JP2006099999A - Electrolyte membrane for polymer electrolyte fuel cell, production method thereof and membrane electrode assembly for polymer electrolyte fuel cell - Google Patents

Abstract

[PROBLEMS] To provide a membrane for a polymer electrolyte fuel cell capable of generating power with high energy efficiency, having high power generation performance regardless of the dew point of a supply gas, and capable of stable power generation over a long period of time. provide.
A cation exchange membrane made of a polymer compound having a sulfonic acid group, which performs an oxidation / reduction reaction in which a standard electrode potential in an aqueous solution is in a range of 1.14 to 1.763 V at 25 ° C. An electrolyte membrane containing a cation is used as an electrolyte membrane for a polymer electrolyte fuel cell. As the cation, for example, cerium ion and manganese ion can be used.
[Selection figure] None

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 a hydrocarbon polymer. In recent years, polymer electrolyte fuel cells using ion-exchange membranes made of these perfluorocarbon polymers are expected to be used as power sources for automobiles and residential markets, etc. . In these applications, since operation with particularly high efficiency is required, operation at a higher voltage is desired and at the same time cost reduction is desired. In addition, from the viewpoint of the efficiency of the entire fuel cell system, operation with low or no humidification is often required.

  However, even in a fuel cell using an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group, the stability is very high when operated under high humidification, but in operating conditions under low or no humidification. It has been reported that the voltage 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. (See Non-Patent Documents 2 and 3).

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 11th Fuel Cell Symposium Lecture Proceedings Page 218 (2004.519) Sponsored by Fuel Cell Development Information Center A. B. LaConti, M.M. Hamdan and R.C. C. McDonald, “Mechanisms of Membrane Degradation for PEMFCs”, Handbook of Fuel Cells: Fundamentals, Technology, and Applications, Vol. 3, p652

  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 fuel with high power generation performance and stable power generation over a long period of time, whether it is operated with low or no humidification or high humidification where the temperature is close to the cell temperature It aims at providing the electrolyte membrane for batteries.

As a degradation mechanism of the polymer electrolyte fuel cell, hydrogen peroxide is detected in the exhaust gas from the anode (hydrogen electrode) (see Non-Patent Document 2), and the decomposition of the membrane is caused by Fe ²⁺ ions present in the membrane. It is considered that hydrogen radicals are reduced by the reaction proceeding in the right direction of the formula (2) by Cu ⁺ ions to generate hydroxy radicals, which accelerate the deterioration of the film (see Non-Patent Document 3). Therefore, in order to suppress the deterioration of the film, while suppressing the hydroxyl radical generation reaction (formula (2)) due to the reaction of hydrogen peroxide in the film, simultaneously the reaction in the right direction shown in the formula (1), That is, the present inventor thought that the reaction for reducing hydrogen peroxide to harmless water should proceed. Here, the standard electrode potential of the formula (1) is 1.763 V in an aqueous solution at 25 ° C., and the standard electrode potential of the formula (2) is 1.14 V in an aqueous solution at 25 ° C. (Electrochemical Handbook 5 Edition, 94 pages, edited by The Electrochemical Society of Japan, published by Maruzensha, 2000. Hereinafter referred to as “Reference 1”).

  The present inventor presents in the ion exchange membrane a specific cation that has a reducing power sufficient to proceed with the reaction of formula (1) and that cannot proceed with the reaction of formula (2) in principle. We thought that deterioration of the film could be suppressed. Specifically, the standard electrode potential has a lower value than the standard electrode potential of formula (1) and a noble value than the standard electrode potential of formula (2), that is, 25 ° C. in an aqueous solution. If a cation (hereinafter referred to as “the present cation”) that undergoes an oxidation / reduction reaction having a standard electrode potential in the range of 1.14 to 1.763 V is present in the membrane, the reaction of formula (1) is thermodynamically performed. It was thought that the reaction of formula (2), which generates a hydroxy radical from hydrogen peroxide, cannot proceed. Here, the cation acts as a reducing agent in the reaction of the formula (1) and is oxidized during the reaction, but is easily reduced to the original state by hydrogen leaking from the anode into the membrane during operation of the fuel cell. It was considered that the reaction of formula (1) can be repeated and the present invention was reached.

