Cell concept with a novel cathode structure and a corresponding cell frame for alkaline water electrolysis

Abstract

The invention provides a cathode structure (1) and a cell frame for an alkaline electrolysis cell (20), wherein the cathode structure (1) comprises a bipolar plate (2) connected to conductor links (3), and wherein the conductor links (3) subdivide an active cell region (6) and are aligned in an electrolyte flow direction (7). The cell frame (10) comprises the cathode structure (1) and has a distributor structure (11), the distributor structure (11) defining an active cell region (6) and being designed to achieve a uniform flow distribution in the cell (20). The invention further provides a process for producing the cell frame (10).

Description

Cell concept with a novel cathode structure and a corresponding cell frame for alkaline water electrolysis The present invention relates to a cell concept for an electrochemical cell, in particular an alkaline electrolysis cell, wherein the seal concept comprises an electrode structure and a cell frame. The present invention further provides a process for producing the cell frame. In view of the energy transition and ongoing climate change, very ambitious efforts are underway to distinctly increase the installed capacity of water electrolyzers, whether via PEM electrolysis or alkaline electrolysis, in the coming years. In this context, there is also a very great need to develop new cell concepts, frames, electrodes, membranes, separators or corresponding sealing components that feature, for example, simpler production, higher efficiency, greater current density and the use of improved materials. If an electrolysis reaction is a reaction in the alkaline range, it is possible to use a diaphragm (also called a separator), or especially also to provide an anion exchange membrane (AEM). If, by contrast, the electrolysis reaction takes place in the acidic region, a proton exchange membrane (PEM) is provided. The producing of green hydrogen from water via the processes mentioned is largely electrolytic nowadays. This is an electrochemical operation in which water is separated into its chemical constituents oxygen and hydrogen. The electrochemical cell reactions or mode of operation or the alkaline electrolysis can be summarized, for example, as follows: Anode electrode 40H- ^ 2H2O + O2 + 4e- Cathode electrode 2H20 + 2e- ^ 20H- + H2 In order to achieve the political goals, especially those of the US Department of Energy, of hydrogen production costs below 2 US$ / kg, technical advances are required in electrolysis systems. In addition to improvements in materials, improvements in the manufacturing processes can result in significant cost reductions and efficiency gains. Hydrogen can be produced by electrolysis of water, using the various technologies mentioned. Alkaline water electrolysis (AEL) is a technology which is already established industrially and has low capital costs resulting from the market readiness of the technology. AEL is also notable for high long-term stability and for the fact that virtually no critical raw materials or costly membrane or electrode materials are required. Known (pressure) cell concepts are based, for example, on nickel-coated steel rings or steel frames which are sealed to one another and electrically separated from one another by flat PTFE seals. As well as known flat seals, O-ring or cord seals that are introduced into corresponding grooves are also known. However, this seal variant is limited to plastic cell frames, since there is frequently no electrical insulation between the cells in an alkaline electrolysis stack. Known electrolysis cells operate in a pressure range between 30 bar and 40 bar and at a temperature of 60 to 100°C. The sealing material may be exposed to the following media: H2, O2, NaOH (30 wt%) and / or KOH. This results in particular demands for the sealing material used. Pressurized AEL systems that are known nowadays achieve current densities of 200 up to a maximum of 400 mA / cm2. These systems are therefore only of limited suitability for an economic (industrial) use of the technology. Sealing concepts for electrolyzers, for example based on fluoro elastomers or PTFE (polytetrafluoroethylene), are known, for example, from: EP 0 276 351 B1, EP 2 734 658 B1, EP 2 993 254 A1, EP 2 993 254 B1. It is an object of the present invention to solve the problems described above, or to specify an improved cell concept for alkaline water electrolysis, which in particular allows the electrolysis to be run at distinctly higher current densities, i.e. of up to or even more than 1 A / cm2. This object is achieved by the subject matter of the independent claims. Advantageous configurations are the subject matter of the dependent claims. One aspect of the present invention relates to an electrode structure, in particular cathode structure, for an alkaline electrolysis cell, in particular a pressurized alkaline electrolysis cell. The cell is preferably provided for water electrolysis and for generation of green hydrogen from renewable energy. The structure of the electrode or cathode structure comprises a bipolar plate connected to flow guide elements. The bipolar plate may consist, for example, of a steel sheet of a few millimeters