KR100810683B1 - High molocular electrolyte membrane for fuel cell, and membrane-electrode assembly thereby, fuel cell - Google Patents

Abstract

A polymer electrolyte membrane for a fuel cell, a membrane electrode assembly containing the polymer electrolyte membrane, and a fuel cell containing the membrane electrode assembly are provided to improve phosphoric acid infiltration and to increase ion conductivity even under the condition of high temperature and no humidification. A polymer electrolyte membrane comprises a polymer film which comprises a polyimide copolymer represented by the formula 1 and a compound represented by the formula 2; and an acid which is infiltrated in the polymer film, wherein A and P are a specific acid dianhydride; B is a group represented by the formula 3; and D is a divalent organic group derived from an aromatic diamine. A membrane electrode assembly comprises the polymer electrolyte membrane; a catalyst layer coated to the both surfaces of the polymer electrolyte membrane by vapor deposition; and a gas diffusion layer arranged at the both sides of the catalyst layer.

Description

Polymer electrolyte membrane for fuel cell, and membrane-electrode assembly using the same, fuel cell {High molocular electrolyte membrane for fuel cell, and membrane-electrode assembly thereby, fuel cell}

1 is a cross-sectional view schematically showing a membrane-electrode assembly (MEA) manufactured using a polymer electrolyte membrane prepared by the above method.

2 is an exploded perspective view schematically showing a fuel cell including the membrane-electrode assembly described above.

FIG. 3 is I-V characteristic data of a fuel cell fabricated using Example 2 of the present invention at 150 ° C. without humidification.

4 is a result of evaluating long-term driving stability of the fuel cell test cell using the polymer electrolyte membrane of Example 2 of the present invention.

<Explanation of symbols for the main parts of the drawings>

10 membrane-electrode assembly 20 bipolar plate

100: polymer electrolyte membrane 110, 110 ': catalyst

120,120 ': gas diffusion membrane

The present invention relates to a polymer electrolyte membrane for a fuel cell, a membrane-electrode assembly, and a fuel cell using the same. More specifically, the present invention can be suitably used in a high temperature non-humidified fuel cell system by expressing the conductivity of hydrogen ions stably at a high temperature. The present invention relates to a polymer electrolyte membrane for fuel cells having improved chemical resistance and physical properties, and a membrane-electrode assembly and a fuel cell using the same.

Polymeric ion exchange membranes have been mainly applied to diffusion dialysis, electrodialysis, and vapor permeation separation, but recently, attention has been focused on the development of polymer electrolyte fuel cells using cation exchange polymers.

A fuel cell is a type of energy conversion device that effectively converts chemical energy stored in fuel into electrical energy and generates electric power by combining hydrogen stored as a gas or methanol stored as a liquid or gas with oxygen. In particular, a proton exchange membrane fuel cell (PEMFC) is a clean energy source that can replace fossil fuels and has excellent power density and energy conversion efficiency.

As electrolytes for such fuel cells, hydrogen ion conductive polymer membranes based on copolymers of perfluorosulphonic acid and tetrafluoroethylene are known. Components of the fuel cell include a polymer electrolyte membrane, an electrode, and a separator for forming a stack.

In general, in order to maximize the surface area of the platinum catalyst, two electrodes, the anode and the cathode, in which nano-sized platinum particles are adsorbed on the surface of a carbon material such as carbon black, are attached to the polymer electrolyte membrane in various ways. membrane-electrode assembly, which is typically in powder form with an effective surface area of several hundred m2 / g, and the platinum particles act as a catalyst for oxidation / reduction reactions.

The construction and performance of such a membrane-electrode assembly are the core of the polymer electrolyte fuel cell technology. The principle of generating electricity in the fuel cell is hydrogen as fuel gas is supplied to the cathode (cathode) as adsorbed on the cathode (cathode) as shown in Scheme 1 and the hydrogen ions and electrons are generated by the oxidation reaction.

<Scheme 1>

2H ₂ → 4H ^{+ +} 4e ^-

At this time, the generated electrons reach the anode along the external circuit, and hydrogen ions pass through the polymer electrolyte membrane and are transferred to the anode. At the anode, as shown in Reaction Formula 2, the oxygen molecules receive electrons transferred to the anode and are reduced to oxygen ions, and the reduced oxygen reacts with hydrogen ions to generate electricity while producing water.

