JP5374094B2 - Electrode paste and method for producing the same, electrode, membrane-electrode assembly, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode which can be simply manufactured and has an excellent binding property, excellent water repellency, excellent water resistance and excellent methanol resistance, and to provide a paste for an electrode suitable for manufacture of the electrode. <P>SOLUTION: A method of manufacturing the paste for electrode has a process of blending, mixing and kneading an electron transportable material supporting a catalyst, a bridging compound (X) having a silicon-oxygen bond, a polymer material (Y) having an acid group and an aqueous dispersion (Z) including a fluorine-based resin which is fiberized by adding shearing force to fiberize the fluorine-based resin. The paste for electrode manufactured by the manufacturing method, the electrode using such the paste for electrode, a membrane-electrode assembly arranging such the electrode on both surfaces of the electrolyte membrane, and a fuel cell having such the membrane-electrode assembly, are provided. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an electrode paste suitable for use in a fuel cell and a method for producing the same, an electrode using the paste, a membrane-electrode assembly using the electrode, and a fuel cell.

Fuel cells are classified according to the type of electrolyte constituting them. For example, a fuel cell whose electrolyte is composed of a solid polymer such as a cation exchange membrane or an anion exchange membrane is called a solid polymer fuel cell (hereinafter abbreviated as “PEFC”).
In general, an electrode of a fuel cell is composed of carbon powder carrying a catalyst such as platinum and a polymer material having an acid group. The current mainstream uses a sulfonated fluororesin (for example, Nafion (registered trademark) manufactured by DuPont) as a polymer material, but in recent years, other polymer materials (for example, hydrocarbon-based materials). The one using an organic silicon compound system) has been actively developed.

For example, an electrode using a sulfonated fluororesin generally has a solution obtained by dissolving the resin in a polar solvent such as alcohol as an electrode binder, and this is mixed with carbon powder carrying a catalyst such as platinum. Then, the obtained mixture is applied on a gas diffusion layer such as carbon paper and heated and pressed.
The electrode thus produced has an ion channel formed by aggregation of sulfonic acid groups, and has high proton conductivity. However, at Tg of 130 ° C. or higher, there is a problem of swelling due to poor high-temperature durability such as denaturation in a short time and a high affinity between methanol and resin used as fuel.

On the other hand, an electrode using an organic silicon compound-based polymer material is prepared by preparing a binder for an electrode containing a crosslinkable compound having a silicon-oxygen bond and a polymer material having an acid group, and platinum or the like. The carbon powder carrying the catalyst and a fluororesin such as polytetrafluoroethylene (PTFE) functioning as a binder and water repellent are mixed, and the resulting mixture is placed on a gas diffusion layer such as carbon paper. It is manufactured by applying and hot pressing.
The electrode produced in this way is excellent in high temperature durability and suppressed swelling due to methanol. However, there are many cases where the conductive polymer material does not have binding properties and water repellency, and a binding component such as PTFE is required, and in addition, sufficient binding properties and water repellency can be expressed. There is a problem that a large amount of PTFE is required.

Therefore, in order to solve such problems of binding properties and water repellency, it has been proposed to use a fluorine-based resin having a property of becoming a fiber by shearing as a polymer material. For example, Patent Document 1 discloses a technique for shearing PTFE by adding liquid paraffin, liquid polyethylene glycol or the like as a kneading aid to a mixture composed of carbon powder, a platinum catalyst and PTFE, and kneading the mixture. .
Japanese Patent Publication No. 6-97612

  However, in the method disclosed in Patent Document 1, it is necessary to process the kneaded product with an ion exchange resin after forming the sheet into a sheet. For this reason, the manufacturing process is complicated and disadvantageous in terms of process efficiency. Patent Document 1 does not mention water resistance and methanol resistance of the electrode.

  The present invention has been made in view of the above circumstances, and an electrode having excellent binding properties, water repellency, water resistance and methanol resistance, and an electrode paste suitable for the production of the electrode, which can be easily manufactured. The issue is to provide.

To solve the above problem,
The invention according to claim 1 is a polymer material having a catalyst-supporting electron-transmitting substance, a crosslinkable compound (X) forming a three-dimensional crosslinked structure by a silicon-oxygen bond, and a sulfonic acid group as an acid group (Y) and an aqueous dispersion (Z) containing polytetrafluoroethylene , which is a fluororesin that is fiberized by application of a shearing force , are kneaded and kneaded to fiberize the fluororesin. This is a method for producing an electrode paste.
The invention according to claim 2, wherein the polymeric material is a monomer containing a sulfonic acid group, electrode according to claim 1, characterized in that it consists of a monomer and containing a silicon atom does not contain a sulfonic acid group It is a manufacturing method of a paste.
According to claim 3 invention, the polymeric material, to claim 1 or 2 polymerizable unsaturated double bonds by the polymerization of monomers having characterized in that it comprises a sulfonic acid group-containing polymer obtained by It is a manufacturing method of the electrode paste as described.
The invention according to claim 4 is characterized in that the crosslinkable compound is 1,2-bis (triethoxysilyl) ethane, 1,6-bis (trimethoxysilyl) hexane, 1,9-bis (triethoxysilyl) nonane, 1,8-bis (triethoxysilyl) octane, 1,8-bis (diethoxymethylsilyl) octane, 1,4-bis (trimethoxysilylethyl) benzene, 1,4-bis (triethoxysilylethyl) benzene 1,8-bis (methyldiethoxysilyl) octane, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dimethyldimethoxysilane, Phenylmethyldimethoxysilane, ethyltrimethoxysilane N-propyltrimethoxysilane, i-propyltrimethoxysilane, n-butyltrimethoxysilane, silicic acid, potassium silicate, and sodium silicate. It is a manufacturing method of the paste for electrodes according to any one of claims 1 to 3.
The invention according to claim 5 is an electrode paste manufactured by the method according to any one of claims 1 to 4.
The invention according to claim 6 is an electrode characterized by using the electrode paste according to claim 5.
The invention according to claim 7 is a membrane-electrode assembly in which the electrode according to claim 6 is arranged on both surfaces of the electrolyte membrane.
The invention according to claim 8 is a fuel cell comprising the membrane-electrode assembly according to claim 7.

