JP2008098179A - Electrolyte membrane for solid polymer electrolyte fuel cell, its manufacturing method, and membrane electrode assembly for polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane for a solid polymer electrolyte fuel cell having high power generation performance independently of the dew point of the supplied gas and capable of generating electric power at a high energy efficiency steadily for a long period. <P>SOLUTION: A cation exchange membrane containing a high molecular compound having sulfonic groups and a hardly-soluble cerium compound is used as an electrolyte membrane for polymer electrolyte fuel cells. In the above cation exchange membrane, it is preferable that the hardly-soluble cerium compound in the cation exchange membrane is 0.3 to 80% of the whole mass of the cation exchange membrane, and that a perfluorocarbon polymer having sulfonic groups is used as the high molecular compound. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 supplied 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 the deterioration of the electrolyte membrane can be remarkably suppressed by containing a poorly soluble cerium compound in the membrane, leading to the present invention.

  The present invention provides an electrolyte membrane for a polymer electrolyte fuel cell, comprising a cation exchange membrane comprising a polymer compound having a sulfonic acid group and a hardly soluble cerium compound. Here, the hardly 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 carbonate, cerium fluoride, cerium fluoride, cerium oxalate, cerium tungstate, and heteropolyacid A cerium salt etc. are mentioned, The 1 or more types of cerium compound chosen from the group which consists of these compounds is especially preferable. Although the valence of cerium in the hardly soluble cerium compound can be in a +3 or +4 valence state, it is not particularly limited in the present invention.

  Further, the present invention is a method for obtaining the above-described 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 to partially remove the sulfonic acid group. Solid polymer form characterized by forming a poorly soluble cerium compound in a film by ion exchange with cerium ions and then immersing in a solution containing a substance that forms a poorly soluble cerium compound by reacting with cerium ions A method for producing an electrolyte membrane for a fuel cell is provided.

  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, There is provided a method for producing an electrolyte membrane for a polymer electrolyte fuel cell, characterized in that the obtained liquid is cast into a membrane.

  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. Disclosed is a method for producing an electrolyte membrane for a polymer electrolyte fuel cell, characterized in that a cerium compound is dispersed and a cast membrane is formed using the obtained liquid.

  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 has excellent durability, Stable power generation is possible for a long time. When any one of the above production methods is employed, the obtained electrolyte membrane can contain the hardly soluble cerium compound uniformly in the membrane with good dispersibility.

Examples of the hardly soluble cerium compound in the present invention include cerium phosphate, cerium phosphate, cerium oxide, cerium hydroxide, cerium hydroxide, cerium carbonate, cerium fluoride, cerium oxalate, and tungstic acid. Examples include cerium and cerium salts of heteropolyacids. 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.

The reason why the electrolyte membrane of the present invention has excellent resistance to hydrogen peroxide or peroxide radicals and excellent durability is not clear, but one of the following mechanisms is considered. For example, cerium ions are generated by dissociation or partial dissolution of a poorly soluble cerium compound in the membrane, and the interaction between the generated cerium ions and —SO ₃ ^— groups results in the formation of sulfonic acid groups. It is considered that some of the ions are ion-exchanged with cerium ions, and the ions effectively improve the hydrogen peroxide or peroxide radical resistance of the electrolyte membrane. Another is considered that the cerium element in the hardly soluble cerium compound has a function of effectively decomposing hydrogen peroxide diffused from the catalyst layer into the film.

  In addition, in addition to imparting excellent resistance to hydrogen peroxide or peroxide radicals to the electrolyte membrane, the poorly soluble cerium compound also functions as a filler, improving the mechanical strength and mechanical stability of the membrane. It is thought that it also contributes to granting. Furthermore, the poorly soluble cerium compound can be present in the cluster region formed by gathering ion exchange groups in the ion exchange resin that constitutes the electrolyte membrane. It can also be present in the part of the main chain that is not. In other words, the poorly soluble cerium compound can be uniformly present in the resin constituting the electrolyte membrane, and can improve the mechanical strength and mechanical stability of the electrolyte membrane more evenly on a micro level. It is thought that.

