JP4946009B2 - ELECTROLYTE MATERIAL FOR SOLID POLYMER TYPE FUEL CELL, METHOD FOR PRODUCING MEMBRANE / ELECTRODE ASSEMBLY FOR SOLID POLYMER TYPE FUEL CELL - Google Patents

Description

  The present invention relates to a method for producing an electrolyte material for a polymer electrolyte fuel cell having excellent stability, and a method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell using the electrolyte material.

  Polymers having sulfonic acid groups (hereinafter referred to as sulfonic acid type polymers) are often used as substrates for cation exchange membranes for salt electrolysis, diaphragms for fuel cells, and the like. In recent years, a fuel cell has attracted attention as a power generation system in which the reaction product is only water in principle and has almost no adverse effect on the global environment. 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. As an electrolyte material for a polymer electrolyte fuel cell, a sulfonic acid type polymer is used for reasons such as heat resistance, chemical resistance, durability, and long-term stability.

  However, it is known that the sulfonic acid type polymer is deteriorated when exposed to a long-term electrode reaction, so that it is difficult to maintain the output as a fuel cell. As a cause of the deterioration of the polymer, at least a part of the terminal group of the polymer main chain is an unstable —COOH group, —COF group, etc., and the main chain is decomposed in a chain from the unstable terminal group. Is mentioned. As a method for stabilizing the terminal group of the polymer, there is a method of fluorinating the polymer (for example, see Patent Document 1). However, this method includes a step of treating the polymer subjected to polymerization with a fluorinating agent such as fluorine gas, and the productivity is lowered.

Japanese Examined Patent Publication No. 46-23245 (Claims)

  An object of this invention is to provide the manufacturing method of the electrolyte material for polymer electrolyte fuel cells excellent in stability which consists of a polymer with few unstable terminal groups.

A first aspect of the present invention is a method for producing a polymer electrolyte fuel cell electrolyte material comprising a polymer having a sulfonic acid group, -SO 2 _X group (X is fluorine atom or chlorine atom) having Perfluorocarbon monomer (A) having an ethylenic double bond (which may contain an etheric oxygen atom) and a double bond and not containing atoms other than carbon, fluorine and oxygen atoms A polymerization step in which at least one perfluorocarbon monomer (B) is copolymerized at a polymerization temperature of 0 to 35 ° C. using a radical polymerization initiator composed of a compound represented by formula (2) or formula (3). This is a method for producing an electrolyte material for a polymer electrolyte fuel cell.
[F (CF ₂ ) _p COO] ₂ (2)
In the formula, p is an integer of 4 to 10.
_{[CF 3 CF 2 CF 2 O} (CF (CF 3) CF 2 O) q CF (CF 3) COO] 2 (3)
In the formula, q is an integer of 0 to 8.

  By using a polymerization temperature of 0 to 35 ° C. in the polymerization step and using a radical polymerization initiator composed of a fluorine-containing compound, the formation of unstable terminal groups of the polymer can be suppressed, and the solid polymer that is resistant to deterioration and excellent in stability. Type fuel cell electrolyte material can be obtained. In addition, the polymer can have a high molecular weight, and an electrolyte material having excellent mechanical strength can be obtained.

  The second aspect of the present invention is a membrane / electrode joint for a polymer electrolyte fuel cell comprising an anode and a cathode each having a catalyst layer containing a catalyst and an electrolyte material, and an electrolyte membrane disposed therebetween. In the method for producing a body, at least one of the electrolyte material constituting the electrolyte membrane, the electrolyte material contained in the anode catalyst layer, and the electrolyte material contained in the cathode catalyst layer is obtained by the method for producing an electrolyte material described above. A method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell, characterized by comprising:

  Since the electrolyte material of the present invention is excellent in stability, when it is contained in a catalyst layer of a fuel cell or used as an electrolyte membrane, a membrane / electrode assembly excellent in durability suitable for maintaining output as a fuel cell Can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the electrolyte material for polymer electrolyte fuel cells excellent in stability which consists of a polymer with few unstable terminal groups is provided. Moreover, a high molecular weight polymer can be obtained and the mechanical stability of the electrolyte material for solid polymer fuel cells can be improved. The membrane / electrode assembly for a polymer electrolyte fuel cell formed using the electrolyte material is excellent in durability and can suitably maintain the output as a fuel cell.

