Method for producing a porous structure, and laser device

Abstract

The invention relates to a method for producing a porous structure (10), in particular for use in a plant for an electrochemical process, in which method a surface (12) of the porous structure (10), which is intended to be in direct contact with a boundary layer in the plant, is irradiated with a laser beam (16) in order to modify the topography of the surface (12).

Description

[0001] METHOD FOR PRODUCING A POROUS STRUCTURE AS WELL AS

[0002] LASER DEVICE

[0003] The invention relates to a method for producing a porous structure, in particular for use in a system for an electrochemical process, and to a laser device for producing a structure, in particular for use in a system for an electrochemical process.

[0004] From EP 4265358 A1 a method for producing a porous structure for transporting a fluid is known, which is in particular intended to form a heat exchanger and / or in contact with which a chemical reaction of the transported fluid can take place.

[0005] The object of the present invention is to create a porous structure which can be contacted with a boundary layer particularly easily over a large area.

[0006] The object of the invention is achieved according to the invention by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the dependent claims, the description, and the drawings. Features, advantages, and possible embodiments set forth in the description for one of the subject matter of the independent claims are to be regarded, at least analogously, as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as of any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the dependent claims.

[0007] The invention relates to a method for producing a porous structure, particularly for use in an electrochemical process. The method may include providing an already porous structure that is further processed by the method. Within the framework of the method, it is provided that a surface of the porous structure, which is intended to be positioned directly adjacent to an interface in the system, is irradiated with a laser beam to modify the surface topography. Thus, within the framework of the method, the laser beam is directed onto the surface of the structure, whereby the surface topography is modified by melting and / or vaporizing material of the structure at the surface by means of the laser beam.The laser beam allows for highly precise modification of the surface topography, ensuring that specifications for contact between the surface and the interface are met with exceptional reliability. For example, it can be specified that the surface of the electrochemical process system must have a particularly large contact area with the interface to achieve a maximum contact area between the structure and the interface. Alternatively or additionally, it can be specified that the surface must seal particularly tightly against the interface to minimize the risk of leakage of a fluid flowing through the porous structure and the interface. The interface defines a region within the electrochemical process system.The process involves modifying the surface under a protective gas atmosphere, particularly nitrogen or argon, using a laser beam. Modifying the surface topography involves melting and / or ablating at least some areas of the structure. The structure can be placed in a flatbed laser system, which then provides the laser beam to modify the surface topography. Alternatively, the surface topography can be modified only in a peripheral area by laser beam irradiation. This means that a central area of ​​the surface can remain unaffected by the laser beam, or that the topography cannot be modified in this central area.This allows the surface to be modified to resemble a tile.

[0008] This process can be used for machining large-area structures. In particular, it is not a process for micromachining or micromaterial processing.

[0009] This process enables particularly good contact properties between the surface of the structure and the interface to which the surface of the structure is to be applied. By modifying the topography of the porous structure's surface, the contact area between the surface and the interface in the electrochemical process can be increased.

[0010] Modifying the surface topography with a laser beam allows for the simultaneous removal of contaminants and / or oxides from the porous structure. This process thus enables highly efficient cleaning of the porous structure's surface, removing contaminants and / or oxides while simultaneously modifying its topography.

[0011] In a possible further development of the invention, a porous transport layer is provided as the porous structure, and / or the system for the electrochemical process is a hydrogen electrolyzer, an electrodialyzer, a capacitive deionizer, an electroosmosis system, or a redox flow battery. The porous transport layer is intended to transport a substance or a mixture of substances, particularly towards the interface. Specifically, the porous transport layer is provided to comprise titanium. It is particularly possible that the porous transport layer is made of titanium or a titanium alloy. For example, the porous transport layer can serve to distribute reaction gases uniformly across the interface. Alternatively or additionally, the porous transport layer can serve to transport a reactant away from the interface.If the porous transport layer is produced as part of the process, then it can be achieved that the porous transport layer can be applied to the boundary layer of the system for the electrochemical process over a particularly large area.

[0012] An electrolyzer is a device that uses electric current to induce a chemical reaction, i.e., a chemical transformation. The electrolyzer is designed to carry out electrolysis. A hydrogen electrolyzer is designed to split water into hydrogen and oxygen. For example, a hydrogen electrolyzer might use a proton exchange membrane. An electrodialyzer is designed to implement an electrochemically driven membrane process by using ion exchange membranes in combination with an electrical potential difference to separate ionic species from uncharged solvents or impurities. A capacitive deionizer is designed to remove ions from an aqueous solution. Similarly, an electrodialyzer is designed to remove ions from an aqueous solution.The electroosmosis system is designed to perform electroosmosis. In electroosmosis, an electric field parallel to a surface is applied, causing an interfacial phenomenon between the capillary wall and an electrolyte solution. Thus, electroosmosis results in the movement of a liquid parallel to a surface by applying an electric field. The electroosmosis system can be used, for example, for electrophoresis. The redox flow battery—more commonly called a liquid battery or wet cell—is a type of accumulator. It stores electrical energy in chemical compounds, with the reactants being dissolved in a solvent. Two energy-storing electrolytes circulate in two separate circuits, between which ion exchange takes place in a galvanic cell via a membrane.In the galvanic cell, the dissolved substances are chemically reduced or oxidized, releasing electrical energy. The use of the porous structure in the hydrogen electrolyzer, electrodialyzer, capacitive deionizer, electroosmosis system, or redox flow battery enables a particularly uniform distribution of reactant or reactant, allowing the respective process to be carried out with high efficiency and reproducibility.