<Scheme 2>

_{^{O 2 + 4e - → 2O 2}} -

^{2O 2 - + 4H + → 2H} 2 O

The fuel cell polymer electrolyte membrane is electrically insulated, but acts as a medium for transferring hydrogen ions (H ⁺ ) from the negative electrode to the positive electrode during battery operation, and simultaneously serves to separate the fuel gas or the liquid from the oxidant gas. Therefore, the fuel cell ion exchange membrane should have excellent mechanical properties and electrochemical stability and low ohmic loss at high current density.

In the early 1960s, many studies on the polymer electrolyte membrane for fuel cells were carried out. However, perfluorinated sulfonic acid was produced by EIDu Pont de Nemours, Inc. in 1968. Nafion has been developed in earnest, and it is mainly applied in fuel cells for installation and portable fuel cells.

However, the fuel cell using Nafion system has a problem of CO poisoning of the electrode catalyst due to the low temperature operation below 80 ° C and the methanol crossover in the direct methanol fuel cell (DMFC). Due to this is a major factor to deteriorate the characteristics of fuel cells and shorten the life cycle, many studies have been conducted to solve this problem.

In addition, in the case of fluorine-based 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 that the synthesis is difficult and the material is expensive, so as to increase the thermal stability of the membrane and lower the cost. A phonated hydrocarbon polymer electrolyte is being developed.

However, since sulfonated hydrocarbon electrolyte membranes are also capable of proton conduction in the presence of water, water dehydration occurs in the membrane at high temperatures of 100 ° C. or higher, and hydrogen ion conductivity rapidly decreases.

In addition, the recent fuel cell system is required to develop a polymer electrolyte membrane for fuel cells suitable for high temperature driving in order to use the power generation efficiency and the array in the domestic fuel cell.

In order to commercialize a fuel cell, durability that does not degrade battery characteristics is very important even for a long time operation, and development of a polymer electrolyte membrane for fuel cells is also required to increase such durability.

The technical problem to be achieved by the present invention is to have a stable hydrogen ion conductivity at a high temperature of more than 150 ℃, not only can express the battery characteristics under high temperature and no humidification conditions, but also to form a new polymer structure with strong chemical and physical properties to form a membrane The present invention provides a polymer electrolyte membrane for a fuel cell which can express the conductivity of hydrogen ions stably at high temperature by improving resistance to radicals that may occur when driving a fuel cell.

Technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

The polymer electrolyte membrane for a fuel cell according to an embodiment of the present invention for solving the above technical problem is to improve the chemical resistance and physical properties of the polymer electrolyte membrane to further include a polyimide of the formula (1) containing phenyl benzimidazole (phenyl benzimidazole) A polyimide copolymer film to which a crosslinking agent containing a reactor, such as an epoxy, a double bond, a triple bond, or a triamine, capable of crosslinking represented by the following formula (2) is added to the copolymer; And an acid impregnated inside the polyimide copolymer film.

<Formula 1>

<Formula 2>

However, in Formula 1, B is a divalent organic group derived from diamino phenyl benzimidazole and is selected from the group represented by the following Formula 3.
In formula (2), R may be any structure such as alicyclic, aromatic, heteroaromatic, and epoxy as a reactor is bifunctional or more than two groups. In addition, R1 can be any structure such as aromatic and heteroaromatic, and the amine is more than trifunctional.

<Formula 3>

In addition, in Formula 1, A and P are tetravalent organic groups derived from dianhydride, and are selected from the group represented by Formula 4 below.

<Formula 4>

In Formula 1, D is a divalent organic group derived from an aromatic diamine, and is one selected from the group represented by Formula 5 below.

<Formula 5>

The functional group of the crosslinking agent having an epoxy reactor represented by the formula (2) is up to 2 to 4, the content of the total polyimide composition is characterized in that it is used up to 40wt% ~ 1wt% relative to the polymer solids.

The functional group of the crosslinking agent having the amine reactor represented by the formula (2) is from 3 to 4, the content of the total polyimide composition is characterized in that used from 40wt% to 1wt% relative to the polymer solids.

Ethinyl aniline represented by the formula (2) is introduced into the terminal monomer during the polymerization, it characterized in that the content of 20 to 2 mol% in mol%.

Maleic anhydride represented by the formula (2) is introduced into the terminal monomer during polymerization, characterized in that the content of 20 to 2 mol% in mol%.

Hereinafter, a method of manufacturing a polymer electrolyte membrane for a fuel cell using the polyimide polymer as described above will be described.

