Gas diffusion layer for an electrolysis cell

Abstract

The invention relates to a gas diffusion layer (5) for an electrolysis cell (1), comprising a fine layer (51) and a coarse layer (52). The fine layer (51) comprises a fine structure with pores of a first pore size, and the coarse layer (52) comprises a coarse structure with pores of a second pore size. The coarse layer (52) comprises a plurality of spiral elements (520), the spiral elements (520) are interwoven, and at least one spiral element (520) is freely movable, in particular freely rotatable, The gas diffusion layer further comprises at least one intermediate layer (53). The at least one intermediate layer (53) comprises an intermediate structure with pores of an intermediate pore size, and the intermediate layer (53) is provided between the fine layer (51) and the coarse layer (52), said intermediate pore size being larger than that of the fine layer (51) and smaller than that of the coarse layer (52).

Description

[0001] Description

[0002] Gas diffusion layer for an electrolysis cell

[0003] The present invention relates to a gas diffusion layer for an electrolysis cell and a method for producing a gas diffusion layer.

[0004] The production of hydrogen from water takes place in electrolytic cells through a process called electrolysis.

[0005] An electrolysis cell comprises two half-cells, an anodic half-cell and a cathodic half-cell, with both half-cells being joined by a membrane. Each half-cell has a bipolar plate that contacts a gas diffusion layer, with the gas diffusion layer contacting the electrode on the membrane or being the electrode itself. The electrode describes the component that is arranged on the catalyst and at which the electrochemical reaction takes place. The arrangement of the electrodes and the application of electric current creates a potential field through which ions move. The movement of the ions takes place in the conductive electrolyte, i.e. the liquid electrolyte in each half-cell, and a potentially solid electrolyte (membrane) that separates the half-cells from one another.The flow of ions through the electrolytes ultimately causes an ion current to flow from one half-cell to the other, producing hydrogen or oxygen at the respective electrodes.

[0006] The cellular reactions of hydrogen and oxygen formation in an alkaline environment are:

[0007] Anode 40H- 2H2O + 02+ 4e-, E=+0.40 V

[0008] Cathode 2H2O + 2e-^ 20H- + H2, E°=- 0.83 V

[0009] Spatial separation of the cellular reactions is made possible by the above-mentioned membrane, which allows ionic transport through the electrolysis cell. In the case of anion exchange membrane electrolysis (AEM water electrolysis), this is achieved through the use of a hydroxide ion-conducting membrane.

[0010] The electrolysis cells are typically connected in series in so-called stacks. Each electrolyzer has one or more stacks.

[0011] An electrolysis cell with its electrodes represents, in particular, an electrical assembly, with electrical resistances or impedances also occurring at the individual components of the assembly. These electrical resistances ultimately determine the operating voltage of the electrolysis cell.

[0012] Two resistances are of particular importance for industrial operation: the activation resistance of the electrolysis reaction and the ohmic resistance of the electrolysis cell. The activation resistance is largely determined by the electrodes, or rather, the catalyst of the electrolysis reaction, and its environment. The ohmic resistance is influenced by all conductive components. In the case of the ohmic resistance, the membrane resistances, or rather, the electrolyte resistances and contact resistances, play a particularly important role.

[0013] The contact resistance between the gas diffusion layer and the bipolar plate is a function of the contact pressure which is applied by tensioning elements such as tension rods, tension springs or tensioning belts.

[0014] According to the state of the art, the gas diffusion layers are made of expanded metal, wire mesh, and rigid, embossed bipolar plates, onto which a metal- or carbon-based fiber fleece is optionally laid. The rigidity of these assemblies is extremely high, while their compressibility is relatively low. This means that, if the plane parallelism is insufficient, the bipolar plates and the gas diffusion layers are pressed together inhomogeneously, resulting in contact surfaces of different sizes. Deviations in the local contact pressure ultimately lead to locally different contact resistances and thus to an undesirable current density distribution, which can, for example, promote melting, welding, or corrosion of the components. This ultimately results in degradation of the electrolyzer.

[0015] To keep contact resistance low, the individual metal layers or wire fibers are currently welded or rigidly woven together. However, this leads to increased rigidity and potential scaling. Gas diffusion layers composed of expanded metal exhibit irreversible settling behavior, or they are plastically deformed under the applied compression.

