Separator plate for an electrolyzer

Abstract

Separator plate (1, 2) for an electrolyzer, wherein the separator plate (1, 2) is formed in at least one layer and comprises at least one layer of titanium, wherein the separator plate (1, 2) has surface structures (100) manufactured by: • Beaming laser pulses onto a surface of the separator plate (1, 2) or a surface of a titanium-containing material layer for the production of the separator plate (1, 2) while generating a laser spot (S1-S4, S21-S24) on the surface, wherein the laser spots (S1-S4, S21-S24) are distributed along at least one first and one second line (L1, L2) and at least one laser spot (S1-S4, S21-S24) is generated overlapping along the corresponding laser spot adjacent to the first and second lines (L1, L2); and wherein the ratio of the size of each laser spot (S1-S4, S21-S24) to a distance (A) of the first and second lines (L1, L2) is at least 1.2.

Description

[0001] The invention relates to a separator plate for an electrolyzer. A method for producing surface structures of a separator plate for an electrolyzer is also disclosed.

[0002] Conventional electrolyzers consist of a stack of individual cells, each comprising a sequence of layers with a separator plate, two media diffusion structures, in particular porous transport layer(s) (PTL) and / or gas diffusion layer(s) (GDL), and a membrane electrode assembly (MEA). This stack of electrochemical cells must be sealed from the outside environment because the media within the cells are kept under increased pressure relative to the external pressure. For this purpose, electrolyzers typically have a cell frame surrounding the outer edge of each individual electrochemical cell stacked on top of each other. The individual cells in the stack are pressed together, for example, by screws between two end plates.

[0003] The individual cells grouped into a stack are each separated by a separator plate. This plate serves both to separate the media and to transmit current or voltage from cell to cell, particularly through the (potentially indirect) contact of the webs between the fluid-carrying channels to the MEAs. The separator plates feature a flow zone, also called a flow field, with a pattern of support structures on their surface. These support structures form channels for supplying and removing fluid. The support structures can, for example, include channels and webs separating them.

[0004] One problem arises from the fact that metals suitable for separator plates from an economic standpoint, which are sufficiently corrosion-resistant to withstand the aggressive conditions typically found in electrolyzers, tend to passivate. Titanium, for example, forms a passivation layer, which provides corrosion resistance.

[0005] A passivation layer, however, leads to a significantly increased electrical contact resistance at the contact surface of a separator plate, thus impairing its function of establishing a low-loss electrical connection. Further challenges arise from the fact that the roughness and thickness of the passivation layer are significant influencing factors for the electrical contact resistance, and that these parameters can vary, for example, between differently shaped surface areas of a separator plate. Furthermore, the base material of the separator plates can vary, particularly with regard to its material-related surface roughness, which can affect both the electrical contact resistance and the aging behavior. Increased roughness results in a larger surface area that can oxidize and, at the same time, fewer physically accessible contact points where electrical current can be transmitted.

[0006] Consequently, the efficiency of electrolyzers with conventional separator plates, and therefore their economic viability, is limited. This efficiency can also fluctuate depending on the influencing factors mentioned.

[0007] DE 10 2021 202 214 A1 teaches the introduction of periodic surface structures in the nanometer to micrometer range, at least in certain areas, to reduce the electrical contact resistance of separator plates. For the sake of clarity, such surface structures in the nanometer to micrometer range are also referred to as microstructures within the scope of this disclosure.

[0008] The object of the present invention is to provide a separator plate with which the efficiency of an electrolyzer can be further improved while maintaining sufficient corrosion resistance. The invention also aims to provide a method for manufacturing such a separator plate.

[0009] This problem is solved by the separator plate according to the main claim and the method for producing a separator plate according to the aspects disclosed herein. Advantageous embodiments of the invention will become apparent with regard to the features of the dependent claims, the following description, and the figures.

[0010] Accordingly, a separator plate for an electrolyzer is proposed, wherein the separator plate is formed in at least one layer and comprises at least one layer of titanium or is made entirely of titanium, wherein the separator plate has surface structures, manufactured by: • Irradiating laser pulses onto a surface of the separator plate or a surface of a titanium-comprising material layer for the production of the separator plate, each time generating a laser spot on the surface, wherein the laser spots are distributed along at least a first and a second line and at least one laser spot is generated overlapping along the corresponding laser spot adjacent to the first and second lines; and wherein the ratio of the size of each laser spot to the distance between the first and second lines is at least 1.2. The ratio may optionally be at most 1.9 or at most 2.

[0011] The laser spots can thus overlap adjacent laser spots along and / or perpendicular to a corresponding first and second line. The overlap in the transverse direction can be achieved through the aforementioned ratio of line spacing to laser spot size.

[0012] It is understood that the laser pulses and laser spots can be generated sequentially. Therefore, the overlaps do not necessarily occur simultaneously. They relate, for example, to the general relative positioning of the impact surfaces of the laser pulses, which are encompassed by the respective laser spots.

[0013] In contrast to existing approaches to surface structuring in the nanometer to micrometer range, i.e., for generating microstructures, the invention adopts a more macroscopic perspective. More precisely, it was recognized that generating the surface structures disclosed herein, particularly the macroscopic ones, optionally including the superimposition of any previously generated, known microstructures, also offers the potential to reduce electrical contact resistances and thus increase efficiency. The macroscopic arrangement relates in particular to the line spacing.

