KR102124789B1 - Preparation Method for Graphenedot-PtNi Hybrid with Sponge Structure and Graphenedot-PtNi Hybrid Catalyst Thereby - Google Patents

Abstract

The present invention relates to a method for preparing a platinum-based nanocomposite having a large effective surface area, a stable and high catalytic activity, and a platinum-based catalyst prepared accordingly, in which a platinum precursor and a nickel precursor are dissolved in a carbon dot solution. The present invention relates to a method for producing a carbon dot-platinum nickel hybrid characterized by reducing and a platinum-based carbon dot-platinum nickel hybrid catalyst prepared thereby.

Description

Preparation method of graphene dot-platinum nickel hybrid of sponge structure and graphene dot-platinum nickel hybrid catalyst produced thereby{Preparation Method for Graphenedot-PtNi Hybrid with Sponge Structure and Graphenedot-PtNi Hybrid Catalyst Thereby}

The present invention relates to a method for producing a platinum-based nanohybrid having a large effective surface area, stability and high catalytic activity, and a platinum-based catalyst prepared accordingly.

A fuel cell is a device that directly converts chemical energy of fuel into electrical and thermal energy by electrochemical reaction, and is considered as a solution to new energy demand. The biggest advantage is that fuel cells can produce electricity without generating pollutants such as high efficiency, high energy density, low operating temperature, low toxicity and by-products generated during hydrocarbon combustion. Among various types of fuel cells, polymer electrolyte fuel cells (PEMFC) are viable candidates for various power applications, and commercialization of PEMFC is considered to be the most promising solution to the rapid increase in energy demand and the deepening of environmental pollution. PEMFC generates power by combining oxidation of fuel by catalyst at the anode and reduction of oxygen (ORR) at the cathode. Since the oxygen reduction reaction is very slow, a positive ORR catalyst is needed to increase the oxygen reduction rate so that the fuel cell can reach a practical level. As for the oxygen reduction reaction, platinum (Pt)-based materials to date are the most practical catalysts, but platinum-based catalysts are limited to applications in a wider range due to the disadvantage that they are too expensive to manufacture commercially viable fuel cells.

Platinum-based catalysts are the most promising catalysts for oxygen reduction reactions or oxidation of methanol and formic acid in alkaline electrolyte solutions. However, since the platinum-based catalyst is likely to be poisoned by CO and/or reaction intermediate adsorbed on the surface, the catalytic activity rapidly deteriorates over the course of the reaction time, even within hundreds of seconds. Accordingly, extensive research has been focused on the development of alternative catalysts in the past decades. A binary catalyst in the form of an alloy of platinum and other metals, such as Pt-Ru, Pt-Pd, Pt-Co, Pt-Ti, Pt-V and Pt-Au, increases the endothelial toxicity of the catalyst and improves activity It is an effective strategy to reduce the use of expensive platinum among catalysts (Korean Patent 10-1137066, US Patent 8603400).

To reduce the aggregation of the binary-based platinum nanoparticle catalyst and increase the conductivity to efficiently flow the current generated by the reaction, such as carbon black, carbon nanotubes, graphene, a reduction product of graphene oxide, amorphous carbon, etc. Catalysts having a platinum-based catalyst supported on a support of a carbon nanomaterial having a surface area have been developed (Korean Patent Registration No. 10-0480969). However, the catalyst supported on the carbon support separates and dissolves the catalyst metal nanoparticles from the carbon support during the operation of the fuel cell, which significantly reduces the effective surface area of the catalyst, which is a major cause of deterioration in fuel cell performance. Furthermore, carbon supports have properties of binding to other materials, resulting in a reduction in effective surface area because they are interposed between many nanocrystals in the production of the working electrode.

