KR20200097670A - Composite polymer electrolyte membrane for fuel cell coated with nanohole graphene sheet, and method of manufacturing the same - Google Patents

Abstract

Disclosed is a composite polymer electrolyte membrane for a fuel cell, comprising a porous fluorine-based polymer support; and a nanohole graphene sheet. The disclosed composite polymer electrolyte membrane for a fuel cell is capable of showing very excellent durability and performance.

Description

Composite polymer electrolyte membrane for fuel cell coated with nano-hole graphene sheet and its manufacturing method {COMPOSITE POLYMER ELECTROLYTE MEMBRANE FOR FUEL CELL COATED WITH NANOHOLE GRAPHENE SHEET, AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to a composite polymer electrolyte membrane for a fuel cell coated with a nano-hole graphene sheet and a method of manufacturing the same. More specifically, the present invention relates to a composite polymer electrolyte membrane for a polymer electrolyte fuel cell (PEMFC) coated with a nano-hole graphene sheet and a method of manufacturing the same.

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a type of fuel cell that is in the spotlight as a next-generation energy source, and is a fuel cell that uses a polymer membrane having hydrogen ion exchange characteristics as an electrolyte. Such a polymer electrolyte fuel cell (PEMFC) includes a polymer electrolyte membrane having characteristics such as high hydrogen ion conductivity, low electronic conductivity and gas permeability, high mechanical strength and dimensional stability, as well as electrical insulation in order to improve initial performance and secure long-term performance. Is required to do.

However, increasing the thickness of the polymer electrolyte membrane for realization of high mechanical strength also increases the resistance of the membrane, which may result in low ionic conductivity of the membrane. That is, it may be quite difficult to implement a polymer electrolyte membrane having high durability while being thinned to have high ionic conductivity.

In addition, since a significant amount of water may be absorbed in the hydrophilic domain of the polymer electrolyte membrane when the fuel cell is driven, the ionic conductivity, mechanical strength, and gas barrier properties of the polymer electrolyte membrane may be greatly reduced. Due to this, the dimensional stability can also be significantly lowered. Therefore, interest in polymer electrolyte membranes that maintain excellent physical properties without being easily decomposed due to electrochemical stress such as hydrolysis and oxidation-reduction reactions during fuel cell operation is increasing.

On the other hand, due to its excellent performance, a perfluorine-based polymer electrolyte membrane such as a single Nafion membrane of DuPont has been commercialized and used most widely. However, in spite of excellent chemical resistance, oxidation resistance, and ion conductivity, the unit cost is high and mechanical and morphological stability are low.Therefore, the demand for new polymer electrolyte membranes having excellent properties as described above and economical is gradually increasing. .

U.S. Patent No. 8,552,075 Korean Patent Publication No. 10-2016-0035565 Korean Patent Publication No. 10-2012-0134164

An object of the present invention is a composite for a fuel cell, including a nano-hole graphene sheet, which has excellent durability and performance compared to its thickness, and allows water to permeate through the nano-holes to enable stable driving of a fuel cell under various humidification conditions. It is to provide a polymer electrolyte membrane and a method of manufacturing the same.

In an exemplary embodiment of the present invention, a porous fluorine-based polymer support; And it provides a composite polymer electrolyte membrane for a fuel cell comprising a; and nano-hole graphene sheet (nanohole graphene sheet).

In an exemplary embodiment of the present invention, in the method for manufacturing a composite polymer electrolyte membrane for a fuel cell described above, the porous fluorine-based polymer support is impregnated with a perfluorine-based sulfonated polymer solution, so that the inside of the pores of the porous fluorine-based polymer support is filled with a perfluorine-based sulfonated polymer. Filling with and forming a perfluorinated sulfonated polymer film on the outer surface; And coating a nano-hole graphene sheet on a porous fluorine-based polymer support having a perfluorine-based sulfonated polymer film formed on the outer surface thereof. It provides a method for producing a composite polymer electrolyte membrane for a fuel cell comprising.

An exemplary embodiment of the present invention provides a membrane electrode assembly including the above-described composite polymer electrolyte membrane for a fuel cell.

An exemplary embodiment of the present invention provides a fuel cell including the membrane electrode assembly described above.

The composite polymer electrolyte membrane for a fuel cell according to the present invention includes a porous fluorine-based polymer support and a graphene sheet having nanoholes, thereby exhibiting very excellent durability and performance compared to the thickness.

Specifically, since the composite polymer electrolyte membrane for a fuel cell contains a graphene sheet, it is possible to improve the durability of the membrane by reducing gas permeation, and it is possible to manufacture a membrane that can prevent degradation of the electrolyte membrane due to little aggregation or denaturation of fillers. Do. That is, it is possible to prevent degradation of performance and durability due to cracking of the film caused by the functional filler applied inside the film.

