Membrane electrode assembly
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- POWERCELL SWEDEN AB
- Filing Date
- 2024-07-05
- Publication Date
- 2026-05-13
Smart Images
Figure SE2024050671_09012025_PF_FP_ABST
Abstract
Description
[0001] Membrane electrode assembly
[0002] Description:
[0003] The present invention relates to a membrane electrode assembly according to the preamble of claim 1. The invention also relates to a fuel cell stack comprising such a membrane electrode assembly.
[0004] Usually, an electric cell stack comprises a plurality of stacked electric plates which are separated from each other by insulating layers. In the special case of a fuel cell stack, the electric plates are bipolar plates, and the insulating layers are multi-layer membrane electrode assemblies. The bipolar plates themselves are a combination of an anode plate and a cathode plate which are fixed to each other, wherein adjacent bipolar plates are then separated, or with other words sandwiched, by the membrane electrode assemblies. The cathode and anodes plate which form the bipolar plates are usually electrically transmitting metal or graphite plates, so called flow field plates, having a flow field for the reactants at one side and a flow field for a cooling fluid on the other side. In the assembled state of the bipolar plates, the flow field plates are placed on top of each other in such a way that the cooling fluid flow fields are facing each other, and the reactant fluid flow fields face the sandwiching membrane electrode assemblies.
[0005] The electric current is produced by the membrane electrode assemblies during operation of the fuel cell stack in the electricity generating subassemblies. The electricity generating subassembly of a membrane electrode assembly comprise an ion-conducting membrane, and two electro catalyst layers being arranged at either side of the membrane serving as anode and cathode. During operation of the fuel cell stack, fuel, particularly hydrogen is provided at the anode, while an oxidant, usually oxygen or air is provided at the cathode.
[0006] At the anode, the electro catalyst, usually a platinum catalyst, causes the hydrogen to split into positive hydrogen ions (protons) and negatively charged electrons. The ion conducting membrane, e.g. the polymer electrolyte membrane (PEM) allows only the positively charged ions to pass through it to the cathode. At the cathode, the electrons and positively charged hydrogen ions combine with oxygen to form water, which flows out of the cell.
[0007] Since the ion conducting membrane allows only the positively charged ions to pass to the cathode, a voltage potential difference is created on both sides of the membrane electrode assembly and therefore between the bipolar plate assemblies.
[0008] During the operation of the electric cell stack, the voltage produced by the stacked cells needs to be monitored for determining whether the stack is operating within its intended operation parameters. For that, it is known that the bipolar plates are equipped with voltage monitoring units, which are fixed to the bipolar plates and are provided with wires for connecting the voltage monitoring units to an external voltage monitoring controller, which monitors and controls the operation of the stack.
[0009] Thereby, it is known to attach the wires, e.g. by soldering or welding, directly at the bipolar plate. It is also known to use pin connections, where the pins are inserted between the plates of the bipolar plates, where they are fixed by friction force or press-fit.
[0010] However, placing and fixing the wires and pins into the fuel cell stack is cumbersome and time-consuming, which makes the stacking process inefficient and slow. Additionally, the known fixation methods are also prone to failure as the wires and pins may come loose from the plates or the wires and pins are misplaced so that they cause failures in the stack.
[0011] Additionally, due to the usually tight stacking of the bipolar plates and associated membrane electrode assemblies, the fuel cell stack lacks the space to fit voltage monitoring interface elements, which might be easier to mount.
[0012] It is also known to arrange and fix an electrical conductor on a foil, which can be arranged between a gas diffusion layer and an adjacent electrode of the membrane electrode assembly so that the electrical conductor is in electric contact with the respective electrode. The electrical conductor extends over the membrane electrode assembly so that the electrical conductor can be connected to a voltage monitoring unit. Disadvantageously, the electrical conductor is easily damaged during assembling of the fuel cell stack and also hinders correct alignment of the membrane electrode assemblies and bipolar plates during the stacking process. It is therefore object of the present invention, to provide solution for the voltage monitoring of the fuel cell stack, which is easily and reliably mounted, without being prone to damage or hindering alignment of the elements.
[0013] This object is solved by a membrane electrode assembly according to claim 1 as well as a fuel cell stack according to claim 13.
[0014] In the following a membrane electrode assembly for a fuel cell stack is disclosed which comprises at least an electricity generating subassembly comprising an ion-conducting membrane, and two electrode catalyst layers being arranged at either side of the membrane serving as anode and cathode. Further, the membrane electrode assembly comprises at least one subgasket surrounding the electricity generating subassembly, wherein at least one subgasket has a first side facing to the electricity generating subassembly and a second side being opposite of the first side and facing away from the electricity generating subassembly.
[0015] It is further proposed to arrange a voltage monitoring interface element at the membrane electrode assembly, itself, instead of at the bipolar plate as known, which is adapted to contact a voltage providing component of the membrane electrode assembly or of the fuel cell stack, wherein the voltage monitoring interface element is entirely arranged at and supported by at least one side of the subgasket, wherein the respective side of the subgasket which supports the voltage monitoring interface element is at least partially exposed towards an external environment for providing a connection area.
[0016] By integrating the voltage monitoring interface element to the membrane electrode assembly, the voltage monitoring interface element is already provided during the assembly of the fuel cell stack. Thereby, the cumbersome attachment of pins or wires to the bipolar plate can be set aside.
[0017] Since the voltage monitoring interface element is entirely supported by a subgasket of the membrane electrode assembly, the voltage monitoring interface element is not protruding over the membrane electrode assembly so that an alignment of the fuel cell stack elements can be performed as usual. Further, by supporting the voltage monitoring element entirely by the subgasket renders the voltage monitoring interface element sufficiently sturdy for avoiding any damage. Nevertheless, easy access to the voltage monitoring interface element is provided by the connecting area where the voltage monitoring interface element is exposed to the environment.
