JP4765401B2 - Method for producing membrane for polymer electrolyte fuel cell and method for producing membrane electrode assembly for polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a method for producing an electrolyte membrane for a polymer electrolyte fuel cell and a method for producing a membrane electrode assembly for a polymer electrolyte fuel cell, which have a high initial output voltage and can obtain a high output voltage over a long period of time .

  A fuel cell is a cell that directly converts the reaction energy of a gas that is a raw material into electric energy. In a hydrogen / oxygen fuel cell, the reaction product is only water in principle and has little influence on the global environment. In particular, polymer electrolyte fuel cells that use solid polymer membranes as electrolytes have been developed for polymer electrolyte membranes with high ionic conductivity, and can operate at room temperature to obtain high output density. With increasing social demand for environmental problems, there is great expectation as a power source for mobile vehicles for electric vehicles and small cogeneration systems.

  In a polymer electrolyte fuel cell, a proton conductive ion exchange membrane is usually used as a solid polymer electrolyte, and an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group is particularly excellent in basic characteristics. In a polymer electrolyte fuel cell, gas diffusible electrode layers are arranged on both surfaces of an ion exchange membrane, and a gas containing hydrogen as a fuel and a gas containing oxygen (such as air) as an oxidant are respectively supplied to an anode and a cathode. To generate electricity.

Since the reduction reaction of oxygen at the cathode of the polymer electrolyte fuel cell proceeds via hydrogen peroxide (H ₂ O ₂ ), hydrogen peroxide or peroxide radicals generated in the catalyst layer There is concern about the possibility of causing deterioration of the electrolyte membrane. Moreover, since oxygen molecules permeate through the membrane from the cathode to the anode, there is a concern that hydrogen peroxide or peroxide radicals may be similarly generated. In particular, when a hydrocarbon-based membrane is used as a solid polymer electrolyte membrane, the stability against radicals is poor, which has been a serious problem in long-term operation.

  For example, the polymer electrolyte fuel cell was first put into practical use when it was used as a power source for a Gemini spacecraft in the United States. At this time, a membrane obtained by sulfonating a styrene-divinylbenzene polymer was used as an electrolyte membrane. However, there was a problem with durability over a long period of time. On the other hand, an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group is known as a polymer that is remarkably excellent in radical stability compared to an electrolyte membrane made of a hydrocarbon-based polymer. In recent years, polymer electrolyte fuel cells using ion-exchange membranes made of these perfluorocarbon polymers are expected to be used as power sources for automobiles and residential markets, etc. . In these applications, since operation with particularly high efficiency is required, operation at a higher voltage is desired and at the same time cost reduction is desired. In addition, from the viewpoint of the efficiency of the entire fuel cell system, operation with low or no humidification is often required.

  However, even in a fuel cell using an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group, the stability is very high when operated under high humidification, but in operating conditions under low or no humidification. It has been reported that the voltage drop is large (see Non-Patent Document 1). That is, under operating conditions with low or no humidification, it is considered that deterioration of the electrolyte membrane proceeds due to hydrogen peroxide or peroxide radicals even in an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group. .

  As a method for suppressing deterioration of an electrolyte membrane composed of an ion exchange membrane made of a perfluorocarbon polymer having a cation exchange group, a method of containing cerium phosphate in an electrolyte membrane or an electrode has been reported (Patent Document 1). reference). As a method for producing an electrolyte membrane containing cerium phosphate, an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group is immersed in an aqueous solution of cerium nitrate, and then contacted with an aqueous solution of phosphoric acid to precipitate cerium phosphate. A method has been reported (see Patent Document 1). In addition, as a method for producing an electrode containing cerium phosphate, a method of forming an electrode by mixing cerium phosphate powder into a solution dispersion of a perfluorocarbon polymer having a sulfonic acid group and coating the solution is reported. (See Patent Document 1).

JP-A-2005-71760 (Claim 2, page 4, lines 19 to 46, page 9, line 20 to page 10, line 7, Example 1 and Example 11) Summary of the 2000 report on research and development results on polymer electrolyte fuel cells sponsored by the New Energy and Industrial Technology Development Organization, page 56, lines 16-24

  A method for producing an electrolyte by immersing an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group in an aqueous solution of cerium nitrate, then contacting the aqueous solution with phosphoric acid, and precipitating cerium phosphate on the membrane includes the following: There was a problem.

  First, it is difficult to deposit cerium phosphate uniformly and uniformly on the film surface, and the deposited cerium phosphate is deposited on the surface of a few microns thick and is easily removed mechanically. End up. Furthermore, when a film swollen in an aqueous solution is dried, deformation occurs, and it is difficult to process the film stably. In addition, in this method, most of the sulfonic acid groups are once replaced with cerium ions, and then hydrolyzed with phosphoric acid to be regenerated into sulfonic acid groups. It was difficult to control the amount of cerium.

