JP2008166117A - Manufacturing method of membrane-electrode assembly for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a membrane-electrode assembly for a fuel cell preventing swelling in the surface direction of an electrolyte membrane in direct applying of catalyst ink to the electrolyte membrane. <P>SOLUTION: The manufacturing method of the membrane-electrode assembly for the fuel cell having a catalyst layer on the surface of an electrolyte membrane contains a process arranging the electrolyte membrane on a substrate which has a surface hardness of pencil hardness 5B or less, and applying catalyst ink containing at least a catalyst component and a solvent to the electrolyte membrane. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a membrane-electrode assembly for a fuel cell.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle and thus exhibit high energy conversion efficiency. A fuel cell is usually configured by laminating a plurality of single cells having a basic structure in which an electrolyte membrane is sandwiched between a pair of electrodes. Among them, a solid polymer electrolyte fuel using a solid polymer electrolyte membrane as an electrolyte membrane Batteries are particularly attracting attention as portable and mobile power sources because of their advantages such as being easy to downsize and operating at low temperatures.

  In the solid polymer electrolyte fuel cell, the electrodes provided on both surfaces of the electrolyte membrane include a catalyst component that has a catalytic action for the electrode reaction that proceeds in each electrode, and usually in order from the solid polymer electrolyte membrane side, It has a multilayer structure in which a catalyst layer containing a catalyst component and a gas diffusion layer for diffusing a reaction gas in the catalyst layer are laminated.

For example, the following methods (1) to (3) are known as a method of providing electrodes having such a multilayer structure on both surfaces of the electrolyte membrane.
(1) First, a catalyst layer sheet prepared by applying and drying a catalyst ink containing a catalyst component on a transfer substrate such as polytetrafluoroethylene, and the surface on which the catalyst layer is formed becomes the electrolyte membrane side. So as to thermocompression-bond with the electrolyte membrane, peel off the substrate from the catalyst layer sheet to produce an electrolyte membrane comprising the catalyst layer, and subsequently join the gas diffusion layer on the catalyst layer,
(2) A method in which a gas diffusion layer having a catalyst layer formed by applying and drying a catalyst ink on the surface and thermocompression bonding with the electrolyte membrane so that the catalyst layer is on the electrolyte membrane side,
(3) A method in which a catalyst ink is directly applied on an electrolyte membrane and dried to form a catalyst layer, and then a gas diffusion layer is bonded onto the catalyst layer.

When a material having a high glass transition temperature is used as the electrolyte contained in the electrolyte membrane and / or the catalyst layer adjacent to the electrolyte membrane, the electrolyte membrane and the catalyst layer are joined by thermocompression bonding as in (1) and (2) above. In this method, the electrolyte membrane and the catalyst layer may not be sufficiently bonded. This is because heating the electrolyte so as to sufficiently soften the electrolyte having a high glass transition temperature may cause deterioration of the electrolyte itself or other constituent materials. As a result, the contact resistance between the electrolyte membrane and the catalyst layer increases, and the power generation efficiency of the fuel cell decreases.
On the other hand, the method (3) in which the catalyst ink is applied directly to the electrolyte membrane surface is easier to secure the bonding property between the electrolyte membrane and the catalyst layer than the methods (1) and (2). It can be said that this method is suitable when an electrolyte having a high glass transition temperature is used.

However, when the catalyst layer is formed on the surface of the electrolyte membrane by the method (3), there is a problem that the electrolyte membrane swells by absorbing the solvent in the catalyst ink when the catalyst ink is applied. The solvent in the catalyst ink applied to the electrolyte membrane evaporates by the drying step subsequent to the catalyst ink application step. At this time, the solvent of the catalyst ink soaked in the electrolyte membrane evaporates, so that the swelled electrolyte membrane Dry and shrink. The swelling and shrinkage of the electrolyte membrane as described above occurs in both the surface direction and the thickness direction of the electrolyte membrane, but wrinkles are generated in the electrolyte membrane due to the shrinkage in the surface direction and are formed on the electrolyte membrane accordingly. Wrinkles and cracks will also occur in the catalyst layer.
Thus, when wrinkles or the like are generated in the electrolyte membrane or the catalyst layer, the adhesion with other layers such as a gas diffusion layer subsequently formed on the catalyst layer is poor, and the performance of the fuel cell is lowered. In addition, the cracking of the catalyst layer may deteriorate the performance of the fuel cell by causing physical damage such as biting into the electrolyte membrane when pressure is applied to the catalyst layer.

