WO2024027985A1

WO2024027985A1 - Humidifying device for a fuel cell unit

Info

Publication number: WO2024027985A1
Application number: PCT/EP2023/066640
Authority: WO
Inventors: Martin Katz; Jochen Wessner
Original assignee: Robert Bosch Gmbh
Priority date: 2022-08-04
Filing date: 2023-06-20
Publication date: 2024-02-08
Also published as: DE102022208114A1

Abstract

The invention relates to a humidifying device (59) for a fuel cell unit (1) for transferring water from the oxidising agent discharged from a fuel cell stack (40) as secondary oxidising agent, to the oxidising agent introduced into the fuel cells stack (40) as primary oxidising agent, comprising a housing (60) which delimits an interior and has a primary inlet opening (64) for introducing the primary oxidising agent into the humidifying device (59), and a primary outlet opening (65) for discharging the primary oxidising agent from the humidifying device (59), and also has a secondary inlet opening (66) for introducing the secondary oxidising agent into the humidifying device (59), and a secondary outlet opening (67) for discharging the secondary oxidising agent from the humidifying device (59), stacked tubes (75) with membrane walls (77) for transferring water from the secondary oxidising agent to the primary oxidising agent through the membrane walls (77), at least one fixing means (68) for fixing the tubes (75) in the interior, at least one sealing means (69), which subdivides the interior into at least one tube interior subspace (82) for passing the oxidising agent through the tubes (75) and into a flow-around interior subspace (83) in which oxidising agent flows around the outer surfaces (77) of the tubes (75), wherein the at least one fixing means (68) and/or the at least one sealing means (69) are formed in multiple parts from stacking elements (70, 90), and the stacking elements (70, 90) are arranged in a stack in the interior.

Description

title

Humidification device for a fuel cell unit

The present invention relates to a humidification device according to the preamble of claim 1, a method for producing a humidification device according to the preamble of claim 8 and a fuel cell unit according to the preamble of claim 15.

State of the art

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

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 oxidizing agents, i.e. a flow space for passing oxidizing agents through, such as air from the environment with oxygen. The gas space for oxidizing agents 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 oxidizing agent, namely oxygen, reaches the cathode of the fuel cells through the gas diffusion layer. In an analogous manner, there is a gas space for fuel. During the To produce a fuel cell unit, individual fuel cells are stacked into a stack as the fuel cell stack.

Channels for oxidizing agents are formed in the fuel cell units. A gas conveying device, in particular a blower, conveys air from the environment as the primary oxidizing agent into the channels for oxidizing agents. After passing the primary oxidant through the oxidant channels in the fuel cell stack, it is discharged into the environment as a secondary oxidant. During the electrochemical reaction, water, particularly in the form of moisture or water vapor, is absorbed by the secondary oxidizing agent. For the operation of the fuel cell unit, it is desirable that the primary oxidizing agent introduced into the fuel cell stack has a high moisture or water content. For this purpose, the secondary oxidizing agent is passed through a humidification device after being discharged from the fuel cell stack and before being discharged into the environment. Furthermore, the primary oxidizing agent is also passed through the humidification device before being introduced into the fuel cell stack. In the humidification device, the water is transferred from the secondary oxidant to the primary oxidant.

A large number of tubes with a membrane effect are arranged in the humidification device with a housing. The housing delimits an interior space and this is divided into two inner pipe compartments and a flushing inner compartment with fixing means and sealant. The fixing agent and the sealing agent are formed of a hardened resin or adhesive. The pipes open into the 2 inner pipe compartments. The primary oxidizing agent is first passed through an inlet opening for the primary oxidizing agent into a first inner tube space and from there into the flow spaces of the tubes. After the primary oxidizing agent has passed through the pipes, ie through the flow spaces of the pipes, it flows into a second inner pipe space and is drained from the humidification device through an outlet opening for the primary oxidizing agent. An inlet opening and an outlet opening for the secondary oxidizing agent open into the inner flushing space. The inner flushing subspace is not divided into any flow subspaces, so that in a smaller flow velocity of the secondary oxidizing agent occurs in the inner flushing subspace with only one flow space because the inner flushing subspace has a large flow cross-sectional area. The pipes are arranged in a disordered manner and stacked in any way with little or no distance between them, so that the outer surfaces of the pipes lie on top of each other to a greater extent. This contact between the outer surfaces of the tubes reduces the transfer of water from the outer surface of the tubes at the wash interior compartment containing the secondary oxidant to the primary oxidant flowing through the tubes. The small diameter of the flow spaces of the tubes causes a large pressure drop of the primary oxidant in the tubes. This disadvantageously requires a large amount of mechanical drive energy for the gas delivery device.

EP 1 261 992 B1 discloses a solid polymer fuel cell system comprising a solid polymer fuel cell and a device for humidifying a reaction gas feed stream, the fuel cell having a reaction gas inlet port and a reaction gas exhaust port and the humidification device having a membrane replacement humidifier.

The CN 211088409 U discloses a humidification device for a fuel cell. A membrane tube bundle is arranged in an interior space delimited by a housing and consists of several membrane tubes. The membrane tubes have micropores. Inlet and outlet openings for air are formed on the housing. Adhesive acts as a fixing and sealing agent to fix the membrane tubes in the housing, to seal and to divide the interior.

Disclosure of the invention

Advantages of the invention

Humidification device according to the invention for a fuel cell unit for transferring water from the oxidizing agent discharged from a fuel cell stack as a secondary oxidizing agent to that in the Fuel cell stack introduced oxidant as the primary oxidant, comprising a housing which delimits an interior, with a primary inlet opening for introducing the primary oxidizing agent into the humidification device, with a primary outlet opening for discharging the primary oxidizing agent from the humidification device, with a secondary inlet opening for introducing the secondary Oxidizing agent into the humidifying device, with a secondary outlet opening for removing the secondary oxidizing agent from the humidifying device, stacked tubes with membrane walls for transferring the water from the secondary oxidizing agent to the primary oxidizing agent through the membrane walls, at least one fixing agent for fixing the tubes in the interior, at least one sealing means, which divides the interior into at least one inner pipe subspace for passing the oxidizing agent through the pipes and into a flushing inner subspace for flushing the outer surfaces of the pipes with oxidizing agent, wherein the at least one fixing means and/or the at least one sealing means is formed in several parts from stacking elements and / or are and the stacking elements are arranged stacked in the interior.

In a further embodiment, contact surfaces formed on the stacking elements, in particular releasably without a material connection, rest on the pipes.

In an additional variant, the geometry of the contact surfaces of the stacking elements is designed to be essentially complementary to the geometry of the outer surfaces of the tubes.

In a supplementary embodiment, the stacking elements are designed as additional components in addition to the tubes.

Preferably, the stacking elements are plate-shaped, in particular strip-shaped, and the tubes, in particular all tubes, are cut by a common fictitious stacking plane between each two immediately adjacent stacked stacking elements. In a further embodiment, stacking surfaces formed on the stacking elements lie on top of one another, in particular releasably without a material connection.

