WO2015099208A1 - Composite membrane prepared by impregnating hydrocarbon-based electrolyte on pan nonwoven fabric supporter and use thereof - Google Patents

Abstract

The present invention relates to a composite electrolyte membrane including a supporter, which is prepared by acidifying a nonwoven fabric formed through electrospinning a polyacrylonitrile (PAN) copolymer solution, and a hydrocarbon-based polymer electrolyte impregnated on the supporter; a novel supporter; a membrane-electrode assembly (MEA) equipped with the composite electrolyte membrane as an electrolyte membrane; and a fuel cell equipped with the MEA, wherein the supporter has improved solvent resistance or strength by forming a hexagonal ring through acidifying the nonwoven fabric formed through electrospinning of the PAN copolymer solution to thereby form a binding between a nitrogen atom of a nitrile group of a side chain and a carbon atom in an adjacent nitrile group. According to the present invention, the composite membrane in which an electrolyte polymer is impregnated on a porous supporter exhibits excellent mechanical properties, dimensional stability, and durability while retaining high porosity.

Description

Composite membrane prepared by impregnating a hydrocarbon-based electrolyte on a PAN nonwoven fabric support and use thereof

The present invention provides a composite electrolyte membrane comprising a support prepared by oxidizing a nonwoven fabric formed by electrospinning a polyacrylonitrile (PAN) copolymer solution and a hydrocarbon-based polymer electrolyte impregnated thereto; Novel fabric formed by electrospinning polyacrylonitrile copolymer solution was oxidized to form hexagonal rings while forming bonds between nitrogen atoms of side chain nitrile groups and carbon atoms of neighboring nitrile groups, thereby improving solvent resistance or strength. Support; A membrane-electrode assembly (MEA) including the composite electrolyte membrane as an electrolyte membrane; And a fuel cell having the membrane-electrode assembly.

Unlike conventional batteries, fuel cells do not require battery replacement or charging, and are devices that convert chemical energy from fuel into electrical energy through chemical reactions with oxygen or other oxidants. The fuel cell is a high efficiency power generation device with energy conversion efficiency of about 60%. It is more efficient than existing internal combustion engines, so it uses less fuel and is a pollution-free energy source that does not generate environmental pollutants such as SO _x , NO _x , and VOC. There is an advantage. In addition, there are additional advantages, such as a variety of raw materials can be used for production, a small area required for production facilities, and a short construction period. Accordingly, fuel cells have a variety of applications ranging from mobile power supplies for portable devices, transport power supplies for automobiles, and the like to distributed generation available for home and power projects. In particular, when the operation of a fuel cell vehicle, a next-generation transportation device, becomes practical, the potential market size is expected to be wide.

The fuel cell comprises a cathode (anode) which produces hydrogen ions and electrons by oxidation of a fuel material, an anode (cathode) and an anode from which the reduction of oxygen or another oxidizing agent occurs by reaction with hydrogen ions and electrons. It includes an electrolyte layer that can efficiently transfer hydrogen ions. In the fuel cell, hydrogen ions and electrons respectively move from the anode to the cathode through an external circuit electrically connected to the electrolyte layer. The fuel cell may use hydrogen, hydrocarbons, alcohols (methanol, ethanol, etc.) as a fuel, and oxygen, air, chlorine, chlorine dioxide, and the like may be used as oxidants.

Fuel cells include Polymer Electrolyte Membrane Fuel Cells (PEMFC), Direct Methanol Fuel Cells (DMFC) and Direct Ethanol Fuel Cells (DEFC), Alkaline Alkaline Fuel Cell (AFC), Phosphoric Acid Fuel Cell (PAFC), Molten Carbonate Fuel Cell (MCFC) and Solid Oxide Fuel Cell (SOFC) Can be. Dual polymer electrolyte fuel cells, direct methanol fuel cells, and direct ethanol fuel cells are capable of operating at relatively lower temperatures than other fuel cells, and are capable of generating power at levels of 1 to 10 kW. In addition, since it can be miniaturized, the output can be improved by stacking and easy to carry, so that it can be usefully used for a notebook or as an auxiliary power supply. Accordingly, in order to reduce the volume of the unit cell, the electrolyte membrane prepared by using the ion conductive polymer between the fuel electrode and the air electrode is placed in the form of a sandwich and pressed to prepare a membrane-electrode assembly in which the fuel electrode-electrolyte membrane-air electrode forms a conjugate. The battery can be constructed. The electrolyte membrane that can be used for the membrane-electrode assembly has a high hydrogen ion transfer capacity while low permeability of the fuel material, as well as high thermal stability, thus stably exhibiting ion conductivity even in a battery driving condition of about 100 ° C. And it is excellent in chemical durability and must be stable without decomposing even under conditions such as prolonged use and acidity.

In particular, proton exchange membrane fuel cells (PEMFCs) are one of the very promising and promising energy technologies because they can directly convert chemical energy into electrical energy for portable electronics, automobiles and large buildings. Among the PEMFC components, a proton exchange membrane (PEM) is a basic element that separates the cathode and the anode, and determines the efficiency and durability of the PEMFC. Nafion, a perfluorosulfonated ionomer, is a membrane material that has been successfully commercialized and used in fuel cells due to its high proton conductivity, low gas permeability, and excellent dimensional stability and cell performance. However, Nafion membranes are expensive and, in addition, their manufacturing process is complex and emits toxic waste. In addition, due to the rapid decrease in hydrogen ion conductivity, softening of the membrane, high methanol permeability, etc., due to the decrease in the moisture content above 100 ℃, there is a big limitation in commercialization of fuel cells.

