Electrochemical cell

Abstract

The invention relates to an electrochemical cell (1), in particular a fuel cell or an electrolysis cell, comprising: two bipolar plates (11, 11') between which a membrane-electrode assembly is arranged, wherein the membrane-electrode assembly comprises a polymer electrolyte membrane (12) and electrodes (12a, 12b) arranged on both sides of the polymer electrolyte membrane (12), said electrodes, when viewed perpendicularly to a plane spanned by the polymer electrolyte membrane (12), being arranged congruently with one another and defining a layer of an active area (2); and at least two frames (3a, 3b) each having a frame opening, wherein an injection-moulded polymer seal (7, 7') is integrally formed on each frame (3a, 3b), said seal extending around the frame opening of that frame and in each case enclosing one of the electrodes (12a, 12b) and at least one planar, fluid-permeable element (4a, 4b) arranged thereon, wherein each seal (7, 7') is provided with first positioning contours (5) extending in the direction of the corresponding frame opening, and, on the at least one planar element (4a, 4b) enclosed by said seal, second positioning contours (6) which cooperate with the first positioning contours, whereby the position of the at least one planar element (4a, 4b) within the frame (3a, 3b) in question is precisely defined.

Description

[0001] Electrochemical cell

[0002] The invention relates to an electrochemical cell, in particular in the form of a fuel cell or an electrolysis cell, comprising two bipolar plates between which a membrane-electrode unit is arranged, wherein the membrane-electrode unit has a polymer electrolyte membrane and electrodes arranged on both sides of the polymer electrolyte membrane, which are arranged congruently perpendicular to a plane spanned by the polymer electrolyte membrane and define a position of an active field, and comprising at least two frames, each of which surrounds one of the electrodes and at least one planar fluid-permeable element arranged thereon.

[0003] Design features of an electrochemical cell, namely a fuel cell, are described, for example, in DE 10 2021 115 559 A1. The fuel cell according to DE 10 2021 115 559 A1 comprises an active field, a bipolar plate extending beyond the active field, and a frame arrangement surrounding the active field. The frame arrangement includes a sealing arrangement, which comprises a corrugated seal when viewed from above against the bipolar plate. In addition to the corrugated seal, a bypass is formed, which follows the contour of the seal. Specifically, the bypass comprises several straight sections and several curved sections. A fluid flows through the bypass, passing through the fuel cell at the edge of the active field.

[0004] US Patent 2005 / 0084734 A1 discloses a polymer electrolyte fuel cell which, in addition to a polymer electrolyte membrane, comprises, among other things, a pair of catalyst layers between which the polymer electrolyte membrane is arranged in a sandwich-like manner, and a pair of gas diffusion electrodes, which are also generally referred to as gas diffusion layers, arranged on the outer surfaces of the catalyst layers. Furthermore, according to US Patent 2005 / 0084734 A1, the fuel cell comprises frame-shaped seals, wherein the seals are placed around the gas diffusion layers, which are rectangular planar components, such that gaps remain between the gas diffusion layers and the seals. According to US Patent 2005 / 0084734 A1, these gaps are partially closed by closing means located at the corners of the gas diffusion layers.

[0005] Possible geometric designs of membrane electrode assemblies (MEAs) intended for use in fuel cells are described in JP 2010-257595 A. According to this, gas diffusion layers belonging to an MEA can have serrated edges, and gas diffusion layers with the same plan view can be arranged congruently on top of each other.

[0006] Various aspects of seals in fuel cell assemblies are addressed in documents DE 10 2015 201 129 A1, JP 2014-229366 A and US 8,003,273 B2. In the latter case, elastically deformable elements are molded onto a frame-shaped seal, pointing inwards, which contact a planar anode or cathode and thus close a gap formed between the seal on the one hand and the anode or cathode on the other.

[0007] Plate-shaped structures intended for use in fuel cells, comprising baffles or deflection devices, are disclosed, for example, in documents WO 2007 / 117739 A2 and DE 10 2009 017 906 A1. In the case of DE 10 2009 017 906 A1, a seal has an internally extending deflection device designed to counteract reactant bypass flow in the fuel cell.

