Heating device for an electrochemical cell stack, fuel cell stack and method for heating

Abstract

The invention relates to a heating device (12) for an electrochemical cell stack, wherein the heating device (12) comprises a heating layer (54) having a first side (56) and an opposite second side (58), a first thermal insulation layer (60) and a second thermal insulation layer (62), the first thermal insulation layer (60) is arranged on the first side (56) of the heating layer (54) and the second thermal insulation layer (62) is arranged on the second side (58) of the heating layer (54), and wherein the heating layer (54) has a central region (64) and an edge region (66), and the first thermal insulation layer (60) has a first gap (68) at the edge region (66) of the heating layer (54) and the second thermal insulation layer (62) has a second gap (70) at the central region (64) of the heating layer (54).

Description

Technical Field

[0001] This invention relates to a heating device for an electrochemical cell stack, wherein the heating device includes a heating layer and a first insulating layer. Furthermore, this invention relates to a fuel cell stack including the heating device and a method for heating components of the fuel cell stack. Background Technology

[0002] A fuel cell is an electrochemical cell that converts the chemical reaction energy of a continuously supplied fuel and oxidant into electrical energy. Therefore, a fuel cell is an electrochemical energy converter. In known fuel cells, hydrogen (H2) and oxygen (O2) are specifically converted into water (H2O), electrical energy, and heat.

[0003] Among these, proton exchange membrane (PEM) fuel cells are known. A PEM fuel cell has a centrally located membrane that is permeable to protons, i.e., hydrogen ions. Thus, the oxidant, particularly oxygen from the air, is spatially separated from the fuel, particularly hydrogen.

[0004] In addition, solid oxide fuel cells, also known as solid oxide fuel cells (SOFCs), are known. Compared with PEM fuel cells, SOFC fuel cells have higher operating temperatures and exhaust gas temperatures, especially for stationary applications.

[0005] A fuel cell has an anode and a cathode. Fuel is supplied to the anode of the fuel cell and catalytically oxidizes into protons in the process of releasing electrons; these protons then reach the cathode. The released electrons are extracted from the fuel cell and flow to the cathode through an external circuit.

[0006] An oxidant, particularly oxygen from the air, is supplied to the cathode of the fuel cell and reacts with protons by absorbing electrons from an external circuit to form water. The resulting water is then extracted from the fuel cell. The overall reaction is:

[0007] O2+4H + +4e — →2H2O

[0008] Here, a voltage is applied between the anode and cathode of the fuel cell. To increase the voltage, multiple fuel cells can be mechanically arranged sequentially into a fuel cell stack, also known as a fuel cell stack, and connected in series electrically.

[0009] Fuel cell stacks typically have end plates that press the individual fuel cells together and stabilize the stack. When no separate current collector is placed between the respective external fuel cell and the end plate, the end plate can also be used as the positive or negative electrode of the fuel cell stack for discharge.

[0010] Electrodes, namely the anode and cathode, and the diaphragm can be structurally combined into a single membrane electrode assembly (MEA), also known as a membrane electrode assembly.

[0011] In addition, fuel cell stacks have bipolar plates, also known as gas distributor plates. Bipolar plates are used to uniformly distribute fuel onto the anode and oxidant onto the cathode. Bipolar plates typically have a surface structure, such as a channel-like structure, for distributing fuel and oxidant onto the electrodes. The channel-like structure also serves to drain water produced during the reaction.

[0012] In addition, the bipolar plate can have a structure that guides the cooling medium through the fuel cell for heat dissipation.

[0013] In addition to guiding the medium for oxygen, hydrogen, and water, the bipolar plates also ensure surface electrical contact with the diaphragm.

[0014] In a fuel cell stack, the fuel cells are typically supplied with a medium, particularly hydrogen and oxygen, through supply or outlet channels arranged perpendicular to the fuel cell membrane. The medium is also exited through these supply or outlet channels. These channels connect to the fuel cell, particularly the bipolar plates, via ports (also called fluid connectors).

[0015] In a fuel cell stack, each fuel cell is typically connected to other fuel cells via a port. From the port, the medium is guided through the port passage into what is actually called the flow field, i.e., the active surface of the bipolar plate.

