JP5427532B2 - Electrode paste, electrode, membrane-electrode assembly, and fuel cell - Google Patents

Description

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

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 sulfonated fluororesin (for example, Nafion (registered trademark) (manufactured by DuPont)) as a polymer material, but recently, other polymer materials (for example, hydrocarbons). A system 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, when the glass transition temperature (Tg) is 130 ° C. or higher, there is a problem of swelling due to poor high-temperature durability, such as degeneration in a short time, and high affinity between methanol and resin used as fuel. It was.

On the other hand, an electrode using a polymer material other than a sulfonated fluororesin is prepared by preparing a solution in which the polymer material is dissolved in a polar solvent such as alcohol to form a binder for an electrode, which carries a catalyst such as platinum. The obtained carbon powder is mixed with a fluorine-based resin such as polytetrafluoroethylene (PTFE) that functions as a binder and a water repellent, and the resulting mixture is applied onto a gas diffusion layer such as carbon paper. It is manufactured by hot pressing.
The electrode produced in this way is excellent in high temperature durability and suppressed swelling due to methanol. However, in many cases, the conductive polymer material does not have a binding property, and therefore, there is a problem that a large amount of PTFE is required.

  Therefore, in order to solve such a problem of binding properties, it has been proposed to use, as a polymer material, a fluorine-based resin having a property of being fiberized by shearing. 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. Yes.

Japanese Patent Publication No. 6-97612

  However, the method disclosed in Patent Document 1 needs to treat the kneaded product with an ion exchange resin after forming the sheet into a sheet. It is also necessary to shear PTFE. Therefore, the manufacturing process is complicated and disadvantageous in terms of process efficiency. Patent Document 1 does not mention the methanol resistance of the electrode. Thus, in the past, there has been no actual proposal of a fuel cell electrode that has sufficient methanol resistance and can be easily manufactured.

  The present invention has been made in view of the above circumstances, and has an excellent methanol resistance and can be easily manufactured, an electrode paste suitable for manufacturing the electrode, a membrane-electrode assembly using the electrode, and It is an object of the present invention to provide a fuel cell using the membrane-electrode assembly.

The invention according to claim 1 carries poly (2-acrylamido-2-methylpropanesulfonic acid) as the acid group-containing polymer material (A) , polyvinyl alcohol as the hydrophilic polymer material (B), and a catalyst. An electrode paste comprising the electron transfer substance (C) thus prepared, wherein the compounding ratio (mass ratio) of the acid group-containing polymer material (A): the hydrophilic polymer material (B) is 55: It is 45-80: 20, The compounding quantity of the said hydrophilic high molecular material (B) with respect to 100 mass parts of electron transport substances (C) which carry | supported the said catalyst is 5 mass parts or more, It is a paste.
The invention according to claim 2 further an electrode paste according to claim 1, characterized in that by blending a surfactant and a fluorine-based resin.
The invention according to claim 3 is an electrode characterized in that the electrode paste according to claim 1 or 2 is heated and solidified.
The invention according to claim 4 is an electrode according to claim 3, wherein the electrode paste is characterized in that it is heated to above 100 ° C..
The invention according to claim 5 is a membrane-electrode assembly in which the electrode according to claim 3 or 4 is arranged on both surfaces of the electrolyte membrane.
A sixth aspect of the present invention is a fuel cell comprising the membrane-electrode assembly according to the fifth aspect.

  According to the present invention, an electrode excellent in methanol resistance can be easily produced. And by using such an electrode, the fuel cell excellent in power generation performance and durability can be manufactured simply and at low cost.

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

The present invention will be described in detail below.
<Paste for electrodes>
The electrode paste of the present invention comprises an acid group-containing polymer material (A), a hydrophilic polymer material (B) not corresponding to the acid group-containing polymer material (A) (hereinafter referred to as “hydrophilic polymer material (B ) ", And an electron transfer material (C) supporting a catalyst (hereinafter abbreviated as" catalyst-supported electron transfer material (C) "), The mixing ratio (mass ratio) of the acid group-containing polymer material (A): the hydrophilic polymer material (B) is 55: 45-80: 20, and 100 parts by mass of the catalyst-carrying electron transfer material (C) The blending amount of the hydrophilic polymer material (B) with respect to is 5 parts by mass or more.

(Acid group-containing polymer material (A))
The acid group-containing polymer material (A) has proton conductivity and is an acid 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. Examples thereof include a polymer material having a group. 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 acid group-containing polymer material (A), a polymer material having a sulfonic acid group is preferable.

