Fuel cell system

Abstract

The invention relates to a fuel cell system (100, 300) having: a fuel cell stack (110) with at least two fuel cells; one or more bipolar plates (150), a respective bipolar plate (150) being arranged between each pair of adjacent fuel cells; a container (130) in which the fuel cell stack (110) is arranged, wherein the container (130) can be filled with a cooling fluid (140) such that the fuel cell stack (110) is surrounded by the cooling fluid (140), and at least one of the bipolar plates (150) has a first fluid line (180) for conducting a first fluid and a second fluid line (220) for conducting a second fluid; and a pressure-equalizing device (250, 310), which is connected to the first fluid line (180), the second fluid line (220), and the container (130) and which is designed to equalize the pressure between the first fluid, the second fluid, and the cooling fluid (140).

Description

[0001] FUEL CELL SYSTEM

[0002] The present invention relates to a fuel cell system and an electrically driven system with a fuel cell system.

[0003] A fuel cell system may comprise a plurality of fuel cells and bipolar plates arranged between adjacent fuel cells.

[0004] Various types of fuel cells are known, for example, those with a polymer electrolyte membrane (PEM) fuel cell, which uses hydrogen as fuel. A fuel cell consists of electrodes, an anode, and a cathode, between which an electrolyte, particularly in the form of a proton-conducting membrane, is arranged. These components form a so-called membrane electrode assembly (MEA for short).

[0005] Since the electrical voltage of a single fuel cell is limited, several fuel cells are connected in series to form a "stack" in order to enable a correspondingly higher voltage. The individual MEAs are separated from each other by bipolar plates, with the bipolar plates connecting the anodes and cathodes of consecutive MEAs to form the series connection. A bipolar plate is responsible for supplying hydrogen and oxidant (especially air or oxygen), removing water, and cooling the fuel cell stack. In addition, the bipolar plate collects the electrodes released from the hydrogen on the anode (hydrogen) side and finally feeds them to the oxidant on the cathode (oxygen) side.

[0006] A bipolar plate can be manufactured from two half-shells that are electrically connected to each other. A cooling medium or fluid can be conducted through cavities, channels, or conduits between the half-shells. A channel structure can be formed on the surfaces facing away from each other, i.e., the anode and cathode sides, to conduct the hydrogen or oxygen to the MEA (usually via a corresponding gas diffusion layer). Bipolar plates made of metal, carbon (graphite / carbon), or composite materials with a graphite or carbon content (carbon composite) are known.

[0007] Bipolar plates made of carbon composite material, in particular, can break relatively easily when subjected to mechanical force. Such mechanical force can be caused by differential pressures between the hydrogen, the oxygen, and the cooling medium, or even by ambient pressure.

[0008] The present invention is based on the object of enabling pressure equalization between different pressures prevailing in a fuel cell system in an improved manner in order to reduce the risk of damage to a bipolar plate due to pressure differences.

[0009] This object is achieved according to the teaching of the independent claims. Various embodiments and further developments of the invention are the subject of the dependent claims.

[0010] A first aspect of the solution relates to a fuel cell system, comprising: (i) a fuel cell stack with at least two fuel cells; (ii) one or more bipolar plates, wherein a bipolar plate is arranged between each two adjacent fuel cells; (iii) a container in which the fuel cell stack is arranged, and wherein the container can be filled with a cooling fluid, in particular an electrically insulating liquid or a gas, in particular air, so that the fuel cell stack is surrounded by the cooling fluid; (iv) wherein at least one of the bipolar plates has a first fluid line for conducting a first fluid, in particular an oxidizing agent, in particular air or oxygen, and a second fluid line for conducting a second fluid, in particular a fuel, in particular hydrogen;(v) a pressure equalization device fluidically connected to each of the first fluid line, the second fluid line, and the container, and configured to equalize the pressure between the first fluid, the second fluid, and the cooling fluid. The terms "comprises," "includes," "includes," "has," "has," "with," or any other variation thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a method or apparatus comprising or having a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or that are inherent in such a method or apparatus.

