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

Description

BACKGROUND

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 matter of the present invention.

The fluid medium can in particular be a gas and/or a liquid, in particular an electrolyte, a catalyst, an analyte, or an educt for the operation of the relevant electrochemical cell.

During electrolysis, in particular water (H₂) or CO or CO₂ electrolysis, and also in fuel cells, inflowing fluid flows have to be distributed as uniformly as possible over the width of the active cell in order to enable and maintain the electrochemical reaction over the entire surface, for example, on the ion or proton exchange membrane, i.e. to guide fresh media thereto and discharge consumed media. Only a uniform media supply or its feed and/or discharge over the entire membrane surface also enables uniform current densities. While maintaining the maximum permissible current density, which is dependent on the respective membrane, the total power of the cell can be maximized without local overload and premature aging connected thereto.

It is advantageous in particular here to increase the flow resistance of distribution channels as much as possible at least downstream in the vicinity of the active cell, in particular in order to prevent or substantially reduce electric parasitic currents.

SUMMARY

It is therefore in particular an object of the present invention to specify an improved, homogenized media distribution for electrochemical cells, which at the same time enables the most robust and compact design possible of the component comprising the cell.

This object is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

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 the supply or feed of the medium to the cell, wherein the fluid inlet branches into a number of N, i.e. at least one, preferably a plurality of, distribution stages, wherein a distribution channel divides from one stage to the next stage into two or more channels of smaller cross section in or along a main flow direction (preferably pointing in the direction of the cell). The distribution channels of the “Nth” stage are configured to distribute the fluid medium (directly) uniformly over a width of the cell element or to supply the electrochemically active part of the cell uniformly.

The advantage of the invention over the prior art relates in particular to the improved possibility for the compact design with substantially homogeneous distribution of the fluid over the cell width at the same time. More robust electrochemical components having greatly improved power density can thus in turn be implemented. Furthermore, the advantage of improved producibility and the possibility of mechanically supporting or compressing cell stacks having multiple cell elements particularly stably against one another results.

In one embodiment, distribution channels of one, in particular the same, stage have substantially the same channel length, preferably along the main flow direction. This embodiment advantageously enables the implementation of the most homogeneous possible fluid distribution.

In one embodiment, the distribution channels of a stage furthermore have substantially equal channel widths and/or channel cross sections. In particular, conventional manufacturing, in particular by milling in plastic plates or plastic injection molding, can be simplified by this embodiment.

In one embodiment, the distribution structure is of symmetrical design from its second stage, in particular completely. In this context, an axis of symmetry preferably refers to an axis parallel to the height and perpendicular to the width of the distribution structure or the cell element. This embodiment also contributes to the task according to the invention of the most homogeneous possible fluid distribution.

In one embodiment, distribution channels from the second stage are arranged distributed uniformly, preferably also equidistantly, over the cell width. This embodiment also advantageously enables the most uniform possible fluid distribution.

In one embodiment, the distribution structure is designed such that a channel course or flow course of the distribution structure, after the branching or upon the transition from one stage to the next stage, is aligned in the direction of the main flow direction again to guide the fluid medium or changes accordingly to this direction.

The channel course or flow course at least partially accordingly does not exactly correspond to the main flow direction, but rather runs partially or somewhat perpendicularly to the latter direction after the branching.

In one embodiment, a height of the distribution structure or an extension of the distribution structure along the main flow direction is less than half the width of the cell element. The distribution structure can be kept compact particularly advantageously by this embodiment and at the same time can be made particularly robustly in cooperation with the further features according to the invention.

In one embodiment, a relative standard deviation or standard deviation in relation to the arithmetic mean value (relStd) or a corresponding variation coefficient of a fluid speed distribution in the intended operation of the distribution structure is less than 0.15. According to this embodiment, it is apparent that the differences in the flow speed (speed and pressure gradients) can advantageously be kept small. The mentioned value relates in particular to a position along the central plane of the channels, i.e. not at their edge (see the special exemplary embodiments of the invention described further below on the basis of the figures).

In one embodiment, the distribution structure in the higher stages or finer branches has connection channels between channel branches of the same stage that extend substantially perpendicularly to the main flow direction, in particular transversely or perpendicularly to this direction, and are configured to homogenize still further a distribution of the fluid medium between the channel branches. Pressure differences or differences in the speed distribution can be reduced still further by these transverse connection channels and the supply of the cell element with the medium can thus furthermore efficiently be standardized.

In one embodiment, the distribution structure is configured to guide a liquid or aqueous electrolyte as the fluid medium to the cell element. This embodiment is particularly advantageous and expedient for the supply of the electrolyte in CO/CO₂ electrolysis.

In an alternative embodiment, the distribution structure is configured for water electrolysis or for the supply of water as a fluid medium to the cell element.