[0013] In a further possible embodiment of the invention, the interface layer is provided by a membrane, a catalyst, or a combination of a membrane and a catalyst. For example, the interface layer can be a membrane coated with a catalyst. For instance, the interface layer can be a proton exchange membrane coated on one side with a cathode catalyst layer and on the other side with an anode catalyst layer. Particularly if the system for the electrochemical process is a hydrogen electrolyzer, this system can be designed to be particularly compact and operated with high efficiency if the interface layer is provided by the combination of the membrane and the catalyst. The interface layer can also be provided by an ionomer.An ionomer is a thin thermoplastic membrane used as the electrolyte in electrolysis. The membrane can thus be a solid electrolyte for the electrochemical process. The ionomer can also be part of a catalyst layer. This process allows the porous structure to be positioned over a particularly large area and / or very close to the interface layer—whether it be a membrane, a catalyst, or a combination of both—by modifying the surface topography. This enables particularly efficient mass transfer from the porous structure to the interface layer.

[0014] In another possible embodiment of the invention, the topography is modified by reducing surface roughness through smoothing. The surface is thus irradiated with a laser beam for smoothing, thereby reducing its roughness. Roughness is the degree of unevenness of a solid surface below the scale of its shape or waviness, but above the irregularity of crystal lattice structures. Roughness is a term from surface physics that describes the unevenness of the surface height. By reducing the roughness, it is possible to ensure that the porous structure, with its surface area, can be placed against the interface over a particularly large area. This allows for a particularly large contact area between the porous structure and the interface.

[0015] In a further possible embodiment of the invention, it is provided that a laser beam is simultaneously directed at the surface of the porous structure, which is intended to be positioned directly adjacent to the interface in the system, and another laser beam is directed at a further surface of the structure opposite the surface. The heat input into the porous structure by the respective laser beams can thus be deterministic and occur on both sides. This allows the topography of the surface and the further surface of the porous structure, which are arranged on opposite sides of the porous structure or which enclose the structure on opposite sides, to be modified particularly quickly, in particular smoothed. This enables the porous structure with its further surface to be applied to another component over a particularly large area.

[0016] In a further possible embodiment of the invention, the surface of a layer-by-layer additively manufactured porous structure is smoothed. In particular, the structure can be produced using selective laser melting (SLM), also known as selective laser melting, or laser metal deposition (LMD). Selective laser melting is a powder bed fusion process, abbreviated as PBF. Laser metal deposition involves material deposition with directed energy input. In the additively manufactured structure, the porosity is precisely controlled. Furthermore, due to the additive manufacturing process, the structure has a particularly precise geometry.As a result of the additive manufacturing of the structure, large surface roughness can occur, which can be smoothed by irradiation with the laser beam as part of the process.

[0017] In this context, a possible further development of the process envisages the layer-by-layer construction of the porous structure from a powder using at least one laser beam in a powder bed-based process. The structure is thus produced within the process by powder bed-based selective laser melting, in particular by melting a metallic material. In this embodiment of the process, the additive manufacturing of the porous structure is therefore an integral part of the process.It is provided that for additive manufacturing using at least one laser beam, an energy input of five to 20 joules per cubic millimeter, in particular an energy input of five to ten joules per cubic millimeter, is introduced during the layer-by-layer construction of the structure, and / or a distance between immediately adjacent melting paths within a layer of the structure is chosen to be greater than twice the diameter of the at least one laser beam for the additive manufacturing of the structure, wherein in particular the distance is at least 0.16 millimeters, in particular 0.2 millimeters to 0.5 millimeters, and / or a layer thickness of the respective applied layer of powder is chosen to be greater than a mean particle diameter, in particular greater than a maximum particle diameter.

[0018] In selective laser melting, a material to be processed is applied in powder form in a thin layer onto a base plate. The powdered material is locally and completely melted by the laser beam and, after solidification, forms a solid layer. The base plate is then lowered by the thickness of one layer, and more powder is applied. This cycle is repeated until all layers of the structure to be produced have been melted. Finally, the finished porous structure is cleaned of excess powder. Subsequently, the surface of the porous structure intended for bonding to the interface is modified in its topography by irradiation with the laser beam.The described manufacturing parameters for additive manufacturing ensure that the porous structure holds together securely, allowing it to be manufactured in one piece, and that the porosity of the structure can be adjusted with exceptional precision. Furthermore, it can be guaranteed that the structure can be completely permeated by a fluid from the outer surface to the surface intended for contact with the interface.