in thickness. Preferably, the area of the bipolar plate also roughly defines an active cell region or an "active field" of the cell. The guide elements also subdivide the active cell region and are aligned in an electrolyte flow direction which is preferably established in operation of the electrochemical cell. In one embodiment, a spacing of the guide elements comprises about 7 cm to 10 cm. The proposed concept of the cathode structure advantageously enables, in particular in cooperation with a corresponding cell frame, efficient and low-wear use of the cell at particularly high current densities. In the case of current densities of more than 1 A / cm2, for example, controlled dissipation of the heat becomes essential; this can likewise be ensured in the concept presented by the finishing and dimensioning of the cathode structure. In addition, a further aspect of the present invention, namely with regard to the production of the corresponding cell frame, advantageously makes it possible to save on material costs and labor costs and to dispense with additional complex work steps that are otherwise required, such as machining steps, in particular for the producing of seal grooves in the cell frame. The cell concept presented is compatible with steel frame constructions for pressure operation at about 30 bar to 40 bar. Furthermore, the concept described, by virtue of the advantageous branching and the progression of the channels, preferably by means of a fluidic system integrated into the cell frame or into the cell (without external "manifolding"), makes it possible to improve (electrolytic) fluid guidance or media supply and media removal, which means that it is advantageously possible to dispense with costly and material-intensive filter press constructions. The present concept can still further enable an efficient "zerogap design" of the electrolysis cell for a particularly high (electrical) system efficiency without excessive ohmic losses. Moreover, the present invention makes it possible to use PFAS-free sealing materials, even in the pressurized AEL. This is because, with the seal concept presented, it is advantageously possible to dispense with what are called PFASs, but nevertheless achieve at least equally good or even improved sealing functionality — compared to conventional solutions. PFAS are per- and polyfluoroalkyl substances. Owing to the persistence of PFAS substances or degradation products thereof in the environment, these substances (also called forever chemicals) are in disrepute, and there are serious risks to the environment and health. In particular, PFAS are suspected of being carcinogenic. The high risk potential of PFAS and, in particular, the high consequential costs entailed by the containment and minimization of damage by spreading, for example through contaminated drinking water, means that extensive bans are likely in the near future. In one configuration of the concept described, every two adjacent guide elements define a separate flow plane for an electrolyte, especially a liquid electrolyte, in the operation of a corresponding electrochemical cell. The guide element concept creates an additional flow plane in which the electrolyte can flow unhindered, thereby assuring efficient heat and gas removal. This is required in particular in the case of or for achievement of high current densities. Furthermore, the design enables efficient removal of gas bubbles from the electrode plane. In known zero-gap systems, gas bubbles have to pass through the electrode structure (expanded metals / foams, etc.) in the plane, which results in a longer residence time. Since the gas bubbles displace the electrolyte, "gassing" of the electrode leads to a significant increase in cell voltage. By contrast, "backflow" behind the electrode structure in the concept described here achieves efficient removal through shorter diffusion distances. In other words, what is advantageously prevented is that gas bubbles become lodged within the electrode structure and hence increase the electrical contact resistance at the corresponding electrode in an efficiency-reducing manner. Rather than gas bubbles being transported away through the electrode space, the guide elements enable defined and efficient gas kinetics. Because the main flow of the electrolyte (and the removal of gas) is advantageously within the defined flow plane, a subatmospheric pressure additionally prevents any significant penetration or lodging of gas bubbles in the actual electrode. In one configuration, the bipolar plate has (only) two opposite straight edges, in particular of equal length, which in particular define a variance from a round cell geometry. In this configuration, the cell or the active cell region is preferably not completely round, but has a round profile, for example, only in regions around the circumference (between the straight edges). The configuration of the bipolar plate with two straight edges advantageously makes it possible to minimize offcuts on cutting to size, in particular by laser cutting. In addition, in particular states of operation, a "gas bar" can be formed in completely round cells, as a result of which the diaphragm loses its blocking effect, and gas exchange between anode and cathode can occur. As a result, safety