JP4910269B2 - ELECTROLYTE MATERIAL FOR SOLID POLYMER TYPE FUEL CELL, METHOD FOR PRODUCING THE SAME, AND MEMBRANE ELECTRODE ASSEMBLY FOR SOLID POLYMER FUEL CELL - Google Patents

Description

  The present invention relates to a membrane electrode assembly for a polymer electrolyte fuel cell and a polymer electrolyte material therefor.

  Hydrogen / oxygen fuel cells are attracting attention as a power generation system that has almost no adverse effect on the global environment because its reaction product is in principle only water. The polymer electrolyte fuel cell was once installed in a spacecraft under the Gemini and Biosatellite programs, but the battery power density at that time was low. Later, higher performance alkaline fuel cells were developed, and alkaline fuel cells have been adopted for space use up to the current space shuttle.

However, in recent years, solid polymer fuel cells have attracted attention again due to technological advances. There are two reasons for this. (1) A highly conductive membrane has been developed as a solid polymer electrolyte. (2) The catalyst used for the gas diffusion electrode layer is supported on carbon, and further coated with an ion exchange resin, an extremely large activity can be obtained.
Many studies have been made on methods for producing membrane electrode assemblies (hereinafter simply referred to as “joints”) of polymer electrolyte fuel cells.

  The polymer electrolyte fuel cell currently being studied has a drawback that it is difficult to effectively use the exhaust heat for auxiliary power of the fuel cell because the operating temperature is as low as 50 to 120 ° C. In order to supplement this, the polymer electrolyte fuel cell is required to have a particularly high power density. Further, as a problem for practical use, there is a demand for the development of a joined body that can obtain high energy efficiency and high power density even under operating conditions with high fuel and air utilization rates.

  Under operating conditions with a low operating temperature and a high gas utilization rate, the electrode porous body is likely to be clogged (flooded) due to the condensation of water vapor, particularly at the cathode where water is generated by the cell reaction. Therefore, in order to obtain stable characteristics over a long period of time, it is necessary to ensure the water repellency of the electrode so that flooding does not occur. This is particularly important for polymer electrolyte fuel cells that can obtain high power density at low temperatures.

  In order to ensure the water repellency of the electrode, it is effective to reduce the ion exchange capacity of the ion exchange resin covering the catalyst in the electrode, that is, to use an ion exchange resin having a low content of ion exchange groups. However, in this case, since the ion exchange resin has a low water content, the conductivity becomes low and the battery performance is lowered. Furthermore, since the gas permeability of the ion exchange resin is lowered, the supply of gas supplied to the catalyst surface through the coated ion exchange resin is delayed. For this reason, the gas concentration at the reaction site decreases and the voltage loss increases, that is, the concentration overvoltage increases and the output decreases.

  Therefore, a resin having a high ion exchange capacity is used as the ion exchange resin for coating the catalyst. In addition, for example, polytetrafluoroethylene (hereinafter referred to as PTFE) and tetrafluoroethylene (hereinafter referred to as TFE) are used. Attempts have been made to suppress flooding by incorporating fluororesin such as a benzene / hexafluoropropylene copolymer and TFE / perfluoro (alkyl vinyl ether) copolymer as a water repellent agent in an electrode, particularly a cathode (for example, Patent Document 1). In the present specification, the A / B copolymer refers to a copolymer comprising a repeating unit based on A and a repeating unit based on B.

  However, if the amount of the water repellent agent in the electrode is increased in order to achieve sufficient water repellency, the water repellent agent is an insulator, so that the electrical resistance of the electrode increases. Moreover, since the electrode becomes thick, gas permeability is lowered, and conversely, the output is lowered. In order to compensate for the decrease in the conductivity of the electrode, for example, it is necessary to increase the conductivity of the carbon material that is the carrier of the catalyst and the ionic conductivity of the ion exchange resin that covers the catalyst. However, it is difficult to obtain an electrode that satisfies both sufficient conductivity and sufficient water repellency, and it has not been easy to obtain a solid polymer fuel cell having high output and long-term stability.

  In addition, a method of mixing fluoride pitch (for example, see Patent Document 2) and a method for fluorinating a catalyst carrier (for example, see Patent Document 3) have been proposed, but the catalyst surface cannot be uniformly coated with an ion exchange resin. There's a problem. In addition, a method of providing a gradient in water repellency with respect to the thickness direction of the electrode (see, for example, Patent Documents 4 and 5) has been proposed, but the manufacturing method is complicated.

  In order to increase the output of the fuel cell, the ion exchange resin in the electrode needs to have high gas permeability and high conductivity, and an ion exchange resin having a high exchange group concentration and a high water content is preferable. However, when an ion exchange resin with a high exchange group concentration is used, the fuel gas permeability and conductivity are high, and the initial output of the fuel cell is high, but flooding is likely to occur, and the output decreases when used for a long time. Cheap.

  In order to solve these problems, the present inventors have proposed a perfluoropolymer having an aliphatic ring structure in the main chain (a polymer in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms). (Patent Document 6). However, although it is improved compared to the chain perfluoropolymer having a sulfonic acid group usually used in solid polymer fuel cells, when the polymer is exposed to more severe conditions, the durability is still sufficient. It wasn't.

JP-A-5-36418 (Claims 1 and 2) Japanese Patent Laid-Open No. 7-212324 (Claims) JP-A-7-192738 (Claims) JP-A-5-251086 (Claim 1) JP-A-7-134993 (Claims) JP 2002-260705 A (Claims)

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a solid polymer fuel cell having high conductivity and high gas permeability of an electrolyte material contained therein and capable of maintaining a high output over a long period of time. An object is to provide a material and a membrane electrode assembly.

  The present invention relates to an electrolyte material comprising a perfluoropolymer having a sulfonic acid group or a sulfonimide group and an aliphatic ring structure in the main chain, comprising 3% hydrogen peroxide and 200 ppm divalent iron ions In a test in which 0.1 g of a polymer is immersed in 50 g of a Fenton reagent solution containing 16 hours at 40 ° C., the fluorine ion elution amount detected in the solution is 0.01% or less of the total fluorine amount in the immersed polymer. An electrolyte material is provided.

The electrolyte material, ing a copolymer comprising repeating units based on a repeating unit Monomer B based on the lower Symbol Monomer A. In the formula, ^{Y 1} is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer from 1 to 12, p is 0 or 1, m + p> 0, Y ² is OH or NHSO ₂ Z, and Z is a C 1-6 perfluoroalkyl group which may contain an etheric oxygen atom. ).
Monomer A: A perfluoromonomer that gives a polymer having a repeating unit containing a ring structure in the main chain by radical polymerization.
Monomer _{^{B: CF 2 = CF- (OCF}} 2 CFY 1) m -O p - (CF 2) a perfluorovinyl ether represented by n _-SO ^{2 Y} 2.

  The present invention also relates to a membrane electrode assembly for a polymer electrolyte fuel cell comprising a membrane solid polymer electrolyte, and a cathode and an anode disposed via the electrolyte, wherein at least one of the cathode and the anode is A membrane electrode assembly for a polymer electrolyte fuel cell comprising a catalyst and the above-described electrolyte material is provided.

  Furthermore, the present invention provides a membrane electrode assembly for a polymer electrolyte fuel cell comprising a membrane solid polymer electrolyte, and a cathode and an anode disposed via the electrolyte, wherein the membrane solid polymer electrolyte card A membrane electrode assembly for a polymer electrolyte fuel cell comprising an electrolyte material is provided.

Furthermore, the present invention provides a method for producing an electrolyte material as described above, wherein after obtaining a perfluoropolymer having —SO ₂ F groups by radical polymerization, the perfluoropolymer is brought into contact with a fluorine gas; Provided is a method for producing an electrolyte material, which comprises converting SO ₂ F groups into sulfonic acid groups or sulfonimide groups.

  According to the present invention, a polymer electrolyte material having high gas permeability and excellent durability can be provided. A membrane electrode assembly for a polymer electrolyte fuel cell having an electrolyte membrane made of the electrolyte material or a membrane electrode assembly for a polymer electrolyte fuel cell having a membrane electrode assembly containing the electrolyte material in an electrode is operated for a long time. Even if the output is reduced, the durability is excellent.