  As a method of suppressing wrinkles of the electrolyte membrane and electrodes due to the swelling / shrinkage of the electrolyte membrane as described above, for example, Patent Document 1 discloses that a solid polymer membrane is formed by evacuation on a porous plate kept at a constant temperature. A method of forming an electrode layer by applying a slurry containing a polymer material to a solid polymer film in a held state has been proposed.

JP 2003-100314 A

  The method described in Patent Document 1 promotes evaporation of the catalyst ink by applying the catalyst ink to the electrolyte membrane in a state where the electrolyte membrane is fixed on the porous plate maintained at a constant temperature by evacuation. It suppresses swelling of the electrolyte membrane. However, since the catalyst ink applied to the electrolyte membrane diffuses into the electrolyte membrane simultaneously with the application, it is difficult to sufficiently suppress the swelling of the electrolyte membrane by the method described in Patent Document 1. As a result, wrinkles, cracks, etc. of the electrolyte membrane and electrode are generated. In addition, although the Example of patent document 1 has the description that an electrolyte membrane is hold | maintained on a porous board via a nylon mesh, there is no description or suggestion about the role of a nylon mesh. .

  The present invention has been accomplished in view of the above circumstances, and is a fuel cell membrane / electrode assembly capable of preventing swelling in the surface direction of an electrolyte membrane when a catalyst ink is directly applied to the electrolyte membrane. An object is to provide a manufacturing method.

  The method for producing a membrane / electrode assembly for a fuel cell according to the present invention comprises a catalyst ink containing at least a catalyst component and a solvent in a state where the electrolyte membrane is disposed on a substrate having a surface hardness of 5B or less. The method includes a step of applying to the electrolyte membrane.

When the electrolyte membrane is disposed on the base material having the surface hardness as described above, the electrolyte membrane is fixed on the base material, and the displacement in the plane direction is limited. By applying the catalyst ink to the electrolyte membrane fixed to the substrate in this way, the electrolyte membrane can be prevented from swelling in the surface direction even if the catalyst ink is absorbed in the electrolyte membrane.
Therefore, according to the present invention, even when an electrolyte membrane that easily swells is used, wrinkles and the like are unlikely to occur in the electrolyte membrane and the catalyst layer, and a membrane / electrode assembly having a uniform catalyst layer can be obtained. it can. In addition, the manufacturing method of the present invention does not require any equipment such as a temperature control device or its condition setting, and is very simple.

  From the viewpoint of adhesion between the electrolyte membrane and the base material, the base material is preferably an elastic body.

  According to the production method of the present invention, when the catalyst ink is directly applied to the electrolyte membrane, even if the electrolyte membrane absorbs the solvent component in the catalyst ink, swelling in the surface direction of the electrolyte membrane is suppressed. Therefore, even when the solvent component absorbed in the electrolyte membrane volatilizes and the electrolyte membrane contracts, the electrolyte membrane is less likely to wrinkle, and the catalyst layer formed on the electrolyte membrane surface is less likely to be wrinkled or cracked. . Therefore, according to the production method of the present invention, by applying the catalyst ink directly to the electrolyte membrane, the uniform catalyst in which the occurrence of wrinkles and cracks is suppressed while maintaining the bondability between the electrolyte membrane and the catalyst layer. A layer can be formed. As a result, it is possible to provide a fuel cell excellent in power generation performance and durability.

  The fuel cell membrane / electrode assembly production method of the present invention is a method for producing a fuel cell membrane / electrode assembly comprising a catalyst layer on the surface of an electrolyte membrane, and the surface hardness is 5B or less of pencil hardness. The method includes a step of applying a catalyst ink containing at least a catalyst component and a solvent to the electrolyte membrane in a state where the electrolyte membrane is disposed on a base material.

