WO2021197746A1

WO2021197746A1 - Fuel cell unit

Info

Publication number: WO2021197746A1
Application number: PCT/EP2021/055352
Authority: WO
Inventors: Thomas Kretschmar; Gerhard Schubert
Original assignee: Robert Bosch Gmbh
Priority date: 2020-04-02
Filing date: 2021-03-03
Publication date: 2021-10-07
Also published as: DE102020204292A1

Abstract

The invention relates to a fuel cell unit (1) as a fuel cell stack (1) for electrochemically producing electrical energy, comprising: - stacked fuel cells (2, 3) having proton-exchange membranes, anodes, cathodes, gas diffusion layers and flow field plates (10); - current lines (43) for electrically connecting to the flow field plates (10) of the fuel cells (2, 3) and for monitoring the fuel cells (2, 3) by sensing at least one parameter of the fuel cells (2, 3); - connecting elements (44) for electrically and mechanically connecting the current lines (43) to the flow field plates (10) so that the current lines (43) are electrically and mechanically connected to the flow field plates (10) by means of the connecting elements (44), the connecting elements (44) being in the form of integral connections (46).

Description

description

title

Fuel cell unit

The present invention relates to a fuel cell unit according to the preamble of claim 1 and a method for producing a fuel cell unit according to the preamble of claim 10.

State of the art

Fuel cell units as galvanic cells convert continuously supplied fuel and oxidizing agent into electrical energy by means of 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 one above the other in a stack as a stack.

For proper and reliable operation of the fuel cell unit, it is necessary to monitor at least one parameter of the fuel cells, for example the voltage and the humidity of the fuel cells. The humidity is indirectly determined, for example, with the impedance as a further parameter. When monitoring the voltage, for example, the voltage applied to the bipolar plates of the fuel cells is conducted by means of power lines to a current collector strip and a cable harness as data transmission devices and from the data transmission devices to a central monitoring unit as Fuel Cell Control Unit transmitted so that the data for the parameter of the voltage is the voltage of the current conducted in power lines itself.

A fuel cell unit with 400 fuel cells arranged one above the other comprises 401 bipolar plates and each bipolar plate is to be connected mechanically and electrically to a power line by means of connecting elements. For this reason, a total of 401 power lines are to be connected to 401 bipolar plates using 401 connecting elements. At the ends of the power lines, pins are designed as connecting elements and these pins are inserted into bores or openings in the bipolar plates. The power lines are thus connected to the bipolar plates with the pins and bores in a form-fitting and / or force-fitting manner. The bipolar plates are approximately 1 mm thick and the bores in the bipolar plates are approximately 0.7 mm in diameter. The pins are manually inserted into the holes in the bipolar plates by skilled workers, so that this work process is time-consuming with a high risk of errors and damage. Automation of this complex work process is difficult if not impossible. This work process thus causes high production costs with a high susceptibility to errors. The fuel cell units are therefore disadvantageously expensive with low reliability.

Disclosure of the invention

Advantages of the invention

Fuel cell unit according to the invention as a fuel cell stack for the electrochemical generation of electrical energy, comprising stacked fuel cells with proton exchange membranes, anodes, cathodes, gas diffusion layers and bipolar plates, power lines for electrical connection to the bipolar plates of the fuel cells and for monitoring the fuel cells by detecting at least one parameter of the fuel cells, connecting elements for the electrical and mechanical connection of the power lines with the bipolar plates, so that the power lines are electrically and mechanically connected to the bipolar plates by means of the connecting elements, the connecting elements as integral connections are formed. Cohesive connections can be produced reliably and automatically, so that the fuel cell unit is inexpensive to produce with great reliability.

In a supplementary variant, the material connections are made by means of welding.

In a further embodiment, the material connections are made by means of laser welding and / or ultrasonic welding.

The bipolar plates, in particular at least 90% or 99% of the bipolar plates, are expediently connected electrically and mechanically by means of one, in particular only one, cohesive connection to each one, in particular only one, power line.