[0008] A fuel cell arrangement described in WO 2022 / 131990 A1 comprises a three-layer membrane electrode arrangement consisting of two electrodes and a membrane. The electrodes each contact a so-called flux field plate. A seal located between the flux field plates is intended to prevent the escape of reactants into the environment. Furthermore, the device according to WO 2022 / 131990 A1 includes a so-called bypass stop element, which is intended to prevent the flow of reactants past flux field structures defined by the flux field plates.

[0009] Various concepts for bonding or welding seals to other fuel cell components in fuel cell assemblies are disclosed in documents DE 11 2005 002 035 B4 and WO 2017 / 055815 A1, respectively. The injection molding of sealing elements for electrochemical units is, for example, known from DE 10 2018 115 987 A1.

[0010] The invention is based on the objective of providing an electrochemical cell that is further developed compared to the aforementioned prior art, particularly with regard to manufacturing aspects, and where a high level of process reliability is also sought under mass production conditions.

[0011] This problem is solved according to the invention by an electrochemical cell, in particular in the form of a fuel cell or an electrolysis cell designed to produce hydrogen from water, with the features of claim 1.

[0012] The electrochemical cell according to the invention comprises two bipolar plates between which a membrane-electrode unit is arranged. The membrane-electrode unit has a polymer electrolyte membrane and electrodes arranged on both sides of the polymer electrolyte membrane. These electrodes are arranged congruently perpendicular to a plane spanned by the polymer electrolyte membrane and define a region of an active field. Here, an "active field" refers to a region of the electrochemical cell in which electrochemical reactions take place. Furthermore, the electrochemical cell comprises at least two frames, each with a frame opening. Each frame has an injection-molded polymer seal molded around the respective frame opening, which surrounds one of the electrodes and at least one planar, fluid-permeable element arranged thereon.Each seal has first positioning contours extending towards the respective frame opening. On the surrounding, at least one flat element, there are second positioning contours that interact with these contours, thus uniquely defining the position of the at least one flat element within the respective frame.

[0013] The electrochemical cell therefore has frames with frame openings that surround an active field, i.e., the area in which the desired electrochemical reactions take place during operation of the electrochemical cell. Within the active field, each electrode has at least one planar, fluid-permeable element, with the frames and the aforementioned planar elements featuring interacting positioning contours that uniquely define the position of the at least one planar element within the respective frame.

[0014] A planar, fluid-permeable element through which a fluid can flow can be in particular in the form of an open-porous transport layer and / or an open-porous gas diffusion layer, both of which are known per se. An open-porous transport layer, which is mostly used in electrolyzers, can be a metallic sintered body and / or a metallic textile material, for example a nonwoven, woven, non-woven fabric, or knitted fabric, and / or expanded metal, in particular titanium or a titanium alloy. An open-porous gas diffusion layer, which is mostly used in fuel cells, can be, in particular, carbon paper or carbon fiber nonwoven.

[0015] This system can utilize multiple stacked, flat elements with identical perimeter dimensions, held within a frame. In each case, at least one flat element possesses sufficient inherent stability to ensure a clear alignment of the second positioning contour formed by this element with the corresponding first positioning contour on the frame. Incorrect assembly of the at least one flat element is therefore inherently impossible. Assembly of the cell components is possible with varying degrees of automation, from manual assembly to semi-automated and fully automated assembly.In all cases, the first positioning contours of the frame and the correspondingly arranged second positioning contours of the planar elements can preferably be distributed around the perimeter of a frame opening in such a way that, in a top view of a flat side of the planar element inserted in the frame, neither mirror symmetry nor rotational symmetry is present.

[0016] According to various possible configurations, each frame, as well as the associated at least one planar element, preferably has a rectangular base shape. Positioning contours are located, for example, asymmetrically on opposite sides of the respective frame and the at least one planar element it surrounds. It is also possible for positioning contours to be located on exactly one side of each frame and the at least one planar element it surrounds.

