KR101189675B1 - Catalyst-coated membrane with integrated sealing material and membrane-electrode assembly produced therefrom - Google Patents

Abstract

The present invention relates to catalyst-coated ion-conductive membranes and electrochemical devices, in particular membrane-electrode assemblies (MEAs) for fuel cells. The catalyst-coated ion-conducting membrane has a thickness at least corresponding to the overall thickness of the catalyst-coated membrane and has a sealing material applied in the edge region on one side of the membrane. Thanks to their simple material-preserving structure, catalyst-coated ion-conductive membranes and membrane-electrode assemblies produced therefrom can be made inexpensively. They are used in PEM fuel cells, direct methanol fuel cells (DMFCs), electrolyzers and other electrochemical devices.

Description

Catalyst-coated membrane with integrated sealing material and membrane-electrode assembly produced therefrom {CATALYST-COATED MEMBRANE WITH INTEGRATED SEALING MATERIAL AND MEMBRANE-ELECTRODE ASSEMBLY PRODUCED THEREFROM}

FIELD OF THE INVENTION The present invention relates to the field of electrochemistry and relates to catalyst-coated membranes and membrane-electrode assemblies for electro-chemical devices such as, for example, fuel cells, electrolyzers or electrochemical sensors. Moreover, a production process of catalyst-coated membrane and membrane-electrode assemblies is disclosed and its use is disclosed.

Fuel cells convert fuel and oxidant into power, heat and water at separate locations at the two electrodes. The fuel used may be hydrogen or a hydrogen-rich gas and the oxydant used may be oxygen or air. The energy conversion process in fuel cells has a particularly high efficiency. For this reason, fuel cells are becoming increasingly important in mobile, stationary and portable applications.

Due to their compact structure, their power density and their high efficiency, membrane fuel cells (PEMFC, DMFC, etc.) are particularly suitable for use in a wide range of applications.

For the purposes of the present invention, a fuel cell stack is a stack of fuel cell units. Hereinafter, the fuel cell unit may be simply called a fuel cell. It is also referred to as separator plates and includes a membrane-electrode assembly ("MEA") located between the dipole plates that acts to bring gas into the unit and conduct current.

The membrane-electrode assembly comprises an ion-conductive membrane provided on two sides with catalyst-coated reaction layers, ie electrodes. One of the reaction layers is configured as an anode for the oxidation of hydrogen and the second reaction layer is configured as a cathode for the reduction of oxygen. Gas diffusion layers (abbreviated as "GDLs") made of carbon fiber felt, carbon fiber paper, or woven carbon fiber fabrics are applied to these catalyst layers. GDLs provide good access of the reactant gases to the electrodes and are easily conducted with current. For the purposes of the present invention, such an arrangement will be referred to as a five-layer membrane-electrode assembly ("5-layer MEA"). In contrast, there is an ion-conductive membrane coated with a catalyst on the front and inverted sides called three-layer CCM (“catalyst-coated membrane”). If only one side of the ion-conductive membrane is coated with a catalyst, it is referred to as a two-layer catalyst-coated membrane ("2-layer CCM").

The anode and cathode generally contain electrocatalysts which catalyze each reaction (oxidation of hydrogen or reduction of oxygen). As catalytically active components, preference is given to using platinum group metals of the Periodic Table of Elements. Most of the catalysts used are supported with catalysts in which catalytically active platinum group metals are applied in finely divided form on the surface of the conductive support material. The average crystal size of the platinum group metals is about 1 to 10 nm. Finely divided conductive carbon blacks have been found to be useful as support materials.

The ion-conductive membrane preferably comprises proton-conducting polymeric materials. These materials will hereinafter be referred to simply as ionomers. Preference is given to using tetrafluoro-ethylene-fluorovinyl ether copolymers which give sulfonic acid groups. This material is marketed, for example, under the name Nafion ^® by DuPont. However, other fluorine-free ionomer materials such as doped sulfonated polyether ketones or doped sulfonated or sulfinated aryl ketones and also doped polybenzimidazoles can also be used. Suitable ion-conductive membranes are described in O. Savadogo, "Journal of New Materials for Electrochemical Systems" I, 47-66 (1998). For use in fuel cells, these membranes generally need to have a thickness of 10 to 200 microns.

The present invention describes catalyst-coated membranes (CCMs) and membrane-electrode assemblies (MEAs) with integrated sealing material. Products according to the invention have a simplified material-preservation structure and can therefore be produced at a lower cost than conventional materials which can be obtained according to the prior art.