Thus, sulfonated poly (arylene ether sulfone), a hydrocarbon-based ionomer that has high thermal resistance, good mechanical strength, low hydrogen permeability and can be produced in an inexpensive production process Sulfonated poly (arylene ether sulfone) (SPAES) has been considered as a PEM material to replace Nafion membranes over the last decades. However, the dimensions of SPAES expand under fully hydrated conditions, reducing fuel cell durability. In order to overcome this drawback, many researchers have studied polyimide (PI), poly (paraphenylene terephthalamide) (PPTA), poly (vinyl alcohol); PVA And multi-fibrous manufactured materials such as polyphenylsulfone (PPS). However, when the high porosity shows a problem that the mechanical properties are lowered, there is an urgent need to develop a porous support and an ion conductor having excellent mechanical properties, dimensional stability, and durability while maintaining high porosity.

The present inventors have tried to find a composite electrolyte membrane that exhibits high conductivity of the polymer electrolyte and at the same time improves its strength by using a support. As a result, the PAN and PMMA copolymers are electrospun to form a nonwoven fabric, and then oxidized and crosslinked in a molecule to increase the strength. The composite electrolyte membrane prepared by impregnating the polymer electrolyte with the support can be increased, and the dimensional change, in particular, the dimensional change in the area direction, which can cause breakage of the electrolyte membrane, significantly reduces the performance even after repeated use several hundred times. It was confirmed that it can be used as a battery separator capable of maintaining the present invention was completed.

An object of the present invention is an electrolyte membrane for a fuel cell, when using a composite membrane impregnated with an electrolyte polymer on a porous support, a porous support and electrolyte that can provide excellent mechanical properties, dimensional stability, durability while maintaining high porosity It is to provide a composite membrane impregnated with a polymer.

The composite membrane impregnated with the electrolyte polymer on the porous support according to the present invention exhibits excellent mechanical properties, dimensional stability, and durability while maintaining high porosity.

1 is a view schematically showing a synthesis process of a PAN copolymer. (a) shows before oxidation and (b) shows PAN copolymer after oxidation.

2 is a view schematically showing the synthesis process of SPAES copolymer.

3 is a view showing SEM images of (a) surface and (b) cross section of the synthesized PAN nonwoven fabric.

4 is a diagram showing the pore size distribution and solubility in NMP of the PAN nonwoven fabric.

5 is a view showing an image of a composite film composed of SPAES50 and PAN nonwoven fabric. (a) is real, (b) is surface, and (c) is cross-sectional image.

6 shows dimensional changes of Nafion 212, SPAES50 and the composite membrane.

Figure 7 is a diagram showing the proton conductivity of Nafion 212, SPAES50 and PAN / SP50 with temperature under 100% relative humidity conditions.

8 is a diagram showing proton conductivity of Nafion 212, SPAES50 and PAN / SP50 according to humidity conditions (80 ° C., 50 kPa back pressure).

9 is a diagram showing the MEA resistance of SPAES50 and PAN / SP50 measured by electrochemical impedance spectroscopy at a DC potential of 0.85 V (70 ° C., 100% relative humidity).

10 shows single cell performance of Nafion 212, SPAES50 and PAN / SP50. (a) shows the result measured in 70 degreeC, 100% relative humidity, and (b) in 70 degreeC and 50% relative humidity conditions.

FIG. 11 shows the results of durability test of SPAES50 and PAN / SP50 using wet-dry cycling including OCV sustain method.

12 is a diagram showing the amount of hydrogen crossover of SPAE50 and PAN / SP50 according to the number of cycles.

A first aspect of the present invention provides a composite electrolyte membrane comprising a support prepared by oxidizing a non-woven fabric formed by electrospinning a polyacrylonitrile (PAN) copolymer solution and a hydrocarbon-based polymer electrolyte impregnated thereto.

The second aspect of the present invention is to oxidize a nonwoven fabric formed by electrospinning a polyacrylonitrile copolymer solution, wherein the polyacrylonitrile copolymer has an alkoxycarbonyl or alk in an ethylene skeleton and a side chain. It comprises 1 to 10% by weight of a unit containing akanonoxy (alkanonoxy), and forming a hexagonal ring by forming a bond between the nitrogen atom of the side chain nitrile group and the carbon atoms of the adjacent nitrile group through oxidation Provided is a porous support that is characteristic.

A third aspect of the present invention provides a membrane-electrode assembly (MEA) comprising the composite electrolyte membrane according to the first aspect as an electrolyte membrane.

A fourth aspect of the present invention provides a fuel cell having the membrane-electrode assembly according to the third aspect.

Hereinafter, the present invention will be described in detail.

The present invention is characterized by providing a porous support by electrospinning and oxidizing a polyacrylonitrile (PAN) polymer solution. The present invention also provides a novel composite electrolyte membrane by impregnating the porous support with a hydrocarbon-based polymer electrolyte, such as a sulfonated poly (arylene ether sulfone) copolymer, as an electrolyte. It is characteristic.

