Stack structure of an electrolyzer or fuel cell

Abstract

The invention relates to a stack structure (20) of an electrolyzer (10) or a fuel cell (10). The stack structure (20) comprises a plurality of individual cells (12) arranged vertically stacked one above the other. The individual cells (12) comprise at least one cathode frame (22), one anode frame (24), at least one bipolar plate (26), at least one gas diffusion layer (28), at least one porous transport layer (30) (PTL), and at least one membrane (38). The stack structure (20) has a first end plate (14) and a second end plate (16), which clamp the individual cells (12) arranged between the end plates (14, 16) against one another using a number of clamping elements (18). At least one circumferential recess (40) is formed in the anode and / or cathode frame (24, 22) of the individual cells (12), which recess is connected to a discharge opening (42).Furthermore, the invention relates to the use of the stack structure (20) in an electrolyzer (10) or in a fuel cell (10).

Description

Technical FieldThe invention relates to a stack structure of an electrolyser or a fuel cell having a multiplicity of individual cells arranged vertically stacked one above the other, each of which has at least one cathode frame, at least one anode frame, at least one bipolar plate, at least one gas diffusion layer, at least one porous transport layer and at least one membrane, the stack structure having a first and a second end plate which, with a number of clamping elements, clamp the individual cells arranged between the end plates against one another. Moreover, the invention relates to the use of the stack structure in an electrolyser or in a fuel cell.Prior ArtFor the production of hydrogen, for example, electrolyzers are used in the context of PEM electrolysis, with which hydrogen having an impurity can be produced from the raw material water with only oxygen as a by-product. In a PEM electrolyser, so-called PEM membranes (proton exchange membranes) are used, which are surrounded by water. When an electric voltage is applied to such a membrane, protons diffuse from the anode through the membrane to the cathode. Oxygen is formed at the anode and hydrogen is formed at the cathode, the two gases being physically separated from one another by the membrane. The gaseous hydrogen is discharged to the cathode side, dried and can be stored.Usually, a plurality of individual cells are used in an electrolyser, each of which comprises a cathode frame, a gas diffusion layer, a membrane, optionally with a catalyst, an anode frame, a porous transport layer and at least one bipolar plate, each of which is stacked one above the other.In each individual cell, a medium, usually water, is transported to the membrane with the catalyst and corresponding reaction products, such as oxygen, hydrogen and water residues, are transported away. This transport of media and away places high demands on the tightness of the individual cells stacked one above the other in the vertical direction. The sealing of the individual cells is made more difficult by the fact that such an electrolysis is usually carried out at elevated pressures (of the order of magnitude of 40 bar) and the tightness must be ensured over the complete service life of a stack structure suitable for electrolysis. The lifetime is currently about 40,000 hours.Disclosure of the InventionAccording to the invention, a stack structure of an electrolyser or a fuel cell is proposed, having a multiplicity of individual cells which are arranged vertically stacked one above the other and each comprise at least one cathode frame, at least one anode frame, at least one bipolar plate, at least one gas diffusion layer, at least one porous transport layer and at least one membrane, wherein the stack structure has a first end plate and a second end plate which, with a number of clamping elements, clamp the individual cells arranged between the end plates against one another. In the anode and / or cathode frame of the individual cells, at least one encircling depression is formed, which is connected to at least one discharge opening.The solution proposed according to the invention makes it possible to collect and discharge gaseous or liquid media, water or water-containing media in each individual cell within the stack structure in a targeted manner. As a result, it is possible to operate such a stack structure with a certain permissible degree of leaks still reliably.In an advantageous development of the stack structure proposed according to the invention, the anode frame and / or the cathode frame are configured vulcanized.In a further advantageous embodiment of the stack structure proposed according to the invention, the at least one encircling depression in the individual cells is designed as a channel or as a groove.In a further advantageous embodiment variant of the stack structure proposed according to the invention, gaseous or liquid media, water or water-containing media are collected in the at least one encircling depression.In the stack structure proposed according to the invention, the at least one discharge opening is advantageously arranged in a corner region of the anode frame and / or cathode frame in the anode frame and / or in the cathode frame.The stack structure proposed according to the invention is advantageously designed in such a way that discharge openings arranged one above the other in each case form at least one discharge channel in the state of the individual cells stacked one above the other.The invention furthermore relates to a method for operating a stack structure, wherein the following method steps are carried out: a) collecting liquid and / or gaseous media, water or aqueous media in which at least one circumferential depression of the individual cells, b) selectively discharging the media collected according to method step a) into a discharge channel, c) determining the quantity of discharged media and d) evaluating the state of the stack structure in order to detect aging effects which are occurring.Finally, the invention relates to the use of the stack structure in an electrolyser for producing gaseous hydrogen or in a fuel cell or in a fuel cell arrangement for driving a vehicle.Advantages of the InventionThe solution proposed according to the invention advantageously makes it possible to collect and specifically discharge leaks occurring with a slight modification of the individual cells arranged in the individual structure. This opens up the possibility of still reliably operating, in particular, a PEM electrolysis stack structure with a certain degree of leaks. Because leaks can be permitted, which can be safely and selectively discharged, higher tolerances of the individual cells stacked one above the other can be permitted. Furthermore, the requirements for the tightness can be somewhat reduced, since higher tolerances can be permitted and a reliable removal of leakage quantities is ensured by means of the solution proposed according to the invention. In a particularly advantageous manner, the at least one encircling depression in the individual cells can be formed as a groove or as a channel, as a channel or the like. In particular, it is possible to connect the at least one encircling depression to a discharge opening which can be formed in particular in the corner region of the surface of the individual cells. In addition to the further media channels for transporting oxygen and hydrogen or water, the discharge channel is formed in that, in the case of individual cells stacked one above the other in the vertical direction, the discharge openings arranged in each case in a corner region are aligned with one another and form a continuous channel within the stack structure proposed according to the invention, which channel extends through said continuous channel substantially from the first, upper end plate to the second, lower end plate.The method proposed according to the invention makes it possible to obtain, from the