Radical scavenger complex, method for producing same, and fuel cell including same

Abstract

The present invention relates to a radical scavenger composite including a longitudinally elongated carbon nanotube having a closed cap structure at one end thereof and a radical scavenger particle located within the cap of the closed cap structure; a method for producing the radical scavenger composite including the steps of providing radical scavenger particles on a substrate surface and growing carbon nanotubes on the surfaces of the radical scavenger particles; and a fuel cell.

Description

[Technical field]

[0001] The present invention relates to an additive complex and a manufacturing method thereof that can prevent chemical deterioration of a polymer electrolyte membrane, and relates to a radical scavenger complex that has improved stability compared to existing radical scavengers, thereby preventing crack generation, performance deterioration, and durability deterioration, and that has the property of maintaining additive performance for a long period of time by preventing additive loss, and has the property of improving performance and durability due to the nanostructure, a manufacturing method thereof, and a fuel cell including the same. [Background technology]

[0002] Fuel cells are cells that directly convert chemical energy generated by the oxidation of fuel into electrical energy, and have been attracting attention as a next-generation energy source due to their high energy efficiency and environmentally friendly characteristics such as low pollutant emissions.

[0003] A fuel cell generally has a structure in which an anode and a cathode are formed on either side of an electrolyte membrane, and such a structure is called a membrane electrode assembly (MEA).

[0004] Fuel cells can be classified into alkaline electrolyte fuel cells, polymer electrolyte membrane fuel cells (PEMFC), etc. depending on the type of electrolyte membrane. Among them, polymer electrolyte fuel cells are in the spotlight as portable, vehicle and home power sources due to their advantages such as a low operating temperature of less than 100℃, fast start-up and response characteristics and excellent durability.

[0005] A representative example of such a polymer electrolyte fuel cell is a proton exchange membrane fuel cell (PEMFC), which uses hydrogen gas as fuel.

[0006] To summarize the reactions that occur in a polymer electrolyte fuel cell, first, when fuel such as hydrogen gas is supplied to the oxidizing electrode, hydrogen ions (H+) and electrons (e-) are generated at the oxidizing electrode through an oxidation reaction of hydrogen. The generated hydrogen ions (H+) are transferred to the reducing electrode through the polymer electrolyte membrane, and the generated electrons (e-) are transferred to the reducing electrode through an external circuit. Oxygen is supplied to the reducing electrode, and the oxygen combines with the hydrogen ions (H+) and electrons (e-) to generate water through the reduction reaction of oxygen.

[0007] In a fuel cell, the reactions at the oxidizing and reducing electrodes are different, and the reactants and by-products are different, so one side and the other side of the polymer electrolyte membrane are exposed to different environments during operation.Fuel cells are structured such that electrode layers are transferred onto both sides of the polymer electrolyte membrane to form a membrane electrode assembly with a laminated structure, a bipolar plate is laminated on the surface, and oxygen and fuel gas are injected through channels formed in the bipolar plate.

[0008] Radicals generated from the electrodes when a fuel cell is operating are known to be the main cause of degradation of the polymer electrolyte membrane. Hydrogen peroxide (H2O2) is generated during the reduction reaction of oxygen at the anode, and the generated hydrogen peroxide produces hydroperoxyl radicals (HO2·) and / or hydroxyl radicals (·OH). The radicals thus generated cause degradation of the ionomer contained in the polymer electrolyte membrane, which has substantial hydrogen ion conductivity, reducing the ionic conductivity of the polymer electrolyte membrane and ultimately causing a decrease in the performance of the fuel cell.

[0009] In order to remove the generated radicals, a method is used in which a radical scavenger, i.e., a substance that captures radicals, is added to the polymer electrolyte membrane or electrode layer to prevent deterioration of the polymer electrolyte membrane and the resulting decrease in fuel cell performance.

[0010] Such a radical-capturing material is called a radical scavenger, and it functions to remove radicals by reacting with the radicals generated at the electrodes before they deteriorate the polymer electrolyte membrane.

[0011] The radical scavenger is added in the form of being coated on the surface of the polymer electrolyte membrane or mixed into the electrode layer, but the radical scavenger added in the form of particles such as metal particles or metal compounds has a problem of being eluted during the operation of the fuel cell. That is, since the amount of the radical scavenger capable of removing radicals decreases, the longer the operation time of the fuel cell, the less the radicals are removed, causing a rapid deterioration in the performance of the fuel cell.

