Fuel cell

Abstract

A fuel cell unit as a fuel cell stack for electrochemically generating electrical energy comprises a fuel cell, wherein the fuel cell comprises a proton exchange membrane, an anode, a cathode, a gas diffusion layer, a bipolar plate, at least one fluid channel for transmitting a fluid, and at least one sealing portion (11) made of a sealing material (42) for sealing the at least one fluid channel (37), wherein particles (41) made of a granular material (43) are arranged in the sealing material (42) of the at least one sealing portion (11) for extending a diffusion path (38) of a fluid sealed by the at least one sealing portion (11).

Description

Technical Field

[0001] The invention relates to a fuel cell unit and a method for producing a fuel cell unit. Background Art

[0002] Fuel cell units, which are galvanic cells, convert continuously supplied fuel and oxidant into electrical energy by means of redox reactions at the anode and cathode. Fuel cells are used in a wide variety of stationary and mobile applications, for example in buildings not connected to the power grid or in motor vehicles, in rail transport, in aviation, in space travel and in shipping.

[0003] In a fuel cell unit, it is necessary to guide a fluid (e.g., water, air, oxygen, hydrogen, or methane) through a fluid channel such as a channel, a gas space, and a pipeline. These fluid channels are sealed by means of a seal made of a sealing material. A significant diffusion occurs due to the relatively large diffusion coefficient of the sealing material used in the seal. In the seal used, the long-term stability relative to the diffusion is critical, so that diffusion occurs only after many years of operation, which is disruptive or harmful to the operation of the fuel cell unit. Therefore, the fuel cell unit does not have the required long-term reliability of 10 to 15 years when used in a motor vehicle, for example.

[0004] DE 10 2006 053 569 A1 describes a sealing arrangement on a separator of a fuel cell.

[0005] DE 10 2004 042 012 A1 discloses a method for orienting a geometrically anisotropic special material in a medium by means of an electric field. Summary of the invention

[0006] The fuel cell unit according to the present invention as a fuel cell stack for electrochemically generating electrical energy comprises a fuel cell, each of which comprises a proton exchange membrane, an anode, a cathode, a gas diffusion layer, a bipolar plate, at least one fluid channel for transmitting a fluid, and at least one sealing part made of a sealing material to seal the at least one fluid channel, wherein particles made of a granular material are arranged in the sealing material of at least one sealing part to extend the diffusion path of the fluid sealed by the at least one sealing part. Based on the extension of the diffusion path and the long-term stability of the granular material of the particles, the sealing part has a very small average diffusion coefficient, for example, in the case of a long-term stability of more than 10 or 15 years.

[0007] In an additional variant, the diffusion coefficient of the granular material of the granules in the respective seal for the fluid to be sealed by the respective seal is smaller than the diffusion coefficient of the sealing material for the fluid to be sealed by the respective seal. In particular, the diffusion coefficient of the granular material is smaller than 90%, 70%, 60%, 50%, 40% or 30% of the diffusion coefficient of the sealing material. Thus, different diffusion coefficients are generated in the seal, in particular, the diffusion coefficients inside the seal differ by at least 10%, 20%, 30%, 50%, 100% or 200%.

[0008] Practically, the aspect ratio of the particles is greater than 1, 2, 5, 7 or 10. For example, if the maximum diameter in the direction of an imaginary plane spanned by the particles is 300 μm and the thickness of the particles perpendicular to the imaginary plane is 30 μm, the aspect ratio is 300:30=10:1=10.

[0009] In an additional variant, the particles are of plate-shaped or needle-shaped design.

[0010] In a supplementary configuration, the imaginary plane opened up by the particles is oriented substantially perpendicularly to the ideal diffusion direction in the respective seal. "Substantially perpendicular" means that the imaginary plane is oriented perpendicularly to the ideal diffusion direction with a deviation of less than 30°, 20°, 10° or 5°. The ideal diffusion direction is the direction of a straight line, ideally represented by a half-straight line, which has the shortest path for the fluid to be sealed to pass through the seal without taking into account the particles. The particles are substantially disk-shaped and / or plate-shaped and / or needle-shaped and thus open up the imaginary plane accordingly.

