JP5079306B2 - Polymer electrolyte membrane for fuel cell, membrane-electrode assembly, and fuel cell - Google Patents

Description

  The present invention relates to a polymer electrolyte membrane for a fuel cell, a membrane-electrode assembly, and a fuel cell, and more particularly to a polymer electrolyte membrane for a fuel cell having a crosslinked structure.

  Regarding polymer electrolyte membranes for fuel cells, many researches on hydrocarbon polymer membranes were conducted in the early development in the 1960s. In 1968, EIDu Pont de Nemours, Inc. As a result of the development of a perfluorinated sulfonic acid (Nafion) membrane made of perfluoronate sulfonic acid, research has been in full swing. The development is progressing.

However, the fuel cell using the Nafion system has a methanol crossover (Direct methanol fuel cell; DMFC) due to the CO poisoning problem of the electrocatalyst with driving below 80 ° C and the direct methanol fuel cell (DMFC). Many studies have been made to solve this problem because cross over) is a major factor that degrades the characteristics of fuel cells and regulates their lifespan.
Recently, in the case of fluorinated polymer electrolyte membranes such as Nafion, there is a problem that there is no thermal stability at a temperature of 90 ° C. or more, and there is a problem that synthesis is difficult and the price of the material is high. Sulfonated hydrocarbon polymer electrolyte membranes have been developed in order to ensure the cost and reduce the cost.
However, since the sulfonated hydrocarbon polymer electrolyte membrane is a system that does not conduct protons without moisture, dehydration occurs inside the membrane when driven at a high temperature of 100 ° C. or higher, and the hydrogen ion conductivity. Have a problem of sudden drop.

In US Pat. No. 5,525,436, a method for producing an electrolyte membrane having hydrogen ion conductivity was proposed by impregnating polybenzimidazole with a strong acid such as phosphoric acid and at a high temperature of 130 ° C. or higher and low humidification. In order for fuel cells to be commercialized in this way, durability that does not deteriorate the characteristics of the battery even during long-term operation has attracted attention as an important characteristic, and many recent research teams have caused the decrease in battery life. Efforts are being made to improve the electrolyte membrane degradation problem, which is expected to be one of the above.
US Pat. No. 5,525,436

The present invention improves the chemical resistance of a polyimide polymer electrolyte membrane containing an imidazole group in Korean Patent Application No. 2006-15710, and ensures a long-term durability. The present invention relates to a membrane, a membrane-electrode assembly using the same, and a fuel cell. More specifically, a new polymer structure having high chemical resistance and high mechanical strength by introducing a polyimide crosslinking agent for a polymer electrolyte membrane. By forming a membrane and improving the resistance to radicals generated when driving a fuel cell, it stably expresses hydrogen ions at high temperatures and is used to suit high-temperature, non-humidified fuel cell systems It is an object of the present invention to provide a polymer electrolyte membrane for a fuel cell, a membrane-electrode assembly using the same, and a fuel cell.
The technical problems to be solved by the present invention are not limited to those described above, and other technical problems that are not mentioned will become clear from the following description.

In order to achieve the above object, the present invention employs the following configuration.
In the polymer electrolyte membrane for a fuel cell of the present invention, the polyimide polymer represented by the following formula (1) is cross-linked by any one of the cross-linking agents of the following formulas (2) to (5). It is characterized by being impregnated.
However, in the following formula (1), B is a structure represented by the following formula (6), and A and P were independently selected from the structures represented by the following formulas (7) to (17). And D is one selected from the structures represented by the following formulas (18) to (25). Moreover, in following formula (1), m is the range of 10,000-1 million, and n is the range of 5000-500000.
Moreover, in Formula (2), R is any of alicyclic, aromatic, and heteroaromatic, and a which shows the number of the epoxy groups which are reactive groups is 2 or more.
Moreover, in Formula (3), R1 is either aromatic or heteroaromatic, and b indicating the number of amine groups as reactive groups is 3 or more.