[0016] Fuel cell stacks typically consist of up to several hundred individual fuel cells stacked on top of each other as so-called sandwiches. Each fuel cell has a membrane electrode assembly and a bipolar plate half on the anode side and a half on the cathode side.

[0017] Supply or outlet channels, also known as medium channels, are typically located at the edges of the fuel cell stack and are used to distribute the medium supplied from outside the fuel cell stack and to outlet the medium again. Supply or outlet channels typically extend vertically through the individual bipolar plates and are created by notches that are arranged overlapping each other to form ports.

[0018] Fuel cell stacks are typically enclosed by two end plates. A current collector is usually arranged adjacent to each of these end plates. The end plates typically have port structures into which energy flows from within the fuel cell stack.

[0019] If a fuel cell stack is put into operation at temperatures below the freezing point of water, frozen water will occur, especially at the port structures. This will also happen when the fuel cell stack can be electrically heated by a heating layer, because the port structures can be thermally insulated by an insulating intermediate layer and thus isolated from the heating device.

[0020] The endplate areas in a fuel cell stack can become so cold, especially during startup at temperatures below 0°C, that it is essential to prevent the water in the fuel cell stack from freezing. This is further described in the article "Development of fuel cell system control for sub-zero environmental conditions" by Maruo et al., SAE Technical Paper, 2017, Published: 10.4171 / 2017-01-1189.

[0021] During startup of a cold fuel cell stack, the fuel cells contained within the stack heat up rapidly, and along with these fuel cells, the areas along the stack direction passing through the ports, or supply and exhaust channels, of the fuel cell stack also heat up. However, the endplates, due to their heat capacity, prevent the edge areas, especially the outer fuel cells, from rapid heating—that is, the rapid heating of the first and last fuel cells in the fuel cell stack, as well as the port structures on the endplates.

[0022] Heating elements, such as heating foils as described in US 9,525,185, can be provided in the endplate region. These heating elements can be arranged between the current collector and the endplate. To prevent the heating foils from primarily heating the endplate, according to US 9,525,185, a thermal barrier is provided between the heating foils and the endplate, such that heat flow proceeds from the heating foils to the current collector and thus towards the cold external fuel cells of the fuel cell stack, while the heat flow from the heating foils towards the endplate is interrupted. Therefore, there is also a risk that water may freeze in the port structure of the endplate during cold start, potentially impairing the medium supply or removal of the fuel cell stack, thereby reducing the efficiency and / or lifespan of the fuel cell stack. Summary of the Invention

[0023] A heating device for electrochemical cell stacks, particularly fuel cell stacks, is proposed, wherein the heating device includes a heating layer having a first side and an opposite second side, a first heat insulation layer and a second heat insulation layer, the first heat insulation layer being disposed on the first side of the heating layer and the second heat insulation layer being disposed on the second side of the heating layer, wherein the heating layer has a central region and an edge region, and the first heat insulation layer has a first notch at the edge region of the heating layer and the second heat insulation layer has a second notch at the central region of the heating layer.

[0024] Furthermore, a fuel cell stack is proposed, comprising at least the following layers in a given order: an end plate having a port structure, a heating device according to the invention, a current collector, a diaphragm electrode assembly, and a bipolar plate, wherein the heating device is arranged between the current collector and the end plate such that a first side of the heating layer points toward the end plate and a second side of the heating layer points toward the current collector.

[0025] The fuel cell stack preferably includes two end plates, two heating devices, and two current collectors, wherein one of the heating devices is preferably arranged between the end plates and the current collectors.

[0026] In a fuel cell stack, a first and / or second insulation layer may be disposed on and bonded to the heating layer, for example, by means of an adhesive. Alternatively, the first insulation layer may be disposed on and bonded to the endplate if necessary. Alternatively, the second insulation layer may be disposed on and bonded to the current collector if necessary. The current collector is preferably a planar component.

[0027] The heating device is preferably a one-piece or multi-piece planar component. Furthermore, the heating layer is preferably implemented as a foil. More preferably, the heating layer is constructed of a flexible material, which is particularly adaptable to the unevenness of the end plate or current collector surface and can adhere to that surface. The heating layer may be constructed of or comprise a conductive polymer, particularly polypropylene (PP) containing fillers such as graphite, which is heated by resistance.