[0011] Preferably, the particles are anisotropically structured.

[0012] In another embodiment, the particle material includes a polarizable material and / or a material having dipole properties, such that the particles as a whole have dipole properties for orienting the particles in an electric field.

[0013] In a supplementary embodiment, the particle material comprises a ferromagnetic material for orienting the particles in a magnetic field.

[0014] Practically, the maximum diameter of the particles is less than 1000 μm, 700 μm, 500 μm or 300 μm.

[0015] In an additional embodiment, the largest diameter of the particles is greater than 5 μm, 10 μm, 100 μm or 200 μm.

[0016] In a supplementary variant, the ratio of the volume fraction and / or mass fraction between the granular material and the sealing material is between 1% and 95%, preferably between 3% and 80%, particularly preferably between 5% and 70%. Thus, for example, if the volume fraction of the total of the granules and / or granular material in the seal is 5 ml and the volume fraction of the sealing material is 20 ml, the ratio is 5 / 20=25%.

[0017] The method according to the present invention for manufacturing a fuel cell unit comprises the following steps: providing components for a fuel cell, providing at least one sealing portion made of a sealing material, assembling the components of the fuel cell into a fuel cell so that at least one fluid channel is sealed by at least one sealing portion, and assembling the fuel cells into a fuel cell unit, wherein a sealing portion is provided so that particles made of a granular material are arranged in the sealing material of at least one sealing portion to extend the diffusion path of the fluid sealed by the sealing portion.

[0018] In an additional configuration, the particles have a maximum diameter in a respective first direction and a minimum diameter in a respective second direction, and the first and second directions are respectively perpendicular to each other and oriented in respective imaginary planes spanned by the particles, and the particles are oriented in the seal with the aid of an electric field and / or a magnetic field, so that the respective first and second directions are oriented substantially perpendicularly to an ideal diffusion direction in a diffusion path in the respective seal.

[0019] In another embodiment, in particular before the components of the fuel cell are assembled, at least one seal is arranged in an electric field and / or a magnetic field, and while the at least one seal is arranged in the electric field and / or the magnetic field, the particles perform a movement, in particular a rotational movement, in the sealing material. The rotational movement leads to an orientation of the particles in the seal, that is, the particles are oriented in the seal according to the description in the present application.

[0020] In a supplementary embodiment, the sealing material of the at least one seal is cured after the particles have been aligned in the at least one seal.

[0021] Preferably, during the assembly of the fuel cells to form a fuel cell unit, at least one fluid channel is sealed by means of at least one seal.

[0022] In another configuration, the particles have a maximum diameter in a respective first direction and a minimum diameter in a respective second direction, and the first and second directions are respectively perpendicular to each other and oriented in a plane, and the particles are arranged in the seal so that the respective first and second directions are oriented substantially perpendicularly to an ideal diffusion direction in the respective seal.

[0023] In an additional variant, the particles are at least partially, in particular completely, constructed from a geometrically anisotropic and / or special material. "Anisotropic" means in particular that the particles have different physical and / or chemical properties based on the particle geometry and / or particle material in different directions in space.

[0024] Practically, the layers to be sealed are the bipolar plates and / or the housing and / or the walls of the channels and / or the walls of the feed lines and / or the walls of the discharge lines.

[0025] In a supplementary variant, the particles comprise, as particle material, layered silicates and / or glass and / or silicon dioxide and / or iron oxide and / or at least one metal and / or titanium dioxide and / or aluminum oxide and / or organic materials (for example liquid crystals).

[0026] In a further specific embodiment, the fuel cell unit described in the present application is produced by means of a method described in the present application for producing a fuel cell unit and / or the method is carried out according to at least one feature of the fuel cell unit described in the present application.

[0027] In a supplementary variant, the fuel cell unit described in the present application is produced by means of the method described in the present application.

[0028] In a further embodiment, during the arrangement of the seal in the electric and / or magnetic field, an imaginary plane spanned by the particles is oriented substantially perpendicularly to an ideal diffusion direction in the respective seal.

[0029] In an additional variant, a proton exchange membrane, an anode, a cathode, a gas diffusion layer and a bipolar plate are provided as components for a fuel cell.