  The acid group-containing polymer material (A) 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 acid group-containing polymer material (A) may further have a hydrophilic group other than the 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 acid group-containing polymer material (A) 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.
Thus, since the acid group-containing polymer material (A) further has a hydrophilic group, the binding force between the catalyst-carrying electron transfer materials (C) described later is further improved, and the water resistance and polarity resistance of the electrode are improved. Solvent property (for example, alcohol resistance) is improved.

  The acid group-containing polymer material (A) may be obtained by polymerizing only a monomer having an acid group (hereinafter abbreviated as monomer (V)), or the monomer (V) and other monomers other than that. A copolymer may be used. 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. Specific examples include a monomer having no acid group; a monomer having no acid group, and a cross-linking agent having a plurality of functional groups capable of binding to other monomers. 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 having a silicon atom can also be used.
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.

  In the present invention, one or a plurality of acid group-containing polymer materials (A) that are further crosslinked with a crosslinking agent may be used as the acid group-containing polymer material (A). 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 acid group-containing polymer material (A) can be easily used even with a simple polymerization controller. Is obtained.

The acid group-containing polymer material (A) 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.
The mass average molecular weight of the acid group-containing polymer material (A) is preferably 1000 to 10000000, and 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.

  In the present invention, it is preferable to use a polymer material (A1) having a smaller mass average molecular weight and a polymer material (A2) having a mass average molecular weight larger than that of the polymer material (A1). More specifically, the mass average molecular weight of the polymer material (A1) is preferably 1000 to 300,000, and more preferably 5,000 to 100,000. The mass average molecular weight of the polymer material (A2) is preferably from 300,000 to 10,000,000, more preferably from 500,000 to 5,000,000. By doing so, the polymer material (A1) easily enters the secondary aggregate (agglomerate) of the catalyst-carrying electron transfer substance (C), which will be described later. Can be further improved. Furthermore, the polymer material (A2) can maintain stable power generation performance even in an environment where the temperature is relatively high and the methanol concentration is high.

(Hydrophilic polymer material (B))
The hydrophilic polymer material (B) is a polymer material not corresponding to the acid group-containing polymer material (A), and is a hydrophilic polymer material having no acid group.
The hydrophilic polymer material (B) is not particularly limited as long as it satisfies the above conditions, and examples thereof include a polymer having a hydrophilic group or a hydrophilic bond in a side chain or main chain.
Moreover, the hydrophilic polymer material (B) may have a crosslinkable group. In this case, in addition to the hydrophilic group, it may have a crosslinkable group, or may have a hydrophilic and crosslinkable group.
As the hydrophilic group, 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 can be exemplified, and a hydroxyl group is particularly preferable.
Examples of the hydrophilic bond include an ether bond, an ester bond, and an amide bond.
The hydrophilic polymer material (B) is preferably a polymer material having a hydroxyl group.

  Preferred examples of the hydrophilic polymer material (B) include polyvinyl alcohol, polyacrylamide, polyvinyl pyrrolidone, polyethylene glycol, and polyglycerol having various molecular weights and degrees of saponification. Since these hydrophilic polymer materials (B) have polar groups, they greatly contribute to the improvement of the adhesion between the acid group-containing polymer material (A) and the catalyst-carrying electron transfer material (C) described later, Thereby, the power generation performance and durability of the electrode are greatly improved.

In the case where the hydrophilic polymer material (B) has a crosslinkable group, the crosslinker used in combination for crosslinking may be appropriately selected according to the type of the crosslinkable group. Preferred examples include dihydrazides, trihydrides. Examples thereof include hydrazides, dicarboxylic acids, tricarboxylic acids, diamines, triamines, dialdehydes, trialdehydes, diglycidyl ethers, triglycidyl ethers, alkoxysilanes, alkoxytitaniums, and alkoxyaluminums. Further, polymers such as polyacrylic acid, acrylic acid-maleic acid copolymer, acrylamide-acrylic acid hydrazide copolymer may be used as a crosslinking agent.
Among these, in particular, polyvinyl alcohol is easily crosslinked by dicarboxylic acids, tricarboxylic acids, dialdehydes, trialdehydes, diglycidyl ethers, triglycidyl ethers, alkoxysilanes, alkoxytitaniums, alkoxyaluminums, and the like.
By crosslinking the hydrophilic polymer material (B), an electrode having excellent durability can be produced even if the heating temperature of the electrode paste is lowered or the heating is omitted.

