KR100967627B1 - Manufacturing Method of Polymer Electrolyte Composite Membrane for Fuel Cell - Google Patents

Abstract

The present invention is impregnated with a porous support containing an ion conductive polymer synthesized using different monomers in a mixed solution containing styrene, vinylpyrrolidone, a crosslinking agent and an initiator, and thermally polymerized by sulfonation to form a hydrogen ion. The present invention relates to a polymer electrolyte composite membrane for a fuel cell and a method of manufacturing the same, which have excellent hydrogen ion conductivity and can simplify the manufacturing process and reduce manufacturing cost. Method for producing a polymer electrolyte composite membrane for a fuel cell containing the styrene-vinylpyrrolidone copolymer, (a-1) impregnating a porous support in a mixed solution consisting of styrene, vinylpyrrolidone, a crosslinking agent and an initiator, (b-1) thermally polymerizing the porous support impregnated in step (a-1) in an oven, and (c-1) treating the styrene-vinylpyrrolidone copolymer composite membrane polymerized in step (b-1). Fonning to introduce the sulfonic acid group, and (d-1) permanently replacing the sulfonated composite membrane in the form of hydrogen ions in (c-1).

Styrene, vinylpyrrolidone, fuel cells, composite membranes.

Description

Manufacturing method of polymer electrolyte composite membrane for fuel cell {PREPARATION METHOD OF POLYMER ELECTROLYTE COMPOSITE MEMBRANES FOR FUEL CELLS}

The present invention relates to a polymer electrolyte composite membrane for a fuel cell and a method for manufacturing the same, and more particularly, to an ion conductive polymer synthesized using different monomers in a mixed solution containing styrene, vinylpyrrolidone, a crosslinking agent and an initiator. By impregnating a porous support containing a thermal support, and then sulfonated and substituted in the form of hydrogen ions, a polymer electrolyte composite membrane for a fuel cell, which has excellent hydrogen ion conductivity and can simplify the manufacturing process and reduce the manufacturing cost, and its manufacture It is about a method.

In general, fuel cells are generally alkaline fuel cells (AFC), phosphate (Phosphoric Acid Fuel Cell (PAFC)), molten carbonate (Molten Carbonate Fuel Cell (MCFC)), solids depending on the type of electrolyte used. Solid Oxide Fuel Cell (SOFC), Direct Methanol Fuel Cell (DMFC), and Polymer Electrolyte Membrane Fuel Cell (PEMFC) are classified. Among the fuel cell types, the polymer fuel cell and the direct methanol fuel cell use polymers as electrolytes, and thus there is no risk of corrosion or evaporation due to electrolytes, and high current density per unit area can be obtained. Compared with the US and Japan, the output characteristics are much higher and the operating temperature is lower than that of the US, Japan, to use them as portable power sources such as automobiles, distributed power sources (on-site) and electronic devices for homes and public buildings. In Europe and other countries, development of this is being actively promoted. In addition, the ion conductive polymer electrolyte membrane is one of the most important key components in determining the performance and price in the polymer electrolyte fuel cell or direct methanol fuel cell.

Currently used polymer electrolyte membranes are mainly Nafion (trade name manufactured by DuPont), Premion (trade name manufactured by Flemion, Asahi Glass), Asiplex (trade name manufactured by Asahi Chemical), and Dow XUS (Dow XUS). , Dow Chemical Co., Ltd.) perfluorosulfonate ionomer membranes such as electrolyte membranes are widely used, but since the price is quite expensive, it is a great difficulty to commercialize the polymer fuel cell as a power source for power generation. It is working as a matter.

On the other hand, as a way to solve such difficulties, hydrocarbon-based polymers such as polyether ether ketone, polysulfone, polyimide, etc., which are relatively inexpensive and have various commercial applications. The research on is active. The polymer is prepared as an ion-conducting polymer by sulfonation and then cast into an electrolyte membrane, which is applied as a fuel cell electrolyte membrane.

