DE102021205986A1 - Method of conditioning an electrochemical cell unit - Google Patents

Abstract

Electrochemical method for conditioning an electrochemical cell unit (53) before putting the electrochemical cell unit (53) into operation for converting electrochemical energy into electrical energy as a fuel cell unit (1) and/or for converting electrical energy into electrochemical energy as an electrolytic cell unit (49) with stacked electrochemical cells and channels for conducting a fuel and/or an electrolyte and channels for conducting an oxidizing agent and/or an electrolyte are formed in the electrochemical cell unit (53), with the steps: providing a conditioning fluid (68), conducting the conditioning fluid (68) through the fuel and/or electrolyte channels and/or passing the conditioning fluid (68) through the oxidant and/or electrolyte channels and adhesion and/or hydration and/or hydration of water and/or moisture to components of the elec trochemical cell unit (53) originating from the conditioning fluid (68), the conditioning fluid (68) being a conditioning liquid (68).

Description

The present invention relates to a method for conditioning an electrochemical cell unit according to the preamble of claim 1 and an electrochemical cell unit 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 multiplicity of fuel cells are arranged in a stack as a stack.

In fuel cell units, a large number of fuel cells are arranged in a fuel cell stack. Inside each fuel cell there is a gas space for oxidizing agent, ie a flow space for conducting oxidizing agent, such as air from the environment with oxygen, through. The oxidant gas space 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. A gas space for fuel is present in an analogous manner.

Electrolytic cell units made up of stacked electrolytic cells, analogous to fuel cell units, are used, for example, for the electrolytic production of hydrogen and oxygen from water. Furthermore, fuel cell units are known which can be operated as reversible fuel cell units and thus as electrolytic cell units. Fuel cell units and electrolytic cell units form electrochemical cell units. Fuel cells and electrolytic cells form electrochemical cells.

During the manufacture of a fuel cell unit, individual fuel cells are stacked into a stack as the fuel cell unit. The components of the fuel cells include anodes, cathodes and proton exchange membranes. After the fuel cells have been arranged to form the stack, these components of the fuel cells have a low level of moisture or a low water content. As a result, the proton exchange membranes would have a low proton conductivity and high ohmic and electrical losses would also occur at the anodes and cathodes. In order to avoid this, conditioning of the fuel cell unit as the stack with a conditioning gas is necessary. During conditioning of the fuel cell assembly, a humidified gas, generally air, is passed through the fuel and oxidant passages. Due to the physically caused low water content as absolute humidity of the humidified gas, it is necessary to conduct the conditioning gas as a conditioning fluid through the channels for fuel and oxidizing agent over a long period of several hours until a sufficient water content of the components anodes, cathodes and proton exchange membrane is present , i.e. H. hydration of these components with water or moisture from the conditioning gas is achieved. In the case of an industrial production of a large number of fuel cell units within several hours, large storage rooms are therefore required in order to keep the fuel cell units produced in the several hours available for carrying out the conditioning. This disadvantageously results in high costs for the production of the fuel cell units, because correspondingly large storage rooms have to be kept available and a large number of devices are required for carrying out the method for simultaneous conditioning of the large number of fuel cell units. In an analogous manner, conditioning is also necessary for electrolytic cell units.

Disclosure of Invention

Advantages of the Invention

Method according to the invention for conditioning an electrochemical cell unit before putting the electrochemical cell unit into operation for converting electrochemical energy into electrical energy as a fuel cell unit and/or for converting electrical energy into electrochemical energy as an electrolysis cell unit with stacked electrochemical cells and in the electrochemical cell unit channels for conducting a fuel and/or or an electrolyte and channels for conducting an oxidizing agent and/or an electrolyte are formed with the steps: providing a conditioning fluid, conducting the conditioning fluid through the channels for fuel and/or electrolyte and/or conducting the conditioning fluid through the channels for oxidizing agent and /or electrolytes and adhesion and/or hydration and/or hydration of water and/or moisture to components the electrochemical cell unit derived from the conditioning fluid, the conditioning fluid being a conditioning liquid. A conditioning liquid with a high mass fraction of water has a greater proportion of water than a conditioning gas. With this, the method for conditioning the electrochemical unit can be carried out in a very short time, for example in half an hour or an hour. Advantageously, no large storage rooms are required for keeping the electrochemical cell units available while the conditioning method is being carried out, and in addition only a small number of devices for carrying out the method have to be kept ready.

In an additional variant, the conditioning liquid has a mass fraction of water of at least 50%, 80%, 90% or 95%.

In an additional embodiment, the conditioning liquid passed through the channels for fuel and/or electrolyte and/or the channels for oxidizing agent and/or electrolyte has a temperature between 50°C and 100°C, in particular between 75°C and 98°C , on. Elevated temperature of the conditioning liquid accelerates adhesion and/or hydration and/or hydration of water and/or moisture to the electrochemical cell unit components.

In another embodiment, the pH of the conditioning liquid is less than 5, 3 or 2.

