Electrochemical cell with support structure

Abstract

Electrochemical cell (2) with a membrane electrode arrangement (6) arranged between two bipolar plates (10). The membrane electrode arrangement (6) has a membrane (5) coated with two electrodes (7, 8) and a frame structure (15). The frame structure (15) encloses the coated membrane (5) at its periphery. A sealing bead (101) is formed on at least one of the bipolar plates (10), which sealingly interacts with the frame structure (15). Adjacent to the sealing bead (101), a support structure (30) is arranged between at least one of the bipolar plates (10) and the frame structure (15).

Description

[0001] The present invention relates to an electrochemical cell with a support structure. State of the art

[0002] Fuel cells, as galvanic cells, convert continuously supplied fuel and oxidant into electrical energy and water through redox reactions at an anode and cathode. Electrolysis cells, for example, are used to electrolytically produce hydrogen and oxygen from water. Fuel cells and electrolysis cells are electrochemical cells and can be constructed in very similar ways: They comprise a membrane electrode assembly arranged between two bipolar plates. The membrane electrode assembly has a membrane coated with two electrodes and a frame structure. The frame structure encloses the coated membrane around its periphery. Sealing beads are formed on the bipolar plates, which interact with the frame structure to form a seal.

[0003] Particularly in a non-active region of the electrochemical cell, harmful fluttering of the frame structure between two bipolar plates can occur. The object of the present invention is to prevent this fluttering. Disclosure of the invention

[0004] For this purpose, the electrochemical cell comprises a membrane electrode assembly arranged between two bipolar plates. The membrane electrode assembly comprises a membrane coated with two electrodes and a frame structure. The frame structure encloses the coated membrane at its periphery. A sealing bead is formed on at least one of the bipolar plates, which sealingly interacts with the frame structure. Adjacent to the sealing bead, a support structure is arranged between at least one of the bipolar plates and the frame structure.

[0005] The support structure thus prevents harmful fluttering of the frame structure between the bipolar plates. This significantly reduces the risk of cracks forming in the frame structure, which usually consists of one or two thermoplastic films. For this purpose, the support structure is arranged very close to the sealing bead, which represents a natural support for the frame structure. At the same time, the sealing bead naturally has an edge that acts as a support surface for the frame structure; if the frame structure were to flutter, it would be exposed to an increased risk of cracks forming, especially in the area of the edge. However, the support structure adjacent to the sealing bead prevents harmful fluttering and thus greater expansion of the frame structure in the area of the edge. An adjacent arrangement is defined as a distance of less than 20 mm.

[0006] The support structure can be formed on the bipolar plate or on the membrane electrode assembly, or be designed as an insert, or as a combination of these features. If necessary, the bipolar plate and / or the membrane electrode assembly must be geometrically adapted to the support structure; the support structure is thus designed in such a way that it does not itself lead to tearing or perforation of the membrane electrode assembly or bipolar plate.

[0007] If the support structure is formed on the frame structure, this can be done as follows, for example: - Gluing one or more materials onto the frame structure - Applying or inserting a (different or the same) material between the layers of the frame structure - Local increase in the position of the frame structure - Local increase in the thickness of the adhesive layer between two layers of the frame structure.

[0008] Typically, the frame structure consists of two bonded layers or films, in which the catalyst-coated membrane is enclosed. Therefore, it is particularly preferred to locally increase the layer thickness of the adhesive between the two films, thereby forming the support structure.

[0009] The support structure can also be formed by locally modifying the material properties of the frame structure and / or bipolar plate. Particularly preferred embodiments are: - Local use of a mechanically more stable adhesive, - Local use of a mechanically more stable layer or film.

[0010] As a result, the more stable adhesive or layer does not deform as much as its surroundings when the electrochemical cell is pressed, thus forming the protruding support structure.

[0011] In advantageous further developments, at least one support structure is arranged on each side of the frame structure. The frame structure is thus supported on both sides by the two support structures, effectively preventing flutter in both directions.

[0012] Particularly preferably, the support structure is arranged adjacent to at least two sealing beads. The sealing beads are either sealing beads for media connections or perimeter sealing beads on the circumference of the active region of the electrochemical cell. Especially between two sealing beads, there is usually a comparatively large area where the frame structure is not supported, especially if this area has a weld seam of the bipolar plate. Metallic bipolar plates are manufactured from two monoplates, usually welded together. Especially directly in the area of the weld seam, it is structurally impossible for the support structure to be formed on the bipolar plate. In such cases, the support structure is advantageously formed on the membrane electrode assembly or designed as an insert.