[0011] Furthermore, unless explicitly stated to the contrary, "or" refers to an inclusive "or" rather than an exclusive "or." For example, a condition A or B is satisfied by one of the following conditions: A is true (or present) and B is false (or absent), A is false (or absent) and B is true (or present), and both A and B are true (or present).

[0012] The terms "a" or "an" as used herein are defined as "one or more." The terms "another" and "another," and any other variations thereof, are defined as "at least one other."

[0013] The term "plurality" as used here is to be understood as meaning "two or more".

[0014] The term “configured” or “set up” to fulfil a specific function (and respective variations thereof), as used here, is to be understood that the corresponding device is already in a design or setting in which it can perform the function or is at least adjustable – i.e. configurable – so that it can perform the function after being set accordingly. The configuration can be carried out, for example, by appropriately setting parameters of a process sequence or of switches or the like for activating or deactivating functionalities or settings. In particular, the device can have a plurality of predetermined configurations or operating modes, so that the configuration can be carried out by selecting one of these configurations or operating modes.The term “fuel cell” as used here refers in particular to a device in which chemical energy is converted directly into electrical energy through an electrochemical reaction of a fuel with an oxidizing agent. For this purpose, an electrolyte layer can be provided in the fuel cell between two layers designed as electrodes. The electrolyte layer is designed, for example, as a polymer electrolyte membrane (PEM), which must be moist during operation in order to be able to conduct protons. A fuel, for example hydrogen, is dissociated at an electrode provided as the anode. The protons produced can diffuse through the PEM to the electrode used as the cathode, where they react with an oxygen atom of the oxidizing agent reduced by the cathode, forming water (formally: 2H). + + 1 / 2O2-H2O).

[0015] The term "electrical insulation," "electrically insulating" (and variations thereof) as used here refers in particular to a physical quantity that indicates how a specific body serving as an insulator at least largely prevents the flow of current when an electrical voltage is applied. In particular, substances or bodies whose electrical conductivity is less than 5 pS / cm under standard conditions (25 °C / 1013 hPa) are referred to as (electrical) insulators or (electrically) insulating.

[0016] The fuel cell system according to the first aspect can achieve pressure equalization between a first fluid, a second fluid, and a cooling fluid. Because the cooling fluid is present in the container, which in turn is exposed to ambient pressure, and is coupled to the pressure equalization device, pressure equalization can be achieved more effectively than in a fuel cell system in which the cooling fluid is only present in cooling lines but not in a container. On the one hand, the effect of ambient pressure can reduce a potential pressure difference compared to a solution without a cooling fluid in a container. On the other hand, the volume of the cooling fluid in the container can better cushion or compensate for pressure fluctuations. For example, this can be advantageous in the case of external mechanical influences, such as vibrations or impacts. Overall, this can extend the service life of the bipolar plate.Preferred embodiments of the fuel cell system are described below, which can be combined with each other as well as with the other aspects described, unless this is expressly excluded or is technically impossible.

[0017] In some embodiments, the pressure equalization device comprises a first pressure equalization module and a second pressure equalization module, which are arranged spatially separated from one another, wherein the first pressure equalization module is fluidically connected to the first fluid line and the container and is configured to bring about pressure equalization between the first fluid and the cooling fluid, and wherein the second pressure equalization module is fluidically connected to the second fluid line and the container and is configured to bring about pressure equalization between the second fluid and the cooling fluid. By spatially separating the first pressure equalization module from the second pressure equalization module, it can be achieved that in the event of a malfunction of one of the two pressure equalization modules, at least the other pressure equalization module can still bring about pressure equalization.Furthermore, pressure equalization can be enabled at different positions within the fuel cell system. This can be advantageous if the respective pressures are not uniform throughout the fuel cell system, i.e., if the pressures of a fluid are location-dependent.