In addition, Teflon is a method for improving redox resistance and thermal / mechanical stability, which are the major disadvantages of the above hydrocarbon-based polymers, and for improving low bonding properties with electrodes due to excessive swelling during membrane electrode assembly (MEA) manufacturing. A method of fabricating a composite membrane by impregnating a perfluorinated or hydrocarbon-based polymer in its pores in a porous support having excellent mechanical, thermal and oxidation resistance has been proposed. Commercialized examples include W.L. Gore & Associates' Gore-select has a thin thickness of 20 to 40㎛ and excellent mechanical and electrochemical properties.

In order to manufacture a membrane that can exhibit better performance of a fuel cell utilizing the excellent properties of the composite membrane as described above, styrene, a hydrocarbon monomer instead of Nafion, is used together with divinylbenzene, a crosslinking agent, with Teflon, polyethylene (PE), and polyvinyl. A method of impregnating and copolymerizing sulfides by impregnating various porous supports such as lidene difluoride (PVDF) has been proposed.

Sponified styrene resins, which are frequently used in the study of such composite membranes, are often copolymerized with divinylbenzene to maintain a membrane shape in water, and form an appropriate ion group as a polymer electrolyte in the resin.

However, these styrene-divinylbenzene copolymers are brittle due to increased brittleness, and have the disadvantage of inferior mechanical stability when mass-produced and processed into electrodes in the form of thin films or composite membranes. It is known that there is a disadvantage that it is not widely commercialized.

Therefore, an object of the present invention, in order to improve the physical properties of the composite membrane using styrene and divinylbenzene introduced into the porous support by introducing a new monomer vinylpyrrolidone (VP) in addition to the two materials in the support and copolymerization, The introduction of vinylpyrrolidone by using the obtained polymer electrolyte composite membrane improves the moisture content and ion exchange capacity of the membrane, and thus has a higher hydrogen ion conductivity than that of the conventional polymer electrolyte composite membrane prepared using styrene-divinylbenzene. It is to provide a composite membrane and a method of manufacturing the same.

A polymer electrolyte composite membrane for a fuel cell containing a styrene-vinylpyrrolidone copolymer according to the present invention for achieving the above object is characterized by forming a membrane by synthesizing a styrene-vinylpyrrolidone copolymer on a porous support.

Herein, the styrene-vinylpyrrolidone copolymer contains 60 to 90 wt.% Of a styrene monomer, 5 to 20 wt.% Of vinyl pyrrolidone, and 5 to 20 wt.% Of a crosslinking agent, and an initiator is added to 100 parts by weight of the monomer. It is preferable to contain the styrene-vinylpyrrolidone copolymer characterized by containing 0.2-1 weight part.

At this time, if the content of vinyl pyrrolidone is less than 5wt.%, The amount is insufficient to obtain a moisture content to improve the ionic conductivity, and if it is more than 20wt%, the ion exchange capacity of the membrane is reduced. In addition, when the content of the crosslinking agent is less than 5 wt%, the crosslinking degree is insufficient, and when the content of the crosslinking agent is more than 20 wt%, the crosslinking degree is too high, thereby reducing the conductivity of the membrane.

In addition, the porous support is preferably at least one selected from polytetrafluoroethylene, polyethylene, polypropylene, and polyvinyl difluoride.

In addition, the styrene monomer is preferably at least one selected from alphamethylstyrene, styrene, and trifluorostyrene.

In addition, the crosslinking agent is preferably any one of divinylbenzene, methylenebisacrylamide and tetramethylenebisacrylamide.

In addition, the initiator is preferably any one of N, N'-azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), cumyl peroxide.

Method for producing a polymer electrolyte composite membrane for a fuel cell containing a styrene-vinylpyrrolidone copolymer according to the present invention for achieving the above object;

(a-1) impregnating a porous support into a mixed solution consisting of styrene, vinylpyrrolidone, a crosslinking agent and an initiator;

(b-1) thermally polymerizing the porous support impregnated in the step (a-1) in an oven;

(c-1) sulfonating the styrene-vinylpyrrolidone copolymer composite membrane polymerized in the step (b-1) to introduce a sulfonic acid group;

(d-1) characterized in that it comprises the step of replacing the sulfonated composite membrane in the form of hydrogen ions in step (c-1) at all times.

