Electrochemical cell unit

Abstract

Electrochemical cell unit (53) for converting electrochemical energy into electrical energy as a fuel cell unit (1) and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit (49), comprising stacked electrochemical cells (52) as a cell stack (61), a first clamping element (33, 34, 35) for applying a compressive force to a first electrochemical cell (52), a second clamping element (33, 34, 36) for applying a compressive force to a last electrochemical cell (52), at least one connecting device (37) subjected to a tensile force, which is in mechanical operative connection with the first and second clamping elements (33, 34, 35, 36), such that, due to the tensile force in the at least one connecting device (37), a compressive force can be applied from the first clamping element (33, 34, 35) to the first electrochemical cell (52) and from the second clamping element (33, 34,36) a pressure force can be applied to the last electrochemical cell (52) such that the at least one cell stack (61) is prestressed, wherein the length of the at least one connecting device (37) is variable by means of a length-changing means (60) integrated into the at least one connecting device (37) in that at least one parameter of the at least one connecting device (37) is controllable and / or adjustable by means of the respective length-changing means (60) and the length of the at least one connecting device (37) depends on the at least one parameter.

Description

[0001] The present invention relates to an electrochemical cell unit according to the preamble of claim 1 and a method for operating an electrochemical cell unit according to the preamble of claim 12. State of the art

[0002] Fuel cell units, as galvanic cells, convert continuously supplied fuel and oxidant into electrical energy and water through redox reactions at an anode and cathode. Fuel cells are used in a wide variety of stationary and mobile applications, for example, in homes without a power grid connection or in motor vehicles, in rail transport, aviation, aerospace, and shipping. In fuel cell units, a large number of fuel cells are arranged in a stack.

[0003] In fuel cell units, a large number of fuel cells are arranged in a fuel cell stack. Within each fuel cell, there is a gas space for the oxidant, i.e., a flow space for the passage of oxidant, such as ambient air with oxygen. The gas space for the oxidant is formed by channels on the bipolar plate and by a gas diffusion layer for a cathode. The channels are thus formed by a corresponding channel structure of a bipolar plate, and the oxidant, namely oxygen, passes through the gas diffusion layer to the fuel cell's cathode. Similarly, a gas space for fuel is formed at an anode.

[0004] Electrolysis cell units consisting of stacked electrolysis cells, similar to fuel cell units, are used, for example, for the electrolytic production of hydrogen and oxygen from water. Furthermore, fuel cell units are known that can be operated as reversible fuel cell units and thus as electrolysis cell units. Fuel cell units and electrolysis cell units form electrochemical cell units. Fuel cells and electrolysis cells form electrochemical cells.

[0005] Channels for fuel, oxidant, and a coolant are formed in the fuel cell stack as a cell stack. Furthermore, electrical current is conducted within the fuel cell stack, particularly by the bipolar plates. To ensure sufficient sealing of the channels and sufficient electrical conductivity of the components of the fuel cell stack, it is necessary to preload the fuel cell stack with a compressive force. For this purpose, an upper first clamping element rests as a clamping plate on the uppermost first fuel cell, and a lower second clamping element rests as a clamping plate on the lowermost last fuel cell. Typically, four connecting devices, such as tie rods or bolts, are arranged outside the fuel cell stack, and these tie rods are subjected to a tensile force.Due to the indirect or direct attachment of the tension rods to the upper and lower clamping elements, this tensile force is transferred to the clamping plates, so that the upper clamping plate applies a compressive force to the upper fuel cell and the lower clamping plate applies a compressive force to the lower fuel cell.

[0006] Furthermore, it is also known to preload a cell stack of a fuel cell unit using tensioning straps as connecting devices. Due to the low elastic properties of these tensioning straps, they do not act directly mechanically on the second, lower tensioning plate, but rather on a preloading plate, a so-called X-plate. Elastic elements are designed as coil springs between the preloading plate and the second, lower tensioning plate. The coil springs ensure that, when the height or expansion of the cell stack is reduced due to the preload and temperature, the preload and compressive forces are only slightly reduced due to the elastic properties of the coil springs.

[0007] The connecting devices, for example in the form of tie rods or tensioning straps, are subject to Hooke's law. The height of the stack is essentially directly proportional to the temperature of the cell stack. Due to Hooke's law, an increase in the temperature of the cell stack causes an increase in the preload of the cell stack with compressive force, and vice versa. This is disadvantageous because it no longer ensures optimal preload of the cell stack, for example for appropriate tightness at seals. Differences in the height of the stack, for example due to manufacturing inaccuracies or different thermal expansions, cause different preloads of the cell stack in a direction parallel to fictitious planes spanned by the components of the cell stack. This can disadvantageously lead to local leaks due to locally insufficient preload.

[0008] DE 10 2019 215 888 A1 shows a fuel cell unit as a fuel cell stack for the electrochemical generation of electrical energy, comprising fuel cells arranged one above the other, an upper clamping element for applying a compressive force to an upper fuel cell, a lower clamping element for applying a compressive force to a lower fuel cell, at least one connecting device which is subjected to a tensile force and which is in mechanical operative connection with the upper and lower clamping elements, so that due to the tensile force in the at least one connecting device a compressive force can be applied from the upper clamping element to the upper fuel cell and a compressive force can be applied from the lower clamping element to the lower fuel cell, wherein the at least one connecting device is arranged within the fuel cell stack.

[0009] DE 10 2022 205 729 A1 discloses an electrochemical cell unit for converting electrochemical energy into electrical energy as a fuel cell unit and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit, comprising stacked electrochemical cells as a cell stack, a first clamping element for applying a compressive force to a first electrochemical cell, a second clamping element for applying a compressive force to a last electrochemical cell, at least one connecting device subjected to a tensile force, which is in mechanical operative connection with the first and second clamping elements, so that due to the tensile force in the at least one connecting device, a compressive force can be applied by the first clamping element to the first electrochemical cell and a compressive force can be applied by the second clamping element to the last electrochemical cell,where the number of connecting devices is greater than eight., Disclosure of the inventionAdvantages of the invention

[0010] An electrochemical cell unit according to the invention, in particular for converting electrochemical energy into electrical energy as a fuel cell unit and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit, comprising stacked electrochemical cells as a cell stack, a first clamping element for applying a compressive force to a first electrochemical cell, a second clamping element for applying a compressive force to a last electrochemical cell, at least one connecting device subjected to a tensile force, which is in mechanical operative connection with the first and second clamping elements, such that, due to the tensile force in the at least one connecting device, a compressive force can be applied by the first clamping element to the first electrochemical cell and a compressive force can be applied by the second clamping element to the last electrochemical cell,so that the cell stack is prestressed with a compressive force, wherein the length of the at least one connecting device is variable by means of a length-changing means integrated into the at least one connecting device, in that at least one parameter of the at least one connecting device is controllable and / or regulatable by means of the respective length-changing means, and the length of the at least one connecting device is dependent on the at least one parameter. The at least one parameter of the at least one connecting device is preferably actively controllable and / or regulatable by means of at least one control and / or regulating unit, in particular independently of the temperature of the cell stack and / or the operating state of the cell stack.

