Fuel cell stack and fuel cell system

Abstract

Fuel cell stack (12) for a fuel cell system, comprising: a plurality of fuel cells (14) arranged in the stacking direction between two end plates (16); a carrier plate (30) with at least one signal input (31) for receiving a voltage signal from at least one fuel cell (14); a voltage measuring unit (33) arranged on the carrier plate (30) and connected to the at least one signal input (31); at least one cooling element (34) in thermal contact with the voltage measuring unit (33), wherein the at least one cooling element (34) has a first section (35) designed to absorb heat from the voltage measuring unit (33) and a second section (36) designed to dissipate heat, characterized in that the voltage measuring unit (33) is traversed by at least one cavity (37), wherein the cooling element (34) is arranged at least in sections in the at least one cavity (37) and is designed as a mounting structure for fastening the voltage measuring unit (33) to the carrier plate (30).

Description

[0001] The invention relates to a fuel cell stack, in particular a fuel cell stack with cooling for an integrated voltage measuring unit, and a fuel cell system with such a fuel cell stack.

[0002] Fuel cells utilize the chemical conversion of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells have a membrane electrode assembly (MEA) with a membrane electrode unit as their core component. The membrane is formed by a proton-conducting membrane (PEM) with catalytic electrodes arranged on both sides. The membrane separates the anode compartment associated with the anode and the cathode compartment associated with the cathode, electrically insulating them. Gas diffusion layers can also be arranged on the sides of the electrodes not facing the membrane.

[0003] During operation of the fuel cell, a hydrogen-containing fuel is fed to the anode, where an electrochemical oxidation of H2 to H + with the release of electrons. A water-bound or water-free transport of the protons H occurs across the electrolytic membrane. + from the anode compartment to the cathode compartment. The electrons provided at the anode are conducted to the cathode via an electrical line. An oxygen-containing operating medium is supplied to the cathode, so that a reduction of O2 to O 2- by absorbing electrons. These oxygen anions react in the cathode compartment with the protons transported across the membrane to form water.

[0004] A state-of-the-art fuel cell stack is Fig. 1. This fuel cell stack 12 has a plurality of individual cells 14 stacked in the stacking direction, two end plates 16, and tension elements 18. The individual cells 14 each have a membrane electrode assembly 20 with a proton-conducting membrane 22 (polymer electrolyte membrane) and electrodes (anode and cathode; not shown) arranged on both sides of the membrane. The electrodes are each arranged between the membrane 22 and a gas diffusion layer 24. The electrodes are either coated on both sides of the membrane 22 or connected to the gas diffusion layers 24 to form so-called gas diffusion electrodes.

[0005] Each membrane electrode assembly 20 is arranged between two bipolar plates 26. The bipolar plates 26 supply the membrane electrode assemblies 20 with the operating media through the gas diffusion layers 24 and generally have suitable channels for this purpose. The fuel cell stack 12 is supplied with its operating media, i.e., the anode operating gas (e.g., hydrogen), the cathode operating gas (e.g., air), and the coolant, via main supply channels that extend through the stack 12 in its entire stacking direction. The main supply channels are formed by superimposing operating media passages arranged in the MEA 20 and the bipolar plates 26. Starting from these operating media passages, the operating media are fed to the individual cells via the bipolar plates.For each operating medium, at least two such main supply channels are provided, namely one for supplying and one for discharging the respective operating medium. Each bipolar plate 26 further electrically connects the two adjacent MEAs 20 and connects them in series. The two terminal bipolar plates 26, also referred to as monopolar plates, are designed to supply an operating medium on one side only to a membrane electrode assembly 20, which is also only connected on one side.

[0006] Between the membrane electrode units 20 and the bipolar plates 26, Fig. 1, seals are arranged which seal the anode and cathode compartments to the outside and prevent the operating media from escaping from the fuel cell stack 12. These seals are provided on the membrane electrode assemblies 20, the bipolar plates 26, or these two components.

[0007] To seal the stack and ensure electrical contact between bipolar plates 26 and membrane electrode assemblies 20, the fuel cell stack 12 is pressed together before commissioning. Typically, the two end plates 16 arranged at the ends of the fuel cell stack 12 are connected by means of tension elements 18. The fuel cell stack 12 is pressed together by introducing tensile forces into the end plates 16 via the tension elements 18. As an alternative to using tension elements 18, spring elements (not shown) can be arranged between one of the end plates 16 and a fixed spring plate or a housing (not shown).