  In the method of mixing a cerium phosphate powder with a dispersion of a perfluorocarbon polymer having a sulfonic acid group and coating the liquid to form an electrode, the cerium phosphate powder is dispersed in a perfluorocarbon polymer dispersion. To disperse finely and uniformly, a special dispersion technique is required. Furthermore, although a method for dispersing high-purity cerium phosphate powder has been proposed, industrial production of high-purity cerium phosphate powder requires a large amount of phosphoric acid waste water and washing water.

  The present invention relates to a method for producing a membrane for a polymer electrolyte fuel cell or a membrane electrode assembly for a polymer electrolyte fuel cell that has high power generation performance and is capable of stable power generation over a long period of time. An object of the present invention is to provide a production method capable of easily and accurately obtaining an electrolyte membrane or a catalyst layer containing cerium phosphate having a uniform particle size.

  The present invention relates to a method for producing an electrolyte membrane for a polymer electrolyte fuel cell comprising a cation exchange membrane comprising a polymer compound having a cation exchange group, and containing cerium phosphate, the method comprising the steps of: After adding cerium carbonate to the molecular compound dispersion and ion-exchanging a part of the cation exchange groups with cerium ions, phosphoric acid or a solution containing phosphoric acid is added to the dispersion, A method for producing an electrolyte membrane for a polymer electrolyte fuel cell is provided, in which cerium phosphate is formed and cast using the obtained liquid composition to produce an electrolyte membrane.

  The present invention also relates to a membrane / electrode assembly for a polymer electrolyte fuel cell comprising an anode and a cathode having a catalyst layer containing a catalyst and an ion exchange resin, and an electrolyte membrane disposed between the anode and the cathode. A method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell, wherein the electrolyte membrane is produced by the method described above.

  Furthermore, the present invention provides a membrane electrode assembly for a polymer electrolyte fuel cell, comprising an anode and a cathode having a catalyst layer containing a catalyst and an ion exchange resin, and an electrolyte membrane disposed between the anode and the cathode. A method for producing a dispersion of a polymer compound having a cation exchange group, wherein cerium carbonate is added to ion-exchange a part of the cation exchange group with cerium ion, and then phosphoric acid or phosphoric acid is contained. A solution is added to the dispersion to form cerium phosphate in the dispersion, and the catalyst is dispersed in the obtained liquid composition and applied to produce at least one of the cathode and the anode. A method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell is provided.

  By the production method of the present invention, an electrolyte membrane in which cerium phosphate is uniformly blended in the membrane can be obtained easily and accurately. In the production method of the present invention, the cerium carbonate and phosphoric acid concentrations can be appropriately adjusted and added according to the ion exchange capacity of the polymer compound having a cation exchange group and the polymer concentration of the dispersion, The cerium phosphate content of the electrolyte membrane obtained by casting can be controlled. Further, an electrolyte membrane having a uniform thickness can be produced by adjusting the concentration of liquid and the amount of coating at the time of cast coating. Similarly, a catalyst layer in which cerium phosphate is uniformly blended can be formed.

  Since the electrolyte membrane or catalyst layer obtained by the production method of the present invention has excellent resistance to hydrogen peroxide or peroxide radicals, a solid electrode comprising the membrane electrode assembly having the electrolyte membrane or catalyst layer of the present invention is provided. Molecular fuel cells are excellent in durability and can stably generate power over a long period of time.

  In the present invention, the cation exchange group of the polymer compound having a cation exchange group is not particularly limited, and examples thereof include a sulfonic acid group, a carboxylic acid group, a sulfonimide group, a phosphonic acid group, and a ketoimide group. In particular, a sulfonic acid group having strong acidity and high chemical stability is preferred. Hereinafter, the polymer compound having a sulfonic acid group will be described as an example.

  Examples of the dispersion medium of the dispersion liquid of the polymer compound having a sulfonic acid group include alcohols and water. In this specification, the dispersion of a polymer compound having a sulfonic acid group includes a solution of the polymer compound having a sulfonic acid group.