[0018] The voltage monitoring interface element itself may be attached to the subgasket, e.g. by gluing.
[0019] Alternatively, is also possible that the voltage monitoring interface element is attached to another voltage providing component of the fuel cell stack and only supported by the subgasket for providing sufficient sturdiness of the voltage monitoring interface element.
[0020] The voltage providing component may be a part of the membrane electrode assembly itself, e.g. an electrode or an optional gas diffusion layer, but can also be provided by an additional component of the fuel cell stack, particularly a bipolar plate. Even if the voltage monitoring interface element may be adapted to come in contact with a bipolar plate, the voltage monitoring interface element itself remains part of the membrane electrode assembly.
[0021] According to a preferred embodiment, the voltage monitoring interface element is arranged at the second side of the subgasket and is adapted to get in direct or indirect contact with a bipolar plate, which, in an assembled state in a fuel cell stack, sandwiches the membrane electrode assembly. By arranging the voltage monitoring interface element at an "outside" of the subgasket, the voltage monitoring interface element is easily accessible for being connected to a voltage monitoring unit.
[0022] According to an alternative or additional arrangement, the membrane electrode assembly may further comprise a gas diffusion subassembly comprising at least an anode sided gas diffusion layer, preferably made of electrically conductive fibers, and a cathode sided gas diffusion layer, preferably made of electrically conductive fibers, wherein the gas diffusion layers sandwich at least the electricity generating subassembly. Since the voltage generated by the membrane electrode assembly is transmitted via the gas diffusion layer to the adjacent bipolar plates, the voltage generated at the respective electrodes can also be monitored at the gas diffusion layer itself. Therefore, it is preferred to arrange the voltage monitoring interface element at the second side of the subgasket, so that the voltage monitoring interface element is in contact with the respective gas diffusion layer
[0023] According to a preferred embodiment, the voltage monitoring interface element is arranged at the first side of the subgasket and in contact with the electricity generating subassembly, particularly with the anode and / or cathode. Thereby, the voltage can be monitored directly at the voltage generating components, so that a significant monitoring can be achieved.
[0024] For exposing at least part of the voltage monitoring interface element to the environment, but still contact the electricity generating subassembly, an embodiment is preferred wherein the at least one subgasket has at least one opening, and the voltage monitoring interface element has a first part which is arranged at the first side of the subgasket, particularly between the anode and / or cathode of the membrane electrode assembly and the respective subgasket, a second part, which extends through the opening in the subgasket and a third part which is arranged at the second side of the subgasket.
[0025] In case there is not only a single subgasket, but the membrane electrode assembly further comprises a subgasket subassembly with an anode sided subgasket surrounding a periphery of the anode and / or a cathode sided subgasket surrounding a periphery of the cathode, the voltage monitoring interface element can be arranged either at the anode sided subgasket or at the cathode side subgasket.
[0026] Thereby it is also possible to arrange the voltage monitoring interface element at the second side of the respective subgasket, particularly between the subgasket and a gas diffusion layer or the bipolar plate. This allows for a simplified access to the connecting area which is exposed to the environment.
[0027] However, it is also possible to arrange the voltage monitoring interface element at the first side of one of the subgaskets and thereby between the anode sided subgasket and the cathode sided subgasket. In this case it is further preferred that one of the subgaskets, either the anode or the cathode side subgasket, is at least partly recessed in relation to the respective other subgasket, thereby exposing the voltage monitoring interface element to the environment. It goes without saying that the recess does not necessarily need to extend over the entire periphery of the subgasket, but can only be provided at a discrete location or at discrete locations of the subgaskets.
[0028] Further, it should be noted the voltage monitoring interface element can be either attached to the electrode or to the respective subgasket or to both.
[0029] It should be further noted that with the integration of the voltage monitoring interface element to the membrane electrode assembly itself and providing a connection area which is exposed to the environment, it is possible to allow for an arrangement of a plurality of voltage monitoring interface elements at a single membrane electrode assembly. Not at least during initial start-up of the fuel cell stack, a plurality of voltage monitoring interface elements can be beneficial.
[0030] Thereby, it should be noted that it is also possible that different arrangements and locations of voltage monitoring elements can be provided at the same membrane electrode assembly or at different membrane electrode assemblies provided in the same fuel cell stack.
[0031] According to a further preferred embodiment, the voltage monitoring interface element might have at least one protruding connecting element which project over the periphery of membrane electrode assembly, wherein at least one of the subgaskets further comprises at least one strip or flag, which protrudes from the periphery of the membrane electrode assembly and supports the protruding connecting element of the voltage monitoring interface element. This strip might be arranged in size and form in such a way that it can sturdily support the protruding connection element of the voltage monitoring interface element.
[0032] As mentioned above, for providing an accessibility of the voltage monitoring interface element to an external voltage monitoring controller it is possible that at least one of the subgaskets has a connection area, in which one of the subgaskets is recessed in relation to the other subgasket, and the voltage monitoring interface element is arranged between the subgaskets and is accessible in the connection area. Thereby, the recess can also be arranged at the above mentioned strip. According to a further preferred embodiment the voltage monitoring interface element is designed as elongated element, which is in contact with at least one of the anode, the cathode, the membrane, the subgaskets, and / or the gas diffusion layers along its length.
[0033] This allows for gathering information on the voltage over an extended range of the membrane electrode assembly, so that it is possible to provide information on the voltage not only in a very limited area but over the whole membrane electrode assembly and particularly over the entire length of an active area defined by the area covered by the electricity generating subassembly.