[0028] The heating layer is, in particular, a surface heating element. The heating layer can be implemented as a resistance heating device, preferably as a separate wire or printed circuit board. Specifically, the resistance heating device has a heating wire between two electrically insulating foils, namely a first thermal insulation layer and a second thermal insulation layer, wherein these foils can have different thicknesses on different sides in order to control the heat flow.

[0029] Alternatively, the heating layer can be implemented using a conductive polymer, also known as a heat-induced thermoplastic, which preferably has a strength of 2 W / cm to 3 W / cm. 2 The conductive polymer is preferably processed into a heating layer by injection molding and / or foil stretching. Preferred matrix materials for the conductive polymer, also known as composite materials, are, for example, rigid polyethylene or high-density polyethylene (HDPE), polyphenylene sulfide (PPS), polypropylene (PP), polyvinylidene fluoride (PVDF), and mixtures thereof. Lower conductivity and higher resistance result in greater heat generation. The conductive polymer further preferably contains conductive filler materials such as conductive carbon black, graphite, and / or metal powders, thereby taking the form of granules.

[0030] The edge and central regions of the heating layer can be connected to a heating circuit, particularly a common heating circuit. Alternatively, the central and edge regions of the heating layer can be connected to different heating circuits.

[0031] Preferably, the central region of the heating layer is surrounded by the edge region of the heating layer. More preferably, if the active surface of the membrane electrode assembly is rectangular, the central region has a rectangular shape, or substantially replicates the geometry of the active surface of the membrane electrode assembly, i.e., the electrochemical active region. In particular, the edge region has the shape of a rectangular frame.

[0032] The first and / or second insulation layers are preferably implemented as coatings for heating layers, end plates, or current collectors. The first and / or second insulation layers preferably comprise ceramics and / or polymers, such as PVDF, polytetrafluoroethylene (PTFE), PP, polyethylene (PE), polyetheretherketone (PEEK), acrylates, and / or polystyrene. More preferably, the first and / or second insulation layers are composed of ceramics and / or polymers, such as PVDF, polytetrafluoroethylene (PTFE), PP, polyethylene (PE), polyetheretherketone (PEEK), acrylates, and / or polystyrene. Polymers are particularly preferred. Furthermore, The foil can be used as a first insulation layer and / or a second insulation layer. In particular, the first insulation layer and the second insulation layer are made of the same material.

[0033] Preferably, the first insulation layer has a first thickness, and the second insulation layer has a second thickness. Preferably, the first thickness and / or the second thickness is in the range of 19 μm to 500 μm.

[0034] In one embodiment, the second thickness deviates from the first thickness by no more than 30% relative to the first thickness.

[0035] Alternatively, the first and second thicknesses can be adjusted according to their positions on the heating layer. Therefore, materials for the first or second insulation layer can be present in the first and second gaps, respectively, each having a reduced or smaller thickness. Preferably, the first thickness of the first insulation layer is smaller in the edge region than in the central region, more preferably at least 30%, particularly at least 60%, and preferably no more than 95% smaller relative to the larger first thickness in the central region. The second thickness of the second insulation layer is preferably smaller in the central region than in the edge region, more preferably at least 30%, particularly at least 60%, and preferably no more than 95% smaller relative to the larger second thickness in the edge region. The thermal resistance of the first or second insulation layer is preferably linearly related to the first or second thickness. For example, a smaller first thickness and / or a smaller second thickness could be 19 μm, while a larger first thickness and / or a larger second thickness could be 60 μm.

[0036] The heating layer has an insulation layer on each of its two sides, wherein the first and second insulation layers preferably overlap by at least less than 30% of the total area of ​​the heating layer, more preferably less than 10%, particularly preferably less than 5%, and especially preferably not overlap. In particular, there is a gap between the first and second insulation layers or between the edge and central regions. The total area of ​​the heating layer can be understood as either the area of ​​the first side or the area of ​​the second side of the heating layer.