In the present invention, cerium carbonate is added and dissolved in a dispersion of a polymer compound having a sulfonic acid group. As cerium carbonate, Ce ₂ (CO ₃ ) ₃ · 8H ₂ O is preferable. When cerium carbonate is added to the dispersion, cerium is present in an ion state in the dispersion, and at least a part of the sulfonic acid group (—SO ₃ H) of the polymer compound is ion-exchanged by cerium ions. It is done. When Ce ₂ (CO ₃ ) ₃ · 8H ₂ O is used, trivalent cerium ions are generated. Many carbonates are generally poorly soluble in water. However, in the case of cerium carbonate, carbon dioxide gas is easily generated by adding water to a dispersion of a polymer compound having a sulfonic acid group. It dissolves as it is generated and ion exchanges part of the sulfonic acid group. When a predetermined amount of phosphoric acid is subsequently added, ion exchange is easily performed again to form a cerium phosphate crystal and stably disperse. If the addition amount of phosphoric acid is in an appropriate range, this solution is applied by a casting method, and the solvent is removed by drying to obtain an electrolyte membrane. In addition to the sulfonic acid group that is a polymer functional group in the electrolyte membrane, Therefore, it is not necessary to wash the excess anion with water. From the viewpoint of production of such a membrane, carbonate is preferable.

  If water is not contained in the dispersion, it may take time for dissolution of cerium carbonate. Therefore, it is preferable to contain water in the dispersion. The amount of water to be contained in the dispersion is appropriately set depending on the ion exchange capacity and concentration of the polymer compound having a sulfonic acid group and the exchange rate with cerium or manganese to be added.

  The solid content concentration of the dispersion of the polymer compound having a sulfonic acid group is not particularly limited, but the polymer compound is 5 to the total mass of the dispersion from the viewpoint that normal cast coating is possible in the subsequent step. It is preferably ˜50%, more preferably 10 to 35%.

  It is preferable to add an amount of cerium carbonate corresponding to 0.5 to 80 equivalents of cerium ion with respect to 100 equivalents of the sulfonic acid group of the polymer compound. The equivalent of cerium ion to 100 equivalent of sulfonic acid group is hereinafter referred to as “substitution rate”. The substitution rate is more preferably 1 to 50 equivalents. If the substitution rate is smaller than this range, sufficient stability against hydrogen peroxide or peroxide radicals may not be ensured. On the other hand, if the substitution rate is larger than this range, aggregates of polymer compounds may be formed.

  Moreover, it is preferable to add the phosphoric acid of the quantity equivalent to 0.5-4 equivalent of phosphate ion with respect to 1 equivalent of cerium ions. More preferably, it is 1-3 equivalents with respect to 1 equivalent of cerium ions. If the ratio is lower than this range, cerium phosphate may not be sufficiently formed. On the other hand, if the ratio is higher than this range, excess phosphoric acid remains, and the catalyst may be poisoned after the membrane / electrode assembly is formed.

The cerium phosphate (cerium (III) phosphate, CePO ₄ ) or cerium phosphate (cerium (IV) phosphate, Ce ₃ (PO ₄ ) ₄ ) formed in the film may be anhydrous, You may have crystal water or hydration water. In the present invention, the effect can be sufficiently obtained regardless of the form of cerium phosphate.

  The solid content concentration of the dispersion to be cast is not particularly limited. The concentration and viscosity can be adjusted so that ordinary cast coating is possible, but from this point of view, the solid content concentration is 5 to 50%, particularly 10 to 35% in terms of mass ratio to the total mass of the liquid composition. It is preferable.

  Since cerium phosphate generally has low electrical conductivity, current shielding occurs depending on the amount added to the film. Therefore, the preferred ratio of cerium phosphate contained in the electrolyte membrane obtained by the production method of the present invention is preferably 0.3 to 20% (mass ratio) of the total mass of the electrolyte membrane, more preferably 0. .4 to 10%, more preferably 0.5 to 5%.

  If the content of cerium phosphate in the film is less than this range, sufficient stability against hydrogen peroxide or peroxide radicals may not be ensured. On the other hand, if the content is larger than this range, current shielding occurs as described above, so that the membrane resistance increases and the power generation characteristics may be deteriorated.

  The electrolyte membrane can also be adjusted to contain cerium phosphate non-uniformly. For example, it is a cation exchange membrane (laminated membrane) composed of two or more layers, and at least one of the layers contains cerium phosphate, that is, cerium phosphate is unevenly distributed in the thickness direction. May be included. Therefore, when it is necessary to increase the durability against hydrogen peroxide or peroxide radicals particularly on the anode side, only the layer closest to the anode can be a layer made of an ion exchange membrane containing cerium phosphate.

  In addition, when the electrolyte membrane obtained by the present invention is a laminated film, the ratio of cerium phosphate to the entire electrolyte membrane should be within the above range, and the cerium phosphate containing layer of cerium phosphate itself contains The rate may be higher than the above range.