The average degree of polymerization of polyvinyl alcohol is preferably 1000 to 5000, and more preferably 3000 to 4500. If the degree of polymerization is too small, the electrode may have poor water resistance, and the output may easily decrease during use as a fuel cell. On the other hand, if the degree of polymerization is too large, the viscosity of the aqueous solution may be too high to produce a sufficiently uniform solution with other materials. In addition, about the mass average molecular weight of polyvinyl alcohol, an approximate value can be calculated by the product of the average degree of polymerization and the average unit molecular weight. Here, the unit of the polyvinyl alcohol is represented by _{(CH 2 CHOH) x (CH} 2 CHOCOCH 3) y, a x + y = 1.
The degree of saponification is not particularly limited, but is preferably as high as possible, preferably 90% or more, and more preferably 98% or more. The higher the degree of saponification, the better the water resistance of the electrode. Note that it is difficult to obtain a saponification degree of 99.99% or more, and the cost increases even if it is available. The saponification degree is expressed by x / (x + y) × 100 (%) by the x and y.

  Polyethylene glycol also has hydroxyl groups that can be crosslinked by various crosslinking agents, and those having various molecular weights are commercially available and can be suitably used. The polyethylene glycol has a mass average molecular weight of preferably 1,000,000 or more, more preferably 2,000,000 or more. The higher the molecular weight, the better the water resistance of the electrode.

  A hydrophilic polymer material (B) 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 compounding ratio (mass ratio) of the acid group-containing polymer material (A): hydrophilic polymer material (B) is 55: 45-80: 20, preferably 60: 40-80: 20, More preferably, it is 65: 35-80: 20.
Usually, when the compounding ratio of the acid group-containing polymer material (A) is large, the power generation performance (output) of the electrode is improved and the durability against methanol tends to be lowered. And when the compounding ratio of an acid group containing polymeric material (A) is small, the durability with respect to methanol of an electrode will improve and it exists in the tendency for electric power generation performance (output) to fall. However, in the present invention, as described later, by making the blending ratio of the hydrophilic polymer material (B) to the catalyst-carrying electron transfer substance (C) a specific value or more, it is surprisingly surprising that the acid group Even if the blending ratio of the containing polymer material (A) is increased, the durability against methanol does not decrease, and the power generation performance (output) of the electrode is further improved.

(Catalyst-supported electron transfer material (C))
The catalyst-carrying electron transfer substance (C) is obtained by carrying a catalyst on an electron transfer substance. When the catalyst has a small diameter, it may be difficult to handle as it is, and in such a case, handling is improved by supporting the catalyst on an electron transfer material. If the catalyst has an electron transfer property and there is no problem in handling, it is possible not to use the electron transfer material.

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.

The catalyst supported on the electron transfer substance promotes proton conduction. Specifically, the reaction of “MeOH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ ” on the anode side and the reaction of “O ₂ + 4H ⁺ + 4e ⁻ → H ₂ O” on the cathode side are promoted, respectively. Those known in the field can be used.
Specific examples of the catalyst include metals such as platinum (Pt), gold (Au), ruthenium (Ru), cobalt (Co), nickel (Ni), iron (Fe), palladium (Pd), and the like. An alloy made of two or more metals selected from the group can be exemplified. 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.

  The catalyst content in the catalyst-carrying electron transfer substance (C) is not particularly limited, but is preferably 20 to 85% by mass, and more preferably 40 to 75% by mass.

  A catalyst carrying | support electron transfer substance (C) 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 types or shapes of at least one of the electron transfer substance and the catalyst are different from each other, it means that “the type of the catalyst-carrying electron transfer substance (C) is different”.

  Moreover, the compounding quantity of the hydrophilic polymer material (B) with respect to 100 mass parts of catalyst carrying | support electron transfer substances (C) is 5 mass parts or more. The upper limit of the amount is preferably 10 parts by mass, and more preferably 7.5 parts by mass. Sufficient durability of the electrode with respect to methanol can be obtained by setting the lower limit value or more. By setting the upper limit value or less, the power generation performance (output) of the electrode is further improved.

(Surfactant)
The electrode paste of the present invention preferably further contains a surfactant.
As the surfactant, known ones such as a cationic surfactant, an anionic surfactant, an amphoteric surfactant, and a nonionic (nonionic) surfactant can be used, and are arbitrarily selected according to the purpose. it can. Of these, nonionic surfactants are preferable, and polyoxyalkylene alkyl ethers, fluorine-based nonionic surfactants, and the like are more preferable.

  The blending amount of the surfactant may be adjusted as appropriate according to the type of other blending components, but is preferably 0.02 to 1% by mass in the electrode paste, and is preferably 0.03 to 0.03. It is more preferably 7% by mass, and particularly preferably 0.04 to 0.4% by mass.

