KR102758384B1 - Cation exchange memgrane for electrolysis based graphene oxide grafted nafion and water electrolysis system thereof - Google Patents

Abstract

The present invention relates to a branched copolymer cation exchange membrane comprising graphene oxide grafted with Nafion and a water electrolysis system using the same. The present invention is composed of a radical-stable fluorene and the entire polymer backbone is composed of only C-C bonds, so that the chemical stability is excellent, and the manufactured composite membrane has the effect of improved hydrogen ion conductivity by including modified graphene oxide.

Description

{CATION EXCHANGE MEMGRANE FOR ELECTROLYSIS BASED GRAPHENE OXIDE GRAFTED NAFION AND WATER ELECTROLYSIS SYSTEM THEREOF}

The present invention relates to a branched copolymer cation exchange membrane comprising graphene oxide grafted with Nafion and a water electrolysis system using the same. The present invention is composed of a radical-stable fluorene and the entire polymer backbone is composed of only C-C bonds, so that the chemical stability is excellent, and the manufactured composite membrane has the effect of improved hydrogen ion conductivity by including modified graphene oxide.

The present invention relates to a cation exchange composite membrane using graphene oxide grafted with a perfluorosulfonic acid ionomer as an additive, and can be applied to a random/branched copolymer polymer-based electrolyte composite membrane and a water electrolysis system, which confirm improved hydrogen ion conductivity after introduction of the additive.

Proton exchange membranes (PEMs), which are key materials used in various energy conversion and storage devices including water electrolysis systems, play a role in selectively transmitting only cations as electrolytes and separators. Therefore, PEMs require the following characteristics: 1) high ion conductivity, 2) outstanding physicochemical stability, 3) easy to scalable mass production, and 4) low cost for production.

The most widely used PEMs today are Nafion®, a perfluorinated electrolyte from Chemers, and Gore-Select®, a perfluorinated porous membrane with a packed structure. Both of these have high ionic conductivity and chemical stability, which makes them suitable for use in most commercial or commissioning fuel cells, redox flow batteries, and electrochemical hydrogen compressor systems. However, all of the existing perfluorinated PEMs suffer from 1) decomposition problems by oxygen radicals, 2) environmental pollution caused by hydrofluoric acid and pollutants during incineration, and 3) high unit costs due to their complex manufacturing processes, which are obstacles to the spread of environmentally friendly, high-efficiency, and low-cost energy conversion and storage systems.

Therefore, the development of a non-perfluorocarbon branched cation exchange membrane that has excellent ion conductivity and cell performance and can be easily utilized as a membrane electrode assembly for polymer electrolyte membrane electrolysis is required. In order to improve the conductivity of the electrolyte membrane and the cell performance of the membrane electrode assembly formed by the same, the development of a composite material that can improve the ion conductivity of the branched polymer is required, and a composite membrane in which the dispersion of the developed composite material is guaranteed should be developed to enable additional performance improvement.

Therefore, in order to develop an electrolyte membrane that satisfies all of the above-described characteristics of a hydrogen ion exchange membrane and can be applied in a water electrolysis system, 1) a polymer material having branched side chains composed of carbon-carbon bonds that are easy to introduce ion exchange functional groups and have excellent chemical stability should be developed, and 3) a composite material that can further improve the performance of a branched cation exchange membrane should be developed to develop a composite membrane thereof, thereby developing an electrolyte material in the form of a composite membrane with improved hydrogen ion conduction characteristics and cell performance.

Korean Patent No. 10-1461417

The present invention has been made to solve the above problems, and the purpose of the present invention is to manufacture an electrolyte membrane into which an ion exchange functional group can be easily introduced.

In addition, it is an object of the present invention to provide a polymer material having a branched side chain composed of carbon-carbon bonds having excellent chemical stability.

In addition, an object of the present invention is to provide a composite membrane using a composite material capable of further improving the performance of a branched cation exchange membrane.

In addition, it is an object of the present invention to provide an electrolyte material in the form of a composite membrane having improved hydrogen ion conducting characteristics and cell performance.

The technical problems to be solved by the invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

<Cation exchange membrane>

A branched copolymer cation exchange membrane comprising a graphene oxide grafted with Nafion according to the present invention,

A first polymer having a repeating unit of the following [chemical formula 1]

It is characterized by including a second polymer manufactured by grafting Nafion onto graphene oxide (GO).

[Chemical Formula 1]

(wherein n is an integer from 1 to 50, m is an integer from 1 to 3, and R is SO ₃ H or CH ₂ -SO ₃ H).

The above Nafion is characterized by having a repeating unit of the following [chemical formula 2].

[Chemical formula 2]

(Here, m is 6.6).

Here, the polymer composite membrane is characterized by having a tensile strength of 14 MPa or more, an elongation of 9.0% or more, an ion exchange capacity (IEC) of 2.0 to 5.0 meq /g, and an ion conductivity of 130 to 300 mS / cm.

By means of solving the above problem, the present invention has the effect of chemical stability because there is no chemically weak bond in the polymer main chain by utilizing an electrophilic substitution reaction under strong acid conditions, rather than developing a cation exchange material through condensation polymerization under a conventional basic catalyst.

In addition, the present invention can manufacture a chemically stable cation exchange membrane composed of radical-stable fluorene and a water electrolysis system using the same.

In addition, the present invention can manufacture a cation exchange membrane having excellent chemical stability because the entire polymer main chain is composed of only carbon single bonds, and a water electrolysis system using the same.

In addition, the present invention can manufacture a molecular electrolyte membrane and a water electrolysis system using the same, which simultaneously improve ion conduction behavior and physicochemical stability due to a distinct hydrophilic or hydrophobic phase separation effect, by using a branched copolymer polymer in which a cation exchange functional group is introduced at the end of the side chain.

In addition, since the present invention is obtained through condensation polymerization at room temperature under an acid catalyst, it is possible to manufacture a molecular electrolyte membrane that is easy to mass-produce and a water electrolysis system using the same.

In addition, the present invention provides a composite membrane manufactured by adding graphene oxide grafted onto Nafion, which exhibits clear nano-phase separation of hydrophilicity and hydrophobicity, thereby exhibiting improved performance compared to a membrane manufactured only with a base polymer to which modified graphene oxide is not added.

