Electrochemical cell with a capacitor, as well as electrochemical system

Abstract

Electrochemical cell (25) comprising a first separator plate (2a), a second separator plate (2b) and a capacitor (30) which is designed to store and release electrical energy, wherein the capacitor (30) is arranged between an outer edge region (14) of the first separator plate (2a) and an outer edge region (15) of the second separator plate (2b), wherein the first separator plate (2a) has a first holding structure (21) for holding the capacitor (30) and / or the second separator plate (2b) has a second holding structure (22) for holding the capacitor (30).

Description

The present invention relates to an electrochemical cell comprising a first separator plate, a second separator plate and a capacitor which is configured to store and emit electrical energy. The invention further relates to an electrochemical system comprising a plurality of stacked electrochemical cells. The electrochemical system can be, in particular, a fuel cell stack or an electrolyser.Fuel cells, in particular fuel cells in PEM technology, which are stacked to form fuel cell stacks having a multiplicity of individual cells, are used, for example, for generating electrical drive power in motor vehicles, such as, for example, passenger cars, commercial vehicles, and also in ships and aircraft. However, the window of suitable operating conditions under which a fuel cell operates optimally is quite narrow. On the other hand, the fuel cells should also be able to bypass rapid load changes and power peaks, particularly in mobile applications.Depending on the operating point, fuel cell stacks require very different volumes of reaction gases and coolant. Fuel cell stacks are advantageously operated in a controllable manner with regard to their medium supply. Reaction times of the fans or pumps supplying the media cannot be avoided, however. Components which are substantially more agile than those currently used are currently not available at reasonable costs. This is tried by designing the fluid volumes according to the response time of the system in order to avoid a harmful undersupply of H 2 or O 2 and to be able to safely remove the increased amount of heat. Frequently, a targeted excess of oxygen is provided which is greater than the excess of hydrogen with respect to the respective operating point. On the other hand, with regard to the component weight to be transported in mobile applications and the costs associated therewith, it is not expedient for the system or its components, in particular pumps and / or fans for the media, to be designed such that they are also designed for the most extreme operating conditions. Therefore, it may occur that if a strongly increasing power is demanded by the system, in a range in which a sufficiently high hydrogen concentration was still present beforehand, the amount of hydrogen present or flowing in no longer suffices as reaction partner for the oxygen supplied on the other side of the PEM. An alternative reactant is then, for example, carbon which serves as a support for the electrochemical catalysts of the fuel cell. The PEM or the carbon support is damaged in this case; in the worst case, perforations of the membrane as such can occur. The catalyst itself, usually predominantly platinum, can also be damaged, for example the surface area available for the catalytic reaction can be reduced or the catalyst can be oxidized. However, it has been shown that often very much larger amounts of media are required only for a limited time.DE 10 2020 007 106 A1 proposes a fuel cell stack having a multiplicity of individual cells which are stacked separately from one another via bipolar plates. In this case, it is provided that the individual cells have a photoelectric voltage generator assigned to them, wherein at least one light source for generating voltage is provided via the photoelectric voltage generators, wherein a sacrificial external current anode can be realized if required via the generated voltage. By way of the effect of an optocoupler, energy can be fed into each of the individual cells of the fuel cell stack in the reverse application. This is independent of the operation of the fuel cell stack. The corresponding voltage can be generated via a light source, if necessary, via the photoelectric voltage generators. As a result, a sacrificial external current anode can be formed in each of the individual cells of the fuel cell stack by generating a voltage during an air / air start via the photoelectric voltage generators and a suitable light source, said voltage counteracting the voltage forming the corrosion potential for the carbon-containing supports of the catalysts. The corrosion can thus be avoided or at least reduced.A disadvantage of this solution is that a plurality of light sources must be provided in order to supply all photoelectric voltage generators in the fuel cell stack with light energy. These light sources must be wired and maintained in the event of service, as a result of which this solution does not necessarily seem practical.The present invention has been devised to solve at least partially the above-described problems and is defined by the subjects of the independent claims. Further developments of the invention are described in the dependent claims and in the following description.According to a first aspect of the present specification, an electrochemical cell is proposed. The electrochemical cell comprises a first separator plate, a second separator plate and a capacitor which is configured to store and emit electrical energy. Here, the capacitor is disposed between an outer edge portion of the first separator plate and an outer edge portion of the second separator plate. Furthermore, the first separator plate has a first holding structure for holding the capacitor and / or the second separator plate has a second holding structure for holding the capacitor.The capacitor makes available a short-term, quickly available power reserve which can emit electrical power during load changes during operation of the electrochemical cell. As a result, for example, the electrochemical system can be dimensioned smaller than conventional electrochemical systems, which are usually designed for a maximum possible load and are thus oversized. Alternatively and / or additionally, particularly expensive agile components can be dispensed with. Moreover, damage to the membrane electrode unit (MEA) or the catalyst can be at least reduced, so that the system provides improved durability.It can be provided that the named holding structures are designed as embossed structures formed into the respective separator plate. The embossed structures can be formed into the separator plate, for example, in the same working step together with other embossed structures, such as channel structures and / or sealing beads. As a result, no additional working steps are necessary in order to form the holding structures.At least one of the holding structures can define a receiving region for the capacitor, wherein the active region of the capacitor and / or the receiving region are laterally delimited by at least one formation formed in the respective separator plate. What is to be limited here is that the capacitor cannot be moved further than the shaping. Lateral tolerances between the capacitor and the shaping can be present here. The shaping can be configured to be circumferential, so that only one circumferential shaping is present; however, a plurality of shapings spaced apart from one another can also be provided. The formation can be designed in some areas as a full bead and / or half bead. The active region of the capacitor forms the region of the capacitor where charge or electrical energy is actually stored and / or discharged again. The receiving region can be further bounded by a bottom surface in the respective separator plate. The bottom surface can extend along or parallel to a separator plate plane, but does not necessarily have to be designed as a planar surface itself, see also below.In some embodiments, at least one of the support structures includes at least one spring structure that is spring-elastic configured to clamp the capacitor. At least one of the spring structures may have a wave-shaped section, for example. The wave-shaped section can extend between the formations and / or along the said bottom surface. Furthermore, the wave-shaped section can have a lower maximum height than the formations. The height is measured perpendicular to the separator plate plane of the first and second separator plates. It can further be provided that at least one of the holding structures is further configured for electrically contacting the capacitor. In particular, the at least one of the spring structures can be designed as a clamping contact. The associated corresponding holding structure has a dual function (holding and electrically contacting) in this case, as a result of which additional elements can be dispensed with. The electrical contacting of the capacitor with the two separator plates can alternatively also be realized by suitable, additional electrical contacts.It can be provided that the first holding structure has first supporting structures and the second holding structure has second supporting structures, wherein the first supporting structures and the second supporting structures typically face one another. In one embodiment, a part of the capacitor is held in position between the mutually facing support structures. For example, a passive region of the capacitor, e.g. a protruding collar of the capacitor, a lateral extension of the capacitor or a line of the capacitor, is clamped or held between the supporting structures. Furthermore, the supporting structures are generally electrically insulated from one another. The electrical insulation can be effected, for example, by a protruding passive, in particular an electrically insulated region of the capacitor or can be realized by means of an insulating coating, which may only be partial, of the first separator plate and / or of the second separator plate.The energy stored in the capacitor may be generated by electrochemical processes in the electrochemical cell. In this case, the electrochemical cell can operate independently of external current sources. Additionally or alternatively, the capacitor can also be charged by a current source from outside the cell, for example before startup, at standstill or else only for absorbing an energy surplus. As soon as the voltage in the electrochemical cell drops below the potential difference of the capacitor, the capacitor can equalize the voltage drop by electron flow in the direction of the electrochemical cells. The capacitor releases the stored energy as electrical energy back to the electrochemical cell. The capacitor of an electrochemical cell is advantageously adapted to the delays in the system and the additional energy required as a result. The capacitor may be or comprise, for example, an electrochemical double layer capacitor, in particular a supercapacitor. The energy stored in the capacitor itself can be electrical energy in the form of an electrical potential or also chemical / electrochemical energy. Batteries, accumulators and conventional capacitors are to be distinguished from this, all of which are based on other memory technologies. However, the differences between the energy stores mentioned are known to a person skilled in the art, for which reason a detailed description is omitted here. Supercapacitors in particular can react very quickly to load changes and thus reduce or minimize the dynamic load on the electrochemical cell. A comparable electrochemical cell, which is intended to dampen the load changes instead of a supercapacitor with a battery, would be significantly larger and heavier with the current battery technology, given the same capacity and dynamics. In addition, power consumption in supercapacitors can be significantly faster compared to batteries.In contrast to batteries, no chemical reactions take place in double layer capacitors during charging and discharging. The main difference between conventional capacitors and supercapacitors is that the latter can store much more energy per volume. This is made possible by the porous surface structure (A) of the electrodes and the dissolved ions in the organic electrolyte and the resulting very small distance (d) of the Helmholtz layer. The basis of the functional principle is charge separation at two electrodes. Besides the two electrodes, a cell of the supercapacitor usually comprises a separator and an electrolyte. The electrodes are usually