WO2021180407A1

WO2021180407A1 - Fuel cell unit

Info

Publication number: WO2021180407A1
Application number: PCT/EP2021/053093
Authority: WO
Inventors: Markus Berger
Original assignee: Robert Bosch Gmbh
Priority date: 2020-03-10
Filing date: 2021-02-09
Publication date: 2021-09-16
Also published as: DE102020203040A1

Abstract

The invention relates to a fuel cell unit as a fuel cell stack for the electrochemical generation of electrical energy, comprising stacked fuel cells, the fuel cells each comprising a proton exchange membrane, an anode, a cathode, a gas diffusion layer, a bipolar plate (10) with three separate channel structures (29) with channels for the separate passage of oxidising agents, fuel and cooling fluid and the channel structures (29) have an inlet region (37) and an outlet region (38) for the oxidising agent, fuel and cooling fluid, at least one feed channel (43) for feeding the oxidising agent as process fluid into the gas spaces for oxidising the fuel cells, at least one feed channel (48) for feeding fuel as process fluid into the gas spaces for fuel of the fuel cells, at least one feed channel (50) for coolant as process fluid for feeding the coolant into a channel for the coolant, distribution structures (45, 46) for conducting and distributing the process fluids from the feed channels (43, 48, 50) into the channel structures (29) of the bipolar plates (10), wherein in each fuel cell in a direction from the feed channels (43, 48, 50) to the inlet region (37) of the channel structures (29) of the bipolar plate (10), a first distribution structure (45) is formed for two process fluids as the first and second process fluid, and a second distribution structure (46) is formed in a direction from the feed channels (43, 48, 50) to the inlet region (37) of the channel structures (29) of the bipolar plate (10) for the first and second process fluid of the first distribution structure (45) and additionally for a third process fluid.

Description

description

title

Fuel cell unit

The present invention relates to a fuel cell unit according to the preamble of claim 1 and a fuel cell system according to the preamble of claim 15.

State of the art

Fuel cell units as galvanic cells convert continuously supplied fuel and oxidizing agent into electrical energy and water 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.

In fuel cell units, a large number of fuel cells are arranged one above the other to form a fuel cell stack. Inside the fuel cells there is a gas space for oxidizing agent, that is to say a flow space for the passage of oxidizing agent, such as air from the environment with oxygen. The gas space for oxidizing agent 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. Due to the electrochemical reaction, water is produced at the cathodes, so that it flows into the gas space for Oxidizing agent, in particular on the gas diffusion layer, leads to an accumulation of water or condensate. The accumulation of water in the area of the cathode, i.e. in particular at the gas diffusion layer for the cathode, leads to an undersupply of the catalyst layer with oxidizing agent due to the flooding of the gas diffusion layer with water, so that the electrical voltage generated by the fuel cell is greatly reduced. Furthermore, this causes increased aging of the fuel cell due to the enrichment with water. For this reason, attempts are made to avoid such accumulations of water in the gas space for oxidizing agents. The air from the environment is introduced into the gas spaces for the oxidizing agent with a gas delivery device, for example a fan or a compressor.

The oxidizing agent is introduced into the gas chambers for oxidizing agent through at least one feed channel and discharged from the gas chambers for oxidizing agent through at least one discharge channel. Extensions are designed as sealing plates in the bipolar plates and the membrane electrode arrangements, and fluid openings are incorporated in the sealing plates. The fluid openings are stacked flush in the fuel cell unit, so that the fluid openings form the at least one supply channel and the at least one discharge channel. Seals are arranged between the sealing plates in the area of the fluid openings so that the oxidizing agent does not get into the spaces between the sealing plates in an uncontrolled manner. The oxidizing agent is introduced into the channels for oxidizing agents from the at least one feed channel. The supply channel for oxidizing agent has a small transverse extent, so that a large transverse distribution is necessary in a distribution structure between the supply channel for oxidizing agent and an inlet region of the channel structure with the channels for oxidizing agent. This is disadvantageous because as a result the oxidizing agent already flows into the channels for oxidizing agents at a different temperature and pressure. This applies analogously to the coolant and the fuel as the further process fluids of the fuel cell, so that these, with the disadvantages mentioned, also flow into the channels for coolant and fuel on the other channel structures of the bipolar plate. Supply and discharge channels for fuel and coolant are designed in an analogous manner as fluid openings on the sealing plates. Due to the introduction of one process fluid only in a partial area as an inlet area at one end of the channel structure, the process fluids do not flow parallel everywhere through the channel structure, so that heat transfer between the process fluids within the channel structures is only possible to a small extent. This leads to large differences in the temperature and humidity in the gas spaces for oxidizing agent and fuel. This reduces the performance of the fuel cell and increases its aging.

