KR101491993B1 - Reinforced composite membrane for fuel cell and membrane-electrode assembly for fuel cell comprising same - Google Patents

Abstract

The present invention relates to a reinforced composite membrane for a fuel cell and a membrane-electrode assembly for a fuel cell comprising the same, wherein the reinforced composite membrane comprises a porous support and an ion conductor filled in the pores of the porous support, The nanofibers of the polymer precursor prepared by electrospinning a precursor solution of the polymer for forming are successively cured while being transferred alternately on and under a plurality of rollers under the application of a winding tension of 1 to 15 N. The randomly arranged polymer nano- Fibers, and has directional mechanical properties.
The reinforced composite membrane is excellent in one-dimensional dimensional stability, so that the polymer electrolyte membrane in a membrane-electrode assembly for a fuel cell is stable in interfacial contact with an electrode when used, and has less deformations under fuel cell operating conditions, thereby improving the performance and durability of the fuel cell. .

Description

TECHNICAL FIELD [0001] The present invention relates to a reinforced composite membrane for a fuel cell and a membrane-electrode assembly for a fuel cell including the same. BACKGROUND ART [0002]

The present invention relates to a reinforced composite membrane for a fuel cell exhibiting excellent one-directional dimensional stability and a membrane-electrode assembly for a fuel cell comprising the same.

Fuel cells convert chemical energy generated by the oxidation of fuel directly into electrical energy. As a result, the fuel cell is attracting attention as a next-generation energy source because of its high energy efficiency and eco-friendly characteristics with less pollutant emissions. Such a fuel cell generally has a structure in which an anode and a cathode are formed on both sides of an electrolyte membrane.

A typical example of a fuel cell for automobiles is a hydrogen ion exchange fuel cell using hydrogen gas as a fuel. Since the electrolyte membrane used in such a hydrogen ion exchange fuel cell is a passage through which hydrogen ions generated in the oxidizing electrode are transferred to the reducing electrode, basically, it should have an excellent hydrogen ion conductivity. In addition, the electrolyte membrane should be excellent in separation ability for separating hydrogen gas supplied to the oxidizing electrode from oxygen supplied to the reducing electrode, and should have excellent mechanical strength, shape stability, and chemical resistance, and should have low resistance loss at high current density And so on. In particular, fuel cells for automobiles should have excellent heat resistance so that the electrolyte membrane is not ruptured when used at high temperature for a long time.

As an electrolyte membrane for a fuel cell currently in use, there is a perfluorosulfonic acid resin (Nafion ™) (hereinafter referred to as "Nafion resin") as a fluororesin. However, since the Nafion resin has a low mechanical strength, pinholes are generated when the Nafion resin is used for a long period of time, resulting in a problem that energy conversion efficiency is deteriorated. In order to reinforce the mechanical strength, there is an attempt to increase the thickness of the Nafion resin. However, in this case, there is a problem that the resistance loss increases and the economical efficiency decreases due to the use of expensive materials.

To solve these problems and to overcome the disadvantages of conventional electrolyte membranes, reinforced composite membranes have been proposed. The reinforced composite membrane is composed of a porous support for improving the dimensional stability, durability, mechanical strength and the like, which is a disadvantage of the electrolyte single membrane, together with the ion conductor which is an electrolyte material. A representative product including a reinforced composite membrane is PRIMEA (TM) manufactured by Gore. The reinforced composite membrane is characterized in that the porous polytetrafluoroethylene resin is compounded with a fluorine-based ion conductor to improve mechanical strength. However, in order to commercialize a fuel cell, the use of a fluorine-based ionic conductor and a fluorine-based porous support is inferior in competitiveness in a situation where cost reduction is required.

Accordingly, inexpensive hydrocarbon-based ionic conductors have been developed to replace expensive fluorine-based ionic conductors, but hydrocarbon-based ionic conductors have a problem in that they are difficult to apply to fluorocarbon-containing porous supports.

Therefore, there is a demand for a porous support that is compatible with hydrocarbon-based ionic conductors, as well as hydrocarbon-based ionic conductors as well as fluorine-based ionic conductors. In addition, since the reinforced composite membrane is applied in the form of a membrane-electrode assembly by bonding electrodes to both surfaces of the reinforced composite membrane when applied to a fuel cell, deterioration in performance and durability of the fuel cell due to poor contact at the interface between the electrode and the reinforced composite membrane A reinforced composite membrane having excellent dimensional stability is required.

Korean Patent Laid-Open Publication No. 2011-0084849 and No. 2011-0120185 disclose a reinforced composite membrane in which a porous support composed of polyimide nanofibers is complexed with an ion conductor.

Korean Patent Laid-Open Publication No. 2011-0084849 (published on July 26, 2011) Korean Patent Laid-Open No. 2011-0120185 (published on November 3, 2011)

It is an object of the present invention to provide a reinforced composite membrane for a fuel cell which has improved one-dimensional dimensional stability and is free from interfacial separation at a contact interface with an electrode.

The present invention also provides a membrane-electrode assembly and a fuel cell for a fuel cell that can improve the durability and performance characteristics of the fuel cell including the reinforced composite membrane.

According to an embodiment of the present invention, there is provided a porous support comprising randomly arranged polymer nanofibers and having a directional mechanical property; And an ion conductor filled in the pores of the porous support, wherein the porous support comprises nanofibers of a polymer precursor prepared by electrospinning a precursor solution containing a precursor of a polymer for forming a porous support, And is continuously cured while being alternately transported on and under a plurality of rollers in a zigzag manner under application of an electric field.

