Metal nanostructures and methods of manufacturing same

Abstract

The invention relates to a metal nanostructure and a method of making the same. A method of making a metal nanostructure is provided that includes reacting a precursor aqueous solution including a metal salt, glycerol, and oxalic acid.

Description

Technical Field

[0001] The present invention relates to metal nanostructures and methods for manufacturing the same. Background Art

[0002] As a method for manufacturing metal nanostructures and catalysts including the same, the "polyol method" is known.

[0003] In the "polyol method", a polyol is used as a reducing agent to reduce a metal salt precursor to prepare metal nanostructures, and the manufactured metal nanostructures are supported on a carbon-based carrier.

[0004] A representative example of the "polyol" used in the polyol method is ethylene glycol, which has a dual function as a solvent and a reducing agent.

[0005] Ethylene glycol has the advantages of low viscosity and excellent reactivity, but has the following disadvantages: it is difficult to handle due to its strong toxicity and high water solubility, and its ability to uniformly control the shape and size of metal nanostructures to uniformly distribute the metal nanostructures is limited. Summary of the Invention

[0006]

Technical Problem

[0007] In order to solve the problems of using ethylene glycol as the "polyol", embodiments have been made.

[0008]

Technical Solution

[0009] In an embodiment, glycerol is used instead of ethylene glycol as the "polyol", and oxalic acid is used as a "reduction aid" for the polyol reaction.

[0010]

Advantageous Effects

[0011] In an embodiment, under the condition where glycerol and oxalic acid coexist, it is easy to control the shape and size of metal nanostructures. Description of the Drawings

[0012] Figure 1 Schematic reaction scheme illustrating a method for manufacturing metal nanostructures according to an embodiment. Detailed Description of the Embodiments

[0013] From the embodiments described in detail with the accompanying drawings, the advantages and features of the present disclosure and the methods for achieving them will become apparent. However, the embodiments may not be limited to the embodiments disclosed below.

[0014] (Definition of Terms)

[0015] Unless otherwise defined, all terms (including technical and scientific terms) used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. Further, unless otherwise defined, all terms defined in commonly used dictionaries are not to be interpreted in an idealized or exaggerated manner.

[0016] Throughout this specification, unless explicitly described to the contrary, "including" any component will be understood to imply further including other components, rather than excluding any other components. Additionally, unless the context clearly indicates otherwise, the singular form is intended to include the plural form.

[0017] In this specification, "particle size" or "average particle size" can be measured by methods well known to those skilled in the art, and for example, can be measured by a particle size analyzer or by a transmission electron microscope or a scanning electron microscope.

[0018] (Method for manufacturing metal nanostructures)

[0019] In the commonly known polyol method, ethylene glycol is used to manufacture metal nanostructures.

[0020] However, ethylene glycol is not only difficult to handle due to its strong toxicity and high water solubility, but also has limited ability to control the shape and size of metal nanostructures. In particular, when the metal nanostructures are used as metal nanostructures for fuel cell monomers or for water electrolysis, the limited ability of ethylene glycol to control the shape and size of metal nanostructures is problematic.

[0021] Specifically, when the shape and size of the metal nanostructures are uneven or large, the metal nanostructures can dissolve out from the catalyst including it, which can damage the polymer electrolyte membrane and can deteriorate the performance and durability of the fuel cell monomer or the water electrolysis device.

[0022] In an embodiment, glycerol is used instead of ethylene glycol as the "polyol", and oxalic acid is used as the "reduction aid" for the polyol reaction.

[0023] Specifically, the embodiment provides a method for manufacturing metal nanostructures, which includes reacting a precursor aqueous solution including a metal salt, glycerol, and oxalic acid.

[0024] More specifically, in the embodiment, under the condition where glycerol and oxalic acid coexist, it is easy to control the shape and size of the metal nanostructures. The process of manufacturing the metal nanostructures and the process of loading the metal nanostructures on a carbonaceous carrier are carried out in situ.

[0025] As a result, the embodiment can provide metal nanostructures with excellent durability. In particular, the metal nanostructures are suitable for use as metal nanostructures for fuel cell monomers or for water electrolysis.

[0026] Hereinafter, the raw materials for the catalyst according to the embodiment and the method for manufacturing a metal nanostructure using these raw materials will be described in detail.

[0027] Metal salt

[0028] The metal salt is a precursor of the metal nanostructure.

[0029] The metal constituting the metal salt may be a noble metal, a transition metal, an alloy thereof, or a mixture thereof.

