KR100508691B1 - Sulfonated poly(aryl ether benzimidazole) electrolyte and its composite membrane for direct methanol fuel cell - Google Patents

Abstract

The present invention relates to a sulfonic acid-containing polyaryletherbenzimidazole electrolyte for a direct methanol fuel cell (DMFC) and an electrolyte composite membrane using the same, and more particularly, to a sulfonic acid-containing poly having excellent properties such as heat resistance, mechanical properties, and solubility. A novel polymer electrolyte comprising aryletherbenzimidazole and a repeating unit of the polymer electrolyte and the above-described polymer electrolyte coated on a support, which significantly reduces ion conductivity and methanol permeability, and thus is useful as an electrolyte membrane of a direct methanol fuel cell (DMFC). It relates to a composite membrane.

Description

Sulfonated poly (aryl ether benzimidazole) electrolyte and its composite membrane for direct methanol fuel cell}

The present invention relates to a sulfonic acid-containing polyaryletherbenzimidazole electrolyte for a direct methanol fuel cell (DMFC) and an electrolyte composite membrane using the same, and more particularly, to a sulfonic acid-containing poly having excellent properties such as heat resistance, mechanical properties, and solubility. A novel polymer electrolyte comprising aryletherbenzimidazole and a repeating unit of the polymer electrolyte and the above-described polymer electrolyte coated on a support, which significantly reduces ion conductivity and methanol permeability, and thus is useful as an electrolyte membrane of a direct methanol fuel cell (DMFC). It relates to a composite membrane.

Unlike ordinary batteries, fuel cells do not require replacement or recharging of batteries. Instead, fuel cells supply fuel such as hydrogen or methanol to convert electrical energy from combustion to electrical energy. Fuel cells have the advantages of high efficiency (up to 60% energy conversion efficiency), the use of various fuels as a pollution-free energy source, a small footprint, and a short construction period. The range of applications ranges from distributed generation to power generation for home and power businesses. In particular, the potential market size is expected to be enormous when the operation of fuel cell vehicles, which is the next generation transportation device, is used in various ways.

There are five major types of fuel cells according to operating temperature and electrolyte: alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), Polymer electrolyte fuel cells (PEMFC) and direct methanol fuel cells (DMFC). Among them, Direct Methanol Fuel Cell (DMFC) was first developed by Kordesh and Marko in 1951 (Oesterr. Chem. Ztg., 1951, 52, 125), because it uses methanol as a direct fuel. It does not need a fuel reformer, making it suitable for powering small portable electronic equipment.

Direct methanol fuel cell (DMFC) is composed of about 45% of the total fuel cell manufacturing cost of the electrolyte membrane assembly (MEA) of the electrolyte membrane and the electrode catalyst for transportation, 56 of which is portable. Occupies% In the development of a direct methanol fuel cell, one of the key elements is the development of an ion conductive polymer electrolyte membrane.

As an ion conductive polymer electrolyte membrane, a hydrocarbon polymer of polystyrene-divinylbenzene sulfonic acid and sulfonated phenol formaldehyde has been studied for the first time. Styrene-based polymers. In the early 1960s, DuPont developed Nafion, a perfluorinated hydrogen ion exchange membrane, and has been used as an ion exchange membrane for fuel cells. Asahi Glass Co., Ltd. developed Flemion with carboxyl group instead of sulfonic acid group as cation exchanger and showed high ion selectivity close to 100%, but lower than Nafion in conductivity. As described above, the perfluorinated polymer electrolyte membrane has chemical resistance, oxidation resistance, excellent ion conductivity, and has advantages as a commercialized material, but it is pointed out that there is a problem of environmental pollution due to high cost and toxic intermediate products generated during manufacturing. It is becoming. In particular, high methanol permeability and 100 when applied for direct methanol fuel cell (DMFC) Due to the sudden decrease in ion conductivity and softening of the membrane due to the decrease in moisture content above ℃ it is acting as an obstacle to commercialization.