  According to the present invention, an electrode having excellent binding properties, water repellency, water resistance and methanol resistance can be easily produced.

Hereinafter, the present invention will be described in detail with reference to the drawings.
<Electrode, membrane-electrode assembly>
FIG. 1 is a schematic view illustrating an electrode of the present invention and a membrane-electrode assembly provided with the electrode. In addition, the electrode and membrane-electrode assembly of the present invention are not limited to those illustrated here, and it is needless to say that a part of the configuration can be appropriately changed within a range not impairing the effects of the present invention.
A catalyst layer 13 is provided on both surfaces of the electrolyte membrane 11, and a gas diffusion layer 14 is provided on the catalyst layer 13 to constitute the membrane-electrode assembly 1. The electrode 10 includes a catalyst layer 13 and a gas diffusion layer 14.
The catalyst layer 13 is formed by solidifying an electrode paste containing an electrode binder and an electron transfer material carrying a catalyst (hereinafter abbreviated as catalyst-supported electron transfer material). As shown in FIG. 1, the catalyst layer 13 has a structure in which the catalyst-carrying electron transfer material 13b is dispersed in the electrode binder solidified material 13a. The catalyst-carrying electron transfer material 13b is continuously present between the electrolyte membrane 11 and the gas diffusion layer 14 in contact with each other.
In FIG. 1, only the structure on the one surface 11a side of the electrolyte membrane 11 in the membrane-electrode assembly 1 is illustrated, but the opposite side to the surface 11a has the same structure. The illustration is omitted here.
Hereinafter, each configuration will be described in more detail.

[Electrolyte membrane]
As the electrolyte membrane 11, a known one can be used, and a proton conductive membrane is particularly suitable. If it is a commercial item, the product made by DuPont and Nafion (trademark) can be illustrated, for example.

[Gas diffusion layer]
The gas diffusion layer 14 is for optimizing the diffusion of a liquid such as gas, methanol, water, and is made of, for example, a porous conductive sheet. However, the gas diffusion layer 14 is not an essential component and may be provided as necessary.
The gas diffusion layer 14 is preferably water-repellent. In particular, in the cathode-side electrode, the generated water may cause flooding. However, by making the gas diffusion layer 14 water repellent, the generated water can be eliminated and the occurrence of flooding can be effectively suppressed. .
The thickness of the gas diffusion layer 14 is preferably 50 to 500 μm, and more preferably 100 to 400 μm.

Further, a conductive intermediate layer (not shown) may be further provided on the surface of the gas diffusion layer 14. As the conductive intermediate layer, a mixture of polytetrafluoroethylene (PTFE) which is a water repellent material and carbon black which is an electron transfer medium is preferable. In this case, the mixing ratio of carbon black and PTFE (carbon black: PTFE, mass ratio) is preferably 3: 7 to 7: 3, more preferably 4: 6 to 6: 4, and 5: 5 is particularly preferred.
The upper limit of the thickness of the conductive intermediate layer is preferably 0.1 mm. By doing in this way, a raise of resistance value can be suppressed and an output can be improved further. On the other hand, the lower limit of the thickness may be appropriately set in consideration of the strength of the conductive intermediate layer and the like.
Carbon black having a specific surface area of 10 m ² / g or more is preferable.

[Catalyst layer]
The catalyst layer 13 can be formed by solidifying an electrode paste containing an electrode binder and a catalyst-carrying electron transfer material.
The thickness of the catalyst layer 13 is preferably 5 to 150 μm, and more preferably 10 to 100 μm.
By using the electrode paste of the present invention, the electrode 10 has excellent binding properties, water repellency, water resistance and methanol resistance, and can be easily manufactured. Hereinafter, the electrode paste will be described in more detail.