The present inventors have disclosed a reinforced composite electrolyte membrane in which a conductive polymer is impregnated into a support having improved strength by crosslinking a nonwoven fabric of a polymer material using a heat treatment or a crosslinking agent through a prior study (Korean Patent No. 10-1279352). However, the heat treatment should be carried out for a long time of several to several ten hours at a high temperature near 300 ℃, when using a crosslinking agent it is inevitable to introduce an additional crosslinking agent and involves a repeated washing process to remove it. That is, such methods require long reactions or additional reagents. However, the support according to the invention can be prepared simply by treating with an oxidizing agent. The oxidant may be an oxygen molecule. That is, it can be performed by heating in an oven containing oxygen, for example, atmospheric conditions. Therefore, oxygen can be oxidized using oxygen in the air as an oxidizing agent only by heating, unless conditions are saturated with vacuum or inert gas.

As shown in FIG. 1, the PAN copolymer, which is a material of the porous support, may form a hexagonal ring as a bond is formed between a nitrogen atom of a side chain nitrile group and a carbon atom of a neighboring nitrile group through an oxidation process. As such, the intramolecular cyclization by oxidation can improve the strength by strengthening the skeleton of the PAN polymer portion, thereby not only reducing the dimensional change of the support but also reducing the cleavage of the polymer strand due to swelling due to moisture. Finally, breakage of the electrolyte membrane can be prevented.

Preferably, the treatment with the oxidant may be performed at 200 to 300 ℃. In addition, the process may be performed for 0.5 to 4 hours. More preferably, it may be performed at 230 to 270 ° C for 1 to 3 hours. In the above process, when the treatment temperature is low or the treatment time is short, the intramolecular cyclization in the PAN polymer portion is insufficient to provide the desired strength as a support or used when impregnating the polymer electrolyte solution. It may be dissolved in a solvent. On the other hand, when the treatment temperature is high or the treatment time is long, the polymer skeleton becomes excessively rigid due to excessive cyclization, so that the polymer skeleton can be easily crushed even by a small force applied without being able to bend flexibly or catch it. Alternatively, porous structures having high porosity may be crushed due to intermolecular crosslinking. Therefore, it is important to find the optimum conditions by appropriately combining the treatment temperature and time.

As described above, when the rigidity of the skeleton is too high, it is difficult to mold due to low flexibility, so that the composite electrolyte membrane prepared by impregnating the electrolyte in the support may not withstand the dimensional change according to conditions such as temperature or humidity. Can be easily broken. Therefore, the PAN copolymer has alkoxycarbonyl or alkanonoxy in the ethylene skeleton and the side chain in order to provide flexibility and hydrophilicity to facilitate molding and improve compatibility with the polymer electrolyte. It is preferable to include 1 to 10% by weight of a unit containing).

Non-limiting examples of units containing alkoxycarbonyl or alkanonoxy in the ethylene skeleton and side chains include methyl methacrylate (MMA) and methyl acrylate (methyl acrylate). , Vinyl acetate, and the like. It is preferable that the said unit is methyl methacrylate.

In a specific embodiment of the present invention, acrylonitrile and methyl methacrylate were mixed and polymerized in a mass ratio of 94: 6 to synthesize a PAN copolymer including 6% by weight of methyl methacrylate.

On the other hand, the concentration of the PAN copolymer solution used for electrospinning for forming into a nonwoven fabric may be 8 to 15% by weight. Preferably it can be used at a concentration of 10% by weight. If the concentration of the copolymer solution is too low, it is difficult to form into a nonwoven fabric having uniform pores that provide high porosity by electrospinning because the viscosity is short and broken. On the other hand, when the concentration is too high, it may be difficult to mold into a nonwoven fabric having uniform pores since the viscosity may be increased and entangled or aggregated may occur.

Preferably, the porous support according to the present invention has 60 to 80% porosity. Due to the presence of pores in the nonwoven fabric and the high porosity, when the electrolyte solution is subsequently impregnated in the preparation of the electrolyte membrane, a large amount of electrolyte may be contained in the pores, thereby canceling the decrease in ion conductivity by the PAN-based copolymer having low proton conductivity. Can be. At this time, if the porosity is less than 60%, it may not contain a sufficient amount of electrolyte, and thus, sufficient conductivity may not be provided as an electrolyte membrane.

In addition, since the porous support prepared through electrospinning and oxidation of the PAN polymer solution according to the present invention exhibits high porosity and has pores of uniform size, the size of the pores is different from that of other nonwoven fabrics in which the pores are not uniform. When forming a composite film impregnated with a polymer, it shows remarkably excellent conductivity and durability.

The porous support according to the present invention preferably has pores having an average diameter of 0.5 to 1.5 μm. If the pores are too small, the impregnation of the electrolyte polymer is not easy. If the pores are too large, the electrolyte polymer does not stay in the pores and flows out so that impregnation is difficult.

Preferably, the porous support according to the present invention has a thickness of 10 to 30 μm. The porous support can provide the mechanical strength or dimensional stability required in the electrolyte membrane of the fuel cell, while the conductivity of the support itself is low, resulting in membrane resistance. Therefore, it is desirable to maintain the mechanical strength but to lower the resistance by minimizing the thickness.