In one embodiment, the distribution structure is producible or produced by an additive production method. The fine branching of the channels and the provision of the channels over a plastic material can in particular be carried out advantageously in an additive manner. Additive production methods (AM: “additive manufacturing”), colloquially also referred to as 3D printing, comprise, for example, as powder bed methods, selective laser melting (SLM) or “fused deposition modeling” (FDM). Additive manufacturing methods have proven in particular to be especially advantageous for components having complex or filigree designs, for example, labyrinthine structures, cooling structures, and/or light construction structures. In particular, additive manufacturing is advantageous due to a particularly short chain of process steps, since a production or manufacturing step of a component can be carried out largely on the basis of a corresponding CAD file and the selection of corresponding manufacturing parameters.

A further aspect of the present invention relates to an electrolyzer, comprising a distribution structure for feeding or supplying the fluid medium to the cell element and an outlet structure designed similarly, in particularly identically thereto, for discharging the fluid medium. With respect to the main flow direction, the outlet structure can accordingly preferably be designed or aligned precisely in the opposite direction, in order to guide the fluid likewise uniformly into a possibly central individual outlet channel again from the cell element, and to discharge it.

A further aspect of the present invention relates to a power-to-X system comprising the described electrolyzer and/or the described distribution structure. “Power-to-X” refers in particular to one or more technology(ies) for the storage or other use of excess current from an oversupply of renewable energies, such as solar energy, photovoltaics, wind power, and/or waterpower. In the present case, such excess current is used in particular for operating the electrochemical cell, preferably an electrolysis cell.

Embodiments, features, and/or advantages which refer in the present case to the distribution structure or a corresponding electrochemical cell can furthermore relate directly to the electrolyzer or the power-to-X system, and vice versa.

The expression “and/or” or “respectively” used here, when it is used in a series of two or more elements, means that each of the listed elements can be used alone, or any combination of two or more of the listed elements can be used.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the invention are described hereinafter on the basis of the figures.

FIG. 1 shows a schematic side view or top view of a conventional distribution structure for electrochemical cells.

FIG. 2 shows a schematic view of a conventional electrochemical cell having a distribution structure similar to FIG. 1.

FIG. 3 shows an alternative embodiment of a conventional distribution structure.

FIG. 4 shows a schematic view of a distribution structure according to the invention for supplying an electrochemical cell with a fluid medium.

FIG. 5 illustrates a schematic view of a distribution structure according to the invention according to an alternative embodiment.

FIG. 6 shows an advantageously compact embodiment of the distribution structure according to the invention.

FIG. 7 illustrates a further advantageously compact embodiment, comprising transverse connection channels, of the distribution structure according to the invention.

FIG. 8 shows still another advantageous embodiment of the distribution structure according to the invention.

FIG. 9 shows still another advantageous embodiment of the distribution structure according to the invention.

FIG. 10 shows still another advantageous embodiment of the distribution structure according to the invention.

FIG. 11 shows still another advantageous embodiment of the distribution structure according to the invention.

FIG. 12 shows the relative standard deviation of simulated fluid speed distributions of the distribution structures according to the invention in a diagram.

DETAILED DESCRIPTION

In the exemplary embodiments and figures, identical or identically acting elements can each be provided with the same reference signs. The illustrated elements and their size ratios in relation to one another are not to be considered to be to scale in principle, rather individual elements can be shown exaggeratedly thick or dimensioned large for better representability and/or for better understanding.

FIGS. 1 to 3 of the following description relate to the prior art or conventional media distributors or distribution structures for electrochemical cells. FIGS. 1 and 2 in particular show a similar embodiment of a conventional media distributor 10′ for electrochemical cells, such as electrolysis cells.

FIG. 1 in particular shows such a distributor having a fluid inlet 11′. Starting from this tubular media inlet, a fan-like widening into a large number of small channels 12′ takes place to cover the cell width (cf. horizontal extension of the cell in FIGS. 1 and 2). It is apparent that the longer channels have a larger cross section in order to obtain approximately equal or standardized flow resistances as the further, shorter channels. Approximately equal volume flows or flow rates can in turn be achieved in this way.

FIG. 2 schematically shows an electrochemical cell 2 of the type mentioned, comprising the distribution structure 10 for the supply with a fluid medium (cf. reference sign M further below). In particular, a complete cell having fluidic inlet and outlets on anode and cathode sides of the membrane cell is indicated. In particular, a similar distributor is configured for the fluid or media outlet (cf. reference sign 3′ in the lower part of the illustration).

The structures shown in the present case on the basis of FIGS. 1 to 3 can preferably be configured for the supply of an electrolysis cell for the water electrolysis and accordingly for the supply and guidance of water to a (PEM) membrane.

