DE102023211053A1 - Electrochemical cell, stacking unit for an electrochemical cell and method for producing such a stacking unit - Google Patents

Abstract

The invention relates to an electrochemical cell (10) comprising a membrane electrode assembly (4) and two bipolar plates (7). The membrane electrode assembly (4) is arranged between the two bipolar plates (7). A sealing bead (71) is formed on the bipolar plate (7).
The membrane electrode assembly (4) comprises a membrane (2), two electrodes (1, 3), a frame (15), and a connecting element (17). The frame (15) has a cutout (18) for an active surface (18) of the membrane electrode assembly (4). The frame (15) is adhesively bonded to the membrane (2) and/or to the first electrode (1) and/or to the second electrode (3) by means of the connecting element (17). The frame (15) comprises only one film (151). The film is adhesively bonded (151) to the sealing bead (71) by means of the connecting element (17).

Description

Technical field

The invention relates to an electrochemical cell, a stacking unit for an electrochemical cell and a method for producing such a stacking unit.

State of the art

Electrochemical cells are electrochemical energy converters and are known in the form of fuel cells or electrolyzers. A fuel cell converts chemical reaction energy into electrical energy. In conventional fuel cells, hydrogen ( _H2 ) and oxygen ( _O2 ) are converted into water ( _H2O ), electrical energy, and heat.

Proton exchange membrane (PEM) fuel cells are among the most common. Proton exchange membrane fuel cells have a centrally located membrane that is permeable to protons, i.e., hydrogen ions. The oxidant, particularly atmospheric oxygen, is thus spatially separated from the fuel, particularly hydrogen.

Fuel cells have an anode and a cathode. The fuel is continuously fed to the anode of the fuel cell and catalytically oxidized, releasing electrons to protons, which are then transferred to the cathode. The released electrons are removed from the fuel cell and flow to the cathode via an external circuit. The oxidant is fed to the cathode of the fuel cell and reacts by absorbing electrons from the external circuit and protons to form water. The resulting water is removed from the fuel cell. The overall reaction is: O ₂ + 4H ⁺ + 4e ^- → 2H ₂ O

A voltage is applied between the anode and cathode of the fuel cell. To increase the voltage, several fuel cells can be mechanically arranged one behind the other to form a fuel cell stack, also known as a stack, an array of electrochemical cells, or a fuel cell assembly, and electrically connected in series.

The electrodes, i.e., the anode and cathode, and the membrane can be structurally combined to form a membrane electrode assembly (MEA). Furthermore, the membrane electrode assembly can include a frame for stabilization.

Stacks of electrochemical cells also feature bipolar plates, also known as gas distribution plates or distributor plates. Bipolar plates serve to evenly distribute the fuel to the anode and the oxidant to the cathode. In addition to conducting oxygen, hydrogen, water, and possibly a coolant, the bipolar plates ensure a flat electrical contact with the membrane.

A stack typically comprises up to several hundred individual electrochemical cells, which are stacked in layers. The individual functional electrochemical cells comprise a membrane electrode assembly and a bipolar plate half on the anode and cathode sides. To form a stack, both functional individual electrochemical cells and stacked units consisting of a bipolar plate and a membrane electrode assembly can be stacked. The function of the electrochemical cells thus only becomes apparent after stacking, when each membrane electrode assembly has a bipolar plate half on both sides.

A stack of electrochemical cells typically has end plates that press the individual cells together and give the stack stability.

Furthermore, electrochemical cells usually comprise diffusion layers arranged between a bipolar plate and a membrane electrode assembly.

Unlike a fuel cell, an electrolyzer is an energy converter that preferentially splits water into hydrogen and oxygen when an electrical voltage is applied. Electrolyzers also feature a membrane electrode assembly, bipolar plates, and diffusion layers.

Electrochemical cells in a stack are often supplied with media, particularly hydrogen and oxygen, or removed from them via media connections arranged perpendicular to the membrane of the electrochemical cells. The media connections are fluidically connected to the electrochemical cells, particularly to the bipolar plates, via ports, also referred to as fluid connections. The media connections are usually located at the edge of the stack and are often created by recesses arranged congruently one above the other, which form the ports. In particular, At the ports, the different media must be sealed against each other and against the environment.

