KR102154101B1 - A composite membrane comprising nonwoven PAN support and hydrocarbon-based electrolyte impregnated therein and the use thereof - Google Patents

Abstract

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 therewith; A new improved solvent resistance or strength by forming a hexagonal ring by oxidizing the nonwoven fabric formed by electrospinning a polyacrylonitrile copolymer solution to form a bond between the nitrogen atom of the side chain nitrile group and the carbon atom of the adjacent nitrile group. Support; A membrane-electrode assembly (MEA) having the composite electrolyte membrane as an electrolyte membrane; And to a fuel cell including the membrane-electrode assembly.
The composite membrane impregnated with an electrolyte polymer on a porous support according to the present invention exhibits excellent mechanical properties, dimensional stability, and durability while maintaining high porosity.

Description

A composite membrane comprising nonwoven PAN support and hydrocarbon-based electrolyte impregnated therein and the 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 therewith; A new improved solvent resistance or strength by forming a hexagonal ring by oxidizing the nonwoven fabric formed by electrospinning a polyacrylonitrile copolymer solution to form a bond between the nitrogen atom of the side chain nitrile group and the carbon atom of the adjacent nitrile group. Support; A membrane-electrode assembly (MEA) having the composite electrolyte membrane as an electrolyte membrane; And to a fuel cell including the membrane-electrode assembly.

The fuel cell is a device for converting chemical energy from the fuel into electrical energy through a chemical reaction with oxygen or with other oxidizing agents, as well as requiring no exchange or charging of the battery, unlike ordinary cells. The fuel cell is a high-efficiency power generation apparatus of this 60% of energy conversion efficiency was increased, the efficiency is less fuel consumption than the conventional internal combustion engine, SO _x, NO _x, pollution-free energy source which does not generate environmental pollutants of VOC such that There is an advantage. In addition, there are additional advantages such as that various raw materials can be used for production, the site area required for production facilities is small, and the construction period is short. Accordingly, the fuel cell has a variety of applications ranging from mobile power sources such as portable devices, transportation power sources such as automobiles, and distributed power generation that can be used for home and power business. In particular, when the operation of a fuel cell vehicle, which is a next-generation transportation device, is put into practice, the potential market size is expected to be wide.

Fuel cells are the anode (anode) that produces hydrogen ions and electrons by oxidation of fuel materials, the cathode (cathode) where the reduction of oxygen or other oxidizing agents by reaction with hydrogen ions and electrons occurs, and the cathode from the anode. It includes an electrolyte layer that can efficiently transfer hydrogen ions. In the fuel cell, hydrogen ions and electrons move from the anode to the cathode through an external circuit electrically connected to the electrolyte layer, respectively. The fuel cell may use hydrogen, hydrocarbon, alcohol (methanol, ethanol, etc.) as fuel, and oxygen, air, chlorine, chlorine dioxide, and the like may be used as the oxidizing agent.

Fuel cells include Polymer Electrolyte Membrane Fuel Cell (PEMFC), Direct Methanol Fuel Cell (DMFC) using alcohol as fuel, Direct Ethanol Fuel Cell (DEFC), alkaline It can be classified into AFC (Alkaline Fuel Cell), Phosphoric Acid Fuel Cell (PAFC), Molten Carbonate Fuel Cell (MCFC), and Solid Oxide Fuel Cell (SOFC). I can. Among them, the polymer electrolyte fuel cell, the direct methanol fuel cell, and the direct ethanol fuel cell can operate at a relatively low temperature compared to other fuel cells, and can generate power with a capacity of 1 to 10 kW. In addition, since it can be miniaturized, it can be stacked to improve output, and since it is easy to carry, it can be usefully used for a notebook computer or as an auxiliary power supply. Accordingly, in order to reduce the volume of the unit cell, an electrolyte membrane prepared by using an ion conductive polymer is placed between the anode and the cathode in a sandwich form, and is compressed to form a membrane-electrode assembly in which the anode-electrolyte membrane-air electrode forms an assembly. Thus, the battery can be configured. The electrolyte membrane that can be used for the membrane-electrode assembly should have high hydrogen ion transfer ability, but low permeability of fuel materials, as well as high thermal stability, and thus stably exhibit ionic conductivity even under battery operating conditions of about 100°C. It has excellent chemical durability and should be stable without decomposition even under long-term use and acidic conditions.

