JP4969083B2 - Electrolyte membrane and fuel cell - Google Patents

Description

  The present invention relates to fuel cells, and more particularly to solid polymer fuel cells and direct methanol fuel cells.

As an electrolyte membrane for a fuel cell, a membrane made of a polymer containing a functional group having a dissociative proton, particularly a polymer having a sulfonic acid group, is known.
Specific examples of the polymer having a sulfonic acid group include a polymer of perfluorosulfonic acid, a polymer in which a sulfonic acid group is introduced by sulfonation into a rigid skeleton such as polyethersulfone, polyetherketone, and polybenzimidazole. Or a polymer in which a side chain having a sulfonic acid group is bonded to the rigid skeleton, styrene sulfonic acid, vinyl sulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid (hereinafter referred to as AMPS), = A polymer of monomers having a C double bond and a sulfonic acid group, a monomer having a C = C double bond and a sulfonic acid group, and a monomer having a C = C double bond but no sulfonic acid group A polymer copolymerized in combination, and the polymer is mixed with divinylbenzene, N, N′-methylenebisacrylamide (hereinafter referred to as MBAA). Examples thereof include polymers crosslinked using a polyfunctional monomer or the like.

  Such a polymer having a sulfonic acid group is used as an electrolyte membrane alone, or for the purpose of suppressing dimensional change during drying-wetting of the membrane, such as water generated in a fuel cell, methanol, and the like. It is used as an electrolyte membrane that is impregnated and filled in a base material that does not easily change its dimensions even when it comes into contact with liquid fuel.

  Since these electrolyte membranes are not thermoplastic to polymers having sulfonic acid groups, (1) after extrusion into a film in the form of a sulfonyl halide precursor, the polymer is hydrolyzed with an alkali in the presence of a swellable solvent. Decompose, ion exchange with acidic solution to make sulfonic acid polymer membrane, (2) Disperse sulfonic acid polymer in solvent, cast into film, evaporate solvent, sulfonic acid polymer (3) A sulfonic acid or a monomer available as a sulfonate is dissolved in water together with a surfactant, impregnated, polymerized and filled into a substrate, and ion exchange is performed with an acid solution as necessary. To make a sulfonic acid polymer membrane (for example, JP-A-2005-71609), (4) Sulfonation of sulfuric acid anhydride, chlorosulfonic acid, etc. by impregnating and polymerizing a sulfonateable monomer on a substrate The performs sulfonated, and the sulfonic acid polymer film (e.g., JP 2001-135328), have been obtained by the method equal.

  In recent years, in polymer electrolyte fuel cells, the hydrogen permeability of the electrolyte membrane has been suppressed to improve durability. In direct methanol fuel cells, the methanol permeability of the electrolyte membrane has been improved to improve fuel efficiency and voltage. There is a need to suppress this. The hydrogen permeability and methanol permeability of the electrolyte membrane can be improved by increasing the thickness of the electrolyte membrane. In this case, however, the proton conductivity of the electrolyte membrane is lowered, and the polymer electrolyte fuel cell and the direct methanol fuel cell are reduced. This is not a preferable solution.

On the other hand, in the electrolyte membrane obtained by the method of (1) to (4) above, a solvent, a sulfonating agent, and water are used at the time of manufacture, so that a portion having high hydrogen permeability or methanol permeability is formed for the following reason. It is thought that it is done.
(A) Hydrogen permeability: When the membrane, dried in the polymer electrolyte fuel cell, where the solvent, water, sulfonating agent used in the production is extracted or evaporated, the hydrogen permeability increases. Cheap.
(B) Methanol permeability: Water penetrates when the fuel electrode side is in direct contact with the methanol aqueous solution in the methanol fuel cell where the solvent, water, and sulfonating agent used in the production are extracted or evaporated. Methanol permeability tends to increase.

In JP-A-2005-71609 described above (3), a polymer of AMPS, which is one type of sulfonic acid monomer, is made into pores of a porous substrate that does not substantially swell with an organic solvent containing methanol or water. There is a description that methanol permeability can be reduced by the filled electrolyte membrane.
However, in this technology, in order to obtain an AMPS polymer, since AMPS is a water-soluble solid, it is necessary to dilute the monomer with about the same weight of water as AMPS, without using water. It cannot be said that it can be polymerized in the base material and the formation of a portion having a high hydrogen permeability or methanol permeability in the electrolyte membrane is not improved.