In particular, the present inventors have made it possible to move water through nanoholes in the graphene sheet, unlike previous studies that were applicable only at low humidity due to the characteristics of graphene, thereby achieving stable driving under various humidification conditions.

Therefore, it is possible to easily implement a membrane electrode assembly having excellent performance and a fuel cell including the same through such a composite polymer electrolyte membrane for a fuel cell.

1 is a diagram showing a method of manufacturing a composite polymer electrolyte membrane for a fuel cell according to an embodiment of the present invention.
2A to 2E show transfer of a single layer nanohole graphene sheet included in the composite polymer electrolyte membrane according to an exemplary embodiment of the present invention to the SiO ₂ surface, or transfer the graphene sheet prior to nanohole generation to the SiO ₂ surface. It is a Raman, TEM, and SAED pattern showing the number and crystallinity of the OM, SEM, AFM images and graphene layers showing the transfer and the surface thereof.
Specifically, Figure 2a is the OM of the upper surface of the graphene sheet measured by transferring the graphene before forming the nanoholes onto SiO ₂ in the embodiment, and Figure 2b is the graphene before forming the nanoholes in the embodiment SiO ₂ phase SEM of the upper surface of the graphene sheet measured by transferring, FIG. 2C shows the AFM analysis result of the upper surface of the graphene sheet measured by transferring graphene onto SiO ₂ before forming nanoholes in the Example. Figure 2d shows the Raman analysis results of the upper surface of the graphene sheet measured by transferring graphene before forming the nanoholes onto SiO ₂ in the Example, and Figure 2e is a TEM of graphene before and after the nanohole formation, It shows the SAED pattern.
3 is a graph showing the water permeation characteristics of the nano-hole graphene sheet of the present invention.
FIG. 4 is a graph showing gas barrier properties of a single layer graphene, a double layer graphene, and a single layer nanohole graphene for hydrogen, nitrogen, and oxygen after coating various graphene on a commercial film.
5A to 5C are high humidification of single cells including a composite polymer electrolyte membrane for a fuel cell manufactured according to an embodiment of the present invention, and a single cell including a pure polymer electrolyte membrane manufactured according to Comparative Examples 1 to 3 It is a graph showing the comparison of performance under conditions.
6A and 6B show low humidification of single cells including a composite polymer electrolyte membrane for a fuel cell manufactured according to an embodiment of the present invention, and a single cell including a pure polymer electrolyte membrane manufactured according to Comparative Examples 1 to 3 It is a graph comparing performance and resistance under conditions.
7A and 7B show accelerated deterioration of single cells including a composite polymer electrolyte membrane for a fuel cell manufactured according to an embodiment of the present invention, and a single cell including a pure polymer electrolyte membrane manufactured according to Comparative Examples 1 to 3 It shows a comparison of the open circuit voltage (ODV) decay and the amount of fluorine ion emission according to the test.
8 is a performance change after an accelerated aging test of a single cell including a composite polymer electrolyte membrane for a fuel cell manufactured according to an embodiment of the present invention, and a single cell including a pure polymer electrolyte membrane manufactured according to Comparative Example 3 It is a graph showing a comparison.
9A and 9B are after an accelerated aging test of a single cell including a composite polymer electrolyte membrane manufactured according to an embodiment of the present invention, and a single cell including a pure polymer electrolyte membrane manufactured according to Comparative Examples 1 to 2. It is an SEM photograph showing the cross section of the film.
Figure 10a shows a porous fluorine-based polymer support, Figure 10b shows a porous fluorine-based polymer support impregnated with an ionomer, and Figure 10c is a composite polymer electrolyte membrane coated with nano-hole graphene on one side of a porous fluorine-based polymer impregnated with an ionomer. This is the picture shown.

Hereinafter, exemplary 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 text are exemplified for purposes of explanation only, and the embodiments of the present invention may be implemented in various forms and should not be construed as being limited to the embodiments described in the text. .

The present invention is not intended to limit the present invention to a specific disclosed form, as various changes can be added and various forms may be added, and all changes, equivalents or substitutes included in the spirit and scope of the present invention It should be understood to include.

In the present specification, "graphene" is a single layer of graphite, meaning that sp ² bonds between carbon atoms are formed in a form in which a hexagonal crystal lattice is repeated, and "graphene sheet" is a very thin layer. As a single flat sheet, it means a two-dimensional carbon material, and the graphene sheet may be laminated in a single layer or a multiple layer.

In the present specification, "nanohole graphene sheet" refers to a graphene sheet including "nanoholes" which are pores having a size of several nanometers.

In the present specification, "complexing" or "complexing occurs" means that the perfluorine-based sulfonated polymer electrolyte (ionomer), which is a polymer electrolyte having hydrogen ion conductivity, is physically and/or chemically bonded to the porous fluorine-based polymer support. It means to be combined to have a function.