[0030] In a further variant, the fuel cell unit comprises at least one connecting device, in particular a plurality of connecting devices, and a tensioning element.

[0031] Practically, the components used in a fuel cell are a proton exchange membrane, an anode, a cathode, a gas diffusion layer and a bipolar plate.

[0032] In another embodiment, the connecting device is designed as a screw and / or in a rod-like manner.

[0033] Practically, the tensioning element is designed as a tensioning plate.

[0034] The fuel cell system according to the present invention, in particular a fuel cell system for a motor vehicle, comprises a fuel cell unit (as a fuel cell stack having a fuel cell), a compressed gas storage device for storing a gaseous fuel, and a gas delivery device for delivering a gaseous oxidant to a cathode of the fuel cell, wherein the fuel cell unit is constructed as a fuel cell unit described in the present application.

[0035] In another variant, the gas conveying device is designed as a ventilator or a compressor.

[0036] In particular, the fuel cell unit comprises at least 3, 4, 5 or 6 connection devices.

[0037] In a further embodiment, the tensioning element is plate-shaped and / or disk-shaped and / or flat and / or is designed as a grid.

[0038] Preferably, the fuel is hydrogen, reformate gas or natural gas.

[0039] Practically, the fuel cell is designed to be essentially flat and / or disk-shaped.

[0040] In a supplementary variant, the oxidant is air containing oxygen or pure oxygen.

[0041] Preferably, the fuel cell unit is a PEM fuel cell unit having a PEM fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Embodiments of the present invention are described in more detail below with reference to the accompanying drawings. It shows:

[0043] Figure 1 A strongly simplified exploded view of a fuel cell system with components of a fuel cell,

[0044] Figure 2 A perspective view of a portion of a fuel cell.

[0045] Figure 3 Longitudinal section of a fuel cell,

[0046] Figure 4 A three-dimensional view of a fuel cell unit as a fuel cell stack (i.e., a fuel cell stack),

[0047] FIG5 is a cross section of a seal known from the prior art, the cross section having a section plane parallel to the diffusion path of the fluid to be sealed by the seal,

[0048] Figure 6 A cross section of the sealing portion in the first embodiment of the fuel cell unit according to the present invention, the cross section having a sectional plane parallel to an ideal diffusion direction of a fluid to be sealed by the sealing portion,

[0049] Figure 7 A cross section of the sealing portion in the second embodiment of the fuel cell unit according to the present invention, the cross section having a sectional plane parallel to an ideal diffusion direction of a fluid to be sealed by the sealing portion,

[0050] Figure 8a seal applied to the carrier layer before the particles are aligned in an electric and / or magnetic field, the seal having the particles integrated into the seal,

[0051] Fig. 9 a seal applied to the carrier layer during the arrangement in the electric and / or magnetic field and after the particles have been aligned, the seal having particles integrated into the seal,

[0052] Fig.10 a seal which is applied to the carrier layer after the particles have been oriented and during the curing of the sealing material of the seal, the seal having the particles integrated into the seal,

[0053] Fig.11 A seal in an assembled fuel cell unit, the seal having particles integrated in a directional manner between a first and a second layer to be sealed,

[0054] Fig.12 Simplified stereoscopic view of particles,

[0055] Fig.13 according to Fig.12 A simplified side view of a particle, and

[0056] Fig.14 Simplified flow chart of a method for manufacturing a fuel cell unit. DETAILED DESCRIPTION

[0057] exist Figures 1 to 3 , the basic structure of a fuel cell 2 as a PEM fuel cell 3 (polymer electrolyte fuel cell 3) is shown. The principle of the fuel cell 2 is to generate electrical energy or electric current by means of an electrochemical reaction. Hydrogen is introduced to the anode 7 as a gaseous fuel and the anode 7 forms the negative electrode. A gaseous oxidant (i.e. air with oxygen) is introduced to the cathode 8, that is, the oxygen in the air provides the required gaseous oxidant. Reduction occurs at the cathode 8 (electron acceptance). Oxidation is carried out at the anode 7 (as electron release).