Typically, the membrane is laminated between two frame foils coated with hot melt adhesive. The hot melt adhesive wets approximately 6% of the membrane's active surface, thereby deactivating the catalyst in this area. Hot melt adhesive is also applied to the frames in the port area. Typically, a frame foil fully coated with hot melt adhesive is laminated on both sides of the membrane.

DE 102 015 100 740 A1 The invention relates to an electrochemical unit for a fuel cell stack, which, for example, has a bonded edge reinforcement layer.

DE 103 61 669 B4 describes a method for producing a seal for fuel cells using an adhesive.

Description of the invention

The invention relates to an electrochemical cell with a membrane electrode assembly and two bipolar plates or distributor plates. The membrane electrode assembly is arranged between the two bipolar plates. A sealing bead is formed on the bipolar plate. The membrane electrode assembly comprises a membrane, two electrodes, a frame, and a connecting element. The frame has a cutout for an active area of the membrane electrode assembly. The frame is glued to the membrane and/or to the first electrode and/or to the second electrode by means of the connecting element. The frame comprises only one film. The film is glued to the sealing bead by means of the connecting element.

The interaction of the sealing bead with the frame serves to seal the electrochemical cell to the outside and the individual media from each other. Typically, an electrochemical cell has several such sealing beads to seal the active area and the media connections. Advantageously, when assembling several electrochemical cells into a cell stack, the foil and the connecting element are arranged and pressed between two sealing beads in such a way that the electrochemical cell is sealed.

The solution proposed by the invention allows fuel cells or electrolyzers to be manufactured using a frame with only one foil, thus reducing material costs. Furthermore, a separate bonding process for applying a diffusion layer can be eliminated. For this purpose, a diffusion layer is advantageously attached to the membrane electrode assembly by means of the connecting element.

Furthermore, a stacking unit for an electrochemical cell is claimed. The stacking unit comprises a membrane-electrode assembly and a bipolar plate. A sealing bead is formed on the bipolar plate. The membrane-electrode assembly has a membrane, two electrodes, a frame, and a connecting element. The frame has a cutout for an active area of the electrochemical cell. The frame is glued to the membrane and/or to the first electrode and/or to the second electrode by means of the connecting element. The frame comprises only one film. The film is glued to the sealing bead by means of the connecting element.

The bonding allows the stacked unit consisting of the bipolar plate and the membrane electrode assembly to be manufactured. Typically, a large number of such stacked units are stacked on top of each other to create a cell stack of electrochemical cells. Such stacked units offer advantages in the manufacturing process, particularly with regard to handling during the stacking of many stacked units into a cell stack.

The connecting element therefore has several functions: bonding parts of the membrane electrode assembly and bonding the membrane electrode assembly to the bipolar plate to form a stacked unit.

In an advantageous embodiment of the electrochemical cell or stacking unit, the connecting element comprises an adhesive selected from, in particular, hot melt adhesives, epoxies, and/or acrylic-based adhesive tapes, which in particular comprise a pressure-sensitive adhesive (PSA). The adhesive in the connecting element allows for variable geometric shaping, forms a media-resistant, cohesive bond, and is easy to handle.

In the electrochemical cell or stacking unit proposed according to the invention, the connecting element preferably forms a sealed connection to a bipolar plate. This design variant eliminates the need for bonding processes on a bipolar plate.

Preferably, the membrane electrode assembly comprises exactly one foil. The membrane electrode assembly can be easily configured in a stacked form using identical parts in an automated manner.

The membrane electrode assembly proposed according to the invention further comprises a diffusion layer on one side of the frame, which in turn is fixed by the connecting element.

1. a) eine Membran, eine erste Elektrode und eine zweite Elektrode, ein Rahmen mit nur einer Folie und ein Verbindungselement bereitgestellt werden,
2. b) mittels des Verbindungselements eine Verbindung zwischen dem Rahmen und der Membran und/oder einer der Elektroden hergestellt wird,
3. c) der Rahmen mittels des Verbindungselements mit einer Bipolarplatte verbunden wird.

