Porous transport layer and production method

Abstract

The invention relates to a porous transport layer (1) for use in an electrolyzer, wherein the transport layer (1) has a plurality of layers (2-4) which are connected to one another, at least one of the layers (2) has a porosity of less than 75%, another layer (3) has a porosity of 75% to 90%, all of the layers (2-4) consist of metal and are integrally bonded to one another, and at least one of the layers (3) consists of a sheet material made of wire or an expanded metal mesh, said sheet material having a main plane and a 3D structuring perpendicular to the main plane such that flow channels are formed in conjunction with an adjacent layer (4, 2).

Description

[0001] Porous transport layer and manufacturing process

[0002] The invention relates to a porous transport layer for use in an electrolyzer and a method for its production.

[0003] The application area of ​​the invention is electrolyzers, in particular water electrolyzers, that is, devices for splitting water into hydrogen and oxygen using electric current, and also a fuel cell operating in reverse. Electrolyzers are classified according to their type: alkaline electrolysis (AEL), proton exchange membrane electrolysis (PEM), and anion exchange membrane electrolysis (AEM). Each electrolyzer has an anode and a cathode, and between the anode and cathode, a separating element that performs various transport functions transverse to its main plane. Depending on the operating principle, a pressure-tight membrane for gases and liquids is used. A porous transport layer, which is in electrically conductive contact with the membrane, borders the membrane. A porous transport layer is described in DE 10 2020 132 271 A1.When liquid water is split, large quantities of gas are produced, approximately 1000 times the volume of the liquid supplied, which must be transported away through the porous transport layer. The transport layer must therefore be designed for both liquid and gas transport.

[0004] The invention is based on the objective of providing a porous transport layer that can be used in various functions in an electrolyzer, either on the anode or cathode side, and that can perform the tasks of mass transport and ion transport between the membrane and the outer cell wall. The porous transport layer should have fine structures on the membrane side and coarser structures on the side facing away from the membrane, while simultaneously being robust and easy to manufacture. A transport layer with these properties should be cost-effective to produce.

[0005] The problem is solved by a porous transport layer with the features of claim 1.

[0006] A method for producing such a transport layer is the subject of claim 9.

[0007] The dependent claims relate to advantageous further developments of the invention.

[0008] The porous transport layer according to the invention is intended for use in an electrolyzer, in particular in a water electrolyzer or a fuel cell. The transport layer comprises several interconnected layers with specific properties. At least one of the layers has a porosity of less than 75%, and another layer has a porosity of 75% to 90%. All layers are made of metal and are bonded together so that they cannot be separated from one another without damage. At least one of the layers consists of a sheet structure made of wire or expanded metal mesh. The sheet structure or expanded metal mesh layer has a main plane and a 3D structuring perpendicular to the main plane, so that flow channels are formed in conjunction with an adjacent layer. The porous transport layer preferably has 2 to 8 layers, in particular 2 to 5, and preferably 3 to 4 layers.Each layer fulfills individually adjustable properties. Preferably, the majority of the layers, or all layers, consist of a wire mesh. A wire mesh is preferably a woven, knitted, or crocheted fabric produced with a specific wire diameter. Depending on the function and positioning of the layer, the mesh can be produced from a wire with a diameter of 0.0125 mm to 2 mm. In particular, the wire diameter is in the range of 0.015 mm to 1.5 mm. Due to the wide range of wire diameters and the 3D structuring of a layer perpendicular to its main plane, it is possible to form directed flow channels, allowing gases generated during electrolysis to easily escape from the transport layer through these flow channels, which preferably run vertically from bottom to top.

[0009] A special feature of the transport layer according to the invention is that, due to the use of wire sheet structures, it is both pressure-resistant and elastically deformable. The elastic deformability protects the transport layer, and also the entire cell or electrolyzer, from pressure-induced damage. Furthermore, the wire sheet structure creates a homogeneous, electrically conductive structure. By selectively choosing and processing the materials used, different porosities between 10% and 90% can be achieved in the individual layers. The combination of differently structured layers has a controllable influence on the flow behavior of the electrolyte and on the properties of the gases produced during the reaction. Each individual layer has a homogeneous material structure.The layers are joined to form a materially bonded overall structure characterized by a precisely controlled porosity. Simultaneously, the division into layers with locally different functions creates the possibility of providing a nearly smooth contact surface, for example, for contact with the separating membrane. Very fine sheet structures with very small wire diameters possess a very high number of contact points, which are evenly distributed and in contact with the membrane.

[0010] Due to the choice of material, the transport layer according to the invention is pressure-stable even at high pressures and has sufficient elasticity to adapt to changing expansions, for example during temperature fluctuations, or to compensate for expansions of adjacent components.