In JP-A-2001-135328 of the above-mentioned (4), a polyolefin porous membrane is used as a base material, and the pores are filled with a polymer of a proton dissociating monomer such as a polymer of a sulfonic acid monomer. A hydrogen gas permeable electrolyte membrane is disclosed, and the proton dissociative functional group including a sulfonic acid group is filled by filling the monomer with a high density without any gaps to the fine pores, and subsequent reaction treatment such as sulfonation. It is described that an electrolyte having low hydrogen gas permeability can be obtained.
However, in this technology, since a reactive agent such as a sulfonating agent is used in the reaction treatment such as sulfonation, it is considered that it is formed when the reactant that has permeated the electrolyte membrane during the reaction treatment is washed and removed. Therefore, it cannot be said that the formation of a portion having high hydrogen permeability or methanol permeability is improved.

As an improvement method of JP 2005-71609 A (3), a method of increasing the hydrophobicity of the electrolyte polymer and decreasing the water absorption of the electrolyte membrane by increasing the number of times the base material is impregnated and filled with the electrolyte polymer. (For example, WO2005 / 76396) is disclosed, and the effect of improving durability is described.
However, in this technology, including when increasing the number of impregnations and fillings, when filling the porous substrate with the electrolyte polymer, if the monomer filling the pores of the porous substrate has a low viscosity, it is porous as it is. Otherwise, a pre-swelled gel is formed in the porous substrate, and water or methanol swells the electrolyte polymer when used as a fuel cell, causing the electrolyte polymer to fall off. There is a description that a solution, particularly an aqueous solution, is preferable because it has an effect of preventing, and when increasing the number of fillings, the use of solvents and water is actively suppressed during production, and hydrogen permeability and methanol permeability are reduced. It does not disclose how to suppress.

  As another solution to the above problem, in Japanese Patent Application Laid-Open No. 2002-83612, the first polymer is embedded by chemical bonding in the pores of the heat-resistant substrate, and further filled with the second polymer, thereby increasing the temperature. There is a proposal that the skeleton of the base material can maintain the membrane structure even underneath, and the proton conductivity can be enhanced while suppressing methanol permeability.

However, in this technique, as a method of filling the second polymer starting from the monomer, after filling the second monomer to be the second polymer into the pores by the subsequent treatment, A polymerization reaction is performed to obtain a second polymer, whereby the second polymer is filled in the pores, thereby suppressing methanol permeability and suppressing polymer elution and outflow in the pores. However, it does not teach a method for suppressing the hydrogen permeability or methanol permeability by actively suppressing the use of solvent or water during production when obtaining the second polymer.
JP 2005-71609 A JP 2001-135328 A WO2005 / 76396 JP 2002-83612 A

  An object of the present invention is to provide an electrolyte membrane with reduced hydrogen permeability and methanol permeability, which increases with the history of production without lowering proton conductivity, and a fuel cell using the electrolyte membrane.

  As a result of studies conducted by the present inventors to solve the above-described problems, a dissociative liquid having a dissociable proton and a C═C double bond is added to the electrolyte membrane precursor having a sulfonic acid group as the first component. An electrolyte membrane characterized in that it is filled with a second component made of a monomer polymer, and the second component is made of a monomer solution polymer containing the dissociable liquid monomer as a main component and substantially free of a solvent. However, it has been found that hydrogen permeability and methanol permeability can be reduced without lowering proton conductivity and can be suitably used for a fuel cell, and the present invention has been completed.

That is, the present invention
(1) The electrolyte membrane precursor having a sulfonic acid group is a first component, dissociative liquid monomer having a dissociative proton and C = C double bond is not more than 75 mol%, the monomer solution containing no solvent An electrolyte membrane in which the first component is filled with the second component, which is a polymer of the monomer, by dipping and polymerizing the monomer ,
(2) The electrolyte membrane precursor having a sulfonic acid group as the first component is converted into a monomer liquid containing 75 mol% or more of a dissociable liquid monomer having a dissociative proton and a C═C double bond, and containing no solvent. A method for producing an electrolyte membrane in which a first component is filled with a second component that is a polymer of a monomer by dipping and polymerizing the monomer;
(3) The present invention relates to a fuel cell using the electrolyte membrane according to (1).