[0011] In a further embodiment, the at least one connecting device is designed as a particularly rigid and / or straight tie rod. Tie rods can be arranged particularly easily outside the cell stack and are inexpensive to manufacture.

[0012] In a supplementary variant, the at least one length-changing means is a cavity filled with a fluid in the at least one connecting device as a cavity connecting device.

[0013] Preferably, the pressure of the fluid in the at least one cavity is controllable and / or regulatable as a parameter of the at least one connecting device and, due to the pressure of the fluid in the at least one cavity, a variable pressure force can be applied by the fluid on an inner side of the cavity connecting device, so that an increase in the pressure of the fluid causes an expansion and enlargement of the length of the at least one connecting device and a reduction in the pressure of the fluid causes a compression and reduction of the length of the at least one connecting device.

[0014] In an additional embodiment, the electrochemical cell unit comprises a compressor, in particular a compressor, for increasing the pressure of the fluid in the cavity to supply the at least one cavity with the fluid under a variable pressure.

[0015] In a further embodiment, the compressor with at least one fluid line is in fluid-conducting connection with the at least one cavity, in particular the compressor with several fluid lines is in fluid-conducting connection with the cavities of several connecting devices.

[0016] In a supplementary variant, the length of the at least one cavity is at least 30%, 50%, 70%, or 90% of the length of the at least one connecting device. The axial walls of the cavity connecting device thus have a large length in the axial direction, allowing for significant expansion or compression of the axial walls.

[0017] In an additional embodiment, at least one cavity is formed on each of the connecting devices.

[0018] In a further embodiment, the at least one length-changing means is designed as at least one heater, in particular at least one electrical resistance heater, for changing the temperature as a parameter of the at least one connecting device, so that by increasing the temperature of the at least one connecting device due to thermal expansion as thermal expansion of the at least one connecting device, the length of the at least one connecting device is increased, and by reducing the temperature of the at least one connecting device due to thermal shrinkage as thermal contraction of the at least one connecting device, the length of the at least one connecting device is reduced.An active reduction of the temperature of the at least one connecting device as an actively controlled and / or regulated parameter occurs, for example, after switching off the at least one heater and / or after reducing the heating power of the at least one heater.

[0019] Preferably, the electrochemical cell unit comprises at least one sensor for detecting the distance between the first and second clamping elements in a direction perpendicular to a fictitious plane spanned by the electrochemical cells, and the length of the at least one connecting device is variable depending on the distance detected by the at least one sensor by changing the at least one parameter.

[0020] In particular, the length of different connecting devices can be varied to achieve a substantially parallel alignment of the first and second clamping elements. A substantially parallel alignment of the first and second clamping elements is defined as a deviation of less than 10°, 5°, 3°, 1°, 0.1°, 0.05°, or 0.01°.

[0021] Inventive method for operating an electrochemical cell unit with stacked electrochemical cells as a cell stack for converting electrochemical energy into electrical energy as a fuel cell unit and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit, comprising the steps of: converting electrochemical energy into electrical energy by passing a fuel through a fuel cell unit or converting electrical energy into electrochemical energy by passing an electrolyte through the electrolysis cell unit, applying a compressive force to a first electrochemical cell with a first clamping element, applying a compressive force to a last electrochemical cell with a second clamping element,at least one connecting device is subjected to a tensile force, and the tensile force in the at least one connecting device is applied by the first clamping element to the first electrochemical cell as a compressive force, and by the second clamping element to the last electrochemical cell as a compressive force, so that the cell stack is prestressed with a compressive force, wherein the length of the at least one connecting device is changed by a length-changing means integrated into the at least one connecting device, by controlling and / or regulating at least one parameter of the at least one connecting device with the length-changing means, and the length of the at least one connecting device is dependent on the at least one parameter.

[0022] In a supplementary variant, each length-changing means comprises a cavity connecting device with a cavity filled with a fluid, and the length of the at least one connecting device is changed by controlling and / or regulating the pressure of the fluid in the at least one cavity as a parameter, and due to the pressure of the fluid in the at least one cavity, a variable pressure force is applied by the fluid to an inner side of the cavity connecting device, and an increase in the pressure of the fluid causes an expansion and enlargement of the length of the at least one connecting device, and a reduction in the pressure of the fluid causes a compression and reduction of the length of the at least one connecting device.

[0023] In an additional embodiment, the length of the at least one connecting device is changed during operation of the electrochemical cell unit by controlling and / or regulating at least one parameter of the at least one connecting device. The operation of the electrochemical cell unit is, in particular, the conversion of electrochemical energy into electrical energy and / or the conversion of electrical energy into electrochemical energy.

[0024] In a further variant, during operation of the electrochemical cell unit, the length of at least one connecting device, preferably a plurality of connecting devices, is changed, in particular simultaneously, with the at least one length-changing means, preferably the plurality of length-changing means, by, in particular simultaneously, introducing the fluid into the at least one cavity in at least one cavity and / or discharging it from the at least one cavity until a substantially parallel alignment of the first and second clamping elements to one another is achieved.

[0025] In a further embodiment, the pressure in the at least one cavity is increased by introducing the fluid through at least one fluid line into at least one cavity and / or the pressure in the at least one cavity is reduced by introducing the fluid from the cavity into at least one fluid line.

[0026] In a further variant, at a substantially constant temperature of the cell stack, in particular with a deviation of less than 30%, 20%, or 10%, the magnitude of the compressive prestress of the cell stack with the clamping elements depends on the length of the at least one connecting device. In particular, the magnitude of the compressive prestress of the cell stack is substantially, in particular with a deviation of less than 30%, 20%, or 10%, indirectly proportional to the length of the at least one connecting device. By increasing the length of the at least one connecting device at a constant temperature of the cell stack, the magnitude of the compressive prestress of the cell stack can be reduced, and vice versa.Changes in the magnitude of the compressive prestress of the cell stack due to a change in temperature can thus be compensated by controlling and / or regulating at least one parameter, so that the cell stack has a substantially constant magnitude of the compressive prestress of the cell stack at different temperatures, for example between 10°C and 60°C, in particular with a deviation of less than 30%, 20% or 10%.