At least one additive, preferably an acid, in particular sulfuric acid, is expediently added to the conditioning liquid. In the proton exchange membranes in particular, acidic properties are necessary for operation, thereby making it necessary to pass an acidic conditioning liquid through the channels in order for the acidic conditioning liquid to adhere to the proton exchange membranes.

In a supplementary embodiment, the conditioning liquid is conducted through the channels in a circuit. Passing the conditioning liquid through the channels in a circuit makes it possible to carry out the method in a particularly simple manner, since this allows the conditioning liquid to be reused continuously.

The pH value of the conditioning liquid is preferably detected by a sensor while the conditioning liquid is being conducted through the channels.

In a further variant, the electrochemical cells each comprise stacked layered components and the components of the electrochemical cells are preferably proton exchange membranes, anodes, cathodes, preferably gas diffusion layers and bipolar plates.

In a supplementary embodiment, the layered electrochemical cells and/or the layered components span fictitious levels.

In a further embodiment, a stack of the electrochemical cells is prestressed with a primary compressive force perpendicular to the imaginary plane before and/or during the passage of the conditioning liquid through the channels and after the passage of the conditioning liquid through the channels and/or after the conditioning liquid is drained off from the channels the compressive force is changed to a secondary compressive force and the secondary compressive force is larger, in particular by 10%, 30% or 50% larger than the primary compressive force. The fuel cell unit as the stack of the electrochemical cells has a greater expansion perpendicular to the imaginary planes during the prestressing with the small primary compressive force than during the prestressing with the larger secondary compressive force. This is due, for example, to the elastic properties of the components and/or seals. During the passage of the conditioning liquid through the channels, swelling of the components, i. H. an increase in the volume of the components. So that this increase in the volume of the components does not cause any damage to the components, it is necessary to be able to provide these components with a sufficient space for increasing the volume by means of the small primary compressive force.

In an additional variant, after the conditioning liquid has been passed through the channels and/or after the conditioning liquid has been discharged from the channels, the water content of the components, in particular the proton exchange membranes and/or anodes and/or cathodes and/or catalyst layers, is greater, in particular by 10%, 50% or 100% greater than before the conditioning liquid was passed through the channels. This increased water content of the components advantageously brings about good proton conductivity in the proton exchange membranes and low ohmic electrical resistance in the anodes and cathodes.

In a further refinement, the conditioning liquid is drawn out of the channels by means of gravity and/or a gas, in particular an inert gas derived. The draining or draining of the conditioning liquid from the channels by gravity is made possible by a corresponding structural design of the electrochemical cell unit, ie the channels allow the conditioning liquid to be drained by gravity due to a corresponding inclination of the channels. The conditioning liquid can either only with the gas, z. B. the inert gas nitrogen, or for a complete discharge of the conditioning liquid is derived by gravity of the rest of the conditioning liquid with the gas from the channels after draining the conditioning liquid.

In a supplementary embodiment, during the passage of the conditioning liquid through the channels, the volume of the components increases due to the adhesion and/or hydration and/or hydration of water and/or moisture on the components, in particular the volume increases by 3%, 5% or 10% to.

In particular, the conditioning liquid is passed through the channels during a period of less than 3 hours, in particular less than 1 hour, 30 minutes or 10 minutes. Due to the short period of time for carrying out the method, only a small number of electrochemical cell units need to be stored while the conditioning method is being carried out.

Electrochemical cell unit according to the invention for converting electrochemical energy into electrical energy as a fuel cell unit and/or for converting electrical energy into electrochemical energy as an electrolysis cell unit, comprising electrochemical cells arranged stacked and the electrochemical cells each comprising layered components arranged stacked and the components of the electrochemical cells preferably proton exchange membranes, anodes , cathodes, preferably gas diffusion layers and bipolar plates, with the electrochemical cell unit being able to carry out a method described in this patent application and/or a stack of the electrochemical cells being prestressed with at least one connecting device with a compressive force perpendicular to imaginary planes and by means of the at least one connecting device the compressive force is variable, so that due to the changed compressive force, the expansion of the St acks can be changed perpendicularly to the fictitious planes.

In a further embodiment, the channels for the process fluids, in particular fuel, oxidizing agent and/or coolant, are formed from a porous, fluid-conducting and/or fluid-permeable material, in particular metal. The channels, in particular in the bipolar plate, are formed, for example, from a porous expanded metal and/or a foam, in particular metal foam.

In a further embodiment, the at least one connecting device comprises one internal thread and one external thread each on two different components, in particular one nut each with the internal thread and one bolt each with the external thread, the connecting device and the internal thread and external thread are screwed into one another and by means of a change With this screw connection between the internal thread and the external thread, the length of the at least one connecting device can be changed perpendicularly to the imaginary planes, so that the compressive force in the electrochemical cell unit can be changed as a result. After carrying out the method for conditioning, only a nut with an internal thread needs to be screwed into an external thread of a rod, for example to increase the compressive force in the electrochemical cell unit.

In an additional variant, a mechanism for changing the distance between the clamping elements, in particular clamping plates, in a direction perpendicular to the fictitious planes is integrated in the at least one connecting device, so that the compressive force for prestressing the stack is preferably changed with the mechanism, in particular after the conditioning liquid has been passed through the channels and/or after the conditioning liquid has been drained from the channels.