In order to manufacture a polymer electrolyte membrane for a fuel cell using the polyimide polymer, a polymer film must first be prepared. As a method for preparing the polymer film, the following two methods can be used according to a polymerization process and a film manufacturing process. have.

The first method is to prepare a polyamic acid, which is a precursor of polyimide, and then cast the solution, apply heat of 200 ° C. or more in a wet film state, and dehydrate the imide ring through dehydration. It is a method of manufacturing the film which has a thickness of 10-500 micrometers after formation and drying.

The second method involves chemical imidization using acetic dianhydride and pyridine in solution, or isoquinoline in acidic solvents such as m-cresol. Solution polymerization using a basic catalyst of (in contrast to the method of using an acidic catalyst in a basic solvent), and a solvent such as toluene in a basic solvent such as N-methylpyrrolidone (N-methyl-2-pyrrolidone) After the imidation reaction was carried out by using the agiotrope phenomenon, the precipitate was obtained to obtain a solid polymer, which was then dissolved and cast in an organic solvent to prepare a film through simple solvent volatilization without imidization reaction. That's how.

However, the second method is limited to the case of using a specific monomer such as alicyclic acid dianhydride because the final polymerized polyimide should be soluble in the organic solvent.

Impregnation of an acid such as phosphoric acid (H ₃ PO ₄ ; phosphoric acid) is required in order to impart hydrogen ions, that is, proton conductivity, to the polymer film prepared by the above methods.

In the present invention, the above prepared polymer film was doped with phosphoric acid having a concentration of 85%, but further modified with phosphoric acid as well as strong acids such as sulfuric acid (H ₂ SO ₄ ) and ethylphosphoric acid. It is possible to impart proton conductivity to the polymer film even if an acid or the like is used.

When the acid film is impregnated with the polymer film as described above, the production of the polymer electrolyte membrane for fuel cell having proton conductivity is completed.

The polyimide structure and the crosslinking agent represented by the following formula (6) are only one example for the purpose of understanding the present invention and do not limit the structure of the polyimide polymer / crosslinker of the present invention.

<Formula 6>

In the method of adding a crosslinking agent, the above four types can be classified into two types and applied.

The first is an epoxy additive or a triamine additive, which does not participate in the polymerization of the polymer and is quantitatively added to the reaction solution in the form of an additive after the polymerization is completed. The amount of the epoxy and triamine crosslinking agent added is 40% to 1%, preferably 30% to 3%, more preferably 20% to 5% by weight of the polymerized polymer.

The second is amine terminal crosslinking or anhydride terminal crosslinking. In the case of the amine terminal crosslinking agent such as ethynylaniline shown in the example, 100 mol% of dianhydride is added during polyimide polymerization, and the synthetic mol% of diamine is added. Introduce from 90% to 99%. The amine terminal crosslinking agent added at this time is added in the amount of 20 mol% to 2 mol%. In the case of an anhydride terminal crosslinking agent such as maleic anhydride, 100 mol% of diamine is introduced in contrast to the amine terminal, and a mole percent of dianhydride is introduced from 90% to 99%. It is added in an amount of 20 mol% to 2 mol%.

The polyimide solution containing the crosslinking agent thus prepared is coated on a glass plate using a casting method, and is gradually heated to a temperature of 300 ° C. or higher to obtain a crosslinked polyimide.

Impregnation of an acid such as phosphoric acid (H ₃ PO ₄ ; phosphoric acid) is required in order to impart hydrogen ions, that is, proton conductivity, to the polymer film prepared by the above methods.

In the present invention, 85% of the phosphoric acid was used to dope the prepared polymer film (crosslinking agent-added polyimide film), but not only phosphoric acid but also strong acids such as sulfuric acid (H ₂ SO ₄ ) and ethyl phos. It is also possible to impart proton conductivity to the polymer film by using a modified acid such as formic acid (Ethylphosphoric acid).

When the polymer film is impregnated with acid as described above, the production of a polymer electrolyte membrane for fuel cell having proton conductivity is completed.

1 is a cross-sectional view schematically showing a membrane-electrode assembly (MEA) manufactured using a polymer electrolyte membrane prepared by the above method.

Referring to FIG. 1, the membrane-electrode assembly 10 of the present invention is a polymer electrolyte membrane 100 for fuel cells, catalyst layers 110 and 110 ′ deposited on both sides of the polymer electrolyte membrane 100, and both sides of the catalyst layer. It includes a gas diffusion layer (120, 120 ') disposed in.

