrangement 4a, 4b are arranged on either side of the sealing layer 1. While FIG. 4A is shown in the uncompressed state, in FIG. 4B the flow region 13 of the sealing layer 1 is already partially compressed in such a way that the height between the bead roofs of the channel beads 15, 15′ plus the thicknesses of the two gas diffusion layers 5a, 5b corresponds to the height between the two outer sides of the two cell frames 3, 3′.

[0061]FIG. 5 shows another sealing layer 1 with cell frames 3, 3′ similar to the arrangement in FIG. 4A. In addition to the sealing layer 1, a further metallic layer 30 is provided, which is arranged above the sealing layer 1 in the region of the cell frames 3, 3′ in the stacking direction of an electrolyzer as viewed from above, in the arrangement shown in FIG. 5. The further metallic layer 30 has a sealing bead 31 with bead feet 37, bead flanks 38 and a bead roof 39. The bead roofs 19 and 39 now lie directly on top of each other, i.e. the two beads 10 and 31 run in opposite directions. FIG. 5 shows both beads in the uncompressed state. Under nominal compression in an electrolyzer, the sealing bead 31 is operated in its elastic region (region A in FIG. 2), while the scaling bead 10 is plastically compressed according to the invention (region B in FIG. 2). To this end, layers 1 and 30 are suitably configured, e.g. by selecting the appropriate layer material, layer thickness, bead geometry, etc.

[0062]FIG. 6A shows another sealing layer 1 according to the invention. FIG. 6A shows an arrangement similar to that in FIG. 5. In this case, however, the sealing layer 1 is only formed in the region of the cell frame 3, while the separator plate 20 is formed without a sealing bead in the region of the cell frame. The sealing bead 10 arranged in the sealing layer 1 is shown in the uncompressed state in FIG. 6. Under nominal conditions for the electrolyzer, the sealing bead 10 is plastically compressed.

[0063]FIG. 6B shows a further embodiment of a sealing layer 1 according to the invention. In FIG. 6B, the cell frame 3 is designed as a sealing layer 1 with the sealing bead 10 to be plastically compressed and is shown in a still uncompressed state. Like the metallic layer in FIG. 6A, the additional metallic layer 30 is designed as a separator plate 20. In contrast to FIG. 6A, the function of the sealing layer 1 is now not performed in a sealing layer separate from the cell frame 3. Rather, the cell frame 3 is designed as a sealing layer 1 according to the invention.

[0064]FIG. 7 shows a further example of a sealing layer according to the invention similar to the example of FIG. 6A. In contrast to FIG. 6A, however, the sealing layer 1 is now welded to the cell frame 3 at welding points 24. Connecting the sealing layer I to the cell frame 3 in this way increases the rigidity of the sealing bead 1.

[0065]FIGS. 8 and 9 show two different sections of a stack of electrochemical cells viewed from above. The electrochemical cells are each formed from a cell frame 3a, a scaling layer 1 as separator layer 21, a further separator layer 22, gas diffusion layers 5a and 5b and a membrane electrode arrangement 4a, which are arranged in the sequence 5b, 21, 22, 5a, 4a. The separator layers 21 and 22 together form a two-layer separator plate or bipolar plate 20. Elements of other electrochemical cells are marked with similar reference symbols in FIGS. 8 and 9. Furthermore, the sectional view of FIGS. 8 and 9 shows a through-opening 25, through which reactants or products can be fed to or from the electrochemical cells in the stacking direction of the electrochemical cells.

[0066]A sealing bead 10 (and 10b) is formed in the sealing layer 1 (and correspondingly in the sealing layer 1b), which runs around the flow region 9 of layer 1 (or flow region 9b of layer 1b). According to the invention, the sealing bead 10 is configured as a sealing bead that is plastically compressed when the stack of electrochemical cells shown in FIG. 8 is compressed. A further bead 31 is arranged opposite the sealing bead 10 in a second layer 22 of the separator plate 20, whereby the beads 10 and 31 lie on top of each other with their bead feet. In this example, the bead 31 is also configured in such a way that it is also plastically compressed when compressed under nominal conditions of the electrolyzer 2.

[0067]FIG. 9 shows the same sequence of electrochemical cells in a different cross-sectional view, as in FIG. 8. The section is now selected so that a section through the channels of the flow region 9 is not shown in layer 22, but in layer 21, which is also configured as scaling layer 1.

[0068]The sealing bead 10 of the layer 21 of the separator plate 20 is, as shown for the similarly designed sealing bead 10b of the layer 21b, runs circumferentially around the flow region 9b of the layer 21b. The bead 10b (and the bead 10 correspondingly) also has an extension that completely surrounds the through-opening 25.

[0069]While FIGS. 8 and 9 show the cell stack in the still uncompressed state, i.e. before the initial one-time compression under nominal operating conditions of the electrolyzer 2, FIGS. 10 and 11 show the arrangement from FIG. 8 and FIG. 9 in the compressed state under standard pressing conditions of a fully assembled electrolyzer 2. In both cases, the beads 10 and 31 are completely compressed to a height of 0 and are therefore plastic. Both the bead 10 and the bead 31 are therefore configured as sealing beads according to the invention, so that in both cases both the layer 21 and the layer 22 are configured as sealing layers according to the invention.

[0070]FIGS. 12 and 13 show a further example of a sequence of electrochemical cells according to the invention in various sections and cross-sections. In principle, the structure of the electrochemical cells in this example is similar to that in FIGS. 8 to 11. In contrast to the previous example, 4 metallic layers are now arranged between the cell frames 3a and 3a′. The layers 21a and 22a of the separator plate 20a are not configured as sealing layers according to the invention with a sealing bead to be plastically compressed. Rather, additional sealing layers 1a and 1a′ are provided on the outside of the separator plate 20, which have sealing beads 10a and 10a′ that are configured according to the invention and run around the flow region 9a. Other electrochemical cells in the cell stack shown are configured accordingly or in the same way.

[0071]FIG. 14 and FIG. 15 each show a representation of a section around the arrangement in FIG. 12 and in FIG. 13 in the region of the through-opening 25, whereby the cell stack is compressed under nominal conditions. In this state, the sealing beads 10a and 10a′ are compressed to height of 0, i.e. plastically compressed.