[0008] The fuel cell stack 12 can further comprise a voltage measuring unit (“cell voltage monitor - CVM”) for monitoring the stack voltage as well as the individual voltage of the fuel cells 14. Such a voltage measuring unit can also perform control functions, such as active or passive balancing between individual fuel cells 14. The voltage measuring unit is preferably arranged on one of the end plates 16 or on the spring plate (not shown). Alternatively, the voltage measuring unit is arranged on a circuit board (also not shown) that extends parallel to a side surface and parallel to the stacking direction of the fuel cell stack 12. The circuit board can comprise contact elements for contacting individual fuel cells 14.A fuel cell stack with such a laterally arranged circuit board with integrated voltage measuring unit for monitoring the cell voltages is disclosed, for example, in DE 10 2009 035 500 A1.

[0009] Due to the heat sensitivity of the electronics used in conventional voltage measurement units, the likelihood of malfunctions increases at higher temperatures. Since heat-resistant electronics are significantly more expensive, the voltage measurement unit is typically located outside the stack package. Alternatively, the stack package is made larger overall to ensure sufficient air cooling of the voltage measurement unit. Both of these options result in increased space requirements for the fuel cell stack.

[0010] It is known from the prior art to use the coolant flow through the main supply channels or the bipolar plates to cool the electronics of a voltage measuring unit. For example, JP 2012 - 227 094 A discloses a fuel cell stack in which voltage measuring units are arranged adjacent to coolant access openings on some of the MEAs. Leaks in the stack can quickly and adversely affect the electronics.

[0011] JP 2014-123 524 A describes a fuel cell system with a fuel cell stack arranged between two end plates. Heat sinks are arranged transversely to the stack direction, each of which contains a control unit arranged in a housing. A voltage measuring unit is arranged on the heat sink, which is traversed by coolant channels arranged between fins and fed by coolant lines. The heat sinks are connected to the end plates via screws.

[0012] JP 2011-014 400 A describes a fuel cell system with a fuel cell stack. A voltmeter comprises a voltmeter and a support element and is attached to a spring plate of the fuel cell stack via the support element. Coolant lines pass through a support plate of the support element and are traversed by a coolant that is either branched off from the main cooling circuit of the fuel cell stack or cooled in isolation from it by a Peltier element.

[0013] The invention is based on the object of overcoming the disadvantages of the prior art and providing a fuel cell stack with an integrated voltage measuring unit, which enables reliable cooling of the voltage measuring unit and compact stack designs.

[0014] This object is achieved by a fuel cell stack having the features of claim 1 and by a fuel cell system having the features of claim 6. It comprises a plurality of fuel cells arranged in the stacking direction between two end plates, wherein it further comprises a carrier plate with at least one signal input for receiving a voltage signal from at least one fuel cell. Preferably, one of the end plates or a spring plate of the fuel cell stack is designed as a carrier plate or the carrier plate is mounted on these stack components. Alternatively, the carrier plate extends parallel to a side surface and parallel to the stacking direction of the fuel cell stack, for example in the form of a side panel.The at least one signal input is preferably connected to a shunt resistor, which is arranged, for example, between two fuel cells, and preferably receives a signal proportional to the current flowing through the shunt.

[0015] According to the invention, a voltage measuring unit is arranged on the carrier plate and connected to the at least one signal input. The voltage measuring unit is further configured to read the at least one voltage signal received via the at least one signal input. For this purpose, the voltage measuring unit has at least one input for receiving at least one voltage signal. Such voltage measuring units (cell voltage monitors - CVMs) are known from the prior art. The structure and interconnection of such voltage measuring units are not the subject of the invention, so a further description thereof is omitted here.

[0016] The fuel cell stack according to the invention further comprises at least one cooling element in thermal contact with the voltage measuring unit, which cooling element has a first section designed to absorb heat from the voltage measuring unit and a second section designed to dissipate heat. According to the invention, the cooling element, in particular also its second section for dissipating absorbed heat, is an integral component of the fuel cell stack. In the fuel cell stack according to the invention, the voltage measuring unit is advantageously not integrated into the layered structure of the stack, but rather arranged on a carrier plate designed as an end plate, spring plate, or side panel. This advantageously ensures electrical insulation and cooling of the voltage measuring unit.