[0014] The surface structures produced according to the invention in this way can also be referred to as macrostructures. The macrostructures can generally differ from the optionally still produced prior art microstructures and / or superimpose them in the manner described here. The macrostructures can generally be larger than the aforementioned microstructures. For example, they can be at least twice as large and, in particular, at least twice as high, deep, and / or wide. Additionally or alternatively, they can be characterized by longer period lengths, in particular by period lengths at least twice as long. The macrostructures can have the following exemplary dimensions, in particular several micrometers, and / or in any case, are not limited to the nanometer range.

[0015] When surface structures, and specifically surface structures generated according to the invention, are mentioned below, these refer to macrostructures of the type described above and not to previously known microstructures. The latter may, however, also be present, particularly in a form superimposed by the macrostructures.

[0016] It can therefore be provided that similar microstructures as in the prior art are generated, in particular the LIPPS structures discussed below, but additionally the macroscopic surface structures disclosed herein, which superimpose the microstructures. The surface structures generated according to the invention and disclosed herein can thus be understood as surface structures that are generated in addition to and / or simultaneously with the previously known microstructures.

[0017] The optionally generated microstructures of the prior art can generally produce an advantageous nanoroughness (i.e., roughness in the nanometer range, for example, with regard to roughness depth). This allows for the creation of a large number of comparably sized electrical contact points on the sheet metal. The microstructures can, in particular, be so-called LIPSS (Laser Induced Periodic Surface Structures). For detailed explanations, details, and definitions on LIPSS, please refer to the following publication: • “Dynamics of the generation and mechanisms of the formation of periodic surface structures in the nanometer range (LIPSS) by irradiation of solids with femtosecond laser pulses”, dissertation by Sandra Höhm, Berlin, 2014 (hereinafter: Höhm 2014), which is made fully part of this disclosure by reference.

[0018] The separator plate is typically laser-surface treated or formed with a laser-surface treated tool in the area of ​​the surface structures generated according to the invention. The spatial period of the microstructures depends, in particular, directly on the wavelength of the laser light used and is usually on the order of the wavelength of the laser light used. According to a further embodiment, the mean spatial period of the microstructures is at least 20%, preferably at least 5%, preferably at least 2% and / or at most 200%, preferably at most 120% of the laser wavelength used.

[0019] In this context, a laser spot is understood to be, in particular, a location on the surface of the separator plate onto which at least one laser pulse is directed, or, in the case of multiple exposures, several laser pulses are directed sequentially. Thus, the laser spot can define and / or encompass the area of ​​impact of a respective laser pulse on the surface.

[0020] The laser pulses can be ultrashort, meaning they have a pulse duration in the picosecond or femtosecond range. The laser pulses can be generated with a repetition rate (pulse frequency) in the kHz-MHz range.

[0021] The diameter of the laser beam and / or a specific laser spot can be, for example, a maximum of 500 µm, a maximum of 300 µm, and / or a minimum of 10 µm. The laser beam can have a Gaussian intensity profile.

[0022] The lines can be generated by traversing or scanning the separator plate surface using the generated laser pulses or laser spots. The traversal speed, which can also be referred to as the scan speed, can be selected and / or varied such that, considering the repetition frequency of the laser pulse generation, the aforementioned multiple exposures of a single laser spot can be achieved. According to one embodiment, the scan speed is between 1.5 and 40 m / s, for example, 15 m / s.

[0023] According to one embodiment, overlaps of the laser spots can occur both along a respective line between the first and second lines, and also perpendicular to these lines. Accordingly, the adjacent laser spots that overlap can be adjacent to each other along a respective line direction and / or perpendicular to a respective line direction.

[0024] Due to the chosen scale ratio, and especially if at least one line has already been scanned and irradiated in the manner described here, an overlap with the laser spots on a correspondingly adjacent line can also be generated. For example, each laser spot on the first line can overlap at least one laser spot on the second line, and / or vice versa.

[0025] The overlaps and spot size-to-line spacing ratio revealed here allow for the creation of macroscopic surface structures that reliably and sustainably reduce electrical contact resistance. However, if even greater overlaps are created between the laser spots, and especially between laser spots on different adjacent lines, for example by further reducing the line spacing, the electrical contact resistance can increase significantly again, particularly on aged surfaces.

[0026] In general, the surface structures produced according to the invention, and more precisely the macrostructures, can extend, for example, along a respective line in the profile in a wave-like or linear fashion. In one embodiment, these surface structures can have depressions and / or elevations. The depressions can run between the elevations and are usually bounded and / or formed by them. The depressions or elevations can run essentially parallel to each other, at least in sections (e.g., parallel to each other or one behind the other). Often, the surface structures form, at least locally, a trench structure with a multitude of elongated depressions, which are essentially parallel to each other. The number of surface structures, depressions, or elevations can be varied as required.The number of indentations can depend on the size of the area that is to have the surface structures.

