DE102021210509A1 - Membrane electrode assembly for an electrochemical cell and method of making an electrochemical cell - Google Patents

Abstract

Membrane-electrode assembly (1) for an electrochemical cell (100), the membrane-electrode assembly (1) having a flat membrane (2), an electrode layer (3) on the cathode side and an electrode layer (4) on the anode side. The two electrode layers (3, 4) are designed differently. A luminescent substance is added to one of the electrode layers (3, 4) in order to distinguish between the cathode and the anode side of the membrane-electrode unit (1).

Description

The invention relates to a membrane-electrode unit for an electrochemical cell and a method for checking and producing such an electrochemical cell with a corresponding membrane-electrode unit.

State of the art

A fuel cell is an electrochemical cell that has two electrodes that are separated from one another by means of an ion-conducting electrolyte. The fuel cell converts the energy of a chemical reaction of a fuel with an oxidant directly into electricity. There are different types of fuel cells.

A special type of fuel cell is the polymer electrolyte membrane fuel cell (PEM-FC). In an active area of a PEM-FC, two porous electrodes with a catalyst layer adjoin a polymer electrolyte membrane (PEM). The PEM-FC also includes gas diffusion layers (GDL) in the active area, which delimit the polymer electrolyte membrane (PEM) and the two porous electrodes with a catalyst layer on both sides. The PEM, the two electrodes with the catalyst layer and optionally also the two GDLs can form a so-called membrane-electrode unit (MEA) in the active area of the PEM-FC. Two opposing bipolar plates (halves), in turn, delimit the MEA on both sides. A fuel cell stack is made up of MEA and bipolar plates arranged alternately one above the other. The fuel, in particular hydrogen, is distributed with an anode plate of a bipolar plate, and the oxidizing agent, in particular air/oxygen, is distributed with a cathode plate of the bipolar plate. In order to electrically insulate adjacent bipolar plates, to stabilize the shape of the MEA and to prevent the fuel or the oxidizing agent from escaping unintentionally, the MEA can be enclosed in a frame-like opening of two foils arranged one on top of the other. The two films of this frame structure are usually made of the same material, for example polyethylene naphthalate (PEN). The two films formed from the same material can dispensably have redundant properties, for example electrical insulating ability (electrically insulating) and/or oxygen impermeability of each of the two films.

In the DE 101 40 684 A1 discloses a membrane-electrode unit for a fuel cell, containing a layered arrangement of an anode electrode, a cathode electrode and a membrane arranged between them, a polymer material being applied to a top and bottom side of the layered arrangement.

The object of the present invention is to make the cathode side of the membrane electrode assembly visually distinguishable from the anode side of the membrane electrode assembly, so that when the membrane electrode assembly is positioned relative to the bipolar plates or distributor plates, the cathode and anode side can be prevented robustly.

Disclosure of Invention

For this purpose, the membrane-electrode unit comprises a flat membrane, an electrode layer on the cathode side and an electrode layer on the anode side. The two electrode layers are designed differently. A luminescent substance is mixed into one of the electrode layers. This makes it possible to distinguish between the cathode and the anode side of the membrane electrode assembly. The electrode layers of electrochemical cells are usually designed differently on the anode and cathode side, for example in the amount of catalysts; however, this cannot be seen with the naked eye. By adding the luminescent substance, optical differentiation can now be carried out easily.

Different luminescent substances can also be added to the two electrode layers. In further embodiments, a number of different electrode layers on the cathode side can also be characterized by different luminescent substances; the same naturally also applies to several different electrode layers on the anode side. As a result, for example, membrane-electrode assemblies for different periods of operation can be distinguished from one another.

The membrane-electrode unit comprises a flat membrane, in particular a polymer electrolyte membrane (PEM). The membrane-electrode unit further comprises two preferably porous electrode layers, each with a catalyst paste, the electrode layers being arranged on the membrane and delimiting it on both sides. One can speak here in particular of an MEA-3. In addition, the membrane electrode assembly can include two gas diffusion layers. In particular, these can delimit the MEA-3 on both sides. One can speak here in particular of an MEA-5.

The electrochemical cell can be, for example, a fuel cell, an electrolytic cell or a battery cell. The fuel cell is in particular a PEM-FC (polymer electrolyte membrane fuel cell). A cell stack comprises, in particular, a multiplicity of electrochemical cells arranged one above the other.

