JP2009104811A - Electrolyte membrane and membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte membrane with excellent low-methanol permeability. <P>SOLUTION: The electrolyte membrane contains a porous base material (A) with an inner communication structure, and a proton-dissociative polymer (B) as well as a non-proton-dissociative polymer (C) with a cross-linking structure contained inside the porous base material (A), with a contact angle of 50 to 70° to 30 mass% methanol aqueous solution, and the membrane electrode assembly is provided with the electrolyte membrane and electrodes. The (A) component is of an organic porous base material, and the (B) component is of a polymer having a cross-linking structure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrolyte membrane suitable for use in fuel cells, particularly solid polymer fuel cells and direct methanol fuel cells, and a method for producing the same.

Conventionally, as an electrolyte membrane for a fuel cell, an electrolyte membrane made of a polymer containing a functional group having a dissociable proton such as a sulfonic acid group is known. In particular, there is a high need for an electrolyte membrane that has high proton conductivity and is prevented from swelling / dissolving in water produced in a fuel cell, liquid fuel typified by methanol, and methanol permeability.
Specific examples of the polymer containing a functional group having a dissociable proton include a polymer of perfluorosulfonic acid, a polyether sulfone, a polyether ketone, a polybenzimidazole, or the like having a dissociable proton by sulfonation. A polymer having a functional group introduced therein, or a polymer in which a side chain having a sulfonic acid group is bonded to the rigid skeleton, styrenesulfonic acid, vinylsulfonic acid, 2-acrylamido-2-methyl-1-propanesulfone Examples thereof include a polymer containing a monomer having a functional group having a C═C double bond and a dissociable proton, such as an acid (hereinafter referred to as AMPS).

  Such a polymer containing a functional group having a dissociative proton may be used alone as an electrolyte membrane. When a polymer containing a functional group having a dissociative proton is used as an electrolyte membrane, a) When the amount of the functional group having a dissociable proton in the polymer is large, high proton conductivity is obtained, but it easily swells and dissolves in water and liquid fuel, and increases methanol permeability; (b) When the amount of the functional group having a dissociable proton in the polymer is small, it becomes difficult to swell and dissolve in water or liquid fuel, and methanol permeability is suppressed, but there is a problem that proton conductivity is also lowered.

  In order to solve the above-mentioned problems, for example, Patent Document 1 discloses that a void of a porous membrane is filled with a monocyclic aromatic polymerizable monomer, a crosslinkable polymerizable monomer, and a polymerizable initiator. Then, a method for producing a diaphragm for a direct liquid fuel cell is disclosed in which the polymerization composition is polymerized and cured, and then a cation exchange group is introduced into a benzene ring derived from the monocyclic aromatic monomer. ing.

  Patent Document 2 discloses a polymer electrolyte membrane containing a polymer of a compound having an acid-generating group and a compound having two or more double bonds in one molecule formed in the polymer, An electrolyte membrane in which the swelling ratio after immersion in water and methanol is controlled within a specific range is disclosed.

  Further, Patent Document 3 discloses a dissociation property having a functional group having a dissociating proton and a C = C double bond in an electrolyte membrane precursor made of a polymer having a cross-linking structure that includes a functional group having a dissociating proton. A composite electrolyte membrane filled with a polymer obtained by polymerizing monomers is disclosed.

JP 2007-234302 A JP 2005-30312 A JP 2007-128764 A

  However, any of the electrolyte membranes described in the above documents still has room for improvement from the viewpoint of methanol permeability.

  In view of the above circumstances, the problem to be solved by the present invention is to provide an electrolyte membrane having excellent low methanol permeability and a method for producing the same.

  As a result of intensive studies on the above problems, the present inventors have found that an electrolyte membrane having a contact angle of 50 to 70 degrees with respect to a 30% by mass methanol aqueous solution has excellent low methanol permeability. The invention has been completed.

That is, the present invention is as follows.
[1]
The electrolyte membrane whose contact angle with respect to 30 mass% methanol aqueous solution is 50-70 degree | times.
[2]
A porous substrate (A) having an internal communication structure;
A proton dissociable polymer (B) and a non-proton dissociable polymer (C) having a crosslinked structure, contained in the porous substrate (A);
The electrolyte membrane according to [1] above, comprising:
[3]
The electrolyte membrane according to the above [2], wherein the component (B) is a polymer having a crosslinked structure.
[4]
The electrolyte membrane according to [2] or [3], wherein the component (A) is an organic porous substrate.
[5]
A membrane electrode assembly comprising the electrolyte membrane according to any one of the above [1] to [4] and an electrode.
[6]
A fuel cell comprising the membrane electrode assembly according to the above [5] and a current collector.

