Distribution structure for electrochemical cells, electrolyser and power-to-x system

Abstract

The invention relates to a distribution structure (10) for an electrochemical cell (30) for supplying a cell element (1) with a fluid medium (M). The distribution structure comprises a fluid inlet (11), which branches into a number of N distribution stages, wherein a distribution channel (12) is divided into two channels of smaller cross section in the main flow direction (S) from one stage (K) to the next stage (K+1), and wherein the distribution channels (12) of the N-th stage of the distribution structure (10) are configured so that the fluid medium (M) is distributed evenly over a width of the cell element (1). The invention further relates to an electrolyser or a corresponding component lighting system comprising the distribution structure.

Description

[0001] Description

[0002] Distribution structure for electrochemical cells, electrolyzer and Power-to-X plant

[0003] The present invention relates to a distribution structure for an electrochemical cell, in particular for an electrolyzer, for supplying one or more cell elements with a fluid medium. Furthermore, a corresponding electrolyzer and a corresponding power-to-X system are the subject of the present invention.

[0004] The fluid medium may in particular be a gas and / or a liquid, in particular an electrolyte, a catalyst, an analyst or a reactant for the operation of the electrochemical cell in question.

[0005] In electrolysis, particularly water (H2) or CO or CCf electrolysis, as well as in fuel cells, incoming fluid streams must be distributed as evenly as possible across the width of the active cell to enable and maintain the electrochemical reaction across the entire surface, for example, at the ion or proton exchange membrane, i.e., to introduce fresh media and remove used media. Only a uniform media supply or its inlet and / or outlet across the entire membrane surface allows for uniform current densities. By adhering to the maximum permissible current density, which depends on the respective membrane, the overall performance of the cell can be maximized without local overloading and the associated premature aging.

[0006] It is particularly advantageous to increase the flow resistance of distribution channels as much as possible, at least downstream in the vicinity of the active cell, in order to prevent or largely reduce electrical parasitic currents. Therefore, it is a particular object of the present invention to provide an improved, homogenized media distribution for electrochemical cells that simultaneously enables the most robust and compact design possible for the component containing the cell.

[0007] This problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are the subject matter of the dependent patent claims.

[0008] One aspect of the present invention relates to a distribution structure for an electrochemical cell, in particular an electrolyzer, for supplying the cell element with the fluid medium. The distribution structure comprises a fluid inlet, preferably a main channel for supplying or feeding the medium to the cell, wherein the fluid inlet branches into N, i.e., at least one, preferably a plurality of, distribution stages, wherein a distribution channel divides into two or more channels of smaller cross-section in or along a main flow direction (preferably pointing toward the cell) from one stage to the next stage. The distribution channels of the "Nth" stage are configured to distribute the fluid medium (directly) evenly across the width of the cell element or to supply the electrochemically active part of the cell evenly.

[0009] The advantage of the invention over the prior art relates in particular to the improved possibility of a compact design with, at the same time, a largely homogeneous distribution of the fluid across the cell width. This in turn makes it possible to produce more robust electrochemical components with a greatly improved power density. Furthermore, there is the advantage of improved manufacturability and the possibility of mechanically supporting or pressing cell stacks with several cell elements against one another in a particularly stable manner. In one embodiment, distribution channels of a stage, in particular of the same stage, have largely the same channel length, preferably along the main flow direction. This embodiment advantageously enables the realization of the most homogeneous fluid distribution possible.

[0010] In one embodiment, the distribution channels of a stage continue to have largely identical channel widths and / or channel cross-sections. This embodiment can simplify conventional manufacturing, particularly by milling into plastic sheets or plastic injection molding.

[0011] In one embodiment, the distributor structure is designed to be symmetrical from its second stage onward, particularly completely. In this context, an axis of symmetry preferably refers to an axis parallel to the height and perpendicular to the width of the distributor structure or cell element. This embodiment also contributes to the inventive objective of achieving the most homogeneous fluid distribution possible.

