JP2010153186A - Proton conductive electrolyte membrane and membrane-electrode assembly using the same, and polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton conductive electrolyte membrane (graft electrolyte membrane) in which a polymer chain having a proton conductive group is graft-polymerized onto a base substance and in which oxidation resistance is more increased than a conventional graft electrolyte membrane. <P>SOLUTION: The electrolyte film is formed by graft-polymerizing a polymer chain having a proton conductive group onto a base substance made of fluororesin or olefin resin, wherein the polymer chain has a styrene derivative unit, in which a tert-butyl group and a proton conductive group are an aromatic ring substituent, as a constituent unit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a proton conductive polymer electrolyte membrane, and a membrane-electrode assembly (MEA) and a polymer electrolyte fuel cell (PEFC) using the same.

  In recent years, fuel cells have attracted attention as the next-generation energy source. In particular, PEFC using a proton conductive polymer membrane as an electrolyte has a high energy density and is expected to be used in a wide range of fields such as household cogeneration systems, power supplies for portable devices, and power supplies for automobiles.

  As a polymer used for the electrolyte membrane, perfluorocarbon sulfonic acid (for example, “Nafion (registered trademark)” manufactured by DuPont) is generally used. A membrane made of perfluorocarbon sulfonic acid is excellent in chemical durability, but a fluororesin as a raw material is not a general-purpose product and is very expensive because its synthesis process is complicated. The high cost of the electrolyte membrane is a major obstacle to the practical use of PEFC. In addition, since the perfluorocarbon sulfonic acid membrane easily permeates methanol, it is a kind of PEFC and is difficult to use as an electrolyte membrane of a direct methanol fuel cell (DMFC) in which a solution containing methanol is supplied to the fuel electrode.

  Against this background, development of hydrocarbon-based polymer electrolyte membranes that are low in cost and suppressed in permeation of methanol is currently underway. As one of the electrolyte membranes, there is a graft membrane (for example, Patent Document 1) in which a polymer chain having a proton conductive group is graft-polymerized on a resin substrate. In the graft membrane, the cost is reduced and methanol permeation is suppressed by using a general fluororesin or olefin resin as a base. By selecting the resin used for the substrate, the strength of the electrolyte membrane can be easily improved. Protons are conducted by polymer chains (graft chains) graft-polymerized on the substrate.

  By the way, during operation of PEFC, hydrogen peroxide and peroxide radicals are generated at the cathode. There is also a report that a part of oxygen that has permeated through the electrolyte membrane is converted into hydroxy radicals at the anode. For this reason, an electrolyte membrane with excellent oxidation resistance is desired, but the oxidation resistance of a general graft membrane is lower than that of a perfluorocarbon sulfonic acid membrane, and when the graft membrane is used as a polymer electrolyte membrane, A decrease in conductivity, that is, a decrease in power generation characteristics tends to occur.

  Patent Document 2 discloses a technique for improving the oxidation resistance of an electrolyte membrane by dispersing and blending a quinone compound having an action of trapping and inactivating radicals. However, since the quinone compound cannot be blended with the graft chain, it is difficult to apply this technique to the graft membrane. Even if the quinone compound is dispersed and blended into the base of the graft membrane, the graft chain responsible for proton conduction is cut by an oxidizing action such as a radical without receiving the benefits of the quinone compound.

  On the other hand, in Patent Document 3, the graft chain is crosslinked by bisvinylphenylethane (BVPE) which is a crosslinking agent. Crosslinking prevents graft chain breakage by hydrogen peroxide or radicals and improves the oxidation resistance of the film. In addition, the graft chain in the electrolyte membrane of patent document 3 has as a structural unit the unit which consists of styrene derivatives, such as styrene, (alpha) -methylstyrene, vinyltoluene, and trifluorostyrene.