  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, a large amount of sulfonic acid groups are ion-exchanged with cerium ions, and sufficient conductivity of hydrogen ions cannot be ensured, resulting in increased membrane resistance and reduced power generation characteristics. Therefore, when a water-soluble cerium compound is contained in the film, it is necessary to strictly control the amount added to the film. Further, when the water-soluble cerium compound is dissociated into ions and dissolved in water in the film, the film strength cannot be improved because it does not have a function as a filler.

  On the other hand, the electrolyte membrane of the present invention can also be adjusted so as to contain a poorly soluble cerium compound non-uniformly. For example, it is a cation exchange membrane (laminated membrane) consisting of two or more layers, and at least one of the layers contains a hardly soluble cerium compound, that is, non-uniformly poorly soluble in the thickness direction. It may contain a cerium compound. 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 a hardly soluble cerium compound. .

  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 is considered to be that even if cerium ions are generated due to dissociation equilibrium, dissolution, or the like, these cerium ions are in a very small amount. That is, the produced cerium ion effectively ion-exchanges with the sulfonic acid in the vicinity of the poorly soluble cerium compound and imparts excellent resistance to hydrogen peroxide or peroxide radicals, but a large amount of sulfonic acid groups are cerium. Since ion exchange is not performed by ions, it is presumed that the membrane resistance does not increase extremely. 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 ratio of the hardly soluble cerium compound contained in the electrolyte membrane is preferably 0.3 to 80% (mass ratio) of the total mass of the cation exchange membrane, more preferably 0.8. It is 4-70%, More preferably, it is 0.5-50%.

  If the content of the poorly soluble cerium compound 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.

  In the case where the electrolyte membrane of the present invention is a laminated film, the ratio of the hardly soluble cerium compound to the whole electrolyte membrane only needs to be within the above range, and the layer containing the hardly soluble cerium compound itself contains the hardly soluble cerium compound. The content rate may be higher than the above range.

Although the method of obtaining the electrolyte membrane of this invention which made the polymer compound which has a sulfonic acid group contain the hardly soluble cerium compound is not specifically limited, For example, the following method is mentioned.
(1) A method of forming a film by a casting method or the like using a liquid obtained by mixing a solution or dispersion of a polymer compound having a sulfonic acid group and a hardly soluble cerium compound. At this time, the sparingly soluble cerium compound may be mixed in advance with a solvent (dispersion medium) capable of dissolving or highly dispersing the compound and then mixed with a solution or dispersion of a polymer compound having a sulfonic acid group.

(2) 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. A method of immersing in a solution containing a substance that reacts with cerium ions to form a hardly soluble cerium compound, thereby precipitating the hardly soluble cerium compound in the film.
(3) A water-soluble cerium compound is added to a dispersion of a polymer compound having a sulfonic acid group, and the sulfonic acid group is ion-exchanged with cerium ions, and then phosphoric acid, oxalic acid, NaF or hydroxide is added to the dispersion. A substance such as sodium that reacts with cerium ions to form a hardly soluble cerium compound or a solution containing the same is added to form a hardly soluble cerium compound in the dispersion, and the resulting solution is used as a casting method. A method of forming a film by, for example.

In the methods (2) and (3), since the polymer compound having a sulfonic acid group is ion-exchanged with cerium ions in a liquid medium (for example, water, alcohol, etc.), it is soluble in the liquid medium. It is necessary to dissolve the cerium compound. Examples of such cerium compounds 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). Examples thereof include cerium sulfate (Ce ₂ (SO ₄ ) ₃ · 8H ₂ O).

  Here, in the case where the electrolyte membrane of the present invention is composed of a laminated film composed of a layer containing a sparingly soluble cerium compound and a layer not containing it, for example, any one of the above-mentioned (1) to (3) A cation exchange membrane containing a hardly soluble cerium compound is prepared by the method. And although it is preferable to produce through the process of laminating this with the cation exchange membrane which does not contain a poorly soluble cerium compound, it is not specifically limited.

