KR20130106073A - Porous support and method for manufacturing same - Google Patents

Abstract

PURPOSE: A porous support is provided to improve adhesion with an ion conductor while improving hydrogen ion conductivity when applied to a reinforced composite film for a fuel cell. CONSTITUTION: A porous support (1) comprises nanofiber (2) on which a minute uneven part (3) is formed on the surface thereof. The nanofiber has the surface roughness of 5 micron or less. The porous support has a porosity of 50-90 %. A manufacturing method of the porous support comprises a step of manufacturing the nanofiber of a polymer precursor by electrospinning a composition for forming nanofiber, including a polymer precursor and a material for forming a minute uneven part; and a step of heat-treating the nanofiber of the manufactured polymer precursor at 350-500 °C.

Description

Porous support and its manufacturing method {POROUS SUPPORT AND METHOD FOR MANUFACTURING SAME}

The present invention relates to a porous support and a method for manufacturing the same, which have a maximized surface area and can improve hydrogen ion conductivity when applied to a reinforced composite membrane for fuel cells, and at the same time, increase binding force with an ion conductor.

Nanofiber has a wide surface area and excellent porosity, and is used for various purposes such as water purification filters, air purification filters, composite materials, battery separators, and the like, and may be particularly useful for reinforcement composite membranes used in fuel cells for automobiles.

Fuel cells are electrochemical devices that operate on hydrogen and oxygen as fuels, and are now becoming environmentally friendly because their products are pure water and reusable heat. In addition, due to its simple operation, high power density and noise, it is widely used as a power source for home, automobile, and power generation.

Fuel cells may be classified into alkali electrolyte fuel cells, direct oxidation fuel cells, and polymer electrolyte membrane fuel cells (PEMFC), depending on the type of electrolyte membrane. Among them, the polymer electrolyte membrane fuel cell is a hydrogen ion ( H ⁺ ) can be operated at room temperature with the principle of generating electricity from the anode (anode) to the cathode (cathode), and has the advantage that the activation time is very short compared to other fuel cells.

The polymer electrolyte membrane fuel cell includes an electricity generating unit including a membrane electrode assembly (MEA) and a separator (also called a bipolar plate) having an anode and a cathode formed therebetween with a polymer electrolyte membrane therebetween; And a fuel supply unit supplying fuel to the electricity generation unit, and an oxidant supply unit supplying an oxidant such as oxygen or air to the electricity generation unit.

The polymer electrolyte membrane may be divided into a single membrane made of a polymer such as fluorine-based or hydrocarbon-based as a conductor of hydrogen ions, and a composite membrane used by combining an organic / inorganic substance or a porous support with the polymer. In the case of a single membrane, DuPont's Nafion ™, which is a perfluorinated polymer, is most used, but has a disadvantage in that the membrane resistance is high due to its high price, low mechanical shape stability, and thick thickness.

To overcome these shortcomings, studies on composite membranes with enhanced mechanical and morphological stability have been actively conducted. Among them, the pore-filled membranes in which the porous support is impregnated with ionic conductors are not only inexpensive but also have performance mechanical and morphological stability. There is much research being done.

Polytetrafluoroethylene (PTFE) is used as a general support for pore filling membranes. However, in the case of PTFE support, there is a problem that the chemical resistance is excellent but the porosity is low as 40 to 60%.

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

SUMMARY OF THE INVENTION An object of the present invention is to provide a porous support and a method for manufacturing the same, which have a maximized surface area and can improve hydrogen ion conductivity when applied to a reinforced composite membrane for fuel cells and at the same time increase binding capacity with an ion conductor.

According to one embodiment of the present invention, the surface includes nanofibers having fine irregularities formed on the surface, and the nanofibers provide a porous support having a surface roughness (Ra) of 5 μm or less.

Preferably, the nanofibers may have a surface roughness (Ra) of 0.001 to 0.5㎛.

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

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

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

The porous support may include a fine iron forming material in the nanofibers.