[0058] The redox equation for the electrochemical process is:

[0059] cathode:

[0060] O2+4H + +4e - →2H2O

[0061] anode:

[0062] 2H2→4H + +4e -

[0063] The total reaction equation of the cathode and anode is:

[0064] 2H2+O2→2H2O

[0065] The standard potential of the electrode pair under standard conditions as the difference in the reversible fuel cell voltage or the no-load voltage of the unloaded fuel cell 2 is 1.23 V. In practice, the theoretical voltage of 1.23 V is not reached. In the idle state and at low currents, voltages of more than 1.0 V can be reached, and when operating at a larger current, voltages between 0.5 V and 1.0 V are reached. The series connection of a plurality of fuel cells 2, in particular a fuel cell unit 1 (a fuel cell stack 1 as a plurality of 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 the respective fuel cell 2.

[0066] The fuel cell 2 further comprises a proton exchange membrane 5 (PEM), which is arranged between an anode 7 and a cathode 8. The anode 7 and the cathode 8 are constructed in a layered or disk-like manner. The PEM 5 serves as an electrolyte, a catalyst carrier and a separator for the reaction gases. In addition, the PEM 5 also serves as an electrical insulator and prevents electrical short circuits between the anode 7 and the cathode 8. Generally, a 50 μm to 150 μm thick proton-conducting membrane made of a perfluorinated and sulfonated polymer is used. The PEM 5 conducts protons H + and essentially blocks the proton H + ions, enabling the PEM-based 5-pair proton H + The PEM 5 is substantially impermeable to the reactant gases oxygen O2 and hydrogen H2, that is, it blocks the flow of oxygen O2 and hydrogen H2 between the gas space 31 with the fuel hydrogen H2 at the anode 7 and the gas space 32 with the air or oxygen O2 as an oxidant at the cathode 8. The proton conductivity of the PEM 5 increases with increasing temperature and increasing water content.

[0067] Electrodes 7, 8 are located on both sides of the PEM 5 facing the gas spaces 31, 32 respectively as anode 7 and cathode 8. The unit composed of PEM 5 and electrodes 7, 8 is called membrane electrode array 6 (MEA). Electrodes 7, 8 are extruded together with PEM 5. Electrodes 7, 8 are carbon particles containing platinum bonded to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride) and / or PVA (polyvinyl alcohol) and hot pressed into microporous carbon fiber mats, glass fiber mats or plastic mats. On electrodes 7, 8, catalyst layers 30 are usually applied on the sides facing the gas spaces 31, 32 respectively. The catalyst layer 30 on the gas space 31 and the fuel on the anode 7 include nano-dispersed platinum-ruthenium on graphitized carbon black particles, and the graphitized carbon black particles are bonded to a binder. The catalyst layer 30 on the gas space 32 and the oxidant on the cathode 8 include similar nano-dispersed platinum. Use e.g. PTFE emulsion or polyvinyl alcohol is used as a binder.

[0068] Gas diffusion layer 9 (Gas Diffusion Layer, GDL) is placed flat on anode 7 and cathode 8. Gas diffusion layer 9 on anode 7 evenly disperses fuel from channel 12 of fuel to catalyst layer 30 on anode 7. Gas diffusion layer 9 on cathode 8 evenly disperses oxidant from channel 13 of oxidant to catalyst layer 30 on anode 7. In addition, GDL 9 is used to extract reaction water in the direction opposite to the flow direction of reaction gas (that is, in the direction from catalyst layer 30 to channel 12, 13 respectively). In addition, GDL 9 keeps PEM 5 in a wet state and conducts current. GDL 9 is constructed, for example, by hydrophobic carbon paper and a bonded carbon powder layer.

[0069] The bipolar plate 10 is located on the GDL 9. The electrically conductive bipolar plate 10 serves as a current collector for water discharge and for conducting the reaction gases via the channel structure 29 and / or the flow field 29 and for discharging waste heat, which is generated at the cathode 8 in particular in the exothermic electrochemical reaction. In order to discharge the waste heat, channels 14 for conveying a liquid or gaseous coolant are inserted into the bipolar plate 10. The channel structure 29 on the gas space 31 for the fuel is composed of channels 12. The channel structure 29 on the gas space 32 for the oxidant is composed of channels 13. For example, metals, electrically conductive plastics and composite materials or graphite are used as materials for the bipolar plate 10.