[0018] In some embodiments, the pressure equalization device comprises a compensation chamber in which pressure equalization between the first fluid, the second fluid, and the cooling fluid can be achieved. This allows the different pressures in this compensation chamber to interact directly with each other. This enables immediate pressure equalization.

[0019] In some embodiments, at least one of the bipolar plates has a cooling line, each of which is fluidly connected to the container via an inlet and an outlet opening. This allows the cooling fluid to flow through the bipolar plate, thereby achieving improved cooling. Furthermore, the pressure of the cooling fluid can act in the cooling line, and pressure equalization takes place accordingly, enabling more effective pressure equalization.

[0020] In some embodiments, the fuel cell system comprises a plurality of spaced-apart seals, in particular sealing lips, each arranged between the container and the at least one bipolar plate, as well as between the inlet and outlet openings of the cooling line. This allows the cooling fluid to be directed more effectively toward the inlet opening and through the fuel cells instead of past them, thereby enabling more effective cooling.

[0021] In some embodiments, the container, in particular the bag, is formed at least partially from a plastic, in particular an elastic plastic. A plastic allows for a comparatively low overall weight of the container. An elastic plastic also allows for better interaction of the container with pressure changes, thus enabling more effective pressure equalization. This also allows the ambient pressure, i.e., air pressure, to act on the container.

[0022] In some embodiments, the container has a corrugated or folded structure, at least in sections. This allows the rigidity of the container to be reduced, thereby improving the container's ability to adapt to pressure changes and enabling even more effective pressure equalization.

[0023] In some embodiments, the fuel cell system comprises a housing with an interior coated with a fluid-tight and electrically insulating lacquer layer, thereby forming the container. This eliminates the need for a separate container and provides a container that requires only minimal additional space.

[0024] In some embodiments, the first fluid line and / or the second fluid line each have a corrugated or folded structure in a region between the at least one of the bipolar plates and an inner wall of the container. This allows the rigidity of the respective fluid line to be reduced, thereby enabling improved pressure adjustment. In some embodiments, the fuel cell system has a control device, wherein the pressure compensation device is signal-connected to the control device, wherein the control device is configured to set a predetermined pressure of the cooling fluid. This allows a predetermined pressure to be actively set.

[0025] A second aspect of the solution relates to an electrically driven system comprising a fuel cell system according to the first aspect.

[0026] In some embodiments, the electrically powered system is designed as a motor vehicle, emergency power generator or power supply system.

[0027] The features and advantages explained with regard to the first aspect of the solution also apply accordingly to the other aspects described.

[0028] Further advantages, features and possible applications emerge from the following description of preferred embodiments in conjunction with the figures.

[0029] This shows

[0030] Fig. 1A schematically shows a fuel cell system in a plan view according to an embodiment;

[0031] Fig. 1B schematically shows a pressure compensation device according to Fig. 1A;

[0032] Fig. 2 shows schematically a fuel cell system in a plan view according to another embodiment; and

[0033] Fig. 3 schematically shows a fuel cell system in a plan view according to another embodiment.

[0034] Throughout the figures, the same reference numerals are used for the same or corresponding elements. Figure 1A schematically shows a top view of a fuel cell system 100 according to one embodiment.

[0035] The fuel cell system 100 comprises a fuel cell stack 110 arranged in a bag 130 filled with a cooling fluid 140, wherein the bag 130 is arranged in a housing 120. The fuel cell system 100 can typically include further components that are known in principle to those skilled in the art and are therefore neither described here nor illustrated in the drawings for the sake of simplicity.

[0036] The fuel cell stack 110 comprises a plurality of fuel cells (not shown here), as explained above, arranged one above the other in the z-direction of the illustrated coordinate system. A bipolar plate 150 is arranged between each two adjacent fuel cells in the fuel cell stack 110, connecting the adjacent fuel cells to one another. The fuel cell stack 110 can typically comprise further components that are known in principle to those skilled in the art and are therefore neither described here nor illustrated in the drawings for the sake of simplicity.