  As the surfactant, one kind may be used alone, or two or more kinds may be used in combination. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

(Fluorine resin)
The electrode paste of the present invention preferably further contains a fluorine resin.
Examples of the fluororesin include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), tetrafluoroethylene / perfluoroalkoxyethylene copolymer ( PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) and the like, and polytetrafluoroethylene (PTFE) is preferred.

  The blending amount of the fluororesin may be appropriately adjusted according to the types of other blending components, but the blending amount with respect to 100 parts by weight of the catalyst-carrying electron transfer substance (C) is 5 to 10 parts by weight. It is preferably 6 to 8 parts by mass. By setting it as such a compounding quantity, the durable fall with respect to methanol is suppressed further, and the electric power generation performance (output) of an electrode improves further.

  A fluorine-type resin 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 electrode paste of the present invention preferably contains both the surfactant and the fluorine resin.

(solvent)
The electrode paste preferably further contains a solvent for dissolving or dispersing the compounding components. The solvent can be arbitrarily selected as long as it does not react with the compounding components, and may be one kind or two or more kinds. Especially, water and alcohol are preferable and it is more preferable to use water and alcohol together. As the alcohol, isopropyl alcohol is preferable.

Although the compounding quantity of a solvent is not specifically limited, It is preferable that it is 70-97 mass% in an electrode paste, and it is more preferable that it is 80-95 mass%.
When water and alcohol are used in combination, the mass ratio of water: alcohol is preferably 5: 5 to 9: 1, and more preferably 6: 4 to 8: 2.

(Other ingredients)
The electrode paste includes an acid group-containing polymer material (A), a hydrophilic polymer material (B), a catalyst-carrying electron transfer substance (C), a surfactant, within a range that does not hinder the effects of the present invention. Other components other than the fluorine-based resin and the solvent may be blended. Examples of other components include the crosslinking agents listed so far.

(Method for producing electrode paste)
The electrode paste of the present invention can be produced by mixing the above-described blending components.
Both the acid group-containing polymer material (A) and the hydrophilic polymer material (B) are preferably blended after being dissolved or dispersed by adding a solvent, preferably water.
The catalyst-carrying electron transfer substance (C) is preferably blended after adding water and / or an organic solvent, preferably water, to wet the catalyst.
Moreover, when mix | blending the said surfactant and / or fluorine-type resin, it is preferable to mix | blend these, after adding a solvent, Preferably water and / or alcohol, and making it melt | dissolve or disperse | distribute.
And at the time of mix | blending each said component, you may mix | blend a solvent separately irrespective of the presence or absence of the solvent addition to these components.

  The electrode paste is prepared by mixing, for example, an acid group-containing polymer material (A), a hydrophilic polymer material (B), and components other than these as required, and mixing them. It is preferable to manufacture by preparing and mixing a catalyst-supporting electron-transmitting substance (C) and, if necessary, other components in the electrode binder.

The electrode binder is used for preparing a liquid or paste electrode paste by mixing with the catalyst-carrying electron transfer substance (C). The following three characteristics are mainly required for the electrode binder.
(I) High affinity for electrode components (II) Electrode paste, high proton conductivity after solidifying this to form a catalyst layer (III) Electrode paste, The catalyst layer formed by solidification is given a strength that is not destroyed by a change in environmental temperature or a pressure increase due to inflow of gas or liquid, and the strength can be maintained for a long time. All of these characteristics are provided, and the electrode paste of the present invention obtained from such an electrode binder can realize an electrode and a fuel cell excellent in power generation performance and durability.

  When preparing an electrode binder, water and / or at the time of blending, regardless of whether or not a solvent is added to the acid group-containing polymer material (A) and the hydrophilic polymer material (B), if necessary. Alternatively, an organic solvent may be added separately. In this case, it is preferable to add water and / or alcohol, and it is more preferable to add water and / or isopropyl alcohol.

  In the case of producing an electrode paste in which the surfactant and / or fluorine resin is blended, the surfactant and / or fluorine resin is blended before and after blending the catalyst-carrying electron transfer substance (C). You may mix | blend in any later stage.

  It is preferable to adjust the blending amount of the solvent in the electrode binder and the water: alcohol mass ratio when water and alcohol are used together as the solvent so that they are within the above ranges when the electrode paste is used.