problems, in particular a risk of explosion, can occur in operation of the cell, since there would otherwise be less or hardly any alkali or less electrolyte in the "cut-off" regions. This effect can be reliably prevented by the proposed shape of the bipolar plate or of the cell. In one configuration, the guide elements are connected to a carrier structure, in particular one attached by welding, at an end facing away from the bipolar plate, wherein the carrier structure in turn bears an electrode structure for the cathode. This configuration enables a particularly appropriate geometry and the formation of advantageous flow kinetics (cf. the described backflow behind the electrode) and electrocatalytic efficiency of the cell. In one configuration, the electron structure has a metal braid, in particular a nickel knit, and, preferably in an interior, a region closest to the separator or diaphragm, a metal weave, in particular a fine nickel weave. This electrode configuration makes it possible in particular to achieve a particularly advantageous electrocatalytic efficiency of the cell. A further aspect of the present invention relates to a cell frame for alkaline electrolysis, especially comprising the cathode structure described. In particular, the cathode structure is welded to the cell frame, or vice versa. The cell frame also comprises a distributor structure or distributor strip which likewise defines the active cell region and is set up to achieve a uniform flow distribution (for the electrolyte) of the cell. The distributor structure may be a diffuser structure, in particular a (slotted) square tube, which in particular distinctly increases, but also homogenizes, the sealing of the cell (see below) and - in particular in association with the guide elements of the cathode structure -the flow of electrolyte in the cell, and hence enables cell operation at the high current densities mentioned. In one configuration, the guide elements are aligned perpendicular to the distributor structure. In one configuration, the cell frame is a ring construction, in particular comprising a nickel-plated steel ring, wherein the distributor structure is arranged within the interior of the ring. In this configuration, the evident benefits of a (partly) round cell, namely the better mechanical force distribution thereof on pressurization, can be exploited, and at the same time the above-described disadvantages or sealing problems can be avoided. In one configuration, the distributor structure defines or integrates distributor channels for guiding the (liquid) electrolyte, wherein the cell frame is also set up such that there is a distributor inlet or distributor outlet channel between every two adjacent guide elements, in particular for the entry of the electrolyte into the active cell region or for the exiting thereof from the active cell region. In particular, the distributor structure of the invention prevents the forming of unfavorable flow pathways (called "z-flow"), for example diagonally and in an uncontrolled manner across the active cell region. Such unguided flow of the electrolyte otherwise inevitably led to a lower electrolytic throughput and to the formation of dead areas in the active field. A further aspect of the present invention relates to an electrolysis cell, in particular for alkaline water electrolysis, comprising at least the cell frame described at the cathode, wherein the cell is also set up for pressures of 30 bar to 40 bar, temperatures of 80°C to 100°C and / or for conducting the media H2, O2 and / or highly concentrated NaOH (e.g. 30 to 35 wt%) or KOH. The electrode structure of the invention is efficient and appropriate to the purposes, in particular at the cathode of alkaline electrolysis cells, since here, for example, twice the amount of the alkali or the electrolyte has to be passed through; consequently, twice the amount of gas is formed than at the anode, for example. However, without restriction of generality, the cathode structure of the invention can in principle also be used at the anode. In one configuration, the electrolysis cell is designed for operation or for achieving current densities above 1 A / cm2. In one configuration, the cell comprises a fluorine-free seal, in particular comprising a PPSU plastic, wherein the seal is set up both for sealing of the cell as a whole and for sealing of the diaphragm of the cell. Alternatively, the sealing effect described can also be achieved by a plurality of fluorine-free individual seals. A further aspect of the present invention relates to a stack or cell stack or a stack arrangement having a plurality, for example dozens, of such electrolysis cells. A further aspect of the present invention relates to an electrolyzer having a plurality of the stacks described. Yet a further aspect of the present invention relates to a method of producing the cell frame or the cell, comprising the providing of a rectangular profile, in particular a jet profile, and the bending of the rectangular profile to a round shape in a roller bending device. The bending to a round shape may, for example, be a profile bending operation of the steel profile via a 3-roll configuration. The method further comprises in particular the cutting of electrolyte channels out of the curved profile