JP2006260811A - Electrolyte membrane for solid polymer fuel cell, manufacturing method thereof, and membrane electrode assembly for solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane for a solid polymer fuel cell capable of generating power at high energy efficiency with high power generating performance irrespective of dew points of supplied gas, and capable of generating stable power over a long period of time. <P>SOLUTION: An electrolyte membrane comprises a cation exchange membrane made of a polymer compound having a sulfonic acid group, contains at least one type selected from a group comprising cerium and manganese ions by 0.3 mole percentage or higher of -SO<SB>3</SB><SP>-</SP>group in the cation exchange membrane and a slightly soluble cerium compound, and is used as the electrolyte membrane for solid polymer fuel cells. In the cation exchange membrane, the slightly soluble cerium compound is preferably contained by 0.3-30% of the total mass of the cation exchange membrane, and perfluorocarbon polymer having a sulfonic acid group is used as the polymer compound. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrolyte membrane for a polymer electrolyte fuel cell that has 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. As a technique for improving such a problem, a method of adding a transition metal oxide or a compound having a phenolic hydroxyl group capable of catalytic decomposition of hydrogen peroxide into a polymer electrolyte membrane (see Patent Document 1), a polymer electrolyte, A method is known in which catalytic metal particles are supported in a membrane and hydrogen peroxide is decomposed (see Patent Document 2). However, although these techniques have an improvement effect in the initial stage, there is a possibility that a serious problem may arise in durability over a long period of time. There is also a problem that the cost becomes high.

  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 the electrolyte membrane made of a hydrocarbon-based polymer as described above. . 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 degradation 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. .

Japanese Patent Laid-Open No. 2001-118591 (Claims 1, 2 to 9 lines) Japanese Patent Laid-Open No. 6-103992 (means for solving the problem, page 2, lines 33-37) 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

  Therefore, the present invention enables power generation with sufficiently high energy efficiency in the practical application of polymer electrolyte fuel cells for in-vehicle and residential markets, and the humidification temperature (dew point) of the supply gas is higher than the cell temperature. Solid polymer type that has high power generation performance and stable power generation over a long period of time, whether it is operated with low or no humidification, or with high humidification where the temperature is close to the cell temperature. It aims at providing the membrane for fuel cells.

  In the fuel cell using an ion exchange membrane made of a polymer compound having a sulfonic acid group, the present inventors diligently studied for the purpose of preventing the membrane from deteriorating under operating conditions with low or no humidity. It has been found that by containing specific ions and a hardly soluble cerium compound in the membrane, the degradation of the electrolyte membrane can be remarkably suppressed and the effect can be maintained for a long period of time.

The present invention comprises a cation exchange membrane made of a polymer compound having a sulfonic acid group, and is selected from the group consisting of cerium ions and manganese ions of 0.3 mol% or more of the —SO ₃ ^— group in the cation exchange membrane. An electrolyte membrane for a polymer electrolyte fuel cell, comprising one or more of the above and a sparingly soluble cerium compound. The cerium ion can take a + 3-valent or + 4-valent state, and the manganese ion can take a + 2-valent or + 3-valent state, but is not particularly limited in the present invention.

The electrolyte membrane of the present invention contains cerium ions or manganese ions, and in particular, by exchanging a part of the sulfonic acid group of the electrolyte membrane with cerium ions or manganese ions, -SO ₃ and ^- interaction with, is estimated to effectively improve the hydrogen peroxide or peroxide radical resistance.

  Since the counter anion is a sulfonic acid group of the electrolyte membrane, cerium ions or manganese ions in the electrolyte membrane should not be able to elute out of the system in principle in order to satisfy the electrical neutrality condition. However, when an actual fuel cell is operated, for example, chloride ions may be mixed as impurity anions. In that case, the cerium ions or manganese ions in the electrolyte membrane combine with chloride ions and dissolve out of the system as water-soluble cerium chloride or manganese chloride. As a result, cerium ions or manganese ions There is a risk that the absolute amount of sulfonic acid groups of the ion-exchanged electrolyte membrane is reduced, and long-term durability is impaired.

  As a measure for preventing this, a method of ion-exchange of a sulfonic acid group with a large amount of cerium ion or manganese ion in the initial stage can be considered. However, if the sulfonic acid group is ion-exchanged with a large amount of cerium ions or manganese ions, sufficient conductivity of hydrogen ions cannot be ensured, resulting in an increase in membrane resistance and a decrease in power generation characteristics. .

  In the present invention, as a result of intensive studies on a method for imparting long-term durability to the electrolyte membrane while suppressing the increase in membrane resistance, a part of the sulfonic acid group of the electrolyte membrane is cerium ion or manganese as long as power generation characteristics are not deteriorated. It has been found that a long-term durability can be remarkably imparted by containing a hardly soluble cerium compound in the electrolyte membrane ion-exchanged with ions.

  That is, in the present invention, as described above, even if cerium ions or manganese ions are dissolved out of the system as water-soluble cerium chloride or manganese chloride, the dissociation equilibrium of the hardly soluble cerium compound contained in the film Thus, cerium ions are dissolved in the membrane for removal, and cerium ions are supplied into the membrane, so that it is possible to provide the electrolyte membrane with extremely long-term durability.