Figure 1 is a schematic diagram of a F1B-SA-10/Nafion-GO(x) polymer composite membrane according to an embodiment of the present invention, where x (a value of 0 to 80) is the wt% content of grafted Nafion in Nafion-GO.
Figure 2 is a schematic diagram of the synthesis of F1BC7Br-10 according to one embodiment of the present invention.
Figure 3 is a schematic diagram of the synthesis of F1B-TA-10 according to one embodiment of the present invention.
FIG. 4 is a schematic diagram of the synthesis of Nafion-GO(x) according to an embodiment of the present invention, where x (a value of 0 to 80) is the wt% content of grafted Nafion in Nafion-GO.
FIG. 5 is a schematic diagram of a manufacturing method of a F1B-SA-10/Nafion-GO(x) polymer composite membrane according to an embodiment of the present invention, where x (a value of 0 to 80) is the wt% content of grafted Nafion in Nafion-GO.
Figure 6 shows the ¹ H NMR analysis results of F1BC7Br-10 and F1B-TA-10 according to one embodiment of the present invention.
Figure 7 shows the FT-IR analysis results of F1BC7Br-10 and F1B-TA-10 according to one embodiment of the present invention.
Figure 8 shows the TGA analysis results of Nafion-GO according to one embodiment of the present invention.
Figure 9 shows the FT-IR analysis results of Nafion-GO according to one embodiment of the present invention.
Figure 10 shows the tensile strength results of F1B-SA-10/Nafion-GO (44) and F1B-SA-10/Nafion-GO (61) according to one embodiment of the present invention.
Figure 11 shows the results of moisture absorption and dimensional change of F1B-SA-10/Nafion-GO(x) according to one embodiment of the present invention.
Figure 12 shows the hydrogen ion conductivity results of F1B-SA-10/Nafion-GO(x) according to one embodiment of the present invention.
Figure 13 shows the results of a water electrolysis cell test of F1B-SA-10/Nafion-GO(x) according to one embodiment of the present invention.

The terms used in this specification will be briefly explained, and the present invention will be described in detail.

The terms used in the present invention are selected from the most commonly used terms in current practice, taking into consideration the functions of the present invention. However, these may vary depending on the intentions of engineers in the field, precedents, the emergence of new technologies, etc. Therefore, the terms used in the present invention should be defined based on the meaning of the terms and the overall content of the present invention, rather than simply the names of the terms.

When a part of a specification is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

Below, with reference to the attached drawings, embodiments of the present invention are described in detail so that those skilled in the art can easily practice the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

The specific details of the present invention, including the problems to be solved, the means for solving the problems, and the effects of the invention, are included in the embodiments and drawings described below. The advantages and features of the present invention, and the methods for achieving them, will become clear with reference to the embodiments described below in detail together with the accompanying drawings.

Hereinafter, the present invention will be described in more detail with reference to the attached drawings.

<Cation exchange membrane>

The branched copolymer cation exchange membrane comprising Nafion grafted graphene oxide according to the present invention is characterized by including a first polymer having a repeating unit of the following [chemical formula 1] and a second polymer manufactured by grafting Nafion onto graphene oxide (GO), as shown in FIG. 1.

The wt% content of the graphene oxide (GO) grafted Nafion in the second polymer is characterized as being 0 to 80.

(wherein n is an integer from 1 to 50, m is an integer from 1 to 3, and R is SO ₃ H or CH ₂ -SO ₃ H).

The above Nafion is characterized by having a repeating unit of the following [chemical formula 2].

(Here, m is 6.6).

Hereinafter, the first polymer shown in [Chemical Formula 1] is F1B-SA-n, the second polymer is described as Nafion-GO(x), and the branched copolymer cation exchange membrane including graphene oxide grafted with Nafion of the present invention is described as F1B-SA-n/Nafion-GO(x). Here, n is an integer from 1 to 50, x is the wt% content of grafted Nafion in Nafion-GO, and x is an integer from 0 to 80.

According to an embodiment of the present invention, a cation exchange membrane was synthesized by synthesizing a comb-shaped precursor copolymer having a side chain terminal that can be modified and consisting only of carbon-carbon bonds using an electrophilic substitution reaction under strongly acidic conditions, rather than developing a cation exchange material through condensation polymerization under a basic catalyst as in the related art. According to the present invention, a cation exchange membrane (Proton Exchange Membrane) promoting microphase separation (hydrophilic/hydrophobic) was developed by introducing a sulfonic acid group to the side chain terminal composed of a chemically stable bond, and graphene oxide (Nafion-GO) introduced with a perfluorosulfonic acid ionomer (Nafion) was manufactured. In addition, the present invention developed a cation exchange membrane for a water electrolysis system by employing this and applied it to a water electrolysis system.

The cation exchange membrane according to one embodiment of the present invention is composed of radical-stable fluorene and is chemically stable. In the case of hydrocarbon-based polymers used in existing cation exchange membranes, they can be obtained through condensation polymerization at high temperature and for a long time under a base catalyst, but in the case of the polymer membrane developed through the present invention, they can be obtained through condensation polymerization at room temperature for 2-3 hours under an acid catalyst.

In addition, the cation exchange membrane according to one embodiment of the present invention has excellent chemical stability because the entire polymer backbone is composed of only carbon single bonds. Recently, various research results have reported that when the polymer used in the CEM contains an aryl ether bond (C _sp2 -O) or a bond with low bond energy (such as a benzylic CH bond), the polymer decomposes under various operating conditions where the CEM is utilized. Therefore, in the present invention, a polymer composed only of carbon-carbon bonds that ultimately do not contain weak bonds that can be decomposed was synthesized to utilize it as a precursor material for the branched polymer to be ultimately developed.

In addition, the cation exchange membrane according to one embodiment of the present invention is a branched copolymer polymer in which a cation exchange functional group is introduced at the end of the side chain. In the case of moisture/electrolyte, which plays an important role in the ion conduction of PEM, it is mostly distributed around the ion exchange functional group. Therefore, the present invention attempted to improve both ion conduction behavior and physicochemical stability due to a distinct hydrophilic/hydrophobic phase separation effect by synthesizing a branched polymer precursor capable of promoting a hydrophilic/hydrophobic micro-phase separation structure.