[0037] The heating layer preferably makes thermal contact with the end plate at the first notch, and with the current collector and, if necessary, with the fuel cell adjacent to the current collector in the fuel cell stack at the second notch, particularly with the membrane electrode assembly adjacent to the current collector. The membrane electrode assembly preferably comprises a polymer electrolyte membrane.

[0038] The first and / or second insulation layers can also be referred to as partial thermal barriers.

[0039] Preferably, relative to the total area of ​​the heating layer, the edge region occupies 5% to 30% of the heating layer, while the central region occupies 70% to 95% of the heating layer.

[0040] Preferably, the first notch of the first insulation layer substantially coincides with the edge region of the heating layer, and / or the second notch of the second insulation layer substantially coincides with the central region of the heating layer.

[0041] The basic overlap can be understood as follows: the first gap covers at least 90%, preferably at least 95%, especially 99% of the area of ​​the edge region, and relative to the total area of ​​the edge region, it does not exceed 10%, preferably not more than 5%, particularly preferably not more than 1%. The corresponding situation applies to the central area of ​​the second insulation layer and the heating layer.

[0042] Furthermore, the central region of the heating layer preferably coincides with the active surface of the membrane electrode assembly. The active surface is particularly understood as a region of the membrane electrode assembly in which, through the current structural design or geometry and current process parameters, the electrochemical reaction can actually take place on at least one side of the membrane. These parameters particularly relate to the membrane, the catalysts on both sides, the medium supply, the electronic contact of the catalyst layer, temperature, and humidification.

[0043] Preferably, the edge region of the heating layer includes ports. More preferably, the edge region of the heating layer includes all ports of the fuel cell stack, which in particular merge into the port structure of the endplate.

[0044] Preferably, the edge region of the heating layer substantially overlaps with or is larger than the port structure of the end plate. More preferably, the edge region of the heating layer is at least 10% larger than the end plate area occupied by the port structure, more preferably at least 30%, and particularly preferably at least 50%.

[0045] The end plate is preferably constructed of a polymer-metal composite material, especially to maintain a low heat capacity. If the end plate is constructed of a polymer-metal composite material, a portion of the end plate may form a first insulation layer.

[0046] Furthermore, the present invention relates to a method for heating components of a fuel cell stack according to the invention, wherein the port structure of the end plate is heated via an edge region of a heating layer, and the active surface of the membrane electrode assembly is heated via a central region of the heating layer. This can be understood as the heat flow between the port structure and the edge region being greater than the heat flow between the port structure and the central region, and vice versa. In particular, the port structure and the active surface are heated via the same heating layer. The membrane electrode assembly is especially a membrane electrode assembly arranged adjacent to a current collector.

[0047] Heating devices can also be used in heat exchangers and / or plate filters.

[0048] Heating of the fuel cell stack is optimized by means of the heating device according to the invention or by means of the fuel cell stack according to the invention and the method according to the invention, especially for the heat flow of auxiliary heating during cold start. The port structure of the end plate and the active area, especially the external fuel cell, can be optimally defrosted or heated by means of only a single heating layer. Accordingly, only one structural element is required for heating.

[0049] Energy requirements are minimized so that not only the active area of ​​the external fuel cell in the fuel cell stack, but also the port structure of the endplate is adequately heated, thus avoiding overheating of the endplate core and edge areas of the fuel cell through the heating layer.

[0050] This reduces or prevents water freezing in the endplates of fuel cells and fuel cell stacks, and consequently, damage to the media supply or evacuation of the fuel cell stack. This results in higher efficiency and increased lifespan for the fuel cell stack.

[0051] In the case of end plates made of polymer-metal composite materials for weight reduction, the heating device according to the invention is particularly advantageous because it reduces heat dissipation from the heated port or the heated port structure. Attached Figure Description

[0052] The embodiments of the present invention are described in detail with reference to the accompanying drawings and the following description.