The mechanical properties may be tensile strength, elongation, or both.

The porous support may have a tensile strength ratio of 5 or less in one direction and in a direction perpendicular to the one direction.

The porosity of the porous support may be 0.2 or more in a direction perpendicular to the one direction and the one direction.

The porous support may include a hydrocarbon-based polymer insoluble in an organic solvent, and may preferably include a polyimide.

The porous support may have a porosity of 50 to 90%.

The porous support may have an average thickness of 5 to 50 탆.

The ionic conductor may be a hydrocarbon-based polymer that is soluble in an organic solvent, and is preferably a sulfonated polyimide, a sulfonated polyaryl ether sulfone, a sulfonated polyether ether ketone, a sulfonated polybenzimidazole, Sulfonated polysulfones, sulfonated polystyrenes, sulfonated polyphosphazenes, and mixtures thereof.

The ionic conductor may be included in an amount of 50 to 99% by weight based on the total weight of the reinforced composite membrane.

The reinforced composite membrane may have a dimensional stability of less than 8% in one direction when swollen in water.

According to another embodiment of the present invention, there is provided a method of manufacturing a polymer precursor comprising the steps of: preparing a polymer precursor nanofiber by electrospinning a precursor solution containing a precursor of a polymer for forming a porous support; Comprising the steps of: preparing a porous support by successively curing while transferring a plurality of rollers on and under a plurality of rollers in a zigzag manner under the application of a tensile force; and filling the pores of the porous support with ionic conductors. do.

The porous support-forming polymer may be a hydrocarbon-based polymer insoluble in an organic solvent.

The precursor solution may include a precursor of the polymer for forming a porous support at a concentration of 5 to 20% by weight based on the total weight of the precursor solution.

The electrospinning process may be performed by applying an electric field of 850 to 3,500 V / cm.

The curing process may be carried out at 80 to 650 ° C.

According to another embodiment of the present invention, there is provided a plasma display panel comprising: an anode electrode and a cathode electrode facing each other; And a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein the polymer electrolyte membrane is the reinforced composite membrane as described above.

According to another embodiment of the present invention, there is provided a fuel cell including the membrane-electrode assembly.

Other details of the embodiments of the present invention are included in the following detailed description.

The reinforced composite membrane is excellent in one-dimensional dimensional stability, so that the polymer electrolyte membrane in a membrane-electrode assembly for a fuel cell is stable in interfacial contact with an electrode when used, and has less deformations under fuel cell operating conditions, thereby improving the performance and durability of the fuel cell. .

1 is a schematic view schematically showing an apparatus for carrying out a continuous zig-zag hardening process in the production of a porous support according to the present invention.
2 is a schematic cross-sectional view of a membrane-electrode assembly in accordance with an embodiment of the present invention.
3 is a photograph of the surface of the porous support prepared in Example 1, observed with a scanning electron microscope (SEM).
FIG. 4 is a graph showing the results of observing the tensile strength and the tensile strength ratio of the porous support prepared in Examples 1 to 3. FIG.
5 is a graph showing the results of observing the elongation and the elongation of the porous support prepared in Examples 1 to 3. FIG.
6 is an SEM photograph of a section of the reinforced composite membrane produced in Example 1. Fig.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

The term "nano," as used herein, refers to nanoscale and includes a size of 1 μm or less.

The term "diameter " as used herein means the length of the minor axis passing through the center of the fiber, and " length " means the length of the major axis passing through the center of the fiber.

Generally, a stack in an automotive fuel cell has a long rectangular shape in the longitudinal direction. Therefore, if the same dimensional stability is applied to each direction of the reinforced composite membrane, deformation in the longitudinal direction is further increased, The durability and the performance of the fuel cell deteriorate. Therefore, there is a demand for a reinforced composite film having better dimensional stability in the longitudinal direction.

On the other hand, in the present invention, when a reinforced composite membrane for a fuel cell is manufactured by using a porous support manufactured by continuously curing a random polyimide nanofiber by alternately zigzagging and transferring a plurality of rollers on and under a controlled winding tension, The dimensional stability is improved and dimensional deformation is small even after interfacial bonding with the electrode. Thus, the present invention has been completed.

That is, the reinforced composite membrane for a fuel cell according to an embodiment of the present invention includes a porous support having randomly arranged polymer nanofibers and having directional mechanical properties; And an ion conductor filled in the pores of the porous support.

The porous support enhances dimensional stability by enhancing the mechanical strength of the reinforced composite membrane and suppressing the volume expansion due to moisture. The porous support is a polymer precursor prepared by electrospinning a solution containing a precursor of a polymer for forming a porous support The nanofibers can be manufactured by successively curing the nanofibers while alternately transferring the nanofibers on and under a plurality of rollers in a staggered manner under the application of a winding tension of 1 to 15N.

The porous support prepared by the above-described production method exhibits orientational mechanical properties including randomly arranged nanofibers. The directional mechanical properties generally mean that the tensile strength and elongation, which show mechanical properties, vary depending on the direction.

It is preferable that the porous support to be applied to the reinforced composite membrane for fuel cells has an optimal ratio of tensile strength and elongation in a certain direction in order to facilitate manufacture and prevent durability and performance deterioration of the fuel cell due to deformation of the electrolyte membrane. Specifically, the porous support has a tensile strength ratio of 5 or less in one direction defined by the following equation (1) and in a direction perpendicular to the one direction.

If the ratio of the tensile strength of the porous support is more than 5, the tensile strength in one direction and the vertical direction is large and the physical properties are biased in one direction, so that it is likely to be cut. As a result, it is difficult to apply the porous support to the ion conductor supporting process during the production of the reinforced composite membrane.