In a further variant, the method is carried out as a manufacturing method during a deactivated state of the electrochemical cell unit.

In a further variant, the conditioning liquid is passed through and/or flooded through and/or into the gas spaces for fuel and/or the conditioning liquid is passed through and/or flooded through and/or into the gas spaces for oxidizing agents. For example, passage of the conditioning liquid through the fuel channels causes passage and/or flooding of the fuel headspaces.

In an additional embodiment, the pH value of the conditioning liquid is recorded while the method is being carried out, and if the pH value recorded is greater than a predetermined target value of the pH value, an acid is added to the conditioning liquid, in particular the acid is admitted until the specified target value of the pH value is reached. An essentially constant pH value, for example 2, can thus be achieved in an advantageous manner for the passage of the conditioning liquid through the channels. Suitably, a substantially constant pH is a pH that differs by less than 30%, 20% or 10%.

In an additional variant, the temperature of the conditioning liquid is recorded with a sensor and a heater is controlled and/or regulated as a function of the recorded temperature of the conditioning liquid, so that the temperature of the conditioning liquid is essentially, in particular with a deviation of less than 30%, 20% or 10%, corresponds to a setpoint of the temperature. The desired value as a specific temperature is between 50°C and 100°C, for example, in particular between 75°C and 98°C.

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

A method described in this patent application can expediently be carried out with the electrochemical cell unit described in this patent application.

In a supplementary variant, the method for conditioning described in this property right application is a production step of a method for producing an electrochemical cell unit, with the electrochemical cells being made available and the electrochemical cells being stacked to form the electrochemical cell unit as a cell stack, preferably before the conditioning method becomes.

The invention also includes 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 computing unit.

The invention also includes 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 property right application when the computer program is carried out on a computer or a corresponding processing unit.

In an additional embodiment, the electrochemical cell unit is a fuel cell unit as a fuel cell stack for converting electrochemical energy into electrical energy and/or an electrolytic cell unit for converting electrical energy into electrochemical energy.

The bipolar plates are expediently designed as separator plates and an electrical insulation layer, in particular a proton exchange membrane, is arranged between each anode and each cathode, and preferably the electrolysis cells each include a third channel for the separate passage of a cooling fluid as the third process fluid.

In an additional variant, the electrolytic cell unit is additionally designed as a fuel cell unit, in particular a fuel cell unit described in this patent application, so that the electrolytic cell unit forms a reversible fuel cell unit.

In a further variant, the first substance is oxygen and the second substance is hydrogen.

In a further variant, the electrolytic cells of the electrolytic cell unit are fuel cells.

In a further variant, the electrochemical cell unit comprises a housing and/or a connection plate. The stack is enclosed by the housing and/or the connection board.

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 store 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 a fuel cell unit described in this patent application and/or Electrolytic cell unit is formed.

Electrolysis system and/or fuel cell system according to the invention, comprising an electrolysis cell unit as an electrolysis cell stack with electrolysis cells, preferably a pressurized gas store for storing gaseous fuel, preferably a gas delivery device for delivering a gaseous oxidizing agent to the cathodes of the fuel cells, a storage container for liquid electrolyte, a pump for delivering the liquid Electrolytes, wherein the electrolytic cell unit is designed as an electrolytic cell unit and/or fuel cell unit described in this patent application.

In a further embodiment, the fuel cell unit described in this patent application also forms an electrolytic cell unit and preferably vice versa.

In a further variant, the electrochemical cell unit, in particular the fuel cell unit and/or the electrolytic cell unit, comprises at least one connecting device, in particular a plurality of connecting devices, and tensioning elements.

Components for electrochemical cells, in particular fuel cells and/or electrolytic cells, preferably insulation layers, in particular proton exchange membranes, anodes, cathodes, preferably gas diffusion layers and bipolar plates, in particular separator plates, are expedient.

In a further embodiment, the electrochemical cells, in particular fuel cells and/or electrolytic cells, each preferably comprise an insulating layer, in particular proton exchange membrane, an anode, a cathode, preferably at least one gas diffusion layer and at least one bipolar plate, in particular at least one separator plate.

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

The clamping elements are expediently designed as clamping plates.

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

In particular, the electrochemical cell unit, in particular a fuel cell unit and/or an electrolytic cell unit, comprises at least 3, 4, 5 or 6 connecting devices.

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

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

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

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

Preferably, the fuel cell unit is a PEM fuel cell unit with PEM fuel cells or an alkaline fuel cell (AFC).

character list

• 1 eine stark vereinfachte Explosionsdarstellung eines elektrochemischen Zellensystems als Brennstoffzellensystem und Elektrolysezellensystem mit Komponenten einer elektrochemischen Zelle als Brennstoffzelle und Elektrolysezelle,
• 2 eine perspektivische Ansicht eines Teils einer Brennstoffzelle und Elektrolysezelle,
• 3 einen Längsschnitt durch elektrochemische Zellen als Brennstoffzelle und Elektrolysezelle,
• 4 eine perspektivische Ansicht einer elektrochemischen Zelleneinheit als Brennstoffzelleneinheit und Elektrolysezelleneinheit als Brennstoffzellenstapel und Elektrolysezellenstapel,
• 5 eine Seitenansicht der elektrochemischen Zelleneinheit als Brennstoffzelleneinheit und Elektrolysezelleneinheit als Brennstoffzellenstapel und Elektrolysezellenstapel,
• 6 eine perspektivische Ansicht einer Bipolarplatte,
• 7 stark vereinfachte Darstellung des elektrochemischen Zellensystems mit einer Vorrichtung zur Durchführung des Verfahrens,
• 8 Darstellung der Verfahrensschritte zur Durchführung des Verfahrens zur Konditionierung der elektrochemischen Zelleneinheit.

