WO2004091024A1

WO2004091024A1 - Catalyst-coated ionomer membranes and membrane-electrode assemblies with components having different colours

Info

Publication number: WO2004091024A1
Application number: PCT/EP2004/002615
Authority: WO
Inventors: Frank Baumann; Ralf Zuber
Original assignee: Umicore AG and Co KG
Current assignee: Umicore AG and Co KG
Priority date: 2003-04-07
Filing date: 2004-03-12
Publication date: 2004-10-21
Anticipated expiration: 2005-10-07
Also published as: DE10315796B4; DE10315796A1

Abstract

The invention relates to the field of electrochemical cells and fuel cells, more specifically to polymer-electrolyte-membrane fuel cells ('PEMFC') and direct methanol fuel cells ('DMFC'). It describes catalyst-coated ionomer membranes ('CCMs') and membrane-electrode-assemblies ('MEAs') embracing two components having different colours. The components having different colours can be gas diffusion layers, protective film layers, sealing layers or gasketing layers. The components having different colours help to distinguish the two reactive sides of the MEA (i.e. the anode side and the cathode side) from each other and thus facilitate the handling properties, particularly in automatic stack assembly lines. The CCMs and MEAs containing these components having different colours can be used for the manufacture of low temperature fuel cell stacks.

Description

Catalyst-coated ionomer membranes and membrane-electrode assemblies with components having different colours

The. invention relates to the field of electrochemical cells and fuel cells, more specifically to polymer-electrolyte-membrane fuel cells ("PEMFC") and direct methanol fuel cells ("DMFC"). It describes catalyst-coated ionomer membranes ("CCMs") and membrane-electrode-assemblies ("MEAs") embracing one or more coloured components. The components with different colours can be protective polymer film layers, sealing layers, gaskets or gas distribution layers and the like. The components with different colours help to distinguish the two reactive sides of the MEA (i.e. the anode side and the cathode side) from each other and thus facilitate the handling properties, particularly in automatic fuel cell stack assembly lines. The catalyst-coated membranes and membrane-electrode-assemblies (MEAs) are used as components iri low temperature fuel cell stacks.

Fuel cells convert a fuel and an oxidising agent into electricity, heat and water at two spatially separated electrodes. The technology of fuel cells is broadly described in the literature, see for example K. Kordesch and G. Simader, "Fuel Cells and its Applications", VCH Verlag Chemie, Weinheim (Germany) 1996.

A catalyst-coated membrane (hereinafter abbreviated "CCM") consists of a polymer electrolyte membrane which is provided on both sides with a catalytically active layer. Generally, the layers are different to each other: One of the layers takes the fόπri of an anode for the oxidation of hydrogen and the second layer takes the form of a cathode for the reduction of oxygen. As the CCM consists of three layers (anode catalyst layer, ionomer membrane and cathode catalyst layer), it is often referred to as "three-layer MEA". As outlined in this invention, the CCM may contain (a) film layer(s) for better handling, protection and sealing of the product. Gas diffusion layers ("GDLs"), sometimes referred to as gas diffusion substrates or backings, are placed onto the anode and cathode layers of the CCM in order to bring the gaseous reaction media (hydrogen and air) to the catalytically active layers and, at the same time, to establish an electrical contact. GDLs usually consist of carbon-based substrates, such as carbon fiber paper or woven carbon fabric, which are highly porous and allow the reaction gases a good access to the electrodes. Furthefmofe they are hydrophobic in order to remove the product water from the fuel cell. GDLs can be coated with a microlayer to improve the contact to the membrane.

A membfane-electfode-assembly ("five-layer MEA") is the central component in a polymef-electrolyte-membfane (PEM) fuel cell and consists of five layers: The anode^' GDL, the anode catalyst layer, the ionomer membrane, the cathode catalyst layer arid the cathode GDL. An MEA can be manufactured by combining a CCM with two GDLs (on the anode and the cathode side) or, alternatively, by combining an ionomer membrane with two catalyst-coated backings (CCBs) at the anode and the cathode side. In both cases, a five-layer MEA product is obtained. When the CCM contains (a) protective film layer(s) integrated in the laminated assembly, the five-layer MEA in turn contains these protective film layer(s) as well.