[0030] The metal constituting the metal salt may be a noble metal, a transition metal, an alloy thereof, or a mixture thereof. Specifically, the noble metal may include platinum (Pt), ruthenium (Ru), osmium (Os), iridium (Ir), palladium (Pd), an alloy thereof, or a mixture thereof, and may be, for example, platinum. In addition, the transition metal may include cobalt (Co), iron (Fe), nickel (Ni), zinc (Zn), tin (Sn), manganese (Mn), copper (Cu), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), yttrium (Y), niobium (Nb), an alloy thereof, or a mixture thereof.

[0031] Meanwhile, the metal salt is in the form of a salt and may include a nitrate, sulfate, acetate, chloride, oxide, or a combination thereof of the metal.

[0032] Specifically, the metal salt is a metal salt including platinum (Pt), and may be dinitro-diamine platinum nitrate, chloroplatinic acid, potassium chloroplatinate, platinum oxalate, monoethanolamine platinum hydroxide, triethanolamine platinum hydroxide, or a combination thereof.

[0033] For example, the metal salt may be dinitro-diamine platinum nitrate. As a more specific example, dinitro-diamine platinum nitrate may be a basic platinum precursor such as (TEA)-2Pt(OH)6, (MEA)-2Pt(OH)6, [Pt(NH3)4]Cl2, [Pt(NH3)4](NO3)2, [Pt(NH3)4](OH)2, Pt(NH3)2Cl2, or (NH4)2[PtCl4].

[0034] Glycerol

[0035] Glycerol is a polyol compound and is represented by the following Chemical Formula 1:

[0036] [Chemical Formula 1]

[0037]

[0038] Glycerol, which is a by-product of biodiesel, can be easily and inexpensively purchased industrially, is less toxic than ethylene glycol, and is therefore used as a food additive.

[0039] Theoretically, since glycerol is a polyol compound, glycerol can be used as a solvent and a reducing agent for reducing metal salts.

[0040] However, the polyol used in the "polyol method" needs to have a low viscosity. Since glycerol has a relatively high viscosity compared to ethylene glycol, glycerol has not been processed in the "polyol method" so far.

[0041] In an embodiment, to reduce the viscosity of glycerol, glycerol is dissolved in water and used in the form of an aqueous solution. Specifically, a precursor aqueous solution including a metal salt, glycerol, and oxalic acid is reacted. More details about this will be described below.

[0042] Meanwhile, glycerol serves as a template and can make the shape and size uniform in the process of converting a metal salt into a metal nanostructure. As a result, by using glycerol, the metal nanostructures can be uniformly distributed.

[0043] Oxalic acid

[0044] Oxalic acid can assist the reducing function of glycerol in the process of converting a metal salt into a metal nanostructure while maintaining the pH of the reaction between the metal salt and glycerol. In this sense, oxalic acid serves as a "reduction aid".

[0045] Specifically, the precursor aqueous solution including a metal salt, glycerol, and oxalic acid may further include formic acid. Here, formic acid can be converted from a part of oxalic acid.

[0046] The molar ratio of the metal salt to oxalic acid can be from 1:0.5 to 1:12, specifically, from 1:3 to 1:10, more specifically, from 1:4 to 1:9, and for example, from 1:5 to 1:7. When within such a range, the role of oxalic acid as a pH adjuster and reduction aid can be improved.

[0047] Manufacturing process of metal nanostructures

[0048] Figure 1 Illustrate a schematic reaction scheme of the reaction of a precursor aqueous solution including a metal salt, glycerol, oxalic acid, and water.

[0049] Specifically, when a part or all of oxalic acid reacts with a part of glycerol and is converted into formic acid, a part of glycerol can react with a part or all of oxalic acid to produce 2-(2,3-dihydroxypropoxy)-2-oxoacetic acid or glycerol monooxalate; 2,3-dihydroxypropyl formate or glycerol monoformate can be produced by the carbon dioxide removal reaction of 2-(2,3-dihydroxypropoxy)-2-oxoacetic acid; and formic acid can be produced by the hydrolysis reaction of 2,3-dihydroxypropyl formate. In this case, glycerol can be regenerated together with formic acid.

[0050] Accordingly, reactions between oxalic acid and glycerol, reactions between metal salts and glycerol, etc. can be carried out in situ.

[0051] The reaction of the precursor aqueous solution including a metal salt, glycerol, and oxalic acid can be carried out under heat treatment conditions.

[0052] The heat treatment can be carried out in a temperature range of 60°C or higher to 150°C or lower, and specifically, can be carried out in a temperature range of 80°C or higher to 100°C or lower, for 1 hour or longer to 24 hours or shorter, specifically, for 3 hours or longer to 10 hours or shorter, and for example, for 5 hours or longer to 8 hours or shorter.