According to another embodiment of the invention, the step of preparing a nanofiber of the polymer precursor by electrospinning the composition for forming a nanofiber comprising a polymer precursor and a fine iron forming material, and the nanofiber of the prepared polymer precursor 350 To provide a method for producing a polymer electrolyte membrane for a fuel cell comprising the step of heat treatment at 500 ℃.

The polymer precursor may be selected from the group consisting of polyamic acid, polyarylethersulfone, polyetheretherketone, polybenzimidazole, polysulfone, polystyrene, polyphosphazene and mixtures thereof.

The polymer precursor may be included in an amount of 5 to 20% by weight based on the total weight of the composition for forming nanofibers.

The fine iron forming material may be a material decomposed in the heat treatment temperature range of 350 to 500 ℃, preferably polyvinylacetate, polyvinylchloride, triazine trichloride, ammonium carbonate, ammonium bicarbonate, ammonium oxalate and mixtures thereof It may be selected from the group consisting of.

The fine iron forming material may be included in an amount of 0.01 to 3% by weight based on the total weight of the composition for forming nanofibers.

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

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

The porous support may have a maximized surface area to improve hydrogen ion conductivity and increase binding force with an ion conductor when applied to a reinforced composite membrane for a fuel cell.

1 is a schematic diagram showing a porous support according to an embodiment of the present invention.
FIG. 2 is a photograph of the surface of the porous support prepared in Example 1 under a scanning electron microscope (SEM). FIG.
Figure 3a is a SEM observation of the cross-section of the reinforced composite membrane before the durability evaluation test for the reinforced composite film comprising a porous support prepared in Example 1, Figure 3b is after the durability evaluation test (after 5 cycles) of the reinforced composite membrane SEM photograph of the cross section.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

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

As used herein, the term "diameter" refers to the length of the short axis passing through the center of the fiber, and the "length" means the length of the long axis passing through the center of the fiber.

The term " surface roughness " as used herein refers to the degree of fine roughness on the surface of a fiber, and is expressed as an arithmetic mean roughness (Ra) value of measured values randomly extracted from fine roughness formed on the fiber surface.

The present invention is characterized by providing a porous support that minimizes the detachment by increasing the binding force between the nanofiber and the ion conductor at the same time to maximize the surface area by forming fine irregularities on the surface of the nanofiber when manufacturing the porous support made of nanofibers. .

1 is a schematic diagram showing a porous support according to an embodiment of the present invention. 1 is only an example for describing the present invention and the present invention is not limited thereto.

Hereinafter, referring to FIG. 1, the porous support 1 according to the exemplary embodiment of the present invention includes a nanofiber 2 in which fine irregularities 3 are formed on a surface thereof.

The porous support 1 serves to enhance dimensional stability by improving mechanical strength of the polymer electrolyte membrane and suppressing volume expansion by moisture, and the porous support 1 is nanofibers 2 produced by electrospinning. Are randomly arranged to form an aggregate of nanofibers, that is, a web of nanofibers, which form a three-dimensional connection structure, wherein the nanofibers 2 have fine grains 3 formed on their surfaces.

The fine iron (3) formed on the surface of the nanofibers, the pyrolysis of the fine iron forming material present on the surface of the nanofibers of the polymer precursor in the subsequent heat treatment process for the nanofibers of the polymer precursor prepared after the electrospinning process of the polymer precursor It is formed. As such, the nanofibers include fine roughness on the surface, thereby increasing the roughness of the surface of the nanofibers and maximizing the surface area. As a result, the loading amount of the ion conductor is increased, thereby increasing the ion conductivity and increasing the binding force between the nanofiber and the ion conductor.

The size and shape of the fine irregularities (3) formed on the surface of the nanofibers (2) is not particularly limited, but the nanofibers (2) including the fine irregularities in consideration of the mechanical strength and surface area of the nanofibers, etc. It is preferable to have surface roughness Ra of 5 micrometers or less. If the surface roughness of the nanofibers exceeds 0.5 μm, the mechanical strength of the porous support may be lowered, and it is not preferable because of difficulty in the electrospinning process and reduction of the binding force between the ion conductor and the nanofibers. More preferably the nanofibers have a surface roughness of 0.001 to 0.5㎛.