In particular, proton exchange membrane fuel cells (PEMFC) are one of the highly anticipated and promising energy technologies as they can directly convert chemical energy into electrical energy for portable electronic devices, automobiles and large buildings. Among the components of PEMFC, a proton exchange membrane (PEM) is a basic element separating the cathode and the anode, and determines the efficiency and durability of PEMFC. Nafion, a perfluorosulfonated ionomer, 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 produces toxic waste. In addition, problems such as a rapid decrease in the hydrogen ion conductivity due to a decrease in water content above 100°C, softening of the membrane, and high methanol permeability are facing a large limit in the commercialization of fuel cells.

Thus, sulfonated poly(arylene ether sulfone), a hydrocarbon-based ionomer that has high thermal resistance, excellent mechanical strength, low hydrogen permeability, and can be manufactured in an inexpensive production process. (Sulfonated poly(arylene ether sulfone); SPAES) has been considered as a PEM material to replace Nafion membranes over the past decade. However, the dimensions of SPAES expand under fully hydrated conditions, reducing the durability of the fuel cell. To overcome these drawbacks, many researchers have tried polyimide (PI), poly(paraphenylene terephthalamide) (PPTA), poly(vinyl alcohol); PVA ) And multi-fibrous manufactured materials such as polyphenylsulfone (PPS). However, when it has a high porosity, the mechanical properties are deteriorated. Therefore, development of a porous support and ion conductor having excellent mechanical properties, dimensional stability, and durability while maintaining high porosity is urgently required.

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

A first aspect of 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 therewith.

In a second aspect of the present invention, a nonwoven fabric formed by electrospinning a polyacrylonitrile copolymer solution is oxidized, and the polyacrylonitrile copolymer has an ethylene skeleton and an alkoxycarbonyl or an Al It contains 1 to 10% by weight of a unit containing alkanonoxy, and forms a hexagonal ring as a bond is formed between the nitrogen atom of the side chain nitrile group and the carbon atom of the adjacent nitrile group through oxidation. It provides a characteristic porous support.

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

A fourth aspect of the present invention provides a fuel cell provided with the membrane-electrode assembly described in 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. In addition, the present invention 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) (SPAES) copolymer, as an electrolyte. It is characterized by doing.

The present inventors disclosed a reinforced composite electrolyte membrane impregnated with a conductive polymer in a support having improved strength by crosslinking a nonwoven fabric made of a polymer material by heat treatment or crosslinking using a crosslinking agent through prior research (Korean Patent No. 10-1279352). However, the heat treatment must be treated at a high temperature near 300° C. for a long time of several to tens of hours, and when a crosslinking agent is used, the introduction of an additional crosslinking agent is inevitable, and a repeated washing process to remove it is involved. That is, such a method requires a long reaction or additional reagents. However, the support according to the present invention can be manufactured simply by treatment with an oxidizing agent. The oxidizing agent may be an oxygen molecule. That is, it can be carried out by heating in an oven under conditions containing oxygen, for example, atmospheric conditions. Therefore, it is possible to oxidize using oxygen in the air as an oxidizing agent by simply heating it unless it is under vacuum or saturated with an inert gas.

As shown in FIG. 1, when the PAN copolymer, which is a material of the porous support, undergoes an oxidation process, a bond is formed between the nitrogen atom of the side chain nitrile group and the carbon atom of the adjacent nitrile group, thereby forming a hexagonal ring. As described above, intramolecular cyclization by oxidation can improve the strength by making the skeleton of the PAN polymer part more rigid, thus reducing the dimensional change of the support as well as reducing the cleavage of the polymer strand due to swelling due to moisture. And, finally, it is possible to prevent breakage of the electrolyte membrane.

Preferably, the process of treating with the oxidizing agent may be performed at 200 to 300°C. 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 PAN polymer portion is not sufficiently cyclized in the molecule due to oxidation, so that the desired strength cannot be provided as a support or is used when impregnating a polymer electrolyte solution. It may dissolve in a solvent. On the other hand, when the treatment temperature is high or the treatment time is long, the polymer skeleton becomes too rigid due to excessive cyclization, so that it cannot be flexibly bent and can easily be broken even by a small force applied so as not to be able to grasp it. Alternatively, a porous structure having a high porosity may be crushed due to crosslinking between molecules. Therefore, it is important to find the optimum conditions by properly combining the treatment temperature and time.