by plasma cutting, laser cutting, water jet cutting or flame cutting. In one configuration, the method subsequently comprises the cathode-side welding of a bipolar plate into the profile ring, and the connection or welding of the guide elements described and of the carrier structure and of the electrode structure as described above. Configurations, features and / or advantages which refer in the present context to the cathode structure or the cell frame likewise relate to the electrolysis cell itself and the production method, and vice versa. The expression "and / or" or "or" used here, when used in a series of two or more elements, means that any of the listed elements can be used alone, or any combination of two or more of the listed elements can be used. Further details of the invention are described hereinafter with reference to the figures. Figure 1 shows a cathode structure of the invention on the basis of a schematic sectional or side view. Figure 2 shows a schematic perspective view of the cell frame of the invention, in particular the cathode side thereof. Figure 3, similarly to figure 4, shows a perspective view of the corresponding anode. Figure 4 schematically indicates an electrolyzer comprising an electrolysis stack of the invention. Figure 5 shows further details of the electrolysis cell of the invention by a schematic view. Figure 6 shows a schematic of a roller bending device and method steps of the invention by a schematic flow diagram. Figures 7 to 9 each show schematically different parameters, such as the volume flow rate of the electrolyte in figure 7, the volume flow rate of a coolant in figure 8, and the diameter of a half-cell in figure 9, each as a function of current density. In the working examples and figures, elements that are the same or have the same effect may each be given the same reference numerals. The elements shown and their proportions to one another should fundamentally not be considered to be true to scale; instead, individual elements may be shown in exaggerated thickness or with large dimensions for better presentability and / or for better understanding. Figure 1 schematically indicates an electrolysis cell 20. The electrolysis cell 20 is preferably an alkaline cell for water electrolysis, which is set up in particular for pressure operation, in particular at pressures of 30 to 40 bar, and temperatures of 80°C to 100°C. One aspect of the present invention relates to the cathode (not explicitly identified) of the cell 20. For this purpose, a cathode structure 1 is shown in the lower region in figure 1. Opposite the cathode or cathode structure 1, for the sake of clarity, an anode 17 is identified, which is separated from the cathode by a separator or a diaphragm 14. The cathode structure 1 includes a bipolar plate 2 (see below in the diagram). The bipolar plate 2 may represent, for example, a bipolar plate of a few millimeters in thickness, in particular 3 mm. Furthermore, the cathode structure 1 comprises guide elements 3, which are in particular welded onto or otherwise bonded to the bipolar plate 2. The guide elements 3 may be welded onto the bipolar plate 2, for example, at a distance of 7 cm to 10 cm. The guide elements 3 may also be produced from a 3 mm flat steel and have a height (cf. vertical extent in figure 1) of 10 mm to 20 mm, preferably 15 mm. The longitudinal axis of the guide elements 3 also preferably extends into the plane of the diagram, i.e. in a flow direction (cf. reference sign 7 in figure 2) for the electrolyte which forms in operation of an electrochemical cell 20 comprising the cathode structure. The flow guide elements 3 thus subdivide an active cell region (cf. reference sign 6 further down) into sections, in particular equidistant sections, with every two adjacent guide elements 3 defining a separate flow plane for the electrolyte (not explicitly indicated by reference signs in the present context) in operation of the corresponding electrochemical cell 20. Accordingly, the guide elements 3 may also function as spacers or partitions. Although this is not explicitly identified by the present figures, the guide elements 3 may be perforated, slotted or otherwise structured. As the next element of the cathode structure 1, the latter has a carrier structure 4, which is indicated by the zigzag-like profile above the guide elements 3. The preferably metallic carrier structure 4 may have a thickness of 2 mm, for example, and be formed by an expanded metal. The carrier structure 4 serves essentially for bearing or spaced-apart bonding of the actual electrode, which is indicated by reference sign 5. In the present context, the electrode or electrode structure 5 comprises a metal braid, for example of thickness about 5 mm to 10 mm, in particular 7 mm, in particular a nickel knit, and further to the inside, i.e. closer to the separator, a metal weave, in particular a fine nickel weave. On the far right in the diagram of figure 1, possible thickness and size ratios of parts of the cathode structure 1 are indicated in millimeters — merely by way of example. Figure 2 shows a further aspect of the present invention, namely a cell frame 10 which is designed to be compatible with the described cathode structure 1. The cell frame 10 has a round shape and preferably consists