KR100942167B1 - Cross-linked aromatic polymer electrolytes and composite membranes using them - Google Patents

Abstract

The present invention relates to a crosslinkable aromatic polymer electrolyte and a composite membrane for a fuel cell using the same, wherein the crosslinkable aromatic polymer containing a protonic acid group having a crosslinking group suitable for a composite membrane used in a fuel cell or the like and a polymer composite membrane for a fuel cell obtained therefrom (electrolyte Membrane).

The protonic acid group-containing crosslinkable aromatic polymer electrolyte is represented by the following Chemical Formula 1, and has a crosslinkable group which is not derived from the protonic acid group and can be directly crosslinked from the polymer subchain. The composite membrane for a fuel cell using the same has excellent ion conductivity, heat resistance, It expresses water resistance and low methanol permeability.

[Formula 1]

Crosslinkable, aromatic polymer, electrolyte, fuel cell, composite membrane

Description

Cross-linked aromatic polymer electrolytes and composite membranes using them}

The present invention relates to a crosslinkable aromatic polymer electrolyte and a composite membrane for fuel cells using the same, and more particularly, to a crosslinkable aromatic polymer containing a protonic acid group having a crosslinking group suitable for a composite membrane used in a fuel cell and the like, and a polymer for a fuel cell obtained therefrom. It relates to a composite membrane (electrolyte membrane).

The crosslinkable aromatic polymer electrolyte containing a protonic acid group is represented by the following Chemical Formula 1, and has a crosslinkable group which is not derived from the protonic acid group and can be crosslinked directly from the polymer subchain. The composite membrane for a fuel cell using the same has excellent ion conductivity, heat resistance, and water resistance. It also expresses low methanol permeability.

[Formula 1]

Generally, highly sulfonated polymers are required to obtain polymer electrolyte membranes with high proton conductivity, but such polymers have a problem of increased hydrophilicity and easy dissolution in water (Japanese Patent Laid-Open No. 10-45913, etc.).

Since a fuel cell is a by-product of water by reaction of fuel and oxygen, a water-soluble polymer cannot be used as a polymer electrolyte membrane for fuel cells. In addition, even if it is not water-soluble, if the hygroscopicity is high, there are problems of swelling of the membrane, a decrease in strength, and crossover of fuel through absorbed water.

In order to control the hygroscopicity or swelling property, membranes have been developed that can be filled with a polymer electrolyte in a porous polymer film to suppress swelling of the polymer electrolyte membrane and thereby reduce fuel crossover (International Patent Publication WO 2003/075385, Japan). Japanese Patent Laid-Open No. 64-22932, Japanese Patent Laid-Open No. 1-158051).

On the other hand, as a polymer electrolyte itself, a method of reducing water solubility and suppressing elution of a polymer by solution fuel and battery reaction by-products without introducing a component that does not have water solubility. Has been attracting attention (see Republic of Korea Patent Registration 10-0660433).

However, such crosslinking has a problem of lowering proton conductivity by directly using protonic acid for crosslinking. In order to solve this problem, WO 2003/033566 discloses a crosslinking mechanism which can be crosslinked during or after film formation, is not derived from protonic acid groups, and does not involve detachment components, and which is directly bonded to an aromatic ring. Although the photocrosslinked aromatic polymer electrolyte membrane was prepared by a crosslinking group having 1 to 10 carbon atoms and a carbonyl group, it was noted that it was possible to prepare a membrane in which at least 10% of the resin was not dissolved in methanol. There is a disadvantage in that the crosslinking reaction is not sufficiently expressed under the same photocrosslinking conditions as the patent contents, and a considerable amount of energy is consumed even in partial crosslinking.

Accordingly, the present invention, in order to solve the problem of the prior art, a proton conductive polymer electrolyte using a crosslinked structure that is not derived from a protonic acid group and does not involve detachment components but expresses crosslinking directly, and a microporous hydrocarbon-based substrate. An object of the present invention is to provide a proton conductive solid polymer electrolyte composite membrane for use in a fuel cell, which is prepared by filling a membrane and thermally crosslinking or photocrosslinking.