In the production method of the present invention, first, a perfluorocarbon monomer (A) having an —SO ₂ X group (X is a fluorine atom or a chlorine atom) and having an ethylenic double bond, a double bond and carbon A polymerization temperature of 0 to 35 ° C. using a radical polymerization initiator composed of a fluorine-containing compound having a molecular weight of 450 or more and at least one perfluorocarbon monomer (B) not containing atoms other than atoms, halogen atoms and oxygen atoms. And undergoing a polymerization step to obtain a polymer having —SO ₂ X groups. Here, the perfluorocarbon monomer (A) may contain an etheric oxygen atom.

As the perfluorocarbon monomer (A), a monomer represented by the formula (1) is preferable.
_{CF 2 = CF (OCF 2 CFY} ) m O k (CF 2) n SO 2 F (1)
In the formula, Y represents a fluorine atom or a trifluoromethyl group, m represents an integer of 0 to 3, k represents 0 or 1, n represents an integer of 1 to 12, and (m + k)> 0.

In particular, the monomer represented by the formula (4) is preferable because the production of the monomer is easy.
_{CF 2 = CFO (CF 2 CF} (CF 3) O) n (CF 2) m SO 2 F (4)
In the formula, m is an integer of 2 to 4, and n is an integer of 0 to 2.
_{Specifically, CF 2 = CFO (CF 2} ) 2 SO 2 F, CF 2 = CFO (CF 2) 3 SO 2 F, CF 2 = CFOCF 2 CF (CF 3) O (CF 2) 2 SO 2 F _{, CF 2 = CFOCF 2 CF (} CF 3) O (CF 2) 3 SO 2 F, CF 2 = CFO (CF 2 CF (CF 3) O) 2 (CF 2) 2 SO 2 F, CF 2 = CFO ( _{CF 2 CF (CF 3) O} ) 2 (CF 2) 3 SO 2 F , and the like.

  Examples of the monomer (B) include the following. Perfluoroolefins such as tetrafluoroethylene, hexafluoropropylene and perfluorobutylethylene. Perfluoroethers such as perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, perfluorobutenyl vinyl ether. Cyclic perfluoro such as perfluoro (1,3-dioxole), perfluoro (2,2-dimethyl-1,3-dioxole), perfluoro- (2-methylene-4-methyl-1,3-dioxolane) Compound.

  Among them, a copolymer of a perfluoroolefin such as tetrafluoroethylene and hexafluoropropylene and a monomer (A), or a multi-component copolymer of these monomers and at least one monomer (B) other than the above-mentioned perfluoroolefin is used. When the polymerization method of the present invention is employed in production, it is preferable to obtain a material suitable as an electrolyte material for a polymer electrolyte fuel cell. Of the perfluoroolefins, tetrafluoroethylene is particularly preferable.

  In the polymer growth reaction of polymerization, a disproportionation reaction occurs when an etheric oxygen atom is bonded to the terminal carbon atom of the growth radical as shown in the following Scheme 1, and the terminal group of the polymer is -COF group or -COOH. May be the basis. Moreover, as shown in the following scheme 2, a polymer having a —COF group or a —COOH group at the end tends to decompose the main chain in a chain manner starting from these end groups. Therefore, it is difficult to stably use a polymer having many terminal groups of -COF groups and -COOH groups as an electrolyte material for a polymer electrolyte fuel cell. In the present invention, the polymerization is carried out at a polymerization temperature of 0 to 35 ° C. At a polymerization temperature higher than 35 ° C., the above disproportionation reaction is more likely to occur, and the number of —COF end groups of the polymer increases. When the polymerization temperature is lower than 0 ° C., the decomposition rate of the radical polymerization initiator is slow. More preferably, it is 10-25 degreeC, Most preferably, it is 10-20 degreeC.

  In the polymerization step, a radical polymerization initiator composed of a fluorine-containing compound having a molecular weight of 450 or more is employed. This polymerization initiator is preferred because it produces a polymer having stable end groups. Moreover, since a chain transfer constant is small, it is preferable that a fluorine-containing compound does not contain a hydrogen atom substantially, and it is more preferable that it is a perfluoro compound.

