KR20190011211A - Preparation Method for Gdot-PtMo Hybrid with Nanosponge Structure and Gdot-PtMo Hybrid Catalyst - Google Patents

Abstract

The present invention relates to a method for manufacturing a platinum-based nanocomposite having a wide effective surface area, stability, and a high catalytic activity, and thus a platinum-based catalyst manufactured by the same. More specifically, the present invention relates to the method for manufacturing a graphenedot-platinum molybdenum hybrid which has a feature of dissolving platinum precursors and molybdenum precursors, mixing the same with a carbon dot and then reducing the same, and a graphenedot-platinum molybdenum hybrid catalyst manufactured by the same.

Description

Plasma molybdenum hybrid of nano sponge structure and a grapindot-platinum molybdenum hybrid catalyst prepared by the same.

The present invention relates to a method for producing a platinum-based nanocomposite having a wide effective surface area, stable and high catalytic activity, and a platinum-based catalyst prepared thereby.

Fuel cells are devices that convert the chemical energy of fuel directly into electricity and heat energy by electrochemical reaction and are considered as a solution to new energy demands. The biggest advantage of fuel cells is that they can produce electricity without generating pollutants such as high efficiency, high energy density, low operating temperature, low toxicity and by-products generated by hydrocarbon combustion. Among various types of fuel cells, polymer electrolyte fuel cells (PEMFC) are viable candidates for various power applications. Commercialization of PEMFC is regarded as the most promising solution for the rapid increase of energy demand and deepening of environmental pollution. PEMFCs generate power by combining the oxidation of fuel by the catalyst at the anode and the reduction of the oxygen at the cathode (ORR). Since the oxygen reduction reaction is very slow, a bipolar ORR catalyst is needed to increase the oxygen reduction rate so that the fuel cell can reach a practical level. Platinum (Pt) -based materials are the most practical catalysts for the oxygen reduction reaction, but platinum-based catalysts are restricted to a wider range of applications due to the disadvantage that they are too expensive to produce commercially feasible fuel cells.

Hydrogen is also attracting attention as a promising renewable energy source with a clean and large energy capacity. Hydrogen evolution reaction (HER) is one of the practical ways to produce hydrogen economically and efficiently. The electrolysis of water using a catalyst is one of the most important hydrogen generation reactions with high energy conversion efficiency.

Platinum-based catalysts are the most promising catalysts for oxygen reduction reactions, oxidation reactions of methanol and formic acid in alkaline electrolyte solutions, and hydrogen generation reactions. However, since the platinum-based catalyst is prone to be poisoned by the CO and / or the reaction intermediate adsorbed on the surface, the catalytic activity rapidly drops within a few hundred seconds, depending on the reaction time. Over the past several decades, extensive research has been focused on the development of alternative catalysts. Binary catalysts in the form of alloys of platinum and other metals such as Pt-Ru, Pt-Pd, Pt-Co, Pt-Ti, Pt-V and Pt-Au increase the endotoxicity of the catalyst, And is an effective strategy for reducing the amount of expensive platinum in the catalyst (Korean Patent No. 10-1707066, USP 8603400).

On the other hand, in order to reduce the aggregation of the binary platinum nanoparticle catalyst and increase the conductivity to efficiently flow the current generated by the reaction, it is preferable to use carbon black, carbon nanotubes, graphene, reduced graphene oxide, amorphous carbon, A catalyst having a platinum-based catalyst supported on a support of a carbon nanomaterial having the same high surface area has been developed (Korean Patent No. 10-0480969). However, the catalyst supported on the carbon support detaches and dissolves the catalyst metal nanoparticles from the carbon support during the operation of the fuel cell, which greatly decreases the effective surface area of the catalyst, which is a major cause of deterioration of fuel cell performance. Furthermore, carbon supports have the property of bonding with other materials, resulting in a reduction in effective surface area since they intercalate between many nanocrystals in the production of the working electrode.