In the present invention, the cation exchange membrane constituting the electrolyte membrane is preferably made of a polymer compound having a sulfonic acid group. The polymer compound having a sulfonic acid group is not particularly limited, but the ion exchange capacity is preferably 0.5 to 3.0 meq / g dry resin, particularly 0.7 to 2.5 meq / g. A dry resin is preferred. From the viewpoint of durability, the polymer compound is preferably a fluorine-containing polymer, and more preferably a perfluorocarbon polymer having a sulfonic acid group (which may contain an etheric oxygen atom). Is not particularly restricted but includes perfluorocarbon polymer _{but, CF 2 = CF- (OCF 2} CFX) m -O p - (CF 2) perfluoro compound represented by n -SO ₃ H (m is 0-3 N represents an integer of 1 to 12, p represents 0 or 1, X represents a fluorine atom or a trifluoromethyl group, and a polymer unit based on tetrafluoroethylene. It is preferable that it is a copolymer containing.

  When the preferable example of the said perfluoro compound is shown more concretely, the compound represented by following formula (i)-(iii) will be mentioned. However, in the following formula, q is an integer of 1 to 8, r is an integer of 1 to 8, and t is an integer of 1 to 3.

  When using the perfluorocarbon polymer which has a sulfonic acid group, you may use what the terminal of the polymer was fluorinated by fluorination after superposition | polymerization. When the terminal of the polymer is fluorinated, the durability against hydrogen peroxide and peroxide radicals is further improved, so that the durability is improved.

  Further, as the polymer compound having a sulfonic acid group, those other than the perfluorocarbon polymer having a sulfonic acid group can be used, for example, having an aromatic ring in the main chain of the polymer or in the main chain and the side chain A polymer compound having a structure in which a sulfonic acid group is introduced into the aromatic ring and having an ion exchange capacity of 0.8 to 3.0 meq / g dry resin can be preferably used. Specifically, for example, the following polymer compounds can be used.

  Sulfonated polyarylene, sulfonated polybenzoxazole, sulfonated polybenzothiazole, sulfonated polybenzimidazole, sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polyphenylenesulfone, sulfonated polyphenyleneoxide, Sulfonated polyphenylene sulfoxide, sulfonated polyphenylene sulfide, sulfonated polyphenylene sulfide sulfone, sulfonated polyether ketone, sulfonated polyether ether ketone, sulfonated polyether ketone ketone, sulfonated polyimide and the like.

The perfluorocarbon polymer having a sulfonic acid group can be obtained by copolymerizing a monomer having a corresponding fluorosulfonyl group (—SO ₂ F group), followed by hydrolysis and acidification treatment.
A polymer compound having a sulfonimide group (—SO ₂ NHSO ₂ R ^f group) is a monomer obtained by converting a —SO ₂ F group of a monomer having a corresponding fluorosulfonyl group (—SO ₂ F group) into a sulfonimide group. It is copolymerized, or corresponding to synthesize a polymer having -SO 2 _F groups, is obtained by converting the -SO 2 _F groups of the polymer. The —SO ₂ F group is converted into a salt-type sulfonimide group (—SO ₂ NMSO ₂ R by reaction with R ^f SO ₂ NHM (R ^f is a perfluoroalkyl group, M is an alkali metal or a quaternary ammonium group). ^f group) and can be converted into an acid form by treatment with an acid such as sulfuric acid, nitric acid or hydrochloric acid.

As a polymer compound having a phosphonic acid group, a copolymer containing a repeating unit based on tetrafluoroethylene and a repeating unit based on CF ₂ ═CFO (CF ₂ ) ₃ PO (OH) ₂ is a preferable example. Can be mentioned.

  The electrolyte membrane obtained by the present invention may be a membrane made of only a polymer compound having a cation exchange group, including cerium phosphate, but may contain other components. For example, a film reinforced with fibers such as polytetrafluoroethylene (hereinafter referred to as PTFE) or other resin such as perfluoroalkyl ether, a woven fabric, a nonwoven fabric, a porous body or the like is used for the liquid composition of the present invention. It can also be applied to the method of film formation.

The polymer electrolyte fuel cell having a membrane electrode assembly obtained by the present invention has the following configuration, for example. That is, a membrane / electrode assembly in which an anode and a cathode having a catalyst layer containing a catalyst and an ion exchange resin are disposed on both surfaces of the electrolyte membrane is provided. The anode and cathode of the membrane electrode assembly are preferably provided with a gas diffusion layer made of carbon cloth, carbon paper or the like outside the catalyst layer (opposite the membrane). Grooves serving as fuel gas or oxidant gas passages are formed on both surfaces of the membrane electrode assembly to form a stack in which a plurality of membrane electrode assemblies are stacked via the separator. Hydrogen gas is supplied, and oxygen or air is supplied to the cathode side. A reaction of H ₂ → 2H ⁺ + 2e ⁻ occurs at the anode, and a reaction of 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O occurs at the cathode, and chemical energy is converted into electric energy.
The membrane electrode assembly of the present invention can also be used in a direct methanol fuel cell that supplies methanol instead of fuel gas to the anode side.