In addition, the porous support has a one-directional orientation defined by the following formula (2) and a longitudinal orientation ratio of at least 0.2 in the one direction.

If the elongation ratio of the porous support is less than 0.2, it is difficult to ensure the dimensional stability of the reinforced composite membrane using the porous support. Particularly, since the dimensional deformation largely occurs in one direction, the performance and durability of the reinforced composite membrane for a fuel cell are lowered.

 The porous support includes a collection of nanofibers, i.e., a web of nanofibers, in which the nanofibers produced by electrospinning are randomly arranged. In consideration of the porosity and thickness of the nanofiber web, the nanofiber was measured for 50 fiber diameters using a scanning electron microscope (JSM6700F, JEOL), and the fiber diameter was measured to be 40 to 5,000 nm It is preferable to have an average diameter. If the average diameter of the nanofibers is less than 40 nm, the mechanical strength of the reinforced composite membrane may deteriorate. If the average diameter of the nanofibers exceeds 5,000 nm, the porosity may be significantly decreased and the thickness may be increased.

The porous support is made of the nanofiber as described above, and thus can have a porosity of 50% or more. As the porous support has a porosity of 50% or more in this way, the porous support has a large specific surface area, so that impregnation of the ion conductor is easy, and as a result, excellent ion conductivity can be exhibited. On the other hand, the porous support preferably has a porosity of 90% or less. If the porosity of the porous support exceeds 90%, the morphology of the porous support may be deteriorated and the post-treatment may not proceed smoothly. The porosity can be calculated according to the ratio of the volume of air to the total volume of the porous support according to Equation (3). In this case, a rectangular volume sample is prepared and measured by measuring the width, length, and thickness, and the air volume can be obtained by subtracting the volume of the polymer inversely calculated from the density after measuring the mass of the sample from the total volume.

In addition, the porous support may have an average thickness of 5 to 50 탆. If the thickness of the porous support is less than 5 탆, the mechanical strength and dimensional stability of the reinforced composite membrane may be significantly deteriorated. On the other hand, when the thickness exceeds 50 탆, resistance loss increases when applied to a reinforced composite membrane, . The thickness of the porous support is more preferably in the range of 10 to 30 占 퐉.

The porous support is insoluble in conventional organic solvents and exhibits excellent chemical resistance and facilitates the ion conductive filling process in the pores of the porous support. In addition, the porous support has hydrophobicity and is free from the possibility of morphological change due to moisture in a high humidity environment It is preferable to include a hydrocarbon-based polymer. The hydrocarbon-based polymer may include nylon, polyimide (PI), polybenzoxazole (PBO), polybenzimidazole (PBI), polyamideimide (PAI), polyethyleneterephtalate ), Polyethylene (PE), polypropylene (PP), copolymers thereof and mixtures thereof. Among these, polyimide polymers having excellent heat resistance, chemical resistance, and shape stability are preferred .

When the porous support comprises polyimide, the porous support preferably has an imidization ratio of 90% or more. The imidization rate can be calculated according to the following equation (4) because the polyimide precursor is converted into an imide group by cyclization reaction through an imidization process such as heat treatment.

However, the weight of the nanofibers before the solvent treatment is measured using nanofibers left in a vacuum oven set at a temperature of 30 ° C for 24 hours or more, and the weight of the nanofibers after the solvent treatment is measured as dimethyl Formaldehyde organic solvent, stirred at room temperature for 24 hours, washed with distilled water more than 5 times, then left in a vacuum oven set at 30 ° C for 24 hours, and then measured using a nanofiber web obtained after solvent treatment.

If the imidization rate is less than 90%, it is difficult to maintain the required properties for a long time because the nanofibers may be damaged by the organic solvent. Accordingly, the polyimide porous support having an imidization ratio after 90% or more of solvent treatment can maintain excellent tensile strength even in a strong acidic environment, which is the driving environment of the fuel cell, and has excellent dissolution resistance to the electrolyte. As a result, And the interface between the electrode and the electrode are not separated, so that excellent ion conductivity can be maintained for a long time. In addition, the polyimide porous support having such excellent acid resistance can improve reliability when it is used in an electrolyte membrane of a fuel cell driven in a strongly acidic environment because it can exhibit excellent performance for a long time.

In order for the porous support to have a thickness of nanofiber having excellent porosity and optimized diameter and to be easily manufactured and to exhibit excellent tensile strength after the wet treatment, the polymer constituting the porous support has a weight of 30,000 to 500,000 g / mol It is preferable to have an average molecular weight. If the weight average molecular weight of the polymer constituting the porous support is less than 30,000 g / mol, porosity and thickness of the porous support can be easily controlled, but tensile strength after porosity and wet treatment may be lowered. On the other hand, when the weight average molecular weight of the polymer constituting the porous support exceeds 500,000 g / mol, the heat resistance may be improved somewhat, but the production process may not proceed smoothly and the porosity may be lowered.

The porous support may have a melting point of 400 ° C or higher, preferably 400 ° C to 800 ° C, as the polymer precursor has a weight average molecular weight in the range as described above and the polymer precursor is converted into a polymer under optimal curing conditions. If the melting point of the porous support is less than 400 ° C, the heat resistance of the porous support may be lowered at a high temperature, and the performance of the fuel cell manufactured using the porous support may deteriorate. In addition, when the heat resistance of the porous support is lowered, the shape is deformed due to abnormal heat generation, thereby deteriorating the performance, and in the worst case, it may rupture and explode.

