KR20220119981A - Palladium-Reduced Graphene Oxide Composite and Preparing Method thereof - Google Patents

Abstract

In a palladium-reduced graphene composite, palladium nanoparticles grow between graphene sheets and receive strong compressive stress. The synthesis of the palladium-reduced graphene composite simultaneously reduces each precursor and uses a small amount of a surface stabilizer to have the advantage of mass-producing the composite and to simplify a process. The palladium-reduced graphene composite can have a fast absorption rate and high stability, and thus can be applied to the field of storing and transporting hydrogen energy in the form of a solid compound.

Description

Palladium-Reduced Graphene Composite and Method for Preparing the Same

Provided are a palladium-reduced graphene composite and a method for preparing the same.

Palladium metal is widely used as a material for theoretical research for the commercialization of solid hydrogen storage materials. Research on improving the hydrogen storage performance of palladium through nanoscale, alloying, and lattice strain of palladium is being conducted. It is known that the lattice transformation of nanoparticles significantly changes the thermodynamic properties of hydrogen absorption and emission. In order to control these nanoparticles, after inducing lattice deformation by arbitrarily applying a compressive stress to the nanoparticles from the outside, research is underway to observe the change in the hydrogen storage properties of the nanoparticles. However, since these studies mainly use metal in the form of a film, they cannot be directly applied to nanoparticles, and there is a limitation that compression occurs only in a specific direction.

According to prior research, in order to synthesize nanoparticles of 30 nm or larger, two steps are required to first synthesize and grow small-sized seed nanoparticles. Since a very large amount of surface stabilizer is required in this step, many synthesis and purification processes are unnecessarily involved. In addition, according to prior research, since the composite synthesis process of palladium nanoparticles and reduced graphene uses a method of independently reducing and mixing each material, the nanoparticles do not enter between the reduced graphene, and the reduced graphene It is adsorbed on the surface of the pin by weak attraction. The composite according to this prior study has poor long-term stability in repeated hydrogen storage cycles, and the hydrogen storage capacity and rate performance are lowered even in a small cycle.

According to the previously published papers on the synthesis of palladium-reduced graphene composites, palladium nanoparticles adsorbed on the surface of reduced graphene are absorbed through the process of independently synthesizing and reducing each material of palladium and reduced graphene and then mixing them. is in an unstable state. However, a number of syntheses of palladium and graphene one-pot processes have been introduced, but according to these synthesis methods, only nanoparticles of 10 nm or less are synthesized, so there is a limit to studying hydrogen storage performance according to various particle sizes. . In addition, the research on the stress and hydrogen storage performance of palladium metal, which was previously published, was mainly performed in the form of a film or an alloy, so it was difficult to apply it to metal nanoparticles of various types and sizes.

As a related prior document, Korean Patent No. 10-1613437 discloses "palladium nanodendrite-graphene nanohybrid-based hydrogen sensor and method for manufacturing the same", and Korean Patent No. 10-1617165 discloses "palladium nanocube-graphene hybrid-based A hydrogen sensor and a method for manufacturing the same” are disclosed.

However, in these prior patents, in order to synthesize a composite of 30 nm or more palladium nanoparticles and reduced graphene, the nanoparticles are first synthesized and then mixed with graphene oxide to remove oxygen functional groups. In this synthesis, since the palladium nanoparticles are adsorbed on the graphene surface rather than growing between the graphene layers, the stability of the composite is poor in the hydrogen absorption and release process. In addition, since the structure of the composite according to this synthesis is not in the form in which the palladium nanoparticles are completely surrounded by graphene, the graphene sheet does not sufficiently transmit the stress, so there is a limit in revealing the relationship between the compressive stress and the hydrogen storage performance. In addition, in the palladium nanoparticle synthesis step, a seed-mediated growth method is used to grow the size of the palladium nanoparticles, and this growth method complicates the overall process together with the step of mixing with the graphene oxide solution. In addition, since the palladium-reduced graphene composite in these prior patents independently proceeds the synthesis of each material, the process is complicated, and it is difficult to control the size of the palladium nanoparticles. Accordingly, this synthesis method acts as a limitation in applying it to the synthesis of other metal nanoparticle composites.

Korean Patent Registration 10-1613437 Korean Patent Registration 10-1617165

Acs Applied Materials & Interfaces, 2016, 8 (39), 25933-25940 Angewandte Chemie International Edition, 2014, 53 (45), 12120-12124 International Journal of Hydrogen Energy, 2016, 41 (4), 2727-2738 Nanoscale, 2014, 6 (21), 13154-13162

One embodiment is for synthesizing a hybrid material wrapped with reduced graphene so that a strong compressive stress can be applied to the palladium nanoparticles.