  The membrane / electrode assembly is obtained in the following manner, for example, according to a normal method. First, a conductive carbon black powder carrying platinum catalyst or platinum alloy catalyst fine particles and an ion exchange resin solution are mixed to obtain a uniform coating solution for forming a catalyst layer (hereinafter referred to as coating solution). For example, a gas diffusion electrode is formed by any of the following methods to obtain a membrane electrode assembly.

  The first method is a method in which the coating 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 to sandwich the coating liquid from both sides of the electrolyte membrane so that the surface to which the coating liquid is applied adheres to the electrolyte membrane after applying and drying the coating solution on two carbon cloths or carbon paper. It is a method to rub 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. In addition, the above coating solution is applied to a separately prepared substrate to produce a catalyst layer, and after joining the electrolyte membrane by a method such as transfer, the substrate is peeled off and sandwiched between the gas diffusion layers. it can.

  The ion exchange resin contained in the catalyst layer is not particularly limited, but is preferably a polymer compound having a cation exchange group constituting the electrolyte membrane in the present invention, and particularly a perfluorocarbon polymer having a sulfonic acid group. It is preferable. The catalyst layer may contain cerium phosphate as in the electrolyte membrane according to the present invention. In such a catalyst layer, since the decomposition of the ion exchange resin is effectively suppressed, the polymer electrolyte fuel cell is further provided with durability. Further, an ion exchange resin not containing cerium phosphate can be used as the electrolyte membrane, and only the catalyst layer can contain cerium phosphate.

  When cerium phosphate is contained in the catalyst layer, cerium carbonate is added to the dispersion of the polymer compound having a cation exchange group, and a part of the cation exchange group is ion-exchanged with cerium ion, and then phosphoric acid is added. Alternatively, a solution containing phosphoric acid is added to the dispersion, cerium phosphate is formed in the dispersion, and a catalyst obtained by dispersing the catalyst in the obtained liquid composition is used as a coating solution in the same manner as described above. A catalyst layer may be formed. In this case, only one of the cathode and the anode can be prepared using the coating solution containing the cerium phosphate, or both the cathode and the anode can be prepared using the coating solution containing the cerium phosphate. You can also

The addition amount of cerium carbonate and the addition amount of phosphoric acid are not particularly limited, but a range similar to the numerical range in the method for producing an electrolyte membrane of the present invention can be preferably employed.
A preferred ratio of cerium phosphate contained in the catalyst layer is preferably 0.1 to 10% (mass ratio), and more preferably 0.3 to 5%. If the content of cerium phosphate in the catalyst layer is less than this range, the above-described effect of cerium phosphate may not be sufficiently obtained, and if the content is more than this range, the resistance may increase. There is.

  Hereinafter, the present invention will be specifically described using Examples and Comparative Examples, but the present invention is not limited thereto. The physical properties of the electrolyte membrane were measured and tested as follows.

<Conductivity>
Electrochimica. Acta. , 43, 24, 3749-3754 (1998), the conductivity at 80 ° C. and 95% RH at an AC resistance of 10 kHz using a four-terminal platinum electrode was measured.

<Fenton test>
The electrolyte membrane whose mass was measured in a dry nitrogen atmosphere was placed in an aqueous solution containing 3% hydrogen peroxide and ferrous sulfate (FeSO ₄ .7H ₂ O) corresponding to 200 ppm of Fe, and 90 ° C., 16 A time immersion test was performed. The fluorine ion concentration in the aqueous solution after the test was measured with a fluorine ion electrode (CE5101-SR, manufactured by Toko Chemical Laboratory Co., Ltd.). The fluorine ion production amount per mass of the membrane was calculated.

[Example 1 (Example)]
In a 300 ml glass round bottom flask, CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H copolymer (ion exchange capacity 1.1 meq / g dry resin) 100 g of a dispersion liquid (hereinafter referred to as “dispersion liquid A”) having a solid content concentration of 30 mass% was prepared by dispersing the above in a mixed liquid of ethanol and water (water: ethanol = 40: 60). To this dispersion A, 1.0 g of cerium carbonate (Ce ₂ (CO ₃ ) ₃ · 8H ₂ O) was added, and the mixture was stirred with a stirrer at room temperature for 4 hours. As a result, a liquid composition in which 30% of the sulfonic acid group of CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H copolymer was ion-exchanged with Ce ³⁺ was obtained. It was.