[0019] In this context, it is particularly intended that, during additive manufacturing, melt tracks are drawn parallel to each other in each layer of the structure, with the orientations of the melt tracks differing between layers. The structure is thus produced layer by layer by creating at least one melt track, and in particular several melt tracks, for building up each layer of the structure. The respective melt tracks are formed by melting and cooling the material used to produce the porous structure. The respective melt tracks can be straight, corrugated, or have any other shape, and it is intended that at least two, and in particular all, melt tracks of a common layer are aligned parallel to each other or run parallel to each other.Melt tracks in different layers of the structure can be oriented obliquely relative to each other with their respective longitudinal orientations, thus differing in their orientation. In particular, it is intended that the longitudinal orientation of melt tracks of immediately adjacent layers is rotated relative to each other by an angle of 30 degrees, 45 degrees, 60 degrees, or 90 degrees about the stacking direction in which the layers are stacked. It is known to adjust the porosity of additively manufactured structures by selecting a prime number, such as 67 degrees, for a rotation angle of as irregular an angle as possible in the longitudinal orientation of melt tracks of immediately adjacent layers, so that the longitudinal orientation of the respective melt tracks is not exactly the same across a particularly large number of layers.Furthermore, a small prime number is not chosen, as otherwise the longitudinal direction of the melt tracks in immediately adjacent layers would not differ sufficiently to create an irregular porosity in the structure. Regular repetition of the same longitudinal direction of the respective melt tracks in each layer of the structure allows a fluid to flow through the structure with particularly low resistance. Rotation angles of 30 degrees, 45 degrees, 60 degrees, and 90 degrees for the longitudinal direction of the melt tracks in immediately adjacent layers enable the creation of a structure with particularly high porosity and simultaneously very high regularity, thereby achieving exceptionally low resistance for a fluid flowing through the structure.

[0020] In a further possible embodiment of the invention, a change in porosity within the structure is generated by changing at least one of the parameters track spacing, laser power, and scan speed within a layer and / or between at least two layers. For example, this porosity change can create at least one stripe in the structure, which may extend within a single layer or through several layers, and which has a higher density compared to the surrounding material of the structure. This stripe can thus be a reinforcing stripe. By providing at least one reinforcing stripe, the structure can be made with particularly high strength.Due to its porosity, the structure exhibits reduced stability. By adjusting the aforementioned parameters during the additive manufacturing process, the porosity can be modified in specific areas of the structure. This can be used both to stabilize the structure and to influence gas drainage and / or liquid flow within the structure when used as intended in the electrochemical plant. Furthermore, a higher density of the structure can facilitate current flow due to lower electrical resistance.

[0021] In this context, a potential further development process could include the additive manufacturing of the structure, at least in one area, with gradually changing porosity. This means that the porosity changes continuously within at least one region of the structure. The change in porosity within the structure can occur in all directions, allowing for the creation of individual reinforcing struts, reinforcements only in a peripheral area of ​​the structure, or reinforcements only with parallel longitudinal directions. By providing for gradually changing porosity in at least one region, a particularly high level of structural stability can be achieved, as large jumps in porosity within this region, and consequently the formation of potential weak points in the structure, can be effectively avoided.Alternatively, the porosity adjustment can be carried out gradually and thus in stages.

[0022] In a further possible embodiment of the invention, the structure is additively built up layer by layer on a bipolar plate. The bipolar plate is, in particular, an electrode of the system for the electrochemical process. Specifically, the bipolar plate is made of a metallic material and / or a carbon-based material. It is possible that the bipolar plate is coated with a catalyst. The bipolar plate can include a gas channel system by means of which, in intended use, a gas or a gas mixture or water can be guided to or from the structure. In particular, it is provided that the structure, with its wider surface opposite the surface intended for contact with the interface layer, rests against the bipolar plate.To achieve a particularly large contact area between the structure's surface and the bipolar plate, the process involves additively building the structure directly onto the bipolar plate, layer by layer. The structure can be additively built onto a flow profile of the bipolar plate, also known as a flow field, and / or the built-up structure can provide or support the functionality of a flow field. The bipolar plate thus serves as a preform for the additive manufacturing of the structure. Specifically, the bipolar plate is designed to be made of titanium. The advantage of additively building the structure directly onto the bipolar plate is that the porous structure is directly bonded to the bipolar plate. Furthermore, the structure does not require the addition of support elements that would need to be removed after additive manufacturing.The structure can therefore be produced additively particularly quickly and connected to the bipolar plate.