[0012] Korean Patent Publication No. 2020-0130179 presents a radical scavenger having radical scavenger particles with a porous protective film on the surface, and discloses a technology to prevent deterioration of fuel cell performance by configuring the radical scavenger to prevent components such as metal ions formed after capturing radicals from dissolving outside the protective film.

[0013] However, when the radical scavenger is produced in the form of a complex having a protective film formed on the surface, additional steps and costs are required for its production, and therefore, there is a need to develop technology that allows the complex to be produced in a simpler manner.

[0014] Therefore, there is a need to develop a method for producing a radical scavenger complex that is easy to produce and has excellent production efficiency while maintaining the radical scavenging effect of the radical scavenger for a long period of time.

[0015] [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Korean Patent No. 1282678

[0017] [Patent Document 2] Korean Patent No. 2044875

[0018] [Patent Document 3] Korean Patent Publication No. 10581099

[0019] [Patent Document 4] Korean Patent Publication No. 2020-0130179 Summary of the Invention [Problem to be solved by the invention]

[0020] The present invention aims to provide a radical scavenger composite and a manufacturing method thereof that can prevent cracking and loss of a radical scavenger, function stably in a membrane electrode assembly, and improve performance and durability.

[0021] Another object of the present invention is to provide a radical scavenger complex having improved physical and chemical stability compared to existing radical scavengers.

[0022] An object of the present invention is to provide a method for producing a radical scavenger complex which can be produced simply and inexpensively and has improved stability. [Means for solving the problem]

[0023] According to one aspect of the present invention, there is provided a radical scavenger complex, comprising: a carbon nanotube having a cap structure with one end closed; and a radical scavenger particle located within the cap of the closed cap structure.

[0024] The carbon nanotubes may be single-walled or multi-walled carbon nanotubes.

[0025] The carbon nanotubes may have a length of 0.3 to 10 μm (micrometers) and a diameter of 100 nm (nanometers) or less.

[0026] The radical scavenger particles may be between 3 and 100 nm (nanometers) in diameter.

[0027] The radical scavenger particles located within the cap may be 55 to 95% by weight based on the total weight of the entire radical scavenger complex particle.

[0028] The radical scavenger complex may be one for use in an electrode in a membrane electrode assembly for a fuel cell.

[0029] According to another aspect of the present invention, there is provided a method for producing a radical scavenger complex, the method including the steps of providing radical scavenger particles on a substrate surface; and growing carbon nanotubes (CNTs) on the surfaces of the radical scavenger particles.

[0030] Providing radical scavenger particles on the surface of the substrate may include applying a solution containing radical scavenger particles to the surface of the substrate.

[0031] The step of growing carbon nanotubes on the surface of the radical scavenger particles may be performed by a tip growth method.

[0032] The step of growing carbon nanotubes on the surface of the radical scavenger particles may include a step of first heat-treating the substrate having the radical scavenger particles provided on its surface; and a step of second heat-treating the first heat-treated substrate at a temperature higher than the first heat-treatment temperature while supplying carbon nanotube precursors.

[0033] The first heat treatment step may be performed at a temperature of 200 to 400° C. in an inert gas atmosphere, and the second heat treatment step may be performed at a temperature of 500 to 1100° C. in a mixed gas atmosphere of hydrogen and an inert gas.

[0034] The carbon nanotube precursor may be at least one selected from the group consisting of ethylene, acetylene, methylacetylene, vinylacetylene, alcohol, phthalocyanine, porphyrin, melamine, cyanamide, and dicyandiamide.

[0035] The carbon nanotube precursor may be at least one selected from the group consisting of ethylene, acetylene, methylacetylene, vinylacetylene, and alcohol, and may be provided in a gaseous state to the second heat treatment step.

[0036] The carbon nanotube precursor is at least one selected from the group consisting of phthalocyanine, porphyrin, melamine, cyanamide, and dicyandiamide, and the carbon nanotube precursor can be provided to the zone where the substrate is located for the second heat treatment step by being heated and vaporized in a second zone separated from the zone where the substrate is located.

[0037] The substrate may be any one selected from the group consisting of a copper (Cu) substrate, an iron (Fe) substrate, a nickel (Ni) substrate, and a silicon (Si) substrate.

[0038] According to yet another aspect of the present invention, there is provided a membrane electrode assembly including the above-described radical scavenger complex.