The present invention dissolves a crosslinkable aromatic polymer electrolyte containing a protonic acid group represented by the formula (1), a monomer having a vinyl group bonded to an aliphatic ring or an aromatic ring, and a radical initiator in a polar solvent, and the solution is formed into pores of a hydrocarbon-based microporous substrate membrane. It is characterized by a composite membrane for a fuel cell produced by optical crosslinking or thermal crosslinking polymerization by impregnation.

The crosslinkable aromatic polymer electrolyte containing a protonic acid group of the present invention has a crosslinkable group which can be directly crosslinked from a polymer sub chain, not derived from a protonic acid group. The composite membrane for a fuel cell using the same has excellent ion conductivity, heat resistance, water resistance, and low methanol permeability. Expresses.

In order to achieve the above object, in the present invention, a polymer electrolyte having an aromatic ring having a vinyl group bonded to a carbon double bond as a secondary chain is prepared by a direct polymerization method, and a porous hydrocarbon together with a vinyl monomer bonded to an aliphatic ring or an aromatic ring using the polymer electrolyte. After filling the base substrate film and thermal crosslinking or photocrosslinking to provide a composite membrane for a solid polymer fuel cell.

Hereinafter, the present invention will be described in more detail.

The polymer electrolyte according to the present invention is a polymer synthesized by a two-step direct polymerization method, in which one part of the main chain repeating structure has an aromatic ring in which a vinyl group, which is a carbon double bond, is bonded as a sub chain, thereby expressing crosslinking due to radical initiation. It is characterized by having the structure of Formula 1.

[Formula 1]

Here, W, X, Y each independently represent one or more of SO2, CO2, CH3-CH2-CH3, CF3-CH2-CF3, S,

Z is one of C-CH3, C-CF3, C-H,

while satisfying the ratio a + c = b + d,

By adjusting the ratio of a and c the sulfonation degree of the polymer is increased or decreased,

It is a synthetic polymer that can increase or decrease the degree of crosslinking of the polymer by adjusting the ratio of b and d,

As a vinyl monomer combined with an aliphatic ring or aromatic ring reacting with

스티렌 모노머,

디비닐벤젠 모노머,

비닐피롤리돈 모노머 등이 사용될 수 있으나 이에 국한되는 것은 아니다.

Styrene monomer,

Divinylbenzene monomer,

Vinylpyrrolidone monomer and the like may be used, but are not limited thereto.

A crosslinkable aromatic polymer electrolyte having a structure of Chemical Formula 1 prepared according to the present invention, one or more monomers and radical initiators of vinyl monomers bonded to an aliphatic ring or an aromatic ring to dimethylacetamide, nitromethylpyrrolidone Dissolved in a polar solvent such as dimethyl sulfoxide, impregnated with pores of a hydrocarbon-based microporous substrate, laminated between PET films, and prepared by photocrosslinking or thermal crosslinking polymerization to be used as a membrane for solid polymer fuel cells. By controlling the mechanical structure of the base film, swelling of the hydrophilic polymer electrolyte can be suppressed and fuel crossover can be greatly reduced.

Carbon double bond portion corresponding to d in the polymer electrolyte structure prepared in the present invention, one of the OH functional groups of 1,1,1-tris (4-hydroxyphenyl) ethane used for polymerization of the main chain with respect to 1 mol of OH 1.1 to 1.5 molar ratios, preferably 1.1 to 1.25 molar ratios of calcium carbonate, substituted with OK in a base atmosphere, followed by direct polymerization with halogen methyl styrene in a solvent of 60 to 100 ^° C. under 50% by weight of a polar solvent, Preferably, the polymer electrolyte of the above structure is prepared by direct polymerization at 70-90 ^° C. for 5-10 hours.

The hydrocarbon-based microporous substrate membrane according to the present invention has a pore volume of 30-70%, more preferably 35-50%, a pore size of 0.05-0.1 micrometer, more preferably 0.07-0.1 micrometer, and a thickness. Hydrocarbon-based membranes such as polyolefins, polyimides, polyamide imides having a value of 10 to 30 micrometers, more preferably 20 to 30 micrometers, are used, but are not limited thereto. By using such a base film, it is possible to improve fuel cell performance by minimizing the thickness of the membrane while increasing the mechanical strength of the membrane beyond the commercial fuel cell membrane.

