Antioxidant with excellent reactive oxygen species-scavenging activity and acid resistance, polymer electrolyte membrane comprising same, and method for preparing same

Abstract

The present invention relates to an antioxidant and, more specifically, to an antioxidant with enhanced antioxidative properties and acid resistance, a polymer electrolyte membrane comprising same, and a method for preparing same, in which the antioxidant exhibits improved proton conductivity and enhanced radical scavenging ability due to a channelized proton transport path, and thus can be used as an excellent antioxidant for a polymer electrolyte membrane.

Description

Antioxidant with excellent active oxygen scavenging ability and acid resistance, polymer electrolyte membrane containing the same, and method for manufacturing the same

[0001] The present invention relates to an antioxidant, and more specifically, to an antioxidant having excellent reactive oxygen species scavenging ability and acid resistance, which can be utilized as an excellent antioxidant for polymer membranes, specifically polymer electrolyte membranes, by improving proton conductivity and enhancing radical scavenging ability due to channeled proton transport pathways, and to a polymer electrolyte membrane containing the same, a polymer membrane, and a method for manufacturing the same.

[0002] A fuel cell is a power generation device that produces electricity through the electrochemical reaction of hydrogen and oxygen from the air, and is well known as an eco-friendly next-generation energy source with high power generation efficiency and no emissions other than water.

[0003] Among them, the Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a new technology with the potential to replace combustion engines with near-zero greenhouse gas emissions.

[0004] Currently, fluorine-based hydrogen ion-conducting polymer materials such as Nafion and hydrocarbon-based materials are known as the most widely used and commercialized polymer electrolyte membranes (PEMs) in polymer electrolyte membrane fuel cells (PEMFCs).

[0005] Because Nafion-based polymer electrolyte membranes (PEMs) possess excellent proton conductivity along with appropriate mechanical and thermal stability, the automotive industry is commercializing Nafion-based PEMFC-powered vehicles.

[0006] However, the actual efficiency and market adoption of PEMFC systems still depend entirely on the chemical durability and proton transfer capacity of the PEM. Since the primary function of the PEM is to limit the mixing of hydrogen (fuel) and air / oxygen (oxidizer), the chemical durability of the PEM is one of the most critical factors in PEMFC systems.

[0007] However, under PEMFC operating conditions with high oxidation levels, Nafion membranes suffer severe chemical degradation due to a lack of chemical durability. The generation of hydrogen peroxide (H2O2) during PEMFC operation is cited as the primary cause. Generally, the incomplete oxygen reduction process occurring at the cathode leads to the formation of hydrogen peroxide, which in turn leads to the production of hydroxide (H2O2). - ) and peroxides (HOO - It forms unwanted single-electron radical species such as ) and attacks the Nafion backbone structure, causing severe degradation of the membrane.

[0008] The reduction potential of hydrogen peroxide (H2O2) (~1.77 V vs. RHE) far exceeds the operating conditions of the PEMFC system, causing the concentration of hydrogen peroxide (H2O2) inside the MEA components to increase.

[0009] Hydrogen peroxide (H2O2) is a highly oxidizing compound that decomposes uniformly or Fe exists as a typical pollutant. 2+ and Cu 2+ They react with transition metal ions such as hydroxyl (-OH) and hydroperoxyl (-OOH) radicals to chemically attack Nafion polymer electrolyte membranes (Nafion PEM), thereby degrading chemical durability and PEMFC performance. Consequently, this chemical degradation caused by radical species eventually leads to the formation of mechanical defects in the membrane and PEMFC failure.

[0010] To mitigate such chemical degradation, various antioxidants have already been applied to Nafion electrolyte membranes. For example, antioxidants acting as hydrogen peroxide decomposers, such as manganese oxide, and antioxidants acting as radical scavengers, such as cerium nitrate hexahydrate and CeO2, have been studied.

[0011] However, adding a large amount of antioxidants has limitations, such as the oxidation of the platinum / carbon electrode inside the membrane electrode assembly (MEA), which reduces long-term stability and significantly lowers proton conductivity. In addition, conventional antioxidants have the problem of potentially significantly reducing the proton transfer capacity of the Nafion membrane.

[0012] The present invention aims to solve the above-mentioned problems by providing an antioxidant with enhanced antioxidant and acid resistance, a polymer electrolyte membrane containing the same, and a method for manufacturing the same, which is designed to suppress the chemical decomposition of electrolyte membranes such as Nafion and hydrocarbon-based materials and to enhance the ability to remove free radicals, thereby improving durability and battery performance by applying an electric field during casting to improve proton conductivity.

[0013] The above and other objects and advantages of the present invention will become apparent from the following description describing preferred embodiments.

[0014] The above objective can be achieved by an antioxidant based on a sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite represented by the following chemical formula 1.

[0015] [Chemical Formula 1] zSa hGO-Ceb(PxOy)

[0016] In the above chemical formula 1,

[0017] 'z' is the content of sulfonated holographic graphene oxide (ShG), ranging from 20 to 200 mg, and

[0018] 'a' is the acid content, ranging from 1 µl / mg to 5 µl / mg of ShG, and

[0019] 'b' is the Ce content, ranging from 1 mmol to 5 mmol (per 100 mg of ShG), and

[0020] 'x' is an integer such that 1≤x<3, and

[0021] 'y' is 1 <y≤7의 정수이다.