[0053] The heat treatment can be carried out in a non-oxidizing atmosphere, for example, in a reducing atmosphere (such as a hydrogen atmosphere).

[0054] In the reaction of the precursor aqueous solution including a metal salt, glycerol, and oxalic acid, due to formic acid converted from a part of oxalic acid and the remaining part of oxalic acid, the pH can be maintained in a range of pH 1 or higher to pH 9 or lower, specifically, can be maintained in a range of pH 2 or higher to pH 5 or lower, and for example, can be maintained in a range of pH 2 or higher to pH 3 or lower. Here, in order to more precisely control the pH within the desired range, a pH regulator such as nitrate, sulfate, acetate, NaOH, or NH4OH can be further used.

[0055] In the reaction of the precursor aqueous solution including a metal salt, glycerol, and oxalic acid, it is necessary to control the viscosity.

[0056] The viscosity of the precursor aqueous solution can be in a range of 10 cP or greater to 1,000 cP or less, specifically, can be in a range of 100 cP or greater to 500 cP or less, and for example, can be in a range of 150 cP or greater to 300 cP or less.

[0057] For viscosity control, based on 100 wt% of the precursor aqueous solution, the water content can be set to 10 wt% or greater to 99 wt% or less, specifically, can be set to 30 wt% or greater to 70 wt% or less, and for example, can be set to 40 wt% or greater to 60 wt% or less.

[0058] Here, the need for viscosity control is as described above.

[0059] (Specific method for manufacturing a catalyst)

[0060] Hereinafter, the method for manufacturing a catalyst according to an embodiment will be described in more detail.

[0061] Reacting a precursor aqueous solution including a metal salt, glycerol, and oxalic acid may include: a first step of preparing an aqueous glycerol solution; a second step of reacting the aqueous glycerol solution prepared in the first step with an aqueous metal salt solution; and a third step of reacting the reaction product of the second step with an aqueous oxalic acid solution.

[0062] First step

[0063] As described above, in an embodiment, to reduce the viscosity of glycerol, glycerol is dissolved in water and used in the form of an aqueous solution.

[0064] In this regard, the aqueous glycerol solution in the first step may include glycerol and water in a weight ratio of 10:90 to 80:20, and specifically may include glycerol and water in a weight ratio of 40:60 to 60:40.

[0065] Second step

[0066] The aqueous metal salt solution in the second step may include a metal salt and water in a weight ratio of 30:70 to 90:10, and specifically may include a metal salt and water in a weight ratio of 50:50 to 70:30.

[0067] The reaction between the slurry prepared in the first step and the aqueous metal salt solution may be carried out under heat treatment conditions.

[0068] The heat treatment may be carried out in a temperature range of 60 °C or higher to 150 °C or lower, and specifically, may be carried out in a temperature range of 80 °C or higher to 110 °C or lower, for 0.1 hour or longer to 24 hours or shorter, specifically, for 3 hours or longer to 10 hours or shorter, and for example, for 5 hours or longer to 8 hours or shorter.

[0069] The heat treatment may be carried out in a non-oxidizing atmosphere, for example, in a reducing atmosphere (such as a hydrogen atmosphere).

[0070] Third step

[0071] The aqueous oxalic acid solution in the third step may include oxalic acid and water in a weight ratio of 1:1 to 1:10, and specifically, may include oxalic acid and water in a weight ratio of 1:3 to 1:8.

[0072] When the reaction product of the second step reacts with the aqueous oxalic acid solution, the molar ratio of the metal salt to oxalic acid may be 1:0.5 to 1:12, specifically, may be 1:3 to 1:10, more specifically, may be 1:4 to 1:9, and for example, may be 1:5 to 1:7. Within such a range, the role of oxalic acid as a pH adjuster and reduction aid can be improved.

[0073] In the third step, an aqueous oxalic acid solution can be supplied at a rate of 10 ml / min to 100 ml / min, and specifically, the aqueous oxalic acid solution can be supplied at a rate of 30 ml / min to 80 ml / min, while controlling within a temperature range of 50 °C to 90 °C, and specifically, controlling within a temperature range of 60 to 80 °C, and then mixing with the reaction product of the second step.

[0074] After the supply is completed, the temperature of the mixture of the reaction product of the second step and the aqueous oxalic acid solution is within the range of 90 °C to 120 °C, and specifically, within the range of 100 °C to 110 °C. While maintaining this temperature range, mixing is carried out for 5 hours to 10 hours so that the nucleation and dispersion of the metal nanostructures can be uniform.

[0075] Fourth step

[0076] After the third step, a fourth step of sequentially performing aging, filtration, rinsing, and drying can be further included. This can be regarded as a post-treatment process to increase the purity of the finally obtained metal nanostructures.