<Paste for electrodes>
The electrode paste contains an electrode binder and a catalyst-carrying electron transfer substance.
The electrode binder includes a crosslinkable compound (X) having a silicon-oxygen bond (hereinafter abbreviated as a crosslinkable compound (X)) and a polymer material (Y) having an acid group (hereinafter referred to as a polymer material). (Abbreviated as (Y)) and an aqueous dispersion (Z) containing a fluororesin that is fiberized by application of shearing force (hereinafter abbreviated as aqueous dispersion (Z)).
The electrode binder is a liquid for mixing with a catalyst-carrying electron transfer substance to prepare a liquid or paste electrode paste. The following three characteristics are mainly required for the electrode binder.
(A) High affinity with electrode components (B) High proton conductivity after solidification and formation of catalyst layer (C) Pressure due to change in ambient temperature or inflow of gas or liquid after solidification The electrode binder according to the present invention has all of these characteristics by including the above-mentioned components, and as a result, can It is possible to realize an electrode and a fuel cell excellent in performance and durability.
Hereinafter, the components contained in the electrode paste will be described in detail.

(Catalyst-supported electron transfer material)
The catalyst-carrying electron transfer substance is a substance in which a catalyst is carried on an electron transfer substance. Since the catalyst has a small diameter and is difficult to handle as it is, it is supported on an electron transfer substance.
The electron-transmitting substance is not particularly limited as long as it has an electron-transmitting property and can carry a catalyst. Among these, carbon and various metals can be exemplified as carbon, and carbon is particularly preferable.
The shape of the electron-transmitting substance is not particularly limited as long as it can support the catalyst, but examples of preferable shapes include particles, plates, and porous bodies, and particles are particularly preferable.

As the catalyst, those known in the fuel cell field can be used. Of these, platinum catalysts and platinum-ruthenium alloy catalysts can be exemplified as preferable ones.
The shape of the catalyst is preferably in the form of particles, and the smaller the average particle diameter, the more preferable. In consideration of handleability, the average particle diameter is preferably 1 to 5 nm. The average particle diameter can be measured with a transmission electron microscope. By using such fine particles, the total surface area of the catalyst can be increased, and a more excellent effect of promoting the reaction can be obtained.

  A catalyst carrying | support electron transfer substance may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose. Here, when the type or shape of at least one of the electron transfer substance and the catalyst is different from each other, it means that “the type of the catalyst-carrying electron transfer substance is different”.

(Crosslinkable compound (X))
The crosslinkable compound (X) is heated in the presence of water and a catalyst, or neutralized with an acid and then heated to form a three-dimensional crosslinked structure with silicon-oxygen bonds. Preferable examples include 1,2-bis (triethoxysilyl) ethane, 1,6-bis (trimethoxysilyl) hexane, 1,9-bis (triethoxysilyl) nonane, 1,8-bis. (Triethoxysilyl) octane, 1,8-bis (diethoxymethylsilyl) octane, 1,4-bis (trimethoxysilylethyl) benzene, 1,4-bis (triethoxysilylethyl) benzene, 1,8- Bis (methyldiethoxysilyl) octane, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dimethyldimethoxysilane, phenylmethyldimethoxysilane, Ethyltrimethoxysilane, n-propyl Pills trimethoxysilane, i- propyl trimethoxy silane, alkoxysilane having an alkoxy silane or a substituent such as n- butyl trimethoxysilane; silicate, potassium silicate, silicate compound, sodium silicate and the like. Here, the “alkoxysilane having a substituent” refers to an alkoxysilane in which an alkoxy group or a hydrogen atom is substituted with a substituent other than these.
Furthermore, preferable examples of the silicate compound include those obtained by neutralizing silicates such as potassium silicate and sodium silicate with an acid, and those obtained by removing metal ions by treatment through an ion exchange resin.
Among these, as the crosslinkable compound (X), alkoxysilane or an alkoxysilane having a substituent is preferable, and alkoxysilane is more preferable.

  Crosslinking compound (X) may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  The blending amount of the crosslinkable compound (X) may be appropriately set in consideration of the types and amounts of other blending components, but is usually preferably 0.1 to 7% by mass in the binder for electrodes. More preferably, the content is 3 to 4% by mass, and particularly preferably 0.5 to 2% by mass. By setting it as such a range, the intensity | strength of a catalyst layer can be improved further.

  The crosslinkable compound (X) may be used in combination with alkoxytitanium, alkoxyaluminum, phosphoric acid, phosphate, tungstic acid or the like that can crosslink with this. When using these compounds together, these compounds may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  Since the crosslinkable compound (X) forms a three-dimensional cross-linked structure by silicon-oxygen bonds as described above, for example, when exposed to high acidity and high temperature and high humidity conditions, or alcohol such as methanol as a fuel. Even when the electrode is used, the electrode can maintain a relatively stable shape.

(Polymer material (Y))
The polymer material (Y) has proton conductivity, and has an acid group such as a sulfonic acid group (sulfo group), a carboxylic acid group (carboxyl group), a phosphoric acid group, a phosphonic acid group, or a phosphinic acid group. The polymer material which has can be illustrated. Preferable examples include vinyl sulfonic acid, allyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, 2- (methacryloyloxy) ethyl sulfonic acid, 3-sulfopropyl methacrylate, 4, Polymers obtained by polymerizing monomers having acid groups such as 4′-diaminostilbenzene-2,2′-disulfonic acid, bis (3-sulfopropyl) itaconate, acrylic acid, methacrylic acid, vinyl phosphoric acid, allyl phosphoric acid; An acid can be illustrated.
Among these, as the polymer material (Y), a polymer material having a sulfonic acid group is preferable.