  According to the present invention, an electrolyte membrane having excellent low methanol permeability can be provided.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

  The electrolyte membrane of the present embodiment has a contact angle with respect to a 30% by mass methanol aqueous solution of 50 to 70 degrees. In the present embodiment, by adjusting the contact angle to the specific range, excellent low methanol permeability can be imparted to the obtained electrolyte membrane. The reason why excellent low methanol permeability is obtained when the contact angle is in the above range is that the electrolyte membrane has a balance between the hydrophobicity derived from the base material and the electrolyte polymer skeleton and the hydrophilicity derived from the proton dissociable group. It is presumed that moderate water repellency is exhibited with respect to the aqueous methanol solution, the solubility of the aqueous methanol solution in the vicinity of the electrolyte membrane surface is lowered, and as a result, the methanol permeability is remarkably reduced.

  Moreover, if the contact angle is outside the above range, the effect of reducing the methanol permeability is insufficient. If the contact angle is 50 degrees or less, the affinity between the polymer constituting the electrolyte membrane and the aqueous methanol solution is Methanol permeability increases because it tends to become stronger. Conversely, if it is 70 degrees or more, it is necessary to take a structure in which a hydrophilic proton-dissociable group is bonded to a water-repellent polymer skeleton. In addition, proton-dissociable groups tend to form large hydrophilic domains (clusters), and methanol has the property of easily passing between large hydrophilic domains containing water, resulting in an increase in methanol permeability. Estimated.

As a method for adjusting the contact angle within the above range, a known hydrocarbon electrolyte membrane known to have a small hydrophilic domain formed by a proton dissociable group can be imparted with a hydrophobic and crosslinked structure. Examples include a method in which a monomer is applied or immersed alone without using a non-polymerizable solvent, polymerized, and impregnated into the hydrocarbon-based electrolyte membrane as a hydrophobic cross-linkable non-electrolyte polymer.
That is, it can be performed by appropriately adjusting the type and amount of the base material and the polymer to be impregnated.

  In the present embodiment, the contact angle means a value obtained by dropping 1 μL of a 30% by mass methanol aqueous solution by the droplet method and measuring the contact angle 20 seconds after landing on the electrolyte membrane surface by the θ / 2 method. To do.

  The electrolyte membrane of the present embodiment may be composed of any component as long as the contact angle with respect to the 30% by mass methanol aqueous solution is 50 to 70 degrees, but the porous substrate (A) having an internal communication structure and Including a proton dissociable polymer (B) and a non-proton dissociable polymer (C) having a crosslinked structure contained in the porous base material (A). It is preferable because good proton conductivity tends to be obtained. Hereinafter, each component will be described.

[(A) component: porous substrate]
The porous substrate having an internal communication structure as the component (A) is a porous substrate having voids due to pores or the like therein, and at least part of the voids through the voids. A known porous substrate can be used without limitation as long as the front and back sides of the substrate are communicated.

The average pore diameter of the void portion of the porous substrate is preferably 0.01 to 2 μm, more preferably 0.015 to 0.4 μm. When the average pore size is 0.01 μm or more, the proton conductivity of the electrolyte membrane tends to increase, and when the average pore size is 2 μm or less, the methanol permeability of the electrolyte membrane tends to decrease.
The average pore diameter here is measured as a volume-based median diameter (μm) by a mercury intrusion method (for example, Autopore 9520 manufactured by Shimadzu Corporation).

The porosity (also referred to as porosity) of the porous substrate is preferably 20 to 95%, more preferably 30 to 90%.
In addition, the porosity here is a value calculated from the thickness and area of the porous substrate by measuring the sample volume (cm3) and weight (g), using the material density of the porous substrate, and using the following equation: It is.
Porosity = {1− (weight / material density) / sample volume} × 100

  The air permeability (JIS P-8117) of the porous substrate is preferably 1500 seconds or less, and more preferably 1000 seconds or less. When the air permeability is within the above range, the electric resistance of the obtained electrolyte membrane tends to be low, and high physical strength tends to be maintained.