largely of a corresponding profile steel or steel ring (cf. description by figure 6 below). A round or partly round cell geometry is found to be distinctly superior to tetragonal or rectangular "cross sections", in particular with regard to the mechanical force ratios, integrity and leaktightness. In an interior of the ring, the cell frame 2 has two opposite distributor structures 11. In principle, the distributor structures 11 or else "diffuser strips" laterally define an active cell region 6. The active cell region 6 in turn preferably corresponds roughly to the area of the bipolar plate 2, which preferably likewise has straight edges along the distributor structures 11, which constitutes a variance from the round cell geometry. In particular, the distributor structures 11 also define a variance of the active cell region 6 from the round or annular geometry of the frame 10. The distributor structures 11 or distributor strips may also consist of a square tube correspondingly slotted for the fluid channels or the electrolyte flow. In particular, the distributor structures 11 enable uniform flow distribution and also mechanically support a seal of the cell 20. Although the described cathode structure 1 cannot be seen completely in figure 2 for the sake of better clarity, the guide elements 3 are apparent, extending essentially perpendicular to the profile (longitudinal axis) of the distributor structures 11. As a feature of the distributor channels 11, figure 2 also shows inlet or outlet openings or corresponding channels 12 through which the inflow of the electrolyte, in particular NaOH or KOH, in operation of the cell 20, or the outflow thereof, can appropriately proceed at relatively high flow rates. A further channel system (internal "manifolding") is likewise not explicitly identified in figure 2 for the sake of better clarity. However, the interacting of the openings 12 of the distributor structure 11 with the described cathode structure 1, or the guide elements 3 thereof, becomes apparent through the position of the channel openings 12. This is because an elongated, roughly oval or crescent-shaped opening 12 (for the inflow or outflow of the electrolyte) is preferably provided between every two guide elements 3. Without restriction of generality, the openings 12 therefore mediate the cathodic linear flow of the electrolyte, either from front to back or vice versa. By means of this cell concept of the invention, the gas throughput and the possible current density of the cell can be increased several times compared to known concepts. In particular, an electrochemical cell equipped with the cathode structure of the invention or with the cell frame of the invention can be operated in particular at current densities of more than 1 A / cm2. Figure 3 indicates, similarly to figure 2, an anode side of the corresponding cell 20, where a cell frame 10 can likewise be used. However, the electrolyte is preferably supplied to the anode via a different channel or inflow system than on the cathode side. For this purpose, the cell frame 10 has the outer openings 15 in the annular frame. Both on the cathode side and on the anode side, inserts or plastic elements, for example made of PPSU, that ensure or improve the sealing of the cell 20 and / or of the diaphragm 14 may be provided in the inlet region and also in the outlet region for the fluids or media. Figure 4 schematically indicates an electrolyzer 40 which comprises a cell stack 30 of electrochemical cells 20 (see above). The advantages of the present invention with reference to the individual cell are therefore exponentiated through the stack up to the overall electrolysis system. Therefore, the present invention enables a significant improvement of the AEL even at an industrialized level and paves the way for the production of green hydrogen (from renewable energy) at particularly high production rates or renewable uptake capacities in the gigawatt range. By virtue of the robust novel but nevertheless on the production side relatively simple and fault-tolerant cell concept, it is possible in particular to achieve high flow rates of the electrolyte, in particular up to or more than 60 l / min. In the present context, this guiding of the electrolyte also influences the cooling of the system, and therefore the flow rate can in particular be reduced only when there is no cooling at the anode, but the cooling is accomplished in another way, for example exclusively on the cathode side. Figure 5 shows only part of the cell 20, namely two seals 13, between which the separator 14 or the diaphragm is disposed, and therefore sealed. The seals are essentially annular flat seals that have recesses in the outer region for anodic fluid supply (similarly to the openings 15 in figure 3). The described seal 13 preferably consists of a PPSU in a singlelayer or multilayer configuration. In the course of the production of the cell 20, the seal 13 may be (hot-)pressed with the diaphragm 14, for example as a (multilayer) PPSU foam. This can be effected in particular by means of heated dies at about 215°C. In contrast to fluorine-free elastomer seals, for example made of EPDM, the "laminate" thus produced is fully compatible with media and advantageously enables mechanical fixing and "padding" of