[0012] In one embodiment, distribution channels from the second stage onward are arranged evenly, preferably equidistantly, distributed across the cell width. This embodiment also advantageously enables the most uniform fluid distribution possible.

[0013] In one embodiment, the distributor structure is designed in such a way that a channel course or flow course of the distributor structure is aligned again in the direction of the main flow direction after the branching or during the transition from one stage to the next stage for guiding the fluid medium, or changes accordingly in this direction.

[0014] Accordingly, the channel or flow path does not correspond exactly to the main flow direction, at least in part, but runs partially or partially perpendicular to the latter direction after the branching. In one embodiment, the height of the distributor structure or an extension of the distributor structure along the main flow direction is less than half the width of the cell element. This embodiment allows the distributor structure to be kept particularly compact and, at the same time, in conjunction with the other features of the invention, to be designed to be particularly robust.

[0015] In one embodiment, a relative standard deviation (re-IStd) or a corresponding coefficient of variation of a fluid velocity distribution during normal operation of the distributor structure is less than 0.15. According to this embodiment, it is evident that the differences in flow velocity (velocity and pressure gradients) can be advantageously kept small. This value refers in particular to a position along the central plane of the channels, i.e., not at their edge (see the specific embodiments of the invention described below with reference to the figures).

[0016] In one embodiment, the distributor structure in the higher stages or finer branches has connecting channels between channel branches of the same stage that run largely perpendicular to the main flow direction, in particular transversely or perpendicularly to this direction. These connecting channels are designed to further homogenize the distribution of the fluid medium between the channel branches. These cross-connecting channels can further reduce pressure differences or differences in velocity distribution, thus further efficiently standardizing the supply of the medium to the cell element.

[0017] In one embodiment, the distribution structure is configured to supply a liquid or aqueous electrolyte as a fluid medium to the cell element. This configuration is particularly advantageous and practical for supplying the electrolyte in CO / CCf electrolysis.

[0018] In an alternative embodiment, the distribution structure is configured for water electrolysis or for supplying water as a fluid medium to the cell element.

[0019] In one embodiment, the distributor structure can be manufactured or produced using an additive manufacturing process. The fine branching of the channels and the provision of the channels via a plastic material can be particularly advantageously achieved by additive means. Additive manufacturing processes (AM), colloquially also referred to as 3D printing, include, for example, powder bed processes such as selective laser melting (SLM) or fused deposition modeling (FDM). Additive manufacturing processes have proven particularly advantageous for complex or delicate components, such as labyrinthine structures, cooling structures, and / or lightweight structures.In particular, additive manufacturing is advantageous due to a particularly short chain of process steps, since a manufacturing or production step of a component can be carried out largely on the basis of a corresponding CAD file and the selection of appropriate manufacturing parameters.

[0020] A further aspect of the present invention relates to an electrolyzer comprising a distribution structure for supplying the fluid medium to the cell element and an outlet structure of the same type, in particular identical to the outlet structure, for discharging the fluid medium. Accordingly, the outlet structure can preferably be designed or oriented in exactly the opposite direction to the main flow direction in order to guide the fluid from the cell element just as uniformly back into a possibly central, individual outlet channel, and to discharge it. A further aspect of the present invention relates to a Power-to-X system comprising the described electrolyzer or the described distribution structure. "Power-fox" refers in particular to one or more technologies for storing or otherwise utilizing surplus electricity from an oversupply of renewable energies, such as solar energy, photovoltaics, wind power, and / or hydropower.In the present case, such excess electricity is used in particular for the operation of the electrochemical cell, preferably an electrolysis cell.

[0021] Configurations, features and / or advantages that relate to the distribution structure or a corresponding electrochemical cell in the present case may also directly affect the electrolyzer or the Power-to-X system, and vice versa.

[0022] The term "and / or" or "respectively," when used in a series of two or more elements, means that any one of the listed elements may be used alone, or any combination of two or more of the listed elements may be used.

[0023] Further details of the invention are described below with reference to the figures.

