Method for producing an open-porous transport layer for use in an electrolysis cell

Abstract

Method for producing an open-porous transport layer (1) for use in an electrolysis cell comprising the following steps: a) Providing at least one wire (2) with a wire thickness in the range of 0.05 to 0.5 mm; b) Winding at least one wire (2) onto a rotating winding body (3, 3a, 3b) to form a wire structure (22) with a maximum mesh size of 2 mm; c) Sintering of the individual wires (2) of the wire structure (22) at their contact points (K) to form a one-piece wire mat (4); and d) Cutting the wire mat (4) and providing the cut wire mat (4') or wire mat pieces (4'') as a plate-shaped open-porous transport layer (1).

Description

[0001] The invention relates to a method for producing an open-porous transport layer for use in an electrolysis cell. The invention further relates to an open-porous transport layer produced according to the method.

[0002] Open-porous transport layers and methods for their production are known.

[0003] US patent 2023 047 374 A discloses a titanium felt compressed from microfibers, forming a random porous structure. This titanium felt serves as an open-porous transport layer, acting as a fluid transport pathway in an electrolyzer or fuel cell between a bipolar plate and the catalyst layer on a polymer electrolyte membrane.

[0004] WO 22 164 896 A1 describes an electrochemical cell or electrolysis cell containing a plurality of compound layers which form a porous transport layer made of an oxidation-resistant metal.

[0005] WO 20 020 467 A1 discloses a process for producing a porous transport layer for an electrochemical cell, in particular an electrolyzer. In this process, a metal powder mixed with a binder is applied to a porous metal layer in the form of a sintered metal plate, a metal fabric or a metal felt, and sintered together after debinding.

[0006] DE 10 2018 105 115 A1 describes an electrode for an electrochemical cell, in particular an electrolyzer, comprising a support element with an active layer containing at least one catalyst. The support element has a decreasing porosity and / or a decreasing pore diameter along its thickness and can be made of stainless steel, titanium, a titanium alloy, nickel, a nickel alloy, or graphite. Furthermore, the support element can be in the form of expanded metal, wire mesh, a metal mesh, a perforated sheet, a nonwoven fabric, a metal foam, or a sintered structure.

[0007] The publication “Porous Transport Layers for Polymer Electrolyte Membrane Water Electrolysis”, Michael Andreas Höh, Volume 388. Forschungszentrum Jülich GmbH, Jülich, 2017, ISBN 978-3-95806-262-7, deals with the production and investigation of differently manufactured porous transport layers.

[0008] The dissertation “Mass transport phenomena in layer systems of an electrolyzer”, Ulla Panchenko, Volume 477, Forschungszentrum Jülich, 12 July 2019, ISBN 978-3-95806-433-1, deals, among other things, with bubble formation and its propagation in the pores of a porous transport layer (PTL).

[0009] Currently available open-porous transport layers in the form of titanium fiber mats have proven to be poorly pressure-resistant, causing them to deform during use in an electrolysis cell. This locally reduces fluid permeability and thus the cell's performance.

[0010] Open-porous transport layers in the form of woven mats made of titanium wires, which are still available on the market, are limited in terms of minimum mesh sizes because the drawn titanium wire is brittle and cannot be woven tightly enough.

[0011] The object of the invention is to provide a method for producing a pressure-stable, open-porous transport layer that can be designed with particularly small openings for fluid passage. Furthermore, the object of the invention is to provide a method for producing an open-porous transport layer according to this method.

[0012] The problem is solved for the process of producing an open-porous transport layer for use in an electrolysis cell by the following steps: a) Providing at least one wire with a wire thickness in the range of 0.05 to 0.5 mm; b) Winding at least one wire onto a rotating winding body to form a wire structure with a maximum mesh size of 2 mm; c) Sintering of the individual wires of the wire structure at their contact points to form a single wire mat; and d) Cutting the wire mat and providing the cut wire mat or wire mat pieces as a plate-shaped open-porous transport layer.

[0013] By using the winding process, even brittle wire materials can be arranged at a desired distance from each other, enabling the production of open-porous transport layers with a wide range of fluid permeabilities and opening sizes. Selected winding parameters, such as wire diameter, winding spacing, and wire crossings at specific angles, etc., allow for very simple and effective control of the properties of the open-porous transport layer. Furthermore, the inventive method makes it possible to produce an open-porous transport layer whose open porosity decreases gradually or continuously across the thickness of the layer by varying the winding parameters from the core to the wire layers built upon it.