In this case the sealing of gas species of the fuel cell from ambient air and other reactive gases is essential for the widespread introduction of safety and fuel cell technology. Therefore, the use of sealing materials and their integration into the structural concept of MEA is very important.

Such structural concepts for membrane-electrode assemblies are described, for example, in US Pat. No. 3,314,697 and European Patent No. 700,108 A2. In this concept, the membrane forms a rim that extends over the electrodes and when the cell is sealed it is clamped between the cell plates and between additional seals if necessary. However, membrane-electrode assemblies (MEAs) with such protruding membrane rims are sensitive to mechanical damage to the membrane during manufacture and assembly. Since the membrane must separate hydrogen and oxygen, the gas species of the reaction gases, damage to the membrane easily leads to damage of the cell. Moreover, the production of such products uses an increasing amount of ion-conductive membrane material due to the area of the protruding rim. Depending on the structure and construction of the MEA, up to 50% or more of the material (based on the active area of the membrane) is required. Thus, for example, an MEA with an active area of 50 cm ² (ie, having dimensions of 7.1 × 7.1 cm) and a rim projecting circumferentially of 0.9 cm has a total area of 64 cm ² . This corresponds to an additional area of 28% (corresponding to an active area of 50 cm ² ) of the membrane required. Ionomer membranes are organic polymers with complex structures and are therefore expensive. Larger membrane rims increase material loss, thus making the overall MEA products more expensive.

EP 586,461 B1 describes a membrane-electrode assembly containing integrated sealing materials. This MEA has a five-layer structure and consists of a cathode composed of a catalyst-coated gas diffusion layer (GDL), an ion-conductive membrane and a once-catalyst-coated gas diffusion layer. In contrast to this patent application, any catalyst-coated membranes (“CCMs”) are used to produce such MEAs. The MEA production process is significantly less flexible and substantially different from the present patent application. In a preferred embodiment of EP 586,461 B1, two layers of sealing material are required, and in a further embodiment, one layer of sealing material is used, but the sealing material is used to produce a composite of the entire MEA. A substantial amount of this material is used because it is applied to the top electrode (i.e. on the top catalyst-coated gas diffusion layer). Since each of the anode, membrane and cathode must have a contact area for the sealing material, there is a large overlap area leading to a significant loss of the active MEA area.

EP 1,037,295 B1 describes the continuous production of catalyst-coated membranes by screen printing. The catalyst layers are printed selectively (ie in a specific pattern) on the membrane in the form of a tape. A margin is produced, consisting of the membrane region and not acting as an active region. Thus, the CCMs produced by this process are expensive and generate relatively expensive material costs.

It is therefore an object of the present invention to provide a catalyst-coated ion-conductive membrane which contains an integrated sealing material and which can be produced simply at low cost. For inexpensive production, the ion-conducting membrane should be coated with the catalyst on the entire front and / or inverting side and without any additional membrane rims. The catalyst-coated ion-conductive membrane should be able to be further processed in a simple process to produce a five-layer membrane-electrode assembly.

This object is achieved by providing a catalyst-coated membrane as claimed in claim 1. Preferred embodiments are described in the subsequent claims. Further claims describe the production of membrane-electrode assemblies provided with these catalyst-coated membranes.

A feature of the catalyst-coated membranes (CCMs) of the present invention is that they comprise a sealing material applied to one side in the edge region of the ion-conductive membrane. The thickness of the sealing material is at least as thick as the coated ion-conductive membrane. The ion-conducting membrane is coated with a catalyst over the entire front and / or inverting side and there is no circumferentially uncoated margin. The drawings below illustrate various embodiments of the invention in more detail.

1A shows a preferred embodiment of a catalyst-coated membrane composed of two layers (“2-layer CCM”). Here, the ion-conductive membrane 1 has a catalyst layer 3 over the entire area of the membrane (ie no margin). Sheet-like sealing material 4 is applied to the uncoated side opposite the membrane.

1B shows a two-layered structure with sealing material 4 in the connected state.

1C shows a five-layer membrane-electrode assembly produced therefrom in a “semi-coexistent” design, which shows a catalyst-coated gas diffusion layer 5 on the front side and a catalyst-free gas diffusion layer 6 on the inverting side. Can be obtained by combining with a two-layer catalyst-coated membrane. The ion-conductive membrane 1 and the gas diffusion layer 5 have different dimensions. The sealing material 4 is integrated into the membrane-electrode assembly and is connected to the interior of the gas diffusion layers 5 and 6 (ie the sides opposite the membrane).