[0039] According to yet another aspect of the present invention, there is provided a fuel cell including the above-described membrane electrode assembly. Effect of the Invention

[0040] The radical scavenger complex according to the present invention can prevent damage to the radical scavenger from external physical and chemical factors, and at the same time, does not affect the radical scavenging effect of the radical scavenger, thereby improving the radical scavenging effect.

[0041] The membrane electrode assembly and fuel cell containing the radical scavenger complex according to the present invention have improved chemical durability.

[0042] The present invention enables the production of a radical scavenger complex by a simple method, and therefore has the effect of improving chemical durability without reducing production efficiency compared to the case where a radical scavenger is used as is. [Brief description of the drawings]

[0043] [Figure 1] FIG. 2 is a vertical cross-sectional view of a membrane electrode assembly.

[0044] [Diagram 2] 1 is a schematic diagram showing the overall configuration of a fuel cell according to an embodiment of the present invention;

[0045] [Diagram 3] FIG. 2 is a schematic diagram showing a process for producing a radical scavenger complex according to the present invention.

[0046] [Figure 4] 1 is a transmission electron microscope (TEM) photograph of a radical scavenger complex prepared according to the present invention.

[0047] [Diagram 5] 1 is a scanning electron microscope (SEM) photograph of an electrode containing a radical scavenger complex prepared according to the present invention.

[0048] [Figure 6]1 shows the results of chemical durability evaluation of membrane electrode assemblies prepared using radical scavengers prepared according to examples and comparative examples of the present invention.

[0049] [Figure 7] 1 shows the performance evaluation results of membrane electrode assemblies prepared using radical scavengers prepared according to the examples and comparative examples of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] Hereinafter, each component of the present invention will be described in more detail so that a person having ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited to the following content.

[0051] The terms "preferred" or "preferably" used herein refer to embodiments of the invention having certain advantages, under particular conditions. However, other embodiments may be preferred, under the same or other conditions. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are not useful, and does not exclude other embodiments within the scope of the invention.

[0052] As used herein, the term "comprising" is used in listing materials, compositions, devices, and methods useful in the present invention, and is not intended to be limiting to the listed examples.

[0053]

[0054] The present invention relates to a method for producing a radical scavenger complex comprising a radical scavenger particle and a carbon nanotube (CNT) wrapping the surface of the radical scavenger particle.

[0055] Carbon nanotubes are porous carbon materials that allow radicals generated during battery operation to come into direct contact with and react with the radical scavenger particles, while preventing the radical scavenger particles from being physically and chemically damaged within the membrane electrode assembly.

[0056] Specifically, the method for preparing a radical scavenger complex according to the present invention includes the steps of providing radical scavenger particles on a surface of a substrate, and growing carbon nanotubes (CNTs) on the surface of the radical scavenger particles.

[0057] The step of providing radical scavenger particles on the surface of the substrate may include applying a solution containing radical scavenger particles to the surface of the substrate. Specifically, the step may include forming seeds for radical scavenger particles and applying a solution containing the seeds to the surface of the substrate. The seeds may become radical scavenger particles during a subsequent heat treatment process.

[0058] After the radical scavenger particles are dispersed on the substrate surface, the carbon nanotubes grow on the surface of the radical scavenger particles into closed structure carbon nanotubes.

[0059] The complex is formed in such a manner that the radical scavenger particles are located within the carbon nanotubes in a closed structure.

[0060] The step of growing the carbon nanotubes can be achieved by various methods without being particularly limited thereto, however, it is preferable that the step of growing the carbon nanotubes on the surface of the radical scavenger particles is performed by a tip growth method.

[0061] When the carbon nanotube is grown by this tip growth method, the radical scavenger particles grow into a complex in the form of being located at the closed cap portion of the carbon nanotube.

[0062] That is, the carbon nanotube has a closed cap structure at one end, and the radical scavenger complex has a structure in which the radical scavenger particles are located at the cap portion of the closed cap structure of the carbon nanotube, and the carbon nanotube is grown underneath the radical scavenger particles.

[0063] Each step in the method for preparing the radical scavenger complex will be described in more detail below.

[0064] Providing radical scavenger particles on the surface of the substrate may include applying a solution containing radical scavenger particles to the surface of the substrate.

[0065] The solution may be applied by a solution process such as spray coating, spin coating, or inkjet printing coating.