[0027] The dimensions of the depressions, particularly their period, generally depend at least on the wavelength of the laser radiation used. Advantageous numerical values ​​are explained below in optional advanced training. The depth is usually measured normal to the area formed by the depressions, or normal to the surface of the separator plate that is free of the periodic surface structures. Additionally or alternatively, the depressions can have a width of, for example, a minimum of 10 µm and / or a maximum of 50 µm. The width is advantageously at least 20% and at most 100% of the laser spot diameter. The width is typically measured at half the height and perpendicular to the local longitudinal direction of the depressions, i.e.,between the plane with the greatest elevation and the plane with the greatest depression, wherein the planes each run parallel to the planar plane of the plate and only one continuously structured area is considered, in particular on a tread surface.

[0028] According to further training, a laser pulse is applied to each laser spot at least three times and / or at most twenty times. In other words, the laser spots can be exposed at least three times and / or at most twenty times. It has been shown that this method allows for the particularly reliable production of surface structures with the advantages revealed here.

[0029] According to a further development, surface structures, and in particular macrostructures, with a first mean spatial period (also referred to here as period length) of at least 2 µm and / or at most 80 µm are produced along each of the first and second lines. The spatial period can denote the maximum distance between two adjacent surface structures of identical or similar shape, for example, between two local maximum heights or local maximum depressions. Due to the manufacturing process, the surface structures are generally not completely identical to each other. Rather, the period can vary along each line. Therefore, this further development considers a mean spatial period.

[0030] According to a further development, surface structures, and in particular macrostructures, with a second mean spatial period that differs from the first mean spatial period are generated along an axis that intersects the first and second lines. This illustrates that, in the present solution, macroscopic aspects of the surface structures generated in a certain surface area have also been recognized as solution-relevant design features. It has been shown that by appropriately varying the mean spatial period along the different axes, the solution to the problem according to the invention is achieved particularly reliably.

[0031] According to a further development, the surface structures produced according to the invention comprise depressions whose maximum depth is no more than 2.5 µm and / or at least 0.7 µm. The depth is to be understood as the distance from a plane parallel to the plate plane, which passes through the maximum elevation of the continuous surface structures, in particular on a web surface.

[0032] According to a further development, the separator plate has a multitude of ribs and channel base surfaces formed between the ribs, wherein the surface structures and in particular macrostructures are formed at least sectionally along a rib surface of the ribs.

[0033] The webs, and in particular their surfaces, can protrude from the channel bases, especially when viewed orthogonally to a plate plane and / or relative to a flat surface of the separator plate. The channels can generally form recessed areas relative to the webs, designed and configured for fluid guidance. The web surfaces can form raised surface areas in at least selected regions of the separator plate. The channel bases can form recessed surface areas in at least selected regions of the separator plate. These selected regions of the separator plate can each encompass several square centimeters, in particular more than 10 cm². 2 They can comprise multiple webs as well as multiple channels. The web surfaces and channel bases can be connected via flanks, which can optionally be assigned to the webs or the channels.

[0034] Additionally or alternatively, the bridge surface can form an installation area for further components of the electrolyzer, in particular for a PTL and / or a GDL.

[0035] The formation of surface structures, at least in sections, along the rib surfaces can mean, in particular, that the electrochemically active area of ​​the separator plate, and according to one variant, only this area, exhibits the surface structures. A media transfer area of ​​the electrolyzer (also referred to as a distribution area), by means of which reaction media or reaction products are supplied to or removed from the electrochemically active area, is preferably not equipped with surface structures or, at most, with surface structures to a significantly reduced extent. This extent can be quantified, for example, by the size of the area within which surface structures are formed, and / or by the spatial density and / or mean spatial period of the surface structures.

[0036] The described concentration of surface structures, and especially macrostructures, in the electrochemically active region takes into account the fact that improvements in electrical contact resistance achieved by these surface structures are less likely to translate into efficiency improvements outside the electrochemically active region. By correspondingly concentrating the surface structures in the electrochemically active region, manufacturing costs can be reduced.

[0037] According to further training, the channel base surfaces have fewer sections with surface structures, and especially macrostructures, compared to the web surfaces. Alternatively or additionally, the channel base surfaces can have smaller sections with surface structures compared to the web surfaces, or even no sections with surface structures at all. This takes into account the fact that the web surfaces can serve as mounting areas for other electrolyzer components, such as a GDL and / or PTL. Accordingly, reductions in electrical contact resistance achieved through the surface structures can directly translate into efficiency improvements.

[0038] According to a further development, the first and second lines each extend along a longitudinal axis of a web. This underlines that the advantageous surface structures according to the invention can be formed particularly within the web surfaces.

[0039] The invention also relates to a separator plate, which is formed in at least one layer, wherein the at least one layer comprises titanium or consists entirely of titanium. The separator plate can comprise surface structures and, in particular, macrostructures along at least a first and second line, with a first mean spatial period of at least 2 µm and / or at most 80 µm, wherein the separator plate has surface structures along an axis that intersects the first and second lines, with a second mean spatial period that differs from the first mean spatial period.