In a supplementary variant, the fuel cell unit comprises a monitoring unit as a computing unit for monitoring the at least one parameter of the fuel cells. The voltage of the fuel cells can preferably be monitored as a parameter of the fuel cells, so that the monitoring unit forms a CVM system (Cell Voltage Monitoring System).

In an additional embodiment, the fuel cell unit comprises a data transmission device for transmitting data with regard to the at least one parameter of the fuel cells to be detected from the power lines to the monitoring unit.

The power lines are expediently electrically and mechanically connected to the data transmission device with additional connection elements.

In a further refinement, the additional connection elements are designed as cohesive connections in accordance with the connection elements described in this patent application.

In an additional variant, the fuel cell unit is produced using a method described in this patent application. Method according to the invention for the production of a fuel cell unit as a fuel cell stack for the electrochemical generation of electrical energy with the following steps: providing a fuel cell unit with stacked fuel cells, the fuel cells comprising proton exchange membranes, anodes, cathodes, gas diffusion layers and bipolar plates, providing power lines for electrical connection with the bipolar plates of the fuel cells and for monitoring at least one parameter of the fuel cells, mechanical and electrical connection of the power lines with the bipolar plates by electrically and mechanically connecting the power lines to the bipolar plates with connecting elements, the connecting elements being formed as integral connections.

The material connections are preferably produced by means of welding, in particular laser welding and / or ultrasonic welding.

In a supplementary embodiment, the material connections are produced by a process unit for producing the material connections, in particular welded connections, being moved in space by a robot. The process unit, for example a laser or an ultrasonic transducer with a sonotrode, is brought into a corresponding process position on the bipolar plate by the robot and the material connection is then established with the temporarily active process unit in the process position. The number of process positions of the process unit during the production of the fuel cell unit corresponds to the number of material connections to be produced for the connecting elements and / or additional connecting elements.

In a further embodiment, one, in particular only one, power line with the robot is brought into mechanical contact with each, in particular only one, bipolar plate and then a material connection is established between the one, in particular only one, power line by means of the process unit and the one, in particular only one, bipolar plate produced. Position data for the geometric arrangement of the bipolar plates of the fuel cell unit and the relative position of the robot to the bipolar plates of the fuel cell unit are preferably stored in a computer and the movement of the robot, in particular the process unit and power lines moved by the robot, is controlled in space as a function of the position data , preferably in an initial phase of the movement of the process unit to one bipolar plate each.

In a further variant, the stacked bipolar plates are optically recorded by a camera, the data from the camera are evaluated by a computer with image processing software and the movement of the robot, in particular that of the robot, is determined by the image processing software moving process unit and power lines, controlled in space. The actual positions for the geometric arrangement of the bipolar plates of the fuel cell unit and / or the actual relative position of the robot to the bipolar plates of the fuel cell unit can be derived from the stored position data for the geometric arrangement of the bipolar plates of the fuel cell unit and / or the stored relative position of the robot to the bipolar plates of the fuel cell unit differ. Due to the optical detection of the actual positions for the geometric arrangement of the bipolar plates of the fuel cell unit and / or the actual relative position of the robot to the bipolar plates of the fuel cell unit, the robot moves, in particular to the process positions of the process unit, in the event of deviations essentially as a function of the actual ones Positions and essentially not as a function of the stored position data. Deviations between the actual and the stored positions of the bipolar plates in the fuel cell unit therefore do not lead to any errors in the production of the integral connections. Since small deviations between the actual and stored positions of the bipolar plates are to be assumed, the final phase of the movement of the robot shortly before reaching the process positions of the process unit is controlled with the recorded actual positions and the initial phase of the movement can be controlled with the stored positions. In the final phase of the movement of the process unit to each bipolar plate, essentially one Direction of movement parallel to the fictitious planes spanned by the bipolar plates.

In a supplementary embodiment, the at least one parameter of the fuel cells monitored with the power lines is the voltage difference between at least two bipolar plates, in particular the voltage differences between at least two immediately adjacent bipolar plates.