In the polymer electrolyte membrane for a fuel cell of the present invention, the polyimide weight when a indicating the number of the epoxy groups is in the range of 2 to 4 and the crosslinking agent represented by the above formula (2) is selected. It is preferable that the content rate of the said crosslinking agent with respect to coalescence is 1-40 mass%.
Moreover, in the polymer electrolyte membrane for fuel cells of the present invention, the polyimide weight when a indicating the number of amine groups is in the range of 3 to 4 and the crosslinking agent represented by the above formula (3) is selected. It is preferable that the content rate of the said crosslinking agent with respect to coalescence is 1-40 mass%.
In the polymer electrolyte membrane for a fuel cell of the present invention, when the crosslinking agent represented by the above formula (4) is selected, the molar ratio of B to the crosslinking agent in the above formula (1) is B: crosslinking agent. It is preferable to adjust so that it may become = 90: 20-99: 2.
In the polymer electrolyte membrane for a fuel cell of the present invention, when the cross-linking agent represented by the above formula (5) is selected, the molar ratio of A and P to the cross-linking agent in the above formula (1) is (A + P). ): Cross-linking agent = 90: 20 to 99: 2 is preferably adjusted.

Next, a membrane-electrode assembly for a fuel cell according to the present invention includes a polymer electrolyte membrane for a fuel cell according to any one of the above, and a pair of catalysts disposed on both surfaces of the polymer electrolyte membrane for a fuel cell. And a gas diffusion layer disposed on the opposite side of the catalyst layer from the polymer electrolyte membrane for a fuel cell.
The fuel cell of the present invention comprises the membrane-electrode assembly described above and bipolar plates disposed on both surfaces of the membrane-electrode assembly.

  According to the polymer electrolyte membrane for a fuel cell in which the crosslinking agent of the present invention is introduced, the polymer electrolyte exhibits excellent phosphoric acid impregnation characteristics and high ionic conductivity even under high temperature non-humidified conditions of 150 ° C. or higher. In addition to providing sufficient characteristics as a membrane, the chemical stability can be improved, and excellent characteristics can be exhibited in that it can be applied to fuel cells to provide stable battery characteristics during long-term operation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an exploded perspective view showing an example of the fuel cell of the present embodiment, and FIG. 2 is a schematic sectional view of a membrane-electrode assembly constituting the fuel cell of FIG.
The fuel cell 1 shown in FIG. 1 has a schematic configuration in which two single cells 11 are sandwiched between a pair of holders 12 and 12. The single cell 11 includes a membrane-electrode assembly 10 and bipolar plates 20, 20 arranged on both sides in the thickness direction of the membrane-electrode assembly 10. The bipolar plates 20 and 20 are made of conductive metal, carbon, or the like, and function as current collectors by being joined to the membrane-electrode assembly 10 respectively, and the catalyst of the membrane-electrode assembly 10. Supply oxygen and fuel to the bed.
The fuel cell 1 shown in FIG. 1 has two single cells 11, but the number is not limited to two, and may be increased to several tens to several hundreds depending on the characteristics required for the fuel cell. .

  As shown in FIG. 2, the membrane-electrode assembly 10 includes a polymer electrolyte membrane for fuel cells (hereinafter referred to as an electrolyte membrane) 100 according to the present invention, and a catalyst layer 110 disposed on both sides in the thickness direction of the electrolyte membrane 100. , 110 ′, the first gas diffusion layers 121, 121 ′ stacked on the catalyst layers 110, 110 ′, and the second gas diffusion layers 120 stacked on the first gas diffusion layers 121, 121 ′, respectively. , 120 ′.

The catalyst layers 110 and 110 ′ function as a fuel electrode and an oxygen electrode, and are each configured to include a catalyst material such as activated carbon and a binder that solidifies and forms the catalyst material. As the binder, a fluororesin excellent in heat resistance may be used, or a material constituting the electrolyte membrane according to the present invention may be used. By using the material constituting the electrolyte membrane as the binder, proton diffusion inside the catalyst layers 110 and 110 ′ is efficiently performed, the impedance of the catalyst layers 110 and 110 ′ is lowered, and the output of the fuel cell is improved.
The first gas diffusion layers 121 and 121 ′ and the second gas diffusion layers 120 and 120 ′ are each formed of, for example, a carbon sheet, and catalyze oxygen and fuel supplied via the bipolar plates 20 and 20. Diffusion over the entire surface of the layers 110, 110 ′.