  The polymer material (Y) may be one obtained by polymerizing one kind of monomer, or may be one obtained by copolymerizing plural kinds of monomers. When a plurality of types of monomers are copolymerized, the combination and ratio of these monomers may be appropriately selected according to the purpose. As a copolymer obtained by copolymerizing a plurality of types of monomers, a compound having a plurality of types of acid groups in one molecule is also preferable. Specifically, a vinyl sulfonic acid-acrylic acid copolymer is preferable. And 2-acrylamido-2-methylpropanesulfonic acid-acrylic acid copolymer and 2-acrylamido-2-methylpropanesulfonic acid-vinyl phosphoric acid copolymer.

The polymer material (Y) may further have a hydrophilic group other than an acid group. Examples of the hydrophilic group include a hydroxyl group, an amino group, an amide group, an oxo group, a carbonyl group, a formyl group, a nitro group, a mercapto group, and the like, and a hydroxyl group, an amino group, and an amide group are more preferable.
The hydrophilic group that the polymer material (Y) has in one molecule may be one kind alone, or two or more kinds. In the case of two or more types, the combination and ratio may be appropriately selected according to the purpose.
Preferred examples of the polymer material containing an acid group and a hydrophilic group include a vinyl sulfonic acid-vinyl alcohol copolymer and a 2-acrylamido-2-methylpropane sulfonic acid-vinyl alcohol copolymer.
As described above, the polymer material (Y) further has a hydrophilic group, so that the binding force between the catalyst-carrying electron transfer materials is further improved, and the water resistance and polar solvent resistance (for example, alcohol resistance) of the electrode is improved. ) Will improve.

  The polymer material (Y) may be obtained by polymerizing only a monomer having an acid group (hereinafter abbreviated as “monomer (V)”) or by copolymerizing the monomer (V) with other monomers. It may be good. The other monomer is not particularly limited as long as the effect of the present invention is not impaired as long as it can be combined with the monomer (V), and can be arbitrarily selected according to the purpose. Specifically, a monomer having no acid group; a crosslinking agent that does not correspond to the monomer (V) and has a plurality of functional groups capable of binding to other monomers can be exemplified. Specific examples of these other monomers include methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylamide, styrene, N, N′-methylenebis (acrylamide), neopentyl glycol diacrylate, 1,4-bis ( Acryloyloxy) butane, 1,3-bis (methacryloyloxy) -2-propanol, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1- (acryloyloxy) -3- (methacryloyloxy) -2-propanol, divinyl Examples thereof include benzene, 3- (methacryloylamino) propyltrimethylammonium chloride, and vinyl methacrylate.

Furthermore, as the “monomer having no acid group”, a monomer (W) having no acid group and containing a silicon atom can be exemplified as a preferable example.
Examples of the monomer (W) include 3- (trimethoxysilyl) propyl acrylate, 3- (methyldimethoxysilyl) propyl acrylate, 3- (triethoxysilyl) propyl acrylate, 3- (methyldiethoxysilyl) propyl acrylate, tri Methoxyvinylsilane, triethoxyvinylsilane, 3- (trimethoxysilyl) propyl methacrylate, 3- (methyldimethoxysilyl) propyl methacrylate, 3- (triethoxysilyl) propyl methacrylate, 3- (methyldiethoxysilyl) propyl methacrylate Preferred examples include rate, p-styryltrimethoxysilane, p-styryltriethoxysilane, and the like.
Examples of the monomer (V) to be copolymerized with the monomer (W) include vinyl sulfonic acid, allyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, and 2- (methacryloyloxy) ethyl sulfonic acid. , 3-sulfopropyl methacrylate, 4,4′-diaminostilbenzene-2,2′-disulfonic acid, bis (3-sulfopropyl) itaconate and the like can be exemplified as preferable examples.

The ratio of the amount of monomer (V) to monomer (W) used (monomer (V): monomer (W), molar ratio) is preferably 99: 1 to 50:50.
With this structure, the polymer material (Y) itself also has a silicon-oxygen cross-linked structure, which suppresses dissolution and swelling due to methanol, etc., improves the acid group concentration, and has high durability and high output. The fuel cell can be obtained.

  In the present invention, one or a plurality of polymer materials (Y) that are further crosslinked with a crosslinking agent may be used as the polymer material (Y). Here, examples of the crosslinking agent include the same ones as described above.

  The monomers exemplified above are available at a relatively low cost and are abundant in variety. Furthermore, since the reaction of the polymerizable unsaturated double bond proceeds relatively easily and the control of the reaction is easy, the desired polymer material (Y) can be easily obtained using a simple polymerization controller. .

A high molecular material (Y) may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.
The mass average molecular weight of the polymer material (Y) is preferably 1000 to 10000000, more preferably 5000 to 5000000.
In addition, in this invention, "mass average molecular weight" shall show the mass average molecular weight in conversion of standard polyethyleneglycol in a gel permeation chromatography (GPC) measurement.