[0027] In an additional embodiment, a method described in this patent application can be carried out with the electrochemical cell unit described in this patent application.

[0028] In a further variant, the process described in this patent application is carried out with an electrochemical cell unit described in this patent application.

[0029] In an additional embodiment, the length of the at least one connecting device is controlled and / or regulated by introducing and / or discharging the fluid into at least one cavity, in particular simultaneously into all cavities, as a function of the temperature and / or the height of the cell stack. An increase in the temperature of the cell stack causes an increase in the height of the cell stack due to thermal expansion, in particular of the bipolar plates. In order to avoid an increase in the compressive prestress of the cell stack, the fluid is introduced into at least one cavity, in particular simultaneously into all cavities, and thus the prestress of the cell stack with compressive force is kept essentially constant.A reduction in the temperature of the cell stack causes a reduction in the height of the cell stack due to temperature compression, particularly of the bipolar plates. To prevent a reduction in the compressive preload of the cell stack, the fluid is discharged from at least one cavity, in particular simultaneously from all cavities, thus keeping the preload of the cell stack with compressive force essentially constant. A substantially constant preload of the cell stack with compressive force preferably means that the preload of the cell stack with compressive force differs by less than 30%, 20%, 10%, 5%, 3%, or 1%.

[0030] In an additional variant, the prestressing of the cell stack with compressive force is kept substantially constant during operation of the electrochemical cell unit and / or in the switched-off state of the electrochemical cell unit by introducing the fluid into at least one cavity of at least one cavity connecting device and / or discharging the fluid and / or by heating at least one connecting device with at least one heating device and / or cooling at least one connecting device by means of a reduced heating power of the at least one heating device or a switched-off at least one heating device.

[0031] In an additional embodiment, the fluid is a liquid, in particular a hydraulic fluid, or a gas, in particular air.

[0032] In a further embodiment, the cavity is completely filled with the fluid.

[0033] In a supplementary variant, increasing the pressure of the fluid in the at least one cavity by introducing the fluid into the at least one cavity and / or reducing the pressure of the fluid in the at least one cavity by discharging the fluid from the at least one cavity can be carried out independently of one another, in particular selectively.

[0034] In a supplementary embodiment, the number of connecting devices is greater than 3, 4, 6 or 10.

[0035] The connecting devices, in particular all connecting devices, are expediently arranged outside the cell stack.

[0036] In a further embodiment, the connecting devices are fixed to the first clamping element and / or second clamping element with fixing elements.

[0037] In a further embodiment, the connecting devices are at least partially, in particular completely, made of metal, in particular steel, aluminum, titanium and / or brass, and / or of fiber-reinforced plastic.

[0038] In an additional variant, the connecting devices are distributed substantially evenly around the cell stack in order to introduce the tensile forces substantially evenly at a respective circumferential edge region of the first and second clamping element. Distributed substantially evenly around the cell stack preferably means that the distance between immediately adjacent connecting devices, which are aligned substantially perpendicular to fictitious planes spanned by the electrochemical cells, is substantially the same. Aligned substantially perpendicular to the fictitious planes preferably means that the alignment deviates by less than 15°, 10° or 5° from a right angle. Distributed substantially evenly around the cell stack preferably means that the distance between immediately adjacent connecting devices that are aligned substantially parallel to one another is substantially the same.Substantially parallel to each other preferably means that the connecting devices are aligned parallel to each other with a deviation of less than 15°, 10° or 5°.

[0039] In particular, the electrochemical cells span fictitious planes.

[0040] Preferably, the at least one connecting device, in particular all connecting devices, is / are oriented substantially perpendicular to the notional planes spanned by the electrochemical cells, in particular with a deviation of less than 30°, 20°, or 10°. Substantially perpendicular to the notional planes preferably means that the orientation deviates from a right angle by less than 30°, 20°, or 10°.

[0041] Advantageously, the at least one connecting device is designed as a tensioning strap.

[0042] In a supplementary embodiment, the electrochemical cells each comprise stacked layered components.

[0043] In a further variant, the components of the electrochemical cells are preferably ion exchange membranes, in particular proton exchange membranes or anion exchange membranes, anodes, cathodes, preferably gas diffusion layers and bipolar plates.

[0044] Preferably, the spring constant of the connecting devices, in particular between fixing elements, is substantially identical. Substantially identical preferably means that the spring constant of the connecting devices differs by less than 30%, 20%, or 10%.

[0045] In an additional embodiment, the elastic modulus of the material of the connecting devices, in particular between the fixing elements, is substantially identical. Substantially identical preferably means that the elastic modulus of the material of the connecting devices differs by less than 30%, 20%, or 10%.

[0046] In an additional embodiment, the elastic modulus of the material of the connecting devices, in particular between fixing elements, is between 30 and 500 GPa, in particular between 60 and 300 GPa.

[0047] In a further embodiment, the clamping elements are designed as clamping plates, clamping grids and / or clamping trusses.

[0048] Preferably, the clamping elements are disc-shaped and / or flat.

[0049] Preferably the fuel is hydrogen, hydrogen-rich gas, reformate gas or natural gas.

[0050] The fuel cells and / or electrolysis cells are expediently designed to be substantially flat and / or disc-shaped.

[0051] In a complementary variant, the oxidizing agent is air with oxygen or pure oxygen.

[0052] Preferably, the fuel cell unit is a PEM fuel cell unit with PEM fuel cells or an alkaline fuel cell (AFC). Short description of the drawings

[0053] In the following, exemplary embodiments of the invention are described in more detail with reference to the accompanying drawings. They show: Fig. 1 a highly simplified exploded view of an electrochemical cell system as a fuel cell system and electrolysis cell system with components of an electrochemical cell as a fuel cell and electrolysis cell, Fig. 2 a perspective view of part of a fuel cell and electrolysis cell, Fig. 3 a longitudinal section through electrochemical cells as fuel cells and electrolysis cells, Fig. 4 a perspective view of an electrochemical cell unit as a fuel cell unit and electrolysis cell unit as a fuel cell stack and electrolysis cell stack, Fig. 5 a longitudinal section of the electrochemical cell unit as a fuel cell unit and electrolysis cell unit as a fuel cell stack and electrolysis cell stack according to Fig. 4 and Fig. 6 a perspective view of a bipolar plate.