In a chain perfluoropolymer having a sulfonic acid group conventionally used for fuel cell applications, a —COOH group, a —CF═CF ₂ group, a —COF group, a CF ₂ H group at the end of a part of the molecular chain. When used as an electrolyte material for polymer electrolyte fuel cells, the polymer gradually decomposes over a long period of operation, resulting in a decrease in power generation voltage or a decrease in membrane strength. The present inventors consider that pinholes, cracks, peeling, etc. occur in the film, and by performing fluorination treatment (contact with fluorine gas) on this polymer or a polymer having a —SO ₂ F group as a precursor thereof. It is proposed that the molecular ends can be perfluorinated and stabilized, and the durability can be greatly improved. However, when the polymer was exposed to harsh operating conditions, the durability was still insufficient. The perfluoropolymer having an alicyclic structure in the main chain and having a sulfonic acid group, when the amount of the unstable functional group is controlled, is significantly higher than the durability improvement by controlling the amount of the functional group of the conventional polymer. It was found that the durability was improved.

  Thus, when the Fenton reagent immersion test was used as an index of the resistance to polymer degradation during fuel cell operation, the results were found to have a good correlation with the durability of the fuel cell, leading to the present invention. In this test, a polymer is immersed in an aqueous solution containing hydrogen peroxide and divalent iron ions, and changes in the polymer before and after immersion are observed. Usually, the hydrogen peroxide solution concentration is 1 to 30%, the divalent iron ion concentration is 10 to 500 ppm, the immersion temperature is 25 to 90 ° C., and the immersion time is 0.5 to 24 hours. A condition is adopted in which 0.1 g of polymer is immersed in 50 g of Fenton reagent solution containing hydrogen oxide water and 200 ppm of divalent iron ions at 40 ° C. for 16 hours. In this test, the polymer degradation is caused by hydroxy radicals or hydroperoxy radicals generated in the Fenton reagent, and the weight loss of the polymer is usually measured because the polymer loses a small weight. However, in the case of a polymer having an ion exchange group, since it is highly hygroscopic, it is difficult to accurately measure the weight even after drying, and it is more sensitive to detect fluorine ions eluted in the Fenton reagent solution during decomposition. Since it is preferable, in this invention, it evaluates by the fluorine ion elution amount.

  The polymer (hereinafter referred to as the present polymer) serving as the electrolyte material of the present invention has a fluorine ion elution amount detected in the solution in this test of 0.01% or less of the total fluorine amount in the immersed polymer. If it is more than 0.01%, the amount of unstable terminal groups is large, and a voltage drop tends to occur during long-time fuel cell operation. More preferably, it is 0.005% or less.

Moreover, the measurement by an infrared spectrum can also be used as a parameter | index of the quantity of an unstable terminal group. In this case, a film of about 50 to 150 μm made of the polymer to be measured is prepared, and the infrared spectrum is measured. This measurement can be performed with a potassium salt of a sulfonic acid group or a sulfonimide group, and in order to reduce the influence on the infrared spectrum by the adsorbed water of the film, the potassium salt type dried using a vacuum dryer or the like. It is preferable to measure in dry nitrogen using the film. In this case, the ratio _I 1690 _{/ I 2350} of the absorbance _{I 2350} of maximum absorbance _{I 1690} and 2350 ± 10 cm ^-1 in the band of the measurement wavenumber 1690 ± 10 cm ^-1 is 0.15 or less, the unstable terminal groups Less polymer is preferable, more preferably 0.1 or less, and still more preferably 0.05 or less. The lower the numerical value, the lower the number of unstable end groups.

In addition, since the absorption having a peak at the measurement wavenumber of 2350 ± 10 cm ⁻¹ is absorption over a wide area, the absorbance I ₂₃₅₀ in this specification is a baseline obtained by connecting a straight line connecting 2740 ± 20 cm ⁻¹ and 2070 ± 20 cm ^−1. The absorbance at the peak position at 2350 ± 10 cm ⁻¹ was a value measured from the baseline. Further, the absorbance _{I 1690} of the peak of the measurement wavenumber 1690 ± 10 cm ^-1 is higher wavenumber of the absorption peak, the straight line connecting the valleys adjacent to each lower wavenumber as a baseline, the peak position in the 1690 ± 10 cm ^-1 Was the value measured from the baseline.

FIG. 1 shows an infrared spectrum of a copolymer of tetrafluoroethylene, perfluoro (2,2-dimethyl-1,3-dioxole) and potassium perfluoro (3,6-dioxa-4-methyl-7-octene) sulfonate. However, the absorbance of each of the measured wave numbers will be specifically described with reference to FIG. In Figure 1, for the peaks at 2350 ± 10 cm ^-1, and around 2740cm ^-1 and around 2070cm ^-1, and with straight lines as can be subtracted tangent to the spectrum, which is the base line 1. The distance from the peak to the baseline 1 is the absorbance I ₂₃₅₀ . For the peak at 1690 ± 10 cm ⁻¹ , a straight line connecting valleys close to the high wave number side and the low wave number side of the absorption peak is defined as the baseline 1 ′, and the distance from the peak to the baseline 1 ′ is the absorbance. I ₁₆₉₀ .

Usually, as a production method of the present polymer, after synthesizing a perfluoropolymer having an aliphatic ring structure in the main chain and having a —SO ₂ F group, a method such as hydrolysis, acidification, or other known groups It is preferable to produce it through a step of converting a —SO ₂ F group into a sulfonic acid group or a sulfonimide group by the conversion method, and to contact with fluorine gas in the middle step. Contact with fluorine gas stabilizes the unstable portion at the end, and can control the degradation of the polymer.

The above fluorination step may be performed after converting the —SO ₂ F group into a sulfonic acid group or a sulfonimide group, but it is preferable in terms of the process to be performed at the stage of the polymer having the —SO ₂ F group. Also preferred is the stability of the substituted functional group. However, it is not limited to this method. However, when a polymer having a sulfonimide group is fluorinated, the NH bond in the sulfonimide group is converted into an NF bond, and therefore an operation for returning to the NH bond is necessary. As this operation, for example, a known method using a malonic acid ester or an aromatic compound can be employed.

  As the fluorine gas used for fluorination, a gas diluted with an inert gas such as nitrogen, helium or carbon dioxide is usually used at a concentration of 0.1% or more and less than 100%, but it may be used without being diluted. The polymer can be contacted with fluorine gas in a bulk state or in a state dispersed or dissolved in a fluorine-containing solvent.

The temperature at which the polymer is fluorinated by contacting with fluorine gas is usually room temperature to 300 ° C, preferably 50 to 250 ° C, particularly 100 to 220 ° C, and more preferably 150 to 200 ° C. If the temperature is too low, the reaction between the fluorine gas and the polymer ends becomes slow, and if the temperature is too high, the —SO ₂ F group may be eliminated. The contact time in the above temperature range is preferably 1 minute to 1 week, particularly preferably 1 to 50 hours.

In the fluorination step, when the polymer is dissolved or dispersed in a fluorinated solvent and fluorinated, for example, the following solvents can be used as the fluorinated solvent.
Polyfluorotrialkylamine compounds such as perfluorotributylamine and perfluorotripropylamine.

Perfluorohexane, perfluorooctane, perfluorodecane, perfluorododecane, perfluoro (2,7-dimethyloctane), 2H, 3H-perfluoropentane, 1H-perfluorohexane, 1H-perfluorooctane, 1H-per Fluorodecane, 1H, 4H-perfluorobutane, 1H, 1H, 1H, 2H, 2H-perfluorohexane, 1H, 1H, 1H, 2H, 2H-perfluorooctane, 1H, 1H, 1H, 2H, 2H-per Fluoroalkanes such as fluorodecane, 3H, 4H-perfluoro (2-methylpentane), 2H, 3H-perfluoro (2-methylpentane) and the like.
3,3-dichloro-1,1,1,2,2-pentafluoropropane, 1,3-dichloro-1,1,2,2,3-pentafluoropropane, 1,1-dichloro-1-fluoroethane Such as chlorofluoroalkane.