In contrast, one-dimensional structural motives, two-dimensional nanosheets, and three-dimensional networks can overcome these shortcomings and improve stability by preserving activity over a long period of time. In particular, when a network structure is formed by using interconnected nanowires to impart porosity in the structure, there is an effect of promoting mass transfer in the electrode. However, it has recently been reported that platinum nanocrystals can be grown on noble metal seeds such as palladium or gold to form three-dimensional dendritic platinum nanostructures . However, very severe reaction conditions are required for the formation of three-dimensional nanostructures, and the problems due to the poisoning of the nanostructured catalyst are not solved, so that the durability is still low. Another approach is to use a repetitive process that uses a template for the channel in a porous material self-assembled structure of a surfactant, or to use other metal nanowires such as silver nanowires or nickel nanowires as a template, or electrospinning . Nevertheless, there remains a problem that the platinum-based nanowires according to the above method are high-density and low-porosity, which can not maximize the structural advantage for improvement of electrocatalyst activity and stability.

On the other hand, carbondot (Cdot) is a new carbon material with unique properties and has attracted much attention because of its potential application in optoelectronics, energy storage and conversion equipment, solar cell, biosensor, and biotech. Carbon Dot is a quasi-spherical carbonaceous nanoparticle containing oxygen that is less than 10 nm in size. Since carbon dots contain a large amount of functional groups containing oxygen on their surface, they have high hydrophilicity and can act as both an electron donor and an electron acceptor. Carbon Dots can also be used as a structure to stabilize metal nanoparticles in aqueous solution by combining with a reducing agent such as ascorbic acid. Carbon Dot has high electrical conductivity, high surface area, low toxicity and chemical stability as well as biocompatibility. The fusion of carbon dot and metal nanoparticles causes inherent property changes in new hybrids, , Electrical and optical performance can be improved. However, very limited research has been conducted on the carbon dot / metal composite yet. For example, Guo et al. ( ACS Catalysis 2015, 5 , 2903.) reported that carbon dots encapsulate the surface of platinum nanoparticles to greatly increase stability. However, carbon nanotubes The dot / metal composite itself did not form a new three-dimensional structure.

Korean Patent No. 10-1137066 United States Patent 8603400 Korean Patent No. 10-0480969

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

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method of preparing a platinum catalyst having a platinum catalyst at a high concentration on a surface thereof, And to provide a platinum-based catalyst produced thereby.

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

Still another object of the present invention is to provide an electrode for a fuel cell comprising the platinum-based catalyst.

In order to accomplish the above object, the present invention relates to a method for preparing a graphenedot-platinum molybdenum hybrid having a nano sponge structure, characterized in that a platinum precursor and a molybdenum precursor are dissolved and then mixed with carbon dots and reduced will be.

The term "hybrid" in the present invention is a term different from a "complex" in which a nanostructure of a platinum molybdenum alloy is simply supported on a carbon support. Usually, when the carbon support is supported on a carbon support, the nanostructure is physically or chemically bonded to the surface of the carbon support while maintaining the shape of the carbon support. For example, when a platinum alloy is supported on a carbon nanotube (CNT), platinum alloy nanoparticles are adsorbed on the surface, but the overall shape of the carbon nanotube retains the shape of the carbon nanotube. On the other hand, in the hybrid of the present invention, the shape of the carbon dot used as the raw material forms the overall shape, and the platinum molybdenum alloy is not adsorbed on the surface thereof, but the graphene dot and platinum Molybdenum is also characterized by the formation of new three-dimensional structures. In the absence of carbon dot, the platinum molybdenum alloy to be produced has a merely aggregated structure, while in the presence of carbon dot, a nano sponge structure is formed (data not shown). This suggests that carbon dots act as a structure directing agent of the nano sponge structure.

Particularly, the graphene-platinum molybdenum hybrid of the nano sponge structure formed by the present invention prevents the platinum nickel alloy nanostructure from being separated, dissolved or poisoned by the solution during encapsulation and encapsulation by the grapindot, Is more excellent. According to the edge partial structure of the graindindd-platinum molybdenum hybrid, the grapindot forming the capsule has a particularly thin layered structure. This means that the multi-layered structure of semi-spherical carbon dot is peeled off in the form of graphene dots on the sheet in the course of the reaction to form a hybrid.

It is more preferable that the carbon dot is a carbon dot doped with a hetero atom. The heteroatom may be at least one selected from the group consisting of, for example, nitrogen, sulfur, phosphorus, and boron. Such doping of hetero atoms not only increases the hydrophilicity of the surface but also improves the properties of the electron donor and the electron acceptor, facilitates introduction of the functional group, and improves the properties of the Cdot. Therefore, the catalytic activity of the grapindow-platinum molybdenum hybrid prepared by the hetero-atom doping is higher than that of carbon dop not doped with the hetero-atom. In the following examples, results for N, S-Cdot were described in detail as heteroatom-doped carbon dots. However, it was confirmed that Cdot or other heteroatom-doped Cdot described in the Examples forms a similar nano sponge structure . Various manufacturing methods have been reported in the prior art for the manufacturing method of Cdot or the method for manufacturing heteroatom-doped Cdot. Since the present invention is not related to the manufacturing method of Cdot or the heteroatom-doped Cdot itself, It is also possible to use a manufactured one. Therefore, a detailed description thereof will be omitted in this specification.