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

• 1 a greatly simplified exploded view of an electrochemical cell system as a fuel cell system and electrolysis cell system with components of an electrochemical cell as a fuel cell and electrolysis cell,
• 2 a perspective view of part of a fuel cell and electrolytic cell,
• 3 a longitudinal section through electrochemical cells as fuel cells and electrolytic cells,
• 4 a perspective view of an electrochemical cell unit as a fuel cell unit and electrolytic cell unit as a fuel cell stack and electrolytic cell stack,
• 5 a side view of the electrochemical cell unit as a fuel cell unit and electrolytic cell unit as a fuel cell stack and electrolytic cell stack,
• 6 a perspective view of a bipolar plate,
• 7 highly simplified representation of the electrochemical cell system with a device for carrying out the method,
• 8th Representation of the process steps for carrying out the process for conditioning the electrochemical cell unit.

In the 1 until 3 the basic structure of a fuel cell 2 is shown 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 H ₂ is passed as a gaseous fuel to an anode 7 and the anode 7 forms the negative pole. A gaseous oxidizing agent, namely air with oxygen, is fed to a cathode 8, ie the oxygen in the air provides the necessary gaseous oxidizing agent. At the cathode 8 there is a reduction (electrons recording) instead. The oxidation as electron release is carried out at the anode 7 .

• Kathode: O₂ + 4 H⁺ + 4 e^- --» 2 H₂O
• Anode: 2 H₂ --» 4 H⁺ + 4 e^-
• Summenreaktionsgleichung von Kathode und Anode: 2 H₂ + O₂ --» 2 H₂O

The redox equations of the electrochemical processes are:

• Cathode: O ₂ + 4 H ⁺ + 4 e ^- --» 2 H ₂ O
• Anode: 2 H ₂ --» 4 H ⁺ + 4 e ^-
• Summation reaction equation of cathode and anode: _{2H2 +} O2 --» _2H2O

The difference between the normal potentials of the pairs of electrodes under standard conditions as a reversible fuel cell voltage or no-load voltage of the unloaded fuel cell 2 is 1.23 V. This theoretical voltage of 1.23 V is not reached in practice. In the idle state and with small currents, voltages of over 1.0 V can be reached and when operating with larger 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 each fuel cell 2.

The fuel cell 2 also includes a proton exchange membrane 5 (proton exchange membrane, PEM), which is arranged between the anode 7 and the cathode 8 . The anode 7 and cathode 8 are in the form of layers or discs. The PEM 5 acts as an electrolyte, catalyst support and separator for the reaction gases. The PEM 5 also acts as an electrical insulator and prevents an electrical short circuit between the anode 7 and cathode 8. In general, 12 μm to 150 μm thick, proton-conducting foils made from perfluorinated and sulfonated polymers are used. The PEM 5 conducts the H ⁺ protons and essentially blocks ions other than H ⁺ protons, so that the charge transport can take place due to the permeability of the PEM 5 for the H ⁺ protons. The PEM 5 is essentially impermeable to the reaction gases oxygen O ₂ and hydrogen H ₂ , ie blocks the flow of oxygen O ₂ and hydrogen H ₂ between a gas space 31 at the anode 7 with fuel hydrogen H ₂ and the gas space 32 at the cathode 8 with air or oxygen O ₂ 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 lie on the two sides of the PEM 5 , each facing towards the gas chambers 31 , 32 . A unit made up of the PEM 5 and the electrodes 7, 8 is referred to as a membrane electrode assembly 6 (membrane electrode assembly, MEA). The electrodes 7, 8 are pressed with the PEM 5. The electrodes 7, 8 are platinum-containing carbon particles bonded to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride) and/or PVA (polyvinyl alcohol) and embedded in microporous carbon fiber, Glass fiber or plastic mats are hot-pressed. A catalyst layer 30 is normally applied to each of the electrodes 7, 8 on the side facing the gas chambers 31, 32. FIG. 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 nanodispersed platinum. For example, Nation®, a PTFE emulsion or polyvinyl alcohol are used as binders.

Deviating from this, the electrodes 7, 8 are constructed from an ionomer, for example Nation®, platinum-containing carbon particles and additives. These electrodes 7, 8 with the ionomer are electrically conductive due to the carbon particles and also conduct the protons H ⁺ and also function as a catalyst layer 30 due to the platinum-containing carbon particles.