The fuel cell 1 including the membrane-electrode assembly 10 operates at a temperature of 100 ° C. to 300 ° C., for example, hydrogen is supplied as fuel to the one catalyst layer side via the bipolar plate 20, and the other catalyst layer side For example, oxygen is supplied as an oxidizing agent through the bipolar plate 20. Then, hydrogen is oxidized in one catalyst layer to generate protons, and the protons pass through the electrolyte membrane 4 to reach the other catalyst layer, and the proton and oxygen react electrochemically in the other catalyst layer. In addition to producing water, it generates electrical energy.
The hydrogen supplied as the fuel may be hydrogen generated by reforming hydrocarbons or alcohols, and the oxygen supplied as the oxidant may be supplied in a state of being included in the air.

Next, the electrolyte membrane 4 provided in the membrane-electrode assembly 1 will be described.
In the electrolyte membrane 4 according to the present invention, the polyimide polymer represented by the following formula (26) is crosslinked by any one of the compounds represented by the following formulas (27) to (30), and the acid It is configured to be impregnated. However, in the following formula (26), B is a structure represented by the following formula (31), and A and P were independently selected from the structures represented by the following formulas (32) to (42). And D is one selected from the structures represented by the following formulas (43) to (50). Moreover, in following formula (26), m is the range of 1000-1 million, n is the range of 5000-500000.
In the formula (27), R is any of alicyclic, aromatic, and heteroaromatic, and a indicating the number of epoxy groups as a reactive group is preferably 2 or more, more preferably in the range of 2-4. preferable.
In the formula (28), R1 is either aromatic or heteroaromatic, and b indicating the number of amine groups as a reactive group is preferably 3 or more, and more preferably in the range of 3-4.

The polyimide polymer represented by the above formula (26) is provided with a benzimidazole group represented by the above formula (31) and a large number of carbonyl groups (C═O groups) in the molecule. Thus, since the polyimide polymer represented by the above formula (26) has a large number of polar functional groups, it can stably hold an acid such as phosphoric acid. In the above formula (26), if m is less than 10000 or n is less than 5000, the heat resistance of the electrolyte membrane is lowered, which is not preferable. If m exceeds 2000000 or n exceeds 1000000, the polyimide polymer Since the solubility with respect to a solvent falls and shaping | molding of an electrolyte membrane becomes difficult, it is not preferable.
This polyimide polymer is produced by reacting a diamine compound having a benzimidazole group with a dicarboxylic acid anhydride such as pyrometic dianhydride to form an imide bond. B in Formula (26) is a structure derived from a diamine compound, and A and P are structures derived from a dicarboxylic acid anhydride.

  Next, the crosslinking agent represented by the formula (27) is an epoxy compound in which a plurality of reactive epoxy groups are bonded to R which is alicyclic, aromatic or heteroaromatic. The epoxy group contained in the epoxy compound reacts with the molecular chain of the polyimide polymer to crosslink the polyimide polymer. 2 or more is preferable and, as for a showing the number of epoxy groups, the range of 2-4 is more preferable. If the number of epoxy groups is less than 2, it is difficult to form a crosslinked structure, which is not preferable. In addition, the upper limit of the number of epoxy groups varies depending on the structure of R. However, when the number of epoxy groups exceeds 4, cross-linking proceeds too much, so that the acid impregnation rate may decrease and proton conductivity may decrease. As an example of the crosslinking agent represented by the formula (27), a compound represented by the following formula (27-1) can be exemplified.