[0040] The invention also relates to a separator plate, which is formed in at least one layer, wherein the at least one layer comprises titanium or consists entirely of titanium, wherein the separator plate has surface structures and in particular macrostructures, manufactured by: - Projecting laser pulses onto a surface of a forming tool, alternately generating a laser spot on the surface, wherein the laser spots are distributed along at least a first and a second line and at least one laser spot is generated overlapping along the corresponding laser spot adjacent to the first and second lines; wherein the ratio of the size of a respective laser spot to a distance between the first and second lines is at least 1.2; and furthermore through: - Transferring the surface structures to a macroscopically shaped separator plate comprising or consisting entirely of titanium using the forming tool. In this case, the separator plate can, for example, first be macroscopically shaped, in particular by embossing or other forming processes; or - Transferring the surface structures onto a titanium-containing or entirely titanium-based material layer using the forming tool and macroscopically forming this material layer using a further forming tool. In this case, forming the material layer into a separator plate and creating its shape and / or structural features can be a subsequent step after generating the surface structures; or - Macroscopic forming of a titanium-containing material layer using the forming tool, in particular forming the separator plate and / or shape and / or structural features of the separator plate, such as webs or channels, while simultaneously transferring the surface structures to the material layer. In this case, one and the same forming tool can, in particular in a single forming step, both macroscopically form the separator plate and transfer the surface structures disclosed herein to it.

[0041] In the preceding examples, macroscopic forming can, in particular, involve shaping a material layer that is initially essentially (for example, with the exception of surface structures) or completely flat into a separator plate. Alternatively or additionally, macroscopic forming can include, in particular, the complete formation of channels, ridges, embossings, or other shape and / or structural features that protrude from a flat surface of the separator plate. Specifically, the electrochemically active area and / or distribution areas of the separator plate described above can each be completely formed by means of macroscopic forming.

[0042] The introduction of surface structures, and especially macrostructures, can be understood as a type of microscopic pressure forming, in comparison to the described shape and / or structural features of the separator plate. This is not contradicted by the fact that macroscopic considerations were also made above, in the relative context of the laser spots and in relation to this context. That is to say, the macroscopic and microscopic considerations in the context of the forming processes described here refer to different and, in particular, larger scales (for example, in the centimeter and millimeter range) than the macroscopic and microscopic considerations when generating the surface structures (which, for example, are in the micrometer and nanometer range).

[0043] It was found that the production of surface structures is reliably successful even with different materials used for the forming tool and the material layer. For example, the forming tools can be made of or comprise hardened steel, especially tool steel, and the material layer can be titanium.

[0044] The invention also relates to a forming tool for introducing surface structures into a separator plate or into a material for producing the separator plate, for example, into a layer of material from which a separator plate is yet to be macroscopically formed. The forming tool has surface structures, and in particular macrostructures, produced by: - Radiation of laser pulses onto a surface of the forming tool, each generating a laser spot on the surface, wherein the laser spots are distributed along at least a first and a second line and at least one laser spot is generated overlapping along the corresponding laser spot adjacent to the first and second lines; wherein the ratio of the size of a respective laser spot to a distance between the first and second lines is at least 1.2.

[0045] Analogous to the above variants, this forming tool can be set up to introduce the surface structures into a macroscopically shaped separator plate or a layer of material that is formed into a separator plate in a subsequent step.

[0046] The invention also relates to a forming tool for introducing surface structures into a separator plate comprising at least one layer of titanium, or into a layer of material comprising titanium for producing a separator plate, wherein the forming tool comprises surface structures and, in particular, macrostructures with a first mean spatial period of at least 2 µm and / or at most 80 µm along at least a first and a second line, wherein the separator plate has surface structures with a second mean spatial period that differs from the first mean spatial period along an axis that intersects the first and second lines.

[0047] According to further training, the forming tool is a roll embossing tool or a stroke embossing tool. Roll embossing and stroke embossing have each proven particularly suitable for producing the surface structures. Generally, the forming tool can be plate- or roller-shaped and / or designed for actuation by a machine press, especially a hydraulic press. Alternatively, the forming process can also be carried out by hydroforming or deep drawing.

[0048] According to further training, the forming tool is also designed for at least partial macroscopic shaping of the separator plate. Macroscopic shaping can be understood as any macroscopic deformation of the type described above, in particular the production of shape and / or structural elements such as webs or channels of the separator plate.

[0049] Alternatively, according to a further development, the forming tool can be configured to transfer the surface structures onto the surface of a macroscopically formed or to-be-formed separator plate. In the latter case, the transfer can occur simultaneously with the forming of the separator plate. For example, the forming tool can be configured to form a separator plate from a material layer that is essentially or completely flat, while simultaneously introducing the surface structures into this material layer.

[0050] According to a further development, the separator plate has a plurality of ribs and channels formed between the ribs, wherein the forming tool only has surface structures in those surface areas which are designed for forming, or in other words, demolding ribs of the separator plate. For example, the tool surface comprises ribs and channels formed complementarily to the separator plate or material layer, and the surface structures are preferably provided exclusively in the area of ​​the channels, i.e., the recesses. The latter are designed for forming ribs in the separator plate or material layer. Alternatively, the surface structures can be formed only in those surface areas which are intended for forming areas of a material layer from which ribs of the separator plate are manufactured.In this case, it may in particular involve a microscopic reshaping of the material layer, in which only the surface structures are introduced into it, without macroscopically reshaping the material layer and in particular not forming the macroscopic shape and / or structural features of a separator plate.

