JP2007329062A - Membrane electrode assembly for direct methanol fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly for a direct methanol fuel cell of small size and high output; and to provide the fuel cell. <P>SOLUTION: In the membrane electrode assembly for the direct methanol fuel cell formed by joining a fuel electrode and a catalyst electrode acting as an air electrode to a solid polymer electrolyte membrane, the concentration of methanol in a methanol aqueous solution fuel supplied to the fuel electrode is 30 mass% or more, and water permeability coefficient of the solid polymer electrolyte member is larger than its methanol permeability coefficient. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a membrane electrode assembly for a direct methanol fuel cell and a direct methanol fuel cell using the same.

With the improvement in performance of portable information devices such as notebook PCs, PDAs, and mobile phones, small and high-capacity power supplies are required. As a promising candidate, expectations for direct methanol fuel cells are increasing. A direct methanol fuel cell is a fuel cell that directly extracts electrical energy from a chemical reaction between methanol and oxygen, and has a feature that it has a high theoretical volumetric energy density and can be used continuously by refueling. Generally, in a direct methanol fuel cell, a membrane electrode assembly is used in which a catalyst electrode serving as a fuel electrode and an air electrode is joined to a solid polymer electrolyte membrane.
Conventionally, a perfluoro-based electrolyte membrane represented by Nafion (trade name) manufactured by DuPont has been mainly used as an electrolyte membrane of a membrane electrode assembly.
However, a membrane electrode assembly using a perfluoro-based electrolyte membrane has a problem that when high-concentration methanol water is used, methanol permeates from the fuel electrode side to the air electrode side and the output decreases. For this reason, it has been necessary to use low-concentration methanol as the fuel, and it has been difficult to reduce the size of the direct methanol fuel cell.

In addition, the following literature is mentioned as a prior art relevant to this invention.
JP 2001-348439 A JP 2002-313364 A JP 2003-82129 A Journal of Applied Polymer Science, Vol. 68, 747-763 (1998)

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a membrane electrode assembly for miniaturizing a direct methanol fuel cell and a fuel cell using the membrane electrode assembly.

  As a result of studying a method for downsizing a direct methanol fuel cell, the present inventors have determined that the concentration of methanol in the fuel supplied to the fuel electrode of the membrane electrode assembly is 30% by mass or more, and the solid polymer electrolyte membrane It has been found that by making the water permeability coefficient larger than the methanol permeability coefficient, preferably 3 times or more, a high power density can be obtained and the direct methanol fuel cell can be miniaturized.

  Further, as such a solid polymer electrolyte membrane, a solid polymer electrolyte membrane obtained by graft polymerization of a radical polymerizable monomer onto a resin film irradiated with radiation, wherein the radical polymerizable monomer has an alkoxysilyl group The present inventors have found that a solid polymer electrolyte membrane containing a radical polymerizable monomer and cross-linked by the reaction of an alkoxysilyl group after graft polymerization is suitable, and has led to the present invention.

Accordingly, the present invention provides the following electrode assembly and fuel cell.
(1) A membrane electrode assembly for a fuel cell in which a fuel electrode and an air electrode catalyst electrode are joined to a solid polymer electrolyte membrane, wherein the methanol concentration in the methanol aqueous solution fuel supplied to the fuel electrode is 30% by mass or more A membrane electrode assembly for a direct methanol fuel cell, wherein the water permeability coefficient of the solid polymer electrolyte membrane is larger than the methanol permeability coefficient.
(2) The membrane electrode assembly for a direct methanol fuel cell as described in (1), wherein the water permeability coefficient of the solid polymer electrolyte membrane is 3 times or more larger than the methanol permeability coefficient.
(3) The solid polymer electrolyte membrane is a solid polymer electrolyte membrane obtained by graft polymerization of a radical polymerizable monomer onto a resin film irradiated with radiation, wherein the radical polymerizable monomer has an alkoxysilyl group. A membrane electrode assembly for a direct methanol fuel cell according to (1) or (2), wherein the membrane electrode assembly is a solid polymer electrolyte membrane that contains a functional monomer and is crosslinked by a reaction of an alkoxysilyl group after graft polymerization.
(4) Direct including the membrane electrode assembly according to (1), (2) or (3) above, wherein the methanol concentration in the aqueous methanol fuel supplied to the fuel electrode is 30% by mass or more Methanol fuel cell.

