KR20040048140A - Preparation of high performance sulfonated polyimides Membranes for Fuel Cell - Google Patents

Abstract

PURPOSE: Provided is a method for making an electrolyte membrane for a fuel cell, which uses polyimide having excellent thermal, chemical and mechanical properties to give a polymeric electrolyte membrane having excellent chemical resistance, heat resistance and heat stress resistance, and high ion-conductivity. CONSTITUTION: The method comprises the step of forming a copolymerized sulfonated polyamic acid(polyimide precursor) by dissolving two different diamines at 30 deg.C under nitrogen atmosphere and mixing thereto a dianhydride. Additionally, a crosslinked type copolymerized sulfonated polyamic acid is formed by a two-step condensation. Both of the sulfonated polyamic acid solutions are directly used to form an electrolyte membrane. Otherwise, the copolymerized sulfonated polyamic acid, the crosslinked type copolymerized sulfonated polyamic acid and an inorganic additive are used to form an organic/inorganic composite electrolyte membrane.

Description

Preparation of high functional sulfonated polyimide electrolyte membrane for fuel cell {Preparation of high performance sulfonated polyimides Membranes for Fuel Cell}

The present invention relates to a heat-resistant, high-performance copolymerized sulfonated polyimide and a crosslinked copolymerized sulfonated polyimide electrolyte membrane having a novel structure, and an organic / inorganic composite electrolyte membrane through blending with a conductive inorganic material for improving conductivity of the electrolyte membrane. It can be used as an electrolyte membrane of a fuel cell converting the chemical energy of the directly into electrical energy by an electrochemical reaction, and in particular, it can be used as a polymer electrolyte fuel cell material and a direct methanol fuel cell electrolyte membrane material.

In general, polymer electrolyte fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) using methanol as fuels use polymer electrolytes. It operates at lower temperatures than solid electrolyte fuel cells, molten carbonate fuel cells, and phosphate fuel cells, and has a high energy density and efficiency, and can quickly change the demands and outputs of high outputs, making it easy to start and stop quickly and be environmentally friendly. It is known as a power generation method. The fuel cell is composed of a polymer electrolyte membrane and an electrode overlapping both surfaces of the electrolyte membrane, and is used in a unit cell or in a form of a laminate thereof.

Currently, Nafion (Nafion, perfluorinated sulfonic acid polymer, DuPont) polymer electrolyte membrane is widely used as commercialized electrolyte membrane, but it is difficult to operate due to high price (900 $ / m2) and rapid water content reduction at temperature above 100 ℃. In the case of direct methanol fuel cell, methanol crossover, which is a permeation of methanol from the anode to the cathode, is occurring, resulting in a rapid decrease in performance. Therefore, platinum catalyst is used as an electrode for high efficiency of fuel cell system operating at low temperature below 100 ℃. In this case, fuel injected into fuel cell to prevent poisoning of electrode surface directly related to electrolyte membrane performance. There is a problem in maintaining a low CO concentration. In particular, an indirect methanol fuel cell system may obtain hydrogen fuel by reforming methanol. In such a case, an expensive CO purification system is required. In addition, the platinum catalyst electrode contaminated by CO has a problem of showing low efficiency because methanol oxidation occurs gradually at a low temperature.

Therefore, when the operating temperature of the fuel cell is increased, the poisoning phenomenon of the platinum catalyst electrode due to CO can be reduced, and the oxidation reaction rate can be greatly increased, thereby increasing the fuel cell operating efficiency. In addition, inexpensive nonmetals can be replaced by electrodes instead of precious metals such as expensive platinum catalysts, thereby making it possible to construct an economical fuel cell system. In addition, the performance of the polymer electrolyte fuel cell is largely dependent on the characteristics of the electrolyte membrane and tends to be largely dependent on the physical, chemical, and thermal characteristics of the electrolyte membrane.

Thus, the present invention provides a novel copolymerized sulfonated polyimide electrolyte membrane that exhibits excellent physical, chemical, and thermal properties as compared to conventional commercialized membranes.

The present invention was derived to solve the above problems, and can be operated in a wide temperature range from room temperature to high temperature using polyimide having excellent physical properties such as thermal, chemical, and mechanical properties, and have low methanol crossover, heat resistance, Polymer electrolyte of fuel cell by preparing copolymerized sulfonated polyimide electrolyte membrane, crosslinking copolymerized sulfonated polyimide electrolyte membrane, and conductive inorganic material with excellent chemical resistance and thermal stress and high ion conductivity There is a technical problem in membrane application.