In the present specification, "hydrogen crossover (H ₂ crossover)" refers to a hydrogen permeation phenomenon that occurs when hydrogen that has not reacted in the anode electrode passes through the polymer electrolyte membrane and passes to the cathode electrode. This hydrogen crossover phenomenon, that is, undesirable gas diffusion from the anode electrode to the cathode electrode, is known to be a major cause of the deterioration of the perfluorine-based electrolyte membrane. In general, the thinner the electrolyte membrane or the polymer electrolyte is impregnated into the support. It can happen more easily if not completely.

Composite polymer electrolyte membrane for fuel cell

The composite polymer electrolyte membrane of the present invention is an electrolyte membrane for a fuel cell, and specifically, is an electrolyte membrane capable of constructing a membrane electrode assembly (MEA) of a polymer electrolyte fuel cell (PEMFC).

In exemplary embodiments of the present invention, a porous fluorine-based polymer support; And it provides a composite polymer electrolyte membrane for a fuel cell comprising a; and nano-hole graphene sheet (nanohole graphene sheet). Since the composite polymer electrolyte membrane for a fuel cell of the present invention includes a graphene sheet, it is possible to improve the durability of the membrane by reducing gas permeation, and to prevent degradation of performance and durability due to the cracking of the membrane caused by the functional filler applied inside the membrane. .

In particular, unlike previous studies that were applicable only at low humidity due to the characteristics of graphene, the graphene sheet includes nanoholes to allow water permeation, so that the water generated during battery operation is easy to be discharged, so stable operation under various humidification conditions Can be achieved.

The porous fluorine-based polymer support is a fluorine-based polymer support having a large number of pores therein, and is chemically stable due to a strong bonding force between carbon and fluorine and a masking effect characteristic of fluorine atoms, and has excellent mechanical properties and hydrogen ion conductivity.

In exemplary embodiments, a perfluorine-based sulfonated polymer resin film filling the inside of the pores of the porous fluorine-based polymer support and covering the outer surface thereof; and further comprising the perfluorine-based sulfonated polymer resin film , The porous fluorine-based polymer support may have substantially no voids therein.

In example embodiments, the nanohole graphene sheet may be a single layer. When the nanoholes are composed of a single layer, the thickness is thin and the water permeability is improved, so that the fuel cell can be stably driven even under various humidification conditions.

In example embodiments, the nanohole graphene sheet may allow water permeation through the nanoholes. Water generated when the fuel cell is driven is discharged through the nanoholes of the nanohole graphene sheet, thereby providing a stable voltage.

In example embodiments, the pore size of the nanohole graphene sheet may be 1 nm to 3 nm. When the pore size is less than 1 nm, water permeation is limited when the fuel cell is driven, and when the pore size is more than 3 nm, the gas blocking effect of graphene may decrease.

In exemplary embodiments, the thickness of the composite polymer electrolyte membrane for a fuel cell may be 5 μm to 30 μm, and specifically 10 μm to 25 μm, or 15 μm to 20 μm. Existing polymer electrolyte membranes for fuel cells, for example, polymer electrolyte membranes made of pure perfluorinated sulfonated polymers such as Nafion electrolyte membranes, generally have a thickness of about 30 μm or more to 50 μm or less for reinforced mechanical properties. However, since an increase in the thickness of the electrolyte membrane increases not only the mechanical properties but also the resistance of the membrane, as the electrolyte membrane has a thicker thickness, the ionic conductivity of the electrolyte membrane may decrease in proportion thereto.

On the other hand, in the case of the composite polymer electrolyte membrane of the present invention, since the graphene sheet is included as described above, it is possible to reduce gas permeation to prevent the hydrogen crossover phenomenon, and there is little aggregation or denaturation caused by the functional filler inside the membrane. It improves the durability of the membrane and prevents performance degradation. Therefore, even if it has a very thin thickness of less than about 30 μm, specifically, about 5 μm or more to less than 30 μm, it may have substantially the same or higher ionic conductivity and mechanical properties as conventional polymer electrolyte membranes for fuel cells. . That is, the composite polymer electrolyte membrane may have very excellent durability and performance compared to the thickness at the same time.

In exemplary embodiments, the porous fluorine-based polymer support may include polytetrafluoroethylene, and in particular, may be treated with acetone, methanol, ethanol, propanol, or hydrogen peroxide. When the hydrophobic polytetrafluoroethylene is included, the porous fluorine-based polymer support is more familiar with air than the perfluorine-based sulfonated polymer and thus has low wettability, so it may be difficult to implement a support without voids. However, by treatment with acetone, methanol, ethanol, propanol, or hydrogen peroxide, the porous fluorine-based polymer support may have improved wettability, and further may not contain impurities on the inside and/or the surface.