In comparison, 1-dimensional structural motifs, 2-dimensional nanosheets, and 3-dimensional networks can overcome these drawbacks and improve stability by preserving activity for a long time. In particular, in the case of a sponge structure in which porosity is imparted in the structure by constructing a network structure using interconnected nanowires, in addition, there is an effect of promoting mass transfer within the electrode. Although not much research has been conducted on the synthesis of a 3D network structure using nanowires, it has recently been reported that platinum nanocrystals can be formed on precious metal seeds such as palladium or gold to form a 3D dendritic platinum nanostructure. . Another approach is to use an iterative process that uses a template for the channel in the self-assembly structure of the porous material of the surfactant, use another metal nanowire as a template, such as silver nanowires or nickel nanowires, or use electrospinning. . Nevertheless, the problem still remains that the platinum-based nanowires by the above method are high-density, low-porosity and thus cannot maximize the structural advantages for improvement of electrocatalytic activity and stability.

Meanwhile, carbondot (Cdot) is a new carbon material with unique properties, and has received a lot of attention because of its potential applicability in optoelectronics, energy storage and conversion equipment, solar cells, biosensors, and biotech. Carbon dot is a quasi-spherical shape carbonaceous nanoparticle containing oxygen, and its size is 10 nm or less. Since carbon dot contains a large amount of functional groups containing oxygen on its surface, it is highly hydrophilic and can act as both an electron donor and an electron donor. Carbon dot can also be used as a structure to stabilize metal nanoparticles in an aqueous solution in combination with a reducing agent such as ascorbic acid. Carbon dot has high electrical conductivity properties, very large surface area, low toxicity, and chemical stability as well as biocompatibility, and the fusion of carbon dot and metal nanoparticles causes intrinsic property changes in new hybrids, resulting in catalyst, It can bring about an improvement in electrical and optical performance. However, only very limited studies have been conducted on the carbon dot/metal composite. For example, Guo et al. ( ACS Catalysis 2015, 5 , 2903.) reported that carbon dot encapsulating the surface of platinum nanoparticles greatly increases stability, but this is carbon as a catalyst supported on carbon nanotubes. The dot/metal complex itself did not form a three-dimensional structure.

Korean Registered Patent 10-1137066 U.S. Patent 8603400 Korean Registered Patent 10-0480969

Guo et al. (ACS Catalysis 2015, 5, 2903.)

In order to solve the problems of the prior art, the present invention has a platinum catalyst at a high concentration on the surface, has a large surface area, has excellent catalytic activity, has high stability and endothelial toxicity, and is also excellent in durability and a method for producing a platinum-based catalyst. It is an object to provide a platinum-based catalyst prepared thereby.

Another object of the present invention is to provide a synthetic method capable of economically producing the platinum-based catalyst in mild conditions by a simple method.

Another object of the present invention is to provide an electrode for a fuel cell including the platinum-based catalyst.

The present invention for achieving the above object relates to a method for producing a nano-sponge structure graphene dot-platinum nickel hybrid, characterized in that the platinum precursor and the nickel precursor are dissolved in a carbon dot solution and then reduced.

In the present invention, "hybrid (hybrid)" is a term distinguished from a "complex" in which a nanostructure of a conventional platinum nickel alloy is simply supported on a carbon support. Usually, when supported on a carbon support, the shape of the carbon support is maintained, and the nanostructures are physically or chemically bonded to the surface. For example, when platinum nickel is supported on a carbon nanotube (CNT), platinum nickel nanoparticles are adsorbed on the surface, but the large overall shape maintains the shape of the carbon nanotube. On the other hand, the hybrid of the present invention is characterized in that the shape of the graphene dot (Gdot) forms an overall shape, and the platinum nickel alloy is not adsorbed on the surface, but the graphene dot-platinum nickel together form a new three-dimensional structure. There is this. Where there is no carbon dot, the platinum nickel alloy produced simply has an agglomerated structure, while in the presence of carbon dot, a nanosponge structure is formed. In addition, as a result of tracking the hybrid manufacturing process over time, carbon dots and platinum nickel nanoparticles form hybrid particles, and then grow into a three-dimensional nanowire network to form nanosponge structures. It suggested that it was working zero.