The hydrocarbon-based microporous substrate membrane is immersed in a solution in which a sulfuric acid concentration of 98% or higher concentration and sulfuric acid chloride of 96% or higher concentration are mixed in a 1 to 1 weight ratio, and preferably 30 to 60 ^o C, preferably 45 to 50 ^o C. After reacting for 5 hours, preferably 3-4 hours, the substrate membrane can be washed with a 2 normal sodium hydroxide solution for at least 1 day to increase the filling rate of the polymer electrolyte and improve the crosslinking density.

The polymer electrolyte and the thermal initiator or photoinitiator prepared above are 30-50% by weight in one of polar solvents such as dimethylacetamide (DMAc), nitromethylpyrrolidone (NMP), and dimethyl sulfoxide (DMSo), preferably The solution is prepared by dissolving to 40-45% by weight, then immersing the sulfonated or pure substrate for 5-60 seconds, preferably 10-30 seconds, and 30-100 micrometers, preferably 30-50 After lamination between two micrometer-thick transparent PET films, it is then thermally cross-linked at 100-110 ^o C for 1-2 hours, or 2,000-10,000 mJ / cm ² , more preferably 2,000 5,000 mJ / cm ² , under nitrogen atmosphere. It is possible to solve the swelling problem of the fluorine-based commercial membrane by irradiating the UV energy of the optical cross-linking to produce a polymer electrolyte composite membrane, the polymer density is increased by the inhibition of mechanical swelling and crosslinking by the substrate. The membrane permeation phenomenon of the fuel containing methanol can be suppressed, and thus, the polymer electrolyte membrane fuel cell including a direct methanol fuel cell can be used to improve the electrical performance of the battery.

Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not restrict | limited at all by this. Various tests and performance evaluations of the ion conductive polymer membranes prepared in Examples and Comparative Examples of the present invention were carried out in the following manner.

1. Tensile strength

The tensile force (kpsi) of the composite membrane (electrolyte membrane) was measured according to the method described in ASTM 882.

2. Proton Conductivity

The membrane prepared in Examples and Comparative Examples was immersed in distilled water at 25 ^° C. for 1 hour, and then placed between two glass substrates on which a rectangular platinum electrode was fixed without removing water from the surface of the membrane to fix the glass substrate. Hz-4 MHz alternating current impedance measurement was performed to measure the proton conductivity of the membrane.

3. Methanol transmittance

The composite membrane sample was mounted in the methanol permeability measuring apparatus shown in FIG. 1, and then 10 wt% methanol solution was placed in a container on the left side of the membrane, and distilled water was placed on the right side of the membrane. As time passes, methanol passes through the membrane sample and moves toward the distilled water. Thus, the methanol permeability of the membrane is measured through gas chromatography after collecting a part of the distilled water side solution after 2 hours at room temperature (kg / m ² · h). Was calculated.

Example

1) Synthesis of Crosslinkable Proton Conductive Polymer Electrolyte

As a one-step polymerization, sulfonated dichlorodiphenylsulfone sodium salt 9.825 g (0.02 mol), 4,4'-dihydroxydiphenylsulfone 2.5027 g (0.01 mol), 1,1,1-tris (4-hydroxyphenyl) ethane 3.0636 g (0.01 mol) Was dissolved completely in 20 ml of nitromethylpyrrolidone and then dispersed in a 200 ml volume three-necked flask equipped with a Dean-stark trap for nitrogen filling and solvent reflux with 2.764 g (0.02 mol) of anhydrous potassium carbonate. 20 ml of toluene was added thereto, and the solution was stirred at room temperature for 1 hour.

While raising the temperature to 145 ^° C. under a nitrogen atmosphere, the water produced by the polymerization reaction was removed using reflux of toluene vaporized together at the azeotropic point. After maintaining the reaction at the same temperature for 5 hours, the temperature was increased to 185 ^° C. and polymerized for 20 hours.

After the polymerization is completed, an appropriate amount of anhydrous potassium carbonate and 20 ml of toluene are further added to replace the OH functional group of unreacted 1,1,1-tris (4-hydroxyphenyl) ethane with OK again. While raising the temperature to 145 ^° C. under a nitrogen atmosphere, substitutions were induced with OK.

