KR101827897B1 - Composite polymer electrolyte membrane for fuel cell, and method of manufacturing the same - Google Patents

Abstract

A composite polymer electrolyte membrane for a fuel cell is manufactured through the following production process: Spraying a hydrogen-ion conductive polymer electrolyte solution on a porous support through a spray process, so that the inside of pores of the porous support is partially Filling with a conductive polymer electrolyte solution; Drying the hydrogen ion conductive polymer electrolyte solution sprayed on the porous support; And a cold isostatic pressing (CIP) process is performed on the porous support in which the pores inside are partially or wholly filled with the proton conductive polymer electrolyte to remove the remaining pores that are not completely filled with the proton conductive polymer electrolyte To do.

Description

Technical Field [0001] The present invention relates to a composite polymer electrolyte membrane for a fuel cell,

The present invention relates to a composite polymer electrolyte membrane for a fuel cell and a method of manufacturing the same. More particularly, the present invention relates to a composite polymer electrolyte membrane for a PEMFC (Polymer Electrolyte Membrane Fuel Cell) and a method of manufacturing the same.

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a type of fuel cell that is attracting attention as a next generation energy source. It is a fuel cell that uses a polymer membrane having hydrogen ion exchange characteristics as an electrolyte. In order to improve initial performance and ensure long-term performance, such a polymer electrolyte fuel cell (PEMFC) includes a polymer electrolyte membrane having not only electrical insulation but also high hydrogen ion conductivity, low electronic conductivity and gas permeability, high mechanical strength and dimensional stability Is required.

On the other hand, as a polymer electrolyte membrane for a polymer electrolyte fuel cell (PEMFC), a pure perfluoropoly sulfonated polymer electrolyte membrane such as a Nafion single membrane of DuPont is currently commercialized and most widely used. However, the pure perfluoropoly sulfonated polymer electrolyte membrane has a high unit cost despite its excellent chemical resistance, oxidation resistance and ion conductivity, has a low mechanical and morphological stability, and has a problem of having a hydrogen ion conductivity which is rapidly reduced at a temperature of 100 ° C or higher , There is an increasing demand for new polymer electrolyte membranes having excellent properties as described above, yet economical.

As one approach to this, research on a composite polymer electrolyte membrane using a porous support has been actively conducted. This can reduce the resistance during operation of the fuel cell, and can be realized to have excellent mechanical and morphological stability while having excellent characteristics as described above. Thus, it is possible to solve various problems of existing polymer electrolyte membranes .

However, since it is considerably difficult to uniformly impregnate the polymer electrolyte uniformly and tightly, that is, completely impregnated into the pores of the porous support, it is practically possible to implement a composite polymer electrolyte membrane.

Korean Patent Publication No. 10-2008-0040225

Effect of triton-X on the preparation of nafion / PTFE composite membrane, Journal of membrane science 237.1 (2004): 1-7

It is an object of the present invention to provide a fuel cell which is realized in the form of a uniform composite thin film including a porous support and has a high hydrogen ion exchange property and low electron conductivity as well as an improved gas permeability and excellent mechanical strength against thickness, To provide a composite polymer electrolyte membrane for a fuel cell which is easy to manufacture and a method for producing the same.

In order to accomplish one object of the present invention, there is provided a method of manufacturing a composite polymer electrolyte membrane for a fuel cell, comprising the steps of: spraying a proton conductive polymer electrolyte solution Injecting the porous support into the pores of the porous support to partially or wholly fill the pores of the porous support with the hydrogen ion conductive polymer electrolyte solution; Drying the hydrogen ion conductive polymer electrolyte solution sprayed on the porous support; And a cold isostatic pressing (CIP) process is performed on the porous support in which the pores inside are partially or wholly filled with the proton conductive polymer electrolyte to remove the remaining pores that are not completely filled with the proton conductive polymer electrolyte To do.

In exemplary embodiments, through the method, the interior of the pores of the porous support can be completely filled with the proton conductive polymer electrolyte.

In exemplary embodiments, the proton conductive polymer electrolyte solution may be a perfluorinated sulfonic acid ionomer (PFSA ionomer) solution, and the porous support may be a porous fluorinated polymer support.

In exemplary embodiments, the perfluorinated sulfonated ionomer solution may comprise about 1 to 20 wt% of a perfluorinated sulfonated ionomer, based on the total weight of the perfluorinated sulfonated ionomer solution.

In exemplary embodiments, during the spray process, the proton conductive polymer electrolyte solution may be injected at a flow rate of about 2 to 6 ml / min under a pressure of about 2 to 4 bar.

In exemplary embodiments, the proton-conducting polymer electrolyte solution may be injected in the direction of gravity.

In exemplary embodiments, the porous support may be treated with acetone, methanol, ethanol, propanol or hydrogen peroxide prior to performing the spray process.