quantity of leaks derived from the stack structure, a conclusion as to the state of aging of individual cells within the stack structure and / or the entire stack structure as such. As a result, aging effects that occur can be detected early, so that remedying measures can be initiated in good time. Furthermore, chemical analysis of the leaks that have occurred, for example elemental analysis by means of ICP-MS, makes it possible to draw conclusions about their cause, such as, for example, membrane degradation and corrosion. Findings about these phenomena are extremely helpful in particular in the development phase and in the definition of shutdown measures or in the risk analysis.Brief Description of the DrawingsEmbodiments of the invention are explained in more detail on the basis of the drawings and the following description.The following are shown: FIG. 1 is a perspective view of an electrolyser, FIG. 2 is a schematic illustration of a single cell within the stack structure according to FIG. 1 ; and FIG. 3 shows a schematic illustration of a cathode frame or anode frame with a circumferential depression for collecting leaks together with the discharge opening.Embodiments of the InventionIn the following description of the embodiments of the invention, identical or similar elements are denoted by identical reference symbols, wherein a repeated description of these elements is omitted in individual cases. The figures only schematically represent the subject matter of the invention.FIG. 1 shows a schematic illustration of an electrolyser in a perspective illustration.The electrolyser 10 shown in Figure 1 comprises a plurality of individual cells 12 stacked one above the other in the vertical direction. The plurality of individual cells 12 of the stack assembly 20 shown in Figure 1 are surrounded by a first, upper end plate 14 and a second, lower end plate 16. The two end plates 14, 16 are braced against one another by a number of clamping elements 18 which are arranged uniformly distributed along the circumference of the first and second end plates 14, 16 and are designed here as screws. The clamping elements 18 could also be designed as clamping straps or the like. A prestressing force is introduced into the stack structure 20 via the clamping elements 18 according to the illustration in FIG. 1, so that the vertically stacked individual cells 12 arranged one above the other bear sealingly against one another.FIG. 2 shows a schematic illustration of individual cells 12 as they are arranged stacked one above the other in the vertical direction in an electrolyser 10 according to the illustration in FIG. 1. Instead of the electrolyser 10, as shown in Figure 1, the stack assembly 20 as shown in Figure 1 could also be that of an electric current generating fuel cell for driving an electric drive of a vehicle.FIG. 2 shows that the single cell 12 usually has a cathode frame 22 and an anode frame 24. Both the cathode frame 22 and the anode frame 24 may be vulcanized. Furthermore, the individual cell 12 according to the schematic illustration in FIG. 1 comprises at least one bipolar plate 26 and at least one gas diffusion layer 28 (GDL) and at least one porous transport layer 30 (PTL).Between the cathode frame 22 and the anode frame 24 there is a membrane 38 which is preferably designed as a proton exchange membrane (PEM) and around which water flows. When an electric voltage is applied to the membrane 38, protons diffuse from the anode side to the cathode side. Oxygen is produced at the anode, and hydrogen is produced at the cathode, which remain physically separated from one another by the membrane 38. The hydrogen is discharged on the cathode side and dried and can be stored.The illustration according to FIG. 2 furthermore shows that the individual cell 12 illustrated there is supplied with water, which is effected via the medium feed 32. Reaction products such as oxygen and hydrogen are discharged via respective exhausts 34, 36, as well as water residues. This transport of the media on and off places very high requirements on the tightness of the individual cells 12 stacked one above the other within the stack structure 20 according to FIG. 1.It can furthermore be seen from the illustration according to FIG. 2 that circumferential depressions 40 can be formed in the cathode frame 22, which is in particular vulcanized, and / or the anode frame 24, which can likewise be vulcanized. According to the sectional illustration of the individual cell 12 according to FIG. 2, these run perpendicular to the plane of the drawing.FIG. 3 shows a schematic illustration of a cathode frame 22 or an anode frame 24, which is provided with at least one circumferential depression 40.It can be seen from the illustration according to FIG. 3 that the encircling depression 40 runs in a surface 46 of the cathode frame 22 and / or of the anode frame 24. This can be designed as a trough-shaped depression, as a groove or also as a channel and preferably runs along the edge region of the vulcanizedly executable cathode frame 22 or of the vulcanizedly executable anode frame 24.The at least one encircling depression 40, which is embodied in the surface 46, comprises within a corner region 48 a discharge opening 42, which is embodied here, for example, in a circular manner. The encircling depression 40, which is provided as a groove, as a channel or with a rounded collar, has, for example, a slight gradient, with the result that it is ensured that gas or liquid media, water or water-containing media can flow to the discharge opening 42.Due to the individual cells 12 arranged vertically one above the other within the stack structure 20 according to FIG. 1, the individual discharge openings 42 in the stack structure 20 lie one above the other. As a result, the discharge openings 42 lying within the corner region 48 are aligned vertically with one another, so that a discharge channel 50 extending from the first, upper end plate 14 to the second, lower end plate 16 is formed from the plurality of individual cells 12 and thus from the plurality of discharge openings 42 aligned with one another. This preferably extends in a corner region 48 of the stack structure 20 according to the illustration in FIG. 1. Thus, leaks can be collected in each case in an individual cell 12 and can be carried away in a targeted manner via the discharge channel 50 formed by the discharge openings 42 lying one above the other.Furthermore, by means of the method according to the invention proposed according to method step a), liquid and / or gaseous media, water or water-containing media can be collected in the at least one circumferential depression 40 of the surface 46 of a respective individual cell 12. According to method step b), the media collected according to method step a) are discharged in a targeted manner into the discharge channel 50, which is formed in the stacked arrangement of the individual cells 12 within the stack structure 20 by the discharge openings 42 lying one above the other. According to method step c), the quantity of the derived media is determined and, from this, according to method step d), an evaluation of the state of the stack structure 20 is carried out. Aging effects can thereby be detected early and corresponding remedial measures can be taken.The stack structure 20 proposed according to the invention is advantageously used in an electrolyser 10 for generating gaseous hydrogen or can be used in a fuel cell which generates current for driving an electrically driven vehicle. In addition, the invention can be used not only in the context of PEM electrolysis or PEM electrolysers, but can also be used in the context of AEM electrolysis. In the context of AEM electrolysis, a membrane type deviating from PEM electrolysis is used.The invention is not limited to the exemplary embodiments described here and the aspects emphasized therein. Rather, within the scope of the claims, a variety of modifications are possible, which are within the scope of specialist activity.