  Particularly in the present invention, it is preferable to use a polymer material (Y1) having a smaller mass average molecular weight and a polymer material (Y2) having a mass average molecular weight larger than that of the polymer material (Y1). More specifically, the mass average molecular weight of the polymer material (Y1) is preferably 1000 to 300000, and more preferably 5000 to 100000. The mass average molecular weight of the polymer material (Y2) is preferably 300,000 to 10,000,000, more preferably 500,000 to 5,000,000. By doing so, the polymer material (Y1) easily enters the secondary aggregate (agglomerate) of the catalyst-carrying electron transfer substance, so that the output can be further improved by effectively using the catalyst. Can do. Furthermore, the polymer material (Y2) can maintain stable power generation performance even in an environment where the temperature is relatively high and the methanol concentration is high.

  The blending ratio of the polymer material (Y) is preferably 0.05 to 5 parts by mass and more preferably 0.1 to 3 parts by mass with respect to 1 part by mass of the crosslinkable compound (X). By setting it as 0.05 mass part or more, the electric power generation performance of an electrode improves further, and melt | dissolution and swelling by methanol etc. of an electrode can be suppressed by setting it as 5 mass parts or less.

The polymer material (Y) may be used in combination with other acid group-containing polymer materials or electrolyte materials known in the fuel cell field having proton conductivity. When these materials are used in combination, these materials may be used alone or in combination of two or more. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.
By using the materials other than the polymer material (Y) in combination, the proton conductivity of the fuel cell can be further improved.

  The water dispersion (Z) improves the shape retention and easy moldability of the electrode by imparting a function of binding the catalyst-carrying electron transfer materials. Further, the compatibility between the crosslinkable compound (X) and the polymer material (Y) is increased, and a more uniform structure is realized. As the fluorine-based resin in the aqueous dispersion (Z), a resin having a property of forming a fiber by applying a shearing force is used. Here, “fibrosis” means that the shape of the fluororesin changes to a fiber shape with a thickness of about 10 nm and a length of about several μm, and the aspect ratio increases. If it has such a characteristic, it can select from a well-known thing and a polyperfluoroalkylene resin is more preferable. That is, as the water dispersion (Z), a fluorine resin dispersion can be used, a polyperfluoroalkylene resin dispersion is preferable, and a PTFE dispersion can be exemplified as a particularly preferable one.

The aqueous dispersion (Z) contains water as a solvent, a fluororesin, and a surfactant as main components. As the fluororesin, those polymerized by a known method may be used, or various commercially available products may be used. In the case of polymerization, for example, a fluorine atom-containing monomer such as tetrafluoroethylene may be emulsion-polymerized in the presence of an appropriate solvent and a surfactant.
In addition, commercially available PTFE dispersions are also available, and preferable ones include “30J” manufactured by Mitsui DuPont Fluoro Chemical Co., “D-1, D-2” manufactured by Daikin Industries, Ltd., “AD938L, AD manufactured by Asahi Glass Co., Ltd. −1, AD639 ”and the like.

  The shape of the fluororesin before fiberization is preferably particulate, and the average particle diameter is preferably 0.1 to 0.8 μm, and preferably 0.2 to 0.4 μm. Is more preferable. When the average particle size is within this range, the stability of the aqueous dispersion (Z) and the dispersibility and stability of the electrode paste during electrode production are further improved. The average particle diameter can be measured with a laser light scattering device or the like.

  The surfactant is preferably a nonionic surfactant. Of these, particularly preferred are polyoxyalkylene alkyl phenyl ethers such as polyoxyethylene alkyl phenyl ethers and polyoxyalkylene alkyl ethers.

The concentration of the fluororesin or surfactant in the aqueous dispersion (Z) is not particularly limited as long as the aqueous dispersion (Z) can exist stably.
Usually, the concentration of the fluororesin is preferably 30 to 80% by mass, more preferably 40 to 75% by mass, and particularly preferably 50 to 70% by mass.
Moreover, it is preferable that the density | concentration of surfactant is 0.2-8 mass%, It is more preferable that it is 0.5-7 mass%, It is especially preferable that it is 1-6 mass%.
In addition, various commercially available fluororesin dispersions are available. For example, a large amount of fluororesin dispersion having a fluororesin concentration of 50 to 65% by mass and a surfactant concentration of 2 to 5% by mass is available. And it can be obtained at low cost.

The mixing ratio of the aqueous dispersion (Z) is preferably 0.1 to 10 parts by mass with respect to 1 part by mass of the catalyst-carrying electron transfer material. By setting it as 0.1 mass part or more, the binding property of catalyst carrying | support electron-transmitting substances improves, and the shape retainability and easy moldability as an electrode improve. Moreover, by setting it as 10 mass parts or less, the resistance of an electrode is suppressed and electric power generation performance improves.
For the same reason, the amount of the fluorine-based resin in the aqueous dispersion (Z) to be blended is 0.05 to 5 parts by mass with respect to 1 part by mass of the catalyst in the catalyst-carrying electron transfer material. It is preferably 0.1 to 3 parts by mass, particularly preferably 0.1 to 1 part by mass.

  A water dispersion (Z) may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

(Other ingredients)
In addition to the catalyst-carrying electron-transmitting substance, the crosslinkable compound (X), the polymer material (Y), and the aqueous dispersion (Z), the electrode paste further contains a solvent for dissolving or dispersing these components. May be included. As the solvent, any solvent can be selected as long as it does not react with the compounding components, but alcohol is preferable, and isopropyl alcohol is more preferable.