[0070] A plurality of fuel cells 2 are arranged one above the other in a fuel cell unit 1 and / or a fuel cell stack and / or a fuel cell stack ( Figure 4 ).exist Figure 12 shows an exploded view of two fuel cells 2 arranged one above the other. The seal 11 seals the gas spaces 31, 32 in a fluid-tight manner. Hydrogen H2 is stored as fuel in a compressed gas storage 21 ( Figure 1 ). From the compressed gas storage 21, the fuel is led via the high-pressure line 18 to the pressure reducer 20 for reducing the pressure of the fuel in the medium-pressure line 17 of about 10 bar to 20 bar. From the medium-pressure line 17, the fuel is led to the injector 19. At the injector 19, the pressure of the fuel is reduced to the intake pressure of between 1 bar and 3 bar. From the injector 19, the fuel is supplied to the supply line 16 for the fuel ( Figure 1 ) and is fed from the feed line 16 into the channel 12 for fuel, which constitutes the channel structure 29 for fuel. As a result, the fuel flows through the gas space 31 for fuel. The gas space 31 for fuel is constituted by the channel 12 and the GDL 9 on the anode 7. After flowing through the channel 12, the fuel that is not consumed in the redox reaction on the anode 7 and (possibly) the water from the controlled humidification of the anode 7 are discharged from the fuel cell 2 through the discharge line 15.

[0071] The gas conveying device 22, which is configured as a ventilator 23 or an air compressor 24, for example, conveys air from the environment as an oxidant into a supply line 25 for the oxidant. From the supply line 25, air is supplied to the channel 13 for the oxidant (the channel forms a channel structure 29 for the oxidant on the bipolar plate 10), so that the oxidant flows through a gas space 32 for the oxidant. The gas space 32 for the oxidant is formed by the channel 13 and the GDL 9 on the cathode 8. After flowing through the channel 13 for the oxidant 32 or the gas space 32, the oxidant that is not consumed on the cathode 8 and the reaction water generated on the cathode 8 due to the electrochemical redox reaction are discharged from the fuel cell 2 through the discharge line 26. The supply line 27 is used to supply the coolant to the channel 14 for the coolant, and the discharge line 28 is used to discharge the coolant guided through the channel 14. For the sake of simplicity, the supply and discharge lines 15, 16, 25, 26, 27, 28 are arranged in a manner similar to the embodiment of the present invention. Figure 1 1 and 12. The fuel cell stack 1 is shown as separate lines and can actually be designed differently in terms of structure, for example as holes in the frame (not shown) or as aligned holes in the end areas (not shown) of the bipolar plates 10 arranged one above the other. The fuel cell stack 1 together with the compressed gas storage 21 and the gas conveying device 22 form a fuel cell system 4. The supply and discharge lines 15, 16, 17, 18, 25, 26, 27, 28 and the channels 12, 13, 14 as well as the gas space 31 for the fuel and the gas space 32 for the oxidant each form a fluid channel 37 for conveying a fluid.

[0072] In the fuel cell unit 1, the fuel cells 2 are arranged between two tensioning elements 33 as tensioning plates 34. The upper tensioning plate 35 is located on the uppermost fuel cell 2, and the lower tensioning plate 36 is located on the lowermost fuel cell 2. The fuel cell unit 1 includes approximately 300 to 400 fuel cells 2, which are not all shown in the drawing for reasons of illustration. Figure 4 . The tensioning element 33 applies pressure to the fuel cell 2, that is, the upper tensioning plate 35 is pressed against the uppermost fuel cell 2 with a pressure and the lower tensioning plate 36 is pressed against the lowermost fuel cell 2 with a pressure. The fuel cell stack 2 is thereby tensioned in order to ensure impermeability to fuel, oxidant and coolant, in particular due to the elastic seal 11, and also to keep the contact resistance inside the fuel cell stack 1 as low as possible. In order to tension the fuel cell 2 with the tensioning element 33, four connecting devices 39 are configured as bolts 40 on the fuel cell unit 1, which are loaded with tensile force. The four bolts 40 are fixedly connected to the tensioning plate 34.