In an additional variant, the stacking elements are formed in one piece with the tubes.

Method according to the invention for producing a humidification device for a fuel cell unit for transferring water from the oxidizing agent discharged from a fuel cell stack as a secondary oxidizing agent to the oxidizing agent introduced into the fuel cell stack as the primary oxidizing agent, with the steps: providing a housing which delimits an interior space, with a primary inlet opening for introducing the primary oxidizing agent into the humidifying device, with a primary outlet opening for discharging the primary oxidizing agent from the humidifying device, with a secondary inlet opening for introducing the secondary oxidizing agent into the humidifying device, with a secondary outlet opening for discharging the secondary oxidizing agent from the humidifying device, providing pipes with membrane walls for transferring the water from the secondary oxidizing agent to the primary oxidizing agent through the membrane walls, providing at least one fixing means for fixing the pipes in the interior, providing at least one sealing agent which divides the interior into at least one Pipe inner subspace for passing the oxidizing agent through the pipes and divided into a flushing inner subspace for flushing the outer surfaces of the pipes with oxidizing agent, assembling the provided components of the humidification device to the humidification device by arranging the pipes in the interior, fixing the pipes with the at least fixing agent in the interior and dividing the interior with the at least one sealant into the at least one inner tube subspace and into a flushing inner subspace, the at least fixing means and/or the at least one sealing means being provided in several parts from stacking elements. In a further embodiment, the fixing of the pipes with the at least fixing means and/or the dividing of the interior space with the at least sealing means into the at least one inner pipe subspace and into the flushing inner subspace is carried out by stacking, in particular strip-shaped, stacking elements and arranging the pipes between two stacking elements become.

In an additional embodiment, the stacking elements are provided by injection molding and/or extrusion, in particular as separate components in addition to the tubes.

In a supplementary variant, the stacking elements are provided in one piece with the tubes, in particular by producing the tubes and the stacking elements using extrusion.

The tubes with at least one stacking element expediently have a first outside diameter on at least a first section in the longitudinal direction of the tubes and have a second outside diameter on at least a second section in the longitudinal direction of the tubes and the second outside diameter is larger than the first outside diameter and at least the membrane wall is formed in a first section and a stacking element is formed on at least one second section.

In a supplementary embodiment, the material for the production of the pipes and stacking elements is passed through a diaphragm with a variable diameter and during the production of the pipes on a section in the longitudinal direction of the pipes without the stacking elements the diaphragm has a first diameter and during the production of the pipes at a section in the longitudinal direction of the tubes with the stacking elements, the aperture has a second diameter and the second diameter of the aperture is larger than the first diameter of the aperture. The diameter of the aperture essentially corresponds, in particular with a deviation of less than 10% or 5%, to the outer diameter of the tubes with the at least one stacking element. In a further embodiment, the fixing of the pipes with the at least one fixing means and/or the dividing of the interior with the at least one sealing means is carried out by placing the stacking surfaces, in particular circumferential radial outer sides, of the stacking elements on stacking surfaces one on top of the other. The preferably ring-shaped stacking elements, each formed in one piece with a tube, preferably have the circumferential radial outside as a stacking surface.

Fuel cell unit according to the invention for the electrochemical generation of electrical energy, comprising stacked fuel cells so that the stacked fuel cells form a fuel cell stack, channels for oxidizing agents integrated into the fuel cell stack, a humidification device for transferring water from the oxidizing agent discharged from the fuel cell stack as a secondary oxidizing agent to the in the oxidizing agent introduced into the fuel cell stack as the primary oxidizing agent, wherein the humidification device is designed as a humidification device described in this patent application and / or the humidification device is produced using a method described in this patent application.

In a further embodiment, the tubes, in particular ends of the tubes, open into the at least one inner tube subspace.

In a further variant, the inner flushing subspace is divided into at least two flow subspaces with at least one sealant to form flow subspaces.

In a further embodiment, the sealing means for forming flow spaces is essentially aligned perpendicular to the longitudinal axes of the pipes, in particular with a deviation of less than 30°, 20° or 10°.

In a complementary variant, the oxidizing agent is in one direction

Essentially, in particular with a deviation of less than 30°, 20° or 10°, can be passed through the flow compartments perpendicular to the longitudinal axes of the pipes.

In an additional embodiment, at least one flow opening is formed in the humidification device for guiding oxidizing agent from one flow subspace into another flow subspace.

Preferably, the at least one flow opening is designed as an interruption of a fastening projection on the housing.

In a further variant, the at least one flow opening is designed as an interruption on the at least one sealing means to form the flow subspaces. The interruption on the at least one sealing means for forming the flow subspaces is designed, for example, as a through hole in the region of one end of the at least one sealing means.

Preferably, two flow openings each open into a flow subspace.

In a further embodiment, a flow opening and the inlet opening for the oxidizing agent or the outlet opening for the oxidizing agent each open into a flow subspace. Preferably, in the flow direction of the oxidizing agent, the inlet opening for the oxidizing agent opens into the first flow subspace and the outlet opening for the oxidizing agent opens into the last flow subspace.

In a further embodiment, the two flow openings open at two opposite end regions, in particular end regions in a direction perpendicular to the longitudinal axes of the tubes, into each one flow subspace. Preferably, the extent of each end region is less than 20% or 10% of the, preferably maximum, extent of the respective flow subspace.

In an additional variant, the flow opening on the one hand and the inlet opening for the oxidizing agent or the outlet opening for the oxidizing agent on the other hand open at two opposite end regions, in particular end regions in a direction perpendicular to the longitudinal axes of the pipes, in each of the flow subspaces.

Preferably, the at least one sealing means for forming partial flow spaces is formed in several parts from stacking elements and the stacking elements are arranged stacked in the interior.

In a further embodiment, at least one sealant for forming flow subspaces is provided and the flushing inner subspace is divided into at least two flow subspaces with at least one sealant for forming flow subspaces.

In a further embodiment, the subdivision of the inner subspace for flushing is carried out into at least two flow subspaces with the at least one sealing means for forming the flow subspaces by stacking, in particular strip-shaped or ring-shaped, stacking elements.

In an additional variant, the at least one sealing means for forming the flow subspaces is made available in several parts from stacking elements.

In a further embodiment, the flow cross-sectional area of a flow opening or the sum of the flow cross-sectional areas from one flow subspace into another adjacent flow subspace is less than 30%, 20% or 10% of the flow cross-sectional area of the flow subspace into which the at least one flow opening opens.

In a further variant, the subdivision of the flushing inner subspace into at least two flow subspaces with the at least one sealant to form the flow subspaces is carried out like the subdivision of the interior with the at least one sealant into the at least one pipe inner subspace and in the flushing inner subspace. In a further variant, the at least one sealing means for forming the flow subspaces is designed like the at least one sealing means for dividing the interior into the at least one pipe inner subspace and the flushing inner subspace.