In one embodiment of the present invention, the PAN copolymer was electrospun to form a nonwoven fabric, and then, the oxidized support was immersed in NMP, which is a solvent for dissolving the polymer electrolyte. As a result, as shown in Figure 4b, even after several weeks it was confirmed that it does not dissolve and maintain a circular shape. Therefore, this invention can provide the support excellent in solvent resistance.

On the other hand, non-limiting examples of the polymer electrolyte that can be impregnated in the support according to the present invention is a hydrocarbon-based polymer electrolyte. Non-limiting examples of hydrocarbon-based polymer electrolytes include sulfonated polyimide, sulfonated poly (arylene ether sulfone) (SPAES), sulfonated polyetheretherketone ether ketone; SPEEK), sulfonated polybenzimidazole (SPBI), sulfonated polysulfone (SPSU), sulfonated polystyrene (SPS), sulfonated polyphosphazene sulfonated polyphosphazene (SPP), sulfonated poly (ether sulfone) (SPES), sulfonated poly (ether ketone) (SPEK), sulfonated polyarylene ether benziimi Sulfonated poly (arylene ether benzimidazole); and SPAEBI. In addition, preferred examples of the hydrocarbon-based polymer electrolyte include sulfonated poly (arylene ether sulfone) copolymers or polymers of the following Chemical Formula 1.

[Formula 1]

In the formula, l, m and n are each independently an integer of 1 or more.

Since the hydrocarbon-based electrolyte including a sulfonated group can interact with the cyano group of the PAN support through the sulfonic acid group, it can provide excellent miscibility when impregnated into the support.

At this time, the sulfonated hydrocarbon-based polymer electrolyte preferably has a degree of 40 to 60 mol% sulfonation. When the sulfonation degree exceeds 60 mol%, the hydrophilicity of the membrane becomes high, so that it may be dissolved in water and eluted without being impregnated in the support, while when the sulfonation degree is less than 40%, the ion conductivity of the membrane may be significantly decreased. .

In one embodiment of the invention, a SPAES copolymer was synthesized that exhibited high conductivity but was not dissolved in a solvent with 50 mol% sulfonation. It was confirmed that the composite membrane prepared by impregnating the SPAES copolymer in the porous support according to the present invention (Example 3) improved not only proton conductivity but also mechanical properties, dimensional stability, and durability. In particular, as a result of measuring the dimensional change in the wet and dry state, it was confirmed that the dimensional change in the area direction that can cause breakage of the electrolyte membrane is significantly reduced to show a lower level than Nafion 212 (Fig. 6). In addition, through the fuel cell drive test, by comparing the properties of the composite membrane prepared according to Example 3 with that of the pure SPAES copolymer polymer membrane, the effect of the porous support according to the invention was confirmed. The dimensional change of the composite membrane decreased from 91% to 51% in water, and the Young's modulus improved almost three times. However, the proton conductivity measured at various temperatures and humidity was reduced in the composite membrane, which is due to the blocking of the proton pathway by the porous support, but because the porous support according to the present invention exhibits improved strength, It can cancel by shortening.

A third aspect of the present invention provides a membrane-electrode assembly (MEA) having a composite electrolyte membrane according to the present invention as an electrolyte membrane.

For example, a membrane-electrode assembly (MEA) may be manufactured by interposing a composite membrane according to the present invention between a cathode and an anode at high temperature. At this time, the pressure during thermal compression is 0.5 to 2 tons (ton), the temperature is preferably 40 to 250 ℃.

The catalyst that can be used in the membrane-electrode assembly may be an alloy catalyst such as Pt, Pt-Ru, Pt-Sn, Pt-Pd, or Pt / C coated with fine carbon particles, Pt-Ru / C, or the like. A metal material such as Ru, Bi, Sn Mo may be deposited on Pt, but any material suitable for oxidation of hydrogen and reduction of oxygen may be used without limitation. You can also use commercially available products from Johnson Matthey, E-Tek, and others. Since the electrode catalysts adhered to both surfaces of the electrolyte membrane act as a cathode and an anode, respectively, they may be used in different amounts depending on the reaction rate at both electrodes, and other types of catalysts may be used.

The membrane-electrode assembly may be manufactured using a method known to those skilled in the art, and various non-limiting examples of the manufacturing method may be used, such as a decal method, a spray method, or a CCG method. In a specific embodiment of the present invention, the membrane-electrode assembly is manufactured using the CCG method, but the method of manufacturing the membrane-electrode assembly is not limited thereto.

Specifically, the non-limiting method of manufacturing the membrane-electrode assembly includes applying a catalyst slurry mixed with a catalyst, a hydrogen ion conductive polymer and a dispersion medium on a GDL and then drying to form a catalyst layer; Stacking the catalyst layer formed on the GDL such that the catalyst layer faces the electrolyte membrane on both surfaces of the composite membrane according to the present invention; And laminating and hot pressing to form a membrane-electrode assembly.

A fourth aspect of the present invention provides a fuel cell having the membrane-electrode assembly according to the present invention.

Preferably, non-limiting examples of a fuel cell having a membrane-electrode assembly according to the present invention include a polymer electrolyte fuel cell (PEMFC) and a direct methanol fuel cell (DMFC). have.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are intended to illustrate the present invention more specifically, but the scope of the present invention is not limited by these examples.