In addition, a cation exchange membrane according to an embodiment of the present invention improved hydrogen ion conductivity and cell performance by modifying graphene oxide through an atom transfer radical attachment method and manufacturing a cation exchange composite membrane utilizing the same. The present invention manufactured a Nafion-GO inorganic additive with commercialized Nafion using an atom transfer radical attachment method (ATRA). When a small amount of Nafion-GO is introduced as an additive and then a composite membrane is manufactured to improve the performance of a polymer that can be utilized in a water electrolysis system, hydrogen ion conductivity characteristics and cell performance can be improved.

The cation exchange membrane of the present invention can exhibit high tensile strength and elongation, ion conductivity, and ion exchange capacity (IEC). The cation exchange membrane including the first polymer having the repeating unit of [Chemical Formula 1] and the second polymer manufactured by grafting Nafion onto graphene oxide (GO) is characterized by having a tensile strength of 14 MPa or more and an elongation of 9.0% or more. The cation exchange membrane including the first polymer having the repeating unit of [Chemical Formula 1] and the second polymer manufactured by grafting Nafion onto graphene oxide (GO) is characterized by having an ion conductivity of 130 to 300 mS/cm under operating conditions in water. In addition, it is characterized by having an ion exchange capacity (IEC) of 2.0 to 5.0 meq/g.

<Method for manufacturing cation exchange membrane>

The method for manufacturing a branched copolymer cation exchange membrane comprising graphene oxide grafted with Nafion according to the present invention is preferably performed by the following steps.

As shown in Figures 2 to 5, each of the above steps is described in detail as follows.

Step 1: Synthesis of fluorene-biphenyl-based polymer (hereinafter, F1BC) ₇ Br-n)

First, the first step (S10) prepares a fluorene-biphenyl-based polymer (F1BC ₇ Br-n), as shown in Fig. 2. The first step (S10) prepares the fluorene-biphenyl-based polymer by reacting 9,9-dimethylfluorene, biphenyl, and 7-bromo-1,1,1-trifluoroheptan-2-one.

More specifically, the first step (S10) is composed of a first step (S11) of reacting 9,9-dimethylfluorene, biphenyl and 7-bromo-1,1,1-trifluoroheptan-2-one as monomers, trifluoromethanesulfonic acid (TFSA) as a catalyst and dichloromethane (DCM) as a solvent, and a first step (S12) of precipitating the polymer solution produced in the first step (S11) in methanol.

In the above-mentioned Step 1-1 (S11), 20 to 25 parts by weight of dichloromethane (DCM) is mixed as a solvent for 1 part by weight of the mixture of 9,9-dimethylfluorene, biphenyl, and 7-bromo-1,1,1-trifluoroheptan-2-one. In addition, the Step 1-1 (S11) is maintained at 4 to 6° C. for 20 to 40 minutes, and then reacted at room temperature for 3 to 4 hours.

In the above step 1-2 (S12), the polymer solution produced in the above step 1-1 is precipitated in methanol, washed several times with methanol, and then dried in a vacuum oven at 35 to 45°C.

Step 2: Preparation of fluorene-biphenyl-based polymer conjugated with thioacetic acid (hereinafter, F1B-TA-n)

Next, the second step (S20) manufactures a fluorene-biphenyl-based polymer having thioacetic acid bound thereto, as shown in Fig. 3. The second step (S20) manufactures a fluorene-biphenyl-based polymer having thioacetic acid bound thereto by reacting the fluorene-biphenyl-based polymer manufactured in the first step (S10) with potassium thioacetate.

More specifically, the second step (S20) is composed of a second-first step (S21) of reacting the F1BC ₇ Br-n manufactured in the first step (S10) with potassium thioacetate, and a second-second step (S22) of precipitating the polymer solution produced in the second-first step (S21) in a solution mixed with methanol and hydrochloric acid.

In the above-mentioned step 2-1 (S21), 5 to 10 parts by weight of tetrahydrofuran (THF) is mixed as a solvent with respect to 1 part by weight of the mixture of F1BC ₇ Br-n and potassium thioacetate. More preferably, 6 parts by weight of tetrahydrofuran (THF) is mixed as a solvent.

After mixing the above mixture, solvent and catalyst, the reaction is performed at 45 to 55°C for 9 to 11 hours. More preferably, the reaction is performed at 50°C for 10 hours to synthesize the product.

In the above step 2-2 (S22), the polymer solution produced in the above step 2-1 is precipitated in a solution mixed with methanol and hydrochloric acid, washed several times with distilled water, and then dried in a vacuum oven at 35 to 45°C.

Step 3: Manufacturing Nafion-Graphene Oxide (hereinafter, Nafion-GO(x))

Next, the third step (S30) manufactures Nafion-graphene oxide (Nafion-GO), as shown in Fig. 4. The third step (S30) manufactures Nafion-graphene oxide (Nafion-GO) by mixing a Nafion solution into a graphene oxide dispersion.

More specifically, the third step (S30) comprises a third-first step (S31) of dispersing graphene oxide in a solvent mixed with isopropanol and water to produce a graphene oxide dispersion, a third-second step (S32) of mixing the Nafion solution into the graphene oxide dispersion, removing oxygen using freeze-pump-thaw, and maintaining a nitrogen atmosphere to produce a graphene oxide-Nafion solution, a third-third step (S33) of adding 2,2'-bipyridyl (BPY) and copper bromide as catalysts to the graphene oxide-Nafion solution from which oxygen has been removed and then reacting, and after the third-third step (S33) reaction, centrifugation is performed. It consists of the 3rd to 4th step (S34) of manufacturing the Nafion-graphene oxide (Nafion-GO) by washing.

The above step 3-1 (S31) prepares the graphene oxide dispersion by mixing isopropanol and water in a volume ratio of 2:1 and then dispersing the mixture using a sonicator for 50 to 70 minutes.

The above 3-2 step (S32) mixes the Nafion solution into the graphene oxide dispersion, then performs freeze-pump-thaw three times to remove oxygen and maintains a nitrogen atmosphere to prepare a graphene oxide-Nafion solution.

The above step 3-3 (S33) is reacted under a nitrogen atmosphere at a temperature of 75 to 85 ℃ for 17 to 19 hours.

The above 3-4 steps (S34) are obtained by washing the Nafion-GO(x) obtained after the reaction using a centrifuge. The Nafion solution was manufactured into 1.5 g and 0.6 g of Nafion-GO(44) and Nafion-GO(61), respectively, depending on the Nafion content.