It is preferable that the porous support is contained in an amount of 1 to 50 wt% based on the total weight of the reinforced composite membrane. If the content of the porous support is less than 1 wt%, the mechanical strength and dimensional stability of the reinforced composite membrane may deteriorate. If the content of the porous support exceeds 50 wt%, the hydrogen ion conductivity of the reinforced composite membrane may decrease .

The porous support includes an aggregate of randomly arranged nanofibers and exhibits a directional mechanical property, thereby improving the one-dimensional stability of the reinforced composite membrane when used as a porous support of a reinforced composite membrane for a fuel cell.

The reinforced composite membrane for a fuel cell according to the present invention also comprises an ion conductor filled in the pores of the porous support.

The ion conductor performs a hydrogen ion conduction function, which is a main function of the polymer electrolyte membrane. The ion conductor can use a hydrocarbon polymer which is excellent in hydrogen ion conductivity and is advantageous in terms of price. Particularly, in consideration of the ease of filling the ion conductor in the pores of the porous support, as described above, it is preferable to use a hydrocarbon-based polymer that is soluble in an organic solvent. Examples of the hydrocarbon-based polymer soluble in the organic solvent include a sulfonated polyimide (S-PI), a sulfonated polyarylethersulfone (S-PAES), a sulfonated polyether ether ketone sulfonated polyetheretherketone (SPEEK), sulfonated polybenzimidazole (SPBI), sulfonated polysulfone (S-PSU), sulfonated polystyrene (S-PS) Sulfonated polyphosphazene, or a mixture thereof may be used, but the present invention is not limited thereto. Here, "solubility" with respect to an organic solvent means melting property at room temperature.

Generally, when operating conditions such as temperature or humidity during operation of the fuel cell are changed, the adhesion between the ion conductor and the porous support may be deteriorated. In the present invention, both the ion conductor and the porous support include a hydrocarbon-based polymer The adhesion between the two is excellent. Specifically, the hydrocarbon-based material contained in the ion conductor is formed into a sulfonated material of the hydrocarbon-based material contained in the porous support, such as S-PI (sulfonated polyimide) as the ionic conductor and PI , The adhesion between the ionic conductor and the porous support is very excellent, and as a result, the separation performance between hydrogen and oxygen is excellent, and a relatively inexpensive hydrocarbon-based resin such as Nafion resin or Teflon resin, Due to the use of polymer materials, it is superior in terms of price competition in mass production.

The ionic conductor may be included in an amount of 50 to 99% by weight based on the total weight of the reinforced composite membrane. If the content of the ionic conductor is less than 50% by weight, the hydrogen ion conductivity of the reinforced composite membrane may be lowered. If the content of the ionic conductor exceeds 99% by weight, the mechanical strength and dimensional stability of the reinforced composite membrane may be deteriorated.

The ion conductor may be formed to a thickness of 1 탆 or more on one surface of the porous support in the manufacturing process, but it is preferable to control the thickness to 30 탆 or less. If the ion conductor is formed on one surface of the porous support to a thickness exceeding 30 mu m, the mechanical strength of the reinforced composite membrane may be deteriorated, leading to an increase in the total thickness of the reinforced composite membrane, have.

The reinforced composite membrane according to the present invention has an excellent mechanical strength of 10 MPa or more because it has the structure in which the ion conductor is filled in the pores of the porous support. As the mechanical strength is increased, the total thickness of the reinforced composite membrane can be reduced to 80 탆 or less. As a result, the hydrogen ion conduction rate is increased and the resistance loss is reduced along with the material cost saving.

Further, the reinforced composite membrane includes a porous support having directional mechanical properties, and thus exhibits excellent dimensional stability under humidifying conditions, specifically, less than 8%, preferably less than 1% when swollen in water. The dimensional stability is a physical property evaluated from the change in length before and after swelling when the reinforced composite membrane is swelled in water according to the following formula (5).

According to another embodiment of the present invention, there is provided a method for preparing a polymer precursor nanofiber comprising the steps of: (1) preparing nanofibers of a polymer precursor by electrospinning a precursor solution containing a precursor of a polymer for forming a porous support, (Step 2) of successively curing while alternately staggering the upper and lower rollers under the application of a coiling tension of 15 N to 15 N to produce a porous support (step 2); and filling the ion conductor in the pores of the porous support (step 3) The present invention also provides a method for producing a reinforced composite membrane for a fuel cell.

In step 1, a precursor solution containing a precursor of a polymer for forming a porous support is electrospun to produce a polymer precursor nanofiber (hereinafter referred to as "nanofiber precursor").

Since the porous support includes a hydrocarbon-based polymer which is insoluble in an organic solvent as a polymer for forming a porous support, it can be prepared without dissolving in an organic solvent or by using a precursor of a polymer for forming a porous support, Followed by formation of a precursor, followed by a predetermined reaction. The precursor of the polymer for forming a porous support may be appropriately selected according to the type of the polymer for forming the porous support, and the specific types of the polymer for forming the porous support are as described above.

For example, a porous support made of polyimide (PI) is formed by electro-spinning polyamic acid (PAA) to form a PAA nanofiber precursor, followed by imidization in a subsequent curing process Can be manufactured.

The polyamic acid may be prepared according to a conventional method. Specifically, the polyamic acid may be prepared by mixing a diamine in a solvent and adding dianhydride thereto followed by polymerization.