made of activated carbon, which has been applied to an aluminum support with a thickness of between 100 and 200 μm. Electrode thicknesses in the nm and μm range are reported in the literature. Due to the high surface area of the activated carbon, many ions can be adsorbed. The activated carbon is often bound by a polymer, the aim here is to hold the particles together and to attach them to the substrate without impairing the porosity. Graphite, conductive polymers and silicon dioxide have been tested as additives. As the electrolyte, acetonitrile is most frequently used as the solvent and tetraethylammonium borofluoride (dissolved salt). The separator serves as a separating material and should be mechanically stable, avoid a potential short circuit of the electrodes, and enable good ion transport. Due to these requirements, polyolefin, paper or fabric impregnated in the electrolyte is frequently used.During charging, the ions present in the electrolyte are attracted and aligned by an electric field from the electrodes. Such a double layer is also called a Helmholtz layer. Positive and negative ions are present in the electrolyte, which are provided by dissociation of the salt dissolved in the electrolyte and which are respectively attracted to the negative and positive electrodes. There is no change in the composition or phase transformation of the active materials. As a result, supercapacitors achieve cycle lives that are higher by two to three orders of magnitude compared to lithium-ion batteries. Designs are cylindrical cells, prismatic cells and PouchAg cells.Furthermore, the first separator plate and / or the second separator plate can have a sealing arrangement for sealing a fluid-conducting region of the respective separator plate. The respective separator plate can further have channel structures for guiding a fluid, for example in the fluid-guiding region. The outer edge region of the respective separator plate can adjoin the sealing arrangement. It should be noted here that at least one holding region defined by the holding structures or the named receiving region is provided outside the sealing arrangement, i.e. between the outer edge and the sealing arrangement. The sealing arrangement and the above-mentioned formations can merge into one another in some embodiments.The receiving region can be formed in a region of the separator plates which protrudes laterally from the electrochemical cell. For example, the separator plates each comprise a protrusion in which the receiving region is formed. Alternatively, it is possible to form the receiving region within an otherwise substantially rectangular surface of the respective separator plate.The outer edge region of the first separator plate and / or the outer edge region of the second separator plate, between which the capacitor is held, is advantageously formed integrally with the first separator plate and / or integrally with the second separator plate. This gives the system higher stability and avoids additional manufacturing steps. Alternatively, the outer edge region can also be connected to the respective separator plate, for example by means of welded connections. This makes it possible to avoid excessive waste in the case of unfavourable overall geometries.Often, the first separator plate is a cathode plate and the second separator plate is an anode plate, or vice versa. The electrochemical cell can also have units known per se, such as a membrane electrode arrangement (MEA) with an electrochemically active membrane together with associated catalyst layers and a frame-shaped reinforcing layer and / or at least one gas diffusion layer, which extend in a planar manner between the two separator plates.According to a further aspect of the present specification, an electrochemical system is proposed which comprises a multiplicity of stacked electrochemical cells of the type described above. Capacitors of adjacent cells can be offset in a direction perpendicular to the stacking direction, in particular arranged alternately, with respect to one another or arranged one above the other in the stacking direction. For the purposes of this specification, adjacent is intended to mean directly adjacent, i.e. without intermediate cell, or indirectly adjacent, so that a further cell can also be arranged between indirectly adjacent cells.The energy stored in the capacitors of the electrochemical system can be generated in particular by electrochemical processes in the electrochemical system itself.The electrochemical system may be a fuel cell stack or an electrolyser.The electrochemical cell may be a fuel cell. However, it can also be a cell of an electrolyser, in particular of a PEM electrolyser. If the separator plates which delimit two cells with respect to one another are configured in two layers in an electrolyser, the foregoing applies directly. If, however, the separator plates which delimit two cells with respect to one another in an electrolyser are of single-layer configuration, the two separator plates which, according to the invention, are assigned to an electrochemical cell belong not only to this one cell, but each of these separator plates belongs to the two cells which delimit them with respect to one another. While stainless steel is preferably used as the material for the separator plates in fuel cells, titanium may be preferred in electrolysers.Exemplary embodiments of the electrochemical cell and of the electrochemical system are illustrated in the appended figures and are explained in more detail with reference to the following description. The following are shown: FIG. 1 is a schematic perspective illustration of an electrochemical system having a plurality of separator plates or bipolar plates arranged in a stack; FIG. 2 is a schematic perspective illustration of two bipolar plates of the system according to the prior art, which bipolar plates consist of two separator plates and have a membrane electrode arrangement (MEA) arranged between the bipolar plates; FIG. 3A is a plan view of a separator plate that is part of an electrochemical cell, according to an embodiment; FIG. 3B is a sectional view along section A-A of FIG. 3A through a portion of an electrochemical cell; FIG. 4A is a plan view of a separator plate which is part of an electrochemical cell according to a further embodiment; FIG. 