[0014] In a preferred embodiment of the method, the winding body is cylindrical, wherein the wire mat is cut once parallel to the axis of rotation of the winding body and formed into a single plate-shaped, open-porous transport layer. The wire mat, which surrounds the circumference of the winding body in a ring-like fashion, is in particular cut longitudinally and bent open so that it is plate-shaped. Subsequently, pressing or rolling, in particular calendering, can be carried out to a predetermined thickness of the open-porous transport layer, preferably simultaneously smoothing the surface of the wire mat that was facing away from the winding body.

[0015] In a further preferred embodiment of the method, the winding body is rectangular, and the wire mesh is cut at each edge of the winding body, forming several flat pieces of wire mesh, each of which constitutes an open-porous transport layer. The winding body can be rotated about a first axis of rotation, and the at least one wire can be wound onto it. Subsequently, the winding body can be rotated about at least one further axis of rotation, oriented perpendicular or tilted to the first axis of rotation, and the at least one wire can be wound further onto it. This allows for a particularly uniform winding of the rectangular winding body with the at least one wire. The flat pieces of wire mesh can be used directly or subjected to compression or rolling, in particular calendering, to achieve a predetermined thickness of the open-porous transport layer.Preferably, the surface of the wire mesh piece facing away from the winding body is smoothed simultaneously.

[0016] In principle, other shaped winding bodies can also be used. However, shapes that result in a rectangular base shape for the wire mat or wire mat pieces, once this has been leveled, have proven effective.

[0017] It has proven effective to wind at least two wires with different diameters. This allows for complex winding patterns and particularly small openings in an open-porous transport layer.

[0018] The wire used is preferably made of titanium or stainless steel, but other wire materials can also be used.

[0019] The wire mesh is preferably designed with a minimum mesh size of 0.03 mm. The open-porous transport layer therefore has openings in the range of 0.03 to 2 mm.

[0020] A single wire is preferably wound with a minimum winding distance between two adjacent wire windings, roughly equal to the wire's diameter. For example, a wire with a diameter of 0.05 mm is wound onto the winding body with a distance of at least 0.05 mm between adjacent wires. Similarly, a wire with a diameter of 2 mm is wound onto the winding body with a distance of at least 2 mm between adjacent wires.

[0021] In particular, several wires can be wound simultaneously or sequentially, interlacing each other. By varying the wire diameters, the spacing between adjacent wires, and the winding pattern, desired types of open-porous transport layers with defined open porosity or defined opening sizes can be easily created.

[0022] The sintering of the individual wires of the wire assembly in step c) of the process at their contact points to form a single wire mat can be achieved, on the one hand, by heating the wire assembly in an oven to an elevated temperature at which the wires sinter together. This can preferably be done under increased gas pressure to accelerate the sintering. Alternatively or in combination with this, the wire can be heated by passing an electric current through it, thereby sintering the wires at the contact points.

[0023] In this process, a temperature-resistant winding body, for example made of ceramic, can be used, which can withstand the sintering of the individual wires of the wire structure into a wire mat without damage and can be reused after the wire mat is removed. Alternatively, the winding body can be made of a material that cannot withstand the sintering of the individual wires of the wire structure into a wire mat without damage. In this case, the wire mat can be removed from the winding body before sintering, provided it is geometrically possible, and the winding body can then be reused. It is also possible to use a thermally decomposable winding body, such as one made of wood, cardboard, wax, or similar materials, in which case the winding body burns out during the sintering of the wires.

[0024] An open-porous transport layer formed according to the inventive method has a thickness in the range of 0.05 to 5 mm.

[0025] Depending on the thickness of the wire structure on the winding body and the selection of wire diameters, desired thicknesses of the open-porous transport layer can be achieved. The thickness can be further reduced by smoothing, especially rolling, although this slightly reduces the open porosity.

[0026] In particular, the open-porous transport layer exhibits decreasing open porosity across its thickness. This is achieved, for example, by following a winding of wire onto the winding body with a large winding spacing with a subsequent winding of wire with a smaller winding spacing, with the winding spacing decreasing with each winding layer. Changing the winding angle and / or reducing the wire diameter also contribute to this effect. Sintering the wires creates a single-piece wire mat from the wire structure, which exhibits a changing or varying open porosity across its thickness.

[0027] The use of an open-porous transport layer produced according to the inventive method in an electrolysis cell, particularly for direct connection to a membrane electrode assembly of the cell, has proven to be especially advantageous. In this case, one side of the open-porous transport layer comes into planar contact with an electrode of the membrane electrode assembly that has a lower open porosity than the opposite side of the open-porous transport layer. This is particularly relevant for an electrolysis cell used to produce hydrogen and oxygen from water.