[0073] 5 shows a section through a seal 11 known from the prior art, made of a sealing material 42, which has a section plane parallel to the diffusion path 38 for the fluid to be sealed. Solids also have a diffusion coefficient, so that the fluid can diffuse through the sealing material 42 on a straight diffusion path 38 as an ideal diffusion direction 53. Due to the straight diffusion path, the fluid that diffuses through the sealing material 42 can travel a small minimum distance, so that a relatively large volume flow of the fluid can diffuse through the sealing material 42.

[0074] exist Figure 6 , a cross section of the sealing portion 11 in a first embodiment of a fuel cell unit 1 according to the invention is shown, the cross section having a sectional plane parallel to an ideal diffusion direction 53 for the fluid to be sealed. The fluid to be sealed, such as the fuel hydrogen H2, the oxidant air or a liquid coolant (such as water with an antifreeze agent) is guided through a fluid channel 37, and the fluid channel 37 is sealed by the sealing portion 11. The sealing portion 11 comprises a sealing material 42, such as a polymer such as PPS (polyphenylene sulfide as a temperature-resistant thermoplastic material), EPDM (ethylene propylene diene rubber as a synthetic rubber) or an adhesive, and furthermore particles 41 made of a granular material 43. The diffusion coefficient of the granular material 43 is much smaller than the diffusion coefficient of the sealing material 42, so that the fluid to be sealed by the sealing portion 11 cannot basically diffuse through the particles 41, so that the diffusion path 38 of the fluid extends basically only in the sealing material 42. As a result, the particles 41 constitute a diffusion barrier for the fluid and the diffusion path 38 thus extends around the particles 41. As a result, in accordance with Figure 6In the seal 11 of FIG. 5 , a longer diffusion path 38 occurs than in the seal 11 according to FIG. 5 . The longer diffusion path 38 results in the seal 11 having a smaller average diffusion coefficient overall than the seal according to FIG. 5 from the prior art.

[0075] exist Figure 7 1 shows a cross section of a seal 11 in a second embodiment of a fuel cell unit 1 according to the invention, the cross section having a section plane parallel to an ideal diffusion direction 53 for the fluid to be sealed. Figure 6 Such a disc-shaped or plate-shaped structure ( Fig.12 ) and has a maximum diameter 46 in a first direction 44 and a minimum diameter 47 in a second direction 45. The first and second directions 44, 45 are perpendicular to each other and are located in an imaginary plane 54 defined by the disk-shaped particles 41 ( Fig.13 ). The maximum diameter is 500 μm and the minimum diameter is 250 μm, so that the particle 41 has an aspect ratio of 2:1 inside the imaginary plane 54. The thickness perpendicular to the imaginary plane 54 is 20 μm, so that the aspect ratio is 500 / 20=25. The first and second directions 44, 45 and the imaginary plane 54 opened by the particle 41 are oriented perpendicular to the ideal diffusion direction 53 to achieve a small diffusion. As a result, the fluid is forced to implement a very long diffusion path 38 through the seal 11, so that the seal 11 has a smaller average diffusion coefficient as a whole. As a result, only very little fluid can diffuse through the seal 11. The particle 41 is constructed by an orientation layer 55 and a diffusion barrier layer 56. The orientation layer 55 is used for orientation in an electric field or a magnetic field. When the particle 41 is arranged in a magnetic field, the orientation layer 55 is, for example, a ferromagnetic layer made of γ-Fe2O3, magnesite, iron, cobalt or nickel. When the particles 41 are arranged in an electric field, the alignment layer 55 is constructed from a polarizable material or a material having dipole properties. This is, for example, a material composed of molecules with polar atomic bonds in which the molecules have an asymmetric structure, such as aluminum chloride (AlCl3). As a diffusion barrier layer 56, a glass or metal layer with, for example, a very small diffusion coefficient, such as iron, brass or copper, can be used.

