KR20070039709A - Method of synthesizing fluorine-based polymer with hydrogen ion conductivity group, polymer elecrolyte and binder comprising polymer obtained from same - Google Patents

Abstract

The present invention relates to a method for producing a fluoro-based polymer having a hydrogen ion conductive group, a polymer electrolyte membrane and a binder for a fuel cell produced by the method, the production method is a compound of formula 2 and the styrene compound of formula 3 In the presence of a transition metal-containing catalyst, a step of preparing a polymer having a YM group of the formula (4) by living radical polymerization in a solvent, and acidifying the polymer having a YM group of the formula (4).

[Formula 1]

[Formula 2]

[Formula 3]

[Formula 4]

(In the above formulas 1 to 4,

R1 and R2 are the same or independently of each other hydrogen or alkyl of C1 to C12,

R3 and R4 are the same or independently of each other hydrogen or an alkyl group of C1 to C12 or a fluoroalkyl group of C1 to C12,

X 1 is hydrogen or F,

Y is a hydrogen ion conductive functional group,

M is an alkali metal,

n is an integer from 50 to 50000, m is an integer from 1 to 1000, k is an integer from 0 or 1)

In the production method of the present invention, a copolymer of polyvinylidene fluoride and polystyrene may be prepared according to desired physical properties, and excellent in solubility, so that the copolymer may be easily manufactured to a desired thickness when preparing a membrane using the copolymer.

Copolymer, polymer electrolyte membrane, fuel cell, living radical polymerization, atomic transfer radical polymerization, PVdF, PSSA

Description

METHOD OF SYNTHESIZING FLUORINE-BASED POLYMER WITH HYDROGEN ION CONDUCTIVITY GROUP, POLYMER ELECROLYTE AND BINDER COMPRISING POLYMER OBTAINED FROM SAME}

[Industrial use]

The present invention relates to a method for producing a fluoro-based polymer having a hydrogen ion conductive group, a polymer electrolyte membrane for a fuel cell and a binder including a polymer prepared by the method, and more particularly, to easily copolymers having desired physical properties. It relates to a method for producing a fluoro-based polymer having a hydrogen ion conductive group that can be produced.

[Prior art]

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy. This fuel cell is a clean energy source that can replace fossil energy, and has a merit that can produce a wide range of outputs by stacking unit cells, and has an energy density of 4-10 times that of a small lithium battery. It is attracting attention as a compact and mobile portable power source.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC) and a direct oxidation fuel cell (Direct Oxidation Fuel Cell). When methanol is used as a fuel in the direct oxidation fuel cell, it is called a direct methanol fuel cell (DMFC).

The polymer electrolyte fuel cell has an advantage of having a high energy density and a high output, but requires attention to handling hydrogen gas and reforms fuel for reforming methane, methanol, natural gas, etc. to produce hydrogen as fuel gas. There is a problem that requires additional equipment such as a device.

On the other hand, the direct oxidation fuel cell has a lower energy density than the polymer electrolyte fuel cell, but it is easy to handle fuel and has a low operating temperature, so that it can be operated at room temperature, in particular, it does not require a fuel reformer.

In such fuel cell systems, the stack that substantially generates electricity comprises several unit cells consisting of a membrane-electrode assembly (MEA) and a separator (also called a bipolar plate). It has a structure laminated to several tens. The membrane-electrode assembly is called an anode electrode (also called a “fuel electrode” or an “oxidation electrode”) and a cathode electrode (also called “air electrode” or “reduction electrode”) with a polymer electrolyte membrane containing a hydrogen ion conductive polymer therebetween. ) Is located.

The principle of generating electricity in a fuel cell is that fuel is supplied to an anode electrode, which is a fuel electrode, adsorbed to a catalyst of the anode electrode, fuel is ionized by an oxidation reaction, and electrons are generated, and the generated electrons are oxidized according to an external circuit. Reaching the cathode, which is the pole, hydrogen ions pass through the polymer electrolyte membrane and are delivered to the cathode. An oxidant is supplied to the cathode, and the oxidant, hydrogen ions, and electrons react on the catalyst of the cathode to generate electricity while producing water.

It is an object of the present invention to provide a method for producing a fluoro-based polymer having a hydrogen ion conductive group which can easily prepare a copolymer having desired physical properties.