[0017] According to the invention, the voltage measuring unit is traversed by at least one cavity, and at least the first section of the at least one cooling element is arranged in this cavity. The cavity particularly preferably extends in an orientation that is at least substantially parallel to the carrier plate. The extension of the at least one cooling element through the voltage measuring unit enables efficient cooling while simultaneously requiring minimal installation space. The voltage measuring unit preferably has at least two such cavities.

[0018] Likewise preferably, the voltage measuring unit is attached to the fuel cell stack, at least also by a positive fit and / or a frictional fit between the at least one cooling element and the at least one cavity, in particular an inner wall of the cavity. The at least one cavity thus serves simultaneously to accommodate mounting structures, for example mounting bolts, and for cooling. The mounting structures are preferably attached to the carrier plate and allow, for example, the voltage measuring unit to be pushed on, wherein they are inserted into the at least one cavity. In this embodiment, the cooling of the voltage measuring unit therefore requires almost no additional installation space.

[0019] According to a preferred embodiment of the invention, the at least one cooling element is designed as a thermally conductive solid body. The cooling element preferably has a thermal conductivity that is greater than the thermal conductivity of the carrier plate and / or the voltage measuring unit. Particularly preferably, the cooling element is made of a highly thermally conductive metal, such as copper or aluminum.

[0020] According to this embodiment, at least the second section of the at least one cooling element is in thermal contact with a Peltier element. The Peltier element is designed to cool the at least one cooling element, preferably all cooling elements, and is preferably supplied with energy for this purpose by the fuel cell stack. The Peltier element is preferably attached to the carrier plate or formed as part of an additional component, for example a housing element, of the fuel cell stack. This embodiment therefore only requires the formation of mounting structures for a voltage measuring unit made of thermally conductive material and the arrangement of an additional Peltier element to ensure autonomous cooling of the voltage measuring unit.

[0021] According to a further embodiment of the fuel cell stack according to the invention, the at least one cooling element is designed as a coolant line. A first section of the at least one coolant line extends through the at least one cavity, and a second section of the at least one coolant line has at least one coolant connection. The absorbed heat is thus preferably dissipated by discharging a heated coolant, for example, to an external heat exchanger. This embodiment therefore only requires the formation of mounting structures for the voltage measuring unit in the form of hollow fluid lines and their connection to a coolant circuit for cooling the voltage measuring unit.

[0022] The coolant circuit for the voltage measuring unit is preferably designed as a bypass or, alternatively, independently of the main coolant circuit of the fuel cell stack. Particularly preferably, the voltage measuring unit is cooled via a coolant tap at the stack inlet of the main coolant circuit, and the heated coolant is returned via a connection at the stack outlet of the main coolant circuit. The advantage of such a coolant bypass to the stack lies in particular in the very short coolant lines. Particularly preferably, the voltage measuring unit has two cavities and two coolant lines extending through these cavities. Each of the two coolant lines has a coolant connection on a first side of the voltage measuring unit. On a second side of the voltage measuring unit, the two coolant lines are fluidly connected to one another.

[0023] According to an example not covered by the invention, the at least one cooling element is designed as a cooling plate. Preferably, at least the first section of the cooling plate is arranged between the carrier plate and the voltage measuring unit. Likewise preferably, the second section extends laterally beyond the voltage measuring unit. Alternatively, the cooling plate is arranged between the voltage measuring unit and a further component of the fuel cell stack, for example a housing part. Likewise preferably, the cooling plate has an angled second section, which particularly preferably extends outwards through the further component (housing part). In this embodiment, the second section is preferably designed as a heat exchanger and has, for example, an enlarged surface.

[0024] In a preferred variant of this example, the cooling plate is in thermal contact with a Peltier element, at least in the second section. The Peltier element is designed to cool the cooling plate and is preferably supplied with energy for this purpose by the fuel cell stack. Furthermore, the cooling plate preferably has a thermal conductivity that is greater than the thermal conductivity of the carrier plate and / or the voltage measuring unit. Particularly preferably, the cooling plate is made of a highly thermally conductive metal, such as copper or aluminum. This embodiment therefore only requires the arrangement of a thin cooling plate between the voltage measuring unit and the carrier plate or the further component and the arrangement of an additional Peltier element to ensure autonomous cooling of the stack.The Peltier element is preferably attached to the carrier plate or formed as part of an additional component, for example a housing element, of the fuel cell stack.