[0034] According to a further preferred embodiment, the voltage monitoring interface element has an elongated main body, which is attached to at least one of the subgaskets and further comprises at least one discrete inner connecting element which extends from the elongated main body in direction of the anode, the cathode, the membrane, and / or the gas diffusion layers and is in contact with at least one of the anode, the cathode, the membrane, and / or the gas diffusion layers.
[0035] The elongated body has the further advantage that it can be connected at different places with external connection elements. This in turn allows for a connection with external connecting elements in an offset way, so that the external connecting elements do not obstruct each other.
[0036] According to a further preferred embodiment, at least a first voltage monitoring interface element and a second voltage monitoring interface element are provided, wherein the at least one first voltage monitoring interface element is arranged at a reactant or coolant inlet side of the membrane electrode assembly and the at least one second voltage monitoring interface element is arranged at a reactant or coolant outlet side of the membrane electrode assembly.
[0037] Gathering voltage information on both the reactants inlet and the outlet side of the membrane electrode assembly and bipolar plate, respectively, allows for an improved monitoring on the voltage distribution over the entire active area.
[0038] According to a further preferred embodiment, the voltage monitoring interface element is a foil made from an electrically conducting material, particularly a silver foil or gold foil, which is attached to at least one of the anode, the cathode, the membrane, the subgaskets, and / or the gas diffusion layers.
[0039] Alternative or additionally, the voltage monitoring interface element is designed as electrically conducting coating, particularly a silver or gold coating, of at least one of the anode, the cathode, the membrane, the subgaskets, and / or the gas diffusion layers.
[0040] A further aspect of the preset invention relates to fuel cell stack comprising a plurality of bipolar plates consisting of an anode plate and a cathode plate, which are attached to each other, wherein the bipolar plates are alternatingly stacked with a plurality of membrane electrode assemblies so that the bipolar plates sandwich the membrane electrode assemblies, wherein a voltage produced by the membrane electrode assembly is monitored by means of a voltage monitoring interface element being arranged at the membrane electrode assembly as mentioned above.
[0041] According to a further preferred embodiment, the fuel cell stack further comprises a voltage monitoring unit comprising a plug-like element having a plurality of contact pin elements which are designed to connect to the voltage monitoring interface element in the connection area, where the voltage monitoring interface element is exposed to the environment. Since the connecting area provided by the voltage monitoring interface element is exposed to the environment, contact with the contact pin elements is facilitated.
[0042] Alternatively or additionally, the plug-like element may also have a plurality of contact clamp elements which are designed to connect to the voltage monitoring interface element by clamping the voltage monitoring interface element in the connection area, where the voltage monitoring interface element is exposed to the environment.
[0043] Further preferred embodiments are defined in the dependent claims as well as in the description and the figures. Thereby, elements described or shown in combination with other elements may be present alone or in combination with other elements without departing from the scope of protection.
[0044] In the following, preferred embodiments of the invention are described in relation to the drawings, wherein the drawings are exemplarily only, and are not intended to limit the scope of protection. The scope of protection is defined by the accompanied claims, only. The figures show:
[0045] Fig. 1 : schematic view of a fuel cell stack with a voltage monitoring arrangement according to the state of the art;
[0046] Fig. 2; schematic top view of a bipolar plate;
[0047] Fig. 3a; a schematic top view of a membrane electrode assembly;
[0048] Fig. 3b: a schematic cross section through the membrane electrode assembly of Fig. 3a;
[0049] Fig. 4: schematic view of a fuel cell stack with a voltage monitoring arrangement according to a first embodiment;
[0050] Fig. 5: schematic view of a fuel cell stack with a voltage monitoring arrangement according to a second embodiment;
[0051] Fig. 6: schematic view of a fuel cell stack with a voltage monitoring arrangement according to a third embodiment;
[0052] Fig. 7: schematic view of a fuel cell stack with a voltage monitoring arrangement according to a fourth embodiment;
[0053] Fig. 8; schematic view of a plug like element with a voltage monitoring arrangement according to a fifth embodiment;
[0054] Fig. 9: schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a first embodiment;
[0055] Fig. 10: schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a second embodiment;
[0056] Fig. 11: schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a third embodiment;
[0057] Fig. 12: schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a fourth embodiment;
[0058] Fig. 13; schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a fifth embodiment;
[0059] Fig. 14: schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a sixth embodiment;
[0060] Fig. 15: schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a seventh embodiment;
[0061] Fig. 16: schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a eighth embodiment;
[0062] Fig. 17: schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a ninth embodiment; and Fig. 18: schematic view of a membrane electrode assembly with a voltage monitoring interface element according to a tenth embodiment.
[0063] In the following same or similar functioning elements are indicated with the same reference numerals.
[0064] Fig. 1 shows a schematic view of a known voltage monitoring arrangement for a fuel cell stack 2 according to the state of the art. The fuel cell stack 2 comprises a plurality of bipolar plates 4-1 to 4-5 sandwiching membrane electrode assemblies 6-1 to 6-5. The bipolar plates 4 themselves are a combination of an anode plate (not illustrated) and a cathode plate (not illustrated) which are fixed to each other. Fig. 2 illustrates such a bipolar plate 4, wherein only the cathode or anode plate is shown. The cathode plates and the anode plates, which form the bipolar plates 4, are usually electrically transmitting metal or graphite plates, so called flow field plates, having a flow field 42 for the reactants at one side and a flow field (not to be seen in the schematic view of Fig. 2) for a cooling fluid on the other side. In the assembled state of the bipolar plates 4, the flow field plates are placed on top of each other in such a way that the cooling fluid flow fields are facing each other, and the reactant fluid flow fields 42 face the sandwiching membrane electrode assemblies 6. The bipolar plates 4 further have manifold inlet openings 44, 45, 46 and manifold outlet openings 47, 48, 49 for the reactants and the coolant, respectively, which are in fluid connection to their respective flow fields 42, and which form in the stacked arrangement tubes for guiding reactants and coolant through the fuel cell stack.