Perfluorodecalin, perfluorocyclohexane, perfluoro (1,2-dimethylcyclohexane), perfluoro (1,3-dimethylcyclohexane), perfluoro (1,3,5-trimethylcyclohexane), perfluorodimethylcyclobutane (structural isomerism) Polyfluorocycloalkanes, etc.).
Polyfluorocyclic ether compounds such as perfluoro (2-butyltetrahydrofuran).

_{n-C 3 F 7 OCH 3} , n-C 3 F 7 OCH 2 CF 3, n-C 3 F 7 OCHFCF 3, n-C 3 F 7 OC 2 H 5, n-C 4 F 9 OCH 3, iso _{-C 4 F 9 OCH 3, n} -C 4 F 9 OC 2 H 5, iso-C 4 F 9 OC 2 H 5, n-C 4 F 9 OCH 2 CF 3, n-C 5 F 11 OCH 3, _{n-C 6 F 13 OCH 3} , n-C 5 F 11 OC 2 H 5, CF 3 OCF (CF 3) CF 2 OCH 3, CF 3 OCHFCH 2 OCH 3, CF 3 OCHFCH 2 OC 2 H 5, n- Hydrofluoroethers such as C ₃ F ₇ OCF ₂ CF (CF ₃ ) OCHFCF ₃ , fluorine-containing low molecular weight polyethers, chlorotrifluoroethylene oligomers, and the like.

Fluorine-containing aromatic compounds such as hexafluorobenzene, trifluoromethylbenzene and 1,4-bistrifluoromethylbenzene.
These may be used alone or in combination of two or more.

In addition to these, a wide range of compounds can be used. 1,1,2-trichloro-1,2,2-trifluoroethane, 1,1,1-trichloro-2,2,2-trifluoroethane, 1,1,1,3-tetrachloro-2,2 Chlorofluorocarbon solvents such as 1,3,3-tetrafluoropropane and 1,1,3,4-tetrachloro-1,2,2,3,4,4-hexafluorobutane can be used technically. From the viewpoint of protecting the global environment, it is not preferable. In addition, the reaction can be performed using liquid or supercritical carbon dioxide.
Among the above-mentioned solvents, a solvent containing a hydrogen atom reacts with fluorine gas, so that it is preferable to use a solvent that does not contain a hydrogen atom.

The polymer fluorinated as described above is, for example, its —SO ₂ F in an alkaline aqueous solution such as NaOH or KOH, or in a mixed solvent of an alcohol such as methanol or ethanol, or a polar solvent such as dimethyl sulfoxide and water. After the group is hydrolyzed, it is acidified with an aqueous solution such as hydrochloric acid or sulfuric acid and converted to a sulfonic acid group. For example, when hydrolyzed with an aqueous KOH solution, the —SO ₂ F group is converted to an —SO ₃ K group, and then the K ion is replaced with a proton. Hydrolysis and acidification are usually performed between 0 ° C and 120 ° C.

Moreover, a well-known method can be used as the conversion method to the sulfonimide group of the polymer fluorinated as mentioned above. For example, US Pat. No. 5,463,005 and Inorg. Chem. 32 (23), page 5007 (1993). That is, a method in which a polymer is contacted with a perfluorosulfonamide such as trifluoromethanesulfonamide, heptafluoroethanesulfonamide, or nonafluorobutanesulfonamide in the presence of a basic compound such as an alkali metal fluoride or an organic amine, or the sulfonamide by the method of contacting an alkali metal salt of the further compound silylated by reacting -SO 2 _F groups in the polymer, after conversion to sulfonimide groups base from a salt form, further hydrochloric acid and an aqueous solution such as sulfuric acid It can be converted into a sulfonimide group by acidification.

In addition, after the fluorinated polymer is contacted with ammonia in a solid state, swollen with a solvent, or dissolved in a solvent, the —SO ₂ F group in the polymer is converted into a sulfonamide group. -SO ₂ F such as trifluoromethanesulfonyl fluoride, heptafluoroethanesulfonyl fluoride, nonafluorobutanesulfonyl fluoride, undecafluorocyclohexanesulfonyl fluoride in the presence of basic compounds such as alkali metal fluorides and organic amines It can also be converted by contacting with a group-containing compound.

  In the case of performing such a conversion reaction to a sulfonimide group, a reaction in which the fluorinated polymer is swollen with a solvent or dissolved in a solvent facilitates the sulfonimide reaction. This is a preferable method. As such a solvent, the solvent illustrated above as a solvent which can be used when, for example, a polymer is dissolved or dispersed in a fluorine-containing solvent and brought into contact with fluorine gas can be used.

  In addition, when the polymer converted into the sulfonimide group to be generated does not dissolve in the above solvent, the reaction field becomes non-uniform as the reaction proceeds, and the imidation reaction may not proceed smoothly. In such a case, it can be said that it is also preferable to use a solvent in which the polymer converted into the generated sulfonimide group dissolves or swells.

  Solvents that can swell or dissolve the polymer converted to sulfonimide groups include acetonitrile, propionitrile, methanol, ethanol, 2-propanol, dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethylacetamide, A polar solvent such as N-methyl-2-pyrrolidone can be used.

Further, CF ₃ CH ₂ OH, CF ₃ CF ₂ CH ₂ OH, H (CF ₂ CF ₂ ) _a CH ₂ OH, CF ₃ (CF ₂ ) _b (CH ₂ ) _c OH, (CF ₃ ) ₂ CHOH, etc. Fluorinated alcohols are also preferred as solvents that can swell or dissolve both fluorinated polymers and polymers converted to sulfonimide groups. However, in formula, a is an integer of 1-5, b is an integer of 1-10, c is an integer of 1-6. In the reaction, these solvents described above can be used alone or in admixture of two or more.

A polymer having a —SO ₂ F group which is a sulfonic acid group, a sulfonimide group or a precursor group thereof to be reacted with fluorine gas is a monomer having a ring structure or a cyclopolymerizable monomer and a sulfonic acid group or a sulfonic acid group. It can be synthesized through a copolymerization step with a monomer having a precursor group. The polymer is preferably a perfluoropolymer obtained by copolymerizing only a perfluoromonomer in consideration of durability as an electrolyte material for a fuel cell and ease of fluorination process. Even a perfluoropolymer having a —COF group, —COOH group, —CF═CF ₂ group, etc. at the end of the polymer main chain and containing a hydrogen atom as a polymerization initiator was used due to a chain transfer reaction or the like. In some cases, a non-perfluoro group based on the polymerization initiator is generated at the polymer main chain terminal, and thus the fluorination effect can be obtained through the fluorination step.

  When a perfluoro compound such as perfluorodiacyl peroxide typified by perfluorobutanoyl peroxide is used as the polymerization initiator, a stable perfluoro group is introduced at the end, and unstable end groups after polymerization are introduced. May decrease. The polymer obtained by such a method can be used as the present polymer without passing through the fluorination step. However, if such a polymer having few unstable end groups is further treated with fluorine gas, it is more easily inactivated. Polymers with very few stable end groups are obtained and preferred.

Although the ring structure in this polymer is not particularly limited, for example, a ring structure represented by the following formula is preferable. In the formula, n is an integer of 1 to 4, R ^f is a C 1-8 perfluoroalkyl group or a perfluoroalkoxy group, and X ¹ and X ² are each independently a fluorine atom or a trifluoromethyl group. is there. In addition, when n is 2 or more in (CX ¹ X ² ) _n , the combination of X ¹ and X ² may be different for each carbon. In any ring structure, a 4- to 7-membered ring is preferable, and a 5-membered or 6-membered ring is particularly preferable in consideration of the stability of the ring.

  Monomers having a comonomer ring structure for obtaining this polymer include perfluoro (2,2-dimethyl-1,3-dioxole) (hereinafter referred to as PDD), perfluoro (1,3-dioxole), Examples include fluoro (2-methylene-4-methyl-1,3-dioxolane) (hereinafter referred to as MMD), 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole, and the like.