[0023] In this context, a further development of the invention may provide that the structure is additively built up directly onto the bipolar plate in the same powder bed in which at least part of the bipolar plate has already been built up layer by layer. For example, at least the flow profile or the gas channel system of the bipolar plate may have been built up layer by layer in the powder bed, with the structure being additively built up directly onto the gas channel system of the bipolar plate. This allows the porosity of the structure to be particularly well adapted to the gas channel system of the bipolar plate. For example, the gas channel system is provided in the system for the electrochemical process for water distribution when the bipolar plate is used as intended. This enables a direct connection of the structure to at least part of the bipolar plate.In particular, the structure is formed integrally with at least part of the bipolar plate. A conventionally manufactured cathode can serve as a preform, onto which the gas channel system, especially for water / gas flow, can then be additively built up layer by layer during intended use. This additive build-up enables flow-optimized channels within the gas channel system and allows for a smooth transition from these channels to the porous structure. This results in particularly good gas exchange and / or gas discharge between the structure and the bipolar plate when the electrochemical process is used as intended. The flow-optimized channels can be designed to gradually increase in size and be built up layer by layer.

[0024] In a further possible embodiment of the invention, it is provided that the laser beam wavelength for smoothing is selected in the range of 0.5 to two micrometers, particularly in the range of one to 1.1 micrometers, and / or the laser beam is pulsed with a pulse duration of one picosecond to one microsecond, particularly with a pulse duration of one to 300 nanoseconds, and / or the laser beam is pulsed with a pulse duration of less than 100 picoseconds, wherein pulse trains of two to 16 pulses are provided, with the time interval between two successive pulse trains being ten to 100 nanoseconds. This ensures that the laser beam introduces only a particularly low amount of heat into the structure, resulting in a particularly low interaction with the structure.Furthermore, the particularly low heat input into the structure effectively limits, and in particular prevents, distortion. Alternatively, a continuously operated laser, a so-called CW laser, can be used, where the heat input is appropriately adjusted via the power and beam geometry in conjunction with the relative motion between the beam and the structure. The power can be controlled via the scanning speed. As an alternative to the additive manufacturing of the porous structure, the porous structure can comprise a nonwoven fabric, for example, a nonwoven fabric made of a titanium-containing material. In particular, the porous structure consists of the nonwoven fabric.

[0025] In a further possible embodiment of the invention, it is provided that surface contaminants, in particular at least one oxide layer on the surface, and / or particles are removed from the surface by means of a further laser process. This further laser process is a process downstream of modifying the surface topography. Thus, the surface of the structure, whose topology has been modified, can be cleaned by means of this further laser process. By removing the oxide layer, the chemical reactivity of the surface can be improved. This further laser process is therefore a downstream laser-based cleaning process. Within the framework of this further laser process, at least one short-pulsed and / or ultrashort-pulsed laser beam can be directed onto the surface of the structure.The duration of the respective laser pulses is specifically shorter than 20 picoseconds and / or the fluence of the respective laser pulses is less than five joules per square centimeter. In this further laser process, the surface can, for example, be irradiated with the laser beam under a noble gas atmosphere.

[0026] In a further possible embodiment of the invention, it is provided that a laser spot is generated on the surface by means of the laser beam, which has a diameter in the range of 5 to 20 pm. The laser beam can have a diffraction coefficient in the range of 1 to 10, in particular in the range of 1 to 5, and especially in the range of 1 to 1.5.

[0027] In another possible embodiment of the invention, it is provided that a quotient of fluence and scan speed of the laser beam in a range of 0.05 to 50 J / cm² is used. 2per m / s, especially in a range of 0.05 to 15 J / cm 2 per m / s, especially in a range of 0.1 to 5 J / cm² 2 per m / s.

[0028] The invention further relates to a laser device for producing a structure, particularly for use in an electrochemical process system. Specifically, the structure is a porous transport layer, particularly for hydrogen electrolysis, electrodialysis, a capacitive ionizer, an electroosmosis system, or a redox flow battery. The laser device is configured to build the porous structure layer by layer using additive manufacturing and to irradiate at least one surface of the porous structure, which is intended to be positioned directly adjacent to an interface in the electrochemical process system, with a laser beam to modify the surface topography.In particular, the laser device is configured to produce the structure using a method as already described in connection with the method according to the invention. The laser device can, in particular, be a flatbed laser system. The laser device is thus configured to both additively produce the structure layer by layer and to smooth the surface of the structure.

[0029] Further features of the invention may become apparent from the following description of the figures and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures themselves, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0030] The drawing shows in:

[0031] Fig. 1 shows a schematic side view of a porous structure which is processed on at least one surface using a laser beam;

[0032] Fig. 2 shows a schematic side view of the porous structure in a first embodiment;

[0033] Fig. 3 shows a schematic side view of the porous structure in a second embodiment; and

[0034] Fig. 4 shows a schematic sectional view of a bipolar plate on which the porous structure is arranged.

