Patent Application
20230395825
The present application claims priority to German Utility Model Application No. 20 2022 103 147.9, entitled “BIPOLAR PLATE FOR AN ELECTROCHEMICAL SYSTEM, AND ASSEMBLY OF SUCH BIPOLAR PLATES”, and filed on Jun. 2, 2022. The entire contents of the above-listed application is hereby incorporated by reference for all purposes.
The present disclosure relates to a bipolar plate for an electrochemical system, and to an assembly of such bipolar plates. Such bipolar plates are used in electrochemical systems, for example in electrolyzers, fuel cells, electrochemical compressors, or redox flow batteries. For this, bipolar plates and membrane electrode assemblies (MEAs) are usually arranged in an alternating fashion with additional components at the respective ends, so as to form a stack of an electrochemical system, and are compressed.
In one type of construction, such bipolar plates comprise at least two separator plates, which are arranged adjacent to each other in a direction perpendicular to the plate plane of the first and/or the second separator plate. These two separator plates are usually joined to each other, for example by welding. If cooling is required, it is possible to pass a coolant between the separator plates. However, such cooling is often not required, such as in the case of electrolyzers.
Each of the separator plates, and thus also the bipolar plate, has an active region which comprises structures, such as embossed channels, for guiding a reaction medium along the outer side of the bipolar plate. These structures are usually designed as flow channels, through which gaseous or also liquid reaction media and reaction products can be passed. These reaction media are supplied to the active region from a through-opening in the respective separator plate via a distribution region. Remaining reaction medium and reaction products are correspondingly discharged via a collection region and a through-opening in the respective separator plate. The distribution regions and/or collection regions also usually have, as fluid-guiding structures, flow channels designed as grooves which are separated from each other by webs. The rear sides of the grooves and webs of the two separator plates span the flow area for coolant in the interior of the bipolar plate.
Adjacent to the through-opening, the two separator plates are arranged bearing directly against each other in a contact plane and are joined to each other in places, such as by welding, for example by welding in a media-tight manner, in order to mechanically support the two separator plates and to seal between the two separator plates. Furthermore, in conventional bipolar plates, the two separator plates are often also joined to each other in the distribution and/or collection region, for example by means of welded joints which, on account of the coolant being guided between the two separator plates, extend only over short sections in order to only minimally impede the coolant flow.
When forming a ready-to-use stack, a membrane electrode assembly is provided between adjacent bipolar plates, which membrane electrode assembly, in the flow region, separates the channels for the passage of the reaction medium in a first bipolar plate from the channels for the passage of another reaction medium in a second bipolar plate, said second bipolar plate being separated from the first bipolar plate only by the membrane electrode assembly. The membrane electrode assembly, typically abbreviated as MEA, extends beyond the active region into the distribution region and possibly the collection region.
In its active region, the MEA usually comprises the actual proton-conducting membrane and the electrodes and catalyst layers applied thereto, to which conductive and gas-permeable layers, so-called gas diffusion layers (GDLs), are applied. In its edge region, the MEA usually comprises a polymer-based film material, which surrounds the active region and in a narrow overlap region overlaps with the materials forming the active region, or with some of these materials, e.g. possibly not with the GDLs. In a stack of an electrochemical system, the MEA defines the spacing between the separator plates. At the same time, gas diffusion layers (GDLs) exhibit relatively large fluctuations in terms of their thickness.