As the porous fluorine-based polymer support has improved wettability, the perfluorine-based sulfonated polymer resin membrane substantially completely fills the inside of the pores of the porous fluorine-based polymer support and sufficiently covers the outer surface of the porous fluorine-based polymer support. Accordingly, substantially no voids may exist inside the composite polymer electrolyte membrane except for the nanohole graphene sheet. As a result, the composite polymer electrolyte membrane may have a high membrane density, and thus may have improved mechanical strength. In addition, since the spacing between the hydrophilic ion domains in the interior thereof is narrowed, the composite polymer electrolyte membrane may have increased ionic conductivity and dimensional stability.

In exemplary embodiments, the perfluorinated sulfonated polymer resin film may include a perfluorinated sulfonic acid ionomer (PFSA), for example, a Nafion ionomer. At this time, the perfluorine-based sulfonated ionomer and the porous fluorine-based polymer support may be strongly bonded to each other to be complex.

Since the composite polymer electrolyte membrane has a structure in which a porous fluorine-based support is impregnated with an ionomer, the amount of perfluorinated sulfonated polymer such as Nafion is reduced, so that the ionomer can be easily hydrated even at low humidity, and the manufacturing cost can be lowered. It can have additional advantages in terms of.

Method for manufacturing composite polymer electrolyte membrane for fuel cell

Referring to FIG. 1, the composite polymer electrolyte membrane of the present invention impregnates the porous fluorine-based polymer support with a perfluorine-based sulfonated polymer solution, filling the pores of the porous fluorine-based polymer support with a perfluorine-based sulfonated polymer, and overfired on the outer surface. Forming a sub-system sulfonated polymer film; And coating a nano-hole graphene sheet on a porous fluorine-based polymer support having a perfluorinated sulfonated polymer film formed on the outer surface thereof. It may be prepared by a method of manufacturing a composite polymer electrolyte membrane for a fuel cell comprising.

In exemplary embodiments, although not particularly shown, before the step of impregnating the perfluorine-based sulfonated polymer solution into the porous support as described above, the porous fluorine-based polymer support is used as acetone, methanol, ethanol, propanol, or hydrogen peroxide. Processing step; may further include. Through this, the porous fluorine-based polymer support may have impurities removed from the inside and/or the surface thereof, and may have improved wettability.

Although not particularly shown, the perfluorine-based sulfonated polymer solution may be impregnated into the porous fluorine-based support through a spray or decal process. Preferably, a perfluorine-based sulfonated polymer solution may be sprayed on a porous support treated with acetone, methanol, ethanol, propanol or hydrogen peroxide through a spray process.

In exemplary embodiments, when performing the spray process, the perfluorine-based sulfonated ionomer solution is based on the total weight of the perfluorinated sulfonated ionomer solution in consideration of dispersibility, in an amount of about 1 to about 20 wt% Sub-system sulfonated ionomers may be included. When the content of the perfluorine-based sulfonated ionomer in the perfluorine-based sulfonated ionomer solution exceeds about 15 wt%, the viscosity of the perfluorine-based sulfonated ionomer solution gradually increases, and the perfluorine-based sulfonated ionomer content is about 20 wt%. If exceeded, the perfluorinated sulfonated ionomer solution may not be sprayed evenly due to the high viscosity.

Through the spraying process, a plurality of pores distributed in a three-dimensional network structure inside the porous fluorine-based support may be filled with the perfluorine-based sulfonated ionomer solution, thereby forming a perfluorine-based sulfonated polymer film on the outer surface.

In exemplary embodiments, in the spraying process, the treated porous fluorine-based polymer support is flatly fixed to a frame manufactured in a predetermined shape, and the treated porous fluorine-based polymer support is fixed at a predetermined distance using a spray gun connected to a gas cylinder. It can be carried out by spraying a perfluorine-based sulfonated ionomer solution.

Thereafter, after sufficiently drying the porous fluorine-based polymer support in which the perfluorine-based sulfonated polymer solution is uniformly impregnated, the nano-hole graphene sheet may be coated.

Although not shown in particular, the step of coating the nanohole graphene sheet on the porous fluorine-based polymer support on which the perfluorine-based sulfonated polymer film is formed on the outer surface may be performed through a process of transferring the nanohole graphene sheet and heat treatment. Specifically, in the coating process, the pores inside the perfluorine-based sulfonated ionomer solution are impregnated into the porous fluorine-based polymer support by a spray impregnation process before, so that the inner pores are filled with the perfluorine-based sulfonated ionomer solution, and a thin layer covering the outer surface. It may be carried out on a porous fluorine-based polymer support on which a resin film is formed.

In example embodiments, prior to the step of coating the nanohole graphene sheet, preparing the nanohole graphene sheet; further comprising, the nanohole graphene sheet Preparing a graphene sheet (nanohole graphene sheet); The step of synthesizing a graphene sheet in a CH ₄ and H ₂ atmosphere after annealing on a copper foil; And generating a nanohole in the graphene sheet using a mild plasma method.