Patent Document 4 discloses a graft film in which a monofunctional monomer and a polyfunctional monomer are sequentially graft-polymerized. The monofunctional monomer is, for example, styrene, α-methylstyrene, trifluorostyrene, and the polyfunctional monomer is, for example, divinylbenzene (DVB).
JP-A-9-102322 JP 2004-247155 A Japanese Patent Laid-Open No. 2006-140086 JP 2006-290159 A

  The present invention relates to a proton conductive polymer electrolyte membrane (graft electrolyte membrane) in which a polymer chain having a proton conductive group is graft-polymerized on a substrate, and an electrolyte membrane having improved oxidation resistance compared to a conventional graft electrolyte membrane The purpose is to provide.

  The proton conductive polymer electrolyte membrane of the present invention is a membrane in which a polymer chain having a proton conductive group is graft-polymerized on a fluororesin or olefin resin substrate, and the polymer chain has a tert-butyl group and a proton conductive group. A styrene derivative unit (unit (A)) having a group as an aromatic ring substituent is included as a structural unit.

  The membrane-electrode assembly of the present invention includes a polymer electrolyte membrane and a pair of electrodes arranged so as to sandwich the electrolyte membrane, and the electrolyte membrane is the proton conductive polymer electrolyte membrane of the present invention. It is.

  A polymer electrolyte fuel cell according to the present invention includes a polymer electrolyte membrane, a pair of electrodes arranged to sandwich the electrolyte membrane, and a pair of separators arranged to sandwich the pair of electrodes. The electrolyte membrane is the proton conductive polymer electrolyte membrane of the present invention.

  In the electrolyte membrane of the present invention, the graft chain has, as a structural unit, a styrene derivative unit (A) having a tert-butyl group and a proton conducting group as a substituent of an aromatic ring. As a result, the electrolyte membrane of the present invention exhibits higher oxidation resistance than conventional graft electrolyte membranes.

  In the graft electrolyte membrane, the graft chain is easily broken by the oxidizing action of hydrogen peroxide and radicals, which is one of the factors that cause the oxidation resistance of the graft electrolyte membrane to be lower than that of the perfluorocarbon sulfonic acid membrane. In a styrene derivative unit that does not have a tert-butyl group as an aromatic ring substituent, such as a polystyrene sulfonic acid unit, the aromatic ring is decomposed by oxidation, and this decomposition leads to graft chain breakage. On the other hand, in the unit (A) having a tert-butyl group as an aromatic ring substituent, it is considered that the CC bond of the tert-butyl group is cleaved before the aromatic ring is decomposed by oxidation. Compared with the case where there is no butyl group, the progress of the decomposition of the aromatic ring and the cleavage of the graft chain is delayed. That is, the tert-butyl group is considered to act as a kind of radical scavenging group, and this action is presumed to improve the oxidation resistance of the electrolyte membrane of the present invention.

  Conventionally, attempts have been made to suppress graft chain breakage due to oxidation by introducing a crosslinked structure into the graft chain. The electrolyte membrane of the present invention is based on a new idea of introducing a radical scavenging group into a styrene derivative unit, and is completely different from the conventional graft electrolyte membrane in its technical idea.

[Proton conducting polymer electrolyte membrane]
(Unit (A))
The styrene derivative unit (A) has a tert-butyl group and a proton conductive group as substituents of the aromatic ring. In the unit (A), typically, one hydrogen atom in the aromatic ring of the unit is substituted by a tert-butyl group, and one hydrogen atom different from this hydrogen atom in the aromatic ring is substituted by a proton conducting group. Has a structure.

  The substitution position of the tert-butyl group in the aromatic ring of the unit (A) is not particularly limited. Typically, it is the p (para) position relative to the vinyl group. At this time, the proton conducting group may be located at a different substitution position from the tert-butyl group, and is usually located at the o (ortho) position with respect to the vinyl group. Such a unit (A) can be formed by graft polymerization of a monomer group containing p-tert-butylstyrene and then introducing a proton conductive group into the p-tert-butylstyrene unit produced by polymerization.

  The proton conductive group is not particularly limited, and is, for example, a sulfonic acid group or a phosphoric acid group, and a sulfonic acid group is preferable because it provides an electrolyte membrane excellent in proton conductivity and handling properties.