  The thickness of the porous substrate is preferably 3 to 120 μm, more preferably 5 to 100 μm, and still more preferably 5 to 70 μm.

  It does not specifically limit as a form of a porous base material, The thing of arbitrary forms, such as a porous film, a woven fabric, a nonwoven fabric, paper, an inorganic film | membrane, can be used. Examples of the material for the porous substrate include organic porous substrates such as thermoplastic resins and thermosetting resins, inorganic porous substrates such as silica and alumina, and mixtures thereof. Among these, since the production is easy and the adhesion strength with the components (B) and (C) described later tends to be high, an organic porous substrate is preferable, and a thermoplastic resin is more preferable.

  Examples of the thermoplastic resin include α such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, and 5-methyl-1-heptene. -Polyolefin resins such as olefin homopolymers or copolymers; Vinyl chloride resins such as polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-olefin copolymers Fluorine such as polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer; -Based resin: nylon 6, nylon 66, etc. Among them, preferred are polyolefin resins, and more preferred are polyethylene resins and polypropylene, since they are excellent in chemical stability and chemical resistance, and can achieve both high mechanical strength and small pore diameter. A resin, more preferably a polyethylene resin.

  The porous substrate can be obtained, for example, by the method described in JP-A-3-64334, JP-A-9-216964, JP-A-11-130899, and the like. In addition, as such a porous substrate, commercially available products can also be used. Etc. can be used.

[(B) component: proton dissociable polymer]
As the proton dissociable polymer as the component (B), for example, a polymer containing a sulfonic acid group, a phosphonic acid group, a carboxylic acid group or the like as a proton dissociable group can be preferably used. Since a better proton conductivity tends to be expressed, it is preferable to use a polymer containing a sulfonic acid group.

  Examples of the polymer containing a sulfonic acid group include a polymer containing a perfluorosulfonic acid, a polymer containing an ether sulfone structure having a sulfonic acid group, a polymer containing an aromatic imide structure having a sulfonic acid group, and a sulfonic acid. A polymer containing an aromatic ether ether ketone structure having a group, a polymer containing 2-acrylamido-2-methylpropanesulfonic acid, a polymer containing polystyrenesulfonic acid, a polymer containing vinylsulfonic acid, and allylsulfonic acid Polymer, polymer containing methallyl sulfonic acid, polymer containing vinyl toluene sulfonic acid, polymer containing vinyl xylene sulfonic acid, polymer containing α-methylstyrene sulfonic acid, polymer containing vinyl naphthalene sulfonic acid, A polymer containing a phenol structure having a sulfonic acid group can be suitably used. That.

  In the present embodiment, the component (B) preferably has a crosslinked structure because the methanol permeability of the obtained electrolyte membrane tends to be further reduced. Examples of the type of cross-linking include cross-linking by covalent bond, cross-linking by hydrogen bond, and cross-linking by coordination bond. From the viewpoint of the strength of the cross-linking structure, cross-linking by covalent bond is preferable. The covalently crosslinked structure of the proton-dissociating polymer (B) can be obtained by, for example, preparing a monomer containing a proton-dissociating functional group and a C═C double bond in advance, divinylbenzene, divinylsulfone, butadiene, isoprene, divinyl. A crosslinked structure is introduced by copolymerizing with a crosslinkable monomer having a plurality of C═C double bonds, such as pyridine, N, N′-methylenebisacrylamide, divinylbiphenyl, triallyl isocyanurate, and trivinylbenzene. A method (for example, cross-linking sulfonated polystyrene with divinylbenzene), a method for introducing a cross-linked structure between a plurality of proton dissociative functional groups (a plurality of sulfonic acids using sulfonated polyether ether ketone and diamine) Sulfonated polyethers that crosslink groups with sulfonamide bonds -Sulfuric acid groups of terketones are desulfurized and condensed to form a sulfonate bond to crosslink), and reactive structures other than proton dissociative functional groups are crosslinked (carbonyl groups in sulfonated aromatic polymers, aromatic A method of forming a cross-linked structure by supplying energy to the alkyl group directly bonded to the ring or an unsaturated bond at the terminal by ultraviolet irradiation or the like, and crosslinking the sulfonated phenol with formaldehyde to form a cross-linked sulfonated phenol resin) Etc., and can be suitably introduced. The introduction ratio of the crosslinked structure is preferably 10 to 50 mol%, more preferably 15 to 45 mol%.