[0053] The attached diagram shows:

[0054] Figure 1 Schematic diagram of a fuel cell stack;

[0055] Figure 2 Side view of a fuel cell stack according to the present invention;

[0056] Figure 3 :according to Figure 2 A top view of the first end plate of the fuel cell stack;

[0057] Figure 4 :according to Figure 2 A top view of the membrane electrode assembly stacked in a fuel cell;

[0058] Figure 5 :according to Figure 2 A top view of the first side of the first heating element of the fuel cell stack;

[0059] Figure 6 Top view of the second side of the first heating device;

[0060] Figure 7 :according to Figure 2 A top view of the second end plate of the fuel cell stack;

[0061] Figure 8 :according to Figure 2 A top view of the first side of the second heating device of the fuel cell stack; and

[0062] Figure 9 Top view of the second side of the second heating device.

[0063] In the following description of embodiments of the invention, the same or similar elements are designated by the same reference numerals, and repeated descriptions of these elements in individual cases are omitted. The accompanying drawings are for illustrative purposes only. Detailed Implementation

[0064] Figure 1 A schematic diagram of a fuel cell stack 4 having multiple fuel cells 3 is shown. Each fuel cell 3 has a membrane 23, two gas diffusion layers 1, an anode side 31, and a cathode side 32. The individual fuel cells 3 are separated from each other by bipolar plates 50, which may include a cooling plate 45.

[0065] The fuel cell stack 4, supplied with hydrogen 40, oxygen 42, and coolant 44, is enclosed by two end plates 48 and has a current collector 52. Different supply sections are separated from each other by seals 46. Heating devices 12 are arranged between the end plates 48 and the current collector 52.

[0066] Figure 2A side view of a fuel cell stack 4 is shown, which has a first end plate 47 and a second end plate 49.

[0067] In addition, the fuel cell stack 4 has two heating devices 12. A first heating device 11 is arranged between a first end plate 47 and a current collector 52. A second heating device 13 is arranged between a second end plate 49 and another current collector 52. Each heating device 12 has a heating layer 54, which has a first side 56 and a second side 58 opposite to the first side 56.

[0068] In addition, the heating device 12 includes a first heat insulation layer 60 and a second heat insulation layer 62. The first heat insulation layer 60 is disposed on the first side 56 of the heating layer 54, and the second heat insulation layer 62 is disposed on the second side 58 of the heating layer 54.

[0069] Each heating layer 54 has a central region 64 and an edge region 66. At the edge region 66 of each heating layer 54, a first heat insulation layer 60 has a first notch 68, and at the central region 64 of each heating layer 54, a second heat insulation layer 62 has a second notch 70. The first notch 68 coincides with the edge region 66, and the second notch 70 coincides with the central region 64.

[0070] The first heat insulation layer 60 has a first thickness 74, and the second heat insulation layer 62 has a second thickness 76, wherein the first thickness 74 is equal to the second thickness 76 in the illustrated embodiment.

[0071] In the fuel cell stack 4, bipolar plates 50 and membrane electrode assemblies 80 are stacked between current collectors 52. One of the bipolar plates 50, membrane electrode assemblies 80, and heating layers 54 has a port 72 that guides through the fuel cell stack 4 and merges into the port structure 78 of the first end plate 47.

[0072] Therefore, the heating device 12 is arranged between the collector 52 and the corresponding end plate 48, such that the first side 56 points to the end plate 48 and the second side 58 points to the collector 52.

[0073] In addition, each of the diaphragm electrode assemblies 80 has an active surface 82, wherein the central region 64 of the heating layer 54 coincides with the active surface 82 of the diaphragm electrode assembly 80.

[0074] The port structure 78 of the first end plate 47 can be heated by means of the edge region 66 of the heating layer 54 of the first heating device 11, and the active surface 82 of the adjacent diaphragm electrode assembly 80 can be heated by means of the central region 64 of the heating layer 54 of the first heating device 11. The first notch 68 of the first heat insulation layer 60 is located at the edge region 66 of the heating layer 54, while the second notch 70 of the second heat insulation layer 62 is located at the central region 64 of the heating layer 54.

[0075] Figure 3 Showing according to Figure 2 A top view of the first end plate 47, the second end plate having a port structure 78.

[0076] Figure 4 Showing according to Figure 2 A top view of the membrane electrode assembly 80 of the fuel cell stack 4, which includes a port 72 and an active surface 82.

