KR100654244B1 - High molocular electrolyte membrane for fuel cell, and membrane-electrode assembly thereby, fuel cell - Google Patents

Abstract

Provided are a polymer electrolyte membrane for a fuel cell, a membrane electrode assembly containing the electrolyte membrane which is excellent in phosphoric acid infiltration, is high in the ion conductivity even under the condition of high temperature and no moisture and is minimized in the deterioration of durability due to the CO poisoning of an electrode, and a fuel cell containing the assembly. The polymer electrolyte membrane comprises a polyimide copolymer film represented by the formula 1; and an acid infiltrated in the polyimide copolymer film, wherein A and P are an acid dianhydride; B is a divalent organic group derived from diaminophenylbenzimidazole represented by the formula 2; and D is a divalent organic group selected from an aromatic diamine. The membrane electrode assembly comprises the polymer electrolyte membrane; a catalyst layer coated on the both sides of the polymer electrolyte membrane by vapor deposition; and a gas diffusion layer located on 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.

3 is I-V characteristic data of a fuel cell manufactured using the polymer electrolyte membrane of Example 1 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 using the same, and a fuel cell, and more particularly, to express hydrogen conductivity stably at a high temperature to be suitably used for a high temperature unhumidified fuel cell system. The present invention relates to a polymer electrolyte membrane for a fuel cell, a membrane-electrode assembly using the same, and a fuel cell.

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, a separator for forming a stack, and the like.

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.

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.

_{^{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 of no thermal stability at a temperature above 90 ° C, a problem of difficulty in synthesis and expensive materials, and sulfonation to increase the thermal stability of the membrane and lower the cost. Hydrocarbon-based polymer electrolytes have been 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.

The present invention provides a polymer electrolyte membrane for a fuel cell having stable hydrogen ion conductivity at a high temperature of 130 ° C. or higher and expressing battery characteristics at high temperature and no humidification conditions, and a membrane-electrode assembly and a fuel cell using the same.

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

     A polymer electrolyte membrane for a fuel cell according to an embodiment of the present invention for solving the above technical problem is impregnated into a polyimide copolymer film of Formula 1, and a polyimide copolymer film including phenyl benzimidazole Contains acids that become.

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 2.

In addition, in Formula 1, A and P are tetravalent organic groups derived from dianhydride, and are selected from the group represented by Formula 3.

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

In Formula 1, the molar ratio of A: P is basically 1: 1, and the sum of the mole% of A and P and the mole% of B and D is 100.

However, if necessary, the molar ratio of 1: 0.9 to 0.9: 1 may be changed in order to prepare the polymer by adjusting the appropriate molecular weight. In this case, the mole% sum of A and P or the mole% sum of B and D may be 100. Maybe not.

In addition, in Formula 1, A and P may be acid dianhydrides having the same chemical structure, or acid dianhydrides having different chemical structures, and when A and P are acid dianhydrides having different chemical structures, The mole% is not the same as the ratio of m and n in Formula 1, the mole% ratio of A and P may be 1: 99%, preferably prepared in a ratio of 30: 70%.

At this time, B may be used from 100 to 10 mol%, D may be used from 0 to 90 mol%, preferably B is used 50 to 100 mol% and D is 0 to 50 mol%, more preferably B Uses 60 to 95 mole percent and D uses 5 to 40 mole percent.

Representative examples of the polyimide polymer that can be prepared by Chemical Formula 1 are shown in Chemical Formula 5 below. However, this is merely an example to help understand the present invention and does not limit the polyimide polymer structure of the present invention.

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 is 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 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.

< Example  1>

1 mol of 6,4'-diamino-2-phenylbenzimidazole represented by the following formula (6) was added as a diamine component while passing nitrogen through a four-necked flask equipped with a stirrer, a temperature controller, a nitrogen gas injection device, and a cooler. 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).

< Example  2>

The same method as in Example 1 was used, but 0.5 mol of 4,4'-diaminodiphenyl ether (cat. No. 00088) and 6,4'-diamino-2-phenylbenzimi were used as diamine components. A polyamic acid solution (PAA-2) was prepared using 0.5 mol of dazole.

< Example  3>

Using the same method as Example 1, using 0.3 mol of 4,4'-diaminodiphenyl ether, 0.7 mol of 6,4'-diamino-2-phenylbenzimidazole, and 1 mol of pyromellitic dianhydride (PMDA) To prepare a polyamic acid solution (PAA-3).

< Example  4>

Using the same method as Example 1, except that 0.3 mol of 4,4'-diaminodiphenylether and 0.7 mol of 6,4'-diamino-2-phenylbenzimidazole, 1,4,5,8-naphthalene tetracarboxylic A polyamic acid solution (PAA-4) was prepared using 1 mol of dianhydride (Ca. No. N0369).

< Example  5>

Using the same method as in Example 1, using 1 mol of 6,4'-diamino-2-phenylbenzimidazole, 1 mol of 1,4,5,8-naphthalene tetracarboxylic dianhydride (PAA-5) Prepared.

< Example  6>

Using the same method as in Example 1, 0.3 mol of 4,4'-diaminodiphenylether and 0.7 mol of 6,4'-diamino-2-phenylbenzimidazole, 3,3 ', 4,4'- A polyamic acid solution (PAA-6) was prepared using 1 mol of benzophenonetetra -carboxylic dianhydride (東京 化成, Cat. No. N0369).

< Example  7>

Using the same method as Example 1, using 1 mol of 6,4'-diamino-2-phenylbenzimidazole, 1 mol of 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride (PAA-7) Was prepared.

Table 1 shows the properties of the polyimide polymer polymer film prepared as in the above embodiments and the impregnation property for phosphoric acid.

As shown in Table 1, it can be seen that the polyimide polymer membrane prepared by the present invention has an excellent impregnation rate in phosphoric acid.

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

As shown in FIG. 3, the fuel cell fabricated using the polymer electrolyte membrane prepared according to Example 1 of the present invention exhibits a voltage value of 600 mV or more over a current of 0 to 0.3 A / cm ² .

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 a high ion conductivity even under a high temperature and no humidification condition of 130 ° C. or more, thereby minimizing the durability degradation of the electrode against CO poisoning. The power generation efficiency and thermal efficiency of the fuel cell can be improved.

Claims (7)

Polyimide copolymer film represented by the above formula; And A polymer electrolyte membrane for a fuel cell comprising an acid impregnated in the polyimide copolymer film. (Wherein A and P are one selected from dianhydrides, B is one selected from the group represented by the following formula, and D is a divalent organic group derived from aromatic diamine). It is one that is chosen.)

The method of claim 1, Wherein A and P is a polymer electrolyte membrane for a fuel cell, characterized in that one selected from the group represented by the following formula.

       The method of claim 1, A and P are acid dianhydrides having the same chemical structure and have a molar ratio of 1: 1. The method of claim 1, A and P are acid dianhydrides having different chemical structures and have a molar ratio of 1: 1. The method of claim 1, D is a polymer electrolyte membrane for a fuel cell, characterized in that one selected from the group represented by the following formula.

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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