  For example, when using cerium phosphate as the poorly soluble cerium compound, any of the methods (1) to (3) can be preferably employed. In particular, in order to uniformly contain cerium phosphate (3) This method is preferred. In this case, for example, by dissolving cerium nitrate in a dispersion of a polymer compound having a sulfonic acid group and then adding phosphoric acid, cerium phosphate can be contained in the liquid. A film containing monocerium can be obtained. When cerium phosphate is contained in the electrolyte membrane, not only can the deterioration of the electrolyte membrane be sufficiently suppressed, but also the drying of the membrane is suppressed even in low-humidity power generation because cerium phosphate has water absorption. It is preferable because power can be generated at a high voltage. Further, cerium hydroxide and a hardly soluble cerium compound having water of crystallization or water of hydration are also preferable because of their high water retention effect.

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, CF 2 = CF- (OCF 2} CFX) m -O p - (CF 2) a perfluorovinyl compound represented by n -SO ₃ H (m is 0 to 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.

  More specifically, preferred examples of the perfluorovinyl compound include compounds represented by the following formulas (i) to (iii). 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 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 diffusing the gas uniformly 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 a hardly soluble cerium compound as in the electrolyte membrane of the present invention. An ion exchange resin containing a hardly soluble cerium compound can be used for both the anode and the cathode, and the decomposition of the resin is effectively suppressed, so that the polymer electrolyte fuel cell is further provided with durability.

  When it is desired to contain a sparingly soluble cerium compound in both the ion exchange resin and the electrolyte membrane in the catalyst layer, for example, a joined body of the catalyst layer and the electrolyte membrane is prepared in advance, and the above-mentioned method (2) It is also possible to contain a hardly soluble cerium compound in the ion exchange resin and the electrolyte membrane.

  The electrolyte membrane of the present invention may be a membrane made only of a polymer compound having a sulfonic acid group, partly containing a hardly soluble cerium compound, but may contain other components, and polytetrafluoroethylene Or a film reinforced with fibers such as other resins such as perfluoroalkyl ether, woven fabric, non-woven fabric, porous body, or the like. Even in the case of a reinforced membrane, the electrolyte membrane of the present invention can be obtained by immersing it in a solution containing cerium ions and then incorporating a poorly soluble cerium compound into the membrane by the method (2) described above. Moreover, the method of forming into a film using the dispersion liquid containing the high molecular compound which disperse | distributed the hardly soluble cerium compound is also applicable.

  Hereinafter, the present invention will be specifically described using Examples (Examples 1 to 6) and Comparative Examples (Examples 7 to 10), but the present invention is not limited to these.

[Example 1]
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. Then, 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).

Then, based on the total weight of the membrane, as containing cerium ions (trivalent) which corresponds to the amount of 3.1%, a cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 24.0mg Dissolved in 500 mL of distilled water, the ion exchange membrane was immersed in this, and stirred with a stirrer at room temperature for 40 hours to ion-exchange part of the sulfonic acid groups in the ion exchange membrane with cerium ions. . Subsequently, this membrane was immersed in a 1 mol / L phosphoric acid aqueous solution at room temperature for 60 hours. When this film was confirmed by X-ray diffraction, 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, 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 ion exchange membrane containing cerium phosphate, the catalyst layers formed on the base film are arranged on both sides of the membrane, and transferred by a hot press method to be used as an anode catalyst layer and a cathode. A membrane catalyst layer assembly was obtained in which the catalyst layers were bonded to both surfaces of the ion exchange membrane. The electrode area was 16 cm ² .

A membrane / electrode assembly is produced by sandwiching the membrane / catalyst layer assembly between two gas diffusion layers made of carbon cloth having a thickness of 350 μm. The membrane / electrode assembly is assembled in a power generation cell and an open circuit test (OCV test) is performed as an acceleration 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 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.