  Furthermore, the present invention is a method for obtaining the above-mentioned electrolyte membrane, in which a slightly soluble cerium compound fine particle is added to and mixed with a dispersion of a polymer compound having a sulfonic acid group, and is hardly soluble in the dispersion. A cerium compound is dispersed, casted using the obtained liquid, and then the obtained film is immersed in a solution containing at least one selected from the group consisting of cerium ions and manganese ions. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell is provided.

  Furthermore, the present invention is a method for obtaining the above electrolyte membrane, which is hardly soluble in a liquid composition comprising a polymer compound having a sulfonic acid group and at least one selected from the group consisting of cerium ions and manganese ions. An electrolyte membrane for a polymer electrolyte fuel cell, characterized in that a hardly soluble cerium compound is dispersed in the liquid composition by adding and mixing fine particles of a cerium compound, and a cast film is formed using the obtained liquid. A manufacturing method is provided.

  Furthermore, the present invention is a method for obtaining the above-mentioned electrolyte membrane, wherein a cation exchange membrane made of a polymer compound having a sulfonic acid group is immersed in a solution containing cerium ions so that a part of the sulfonic acid group is cerium. After ion exchange with ions, immerse in a solution containing a substance that forms a sparingly soluble cerium compound by reacting with cerium ions to form a sparingly soluble cerium compound in the membrane, and then the cation exchange membrane is cerium ion And a method for producing an electrolyte membrane for a polymer electrolyte fuel cell, which is immersed in a solution containing at least one selected from the group consisting of manganese ions.

  Furthermore, the present invention is a method for obtaining the above-described electrolyte membrane, wherein a cerium compound that is soluble in the dispersion is added to the dispersion of the polymer compound having a sulfonic acid group, and a part of the sulfonic acid group is removed. After ion exchange with cerium ions, a solution or solid containing a substance that forms a sparingly soluble cerium compound by reacting with cerium ions is added to the dispersion to form a sparingly soluble cerium compound in the dispersion, A solid polymer fuel cell comprising: casting a film using the obtained liquid; and immersing the obtained film in a solution containing at least one selected from the group consisting of cerium ions and manganese ions A method for manufacturing an electrolyte membrane for use is provided.

  Since the electrolyte membrane of the present invention has excellent resistance to hydrogen peroxide or peroxide radicals, the polymer electrolyte fuel cell comprising the membrane electrode assembly having the electrolyte membrane of the present invention is excellent in durability, Stable power generation is possible for a long time.

  Although the method to make the high molecular compound which has a sulfonic acid group contain 1 or more types chosen from the group which consists of a cerium ion and a manganese ion is not specifically limited, 1 type or more chosen from the group which consists of a cerium ion and a manganese ion is included A solution containing at least one selected from the group consisting of water-soluble salts and cerium ions and manganese ions is used, and examples thereof include the following methods. (I) A water-soluble salt containing at least one selected from the group consisting of cerium ions and manganese ions is added to the dispersion of the polymer compound having a sulfonic acid group and selected from the group consisting of cerium ions and manganese ions. Or a mixture of a polymer compound having a sulfonic acid group and a solution containing one or more selected from the group consisting of cerium ions and manganese ions, A method of forming a film by a casting method or the like using the obtained liquid. (Ii) A method of immersing a film made of a polymer compound having a sulfonic acid group in a solution containing one or more selected from the group consisting of cerium ions and manganese ions.

Here, the cerium ion may be +3 or +4, and various water-soluble cerium salts are used to obtain a solution containing cerium ions. Specific examples of salts containing trivalent cerium ions include cerium acetate (Ce (CH ₃ COO) ₃ .H ₂ O), cerium chloride (CeCl ₃ .6H ₂ O), and cerium nitrate (Ce (NO _{3) 3 · 6H 2 O)} , and the like, cerium sulfate _{(Ce 2 (SO 4) 3} · 8H 2 O) is. Examples of the salt containing tetravalent cerium ions include cerium sulfate (Ce (SO ₄ ) ₂ .4H ₂ O), diammonium cerium nitrate (Ce (NH ₄ ) ₂ (NO ₃ ) ₆ ), and tetraammonium cerium sulfate. (Ce (NH ₄ ) ₄ (SO ₄ ) ₄ ) · 4H ₂ O) and the like. Examples of the organometallic complex salt of cerium include cerium acetylacetonate (Ce (CH ₃ COCHCOCH ₃ ) ₃ .3H ₂ O). Of these, cerium nitrate and cerium sulfate are particularly preferred because they are easy to handle. Further, nitric acid or sulfuric acid generated when ion exchange of a polymer compound having a sulfonic acid group in these aqueous solutions is preferable because it can be easily dissolved and removed in the aqueous solution.