(Graft chain)
The graft chain in the electrolyte membrane of the present invention has a unit (A) as a structural unit. Such a graft chain can be formed by graft polymerization of a monomer group containing a monomer (monomer (B)) that becomes a unit (A) by polymerization and introduction of a proton conductive group onto a substrate.

  The monomer (B) is, for example, p-tert-butylstyrene.

  The graft chain may contain a structural unit other than the unit (A) as long as the function as an electrolyte membrane can be maintained, and may have a structural unit derived from a polyfunctional monomer, for example. In this case, depending on the type of the polyfunctional monomer, a crosslinked structure is formed between adjacent graft chains, and the oxidation resistance of the electrolyte membrane is further improved. In addition, since the swelling of the membrane is suppressed by the cross-linked structure, the methanol permeability of the electrolyte membrane is further reduced, and the thermal stability thereof is improved.

  The polyfunctional monomer is not particularly limited. For example, divinyl sulfone, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, divinylbenzene (DVB), 1,2-bis (p-vinylphenyl) ethane, cyclohexanedi Methanol divinyl ether, phenylacetylene, diphenylacetylene, 1,4-diphenyl-1,3-butadiene, diallyl ether, 2,4,6-triallyloxy-1,3,5-triazine, triallyl-1,2,4 -Benzene tricarboxylate, triallyl-1,3,5-triazine-2,4,6-trione, butadiene, isobutene.

  When the graft chain has a structural unit derived from a polyfunctional monomer (unit (C)), the proportion of the unit (C) in all the structural units constituting the graft chain is, for example, 0.5 to 20 mol%. 1.0 to 10 mol% is preferable.

(Substrate)
The substrate in the electrolyte membrane of the present invention is made of a fluororesin or an olefin resin. Fluororesin and olefin resin are excellent in chemical durability, and a graft electrolyte membrane based on these resins is suitable for use as a polymer electrolyte membrane for fuel cells.

  Examples of fluororesins include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene. -Perfluoroalkyl vinyl ether copolymer (PFA) and at least one selected from ethylene-chlorotrifluoroethylene (ECTFE).

  The olefin resin is at least one selected from, for example, polyethylene (PE) and polypropylene (PP).

  The substrate may have a crosslinked structure of these resins, and in this case, the oxidation resistance of the electrolyte membrane is further improved. In addition, since the swelling of the membrane is suppressed by the cross-linked structure, the methanol permeability of the electrolyte membrane is further reduced, and the thermal stability thereof is improved.

  This crosslinked structure can be formed by a known method. For example, a method for crosslinking PTFE is disclosed in JP-A-6-116432, and a method for crosslinking FEP and PFA is disclosed in JP-A-11-49867.

  The shape of the substrate is a film, but the thickness and the size viewed from the direction perpendicular to the main surface can be appropriately determined based on the desired thickness and size of the electrolyte film.

  One important characteristic of the electrolyte membrane is membrane resistance (resistance to proton conduction). In order to reduce the membrane resistance, the electrolyte membrane should be thin. However, if it is excessively thin, the strength of the film is reduced, and breakage or pinholes are likely to occur. For this reason, the thickness of the electrolyte membrane is preferably about 10 to 200 μm, more preferably about 20 to 150 μm. When a polymer chain is graft-polymerized on the substrate and a proton conductive group is introduced into the polymer chain, the finally obtained electrolyte membrane becomes thicker than the substrate. Considering this, the thickness of the substrate is preferably about 8 to 180 μm, more preferably about 18 to 135 μm.

  The graft ratio in the electrolyte membrane of this invention is 5-70 weight%, for example, and 8-40 weight% is preferable. In the production method described later, the graft ratio can be adjusted by changing the radiation dose to the substrate, the polymerization temperature and / or polymerization time of the monomer group, and the type of solvent (polymerization solvent) of the monomer group.

  The proton conductivity (25 ° C.) of the electrolyte membrane of the present invention is usually 0.03 S / cm or more, and is 0.90 S / cm or more depending on the configuration of the membrane. Since the proton conductivity of the electrolyte membrane is affected by the amount of graft chains introduced into the membrane, it is necessary to appropriately control the membrane graft rate in accordance with the desired proton conductivity.