When heteroatom-doped Cdot is used, the doping amount of hetero atoms is preferably 20 wt% or less with respect to carbon. When the doping amount of hetero atoms is too high, the formation of Cdot is difficult and the effect as a structure directing agent in reducing platinum precursor and molybdenum precursor is decreased.

The platinum precursor includes platinum ions, and any platinum precursor can be used as long as it can be reduced to platinum by a reduction reaction. Specific examples of the platinum precursor include tetrachloroplatinic acid (H ₂ PtCl ₄ ), hexachloroplatinic acid (H ₂ PtCl ₆ ), potassium tetrachloroplatinate (K ₂ PtCl ₄ ), potassium hexachloroplatinate (K ₂ PtCl ₆ ) (PtCl ₂ ), platinum tetrachloride (PtCl ₄ ), or a mixture thereof, but is not limited thereto.

The molybdenum precursor also contains molybdenum ions, and any molybdenum precursor can be used as long as it can be reduced to molybdenum by a reduction reaction. Examples of the molybdenum precursor include lithium molybdate (Li ₂ MoO ₄ ), calcium molybdate (CaMoO ₄ ), potassium molybdate (K ₂ MoO ₄ ), sodium molybdate (Na ₂ MoO ₄ ), molybdenum chloride (MoCl ₅ , MoCl ₃ , MoOCl ₄ ), or mixtures thereof, but are not limited thereto.

Preferably, the reaction is carried out using 1 to 200 parts by weight of carbon black and 10 to 300 parts by weight of molybdenum precursor based on 100 parts by weight of the platinum precursor. If the content of carbon dot is too small, the function as a structure directing agent is not sufficient and it is difficult to form a nano sponge structure. When the content of carbon dot is too large, the content of metal exhibiting catalytic activity becomes relatively small, . The nano sponge structure was formed regardless of the ratio of platinum and molybdenum. When the proportion of molybdenum precursor was too small, not only the catalyst price rose but also the catalytic activity was decreased. When the molybdenum precursor ratio was too high, .

The reduction of the platinum precursor and the molybdenum precursor may be carried out by any method used in the production of a conventional platinum / molybdenum binary metal nano alloy. That is, this may be accomplished by a simple heating reaction or by additionally adding a reducing agent. Examples of the reducing agent include one selected from the group consisting of formic acid, ascorbic acid, citric acid, oleylamine, formaldehyde, sodium borohydride, aluminum borohydride, lithium aluminum hydride and 2-methyl- It is possible to use a mixture of two or more, but is not limited thereto. The temperature for the reduction reaction is 20 to 180 占 폚, and suitable conditions may be selected depending on the use of the reducing agent and the type of the reducing agent to be used.

The present invention also relates to a graphene-platinum molybdenum hybrid catalyst having a nano sponge structure and a catalyst electrode to which the catalyst is applied, characterized in that a platinum molybdenum alloy having a nano sponge structure is encapsulated by grapindot. More preferably, the graphene dot is a hetero-doped graphene dot.

The grapindow-platinum molybdenum hybrid catalyst of the present invention can be used in all fields where a platinum catalyst is used. That is, the catalyst may be used as a catalyst for an oxygen reduction reaction at the cathode of a fuel cell, an oxidation reaction of methanol or formic acid, a hydrogen generation reaction, and the like, but is not limited thereto. Since the grapindow-platinum molybdenum hybrid according to the present invention has a porous nano-sponge structure, the electrochemically effective surface area is wide and the catalytic activity is high due to the additional electric conductivity characteristic of the grapindock. The Gdot-PtMo catalyst of the present invention was evaluated on the catalytic activity of hydrogen generation reaction and oxygen reduction reaction in an acidic or alkaline aqueous solution. As a result, the content of platinum was lower than that of commercial cPt / C containing 20w% of platinum The maximum current density was high and the durability was remarkable. In particular, the atomic ratio of platinum to molybdenum is preferably 50:50 to 90:10, more preferably 60:40 to 90:10.