Since the nanofibers 2 are used in the manufacture of a fine uneven iron forming material and a polymer precursor, the nanofibers 2 may include a fine uneven iron forming material present in the nanofibers and not pyrolyzed in a subsequent heat treatment process. In this way, even though the fine iron-forming material remains in the nanofibers, due to the excellent chemical and heat resistance properties of the nanofiber forming polymer, the micro-irons are not affected by the fine iron-forming material present in the fiber, and the pores are formed in the fiber. Compared with the formed porous nanofibers can exhibit better mechanical strength.

In addition, in consideration of the porosity and thickness of the porous support 1, the nanofibers 2 including fine iron on the surface were measured for 50 fiber diameters by using an scanning electron microscope (Scanning Electron Microscope, JSM6700F, JEOL). When it calculates from the average, it is preferable to have an average diameter of 40-1,000 nm. If the average diameter of the nanofibers is less than 40nm, the mechanical strength of the polymer electrolyte membrane may be lowered. If the average diameter of the nanofibers exceeds 1,000nm, the porosity of the support may be significantly reduced and the thickness may be thickened.

The nanofibers 2 are randomly arranged during electrospinning to form a web having a three-dimensional connection structure, wherein the web includes pores 4 formed by crossing between the nanofibers.

The pores 4 may exist as independent pores in the web of nanofibers, may form pores together with uneven portions formed on the surface of the nanofibers, and may also be three-dimensionally connected between the pores. The pores 4 are formed to have a uniform density in the porous support 1, the ion conductors filled in the pores during the filling of the ion conductor can be uniformly distributed, as a result of the overall hydrogen ion conductivity of the polymer electrolyte membrane It is preferable because it can be made uniform.

The size of the pores 4 formed in the porous support 1 is not particularly limited, but is formed in the diameter range of 0.05 to 10 ㎛ considering the mechanical strength of the porous support and the hydrogen ion conductivity when applied to the polymer electrolyte membrane. It is preferable to be. When the pore diameter is less than 0.05 μm, the hydrogen ion conductivity of the polymer electrolyte membrane may be lowered. When the pore diameter exceeds 10 μm, the mechanical strength characteristics of the polymer electrolyte membrane may be lowered and the volume change rate may be increased.

The porous support 1 may have a porosity of 50% or more by including the nanofibers 2 and the pores 4 as described above. As described above, as the porous support has a porosity of 50% or more, the porous support has a large specific surface area, so that the ion conductor can be easily impregnated, and as a result, it can exhibit excellent hydrogen ion conductivity. On the other hand, the porous support 1 preferably has a porosity of 90% or less. If the porosity of the porous support 1 exceeds 90%, the morphological stability may be lowered, and thus the subsequent process may not proceed smoothly. The porosity is calculated by the ratio of the air volume to the total volume according to the following equation (1). In this case, the total volume was calculated by measuring the width, length, and thickness of the sample in the form of a rectangular shape, the air volume can be obtained by subtracting the volume of the polymer inverted 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㎛. When the thickness of the porous support is less than 5 μm, the mechanical strength and dimensional stability may be significantly decreased. On the other hand, when the thickness is more than 50 μm, the resistance loss may increase when applied to the polymer electrolyte membrane, and the weight and integration may be reduced. . More preferred thickness of the porous support is in the range of 10 to 50 mu m.

The porous support 1 is insoluble in a conventional organic solvent and thus exhibits excellent chemical resistance, and facilitates the ion conductor filling process in the pores of the porous support 1, and has a hydrophobic property to moisture in a high humidity environment. It is preferable to include the hydrocarbon type polymer which does not have a possibility of morphological modification by. The hydrocarbon-based polymer may be nylon, polyimide (PI), polybenzoxazole (polybenzoxazole, PBO), polybenzimidazole (polybenzimidazole, PBI), polyamideimide (PAI), polyethylene terephthalate (polyethyleneterephtalate). ), Polyethylene (PE), polypropylene (PP), copolymers thereof, or a mixture thereof may be used. Among these, polyimide polymers having better heat resistance, chemical resistance, and morphological stability are preferable. .