In a further embodiment, the power lines are electrically and mechanically connected to the data transmission device with additional connection elements and the additional connection elements are designed and / or produced as material connections according to the connection elements described in this patent application.

Expediently, all of the bipolar plates are electrically and mechanically connected to one power line each by means of a material connection.

The fuel cell unit preferably comprises at least one generator for generating a monitoring signal, in particular alternating current, and with the at least one data transmission device and the power lines, the monitoring signal can be transmitted from the at least one generator to the bipolar plates for applying the monitoring signal to the bipolar plates, in particular for detecting the impedance as a parameter of the fuel cell.

In a further variant, the at least one data transmission device is designed as at least one current collector strip with power lines and / or as at least one CAN interface and / or at least one LIN interface and / or at least one radio transmission means. The radio transmission medium transmits the data by radio, for example with WLAN or Bluetooth.

In a further embodiment, the bipolar plates and the power lines, in particular an end section of the power lines, are made of the same material, in particular metal, conductive plastic, composite materials or graphite, educated. In this way, the material connections of the connecting elements can be formed from the same material.

In a further embodiment, the contact surfaces of the current collector strip and the power lines, in particular an end section of the power lines, are made from the same material, in particular metal, conductive plastic, composite materials or graphite. The material connections of the additional connecting elements can thus be formed from the same material.

In a supplementary embodiment, the at least one parameter is the electrical voltage and / or the impedance of at least one monitored fuel cell.

In a further variant, the fuel cell unit comprises at least one connection device, in particular several connection devices, and tensioning elements.

Components for fuel cells are useful

Proton exchange membranes, anodes, cathodes, gas diffusion layers and bipolar plates.

In a further embodiment, the fuel cells each comprise a proton exchange membrane, an anode, a cathode, at least one gas diffusion layer and at least one bipolar plate.

In a further embodiment, the connecting device is designed as a bolt and / or is rod-shaped.

The clamping elements are expediently designed as clamping plates.

Fuel cell system according to the invention, in particular for a motor vehicle, comprising a fuel cell unit as a fuel cell stack with fuel cells, a compressed gas reservoir for storing gaseous fuel, a gas delivery device for delivering a gaseous oxidizing agent to the cathodes of the fuel cells, the Fuel cell unit is designed as a fuel cell unit described in this patent application.

In a further variant, the gas delivery device is designed as a fan or a compressor.

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

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

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

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

In a supplementary variant, the oxidizing agent is air with oxygen or pure oxygen.

The fuel cell unit is preferably a PEM fuel cell unit with PEM fuel cells.

The invention further comprises a computer program with program code means which are stored on a computer-readable data carrier in order to carry out a method described in this patent application when the computer program is carried out on a computer or a corresponding processing unit.

Part of the invention is also a computer program product with program code means that are stored on a computer-readable data carrier in order to carry out a method described in this patent application when the computer program is carried out on a computer or a corresponding processing unit. Brief description of the drawings

In the following, exemplary embodiments of the invention are described in more detail with reference to the accompanying drawings. It shows:

Fig. 1 is a greatly simplified exploded view of a

Fuel cell system with components of a fuel cell,

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

3 shows a longitudinal section through a fuel cell,

4 shows a perspective view of a fuel cell unit as a fuel cell stack, i.e. H. a fuel cell stack,

FIG. 5 shows a section through the fuel cell unit according to FIG. 4,

FIG. 6 shows a section through the fuel cell unit, showing FIG

Power lines, a data transmission device and a monitoring unit for monitoring at least one parameter of the fuel cells and

7 shows a greatly simplified representation of a robot.