  Next, the crosslinking agent represented by the formula (28) is an amine compound in which a plurality of amine groups as reactive groups are bonded to R1 which is either aromatic or heteroaromatic. The amine group contained in the amine compound reacts with the molecular chain of the polyimide polymer to crosslink the polyimide polymer. As for b which shows the number of amine groups, 3 or more are preferable and the range of 3-4 is more preferable. If the number of amine groups is less than 3, it is difficult to form a crosslinked structure, which is not preferable. In addition, the upper limit of the number of amine groups varies depending on the structure of R1, but when the number of amine groups exceeds 4, crosslinking proceeds too much, so that the acid impregnation rate may decrease and proton conductivity may decrease. As an example of the crosslinking agent represented by the formula (28), a compound represented by the following formula (28-1) can be exemplified.

  The content of the crosslinking agent represented by the formula (27) or (28) with respect to the polyimide polymer is preferably in the range of 1 to 40% by mass, more preferably in the range of 3% to 30% by mass, and 5 to 20% by mass. Is particularly ideal and preferred. If the content is less than 1% by mass, crosslinking is insufficient and the durability of the electrolyte membrane 4 is lowered, which is not preferable. On the other hand, if the content exceeds 49% by mass, crosslinking is excessively advanced, the acid impregnation rate is lowered, and the proton conductivity is lowered.

Next, the crosslinking agent shown in Formula (29) is p-ethynylaniline in which an amine group and an ethynyl group are bonded to a benzene ring. In the crosslinking mechanism by p-ethynylaniline, first, the amine group in the molecule is bonded to the end of the polyimide polymer molecular chain. At this time, a dicarboxylic acid anhydride may be located at the end of the polyimide polymer. The amine group of p-ethynylaniline reacts with the dicarboxylic anhydride to form an amide bond. Next, the ethynyl group in a form bonded to the end of the polymer undergoes a polymerization reaction with the ethynyl group at the other end of the polymer, thereby cross-linking the polymers at each end.
Moreover, the crosslinking agent shown in Formula (30) is maleic anhydride. In the crosslinking mechanism by maleic anhydride, first, the carbonyl group in the molecule is bonded to the end of the molecular chain constituting the polyimide polymer. At this time, a diamine compound may be located at the end of the polyimide polymer. The carbonyl group of maleic anhydride reacts with the amine group of the diamine compound to form an amide bond. Next, the intramolecular double bond of maleic anhydride in a form bonded to the end of the polymer undergoes a polymerization reaction with the double bond at the other end of the polymer, whereby the polymers are cross-linked at each end.

When the crosslinking agent represented by the above formula (29) is selected, the content ratio of the crosslinking agent is such that the molar ratio of B to the crosslinking agent in the above formula (26) is B: crosslinking agent = 90: 20 to 99: 2. It is adjusted to become.
Similarly, when the crosslinking agent represented by the above formula (30) is selected, the content of the crosslinking agent is such that the molar ratio of A and P to the crosslinking agent in the above formula (26) is (A + P): crosslinking agent = It is adjusted to be 90:20 to 99: 2.
In addition, the molar amount of B in Formula (26) is an amount corresponding to the molar amount of a diamine compound, and the molar amount of A and P is an amount corresponding to the molar amount of a dicarboxylic anhydride.
When the molar ratio of the crosslinking agent is less than the above range, crosslinking is insufficient and durability of the electrolyte membrane 4 is lowered, which is not preferable. On the other hand, when the molar ratio of the cross-linking agent is excessive from the above range, the cross-linking proceeds excessively, the acid impregnation rate decreases, and the proton conductivity decreases, which is not preferable.

  Next, examples of the acid impregnated in the polyimide polymer include phosphoric acid, phosphonic acid, sulfuric acid, ethylphosphoric acid, trifluoroacetic acid, trifluoromethanesulfonic acid, trifluoromethanesulfimidic acid, and phosphotungstic acid. From the viewpoints of heat resistance, corrosivity, volatility, and conductivity, phosphoric acid is preferred. Any of these acids is impregnated (doped) into a polyimide polymer to develop proton conductivity. The acid doping ratio is preferably in the range of 50% to 400%, more preferably in the range of 100% to 300%, although it depends on the type of acid. If the doping rate is too low, the proton conductivity is lowered, which is not preferred. If the doping rate is too high, the mechanical strength of the electrolyte membrane is lowered, which is not preferred.