[0035] Identical or functionally equivalent elements are designated with the same reference numerals in the figures. Figure 1 shows a porous structure 10. This porous structure 10 is, in this case, a porous transport layer for an electrochemical process system, in particular for a hydrogen electrolyzer. Alternatively, the structure 10 could be a porous transport layer for an electrodialyzer, a capacitive deionizer, an electroosmosis system, or a redox flow battery. The porous structure 10 has a first surface 12 on one side and a second surface 14 on the opposite side. The first surface 12 is designed to be oriented against an interface layer of the electrochemical process system when used as intended.This interface layer is, in particular, a membrane, a catalyst, or a combination of a membrane and a catalyst. Specifically, the interface layer is intended to be an ionomer, and thus a thin thermoplastic membrane as the electrolyte. To produce the porous structure 10, the first surface 12 is irradiated with a laser beam 16, thereby modifying the topography of the first surface 12. In this case, the topography is modified by smoothing to reduce the roughness of the first surface 12. For particularly fast processing of the porous structure 10, the first surface 12 and the second surface 14 can be irradiated simultaneously with separate laser beams.This allows the topography of the first surface 12 and the topography of the second surface 14 to be modified simultaneously.

[0036] In particular, it is intended that the porous structure 10 is built up layer by layer in an additive manufacturing process. Specifically, it may be intended that the structure 10 is additively manufactured from a titanium-containing material. This allows the structure 10 to exhibit particularly high permeability and particularly low flow resistance for a fluid flowing through it. The functionality of the structure 10 can be influenced by adjusting the respective parameters during its additive manufacturing.

[0037] It can be envisaged that the porous structure 10 is built up layer by layer from a powder, in particular a titanium-containing powder, using at least one laser beam in a powder bed-based process. It is possible that the same laser device is used both to additively build up the structure 10 and to smooth the topography of the first surface 12.

[0038] In the powder bed-based process, an energy input of five to 20 joules per cubic millimeter, in particular five to ten joules per cubic millimeter, can be introduced into the powder by means of at least one laser beam. Furthermore, it is possible to choose a distance between immediately adjacent melt tracks within a layer of structure 10 that is greater than twice the diameter of the at least one laser beam. In particular, the distance is at least 0.16 millimeters, and more specifically 0.2 to 0.5 millimeters. Additionally, the layer thickness of the respective applied layer of powder can be chosen to be greater than a mean particle diameter, and in particular greater than a maximum particle diameter. The layer thickness is thus adapted to the particle diameter of the powder used. The particle size of the powder determines the possible porosity and topography of the surfaces of structure 10.It may be intended that the layer thickness is greater than 60 micrometers, in particular greater than 120 micrometers, for coarse powder.

[0039] Furthermore, it can be provided that, during additive manufacturing, melt tracks in each layer of structure 10 are drawn parallel to each other, with the orientations of the melt tracks differing between layers. In particular, it is provided that the longitudinal direction of melt tracks of immediately adjacent layers is rotated relative to each other by an angle of 30 degrees, 45 degrees, 60 degrees, or 90 degrees about a stacking direction in which the layers are stacked.

[0040] By regularly repeating the respective exposure directions and thus the longitudinal direction of the melt tracks of layers in structure 10 through rotation angles of 30, 45, 60, or 90 degrees, a particularly low flow resistance can be achieved when a fluid flows through structure 10. Adjusting the aforementioned characteristics for the additive manufacturing of structure 10—namely, the energy input, the spacing of immediately adjacent melt tracks, the layer thickness, and the rotation angle of the longitudinal direction of melt tracks of immediately adjacent layers—enables continuous channels in structure 10 for effective depowder removal and, when used as intended in the electrochemical process system, for good fluid permeability, particularly good mass permeability.Due to continuous melt paths in the respective layers, the 3D-printed structure 10 has a particularly low flow resistance while simultaneously exhibiting particularly high water permeability due to its high porosity.

[0041] Irregular powder particles, in particular, can lead to a rough surface of structure 10. Therefore, post-treatment of at least the first surface 12 of structure 10 is necessary to prevent structure 10 from puncturing a membrane of the electrochemical process system. This post-treatment of at least the first surface 12 involves smoothing by melting and / or ablating the surface using a laser beam. This laser beam is provided, in particular, by a high-power laser.

[0042] As shown in Figures 2 and 3, the structure 10 can be produced with regions of different porosities. In Figures 2 and 3, the structure 10 is shown with a view of the first surface 12. In Figure 2, the structure 10 has five regions of different porosities. In a first region 18, the structure 10 has a porosity of ten percent. In a second region 20, the structure 10 has a porosity of 20 percent. In a third region 22, the structure 10 has a porosity of 30 percent. In a fourth region 24, the structure 10 has a porosity of 40 percent. In a fifth region 26, the structure 10 has a porosity of 50 percent. In the embodiment of structure 10 shown in Fig. 3, the structure 10 has only four regions with different porosities, namely the first region 18, the second region 20, the third region 22, and the fourth region 24. In the embodiment shown in Fig.In the embodiment shown in Fig. 2, the structure 10 has a porosity of 50 percent in a central region and areas of reduced porosity in opposing edge regions. The areas 18 to 24 of reduced porosity stabilize the structure 10 in the opposing edge regions, with the porosity decreasing with decreasing distance to the respective edges of the structure 10 that bound each edge region on at least one side. In the embodiment shown in Fig. 3, the areas 18 to 22 extend in a frame-like manner around the fourth area 24. The structure 10 is thus stabilized in a frame-like manner by the areas of reduced porosity. Here, the porosity decreases with decreasing distance to the respective edges of the structure 10 that bound each edge region.The change in porosity within structure 10 can be generated by changes in the track spacing and / or the laser power and / or the scanning speed within a layer and / or between at least two layers. It is possible that structure 10 is additively manufactured at least in one region with gradually changing porosity.