One embodiment is to control the compressive stress only by the size of palladium.

In addition to the above tasks, the embodiment according to the present invention may be used to achieve other tasks not specifically mentioned.

The palladium-reduced graphene composite according to an embodiment includes the first palladium nanoparticles, the second palladium nanoparticles spaced apart from the first palladium nanoparticles, the upper portion of the first palladium nanoparticles, and the upper portion of the second palladium nanoparticles It includes a first reduced graphene surrounding, and a second reduced graphene surrounding the lower portion of the first palladium nanoparticles and the lower portion of the second palladium nanoparticles.

The first reduced graphene and the second reduced graphene may each have a reticulated structure.

The first reduced graphene and the second reduced graphene may be spaced apart from each other.

The first palladium nanoparticles may receive a clamping force in the lower direction by the first reduced graphene, and may receive a clamping force in the upper direction by the second reduced graphene.

The first palladium nanoparticles may receive a lateral force in the horizontal direction by the first reduced graphene, and may receive a lateral force in the horizontal direction by the second reduced graphene.

Each of the first palladium nanoparticles and the second palladium nanoparticles may have a cube-shaped structure.

Each of the first palladium nanoparticles and the second palladium nanoparticles may have a spherical structure.

The palladium-reduced graphene composite according to an embodiment has a cube-shaped structure, has a plurality of palladium nanoparticles arranged in layers, and has a net-like structure, and the first reduction surrounding the upper portion of the plurality of palladium nanoparticles Graphene, and having a net-like structure, includes a second reduced graphene surrounding the lower portion of the plurality of palladium nanoparticles.

The first reduced graphene may surround the plurality of palladium nanoparticles while in contact with the upper portion of the plurality of palladium nanoparticles along the cube-shaped shape of the plurality of palladium nanoparticles.

The second reduced graphene may surround the plurality of palladium nanoparticles while in contact with the lower portion of the plurality of palladium nanoparticles along the cube-shaped shape of the plurality of palladium nanoparticles.

Each of the plurality of palladium nanoparticles may have a size of about 25 nm to about 80 nm.

The palladium-reduced graphene composite according to an embodiment has a spherical structure, a plurality of palladium nanoparticles arranged in layers, a network-like structure, and a first reduced graph surrounding the upper portion of the plurality of palladium nanoparticles. It has a fin, and a net-like structure, and includes a second reduced graphene surrounding the lower portion of the plurality of palladium nanoparticles.

The first reduced graphene may surround the plurality of palladium nanoparticles while in contact with the upper portion of the plurality of palladium nanoparticles along the spherical shape of the plurality of palladium nanoparticles.

The second reduced graphene may surround the plurality of palladium nanoparticles while in contact with the lower portion of the plurality of palladium nanoparticles along the spherical shape of the plurality of palladium nanoparticles.

Each of the plurality of palladium nanoparticles may have a size of about 2 nm to about 4 nm.

Palladium-reduced graphene composite manufacturing method according to an embodiment, dissolving graphene oxide powder in a solvent to prepare a graphene oxide solution, dissolving a palladium salt in a solvent to prepare a palladium precursor solution, graphene oxide After adding a reducing agent and a surface stabilizer to the pin solution, heating, and adding a palladium precursor solution to obtain a palladium-reduced graphene composite.

The palladium-reduced graphene composite may be prepared by a reduction reaction in a one-pot process.

The reducing agent may be ascorbic acid, and the surface stabilizer may be potassium bromide.

Palladium-reduced graphene composite manufacturing method according to an embodiment comprises the steps of preparing a palladium precursor solution by dissolving a palladium salt in a solvent, adding graphene oxide powder to the palladium precursor solution and stirring, palladium precursor-graphene oxide Obtaining a pin composite, drying the palladium precursor-graphene oxide composite to obtain a palladium precursor-graphene oxide composite powder, and heating the palladium precursor-graphene oxide composite powder to a reduction reaction, palladium-reduced graph and obtaining a pin composite.

The reduction reaction may occur in a one-pot process, and the reduction reaction may occur at 250 degrees Celsius to 350 degrees Celsius for 1 hour to 3 hours.

According to one embodiment, palladium nanoparticles having a size of 30 nm or more can be synthesized at a time by using a small amount of a surface stabilizer.

According to an embodiment, since the palladium nanoparticles are synthesized in one-pot with graphene oxide, the palladium nanoparticles may grow between the graphene sheets.