Examples of the dianhydride include pyromellitic dianhydride (PMDA), 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride (3,3', 4,4'-benzophenonetetracarboxylic dianhydride, BTDA ), 4,4'-oxydiphthalic anhydride (ODPA), 3,4,3 ', 4'-biphenyltetracarboxylic acid anhydride (3,4,3', 4 ' -biphenyltetracarboxylic dianhydride (BPDA), bis (3,4-dicarboxyphenyl) dimethylsilane dianhydride (SiDA), and mixtures thereof. Examples of the diamine include 4,4'-oxydianiline (ODA), p-phenylene diamine (p-PDA), o-phenylene diamine diamine, o-PDA), and mixtures thereof. The solvent for dissolving the polyamic acid may include m-cresol, N-methyl-2-pyrrolidone (NMP), dimethyl (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), acetone, diethyl acetate, tetrahydrofuran (THF), chloroform, gamma -butyrolactone and mixtures thereof A solvent may be used.

The precursor solution containing the precursor of the polymer for forming a porous support may be prepared by dissolving the precursor of the polymer for forming a porous support in a conventional organic solvent such as NMP, DMF, DMAc, DMSO, or THF.

At this time, the precursor of the polymer for forming a porous support is preferably contained in a concentration of 5 to 20% by weight based on the total weight of the precursor solution. If the concentration of the precursor solution is less than 5% by weight, the spinning does not proceed smoothly. Therefore, fibers having no fiber formation or having a uniform diameter can not be produced, whereas when the concentration of the precursor solution is 20% The discharge pressure may increase suddenly, which may result in inefficiency or poor performance.

Then, the prepared precursor solution is spun using a conventional electrospinning apparatus to prepare a nanofiber precursor.

Specifically, the precursor solution is supplied in a predetermined amount to a radiation part using a metering pump in a solution tank storing a spinning solution, the precursor solution is discharged through a nozzle of the spinning part, and a nanofiber precursor , And additionally, such a solidified nanofiber precursor can be focused on a collector having a releasing film to produce a fiber aggregate.

At this time, the intensity of the electric field between the radiation part and the collector applied by the high voltage generating part is preferably 850 to 3,500 V / cm. If the electric field intensity is less than 850 V / cm, since the precursor solution is not continuously discharged, it is difficult to produce nanofibers of uniform thickness, and since the nanofibers formed after spinning can not be smoothly focused on the collector It may be difficult to produce a fibrous aggregate. On the other hand, if the electric field intensity exceeds 3,500 V / cm, the nanofibers can not be accurately placed on the collector, so that a fiber aggregate having a normal shape can not be obtained.

Through the spinning process, a nanofiber precursor having a uniform fiber diameter, preferably an average diameter of 0.01 to 5 탆, is prepared, and the nanofiber precursor is randomly arranged to form a fibrous aggregate, i.e., a web.

In step 2, the nanofiber precursor is successively cured while alternately moving on and under a plurality of rollers in a zigzag manner under the application of a winding tension of 1 to 15 N.

Since the precursor of the polymer is used for forming the porous support by electrospinning in the production method of the present invention, in order to convert the precursor into the polymer for forming the porous support, a curing process is performed as an additional process for the nanofiber precursor do. For example, when nanofibers or fibrous assemblies produced by the electrospinning are made of polyimide precursors, they are converted to polyimides through imidization during the curing process.

Accordingly, it is preferable that the temperature during the curing process is appropriately controlled in consideration of the conversion ratio of the polymer precursor to the polymer. Concretely, it is preferable that the curing process is carried out at 80 to 650 ° C. When the curing temperature is lower than 80 ° C, the polymer conversion rate is lowered. As a result, the heat resistance and chemical resistance of the porous support may deteriorate. When the curing temperature exceeds 650 ° C, the physical properties of the porous support There is a risk of degradation.

1 is a schematic view schematically showing an apparatus for carrying out a continuous zig-zag hardening process in the production of a porous support according to the present invention.

1, a nanofiber precursor or fiber aggregate 12 produced by electrospinning is placed in a curing apparatus 10 having a plurality of rolls 11 installed up and down so as to enable zigzag transfer And then the upper and lower rollers are alternately and zigzagly transported with a later-controlled winding tension.

At this time, the winding tension is preferably 1 to 15N. If the coiling tension is less than 1N, the nanofiber precursor may not be transferred in the coin furnace, and if it is more than 15N, the nanofiber precursor or the fibrous aggregate is deformed to make it difficult to obtain a uniform thickness, Is lowered, tensile strength may be lowered.

By thus transferring the nanofiber precursor or the fibrous aggregate thereof in a zigzag manner with an optimum winding tension, the porous support exhibits a directional mechanical property in spite of the fact that the nanofibers constituting the porous support are fibrous in a random arrangement. As a result, it is possible to remarkably improve the unidirectional dimensional stability of the reinforced composite membrane when used as a reinforced composite membrane for a fuel cell in which an ion conductor is complexed with a porous support.

In step 3, the ion conductor is filled in the pores of the prepared porous support.

The ion conductor may be filled by a method in which the porous support is supported on an ion conductor solution prepared by dissolving an ion conductor in a solvent, but the present invention is not limited thereto, and a spray process, a screen printing process, a doctor blade process, Various methods known in the art can be used. When the above-mentioned supporting step is used, it is preferable to carry out the supporting step for 2 to 5 times at room temperature for 5 to 30 minutes.

The ion conductor solution can be prepared by dissolving an ion conductor in an organic solvent. The organic solvent may be N-methyl-2-pyrrolidinone (NMP), dimethylformamide (DMF), or dimethyl acetamide (DMA) , But it is not necessarily limited thereto.

The ion conductor may be the same as that described above.