In the illustrative embodiments, the cold isostatic pressing (CIP) process is a process wherein the porous support, in which the pores are partially or wholly filled with hydrogen-ion conductive polymer electrolyte, is sealed in a rubber-made container, To adhere the porous support to the container using a vacuum pump; And applying a isostatic pressure to the container containing the porous support using a cold isostatic pressing device containing a buffer solution.

In exemplary embodiments, the isotropic pressure may be between about atmospheric pressure and 300 MPa isotropic pressure.

A composite polyelectrolyte membrane for a fuel cell according to exemplary embodiments for achieving an object of the present invention is manufactured through the above-described manufacturing method, and comprises a porous support; And a proton conductive polymer electrolyte which completely fills the inside of the pores of the porous support. The composite polymer electrolyte membrane of about 0.5mA / cm ² of hydrogen crossover current density (H ₂ crossover current density) value equal to or less than can be represented.

In exemplary embodiments, the porous support may be a porous fluorinated polymeric support and may be treated with acetone, methanol, ethanol, propanol or hydrogen peroxide.

In exemplary embodiments, the proton conductive polymer electrolyte may be a perfluorinated sulfonic acid ionomer (PFSA ionomer), and the proton conductive polymer electrolyte may be combined with the porous support.

In exemplary embodiments, the composite polyelectrolyte membrane may have a thickness of less than about 10 [mu] m to less than 25 [mu] m.

In the exemplary embodiments, the composite polymer electrolyte membrane may constitute a membrane electrode assembly of a polymer electrolyte fuel cell.

The composite polyelectrolyte membrane for a fuel cell according to the present invention can be manufactured in the form of a uniform composite membrane containing a porous support by sequentially performing a treatment process, a spray process, a drying process, and a cold isostatic pressing process. Particularly, by performing the cold isostatic pressing process after the spraying process, the interior of the porous support pores distributed in a three-dimensional net structure, rather than a simple vertical direction, is exposed to a hydrogen ion conductive polymer electrolyte I.e., substantially completely filled with water. Accordingly, the composite polymer electrolyte membrane may not substantially contain residual pores or voids that are not sufficiently filled with the proton conductive polymer electrolyte, and physical and / or chemical damage or deterioration may not occur. As a result, the composite polymer electrolyte membrane can have improved hydrogen ion exchange characteristics, electron conductivity, mechanical strength, dimensional stability, and particularly, a low gas permeability, which is superior to or better than that of conventional polymer electrolyte membranes for fuel cells.

In addition, since the composite polymer electrolyte membrane can be manufactured using a hydrogen ion conductive electrolyte such as a high-priced perfluorocarbon sulfonated ionomer in a minimum amount, the polymer electrolyte membrane can have an additional advantage in terms of price competitiveness compared to a conventional polymer electrolyte membrane for a fuel cell.

Therefore, a membrane electrode assembly having excellent performance and a fuel cell including the membrane electrode assembly can be easily realized through the composite polymer electrolyte membrane for a fuel cell.

1 is a schematic diagram showing a cold isostatic pressing (CIP) process for producing a composite polymer electrolyte membrane according to exemplary embodiments of the present invention.
FIG. 2 is a schematic diagram showing a hot pressing process used for manufacturing a conventional composite polymer electrolyte membrane.
3 is a SEM photograph showing the surfaces (a, c and e) and cross sections (b, d and f) of the composite polymer electrolyte membranes prepared according to Examples and Comparative Examples 1 and 2.
4 is a graph showing a current-voltage change (a) and a power density change (b) of the composite polymer electrolyte membranes prepared according to Examples and Comparative Examples 1 and 2.
5 is a graph showing the electrochemical characteristics of a single cell including a composite polymer electrolyte membrane prepared according to Examples and Comparative Examples 1 and 2, measured through a cyclic voltammetry (CV) It is a graph.
6 is a graph showing the hydrogen crossover current density of single cells comprising the composite polymer electrolyte membranes prepared according to Examples and Comparative Examples 1 and 2, measured through Linear Sweep Voltammetry (LSV) (H ₂ crossover current density).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The embodiments of the present invention disclosed in the present specification are for illustrative purposes only and the embodiments of the present invention can be embodied in various forms and should not be construed as limited to the embodiments described in the text .

It is to be understood that the invention is not to be limited to the specific forms disclosed, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention, As will be understood by those skilled in the art.

The combination or complexation in the present specification means that the perfluoropolyether sulfonate polymer electrolyte (ionomer), which is a polymer electrolyte having proton conductivity, is physically and / or chemically bonded to the porous fluorinated polymer scaffold to have a more effective function .

The hydrogen cross-over (H ₂ crossover) in the description field, an anode (anode) means a hydrogen permeable phenomenon occurs going beyond the cathode (cathode) electrode is a hydrogen has not reacted at the electrode through the electrolyte membrane polymer and, through which the polymer electrolyte The gas permeability of the membrane can be measured. Such a hydrogen crossover phenomenon, that is, an undesirable gas diffusion from the anode electrode to the cathode electrode is known to be a main cause of the deterioration of the perfluorinated electrolyte membrane, and generally, the thinner the thickness of the electrolyte membrane, the easier it is. In the present invention, in order to confirm the occurrence of the hydrogen crossover phenomenon and the hydrogen crossover current density, hydrogen is supplied to the anode electrode and nitrogen is supplied to the cathode electrode, and a voltage of 0V to 0.6V (vs. Anode) section of the battery.