4B is a sectional view taken along section B-B of FIG. 4A through a portion of an electrochemical cell; FIG. 5A is a plan view of a separator plate which is a component of an electrochemical cell according to a further embodiment; FIG. 5B is a cross-sectional view taken along section C-C of FIG. 5A through a portion of an electrochemical cell; FIG. 5C is a cross-sectional view taken along a section similar to the section D-D of FIG. 5A through a portion of an alternative embodiment of an electrochemical cell; FIG. 6 shows a sectional illustration of an alternative embodiment of an electrochemical cell, in which only one of the two separator plates delimiting the cell has a holding structure for a capacitor; FIG. 7 shows a schematic illustration of an outer contour of a separator plate; and FIG. 8 shows a schematic illustration of an outer contour of a further separator plate.Here and in the following, recurring features in different figures are each denoted by the same or similar reference numerals. In part, for the sake of clarity, the repeated use of reference symbols in subsequent figures is omitted.FIG. 1 shows an electrochemical system 1 having a plurality of identically constructed metallic bipolar plates 2 which consist of separator plates 2 a, 2 band together with membrane electrode units 10 and gas diffusion layers form electrochemical cells 25 which are arranged in a stack 6 and are stacked along a z-direction 7. The bipolar plates 2 of the stack 6 are clamped between two end plates 3, 4. The z-direction 7 is also called the stacking direction. In the present example, the system 1 is a fuel cell stack. Two separator plates 2 a, 2 b, which are closest to one another, of two adjacent bipolar plates 2 of the stack each delimit an electrochemical cell 25, which serves, for example, for the conversion of chemical energy into electrical energy. To form the electrochemical cells 25 of the system 1, a membrane electrode unit (MEA) 10 is arranged in each case between adjacent bipolar plates 2 of the stack, which is sometimes also called a membrane electrode arrangement. The MEAs typically each include at least one membrane, e.g., an electrolyte membrane. Furthermore, a gas diffusion layer (GDL) may be arranged on one or both surfaces of the MEA, not shown in FIGS. 1 and 2.In alternative embodiments, the system 1 can likewise be designed as an electrolyser. Separator plates can likewise be used in this case. The structure of these separator plates can then correspond to the structure of the separator plates 2 a, 2 b, explained in more detail here, even if the media guided onto or through the separator plates in an electrolyser can respectively differ from the media used for a fuel cell system.The z-axis 7 together with an x-axis 8 and a y-axis 9 span a right-handed Cartesian coordinate system. The separator plates 2 a, 2 bdefine a plate plane at their contact plane, wherein the plate planes are each aligned parallel to the x-y plane and thus perpendicular to the stacking direction or to the z-axis 7. The end plate 4 has a plurality of media connections 5, via which media can be supplied to the system 1 and via which media can be discharged from the system 1. These media that can be supplied to the system 1 and discharged from the system 1 can comprise, for example, fuels such as molecular hydrogen or methanol, reaction gases such as air or oxygen, reaction products such as water vapor or depleted fuels or coolants such as water and / or glycol. In this case, gases are frequently supplied by means of blowers and / or compressors, while the supply of coolant is usually effected with the aid of at least one pump.FIG. 2 shows in perspective two adjacent bipolar plates 2 of an electrochemical system of the type of the system 1 from FIG. 1 and a membrane electrode unit (MEA) 10 known from the prior art arranged between these adjacent bipolar plates 2, wherein the MEA 10 in FIG. 2 is covered for the most part by the separator plate 2 facing the observer. The bipolar plate 2 is formed from two separator plates 2 a, 2 bassembled together in a materially bonded manner (see, for example, FIG. 3 ), of which only the first separator plate 2 afacing the observer is visible in FIG. 2, and covers the second separator plate 2 b. The separator plates 2 a, 2 bmay each be manufactured from a metal sheet, e.g. from a stainless steel sheet. The separator plates 2 a, 2 bmay be welded to one another, for example, by laser welding connections. Two separator plates 2 a, 2 b, which are closest to one another, together with the MEA 10 and any GDLs present, but not shown here, form an electrochemical cell 25.The separator plates 2 a, 2 bhave through-openings which are aligned with one another and form through-openings 11 a- cof the bipolar plate 2. When stacking a plurality of plates of the bipolar plate 2 type, the through-openings 11 a- cform lines that extend through the stack 6 in the stacking direction 7 (see FIG. 1 ). Typically, each of the conduits formed by the through openings 11 a- cis each in fluid communication with one of the ports or media ports 5 in the end plate 4 of the system 1. The lines formed by the through openings 11 b, 11 c, on the other hand, can be designed to supply the electrochemical cells 25 of the fuel cell stack 6 of the system 1 with fuel and with reaction gas and to discharge the reaction products from the stack. The medium-carrying through-openings 11 a- 11 care formed substantially parallel to the plate plane.In order to seal the through-openings 11 a- cto the interior of the stack 6 and to the environment, the first separator plates 2 aeach have sealing arrangements in the form of sealing beads 12 a- cwhich are arranged in each case around the through-openings 11 a- cand which in each case completely surround the through-openings 11 a- c. The second separator plates 2 bhave corresponding sealing beads (not shown) on the rear side of the bipolar plates 2 facing away from the observer of FIG. 2 for sealing the through-openings 11 a- c.In an electrochemically active region 18, the first separator plates 2 acomprise, on their front side facing the observer of FIG. 2, a flow field 17 with structures for guiding a reaction medium along the front side of the separator plate 2 a. These structures are provided in FIG. 2 by a multiplicity of webs and channels