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 conducted as a gaseous fuel at an anode 7 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 uptake) takes place at the cathode 8. The oxidation as the release of electrons is carried out at the anode 7. The redox equations for the electrochemical processes are:

Cathode:

0 ₂ + 4 H ⁺ + 4 e- - »2 H ₂ 0

Anode:

2 H ₂ - »4 H ⁺ + 4 e-

Sum reaction equation of cathode and anode: 2 H ₂ + 0 _{2 ~} »2 H ₂ 0

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

The fuel cell 2 also comprises a proton exchange membrane 5 (Proton Exchange Membrane, PEM), which is arranged between the anode 7 and the cathode 8. The anode 7 and cathode 8 are layered or disk-shaped. The PEM 5 acts as an electrolyte, catalyst carrier and separator for the reaction gases. The PEM 5 also functions as an electrical insulator and prevents an electrical short circuit between the anode 7 and cathode 8. In general, proton-conducting foils made of perfluorinated and sulfonated polymers are 12 μm to 150 μm thick. The PEM 5 conducts the protons H ⁺ and essentially blocks ions other than protons H ⁺ , so that the charge transport can take place due to the permeability of the PEM 5 for the protons H ^+. The PEM 5 is essentially impermeable to the reaction gases oxygen O2 and hydrogen H2, ie it blocks the flow of oxygen O2 and hydrogen H2 between one 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 the oxidizing agent. The proton conductivity of the PEM 5 increases with increasing temperature and increasing water content.

The electrodes 7, 8 as the anode 7 and cathode 8 rest on the two sides of the PEM 5, each facing the gas spaces 31, 32. A unit composed of the PEM 5 and the electrodes 6, 7 is referred to as a membrane electrode arrangement 6 (membrane electrode array, MEA). The electrodes 7, 8 are pressed with the PEM 5. The electrodes 6, 7 are platinum-containing carbon particles attached to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene copolymer),

PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride) and / or PVA (polyvinyl alcohol) are bound and hot-pressed in microporous carbon fiber, glass fiber or plastic mats. A catalyst layer 30 is normally applied to each of the electrodes 6, 7 on the side facing the gas spaces 31, 32. The catalyst layer 30 on the gas space 31 with fuel on the anode 7 comprises nanodisperse platinum ruthenium on graphitized soot particles which 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. Nafion®, a PTFE emulsion or polyvinyl alcohol, for example, are used as binders.

A gas diffusion layer 9 (gas diffusion layer, GDL) rests 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 oxidizing agent from channels 13 for oxidizing agent evenly onto the catalyst layer 30 on the cathode 8. The GDL 9 also draws off water of reaction in the opposite direction to the direction of flow of the reaction gases, i. H. in one direction each 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 is composed, for example, of a hydrophobized carbon paper and a bonded layer of carbon powder. The fuel cells 2 are layered and disk-shaped and this also applies to the components proton exchange membranes 5, anodes 7, cathodes 8, gas diffusion layers 9 and bipolar plates 10. The fuel cells 2 and the Components of the fuel cells 2 span fictitious planes 54 which are aligned parallel to one another.

A bipolar plate 10 rests on the GDL 9. The electrically conductive bipolar plate 10 serves as a current collector, to drain water and to conduct the reaction gases through a channel structure 29 and / or a flow field 29 and to dissipate the waste heat that occurs in particular during the exothermic electrochemical reaction at the cathode 8. In order to dissipate the waste heat, channels 14 for the passage of a liquid or gaseous coolant are incorporated into the bipolar plate 10. The channel structure 29 on the gas space 31 for fuel is formed by channels 12. The channel structure 29 in the gas space 32 for oxidizing agent is formed by channels 13. For example, metal, conductive plastics and composite materials or graphite are used as the material for the bipolar plates 10.