  The production method of the present invention is characterized in that when the catalyst ink is directly applied to the surface of the electrolyte membrane 1, the electrolyte membrane 1 is disposed on a soft substrate 2 having a low surface hardness (see FIG. 1). ). The electrolyte membrane disposed on such a base material is in a state of being fixed on the base material due to the adhesiveness between the base material and the displacement in the surface direction is limited.

  According to the present invention, in a state where the electrolyte membrane is arranged on such a base material, the catalyst membrane is applied to the electrolyte membrane, so that even if the solvent in the catalyst ink soaks into the electrolyte membrane, the electrolyte membrane is based on the electrolyte membrane. Since it is firmly fixed on the material, swelling in the surface direction of the electrolyte membrane can be suppressed. Therefore, when the solvent in the catalyst ink is removed from the electrolyte membrane in the drying step, there is little shrinkage in the surface direction of the electrolyte membrane.

  As described above, according to the present invention, it is possible to suppress swelling in the surface direction of the electrolyte membrane during application of the catalyst ink, which is a major cause of wrinkles and cracks in the electrolyte membrane and the catalyst layer. That is, according to the production method of the present invention, a uniform catalyst layer can be formed while ensuring the bonding property between the electrolyte membrane and the catalyst layer by applying the catalyst ink to the electrolyte membrane. Therefore, it is possible to prevent a decrease in power generation performance of the fuel cell due to wrinkles or cracks in the electrolyte membrane and the catalyst layer.

In addition, according to the present invention, it is possible to form a catalyst layer by directly applying a catalyst ink even on an electrolyte membrane that swells easily because it has been difficult to apply the catalyst ink directly because of its high swelling property. It becomes.
In addition, the manufacturing method of the present invention can sufficiently prevent swelling in the lateral direction of the electrolyte membrane without particularly providing a device for controlling the temperature of the electrolyte membrane or a device for evacuating the electrolyte membrane. Since it is simple and simple, the cost can be reduced and the manufacturing process can be simplified.

The base material used in the present invention has a surface hardness of 5B or less, and can suppress swelling in the surface direction of the electrolyte membrane disposed on the base material.
Here, the surface hardness of 5B or less means that when the pencil hardness is measured according to the scratch hardness (pencil method) of JIS K5600-5-4, the surface of the substrate is softened with a pencil softer than 5B or 5B. It means being scratched. The pencil hardness is evaluated in 17 stages of 9H to H, F, H, HB, and B to 6B in order from the hardness side.

  The base material preferably has the surface hardness as described above and does not swell more than the electrolyte membrane in the surface direction due to absorption of the solvent. Even if the swelling in the surface direction of the electrolyte membrane is relatively suppressed on the base material due to the adhesion between the base material and the electrolyte membrane, the electrolyte membrane also expands and contracts as the base material expands and contracts in the surface direction. Because it ends up.

  The base material should just have the above properties, and there is no limitation in particular in a material and a shape. Further, the base material may be installed on the surface of an apparatus or the like for disposing an electrolyte membrane, or may be integrally formed on the surface of an apparatus or the like for disposing an electrolyte membrane.

  For example, as a material of the base material, silicone rubber or the like can be used. Silicone rubber can be suitably used because of its excellent heat resistance and chemical resistance. Silicone rubber has a functional group related to adhesion on the surface, has a low glass transition temperature, and has a property of easily fixing the electrolyte membrane, and exhibits a particularly high electrolyte membrane swelling suppression effect. . In addition, an elastic body such as silicone rubber can conform to the shape of the electrolyte membrane and be in close contact with the electrolyte membrane, thereby suppressing swelling in the surface direction more reliably. Furthermore, since the silicone rubber does not have water absorption, it is suitable as a base material from the viewpoint that it does not swell in the surface direction when the catalyst ink is applied.

In order to promote the volatilization of the solvent from the electrolyte membrane, the catalyst ink may be applied while evacuating the electrolyte membrane. By evacuating the electrolyte membrane, the solvent of the catalyst ink soaked into the electrolyte membrane can be quickly removed, and swelling of the electrolyte membrane can be suppressed.
When the electrolyte membrane is evacuated, a substrate having air permeability is used. Examples of the base material having air permeability include those provided with through holes and those having a mesh shape. The density, size, and the like of the through holes provided in the substrate are not particularly limited, and may be set as appropriate in consideration of the strength of the electrolyte membrane, the strength of the substrate, and the like.
If the base material 2 provided with such a through hole is evacuated through, for example, the porous plate 3 or the like, the electrolyte membrane 1 disposed thereon can also be evacuated (see FIG. 2).