[0024] Figure 1 shows a schematic side view and top view of a conventional distribution structure for electrochemical cells.

[0025] Figure 2 shows a schematic view of a conventional electrochemical cell with a manifold structure similar to Figure 1.

[0026] Figure 3 shows an alternative embodiment of a conventional distributor structure. Figure 4 shows a schematic view of a distributor structure according to the invention for supplying an electrochemical cell with a fluid medium.

[0027] Figure 5 indicates a schematic view of a distributor structure according to the invention according to an alternative embodiment.

[0028] Figure 6 shows an advantageously compact design of the distributor structure according to the invention.

[0029] Figure 7 indicates a further advantageously compact embodiment of the distributor structure according to the invention which has cross-connection channels.

[0030] Figure 8 shows yet another advantageous embodiment of the distribution structure according to the invention.

[0031] Figure 9 shows yet another advantageous embodiment of the distribution structure according to the invention.

[0032] Figure 10 shows yet another advantageous embodiment of the distributor structure according to the invention.

[0033] Figure 11 shows yet another advantageous embodiment of the distributor structure according to the invention.

[0034] Figure 12 shows the relative standard deviation of simulated fluid velocity distributions of the distributor structures according to the invention in a diagram.

[0035] In the exemplary embodiments and figures, identical or equivalent elements may be provided with the same reference numerals. The illustrated elements and their relative sizes are generally not to be considered true to scale; rather, individual elements may be exaggeratedly thick or oversized for clarity and / or clarity.

[0036] Figures 1 to 3 of the following description refer to the prior art, or rather, to conventional media distributors or distributor structures for electrochemical cells. Figures 1 and 2 show, in particular, a similar design of a conventional media distributor 10' for electrochemical cells, such as electrolysis cells.

[0037] Figure 1 shows, in particular, such a distributor with a fluid inlet 11'. Starting from this tubular media inlet, a fan-like expansion occurs into a plurality of small channels 12' to cover the cell width (cf. horizontal expansion of the cell in Figures 1 and 2). It is evident that the longer channels have a larger cross-section in order to achieve approximately the same or uniform flow resistance as the other, shorter channels. This, in turn, allows approximately equal volume flows or flow rates to be achieved.

[0038] Figure 2 schematically shows an electrochemical cell 2' of the aforementioned type, comprising the distributor structure 10' for supplying a fluid medium (see reference symbol M below). In particular, a complete cell with fluid inlets and outlets on the anode and cathode sides of the membrane cell is indicated. A similar distributor is provided for the fluid or media outlet (see reference symbol 3' in the lower part of the illustration).

[0039] The structures shown here with reference to Figures 1 to 3 can preferably be configured to supply an electrolysis cell for water electrolysis and accordingly to supply and guide water to a (PEM) membrane. Figure 3 shows an alternative conventional distributor design, whereby the distributor can also consist of a section with a large cross-section (and low flow resistance), which is then used for distribution across the width, and small, similar channels branching off from this (with correspondingly large flow resistance). The small, similar channels expediently supply the individual cell sections across the width. The flow resistance to an individual cell section is dominated by the small channels and is almost constant across the entire width.

[0040] Such distribution structures are in principle suitable for supplying fluids according to a combination of low and high flow resistances.

[0041] Both distribution variants presented above are suitable for evenly supplying cells with a comparatively small width. However, problems arise when large cell widths need to be supplied without the distribution structure assuming excessive vertical expansion.

[0042] In the variant illustrated in Figures 1 and 2, the length ratio of the longest to the shortest supply channel increases with the cell width. Since the channels all branch off from the same inlet, this requires a correspondingly large ratio of the channel widths (or channel cross-sections) to adjust the flow resistances accordingly. Due to manufacturing constraints, technical limitations have been reached for the smallest channel width.