[0016] Based on the known prior art, it is an object of the present invention to provide an improved gas diffusion layer and a corresponding manufacturing method.

[0017] The problem is solved by a gas diffusion layer having the features of claim 1. Advantageous further developments emerge from the subclaims, the description and the figures.

[0018] Accordingly, a gas diffusion layer for an electrolysis cell is proposed, comprising a fine layer and a coarse layer, wherein a fine layer comprises a fine structure with fine pores and a coarse layer comprises a coarse structure with coarse pores, wherein the coarse layer comprises a plurality of spiral elements, wherein the spiral elements are woven, wherein at least one spiral element is freely movable, in particular is freely rotatable, wherein the gas diffusion layer further comprises at least one intermediate layer, wherein the at least one intermediate layer comprises an intermediate structure with pores of an intermediate pore size, wherein the intermediate layer is arranged between the fine layer and the coarse layer, wherein the intermediate pore size is larger than that of the fine layer and wherein the intermediate pore size is smaller than that of the coarse layer.

[0019] The gas diffusion layer is arranged between the bipolar plate and the membrane of the electrolysis half-cell. The gas diffusion layer's task is to ensure a uniform current distribution across the membrane, allowing the ions from the electrolysis reaction to propagate evenly through the membrane. At the same time, the gas diffusion layer must be porous or perforated to allow the ions to be transported through the pores.

[0020] The bipolar plate is in electrical contact with the coarse layer of the gas diffusion layer, and the coarse layer is typically in electrical contact with the fine layer via the intermediate layer, and the fine layer is in mechanical contact with the membrane. However, the coarse layer can also be in electrical contact with the bipolar plate via another layer. The contacts are provided by a mechanical contact pressure, which can be applied to the half-cell by means of clamping elements such as tension rods, tension springs, or tension belts.

[0021] Due to the resulting variable contact pressure, the contact resistance between the bipolar plate and the coarse layer, between the coarse layer and the intermediate layer, and between the intermediate layer and the fine layer is also variable. To a certain extent, greater contact pressure can increase the contact area between the components, resulting in a lower contact resistance with the same conductivity.

[0022] The coarse layer has a coarse structure with a spring property along the surface normal of the coarse layer. This allows a homogeneous contact resistance to be generated along the contact surface even when the contact pressure is inhomogeneous along the surface normal of the layer. The fine layer has a fine structure that provides the most homogeneous current distribution possible. The fine layer is typically made from a fleece of conductive fibers, which, however, do not have the necessary mechanical stability on their own and are therefore electrically contacted with the coarse layer via the intermediate layer.

[0023] The coarse structure of the coarse layer includes, in particular, large pores, while the fine structure has fine pores. A pore is a recess in the surface of the respective layer. A coarse pore is simply a larger recess than a fine pore.

[0024] The coarse layer comprises a large number of spiral elements. The spiral elements wind along the spiral axis around the spiral axis. The spiral elements are characterized by their handedness. For example, the spiral elements wind clockwise or counterclockwise around the spiral axis. The spiral elements are further characterized by the number of turns per path along the spiral axis, or the turn length, and by the turn diameter, i.e. twice the radial distance of the turn from the spiral axis. In the spiral structure, the spirals are woven perpendicular to one another. This type of weaving allows the individual spiral to be movable, but the combination of spirals forms a dimensionally stable fabric.

[0025] Thus, in principle, the individual spiral element is freely rotatable, since it could be unscrewed from the coarse position by rotating it around the spiral axis.

[0026] Particularly preferably, each spiral element is freely movable. This makes it possible, in particular, to provide a gas diffusion layer which, through a suitable choice of spiral elements, has a high degree of mechanical mobility perpendicular to the fabric plane relative to the other mechanical components. This means that local flat tolerances can be compensated. This is particularly true when large-area cells have to be produced. The elastic deformability of the spiral fabric under compressive stress is therefore particularly advantageous.

[0027] The spiral structure ensures uniform contact between the bipolar plate and the gas diffusion layer.