Another object of the present invention is to provide a polymer electrolyte membrane for a fuel cell comprising a polymer prepared by the above production method.

Still another object of the present invention is to provide a binder for a fuel cell comprising a polymer prepared by the above production method.

In order to achieve the above object, the present invention is to prepare a polymer having a YM group of the formula (4) by living radical polymerization in a solvent in the presence of a transition metal-containing catalyst of the compound of formula (2) and styrene compound of the formula (3) It provides a method for producing a fluoro-based polymer having a hydrogen ion conductive group of the general formula (1) comprising the step of acidifying the polymer having a YM group of the general formula (4).

[Formula 1]

[Formula 2]

[Formula 3]

[Formula 4]

(In the above formulas 1 to 4,

R1 and R2 are the same or independently of each other hydrogen or alkyl of C1 to C12,

R3 and R4 are the same or independently of each other hydrogen or an alkyl group of C1 to C12 or a fluoroalkyl group of C1 to C12,

X 1 is hydrogen or F,

Y is a hydrogen ion conductive functional group,

M is an alkali metal,

n is an integer from 50 to 50000, m is an integer from 1 to 1000, k is an integer from 0 or 1)

The prepared fluoropolymer may be usefully used as a polymer electrolyte membrane for fuel cells or as a binder.

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

In general, perfluorosulfonic acid is mainly used as a polymer electrolyte membrane for fuel cells, but researches to replace it are being conducted. Among them, polyvinylidene fluoride has attracted much attention as a membrane material because of its excellent chemical resistance, oxidation stability, and excellent tensile strength, and polystyrene sulfonic acid is attracting attention as a hydrogen ion conductor for fuel cells due to its excellent hydrogen ion conductivity. I am getting it.

Therefore, attempts have been made to prepare copolymers of polyvinylidene fluoride and polystyrene sulfonic acid and use them as polymer electrolyte membranes for fuel cells. The conventional production method was a method of preparing a polyvinylidene fluoride film and introducing a functional group capable of initiating radical polymerization by gamma ray, corona treatment, plasma treatment, and the like, and polymerizing with the styrene sulfonic acid monomer. However, this method has a limitation in controlling the film thickness since the crosslinking reaction is performed after the plasma treatment, and the film thickness is generally controlled by concentration or amount after dissolving the polymer in a solvent. The film is cross-linked and insoluble, so that the film thickness cannot be controlled. In addition, the decomposition reaction of the membrane chain is accompanied with the problem of brittle (brittle) when thickening the membrane at the same time. Therefore, the polymer electrolyte membrane prepared by the conventional method is difficult to control the film thickness and difficult to control the structure there was a limit to use as a polymer electrolyte membrane for fuel cells.

In the present invention, the physical properties can be adjusted as desired, and solubility in various solvents such as dimethoxyformamide, dimethyl acetate, and N-methylpyrrolidone can be easily controlled, and the film thickness can be controlled. It provides a method for producing a polymer electrolyte membrane that can easily prepare a polymer electrolyte membrane having the desired physical properties.

The manufacturing method of the polymer electrolyte membrane of the present invention is as follows.

In the presence of a transition metal-containing catalyst, a compound of Formula 2 and a styrene compound of Formula 3 have a YM group represented by the following formula (4) by living radical polymerization and atom transfer radical polymerization in a solvent. Prepare a polymer.

[Formula 2]

[Formula 3]

 [Formula 4]

In Chemical Formulas 2 to 4,

R1 and R2 are the same or independently of each other hydrogen or alkyl of C1 to C12,

R3 and R4 are the same or independently of each other hydrogen or an alkyl group of C1 to C12 or a fluoroalkyl group of C1 to C12,

X 1 is hydrogen or F,

Y is a hydrogen ion conductive functional group,

M is an alkali metal,

n is an integer of 50-500000, m is an integer of 1-1000, k is an integer of 0 or 1.

The Y is preferably selected from the group consisting of SO ₃ , COO, PO ₃ , the M is preferably Na, Li, K or Ca.

CuCl, CuBr, NiCl or FeCl ₂ may be used as the transition metal-containing catalyst, and N-methylpyrrolidone, dimethyl acetate, dimethylformamide or toluene may be used as the solvent.