[0043] Figure 4 illustrates how the structure 10 is additively built up layer by layer on a bipolar plate 27. The structure 10 can thus be directly additively built up layer by layer on the bipolar plate 27, in particular at least on a portion of the bipolar plate 27, specifically on a gas channel system 28 of the bipolar plate 27. In particular, it is possible for the structure 10 to be additively built up layer by layer directly onto the bipolar plate 27 in the same powder bed in which at least a portion of the bipolar plate 27 has already been built up layer by layer. In the present case, it is possible for the gas channel system 28 to be additively built up layer by layer onto a cathode 30 of the bipolar plate 27, and for the structure 10 to be built up layer by layer onto the gas channel system 28. Here, the gas channel system 28 and the structure 10 can be built up in the same powder bed.Thus, the structure 10 can be directly printed onto the bipolar plate 27, which in particular comprises titanium, as a preform. A portion of the bipolar plate 27, especially a water distribution layer, can also be printed, thereby achieving a direct bond between the structure 10 and the water distribution layer.

[0044] As a further process step after the printing of structure 10, the laser beam 16 is used to optimize at least the first surface 12. The first surface 12 is melted and / or ablated over a large area, resulting in stronger particle bonding and a smoother surface. This smoothed first surface 12 allows for a particularly good bond with surrounding components, in this case the interface, and prevents damage to the membrane. Damage to the membrane could lead to a short circuit in one of the electrolyzer cells.

[0045] A wavelength of the laser beam 16 in the range of 0.5 to two micrometers, especially in the range of one to

[0046] 1.1 micrometers, are selected and / or the laser beam 16 is pulsed with a pulse duration of one picosecond to one microsecond, in particular with a pulse duration of ten nanoseconds to 500 nanoseconds, and / or the laser beam 16 is pulsed with a pulse duration of less than 100 picoseconds, wherein pulse trains of two to 16 pulses are provided and a time interval between two successive pulse trains is ten to 100 nanoseconds.

[0047] It is possible to remove surface contaminants, particularly at least one oxide layer, and / or particles from the first surface 12 by means of a further laser process that differs from the modification of the first surface 12's topology. Additionally, surface properties of the first surface 12, such as laser-induced periodic surface structures, can be adjusted, or a change in the surface chemistry of the first surface 12 can be induced by modifying a process gas atmosphere. In particular, a continuous-wave laser (CW laser) can be used for the further laser process. Here, the heat input can be appropriately adjusted via the power and beam geometry in conjunction with the relative motion between the laser beam and the structure 10. The power can be controlled via the scanning speed.

[0048] Contaminants on the first surface 12, in particular oxide layers, which could increase the electrical resistance of a contact and thereby reduce the efficiency of electrolysis, can be removed when modifying the topography of the first surface 12 using the laser beam. This allows contact between the structure 10, in particular the porous transport layer, and the interface, such as the ionomer or the catalyst, to be made with particularly low electrical resistance. In a suitable process environment—in particular by selecting a gas or liquid in which the laser processing of the surface is carried out—the modification of the topography can be combined or supplemented with a change in the surface chemistry by locally heating the workpiece.This allows the removal of gaseous reactants as well as the introduction of liquids via the porous structure to be improved not only by the porosity and a micro- and nanoscale topography of the porous surface, but also by the surface chemistry, for example by generating locally hydrophilic and / or hydrophobic areas.

[0049] The strength or type of topographic modification can be specifically adjusted. It is possible to process both sides of the structure 10, whereby the first surface 12 and the second surface 14 are optimized according to their respective individual requirements by irradiation with at least one laser beam each. In this case, it is intended that, when used as intended in the electrochemical process system, the second surface 14 will be positioned against the bipolar plate 27, in particular against the gas channel system 28 of the bipolar plate 27. On the second surface 14, which, when used as intended in the system, faces the gas channel system 28, a particularly efficient water flow can be achieved with a very coarse structuring of the structure 10.By at least slightly melting the first surface 12, particularly good electrical contact between the first surface 12 and the interface can be achieved. This modification allows for targeted adjustment of the flatness of the respective surfaces 12 and 14. Water permeability can be maintained through the targeted input of thermal energy. The laser beam 16 enables energy to be introduced deterministically into the structure 10. Processing both sides of the structure 10, and thus simultaneously processing the first surface 12 and the second surface 14, allows for a particularly homogeneous heat input into the structure 10 from opposite sides, thereby minimizing distortion of the structure 10 due to heat absorbed in the material.By increasing the melting of the structure 10 at the second surface 14, channel-shaped structures can be introduced into the structure 10, by means of which water can be directed into the structure 10.