Analysis result of differential scanning thermal analyzer (DSC) of copolymerized sulfonated polyimide precursor (polyamic acid) powder according to the present invention

Analysis result of infrared spectroscopy (FT-IR) of copolymerized sulfonated polyimide electrolyte membrane according to the present invention

Analysis result of the gravimetric thermal analyzer (TGA) of the copolymerized sulfonated polyimide electrolyte membrane according to the present invention

The present invention provides an organic-inorganic composite electrolyte through blending a copolymerized sulfonated polyimide having a repeating unit represented by the following formula (1) with a crosslinked copolymerized sulfonated polyimide electrolyte membrane represented by the formula (2) and a conductive inorganic material. Provide a membrane.

In the above formula,

Ar is , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Ar ’

, , , ,

Ar ” , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,-(CH ₂ ) _n- (n = 4 to 10)

In the above formula,

Ar is the same as Ar of Formula (1);

Ar ’

, , , , , ,

Ar ”

, , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

, , , , , , , , , , , , , , , , , , , , , , , , , , ,-(CH ₂ ) _n- (n = 4 to 10)

B is

, , ,

Here, the molecular weight of the copolymerized sulfonated polyimide represented by the general formula (1) and the crosslinked copolymerized sulfonated polyimide represented by the general formula (2) may reach 10,000 to several hundred thousand.

In the present invention, a sulfonated polyimide containing a sulfone group was prepared to prepare a polymer electrolyte membrane for a fuel cell. A crosslinking sulfonated polyimide electrolyte membrane such as Formula (2) crosslinked using a crosslinking agent B with a copolymerized sulfonated polyimide electrolyte membrane such as Formula (1) suitable as a polymer electrolyte for fuel cells, and blended with a conductive inorganic material. Inorganic composite electrolyte membrane was synthesized.

In the preparation of the polymer electrolyte membrane, the organic solvent is used to dissolve diamine and dianhydride, and the usable organic solvent is N-methylpyrrolidone (NMP), N, N'- including meta-cresol. Dimethylacetamide (DMAc), dimethylsulfuroxide (DMSO), and the like can be used, and meta cresol (m-Cresol) and the remaining organic solvents can be mixed and used in an appropriate ratio.

As the trialkylamine according to the present invention, any of triethylamine, trimethylamine and tripropylamine may be used.

On the other hand, the inorganic additive according to the present invention is a material added to improve the ionic conductivity of the electrolyte membrane for fuel cells, copolymerized sulfonated polyimide and crosslinked copolymerized sulfonated polyimide prepared by the reaction of the diamine and dianhydride Depending on the amount of crosslinking agent used for the preparation, usually 1 to 99% is available, and the usable materials include H _m (X _x Y _y O _z ) (nH 2 O), where X is B, Al, Ga, Si, Ge, Sn, P, As, Sb, Te, and the first, second, and third group transition elements, and Y are mixed with heteropolyacids such as the first, second, and third group transition elements, and the ionic conductivity is increased according to the addition of the inorganic material. Can be increased.

Hereinafter, a sulfonated polyimide manufacturing method according to the present invention will be described.

Two different diamines were mixed in an organic solvent at 30 ° C. under a nitrogen atmosphere, and then dissolved in an organic solvent. Then, dianhydride was mixed with the mixture, followed by sufficiently stirring at 0 ° C. to room temperature, thereby preparing Formula (3). After the stirring was completed, the reaction product was prebaked at 80 ° C. for 1 hour using a spin coater or a doctor blade at 80 ° C. in a hot plate or vacuum oven, and then heated up to 150 ° C. to 300 ° C. It is sufficiently thermoset between temperatures of to prepare a stabilized copolymerized sulfonated polyimide electrolyte membrane of the formula (1).

Two different diamines were mixed in an organic solvent at 30 ° C. under a nitrogen atmosphere, and then dissolved in an organic solvent. Then, dianhydride was mixed with the mixture, and the mixture was sufficiently stirred at 0 ° C. to room temperature to prepare Chemical Formula (4). After the reaction was completed by the addition of the crosslinking agent B, the reaction formula (5) was reacted by using a spin coater or a doctor blade, and an electrolyte membrane having a thickness of several μm to several hundred μm was used for one hour on a hot plate or a vacuum oven. After prebaking at 80 ° C., the temperature is raised, and then sufficiently thermoset and crosslinked at a temperature of 150 ° C. to 300 ° C. to prepare a stabilized crosslinked copolymer sulfonated polyimide electrolyte membrane of the formula (2).