In particular, the nano-sponge-structured graphene dot-platinum nickel hybrid formed by the present invention has a platinum nickel alloy nanostructure surrounded by encapsulation (encapsulation, encapsulating), so that the platinum nickel alloy nanostructure is more durable than conventional composites. Do.

The carbon dot is a carbon atom doped with a hetero atom, that is, a carbon dot doped with nitrogen (N-Cdot), a carbon doped with sulfur (S-Cdot), or a carbon dot doped with nitrogen and sulfur simultaneously It is more preferable that it is (N,S-Cdot). Doping of heteroatoms such as nitrogen and sulfur not only increases the hydrophilicity of the surface, but also improves the properties of Cdot, such as improving the properties as electron donors and electron donors and facilitating the introduction of functional groups. Therefore, since the catalytic activity is more increased when the heteroatom is doped than when the carbon dot in which the heteroatom is not doped is used, in the following example, the results for N-Cdot as the carbon dot doped with the heteroatom are described in detail. In the case of the described Cdot, S-Cdot, N,S-Cdot, it was confirmed that a similar nanowire network structure was formed. The manufacturing method of Cdot or the manufacturing method of Cdot doped with heteroatoms has been reported in the prior art, and the present invention is not related to the manufacturing method of Cdot or Cdot itself doped with heteroatoms. It is irrelevant to use the manufactured one. Therefore, detailed description of the manufacturing method thereof is omitted in this specification.

When using Cdot doped with a hetero atom, the doping amount of nitrogen and/or sulfur, which is a hetero atom, is preferably 20% by weight or less relative to carbon. When the doping amount of the hetero atom is too large, Cdot formation is difficult, and the effectiveness as a structure inducing agent is reduced when the platinum precursor and the nickel precursor are reduced.

The platinum precursor contains platinum ions, and any one that can be reduced to platinum by a reduction reaction can be used. Specific examples of the platinum precursor are tetrachloroplatinic acid (H ₂ PtCl ₄ ), hexachloroplatinic acid (H ₂ PtCl ₆ ), tetrachloroplatinic acid potassium (K ₂ PtCl ₄ ), potassium hexachloroplatinate (K ₂ PtCl ₆ ), platinum chloride (PtCl ₂ ), platinum tetrachloride (PtCl ₄ ) or a mixture thereof may be used, but is not limited thereto.

The nickel precursor also contains nickel ions, and any material that can be reduced to nickel by a reduction reaction can be used. Examples of the nickel precursor may be nickel chloride (NiCl ₂ ), nickel nitride (Ni(NO ₃ ) ₂ ), nickel sulfate (NiSO ₄ ), or a mixture thereof, but is not limited thereto.

It is preferable to use 1 to 200 parts by weight of carbon dots and 20 to 200 parts by weight of nickel precursors with respect to 100 parts by weight of the platinum precursor. When the content of Cdot was too small, it was difficult to form a nano-sponge structure due to insufficient action as a structure-inducing agent. When the content of Cdot was too large, the catalytic activity was lowered because the content of the metal exhibiting catalytic activity was relatively small. . When the ratio of the nickel precursor was too small, the price of the catalyst was increased, and the production reaction of the Gdot-PtNi hybrid was too slow, and when the ratio of the nickel precursor was too large, the catalyst activity was lowered.

Reduction of the platinum precursor and nickel precursor may be performed using any method used in the preparation of a conventional platinum/nickel bimetallic nanoalloy. That is, it can be achieved by a simple heating reaction or by additionally administering a reducing agent. As the reducing agent, one selected from the group consisting of formic acid, ascorbic acid, citric acid, oleylamine, formaldehyde, sodium borohydride, aluminum borohydride, lithium aluminum hydride, 2-methyl-2-pyrrolidine or It is possible to use a mixture of two or more, but is not limited thereto. The temperature during the reduction reaction is 20 to 180°C, and appropriate conditions may be selected depending on whether a reducing agent is used or not, depending on the type of reducing agent used.

The conditions during the reduction reaction influenced the elemental ratio of platinum and nickel in the graphene dot-platinum nickel hybrid. That is, it was confirmed that as the reduction reaction temperature increased, the content ratio of platinum to nickel decreased. This means that the composition in the hybrid can be easily controlled by controlling the reduction reaction temperature.