running between the webs and bounded by the webs. On the front side of the bipolar plates 2 facing the observer of FIG. 2, the first separator plates 2 aalso each have a distribution and collection region 20. Distribution or collection areas 20 each comprise structures which are configured to distribute a medium introduced into the distribution area 20 starting from a first of the two passage openings 11 bvia the active area 18 or to collect or bundle a medium flowing from the active area 18 towards the second of the passage openings 11 b. The fluid-conducting structures of both distribution or collection regions 20 are likewise provided in FIG. 2 by webs and channels running between the webs and bounded by the webs.The sealing beads 12 a- 12 chave feedthroughs 13 a- 13 cthat allow medium to pass through the sealing beads 12 a- 12 c.The first separator plates 2 afurther comprise a further sealing arrangement in the form of a perimeter bead 12 d, which circulates around the flow field 17 of the active region 18, the distribution and collection regions 20 and the through-openings 11 b, 11 cand seals them with respect to the through-opening 11 a, i.e. with respect to the coolant circuit, and with respect to the environment of the system 1. The second separator plates 2b each comprise respective perimeter beads. The structures of the active region 18, the distribution structures of the distribution and collection region 20 and the sealing beads 12 a- dare each formed integrally with the separator plates 2 aand are formed into the separator plates 2 a, for example in an embossing or deep-drawing process or by means of hydroforming. The same applies to the corresponding structures of the second separator plates 2 b.The two through-openings 11 bor the lines formed by the through-openings 11 bthrough the plate stack of the system 1 are each in fluid communication with one another via feedthroughs 13 bin the sealing beads 12 b, via the distribution structures of the distribution or collection region 20 and via the flow field 17 in the active region 18 of the first separator plates 2 afacing the observer of FIG. 2. In an analogous manner, the two through-openings 11 cor the lines formed by the through-openings 11 care each in fluid communication with one another through the plate stack of the system 1 via corresponding bead feedthroughs, via corresponding distribution and collection structures and via a corresponding flow field on an outer side of the second separator plates 2 bfacing away from the observer of FIG. 2. The through-openings 11 a, on the other hand, or the lines formed by the through-openings 11 athrough the plate stack of the system 1 are each in fluid communication with one another via a cavity 19 enclosed or enclosed by the separator plates 2 a, 2 b. This cavity 19 serves in each case for guiding a coolant through the bipolar plate 2, in particular for cooling the electrochemically active region 18 of the separator plates 2 a, 2 b.In the following, the sealing beads 12 a, 12 b, 12 c, 12 dare also collectively described as a sealing arrangement 12. The sealing arrangement 12 thus comprises only one, at least one or all of the sealing beads 12 a- d. Overall, the sealing arrangement 12 defines a fluid-conducting region 16 of the respective plate, within which the media (cooling fluid, reactants, product media) flow or are conducted.The described separator plates 2 a, 2 b,as well as the periphery of the fuel cell stack 1, i.e. for example fans and pumps, are usually designed for a specific load range of the electrochemical system 1. In order to cover an upper load range as well, the periphery of the fuel cell stack, as well as the passage openings 11 a- cof the separator plates 2 a, 2 b, are usually oversized, so that adequate cooling for the increased amount of heat generated in the upper load range is ensured and undersupply of reactants can be avoided. It would be desirable for some applications if the electrochemical system could be made more compact while at the same time operating safely.The present application was designed to at least partially solve this problem. Various embodiments are illustrated in FIGS. 1 and 3A to 8 and are explained in more detail below. The separator plates 2 a, 2 bshown in FIGS. 3A to 8 can have individual, multiple or all features of the separator plates 2 a, 2 bof FIG. 2. In addition, a capacitor 30 is also provided, which is accommodated by the first separator plate 2 aand / or the second separator plate 2 b. The capacitors 30 are arranged between the outer edge regions of the respective separator plates 2 a, 2 b,and the electrochemically active region of the respective cells 25 is thus removed from the regions relevant for the accommodation of the capacitors 30 and shown here in terms of the center of gravity. The cells 25 are thus usually only indicated. With regard to the group of figures 5, the following is to be pointed out: the top view of FIG. 5A can correspond on the one hand to an exemplary embodiment as is illustrated in the sectional illustration in FIG. 5B. Alternatively, the top view of FIG. 5A can also correspond to an exemplary embodiment, as is shown in the sectional illustration in FIG. 5C.According to the embodiments of FIGS. 1 and 3A to 8, an electrochemical cell 25 is provided, which comprises a first separator plate 2 a, a second separator plate 2 band a capacitor 30. The capacitor 30 is preferably a supercapacitor. If nothing is explained further below in the context of the term "capacitor", this is also preferably a supercapacitor. The capacitor 30 is configured to store and discharge electric energy. The capacitor 30 is disposed between an outer peripheral portion 14 of the first separator plate 2 aand an outer peripheral portion 15 of the second separator plate 2 b.The separator plates 2 a, 2 bhave in each case a sealing arrangement 12 for sealing a fluid-conducting region 16 of the separator plate 2 a, 2 b. Usually, a sealing arrangement 12' designed as a half bead is additionally present along the outer edge of the separator plates 2a, 2b, which in some cases has not only a sealing but in particular a supporting function. The respective separator plate 2 a, 2 bfurther includes channel structures 46 for guiding a fluid. The respective outer edge region 14, 15 is located outside the fluid-conducting