When the porous support 1 includes polyimide, the porous support preferably has an imidation ratio of 90% or more. The imidation ratio is a precursor of the polyimide is converted into an imide group by a cyclization reaction occurs through an imidization process such as heat treatment, it can be calculated according to the following equation (2).

However, the weight of the nanofibers before the heat treatment is measured by using the nanofibers left at least 24 hours in a vacuum oven set at a temperature of 30 ℃, the weight of the nanofibers after the heat treatment is a dimethylformamide organic After immersion in a solvent for 24 hours at room temperature and stirred for 5 or more times in distilled water and then left for 24 hours in a vacuum oven set to a temperature of 30 ℃ measured by using a nanofiber web obtained after the solvent treatment.

If the imidation ratio is less than 90%, it is difficult to maintain the required physical properties for a long time because the nanofibers may be damaged by the organic solvent. Therefore, the polyimide porous support having an imidation ratio after 90% or more solvent treatment as described above can maintain excellent tensile strength even in a strongly acidic state, which is a driving environment of a fuel cell, and has excellent dissolution resistance to an electrolyte. Since the interface between the electrode and the electrode is not separated, excellent ionic conductivity can be maintained for a long time. In addition, the polyimide porous support having such excellent acid resistance can improve reliability because it can express excellent performance for a long time when used in the electrolyte membrane of a fuel cell driven in a strong acid environment.

The porous support 1 has nanoporous thickness and thickness with excellent porosity and optimized diameter, is easy to manufacture, and in order to exhibit excellent mechanical strength after wet treatment, the polymer constituting the porous support 1 is 30,000 to 30,000. It is preferred to have a weight average molecular weight of 500,000 g / mol. If the weight average molecular weight of the polymer constituting the porous support is less than 30,000 g / mol, the porosity and thickness of the porous support can be easily controlled, but the mechanical strength may be reduced after the porosity and the wet treatment. On the other hand, if the weight average molecular weight of the polymer constituting the porous support exceeds 500,000g / mol, heat resistance may be somewhat improved, but the tensile strength may be lowered after the porosity and wet treatment without a smooth manufacturing process. .

In addition, the porous support 1 has a weight average molecular weight in the range as described above and as the polymer precursor is converted into a polymer under the optimal curing conditions, it may have a melting point of 400 ℃ or more, preferably 400 to 800 ℃ have. If the melting point of the porous support is less than 400 ° C., the heat resistance may be easily deformed at high temperatures as the heat resistance thereof is lowered. Accordingly, the fuel cell manufactured using the porous support may degrade performance. In addition, when the heat resistance of the porous support is deteriorated, the shape is deformed by abnormal heat generation, thereby degrading the performance, and in severe cases, may burst and explode.

In general, the adhesion between the ion conductor and the porous support may decrease when operating conditions such as temperature or humidity are changed during operation of the fuel cell. In the present invention, fine iron is formed on the surface of the nanofibers constituting the porous support. As a result, the binding force between the two can be increased.

The porous support according to the present invention as described above exhibits excellent mechanical strength of 40MPa or more. As the mechanical strength is improved, the thickness of the entire polymer electrolyte membrane can be reduced to 80 μm or less when applied to the polymer electrolyte membrane. As a result, the hydrogen ion conduction rate is increased and the resistance loss is reduced while saving the material cost.

In addition, the porous support has excellent durability, and when applied to the polymer electrolyte membrane, can inhibit the three-dimensional expansion of the polymer electrolyte membrane due to moisture, so that the length and thickness expansion ratio are relatively low. Specifically, the porous support shows excellent dimensional stability of 5% or less when swollen in water after filling the ion conductor. The dimensional stability is a physical property evaluated according to Equation 3 below from the change in length before and after swelling when the porous support is swelled in water after the ion conductor is filled.

According to another embodiment of the present invention, the step of preparing a nanofiber of the polymer precursor by electrospinning the composition for forming a nanofiber including the polymer precursor and the fine iron forming material (step 1) and the nanoparticles of the prepared polymer precursor Heat treating the fibers at 350 to 500 ° C.