Therefore, usually just enough space is provided between bipolar plates in the thickness direction of the stack that, on the one hand, there is sufficient space in the active region to accommodate the relevant section of the MEA and, on the other hand, there is just enough space for defined compression of this section of the MEA. As a result, more space is sometimes reserved in the distribution and collection region than would in fact be necessary for the latter to function. If an MEA has an above-average thickness in the active region, this results in a lot of installation space in the distribution or collection region; if the MEA has a below-average, thin active region, this results in little installation space in the distribution or collection region. In the case of conventional plates, therefore, the bipolar plates are designed in such a way that the separator plates thereof partially come to bear against each other both in the active region and in the distribution or collection region and are at least partially welded to each other in these regions. However, pressure fluctuations in the coolant passed between the bipolar plates of a stack cause the separator plates to move relative to each other and expose the joints between the separator plates of a bipolar plate, for example welded joints in the distribution or collection region; for instance, if the spacing between mutually closest bipolar plates may be large in the region of the distribution or collection region, dynamic pressure fluctuations and loads occur which may lead to breakage of the welded joint and possibly even to perforation of one of the separator plates at the damaged joint.
An object of the present disclosure is therefore to provide a bipolar plate and assemblies containing the latter, in which thickness fluctuations of the membrane electrode assembly, for example of at least one of the gas diffusion layers thereof, have no destructive effect, or only a minor destructive effect, on the bipolar plate, such as during dynamic operation.
This object and others are achieved by embodiments of bipolar plates and systems comprising bipolar plates described herein.
The bipolar plate according to the present disclosure is suitable, inter alia, for an electrochemical system, such as for an electrolyzer, a fuel cell, an electrochemical compressor, or a redox flow battery.
It comprises at least a first and a second separator plate, which are arranged adjacent to each other in a direction perpendicular to the plate plane of the first and/or the second separator plate. In a plan view of this assembly of the two separator plates, each of the separator plates has at least two through-openings for passing a respective reaction medium through the separator plate. Typically, however, the separator plates have up to six such through-openings, via which two different reaction media and optionally a cooling fluid can be supplied and these two reaction media and/or the reaction products thereof and also the cooling fluid can also be discharged again; sometimes even more than two through-openings are provided for a medium. The following description refers to the aforementioned at least two through-openings for two different reaction media, for example for supplying the latter. However, one, some or all of the additional through-openings in the separator plates for discharging the reaction media or for supplying or discharging other media, and regions adjacent thereto, such as distribution regions or collection regions, may be designed in the same way.
Furthermore, the separator plates have an active region with structures for guiding a reaction medium along the surface of the separator plate that is located on the outer side of the bipolar plate. Different reaction media are guided through the active region on the outer side of each of the two separator plates, wherein in each case one of the two through-openings in the separator plates is used to supply or discharge one of the reaction media to or from the outer side of one of the separator plates.
For each of the separator plates, therefore, the reaction medium is guided on the outer side of the bipolar plate according to the present disclosure. In other words, on the two outer sides of the bipolar plate, flow channels are formed in each of the separator plates, for example by embossing, in each of which flow channels a reaction medium from one of the through-openings can be guided. The electrochemical reaction intended to take place in the electrochemical system between the reaction media separated by the MEA takes place in this active region; more precisely, protons pass through the MEA and thus enable the electrochemical reaction.
Furthermore, each of the separator plates has a distribution or collection region with structures for guiding the reaction medium from one of the aforementioned through-openings to the active region or from the active region to the through-opening. By way of example, as structures for guiding the reaction medium in the distribution or collection region, flow channels arranged on the outer side of the bipolar plate are provided for the reaction medium. If the bipolar plate or the separator plates thereof have additional through-openings with adjacent distribution regions or collection regions, these distribution regions or collection regions may also be designed in the same way as the distribution region described below. While the through-openings are arranged next to each other in a plan view of a bipolar plate, the distribution regions or collection regions at least partially overlap and extend in different planes. Bipolar plates usually have two areas in which distribution or collection regions overlap; in the case of fuel cells, usually three media systems are separated from each other in the distribution or collection regions, but are routed spatially one above the other in the stacking direction.
The present disclosure will be described below on the basis of a distribution region which is fluidically connected to one of the through-openings. However, whenever a distribution region is mentioned below, this could also be a collection region instead of a distribution region.