[0022] The above objective is a method for manufacturing an antioxidant represented by Chemical Formula 1, wherein

[0023] This can be achieved by a method for preparing an antioxidant based on a sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite, comprising the steps of: preparing a first mixture by ultrasonically treating a graphene oxide dispersion and then mixing it with hydrogen peroxide; preparing a holographic graphene oxide by stirring the first mixture and then centrifuging it; modifying the holographic graphene oxide by acid treatment; preparing a second mixture containing cerium polyphosphate by dispersing a cerium salt in a solvent and adding phosphoric acid dropwise under stirring; preparing a third mixture by mixing the acid-treated holographic graphene oxide with the second mixture; stirring the third mixture to obtain a powder-form mixture; and washing and drying the powder-form mixture.

[0024] The above acid treatment is characterized by adding the above-mentioned holographic graphene oxide (hGO) into an acidic solution, followed by ultrasonic treatment and stirring.

[0025] The above cerium salt is cerium sulfate octahydrate (Ce(SO4) 2· It is characterized by being any one selected from H2O), cerium oxide, ammonium cerium nitrate, cerium tetrais(diisoporpylamide), and cerium nitrate hexahydrate.

[0026] The above objective can be achieved by a method for manufacturing an electrolyte membrane containing a sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite-based antioxidant, characterized by comprising the steps of: preparing a fourth solution by drying the solvent of an ionomer dispersion to evaporate; preparing a fifth solution by adding a sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite-based antioxidant to a solvent and sonicating it; preparing a mixed solution by mixing, stirring, and sonicating the fourth solution and the fifth solution; preparing a concentrated solution by heating the mixed solution under stirring conditions to evaporate the solvent; preparing a porous membrane by casting the concentrated solution onto a porous reinforcing layer; applying a magnetic field and an electric field to the porous membrane; and drying the porous membrane.

[0027] According to the present invention, by preparing a new type of cerium polyphosphate-double-modified graphene oxide nanocomposite, proton conductivity is improved and radical scavenging ability is enhanced due to channeled proton transport pathways, thereby enabling it to be utilized as an excellent antioxidant for polymer electrolyte membranes.

[0028] A sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite prepared according to one embodiment of the present invention is designed to enhance the ability to suppress chemical decomposition of electrolyte membranes, such as Nafion and hydrocarbon-based ones, and to remove free radicals, thereby improving proton conductivity by applying an electric field during casting, which can significantly improve chemical durability and battery performance.

[0029] However, the effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description below.

[0030] Figure 1 is a diagram showing images of graphene oxide (GO), holy graphene oxide (hGO), and acid-treated graphene oxide (ShGO) at the synthesis step of Preparation Example 1, respectively, analyzed using a field emission scanning electron microscope (FESEM).

[0031] Figure 2 is a graph showing the XRD analysis (X-ray diffraction analysis) results of a sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite prepared according to Preparation Example 1.

[0032] Figure 3 is a graph showing the results of the three-dimensional XPS (X-ray photoelectron spectroscopy) spectrum analysis of the sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite prepared according to Preparation Example 1.

[0033] Figure 4 is a diagram showing details of the three-dimensional XPS (X-ray photoelectron spectroscopy) analysis of the sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite prepared according to Preparation Example 1.

[0034] Figure 5 is a schematic diagram showing the process for applying an electric field during Nafion casting in the process of Manufacturing Example 2.

[0035] Figure 6 is a digital image showing the results of Experimental Example 1.

[0036] Figure 7 is a graph of the ultraviolet-visible light spectrum showing the results of Experimental Example 1.

[0037] Figure 8 is a graph showing the proton conductivity values ​​of Experimental Example 2.

[0038] Figure 9 is a graph showing the fluoride ion emission rate (FER) analysis results of Experimental Example 3.

[0039] Figure 10 is a graph showing the results of the battery performance (voltage) evaluation of Experimental Example 4.

[0040] Figure 11 is a graph showing the results of the battery performance (power density) evaluation of Experimental Example 4.

[0041] Figure 12 is a graph showing the results of analyzing the battery performance (hydrogen crossover current density (HCCD)) of Experimental Example 4.

[0042] The present invention will be described in detail below with reference to the embodiments and drawings. These embodiments are presented merely as examples to explain the invention more specifically, and it will be obvious to those skilled in the art that the scope of the invention is not limited by these embodiments.

[0043] Furthermore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains, and in the event of a conflict, the description in this specification including definitions shall prevail.

[0044] To clearly explain the proposed invention in the drawings, parts unrelated to the description have been omitted, and similar parts throughout the specification have been assigned similar reference numerals. Furthermore, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Additionally, the term "part" as described in the specification refers to a single unit or block that performs a specific function.

[0045] In each step, identification codes (1st, 2nd, etc.) are used for convenience of explanation and do not describe the order of the steps; the steps may be performed differently from the specified order unless a specific order is clearly indicated in the context. That is, the steps may be performed in the same order as specified, substantially simultaneously, or in the reverse order.