[0025] In a likewise preferred variant of this example, the cooling plate is traversed by at least one coolant channel and has at least one coolant connection in the second section for supplying coolant into the at least one coolant channel. Particularly preferably, the coolant channels are formed in a meandering manner within the cooling plate. The coolant channels can be formed as pipes cast into the cooling plate or as fully embedded cavities of a monolithic cooling plate. Likewise preferably, the coolant channels are recesses formed, for example, engraved, on one side of the cooling plate, which are only sealed when the voltage measuring unit is applied to the cooling plate.

[0026] The invention also relates to a fuel cell system with a fuel cell stack as described above. The fuel cell system preferably has an anode supply, a cathode supply, and a main coolant circuit for supplying the fuel cell stack with its operating media. The coolant circuit for the at least one cooling element of the fuel cell stack designed to cool the voltage measuring unit is preferably designed to be independent of the main coolant circuit. Alternatively, the coolant circuit for the at least one cooling element designed to cool the voltage measuring unit is designed as a bypass of the main coolant circuit. Particularly preferably, the voltage measuring unit is cooled via a coolant tap at the stack inlet of the main coolant circuit, and the heated coolant is returned via a connection at the stack outlet of the main coolant circuit.The advantage of such a coolant bypass to the stack lies in the very short coolant lines.

[0027] Further preferred embodiments of the invention emerge from the remaining features recited in the subclaims. The various embodiments of the invention recited in this application can be advantageously combined with one another, unless otherwise stated in individual cases.

[0028] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show: Fig. 1 shows a representation of a fuel cell stack according to the prior art; Fig. 2 (A) a plan view and (B) a cross section through a support plate of a fuel cell stack according to a first embodiment; Fig. 3 (A) a plan view and (B) a cross section through a support plate of a fuel cell stack according to a second embodiment; Fig. 4 (A) a plan view and (B) a cross-section through a support plate of a fuel cell stack not covered by the invention; and Fig. 5 (A) a plan view and (B) a cross section through a support plate of a fuel cell stack not covered by the invention.

[0029] Fig. 1 shows a fuel cell stack 10 according to the prior art and has already been explained in the introduction.

[0030] The Fig. 2 to Fig. 5 each show (A) a plan view and (B) a cross-section through a carrier plate 30 of a fuel cell stack 12, as shown for example in Fig. 1 shown.

[0031] The carrier plate 30 can be one of the Fig. 1 or be mounted on one of them. Alternatively, the support plate 30 can be designed as an additional spring plate (“spring cap”), which is fixed substantially plane-parallel to one of the end plates 16 and is connected to it via spring elements. Furthermore, the support plate 30 can also be designed as a side panel of the Fig. 1, which is aligned substantially parallel to the tension elements 18 shown.

[0032] The Fig. 2 to Fig. 5 have a plurality of signal inputs 31 for receiving voltage signals from the plurality of fuel cells 14 of the fuel cell stack 12. As shown in the Fig. 2 to Fig. 5, the signal inputs are each a plurality of contact metallizations of a circuit carrier, which are arranged in the edge region of the carrier plate 30.

[0033] Furthermore, a voltage measuring unit 33 is arranged on each of the support plates 30. This voltage measuring unit is a cell voltage meter for detecting the voltage of a plurality of fuel cells 14 of the fuel cell stack 12. The voltage measuring unit 33 is connected to the circuit carrier of the signal inputs 31 via a broadband bus connection 32 and receives the voltage signals of the fuel cells 14 for further processing.

[0034] As can be seen particularly in the cross sections of the support plate 30 in the Fig. 2 (B) to Fig. 5 (B), the voltage measuring unit 33 further comprises two cavities 37 extending through the voltage measuring unit 33 in a longitudinal direction of the voltage measuring unit 33 parallel to the support plate 30. These cavities 37 are generally used to mount the voltage measuring unit 33 on the support plate 30 by sliding them onto mounting bolts 43 that are attached to the support plate 30 and extend parallel to its surface.

[0035] Fig. Figure 2 shows a first embodiment of a support plate 30 of a fuel cell stack 12 according to the invention, wherein the mounting bolts 43 are designed as cooling elements 34 made of a highly thermally conductive copper alloy. A first section 35 of the cooling elements 34 is arranged within the cavities 37 and is designed to absorb heat from the voltage measuring unit 33. A second section 36 of the cooling elements 34 extends in the lateral direction beyond the dimension of the voltage measuring unit 33. This projection 36 of the cooling elements 34 is in thermal contact with a Peltier element 38 and is thus designed to release or dissipate heat. The Peltier element is preferably designed as a component of an additional housing part (not shown) to be placed on the support plate 30 and is therefore only visible as a projection in the top view of the Fig. 2 (A). The Peltier element 38 is preferably electrically powered by the fuel cell stack 12.