[0028] According to the invention, the gas diffusion layer also comprises an intermediate layer comprising an intermediate structure with pores of an intermediate pore size. This may mean that the intermediate pore size is larger than that of the fine layer and that the intermediate pore size is smaller than that of the coarse layer.

[0029] For example, the intermediate structure can be finer-meshed than the coarse structure and coarser-meshed than the fine structure.

[0030] The intermediate layer is placed between the fine layer and the coarse layer. In this way, the local current density between the individual layers can be adjusted to a certain extent. If the coarse layer were placed directly on the fine layer, the number of current-carrying contact points would be limited by the coarse structure of the coarse layer. The entire current would therefore have to flow through a limited number of current-carrying contact points through the gas diffusion layer, which leads to high current densities at each contact point between the coarse layer and the fine layer. The high current density in the fine layer, for example, can lead to damage to the fleece due to the fine structure of the conductive fleece.

[0031] However, if an intermediate layer is arranged between the coarse layer and the fine layer, wherein the intermediate pore size is larger than that of the fine layer and smaller than that of the coarse layer, the number of current-carrying contact points between the coarse layer and the fine layer is increased, so that the current density at each contact point is lower, which can prevent damage. The gas diffusion layer can have at least two intermediate layers, wherein the at least two intermediate layers have different pore sizes, wherein the intermediate layers are arranged such that they have an increasing pore size with increasing distance from the fine layer.

[0032] Equivalently, the layers can also have decreasing pore sizes with increasing distance from the coarse layer.

[0033] By means of additional intermediate layers, the above improvement can be further adjusted between the individual layers, so that the gas diffusion layer can be operated with as little damage as possible.

[0034] For example, the gas diffusion layer may have a total of four or five layers.

[0035] The spiral elements of the coarse structure can convert a deformation force perpendicular to the spiral axis into a torsion around the spiral axis.

[0036] When heat is introduced into the structure, which is triggered by the cell's internal resistance, especially at higher current densities, the spiral wire expands longitudinally. This results in the spiral elements being stretched along the spiral axis.

[0037] When the coarse layer is loaded along the surface normal to the layer, elastic deformation occurs due to the spring action of the spiral element windings. For example, the winding diameter of the spiral element is locally reduced (compressed) by the load. Along the spiral axis, this results in torsion, while the winding length remains constant.

[0038] This deformation is preferably completely reversible, so that the original number of turns and the original position are restored upon subsequent unloaded coarse position. The reversibility of the spiral is based on the spring constant of the spiral element.

[0039] This ensures minimal lateral expansion of the coarse layer under load, meaning that the adjacent structures of the electrolysis cell, such as the cell frame, are subjected to little or no mechanical stress and the risk of assemblies or components becoming mechanically jammed is reduced.

[0040] In contrast to the rigid expanded metal layers, wire mesh or folded sheets of the state of the art, compression does not lead to material stresses and thus not to inhomogeneous pressure peaks, which in the worst case lead to mechanical wedging in the electrolyzer.

[0041] During pressurized operation of the electrolyzer, differential pressures can also occur between the anodic and cathodic half-cells. The described gas diffusion layers, with their multilayered structure consisting of a fine structure, intermediate structure, and coarse structure, can provide dynamic and local support for the membrane, ensuring that it can withstand the forces in the electrolyzer and is not subjected to unnecessary mechanical stress.

[0042] The spiral elements can be woven together, with at least one node point existing per turn of the spiral element, in that four spiral elements are frictionally connected to one another, with the first and the second spiral element running parallel to one another, in particular being wound together in a double helix manner, with the third and the fourth spiral element running parallel to one another, in particular being wound together in a double helix manner, with the third spiral element and the fourth spiral element running perpendicular to the first spiral element and to the second spiral element.

[0043] The connection of the spiral elements is frictionally engaged if it is detachable, can withstand dynamic loads and there is no play in the spiral elements. This weave allows each individual spiral element of the coarse structure to be flexibly movable. Flexible movement means that the spiral can rotate about its spiral axis but can also be stretched or compressed along its spiral axis, in particular it can be twisted. Thus each spiral element of the coarse structure has a degree of freedom of movement along the spiral axis but also a degree of freedom of rotation about the spiral axis.