  The present invention relates to a cation exchange membrane comprising a polymer compound having a sulfonic acid group, which performs an oxidation / reduction reaction in which a standard electrode potential in an aqueous solution is in a range of 1.14 to 1.763 V at 25 ° C. An electrolyte membrane for a polymer electrolyte fuel cell, a membrane electrode assembly for a polymer electrolyte fuel cell comprising the electrolyte membrane, and a method for producing the same.

  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.

  What can be used as the present cation, its redox reaction and its standard electrode potential are shown in the following formulas (3) to (8). The standard electrode potential is indicated next to the equation (Source: Reference 1).

  Among these, from the viewpoint of safety and handleability, the cation is preferably at least one selected from the group consisting of cerium ions and manganese ions. Here, when the cation is contained in the membrane, it may be in a reduced state or an oxidized state. That is, the cerium ion may be +3 or +4, and the manganese ion may be +2 or +3.

  Even if the standard electrode potential is a cation that undergoes oxidation / reduction outside the range of 1.14 to 1.763 V, a complex ion is formed by coordinating or binding various compounds such as ligands to the cation. If the standard electrode potential when the complex ion is oxidized and reduced is in the range of 1.14 to 1.763 V, the complex ion can be used as the present cation.

  In addition to the cation that causes a redox reaction in which the oxidized state and the reduced state are cations as described above, a compound that is a cation in the reduced state but becomes a compound such as an oxide in the oxidized state has a standard electrode potential of 1. If it is in the range of .14 to 1.763 V, it can be used as the present cation. Examples of such redox reaction of the present cation are given below. In the formulas (9) to (11), the reductant is a cation and the oxidant is a combination of oxides, and the standard electrode potential is shown beside the formula. It is considered that such a system can also promote the reaction of reducing hydrogen peroxide to harmless water (Source: Reference 1).

  The cation may exist in any state in the electrolyte membrane as long as it is present as an ion, but as one state, a part of the sulfonic acid group in the electrolyte membrane is ion-exchanged with the cation to be present. be able to. When both the oxidant and the reductant are cations, the cation is likely to exist in a stable state by ion exchange with the proton of the sulfonic acid group, and it is considered that it does not elute out of the system. This is preferable because it can have an excellent structure with respect to hydrogen oxide or peroxide radicals.

For example, when the cation is a cerium ion and the cerium ion is trivalent, when the sulfonic acid group is ion-exchanged by the cerium ion, Ce ³⁺ is bonded to _three —SO ₃ ^— as shown below.

  The electrolyte membrane of the present invention need not contain the present cation uniformly. For example, it is a cation exchange membrane (laminated membrane) composed of two or more layers, and has at least one layer containing the present cation instead of all the layers, that is, the present cation is unevenly distributed in the thickness direction. May be included. Therefore, particularly 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 is made of an ion exchange membrane containing the present cation, and the other layers are It can also be comprised with the film | membrane which consists of a high molecular compound which has a sulfonic acid group which does not contain this cation.

The method for obtaining the electrolyte membrane of the present invention by incorporating the present cation in the polymer compound having a sulfonic acid group is not particularly limited, and examples thereof include the following methods. (1) A method of immersing a film made of a polymer compound having a sulfonic acid group in a solution containing the present cation. (2) After adding a salt containing the present cation to the dispersion of the perfluorocarbon polymer having a sulfonic acid group to contain the present cation in the dispersion, or having a sulfonic acid group and the solution containing the present cation A method in which a dispersion of a polymer compound is mixed to contain the present cation, and then the resulting solution is used to form a film by a casting method or the like. (3) A method in which an organic metal complex salt containing the cation is brought into contact with a cation exchange membrane composed of a polymer compound having a sulfonic acid group to contain the cation. (4) By adding a metal (for example, cerium metal or manganese metal) that can become the present cation to the dispersion liquid of the perfluorocarbon polymer having a sulfonic acid group, the cation is reacted with the metal. Method to contain.
In the electrolyte membrane containing the present cation obtained by the above method, it is considered that a part of the sulfonic acid group is ion-exchanged by the present cation.