  Next, a method for manufacturing the electrolyte membrane 4 according to the present invention will be described. In order to produce a polymer electrolyte membrane for a fuel cell using the above polyimide polymer, a polymer film must first be produced. A method for producing this polymer film is generally widely known. You can choose the method you have. This is the method described in Korean Patent Application 2006-15710 filed earlier. However, with respect to the method of adding a crosslinking agent, the above four types of crosslinking agents can be broadly classified and applied.

The first is a case where a crosslinking agent comprising an epoxy compound represented by the above formula (27) or an amine compound represented by the above formula (28) is used. In this case, first, a polyimide polymer is prepared by reacting a diamine compound having a benzimidazole group with a dicarboxylic acid anhydride such as pyrometic dianhydride in a solvent such as N-methyl-2-pyrrolidone. Form.
Next, after the polymerization is completed, a crosslinking agent composed of an epoxy compound or an amine compound is added. As described above, the addition amount is preferably in the range of 1 to 40% by mass, more preferably in the range of 3% by mass to 30% by mass, and particularly preferably 5 to 20% by mass with respect to the polyimide polymer.
Thereafter, a solvent containing a polymer and a crosslinking agent is cast on a glass plate or the like, and is crosslinked stepwise at a temperature of 300 ° C. or higher to form a crosslinked film. Thereafter, the electrolyte membrane according to the present invention is manufactured by impregnating the crosslinked membrane with an acid.

The second is a case where the crosslinking agent represented by the above formula (28) or the above formula (29) is used.
When a monofunctional amine terminal cross-linking agent such as p-ethynylaniline represented by the above formula (28) is used, a dicarboxylic acid anhydride such as pyrometic dianhydride is used in a solvent such as N-methyl-2-pyrrolidone. In addition to 100% of the theoretical molar amount necessary for the polymerization of the polyimide polymer, 90% to 99% of the theoretical molar amount necessary for the polymerization of the polyimide polymer is added to the diamine compound. Furthermore, the monofunctional amine terminal crosslinking agent is added in an amount of 2 to 20% of the theoretical molar amount depending on the addition amount of the diamine compound. Thereby, the molar ratio of B in Formula (26) and a crosslinking agent is adjusted to B: crosslinking agent = 90: 20-99: 2.
Thereafter, a solvent containing a dicarboxylic acid anhydride, a diamine compound and a crosslinking agent is cast on a glass plate and the like, and the polyimide polymer is polymerized and polymerized by stepwise heating at a temperature of 300 ° C. or higher. To form a crosslinked film. Thereafter, the electrolyte membrane according to the present invention is manufactured by impregnating the crosslinked membrane with an acid.

When an acid anhydride terminal cross-linking agent such as maleic anhydride represented by the above formula (29) is used, a diamine compound is added to a solvent such as N-methyl-2-pyrrolidone at 100% of the theoretical molar amount. At the same time, dicarboxylic acid anhydride such as pyrometic dianhydride is added from 90% to 99% of the theoretical molar amount necessary for polyimide polymerization. Furthermore, an acid anhydride terminal cross-linking agent is added in an amount of 20% to 2% depending on the amount of dicarboxylic acid anhydride added. Thereby, the molar ratio of A and P in Formula (26) and a crosslinking agent is adjusted to (A + P): crosslinking agent = 90: 20-99: 2 Then, dicarboxylic acid anhydride, a diamine compound, and a crosslinking agent Is cast onto a glass plate or the like and heated stepwise at a temperature of 300 ° C. or higher to polymerize the polyimide polymer and crosslink the polymer to form a crosslinked film. Thereafter, the electrolyte membrane according to the present invention is manufactured by impregnating the crosslinked membrane with an acid.