  The content of the component (B) contained in the porous substrate (A) is preferably 15 to 4000% by mass, more preferably 25 to 2000% by mass, and further preferably 35 to 900% by mass. When the content of the component (B) is 15% by mass or more, the proton conductivity of the electrolyte membrane tends to be favorable, and when it is 4000% by mass or less, the methanol permeability of the electrolyte membrane tends to decrease. .

[Component (C): Non-proton dissociable polymer having a crosslinked structure]
Examples of the aprotic dissociative polymer having a crosslinked structure as component (C) include N, N′-methylenebisacrylamide, divinylbenzene, trivinylbenzene, α- and ω-terminated alkanes having both terminals α and ω vinylated. , Α and ω both ends of (meth) acrylated C2 or more diol and di (meth) acrylate compound condensed with two or more molecules of diol, trimethylolpropane tri (meth) acrylate and its ethylene oxide or propylene oxide It is obtained by polymerizing a compound having a plurality of double bonds, such as a modified product, triallyl isocyanurate, tri (meth) acrylate isocyanurate, pentaerythritol in which all hydroxyl groups are (meth) acrylated, and condensates thereof. A polymer is preferred. These compounds having a plurality of double bonds can be used in combination of two or more. In addition, styrene derivatives that do not contain a plurality of double bonds may be mixed as impurities, such as commercially available divinylbenzene, but they may be used without removing these impurities. Furthermore, in the production of the electrolyte membrane, a monomer that does not contain a plurality of double bonds, such as a styrene monomer, within a range not exceeding the total amount of compounds having a plurality of double bonds, is a monomer that forms component (C). For the purpose of adjusting the viscosity of the mixture, a cross-linked structure can be imparted in combination. Among them, from the viewpoint of reducing methanol permeability, divinylbenzene, trivinylbenzene, α- and ω-terminated vinylphenoxylated C2 or higher alkanes and isocyanuric acids that do not contain amide, ether, and ester functional groups. A polymer composed of a hydrophobic compound that does not mix with water, such as triallyl, is preferred.

  The content of the component (C) contained in the porous substrate (A) is preferably 0.01 to 5% by mass, more preferably 0.05 to 4% by mass, and still more preferably 0.1 to 5% by mass. 3% by mass. When the content of the component (C) is 5% by mass or less, the amount of the component (C) attached to the electrolyte membrane is not too much, and the proton conductivity of the electrolyte membrane tends to be good, and 0.01% by mass The above is preferable because the methanol permeability reduction effect of the electrolyte membrane by the component (C) tends to be larger.

[Manufacture of electrolyte membrane]
The manufacturing method of the electrolyte membrane of the present embodiment is not particularly limited, but for example, the following methods (I) and (II) can be employed.
(I) a first filling step of filling a monomer (b) that forms a proton dissociable polymer (B) inside a porous substrate (A) having an internal communication structure;
A first polymerization step of polymerizing the monomer (b) to form a proton dissociable polymer (B) after the first filling step;
After the first polymerization step, a second filling step of filling the monomer (c) that forms the aprotic dissociative polymer (C) having a crosslinked structure;
A second polymerization step of polymerizing the monomer (c) to form an aprotic dissociable polymer (C) having a crosslinked structure after the second filling step;
A production method comprising:
(II) a first filling step of filling the monomer (b) that forms the proton dissociable polymer (B) inside the porous substrate (A) having an internal communication structure;
A first polymerization step of polymerizing the monomer (b) to form a polymer after the first filling step;
After the first polymerization step, a proton dissociable group introduction step of introducing a proton dissociable group into the polymer to form a proton dissociable polymer (B);
A second filling step of filling the monomer (c) that forms the aprotic dissociable polymer (C) having a crosslinked structure after the proton dissociable group introduction step;
A second polymerization step of polymerizing the monomer (c) to form an aprotic dissociable polymer (C) having a crosslinked structure after the second filling step;
Manufacturing method.