  A polymerization initiator having a low molecular weight is easily vaporized to cause a polymerization reaction in the gas phase, and easily produces a polymer having an abnormal composition that is different in composition and molecular weight from the polymer obtained by the desired polymerization reaction. This hinders the desired polymerization reaction and contaminates the polymerization apparatus, leading to a decrease in productivity. In addition, the polymer having an abnormal composition becomes a defect site when a polymer having a sulfonic acid group containing the polymer is used as an electrolyte membrane. When a fuel cell is operated using such an electrolyte membrane, the membrane is damaged from the defective part, the operation itself becomes impossible, or hydrogen peroxide is generated due to the reaction between the leaked oxygen gas and hydrogen gas, resulting in deterioration of the membrane. Invite to accelerate. Therefore, in the present invention, a polymerization initiator having a relatively low vapor pressure and a molecular weight of 450 or more is used to prevent a polymerization reaction in the gas phase portion.

Specifically, bis (fluoroacyl) peroxides represented by formula (2) or formula (3) are preferable.
[F (CF ₂ ) _p COO] ₂ (2)
In the formula, p is an integer of 4 to 10.
_{[CF 3 CF 2 CF 2 O} (CF (CF 3) CF 2 O) q CF (CF 3) COO] 2 (3)
In the formula, q is an integer of 0 to 8.

Specific examples of bis (fluoroacyl) peroxides include [CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) COO] ₂ , [CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COO] ₂ , etc. are mentioned.

  The 10-hour half-life temperature of the radical polymerization initiator is preferably -20 to 40 ° C. The 10-hour half-life temperature refers to a temperature at which the amount of initiator becomes half after 10 hours from the start of polymerization. When the decomposition reaction temperature of the initiator is significantly lower than the polymerization temperature, it is necessary to use a large amount of initiator because the radical generation efficiency is low. When the decomposition reaction temperature of the initiator is significantly higher than the polymerization temperature, the polymerization time is long, and the production efficiency is low, which is industrially disadvantageous. More preferably, it is -10-35 degreeC.

  The amount of radical polymerization initiator used is preferably 0.01 to 1%, more preferably 0.01 to 0.5%, based on the amount of perfluorocarbon monomer. If the amount of the polymerization initiator is too small, the molecular weight of the polymer to be produced becomes too large, the workability is deteriorated, and it may be difficult to form an electrolyte membrane. If the amount of the polymerization initiator is too large, the molecular weight of the polymer to be produced becomes small, and there is a possibility that the strength that can be used as an electrolyte material for a polymer electrolyte fuel cell cannot be obtained.

  In the polymerization step, known polymerization methods such as suspension polymerization, solution polymerization, emulsion polymerization, bulk polymerization and the like can be adopted as the polymerization method for copolymerizing the above monomers, but solution polymerization or bulk polymerization is particularly preferable. In suspension polymerization and emulsion polymerization, since water is used as a polymerization medium, it is difficult to dissolve the perfluorocarbon monomer in the polymerization medium, and it is difficult to perform polymerization stably.

  As a polymerization medium in the case of solution polymerization, a fluorine-containing organic solvent having a small chain transfer constant is preferable. In particular, at least one selected from the group consisting of a C 3-10 perfluorocarbon, a C 3-10 hydrofluorocarbon, a C 3-10 hydrochlorofluorocarbon, and a C 3-10 chlorofluorocarbon is preferred. These halogenocarbons can be preferably used in any of linear, branched or cyclic structures, and may contain etheric oxygen atoms in the molecule, but are preferably saturated compounds.