According to one embodiment, by controlling only the amount of the surface stabilizer, it is possible to synthesize the cube-shaped palladium nanoparticles having a size of about 24 nm to about 80 nm.

According to an embodiment, since the synthesis of the complex is based on an aqueous solution and each precursor is reduced at the same time, it is advantageous for mass production of the complex and the process can be simplified.

According to one embodiment, a composite having a fast absorption rate and high stability without storage loss can be manufactured, and this composite can be applied to the field of storing/transporting hydrogen energy.

1 is a schematic diagram of a palladium nanocube-reduced graphene composite according to an embodiment.
2 is a palladium nano spherical-reduced graphene composite according to an embodiment.
3 to 5b are TEM images of a palladium nanocube-reduced graphene composite according to an embodiment.
6 and 7 are palladium nano-spherical-reduced graphene composites according to an embodiment, showing TEM images.
8 is an XRD graph of a palladium nanocube-reduced graphene composite according to an embodiment.
9 is an XRD graph of a palladium nano spherical-reduced graphene composite according to an embodiment.
10 and 11 are XPS graphs confirming the presence or absence of reduction of graphene oxide.
12 to 16 are results of PCT (Pressure-composition-temperature) measurement for the cube-shaped palladium-reduced graphene composite according to an embodiment.
17 and 18 are spherical palladium-reduced graphene composites according to an embodiment, showing results of kinetics and PCT measurement.

With reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and the same reference numerals are used for the same or similar components throughout the specification. In addition, in the case of a well-known known technology, a detailed description thereof will be omitted.

Throughout the specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

Then, a palladium-reduced graphene composite according to an embodiment and a method for manufacturing the same will be described in detail.

Referring to FIG. 1 , the palladium-reduced graphene composite has a cube-shaped structure, a plurality of palladium nanoparticles arranged in layers, and a plurality of network-type structures surrounding the upper and lower portions of the plurality of palladium nanoparticles, respectively. of reduced graphene.

A plurality of cube-shaped palladium nanoparticles may be spaced apart from each other. A plurality of reduced graphene may be in the form of a sheet having a net-like structure, respectively, and may be spaced apart from each other in a vertical direction.

The plurality of reduced graphene may surround the plurality of palladium nanoparticles while in contact with the upper and lower surfaces of the plurality of palladium nanoparticles along the cube-shaped shape of the plurality of palladium nanoparticles.

Each of the cube-shaped palladium nanoparticles may have a size of about 25 nm to about 80 nm. Specifically, each of the cube-shaped palladium nanoparticles may have a size of about 30 nm to about 65 nm.

The plurality of cube-shaped palladium nanoparticles may receive a clamping force in the upper and lower directions by the plurality of reduced graphenes. In addition, the plurality of cube-shaped palladium nanoparticles may receive a lateral force in the horizontal direction by the plurality of reduced graphenes.

Referring to FIG. 2 , the palladium-reduced graphene composite has a spherical structure, a plurality of palladium nanoparticles arranged in layers, and a plurality of net-like structures surrounding the upper and lower portions of the plurality of palladium nanoparticles, respectively. reduced graphene.

The plurality of spherical palladium nanoparticles may be spaced apart from each other. A plurality of reduced graphene may be in the form of a sheet having a net-like structure, respectively, and may be spaced apart from each other in a vertical direction.

The plurality of reduced graphene may surround the plurality of palladium nanoparticles while contacting the upper and lower surfaces of the plurality of palladium nanoparticles along the spherical shape of the plurality of palladium nanoparticles.

Each of the plurality of spherical palladium nanoparticles may have a size of about 2 nm to about 4 nm.

The plurality of spherical palladium nanoparticles may receive a clamping force in the upper and lower directions by the plurality of reduced graphenes. In addition, the plurality of spherical palladium nanoparticles may receive a lateral force in the horizontal direction by the plurality of reduced graphenes.

The palladium-reduced graphene composite according to an embodiment and the hydrogen storage performance due to its stress effect may be applied to designing a material for a solid hydrogen storage system. Since cube-shaped or spherical nanoparticles are used rather than films or alloys, the intrinsic effect of metal nanoparticles compared to metal bulk or film is maintained, and at the same time, stress can be controlled by easily adjusting the size of the nanoparticles. By using this, it can be applied to various metal nanoparticle-based hybrid materials, contributing to building a system showing optimal hydrogen storage performance.

The size of the nanoparticles is an essential factor in controlling the effect of stress on hydrogen storage performance. According to the prior art, in the hybrid material based on the existing graphene derivative, the nanoparticles cannot grow in the graphene sheet because each component is independently synthesized, reduced, and then mixed. In addition, this limits the study of the stress effect on hydrogen storage corresponding to various particle sizes.