DE 102006 019 114 A1 discloses a fuel cell system with a plurality of fuel cells, each of the fuel cells comprising a membrane electrode arrangement, an anode catalyst layer on a first side of the membrane electrode arrangement and a cathode catalyst layer on a second side of the membrane electrode arrangement, the plurality of fuel cells in at least two stages are arranged, wherein the plurality of fuel cells are arranged in each of the at least two stages in a parallel arrangement and the stages are arranged in a series arrangement, wherein a first stage has a first plurality of fuel cells and a second stage has a second plurality of fuel cells wherein the first plurality of fuel cells comprises a greater number of fuel cells than the second plurality of fuel cells; an anode gas inlet manifold in communication with the first stage; at least one anode gas inlet / discharge manifold, the anode gas inlet / discharge manifold allowing anode exhaust gas to exit the first stage and allowing the anode exhaust gas to enter the second stage; and an anode gas discharge manifold in communication with the second stage.

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, the fuel cells each comprising a proton exchange membrane, an anode, a cathode, a Gas diffusion layer, a bipolar plate with three separate channel structures with channels for the separate passage of oxidizing agent, fuel and cooling fluid and the channel structures have an inlet area and an outlet area for the oxidizing agent, the fuel and the cooling fluid, at least one feed channel for the supply of oxidizing agent as process fluid into the Gas chambers for oxidizing agent of the fuel cells, at least one feed channel for feeding fuel as process fluid into the gas chambers for fuel of the fuel cells, at least one feeding channel for coolant as process fluid for feeding the coolant into a channel for coolant, distribution structures for feeding and distributing the process fluids from the feed channels into the channel structures of the bipolar plates, with a first distribution structure for between two ei process fluids are formed as first and second process fluids and a second distribution structure for the first and second process fluids of the first distribution structure and additionally for a third process fluid is formed in a direction from the supply channels to the inlet area of the channel structures of the bipolar plate.

In a supplementary embodiment, the second distribution structure is formed between the first distribution structure and the inlet region of the channel structures of the bipolar plate.

In a further embodiment, the first distribution structure is formed only for the first and second process fluid, so that only first and second distribution channels for the first and second process fluid are formed in the first distribution structure.

In an additional variant, the supply channels for the first and second process fluids of the first distribution structure are formed in the first distribution structure.

In a supplementary embodiment, the at least one supply channel for the third process fluid is formed, in particular exclusively, in the second distribution structure. Separate first and second distribution channels for the first and second process fluid are preferably formed in the first distribution structure, and the first and second distribution channels are formed separately from one another in a direction perpendicular to fictitious planes spanned by the fuel cells.

In a further embodiment, separate first, second and third distribution channels for the first, second and third process fluid are formed in the second distribution structure.

In a further variant, two of the first, second and third distribution channels are formed separately from one another in a direction perpendicular to the fictitious planes spanned by the fuel cells and / or one of the first, second and third distribution channels in a direction parallel to the fictitious planes spanned by the fuel cells is formed next to one of the other first, second or third distribution channels.

In an additional embodiment, the first, second and third distribution channels are aligned as longitudinal channels in the second distribution structure essentially parallel to one another. Substantially means preferably with a deviation of less than 30 °, 20 ° or 10 °.

The fuel cell unit, in particular the fuel cells, expediently has a longitudinal extent in a longitudinal direction and a transverse extent in a transverse direction, and the longitudinal and transverse directions are mutually perpendicular and parallel to the fictitious planes spanned by the fuel cells.

In a further embodiment, when the first and second distribution structure are formed between a transverse side of the fuel cell unit and the channel structure of the bipolar plate, the transverse extent of the first and second distribution structure essentially corresponds to the transverse extent of the inlet area of the channel structure. Substantially means preferably with a deviation of less than 30%, 20% or 10%. In a supplementary embodiment, the first process fluid is the oxidizing agent, the second process fluid is the coolant and the third process fluid is the fuel.