[0046] All technical terms used in this invention, unless otherwise defined, are used in the sense generally understood by those skilled in the art in the relevant field of this invention. Additionally, while preferred methods or samples are described herein, similar or equivalents are also included within the scope of this invention. The contents of all publications cited as references in this specification are incorporated by reference in their entirety into this invention.

[0047]

[0048] Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the attached drawings. However, the present invention may not be limited to these embodiments and examples and drawings.

[0049] Antioxidants

[0050] An antioxidant for a fuel cell according to one embodiment of the present invention is a sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite-based antioxidant, represented by the following chemical formula 1:

[0051] <Chemical Formula 1>

[0052] zS a hG-Ce b (P x O y )

[0053] In the above chemical formula 1,

[0054] 'z' represents the content of sulfonated holographic graphene oxide (ShG) in the antioxidant, and may be, for example, 20 to 200 mg, specifically 10 to 100 mg.

[0055] 'a' means acid content, and specifically, acid content may mean the amount of acid added for sulfonate functionalization, namely chlorosulfonic acid. For example, it may be 1 µl / mg to 5 µl / mg of ShG.

[0056] 'b' indicates the Ce content, for example, 1 mmol to 5 mmol (per 100 mg of ShG), and

[0057] 'x' can be an integer such that 1≤x<3.

[0058] 'y' is 1 <y≤7의 정수일 수 있다.

[0059] The above-mentioned sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite is a novel antioxidant having a porous structure and modified (functionalized) by acidification, and by exhibiting high radical scavenging characteristics and proton conductivity, it can have the effect of improving the chemical durability of polymer electrolyte membranes.

[0060] Method for manufacturing antioxidants

[0061] An antioxidant for a fuel cell according to one embodiment of the present invention is an antioxidant based on a sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite represented by Chemical Formula 1, and one embodiment of the method for manufacturing the same is as follows.

[0062] Step (S10) of preparing a first mixture by ultrasonically treating a graphene oxide dispersion and then mixing it with hydrogen peroxide;

[0063] Step (S20) of preparing a holly graphene oxide by stirring the first mixture and then centrifuging it;

[0064] A step of modifying the above-mentioned holographic graphene oxide by acid treatment (S30);

[0065] Step (S40) of preparing a second mixture containing cerium polyphosphate by dispersing a cerium salt in a solvent and adding phosphoric acid dropwise under stirring;

[0066] Step (S50) of preparing a third mixture by mixing acid-treated holographic graphene oxide with a second mixture;

[0067] A step (S60) of stirring the above third mixture to obtain a mixture in powder form; and

[0068] It may include the step (S70) of washing and drying the above powder-form mixture.

[0069] More specifically, in the step of preparing the first mixture, which is step S10, the graphene oxide may be included in an amount of 0.1 to 50.0 parts by weight (relative to 100 parts by weight of the first mixture).

[0070] The solvent in the graphene oxide dispersion above can be selected from the group consisting of, for example, deionized water (DI water), methanol, ethanol, and isopropanol.

[0071] The above ultrasonication may be performed using a conventional ultrasonic treatment device, for example, for 1 to 8 hours.

[0072] In the above S20 step, it is preferable that the stirring of the first mixture be performed vigorously for 3.5 to 4.5 hours at, for example, 45 to 50°C.

[0073] After stirring, the first mixture can be cooled to room temperature (19–24°C) and centrifuged to obtain holographic graphene oxide (hGO). The holographic graphene oxide (hGO) may refer to graphene oxide having an internal porous structure.

[0074] Specifically, the above-mentioned holy graphene oxide (hGO) may be a form of graphene oxide in which hexadentate carbon atoms are removed from the GO layer during peroxidation with H2O2, thereby forming a defect on the surface and a hole-like structure.

[0075] In the above S30 step, the holographic graphene oxide (hGO) can be modified by acid treatment. That is, the antioxidant according to one embodiment of the present invention can further enhance radical scavenging ability by performing acid functionalization on the holographic graphene oxide (hGO) through acidic surface treatment.

[0076] The above acidic functionalization may be phosphorylation (-PO3H), sulfonation (-SO3H), or carboxylation (-COOH) of the above-mentioned holographic graphene oxide (hGO).

[0077] A method for performing the above acid treatment may include a process of adding the above-mentioned holographic graphene oxide (hGO) into an acidic solution, followed by ultrasonical treatment and stirring.

[0078] Preferably, the acidic component may be a chlorosulfonic acid solution of a sulfonic acid solution, and sulfonate groups may be functionalized in the hGO layer. This can provide additional acidic functional groups to the antioxidant, which helps improve the proton conductivity of the PEM.

[0079] In other words, acid functionalization in the present invention refers to surface functionalization of an hGO layer having acidic sulfonate groups, and such functional groups can improve the proton conductivity of the membrane by providing additional active sites for proton transfer.

[0080] Generally, the addition of antioxidants such as oxides and hydroxides creates obstacles in the proton conduction pathways, thereby reducing the proton conductivity of the membrane; however, in this case, the antioxidants can provide additional active sites for proton transport. Furthermore, the presence of GO structures can incorporate radical relaxation capabilities, further enhancing membrane properties that are more suitable for PEMFC applications.