In advantageous embodiments, the luminescent substance is introduced into the anode-side electrode layer of a fuel cell. Fewer catalyst particles are usually introduced there, so that more free space is available, as it were. If it is an electrolytic cell, then the luminescent substance is preferably introduced into the electrode layer on the cathode side.

In advantageous developments, the luminescent substance is arranged in a catalyst paste of the electrode layer. The luminescent substance is particularly preferably mixed with the catalyst ink so that it is formed as a component of the catalyst paste when the catalyst ink is applied to the electrode layer. This is a very simple and inexpensive manufacturing process, which is used in any case for the manufacturing process of a membrane-electrode assembly.

The invention also includes methods for producing or checking an electrochemical cell with a membrane-electrode assembly according to one of the above statements.

• • Positionierung der kathodenseitigen Verteilerplatte zu der kathodenseitigen Elektrodenschicht und/oder
• • Positionierung der anodenseitigen Verteilerplatte zu der anodenseitigen Elektrodenschicht und
• • Optische Überprüfung der anodenseitigen und/oder kathodenseitigen Anordnung, wobei der lumineszierende Stoff der anodenseitigen und/oder kathodenseitigen Elektrodenschicht mit einer Lichtquelle bestrahlt wird.

The method for checking the assembly of an electrochemical cell with a membrane-electrode assembly and a cathode-side distributor plate and an anode-side distributor plate is characterized by the following method steps:

• • Positioning of the cathode-side distributor plate to the cathode-side electrode layer and/or
• • Positioning of the anode-side distributor plate to the anode-side electrode layer and
• • Optical inspection of the anode-side and/or cathode-side arrangement, the luminescent substance of the anode-side and/or cathode-side electrode layer being irradiated with a light source.

This ensures that the cathode-side electrode layer and the cathode-side distributor plate are arranged in the cathode compartment of the electrochemical cell, and the anode-side electrode layer and the anode-side distributor plate are arranged in the anode compartment of the electrochemical cell.

However, a method is also conceivable which, for the assembly of the electrochemical cell or for the stacking process of several membrane-electrode units and distributor plates or bipolar plates to form a cell stack, the membrane-electrode units and/or distributor plates or bipolar plates according to luminescent substance aligns. Here, too, it is ensured that the cathode-side electrode layer and the cathode-side distributor plate are arranged in the cathode compartment of the electrochemical cell, and the anode-side electrode layer and the anode-side distributor plate are arranged in the anode compartment of the electrochemical cell.

• • Detektion der kathodenseitigen Elektrodenschicht und/oder der anodenseitigen Elektrodenschicht der Membran-Elektroden-Anordnung, wobei der lumineszierende Stoff der anodenseitigen und/oder kathodenseitigen Elektrodenschicht mit einer Lichtquelle bestrahlt wird.
• • Positionierung der kathodenseitigen Verteilerplatte zu der kathodenseitigen Elektrodenschicht.
• • Positionierung der anodenseitigen Verteilerplatte zu der anodenseitigen Elektrodenschicht.

The corresponding process for producing the electrochemical cell is characterized by the following process steps:

• • Detection of the cathode-side electrode layer and/or the anode-side electrode layer of the membrane-electrode assembly, the luminescent substance of the anode-side and/or cathode-side electrode layer being irradiated with a light source.
• • Positioning of the cathode-side spreader plate to the cathode-side electrode layer.
• • Positioning of the anode-side distributor plate to the anode-side electrode layer.

In all methods, a UV light source is preferably used as the light source. This is a cheap and robust light source to allow the luminescent substance to emit light in a visually recognizable manner.

Further measures improving the invention result from the following description of some exemplary embodiments of the invention, which are described with the figures. All of the features and/or advantages resulting from the claims, the description or the drawings, including structural details, spatial arrangements and method steps, can be essential to the invention both on their own and in various combinations. It should be noted that the figures are only descriptive and are not intended to limit the invention in any way.

• 1 einen Schnitt durch eine aus dem Stand der Technik bekannte elektrochemische Zelle, wobei nur die wesentlichen Bereiche dargestellt sind.
• 2 einen Schnitt durch eine Membran-Elektroden-Einheit, wobei nur die wesentlichen Bereiche dargestellt sind.

They show schematically:

• 1 a section through an electrochemical cell known from the prior art, with only the essential areas being shown.
• 2 a section through a membrane electrode assembly, with only the essential areas are shown.