According to an embodiment, the optimized size of various metal nanoparticles used in a solid hydrogen storage material may be presented by controlling the stress effect on nanoparticles of various sizes of 100 nm or less.

According to one embodiment, reduced graphene serves to transfer a strong compressive stress effect to the palladium nanoparticles in all directions, thereby changing the thermodynamic properties of hydrogen absorption and release.

When the palladium-reduced graphene composite according to an embodiment has a cubic structure, the equilibrium pressure gradually increases in the hydrogen absorption process, which contributes to a rapid phase change without loss of thermodynamic storage performance. In addition, the equilibrium pressure decreases during the hydrogen release process, which increases the enthalpy of the (de)hydrogenation process, and can increase the applicability to alanate-based metal complexes, which were difficult to commercialize due to an unstable phase.

When the palladium-reduced graphene composite according to an embodiment has a spherical structure, the above-described compressive stress effect causes a tensile strain of about 3.3% to about 5.4%, and the nanoscale effect works together, so that the It indicates a faster rate of hydrogen absorption. By absorbing about 0.57 hydrogen atoms per palladium atom in about 5 minutes under a hydrogen atmosphere of 100 degrees Celsius and 2.2 bar, the initial hydrogen absorption rate is about 3 times faster than that of conventional palladium nanoparticles.

According to one embodiment, in the method of synthesizing the complex having a cube structure, the process is very simple because the palladium precursor and the graphene oxide dispersion solution are mixed together and reduced at the same time. As a surface stabilizer, small molecule potassium bromide (KBr) is used, not cetyltrimethylammonium bromide (CTAB), which has a long chain structure. The particle size can be controlled. By controlling the intensity of the stress received from reduced graphene according to the size of the nanoparticles, the hydrogen storage performance can be evaluated, which can be applied to various metal nanoparticles and contribute to constructing a solid hydrogen storage system with optimal performance.

According to an embodiment, the palladium precursor and graphene oxide are simultaneously reduced based on one-pot synthesis, and for example, in the case of a complex having a cube structure, only the amount of the surface stabilizer is adjusted to have a size of about 24 nm to about 80 nm. Particles can be synthesized, and these nanoparticles have a shape surrounded by reduced graphene. Furthermore, nanoparticles having a cubic structure having a size of about 30 nm to about 65 nm can be synthesized by controlling only the amount of the surface stabilizer. In addition, nanoparticles having a spherical structure of about 2 nm to about 4 nm can be synthesized by one process, and these nanoparticles have a form surrounded by reduced graphene. In addition, in the case of composites having a cubic structure or a spherical structure, the relationship between the stress effect and hydrogen storage performance according to the nanoparticle size is presented.

According to one embodiment, since the composite can be synthesized at the same time and the size of the surrounded nanoparticles can be easily adjusted, it is advantageous in terms of simplification of the process for mass production. Both the spherical palladium nanoparticles or the cubic palladium nanoparticles are surrounded by reduced graphene, and the correlation between the compressive stress and the nanoparticle size is presented for the first time. In particular, when the tensile strain of the composite having a spherical structure is observed with a high-resolution transmission electron microscope, changes in the hydrogen absorption rate and thermodynamic properties are clearly shown.

According to an embodiment, a composite of palladium nanoparticles having a size of about 30 nm or more and reduced graphene may be synthesized at the same time to have a form surrounded by nanoparticles, and this embodiment has not yet been reported.

According to an embodiment, a palladium nanocube-reduced graphene composite (31, 45, 65 nm) may be prepared.

According to the prior art, the synthesis of a 10-15 nm palladium nanocube and reduced graphene composite has been reported.

However, according to one embodiment, 1) a composite can be synthesized so that a nanocube of 30 nm or more can be wrapped with reduced graphene, and 2) the cube size can be controlled by adjusting only the amount of a surface stabilizer or capping agent. 3) because the palladium nanoparticles are not simply attached to graphene, but are completely surrounded, the palladium nanoparticles can be subjected to sufficient stress, and 4) during the hydrogen release and absorption process of several cycles. The shape of the palladium nanoparticles may be continuously maintained.

According to the prior art, the stress-hydrogen storage characteristic relationship has been previously reported, but the study mainly focuses on the film form. Recently, the improvement of hydrogen storage properties through nanoscaling has been led, but it is difficult to directly apply the study in the form of films to nanoparticles.

However, according to an embodiment, a basis applicable to other nano-metal hydrides may be presented as a method of utilizing cube-shaped palladium nanoparticles.