  Employing such a production method means that, after the step of introducing a proton dissociable group, a void formed by the elimination of a solvent that may be used to dissolve the monomer (b) during the first filling step. It is preferable from the viewpoint of filling a loose structure that easily allows methanol permeation, which is likely to occur during a washing step with water that may be employed, with polymer (C), densifying the electrolyte membrane, and suppressing methanol permeability.

  The proton dissociative polymer (B) is polymerized in advance using the monomer (b) having a proton dissociable group, or polymerized using a monomer (b) having no proton dissociable group. It is prepared by introducing a proton dissociable group into the obtained polymer.

  As the monomer (b), examples of the monomer having a proton dissociable group include sulfones such as vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, and 2- (meth) acrylamide-2-methylpropane sulfonic acid. Acidic monomers; carboxylic acid monomers such as acrylic acid, methacrylic acid, and vinyl benzoic acid; known C═C double bonds such as phosphonic acid monomers such as vinylphosphonic acid and styrenephosphonic acid And compounds having a sulfonic acid, carboxylic acid, or phosphonic acid group.

  On the other hand, as a monomer having no proton dissociable group, for example, styrene, o-, m-, p-methylstyrene, 2,4-dimethylstyrene, 1,2,4-trimethylstyrene, 1,3,4 -Trimethylstyrene, 2-ethyl-4-methylstyrene, 2-propyl-4-methylstyrene, 2-butyl-4-methylstyrene, 2-chloro-4-methylstyrene, p-methyl-α-methylstyrene, etc. A vinyl aromatic compound is mentioned. The above monomers may be used alone or in combination of two or more.

  As the monomer (b), it is preferable to use a hydrophobic vinyl monomer because it is easy to fill the porous substrate and the proton conductivity of the obtained electrolyte membrane tends to be good. Examples of such a hydrophobic vinyl monomer include the above-mentioned hydrophobic vinyl aromatic compounds such as styrene and methylstyrene and divinylbenzene, trivinylbenzene, C2 or more in which both α and ω terminals are vinylphenoxylated. It is preferable to use a hydrophobic cross-linking agent such as alkane in combination.

  As a method of filling the monomer (b) inside the porous substrate (A), a known method such as an immersion method or a coating method can be used as a monomer liquid (liquid monomer) by dissolving only in the monomer or in a solvent. Then, the porous substrate as component (A) is impregnated. When using a solvent during impregnation, polar solvents such as water, alcohols, dimethyl sulfoxide and the like that can easily penetrate into the porous base material can be suitably used. Since the methanol permeability of the resulting electrolyte membrane may be increased by removing the solvent during use, it is preferable to impregnate without using a solvent. If necessary, a small amount of additives such as a surfactant and a plasticizer can be used.

  The method for polymerizing the monomer (b) filled in the voids of the porous substrate (A) is not particularly limited, and a known method may be appropriately employed depending on the types of the monomer and the polymerization initiator. For example, when an organic peroxide is used as the polymerization initiator, a heating polymerization method (thermal polymerization) is generally used. This method is preferable because it is easy to operate and can be relatively uniformly polymerized. In the polymerization, in order to prevent polymerization inhibition due to oxygen and to obtain smoothness of the surface, it is preferable to perform polymerization after covering the porous substrate filled with the monomer (b) with a film of polyester or the like. By covering the porous substrate with a film, excess monomer is excluded from the porous substrate, and a thin and uniform electrolyte membrane tends to be obtained.

  As the polymerization initiator, an organic peroxide is preferably used. For example, octanoyl peroxide, lauroyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, t-butylperoxyiso Examples thereof include radical polymerization initiators such as butyrate, t-butyl peroxylaurate, t-hexyl peroxybenzoate, and di-t-butyl peroxide.

  Although the usage-amount of a polymerization initiator is suitably changed according to the kind of monomer or polymerization initiator, Preferably it is 0.1-20 mass parts with respect to 100 mass parts of monomer components, More preferably, it is 0.00. 5 to 10 parts by mass.

  The polymerization temperature at the time of thermal polymerization is not particularly limited, and a known temperature condition may be appropriately selected, but is preferably 50 to 150 ° C, more preferably 60 to 120 ° C. The polymerization time is preferably 10 minutes to 10 hours.