As described above, the grapindow-platinum molybdenum hybrid produced by the method of the present invention has a wide effective surface area due to the nano sponge structure and accelerates the transfer of electrons due to the electrical conductivity of the grapindock, and thus the catalytic activity is excellent. In addition, the grapindot-platinum molybdenum hybrid can be used as a platinum-based catalyst because it has improved durability because it encapsulates a thin sheet-like graphene dot nano sponge structure to prevent separation / dissolution in solution and has excellent endotoxicity.

Further, the grapindow-platinum molybdenum of the present invention is not only simple to manufacture but also can be economically produced by mild reaction conditions.

1 is an electron microscope image of Gdot-PtMo prepared according to one embodiment of the present invention.
Figure 2 shows HAADF-STEM, EDS element mapping and HR-TEM image of Gdot-PtMo.
3 shows XRD, XPS and Raman spectra of Gdot-PtMo.
4 is a graph showing electrochemical characteristics of Gdot-PtMo.
Figure 5 is a CV curve showing the durability of cPt / C.
6 shows a polarization curve and a Tafel plot showing the electrochemical characteristics of the hydrogen evolution reaction of Gdot-PtMo.
7 is a polarization curve showing the electrochemical characteristics of the Gdot-PtMo oxygen reduction reaction.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these embodiments are merely examples for explaining the content and scope of the technical idea of the present invention, and thus the technical scope of the present invention is not limited or changed. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea of the present invention based on these examples.

[Example]

Example 1: Preparation of a grapindot-platinum molybdenum hybrid

1) Preparation of nitrogen, sulfur doped grapindot-platinum molybdenum hybrid

Preparation of nitrogen, sulfur-doped carbon dot (Cdot)

Carbon Dot (Cdot) was simultaneously doped with nitrogen and sulfur according to the method described in Angewandte Chemie International Edition 2013, 52 , 7800. Briefly, 2 g of citric acid mohohydrate and 1 g of L-cysteine were dissolved in 20 mL of DI water. The solution was treated at 70 DEG C for 12 hours to evaporate the solvent. The remaining residue was placed in an autoclave, heated at a rate of 4.3 DEG C / min, and hydrothermally reacted at 200 DEG C for 3 hours. The black syrupy product was diluted with 1100 mL DI water. The diluted solution was dialyzed against a secondary DI number through a dialysis membrane (5 kDa MWCO). The dialysis solution was lyophilized to obtain yellow Cdot. The prepared Cdot had a spherical shape with an average particle diameter of 7 nm (detailed data not shown).

Preparation of Nitrogen, Sulfur Doping Grading Dot-Platinum Molybdenum Hybrid (Gdot-PtMo)

(H ₂ PtCl ₆ , Sigma-Aldrich) and 20 mM molybdenum chloride (MoCl ₅ , manufactured by Sigma-Aldrich) were added to a 500 ml round-bottomed flask equipped with a solution of 28.1 mg of nitrogen and sulfur-doped Cdot prepared in 1) Alfa Aesar) were administered in the ratios shown in Table 1 below. The reaction mixture was sonicated for 30 minutes to produce a clear pale yellow solution. The solution was stirred with 20 ml of 50 mM NaBH ₄ and further stirred at 70 ° C for 3 hours with the lid covered until the whole solution turned black. The black precipitate was obtained by centrifugation at 500 rpm for 5 minutes, washed several times with water and ethanol, and dried at 70 ° C for 2 hours.

2) Preparation of a Grindindod-platinum molybdenum hybrid

Manufacture of carbon dot (Cdot)

Carbon Dot (Cdot) was prepared using microwaves according to the method described in Carbon 2016, 96, 139-144. Briefly, 3 g of citric acid (Duksan Chemical) and 3 g of urea (Shinyo Chemical) were added to 10 mL of DI water and vigorously stirred, 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 Cdots were collected and dried in a vacuum oven.

The dried Cdot was dispersed in ethanol and dropped on a mica substrate to prepare a sample. AFM images were obtained in a tapping mode using a MultiMod 8 (Bruker) microscope. As a result of the observation, it was confirmed that the prepared Cdot had an average particle diameter of 1.2 nm and a spherical shape showing a Gaussian distribution.