[0066] The solution containing the radical scavenger particles may contain at least one solvent selected from water, alcohol, hexane, dimethylacetamide, dimethylsulfoxide, dimethylformamide, methylpyrrolidine, and a mixed solvent thereof.

[0067] The solution containing the radical scavenger particles may further include an auxiliary additive such as urea, which facilitates the formation of seeds from the precursor of the radical scavenger particles and allows the surface of the radical scavenger particles to be capped with carbon.

[0068] More specifically, the step of growing carbon nanotubes on the surface of the radical scavenger particles may include a first heat-treatment step (hereinafter also referred to as the first heat-treatment step) of the substrate having the radical scavenger particles provided on its surface; and a second heat-treatment step (hereinafter also referred to as the second heat-treatment step) of the first heat-treated substrate at a temperature higher than the first heat-treatment temperature while supplying a carbon nanotube precursor.

[0069] The first heat treatment step is performed in an inert gas atmosphere, e.g., a nitrogen atmosphere, at a temperature of 200 to 400° C. The first heat treatment step is performed for 1 to 4 hours. The second heat treatment step is performed in a hydrogen and inert gas mixture atmosphere, e.g., a hydrogen / nitrogen mixture atmosphere, at a temperature of 500 to 1100° C. The second heat treatment step is performed for 1 to 20 minutes.

[0070] Preferably, the first heat treatment step is performed at a temperature of 250 to 350° C. for 1.5 to 3.5 hours, and the second heat treatment step is performed at a temperature of 750 to 1050° C. for 2 to 15 minutes. If the first and second heat treatment temperatures are lower than the above temperatures, capping and growth of carbon nanotubes may not be performed well or the density and diameter of carbon nanotubes may decrease. If the temperatures are higher than the above temperatures, urea may not be capped with carbon or carbon nanotubes may grow excessively.

[0071] If the heat treatment is performed for a time shorter than the above range, capping and growth of carbon nanotubes may not be performed well, whereas if the heat treatment is performed for a time longer than the above range, carbon nanotubes may grow excessively.

[0072] The carbon nanotube growth steps including the first and second heat treatments are performed in a tube-shaped furnace. If necessary, a furnace having two heat treatment zones may be used, particularly for performing the thermal vaporization of the carbon nanotube precursor described below. For example, the carbon nanotube precursor is placed at the front end of the furnace, a substrate having radical scavenger particles dispersed on its surface is placed at the rear end, and the first heat treatment is performed at the rear end, and the carbon nanotube precursor is heated and vaporized at the front end and flows to grow carbon nanotubes on the radical scavenger particles on the substrate surface at the rear end of the furnace by the second heat treatment. That is, carbon nanotubes can be grown by deposition.

[0073] The carbon nanotube precursor is not particularly limited and may be a carbon precursor or a carbon / nitrogen precursor, for example, at least one selected from the group consisting of ethylene, acetylene, methylacetylene, vinylacetylene, alcohol, phthalocyanine, porphyrin, melamine, cyanamide, and dicyandiamide.

[0074] In an embodiment, the carbon nanotube precursor may be at least one selected from the group consisting of ethylene, acetylene, methylacetylene, vinylacetylene, and alcohol, and may be provided in a gaseous state to the second heat treatment step.

[0075] In one embodiment, the carbon nanotube precursor is at least one selected from the group consisting of phthalocyanine, porphyrin, melamine, cyanamide, and dicyandiamide, and the carbon nanotube precursor may be heated and vaporized in a second zone separated from the zone in which the substrate is located, and thereby provided to the zone in which the substrate is located for the second heat treatment step.

[0076] The carbon nanotubes constituting the radical scavenger complex may be either single-walled carbon nanotubes or multi-walled carbon nanotubes, and the complex added to one membrane electrode assembly does not necessarily have to be composed of carbon nanotubes of the same type, and may be of a mixed type.

[0077] In the radical scavenger complex, the length of the carbon nanotube may be 0.3 to 10 μm (micrometers), preferably 0.4 to 5 μm, and most preferably 0.5 to 3 μm.

[0078] If the length is longer than the above range, there is a problem that dispersibility decreases when the radical scavenger complex is added to the polymer electrolyte membrane or the catalyst layer of the electrode of the membrane electrode assembly, and the effect of improving performance and durability may be hindered. Therefore, it is preferable to configure the length within the above range. If the length is shorter than the above range, the radical scavenger particles cannot be sufficiently protected, and the effect of improving stability and suppressing performance deterioration of the complex is negligible, and the function as a structure cannot be fulfilled, resulting in no effect of improving performance and durability.