FIG. 3 shows an alternative conventional distribution design, wherein the distributor can also consist of a section of large cross section (and low flow resistance), using which the distribution in the width is then carried out, and small similar channels branching off therefrom (having correspondingly high flow resistance). The small similar channels expediently supply the individual cell sections in the width. The flow resistance to a single cell section is dominated here by the small channels and is nearly constant over the entire width.

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

Both distribution variants described above are suitable for supplying cells with comparatively small width uniformly. If large cell widths have to be supplied without the distribution structure assuming an excessively large vertical extension, however, problems result.

In the variant illustrated in FIGS. 1 and 2, the length ratio of the longest relative 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 the channel cross sections) in order to equalize the flow resistances accordingly. In any case, technical limits are reached with respect to manufacturing for the smallest channel width.

In the second variant shown in FIG. 3, the flow resistance of the section for the distribution in the width is disadvantageously no longer negligible for large cell widths, or has too much difference for sections close to the inlet and those arranged farther away from the inlet to achieve a sufficiently uniform media distribution.

Support structures are identified with the reference sign 15 in FIG. 3 and are used to receive plungers or mechanical supports. The mechanical stable mounting of each individual electrolysis cell becomes evident upon the observation of required fluid pressures of multiple bar

FIG. 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 design of electrochemical cells which use the distribution structure according to the subject matter of the invention.

A distribution structure 10 for an electrochemical cell, such as an electrolyzer 30, is thus presented which is configured to supply a cell element 1 with a fluid medium M and comprises a fluid inlet 11, which branches into a number of N distribution stages, wherein one 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. Moreover, the distribution channels 12 of the Nth stage of the distribution structure 10 are configured to distribute the fluid medium M particularly uniformly over a width B of the cell element 1.

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 distribution design therefore (as shown)—in the case of the fluid supply of a cell for CO₂/CO electrolysis with liquid electrolyte—is slightly asymmetrical, since a completely symmetrical channel assembly is not implementable by manufacturing. For this purpose, the first stage (branching) in the example was designed having channels and channel widths of different lengths in order to obtain equal flow resistances for this section or compensate for corresponding differences.

The manufacturing in this operating mode, according to which typically carbon dioxide is formed in the channel and has to be discharged as it were via one outlet, requires the guidance of multiple media, strictly speaking, in particular that of an analyte, a catalyst, and a gaseous medium. On the basis of this example, a person skilled in the art also recognizes the practical difficulty, the stability over time. In this regard, gas bubbles can unfavorably close small channels, which in turn results in inhomogeneities in the media supply and in the current density of the cell and in corresponding degradation and premature aging.

After this first stage, in which the channel cross sections are (still) relatively large, a substantially symmetrical, tree-like distribution structure is shown in FIG. 4, which—shown by way of example—branches into seven (N=7) stages, in order to then deliver the fluid or medium to be guided and distributed uniformly at the active cell surface 1.

Distribution channels 12 of each stage have substantially the same channel length 1 here (cf. horizontal channel extension in FIG. 5). This also substantially applies in this and the embodiments described hereinafter to the corresponding channel widths b or corresponding cross sections, due to which substantially equal flow resistances are obtained and furthermore a uniform fluid distribution is ensured over the cell width.

Furthermore, the distribution channels 12 are arranged distributed substantially uniformly over the cell width B approximately from the second stage.

After or upon the branching 13 of one stage K≥2 to the next stage K+1, an electrolytic medium to be guided by the distribution structure expediently does not strictly follow the main flow direction identified by S. Instead, upon the transition to the next (K+1st) stage, a deflection of the channel 12 or alignment of the corresponding flow M then again preferably takes place in or parallel to the main flow direction S.

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, from the sixth to the seventh stage into 64 channels, so that after the seventh stage, finally 128 equivalent distribution channels are present for the supply of the cell element 1. In other words, branching or multiplication of the distribution channels takes place in powers of two, wherein the exponent represents the number of the stages and the power (for the base 2) represents the number of the channels of the effective and last stage. Without restriction of the generality and deviating from the basic concept of the invention, branching into, for example, three or more channels can also take place.

A speed distribution of the fluid medium can be calculated and/or estimated from a flow dynamics simulation (CFD), wherein the flow dynamics are preferably assumed in the central plane of the channels (cf. the depth in the plane of illustration and the coordinate system at the bottom left). It can be seen that the speeds in the channels (and therefore also the volume flow) are substantially equal. As a measure, the relative standard deviation of the speed (with respect to the mean value) in the channel center over all 128 channels can be used. For this structure (cf. FIGS. 4, 5 and point “A” in the diagram of FIG. 12), this is relStd=0.0482.

FIG. 6 shows, in contrast to the illustration of FIG. 5, that the speed distribution becomes significantly more inhomogeneous when the structure described above is compressed with respect to the vertical extension in order to make the structure more compact. A height H2 of the distribution structure from FIG. 6 is accordingly shown smaller for this purpose than the height H1 of the structure from FIG. 5 (cf. the arrow lengths at the right image edge in each case).