region 16 of the respective separator plate 2 a, 2 bdefined by the bead arrangement 12 and often adjoins the fluid-conducting region 16 of the plate 2 a, 2 bor the bead arrangement 12. In some embodiments, the separator plate 2 a, 2 bincludes the fluid-conducting region 16 and the outer edge region 14, 15, or consists only of these two regions. Alternatively, at least one further region of the separator plate 2 a, 2 bmay be provided between the fluid-conducting region 16 and the outer edge region 14, 15.The first separator plate 2 aincludes a first holding structure 21 for holding the capacitor 30. Alternatively or additionally, the second separator plate 2 bhas a second holding structure 22 for holding the capacitor 30. The named holding structures 21, 22 can be designed as embossed structures formed into the respective separator plate 2 a, 2 b. The holding structures 21, 22 are thus an integral part of the separator plate 2 a, 2 b. The term "embossing" used in this specification is intended to include forming methods such as lifting or roll embossing, deep drawing and / or hydroforming, so that this specification is not limited to a specific forming method for the embossing structures. Other embossing structures include, for example, the sealing assembly 12 and the channel structures 46.The support structures 21, 22 define a receiving region 26 for the capacitor 30 in which the capacitor 30 is received and held. For simplification, reference is made below to the holding structure 21, 22, wherein this can mean only one, at least one or both of the holding structures 21, 22. This applies analogously to further structures which are described in the singular.The holding structures 21, 22 can be formed in outer edge regions 14, 15 of separator plates 2 a, 2 b, cf. FIG. 4A. The resulting separator plates 2 a, 2 bmay thus be integrated into existing electrochemical systems 1. Alternatively, it can also be provided that the outer edge region 14, 15 has a protrusion 45 which protrudes laterally from the separator plate 2 a, 2 b, cf. FIGS. 1 and 3A. The dashed line in FIG. 1 indicates the boundary of the protrusion 45; a corresponding protruding region is not present in a stack with separator plates according to FIG. 2. The receiving region 26 can be provided at least partially or completely in the region of the protrusion 45. In the embodiment of FIG. 5A, the supporting structures 23, 24 of the holding structures 21, 22 end in sections substantially flush with the edges of the separator plate 2 a, 2 b.The capacitor 30 may include an active region 31 and a passive region 32. The active region 31 of the capacitor 30 typically forms the region of the capacitor 30 in which a portion of the electrical energy released in the electrochemical cell 25 is stored or can be released again by discharging the capacitor 30. No energy storage takes place in the passive region 32; the passive region 32 is used only for the insulation and the mounting of the capacitor 30 between the supporting structures 23, 24.The support structure 21, 22 may include a bottom surface 35, 36 and sidewalls 27, 28. In the figures, the side walls are formed by formations 27, 28 designed as beads, in particular by side flanks of these beads. The formation 27, 28 can be designed in some regions as a full bead with two side flanks and / or half bead with one side flank. The capacitor 30, in particular the active region 31 of the capacitor 30, can be bounded laterally by at least one formation 27, 28 formed in the respective separator plate 2 a, 2 b. In a region between the bottom surface 35 and the bead arrangement 12, the formation 27, 28 can be designed as a full bead with two bead flanks. In the example of FIG. 4A / B, it is shown that the structure forming the shaping 27, 28 is identical to or part of the sealing structure 12. In a region between the bottom surface 35, 36 and the outer edge 43, 44 of the separator plate 2 a, 2 b, the formation 27, 28 can be configured as a half bead with only one bead flank, cf. FIG. 4B, or as a full bead with two bead flanks, cf. FIGS. 3B, 5B, 6.The support structures 21, 22 may include support structures 23, 24 facing each other. In the region of the supporting structures 23, 24, the two supporting structures 23, 24 of the supporting structures 21, 22 are supported on one another. Often, the support structures 23, 24 are electrically insulated from one another. For this purpose, the separator plate 2 a, 2 bmay have a coating 41, 42 which is arranged at least in regions on the respective separator plate 2 a, 2 b, in particular in the region of the supporting structures 23, 24, cf. FIGS. 4A, 4B, but often also beyond this, such that the entire outer edge region 14, 15 may be provided with the coating 41, 42, cf. FIG. 4A. Alternatively or additionally, the capacitor 30 can have an electrically insulating cladding 40, cf. FIGS. 3B, 5B, 5C.A part of the capacitor 30, in particular the passive region 32 of the capacitor, such as a protruding collar or a lateral extension of the capacitor 30, can be held between the mutually facing support structures 23, 24 in some embodiments, cf. FIGS. 3B, 5B. For this purpose, it is advantageous if the supporting structures 23, 24 are supported on one another in a resilient manner. The supporting structures 23, 24 can be designed as bead roofs of the full beads or half beads of the shaped portion 27, 28. The sealing arrangement 12 and individual elements of said holding structures 21, 22, such as the supporting structures 23, 24, may merge into one another in some embodiments. For example, the sealing arrangement 12 designed as a full bead and the sealing arrangement 12' designed as a half bead, which is not arranged in the fluid-conducting region 16, but in the outer edge region 14 or 15, respectively, simultaneously form the formations 27, 28 in FIG. 4B. It should be noted that at least the receiving region 26 is normally provided outside the fluid-conducting region 16 and the sealing arrangement 12, see FIGS. 3A-6.In the sectional view of FIG. 3B, a part of the MEA 10 can also be seen. This is a reinforcing edge which reinforces the membrane of the MEA 10 and is typically manufactured from an electrically insulating material.Furthermore, the holding structure 21, 22 has a spring structure 33, 34 which is designed to be resilient in order