The catalyst layers 110, 110 'may comprise platinum, ruthenium, osmium, platinum-ruthenium alloys, platinum-osmium alloys, platinum-palladium alloys, or platinum-M alloys (M = Ga, Ti, V, Cr, Mn, Fe, Co). , At least one catalyst selected from the group consisting of Ni, Cu, and Zn), and is prepared by mixing the catalyst with carbon black.

Gas diffusion layers (GDLs) 120 and 120 'are disposed on both surfaces of the catalyst layers 110 and 110'.

The gas diffusion layers 120 and 120 'serve to smoothly supply the hydrogen gas and the oxygen gas supplied from the outside to the catalyst layer to assist in the formation of the three-phase interface of the catalyst-electrolyte membrane-gas, and the carbon paper or carbon It is preferable to make with a carbon cloth.

Further, in order to assist diffusion of hydrogen gas and oxygen gas between the catalyst layers 110 and 110 ′ and the gas diffusion layers 120 and 120 ′, a micro porous layer (MPL) 121 and 121 ′ may further be included. It may be.

2 is an exploded perspective view schematically showing a fuel cell including the membrane-electrode assembly described above.

Referring to FIG. 2, the fuel cell 1 of the present invention includes a membrane-electrode assembly 10 and a bipolar plate 20 disposed on both sides of the membrane-electrode assembly.

Hereinafter, the configuration and effects of the present invention will be described in detail with specific examples and comparative examples. However, the following examples are merely provided to more clearly understand the present invention and do not limit the scope of the present invention.

One. In the present invention  According to the polymer Electrolyte membrane  To explain the effect Examples  And Comparative example

< Comparative example >

1 mol of 6,4'-diamino-2-phenylbenzimidazole represented by the following formula (7) was passed through the four-necked flask equipped with the stirrer, the temperature controller, the nitrogen gas injection device, and the cooler as a diamine component. N-methyl-2-pyrrolidone (NMP; Junsei chemical) was added and dissolved.

 1 mole of pyromellitic dianhydride (PMDA; Cat. No. B0040) was added thereto, followed by vigorous stirring. The solid content at this time is 15% by weight in mass ratio, the reaction was carried out for 24 hours while maintaining the temperature below 25 ℃ to prepare a polyamic acid solution (PAA-1).

<Formula 7>

< Example  1>

After preparing a polyimide in the same manner as in Comparative Example, N-methyl-2-pyrrolidone was 20% by mass of 15% by weight of Isocyanuric Acid Triglycidyl Ester (Tokyo Chemical, Cat.No. I0428) After dissolving in (NMP; Junsei chemical), the solution was stirred vigorously with a mechanical stirrer for 6 hours to prepare a uniform polymer solution.

< Example  2>

After preparing a polyimide in the same manner as in Comparative Example, Isocyanuric Acid Triglycidyl Ester (Tokyo Chemical, Cat. No. I0428) was prepared with N-methyl-2-pyrrolidone (5 wt% to 15 wt%). NMP; Junsei chemical)) was added and then vigorously stirred for 6 hours with a mechanical stirrer to prepare a uniform polymer solution.

< Example  3>

After preparing a polyimide in the same manner as in Comparative Example, Melamine Monomer (東京 化成, Cat. No. T0337) was prepared with N-methyl-2-pyrrolidone (NMP; Junsei chemical) was dissolved and added, and then vigorously stirred for 6 hours with a mechanical stirrer to prepare a uniform polymer solution.

< Example  4>

Polymerizing polyimide in the same manner as in Comparative Example, using 0.95 mol of 6,4'-diamino-2-phenylbenzimidazole and 0.1 mol of 4-Ethynylaniline (東京 化成, Cat. No. E0505) Polyamic acid solution was prepared.

< Example  5>

The polyimide was polymerized in the same manner as the comparative example, but 0.95 mol of pyromellitic dianhydride (PMDA; Tokyo, Cat. No. B0040) was used, and 0.1 mol of maleic anhydride (cat. No. M0005) was used. To prepare a polyamic acid solution.

Table 1 shows the results of testing the chemical resistance of the crosslinked polyimide of the Comparative Example and Examples 1 to 5 of the present invention.