[0077] Fifth step

[0078] The metal nanostructures obtained after the third step or the fourth step can be dispersed on a carrier to increase the activated surface area. Specifically, a carbon material, a metal oxide, or a combination thereof can be used as the carrier. For example, after dispersing a high-surface-area carbon material with a size of 5 μm or less in water, the dispersion of the high-surface-area carbon material is added to the metal nanostructure solution to form a material in which the metal nanostructures are loaded on the high-surface-area carbon material. The obtained product can be used as a catalyst for fuel cell monomers or a catalyst for water electrolysis.

[0079] Meanwhile, after adding the dispersion of the high-surface-area carbon material to the metal nanostructure solution, nano-grinding can be carried out so that the size of the solid particles is less than 1 μm.

[0080] (Metal nanostructures)

[0081] In an embodiment, metal nanostructures that inevitably further include glycerol in an amount greater than 0 ppm and less than 40 ppm are provided.

[0082] The metal nanostructures of the embodiment can be manufactured by the above method and can be in an activated state. The activated metal nanostructures strongly adsorb the materials used in the manufacturing process. Accordingly, when analyzing the metal nanostructures of the embodiment, the materials used in the manufacturing process can be detected.

[0083] Residual amount of glycerol

[0084] According to the above method, since glycerol is used as a solvent and a reducing agent, glycerol inevitably remains on the surface of the finally obtained metal nanostructure.

[0085] In the metal nanostructure of the embodiment, the residual amount of glycerol can be measured by the LC-MS method. Specifically, 10 g of the sample is treated with 100 g of water (H2O) and 5 g of ethanol, and then heated at about 90 °C for 4 hours. In this process, the glycerol remaining on the surface of the metal nanostructure is released by water and ethanol.

[0086] The released glycerol is measured by LC-MS and HPLC. Here, a dimethylpolysiloxane column as a non-polar column is used, a toluene standard solution with a concentration of 4 g / L is used, and the amount of added toluene is standardized to 4 μg to measure the peaks of organic compounds. In the chromatogram obtained above, the areas between n-hexane and n-hexadecane are added up, converted into the mass unit of toluene, and the amount of glycerol is calculated. Based on the amount (g) of the sample used in the experiment, the amount of glycerol (μg) is expressed in ppm, ppb or wt%.

[0087] As a result of the LC-MS measurement as described above, in the metal nanostructure of the embodiment, the residual amount of glycerol can be greater than 0 ppm and less than 50 ppm, specifically, greater than 0 ppm and less than 40 ppm, and more specifically, can be 0 ppm or greater to 30 ppm or less.

[0088] Residual amount of reactants

[0089] According to the above method, in addition to glycerol, metal salts, oxalic acid, formic acid, etc. are used as reactants. Accordingly, according to the above method, the reactants may inevitably or selectively remain on the surface of the finally obtained metal nanostructure.

[0090] The residual amount of the reactants can also be measured by the LC-MS method. The specific LC-MS measurement method is the same as above, except that "glycerol" is changed to each of the reactants.

[0091] Specifically, in the metal nanostructure of the embodiment, the residual amount of oxalic acid can be 0 ppb or greater to less than 20 ppb, specifically, 0 ppb or greater to 15 ppb or less, or 0 ppb or greater to 10 ppb or less.

[0092] Residual amount of pH regulator

[0093] According to the above method, since pH regulators such as nitrates, sulfates, acetates, NaOH or NH4OH can be further used, the pH regulators may also optionally remain. The residual amount of the pH regulator can also be measured by the LC-MS method. The specific LC-MS measurement method is the same as above, except that "glycerol" is changed to the pH regulator.

[0094] Residual amount of nitrogen compound

[0095] In the case where ethylene glycol is used according to the commonly known "polyol" method, when using basic platinum precursors such as (TEA)-2Pt(OH)6, (MEA)-2Pt(OH)6, [Pt(NH3)4]Cl2, [Pt(NH3)4](NO3)2, [Pt(NH3)4](OH)2, Pt(NH3)2Cl2 or (NH4)2[PtCl4], an excessive amount of nitrogen compounds will inevitably remain on the surface of the finally obtained metal nanostructures.

[0096] However, in the case where glycerol is used instead of ethylene glycol according to the above method, even when using basic platinum precursors, the amount of nitrogen compounds remaining in the finally obtained metal nanostructures can be reduced.

[0097] As a result, in the metal nanostructures of the embodiments, the maximum residual amount of nitrogen compounds can be 0 ppm or more and 50 ppm or less.

