FUEL CELL STACK, FUEL CELL DEVICE AND MOTOR VEHICLE WITH A FUEL CELL DEVICE

Description

[0001] The invention relates to a fuel cell stack comprising a plurality of fuel cells arranged in the stack direction and clamped by clamping elements, at least one of which, preferably each, has a cell voltage tap for electrical connection to a cell monitoring unit. The at least one cell voltage tap is mechanically secured with respect to the connection to the fuel cells by at least one of the clamping elements. The invention further relates to a fuel cell device and a motor vehicle having a fuel cell device.

[0002] Fuel cells are used for the chemical conversion of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain a membrane electrode assembly as their core component. This assembly consists of a proton-conducting membrane and an electrode arranged on either side of the membrane, namely an anode and a cathode. Gas diffusion layers can also be arranged on either side of the membrane electrode assembly, on the sides of the electrodes facing away from the membrane. To increase performance, several fuel cells can be connected in series to form a fuel cell stack.

[0003] During operation, the fuel, in particular hydrogen (H 2 ) or a hydrogen-containing gas mixture, is fed to the anode, where an electrochemical oxidation of H 2 to H +< takes place with the release of electrons e-. Across the membrane, which separates the reaction chambers from each other in a gas-tight manner and electrically insulates them, a water-bound or water-free transport of the protons H +< - from the anode chamber to the cathode chamber takes place. The electrons provided at the anode are conducted to the cathode via an electrical line. Oxygen or an oxygen-containing gas mixture is fed to the cathode, so that a reduction of O 2 to O 2 -< O2- takes place with the absorption of electrons. At the same time, the oxygen anions in the cathode compartment react with the protons transported across the membrane to form water. Careful temperature management is also required here, so that in addition to the reactants, a coolant for appropriate temperature control of the fuel cell stack is fed separately from the reactants to the respective active areas of the fuel cells, with supply and removal via so-called media guides. In addition to the membrane electrode arrangement, a fuel cell therefore usually has a bipolar plate in which an inlet line, an outlet line, and at least one media channel are formed for each medium, which in the case of the reactants is usually expanded to form a flow field.

[0004] The majority of fuel cells combined in a fuel cell stack are generally pressed together using clamping elements with a force in the range of several 10,000 N in order to achieve sufficient contact pressure on the catalyst-coated membrane to reduce ohmic losses and to avoid leaks by means of the high compression.

[0005] In a fuel cell stack, the electrical voltages of each individual fuel cell are monitored to diagnose fault-free operation. For this purpose, each individual fuel cell is electrically contacted and connected to a cell monitoring unit. This electrical contact requires compliance with appropriate quality requirements, particularly when the fuel cell stack is used in a fuel cell device for a motor vehicle. When using connectors for each of the fuel cells, a locking connector is generally required to ensure that the electrical contact is not impaired under the influence of vibrations or mechanical shocks. However, there is limited installation space available on the bipolar plates used, and their complexity is further increased.Another disadvantage in terms of design and assembly effort is that there are usually cable connections between the connectors and the cell monitoring unit.

[0006] DE 10 2017 215 560 A1 shows a fuel cell stack with a tensioning device comprising a tension body, wherein a cable for a cell monitoring unit is attached to the tension body. EP 1 037 296 A1 discloses a fuel cell stack in which the individual fuel cells are clamped together by means of tension rods. The tension rods also serve as busbars. EP 3 035 430 A1 discloses an electrically conductive tensioning element that serves to contact one of the busbars. US 2007 / 0087237 A1 shows a fuel cell stack in which the end plates are clamped by tension rods. Holes are formed in the tension rods for the passage of electrical connections for a cell monitoring unit.

[0007] US 2005 / 213409 A1 relates to a fuel cell stack provided with a plurality of stacked separators, comprising: terminals extending from the separators; a package in which a plurality of through-holes through which the terminals are inserted are formed; a package case having a concave portion wrapping side surfaces of the package and supporting a bottom surface of the package, and through-holes through which the terminals are inserted; and a connecting member having a pressing surface pressing an upper surface of the package, wherein inner surfaces of the through-holes in the package are in contact with outer surfaces of the terminals without a gap.

[0008] JP 2014007152 A discloses a fuel cell comprising a membrane electrode assembly, a frame, a first separator, a second separator, and a housing. In the fuel cell, a support of the frame protrudes so as to be disposed between an end portion of the second separator and a top plate of the housing. The support of the frame also supports the end portion of the second separator.