[0036] Fig. 3 shows a second embodiment of a support plate 30 of a fuel cell stack 12 according to the invention, wherein the mounting bolts 43 are replaced by cooling elements 34 in the form of coolant lines 39. A first section 35 of the coolant lines 39 is arranged within the cavities 37 and is designed to absorb heat from the voltage measuring unit 33. Second sections 36 of the coolant lines 39 extend in the lateral direction on both sides beyond the dimension of the voltage measuring unit 33. On one side of the voltage measuring unit 33, the coolant lines 39 in the second section 36 have coolant connections 40 for connecting a coolant supply to the lines 39. On the opposite side of the voltage measuring unit 33, the lines 39 in the second section 36 are connected to one another.

[0037] Fig. 4 shows a support plate 30 of a fuel cell stack 12, which is not covered by the invention. A cooling plate 41 is arranged as a cooling element 34 and independently of the mounting bolts 43 on the support plate 30. The cooling plate 41 is made of a highly thermally conductive copper alloy. At least a first section 35 of the cooling plate 41 is arranged between the voltage measuring unit 33 and the support plate 30 and is designed to absorb heat from the voltage measuring unit 33. A second section 36 of the cooling plate 41 projects laterally beyond the voltage measuring unit 33 and is in thermal contact with a Peltier element 38. The Peltier element is designed to cool the cooling plate 41 and is preferably electrically powered by the fuel cell stack 12 for this purpose.

[0038] Fig.5 shows a support plate 30 of a fuel cell stack 12, which is not covered by the invention. Again, a cooling plate 41 is arranged as a cooling element 34 and independently of the mounting bolts 43 on the support plate 30. At least in a first section 35 arranged between the voltage measuring unit 33 and the support plate 30, the cooling plate 41 has a plurality of meandering coolant channels 42. The channels 42 are completely enclosed by the cooling plate 41 made of die-cast aluminum and manufactured, for example, using lost cores. The plurality of channels 42 are connected to one another and to two coolant connections 40 arranged in a second section 36 of the cooling plate 41, so that a coolant circuit is formed through the cooling plate 41.By means of a coolant conveyed through the coolant channels 42, heat is absorbed by the voltage measuring unit 33 in the first section 35 and removed from the voltage measuring unit 33 in the second section 36 via one of the coolant connections 40, for example in the direction of an external heat exchanger.

Claims

[1] Fuel cell stack (12) for a fuel cell system, comprising: a plurality of fuel cells (14) arranged in the stacking direction between two end plates (16); a carrier plate (30) with at least one signal input (31) for receiving a voltage signal from at least one fuel cell (14); a voltage measuring unit (33) arranged on the carrier plate (30) and connected to the at least one signal input (31); at least one cooling element (34) in thermal contact with the voltage measuring unit (33), wherein the at least one cooling element (34) has a first section (35) designed to absorb heat from the voltage measuring unit (33) and a second section (36) designed to dissipate heat, characterized by , that the voltage measuring unit (33) is traversed by at least one cavity (37), wherein the cooling element (34) is arranged at least in sections in the at least one cavity (37) and is designed as a mounting structure for fastening the voltage measuring unit (33) to the carrier plate (30). [2] Fuel cell stack (12) according to claim 1, wherein the at least one cooling element (34) is formed from a thermally conductive material and is in thermal contact with a Peltier element (38) in the second section (36). [3] Fuel cell stack (12) according to claim 1 or 2, wherein the at least one cooling element (34) is designed as a coolant line (39) and has at least one coolant connection (40) in the second section (36). [4] Fuel cell stack (12) according to one of claims 1 to 3, wherein the voltage measuring unit (33) is fastened to the fuel cell stack (12) by positive and / or frictional engagement of the at least one cooling element (34) and the at least one cavity (37). [5] Fuel cell stack (12) according to claim 2, wherein the thermally conductive material is copper and / or the Peltier element (38) is formed as part of a housing element of the fuel cell stack (12). [6] Fuel cell system with a fuel cell stack (12) according to one of claims 1 to 5.

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