[0065] Fig. 3 illustrates schematically a membrane electrode assembly 6 in top view (see Fig. 3a) and cross sectional view (see Fig. 3b).
[0066] Analogously, to the bipolar plate 4, also the membrane electrode assembly has manifold inlet openings 64, 65, 66 and manifold outlet openings 67, 68, 69 for the reactants and the coolant, which form, together with the manifolds of the bipolar plate, in the stacked arrangement tubes for guiding reactants and coolant through the fuel cell stack. The membrane electrode assembly 6 further comprises an active area 62, which is covered by the flow field 42 of the bipolar plate, and which constitutes the location, where the electricity is generated, which will be described in detail with reference to Fig. 3b. As can be seen in Fig. 3b, the membrane electrode assembly 6 usually comprises an electricity generating subassembly 14 comprising an ion-conducting membrane 16, and two electro catalyst layers 18, 20 being arranged at either side of the membrane serving as anode 18 and cathode 20. The electricity generating subassembly 14 constitute the active area 62 of the fuel cells, and is usually arranged in the area of the reactants' flow fields 42 provided by the bipolar plates 4. For distributing reactants uniformly over the membrane electrode assembly 6, the membrane electrode assembly 6 may further comprise gas diffusion layers 22, 24, which are in contact with the electricity generating subassembly 14 and the bipolar plates 4. Further, the gas diffusion layers 22, 24 extend over at least the active areas 62 and are arranged at both the cathode side and the anode side of the electricity generating subassembly 14, thereby sandwiching the electricity generating subassembly 14. The gas diffusion layers 22, 24 are usually made from an electrically conducting material and provide the voltage transfer from the electricity generating subassembly 14 to the bipolar plates 4.
[0067] Additionally, the membrane electrode assembly 6 comprises an anode sided subgasket 26 and a cathode sided subgasket 28, which surround the electricity generating subassembly 14 frame-like, as is illustrated in Fig. 3a, and extend over the whole bipolar plate. The subgaskets 26; 28 each have a first side 26-1 and 28-1 which face to the anode and the cathode of the membrane electrode assembly 6, and a second side 26-2; 28-2 which face to the gas diffusion layers 22; 24. As the subgaskets 26; 28 may be made from an electrically insulating material they may also serve as electrical insulation between adjacent bipolar plates 4, for avoiding short circuits. Therefore, the membrane electrode assemblies 6 and particularly the subgaskets 26, 28 of the membrane electrode assemblies 6 do not only cover the bipolar plates 4, but protrude over the bipolar plates 4, as is illustrated in Fig. 1.
[0068] The fuel cell stack 2 generates a total voltage as a result of individual voltages of each electricity generating subassembly 14, which are accumulated and transferred by means of the bipolar plates 4. As the electricity generating subassembly 14 and the bipolar plates 4 may wear over time, it is necessary to monitor the generated voltages for ensuring the performance of the fuel cell stack. For this purpose, it is known to provide at each bipolar plate 4-1 - to 4-5 with a voltage monitoring unit 8-1 to 8-5. Each voltage monitoring unit 8-1 to 8-5 comprises a voltage monitoring interface element 10-1 to 10-5, each of which is connected to a bipolar plate 4-1 to 4-5, for example in the form of a pin, as shown in Fig. 1 , or any other kind of connection or may be directly welded to or molded into the bipolar plate 4. Via the voltage monitoring interface elements 10-1 to 10-5, the respective voltages of the bipolar plates 4-1 to 4-5 and the electricity generating subassembly 14 are tapped and transmitted to an externally or internally arranged control unit 12.
[0069] As mentioned above and as can be further seen in Fig. 1 , the membrane electrode assemblies 6-1 to 6-5 extend over the bipolar plates 4-1 to 4-5, which hinders inserting or attaching the voltage monitoring interface element 10-1 to 10-5 into / to the bipolar plates 4-1 to 4-5.
[0070] Therefore, it has been suggested by the inventor to arrange the voltage monitoring interface element at the membrane electrode assembly 6 and not at the bipolar plate 4. Since the membrane electrode assembly 6 is usually quite thin, the voltage monitoring interface element needs also to be quite thin, which in turn renders the voltage monitoring interface element prone to damage. It is therefore further suggested by the inventor to arrange the voltage monitoring interface element entirely at the subgasket so that the subgasket can support the voltage monitoring interface element and thereby increase its sturdiness.
[0071] Figs. 4 to 18 illustrate various embodiments of fer monitoring a voltage by means of a voltage monitoring interface element which is arranged at the membrane electrode assembly 6 and particularly at the subgasket and is supported by the subgasket.
[0072] Figs. 4 to 7 illustrates also a fuel cell stack 2 comprising a plurality of bipolar plates 4-1 to 4-6 sandwiching the membrane electrode assemblies 6-1 to 6-6. It is further illustrated in Figs. 4 to 18 that the membrane electrode assemblies 6-1 to 6-6 and particularly the subgaskets are provided with a voltage monitoring interface element 10-1 to 10-6, wherein the voltage monitoring interface element 10 is made from an electrically conducting material, e.g. a gold or silver foil or coating, and is in contact with an electrically conducting material present in the membrane electrode assembly 6, particularly with the anode / cathode material, 18; 20 and / or the gas diffusion layers 22; 24.