[0054] In the Fig. Figures 1 to 3 show the basic structure of a fuel cell 2, a PEM fuel cell 3 (polymer electrolyte fuel cell 3). The principle of fuel cells 2 is that electrical energy or electrical current is generated by means of an electrochemical reaction. Hydrogen H2 is fed to an anode 7 as a gaseous fuel, and the anode 7 forms the negative pole. A gaseous oxidant, namely air with oxygen, is fed to a cathode 8; that is, the oxygen in the air provides the necessary gaseous oxidant. Reduction (electron absorption) takes place at the cathode 8. Oxidation, as electron release, takes place at the anode 7.

[0055] The redox equations of the electrochemical processes are: Cathode: O2+ 4 H + + 4e - → 2 H2O

[0056] Anode: 2 H2 → 4 H + + 4 e -

[0057] Total reaction equation of cathode and anode: 2 H2 + O2 → 2 H2O

[0058] The difference between the normal potentials of the electrode pairs under standard conditions as the reversible fuel cell voltage or open-circuit voltage of the unloaded fuel cell 2 is 1.23 V. This theoretical voltage of 1.23 V is not achieved in practice. In the idle state and at low currents, voltages above 1.0 V can be achieved, and during operation with higher currents, voltages between 0.5 V and 1.0 V are achieved. The series connection of several fuel cells 2, in particular a fuel cell unit 1 as a fuel cell stack 1 of several stacked fuel cells 2, has a higher voltage, which corresponds to the number of fuel cells 2 multiplied by the individual voltage of each fuel cell 2.

[0059] The fuel cell 2 also includes a proton exchange membrane 5 (Proton Exchange Membrane, PEM), which is arranged between the anode 7 and the cathode 8. The anode 7 and cathode 8 are layered or disc-shaped. The PEM 5 acts as an electrolyte, catalyst support, and separator for the reaction gases. The PEM 5 also acts as an electrical insulator and prevents an electrical short circuit between the anode 7 and cathode 8. Generally, 12 µm to 150 µm thick, proton-conducting films made of perfluorinated and sulfonated polymers are used. The PEM 5 conducts the protons H + and blocks ions other than protons H + essentially, so that due to the permeability of the PEM 5 for the protons H +the charge transport can take place. The PEM 5 is essentially impermeable to the reaction gases oxygen O2 and hydrogen H2, i.e., it blocks the flow of oxygen O2 and hydrogen H2 between a gas space 31 at the anode 7 containing hydrogen H2 as fuel and the gas space 32 at the cathode 8 containing air or oxygen O2 as oxidizing agent. The proton conductivity of the PEM 5 increases with increasing temperature and increasing water content.

[0060] On both sides of the PEM 5, each facing the gas spaces 31, 32, are the electrodes 7, 8, serving as the anode 7 and cathode 8. A unit comprising the PEM 5 and the electrodes 7, 8 is referred to as a membrane electrode assembly (MEA). The electrodes 7, 8 are constructed from an ionomer, for example Nafion®, platinum-containing carbon particles, and additives. These electrodes 7, 8 with the ionomer are electrically conductive due to the carbon particles and also conduct the protons H + and additionally function as a catalyst layer 30 due to the platinum-containing carbon particles. Membrane electrode assemblies 6 with these electrodes 7, 8 and the PEM 5 form membrane electrode assemblies 6 as a CCM (catalyst coated membrane).

[0061] A gas diffusion layer 9 (GDL) lies on the anode 7 and the cathode 8. The gas diffusion layer 9 on the anode 7 evenly distributes the fuel from fuel channels 12 to the anode 7. The gas diffusion layer 9 on the cathode 8 evenly distributes the oxidant from oxidant channels 13 to the cathode 8. The GDL 9 also draws off reaction water in the opposite direction to the flow of the reaction gases, i.e., in one direction from the electrodes 7, 8 to the channels 12, 13. Furthermore, the GDL 9 keeps the PEM 5 moist and conducts the current.

[0062] A bipolar plate 10 rests on the GDL 9. The electrically conductive bipolar plate 10 serves as a current collector, for water drainage and for conducting the reaction gases as process fluids through the channel structures 29 and / or flow fields 29, and for dissipating the waste heat, which occurs particularly during the exothermic electrochemical reaction at the cathode 8. To dissipate the waste heat, channels 14 are incorporated into the bipolar plate 10 as a channel structure 29 for conducting a liquid or gaseous coolant as a process fluid. The channel structure 29 at the gas space 31 for fuel is formed by channels 12. The channel structure 29 at the gas space 32 for oxidizing agent is formed by channels 13. The materials used for the bipolar plates 10 include, for example, metal, conductive plastics and composite materials, or graphite.

[0063] In a fuel cell unit 1, several fuel cells 2 are arranged in alignment stacked manner ( Fig. 4 and Fig. 5). The stacked fuel cells 2 form a cell stack 61. In Fig. 1 shows an exploded view of two aligned stacked fuel cells 2. Seals 11 seal the gas chambers 31, 32 or channels 12, 13 in a fluid-tight manner. In a compressed gas storage 21 ( Fig. 1) Hydrogen H2 is stored as a fuel at a pressure of, for example, 350 bar to 700 bar. From the compressed gas storage 21, the fuel is fed through a high-pressure line 18 to a pressure reducer 20 to reduce the pressure of the fuel in a medium-pressure line 17 from approximately 10 bar to 20 bar. From the medium-pressure line 17, the fuel is fed to an injector 19. At the injector 19, the pressure of the fuel is reduced to an injection pressure between 1 bar and 3 bar. From the injector 19, the fuel is fed to a supply line 16 for fuel ( Fig. 1) and from the supply line 16 to the fuel channels 12, which form the fuel channel structure 29. The fuel thereby flows through the fuel gas space 31. The fuel gas space 31 is formed by the channels 12 and the GDL 9 at the anode 7. After flowing through the channels 12, the fuel not consumed in the redox reaction at the anode 7 and, if applicable, water from a controlled humidification of the anode 7 are discharged from the fuel cells 2 through a discharge line 15.