[0098] The maximum residual amount of nitrogen compounds can be measured by the N2-TPD method. For example, the maximum residual amount of nitrogen compounds can be determined by the following method: 0.1 g of the sample is loaded into a vertical flow reactor using quartz wool, 2 L of N2 gas is transferred to the reactor at a heating rate of 10 °C / min until the temperature rises to 400 °C, and then the exhaust gas is measured using an MKS FT-IR analyzer.

[0099] Shape and size of metal nanostructures

[0100] When using ethylene glycol and polyvinylpyrrolidone according to the commonly known "polyol" method, it is difficult to uniformly control the shape and size of the metal nanostructures in the finally obtained catalyst to achieve uniform dispersion.

[0101] However, when using glycerol and oxalic acid according to the above method, the shape and size of the finally obtained metal nanostructures can be uniformly controlled to achieve uniform dispersion. As a result, the metal nanostructures of the embodiments can be spherical metal nanoparticles.

[0102] When performing XRD analysis on the metal nanostructures of the embodiments, the grain diameter of the (111) plane can be 0.1 nm or greater up to 20 nm or less, specifically, 0.5 nm or greater up to 15 nm or less, and for example, 1 nm or greater up to 10 nm or less.

[0103] Here, the "grain diameter" refers to the size of the crystal connected to the (111) plane of the metal nanostructure. The grain diameter can be calculated from the half-width of the XRD peak of the metal nanostructures of the embodiments by the Scherrer equation.

[0104] In addition, when performing TEM analysis on the metal nanostructures of the embodiments, the particle size to be observed can be 0.1 nm or greater up to 20 nm or less, specifically, 0.5 nm or greater up to 15 nm or less, and for example, 1 nm or greater up to 10 nm or less.

[0105] Weight retention rate during heat treatment of metal nanostructures

[0106] When using glycerol and oxalic acid according to the above method, weight loss of the obtained final metal nanostructures can be inhibited.

[0107] When performing heat treatment at 250 °C, the metal nanostructures of the embodiments can have a weight retention rate of 97 wt% to 100 wt%, and the weight retention rate is measured according to Equation 1:

[0108] [Equation 1]

[0109] Weight retention rate of the metal nanostructures = 100 × (A - B) / A

[0110] In Equation 1,

[0111] A is the weight of the metal nanostructures before heat treatment, and

[0112] B is the weight of the metal nanostructures after heat treatment.

[0113] (Catalyst)

[0114] The above metal nanostructures are suitable for use as metal nanostructures for fuel cell monomers or metal nanostructures for water electrolysis.

[0115] Accordingly, as an embodiment, a catalyst including the above metal nanostructures is provided.

[0116] Carbonaceous carrier

[0117] The carrier can be a carbon-based carrier.

[0118] The carbonaceous support may include carbon black, graphite, carbon nanofibers, graphitized carbon nanofibers, carbon nanotubes, carbon nanohorns, carbon nanowires, or a combination thereof. Carbon black may include, for example, Denka black, Ketjen black, acetylene black, channel black, furnace black, lamp black, thermal black, or a combination thereof.

[0119] The specific surface area of the carbonaceous support may be from 250 m 2 / g to 1,200 m 2 / g. When the specific surface area of the carbonaceous support is 250 m 2 / g or greater, the area attached to the metal nanostructure can be increased, and the effective surface area can be increased by highly dispersing the metal nanostructure. At the same time, when the specific surface area of the carbonaceous support is greater than 1,200 m 2 / g, when forming an electrode for a fuel cell single cell, the presence rate of ultra-fine pores that are difficult for an ion exchange resin to penetrate (less than about 20 Å) increases, which can reduce the utilization efficiency of the catalyst.

[0120] The catalyst of the embodiment may include a metal and a carbonaceous support in a weight ratio of 30:70 to 95:5, 40:60 to 95:5, or 50:50 to 95:5. This can be appropriately adjusted considering the performance of the catalyst.

[0121] (Catalyst, Electrode for Fuel Cell Single Cell, Membrane-Electrode Assembly, and Fuel Cell Single Cell)

[0122] The embodiment provides an electrode for a fuel cell single cell including the above catalyst and an ion-crosslinked polymer mixed with the catalyst.

[0123] The embodiment provides a membrane-electrode assembly including an anode and a cathode facing each other and an ion exchange membrane between the anode and the cathode, wherein the anode, the cathode, or both correspond to the above electrode for a fuel cell single cell.

[0124] The embodiment provides a fuel cell single cell including the membrane-electrode assembly.

[0125] Since the electrode, the membrane-electrode assembly, and the fuel cell single cell are the same as the general electrode, membrane-electrode assembly, and fuel cell single cell for a fuel cell single cell, except that they include the above catalyst, a detailed description thereof is omitted.

