Method for producing metal nanoparticle-graphene composite using electrodeposition

Abstract

The present invention provides a method for forming a metal nanoparticle-graphene composite using electroplating. To this end, the method of the present invention comprises the steps of: preparing a base material; coating graphene onto the base material; and forming a metal nanoparticle-graphene composite by depositing metal nanoparticles onto the graphene coating by electroplating. According to the present invention, the corrosion resistance of the base material can be improved, and the catalytic reaction can be enhanced when used as a water electrolysis electrode or sensor material.

Description

Technology Field

[0001] The present invention relates to a method for forming a metal nanoparticle-graphene composite, and more specifically, to a method for forming a metal nanoparticle-graphene composite using electroplating. Background Technology

[0002] Metal nanoparticles exhibit properties not found in bulk metals and are utilized in various fields, including catalytic reactions, sensors, and semiconductor devices. For example, in the field of water electrolysis electrodes, metal nanoparticles are actively used to enhance the catalytic properties of metals and reduce the use of precious metals. In the sensor field, they are used to fabricate photosensors utilizing the interaction between metal nanoparticles and visible light, or in biosensors by inducing oxidation / reduction reactions of specific organic molecules through metal nanoparticles.

[0003] Chemical synthesis methods involving the reduction of metal ions using reducing agents are widely utilized for the synthesis of metal nanoparticles. Citric acid, hydrazine, and sodium borohydride are primarily used as reducing agents, and synthesis is performed using hydrothermal reactions to accelerate the reaction in solution.

[0004] However, the synthesis of metal nanoparticles via such chemical methods has limitations regarding process control and uniform dispersion. When metal nanoparticles are synthesized onto a substrate via chemical methods, the nucleation energy at heterointerfaces is lower than that of a single metal ion forming a crystal nucleus. This leads to the problem of product formation within the synthesis reactor, resulting in reduced yield. Furthermore, due to their high surface energy, metal nanoparticles tend to aggregate, requiring an additional dispersion process to attach them to the substrate. If uniform dispersion is not achieved, the aggregated metal nanoparticles lose the properties inherent to nano-sized metals, thereby limiting their utilization as nanoparticles. The problem to be solved

[0005] The present invention aims to provide a method for forming a metal nanoparticle-graphene composite by bonding metal nanoparticles to graphene in order to improve the catalytic properties of metal nanoparticles, in order to solve the problems of the aforementioned prior art. means of solving the problem

[0006] To solve the above problem, the present invention provides a method for forming a metal nanoparticle-graphene composite comprising the following steps.

[0007] Step of preparing the base material;

[0008] A step of coating graphene onto the above-mentioned substrate;

[0009] A step of forming a metal nanoparticle-graphene composite by depositing metal nanoparticles onto the graphene coating by electroplating.

[0010] This invention utilizes the acceleration of nucleation through defects within graphene to overcome the problems of conventional chemical synthesis methods. Defects present within graphene are unstable, resulting in low adsorption and nucleation energies for metal ions; consequently, metal nanoparticles are formed only at these specific sites. Therefore, by utilizing these defects, metal nanoparticles can be uniformly dispersed on the graphene, eliminating the need for additional dispersion and attachment processes onto the substrate. Consequently, a metal nanoparticle-graphene composite with uniformly dispersed metal nanoparticles can be formed.

[0011] In the present invention, graphene contributes to the uniform formation of metal nanoparticles. When metal nanoparticles are formed directly on a substrate without graphene, the particles are not uniformly distributed; however, when graphene is present, nanoparticles can be formed uniformly on the graphene. Additionally, when graphene is coated on a substrate, the graphene layer acts as a corrosion-preventing layer or a gas diffusion-preventing layer for the substrate.

[0012] However, since corrosion-causing agents can penetrate the substrate through defects present in graphene, this alone is insufficient for blocking ability; therefore, the additional formation of metal nanoparticles is desirable.

[0013] Meanwhile, when metal nanoparticles are formed on graphene according to the present invention, defects and impurities in the graphene are removed. Generally, graphene does not possess a perfectly hexagonal structure in all regions; instead, it exists in a state where the hexagonal structure is partially destroyed due to the presence of voids or the addition of impurities. Such defects in graphene have an adverse effect that reduces electrical conductivity.