[0044] Such a weave in particular provides a coarse structure whose freely movable spiral elements offer a more homogeneous contact pressure of the adjacent components and a better tolerance compensation.

[0045] For example, the coarse layer can have a tolerance compensation of between 100 pm and 500 pm, preferably 200 pm. For example, the coarse layer can have a tolerance compensation of at least 5%, preferably 10%, particularly preferably at least 20% of the thickness of the coarse layer.

[0046] The wire diameter can be between 0.3mm and 1.5mm, for example 0.7mm and / or the mesh size can be between 2mm and 10mm, for example 6mm and / or the hole opening can be between 2mm and 8mm, for example 3.5mm and / or the thickness of the coarse layer can be between 3mm and 10mm, for example 5mm.

[0047] This allows the compressibility and clamping force to be adjusted. In particular, the contact resistance can be adjusted by selecting the appropriate parameters.

[0048] In a particularly preferred variant for anion exchange membrane electrolysis, the wire thickness is 0.7 mm, the mesh size is 6 mm, the hole opening is 3.5 mm and the total thickness is 5 mm.

[0049] In a particularly preferred variant for proton exchange membrane electrolysis, the wire thickness is 0.5 mm, the mesh size is 6 mm, the hole opening is 3.5 mm and the total thickness is 5 mm.

[0050] The coarse pores of the coarse layer can have a diameter that is 100 to 1000 times the diameter of the fine pores of the fine layer.

[0051] This already ensures a more homogeneous current density distribution, so that voltage peaks in particular are avoided and the service life of the electrolysis cell is increased.

[0052] The current density distribution can be further homogenized by the intermediate layers with pores whose diameters are smaller than 100 to 1000 times the diameter of the fine pores.

[0053] It is also possible to further improve the current density distribution by coating the individual layers. The coating allows the coarse layer and / or another layer to also serve as an electrocatalyst. Overall, with a coating, the entire gas diffusion layer can also serve as an electrocatalyst.

[0054] The fine structure of the fine layer can comprise fibrous and / or powder-like structures, with a fiber thickness between 10 and 50 μm, and / or perforated sheets with a hole diameter between 2 and 10 mm, and / or braided, fine-mesh net structures, and / or knitted layers. Furthermore, the fine layer can have a thickness between 0.2 and 1 mm.

[0055] This allows for very good transverse conductivity, i.e., conductivity in the layer, and thus a very good current distribution. The current flowing from the contact points to the electrolyzer electrodes is distributed evenly with this structure.

[0056] Preferred are fibrous structures, which are generally formed as nonwovens. The intermediate structure of the at least one intermediate layer can comprise various structures depending on the desired pore size, for example, fine-mesh spiral braids, expanded metal sheets, perforated metal sheets, braided fine-mesh net structures, wire mesh, knitted wire mesh, fibrous and / or powder-like structures.

[0057] For example, a first intermediate layer can be a perforated sheet, a second intermediate layer can be a fine-meshed spiral mesh and a third intermediate layer can be a wire mesh.

[0058] It has been shown that by combining the coarse layer with an intermediate layer, for example an expanded metal sheet with a mesh size of 2.5 x 2 mm 2 and a very fine fine layer, for example a fleece structure made of stainless steel fleece or carbon fleece, creates a very homogeneous pressure distribution on the membrane.

[0059] The fine layer, intermediate layer, and coarse layer can be made from a NiCr-based steel. However, for the fiber and wire thicknesses mentioned above, other metals such as Ni, Ti, or alloys (e.g., 1.4404, 1.4571, 1.4550, 1.4541, 1.4539, 2.4816, 2.4066, 2.4819) can also be used.

[0060] The fine layer, the at least one intermediate layer, and the coarse layer can, in particular, be sintered together instead of welded together (see below). The fine layer, the at least one intermediate layer, and the coarse layer can also simply be placed on top of one another.

[0061] The above-mentioned object is further achieved by a method for producing a gas diffusion layer having the features of claim 12. Advantageous developments of the method emerge from the subclaims as well as the present description and the figures.