A plurality of fuel cells 2 are arranged one above the other in a fuel cell unit 1 and / or a fuel cell stack 1 and / or a fuel cell stack 1 (FIG. 4). 1 shows an exploded view of two fuel cells 2 arranged one above the other. A seal 11 seals the gas spaces 31, 32 in a fluid-tight manner. In a compressed gas reservoir 21 (FIG. 1), hydrogen H2 is stored as fuel at a pressure of, for example, 350 bar to 700 bar. From the pressurized gas reservoir 21, the fuel is passed through a high pressure line 18 to a pressure reducer 20 to reduce the pressure of the fuel in a medium pressure line 17 from approximately 10 bar to 20 bar. 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. From the injector 19, the fuel is fed to a feed line 16 for fuel (FIG. 1) and from the feed 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 flowing through the channels 12, the fuel not consumed in the redox reaction at the anode 7 and possibly water from a controlled humidification of the anode 7 is diverted from the fuel cells 2 through a discharge line 15. A gas delivery device 22, for example designed as a fan 23 or a compressor 24, delivers air from the environment as an oxidizing agent into a supply line 25 for oxidizing agent. From the supply line 25, the air is fed 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 flowing through the channels 13 or the gas space 32 for the oxidizing agent 32, the oxidizing agent not consumed at the cathode 8 and the water of reaction arising at the cathode 8 due to the electrochemical redox reaction are discharged from the fuel cells 2 through a discharge line 26. A feed line 27 is used to feed coolant into the channels 14 for coolant and a discharge line 28 is used to discharge the coolant conducted through the channels 14. The supply and discharge lines 15, 16, 25, 26, 27, 28 are shown in FIG End region (not shown) of bipolar plates 10 lying on top of one another. The fuel cell stack 1 together with the compressed gas storage device 21 and the gas delivery device 22 form 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 uppermost fuel cell 2 and a lower clamping plate 36 rests on the lowermost fuel cell 2. The fuel cell unit 1 comprises approximately 300 to 400 fuel cells 2, which are not all shown in FIG. 4 for reasons of drawing. The clamping elements 33 apply a compressive force to the fuel cells 2, ie the upper clamping plate 35 rests on the uppermost fuel cell 2 with a compressive force and the lower clamping plate 36 rests on the lowermost fuel cell 2 with a compressive force. The fuel cell stack 2 is thus braced in order to ensure the 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 1 as small as possible. To brace the fuel cells 2 with the tensioning elements 33 are formed on the fuel cell unit 1 four connecting devices 39 as bolts 40, which are subject to tension. The four bolts 40 are firmly connected to the chipboard 34.

At least one parameter of the fuel cell unit 1 is monitored by a monitoring unit 37 (FIG. 6). The voltage of the fuel cells 2 is monitored as an essential parameter, i. H. the difference between the voltage between two bipolar plates 10. The monitoring unit 37 (FCCU, Fuel Cell Control Unit) thus forms in particular a CVM system (Cell Voltage Monitoring System). All of the bipolar plates 10 are electrically and mechanically connected to power lines 43, and the power lines 43 are electrically connected to the monitoring unit 37 by means of a data transmission device 38. Each power line 43 is thus electrically connected to the monitoring unit 37 in order to detect the at least one parameter. The data transmission device 38 is formed by a current collector strip 41 with contact surfaces 42 and a cable harness 47. The power lines 43 are electrically and mechanically connected to the bipolar plates 10 by connecting elements 44 as material connections 46. The current collector strip 41 is electrically connected to the monitoring unit 37 by the cable harness 47. Each bipolar plate 10 is connected to a power line 43 by means of a material connection 46. The power lines 43 are mechanically and electrically connected to the contact surfaces 42 of the current collector strip 41 by additional connecting elements 45. The number of contact surfaces 42 corresponds to the number of power lines 43 and each power line 43 is connected to a contact surface 42. The additional connection elements 45 are identical to the connection elements 44 as material connections 46. The bipolar plates 10, the power lines 43 and the contact surfaces 42 are made of identical electrically conductive material, in particular metal.

The number of bipolar plates 10 thus corresponds to the number of power lines 43, the number of connecting elements 44 and the number of additional connecting elements 45 the monitoring unit 37 outputs an error message. During the production of the fuel cell unit 1, fuel cells 2 are stacked to form the fuel cell unit 1 as a fuel cell stack 1, ie the fuel cell unit 1 with the stacked fuel cells 2 is made available. A robot 48 comprises robot arms 49 and robot joints 50. A process unit 52 as a laser 53, a camera 51 and gripping tongs 56 are attached to an end region of a last robot arm 49. The gripping tongs 56 are fastened to the last robot arm 49 by means of a motor-driven ball joint (not shown). The robot 48 controls a computer 55 with a processor and a data memory. Position data on the intended geometric arrangement of the bipolar plates 10 and / or on the relative position of the robot 48 to the fuel cell unit 1 are stored in the data memory. The camera 51 optically captures images of the bipolar plates 10 and the actual relative position of the bipolar plates 10 to the robot 48 is captured with image processing software in the computer 55. The movement of the robot 48 is thus controlled as a function of the intended position data stored in the data memory and / or the data on the actual position of the bipolar plates 10 relative to the robot 48 determined by the image processing software certain data on the actual position of the bipolar plates 10 relative to the robot 48 are corrected, so that advantageously deviations in the geometric arrangement of the bipolar plates 10 due to manufacturing inaccuracies have no effect on the production.