Membrane electrode assemblies 6 with these electrodes 7, 8 comprising the ionomer form membrane electrode assemblies 6 as a CCM (catalyst coated membrane).

On the anode 7 and the cathode 8 there is a gas diffusion layer 9 (gas diffusion layer, GDL). The gas diffusion layer 9 on the anode 7 distributes the fuel from fuel channels 12 evenly onto the catalyst layer 30 on the anode 7. The gas diffusion layer 9 on the cathode 8 distributes the oxidant from oxidant channels 13 evenly onto the catalyst layer 30 on the cathode 8. The GDL 9 also withdraws reaction water in the reverse 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 wet and conducts the current. The GDL 9 is constructed, for example, from hydrophobic carbon paper as the carrier and substrate layer and a bonded carbon powder layer as the microporous layer.

A bipolar plate 10 rests on the GDL 9 . The electrically conductive bipolar plate 10 serves as a current collector, for water drainage and for conducting the reaction gases as process fluids through the channel structures 29 and/or flow fields 29 and for dissipating the waste heat, which occurs 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 conducting a liquid or gaseous coolant as the process fluid. The channel structure 29 in the gas space 31 for fuel is formed by channels 12 . The channel structure 29 in the gas space 32 for the oxidizing agent is formed by channels 13 . Metal, conductive plastics and composite materials or graphite, for example, are used as the material for the bipolar plates 10 .

In a fuel cell unit 1 and/or a fuel cell stack 1 and/or a fuel cell stack 1, a plurality of fuel cells 2 are arranged stacked in alignment ( 4 and 5 ). In 1 is an exploded view of two aligned stacked fuel cells 2 shown. Seals 11 seal the gas chambers 31, 32 or channels 12, 13 in a fluid-tight manner. In a compressed gas accumulator 21 ( 1 ) hydrogen H ₂ is stored as a fuel at a pressure of, for example, 350 bar to 700 bar. From the compressed 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 routed to an injector 19 from the medium-pressure line 17 . At the injector 19, the pressure of the fuel is reduced to an injection pressure of between 1 bar and 3 bar. From the injector 19, the fuel is supplied to a supply line 16 for fuel ( 1 ) and from the supply line 16 to the channels 12 for fuel, which form the channel structure 29 for fuel. As a result, the fuel 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 any water from controlled humidification of the anode 7 are discharged from the fuel cells 2 through a discharge line 15 .

A gas conveying device 22, embodied for example as a fan 23 or a compressor 24, conveys air from the environment as oxidizing agent into a supply line 25 for oxidizing agent. The air is supplied from the supply line 25 to the channels 13 for oxidizing agent, which form a channel structure 29 on the bipolar plates 10 for oxidizing agent, so that the oxidizing agent flows through the gas space 32 for the oxidizing agent. The gas space 32 for the oxidizing agent is formed by the channels 13 and the GDL 9 on the cathode 8 . After the oxidizing agent 32 has flowed through the channels 13 or the gas space 32, the oxidizing agent not consumed at the cathode 8 and the water of reaction formed at the cathode 8 due to the electrochemical redox reaction are discharged from the fuel cells 2 through a discharge line 26. A supply line 27 is used to supply 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 in 1 shown as separate lines for reasons of simplification. At the end area in the vicinity of the channels 12, 13, 14 are in the stack as a stack of the fuel cell unit 1 aligned fluid openings 41 on sealing plates 39 as an extension at the end area 40 of the bipolar plates 10 ( 6 ) and membrane electrode assemblies 6 (not shown) are formed.

The fuel cells 2 and the components of the fuel cells 2 are disk-shaped and span imaginary planes 59 aligned essentially parallel to one another. The aligned fluid openings 41 and seals (not shown) in a direction perpendicular to the notional planes 59 between the fluid openings 41 thus form an oxidant supply duct 42, an oxidant discharge duct 43, a fuel supply duct 44, a fuel discharge duct 45, a Supply channel 46 for coolant and a discharge channel 47 for coolant. The supply and discharge lines 15, 16, 25, 26, 27, 28 outside the stack of the fuel cell unit 1 are designed as process fluid lines. The supply and discharge lines 15, 16, 25, 26, 27, 28 outside the stack of the fuel cell unit 1 open into the supply and discharge channels 42, 43, 44, 45, 46, 47 inside the stack of the fuel cell unit 1. The fuel cell stack 1 together with the compressed gas reservoir 21 and the gas delivery device 22 forms a fuel cell system 4.

The fuel cells 2 are arranged as clamping plates 34 between two clamping elements 33 in the fuel cell unit 1 . A first clamping plate 35 lies on the first fuel cell 2 and a second clamping plate 36 lies on the last fuel cell 2 . The fuel cell unit 1 comprises approximately 200 to 400 fuel cells 2, not all of which are shown in 4 and 5 are shown. The clamping elements 33 apply a compressive force to the fuel cells 2, ie the first clamping plate 35 rests on the first fuel cell 2 with a compressive force and the second clamping plate 36 rests on the last fuel cell 2 with a compressive force. The fuel cell stack 2 is thus braced to ensure the tightness of the fuel, the oxidizing agent and the coolant, in particular due to the elastic seals 11, and also to keep the electrical contact resistance within the fuel cell stack 1 as small as possible. To brace the fuel cells 2 with the tensioning elements 33, four connecting devices 37 are designed as bolts 38 on the fuel cell unit 1, which are subjected to tensile stress. The four bolts 38 are connected to the chipboards 34 .