The more compact technical embodiment is thus identified together with the speed distribution in FIG. 6, wherein the same parameters are shown. This is also reflected by the substantially (factor 7) higher relative standard deviation of the speed in the channel center, which is relStd=0.337 (cf. point “B” in the diagram of FIG. 12).

One cause of the greater scattering (inhomogeneity) in the fluid dynamics is that the greatly shortened vertical channel sections before the next branching are not sufficient to also absorb the momentum of the flow in the horizontal direction. The branches or channel sections lying in the flow direction thus each receive a greater fluid proportion. One remedying measure is the variant already shown in FIG. 5 having a lengthening of the vertical extension, which is counter to the requirement for compact vertical dimensions, however.

FIG. 6 shows in particular a distribution structure 10 having more complex design or assembly, namely one of this kind, wherein a height H of the distribution structure is less than half the width of the cell element 1.

According to one advantageous embodiment of the present invention of the distribution structure 10, a relative standard deviation of a fluid speed distribution in the intended operation of the distribution structure 10 is less than 0.34, preferably less than 0.15,particularly preferably less than 0.1.

FIG. 7 shows, according to one exemplary embodiment of the present invention, that horizontally extending (transverse) connection channels were introduced into the design, in particular between channels of the last and seventh stage, in order to homogenize the distribution still further. According to the embodiment of FIG. 7, the relative standard deviation is relStd=0.137 (cf. point “C” in the diagram of FIG. 12).

The following figures also indicate on the basis of the fluid paths accented in the drawings results of further CFD simulations with precisely the same parameters (flow rate and fluid properties), as in the preceding simulations and examples.

In the embodiment variants mentioned hereinafter on the basis of FIGS. 7 to 10, in the distribution areas of increasingly lower stage, further transverse connection channels 14 were successively introduced into the branching stages. In other words, fluidic connections were configured rising per stage between adjacent branches of distribution channels 12 of the same stage, which can advantageously equalize pressure or flow gradients during the supply of the cell element 1.

FIG. 8 shows transverse connection channels 14 in the seventh and sixth stage. According to the embodiment of FIG. 8, the mentioned relative standard deviation is relStd=0.10 (cf. point “D” in the diagram of FIG. 12).

FIG. 9 shows transverse connection channels 14 in the seventh, sixth, and fifth stage. According to the embodiment of FIG. 9, the relative standard deviation is relStd=0.0834 (cf. point “E” in the diagram of FIG. 12).

FIG. 10 shows transverse connection channels 14 in the seventh, sixth, fifth, and fourth stage. According to the embodiment of FIG. 10, the relative standard deviation is relStd=0.0781 (cf. point “F” in the diagram of FIG. 12).

According to the illustration of FIG. 11, the relative standard deviation of the speed distribution at relStd=0.0749 (cf. point “G” in the diagram of FIG. 12) is most favorable for the goal according to the invention of homogeneous media distribution. The connection channels 14 exist here starting from the seventh stage into five directly subordinate (directed upstream) stages.

The clearest improvement in the homogeneity is achieved according to experience by the transverse channels in the seventh (cf. FIG. 10). However, all further additionally introduced transverse channels also result in a further improvement of the homogeneity of the speed distribution and therefore the media supply over the cell width.

According to the concept of the invention, the described channels 14 extending horizontally or transversely to the main flow S do not necessarily have to be provided in each branch, however, wherein this can be required in principle for flow distribution.

For the cell dimensions described in the present case, an exemplary cell width of approximately 1.40 m×1.40 m in height (and width) and of 2⁷=128 distribution channels 12 is assumed. This essentially results in a channel cross section of somewhat greater than 10 mm.

As described above, the distribution structure 10 can be configured to supply a liquid electrolyte as a fluid medium to the cell element 1 (cf. FIGS. 1 to 3 as described above).

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

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 an equivalently designed outlet structure 20 for discharging the fluid medium M (cf. FIG. 11).

A further aspect of the present invention relates to a power-to-X system 100 comprising an electrolyzer 30. Corresponding power-to-X technologies are essential for changing over large or all parts of the energy supply system to the largest possible proportion of renewable energies in the course of necessary measures for decarbonization, which, among other things, can compensate for an excess of partially renewable energies or balance out their fluctuation so that the excess energy can be used on the contrary for producing green or synthetic fuels. A bundle of approximately 100 (in the plane of illustration) arrayed elements 1, for example, is characteristic of a so-called “stack” of electrolysis cells used in a power-to-X system.

A further aspect of the present invention relates to an embodiment of the distribution structure which is produced by an additive production method. An expedient alternative can be specified thereby, for example, in relation to the conventional production via milling from a plastic plate or via plastic injection molding.