  The electrolyte membrane of the present invention has a methanol permeability lower than that of a perfluorocarbon sulfonic acid membrane, and can be suitably used for DMFC.

(Production method)
The method for producing the electrolyte membrane of the present invention is not particularly limited, and a known method for producing a graft electrolyte membrane can be applied.

  Specific examples are shown below.

  First, a substrate made of a fluororesin or an olefin resin is irradiated with radiation. The radiation is generally an electron beam or γ-ray. The irradiation temperature is about −10 to 80 ° C., preferably room temperature. The irradiation dose is, for example, 1 to 500 kGy. Radiation may be irradiated in air, but irradiation is preferably performed in an inert gas atmosphere.

  Next, the monomer group containing the monomer (B) is graft-polymerized on the substrate. The method of graft polymerization is not particularly limited, and for example, the substrate after irradiation may be immersed in a monomer group from which oxygen has been removed by freezing, boiling or bubbling with an inert gas. The monomer group to be graft-polymerized preferably contains the above-described polyfunctional monomer in addition to the monomer (B). In this case, a graft chain having a crosslinked structure can be formed.

  When graft polymerization is not performed immediately after irradiation, the substrate after irradiation may be temporarily stored at a temperature lower than the glass transition temperature of the resin constituting the substrate.

  In graft polymerization, the monomer group solvent (polymerization solvent) should be selected appropriately in consideration of chain transfer constants when the monomer undergoes radical polymerization, solubility and swelling in the substrate, and the boiling point of the solvent. There is. In the electrolyte membrane of the present invention, the solvent during graft polymerization is preferably a mixed solvent of an alcohol having 4 or less carbon atoms (solvent 1) and an aromatic hydrocarbon and / or chlorinated hydrocarbon (solvent 2). The solvent 1 is at least one selected from, for example, methanol, ethanol, and isopropyl alcohol. The solvent 2 is at least one selected from xylene, toluene, ethylbenzene, chloroform and o-dichlorobenzene. The solvent 2 is preferably 10 to 200% by weight of the total amount of the monomers in the monomer group, and preferably 5 to 90% by weight of the total amount of the solvent 1 and the solvent 2 in the mixed solvent. If the content of the solvent 2 in the mixed solvent becomes excessively small, the amount of polymer (homopolymer) that is not graft-polymerized on the substrate increases, making it difficult to proceed with stable graft polymerization. On the other hand, when the content of the solvent 2 in the mixed solvent becomes excessively large, graft polymerization is inhibited.

  In the above example, radiation irradiation and graft polymerization are performed separately (pre-irradiation method). Pre-irradiation can reduce the amount of homopolymer produced. The pre-irradiation method mainly includes two methods (polymer radical method and peroxide method), and any method may be used. The polymer radical method is a method in which an alkyl radical generated on a substrate by radiation irradiation is used as it is as an active point of graft polymerization. The peroxide method is a method in which an alkyl radical generated by irradiation with radiation is changed to peroxide by temporarily exposing the substrate to an oxygen-containing atmosphere and used as an active point for graft polymerization.

  Next, the substrate after graft polymerization is washed with a solvent such as toluene to remove the unreacted monomer group remaining on the substrate.

  Next, a proton conductive group is introduced into the graft chain, more specifically into the structural unit derived from the monomer (B). The introduction of the proton conductive group may be performed according to a known method. JP-A-2001-348439 discloses a method for introducing a sulfonic acid group as a proton conducting group. Specifically, the substrate after graft polymerization is immersed in a chlorosulfonic acid solution having a concentration of 0.2 to 0.5 mol / L using 1,2-dichloroethane as a solvent, and the reaction temperature is 10 to 80 ° C. React for ~ 48 hours. After the reaction, the substrate is sufficiently washed with water to remove unreacted chlorosulfonic acid. The sulfonating agent is not limited to a dichloroethane solution of chlorosulfonic acid, but may be any substance that can introduce a sulfonic acid group as a proton conductive group, such as concentrated sulfuric acid, fuming sulfuric acid, sulfur trioxide, sodium thiosulfate, and mesitylenesulfonic acid.