<Method for producing electrode paste>
The method for producing an electrode paste of the present invention comprises a catalyst-supporting electron-transmitting substance, a crosslinkable compound (X), a polymer material (Y), and an aqueous dispersion (Z) containing the fluororesin. It has the process of mix | blending and knead | mixing and making the said fluororesin fiber.
The method for blending the components is not particularly limited. For example, the catalyst-carrying electron transfer substance, the crosslinkable compound (X), the polymer material (Y) and the water dispersion (Z) may be blended at once or in any order, or the catalyst-carrying electron transfer property. Two or more components selected from the group consisting of a substance, a crosslinkable compound (X), a polymer material (Y), and an aqueous dispersion (Z) are blended in advance and added to the remaining components. May be. In addition, two types of premixed two components selected from the group consisting of a catalyst-supporting electron transfer substance, a crosslinkable compound (X), a polymer material (Y), and an aqueous dispersion (Z) were prepared. , One may be added to the other.
Further, for example, as described above, when other components are also used, each component may be blended as described above, including other components.
The catalyst-supporting electron transfer material is preferably blended after wetting by adding water and / or an organic solvent, preferably water.
Further, the crosslinkable compound (X), the polymer material (Y), the aqueous dispersion (Z), and other components may be added after adding water and / or an organic solvent, preferably as a solution.
Furthermore, you may add water and / or an organic solvent separately at the time of a mixing | blending as needed.
The organic solvent can be arbitrarily selected as long as it does not react with each compounding component, but alcohol is preferable and isopropyl alcohol is more preferable.

Each component may be blended while mixing, or all components may be blended and then mixed. By mixing in this way, a compounding component can be disperse | distributed uniformly.
The mixing method is not particularly limited, and for example, a known method using a stirrer, an ultrasonic disperser, an ultrasonic homogenizer, a self-revolving mixer or the like may be applied.

  The blend of each component may be adjusted in concentration by removing a part of the solvent (drying) before kneading or adding a solvent separately. The solvent to be added may be the same as that described above as added at the time of blending.

The method for kneading the blend is not particularly limited as long as it can apply a shearing force sufficient to fiberize the fluororesin contained in the aqueous dispersion (Z). As a preferable method, specifically,
(I) A method of placing the compound on a plate such as a metal plate and kneading using a spatula such as a metal spatula (ii) Kneading the compound in a mortar made of agate or the like using a pestle or the like Method (iii) A method of kneading the compound in a roll type or screw type kneader can be exemplified.

  The kneading conditions may be set as appropriate for each kneading method. For example, in the case of (i), the kneading time is preferably 1 to 10 minutes, and more preferably 2 to 5 minutes. By setting it as 1 minute or more, the said fluororesin can fully be fiberized and high binding property and water repellency can be expressed. Moreover, by setting it as 10 minutes or less, it can suppress that the paste for electrodes becomes hard too much, and can perform the application | coating process mentioned later easily. The temperature at the time of kneading may be arbitrarily set within a range where the compound and the electrode paste do not deteriorate or become too hard, preferably 10 to 40 ° C., more preferably about room temperature.

  According to the method for producing an electrode paste of the present invention, the fluorine-containing resin contained in the aqueous dispersion (Z) is sufficiently fiberized by applying a shearing force by kneading the compounding components. Therefore, the adhesiveness and water repellency of the electrode are improved. In addition, since the fiber is sufficiently formed, the amount of the fluororesin used can be greatly reduced as compared with the conventional case. Moreover, an electrode is excellent in polar solvent tolerance, especially water resistance and methanol resistance by using combining a crosslinkable compound (X), polymeric material (Y), and an aqueous dispersion (Z). Furthermore, since the electrode paste can be produced simply by kneading the blended components, the electrode production process can be simplified.

<Method for producing electrode and membrane-electrode assembly>
The electrode of the present invention can be produced using the electrode paste of the present invention. Specifically, a method of heat-curing the electrode paste can be exemplified, and it is preferable that the electrode paste is applied to a predetermined portion and then heat-cured according to a desired configuration of the membrane-electrode assembly. For example, the membrane-electrode assembly 1 shown in FIG. 1 can be manufactured by the following method. That is, an electrode paste is applied on the gas diffusion layer 14 and heated to form the electrode 10. Next, two such electrodes 10 are used, and the surface opposite to the gas diffusion layer 14 side is brought into contact with both surfaces of the electrolyte membrane 11 one by one and heated to join them. . Alternatively, the electrode paste is applied to both surfaces of the electrolyte membrane 11 and bonded by heating, and then the surface opposite to the bonded surface of the bonded electrode paste is brought into contact with the gas diffusion layer 14 respectively. The electrode 10 and the membrane-electrode assembly 1 may be formed simultaneously by heating. As a result, the electrode binder in the electrode paste is solidified to form the catalyst layer 13 and further the electrode 10, whereby the membrane-electrode assembly 1 is obtained.