Manganese ions may be +2 or +3, and various water-soluble manganese salts are used to obtain a solution containing manganese ions. Specific examples of salts containing divalent manganese ions include manganese acetate (Mn (CH ₃ COO) ₂ .4H ₂ O), manganese chloride (MnCl ₂ .4H ₂ O), manganese nitrate (Mn (NO _{3) 2 · 6H 2 O)} , and the like manganese sulfate _{(MnSO 4 · 5H 2 O)} . Examples of the salt containing trivalent manganese ions include manganese acetate (Mn (CH ₃ COO) ₃ .2H ₂ O). Examples of the organometallic complex salt of manganese include manganese acetylacetonate (Mn (CH ₃ COCHCOCH ₃ ) ₂ ). Of these, manganese nitrate and manganese sulfate are particularly preferred because they are easy to handle. Further, nitric acid or sulfuric acid generated when ion exchange of a polymer compound having a sulfonic acid group in these aqueous solutions is preferable because it can be easily dissolved and removed in the aqueous solution.

For example, when the cerium ions are trivalent, the sulfonic acid groups are ion-exchanged with cerium ions, replaced the three protons and cerium ions, Ce ³⁺ is three -SO ₃ ^- but it is bonded to , It may not be completely ion-exchanged. Further, for example, when the manganese ion is +2 valent, when the sulfonic acid group is ion-exchanged by the manganese ion, two protons and manganese ions are replaced, and Mn ²⁺ is bonded to two —SO ₃ ^—. However, it may not be completely ion-exchanged.

In the present invention, the cerium ion or manganese ion contained in the electrolyte membrane is 0.3 mol% or more of the —SO ₃ ^— group in the membrane (hereinafter, this ratio is referred to as “cerium ion or manganese ion content”). That said.) The lower limit of the content of trivalent or tetravalent cerium ions is preferably 0.7 mol% or more, more preferably 1 mol% or more, and the upper limit is preferably 30 mol% or less, more preferably 16 mol% or less. 13 mol% or less is more preferable. The content of divalent or trivalent manganese ions is preferably 0.5 mol% or more, more preferably 1 mol% or more, still more preferably 1.5 mol% or more, and the upper limit is 45 mol% or less. Is preferable, 25 mol% or less is more preferable, and 20 mol% or less is more preferable.

  If the content of cerium ions or manganese ions is smaller than the above range, sufficient stability against hydrogen peroxide or peroxide radicals may not be ensured. On the other hand, if the content of cerium ions or manganese ions is larger than the above range, sufficient conductivity of hydrogen ions cannot be ensured, resulting in an increase in membrane resistance and a decrease in power generation characteristics.

The poorly soluble cerium compound in the present invention means a cerium compound having a solubility in water at 25 ° C. of 0.1 g or less with respect to 100 g of water. Specifically, cerium phosphate, cerium phosphate, cerium oxide, cerium hydroxide, cerium hydroxide, cerium hydroxide, cerium carbonate, cerium fluoride, cerium oxalate, cerium tungstate, and heteropolyacid A cerium salt etc. are mentioned. These may be anhydrous and may have water of crystallization or water of hydration. The valence of cerium of the hardly soluble cerium compound may be +3 or +4. For example, in the case of cerium oxide, Ce ₂ O ₃ or CeO ₂ may be used.

  Here, the cerium ion generated by dissociation equilibrium of the hardly soluble cerium compound or the cerium ion generated by dissolving the hardly soluble cerium compound in the film may be +3 or +4. In addition, it is considered that the hardly soluble cerium compound also functions as a filler and contributes to the improvement of the mechanical strength of the film and the provision of mechanical stability.

  On the other hand, when a water-soluble cerium compound is contained in the cation exchange membrane, the cerium compound is easily dissociated into ions by water generated by power generation or water supplied to the membrane by gas humidification. Ions are generated. As a result, in addition to the exchange groups that have already been ion-exchanged, a large amount of sulfonic acid groups will be ion-exchanged by cerium ions, so that sufficient conductivity of hydrogen ions cannot be ensured and membrane resistance will increase. As a result, power generation characteristics may be reduced.

  In the present invention, even if a poorly soluble cerium compound is present in a large amount in the membrane, it does not extremely impair proton conductivity. The reason for this is that even if cerium ions are generated due to dissociation equilibrium, dissolution, etc., the total amount of these cerium ions is 0.1 mol relative to the number of sulfonic acid groups in the cation exchange membrane. % Or less. Therefore, even if the amount of the poorly soluble cerium compound added to the film is widely changed, it is possible to suppress an extreme increase in film resistance, so that the film or membrane electrode junction has excellent resistance to hydrogen peroxide or peroxide radicals. The production of the body is very easy.

  On the other hand, since poorly soluble cerium compounds generally have low electrical conductivity, current shielding occurs depending on the amount added to the film. Therefore, in the present invention, the preferred proportion of the poorly soluble cerium compound contained in the electrolyte membrane is preferably 0.3 to 30% (mass ratio) of the total mass of the cation exchange membrane, more preferably 0.8. 4 to 20%, more preferably 0.5 to 10%. If the content of the hardly soluble cerium compound in the film is less than this range, there is a possibility that sufficient stability against hydrogen peroxide or peroxide radicals cannot be ensured over a long period of time. On the other hand, when 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.