By generating nanoholes using the mild plasma method, the gas barrier effect of graphene is maintained and the water permeation performance of the composite membrane is improved, thereby enabling stable fuel cell operation. In addition, the size of the nanohole can be controlled by oxygen flow rate, power, exposure time, etc. in the plasma process step. Specifically, using Femto Science's Cute, while maintaining 90 to 110 sccm O2 and 10 to 110 W power, a nanohole graphene sheet can be formed on the synthesized graphene for about 20 to 40 seconds through oxygen plasma treatment. have.

As described above, the composite polymer membrane for a fuel cell of the present invention includes a nano-hole graphene sheet in a porous fluorine-based support, thereby reducing gas permeation and allowing water to move through the nano-holes. Can represent.

In addition, since the composite polymer electrolyte membrane impregnates the porous fluorine-based support with an expensive perfluorinated sulfonated ionomer, it is easy to hydrate the ionomer even at low humidity and lowers the manufacturing cost, so it is price competitive compared to the conventional polymer electrolyte membrane for fuel cells. Can have additional advantages in terms of

On the other hand, until now, only the composite polymer electrolyte membrane for a fuel cell and a method of manufacturing the same have been described, but the membrane electrode assembly including the composite polymer electrolyte membrane as described above, and all fuel cells including the same, for example, a polymer electrolyte fuel cell (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 implementation. However, the examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

[ Example ]

After fixing a porous polytetrafluoroethylene membrane having a thickness of 10 μm on a glass substrate, impurities were removed by immersing in acetone for 20 minutes at room temperature.

Nafion ionomer solution (EW1100 5wt%, DuPont) was impregnated into a polytetrafluoroethylene porous membrane through a spray process. Accordingly, a thin resin film was formed that fills the inside of the pores of the polytetrafluoroethylene porous film and covers the outer surface. The resin-impregnated polytetrafluoroethylene porous membrane was dried at 80° C. for 4 hours or more, and an impregnated membrane having a thickness of 20 μm was prepared.

Nano hole Graphene Sheet synthesis

First, in order to synthesize the graphene sheet, the copper foil was pretreated with dilute nitric acid and washed with distilled water, acetone, and isopropyl alcohol. The copper foil was heat-treated at 1000° C. for 30 minutes in a hydrogen atmosphere and annealed. Then, graphene synthesis was performed for 30 minutes in CH ₄ and H ₂ environments. After the growth step, the CVD furnace is rapidly cooled to room temperature.

Thereafter, in order to generate nanoholes in the synthesized graphene sheet, nanoholes are generated in graphene synthesized on a copper catalyst through a mild plasma method. The pore size and distribution of the nano-hole graphene sheet can be controlled by oxygen flow rate, power, and exposure time in the plasma process step. Specifically, using Femto Science's Cute, while maintaining 100 sccm O2 and 100 W power, a nanohole graphene sheet was formed on the synthesized graphene for about 30 seconds through oxygen plasma treatment.

Nano hole Graphene Sheet coating process

The synthesized graphene was transferred onto a polytetrafluoroethylene composite polymer electrolyte membrane impregnated with an ionomer through a polymethylmethacrylate-assisted (PMMA-assisted) method. Specifically, PMMA was spin-coated on the nanohole graphene sheet and dried at 80°C to remove the solvent. After etching the copper foil with FeCl ₃ solution, rinse the etching solution with dilute hydrochloric acid and distilled water, transfer the nanohole graphene sheet to the polytetrafluoroethylene composite polymer electrolyte membrane impregnated with ionomer, and heat treatment, and then remove PMMA through toluene. I did.

Accordingly, a composite polymer electrolyte membrane having a final thickness of 20 μm was prepared.

Cell Produce

Thereafter, a membrane electrode assembly and a unit cell including the same were manufactured by performing the following processes using the prepared composite polymer electrolyte membrane.

A 46.5wt% Pt/C catalyst was added to an isopropyl alcohol solvent together with a Nafion ionomer solution, and then mixed for 30 minutes in an ultrasonic mixer to prepare a catalyst slurry. After spreading and fixing the prepared composite polymer electrolyte membrane, the catalyst slurry was directly applied to the composite polymer electrolyte membrane through a hand spray method using a spray gun. At this time, the catalyst loading amount of the anode was 0.2 mgpt/cm ² , the catalyst loading amount of the cathode was 0.4 mgpt/cm ² , and the active area was 1 cm ² . Accordingly, a membrane electrode assembly (MEA) including an anode electrode and a cathode electrode disposed to face each other, and the composite polymer electrolyte membrane disposed therebetween was fabricated.

A unit cell is fabricated by naturally drying the produced membrane electrode assembly (MEA) until all solvents in the catalyst solution evaporate, and then fastening it with a pressure of 70 In*lb using a gasket and a bipolar plate. I did.