[0043] In the second variant, shown in Figure 3, the flow resistance of the section for width distribution is disadvantageously no longer negligible for large cell widths, or rather, the flow resistance differs too much between sections close to the inlet and those located farther from the inlet to achieve a sufficiently uniform media distribution. Support structures are designated by reference numeral 15 in Figure 3 and serve to accommodate pistons or mechanical supports. The mechanically stable mounting of each individual electrolysis cell becomes evident when considering the necessary fluid pressures of several bar.

[0044] Figure 4 now shows a distribution structure according to the invention which solves the above-mentioned technical difficulties and, in particular, enables a compact, robust and supply-efficient construction of electrochemical cells which use the distribution structure according to the invention.

[0045] Thus, a distribution structure 10 for an electrochemical cell, such as an electrolyzer 30, is presented, which is configured to supply a cell element 1 with a fluid medium M and comprises a fluid inlet 11 branching into a number N of distribution stages, wherein a distribution channel 12 divides in the main flow direction S from one stage K to the next stage K+1 into two or more channels of smaller cross-section. In addition, the distribution channels 12 of the Nth stage of the distribution structure 10 are configured to distribute the fluid medium M particularly evenly across a width B of the cell element 1.

[0046] Two downstream distribution channels of the first stage originate from the channel inlet 11 (cf. N=1, left in the illustration). In this stage the distributor design is therefore (as shown) - in the case of the fluid supply to a cell for CO2 / CO electrolysis with liquid electrolyte - slightly asymmetrical, since a completely symmetrical channel configuration is not feasible from a manufacturing perspective. For this reason the first stage (branching) in the example was designed with channels of different lengths and widths in order to achieve the same flow resistances for this section or to compensate for corresponding differences. Production in this operating mode, according to which carbon dioxide is usually formed in the channel and has to be discharged via an outlet, strictly speaking requires the guidance of several media, in particular those of an analyser, a catalyst and a gaseous medium.From this example, the expert also recognizes the practical difficulty of temporal stability. In this regard, gas bubbles can unfavorably close small channels, which in turn leads to inhomogeneities in the media supply as well as in the current density of the cell and to corresponding degradation and premature aging.

[0047] After this first stage, in which the channel cross-sections are (still) relatively large, Figure 4 shows a largely symmetrical, tree-like distribution structure, which - shown as an example - branches out into seven (N=7) stages in order to then deliver the fluid or medium to be guided and distributed evenly to the active cell surface 1.

[0048] Distribution channels 12 of each stage have substantially the same channel length 1 (cf. horizontal channel extension in Figure 5). The same applies in this and the embodiments described below to the corresponding channel widths b and corresponding cross-sections, whereby substantially equal flow resistances are obtained and a uniform fluid distribution across the cell width is further ensured.

[0049] Furthermore, from approximately the second stage onwards, the distribution channels 12 are arranged to be distributed largely evenly over the cell width B.

[0050] After or at the branching 13 of a stage Kb2 to the next stage K+1, an electrolytic medium to be conducted from the distributor structure expediently does not strictly follow the main flow direction marked S. Instead, at the transition to the next (K+1st) stage, the channel 12 is again deflected or the corresponding flow M is aligned preferably in or parallel to the main flow direction S.

[0051] In this manner, the distribution channels 12 branch from the second to the third stage into four channels, from the third to the fourth stage into eight channels, from the fourth to the fifth stage into 16 channels, from the fifth to the sixth stage into 32 channels, and from the sixth to the seventh stage into 64 channels, so that after the seventh stage there are finally 128 identical distribution channels to supply cell element 1. In other words, the distribution channels are branched or multiplied in powers of two, where the exponent represents the number of stages and the power (to the base 2) the number of channels of the effective and final stage. Without limiting the generality and deviating from the basic idea of ​​the invention, branching can also occur, for example, into three or more channels.

[0052] A velocity distribution of the fluid medium can be calculated and / or estimated from a fluid dynamics simulation (CFD), whereby the flow dynamics are assumed to be preferably in the central plane of the channels (see the depth in the representation plane and the coordinate system at the bottom left). It can be seen that the velocities in the channels (and thus also the volume flow) are largely the same. The relative (relative to the mean) standard deviation of the velocity in the center of the channel across all 128 channels can be used as a measure. For this structure (see Figures 4, 5 and point "A" in the diagram of Figure 12), this is relStd=0.0482.