The present invention also relates to a nanosponge structure graphene dot-platinum nickel hybrid catalyst.

In the graphene dot-platinum nickel hybrid catalyst according to the present invention, the platinum nickel alloy nanostructure is encapsulated by graphene dot, preventing separation, dissolving, or poisoning as a solution during the reaction, thereby providing excellent durability. According to a detailed structural analysis of the graphene dot-platinum nickel hybrid, the graphene dot forming the capsule has a single-layer graphene dot structure with little defect.

In the present invention, the platinum nickel alloy nanostructure may be a 3D nanowire network structure, and the nanowire network has a nanosponge structure encapsulated by graphene dots. The nanowire has a core-shell structure composed of a platinum nickel alloy core and a platinum-rich shell as a whole. The core-shell structure as described above has an effect of further increasing the catalytic activity because platinum having a high catalytic activity is present in a higher concentration in the surface shell.

The graphene dot is more preferably a graphene dot doped with a hetero atom. Doping of a hetero atom such as nitrogen or sulfur not only increases the hydrophilicity of the surface, but also improves the properties of Gdot, such as improving the properties as an electron donor and electron donor and facilitating the introduction of functional groups. Therefore, in the case of graphene dots doped with heteroatoms, catalytic activity is more excellent than hybrids using graphene dots in which heteroatoms are not doped.

The graphene dot-platinum nickel hybrid catalyst of the present invention can be used in all fields where platinum-based catalysts are used. That is, it may be used as a catalyst for the oxygen reduction reaction at the anode of the fuel cell, or may exemplify an oxidation reaction of methanol or formic acid, a hydrogen generation reaction, but is not limited thereto.

Accordingly, the present invention provides an electrode of a fuel cell including the graphene dot-platinum nickel hybrid catalyst. A graphene dot-platinum nickel hybrid catalyst layer is formed on the electrode, and when the ionic liquid coating layer is additionally included on the catalyst layer, electrochemical activity and durability can be further increased.

As described above, the graphene dot-platinum nickel hybrid produced by the method of the present invention has a large effective surface area due to a three-dimensional nanosponge structure, and has excellent catalytic activity because it accelerates the movement of electrons due to the electrical conductivity of graphene dots. Among the hybrid structures, the platinum nickel alloy is concentrated with platinum having high catalytic activity on its surface, and can effectively utilize the catalytic activity of expensive platinum. In a hybrid structure, the platinum nickel alloy is encapsulated in graphene dots to prevent separation/dissolution in a solution, and since it has excellent endothelial toxicity, durability can be improved and useful as a platinum-based catalyst.

In addition, the graphene dot-platinum nickel of the present invention is not only a simple method of production, but it is possible to economically prepare a platinum-based catalyst due to the mild reaction conditions.

1 is a SEM and TEM image of Gdot-PtNi prepared by an embodiment of the present invention.
2 is a TEM, EDX element mapping image and XRD spectrum of Gdot-PtNi.
3 is a TEM image showing the formation of a Gdot-PtNi nanowire network over time.
4 is a TEM image showing the effect of Cdot on the formation of a three-dimensional nanowire network structure.
5 is a TEM image and EDX element mapping image of Gdot-PtNi according to the temperature of the reduction reaction.
6 is a TEM image showing the detailed structure of Gdot-PtNi.
7 is an EDX elemental mapping image showing the detailed structure of Gdot-PtNi.
8 is a Raman and XPS spectrum of Cdot before and after the reduction reaction.
Figure 9 is a reaction solution photograph showing the difference in reaction rate according to the platinum / nickel ratio.
10 is a schematic diagram showing the formation of Gdot-PtNi hybrid.
11 is a graph showing the electrochemical properties of Gdot-PtNi.
12 is a graph and images showing the electrochemical properties and durability of Gdot-PtNi electrode by ionic liquid.