[0014] However, structural defects in graphene are structurally unstable, making them susceptible to the formation of metal particles. As metal nanoparticles form, these defects are masked, stabilizing the graphene and enhancing its ability to block corrosion-inducing factors. Furthermore, stabilizing the structure in this way through electroplating also increases electrical conductivity. This is because metal nanoparticles are formed by utilizing the structural or chemical defects of graphene. In other words, since the nucleation of metal nanoparticles occurs at the defect sites of graphene, the defects are eliminated, resulting in a further stabilization effect.

[0015] In addition, when metal particles are formed using electroplating according to the present invention, the purity of the graphene is also increased.

[0016] Meanwhile, since the present invention utilizes electroplating, the metal serving as the base material can be any metal that conducts electricity and is capable of electroplating, and is not limited to a specific metal. In addition, the metal forming the nanoparticles bonded to the graphene can also be any metal that is capable of electroplating.

[0017] In the present invention, it is preferable to form graphene into multiple layers. In this case, metal nanoparticles can be formed between the layers of graphene, resulting in a uniform and dense structure compared to when formed as a single layer. The method of forming graphene into multiple layers is not particularly limited. For example, chemical vapor deposition (CVD), spin coating, dip coating, spray coating, etc., may be used. Among these, using spray coating is particularly preferred because it enables efficient multilayer formation through a simple process.

[0018] On the other hand, graphene is hydrophobic and tends to aggregate and settle rather than disperse uniformly. In other words, when coating with standard graphene, the material disperses in an aggregated state, resulting in an uneven coating on the substrate in an aggregated state. While the concentration of the graphene dispersion can be lowered to address this, it prolongs the time required to form multilayer graphene. Furthermore, if a dispersant is added, the agent is also coated onto the material, leading to issues such as reduced electrical conductivity and lack of uniformity.

[0019] To solve these problems, it is preferable to use high-solubility graphene having high solubility in a spray solution for the graphene used in the present invention. It is preferable to add sulfur and oxygen to the high-solubility graphene so that the aggregation of graphene is resolved and a uniform coating can be achieved. Effects of the invention

[0020] According to the present invention, since metal nanoparticles are bonded to defects in graphene, adhesion is enhanced, and thus the corrosion resistance of the base material can be improved.

[0021] In addition, metal nanoparticles uniformly dispersed on graphene can lower the activation energy, thereby enhancing catalytic reactions when used as water electrolysis electrodes or sensor materials.

[0022] In addition, the defects of the graphene coated on the substrate can be reduced and its purity increased, thereby improving physical properties.

[0023] In addition, water electrolysis electrodes with improved electrical conductivity can be obtained. Brief explanation of the drawing

[0024] Figure 1 is an electron microscope image showing the side cross-section of a sample in which a metal nanoparticle-graphene composite is formed on a substrate according to an embodiment of the present invention, and a sample in which metal nanoparticles are formed on a substrate without graphene as a comparative example. FIG. 2 is an electron microscope image showing (a) the surface immediately after formation and (b) the surface after a corrosion test for samples composed of metal nanoparticles / graphene / matrix material according to an embodiment of the present invention, and substrate, graphene / matrix material, and metal nanoparticles / matrix material according to a comparative example. Figure 3 is a surface photograph after a corrosion test and an accelerated corrosion simulation test for samples composed of metal nanoparticles / graphene / matrix according to an embodiment of the present invention, and substrate, graphene / matrix, and metal nanoparticles / matrix, respectively, according to a comparative example. Figure 4 is a graph showing the results of measuring the current while scanning the voltage for specimens of the embodiment and comparative example of the present invention. Figure 5 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis results for samples of the embodiment and comparative example of the present invention immediately after deposition and after an accelerated corrosion simulation experiment. Figure 6 is a graph showing the results of inductively coupled plasma (ICP) mass spectrometry after an accelerated corrosion simulation experiment and the state immediately after deposition for samples of the embodiment and comparative example of the present invention. Figure 7 is a graph showing what bonds exist with carbon within the bond energy range of carbon through XPS analysis of samples of the embodiments and comparative examples of the present invention. Figure 8 is a schematic diagram showing the process of corrosion-inducing factors acting on single-layer graphene and multilayer graphene. FIG. 9 is an electron microscope image showing the amount of spray solution injected and the layer structure of graphene formed on the substrate according to the second embodiment of the present invention. FIG. 10 is an electron microscope image showing the coating surface of (a) a case where ordinary graphene is spray-coated and (b) a case where highly soluble graphene is coated according to an example. Specific details for implementing the invention