When, for example, cerium ions are included in the electrolyte membrane as the cation, the salt used may be +3 or +4, and various 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 +4 valent 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 preferable because they are water-soluble and 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.

When the cation is manganese ion, the valence may be +2 or +3, and various manganese salts are used to obtain a solution containing manganese ions. Specific examples of the salt containing +2 valent 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 preferable because they are water-soluble and 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.

Here, for example, when the manganese ion is +2, 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 ^—. become.

In the present invention, when the present cation contained in the electrolyte membrane is a cation in both the oxidized state and the reduced state, 1 to 90 equivalents of the —SO ₃ ^— group in the membrane when converted into the reduced state It is preferable that an amount corresponding to% is included. Here, for example, in the case of cerium ions, there are trivalent and tetravalent states in the film, but the reduced state refers to trivalent cerium, and the above ratio is the ratio of equivalents calculated as trivalent cerium ions. Show. That is, for example, cerium ions are -SO ₃ in the film ^- that contained 1 mole% of groups, cerium ions are -SO ₃ in the film ^- it is synonymous with included 3 equivalent percent of the group. If the proportion of the present cation contained in the electrolyte membrane is low, sufficient stability against hydrogen peroxide or peroxide radicals may not be ensured. On the other hand, if this ratio is too high, sufficient conductivity of hydrogen ions cannot be ensured, resulting in an increase in membrane resistance and a decrease in power generation characteristics. More preferably, the said ratio is 2-50 equivalent%, More preferably, it is 3-40 equivalent%.

When the electrolyte membrane of the present invention is a laminated membrane, the ratio of the present cation to the —SO ₃ ^— group of the entire electrolyte membrane may be in the above range, and the layer of the present cation containing the present cation itself The content rate may be higher than the above range. In addition, as a method for producing the laminated film, for example, a cation exchange membrane containing the present cation is produced by any one of the methods (1) to (4) described above, and the cation exchange membrane not containing the present cation is laminated. However, it is not particularly limited.

In the present invention, the polymer compound having a sulfonic acid group before containing the cation is not particularly limited, but the ion exchange capacity is preferably 0.5 to 3.0 meq / g dry resin, particularly 0. It is preferably 7 to 2.5 meq / g dry resin. From the viewpoint of durability, the polymer compound is preferably a fluorine-containing polymer, and more preferably a perfluorocarbon polymer (which may contain an etheric oxygen atom). No particular limitation is imposed on the perfluorocarbon polymer _{but, CF 2 = CF- (OCF 2} CFX) m -O p - (CF 2) a perfluorovinyl compound represented by n -SO ₃ H (m is 0-3 N represents an integer of 1 to 12, p represents 0 or 1, X represents a fluorine atom or a trifluoromethyl group, and a polymer unit based on tetrafluoroethylene. It is preferable that it is a copolymer containing.

  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.

  In addition, as the polymer compound having a sulfonic acid group before containing the cation, those other than the perfluorocarbon polymer having a sulfonic acid group can be used, for example, in the main chain of the polymer or in the main chain and the side chain. A polymer having an aromatic ring and 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 A compound 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. In the second method, the dispersion is applied on two carbon cloths or carbon paper, and then sandwiched from both sides of the ion exchange membrane so that the surface on which the dispersion is applied is in close contact with the ion exchange membrane. It is a method to rub. Here, the carbon cloth or the carbon paper has a function as a gas diffusion layer and a function as a current collector for 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. .

  The ion exchange resin contained in the catalyst layer is not particularly limited, but is preferably a perfluorocarbon polymer having a sulfonic acid group. The ion exchange resin in the catalyst layer may contain the present cation similarly to the electrolyte membrane of the present invention. Since the ion exchange resin containing the present cation can be used for both the anode and the cathode, and the decomposition of the resin is effectively suppressed, the solid polymer fuel cell is further provided with durability.

  When it is desired to contain the present cation 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 joined body is immersed in a solution containing the present cation. It is also possible to make it.