[0013] In advantageous further developments, the sealing beads are arranged mirror-symmetrically on both sides of the frame structure. The frame structure is thus supported in the same way on both sides. The support structure is arranged adjacent to at least two sealing beads on each side of the frame structure. Short description of the drawings

[0014] In the following, exemplary embodiments of the invention are described in more detail with reference to the accompanying drawings. They show: Fig. 1 a basic structure of an electrochemical cell designed as a fuel cell in cross section, with only the essential areas shown. Fig. 2 a perspective, schematic view of a bipolar plate, showing only the essential areas. Fig. 3 a cross-sectional view of a membrane electrode assembly according to the prior art, with only the essential areas being shown. Fig. 4 is a cross-sectional view of an electrochemical cell according to the prior art, with only the essential areas shown. Fig. 5 is a perspective, schematic view of a bipolar plate according to an embodiment of the invention, with only the essential areas being shown. Fig. 6 a cross-sectional view of an electrochemical cell according to the invention, with only the essential areas being shown.

[0015] In Fig. Figure 1 shows the basic structure of an electrochemical cell 2 designed as a fuel cell, particularly in the so-called active region. The principle of fuel cells 2 is that electrical energy or electrical current is generated by means of an electrochemical reaction. Hydrogen as a gaseous fuel is fed to an anode 7, and the anode 7 forms the negative pole. A gaseous oxidizing agent, namely air with oxygen, is fed to a cathode 8, i.e. the oxygen in the air provides the necessary gaseous oxidizing agent. Reduction (electron absorption) takes place at the cathode 8. Oxidation (electron loss) takes place at the anode 7.

[0016] A fuel cell unit 1 is a series connection of several fuel cells 2 and is often referred to as a fuel cell stack 1. The fuel cell stack 1 is created by stacking several individual cells 2 in the z-direction.

[0017] The electrochemical cell 2 comprises a membrane 5, which is arranged between the anode 7 and the cathode 8. The anode 7 and the cathode 8 are layered or disc-shaped. The membrane 5 functions as an electrolyte, catalyst carrier and separator for the reaction gases. The membrane 5 also functions as an electrical insulator and prevents an electrical short circuit between the anode 7 and the cathode 8. The membrane 5 is essentially impermeable to the reaction gases oxygen O2 and hydrogen H2 as well as water, i.e. it blocks the flow of oxygen, hydrogen and water between a gas space 31 at the anode 7 (in the case of a fuel cell with hydrogen as fuel) and the gas space 32 at the cathode 8 (in the case of a fuel cell with air or oxygen as the oxidizing agent). The proton conductivity of the membrane 5 increases with increasing temperature and increasing water content.

[0018] On both sides of the membrane 5, each facing the gas spaces 31, 32, are the electrodes 7, 8, serving as the anode 7 and cathode 8. A unit comprising the membrane 5 and the electrodes 7, 8 is referred to as a membrane electrode assembly (MEA). The electrodes 7, 8 are, for example, platinum-containing carbon particles bonded to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride), and / or PVA (polyvinyl alcohol) and hot-pressed into microporous carbon fiber, glass fiber, or plastic mats.

[0019] A gas diffusion layer 9 (GDL) lies on the anode 7 and the cathode 8. The gas diffusion layer 9 on the anode 7 of an electrochemical cell 2 designed as a fuel cell distributes the fuel from channels 12 for fuel evenly to the catalysts on the anode 7. The gas diffusion layer 9 on the cathode 8 distributes the oxidant from channels 13 for oxidant evenly to the catalysts on the cathode 8. The GDL 9, in particular on the cathode 8, also draws off reaction water in the opposite direction to the flow direction of the reaction gases, i.e. in a direction from the cathode 8 to the channels 13. Furthermore, the GDL 9 keeps the membrane 5 moist and conducts the current. The GDL 9 is constructed, for example, from a hydrophobized carbon paper as a carrier and substrate layer and a bonded carbon powder layer as a microporous layer.