[0064] A gas conveying device 22, embodied, for example, as a blower 23 or a compressor 24, conveys air from the environment as the oxidant into an oxidant supply line 25. From the supply line 25, the air is fed to the oxidant channels 13, which form a channel structure 29 on the oxidant bipolar plates 10, so that the oxidant flows through the oxidant gas space 32. The oxidant gas space 32 is formed by the channels 13 and the GDL 9 at the cathode 8. After flowing through the channels 13 and the oxidant gas space 32, the oxidant not consumed at the cathode 8 and the reaction water produced at the cathode 8 due to the electrochemical redox reaction are discharged from the fuel cells 2 through a discharge line 26.A supply line 27 serves to supply coolant into the coolant channels 14, and a discharge line 28 serves to discharge the coolant passed through the channels 14. The supply and discharge lines 15, 16, 25, 26, 27, 28 are shown in . Fig. 1 are shown as separate lines for simplification reasons. At the end area near the channels 12, 13, 14, aligned fluid openings 41 are provided on sealing plates 39 in the stack of the fuel cell unit 1 as an extension at the end area 40 of the superimposed bipolar plates 10 ( Fig. 6) and membrane electrode assemblies 6 (not shown). The fuel cells 2 and the components of the fuel cells 2 are disk-shaped and span fictitious planes 59 that are essentially parallel to one another. The aligned fluid openings 41 and seals (not shown) in a direction perpendicular to the fictitious planes 59 between the fluid openings 41 thus form a supply channel 42 for oxidizing agent, a discharge channel 43 for oxidizing agent, a supply channel 44 for fuel, a discharge channel 45 for fuel, a supply channel 46 for coolant, and a discharge channel 47 for coolant. The supply and discharge lines 15, 16, 25, 26, 27, 28 outside the stack of the fuel cell unit 1 are designed as process fluid lines.The supply and discharge lines 15, 16, 25, 26, 27, 28 outside the stack of the fuel cell unit 1 open into the supply and discharge channels 42, 43, 44, 45, 46, 47 within the stack of the fuel cell unit 1. The fuel cell stack 1 together with the compressed gas storage device 21 and the gas conveying device 22 forms a fuel cell system 4.

[0065] In the fuel cell unit 1, the fuel cells 2 are arranged between two clamping elements 33 as clamping plates 34. A first upper clamping plate 35 rests on the first upper fuel cell 2 and a second lower clamping plate 36 rests on the last lower fuel cell 2. The fuel cell unit 1 comprises approximately 200 to 400 fuel cells 2, which for graphic reasons are not all shown in Fig. 4 and Fig. 5 are shown. The clamping elements 33 apply a compressive force to the fuel cells 2, i.e. the first clamping plate 35 rests with a compressive force on the first fuel cell 2 and the second clamping plate 36 rests with a compressive force on the last fuel cell 2. The fuel cell stack 2 is thus clamped in order to ensure the tightness for the fuel, the oxidizing agent and the coolant, in particular due to the elastic seals 11, and also to keep the electrical contact resistance within the fuel cell stack 1 as low as possible. In order to clamp the fuel cells 2 with the clamping elements 33, connecting devices 37 are designed on the fuel cell unit 1 as bolts 38 which are subjected to tensile stress and thus form tie rods 38. The bolts 38 are firmly connected to the clamping plates 34.The clamping elements 33 are each electrically insulated from the fuel cells 2 by an insulating layer 84 to prevent an electrical short circuit due to the electrically conductive clamping elements 33 and bolts 38. Recesses 64 are formed on the clamping elements 37. The tension rods 38 have a head 62 at an upper end region. An external thread is machined into a lower end region of the tension rods 38, and a nut 63 is screwed into this external thread. The head 62 of each tension rod 38 is arranged in a recess in the first, upper clamping plate 35, and the nut 63 is arranged in the recess 64 of the second, lower clamping plate 36.By screwing the nut 63 into the thread of the tension rod 38, the distance between the first and second clamping plates 35, 36 can be reduced and thus the preload and the compressive forces within the cell stack 61 can be increased and vice versa during the manufacture of the fuel cell unit 1 and during the operation of the fuel cell unit 1.

[0066] In Fig. 6 shows the bipolar plate 10 of the fuel cell 2. The bipolar plate 10 comprises the channels 12, 13 and 14 as three separate channel structures 29. The channels 12, 13 and 14 are in Fig. 6 is not shown separately, but merely simplified as a layer of a channel structure 29. The fluid openings 41 on the sealing plates 39 of the bipolar plates 10 and membrane electrode assemblies 6 (not shown) are arranged in an aligned stack within the fuel cell unit 1, so that supply and discharge channels 42, 43, 44, 45, 46, 47 are formed. Seals (not shown) are arranged between the sealing plates 39 for fluid-tight sealing of the supply and discharge channels 42, 43, 44, 45, 46, 47 formed by the fluid openings 41.

[0067] Since the bipolar plate 10 also fluid-tightly separates the gas chamber 31 for fuel from the gas chamber 32 for oxidizing agent and furthermore fluid-tightly seals the channel 14 for coolant, the term separator plate 51 can also be used for the bipolar plate 10 for fluid-tight separation of process fluids. Thus, the term separator plate 51 is also subsumed under the term bipolar plate 10, and vice versa. The channels 12 for fuel, the channels 13 for oxidizing agent, and the channels 14 for coolant of the fuel cell 2 are also formed on the electrochemical cell 52, but with a different function.

[0068] The fuel cell unit 1 can also be used and operated as an electrolysis cell unit 49, i.e., it forms a reversible fuel cell unit 1. Some features are described below that enable the operation of the fuel cell unit 1 as an electrolysis cell unit 49. A liquid electrolyte, namely highly diluted sulfuric acid with a concentration of approximately c (H2SO4)=1 mol / l, is used for electrolysis. A sufficient concentration of oxonium ions H3O + in the liquid electrolyte is necessary for electrolysis.