[0062] Accordingly, a manufacturing method of a gas diffusion layer is proposed, wherein the fine layer, the at least one intermediate layer and the coarse layer are sintered together, in particular fusion-sintered.

[0063] During sintering, the fine layer, at least one intermediate layer, and the coarse layer are placed on top of each other and then baked together. The fine layer, at least one intermediate layer, and the coarse layer are not welded together, but are bonded together.

[0064] This prevents the formation of mixed phases in the metal structure in the gas diffusion layer. Such mixed phases can be triggered, for example, by high local heat input when the expanded metal layers are welded together. Such mixed phases can prevent the formation of passivation layers and, due to the lack of passivation, promote corrosion. Accordingly, sintering the layers enables the formation of a uniform passivation layer, which can protect the gas diffusion layer against corrosion.

[0065] Furthermore, the fine layer, the at least one intermediate layer and the coarse layer form a materially bonded individual component and a functional unit.

[0066] The fine layer, at least one intermediate layer and the coarse layer can be sintered in a protective gas atmosphere.

[0067] Sintering in a protective gas atmosphere results in the fine layer, at least one intermediate layer and the coarse layer bonding together via diffusion, but due to the lack of oxygen and the rather mild temperatures, no scale or oxide deposits are formed.

[0068] The bond during sintering is always material-to-material, thus providing optimal contact with minimal contact resistance between the components. The surfaces of the fine layer, at least one intermediate layer, and the coarse layer can be degreased and pickled in advance to facilitate the sintering of wires, fibers, and other structures.

[0069] The sintering temperature can be between 700°C and 1200°C, preferably 900°C and / or the fine layer, the at least one intermediate layer and the coarse layer can be sintered at a pressure between 10MPa and 100MPa, preferably 40MPa and / or the heating rate can be 50°C / min.

[0070] Preferred sintering parameters are a sintering temperature of 900°C at a pressure of 40 MPa and heating rates of 50°C / min. This allows the spiral elements to still move freely, even though they are sintered to the fine layer at certain contact points. The properties of the fine layer's improved cross-flow conductivity are now combined with reversible compressibility, tolerance compensation, and thus more homogeneous contact.

[0071] The gas diffusion layer can be coated with Ni and / or NiP and / or NiTi and / or NiFe.

[0072] This allows the current carrying capacity and the ohmic resistance of the gas diffusion layer to be reduced, while the nickel-based coating simultaneously has wear-inhibiting properties, such as abrasion and corrosion protection.

[0073] The coating can be deposited electrolessly, galvanically or by gas phase processes, in particular sputtering, arc evaporation or electron beam evaporation.

[0074] A further aspect of the invention relates to an electrolysis cell with a gas diffusion layer according to the invention.

[0075] Short description of the characters

[0076] Preferred further embodiments of the invention are explained in more detail by the following description of the figures. Figure 1 shows a schematic structure of an electrolyzer half-cell.

[0077] Figure 2A, B is a schematic representation of the first

[0078] spiral structure;

[0079] Figure 3A, B shows a schematic representation of the deformation in the z-direction and rotation of the spiral structure;

[0080] Figure 4 Results of a contact pressure test, left: gas diffusion layer according to the state of the art, right: gas diffusion layer according to the invention;

[0081] Figure 5 shows a compression deformation characteristic of the gas diffusion layer according to the invention;

[0082] Figure 6A, B a fine structure of the fine layer; and

[0083] Figure 7 shows the differences in the manufacturing technology of an electrolysis cell with respect to a CCM and CCS design.

[0084] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the different figures are provided with identical reference numerals, and a repeated description of these elements is partially omitted to avoid redundancies.

[0085] Figure 1 shows a schematic diagram of an electrolysis cell 1 according to the invention. The electrolysis cell 1 is divided into an anodic half-cell 10 and a cathodic half-cell 12, with both cells converging at the membrane 6. Each half-cell 10, 12 has a bipolar plate 2 that contacts a gas diffusion layer 5, wherein the gas diffusion layer 5 has a fine layer 51, an intermediate layer 53, and a coarse layer 52. The cell frame 3 and seals 4 are arranged between the bipolar plate 2 and the gas diffusion layer 5. The two half-cells 10, 12 are pressed together by fastening means such as tension rods 7, so that the components of the electrolysis cell 1 are in mechanical or electrical contact with one another (provided they are conductive).