The channels in the distribution region are designed as grooves which are formed in the respective separator plate, for example by embossing, said grooves being separated from each other by corresponding webs which project towards the outside of the bipolar plate. The channels in the distribution or collection region of the separator plate of a bipolar plate may extend parallel to each other, at an angle to each other, in a manner curved by different radii to each other, or in a manner arranged completely randomly in relation to each other. The same applies when considering individually the other separator plate of the bipolar plate. For instance, the channels of the distribution region of the separator plate under consideration may extend as a set in parallel with each other over large areas of the distribution region; however, when the structures of a distribution region are projected into a common plane with an adjacent distribution region containing the set, channels of the adjacent distribution or collection region of the other separator plate of the bipolar plate may extend thereacross, for example at a positive angle.
The problem that arises when the installation space available between the reinforcing edges of different cells in the area of a distribution or collection region differs greatly in the thickness direction in order to compensate for any fluctuations in the MEA thickness in the active region, as described above, is now solved by the present disclosure in that the distribution or collection regions of at least one of the two separator plates, possibly even of each of the two separator plates, has/have at least one compensating region in which flow channels may be formed in a way. If compensating regions are provided in both separator plates, these compensating regions need not be arranged congruently in a plan view looking toward the plane of the bipolar plate. However, these compensating regions may at least partially overlap. For instance, a pairwise arrangement of partially or completely overlapping compensating regions of adjacent separator plates is advantageous. In principle, however, it is also possible to form the entire compensating region in just one separator plate.
According to the present disclosure, the flow channels in the compensating regions are designed in such a way that, in the non-compressed state, the rear sides of the channel bottoms of the flow channels of the separator plate are spaced apart from the rear sides of the channel bottoms of the flow channels of the adjacent separator plate. Here, the rear side is in principle considered to be that surface or place on a separator plate that does not face outwards in the bipolar plate, but rather is located in the interior of the bipolar plate. Usually, oxidizing agents and reducing agents and reaction products thereof are guided on the outward-facing surfaces of a bipolar plate, while cooling medium is guided in the interior, e.g. on the rear side of the separator plates. Given a substantially constant material thickness, a smallest possible spacing from the adjacent separator plate of the bipolar plate on the rear side is formed by those regions which, on the outer side, form the deepest regions of the respective channels or channel bottoms.
Since, in the region of the channel bottoms of the flow channels, the separator plates do not bear directly against each other in the compensating regions in the unassembled state, this results in a spacing between the two separator plates in the overlapping areas in the compensating region, by virtue of which it is possible to compensate for thickness fluctuations in a membrane electrode assembly.
This applies both in overlapping and in non-overlapping sections of the compensating regions, since in both cases the two separator plates are spaced apart from each other there in the unassembled state.
In the present disclosure, the expression “in the unassembled state” refers to the fact that the bipolar plate has not yet been compressed for final assembly of an electrochemical system. This means that a single bipolar plate may be in the unassembled state. However, this also applies to the bipolar plates in a stack of bipolar plates arranged one above the other, provided that the stack has not yet been compressed.
The channel bottoms may be straight or curved in cross-section, for example curved in a convex or concave manner.
Formed between the separator plates of a bipolar plate, outside of the compensating regions, is a contact plane at which the separator plates bear directly against each other with their rear sides/inner sides. This may take place in the area of sealing beads, which are intended to seal between the separator plates in a fluid-tight manner where necessary. The contact plane is formed in the region of the bead feet, e.g. directly adjacent to the sealing bead. Such sealing beads may be, for example, sealing beads around the through-openings, or a bead extending around the entire bipolar plate at its outer edge, a so-called perimeter bead. Adjacent to edge flanks of the distribution region, the separator plates may likewise come to bear partially against each other and form a contact plane.