[0076] exist Figures 8 to 11, the steps for producing a seal 11 with oriented particles 41 are shown. First, provision 57 of an uncured sealing material 42 with particles 41 is carried out. The sealing material 42 with integrated particles 41 is applied 58 to a carrier layer 48 as a first layer 49 to be sealed, for example by means of a dispenser. The first layer 49 to be sealed is a bipolar plate 10. Subsequently, a pole plate 51 is moved over the sealing material 42 with particles 41 and a voltage is applied between the pole plate 51 and the bipolar plate 10, so that an electrostatic field is formed between the positively charged pole plate 51 and the bipolar plate 10 as a negatively charged pole plate 52 with the applied sealing material 42, the electrostatic field having a voltage between 10 and 11. 2 Up to 10 6 V / m. Differently, it can also involve an alternating electric field. The sealing material 42 as a fluid medium is Fig. 9 The particles 41 are not yet hardened and have sufficient viscosity so that the particles 41 can perform movement, especially rotational movement, in the sealing material 42 and according to the Fig. 9 59 in the illustration, so that the imaginary plane 54 formed by the particles 41 is oriented substantially perpendicularly to the ideal diffusion direction 53. The sealing material 42 is then hardened 60, for example thermally or by means of radiation. After hardening 60 of the sealing material 42 with the oriented particles 41, the fuel cell unit 1 is assembled so that the second layer 50 to be sealed is placed as a bipolar plate 10 on the seal 11, that is, the seal 11 is arranged 61 between the two layers 49, 50 to be sealed. In contrast to the exemplary embodiment shown above, in Figure 8 In the method steps shown in , a sealing material 42 with unoriented particles 41 can be applied to a carrier layer 48, which is not used as a layer 49 to be sealed later, in particular not a bipolar plate 10, so that after the particles 41 are oriented and the sealing material 42 is hardened, the seal 11 is removed from the carrier layer 48 and placed on the layers 49, 50 to be sealed, in particular arranged 61 between two layers 49, 50 to be sealed.

[0077] In another embodiment not shown, similar to that described above, Fig. 9 According to the exemplary embodiment in FIG. 4 , the sealing material 42 having the particles 41 is arranged in a magnetic field to orient the particles 41 .

[0078] Overall, the fuel cell unit 1 according to the invention and the method according to the invention for producing a fuel cell unit 1 have important advantages. As the sealing material 42 in the seal 11, due to the required properties of the sealing material 42, it is necessary to use a sealing material 42 with a relatively large diffusion coefficient, because, for example, glass is not used as the sealing material 42. The oriented particles 41 have a very small diffusion coefficient and greatly increase the length of the diffusion path 38, so that the seal 11 has a much smaller average diffusion coefficient than in the prior art design consisting only of a sealing material 42 without particles 41.

Claims

1. A fuel cell unit (1) as a fuel cell stack for electrochemically generating electrical energy, the fuel cell unit comprising - A fuel cell (2), wherein the fuel cell (2) comprises a proton exchange membrane (5), an anode (7), a cathode (8), a gas diffusion layer (9), and a bipolar plate (10), - at least one fluid channel (37) for conveying a fluid, at least one sealing portion (11) made of a sealing material (42) for sealing the at least one fluid channel (37), in, Particles (41) made of a granular material (43) are arranged in the sealing material (42) of the at least one sealing portion (11) for extending a diffusion path (38) of a fluid sealed by the at least one sealing portion (11). It is characterized in that An imaginary plane (54) spanned by the particles (41) is oriented substantially perpendicularly to an ideal diffusion direction (53) in the respective seal (11).

2. The fuel cell unit according to claim 1, It is characterized in that The diffusion coefficient of the particle material (43) of the particles (41) in the corresponding sealing portion (11) for the fluid to be sealed by the corresponding sealing portion (11) is smaller than the diffusion coefficient of the sealing material (42) for the fluid to be sealed by the corresponding sealing portion (11).

3. The fuel cell unit according to claim 1 or 2, It is characterized in that The aspect ratio of the particle (41) is greater than 1.

4. The fuel cell unit according to claim 3, It is characterized in that The aspect ratio of the particle (41) is greater than 2.