[0086] The tension rod 7 therefore builds up a contact pressure which is to be distributed homogeneously in the electrolysis cell 1. However, due to manufacturing tolerances, voltage peaks in the material in the electrolysis cell 1 can occur, particularly in the area of ​​the gas diffusion layers 5, so that an inhomogeneous distribution of the contact resistance between the electrical components 6, 51, 52 of the cell also occurs, which can result in damage.

[0087] Figure 1 also schematically shows that the intermediate layer 53 is arranged between the fine layer 51 and the coarse layer 52. The hatching schematically illustrates that the interpore size of the pores of the intermediate layer 53 is larger than the pore size of the fine layer 51 and smaller than that of the coarse layer 52.

[0088] In a sense, the layers are arranged in such a way that there is a decreasing gradient of pore size from the bipolar plate 2 to the membrane 6. The gas diffusion layer 5 thus becomes increasingly fine-meshed from the bipolar plate 2 to the membrane 6.

[0089] Figure 2 shows the coarse layer 52. The coarse layer 52 comprises a plurality of spiral elements 520 that are freely movable and, in particular, freely rotatable or freely twistable.

[0090] For example, the first spiral element 521 and the second spiral element 522 run parallel to each other. In particular, the spiral axes of the spiral elements 521, 522 coincide. The two spiral elements 521, 522 form a double helix structure because they are intertwined.

[0091] The same applies to the third spiral element 523 and the fourth spiral element 524. The first and second spiral elements 521, 522 are perpendicular to the third and fourth spiral elements 523, 524. In particular, the spiral elements 521, 522, 523, 524 form a node K in which all spiral elements are frictionally connected to one another.

[0092] A frictional connection is achieved, for example, in that the first spiral element 521 is guided at the node K under the third spiral element 523 and above the fourth spiral element 524, while the second spiral element 522 is guided above the third spiral element 523 and below the fourth spiral element 524. At the same time, the third spiral element 523 is guided at the node K under the second spiral element 522 and above the first spiral element 521, while the fourth spiral element 522 is guided above the second spiral element 523 and below the first spiral element 524.

[0093] Figure 2B shows a corresponding photograph of such interwoven spiral elements 520.

[0094] Figure 3 shows the effect of torsion of a spiral element 520 due to vertical pressure in an FEM simulation, with the deformation in the x-direction being shown in Figure 3A and the deformation in the z-direction in Figure 3B. The turns of the spiral element 520 adapt to the contact surface due to the pressure exerted, thereby compensating for any elevations or depressions in the respective contact surface. This results in an overall uniform contact surface. This occurs, for example, by twisting the spiral element 520 along the spiral axis, i.e. the spiral locally adjusts its number of turns (dark discoloration). The manufacturing tolerances of adjacent parts and components can therefore be selected in a much more production-friendly and therefore more economically viable manner. This can lead to a considerable cost reduction, particularly for components with a correspondingly large extent.Tolerance compensation in the range of 100 pm - 500 pm, preferably 200 pm, is possible. The tolerance compensation can also amount to at least 5%, preferably 10%, and particularly preferably at least 20% of the thickness of the coarse layer.

[0095] Figure 4 shows a pressure test of the homogeneous contact. In Figure 4, on the left, a conventional coarse layer 52 consisting of expanded metal is shown, while on the right the innovative coarse layer 52 made of interwoven spiral elements 520 is shown. The dots on the underlying sheets show the contact points of the two coarse layers 52. The blacker the color, the higher the contact pressure. The uniform dot size achieved with the coarse layer made of interwoven spiral elements is noteworthy, while on the left clear differences in shape and size can be seen. Accordingly, a significant improvement in contact resistance is achieved with the innovative spiral structure.

[0096] In an analogous way, the improvement in contact by the intermediate layers 53 can be understood from Figure 4. While in Figure 4 on the left there are still a few coarse contact points that enable electrical conduction through the gas diffusion layer 5, the number of contact points in Figure 4 on the right is already considerably greater. By arranging layers 51, 53, 52 with different pores one above the other, a constantly growing number of contact points is provided between the layers, so that the current flow between the layers to the fine layer 51 is evened out, in particular homogenised, whereby current peaks and thus damage are avoided.