Claims

Stack structure (20) of an electrolyser (10) or of a fuel cell (10) having a multiplicity of individual cells (12) which are arranged vertically one above the other and which each comprise a cathode frame (22), an anode frame (24), at least one bipolar plate (26), at least one gas diffusion layer (28), at least one porous transport layer (30) and a membrane (38), wherein the stack structure (20) has a first end plate (14) and a second end plate (16) which, with a number of clamping elements (18), clamp the individual cells (12) arranged between the end plates (14, 16) against one another, characterized in that at least one encircling depression (40) which is connected to at least one discharge opening (42) is formed in the anode frame and / or in the cathode frame (22, 24) of the individual cells (12).Stack assembly (20) according to claim 1, characterized in that the anode and / or the cathode frame (24, 22) is vulcanized.Stack structure (20) according to Claims 1 and 2, characterized in that the at least one encircling depression (40) is designed as a channel (44) or as a groove (44).Stack structure (20) according to Claims 1 to 3, characterized in that gaseous or liquid media, water or water-containing media are collected in the at least one encircling depression (40).Stack structure (20) according to Claims 1 to 4, characterized in that in the anode frame and / or in the cathode frame (24, 22) the at least one discharge opening (42) is arranged in a corner region (48) of the anode frame and / or of the cathode frame (24, 22).The stack structure (20) according to claims 1 to 5, characterized in that in the stacked state of the individual cells (12), discharge openings (42) lying one above the other each form at least one discharge channel (50).Method for operating a stack structure (20) according to one of Claims 1 to 6, having the following method steps: a) collecting liquid and / or gaseous media, water or aqueous media in the at least one circumferential depression (40) of the individual cells (12), b) selectively discharging the media collected according to method step a) into at least one discharge channel (50), c) determining the quantity of discharged media and d) evaluating the state of the stack structure (20) in order to detect aging effects which are occurring.Use of the stack assembly (20) according to any one of claims 1 to 6 in an electrolyser (10) for producing gaseous hydrogen.Use of the stack assembly (20) according to any one of claims 1 to 6 in a fuel cell (10) for driving a vehicle.

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