As described above, when the stiffness of the skeleton is too high, it may be difficult to mold and be broken due to low flexibility, and the composite electrolyte membrane manufactured by impregnating the support with an electrolyte cannot withstand dimensional changes according to conditions such as temperature or humidity. It can be easily broken. Accordingly, in order to provide flexibility and hydrophilicity to facilitate molding and to improve compatibility with a polymer electrolyte, the PAN copolymer has alkoxycarbonyl or alkanonoxy It is preferable to include 1 to 10% by weight of the unit containing).

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

In a specific example of the present invention, a PAN copolymer containing 6% by weight of methyl methacrylate was synthesized and used by polymerization by mixing acrylonitrile and methyl methacrylate at a mass ratio of 94:6.

Meanwhile, the concentration of the PAN copolymer solution used for electrospinning for molding into a nonwoven fabric may be 8 to 15% by weight. Preferably it can be used in a concentration of 10% by weight. If the concentration of the copolymer solution is too low, the viscosity is low and it is cut short, so it is difficult to form a nonwoven fabric having uniform pores that provides high porosity by electrospinning. On the other hand, if the concentration is too high, the viscosity may increase, resulting in a phenomenon such as agglomeration or agglomeration, so it is difficult to form a nonwoven fabric having uniform pores.

It is preferable that the porous support according to the present invention has 60 to 80% porosity. Due to the presence of pores and high porosity in the nonwoven fabric, a large amount of electrolyte may be contained in the pores when the electrolyte solution is impregnated in the subsequent manufacturing of the electrolyte membrane, so that the decrease in ionic conductivity due to the PAN-based copolymer with low proton conductivity will be offset. I can. At this time, if the porosity is less than 60%, a sufficient amount of electrolyte cannot be contained, and thus sufficient conductivity cannot be provided as an electrolyte membrane, and if the porosity exceeds 80%, the strength of the support is lowered and thus it cannot function as a support.

In addition, the porous support produced by electrospinning and oxidation of the PAN polymer solution according to the present invention exhibits high porosity and has pores of a uniform size, so that the electrolyte is compared with other nonwoven fabrics having a non-uniform pore size. When forming a polymer-impregnated composite film, it exhibits 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, impregnation of the electrolyte polymer is not easy, and if the pores are too large, the electrolyte polymer does not stay in the pores and flows out, making impregnation difficult.

It is preferable that the porous support according to the present invention has a thickness of 10 to 30 μm. While the porous support can provide the mechanical strength or dimensional stability required in the electrolyte membrane of a fuel cell, the support itself has low conductivity, resulting in membrane resistance. Therefore, it is preferable to maintain the mechanical strength, but to minimize the thickness to lower the resistance.

In an embodiment of the present invention, it was confirmed whether the PAN copolymer was electrospun to form a nonwoven fabric, and then the oxidized support was immersed in NMP, a solvent for dissolving the polymer electrolyte, to dissolve. As a result, as shown in FIG. 4B, it was confirmed that it was not dissolved and maintained the original shape even after several weeks had passed. Therefore, the present invention can provide a support having excellent solvent resistance.

Meanwhile, a non-limiting example of a polymer electrolyte that can be impregnated into 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 polyether ketone (sulfonated poly(ether)). 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 etherbenzimi Dazole (sulfonated poly(arylene ether benzimidazole); SPAEBI). In addition, a preferred example of the hydrocarbon-based polymer electrolyte is a sulfonated poly(arylene ether sulfone) copolymer or a polymer represented by the following formula (1).

[Formula 1]

In the above 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 a sulfonic acid group, when impregnated into the support, excellent miscibility can be provided.

At this time, it is preferable that the sulfonated hydrocarbon-based polymer electrolyte has a degree of sulfonation of 40 to 60 mol%. If the degree of sulfonation exceeds 60% by mole, the hydrophilicity of the membrane becomes high, so that it is dissolved in water and may not be impregnated in the support and may be eluted, whereas if the degree of sulfonation is less than 40%, the ionic conductivity of the membrane may be significantly lowered .