[0097] Figure 5 shows a series of tests on the setting behavior of the coarse layer. A coarse layer with a wire thickness of 0.7 mm, a mesh size of 6 mm, a hole opening of 3.5 mm, and a total thickness of 5 mm was used.

[0098] Settling behavior involves investigating the irreversible compression of the coarse layer under periodic loading. In this case, a pressure of between 0.6 MPa and 2.5 MPa was periodically applied. The coarse layer exhibits a settling behavior of approximately 20 pm after 100 cycles of complete unloading. A cyclic loading test with 10,000 cycles shows a settling behavior of only 24 pm, with almost ideal elastic behavior being observed across the entire working range of the coarse layer.

[0099] The spring constant in this range is 8.7 MPa / mm. The coarse layer can therefore be used in a pressure range from 0.5 MPa to 5 MPa. A pressure range between 1.0 MPa and 3.5 MPa is particularly preferred.

[0100] Due to the spiral-shaped coarse layer 52, the gas diffusion layers therefore exhibit a certain dimensional stability in the event of pressure fluctuations in the electrolyzer or in the event of cyclical mechanical loading of the electrolyzer, so that the corresponding contact pressure is kept constant.

[0101] Figure 6A shows a microscopic image of a fine layer 1 with a fine structure that enables a homogeneous power supply. The fine layer 51 is mechanically and electrically contacted via the intermediate layer 53, as shown in Figure 6B. Similarly, the intermediate layer 53 is contacted with the coarse layer 52 (not shown).

[0102] The fine structure of the fine layer 51 differs from the coarse structure of the coarse layer 52 in that the fibers are not processed systematically, but randomly into a fabric. The result is random interweaving and a significantly higher tortuosity of the fabric. The macroscopic appearance of the fine structure nevertheless appears homogeneous due to the size ratios, although the fibers have a chaotic, inhomogeneous appearance at the microscopic level. By choosing a fiber thickness between 10 pm and 50 pm and a thickness of the fine layer between 0.2 mm and 1 mm, very good transverse conductivity, i.e. conductivity in the horizontal direction and thus a distribution of the current, can be achieved. The gas diffusion layer is suitable for polymer membrane electrolysis, in particular with acidic proton exchange membranes or alkaline anion exchange membranes, depending on the material selected.Application in alkaline electrolysis with diaphragms is also possible.

[0103] Figure 7 also shows two possible manufacturing processes for the electrolysis cell.

[0104] In the so-called CCS design (Catalyst Coated Substrate), the gas diffusion layer 5 is coated with an electrocatalyst and then pressed with the diaphragm or membrane 6.

[0105] In the CCM design (Catalyst Coated Membrane), the membrane 6 is coated with the electrocatalyst and then pressed onto the uncoated gas diffusion layer 5. Combinations of both designs are possible. Industrial production currently uses standardized processes for cost reasons.

[0106] Due to the fine structure of the fine layer 51, which already has a high surface area in its initial state due to the fibers, it can be coated with catalysts for use in alkaline environments and then serve as an electrode itself. Together with a prior adhesive coating, this layer combination enables a combined multilayer electrode design that contacts and mechanically supports the membrane 6.

[0107] Where applicable, all individual features shown in the embodiments can be combined and / or exchanged without departing from the scope of the invention.

Claims

Patent claims 1. Gas diffusion layer (5) for an electrolysis cell (1), comprising a fine layer (51), a coarse layer (52), wherein the fine layer (51) comprises a fine structure with pores of a first pore size, wherein the coarse layer (52) comprises a coarse structure with pores of a second pore size, wherein the coarse layer (52) comprises a plurality of spiral elements (520), wherein the spiral elements (520) are woven, wherein at least one spiral element (520) is freely movable, in particular freely rotatable, wherein the gas diffusion layer further comprises at least one intermediate layer (53), wherein the at least one intermediate layer (53) comprises an intermediate structure with pores of an intermediate pore size, wherein the intermediate layer (53) is arranged between the fine layer (51) and the coarse layer (52), wherein the intermediate pore size is larger than that of the fine layer (51) and wherein the intermediate pore size is smaller than that of the coarse layer (52) is.