The polymer electrolyte membrane applied to the fuel cell should play a role in preventing the migration of the fuel from the anode to the cathode in addition to serving as a hydrogen ion transport membrane. Therefore, the polymer membrane used in the fuel cell should have chemical, thermal, mechanical and electrochemical stability as well as hydrogen ion conductivity as a cation exchange membrane.

In order to make up for the shortcomings of perfluorinated polymer membranes, polymer electrolyte membranes in which carboxyl groups and sulfonic acid groups have been introduced into aromatic ring polymers have been studied. Examples include sulfonated polyarylether sulfones (Journal of Membrane Science, 83, 211, 1993), sulfonated polyetherether ketones (JP-A 6-93114, USP 5,438,082), sulfonated polyimides (USP 6,245,881), and the like. have. However, dehydration reaction by acid or heat is liable to occur in the process of introducing sulfonic acid group into aromatic ring, and hydrogen ion conductivity is greatly influenced by water molecules. Reducing methanol permeability of the polymer membrane generally results in lowering water permeability or hydrophilicity. Therefore, in order to lower fuel permeability, a situation arises where sacrifice of ion conductivity occurs, and no clear alternative has been prepared. Also, they are not durable enough for use as fuel cell membranes.

On the other hand, aromatic polybenzimidazole or sulfonic acid-containing polybenzimidazole is known as a high heat resistant and highly durable material. As a representative example, published by Keikichi Uno et al., It is known that 3,3'-diaminobenzidine and 3,5-dicarboxybenzenesulfonic acid or 4,6-dicarboxylic acid-1,3-benzene disulfonic acid. Synthesis has been reported (Journal Polymer Science, Polymer Chemistry Edition 15, 1309, 1977). U.S. Patent 5,312,895 also reports synthesis from 1,2,4,5-benzenetetramine and 2,5-dicarboxybenzenesulfonic acid. However, these reports do not disclose electrochemical properties, and at the same time, the molecular design considering heat resistance, mechanical properties, ion conductivity and processability is not available, and these characteristics are inferior to those used as polymer electrolyte membranes.

In addition, the synthesis of polybenzimidazole by direct reaction with sulfuric acid has been reported (Solid state Ionics 106, 219, 1998). However, this method yields a low sulfonic acid group introduction rate and a weak brittle membrane. However, since polybenzimidazole has a NH bond having substitution activity, it can react with sulfone or bromobenzylsulfonate under basic atmosphere (LiH) to form a CN bond. By this method, polybenzimidazole having derivatives such as propyl sulfonic acid and benzyl sulfonic acid in the side chain can be synthesized (Solid State Ionics, 97, 323, 1997). However, this method has a disadvantage in that the ion conductivity is not large and the durability is low at low temperatures.

In addition, it has been reported that impregnated sulfuric acid or phosphoric acid may exhibit high hydrogen ion conductivity at high temperature in order to pay attention to the excellent heat resistance and mechanical properties of polybenzimidazole in nature (USP 5,529,436). 100 in this way It is difficult to apply the electrolyte membrane for low temperature fuel cell at low temperature below ℃, it is difficult to apply the electrolyte membrane for low temperature fuel cell, so it is not easy to manufacture the membrane due to poor solubility, and the low molecular ion conductor diffuses out of the membrane, thereby reducing the ion conductivity.

The present invention solves the problems of the conventional direct methanol fuel cell (DMFC) polymer electrolyte, while maintaining the hydrogen ion conductivity in the polymer electrolyte while significantly lowering the permeability of the fuel (methanol) polymer electrolyte for direct methanol fuel cell (DMFC) The present invention has been completed by the development.

Therefore, an object of the present invention is to provide a polymer electrolyte of a novel sulfonic acid polyaryletherbenzimidazole having excellent solubility and ion conductivity.

In addition, the present invention is a thin coating of the sulfonic acid polyaryletherbenzimidazole to the support to minimize the reduction in ion conductivity, while at the same time significantly reducing the permeability of methanol, and does not occur in distilled water or methanol for direct methanol fuel cell (DMFC) Another object is to provide an electrolyte composite membrane.