  When cerium phosphate is included in the electrolyte membrane as a poorly soluble cerium compound, not only can the electrolyte membrane be sufficiently prevented from degrading, but the membrane can also be used in power generation with low humidity because the cerium phosphate has water absorption. Is preferable because drying of the water is suppressed and power can be generated at a high voltage. In addition, a poorly soluble cerium compound having crystal water or hydrated water is also preferable because of its high effect of water retention.

The method for obtaining the electrolyte membrane of the present invention containing at least one selected from the group consisting of cerium ions and manganese ions and a hardly soluble cerium compound in the polymer compound having a sulfonic acid group is not particularly limited. The following methods are mentioned.
(1) A poorly soluble cerium compound is dispersed in a liquid composition containing a polymer compound having a sulfonic acid group and at least one selected from the group consisting of cerium ions and manganese ions, and then the obtained liquid is used. A method for forming a film by a casting method or the like.
At this time, the hardly soluble cerium compound may be mixed in advance with a solvent (dispersion medium) capable of highly dispersing the compound and then mixed with a dispersion of a polymer compound having a sulfonic acid group.

  (2) After dispersing a sparingly soluble cerium compound in a dispersion or solution of a polymer compound having a sulfonic acid group, the resulting solution is used to form a film by a casting method or the like. A method in which a part of a sulfonic acid group is ion-substituted by dipping in a solution containing at least one selected from the group consisting of manganese ions.

  (3) After immersing a membrane made of a polymer compound having a sulfonic acid group in a solution containing cerium ions to contain cerium ions in the membrane, phosphoric acid, oxalic acid, NaF, sodium hydroxide, etc. The film is immersed in a solution containing a substance that reacts with cerium ions to form a hardly soluble cerium compound, and the hardly soluble cerium compound is deposited in the film, and then the film is selected from the group consisting of cerium ions and manganese ions A method in which a part of a sulfonic acid group is ion-substituted by dipping in a solution containing one or more kinds.

  (4) A cerium compound that can be dissolved in the dispersion is added to the dispersion of the polymer compound having a sulfonic acid group, and the sulfonic acid group is ion-exchanged with cerium ions, and then phosphoric acid and oxalic acid are added to the dispersion. A solution obtained by adding a substance that reacts with cerium ions to form a hardly soluble cerium compound, such as NaF or sodium hydroxide, or a solution containing the same, to form a hardly soluble cerium compound in the dispersion. A film is formed by using a casting method or the like, and the obtained film is immersed in a solution containing one or more selected from the group consisting of cerium ions and manganese ions, and a part of the sulfonic acid group is ion-substituted.

In the methods of (3) and (4), after a cerium ion is once contained in a polymer compound having a sulfonic acid group, a hardly soluble cerium compound is formed by a substance that reacts with cerium ions to form a hardly soluble cerium compound. It is generated. The cerium ion mentioned here can also be contained by using a water-soluble salt containing cerium ions in the same manner as the cerium ions finally contained in the electrolyte membrane. Examples of water-soluble salts containing cerium ions include cerium acetate (Ce (CH ₃ COO) ₃ .H ₂ O), cerium chloride (CeCl ₃ .6H ₂ O), and cerium nitrate (Ce (NO ₃ ) ₃ .6H. ₂ O) cerium sulfate (Ce ₂ (SO ₄ ) ₃ · 8H ₂ O) and the like.
In the above methods (1) to (4), the method (1) is preferred because it can uniformly contain hardly soluble cerium and is a simple method.

  The electrolyte membrane of the present invention can also be adjusted so that it contains non-uniformly one or more selected from the group consisting of cerium ions and manganese ions and a poorly soluble cerium compound. For example, a cation exchange membrane (laminated film) composed of two or more layers, and at least one layer selected from the group consisting of cerium ions and manganese ions instead of all the layers, and a poorly soluble cerium compound 1 or more selected from the group consisting of cerium ions and manganese ions and a poorly soluble cerium compound may be included. Therefore, in particular, when it is necessary to increase the durability against hydrogen peroxide or peroxide radicals on the anode side, only the layer closest to the anode has at least one selected from the group consisting of cerium ions and manganese ions, and is hardly soluble. It can also be set as the layer which consists of an ion exchange membrane containing a cerium compound. One or more selected from the group consisting of cerium ions and manganese ions and a sparingly soluble cerium compound may be contained in separate layers of the laminated film.

  Here, when the electrolyte membrane of the present invention is composed of a laminated film composed of a layer containing one or more selected from the group consisting of cerium ions and manganese ions and a hardly soluble cerium compound, and a layer not containing it, a production method thereof For example, a cation exchange membrane containing at least one selected from the group consisting of cerium ions and manganese ions and a hardly soluble cerium compound by any one of the methods (1) to (4) described above is prepared. deep. And although it is preferable to produce through the process of laminating | stacking this with the cation exchange membrane which does not contain a cerium ion, a manganese ion, or a hardly soluble cerium compound, it is not specifically limited.

The polymer compound having a sulfonic acid group in the present invention 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 mm. Equivalent / g 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 0 to 12, p represents 0 or 1, and when n = 0, p = 0 and m = 1 to 3, X represents a fluorine atom or a trifluoromethyl group. A copolymer containing a repeating unit based on tetrafluoroethylene and a repeating unit based on tetrafluoroethylene.