[0025] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings.

[0026] First embodiment

[0027] In this embodiment, a base material was prepared first. Stainless steel (316L) was used as the base material.

[0028] Next, graphene was formed on the base material by spray coating.

[0029] A graphene solution for spray coating was prepared by incorporating graphene at a concentration of 0.89 g / ml into an ethanol solvent, and ultrasonic dispersion was performed for 30 minutes to ensure uniform dispersion of the graphene within the ethanol. Subsequently, the prepared solution was injected into a solution holder, and 1 ml was sprayed at a distance of approximately 15 cm from the substrate at a temperature of 25°C using nitrogen as the spraying gas for the spray coating. As a result, a graphene-coated substrate was obtained.

[0030] Next, an electroplating process was performed to plate metal nanoparticles onto the graphene coated on the substrate as described above. In this embodiment, gold (Au) was used as the metal nanoparticle.

[0031] The solution used for electroplating consisted of 30.42 M Na2S2O, 30.42 M Na2SO3, and 40.005 M HAuCl, with water as the solvent. Electroplating was performed at -100 mA / cm² at 25°C while stirring the solution at 300 RPM with a magnetic bar. 2It was carried out by applying a current density of 5 seconds. A graphene-coated stainless steel substrate served as the electrode, a platinum electrode as the counter electrode, and Ag / AgCl as the reference electrode. The residual solution on the plated surface was removed by water spraying.

[0032] Meanwhile, as a comparative example, a sample in which metal nanoparticles were formed directly on a substrate without graphene and a sample in which only graphene was coated on a substrate were prepared, respectively, and their microstructures and physical properties were compared.

[0033] Figure 1 is an electron microscope image showing the side cross-section of a sample in which a metal nanoparticle-graphene composite is formed on a substrate according to an embodiment of the present invention, and a sample in which metal nanoparticles are formed on a substrate without graphene as a comparative example.

[0034] In the example shown in the lower photograph, graphene (G) is formed on a substrate and gold (Au) is plated as metal nanoparticles (Me), whereas in the comparative example shown above, gold (Au) is formed directly on the substrate. In the example, graphene is evenly coated on the substrate and gold (Au) is well dispersed within the graphene, whereas in the comparative example, there are areas on the substrate where gold (Au) is not plated.

[0035] FIG. 2 is an electron microscope image showing (a) the surface immediately after formation and (b) the surface after a corrosion test for samples composed of metal nanoparticles / graphene / matrix material according to an embodiment of the present invention, and substrate, graphene / matrix material, and metal nanoparticles / matrix material according to a comparative example.

[0036] It can be confirmed that while corrosion occurred in the sample consisting solely of SUS substrate, delamination occurred in the graphene / substrate sample, and corrosion (indicated by stains in the photo) also occurred in the metal nanoparticle / substrate sample, no corrosion occurred in the example composed of metal nanoparticles, graphene, and substrate.

[0037] Figure 3 is a surface photograph after performing a corrosion test and an accelerated corrosion simulation test on samples composed of metal nanoparticles / graphene / matrix according to an embodiment of the present invention, and substrate, graphene / matrix, and metal nanoparticles / matrix, respectively, according to a comparative example.

[0038] It can be seen that in the case of the metal nanoparticle / graphene / matrix material sample according to the example, there is no damage caused by exfoliation or corrosion in any case compared to other samples.