Specific examples of the polymerization medium include the following. Examples of the perfluorocarbon include perfluorocyclobutane, perfluorohexane, perfluoro (dipropyl ether), perfluorocyclohexane, perfluoro (2-butyltetrahydrofuran) and the like. As the hydrofluorocarbon, the number of fluorine atoms in the molecule is preferably larger than that of hydrogen atoms, and CH ₃ OC ₂ F ₅ , CH ₃ OC ₃ F ₇ , C ₅ F ₁₀ H ₂ (more preferably CF ₃ CFHCCFHCF ₂ CF ₂ CF ₃ ), C ₆ F ₁₃ H (more preferably, CF ₃ CF ₂ CF ₂ CF ₂ CF ₂ CF ₂ CF ₂ H), C ₆ F ₁₂ H ₂ (more preferably, CF ₂ HCF ₂ CF _{2 CF 2 CF 2 CF 2 H} ) , and the like. The hydrochlorofluorocarbon preferably has 3 or less hydrogen atoms, and examples thereof include CHClFCF ₂ CF ₂ Cl. Examples of the chlorofluorocarbon include 1,1,2-trichlorotrifluoroethane. Particularly preferred solvents are CHClFCF ₂ CF ₂ Cl, CF ₃ CF ₂ CF ₂ CF ₂ CF ₂ CF ₂ H.

  The amount of the polymerization medium used is preferably 10 to 90% by volume with respect to the polymerization tank volume, and more preferably 30 to 70%. When the amount of the polymerization medium is small, the amount of perfluorocarbon monomer that can be dissolved in the polymerization medium is also small, and the resulting polymer is small, so that the production efficiency is low and industrially disadvantageous. On the other hand, if the amount of the polymerization medium is too large, it becomes difficult to uniformly stir the whole. In the case of suspension polymerization and emulsion polymerization, water can be mentioned as a substantial polymerization medium.

  In the polymerization step, it is preferable that substantially no chain transfer agent is used. This is because when a chain transfer agent is used, a hydrogen atom is introduced into the terminal group of the polymer and may become unstable.

  The polymerization pressure is preferably 0.05 to 10 MPa. If the polymerization pressure is too low, it becomes difficult to control the reaction, and if the polymerization pressure is too high, it is not preferable for production equipment. More preferably, 0.1 to 2.5 MPa is employed.

As an index of the amount of unstable terminal groups of the polymer in the present invention, measurement by infrared spectroscopy can be used. As measurement by infrared spectroscopy, FT-IR measurement can be suitably employed. It is carried out by preparing a film of about 50 to 200 μm consisting of a polymer having a —SO ₃ K group of potassium salt type obtained by hydrolyzing a polymer having a —SO ₂ X group, and measuring its infrared spectrum. . In order to reduce the influence of the adsorbed water on the infrared spectrum of the film, it is preferable to measure in dry nitrogen using a film dried using a vacuum dryer or the like.

Read the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ defined in the infrared spectrum as follows:
I ₁₆₉₀ : maximum absorbance in the band of wave number 1690 ± 10 cm ⁻¹ ,
I ₂₃₅₀ : Maximum absorbance in the band of wave number 2350 ± 10 cm ⁻¹ .
The wave number 1690 ± 10 cm ⁻¹ corresponds to the absorption of —COOK, and the wave number 2350 ± 10 cm ⁻¹ corresponds to the absorption of the main chain —CF ₂ —. Since —COOK is derived from —COF and —COOH which are unstable terminal groups of the polymer, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ represents the relative amount of the unstable terminal group to the polymer main chain (—CF ₂ —). That is, it means that the lower the numerical value of this ratio, the smaller the amount of unstable terminal groups of the polymer. In order to use a polymer as an electrolyte material for a polymer electrolyte fuel cell, I ₁₆₉₀ / I ₂₃₅₀ is preferably 0.10 or less, and more preferably 0.05 or less.

A method of reading the absorbance I ₁₆₉₀ and the absorbance I ₂₃₅₀ from the infrared spectrum in this specification will be described with reference to FIGS. FIG.1 and FIG.2 is a figure which shows the infrared spectrum measured about the electrolyte material (polymer) produced by the manufacturing method of this invention in Example 31 mentioned later. 1 shows a range of wave numbers 2100 to 1600 cm ⁻¹ , and FIG. 2 shows a range of wave numbers 2800 to 2000 cm ⁻¹ . As illustrated in FIG. 1, the absorbance I ₁₆₉₀ is based on the absorbance at the peak position at 1690 ± 10 cm ⁻¹ with the straight line connecting the valleys close to the high wave number side and the low wave number side of the absorption peak as the base line. The value measured from the line. In addition, as illustrated in FIG. 2, the absorbance I ₂₃₅₀ is based on the straight line connecting 2740 ± 20 cm ⁻¹ and 2070 ± 20 cm ⁻¹ as the baseline, and the absorbance at the peak position at 2350 ± 10 cm ⁻¹ as the baseline. The value measured from