In 6 the bipolar plate 10 of the fuel cell 2 is shown. The bipolar plate 10 includes the channels 12, 13 and 14 as three separate channel structures 29. The channels 12, 13 and 14 are in 6 not shown separately, but only in simplified form as a layer of a channel structure 29. The fluid openings 41 on the sealing plates 39 of the bipolar plates 10 and membrane electrode arrangements 6 (not shown) are arranged stacked in alignment within the fuel cell unit 1, so that supply and discharge channels 42, 43, 44, 45, 46, 47. Seals (not shown) are arranged between the sealing plates 39 for fluid-tight sealing of the supply and discharge channels 42, 43, 44, 45, 46, 47 formed by the fluid openings 41.

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

The fuel cell unit 1 can also be used and operated as an electrolytic cell unit 49, ie forms a reversible fuel cell unit 1. A number of features that allow the fuel cell unit 1 to be operated as an electrolytic cell unit 49 are described below. A liquid electrolyte, namely highly diluted sulfuric acid with a concentration of approximately c(H ₂ SO ₄ )=1 mol/l, is used for the electrolysis. A sufficient concentration of oxonium ions H ₃ O ⁺ in the liquid electrolyte is necessary for the electrolysis.

• Kathode: 4 H₃O⁺ + 4 e^- --» 2 H₂ + 4 H₂O
• Anode: 6 H₂O --» O₂ + 4 H₃O⁺ + 4 e^-
• Summenreaktionsgleichung von Kathode und Anode: 2 H₂O --» 2 H₂ + O₂

The following redox reactions take place during electrolysis:

• Cathode: 4 H ₃ O ⁺ + 4 e ^- --» 2 H ₂ + 4 H ₂ O
• Anode: 6 H ₂ O --» O ₂ + 4 H ₃ O ⁺ + 4 e ^-
• Summation reaction equation of cathode and anode: 2H2O --» _{2H2 + O2}

The polarity of the electrodes 7, 8 with electrolysis when operating as an electrolytic cell unit 49 is reversed (not shown) as when operating as a fuel cell unit 1, so that in the channels 12 for fuel, through which the liquid electrolyte is conducted, at the cathodes Hydrogen H ₂ is formed as a second substance and the hydrogen H ₂ is taken up by the liquid electrolyte and transported in dissolved form. Analogously, the liquid electrolyte is conducted through the channels 13 for oxidizing agent and oxygen O ₂ is formed as the first substance at the anodes in or at channels 13 for oxidizing agent. The fuel cells 2 of the fuel cell unit 1 function as electrolytic cells 50 during operation as an electrolytic cell unit 49. The fuel cells 2 and electrolytic cells 50 thus form electrochemical cells 52. The oxygen O ₂ formed is absorbed by the liquid electrolyte and transported in dissolved form. The liquid electrolyte is stored in a storage tank 54 . In 1 For reasons of simplification in the drawing, two storage tanks 54 of the fuel cell system 4 are shown, which also functions as an electrolytic cell system 48 . The 3-way valve 55 on the fuel supply line 16 is switched over during operation as an electrolytic cell unit 49, so that the liquid electrolyte is introduced into the fuel supply line 16 from the storage tank 54 with a pump 56 and not fuel from the compressed gas storage tank 21 . A 3-way valve 55 on the supply line 25 for oxidant is switched over during operation as an electrolytic cell unit 49, so that the liquid electrolyte with the pump 56 from the storage tank 54 is fed into the supply line 25 for oxidant rather than oxidant as air from the gas delivery device 22 is initiated. The fuel cell unit 1, which also functions as an electrolytic cell unit 49, has optional modifications to the electrodes 7, 8 and the gas diffusion layer 9 compared to a fuel cell unit 1 that can only be operated as a fuel cell unit 1: for example, the gas diffusion layer 9 is not absorbent, so that the liquid electrolyte easy to completely drain or the gas diffusion layer 9 is not formed or the gas diffusion layer 9 is a structure on the bipolar plate 10. The electrolytic cell unit 49 with the storage tank 54, the pump 56 and the separators 57, 58 and preferrably wise the 3-way valve 55 forms an electrochemical cell system 60.

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

In a further exemplary embodiment, which is not shown, the fuel cell unit 1 is designed as an alkaline fuel cell unit 1 . Potassium hydroxide solution is used as a mobile electrolyte. The fuel cells 2 are stacked. A monopolar cell structure or a bipolar cell structure can be formed. The potassium hydroxide solution circulates between an anode and cathode and transports reaction water, heat and impurities (carbonates, dissolved gases) away. The fuel cell unit 1 can also be used as a reversible fuel cell unit 1, i. H. as an electrolytic cell unit 49.