to clamp the capacitor 30. For this purpose, the spring structure 33, 34 can have a wave-shaped section 29 or can be configured in a wave-shaped manner overall. The wave-shaped section 29 usually extends partially (cf. FIG. 3B ) or completely (cf. FIGS. 4B, 5B ) along the bottom surface 35, 36 of the holding structure 21, 22, for example within a region bounded by the shaping 27, 28. Furthermore, the wave-shaped section 29 has a lower maximum height than the respective formation 27, 28, wherein the height in the z-direction is measured perpendicular to the plate plane E of the first separator plate 2 aand the second separator plate 2 b. The maximum height thus describes here the maximum extent of the respective element perpendicular to the plate plane E. The plate plane E and the z-direction perpendicular thereto are indicated in FIG. 3B for clarity. The separator plate plane E of the respective separator plate 2 a, 2 bis determined in regions in which it is planar and does not comprise any embossed structures.The holding structure 21, 22 can be further configured for electrically contacting the capacitor 30. The electrical contacting of the capacitor 30 can be realized in particular by the resilient part of the holding structure 21, 22, i.e. by the spring structures 33, 34, wherein the spring force of the spring structures 33, 34 ensures that the capacitor 30 is always in electrical contact with the respective separator plate 2 a, 2 b. The spring structure 33, 34 is thus preferably designed as a clamping contact. This eliminates the need for additional electrical wiring of the capacitor 30 to the separator plate 2 a, 2 b.Overall, at least one or each holding structure 21, 22, i.e. at least one of the following elements, can have: formation 27, 28, bottom surface 35, 36, supporting structure 23, 24, insulating coating 41, 42 and / or spring structure 33, 34.The capacitor 30 may be or comprise an electrochemical double layer capacitor, in particular a supercapacitor. Advantageously, energy may be generated by electrochemical processes in the electrochemical cell 25 and subsequently stored in the capacitor 30. In particular, the energy stored in the capacitor 30 is generated at least by electrochemical processes in the electrochemical system 1. Alternatively, an additional or external current source can also be provided and provide for the charging of the capacitor 30.Conventional supercapacitors can be used for the capacitor 30. Thus, the capacitor 30 usually has a separator 39 and two opposing electrodes 37, 38, wherein the separator 39 separates the two electrodes 37, 38 from one another. For further features and properties of capacitor 30, reference may be made to Andrew F. Burke, Jingyuan Zhao, Past, present and future of electrochemical capacitors: Technologies, performance and application, Journal of Energy Storage, 35 (2021) 102310.The embodiment of FIG. 6 differs from the embodiments of FIGS. 3A-5C in that only one of the two separator plates 2c, 2b or 2c', 2b' or 2c", 2b" of a bipolar plate 2, namely the separator plate 2b or 2b' or 2b", forms a receiving region 26 with formations 27 for the capacitor 30. The separator plates 2c, 2c' and 2c", unlike the separator plates 2a of the preceding embodiments, do not extend into the region in which the capacitor or capacitors 30 are accommodated. The designation of the separator plates 2b, 2b', 2b", 2c, 2c', 2c" differs here correspondingly from the designation of the separator plates in the preceding embodiments. The holding structure 22 of the separator plate 2b' merely has a bottom surface 36 with a spring structure 34, but does not have any shaping 27, 28. Optionally or alternatively, the separator plate 2b' can also be designed completely as a flat surface in the region of the capacitor 30. The separator plates 2b, 2b' are designed in the receiving regions 26 in a manner similar to the corresponding sections of the separator plates 2a, 2b of the preceding embodiments and substantially mirror-symmetrical to one another. The embodiment of FIG. 6 is thus distinguished from the other embodiments in that here the separator plate 2b' forms the first separator plate, the first retaining structure and the separator plate 2b forms the second separator plate, which has the second retaining structure for retaining the capacitor 30. The two separator plates 2b, 2b' are thus each anode plates or each cathode plate.FIGS. 7 and 8 show only outer contours of a separator plate 2 a. A pair of possible positions for the projections 45 can be seen, wherein the projections 45 in FIGS. 7 to 8 are optionally arranged in such a way that the outer contours 7, 8 are designed to be rotationally symmetrical. The projections 45 of a separator plate 2a do not all have to accommodate a capacitor 30. Rather, for space reasons in the electrochemical system 1, the projections 45 can alternately receive a capacitor 30.It should be noted here that the separator plate 2 a, 2 bshown in the group 5 of figures is likewise configured rotationally symmetrically.The first separator plate 2 amay be configured as a cathode plate while the second separator plate 2 bis an anode plate, or vice versa. When assembling the electrochemical cells 25, finished capacitors 30 or capacitor packs are preferably used, which are then arranged between the separator plates 2 a, 2 b.The outer edge region 14 of the first separator plate 2 aand / or the outer edge region 15 of the second separator plate 2 b, between which the capacitor is held, is formed integrally with the first separator plate 2 aand integrally with the second separator plate 2 bin all the exemplary embodiments shown. This gives the system 1 higher stability and avoids additional production steps.According to one aspect, an electrochemical system 1 comprising a plurality of stacked electrochemical cells 25 of the type described above is proposed. In this case, capacitors 30 of adjacent cells 25 are offset in a direction perpendicular to the stacking direction, in particular arranged alternately, with respect to one another or arranged one above the other in the stacking direction.FIG. 5C shows an embodiment in which capacitors 30 in the electrochemical system are arranged between every second plate pair of separator plates 2 a, 2 b, which are associated with two different bipolar plates 2 and are closest