The present invention is a polymer electrolyte comprising a sulfonic acid-containing polyaryletherbenzimidazole represented by Formula 1 as a repeating unit:

In Formula 1, Y is selected from -S-, -SO _2- , -C = O- and -P (O) (C ₆ H ₅ )-or a combination thereof, and Z is a bond ), -O-, -SO _2- , -C = O- and -C (CF ₃ ) ₂ , n + m = k and n / n + m is between 0.001 and 1 (preferably 0.2 To 0.6).

The present invention also includes an electrolyte composite membrane in which the sulfonic acid-containing polyaryletherbenzimidazole electrolyte is coated on one or both surfaces of the support.

Referring to the present invention in more detail as follows.

The present invention relates to a polymer electrolyte repeating a sulfonic acid-containing polyaryletherbenzimidazole represented by Chemical Formula 1 and an electrolyte composite membrane using the same as a coating film.

Briefly illustrating a method for preparing a polymer electrolyte according to the present invention is shown in Scheme 1.

In Reaction Scheme 1, Y, Z, n, m and k are as defined above, respectively, and X is a halogen atom or a nitro group including Cl, F, Br as leaving group.

According to the preparation method according to Scheme 1, the polymer electrolyte of the present invention is a sulfonated aromatic monomer represented by Formula 2, an unsulfonated aromatic monomer represented by Formula 3, and bis (hydroxy) represented by Formula 4 It is obtained by the direct polymerization method from benzimidazole).

The monomer represented by the formula (2) or (3) can be prepared and used by a general production method as a known compound, as the activator (Y) -S-, -SO _2- , -C = O- and -P (O) (C ₆ H ₅ ) — is bonded and has a form in which a halogen atom or a nitro group is bonded as the leaving group (X). The activator (Y) or leaving group (X) of the monomer represented by Formula 2 or Formula 3 may be the same as or different from each other. In addition, the aromatic monomer containing the sulfonic acid represented by the formula (2) can be prepared by the known sulfonation method of the unsulfonated aromatic monomer represented by the formula (3). Moreover, although represented by the phenyl group as an aromatic ring, other aromatic structures, for example, may include a phenyl group, naphthyl, terphenyl, and combinations thereof.

The reaction molar ratio of the sulfonated aromatic monomer represented by the formula (2), the unsulfonated aromatic monomer represented by the formula (3) and the bis (hydroxybenzimidazole) represented by the formula (4) is n / n + m = 0.001 to It is quantitatively used within the range of 1 and satisfying n + m = k.

The polymer represented by Chemical Formula 1 prepared by the method as described above has an intrinsic viscosity measured in 1-methyl-2-pyrrolidinone (NMP) solvent of 0.1 or more (preferably 0.3 to 2.0), and water or methanol It is insoluble in properties. In addition, the polymer represented by the formula (1) is excellent in solubility and ion conductivity, it is also suitable for use as an ion exchange membrane for fuel cells by molding into a film or film form.

On the other hand, the present invention includes an electrolyte composite membrane prepared by coating the polymer represented by the formula (1) on the surface of the support.

That is, the polymer represented by Chemical Formula 1 is used in the preparation of the composite membrane in the form of a salt. The polymer electrolyte is dissolved in a polar solvent and then filtered using a membrane filter. The polymers of the filtered salt forms and swollen for 1 to 24 hours in a polar solvent, and then spin coating or casting to Nafion the support surface, removing the solvent, 0.5 MH ₂ SO _4, such as room temperature or elevated temperatures (100, using the In the form of sulfonic acid to obtain an electrolyte composite membrane. The removal of the solvent is preferably carried out by drying in view of the uniformity of the membrane, and is preferably dried at a temperature as low as possible under reduced pressure in order to avoid decomposition and deterioration of the solvent. Moreover, the method of leaving it to stand in air or inert gas for a suitable time can also be used. As the polar solvent, 1-methyl-2-pyrrolidinone (NMP), N, N-dimethylacetamide (DMAc), N, N-diethylacetamide, N, N-dimethylformamide (DMF), hexa Methylphosphoramide (HMPTA), methanesulfonic acid, H ₂ SO ₄ and the like can be selected and used.