  The electrolyte membrane of the present invention may be a membrane made only of a polymer compound having a sulfonic acid group, partly containing the present cation, but may contain other components, such as polytetrafluoroethylene or It may be a membrane reinforced with fibers such as other resins such as fluoroalkyl ether, woven fabric, nonwoven fabric, porous body and the like. Even in the case of a reinforced membrane, the electrolyte membrane of the present invention can be obtained by immersing a cation exchange membrane having a reinforced sulfonic acid group in a solution containing the present cation. Moreover, the method of forming into a film using the dispersion liquid containing the high molecular compound ion-exchanged with this cation is also applicable.

  In the electrolyte membrane of the present invention, the presence of the cation in the membrane suppresses the generation reaction of hydroxyl radicals due to the reaction of hydrogen peroxide in the membrane (formula (2)), and at the same time harms hydrogen peroxide. It is considered that the reaction (formula (1)) for reducing to pure water proceeds. As long as hydrogen is present in the membrane, the cation can be present in the membrane in a reduced state, and as a result, the reaction for reducing hydrogen peroxide to harmless water (formula (1)) is continuously performed. It is considered that the film can be made to progress and the decomposition of the film can be suppressed. In addition, when the cation is present in an ion exchange membrane having a sulfonic acid group and is ion-exchanged with a proton bonded to the sulfonic acid group of the membrane, unless an operation such as washing the membrane with an acid is performed. It is considered that this cation does not elute out of the membrane due to the electrically neutral condition. Therefore, it is possible to suppress the decomposition of the membrane over a long period of time even in the operating state of the fuel cell and in the open circuit state.

Therefore, the electrolyte membrane of the present invention has excellent resistance to hydrogen peroxide or peroxide radicals. Further, even if impurities such as Fe ²⁺ ions and Cu ²⁺ ions exist in the film and the reaction of the formula (2) proceeds by the ions of the impurities to reduce hydrogen peroxide to generate hydroxy radicals, The radical is generated by a reaction of OH · + H ⁺ + e ⁻ → H ₂ O (formula (12)), and the standard electrode potential occurs at a noble potential of 2.38V. Since this reaction has such a very noble potential, it is considered that the reaction of the formula (12) in which the hydroxy radical is reduced by the presence of this cation easily proceeds.

  Hereinafter, the present invention will be specifically described using Examples (Examples 1 to 10) and Comparative Examples (Examples 11 to 14), but the present invention is not limited thereto.

[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).

Next, as containing cerium ions, which corresponds to 30% of the amount of the sulfonic acid groups of the membrane (+3), cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O) distilled 12.0mg of 500mL It melt | dissolved in water, the said ion exchange membrane was immersed in this, and it stirred using the stirrer at room temperature for 40 hours, and contained the cerium ion in the ion exchange membrane. In addition, as a result of analyzing the cerium nitrate solution before and after immersion by ion chromatography, it was found that the cerium ions in the ion exchange membrane were 28 equivalent% of the —SO ₃ ^— group (hereinafter, this ratio was referred to as “cerium ion”). "Content rate").