In a further embodiment, the supply channels are arranged next to one another in the longitudinal direction and essentially centrally in the transverse direction, preferably when the inlet area is designed with an extension predominantly in the transverse direction between the transverse side of the fuel cell and the channel structure. Essentially centered preferably means that in a section parallel to the fictitious planes spanned by the fuel cells, the centers or focal points of the feed channels are at a distance from a central longitudinal center line of the fuel cells that is less than 30%, 20% or 10% of half the Transverse expansion of the fuel cells.

In a further embodiment, the transverse extent or the sum of the transverse extent of the at least one feed channel for oxidizing agent essentially corresponds to the transverse extent of the inlet area of the channel structure, preferably when the inlet area is formed with an extent predominantly in the transverse direction between the transverse side of the fuel cell and the channel structure. Substantially means preferably with a deviation of less than 30%, 20% or 10%. There is thus essentially no transverse distribution of the oxidizing agent from the at least one feed channel to the inlet region of the channel structure necessary.

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 storage device 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 being designed as a fuel cell unit described in this patent application.

In a further embodiment, the feed channels are arranged next to one another in the transverse direction and essentially in the middle in the longitudinal direction, preferably when the inlet area is formed with an extension predominantly in the longitudinal direction between the longitudinal side of the fuel cell and the channel structure. Essentially centered preferably means that in a section parallel to the fictitious planes spanned by the fuel cells, the centers or focal points of the feed channels are at a distance from a central transverse center line of the fuel cells that is less than 30%, 20% or 10% of half the Longitudinal expansion of the fuel cells.

In a further embodiment, in the longitudinal direction from the transverse side to the inlet area of the channel structure of the bipolar plate, first the at least one supply channel for oxidizing agent and then the at least one supply channel for coolant are formed in the first distribution structure and then in the longitudinal direction the at least one supply channel for fuel in the second distribution structure .

In a further embodiment, when the first and second distribution structure is formed between a longitudinal side of the fuel cell unit and the channel structure of the bipolar plate, the longitudinal extent of the first and second distribution structure essentially corresponds to the longitudinal extent of the inlet area of the channel structure. Substantially means preferably with a deviation of less than 30%, 20% or 10%.

In a further embodiment, in the transverse direction from the longitudinal side to the inlet area of the channel structure of the bipolar plate, first the at least one supply channel for oxidizing agent and then the at least one supply channel for coolant are formed in the first distribution structure and then in the transverse direction the at least one supply channel for fuel in the second distribution structure.

In a further embodiment, the longitudinal extent or the sum of the longitudinal extents of the at least one feed channel for fuel essentially corresponds to the longitudinal extent of the inlet area of the channel structure, preferably when the inlet area is formed with an extent predominantly in the longitudinal direction between the longitudinal side of the fuel cell and the channel structure. Substantially means preferably with a deviation of less than 30%, 20% or 10%. It is therefore in the Substantially no longitudinal distribution of the fuel from the at least one feed channel to the inlet region of the channel structure is necessary.

The transverse extent or the sum of the transverse extent of the at least one supply channel for coolant is expediently smaller than 90%, 70% or 50% of the transverse extent of the inlet area of the duct structure.

In a further variant, the transverse extent or the sum of the transverse extent of the at least one feed channel for fuel is smaller than 90%, 70% or 50% of the transverse extent of the inlet area of the duct structure.

In an additional embodiment, the at least one supply channel and / or discharge channel for oxidizing agent and / or fuel and / or coolant is oriented essentially perpendicular to the fictitious planes spanned by the fuel cells. The orientation of the at least one supply channel and / or discharge channel for oxidizing agent and / or fuel and / or coolant is the longitudinal axis and / or the flow direction of the process fluid in the supply channel and / or discharge channel. Substantially perpendicular means preferably with a deviation of less than 30 °, 20 ° or 10 °.

In an additional embodiment, the transverse extent of the inlet area essentially corresponds to the transverse extent of the channel structure when the inlet area is formed between the transverse sides of the fuel cell and the channel structure.

In an additional embodiment, the longitudinal extent of the inlet area corresponds essentially to the longitudinal extent of the channel structure when the inlet area is formed between the longitudinal sides of the fuel cell and the channel structure.

In a supplementary embodiment, all channels for oxidizing agent, fuel and coolant in the channel structures of the bipolar plates are designed so that the oxidizing agent, fuel and coolant flow through the channels essentially in parallel. Essentially parallel means preferably with a deviation of less than 30 °, 20 ° or 10 °.