Step 4: Manufacturing of polymer membrane (hereinafter, F1B-SA-n/Nafion-GO( x ))

Next, the fourth step (S40) manufactures a polymer membrane, F1B-SA-n/Nafion-GO(x), as shown in Fig. 5. The fourth step (S40) mixes the thioacetic acid-bound fluorene-biphenyl-based polymer manufactured in the second step (S20) and the Nafion-graphene oxide (Nafion-GO) manufactured in the third step (S30) to manufacture a polymer membrane. It is preferable to mix 80 to 120 parts by weight of the Nafion-GO(x) with respect to the F1B-SA-n.

More specifically, in step 4-1 (S41), the Nafion-graphene oxide (Nafion-GO) manufactured in step 3 (S30) is dispersed in a dimethylformamide solvent to manufacture a Nafion-graphene oxide (Nafion-GO) dispersion, the fluorene-biphenyl-based polymer combined with thioacetic acid manufactured in step 2 (S20) is mixed with the Nafion-graphene oxide (Nafion-GO) dispersion, and then vacuum-dried to manufacture a Nafion-graphene oxide (Nafion-GO) composite membrane, and in step 4-2 (S42), the Nafion-graphene oxide (Nafion-GO) composite membrane is mixed with formic acid and distilled water, heated, and then hydrogen peroxide is added dropwise to react at a temperature of 65 to 75°C for 5 to 7 hours to manufacture the polymer membrane. It consists of Step 4-3 (S43).

The above step 4-1 (S41) prepares the Nafion-graphene oxide (Nafion-GO) dispersion by dispersing it five times for 20 to 40 minutes using a sonicator.

The above step 4-2 (S42) manufactures the Nafion-graphene oxide (Nafion-GO) composite membrane by stirring at room temperature for 50 to 70 minutes and then vacuum drying at a temperature of 55 to 65°C for 5 to 7 hours.

In the above step 4-3 (S43), the manufactured Nafion-graphene oxide (Nafion-GO) composite membrane is placed in a colorimetric tube and heated at a temperature of 65 to 75°C for 5 to 7 hours, then the hydrogen peroxide is added dropwise to cause a reaction, and then the membrane is washed several times with distilled water and then dried to obtain the polymer membrane.

Here, x of the Nafion-GO(x) is the wt% content of the graphene oxide (GO) grafted Nafion, and x is characterized as being 0 to 80.

<Cation exchange membrane electrolysis device>

The branched copolymer cation exchange membrane comprising the graphene oxide grafted with Nafion according to the present invention described above is included in the present invention if it is used for ion exchange in its intended use. Preferably, it can be usefully applied to electrolysis of water (water electrolysis). Therefore, the present invention can provide a water electrolysis device comprising the cation exchange membrane.

The present invention relates to a branched copolymer cation exchange membrane electrolysis device comprising grafted graphene oxide and Nafion, characterized in that it comprises a first polymer having a repeating unit of the following [chemical formula 1] and a second polymer manufactured by grafting Nafion onto graphene oxide (GO).

The wt% content of the graphene oxide (GO) grafted Nafion in the second polymer is characterized as being 0 to 80.

[Chemical Formula 1]

(wherein n is an integer from 1 to 50, m is an integer from 1 to 3, and R is SO ₃ H or CH ₂ -SO ₃ H).

The above Nafion is characterized by having a repeating unit of the following [chemical formula 2].

[Chemical formula 2]

(Here, m is 6.6).

Meanwhile, the water electrolysis device and fuel cell according to the present invention may have a conventional structure, and are included in the present invention if they use the cation exchange membrane according to the present invention as an electrolyte.

The electrolysis device according to the present invention may be configured to include, for example, at least a membrane-electrode assembly (MEA) having an electrolyte membrane, and anode and cathode catalyst layers formed on both surfaces of the electrolyte membrane, as is conventional, and may include a frame, a separator, an MEA support, and a gasket (packing), etc. arranged in a form that allows the supply and discharge of electrons, reactants, and products.

At this time, the electrolyte membrane constituting the membrane-electrode assembly (MEA) is composed of a fluorene and biphenyl-based branched copolymer cation exchange membrane according to the present invention.

In addition, the fuel cell according to the present invention may have a membrane electrode assembly (MEA) including, for example, a polymer electrolyte fuel cell (PEFC) having a conventional structure, an electrolyte membrane, a catalyst layer bonded to both sides of the electrolyte membrane, and a gas diffusion layer bonded to the outside of the catalyst layer. A separator may be arranged in the membrane electrode assembly (MEA), and a gas path for supplying a fuel gas or an oxidizer gas may be formed at a contact portion between the membrane electrode assembly (MEA) and the separator or within the separator. In addition, the fuel electrode to which a fuel gas such as hydrogen or methanol is supplied, and an oxygen electrode to which an oxidizer gas such as air or oxygen is supplied, have. At this time, the electrolyte membrane constituting the membrane electrode assembly (MEA) is composed of a cation exchange membrane according to the present invention.

<Cation Exchange Membrane Fuel Cell>

The branched copolymer cation exchange membrane comprising the Nafion grafted graphene oxide according to the present invention described above is included in the present invention if it is used for ion exchange in its intended use. Preferably, a fuel cell system including a fuel cell can be provided. Accordingly, the present invention can provide a fuel cell including the cation exchange membrane.

A branched copolymer cation exchange membrane fuel cell comprising Nafion-grafted graphene oxide according to the present invention is characterized by comprising a first polymer having a repeating unit of the following [chemical formula 1] and a second polymer manufactured by grafting Nafion onto graphene oxide (GO).

The wt% content of the graphene oxide (GO) grafted Nafion in the second polymer is characterized as being 0 to 80.

[Chemical Formula 1]

(wherein n is an integer from 1 to 50, m is an integer from 1 to 3, and R is SO ₃ H or CH ₂ -SO ₃ H).

The above Nafion is characterized by having a repeating unit of the following [chemical formula 2].

[Chemical formula 2]

(Here, m is 6.6).