The term 'cold isothatic pressing (CIP)' as used herein means a process of uniformly delivering a high pressure in all directions to a desired material by using a liquid such as water as a pressure medium.

Composite Polymer Electrolyte Membrane for Fuel Cell

The composite polymer electrolyte membrane of the present invention is an electrolyte membrane for a fuel cell, specifically, an electrolyte membrane capable of forming a membrane electrode assembly (MEA) of a polymer electrolyte fuel cell (PEMFC). The composite polymer electrolyte membrane includes a porous support and a proton conductive polymer electrolyte. At this time, the inside of the pores of the porous support may be uniformly and closely filled with the hydrogen-ion conductive polymer electrolyte, that is, substantially completely, so that the composite polymer electrolyte membrane may have substantially no residual pores or voids. Therefore, since the composite polymer electrolyte membrane of about 0.5mA / cm ² of hydrogen crossover current density of less than the indicated (H ₂ crossover current density) of the low gas permeability it is extremely excellent in gas permeability.

The porous support has hydrogen ion conductivity. In addition, it has a plurality of pores in a three-dimensional network structure inside, and contributes to enhancement of mechanical strength and morphological stability of the composite polymer electrolyte membrane. As such a porous support, for example, a porous fluorinated polymer support such as a porous polytetrafluoroethylene (PTFE) support may be used. The porous fluorocarbon polymer scaffold is chemically stable due to the strong binding force between carbon and fluorine and the blocking effect, which is a characteristic of fluorine atoms, and is excellent in both mechanical properties and hydrogen ion conductivity, and thus can be usefully used in the present invention.

In exemplary embodiments, the porous support may be one treated with acetone, methanol, ethanol, propanol or hydrogen peroxide. Porous fluorinated polymer scaffolds such as porous polytetrafluoroethylene (PTFE) scaffolds have hydrophobicity, so they are more familiar with air than the hydrophilic conductive polymer electrolyte, and have lower wettability. Therefore, it may be difficult to realize a composite polymer electrolyte membrane having a uniform and dense internal structure without residual pores or voids, despite the advantages described above. However, by treating with acetone, methanol, ethanol, propanol or hydrogen peroxide, the porous fluorinated polymer scaffold may have improved wettability and may further contain no impurities on the interior and / or the surface.

The improved wettability of the porous fluorinated polymer scaffold is advantageous for filling the pores of the porous fluorinated polymer scaffold more uniformly and densely, that is, substantially completely with the hydrogen ion conductive electrolyte. Accordingly, the composite polymer electrolyte membrane can have a high film density, and as a result, can have a further improved mechanical strength. In addition, since the interval between the hydrophilic ion domains is narrowed within the polymer electrolyte membrane, the composite polymer electrolyte membrane can have increased ionic conductivity and dimensional stability.

The proton conductive polymer electrolyte may be a perfluorinated sulfonic acid ionomer (PFSA ionomer) such as a Nafion ionomer. Since the perfluorinated sulfonated ionomer (PFSA) has the same structure as the main chain of polytetrafluoroethylene (PTFE), it can have a high chemical affinity for the porous fluorinated polymer scaffold. Therefore, the perfluorinated sulfonated ionomer (PFSA ionomer) and the porous fluorinated polymer scaffold can be strongly bonded to each other to be complexed, and this combination can ultimately contribute to the improved stability of the composite polymer electrolyte membrane.

The composite polymer electrolyte membrane can be formed in a thin film form without having deteriorated properties such as low hydrogen ion exchange characteristics, high electron conductivity and gas permeability due to electrolyte shortage, and the inside of all the pores of the porous fluorine- May contain a perfluorinated sulfonated ionomer in a suitable amount that can be filled. On the other hand, the performance of the composite polymer electrolyte membrane can be improved in proportion to the content of the perfluorinated sulfonated ionomer. However, if an excessive amount of perfluorinated sulfonated ionomer is contained in excess, the manufacturing cost may increase, Implementation of a polymer electrolyte membrane may be difficult.

The composite polymer electrolyte membrane may have a thickness of, for example, less than about 10 占 퐉 to less than 25 占 퐉. Conventional polymer electrolyte membranes for fuel cells, such as Nafion electrolyte membranes, generally have a thicker thickness of about 25 탆 or more for enhanced mechanical properties, which are composed of a pure perfluoropoly sulfonated polymer electrolyte. However, since the increase in the thickness of the electrolyte membrane increases not only the mechanical characteristics but also the resistance of the membrane, the ionic conductivity of the electrolyte membrane may decrease in proportion to the thickness of the electrolyte membrane. On the other hand, since the composite polymer electrolyte membrane of the present invention has a high film density and mechanical properties as described above, it has a relatively thin thickness of, for example, about 10 탆 to less than 25 탆, And may have ion conductivity and mechanical properties substantially equal to or higher than those of the polymer electrolyte membranes. That is, the composite polymer electrolyte membrane can have hydrogen ion exchange property and mechanical strength which are excellent in the thickness.