Looking at each step below, step 1 is a step of producing a nanofiber of the polymer precursor by electrospinning the composition for forming the nanofiber comprising the polymer precursor and fine iron forming material.

Since the porous support according to the present invention includes a hydrocarbon-based polymer that is insoluble in an organic solvent, it is prepared without dissolving in an organic solvent or after forming nanofibers of a polymer precursor using a polymer precursor that is well soluble in an organic solvent. It can be prepared through the subsequent reaction of. The polymer precursor may be appropriately selected and used according to the type of the polymer for forming the porous support, and the specific kind of the polymer for forming the porous support is as described above.

For example, the porous support made of PI (Polyimide) is electrospinning polyamic acid (PAA) to form a PAA nanofiber precursor, followed by imidization reaction in a subsequent heat treatment process. Can be prepared.

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

Examples of the dianhydride include pyromellyrtic 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 anhydride (3,4,3', 4 ') Compounds selected from the group consisting of -biphenyltetracarboxylic dianhydride (BPDA), and bis (3,4-dicarboxyphenyl) dimethylsilane dianhydride (SiDA) and mixtures thereof can be used. In addition, the diamine is 4,4'-oxydianiline (4,4'-oxydianiline, ODA), p-phenylene diamine (p-phenylene diamine, p-PDA), o-phenylene diamine (o-phenylene diamine, o-PDA) and mixtures thereof may be used, and the solvent for dissolving the polyamic acid may be m-cresol, N-methyl-2-pyrrolidone (NMP) or dimethyl. Dimethylamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, diethyl acetate, tetrahydrofuran (THF), chloroform, γ-butyrolactone and mixtures thereof Solvents may be used.

In addition to the polyamic acid, polyaryl ether sulfone, polyether ether ketone, polybenzimidazole, polysulfone, polystyrene, polyphosphazene or a mixture thereof may be used as a polymer precursor for forming nanofibers.

The composition for forming nanofibers may be prepared by dissolving the polymer precursor and the fine iron forming material in a conventional organic solvent such as NMP, DMF, DMAc, DMSO, and THF.

At this time, the polymer precursor is preferably included in an amount of 5 to 20% by weight based on the total weight of the composition for forming nanofibers. If the content of the polymer precursor is less than 5% by weight, since spinning does not proceed smoothly, there is a fear that a fiber is not formed or a nanofiber having a non-uniform fiber diameter may be manufactured, whereas the content of the polymer precursor is 20 When the weight percentage is exceeded, as the discharge pressure increases rapidly, spinning may not be performed or processability may be reduced.

The fine irregularity forming material is decomposed by a subsequent heat treatment process to form pores on the surface of the nanofibers, and may be used without particular limitation as long as it is degradable in a heat treatment temperature range of 350 to 500 ° C. Specifically, those selected from the group consisting of polyvinyl acetate, polyvinyl chloride, triazine trichloride, ammonium carbonate, ammonium bicarbonate, ammonium oxalate and mixtures thereof can be used.

In addition, since fine fine iron is formed on the surface of the nanofibers by thermal decomposition of the fine fine iron forming material, it is preferable to appropriately adjust the content of fine fine iron forming material. Specifically, the fine iron forming material is preferably included in an amount of 0.01 to 3% by weight based on the total weight of the nanofiber forming composition. If the content of the micro-concave forming material is less than 0.01%, the effect of increasing the surface area is insignificant due to the low rate of formation of the micro-convex portion formed on the surface of the nanofibers, while the discharge pressure when the content of the micro-convex forming material exceeds 3%. As the rapid increase, the spinning may not be performed or the processability may be lowered, and the formation rate of the fine concavo-convex portion formed on the nanofibers may be excessively high, thereby lowering the mechanical strength of the porous support.

Subsequently, the prepared nanofiber forming composition is spun using a conventional electrospinning apparatus to prepare nanofibers of a polymer precursor.

Specifically, in the solution tank in which the composition for storing the nanofibers is formed, the nanofiber forming composition is supplied to the spinning unit using a metering pump in a predetermined amount, and the nanofiber forming composition is discharged through the nozzle of the spinning unit. The nanofibers of the solidified polymer precursor are simultaneously formed with scattering, and additionally, the nanofibers of the solidified polymer precursor can be focused in a collector having a releasing film to prepare a fiber aggregate.