The power lines 43 are stored in a container (not shown). The gripping tongs 56 each grip a power line 43 and leads one end of the power line 43 to the outside of a bipolar plate 10 by means of a controlled movement of the robot 48. The laser 53 is then aligned and switched on while the power line 43 is fixed by the gripping tongs 56 to the bipolar plate 10 is, so that the laser beam emitted by the laser 53 is directed to the end of the power line 43, which rests on the outside of the bipolar plate 10. The laser beam has a power of approximately one to a few kW with a diameter of a few tenths of a millimeter, so that the metal of the end of the power line 43 and im Essentially, the metal on the outside of the bipolar plate 10 melts locally and the material connection 46 is produced as a welded connection with laser welding between the bipolar plate 10 and the power line 43. This process is automatically repeated by the robot 48 for each bipolar plate 10 until all of the bipolar plates 10 are each connected to a power line 43. In a manner analogous to the way in which the connecting elements 44 are produced as material connections 46 between the bipolar plates 10 and the power lines 43, the additional connection elements 45 are produced as material connections 46 between the other ends of the power lines 43 and the contact surfaces 42 of the current collector strip 41. Each power line 43 is electrically and mechanically connected to a respective contact surface 42.

In a further exemplary embodiment, not shown, the process unit 52 is designed as an ultrasonic transducer and a sonotrode. Otherwise, this exemplary embodiment of the production corresponds to the exemplary embodiment described above with the laser 53 as the process unit 52. A generator generates a high-frequency alternating current which generates an ultrasonic oscillation in the ultrasonic transducer with piezoelectric and magnetostrictive effects. This ultrasonic oscillation is transmitted to the sonotrode and the sonotrode is placed by the robot 48 on the power line 43, which is arranged between the outside of the bipolar plate 10 and the sonotrode. In this way, material connections 46 as the connecting elements 44 between the bipolar plates 10 and the power lines 43 are produced by means of ultrasonic welding. In an analogous manner, the additional connecting elements 45 are produced between the other ends of the power lines 43 and the contact surfaces 42 by means of ultrasonic welding. In the case of ultrasonic welding, the joining partners, ie the bipolar plates 10 and power lines 43, are essentially connected to one another by interlocking and interlocking through plastic flow without the material melting as in laser welding. In this way, material connections 46, which are made with laser welding or ultrasonic welding, can also be distinguished from one another structurally by a material test, for example with a visual test with a microscope, acoustic emission analysis, time-domain reflectometry or ultrasound, after production. Viewed overall, the fuel cell unit 1 according to the invention and the method according to the invention for producing the fuel cell unit 1 are associated with significant advantages. The connecting elements 44 between the bipolar plates 10 and a first end of the power lines 43 and the additional connecting elements 45 between a second end of the power lines 43 and the contact surfaces 42 are automatically produced as material connections 46 by a robot 48 with a process unit 52. The connecting elements 44 and additional connecting elements 45 have no manually caused manufacturing errors due to the automated production and are inexpensive to manufacture. As robots 48, simple built robots 48 can also be used, which can essentially only execute straight-line movements parallel and perpendicular to the fictitious planes 54, so that the production costs can be reduced even further.