[0069] During electrolysis, the following redox reactions take place: Cathode: 4 H3O + + 4 e - → 2 H2 + 4 H2O

[0070] Anode: 6 H2O → O2 + 4 H3O + + 4 e -

[0071] Total reaction equation of cathode and anode: 2 H2O →2 H2 + O2

[0072] The polarity of the electrodes 7, 8 with electrolysis when operated as an electrolysis cell unit 49 is reversed (not shown) to that when operated as a fuel cell unit 1, so that in the channels 12 for fuel, through which the liquid electrolyte is passed, hydrogen H2 is formed as a second substance at the cathodes, and the hydrogen H2 is absorbed by the liquid electrolyte and transported along in dissolved form. Analogously, the liquid electrolyte is passed through the channels 13 for oxidizing agents and oxygen O2 is formed as the first substance at the anodes in or on channels 13 for oxidizing agents. The fuel cells 2 of the fuel cell unit 1 function as electrolysis cells 50 when operated as an electrolysis cell unit 49. The fuel cells 2 and electrolysis cells 50 thus form electrochemical cells 52. The oxygen O2 formed is absorbed by the liquid electrolyte and transported along in dissolved form.The liquid electrolyte is stored in a storage container 54. In . Fig. For the sake of simplicity, Figure 1 shows two storage tanks 54 of the fuel cell system 4, which also functions as an electrolysis cell system 48. A 3-way valve 55 on the fuel supply line 16 is switched during operation as an electrolysis cell unit 49, so that not fuel from the compressed gas storage device 21, but rather the liquid electrolyte is fed from the storage tank 54 into the fuel supply line 16 by a pump 56. A 3-way valve 55 on the oxidizing agent supply line 25 is switched during operation as an electrolysis cell unit 49, so that not oxidizing agent as air from the gas delivery device 22, but rather the liquid electrolyte is fed from the storage tank 54 into the oxidizing agent supply line 25 by the pump 56.The fuel cell unit 1, which also functions as an electrolysis cell unit 49, has, in comparison to a fuel cell unit 1 that can only be operated as a fuel cell unit 1, optional modifications to the electrodes 7, 8 and the gas diffusion layer 9: for example, the gas diffusion layer 9 is not absorbent, so that the liquid electrolyte easily drains off completely, or the gas diffusion layer 9 is not formed, or the gas diffusion layer 9 is a structure on the bipolar plate 10.

[0073] A hydrogen separator 57 is arranged on the fuel discharge line 15. The separator 57 separates the hydrogen from the electrolyte with hydrogen, and the separated hydrogen is introduced into the compressed gas reservoir 21 by a compressor (not shown). The electrolyte discharged from the hydrogen separator 57 is then fed back to the electrolyte storage container 54 via a line. The hydrogen separated at the separator 57 can be fed to the compressed gas reservoir 21 by a compressor (not shown). An oxygen separator 58 is arranged on the fuel discharge line 26. The separator 58 separates the oxygen from the electrolyte with oxygen, and the separated oxygen is fed into a compressed gas reservoir (not shown) by a compressor (not shown).The oxygen in the compressed gas storage tank for oxygen (not shown) can optionally be used to operate the fuel cell unit 1 by feeding the oxygen into the oxidant supply line 25 via a line (not shown) when operating as a fuel cell unit 1. The electrolyte discharged from the oxygen separator 58 is then fed back to the electrolyte storage tank 54 via a line. The channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 are designed such that after use as an electrolysis cell unit 49 and the pump 56 is switched off, the liquid electrolyte flows completely back into the storage tank 54 due to gravity.Optionally, after use as an electrolysis cell unit 49 and before use as a fuel cell unit 1, an inert gas is passed through the channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 to completely remove the liquid electrolyte before the gaseous fuel and oxidant are passed through. The fuel cells 2 and the electrolysis cells 2 thus form electrochemical cells 52. The fuel cell unit 1 and the electrolysis cell unit 49 thus form an electrochemical cell unit 53. The channel 12 for fuel and the channel for oxidant thus form channels 12, 13 for passing the liquid electrolyte during operation as an electrolysis cell unit 49, and this applies analogously to the supply and discharge lines 15, 16, 25, 26. For process-related reasons, an electrolysis cell unit 49 normally does not require channels 14 for passing coolant.In an electrochemical cell unit 49, the channels 12 for fuel also form channels 12 for passing fuel and / or electrolyte, and the channels 13 for oxidant also form channels 13 for passing fuel and / or electrolyte.

[0074] In a further embodiment not shown, the fuel cell unit 1 is designed as an alkaline fuel cell unit 1. Potassium hydroxide solution is used as the mobile electrolyte. The fuel cells 2 are arranged in stacks. A monopolar or bipolar cell structure can be used. The potassium hydroxide solution circulates between an anode and cathode and transports away reaction water, heat, and impurities (carbonates, dissolved gases). The fuel cell unit 1 can also be operated as a reversible fuel cell unit 1, i.e., as an electrolysis cell unit 49.

[0075] In the Fig. 4 and Fig.The exemplary embodiment of the fuel cell unit 1 shown in Figure 5 has four connecting devices 37 in the form of bolts 38 and thus tie rods 38. The diameter of the tie rods 38 is approximately 5 mm outside a cavity connecting device 72 in the form of a cavity tie rod 73. The diameter of the tie rods 38 on the cavity connecting device 72 is approximately 30 mm. All tie rods 38 have an identical diameter. The tie rods 38 are positively connected to the first clamping plate 35 on the first upper clamping plate 35 by means of the head 62 as a fixing element 65. The head 62 rests on the recess 64. The tie rods 38 are positively connected to the second clamping plate 36 on the second lower clamping plate 36 by means of the nut 63 as the fixing element 65. The nut 63 rests on the recess 64.The recesses 64 have an area with a larger diameter as a blind hole in which the head 62 and the nut 63 are arranged and an area with a smaller diameter as a through hole, which is slightly larger than the diameter of the tie rods 38. The tie rods 38 are guided through this area with the smaller diameter of the recesses 64. The tie rods 38 are thus fixed to the clamping elements 33 with the fixing elements 65 and the spring constant D of the connecting devices 37 results from the length L of the connecting devices 37 between the two fixing elements 65 as the head 62 and the nut 63, the cross-sectional area A of the connecting devices 37 and the modulus of elasticity E of the material of the connecting devices 37. D=E×AL

[0076] The spring constant of the tension rod 38 is different at the cavity connection device 72 as the pressure vessel 67 and outside the cavity connection device 72 with the solid profile. The equivalent spring constant of each tension rod 38 is to be determined from the series connection of the individual spring constants at the different axial sections of the tension rod 38. The elastic properties of the tension rods 38 thus cause them to replace coil springs and thus additionally function as expansion rods 38. The tension rods 38 are aligned essentially perpendicular to the fictitious plane 59, ie the tension rods 38 are aligned at an angle α = 90° to the fictitious plane 59.