The fuel cell system according to the present invention may have a conventional structure, and if the fuel cell according to the present invention is used as the fuel cell constituting it, it is included in the present invention. For example, the fuel cell system according to the present invention may include a fuel cell, a hydrogen generation device which generates hydrogen from a raw material gas and supplies hydrogen to a fuel electrode of the fuel cell, an oxidizer gas supply device which supplies an oxidizer gas (air, oxygen, etc.) to an oxygen electrode of the fuel cell, a fuel gas opening/closing means for opening and closing the inlet/outlet of the fuel electrode, an oxidizer gas opening/closing means for opening and closing the inlet/outlet of the oxygen electrode, a hydrogen opening/closing means for opening and closing the inlet/outlet of the hydrogen generation device, a control device for controlling the opening/closing operations of the fuel gas opening/closing means, the oxidizer gas opening/closing means, and the hydrogen opening/closing means, etc. In this case, the fuel cell is configured as a fuel cell including the fluorene and biphenyl-based branched copolymer cation exchange membrane according to the present invention. In addition, a water electrolysis device according to the present invention can be applied as the hydrogen generation device constituting the fuel cell system according to the present invention.

Hereinafter, the present invention will be described in more detail through examples. The purpose, features, and advantages of the present invention will be easily understood through the following examples. The present invention is not limited to the examples described herein, and may be embodied in other forms. The examples introduced herein are provided so that the idea of the present invention can be sufficiently conveyed to those skilled in the art to which the present invention pertains. Therefore, the present invention should not be limited by the following examples.

Example 1: Fluorene-biphenyl-based polymer (hereinafter, F1BC) ₇ Br-10 and F1BC ₇ Manufacturing of Br-30)

F1BC ₇ Br-10 was synthesized using 9,9-Dimethylfluorene (1 g, 5.15 mmol), Biphenyl (7.14 g, 46.33 mmol), and 7-Bromo-1,1,1-trifluoroheptan-2-one (13.99 g, 56.62 mmol) as monomers, trifluoromethanesulfonic acid (TFSA) (77.25 g, 514.75 mmol) as a catalyst, and 23 wt% dichloromethane (DCM) based on the weight of monomers as a reaction solvent at 5 ℃, 30 min, then reacted at RT, 3 h 30 min. After the reaction, the resulting polymer solution was precipitated in methanol (1300 mL), washed several times with methanol, and then dried in a vacuum oven at 40 ℃.

F1BC ₇ Br-30 was synthesized using 9,9-Dimethylfluorene (2 g, 10.29 mmol), Biphenyl (3.70 g, 24.02 mmol), and 7-Bromo-1,1,1-trifluoroheptan-2-one (9.33 g, 37.75 mmol) as monomers, TFSA (51.50 g, 343.17 mmol) as a catalyst, and 23 wt% DCM based on the weight of monomers as a reaction solvent at 5 ℃, 30 min, and then reacted at RT for 3 h. The precipitation and obtaining methods are the same as above.

Example 2: Preparation of fluorene-biphenyl-based polymers bonded with thioacetic acid (hereinafter, F1B-TA-10 and F1B-TA-30)

F1B-TA-10 was synthesized by reacting previously synthesized FL1C ₇ Br-10 (2 g, 5.16 mmol) and potassium thioacetate (1.12 g, 9.81 mmol) as reactants and 6 wt% tetrahydrofuran (THF) as a reaction solvent based on the weight of the reactants at 50 °C for 10 h. After the reaction, the produced polymer solution was precipitated in a solution of methanol (1000 mL) and hydrochloric acid (100 mL, 2 M), washed several times with distilled water, and then dried in a vacuum oven at 40 °C.

F1B-TA-30 was synthesized by reacting previously synthesized FL1C7Br-30 (2 g, 5.06 mmol) and potassium thioacetate (1.04 g, 9.11 mmol) as reactants and 6 wt% tetrahydrofuran (THF) as a reaction solvent based on the weight of the reactants at 50 ℃ for 10 h, and the precipitation and yielding methods are the same as above.

Example 3: Preparation of Nafion-Graphene Oxide (hereinafter, Nafion-GO(x))

Graphene oxide (GO, 0.1 g) was dispersed in a solvent of isopropanol: water = 2:1 (v/v), 20 ㎖ using a sonicator for 1 hour to prepare a dispersion solution. After adding Nafion solution (D2020), internal oxygen was removed through three freeze-pump-thaw cycles, and a nitrogen atmosphere was maintained. Then, 2,2'-bipyridyl (BPY, 0.05 g) and copper bromide (CuBr, 0.062 g) were added as catalysts and reacted at 80 ℃ for 18 h under a nitrogen atmosphere to synthesize. After the reaction, Nafion-GO(x) was washed and obtained using a centrifuge.

Nafion solution was used in amounts of 1.5 g and 0.6 g, respectively, depending on the Nafion content of Nafion-GO (Nafion-GO(44), Nafion-GO(61)).

Example 4: Polymer membrane (hereinafter, F1B-SA-n/Nafion-GO( x )) manufacturing

F1B-SA-10/Nafion-GO(x) was prepared by the following method.

The previously synthesized Nafion-GO(x) (5 mg) and DMF (9.5 g) were placed in a 20 mL vial and sonicated 5 times for 30 minutes to prepare a Nafion-GO dispersion. After that, F1B-TA-10 (0.5 g) was added to the dispersion, stirred at room temperature for 1 h, poured into a 10 cm diameter petri dish, and dried under vacuum at 60 °C for 6 h to prepare a F1B-TA-10/Nafion-GO(x) composite membrane. The prepared composite membrane was poured into a 100 mL colorimetric tube with a solution of 15 mL of formic acid (HCOOH) and 45 mL of distilled water, and then heated to 60 °C. After that, a 8x8 ㎠, 50 ㎖ composite membrane was placed in a colorimetric tube, maintained at 10 m, 30 mL of hydrogen peroxide was slowly added, and the reaction was performed at 70 ℃ for 6 h. After the reaction, the membrane was washed several times with distilled water and then dried to produce F1B-SA-10/Nafion-GO (44) and F1B-SA-10/Nafion-GO (61).

Below, ^1H NMR, FT-IR, TGA, mechanical property evaluation, water absorption, ion exchange capacity, hydrogen ion conductivity, and water electrolysis cell tests were performed using the previously implemented examples.

Experimental Example 1: F1BC ₇ Br-10 and F1B-TA-10 ¹ H NMR analysis results

The results of ¹ H-NMR confirmation of F1BC ₇ Br-10 and F1B-TA-10 are shown in Fig. 6. The progress of the reaction was determined through the change in the NMR peak of CH ₂ (11) next to the modifiable position (-Br) of the F1BC ₇ Br-10 branch terminal.