  The comonomer cyclopolymerizable monomer for obtaining this polymer includes perfluoro (3-butenyl vinyl ether) (hereinafter referred to as BVE), perfluoro [(1-methyl-3-butenyl) vinyl ether], perfluoro. (Allyl vinyl ether), 1,1 ′-[(difluoromethylene) bis (oxy)] bis [1,2,2-trifluoroethene] and the like can be exemplified.

  Specific examples of the repeating unit based on the monomer having a cyclic structure or the cyclopolymerizable monomer described above include, for example, a repeating unit based on PDD is represented by formula 5, a repeating unit based on BVE is represented by formula 6, and a repeating unit based on MMD is represented by formula 7. As used herein, the term “perfluoropolymer having an aliphatic ring structure” refers to a perfluoropolymer containing a repeating unit having a ring structure that does not contain an unsaturated bond.

As the monomer having a sulfonic acid group, a sulfonimide group or a precursor group of these groups to be reacted with a monomer having a ring structure or a cyclopolymerizable monomer, perfluorovinyl ether having a —SO ₂ F group is preferably exemplified. ^{_{Specifically, CF 2 = CF- (OCF 2}} CFY 1) m -O p - (CF 2) n perfluorovinylether (wherein represented by -SO ₂ F, ^{Y 1} is a fluorine atom or a trifluoromethyl And m is an integer of 0 to 3, n is an integer of 1 to 12, p is 0 or 1, and m + p> 0. Of the perfluorovinyl ethers, compounds of formulas 8 to 10 are preferred. However, in Formula 8-10, q is an integer of 1-8, r is an integer of 1-8, s is 2 or 3. When polymerized using a monomer having —SO ₂ F group, it is converted into —SO ₃ H group or sulfonimide group by usually hydrolysis, acidification treatment or known reaction to obtain an electrolyte material. That, _CF 2 ₌ CF- in the polymer as a electrolyte material ^{_{(OCF 2 CFY 1) m -O}} p - (CF 2) repeating units based on n -Z (Z is a sulfonic acid group or a sulfonimide group) It is preferably included.

Moreover, the monomer represented by following formula 11-13 other than the said monomer can also be used. In the formula, Y ² and Y ³ are each a fluorine atom or a trifluoromethyl group, t and x are integers of 0 to 2, and u, v, and w are integers of 1 to 12. More specifically, monomers represented by formulas 14 to 17 are listed.

In particular, as this polymer, perfluoro (3-butenyl vinyl ether), perfluoro (2,2-dimethyl-1,3-dioxole), perfluoro (1,3-dioxole), 2,2,4-trifluoro Repeating units based on monomers selected from the group consisting of -5-trifluoromethoxy-1,3-dioxole and perfluoro (2-methylene-4-methyl-1,3-dioxolane); and perfluoro (3,6 - dioxa-4-methyl-7-octene) sulfonic acid _{(CF 2 = CFOCF 2 CF (} CF 3) O (CF 2) 2 SO 3 H) or perfluoro (3-oxa-4-pentene) sulfonic acid (CF ₂ = _{CFO (CF 2)} is preferably a polymer comprising a repeating unit based on 2 _SO 3 H).

This polymer is synthesized through a copolymerization step of the above-mentioned cyclic monomer or cyclopolymerizable monomer and a monomer having a —SO ₂ F group as represented by, for example, formulas 8 to 10, but the strength is adjusted. For example, other radically polymerizable monomers such as tetrafluoroethylene may be copolymerized. When this polymer is composed only of a repeating unit based on a monomer having a ring structure and a repeating unit based on a monomer having a sulfonic acid group or a sulfonimide group, the skeleton tends to be rigid, and the fuel cell membrane or catalyst layer This is because the film and the catalyst layer may be fragile.

  However, this polymer is excellent in water repellency by passing through a fluorination step after polymerization, and when used as an electrolyte for a cathode of a fuel cell, improves the output of the fuel cell and shows stable characteristics over a long period. When the monomer is copolymerized, the content of the repeating unit based on the other monomer in the polymer is 35% or less, particularly 20% or less, so as not to impair its excellent output characteristics. It is preferable to do so.

Examples of the copolymerizable monomer include TFE, chlorotrifluoroethylene, vinylidene fluoride, hexafluoropropylene, trifluoroethylene, vinyl fluoride, and ethylene. _Further, the compound represented by ^{_{CF 2 = CFOR f1, CH 2}} = CHR f2, CH 2 = CHCH 2 R f2 may be used. However, R ^f1 is a C 1-12 perfluoroalkyl group, may have a branched structure, and may contain an etheric oxygen atom. R ^f2 is a C 1-12 perfluoroalkyl group. Among these, the use of perfluoromonomer is preferable from the viewpoint of durability because the reaction with fluorine gas is easy. Of these, TFE is preferred because it is readily available and has high polymerization reactivity.

As the compound represented by CF ₂ ═CFOR ^f1 in the monomer, a perfluorovinyl ether compound represented by CF ₂ ═CF— (OCF ₂ CFX) _y —O—R ^f4 is preferable. However, in the formula, y is an integer of 0 to 3, X is a fluorine atom or a trifluoromethyl group, and R ^f4 is a linear or branched perfluoroalkyl group having 1 to 12 carbon atoms (hereinafter referred to as the present invention). In the specification, R ^f4 is used in the same meaning.). Especially, the compound represented by Formula 18-20 is mentioned preferably. However, in formula, a is an integer of 1-8, b is an integer of 1-8, c is 2 or 3.

  In order to increase the strength of the membrane or catalyst layer using the present polymer, the number average molecular weight of the present polymer is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 20,000 or more. Moreover, since a moldability and the solubility to the solvent mentioned later may fall when molecular weight is too large, molecular weight is preferable 5000000 or less, and it is more preferable that it is 2000000 or less.

  The content of the repeating unit based on the monomer having a ring structure in the present polymer is preferably 0.5 to 80 mol%, 1 to 80 mol%, further 4 to 70 mol%, and further 10 to 70 mol%. And more preferred. Even if a small amount of a repeating unit based on a monomer having a ring structure is contained, there is an effect of improving the durability, but if it is less than 0.5%, the effect may not easily appear. In addition, the more repeating units based on a monomer having a ring structure, the more excellent the durability of the present polymer in a severe environment (for example, at a high temperature). On the other hand, when there are too many repeating units having a ring structure, the number of sulfonic acid groups in the polymer is decreased, and the ion exchange capacity is decreased, which may lower the conductivity.

Moreover, when using this polymer as an electrolyte membrane, the use temperature may become a high temperature of 100 degreeC or more especially. Therefore, the softening temperature of the electrolyte membrane is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, and particularly preferably 120 ° C. or higher. The softening temperature can be measured by a dynamic viscoelasticity measuring method. In this specification, the storage elastic modulus of the acidified film is measured under the conditions of dynamic viscoelasticity measurement at 1 Hz and a temperature increase rate of 2 ° C./min, a tangent at 50 ° C., and a storage elastic modulus of 5 × 10 ⁷ Pa. The intersection with the tangent at is the softening temperature. In addition, since some polymers are difficult to measure dynamic viscoelasticity, such polymers can be measured by the TMA method to obtain a softening temperature.
In this case, the content of the repeating unit based on the monomer having a ring structure is preferably 20 mol% or more, more preferably 30 mol% or more, and particularly preferably 40 mol% or more.

  Furthermore, when this polymer contains a repeating unit based on a copolymerizable monomer such as TFE, the repeating unit is preferably contained in an amount of 5 to 85 mol%. When it is less than 5 mol%, for example, when used as an electrolyte membrane, the toughness of the membrane may not be sufficient. When it is more than 85 mol%, the repeating unit having a ring structure and the sulfonic acid group in the polymer are decreased, and the effect expected in the present invention may not be exhibited. More preferably, it is 10-80 mol%, More preferably, it is 10-70 mol%. Further, in order to obtain a polymer having a high softening temperature, it is preferably 10 to 70 mol%, more preferably 10 to 60 mol%, and particularly preferably 10 to 50 mol%.

  Moreover, it is preferable that the repeating unit which has a sulfonic acid group or a sulfonimide group is contained so that the ion exchange capacity of this polymer may be 0.7-2.5 meq / g dry resin, 0.9-1 More preferably, it is contained so as to be 5 meq / g dry resin. If the ion exchange capacity is too low, the conductivity of the polymer as the electrolyte material will be low. If it is too high, the water repellency will be poor and the durability will be poor when used in a fuel cell, and the polymer strength may be insufficient. is there.