[0077] The tie rods 38 are formed into a total of three sections in the axial direction of the tie rods 38. In the vicinity of the clamping plates 38, the tie rods 38, as the connecting devices 37, are formed as a solid profile without a cavity 66 as a pressure vessel 67, i.e., not as a cavity connecting device 72 and not as a cavity tie rod 73. Between these two sections near the clamping plates 38 with the solid profile of the tie rods 38, a length-changing means 60 is formed. The length-changing means 60 encompasses the cavity 66. The cavity 66 is delimited by inner sides 81 of walls 68 of the pressure vessel 67. The walls 68 are axial walls 69 in an axial direction of the tie rods 38 and radial walls 70 in a radial direction perpendicular to the longitudinal axis of the tie rods 38. The radial walls 70 are disc-shaped and the axial walls 69 are circular in cross section, ieare cylindrical in shape. A fluid opening 71 is formed in a wall 68 of the cavity tie rod 73 for introducing a fluid into the cavity 66 and for discharging a fluid from the cavity 66. The flood opening 71 is connected in a fluid-tight manner to a fluid line 74. In all connecting devices 37, a cavity connecting device 72 is formed with the cavity 66 delimited by the pressure vessel 67, each having a fluid opening 71. The fluid openings 71 of the connecting devices 37 are fluidly connected to a compressor 78, for example a compressor, via the fluid lines 74. The fluid, namely a hydraulic fluid, is held in a storage space 79. A pressure sensor 75 and a closing element 76 are formed in the fluid lines 74 to each cavity connecting device 72.The pressure sensor 75 detects the pressure of the fluid in the cavity 66, and with the closing element 76 as a valve 77, the fluid line 74 leading into the fluid opening 71 can be closed and reopened in a fluid-tight manner. Alternatively (not shown), the pressure sensor 75 can also be arranged on the cavity connection device 72, for example, within the cavity 66, or the pressure sensor 75 can be fluidly connected to the cavity 66 via a sensor channel. A sensor 80 is arranged on the lower clamping plate 34 near the tension rods 38 for detecting the distance between the clamping plates 34 in a direction perpendicular to the fictitious plane 59.

[0078] During operation of the electrochemical cell unit 53, i.e. during the conversion of electrochemical energy into electrical energy as fuel cell unit 1 or during the conversion of electrical energy into electrochemical energy as electrolysis cell unit 49, the temperature of the cell stack 61 is recorded using a temperature sensor 82 and the data on the temperature of the cell stack 61 is transmitted to a control and / or regulating unit 83 via data lines (not shown). In the control and / or regulating unit 83, the change in the height of the cell stack 61, i.e. the extension of the cell stack 61 perpendicular to the fictitious plane 59, is determined from the change in the temperature of the cell stack 81 using stored data. The height of the cell stack 61 is essentially directly proportional to the temperature of the cell stack 61 and also depends on the equivalent spring constants of the tension rods 38.Corresponding data from empirical measurements and / or calculations are stored in the control and / or regulation unit 83. The temperature sensor 82 thus indirectly also forms a sensor for detecting the height of the cell stack 61. The cell stack 61 is intended to be preloaded with a substantially constant compressive force. However, due to spring laws such as Hooke's law, the tension rods 38, as fictitious spring elements, nevertheless cause an increase in the compressive force with which the cell stack 61 is preloaded when the height of the cell stack 61 increases. Conversely, when the height of the cell stack 61 decreases due to cooling of the cell stack 61, the compressive force with which the cell stack 61 is preloaded is reduced.

[0079] The length of the connecting devices 37 can be changed with the integrated length-changing means 60 by changing a parameter. To increase the length of the connecting devices 37 as the tie rods 38, the closing element 76 is opened, and the compressor 78 introduces the fluid as the hydraulic fluid through the fluid opening 71, so that the pressure of the hydraulic fluid in the cavity 66 increases as a parameter of the connecting device 37, thus exerting a greater compressive force on the inner side 81 of the pressure vessel 67. In particular, the compressive force of the hydraulic fluid acting on the radial walls 70 causes an increase in the tensile force in the axial walls 69 of the cavity connecting device 72 and thus an expansion of the axial walls 69.Conversely, when the compressor 78 is switched off and the closing element 76 is opened, hydraulic fluid can be discharged from the cavity 66, thereby reducing the pressure of the hydraulic fluid in the cavity 66 as a parameter of the connecting device 37 and reducing the tensile force in the axial walls 69 of the cavity connecting device 72, thus causing compression of the axial walls 69. The cavity 66 is completely filled with the hydraulic fluid as the fluid.

[0080] The control and / or regulating unit 83 thus changes the length of the connecting devices 37 depending on the temperature and the cell stack 61. The length of the connecting devices 37 is actively controlled and / or regulated by changing the pressure of the fluid in the cavity 66 as a parameter of the connecting device 37, so that the compressive prestress in the cell stack 61 can be kept substantially constant even in the event of a temperature-related change in the height of the cell stack 61.

[0081] Optionally, the distance between the clamping plates 34, i.e., the first clamping plate 35 and the second clamping plate 36, is additionally detected with the sensors 80 at the end regions near the connecting devices 37. These four detected distances are transmitted to the control and / or regulating unit 83 via data lines (not shown). The differences between these four distances are calculated in the control and / or regulating unit 83, and if a predetermined limit value of this difference is exceeded, the length of at least one connecting device 37 is selectively and actively changed in order to maintain a substantially parallel alignment of the two clamping plates 34 to one another.For example, if the distance between one connecting device 37 and the other three connecting devices 37 is too small, the closing element 76 on this connecting device 37 is opened, and hydraulic fluid is introduced into the cavity 66 until the difference between the distances again falls below or reaches the predetermined limit. The hydraulic fluid can thus be selectively introduced into at least one cavity 66 and / or discharged from at least one cavity 66 by means of the opening or closing of one closing element 76 and the operation of the compressor 78.