In the F1B-TA-10 data, it was confirmed that the synthesis was achieved with 100% conversion through the complete shift (11') of the 11th peak and the generation of the 12th peak of F1BC ₇ Br-10, which was the material before the reaction.

Experimental Example 2: F1BC ₇ FT-IR analysis results of Br-10 and F1B-TA-10

As shown in Fig. 7, the FT-IR of F1BC ₇ Br-10 and F1B-TA-10 confirmed the CH peak around 3000-2840 cm ^-1 , and the C=O peak around 1725-1705 cm ^-1 , confirming the change in the terminal functional group.

Experimental Example 3: TGA analysis results of Nafion-GO(44) and Nafion-GO(61)

The TGA of the electrolyte membrane was measured by the following method. The temperature was increased from room temperature to 120 ℃ at 20 ℃ min ^-1 and maintained for 10 min to remove residual moisture and stabilize. After that, it was cooled to 60 ℃ at 20 ℃ min ^-1 and the weight change of the polymer sample was measured from 60 to 700 ℃ at 10 ℃ min ^-1 in a nitrogen atmosphere.

As shown in Fig. 8, Nafion-GO(x) showed decomposition of Nafion between 330°C and 600°C, and the Nafion content of Nafion-GO(x) was confirmed through the weight change between 330°C and 600°C. As a result, the Nafion contents of Nafion-GO(x) were confirmed to be 44 wt% and 61 wt% for Nafion-GO(44) and Nafion-GO(61), respectively.

Experimental Example 4: FT-IR analysis results of Nafion-GO(44) and Nafion-GO(61)

As shown in Fig. 9, the FT-IR results of Nafion-GO (44) and Nafion-GO (61) show that the C=C peak of GO is observed around 1720 cm ^-1 , and the -CF ₂ - peak of the Nafion chain is observed between 1113 cm ^-1 and 1164 cm ^-1 , confirming that Nafion-GO (44) and Nafion-GO (61) were successfully synthesized.

In addition, when comparing Nafion-GO(44) and Nafion-GO(61), the peak between 1113 cm ^-1 and 1164 cm ^-1 was stronger in Nafion-GO(61) than in Nafion-GO(44), confirming that Nafion-GO has a high content of Nafion.

Experimental Example 5: Mechanical Properties Evaluation of F1B-SA-10/Nafion-GO(44) and F1B-SA-10/Nafion-GO(61) Polymer Membranes

To measure the mechanical properties, a 250 N load cell was attached to the LLOYD UTM LS1 device, and specimens cut according to ASTM D 638 type Ⅴ were clamped. The extension rate was 5 mm/min, and more than 6 specimens for each type of electrolyte membrane were measured to obtain the strain-stress curve and the average and standard deviation of the Young's modulus and elongation.

Sample Tensile Strength
(MPa) Young's Modulus
(MPa) Elongation at Break
(%) F1B-SA-10/
Nafion-GO(44) 16.0 ± 0.9 542.9 ± 30.3 9.6 ± 1.0 F1B-SA-10/
Nafion-GO(61) 14.1 ± 0.5 550.2 ± 35.2 10.9 ± 0.8

As shown in Table 1 and Fig. 10, the tensile strengths of F1B-SA-10/Nafion-GO (44) and F1B-SA-10/Nafion-GO (61) were 16.0 MPa and 14.1 MPa, respectively, and the elongations were 9.6% and 10.9%, respectively.

Experimental Example 6: Water Absorption and Dimensional Changes of F1B-SA-10/Nafion-GO(x) Polymer Membranes

The moisture absorption and dimensional change were measured by the following method. The membrane dried in a desiccator was cut into 1 cm × 4 cm sizes, and the thickness and weight of the dried membrane were measured. After that, the membrane whose area, thickness, and weight were measured in the dried state were placed in a vial, filled with distilled water, and placed in a drying oven at 30 °C and 80 °C, respectively. After 12 h, the swollen membrane was taken out of the oven, and the area, thickness, and weight were measured, and the dimensional change was measured using the following formula. Measurements were performed three times for each sample.

Water uptake [%] = [(W _wet - W _dry ) / W _dry ] × 100

Change in dimension [%] = [((A _wet × T _wet ) - (A _dry × T _dry )) / (A _dry × T _dry )] × 100

(Here, W _dry and W _wet are the weights of the dried and swollen membranes, A _dry and A _wet are the areas of the dried and swollen membranes, and T _dry and T _wet are the thicknesses of the dried and swollen membranes.)

SAMPLE WU (%) △V (%) △A (%) 30℃ 80℃ 30℃ 80℃ 30℃ 80℃ F1B-SA-10 Pristine 50.8 58.6 56.1 70.1 37.0 48.7 F1B-SA-10/
Nafion-GO(44) 44.8 65.5 48.7 49.6 26.5 30.0 F1B-SA-10/
Nafion-GO(61) 71.6 84.0 65.8 84.6 38.3 52.6 Nafion 212 13.3 27.7 18.3 51.3 14.6 28.0

As shown in Table 2 and Fig. 11, for the composite membrane with a low Nafion content of Nafion-GO, the dimensional change is confirmed to be reduced compared to the existing pristine membrane, whereas for the composite membrane with a high Nafino content of Nafion-GO, the dimensional change is confirmed to be increased.

Experimental Example 7: Measurement of ion exchange capacity of F1B-SA-10/Nafion-GO(x) polymer membrane

To measure the ion exchange capacity, the weight of the dried cation exchange membrane was measured, placed in a 30 ml vial, 15 ml of 1 M NaCl solution was added, and the sample was prepared by stirring at 60℃ for more than 6 h. The volume of NaOH added until the pH of the solution containing the cation exchange membrane became 7.0 was confirmed using an automatic potentiometric titrator (TITRANDO 888) for 0.01 M NaOH solution, and the calculation was made using the following formula.

IEC _w = ( C _NaOH * ΔV _NaOH / W _s ) * 1000 [meq/g]

(Here, C _NaOH is the NaOH concentration (0.01 M), △V _NaOH is the NaOH volume, and W _s is the weight of the dried membrane.)

Sample Theoretical IEC
(meq /g) Experimental IEC
(meq /g) F1B-SA-10 Pristine 2.57 2.19 ± 0.00 F1B-SA-10/
Nafion-GO(44) 2.04 ± 0.17 F1B-SA-10/
Nafion-GO(61) 2.04 ± 0.03

As shown in Table 3, F1B-SA-10/Nafion-GO(x) showed a slightly decreased IEC compared to the conventional F1B-SA-10 Pristine membrane.