According to the fuel cell polymer electrolyte composite membrane according to the present invention and a method for manufacturing the same, in order to improve the mechanical properties of the polymer electrolyte composite membrane, PTFE, PE, which are porous supports, and vinylpyrrolidone monomers are used together, -It has better ionic conductivity than composite membrane made using only divinylbenzene, but it can reduce the manufacturing cost due to simple manufacturing process and thinning and can expect to develop continuous manufacturing process.

Hereinafter, one preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

In this invention, the mixed solution which mixed the styrene and vinylpyrrolidone monomer, a crosslinking agent, and an initiator is produced. At this time, the ratio of the monomer in the mixed solution contains 60 to 90 parts by weight of styrene, 5 to 20 parts by weight of vinyl pyrrolidone, 5 to 20 parts by weight of divinylbenzene, and 100 parts by weight of the monomer solution, based on 100 parts by weight of the total solution. 0.2 to 1 (preferably 0.25) parts by weight of initiator.

Herein, the styrene monomer is at least one selected from alphamethylstyrene, styrene, and trifluorostyrene.

As such, by using a predetermined amount of the vinylpyrrolidone monomer having excellent moisture retention together with the styrene monomer, the water content and the ion exchange ability are improved to have high ion conductivity.

The crosslinking agent for the polymerization plays a role in determining the swelling degree and the mechanical properties of the membrane according to the amount of crosslinking degree of the composite membrane and its type may be divinylbenzene, methylenebisacrylamide, tetramethylenebisacrylamide, etc. It does not limit a kind, It is most preferable to use divinylbenzene in this invention. In addition, an initiator for polymerization may be used without particular limitation, and in the present invention, N, N′-azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), cumyl peroxide, and the like may be used.

Hereinafter, a method of manufacturing a polymer electrolyte composite membrane for a fuel cell according to the present invention will be described in more detail.

First, the porous support is impregnated into the mixed solution of styrene and vinylpyrrolidone monomer, crosslinking agent, and initiator as described above to allow the mixed solution to fully penetrate the support, and then onto the PET film and cover the PET film again. After the solution is evenly pushed with a push rod to allow the solution to be buried between the films, the polymer is thermally polymerized at 60 ° C. to 120 ° C. for at least 1 hour in an oven to prepare a composite membrane in which the pores in the porous support are filled with polymer. At this time, the thermal polymerization effect through an efficient initiation reaction cannot be obtained at a polymerization temperature of 60 ° C. or lower, and a problem occurs in the thermal stability of the manufactured film at 120 ° C. or higher.

Here, the support is used a material excellent in chemical resistance, oxidation resistance and thermal / mechanical stability, for example, polytetrafluoroethylene, polyethylene, polypropylene, polyvinyl difluoride may be used.

Next, for sulfonation of the composite membrane, an acid solution containing chlorosulfonic acid was prepared using dichloroethane (DCE) as a solvent, and the composite membrane was precipitated in the solution and allowed to stand for 24 hours to be sulfonated, and then acetone was removed to remove residual acid. And several times using ultrapure water. In order to replace the sulfon group with hydrogen ion form, it was left for 4-8 hours in 2N NaOH solution, and then immersed in 2N HCl solution for 10-12 hours and washed several times with ultrapure water. At this time, the acid solution is subjected to sulfonation reaction with 0.5 to 30 wt.% Chlorosulfonic acid solution prepared using dichloroethane as a solvent. When the concentration of the chlorosulfonic acid solution is 0.5 wt% or less, sufficient sulfonation reaction does not occur. At 30 wt% or more, the side reaction causes the membrane to be brittle, resulting in deterioration of mechanical properties.

In the same manner as above, a polymer electrolyte composite membrane having a thickness of 30 to 40 μm containing a copolymer of styrene and vinyl pyrrolidone may be prepared.