[0073] As can be further seen in Fig. 4, for monitoring the voltage, the voltage monitoring interface element 10 shall be contactable by a voltage monitoring unit 8, which may be designed as a plug-like element 82 having a plurality of comb-like support elements 84, which may be designed as rods 84-1 to 84-5 extending from a base body 86. Thereby the rods 84 may be designed for contacting the voltage monitoring interface elements 10-1 to 10-5 arranged at the membrane electrode assemblies 6-1 to 6-5 directly, and / or may be designed as support elements for providing a contact possibility to the voltage monitoring interface element 10. Since the membrane electrode assemblies 6-1 to 6-5 and in particular the subgasket are extending over the periphery of the respective bipolar plates 4-1 to 4-5 the voltage monitoring interface element 10 is exposed to the environment and easily accessible and can be contacted without problem by means of the plug-like element 82. Further plug-like elements 82-2 ... (not illustrated) may be arranged below or above the illustrated plug-like element 82 and may be adapted to contact further membrane electrode assemblies, e.g. 6-6 ...
[0074] As mentioned above the support elements 84-1 to 84-5 of Fig. 4 may be designed as rods which provide contact elements for the voltage monitoring interface element 10, as is illustrated in Fig. 4. However, the support elements 84 can also be designed for interacting with additional electrical contact elements 88, as is illustrated in Figs. 5 and 6.
[0075] As can be seen in Fig. 5, the voltage monitoring unit 8 further comprise electric contact elements 88, e.g. in the form of pins 88-1 to 88-5, which may be inserted into the main body 86 and are designed to contact the voltage monitoring interface elements 10-1 to 10-5. Thereby it is preferred that the pins 88 are inserted between the support element 84 and the voltage monitoring interface element 10 so that the support element 84 ensures that the pins 88 remains in contact with the voltage monitoring interface element 10.
[0076] Alternatively or additionally, the voltage monitoring unit 8, and particularly the plug-like element 82 may further comprise clamping elements 89, which ensure that the membrane electrode assembly 6 is clamped between the clamping element 89 and the support element 84, as is illustrated in Fig. 6.
[0077] As is further illustrated in Fig. 6, the electric contact elements 88, namely the pins of the plug-like element do not necessarily extend through the main body 86, as is illustrated in Fig. 5, but may be embedded in the main body 86 and can be interconnected for transferring the voltage measurement to a control unit.
[0078] As is further illustrated in Fig. 7, the support elements 84, the electric contact elements 88 and / or the clamping elements 89 may be offset to each other for ensuring that even with the small dimensions of membrane electrode assembly 6 and bipolar plate 4 each membrane electrode assembly 6 may be contacted by a the support element 84 directly or by means of an additional electric contact element 88 at its voltage monitoring interface element 10. As can be further seen in Fig.8, the support elements 84 may also have different length, which also allows for a contacting of the voltage monitoring interface element 10 at different locations.
[0079] Figs. 9 to 12 illustrate different embodiments for integrating the voltage monitoring interface element 10 into the membrane electrode assembly 6. As mentioned above, the membrane electrode assembly 6 usually comprises an ion-conducting membrane 16, and two electro catalyst layers 18, 20 being arranged at either side of the membrane serving as anode 18 and cathode 20. The illustrated membrane electrode assembly 6 further comprises gas diffusion layers 22, 24, which are in contact with the electricity generating subassembly 14 and the bipolar plates 4. The gas diffusion layers 22, 24 are usually made from an electrically conducting material and provide the voltage transfer from the electricity generating subassembly 14 to the bipolar plates 4. Thus, both the gas diffusions layer 22, 24 and the electro-catalyst layers 18, 20 provide information on the voltage of the unit fuel cell. Therefore, both may serve as voltage information providing elements, which may be used for monitoring the voltage produced by the electricity subassembly 14.
[0080] Further and as also mentioned above, the membrane electrode assembly 6 comprises subgaskets 26; 28 which are made from an electrically insulating material and also serve as electrical insulation between adjacent bipolar plates 4, for avoiding short circuits. As mentioned above with reference to Fig. 3b, the subgaskets 26; 28 further each comprise a first side 26-1 ; 28-1 facing the electrodes 18; 20 of the membrane electrode assembly 6 and a second side 26-2; 28-2 facing the gas diffusion layer 22, 24, respectively. Since the subgaskets 26; 28 surround the active area of the membrane electrode assembly 6 framelike and protrude over the bipolar plate 2, they provide the ideal location for arranging and supporting the voltage monitoring interface element. The voltage monitoring interface element is then on the one side in contact with a voltage providing component of the fuel cell stack, e.g. the anode / cathode, the gas diffusion layer and / or the bipolar plate. On the other side the voltage monitoring interface element is exposed to the environment and provides a connection area for e.g. the contact elements of the plug-like element 82. As the gas diffusion layers 22, 24 and the electro catalyst layers 18; 20 provide information on the voltage, it is also possible to arrange the voltage monitoring interface element 10 at the gas diffusion layers 22, 24 and / or the electro catalyst layers 18; 20.
[0081] According to a first embodiment and as is illustrated in Fig. 9, the voltage monitoring interface element 10 may be arranged in electrical contact with the gas diffusion layer 22. For that, the voltage monitoring interface element 10 may be a foil or coating made from an electrically conducting material, e.g. silver or gold, which is arranged / attached to the subgasket 26. In the illustrated embodiment the voltage monitoring interface element 10 is arranged between the gas diffusion layer 22 and the subgasket 26.