  Examples of the proton-dissociable group introduced into the polymer after polymerization using the monomer (b) having no proton-dissociable group include a sulfonic acid group, a carboxylic acid group, and a phosphonic acid group. Among them, a sulfonic acid group is preferable because proton conductivity of the obtained electrolyte membrane tends to be good.

  As a method for introducing a sulfonic acid group into a polymer, for example, as a method for introducing a sulfonic acid group into a benzene ring, for example, a method of reacting a sulfonating agent such as concentrated sulfuric acid, fuming sulfuric acid, sulfur dioxide, chlorosulfonic acid, etc. Etc. Examples of the method for introducing a phosphonic group into the benzene ring include a method in which the polymer is reacted with phosphorus trichloride in the presence of anhydrous aluminum chloride and then hydrolyzed in an alkaline aqueous solution. Furthermore, as a method of introducing a carboxylic acid group into the benzene ring, a method of halogenating by contacting with a halogen gas in the presence of a catalyst such as iron halide, further reacting with alkyllithium, and then reacting with carbon dioxide. Etc.

  In the present embodiment, the first filling step and the first polymerization step, or the first filling step, the first polymerization step, and the proton dissociable group introduction step, into the porous substrate (A), After the formation of the proton dissociable polymer (B), a second filling step of filling the monomer (c) that forms the non-proton dissociating polymer (C) having a crosslinked structure, and after the second filling step The second polymerization step of polymerizing the monomer (c) to form the aprotic dissociable polymer (C) having a crosslinked structure is carried out.

  Examples of the monomer (c) include N, N′-methylenebisacrylamide, divinylbenzene, trivinylbenzene, C2 or higher alkane in which both ends of α and ω are vinylphenoxylated, and both ends of α and ω are (meth). Diacrylated C2 or higher diol and di (meth) acrylate-based compounds in which two or more diols are condensed, trimethylolpropane tri (meth) acrylate and its modified products by ethylene oxide or propylene oxide, triallyl isocyanurate, triisocyanurate A compound having a plurality of double bonds, such as (meth) acrylate, pentaerythritol in which all hydroxyl groups are (meth) acrylated, and a condensate thereof can be used. And methanol permeation of the resulting electrolyte membrane Because There is a tendency to decrease, divinylbenzene, trivinylbenzene, alpha, omega both ends vinylphenoxy reduction has been C2 or more alkanes, such as triallyl isocyanurate, hydrophobic crosslinking agent immiscible with water is preferred.

  As a method of filling the monomer (c) into the porous substrate (A), a method similar to the method of filling the monomer (b) can be used. The monomer impregnated in the porous substrate (A) As a method for polymerizing (c), the same polymerization method as described above can be used.

[Membrane electrode assembly, fuel cell]
The electrolyte membrane obtained as described above is washed, cut, and the like as necessary, and can be used as a diaphragm for a fuel cell according to a conventional method as described below.

  The fuel cell of the present embodiment can be manufactured by attaching gas diffusion electrodes to both surfaces of the electrolyte membrane (manufacturing the membrane electrode assembly) and then sandwiching the entire membrane with a current collector according to a known method. . In accordance with a known method, the gas diffusion electrode is prepared by using carbon black powder carrying fine particles made of platinum or an alloy of platinum and a dissimilar metal such as ruthenium, a polymer containing a functional group having a known dissociative proton, or PTFE. And a porous sheet held by a hydrophobic resin binder. The gas diffusion electrode may be formed by a known method, for example, by preparing a gas diffusion electrode on a support in advance and then closely adhering to the electrolyte membrane by hot pressing, or directly forming it on the electrolyte membrane by screen printing. Adhere to.

  The current collector is made of a conductive material such as a conductive carbon plate, and a groove serving as a flow path for fuel gas or liquid is formed on the cathode side and an oxidant gas is formed on the anode side.