  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.

  In addition, as the polymer compound having a sulfonic acid group, those other than the perfluorocarbon polymer having a sulfonic acid group can be used. 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 polymer electrolyte fuel cell having the electrolyte membrane of 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 arranged on both surfaces of the electrolyte membrane of the present invention 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 electrolyte membrane of the present invention can also be used in a direct methanol fuel cell in which methanol is supplied to the anode side instead of fuel gas.

  The catalyst layer described above 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 a solution of a perfluorocarbon polymer having a sulfonic acid group are mixed to obtain a uniform dispersion. For example, by any of the following methods: A gas diffusion electrode is formed to obtain a membrane electrode assembly.

  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. Here, the carbon cloth or the carbon paper has a function as a gas diffusion layer and a function as a current collector for uniformly diffusing the gas by the layer containing the catalyst. In addition, a method can be used in which a catalyst layer is prepared by applying the dispersion to a separately prepared substrate, bonded to the electrolyte membrane by a method such as transfer, and then peeled off and sandwiched between the gas diffusion layers. .

  Although the ion exchange resin contained in the catalyst layer is not particularly limited, it is preferably a perfluorocarbon polymer having a sulfonic acid group, like the resin constituting the electrolyte membrane. The ion exchange resin in the catalyst layer may contain at least one ion selected from the group consisting of cerium ions and manganese ions and a hardly soluble cerium compound, as in the electrolyte membrane of the present invention. An ion exchange resin containing one or more ions selected from the group consisting of cerium ions and manganese ions and a sparingly soluble cerium compound can be used for both the anode and the cathode, and the decomposition of the resin is effectively suppressed. The polymer electrolyte fuel cell is further provided with durability.

  When it is desired to contain one or more ions selected from the group consisting of cerium ions and manganese ions and a sparingly soluble cerium compound in both the ion exchange resin and the electrolyte membrane in the catalyst layer, for example, between the catalyst layer and the electrolyte membrane A joined body is prepared in advance, and the ion exchange resin in the catalyst layer and one or more ions selected from the group consisting of cerium ions and manganese ions and a sparingly soluble cerium compound in the catalyst layer by the method of (3) above. It can also be included.

  The electrolyte membrane according to the present invention is a membrane that is formed only of a polymer compound having a sulfonic acid group, including one or more ions selected from the group consisting of cerium ions and manganese ions and a hardly soluble cerium compound. However, it may contain other components, and is a membrane reinforced with fibers, woven fabrics, nonwoven fabrics, porous bodies, etc., such as other resins such as polytetrafluoroethylene and perfluoroalkyl ether. Also good.

  Hereinafter, the present invention will be specifically described using Examples (Examples 1 to 3) and Comparative Examples (Examples 4 and 5), but the present invention is not limited thereto.

[Example 1]
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) 300 g ethanol 420 g water 280 g Was placed in a 2 L autoclave, sealed, and mixed and stirred at 105 ° C. for 6 hours with a double helical blade to obtain a uniform liquid (hereinafter referred to as “solution A”). The solid content concentration of Solution A was 30%.

A 300 ml glass round bottom flask was charged with 100 g of the above solution A and 1.43 g of cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O), and 8 ml at room temperature with a polytetrafluoroethylene meniscus blade. The mixture was stirred for a time to obtain a uniform liquid (hereinafter referred to as solution B).

Here, the content rate of the cerium ion which will be contained in a polymer electrolyte membrane was measured. The above solution B is coated on a sheet (trade name: Aflex 100N, manufactured by Asahi Glass Co., Ltd., hereinafter also referred to simply as an ETFE sheet) with a die coater on a sheet of 100 μm ethylene / tetrafluoroethylene copolymer to form a cast film. Then, after preliminary drying at 80 ° C. for 10 minutes, drying was performed at 120 ° C. for 10 minutes to obtain a polymer electrolyte membrane having a thickness of 50 μm. From this polymer electrolyte membrane, a 5 cm × 5 cm size membrane was cut out and allowed to stand in dry nitrogen for 16 hours. Then, the mass was precisely weighed and impregnated in a 0.1 N aqueous hydrochloric acid solution, and cerium ions were added. A completely extracted liquid was obtained. As a result of calculating this liquid by measuring by ICP spectroscopy, the content of cerium ions in the polymer electrolyte membrane was 10.2 mol% of the —SO ₃ ^— group in the membrane.

Next, 100 g of the solution B and 0.5 g of cerium oxide fine powder (CeO ₂ , manufactured by Junsei Chemical Co., Ltd., average particle size 0.4 μm) were charged into a 300 ml glass round bottom flask and mixed. This mixture was further mixed and pulverized using an ultrasonic generation homogenizer (US-600T: manufactured by Nippon Seiki Co., Ltd.) to obtain a translucent dispersion in which cerium oxide particles were dispersed. This solution was applied in the same manner and cast to obtain a polymer electrolyte membrane having a thickness of 50 μm and a cerium oxide content of 1.6% of the total mass of the membrane.