[0082] As can be further seen in Fig. 9, the voltage monitoring interface element 10 covers at least partly the second side 26-2 of the subgasket 26 particularly in peripheral area of the subgasket 26. It is further illustrated that the voltage monitoring interface element 10 is supported over its entirety by the subgasket 26 and is exposed to the environment in a connection area 11 , so that the voltage monitoring interface element 10 may be contacted by the voltage monitoring unit 8, as explained above in relation to Figs. 4 to 8.
[0083] Fig. 10 illustrates an embodiment, where the voltage monitoring interface element 10 may be in contact with both the anode 18 and the anode sided gas diffusion layer 22. For that, the anode sided subgasket 26 has an opening 30 through which the voltage monitoring interface element 10 may be led. Further, the voltage monitoring interface element 10 has a first part 10a which is arranged at the first side 26-1 of the subgasket 26 and is in electric contact with the anode layer 18, a second part 10b which extends through the opening in the subgasket 26, and a third part 10c, which is arranged at the second side 26-2 of the subgasket 26 and in electric contact with the gas diffusion layer 22. Again, the voltage monitoring interface element is supported over its entirety by the subgasket 26, but is equipped with a connection area 11 which is exposed to the environment so that the voltage monitoring interface element 10 may be contacted from the outside, e.g. by the voltage monitoring unit 8. The second part 10b of the voltage monitoring interface element 10 may be a foil or a coating, or even a wire, which extends through the subgasket 26 and connects two more widespread parts 10 a, 10c of the voltage monitoring interface element 10. It goes without saying that alternatively or additionally, the voltage monitoring interface element 10 may be arranged at and may be in electrical contact with the cathode 20 and / or the cathode sided gas diffusion layer 28. It should be further noted that it is also possible that the first part 10a of the voltage monitoring interface element 10 may be arranged at the gas diffusion layer 22; 24 and the third part 10c is arranged at the electro catalyst layer 18; 20. However, in this case, further measures needs to be taken for exposing the voltage monitoring element 10 to the environment as will be explained further below with reference to Fig. 11 and 12.
[0084] Fig. 11 illustrates an embodiment, where the voltage monitoring interface element 10 is arranged in electrical contact with the electro catalyst layer 18; 20, only. As illustrated, the voltage monitoring interface element 10 may be a coating or a foil which is e.g. attached to and supported by the subgasket 26 at the electricity subassembly 14 facing first side 26-1 of the subgasket 26. It is further illustrated in the embodiment of Fig. 10, that the electricity subassembly 14 does not extend as far as the subgasket 26, 28 and the subgaskets 26, 28 contact each other in the periphery of the membrane electrode assembly 6.
[0085] For picking off the voltage information from the voltage monitoring interface element 10 and exposing the voltage monitoring interface element to the environment, one of the subgaskets 26, 28 may be provided with an area in which an edge 32 of one of the subgaskets 26 is recessed compared to an edge 34 of the other subgasket 28 so that, the voltage monitoring interface element 10 is exposed and can be accessed directly in the connection area 11 , as is illustrated in Fig. 11.
[0086] It goes without saying that the recess does not necessarily need to extend over the entire periphery of the subgasket, but can only be provided at a discrete location or at discrete locations so that in one area the edges 32, 34 of the subgasket 26; 28 are flush and, in other areas, one of the edges 32; 34 of the subgaskets 26; 28 is recessed.
[0087] Fig. 12 illustrates an embodiment, where the voltage monitoring interface element 10 is arranged around the electro catalyst layer, e.g. anode 18, in a frame like manner. Thereby, the voltage monitoring interface element 10 may be completely embedded into the electricity generating subassembly 14. However, also in this case the voltage monitoring interface element is supported by the subgasket 16; 28 for providing sufficient sturdiness. For providing access to such a voltage monitoring interface element 10 the edges 32, 34 of the subgaskets 26 and 28 are again recessed in at least one area, so that the voltage monitoring interface element 10 is exposed to the environment in the connecting area 11 .
[0088] It goes without saying that also combinations of embodiments as illustrated in Figs. 11 and 12 may be possible.
[0089] Figs. 13 to 18 illustrate top views of a membrane electrode assembly 6, with different embodiments for the voltage monitoring interface element 10.
[0090] As can be seen in Fig. 13 and is illustrated in the cross sections of Figs. 11a and 12c, the voltage monitoring interface element 10 may extend to the edges 32, 34 of the subgaskets 26; 28. As can be further seen in Fig: 13, the voltage monitoring interface element 10 extends over the whole length of the active area 62 provided by the electricity generating subassembly 14, which allows for gaining information on the voltage over the entire length of the membrane electrode assembly. This is particularly interesting during a start up phase, as the voltage at the inlet region 61 may differ from the voltage at the outlet region 63 of the active area 62.
[0091] Alternatively, and as illustrated in Fig. 14 and in the cross sections of Fig. 11 and 12, it is also possible that the voltage monitoring interface element 10 does not extend to the edges 32, 34 of the subgaskets but terminates before. Also in this case, it is advantageous that the voltage monitoring interface element 10 extend over the whole length of the active area 62. Nevertheless, also in this case, the one of the subgaskets may be recessed for providing a connection are of the voltage monitoring interface element which is exposed to environment.
[0092] Further, by the extending voltage monitoring interface element 10, e.g. over the whole length of the active area, it is possible that the voltage monitoring interface elements 10 of adjacent unit fuel cells may be contacted in different locations (see e.g. Fig. 7) along the length of the voltage monitoring interface element 10.