At this time, the intensity of the electric field between the radiator and the collector applied by the high voltage generator is preferably 850 to 3,500V / cm. If the strength of the electric field is less than 850 V / cm, it is difficult to manufacture nanofibers having a uniform thickness because the composition for forming nanofibers is not continuously discharged, and the nanofibers formed after spinning are smoothly focused on the collector. It can be difficult to manufacture a fiber aggregate because it cannot. On the other hand, when the strength of the electric field exceeds 3,500 V / cm, the fiber aggregate having a normal shape cannot be obtained because the nanofibers are not accurately seated in the collector.

Through the spinning process, a nanofiber of a polymer precursor having a uniform fiber diameter, preferably an average diameter of 0.01 to 5 μm is prepared, and the nanofibers are randomly arranged to form a fiber aggregate, that is, a web.

In step 2, a porous support is prepared by performing heat treatment on the nanofibers of the polymer precursor.

In the manufacturing method of the present invention, since the polymer precursor is used to form the porous support through electrospinning, a heat treatment process is performed as an additional process for the nanofibers of the polymer precursor to convert the polymer precursor into the polymer for forming the porous support. Conduct. For example, when the nanofibers or fiber aggregates produced by electrospinning are made of polyimide precursors, they are converted into polyimides through imidization during the curing process. In addition, during the heat treatment process, the microfiber forming material located on the surface of the nanofiber precursor is decomposed along with the conversion of the polymer precursor.

Accordingly, the temperature during the heat treatment process is preferably adjusted in consideration of the conversion rate of the polymer precursor into the polymer and the decomposition of the fine concavo-convex forming material. Specifically, it is preferable to perform a heat treatment process at 350 to 500 ° C. If the temperature is less than 350 ℃ during the heat treatment, the polymer conversion rate is low, and as a result, the heat resistance and chemical resistance of the porous support may be lowered, and the decomposition rate of the fine iron forming material is lowered, and thus the fine iron formation rate on the surface of the nanofiber is increased. Can be degraded. In addition, when the temperature exceeds 500 ° C. during heat treatment, there is a concern that the support may be destroyed due to the decrease in the molecular weight of the polymer due to thermal decomposition.

The porous support prepared by the manufacturing method as described above includes nanofibers formed with fine irregularities on its surface and exhibits a maximum specific surface area. As a result, the hydrogen support can be improved when applied to a polymer electrolyte membrane. In addition, there is no fear of desorption due to increased binding strength between the nanofiber and the ion conductor. As a result, the performance and durability of the fuel cell can be improved.

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

In a solution prepared by dissolving polyamic acid in dimethylformamide at 13% by weight, polyvinylacetate (polyvinyl acetate) was added at 1% by weight to prepare a spinning solution of 45,000 cps. After transporting the prepared spinning solution to the solution tank, it was supplied to the spinning chamber consisting of 20 nozzles and applied a high voltage of 1kV through a quantitative gear pump to produce a nanofiber precursor web. At this time, the supply amount of the spinning solution was 1.5 ml / min. The prepared nanofiber precursor web was heated at 420 ° C. to decompose the vinyl acetate resin on the surface of the nanofibers, thereby preparing a web of nanofibers having fine roughness as a porous support. The porosity of the prepared porous support was 85%, and the average thickness was 25 μm. In addition, the average diameter of the nanofibers constituting the porous support was 800 ± 50 nm.

Example  2

A porous support was prepared in the same manner as in Example 1, except that a spinning solution prepared by dissolving polyvinyl acetate in 0.5% by weight was used.

The porosity of the prepared porous support was 83%, the average thickness was 25㎛. In addition, the diameter of the nanofibers constituting the porous support was 800 ± 50 nm.

Comparative Example  One

A porous support was prepared in the same manner as in Example 1, except that a spinning solution prepared by dissolving polyamic acid in dimethylformamide without using polyvinyl acetate was used.