Preparation of Graded-Platemolybdenum Hybrid (Gdot-PtMo)

The Gdot-PtMo hybrid was prepared in the same manner as in the preparation of the nitrogen-sulfur-doped Gdot-PtMo hybrid except that the Cdot prepared above was used in place of the nitrogen, sulfur-doped Cdot.

Example 2: Physical and chemical characterization of grapindot-platinum molybdenum hybrid

The morphology of Gdot-PtMo prepared in Example 1 was analyzed by field emission scanning electron microscope (FE-SEM, JSM-7000F, JEOL, Japan), transmission electron microscope (TEM, JEM-2010HR) and high resolution transmission electron microscope , JEM-2100F, JEOL, Japan). Samples were dispersed in ethanol and dropped onto carbon coated copper TEM grid (Ted Pella, Redding, USA) and dried at normal temperature and pressure.

1 is an SEM, TEM and HR-TEM image of Production Example 4, and d to f are electron microscopic images of Gdot-PtMo prepared in 1) of Example 1, TEM images of Example 3 and Preparation Example 5 show that the product forms a porous nanosponge structure by a three-dimensional network as a whole regardless of the ratio of Pt / Mo.

2 shows an HAADF-STEM image (a), an EDS element mapping image (b to f), and an HR-TEM image of Gdot-PtMo of Production Example 4. The HAADF-STEM image shows that a uniform porous nano-sponge structure is formed by the metal, and it can be confirmed that the EDS mapping forms platinum and molybdenum uniformly dispersed throughout the sponge structure to form a PtMo alloy structure. The EDS mapping image of c indicates that the PtMo nano sponge structure is embedded in the carbon matrix. This can also be seen in the HR-TEM image of g, HR-TEM image shows that the core structure of PtMo is encapsulated by a transparent sheet-like Gdot shell. According to a preliminary experiment, Pt plays an important role in peeling the Cdot in the growth of the hybrid crystal to encapsulate the alloy structure by the Gdot on the sheet (detailed data in the inventor's patent application 10-2018-0068113). The lattice spacings of 0.231 and 0.195 nm observed in the HR-TEM correspond to the Pt cube, and the lattice spacing of Mo was not observed separately, indicating that the PtMo alloy retained the crystal structure of Pt. The broad peak near 23 ° is due to Gdot and shows the presence of a carbon layer.

The crystal structure of the Gdot-PtMo hybrid was further confirmed by X-ray diffraction analysis and XPS and Raman spectra. 3 is an XRD spectrum (a), an XPS spectrum (c to d), and a Raman spectrum (e) showing the results.

All the Gdot-PtMo hybrids of Production Examples 1 to 5 showed XRD patterns corresponding to the face-centered cubic (fcc) Pt structures corresponding to (111), (200) and (311). No XRD pattern corresponding to Mo or its oxide was observed. The properties of the Gdot-PtMo hybrids calculated from the XRD pattern are shown in Table 2 below. In Table 2 below, the average crystallite size was calculated using the (111) peak. (111) peak gradually became broader with increasing molybdenum ratio, indicating that the average crystal size gradually decreased. It was also shown that as the Mo content increased, the 2θ value of the (111) peak also increased and the lattice constant decreased as the Pt was replaced with Mo in the crystal lattice.

3B to 3D show the XPS spectrum of Production Example 4, which shows that graphite carbon is the main component of carbon from the main peak of C1s observed at 284.6 eV. FIG. 3, which is a Raman spectrum of Production Example 4, shows both the G band and the D band, showing amorphous carbon together with the crystal form. The ratio of I _D / I _G in Gdot-PtMo was about 0.5, which was slightly less than 0.67 of Gdot. In the hybrid manufacturing process, a spherical Cdot with a multi-layer structure was peeled and reduced and partly converted to sp ² carbon, And the like.

Example 3 Evaluation of Catalytic Activity for Hydrogen Generation and Oxygen Reduction

Manufacture of working electrode

A stock solution was prepared by mixing 10 ml 2-propanol with 39.8 ml DI water (DI) and 0.2 ml 5w% Nafion solution. 1 ml of the stock solution and 1.8 mg of Gdot-PtMo of the preparation example were placed in a 2 ml vial and mixed using a Vortex mixer-KMC-1300V for 5 minutes. Then, ultrasonic treatment was performed at a temperature of 30 캜 or lower for 1 hour to prepare a homogeneous catalyst ink.