[0051] Within the scope of the above examples, particular attention can be paid to the webs and channels that are formed on the side of the material layer into which the forming tool engages and / or which comes into contact with surface areas of the forming tool that have surface structures and, in particular, macrostructures.

[0052] A method according to any of the following aspects is also disclosed. All variants and embodiments of the features of a separator plate and a forming tool disclosed herein may also apply for identical or comparable method features. In particular, the method may be disclosed for manufacturing a separator plate according to any embodiment disclosed herein and / or may include any manufacturing measures and features disclosed for this purpose. Additionally or alternatively, the method may be carried out using any forming tools disclosed herein.

[0053] In particular, the following aspects are revealed: 1. Method for producing surface structures and in particular macrostructures of a separator plate for an electrolyzer, wherein the separator plate is formed in at least one layer and comprises at least one layer of titanium, comprising the method: • Beaming laser pulses onto a surface of the separator plate or a surface of a titanium-containing material layer to produce the separator plate, thereby generating a laser spot on the surface, wherein the laser spots are distributed along at least a first and a second line and at least one laser spot is generated overlapping along a corresponding laser spot adjacent to the first and second lines; and wherein the ratio of the size of a respective laser spot to a distance between the first and second lines is at least 1.2. 2. Procedure according to aspect 1, where the first and second lines are at least partially straight and / or parallel and / or concentric to each other. 3. Procedure according to aspect 1 or 2, wherein a laser pulse is applied to each laser spot at least three times and / or at most twenty times. 4. Procedure according to one of the preceding aspects, wherein surface structures with a first mean spatial period of at least 2 µm and / or at most 80 µm are generated along each of the first and second lines. 5. Procedure according to aspect 4, wherein, along an axis that intersects the first and second lines, surface structures with a second mean spatial period are generated that differs from the first mean spatial period. 6. Procedure according to one of the preceding aspects, wherein the generated surface structures include depressions whose maximum depth is not more than 2.5 µm and / or at least 0.7 µm. 7. Procedure according to one of the preceding aspects, wherein the separator plate has a plurality of ribs and channel bases formed between the ribs, wherein the surface structures are formed at least sectionally along the rib surfaces. 8. Procedure according to aspect 7, where, with regard to the channel base areas and in comparison to the bridge surfaces, fewer sections with surface structures or smaller dimensioned sections with surface structures or no sections with surface structures are formed. 9. Procedure according to aspect 7 or 8, where the first and second lines extend along a longitudinal axis of a bridge. 10. Method for producing surface structures of a separator plate for an electrolyzer, wherein the separator plate is formed in at least one layer and comprises at least one layer of titanium, comprising the method: • Beaming laser pulses onto a surface of a forming tool, each generating a laser spot on the surface, wherein the laser spots are distributed along at least a first and a second line and at least one laser spot is generated overlapping along the corresponding laser spot adjacent to the first and second lines; wherein the ratio of the size of a respective laser spot to a distance between the first and second lines is at least 1.2; and further showing: • Transferring the surface structures onto a macroscopically shaped separator plate encompassing titanium using the forming tool; or • Transferring the surface structures to a titanium-containing material layer using the forming tool and macroscopically forming this material layer using another forming tool; or • Macroscopic forming of a titanium-containing material layer using the forming tool while simultaneously transferring the surface structures to the material layer. 11. Procedure according to aspect 10, where the forming tool is a roll stamping tool or a stroke stamping tool.

[0054] The electrolyzer can be used to produce hydrogen and oxygen, as well as carbon monoxide or other basic materials.

[0055] The invention is explained below with reference to the accompanying schematic figures. The same reference numerals can be used across all figures for similar or equivalent features. Fig. Figure 1 shows an exploded view of a single electrochemical cell of an electrolyzer, comprising separator plates according to an embodiment of the invention. Fig. Figure 2 is a sectional view of a portion of a stack of electrochemical cells, as shown in the example from Fig. 1 are trained. Fig. Figure 3 is a detailed view of a surface area of ​​a separator plate, as used in the electrochemical cell made of Fig. 1 can be used, wherein the surface area has surface structures produced according to the invention. Fig. 4A-C show a survey area ( Fig. 4A) of the surface area Fig. 3 and a height profile measured therein when surveying along a first axis ( Fig. 4B-C). Fig. 5A-C show a survey area ( Fig. 5A) of the surface area Fig. 3 and a height profile measured therein when surveying along a second axis ( Fig. 5B-C).

[0056] Fig. Figure 1 shows an exploded view of an electrochemical single cell 9, wherein the single cell 9 is part of an electrochemical system in the form of an electrolyzer. Electrolyzers typically comprise a plurality of such single cells 9 in a stacked arrangement; see also the one discussed below. Fig. 2. The single cell 9 comprises two separator plates 1 and 2, two cell frames 42 and 44, a sealing layer 45, and a membrane electrode assembly 40 with media diffusion structures 41 and 43. The media diffusion structure 43 comprises, for example, layers of carbon fleece and is, for example, a GDL, while the media diffusion structure 41 comprises metal, e.g., titanium, and is, for example, a PTL. The separator plate 1 is, for example, arranged on the anode side of the single cell 9. In the illustrated embodiment, the separator plate 2 is arranged on the cathode side of the single cell 9. The individual layers shown are pressed together to form a compact single cell 9. Each layer has fluid feedthroughs 46, 47, 50 arranged in alignment above and below each other for introducing and removing water, oxygen, and hydrogen, as well as positioning holes 48.