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, using the above-described polymer electrolyte membrane containing cerium ions and cerium oxide, the catalyst layers formed on the above-mentioned substrate film are respectively disposed on both sides of this membrane, and the catalyst layer is formed into a membrane by hot pressing. The membrane catalyst layer assembly was obtained by transferring and joining the anode catalyst layer and the cathode catalyst layer to both surfaces of the polymer electrolyte membrane. The electrode area was 16 cm ² .

This membrane / catalyst layer assembly is sandwiched between two gas diffusion layers made of carbon cloth having a thickness of 350 μm to produce a membrane / electrode assembly, which is then sandwiched between separators to complete a single cell. OCV test). 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 120 ° C., and the anode gas. The dew point was 73 ° C. (relative humidity 18%) and the dew point of the cathode gas was also 73 ° C. The battery was operated for 100 hours 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.

Next, a membrane electrode assembly was prepared in the same manner as described above, sandwiched between separators to complete a single cell, and a durability test was performed under operating conditions at high temperature and low humidity. The test conditions were as follows: both the anode and the cathode were pressurized to 0.2 MPa, hydrogen (utilization rate 50%) and air (utilization rate 50%) were supplied, and the solid density at a current density of 0.2 A / cm ² at a cell temperature of 120 ° C. The initial characteristics and durability of the molecular fuel cell were evaluated. Hydrogen and air are humidified and supplied to the cell so that the anode side has a dew point of 105 ° C. (relative humidity 60%) and the cathode side also has a dew point of 105 ° C., respectively. The relationship with the cell voltage was measured. The results are shown in Table 2.

In addition, a durability test with high humidification was also performed. The test conditions were as follows: hydrogen (utilization rate 70%) and air (utilization rate 40%) were supplied at normal pressure, the initial temperature of the polymer electrolyte fuel cell at a cell temperature of 80 ° C. and a current density of 0.2 A / cm ² Characteristic evaluation and durability evaluation were performed. The anode side has a dew point of 80 ° C. (relative humidity 100%), and the cathode side also has a dew point of 80 ° C. to humidify and supply hydrogen and air into the cell. The relationship was measured. The results are shown in Table 3.

[Example 2]
Cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 10.0g was dissolved in distilled water of 500 mL, was added dropwise phosphorus acid solution 1 mol / L therein, to give a white precipitate. 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, 2.00 g of the above-mentioned cerium phosphate was added to 100 g of the solution A, and the liquid composition in which the cerium phosphate was dispersed by stirring for 8 hours at room temperature with a polytetrafluoroethylene meniscus blade. I got a thing. Next, this liquid composition was coated on a 100 μm ETFE sheet with a die coater, cast into a film, pre-dried at 80 ° C. for 10 minutes, then dried at 120 ° C. for 10 minutes, and further at 150 ° C. for 30 minutes. The polymer electrolyte membrane was obtained with a film thickness of 50 μm and a cerium phosphate content of 6.2% of the total mass of the membrane.

  From this polymer electrolyte membrane, a membrane having a size of 5 cm × 5 cm was cut out and allowed to stand in dry nitrogen for 16 hours, and then the mass was measured in dry nitrogen to be 0.260 g. The amount of sulfonic acid groups in this membrane is determined by the following formula. 0.260 * (1-0.062) * 1.1 (milli equivalent / g dry resin) = 0.268 (milli equivalent).

Next, to include the polymer electrolyte membrane of the sulfonic acid group amount of cerium corresponds to the amount of 10 mole% ionic (+3), cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 11.7mg Was dissolved in 500 mL of distilled water. The polymer electrolyte membrane was immersed in this aqueous solution and stirred with a stirrer at room temperature for 40 hours to ion-exchange part of the sulfonic acid group of the polymer electrolyte membrane with cerium ions. In addition, as a result of analyzing the cerium nitrate solution before and after immersion by ion chromatography, it was found that the content of cerium ions in the polymer electrolyte membrane was 9.3 mol% of the —SO ₃ ^— group in the membrane.
Using this membrane, a membrane / catalyst layer assembly was obtained 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 Tables 1 to 3 were obtained.

[Example 3]
60 g of granular polyetheretherketone (Pick-450P manufactured by Victrex, UK) is added to 1200 g of 98% sulfuric acid in small portions at room temperature and stirred at room temperature for 60 hours to introduce sulfonic acid groups into the polyetheretherketone. A solution of the obtained polymer compound was obtained. Next, this solution was gradually added dropwise to 5 L of distilled water while cooling, thereby precipitating a polyether ether ketone having a sulfonic acid group, and separating by filtration. Next, this was washed with distilled water until the washing liquid became neutral, and then dried under vacuum at 80 ° C. for 24 hours to obtain 48 g of polyetheretherketone having sulfonic acid groups.

  Next, about 1 g of this compound was precisely weighed and then immersed in 500 mL of a 1N aqueous sodium chloride solution and reacted at 60 ° C. for 24 hours to ion-exchange sulfonic acid groups with sodium ions. After cooling this sample to room temperature, it was thoroughly washed with distilled water, and the ion exchange capacity was obtained by titrating the ion-exchanged 1N aqueous sodium chloride solution and the washed distilled water with 0.01N sodium hydroxide. It was. The ion exchange capacity was 1.6 meq / g dry resin.