[0079] Meanwhile, in the present invention, the substrate may be any one selected from the group consisting of a copper (Cu) substrate, an iron (Fe) substrate, a nickel (Ni) substrate, and a silicon (Si) substrate. Preferably, a copper or nickel substrate may be used. More preferably, a copper substrate may be used.

[0080] When using other substrates, there is a problem that the carbon nanotubes do not grow selectively on the surface of the radical scavenger particles but grow randomly, so it is preferable to use a copper substrate as much as possible for production.

[0081] In the present invention, the radical scavenger particles can be used without any particular limitation as long as they are additives or particles having radical scavenging ability, and any substance can be used as a component of the composite in the present invention. For example, the radical scavenger particles may be one or more selected from the group consisting of transition metals, noble metals, ions thereof, salts thereof, oxides thereof, nitrides thereof, and complexes thereof.

[0082] The transition metal may be, but is not limited to, cerium (Ce), manganese (Mn), tungsten (W), cobalt (Co), vanadium (V), nickel (Ni), chromium (Cr), zirconium (Zr), yttrium (Y), iridium (Ir), iron (Fe), titanium (Ti), molybdenum (Mo), lanthanum (La), or neodymium (Nd).

[0083] The noble metal may be, but is not limited to, silver (Au), platinum (Pt), ruthenium (Ru), palladium (Pd), or rhodium (Rh).

[0084] The transition metal or noble metal salt may be a carbonate, acetate, chloride, fluoride, sulfate, phosphate, nitrate, tungsten oxide, hydroxide, ammonium acetate, ammonium sulfate, or acetylacetonate, but this is by way of example only and is not intended to be limiting, and various radical scavenger particles may be used.

[0085] Meanwhile, the radical scavenger particles may have a diameter of 3 to 100 nm (nanometers), preferably 4 to 80 nm, and most preferably 5 to 60 nm.

[0086] If the diameter is smaller than the above range, there is a problem that the radical scavenger particles are not positioned inside the carbon nanotube, and if the diameter is larger than the above range, there is a problem that the radical scavenger particles are not completely encapsulated by the carbon nanotube, and the radical scavenger particles are not positioned on the closed cap structure side of the carbon nanotube.

[0087] The radical scavenger particles located within the cap may be in an amount of 55 to 95% by weight, specifically 60 to 90% by weight, based on the total weight of the entire radical scavenger complex particle.

[0088] By setting the amount of the radical scavenger particles located within the caps of the carbon nanotubes within the above range, the performance and life of the fuel cell according to the present invention can be effectively improved.

[0089] The porous protective film has an advantage in that it can prevent the dissolution of the radical scavenger particles by reducing the mobility of the radical scavenger particles, and can improve stability by suppressing reactions with reactive species other than radicals.

[0090] In the present invention, the radical scavenger complex may have a carbon nanotube diameter of 110 nm or less in a final completed state, for example, 4 to 110 nm, preferably 5 to 90 nm, and most preferably 6 to 70 nm.

[0091] If the diameter is larger than the diameter of the carbon nanotube, there may be a problem that the radical scavenger particles flow into the pores of the carbon nanotube, but since the diameter of the carbon nanotube is determined according to the size of the radical scavenger, the lower limit of the diameter is not particularly limited.

[0092] In this way, the radical scavenger produced by the above-mentioned method for producing a radical scavenger complex prevents deterioration of the polymer electrolyte membrane and the ionomer binder, thereby preventing a decrease in fuel cell performance, and also maintains its radical scavenging performance without being eluted, thereby preventing a decrease in the performance and lifespan of the fuel cell.

[0093] In addition, since the radical scavenger complex is made of carbon nanotubes, it acts as a structural member within the electrode, improving performance and durability.

[0094]

[0095] The invention will now be explained in more detail with reference to the drawings.

[0096] However, this is merely an example for understanding the present invention, and does not limit the scope of the present invention.