By repeating the operation of forming the electrolyte membrane, a single-sided or double-sided composite membrane can be manufactured. The thickness of the coating film of the finally prepared electrolyte composite membrane is preferably as thin as possible in terms of ion conductivity, but more preferably 0.1 μm to 1000 μm, particularly preferably 1 μm to 200 μm.

The electrolyte composite membrane of the present invention prepared in the above is excellent in heat resistance and mechanical properties without peeling even in distilled water or boiling methanol at 100 ° C., and also has high ion conductivity of 0.03 S / cm or more (preferably 0.05 to 1.50 S / cm). The methanol permeability of the composite membrane was significantly reduced to 50% or less compared to that of Nafion, which is a conductive material and a support. These results indicate that the NH group and the sulfonic acid group of the imidazole in the polymer electrolyte represented by Chemical Formula 1 form a salt to prevent peeling even though the hydrogen ion conductivity is slightly reduced, and exhibits excellent mechanical properties and shows methanol permeation. It is because of the characteristic to suppress.

In addition, the following experiment was performed to measure the water absorption rate of the prepared electrolyte membrane and composite membrane: The acid treated membrane was washed several times with distilled water, and then immersed in distilled water purified in a beaker at room temperature for 24 hours and then taken out. Remove water from the surface and weigh it (W _wet ). It is then dried in a reduced pressure dryer at 120 ° C. for 24 hours and weighed (W _dry ). And water absorption was calculated by the following equation (1).

In addition, in order to measure the ion conductivity of the prepared electrolyte membrane and composite membrane, a measurement cell as shown in Figure 6 was prepared and measured using a Solatron 1260 Impedance / Gain-Phase analyzer. Impedance spectrum was recorded from 10 MHz to 10 Hz. Ion conductivity was calculated by the following equation.

In Equation 2, R is the resistance (ohm), L is the distance between the electrodes (cm), A is the cross-sectional area (cm ² ) of the film.

In addition, methanol permeability was measured by gas chromatograph (GC) by mounting an electrolyte membrane between a constant concentration of methanol and water, and the amount of methanol permeated over time was calculated by the following equation (3).

In Equation 3, a is the slope in the time-concentration graph, V _B is the volume of the permeate side (cm ³ ), L is the thickness of the membrane (cm), A is the membrane area (cm ² ), C _A is The concentration of methanol used.

 The present invention as described above will be described in more detail based on the following examples, but the present invention is not limited thereto.

Example 1 Preparation of Monomer

(1) Synthesis of 5,5-bis [2-4 (hydroxyphenyl) benzimidazole] (BHPB)

25.80 g of 3,3'4,4'-tetraaminobiphenyl, 52.62 g of phenyl-4-hydroxybenzoate, 95.30 g of diphenylsulfone, 100 mL of toluene were added to add 150 2.5 hours of reaction at room temperature to remove toluene and 250 The reaction was heated for 1.5 hours for 1.5 hours. Cooled to precipitate with acetone and toluene and 110 It dried on the vacuum evaporator of degreeC, and obtained BHPB. ¹ H-NMR spectra for the prepared monomers are attached as FIG. 1.

(2) Synthesis of 5,5-bis [2-4 (hydroxyphenylsulfon) benzimidazole] (BHPSB)

Prepared in the same manner as in (1), except that 5,5-bis [2 using 3,3'4,4'-tetraaminodiphenylsulfone instead of 3,3'4,4'-tetraaminobiphenyl. -4 (hydroxyphenylsulfone) benzimidazole] was prepared.

(3) Synthesis of Disulfonated Difluorodiphenylsulfone (SDFDPS)

Add 7.5 g of 4,4'-difluorodiphenylsulfone (DFDPS) and 15 mL of fuming sulfuric acid to a 100 mL flask and add 120 After reacting at 6 ° C. for 6 hours, it was poured into iced water bath and precipitated by addition of NaCl. Then filtered, washed, dried and dissolved in distilled water and neutralized with 2N NaOH. The precipitate formed was filtered and dried in a reduced pressure drier.