Example 1: Material

4,4'-Difluorodiphenyl sulfone (DFDPS) was purchased from Solvay Advanced Polymers (USA) and recrystallized from ethanol. 3,3'-disulfonated-4,4'-difluorodiphenyl sulfone (3,3'-disulfonated-4,4'-difluorodiphenyl sulfone; SDFDPS) was synthesized according to a known method. 4,4'-Bisphenol (4,4'-Bisphenol; BP, TCI) was also recrystallized from ethanol to increase the purity. N-methyl-2-pyrrolidone (NMP, Junsei), anhydrous toluene (Aldrich), 95-97% sulfuric acid (Merck), dimethylsulfoxide (DMSO, Aldrich), dimethyl Formamide (dimethylformamide; DMF, Aldrich) and azobisisobutyronitrile (AIBN, Aldrich) were used without further processing. Anhydrous potassium carbonate (K ₂ CO ₃ , Aldrich) was dried for 48 hours at 200 ° C. in vacuo before use. Acrylonitrile (AN) and methyl methacrylate (MMA) were purchased from South Korea. For the electrospinning process, stainless steel needles (internal diameter 0.51 mm, external diameter 0.81 mm and length 13 mm) were used (MN-21G-13, Iwashita Engineering, Japan).

Example 2 Preparation of PAN Nonwovens

Polyacrylonitrile (PAN) copolymers were synthesized using AN and MMA monomers at a mass ratio of 94: 6 and are schematically illustrated in FIG. 1A. First, AN (70.5 g) and MMA (4.5 g) monomers were added to a four neck flask equipped with a mechanical stirrer in a nitrogen atmosphere. Deionized water (279.0 g) was added to the reactor. The reactor was heated to 70 ° C. and a 20 wt% AIBN (0.8 g) solution dissolved in DMF was added to the mixture and stirred for 30 minutes. The polymerized sample was filtered and washed thoroughly three or four times with methanol to remove the remaining reactants. It was then dried for 48 hours at 50 ° C. under convection.

Thereafter, a PAN nonwoven fabric was manufactured using the electrospinning method. In response to the tensile force formed by the applied electric field, a 10 wt% PAN solution dissolved in DMSO was released from the syringe. The electrospun fibers were collected on a cylindrical drum collector. The electrical voltage was 10 kV and a syringe pump (KD Scientific-100, USA) was used to supply the solution at a constant throughput. The distance from the nozzle tip to the collector was fixed at 10 cm. The PAN nonwoven formed was dried at 160 ° C. for 2 hours under vacuum to remove excess solvent. Finally, the dried PAN nonwoven fabric was oxidized by treatment with an oxidizer at 240 ° C. for 1.5 hours (FIG. 1B). Specifically, the mixture was treated at 240 ° C. for 1.5 hours in an oven containing oxygen.

Example 3: Preparation of Membranes

Aromatic nucleophilic step-growth polymerization using SDFDPS, DFDPS and BP in a four-necked flask equipped with a mechanical stirrer, argon gas inlet, condenser and Dean-Stark trap To synthesize SPAES50. 2 schematically shows a SPAES50 copolymer synthesis method used as an ionomer for producing a composite membrane. In order to form a flat film, a composite film was prepared by impregnating a solution of 15 wt% of a polymer (SPAES50) dissolved in NMP into a PAN nonwoven fabric prepared according to Example 2 using a bar coating method. . The polymer solution together with the PAN nonwoven was dried in an oven at 80 ° C. for 6 hours on glass, and the membrane thus prepared was subsequently dried at 120 ° C. under vacuum for 12 hours to completely remove excess solvent. Finally, the membrane was acidified in 1.5 M sulfuric acid for 24 hours and then washed with deionized water for 24 hours at room temperature.

Example 4: Characterization of the Membrane

The molecular weight (Mw) of the PAN copolymer synthesized according to Example 2 was confirmed by gel permeation chromatography (GPC, Waters, Tosoh). The pore size distribution of the PAN nonwovens was measured using a high order capillary flow porometer (ACFP-1500AE, wet up / dry up method using Galwick solution). The dimensional change (area, thickness and volume) and the amount of water uptake were determined from the difference in volume and mass between the wet membrane in the fully hydrated state and the dry membrane measured after vacuum drying at 120 ° C. A mechanical testing instrument (LLOYD instrument LR5K) was used to confirm the mechanical properties of the membrane at a crosshead speed of 50 mm / min at 25 ° C. in a fully hydrated state.

Scanning electron microscopy (SEM, XL-30S FEG, Philips) was used to observe the surface and cross-sectional images of the PAN nonwoven fabric and composite membrane. Prior to SEM image processing, the samples were coated with platinum for 2 minutes in vacuo using a sputter coating machine (Sputter Coater, Q150T ES, Quorumtech, USA).