In the case of the organic-inorganic composite electrolyte membrane using an inorganic substance, Chemical Formulas (3), (4), and (5) are prepared, and the inorganic additive H _m (X _x Y _y O _z ) (nH 2 O) is added at various composition ratios.

Thus, the prepared electrolyte membrane can achieve characteristics change by controlling thickness and process temperature, and can be adjusted according to use temperature and need.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the following examples are only for illustrating the present invention in detail and are not intended to limit the scope of the present invention by these examples.

<Example 1>

Preparation of copolymerized sulfonated polyimide precursor (polyamic acid) powder

The reaction of the copolymerized sulfonated polyimide was carried out in a 100 ml reactor equipped with a mechanical stirrer, an inlet for inert gas such as nitrogen, and a sample inlet, and an oil bath capable of maintaining a constant reaction temperature was used.

0.631 g (3.15 mmol) of 4,4'-oxydiphenylenediamine (4,4'-ODA) (Aldrich, USA) was added to a reactor filled with 9 ml of meta-cresol (TCI, Japan) at 30 ° C. After dissolving, 0.465 g (1.35 mmol) of 4,4'-diamino biphenyl-2,2'-disulfonic acid (BDSA) (TCI, Japan) was added and dissolved. At this time, 0.375 ml (2.7 mmol) of triethylamine (Aldrich, USA) was added to increase the solubility of 4,4'-diamino biphenyl-2,2'-disulfonic acid (BDSA). And, for the composition of the mixed solvent, 9 ml of meta-cresol and the same amount of N-methylpyrrolidone (NMP) (Lancaster, USA) is added. 2 g (4.5 mmol) of 4,4 '-(hexafluoroisopropylene) diphthalic anhydride (6FDA) (Aldrich, USA) was slowly added dropwise to the completely mixed mixture, followed by reaction with sufficient stirring at 0 ° C to room temperature. . Then, an excess of ethyl acetate was added to the reaction mixture after the reaction was completed, and a pink precipitate was obtained with rapid stirring. The precipitate obtained at all times was filtered through a vacuum filter, washed several times with ethyl acetate, and the washed precipitate was dried sufficiently in a vacuum oven at 30 ° C. to 100 ° C. to obtain a polyamic acid powder. The thermosetting temperature of the prepared copolymerized sulfonated polyamic acid was made between 150 ° C. and 300 ° C. and is shown in FIG. 1.

<Example 2>

Identification of Copolymerized Sulfonated Polyimides

After the copolymer sulfonated polyamic acid powder obtained in Example 1 was dissolved in NMP or the copolymer sulfonated polyamic acid solution before precipitation in Example 1 was poured onto the wafer, the wafer was 100 to 5000 rpm using a spin coater. The thickness of the film is controlled by appropriately rotating at a speed of about 5 to 60 seconds, and the mixture dispersed on the wafer by the rotation of the spin coater is prebaked at 80 ° C. for 1 hour in a vacuum oven, and then the temperature is between 150 ° C. and 300 ° C. It was sufficiently thermally cured at to prepare a brown sulfonated polyimide electrolyte membrane having a thickness of about 10㎛. The obtained copolymerized sulfonated polyimide electrolyte membrane was analyzed using infrared spectroscopy (FT-IR) (ATI Mattsion Co., USA) to confirm the conversion of polyamic acid to copolymerized sulfonated polyimide. The analysis results by the infrared spectroscopy are shown in FIG. 2.

<Example 3>

Preparation and Characterization of Copolymerized Sulfonated Polyimide Electrolyte Membrane

The copolymer sulfonated polyamic acid powder obtained in Example 1 was dissolved in NMP, or the copolymer sulfonated polyamic acid solution before precipitation in Example 1 was prepared using a spin coater or a doctor blade to obtain a thickness of several micrometers to several hundred micrometers. The electrolyte membrane was prebaked at 80 ° C. for one hour on a hot plate or vacuum oven, and then heated to a sufficient temperature and heated to a temperature of 150 to 300 ° C. to prepare a brown sulfonated polyimide electrolyte membrane. The membranes thus prepared are shown in Table 1, ion exchange capacity (IEC), hydrogen ion conductivity, and water content in Table 2, and analyzed by gravimetric thermal analyzer (TGA) to confirm thermal stability. 3 is shown.

Copolymerization sulfonated polyimide electrolyte membrane having various composition ratios may be prepared by adjusting the composition ratio of diamines in the same manner as described above.