Claims

Expectations

1. Fuel cell unit (1) as a fuel cell stack (1) for the electrochemical generation of electrical energy, comprising

- stacked fuel cells (2, 3) with proton exchange membranes (5), anodes (7), cathodes (8), gas diffusion layers (9) and bipolar plates (10),

- Power lines (43) for the electrical connection to the bipolar plates (10) of the fuel cells (2, 3) and for monitoring the fuel cells (2, 3) by means of a detection of at least one parameter of the fuel cells (2, 3),

- Connecting elements (44) for the electrical and mechanical connection of the power lines (43) to the bipolar plates (10), so that the power lines (43) are electrically and mechanically connected to the bipolar plates (10) by means of the connecting elements (44), characterized in that, that the connecting elements (44) are designed as cohesive connections (46).

2. Fuel cell unit according to claim 1, characterized in that the material connections (46) are made by welding.

3. Fuel cell unit according to claim 1 or 2, characterized in that the material connections (46) are made by means of laser welding and / or ultrasonic welding.

4. Fuel cell unit according to one or more of the preceding claims, characterized in that the bipolar plates (10), in particular at least 90% or 99% of the bipolar plates (10), electrically by means of a cohesive connection (46) each with a power line (43) and are mechanically connected.

5. Fuel cell unit according to one or more of the preceding claims, characterized in that the fuel cell unit (1) comprises a monitoring unit (37) as a computing unit for monitoring the at least one parameter of the fuel cells (2, 3).

6. Fuel cell unit according to claim 5, characterized in that the fuel cell unit (1) has a data transmission device (38) for transmitting data regarding the at least one parameter of the fuel cells (2, 3) to be detected from the power lines (43) to the monitoring unit (37 ) includes.

7. Fuel cell unit according to claim 6, characterized in that the power lines (43) are electrically and mechanically connected to the data transmission device (38) with additional connecting elements (45) are.

8. The fuel cell unit according to claim 7, characterized in that the additional connecting elements (45) are designed according to the cohesive connections (46) according to claims 1 to 3.

9. Fuel cell unit according to one or more of the preceding claims, characterized in that the fuel cell unit (1) is produced using a method according to one or more of claims 10 to 15.

10. A method for producing a fuel cell unit (1) as a fuel cell stack (1) for the electrochemical generation of electrical energy with the following steps: providing a fuel cell unit (1) with stacked fuel cells (2, 3), the fuel cells (2, 3) comprising proton exchange membranes (5), anodes (7), cathodes (8), gas diffusion layers (9) and bipolar plates (10), providing power lines (43) for electrical connection with the bipolar plates (10) of the fuel cells (2, 3) and for monitoring at least one parameter of the fuel cells (2, 3), mechanical and electrical connection of the power lines (43) to the bipolar plates (10) by connecting the power lines (43) electrically and mechanically with connecting elements (44) to the bipolar plates (10) are characterized in that the connecting elements (44) are designed as cohesive connections (46).

11. The method according to claim 10, characterized in that the material connections (46) are produced by means of welding, in particular laser welding and / or ultrasonic welding.

12. The method according to claim 10 or 11, characterized in that the material connections (46) are produced by a process unit (52) for producing the material connections (46), in particular welded connections (46), by a robot (48) in space is moved.

13. The method according to claim 12, characterized in that each one power line (43) with the robot (48) is brought into mechanical contact with a respective bipolar plate (10) and then by means of the process unit (52) a material connection (46) between each one power line (43) and each one bipolar plate (10) is produced.

14. The method according to claim 12 or 13, characterized in that in a computer (55) position data for the geometric arrangement of the bipolar plates (10) of the fuel cell unit (1) and the relative position of the robot (48) to the bipolar plates (10) Fuel cell unit (1) are stored and the movement of the robot (48), in particular of the process unit (52) and power lines (43) moved by the robot (48), is controlled in space as a function of the position data.

15. The method according to one or more of claims 12 to 14, characterized in that the stacked bipolar plates (10) are optically captured by a camera (51), the data from the camera (51) evaluated by a computer (55) with image processing software and the movement of the robot (48), in particular of the process unit (52) and power lines (43) moved by the robot (48), is controlled in space as a function of the data on the position of the bipolar plates (10) determined by the image processing software.