  In the production method of the present invention, the electrolyte membrane that can be used is not particularly limited. For example, in addition to a fluorine-based polymer electrolyte such as perfluorocarbon sulfonic acid resin represented by Nafion (trade name, manufactured by DuPont). Hydrocarbon polymer electrolytes and the like can also be used. Here, the hydrocarbon-based polymer electrolyte typically does not contain any fluorine, but may be partially substituted with fluorine. Specifically, polyether ether ketone, polyether ketone, polyether sulfone may be used. , Engineering plastics such as polyphenylene sulfide, polyphenylene ether, polyparaphenylene, etc. and general purpose plastics such as polypropylene and polystyrene introduced proton conductive groups such as sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, boronic acid groups, etc. Can be mentioned.

As described above, according to the present invention, since the swelling in the surface direction of the electrolyte membrane can be suppressed, even if the electrolyte membrane is easily swelled, the catalyst ink is directly applied and the electrolyte membrane-catalyst layer bonding is performed. The body can be formed. For example, even an electrolyte membrane having a swelling rate (length) of 20% or more when impregnated in water at 80 ° C. for 1 hour can prevent swelling in the production method of the present invention, and should be suitably used. Can do.
Examples of the electrolyte membrane that easily swells include, generally, a membrane having a high ion exchange capacity.

  Among them, glass transition temperature is high, such as sulfonated polyetheretherketone (sulfonated PEEK) and sulfonated polyethersulfone (sulfonated PES) having high ion exchange capacity, and the catalyst layer. Since the bondability by thermocompression bonding is low, it is preferable to form the catalyst layer by a method of directly applying the catalyst ink to the electrolyte membrane, but even when using an electrolyte membrane that easily swells, according to the present invention, the electrolyte membrane By suppressing the swelling in the surface direction, a uniform catalyst layer can be formed, and the electrolyte membrane and the catalyst layer can be bonded well.

  The catalyst ink contains at least a catalyst component and a solvent. The catalyst component is not particularly limited as long as it has a catalytic action for the hydrogen oxidation reaction at the fuel electrode and the oxygen reduction reaction at the oxidant electrode. For example, platinum, ruthenium, iron, nickel, manganese And an alloy of a metal such as platinum and the like. These catalyst components are usually used by being supported on a conductive material such as a carbon material such as carbon particles or carbon fibers. The amount of the catalyst component contained in the catalyst ink is not particularly limited, but is usually about 20 to 70% by weight.

  The catalyst ink generally contains an ion conductive material in addition to the catalyst component and the solvent. The ion conductive material can be appropriately selected from materials used for the electrolyte membrane, and examples thereof include the fluorine-based polymer electrolyte and the hydrocarbon-based polymer electrolyte as described above. The amount of the ion conductive material contained in the catalyst ink is not particularly limited, but is usually about 5 to 30% by weight.

  The catalyst ink is obtained by mixing and dispersing a catalyst component, an ion conductive material, and, if necessary, other materials such as a water repellent polymer and a binder in a solvent. Examples of the solvent include alcohols such as ethanol, methanol, propanol, and propylene glycol, organic solvents such as dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP), and mixtures of organic solvents and water containing these alcohols. However, it is not limited to these.

  As a method of applying the catalyst ink on the electrolyte membrane, a general method may be used, and examples thereof include a spray method, a screen printing method, and a die coating method. The spray method is particularly preferred because of its high convenience and good power generation characteristics of the resulting fuel cell.

  A catalyst ink is applied to the electrolyte membrane disposed on the substrate, followed by drying to form a catalyst layer on the electrolyte membrane. Usually, a catalyst layer is also formed on the other surface in the same manner. The electrolyte membrane thus formed with the catalyst layer can be joined so as to be sandwiched between a pair of gas diffusion layer sheets to form a membrane-electrode assembly.