Hereinafter, the present invention will be described in more detail with reference to the attached examples. However, these examples are merely examples for easily explaining the contents and scope of the technical spirit of the present invention, and the technical scope of the present invention is not limited or changed thereby. It will be obvious to those skilled in the art that various modifications and changes are possible within the scope of the technical spirit of the present invention based on these examples.

[Example]

Example 1: Preparation of graphene dot-platinum nickel hybrid

1) Preparation of nitrogen-doped graphene dot-platinum nickel hybrid

Preparation of nitrogen-doped carbon dot (N-Cdot)

A nitrogen-doped carbon dot (N-Cdot) was prepared according to the method described in Angewandte Chemie International Edition 2013, 52 , 7800. Briefly, 4 g citric acid mohohydrate and 1.24 g glycine were dissolved in 10 mL of distilled water. The solution was treated at 70° C. for 12 hours to evaporate the solvent, and the remaining residue was placed in an autoclave and heated at a rate of 4.3° C./min to perform a hydrothermal reaction at 200° C. for 3 hours. The product in black syrup was neutralized with a 1.0M NaOH solution and diluted with 100 mL distilled water. The diluted solution was dialyzed against secondary distilled water through a dialysis membrane (5 kDa MWCO). The dialysate was lyophilized to obtain yellow N-Cdot.

As a result of observing the produced N-Codt by TEM, it was spherical with a diameter of 1.5 to 2.5 nm. According to the HR-TEM image, a lattice fringe was continuously formed on the entire particle with a graphite {100} plane spaced about 0.21 nm apart. The N-Cdot solution exhibited a yellow color, and when irradiated with UV at 365 nm, exhibited a maximum emission wavelength of about 500 nm and emitted blue light. On the XPS spectrum of the prepared N-Cdot, peaks due to C 1s, N 1s, and O 1s were observed at 286.44, 399.82, and 533.09eV, respectively. The ratios of C, N, and O calculated from the XPS spectrum were 84.35, 5.29, and 9.36 atom%, respectively. In the XRD spectrum of N-Cdot, a broad peak centered at 2θ=20° was observed, due to the graphene structure. On the FT-IR spectrum, peaks corresponding to the vibrations of -CH _2- , -OH, -NH ₂ , -NH ₃ ⁺ , C=O, NH, CN, and amide were observed, and nitrogen was successfully doped into the Cdot, and oxygen It was confirmed that a number of functional groups including nitrogen and.

Preparation of Graphene Dot-Platinum Nickel Hybrid Using Nitrogen Doped Carbon Dot

In a 30 mL vial, a solution in which 2.5 mg of N-Cdot prepared above was dispersed in 20 ml distilled water and 20 mg of hexachloroplatinic acid (H ₂ PtCl ₆ , Sigma-Aldrich) and 20 mg of nickel chloride (NiCl ₂ , Sigma-Aldrich) were administered. The reaction mixture was sonicated for 15 minutes to prepare a transparent pale yellow solution. 1 mL of formic acid (88% ACS reagent) was added to the solution, the vial was capped and stirred for 15 minutes, and then left at 30°C for 3 days. After 3 days, a black precipitate was obtained by centrifugation at 7000 rpm, washed several times with ethanol, and dried at 70° C. for 2 hours.

2) Preparation of graphene dot-platinum nickel hybrid

Manufacturing of carbon dot

Carbon 2016, 96, carbon dot (Cdot) was prepared using a microwave according to the method described in 139-144. Briefly, 3 g of citric acid (Ducsan Chemical) and 3 g of urea (Shinyo Chemical) were added to 10 mL of distilled water and stirred vigorously, followed by treatment in a microwave oven (700 W) for 4 minutes. The resulting dark brown solution was cooled to room temperature and centrifuged at 7000 rpm for 30 minutes to remove large black aggregates. The supernatant containing Cdot was neutralized with bicarbonate water and washed several times with DI water. The black Cdot was collected and dried in a vacuum oven.