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 ions, the catalyst layers formed on the base film are respectively disposed on both sides of the membrane, and transferred by a hot press method to be the anode catalyst layer and the cathode catalyst. A membrane catalyst layer assembly was obtained in which the 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, and 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 were measured. 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]
Instead of using the aqueous solution of cerium nitrate used in Example 1, an aqueous solution in which 9.8 mg of cerium sulfate (Ce ₂ (SO ₄ ) ₃ · 8H ₂ O) containing cerium ions (+ trivalent) was dissolved in 500 mL of distilled water was used. In the same manner as in Example 1, the same commercially available ion exchange membrane as used in Example 1 is treated to obtain a membrane having a cerium ion content of 28 equivalent%. Next, using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1, and a membrane / electrode assembly is further obtained. 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 3]
Instead of the cerium nitrate aqueous solution used in Example 1, except that an aqueous solution in which 8.0 mg of cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O) was dissolved in 500 mL of distilled water was used, The same commercially available ion exchange membrane as used in Example 1 was treated to obtain a membrane having a cerium ion content of 19 equivalent%. Next, using this membrane, a membrane / catalyst layer assembly was obtained in the same manner as in Example 1, and a membrane / electrode assembly was further 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 4]
Instead of the cerium nitrate aqueous solution used in Example 1, a solution similar to Example 1 was used except that 4.0 mg of cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O) was dissolved in 500 mL of distilled water. The same commercially available ion exchange membrane as used in Example 1 is treated to obtain a membrane having a cerium ion content of 10 equivalent%. Next, using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1, and a membrane / electrode assembly is further obtained. 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 a solid polymer 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 is ion-exchanged with cerium ions, is produced as follows. did. That is, by adding 60 g of granular commercially available polyetheretherketone (manufactured by Victrex, UK, PEEK-450P) to 1200 g of 98% sulfuric acid little by little at room temperature and stirring at room temperature for 60 hours to obtain a uniform solution, 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 to remove it, 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 protons and sodium ions of sulfonic acid groups. 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, the 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, which is casted on a substrate made of polytetrafluoroethylene at room temperature. After film formation, the film was dried at 100 ° C. for 10 hours in a nitrogen atmosphere to evaporate NMP, thereby obtaining a film having a thickness of 50 μm. Next, this film was cut into a size of 5 cm × 5 cm (area: 25 cm ² ), and the weight of the entire film was measured in the same manner as in Example 1. As a result, it was 0.168 g. The amount of sulfonic acid groups in this membrane is determined by the following formula.
0.168 * 1.6 (1.1 milliequivalent / g dry resin) = 0.269 (milliequivalent).

Aqueous solution of Ce ions cerium nitrate containing _{(+3) (Ce (NO 3) 3} · 6H 2 O) 12.0mg dissolved in distilled water of 500mL corresponding to an amount of about 30% of the sulfonic acid groups of the membrane Then, the ion exchange membrane is immersed and stirred with a stirrer at room temperature for 40 hours to obtain a membrane having a cerium ion content of 31 equivalent%. Next, using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1, and a membrane / electrode assembly is further obtained. 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 6]
In the same manner as in Example 1 except that an aqueous solution in which 12.0 mg of manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O) was dissolved in 500 mL of distilled water was used instead of the cerium nitrate aqueous solution used in Example 1, The same commercially available ion exchange membrane as used in Example 1 was treated. It was found that the manganese ion content of this ion exchange membrane (the ratio of manganese ions to the number of —SO ₃ ^— groups in the membrane) was 28 equivalent%. Next, using this membrane, a membrane / catalyst layer assembly was obtained in the same manner as in Example 1. The membrane electrode assembly was evaluated in the same manner as in Example 1. As shown in Tables 1 to 3, became.

[Example 7]
Instead of the manganese nitrate aqueous solution used in Example 6, a solution similar to Example 1 was used except that 10.0 mg of manganese sulfate (MnSO ₄ .5H ₂ O) containing manganese ions (+2 valent) was dissolved in 500 mL of distilled water. Then, the same commercially available ion exchange membrane as that used in Example 1 is treated to obtain a membrane having a manganese ion content of 28 equivalent%. Next, using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1, and a membrane / electrode assembly is further obtained. 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 8]
In the same manner as in Example 1 except that an aqueous solution in which 8.0 mg of manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O) was dissolved in 500 mL of distilled water was used instead of the aqueous manganese nitrate solution used in Example 6, The same commercially available ion exchange membrane as that used in Example 1 was treated to obtain a membrane having a manganese ion content of 19 equivalent%. Next, using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1, and a membrane / electrode assembly is further obtained. 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 9]
In the same manner as in Example 1 except that an aqueous solution in which 4.0 mg of manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O) was dissolved in 500 mL of distilled water was used instead of the manganese nitrate aqueous solution used in Example 6, The same commercially available ion exchange membrane as that used in Example 1 is treated to obtain a membrane having a manganese ion content of 10 equivalent%. Next, using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1, and a membrane / electrode assembly is further obtained. 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]
Using the ion exchange membrane made of polyetheretherketone having sulfonic acid groups obtained in Example 5, manganese ions (+2 corresponding to about 30% of the amount of sulfonic acid groups in this membrane were obtained in the same manner as in Example 6. an aqueous solution of manganese nitrate _{(Mn (NO 3) 2 ·} 6H 2 O) 12.0mg dissolved in distilled water of 500mL containing valence), and immersing the ion-exchange membrane, at room temperature for 40 hours, stirring with a stirrer Thus, a film having a manganese ion content of 31 equivalent% is obtained. Next, 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 11]
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 / 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 12]
In the same manner as in Example 1, 9.8 mg of calcium nitrate (Ca (NO ₃ ) ₂ .4H ₂ O) containing calcium ions (+2) was distilled from 500 mL of the same commercially available ion exchange membrane as used in Example 1. It is immersed in an aqueous solution dissolved in water to obtain a membrane having a calcium ion content (the ratio of calcium ions to the number of —SO ₃ ^— groups in the membrane) of 21 equivalent%. Calcium ions do not cause a redox reaction in an aqueous solution. Next, using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1, and a membrane / electrode assembly is further obtained. 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 13]
In the same manner as in Example 1, 10.3 mg of copper sulfate (CuSO ₄ .5H ₂ O) containing copper ions (+2) was dissolved in 500 mL of distilled water using the same commercially available ion exchange membrane as used in Example 1. Immersion in an aqueous solution yields a film having a copper ion content of 29 equivalent% (ratio of copper ions to the number of —SO ₃ ^— groups in the film). Next, using this membrane, a membrane / catalyst layer assembly is obtained in the same manner as in Example 1, and a membrane / electrode assembly is further obtained. 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. Although copper ions cause a reaction of Cu ²⁺ + e ⁻ → Cu ^{+ in} an aqueous solution, the standard electrode potential of this reaction is 0.159 V, and the copper ions correspond to a comparative example of the present invention.