  According to the present invention, a direct methanol fuel cell having a small size and a high output can be obtained.

The membrane electrode assembly according to the present invention is obtained by joining a catalyst electrode to be a fuel electrode and an air electrode to a solid polymer electrolyte membrane.
In this case, any solid polymer electrolyte membrane may be used as long as the water permeability coefficient is larger than the methanol permeability coefficient, but preferably the solid polymer electrolyte membrane is radically polymerizable to the resin film irradiated with radiation. A solid polymer electrolyte membrane obtained by graft polymerization of a monomer, wherein the radical polymerizable monomer contains a radical polymerizable monomer having an alkoxysilyl group, and is crosslinked by the reaction of the alkoxysilyl group after the graft polymerization It is a membrane. In such a solid polymer electrolyte membrane, the water permeability coefficient is larger than the methanol permeability coefficient. Therefore, it is considered that the concentration of methanol permeated to the air electrode side is reduced and the overvoltage of the air electrode is reduced.
In addition, since silanol groups and siloxane bonds derived from alkoxysilyl groups are present in the solid polymer electrolyte membrane, it is considered that the hydrophilic domains in the membrane increase and water can easily permeate.

In this case, as a method for producing a solid polymer electrolyte membrane by graft polymerization of a polymerizable monomer to the resin film irradiated with the radiation,
Irradiating the resin film with radiation;
A step of graft-polymerizing a polymerizable monomer having an alkoxysilyl group alone or a polymerizable monomer having the alkoxysilyl group and another polymerizable monomer on a resin film irradiated with radiation;
A step of crosslinking by reaction of an alkoxysilyl group;
When the polymerizable monomer is a monomer having no ion conductive group, it is preferable to employ a step of introducing an ion conductive group.

  Here, as the resin film, it is preferable to use a film or sheet made of a fluororesin. Among fluororesins, it has excellent film properties and is suitable for radiation graft polymerization, so polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene -Tetrafluoroethylene copolymers are preferred. These resins may be used alone or in appropriate combination.

  Moreover, 10-200 micrometers is preferable and, as for the film thickness of a resin film, 20-100 micrometers is more preferable.

  The resin film is first irradiated with radiation, for example, at room temperature. As the radiation, electron beams, γ rays, and X-rays are preferable, and electron beams are particularly preferable. The amount of irradiation depends on the type of radiation, and further on the type and thickness of the resin film. For example, when the above-mentioned fluorine-based resin film is irradiated with an electron beam, 1 to 200 kGy is preferable, and 1 to 100 kGy is more preferable.

  Further, the irradiation with radiation is preferably performed in an inert gas atmosphere such as helium, nitrogen, or argon gas, and the oxygen concentration in the gas is preferably 100 ppm or less, and particularly preferably 50 ppm or less. There is no.

  Next, the resin film irradiated with the radiation is grafted with a polymerizable monomer including a polymerizable monomer having an alkoxysilyl group.

  As the polymerizable monomer having an alkoxysilyl group, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (βmethoxyethoxy) silane, γ-acryloxypropylmethyldimethoxysilane, γ-acryloxypropylmethyldiethoxysilane, γ- Acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltri Ethoxysilane, γ- (acryloxyethoxy) propyltrimethoxysilane, γ- (acryloxyethoxy) propyltriethoxysilane, γ- (methacryloxyethoxy) propyltri Tokishishiran, .gamma. (methacryloxyethoxy) propyltriethoxysilane, hexenyltrimethoxysilane, hexenyl triethoxy silane, decenyl trimethoxysilane can be mentioned decenyl triethoxysilane. Among them, trimethoxysilyl styrene, triethoxysilyl styrene, vinyl benzyl trimethoxy silane, vinyl benzyl triethoxy silane, vinyl phenethyl trimethoxy silane, vinyl phenethyl triethoxy silane having vinyl phenyl group in the molecule are included in the graft film. This is preferable because the content of the alkoxysilyl group can be greatly increased. These polymerizable monomers having an alkoxysilyl group may be used alone or in appropriate combination.