Furthermore, the invention relates to a method for producing a stacking unit, wherein

1. a) a membrane, a first electrode and a second electrode, a frame with only one foil and a connecting element are provided,
2. b) a connection is established between the frame and the membrane and/or one of the electrodes by means of the connecting element,
3. c) the frame is connected to a bipolar plate by means of the connecting element.

In an advantageous embodiment of the method proposed according to the invention, a frame-shaped structure of the connecting element is produced by punching, cutting or lasering a full-surface adhesive substrate.

In the method proposed according to the invention, the connecting element is produced by coating the frame, in particular by means of screen printing, spraying, dispensing, doctoring or jetting.

The stacking unit proposed according to the invention enables a leaner process chain to be realized due to the elimination of gluing processes.

Short description of the drawings

Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

• 1 eine schematische Darstellung einer elektrochemischen Zelle aus dem Stand der Technik, wobei nur die wesentlichen Bereiche dargestellt sind.
• 2 eine schematische Darstellung der Herstellung einer Membran-Elektroden-Einheit gemäß dem Stand der Technik.
• 3 eine Querschnittsansicht einer Membran-Elektrodeneinheit gemäß dem Stand der Technik, wobei nur die wesentlichen Bereiche dargestellt sind.
• 4 eine Querschnittsansicht einer Membran-Elektrodeneinheit gemäß einem nicht vorveröffentlichten Stand der Technik, wobei nur die wesentlichen Bereiche dargestellt sind.
• 5 eine prinzipielle Draufsicht auf einen Bipolarplatte nach dem Stand der Technik, wobei nur die wesentlichen Bereiche gezeigt sind.
• 6 eine Querschnittsansicht einer Membran-Elektrodeneinheit, wobei nur die wesentlichen Bereiche dargestellt sind.
• 7 einen schematischen Schnitt durch eine erfindungsgemäße elektrochemische Zelle, wobei nur die wesentlichen Bereiche dargestellt sind.

They show:

• 1 a schematic representation of a prior art electrochemical cell, showing only the essential areas.
• 2 a schematic representation of the production of a membrane electrode assembly according to the prior art.
• 3 a cross-sectional view of a membrane electrode assembly according to the prior art, with only the essential areas being shown.
• 4 a cross-sectional view of a membrane electrode assembly according to a non-prepublished prior art, wherein only the essential areas are shown.
• 5 a basic plan view of a bipolar plate according to the state of the art, with only the essential areas shown.
• 6 a cross-sectional view of a membrane electrode assembly, showing only the essential areas.
• 7 a schematic section through an electrochemical cell according to the invention, with only the essential areas being shown.

1 shows an electrochemical cell 10 in the form of a fuel cell. The electrochemical cell 10 has a membrane 2 as the electrolyte. The membrane 2 separates a cathode compartment 6 from an anode compartment 8. In the cathode compartment 6 and the anode compartment 8, an electrode 1, 3, a diffusion layer 5, and a bipolar plate 7 are arranged on the membrane 2. The composite of membrane 2 and the electrodes 1, 3 is part of a membrane-electrode assembly 4.

A bipolar plate 7 often consists of a bipolar plate half of an electrochemical cell and a bipolar plate half of the adjacent electrochemical cell. The two plate halves are connected, for example, by welding, and can form cooling channels in the resulting space.

Media 29 are supplied to the bipolar plates 7. Oxygen passes through the bipolar plate 7 in the cathode chamber 6 to the cathode-side diffusion layer 5, and hydrogen passes through the bipolar plate 7 of the anode chamber 8 to the corresponding anode-side diffusion layer 5.

2 shows the production of a membrane electrode assembly 4 according to the prior art, wherein a membrane 2 coated with electrodes 1, 3 is arranged between two frames 15 or two foils, each having two port areas 19. The two foils of the frame 15 further each have a cutout 18, which, after assembly of the electrochemical cell 10, delimits an active area of the membrane electrode assembly 4 or the electrochemical cell 10. In the active area, the reaction educts pass through the diffusion layers 5 to the electrodes 1, 3, and the reaction products are removed from the electrodes 1, 3.