the diaphragm. Compared to flat PTFE seals, the concept described here advantageously has distinctly lower creep, if any, in pressure applications. This in turn advantageously reduces the otherwise required mechanical retensioning of the stacks. The cell design described here thus also enables the use of fluorine-free seals, preferably in combination with pressureresistant nickel-plated steel ring cells. The production method for the cell frame 10 is also described in detail with reference to figure 6. This shows parts of a roller bending device 100 in simplified form. This device is preferably provided for bending of profiled steels to a round shape. In S1, the method of the invention comprises the providing of a rectangular profile 10, in particular steel profile 10. In S2, the method further comprises the bending of the rectangular profile 10 to a round shape in a roller bending device 100 and, in S3, the cutting of electrolyte channels 16 out of the rounded profile 10. A profile steel or steel ring which is to form the cell frame 10 at a later stage is preferably bent to a round shape from a 3 mm-thick rectangular profile over and above an outer diameter of about 1 m. This method advantageously makes it possible to save on material and machining costs by comparison with conventional methods. In known methods of producing steel ring cells, corresponding blanks are cut from tubes and the sealing grooves and media channels are subsequently integrated by machining. The manufacture described here, on the other hand, is based on simple bending of steel tube profiles to a round shape. Cutouts for electrolyte channels can be subsequently integrated by plasma cutting, laser cutting, water jet cutting or flame cutting. Cell frames with an outer diameter of more than 1 m can preferably be cut out of sheets of heavy plate by flame cutting and deburred. Alternatively, smaller cells can also be produced by welding of curved partsegments. It is not ruled out that profile rings may also be composed of a plurality of bent segments or L-shaped profiles. This is particularly relevant for relatively small ring diameters with critical bending radii. In general, profiles are bent with a plurality of settings of the rollers. The bipolar plate 2 (containing in particular also the further elements of the cathode structure 1) can subsequently be welded into the ring 10. For this purpose, the components are preferably preheated to at least 180°C. Welding methods employed may be those called MIG or MAG methods with a rapidly pulsed arc, in order to largely prevent thermal warpage or post-processing. It is then possible, in the course of the production of the cell, to weld the guide elements 3 onto the bipolar plate 2 on the cathode side. In one modification, after the bipolar plate 2 has been welded into the ring, it is also possible to correspondingly weld in the described carrier structure 4 and the electron structure 5. In addition, insulation sections (not explicitly identified in the present context) can be integrated into the steel ring profile. These can be created, for example, by tapering of hoses or by potting of the structure by means of epoxy resin. The cell design described here particularly advantageously enables the use of inexpensive structural steels and profile steels. The cells thus constructed have high compressive strength, since the bipolar plate and also the welded-in transverse profiles largely reliably compensate for the forces acting outward. Furthermore, the method of the invention advantageously considerably reduces offcut material compared to conventional production techniques. Figure 7 shows a diagram with illustrative data of the volume flow rate of the electrolyte, plotted against current density J. The initially proportional progression suggests that achievement of high current densities correspondingly requires high flow rates, but these are indeed achievable through the concept presented. Figure 8 shows a similar dependence as shown by figure 7 for the cooling flow rate too as a function of current density. Figure 9 also shows similar behavior of the half-cell thickness d of the "catholyte" or of the corresponding chamber thickness as a function of the current density. The parameter of halfcell or catholyte thickness shown may correspond roughly to the height of the guide elements 3 (see above). All the data shown in figures 7 to 9 correspond to a design of the cell configuration at atmospheric pressure (about 1 bar). It is apparent that the desired current densities of up to about 1 A / cm2 are thus achievable with the respectively plotted parameters even without pressure operation of the cell. Accordingly, the cell concept presented is of quite generous dimensions, and it becomes evident that the advantages of the invention certainly become evident in pressure operation, for example above one bar to 20 bar, or even in a range between 30 bar and 40 bar, although no explicit data are described in this regard. The person skilled in the art is aware that pressure operation prevents in particular the forming of large gas bubbles and thus considerably reduces ohmic losses. In other words, the efficiency of the cell is advantageously increased without significant losses in lifetime by means of pressure operation.