Hereinafter, the present invention will be described in detail with reference to the following examples, but the present invention is not limited only to the following examples.

Example 1

A monomer solution was prepared by mixing styrene (vinyl pyrrolidone (vp): divinylbenzene (DVB) in a weight ratio of 90: 0: 10, 85: 5: 10, and 90: 5: 5, respectively. N, N'-azobisisobutyronitrile (AIBN) was added at a ratio of 0.25% by weight based on the total weight of. The solution was impregnated with a 40 μm-thick polytetrafluoroethylene-based porous support to sufficiently infiltrate the monomer solution into the support, and then the support was sandwiched between polyethylene terephthalate (PET) films and thermally polymerized in a 110 ° C. oven. Was performed. Upon completion of the polymerization, the polyethylene terephthalate film was removed and immersed in a 5 wt% chlorosulfonic acid solution prepared using dichloroethane as a solvent at room temperature for 24 hours to proceed with sulfonation of the polymer. After sulfonation was completed, washed several times with acetone and ultrapure water and then stored.

This process produced a PTFE / sulfonated styrene-vinylpyrrolidone composite membrane having a film thickness of approximately 40 μm. The composite membrane thus prepared was analyzed for SEM, water content, ion exchange capacity and conductivity, and the results are shown in FIG. 1 and Table 1 below.

(A) and (b) of FIG. 1 are SEM images of the PTFE / styrene-vinylpyrrolidone composite membrane prepared according to Example 1, and it can be seen that phase separation and pinholes are not found in the membrane.

The water content, ion exchange capacity and conductivity of the PTFE / sulfonated styrene-vinylpyrrolidone composite membrane were measured by the following method, and the results are shown in Table 1.

1) Moisture content: Soak the composite membrane in ultrapure water for more than 24 hours to allow the membrane to have enough water. Remove moisture from the surface of the membrane and measure its weight (wet weight, Ww). The membrane is placed in a vacuum oven at 120 ° C. and dried for at least 12 hours and weighed (dry weight, Wd). The moisture content is obtained by substituting Equation 1 below.

2) Ion-exchange capacity: Soak the composite membrane in 1.0 M HCl for 24 hours so that functional groups in the ion-exchange membrane exist in acid form (eg -SO3H). Wash the membrane in equilibrium with acid solution with distilled water and remove all the acid solution remaining on the membrane surface. Remove The membrane is again immersed in 50 mL of 1.0 M NaCl for 24 hours to replace the cations in the NaCl solution with the hydrogen ions in the polymer electrolyte membrane. In this process, the volume of the salt solution must be known correctly to later calculate the exact moles of hydrogen ions. The NaCl solution is titrated with 0.01 M NaOH to determine the amount of hydrogen ions replaced again. The re-substituted membrane is dried, weighed, and the ion exchange capacity is calculated by the following equation.

Where V = replacement salt solution volume (mL), C = hydrogen ion concentration (meq / mL), and W = weight of the dry membrane.

3) Hydrogen ion conductivity: After impregnating the ultrapure water at room temperature for more than 24 hours, the surface water was removed and the resistance was measured by impedance spectroscopy using a four-electrode system measuring device.

       Where σ = hydrogen ion conductivity (S / cm), L = length between the Pt wires of the measuring cell (cm), R = measured resistance (Ω), W = film width (cm), d = film thickness ( cm).

Mixed Solution Composition (wt%) Water content
(%) Ion exchange capacity (meq / g)
Hydrogen ion
conductivity
(S / cm)
(S / cm) division Styrene VP DVB Comparative Example 1-1 90 0 10 32.37 1.40 0.0526 Example 1-1 85 5 10 31.21 1.83 0.0499 Example 1-2 90 5 5 62.50 1.84 0.0905

As shown in the above table, it can be seen that the ion exchange capacity increases when vinylpyrrolidone is used in combination with styrene alone (Comparative Example 1-1) (Examples 1-1 and 1-2). ), The composite membrane of Example 1-2 showed much higher hydrogen ion conductivity and water content than when styrene was used alone.