In a further variant, the fuel cell unit comprises at least one discharge channel for discharging fuel from the fuel cells.

In a supplementary embodiment, the fuel cell unit comprises at least one discharge channel for discharging coolant from the fuel cells.

In a further variant, in the first distribution structure and / or second distribution structure, the first distribution channels and / or second distribution channels and / or third distribution channels are formed separately from one another in two or three levels in a direction perpendicular to the fictitious levels spanned by the fuel cells.

In a further variant, in the first distribution structure and / or second distribution structure, the first distribution channels and / or second distribution channels and / or third distribution channels are in at least one direction parallel to the fictitious planes spanned by the fuel cells next to another first, second or third distribution channel trained on one level.

In a further embodiment, at least one, in particular all of the features disclosed in this property right with regard to a fuel cell are embodied in all fuel cells of the fuel cell unit.

In an additional embodiment, the fuel cells of the fuel cell unit are stacked in alignment, in particular one on top of the other.

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 and / or is designed as a tensioning belt.

The clamping elements are expediently designed as clamping plates.

In a further variant, the gas delivery device is designed as a fan and / or a compressor and / or a pressure vessel with an oxidizing agent.

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.

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,

6 shows a plan view of a bipolar plate of the fuel cell unit according to the invention in a first exemplary embodiment,

7 shows an enlarged plan view of the bipolar plate of the fuel cell unit according to the invention in the first exemplary embodiment,

8 shows a section A-A according to FIG. 7 of the bipolar plate,

9 shows a section B-B according to FIG. 7 of the bipolar plate,

FIG. 10 shows a section C-C according to FIG. 7 of the bipolar plate and FIG

11 shows an enlarged plan view of the bipolar plate of the fuel cell unit according to the invention in the second exemplary embodiment.

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 fed to an anode 7 as a 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 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 stacked fuel cells 2, 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 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 are 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 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 a gas space 31 at the anode 7 with hydrogen H2 fuel and the gas space 32 at the cathode 8 with air or Oxygen O2 as an 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 assembly 6 (Membrane Electrode Assembly, MEA). The electrodes 7, 8 are pressed with the PEM 5. The electrodes 6, 7 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 are encapsulated in microporous carbon fiber, Glass fiber or plastic mats are hot-pressed. 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 water of reaction in the opposite direction to the direction of flow of the reaction gases, ie 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.

A bipolar plate 10 rests on the GDL 9. The electrically conductive bipolar plate 10 serves as a current collector, for water drainage and for conducting the reaction gases as process fluids through the channel structures 29 and / or flow fields 29 and for dissipating the waste heat that occurs in particular during the exothermic electrochemical reaction at the cathode 8. In order to dissipate the waste heat, channels 14 are incorporated into the bipolar plate 10 as a channel structure 29 for the passage of a liquid or gaseous coolant as a process fluid. 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 stacked in a fuel cell unit 1 and / or a fuel cell stack 1 and / or a fuel cell stack 1 (FIG. 4). In Fig. 1, an exploded view of two stacked fuel cells 2 is shown. 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 if necessary, 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. 1 as separate lines for reasons of simplicity and are actually structurally at the end area near the channels 12, 13, 14 as aligned fluid openings 42 on sealing plates 41 designed as an extension at the end region of the superimposed bipolar plates 10 (FIGS. 6 and 7) and membrane electrode arrangements 6 (not shown). 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 200 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. So that the fuel cell stack 2 is braced to the tightness for the To ensure 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, four connecting devices 39 are designed as bolts 40 on the fuel cell unit 1, which are subject to tensile stress. The four bolts 40 are firmly connected to the chipboard 34.

FIGS. 1 to 5 merely serve to illustrate the basic mode of operation of fuel cells 2 and features essential to the invention are partially not shown in FIGS. 1 to 5.

In FIGS. 6 to 10, a fuel cell 2 of a fuel cell unit 1 according to the invention is shown in a first exemplary embodiment. The bipolar plate 10 is constructed from two reshaped plates, namely an upper plate and a lower plate (FIGS. 2 and 3), so that the channels 12, 13 and 14 are formed as three separate channel structures 29 in the bipolar plate 10. The fluid openings 42 on the sealing plates 41 of the bipolar plates 10 and membrane electrode assemblies 6 are stacked in an aligned manner within the fuel cell unit 1 so that feed and discharge channels 43, 44, 48, 49, 50, 51 are formed. Seals (not shown) are arranged between the sealing plates 41 for the fluid-tight sealing of the supply and discharge channels 43, 44, 48, 49, 50, 51 formed by the fluid openings 42.