[Membrane-electrode assembly]
An example of the membrane-electrode assembly (MEA) of the present invention is shown in FIG.

  The MEA 1 shown in FIG. 1 includes an electrolyte membrane 2 and a pair of electrodes (an anode electrode 3 and a cathode electrode 4) arranged so as to sandwich the electrolyte membrane 2. The electrolyte membrane 2 and the electrodes 3 and 4 are Are joined together. Here, the electrolyte membrane 2 is the above-described electrolyte membrane of the present invention, and the MEA 1 has high oxidation resistance. Therefore, by incorporating the MEA 1 into the PEFC, it is possible to extend the life of the PEFC and improve the power generation characteristics. Moreover, MEA1 is suitable for DMFC because of its low methanol permeability.

  The configurations of the anode electrode (fuel electrode) 3 and the cathode electrode (oxidation electrode) 4 may be the same as those of a general MEA anode electrode and cathode electrode, respectively.

  The MEA 1 can be formed by a known method such as hot pressing the electrolyte membrane 2 and the electrodes 3 and 4.

[Polymer electrolyte fuel cell]
An example of the polymer electrolyte fuel cell (PEFC) of the present invention is shown in FIG.

  The fuel cell 11 shown in FIG. 2 sandwiches the electrolyte membrane 2, a pair of electrodes (anode electrode 3 and cathode electrode 4) disposed so as to sandwich the electrolyte membrane 2, and the pair of electrodes. It is provided with a pair of separators (anode separator 5 and cathode separator 6) arranged, and each member is joined in a state where pressure is applied in a direction perpendicular to the main surface of the member. The electrolyte membrane 2 and the electrodes 3 and 4 constitute the MEA 1. Here, the electrolyte membrane 2 is the above-described electrolyte membrane of the present invention, whereby the fuel cell 11 has a long life and improved power generation characteristics.

  The configurations of the anode electrode (fuel electrode) 3, the cathode electrode (oxidation electrode) 4, the anode separator 5 and the cathode separator 6 may be the same as those of each member in a general PEFC.

  The fuel cell of the present invention may include members other than the members shown in FIG. 2 as necessary.

  The PEFC 11 shown in FIG. 2 is a so-called single cell, but the fuel cell of the present invention may be a stack in which a plurality of such single cells are stacked.

  The fuel cell of the present invention can be formed by a known method.

  The examples illustrate the invention in more detail. The present invention is not limited to the examples shown below.

  First, an evaluation method of the electrolyte membrane produced in this example is shown.

(Graft rate)
The graft ratio of the electrolyte membrane was determined by the following formula (1).
Graft ratio _{(wt%) = (W 2 -W 1} ) / W 1 × 100 (1)

In formula (1), W ₁ is the dry weight (g) of the substrate before graft polymerization, and W ₂ is the dry weight (g) of the substrate after graft polymerization and before introduction of the proton conductive group.

(Proton conductivity: σ)
A pair of glass cells having the same shape (cylindrical shape) were connected to each other at the opening using the produced electrolyte membrane as a partition wall. A measurement electrode was disposed inside each cell. Next, both cells were filled with a 1 mol / L sulfuric acid aqueous solution and allowed to stand for several minutes until the electrolyte membrane became compatible with the sulfuric acid aqueous solution, and then a current was applied between the measuring electrodes using a potentiostat (HABF-5001 manufactured by Hokuto Denko). Then, the potential difference between the measurement electrodes generated at that time was measured using a voltmeter (HE-104). A resistance value R ₁ between the measurement electrodes was obtained from the value of the applied current and the value of the measured potential difference. Next, a pair of glass cells were connected in a state where no electrolyte membrane was disposed, and a resistance value R ₂ between the measurement electrodes was obtained by the same method as described above. The value obtained by subtracting R ₂ from the obtained resistance value R ₁ was defined as the membrane resistance value R _m of the electrolyte membrane. The resistance values R ₁ and R ₂ were measured at room temperature (25 ° C.).