The ion conductor may be contained in the ion conductor solution in an amount of 5 to 40% by weight. When the ionic conductor is contained in an amount of less than 5% by weight, the ionic conductor may not be sufficiently filled in the pores of the porous support to form an empty space. When the ionic conductor is more than 40% by weight, It may be too high to fill the pores of the porous support.

After the ion conductor solution is filled, the organic solvent in the ion conductor solution is removed so that the ion conductor is filled in the pores of the porous support. Therefore, the method of preparing the reinforced composite membrane according to the present invention may further include a step of removing the organic solvent after filling the ion conductor, and the organic solvent removing step may be performed in a vacuum oven at 60 to 150 ° C. for 2 to 15 hours Process.

The reinforced composite membrane produced by the above-described production method is excellent in one-dimensional dimensional stability, so that the polymer electrolyte membrane in the membrane-electrode assembly for a fuel cell is stable in interfacial contact with the electrode when used, The performance and durability of the battery can be improved.

According to another embodiment of the present invention, there is provided a membrane-electrode assembly and a fuel cell for a fuel cell including the reinforced composite membrane as a polymer electrolyte membrane.

Specifically, the membrane-electrode assembly includes the reinforced composite membrane as the polymer electrolyte membrane positioned between the anode and the cathode, and between the anode and the cathode.

2 is a schematic cross-sectional view of a membrane-electrode assembly in accordance with an embodiment of the present invention. 2, the membrane-electrode assembly 100 according to an embodiment of the present invention includes a polymer electrolyte membrane 50 and the fuel cell electrode 20 (see FIG. 2) disposed on both sides of the polymer electrolyte membrane 50 , 20 '). The electrode includes an electrode substrate 40, 40 'and a catalyst layer 30, 30' formed on the surface of the electrode substrate. The electrode substrate 40, 40 'and the catalyst layer 30, 30' (Not shown) containing conductive fine particles, such as carbon powder, carbon black, etc., to facilitate the diffusion of the materials in the substrate.

The membrane-electrode assembly 100 includes a polymer electrolyte membrane 50 disposed on one surface of the membrane electrode assembly 40 and having an electrode substrate 40 and an electrode (Or cathode) electrode 20 is disposed on the other surface of the polymer electrolyte membrane 50 and passes through the polymer electrolyte membrane 50 and the electrode substrate 40 ' The electrode 20 'that causes a reduction reaction to generate water from the oxidant transferred to the cathode 30' is referred to as a cathode electrode (or an anode electrode).

The catalyst layers 30 and 30 'of the anode and cathode electrodes 20 and 20' include a catalyst. Any of the catalysts which can participate in the reaction of the battery and can be used as a catalyst of a fuel cell can be used. Specific examples of the platinum-based catalyst include platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum-M alloy (M is Ga, Ti, V At least one transition metal selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Mo, W and Rh) may be used. Specific examples thereof include Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni and Pt / Ru / Sn / W. Such a catalyst may be used as the catalyst itself (black) or may be supported on a carrier. The carrier may be a carbonaceous material such as graphite, denka black, ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanoballs, or activated carbon, or may be alumina, silica, zirconia, Or an inorganic fine particle such as titania may be used.

The catalyst layers 30 and 30 'may further include a binder resin for improving adhesion between the catalyst layer and the polymer electrolyte membrane and for transferring hydrogen ions. The binder resin may be the same as the ionic conductor used in the production of the reinforced composite membrane.

A porous conductive base material may be used as the electrode base material 40 or 40 'so that hydrogen or oxygen can be supplied smoothly. As a typical example thereof, a metal film is formed on the surface of a cloth formed of a porous film or polymer fiber composed of carbon paper, carbon cloth, carbon felt or metal cloth ) May be used, but the present invention is not limited thereto. It is preferable that the electrode substrate is subjected to water repellency treatment with a fluorine-based resin because it is possible to prevent the reactant diffusion efficiency from being lowered due to water generated when the fuel cell is driven. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxyvinyl ether, fluorinated ethylene propylene ( Fluorinated ethylene propylene), polychlorotrifluoroethylene, or copolymers thereof.

The membrane-electrode assembly may be manufactured according to a conventional method for manufacturing a membrane-electrode assembly for a fuel cell, except that the reinforced composite membrane is used as the polymer electrolyte membrane.

A fuel cell according to another embodiment of the present invention provides a fuel cell including a membrane-electrode assembly including the reinforced composite membrane as a polymer electrolyte membrane.

Specifically, the fuel cell includes at least one electricity generating unit for generating electricity through an oxidation reaction of the fuel and a reduction reaction of the oxidant; A fuel supply unit for supplying fuel to the electricity generation unit; And an oxidizing agent supply unit for supplying an oxidizing agent such as oxygen or air to the electricity generating unit, wherein the electricity generating unit includes a separator for supplying fuel and an oxidant to both the membrane electrode assembly and the membrane electrode assembly. In the present invention, hydrogen or hydrocarbon fuel in a gaseous or liquid state can be used as the fuel. Representative examples of the hydrocarbon fuel include methanol, ethanol, propanol, butanol or natural gas.

Since the separator, the fuel supply unit and the oxidant supply unit constituting the electricity generating unit in the fuel cell are used in a conventional fuel cell, except that the membrane-electrode assembly according to an embodiment of the present invention is used, Detailed description thereof will be omitted.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example  One

Polyamic acid was dissolved in a dimethylformamide solution to prepare 5 liters of spinning solution of 480 poise at 13 wt%. The prepared spinning solution was transferred to a solution tank, which was supplied through a metering gear pump to a spinning chamber having 20 nozzles and a high voltage of 46 kV to spin the nanofibers precursor. At this time, the supply amount of the solution was 1.5 ml / min.