1 shows schematically an electrochemical cell 100 known from the prior art in the form of a fuel cell, only the essential areas being shown. The fuel cell 100 has a membrane 2, in particular a polymer electrolyte membrane. A cathode space 100a is formed on one side of the membrane 2 and an anode space 100b on the other side.

An electrode layer 3, a diffusion layer 5 and a distributor plate 7 are arranged in the cathode chamber 100a, pointing outwards from the membrane 2--ie in the normal direction or stacking direction z. Analogously, an electrode layer 4, a diffusion layer 6 and a distributor plate 8 are arranged in the anode chamber 100b, pointing outwards from the membrane 2. The membrane 2 and the two electrode layers 3, 4 form a membrane-electrode assembly 1. Optionally, the two diffusion layers 5, 6 can also be part of the membrane-electrode assembly 1. Optionally, one or both diffusion layers 5, 6 can also be omitted if the distributor plates 7, 8 can ensure sufficiently homogeneous gas feeds.

The distributor plates 7, 8 have ducts 11 for the supply of gas--for example air in the cathode space 100a and hydrogen in the anode space 100b--to the diffusion layers 5,6. The diffusion layers 5, 6 typically consist of a carbon fiber fleece on the channel side--ie towards the distributor plates 7, 8--and on the electrode side--ie towards the electrode layers 3, 4--of a microporous particle layer.

The distributor plates 7 , 8 have the channels 11 and thus implicitly also the webs 12 adjoining the channels 11 . The undersides of these webs 12 consequently form a contact surface 13 of the respective distributor plate 7, 8 with the underlying diffusion layer 5, 6.

Usually, the cathode-side distributor plate 7 and the anode-side distributor plate 8 differ from one another; Advantageously, the cathode-side distributor plate 7 of an electrochemical cell 100 and the anode-side distributor plate 8 of the adjacent electrochemical cell are firmly connected, for example by welded joints, and are thus combined to form a bipolar plate.

2 shows a vertical section of the membrane-electrode assembly 1 of an electrochemical cell 100, in particular a fuel cell, in an edge area, only the essential areas being shown. The membrane-electrode assembly 1 has the flat membrane 2, for example a polymer electrolyte membrane (PEM), and the two porous electrode layers 3 and 4, each with a catalyst layer, the electrode layers 3 and 4 each on one side or surface of the Membrane 2 are arranged. Furthermore, the electrochemical cell 100 has the two diffusion layers 5 and 6, which can also belong to the membrane-electrode assembly 1, depending on the design.

The membrane electrode assembly 1 is surrounded on its periphery by the frame structure 16, which is also referred to as a subgasket. The frame structure 16 is used for rigidity and tightness of the membrane electrode assembly 1 and is a non-active area of the electrochemical cell 100.

The frame structure 16 is particularly U-shaped or Y-shaped in section, with a first leg of the U-shaped frame section being formed by a first film 161 made of a first material W1 and a second leg of the U-shaped frame section being formed by a second Foil 162 is formed from a second material W2. In addition, the first foil 161 and the second foil 162 are glued together by means of an adhesive 163 made of a third material W3. The first material W1 and the second material W2 are often identical and are made of a thermoplastic polymer, for example PEN (polyethylene naphthalate).

The two diffusion layers 5 and 6 are inserted into the frame structure 16 , usually in such a way that they are in contact with an electrode layer 3 , 4 each over an active surface 21 of the membrane-electrode assembly 1 . The electrode layers 3, 4 have a catalyst paste 31, 41 in which catalysts, usually catalyst particles, are embedded.

If the electrode layers 3, 4 are covered by the frame structure 16, this is a non-active edge area 22 of the membrane electrode assembly 1. In the non-active edge area 22, no reaction fluids reach the electrode layers 3, 4 or catalyst pastes 31, 41 embedded catalysts; thus no chemical reactions take place in the edge area 22, the current density of the electrochemical cell 100 therefore drops very sharply here relative to the active surface 21 or is even zero.