[0020] A bipolar plate 10 rests on the GDL 9. The electrically conductive bipolar plate 10 serves as a current collector, for water drainage and for conducting the reaction gases as process fluids through the channel structures 12, 13, 14, and for dissipating the waste heat, which occurs particularly during the exothermic electrochemical reaction at the cathode 8. To dissipate the waste heat, channels 14 are incorporated into the bipolar plate 10 for conducting a liquid or gaseous coolant as a process fluid. The channel structure in the gas space for fuel is formed by channels 12. The channel structure in the gas space 32 for oxidizing agent is formed by channels 13. The materials used for the bipolar plates 10 include, for example, metal, conductive plastics, composite materials, and / or graphite.

[0021] In a fuel cell unit 1, several fuel cells 2 are arranged in alignment and stacked.

[0022] An electrolysis cell unit 1 is basically constructed in a very similar way and could therefore also be Fig. 1. However, for electrochemical cells 2 designed as electrolysis cells, it is common for their bipolar plates 10 not to have channel structures 14 for coolant, but rather the cooling function is provided by the process water, i.e., via the channel structures 12 on the anode 7 side. Hydrogen is removed from the electrolysis cell 2 via the channel structure 13 on the cathode 8 side. A bipolar plate 10 for an electrolysis cell can therefore also consist of a single metallic sheet.

[0023] Fig. 2 shows a perspective view of a bipolar plate 10 in a schematic representation. The bipolar plate 10 of the Fig. 2 is preferably suitable for an electrochemical cell 2 designed as a fuel cell. In the center of the bipolar plate 10 is the preferably rectangular active region 21 with the schematically indicated channel structures 12, 13. In the embodiment of the Fig. 2, the bipolar plate 10 has three media connections 31, 32, 33 on its narrow left end face for the supply of the media fuel, oxidant, and coolant, and three media connections 41, 42, 43 on its narrow right end face for the discharge of the media fuel, oxidant, and coolant. The area of the media connections 31, 32, 33, 41, 42, 43 is also referred to as the port area 23.

[0024] Between the media connections 31, 32, 33, 41, 42, 43 or the port area 23 and the active area 21, the so-called distribution area 22 is formed, which serves for the distribution (supply side) or the collection (discharge side) of the media from the comparatively narrow media connections 31, 32, 33, 41, 42, 43 to the comparatively wide active area 21, i.e. in the representation of the Fig. 2 in the y-direction.

[0025] A membrane electrode assembly 6 interacting with this bipolar plate 10 has, in principle, a very similar structure: media connections 31, 32, 33, 41, 42, 43 are formed on the end faces. In the area of the media connections 31, 32, 33, 41, 42, 43 or the port area 23 and the distributor area 22, the membrane electrode assembly 6 has, in particular, a frame structure; in the area of the active area 21, the membrane electrode assembly 6 has, in particular, the membrane 5, the anode 7, and the cathode 8.

[0026] In the execution of the Fig. 2, each media connection 31, 32, 33, 41, 42, 43 is circumferentially surrounded by a sealing contour as a sealing bead 101_31, 101_32, 101_33, 101_41, 101_42, 101_43; the sealing bead 101_31, for example, serves to seal the media connection 31. Furthermore, a sealing bead 101_10 is arranged on the circumference of the bipolar plate 10, which serves in particular to seal the active region 21 and the distributor region 22; this outer sealing bead 101_10 can also be referred to as a perimeter bead or perimeter sealing bead.

[0027] In alternative designs, the perimeter bead 101_10 does not have to enclose all media connections of the port area 23, but can also omit individual media connections.

[0028] Fig. 3 shows a cross-sectional view of a membrane electrode assembly 6 according to the prior art. The frame structure 15 of the membrane electrode assembly 6 has two films 151, 152. A connecting element 17 in the form of an adhesive is attached to each of the two films 151, 152, which bonds the frame structure 15 to the electrodes 7, 8 and extends into the port region 23 of the frame structure 15. Furthermore, an inactivated region 26 of the two electrodes 7, 8 is identified, which is covered by the connecting element 17. The active region 21, on the other hand, is covered neither by the connecting element 17 nor by the frame structure 15 and therefore characterizes the active area of the membrane electrode assembly 6. The frame structure 15 thus encloses the coated membrane 5 at its periphery, i.e., in the non-active region.