[0081] In the above S40 step, the cerium salt may be any one selected from cerium sulfate octahydrate (Ce(SO4)2H2O), cerium oxide, ammonium cerium nitrate, and cerium tetrais(diisoporpylamide).

[0082] The above solvent may be DI water.

[0083] Based on 100 parts by weight of the second mixture above, the cerium polyphosphate may be included in an amount of, for example, 0.1 to 50.0 parts by weight.

[0084] After adding hydrogen peroxide to the second mixture above and performing stirring, cerium ions (Ce 3+ It can oxidize ). That is, the hydrogen peroxide is added to control the transition from trivalent cerium to tetravalent cerium in the acidic environment of the ionomer solution, and subsequently, phosphoric acid can be further added.

[0085] In the above S50 step, when preparing the acid-treated holographic graphene oxide and the second mixture, stirring may be performed, and the stirring may be carried out at 500 to 800 rpm for 60 minutes to 120 minutes.

[0086] In the above S60 step, during the process of obtaining the powder-form mixture, stirring may be performed for, for example, at 55 to 65°C for 11 to 13 hours.

[0087] In the above S70 step, in the step of washing and drying the powder-form mixture, deionized water (DI water) may be used for washing, and drying may be carried out at 80 to 100°C.

[0088] Method for manufacturing a polymer electrolyte membrane containing an antioxidant

[0089] The antioxidant based on the sulfonated holy graphene oxide-cerium polyphosphate nanocomposite prepared in this manner can be used by impregnating it into an electrolyte membrane containing an ionomer. Accordingly, the electrolyte membrane of the present invention comprises an ionomer and the antioxidant. As an embodiment of a method for preparing an electrolyte membrane comprising such an ionomer and the antioxidant,

[0090] A step of preparing a fourth solution by drying the ionomer dispersion so that the solvent evaporates;

[0091] A step of preparing a fifth solution by adding the above-mentioned sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite-based antioxidant to a solvent and sonicating it;

[0092] A step of preparing a mixed solution by mixing the above-mentioned fourth solution and fifth solution, stirring, and ultrasonically treating;

[0093] A step of preparing a concentrated solution by heating the above-mentioned mixed solution under stirring conditions to evaporate the solvent;

[0094] A step of manufacturing a porous membrane by casting the above concentrated solution onto a porous reinforcing layer;

[0095] A step of applying a magnetic field and an electric field to the porous membrane; and

[0096] It may include a step of drying the porous membrane.

[0097] More specifically, in the step of preparing the fourth solution, the drying may be carried out at 60 to 80°C so that the solvent evaporates.

[0098] The above drying is characterized by 80% of the solvent evaporating, leaving 20% ​​of the ionomer dispersion.

[0099] In the step of preparing the fifth solution above, the solvent may be any one selected from the group consisting of N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO).

[0100] The above ultrasonic treatment may be carried out for 30 minutes to 2 hours.

[0101] In the step of preparing a mixed solution by mixing, stirring, and ultrasonically treating the above-mentioned fourth solution and fifth solution, the stirring may be carried out at 500 to 800 rpm for 60 to 120 minutes.

[0102] In the step of preparing a concentrated solution by heating the above-mentioned mixed solution under stirring conditions to evaporate the solvent, the evaporation of the solvent may proceed until only 40% of the solution remains.

[0103] In the step of manufacturing a porous membrane by casting the above concentrated solution onto a porous reinforcing layer, the porous reinforcing layer may be any one selected from polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (e-PTFE), polyethylene (PE), polypropylene (PP), polyphenylene oxide (PPO), polybenzimidazole (PBI), or a combination thereof.

[0104] The above casting is characterized by using a doctor blade that moves at a constant speed to disperse the concentrated solution into a porous reinforcing layer.

[0105] The porous reinforcing layer has a thickness of 1 to 20 μm, the doctor blade speed moves at 0.004 to 0.02 cm / sec, and the doctor blade has a thickness of 10 to 40 μm.

[0106] In the step of applying an electric field and a magnetic field to the electrolyte membrane, the electric field is applied in the vertical direction of the porous membrane by electrically connecting a function generator to the electrolyte membrane with an AC voltage and AC frequency within a range greater than 0 and equal to or less than 20V, and most preferably, an electric field of 5V is applied in the vertical direction of the porous membrane.

[0107] The above magnetic field is applied in the horizontal direction of the electrolyte membrane, most preferably within a range greater than 0 and equal to or less than 5T, with a magnetic field of 0.1T being most preferably applied.

[0108] The above AC frequency is characterized as being 10 to 100 kHz.

[0109] The above electric and magnetic fields are sustained only during the casting and drying process and can be applied simultaneously or one at a time.

[0110] This combination of electric and magnetic fields is used to synergistically align proton channels and antioxidants inside the ion exchange membrane.

[0111] In the step of drying the electrolyte membrane, the drying is performed at room temperature for 2 to 4 hours, and then at 80 to 100°C for 2 to 4 hours and at 120 to 150°C for 15 to 30 minutes.