[0077] Figure 5 Showing according to Figure 2 A top view of the first side 56 of the first heating device 11. The central region 64 is covered by the first heat insulation layer 60, while the edge region 66 of the heating layer 54 is exposed and can emit heat flow, thereby heating the port structure 78 of the first end plate 47.

[0078] Figure 6 Showing according to Figure 2 A top view of the second side 58 of the first heating element 11 of the fuel cell stack 4. Port 72 is located in the edge region 66 of the heating layer 54, which is covered by the second insulation layer 62.

[0079] The second notch 70 is located in the central region 64 of the heating layer 54, so that the heating layer 54 can emit heat in the central region 64, thereby heating the active surface 82 of the adjacently arranged diaphragm electrode assembly 80.

[0080] Figure 7 A top view of the second end plate 49 is shown.

[0081] Figure 8 Showing according to Figure 2 A top view of the first side 56 of the second heating device 13, which is arranged on the second end plate 49, and... Figure 9 Showing according to Figure 2 A top view of the second side 58 of the second heating device 13. Figure 8 Basically corresponding to Figure 5 ,and Figure 9 Basically corresponding to Figure 6 However, the difference is that, unlike the first heating device 11, the second heating device 13 does not have a port 72.

[0082] The invention is not limited to the embodiments and aspects highlighted herein. Rather, various modifications are possible within the scope of the claims, and these modifications are all within the capabilities of those skilled in the art.

Claims

1. A heating device (12) for stacking electrochemical cells, wherein, The heating device (12) includes a heating layer (54) having a first side (56) and an opposite second side (58), a first heat insulation layer (60) and a second heat insulation layer (62), wherein the first heat insulation layer (60) is disposed on the first side (56) of the heating layer (54) and the second heat insulation layer (62) is disposed on the second side (58) of the heating layer (54), wherein the heating layer (54) has a central region (64) and an edge region (66), and the first heat insulation layer (60) has a first notch (68) at the edge region (66) of the heating layer (54) to expose the edge region (66) of the heating layer (54), and the second heat insulation layer (62) has a second notch (70) at the central region (64) of the heating layer (54) to expose the central region (64) of the heating layer (54).

2. The heating device (12) according to claim 1, characterized in that, The first notch (68) of the first heat insulation layer (60) substantially coincides with the edge region (66) of the heating layer (54) and / or the second notch (70) of the second heat insulation layer (62) substantially coincides with the central region (64) of the heating layer (54).

3. The heating device (12) according to claim 1 or 2, characterized in that, The edge region (66) of the heating layer (54) includes a port (72).

4. The heating device (12) according to claim 1 or 2, characterized in that, Relative to the total area of ​​the heating layer (54), the edge region (66) of the heating layer (54) occupies 10% to 30% respectively, while the central region (64) of the heating layer (54) occupies 70% to 90% respectively.

5. The heating device (12) according to claim 1 or 2, characterized in that, The heating layer (54) is constructed of a flexible material.

6. The heating device (12) according to claim 1 or 2, characterized in that, The heating layer (54) comprises a conductive polymer.

7. A fuel cell stack (4) comprising at least the following layers in a given order: An end plate (48) having a port structure (78), a heating device (12) according to any one of claims 1 to 6, a collector (52), a diaphragm electrode assembly (80), and a bipolar plate (50), wherein, The heating device (12) is arranged between the collector (52) and the end plate (48) such that the first side (56) of the heating layer (54) points to the end plate (48) and the second side (58) of the heating layer (54) points to the collector (52).

8. The fuel cell stack (4) according to claim 7, characterized in that, The central region (64) of the heating layer (54) substantially overlaps with the active surface (82) of the diaphragm electrode assembly (80).

9. The fuel cell stack (4) according to claim 7 or 8, characterized in that, The end plate (48) is constructed of a polymer-metal composite material.

10. A method for heating components of a fuel cell stack (4), said method being carried out using a fuel cell stack according to any one of claims 7 to 9, wherein, The port structure (78) of the end plate (48) is heated by means of the edge region (66) of the heating layer (54), and the active surface (82) of the diaphragm electrode assembly (80) is heated by means of the central region (64) of the heating layer (54).

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