  Further, the other polymerizable monomer is preferably a monofunctional polymerizable monomer, such as styrene monomer such as styrene, α-methylstyrene, trifluorostyrene, sulfonic acid group, sulfonic acid amide group, carboxylic acid group, phosphoric acid. And monomers having an ion conductive group such as a quaternary ammonium base (sodium acrylate, sodium acrylamidomethylpropanesulfonate, sodium styrenesulfonate, etc.) can be used alone or in appropriate combination. In addition, a polyfunctional polymerizable monomer can be used by utilizing the difference in the reactivity of the functional group.

  In addition, when other polymerizable monomer M2 is used in combination with polymerizable monomer M1 having an alkoxysilyl group in this way, the ratio is appropriately selected, but preferably M1: M2 is in a molar ratio of 5:95 to 50: 50, in particular 10:90 to 40:60.

  The grafting method is performed, for example, by immersing a resin film irradiated with radiation in a solution containing a polymerizable monomer having an alkoxysilyl group and another polymerizable monomer, and 10 to 10 at 50 to 80 ° C. in a nitrogen atmosphere. What is necessary is just to heat for 20 hours. The graft rate is preferably 10 to 100%.

  Here, the usage-amount of the polymerizable monomer grafted to the resin irradiated with radiation is 1,000 to 100,000 parts by weight, particularly 4,000 to 20,000 parts by weight of the polymerizable monomer with respect to 100 parts by weight of the resin film. It is preferable to use a part. If the amount of the monomer is too small, the contact may be insufficient. If the amount is too large, the monomer may not be used efficiently.

  In graft polymerization of these polymerizable monomers, a polymerization initiator such as azobisisobutyronitrile may be appropriately used as long as the object of the present invention is not impaired.

  Furthermore, a solvent can be used during the grafting reaction, and the solvent is preferably one that uniformly dissolves the monomer, for example, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate and butyl acetate, methyl alcohol and ethyl alcohol , Alcohols such as propyl alcohol and butyl alcohol, ethers such as tetrahydrofuran and dioxane, aromatic hydrocarbons such as N, N-dimethylformamide, N, N-dimethylacetamide, benzene, toluene and xylene, n-heptane, n -Aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane, or a mixed solvent thereof can be used. The monomer / solvent (mass ratio) is preferably from 0.01 to 1. When the monomer / solvent (mass ratio) is larger than 1, it is difficult to adjust the number of monomer units of the graft chain, and when it is smaller than 0.01, the graft ratio may be too low. A more desirable range is 0.03 to 0.5.

  Next, the grafted resin film is subjected to crosslinking by a reaction of an alkoxysilyl group, for example, hydrolysis and dehydration condensation. The hydrolysis may be performed, for example, by immersing the grafted resin film in a mixed solution of hydrochloric acid and dimethylformamide (DMF) at room temperature for 10 to 20 hours. In the dehydration condensation, the resin film after hydrolysis is heated for several hours (usually 2 to 8 hours) at 100 to 200 ° C. in an inert gas atmosphere under reduced pressure (usually 1 to 10 Torr) or atmospheric pressure. do it. At this time, a tin-based catalyst such as dibutyltin dilaurate can also be used to advance the reaction under mild conditions.

  Furthermore, in the case of a monomer having no ion conductive group (for example, the above styrene monomer), an ion conductive group such as a sulfonic acid group, a carboxylic acid group, or a quaternary ammonium base is introduced into the graft chain. A solid polymer electrolyte membrane is obtained. The introduction method of the sulfonic acid group is the same as the conventional method. For example, it may be sulfonated by contacting with chlorosulfonic acid or fluorosulfonic acid. In addition, sulfonation can be performed before dehydration condensation, and hydrolysis can be omitted.

  Further, the crosslinking density can be further increased by immersing the grafted resin film in alkoxysilane and cohydrolyzing and codehydrating with the alkoxysilyl group of the graft chain. Examples of the alkoxysilane include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dimethyldimethoxysilane, and dimethyldiethoxysilane. In this case, the amount of alkoxysilane used is that 1,000 to 10,000 parts by mass of alkoxysilane is used with respect to 100 parts by mass of the resin film, and 0.1 to 20% by mass of alkoxysilane is impregnated in the resin film. preferable.

  The solid polymer electrolyte membrane thus obtained has an increased crosslink density and a greatly reduced water swelling and methanol permeability. In this case, as described above, the water permeability coefficient is larger than the methanol permeability coefficient, and usually the water permeability coefficient is 3 times or more, particularly 3 to 30 times the methanol permeability coefficient.