[0009] DE 10 2018 127490 A1 relates to a fuel cell that can have a voltage sensing cell connector that is reliably held to the fuel cell without increasing the thickness of the fuel cell to a thickness greater than that originally required for power generation. The fuel cell includes a recessed portion into which a cell connector can be inserted. A guide portion formed from a part of a separator is formed in the recessed portion, which guide portion can guide a cell connector inserted into the recessed portion. In a portion of the recessed portion opposite the second extension portion, a projection forming part of an insulating resin sheet or resin layer disposed between a pair of separators protrudes toward the second extension portion.

[0010] It is the object of the present invention to provide an improved fuel cell stack, an improved fuel cell device and a motor vehicle with a fuel cell device which mitigate or even eliminate the above-mentioned disadvantages.

[0011] This object is achieved by a fuel cell stack having the features of claim 1, by a fuel cell device having the features of claim 6, and by a motor vehicle having the features of claim 7. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0012] The fuel cell stack mentioned above is characterized by the fact that the mechanical securing of the cell voltage taps is realized by an existing, essential component that, due to its intended use, is mechanically very robust and stable. Any change in the position of the cell voltage taps is prevented by the clamping element.

[0013] It is preferred if each cell voltage tap comprises a plug for a plug connection, and if the plugs are pre-assembled on the clamping element, since in this way the clamping element can also be used as an assembly aid and the production of the fuel cell stack is simplified while reducing costs.

[0014] In this context, it is advantageous if the clamping element has feedthroughs for cables leading to the cell monitoring unit in order to be able to establish the required connections in a short distance and protected against external influences.

[0015] According to a further embodiment, it is possible for each connector to be arranged on one of the fuel cells, and for a fastening part for the connectors to be accommodated in the clamping element for the electrical connections to the cell monitoring unit. The connectors are formed by sockets, and the fastening part is formed by an injection-molded part through which the electrical connections are routed to a circuit board connected to the cell monitoring unit.

[0016] According to a further preferred embodiment, the plugs and the fastening part can be combined integrally in one component.

[0017] The fuel cells are clamped between end plates by the clamping elements, which are designed as rigid tension bands, so that they have a high mechanical load capacity and are suitable for securing the position of the plugs or sockets.

[0018] The above-mentioned effects and advantages also apply mutatis mutandis to a fuel cell device having such a fuel cell stack and to a motor vehicle having such a fuel cell device.

[0019] The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures, can be combined not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also to be considered encompassed and disclosed by the invention that are not explicitly shown or explained in the figures, but which emerge and can be produced through separate feature combinations from the explained embodiments. Further advantages, features, and details of the invention emerge from the claims, the following description of preferred embodiments, and from the drawings. In the drawings: Fig. 1a schematic representation of a fuel cell stack constructed from a plurality of fuel cells that are pressed together by clamping elements that also serve to secure plug connections, Fig. 2 one of the Figure 1 corresponding representation with plugs mounted on the fuel cells, which are connected to the cell voltage monitoring unit by connecting elements assigned to a clamping element, and Fig. 3 one of the Figure 1 corresponding representation in which the plug and a fastening part are integrated into a clamping element.

[0020] A fuel cell device comprises a fuel cell stack 1 with a plurality of fuel cells 2 arranged in the stacking direction.

[0021] Each of the fuel cells 2 comprises an anode, a cathode, and a proton-conductive membrane separating the anode from the cathode. The membrane is formed from an ionomer, preferably a sulfonated polytetrafluoroethylene (PTFE) polymer or a perfluorinated sulfonic acid (PFSA) polymer. Alternatively, the membrane can also be formed as a sulfonated hydrocarbon membrane.

[0022] Fuel, particularly hydrogen from a fuel tank, can be supplied to the anode via an anode chamber. In a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules are split into protons and electrons at the anode. The PEM allows the protons to pass through but is impermeable to the electrons. The following reaction, for example, occurs at the anode: 2H 2 -> 4H +< + 4e -< (oxidation / electron release). While the protons pass through the PEM to the cathode, the electrons are conducted to the cathode or an energy storage device via an external circuit.

[0023] The cathode gas (for example oxygen or oxygen-containing air) can be supplied to the cathode via a cathode chamber, so that the following reaction takes place on the cathode side: O 2 + 4H +< +4e -< -> 2H 2 O (reduction / electron absorption) The fuel cell stack 1 also has a clamping device formed by clamping elements 3 for compressing the fuel cells 2.