As described above, the composite polymer electrolyte membrane of the present invention is realized in the form of a uniform composite thin film including a porous support, which not only has excellent mechanical strength against thickness, but also has a high hydrogen ion exchange property and low electron conductivity, Respectively. In addition, since the composite polymer electrolyte membrane has excellent characteristics as described above in comparison with a conventional polymer electrolyte membrane while containing a relatively high amount of perfluorinated sulfonated ionomer (e.g., Nafion ionomer) in a relatively small amount It can have additional advantages in terms of price competitiveness.

Accordingly, it is possible to easily realize a membrane electrode assembly (MEA) having excellent performance and a fuel cell including the same. Particularly, since the composite polymer electrolyte membrane has high mechanical strength, the fuel cell stack can be easily manufactured without damaging the electrolyte membrane.

METHOD FOR PRODUCING POLYMER ELECTROLYTE MEMBRANE FOR FUEL CELL

The composite polymer electrolyte membrane of the present invention can be produced by performing the following processes with reference to FIG.

Although not specifically shown, the porous support as described above is treated with acetone, methanol, ethanol, propanol or hydrogen peroxide.

In exemplary embodiments, the porous fluoropolymer support may be washed with acetone, methanol, ethanol, propanol or hydrogen peroxide as the porous support. Accordingly, the porous fluorocarbon polymer scaffold can have impurities removed from the inside and / or the surface thereof, and can have improved wettability.

Although not specifically shown, a hydrogen ion conductive electrolyte solution is sprayed through a spray process onto a porous support treated with acetone, methanol, ethanol, propanol or hydrogen peroxide. The proton conductive electrolyte solution is a solution containing the same proton conductive electrolyte as described above, for example, a solution of a perfluorinated sulfonated ionomer (PFSA ionomer) can be used. Through the spray process, a plurality of pores distributed in a three-dimensional net structure inside the porous support may be at least partially filled with the hydrogen ion conductive electrolyte solution (perfluorinated sulfonated ionomer solution).

In exemplary embodiments, the spraying process may be performed by fixing the treated porous fluoropolymer support to a mold made in a predetermined shape, fixing the porous fluoropolymer support to a predetermined shape using a spray gun connected to a gas cylinder, And spraying a perfluorinated sulfonated ionomer solution. At this time, the perfluorinated sulfonated ionomer solution can be sprayed at a flow rate of about 2 to 6 ml / min under a pressure of about 2 to 4 bar so that the porous fluorocarbon based support can be evenly sprayed without being damaged. In particular, in one embodiment, the perfluorinated sulfonated ionomer solution may be injected in the direction of gravity. In this case, when the perfluorinated sulfonated ionomer solution is injected into the injected perfluorinated sulfonated ionomer solution in the same direction and the injected perfluorinated sulfonated ionomer solution is injected in a direction other than the direction of gravity, The inside of the pores of the support can be more effectively filled.

On the other hand, in exemplary embodiments, in performing the spray process, the perfluorinated sulfonated ionomer solution may contain about 1 to about 20 wt%, based on the total weight of the perfluorinated sulfonated ionomer solution, Of a perfluorinated sulfonated ionomer. When the content of the perfluorinated sulfonated ionomer in the perfluorinated sulfonated ionomer solution exceeds about 15 wt%, the viscosity of the perfluorinated sulfonated ionomer solution gradually increases and the perfluorinated sulfonated ionomer content increases to about 20 wt% %, The perfluorinated sulfonated ionomer solution may not be uniformly sprayed due to the high viscosity.

Although not specifically shown, the hydrogen ion conductive polymer electrolyte solution sprayed on the porous support is dried through a drying process. Thus, the solvent in the solution is volatilized and only the hydrogen ion conductive polymer electrolyte, for example, the perfluorinated sulfonated ionomer, as described above, may remain in the porous support pores.

In exemplary embodiments, the drying process may be performed by placing a porous fluoropolymer support, in which pores at least partially filled with the perfluorocompound sulfonated ionomer solution, into an oven and then primarily drying for about 1 to 2 hours , Followed by secondary drying for a longer time than the primary drying, for example, about 12 hours. At this time, the primary drying and the secondary drying may both be performed sufficiently at a temperature at which the solvent in the solution can sufficiently volatilize and the perfluorinated sulfonated ionomer is not decomposed or changed by heat, for example, about 60 ° C.

Referring to FIG. 1, a cold isostatic pressing (CIP) process is performed on a porous support in which pores at least partially filled with the proton conductive polymer electrolyte. Accordingly, residual pores which may not be completely filled with the proton conductive polymer electrolyte may be removed from the above-described processes.