[ Comparative example One- Nano hole not included Graphene Composite polymer electrolyte membrane including sheet]

Membrane electrode assembly by performing the same process as in Example except that the "composite polymer electrolyte membrane including the graphene sheet in the step before the nanohole generation process" was used instead of the composite polymer electrolyte membrane coated with the nanohole graphene layer. (MEA) and a unit cell including the same were prepared.

[ Comparative example 2- Graphene Composite polymer electrolyte membrane without sheet coating]

A membrane electrode assembly (MEA) and a membrane electrode assembly (MEA) including the same were performed by performing the same process as in the embodiment, except for using a "composite polymer electrolyte membrane without coating a graphene sheet" instead of a composite polymer electrolyte membrane coated with a graphene layer. A unit cell was prepared.

[ Comparative example 3-commercially available electrolyte membrane]

Membrane electrode by performing the same process as in the Example except for using a 25 μm Nafion 211 (DuPont) electrolyte membrane made of perfluorinated sulfonated polymer instead of a 20 μm thick composite polymer electrolyte membrane coated with a graphene layer. A conjugate (MEA) and a unit cell including the same were prepared.

Experimental example : Composite polymer electrolyte membrane Graphene Structure evaluation

In order to analyze the graphene layer of the composite polymer electrolyte membrane, the structure of the surface was observed using an optical microscope (OM), a scanning electron microscope (SEM), and an atomic force microscope (AFM). , Raman spectroscopy, and a selected area diffraction pattern (SAED) analysis using a transmission electron microscope (TEM) was performed. The results are as shown in FIGS. 2A to 2E.

Specifically, FIG. 2A shows the result of OM observation on the upper surface of graphene, which has not undergone a process of piercing nanoholes through plasma treatment, on a SiO ₂ substrate, and FIG. 2B shows the result of SEM analysis, FIG. 2c shows the AFM analysis results. More specifically, graphene synthesis for 30 minutes in a CH ₄ and H ₂ environment in a CVD heating furnace and an image immediately after cooling.

Referring to FIG. 2A taken in the step before nanohole formation in the embodiment, graphene wrinkles generated by the thermal expansion coefficient of the copper substrate and graphene during graphene growth exist in the shape of a solid line, and also in FIG. All of the thin lines were graphene wrinkles and a bilayer was observed little by little. Figure 2c is also confirmed wrinkles (wrinkle), shows a clean surface in addition to the wrinkles (wrinkle).

Figure 2d confirmed that the graphene coated on the prepared composite polymer electrolyte membrane was synthesized as a single layer having high crystallinity. Specifically, in the Raman analysis, the peak observed around 1350 is a peak indicating a graphene defect, and in the case of FIG. 2D, it can be seen that graphene with almost no defects was synthesized by seeing that there is no 1350 peak, and the 2D peak (around 2680) ), it can be seen that a single layer of graphene was synthesized through the fact that the ratio of the peak observed in the G peak (near 1585) is 2:1. In addition, in the SAED pattern, a 6-fold symmetric structure of graphene was confirmed, and through this, it was found that graphene with high crystallinity was synthesized.

Figure 2e shows the TEM and SAED pattern of graphene before and after nanohole generation, and nanoholes at the level of 1 to 3 nm that were not observed in graphene (left) before nanohole generation (right) are generated through the plasma method. It can be confirmed.

Test example : Nano hole Graphene Sheet Water permeation Property evaluation

In order to confirm the water permeation properties of graphene and nano-hole graphene sheets, water permeation characteristics were evaluated by analyzing the amount of water reduction per hour in a container made to allow water to escape only through graphene. Specifically, a silicon chip having a hole having a diameter of about 5 μm was prepared, a single-layer graphene sheet (not including nanoholes) and a nanohole graphene sheet were transferred thereon, and then the amount of water reduction in the container was measured at room temperature. The water permeability performance of each graphene was evaluated.

Referring to FIG. 3, the water permeability of single-layered graphene (not including nanoholes) was measured to be 2.4 g/day, and of a single-layered nanohole graphene sheet manufactured through mild plasma treatment. In the case of the case, the water permeation property of 4 g/day was shown, which is about 67% improved compared to single-layer graphene. Therefore, it can be seen that the water permeability is greatly improved by including nanoholes in the graphene sheet.

Test example : Evaluation of gas permeability of composite polymer electrolyte membrane

In order to confirm the gas barrier effect of 2D graphene with an atomic-level layer structure, a graphene sheet (not including nanoholes) in a commercial film (pure Nafion film) is a single layer, a double layer, and a nanohole graphene sheet. After each coating with a single layer, the gas permeability to several gases was measured. Specifically, if a small pressure is applied to the top of the membrane after maintaining the lower part of the permeate cell at high vacuum, gas permeation occurs due to the pressure difference between the top and the bottom of the membrane. The gas permeability was measured by the method. The results are as shown in FIG. 4.