2. Gas diffusion layer (5) for an electrolysis cell (1) according to claim 1, characterized in that the gas diffusion layer (5) has at least two intermediate layers (53, 53'), wherein the at least two intermediate layers (53, 53') have different pore sizes, wherein the intermediate layers are arranged such that they have an increasing pore size with increasing distance from the fine layer (51).

3. Gas diffusion layer (5) according to one of the preceding claims, characterized in that the spiral elements (520) have a spiral axis and are designed to convert a deformation force perpendicular to the spiral axis into a rotation and / or torsion about the spiral axis.

4. Gas diffusion layer (5) according to one of the preceding claims, characterized in that the spiral elements (520) are interwoven with each other, wherein at least one node point (K) exists per turn of each spiral element, in that four spiral elements (521, 522, 523, 624) are frictionally connected to each other, - wherein the first spiral element (521) and the second spiral element (522) run parallel to each other, in particular are wound together in a double helix manner, - wherein the third spiral element (523) and the fourth spiral element (524) run parallel to each other, in particular are wound together in a double helix manner, - wherein the third spiral element (523) and the fourth spiral element (524) run perpendicular to the first spiral element (521) and the second spiral element (522).

5. Gas diffusion layer (5) according to one of the preceding claims, characterized in that - the wire diameter is between 0.3mm and 2.5mm, - the mesh size is between 1mm and 20mm, - the hole opening is between 1mm and 15mm, - the thickness of the coarse layer (52) is between 3mm and 10mm.

6. Gas diffusion layer (5) according to one of the preceding claims, characterized in that the coarse pores have a diameter which corresponds to 100 times to 1000 times the diameter of the fine pores.

7. Gas diffusion layer (5) according to one of the preceding claims, characterized in that a coating of at least one of the layers, comprising the fine layer, the at least one intermediate layer and the coarse layer, is an electrocatalyst.

8. Gas diffusion layer (5) according to one of the preceding claims, characterized in that the coarse layer (52) has a tolerance compensation of at least 5%, preferably of 10%, particularly preferably of at least 20% of the thickness of the coarse layer (52).

9. Gas diffusion layer (5) according to one of the preceding claims, characterized in that the fine structure of the first layer (51) comprises fibrous and / or powder-like structures, wherein the fiber thickness is between 10pm and 50pm and / or comprises perforated sheets with a hole diameter between 2mm and 10mm and / or comprises braided fine-machine mesh structures and / or knitted structures.

10. Gas diffusion layer (5) according to one of the preceding claims, characterized in that the fine layer (51) has a thickness between 0.2 and 1 mm.

11. Gas diffusion layer (5) according to one of the preceding claims, characterized in that the fine layer (51), the at least one intermediate layer (53) and the coarse layer (52) are sintered together, in particular diffusion sintered.

12. Manufacturing method of a gas diffusion layer (5) according to one of the preceding claims, characterized in that the fine layer (51), the at least one intermediate layer (53) and the coarse layer (52) are sintered together, in particular diffusion sintered, wherein the sintering temperature is between 700°C and 1200°C, preferably 900°C and / or the fine layer (51) which has at least one intermediate layer (53) and the coarse layer (52) are sintered in a protective gas atmosphere and / or - the fine layer (51), the at least one intermediate layer (53) and the coarse layer (52) are sintered with a pressure between 10MPa and 100MPa, preferably 40MPa and / or - the heating rate is 50°C / min.

13. Manufacturing method according to claim 10, characterized in that the gas diffusion layer (5) is coated with Ni and / or NiP and / or NiTi and / or NiFe.

14. Manufacturing method according to claim 11, characterized in that the coatings are deposited electrolessly, galvanically or by gas phase processes, in particular sputtering, arc evaporation or electron beam evaporation.

15. Electrolysis cell (1) with a gas diffusion layer (5) according to one of claims 1 to 10 and an electrolysis membrane, wherein the gas diffusion layer is arranged such that the pore size decreases with increasing distance from the electrolysis membrane.

Images