In an additional embodiment, the inner flushing subspace is divided into the at least two flow subspaces in the direction of the longitudinal axes of the pipes with the at least one sealing means for forming the flow subspaces.

Preferably, the oxidizing agent flows through adjacent flow subspaces of the inner flushing subspace in the opposite direction, preferably perpendicular to the longitudinal axis of the pipes.

In a supplementary variant, the stacking elements are essentially rectangular in shape.

In an additional embodiment, the stacking elements lie on one another with a prestressing force, so that the stacking surfaces of the stacking elements lie on one another with a compressive force and/or the contact surfaces of the stacking elements rest on the outer surfaces of the tubes with a compressive force. The prestressing force is actively applied to the stacking elements and does not include the gravity of the stacking elements.

In an additional embodiment, the prestressing force is applied to the stacked stacking elements from the housing to the stacking elements.

In a further embodiment, the cross-sectional shape of the tubes is circular, rectangular, in particular square, and/or elliptical. The pipes have any cross-sectional shape.

In a further embodiment, the stacking elements are at least partially, in particular completely, made of plastic, in particular thermoplastic. In an additional embodiment, the membrane walls of the tubes have micropores and/or microopenings. Through the micropores and/or microopenings, the water, in particular in the form of water vapor or moisture, can pass through the membrane walls from the secondary oxidizing agent to the primary oxidizing agent.

In a further embodiment, the stacking elements, in particular the stacking elements as complementary components to the tubes, are flat and/or disk-shaped and/or plate-shaped and/or strip-shaped.

In a further embodiment, the stacking elements, in particular the stacking elements formed in one piece with the tubes, are essentially ring-shaped.

The membrane walls are expediently made of plastic, in particular polysulfones.

Preferably, stacking surfaces of the stacking elements lie on top of each other.

In a further variant, the contact surfaces of the stacking elements are essentially formed parallel to the outer surfaces of the tubes, in particular with a deviation of less than 30°, 20° or 10°.

In a further embodiment, the contact surfaces of the stacking elements are concavely curved, in particular the radius of curvature of the contact surfaces essentially corresponds, in particular with a deviation of less than 30%, 20% or 10%, to the radius of curvature of the outer surfaces of the tubes.

In a further embodiment, the number of stacking elements is larger or smaller than the number of tubes, in particular the number of stacking elements is larger than 2 times, 3 times, 5 times or 7 times the number of tubes. Preferably the number of stacking elements is greater than 10, 30, 50, 100, 300, 500, 1000 or 1500.

At least 50%, 70% or 90% of the sum of the areas of the outer surfaces of the pipes are expediently arranged in the at least one inner flushing space.

In an additional embodiment, the tubes have an inner diameter of the flow space greater than 0.4 mm, 0.6 mm, 0.7 mm, 0.8 mm or 1 mm.

The humidification device expediently comprises at least 10, 30, 50, 100, 300, 500, 1000 or 2000 tubes.

In a supplementary embodiment, the distance, in particular the minimum distance, perpendicular to the longitudinal axis of the tubes is essentially identical, in particular with a deviation of less than 30%, 20% or 10%.

Preferably, the length of the tubes is greater than 5 times, 10 times, 50 times, 100 times, 200 times or 300 times the outside diameter of the tubes.

In a further embodiment, the tubes are arranged essentially straight in the interior space delimited by the housing. Substantially straight tubes preferably means that the radius of curvature of the tubes is larger than the, in particular the smallest or largest, distance between two fixing means in the direction of the longitudinal axis of the tubes.

In an additional embodiment, the tubes are connected to one another in a form-fitting and/or force-fitting manner by means of the stacking elements. The stacking elements lie on top of each other on the stacking surfaces and the stacking elements are connected to one another in a form-fitting and/or force-fitting manner on the stacking surfaces, so that the tubes are connected to one another in a form-fitting and/or force-fitting manner by means of the stacking elements. In an additional embodiment, the primary oxidizing agent can be conducted through the flow spaces of the pipes and the at least one inner pipe subspace and the secondary oxidizing agent can be conducted through the flushing inner subspace.

In an additional embodiment, the secondary oxidizing agent can be conducted through the flow spaces of the pipes and the at least one inner pipe subspace and the primary oxidizing agent can be conducted through the flushing inner subspace.

In an additional embodiment, in the one-piece design of the stacking elements together with the tubes, the stacking elements are designed in several parts in that the tubes are individual components, so that the at least one stacking element formed on the tubes are different multi-part components on the different tubes.

In an additional embodiment, with a one-piece design of the stacking elements on the tubes, the stacking elements are cohesively connected to the tubes.

In a further variant, when the stacking elements are designed as complementary components to the tubes, the stacking elements are connected to the tubes in a form-fitting and/or force-fitting manner, but preferably not in a material-locking manner.

In a further embodiment, the distances L _x in the direction of the longitudinal axes of the tubes between the sealing means and/or between the fixing means and/or between the stacks of stacking elements are different, in particular these differ by at least 30%, 20% or 10%. Advantageously, the sections of the tubes between the stacks of stacking elements have a different natural frequency, so that the sections of the tubes between the stacks of stacking elements do not have identical resonance frequencies. In a further variant, the gas delivery device is designed as a blower or a compressor.

In particular, the fuel cell unit comprises at least 3, 4, 5 or 6 connection devices.

In a further embodiment, the clamping elements are plate-shaped and/or disk-shaped and/or flat and/or designed as a grid.

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

The fuel cells and/or components are expediently designed to be essentially flat and/or disk-shaped.

In a complementary variant, the oxidizing agent is air, air with an increased or reduced oxygen content compared to air or pure oxygen.

Preferably, the fuel cell unit is a PEM fuel cell unit with PEM fuel cells (polymer electrolyte membrane fuel cell).

Brief description of the drawings

Exemplary embodiments of the invention are described in more detail below with reference to the accompanying drawings. It shows:

Fig. 1 is a highly simplified exploded view of a

Fuel cell system with components of a fuel cell,

2 is a perspective view of part of a fuel cell,

3 shows a longitudinal section through a fuel cell,

4 is a perspective view of a fuel cell stack without a housing, 5 shows a section through a fuel cell unit with housing,

6 is a greatly simplified perspective view of a bipolar plate,

7 shows a longitudinal section through a humidification device in a first exemplary embodiment,

8 shows a section AA through a fixing and sealing means and tubes of the humidification device according to FIG. 7,

9 is an exploded view of the fixing and sealing means according to FIG. 8 with pipes,

10 is a top view of a first stacking element of the fixing and sealing means according to FIG. 8,

11 shows a longitudinal section through the humidification device in a second exemplary embodiment,

12 shows a longitudinal section through the humidification device in a third exemplary embodiment,

13 shows a cross section through the fixing and sealing means and the tube of the humidification device according to FIG. 12,

14 shows a section BB through a fixing and sealing means and tubes of the humidification device according to FIG. 12,

15 shows a cross section through the fixing and sealing means and the pipe in a further exemplary embodiment,

Fig. 16 shows a longitudinal section of the pipe with fixing and sealing means according to Figs. 14 and 15. 1 to 3 show the basic structure of a fuel cell 2 as 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 passed to an anode 7 as gaseous fuel and the anode 7 forms the negative pole. A gaseous oxidizing agent, namely air with oxygen, is passed to a cathode 8, ie the oxygen in the air provides the necessary gaseous oxidizing agent. A reduction (electron absorption) takes place at the cathode 8. The oxidation as electron release is carried out at the anode 7.