The dried Cdot was dispersed in ethanol and dropped on a mica substrate to prepare a sample, and then an AFM image was obtained in a tapping mode using a MultiMod 8 (Bruker) microscope. As a result of the observation, it was confirmed that the manufactured Cdot had an average particle diameter of 1.2 nm and a spherical shape representing a Gaussian distribution (detailed data not shown).

Preparation of graphene dot-platinum nickel hybrid (Cdot-PtNi)

Gdot-PtNi was prepared by the same method as that of nitrogen-doped graphene dot-platinum nickel hybrid, except that Cdot prepared above was used instead of N-Cdot.

Example 2: Analysis of physical and chemical properties of graphene dot-platinum nickel hybrid

The morphology characteristics of Gdot-PtNi prepared in 1) of Example 1 were field-radiation scanning electron microscope (FE-SEM, JSM-7000F, JEOL, Japan) and transmission electron microscope (TEM, JEM-2010HR), high-resolution transmission electrons. It was analyzed with a microscope (HRTEM, JEM-2100F, JEOL, Japan) and an X-Pert PRO MPD high-performance X-ray diffractometer (Cu-Kα radication). The sample was dispersed in ethanol and added dropwise to a carbon-coated copper TEM grid (Ted Pella, Redding, USA) and dried at room temperature and pressure. 1 shows the result, (a) is an SEM image, (b) to (d) are TEM images, and (e) to (f) are HRTEM images. 1, it can be seen that the Gdot-PtNi prepared in Example 1 forms a porous sponge structure as a whole, and according to the expanded structure analysis, it can be confirmed that the nanowires form a three-dimensional network. The nanowire was about 3 nm thick. In addition, it can be seen that the PtNi nanosponge structure is surrounded by a graphene layer, and PtNi exhibited polycrystalline having (111) and (200) planes.

Figure 2 shows the TEM image of the structure of Gdot-PtNi and EDX element mapping image and XRD spectrum. As can be seen in FIG. 2, Gdot-PtNi has a nanowire network structure, and carbon, platinum, and nickel are evenly dispersed throughout the nanowire. In addition, it can be seen that the PtNi nanosponge structure has a Pt-enriched shell structure. The weak and broad C(002) peak at the 2θ value of about 26 in the XRD spectrum shows that the graphene layer was formed, indicating that the PtNi alloy of FCC structure of Cdot-PtNi nanostructure was formed.

3 is a TEM image showing the hybrid formation process according to the reaction time of Gdot-PtNi. At 24 hours of the reaction, PtNi alloy nanoparticles and carbon dots form a hybrid, but do not form a nanowire network structure. It can be seen that the reaction time elapses and the nanoparticles begin to grow into nanowires at 24.5 hours, and the length of the nanowires increases at 25 hours of reaction.

4A to 4C are SEM images showing the effect of Cdot on the formation of a 3D nanosponge structure. In the presence of Cdot, PtNi nanoparticles form a 3D nanosponge structure (Fig. 4A), but without Cdot It can be seen that PtNi nanoparticles exist in a simple aggregated state (b, c in FIG. 4). Specifically, PtNi particles generated in the absence of Cdot are aggregated about 200 nm in size by agglomeration of PtNi nanoparticles with a size of about 5 nm as can be seen in the HR-TEM image (d to f in FIG. 4). Doing.

The results of FIGS. 3 and 4 suggested that Cdot and PtNi alloy nanoparticles that existed separately form a sponge structure by acting as a structure-directing agent of a 3D network structure.

5 is an image showing the TEM image and EDS mapping of Gdot-PtNi according to the temperature of the reduction reaction. 5) a), b), and c) are TEM images of Gdot-PtNi prepared at 20°C, 30°C, and 40°C, respectively, and d), e), and f) are 20°C, 30°C, and 40°C, respectively. It is an image showing the EDX mapping of Gdot-PtNi prepared in. According to FIG. 5, it can be seen that the ratio of Pt to Ni decreases as the reaction temperature increases during reduction.