In the exemplary embodiments, the cold isostatic pressing (CIP) process is a process in which a porous fluorinated polymeric support, in which the pores therein are at least partially filled with a perfluorinated sulfonated ionomer, The porous fluoropolymer support was brought into close contact with the container (frame) using a vacuum pump so that the pressure could be evenly received, and then the porous fluoropolymer support was attached to the container using a cold isostatic pressing device containing a buffer solution. It is possible to proceed by applying an isotropic pressure to a container (frame) containing the polymer scaffold. At this time, since the porous fluorinated polymer scaffold is enclosed in the container (frame), it may not be contaminated by the buffer solution.

In exemplary embodiments, the isotropic pressure may be between about atmospheric pressure and 300 MPa isotropic pressure. For example, since a high pressure of about 250 MPa can be applied to the porous fluoropolymer support uniformly in all directions, residual pores that may be present because of not being completely filled with the perfluorinated sulfonated ionomer can be effectively removed.

Unlike the production method of the present invention as described above, in the production of a polymer electrolyte membrane for a fuel cell, particularly a composite polymer electrolyte membrane, conventionally, a dipping process, a casting process, a coating process ). However, such processes may be difficult to fill the inside of the pores of the porous support containing a fluorine-based polymer such as a porous support, particularly hydrophobic polytetrafluoroethylene, with a hydrophilic polymer electrolyte (hydrogen ion conductive polymer electrolyte). When the pores of the porous support are not sufficiently filled, residual pores are present in the composite polymer electrolyte membrane, thereby deteriorating the performance of the membrane due to the permeation of the fuel. In addition, since the radical of the fuel cell, including the composite polymer electrolyte membrane, And can act as a cause of deteriorating the film.

Moreover, the dipping process, casting process, coating process and the like are generally required to be repeated several times, resulting in complications during manufacture, and nonetheless, the polymer electrolyte There may be residual pores that are not sufficiently filled and the post-treatment process such as a hot pressing process must be additionally performed after the execution of the processes.

However, this thermocompression process is a process which is carried out by placing a porous support, in which the internal pores are at least partially filled with a polymer electrolyte, between two hot plates and applying pressure thereto, Through this, pressure is normally applied only in a simple vertical direction. Therefore, there may still be a limit to the removal of a large number of pores (residual pores which are not completely filled with the proton conductive polymer electrolyte), which are distributed in a three-dimensional net structure rather than a simple vertical direction.

In addition, the porous support and the polymer electrolyte can be easily damaged by heat and pressure during the thermocompression process. For example, a perfluorinated sulfonated ionomer used as a polymer electrolyte has a sulfonic acid group and thus has a characteristic of being decomposed at a temperature above a certain temperature because it is temperature-sensitive. Therefore, in order to prevent decomposition of the polymer electrolyte by the heat applied during the thermocompression process, various factors such as the glass transition temperature and the decomposition temperature of the polymer electrolyte should be considered. In order to investigate the thermal characteristics of the polymer electrolyte, (Differential scanning calorimetry, DSC) or thermogravimetric analysis (TGA).

Particularly, in order to perform a thermocompression process at a high temperature of 200 ° C or more, a process of replacing a polymer electrolyte, for example, a perfluorinated sulfonated ionomer, into a heat-resistant form is required. That is, a further step of replacing H + ions with Na + ions in the sulfonic acid group (-SO ₃ H) is required. Since the replacement process requires a long time, the composite polymer electrolyte membrane produced through the process is inevitably disadvantageous for mass production .

As a result, the temperature and pressure that can be applied through the thermocompression process are not sufficiently high, and thus it is difficult to easily manufacture a composite polymer electrolyte membrane having excellent performance without defects in the conventional manufacturing method.

However, the composite polymer electrolyte membrane according to the present invention can be produced in the form of a uniform composite membrane containing a porous support by sequentially performing the above-mentioned treatment process, spray process, drying process, and cold isostatic pressing process . Particularly, by performing the cold isostatic pressing process after the spraying process, the interior of the porous support pores distributed in a three-dimensional net structure, rather than a simple vertical direction, is exposed to a hydrogen ion conductive polymer electrolyte I.e., substantially completely filled with water. Therefore, the composite polymer electrolyte membrane may not substantially contain residual pores or voids that are not sufficiently filled with the proton conductive polymer electrolyte, and physical and / or chemical damage or deterioration may not occur. As a result, the composite polymer electrolyte membrane can have improved hydrogen ion exchange characteristics, electron conductivity, mechanical strength, dimensional stability, and particularly, a low gas permeability, which is superior to or better than that of conventional polymer electrolyte membranes for fuel cells.

In addition, since the composite polymer electrolyte membrane can be manufactured using a hydrogen ion conductive electrolyte such as a high-priced perfluorocarbon sulfonated ionomer in a minimum amount, the polymer electrolyte membrane can have an additional advantage in terms of price competitiveness compared to a conventional polymer electrolyte membrane for a fuel cell.