[0017] According to the invention, the first positioning contours of each frame are formed by a seal located on the frame. This polymeric, in particular elastomeric, seal is molded onto a base body of the frame by means of an injection molding process. The seal surrounds the active field of the electrochemical cell in a ring-like manner. In particular, the seal is injection-molded or molded onto an edge of the frame that surrounds the frame opening.

[0018] A positioning contour preferably has a triangular base shape. Rounded positioning contours, for example semicircular ones, are also possible. The first positioning contours of the frame are directed inwards, i.e., towards the active field. The second positioning contours of the at least one planar element are present as recesses at the edge of this at least one element and allow the first positioning elements to engage in these recesses. The first and second positioning contours can thus be realized by various types of coordinated key-lock structures. A channel can be formed between the first positioning contour of the respective frame and the second positioning contour of the at least one planar element it surrounds.The channel can extend beyond the positioning contours between the frame and the planar element and, in particular, can be configured as a bypass channel at the edge of the active field. Compared to a straight bypass channel, the positioning contours result in increased flow resistance in the bypass channel and thus reduced bypass flow. This reduced flow in the bypass channel is ideally accompanied by increased flow in the at least one planar, fluid-permeable element, which is specifically designed as an open-porous transport layer and / or an open-porous gas diffusion layer.

[0019] In principle, metallic or non-metallic materials, especially plastics, are suitable for manufacturing the frames, with the choice of material depending primarily on the required electrical conductivity of the frames. Each frame can be constructed of a single material or a combination of materials. A large number of identical and / or different frames can be used within a stack of electrochemical cells. Frames with thicknesses ranging from the millimeter range to several millimeters can be used to match the thickness of the at least one planar element used.

[0020] Several embodiments of the invention are explained below with reference to Figures 1 to 4. These show:

[0021] Fig. 1 shows a section of several components of an electrochemical cell in a top view.

[0022] Fig. 2 shows partially enlarged features of the components according to Figure 1.

[0023] Fig. 3 shows partially enlarged features of the further components according to Figure 1, including a bypass channel between a frame and a planar fluid-permeable element, and Fig. 4 shows an electrochemical cell in the form of an electrolysis cell in cross-section.

[0024] Unless otherwise stated, the following explanations apply to all figures. Corresponding or essentially equivalent parts are marked with the same reference symbols in all figures.

[0025] An electrochemical cell, designated by reference numeral 1 (see Figure 4, which shows a cross-sectional view of an electrolysis cell), is part of a cell stack 10, also referred to as a stack 10. For the sake of simplicity, means for supplying and removing operating and cooling media for the operation of the electrochemical cell are not shown here. Regarding the basic structure and function of an electrochemical cell stack 10, particularly in the form of an electrolysis cell for the electrolysis of water, reference is made to the prior art cited above.

[0026] The electrochemical cell 1 comprises two bipolar plates 11, 11', between which a membrane electrode assembly is arranged. The membrane electrode assembly has a polymer electrolyte membrane 12 and electrodes 12a, 12b arranged on either side of the polymer electrolyte membrane 12. These electrodes are arranged congruently perpendicular to a plane spanned by the polymer electrolyte membrane 12 and define a position of an active field 2. Furthermore, at least two frames 3a, 3b are provided, each surrounding one of the electrodes 12a, 12b and at least one planar fluid-permeable element 4a, 4b arranged thereon. The respective electrode 12a, 12b and the adjacent planar fluid-permeable element 4a, 4b are thus located within a frame opening of the respective frame 3a, 3b.Each frame 3a, 3b has first positioning contours 5 which interact with second positioning contours 6 on the at least one planar element 4a, 4b surrounding it. This uniquely defines the position of the at least one planar element 4a, 4b within the respective frame 3a, 3b. In this example, the polymer electrolyte membrane 12 is held by a sealing frame 15a, 15b, 15c made of plastic films, also known as a "subgasket" or sub-seal. The plastic films of the sealing frame 15a, 15b, 15c can be integrally bonded to the polymer electrolyte membrane 12 or exist as separate film frames.