In 7 the electrochemical cell system 60 is shown with a device for carrying out a method for conditioning the electrochemical cell unit 53 as a fuel cell unit 1. The device comprises a storage container 67 which is filled with a conditioning liquid 68 as essentially water. The storage container 67 essentially enables the conditioning liquid 68 to be made available 73 for the electrochemical cell units 53 to be conditioned one after the other. the fuel supply line 16 and the fuel discharge line 15, and these lines 15, 16, 25 and 26 are in 7 not shown on the electrochemical cell system 60. An orifice 61 is formed in fuel supply line 16 , an orifice 62 is formed in oxidant supply line 25 , an orifice 63 is formed in fuel discharge line 15 , and an orifice 64 is formed in oxidant discharge line 26 . Lines 65 for a conditioning liquid open into these openings 61, 62, 63, 64. In the lines 65 in the area of the openings 61, 62, 63, 64 there are closing elements 66 for opening and closing the lines 65, so that when the closing elements 66 are closed another fuel cell unit 1 can simply be connected hydraulically to the device. The closing elements 66 are designed, for example, as a cock or a valve. A circulating pump 69 is installed in each of two lines 65 for the conditioning liquid 58 . In addition, a sensor 70 for detecting the pH value is installed in a line 65 which opens into the storage container 67 . In addition, an addition device 71 for adding acid as an additive to the conditioning liquid 68 is built into the storage tank 67 . If the pH value of the conditioning liquid 68 deviates from a target value, for example a pH value of 2, for example when a pH value of 2.5 is reached, with the addition device 71 added the acid as the additive. A substantially constant pH value of the conditioning liquid 68 can thus be ensured while the method is being carried out. In addition, a heater 72 is built into the storage container 67 for heating the conditioning liquid to 90°C. The temperature of the conditioning liquid is detected by a temperature sensor, not shown, and if the temperature of the conditioning liquid deviates from a predetermined desired value, the heater 72 is switched on or off. The conditioning liquid can thus be conducted through the channels 12, 13 at a substantially constant temperature of 90°C.

Passing 74 of the conditioning liquid 68 through the channels 12 for fuel and simultaneously passing 75 of the conditioning liquid 68 through the channels 13 for oxidizing agent is carried out. The conditioning liquid 68 is circulated through the channels 12, 13, the lines 65 and the storage tank 68. When the method for conditioning the electrochemical cell unit 53 as the fuel cell unit 1 is carried out, very rapid hydration 76 and adhesion 76 of the proton exchange membranes 5 occur due to the passage 75 of the conditioning liquid 68 at the high temperature of 90°. As a result, a sufficient water content of the proton exchange membranes 5 for good proton conductivity is already reached in approximately 5 minutes (min) after the start of the method for conditioning the fuel cell unit 1 . During this time, a sufficient water content of the anodes 7 and cathodes 8 can also be achieved for a small ohmic and electrical resistance of the anodes 7 and cathodes 8. During the hydration of the proton exchange membranes 5, the anodes 7 and cathodes 8, the volume increases as a result of these components 5, 7 and 8. So that this increase in the volume of these components 5, 7 and 8 does not lead to damage to these components 5, 7 and 8, the fuel cell stack 1 as the fuel cell stack 1 is initially subjected to a small primary compressive force from the connecting devices 37 before and during the implementation of the method . The prestressing of the fuel cell stack 1 with the small primary compressive force causes a large expansion of the fuel cell stack 1 perpendicular to the imaginary planes 59, so that the components 5, 7 and 8 have sufficient space for the increase in volume, i. H. for expansion, is available. Only after the end of the procedure, i. H. draining the conditioning liquid 68 from the channels 12, the compressive force is increased from the small primary compressive force to a larger secondary compressive force. The rods 38 or bolts 38 of the connecting devices 37 have an external thread (not shown) at one end region, into which an internal thread of a nut (not shown) is screwed. By simply screwing the nuts into the external thread of the bolts 38, the compressive force in the fuel cell stack 1 can be increased. The high secondary compressive force for prestressing the fuel cell stack 1 is necessary for the operation of the fuel cell unit 1 so that the seals 11 are reliably fluid-tight and a low electrical and ohmic resistance occurs in the fuel cell stack 1 .

The method for conditioning can also be carried out in an analogous manner in the case of an electrolytic cell unit 49 . Before the electrolytic cell unit 49 is put into operation during production, the conditioning liquid 68 is passed through the channels 12, 13 for the electrolyte.

Considered overall, the method according to the invention for conditioning the electrochemical cell unit 53 and the electrochemical cell unit 53 according to the invention have significant advantages. The conditioning of the electrochemical cell unit 53 with the conditioning liquid 68 at approximately 90° C. enables the water content of the components 5, 6, 7, 8, 9, 10, 51 of the electrochemical cell unit 53 to be increased very quickly 53 only a very small number of electrochemical cell units 53 are kept available simultaneously while the method for conditioning is being carried out. The costs for the production of the electrochemical cell units 53 can thus be significantly reduced in an advantageous manner.