The glacier carbon rotating disk electrode was polished with a 1 탆 polished diamond suspension and then polished with a 0.05 탆 Al ₂ O ₃ particle suspension. The polished electrode was washed with DI water, sonicated for 5 minutes with DI water, washed again with DI water, and dried at room temperature for 30 minutes.

3 [mu] l of the catalyst ink prepared above was drop-cast onto a dry glacier carbon electrode, and the catalyst film was dried at room temperature for 30 minutes to prepare a working electrode. The loading amount of the catalyst was 76 占 퐂 / cm2.

Electrochemical measurement

Electrochemical measurements were performed in a three electrode cell with an ALS rotary disk electrode (RDE) device and an IVIUM potential potentiostat. Ag / AgCl (3M Cl ^- ) and Hg / HgO were used as reference electrodes in acidic and alkaline electrolytes, respectively, using platinum mesh as a counter electrode and 0.5MH ₂ SO ₄ or 0.1M KOH aqueous solution as the electrolyte. Respectively.

The three-electrode cell was purged with ultra-pure nitrogen for 30 minutes to measure the cyclic voltamogram (CV), and a scanning speed of 50 mV / s within the range of 0.05 V to 1.20 V . The electrocatalytic activity of the catalyst was scanned by linear sweep voltammetry (LSV) at a scan rate of 5 mV / s while rotating at a speed of 1000 rpm to remove hydrogen generated at the surface of the electrode.

For comparison, a working electrode was prepared using a commercial Pt / C (cPt / C) catalyst (20% Pt on Vulcan XC-72, Alfa Aesar) instead of Gdot-PtMo and electrochemical measurements were performed by the same method Respectively.

Fig. 4 is the CV curve (a) measured by the above method in 0.1 M KOH aqueous solution and the calculated electrochemical surface area (ECSA) (b). The Gdot-PtMo of Production Example 4 exhibited the highest redox peak charge on proton adsorption / desorption on the catalyst surface, suggesting that absorption and dissolution equilibrium of proton is easily formed on the surface compared to other catalysts. The anodic peak at E ~ 0.85V corresponds to the formation of the PtMo surface oxide and the cathodic peak at 0.77V corresponds to the reduction peak of the PtMo surface oxide. (b) shows the effective surface area of the catalyst calculated from the CV curve, and Production Examples 1 and 3 showed 56.5 and 59.2 m 2 / g, respectively, similar to the commercial cPt / C catalyst (58.1 m 2 / g) Were 67.5 and 63.1 ㎡ / g, respectively.

Fig. 4 (c) shows the result of durability test for the catalyst of Production Example 4. As a result, the effective surface area reduction after 5000 cycles was about 15%. On the other hand, the reduction of the effective surface area calculated from FIG. 5 showing the results of the durability test is about 40%, indicating that the durability of the Gdot-PtMo catalyst is remarkable. c shows an HR-TEM image of Gdot-PtMo after 5000 cycles showing that the porous structure and encapsulation by Gdot are well maintained, and it can be further confirmed that the stability is excellent.

4 (d) is a Nyquist plot measured using an electrochemical impedance spectroscope (EIS) for a range of 100 kHz to 0.1 Hz under 0.1 m KOH aqueous solution and -100 mV overvoltage (?). The Nyquist plot consists of two semicircles, the first semicircle of the high frequency region being related to the porosity of the surface, and the semicircle of the low frequency region being related to the charge transfer characteristic. The magnitude of the resistance value R _ct associated with charge transfer was much smaller than that of cPt / C in Examples 4 and 5, indicating that the charge transfer capability and the catalytic activity were high. Table 3 below summarizes the electrochemical impedence spectroscopy (EIS) data fitting parameters of the catalysts calculated from the Nyquist plot.

6 and Table 4 show the electrochemical catalytic activity for the oxygen generation reaction (HER) in 0.5M H ₂ SO ₄ or 0.1M KOH aqueous solution by the linear main prior art method.

FIG. 6 (a) is a polarization curve in an aqueous solution of 0.5 MH ₂ SO ₄ , and the cPt / C catalyst exhibited a very high activity for the HER reaction with an initiation potential of almost 0 mV. The Gdot-PtMo of Production Example 4 exhibited very excellent catalytic activity at an initial voltage of -11 mV and an overvoltage of -32 V at a current density of 10 mA / cm 2. In contrast, Production Example 1, Production Example 3 and cPt / C required higher overvoltages of -47, -40, and -42 mV at the same current density, respectively. These catalyst properties are shown in Table 4. From these, it can be confirmed that Gdot-PtMo of Production Example 4 exhibits the best catalytic activity for HER under acidic conditions.