A high molecular weight polymer can be obtained by the polymerization step in the present invention. The molecular weight of the polymer in the present invention can be evaluated by the value of T _Q is an index of melt fluidity. _TQ is measured at the stage of the polymer having —SO ₂ F groups before hydrolysis and acidification. T _Q is defined as a temperature (° C.) indicating a capacity flow rate of 100 mm ³ / sec. The capacity flow rate is a value obtained by causing the polymer to melt and flow out from a nozzle having a length of 1 mm and an inner diameter of 1 mm under a pressure of 2.94 MPa, and the flowing polymer is expressed in units of mm ³ / sec. Generally higher molecular weight T _Q is high is large, the has a practically sufficient strength as an electrolyte membrane, the lower limit of the range of T _Q electrolyte material preferably 180 ° C. or higher, more preferably 200 ° C. or higher, more preferably 220 It is above ℃.

On the other hand, the upper limit of the range of T _Q of the electrolyte material is dependent on the method of forming a film when used as an electrolyte membrane. In order to obtain a film by melt molding, from the viewpoint prevent decomposition of the -SO 2 _F groups in the polymer, also hydrolyze the polymer having -SO 2 _F groups, treated acid form, film by the casting method when obtaining, from the viewpoint of ensuring the solubility or dispersibility in a solvent, the upper limit of T _Q is preferably 400 ° C.. The electrolyte material of the invention, it is preferred that T _Q hydrolysis the polymer having -SO 2 _F groups in the above range, obtained by treating an acid form.

The ion exchange capacity (hereinafter also referred to as AR) of the electrolyte material obtained by hydrolyzing and acidifying the polymer having —SO ₂ F groups obtained by the present invention is not particularly limited, but is usually 0.00. Often 5 to 3.0 meq / g dry resin. Conventionally, it has been difficult to obtain a high molecular weight when trying to obtain an electrolyte material having a relatively high ion exchange capacity. However, a relatively high ion exchange capacity (for example, 1.2 to 1.. It was found that even a resin having a weight of 8 meq / g dry resin can be made to have a high molecular weight. According to the production method of the present invention, it is possible to provide an electrolyte material for a polymer electrolyte fuel cell having high ion exchange capacity, low electrical resistance, high molecular weight, excellent mechanical strength, and durability.

The polymer obtained by the above polymerization step is usually hydrolyzed and acidified to convert the —SO ₂ X group into an —SO ₃ H group. Since the obtained sulfonic acid type polymer is excellent in stability, the polymer electrolyte fuel cell using this sulfonic acid type polymer as an electrolyte material is excellent in durability.

In the hydrolysis, for example, in a solution of a base such as NaOH or KOH using water or a mixture of water and an alcohol (such as methanol or ethanol) or a polar solvent (such as dimethyl sulfoxide) as a solvent, The —SO ₂ X group is converted to —SO ₃ Na group, —SO ₃ K group or the like. In the subsequent acidification treatment, an —SO ₃ Na group or the like in the polymer is acidified in an aqueous solution of an acid such as hydrochloric acid, nitric acid, or sulfuric acid, and converted to —SO ₃ H group (sulfonic acid group). The The hydrolysis or acidification treatment is usually performed at 0 to 120 ° C.

The electrolyte material according to the present invention can be formed into a film and used as a solid polymer electrolyte membrane. A polymer having a —SO ₂ X group or the like can be formed into a film by melt extrusion or heating press, followed by hydrolysis and then acidification treatment to obtain an electrolyte membrane. Alternatively, a polymer having —SO ₂ X group or the like may be hydrolyzed and acidified in a powder state to obtain an electrolyte material, and then dissolved in a solvent to form a film by a casting method. In this case, the electrolyte membrane can be reinforced with a polytetrafluoroethylene porous body, polytetrafluoroethylene fiber (fibril), or the like.