[0057] By projecting the cell frame 44 onto the separator plate 2, an outer edge of the flow field 32 of the separator plate 2 is defined. By projecting the cell frame 42 onto the separator plate 1, an outer edge of the flow field 31 of the separator plate 1 is defined. The projections are preferably orthogonal to the respective plane within which the cell frames 42 and 44 extend.

[0058] The cell frame 42 has distribution channels (not shown) for distributing the introduced water. The through-openings 46, 47 are in fluid communication with the flow field 31 so that a medium can be directed from the through-opening 46 to the flow field 31 or from the flow field 31 to the through-opening 47. When an electrical potential is applied, hydrogen (or oxygen) can be produced from the supplied water in the electrolyzer. This can be discharged through the distribution channels 49 in the cell frame 44. Subsequently, the hydrogen can leave the cell through the through-openings 50. While the in Fig. Although the separator plates 1, 2 shown in Figure 1 have a round outer contour, other shapes are also possible. For example, the separator plates 1, 2 can have an essentially rectangular outer contour.

[0059] Fig. 2 is a cross-sectional view through a section of an electrochemical system in which several individual cells 9 are made up of Fig. 1 are stacked on top of each other. However, only partial sequences of selected layers or individual cells 9 of this electrochemical system are shown, and the view includes significantly more individual cells 9 and separator plates 1,2.

[0060] The section view from Fig. 2 contains a plurality of individual cells 9. The separator plates 1, 2, which delimit each individual cell 9, are again visible. Between each pair of separator plates 1, 2, and thus within an electrochemical cell 9, a sequence of components 41, 40, 43 of the type described above is arranged and, more precisely, stacked layer by layer on top of each other.

[0061] The section view from Fig. 2 contains partial areas of the flux fields 31, 32 of the respective separator plates 1,2 and thus at least partially represents the electrochemically active area of ​​the individual cells 9.

[0062] It can be seen that the separator plates 1, 2 are uneven in the areas shown. More precisely, they have a sequence of ribs 53 and channels 51 formed between these ribs 53. Only selected of these are marked with a corresponding reference symbol. Furthermore, for explanatory purposes, the following are shown in Fig. 2 sides of the separator plates 1,2 pointing into the interior of a single cell 9 are considered.

[0063] Canals 51 are opposite piers 53 in Fig. The ribs 53 are lowered, with the lowest area being formed by a channel base 52. Their highest area comprises a rib surface 54, against which an opposing media diffusion structure 41, 43 abuts. An electrically conductive contact with the adjacent media diffusion structure 41, 43 is established via the rib surface 54. Adjacent rib surfaces 54 and channel bases 52 are connected by means of flanks that are not separately referenced and which can be considered, for example, as either part of the ribs 53 or the channels 51.

[0064] The channels 51 and webs 53 are each elongated. An exemplary longitudinal axis L of one of the webs 53 runs, as with all other webs 53 and channels 51, orthogonally to the image plane.

[0065] On the bridge surfaces 54 and especially exclusively there and / or at least not also on the canal bottom surfaces 52, in Fig. 2 surface structures not shown separately 100 and in particular macrostructures are formed.

[0066] Fig. Figure 3 shows a top view of a part of a web surface 54, as it appears in one of the webs 53 made of Fig. 2 may be provided. The area shown does not extend over the entire width of a web surface 54, nor over the entire length, but is significantly smaller in comparison.

[0067] The following will be based on Fig. 3. First, a manufacturing process for surface structures 100 using laser beam processing was discussed. Based on the Fig. 4A-C and 5A-C then explain details of the surface structures 100 as such.

[0068] In Fig. Figure 3 shows sections of two lines L1 and L2, which are depicted as straight lines only as examples. These extend parallel to the longitudinal axis L of the web surface 54 and the associated web 53, see also Fig. 2. They have a greater length than shown and extend at least along the entire depicted area of ​​the web surface 54 and, for example, along the entire web surface 54. A distance A between lines L1 and L2, measured orthogonally to each of the lines L1 and L2 as well as along the web surface 54, is also shown. For example, the distance A here is 40 µm. The diameter of a laser spot is given here as D; in this example, it is 50 µm.

[0069] Laser spots S1-S4 and S21-S24 are distributed along each line L1, L2. In particular, this can be done such that the distances measured along each line between the centers of the individual laser spots S1-S4 and S21-S24 (not shown) are constant. The distances between the adjacent and, in particular, immediately adjacent laser spots S1-S4 and S21-S24 along a line L1, L2 are chosen such that at least immediately adjacent laser spots S1-S4 and S21-S24 overlap along this line L1, L2. Selected overlap regions O1 are Fig. 3 marked accordingly. In the example shown, these distances are chosen to be so small that there are overlaps between, for example, laser spot S2, S22 and all remaining laser spots S1-S4 or S21-S24 distributed along a corresponding line L1 or L2.