  The electrolyte membrane of the present invention is a second component comprising a polymer of a monomer liquid that contains a dissociable liquid monomer as a main component and substantially does not contain a solvent with respect to the electrolyte membrane precursor having a sulfonic acid group as the first component. In the production of the electrolyte membrane precursor, the monomer liquid is substantially added to the hydrogen permeable or methanol permeable portion formed in the electrolyte membrane precursor by water, a solvent or a sulfonating agent. Since the polymerization and filling without using a solvent is possible, hydrogen permeability and methanol permeability can be suppressed without lowering proton conductivity, and it can be suitably used for a fuel cell.

  The present invention will be specifically described below. The electrolyte membrane of the present invention includes an electrolyte membrane precursor having a sulfonic acid group as a first component, and a polymer of a liquid monomer having a dissociable proton and a C = C double bond, which is filled in the electrolyte membrane precursor. An electrolyte membrane comprising: a second component comprising: a polymer of a monomer liquid containing the dissociative liquid monomer as a main component and substantially free of a solvent. is there. More specifically, the electrolyte membrane of the present invention is formed in water, a solvent, or a sulfonating agent, which is formed with water, a solvent, or a sulfonating agent at the time of producing the electrolyte membrane precursor as the first component. The second component composed of the liquid monomer was impregnated as a monomer liquid substantially free from a solvent, polymerized, and filled, and the hydrogen permeability and methanol permeability were suppressed without reducing proton conductivity. It is an electrolyte membrane.

The electrolyte membrane precursor having a sulfonic acid group as the first component used in the present invention is an electrolyte membrane precursor obtained by any one of the following methods (1) to (4).
(1) Extruded into a film in the form of a sulfonyl halide precursor, then hydrolyzed with an alkali in the presence of a swellable solvent, ion exchanged with an acidic solution, and made into a sulfonic acid polymer membrane (Example: perfluorosulfonic acid polymer membrane), (2) A sulfonic acid polymer dispersed in a solvent, cast into a film, and then evaporated to give a sulfonic acid polymer membrane (eg, sulfonation) (Polyethersulfone membrane, sulfonated polyimide membrane, sulfonated polyetheretherketone membrane), (3) A monomer available as sulfonic acid or sulfonate is dissolved in water together with a surfactant, impregnated into a substrate and polymerized If necessary, ion exchange is performed with an acidic solution to obtain a sulfonic acid polymer membrane (eg, polyethylene microporous membrane impregnated and polymerized with AMPS), 4) Impregnated base material with a sulfonateable monomer, polymerized, and sulfonated with a sulfonating agent such as sulfuric anhydride or chlorosulfonic acid to give a sulfonic acid polymer film (eg, styrene, divinylbenzene) Impregnated polymerized and sulfonated polyethylene microporous membrane, hydrofluorinated polyethylene microporous membrane impregnated with perfluorosulfonic acid polymer). If necessary, a plurality of the electrolyte membrane precursors obtained by any of the methods (1) to (4) may be laminated and used in combination.