In one embodiment of the present invention, a SPAES copolymer having a 50 mol% sulfonation degree was synthesized so as to exhibit high conductivity but not dissolve in a solvent. It was confirmed that the composite membrane prepared by impregnating the SPAES copolymer into the porous support according to the present invention (Example 3) improved mechanical properties, dimensional stability, and durability as well as proton conductivity. In particular, as a result of measuring the dimensional change in wet and dry conditions, it was confirmed that the dimensional change in the area direction that may cause breakage of the electrolyte membrane was significantly reduced, indicating a lower level than Nafion 212 (FIG. 6). Further, through a fuel cell driving test, the properties of the composite membrane prepared according to Example 3 were compared with those of the pure SPAES copolymer polymer membrane, and the effect of the porous support according to the present invention was confirmed. The dimensional change of the composite membrane decreased from 91% to 51% in water, and the Young's modulus showed an almost three-fold improvement. However, the proton conductivity measured at various temperatures and humidity decreased in the composite membrane, which is due to the blocking of the proton path by the porous support, but the porous support according to the present invention exhibits improved strength, so that the It can be offset by shortening.

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

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

The catalyst that can be used in the membrane-electrode assembly is an alloy catalyst such as Pt, Pt-Ru, Pt-Sn, Pt-Pd, or Pt/C, Pt-Ru/C coated with fine carbon particles, or Pb, Metal materials such as Ru, Bi, Sn and Mo may be deposited on Pt to be used, but any material suitable for oxidation of hydrogen and reduction of oxygen may be used without limitation. You can also use those sold commercially by Johnson Matthey, E-Tek, etc. Since the electrode catalyst adhered to both sides of the electrolyte membrane acts as a cathode and an anode, respectively, it may be used in different amounts depending on the reaction rate at both electrodes, and different types of catalysts may be used.

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

Specifically, a non-limiting method of manufacturing the membrane-electrode assembly may include applying a catalyst slurry in which a catalyst, a hydrogen ion conductive polymer, and a dispersion medium are mixed on a GDL, followed by drying to form a catalyst layer; Stacking the catalyst layers formed on the GDL on both surfaces of the composite membrane according to the present invention, with the catalyst layers facing the electrolyte membrane; And hot pressing after lamination to form a film-electrode assembly.

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

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

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

1 is a diagram schematically showing the synthesis process of the PAN copolymer. (a) shows the PAN copolymer before oxidation and (b) after the oxidation.
2 is a diagram schematically showing the synthesis process of the SPAES copolymer.
3 is a diagram showing SEM images of the (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 diagram showing an image of a composite film composed of SPAES50 and PAN nonwoven fabric. (a) shows the real object, (b) shows the surface, and (c) shows the cross-sectional image.
6 is a diagram showing the dimensional change of Nafion 212, SPAES50, and composite membranes.
7 is a diagram showing the proton conductivity of Nafion 212, SPAES50, and PAN/SP50 according to temperature under 100% relative humidity conditions.
8 is a diagram showing the 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 is a diagram showing single cell performance of Nafion 212, SPAES50, and PAN/SP50. (a) shows the results measured under conditions of 70°C and 100% relative humidity, and (b) at 70°C and 50% relative humidity.
11 is a diagram showing the results of durability tests of SPAES50 and PAN/SP50 using wet-dry cycling including OCV sustaining method.
12 is a diagram showing the amount of hydrogen crossover of SPAE50 and PAN/SP50 according to the number of cycles.

Hereinafter, the present invention will be described in more detail through examples. These examples are for explaining the present invention more specifically, and the scope of the present invention is not limited by these examples.

Example 1: substance

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 with 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 additional procedures. Anhydrous potassium carbonate (K ₂ CO ₃ , Aldrich) was dried at 200° C. for 48 hours in vacuum before use. Acrylonitrile (AN) and methyl methacrylate (MMA) were purchased from Samjeon Chemical (South Korea). For the electrospinning process, a stainless steel needle (stainless steel needle, MN-21G-13, Iwashita Engineering, Japan) having an inner diameter of 0.51 mm, an outer diameter of 0.81 mm, and a length of 13 mm was used.

Example 2: PAN Non-woven( nonwoven ) Of manufacture

A polyacrylonitrile (PAN) copolymer was synthesized using AN and MMA monomers in a mass ratio of 94:6, which is schematically shown in FIG. 1A. First, AN (70.5 g) and MMA (4.5 g) monomers were added to a four-necked 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 three or four times with methanol to remove the remaining reactants. Then, it was dried at 50° C. for 48 hours under convection.