Although the composite polymer electrolyte membrane for a fuel cell and the method for producing the same have been described so far, membrane electrode assemblies composed of the composite polymer electrolyte membrane as described above, and all fuel cells including the same, for example, polymer electrolyte fuel cells PEMFC) is also included in the scope of the present invention will be apparent to those skilled in the art.

The present invention will be described in more detail through the following embodiments. However, the examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

[Example]

The porous polytetrafluoroethylene support (GORE PTFE, GMM-405) was washed with acetone (Sigma Aldrich) to remove impurities and improve wettability.

 The porous polytetrafluoroethylene support washed with acetone was fixed flat and firmly using a Teflon tape to a frame made to have a uniform shape. Then, a spray gun (EWATA spray gun, W-300-101G ), Nafion resin solution (5 wt% of Nafion perfluorinated resin solution, Sigma Aldrich) was evenly sprayed on a porous polytetrafluoroethylene support at a certain distance. At this time, the Nafion resin solution was sprayed at a flow rate of 2 to 6 ml / min under a pressure of 2 to 4 bar in the gravity direction.

The porous polytetrafluoroethylene support onto which the Nafion resin solution was sprayed was first dried in an oven at 60 ° C for 1 hour and then dried in a vacuum oven at the same temperature for 12 hours for 12 hours to remove the solvent in the sprayed Nafion resin solution All were volatilized. Thus, the porous polytetrafluoroethylene support was impregnated with 0.097 g of Nafion ionomer, and the porous polytetrafluoroethylene support having the pores therein filled with Nafion ionomer had a thickness of 20 μm.

Then, the porous polytetrafluoroethylene support having pores filled with Nafion ionomers was sealed in a frame made of a rubber material so as not to be contaminated by the buffer solution, and the porous polytetrafluoroethylene support was completely adhered to the frame by using a vacuum pump To receive. The frame containing the porous polytetrafluoroethylene support was placed in a cold isostatic pressing (CIP) apparatus and a pressure of 250 MPa was applied for 5 minutes.

A composite polymer electrolyte membrane having a thickness of 20 袖 m was finally prepared through the above-described processes, and then the membrane electrode assembly and the unit cell including the membrane electrode assembly were prepared by using the following processes.

A catalyst solution was prepared by dissolving 46.5 wt% Pt / C catalyst in Nafion ionomer and isopropyl alcohol (Sigma Aldrich) solvent. The composite polymer electrolyte membrane was spread and fixed, and then the catalyst solution was sprayed onto the composite polymer electrolyte membrane using a spray gun for catalyst separation. At this time, the catalyst loading amount of the anode was 0.2 mg _pt / cm ² , the catalyst loading amount of the cathode was 0.4 mg _pt / cm ² , and the active area was 1 cm ² . Thereafter, the solvent of the catalyst solution is naturally dried until all of the solvent evaporates, thereby forming a membrane electrode assembly (membrane) assembly including an anode electrode and a cathode electrode arranged to face each other, and a composite polymer electrolyte membrane interposed therebetween, electrode assembly, MEA) were fabricated.

The prepared membrane electrode assembly (MEA) was sequentially tightened at a pressure of 30 In * lb, 50 In * lb, and 70 In * lb by using a gasket made of Teflon and a bipolar plate made of carbon A single cell was fabricated.

[Comparative Example 1]

Except that the cold isostatic pressing step was carried out, a 20 μm thick composite polymer electrolyte membrane containing 0.097 g of Nafion ionomer was prepared.

In addition, a membrane electrode assembly (MEA) and a unit cell including the membrane electrode assembly (MEA) were fabricated using the prepared composite polymer electrolyte membrane.

[Comparative Example 2]

After the drying step, a thermo-compression process was performed in place of the cold isostatic pressing process to prepare a 20 μm thick composite polymer electrolyte membrane containing 0.097 g of Nafion ionomer. At this time, the thermocompression bonding process was performed by weighing 3 tons at 110 캜, which is a temperature near the glass transition temperature of the Nafion ionomer. (Through the thermocompression process, the pressure applied per area on the porous polytetrafluoroethylene support in which the internal pores are filled with Nafion ionomer is about 1.3 MPa in terms of Pa pressure unit)

In addition, a membrane electrode assembly (MEA) and a unit cell including the membrane electrode assembly (MEA) were fabricated using the prepared composite polymer electrolyte membrane.

Experimental Example: Evaluation of Microstructure of Composite Polymer Electrolyte Membrane

In order to evaluate the microstructure of the composite polymer electrolyte membrane, the surface and cross-section of the composite polymer electrolyte membranes prepared according to Examples and Comparative Examples 1 and 2 (the cross-section perpendicular to the plane of the injected Nafion ionomer solution) Were observed and compared using a scanning electron microscope (SEM). The result is as shown in Fig.

3 (a) and 3 (b) are SEM photographs each showing a surface and a cross section of the composite polymer electrolyte membrane prepared according to the embodiment, and FIGS. 3 (c) and 3 (E) and (f) are SEM micrographs showing the surface and cross-section of the composite polymer electrolyte membrane prepared according to Comparative Example 1, respectively.