4, in the case of a film coated with a single layer of a nanohole graphene sheet for hydrogen, nitrogen, and oxygen (shown as 211-Hole Mono GN on the drawing), a commercial film without any treatment (pure Nafion film , Compared with the gas permeability of Dupont's NRE-211, shown as 211-None on the drawing), the gas permeability was reduced by 14%, 50%, and 22%, and graphene sheets (not including nanoholes) In the case of a film coated with a single layer (shown as 211-Mono GN on the drawing), the gas permeability decreased by 28%, 50%, and 30%, and a graphene sheet (not including nanoholes) was coated with a double layer. In the case of the membrane (indicated by 211-Bi GN on the drawing), it was confirmed that the gas permeability was reduced to 57%, 80%, and 65%.

From the above results, it can be seen that the gas barrier effect was exhibited only by coating a very thin graphene surface. Considering that the hydrogen crossover phenomenon, that is, undesirable gas diffusion from the anode electrode to the cathode electrode, is known to be a major cause of the deterioration of the perfluorine-based electrolyte membrane, when the graphene sheet is included, the initial gas permeability is low. Can be predicted to have a positive effect on long-term durability.

Test example : Performance evaluation of composite polymer electrolyte membrane

In order to evaluate the performance of the composite polymer electrolyte membrane, a single cell including the composite polymer electrolyte membrane prepared according to the Examples and the single cells including the pure polymer electrolyte membrane prepared according to Comparative Examples 1 to 3 were operated. The current-voltage change was measured. At this time, hydrogen at a flow rate of 200 cc/min was supplied to the anode electrode and air at a flow rate of 600 cc/min was supplied to the cathode electrode, and the unit cells were moved from OCV to 0.4 V under conditions of humidification at 80° C. RH 100% and 50%. The voltage was changed at a rate of 20 mV/s until. The results are as shown in FIGS. 5A to 5C, 6A and 6B.

Referring to FIG. 5A, a unit cell including a composite polymer electrolyte membrane manufactured according to the Example at a battery voltage of 0.6V under operating conditions of 100% relative humidity exhibits a performance of 0.941 A/cm ² , according to Comparative Examples 1 to 3 It indicated the performance of the unit cell containing the prepared composite polymer electrolyte membrane jideuleun each of ^{0.927 a / cm 2, 1.127 a} / cm 2 and 1.1 a / cm ^2, So the performance degradation of the unit cell of the fin sheet applied to check that the almost no Could

Specifically, in the case of Comparative Example 1 without nanoholes while obtaining the IV-curve, a fairly unstable cycle was performed as shown in FIG. 5B. On the other hand, in the case of the single cell applied with the composite polymer electrolyte membrane of the embodiment, a stable electrochemical test as shown in FIG. 5C was possible. Through this, it can be predicted that the nanoholes of the graphene sheet facilitated the discharge of the generated water.

Referring to FIG. 6A, while the single cell including the composite polymer electrolyte membrane manufactured according to the Example at a battery voltage of 0.6V under 50% relative humidity operating conditions showed a performance of 0.54 A/cm ² , Comparative Examples 1 to 3 It was confirmed that the single cells including the pure polymer electrolyte membrane prepared accordingly exhibited the performance of 0.54 A/cm ² , 0.54 A/cm ² and 0.32 A/cm ² , respectively.

Through this, when a gas barrier material is applied using the composite polymer electrolyte membrane according to the present invention, it is possible to maintain performance without a separate functionalization process, and a membrane electrode assembly (MEA) having much better performance than a commercial electrolyte membrane and including the same It was found that a polymer electrolyte fuel cell (PEMFC) can be implemented. Also in FIG. 6B, the ohmic resistance indicated by the x-intercept at high frequencies shows similar values in Comparative Example 2, Comparative Example 1, and Example, which is also a result supporting this.

Test example : Durability evaluation of composite polymer electrolyte membrane

In order to actually compare the effect of the nanohole graphene sheet on the durability of the unit cell under the accelerated aging conditions of low humidification and high voltage, the MEA chemical durability test was tested according to the DOE protocol. Specifically, in this experiment, hydrogen and air were supplied at a rate of 10/10 at a flow rate equivalent to 0.2A/cm ² , and at this time, the temperature of the unit cell was 90°C, 1.5 bar, and the relative humidity was RH 30 for both anode and cathode. It was set to %. The endurance test was carried out for 96 hours, and in the case of Comparative Examples 1 and 2, the OCV fell below 0.7V and the test was stopped.

7A shows the OCV reduction rate according to the accelerated aging test of the membrane electrode assembly. First, comparing the initial OCV values, the composite polymer electrolyte membrane according to the embodiment of the present invention was able to confirm the gas barrier effect through the initial OCV enhancement.