[0011] The sheet material is in particular a fabric. Alternatively, if it is an expanded metal mesh, it is preferably made from a sheet with a thickness of 0.1 mm to 1 mm.

[0012] In an advantageous embodiment of the invention, one layer consists of a metal fiber fleece, wherein the fiber thicknesses are in the range of 2 pm to 60 pm and wherein the metal fiber fleece has a thickness of 0.15 mm to 1 mm. A metal fiber fleece can be produced from scraped or drawn fibers or a mixture thereof. The porous transport layer can have a total thickness of preferably 0.5 mm to 12 mm.

[0013] In an advantageous embodiment of the invention, the porous transport layer is joined to a fluid-tight outer wall. In this case, the outer wall is not porous, but is bonded to the at least two further porous layers of the transport layer. The porous transport layer with the outer wall forms a structural component whose function is enhanced. Hereinafter, the term "porous transport layer" will also be used for this structural component.

[0014] The outer wall can be, for example, a sheet metal part, especially a smooth one. This could be the outer wall of the cell. Alternatively, the outer wall could be a bipolar plate. The connection to the outer wall expands the porous transport layer into a transport structure. This transport structure is characterized by the fact that it encompasses both the porous transport layer and the non-porous outer wall / bipolar plate. This enables cost-effective manufacturing not only of the porous transport layer but of the entire electrolyzer.

[0015] The transport layer according to the invention integrates various functions and properties into a single component, which also simplifies the assembly of the electrolyzer, particularly when the transport layer is already bonded to an outer sheet metal wall. The transport layer according to the invention utilizes layers made of different materials. The combination of materials with different mechanical and technological properties leads to optimal utilization of the available installation space. This combination of different materials allows for the desired adjustment of sometimes contradictory properties required of porous transport layers. The porous transport layer can be impermeable to substances and media on one side and open on the opposite side to ensure mass transport.Lower surface roughness can be achieved against the membrane of an electrolyzer, whereas greater roughness is achieved against the outer cell wall. The cross-sectional structure can range from coarser to finer structures in the orientation from the cell wall towards the membrane, in order to ensure targeted distribution of the electrolyte or other media.

[0016] The individual layers are bonded together using a material-bonded process, particularly through diffusion, fusion, welding, or brazing. The bond can be applied across the entire surface or at specific points. The resulting transport layer can be easily handled and further processed as a complete component. It is highly customizable and cost-effective to manufacture.

[0017] The transport layer is characterized in particular by the fact that a layer of a sheet-like wire structure has been plastically deformed for the purpose of improving the conductivity of substances, gases, and fluids and increasing elasticity, resulting in a 3D structure perpendicular to the main plane. This 3D structuring increases the thickness of the individual layer compared to its undeformed initial thickness.

[0018] Layers of metal mesh can be produced using various weave types, such as plain weave, twill weave, or specially woven weaves. Individual layers may be calendered to achieve a smooth surface or defined thickness.

[0019] Metal fiber nonwovens made from different fiber thicknesses (2 pm to 60 pm) can exhibit varying porosities. Preferably, metal fiber nonwovens are sintered and calendered to achieve defined thicknesses between 0.15 mm and 1 mm.

[0020] Knitted fabrics with various mesh shapes are also considered sheet structures made of wire. Wire diameters of 0.10 mm to 1.5 mm are particularly common in this context. Knitted fabrics can have a thickness of up to 12 mm. The invention also takes into account that at least one optional layer can consist of a perforated sheet. Such a perforated sheet can have openings produced by punching, etching, laser cutting, or laser drilling, with sheet thicknesses of 0.1 mm to 1 mm.

[0021] When using expanded metal mesh, different mesh shapes are also conceivable in order to achieve different porosities depending on the degree of expansion. The sheet thicknesses used are preferably in the range of 0.1 mm to 1 mm.

[0022] Depending on the location and intended use, materials such as titanium, steel alloys, stainless steel alloys or nickel or nickel alloys (Ni99,2, Ni99,6) can be used for the porous transport layer.

[0023] To optimize mass transport, the 3D structures in the relevant surface structure can be produced by profile rolling, corrugating, folding, deep drawing or pressing.

[0024] An example of a porous transport layer according to the invention comprises, for example, a corrugated open wire mesh with vertical nonwoven channels in the form of 3D structures perpendicular to the main plane. Adjacent to the highly porous corrugated open wire mesh are two sintered fine wire mesh layers, followed by a sintered calendered metal fiber nonwoven. Additionally, a further layer can be added to increase the number of contact points or reactions with the membrane that follows the fine layer. The corrugated open wire mesh with the vertical flow channels can optionally be connected to the cell outer wall. This can be a closed sheet. An alternative example shows a wire mesh with a suitable channel structure extending from the cell outer wall.The cell consists of a bonding layer, followed by a porous metal medium to increase stability and achieve homogeneous dispersions, and a third layer of a porous metal medium in the form of a fabric, expanded metal mesh, or laser-cut structure with an additional coating. In the installed position, the membrane is applied to this third layer. As in the first embodiment, the cell outer wall can be bonded to the channeled wire mesh with the 3D structuring, in particular by welding.