  As the gas diffusion layer sheet for forming the gas diffusion layer, a gas diffusion property that can efficiently supply gas to the catalyst layer, conductivity, and strength required as a material constituting the gas diffusion layer, for example, Carbonaceous porous bodies such as carbon paper, carbon cloth, carbon felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, lead alloy, titanium, niobium , Tantalum, iron, stainless steel, gold, platinum, and the like, and those made of a conductive porous material such as a metal mesh or a metal porous material. The thickness of the conductive porous body is preferably about 50 to 300 μm.

  The gas diffusion layer sheet may be composed of a single layer of the conductive porous body as described above, but a water repellent layer may be provided on the side facing the catalyst layer. The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, water-repellent resin such as polytetrafluoroethylene (PTFE), and the like. The water-repellent layer is not necessarily required, but it can improve the drainage of the gas diffusion layer while maintaining an appropriate amount of water in the catalyst layer and the electrolyte membrane. There is an advantage that electrical contact can be improved.

  The method for forming the water repellent layer on the conductive porous body is not particularly limited. For example, water repellent obtained by mixing conductive particles such as carbon particles, water repellent resin, and other components as necessary with an organic solvent such as ethanol, propanol, propylene glycol, water or a mixture thereof. The layer ink may be applied to at least the side of the conductive porous body facing the catalyst layer, and then dried and / or fired.

  The shape of the water repellent layer is not particularly limited, and may be, for example, a shape that covers the entire surface of the conductive porous layer on the catalyst layer side or a shape having a predetermined pattern such as a lattice shape. The thickness of the water repellent layer may usually be about 1 to 50 μm. Examples of the method for applying the water repellent layer ink to the conductive porous body include a screen printing method, a spray method, a doctor blade method, a gravure printing method, and a die coating method.

  In addition, the conductive porous body is formed by impregnating and applying a water-repellent resin such as polytetrafluoroethylene to the side facing the catalyst layer with a bar coater or the like, so that the moisture in the catalyst layer is efficiently removed from the gas diffusion layer. It may be processed so as to be discharged well, or a layer other than the above can be provided.

(Example)
An electrode catalyst was prepared by supporting 45% by weight of platinum-based catalyst particles having an average particle diameter of 3 nm on carbon black. This electrode catalyst and perfluorocarbon sulfonic acid resin solution (manufactured by Aldrich) were mixed so that carbon black: perfluorocarbon sulfonic acid resin (weight ratio) = 1: 1. Ethanol was added here, and it stirred for predetermined time using the ultrasonic cleaning apparatus, and produced the catalyst ink.

A sulfonated polyetheretherketone membrane (Victrex, sulfonation rate 50%, film thickness 50 μm) was placed on a silicone rubber (surface hardness: pencil hardness 5B).
The catalyst ink obtained above was sprayed directly on the surface of the sulfonated polyether ether ketone membrane and dried at 50 ° C. for 24 hours to form a catalyst layer.
The obtained catalyst layer was uniformly formed on the surface of the sulfonated polyether ether ketone membrane, and no wrinkles were generated on the membrane and the catalyst layer.

(Comparative example)
In the examples, the sulfonated poly (ether ether ketone) membrane was placed on a nylon mesh (surface hardness: pencil hardness F) instead of being placed on the silicone rubber and fixed with a clip. A catalyst layer was formed on the ether ether ketone membrane.
Many wrinkles were seen in the obtained membrane and catalyst layer. This is because when the catalyst ink was applied, the film was not sufficiently fixed, so the film that absorbed the solvent in the catalyst ink swelled in the surface direction and contracted by drying.

It is a figure explaining an example of the manufacturing method of the fuel cell of this invention. It is a figure explaining the other example of the manufacturing method of the fuel cell of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Base material 3 ... Porous board

Claims (2)

A method for producing a membrane / electrode assembly for a fuel cell comprising a catalyst layer on the surface of an electrolyte membrane,
A fuel comprising a step of applying a catalyst ink containing at least a catalyst component and a solvent to the electrolyte membrane in a state where the electrolyte membrane is disposed on a substrate having a surface hardness of 5B or less in pencil hardness. Manufacturing method of battery membrane / electrode assembly.   The method for producing a membrane / electrode assembly for a fuel cell according to claim 1, wherein the substrate is an elastic body.

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