In the case of the cube-shaped palladium-reduced graphene composite according to an embodiment, it is confirmed through the TEM image that the cube-shaped palladium nanoparticles are well surrounded by the reduced graphene, and it is confirmed that it is a palladium metal through XRD analysis, And it is confirmed that graphene oxide is properly reduced to reduced graphene through XPS analysis.

In the case of a cube-shaped palladium-reduced graphene composite according to an embodiment, hydrogen absorption and release phenomena are observed through PCT analysis.

The width of the pressure hysteresis increases and the slope becomes larger than that of the conventional palladium metal, which means that it is under sufficient pressure.

The hysteresis width has a constant trend according to the size, which means that a simple size adjustment causes a change in the hydrogen storage characteristics.

Through enthalpy calculation, it can be confirmed that the enthalpy is increased compared to the conventional palladium metal, which means that the metal hydride phase is more stable. In addition, it indicates that there is a possibility that the composite according to an embodiment may be applied to the alanate series (LiAlH ₃ ), which had limitations in hydrogen storage research as a very unstable phase in the prior art.

According to an embodiment, a palladium nanosphere (sphere)-reduced graphene composite (3 to 4 nm) may be prepared.

According to one embodiment, 1) a composite can be synthesized so that about 3 to 4 nm palladium nanospheres can be wrapped with reduced graphene, and 2) palladium nanoparticles are not simply attached to graphene, but are formed by graphene. Because it is completely enclosed, the palladium nanoparticles can be subjected to sufficient stress, and 4) the shape of the palladium nanoparticles can be maintained continuously during the hydrogen release and absorption process of several cycles.

According to an embodiment, a method using spherical palladium nanoparticles may provide a basis for application to other nano-metal hydrides.

Strain analysis applied to palladium is specifically performed through HRTEM analysis and simulation. Linking the strains subjected to palladium to hydrogen storage properties by correlating with actual hydrogen absorption and release experiments through PCT analysis.

In the case of the spherical palladium-reduced graphene composite according to an embodiment, as a result of kinetics analysis, the hydrogen storage capacity is improved to about 2 times that of the conventional palladium metal, and the hydrogen absorption rate is increased.

In the case of the spherical palladium-reduced graphene composite according to an embodiment, it is confirmed that the spherical palladium nanoparticles are well surrounded by the reduced graphene through the TEM image, and it is confirmed that it is a palladium metal through XRD analysis, and XPS Through analysis, it is confirmed that graphene oxide is properly reduced to reduced graphene.

In the case of a spherical palladium-reduced graphene composite according to an embodiment, it is confirmed that the palladium nanoparticles are subjected to tensile strain through lattice parameter analysis by HRTEM.

In the case of a spherical palladium-reduced graphene composite according to an embodiment, a hydrogen absorption phenomenon is observed through kinetic analysis. For example, improved storage capacity and improved absorption rates are observed.

In the case of a spherical palladium-reduced graphene composite according to an embodiment, hydrogen absorption and release phenomena are observed through PCT analysis.

Palladium-reduced graphene composite manufacturing method according to an embodiment, dissolving graphene oxide powder in a solvent to prepare a graphene oxide solution, dissolving a palladium salt in a solvent to prepare a palladium precursor solution, graphene oxide After adding a reducing agent and a surface stabilizer to the pin solution, heating and adding a palladium precursor solution to obtain a palladium-reduced graphene composite.

Here, the palladium-reduced graphene composite is prepared by a reduction reaction in a one-pot process.

For example, the reducing agent may be ascorbic acid, and the surface stabilizer may be potassium bromide.

A small amount of the surface stabilizer may be used, for example, about 45 wt% to about 71 wt% based on the total weight of the composite. When used in an amount less than the lower limit, each facet of the particle is not distinguished, so it can be synthesized in a shape close to a spherical shape. can clump together

After adding a reducing agent and a surface stabilizer to the graphene oxide solution, it is heated to about 70 degrees Celsius to about 90 degrees Celsius, and after adding the palladium precursor solution, it is heated to about 70 degrees Celsius to about 90 degrees Celsius for about 2 hours to about 4 hours can be reacted during

Palladium-reduced graphene composite manufacturing method according to an embodiment comprises the steps of preparing a palladium precursor solution by dissolving a palladium salt in a solvent, adding graphene oxide powder to the palladium precursor solution and stirring, palladium precursor-graphene oxide Obtaining a pin composite, drying the palladium precursor-graphene oxide composite to obtain a palladium precursor-graphene oxide composite powder, and heating the palladium precursor-graphene oxide composite powder in a hydrogen atmosphere for a reduction reaction, palladium -Contains the step of obtaining a reduced graphene composite.