[0093] Instead of contacting the active area 62 along the whole length it is also possible that the voltage monitoring interface element 10 has voltage monitoring interface element connecting elements 13, which are in contact with the active area 62. Thereby, it is possible to have a plurality of contact elements as is illustrated in Fig. 15 or only a single contact element as is illustrated in Fig. 16.
[0094] Besides the arrangement of the voltage monitoring interface element 10 at the long side of the membrane electrode assembly 6 and therefore the long side of the active area 62, it is also possible to arrange the voltage monitoring interface element 10 in the area of the manifold openings 64 - 69. Fig. 17 and Fig. 18 illustrate two embodiments with the voltage monitoring interface element 10 arranged in the region of the manifold openings 64 - 69.
[0095] As is illustrated in Fig. 17, the voltage monitoring interface element 10 may be designed as elongated element which is connected to the active are 62 by means of a connecting element 13. The elongation of the voltage monitoring interface element 10 allows again the contacting in different locations from unit fuel cell to unit fuel cell as mentioned above.
[0096] Alternative and as illustrated in Fig. 18, it is also possible to design discrete voltage monitoring flags or strips 10-1 , 10-2, 10-3, which stick out from the membrane electrode assembly 6 and may be contacted or integrated into specially designed voltage monitoring units 8. The strips 10-1 to 10-3 may be supported by strips or flags 31 -1 to 31-3 made from the subgasket 28; 26.
[0097] Even if in Figs. 17 and 18 the voltage monitoring interface element 10 is only illustrated as being arranged at the inlet side of the membrane electrode assembly 6, it is also possible to arrange the voltage monitoring interface element 10 at the outlet side of the membrane electrode assembly or even on both, the inlet and the outlet side.
[0098] In all cases it is also possible that parts of one of the subgaskets are recessed so that the voltage monitoring interface element 10 is exposed for direct access.
[0099] Alternatively, the voltage monitoring interface element is arranged at the second side 26-2; 28-2 of the respective subgasket 26; 28.
[0100] By providing a voltage monitoring interface element 10 at the membrane electrode assembly 6 directly, a voltage monitoring arrangement may be presented which can be easily manufactured during manufacturing of the membrane electrode assembly 6 itself. As the membrane electrode assembly 6 usually extends over the bipolar plate 4, the voltage monitoring interface element 10, which is provided at the membrane electrode assembly 6, can be accessed in a simple way. For providing sufficient sturdiness of the voltage monitoring interface element even if it is located at the thin membrane electrode assembly, the voltage monitoring interface element is supported over its entirety by the subgasket and has a connecting area in which the voltage monitoring interface element is exposed to the environment for easy access. Further due to the elongated shape of the voltage monitoring interface element 10 or due to the possibility to arrange a voltage monitoring interface element 10 at both, the inlet and the outlet side of the membrane electrode assembly 6, information on voltage differences over the whole unit fuel cell can also be gained, which is particularly important during start up or for determining a wear of the fuel cell stack or the unit fuel cells.
[0101] Reference numerals
[0102] 2 fuel cell stack
[0103] 4 bipolar plates
[0104] 6 membrane electrode assemblies
[0105] 8 voltage monitoring unit
[0106] 10 voltage monitoring interface elements
[0107] 11 connecting area
[0108] 13 connecting element
[0109] 12 externally or internally arranged control unit
[0110] 14 electricity generating subassembly
[0111] 16 ion-conducting membrane
[0112] 18 electro catalyst layer, anode
[0113] 20 electro catalyst layer, cathode
[0114] 22, 24 gas diffusion layers
[0115] 26 anode sided subgasket
[0116] 28 cathode sided subgasket
[0117] 26-1; 28-1 first side of the subgasket
[0118] 26-2, 28-2 second side of the subgasket
[0119] 30 opening
[0120] 31 subgasket flags
[0121] 32, 34, 36 edges
[0122] 42 flow fields
[0123] 44, 45, 46 bipolar plate inlet openings
[0124] 47, 48, 49 bipolar plate outlet openings
[0125] 61 membrane electrode assembly inlet region
[0126] 62 membrane electrode assembly active area
[0127] 63 membrane electrode assembly outlet region
[0128] 64, 65, 66 membrane electrode assembly inlet openings
[0129] 67, 68, 69 membrane electrode assembly outlet openings
[0130] 82 plug-like element
[0131] 84 comb-like support elements, rods
[0132] 86 base body
[0133] 88 electrical contact elements, pins
[0134] 89 clamping element
Claims
Membrane electrode assemblyClaims:1 . Membrane electrode assembly (6) for a fuel cell stack (2) comprising at least an electricity generating subassembly (14) comprising an ion-conducting membrane (16), and two electro catalyst layers (18, 20) being arranged at either side of the membrane serving as anode (18) and cathode (20), wherein the membrane electrode assembly further comprises at least one subgasket (26) surrounding the electricity generating subassembly (14), wherein at least one subgasket (26, 28) has a first side (26-1 ; 28-1) facing to the electricity generating subassembly (14) and a second side (16-2; 28-2) being opposite of the first side and facing away from the electricity generating subassembly (14), characterized in that at least one voltage monitoring interface element (10) is arranged at the membrane electrode assembly (6), which is adapted to contact a voltage providing component of the membrane electrode assembly (6) or of the fuel cell stack, wherein the voltage monitoring interface element (10) is entirely arranged at and supported by at least one side of the subgasket (26; 28), wherein the respective side (26-1 , 28-1 ; 26-2, 28- 2) of the subgasket (26; 28) which supports the voltage monitoring interface element (10) is at least partially exposed towards an external environment for providing a connection area (11).