  For the polymerization for obtaining this polymer, conventionally known methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization can be employed. Polymerization is performed under conditions where radicals are generated, and a method of irradiating radiation such as ultraviolet rays, γ rays, electron beams, etc., and a method of adding a radical initiator used in normal radical polymerization are common. The polymerization temperature is usually about 20 to 150 ° C. Examples of radical initiators include bis (fluoroacyl) peroxides, bis (chlorofluoroacyl) peroxides, dialkyl peroxydicarbonates, diacyl peroxides, peroxyesters, azo compounds, and persulfates. Can be mentioned.

  In the solution polymerization, the boiling point of the solvent used is usually 20 to 350 ° C., preferably 40 to 150 ° C., from the viewpoint of handleability. Examples of the solvent that can be used include the same solvents as the fluorine-containing solvents exemplified as suitable fluorine-containing solvents when the fluorination of the polymer is performed in a fluorine-containing solvent. That is, a polyfluorotrialkylamine compound, a perfluoroalkane, a hydrofluoroalkane, a chlorofluoroalkane, a fluoroolefin having no double bond at the molecular chain end, a polyfluorocycloalkane, a polyfluorocyclic ether compound, a hydrofluoroether, Fluorine-containing low molecular weight polyether, t-butanol and the like can be mentioned. These may be used alone or in combination of two or more. In addition, polymerization can also be performed using liquid or supercritical carbon dioxide.

  The present polymer can be dissolved or well dispersed in an organic solvent having —OH groups. The solvent is preferably an organic solvent having an alcoholic —OH group. Specifically, methanol, ethanol, 1-propanol, 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoro-1-propanol, 2,2,3,3-tetrafluoro -1-propanol, 4,4,5,5,5-pentafluoro-1-pentanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 3,3,3-trifluoro -1-propanol, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexanol, 3,3,4,4,5,5,6,6,7,7,8 , 8,8-tridecafluoro-1-octanol and the like. In addition to alcohol, an organic solvent having a carboxyl group such as acetic acid can also be used, but is not limited thereto.

The organic solvent having an —OH group may be used by mixing a plurality of solvents, or may be used by mixing with water or another fluorine-containing solvent. Examples of the other fluorine-containing solvent include the same solvents as the fluorine-containing solvent exemplified as a preferable fluorine-containing solvent when the fluorination of the polymer is performed in the fluorine-containing solvent. When a mixed solvent is used, the organic solvent having an —OH group is preferably contained in an amount of 10% or more, particularly 20% or more of the total mass of the solvent.
When a mixed solvent is used, the present polymer may be dissolved or dispersed in the mixed solvent from the beginning, but after dissolving or dispersing in the organic solvent having an —OH group, another solvent may be mixed.

The temperature for dissolving or dispersing is preferably in the range of 0 ° C. to 250 ° C., and particularly preferably 20 to 150 ° C. under atmospheric pressure or under conditions of hermetically pressurized such as an autoclave.
Further, an aqueous dispersion substantially free of an organic solvent can be prepared by dissolving or dispersing the present polymer in an alcohol solvent having a boiling point lower than that of water and then adding water to distill off the alcohol. .

  When a cathode of a polymer electrolyte fuel cell is produced using the liquid composition obtained by dissolving or dispersing the present polymer as described above, a cathode excellent in gas diffusibility and water repellency can be obtained. The concentration of the present polymer in the liquid composition is preferably 1 to 50%, particularly 3 to 30% of the total mass of the liquid composition. If the concentration is too low, for example, a large amount of an organic solvent is required at the time of producing the cathode, and if the concentration is too high, the viscosity of the solution is too high and the handleability is deteriorated.

  In the present invention, for example, a conductive carbon black powder carrying platinum catalyst fine particles is mixed and dispersed in a liquid composition containing the present polymer. A membrane-electrode assembly for a polymer electrolyte fuel cell can be obtained by any one of the two methods. The first method is a method in which the above dispersion is applied to both surfaces of a cation exchange membrane to be a membranous solid polymer electrolyte, dried, and then adhered with carbon cloth or carbon paper. The second method is a method in which the dispersion is applied and dried on carbon cloth or carbon paper, and is then adhered to the cation exchange membrane.

  In the polymer electrolyte fuel cell of the present invention, the catalyst contained in the cathode and the ion exchange resin as the electrolyte material have a mass ratio of catalyst: ion exchange resin = 40: 60 to 95: 5. It is preferable from the viewpoint of conductivity and water discharge. In addition, the mass of the catalyst here includes the mass of the carrier in the case of a supported catalyst supported on a carrier such as carbon.

Further, the ion exchange resin in the cathode may be made of a resin of the present polymer alone, but may be a mixture of a perfluoropolymer having a sulfonic acid group known in the art and the present polymer. Examples of the conventionally known polymers, tetrafluoroethylene and _{CF 2 = CF- (OCF 2 CFY} ) m -O p - (CF 2) a perfluorovinyl ether (wherein represented by n -SO ₃ H, Y is fluorine An atom or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer of 1 to 12, p is 0 or 1, and m + p> 0). Is done. Particularly preferred is a polymer having a sulfonic acid group obtained by obtaining a copolymer of tetrafluoroethylene and a monomer represented by the above formulas 1 to 3, and hydrolyzing and copolymerizing it.

  When a conventionally known polymer is mixed and used for the cathode, the proportion of this polymer is preferably 20% or more, particularly 50% or more of the total mass of the ion exchange resin in the cathode.

  The anode in the present invention may be the same as the cathode, but may be composed of a conventionally used gas diffusion electrode or the like. The anode is formed in the same process as the cathode, and a membrane-electrode assembly is obtained in which the anode is disposed on one side of the membrane and the cathode is disposed on the other side. The polymer is an electrolyte material for a polymer electrolyte fuel cell, but may be contained in the anode instead of the cathode, or may be used as a material for an ion exchange membrane that is a membrane-like solid polymer electrolyte. Alternatively, only the ion exchange membrane may be composed of the present polymer, and another resin such as a conventionally known electrolyte material may be used for the cathode and the anode.

  The obtained membrane-electrode assembly is sandwiched between separators made of a conductive carbon plate or the like in which a groove serving as a passage for an oxidant gas (air, oxygen, etc.) containing fuel gas or oxygen is formed. By being incorporated, the polymer electrolyte fuel cell of the present invention can be obtained. The polymer electrolyte fuel cell to which the electrolyte material of the present invention is applied is not limited to a hydrogen / oxygen fuel cell. Application to a direct methanol fuel cell (DMFC) or the like is also possible.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to Examples (Examples 1 to 10, 13) and Comparative Examples (Examples 11 and 12), but the present invention is not limited to these.
In the following examples, the following abbreviations are used.
PSVE: CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F,
PSVE2: CF ₂ = CFOCF ₂ CF ₂ OCF ₂ CF ₂ SO ₂ F,
_{IPP: (CH 3) 2 CHOC} (= O) OOC (= O) OCH (CH 3) 2,
PFB: CF ₃ CF ₂ CF ₂ C (═O) OOC (═O) CF ₂ CF ₂ CF ₃
HCFC141b: CH ₃ CCl ₂ F (Asahi Glass Co., Ltd.)
HCFC225cb: CClF ₂ CF ₂ CHClF (Asahi Glass Co., Ltd.)
DMSO: dimethyl sulfoxide.

[Example 1]
Synthesis of PDD / PSVE copolymer 26.0 g of PDD, 127.8 g of PSVE, and 0.46 g of IPP were placed in an autoclave with an internal volume of 200 ml. After degassing, the mixture was compressed to 0.3 MPa with nitrogen. Polymerization was started by heating and stirring at 40 ° C. After 10 hours, the polymerization was stopped by cooling and purging, and after dilution with HCFC225cb, precipitation was performed by adding it to hexane, followed by washing twice with hexane and once with HCFC141b. After filtration, it was vacuum-dried at 80 ° C. for 16 hours to obtain 41.6 g of a white polymer. The sulfur content was determined by elemental analysis, and the ratio of PDD / PSVE and the ion exchange capacity were determined to be 56.5 / 43.5 (molar ratio) and 1.31 meq / g dry resin, respectively. Moreover, when the molecular weight was measured by GPC, the number average molecular weight in terms of polymethyl methacrylate was 33,000.