When producing an electrode paste from an electrode binder, for example, an electrode binder and a catalyst-carrying electron transfer substance (C) are blended, and if necessary, other components are blended and mixed. Can be manufactured.
At this time, the electrode binder may be added after adding water and / or an organic solvent.
Further, if necessary, a solvent may be separately added during the blending of the electrode binder and the catalyst-carrying electron transfer substance (C) regardless of the presence or absence of the solvent. The solvent can be arbitrarily selected as long as it does not react with the compounding components, but water and alcohol are preferable, and two or more solvents may be used in combination. As the alcohol, isopropyl alcohol is preferable.

When preparing the electrode paste or the electrode binder, each component may be mixed while mixing, or all components may be mixed before mixing. 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.

  For example, the electrode paste of the present invention does not need to be fiberized by shearing the resin in order to improve the binding property of the electrode. Therefore, raw materials necessary for shearing are not required, and the electrode can be easily manufactured. Further, as will be described later in the electrode manufacturing method, it can be sufficiently solidified without using a crosslinking agent. And even if the compounding ratio of the acid group-containing polymer material (A) is increased by setting the compounding ratio of the catalyst-carrying electron transfer substance (C) to the hydrophilic polymer material (B) to a specific value or more. Further, the durability against methanol is not lowered, and the power generation performance (output) of the electrode is further improved.

<Electrode, membrane-electrode assembly>
The electrode of the present invention is characterized in that the electrode paste of the present invention is heated and solidified. And it can manufacture by apply | coating the paste for electrodes to a predetermined location according to the structure of a desired membrane-electrode assembly, and heating and solidifying this.
The membrane-electrode assembly of the present invention is characterized in that the electrode of the present invention is disposed on both surfaces of an electrolyte membrane.
Hereinafter, it demonstrates in detail, referring drawings.

FIG. 1 is a schematic view illustrating an electrode of the present invention and a membrane-electrode assembly provided with the electrode. In addition, it cannot be overemphasized that a part of structure can be suitably changed in the range which is not limited to what is shown here and the electrode and membrane-electrode assembly of this invention do not impair the effect of this 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 is constituted by the catalyst layer 13 and the gas diffusion layer 14. However, the gas diffusion layer 14 is not an essential component and may be provided as necessary. Therefore, an electrode may be constituted only by the catalyst layer 13.
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, Nafion (trademark) (made by DuPont) can be illustrated.

[Catalyst layer]
The catalyst layer 13 is obtained by heating and solidifying the electrode paste of the present invention.
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 substance 13b is continuously present in contact with each other between the electrolyte membrane 11 and the gas diffusion layer.
The thickness of the catalyst layer 13 is preferably 5 to 150 μm, and more preferably 10 to 100 μm.
The hydrophilic polymer material (B) in the electrode binder acts as a binder and improves the binding between the acid group-containing polymer material (A) and the catalyst-carrying electron transfer substance in the electrode paste. Therefore, the electrode 10 has excellent methanol resistance. As a result, the catalyst layer 13 has excellent binding properties with the electrolyte membrane 11 and a gas diffusion layer 14 described later.

[Gas diffusion layer]
The gas diffusion layer 14 is for optimizing the diffusion of a gas or a liquid such as methanol or water, and is composed of, for example, a porous conductive sheet.
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 between the gas diffusion layer 14 and the catalyst layer 13. 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.

The electrode 10 and the membrane-electrode assembly 1 can be manufactured, for example, by the following method.
That is, the electrode paste is applied on the gas diffusion layer 14 and is heated and solidified to form the catalyst layer 13 and the electrode 10. Next, using two such electrodes 10, the surface opposite to the gas diffusion layer 14 side (the surface of the catalyst layer 13) is brought into contact with both surfaces of the electrolyte membrane 11 one by one and heated. The membrane-electrode assembly 1 is obtained by bonding.
Alternatively, the electrode paste is applied to both surfaces of the electrolyte membrane 11 and bonded by heating, and then the surface (exposed surface) opposite to the bonded surface of the bonded electrode paste is exposed to the gas diffusion layer 14. The catalyst layer 13, the electrode 10, and the membrane-electrode assembly 1 may be formed at the same time by being brought into contact with heating and solidifying.

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 when forming the electrode 10 is not particularly limited as long as solidification proceeds sufficiently, but is preferably 100 ° C. or higher. By setting it as such temperature, even if it does not use a crosslinking agent, it can fully solidify (harden). 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.
The heating time of the electrode paste at the time of forming the electrode 10 may be appropriately set according to the heating temperature, but is preferably 2 to 30 minutes, and more preferably 3 to 15 minutes.
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, heating and solidifying the paste, and then pressing it onto 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.