[0025] Another example of 3D structuring can be honeycomb or spherically structured wire mesh; here too, the structuring is perpendicular to the main plane.

[0026] The invention is explained in more detail below with reference to the exemplary embodiments shown in the figures.

[0027] Figure 1 shows an example of a porous transport layer 1 in the form of a multilayer porous structural element, oriented with its upper surface facing the viewer towards a membrane (not shown in detail). The porous transport layer 1 shown here consists of three layers 2, 3, 4, each made of wire meshes that become progressively finer towards the membrane with respect to roughness, pore channels, and wire diameter. The wire diameters range from 0.05 mm to 0.5 mm. The pore channels in the finest layer 2 have a fineness of 14 pm. The last layer 2, adjacent to the membrane, should have pore channels ranging from 2 pm to 200 pm, preferably from 3 pm to 100 pm, and more preferably from 5 pm to 25 pm. The last layer 2 preferably has a smooth surface with roughnesses of Ra < 50 pm, preferably Ra < 25 pm, and particularly Ra < 10 pm.

[0028] Although three layers 2, 3, 4 are shown in this embodiment, the number of layers can range from 2 to 8; five individual layers are preferred. Three suitable individual layers for creating the porous transport layer 1 are particularly advantageous. A key feature of the invention is a three-dimensionally deformed individual layer. In this case, it is the middle layer 3, designated by reference numeral 3, which, through its combination with the two adjacent layers 2, 4, forms flow channels. Furthermore, the middle layer 3, due to its geometric shape, is crucial for the elasticity of the overall component. Cyclic threshold loads of more than 2.0 MPa, preferably more than 2.8 MPa, and preferably more than 3.5 MPa can be withstood for 50,000 cycles. After loading, the pressure relaxation is less than 0.25 MPa, preferably less than 0.1 MPa. The 3D structuring can be undirected, for example in the form of a honeycomb structure.Preferably, it is oriented as shown in Figure 1. There, a channel structure in the form of a wave structure is shown. The deformation of the middle layer 3 increases its thickness perpendicular to the transport layer 1 by 150% to 2500%, preferably by 200% to 1500%, and particularly by 600% to 1000%. This in turn results in a porosity of this layer of up to 95%, preferably up to 92%.

[0029] The third layer 4 in Figure 1 is purely functional as the separating layer from the cell wall (not shown in detail). The third layer 4 is shown at the bottom of the image plane in Figure 1. In this case, it consists of a single porous layer of wire mesh, but it can also be made of a composite layer. This final composite layer can comprise one to three single layers. The final, outermost layer of such a composite layer can be made of sheet metal. In this case, the sheet metal does not have porous properties.

[0030] The separating layer serves to fix the three-dimensionally deformed middle layer 3 between the two adjacent layers 2 and 4, preventing any relative movement between layers 2 and 4. Simultaneously, the material flow is directed away from the cell wall by a porous separating layer and into the middle region of the porous transport layer 1. The porosity of layer 4 is preferably between 20% and 80%, more preferably between 20% and 75%, and particularly between 20% and 55%. The layer 4 shown here, in the form of the separating layer, consists of a single-layer wire mesh with a porosity of 53% and a pore channel or mesh size of 1.00 mm.

[0031] The embodiment shown in Figure 2 depicts a cross-section of a porous transport layer 5. The upper side in the plane of the image is oriented towards the membrane of an electrolyzer (not shown in detail). In this embodiment as well, the porous transport layer 5 changes its properties from layer 9, located at the bottom of the image plane, to layer 6, located at the top of the image plane. Figure 2 shows a combination of a wire mesh and a metal fiber fleece, with the porous transport layer 5 becoming progressively finer in terms of roughness, pore channels, and wire diameter. The wire diameter of the metal mesh is 0.125 mm, and the pore channels have a diameter of 250 pm. The porosity is 70%. The metal fiber fleece of layer 6 consists of scraped fibers with a fiber diameter of 15 pm. The pore channels there have a diameter of 14 pm. The porosity is 55%.

[0032] The metal fiber fleece in layer 6 is followed by the 3-dimensionally shaped middle layer 7. Reference is made to the explanations in Figure 1 regarding the middle layer 7, since layer 7 has the same function and properties and is dimensioned in the same way.

[0033] In the lower plane of the image, the separating layer functionally adjoins the cell wall. Unlike the embodiment shown in Figure 1, this separating layer is formed from two separate layers, 8 and 9. It consists of a two-layer wire mesh. The lower layer, 9, has a porosity of 53% and a pore channel of 1.0 mm. The mesh, or layer 8, located between the corrugated layer 7 and the lower layer 9, has a porosity of 63% and a pore channel of 0.3 mm.