[0028] The Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9, Fig. 10 to Fig. Figure 11 is intended to illustrate the inventive method and the resulting open-porous transport layer by way of example. For instance, it shows Fig. 1. An arrangement for carrying out steps a) and b) of the method using a cylindrical winding body, Fig. 2 a further arrangement for carrying out steps a) and b) of the method with a cylindrical winding body, Fig. 3 a further arrangement for carrying out steps a) and b) of the method with a cylindrical winding body, Fig. 4 an arrangement for carrying out steps a) and b) of the method with a rectangular winding body, Fig. 5 a further arrangement for carrying out steps a) and b) of the method with a rectangular winding body, Fig. 6 an order to carry out step c) of the procedure, Fig. 7 a further order for the implementation of step c) of the procedure, Fig. 8 an arrangement for carrying out step d) of the method on a cylindrical winding body, Fig. 9 the cut wire mat removed from the winding body Fig. 8 in the top view, Fig. 10 an arrangement for carrying out step d) of the method on a rectangular winding body, Fig. 11 the cut wire mat removed from the winding body Fig. 10 in the top view, which forms an open-porous transport layer.

[0029] Fig. Figure 1 shows an arrangement for carrying out steps a) and b) of the method using a cylindrical winding body 3. The winding body 3 rotates about its axis of rotation 5 (see arrow), while a wire 2 is wound onto the circumference of the winding body 3 with a winding spacing WA between the adjacent wires 2. The adjacent and overlapping wire sections form contact points K (compare Figure 1). Fig. 3), which can be sintered together. The wire 2 is wound up until a wire structure 22 (compare Fig. 6) is present.

[0030] Fig. Figure 2 shows a further arrangement for carrying out steps a) and b) of the method using a cylindrical winding body. Figure 3. Same reference numerals as in Fig. 1 denotes identical elements. Here, a wire 2 and a thinner wire 2' are wound simultaneously onto the winding body 3, lying side by side in a first layer on the winding body 3 (see enlarged section). In the second layer, the winding is such that the wire 2 lies over the thinner wire 2' and vice versa. The adjacent and overlapping wire sections form contact points K (compare Fig. 3), which can be sintered together. The wire 2, 2' is wound up until a wire structure 22 (compare Fig. 6) is present.

[0031] Fig. Figure 3 shows a further arrangement for carrying out steps a) and b) of the method with a cylindrical winding body 3. Same reference numerals as in Fig. 1 and Fig. 2 denote identical elements. Here, a wire 2' is wound onto the winding body 3, and a thicker wire 2 is wound onto this, with the wires 2 and 2' crossing over each other and forming additional contact points K. The wire 2 and 2' are wound until a wire structure 22 (compare Fig. 6) is present.

[0032] Fig. Figure 4 shows an arrangement for carrying out steps a) and b) of the method with a rectangular winding body 3'. The winding body 3' is square and flat. The winding body 3' is first rotated about the axis of rotation 5 and a wire 2' is wound onto it. Subsequently, the winding body 3' is rotated about the axis of rotation 5', which is perpendicular to it, and the wire 2, which is thicker than wire 2', is wound onto it. The wire 2, 2' is wound onto it until a wire structure 22 (compare Figure 4) is formed. Fig. 6) is present.

[0033] Fig. Figure 5 shows a further arrangement for carrying out steps a) and b) of the method with a rectangular coiled body 3'. Same reference numerals as in Fig. The 5 denote identical elements. The winding body 3' is square and flat. The winding body 3' is first rotated around the axis of rotation 5, and a wire 2 and then a thinner wire 2' with a smaller winding spacing WA are wound onto it. The winding body 3' is then rotated around the perpendicular axis of rotation 5'. Again, the wire 2 and then the thinner wire 2' with a smaller winding spacing WA are wound onto it. The wire 2, 2' is wound until a wire structure 22 (compare Fig. 6) is present.

[0034] Fig. Figure 6 shows an arrangement for carrying out step c) of the method, wherein the cylindrical winding body 3 is shown as an example. Fig. Figure 2 shows the following. However, any other shape of winding body can also be present, supporting a wire structure 22 formed by winding. The winding body 3, including the wire structure 22, was placed in a furnace 30 and heated to a sintering temperature for the wire 2, 2'. In particular, the pressure in the furnace chamber can be increased to accelerate the sintering process. An inert furnace atmosphere has also proven effective in preventing surface oxidation of the wires 2, 2'. During sintering, the wires 2, 2' of the wire structure 22 bond together at the contact points K to form a stable wire mat 4, see Figure 2. Fig. 8.