Experimental Example 8: Hydrogen ion conductivity of F1B-SA-10/Nafion-GO(x) polymer membrane

To measure hydrogen ion conductivity, a 0.5 × 3 ㎠ sample was prepared and attached to a 4-probe cell, and then measured using electrochemical spectroscopy (SP-240, Bio Logic Science Instrument, France). The measurement conditions were 100% RH conditions with the cell placed in double-distilled water, and the resistance value according to the temperature change from 30 ℃ to 90 ℃ was measured and calculated using the following formula.

Proton conductivity (σ) [mS cm ^-1 ] = d/RS

(Here, D is the distance between the electrodes, R is the resistance value, and S is the thickness*width of the sample)

The resistance value was measured at each temperature from 30 ℃ to 90 ℃ in distilled water containing the cell, at 10 ℃ intervals, and the resistance value was measured and recorded six times at each temperature.

F1B-SA-10 F1B-SA-10
/Nafion-GO(44) F1B-SA-10
/Nafion-GO(61) Nafion 212 30 116.7 ± 2.7 139.6 ± 1.8 151.4 ± 1.7 76.3 ± 0.5 40 138.0 ± 1.8 158.7 ± 2.6 171.7 ± 2.3 91.5 ± 1.7 50 157.4 ± 1.1 182.9 ± 2.8 195.3 ± 2.5 105.3 ± 2.0 60 173.0 ± 1.7 211.4 ± 2.3 222.0 ± 2.6 125.4 ± 1.8 70 194.1 ± 1.6 234.1 ± 2.1 248.5 ± 1.9 139.2 ± 1.4 80 215.0 ± 1.4 260.7 ± 2.7 272.0 ± 2.6 161.4 ± 3.1 90 226.4 ± 2.5 278.2 ± 1.3 294.4 ± 1.5 185.8 ± 3.5

As shown in Table 4 and Fig. 12, F1B-SA-10/Nafion-GO(x) exhibited improved hydrogen ion conductivity compared to the conventional F1B-SA-10 pristine, and it was confirmed that the higher the Nafino content of Nafion-GO, the higher the hydrogen ion conductivity.

Experimental Example 9: Water electrolysis cell test of F1B-SA-10/Nafion-GO(x) polymer membrane

For the electrolysis cell test, a membrane electrode assembly (MEA) was used for the cell test by assembling a gas diffusion layer (JNT30-A3, JNTG, Korea), a rubber gasket, a graphite bipolar plate, and an aluminum end plate.

Polarization curves were obtained at a constant gas flow rate ( _H2 : 100 sccm, Air: 200 sccm) using a test device (Z010-100, SCITHEC KOREA), and electrochemical impedance spectroscopy was performed at 0.6 V with an amplitude of 90 mV, and a potentiostat (SP-300, Biologic, France) was used in the frequency range of 100 kHz to 50 mHz.

Sample Current Density
(A/㎠) @1.6 v @2.0 v F1B-SA-10 Pristine 0.813 3.17 F1B-SA-10/
Nafion-GO(44) 0.978 3.64

As shown in Table 5 and Fig. 13, F1B-SA-10/Nafion-GO(x) showed improved water electrolysis cell performance compared to the conventional F1B-SA-10 pristine membrane.

By means of solving the above problem, the present invention has the effect of chemical stability because there is no chemically weak bond in the polymer main chain by utilizing an electrophilic substitution reaction under strong acid conditions, rather than developing a cation exchange material through condensation polymerization under a conventional basic catalyst.

In addition, the present invention can manufacture a chemically stable cation exchange membrane composed of radical-stable fluorene and a water electrolysis system using the same.

In addition, the present invention can manufacture a cation exchange membrane having excellent chemical stability because the entire polymer main chain is composed of only carbon single bonds, and a water electrolysis system using the same.

In addition, the present invention can manufacture a molecular electrolyte membrane and a water electrolysis system using the same, which simultaneously improve ion conduction behavior and physicochemical stability due to a distinct hydrophilic or hydrophobic phase separation effect, by using a branched copolymer polymer in which a cation exchange functional group is introduced at the end of the side chain.

In addition, since the present invention is obtained through condensation polymerization at room temperature under an acid catalyst, it is possible to manufacture a molecular electrolyte membrane that is easy to mass-produce and a water electrolysis system using the same.

In addition, the present invention provides a composite membrane manufactured by adding graphene oxide grafted onto Nafion, which exhibits clear nano-phase separation of hydrophilicity and hydrophobicity, thereby exhibiting improved performance compared to a membrane manufactured only with a base polymer to which modified graphene oxide is not added.

In this way, it will be understood by those skilled in the art that the technical configuration of the present invention described above can be implemented in other specific forms without changing the technical idea or essential features of the present invention.

Therefore, the embodiments described above should be understood as illustrative and not restrictive in all respects, and the scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

delete

Claims (20)

A first polymer having a repeating unit of the following [chemical formula 1]
A second polymer comprising Nafion grafted onto graphene oxide (GO) ,
The tensile strength is 14.1 to 16.0 MPa, and the elongation is 9.6 to 10.9 %.
A branched copolymer cation exchange membrane comprising Nafion-grafted graphene oxide, characterized in that the ionic conductivity at 80°C is 260.7 to 272.0 mS/cm :
[Chemical Formula 1]

(wherein n is an integer from 1 to 50, m is an integer from 1 to 3, and R is SO ₃ H or CH ₂ -SO ₃ H).
In paragraph 1,
The above Nafion is a branched copolymer cation exchange membrane including Nafion-grafted graphene oxide, characterized by having a repeating unit of the following [chemical formula 2]:
[Chemical formula 2]