The bipolar plates 10 (FIGS. 6 and 7) and membrane electrode arrangements 6 are essentially rectangular and have a longitudinal extent as a length in a longitudinal direction 57 and a transverse extent in a transverse direction 58. The essentially layered bipolar plates 10, membrane electrode arrangements 6 and gas diffusion layers 9 span fictitious planes 52. A direction 53 is oriented perpendicular to the fictitious planes 52. The drawing planes of FIGS. 6 and 7 are aligned in the fictitious planes 52 or parallel to them.

The fuel cell unit 1, the fuel cells 2 and the bipolar plates 10 with the sealing plates 41 have two opposite longitudinal sides 55 opposite one another in the transverse direction 58 as ends in the transverse direction 58 and two opposite transverse sides 56 opposite one another in the longitudinal direction 57 as Ends in the longitudinal direction 57. Between the transverse side 56 shown on the left in FIGS. 6 and 7 and an inlet area 37 on the channel structure 29 for introducing a first process fluid as the oxidizing agent into the channels 13, a second process fluid as the coolant in the channels 14 and a third process fluid as the fuel A first distribution structure 45 and a second distribution structure 46 are formed in the channels 12. A supply channel 43 for oxidizing agent and a supply channel 50 for coolant are arranged in the first distribution structure 45. A feed channel 48 for fuel is formed in the second distribution structure 46. The transverse extent 69 of the inlet area 37 of the channel structure 29 corresponds to the transverse extent 70 of the outlet area 38 of the channel structure 29 and is slightly smaller than the transverse extent of the bipolar plate 10, i.e. the distance in the transverse direction 58 between the two longitudinal sides 55. The transverse extents 69, 70 correspond to the transverse extent 68 of the channel structure 29, i.e. h the inlet and outlet areas 37, 38 are formed on the entire end area in the longitudinal direction 57 of the channel structure 29. The longitudinal extent 67 of the channel structure 29 is approximately 60% to 90% of the longitudinal extent of the bipolar plate 10. The longitudinal extent 71 of the first distribution structure 45 is significantly larger, approximately 2 times greater than the longitudinal extent 73 of the second distribution structure 46, since in the First distribution structure 45 in the longitudinal direction 57, the supply channel 43 for oxidizing agent and the supply channel 50 for coolant are arranged side by side. The transverse extent 72 of the first distribution structure 45 corresponds to the transverse extent 74 of the second distribution structure 46 and the transverse extents 72, 74 of the first and second distribution structures 45, 46 are essentially identical to the transverse extent 69 of the inlet region 37 of the channel structure 29.

The transverse dimension 85 of the feed channel 43 for oxidizing agent is only slightly smaller than the transverse dimension 69 of the inlet area 37 of the channel structure, so that for the guidance of the oxidizing agent from the feed channel 43 for oxidizing agent into the channels 13 for oxidizing agent, which begin at the inlet area 37, in Substantially no transverse distribution of the oxidizing agent in transverse direction 58, but essentially only a longitudinal distribution or longitudinal line in longitudinal direction 57 is necessary. For this reason, there are essentially only first distribution channels 59 as the first longitudinal distribution channels from the supply channel 43 to the inlet region 37 62 routed for the first process fluid as the oxidizer. The first distribution channels 59 as the first longitudinal distribution channels 62 are formed in the first distribution structure 45 and the second distribution structure 46.

The transverse dimension 86 of the supply channel 50 for coolant is significantly smaller than the transverse dimension 69 of the inlet area 37 of the channel structure, so that for the guiding of the coolant from the supply channel 50 for coolant into the channels 14 for coolant, which begin at the inlet area 37, both a Transverse distribution of the coolant in the transverse direction 58 as well as a longitudinal distribution or longitudinal line in the longitudinal direction 57 is necessary. For this reason, from the supply channel 50 to the inlet region 37, second distribution channels 60 are routed as second longitudinal distribution channels 63 in the longitudinal direction 57 and second transverse distribution channels 64 in the transverse direction 58 for the second process fluid as the coolant. The second transverse distribution channels 64 are formed only in the first distribution structure 45 and the second longitudinal distribution channels 63 are formed in the first and second distribution structures 45, 46. The second transverse distribution channels 64 open into the supply channel 50 for coolant, so that the coolant flows from the supply channel 50 first into the second transverse distribution channels 64 and then into the second longitudinal distribution channels 63.