The Tafel slope is an important parameter for the evaluation of the HER mechanism such as the rate determining step, and FIG. 6b shows a Tafel plot for the HER reaction in 0.5M H ₂ SO ₄ aqueous solution. The Tafel slope of cPt / C was 36 mV / dec, which was close to the theoretical value. On the other hand, the Gdot-PtMo of Production Example 4 had a smaller value of 32 mV / dec, and the exchange current density was 0.91 mA / cm 2 higher than 0.75 mA / cm 2 of cPt / C. This means that the Gdot-PtMo nano-sponge catalyst follows the Volmer-Tafel mechanism, which is the rate-determining step of hydrogen evolution.

FIG. 6C is a graph showing the durability of the catalyst against the HER reaction in the 0.5M H ₂ SO ₄ aqueous solution. As a result, it was confirmed that the durability was very good since there was almost no change in the initiation potential or the current density after 5000 cycles. In addition, in Fig. 6 (d), which is a chronoamperometric measurement showing a comparison of the current density with time at an over-voltage of -35 mV, the cPt / C catalyst shows a significant drop in current density within 10 hours, whereas Gdot- Did not change significantly for 48 hours after a slight loss at 5 hours. As can be seen from the inside drawing of FIG. 6D, the release of a large amount of hydrogen bubbles was confirmed. This durability can be interpreted because the above-mentioned PtMo alloy is surrounded by Gdot and the toxicity is lowered.

6 and 7 show polarization curves and Tafel plots for the hydrogen generation reaction in 0.1 M KOH aqueous solution, respectively. In the alkali medium, Gdot-PtMo of Production Example 4 also showed excellent catalytic activity.

After the completion of the measurement, the disk electrode was saturated with oxygen for at least 30 minutes to measure the catalytic activity for the oxygen reduction reaction (ORR). The disk electrode was scanned at a scanning speed of 50 mV / s in a typical polarization program in the range of 0.05 to 0.92 V And anodically. The ORR polarization curve was obtained at a rotational speed of 1600 rpm. 7 shows the polarization curve for the oxygen reduction reaction, wherein a) is a 0.5M H ₂ SO ₄ aqueous solution and b) is a measurement result in 0.1M KOH aqueous solution. The ORR polarization curve also shows that Gdot-PtMo of Production Example 4 is electrochemically more sensitive than cPt / C and is more efficient as a catalyst for ORR reaction.

Claims (8)

Platinum precursor and molybdenum precursor are dissolved and then mixed with carbon dot for reduction. The present invention also provides a method for producing a graphene-platinum molybdenum hybrid having a nano sponge structure.
The method according to claim 1,
Wherein the grapindow-platinum molybdenum hybrid is encapsulated with a nano-sponge platinum molybdenum alloy by grapindock. 2. The method of claim 1, wherein the graphene-platinum molybdenum hybrid is a graphene-platinum molybdenum hybrid.
3. The method according to claim 1 or 2,
Wherein the carbon dot is doped with at least one hetero atom selected from the group consisting of nitrogen, sulfur, phosphorus, and boron.
3. The method according to claim 1 or 2,
Platinum molybdenum hybrid according to claim 1, wherein 1 to 200 parts by weight of carbon dots and 10 to 300 parts by weight of a molybdenum precursor are used relative to 100 parts by weight of the platinum precursor.
Platinum molybdenum hybrid catalyst having a nano sponge structure is characterized in that a platinum molybdenum alloy having a nano sponge structure is encapsulated by grapindot.
6. The method of claim 5,
Platinum molybdenum hybrid catalyst having a nano sponge structure, wherein the atomic ratio of platinum to molybdenum in the platinum molybdenum alloy is 50:50 to 90:10.
The method according to claim 5 or 6,
Wherein the graphene dot is doped with at least one hetero atom selected from the group consisting of nitrogen, sulfur, phosphorus, and boron, and a grapindow-platinum molybdenum hybrid catalyst having a nano sponge structure.
A catalyst electrode comprising the grapindot-platinum molybdenum hybrid catalyst of claim 5 or 6.

Images