In many electrochemical cells 100, the electrode layer 3 on the cathode side differs from the electrode layer 4 on the anode side. The differences can relate to the layer thickness and/or the material, for example. This can generally apply to the electrode layers 3, 4 and/or also to the catalyst pastes 31, 41 in particular. example For example, it is common for electrochemical cells 100 configured as fuel cells that the catalyst paste 31 on the cathode side contains more catalyst paste than the catalyst paste 41 on the anode side. It is therefore absolutely necessary for the stacking process to orient the catalyst paste 31 on the cathode side accordingly to the distributor plate 7 on the cathode side, so that both are arranged in the cathode space 100a of the electrochemical cell 100 . The same applies, of course, to the anode-side catalyst paste 41 and the anode-side distributor plate 8, which are to be arranged in the anode space 100b. Interchanging the two catalyst pastes 31, 41 would at least result in a loss of efficiency, but can even lead to failure of the electrochemical cell 100; If the cathode-side catalyst paste 41 were arranged in the anode chamber 100b, then an unnecessarily large number of expensive catalyst particles, which consist of platinum, for example, would be introduced there.

According to the invention, at least one of the electrode layers 3, 4 now has a luminescent substance. The added substance can be phosphorescent or fluorescent. Advantageously, the luminescent substance is added to the electrode layer 4 on the anode side. This usually contains fewer catalyst particles, ie has a lower catalyst density, and as a result has more free space available for the arrangement of further particles and substances, such as the luminescent substance.

The correct positioning of the distributor plates 7, 8 in relation to the membrane electrode assembly 1 can therefore be checked by the luminescent substance or also controlled during assembly. The distinction between the cathode and anode side is thus already given early on during the manufacturing processes of the cell stack, for example from the application of the catalyst paste 31, 41 to the electrode layer 3, 4 if the luminescent substance is just the catalyst paste 31, 41 mixed.

Furthermore, it is even possible to identify different catalyst pastes 31 on the cathode side or different catalyst pastes 41 on the anode side by means of differently luminescent substances. In this way, for example, membrane-electrode assemblies for passenger car applications can be distinguished from truck applications.

QUOTES INCLUDED IN DESCRIPTION

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

Patent Literature Cited

• DE 10140684 A1 [0004]

Claims (6)

Membrane-electrode unit (1) for an electrochemical cell (100), wherein the membrane-electrode unit (1) has a flat membrane (2), a cathode-side electrode layer (3) and an anode-side electrode layer (4), wherein the the two electrode layers (3, 4) are designed differently, characterized in that a luminescent substance is added to one of the electrode layers (3, 4). Membrane electrode assembly (1) after claim 1 characterized in that the luminescent substance is added to the anode-side electrode layer (4). Membrane electrode assembly (1) after claim 1 or 2 characterized in that the luminescent substance is arranged in a catalyst paste (31, 41) of the electrode layer (3, 4). Method for checking the assembly of an electrochemical cell (100) with a membrane-electrode assembly (1) according to one of Claims 1 until 3 , wherein the membrane-electrode unit (1) has a flat membrane (2), an electrode layer (3) on the cathode side and an electrode layer (4) on the anode side, the two electrode layers (3, 4) being designed differently, with one of the electrode layers (3, 4) a luminescent substance is added, the electrochemical cell (100) having a cathode-side distributor plate (7) and an anode-side distributor plate (8), characterized by the following method steps: positioning the cathode-side distributor plate (7) to the cathode-side electrode layer (3) and/or positioning of the anode-side distributor plate (8) to the anode-side electrode layer (4). • Optical inspection of the anode-side and/or cathode-side arrangement, the luminescent substance of the anode-side and/or cathode-side electrode layer (3, 4) being irradiated with a light source. Method for producing an electrochemical cell (100) with a membrane electrode assembly (1) according to one of Claims 1 until 3 , wherein the membrane-electrode unit (1) has a flat membrane (2), an electrode layer (3) on the cathode side and an electrode layer (4) on the anode side, the two electrode layers (3, 4) being designed differently, with one of the electrode layers (3, 4) a luminescent substance is added, the electrochemical cell (100) having a cathode-side distributor plate (7) and an anode-side distributor plate (8), characterized by the following method steps: • Detection of the cathode-side electrode layer (3) and/or the anode-side electrode layer (4) of the membrane-electrode assembly (1), the luminescent substance of the anode-side and/or cathode-side electrode layer (3, 4) being irradiated with a light source. • Positioning of the cathode-side distributor plate (7) to the cathode-side electrode layer (3). • Positioning of the anode-side distributor plate (8) to the anode-side electrode layer (4). procedure after claim 4 or 5 , wherein the light source is a UV light source.

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