The equivalent titer of sulfonic acid groups per unit mass of membrane (1 g) was measured with an automatic titrator (Metroohm 794 Basic Titrino) and expressed as ion exchange capacity (IEC). AC impedance analyzer (SP) using a 4-probe conductivity cell with varying temperature (from 25 ° C. to 80 ° C.) at 100% relative humidity in the in-plane direction over a frequency range of 0.1 Hz to 4 MHz. The proton conductivity of the membrane was measured using an Impedance / Gain Phase Analyzer. Equilibration was performed for 1 hour in a temperature chamber (ESPEC, SH-241) before each measurement. Proton conductivity was calculated using the following formula (1):

Proton Conductivity (S / cm) = l / R × S (1)

Where l is the distance between the electrodes, R is the electrochemical impedance spectroscopy (EIS) curve (x axis = real part (Z '), y axis = imaginary part (Z' ') using the intercept x value The calculated membrane resistance, and S, is the cross-sectional surface area of the membrane, and the in-plane conductivity system (BekkTech, BT) that can control humidity conditions using the same 4-probe. Proton conductivity was measured under various conditions (relative humidity 20% to 80%) at 80 ° C.

Example 5: Preparation of MEA using PAN copolymer based composite membrane

Example 3 with gas-diffusion layers coated with Pt / C and Nafion binder (50 wt% Pt / C, 0.4 mg Pt / cm ² , FuelCellPower Inc.) to evaluate single cell performance The membrane electrode assembly (MEA) was prepared using the composite membrane prepared in the above as an electrolyte membrane. The active surface area of the electrode was 25 cm ² . The membrane electrode assembly prepared above was activated for 24 hours at 70 ° C. with hydrogen at the cathode and at the anode (stoichiometric coefficient = 1.2 / 2). Subsequently, the test station (FCT-TS300, Fuel Cell Technologies, Inc.) was used to provide 0.5 m to 50 mV steps per 25 seconds at a backpressure of 0, 70 ° C. and 100% relative humidity for the membrane electrode assembly. It was evaluated electrochemically by cycling between 1.0 V. In addition, electrochemical impedance spectroscopy measurements were performed to observe the resistance of the through-plane MEA at a DC potential of 0.85 V with an AC frequency ranging from 10 mHz to 1 MHz. After purging with nitrogen for 30 minutes, the DC power supply (Agilent N5744A) degree of hydrogen crossover was measured. A working electrode and a reference electrode were connected to the anode and the cathode, respectively, and a potential of 0.15 to 0.3 V was applied to the single cell. The current generated as the hydrogen passed through the membrane from the cathode oxidized at the anode.

result

The morphological properties of the electrospun PAN nonwovens with appropriate feasible oxidative stability of 450 kg / mol of molecular weight (Mw) prepared according to Example 2 were analyzed using SEM images. 3a and b show SEM images of the surface and cross section of a PAN nonwoven fabric (thickness = 18 ± 2 μm) successfully formed in the form of a multifibrous nonwoven fabric. The diameters of the fibers in the PAN nonwovens were determined to range from 600 nm to 1200 nm, and the PAN fibers appeared to be somewhat dissolved and bound to each other. The pore size and pore size distribution of the PAN nonwoven fabric were quantitatively analyzed and the results are shown in FIG. 4A. The average pore diameter of the PAN nonwovens was about 1 μm and uniformly distributed in the range of 0.5 μm to 1.5 μm. In addition, it was confirmed to have a porosity of 80% by using the weight and volume of the PAN nonwoven fabric.

In order to confirm the resistance of the organic solvent, solubility test was performed using NMP, which is a solvent used for forming a composite film using the SPAES50 copolymer. 4b shows an image of PAN nonwoven fabric after soaking in NMP solvent. As a result, PAN nonwovens were found to be insoluble in NMP and therefore suitable for inclusion in SPAES50 solution. From the above results, it was confirmed that a remarkable nonwoven material having nano-sized fibers and an elaborate pore structure can be used for the proton exchange composite membrane.

5 is a view showing a real image and a SEM image of the surface and side of the composite film (hereinafter referred to as PAN / SP50) prepared by using a PAN nonwoven fabric and SPAES50 according to Example 3. The composite film is black due to the oxidative PAN substrate (FIG. 5A). SPAES50 copolymer was successfully impregnated into PAN nonwovens (FIG. 5B). The pores of the PAN nonwoven fabric did not appear on the surface of the composite membrane. It was confirmed that the PAN nonwoven fabric was well mixed with the SPAES50 copolymer from the cross-sectional shape located at the center of the membrane. The thickness of the composite membrane was about 35 μm (FIG. 5C).

In general, multifibrous substrates contribute to strengthening the mechanical properties of the polymer composite membrane. In order to confirm the mechanical change, the tensile test of the composite membrane was performed in a fully hydrated state at room temperature. The results are shown in Table 1 below. Young's modulus and yield strength of membranes for use in PEMFCs are important factors for durability in operation. When a change is caused by an external force, these properties indicate the degree of durability and the limits of restorability. In the case of the composite membrane according to Example 3, the Young's modulus of PAN / SP50 due to the use of a multi-fibrous material having a rigid filler effect, that is, a PAN nonwoven fabric (Young's modulus 704.6 MPa) as a support (692.1 MPa) was significantly higher than the value for SPAES50 (244.6 MPa) and Nafion 212 (112.6 MPa). In addition, the yield strength of the membrane showed a tendency similar to Young's modulus. The yield strength of PAN / SP50 (13.8 MPa) was improved by 50% over the values for SPAES50 (9.2 MPa) and Nafion 212 (9.0 MPa). This mechanical property is an important factor in the operation of the PEMFC under extreme conditions. Another property involved in durability is the dimensional change in water. To achieve optimal proton conduction, the membrane needs water while the PEMFC is operating. Thus, the membrane absorbs water through sulfonic acid groups and expands in volume due to the absorbed water. However, this expanded membrane weakens as the amount of water absorbed increases. 6 shows the dimensional change of the composite membrane and the pure polymer membrane in comparison with Nafion 212. The high dimensional change of SPAES50 decreased from 91% to 50% in PAN / SP50, and the value for PAN / SP50 was similar to that for Nafion 212. In particular, a significant decrease was seen in the area-based variation of PAN / SP50, which is inferred to be due to the swelling of the membrane being suppressed by the PAN nonwovens, as shown in FIG. 6. The area-based expansion rate of PAN / SP50 was around 19%, which is lower than the 26% value for Nafion 212. From this, it was confirmed that the water absorption is involved in the dimensional change, the measured values are shown in Table 1 below.