The redox equations for electrochemical processes are:

Cathode:

O ₂ + 4 H ⁺ + 4 e- -» 2 H ₂ O

Anode:

2 H ₂ -» 4 H ⁺ + 4 e-

Cumulative reaction equation of cathode and anode: 2 H ₂ + O ₂ -» 2 H ₂ O

The difference in the normal potentials of the electrode pairs under standard conditions as the reversible fuel cell voltage or no-load voltage of the unloaded fuel cell 2 is 1.23 V. This theoretical voltage of 1.23 V is not achieved in practice. In idle mode and with small currents, voltages of over 1.0 V can be achieved and in operation with larger currents, voltages between 0.5 V and 1.0 V can be achieved. The series connection of several fuel cells 2, in particular a fuel cell unit 1 with a fuel cell stack 40 of several fuel cells 2 arranged one above the other, has a higher voltage, which corresponds to the number of fuel cells 2 multiplied by the individual voltage of each fuel cell 2.

The fuel cell 2 also includes a proton exchange membrane 5

(Proton Exchange Membrane, PEM), which is between the anode 7 and the Cathode 8 is arranged. The anode 7 and cathode 8 are layer-shaped or disk-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. In general, 12 pm to 150 pm thick, proton-conducting films made of perfluorinated and sulfonated polymers are used. The PEM 5 conducts the protons H ⁺ and essentially blocks ions other than protons H ⁺ so that charge transport can take place due to the permeability of the PEM 5 to the protons H ⁺ . The PEM 5 is essentially impermeable to the reaction gases oxygen O2 and hydrogen H2, that is, it blocks the flow of oxygen O2 and hydrogen H2 between a gas space 31 on the anode 7 with fuel hydrogen H2 and the gas space 32 on the cathode 8 with air or Oxygen O2 as an oxidizing agent. The proton conductivity of PEM 5 increases with increasing temperature and increasing water content.

The electrodes 7, 8 lie on the two sides of the PEM 5, each facing the gas spaces 31, 32, as the anode 7 and cathode 8. A unit consisting of the PEM 5 and anode 7 and cathode 8 is referred to as a membrane electrode assembly 6 (membrane electrode assembly, MEA). The electrodes 7, 8 are pressed with the PEM 5. The electrodes 7, 8 are platinum-containing carbon particles that are bound to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride) and / or PVA (polyvinyl alcohol) and in microporous carbon fiber, Fiberglass or plastic mats are hot-pressed. A catalyst layer 30 is normally applied to the electrodes 7, 8 on the side facing the gas spaces 31, 32 (not shown). The catalyst layer 30 on the gas space 31 with fuel on the anode 7 comprises nanodispersed platinum-ruthenium on graphitized soot particles that are bound to a binder. The catalyst layer 30 on the gas space 32 with oxidizing agent on the cathode 8 analogously comprises nanodisperse platinum. Nation®, a PTFE emulsion or polyvinyl alcohol, for example, are used as binders.

Deviating from this, the electrodes 7, 8 are made up of an ionomer, for example Nation®, platinum-containing carbon particles and additives. This Electrodes 7, 8 with the ionomer are electrically conductive due to the carbon particles and also conduct the protons H ⁺ and also function as a catalyst layer 30 due to the platinum-containing carbon particles (FIGS. 2 and 3). Membrane electrode arrangements 6 with these electrodes 7, 8 comprising the ionomer form membrane electrode arrangements 6 as CCM (catalyst coated membrane).

A gas diffusion layer 9 (Gas Diffusion Layer, GDL) lies on the anode 7 and the cathode 8. The gas diffusion layer 9 on the anode 7 distributes the fuel from channels 12 for fuel evenly onto the catalyst layer 30 on the anode 7. The gas diffusion layer 9 on the cathode 8 distributes the oxidant from channels 13 for oxidant evenly onto the catalyst layer 30 on the cathode 8. The GDL 9 also draws off reaction water in the opposite direction to the direction of flow of the reaction gases, i.e. H. in one direction from the catalyst layer 30 to the channels 12, 13. Furthermore, the GDL 9 keeps the PEM 5 moist and conducts the current. The GDL 9, for example, is made of hydrophobic carbon paper and a bonded carbon powder layer.

A bipolar plate 10 rests on the GDL 9. The electrically conductive bipolar plate 10 serves as a current collector, for dissipating water and for guiding the reaction gases through a channel structure 29 and/or a flow field 29 and for dissipating the waste heat, which occurs in particular in the exothermic electrochemical reaction at the cathode 8. To dissipate the waste heat, channels 14 are incorporated into the bipolar plate 10 for the passage of a liquid or gaseous coolant. The channel structure 29 on the gas space 31 for fuel is formed by channels 12. The channel structure 29 on the gas space 32 for oxidizing agents is formed by channels 13. The materials used for the bipolar plates 10 are, for example, metal, conductive plastics and composite materials or graphite. The bipolar plate 10 thus comprises the three channel structures 29, formed by the channels 12, 13 and 14, for the separate passage of fuel, oxidizing agent and coolant. In a fuel cell unit 1 with fuel cell stack 40 and/or a fuel cell stack 40, a plurality of fuel cells 2 are arranged stacked in alignment (FIG. 4). The fuel cells 2 and the components 5, 6, 7, 8, 9, 10 of the fuel cells 2 are layered and/or disk-shaped and span fictitious levels 37 (Fig. 3). The components 5, 6, 7, 8, 9, 10 of the fuel cells 2 are proton exchange membranes 5, anodes 7, cathodes 8, gas diffusion layers 9 and bipolar plates 10.

1 shows an exploded view of two stacked fuel cells 2. A seal 11 seals the gas spaces 31, 32 in a fluid-tight manner. Hydrogen H2 is stored as fuel at a pressure of, for example, 350 bar to 800 bar in a compressed gas storage 21 (FIG. 1). From the compressed gas storage 21, the fuel is passed through a high-pressure line 18 to a pressure reducer 20 in order to reduce the pressure of the fuel in a medium-pressure line 17 from approximately 10 bar to 20 bar. The fuel is fed from the medium pressure line 17 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. The fuel is supplied from the injector 19 to a supply line 16 for fuel (FIG. 1) and from the supply line 16 to the channels 12 for fuel, which form the channel structure 29 for fuel. The fuel thereby flows through the gas space 31 for the fuel. The gas space 31 for the fuel is formed by the channels 12 and the GDL 9 on the anode 7. After the flow through the channels 12, the fuel not used in the redox reaction at the anode 7 and, if necessary, water from a controlled humidification of the anode 7 are discharged from the fuel cells 2 through a discharge line 15.