10 g of the polymer was placed in a 2000 ml Hastelloy autoclave and degassed, and then fluorine gas (20% by volume) diluted with nitrogen gas to a gauge pressure of 0.3 MPa was introduced and maintained at 180 ° C. for 4 hours. Next, it was immersed in a solution of KOH / H ₂ O / DMSO = 11/59/30 (mass ratio) and hydrolyzed by maintaining at 90 ° C. for 17 hours. Next, the temperature was returned to room temperature, followed by washing with water three times, and further immersed in 3N hydrochloric acid at room temperature for 2 hours and further washed with water. This hydrochloric acid immersion and water washing were performed three times in total, and finally three times. This was vacuum dried at 80 ° C. to form an acid form, dried, and then dissolved in ethanol to obtain a transparent 10% solution. A cast film having a thickness of 200 μm was prepared from this solution and heated at 160 ° C. for 30 minutes. The cast film was set in TMA (manufactured by Mac Science). Using a 1 mmφ quartz probe, the cast film was loaded with a weight of 3.5 g and heated at 5 ° C./min. When the temperature at which the thickness of the film began to rapidly decrease due to penetration of the probe into the cast film was measured as the softening point, the softening temperature of this polymer was 150 ° C.

Further, the PDD / PSVE copolymer before acidification treated with fluorine gas was hot-pressed to produce a film having a thickness of 100 μm, which was KOH / H ₂ O / DMSO = 11/59/30 (mass Ratio) and kept at 90 ° C. for 17 hours for hydrolysis. Next, the temperature was returned to room temperature, followed by washing with water three times, and further immersed in 3N hydrochloric acid at room temperature for 2 hours and further washed with water. This hydrochloric acid immersion and water washing were performed three times in total, and finally three times of water washing were performed. This was vacuum-dried at 80 ° C. to obtain an acid-type dry film. 0.1 g of this film was cut out and tested by immersing in 50 g of Fenton reagent solution containing 3% aqueous hydrogen peroxide and 200 ppm of divalent iron ions at 40 ° C. for 16 hours, and elution of fluorine ions detected in the solution The proportion of the total amount of fluorine in the soaked polymer was measured. The elution ratio of fluorine ions was 0.004%.

The acid type film was cut out, immersed in a 0.1 M KOH aqueous solution at room temperature for 30 minutes, washed with water, and then vacuum dried at 110 ° C. to obtain a K salt type film. When the infrared spectrum of this film was measured, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.06.

[Example 2]
Synthesis of BVE / PSVE copolymer In a 300 ml flask, under a nitrogen atmosphere, 120.0 g of BVE, 128.5 g of PSVE, and 0.76 g of IPP were placed, and polymerization was started by heating to 40 ° C and stirring. did. After 16.7 hours, the polymerization was stopped, the mixture was poured into hexane to precipitate, and further washed with hexane three times. After filtration, it was vacuum dried at 80 ° C. for 16 hours to obtain 47.8 g of a white polymer.

  The sulfur content was determined by elemental analysis, and the BVE / PSVE ratio and the ion exchange capacity were determined. BVE / PSVE = 67.0 / 33.0 (molar ratio) and 0.99 meq / g dry resin, respectively. Met. Moreover, when the molecular weight was measured by GPC, the number average molecular weight in terms of polymethyl methacrylate was 29,000. 10 g of the polymer was placed in a 2000 ml Hastelloy autoclave and degassed, and then fluorine gas (20% by volume) diluted with nitrogen gas to a gauge pressure of 0.3 MPa was introduced and maintained at 180 ° C. for 4 hours. It was hydrolyzed with alkali, acidified and dried, and then dissolved in ethanol to obtain a transparent 10% solution. The softening temperature of this polymer determined in the same manner as in Example 1 was 110 ° C.

When the Fenton test was conducted on the obtained polymer in the same manner as in Example 1, the fluorine ion elution ratio was 0.004%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.05.

[Example 3]
Synthesis of TFE / PDD / PSVE Copolymer An autoclave having an internal volume of 200 ml was charged with 14.30 g of PDD, 52.64 g of PSVE, 76.94 g of HCFC225cb, and 0.36 g of IPP and freeze-deaerated. After introducing 5.9 g of TFE, the temperature was raised to 40 ° C. to initiate polymerization. At this time, the pressure was 0.26 MPa (gauge pressure). The reaction was carried out at 40 ° C. for 10 hours, and the reaction was stopped when the pressure reached 0.07 MPa (gauge pressure). The polymerization solution was diluted with HCFC225cb, aggregated with hexane, and further washed with hexane three times. Vacuum drying was performed overnight at 80 ° C. Yield 25.03 g (Yield 34.4%).

^{When the} polymer composition was determined by ¹⁹ F-NMR, it was TFE / PDD / PSVE = 42/35/22 (molar ratio), and the ion exchange capacity was 0.98 meq / g dry resin. Moreover, the number average molecular weight of polymethyl methacrylate conversion by GPC was 53,000, and the weight average molecular weight was 83,000. 10 g of this polymer was put into a 2000 ml Hastelloy autoclave, degassed, and then fluorine gas (20% by volume) diluted with nitrogen gas to a gauge pressure of 0.3 MPa was introduced and maintained at 180 ° C. for 4 hours. Next, it was hydrolyzed with alkali, acidified and dried, and then dissolved in ethanol to obtain a transparent 12% solution.

Further, a film having a thickness of 100 μm was produced by hot pressing using a polymer obtained by treatment with fluorine gas. This was immersed in a solution of KOH / H ₂ O / DMSO = 11/59/30 (mass ratio) and kept at 90 ° C. for 17 hours for hydrolysis. It returned to room temperature and washed with water 3 times. Further, it was immersed in 2N sulfuric acid at room temperature for 2 hours and washed with water. This sulfuric acid immersion and water washing were each performed a total of 3 times, and finally water washing was further performed 3 times. It was air-dried at 80 ° C. for 16 hours and further vacuum-dried at 80 ° C. to obtain an acid-type dry film. When the dynamic viscoelasticity was measured and the softening temperature was determined, the softening temperature of this polymer was 120 ° C.

When the Fenton test was conducted on the obtained polymer in the same manner as in Example 1, the fluorine ion elution ratio was 0.004%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.07.

[Example 4]
Synthesis of TFE / PDD / PSVE copolymer part 2 The same as Example 3 except that 9 g of TFE, 24.4 g of PDD, 102.6 g of PSVE, 0.08 g of IPP were used, and HCFC225cb was not used. Polymerization was carried out by the method. Polymerization was carried out at 40 ° C. for 12 hours to complete the reaction. The polymerization solution was diluted with HCFC225cb, aggregated with hexane, and further washed with hexane three times. Vacuum drying was performed overnight at 80 ° C. Yield 37.8 g (Yield 27.7%).

  The molecular weight and composition were measured in the same manner as in Example 3. The composition of the obtained polymer was TFE / PDD / PSVE = 36/41/23, and the ion exchange capacity was 0.97 meq / g dry resin. The number average molecular weight was 160,000 and the weight average molecular weight was 280,000. The obtained polymer was heat-treated at 240 ° C. under reduced pressure for 4 hours, and then treated with fluorine gas in the same manner as in Example 3.

The polymer obtained was subjected to hydrolysis and acidification treatment in the same manner as in Example 1 and subjected to a Fenton test. As a result, the fluorine ion elution ratio was 0.004%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.06.

[Example 5]
Synthesis of TFE / PDD / PSVE2 Copolymer Polymerization was conducted in the same manner as in Example 4 using 6 g of TFE, 16.5 g of PDD, 68.3 g of PSVE2, and 0.05 g of IPP. The polymerization was carried out at 40 ° C. for 20 hours. The polymerization solution was diluted with HCFC225cb, aggregated with hexane, and further washed with hexane three times. Vacuum drying was performed overnight at 80 ° C. Yield 27.3 g (Yield 30.1%).