The proton conductivity (S / cm ² ) of the electrolyte membrane was determined from the following formula (2). X in Formula (2) is the area of the partition wall in the electrolyte membrane (measurement area: cm ² ).
Proton conductivity (S / cm ² ) = 1 / R _m / X (2)

(Methanol permeability)
A pair of glass cells having the same shape were connected to each other at the opening using the manufactured electrolyte membrane as a partition. The area Y of the partition wall in the electrolyte membrane was 9.61 cm ² . Next, 140 g of water was poured into one cell P and 200 g of water was poured into the other cell Q, and the surface of the electrolyte membrane was made to conform to water, and the whole was stabilized at 60 ° C. by a thermostatic bath. Next, 60 g of methanol at 60 ° C. was quickly charged into the cell P, and the amount of methanol permeated through the electrolyte membrane to the cell Q side was quantified at regular intervals, with the time of charging being set to 0:00. Methanol was quantified by gas chromatography (GC), and a calibration curve prepared from GC measurement on a methanol aqueous solution having a predetermined concentration was used for quantification. The quantified amount of methanol was plotted against the elapsed time, and the methanol permeability (mmol / cm ² / Hr) of the electrolyte membrane was determined from the slope of the plot by the following formula (3).
Methanol permeability = slope of plot (mmol / hr) / area Y (3)

(Oxidation resistance)
The oxidation resistance of the electrolyte membrane was evaluated by its weight half time (Hr). The half weight time was determined as follows.

First, the produced electrolyte membrane was cut into a size of about 3 cm × 4 cm, and its dry weight W ₃ was determined.

Next, the weighed electrolyte membrane is immersed in 16.3 g of an aqueous hydrogen peroxide solution (containing iron sulfate (I) having a concentration of 3% by weight and a concentration of 30 ppm by weight), and the whole is maintained at 60 ° C. by a thermostatic bath. Then, after the immersion, the dry weight W ₄ of the electrolyte membrane was measured every predetermined time. The dry weight W ₄ was measured after the electrolyte membrane was thoroughly washed with RO water (reverse osmosis membrane treated water) and then dried.

Next, when the weight retention rate (= (W ₃ −W ₄ ) / W ₃ ) of the electrolyte membrane at the measurement timing of each dry weight W ₄ is obtained, and each value is approximated to the following equation (4) The coefficient Z was defined as the weight half time of the electrolyte membrane. T in Formula (4) is the elapsed time from the start of immersion.
(Weight reduction rate at time t) = 1−1 / (1 + EXP (− (t−Z))) (4)

Example 1
A PVdF film (thickness 50 μm) as a substrate was cut into a 10 cm square, and the film was irradiated with an electron beam (acceleration voltage 250 kV) with a dose of 30 kGy at room temperature in the air. The irradiated film was cooled to a dry ice temperature (−79 ° C.) and stored at that temperature until the start of graft polymerization.

  Separately, a polymerization solution was prepared by mixing 160 g of p-tert-butylstyrene, 5.55 g of divinylbenzene (DVB), 48 g of methanol and 112 g of ethylbenzene as a monomer group to be graft-polymerized on the substrate.

  Next, the prepared polymerization solution is put into a separable flask equipped with a reflux tube, heated and refluxed under atmospheric pressure, and the film after irradiation is immersed in this for 270 minutes, and p-tert-butylstyrene and DVB was graft polymerized.

  After the completion of the polymerization, the film was taken out from the flask, washed with toluene for 1 hour and methanol for 10 minutes, and then dried with a drier maintained at 60 ° C. to give a PVdF substrate with p-tert-butylstyrene units and DVB units. A graft film was obtained in which a polymer chain having a structural unit as a structural unit was graft-polymerized. The graft ratio of this membrane was 29% by weight.

  Next, the obtained graft membrane was immersed in an o-dichlorobenzene solution (concentration 0.2 mol / L) of 1,3,5-trimethylbenzene-2-sulfonic acid at 135 ° C. for 30 minutes to form a polymer chain. A sulfonic acid group was introduced. Thereafter, the sulfonic acid group-introduced film was washed twice with isopropyl alcohol (30 minutes per time) and with warm water at 60 ° C. for 30 minutes, and then dried with a drier kept at 60 ° C. As a result, a graft membrane having a sulfonic acid group introduced therein was obtained.