  The purpose of impregnating the cross-linked membrane with acid is to impart hydrogen ions, that is, proton conductivity to the cross-linked membrane. As the acid, for example, impregnation with a strong acid such as phosphoric acid is preferable. In the present invention, phosphoric acid having a concentration of 85% may be used, the cross-linked membrane produced above may be doped, or a modified acid such as sulfuric acid or ethylphosphoric acid may be used as a proton. It is possible to impart conductivity.

As described above, when the polymer film is impregnated with an acid, the production of the electrolyte membrane 4 according to the present invention having proton conductivity is completed.
Then, the membrane-electrode assembly 10 shown in FIG. 2 is manufactured using the manufactured electrolyte membrane 4, and the fuel cell 1 according to the present invention shown in FIG. 1 is further manufactured using this membrane-electrode assembly 10. To manufacture.

As described above, according to the electrolyte membrane, since the polyimide polymer is crosslinked by any one of the above-described formulas (27) to (30), the oxidation resistance, etc. Chemical stability is improved. Thereby, the durability of the fuel cell using the electrolyte membrane according to the present invention can be improved.
Moreover, since the polyimide polymer is impregnated with an acid, proton conductivity can be increased.
Furthermore, since the benzimidazole group represented by the above formula (31) is introduced into the polyimide polymer, the heat resistance can be improved and it can be suitably used as an electrolyte for a fuel cell.
Moreover, in said electrolyte membrane, since content of a crosslinking agent is made into the predetermined range, chemical stability and proton conductivity can be improved more.

  Hereinafter, the configuration and effects of the present invention will be described in more detail by way of specific examples and comparative examples of the present invention. However, the following examples are provided for a clearer understanding of the present invention, and do not limit the scope of the present invention.

"Example 1"
6,4′-Diamino-2-phenyl represented by the following formula (51) as a diamine compound while passing nitrogen through a four-necked flask equipped with a stirrer, a temperature control device, a nitrogen gas injection device and a cooler. 1 mol of benzimidazole was added, and further N-methyl-2-pyrrolidone (hereinafter referred to as NMP) was added to dissolve the diamine compound. Thereafter, 1 mol of pyrometic dianhydride (hereinafter referred to as “Catalog No. B0040” manufactured by Tokyo Chemical Industry Co., Ltd.) was added and vigorously stirred. The solid content at this time was 15% by weight in terms of mass ratio, and a polyamic acid solution was prepared by reacting for 24 hours while maintaining the temperature below 25 ° C.
Next, an isocyanuric acid triglycidyl ether (Isocyanuric Acid Triglycidyl Ester (Tokyo Kasei Co., Ltd., Cat. No. I0428)) in an amount of 20% based on the above solid content is dissolved in NMP to a concentration of 15% by mass. The solution was mixed with this polyamic acid solution. After mixing, the mixture was vigorously stirred for 6 hours with a mechanical stirrer to produce a uniform polymer solution.
Thereafter, the polymer solution was cast on a glass plate and heated at 300 ° C. to produce a crosslinked film of Example 1 having a thickness of 28 μm.

"Example 2"
Except that 5% isocyanuric acid triglycidyl ether was dissolved in NMP to give a solution having a concentration of 15% by mass and mixed with this solution polyamic acid solution. Thus, a crosslinked film of Example 2 was produced.

"Example 3"
First, a polyamic acid solution was prepared in the same manner as in Example 1.
Next, a 10% amount of melanin monomer (Melamine Monomer (Tokyo Kasei Co., Ltd., Cat. No. T0337)) is dissolved in NMP to obtain a solution having a concentration of 15% by mass. After mixing, the mixture was mixed vigorously with a mechanical stirrer for 6 hours to produce a uniform polymer solution.
Thereafter, the polymer solution was cast on a glass plate and heated at 300 ° C. to produce a crosslinked film of Example 3 having a thickness of 27 μm.