In the same manner, sulfonated dihalide derivatives were synthesized.

Example 2 Preparation of Polymer

For the preparation of sulfonated polyarylbenzimidazole polymers, difluorodiphenylsulfone (DFDPS), disulfonated difluorodiphenylsulfone (SDFDPS) and 5,5-bis [2-4 (hydroxyphenyl) benz Imidazole] (BHPB) by controlling the molar ratio. The amount of sulfonated dihalide was adjusted to 0, 10, 20, 30, 40, 50 and 60 mo% based on the total amount of dihalide monomers, and synthesized by nucleophilic aromatic substitution. The solvent used was DMAc or NMP with toluene added as an azeotropic derivative, and in the presence of anhydrous potassium carbonate 160 ℃ 190 The reaction was carried out at < RTI ID = 0.0 > Sulfonated dihalides with substituents are generally less reactive and therefore have a higher reaction temperature than 190 to obtain a high molecular weight polymer. It was required up to C and precipitated in water after the reaction to give a polymer. The monomers and polymers produced^OneThe structure was confirmed by H-NMR and FT-IR. In addition, the synthesis and analysis results of the prepared polymer are shown in Table 1 below.

Example 3: Preparation of sulfonic acid containing polyaryletherbenzimidazole electrolyte membrane

The polymer prepared in Example 2 was dissolved in NMP, filtered using a 0.45 μm PTFE membrane filter, and then cast on a clean plate glass support. Solvent 50 in a reduced pressure oven Removal was carried out at or below. 100 after membrane manufacturing Acid treatment was carried out using 0.5 MH ₂ SO ₄ at ₄ ° C. for 4 hours to convert to acid form. At this time, the thickness of the final film was about 120 ㎛. Physical properties evaluation results of the prepared electrolyte membrane are shown in Table 2 below.

Example 4 Preparation of Composite Membrane

The polymer prepared in Example 2 was dissolved in hexamethylphosphoramide (HMPTA) and filtered using a 0.45 μm PTFE membrane filter. Swell for 24 hours in hexamethylphosphoramide (HMPTA), cast on a fixed Nafion 117 scaffold, remove solvent and remove 100 A composite membrane converted to the sulfonic acid form was obtained using 0.5 MH ₂ SO ₄ at ° C. At this time, the thickness of the final coated portion was adjusted to 5 ㎛ to 20 ㎛. In addition, the same operation was repeated to cast both sides to prepare a double-sided composite membrane. Physical property evaluation results of the prepared composite membrane are shown in Table 3 below.

Example 5 Preparation of Polymers, Electrolyte Membranes, and Composite Membranes

In preparing the polymer in the same manner as in Example 2, bis (hydroxyphenylbenzimide) and hexafluorobisphenol A (HFBA) were added at the same molar ratio to prepare a polymer, and in the same manner as in Example 3 An electrolyte membrane was prepared. Subsequently, in preparing the composite film in the same manner as in Example 4, NMP was used as the coating and swelling solvent, and spin coating was used. Synthesis and analysis results of the prepared polymers and the evaluation of the properties of the electrolyte membrane are shown in Table 4, and the results of the evaluation of the properties of the composite membrane are shown in Table 5 below.

Example 6 Preparation of Polymers and Composite Membranes

In preparing the polymer in the same manner as in Example 2, the polymer was prepared by adding BHPSB instead of BHPB, followed by spin coating in the same manner as in Example 5 to prepare a composite membrane. Physical property evaluation results of the prepared composite membrane are shown in Table 6 below.

Comparative Example 1

A polymer was prepared in the same manner as in Example 2, except that hexafluorobisphenol A (HFBA) was used alone without adding bis (hydroxyphenylenebenzimidazole), and 40 mol% of sulfonic acid dihalide and bisulfonated. The polymer was prepared using 60 mol% dihalide. Subsequently, Nafion 117 was coated in the same manner as in Example 5 to prepare a composite membrane.