[0070] Laser pulses can be repeatedly directed onto each of the laser spots S1-S4, S21-S24, i.e., multiple exposures occur. The traverse speed or scan speed of the respective lines L1, L2 is appropriately selected for this purpose. Alternatively, single exposure, for example of individual laser spots, is also possible. The power of the laser pulses is selected such that the material of the web surface in the area of ​​the laser spots can be modified at least partially (i.e., not across the entire sheet thickness). This allows surface structures 100 and, in particular, macrostructures according to any of the examples disclosed herein to be generated, which deviate, in particular, from the web surface 54 that is usually initially flat and / or has a purely material-related roughness.The average power density is in the range of at least 5 watts and at most 30 watts, taking into account the ultra-short duration of the laser pulses.

[0071] To generate preferred surface structures 100, and in particular macrostructures, the solution disclosed here further proposes selecting the distance A between lines L1 and L2 such that overlaps of laser spots S1-S4 and S21-S24 are also generated, which are adjacent to each other when viewed transversely to the respective lines L1 and L2, i.e., also overlaps of laser spots S1-S4 and S21-S24 that are located on different lines L1 and L2. Selected of these overlap regions are shown in Fig. 3 is labelled O2. In the example shown, it is again possible that laser spots S1-S4, S21-S24 of a first line L1 overlap with several laser spots of the corresponding second line L2, and vice versa.

[0072] In particular, the invention proposes that the ratio of the size of a respective laser spot to the distance between the first and second lines is at least 1.2 and / or at most 1.9 and / or at most 2. This has proven to be a particularly suitable process window in order to sustainably reduce the electrical contact resistance even with increasing aging and corresponding increase in passivation.

[0073] The Fig. Sections 4A-C relate to a surface topography measurement of the surface structures 100 generated in this way and in particular macrostructures during a measurement along a first axis A1 or several lines running parallel to it. Fig. Figure 4A shows a measuring area M1 extending along the longitudinal axis L, in which the measurement is carried out, wherein Fig. Figure 4B depicts axis A1, along which the measurement is taken, and along which parallel lines are also drawn but without their own reference marker. All of these measurement lines generally run parallel to lines L1 and L2. Fig. 3. In Fig. Figure 4B shows a measurement diagram of the surface topography measurement obtained by averaging the aforementioned measurements, which is shown in Fig. 4C is shown enlarged.

[0074] In Fig. 4C represents the surface topography as a height value or profile height in micrometers plotted along the vertical axis. This height is measured relative to a plane of the web surface 54 and / or a plane of the separator plate 1,2. The horizontal axis of the measurement diagram in Fig. 4C indicates positions along axis A1, with the values ​​also given in micrometers and referenced to an initial reference point of 0 µm. It is evident that, compared to conventional material roughness measurements, more pronounced height variations occur along axis A1, exhibiting a certain periodicity. This periodicity particularly concerns the occurrence of locally maximum amplitudes in the measurement curve. Exemplary period lengths P1, from which a mean period can be determined, are shown.

[0075] The Fig. 5A-C show essentially analogous views to the Fig. 4A-C. However, they concern a surface topography measurement in a measurement area M2 extending transversely to the longitudinal axis L and also along a corresponding axis A2 extending transversely to the longitudinal axis L or its parallels. Again, in Fig. 5B shows the obtained measurement diagram schematically, that in Fig. The diagram is shown enlarged at 5C. The axes of this measurement diagram are analogous to Fig. 4C defined.

[0076] Once again, a significant variation in height is evident, particularly in comparison to an underlying material roughness that is not shown separately. The height fluctuations, or in other words, the locally maximum amplitudes of the measurement curve, are higher than in the case of Fig. 4C. The range of exemplary periods P2 and, in particular, a mean period determinable from them, according to which the described locally maximum amplitudes occur, is significantly larger than in the case of Fig. 4C.

[0077] The result shows that the surface structures 100, and in particular macrostructures, are characterized by spatially, i.e., in the scan direction and orthogonally to the scan direction of the laser irradiation, differing periods of their profile depths, and especially by differing mean periods. The latter are in the Fig. 4A-C and 5A-C are not listed separately, but are nevertheless evident from these.

[0078] The averaging of measurements from seven lines parallel to axes A1 and A2 is merely an example. A different, particularly smaller, number of lines can also be averaged. It is also possible to measure only along axes A1 and A2. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 202 214 A1

[0007] Cited non-patent literature

[0000] Dynamics of the generation and mechanisms of the formation of periodic surface structures in the nanometer range (LIPSS) by irradiation of solids with femtosecond laser pulses”, Dissertation by Sandra Höhm, Berlin, 2014

[0017]

Claims

[1] Separator plate (1, 2) for an electrolyzer, wherein the separator plate (1, 2) is formed in at least one layer and comprises at least one layer of titanium, wherein the separator plate (1, 2) has surface structures (100) manufactured by: • Beaming laser pulses onto a surface of the separator plate (1, 2) or a surface of a titanium-containing material layer for the production of the separator plate (1, 2) while generating a laser spot (S1-S4, S21-S24) on the surface, wherein the laser spots (S1-S4, S21-S24) are distributed along at least one first and one second line (L1, L2) and at least one laser spot (S1-S4, S21-S24) is generated overlapping along the corresponding laser spot adjacent to the first and second lines (L1, L2); and wherein the ratio of the size of each laser spot (S1-S4, S21-S24) to a distance (A) of the first and second lines (L1, L2) is at least 1.