From the report that Guo et al. reported that Cdot encapsulated Pt in Pt@Cdot/CNT and supported on carbon nanotubes, HRTEM and EDS mapping of the edge portion of the nanowire to Cdot encapsulated PtNi in the nanowire network also in the present invention. It was confirmed by. FIG. 6 is an HRTEM image of the edge region, and FIG. 7 shows EDS mapping. In FIG. 6, a) and b) are TEM images of Cdot, c) are TEM images of reduced Cdot, and d) to f) are TEM images of the edge portion of Gdot-PtNi. According to FIGS. 6 and 7, it can be seen that PtNi alloy nanoparticles have a PtNi core-Pt rich shell structure because Ni is more concentrated in the core portion of the particles, and Gdot encapsulates PtNi alloy particles.

In the TEM, it was observed that the Cdot of the edge portion has a single-layer graphene structure, and Raman spectroscopy and XPS spectroscopy were performed to further confirm the structural characteristics of the Cdot. 8, a) and c) are Cdot Raman spectrum and XPS spectrum, respectively, b) and d) are Gdot-PtNi Raman spectrum and XPS spectrum, respectively. In the Raman spectrum of FIG. 8, the I _D /I _G value was reduced to 0.67 for Cdot and 0.15 for Cdot-PtNi, showing that the intensity of the D peak was significantly reduced and structural defects were significantly reduced, and graphene in the XPS spectrum The peak ratio for the intrinsic C=C bond was greatly increased, and Cdot was also reduced in the hybrid production process to decrease the proportion of CO and C=O groups, which are oxygen-containing functional groups. This means that the multi-layer structure of Codt is exfoliated and sp3 carbon is present in the form of graphene dots (grephenedot, Gdot) converted to sp2 carbon.

Example 3: Generation of graphene dot-platinum nickel hybrid according to platinum/nickel ratio

The total weight of the platinum precursor and the nickel precursor was maintained at 40 mg, and a graphene dot-platinum nickel hybrid was prepared by the same method as 2) in Example 1, except that the molar ratio of the platinum precursor/nickel precursor was changed. Figure 9 shows the color change of the reaction solution over time, it can be seen that the reaction is delayed as the proportion of the platinum precursor decreases. Although not separately shown, the Cdot solution containing no platinum precursor and the mixed solution of the Cdot and nickel precursor did not change color after 7 days, and the Gdot-PtNi hybrid was not formed.

As a result of observing the Gdot-PtNi hybrid by HR-TEM, it was confirmed that all of them had a nano-sponge structure (data not shown). The Pt/Ni ratio in the Cdot-PtNi hybrid by TEM-EDS analysis is shown in Table 1 below.

Summarizing the above results, platinum causes the exfoliation of graphene, and in the exfoliated graphene, the PtNi alloy grows as a nanowire by graphene, and the Gdot-PtNi nanosponge structure is formed while the graphene is wrapped. Is fed. 10 is a schematic diagram of the formation of such a Gdot-PtNi nanosponge structure.

Example 4: Evaluation of catalytic activity for oxygen reduction reaction

Preparation of working electrode

A stock solution was prepared by mixing 10 ml 2-propanol with 29.8 ml distilled water (DI) and 0.2 ml 5w% Nafion solution. 0.5 ml of stock solution and 0.5 mg Gdot-PtNi were placed in a 2 ml vial and mixed for 5 minutes using a Vortex Mixer-KMC-1300V. Subsequently, a homogeneous catalyst ink was prepared by treating with a sonicator for 30 minutes at a temperature of 30°C or less.

The glass carbon rotating disk electrode was polished with a 1 μm abrasive diamond suspension, followed by a 0.05 μm Al ₂ O ₃ particle suspension. The polished electrode was washed with distilled water, sonicated with distilled water for 5 minutes, then washed with distilled water, and dried at room temperature for 30 minutes.

After the 3 µl catalyst ink prepared above was dropped-cast onto a dry glassy carbon electrode, the catalyst film was dried at room temperature for 30 minutes to prepare a working electrode.