Composition 6FDA ODPA BDSA ODA MDA 6FDO506DEO606FDO706FDO80 100100100100 50403020 50607080 ODM50ODM60ODM70ODM80 100100100100 50403020 50607080

25 ℃ 40 ℃ 60 ℃ 80 ℃ IEC Nafion115 Conductivity (Scm ^-1 ) 1.36 × 10 ^-2 2.10 × 10 ^-2 2.41 × 10 ^-2 3.54 × 10 ^-2 1.2 Water uptake (%) 23.09 24.39 25.65 29.07 6FDO50 Conductivity (Scm ^-1 ) 3.94 × 10 ^-3 6.96 × 10 ^-3 8.16 × 10 ^-3 9.16 × 10 ^-3 1.69 Water uptake (%) 13.24 15.24 15.58 17.54 6FDO60 Conductivity (Scm ^-1 ) 1.93 × 10 ^-3 2.96 × 10 ^-3 4.34 × 10 ^-3 5.24 × 10 ^-3 1.365 Water uptake (%) 11.7 12.00 12.58 14.24 6FDO70 Conductivity (Scm ^-1 ) 1.51 × 10 ^-4 1.81 × 10 ^-4 2.36 × 10 ^-4 4.10 × 10 ^-4 0.92 Water uptake (%) 8.03 8.75 8.78 9.52 6FDO80 Conductivity (Scm ^-1 ) 1.40 × 10 ^-5 1.93 × 10 ^-5 2.57 × 10 ^-5 3.39 × 10 ^-5 0.68 Water uptake (%) 4.82 5.74 6.29 8.16

25 ℃ 40 ℃ 60 ℃ 80 ℃ IEC Nafion 115 Conductivity (Scm ^-1 ) 1.36 × 10 ^-2 2.10 × 10 ^-2 2.41 × 10 ^-2 3.54 × 10 ^-2 1.2 Water uptake (%) 23.09 24.39 25.65 29.07 ODM50 Conductivity (Scm ^-1 ) 4.79 × 10 ^-3 7.15 × 10 ^-3 8.82 × 10 ^-3 1.27 × 10 ^-2 1.74 Water uptake (%) 18.14 19.05 21.84 22.7 ODM60 Conductivity (Scm-1) 2.34 × 10 ^-3 3.20 × 10 ^-3 4.69 × 10 ^-3 6.05 × 10 ^-3 1.42 Water uptake (%) 14.75 15.95 16.52 18.38 ODM70 Conductivity (Scm ^-1 ) 2.71 × 10 ^-4 3.31 × 10 ^-4 4.16 × 10 ^-4 6.05 × 10 ^-4 1.05 Water uptake (%) 9.57 10.53 10.83 11.16 ODM80 Conductivity (Scm ^-1 ) 2.73 × 10 ^-5 3.15 × 10 ^-5 3.85 × 10 ^-5 4.97 × 10 ^-5 0.73 Water uptake (%) 5.85 6.57 7.14 7.83

<Example 4>

Preparation of Crosslinked Copolymer Sulfonated Polyimide Electrolyte Membrane

The reaction of the crosslinked copolymer sulfonated polyimide was carried out in a 100 ml reactor equipped with a mechanical stirrer, an inlet for inert gas such as nitrogen, and a sample inlet, and an oil bath capable of maintaining a constant reaction temperature was used.

0.342 g (2.25 mmol) and 4,4 crosslinkable 3,5-diamino benzoic acid (DBA) (Aldrich, USA) in a reactor filled with 18 ml of N-methylpyrrolidone (NMP) (Lancaster, USA) at room temperature 0.45 g (2.25 mmol) of '-oxydiphenylenediamine (4,4'-ODA) (Aldrich, USA) is added to dissolve completely. 2 g (4.5 mmol) of 4,4 '-(hexafluoroisopropylene) diphthalic dianhydride (6FDA) (Aldrich, USA) was slowly added dropwise to the completely mixed mixture, followed by reaction with sufficient stirring at 0 ° C to room temperature. . Then, add 0.239 g (1.125 mmol) of N, N-bis (2-hydroxyethyl) -2-aminoethanesulfonic acid (BES) as a crosslinking agent and stir for at least 3 hours. Then, the obtained solution was prebaked at 80 ° C. for 1 hour in a hot plate or vacuum oven using a spin coater or a doctor blade, and then heated up to a temperature of 150 to 300 ° C. It was thermally cured and crosslinked sufficiently to prepare a brown crosslinked sulfonated polyimide electrolyte membrane.