[0039] Figure 4 is a graph showing the results of measuring the current while scanning the voltage for specimens of the embodiment and comparative example of the present invention.

[0040] The diagram shows the results of measuring the corresponding current while scanning the voltage from -0.3V to 0.6V, and the corrosion current and corrosion voltage can be identified through the tangents of the formed peaks. The x-axis value of the tangent intersection point represents the corrosion current, and the y-axis value represents the corrosion voltage. A higher corrosion voltage indicates that corrosion does not occur thermodynamically well, while a lower corrosion current indicates a slower corrosion rate. Therefore, the value (blue line) of the metal nanoparticle / graphene / substrate (Me / G / Substrate) sample in the example, which has the lowest corrosion current and the highest corrosion voltage, indicates that the corrosion resistance is the best compared to samples composed of the substrate (SUS) (black line), graphene / substrate (G / Substrate) (red line), and metal nanoparticle / substrate (Me / Substrate) (green line).

[0041] In addition, the efficiency of corrosion resistance improvement can be calculated through the corrosion current using the values ​​obtained from the table below. That is, I corr : Corrosion current, E corr : Corrosion voltage, β a : Slope of the upper tangent, β c : Slope of the lower tangent, I corr : Corrosion current of the sample, I 0 corr : It is the corrosion current of SUS, and R p is R p = (βßa x β c ) / {2.3 xi corr x (β a + βß c It is calculated as )}, and the corrosion resistance improvement efficiency PE = 100 x (1-I corr / I 0 corr It is obtained using the formula ), and according to this, it was confirmed that the corrosion resistance of the metal nanoparticle / graphene / matrix specimen increased by 96.4%.

[0042] Sample Ecorr (mV) Icorr (uA / cm) βa (mV) βc (mV) PE (%) SUS -0.287 66.96 76.39865 36.5614 - G / SUS -0.279 62.67 80.07938 36.69999 6.4% Me / SUS -0.004 4.22 104.813 80.16572 93.7% Me / G / SUS 0.164 2.43 95.12009 75.21975 96.4%

[0043] Figure 5 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis results for samples of the embodiment and comparative example of the present invention immediately after deposition and after an accelerated corrosion simulation experiment.

[0044] From the graph, after the accelerated corrosion simulation experiment, the Fe component of the base material was exposed and detected due to delamination in other samples, whereas no Fe element was detected in the sample of the example. This means that the sample according to the example exhibits the best corrosion protection performance.

[0045] Figure 6 is a graph showing the results of inductively coupled plasma (ICP) mass spectrometry after an accelerated corrosion simulation experiment and the state immediately after deposition for samples of the embodiment and comparative example of the present invention.

[0046] From the graph, the amount of metal ions dissolved from the base material during accelerated corrosion simulation experiments according to the examples was lowest in the sample of the example formed of metal nanoparticles / graphene / base material. Specifically, Fe and Ni were significantly low, while Cr appeared similar, indicating that the overall amount was the lowest. From this, it was confirmed that the corrosion resistance of the example sample was the best.

[0047] Figure 7 is a graph showing what bonds exist with carbon within the bond energy range of carbon through XPS analysis of samples of the embodiments and comparative examples of the present invention.

[0048] In the diagram, a decrease in the CC peak indicates a reduction in structural defects, while a decrease in the COH and COO peaks indicates a reduction in oxygen impurities.

[0049] Oxygen present in graphene possesses COO- or CO- bonds. Both bonds are electrically negative and serve to trap metal cations in solution. Therefore, metal nucleation is more easily initiated at COO- or CO- than at defect-free carbon hexagonal structures. Consequently, metal particles are primarily generated at COO- or CO-, which physically shield the COO- or CO-, resulting in the disappearance of oxygen. Additionally, during metal nanoparticle plating, oxygen is reduced not only by the physical shielding of the nanoparticles but also by the desorption and disappearance of oxygen itself through electrochemical reactions.

[0050] In the table below, the ratio of C / O is higher at 7.79 in the metal nanoparticle / graphene / matrix (Au / G / SUS) sample compared to 4.25 in the graphene / matrix (G / SUS) sample, indicating the reduction of graphene.