5. The fuel cell unit according to claim 3, It is characterized in that The aspect ratio of the particle (41) is greater than 5.

6. The fuel cell unit according to claim 3, It is characterized in that The aspect ratio of the particle (41) is greater than 7.

7. The fuel cell unit according to claim 3, It is characterized in that The aspect ratio of the particle (41) is greater than 10.

8. The fuel cell unit according to claim 1 or 2, It is characterized in that The particles (41) are plate-shaped or needle-shaped.

9. The fuel cell unit according to claim 1 or 2, It is characterized in that The particles (41) are anisotropically structured.

10. The fuel cell unit according to claim 1 or 2, It is characterized in that The particle material (43) includes a polarizable material and / or a material having dipole properties, so that the particles (41) as a whole have dipole properties for orienting the particles (41) in an electric field.

11. The fuel cell unit according to claim 1 or 2, It is characterized in that The particle material (43) includes a ferromagnetic material for orienting the particles in a magnetic field.

12. The fuel cell unit according to claim 1 or 2, It is characterized in that The maximum diameter (46) of the particles (41) is less than 1000 μm.

13. The fuel cell unit according to claim 12, It is characterized in that The maximum diameter (46) of the particles (41) is less than 700 μm.

14. The fuel cell unit according to claim 12, It is characterized in that The maximum diameter (46) of the particles (41) is less than 500 μm.

15. The fuel cell unit according to claim 12, It is characterized in that The maximum diameter (46) of the particles (41) is less than 300 μm.

16. The fuel cell unit according to claim 1 or 2, It is characterized in that The maximum diameter (46) of the particles (41) is greater than 5 μm.

17. The fuel cell unit according to claim 16, It is characterized in that The maximum diameter (46) of the particles (41) is greater than 10 μm.

18. The fuel cell unit according to claim 16, It is characterized in that The maximum diameter (46) of the particles (41) is greater than 100 μm.

19. The fuel cell unit according to claim 16, It is characterized in that The maximum diameter (46) of the particles (41) is greater than 200 μm.

20. The fuel cell unit according to claim 1 or 2, It is characterized in that The ratio of the volume fraction and / or the mass fraction between the granular material (43) and the sealing material (42) is between 1% and 95%.

21. The fuel cell unit according to claim 20, It is characterized in that The ratio of the volume fraction and / or the mass fraction between the granular material (43) and the sealing material (42) is between 3% and 80%.

22. The fuel cell unit according to claim 20, It is characterized in that The ratio of the volume fraction and / or the mass fraction between the granular material (43) and the sealing material (42) is between 5% and 70%.

23. A method for manufacturing a fuel cell unit (1), comprising the following steps: - providing a component for a fuel cell (2), - providing at least one sealing portion (11) made of a sealing material (42), - assembling the components of the fuel cell (2) into the fuel cell (2), so that at least one fluid channel (37) is sealed by the at least one sealing portion (11), - assembling the fuel cells (2) into the fuel cell unit (1), in, The sealing portion (11) is provided such that particles (41) made of a granular material (43) are arranged in the sealing material (42) of at least one of the sealing portions (11) for extending a diffusion path (38) of a fluid sealed by the sealing portion (11), It is characterized in that The particles (41) have a maximum diameter (46) in a respective first direction (44) and a minimum diameter (47) in a respective second direction (45), and the respective first and second directions (44, 45) are perpendicular to each other and oriented in a respective imaginary plane (54) spanned by the particles (41), and the particles (41) in the seal (11) are oriented by means of an electric field and / or a magnetic field, so that the respective first and second directions (44, 45) are oriented substantially perpendicularly to an ideal diffusion direction (53) in the respective seal (11).

24. The method according to claim 23, It is characterized in that Before the components of the fuel cell (2) are assembled, the at least one seal (11) is arranged in the electric field and / or magnetic field.

25. The method according to claim 23, It is characterized in that While the at least one seal (11) is arranged in the electric and / or magnetic field, the particles (41) execute a rotational movement in the sealing material (42).

26. The method according to any one of claims 23 to 25, It is characterized in that After the particles (41) have been oriented in the at least one seal (11), the sealing material (42) of the at least one seal (11) is cured.

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