The anode and cathode electrode layers generally comprise different electro-catalysts, which catalyze the respective reaction (oxidation of hydrogen at the anode and. reduction of oxygen at the cathode). The metals of the platinum group of the" periodic table are preferably used as the catalytically active components. For the most partj supported catalysts are used, in which the catalytically active platinum group metals have been fixed in nano-sized particle form to the surface of a conductive support material. The average particle size of the platinum group metal is between about 1 arid 10 nm. Carbon blacks with particle sizes of 10 to 100 nm and high electrical conductivity have proven to be suitable as support materials.

The polymer electrolyte membrane consists of proton-conducting polymer materials.

These materials are also referred to below as ionomer membranes. Tetrafluόrόethyiene- fluorovinyl-ether copolymer with sulfonic acid groups is preferably used. This material is marketed for example by E.I. DuPont under the trade name Nafiόn^®. However, other, especially fluorine-free, ionomer materials such as sulfonated polyether ketόries or afyl ketones or acid-doped polybenzimidazoles may also be used. Suitable ioiiόmer materials are described by O. Savadogo in "Journal of New Materials for Electrochemical Systems" I, 47-66 (1998). For application in fuel cells, these membranes generally have a thickness between 10 and 200 μm. In the construction of a PEMFC stack, several membrane-electrode-assemblies and bipolar plates are stacked in series to obtain the desired voltage output. Generally, these components (predominantly CCMs, MEAs and bipolar plates) are sealed against leakage to the environment and against intermixing of the reactants (hydrogen and Oxygen/air) with gas-tight seals. The technology for manufacturing fuel cell components and sealings is well described in the literature.

hi US 6,500,217 Bl a continuous method for the manufacture of catalyst-coated membranes by applying electrode layers to a polymer electrolyte membrane strip is disclosed.

US 2002/0064593 Al, teaches a continuous process for producing 5-layef MEAs for fuel cells.

In US 3,134,697, a sealing function is conventionally achieved by Using pre-cut frames of polymer material and placing these frames around the electrodes of the fuel cell between the membrane and the bipolar plates of the cell.

EP 690 519 addresses the stabilisation of the membrane in the inactive sealing region. It relates to an assembly consisting of at least one seal layer in a solid polymer ioή exchange layer wherein the seal layers cover essentially only the region of the ioή exchange layer which is to be sealed. The sealing layer is made of polytetrafluoroethylene (PTFE) film having one surface coated and partially impregnated with the ionomer material.

WO 00/10216 describes a membrane electrode gasket assembly having a gasket and a sub-gasket to seal the MEA and to protect it from possible edge failures. The gasket material typically consists of expanded polytetrafluoroethylene (e-PTFE) soaked with a solution of ionomer for better adhesion.

EP 1 184925 A2 describes a method of the manufacture of PEMFC stacks by assembUng MEAs and bipolar plates, characterised by a characteristic compression process.

Generally, in the PEM stack assembly process, the MEAs must be assembled with bipolar plates in a certain well defined order to build the stack. Depending oil the power output required, a certain number of MEAs (sometimes up to 100 MEAs for a 50 kW stack) are stacked onto each other. In this process, the anode side of the MEA (i.e. the side where the hydrogen containing feed gas enters the stack) is always separated from the cathode side (i.e. the air supply side). In the stack assembly, the MEAs are connected electrically in "series" in the following way: anode - membrane - cathode // bipolar plate // anode - membrane - cathode // bipolar plate // etc.