3 shows a 2 corresponding cross-sectional view of a membrane electrode assembly 4 according to the prior art. The frame 15 has two foils 151, 152. Attached to each of the two foils 151, 152 is a connecting element 17 in the form of an adhesive, which bonds the frame 15 to the electrodes 1, 3 and extends into the port area 19 of the frame 15. Furthermore, an inactivated area 26 of the second electrode 3 is marked, which is covered by the connecting element 17. The cutout 18, on the other hand, is covered neither by the connecting element 17 nor by the frame 15 and therefore marks the active area of the membrane electrode assembly 4.

From the unpublished DE102023200374A1 Furthermore, a membrane electrode assembly 4 with a frame 15 is known, which has only a single foil 151. This is in 4 in a corresponding cross-sectional view of a membrane electrode assembly 4, wherein only the essential areas are shown.

The connecting element 17 is applied to both sides of one film 151, so that the frame 15 can be bonded to the first electrode 1 on the one hand, and to the two diffusion layers 5 on the other. The active area of the membrane electrode assembly 4 is thus somewhat larger than defined by the cutout 18 of the film 151 at the first electrode 1, since the second electrode 3 is not covered by the connecting element 17 or by the frame 15. Due to transverse diffusion of the fluids, the active area will thus extend somewhat further in the x-direction to the edge of the membrane electrode assembly 4 than indicated by the cutout 18.

In the case of an electrochemical cell 10 designed as a fuel cell, the first electrode 1, designed as a cathodic electrode, is covered by the frame 15, and the second electrode 3, designed as an anodic electrode, is not covered by the frame 15. This ensures that a local hydrogen deficiency cannot occur at any location on the active surface.

5 shows a top view of a bipolar plate 7 of an electrochemical cell 10. The bipolar plate 7 has a cutout 18, which later defines the active region of the electrochemical cell 10. Furthermore, two port regions 19 are formed in the bipolar plate 7, each having three media connections 190. The so-called distribution region 20 is formed between the port region 19 and the active region 18. There, the media are distributed from the individual media connections 190 across the entire width of the active region 18. The distribution region 20 is typically defined by a channel structure of the bipolar plate 7.

Furthermore, in 5 a sealing contour 70 is shown, which seals the electrochemical cell 10 to the outside. In the embodiment of the 5 In addition to the active area 18, the sealing contour 70 also encloses all media connections 190. In alternative embodiments, the sealing contour 70 can also enclose only a few or no media connections 190 and further sealing contours 70 can also be arranged, for example, around individual media connections 190.

6 shows a membrane electrode assembly 4, which is applied to a frame 15 provided with the connecting element 17 on one side and subsequently covered by a diffusion layer 5. The frame 15 has only a single film 151. In the illustration, position 42 designates an additional adhesive that connects the lower of the two diffusion layers 5 to the film 151.

7 shows a schematic section through an electrochemical cell 10 according to the invention in the edge region, with only the essential areas being shown. The membrane electrode assembly 4 is embedded in the frame 15 on the connecting element 17 containing adhesive. The composite comprising the frame 15, the connecting element 17, and the membrane electrode assembly 4 is provided on both sides with the diffusion layer 5; for this purpose, the diffusion layer 5 is bonded to the film 151 with the additional adhesive 42.

The bipolar plate 7 has a sealing bead 71 in the non-active area of the electrochemical cell 10. The frame 15 of the membrane electrode assembly 4 is pressed between two sealing beads 71 of two bipolar plates 7; this seals the electrochemical cell 10 to the outside. Analogous sealing beads 71 can also be used to seal media connections190.

According to the invention, the frame 15 is glued to the sealing bead 71 of the bipolar plate by means of the connecting element 17. The frame 15 is thus connected to a sealing bead 71 of a bipolar plate 7 (in the illustration of the 7 The upper bipolar plate is bonded to the other sealing bead 71 of the other bipolar plate 7 and presses together. Consequently, the upper bipolar plate 7 and the membrane electrode assembly 4 form a stacking unit 11; functionally, in these embodiments, the electrochemical cells 10 are only created when two or more stacking units 11 are stacked.