In the first distribution structure 45, the first distribution channels 59 and the second distribution channels 60 are formed separately from one another in the direction 53 perpendicular to the fictitious planes 52 spanned by the fuel cells 2 in two different planes (FIG. 8). In the second distribution structure 46, the first and second distribution channels 59, 60 are arranged next to one another in a direction parallel to the fictitious planes 52 in one plane (FIGS. 9 and 10). In the second distribution structure 46, on the one hand the first and second distribution channels 59, 60 and on the other hand the third distribution channels 61 in the direction 53 perpendicular to the fictitious planes 52 spanned by the fuel cells 2 are formed separately from one another in two different planes (FIG. 10).

The transverse extent 87 of the feed channel 48 for fuel is significantly smaller than the transverse extent 69 of the inlet region 37 of the duct structure, so that for guiding the fuel from the feed duct 48 for fuel into the channels 12 for fuel, which begin at the inlet area 37, both a transverse distribution of the coolant in the transverse direction 58 and a longitudinal distribution or longitudinal line in the longitudinal direction 57 is necessary guided as third longitudinal distribution channels 65 in longitudinal direction 57 and third transverse distribution channels 66 in transverse direction 58 for the third process fluid as the fuel. The third distribution channels 61 as the third longitudinal distribution channels 65 and the third transverse distribution channels 66 are only formed on the second distribution structure 46 because the supply channel 48 for fuel is formed in the second distribution structure 46. The third transverse distribution channels 66 open into the supply channel 48 for fuel, so that the fuel from the supply channel 48 first flows into the third transverse distribution channels 66 and then into the third longitudinal distribution channels 65.

The process fluids, namely the oxidizing agent, the coolant and the fuel, are introduced into the channels 13 at the end region of the second distribution structure 46 from the first longitudinal distribution channels 62 for the oxidizing agent, introduced into the channels 14 from the second longitudinal distribution channels 63 for the coolant and from the third longitudinal distribution channels 65 for the fuel introduced into the channels 12. After the process fluids have flowed through the channels 12, 13, 14, they occur, i. H. the process fluids, again at the outlet area 38 from the channel structure 29 of the bipolar plate 10. A first collection structure 75 and a second collection structure 76 are formed between the outlet region 38 and the transverse side 56 shown on the right in FIGS. 6 and 7. The first collection structure 75 is essentially axially symmetrical and / or complementary to the first distribution structure 45, and the second collection structure 76 is essentially axially symmetrical and / or complementary to the second distribution structure 46. The discharge channel 44 for oxidizing agent and the discharge channel 51 for coolant are therefore arranged in the first collection structure 75. The discharge channel 49 for fuel is formed in the second collection structure 76.

The transverse dimension of the discharge channel 44 for oxidizing agent is only slightly smaller than the transverse dimension 70 of the outlet region 38 of FIG Channel structure 29, so that essentially no transverse distribution of the oxidizing agent in the transverse direction 58 is necessary for guiding the oxidizing agent from the channels 13 for oxidizing agents, which end at the outlet region 38, to the discharge channel 44 for oxidizing agents, but essentially only a longitudinal distribution or distribution. Longitudinal line in the longitudinal direction 57. For this reason, essentially only first collection ducts 77 are routed from the outlet region 38 to the discharge duct 44 as first longitudinal collection ducts 80 for the first process fluid as the oxidizing agent. The first collection channels 77 as the first longitudinal collection channels 80 are formed in the first collection structure 75 and the second collection structure 76.

The transverse dimension of the discharge channel 51 for coolant is significantly smaller than the transverse dimension 70 of the outlet area 38 of the channel structure, so that for the conduction of the coolant from the channels 14 for coolant, which end at the outlet area 38, into the discharge channel 51 for coolant, both a Cross collection of the coolant in the transverse direction 58 is necessary, as is a longitudinal collection or longitudinal line in the longitudinal direction 57. For this reason, second collection channels 78 are led from the outlet area 38 into the discharge channel 51 as second longitudinal collection channels 81 in the longitudinal direction 57 and second cross collection channels 82 in the transverse direction 58 for the second process fluid as the coolant. The second transverse collection channels 82 are formed only in the first collection structure 75, and the second longitudinal collection channels 81 are formed in the first and second collection structures 75, 76. The second cross-collection channels 82 open into the discharge channel 51 for coolant, so that the coolant flows from the channels 14 first into the second longitudinal collection channels 81, then into the second cross-collection channels 82 and from the second cross-collection channels 82 into the discharge channel 51 for coolant.