Example 4
In the same manner as in Example 1, while passing nitrogen through a four-necked flask equipped with a stirrer, a temperature controller, a nitrogen gas injection device and a cooler, 6,4′-diamino-2-phenylbenzimidazole 0 .95 mol was added, and NMP was further added to dissolve the diamine compound. Thereafter, 1 mol of pyrometic dianhydride and 0.1 mol of 4-ethynylaniline (Tokyo Kasei Co., Ltd., Cat. No. E0505) were added and stirred vigorously. The polyamic acid solution was prepared by reacting for 24 hours while maintaining below.
Thereafter, the polyamic acid solution was cast on a glass plate and heated at 300 ° C. to produce a crosslinked film of Example 4 having a thickness of 31 μm.

"Example 5"
In the same manner as in Example 1, while passing nitrogen through a four-necked flask equipped with a stirrer, a temperature controller, a nitrogen gas injection device and a cooler, 6,4′-diamino-2-phenylbenzimidazole 1 Mole was added, and NMP was further added to dissolve the diamine compound. Thereafter, 0.95 mole of pyrometic dianhydride and 0.1 mole of maleic anhydride (Maleic anhydride (Tokyo Kasei Co., Ltd., Cat. No. M0005)) were added and stirred vigorously. The polyamic acid solution was prepared by reacting for 24 hours while maintaining below.
Thereafter, the polyamic acid solution was cast on a glass plate and heated at 300 ° C. to produce a crosslinked film of Example 5 having a thickness of 27 μm.

“Comparative Example 1”
In the same manner as in Example 1, while passing nitrogen through a four-necked flask equipped with a stirrer, a temperature controller, a nitrogen gas injection device and a cooler, 6,4′-diamino-2-phenylbenzimidazole 1 Mole was added, and further N-methyl-2-pyrrolidone (hereinafter referred to as NMP) was added to dissolve the diamine compound. Thereafter, 1 mol of pyrometic dianhydride was added and vigorously stirred. While maintaining the temperature of this solution below 25 ° C., a reaction was carried out for 24 hours to prepare a polyamic acid solution.
Thereafter, the polyamic acid solution was cast on a glass plate and heated at 300 ° C. to produce an uncrosslinked film of Comparative Example 1 having a thickness of 32 μm.

"Fenton test"
A chemical resistance test was performed on the crosslinked films of Examples 1 to 5 and the uncrosslinked film of Comparative Example 1. The chemical resistance test was performed through a Fenton experiment. FeSO ₄ was dissolved in hydrogen peroxide at a concentration of 20 ppm to prepare a Fenton test solution, and each of the prepared crosslinked films was poured into the Fenton test solution. The Fenton test solution containing the crosslinked film was warmed with a hot water bath at 80 ° C. and stirred for 6 hours using a shaker. After stirring, the crosslinked film in the solution was taken out, washed with water, dried in a vacuum oven at 60 ° C. for 3 hours, and the weight of the crosslinked film was measured. The results are shown in Table 1.

  As shown in Table 1, it was found that the crosslinked films of Examples 1 to 5 had a high mass maintenance rate of 78 to 94% and were excellent in oxidation resistance. On the other hand, the uncrosslinked film of Comparative Example 1 was shattered after the Fenton test, making it impossible to measure the mass itself. This is presumably because the film of Comparative Example 1 was not crosslinked at all and the chemical resistance was lowered. In addition, about the film | membrane of Examples 1-5 and the comparative example 1, as shown in Table 1, all the film formability by the casting method was favorable.

“Characteristics of electrolyte membrane”
The crosslinked membrane of Example 2 and the crosslinked membrane of Comparative Example 1 were impregnated with phosphoric acid having a concentration of 85% to obtain an electrolyte membrane.
The obtained electrolyte membrane was sandwiched between commercially available fuel cell electrodes (Electrochem), and a carbon sheet was stacked on the electrode to form a membrane-electrode assembly. Two membrane-electrode assemblies were prepared, and each membrane-electrode assembly was sandwiched between a pair of bipolar plates to produce a fuel cell as shown in FIG. Then, a power generation test was performed by supplying hydrogen as a fuel and air as an oxidant to the fuel cell under conditions of 150 ° C. and no humidification.