[0037] The bipolar plate 150 has an oxidant line 180 through which an oxidant, in particular air, can be supplied to a cathode of a fuel cell. The bipolar plate 150 further has a fuel line 220 through which a fuel, in particular hydrogen, can be supplied to an anode of a fuel cell. The bipolar plate 150 further has two cooling lines 155 through which a cooling fluid 140 can be passed to cool the fuel cell. The schematically illustrated arrangement of the cooling lines 155 in the bipolar plate 150 is to be understood as an example. The cooling lines 155 can equally well extend through the bipolar plate 150 over a different area and with a different path geometry.

[0038] According to the present exemplary embodiment, the fuel cell stack 110 is surrounded by the cooling fluid 140. The cooling fluid 140 can, in particular, be an electrically insulating liquid with good thermal conductivity, in particular based on ethylene glycol. Alternatively, a gas, in particular air, can also be used as the cooling fluid. The cooling fluid 140 is supplied to the bag 130 via a cooling fluid inlet line 145. The cooling fluid can be led out of the bag 130 via a cooling fluid outlet line (not shown here), for example, when the cooling fluid 140 is replaced. The fuel cell stack 110 can be cooled or heated by the cooling fluid 140. Furthermore, the cooling fluid 140, in particular when using a liquid cooling fluid 140, can also ensure that less hydrogen diffuses out of the fuel cell stack 110 at a lower rate.

[0039] The fuel cell system 100 according to the present embodiment has a pressure equalization device with a first pressure equalization module 160 and a second pressure equalization module 200.

[0040] The first pressure equalization module 160 has a first equalization chamber 170 and a first piston 165, which is movable in the x-direction within the first equalization chamber 170. The first piston 165 divides the first equalization chamber 170 into two sections or sub-chambers, the size of which each depends on a position of the first piston 165 in the first equalization chamber 170. The first equalization chamber 170 has a first module opening 175 on one side, through which one of the two sections is fluidically connected to the cooling fluid 140 in the bag 130. As a result, this section is filled with cooling fluid and has a pressure equal to the pressure of the cooling fluid 140 in the bag 130. The oxidant line 180, which is fluidically connected to this section, leads through the other of the two sections.As a result, this section is filled with the oxidant and has a pressure equal to the pressure of the oxidant in the bipolar plate 150. When the bipolar plates 150 of the fuel cell stack 110 are fluidically connected, the respective bipolar plates 150 have this pressure of the oxidant.

[0041] The movable first piston 165 enables pressure equalization between the pressure of the oxidizing agent and the pressure of the cooling fluid. If a pressure difference occurs, the piston moves accordingly toward the lower pressure.

[0042] The second pressure equalization module 200 has a second equalization chamber 210 and a second piston 205, which is movable in the x-direction within the second equalization chamber 210. The second piston 205 divides the second equalization chamber 210 into two sections, the size of each of which depends on a position of the second piston 205 in the second equalization chamber 210. The second equalization chamber 210 has a second module opening 215 on one side, through which one of the two sections is fluidically connected to the cooling fluid 140 in the bag 130. As a result, this section is filled with cooling fluid and has a pressure equal to the pressure of the cooling fluid 140 in the bag 130. A fuel line 220 leads through the other of the two sections and is fluidically connected to this section. As a result, this section is filled with the fuel and has a pressure equal to the pressure of the fuel in the bipolar plate 150.Furthermore, the fuel line 220 is fluidically connected to the other of the two sections. As a result, this section is filled with fuel and has a pressure equal to the fuel pressure in the bipolar plate 150. When the bipolar plates 150 of the fuel cell stack 110 are fluidically connected, the respective bipolar plates 150 have this fuel pressure accordingly.

[0043] The movable second piston 205 enables pressure equalization between the pressure of the fuel and the pressure of the cooling fluid 140. If a pressure difference occurs, the piston moves accordingly toward the lower pressure.

[0044] Furthermore, the ambient pressure acts on the housing 120 and the bag 130 of the fuel cell system 100, whereby a supporting pressure is formed on the bag 130, which can lead to smaller pressure fluctuations.