By adjusting the composition ratio of the diamine and the composition ratio of the crosslinking agent in the above manner it can be prepared a cross-linked copolymer sulfonated polyimide electrolyte membrane having a variety of composition ratios.

Example 5

Preparation of Organic / Inorganic Composite Electrolyte Membrane

To the solution obtained in the same manner as in Example 4, 0.086 g of H ₃ PW ₁₂ O ₄₀ (29H ₂ O), which is an inorganic substance of 30% by weight of the crosslinking agent, was sufficiently stirred. Then, the obtained solution was prebaked at 80 ° C. for 1 hour in a hot plate or vacuum oven using a spin coater or a doctor blade, and then heated up to a temperature of 150 to 300 ° C. It was sufficiently thermally cured and crosslinked between to prepare a brown organic-inorganic composite electrolyte membrane.

By adjusting the composition ratio of the copolymerized sulfonated polyamic acid solution or the crosslinking agent and the inorganic substance by the above method, an organic-inorganic composite electrolyte membrane having various composition ratios can be prepared.

The electrolyte membrane for a fuel cell according to the present invention is an electrolyte membrane capable of showing various characteristics according to a process (curing temperature) and a membrane manufacturing method (thickness control), and thus, the required molar ratio may be changed and manufactured to improve the required characteristics. In particular, it has low electrical resistance (high conductivity), high mechanical strength and uniform thickness based on excellent physical properties such as excellent heat resistance, chemical resistance and thermal stress, and can maintain thermal stability and high ion exchange ability even at high temperatures of 100 ° C. or higher. In addition, it can be said that it is possible to apply to high efficiency high performance polymer electrolyte membrane for fuel cell by reducing methanol crossover phenomenon.

Claims (4)

A method of preparing a copolymerized sulfonated polyimide precursor (polyamic acid) having a repeating unit of formula (3) through a two-step condensation reaction as follows; In the above formula, Ar is , , , , , , , , , , , , , , , , , , , , , , , , , , , , Ar ’ , , , , Ar ” , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,-(CH ₂ ) _n- (n = 4 to 10) In the same manner as in Examples 1 and 2, two different types of diamines were dissolved under a nitrogen atmosphere at 30 ° C., and then dianhydride was mixed in the mixture, and the mixture was sufficiently stirred at 0 ° C. to room temperature. A method of making a fonned polyimide precursor (polyamic acid). The solution itself may be used and precipitated in ethyl acetate to prepare a copolymer sulfonated polyimide precursor (polyamic acid) powder, which may be dissolved in an organic solvent such as NMP to prepare a solution. Method for producing a crosslinked copolymer sulfonated polyimide precursor (polyamic acid) having a repeating unit of formula (4), (5) through the following two-step condensation reaction; In the above formula, Ar is the same as Ar of Formula (1); Ar ’ , , , , , , Ar ” , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,-(CH ₂ ) _n- (n = 4 to 10) B is , , , After preparing a solution of the copolymerized sulfonated polyimide precursor (polyamic acid) of the formula (4) by the same method as in claim 1, the crosslinking agent (B) was added thereto and stirred sufficiently to form a crosslinked copolymerized sulfonated polyimide precursor of the formula (5) ( Polyamic acid) solution. Claims 1 and 2, the copolymerization of the formula (3), (4), (5) and the production method further comprising an inorganic additive in the sulfonated polyimide precursor (polyamic acid) solution. The inorganic additive is H _m (X _x Y _y O _z ) (nH ₂ O) and X is B, Al, Ga, Si, Ge, Sn, P, As, Sb, Te and the 1, 2, 3 group transition Any one selected from the elements, Y is any one selected from the first, second, third group transition elements. A solution containing a copolymer sulfonated polyamic acid solution prepared according to claim 1, a crosslinked copolymer sulfonated polyamic acid solution prepared according to claim 2, and an inorganic additive prepared according to claim 3 is used by using a spin coater or a doctor blade. After prebaking at 80 ° C. in a hot plate or vacuum oven for 1 hour, the temperature was raised, and then sufficiently thermoset and crosslinked at a temperature of 150 to 300 ° C. to stabilize the copolymer of Chemical Formula (1) having a thickness of several μm to several hundred μm. A method for producing an ionized polyimide electrolyte membrane, a crosslinked copolymer sulfonated polyimide electrolyte membrane of formula (2), and an organic / inorganic composite electrolyte membrane and an prepared electrolyte membrane.