A gas conveying device 22, for example designed as a blower 23 or a compressor 24, conveys air from the environment as oxidizing agent into a supply line 25 for oxidizing agent. From the supply line 25, the air is supplied to the channels 13 for oxidizing agents, which form a channel structure 29 on the bipolar plates 10 for oxidizing agents, so that the oxidizing agent flows through the gas space 32 for the oxidizing agent. The gas space 32 for the oxidizing agent is formed by the channels 13 and the GDL 9 on the cathode 8. After the oxidizing agent 32 has flowed through the channels 13 or the gas space 32, the oxidizing agent not consumed at the cathode 8 and the reaction water formed at the cathode 8 due to the electrochemical redox reaction are drained out of the fuel cells 2 through a discharge line 26. A supply line 27 is used to supply coolant into the channels 14 for coolant and a Discharge line 28 serves to drain away the coolant passed through channels 14. The supply and discharge lines 15, 16, 25, 26, 27, 28 are shown as separate lines in FIG Aligned fluid openings 52 on sealing plates 50 are formed as an extension at the end region 51 of the bipolar plates 10 (FIG. 6) and membrane electrode arrangements 6 (not shown) lying one on top of the other. The fuel cells 2 and the components of the fuel cells 2 are disc-shaped and span fictitious planes 37 that are essentially parallel to one another. The aligned fluid openings 52 and seals (not shown) in a direction perpendicular to the fictitious planes 37 between the fluid openings 52 thus form an oxidant supply channel 53, an oxidant discharge channel 54, a fuel supply channel 55, a fuel discharge channel 56, etc Supply channel 57 for coolant and a discharge channel 58 for coolant. The supply and discharge lines 15, 16, 25, 26, 27, 28 outside the fuel cell stack 40 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 fuel cell stack 40 of the fuel cell unit 1 open into the supply and discharge channels 53, 54, 55, 56, 57, 58 within the fuel cell stack 40 of the fuel cell unit 1. The Fuel cell stack 40 as fuel cell unit 1 together with the compressed gas storage 21 and the gas delivery device 22 forms a fuel cell system 4.

In the fuel cell unit 1, the fuel cells 2 are arranged between two clamping elements 33 as clamping plates 34. An upper clamping plate 35 rests on the top fuel cell 2 and a lower clamping plate 36 rests on the bottom fuel cell 2. The fuel cell unit 1 comprises approximately 200 to 400 fuel cells 2, not all of which are shown in FIGS. 4 to 5 for illustrative reasons. The clamping elements 33 apply a compressive force to the fuel cells 2, ie the upper clamping plate 35 rests on the topmost fuel cell 2 with a compressive force and the lower clamping plate 36 rests on the lowest fuel cell 2 with a compressive force. The fuel cell stack 40 is thus braced in order to ensure tightness for the Fuel, the oxidizing agent and the coolant, in particular due to the elastic seal 11, and also to keep the electrical contact resistance within the fuel cell stack 40 as small as possible. To clamp the fuel cells 2 with the clamping elements 33, four connecting devices 38 are designed as bolts 39 on the fuel cell unit 1, which are subject to tension. The four bolts 39 are firmly connected to the clamping plates 34.

The fuel cell stack 40 is arranged in a housing 42 (FIG. 5). The housing 42 has an inside 43 and an outside 44. A space 41 is formed between the fuel cell stack 40 and the housing 42. The housing 42 is also formed by a connection plate 47 made of metal, in particular steel. The remaining housing 42 without the connection plate 47 is attached to the connection plate 47 with fixing elements 48 as screws 49. An opening 45 for introducing oxidizing agent into the channels 13 for oxidizing agent is formed in the connection plate 47 and in the lower clamping plate 36. In addition, an opening 46 for discharging oxidizing agent from the channels 13 for oxidizing agent is formed in the connection plate 47 and in the lower clamping plate 36. In the connection plate 47 and the lower clamping plate 36 as the clamping element 33, further openings, not shown, are formed for introducing fuel, for discharging fuel, for introducing coolant and for discharging coolant. This means that a total of 6 openings are formed in the connection plate 47 and the lower clamping plate 36 (not shown).

The oxidizing agent introduced into the fuel cells 2 is the primary oxidizing agent and the oxidizing agent discharged from the fuel cells 2 is the secondary oxidizing agent. The fuel cells 2 are stacked to form a fuel cell stack 40. The primary oxidizing agent is introduced from the gas conveyor 22 through the supply line 25 into the channels 13 for oxidizing agent and passed through a humidification device 59 before being introduced into the channels 13 for oxidizing agent. The secondary oxidant is discharged to the environment through the oxidant and water discharge line 26 after passing through the opening 46 for discharging the oxidant and before being discharged to the environment through the Humidification device 59 directed. In the humidification device 59, the water, in particular in the form of moisture or water vapor, is transferred from the secondary oxidizing agent to the primary oxidizing agent.

In Fig. 6, the bipolar plate 10 of the fuel cell 2 is shown in a highly simplified and schematic manner. The bipolar plate 10 includes the channels 12, 13 and 14 as three separate channel structures 29. The channels 12, 13 and 14 are not shown separately in FIG Bipolar plates 10 and membrane electrode arrangements 6 (not shown) are arranged in an aligned stacked manner within the fuel cell unit 1, so that supply and discharge channels 53, 54, 55, 56, 57, 58 are formed. Seals (not shown) are arranged between the sealing plates 50 of the bipolar plate 10 for fluid-tight sealing of the

Fluid openings 52 are formed by supply and discharge channels 53, 54, 55, 56, 57, 58. The channels 14 for the coolant are actually formed between a first plate and a second plate (not shown) of the bipolar plate 10.

A first structural exemplary embodiment of the humidification device 59 is shown in FIGS. 7 to 10. The humidification device 59 includes a housing 60 made of metal or plastic. The housing 60 comprises a top wall 61 as a, preferably removable and/or lockable, lid, a bottom wall 62 and side walls 63. The housing 60 delimits an interior with the top wall 61, the bottom wall 62 and the side walls 63 and the interior is divided into two Pipe inner subspaces 82 and a flushing inner subspace 83 are divided. Formed on the housing are an inlet port 64 for the primary oxidant, an outlet port 65 for the primary oxidant, an inlet port 66 for the secondary oxidant and an outlet port 67 for the secondary oxidant. A large number of tubes 75 are arranged stacked in the interior space delimited by the housing 60. The tubes 75 each have a longitudinal axis 89 (FIG. 16) and the tubes 75 and thus also the longitudinal axes 89 of the tubes 75 are aligned essentially parallel to one another, in particular with a deviation of less than 30°, 20° or 10° . The tubes 75 have an outer surface 76 on the outside and are essentially circular in cross section Membrane wall 77 is formed. The membrane wall 77 delimits a flow space 86 on the inside for the primary oxidizing agent to pass through. The membrane walls 77 have micropores and microopenings for the passage of moisture or water from the inner subspace 83 with secondary oxidizing agent into the flow spaces 86 of the tubes 75 with primary oxidizing agent.