[0053] In contrast to the representation in Figure 5, Figure 6 shows that the velocity distribution becomes significantly more inhomogeneous when the structure shown above is compressed in terms of its vertical extension to make the structure more compact. The height H2 of the distribution structure in Figure 6 is shown correspondingly smaller than the height H1 of the structure in Figure 5 (see the arrow lengths on the right edge of the image).

[0054] The more compact technical design, including the velocity distribution, is shown in Fig. 6, where the same parameters are shown. This is also reflected by the significantly higher (factor of 7) relative standard deviation of the velocity in the center of the channel, which amounts to rel-lStd=0.337 (cf. point "B" in the diagram in Figure 12).

[0055] One reason for the greater scatter (inhomogeneity) in fluid dynamics is that the significantly shortened vertical channel sections before the next branch are insufficient to absorb the flow momentum in the horizontal direction. As a result, the branches or channel sections located in the flow direction each receive a larger proportion of fluid. One remedy is the variant already shown in Figure 5, with an extension of the vertical extent, which, however, contradicts the requirement for compact vertical dimensions.

[0056] Figure 6 shows in particular a distribution structure 10 with a more complex design or assembly, namely one in which a height H of the distribution structure is smaller than half the width of the cell element 1.

[0057] According to an advantageous embodiment of the present invention of the distributor structure 10, a relative standard deviation of a fluid velocity distribution during intended operation of the distributor structure 10 is less than 0.34, preferably less than 0.15, particularly preferably less than 0.1.

[0058] Figure 7 shows, according to an exemplary embodiment of the present invention, horizontally extending (transverse) connecting channels were incorporated into the design, particularly between the channels of the last and seventh stages, to further homogenize the distribution. According to the embodiment of Figure 7, the relative standard deviation relStd=0.137 (cf. point "C" in the diagram of Figure 12).

[0059] The following figures, based on the graphically accentuated fluid paths, also indicate results of further CFD simulations with exactly the same parameters (flow rate and fluid properties) as in the previous simulations and examples.

[0060] In the design variants described below with reference to Figures 7 to 10, additional cross-connection channels 14 were successively introduced into the branching stages in the distribution areas of increasingly lower stages. In other words, fluidic connections were established in descending order per stage between adjacent branches of distribution channels 12 of the same stage, which can advantageously compensate for pressure or flow gradients when supplying the cell element 1.

[0061] Figure 8 shows cross-connection channels 14 in the seventh and sixth stages. According to the configuration of Figure 8, the relative standard deviation relStd=0.10 (see point "D" in the diagram of Figure 12).

[0062] Figure 9 shows cross-connection channels 14 in the seventh, sixth, and fifth stages. According to the configuration of Figure 9, the relative standard deviation is relStd=0.0834 (cf. point "E" in the diagram of Figure 12).

[0063] Figure 10 shows cross-connection channels 14 in the seventh, sixth, fifth, and fourth stages. According to the configuration of Figure 10, the relative standard deviation is re-lStd=0.0781 (cf. point "F" in the diagram of Figure 12).

[0064] According to the representation in Figure 11, the relative standard deviation of the velocity distribution with re- lStd=0.0749 (cf. point "G" in the diagram of Figure 12) is most favorable for the inventive goal of homogeneous media distribution. The connecting channels 14 exist here starting from the seventh stage in five immediately subordinate (upstream) stages.

[0065] Experience has shown that the most significant improvement in homogeneity is achieved by the transverse channels in the seventh cell (see Figure 10). However, all additional transverse channels also lead to a further improvement in the homogeneity of the velocity distribution and thus in the media supply across the cell width.

[0066] According to the inventive concept, the described channels 14 running horizontally or transversely to the main flow S do not necessarily have to be provided in every branch, although this can generally be beneficial for flow distribution.