[0050] If structure 10 is manufactured using a process such as laser cladding or selective laser melting in the laser device, then the modification of the topography of at least the first surface 12 of structure 10 can be performed directly after the structure 10 is built using the laser device. Thus, a protective gas atmosphere from the additive manufacturing process of structure 10 can be used for the thermal surface treatment during the modification of the topography of at least the first surface 12. Using coarse powder allows for increased productivity in the build rate while simultaneously reducing material costs. Furthermore, it is possible to manufacture structure 10 in a particularly small number of process steps. Both laser metal fusion and laser metal deposition are 3D printing processes.Laser Metal Fusion (LMF) is also known as Selective Laser Melting, and Laser Metal Deposition (LMD) is also known as laser cladding. Porous transport layers are part of a hydrogen electrolysis cell and are typically sintered from titanium. Requirements for a porous transport layer include the highest possible permeability to water and gases, combined with low electrical resistance. Particularly when sintering a porous transport layer from titanium fibers, these layers can have a rough and highly fractured surface. This makes them only conditionally suitable for contacting other layers, such as catalysts or contact layers. The information in connection with the figures...The described method enables improved contact between the structure 10, used as a porous transport layer, and the interface by means of laser treatment of the first surface 12, which smooths existing surface structures of the structure 10, thereby achieving particularly good performance of the hydrogen electrolysis cell.

[0051] The described invention is based on the understanding that hydrogen is considered an ideal energy carrier for storing renewable energies. Water electrolysis based on proton exchange membranes (PEM) enables the production of hydrogen with high product purity, high load flexibility, high efficiency, and relatively low operating costs. This type of water electrolysis is therefore considered very promising, especially in connection with the use of renewable energies.

[0052] Although the majority of hydrogen produced today is obtained through steam reforming, a significant increase in hydrogen production via electrolysis using renewable energy is anticipated. Numerous development projects and activities are focused on reducing production costs. A fundamental understanding of the performance losses and aging processes occurring in the cell components—catalyst, membrane, and porous transfer layer (PTL)—is crucial for further improving this technology while simultaneously reducing costs.

[0053] Porous transport layers are the liquid / gas diffusion layers, which are critical components in water electrolyzers. In the cell structure, these components are located between the catalyst layer and the respective flow field. The diffusion layers must meet a wide range of requirements – good electrical contact and conductivity, high porosity for the necessary mass transport of water and gas, mechanical stability, and corrosion resistance at high temperatures (80°C) and low pH values.

[0054] Additive manufacturing enables the production of porous components. In this process, a laser is used to partially fuse the material. Various additive manufacturing methods can produce such structures. These methods include powder bed fusion (LMF) and laser deposition (LMD). Additive manufacturing using LMF or SML is a powder bed-based process. Metal powder is applied layer by layer and melted by a laser. The laser melts the metal powder, potentially generating local temperatures exceeding 2000°C. Due to the high speed at which the laser scans the surface (1-2 m / s), the molten material cools very rapidly, resulting in a fine microstructure. The process takes place in a sealed chamber under a protective gas atmosphere to prevent oxidation during melting.

[0055] To create structure 10, titanium grade 1 metal powder can be applied layer by layer using argon as a protective gas and fused with a laser. The resulting porosity depends on: the type of powder used, the energy input, the track spacing of the laser paths, the layer thickness of the powder application, and the rotation angle of the exposure direction after each layer. For a PTL (percutaneous transluminal laser), the goal is to achieve the most open porosity possible with high electrical conductivity and / or low electrical resistance.

[0056] With a volume energy input of 5 to 20 J / mm² 3 , especially from 5 to 10 J / mm 3An open porosity can be achieved (transparent at a component thickness of 1 mm, porosity >30%). The track spacing of the individual laser paths is at least twice the laser beam diameter to create gaps / pores between the individual melted paths. With a typical laser beam diameter of 80 pm, a track spacing of at least 0.16 pm is selected. Open porosity can be achieved with track spacings between 0.2 and 0.5 mm. In particular, it is intended that both requirements – and thus energy and track spacing – are met simultaneously.

[0057] If the layer thickness is chosen to be at least as large as the maximum particle diameter, then a consistently open porosity can be achieved (e.g., with a maximum particle diameter of 45 pm, a layer thickness of 60 pm to 80 pm is chosen). This reliably ensures that all non-adherent particles are removed, which is important for the subsequent use of structure 10. The high layer thickness creates channels between the individual layers of structure 10, thus ensuring good water flow through structure 10 when used as intended.

[0058] LMF standard powders are spherical and have a diameter distribution of 15–45 µm or 15–62 µm. In this case, a layer thickness of 80 µm is sufficient for open porosity. Alternatively, coarser spherical powders with a diameter distribution of 45–106 µm can be used. In this case, a layer thickness of at least 120 µm is required. Higher layer thicknesses, such as 160 µm, also allow for good powder removal after printing. Alternatively, non-spherical, i.e., irregular, particles can be used. Even then, a porous structure is possible with a suitable layer thickness.