In addition, in the OCV reduction rate, which is one of the measures of deterioration of the film, Comparative Example 1: 3.4 mV/h, Comparative Example 2: 6.25 mV/h, Comparative Example 3: 1.38 mV/h, whereas the present invention In the case of the composite polymer electrolyte membrane including the nanohole graphene sheet according to the embodiment of, the OCV decay rate was 0.375 mV/h. This is a value that is about 16 times or more improved in durability compared to Comparative Example 2 by the application of the nano-hole graphene sheet, and in particular, it is about 9 times improved compared to Comparative Example 1 without nano holes. Therefore, it is predicted that the durability could be further improved by providing a nano-hole not only to block gas but also to enable flexible fuel cell operation in the long term.

The amount of fluorine ions released from the perfluorine-based electrolyte membrane during fuel cell operation is a good measure of the degree of degradation of the electrolyte membrane. 7B shows the amount of fluorine ion emission changed after 24, 48, 72, and 96 hours of accelerated deterioration test of the membrane electrode assembly including the composite polymer electrolyte membranes of Examples and Comparative Examples 1 to 3; While the membrane electrode assembly unit cell of the comparative example showed a high amount of fluorine ion emission, it can be seen that almost no fluorine ions were detected in the condensed water after the unit cell operation of the example. Through this, it can be predicted that the deterioration of the film is greatly reduced.

8 shows performance changes before and after the accelerated aging test of the membrane electrode assembly. Comparative Example 3 decreased to 0.15 times the initial performance after the accelerated aging test, while in the case of the Example, it was confirmed that the performance was maintained as much as 0.75 times the initial performance.

9A and 9B are SEM photographs showing a cross section of an electrolyte membrane before and after the accelerated degradation test of the membrane electrode assembly. 9A is a cross-sectional view of a composite polymer electrolyte membrane manufactured according to an embodiment of the present invention, and FIG. 9B is a cross-sectional view of a polymer electrolyte membrane of Comparative Example 3. FIG. In the case of Comparative Example 3, the film thinning phenomenon and several holes and cracks were generated, whereas in the case of the Example, it was confirmed that there was no significant difference between before and after the accelerated aging test.

Claims (13)

Porous fluorine-based polymer support; And
A composite polymer electrolyte membrane for a fuel cell comprising a nanohole graphene sheet.
The method of claim 1,
A perfluorinated sulfonated polymer resin membrane filling the pores of the porous fluorine-based polymer support and covering the outer surface thereof;
The method of claim 1,
The nanohole graphene sheet (nanohole graphene sheet) is a composite polymer electrolyte membrane for a fuel cell, characterized in that the single layer.
The method of claim 1,
The nanohole graphene sheet is a composite polymer electrolyte membrane for a fuel cell, characterized in that water can permeate through the nanoholes.
The method of claim 1,
A composite polymer electrolyte membrane for a fuel cell, characterized in that the pore size of the nanohole graphene sheet is 1 nm to 3 nm.
The method of claim 1,
The composite polymer electrolyte membrane for a fuel cell, wherein the thickness of the composite polymer electrolyte membrane for a fuel cell is 5 μm to 30 μm.
The method of claim 1,
The porous fluorine-based polymer support includes polytetrafluoroethylene and is treated with acetone, methanol, ethanol, propanol, or hydrogen peroxide.
The method of claim 2,
The perfluorinated sulfonated polymer resin film includes a perfluorinated sulfonic acid ionomer (PFSA),
A composite polymer electrolyte membrane for a fuel cell, characterized in that the perfluorinated sulfonated ionomer and the porous fluorine-based polymer support are combined to form a composite.
In the method for producing a composite polymer electrolyte membrane for a fuel cell according to any one of claims 1 to 8,
Impregnating the porous fluorine-based polymer support with a perfluorine-based sulfonated polymer solution, filling the pores of the porous fluorine-based polymer support with a perfluorine-based sulfonated polymer, and forming a perfluorine-based sulfonated polymer film on the outer surface; And
Coating a nano-hole graphene sheet on a porous fluorine-based polymer support on which a perfluorine-based sulfonated polymer film is formed on the outer surface; a method for producing a composite polymer electrolyte membrane for a fuel cell comprising.
The method of claim 9,
Before the step of impregnating the perfluorine-based sulfonated polymer solution,
Treating the porous fluorine-based polymer support with acetone, methanol, ethanol, propanol, or hydrogen peroxide; a method for producing a composite polymer electrolyte membrane for a fuel cell further comprising.
The method of claim 9,
Before the step of coating the nanohole graphene sheet,
Preparing the nanohole graphene sheet (nanohole graphene sheet); Including, further comprising, preparing the nanohole graphene sheet (nanohole graphene sheet);
Synthesizing a graphene sheet in a CH ₄ and H ₂ atmosphere after annealing on a copper foil; And
The method of manufacturing a composite polymer electrolyte membrane for a fuel cell comprising: generating nanoholes in the graphene sheet by using oxygen plasma treatment.
A membrane electrode assembly comprising the composite polymer electrolyte membrane for a fuel cell according to any one of claims 1 to 8.
A fuel cell comprising the membrane electrode assembly according to claim 12.

Images