  In the present invention, the viscosity of the dissociative liquid monomer having a dissociable proton and a C═C double bond constituting the polymer of the second component is used for the electrolyte membrane precursor when used as a monomer liquid. In order to maintain a good impregnation property, it is preferable that the liquid is 100 cP or less at 40 ° C., more preferably 10,000 cP or less, and still more preferably 1000 cP or less. As examples of such dissociable liquid monomers, vinyl sulfonic acid, vinyl phosphonic acid, acrylic acid, methacrylic acid, vinyl acetic acid and the like are preferably used. If necessary, a plurality of these dissociable liquid monomers may be used in combination with the monomer liquid. If necessary, a non-dissociable monomer having at least one C═C double bond that can be dissolved in the dissociable liquid monomer is added to the weight of the dissociable liquid monomer in the monomer liquid. It may be dissolved in the monomer solution within a range not exceeding 1, copolymerized and used in combination. The viscosity of the monomer liquid is preferably a liquid of 100000 cP or less, more preferably 10,000 cP or less, and still more preferably 1000 cP or less at 40 ° C. in order to maintain good impregnation into the electrolyte membrane precursor. Since the monomer liquid is in a liquid state, the total amount of the dissociable liquid monomer and the non-dissociable monomer as main components is preferably 90 wt% even without substantially using a solvent such as water or an organic solvent. More preferably, the electrolyte membrane precursor can be directly impregnated at a high concentration of 95 wt% or more, and when the monomer liquid is polymerized to form a polymer, the solvent does not fall off, and the electrolyte membrane hydrogen obtained Permeability and methanol permeability can be suppressed. In addition to the dissociable liquid monomer, a small amount of a polymerization initiator or an additive such as a surfactant to be mentioned below may be used in combination.

In the present invention, the monomer liquid containing the dissociated liquid monomer and substantially free of the solvent is either (i) directly on the electrolyte membrane precursor irradiated with high energy rays or (ii) together with the radical polymerization initiator. Then, the electrolyte membrane precursor is impregnated and polymerized as a monomer solution, thereby forming a polymer and filling the electrolyte membrane precursor.
As the high energy rays that can be used in the method (i), known high energy rays such as plasma, ultraviolet rays, electron beams, and γ rays can be used. These high energy rays excite the electrolyte membrane precursor to generate a reaction initiation point, which reacts with the monomer liquid, so that the polymer of the monomer liquid can be obtained without using a polymerization initiator. It is formed.

As a radical polymerization initiator that can be used in the method (ii), a known radical polymerization technique can be used. Specific examples include heat-initiated polymerization and photoinitiated polymerization such as ultraviolet rays. Examples of the radical polymerization initiator for heat-initiated polymerization include the following.
Persulfates such as ammonium persulfate, potassium persulfate and sodium persulfate. Organic peroxides such as di-t-butyl peroxide. These radical polymerization initiators may be used alone or in combination of two or more.

  Specific examples of radical photopolymerization initiators include benzoin ether initiators such as benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether, which are generally used for ultraviolet polymerization, 2-hydroxy-2-methyl-1- Phenylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, 4- (2-hydroxyethoxy) -phenyl (2-hydroxy-2-propyl) ketone, 2-methyl-1- (4- (methylthio) phenyl) -2-mon Acetophenone-based initiators such as folinopropane-1, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) butanone-1, diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, o -Methyl benzoylbenzoate, 4-ben Benzophenone initiators such as yl-4′-methyldiphenyl sulfide, (4-benzoylbenzyl) trimethylammonium chloride, 4,4′-dimethylaminobenzophenone, 4,4′-diethylaminobenzophenone, isopropylthioxanthone, diethylthioxanthone, thioxanthone, etc. And thioxanthone initiators, benzyl, quinone, thioacridone, and derivatives thereof. It is preferable that the polymerization initiator can be directly dissolved in the monomer liquid used without substantially containing a solvent. Moreover, it is preferable that the usage-amount of a polymerization initiator is 5 mass% or less of this monomer liquid.

  The monomer solution is used substantially free of a solvent, but the electrolyte membrane precursor is sufficient before filling with the monomer solution to prevent excess solvent from being taken into the resulting electrolyte membrane. It is preferably dried. As a drying method, known hot air drying and vacuum drying can be used within a range of conditions that do not cause alteration of the electrolyte membrane precursor.

The following examples and comparative examples illustrate the present invention. Note that this example does not limit the scope of the invention.
Measurement of proton conductivity The proton conductivity (S / cm) in the direction of the membrane surface in water at 40 ° C. was obtained from the AC impedance measured by the 4-terminal method, and this value was divided by the membrane thickness (cm) to obtain proton conductivity ( S / cm ² ).
Measurement of methanol permeability The membrane was set in a cell in a chamber controlled at 40 ° C., a 30 wt% aqueous methanol solution was circulated on the upper surface of the membrane, dry helium was allowed to flow on the lower surface of the membrane, and methanol was permeated and vaporized. The helium flowed on the lower surface of the membrane was sampled at regular intervals by a hexagonal valve equipped with a gas sampler, and the amount of methanol in the helium was quantified with a gas chromatograph. The change in the amount of methanol over time was followed, and the methanol permeability was determined from the amount of methanol when the amount became constant.