Thereafter, a PAN nonwoven fabric was manufactured using an electrospinning method. In response to the tensile force formed by the applied electric field, a 10% by weight PAN solution dissolved in DMSO was released from the syringe. The electrospun fibers were collected on a cylindrical drum collector. The electric 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 formed PAN nonwoven fabric was dried at 160° C. for 2 hours under vacuum to remove excess solvent. Finally, the dried PAN nonwoven fabric was oxidized by treating with an oxidizer at 240° C. for 1.5 hours (FIG. 1B). Specifically, it was treated for 1.5 hours at 240°C in an oven containing oxygen.

Example 3: Preparation of the membrane

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

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 nonwoven fabric was measured using an advanced capillary flow porometer (ACFP-1500AE, wet up/dry up method using a 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 fully hydrated wet film and the dry film measured after vacuum drying at 120°C. The mechanical properties of the membrane were confirmed with a crosshead speed of 50 mm/min at 25° C. in a fully hydrated state using a material testing instrument (LLOYD instrument LR5K).

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

The equivalent 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). Using a 4-probe conductivity cell, an AC impedance analyzer (SP) with a temperature change (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. -300, Impedance/gain phase analyzer) was used to measure the proton conductivity of the membrane. It was equilibrated 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 electrodes, R is an electrochemical impedance spectroscopy (EIS) curve (x-axis = real part (Z'), y-axis = imaginary part (Z'') using the x-axis intercept value The calculated membrane resistance, and S is the cross-sectional surface area of the membrane, and an in-plane conductivity system (BekkTech, BT) that can control the humidity conditions using the same 4-probe. -512) was measured for proton conductivity under various conditions (from 20% relative humidity to 80%) at 80°C.

Example 5: PAN Copolymer based Composite membrane Used MEA Manufacture of

In order to evaluate single cell performance, 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.) Membrane electrode assemblies (MEA) were manufactured using the composite membrane prepared by as an electrolyte membrane. The active surface area of the electrode was 25 cm ² . The prepared membrane electrode assembly was activated with hydrogen at the cathode and air at the anode at 70° C. for 24 hours (stoichiometric coefficient = 1.2/2). Then, using a test station (FCT-TS300, Fuel Cell Technologies, Inc.), the backpressure for the membrane electrode assembly was 0, 70° C., at 100% relative humidity, at a stepwise change of 50 mV per 25 seconds from 0.5 V to 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 in the range of 10 mHz to 1 MHz. After purging with nitrogen for 30 minutes with the anode, the degree of hydrogen crossover of a DC power supply (Agilent N5744A) was measured. A working electrode and a reference electrode were connected to the positive and negative electrodes, respectively, and a potential of 0.15 to 0.3 V was applied to the single cell. The current generated when hydrogen passed through the film from the cathode oxidized at the anode was recorded.

result

The morphological properties of the electrospun PAN nonwoven fabric having a feasible oxidative stability of 450 kg/mol molecular weight (Mw) prepared according to Example 2 were analyzed using SEM images. 3A and 3B 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. In the PAN nonwoven fabric, the diameter of the fibers was determined in the range of 600 nm to 1200 nm, and the PAN fibers were somewhat dissolved and appeared to bind 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 nonwoven fabric was about 1 μm, and was uniformly distributed in the range of 0.5 μm to 1.5 μm. In addition, it was confirmed that it had a porosity of 80% using the weight and volume of the PAN nonwoven fabric.

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

5 is a diagram showing a real image and SEM images of the surface and side surfaces of a composite film (hereinafter referred to as PAN/SP50) manufactured using a PAN nonwoven fabric and SPAES50 according to Example 3. The composite film has a black color due to the oxidative PAN substrate (FIG. 5A). The SPAES50 copolymer was successfully impregnated into the PAN nonwoven (FIG. 5B ). Pore 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 positioned at the center of the membrane. The thickness of the composite film was about 35 μm (Fig. 5c).