FIG. 3 is a graph showing IV characteristics when a fuel cell manufactured using the electrolyte membrane of Example 2 is generated under a non-humidified condition at 150 ° C. As shown in FIG. 3, it can be seen that the fuel cell manufactured using the electrolyte membrane of Example 2 shows a voltage of 670 mV or more at a current density of 0.3 A / cm ² .
FIG. 4 shows the results of evaluating the long-term driving stability of the fuel cell using the electrolyte membrane of Example 2. In the case of Comparative Example 1 in which no cross-linking agent is introduced into the polyimide polymer, the durability of less than 300 hours is exhibited. On the other hand, when the electrolyte membrane of Example 2 is applied, the long-term operation condition is a current density of 0.2 A / cm ^2. The durability was 3500 hours or longer, and it was found that the durability was sufficient.

FIG. 1 is a perspective exploded view showing a main part of a fuel cell according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the membrane-electrode assembly provided in the fuel cell of FIG. FIG. 3 is a graph showing the current density dependence (IV characteristics) of the voltage of the fuel cell using the electrolyte membrane of Example 2. FIG. 4 is a graph showing the relationship between the voltage of the fuel cell using the electrolyte membrane of Example 2 and the operation time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 10 ... Membrane-electrode assembly, 20 ... Bipolar plate, 100 ... Electrolyte membrane (polymer electrolyte membrane for fuel cells), 110, 110 '... Catalyst layer, 120, 120', 121, 121 '... Gas diffusion layer

Claims (7)

A polyimide polymer represented by the following formula (1) is crosslinked by any one of the following formulas (2) to (5) and impregnated with an acid. Polymer electrolyte membrane.
However, in the following formula (1), B is a structure represented by the following formula (6), and A and P were independently selected from the structures represented by the following formulas (7) to (17). And D is one selected from the structures represented by the following formulas (18) to (25). Moreover, in following formula (1), m is the range of 10,000-1 million, and n is the range of 5000-500000.
Moreover, in Formula (2), R is any of alicyclic, aromatic, and heteroaromatic, and a which shows the number of the epoxy groups which are reactive groups is 2 or more.
Moreover, in Formula (3), R1 is either aromatic or heteroaromatic, and b indicating the number of amine groups as reactive groups is 3 or more.

  A indicating the number of the epoxy groups is in the range of 2 to 4, and the content of the crosslinking agent relative to the polyimide polymer when the crosslinking agent represented by the formula (2) is selected is 1 to 40% by mass. The polymer electrolyte membrane for fuel cells according to claim 1, wherein the polymer electrolyte membrane is for fuel cells.   A indicating the number of amine groups is in the range of 3 to 4, and the content of the cross-linking agent relative to the polyimide polymer when the cross-linking agent represented by the formula (3) is selected is 1 to 40% by mass. The polymer electrolyte membrane for fuel cells according to claim 1, wherein the polymer electrolyte membrane is for fuel cells.   When the crosslinking agent represented by the above formula (4) is selected, the molar ratio of B to the crosslinking agent in the above formula (1) is adjusted to be B: crosslinking agent = 90: 20 to 99: 2. The polymer electrolyte membrane for a fuel cell according to claim 1, wherein   When the crosslinking agent represented by the above formula (5) is selected, the molar ratio of A and P in the formula (1) to the crosslinking agent is (A + P): crosslinking agent = 90: 20 to 99: 2. The polymer electrolyte membrane for a fuel cell according to claim 1, wherein the polymer electrolyte membrane is adjusted to   The polymer electrolyte membrane for fuel cells according to any one of claims 1 to 5, a pair of catalyst layers disposed on both surfaces of the polymer electrolyte membrane for fuel cells, and the catalyst layer for the fuel cell A membrane-electrode assembly comprising a gas diffusion layer disposed on the opposite side of the polymer electrolyte membrane.   A fuel cell comprising the membrane-electrode assembly according to claim 6 and a bipolar plate disposed on both surfaces of the membrane-electrode assembly.

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