[Example 14]
A membrane / catalyst layer assembly was obtained in the same manner as in Example 5 except that the ion exchange membrane comprising a polyether ether ketone having a sulfonic acid group obtained in Example 5 was used without being treated with cerium ions, and a membrane electrode was further obtained. Obtain a zygote. 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 (10)

  A cation exchange membrane made of a polymer compound having a sulfonic acid group, which contains a cation that performs an oxidation / reduction reaction in which a standard electrode potential in an aqueous solution is in a range of 1.14 to 1.763 V at 25 ° C. An electrolyte membrane for a polymer electrolyte fuel cell.   The electrolyte membrane for a polymer electrolyte fuel cell according to claim 1, wherein the cation is at least one selected from the group consisting of cerium ions and manganese ions.   The solid polymer according to claim 1 or 2, comprising 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 the cation. Electrolyte membrane for fuel cell. The cation is present as a cation in an oxidized state or a reduced state, and the content in the membrane includes an amount corresponding to 1 to 90 equivalent% of the —SO ₃ ^— group in the membrane in the reduced state. The electrolyte membrane for polymer electrolyte fuel cells according to any one of?   The polymer membrane for a polymer electrolyte fuel cell according to any one of claims 1 to 4, wherein the polymer compound 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 electrolyte membrane for a polymer electrolyte fuel cell according to claim 5.   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 4, wherein the exchange capacity is 0.8 to 3.0 meq / g dry resin.   The method for producing an electrolyte membrane according to any one of claims 1 to 7, wherein a cation exchange membrane comprising a polymer compound having a sulfonic acid group has a standard electrode potential of 1.14 in an aqueous solution at 25 ° C. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell, wherein the membrane is immersed in an aqueous solution containing a cation that undergoes an oxidation / reduction reaction in a range of ˜1.763V.   The method for producing an electrolyte membrane according to any one of claims 1 to 7, wherein a standard electrode potential in an aqueous solution is 1 at 25 ° C and a solution obtained by dissolving or dispersing a polymer compound having a sulfonic acid group in a solvent An electrolyte membrane for a polymer electrolyte fuel cell, characterized in that a coating liquid containing a cation that performs an oxidation / reduction reaction in the range of .14 to 1.763 V is prepared, and the coating liquid is cast into a film. Manufacturing method. A membrane electrode assembly comprising a cathode and an anode having a catalyst layer containing a catalyst, and a solid polymer electrolyte membrane disposed between the cathode and the anode, wherein the solid polymer electrolyte membrane is defined in claims 1 to 7. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising the electrolyte membrane according to any one of the above.