  The electrolyte material according to the present invention is used as a material constituting a membrane / electrode assembly for a polymer electrolyte fuel cell. The membrane / electrode assembly for a polymer electrolyte fuel cell comprises an anode and a cathode each having a catalyst layer containing a catalyst and an electrolyte material, and an electrolyte membrane disposed therebetween. A solid polymer type wherein at least one of the electrolyte material constituting the electrolyte membrane, the electrolyte material contained in the anode catalyst layer, and the electrolyte material contained in the cathode catalyst layer is produced by the method for producing an electrolyte material of the present invention. The fuel cell membrane / electrode assembly is preferable because it hardly deteriorates in the operating environment of the fuel cell. It is particularly preferable that the electrolyte material constituting the electrolyte membrane, the electrolyte material contained in the anode catalyst layer, and the electrolyte material contained in the cathode catalyst layer are all produced by the method for producing an electrolyte material of the present invention.

  The membrane / electrode assembly for a polymer electrolyte fuel cell can be obtained in the following manner, for example, according to a usual method. First, obtain a uniform dispersion composed of a liquid composition containing a conductive carbon black powder carrying platinum catalyst or platinum alloy catalyst fine particles and an electrolyte material, and form a gas diffusion electrode by one of the following methods: Thus, a membrane / electrode assembly is obtained.

  The first method is a method in which the dispersion liquid is applied to both surfaces of the electrolyte membrane, dried, and then both surfaces are adhered to each other with two carbon cloths or carbon paper. The second method is a method in which the dispersion liquid is applied onto two carbon cloths or carbon papers and then sandwiched from both surfaces of the electrolyte membrane so that the surface on which the dispersion liquid is applied is in close contact with the electrolyte membrane. It is. The third method is to apply the above dispersion on a separately prepared substrate film and dry it to form a catalyst layer, then transfer the electrode layer to both sides of the electrolyte membrane, and then add two sheets of carbon cloth or carbon paper This is a method of sticking both sides together. Here, the carbon cloth or the carbon paper has a function as a gas diffusion layer and a function as a current collector for diffusing the gas uniformly by the layer containing the catalyst.

  The obtained membrane / electrode assembly is formed with a groove serving as a passage for fuel gas or oxidant gas, sandwiched between separators, and incorporated into a cell to obtain a polymer electrolyte fuel cell. Hydrogen gas is supplied to the anode side of the membrane-electrode assembly, and oxygen or air is supplied to the cathode side.

In order to describe the present invention in more detail, examples and comparative examples are shown below.
_{T Q} of the polymer was measured using a Flow Tester CFT-500D (manufactured by Shimadzu Corporation).
The AR of the polymer was determined by immersing the polymer in a solution containing NaOH / water in a constant concentration as a solvent and hydrolyzing it, and back titrating the solution.

[Example 1]
97.74 g of CHClFCF ₂ CF ₂ Cl (hereinafter referred to as HCFC-225cb) is added to a 1 L stainless steel reactor having a stirrer, CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F (hereinafter referred to as “HFCFC-225cb”). , PSVE) was introduced, and the inside was deaerated. Thereafter, tetrafluoroethylene (hereinafter referred to as TFE) was charged at an internal temperature of 20 ° C. until the pressure became 0.33 MPaG (gauge pressure, the same applies hereinafter). Next, 3.3 g of a solution in which [CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COO] ₂ as an initiator was dissolved in HCFC-225cb at a concentration of 8% by mass was charged to initiate polymerization. did. As the polymerization progressed, the pressure decreased, so TFE was continuously added to keep the pressure constant. When the amount of TFE charged later became 50 g, the internal temperature was cooled to 10 ° C., unreacted TFE was discharged, and the pressure vessel was opened.

Methanol was put into the slurry-like contents in the pressure vessel and stirred to coagulate and settle the polymer. This polymer was dried at 80 ° C. for 10 hours to obtain 119.1 g of a TFE / PSVE copolymer as a white powder. No scale could be confirmed in the polymer obtained. _{T Q} is 304.5 ° C. the polymer, AR was 1.288 meq / g dry resin.

The obtained polymer was formed into a film at 300 ° C. and pressure-cooled to prepare a sheet having a thickness of about 0.1 mm. The sheet was then placed in an oven at 300 ° C. in air for 4 hours to oxidize the terminal —COF groups to —COOH groups. Further, the sheet was immersed in a 20% by mass aqueous solution of KOH and allowed to stand at 80 ° C. for 24 hours to hydrolyze —COOH groups to —COOK groups. When FT-IR measurement was performed on this film, the absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.12.