Next, the nanofiber precursor was transferred to a continuous curing furnace maintained at a temperature of 420 DEG C by a curing apparatus as shown in Fig. 1 for 6 minutes alternately in a zigzag manner on a plurality of rollers, A porous support composed of nanofibers was prepared. At this time, the winding tension was 10N.

The prepared porous support was immersed in ion-conductive solution dissolved in 5% by weight of sulfonated polyarylethersulfone (S-PAES) twice for 30 minutes, then left under reduced pressure for 1 hour, And dried at 80 DEG C for 10 hours to prepare a reinforced composite membrane. At this time, the weight per unit area of the polyimide nanofiber was 6.8 gsm, and the weight of the sulfonated polyaryl ether sulfone was 65 mg / cm ² .

An electrode layer was formed on the prepared composite membrane using the decal method to prepare a membrane-electrode assembly. At this time, the catalyst layer of the electrode is formed by applying a composition for forming a catalyst layer containing Pt / carbon catalyst to a release film and then drying the catalyst layer to form a catalyst layer. The catalyst layer and the reinforced composite membrane face each other on both surfaces of the release film coated with the catalyst layer And hot pressing was performed at a pressure of 5 kg / cm < ² > and a temperature of 100 DEG C to transfer the catalyst layer to both sides of the reinforced composite membrane. Next, a gas diffusion layer (GDL) was bonded to both sides of the reinforced composite membrane to which the catalyst layer was bonded to prepare a membrane - electrode assembly. At this time, the loading amount of the catalyst was 0.5 mg / cm ² .

Example  2

A membrane-electrode assembly was prepared in the same manner as in Example 1, except that the coiling tension for the nanofiber precursor was 1N.

Example  3

A membrane-electrode assembly was prepared in the same manner as in Example 1, except that the coiling tension for the nanofiber precursor was 15 N.

Comparative Example  One

A polyimide porous support was prepared in the same manner as in Example 1 except that the nanofibers were transferred only onto a plurality of rollers during curing of the nanofiber precursor.

Comparative Example  2

A membrane-electrode assembly was prepared in the same manner as in Example 1, except that a single membrane was prepared from an ion conductor without using a porous support. The thickness of the prepared single film was 30 탆.

Test Example  1: Evaluation of porous support

The surface of the porous support prepared in Example 1 was observed with a scanning electron microscope (SEM). The results are shown in Fig.

As shown in FIG. 3, it can be confirmed that the nanofibers having a nano-level diameter are randomly arranged in the porous support.

The average thickness, thickness variation and porosity of the porous support prepared in Examples 1 to 3 and Comparative Example 1 were measured, and the results are shown in Table 1 below.

The average thickness of the porous support was measured at intervals of 1 cm using a thickness measuring device (Digimatic Indicator 547-401, MITUTOYO Co.) at a sample of 30 × 50 cm ² , and the average value thereof was calculated.

Average thickness
(탆) Thickness deviation
(탆) Porosity
(%) Example 1 22 ± 1 78 Example 2 23 ± 1 80 Example 3 22 ± 1 75 Comparative Example 1 30 ± 7 ND

In Table 1, "ND" means that porosity is not measured because porosity reliability is lowered due to a large volume change of the support itself.

As shown in Table 1, the porous supports of Examples 1 to 3 produced by alternately feeding the nanofiber precursors on and under a plurality of rollers in a zigzag manner exhibited almost uniform thickness with a thickness deviation of +/- 1, while the nanofiber precursor In the case of the porous support of Comparative Example 1 manufactured by transferring only a plurality of rollers over a plurality of rollers, the thickness variation was large due to the wrinkles caused by the shrinkage of the nanofibers in the curing process and the apparent average thickness was increased, It was difficult to manufacture the electrode assembly.

(X direction / Y direction) and elongation (X direction / Y direction) of the porous support prepared in Examples 1 to 3 according to ASTM 638 using a Universal Test Machine (Instron 4303, Instron) The conditions for measurement were as follows.

Measurement speed: 25 cm / min

Grip interval: 6.35 cm

Temperature and humidity: 25 ° C × 50%

The measurement results are shown in Table 2 below, and Figs. 4 and 5.

FIG. 4 is a graph showing the results of observing the tensile strength and the tensile strength ratio of the porous support prepared in Examples 1 to 3, and FIG. 5 is a graph showing the results of observation of elongation and reinforcement ratio.

Seal
Intensity ratio The tensile strength
(MPa) Shinobi Shinto (%) X Y X Y Example 1 2.3 37 16 0.4 4.4 11.0 Example 2 1.6 23 14 0.4 6.1 13.9 Example 3 4.0 40 10 0.2 3.2 15.0

As shown in Table 2 and FIGS. 4 and 5, the porous supports of Examples 1 to 3 according to the present invention had a tensile strength ratio of 5 or less and a new aspect ratio of 0.2 or more.

Test Example  2: Reinforced composite membrane  evaluation

The sections of the reinforced composite membrane prepared in Example 1 were observed with a scanning electron microscope (SEM). The results are shown in Fig.

As shown in FIG. 6, it can be seen that the ion conductor is densely packed in the pores of the porous support.

In order to evaluate the dimensional stability improvement effect of the reinforced composite membrane according to the present invention, the reinforced composite membrane prepared in Examples 1 to 3 was evaluated for dimensional stability by the following method. The results are shown in Table 3.