Table 1 membrane IEC (meq / g) Water absorption rate (wt%) Dimensional change (volume%) Young's modulus (MPa) Yield strength (MPa) Activation energy (E _a , kJ / mol) Nafion 212 0.90 24 43 112.6 ± 8.4 9.0 ± 0.1 10.9 ± 0.6 SPAES50 2.01 76 91 244.6 ± 37.6 9.2 ± 0.1 10.7 ± 0.7 PAN / SP50 1.71 51 50 692.1 ± 38.9 13.8 ± 0.1 15.7 ± 0.3 PAN Nonwovens - - - 704.6 ± 37.6 15.8 ± 0.3 -

The proton conductivity of the composite membrane was confirmed by varying the temperature under completely hydrated conditions, and the results are shown in FIG. 7 in comparison with the pure polymer membrane and Nafion 212. As the temperature increased from 25 ° C. to 80 ° C., the proton conductivity of all the membranes used for the measurement increased. Proton conductivity of PAN / SP50 was 0.062 S / cm and 0.164 S / cm at 25 ° C and 80 ° C at 100% relative humidity, respectively, lower than the values for SPAES50 (0.092 S / cm and 0.181 S / cm). . The IEC value of PAN / SP50 was also 1.71 meq / g, lower than the value for SPAES50 (2.01 meq / g), as expected. Therefore, the decrease in the proton conductivity of the composite membrane can be determined by the porosity of the PAN nonwoven fabric. Although the proton conductivity of PAN / SP50 decreased compared to SPAES50, the value was close to that for Nafion 212 at 80 ° C / 100% relative humidity. In order to confirm the temperature dependence of the proton conductivity, the slope of the proton conductivity shown with respect to the inverse of the absolute temperature was calculated to confirm the activation energy (E _a ). Nafion 212 (10.9 kJ / mol) and SPAES50 (10.7 kJ / mol) showed similar activation energies, while PAN / SP50 showed increased activation energies up to 15.7 kJ / mol. It is described together in Table 1 above. These results indicate that the PAN nonwoven fabric in the composite membrane increases the minimum energy for proton transport and decreases the proton conductivity. In addition, in order to confirm the proton conductivity at low relative humidity, experiments were performed at 20% and 80% relative humidity. As a result, as the relative humidity decreases, the number of water molecules around the membrane that can transport the protons decreases significantly, so that the proton conductivity in all the membranes decreases as the humidity decreases. At low relative humidity, SPAES50 exhibited particularly lower proton conductivity than Nafion 212, which may be due to ineffective connectivity of the proton pathway by sulfonic acid groups of SPAES50 compared to Nafion 212. PAN / SP50 had the lowest connectivity among the membranes used for the measurement because the PAN nonwovens act as proton barriers and thus exhibited the lowest proton conductivity at low relative humidity (FIG. 8).

To check the ohmic and interfacial contact resistance (OCR) of the MEA surface, the EIS technique was used. OCR is an important property involved in the improved performance of the MEA and is calculated by the high frequency intercept value of x axis (Z _Re ). When using the same catalyst system in the MEA, OCR is affected by membrane resistance. 9 shows OCR of SPAES50 and PAN / SP50 at 70 ° C./100% relative humidity, 0.0072 Ω and 0.0092 Ω, respectively. The results indicate that SPAES50 has about 20% higher proton conductance than PAN / SP50, calculated from the inverse of the OCR value. This difference in performance is due to the porosity of the PAN nonwovens. Subsequently, the performance of the single cell with SPAES50, PAN / SP50, and Nafion 212 was confirmed by comparing the pure polymer membrane with the composite membrane. The current density of PAN / SP50 at 70 ° C./100% relative humidity was 1012 mA / cm ² at 0.6 V, slightly lower than the value for SPAES50 (1109 mA / cm ² ) (FIG. 10). However, PAN / SP50 showed a performance comparable to Nafion 212 (1053 mA / cm ² at 0.6V). This indicates that cell performance levels correlate with proton conductivity results (FIG. 10A). The relative performance improvement of PAN / SP50 is due to the thinner molding compared to SPAES50 (45 μm) and Nafion 212 (50 μm), and consequently the cell resistance can be reduced by shortening the proton path. When the measurement conditions are 70 ° C / 50% relative humidity, the performance of SPAES50 (788 mA / cm ² ) and PAN / SP50 (691 mA / cm ² ) at 0.6 V is lower than Nafion 212 (884 mA / cm ² ). Therefore, in the case of low relative humidity conditions, the result was the same as for the proton conductivity.