[0045] Instead of the bag 130, a fluid-tight and electrically insulating lacquer layer can be applied to an inner side of the housing 120, and the housing 120 with the lacquer layer is filled with the cooling fluid 140 (not shown here).

[0046] The first pressure compensation module 160 and the second pressure compensation module 200 together form a pressure compensation device 250 for the fuel cell system 100 according to a first embodiment. For reasons of clarity, this pressure compensation device 250 is shown separately in Fig. 1B instead of in Fig. 1A. Fig. 1B schematically shows the pressure compensation device 250 according to a first embodiment, which comprises the first pressure compensation module 160 and the second pressure compensation module 200 according to Fig. 1A.

[0047] Fig. 2 shows a fuel cell system 100 in a plan view according to a further embodiment. The embodiment according to Fig. 2 is a further development of the embodiment of Fig. 1A. The pressure equalization device 250 according to Fig. 1A or 1B is used unchanged in the embodiment according to Fig. 2. According to the embodiment of Fig. 2, a plurality of sealing lips 240 is additionally provided. These sealing lips 240 are each arranged at a distance from one another along outer sides of the fuel cell stack 110 in order to enable a more effective supply of the cooling fluid to a cooling line 155 of the bipolar plate 150 and to prevent the cooling fluid 140 from flowing past the cooling line 150. This supply of the cooling fluid 140 to the cooling line 155 is indicated by an arrow. Likewise, the outflow of the cooling fluid 140 from the cooling line 155 is indicated by an arrow.

[0048] Fig. 3 shows a fuel cell system in a plan view according to another embodiment.

[0049] In contrast to the exemplary embodiment of Fig. 1A or 1B, the fuel cell system 300 has a pressure equalization device 310 according to a further embodiment with a third equalization chamber 315, with a movable first piston 165 and a movable second piston 205. The movable first piston 165 and the movable second piston 205 divide the third equalization chamber 315 into three sections, wherein the size of the individual sections depends on a position of the movable first piston 165 and the movable second piston 205.

[0050] The third compensation chamber 315 has an opening 320 on one side, through which a first of the three sections is fluidically connected to the cooling fluid 140 in the bag 130. As a result, this first section is filled with cooling fluid and has a pressure equal to the pressure of the cooling fluid 140 in the bag 130. A fuel line 220 leads through a second of the three sections. Fuel, in particular hydrogen, is supplied to an anode of a fuel cell through this fuel line 220 and via the adjoining fuel outlet 230. Furthermore, the fuel line 220 is fluidically connected to the second of the three sections. As a result, this second section is filled with fuel and has a pressure equal to the pressure of the fuel in the bipolar plate 150.

[0051] An oxidant outlet 190 of an oxidant line 180 extends through a third of the three sections. An oxidant is supplied to a cathode of the fuel cell through this oxidant outlet 190. Furthermore, the oxidant outlet 190 is fluidically connected to the third of the three sections. As a result, this third section is filled with the oxidant and has a pressure equal to the pressure of the oxidant in the bipolar plate 150.

[0052] In the third compensation chamber 315, three sections are formed by the first piston 165 and the second piston 205, with the pressure of the cooling fluid 140 prevailing in the first section, the pressure of the fuel in the second section, and the pressure of the oxidant in the third section. The movable pistons 165, 205 ensure pressure equalization in the third compensation chamber 315 between the pressures of the oxidant, the fuel, and the cooling fluid 140.

[0053] Likewise, in this embodiment, the sealing lips 240 can be arranged according to Fig. 2.

[0054] While at least one exemplary embodiment has been described above, it should be appreciated that a wide variety of variations exist. It should also be understood that the described exemplary embodiments are merely non-limiting examples and are not intended to limit the scope, applicability, or configuration of the devices and methods described herein. Rather, the foregoing description will provide one skilled in the art with guidance for implementing at least one exemplary embodiment, it being understood that various changes in the operation and arrangement of the elements described in an exemplary embodiment may be made without departing from the subject matter as defined in the appended claims, as well as their legal equivalents.