[0034] The embodiment shown in Figure 3 illustrates another embodiment of a porous transport layer 10 with a 3-dimensionally shaped middle layer 12. Reference is made to the explanations of Figures 1 and 2. In this case, the separating layer 11 is located in the upper plane of the image, thus in the opposite direction to Figures 1 and 2, where the separating layer is located at the bottom. In this case, the separating layer is a single layer consisting of a sheet with a thickness of 0.5 mm. The porous transport layer 10 is functionally extended into a transport structure by the sheet. This sheet layer is designated by the reference numeral 11. Layers 11 to 13 are bonded together. This fixes the adjacent layers so that no relative movement can occur. At the same time, the material flow is guided through the porous 3D-structured middle layer 12.

[0035] In the lower plane of the image is the side of the transport layer 10 oriented towards the membrane (not shown in detail). It is a two-layer structure, comprising a layer 13 consisting of a wire mesh and a metal fiber fleece arranged underneath, which is not visible in this illustration.

[0036] The gradation of wire mesh and metal fiber fleece is such that progressively finer dimensions are achieved with regard to roughness, pore channels, and wire diameter. The wire thickness of layer 13 of the wire mesh is 0.125 mm, and the pore channels have a diameter of 250 µm. The porosity is 70%. The adjacent metal fiber fleece consists of scraped fibers with a fiber diameter of 15 µm, an average pore channel diameter of 14 µm, and a porosity of 55%.

[0037] Figure 4 shows, viewed from the positive side, an example of a 3D structuring in the form of a wire mesh with a hexagonal structure, a wire diameter of 0.16 mm, a 200% increase in the initial thickness, and a porosity of 85%. It can serve as a middle layer, featuring a main plane and a 3D structuring perpendicular to its main plane, so that, in conjunction with an adjacent layer, flow channels are formed.

[0038] Figures 5 to 7 show three further examples of 3D structuring in the form of a wire mesh with a spherical structure or with spherical cap-shaped protrusions, with a wire diameter of 0.16 mm, a 200% increase in the initial thickness, and a porosity of 85%. The wire mesh can serve as an intermediate layer, featuring a main plane and a 3D structure perpendicular to its main plane, so that, in conjunction with an adjacent layer, flow channels are formed.

Claims

Patent claims 1. Porous transport layer (1, 5, 10) for use in an electrolyzer, wherein the transport layer (1, 5, 10) has several interconnected layers, wherein at least one of the layers (2, 6, 13) has a porosity of less than 75% and another layer (3, 7, 8, 9, 12) has a porosity of 75% to 90%, wherein all layers (2-4, 6-9, 11-13) are made of metal and are metallurgically bonded together, wherein at least one of the layers (3, 7, 12) consists of a planar structure made of wire or of an expanded metal mesh having a main plane and a 3D structuring perpendicular to its main plane, such that flow channels are formed in conjunction with an adjacent layer (2, 4, 8, 13).

2. Porous transport layer (1 , 5, 10) according to claim 1 , characterized in that the metallic sheet structure is a woven, knitted or crocheted fabric with a wire diameter of 0.015 mm to 2 mm, in particular with a wire diameter of 0.015 mm to 1.5 mm.

3. Porous transport layer (1 , 5, 10) according to claim 1 or 2, characterized in that the expanded metal mesh is made from a sheet with a sheet thickness of 0.1 to 1 mm.

4. Porous transport layer (1 , 5, 10) according to one of claims 1 to 3, characterized in that a layer (6) consists of a metal fiber fleece, wherein the fiber thicknesses are in a range of 2 pm to 60 pm and wherein the metal fiber fleece has a thickness of 0.15 mm to 1 mm.

5. Porous transport layer (1 , 5, 10) according to one of claims 1 to 4, characterized in that the transport layer (1 , 5, 10) has 2 to 8 layers (2-4; 6-9; 12-13), with a total thickness of the porous transport layer (1 , 5, 10) of 0.5 to 12 mm.

6. Porous transport layer (1 , 5, 10) according to any one of claims 1 to 5, characterized in that it is joined with a fluid-tight outer wall.

7. Porous transport layer (1 , 5, 10) according to one of claims 1 to 6, characterized in that the materials of the individual layers have a coating.

8. Method for producing a porous transport layer (1 , 5, 10) according to one of claims 1 to 7 characterized in that the 3D structuring is produced by one or more of the following manufacturing processes: profile rolling, corrugation, folding, deep drawing, pressing.

9. Method according to claim 8, characterized in that all layers (2-4, 6-9, 11-13) are joined together by material bonding.

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