  Next, 40 g of the polyether ether ketone having a sulfonic acid group is dissolved in 360 g of N-methyl-2-pyrrolidone (NMP) to form a 10% solution (hereinafter referred to as solution C). After adding 3.1 g of the cerium phosphate obtained in Example 2 to 100 g of this solution C, this was cast on a substrate made of polytetrafluoroethylene at room temperature, and then at 100 ° C. in a nitrogen atmosphere. NMP was evaporated by drying for 10 hours to obtain a polymer electrolyte membrane having a thickness of 50 μm and a cerium phosphate content of 3.0% of the total mass of the membrane. A film having a size of 5 cm × 5 cm was cut out from the polymer electrolyte membrane, left in dry nitrogen for 16 hours, and then precisely weighed to find 0.171 g. The amount of sulfonic acid groups in this membrane is determined by the following formula. 0.171 ÷ 1.03 × 1.6 (1.1 milliequivalent / g dry resin) = 0.266 (milliequivalent).

Next, dissolving the cerium nitrate containing a sulfonic acid group amount of cerium corresponds to about 10 mole% ionic (+3 valence) of the membrane _{(Ce (NO 3) 3 ·} 6H 2 O) 12.0mg of distilled water 500mL To do. The polymer electrolyte membrane is immersed in this aqueous solution and stirred with a stirrer at room temperature for 40 hours to obtain a polymer electrolyte membrane having a cerium ion content of 10 mol% of the —SO ₃ ^— group in the membrane. obtain.
Using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1 to further obtain a membrane / electrode assembly. When this membrane electrode assembly is evaluated in the same manner as in Example 1, the results shown in Tables 1 to 3 are obtained.

[Example 4]
As a polymer electrolyte membrane, a 50 μm-thick 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, , A size of 5 cm × 5 cm (area 25 cm ² ) was used. The total weight of this film was allowed to stand in dry nitrogen for 16 hours and then measured in dry nitrogen, and it was 0.251 g. The amount of sulfonic acid groups in this membrane is determined by the following formula.
0.251 × 1.1 (1.1 milliequivalent / g dry resin) = 0.276 (milliequivalent).

Next, cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 24.0mg dissolved in distilled water of 500 mL, and immersing the ion-exchange membrane in this, 40 hours at room temperature, stirred using a stirrer Then, a part of the sulfonic acid group in the ion exchange membrane was ion-exchanged with cerium ions. Next, this membrane was immersed in a 1 mol / L phosphoric acid aqueous solution at room temperature for 60 hours. This film was dried in air at 120 ° C. for 10 hours, then cooled and confirmed by X-ray diffraction. As a result, it was confirmed that cerium phosphate was precipitated in the film. The content ratio of this cerium phosphate with respect to the total mass of the film was 5.2%.

Next, 12.0 mg of manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O) was added to 500 mL of distilled water so as to contain manganese ions (+2 valence) corresponding to 15 mol% of the sulfonic acid group amount of the membrane. Then, the ion exchange membrane was immersed in this, and stirred at room temperature for 40 hours using a stirrer to ion-exchange some of the sulfonic acid groups of the ion exchange membrane with manganese ions. As a result of analyzing the manganese nitrate solution before and after immersion by ion chromatography, it was found that the content of manganese ions in this ion exchange membrane was 14 mol% of the —SO ₃ ^— group in the membrane.

  Using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1 to further obtain a membrane / electrode assembly. When this membrane electrode assembly is evaluated in the same manner as in Example 1, the results shown in Tables 1 to 3 are obtained.

[Example 5]
As the polymer electrolyte membrane, the same commercially available ion exchange membrane as that used in Example 4 was used without any treatment, and then a membrane-catalyst layer assembly was obtained using this membrane in the same manner as in Example 1. Further, a membrane electrode assembly was obtained. When this membrane electrode assembly was evaluated in the same manner as in Example 1, the results shown in Tables 1 to 3 were obtained.

[Example 6]
The solution C obtained in Example 3 was cast on a substrate made of polytetrafluoroethylene at room temperature, then dried at 100 ° C. for 10 hours in a nitrogen atmosphere to evaporate NMP, and a polymer electrolyte membrane having a thickness of 50 μm Got. Next, a membrane having a size of 5 cm × 5 cm is cut out from this membrane, and a membrane / catalyst layer assembly is obtained in the same manner as in Example 1 to further obtain a membrane / electrode assembly. When this membrane electrode assembly is evaluated in the same manner as in Example 1, the results shown in Tables 1 to 3 are obtained.

  From the results of the above examples and comparative examples, in the open circuit test (OCV test) of high temperature and low humidity, which is an accelerated test, the conventional electrolyte membrane deteriorated and hydrogen leakage increased, but the electrolyte of the present invention It can be seen that the membrane exhibits exceptional durability. In addition, in a low humidification operation (60% relative humidity) under 120 ° C. pressure (0.2 MPa), the conventional electrolyte membrane has pores in the membrane in 100 hours or 20 hours, and power generation is impossible. The membrane showed extremely excellent durability and was able to generate power for 2000 hours or more. In addition, it is recognized that excellent durability is exhibited even in high-humidity power generation at 80 ° C. and normal pressure.