[Reference Example 1]
(Preparation of electrolyte membrane precursor)
A polyethylene microporous film (thickness 38 μm, porosity 43%, air permeability 610 seconds / 100 cc), AMPS 87 mol%, MBAA 13 mol% monomer 49 wt%, fluorosurfactant 1 wt%, photopolymerization initiator 1 wt%, water After dipping in a monomer solution consisting of 49 wt% and pulling it up, a high pressure mercury lamp was irradiated for 3 minutes to polymerize AMPS and MBAA. The obtained electrolyte membrane precursor had a proton conductivity of 25 S / cm ² and a methanol permeability of 17 kg / m ² · day.

[Example 1]
The electrolyte membrane precursor of Reference Example 1 was dried at 40 ° C. for 18 hours, irradiated with 100 kGy of gamma rays at room temperature in a nitrogen atmosphere, immersed in a monomer liquid composed of vinyl sulfonic acid, pulled up, and then heated in an oven at 50 ° C. for 18 hours. Heated for hours to polymerize vinyl sulfonic acid. The obtained electrolyte membrane had a proton conductivity of 29 S / cm ² and a methanol permeability of 10 kg / m ² · day.

[Example 2]
The electrolyte membrane precursor of Reference Example 1 was dried at 40 ° C. for 18 hours, irradiated with 100 kGy of gamma rays at room temperature in a nitrogen atmosphere, immersed in a monomer solution consisting of 75 mol% of vinyl sulfonic acid and 25 mol% of MBAA, and then pulled up. The mixture was heated in an oven at ° C for 18 hours to polymerize vinyl sulfonic acid. The obtained electrolyte membrane had proton conductivity of 26 S / cm ² and methanol permeability of 9 kg / m ² · day.

[Comparative Example 1]
The electrolyte membrane precursor of Reference Example 1 was dried at 40 ° C. for 18 hours, then irradiated with 100 kGy of gamma rays at room temperature in a nitrogen atmosphere, and immersed in a monomer solution composed of an aqueous vinyl sulfonate solution (containing 25 wt% sodium vinyl sulfonate). After being pulled up, it was heated in an oven at 50 ° C. for 18 hours to polymerize sodium vinyl sulfonate. The obtained membrane was ion-exchanged with dilute sulfuric acid to obtain an electrolyte membrane. The electrolyte membrane had proton conductivity of 27 S / cm ² and methanol permeability of 15 kg / m ² · day.

[Comparative Example 2]
After the electrolyte membrane precursor of Reference Example 1 was dried at 40 ° C. for 18 hours, it was immersed in a monomer liquid consisting of AMPS 87 mol%, MBAA 13 mol% monomer 49 wt%, photopolymerization initiator 1 wt%, water 49 wt%, and then pulled up. A mercury lamp was irradiated for 3 minutes to polymerize AMPS and MBAA. The obtained electrolyte membrane had a proton conductivity of 27 S / cm ² and a methanol permeability of 14 kg / m ² · day.

  The electrolyte membrane and fuel cell of the present invention can be suitably used in the field of fuel cells, particularly solid polymer fuel cells and direct methanol fuel cells.

Claims (3)

An electrolyte membrane precursor having a sulfonic acid group is a first component, dissociative liquid monomer having a dissociative proton and C = C double bond is not more than 75 mol%, was immersed in a monomer solution containing no solvent, An electrolyte membrane in which a first component is filled with a second component that is a polymer of the monomer by polymerizing the monomer . The electrolyte membrane precursor having a sulfonic acid group as the first component is immersed in a monomer liquid containing 75 mol% or more of a dissociable liquid monomer having a dissociable proton and a C═C double bond, and not containing a solvent, The manufacturing method of the electrolyte membrane which makes the 1st component be filled with the 2nd component which is a polymer of a monomer by polymerizing a monomer.  A fuel cell using the electrolyte membrane according to claim 1.