  In the present invention, a catalyst electrode serving as a fuel electrode and an air electrode is joined to the solid polymer electrolyte membrane. In this case, the catalyst electrode is formed of a porous electrode substrate and a catalyst layer. As the porous electrode substrate, carbon paper, carbon cloth or the like is preferably used. The catalyst layer preferably contains catalyst particles and a solid polymer electrolyte.

  In this case, examples of the catalyst particles include platinum and platinum alloys. Examples of platinum alloys include alloys of platinum and at least one metal selected from ruthenium, palladium, rhodium, iridium, osmium, molybdenum, tin, cobalt, nickel, iron, chromium, and the like. In this case, the platinum alloy is preferably one containing 5% by mass or more, particularly 10% by mass or more of platinum.

  The platinum, platinum alloy or the like may be in the form of fine particles, or may be supported on an electrically conductive carrier such as carbon black or carbon nanotube. Alternatively, a supported state and an unsupported state may be mixed.

On the other hand, examples of the solid polymer electrolyte include perfluoro-based electrolytes typified by Nafion (trade name, manufactured by DuPont), hydrocarbon-based electrolytes typified by styrenesulfonic acid-butadiene copolymers, and sulfonic acid group-containing alkoxysilanes. Inorganic / organic hybrid electrolytes typified by copolycondensates of silyl and terminal silylated organic oligomers are preferably used.
In addition to the above components, inorganic oxide fine particles such as silica and titania can be blended for the purpose of imparting hydrophilicity.

  Furthermore, a solvent can be used for the catalyst paste forming the catalyst layer for the purpose of improving the coating property when the catalyst paste is applied to the electrode and / or the electrolyte membrane. As the solvent, those that uniformly dissolve the solid polymer electrolyte and the like are preferable. For example, alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, ethylene glycol, glycerol, acetone, Ketones such as methyl ethyl ketone, esters such as ethyl acetate and butyl acetate, ethers such as tetrahydrofuran and dioxane, aromatic hydrocarbons such as benzene and toluene, aliphatic or alicyclic such as n-heptane, n-hexane and cyclohexane Polar solvents such as hydrocarbon, water, dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethylacetamide, formamide, N-methylformamide, N-methylpyrrolidone, ethylene carbonate, propylene carbonate And the like. These can be used alone or in admixture of two or more. Of these, polar solvents such as isopropyl alcohol, water and N, N-dimethylformamide are desirable.

  Moreover, in order to increase the porosity in the catalyst layer and facilitate the movement of water, it is also possible to add a fluororesin. Examples of fluororesins include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polychlorotrifluoroethylene (PCTFE), ethylene-tetra Fluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), trifluoroethylene-ethylene copolymer (ECTFE), etc. are used, and these may be used alone or in combination of two or more. Can do. In addition, as these fluororesins, the commercial item about the polystyrene conversion number average molecular weight 100,000-600,000 by GPC can be used.

  The amount of the above-mentioned components can be selected within a wide range, but the solid polymer electrolyte is 10 to 1,000 parts by weight and the solvent is 0 to 5,000 parts by weight, particularly 100 to 1,1 parts per 100 parts by weight of catalyst particles. 000 parts by mass and the fluororesin component are preferably used in an amount of 10 to 400 parts by mass, particularly 40 to 130 parts by mass.

  The catalyst paste is applied onto the electrolyte membrane or the porous electrode substrate, and when a solvent is added to the paste, the solvent is removed and a catalyst layer is formed by a conventional method.

The catalyst layer is formed on at least one of the electrolyte membrane and the electrode substrate, and the membrane / electrode assembly can be obtained by sandwiching both surfaces of the electrolyte membrane with the electrode substrate and hot pressing. The temperature during hot pressing is appropriately selected depending on the components in the electrolyte membrane or catalyst paste to be used, the type of fluorine resin, and the mixing ratio, but the desirable temperature range is 50 to 200 ° C, more desirably 80 to 180 ° C. is there. If it is less than 50 ° C, bonding may be insufficient, and if it exceeds 200 ° C, the resin component in the electrolyte membrane or the catalyst layer may be deteriorated. The pressure level is appropriately selected depending on the components in the electrolyte membrane and / or the catalyst paste, the type and blending ratio of the fluororesin, and the type of the porous electrode substrate, but the preferable pressure range is 1 to 100 kgf / cm ^2. More desirably, it is 10 to 100 kgf / cm ² . If it is less than 1 kgf / cm ² , the bonding may be insufficient, and if it exceeds 100 kgf / cm ² , the porosity of the catalyst layer and the electrode substrate may decrease, and the performance may deteriorate.