At least in the non-compressed state, e.g., in the so-called “unassembled” state, the bipolar plate according to the present disclosure creates a free gap between the channel bottoms of adjacent separator plates in the at least one compensating region, which gap serves for tolerance compensation of thickness fluctuations of a membrane electrode assembly. For instance, this prevents the adjacent separator plates from being in the main line of force in the compensating regions when compressing a stack of bipolar plates. For example under dynamic loads, as occur for example and, for instance, when a coolant is introduced between the separator plates of a bipolar plate during operation, the risk of destruction of the bipolar plate is thereby reduced, while the latter is still inexpensive to manufacture and of simple design. According to the present disclosure, the compensating region in a separator plate may extend over the entire distribution region or else only over part of the distribution region, both transversely to the direction of extension of the flow channels in the distribution region and along the extension of the flow channels in the distribution region.
If the compensating region extends over only part of the distribution region, such as only over a section of the distribution region transversely to the direction of extension of the flow channels, one or more channels of the distribution region that are not part of the compensating region may not be set back from the contact plane, e.g. the rear side of the channel bottoms thereof may not be spaced apart from the contact plane, so that the rear sides of their channel bottoms bear against each other and rest against each other in the contact plane. The webs delimiting one or more of these channels may also have a deeper embossing on the gas side of the distribution region than the embossing of the channels in the compensating region. For instance, the web delimiting this or these channels towards the compensating region may have a deeper embossing. This design of the channels and webs in the distribution region adjacent to the compensating region enables the compensating region to act as a bending beam with a lateral through these channels and webs adjacent to the compensating region, and to create an elastic support effect to prevent the distribution region from collapsing at excessive gas pressures.
As an alternative or in addition, the compensating region may for example extend over a length L, where L≥50% of the length of a flow channel or advantageously L≥75% of the length of a flow channel. The compensating region may in this case extend from the area around a through-opening, such as from a sealing structure surrounding the through-opening, for example a weld seam or a sealing bead or an elastomer bead, into the distribution or collection region.
If, in the flow direction, the compensating region starts directly at one of the edges of the distribution region, the flow channels in the compensating region may be designed to be less deep than the outermost flank of one or both of the two outermost flow channels, the outermost flank or the outermost flow channel being considered in such a way that “outermost” is considered in the direction perpendicular to the direction of extension of the flow channels in the distribution region, possibly the direction of extension of at least one flow channel if the flow channels are not parallel. In other words, in this case, the transition from the channel bottom rear side plane to the contact plane between the adjacent separator plates takes place in the edge area of the flow region. Advantageously, the depth of the flow channels in the compensating region may be less deep, by 30 to 150 μm, than the height of the outer flank of one or both of the two outermost webs of the distribution region and/or than the height of a sealing structure surrounding the through-opening. Since the outermost web or the sealing structure defines the contact plane, the result is that, according to the present disclosure, the rear sides of the bottoms of the flow channels do not bear against each other in the compensating regions of the two separator plates in the non-compressed state. What is not meant here, however, is the transition regions in which the channels and/or webs extend out of the plate plane at the start or end of the flow channels—as viewed in the flow direction—e.g. the plate material is shaped out of the plate plane in order to form the channels, and consequently the rear sides of the bottoms of the flow channels also do not bear against each other in these transition regions.
The sealing structures may together have a height HD* between the outward-facing surfaces of the separator plates of the bipolar plates, where HD*≤1200 μm, in the individual separator plates such as 400μm≤HD≤600 μm in the unassembled state of the bipolar plate, and/or where HD*≤1140 μm, for example 330 μm≤HD≤570 μm, in the state compressed under the final assembly pressure. The first-mentioned number HD* (1200 μm or 1140 μm) may relate to the sealing elements of a bipolar plate; the next-mentioned numerical ranges HD may relate to the sealing elements in separator plates, e.g. such as single-layer plates.