[0055] LIST OF REFERENCE SYMBOLS

[0056] 100, 300 fuel cell system

[0057] 110 fuel cell stacks

[0058] 120 housings

[0059] 130 bags

[0060] 140 cooling fluid

[0061] 145 Cooling fluid inlet line

[0062] 150 bipolar plate

[0063] 155 Cooling line

[0064] 160, 200 First, second pressure equalization module

[0065] 165, 205 First, second piston

[0066] 170, 210 First, second compensation room

[0067] 175, 215 First, second module opening

[0068] 180 Oxidant line

[0069] 190 Oxidant outlet

[0070] 220 fuel line

[0071] 230 fuel outlet

[0072] 240 sealing lip

[0073] 250, 310 pressure equalization device

[0074] 315 Third compensation area

[0075] 320 opening

Claims

CLAIMS 1. A fuel cell system (100, 300), comprising: a fuel cell stack (110) with at least two fuel cells; one or more bipolar plates (150), wherein a bipolar plate (150) is arranged between each two adjacent fuel cells; a container (130) in which the fuel cell stack (110) is arranged, and wherein the container (130) can be filled with a cooling fluid (140) so that the fuel cell stack (110) is surrounded by the cooling fluid (140); wherein at least one of the bipolar plates (150) has a first fluid line (180) for conducting a first fluid and a second fluid line (220) for conducting a second fluid; a pressure equalization device (250, 310) which is fluidically connected to the first fluid line (180), the second fluid line (220) and the container (130) in each case, and which is configured to bring about a pressure equalization between the first fluid, the second fluid and the cooling fluid (140).

2. Fuel cell system (100, 300) according to claim 1, wherein the pressure equalization device (250) has a first pressure equalization module (160) and a second pressure equalization module (200) which are arranged spatially separated from one another, wherein the first pressure equalization module (160) is fluidically connected to the first fluid line (180) and the container (130) and is designed to bring about pressure equalization between the first fluid and the cooling fluid (140), and wherein the second pressure equalization module (200) is fluidically connected to the second fluid line (220) and the container (130) and is designed to bring about pressure equalization between the second fluid and the cooling fluid (140).

3. Fuel cell system (100, 300) according to claim 1, wherein the pressure equalization device (310) has a compensation chamber (315) in which the pressure equalization between the first fluid, the second fluid and the cooling fluid (140) can be brought about.

4. Fuel cell system (100, 300) according to one of the preceding claims, wherein the at least one of the bipolar plates (150) has a cooling line (155) which is fluidically connected to the container (130) via an inlet opening and an outlet opening.

5. Fuel cell system (100, 300) according to claim 4, comprising a plurality of spaced-apart seals (240) each arranged between the container (130) and the at least one bipolar plate (150) and between the inlet opening and the outlet opening of the cooling line (115).

6. Fuel cell system (100, 300) according to one of the preceding claims, wherein the container (130) is formed at least partially from a plastic.

7. Fuel cell system (100, 300) according to one of the preceding claims, wherein the container has at least in sections a corrugated or folded structure.

8. Fuel cell system (100, 300) according to one of the preceding claims, comprising a housing (120) with an inner side coated with a fluid-tight and electrically insulating lacquer layer, whereby the container (130) is formed.

9. Fuel cell system (100, 300) according to one of the preceding claims, wherein the first fluid line (180) and / or the second fluid line (220) each have a corrugated or folded structure in a region between the at least one of the bipolar plates (150) and an inner wall of the container (130).

10. Fuel cell system (100, 300) according to one of the preceding claims, comprising a control device, wherein the pressure compensation device (310) is signal-connected to the control device, wherein the control device is configured to set a predetermined pressure of the cooling fluid (140).

11. An electrically driven system comprising a fuel cell system (100, 300) according to any one of the preceding claims.

12. An electrically driven system according to claim 11, which is used as a motor vehicle, emergency power generator or power supply system.

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