A change by mistake of the anode and cathode side of the MEA / CCM during stack assembly could lead to severe failures in the complete PEM stack. The anode side of the MEA, usually containing CO-tolerant PtRu-electrocatalysts, would be exposed to air (i.e. oxidized) and the cathode side would get in contact with hydrogen. As a result of such a type of fault in assembly, the performance and reliability of the stack is severely affected. The stack has to be disassembled and rebuilt with the MEA assembled properly in series. Thus, this type of fault must be completely avoided.

When the PEM stack is assembled manually, considerable care must be taken to identify the correct side (i.e. the anode side or cathode side) of the MEA / CCM prior to the assembly of the stack. This can be a very time-consuming process, which could lead to long assembly times and thus to high labour costs associated with this process.

Given this background, it is an object of the present invention to make available MEAs and CCMs which allow a better, safer and faster handling in PEMFC stack assembly. Better handling and faster processing is most important in large scale continuous production of CCMs and MEAs as necessary for the future widespread commercialisation of fuel cells.

This problem was solved by providing CCMs and MEAs containing components with different colours. For example, to better distinguish the anode side of the MEA from the cathode side,, the anode side can be identified by using e.g. a black coloured polymer film layer as protective film layer and the cathode side can be identified by using, e.g. a white polymer film.

The term "having different colours" in the present invention means any difference in the properties, e.g. of the surface and/or appearance, of the component, which can be Used to visually distinguish the two sides of the product.

Suitable properties can be the colour (black, red, white, transparent etc), roughness (e.g. smooth, rough or textured), transparency (e.g. opaque, high or low) of, more generally, appearance (e.g. shiny, glossy, bright, dark). Preferably the distinguishing property is a difference in colour. Although the colour properties are referred to throughout this application, it is to be understood that any of the above properties can also be Used. The difference in the above-mentioned properties of the two components should be sufficient to allow a differentiation by automatic sensors or similar recognition systems. The applicable CUE Standards may act as a guideline for suitable colour differences.

Among the colour models most preferred is the CIELAB colour model, hi this system, colour differences are documented by three values (L* = lightness, a* = red to green, and b* = blue to yellow). The central vertical axis ("grey scale axis") represents lightness (signified as L*), whose values run from 0 (black) to 100 (white). Typically, differences of ΔL = +/- 5 can be detected by the naked eye and by suitable colour recognition sensors. On the a* to -a* axis, positive values indicate amount of red, while negative values indicate amount of green. On the b* to -b* axis, yellow is positve and blue is negative. Typically, differences of Δ a* and Δ b* of +/- 5 Units can be detected by the naked eyeand by suitable colour sensor systems.

The colour differences of the components may be detected by visual light (VIS), by UV light, by IR, or by other suitable spectroscopic methods. The suitable pigments and colouring agents are selected accordingly.

hi fully automated continuous production lines* robots equipped with suitable recognition systems can easily distinguish the anode and cathode sides of MEAs and/of CCMs by the different properties associated with them. Consequently, the stack assembly process can be made faster, safer and more economical. The same holds- true for manual stack assembly, where the worker can easily distinguish the two different sides of the MEA by the naked eye and assemble the MEA in the proper fashion.

The components added to the CCM and/or MEA are generally present in a flat forfii, perferably in film or layer form. The components can be protective polyή er film layers, sealing layers, gaskets or gas distribution layers and the like.

In one embodiment of the present invention, the components are a protective polymer material, fof example out of pre-cut polymer films. These films are furnished hi two different colours and are used for the two different sides of the MEA.

In another embodiment of the pfesent invention, the layered component can be made out of different types- of adhesives, for example silicon adhesives. Two adhesives having different colours are used as gasket materials to seal the MEA in the PEM stack.

In yet another embodiment, the components can be a GDL (Gas ^"Diffusion Layer), which comprises sealing components with different colours. Furthermore, it is an object of the present invention to provide a process fof the manufacture of the improved MEA and CCM products containing the components having different colours.