In the same manner as in Example 3, molecular weight / composition measurement and fluorine gas treatment were performed. The composition of the obtained polymer was TFE / PDD / PSVE2 = 36/39/26, and the ion exchange capacity was 1.11 meq / g dry resin. The number average molecular weight was 167,000 and the weight average molecular weight was 870,000. When the obtained polymer was hydrolyzed and acidified in the same manner as in Example 1 and subjected to a Fenton test, the fluorine ion elution ratio was 0.007%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.1.

[Example 6]
Synthesis of TFE / MMD / PSVE Copolymer An autoclave having an internal volume of 200 ml was charged with 14.1 g of MMD, 78.0 g of PSVE, and 0.3 g of an HCFC225cb solution containing 3% by mass of PFB, followed by freeze degassing. After introducing 14.1 g of TFE, polymerization was carried out at 20 ° C. for 22 hours. The polymerization solution was diluted with HCFC225cb, aggregated with hexane, and further washed with hexane three times. Vacuum drying was performed overnight at 80 ° C. Yield 2.2g.

The obtained polymer was subjected to molecular weight / composition measurement and fluorine gas treatment in the same manner as in Example 3. The composition of the obtained polymer was TFE / MMD / PSVE = 30/47/23 (molar ratio), and the ion exchange capacity was 0.93 meq / g dry resin. Moreover, the number average molecular weight of polymethyl methacrylate conversion by GPC was 155,000, and the weight average molecular weight was 239,000. When the obtained polymer was hydrolyzed and acidified in the same manner as in Example 1 and subjected to a Fenton test, the fluorine ion elution ratio was 0.001%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.015.

[Example 7]
Synthesis of TFE / MMD / PSVE Copolymer No. 2 0.77 MMD, 92.6 g PSVE, 50.8 g HCFC225cb, and 2.57 g HCFC-225cb solution containing 3% by mass of PFB in an autoclave with an internal volume of 200 ml And freeze degassed. The temperature was raised to 40 ° C. and TFE was introduced until the pressure reached 0.5 MPa, and then polymerization was carried out at 40 ° C. for 7 hours while introducing TFE while maintaining this pressure. The polymerization solution was aggregated with HCFC141b and washed three times with HCFC141b. Vacuum drying was performed overnight at 80 ° C. Yield 19.9 g.

The obtained polymer was hydrolyzed with an aqueous KOH solution and titrated with aqueous hydrochloric acid to obtain an ion exchange capacity of 1.06 meq / g dry resin. Furthermore, when the polymer composition was determined by ¹⁹ F-NMR, it was TFE / MMD / PSVE = 77/5/18 (molar ratio). This polymer was treated with fluorine gas in the same manner as in Example 3. When the obtained polymer was hydrolyzed and acidified in the same manner as in Example 1 and subjected to a Fenton test, the fluorine ion elution ratio was 0.001%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.02.

[Example 8]
Synthesis of TFE / MMD / PSVE Copolymer No. 3 2.62 g of HCFC-225cb solution containing 0.4 g of MMD, 93.0 g of PSVE, 53.3 g of HCFC225cb, and 3% by mass of PFB in an autoclave having an internal volume of 200 ml And freeze degassed. The temperature was raised to 40 ° C. and TFE was introduced until the pressure reached 0.45 MPa, and then polymerization was carried out at 40 ° C. for 7 hours while introducing TFE while maintaining this pressure. The polymerization solution was aggregated with HCFC141b and washed three times with HCFC141b. Vacuum drying was performed overnight at 80 ° C. Yield 16.7g.

The obtained polymer was hydrolyzed with an aqueous KOH solution and titrated with aqueous hydrochloric acid to obtain an ion exchange capacity of 1.04 meq / g dry resin. Furthermore, when the polymer composition was determined by ¹⁹ F-NMR, it was TFE / MMD / PSVE = 74/8/18 (molar ratio). This polymer was treated with fluorine gas in the same manner as in Example 3. When the obtained polymer was hydrolyzed and acidified in the same manner as in Example 1 and subjected to a Fenton test, the fluorine ion elution ratio was 0.001%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.01.

[Example 9]
TFE / MMD / PSVE part 4
An autoclave having an internal volume of 200 ml was charged with 2.4 g of MMD, 91.8 g of PSVE, 55.2 g of HCFC-225cb, and 2.66 g of an HCFC225cb solution containing 3% by mass of PFB, followed by freeze degassing. The temperature was raised to 40 ° C. and TFE was introduced until the pressure reached 0.40 MPa, and then polymerization was carried out while introducing TFE while maintaining this pressure. The polymerization time was 7 hours at 40 ° C. The polymerization solution was aggregated with HCFC141b and washed three times with HCFC141b. Vacuum drying was performed overnight at 80 ° C. Yield 14.9g.

The obtained polymer was hydrolyzed with a KOH aqueous solution and titrated with hydrochloric acid water to obtain an ion exchange capacity of 1.13 meq / g dry resin. Furthermore, when the polymer composition was determined by ¹⁹ F-NMR, it was TFE / MMD / PSVE = 61/16/23 (molar ratio). This polymer was treated with fluorine gas in the same manner as in Example 3. When the obtained polymer was hydrolyzed and acidified in the same manner as in Example 1 and subjected to a Fenton test, the fluorine ion elution ratio was 0.003%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.04.

[Example 10]
TFE / BVE / PSVE copolymer HCFC- containing 38.6% by weight of 48.6 g BVE, 86.4 g PSVE, 86.2 g 1,1,2-trichlorotrifluoroethane, and PFB in an autoclave with an internal volume of 200 ml 0.75 g of 225cb solution was added and freeze degassed. The temperature was raised to 30 ° C. and TFE was introduced until the pressure reached 0.15 MPa, and then polymerization was carried out while introducing TFE while maintaining this pressure. The polymerization time was 30 ° C. for 16 hours. The polymerization solution was aggregated with hexane and washed three times with hexane. Vacuum drying was performed overnight at 80 ° C. Yield 8.3g.

The obtained polymer was hydrolyzed with an aqueous KOH solution and titrated with aqueous hydrochloric acid to obtain an ion exchange capacity of 0.95 meq / g dry resin. Furthermore, when the polymer composition was determined by ¹⁹ F-NMR, it was TFE / BVE / PSVE = 61/20/19 (molar ratio). This polymer was treated with fluorine gas in the same manner as in Example 3. When the obtained polymer was hydrolyzed and acidified in the same manner as in Example 1 and subjected to a Fenton test, the fluorine ion elution ratio was 0.001%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.01.

[Example 11]
The polymer polymerized in Example 4 was recovered without treatment with fluorine gas. The composition and molecular weight were the same. When the obtained polymer was hydrolyzed and acidified in the same manner as in Example 1 and subjected to the Fenton test, the elution ratio of fluorine ions was 0.043%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.61.

[Example 12]
10 g of copolymer powder consisting of TFE and PSVE (ion exchange capacity 1.1 meq / g dry resin when converted to acid form and measured, hereinafter referred to as copolymer A) in a vacuum oven at a pressure of 10 Pa, Heat treatment was performed at 250 ° C. for 4 hours. Thereafter, fluorine gas treatment was performed in the same manner as in Example 3. The polymer obtained was hydrolyzed and acidified in the same manner as in Example 1 and subjected to a Fenton test. As a result, the fluorine ion elution ratio was 0.002%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.03.

Moreover, when the Fenton test was done similarly about the copolymer A, the fluorine ion elution ratio was 0.04%. Further, when the infrared spectrum was measured in the same manner as in Example 1, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.57.