[0112] This multi-stage drying process is intended to remove volatile impurities.

[0113] The ionomer used in the electrolyte membrane prepared in this way is selected from the group consisting of perfluorosulfonic acid-based ionomers, hydrocarbon-based ionomers, and mixtures thereof.

[0114] Membrane-electrode assemblies and fuel cells

[0115] Furthermore, the electrolyte membrane impregnated with the antioxidant may be used in a membrane-electrode assembly, wherein the membrane-electrode assembly of the present invention comprises an electrolyte membrane containing the antioxidant; and a pair of electrodes provided on both sides of the electrolyte membrane; and the membrane-electrode assembly may be used in a fuel cell.

[0116] According to one embodiment of the present invention, the electrolyte membrane may comprise 0.1 to 10 weight% of the antioxidant, and the membrane-electrode assembly may comprise 0.1 to 50.0 weight% of the electrolyte membrane.

[0117] Hereinafter, the structure of the present invention and the resulting effects are to be explained in more detail through specific embodiments and comparative examples. However, these embodiments are intended to explain the present invention more specifically, and the scope of the present invention is not limited to these embodiments.

[0118] [Preparation Example 1 : zS a hG-Ce b (P x O y ) manufacturing]

[0119] zS a hGO synthesis

[0120] After sonicating an aqueous dispersion of graphene oxide flakes (GO) for 1 hour, a first mixture was prepared by adding 2 ml of 30 wt.% hydrogen peroxide (H2O2) to the GO dispersion and vigorously stirring at 50°C for 4 hours. Subsequently, the first mixture was cooled to room temperature (19–24°C) and centrifuged. The separated hGO was washed with water and ethanol and dried at 50°C for 12 hours.

[0121] Then, for acidification modification, hGO was sonicated in DMAc (dimethylacetamide) for 15 minutes and stirred for an additional 30 minutes. Subsequently, 'a' ml of 5% chlorosulfonic acid was added and refluxed for 4 to 10 hours. Afterward, the final solution was centrifuged and washed with DI water and ethanol, and the resulting solid material was dried under vacuum at 50°C for 12 hours.

[0122] zS a hG-Ce b (P x O y ) Synthesis

[0123] zS synthesized according to the manufacturing method described above a A dispersion of hGO was prepared through ultrasonic treatment and stirring.

[0124] Then, a cerium(III) metal precursor at concentration b was mixed with 100 ml of DI water and stirred for 5 minutes. 0.2 mmol of hydrogen peroxide was added to this, and stirring was continued for another 30 minutes to form Ce 3+ The ions were oxidized. Then, 1 mmol of phosphoric acid was added to obtain a second mixture, which was refluxed at 60°C for 4 to 6 hours while continuously stirring. Subsequently, the product was separated by centrifugation and washed at least twice each with DI water and ethanol. Thus, a white solid paste was obtained.

[0125] Next, a mixture was prepared by mixing the solid paste with a dispersion of zSa hGO, stirring at 60°C for 12 hours, separating the solid nanocomposite, and washing the solid powder to obtain the final material, the zSa hGO-Ceb(PxOy) nanocomposite. The ShG content 'z', the acid content 'a', and the Ce content 'b' are shown in Table 1 below.

[0126] Antioxidant Chemical Formula a(μl / mg)b(mmol)Z(mg) Example 1 Z1 S a2 HG-Ce b1 (P x O y )1-51-210 Example 2 Z2 S a2 hG-Ce b1 (P x O y )1-51-2100 Example 3 Z3 S a2 hG-Ce b1 (P x O y )1-51-250 Example 4 Z2 S a1 hG-Ce b1 (P x O y )1-51-2100 Example 5 Z2 S a2 hG-Ce b1 (P x O y )1-51-2100 Example 6 Z2 S a3 hG-Ce b1 (P x O y )1-51-2100 Example 7 Z2 S a2 hG-Ce b2 (P x O y )1-51-2100 Example 8 Z2 S a2 hG-Ce b3 (P x O y )1-51-2100 Example 9 Z2 S a2 hG-Ceb4 (P x O y )1-51-2100Comparative Example 1CeO2-1-

[0127] Figure 1 is a diagram showing FESEM analysis images of graphene oxide (GO), holy graphene oxide (hGO), and acid-treated graphene oxide (ShGO) at the synthesis step of Preparation Example 1, respectively.

[0128] Referring to Figure 1, FESEM analysis confirmed that the structure of graphene oxide (GO) was modified to form holy graphene oxide (HGO) and acid-treated graphene oxide (ShGO). In particular, it was confirmed that the hexagonal carbon structure was removed from the surface of graphene oxide (GO) and pores were formed to form holy graphene oxide (HGO).

[0129] Figure 2 is a graph showing the XRD analysis (X-ray diffraction analysis) results of a sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite prepared according to Preparation Example 1.

[0130] Referring to FIG. 2, XRD analysis results show that the sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite (zSahG-Ce) prepared according to the method of Preparation Example 1 b It can be confirmed that (PxOy)) was synthesized.