The present invention comprises three major preferred embodiments, Which are described hereinafter to illustrate the invention. However, the invention is not restricted to these preferred embodiments. i

In embodiment 1 (ref. to Figure 1) of the present invention, the components having different colours are made from two types of pasty or liquid adhesive materials with different colours (4a, 4b). When applied to the 5-layer MEA, containing a CCM with an ionomer membrane (1), two catalyst layers (2) and two gas diffusion layers (3), for example by injection moulding or by paste application, they act as a gas-tight seal. The MEA can be made in various designs, including coextensive or non-coexteήsive designs.

In embodiment 2 of the present invention, gas tight sealing materials, for example pre- cut sealing films, are applied in two different colours to each side of the MEA as shown in Figure 2. It shows a schematic drawing (cross section) of a catalyst-coated membrane (CCM) according to the second embodiment of the present invention. The ionomer membrane (1) is coated on both sides with electrode layers (2) forming the active area of the catalyst-coated membrane. Two frames of protective film layers (3) with different colours (3a: colour 1; 3b: colour 2) are applied on both sides to the passive afea of the membrane (1). The protective film may be made from a polymer which is more rigid than the ionomer membrane. The thickness of the protective film is in the range of 10 μm to 150 μm (preferably in the range of 80 to 120 μfn) and can constitute a protection for the ionomer membrane against pressure, impact, wear, heat, drying out etc. The protective film layef is tightly fixed onto the membrane and ϊhay overlap with the electrode layer. It can be pre-shaped and heat-laminated or attached by an adhesive onto the membrane.

In embodiment 3 (ref. to Figure 3), the gas diffusion layers contain sealing materials with different colours. It is feasible to apply a sealing material in the form of a coloured liquid, to press the coloured liquid into the GDL and to cure the Hquid providing a solid protective film penetrating the GDL. By soaking the GDLs with liquid sealant having different colours, GDLs with differently coloured sides can be produced. Alternatively, the pre-cut sealing films can be applied in two different colours to each side of the 5- layer MEA (i.e. on the top of the anode GDLs and on the top of the cathode GDL from the reversed side). Subsequently, this assembly can be treated by a lamination process involving heat and pressure. After lamination, the GDL appears impregnated όή both sides with the protective film material having different colours in the sealing areas of the MEA. Thus, the different sides of the MEA can be easily distinguished by their colour.

According to this invention, useful sealing and protecting polynϊeϊ materials can be in film, foil or sheet form. Alternatively they could be available in paste or liquid form for printing, brashing or stamping application. Generally, all materials should be stable and resistant to the operating conditions of membrane fuel cells, i.e. PEM and DMFC types. Furthermore, the materials should have high endurance and lifetime as well as high purity in respect to trace contaminants, residual volatile cofnponents and Other inorganic or organic materials, which could be leached out during operation of the fuel cell.

Preferred materials for polymer film layers are organic thermoplastic or duroplastic polymers such as polytetrafluoroethylene, PVDF, polyethylene, polypropylene, polyester, polyamide, co-polyamide, polyamide elastomers, polyimide, polyurethan'e, polyurethane elastomers, silicones, silicon rubbers, silicon-based elastomers and the like. For example, suitable polyurethane films are available on the market and can be obtained in various colours specified by the vendor.

Suitable colouring agents should be resistant to acid and substantially insoluble in water. Furthermore they should be stable to the operating conditions of a fuel cell particularly in respect to endurance and ageing resistance. Examples of suitable colouring agents are acid-resistant inert organic or inorganic colouring agents and pigments, as commercially available on the market.

Suitable colouring agents or pigments may be active in visible light, UV light, IR light or in any other area of the spectrum.