Next, a membrane electrode assembly was prepared in the same manner as described above and incorporated in a power generation cell, and an endurance test under operating conditions with low humidification was performed. The test conditions were as follows: hydrogen (utilization 70%) / air (utilization 40%) was supplied at normal pressure, and the initial state 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. Hydrogen and air were humidified and supplied into the cell with a dew point of 80 ° C. on the anode side and a dew point of 50 ° C. on the cathode side, respectively. The results are shown in Table 2. Further, under the above-described cell evaluation conditions, the relationship between the cell voltage at the initial stage of operation and the elapsed time after the start of operation and the cell voltage was measured in the same manner except that the dew point on the cathode side was changed to 80 ° C. The evaluation results are shown in Table 3.

[Example 2]
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). For this dispersion, containing cerium ions corresponding to 2.8% of the mass of the copolymer, cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) dissolved 2.64g of distilled water 50mL The solution was added and mixed with a stirrer at room temperature for 10 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, 5.0 g of a 1 mol / L phosphoric acid aqueous solution was added dropwise to the liquid composition while stirring, and stirring was further continued at room temperature for 2 hours. Precipitation of fine white particles was observed from the start of dropping, and finally, a white liquid composition 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. Next, this composition 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, pre-dried at 80 ° C. for 10 minutes, then dried at 120 ° C. for 10 minutes, and further annealed at 120 ° 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 cerium phosphate contained 4.7% with respect to the total mass of the membrane.

  A membrane having a size of 5 cm × 5 cm was cut out from this polymer electrolyte membrane, and a membrane / electrode 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]
Cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) 10.0g was dissolved in distilled water of 500 mL, the aqueous solution of phosphoric acid 1 mol / L therein and 100g added dropwise 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, 100 g of dispersion A and 2.00 g of cerium phosphate obtained above were charged into a 300 ml glass round bottom flask and stirred for 8 hours at room temperature to disperse cerium phosphate. A liquid composition is obtained. 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. To obtain a polymer electrolyte membrane having a thickness of 50 μm and a content of cerium phosphate of 6.2% of the total mass of the membrane. A membrane having a size of 5 cm × 5 cm is cut out from the polymer electrolyte membrane, and a membrane electrode assembly is obtained in the same manner as in Example 1. 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]
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) ) Is dispersed in ethanol with a solid content concentration of 9.5% by mass, and 0.30 g of powdered cerium carbonate hydrate (Ce ₂ (CO ₃ ) ₃ · 8H ₂ O) is charged. The mixture was mixed and pulverized using an ultrasonic generation homogenizer (trade name: US-600T: manufactured by Nippon Seiki Co., Ltd.) to obtain a translucent dispersion in which cerium carbonate particles were dispersed. Next, this composition was coated on a 100 μm ETFE sheet with a die coater to form a cast film.

  This is dried at 80 ° C. for 30 minutes and further annealed at 150 ° C. for 30 minutes to obtain a polymer electrolyte membrane having a film thickness of 50 μm and a cerium carbonate hydrate content of 3.2% of the total mass of the membrane. A membrane having a size of 5 cm × 5 cm is cut out from the polymer electrolyte membrane, and a membrane electrode assembly is obtained in the same manner as in Example 1. 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]
In a 300 ml glass round bottom flask, 100 g of dispersion A and 0.5 g of cerium oxide fine powder (CeO ₂ , Junsei Chemical Co., Ltd., average particle size 0.4 μm) were charged 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 as in Example 2 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. A membrane having a size of 5 cm × 5 cm was cut out from this polymer electrolyte membrane, and a membrane / electrode 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 6]
As the electrolyte membrane, a 50 μm-thick ion exchange membrane made of a polymer compound of polyether ether ketone having a sulfonic acid group, in which a part of the sulfonic acid group was ion-exchanged with a sparingly soluble cerium compound, was prepared as follows. . That is, 60 g of granular commercially available polyetheretherketone (trade name: PEEK-450P, manufactured by Victrex) is added little by little to 1200 g of 98% sulfuric acid at room temperature, and stirred at room temperature for 60 hours to obtain a uniform solution. Thus, a solution of a polymer compound in which a sulfonic acid group was introduced into polyether ether ketone was obtained. Next, while cooling this solution, it was dropped into 5 L of distilled water for removal, thereby precipitating polyether ether ketone having a sulfonic acid group, and separating by filtration. Next, this was washed with distilled water until 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, a polyether ether ketone having a sulfonic acid group is dissolved in N-methyl-2-pyrrolidone (NMP) to obtain a solution of about 10% by mass, and the cerium phosphate obtained in Example 3 is added thereto. And mix. This was cast into a substrate made of polytetrafluoroethylene at room temperature, dried in a nitrogen atmosphere at 100 ° C. for 10 hours to evaporate NMP, and the content of cerium phosphate in the film at a thickness of 50 μm Gives a polymer electrolyte membrane of 3.0% of the total mass of the membrane. A membrane having a size of 5 cm × 5 cm is cut out from the polymer electrolyte membrane, and a membrane electrode assembly is obtained in the same manner as in Example 1. 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 7]
As the solid polymer electrolyte membrane, the same commercially available ion exchange membrane as that used in Example 1 was used without any treatment, and then 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 Tables 1 to 3 were obtained.