[0131] Figure 3 is a graph showing the results of the three-dimensional XPS spectrum analysis of a sulfonated holographic graphene oxide-cerium polyphosphate nanocomposite prepared according to Preparation Example 1, and Figure 4 is a diagram showing detailed information regarding the three-dimensional XPS spectrum analysis.

[0132] Referring to FIGS. 3 and 4, in the case of Example 7, through the decomposed Ce 3d XPS results, cerium ions in the nanocomposite, i.e., Ce 4+ (74.43%) and Ce 3+ The presence of (25.57%) was confirmed. This is due to Ce resulting from oxidation. +3 From Ce +4This suggests that changes in the atomic state between them can create excellent potential for radical removal.

[0133] [Preparation Example 2 : zS a hG-Ce b (P x O y [Preparation of polymer electrolyte membranes containing )]

[0134] First, a perfluorosulfonic acid (PFSA) solution (5–50 w / w% DuPont) was placed in a vial and stirred at 80°C for 1 hour.

[0135] Then, each antioxidant of Table 1 was mixed with 6 ml of DMAc solvent (DMAc, 99.8%, Sigma-Aldrich) in another beaker and sonicated for 30 minutes to prepare a dispersion of each antioxidant.

[0136] Next, each antioxidant dispersion was added to the PFSA solution and stirred again at 80°C for 1 hour.

[0137] Then, the mixed slurry was poured onto a PTFE film attached to a metal plate, and both sides were cast to an optimized thickness of 23 μm using a knife coater and dried at 80°C for 2 hours, followed by drying the membrane at 120°C for 20 minutes. Afterward, the entire membrane was peeled off. The thickness of the membrane was measured to be 16 ± 2 μm. The component composition of each fabricated polymer electrolyte membrane is shown in Table 2 below.

[0138] Meanwhile, in Table 2, Comparative Example 2 refers to a reinforced PSFA membrane, Comparative Example 3 refers to a Nafion (Nafion 211) membrane (25.4 μm), and Comparative Example 4 refers to a reinforced Nafion (Nafion) membrane using a CeO2 antioxidant. Examples 4-1 to 7-1 represent polymer electrolyte membranes to which the antioxidants of Table 1 described above have been applied, respectively.

[0139] In addition, a polymer electrolyte membrane was fabricated by applying an electric field. Direct current was applied as shown in Fig. 5 to align the polymer active channels by increasing proton conductivity. Prior to applying the electric field, a process of washing the metal substrate with ethanol was performed. Once washing was complete, a Nafion antioxidant solution was first cast using a doctor blade. Then, PTFE was placed on top of the cast solution to complete pore filling on the bottom surface.

[0140] An electric field was applied during the secondary coating of the Nafion casting method as shown in Fig. 5. The metal plate was connected to the negative terminal, and the casting blade was connected to the positive terminal of the DC power supply. Before casting, the DC power supply was set to 3V and 0.2-1.5A. Then, the Nafion antioxidant solution was poured onto the top surface of the PTFE, and the DC power supply was turned on to cast at a speed of 3-10 mm per second. The polymer electrolyte membrane to which the electric field was applied is Example 7-2 in Table 2 below.

[0141] Polymer electrolyte membrane chemical formula Content of antioxidant (AO) (based on total membrane weight) Example 4-1 Nafion / PTFE-z2S a1 hG-Ce b1 (P x O y )1 wt% Example 7-1 Nafion / PTFE- z2 S a2 hG-Ce b2 (P x O y )1 wt% Example 6-1 Nafion / PTFE-z2S a3 hG-Ce b1 (P x O y )1 wt% Example 1-1 Nafion / PTFE- z1 S a2 hG-Ce b1 (P x O y )1 wt% Example 2-1 Nafion / PTFE- z2 S a2 hG-Ce b1 (Px O y )1 wt% Example 3-1 Nafion / PTFE- z3 S a2 hG-Ce b1 (P x O y )1 wt% Example 5-1 Nafion / PTFE- z2 S a2 hG-Ce b1 (P x O y )1 wt% Example 8-1 Nafion / PTFE- z2 S a2 hG-Ce b3 (P x O y )1 wt% Example 9-1 Nafion / PTFE- z2 S a2 hG-Ce b4 (P x O y )1 wt% Example 7-2 Nafion / PTFE- z2 S a2 hG-Ce b2 (P x O y ) / EF1 wt% Comparative Example 2 Nafion / PTFE (No AO) 1 wt% Comparative Example 3 Nafion film 1 wt% Comparative Example 4 CeO2 film 1 wt%

[0142]

[0143] <Experimental Example 1: Evaluation of Antioxidant Activity>

[0144] A methyl violet test was performed to measure the antioxidant activity of each antioxidant (Table 1) prepared according to Preparation Example 1. The methyl violet test is a method that can quickly and effectively evaluate the radical scavenging properties of a substance by visually observing the color change of the methyl violet dye. When the antioxidant activity of the sample increases, the original purple color of the methyl violet is maintained, and when the antioxidant activity decreases, the purple color becomes pale and then changes to colorless.

[0145] The reaction solution for photometric measurement contains 1.2 x 10 -5 M(MV), 0.15 mM FeSO4· 7H2O, 1.0 M H2O2 (MV / HP / Fe), and 0.1 M Tris-HCl buffer (pH 4.7) were used together, and for Comparative Example 1 and Example 7, the color change was observed at room temperature for a certain period of time.