In a polymer electrolyte fuel cell, for example, hydrogen gas is supplied to the cathode side and air is supplied to the anode side, and electric energy is generated by the following reaction.
Cathode: H ₂ → 2H ⁺ + 2e ⁻
Anode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O

In a direct methanol fuel cell, for example, an aqueous methanol solution is supplied to the cathode side and air is supplied to the anode side, and electric energy is generated by the following reaction.
Cathode: CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻
Anode: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O

Hereinafter, the present embodiment will be described in more detail with reference to examples.
[Measuring method]
The measuring method of the physical property etc. in this specification is as follows.
(Measurement of contact angle)
Using an automatic contact angle system CA-V150 manufactured by Kyowa Interface Science Co., Ltd., 1 μl of a 30% by mass methanol aqueous solution is dropped by the droplet method, and the contact angle 20 seconds after landing on the electrolyte membrane surface is θ / 2. Measured by the method.
(Measurement of methanol permeability)
An electrolyte membrane is sandwiched between a glass H-type cell, a 30% by weight aqueous methanol solution is added to one side cell (A), ion-exchanged water is added to the opposite side cell (B), and the cells on both sides are agitated. The change in methanol concentration with time was quantified with a gas chromatograph to determine methanol permeability. The measured value of each electrolyte membrane was divided by the value measured in the same manner for Nafion (registered trademark) 117 manufactured by DuPont, USA, and normalized as a relative value.
(Measurement of proton conductivity)
The proton conductivity (S / cm) in the direction of the membrane surface at 40 ° C. in water was determined from the AC impedance measured by the 4-terminal method using a 1280B chemical impedance analyzer manufactured by Solartron, England, and this value was obtained as the membrane thickness (cm). The proton conductivity (S / cm ² ) was divided. The measured value of each electrolyte membrane was divided by the value measured in the same manner for Nafion (registered trademark) 117 manufactured by DuPont, USA, and normalized as a relative value.

[Comparative Example 1]
Polyethylene microporous membrane (thickness: 16 μm, porosity: 41%, air permeability: 250 sec / 100 cc), 60 parts by mass of methylstyrene (mixed product of Wako Pure Chemical Industries, m-form: about 60%, p-form: about 40%) , Divinylbenzene (DVB) (manufactured by Wako Pure Chemical Industries, Ltd., isomer mixture having a content of about 55%), t-butylperoxy-2-ethylexanoate (manufactured by NOF Corporation, trade name) “Perbutyl O” (content 97% or more) impregnated with 5 parts by mass of a monomer liquid, pulled up, sandwiched between two polyethylene terephthalate films (hereinafter referred to as “PET film”), and in nitrogen atmosphere at 80 ° C. for 5 hours Polymerized. The obtained film was peeled off from the PET film and immersed in a 1: 1 mixture of 98% concentrated sulfuric acid and chlorosulfonic acid having a purity of 90% or more at 40 ° C. for 60 minutes to sulfonate the benzene ring, and the electrolyte membrane was Obtained. The obtained electrolyte membrane had a contact angle of 32 degrees, proton conductivity of 4.4 relative to Nafion (registered trademark) 117, and methanol permeability of 0.2 relative to Nafion (registered trademark) 117. 23.

[Comparative Example 2]
Polyethylene microporous membrane (thickness 25 μm, porosity 36%, air permeability 700 sec / 100 cc), 60 parts by mass of methylstyrene (similar to that used in Comparative Example 1), divinylbenzene (DVB) (used in Comparative Example 1) After impregnating the monomer liquid consisting of 40 parts by mass and 5 parts by mass of t-butylperoxy-2-ethylexanoate (similar to that used in Comparative Example 1) as a polymerization initiator and pulling it up The film was sandwiched between two PET films and polymerized at 80 ° C. for 5 hours in a nitrogen atmosphere. The obtained film was peeled off from the PET film and immersed in a 1: 1 mixture of 98% concentrated sulfuric acid and chlorosulfonic acid having a purity of 90% or more at 40 ° C. for 60 minutes to sulfonate the benzene ring, and the electrolyte membrane was Obtained. The obtained electrolyte membrane had a contact angle of 42 degrees, proton conductivity of 3.3 relative to Nafion (registered trademark) 117, and methanol permeability of 0.2 relative to Nafion (registered trademark) 117. There were 50.

[Example 1]
The electrolyte membrane of Comparative Example 1 is 100 parts by mass of divinylbenzene (similar to that used in Comparative Example 1) and t-butylperoxy-2-ethylexanoate (as used in Comparative Example 1 as a polymerization initiator). Similarly) After impregnating the monomer liquid consisting of 5 parts by mass and pulling it up, it was sandwiched between two PET films and polymerized at 80 ° C. for 5 hours in a nitrogen atmosphere. The obtained membrane was peeled from the PET film to obtain the electrolyte membrane of the present embodiment. The obtained electrolyte membrane had a contact angle of 58 degrees, proton conductivity of 3.6 relative to Nafion (registered trademark) 117, and methanol permeability of 0.2 relative to Nafion (registered trademark) 117. 08.