[Example 8]
A 300 ml glass round bottom flask was charged with 100 g of dispersion A and 1.00 g of powdered zirconium phosphate (Daiichi Rare Element Chemical Co., Ltd.) and stirred at room temperature for 8 hours with a PTFE meniscus blade. Thus, a liquid composition in which zirconium phosphate was dispersed was obtained. 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. Thus, a solid polymer electrolyte membrane having a thickness of 50 μm and a zirconium phosphate content of 3.2% of the total mass of the membrane was obtained. A membrane having a size of 5 cm × 5 cm is cut out from the polymer electrolyte membrane, and a membrane / catalyst layer assembly is 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 9]
A 300 ml glass round bottom flask was charged with 100 g of dispersion A and 1.00 g of powdered silicon dioxide (manufactured by Kanto Chemical Co., Inc., average particle size 1.0 μm), and at room temperature with a PTFE meniscus blade. Stir for 8 hours to obtain a liquid composition in which silicon dioxide is dispersed. 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. To obtain a solid polymer electrolyte membrane having a thickness of 50 μm and a silicon dioxide content of 3.2% of the total mass of the membrane. A membrane having a size of 5 cm × 5 cm is cut out from the electrolyte membrane, and a membrane / catalyst layer assembly is obtained in the same manner as in Example 1. 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 10]
A membrane / catalyst layer assembly was obtained in the same manner as in Example 5 except that the ion exchange membrane comprising the polyether ether ketone having a sulfonic acid group obtained in Example 6 was used as it was without containing anything. Get the body. 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.

  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 low humidification power generation and high humidification power generation.

Claims (8)

  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. A solid or a solid containing a substance that forms a soluble cerium compound is added to the dispersion to form a hardly soluble cerium compound in the dispersion, and the resulting liquid is used to form a film. A method for producing an electrolyte membrane for a polymer fuel cell.   2. The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to claim 1, wherein the obtained liquid is cast into a membrane.   The refractory cerium compound is selected from the group consisting of cerium phosphate, cerium oxide, cerium hydroxide, cerium carbonate, cerium oxalate, cerium fluoride, cerium tungstate, and cerium salts of heteropolyacids. Item 3. The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to Item 1 or 2.   2. 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 contains a hardly soluble cerium compound. 4. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to any one of 3 above.   The production of an electrolyte membrane for a polymer electrolyte fuel cell according to any one of claims 1 to 4, wherein the hardly soluble cerium compound is contained in an amount of 0.3 to 80% of the total mass of the cation exchange membrane. Method.   The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to any one of claims 1 to 5, wherein the polymer compound having a sulfonic acid group is a fluoropolymer having a sulfonic acid group.   The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to any one of claims 1 to 6, wherein the fluorinated polymer having a sulfonic acid group is a perfluorocarbon polymer having a sulfonic acid group. The perfluorocarbon _{polymer, 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 represents an integer of 1 to 12, p represents 0 or 1, and X represents a fluorine atom or a trifluoromethyl group.) and a copolymer comprising a polymer unit based on tetrafluoroethylene The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to any one of claims 1 to 7.