Here, the palladium precursor-reduced graphene composite is prepared by a reduction reaction in a one-pot process.

The reduction reaction may occur at about 250 degrees Celsius to about 350 degrees Celsius for about 1 hour to about 3 hours.

After adding the graphene oxide powder to the palladium precursor solution, the graphene exfoliation and the mixture may be stirred at room temperature for about 2 hours to about 4 hours.

Hereinafter, the present invention will be described in more detail by way of examples, but the following examples are only examples of the present invention, and the present invention is not limited thereto.

Example

Preparation of Palladium Nanocube-Reduced Graphene Composite

Potassium chloride (KCl), palladium chloride (PdCl ₂ ), ascorbic acid, potassium bromide (KBr) are Sigma-Aldrich products, graphene oxide powder (Graphene oxide powder) , GO) is a product of Standard Graphene Inc.

32 mL of GO solution was prepared by ultrasonically dispersing 1.2 mg/mL GO powder in DI water.

A palladium precursor aqueous solution is synthesized. Add 182 mg PdCl ₂ and 153 mg KCl to 12.6 mL DI water and react with ultrasonic stirring at room temperature for about 2 hours to synthesize K ₂ PdCl ₄ (aq), a palladium precursor.

In 32 mL of GO(aq), 240 mg of ascorbic acid as a reducing agent and 500 mg of KBr as a capping agent are added, heated to about 80 degrees Celsius while stirring with a magnetic bar, and maintained for about 10 minutes to prepare an aqueous solution.

In the one-pot process, 12.5 mL of K ₂ PdCl ₄ (aq), a palladium precursor solution, was added to the prepared aqueous solution through a needle, and then reacted at about 80 degrees Celsius for about 3 hours.

After washing with DI water and ethanol, it is dried in a vacuum oven at about 60 degrees Celsius for one day.

A cube-shaped palladium-reduced graphene composite powder (rGO-Pd powder) is prepared, and the composite has an edge size of about 31 nm. Referring to FIG. 3 , a TEM image of a cube-shaped palladium-reduced graphene composite having a size of about 31 nm and a size distribution of nanoparticles are confirmed. In addition, referring to FIG. 8 , the crystal structure of the palladium nanoparticles is confirmed through XRD analysis of the cube-shaped palladium-reduced graphene composite.

A cube-shaped palladium-reduced graphene composite powder is prepared in the same manner as for the rest, except that the amount of KBr to be input is 1000 mg, and at this time, the composite is about 45 nm. Referring to FIG. 4 , a TEM image of a cube-shaped palladium-reduced graphene composite having a size of about 45 nm and a size distribution of nanoparticles are confirmed.

A cube-shaped palladium-reduced graphene composite powder is prepared in the same manner as for the rest, except that the amount of KBr to be input is 1500 mg, in which case the composite is about 65 nm. Referring to FIG. 5a , a TEM image of a cube-shaped palladium-reduced graphene composite having a size of about 65 nm and a size distribution of nanoparticles are confirmed.

Accordingly, by adjusting the amount of the capping agent, it is possible to control the size of the palladium nanoparticles.

In addition, referring to FIG. 5b , in the case of a cube-shaped palladium-reduced graphene composite, since the palladium precursor solution and the graphene oxide solution are mixed and reduced in a one-pot process, the palladium-reduced graphene composite is formed with various crystalline zone axes. Even in the case of tilting, the palladium nanoparticles are well surrounded by reduced graphene. For example, palladium nanoparticles are surrounded by reduced graphene at (112) crystal band axes, (013) crystal band axes, and (001) crystal band axes. Accordingly, the palladium nanoparticles can be sufficiently stressed by the reduced graphene in all directions, and aggregation between the palladium nanoparticles can be reduced for several cycles in the hydrogen absorption and release process.

In contrast, in the case of a conventional palladium-graphene composite, palladium nanoparticles are synthesized by reducing the palladium precursor solution, and the synthesized palladium nanoparticles are supported again in a graphene oxide solution and then reduced, palladium-reduced graphene composites is created Due to such a conventional manufacturing method, the palladium nanoparticles are attached to the surface of the reduced graphene, and the reduced graphene does not surround the palladium nanoparticles in various directions. In addition, in the case of the conventional palladium-reduced graphene composite, aggregation between the palladium nanoparticles is increased during the hydrogen absorption and release process.