[0027] The active field of the electrochemical cell 1 is designated by 2, that is, a planar area in which the desired electrochemical reactions take place, in this case, the generation of hydrogen and oxygen from water using electrical energy. In the arrangement according to Figure 4, the polymer electrolyte membrane 12 spans a plane in which the active field 2 extends. The stacking direction of the cell stack 10, which comprises at least one cell 1, forms a surface normal to this plane. Further electrochemical cells 1 can be stacked on top of each other between the end plates 13, 13', which serve to clamp and seal the electrochemical cell(s) 1 via clamping elements 14.In this process, on the side of the bipolar plate 11 facing the end plate 13, all cell components arranged between the end plate 13 and the bipolar plate 11 would connect to it at least once more in order to form a cell stack 10 comprising at least two electrochemical cells 1.

[0028] The active field 2 and the electrodes 12a, 12b of cell 1 are surrounded by frames 3a, 3b, and are therefore located within the respective frame openings. Figures 1 to 3, described below, show only partial components of the electrochemical cell 1 according to Figure 4, in a top view of frame 3a and the planar element 4a. The partial view of frame 3a shows a square opening for receiving the planar element 4a with clearly visible rounded corners.

[0029] The planar, fluid-permeable elements 4a, 4b each have the form of an open-porous transport layer (PTL) through which the operating medium flows. The two open-porous transport layers 4a, 4b of one and the same cell 1 are separated from each other in a manner known per se by the proton- or anion-permeable polymer electrolyte membrane 12.

[0030] During the assembly of the cell stack 10, the planar, fluid-permeable elements 4a, 4b are inserted into the frames 3a, 3b in a defined manner. For this purpose, the first positioning contours 5 are present on the frames 3a, 3b, and the second positioning contours 6 are present on the planar elements 4a, 4b. In the exemplary embodiments, the positioning contours 5, 6 are rounded triangular contours. Here, the first positioning contours 5 on the frame 3a, shown in detail, are formed as projections, and the corresponding second positioning contours 6 on the adjacent planar element 4a are formed as recesses, i.e., indentations.

[0031] In each embodiment, the positioning contours 5, 6 are distributed asymmetrically around the frame opening of the frame 3a and at the edge of the planar element 4a, respectively. This asymmetry is illustrated by dashed guidelines in Fig. 1. As can be seen in Fig. 1, two pairs of positioning contours 5, 6 are located on the left side of the frame 3a and the planar element 4a. On the opposite right side, there is only a single pair of positioning contours 5, 6. The other two sides of the frame 3a and the planar element 4a are free of positioning contours. This arrangement of the positioning contours 5, 6, or a different arrangement thereof, can also be chosen for the frame 3b and the planar element 4b, which are not visible in the top view.

[0032] The choice of identical frames 3a, 3b and identical perimeter shapes of the planar elements 4a, 4b leads to a simplification of the stacking process and a reduction in the number of different components required for a cell stack 10.

[0033] In contrast to the representation in Fig. 1, only a single pair of positioning contours 5, 6 is visible in an enlarged view in Fig. 2. Fig. 3 shows a number and arrangement of two positioning contours 5, 6 in an enlarged view. A seal 7 is associated with frame 3a, which is injection-molded onto a base body 8a of frame 3a. A seal 7' is associated with frame 3b, which is injection-molded onto a base body 8b of frame 3b. The positioning contours 5 are formed integrally with and through the seals 7, 7'.

[0034] As can be seen particularly from Figures 2 and 3, a channel 9 is formed between the seal 7, including the triangular first positioning contours 5, on the one hand, and the edge of the planar element 4a on the other. This channel 9 is a bypass channel through which the operating medium flows at the edge of the active field 2. The positioning contours 5 and 6 increase the flow resistance in the bypass channel 9 and thus have an additional function beyond their assembly function, which comes into play during the operation of the cell stack 10.