2A shows a further preferred embodiment of the present invention. The catalyst-coated membrane used here consists of three layers ("3-layer CCM"). An ion-conductive membrane 1 is provided on the front side 2 with the catalyst layer and on the reverse side 3 with the catalyst layer. Both catalyst layers are applied over the entire area of the membrane, ie there is no uncoated membrane margin. Sheet-like sealing material 4 is applied to one side of the CCM.

2B shows a three-layered structure with sealing material 4 in the connected state.

2C shows a five-layer membrane-electrode assembly produced therefrom, which shows a three-layer catalyst-coated membrane with a catalyst-free gas diffusion layer 5 on the front side and a catalyst-free gas diffusion layer 6 on the inverting side. It is obtained by combining with ("3-layer CCM"). Here too, the sealing material 4 is integrated into the membrane-electrode assembly and connected to the interior (ie sides opposite the membrane) of the gas diffusion layers 5 and 6.

Catalyst-coated ion-conductive membranes can be produced by an inexpensive process because full-area coating of the membrane surface can be performed. CCMs with different formats and patterns can be obtained by simple cutting or stamping from the coated membrane over its entire area. Coating of the membrane by screen printing does not require expensively produced screens and no dimensional problems arise. Significant savings of expensive membrane materials are achieved because no membrane margin occurs. Moreover, the sealing material is also used in a cost-saving form, only to provide contact on the interior of the gas diffusion layers. The catalyst-coated ion-conductive membranes can be further processed in a simple process (e.g., by overlapping in the fuel cell stack, by adhesive bonding, by pressing or lamination) to produce a five-layer membrane-electrode assembly. have. If necessary, the entire process can be carried out in continuous mode.

It has been found advantageous for the sealing material to be formed as a sheet and to be applied to the membrane within a certain minimum width edge region. The sealing material advantageously overlaps the ion-conducting membrane at the edge with a width of at least 1 mm.

The thickness d _D of the sealing material is advantageously at least as large as the total thickness d _CCM of the catalyst-coated ion-conducting membrane. This achieves an airtight, strong and durable combination of the components. For example, used is a membrane made of Nafion 112 ^® (DuPont) having a 50 micron thickness, for a case in which a catalyst layer of the full 15 micron thick coating example, the coated ion-total layer thickness of the conductive membrane (d _CCM ) Is 65 microns. Thus, the thickness d _D of the sealing material should likewise be at least 65 microns. The smaller the thickness of the sealing material leads to damage to the catalyst layers, the larger the layer thickness (i.e. 50% greater than the total thickness of the CCM) leads to unnecessary consumption of material and also to dimensional problems. .

As the sealing material, it is possible to use polymers which do not release substrates which may interfere with electrocatalytic decomposition under the operating conditions of the fuel cell or otherwise adversely affect the function of the fuel cell. The polymers should be able to provide an airtight contact between the gas diffusion structures and the active catalyst layers. A further important feature of these polymers is their ability to form strong integrated bonds with the polymer electrolyte membrane. Possible sealing materials are polyethylenes, polypropylenes, polyamides, polyurethanes, thermoplastic polymers and / or copolymers of the class of polyesters, elastomers such as silicone rubber, EPDM, and epoxy resins and sheaths. Thermosetting materials such as no-acrylates.

To apply the sealing material, the polymer can be used in the form of a precut film or as a liquid or molding composition. When a precut film is used for the production process, the ion-conductive membrane can be placed with a suitably precut frame of sealing material in the press. This frame is cut such that its inner open area corresponds to the dimensions of the desired active area of the MEA. The sealing material is then applied by heating under pressure. To carry out this process, heatable hydraulic presses, calendars, rollers, roller presses or other lamination devices may be used, all of which may suitably be operated continuously. Pressing pressure is referred to as area pressure in the present patent application. The area pressure used (based on the window area of the sealing material) is in the range of 50 to 300 N / cm ² . The temperature is in the range of 20 to 200 ° C. The pressing time is preferably in the range of 1 to 10 minutes.

Subsequent further processing of the catalyst-coated membranes to produce membrane-electrode assemblies can be performed using the same devices. For this purpose, the area pressure used (based on the total area of the larger gas diffusion layer) is preferably in the range of 50 to 200 N / cm ² .

However, it is also possible to combine the gas diffusion layers required for catalyst-coated membranes, sealing materials and multilayer structures and to produce a five-layer membrane-electrode assembly in a single step (ie single-stage production). The values for the area pressure are then selected within this range.

The five-layer membrane-electrode assemblies can be of "coexistent" design or "semi-coexistent" design. "Co-existence" means that the GDLs cover the entire area of the ion-conducting membrane, while "semi-co-existence" means that the ion-conducting membrane and the GDLs have different dimensions.