[0035] Fig. Figure 7 shows a further arrangement for carrying out step c) of the method, again using a cylindrical winding body 3 as an example. However, any other shape of winding body can also be used, supporting a wire structure 22 formed by winding. The wires 2 on the winding body 3 are connected to a current source 40. The current flowing through the wire 2 heats the wire 2 and ultimately leads to the sintering of the wires 2 together in the area of ​​the contact points K.

[0036] Fig. Figure 8 shows an arrangement for carrying out step d) of the method on a cylindrical winding body 3, in which the formed one-piece wire mat 4 is cut. For this purpose, a cutting device 50 is provided which cuts the wire mat 4 parallel to the axis of rotation 5 of the winding body 3 between the end faces of the winding body 3. The cut wire mat 4' is bent open and removed from the winding body 3. Fig. Figure 9 shows the cut wire mat 4' removed from the winding body 3. Fig. 8 in the top view. To create a flat, plate-shaped, open-porous transport layer 1 (compare Fig. 11) to produce from it, the separated wire mat 4 is rolled, in particular calendered.

[0037] Fig. Figure 10 shows an arrangement for carrying out step d) of the method on a rectangular winding body 3'. For this purpose, a cutting device 50 is provided which cuts the wire mat 4 on the circumference of the flat winding body 3', so that two flat wire mat pieces 4'' are present. The wire mat pieces 4'' already have a plate-like shape and can be used as an open-porous transport layer 1 without further processing.

[0038] Fig. 11 shows one of the wire mesh pieces 4'' made of Fig. 10 in the top view, which forms an open-porous transport layer 1. To improve the flatness and surface quality of the open-porous transport layer 1, this will also be smoothed subsequently.

[0039] If a rectangular winding body is used that is not flat but cuboid or cube-shaped, the cutting device can sever the edges of the wire mat at one top and one bottom edge of the cuboid or cube and then cut the remaining wire mat section surrounding the cuboid or cube along one edge. This results in at least two equally sized, plate-shaped pieces of wire mat and at least one additional piece of wire mat, which can either be further divided into plate-shaped pieces or flattened entirely without further cutting. Reference symbol list 1 open-porous transport layer 2.2' wire 3, 3' winding body 4 wire mat 4' cut wire mat 4'' wire mesh piece 5.5' axis of rotation 22 wire structures 30 oven 40 Power source 50 cutting device K Contact point WA winding distance

Claims

[1] Method for producing an open-porous transport layer (1) for use in an electrolysis cell comprising the following steps: a) Providing at least one wire (2) with a wire thickness in the range of 0.05 to 0.5 mm; b) Winding at least one wire (2) onto a rotating winding body (3, 3a, 3b) to form a wire structure (22) with a maximum mesh size of 2 mm; c) Sintering of the individual wires (2) of the wire structure (22) at their contact points (K) to form a one-piece wire mat (4); and d) Cutting the wire mat (4) and providing the cut wire mat (4') or wire mat pieces (4'') as a plate-shaped open-porous transport layer (1). [2] Method according to claim 1, wherein the winding body (3a) is cylindrical, wherein the wire mat (4) is cut once parallel to the axis of rotation (5) of the winding body (3a) and is formed into a single plate-shaped open-porous transport layer (1). [3] Method according to claim 1, wherein the winding body (3b) is rectangular and the wire mat (4) is cut at each edge of the winding body (3b), forming several flat wire mat pieces (4'') which each form an open-porous transport layer (1). [4] Method according to any one of claims 1 to 3, wherein the plate-shaped open-porous transport layer (1) is calendered. [5] Method according to any one of claims 1 to 4, wherein at least two wires (2, 2') with different wire diameters are wound up. [6] Method according to any one of claims 1 to 5, wherein wire (2, 2') of titanium or stainless steel is wound. [7] Method according to any one of claims 1 to 6, wherein the wire mat (4) is formed with a minimum mesh size of 0.03 mm. [8] Method according to any one of claims 1 to 7, wherein a single wire (2) is wound with a minimum winding distance (WA) between two adjacent wire windings in the region of the wire diameter of the wire (2). [9] Method according to any one of claims 1 to 8, wherein several wires (2) are wound simultaneously or successively, which are wound in a crisscrossing manner. [10] Open-porous transport layer (1) formed according to a method according to any one of claims 1 to 9 and having a thickness in the range of 0.05 to 5 mm.

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