After the reaction was completed, the polymer solution was cooled to room temperature, and 40 ml of nitromethylpyrrolidone was further added dropwise to dilute the polymer solution. A membrane filter was used to remove unreacted potassium carbonate and potassium chloride by-products. Was poured into an appropriate amount of isopropyl alcohol to precipitate the polymer electrolyte at the same time as removing the unreacted monomer.

The precipitated polymer electrolyte was vacuum dried at 120 ^° C. for 12 hours, weighed to confirm the yield, the polymer electrolyte equivalent was calculated, and then 2- to 3-fold chloromethyl relative to 1 equivalent of functional groups substituted by OK by two-step polymerization. Into a 200 ml flask with styrene was dissolved again in NMP at a concentration of 50 wt%.

The polymer was directly polymerized at 70-90 ^o C for 5-10 hours to prepare a polymer electrolyte of the above structure.

After precipitating and drying the finally prepared polymer electrolyte using the same method as in step 1, to dissolve the vinyl monomer having a vinyl group bonded to the polymer electrolyte and an aliphatic ring or aromatic ring in a polar solvent to fill the porous substrate, The polymer electrolyte is dissolved in dimethyl acetate at a concentration of 40 wt% and the vinyl monomer at a concentration of 3-10 parts by weight relative to 100 parts by weight of the polymer electrolyte.

2) Hydrophilic Treatment of Microporous Hydrocarbon Base Membrane

After cutting the microporous polyethylene base film (Asahi Kasei Chemicals, Japan) having a pore volume of 30%, an average pore size of 0.1 micrometer, and a thickness of 30 micrometer (Asahi Kasei Chemicals, Japan) into a suitable size, sulfuric acid having a concentration of 98% or more and sulfuric acid chloride of 96% or more The substrate was immersed in a solution mixed at a weight ratio of 1 to 1, and reacted at 40 ^° C. for 3 hours to hydrophilize the substrate. In order to remove the chloride remaining in the hydrophilized substrate membrane was washed with a sodium hydroxide solution of 2 normal concentration for at least 1 day, and then dried in a 70 ^° C oven for 2 hours or more to prepare a sulfonated hydrophilic substrate membrane.

3) Pore filling and thermal crosslinking or optical crosslinking of synthetic polymer electrolyte

After dissolving an appropriate amount of radical initiator (thermal initiator or photoinitiator) in the polymer electrolyte and vinyl monomer dissolution solution prepared in 1), the substrate membrane prepared in 2) was immersed for 30 seconds to completely fill the polymer electrolyte in the micropores.

Substrate filled with a polymer electrolyte was placed between two PET films 50 micrometers thick, and then the PET film was completely adhered to remove the excess polymer electrolyte solution, using a 100-110 ^o C oven under a nitrogen atmosphere. The polymer electrolyte composite membrane was prepared by time cross-linking or UV-curing at 2,000-5,000 mJ / cm ² into a curing ultraviolet (UV) irradiation apparatus having a wavelength of 340 nm.

After the PET film was removed, the polymer on the surface was removed with water, and the polymer electrolyte was completely replaced with acid by putting in 2 normal hydrochloric acid.

Tensile strength, proton conductivity, methanol permeability, membrane area increase rate (swelling degree) for distilled water and methanol were measured and the results are shown in Table 1 below.

In addition, in order to confirm the solubility in the polar solvent of the prepared cross-linked polymer electrolyte composite membrane, 1 day in distilled water at room temperature (1) and 70 ^° C (2), 1 hour in distilled water at 100 ^° C (3), room temperature dimethyl After immersing in an acetate solvent (4) for 1 day, washing and drying with water were measured to weigh the result, and the result of comparing the remaining polymer electrolyte is shown in FIG. 2.

Comparative example

Tensile strength, proton conductivity, methanol permeability, membrane area swelling degree after 1 hour immersion in distilled water and methanol of a commercially available ion exchange membrane, Nafion 117 membrane (Dupont, USA) are shown in Table 1 below and compared with Examples.