[Example 2]
The electrolyte membrane of Comparative Example 2 was impregnated with the same monomer solution as in Example 1, pulled up, sandwiched between two PET films, and polymerized at 80 ° C. for 5 hours in a nitrogen atmosphere. The obtained membrane was peeled from the PET film to obtain the electrolyte membrane of the present embodiment. The obtained electrolyte membrane had a contact angle of 58 degrees, proton conductivity of 1.5 relative to Nafion (registered trademark) 117, and methanol permeability of 0.2 relative to Nafion (registered trademark) 117. It was 15.

[Example 3]
The electrolyte membrane of Comparative Example 2 was prepared by using 100 parts by mass of isocyanuric acid triallyl (TAIC) (produced by Tokyo Chemical Industry Co., Ltd., content of 97% or more) and t-butylperoxy-2-ethylexanoate (Comparative Example) as a polymerization initiator. (Similar to that used in No. 1) 30 parts by mass of a monomer liquid was impregnated, pulled up, sandwiched between two PET films, and polymerized at 80 ° C. for 5 hours in a nitrogen atmosphere. The obtained membrane was peeled from the PET film to obtain the electrolyte membrane of the present embodiment. The obtained electrolyte membrane had a contact angle of 51 degrees, proton conductivity of 2.4 relative to Nafion (registered trademark) 117, and methanol permeability of 0.2 relative to Nafion (registered trademark) 117. 18

[Comparative Example 3]
The electrolyte membrane of Comparative Example 2 was prepared by using 100 parts by mass of a styrene monomer (manufactured by Wako Pure Chemical Industries, Ltd. content: 99% or more) and t-butylperoxy-2-ethylexanoate (used in Reference Example 1) as a polymerization initiator. (Similar to the above) The polymer liquid was impregnated with 5 parts by mass, pulled up, sandwiched between two PET films, and polymerized at 80 ° C. for 5 hours in a nitrogen atmosphere. The obtained membrane was peeled from the PET film to obtain the electrolyte membrane of the present embodiment. The obtained electrolyte membrane had a contact angle of 41 degrees, proton conductivity of 1.6 relative to Nafion (registered trademark) 117, and methanol permeability of 0.2 relative to Nafion (registered trademark) 117. 35.

[Comparative Example 4]
A commercially available electrolyte membrane Nafion (registered trademark) 117 manufactured by DuPont USA was obtained, and the contact angle measured in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 3 was 74 degrees.

As is clear from the results in Table 1, the electrolyte membranes of Examples 1 to 3 having a contact angle of 50 to 70 degrees with respect to a 30% by mass methanol aqueous solution maintain good proton conductivity and have remarkable methanol permeability. It was reduced to.
On the other hand, although the electrolyte membranes of Comparative Examples 1 to 3 having a contact angle of less than 50 degrees had good proton conductivity, the effect of reducing methanol permeability was insufficient.
Moreover, the electrolyte membrane of Comparative Example 4 having a contact angle exceeding 70 degrees was inferior in both proton conductivity and methanol permeability.

  The electrolyte membrane of the present invention has excellent low proton permeability, and has industrial applicability as an electrolyte membrane for fuel cells, particularly solid polymer fuel cells and direct methanol fuel cells.

Claims (6)

  The electrolyte membrane whose contact angle with respect to 30 mass% methanol aqueous solution is 50-70 degree | times. A porous substrate (A) having an internal communication structure;
A proton dissociable polymer (B) and a non-proton dissociable polymer (C) having a crosslinked structure, contained in the porous substrate (A);
The electrolyte membrane according to claim 1, comprising:   The electrolyte membrane according to claim 2, wherein the component (B) is a polymer having a crosslinked structure.   The electrolyte membrane according to claim 2 or 3, wherein the component (A) is an organic porous substrate.   A membrane electrode assembly comprising the electrolyte membrane according to any one of claims 1 to 4 and an electrode.   A fuel cell comprising the membrane electrode assembly according to claim 5 and a current collector.