Next, 3.3 g of a 1 mol / L phosphoric acid (H ₃ PO ₄ ) aqueous solution (PO ₄ ³⁻ / Ce ³⁺ = 1/1 molar ratio) was added dropwise to the liquid composition with stirring, and further at room temperature for 2 hours. Stirring was continued. Precipitation of fine white particles was observed from the start of dropping, and finally, a white liquid composition (hereinafter referred to as liquid composition B) that was uniformly and stably dispersed was obtained. As a result of identifying the white particles by X-ray diffraction, it was confirmed that the particles were cerium phosphate. When the particle size distribution of the liquid composition B was measured with Microtrac (manufactured by Nikkiso Co., Ltd., solvent: ethanol / water = 1/1), the average particle size was 0.8 μm (standard deviation 0.2). It was. Even when the liquid composition B was allowed to stand at room temperature for 1 week, there was no change in the particle size distribution.

  Next, the liquid composition B was coated on a sheet (trade name: Aflex 100N, manufactured by Asahi Glass Co., Ltd., hereinafter simply referred to as ETFE sheet) made of a 100 μm ethylene / tetrafluoroethylene copolymer with a die coater. The film was cast and pre-dried at 80 ° C. for 10 minutes, then dried at 120 ° C. for 10 minutes, and further annealed at 150 ° C. for 30 minutes to obtain a solid polymer electrolyte membrane having a thickness of 50 μm. When white particles present in the film were identified by X-ray diffraction, it was confirmed to be ceric phosphate. The polymer electrolyte membrane was dried in nitrogen, then immersed in concentrated nitric acid (14 mol / L), and a solution in which all of cerium phosphate was dissolved was measured by ICP spectroscopic analysis. From the result, it was found that 2.5% of cerium phosphate was contained with respect to the total mass of the film. The conductivity of the obtained film was 0.20 S / cm. Further, the fluorine ion production amount per mass of the film in the Fenton test was 0.002%.

Next, 5.1 g of distilled water was added to 1.0 g of catalyst powder (manufactured by N.E. Chemcat Co.) supported by platinum so that 50% of the total mass of the catalyst was contained in a carbon support (specific surface area 800 m ² / g). Mixed. CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H copolymer (ion exchange capacity 1.1 meq / g dry resin) is dispersed in ethanol in this mixed solution. 5.6 g of a liquid having a solid content concentration of 9% by mass was mixed. This mixture was mixed and pulverized using a homogenizer (trade name: Polytron, manufactured by Kinematica) to prepare a coating solution for forming a catalyst layer.

This coating solution was applied onto a polypropylene base film with a bar coater, and then dried in an oven at 80 ° C. for 30 minutes to produce a catalyst layer. In addition, when the amount of platinum per unit area contained in the catalyst layer was calculated by measuring the mass of only the base film before formation of the catalyst layer and the mass of the base film after formation of the catalyst layer, 0.5 mg / Cm ² .

Next, from the electrolyte membrane containing cerium phosphate described above, a membrane having a size of 5 cm × 5 cm is cut out, and catalyst layers formed on the base film are disposed on both sides of the membrane, respectively, and a hot press method is performed. Was transferred to obtain a membrane catalyst layer assembly in which the anode catalyst layer and the cathode catalyst layer were bonded to both surfaces of the ion exchange membrane, respectively. The electrode area was 16 cm ² .

This membrane / catalyst layer assembly is sandwiched between two gas diffusion layers made of carbon cloth with a thickness of 350 μm to produce a membrane / electrode assembly, a power generation cell is completed, and an open circuit test (OCV test) is performed as an acceleration test. Went. In the test, hydrogen (utilization rate 70%) and air (utilization rate 40%) corresponding to a current density of 0.2 A / cm ² were supplied to the anode and the cathode, respectively, the cell temperature was 90 ° C., and the anode gas. The dew point was 60 ° C., the dew point of the cathode gas was 60 ° C., 100 hours of operation was performed in an open circuit state without power generation, and the voltage change during that time was measured. Also, before and after the test, hydrogen was supplied to the anode and nitrogen was supplied to the cathode, and the amount of hydrogen gas leaking from the anode to the cathode through the membrane was analyzed to examine the degree of membrane degradation. The results are shown in Table 1.