The electrode paste may be applied by a known method, and specific examples of the application method include a paste method, a bar coating method, a spray method, and a screen printing method.
The heating temperature of the electrode paste is preferably 100 ° C. or higher. By doing in this way, heat hardening fully advances. The upper limit of the heating temperature is not particularly limited as long as the physical properties of the film and the gas diffusion layer are not impaired, but it is usually preferably 200 ° C.
Moreover, it is preferable to pressurize simultaneously when heating the electrode paste. By heating and pressing in this manner, the adhesion between the catalyst-carrying electron-transmitting substances is improved and the electron-transmitting property is improved. The pressure at the time of pressurization is preferably adjusted as appropriate according to the pressurization method and the type of the electrode, but is usually preferably 0.16 kN / cm ² or more. The upper limit of the pressure is not particularly limited as long as the electrode is not destroyed.

  Further, the electrode paste may be transferred by applying it on another base material without being directly applied to the target portion, applying the heat paste to the target portion, and then pressing it on the target portion. By such a method, for example, it can be transferred to both the gas diffusion layer 14 and the electrolyte membrane 11 in FIG.

  Here, although the manufacturing method of the electrode provided with the gas diffusion layer and the membrane-electrode assembly has been described, in the case where the gas diffusion layer is not provided, the electrode is formed in the same manner as above except that the gas diffusion layer is not used. And a membrane-electrode assembly may be manufactured.

<Fuel cell and manufacturing method thereof>
A fuel cell according to the present invention includes the membrane-electrode assembly according to the present invention. And the fuel cell of this invention can be manufactured by a well-known method except using this membrane-electrode assembly.
The electrode of the present invention can be easily manufactured and has excellent binding properties, water repellency, water resistance and methanol resistance. Therefore, a fuel cell using such an electrode can be manufactured at low cost and has power generation performance. And it has excellent durability.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples.
<Preparation of electrode paste, electrode, and membrane-electrode assembly>
[Example 1]
(1) Preparation of electrode binder
10.0 g poly (2-acrylamido-2-methylpropanesulfonic acid) (mass average molecular weight 2000000) (diluted 15% by mass aqueous solution made by Aldrich to 2.5% by mass with water), 0.25 g tetramethoxysilane Then, 10.0 g of isopropyl alcohol was added and mixed with an ultrasonic homogenizer.
(2) Preparation of Electrode Paste 0.75 g of water was added to 0.15 g of catalyst-supporting carbon (platinum-ruthenium-supporting carbon, TEC61E54 Pt 30 mass% Ru 23 mass% manufactured by Tanaka Kikinzoku Co., Ltd.) and moistened. The electrode binder 2.00 g, PTFE dispersion (manufactured by Asahi Glass Co., Ltd., AD938L, PTFE content 55-60 mass%, surfactant concentration 3 mass% diluted to 4 times by mass ratio) 1) 0.20 g and 0.75 g of isopropyl alcohol were added, followed by ultrasonic dispersion.
Next, after the mixture was dried in air, 0.4 g of water and 0.4 g of isopropyl alcohol were added.
Next, the mixture was placed on a metal plate and kneaded with a metal spatula for 3 minutes at room temperature to apply a shearing force to produce an electrode paste.
(3) Production of electrode The produced electrode paste was thinly and uniformly applied on a gas diffusion layer (TGP-H060, thickness 200 μm). A jig and a spatula were used for application. Next, this was pressed for 3 minutes with a hot press (manufactured by Shinto Kogyo Co., Ltd.) at 120 ° C. to 1 kN to produce an anode electrode having a catalyst layer thickness of about 50 μm. The platinum amount of the anode electrode was 1.0 mg / cm ² , and the ruthenium amount was 0.6 mg / cm ² .
(4) Production of membrane-electrode assembly The produced anode electrode and a commercially available cathode electrode (GDE400-3, manufactured by Paramount Energy Co., Ltd.) were cut into 2.5 cm square, and Nafion 117 (registered trademark) (DuPont) as an electrolyte membrane. To produce a membrane-electrode assembly. The joining at this time was performed by pressing for 3 minutes under the condition of 140 ° C.-1.5 kN with the hot press machine.

[Example 2]
In “(2) Preparation of electrode paste”, the same as Example 1 except that the catalyst-supporting carbon, the electrode binder, the PTFE dispersion, and isopropyl alcohol were mixed and then kneaded using an agate mortar. In addition, an electrode paste, an electrode, and a membrane-electrode assembly were prepared.

[Comparative Example 1]
In “(2) Preparation of electrode paste”, as in Example 1, except that the catalyst-supporting carbon, the electrode binder, the PTFE dispersion, and isopropyl alcohol were mixed and then kneading was not performed. Pastes, electrodes, and membrane-electrode assemblies were prepared.

[Comparative Example 2]
An electrode paste, an electrode, and a membrane-electrode assembly were prepared in the same manner as in Comparative Example 1 except that 3 times the amount of PTFE was used.

[Comparative Example 3]
An electrode paste, an electrode, and a membrane-electrode assembly were prepared in the same manner as in Example 1 except that a commercially available anode electrode (GDE400-4, manufactured by Paramount Energy) using a sulfonated fluororesin solution as a binder was used. did.