[0126]

Mode of Invention

[0127] Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to specifically illustrate or explain the present invention, and are not intended to limit the scope of the present invention.

[0128] Example 1

[0129] (1) Prepare an aqueous glycerol solution containing glycerol and water (H2O) mixed at a weight ratio of 50:50 using a high-shear dispersion mixer. Wet stir the aqueous glycerol solution.

[0130] (2) Prepare an aqueous metal salt solution in which the metal salt and water (H2O) are mixed at a weight ratio of 50:50. Add the aqueous metal salt solution to the aqueous glycerol solution and heat to 100 °C for 1 hour. When adding the aqueous metal salt solution, set the weight ratio of the metal salt to glycerol to 60:40.

[0131] (3) Prepare an aqueous oxalic acid solution in which oxalic acid and water (H2O) are mixed at a weight ratio of 1:5. After heating the aqueous oxalic acid solution to 70 °C, pump the heated aqueous oxalic acid solution into the mixture where step (2) is completed. Here, considering the size distribution of the final metal nanostructures, set the molar ratio of the metal salt to oxalic acid to 1:2.

[0132] (4) Treat the final reaction mixture at 100 °C for 5 hours, cool to room temperature, and age for 12 hours with stirring at 500 rpm. Filter the aged metal nanostructure slurry and rinse with hot water to remove water, oxalic acid, and its derivatives. The filtered cake of the rinsed metal nanostructures reaches a final pH of 6.5. Vacuum dry the filtered cake of the metal nanostructures reaching the above pH at 100 °C.

[0133] Example 2

[0134] Manufacture the metal nanostructures in the same manner as in Example 1, except that the weight ratio of glycerol to water (H2O) in step (1) is changed to 40:60.

[0135] Example 3

[0136] Prepare the metal nanostructures in the same manner as in Example 1, except that the weight ratio of glycerol and water (H2O) in step (1) is changed to 60:40.

[0137] Comparative Example 1

[0138] (1) Prepare an aqueous ethylene glycol solution.

[0139] (2) Prepare an aqueous metal salt solution in which the metal salt and water (H2O) are mixed at a weight ratio of 50:50. Add the aqueous metal salt solution to the aqueous ethylene glycol solution and heat to 100 °C for 1 hour.

[0140] (3) Adjust the final reaction mixture to pH 9.5, heat it at 180 °C for 5 hours, cool it to room temperature, and age it for 12 hours with stirring at 500 rpm. Filter the aged metal nanostructures and rinse them with hot water to remove water and oxalic acid and its derivatives. The filter cake of the rinsed metal nanostructures reaches a final pH of 5. Vacuum-dry the filter cake of the metal nanostructures that have reached the above pH at 100 °C, and then further dry it in an oven dryer purged with N2 at 200 °C for 12 hours.

[0141] [Evaluation Example 1: Evaluation of the Performance of Metal Nanostructures]

[0142] Evaluation Example 1-1: Residual Amount of Each Material Remaining on the Surface of Metal Nanostructures

[0143] For the metal nanostructures of the Examples and Comparative Examples, the residual amount of each material remaining on the surface of the metal nanostructures was evaluated according to the following method, and the evaluation results are shown in Table 1.

[0144] (1) Glycerol and Oxalic Acid

[0145] For the catalysts of the Examples and Comparative Examples, the residual amount of each of glycerol and oxalic acid was evaluated. The residual amount of each material can be measured by the LC-MS method.

[0146] Specifically, treat 10 g of the sample with 100 g of water (H2O) and 5 g of ethanol, and then heat it at about 90 °C for 4 hours. In this process, the glycerol remaining on the surface of the metal nanostructures is released by water and ethanol.

[0147] Measure the released glycerol by LC-MS and HPLC. Here, a dimethylpolysiloxane column, which is a non-polar column, is used, a toluene standard solution with a concentration of 4 g / L is used, and the amount of added toluene is standardized to 4 μg to measure the peaks of organic compounds. In the chromatogram obtained above, add the areas between n-hexane and n-hexadecane, convert them into the mass unit of toluene, and calculate the amount of glycerol. Based on the amount (g) of the sample used in the experiment, express the amount (μg) of glycerol in ppm units.

[0148] In addition, measure oxalic acid in the same way as glycerol, and express it in ppb and wt% units, respectively.

[0149] (2) Nitrogen Compounds

[0150] Meanwhile, evaluate the maximum residual amount of nitrogen compounds for the metal nanostructures of the Examples and Comparative Examples.