  Thus, the electrode 10 can be manufactured simply by solidifying the paste by using the electrode paste of the present invention, and can be manufactured simply and at low cost. Moreover, the obtained electrode 10 has excellent methanol resistance as described above.

<Fuel cell>
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.
Specifically, a pair of separators serving as fuel and air (oxygen) passages were installed outside the membrane-electrode assembly, and a current collecting plate for taking out current was installed outside these separators. The thing of a form can be illustrated.
Further, the membrane-electrode assembly is used as a unit cell, and a pair of separators serving as fuel and oxygen (air) passages are provided outside the unit cell, and a plurality of adjacent unit cells are connected to each other. it can.
Since the fuel cell of the present invention uses an electrode having excellent methanol resistance, it has excellent power generation performance and durability. Furthermore, since the electrode is inexpensive, it can be manufactured at low cost.

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 binder, electrode paste, electrode and membrane-electrode assembly>
[Example 1]
(1) Preparation of electrode binder Poly (2-acrylamido-2-methylpropanesulfonic acid) (mass average molecular weight 2000000) (Aldrich 15% by weight aqueous solution) 3.0 g, polyvinyl alcohol (Aldrich) Water was added to form a 7% by mass aqueous solution. Polyvinyl alcohol had a mass average molecular weight of 146000 to 186000, a saponification degree of 99% or more) 2.14 g and 6.86 g of water were added, and “poly (2-acrylamide- “2-methylpropanesulfonic acid): polyvinyl alcohol (mass ratio)” was adjusted to be “75:25”, and this was mixed with a self-revolving mixer.
Next, to the obtained mixture 10.0 g, FC-4430 (water-based surfactant added by Sumitomo 3M Ltd. to make a 10% by mass aqueous solution) 0.20 g, PTFE dispersion (Asahi Glass Co., Ltd., AD938L, PTFE content 55-60 mass%, surfactant concentration 3 mass% diluted 4 times by mass ratio) 1.00 g), 0.80 g water and 8.0 g IPA In addition, it was mixed with a revolving mixer to obtain a binder for electrodes.
(2) Preparation of Electrode Paste 1.0 g of water was added to 0.2 g of catalyst-supporting carbon (platinum-ruthenium-supporting carbon, TEC61E54, Tanaka Kikinzoku Co., Ltd., Pt 30 mass%, Ru 23 mass%) and moistened. After adding 2.0 g of the electrode binder to this, mixing by an auto-revolving mixer and ultrasonic dispersion were performed to prepare an electrode paste. Table 1 shows the mixing ratio of each component.
(3) Production of electrode The produced electrode paste was thinly and uniformly applied on a gas diffusion layer (TGP-H060, thickness 200 μm). Area of the coated surface was 36cm ^2. A jig and a spatula were used for application. Next, this was dried at room temperature for 1 hour, and further pressed with a hot press machine (manufactured by Shinto Kogyo Co., Ltd.) at 120 ° C.-1 kN for 10 minutes 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) which is an electrolyte membrane. And a membrane-electrode assembly was produced. The joining at this time was performed by pressing for 3 minutes at 140 ° C. and 1 kN with the hot press.

[Example 2]
(1) Preparation of electrode binder Poly (2-acrylamido-2-methylpropanesulfonic acid) (mass average molecular weight 2000000) (Aldrich 15% by weight aqueous solution) 3.0 g, polyvinyl alcohol (Aldrich) Water was added to give a 7% by weight aqueous solution, polyvinyl alcohol had a mass average molecular weight of 146000 to 186000, a saponification degree of 99% or more) 3.47 g and 7.39 g of water were added, and “poly (2-acrylamide- “2-methylpropanesulfonic acid): polyvinyl alcohol (mass ratio)” was adjusted to be “65:35”, and this was mixed with a self-revolving mixer.
Next, to the obtained mixture 10.0 g, FC-4430 (added water to a fluorosurfactant manufactured by Sumitomo 3M to make a 10% by mass aqueous solution) 0.28 g, PTFE dispersion (manufactured by Asahi Glass Co., Ltd., AD938L, PTFE content 55-60 mass%, surfactant concentration 3 mass% diluted 4 times by mass ratio) 1.40 g, and 5.13 g water and 11.2 g IPA In addition, it was mixed with a revolving mixer to obtain a binder for electrodes.
(2) Preparation of electrode paste to (4) Preparation of membrane-electrode assembly As in Example 1, except that the electrode binder was used, an electrode paste, an electrode, and a membrane-electrode assembly were prepared. did.