[Example 2 (comparative example)]
As the solid polymer electrolyte membrane, the same commercially available ion exchange membrane as that used in Example 1 was used without any treatment. The conductivity of the film was 0.29 S / cm. Further, the fluorine ion production amount per mass of the film in the Fenton test was 0.037%.
Next, a membrane / electrode assembly was obtained using this membrane in the same manner as in Example 1. When this membrane electrode assembly was evaluated in the same manner as in Example 1, the results shown in Table 1 were obtained.

[Examples 3 to 6]
The same method as in Example 1 except that in Example 1, the ion exchange capacity of the polymer compound having a sulfonic acid group, the substitution rate with Ce ³⁺ , and the addition amount of phosphoric acid were changed to various combinations shown in Table 2. Thus, an electrolyte membrane was obtained, and conductivity measurement and Fenton test were performed. The results are shown in Table 2 together with the results of Example 2.
It turns out that the production | generation of a fluorine ion is suppressed by ion-substituting with cerium, and also using cerium phosphate salt. When the ion exchange is performed with cerium, the conductivity decreases, but recovery is observed by addition of phosphoric acid. Thus, in the manufacturing method of this invention, adjustment of content of the cerium phosphate in a film | membrane can be controlled easily.

[Example 7 (comparative example)]
As a solid polymer electrolyte membrane, an ion exchange membrane (trade name: Flemion, manufactured by Asahi Glass Co., Ltd., ion exchange capacity 1.1 milliequivalent / g dry resin) made of a perfluorocarbon polymer having a sulfonic acid group was used. A size of 7.5 cm × 7.5 cm was used. The total weight of the film was allowed to stand in dry nitrogen for 16 hours and then measured in dry nitrogen to find 0.56 g. The amount of sulfonic acid groups in this membrane is determined by the following formula.
0.56 × 1.1 (1.1 milliequivalent / g dry resin) = 0.62 (milliequivalent).

Next, this film was immersed in an aqueous solution in which cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O) was dissolved so that the cerium ion concentration was 0.05 wt%, and heated at 90 ° C. for 2 hours. Next, the membrane was immersed in a 0.1 mol / L phosphoric acid (H ₃ PO ₄ ) aqueous solution and hydrolyzed at 90 ° C. for 1 hour. The film gradually became white and cerium phosphate was deposited on the film surface. Furthermore, after washing several times with ion-exchanged water, it was heated in ion-exchanged water at 90 ° C. for 30 minutes to remove excess H ₃ PO ₄ . The membrane was again left in dry nitrogen for 16 hours and then measured in dry nitrogen. The change in membrane weight was 5.6%.

The cerium phosphate deposited on the surface layer had mottled and uneven parts, and some parts were lost when wiped with water. When the conductivity of the film was measured, it was as low as 0.05 S / cm. This is the same value even when the surface layer of cerium phosphate is removed, and it is considered that a large amount of cerium ions taken in the film remain, that is, hydrolysis by H ₃ PO ₄ was insufficient.

[Example 8 (comparative example)]
Dissolve 10.0 g of cerium nitrate (Ce (NO ₃ ) ₃ · 6H ₂ O) in 500 mL of distilled water, add 100 g of 1 mol / L phosphoric acid (H ₃ PO ₄ ) aqueous solution dropwise, and add white precipitate Got. This was washed with water, repeatedly washed with water and filtered until the pH reached 7, and dried at 80 ° C. As a result of identifying this crystal by X-ray diffraction, it was confirmed that it was ceric phosphate.

  Next, a 300 ml glass round bottom flask was charged with 100 g of dispersion A and 0.75 g of the first cerium phosphate obtained above, and stirred for 8 hours at room temperature with a magnetic stirrer to obtain cerium phosphate. A liquid composition in which was dispersed was obtained. When the particle size distribution of the liquid composition was measured with Microtrac (solvent: ethanol / water = 1/1), the average particle size was 10 μm (standard deviation 0.2). When this solution was allowed to stand for 1 week, partial sedimentation was observed. When the particle size distribution was measured by stirring again, the average particle size was 13 μm.

Next, this composition was coated on a 100 μm ETFE sheet with a die coater to form a cast film, pre-dried at 80 ° C. for 10 minutes, dried at 120 ° C. for 10 minutes, and further annealed at 150 ° C. for 30 minutes. As a result, a polymer electrolyte membrane having a film thickness of 50 μm and a cerium phosphate content of 2.5% of the total mass of the membrane was obtained.
The obtained film gave a substantially uniform appearance, but spots and spots were partially formed. The conductivity of the relatively uniform region of the film was 0.21 S / cm.