[0097] 1 is a schematic cross-sectional view of a membrane electrode assembly according to the present invention. Referring to FIG. 1, the membrane electrode assembly 100 includes the polymer electrolyte membrane 50 and electrodes 20, 20' disposed on both sides of the polymer electrolyte membrane 50. The electrodes 20, 20' include electrode substrates 40, 40' and catalyst layers 30, 30' formed on the surfaces of the electrode substrates 40, 40', and may further include a microporous layer (not shown) containing conductive fine particles such as carbon powder or carbon black between the electrode substrates 40, 40' and the catalyst layers 30, 30' to facilitate diffusion of materials in the electrode substrates 40, 40'.

[0098] In the membrane electrode assembly 100, the electrode 20 disposed on one side of the ion exchange membrane 50 and performing an oxidation reaction to generate hydrogen ions and electrons from the fuel transferred to the catalyst layer 30 through the electrode substrate 40 is referred to as an anode electrode, and the electrode 20' disposed on the other side of the ion exchange membrane 500 and performing a reduction reaction to generate water from the hydrogen ions supplied through the ion exchange membrane 50 and the oxidant transferred to the catalyst layer 30' through the electrode substrate 40' is referred to as a cathode electrode.

[0099] The electrode substrates 40, 40' may be porous conductive substrates so that hydrogen or oxygen can be smoothly supplied. Representative examples include, but are not limited to, carbon paper, carbon cloth, carbon felt, or metal cloth (a porous film made of metal cloth in a fibrous state or a cloth made of polymeric fiber on which a metal film is formed). In addition, it is preferable to use electrode substrates 40, 40' that are water-repellent treated with fluorine-based resin, since this prevents the reactant diffusion efficiency from decreasing due to water generated during the operation of the fuel cell.

[0100] The fluorine-based resin may be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkylvinyl ether, polyperfluorosulfonyl fluoride alkoxyvinyl ether, fluorinated ethylene propylene, polychlorotrifluoroethylene, or a copolymer thereof.

[0101] A fuel cell according to an embodiment of the present invention includes the membrane electrode assembly, and may be, for example, a fuel cell that uses hydrogen gas as fuel.

[0102] FIG. 2 is a schematic diagram showing the overall configuration of a fuel cell according to an embodiment of the present invention.

[0103] Referring to FIG. 2, the fuel cell 200 includes a fuel supply unit 210 that supplies a mixed fuel obtained by mixing fuel and water, a reformer 220 that reforms the mixed fuel to generate a reformed gas including hydrogen gas, a stack 230 in which the reformed gas including hydrogen gas supplied from the reformer 220 undergoes an electrochemical reaction with an oxidant to generate electrical energy, and an oxidant supply unit 240 that supplies an oxidant to the reformer 220 and the stack 230.

[0104] The stack 230 includes a plurality of unit cells that generate electrical energy by inducing an oxidation / reduction reaction between the reformed gas, including hydrogen gas, supplied from the reformer 220 and an oxidant supplied from the oxidant supplying unit 240 .

[0105] Each unit cell means a unit cell that generates electricity, and includes the membrane electrode assembly that oxidizes / reduces oxygen in the reformed gas containing hydrogen gas and the oxidant, and a separator plate (also called a bipolar plate, hereinafter referred to as "separator plate") for supplying the reformed gas containing hydrogen gas and the oxidant to the membrane electrode assembly. The separator plates are placed at the center of the membrane electrode assembly and on both sides of it. Here, the separator plates located at the outermost sides of the stack are particularly referred to as end plates.

[0106] Of the separation plates, the end plate includes a pipe-shaped first supply pipe 231 for injecting reformed gas containing hydrogen gas supplied from the reforming section 220, and a pipe-shaped second supply pipe 232 for injecting oxygen gas, and the other end plate includes a first exhaust pipe 233 for discharging reformed gas containing hydrogen gas that ultimately remains unreacted in the multiple unit cells to the outside, and a second exhaust pipe 234 for discharging oxidant that ultimately remains unreacted in the unit cells to the outside.

[0107] FIG. 3 is a schematic diagram showing the process for producing the radical scavenger complex according to the present invention.

[0108] First, radical scavenger particles are dispersed on a copper substrate, and carbon nanotubes having a cap structure that is closed in the height direction based on the copper substrate are grown on the surfaces of the radical scavenger particles.

[0109] The length of the carbon nanotube gradually increases using the tip growth method, and at this time, the radical scavenger particles grow while positioned in the cap portion of the closed cap structure. Finally, after the growth of the carbon nanotube is completed, it is obtained as an independent composite separated from the copper substrate by scratching with a knife or applying ultrasound in water.