[Example 3]
(1) Preparation of electrode binder Poly (2-acrylamido-2-methylpropanesulfonic acid) (mass average molecular weight 2000000) (Aldrich 15% by weight aqueous solution) 3.0 g, polyvinyl alcohol (Aldrich) Water was added to give a 7% by weight aqueous solution, polyvinyl alcohol had a mass average molecular weight of 146000 to 186000, a saponification degree of 99% or more) 3.47 g and 7.39 g of water were added, and “poly (2-acrylamide- “2-methylpropanesulfonic acid): polyvinyl alcohol (mass ratio)” was adjusted to be “65:35”, and this was mixed with a self-revolving mixer.
Subsequently, 10.05 g of the obtained mixture was added with 0.35 g of FC-4430 (added to a fluorosurfactant manufactured by Sumitomo 3M to make a 10% by mass aqueous solution), PTFE dispersion (manufactured by Asahi Glass Co., Ltd., AD938L, PTFE content 55-60 mass%, surfactant concentration 3 mass% diluted 4 times by mass) 1.75 g is added, and water 8.92 g and IPA 14.0 g are further added. In addition, it was mixed with a revolving mixer to obtain a binder for electrodes.
(2) Preparation of electrode paste to (4) Preparation of membrane-electrode assembly As in Example 1, except that the electrode binder was used, an electrode paste, an electrode, and a membrane-electrode assembly were prepared. did.

[Example 4]
(1) Preparation of electrode binder Poly (2-acrylamido-2-methylpropanesulfonic acid) (mass average molecular weight 2000000) (Aldrich 15% by weight aqueous solution) 3.0 g, polyvinyl alcohol (Aldrich) Water was added to give a 7% by mass aqueous solution, and polyvinyl alcohol had a mass average molecular weight of 146000 to 186000, a saponification degree of 99% or more) and 1.61 g of water and 2.89 g of water were added, and “poly (2-acrylamide- “2-methylpropanesulfonic acid): polyvinyl alcohol (mass ratio)” was adjusted to be “80:20”, and this was mixed with a self-revolving mixer.
Next, to the obtained mixture 10.0 g, FC-4430 (added water to a fluorosurfactant manufactured by Sumitomo 3M to make a 10% by mass aqueous solution) 0.24 g, PTFE dispersion (Asahi Glass Co., Ltd., AD938L, PTFE content of 55-60 mass%, surfactant concentration of 3 mass% diluted 4 times by mass ratio) 1.20 g, and 2.98 g of water and 9.62 g of IPA In addition, it was mixed with a revolving mixer to obtain a binder for electrodes.
(2) Preparation of electrode paste to (4) Preparation of membrane-electrode assembly As in Example 1, except that the electrode binder was used, an electrode paste, an electrode, and a membrane-electrode assembly were prepared. did.

[Comparative Example 1]
(1) Preparation of electrode binder Poly (2-acrylamido-2-methylpropanesulfonic acid) (mass average molecular weight 2000000) (Aldrich 15% by weight aqueous solution) 3.0 g, polyvinyl alcohol (Aldrich) Water was added to give a 7% by weight aqueous solution, polyvinyl alcohol had a mass average molecular weight of 146000 to 186000, a saponification degree of 99% or more) 3.47 g and 7.39 g of water were added, and “poly (2-acrylamide- “2-methylpropanesulfonic acid): polyvinyl alcohol (mass ratio)” was adjusted to be “65:35”, and this was mixed with a self-revolving mixer.
Then, 10.0 g of the obtained mixture was added with 0.4 g of FC-4430 (added to a fluorosurfactant manufactured by Sumitomo 3M to make a 10 mass% aqueous solution), PTFE dispersion (manufactured by Asahi Glass Co., Ltd., AD938L, PTFE content 55-60% by mass, surfactant concentration 3% by mass diluted 4 times by weight) 2.00 g, and 11.6 g water and 16.0 g IPA In addition, it was mixed with a revolving mixer to obtain a binder for electrodes.
(2) Preparation of electrode paste to (4) Preparation of membrane-electrode assembly As in Example 1, except that the electrode binder was used, an electrode paste, an electrode, and a membrane-electrode assembly were prepared. did.