Referring to FIG. 3, there were a large number of residual pores not sufficiently filled with Nafion ionomer on the surface and cross section of the composite polymer electrolyte membrane prepared according to Comparative Example 1, and the composite polymer electrolyte membrane prepared according to Comparative Example 2 had 1, residual pores were not present on the surface but residual pores were still present on the surface. On the other hand, the composite polyelectrolyte membrane prepared according to the Example did not show a large difference in morphology on the surface of the composite polymer electrolyte membrane prepared according to Comparative Example 2 (see comparison between (a) and (b)), (D), the interval between the results in the transverse direction was remarkably reduced in (b), and it was confirmed that there was almost no existence.

Accordingly, the inside of the pores of the porous support can be more uniformly and closely filled with the proton conductive polymer electrolyte through the cold isostatic pressing process of the present invention than the conventional thermocompression process. As a result, a thin polymerized composite electrolyte Can be easily produced.

Experimental Example: Performance Evaluation of Composite Polymer Electrolyte Membrane I

In order to evaluate the performance of the composite polymer electrolyte membrane, the change in the current-voltage (IV) was measured by operating the unit cells (sigle cells) including the composite polymer electrolyte membrane prepared according to the Examples and Comparative Examples 1 and 2, The density change was measured. At this time, 200cc / min of hydrogen was supplied to the anode, 600cc / min of air was supplied to the cathode, and the current was changed from 0 A to 2.5 A at a rate of 50 mA / s while the corresponding cells were operated. The results are as shown in Fig. 4 and [Table 1]. Specifically, a current-voltage (I-V) variation is shown in FIG. 4 (a) and a power density variation is shown in (b). On the other hand, the performance of the composite polymer electrolyte membrane in the current-voltage (I-V) curve was evaluated based on the OCV (open circuit voltage) and the current density value at 0.6V.

Example Comparative Example 1 Comparative Example 2 Open circuit voltage (OCV) 0.957 0.942 0.952 ^{A / cm 2 @ 0.6V (I} -Vcurve) 1.456 1.231 1.241 ^{mA / cm 2 @ 0.4V (LSV} ) - 1.51 0.78 Maximum power density (W / cm ² ) 1.013 0.887 0.874 Thickness (μm) 20 20 20

Referring to FIG. 4 and Table 1, the performance of the unit cell according to Comparative Example 2 was better than that of the unit cell according to Comparative Example 1, and the single cell according to the Example was significantly superior to the single cell according to Comparative Example 2 (See Fig. 4 (a)).

Particularly, a power density is a product of a current density and a voltage. The performance of the unit cell is evaluated based on a maximum power density. The maximum power density value The higher the performance of the unit cell, the better. 4 (b), the maximum power density of the single cell according to Comparative Example 2 is slightly lower than the maximum power density of the single cell according to Comparative Example 1, slightly different from the tendency shown in (a) , It was confirmed that the maximum power density of the single cell according to the embodiment was significantly higher than the maximum power density of the single cells according to Comparative Examples 1 and 2, and a similar tendency still appeared even in the case of (b).

The composite polyelectrolyte membranes according to Examples and Comparative Examples 1 to 2 contain Nafion ionomers in the same contents and have the same thicknesses. Therefore, the performance characteristics of the single cells as described above may vary depending on the electrolyte membrane morphology It can be understood that it is the origin.

Experimental Example: Performance Evaluation of Composite Polymer Electrolyte Membrane II

In order to evaluate the performance of the composite polyelectrolyte membrane, cyclic voltammetry (CV) and linear sweep voltammetry were performed on the unit cells including the composite polymer electrolyte membrane prepared according to Examples and Comparative Examples 1 and 2, , LSV) were performed. At this time, hydrogen at a flow rate of 200 cc / min was supplied to the anode, and nitrogen at a flow rate of 600 cc / min was supplied to the cathode. The results are shown in Figs. 5, 6, and Table 1.

5 is a graph comparing electrochemical characteristics of the unit cells measured using the cyclic voltammetry (CV) method. FIG. 6 is a graph showing the electrochemical characteristics of the unit cells measured using the cyclic voltammetry (CV) (H ₂ crossover current density) of the hydrogen crossover.

Referring to FIG. 5, the electrochemical active region of the catalyst can be confirmed by observing the adsorption / desorption reaction between the hydrogen supplied during the operation of the unit cell and the platinum electrode of the unit cell through the cyclic voltammetry (CV) method. The graph shows the fifth measured value after ensuring reproducibility by measuring a total of 5 times at a potential scanning speed of 50 mV / s from 0.05 V to 1.2 V. The electrochemically active surface was evaluated based on the hydrogen desorption peaks observed from 0.05V to 0.35V. As a result of comparing the platinum active area in the graph of the circulating current voltage (CV) for the unit cells according to Examples and Comparative Examples 1 and 2, it was found that the electrochemically active regions of the platinum catalyst coincide with each other in each of Examples and Comparative Examples 1 and 2 . It can be seen from the above that the performance of the single cells according to Examples and Comparative Examples 1 and 2 is attributable to the characteristics of the electrolyte membrane included in the cells, not the catalyst.