The present disclosure additionally relates to an assembly of bipolar plates, comprising at least two bipolar plates, wherein the two bipolar plates are arranged adjacent to each other in a direction perpendicular to the plate plane, with the interposition of a reinforcing edge of a membrane electrode assembly. This perspective enables the MEA to be considered as the center of a unit within a fuel cell stack, whereas the previous perspective considers the bipolar plate as the center of a unit. When considering the MEA as the center of a unit, the bipolar plates adjacent thereto may be designed in such a way that they each have a sealing structure surrounding the through-opening, said sealing structures being arranged adjacent to each other in a direction perpendicular to the plate plane and sealing between the two bipolar plates. Here, the two sealing structures of the mutually facing separator plates of the first and second bipolar plate together have a total height HG, where 800 μm≤HG≤1200 μm in the unassembled state of the separator plate, and/or where 660 μm≤HG≤1140 μm in the state compressed under the final assembly pressure. This height is given as the height spanned between the sealing structures, minus the thickness of the MEA.
To seal between adjacent bipolar plates, sealing structures may also be provided on the outer surfaces of the separator plates, for example elastomer seals or beads integrally formed in the separator plate. In the assembled state, these then provide sealing between adjacent bipolar plates in a fluid-tight manner, such as towards the reinforcing edge of the MEA, for example circumferentially around through-openings in an intrinsically closed fashion.
A bipolar plate assembly according to the present disclosure comprises at least two of the above-described bipolar plates according to the present disclosure, which are arranged adjacent to each other, wherein located between these is a membrane-electrode assembly, the reinforcing edge of which is gripped by the two bipolar plates.
When a stack of alternately arranged bipolar plates and MEAs is compressed, the compensating regions formed in the separator plates of the bipolar plates can absorb and compensate for thickness fluctuations of the membrane electrode assembly.
Since adjacent separator plates of a bipolar plate do not come into contact with each other in the compensating regions in the unassembled state, e.g. the separator plates are not joined in a materially bonded manner in the compensating regions, dynamic loads in the compensating regions also do not lead to destruction of the separator plates and thus of the bipolar plate.
Examples of bipolar plates according to the present disclosure and of bipolar plate assemblies according to the present disclosure will be given below. Here, identical and similar elements of the separator plates and bipolar plates and assemblies will be provided with identical or similar reference signs, and therefore the description thereof will not always be repeated. The following examples include the features according to the present disclosure together with one or more optional enhancements or developments according to the present disclosure. However, it is possible also to use individual elements of these improvements and developments independently of the other elements of the respective examples or also in combination with some of the other elements of the same example or of other examples and to further improve the present disclosure as a result.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
Alternatively, the system 1 shown in
The z-axis 7, together with an x-axis 8 and a y-axis 9, spans a right-handed Cartesian coordinate system. The bipolar plates 2 each define a plate plane E (cf.
The separator plates 2a, 2b have through-openings, which are aligned with each other and form through-openings 11a-c of the bipolar plate 2. When a plurality of bipolar plates of the same type as the bipolar plate 2 are stacked, the through-openings 11a-c together with aligned through-openings in the reinforcing edges of the MEAs form lines which extend through the stack 6 in the stacking direction 7 (see
In order to seal off the through-openings 11a-c with respect to the interior of the stack 6 and with respect to the surrounding environment, the first separator plates 2a may each have sealing arrangements in the form of sealing beads 12a-c, which are arranged in each case around the through-openings 11a-c and in each case completely surround the through-openings 11a-c. On the rear side of the bipolar plates 2, facing away from the viewer of
In an electrochemically active region 18, the first separator plates 2a have, on the front side thereof facing towards the viewer of
In such a conventional bipolar plate, the two separator plates 2a and 2b bear directly against each other and support each other in the region of the bottoms of the channels in the distribution regions 20. The two separator plates 2a and 2b are usually joined to each other at contact points in the distribution regions 20, such as by welding.