[0151] The maximum residue amount of the nitrogen compound can be measured by the N2-TPD method. For example, the maximum residue amount of the nitrogen compound can be determined by the following method: Charge 0.1 g of the sample into a vertical flow reactor using quartz wool, transfer 2 L of N2 gas to the reactor at a heating rate of 10 °C / min until the temperature rises to 400 °C, and then measure the exhaust gas using an MKS FT-IR analyzer.

[0152] (Table 1)

[0153] Glycerol (ppm) Oxalic acid (ppb) Nitrogen compound (maximum ppm) Example 1 18 3.4 24 Example 2 9 2.1 21 Example 3 21 6.5 19 Comparative Example 1 0 0 168

[0154] Evaluation Examples 1-2: Grain diameter, particle size, and weight retention rate of metal nanostructures

[0155] For the metal nanostructures of the examples and comparative examples, the grain diameter, particle size, and weight retention rate were evaluated according to the following method, and the evaluation results are shown in Table 2.

[0156] (1) Grain diameter

[0157] For the metal nanostructures of the examples and comparative examples, the grain diameter of the (111) plane was evaluated by XRD analysis.

[0158] (2) Particle size

[0159] For the metal nanostructures of the examples and comparative examples, the particle size was evaluated by TEM analysis.

[0160] (3) Weight retention rate during heat treatment

[0161] Each of the metal nanostructures of the examples and comparative examples was heat-treated at 250 °C, and the weight retention rate was evaluated according to Equation 1:

[0162] [Equation 1]

[0163] Weight retention rate = 100 × (A - B) / A

[0164] In Equation 1,

[0165] A is the weight of the metal nanostructure before heat treatment, and

[0166] B is the weight of the metal nanostructure after heat treatment.

[0167] (Table 2)

[0168]

[0169] Evaluation Example 1-3: Modification and evaluation of the manufacturing process (1)

[0170] A metal nanostructure was fabricated in the same manner as in Example 1, except that the molar ratio of the metal salt to oxalic acid in the precursor aqueous solution was changed according to Table 3.

[0171] The grain diameter of the (111) plane of the metal nanostructure was evaluated in the same manner as in Evaluation Example 2, and the results are shown in Table 3.

[0172] (Table 3)

[0173]

[0174] Evaluation Examples 1 - 4: Modification and Evaluation of the Manufacturing Process (2)

[0175] A metal nanostructure was fabricated in the same manner as in Example 1, except that the weight ratio of oxalic acid / metal and metal in the precursor aqueous solution was changed according to Table 4.

[0176] The (111) grain diameter of the metal nanostructure was evaluated in the same manner as in Evaluation Example 2, and the particle size of the nanostructure was confirmed by SEM, and the results are shown in Table 4.

[0177] (Table 4)

[0178]

[0179] [Evaluation Example 2: Performance Evaluation of Metal Nanostructures When Applied to a Fuel Cell Monomer]

[0180] For the catalysts of the examples, the performance of the metal nanostructures when applied to a fuel cell monomer was measured, and the results are shown in Table 5.

[0181] (1) Method for Manufacturing a Fuel Cell Monomer

[0182] The catalyst loading of the anode was 0.1 mg / cm based on Pt 2 , and the anode was produced by a printing method. Nafion ion cross - linked polymer (5 wt% Nafion Dispersion, DuPont, USA) was used, and the ratio of ion cross - linked polymer / carbon was 0.9.

[0183] The catalyst loading of the cathode was 0.35 mg / cm based on Pt 2 , and the cathode was produced by a printing method. Nafion ion cross - linked polymer (5 wt% Nafion Dispersion, DuPont, USA) was used, and the ratio of ion cross - linked polymer / carbon was 0.9.

[0184] The catalyst in each of the anode and cathode was a mixture of each nanostructure of the examples and comparative examples and a carbon - based carrier with a weight ratio of 70:30.

[0185] As the electrolyte membrane for producing a membrane - electrode assembly (MEA), the NRE211 product (DuPont) is used.

[0186] The anode and cathode are placed on both sides of the electrolyte membrane, and then pressed at a pressure of 30 bar and 150 °C for 10 minutes to produce a membrane - electrode assembly (MEA).

[0187] (2) Evaluation method of fuel cell single cell

[0188] A 5 cm × 5 cm single cell is connected to a voltmeter and an ammeter. The voltage and current at different points on the IV curve are measured using the voltmeter and ammeter. The measured values of the voltage and current at each point of the IV curve are recorded and plotted on a graph to draw the IV curve, with voltage on the y - axis and current on the x - axis. Here, RH100% indicates 100% relative humidity.

[0189] Meanwhile, in order to measure the open - circuit voltage (OCV), first, the voltmeter is connected to the fuel cell single cell without connecting a load. The voltmeter reads the highest voltage that the single cell can generate.