[0146] Figure 6 is a digital image showing the results of Experimental Example 1, and Figure 7 is a graph of the ultraviolet-visible light spectrum showing the results of Experimental Example 1.

[0147] Referring to FIG. 6, (A) and (B) are reference methyl violet with and without Fenton reagent, respectively. In the case of (C), Comparative Example 1 was used as an antioxidant, and in the case of (D), Example 7 is shown to have been decomposed as an antioxidant.

[0148] Referring to Fig. 7, ultraviolet-visible spectroscopic analysis (Shimadzu, Japan) was performed to compare antioxidant activity more precisely. When the reaction was maintained for 24 hours without an antioxidant, a unique absorption wavelength (582 nm) of methyl violet was observed, which was not present in the standard methyl violet solution (MV / HP / Fe). In the case of the MV solution with added antioxidant, after 24 hours of reaction, the sample was centrifuged to remove the antioxidant and the supernatant was collected.

[0149] As shown in Fig. 7, the absorption intensity of each supernatant was observed, and in the case of Examples 1 to 9, each solution contained a similar amount of antioxidant, indicating excellent antioxidant activity. Among them, in the case of Example 7, it was confirmed that it exhibited significantly higher absorbance than Comparative Example 1.

[0150] <Experimental Example 2: Measurement of Proton Conductivity>

[0151] The proton conductivity of each polymer electrolyte membrane (Table 2) prepared according to Preparation Example 2 was measured. In-plane proton conductivity measurements were performed at 60°C with 100% humidity.

[0152] First, each polymer electrolyte membrane sample (Table 2) was stored inside a membrane conductivity chamber (MCC) containing a platinum electrode and then placed inside a cell stack under the required temperature and humidity conditions. Subsequently, the electrochemical impedance spectrum (EIS) was measured using a potentiometer, and the proton conductivity was measured. The proton conductivity of each sample was measured after the necessary pretreatment.

[0153] σ=L / (RХWХt)

[0154] σ represents the proton conductivity (cm) of the polymer electrolyte membrane, L and W represent the distance between the two platinum electrodes and the width of the sample (cm), R represents the resistance (Ω), and t represents the thickness of the membrane (cm).

[0155] Figure 8 is a graph showing the proton conductivity values, which are the results of Experimental Example 2.

[0156] Referring to FIG. 8, the maximum proton conductivity of Comparative Example 3 is 0.12 Scm -1 In contrast, the proton conductivity of Comparative Example 4 is 0.062 Scm -1 It was measured as such. Generally, Comparative Example 4 may be a standard antioxidant with maximum antioxidant activity, and there was a loss of ~48% compared to the proton conductivity of Comparative Example 3 and ~19% compared to the membrane of Comparative Example 2.

[0157] Meanwhile, it was confirmed that the polymer electrolyte membranes of Examples 4-1 to 9-1 exhibited superior proton conductivity compared to Comparative Example 2. Additionally, it was confirmed that Example 7-2, to which an electric field was applied, showed a 10% increase in proton conductivity compared to Example 7-1, which had the same composition but no electric field was applied.

[0158] <Experimental Example 3: Long-term Durability Evaluation>

[0159] Long-term durability (chemical durability) was evaluated for each polymer electrolyte membrane (Table 2) prepared according to Preparation Example 2. As an evaluation method, the fluorine emission rate (FER) was measured by reacting with a Fenton solution.

[0160] For the measurement method, first, DI water and hydrogen peroxide were mixed in a weight ratio of 1:0.1, and 10 mg / L of FeSO4·7H2O was added to the mixture to prepare a Fenton solution. Then, each polymer electrolyte membrane listed in Table 2 was added to the Fenton solution. The fluoride leaching rate (FER) reaction was carried out at 80°C for 100 hours, and the fluoride ion concentration was measured after the reaction.

[0161] Figure 9 is a graph showing the fluorine leaching rate (FER) value, which is the result of Experimental Example 3.

[0162] Referring to FIG. 9, each polymer electrolyte membrane of Examples 4-1 to 7-2 of Table 2 above exhibited superior antioxidant activity compared to Comparative Example 2 and Comparative Example 3, which lacked antioxidants. Among them, Example 7-1 showed the lowest FER value, exhibiting a fluorine emission amount 2.14 times lower than Comparative Example 2, 2.33 times lower than Comparative Example 3, and 1.62 times lower than Comparative Example 4. Meanwhile, the membrane of Example 7-2 to which an electric field was applied showed antioxidant ability similar to that of the membrane of Example 7-1, proving that the application of an electric field does not compromise the structural integrity of the composite electrolyte membrane.

[0163] <Experimental Example 4: Fuel Cell Performance Analysis>

[0164] Fuel cell performance evaluation was performed on fuel cells containing each polymer electrolyte membrane (Table 2) prepared according to Preparation Example 2.