[0029] Fig. 4 shows, by way of example, a section of an electrochemical cell 2 in a vertical section to illustrate the sealing concept of the electrochemical cell 2. The sealing of the electrochemical cell 2 is ensured by the interaction of the frame structure 15 with the bipolar plate 10, in particular with a sealing bead 101 formed on one of the bipolar plate 10. For this purpose, the bipolar plate 10 has the sealing bead 101, on which a sealing coating 102 is particularly preferably applied. The frame structure 15, in the embodiment of Fig. 4 consisting of two foils 151, 152 with a connecting element 17 interposed, is pressed in the port area 23 between two sealing beads 101 and thus seals the cell 2 to the outside.

[0030] Out of Fig. 4 shows that in an area 24 adjacent to the sealing bead 101, the frame structure 15 virtually hangs in the air. During operation of the electrochemical cell 2, particularly at different pressures on the anode and cathode sides, a kind of fluttering of the frame structure 15 can occur.

[0031] According to the invention, the frame structure 15 is therefore stabilized or supported in the adjacent area 24 by means of a support structure. Fig. 5 a support structure 30 formed on the bipolar plate 10 in the adjacent region 24 of the outer sealing bead 101_10. The support structure 30 supports the frame structure 15 of the membrane electrode arrangement 6 in the assembly of the electrochemical cell 2. Preferably, the support structure 30 is arranged in the adjacent region of several sealing beads 101; in the embodiment of the Fig. 5, the support structure 30 is arranged between three sealing beads 101_10, 101_31, 101_32. In such areas, channels 12, 13 are typically not formed on the bipolar plate 10, which could also provide support for the frame structure 15.

[0032] In alternative embodiments, the support structure 30 can also be formed on the membrane electrode assembly 6 or on its frame structure 15, or can be inserted as a separate insert between the bipolar plate 10 and the frame structure 15. This is particularly advantageous if the adjacent region 24 coincides with a weld seam of a bipolar plate 10 consisting of two metallic sheets.

[0033] Fig.6 shows a vertical section of an electrochemical cell 2 according to the invention in its port region 23, with only the essential regions being illustrated. The frame structure 6 of the membrane electrode assembly 6 is inserted between two bipolar plates 10 and cooperates sealingly with the sealing beads 101. Two sealing beads 101_31, 101_32 for two media connections 31, 32 are shown as examples. Adjacent to the two sealing beads 101_31, 101_32 or between them, a support structure 30 is inserted between the frame structure 15 and the bipolar plate 10 on each side of the frame structure 15. The support structure 30 thus prevents harmful fluttering of the frame structure 15 between the bipolar plates 10. Preferably, the support structure 30 has a distance of less than 10 mm from the sealing beads 101_31, 101_32.

Claims

[1] Electrochemical cell (2) with a membrane electrode arrangement (6) arranged between two bipolar plates (10), wherein the membrane electrode arrangement (6) comprises a membrane (5) coated with two electrodes (7, 8) and a frame structure (15), wherein the frame structure (15) encloses the coated membrane (5) at its periphery, wherein a sealing bead (101) is formed on at least one of the bipolar plates (10), wherein the sealing bead (101) cooperates sealingly with the frame structure (15), characterized by that a support structure (30) is arranged adjacent to the sealing bead (101) between at least one of the bipolar plates (10) and the frame structure (15). [2] Electrochemical cell (2) according to claim 1 characterized by that the support structure is formed on the bipolar plate (10). [3] Electrochemical cell (2) according to claim 1 or 2 characterized by that the support structure is formed on the frame structure (15). [4] Electrochemical cell (2) according to claim 3 characterized by that the support structure is designed as a local increase in the thickness of an adhesive layer between two layers of the frame structure (15). [5] Electrochemical cell (2) according to one of claims 1 to 4 characterized by that the support structure is designed as an insert. [6] Electrochemical cell (2) according to one of claims 3 to 5 characterized by that the support structure is arranged adjacent to a weld seam of the bipolar plate (10), wherein the bipolar plate (10) is made of metal. [7] Electrochemical cell (2) according to one of claims 1 to 6 characterized by that at least one support structure (30) is arranged on each side of the frame structure (15). [8] Electrochemical cell (2) according to one of claims 1 to 7 characterized bythat the support structure (30) is arranged adjacent to at least two sealing beads (101_10, 101_31, 101_32, 101_33, 101_41, 101_42, 101_43). [9] Electrochemical cell (2) according to claim 8 characterized by that on each side of the support structure (30) at least two sealing beads (101_10, 101_31, 101_32, 101_33, 101_41, 101_42, 101_43) are arranged adjacent to the support structure (30).

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