  In this way, a membrane electrode assembly as shown in FIG. 1 is obtained. Here, in FIG. 1, 1 is a cathode (air electrode) made up of a porous electrode substrate 2 made of carbon paper, carbon cloth, etc. and a catalyst layer 3, and 4 is a porous electrode base made up of carbon paper, carbon cloth, etc. An anode (fuel electrode) 7 composed of the material 5 and the catalyst layer 6 is a solid polymer electrolyte membrane. In this case, a water repellent layer can be interposed between the catalyst layer 3 and the porous electrode substrate 2 and between the catalyst layer 6 and the porous electrode substrate 5, respectively.

  The direct methanol fuel cell of the present invention is constructed according to a known method except that the membrane electrode assembly is used. In the present invention, the methanol concentration in the fuel is 30 as the methanol aqueous solution fuel supplied to the fuel electrode. The mass density is 100% by mass or more, preferably 40 to 100% by mass, and more preferably 50 to 100% by mass. Thus, by setting the methanol concentration high, a high output density is achieved. In this case, the use of the membrane electrode assembly described above makes it possible to use a high-concentration fuel with a small reduction in output due to methanol permeation from the fuel electrode side to the air electrode side.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Example 1]
[I] Synthesis of solid polymer electrolyte membrane (1) Styrene-trimethoxysilylstyrene copolymer graft Low-voltage electron beam irradiation on an ethylene-tetrafluoroethylene copolymer membrane (manufactured by Norton) having a length of 5 cm, a width of 6 cm, and a thickness of 25 μm An electron beam with an accelerating voltage of 100 kV was irradiated with an apparatus (light beam L manufactured by Iwasaki Electric Co., Ltd.) in a nitrogen atmosphere so that the absorbed dose was 50 kGy.
An initiator solution was prepared by dissolving 15 mg of azobisisobutyronitrile in 7.5 g of toluene.
In a test tube equipped with a three-way cock, the above membrane, 3.9 g of styrene, 2.1 g of trimethoxysilylstyrene, 1.0 g of initiator solution, and 17.0 g of toluene were bubbled with nitrogen for 0.5 hours at room temperature. The three-way cock was closed and graft polymerization was performed in a 63 ° C. oil bath for 16 hours.
The co-graft membrane was washed with xylene and dried under reduced pressure at 100 ° C. for 4 hours.
The total graft ratio determined by the following formula from the change in the mass of the membrane before and after the grafting was 23% by mass.
Total graft ratio = (post-graft membrane mass−pre-graft membrane mass) / pre-graft membrane mass The graft rate of trimethoxysilylstyrene determined from the methoxy group absorption intensity in the IR absorption spectrum was 5% by mass.

(2) Crosslinking of styrene-trimethoxysilylstyrene co-graft membrane 3 g of 2M hydrochloric acid and 22 g of N, N-dimethylformamide were mixed.
The co-graft membrane and the above mixed solution were placed in a test tube and immersed for 5 hours at room temperature, and then the membrane was crosslinked by heating at 200 ° C. for 3 hours in reduced pressure (5 Torr).

(3) Sulfonation of cross-linked styrene-trimethoxysilylstyrene cograft membrane 0.6 g of chlorosulfonic acid and 25 mL of dichloroethane were mixed to prepare a chlorosulfonic acid / dichloroethane solution.
The cross-linked membrane and the above solution were put into a test tube equipped with a Dimroth condenser, and sulfonated in a 50 ° C. oil bath for 6 hours.
The sulfonated membrane was washed with dichloroethane and pure water.
A sulfonated membrane and 300 mL of pure water were placed in a beaker and hydrolyzed in a thermostatic bath at 50 ° C. for 22 hours to obtain an electrolyte membrane.
The electrolyte membrane was washed with pure water and dried under reduced pressure at 100 ° C. for 3 hours.