[0024] The terminal fuel cells 2 are assigned end plates 4 to which the clamping device is connected for the force introduction, with the media guides 5 (only in Fig. 3shown) for the fuel, the oxidizing agent and a coolant are arranged, in the embodiments shown in the drawing on the left end plate 4. The tensioning elements 3 are formed as rigid tension bands, which can in particular be made of metal with the corresponding mechanical properties with regard to strength and flexural rigidity.

[0025] The fuel cell stack 1 preferably further comprises a cell voltage tap 6 for each of the fuel cells 2 for electrical connection to a cell monitoring unit 7, thus enabling diagnosis of fault-free operation. The cell voltage taps 6 are mechanically secured with respect to the connection to the fuel cells 2 by at least one of the clamping elements 3.

[0026] Figure 1shows an embodiment in which each cell voltage tap 6 comprises a connector 8 for a plug connection, so that in this embodiment, the additional mechanical security is paramount. Additionally, however, the connectors 8 can also be pre-assembled on the clamping element 3 in order to use the clamping element 3 as an assembly aid, with the clamping element 3 having feedthroughs for cables routed to the cell monitoring unit 7.

[0027] The Figure 2shows an embodiment in which each plug 8 is arranged on one of the fuel cells 2, wherein a fastening part 9 for the plugs 8 is accommodated in the clamping element 3 for the electrical connections to the cell monitoring unit 7, namely in that the plugs 8 are formed by sockets 10 and the fastening part 9 by an injection-molded part 11, through which the electrical connections are led to a printed circuit board 12 which is electrically and in particular mechanically connected to the cell monitoring unit 7.

[0028] Figure 3 shows an embodiment in which the connectors 6 and the fastening part 9 are further combined in a component 13 that is integrated into the clamping element 3. The contacting is implemented on the component 13 with a projection 14, so that the connection to the cell monitoring unit 7 can be realized with solder contacts via the printed circuit board 12.

[0029] Fuel cell devices with such a fuel cell stack show their advantages particularly when used in a motor vehicle, since there are particular mechanical loads and vibrations. LIST OF REFERENCE SYMBOLS:

[0030] 1Fuel cell 2Electrolyte membrane 3First side of the membrane 4Electrode / anode 5Second side of the membrane 6Electrode / cathode 7Anode-side gas diffusion layer 8Cathode-side gas diffusion layer 9Bipolar plate fuel gas 10Bipolar plate cathode gas 11Fuel flow field 12Cathode gas flow field 13Catalyst particles 14Carrier particles 15Ionomer binder 16Catalyst paste 17Application agent 18Chamber 19Drying unit 20Film web 21Conveying direction 22Flow direction 23Electrolyte membrane feed device 24Web path 25Coil 26Cut-out 27Edge

Claims

1. A fuel cell stack (1) having a plurality of fuel cells (2) which are arranged in stacking direction, are clamped by means of clamping elements (3) and of which at least one, preferably each, has a cell voltage contact (6) for electrical connection to a cell monitoring unit (7), the at least one cell voltage contact (6) being mechanically secured by at least one of the clamping elements (3) with respect to the connection to the fuel cells (2), characterized in that each cell voltage contact (6) comprises a plug (8) for a plug connection, and in that the plugs (8) are preassembled on the clamping element (3), or in that each plug (8) is arranged on one of the fuel cells (2), and in that a mounting part (9) for the plugs (8) is accommodated in the clamping element (3) for the electrical connections to the cell monitoring unit (7).

2. The fuel cell stack (1) according to claim 1, characterized in that the clamping element (3) has bushings for cables routed to the cell monitoring unit (7).

3. The fuel cell stack (1) according to claim 1, characterized in that the plugs (8) are formed by sockets (10) and the mounting part (9) is formed by an injection-molded part (11)through which the electrical connections are routed to a printed circuit board (12) which is connected to the cell monitoring unit (7).

4. The fuel cell stack (1) according to claim 1, characterized in that the plugs (8) and the mounting part (9) are integrally combined in one component (13).

5. The fuel cell stack (1) according to any one of claims 1 to 4, characterized in that the fuel cells (2) are braced between end plates (4) by the clamping elements (3), which are formed as rigid tension bands.

6. A fuel cell device comprising a fuel cell stack (1) according to any one of claims 1 to 5.

7. A motor vehicle with a fuel cell device according to claim 6.