Electrochemical measurement

Electrochemical measurements were performed in a 3-electrode cell with an ALS rotating disk electrode (RDE) device and an IVIUM potentiostat. The baekgeumheuk portion platinum (Pt platinized) mesh as a counter ^{electrode, Ag / AgCl (3M Cl -} ) reference electrode with a, was used 0.1M HClO ₄ aqueous solution as an electrolyte.

For cyclic volatmogram (CV) measurement, the 3-electrode cell is purged for 30 minutes with ultrapure nitrogen, and during the measurement, purge nitrogen and scan rate of 50 mV/s within the range of 0.05V to 1.20V It was carried out with 10 cycles. When the CV measurement was completed, it was allowed to saturate with oxygen for at least 30 minutes before measuring the ORR activity. For ORR measurement, the disk electrode was anodically scanned at a scan rate of 20 mV/s with a conventional polarization program in the range of 0.05 to 0.92 V. The ORR polarization curve was obtained at a rotation speed of 1600 rpm.

For comparison, a working electrode was prepared using PtNi prepared in the absence of Cdot instead of Gdot-PtNi and a commercially available Pt/C (c-Pt/C) catalyst (20% Pt on Vulcan XC-72, Alfa Aesar). Then, electrochemical measurement was performed by the same method.

10 is a graph showing the CV curve measured by the above method and the electrochemical effective surface area (ESCA), catalytic activity and polarization curve calculated therefrom. 11 shows that Gdot-PtNi is electrochemically more sensitive than PtNi or c-PtC, and also shows that the effective surface area (ESCA) or catalytic activity is remarkably high, which is useful as an electrocatalyst. In addition, even after repeated use of 3000 cycles, the Gdot-PtNi hybrid catalyst (e of FIG. 11) exhibits excellent durability due to a markedly small change in catalytic activity compared to the PtNi catalyst (f of FIG. 11) prepared without Cdot. Can be.

In order to confirm whether the ionic liquid can further increase the effectiveness of Gdot-PtNi, one drop of the ionic liquid was dropped on the Gdot-PtNi layer during working electrode manufacturing, followed by drying for 15 minutes. Then, while purging nitrogen, CV was measured at 50 cycles at a scan rate of 50 mV/s within a range of 0.05 V to 0.92 V. 12 is a measure of the electrochemical activity by the ionic liquid, the ionic liquid, as well as the electrochemical activity, it was confirmed that the durability is more excellent by increasing the electrochemical stability by repeated use.

Claims (11)

By dissolving a platinum precursor and a nickel precursor in a carbon dot solution, and then reducing it using formic acid,
A method of manufacturing a nanosponge structure graphene dot-platinum nickel hybrid, wherein the nanosponge structure platinum nickel alloy by three-dimensional networking of nanowires is encapsulated by a single layer graphene dot.
delete According to claim 1,
The carbon dot is a method of manufacturing a graphene dot-platinum nickel hybrid of nanosponge structure, characterized in that nitrogen or sulfur, which is a hetero atom, is doped with nitrogen and sulfur at the same time.
According to claim 1,
Method for producing a nano-sponge graphene dot-platinum nickel hybrid, characterized in that 1 to 200 parts by weight of carbon dot and 20 to 200 parts by weight of nickel precursor are used with respect to 100 parts by weight of the platinum precursor.
The nanosponge-structured graphene-dot-platinum nickel hybrid catalyst, characterized in that the nano-sponge-structured platinum-nickel alloy by nanowire 3D networking is encapsulated by a single-layer graphene-dot.
delete delete The method of claim 5,
The nanowire is a graphene dot-platinum nickel hybrid catalyst, characterized in that it has a core-shell structure composed of a platinum nickel alloy core and a platinum-rich shell.
The method of claim 5,
The graphene dot is a graphene dot-platinum nickel hybrid catalyst, characterized in that the hetero atom is nitrogen or sulfur or nitrogen and sulfur are doped at the same time.
A fuel cell electrode comprising the graphene dot-platinum nickel hybrid catalyst of claim 5 or 9.
The method of claim 10,
A fuel cell electrode further comprising an ionic liquid coating layer.

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