Preparation of Palladium Nanospherical-Reduced Graphene Composite

Palladium chloride, hydrochloric acid (hydrochloric acid, HCl, 36.5-38.0% is a product of Sigma-Aldrich, and graphene oxide powder is a product of Standard Graphene Inc.)

Add 302.8 mg PdCl ₂ and 277.6 μL HCl to 300 mL DI water and react with ultrasonic stirring at room temperature for about 2 hours to synthesize H ₂ PdCl ₄ (aq), a palladium precursor.

In a one-pot process, 240 mg of GO powder is added to 300 mL of H ₂ PdCl ₄ (aq), and ultrasonically stirred at room temperature for about 3 hours.

After washing with DI water, it is dried in a vacuum oven at about 60 degrees Celsius for one day.

The dried powder is subjected to a reduction reaction (4% H ₂ /96% N ₂ gas condition) at about 300 degrees Celsius in a tube furnace for about 2 hours.

Referring to FIG. 6 , a TEM image of a spherical palladium-reduced graphene composite having a size of about 3 nm and a size distribution of nanoparticles are confirmed. Referring to FIG. 7 , it is confirmed that the spherical palladium nanoparticles are surrounded by the reduced graphene layer. In addition, referring to FIG. 9 , the crystal structure of the palladium nanoparticles is confirmed through XRD analysis of the spherical palladium-reduced graphene composite.

10 and 11 , in the composite according to an embodiment, the presence or absence of reduction of graphene oxide is confirmed.

Hydrogen storage properties

For the cube-shaped palladium-reduced graphene composite prepared in the above-described embodiment, the results of PCT (Pressure-composition-temperature) measurement using HyEnergy Sieverts PCT Pro-2000 are shown in FIGS. 12 to 16 .

12 to 14 show the results of experiments on the absorption and release of hydrogen at 98 degrees Celsius, 112 degrees Celsius, and 128 degrees Celsius, respectively. The hydrogen concentration when equilibrium is achieved by flowing hydrogen gas of a constant pressure step through the sample is recorded (Sievert's equation). Before the experiment, a process for activating the sample is required, and the evacuation process is performed at 98 degrees Celsius for 1 hour or more, and the metal is hydrogenated at a hydrogen pressure of 1 MPa.

Referring to FIG. 15 , it is confirmed that as the size of the composite decreases, the compressive stress increases and the hysteresis width increases. Accordingly, simple compressive stress control is possible by adjusting the size of the composite. This trend is due to the use of reduced graphene. As the graphene in the composite according to an embodiment is reduced, the layer spacing is reduced, so that the regularity between the layers is changed. For example, as the size of nanoparticles trapped in the composite increases, graphene does not sufficiently wrap it, so that the interlayer regularity decreases, and accordingly, the pressure that can be applied decreases. Accordingly, the hysteresis phenomenon is reduced. According to an embodiment, a platform applicable to metal hydride-2D composites other than palladium may be presented.

Referring to FIG. 16 , the result of calculating the enthalpy between the metal and the metal hydride is shown by applying the equilibrium pressure and temperature obtained from the PCT analysis to the vant Hoff equation. When the pure palladium nanoparticles and the composite according to an embodiment are compared, an increase in enthalpy is confirmed. This means that the phase of the metal hydride is stabilized. Accordingly, the composite according to an embodiment may present the possibility of compatibility with respect to the alanate-based metal complex, which has been limited in practical application as a conventionally too unstable phase.

For the spherical palladium-reduced graphene composite having a size of about 3 nm prepared in the above-mentioned Example, the results of kinetics and PCT measurement using HyEnergy Sieverts PCT Pro-2000 are shown in FIGS. 17 and 18. indicates. In the kinetics experiment, while flowing the sample with a hydrogen pressure gas of 2.2 bar at 100 degrees Celsius, the hydrogen absorption phenomenon is observed as the storage capacity over time. The PCT experimental conditions are the same as for the above-described cube-shaped palladium-reduced graphene composite.

Referring to FIGS. 17 and 18 , a fast hydrogen absorption rate is confirmed through chitetics analysis of the spherical complex. Hydrogen absorption due to tensile strain during compressive stress is promoted. The interaction between palladium and reduced graphene allows electrons of palladium to move to graphene, allowing more hydrogen to bind, thereby improving hydrogen storage capacity. In addition, the composite according to one embodiment, due to an increase in enthalpy, may suggest the possibility of compatibility for alanate-based metal complex compounds.