In general, the multi-fibrous substrate contributes to strengthening the mechanical properties of the polymer composite membrane. In order to confirm the mechanical change, the tensile strength test of the composite membrane was performed in a completely hydrated state at room temperature. The results are shown in Table 1 below. The Young's modulus and yield strength of a film for use in PEMFC are important factors for durability during driving. When a change is caused by an external force, these properties represent 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 the value for Nafion 212 (112.6 MPa). In addition, the yield strength of the film showed a similar tendency to the 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). These mechanical properties are an important factor in operating PEMFC under extreme conditions. Another property involved in durability is the dimensional change in water. In order to achieve optimal proton conduction, the membrane needs water while PEMFC is running. Thus, the membrane absorbs water through sulfonic acid groups and the volume expands due to the absorbed water. However, this expanded membrane weakens as the amount of absorbed water increases. 6 shows the dimensional change of the composite membrane and the pure polymer membrane compared with Nafion 212. The high dimensional change of SPAES50 decreased from 91% to 50% in PAN/SP50, and it was confirmed that 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 because the swelling of the membrane is inhibited by the PAN nonwoven fabric, as shown in FIG. 6. The area-based expansion rate of PAN/SP50 was around 19%, which was lower than the 26% value for Nafion 212. From this, it was confirmed that the water absorption rate is involved in the dimensional change, and the measured values are shown in Table 1 below.

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 nonwoven - - - 704.6±37.6 15.8±0.3 -

The proton conductivity of the composite membrane was confirmed while changing the temperature in the fully hydrated condition, and the results are shown in FIG. 7 compared with the pure polymer membrane and Nafion 212. As the temperature increased from 25°C to 80°C, the proton conductivity of all membranes used for the measurement increased. The proton conductivity of PAN/SP50 was 0.062 S/cm and 0.164 S/cm, respectively, at 25°C and 80°C at 100% relative humidity, and both were lower than the values for SPAES50 (0.092 S/cm and 0.181 S/cm). . The IEC value for PAN/SP50 was also 1.71 meq/g, which, as expected, was lower than the value for SPAES50 (2.01 meq/g). Therefore, the degree of decrease in 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 of 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 plotted against the inverse of the absolute temperature was calculated to determine the activation energy (E _a ). Nafion 212 (10.9 kJ/mol) and SPAES50 (10.7 kJ/mol) recorded similar activation energy, but PAN/SP50 showed increased activation energy up to 15.7 kJ/mol. This is also described in Table 1 above. These results indicate that the PAN nonwoven fabric increases the minimum energy for proton transport and decreases the proton conductivity in the composite membrane. In addition, in order to confirm the proton conductivity at low relative humidity, experiments were performed under conditions of 20% and 80% relative humidity. As a result, as the relative humidity decreases, the number of water molecules around the membrane capable of transporting protons decreases significantly, and thus the proton conductivity in all membranes decreases as the humidity decreases. At low relative humidity, SPAES50 exhibited a 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 has the lowest connectivity among the membranes used in the measurement, since the PAN nonwoven fabric acts as a proton barrier, thus exhibiting the lowest proton conductivity at low relative humidity (FIG. 8).

In order 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 MEA and is calculated by the high frequency intercept value of x axis (Z _Re ). When using the same catalyst system in MEA, OCR is affected by membrane resistance. 9 shows the OCR of SPAES50 and PAN/SP50 at 70° C./100% relative humidity, each of which was 0.0072 Ω and 0.0092 Ω. The results are calculated from the reciprocal of the OCR value, indicating that SPAES50 has a proton conduction ability that is about 20% higher than that of PAN/SP50. This difference in performance is due to the porosity of the PAN nonwoven. Then, the performance of the single cell equipped with SPAES50, PAN/SP50 and Nafion 212 was confirmed by comparing the pure polymer membrane and the composite membrane. At 70° C./100% relative humidity, the current density of PAN/SP50 was 1012 mA/cm ² at 0.6 V, which was slightly lower than the value for SPAES50 (1109 mA/cm ² ) (FIG. 10). However, PAN/SP50 showed comparable performance to Nafion 212 (1053 mA/cm ² at 0.6V). This indicates that the cell performance level correlates with the proton conductance results (FIG. 10A). The relative performance improvement of PAN/SP50 is because it can be molded thinner compared to SPAES50 (45 μm) and Nafion 212 (50 μm), and consequently, cell resistance can be reduced by shortening the proton path. When the measurement conditions are 70℃/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 that of Nafion 212 (884 mA/cm ² ). Therefore, in the low relative humidity condition, the same result was obtained for the proton conductivity.