Claims (15)

Method for conditioning an electrochemical cell unit (53) before putting the electrochemical cell unit (53) into operation for converting electrochemical energy into electrical energy as a fuel cell unit (1) and/or for converting electrical energy into electrochemical energy as an electrolytic cell unit (49) with stacked electrochemical cells ( 52) and in the electrochemical cell unit (53) channels (12) for conducting a fuel and/or an electrolyte and channels (13) for conducting an oxidizing agent and/or an electrolyte are formed with the steps: - providing a conditioning fluid ( 68), - passing the conditioning fluid (68) through the channels (12) for fuel and/or electrolyte and/or passing the conditioning fluid (68) through through the channels (13) for oxidizing agent and/or electrolyte and - adhesion and/or hydration and/or hydration of water and/or moisture to components (5, 6, 7, 8, 9, 10, 51) of the electrochemical cell unit ( 53) which originates from the conditioning fluid (68), characterized in that the conditioning fluid (68) is a conditioning liquid (68). procedure after claim 1 , characterized in that the conditioning liquid (68) has a mass fraction of water of at least 50%, 80%, 90% or 95%. procedure after claim 1 or 2 , characterized in that the conditioning liquid (68) passed through the channels (12) for fuel and/or electrolytes and/or through the channels (13) for oxidizing agents and/or electrolytes has a temperature between 50°C and 100°C, in particular between 75°C and 98°C. Method according to one or more of the preceding claims, characterized in that the pH value of the conditioning liquid (68) is less than 5, 3 or 2. Method according to one or more of the preceding claims, characterized in that at least one additive, preferably an acid, in particular sulfuric acid, is added to the conditioning liquid (68). Method according to one or more of the preceding claims, characterized in that the conditioning liquid (68) is conducted in a circuit through the channels (12, 13). Method according to one or more of the preceding claims, characterized in that the pH value of the conditioning liquid (68) is detected with a sensor (70) while the conditioning liquid (68) is being passed through the channels (12, 13). Method according to one or more of the preceding claims, characterized in that the electrochemical cells (52) each comprise stacked layered components (5, 6, 7, 8, 9, 10, 51) and the components (5, 6, 7, 8, 9, 10, 51) of the electrochemical cells (52) are preferably proton exchange membranes (5), anodes (7), cathodes (8), preferably gas diffusion layers (9) and bipolar plates (10). procedure after claim 8 , characterized in that the layered electrochemical cells (52) and/or the layered components (5, 6, 7, 8, 9, 10, 51) span imaginary planes (59). procedure after claim 9 , characterized in that a stack (1, 49, 53) of the electrochemical cells (52) with a primary compressive force perpendicular to the imaginary plane (59) before and / or during the passage of the conditioning liquid through the channels (12, 13) is prestressed and after the conditioning liquid (68) has been passed through the channels (12, 13) and/or after the conditioning liquid (68) has been discharged from the channels (12, 13), the pressure force is changed to a secondary pressure force and the secondary pressure force is greater, in particular by 10%, 30% or 50%, than the primary compressive force. Method according to one or more of the preceding claims, characterized in that after the conditioning liquid (68) has been passed through the channels (12, 13) and/or after the conditioning liquid (68) has been discharged from the channels (12, 13), the water content of the components (5, 6, 7, 8, 9, 10, 51), in particular the proton exchange membranes (5) and/or anodes (7) and/or cathodes (8) and/or catalyst layers (30), is larger, in particular is 10%, 50% or 100% greater than before the conditioning liquid (68) was passed through the channels (12, 13). Method according to one or more of the preceding claims, characterized in that the conditioning liquid (68) is drained from the channels (12, 13) by means of gravity and/or a gas, in particular an inert gas. The method according to one or more of the preceding claims, characterized in that during the passage of the conditioning liquid (68) through the channels (12, 13) the volume of the components (5, 6, 7, 8, 9, 10, 51) due to the Adhesion and/or hydration and/or hydration of water and/or moisture to the components (5, 6, 7, 8, 9, 10, 51) increases, in particular the volume increases by 3%, 5% or 10%. Method according to one or more of the preceding claims, characterized in that the conditioning liquid (68) is passed through the channels (12, 13) for a period of less than 3 hours, in particular less than 1 hour, 30 minutes or 10 minutes . Electrochemical cell unit (53) for converting electrochemical energy into electrical energy as a fuel cell unit (2) and/or for converting electrical energy into electrochemical energy as an electrolytic cell unit (49), comprising send - stacked electrochemical cells (52) and the electrochemical cells (52) each stacked layered components (5, 6, 7, 8, 9, 10, 51) and - the components (5, 6, 7, 8, 9, 10, 51) of the electrochemical cells (52) are preferably proton exchange membranes (5), anodes (7), cathodes (8), preferably gas diffusion layers (9) and bipolar plates (10, 51), characterized in that with the electrochemical cell unit (53) a method can be carried out according to one or more of the preceding claims and/or a stack (1, 49, 53) of the electrochemical cells (52) with at least one connecting device (37) with a compressive force perpendicular to imaginary planes (59) is prestressed and by means of the at least one connecting device (59) the compressive force can be changed, so that due to the changed compressive force the expansion of the stack (1, 49, 53) perpendicular to the imaginary planes (59) can be changed.

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