Gas diffusion layers (GDLs) may be composed of porous electrically conductive materials such as woven carbon fiber fabrics, carbon fiber felts or carbon fiber papers. They may, if desired, be waterproofed and / or have additional microlayers applied to the side in contact with the ion-conductive membrane. Moreover, it may be provided with a catalyst layer. Such gas diffusion layers are currently commercially available.

Catalyst-coated ion-conductive membranes (CCMs) and membrane-electrode assemblies produced therefrom are used in PEM fuel cells, direct current methanol fuel cells (DMFCs), electrolyzers and other electrochemical devices.

The following examples illustrate the invention.

Example 1

a) production of 3-layer CCM with integrated sealing material

A three-layer membrane (CCM type for hydrogen / air operation; Umicore AG & Co KG, Hanau) coated with catalyst over its entire area is used as starting material. The Pt load of the CCM is 0.2 mg Pt / cm ² on the anode side and 0.4 mg Pt / cm ² on the cathode side (ie total load = 0.6 mg Pt / cm ² ). The dimensions are 72 x 72 mm, the membrane thickness is 25 microns, and the total thickness of the catalyst layers is 22 microns. The sealing rim of polyamide (Vestamelt 3261, Degussa, Dusseldorf) with a thickness of 50 microns, an inner window size of 68 x 68 mm and an outer dimension of 100 x 100 mm is concentrated on the CCM and two PTFE of hot press Pressed between the plates. The hot press is set such that it applies an area pressure of 250 N / cm ² based on the area of the sealing rim. The temperature is 160 ° C. and the pressing time is 2 minutes. After slow cooling, the structure is obtained from the press.

b) production of 5-layer MEA (semi-idle design)

A three-layer CCM with a sealing rim applied on one side has two catalyst-free gas diffusion layers (30 BC type, with dimensions 72 x 72 mm (anode) and 76 x 76 mm (cathode) SGL-carbon, Meitingen) is concentrated. This structure is sequentially pressed in the hot press for 3 minutes at 135 ° C. by a hot press set to apply an area pressure of 100 N / cm ² based on the area of the larger gas diffusion layer. Slow cooling yields a five-layer MEA in which the individual components are firmly bound.

c) electrochemical measurements

A five-layer MEA is built into a single cell in a PEM fuel cell test station and tested under hydrogen / air conditions (pressure: 1 bar, temperature: 70 ° C.). A cell voltage of 715 mV is obtained at a current density of 600 mA / cm ² . This corresponds to a good power density of 0.43 W / cm ² .

Example 2

a) production of two-layer CCM with integrated sealing material

A 50 micron thick ionomer membrane is coated with the catalyst layer by continuous screen printing. A cathode layer having a Pt load of 0.4 mg of Pt / cm ² and a thickness of 15 microns is applied. After drying, 72 x 72 mm of active area is stamped from this structure. Polyamide sealing rims (see Example 1; window size 68 x 68 mm; thickness: 75 microns; external dimensions 100 x 100 mm) are concentrated on the uncoated membrane side, and the overall structure is two in a hot press. Pressed between PTFE plates. The interview pressure is 250 N / cm ² based on the entire area of the sealing rim, the temperature is 160 ° C. and the pressing time is 2 minutes. After slow cooling, a two-layer CCM is obtained from the press.

b) production of 5-layer MEA

A large gas diffusion layer (30 BC type, SGL-carbon, Meitingen) for the anode is provided over its entire area with the catalyst layer (Pt load = 0.2 mg / cm ² ). After drying, smaller GDLs are stamped with dimensions of 76 x 76 mm. As a gas diffusion layer for the cathode, a catalyst-free GDL with dimensions of 76 x 76 mm is used. The anode gas diffusion layer, the two-layer CCM and the cathode gas diffusion layer are stacked on top of each other to concentrate the active region and bring the anode catalyst layer into contact with the uncoated membrane side. This structure is sequentially pressed in a hot press at 135 ° C. for 3 minutes. Interview pressure (based on the area of the gas diffusion layer) is 100 N / cm ² . Slow cooling results in a 5-layer MEE in which the individual components are firmly bound.

c) electrochemical measurements

A five-layer MEA is built into a single cell in a PEM fuel cell test station and tested under hydrogen / air conditions (pressure: 1 bar, temperature: 70 ° C.). A cell voltage of 705 mV is obtained at a current density of 600 mA / cm ² . This corresponds to a good power density of 0.42 W / cm ² .