[0082] Overall, the electrochemical cell unit 53 according to the invention and the method according to the invention for operating an electrochemical cell unit 53 offer significant advantages. The length of the connecting devices 37 can be actively controlled and / or regulated using the length-changing means 60. This advantageously makes it possible to achieve a substantially constant prestressing of the cell stack 61 with compressive force even when the height of the cell stack 61 changes due to temperature changes in the cell stack 61. Furthermore, in the event of deviations in the parallelism between the first clamping plate 35 and the second clamping plate 36, the length of at least one connecting device 37 can be selectively changed, thus aligning the two clamping plates 34 substantially parallel to one another again. QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] DE 10 2019 215 888 A1

[0008] DE 10 2022 205 729 A1

[0009]

Claims

[1] Electrochemical cell unit (53) comprising - stacked electrochemical cells (52) as a cell stack (61), - a first clamping element (33, 34, 35) for applying a compressive force to a first electrochemical cell (52), - a second clamping element (33, 34, 36) for applying a compressive force to a last electrochemical cell (52), - at least one connecting device (37) subjected to a tensile force, which is in mechanically operative connection with the first and second clamping elements (33, 34, 35, 36), so that due to the tensile force in the at least one connecting device (37), a compressive force can be applied by the first clamping element (33, 34, 35) to the first electrochemical cell (52) and a compressive force can be applied by the second clamping element (33, 34, 36) to the last electrochemical cell (52), so that the cell stack (51) is prestressed with a compressive force, characterized bythat the length of the at least one connecting device (37) is variable with a length-changing means (60) integrated into the at least one connecting device (37), in that at least one parameter of the at least one connecting device (37) is controllable and / or regulatable with the respective length-changing means (60) and the length of the at least one connecting device (37) is dependent on the at least one parameter. [2] Electrochemical cell unit according to claim 1, characterized by that the at least one connecting device (37) is designed as a, in particular rigid and / or straight, pull rod (38). [3] Electrochemical cell unit according to claim 1 or 2, characterized by that the at least one length-changing means (60) is a cavity (66) filled with a fluid in the at least one connecting device (37) as a cavity connecting device (72). [4] Electrochemical cell unit according to claim 3, characterized by that the pressure of the fluid in the at least one cavity (66) is controllable and / or regulatable as a parameter of the at least one connecting device (37) and, due to the pressure of the fluid in the at least one cavity (66), a variable pressure force can be applied by the fluid to an inner side (81) of the cavity connecting device (72), so that an increase in the fluid pressure causes an expansion and increase in the length of the at least one connecting device (37) and a reduction in the fluid pressure causes a compression and reduction in the length of the at least one connecting device (37). [5] Electrochemical cell unit according to claim 3 or 4, characterized bythat the electrochemical cell unit (52) comprises a compressor (78), in particular a compressor, for increasing the fluid pressure in the cavity (66) for supplying the at least one cavity (66) with the fluid under a variable pressure. [6] Electrochemical cell unit according to claim 5, characterized by that the compressor (78) is in fluid-conducting connection with the at least one cavity (66) by means of at least one fluid line (74), in particular the compressor (78) is in fluid-conducting connection with the cavities (66) of a plurality of connecting devices (37) by means of a plurality of fluid lines (74). [7] Electrochemical cell unit according to one or more of the preceding claims, characterized by that the length of the at least one cavity (66) is at least 30%, 50%, 70% or 90% of the length of the at least one connecting device (37). [8] Electrochemical cell unit according to one or more of the preceding claims, characterized by that at least one cavity (66) is formed on each of the connecting devices (37). [9] Electrochemical cell unit according to one or more of the preceding claims, characterized byin that the at least one length-changing means (60) is designed as at least one heater, in particular as at least one electrical resistance heater, for changing the temperature as a parameter of the at least one connecting device (37), so that by increasing the temperature of the at least one connecting device (37) due to thermal expansion as thermal expansion of the at least one connecting device (37) the length of the at least one connecting device (37) is increased, and by reducing the temperature of the at least one connecting device (37) due to thermal shrinkage as thermal contraction of the at least one connecting device (37) the length of the at least one connecting device (37) is reduced. [10] Electrochemical cell unit according to one or more of the preceding claims, characterized bythat the electrochemical cell unit (52) comprises at least one sensor (80) for detecting the distance between the first and second clamping elements (33, 34, 35, 36) in a direction perpendicular to a fictitious plane (59) spanned by the electrochemical cells (52) and the length of the at least one connecting device (37) is variable as a function of the distance detected by the at least one sensor (80) by changing the at least one parameter. [11] Electrochemical cell unit according to claim 10, characterized by that the length of different connecting devices (37) can be varied differently until a substantially parallel alignment of the first and second clamping elements (33, 34, 35, 36) to one another is present. [12] Method for operating an electrochemical cell unit (53) with stacked electrochemical cells (52) as a cell stack (61) for converting electrochemical energy into electrical energy as a fuel cell unit (1) and / or for converting electrical energy into electrochemical energy as an electrolysis cell unit (49), comprising the steps: - converting electrochemical energy into electrical energy by passing a fuel through a fuel cell unit (1) or converting electrical energy into electrochemical energy by passing an electrolyte through the electrolysis cell unit (49), - a compressive force is applied to a first electrochemical cell (52) by means of a first clamping element (33, 34, 35), - a second clamping element (33, 34, 36) is used to apply a compressive force to a last electrochemical cell (52), - at least one connecting device (37) is subjected to a tensile force, and the tensile force in the at least one connecting device (37) is applied by the first clamping element (33, 34, 35) to the first electrochemical cell (52) as a compressive force and by the second clamping element (33, 34, 36) to the last electrochemical cell (52) as a compressive force, so that the cell stack (61) is prestressed with a compressive force, characterized by that the length of the at least one connecting device (37) is changed by means of a length-changing means (60) integrated into the at least one connecting device (37), in that at least one parameter of the at least one connecting device (37) is controlled and / or regulated by means of the respective length-changing means (60), and the length of the at least one connecting device (37) is dependent on the at least one parameter. [13] Method according to claim 12, characterized byin that each length-changing means (60) comprises a cavity connecting device (72) with a cavity (66) filled with a fluid, and the length of the at least one connecting device (37) is changed by controlling and / or regulating the pressure of the fluid in the at least one cavity (66) as a parameter, and due to the pressure of the fluid in the at least one cavity (66), a variable pressure force is applied by the fluid to an inner side (81) of the cavity connecting device (72), and an increase in the pressure of the fluid causes an expansion and enlargement of the length of the at least one connecting device (37), and a reduction in the pressure of the fluid causes a compression and reduction of the length of the at least one connecting device (37). [14] Method according to claim 12 or 13, characterized bythat during operation of the electrochemical cell unit (53) the length of the at least one connecting device (37) is changed by controlling and / or regulating at least one parameter of the at least one connecting device (37). [15] Method according to one or more of claims 12 to 14, characterized by that during operation of the electrochemical cell unit (53) the length of at least one connecting device (37), preferably a plurality of connecting devices (37), is changed, in particular simultaneously, with the at least one length-changing means (60), preferably the plurality of length-changing means (60), by, in particular simultaneously, in at least one cavity (66), the fluid is introduced into the at least one cavity (66) and / or is discharged from the at least one cavity (66) until a substantially parallel alignment of the first and second clamping elements (33, 34, 35, 36) to one another is achieved.

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