The electrolyte membrane of 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 of the present invention has long-term durability in both high temperature low humidification power generation and high humidification power generation.

Claims (14)

Consists cation exchange membrane made of a polymer compound having a sulfonic acid group, -SO ₃ in the cation exchange membrane ^- at least one member selected from the group consisting of more than 0.3 mol% of cerium ions and manganese ions based on And an electrolyte membrane for a polymer electrolyte fuel cell, comprising a hardly soluble cerium compound.   2. The solid according to claim 1, wherein the hardly soluble cerium compound is selected from the group consisting of cerium phosphate, cerium oxide, cerium hydroxide, cerium carbonate, cerium oxalate, cerium fluoride, cerium tungstate and a cerium salt of heteropolyacid. Electrolyte membrane for polymer fuel cells.   A cation exchange membrane in which two or more layers of a polymer compound having a sulfonic acid group are laminated, and at least one of the two or more layers is at least one selected from the group consisting of cerium ions and manganese ions; The electrolyte membrane for a polymer electrolyte fuel cell according to claim 1 or 2, comprising a hardly soluble cerium compound. Solid polymer electrolyte membrane according to claim 1 containing 0.3 to 30 mol% of the groups ^- -SO ₃ of cerium ions wherein in the cation exchange membrane. -SO ₃ of manganese ions the in the cation exchange membrane ^- a solid polymer electrolyte membrane according to claim 1 containing 0.5 to 45 mol% of the groups.   The electrolyte membrane for a polymer electrolyte fuel cell according to any one of claims 1 to 5, wherein the hardly soluble cerium compound is contained in an amount of 0.3 to 30% of the total mass of the cation exchange membrane.   The polymer membrane for a polymer electrolyte fuel cell according to any one of claims 1 to 6, wherein the polymer compound having a sulfonic acid group is a perfluorocarbon polymer having a sulfonic acid group. The perfluorocarbon polymer is
_{CF 2 = CF- (OCF 2 CFX} ) m -O p - (CF 2) a perfluorovinyl compound represented by n -SO ₃ H (m is an integer of 0 to 3, n is from 0 to 12 integer P represents 0 or 1, and when n = 0, p = 0 and m = 1 to 3, and X represents a fluorine atom or a trifluoromethyl group.) The electrolyte membrane for a polymer electrolyte fuel cell according to claim 7, which is a copolymer containing a repeating unit based on ethylene.   The polymer compound having a sulfonic acid group has an aromatic ring in the main chain of the polymer or in the main chain and side chain, and a structure in which the sulfonic acid group is introduced into the aromatic ring, The electrolyte membrane for a polymer electrolyte fuel cell according to any one of claims 1 to 6, wherein the exchange capacity is 0.8 to 3.0 meq / g dry resin. A method for producing an electrolyte membrane according to any one of claims 1 to 9,
In a liquid composition comprising a polymer compound having a sulfonic acid group and at least one selected from the group consisting of cerium ions and manganese ions,
Disperse the hardly soluble cerium compound in the liquid composition by adding and mixing fine particles of the hardly soluble cerium compound,
A method for producing an electrolyte membrane for a polymer electrolyte fuel cell, comprising casting a film using the obtained liquid. A method for producing an electrolyte membrane according to any one of claims 1 to 9,
In the dispersion of the polymer compound having a sulfonic acid group, the hardly soluble cerium compound is dispersed in the dispersion by adding and mixing fine particles of the hardly soluble cerium compound.
After casting a film using the obtained liquid,
A method for producing an electrolyte membrane for a polymer electrolyte fuel cell, wherein the obtained membrane is immersed in a solution containing one or more selected from the group consisting of cerium ions and manganese ions. A method for producing an electrolyte membrane according to any one of claims 1 to 9,
A cation exchange membrane made of a polymer compound having a sulfonic acid group,
After immersing in a solution containing cerium ions and ion-exchanging a part of the sulfonic acid group with cerium ions, it is immersed in a solution containing a substance that forms a sparingly soluble cerium compound by reacting with cerium ions. Forms a sparingly soluble cerium compound in
Next, the method for producing an electrolyte membrane for a polymer electrolyte fuel cell, wherein the cation exchange membrane is immersed in a solution containing one or more selected from the group consisting of cerium ions and manganese ions. A method for producing an electrolyte membrane according to any one of claims 1 to 9,
It is difficult to react with cerium ions after adding a cerium compound that can be dissolved in the dispersion of the polymer compound having a sulfonic acid group and exchanging a part of the sulfonic acid group with cerium ions. Adding a solution or solid containing a substance that forms a soluble cerium compound to the dispersion to form a sparingly soluble cerium compound in the dispersion;
After casting a film using the obtained liquid,
A method for producing an electrolyte membrane for a polymer electrolyte fuel cell, wherein the obtained membrane is immersed in a solution containing one or more selected from the group consisting of cerium ions and manganese ions. 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 electrolyte membrane disposed between the anode and the cathode, wherein the electrolyte membrane is claimed. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising the electrolyte membrane according to any one of 1 to 9.