With respect to the other properties, which can be used to distinguish the components, the materials of the components can be selected and processed accordingly. Fof example, to achieve a difference in surface roughness casting, embossing or any othef suitable technique can be used. A difference in transparency can be achieved by adding, e.g. ^"particulate matter. Finally, a difference in appearance can be reached by suitable methods depending on the composition of the component. All types of commercially available GDLs as well as other suitable materials can be used for the formation of components having different colours for use in this invention. As base materials for GDLs, woven carbon cloth, non-woven carbon fiber layers of carbon fiber papers can be used. Typical GDL base materials are Toray TGP-H-060 or Textron AvCarb 1071 HCB supplied by Textron Inc. The gas distribution layers may be hydrophobically treated. They may comprise additional carbon black microlayefs and catalyst layers, if necessary.

The bonding of the components having different colours (i.e. GDLs, protective layers, seal films etc) to the CCM can be conducted by application of pressure and heat (for example in a lamination process). Appropriate bonding or laminating conditions should be adapted to the mechanical stability of the base material of the components. It is also possible to bond the components by application of adhesives or glues and the like.

The following examples describe the invention in more detail. These examples are presented to aid in an understanding of the present invention and are not intended to, and should not be construed to, limit the invention in any way.

EXAMPLES

Example 1;

The catalyst-coated membrane used in this example was manufactured according to U.S. Patent No. 6,309,772. A 40 wt.% Pt/Vulcan XC72 catalyst was used as a cathode catalyst, and 40 wt.% PtRu (l:l)/Vulcan XC72 was employed for the anode side. The CCM product is available from OMG AG & Co. KG under the designation "CCM-Type 7C" and was used with a 100 cm² (10 x 10 cm) of active area. The passive area (the non-coated area) of the CCM had a size of 1.0 cm in width, resulting in overall CCM dimensions of 12 x 12 cm with the active area centered in the middle.

Polyurethane-based film materials (PU film white and PU film black) with a thickness of 50 μm were used as a protective film layer.

The catalyst-coated membrane was placed between a frame of black protective film material on the cathode side and a frame of white protective film material on the anode side, and the assembly was covered by two sheets of PTFE blanks. The protective film frames were positioned with respect to the catalyst-coated membrane so that the peripheral membrane rim was completely covered, and a 2 mm broad fegiofi of the active area overlapped with the inner edge of the frame Of protective film όή both sides of the CCM. Lamination of the package was performed at 27 bar and a temperature of 145°C for 2 minutes.

A catalyst coated membrane (CCM) with a white protective layef on the anode side and a black protective layer at the cathode side was obtained. The CCM and two gas diffusion layers (GDLs), one on the anode and one on the cathode side, were mounted into a PEM single cell and tested in hydrogen/air operation at 2.7 bar operating pfessu at 70°C cell temperature. The electrical performance was in the range of 650 mV at a current density of 600 mA/cm².

Due to the colour differences of both sides, the MEA assembly was fast and easy.

Example 2:

The catalyst-coated membrane (CCM) used in this example was identical to the one used in example 1, however, instead of protective film layers with different colours, differently coloured gasket layers (i.e. seal layers) are applied to the CCM. Elastomer materials (Silicon Elastomer VMQ 0,4 mm thick, red coloured and black coloured) were used as seal layers for the PEM fuel celi. The elastomer was cut to rectangular frames of 2 mm width with a 74 mm to 74 mm wide opening. One frame of red coloured elastomer material and one frame of black coloured elastomer material wefe provided. Both frames were brush-coated with liquid adhesive on one surface. The catalyst-coated membrane was then placed between the frames with the coated frame surface directed to the membrane. The red seal frame was placed onto the cathode side and the black seal frame onto the anode side of the CCM, and the assembly was covered by two sheets of PTFE blanks. The seal frames were positioned onto the ήiembfane peripheral rim of the catalyst-coated membrane so that they closely enveloped the active catalyst coated area on both sides of the CCM. Lamination of the package was completed at 10 bar at room temperature for 2 minutes.