The sealing beads 12a-12c have passages 13a-13c which serve to pass media through the sealing beads. By way of example, the passages 13a enable coolant to pass between the through-opening 12a and the distribution region 20, so that the coolant enters the distribution region between the separator plates and is guided out therefrom. Furthermore, the passages 13b enable hydrogen to pass between the through-opening 12b and the distribution region on the upper side of the upper separator plate 2a. The passages 13c enable air, for example, to pass between the through-opening 12c and the distribution region 20, so that air enters the distribution region 20 on the underside of the lower separator plate 2b and is guided out from this distribution region 20. The through-openings 11a or the lines through the plate stack of the system 1 that are formed by the through-openings 11a are in each case fluidically connected to each other via a cavity 19 which is enclosed by the separator plates 2a, 2b. If necessary, this cavity 19 can serve to guide a coolant through the bipolar plate 2, for example in order to cool the electrochemically active region 18 of the bipolar plate 2.
The first separator plates 2a each also have a further sealing arrangement in the form of a perimeter bead 12d, which extends around the flow field 17 of the active region 18 and also around the distribution or collection region 20 and the through-openings 11b, 11c and seals these off with respect to the through-opening 11a, that is to say with respect to the coolant circuit, and with respect to the environment surrounding the system 1. The second separator plates 2b each comprise corresponding perimeter beads 12d. In alternative plate designs, the perimeter bead may also enclose the coolant openings and thus the entire coolant circuit. The structures of the active region 18, the webs and channels of the distribution or collection region 20 and the sealing beads 12a-d are each formed in one piece with the separator plates 2a and are integrally formed in the separator plates 2a, for example in an embossing, deep-drawing or hydroforming process. The same applies to the corresponding distributing structures and sealing beads of the second separator plates 2b.
For instance in the case of a fuel cell, the separator plates 2a, 2b of the bipolar plate 2 may each be formed, for example, from a stainless steel sheet having a thickness of less than 100 μm. In the case of an electrolyzer, it is possible to use either sheets made of a titanium alloy or sheets made of fully coated stainless steel. The sheet thicknesses are usually greater in electrolyzers; for example, they can be 100-800 μm, 150-500 μm, for example 200-300 μm. The bipolar plate 2 usually has a substantially rectangular shape, but it may also be round or oval, such as in the case of electrolyzers.
In the embodiment of
Using the uppermost bipolar plate 2 in the drawing as an example, the structure of the bipolar plate will now be explained. This is identical for the adjacent bipolar plates.
The bipolar plate 2 comprises two separator plates 2a and 2b, which are arranged adjacent to each other. These each have a sealing bead 12b and 12b′ surrounding the through-opening 11b, the sealing beads being designed as full beads and surrounding the through-opening 11b in an intrinsically closed manner. The two separator plates 2a and 2b are joined by means of a weld seam 14′ around at least part of the circumference surrounding the full beads 12b, 12b′. A welded joint 14″, which likewise joins the separator plates 2a and 2b, also extends between the perimeter bead 12d and the embossment 25 on the outer edge 24 of the bipolar plate 2.
Arranged between the sealing bead 12b and the active region 18 is the distribution region 20, in which webs 21 and channels 22 are formed by embossing. At the base of the channels 22, the adjacent separator plates 2a and 2b are welded to each other at weld spots 14. In the separator plate 2a shown at the top in
If coolant is not just introduced into the intermediate space 19 between the separator plates 2a and 2b, but rather is introduced at greatly fluctuating pressures depending on other operating parameters, then the separator plates, if not fixed to each other by means of welded joints 14 as in
Conventional designs also have the problem that, due to the distance between the MEA reinforcing edge 16 and the webs 21 of the distribution or collection region 20, the MEA reinforcing edge 16 does not have any defined support and therefore may flutter.
The embodiment of
It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. Moreover, unless explicitly stated to the contrary, the terms “first,” “second,” “third,” and the like are not intended to denote any order, position, quantity, or importance, but rather are used merely as labels to distinguish one element from another. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.
As used herein, the term “approximately” or “substantially” is construed to mean plus or minus five percent of the range unless otherwise specified.
The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20 2022 103 147.9 | Jun 2022 | DE | national |