The transverse extent of the discharge channel 49 for fuel is significantly smaller than the transverse extent 70 of the outlet area 38 of the duct structure, so that there is both a transverse distribution for guiding the fuel from the ducts 12, which end at the outlet area 38, into the discharge duct 49 for fuel of the coolant in the transverse direction 58 is necessary, as well as a longitudinal distribution or longitudinal line in the longitudinal direction 57. For this reason, third collection channels 79 are from the outlet region 38 to the discharge channel 49 guided as third longitudinal collection channels 83 in the longitudinal direction 57 and third transverse collection channels 84 in the transverse direction 58 for the third process fluid as the fuel. The third collection channels 79 as the third longitudinal collection channels 83 and the third transverse collection channels 84 are only formed on the second collection structure 76 because the discharge channel 49 for fuel is formed in the second collection structure 76.

The third cross-collection channels 84 open into the discharge channel 49 for fuel, so that the fuel from channels 12 first flows into the third longitudinal collection channels 83, then into the third cross-collection channels 84 and from the third cross-collection channels 84 into the discharge channel 49 for fuel.

In the first exemplary embodiment described above, the first and second distribution structures 45, 46 are arranged between the transverse sides 56 and the channel structure 29, so that the process fluids flow in the longitudinal direction 57 essentially in parallel through the channel structure 29 and the inlet and outlet areas 37, 38 extends in the transverse direction. In the first exemplary embodiment, the transverse extent of the inlet and outlet areas 37, 38 essentially corresponds to the transverse extent 68 of the channel structure 29.

In FIG. 11, the bipolar plate 10 of the fuel cell unit 1 is shown in a second exemplary embodiment. The fuel cell unit 1 essentially corresponds to the first exemplary embodiment with a geometrically different arrangement of the feed channel 48 for fuel, the feed channel 50 for coolant, the discharge channel 49 for fuel and the discharge channel 51 for coolant.

In a second exemplary embodiment, not shown, the first and second distribution structures 45, 46 are arranged between the longitudinal sides 55 and the channel structure 29, so that the process fluids flow in the transverse direction 58 essentially in parallel through the channel structure 29 and the inlet and outlet areas 37, 38 extends in the longitudinal direction. In the second exemplary embodiment, not shown, the longitudinal extent of the inlet and outlet areas 37, 38 essentially corresponds to the longitudinal extent 67 of the channel structure 29. Viewed overall, the fuel cell unit 1 according to the invention and the fuel cell system 4 according to the invention are associated with significant advantages. All process fluids are in the first and second distribution structure 45, 46 over the entire transverse extent 69 of the

Inlet area 37 distributed so that all process fluids with respect to the volume flow evenly distributed over the transverse direction 58 flow into the inlet area 37 of the channel structure 29 parallel to one another. In this way, the process fluids can distribute the entire channel structures 29 uniformly with respect to the volume flow over the transverse direction 58 through the

Flow through channel structures 29 and in this way emerge again from the outlet region 38 into the first and second collection structure 75, 76. This advantageously results in small differences in temperature and humidity in the gas spaces 31, 32 for oxidizing agent and fuel as well as in the channels 14 for coolant. This shows the

Fuel cell unit 1 has a large output per unit mass with a slight aging during operation.