Test Example  One

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. 2, it was confirmed that fine roughness was formed on the surface of the nanofibers constituting the porous support.

In addition, fine irregularities formed on the surface of the nanofibers constituting the porous supports of Examples 1 and 2 were measured by a contact method using an atomic force microscope (AFM) (AutoProbe M5, manufactured by PSIA). .

As a result, the surface roughness Ra of the nanofibers constituting the porous support of Example 1 was 0.1 μm, and the surface roughness Ra of the nanofibers constituting the porous support of Example 2 was 0.06 μm. In addition, it was confirmed that fine irregularities formed on the surface of the nanofibers constituting the porous supports of Examples 1 and 2 are uniformly distributed throughout the nanofibers.

Test Example  2

Hydrogen ion conductivity was evaluated in the preparation of the reinforced composite membrane using the porous support according to the present invention.

In detail, the porous supports prepared in Examples 1, 2 and Comparative Example 1 are placed in a Petri dish, respectively, and 5 wt% of Nafion solution can be impregnated with 0.06 g of Nafion per unit area (cm ² ) of the web. It was put in, and dried in at least 60 hours at 60 ℃ using an oven to prepare a reinforced composite film. Each of the prepared reinforced composite membranes were immersed in 1 mol of sulfuric acid solution for 3 hours to sufficiently activate hydrophilic groups, and then wiped the surface with ultrapure water to prepare a sample for measuring conductivity. In addition, a polymer electrolyte membrane in which Dupont's Nafion 117 membrane was immersed in ultrapure water for 3 hours or more so that sufficient water was present in the membrane was used as Comparative Example 2.

Ion conductivity was measured at 25 ° C. and 80 ° C. by a 90% humidification and four-electrode method using a resistance measuring device. The results are shown in Table 1 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 25 ℃ (Scm ^-1 ) 0.07 0.07 0.07 0.07 80 ℃ (Scm ^-1 ) 0.097 0.094 0.087 0.1

As shown in Table 1, the reinforced composite membrane comprising the porous supports of Examples 1 and 2 and the reinforced composite membrane comprising the porous support of Comparative Example 1, the fluorine-based system of Comparative Example 2 known to exhibit excellent hydrogen ion conductivity Compared with the polymer electrolyte membrane, the hydrogen ion conductivity was shown to be equivalent at 25 ° C. However, the reinforced composite membrane including the porous supports of Examples 1 and 2 at 80 ° C. high temperature showed the same level of hydrogen ion conductivity as the fluorine-based polymer electrolyte membrane of Comparative Example 2, while the reinforced composite including the porous support of Comparative Example 1 The composite membrane exhibited a significantly lowered ion conductivity compared to the fluorine-based polymer electrolyte membrane of Comparative Example 2 due to the difference in surface roughness of the nanofibers constituting the porous support and the difference in the ion conductor loading.

Test Example  3

Using the porous support according to the present invention was evaluated whether or not the detachment phenomenon occurs when manufacturing the reinforced composite membrane in the following manner.

After drying the reinforced composite membrane prepared in Test Example 2 in a 60 ℃ oven for 6 hours or more and storing it for 2 hours at 80 ℃ hot water once and repeatedly performed 5 times using the UTM-3365 device for the resulting polymer electrolyte membrane. Tensile strength was measured. The results are shown in Table 2 below.

<Taliness phenomenon>

× No tally effect

○ Tally outbreak

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Before evaluation After conducting five times Before evaluation After conducting five times Before evaluation 5 times Before evaluation After conducting five times Tensile Strength (MPa) 47.18 32.12 44.24 29.6 42.02 23.14 36.02 23.04 Tally × × × × × ○ × ×

As shown in Table 2, the reinforced composite membrane including the porous supports of Examples 1 and 2 according to the present invention has improved binding force between the ion conductor and the nanofibers due to fine roughness formed on the surface of the nanofibers, Comparative Example 1 and It showed improved mechanical properties compared to the reinforced composite membrane including the support of 2 and the polymer electrolyte membrane of Comparative Example 2, and even after the durability evaluation, no delamination between the ion conductor and the nanofibers was observed.