Claims (17)

An ion-conductive membrane 1 having a front side and an opposite side; At least one catalyst layer 3; And A sealing material (4), The sealing material 4 is applied to the edge region of the ion-conducting membrane 1 and with the ion-conductive membrane 1 in the edge region up to at least 1 mm wide on either one of the front and the opposite side. Overlapping, catalyst-coated ion-conductive membrane for electrochemical devices. The catalyst-coated ion-conductive membrane of claim 1, wherein the thickness (d _D ) of the sealing material (4) corresponds at least to the thickness (d _CCM ) of the catalyst-coated ion-conductive membrane. The catalyst-coated ion-conductive membrane of claim 1, wherein the at least one catalyst layer comprises noble metal based catalysts and is applied over the entire area of the ion-conductive membrane. 4. The catalyst-coated ion-conductive membrane according to any one of claims 1 to 3, comprising both a catalyst layer (2) on the front side and a catalyst layer (3) on the opposite side of the ion-conductive membrane. The sealing material of claim 1, wherein the sealing material is polyethylene, polypropylenes, polytetrafluoroethylenes, PVDF, polyesters, polyamides, polyamide elastomers, polyimides And elastomers from the group consisting of polyurethanes or copolymers, silicones, silicone elastomers, EPDM, fluorinated elastomers, perfluorinated elastomers, chloroprene elastomers, fluorosilicone elastomers from the group consisting of polyurethanes Or thermoset polymers from the group consisting of epoxy resins, phenolic resins and cyano-catalysts. The ion-conducting membrane of claim 1, wherein the ion-conducting membrane is proton-conductive perfluorinated polymerizable sulfonic acid compounds, doped polybenzimidazoles, polyether ketones, polysulfones or ion-conductive A catalyst-coated ion-conducting membrane comprising organic polymers having ceramic materials. An ion-conductive membrane 1 having a front side and an opposite side; A first catalyst layer (2) on the front side; A second catalyst layer (3) on the opposite side; A first gas diffusion layer (5) on the front side; A second gas diffusion layer (6) on the opposite side; And A sealing material (4), The sealing material (4) is in contact with the interior of each of the gas diffusion layers (5 and 6) in an edge region up to at least 1 mm wide. 8. The membrane electrode assembly of claim 7, wherein the gas diffusion layers (5 and 6) comprise porous electrically conductive materials with woven carbon fiber fabrics, carbon fiber felts or carbon fiber papers. Providing an ion-conductive membrane 1 having at least one catalyst layer applied over the whole area; And A catalyst-coating with integrated sealing material, comprising applying a sealing material 4 to the edge region of the ion-conductive membrane 1 on one side with the aid of elevated or elevated temperature or elevated and elevated temperature. Process of prepared ion-conductive membrane. Providing a catalyst-coated ion-conductive membrane having a sealing material as claimed in claim 1, and A membrane with an integrated sealing material, comprising applying gas diffusion layers 5 and 6 to the front and opposite sides of the catalyst-coated ion-conductive membrane with the aid of elevated or elevated or elevated and elevated temperatures. Manufacturing process of the electrode assembly. Providing an ion-conductive membrane 1 having at least one catalyst layer applied over the whole area, Placing a sealing material 4 on one side of the edge region of the ion-conductive membrane 1, wherein the sealing material 4 is at least 1 mm wide on the one side in the edge region Placing it so as to overlap with the conductive membrane 1, Placing gas diffusion layers 5 and 6 on the front and opposite sides of the catalyst-coated ion-conductive membrane, -Joining the structure at elevated or elevated or elevated and elevated temperatures, a process for manufacturing a membrane-electrode assembly with an integrated sealing material. 10. The integrated sealing material of claim 9, wherein the pressure (quoted as area pressure based on the frame area of the sealing material) is in the range of 50 to 300 N / cm ² and the temperature range is 20 to 200 ° C. Process for preparing a catalyst-coated ion-conductive membrane having The integrated seal according to claim 10 or 11, wherein the pressure (quoted as the area pressure based on the area of the gas diffusion layer) is in the range of 50 to 200 N / cm ² and the temperature range is 20 to 200 ° C. Process for the manufacture of membrane-electrode assembly with ring material. Catalytically-coated ion-conductive, characterized in that the catalyst-coated ion-conductive membranes as claimed in claim 1 are used for producing membrane-electrode assemblies of electrochemical devices. Method of Using Membranes. Method of using membrane-electrode assemblies, characterized in that the membrane-electrode assemblies according to claim 7 are used for producing electrochemical devices. delete delete

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