[0190] (Table 5)

[0191]

[0192] Results

[0193] According to Tables 1 to 5, the embodiments represented by the examples can easily control the shape and size of metal nanostructures under the conditions where glycerol and oxalic acid co - exist.

[0194] If the metal nanostructures with controlled shape and size are loaded on a carbon - based carrier, the embodiments can provide a catalyst with excellent performance and durability. In particular, the metal nanostructures are suitable for use as metal nanostructures for fuel cell single cells or metal nanostructures for water electrolysis.

[0195] Although the present invention has been described in connection with presently contemplated embodiments, it should be understood that the present invention is not limited to the disclosed embodiments, but rather, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims.

Claims

1. A method for manufacturing a metal nanostructure, comprising reacting a precursor aqueous solution including a metal salt, glycerol, and oxalic acid.

2. The method according to claim 1, wherein the molar ratio of the metal salt to the oxalic acid is from 1:0.5 to 1:

12.

3. The method according to claim 1, wherein the precursor aqueous solution including the metal salt, glycerol, and oxalic acid further includes formic acid.

4. The method according to claim 3, wherein the formic acid is converted from a part of the oxalic acid.

5. The method according to claim 1, wherein the viscosity of the precursor aqueous solution including the metal salt, glycerol, and oxalic acid is 10 cP or more and 1000 cP or less.

6. The method according to claim 1, wherein based on 100 wt% of the precursor aqueous solution including the metal salt, glycerol, and oxalic acid, the water content is 10 wt% or more and 99 wt% or less.

7. The method according to claim 1, wherein the reaction of the precursor aqueous solution including the metal salt, glycerol, and oxalic acid is carried out in a temperature range of 60°C or higher and 150°C or lower.

8. The method according to claim 1, wherein the reaction of the precursor aqueous solution including the metal salt, glycerol, and oxalic acid includes: a first step of preparing a glycerol aqueous solution; a second step of reacting the glycerol aqueous solution prepared in the first step with a metal salt aqueous solution; and a third step of reacting the reaction product of the second step with an aqueous oxalic acid solution.

9. The method according to claim 8, wherein in the first step, the glycerol aqueous solution includes glycerol and water in a weight ratio of 10:90 to 80:

20.

10. The method according to claim 8, wherein in the second step, the metal salt aqueous solution includes the metal salt and water in a weight ratio of 30:70 to 90:

10.

11. The method according to claim 8, wherein the reaction between the slurry prepared in the first step and the metal salt aqueous solution is carried out in a temperature range of 60°C to 150°C for 0.1 hour to 24 hours.

12. The method according to claim 8, wherein in the third step, the aqueous oxalic acid solution includes oxalic acid and water in a weight ratio of 1:1 to 1:

10.

13. The method according to claim 8, wherein in the third step, the aqueous oxalic acid solution is added in a state where the temperature of the aqueous oxalic acid solution is controlled within a range of 50°C to 90°C, and the reaction product of the second step and the aqueous oxalic acid solution are mixed for 5 hours to 10 hours while maintaining the temperature of the mixture of the reaction product of the second step and the aqueous oxalic acid solution within a range of 90°C to 120°C.

14. The method according to claim 1, further comprising: a fourth step of aging, filtering, rinsing, and drying in sequence after the third step.

15. The method according to claim 1, further comprising: Disperse the metal nanostructure obtained after the third step or the fourth step on a carrier that is a carbon material, a metal oxide, or a combination thereof.

16. A metal nanostructure inevitably includes glycerol in an amount greater than 0 ppm and less than 50 ppm.

17. The metal nanostructure according to claim 16, wherein the metal nanostructure inevitably further includes oxalic acid in an amount of 0 ppb or greater and less than 20 ppb.

18. The metal nanostructure according to claim 16, wherein when measured by XRD analysis, the grain diameter of the (111) plane of the metal nanostructure is 0.1 nm or greater and 20 nm or less.

19. The metal nanostructure according to claim 16, wherein when measured by TEM analysis, the particle size of the metal nanostructure is 0.1 nm or greater and 20 nm or less.

20. The metal nanostructure according to claim 16, wherein when heat-treated at 250 °C, the metal nanostructure has a weight retention rate of 97 wt% to 100 wt%, and the weight retention rate is measured according to Equation 1: [Equation 1] Weight retention rate of metal nanostructure = 100×(A - B) / A Among them, In Equation 1, A is the weight of the metal nanostructure before the heat treatment, and B is the weight of the metal nanostructure after the heat treatment.

21. The metal nanostructure according to claim 16, wherein the metal nanostructure is a metal nanostructure for a fuel cell single cell or a metal nanostructure for water electrolysis.

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