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

Claims (21)

first palladium nanoparticles,
The second palladium nanoparticles spaced apart from the first palladium nanoparticles,
The first reduced graphene surrounding the upper portion of the first palladium nanoparticles and the upper portion of the second palladium nanoparticles, and
The second reduced graphene surrounding the lower portion of the first palladium nanoparticles and the lower portion of the second palladium nanoparticles
A palladium-reduced graphene composite comprising a.
In claim 1,
The first reduced graphene and the second reduced graphene each have a palladium-reduced graphene composite having a net-like structure.
In claim 2,
The first reduced graphene and the second reduced graphene are palladium-reduced graphene composites that are spaced apart from each other.
In claim 2,
The first palladium nanoparticles receive a clamping force in the lower direction by the first reduced graphene, and receive a clamping force in the upper direction by the second reduced graphene palladium-reduced graphene composite .
In claim 4,
The first palladium nanoparticles receive a lateral force in the horizontal direction by the first reduced graphene, and receive a lateral force in the horizontal direction by the second reduced graphene palladium-reduced graphene composite .
In claim 5,
The palladium-reduced graphene composite of the first palladium nanoparticles and the second palladium nanoparticles each having a cube-shaped structure.
In claim 5,
The first palladium nanoparticles and the second palladium nanoparticles each have a spherical structure palladium-reduced graphene composite.
A plurality of palladium nanoparticles having a cube-shaped structure and arranged in layers,
A first reduced graphene having a net-like structure and surrounding the upper portion of the plurality of palladium nanoparticles, and
Second reduced graphene having a network structure and surrounding the lower portion of the plurality of palladium nanoparticles
A palladium-reduced graphene composite comprising a.
In claim 8,
The first reduced graphene is a palladium-reduced graphene composite that surrounds the plurality of palladium nanoparticles while in contact with the upper portions of the plurality of palladium nanoparticles along the cube-shaped shape of the plurality of palladium nanoparticles.
In claim 9,
The second reduced graphene is a palladium-reduced graphene composite that surrounds the plurality of palladium nanoparticles while in contact with the lower portions of the plurality of palladium nanoparticles along the cube-shaped shape of the plurality of palladium nanoparticles.
In claim 10,
The size of each of the plurality of palladium nanoparticles is 25 nm to 80 nm palladium-reduced graphene composite.
A plurality of palladium nanoparticles having a spherical structure and arranged in layers,
A first reduced graphene having a net-like structure and surrounding the upper portion of the plurality of palladium nanoparticles, and
Second reduced graphene having a network structure and surrounding the lower portion of the plurality of palladium nanoparticles
A palladium-reduced graphene composite comprising a.
In claim 12,
The first reduced graphene is a palladium-reduced graphene composite that surrounds the plurality of palladium nanoparticles while in contact with the upper portions of the plurality of palladium nanoparticles along the spherical shape of the plurality of palladium nanoparticles.
In claim 13,
The second reduced graphene is a palladium-reduced graphene composite that surrounds the plurality of palladium nanoparticles while in contact with the lower portions of the plurality of palladium nanoparticles along the spherical shape of the plurality of palladium nanoparticles.
15. In claim 14,
The size of each of the plurality of palladium nanoparticles is 2 nm to 4 nm palladium-reduced graphene composite.
Dissolving the graphene oxide powder in a solvent to prepare a graphene oxide solution,
Dissolving a palladium salt in a solvent to prepare a palladium precursor solution,
After adding a reducing agent and a surface stabilizer to the graphene oxide solution, heating, and adding the palladium precursor solution to obtain a palladium-reduced graphene composite
A palladium-reduced graphene composite manufacturing method comprising a.
17. In claim 16,
The palladium-reduced graphene composite is a palladium-reduced graphene composite manufacturing method that is produced by a reduction reaction in a one-pot process.
In claim 17,
The reducing agent is ascorbic acid, and the surface stabilizer is potassium bromide. Palladium-reduced graphene composite manufacturing method.
Dissolving a palladium salt in a solvent to prepare a palladium precursor solution,
After adding graphene oxide powder to the palladium precursor solution and stirring, obtaining a palladium precursor-graphene oxide composite;
Drying the palladium precursor-graphene oxide composite to obtain a palladium precursor-graphene oxide composite powder, and
Heating the palladium precursor-graphene oxide composite powder for a reduction reaction to obtain a palladium-reduced graphene composite
A palladium-reduced graphene composite manufacturing method comprising a.
In paragraph 19,
The palladium-reduced graphene composite is a palladium-reduced graphene composite manufacturing method that is produced by a reduction reaction in a one-pot process.
21. In claim 20,
The reduction reaction is palladium-reduced graphene composite manufacturing method that occurs at 250 degrees Celsius to 350 degrees Celsius for 1 hour to 3 hours.

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