Example Comparative example Tensile strength (kpsi) 23.0 (MD), 20.0 (TD) 6.3 (MD), 4.7 (TD) Proton Conductivity (S / cm) 0.08 0.08 Methanol Permeability (kg / m ² · h) 0.10 0.28 Unit Area Swelling% Room temperature distilled water 9 30 70 ^o C distilled water 12 55 Methanol 10 50 MD: machine direction TD: transverse direction

As can be seen from Table 1, the optical cross-linked polymer electrolyte composite membrane of the embodiment prepared in the present invention was very excellent in tensile strength compared to the membrane of the comparative example commercialized, methanol permeability 1/3 level compared to the membrane of the comparative example It is expected to be able to replace the commercial membrane of the comparative example as a low cost and environmentally friendly hydrocarbon fuel cell membrane.

As can be seen from FIG. 2, it can be seen that the crosslinked polymer electrolyte composite membrane prepared according to the present invention is hardly soluble in hot distilled water as well as an organic solvent, despite having sufficient crosslinking to contain a high protonic acid group.

1 is a schematic diagram of a device for measuring the methanol permeability of the polymer composite membrane prepared in Examples and Comparative Examples of the present invention.

Figure 2 is a day, 100 ^o C (3) distilled water at room temperature (1) and 70 ^o C (2) distilled water in order to confirm the solubility in the polar solvent of the cross-linked polymer electrolyte composite membrane prepared in an embodiment of the present invention It is a graph showing the amount of residual polymer electrolyte change after immersion in dimethyl acetate solvent (4) at room temperature for 1 hour at 1 hour.

Claims (8)

Crosslinkable aromatic polymer electrolyte containing a protonic acid group represented by the following formula (1) [Formula 1]

Where W, X, Y each independently represent one or more of SO ₂ , CO ₂ , CH ₃ -CH ₂ -CH ₃ , CF ₃ -CF ₂ -CF ₃ , S, Z is any one of C-CH ₃ , C-CF ₃ , CH, while satisfying the ratio a + c = b + d, By adjusting the ratio of a and c the sulfonation degree of the polymer is increased or decreased, The degree of crosslinking of the polymer may be increased or decreased by adjusting the ratio of b and d. Photocrosslinking by impregnating the pores of the hydrocarbon-based microporous substrate membrane with a crosslinkable aromatic polymer electrolyte having a structure of Formula 1, a monomer having a vinyl group bonded to an aliphatic ring or an aromatic ring, and a solution in which a radical initiator is dissolved in a polar solvent Or composite membrane for fuel cell prepared by thermal crosslinking polymerization The method of claim 2, As the microporous substrate, a composite membrane for a fuel cell, characterized in that a porous hydrocarbon membrane having a pore volume of 30 to 70%, a pore size of 0.05 to 0.1 micrometers, and a thickness of 10 to 30 micrometers is used. The method of claim 2, The hydrocarbon-based microporous substrate membrane is immersed in a solution in which a sulfuric acid concentration of 98% or more and a sulfuric acid chloride of 96% or more are mixed in a one-to-one weight ratio to sulfonate to improve the filling rate of the polymer electrolyte. membrane The method of claim 2, The hydrocarbon-based microporous substrate membrane was immersed in a polymer electrolyte solution for 10-30 seconds, laminated between two transparent PET films having a thickness of 30-50 micrometers, and then heated at 100-110 ^o C for 1-2 hours under a nitrogen atmosphere. Composite membrane for fuel cell, characterized in that crosslinking The method of claim 2, The hydrocarbon-based microporous substrate membrane was immersed in a polymer electrolyte solution for 10-30 seconds, laminated between two transparent PET films 30-50 micrometers thick, and then subjected to ultraviolet energy of 2,000-10,000 mJ / cm ² under a nitrogen atmosphere. Composite membrane for fuel cell, characterized in that light irradiated by cross-linking The method according to any one of claims 2 to 6, The composite membrane has a proton conductivity of 0.05 S / cm or more at room temperature in a state of being swollen in water. The method according to any one of claims 2 to 6, The composite membrane is a fuel cell composite membrane, characterized in that the area increase rate of 20% or less in a state of swelling in water or methanol of 70 ^° C or less for 1 hour or more.

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