The tubes 75 are fixed to one another and to the housing 60 with stacking elements 70. The stacking elements 70 are essentially strip-shaped and rectangular. First stacking elements 87 are designed as intermediate stacking elements 87 and are arranged between layers of tubes 75. At the end region of stacked first stacking elements 87 as intermediate stacking elements 87, second stacking elements 88 are arranged as end stacking elements 88. The intermediate stacking elements 87 and the end stacking elements 88 are stacking elements 70. The end regions of the stacked stacking elements 70 are formed in a direction perpendicular to the longitudinal axis 89 of the tubes 75. Contact surfaces 71 and stacking surfaces 72 are formed on two opposite sides of the intermediate stacking elements 87. The outer surfaces 76 of the tubes 75 lie on the contact surfaces 71 for the positive fixation of the tubes 75 on the contact surfaces 71. The intermediate stacking elements 87 lie on one another on the stacking surfaces 72. The geometry of the contact surfaces 71 is designed to be complementary to the geometry of the outer surface 76 of the tubes 75. The outer surface 76 of the tubes 75 is designed to be convexly curved and the contact surface 71 of the stacking elements 70 is designed to be concavely curved. The radius of curvature of the outer surface 76 of the tubes 75 corresponds to the radius of curvature of the contact surface 71 of the stacking elements 70. The stacked

Stacking elements 70 thus serve as fixing means 68 for positively fixing the tubes 75 in the interior of the housing 60.

In addition, the stacking elements 70 also function as sealing means 69 for the essentially fluid-tight separation of the interior of the housing 60 into the flushing inner subspace 83 and the two inner pipe subspaces 82. The stacked stacking elements 70 shown on the left and right in FIG. 7 serve for the fluid-tight separation of one inner pipe subspace 82 each dem Flushing inner part space 83. The end stacking element 88 at the bottom is fixed in a form-fitting manner in a circumferential fastening recess 85 in the bottom wall 82 of the housing 60. The end stacking element 88 at the top rests on a circumferential fastening projection 84 on the top wall 61. The distance between the fastening projection 84 and the fastening recess 85 is selected such that a prestressing force is applied to the stacked stacking elements 70 by the fastening projection 84 and the fastening recess 85. The stacking surfaces 72 of the stacking elements 70 and the outer surfaces 76 of the tubes 75 as well as contact surfaces 71 of the stacking elements 70 thus rest on one another with a greater compressive force than would result from the gravity of the stacking elements 70 and the tubes 75. The tubes 75 are therefore also fixed to a considerable extent in a non-positive manner on the outer surfaces 76 on the contact surfaces 71 of the stacking elements 70. The stacking elements 70 span a fictitious plane 74 and this fictitious plane 74 is essentially aligned parallel to the longitudinal axis 89 of the tubes 75, in particular with a deviation of less than 30°, 20° or 10°. A fictitious stacking plane 73 of the tubes 75, which is aligned parallel to the fictitious plane 74, intersects all of the tubes 75 between 2 intermediate stacking elements 87 as a layer of tubes 75. The tubes 75 are thus arranged in layers between each 2 intermediate stacking elements 87. Analogously, a layer of tubes 75 is also arranged between the intermediate stacking element 87 and the end stacking element 88.

The flushing inner subspace 83 is divided into 2 flow subspaces 91 by an additional stack of stacking elements 70 and these 2 flow subspaces 91 of the flushing inner subspace 83 have approximately a length Li and a length L2 in the direction of the longitudinal axis 89 of the tubes 75. The additional stack of stacking elements 70 thus forms a sealing means 69 for forming the flow subspaces 91. The additional stack of stacking elements 70 is arranged approximately centrally between the stack of stacking elements 70 shown on the left and right in FIG. 7. These centrally stacked stacking elements 70 are fixed at the bottom in the same way as the fastening recess 85 on the bottom wall 82 of the housing 60. The fastening projection 84 lies intermittently on the upper end stacking element 88 of the middle stack of stacking elements 70 as flow openings 92 on the end stacking element 88, so that the secondary oxidizing agent introduced through the inlet opening 66 for secondary oxidizing agent initially only flows around the right flow subspace 91 according to FIG the interruptions are introduced as flow openings 92 in the left flow subspace 91 of the flushing inner subspace 83 and flows around the pipes 75 between the middle and left stack of stacking elements 70 and is then discharged out of the humidification device 59 through the outlet opening 67. The stack of stacking elements 70 shown on the left and right in FIG 91 of the interior flushing compartment 83.

The primary oxidizing agent is thus introduced through the inlet opening 64 into the inner pipe subspace 82 shown on the left in FIG. 7 and is introduced from this inner pipe subspace 82 into the flow spaces 86 of the pipes 75. After passing the primary oxidizing agent through the flow spaces 86, the primary oxidizing agent is collected again in the inner tube space 82 shown on the right in FIG. 7 and discharged from the humidification device 59 through the outlet opening 65. While the primary oxidizing agent is passing through the tubes 75, the secondary oxidizing agent is simultaneously introduced through the inlet opening 66 and discharged through the outlet opening 67, so that the outer surfaces 76 of the tubes 75 are washed around by the secondary oxidizing agent and thus the water is absorbed by the secondary oxidizing agent the primary oxidizing agent is transferred. The centrally arranged stack of stacking elements 70 serves not only as a sealing means 69, but also as a fixing means 68, so that the tubes 75 are fixed with a small distance Li and l_2 in the direction of the longitudinal axis 89 on the fixing means 68 as the stacks of stacking elements 70 and thus there is a slight deflection, ie the outer surfaces 76 of the tubes 75 have no contact with one another and so that the entire outer surface 76 of the tubes 75 can function to transfer water from the secondary oxidant to the primary oxidant. Due to the subdivision of the internal flushing subspace 83 into two flow subspaces 91, the secondary oxidizing agent has a high flow velocity in the internal flushing subspace 83, so that the transfer of water from the secondary oxidizing agent to the primary oxidizing agent is significantly improved. Due to the high effectiveness of the transfer of water from the secondary oxidizing agent to the primary oxidizing agent, the inner diameter of the flow space 86 of the tubes 75 can be made correspondingly large, so that a small pressure drop of the primary oxidizing agent occurs when it passes through the tubes 75 and therefore advantageously little mechanical energy is necessary to operate the gas delivery device 22. The small distance Li and l_2 between the stacks of stacking elements 70 in the direction of the longitudinal axis 89 of the tubes 75 causes a small natural frequency of the tubes 75, so that no resonance occurs when excited with mechanical vibrations and therefore essentially no disadvantageous mechanical vibrations of the tubes 75 occur between the stacks of stacking elements 70.