[0035] A channel 9' is also formed between the seal 7', including the first positioning contours 5 formed by it, on the one hand, and the edge of the planar element 4b on the other, as shown in Figure 4. This channel 9' is also a bypass channel through which the operating medium flows at the edge of the active field 2. The positioning contours 5 and 6 also increase the flow resistance in the bypass channel 9' at this point and thus have an additional function beyond their assembly function, which comes into play during the operation of the cell stack 10.

[0036] The positioning contours 5, 6 shown in Figures 1 to 3 are merely examples; any type of key-lock structure or interlocking structures can be used.

[0037] List of reference symbols for electrochemical cells

[0038] Active field a, 3b Frame a, 4b Flat fluid-permeable element, open-porous transport layer First positioning contour on the frame Second positioning contour on the flat element, 7' Injection-molded polymer seal a, 8b Base body of the frame, 9' Channel, bypass channel 0 Cell stack, Stack 1, 11' Bipolar plate 2 Polymer electrolyte membrane 2a, 12b Electrode 3, 13' End plate 4 Clamping element 5a, 15b, 15c Sealing frame

Claims

Patent claims 1. Electrochemical cell (1), in particular a fuel cell or an electrolysis cell, comprising two bipolar plates (11, 11') between which a membrane electrode assembly is arranged, wherein the membrane electrode assembly has a polymer electrolyte membrane (12) and electrodes (12a, 12b) arranged on both sides of the polymer electrolyte membrane (12) on this membrane, which are arranged congruently perpendicular to a plane spanned by the polymer electrolyte membrane (12) and define a position of an active field (2), and comprising at least two frames (3a, 3b) each with a frame opening, wherein an injection-molded polymer seal (7, 7') surrounding the respective frame opening is formed on each frame (3a, 3b), each of which surrounds one of the electrodes (12a, 12b) and at least one planar fluid-permeable element (4a, 4b) arranged thereon, wherein on each seal (7,7') first positioning contours (5) extending in the direction of the respective frame opening and second positioning contours (6) cooperating with the at least one planar element (4a, 4b) surrounded thereby, whereby the position of the at least one planar element (4a, 4b) in the respective frame (3a, 3b) is uniquely determined.

2. Electrochemical cell (1 ) according to claim 1 , characterized in that the planar fluid-permeable element (4a, 4b) is designed as an open-porous transport layer.

3. Electrochemical cell (1 ) according to claim 1 or 2, characterized in that the respective cooperating first positioning contours (5) and second positioning contours (6) are neither arranged in a mirror-symmetric nor a rotationally symmetric arrangement relative to each other when viewed perpendicular to the plane spanned by the polymer electrolyte membrane (12).

4. Electrochemical cell (1 ) according to claim 3, characterized in that the frame (3a, 3b) as well as the planar element (4a, 4b) has a rectangular basic shape and positioning contours (5, 6) are located asymmetrically on opposite sides of the frame (3a, 3b) and the planar element (4a, 4b).

5. Electrochemical cell (1 ) according to claim 3, characterized in that the positioning contours (5, 6) are located on exactly one side of the respective frame (3a, 3b) and the respective planar element (4a, 4b).

6. Electrochemical cell (1 ) according to one of claims 1 to 5, characterized in that each first position contour (5) is designed to engage in each of the second position contours (6).

7. Electrochemical cell (1 ) according to one of claims 1 to 6, characterized in that the positioning contours (5, 6) have a triangular basic shape.

8. Electrochemical cell (1 ) according to one of claims 1 to 7, characterized in that a channel (9, 9') is formed between the first positioning contour (5) and the associated second positioning contour (6).

9. Electrochemical cell (1 ) according to claim 8, characterized in that the channel (9, 9') extends outside the positioning contours (5, 6) between the respective frame (3, 3') and the respective planar element (4a, 4b).

10. Electrochemical cell (1 ) according to claim 9, characterized in that the channel (9, 9') is designed as a bypass channel.

11. Electrochemical cell (1) according to one of claims 1 to 10, characterized in that the polymeric seal (7, 7') is formed on an edge running around the frame opening in the respective frame (3a, 3b).

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