In addition, the polymerization process is carried out under a temperature condition of 30 to 250 ℃. If the polymerization process is carried out under conditions outside the above temperature range, the polymerization does not proceed well or side reactions occur, which is not preferable.

Subsequently, the prepared polymer having the YM group of Formula 4 is acidified to prepare a fluoro-based polymer having the YH group of Formula 1.

[Formula 1]

In Formula 1, R1, R2, Y, n, and m are the same as defined above.

The acidification process can be carried out using an acid such as H ₂ SO ₄ , HCl or phosphoric acid. This acidification step may be carried out by dipping the prepared polymer in the acid, or when using it as an electrolyte membrane, after the membrane is prepared, the membrane may be dipped in the acid. Of course, when the membrane is prepared, the polymer may be subjected to acid treatment first, and then the membrane may be prepared from the acid-treated polymer.

The prepared polymer of Formula 1 may be usefully used as a binder of a polymer electrolyte membrane or a catalyst layer for a fuel cell.

When preparing a polymer electrolyte membrane, the polymer of Chemical Formula 1 is dissolved in an organic solvent, and the solution is filmed to prepare a polymer electrolyte membrane.

N-methylpyrrolidone, dimethyl acetate or dimethyl fluoride may be used as the organic solvent.

Alternatively, the polymer having the YM group of Formula 4 may be dissolved in an organic solvent, and the solution may be filmed first, followed by acidification of the film to prepare a polymer electrolyte membrane having the fluoropolymer of Formula 1.

The polymer electrolyte membrane prepared by this process is not in a crosslinked form, and a crosslinked polymer electrolyte membrane may be prepared by further using a compound represented by Chemical Formula 5 in the living radical polymerization reaction. Alternatively, the prepared polymer electrolyte membrane may be plasma treated to produce a cross-linked polymer electrolyte membrane.

[Formula 5]

(In Formula 5, R3 and R4 are the same as defined above, A is vinyl)

The number average molecular weight of the polymer electrolyte membrane produced by this process is 5000 to 300,000, which is much smaller than the number average molecular weight of 100000 to 500000 of the polymer electrolyte membrane prepared according to the conventional method, so that the solubility is excellent.

Since the polymer of Formula 1 of the present invention is used as a polymer electrolyte membrane or a catalyst layer binder, the polymer of Formula 1 of the present invention is included in a membrane-electrode assembly for a fuel cell. The membrane-electrode assembly includes an anode electrode and a cathode electrode positioned opposite each other, and includes a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode. When the polymer of Formula 1 of the present invention is used as the catalyst layer binder, the polymer is included in the anode electrode and the cathode electrode.

The anode electrode and the cathode electrode include an electrode substrate and a catalyst layer formed on the electrode substrate.

The catalyst in the catalyst layer is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Preference is given to using at least one member selected from the group consisting of at least one transition metal selected from the group consisting of Cu and Zn. As described above, the anode electrode and the cathode electrode may use the same material, but in order to prevent the catalyst poisoning caused by CO generated during the anode electrode reaction in the direct oxidation fuel cell, a platinum-ruthenium alloy catalyst is used as the anode. It is more preferable as an electrode catalyst.

In addition, such a metal catalyst may be used as the metal catalyst (black) itself, or may be supported on a carrier. As the carrier, carbon such as acetylene black, denka black, activated carbon, ketjen black, graphite may be used, or inorganic fine particles such as alumina, silica, titania, zirconia may be used, but carbon is generally used.

The electrode substrate plays a role of supporting the electrode and diffuses the fuel and the oxidant to the catalyst layer, thereby serving to easily access the fuel and the oxidant to the catalyst layer. The electrode substrate is a conductive substrate, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (porous film or polymer fiber composed of metal cloth in a fibrous state). The metal film is formed on the surface of the cloth formed of (referred to as a metalized polymer fiber) may be used, but is not limited thereto.

In addition, it is preferable to use a water-repellent treatment with a fluorine-based resin as the electrode base material, since the gas diffusion efficiency can be prevented from being lowered by water generated when the fuel cell is driven. As the fluorine-based resin, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, fluoroethylene polymer, or the like may be used.