On the other hand, the LSV was performed at a potential scanning speed of 2 mV / s in a voltage range from 0.0 V to 0.6 V, whereby hydrogen which did not react at the anode was transmitted to the cathode and reacted with the cathode electrode layer the hydrogen crossover current density (H ₂ crossover current density) was measured. At this time, the hydrogen crossover current density was evaluated based on a battery voltage of 0.4 V (see Table 1), and hydrogen gas could easily permeate through the electrolyte membrane as the hydrogen crossover current density became higher (the electrolyte membrane was high Gas permeability ").

Referring to FIG. 6, the hydrogen crossover current density at 0.4 V was 1.51 mA / cm ² according to Comparative Example 1, and the unit cell according to Comparative Example 2 was reduced by about 50% Lt; ² > / cm < ² > This means that the hydrogen purity of the composite polymer electrolyte membrane can be lowered by removing residual pores to some extent through the thermocompression process.

However, it was confirmed that the unit cell according to the Example exhibited a negative value of the hydrogen crossover current density, and thus showed a distinct difference from the single cells according to Comparative Examples 1 and 2. This means that hydrogen gas permeation into the composite polymer electrolyte membrane does not occur because the residual pores are not substantially present in the composite polyelectrolyte membrane manufactured through the cold isostatic pressing process. These results are consistent with the result of the microstructure evaluation of the composite polymer electrolyte membrane as shown in FIG.

Claims (14)

Spraying a hydrogen ion conductive polymer electrolyte solution onto a porous support through a spray process to fill the pores of the porous support with the hydrogen ion conductive polymer electrolyte solution partly or wholly;
Drying the hydrogen ion conductive polymer electrolyte solution sprayed on the porous support; And
A cold isostatic pressing (CIP) process is performed on a porous support having pores filled in with the proton conductive polymer electrolyte partially or entirely to remove residual pores that are not completely filled with the proton conductive polymer electrolyte Wherein the composite polymer electrolyte membrane for fuel cells comprises: The method according to claim 1,
Wherein the pores of the porous support are completely filled with the proton conductive polymer electrolyte through the above method. The method according to claim 1,
The hydrogen ion conductive polymer electrolyte solution is a perfluorinated sulfonic acid ionomer (PFSA ionomer) solution,
Wherein the porous support is a porous fluorinated polymer support. The method of claim 3,
Wherein the perfluorinated sulfonated ionomer solution comprises 1 to 20 wt% of a perfluorinated sulfonated ionomer based on the total weight of the perfluorinated sulfonated ionomer solution. The method according to claim 1,
Wherein the hydrogen ion conductive polymer electrolyte solution is injected at a flow rate of 2 to 6 ml / min under a pressure of 2 to 4 bar during the spraying process. 6. The method of claim 5,
Wherein the hydrogen-ion conductive polymer electrolyte solution is injected in a gravity direction. The method according to claim 1,
Prior to performing the spray process,
Further comprising treating the porous support with acetone, methanol, ethanol, propanol or hydrogen peroxide. The method according to claim 1,
The cold isostatic pressing process (CIP)
Sealing the porous support, which is partially or entirely filled with the proton conductive polymer electrolyte, in a rubber-made container, and bringing the porous support into close contact with the container using a vacuum pump so that pressure can be uniformly received; And
And applying an isostatic pressure to the container containing the porous support by using a cold isostatic pressing device containing a buffer solution. ≪ RTI ID = 0.0 > 11. < / RTI > 9. The method of claim 8,
Wherein the isotropic pressure is an isostatic pressure of atmospheric pressure to 300 MPa. A composite polymer electrolyte membrane produced by the method according to any one of claims 1 to 9, wherein the composite polymer electrolyte membrane comprises
A porous support; And
And a proton conductive polymer electrolyte which completely fills the inside of the pores of the porous support,
0.5mA / cm ² below the hydrogen crossover current density (H ₂ crossover current density) indicating a composite polymer electrolyte membrane for fuel cells of. 11. The method of claim 10,
Wherein the porous support is a porous fluorinated polymer support and is treated with acetone, methanol, ethanol, propanol or hydrogen peroxide. 11. The method of claim 10,
Wherein the hydrogen-ion conductive polymer electrolyte is a perfluorinated sulfonic acid ionomer (PFSA ionomer), and is combined with the porous support to form a complex polymer electrolyte membrane for a fuel cell. 11. The method of claim 10,
Wherein the composite polymer electrolyte membrane has a thickness of less than 10 占 퐉 to 25 占 퐉. 11. The method of claim 10,
The composite polymer electrolyte membrane is a membrane electrode assembly of a polymer electrolyte fuel cell.

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