Specifically, a reinforced composite membrane cut into 30 cm × 50 cm was placed in a thermo-hygrostat maintained at a temperature of 80 ° C. and a relative humidity of 90%, which is a general operating environment of the fuel cell, and left for 4 hours. And the value measured before the humidification treatment were applied to the following expression (6).

In Equation (6), La is the length of the reinforced composite membrane after the humidifying treatment, and Lb is the length of the reinforced composite membrane before the humidifying treatment.

Dimensional stability
(%) Swelling dimension
(cm) X Y X Y Example 1 0.2 4.5 50.12 31.35 Example 2 0.3 5.2 50.15 31.57 Example 3 0.2 6.9 50.11 32.07

As shown in Table 3, the reinforced composite membranes prepared using the porous supports of Examples 1 to 3 exhibited excellent dimensional stability due to small dimensional change with respect to one direction.

Test Example  3: Just- Electrode assembly  evaluation

In order to evaluate the durability of the membrane-electrode assembly according to the present invention, the following experiments were conducted to observe whether the interface between the reinforced composite membrane and the electrode in the membrane-electrode assembly was separated. The results are shown in Table 4.

After the cells were dried in a vacuum oven at 50 캜 for 2 hours and immersed in ultra-pure water at room temperature for 2 hours, one cycle was performed. After 3, 5, 10 and 15 cycles, the interface separation between the reinforced composite membrane and the electrodes was visually confirmed.

durability 3 cycles 5 cycles 10 cycles 15 cycles Example 1 O O O O Example 2 O O O X Example 3 O O O O Comparative Example 2 X - - -

As shown in Table 4, in the membrane-electrode assemblies of Examples 1 to 3, separation did not occur at the interface between the reinforced composite membrane and the electrode even for 10 cycles or more. However, in Comparative Example 2 containing the polymer electrolyte membrane composed of the ion conductor single membrane Interfacial separation occurred in the third cycle of the membrane electrode assembly.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

10 Curing device
11 Roll
12 Nanofibers of polymer precursors
100 membrane-electrode assembly
20, 20 'electrode
30, 30 '
40, 40 'electrode substrate
50 Polymer electrolyte membrane

Claims (19)

A porous support comprising randomly arranged polymeric nanofibers and having directional mechanical properties; And
And an ion conductor filled in the pores of the porous support,
The porous support is prepared by electrospinning a precursor solution containing a precursor of a polymer for forming a porous support, and transferring nanofibers of the polymer precursor in a zigzag manner alternately on and under a plurality of rollers under the application of a winding tension of 1 to 15 N, A reinforced composite membrane produced by the above method,
Wherein the reinforced composite membrane has a one-dimensional dimensional stability of 0 to 8% when swollen in water. The method according to claim 1,
Wherein the mechanical properties are tensile strength, elongation, or both. The method according to claim 1,
Wherein the porous support has a tensile strength ratio of 1.6 to 5 in one direction and a direction perpendicular to the one direction. The method according to claim 1,
Wherein the porous support has a one-way orientation and a new orientation ratio of 0.2 to 0.4 in a direction perpendicular to the one direction. The method according to claim 1,
Wherein the porous support comprises a hydrocarbon-based polymer insoluble in an organic solvent. The method according to claim 1,
Wherein the porous support comprises polyimide. The method according to claim 1,
Wherein the porous support has a porosity of 50 to 90%. The method according to claim 1,
Wherein the porous support has an average thickness of 5 to 50 占 퐉. The method according to claim 1,
Wherein the ionic conductor is a hydrocarbon-based polymer that is soluble in an organic solvent. The method according to claim 1,
The ionic conductor may be selected from the group consisting of sulfonated polyimide, sulfonated polyaryl ether sulfone, sulfonated polyether ether ketone, sulfonated polybenzimidazole, sulfonated polysulfone, sulfonated polystyrene, sulfonated polyphosphate Zirconium oxide, zirconium oxide, zirconium oxide, zirconium oxide, zirconium oxide, zirconium oxide, zirconium oxide, zirconium oxide, zirconium oxide, zirconia, The method according to claim 1,
Wherein the ionic conductor is contained in an amount of 50 to 99 wt% based on the total weight of the reinforced composite membrane. delete Preparing a polymer precursor nanofiber by electrospinning a precursor solution containing a precursor of a polymer for forming a porous support,
Continuously curing the prepared nanofibers of the polymer precursor while alternately zigzag and transferring on and under a plurality of rollers under the application of a winding tension of 1 to 15 N to prepare a porous support; and
Filling the pores of the porous support with an ion conductor
≪ RTI ID = 0.0 > 1, < / RTI &
The reinforced composite membrane has a dimensional stability of 0 to 8% in one direction when swollen in water Method for manufacturing reinforced composite membrane for fuel cells 14. The method of claim 13,
Wherein the polymer for forming a porous support is a hydrocarbon-based polymer insoluble in an organic solvent. 14. The method of claim 13,
Wherein the precursor solution comprises a precursor of a polymer for forming a porous support in an amount of 5 to 20% by weight based on the total weight of the precursor solution. 14. The method of claim 13,
Wherein the electrospinning process is performed by applying an electric field of 850 to 3,500 V / cm. 14. The method of claim 13,
Wherein the curing step is carried out at 80 to < RTI ID = 0.0 > 650 C. < / RTI > An anode electrode and a cathode electrode positioned opposite to each other; And
And a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode,
The membrane-electrode assembly for a fuel cell according to claim 1, wherein the polymer electrolyte membrane is the reinforced composite membrane according to claim 1. A fuel cell comprising the membrane-electrode assembly according to claim 18.

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