In addition, the cross section of the reinforced composite membrane including the porous support of Example 1 before and after the durability test was observed by scanning electron microscopy (SEM). The results are shown in Figures 3a and 3b.

Figure 3a is a SEM observation of the cross-section of the reinforced composite membrane before the durability evaluation test for the reinforced composite film comprising a porous support prepared in Example 1, Figure 3b is after the durability evaluation test (after 5 cycles) of the reinforced composite membrane SEM photograph of the cross section.

3A and 3B, it was confirmed that no desorption phenomenon between the ion conductor and the nanofibers was observed in the reinforced composite membrane including the porous support of Example 1 even after the durability evaluation.

Test Example  4

In order to evaluate the morphological stability of the reinforced composite membrane using the porous support according to the present invention, each of the reinforced composite membrane prepared in Test Example 1 was dried for 6 hours at a temperature of 50 ℃ in a hot air oven and then 24 hours in ultrapure water The dimensional change was measured by dipping. The results are shown in Table 3 below.

After drying (cm) After dipping (cm) Dimensional change ratio (%) X Y X Y X Y Example 1 5 5 5 5.15 0 3 Example 2 5 5 5 5.2 0 4 Comparative Example 1 5 5 5 5.2 0 4 Comparative Example 2 5 5 5.5 5.5 10 10

As shown in Table 3, the reinforced composite membrane including the porous supports of Examples 1 and 2 according to the present invention is significantly improved compared to Comparative Example 2 including the electrolyte membrane of the fluorine-based polymer known to exhibit excellent hydrogen ion conductivity. Morphological stability.

From the above experimental results, the porous support according to the present invention exhibits excellent hydrogen ion conductivity by having a surface area maximized by the fine concavo-convex formed on the surface of the nanofiber forming the porous support when applied to the reinforced composite membrane for fuel cells, In addition, the binding force with the ion conductor is increased, there is no fear of detachment, and it can be seen that it shows excellent shape stability.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of right.

1 porous support
2 nanofibers
3 fine iron
4 pore

Claims (14)

Contains nanofibers with fine grains on the surface,
The nanofiber is a porous support having a surface roughness (Ra) of 5 μm or less. The method of claim 1,
The nanofiber is a porous support having a surface roughness (Ra) of 0.001 to 0.5㎛. The method of claim 1,
The porous support is a porous support comprising a hydrocarbon-based polymer insoluble in an organic solvent. The method of claim 1,
The porous support comprises a polyimide. The method of claim 1,
The porous support is one having a porosity of 50 to 90%. The method of claim 1,
The porous support is one having an average thickness of 5 to 50㎛. The method of claim 1,
The porous support is a porous support that includes a fine iron forming material in the nanofibers. Preparing a nanofiber of a polymer precursor by electrospinning a composition for forming a nanofiber including a polymer precursor and a fine iron forming material, and
Heat-treating the nanofibers of the prepared polymer precursor at 350 to 500 ° C
Method for producing a porous support comprising a. 9. The method of claim 8,
The polymer precursor is selected from the group consisting of polyamic acid, polyaryl ether sulfone, polyether ether ketone, polybenzimidazole, polysulfone, polystyrene, polyphosphazene and mixtures thereof. 9. The method of claim 8,
The polymer precursor is a method for producing a porous support is contained in an amount of 5 to 20% by weight based on the total weight of the composition for forming nanofibers. 9. The method of claim 8,
The fine iron forming material is a method of producing a porous support is a material that is decomposed in the heat treatment temperature range of 350 to 500 ℃. 9. The method of claim 8,
The fine iron forming material is a polyvinylacetate, polyvinyl chloride, triazine trichloride, ammonium carbonate, ammonium bicarbonate, ammonium oxalate, and a mixture thereof. 9. The method of claim 8,
The fine iron forming material is a material is a method for producing a porous support that is included in an amount of 0.01 to 3% by weight based on the total weight of the composition for forming nanofibers. 9. The method of claim 8,
The electrospinning process is a method of producing a porous support that is carried out by applying an electric field of 850 to 3,500V / cm.

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