[0059] REFERENCE MARK LIST

[0060] 10 Structure

[0061] 12 first surface 14 second surface

[0062] 16 Laser beam

[0063] 18 first area

[0064] 20 second area

[0065] 22 third area 24 fourth area

[0066] 26 fifth area

[0067] 27 Bipolar plate

[0068] 28 Gas duct system

[0069] 30 Cathode

Claims

PATENT CLAIMS 1. Method for producing a porous structure (10), in particular for use in an apparatus for an electrochemical process in which a surface (12) of the porous structure (10), which is intended to be located directly adjacent to an interface in the apparatus, is irradiated with a laser beam (16) for the purpose of modifying the topography of the surface (12).

2. Method according to claim 1, characterized in that a porous transport layer is produced as the porous structure (10) and / or the apparatus for the electrochemical process is a hydrogen electrolyzer or an electrodialyzer or a capacitive deionizer or an electroosmosis system or a redox flow battery.

3. Method according to claim 1 or 2, characterized in that the boundary layer is provided by a membrane or a catalyst or a combination of a membrane and a catalyst.

4. Method according to one of the preceding claims, characterized in that the topography is modified by reducing the roughness of the surface (12) by smoothing.

5. Method according to one of the preceding claims, characterized in that simultaneously the laser beam (16) is directed onto the surface (12) of the porous structure (10), which is provided to be positioned directly at the interface in the system, and a further laser beam is directed onto a further surface (14) of the structure (10) opposite the surface (12).

6. Method according to one of the preceding claims, characterized in that the surface (12) of a layered additively manufactured porous structure (10) is smoothed.

7. Method according to claim 6, characterized in that the porous structure (10) is built up layer by layer from a powder using at least one laser beam in a powder bed-based process and at least one of the following manufacturing parameters for additive manufacturing is set: an energy input of 5 to 20 J / mm² is applied by means of the at least one laser beam. 3 , especially from 5 to 10 J / mm 3 , introduced; a distance between immediately adjacent melt tracks within a layer of the structure (10) is chosen to be greater than twice the diameter of the at least one laser beam, in particular the distance is at least 0.16 mm, in particular 0.2 mm to 0.5 mm; a layer thickness of the respective applied layer of powder is chosen to be greater than a mean particle diameter, in particular greater than a maximum particle diameter.

8. Method according to claim 6 or 7, characterized in that during additive manufacturing, melt tracks are drawn parallel to each other in each layer of the structure (10), wherein the orientations of the melt tracks differ from each other in layers that are not directly adjacent to each other, wherein it is particularly provided that the longitudinal extension direction of melt tracks of layers that are directly adjacent to each other is rotated to each other by an angle of 30° or 45° or 60° or 90° about a stacking direction in which the layers are stacked on top of each other.

9. Method according to one of claims 6 to 8, characterized in that a change in the porosity within the structure (10) is achieved by changing at least one of the parameters: Track spacing Laser power Scan speed, is generated within a layer and / or between at least two layers.

10. Method according to one of claims 6 to 9, characterized in that the structure (10) is additively produced at least in an area with gradually changing porosity.

11. Method according to one of claims 6 to 10, characterized in that the structure (10) is additively built up layer by layer on a bipolar plate (27).

12. Method according to claim 11, characterized in that the structure (10) is additively built up layer by layer directly onto the bipolar plate (27) in the same powder bed in which at least part of the bipolar plate (27) has already been built up layer by layer.

13. Method according to one of the preceding claims, characterized in that at least one of the following processing parameters is selected as the processing parameter for smoothing: Wavelength of the laser beam (16) in the range of 0.5 - 2 micrometers, in particular 1-1.1 micrometers, The laser beam (16) is pulsed with a pulse duration of 1 picosecond to 1 microsecond, in particular with a pulse duration of 10 nanoseconds to 500 nanoseconds. The laser beam (16) is pulsed with a pulse duration of less than 100 picoseconds, with pulse trains of 2 to 16 pulses being provided, wherein the time interval between two successive pulse trains is 10 to 100 nanoseconds.

14. Method according to one of the preceding claims, characterized in that by means of a further laser process, impurities of the surface (12), in particular at least one oxide layer of the surface (12), and / or particles of the surface (12) are removed.

15. Method according to one of the preceding claims, characterized in that a laser spot is generated on the surface (12) by means of the laser beam (16) which has a diameter in a range of 5 to 20 pm.

16. Method according to one of the preceding claims, characterized in that a quotient of fluence and scan speed of the laser beam (16) in a range of 0.05 to 50 J / cm 2 per m / s, especially in a range of 0.05 to 15 J / cm 2 per m / s, especially in a range of 0.1 to 5 J / cm² 2 per m / s.

17. Laser device for producing a structure (10), in particular for use in a plant for an electrochemical process, wherein the laser device is configured to build up the porous structure (10) layer by layer by additive manufacturing and to irradiate at least one surface (12) of the porous structure (10), which is intended to be located directly adjacent to an interface in the plant for the electrochemical process, with a laser beam (16) for a modification of the topography of the surface (12).

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