Example 2

In Example 1, a composite membrane was prepared by using a polyethylene support having a thickness of 30 μm instead of the PTFE support, and the results were shown in Table 2 below.

Mixed Solution Composition (wt%) Water content
(%) Ion exchange capacity
(meq / g) Hydrogen ion
conductivity
(S / cm) division Styrene VP DVB Comparative Example 2-1 90 0 10 15.22 1.48 0.0175 Example 2-1 85 5 10 20.41 2.06 0.0224 Example 2-2 90 5 5 21.74 1.49 0.0155

As shown in Table 2 above, it can be seen that the ion exchange capacity and conductivity were increased when vinyl pyrrolidone was used together (Example 2-1) than when styrene was used alone (Comparative Example 2-1).

Although the present invention has been described in detail with reference to various embodiments, it is not intended to limit the present invention only to illustrate the present invention, and various changes and modifications can be made by those skilled in the art without departing from the gist and scope of the present invention. Of course, this is also within the scope of the present invention.

1 is a view showing a photograph measured by Scanning Electron Microscope (SEM) of the surface of the porous support (PTFE support) according to the present invention,

FIG. 2A is a photograph taken by a scanning electron microscope (SEM) of the surface of the PTFE / sulfonated styrene-vinylpyrrolidone composite membrane, and FIG. 2B is a cross-sectional photograph of FIG. 2A.

Claims (11)

delete delete delete delete delete delete (a-1) impregnating a porous support into a mixed solution consisting of styrene, vinylpyrrolidone, a crosslinking agent and an initiator; (b-1) thermally polymerizing the porous support impregnated in the step (a-1) in an oven; (c-1) sulfonating the styrene-vinylpyrrolidone copolymer composite membrane polymerized in the step (b-1) to introduce a sulfonic acid group; (d-1) replacing the sulfonated composite membrane in the form of hydrogen ion at step (c-1) at all times, In the step of introducing the sulfonic acid group, in order to sulfonate the styrene-vinylpyrrolidone copolymer composite membrane using dichloroethane (DCE) as a solvent to make an acid solution containing chlorosulfonic acid and precipitate the composite membrane in the solution and left for 24 hours After sulfonation, a method of producing a polymer electrolyte composite membrane for a fuel cell containing a styrene-vinylpyrrolidone copolymer, which is washed several times with acetone and ultrapure water to remove residual acid. 8. The polymer electrolyte for fuel cell containing styrene-vinylpyrrolidone copolymer according to claim 7, wherein in the thermal polymerization step, the impregnated porous support is thermally polymerized in the oven at 60 ° C. to 120 ° C. for at least 1 hour. Method for producing a composite membrane. delete (a-1) impregnating a porous support into a mixed solution consisting of styrene, vinylpyrrolidone, a crosslinking agent and an initiator; (b-1) thermally polymerizing the porous support impregnated in the step (a-1) in an oven; (c-1) sulfonating the styrene-vinylpyrrolidone copolymer composite membrane polymerized in the step (b-1) to introduce a sulfonic acid group; (d-1) replacing the sulfonated composite membrane in the form of hydrogen ion at step (c-1) at all times, In the step of introducing the sulfonic acid group, the sulfonated composite membrane was left for 4 to 8 hours in 2 N NaOH solution to replace the sulfonated composite membrane in the form of hydrogen ions, and then immersed in 2 N HCl solution for 10 to 12 hours and then several times with ultrapure water. A method for producing a polymer electrolyte composite membrane for a fuel cell containing a styrene-vinylpyrrolidone copolymer, characterized by washing and storing. The method of claim 7, wherein the dichloroethane (DCE) as a solvent in the step of making an acid solution containing chlorosulfonic acid, immersed in 0.5 ~ 30wt.% Chlorosulfonic acid solution prepared using dichloroethane as a solvent at room temperature A method for producing a polymer electrolyte composite membrane for a fuel cell, which is left for 24 hours to undergo sulfonation of a polymer.

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