A second structural exemplary embodiment of the humidification device 59 is shown in FIG. Essentially only the differences from the first exemplary embodiment according to FIGS. 7 to 10 are described below. Five stacks of stacking elements 70 are arranged in the interior of the housing 60. The stacks of stacking elements 70 arranged on the left and right in Fig. 11 have the same function as in the first exemplary embodiment, ie serve as fixing means 68 for the pipes 75 and as sealing means 69 for fluid-tight sealing of the flushing inner part space 83 from the 2 pipe inner part spaces 82. In In the longitudinal direction of the tubes 75, three further stacks of the stacking elements 70 are formed between these stacks of stacking elements 70 arranged on the left and right in FIG. 11. The further stack of stacking elements 70 thus forms sealing means 69 for forming the flow subspaces 91. These divide the flushing inner subspace 83 in the direction of the longitudinal axis 89 of the pipes 75 into 4 flow subspaces 91. The secondary oxidizing agent introduced through the inlet opening 66 is from these 3 stacks in the flow direction deflected so that the secondary oxidizing agent in the 4 flow subspaces 91 is essentially perpendicular to the longitudinal axis 89 of the tubes 75 flows through the flow subspaces 91 and flows in the opposite direction in adjacent flow subspaces 91. For this purpose, corresponding interruptions are formed as flow openings 92 on each fastening projection 84 on the top wall 61 and the bottom wall 62, so that the secondary oxidizing agent can flow from one flow subspace 91 into the adjacent flow subspace 91. From the last flow subspace 91, the secondary oxidizing agent is discharged from the humidification device 59 through the outlet opening 67. Due to the large number of stacks of stacking elements 70, the flow subspaces 91 have a smaller volume and a small flow cross-sectional area than in the first exemplary embodiment, so that the secondary oxidizing agent is passed at a high flow velocity through one flow subspace 91 between the stacks of stacking elements 70. This high flow rate of the secondary oxidant increases the transferability of the water from the secondary oxidant to the primary oxidant. The distances Li to L4 in the direction of the longitudinal axis 89 between the stacks of the stacking elements 70 of the tubes 75 are very small, so that only small bending moments are absorbed by the tubes 75 and thus also the bends of the tubes 75 in a direction perpendicular to the longitudinal axis 89 of the tubes 75 is very small. Even with a small distance between the outer surfaces 76 of the tubes 75, contact between the outer surfaces 76 of the tubes 75 is thus excluded and the entire outer surface 76 of the tubes 75 can therefore function to transfer moisture from the secondary oxidizing agent to the primary oxidizing agent. The small and different distances Li to L4 in the direction of the longitudinal axis 89 between the stacks of the stacking elements 70 of the tubes 75 also cause the tubes 75 to have a very high natural frequency with regard to mechanical vibrations, so that resonance is essentially excluded when the tubes 75 are excited to vibrate can be. The different distances Li to L4 thus cause different natural frequencies of the tubes 75 to be present and therefore no pronounced and identical resonance frequencies for the sections of the tubes 75 between the stacks of the stacking elements 70 occur. A third structural exemplary embodiment of the humidification device 59 is shown in FIGS. 12 to 16. Essentially only the differences from the second exemplary embodiment according to FIG. 11 are described below. In this third exemplary embodiment, the stacking elements 70, 90 are formed in one piece with the tubes 75. The tubes 75 with integrated stacking elements 70, 90 are produced by extrusion. A diaphragm (not shown) is formed on an extrusion tool. The diameter of the aperture, which is circular, can be changed. The tube 75 together with the stacking elements 70, 90 has 2 different outer diameters 80, 81, namely a first smaller outer diameter 80 and a second, larger outer diameter 81. The first outer diameter 80 is formed on the tube 75 without the stacking element 90, ie on the membrane wall 77 for the transmission and passage of the water. The second outer diameter 81 is present on the stacking element 90.

During the production of the tube 75 with the stacking elements 90, the material for the tube 75 with the stacking elements 90 is conveyed through the aperture and during conveying the diameter of the aperture is changed so that with a diameter of the aperture with the second outer diameter 81, the tube 75 is extruded together with the stacking element 90 and with a diameter of the aperture with the first diameter 80, the tube 75 is extruded without the stacking element 90. The tube 75 is thus divided in the direction of the longitudinal axis 89 of the tube 75 into first sections 78 with the small first outside diameter 80 and into second sections 79 with the large second outside diameter 81. The plastic material of the pipe 75 is conveyed with a screw conveyor (not shown) through the aperture of the extrusion tool (not shown) and during the period of the aperture with the larger second outer diameter 81, the screw conveyor has a greater conveying speed or larger volume flow than during the period the aperture with the smaller first outer diameter 80. With the extrusion tool, only one tube 75 is produced at a time, ie the extrusion tool only has one aperture whose diameter can be changed. 15 shows an exemplary embodiment of the stacking elements 90 with a stacking surface 72 which is circular in cross section. In the exemplary embodiment shown in FIG. 13, the stacking surfaces 72 of the stacking elements 90 are hexagonal in cross section. When stacking the stacking elements 90 shown in FIG. 13, essentially no cavities occur between the stacking surfaces 72 due to the geometry of the stacking surfaces 72, provided only stacking elements 90 with the hexagonal geometry are used on the stacking surface 72. When stacking the stacking elements 90 shown in FIG. 15 with the circular stacking surface 72 as the radial outer surface of the stacking elements 90, cavities occur between the stacking surfaces 72. In Fig. 12 the humidification device 59 is shown with the tubes 75 shown in Fig. 6. Only the stack of stacking elements 70 on the left is designed in several parts in addition to the tubes 75 according to the first and second exemplary embodiments. The other stacks of the stacking elements 90 are formed in one piece by the stacking elements 90 together with the tubes 75.

Viewed overall, there are significant advantages associated with the humidification device 59 according to the invention, the method according to the invention for producing the humidification device 59 and the fuel cell unit 1 according to the invention. The fixing means 68 and the sealing means 69 are formed in several parts by the stacking elements 70, 90. The tubes 75 can thereby advantageously be arranged in a simple manner in the interior of the housing 60 at a precisely predetermined, in particular constant, distance from one another on the outer surfaces 76. Contact between the outer surfaces 76 of the tubes 75 can thereby essentially be avoided, so that the entire outer surface 76 of the tubes 75 can be used for the passage or diffusion of the water through the membrane walls 77. This means that the inner diameter of the flow space 86 of the tubes 75 can be made correspondingly larger, so that small pressure losses occur when the oxidizing agent is passed through the flow spaces 86 of the tubes 75. The additional stacks of stacking elements 70, 90 divide the inner flushing subspace 83 in the longitudinal direction of the longitudinal axis 89 of the pipes 75 into flow subspaces 91. This subdivision into the Flow subspaces 91 increases the flow velocity of the oxidizing agent in the flow subspaces 91 and the natural frequency of the tubes 75. This can improve the transfer of water from the secondary oxidizing agent to the primary oxidizing agent and reduce the susceptibility of the humidifying device 59 to resonance in the event of mechanical vibrations.