[0110] Fig. 4 is a transmission electron microscope (TEM) photograph of the radical scavenger complex prepared according to the present invention. As can be seen in Fig. 4, the complex prepared sequentially according to the process of Fig. 3 is prepared in the form of a complex in which the radical scavenger particles are located in the cap portion of the closed cap structure.

[0111] 5 is a scanning electron microscope (SEM) image of an electrode prepared using the radical scavenger complex prepared according to the present invention, which shows that the radical scavenger complex in the form of carbon nanotubes is observed in the electrode.

[0112] The present invention will be described in more detail below based on examples. However, this is merely an illustrative description for understanding the present invention, and the scope of the present invention is not limited to the following examples.

[0113]

[0114] [Example]

[0115] Dissolve 1.0g of urea in a water-alcohol mixed solution. Add 1g of Ce(NO2)3·6H2O to the mixed solution and stir at 100℃ for 3 hours to form CeOx seeds. Spray the solution onto a copper substrate and dry it. Place the copper substrate coated with the CeOx seeds into a tube-shaped furnace.

[0116] The furnace is subjected to a heat treatment in a nitrogen atmosphere at 300° C. for 2 hours.

[0117] Furthermore, heat treatment is performed at 1,000°C for 10 minutes in an atmosphere of C2H4 gas and a 5% H2 / N2 mixed gas.

[0118] When the carbon nanotubes had grown to a length of 3 μm, a process of scraping with a knife (a process of separating the composite from the substrate) was carried out to obtain a composite. At this time, the carbon nanotubes in the composite were formed as multi-walled carbon nanotubes, and the diameter of the composite was about 20 nm. A closed cap structure was observed at one end of the carbon nanotubes, and the ratio of radical scavenger particles located within the cap of the cap structure was about 60 to 90% by weight.

[0119]

[0120] [Comparative Example 1]

[0121] Carbon nanofibers loaded with radical scavenger were manufactured according to the disclosure of prior art 1 (Korean Patent No. 1282678), and carbon nanofibers with a length of 10 μm and a diameter of 30 nm were obtained in which 30% of 10 nm radical scavenger was loaded.

[0122]

[0123] [Comparative Example 2]

[0124] The radical scavenger having a porous carbon coating layer of the prior art 3 (Korean Patent Publication 10-2017-0127250) was prepared as follows: dopamine was added to a tris-HCl buffer solvent to prepare a carbon precursor coating composition, and catalyst particles capable of decomposing peroxides or radicals, such as CeO2, were added to the carbon precursor coating composition. In this case, the carbon precursor coating composition contains 0.3 parts by weight of the carbon precursor for 100 parts by weight of the catalyst particles. The carbon precursor coating composition to which the catalyst particles were added was stirred at 250 rpm at 25°C for 12 hours, stabilized at 250°C in a nitrogen atmosphere, and carbonized at 700°C in a nitrogen atmosphere to prepare a radical decomposition catalyst in which a porous carbon coating layer was formed on the surface of the catalyst particles.

[0125]

[0126] [Comparative Example 3]

[0127] A radical scavenger composite was prepared in the same manner as in the Example, except that the step of heat treating the furnace in a nitrogen atmosphere at 300°C for 2 hours was omitted. In the prepared radical scavenger composite, no closed cap structure was observed at one end of the carbon nanotube, and the proportion of radical scavenger particles located at one end was about 5 to 35 wt%.

[0128]

[0129] [Experimental Method]

[0130] [Experimental Example 1: Evaluation of Chemical Durability of Membrane Electrode Assembly]

[0131] The membrane electrode assemblies were manufactured using the radical scavengers manufactured according to the comparative example and the example. Three membrane electrode assemblies were manufactured under the same conditions and methods, but the radical scavenger of comparative example 2 was used in bulk, and the amount actually added was greater than that of the membrane electrode assemblies using comparative example 1 and the example. The chemical durability of the membrane electrode assemblies was evaluated according to the durability evaluation protocol of the U.S. Department of Energy (DOE). Specifically, to evaluate the chemical durability of the membrane electrode assemblies, the voltage retention was measured while performing the OCV hold method, and the measured values ​​are shown in FIG. 6. It can be seen from FIG. 6 that in the case of comparative example 1, the voltage suddenly decreased after 500 hours, whereas in the case of using the radical scavenger of example 1 of the present invention, the voltage was stably maintained even after 800 hours.