• - dem Zusammenbau der Membran-Elektroden-Einheit 4, indem der Rahmen 15 an der Membran 2 und/oder an der ersten Elektrode 1 und/oder an der zweiten Elektrode 3 befestigt ist,
• - dem Befestigen einer Diffusionslage 5 an der Membran-Elektroden-Einheit 4 und
• - dem Befestigen der Membran-Elektroden-Einheit 4 an einer Bipolarplatte 7 zur Bildung einer Stapeleinheit 11.

The connecting element 17 therefore serves

• - the assembly of the membrane electrode unit 4 by attaching the frame 15 to the membrane ran 2 and/or to the first electrode 1 and/or to the second electrode 3,
• - attaching a diffusion layer 5 to the membrane electrode assembly 4 and
• - attaching the membrane electrode assembly 4 to a bipolar plate 7 to form a stacking assembly 11.

In the execution of the 7 The sealing bead 71 has a sealant 72. This can be, for example, an elastomer seal or a synthetic rubber. However, the sealant 72 can also be omitted, since the connections between the sealing bead 71 and the film 151, and especially between the sealing bead 71 and the connecting element 17, can be designed to be media-tight.

The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, numerous modifications are possible within the scope of the claims, which are within the scope of expert practice.

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102 015 100 740 A1 [0014]
• DE 103 61 669 B4 [0015]
• DE 102023200374A1 [0037]

Claims (7)

Electrochemical cell (10) with a membrane electrode assembly (4) and two bipolar plates (7), wherein the membrane electrode assembly (4) is arranged between the two bipolar plates (7), wherein a sealing bead (71) is formed on the bipolar plate (7), wherein the membrane electrode assembly (4) comprises a membrane (2), two electrodes (1, 3), a frame (15) and a connecting element (17), wherein the frame (15) has a cutout (18) for an active surface of the electrochemical cell (10), wherein the frame (15) is adhesively bonded to the membrane (2) and/or to the first electrode (1) and/or to the second electrode (3) by means of the connecting element (17), wherein the frame (15) comprises only one film (151), characterized in that the film (151) is adhesively bonded to the sealing bead (71) by means of the connecting element (17). Electrochemical cell (10) according to Claim 1 characterized in that the connecting element (17) comprises an adhesive which is selected from in particular hot melt adhesives, epoxies and/or acrylic-based adhesive tapes which in particular contain a pressure-sensitive PSA adhesive (Pressure Sensitive Adhesive). Electrochemical cell (10) according to one of the Claims 1 or 2 characterized in that a diffusion layer (5) is attached to the membrane electrode unit (4) by means of the connecting element (17). Stacking unit (11) for an electrochemical cell (10), wherein the stacking unit (11) comprises a membrane-electrode unit (4) and a bipolar plate (7), wherein a sealing bead (71) is formed on the bipolar plate (7), wherein the membrane-electrode unit (4) comprises a membrane (2), two electrodes (1, 3), a frame (15) and a connecting element (17), wherein the frame (15) has a cutout (18) for an active area of the electrochemical cell (10), wherein the frame (15) is adhesively bonded to the membrane (2) and/or to the first electrode (1) and/or to the second electrode (3) by means of the connecting element (17), wherein the frame (15) comprises only one film (151), characterized in that the film (151) is adhesively bonded to the sealing bead (71) by means of the connecting element (17). Stacking unit (11) after Claim 4 characterized in that the connecting element (17) comprises an adhesive which is selected from in particular hot melt adhesives, epoxies and/or acrylic-based adhesive tapes which in particular contain a pressure-sensitive PSA adhesive (Pressure Sensitive Adhesive). Stacking unit (11) according to one of the Claims 4 or 5 characterized in that a diffusion layer (5) is attached to the membrane electrode unit (4) by means of the connecting element (17). Method for producing a stacking unit (11) according to a Claims 4 until 6 , wherein a) a membrane (2), a first electrode (1) and a second electrode (3), a frame (15) with only one film (151) and a connecting element (17) are provided, b) by means of the connecting element (17) a connection is made between the frame (15) and the membrane (2) and/or one of the electrodes (1, 3), c) the frame (15) is connected to a bipolar plate (7) by means of the connecting element (17).

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