On the other hand, the obtained polymer was pressed at 300 ° C. to prepare a film having a thickness of 100 μm, which was immersed in a solution of KOH / H ₂ O / DMSO = 11/59/30 (mass ratio), and at 90 ° C. It was kept for 17 hours and hydrolyzed. Next, the temperature was returned to room temperature and washing with water was performed 3 times. Then, it was immersed in 3N hydrochloric acid at room temperature for 2 hours and washed with water a total of 3 times, and finally further washed with water 3 times. It was vacuum dried at 80 ° C., to obtain a film comprising a polymer having a -SO 3 _H group. 0.1 g of this film was cut out and immersed for 16 hours at 40 ° C. in 50 g of a Fenton reagent solution containing 3% hydrogen peroxide solution and 200 ppm of divalent iron ions. When the fluorine ion concentration in the solution was measured with an ion meter and the fluorine ion elution amount was calculated, it was 0.001% of the total fluorine amount in the immersed polymer.

[Example 2]
38.75 g of HCFC-225cb and 719.0 g of PSVE were added, TFE was charged until the pressure became 0.36 MPaG, and [CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) as an initiator _{COO] 2} 13.5 mass% concentration with HCFC-225cb was dissolved in a solution of 12.4g were charged, except that the TFE amount of post-charged was 13.5g and the polymerization in the same manner as in example 1, white 39.2 g of TFE / PSVE copolymer as a powder was obtained. No scale could be confirmed in the polymer obtained. T _Q of the polymer was unclear exceeds the measurable limit of the measuring device. AR was 1.150 meq / g dry resin.

A sheet was prepared from the obtained TFE / PSVE copolymer in the same manner as in Example 1, processed, and subjected to FT-IR measurement. The absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.05.
The fluorine ion elution amount measured and calculated in the same manner as in Example 1 was 0.003% of the total fluorine amount in the polymer.

[Example 3]
Using a 2.5 L stainless steel reactor having a stirrer, 212.91 g of HCFC-225cb and 1738.60 g of PSVE were charged, TFE was charged until the pressure became 0.21 MPaG, and [CF ₃ CF ₂ as an initiator was used. CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COO] ₂ was dissolved in HCFC-225cb at a concentration of 5.2% by mass, 17.865 g, and the amount of TFE after charging was set to 33.0 g. Except for this, polymerization was carried out in the same manner as in Example 1 to obtain 55.0 g of a TFE / PSVE copolymer as a white powder. No scale could be confirmed in the polymer obtained. _{T Q} is 229.3 ° C. the polymer, AR was 1.403 meq / g dry resin.

A sheet was prepared from the obtained TFE / PSVE copolymer in the same manner as in Example 1, processed, and subjected to FT-IR measurement. The absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.02.
The fluorine ion elution amount measured and calculated in the same manner as in Example 1 was 0.001% of the total fluorine amount in the polymer.

[Comparative Example 1]
77.65 g of HCFC-225cb and 147.62 g of PSVE were put into a 0.2 L stainless steel reactor having a stirrer, and deaeration was performed. Thereafter, TFE was charged at an internal temperature of 30 ° C. until the pressure reached 0.33 MPaG. Next, 4.92 g of a solution in which (CF ₃ CF ₂ CF ₂ COO) ₂ as an initiator was dissolved in HCFC-225cb at a concentration of 3% by mass was charged and polymerization was started. As the polymerization progressed, the pressure decreased, so TFE was continuously added to keep the pressure constant. When the amount of TFE to be charged later became 11.1 g, the internal temperature was cooled to 10 ° C., unreacted TFE was discharged, and the pressure vessel was opened.

Methanol was put into the slurry-like contents in the pressure vessel and stirred to coagulate and settle the polymer. This polymer was dried at 80 ° C. for 10 hours to obtain 15.9 g of a TFE / PSVE copolymer as a white powder. Scale was generated in the obtained polymer. T _Q of the polymer was unclear exceeds the measurable limit of the measuring device. AR was 0.896 meq / g dry resin.