The catalyst-coated membrane with attached seal frames and two GDLs were again mounted into a PEM single cell and tested in hydrogeή/aif operation at 1.0 bar / 7 °C for an extended period of 300 hours. An excellent long-term performance was obtained. Microscopic inspection of the catalyst-coated membrane showed no indications for damage, either in the seal frames or at the interface between seal frame and active area of the CCM. Example 3:

A catalyst-coated membrane (CCM, type 7C, OMG AG & CO KG, HanaU) was transferred into a 5-layer MEA by attaching two GDL base materials (Tofay TGP-H- 060) to both sides of the CCM. The gas distribution layef s were hydf ophόbically t ated and comprised an additional carbon black microlayef. Two frames of polyurefhane- based film materials (PU-type white and PU-type black) with a thickness of 150 μm were applied onto both GDLs. This seven layer-sahdwich assembly was laminated at 200 °C at pressure of 30 bar for 2 minutes. After this process, a bicoldur 5-layef MEA was obtained. Due to the different coloufs of the film materials, the anode and the cathode side of the MEA could be easily distinguished.

Example 4;

A catalyst-coated membrane (CCM, type 7C, OMG AG & CO KG, Hanau) was transferred into a 5-layer MEA by attaching two GDL base materials (Toray TGP-H- 060) to both sides of the CCM. The gas distribution layers were hydrophobically treated and comprised an additional carbon black micfolayer. The 5-layer MEA was transferred into a suitable mould and a bi-coloured sealing rim was applied by means of injection moulding around the outer edge of the MEA.

Claims

1. Catalyst-coated membrane for use in an electrochemical cell, comprising an ionomer membrane coated with catalyst layers on both sides of the membfane surface and two components, one attached to the front surface and one attached to the back surface of said catalyst-coated membrane, wherein the t o components have different colours.

2. Catalyst-coated membrane according to claim 1, wherein one of the components having different colours comprises one or more acid resistant, watef-insόluble colouring agents.

3. Catalyst-coated ionomer membrane according to claim 1, wherein the components having different colours are gas diffusion layers, protective film layers, sealing layers and/or gasketing layers.

4. Catalyst-coated membrane according to claim 1, wherein the components having different colours are protective film layers, sealing layers aήd/or gasketing layers which comprise polytetrafluoroethylene, PVDF, polyethylene, polypfopylefie, polyester, polyamide, co-polyamide, polyamide elastomers, polyimides, polyurethanes, polyurethane elastomers, silicones, silicon rubbers, or silicon based elastomers.

5. Catalyst-coated membrane according to claim 1, wherein the components having different colours are gas diffusion layers which comprise carboii fibef papers, woven carbon cloths, non-woven carbon fabrics or carbon fiber fleeces.

6. Membrane-electrode-assembly for use in an electrochemical cell, comprising an ionomer membrane coated with catalyst layers on both sides of the membfane surface, two gas diffusion layers covering the catalyst layefs of said catalyst- coated membrane, and two components, one attached to the front surface and one attached to the back surface of said catalyst-cόated membfane, wherein the two components have different colours.

7. A process for manufacturing a catalyst-coated membrane according to any of claims 1 to 5, wherein the components having different colours are assembled with the catalyst-coated membrane by a process involving pressure and heat.

8. A process for manufacturing a catalyst-coated membrane accofding to claim 7, wherein the process is a lamination process involving pressure in the range of 10 to 100 bar and temperatures in the range of 20 to 300°C.

9. A process for manufacturing a membrane-electrode-assembly according to claim 7, wherein the catalyst-coated membrane, the gas diffusion layers and the components having different colours are assembled by a process involving pressure and heat.

10. A process for manufacturing a membrane-electrode-assembly according to claim 9, wherein the process is a lamination process involving pressure in the range of 10 to 100 bar and temperatures in the range of 20 to 300°C.

11. Use of a catalyst-coated membrane according to any of claims 1 to 5 for the manufacture of a PEM or DMFC fuel cell stack.

12. Use of a membrane-electrode-assembly according to claim 6 for the manufacture of a PEM or DMFC fuel cell stack.