[0067] The cell dimensions described here assume an exemplary cell width of approximately 1.40 mx 1.40 m in height (and width) and 2 7 =128 distribution channels 12. This essentially results in a channel cross-section of just over 10 mm.

[0068] As described above, the distributor structure 10 can be configured to supply a liquid electrolyte as a fluid medium to the cell element 1 (cf. Figures 1 to 3 as described above).

[0069] Alternatively, the distribution structure 10 can be configured to supply water as a fluid medium to the cell element 1 for water electrolysis.

[0070] A further aspect of the present invention relates to an electrolyzer 30, comprising a distributor structure 10 for supplying the fluid medium M into the cell element 1 and a similarly designed outlet structure 20 for discharging the fluid medium M (see Figure 11). A further aspect of the present invention relates to a Power-to-X system 100 comprising an electrolyzer 30. For the conversion of large or all parts of the energy supply system to the largest possible proportion of renewable energies as part of necessary decarbonization measures, corresponding Power-to-X technologies are essential, which, among other things, can compensate for a surplus of partially renewable energies or balance their fluctuations by using the surplus energy in return for the production of green or synthetic fuels.A characteristic feature of a so-called "stack" of electrolysis cells used in a Power-to-X plant, for example, is a bundle of approximately 100 elements arranged in a row (in the plane of the image) 1.

[0071] A further aspect of the present invention relates to a configuration of the distributor structure produced by an additive manufacturing process. This provides a practical alternative, for example, to conventional manufacturing methods such as milling from a plastic sheet or plastic injection molding.

Claims

Patent claims 1. Distribution structure (10) for an electrochemical cell (30) for supplying a cell element (1) with a fluid medium (M) comprising a fluid inlet (11) which branches into a number of N distributor stages, wherein a distributor channel (12) divides in the main flow direction (S) from one stage (K) to the next stage (K+l) into two channels of smaller cross-section, and wherein the distributor channels (12) of the Nth stage of the distributor structure (10) are arranged to distribute the fluid medium (M) uniformly over a width (B) of the cell element (1).

2. Distributor structure (10) according to claim 1, wherein distributor channels of a stage have largely the same channel length (1).

3. Distributor structure (10) according to claim 1 or 2, wherein distributor channels of a stage have largely equal channel widths (b).

4. Distributor structure (10) according to one of the preceding claims, wherein the distributor structure is symmetrical from its second stage onwards.

5. Distributor structure (10) according to one of the preceding claims, wherein distributor channels from the second stage onwards are arranged evenly distributed over the cell width (B).

6. Distributor structure (10) according to one of the preceding claims, wherein a channel of the distributor structure (10) is aligned again in the direction of the main flow direction (S) after the branching (13) of a stage (Kb2) to the next stage (K+l).

7. Distributor structure (10) according to one of the preceding claims, wherein a height (H) of the distributor structure is less than half the width of the cell element (1) .

8. Distributor structure (10) according to claim 7, wherein a relative standard deviation of a fluid velocity distribution in the intended operation of the distributor structure (10) is less than 0.

15.

9. Distributor structure (10) according to one of the preceding claims, which in the higher stages has connecting channels (14) extending largely perpendicular to the main flow direction (S) between channel branches of the same stage, which are arranged to homogenize a distribution of the fluid medium (M) between the channel branches.

10. Distributor structure (10) according to one of the preceding claims, which is configured to supply a liquid electrolyte as a fluid medium to the cell element (1).

11. Distributor structure (10) according to one of claims 1 to 9, which is configured to supply water as a fluid medium to the cell element (1) for water electrolysis.

12. Distributor structure (10) according to one of the preceding claims, which is produced by an additive manufacturing process.

13. Electrolyzer (30) , comprising a distributor structure (10) according to one of the preceding claims for supplying the fluid medium (M) into the cell element (1) and a similarly designed outlet structure (20) for discharging the fluid medium (M) .

14. Power-to-X plant (100) comprising an electrolyzer (30) according to claim 13.

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