Except that the obtained TFE / PSVE copolymer was formed into a film at 280 ° C., a sheet was prepared and processed in the same manner as in Example 1, and FT-IR measurement was performed. The absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 0.14.
Further, the fluorine ion elution amount measured and calculated in the same manner as in Example 1 was 0.007% of the total fluorine amount in the polymer.

[Comparative Example 2]
TFE / PSVE copolymer 105, a white powder, was prepared in the same manner as in Example 1 except that 232.9 mg of azoisobutyronitrile as a polymerization initiator was charged, the polymerization temperature was 70 ° C., and the polymerization pressure was 1.15 MPaG. 0.0 g was obtained.
_{T Q} is 220 ° C. The resulting polymer, AR was 1.100 meq / g dry resin.

A sheet was prepared, processed and subjected to FT-IR measurement in the same manner as in Example 1 except that the obtained TFE / PSVE copolymer was formed into a film at 250 ° C. The absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ was 1.45.
Further, the fluorine ion elution amount measured and calculated in the same manner as in Example 1 was 0.04% of the total fluorine amount in the polymer.

  Since the electrolyte material for a polymer electrolyte fuel cell obtained by the production method of the present invention has few unstable terminal groups contained in the molecule and is excellent in stability, the solid polymer constituted using this electrolyte material As a membrane-electrode assembly for a fuel cell, it can be suitably used for operation at high temperatures.

The figure which shows the infrared spectrum (wavenumber 2100-1600cm < ^-1 >) measured about the polymer obtained in Example 1. FIG. The figure which shows the infrared spectrum (wave number 2800-2000cm < ^-1 >) measured about the polymer obtained in Example 1. FIG.

Claims (4)

A method for producing an electrolyte material for a polymer electrolyte fuel cell comprising a polymer having a sulfonic acid group,
A perfluorocarbon monomer (A) having an —SO ₂ X group (X is a fluorine atom or a chlorine atom) and having an ethylenic double bond (which may contain an etheric oxygen atom); A radical polymerization initiator comprising a compound represented by the formula (2) or the formula (3) with at least one perfluorocarbon monomer (B) having at least one of carbon atoms, fluorine atoms and oxygen atoms. And a polymerization step of copolymerizing at a polymerization temperature of 0 to 35 ° C. to produce an electrolyte material for a polymer electrolyte fuel cell.
[F (CF ₂ ) _p COO] ₂ (2)
In the formula, p is an integer of 4 to 10.
_{[CF 3 CF 2 CF 2 O} (CF (CF 3) CF 2 O) q CF (CF 3) COO] 2 (3)
In the formula, q is an integer of 0 to 8. The said perfluorocarbon monomer (A) is a monomer represented by Formula (1), and the said perfluorocarbon monomer (B) is tetrafluoroethylene, The manufacture of the electrolyte material for polymer electrolyte fuel cells of Claim 1 Method.
_{CF 2 = CF (OCF 2 CFY} ) m O k (CF 2) n SO 2 F (1)
In the formula, Y represents a fluorine atom or a trifluoromethyl group, m represents an integer of 0 to 3, k represents 0 or 1, n represents an integer of 1 to 12, and (m + k)> 0. The solid polymer according to claim 1 or 2 , wherein the polymer having a sulfonic acid group of the polymer as a potassium salt type has an absorbance ratio I ₁₆₉₀ / I ₂₃₅₀ defined as follows in an infrared spectrum of 0.10 or less. Of manufacturing electrolyte material for fuel cell
I ₁₆₉₀ : maximum absorbance in the band of wave number 1690 ± 10 cm ⁻¹ ,
I ₂₃₅₀ : Maximum absorbance in the band of wave number 2350 ± 10 cm ⁻¹ . In a method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell comprising an anode and a cathode each having a catalyst layer containing a catalyst and an electrolyte material, and an electrolyte membrane disposed therebetween, the electrolyte membrane comprises: electrolyte material constituting, characterized in that at least one electrolyte material of the electrolyte material contained in the electrolyte material and the cathode catalyst layer included in the anode catalyst layer is prepared by a process according to any of claims 1 to 3 A method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell.

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