Chemical resistance test was performed through the Fenton experiment. FeSO ₄ was dissolved in hydrogen peroxide at a concentration of 20 ppm to prepare a Fenton test solution, and each prepared polyimide film was added to a test solution contained in different containers. Fenton test solution containing a polyimide film was shaken for 6 hours using a shaker (shaker) while applying a temperature in a water bath at 80 ℃. After 6 hours, the 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 final remaining film was measured.

As shown in Table 1, when the crosslinking agent was not added to the polyimide copolymer as in the comparative example, it was found that the film was very brittle after the Fenton test, and the mass loss rate was so large that it was impossible to measure.

In contrast, in Examples 1 to 5 in which the crosslinking agent was added to the polyimide copolymer, the mass retention rate was relatively high even after the Fenton test, and in particular, in Example 1, the mass retention rate reached 94%. .

FIG. 3 is I-V characteristic data of a fuel cell fabricated using the polymer electrolyte membrane of Example 2 of the present invention under a humidified condition of 150 ° C. FIG.

As shown in FIG. 3, the fuel cell fabricated using the polymer electrolyte membrane prepared according to Example 2 of the present invention exhibits a voltage value of 670 mV or more at a current density of 0.3 A / cm ² .

4 is a result of evaluating long-term driving stability of the fuel cell test cell using the polymer electrolyte membrane of Example 2.

However, although not shown in FIG. 4, the comparative example in which the crosslinking agent was not introduced into the polyimide showed a durability of less than 300 hours, whereas the film of Example 2 containing the crosslinking agent was applied to have a current density of 0.2 A / cm ² . It can be seen that the durability is greatly improved to more than 3,500 hours under long term operating conditions.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings and tables, the present invention is not limited to the above embodiments, but may be manufactured in various forms, and common knowledge in the art to which the present invention pertains. Those skilled in the art can understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

According to the polymer electrolyte membrane for a fuel cell according to the embodiment of the present invention, it shows an excellent phosphoric acid impregnation rate, and also exhibits high ionic conductivity even under high temperature and no humidification conditions of 150 ° C. or higher, thereby providing sufficient characteristics as a polymer electrolyte membrane. In addition, the chemical resistance and physical properties are improved, and thus, the fuel cell can be applied to a fuel cell, thereby providing excellent characteristics such as providing stable battery characteristics even during long-term operation.

Claims (7)

A polymer film to which a compound represented by the following formula (2) is added to a polyimide copolymer represented by the following formula (1); And A polymer electrolyte membrane for a fuel cell comprising an acid impregnated in the polymer film. <Formula 1>

(However, in Formula 1, A and P are one selected from dianhydride represented by Formula 4 below, and in Formula 1, B is one selected from the group represented by Formula 3 below. D is one selected from divalent organic groups derived from aromatic diamine represented by the following formula (5).) <Formula 2>

In Chemical Formula 2, R may have any structure such as alicyclic, aromatic, heteroaromatic, and epoxy as a reactor. In addition, R1 can be any structure such as aromatic and heteroaromatic, and the amine is more than trifunctional. <Formula 3>

<Formula 4>

<Formula 5>

The method of claim 1, The functional group of the crosslinking agent having an epoxy reactor represented by the formula (2) is up to 2 to 4, the content of the total polyimide composition is 40wt% ~ 1wt% compared to the polymer solids, the polymer electrolyte membrane for a fuel cell.        The method of claim 1, The functional group of the crosslinking agent having an amine reactor represented by the formula (2) is from 3 to 4, the content of the total polyimide composition is 40wt% to 1wt% of the polymer solids, characterized in that the polymer electrolyte membrane for fuel cells. The method of claim 1, Ethyl aniline represented by the formula (2) is introduced as a terminal monomer during polymerization, the polymer electrolyte membrane for a fuel cell, characterized in that the content of 20 to 2 mol% in mol%. The method of claim 1, Maleic anhydride represented by the formula (2) is introduced as a terminal monomer during polymerization, the polymer electrolyte membrane for a fuel cell, characterized in that the content of 20 to 2 mol% in mol%. A polymer electrolyte membrane for a fuel cell according to any one of claims 1 to 5; A catalyst layer coated on both surfaces of the polymer electrolyte membrane; And Membrane-electrode assembly comprising a gas diffusion layer disposed on both sides of the catalyst layer. The membrane-electrode assembly of claim 6; And A fuel cell comprising a bipolar plate disposed on both sides of the membrane-electrode assembly.

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