to one another. The outer edge of the remaining plate pairs does not extend into the illustrated receiving region 21, 22, but is cut out in this region. Preferably, on a second outer edge, for example the outer edge, on which the section C-C is indicated in FIG. 5A, corresponding receiving regions 21, 22 are provided in the remaining plate pairs. This makes it possible to accommodate capacitors 30 with a greater overall height than is possible, for example, in FIGS. 3B and 4B. Due to the rotational symmetry of the separator plates 2 a, 2 b, identical parts can nevertheless be used.For all of the aforementioned exemplary embodiments, as soon as the voltage in the stack 1 drops, the capacitors 30 can temporarily compensate for this and thus counteract damage to the system.List of reference numbers:1 Electrochemical system 2 Separator plate or bipolar plate 2 aFirst individual plate 2 bSecond individual plate 3 End plate 4 End plate 5 Media connection 6 Stack 7 z-direction 8 x-direction 9 y-direction 10 Membrane electrode unit 11 a- c Through-openings 12 Sealing arrangement 12 a- d Sealing beads 13 a- c Feedthroughs 14 Outer edge region of the first individual plate 15 Outer edge region of the second individual plate 16 Fluid-conducting region 17 Flow field 18 Electrochemically active region 19 Cavity 20 Distribution or collection region 21 First retaining structure 22 Second retaining structure 23 First supporting structure 24 Second supporting structure 25 Electrochemical cell 26 Receiving region 27 Formation 28 Formation 29 Corrugated section 30 Capacitor 31 Active region of the capacitor 32 Passive region of the capacitor 33 Spring structure 34 Spring structure 35 Bottom surface 36 Bottom surface 37 Electrode 38 electrode 39 separator 40 insulating jacket 41 insulating coating 42 insulating coating 43 outer edge 44 outer edge 45 protrusion 46 channel structures E plate planeReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2020 007 106 A1

[0004] Cited Non-Patent LiteratureAndrew F. Burke, Jingyuan Zhao, Past, present and future of electrochemical capacitors: Technologies, performance and application, Journal of Energy Storage, 35 (2021) 102310

[0053]

Claims

Electrochemical cell (25) comprising a first separator plate (2a), a second separator plate (2b) and a capacitor (30) configured to store and discharge electrical energy, wherein the capacitor (30) is arranged between an outer edge region (14) of the first separator plate (2a) and an outer edge region (15) of the second separator plate (2b), wherein the first separator plate (2a) has a first holding structure (21) for holding the capacitor (30) and / or the second separator plate (2b) has a second holding structure (22) for holding the capacitor (30).Electrochemical cell (25) according to claim 1, wherein said support structures (21, 22) are configured as embossed structures formed in the respective separator plate (2a, 2b).Electrochemical cell (25) according to one of the preceding claims, wherein at least one of the holding structures (21, 22) defines a receiving region (26) for the capacitor (30), wherein the active region (31) of the capacitor (30) is laterally delimited by at least one formation (27, 28) formed in the respective separator plate.The electrochemical cell (25) according to any of the preceding claims, wherein the first support structure (21) comprises first support structures (23) and the second support structure (22) comprises second support structures (24), and the first and second support structures (23, 24) face each other, wherein the support structures (23, 24) are electrically insulated from each other.Electrochemical cell (25) according to any of the preceding claims, wherein at least one of the support structures (21, 22) comprises at least one spring structure (33, 34) which is spring-elastic configured to clamp the capacitor (30).The electrochemical cell (25) according to any one of the preceding claims, wherein at least one of the spring structures (33, 34) comprises at least one wave-shaped portion (29).Electrochemical cell (25) according to claim 6 when dependent on claim 3, wherein the wave-shaped section (29) extends within the at least one formation (27, 28) or between at least two formations (27, 28) and has a lower maximum height than the respective formation (27, 28), wherein the height is measured perpendicular to the plate plane of the first separator plate (2a) and the second separator plate (2b).The electrochemical cell (25) according to any of the preceding claims, wherein at least one of the support structures (21, 22) is further configured to electrically contact the capacitor (30).Electrochemical cell (25) according to one of the preceding claims, wherein the capacitor (30) is or comprises an electrochemical double layer capacitor, in particular a supercapacitor.Electrochemical cell (25) according to one of the preceding claims, wherein the first separator plate (2a) and / or the second separator plate (2b) has a sealing arrangement (12, 12'), in particular for sealing a fluid-conducting region (16) of the respective separator plate (2a, 2b), wherein the outer edge region (14, 15) of the respective separator plate (2a, 2b) adjoins the sealing arrangement (12, 12').The electrochemical cell (25) according to any one of the preceding claims, wherein the first separator plate (2a) is a cathode plate and the second separator plate (2b) is an anode plate.Electrochemical cell (25) according to one of the preceding claims, wherein the outer edge region (14) of the first separator plate (2a) and / or the outer edge region (15) of the second separator plate (2b) between which the capacitor (30) is held is formed integrally with the first separator plate (2a) and / or integrally with the second separator plate (2b).Electrochemical system (1) comprising a plurality of stacked electrochemical cells (25) according to one of the preceding claims, wherein capacitors (30) of adjacent cells (25) are arranged offset, in particular alternating, to one another in a direction perpendicular to the stacking direction or are arranged one above the other in the stacking direction.The electrochemical system (1) according to the preceding claim, wherein the energy stored in the capacitors (30) is generated by electrochemical processes in the electrochemical system (1).

Images