Claims

Expectations

1 . Humidifying device (59) for a fuel cell unit (1) for transferring water from the oxidizing agent discharged from a fuel cell stack (40) as a secondary oxidizing agent to the oxidizing agent introduced into the fuel cell stack (40) as a primary oxidizing agent, comprising

- a housing (60), which delimits an interior space, with a primary inlet opening (64) for introducing the primary oxidizing agent into the humidifying device (59), with a primary outlet opening (65) for discharging the primary oxidizing agent from the humidifying device (59), with a secondary inlet opening (66) for introducing the secondary oxidizing agent into the humidifying device (59), with a secondary outlet opening (67) for discharging the secondary oxidizing agent from the humidifying device (59),

- stacked tubes (75) with membrane walls (77) for transferring the water from the secondary oxidizing agent to the primary oxidizing agent through the membrane walls (77),

- at least one fixing means (68) for fixing the pipes (75) in the interior,

- at least one sealing means (69), which divides the interior into at least one inner pipe subspace (82) for passing the oxidizing agent through the pipes (75) and into a flushing inner subspace (83) for flushing the outer surfaces (77) of the pipes (75) with oxidizing agent , characterized in that the at least one fixing means (68) and/or the at least one sealing means (69) are formed in several parts from stacking elements (70, 90) and the stacking elements (70, 90) are stacked in the Interior are arranged. Humidification device according to claim 1, characterized in that contact surfaces (71) formed on the stacking elements (70), in particular releasably without a material connection, rest on the tubes (75). Humidification device according to claim 1 or 2, characterized in that the geometry of the contact surfaces (71) of the stacking elements (70) is designed to be essentially complementary to the geometry of the outer surfaces (76) of the tubes (75). Humidification device according to one or more of the preceding claims, characterized in that the stacking elements (70) are designed as additional components in addition to the tubes (75). Humidification device according to one or more of the preceding claims, characterized in that the stacking elements (70) are plate-shaped, in particular strip-shaped, and the tubes (75), in particular all tubes (75), between each two immediately adjacent stacked stacking elements (70). two immediately adjacent stacked stacking elements (70) from a common fictitious stacking level (73) are cut. Humidification device according to one or more of the preceding claims, characterized in that stacking surfaces (72) formed on the stacking elements (70, 90), in particular releasably without a material connection, lie on top of each other. Humidification device according to one or more of the preceding claims, characterized in that the stacking elements (90) are formed in one piece with the tubes (75). Method for producing a humidification device (59) for a fuel cell unit (1) for transferring water from the oxidizing agent discharged from a fuel cell stack (40) as a secondary oxidizing agent to the oxidizing agent introduced into the fuel cell stack (40) as a primary oxidizing agent with the steps:

- providing a housing (60), which delimits an interior space, with a primary inlet opening (64) for introducing the primary oxidizing agent into the humidification device (59), with a primary outlet opening

(65) for discharging the primary oxidizing agent from the humidification device (59), with a secondary inlet opening

(66) for introducing the secondary oxidizing agent into the humidification device (59), with a secondary outlet opening

(67) for removing the secondary oxidizing agent from the humidification device (59), - providing pipes (75) with membrane walls (77) for transferring the water from the secondary oxidizing agent to the primary oxidizing agent through the membrane walls (77),

- provide at least one fixing means (68) for fixing the pipes (75) in the interior,

- provide at least one sealant (69), which divides the interior into at least one inner pipe subspace (82) for passing the oxidizing agent through the pipes (75) and into a flushing inner subspace (83) for flushing around the outer surfaces (76) of the pipes (75) divided with oxidizing agent,

- Assembling the provided components of the humidification device (59) to the humidification device (59) by arranging the tubes (75) in the interior, fixing the tubes (75) with the at least one fixing means (68) in the interior and dividing the Interior with the at least one sealing means (69) in the at least one inner pipe sub-space (82) and in a flushing inner sub-space (83), characterized in that the at least fixing means (68) and / or the at least one sealing means (69) are available in several parts from stacking elements is provided. Method according to claim 8, characterized in that fixing the pipes (75) with the at least fixing means (68) and/or dividing the interior space with the at least sealing means (69) into the at least one inner pipe subspace (82) and into the flushing inner subspace ( 83) is carried out by stacking, in particular strip-shaped, stacking elements (70) and the tubes (75) between two stacking elements (70). to be ordered. Method according to claim 8 or 9, characterized in that the stacking elements (70, 90) are provided by means of injection molding and/or extrusion, in particular as separate components in addition to the tubes (75). Method according to one or more of claims 8 to 10, characterized in that the stacking elements (90) are provided in one piece with the tubes (75), in particular by producing the tubes (75) and the stacking elements (90) using extrusion. Method according to claim 11, characterized in that the tubes (75) with at least one stacking element (90) have a first outside diameter (80) on at least one first section (78) in the longitudinal direction of the tubes (75) and on at least one second section ( 79) have a second outside diameter (81) in the longitudinal direction of the tubes (75) and the second outside diameter (81) is larger than the first outside diameter (80) and on which at least one first section (78) the membrane wall (77) is formed and on which at least one second section (79) a stacking element (90) is formed. Method according to claim 11 or 12, characterized in that the material for the production of the tubes (75) and stacking elements (90) is passed through a diaphragm with a variable diameter and during the production of the tubes (75) on a section (78) in the longitudinal direction of the tubes (75) without the stacking elements ( 90) the aperture has a first diameter (80) and during the production of the tubes (75) on a section (79) in the longitudinal direction of the tubes (75) with the stacking elements (90), the aperture has a second diameter (81) and the second diameter (81) of the aperture is larger than the first diameter (80) of the aperture. Method according to one or more of claims 8 to 13, characterized in that the fixing of the tubes (75) with the at least one fixing means (68) and/or the dividing of the interior with the at least one sealing means (69) is carried out by the stacking surfaces (72), in particular circumferential radial outer sides, of the stacking elements (70, 90) are placed one on top of the other on stacking surfaces (72). Fuel cell unit (1) for the electrochemical generation of electrical energy, comprising stacked fuel cells (2), so that the stacked fuel cells form a fuel cell stack form channels (13) integrated into the fuel cell stack for oxidizing agents, a humidifying device (59) for transferring water from the oxidizing agent discharged from the fuel cell stack as a secondary oxidizing agent to the oxidizing agent introduced into the fuel cell stack as a primary oxidizing agent, characterized in that the humidifying device ( 59) according to one or more of the Claims 1 to 7 is designed and/or the humidification device (59) is produced using a method according to one or more of claims 8 to 14.