Comparative Example 2

A polymer was prepared in the same manner as in Example 2, except that 4,4-dihydroxybiphenyl was used alone without adding bis (hydroxyphenylenebenzimidazole), and 40 mole% of sulfonic acid dihalide was used. The polymer was prepared using 60 mol% of fonned dihalide. Subsequently, Nafion 117 was coated in the same manner as in Example 5 to prepare a composite membrane.

Comparative Example 3

100 commercially available Nafion 117 (EW-1100, 180 μm thick) membranes manufactured by DuPont Treatment with 0.5 M sulfuric acid at 4 ° C. for 4 hours to remove Nafion membrane surface contaminants and stored in deionized water. The polymer electrolyte membrane performances were all evaluated by the same method.

  Evaluation results of the properties of the membranes prepared in Comparative Examples 1 to 3 are shown in Table 7 below.

As described above, the electrolyte composite membrane prepared using the sulfonic acid-containing polyaryletherbenzimidazole polymer according to the present invention has excellent ion conductivity and significantly reduces methanol permeability, thereby increasing the polymer electrolyte for direct methanol fuel cell (DMFC). The performance of the membrane can be greatly improved.

1 is a ¹ H-NMR spectrum of a 5,5-bis [2-4 (hydroxyphenyl) benzimidazole] (BHPB) monomer prepared in Example 1. FIG.

2 is a ¹ H-NMR spectrum of the sulfonic acid-containing polyaryletherbenzimidazole (BDFS) prepared in Example 2. FIG.

3 is a result of TGA analysis of sulfonic acid-containing polyaryletherbenzimidazole (HBDFH) prepared in Example 5. FIG.

4 shows the results of comparative analysis of sulfonic acid sodium salt form prepared in Example 5 with polyaryletherbenzimidazole (HBDFH) in sulfonic acid form by TGA.

FIG. 5 is an FT-IR spectrum according to sulfonation degree of sulfonic acid-containing polyaryletherbenzimidazole (HBDFH) prepared in Example 5. FIG.

6 is a schematic diagram of the structure of a cell for measuring the conductivity of a sulfonic acid-containing polyaryletherbenzimidazole electrolyte membrane and a composite membrane.

7 is an electron scanning microscope (SEM) photograph of the sulfonic acid-containing polyaryletherbenzimidazole (BDFS) composite membrane prepared in Example 4. FIG.

[Description of Major Symbols in Drawing]

1. Teflon block 2. Thumbscrew

3. Empty space to maintain equilibrium with the surroundings

4. Membrane sample 5. Black platinum (Pt) electrode

Claims (7)

A polymer electrolyte comprising a sulfonic acid-containing polyaryletherbenzimidazole represented by the following Formula 1 as a repeating unit: [Formula 1] In Formula 1, Y is selected from -S-, -SO _2- , -C = O- and -P (O) (C ₆ H ₅ )-or a combination thereof, and Z is a bond ), -O-, -SO _2- , -C = O- and -C (CF ₃ ) ₂ , n + m = k and n / n + m are in the region between 0.001 and 1. 2. The polymer electrolyte according to claim 1, wherein n / n + m is in a 0.2 to 0.6 region. The polymer electrolyte according to claim 1, wherein the intrinsic viscosity measured in 1-methyl-2-pyrrolidinone (NMP) is 0.1 or more and insoluble in water and methanol. Electrolyte membrane, characterized in that consisting of the sulfonic acid-containing polyaryletherbenzimidazole electrolyte selected from claim 1 to 3. An electrolyte composite membrane, wherein a sulfonic acid-containing polyaryletherbenzimidazole electrolyte selected from claims 1 to 3 is coated on one or both surfaces of a Nafion support. 6. The electrolyte composite membrane according to claim 5, wherein the ion conductive electrolyte coating membrane has a thickness of 1 µm to 200 µm. The method of claim 5, wherein the ion conductivity of the composite membrane is 0.03 S / cm or more, methanol permeability is reduced to 50% or less than Nafion, 100 Electrolyte composite membrane, characterized in that the peeling does not occur in distilled water or boiled methanol at ℃.