[0132]

[0133] [Experimental Example 2: Performance evaluation of membrane electrode assembly]

[0134] After preparing a membrane electrode assembly using the radical scavengers prepared according to the comparative example and the examples, the performance of the membrane electrode assembly was evaluated under conditions of 65°C, 50 / 50 RH, and normal pressure, and the results are shown in Figure 7. From Figure 7, it can be seen that in the case of the example containing the radical scavenger inside the carbon nanotube, there is no decrease in performance due to the increased stability of the radical scavenger, as compared to Comparative Example 1, in which the radical scavenger dissolves during fuel cell operation and inhibits the activity of the fuel cell catalyst, and the performance is improved compared to Comparative Example 2 due to the increased conductivity and improved stability of the catalyst layer due to the structural characteristics of the carbon nanotube.

Claims

1. A carbon nanotube having a cap structure with one end closed, and A radical scavenger complex comprising a radical scavenger particle located within the cap of said closed cap structure.

2. 2. The radical scavenger complex of claim 1, wherein the carbon nanotube is a single-walled carbon nanotube or a multi-walled carbon nanotube.

3. 2. The radical scavenger complex of claim 1, wherein the carbon nanotube has a length of 0.3 to 10 μm (micrometers) and a diameter of 100 nm (nanometers) or less.

4. 2. The radical scavenger complex of claim 1, wherein the radical scavenger particles have a diameter of 3 to 100 nm (nanometers).

5. 2. The radical scavenger complex of claim 1, wherein the radical scavenger particles located within the cap are 55 to 95% by weight based on the total weight of the radical scavenger complex particles.

6. 10. The radical scavenger complex of claim 1 for use in an electrode in a membrane electrode assembly for a fuel cell.

7. providing radical scavenger particles to a surface of the substrate; and growing carbon nanotubes (CNTs) on the surfaces of the radical scavenger particles; A method for producing a radical scavenger complex comprising:

8. The method of claim 7, wherein the step of providing the radical scavenger particles on the surface of the substrate comprises applying a solution containing the radical scavenger particles to the surface of the substrate.

9. The step of growing carbon nanotubes on the surface of the radical scavenger particles comprises: The method for producing the radical scavenger complex according to claim 7, which is carried out by a tip growth method.

10. The step of growing carbon nanotubes on the surface of the radical scavenger particles comprises: subjecting the substrate having the radical scavenger particles provided thereon to a first heat treatment; and The method for producing a radical scavenger complex according to claim 7, further comprising the step of subjecting the substrate that has been subjected to the first heat treatment to a second heat treatment at a temperature higher than the first heat treatment temperature while supplying a carbon nanotube precursor.

11. 11. The method of claim 10, wherein the first heat treatment step is performed at a temperature of 200 to 400° C. in an inert gas atmosphere, and the second heat treatment step is performed at a temperature of 500 to 1100° C. in a mixed gas atmosphere of hydrogen and an inert gas.

12. The method for producing a radical scavenger complex according to claim 10, wherein the carbon nanotube precursor is at least one selected from the group consisting of ethylene, acetylene, methylacetylene, vinylacetylene, alcohol, phthalocyanine, porphyrin, melamine, cyanamide, and dicyandiamide.

13. The method for producing a radical scavenger complex according to claim 10, wherein the carbon nanotube precursor is at least one selected from the group consisting of ethylene, acetylene, methylacetylene, vinylacetylene, and alcohol, and is provided in a gaseous state to the second heat treatment step.

14. The carbon nanotube precursor is at least one selected from the group consisting of phthalocyanine, porphyrin, melamine, cyanamide, and dicyandiamide; The method for producing a radical scavenger complex according to claim 10, wherein the carbon nanotube precursor is heated and vaporized in a second zone separated from the zone in which the substrate is located, and thereby provided to the zone in which the substrate is located for the second heat treatment step.

15. The method for producing a radical scavenger complex according to claim 7, wherein the substrate is any one selected from the group consisting of a copper (Cu) substrate, an iron (Fe) substrate, a nickel (Ni) substrate, and a silicon (Si) substrate.

16. A membrane electrode assembly comprising the radical scavenger complex according to claim 1.

17. A fuel cell comprising a membrane electrode assembly according to claim 16.

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