2. [2] Separator plate (1, 2) according to claim 1, wherein the first and the second line (L1, L2) are at least partially straight and / or parallel and / or concentric to each other. [3] Separator plate (1, 2) according to claim 1 or 2, wherein a laser pulse is directed at each of the laser spots (S1-S4, S21-S24) at least three and / or at most twenty times. [4] Separator plate (1, 2) according to one of the preceding claims, wherein surface structures (100) with a first mean spatial period of at least 2 µm and / or at most 80 µm are generated along a respective first and second line (L1, L2). [5] Separator plate (1, 2) according to claim 4, wherein surface structures (100) with a second mean spatial period different from the first mean spatial period are generated along an axis (A2) which intersects the first and second lines (L1, L2). [6] Separator plate (1, 2) according to one of the preceding claims, wherein the generated surface structures (100) comprise depressions whose maximum depth is not more than 2.5 µm and / or at least 0.7 µm. [7] Separator plate (1, 2) according to one of the preceding claims, wherein the separator plate (1, 2) has a plurality of webs (53) and channel base surfaces (52) formed between the webs (53), wherein the surface structures (100) are formed at least sectionally along web surfaces (54) of the webs (53). [8] Separator plate (1, 2) according to claim 7, wherein the channel base surfaces (52) have fewer sections with the surface structures (100) compared to the web surfaces (54); or have smaller dimensioned sections with the surface structures (100); or have no sections with the surface structures (100). [9] Separator plate (1, 2) according to claim 7 or 8, wherein the first and second lines (L1, L2) extend along a longitudinal axis (L) of a web (53). [10] Separator plate (1, 2) for an electrolyzer, wherein the separator plate (1, 2) is formed in at least one layer and comprises at least one layer of titanium, wherein the separator plate (1, 2) along at least one first and second line (L1, L2) comprises surface structures (100) with a first mean spatial period of at least 2 µm and / or at most 80 µm, wherein the separator plate (1, 2) has surface structures (100) along an axis which intersects the first and second line (L1, L2) with a second mean spatial period which is different from the first mean spatial period. [11] Separator plate (1, 2) for an electrolyzer, wherein the separator plate (1, 2) is formed in at least one layer and comprises at least one layer of titanium, wherein the separator plate (1, 2) has surface structures (100), manufactured by: - Irradiation of laser pulses onto a surface of a forming tool, generating a laser spot (S1-S4, S21-S24) on the surface, wherein the laser spots (S1-S4, S21-S24) are distributed along at least a first and a second line (L1, L2) and at least one laser spot (S1-S4, S21-S24) is generated overlapping along the corresponding laser spot adjacent to the first and second lines (L1, L2); wherein the ratio of the size of a respective laser spot (S1-S4, S21-S24) to a distance (A) of the first and second lines (L1, L2) is at least 1.2; and furthermore through: - Transferring the surface structures (100) onto a macroscopically shaped separator plate (1, 2) comprising titanium using the forming tool; or - Transferring the surface structures (100) onto a titanium-containing material layer using the forming tool and macroscopically forming this material layer using another forming tool or - macroscopic forming of a titanium-containing material layer using the forming tool while simultaneously transferring the surface structures (100) to the material layer. [12] Forming tool for introducing surface structures (100) into a separator plate (1, 2) or into a material for producing the separator plate (1, 2), wherein the forming tool has surface structures (100), produced by: - Radiation of laser pulses onto a surface of the forming tool, each generating a laser spot (S1-S4, S21-S24) on the surface, wherein the laser spots (S1-S4, S21-S24) are distributed along at least a first and a second line (L1, L2) and at least one laser spot (S1-S4, S21-S24) is generated overlapping along the corresponding laser spot adjacent to the first and second line (L1, L2); wherein the ratio of the size of each laser spot (S1-S4, S21-S24) to a distance (A) of the first and second line (L1, L2) is at least 1.

2. [13] Forming tool for introducing surface structures (100) into a separator plate (1, 2) comprising at least one layer of titanium, or into a layer of material comprising titanium for producing a separator plate (1, 2), wherein the forming tool comprises surface structures (100) with a first mean spatial period of at least 2 µm and / or at most 80 µm along at least a first and a second line (L1, L2), wherein the separator plate (1, 2) has surface structures (100) with a second mean spatial period that is different from the first mean spatial period along an axis that intersects the first and second lines (L1, L2). [14] Forming tool according to claim 12 or 13, wherein the forming tool is a roll forming tool or a stroke forming tool. [15] Forming tool according to one of claims 12-14, wherein the forming tool is also configured for at least partially macroscopic shaping of the separator plate (1, 2); or wherein the forming tool is configured to transfer the surface structures (100) onto the surface of a macroscopically shaped or to be shaped separator plate (1, 2). [16] Forming tool according to one of claims 12-15, wherein the separator plate (1, 2) has a plurality of webs (53) and channels (54) formed between the webs (53), wherein the forming tool has surface structures (100) only in such surface areas which are designed for forming webs (53) of the separator plate (1, 2) or for forming areas of a material layer from which webs (53) of the separator plate (1, 2) are made.

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