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), the fuel cells (2) each comprising a proton exchange membrane (5), an anode (7), a cathode (8), a gas diffusion layer (9), a bipolar plate (10) with three separate channel structures (29) ) with channels (12, 13, 14) for the separate passage of oxidizing agent, fuel and cooling fluid and the channel structures (29) have an inlet area (37) and an outlet area (38) for the oxidizing agent, fuel and cooling fluid,

- At least one feed channel (43) for feeding oxidizing agent as process fluid into the gas spaces (32) for oxidizing agent of the fuel cells (2),

- At least one feed channel (48) for feeding fuel as process fluid into the gas spaces (31) for fuel of the fuel cells (2),

- At least one supply channel (50) for coolant as process fluid for supplying the coolant into a channel (14) for coolant,

- Distribution structures (45, 46) for conducting and distributing the process fluids from the supply channels (43, 48, 50) into the channel structures (29) of the bipolar plates (10), characterized in that in each case one fuel cell (2) in one direction of the supply channels (43, 48, 50) to the inlet area (37) of the channel structures (29) of the bipolar plate (10) a first distribution structure (45) is formed for two process fluids as first and second process fluid and in one direction from the supply channels (43 , 48, 50) to the inlet area (37) of the channel structures (29) of the bipolar plate (10) a second distribution structure (46) for the first and second process fluids of the first Distribution structure (45) and is also designed for a third process fluid.

2. Fuel cell unit according to claim 1, characterized in that the second distribution structure (46) is formed between the first distribution structure (45) and the inlet region (37) of the channel structures (29) of the bipolar plate (10).

3. Fuel cell unit according to one or more of the preceding claims, characterized in that the first distribution structure (45) is designed only for the first and second process fluid, so that in the first distribution structure (45) only first and second distribution channels (59, 60) are designed for the first and second process fluid.

4. Fuel cell unit according to one or more of the preceding claims, characterized in that the supply channels (43, 48, 50) for the first and second process fluids of the first distribution structure (45) are formed in the first distribution structure (45).

5. Fuel cell unit according to one or more of the preceding claims, characterized in that the at least one feed channel (43, 48, 50) for the third process fluid, in particular exclusively, is formed in the second distribution structure (46).

6. Fuel cell unit according to one or more of the preceding claims, characterized in that separate first and second distribution channels (59, 60) for the first and second process fluid and the first and second distribution channels (59, 60) are formed in the first distribution structure (45) ) are formed separately from one another in a direction (53) perpendicular to fictitious planes (52) spanned by the fuel cells (2).

7. Fuel cell unit according to one or more of the preceding claims, characterized in that separate first, second and third distribution channels (59, 60, 61) for the first, second and third process fluid are formed in the second distribution structure (46).

8. Fuel cell unit according to claim 7, characterized in that two of the first, second and third distribution channels (59, 60, 61) formed separately from one another in a direction (53) perpendicular to the fictitious planes (52) spanned by the fuel cells (2) are.

9. Fuel cell unit according to one or more of the preceding claims, characterized in that the first, second and third distribution channels (59, 60, 61) as longitudinal distribution channels (62, 63, 65) in the second distribution structure (46) are aligned essentially parallel to one another.

10. Fuel cell unit according to one or more of the preceding claims, characterized in that the fuel cell unit (1), in particular the fuel cells (2), has a longitudinal extent in a longitudinal direction (57) and a transverse extent in a transverse direction (58) and the longitudinal direction ( 57) and transverse direction (58) are aligned perpendicular to one another and parallel to the fictitious planes (52) spanned by the fuel cells (2).

11. The fuel cell unit according to claim 10, characterized in that when the first and second distribution structure (45, 46) are formed, the transverse extent (72) between a transverse side (56) of the fuel cell unit (1) and the channel structure (29) of the bipolar plate (29) , 74) of the first and second distribution structure (45, 46) essentially corresponds to the transverse extent (69) of the inlet area (37) of the channel structure (29).

12. Fuel cell unit according to one or more of the preceding claims, characterized in that the first process fluid is the oxidizing agent, the second process fluid is the coolant and the third process fluid is the fuel.

13. Fuel cell unit according to one or more of the preceding claims, characterized in that the feed channels (43, 48, 50) are arranged next to one another in the longitudinal direction (57) and essentially centrally in the transverse direction.

14. Fuel cell unit according to one or more of claims 11 to 13, characterized in that the transverse extent (85) or the sum of the transverse extents of the at least one feed channel (43) for oxidizing agent is essentially the transverse extent (69) of the inlet region (37) of the channel structure (29) corresponds.

15. Fuel cell system (4), in particular for a motor vehicle, comprising

- A fuel cell unit (1) as a fuel cell stack with fuel cells (2),

- A compressed gas storage (21) for storing gaseous fuel,

- A gas delivery device (22) for delivering a gaseous oxidizing agent to the cathodes (8) of the fuel cells (2), characterized in that the fuel cell unit is designed as a fuel cell unit according to one or more of the preceding claims.