  Next, a graft electrolyte membrane (Example 1) was obtained by immersing the obtained graft membrane in an aqueous HCl solution (concentration 1N) at room temperature for 3 hours.

(Comparative Example 1)
An electrolyte membrane (Comparative Example 1) was obtained in the same manner as in Example 1 except that p-methylstyrene was used in place of p-tert-butylstyrene and the graft polymerization time was 45 minutes.

(Comparative Example 2)
An electrolyte membrane (Comparative Example 2) was obtained in the same manner as in Example 1 except that styrene was used in place of p-tert-butylstyrene and the graft polymerization time was 20 minutes.

(Comparative Example 3)
An electrolyte membrane (Comparative Example 3) was obtained in the same manner as in Example 1 except that 4-acetoxystyrene was used in place of p-tert-butylstyrene and the graft polymerization time was 20 minutes.

  Table 1 below shows the results of evaluation of the proton conductivity, methanol permeability, and weight half-life, which are indicators of oxidation resistance, of the electrolyte membranes of Example 1 and Comparative Examples 1 to 3. Table 1 also shows the results of evaluating proton conductivity and methanol permeability for an electrolyte membrane made of Nafion 112 (manufactured by DuPont), which is perfluorocarbon sulfonic acid, as a reference example.

  As shown in Table 1, the weight half time of Example 1 was larger than that of Comparative Examples 1 to 3, and an electrolyte membrane excellent in oxidation resistance could be realized. Moreover, the methanol transmittance | permeability of Example 1 became small compared with Comparative Examples 1-3 and the reference example. Looking at the proton / methanol selective permeability represented by the ratio of proton conductivity to methanol permeability (= proton conductivity / methanol permeability), the value of Example 1 is the value of Comparative Examples 1 to 3 and the reference example. The electrolyte membrane of Example 1 was found to be suitable for DMFC, which was considerably larger than the value.

  The proton conductive polymer electrolyte membrane of the present invention can be suitably used for PEFC (particularly DMFC using methanol-containing solution as fuel).

It is a schematic diagram which shows an example of the membrane-electrode assembly of this invention. It is a schematic diagram which shows an example of the fuel cell of this invention.

Explanation of symbols

1 Membrane-electrode assembly (MEA)
2 Polymer electrolyte membrane (PEM)
3 Anode electrode 4 Cathode electrode 5 Anode separator 6 Cathode separator 11 Polymer electrolyte fuel cell (PEFC)

Claims (6)

A proton conductive polymer electrolyte membrane in which a polymer chain having a proton conductive group is graft-polymerized to a fluororesin or olefin resin substrate,
The proton conductive polymer electrolyte membrane, wherein the polymer chain has a styrene derivative unit having a tert-butyl group and a proton conductive group as a substituent of an aromatic ring as a constituent unit.   The fluororesin is polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene- 2. The proton conductive polymer electrolyte membrane according to claim 1, which is at least one selected from a perfluoroalkyl vinyl ether copolymer (PFA) and ethylene-chlorotrifluoroethylene (ECTFE).   The proton conductive polymer electrolyte membrane according to claim 1, wherein the olefin resin is at least one selected from polyethylene (PE) and polypropylene (PP).   The proton conductive polymer electrolyte membrane according to claim 1, wherein the proton conductive group is a sulfonic acid group or a phosphoric acid group. A polymer electrolyte membrane, and a pair of electrodes arranged to sandwich the electrolyte membrane,
The membrane-electrode assembly in which the electrolyte membrane is the proton conductive polymer electrolyte membrane according to any one of claims 1 to 4. A polymer electrolyte membrane;
A pair of electrodes arranged to sandwich the electrolyte membrane;
A pair of separators arranged to sandwich the pair of electrodes, and
A polymer electrolyte fuel cell, wherein the electrolyte membrane is the proton conductive polymer electrolyte membrane according to any one of claims 1 to 4.

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