In addition, a microporous layer may be further included to enhance the gas diffusion effect in the electrode substrate. These microporous layers are generally conductive powders of small particle size, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotubes, carbon nanowires, carbon nano horns. -horn or carbon nano ring. The microporous layer is prepared by coating a composition including a conductive powder, a binder resin, and a solvent on the gas diffusion layer. As the binder resin, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, cellulose acetate, and the like may be preferably used. The solvent may be ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, or the like. Alcohol, water, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone and the like can be preferably used. The coating process may be screen printing, spray coating, or coating using a doctor blade according to the viscosity of the composition, but is not limited thereto.

The fuel cell system of the present invention includes at least one electricity generating portion, a fuel supply portion and an oxidant supply portion.

The electricity generating portion includes a membrane-electrode assembly and a separator (also called bipolar plate). The membrane-electrode assembly includes a polymer electrolyte membrane and cathode and anode electrodes existing on both sides of the polymer electrolyte membrane. The electricity generation unit serves to generate electricity through the oxidation reaction of the fuel and the reduction reaction of the oxidant.

The fuel supply unit serves to supply fuel to the electricity generation unit, and the oxidant supply unit serves to supply an oxidant such as oxygen or air to the electricity generation unit.

In the present invention, the fuel may include hydrogen or hydrocarbon fuel in gas or liquid state. Representative examples of the hydrocarbon fuel include methanol, ethanol, propanol, butanol or natural gas.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

(Example 1)

Styrene sulfonic acid in which R 1 and R 2 is H, n is 15,000, and R 3 and R 4 in H, Y is SO ₃ , and M is Na, is a CuCl catalyst and N-methyl pyrrolidone solvent. In the living radical polymerization, a copolymer of polyvinylidene fluoride and polystyrene sulfonic acid in which R1 and R2 are H, n is 15,000 and m is 100, Y is SO ₃ , and M is Na in the following Chemical Formula 4 was prepared.

After dissolving the copolymer of Formula 4 in dimethyl acetate and casting on a glass plate to form a polymer membrane, the membrane thus prepared is immersed in 1N H ₂ SO ₄ solution for 24 hours to acidify to R1 and R2 in Formula 1 And Y is SO ₃ , n is 15,000, and m is 100. A polymer electrolyte membrane for a fuel cell of a copolymer of polyvinylidene fluoride and polystyrene sulfonic acid is prepared.

The production method of the present invention can produce a hydrogen ion conductive fluoro-based polymer according to the desired physical properties, and excellent solubility, it is easy to manufacture to the desired thickness when producing a membrane using the polymer.

Claims (8)

Preparing a polymer having a YM group represented by the following Chemical Formula 4 by living radical polymerization in a solvent in the presence of a transition metal-containing catalyst with a polymer of the following Chemical Formula 2 and a styrene compound of the following Chemical Formula 3; Acidifying the polymer having a YM group of the formula Method for producing a polymer having a hydrogen ion conductive group of the formula (1) comprising a step. [Formula 1]

[Formula 2]

[Formula 3]

[Formula 4]

(In the above formulas 1 to 4, R1 and R2 are the same or independently of each other hydrogen or alkyl of C1 to C12, R3 and R4 are the same or independently of each other hydrogen or an alkyl group of C1 to C12 or a fluoroalkyl group of C1 to C12, X 1 is hydrogen or F, Y is a hydrogen ion conductive functional group, M is an alkali metal, n is an integer from 50 to 50000, m is an integer from 1 to 1000, k is an integer from 0 or 1) The method of claim 1, Wherein Y is selected from the group consisting of SO ₃ , COO and PO _{3 The} method of producing a polymer having a hydrogen ion conductive group. The method of claim 1, M is a method for producing a polymer having a hydrogen ion conductive group is selected from the group consisting of Na, K, Li and Ca. The method of claim 1, The living radical polymerization is a method for producing a polymer having a hydrogen ion conductive group that is carried out at a temperature of 50 to 250 ℃. The method of claim 1, The copolymer of polyvinylidene fluoride and polystyrene sulfonic acid is a method for producing a polymer having a hydrogen ion conductive group for a polymer electrolyte membrane or a binder for a fuel cell. The method of claim 1, The method of producing a polymer having a hydrogen ion conductive group to further use a compound of the formula (5) in the living radical polymerization process. [Formula 5]

(In Formula 5, A is vinyl)  A high molecular electrolyte membrane for a fuel cell comprising the polymer of any one of claims 1 to 6.   A fuel cell binder comprising the polymer of any one of claims 1 to 6.