11 shows the results of testing the film durability while driving the cell under a rigorous condition. The endurance protocol used was a method using hydration / dehydration cycling and the OCV hold method to simultaneously identify physical and chemical damage characteristics. The hydration / dehydration cycle time was 10 minutes in total (5 minutes each). The SPAES50 dropped below 0.9 V after about 500 cycles, while the PAN / SP50 continued up to 1000 cycles due to the PAN nonwoven fabric reinforcement effect. This indicates that the polymer nanofibers can improve the durability of the membrane while driving PEMFC under various conditions. Hydrogen crossmixing results from the diffusion of hydrogen gas through the membrane from the cathode to the anode. Membrane damage in PEMFC can be confirmed by determining whether diffusion of the hydrogen gas occurs. 12 shows hydrogen cross-mixing of SPAES50 and PAN / SP50 according to the hydration / dehydration cycle. Initial hydrogen cross-mix levels of SPAES50 and PAN / SP50 were hardly noticeable. This was confirmed with low current density (0.001 A / cm ² ). However, after 500 cycles, hydrogen cross-mixing of SPAES50 markedly increased to 0.012 A / cm ² . For PAN / SP50, it increased to 0.006 A / cm ² after 1000 cycles, which was only half the value measured after 500 cycles of SPAES50. In addition to reducing OCV, hydrogen cross-mixing clearly demonstrated membrane damage during fuel cell operation. Analysis of single cell performance and durability evaluation results of SPAES50 and PAN / SP50 confirmed that the composite membrane including the electrospun PAN nonwoven fabric can be usefully used for PEMFC.

conclusion

New composite membranes have been successfully developed by impregnating SPAES50 in PAN resin nonwovens. The PAN nonwoven fabric for producing composite membranes suitable for long time operation under various conditions was produced by electrospinning. PAN nonwovens were analyzed by measuring fiber thickness, pore size and porosity. The introduction of PAN nonwovens was found to be an effective means to improve dimensional stability as well as mechanical properties. However, blocking proton conduction path by PAN nonwoven fabric decreased proton conductivity in composite membrane compared to pure polymer membrane. For single cell driving, composite membranes not only showed improved durability compared to pure polymer membranes but also showed similar levels of performance. The excellent durability of the composite membrane was again confirmed by hydrogen cross mixing. This advantage of composite membranes using PAN nonwovens can improve membrane technology for PEMFC applications.

Claims (14)

A composite electrolyte membrane comprising a support prepared by oxidizing a non-woven fabric formed by electrospinning a polyacrylonitrile (PAN) copolymer solution and a hydrocarbon-based polymer electrolyte impregnated thereto. The method of claim 1, The oxidation is a composite electrolyte membrane that is carried out at 200 to 300 ℃, 0.5 to 4 hours. The method of claim 1, A composite electrolyte membrane that forms a hexagonal ring by forming a bond between the nitrogen atom of the side chain nitrile group and the carbon atom of the neighboring nitrile group by the oxidation. The method of claim 1, The PAN copolymer is a composite electrolyte membrane, characterized in that it comprises 1 to 10% by weight of a unit containing an alkoxycarbonyl (alkoxycarbonyl) or alkanonoxy (alkanonoxy) in the ethylene (ethylene) skeleton and the side chain. The method of claim 4, wherein Units containing alkoxycarbonyl or alkanonoxy in the ethylene skeleton and side chain are methyl methacrylate (MMA), methyl acrylate and vinyl acetate (vinyl). acetate) is selected from the group consisting of. The method of claim 1, The concentration of the PAN copolymer solution is a composite electrolyte membrane, characterized in that 8 to 15% by weight. The method of claim 1, The support is a composite electrolyte membrane, characterized in that it has a 60 to 80% porosity (porosity). The method of claim 1, The support is a composite electrolyte membrane, characterized in that having an average diameter of 0.5 to 1.5 μm pores. The method of claim 1, Composite electrolyte membrane characterized in that it has a thickness of 10 to 30 μm. The method of claim 1, The hydrocarbon-based electrolyte is a sulfonated poly (arylene ether sulfone) (SPAES) copolymer or a composite electrolyte membrane, characterized in that the polymer of Formula 1: [Formula 1]

In the formula, l, m and n are each independently an integer of 1 or more. The method of claim 1, The hydrocarbon-based polymer electrolyte is characterized in that it has a 40 to 60 mol% sulfonation degree composite electrolyte membrane. Oxidized nonwoven fabric formed by electrospinning a polyacrylonitrile copolymer solution, The polyacrylonitrile copolymer includes an monomer containing 1 to 10% by weight of an ethylene backbone and an alkoxycarbonyl or alkanonoxy in the side chain. A porous support characterized in that a bond is formed between a nitrogen atom of a group and a carbon atom of a neighboring nitrile group to form a hexagonal ring. A membrane-electrode assembly (MEA) comprising the composite electrolyte membrane according to any one of claims 1 to 11 as an electrolyte membrane. A fuel cell comprising the membrane-electrode assembly according to claim 13.

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