[Comparative Example 2]
(1) Preparation of electrode binder Poly (2-acrylamido-2-methylpropanesulfonic acid) (mass average molecular weight 2000000) (Aldrich 15% by weight aqueous solution) 3.0 g, polyvinyl alcohol (Aldrich) Water was added to give a 7% by weight aqueous solution, polyvinyl alcohol had a mass average molecular weight of 146000 to 186000, a saponification degree of 99% or more) 6.43 g, and water 8.57 g were added, and “poly (2-acrylamide- “2-methylpropanesulfonic acid): polyvinyl alcohol (mass ratio)” was adjusted to be “50:50”, and this was mixed with a self-revolving mixer.
Then, 10.0 g of the obtained mixture was added with 0.4 g of FC-4430 (added to a fluorosurfactant manufactured by Sumitomo 3M to make a 10 mass% aqueous solution), PTFE dispersion (manufactured by Asahi Glass Co., Ltd., AD938L, PTFE content 55-60% by mass, surfactant concentration 3% by mass diluted 4 times by weight) 2.00 g, and 11.6 g water and 16.0 g IPA In addition, it was mixed with a revolving mixer to obtain a binder for electrodes.
(2) Preparation of electrode paste to (4) Preparation of membrane-electrode assembly As in Example 1, except that the electrode binder was used, an electrode paste, an electrode, and a membrane-electrode assembly were prepared. did.

[Comparative Example 3]
A membrane-electrode assembly was produced in the same manner as in Example 1 except that a commercially available anode electrode (GDE400-4, manufactured by Paramount Energy Co., Ltd.) using a sulfonated fluororesin solution as a binder was used.

<Evaluation of electrode and membrane-electrode assembly>
The electrode and the membrane-electrode assembly were evaluated according to the following procedure.
(I) Evaluation of initial power generation performance of electrode by comparison of relative output The membrane-electrode assemblies of Examples 1 to 3 and Comparative Examples 1 to 3 are set in a single cell for fuel cells (JARI standard cell) by a prescribed method. did. 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 maximum output was measured by measuring the cell IV. Then, assuming that the output when the membrane-electrode assembly of Comparative Example 3 is used is 100, the relative output when the membrane-electrode assemblies of Examples 1 to 3 and Comparative Examples 1 and 2 are used is calculated. did. The results are shown in Table 2.

(II) Evaluation of electrode durability-1 by immersion in aqueous methanol solution The electrodes of Examples 1 to 3 and Comparative Examples 1 to 3 were immersed in 200 mL of a 50% by weight aqueous methanol solution, and then in an oven at 80 ° C for 24 hours. Heated. 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 2.
○ ・ ・ ・ ・ No elution △ ・ ・ ・ ・ Slight elution × ・ ・ ・ ・ Remarkably elution

(III) Evaluation of Durability of Electrode by Immersion in Aqueous Methanol Solution-2 For the electrode immersed in the methanol aqueous solution in (II), in order to evaluate the durability from the power generation performance, the method of (I), Maximum output was measured. And the output maintenance rate (%) after immersion was computed by making the output before immersion 100%, respectively. The results are shown in Table 2.

As is clear from the above results, the electrodes of Examples 1 to 4 have an initial power generation performance equivalent to or higher than that of the electrode of Comparative Example 3, and do not elute into the methanol aqueous solution and hardly swell. The output maintenance factor which is equal to or better than the electrodes of Comparative Examples 1 to 3 was shown. The electrodes of Examples 1 to 4 were clearly superior to the electrodes of Comparative Examples 1 to 3 in that both the initial power generation performance and durability were high.
In addition, if a predetermined amount or more of polyvinyl alcohol is present relative to platinum-ruthenium-supported carbon, the output retention rate is lowered even if the ratio of poly (2-acrylamido-2-methylpropanesulfonic acid) is increased. It was confirmed that the initial power generation performance was improved.

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

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 (6)

Poly (2-acrylamido-2-methylpropanesulfonic acid ) as the acid group-containing polymer material (A) , polyvinyl alcohol as the hydrophilic polymer material (B), and an electron transfer material carrying a catalyst (C) An electrode paste comprising:
The mixing ratio (mass ratio) of the acid group-containing polymer material (A): the hydrophilic polymer material (B) is 55: 45-80: 20,
An electrode paste, wherein a blending amount of the hydrophilic polymer material (B) is 5 parts by mass or more with respect to 100 parts by mass of the electron transfer material (C) carrying the catalyst. Furthermore, surfactant and fluorine resin are mix | blended, The paste for electrodes of Claim 1 characterized by the above-mentioned. An electrode, wherein the electrode paste according to claim 1 or 2 is heated and solidified. The electrode according to claim 3 , wherein the electrode paste is heated to 100 ° C. or higher. A membrane-electrode assembly, wherein the electrode according to claim 3 or 4 is disposed on both surfaces of an electrolyte membrane. A fuel cell comprising the membrane-electrode assembly according to claim 5 .

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