[Example 13]
After 0.16 g of the polymer treated with fluorine gas obtained in Example 4 was dissolved in 2.7 g of 1,3-bistrifluoromethylbenzene, 2.7 g of dimethyl sulfoxide was gradually added to obtain a suspension of the polymer. Obtained. To this were added 0.24 g of trifluoromethanesulfonamide and 0.15 g of triethylamine, and the mixture was stirred at 100 ° C. for 48 hours. The obtained reaction liquid was uniformly transparent. This solution was applied onto a substrate and dried, then washed with 3N hydrochloric acid three times, further treated with water three times, again immersed in a 20% aqueous KOH solution, washed with water and dried. As a result of infrared spectrum measurement of the obtained film, 50% of SO ₂ F groups in the polymer were converted to SO ₃ K, and 50% was converted to —SO ₂ NKSO ₂ CF ₃ (a potassium salt of sulfonimide). It was confirmed that The absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.06.

[Fuel cell fabrication and electrolyte material durability evaluation test]
The fuel cell was assembled as follows. CF ₂ = CF ₂ to based repeating units _{CF 2 = CF-OCF 2 CF} (CF 3) O (CF 2) 2 SO 3 consisting of repeating units based on H copolymer (ion exchange capacity: 1.1 meq / Gram dry resin) and platinum-supported carbon were mixed at a mass ratio of 1: 3, and further mixed with ethanol to prepare a coating solution. This coating solution was applied onto an ethylene-tetrafluoroethylene film substrate by a die coating method and dried to obtain an electrode layer having a thickness of 10 μm and a platinum carrying amount of 0.5 mg / cm ² .

Next, about each polymer obtained in Examples 4-12, it hot-pressed and produced the film of thickness 50 micrometers, respectively. This was immersed in a solution of KOH / H ₂ O / DMSO = 15/55/30 (mass ratio) and kept at 80 ° C. for 17 hours for hydrolysis. This was returned to room temperature, washed with water three times, and further immersed in 3 mol / L hydrochloric acid at room temperature for 2 hours for washing with water. This hydrochloric acid immersion and water washing were performed three times in total, and finally three times of water washing were performed. The electrolyte membrane was obtained by air drying at 60 ° C. for 16 hours. Further, an electrolyte membrane was obtained in the same manner for the copolymer A of Example 12 (without fluorination treatment).

  Next, the two electrode layers obtained as described above were pressed with the electrolyte membrane sandwiched between them so that the electrode layers face each other, and the electrode layer was transferred to the membrane Was prepared for each example. Further, a carbon cloth was disposed on both outer sides as a gas diffusion layer to produce a membrane electrode assembly.

A solid polymer fuel cell having an effective membrane area of 25 cm ² is disposed on both outer sides of the membrane electrode assembly by a carbon plate separator in which gas channel narrow grooves are cut into a zigzag shape, and further on the outer side of the heater. Assembled.

  The durability was evaluated by the following method. With the circuit open, the temperature of the fuel cell was maintained at 90 ° C., and air containing water vapor at a dew point of 50 ° C. was supplied to the cathode and hydrogen containing water vapor at a dew point of 50 ° C. was supplied at 50 ml / min. After continuing the operation for the time shown in the table in this state, the fuel cell was disassembled, and the deterioration state of the electrolyte membrane was measured by mass measurement. The results are shown in the table. Here, the mass reduction rate is a value obtained by dividing mass reduction (%) by operating time (h). In addition, when the same evaluation is performed on Example 13, a result equivalent to Example 4 is expected.

  The electrolyte material of the present invention has an aliphatic ring structure in the main chain, is excellent in gas diffusibility, is highly fluorinated, has excellent water repellency, and has a stabilized terminal. The fuel cell having this electrolyte material is excellent in durability even when operated for a long period of time.

Further, the present invention is used conventionally tetrafluoroethylene _{/ CF 2 = CFCF 2 CF (} CF 3) O (CF 2) 2 SO 3 softening temperature of the H copolymer is high acid polymer can be provided. Conventional polymers begin to have a sudden drop in elastic modulus from around 80 ° C., and their softening temperature is close to the operating temperature of the fuel cell, so that when used as an electrolyte for a fuel cell, physical properties such as swelling tend to change over time. In terms of durability, problems are likely to occur, and operation at a temperature of 80 ° C. or higher is difficult. On the other hand, when the electrolyte material of the present invention having a high softening temperature is used as an electrolyte polymer contained in an electrolyte membrane or electrode of a fuel cell, there is no change in physical properties over time, so that high durability is obtained. It is also possible to operate the cell at a temperature higher than 80 ° C.

The figure which shows the infrared spectrum of the copolymer of tetrafluoroethylene, perfluoro (2,2- dimethyl- 1, 3-dioxole), and potassium perfluoro (3, 6- dioxa-4-methyl-7-octene) sulfonate. .

Explanation of symbols

1,1 ': Baseline

Claims (10)

An Fenton reagent comprising a perfluoropolymer having a sulfonic acid group or a sulfonimide group and having an aliphatic ring structure in the main chain, comprising 3% hydrogen peroxide and 200 ppm divalent iron ions in a study in solution 50g immersed 16 hours polymer 0.1g at 40 ° C., fluoride ion-elution amount detected in the solution state, and are 0.01% or less of the total amount of fluorine in the soaked polymer,
The perfluoropolymer electrolyte material characterized Rukoto such a copolymer comprising repeating units based on a repeating unit Monomer B based on the following monomer A (In the formula, Y ¹ is a fluorine atom or a trifluoromethyl A methyl group, m is an integer of 0 to 3, n is an integer of 1 to 12, p is 0 or 1, m + p> 0, Y ² is OH or NHSO ₂ Z, and Z is C1-C6 perfluoroalkyl group which may contain an etheric oxygen atom.) .
Monomer A: A perfluoromonomer that gives a polymer having a repeating unit containing a ring structure in the main chain by radical polymerization.
Monomer _{^{B: CF 2 = CF- (OCF}} 2 CFY 1) m -O p - (CF 2) a perfluorovinyl ether represented by n _-SO ^{2 Y} 2. The perfluoropolymer has a ratio I ₁₆₉₀ / I ₂₃₅₀ of a maximum absorbance I _{1690 in} a band of 1690 ± 10 cm ^{−1 and} an absorbance I _{2350 in} a band of 2350 ± 10 cm ⁻¹ in an infrared spectrum of 0.15 or less. Item 12. The electrolyte material according to Item 1. The electrolyte material according to claim 1 or 2 , wherein the repeating unit based on the monomer A is represented by any one of the following formulas (1) to (4), wherein n is an integer of 1 to 4, ^f is a ^C 1-8 perfluoroalkyl group or perfluoroalkoxy group, and X ¹ and X ² are each independently a fluorine atom or a trifluoromethyl group, and (CX ¹ X ² ) _n is n Is 2 or more, the combination of X ¹ and X ² may be different for each carbon).

The electrolyte material according to claim 1 or 2 , wherein the repeating unit based on the monomer A is represented by any one of the following formulas (5) to (7).

0.5 to 80 mol% of repeating units based on the monomer A, 5 to 40 mol% of repeating units based on the monomer B, and an ion exchange capacity of 0.7 to 2.5 meq / g dry resin The electrolyte material according to any one of claims 1 to 4 . 0.5 to 70 mol% of repeating units based on the monomer A, 5 to 40 mol% of repeating units based on the monomer B, and 5 to 90 mol% of repeating units based on tetrafluoroethylene, and having an ion exchange capacity the electrolyte material according to any one of claims 1 to 4, which is 0.7 to 2.5 meq / g dry resin. The electrolyte material according to claim 1-6 a number average molecular weight of 20,000 to 2,000,000. 2. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising a membrane-like solid polymer electrolyte, and a cathode and an anode disposed via the electrolyte, wherein at least one of the cathode and the anode is a catalyst. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising the electrolyte material according to any one of 7 to 7 . A film-like solid polymer electrolyte, the polymer electrolyte fuel cell membrane electrode assembly comprising a cathode and an anode are disposed through the electrolyte, the film-like solid polymer electrolyte according to claim 1 to 7 A membrane electrode assembly for a polymer electrolyte fuel cell, comprising the electrolyte material according to any one of the above. A manufacturing method of the electrolyte material according to any one of claims 1 to 7 perfluoropolymer having -SO 2 _F groups after obtaining by radical polymerization, by contacting the perfluoropolymer with fluorine gas, then A method for producing an electrolyte material, wherein the —SO ₂ F group is converted into a sulfonic acid group or a sulfonimide group.

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