Claims

1. A cathode structure (1) for an alkaline electrolysis cell (20), wherein the cathode structure (1) comprises a bipolar plate (2) connected to guide elements (3), wherein the guide elements (3) subdivide an active cell region (6) and are aligned in an electrolyte flow direction (7), and wherein the bipolar plate (2) has two opposite straight edges which in particular define a variance from a round cell geometry.

2. The cathode structure (1) as claimed in claim 1, wherein every two adjacent guide elements (3) define a separate flow plane for an electrolyte in the course of operation of a corresponding electrochemical cell (20).

3. The cathode structure (1) as claimed in either of the preceding claims, wherein the guide elements (3) are connected to a carrier structure (4) at an end facing away from the bipolar plate (2), wherein the carrier structure (4) bears an electrode structure (5) for the cathode.

4. The cathode structure (1) as claimed in claim 3, wherein the electrode structure (5) comprises a metal braid, in particular a nickel knit, and a metal mesh, in particular a fine nickel mesh.

5. A cell frame (10) for an alkaline electrolysis cell (20), wherein the cell frame (10) comprises the cathode structure (1) as claimed in any of the preceding claims, and a distributor structure (11), wherein the distributor structure (11) defines an active cell region (6) and is set up to achieve a uniform flow distribution of the cell (20).

6. The cell frame (10) as claimed in claim 5, wherein the guide elements (3) are aligned perpendicular to the distributor structure (11).

7. The cell frame (10) as claimed ring construction, in particular steel ring, wherein the distributor interior of the ring.in claim 5 or 6, which is a comprising a nickel-plated structure (11) is within the8. The cell frame (10) as claimed in any of claims 5 to 7, wherein the distributor structure (11) defines distributor channels for guiding an electrolyte, wherein the cell frame (10) is set up such that there is a distributor inlet or distributoroutlet channel (12) between every two adjacent guide elements(3).

9. An electrolysis cell (20), especially for alkaline water electrolysis, comprising, on the cathode side, a cell frame (10) as claimed in any of claims 5 to 8, wherein the cell (20) is set up for pressures of 30 bar to 40 bar, temperatures of 80°C to 100°C, and / or for carrying the media H2, O2, and / or highly concentrated NaOH or KOH.

10. The electrolysis cell (20) as claimed in claim 9, having a fluorine-free seal (13), especially comprising a PPSU plastic, wherein the seal (13) is set up both for sealing of the cell (20) as a whole and for sealing of a diaphragm (14) of the cell (20).

11. A stack arrangement (30) having a plurality of electrolysis cells (10) as claimed in claim 10.

12. An electrolyzer (40) having a plurality of stacks (30) as claimed in claim 11.

13. A method of producing a cell frame (10) as claimed in any of claims 5 to 8, comprising the steps of:-  (S1) providing a rectangular profile (10), in particular asteel profile,-   (S2) bending the rectangular profile (10) to a round shapein a roller bending device (100), and- (S3) cutting electrolyte channels (16) out of the rounded profile (10) by plasma cutting, laser cutting, waterjet cutting or flame cutting.

14. The method as claimed in claim 13, wherein a bipolar plate (2) is subsequently welded into the profile ring on a cathode side, and then the guide elements (3), and in particular the carrier structure (4) and the electron structure (5) as claimed in any of claims 1 to 4, are welded or bonded.

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