2. Membrane electrode assembly (6) according to claim 1 , wherein at least one of the at least one voltage monitoring interface element (10) is arranged at the second side (26-2; 28-2) of the subgasket (26; 28) and adapted to get in direct or indirect contact with a bipolar plate sandwiching the membrane electrode assembly (6) in the assembled state of a fuel cell stack.
3. Membrane electrode assembly (6) according to claim 1 or 2, wherein the membrane electrode assembly (6) further comprises an anode sided gas diffusion layer (26), preferably made of electrically conductive fibers, and a cathode sided gas diffusion layer (28), preferably made of electrically conductive fibers, wherein the gasdiffusion layers (22, 24) sandwich at least the electricity generating subassembly (14), and wherein at least one of the at least one voltage monitoring interface element (10) is arranged at the second side of the subgasket and is in contact with the anode sided (26) and / or cathode sided (28) gas diffusion layer.
4. Membrane electrode assembly (6) according to any one of the preceding claims, wherein at least one of the at least one voltage monitoring interface element (10) is arranged at the first side (26-1 ; 28-1) of the at least one subgasket (26; 28) and is in contact with at least one of the electro catalyst layers (18, 20) of the electricity generating subassembly (14), particularly in contact with the anode (18) and / or cathode (20).
5. Membrane electrode assembly (6) according to claim 4, wherein the membrane electrode assembly (6) further comprises an anode sided subgasket (26) surrounding a periphery of the anode (18), and a cathode sided subgasket (28) surrounding a periphery of the cathode (20), and wherein the at least one voltage monitoring interface element (10) is arranged between the anode sided subgasket (26) and the cathode sided subgasket (28), and wherein one of the subgaskets (26, 28) is recessed in relation to the other subgasket (26, 28) in at least one location for forming the connection area (11), in which the voltage monitoring interface element (10) is exposed to the environment.
6. Membrane electrode assembly (6) according to any one of the preceding claims, wherein the at least one subgasket (26, 28) has at least one tunnel-like opening (30) extending from the first (26-1 ; 28-1) to the second side (26-2; 28-2) of the subgasket (26; 28), and at least one of the at least one voltage monitoring interface element (10) has a first part (19a) which is arranged at the first side (16-1 ; 28-1) of the subgasket (26; 28) and is in contact with the electro catalyst layer (18, 20), a second part (10b) which extends through the tunnel-like opening (30) in the subgasket (26, 28), and a third part (10c) which is arranged at the second side (16-2; 28-2) of the subgasket and is exposed to the environment for providing the connection area (11).
7. Membrane electrode assembly (6) according to any one of the preceding claims, wherein at least one of the subgaskets (26, 28) further comprises at least one strip (31) which protrudes from the periphery of the membrane electrode assembly (6),and wherein the voltage monitoring interface element (10) has at least one protruding connecting element which projects over the periphery of the membrane electrode assembly (6), wherein preferably a size and / or form of the at least one strip (31) of the subgasket is designed for supporting the at least one protruding connecting element.
8. Membrane electrode assembly (6) according to any one of the preceding claims, wherein the voltage monitoring interface element (10) is designed as elongated element having a length, which is along its length in contact with at least one of the anode (18), the cathode (20), the membrane (6), the subgaskets (26, 28), and / or the gas diffusion layers (22, 24).
9. Membrane electrode assembly (6) according to any one of claim 1 to 8, wherein the voltage monitoring interface element (10) has an elongated main body (86), which is attached to the at least one subgaskets (26, 28) and further comprises at least one discrete inner electric connecting element (13) which extends from the elongated main body (86) in direction of the anode (18), the cathode (20), the membrane (6), and / or the gas diffusion layers and is in contact with at least one of the anode (18), the cathode (20), the membrane (6), and / or the gas diffusion layers (22, 24).
10. Membrane electrode assembly (6) according to any one of the preceding claims, wherein at least a first voltage monitoring interface element (10) and a second voltage monitoring interface element (10) are provided wherein the at least one first voltage monitoring interface element (10) is arranged at a reactant or coolant inlet side (61) of the membrane electrode assembly (6) and the at least one second voltage monitoring interface element (10) is arranged at a reactant or coolant outlet side (63) of the membrane electrode assembly (6).11 . Membrane electrode assembly (6) according to any one of the preceding claims, wherein the voltage monitoring interface element (10) is designed as electrically conducting coating, particularly a silver or gold coating, of the at least one subgasket.
12. Membrane electrode assembly (6) according to any one of the preceding claims, wherein the voltage monitoring interface element (10) is a foil made from anelectrically conducting material, particularly a silver foil or gold foil, which is attached to at least one of the anode (18), the cathode (20), the membrane (6), the subgaskets (26, 28), and / or the gas diffusion layers (22, 24).
13. Fuel cell stack (2) comprising a plurality of bipolar plates consisting of an anode plate (18) and a cathode plate (20), which are attached to each other, wherein the bipolar plates are alternatingly stacked with a plurality of membrane electrode assemblies so that the bipolar plates sandwich the membrane electrode assemblies (6), characterized in that the membrane electrode assembly (6) is a membrane electrode assembly according to any one of claim 1 to 12.
14. Fuel cell stack (2) according to claim 13, further comprising a voltage monitoring unit (8) comprising a plug-like element (82) having a plurality of contact pin elements (84) which are designed to connect to the voltage monitoring interface element (10) in the connection area, where the voltage monitoring interface element is exposed to the environment.
15. Fuel cell stack (2) according to claim 13, further comprising a voltage monitoring unit (8) comprising a plug-like element (82) having a plurality of contact clamp elements (84) which are designed to connect to the voltage monitoring interface element (10) by clamping the voltage monitoring interface element (10) in the connection area, where the voltage monitoring interface element is exposed to the environment.