[II] Measurement of Water Permeability Coefficient and Methanol Permeability Coefficient of Electrolyte Membrane 60 mL of 32 mass% methanol water and 60 mL of pure water are separated by the electrolyte membrane obtained in [I], and the methanol water side is separated at regular intervals at room temperature. The water permeation coefficient and the methanol permeation coefficient were determined by gas chromatography quantifying the concentration of methanol permeating through the membrane and exiting to the pure water side and the concentration of methanol remaining on the methanol water side. The results are shown in Table 1.

[III] Production of Membrane Electrode Assembly A paste made of Johnson Massey's PtRu black HiSPEC6000 (trade name) and DuPont's Nafion solution (trade name) is added to Toray's carbon paper TGP-H-060 (trade name). The catalyst electrode (A) for the fuel electrode was prepared by applying the PtRu black amount to 7 mg / cm ² and drying.
Similarly, paste made of Toray's carbon paper TGP-H-060 (trade name), Johnson Massey's Pt black HiSPEC 1000 (trade name) and DuPont's Nafion solution (trade name), with a Pt black amount of 7 mg. The catalyst electrode (C) for the air electrode was produced by applying the solution to / cm ² and drying.
Sandwiched between the electrolyte membrane and the area of 5 cm ² catalyst electrode prepared by the method of [I] (A) a catalyst electrode (C), 150 ℃, hot-pressed at 50 kgf / cm ^2, to obtain a membrane electrode assembly.

[IV] Membrane / electrode assembly of power generation evaluation [III] is incorporated into a fuel cell FC-05-01SP (trade name) manufactured by Electrochem, and 0.5 mL of methanol water having a concentration of 3 to 100% by mass on the fuel electrode side. In addition to supplying at / min, dry air was supplied to the air electrode side at 0.44 L / min (standard state conversion) to generate electricity at 30 ° C. The power generation output was measured with an electronic load device 890CL (trade name) manufactured by Scribner. The maximum power density at each methanol concentration is shown in FIG.

[Comparative Example 1] Membrane electrode assembly of perfluoro-based electrolyte membrane In the same manner as [III] in Example 1, Nafion 112 (trade name) manufactured by DuPont was used as a catalyst electrode (A) and a catalyst electrode (C) having an area of 5 cm ^2. And hot-pressed at 130 ° C. and 50 kgf / cm ² to obtain a membrane / electrode assembly. This membrane / electrode assembly was subjected to power generation evaluation under the same conditions as [IV] of Example 1.
The water permeation coefficient and methanol permeation coefficient of Nafion 112 manufactured by DuPont are shown in Table 1, and the results of power generation evaluation of this membrane electrode assembly are shown in FIG.

It is sectional drawing which shows an example of an electrode and membrane assembly. 4 is a graph showing the maximum output density at a methanol concentration in Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cathode 2 Porous electrode base material 3 Catalyst layer 4 Anode 5 Porous electrode base material 6 Catalyst layer 7 Solid polymer electrolyte membrane

Claims (4)

  A membrane electrode assembly for a fuel cell in which a catalyst electrode to be a fuel electrode and an air electrode is joined to a solid polymer electrolyte membrane, wherein the methanol concentration in the methanol aqueous solution fuel supplied to the fuel electrode is 30% by mass or more, A membrane electrode assembly for a direct methanol fuel cell, wherein the water permeability coefficient of the solid polymer electrolyte membrane is larger than the methanol permeability coefficient.   2. The membrane electrode assembly for a direct methanol fuel cell according to claim 1, wherein the water permeability coefficient of the solid polymer electrolyte membrane is at least 3 times larger than the methanol permeability coefficient.   The solid polymer electrolyte membrane is a solid polymer electrolyte membrane obtained by graft polymerization of a radical polymerizable monomer onto a resin film irradiated with radiation, wherein the radical polymerizable monomer has a radical polymerizable monomer having an alkoxysilyl group. The membrane electrode assembly for a direct methanol fuel cell according to claim 1 or 2, wherein the membrane electrode assembly is a solid polymer electrolyte membrane that is crosslinked by a reaction of an alkoxysilyl group after graft polymerization. A direct methanol fuel cell comprising the membrane electrode assembly according to claim 1, wherein the methanol concentration in the methanol aqueous solution fuel supplied to the fuel electrode is 30% by mass or more.

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