Example 9 (Example)
Distilled water (5.1 g) was mixed with 1.0 g of a catalyst powder (manufactured by NP Chemcat) on which platinum was supported so that 50% of the total mass of the catalyst was contained in a carbon support (specific surface area 800 m ² / g). The liquid mixture B1.3g produced in Example 1 was mixed with this liquid mixture. This mixture was mixed and pulverized using a homogenizer (trade name: Polytron, manufactured by Kinematica) to prepare a catalyst layer forming coating solution.

This coating solution was applied onto a polypropylene base film with a bar coater, and then dried in an oven at 80 ° C. for 30 minutes to produce a catalyst layer. In addition, when the amount of platinum per unit area contained in the catalyst layer was calculated by measuring the mass of only the base film before formation of the catalyst layer and the mass of the base film after formation of the catalyst layer, 0.5 mg / Cm ² .

Next, as a solid polymer electrolyte membrane, an ion exchange membrane having a thickness of 50 μm made of a perfluorocarbon polymer having a sulfonic acid group (trade name: Flemion, manufactured by Asahi Glass Co., Ltd., ion exchange capacity 1.1 meq / g dry resin) ), And a catalyst layer formed on a base film is disposed on both sides of the membrane, and transferred by a hot press method to be an anode catalyst layer and a cathode catalyst layer. A membrane-catalyst layer assembly was obtained by bonding to the both surfaces of the ion exchange membrane. The electrode area was 16 cm ² . When the same evaluation as in Example 1 was performed, the results shown in Table 3 were obtained.

The electrolyte membrane or electrode obtained by the present invention is extremely excellent in durability against hydrogen peroxide or peroxide radicals generated by power generation of a fuel cell. Therefore, the polymer electrolyte fuel cell including the membrane electrode assembly having the electrolyte membrane or electrode has long-term durability even in low humidification power generation.

Claims (10)

A method for producing an electrolyte membrane for a polymer electrolyte fuel cell comprising a cation exchange membrane comprising a polymer compound having a cation exchange group and containing cerium phosphate,
After adding cerium carbonate to a dispersion of a polymer compound having a cation exchange group and ion-exchanging a part of the cation exchange group with cerium ion, phosphoric acid or a solution containing phosphoric acid is added to the dispersion. Then, cerium phosphate is formed in the dispersion, and the obtained liquid composition is cast to form an electrolyte membrane, thereby producing an electrolyte membrane for a polymer electrolyte fuel cell, Method.   2. The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to claim 1, wherein the cation exchange group is a sulfonic acid group.   The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to claim 2, wherein the polymer compound having a sulfonic acid group is dispersed in a liquid containing water.   The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to claim 2 or 3, wherein an amount of cerium carbonate corresponding to 0.5 to 80 equivalents of cerium ions is added to 100 equivalents of the sulfonic acid group of the polymer compound. .   The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to any one of claims 2 to 4, wherein an amount of phosphoric acid corresponding to 0.5 to 4 equivalents of phosphate ions is added to 1 equivalent of cerium ion.   The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to any one of claims 2 to 5, wherein cerium phosphate is contained in an amount of 0.3 to 20% of the total mass of the electrolyte membrane.   The electrolyte membrane for a polymer electrolyte fuel cell according to any one of claims 2 to 6, wherein the polymer compound comprises a perfluorocarbon polymer having a sulfonic acid group (which may contain an etheric oxygen atom). Manufacturing method. The polymer compound includes a perfluoro compound represented by a repeating unit based on tetrafluoroethylene and CF ₂ ═CF— (OCF ₂ CFX) _m —O _p — (CF ₂ ) _n —SO ₃ H (X is a fluorine atom) Or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer of 1 to 12, and p is 0 or 1. Item 8. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to any one of Items 2 to 7. A method for producing a membrane electrode assembly for a polymer electrolyte fuel cell, comprising an anode and a cathode having a catalyst layer containing a catalyst and an ion exchange resin, and an electrolyte membrane disposed between the anode and the cathode. ,
A method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell, wherein the electrolyte membrane is produced by the method according to claim 1. A method for producing a membrane electrode assembly for a polymer electrolyte fuel cell, comprising an anode and a cathode having a catalyst layer containing a catalyst and an ion exchange resin, and an electrolyte membrane disposed between the anode and the cathode. ,
After adding cerium carbonate to a dispersion of a polymer compound having a cation exchange group and ion-exchanging a part of the cation exchange group with cerium ion, phosphoric acid or a solution containing phosphoric acid is added to the dispersion. And forming at least one of the cathode and the anode by forming cerium phosphate in the dispersion, dispersing the catalyst in the obtained liquid composition, and coating the solid. A method for producing a membrane electrode assembly for a polymer fuel cell.