11 shows the results of testing the membrane durability while driving the cell under a rigorous condition. The durability protocol used was a method using hydration/dehydration cycling and OCV hold method to simultaneously check physical and chemical failure characteristics. The hydration/dehydration cycle time was a total of 10 minutes (5 minutes each). SPAES50 decreased to less than 0.9 V after about 500 cycles, while PAN/SP50 continued up to 1000 cycles due to the reinforcing effect of PAN nonwoven fabric. This indicates that the polymer nanofibers can improve the durability of the membrane while operating the PEMFC under various conditions. Hydrogen cross-mixing occurs as the diffusion of hydrogen gas through the membrane from the cathode to the anode. In PEMFC, membrane damage can be confirmed by determining whether or not diffusion of the hydrogen gas occurs. Figure 12 shows the hydrogen cross-mixing of SPAES50 and PAN/SP50 according to the hydration/dehydration cycle. The initial levels of hydrogen cross-mixing of SPAES50 and PAN/SP50 were hardly noticeable. This was confirmed as a low current density (0.001 A/cm ² ). However, after 500 cycles, the hydrogen cross-mixing of SPAES50 increased significantly to 0.012 A/cm ² . For PAN/SP50, it increased to 0.006A/cm ² after 1000 cycles, which was only half of the value measured after 500 cycles of SPAES50. In addition to reducing OCV, hydrogen cross-mixing clearly demonstrated membrane damage during fuel cell operation. Through the analysis of the single cell performance and durability evaluation results of SPAES50 and PAN/SP50, it was confirmed that the composite membrane including the electrospun PAN nonwoven fabric can be usefully used for PEMFC.

conclusion

A novel composite film was successfully developed by impregnating SPAES50 into the PAN resin nonwoven fabric. The PAN nonwoven fabric for manufacturing a composite film suitable for long-time driving under various conditions was manufactured by electrospinning. The PAN nonwoven fabric was analyzed by measuring the fiber thickness, pore size and porosity. It was confirmed that the introduction of PAN nonwoven fabric is an effective means to improve not only mechanical properties but also dimensional stability. However, by blocking the proton conduction path by the PAN nonwoven fabric, the proton conductance was decreased in the composite membrane compared to the pure polymer membrane. For single cell driving, the composite membrane not only exhibited improved durability compared to the pure polymer membrane, but also exhibited similar levels of performance. The excellent durability of the composite membrane was confirmed again by hydrogen cross-mixing. This advantage of the composite membrane using PAN nonwoven fabric can improve the membrane technology for PEMFC application.

Claims (14)

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 therewith,
The PAN copolymer contains 1 to 10% by weight of a unit including alkoxycarbonyl or alkanonoxy in an ethylene skeleton and side chain,
The oxidation is a composite electrolyte membrane, characterized in that it is carried out for 0.5 to 4 hours at 200 to 300 ℃.
delete The method of claim 1,
The composite electrolyte membrane to form a hexagonal ring by forming a bond between the nitrogen atom of the side chain nitrile group and the carbon atom of the adjacent nitrile group by the oxidation.
delete The method of claim 1,
Units containing alkoxycarbonyl or alkanonoxy in the ethylene skeleton and side chains are methyl methacrylate (MMA), methyl acrylate, and vinyl acetate. acetate) will be selected from the group consisting of a composite electrolyte membrane.
The method of claim 1,
The composite electrolyte membrane, characterized in that the concentration of the PAN copolymer solution is 8 to 15% by weight.
The method of claim 1,
The composite electrolyte membrane, characterized in that the support has a porosity of 60 to 80%.
The method of claim 1,
The composite electrolyte membrane, characterized in that the support has pores with an average diameter of 0.5 to 1.5 μm.
The method of claim 1,
A composite electrolyte membrane characterized by having 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 it is a polymer of the following formula (1):
[Formula 1]

In the above formula, l, m and n are each independently an integer of 1 or more.
The method of claim 1,
The composite electrolyte membrane, characterized in that the hydrocarbon-based polymer electrolyte has a degree of sulfonation of 40 to 60 mol%.
A nonwoven fabric formed by electrospinning a polyacrylonitrile copolymer solution is oxidized,
The polyacrylonitrile copolymer contains 1 to 10% by weight of a unit including alkoxycarbonyl or alkanonoxy in an ethylene skeleton and side chain, and the side chain nitrile through oxidation A porous support, characterized in that a hexagonal ring is formed while a bond is formed between the nitrogen atom of the group and the carbon atom of the adjacent nitrile group, and the oxidation is performed at 200 to 300° C. for 0.5 to 4 hours.
A membrane-electrode assembly (MEA) comprising the composite electrolyte membrane according to any one of claims 1, 3, and 5 to 11 as an electrolyte membrane.
A fuel cell comprising the membrane-electrode assembly according to claim 13.

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