(Here, m is 6.6).
delete In paragraph 1,
The above cation exchange membrane is,
A branched copolymer cation exchange membrane comprising Nafion-grafted graphene oxide, characterized in that the ion exchange capacity (IEC) is 2.0 to 5.0 meq/g.
delete A first step of producing a fluorene-biphenyl-based polymer by reacting 9,9-dimethylfluorene, biphenyl, and 7-bromo-1,1,1-trifluoroheptan-2-one;
A second step of producing a fluorene-biphenyl-based polymer having thioacetic acid bonded thereto by reacting the fluorene-biphenyl-based polymer produced in the first step with potassium thioacetate;
The third step of producing Nafion-GO by mixing Nafion solution into graphene oxide dispersion;
A fourth step of manufacturing a polymer membrane by mixing the fluorene-biphenyl-based polymer combined with thioacetic acid manufactured in the second step and the Nafion-graphene oxide (Nafion-GO) manufactured in the third step ;
The fourth step above is,
Step 4-1 of preparing a Nafion-graphene oxide (Nafion-GO) dispersion by dispersing the Nafion-GO prepared in the above step 3 in a dimethylformamide solvent;
Step 4-2 of manufacturing a Nafion-GO composite membrane by mixing the fluorene-biphenyl-based polymer combined with thioacetic acid manufactured in the second step into the Nafion-GO dispersion and then vacuum drying;
A method for producing a branched copolymer cation exchange membrane including Nafion-grafted graphene oxide, characterized in that it comprises a step 4-3 of producing the polymer membrane by mixing the Nafion-GO composite membrane with formic acid and distilled water, heating it, and then adding hydrogen peroxide dropwise thereto and reacting it at a temperature of 65 to 75° C. for 5 to 7 hours .
In paragraph 6,
The above first step is,
Step 1-1 of reacting by mixing 9,9-dimethylfluorene, biphenyl and 7-bromo-1,1,1-trifluoroheptan-2-one as monomers, trifluoromethanesulfonic acid (TFSA) as a catalyst and dichloromethane (DCM) as a solvent; and
A method for producing a branched copolymer cation exchange membrane comprising Nafion-grafted graphene oxide, characterized by comprising a step 1-2 of precipitating the polymer solution produced in the step 1-1 in methanol.
In paragraph 6,
The second step above is,
Step 2-1 of mixing the fluorene-biphenyl-based polymer manufactured in the above step 1 with potassium thioacetate as a reactant and tetrahydrofuran (THF) as a solvent; and
A method for manufacturing a branched copolymer cation exchange membrane including graphene oxide grafted with Nafion, characterized by including a step 2-2 of precipitating the polymer solution produced in the step 2-1 in a solution mixed with methanol and hydrochloric acid.
In paragraph 6,
The third step above is,
Step 3-1 of producing a graphene oxide dispersion by dispersing graphene oxide in a solvent mixed with isopropanol and water;
Step 3-2 of producing a graphene oxide-Nafion solution by mixing the Nafion solution into the graphene oxide dispersion, removing oxygen using freeze-pump-thaw, and maintaining a nitrogen atmosphere;
Step 3-3 of adding 2,2'-bipyridyl (BPY) and copper bromide as catalysts to the above-mentioned oxygen-removed graphene oxide-Nafion solution and then reacting;
A method for producing a branched copolymer cation exchange membrane including Nafion-grafted graphene oxide, characterized in that it comprises a step 3-4 of producing Nafion-graphene oxide (Nafion-GO) by washing with a centrifuge after the step 3-3 reaction.
In Article 9,
The above step 3-1 is,
A method for producing a branched copolymer cation exchange membrane including Nafion-grafted graphene oxide, characterized in that isopropanol and water are mixed in a volume ratio of 2:1.
In Article 9,
The above step 3-1 is,
A method for producing a branched copolymer cation exchange membrane including Nafion-grafted graphene oxide, characterized in that the graphene oxide dispersion is produced by dispersing the graphene oxide using a sonicator for 50 to 70 minutes.
In Article 9,
The above step 3-3 is,
A method for producing a branched copolymer cation exchange membrane comprising a graphene oxide grafted with Nafion, characterized in that the reaction is performed under a nitrogen atmosphere at a temperature of 75 to 85° C. for 17 to 19 hours.
delete In paragraph 6 ,
The above step 4-1 is,
A method for producing a branched copolymer cation exchange membrane including Nafion-grafted graphene oxide, characterized in that the Nafion-GO dispersion is produced by dispersing the Nafion-GO dispersion using a sonicator for 20 to 40 minutes.
In paragraph 6 ,
The above step 4-2 is,
A method for producing a branched copolymer cation exchange membrane including Nafion-grafted graphene oxide, characterized in that the Nafion-GO composite membrane is produced by stirring for 50 to 70 minutes and then vacuum drying at a temperature of 55 to 65° C. for 5 to 7 hours.
In paragraph 6 ,
The above step 4-3 is,
A method for producing a branched copolymer cation exchange membrane comprising Nafion-grafted graphene oxide, characterized in that the polymer membrane is produced by reacting at a temperature of 65 to 75° C. for 5 to 7 hours.
A first polymer having a repeating unit of the following [chemical formula 1]
A polymer composite membrane including a second polymer manufactured by grafting Nafion onto graphene oxide (GO) ,
The tensile strength is 14.1 to 16.0 MPa, and the elongation is 9.6 to 10.9 %.
A water electrolysis device comprising a branched copolymer cation exchange membrane comprising Nafion grafted graphene oxide, characterized in that the ionic conductivity is 260.7 to 272.0 mS/cm at 80°C :
[Chemical Formula 1]

(wherein n is an integer from 1 to 50, m is an integer from 1 to 3, and R is SO ₃ H or CH ₂ -SO ₃ H).
In Article 17,
The above Nafion is a branched copolymer cation exchange membrane electrolysis device including a graphene oxide grafted with Nafion, characterized in that it has a repeating unit of the following [chemical formula 2]:
[Chemical formula 2]

(Here, m is 6.6).
A first polymer having a repeating unit of the following [chemical formula 1]
A polymer composite membrane including a second polymer manufactured by grafting Nafion onto graphene oxide (GO) ,
The tensile strength is 14.1 to 16.0 MPa, and the elongation is 9.6 to 10.9 %.
A branched copolymer cation exchange membrane fuel cell comprising Nafion-grafted graphene oxide, characterized in that the ionic conductivity at 80°C is 260.7 to 272.0 mS/cm :
[Chemical Formula 1]

(wherein n is an integer from 1 to 50, m is an integer from 1 to 3, and R is SO ₃ H or CH ₂ -SO ₃ H).
In Article 19,
The above Nafion is a branched copolymer cation exchange membrane fuel cell including Nafion-grafted graphene oxide, characterized in that it has a repeating unit of the following [chemical formula 2]:
[Chemical formula 2]

(Here, m is 6.6).