<Evaluation of electrode paste, electrode and membrane-electrode assembly>
The electrode paste, electrode, and membrane-electrode assembly were evaluated according to the following procedure.
(I) Evaluation of electrode durability by immersion in aqueous methanol solution The electrodes of Examples 1 and 2 and Comparative Examples 1 to 3 were immersed in 200 mL of an aqueous methanol solution (4 mass%, 50 mass%), and an oven at 80 ° C. For 24 hours. Then, the degree of elution of the electrode into the aqueous methanol solution and the state of the electrode after immersion were examined, and the durability of the electrode was evaluated according to the following criteria from the viewpoints of changes in the weight of the electrode and changes in the components of the aqueous methanol solution. The results are shown in Table 1.
○ ・ ・ ・ ・ No elution △ ・ ・ ・ ・ Slight elution × ・ ・ ・ ・ Remarkably elution

The electrodes of Examples 1 and 2 did not elute into an aqueous methanol solution and were hardly swollen.
The electrode of Comparative Example 1 was remarkably eluted in a methanol aqueous solution and swollen vigorously.
The electrode of Comparative Example 2 was less extensive than the electrode of Comparative Example 1, but it eluted significantly into the aqueous methanol solution and swelled violently.
The electrode of Comparative Example 3 did not elute into the 4% by mass methanol aqueous solution, but slightly eluted into the 50% by mass methanol aqueous solution and swollen.

(II) Evaluation of electrode durability by comparison of relative output The membrane-electrode assemblies of Examples 1-2 and Comparative Examples 1-3 were set in a single cell for fuel cells (JARI standard cell) by a prescribed method. . This cell is set in a fuel cell power generation evaluation apparatus (NF circuit block design As-510), the cell temperature is 35 ° C., the concentration of methanol is 10 mass%, the flow rate is 0.5 ml / min, and the air flow rate is The operation was set at 200 ml per minute, and the cell's IV was measured to compare the maximum output. And in order to evaluate durability of an electrode from electric power generation performance, the output before immersion was set to 100, and the relative output after immersion was computed. The results are shown in Table 2.

The electrodes of Examples 1 and 2 maintained a high output even when immersed, and had a good relative output equivalent to that of the electrode of Comparative Example 3.
On the other hand, the relative outputs of the electrodes of Comparative Examples 1 and 2 were reduced by 20% or more, and when the PTFE was not sheared or when a large amount of PTFE was used, the decrease in output could not be suppressed. It was.

(III) Confirmation of fiberization state of PTFE by FE-SEM Part of the electrode pastes of Examples 1-2 and Comparative Examples 1-3 immediately before application to the gas diffusion layer were set on a sample stage. After drying this all day and night, it was observed with a field emission scanning electron microscope (FE-SEM, manufactured by JEOL, JSM-6700F). The results are shown in Table 3.

  The present invention is applicable to a polymer electrolyte fuel cell.

It is the schematic which illustrates the electrode of this invention and a membrane-electrode assembly provided with the same.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Membrane-electrode assembly, 10 ... Electrode, 11 ... Electrolyte membrane, 11a ... One surface of electrolyte membrane, 13 ... Catalyst layer, 13a ... Solidified binder for electrode , 13b ... catalyst-carrying electron transfer material, 14 ... gas diffusion layer

Claims (8)

An electron transfer material carrying a catalyst, a crosslinkable compound (X) that forms a three-dimensional crosslinked structure by silicon-oxygen bonds, a polymer material (Y) having a sulfonic acid group as an acid group , and a shearing force An electrode paste comprising a step of blending and kneading an aqueous dispersion (Z) containing polytetrafluoroethylene , which is a fluororesin that is made into a fiber by application, and fiberizing the fluororesin Manufacturing method. Wherein the polymeric material is a monomer containing a sulfonic acid group, a manufacturing method of electrode paste according to claim 1, characterized in that it consists of a monomer containing and silicon atoms containing no sulfonic acid group. The method for producing an electrode paste according to claim 1 or 2 , wherein the polymer material contains a sulfonic acid group-containing polymer obtained by polymerizing a monomer having a polymerizable unsaturated double bond. . The crosslinkable compound is
1,2-bis (triethoxysilyl) ethane, 1,6-bis (trimethoxysilyl) hexane, 1,9-bis (triethoxysilyl) nonane, 1,8-bis (triethoxysilyl) octane, 8-bis (diethoxymethylsilyl) octane, 1,4-bis (trimethoxysilylethyl) benzene, 1,4-bis (triethoxysilylethyl) benzene, 1,8-bis (methyldiethoxysilyl) octane, Tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dimethyldimethoxysilane, phenylmethyldimethoxysilane, ethyltrimethoxysilane, n-propyltri Methoxysilane, i-p It is any one or more selected from the group consisting of pyrtrimethoxysilane, n-butyltrimethoxysilane, silicic acid, potassium silicate, and sodium silicate. The manufacturing method of the paste for electrodes as described in any one of. An electrode paste produced by the method according to any one of claims 1 to 4. An electrode using the electrode paste according to claim 5. A membrane-electrode assembly, wherein the electrode according to claim 6 is disposed on both surfaces of an electrolyte membrane. A fuel cell comprising the membrane-electrode assembly according to claim 7.

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