[0165] The cell performance was measured using a fuel cell station supplied by Wonatech of Korea, when the polymer electrolyte membrane according to Preparation Example 2 of the present invention was used. The prepared polymer electrolyte membrane and two GDEs (carbon paper type, negative electrode 0.3 mg / cm²) hot-pressed at 120°C and 12 MPa pt 2 , anode 0.1mg / cm² pt 2 A membrane electrode assembly (MEA) was prepared using ). Performance was measured in air and H2 at a stoichiometric ratio of 1:2.

[0166] Figure 10 is a graph showing the results of the battery performance (voltage) evaluation of Experimental Example 4, and Figure 11 is a graph showing the results of the battery performance (power density) evaluation of Experimental Example 4.

[0167] Referring to FIGS. 10 and FIGS. 11 together, Example 7-2 has a current density of 1.21 A / cm² at 0.6 V compared to Comparative Example 2. 2 and Peak Power Density (PPD) 0.744 W / cm² 2 It was confirmed that it exhibited higher battery performance.

[0168] Figure 12 is a graph showing the results of analyzing the battery performance (hydrogen crossover current density (HCCD)) of Experimental Example 4.

[0169] Referring to FIG. 12, the hydrogen crossover current density (HCCD) before and after the 72-hour accelerated degradation test (ADT) was analyzed for fuel cells equipped with the polymer electrolyte membranes of Comparative Example 2 and Example 7-2. As a result, Example 7-2 showed 0.55 HCCD mA / cm² 2 We were able to confirm an excellent current density (HCCD) limit of 46% increased.

[0170] In this specification, only a few examples among the various embodiments performed by the inventors are described; however, the technical concept of the present invention is not limited or restricted thereto, and it is obvious that it can be modified and implemented in various ways by those skilled in the art.

Claims

1. Antioxidant based on a sulfonated holographic graphene oxide-mixed cerium phosphate nanocomposite represented by the following chemical formula 1: [Chemical Formula 1] zS a hGO-Ce b (P x O y ) In the above chemical formula 1, 'z' is the content of sulfonated holographic graphene oxide (ShG), ranging from 20 to 200 mg, and 'a' is the acid content, ranging from 1 µl / mg to 5 µl / mg of ShG, and 'b' is the Ce content, ranging from 1 mmol to 5 mmol (per 100 mg of ShG), and 'x' is an integer such that 1≤x<3, and 'y' is 1 <y≤7의 정수이다.

2. A method for manufacturing an antioxidant represented by Chemical Formula 1 of Claim 1, wherein A step of preparing a first mixture by ultrasonically treating a graphene oxide dispersion and then mixing it with hydrogen peroxide; A step of preparing holly graphene oxide by stirring the first mixture and then centrifuging; A step of modifying the above-mentioned holographic graphene oxide by acid treatment; A step of preparing a second mixture containing mixed cerium phosphate by dispersing a cerium salt in a solvent and adding phosphoric acid dropwise under stirring; A step of preparing a third mixture by mixing acid-treated holographic graphene oxide with a second mixture; A step of stirring the above third mixture to obtain a mixture in powder form; and A method for preparing an antioxidant based on a sulfonated holographic graphene oxide-mixed cerium phosphate nanocomposite, comprising the step of washing and drying the above powder-form mixture.

3. In Paragraph 2, A method for preparing an antioxidant based on a sulfonated holographic graphene oxide-mixed cerium phosphate nanocomposite, characterized by the above acid treatment being the addition of the holographic graphene oxide (hGO) into an acidic solution, followed by ultrasonic treatment and stirring.

4. In Paragraph 2, A method for preparing an antioxidant based on a sulfonated holographic graphene oxide-mixed cerium phosphate nanocomposite, characterized in that the cerium salt is selected from any one of cerium sulfate octahydrate (Ce(SO4)·2H2O), cerium oxide, ammonium cerium nitrate, and cerium tetrais(diisoporpylamide).

5. A step of preparing a fourth solution by drying the ionomer dispersion so that the solvent evaporates; A step of preparing a fifth solution by adding the antioxidant based on the sulfonated holographic graphene oxide-mixed cerium phosphate nanocomposite according to claim 1 to a solvent and sonicating it; A step of preparing a mixed solution by mixing the above-mentioned fourth solution and fifth solution, stirring, and ultrasonically treating; A step of preparing a concentrated solution by heating the above-mentioned mixed solution under stirring conditions to evaporate the solvent; A step of manufacturing a porous membrane by casting the above concentrated solution onto a porous reinforcing layer; A step of applying a magnetic field and an electric field to the porous membrane; and A method for preparing a polymer electrolyte membrane comprising a sulfonated holographic graphene oxide-mixed cerium phosphate nanocomposite-based antioxidant, characterized by including the step of drying the porous membrane.

6. Polymer electrolyte membrane manufactured according to paragraph 5.

7. In Paragraph 6, A polymer electrolyte membrane characterized in that, with respect to the total weight of the polymer electrolyte membrane, the antioxidant is included in an amount of 0.1 to 10 weight%.

8. A polymer electrolyte membrane manufactured according to paragraph 6; and, A membrane-electrode assembly for a fuel cell, characterized by being composed of a pair of electrodes provided on both sides of the polymer electrolyte membrane.

9. A fuel cell comprising a membrane-electrode assembly according to paragraph 8.

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