[0051] Therefore, it can be seen that after plating with metal nanoparticles, oxygen, an impurity within the graphene, is reduced, resulting in structural stabilization and increased purity.

[0052] G / SUS Au / G / SUS Atomic % C 78.39 77.38 O 18.42 9.93 Atomic ratio C / O 4.25 7.79 Peak area ratio CC / C=C 0.129336 0.095028 C-OH / C=C 0.361602 0.115565 C(O)O / C=C 0.089024 0.017704

[0053] Second embodiment

[0054] In the second embodiment of the present invention, other conditions were kept the same as in the first embodiment, and the difference between forming graphene as a multilayer and as a single layer was examined. As a method for forming a multilayer, changes in the graphene layer were confirmed by varying the amount of solution injected during spray coating.

[0055] Figure 8 is a schematic diagram illustrating the process by which corrosion-inducing agents act on single-layer graphene and multilayer graphene. In the case of single-layer graphene, theoretically, as shown in the left figure of the diagram, it is known to have excellent corrosion prevention effects due to its dense hexagonal structure. However, in reality, as shown in the middle figure, not all hexagonal structures are perfect and defects exist due to breakdowns in the middle; thus, corrosion-inducing agents pass through these defects, causing corrosion of the substrate. At this time, corrosion is accelerated because the low electrical resistance of single-layer graphene rapidly supplies the electrons required for the electrochemical reaction for corrosion. Therefore, as shown in the right figure, forming graphene into multiple layers complicates the pathways for corrosion-inducing agents, thereby delaying corrosion.

[0056] However, since the defects themselves do not disappear in multilayer graphene, in this embodiment, the electroplating solution penetrated between each graphene layer through these defects, and gold nanoparticles were smoothly formed at the defect sites. This is because perfect graphene has low surface energy, which hinders the nucleation of gold nanoparticles, whereas defects within the graphene have very high surface energy, which is favorable for the nucleation of gold nanoparticles.

[0057] FIG. 9 is an electron microscope image showing the amount of spray solution injected and the layer structure of graphene formed on the substrate according to the second embodiment of the present invention.

[0058] In the drawing, the black area at the bottom is the base material, SUS, and the black ellipses with irregular shapes and sizes from top to bottom are metal nanoparticles. Additionally, the section showing slight stripes with heights indicated by red lines corresponds to graphene.

[0059] Numbers 1 to 4 in the drawing represent cases where the spray solution is 0.05 ml, 0.1 ml, 0.5 ml, and 1 ml, respectively. In case 1, the graphene is formed as a single layer of less than 1 nm. Here, "single layer" does not refer to a perfect single layer, but rather to a layer of about 1 to 5 layers; however, since it is difficult to form a structure with metal nanoparticles interposed between the layers at this level, it is referred to as a single layer. In case 2, the space between the upper and lower particles of the coated graphene is formed as a multilayer with a thickness of about 5 nm. In case 3, the graphene is a multilayer with a thickness of about 20 nm between the upper and lower particles, and in case 4, the space between the uppermost graphene particle and the lowermost graphene particle is formed as the thickest multilayer with a thickness of about 50 nm.

[0060] The reason the number of graphene layers increases as the thickness increases by increasing the injection amount of the spray solution is that when the injection amount increases, the graphene is coated preferentially on the substrate, followed immediately by the coating. One layer of graphene is approximately 0.33 nm thick, and the number of layers increases proportionally to the thickness of the coated graphene. In Figure 4, graphene is formed with a thickness of approximately 50 nm, which is about 150 layers. It can also be observed that metal nanoparticles are dispersed between some of the layers of the graphene formed in this way.

[0061] If the thickness of the graphene is too thin, the corrosion resistance ability is reduced, and if it is too thick, the graphene is exfoliated from the substrate when forming metal nanoparticles through plating. Therefore, it is necessary to appropriately adjust the thickness of the graphene, and 20 to 50 nm, more preferably 50 nm, is the optimal thickness for forming multilayer graphene-metal nanoparticles.

[0062] In the second embodiment, as a result of depositing gold nanoparticles between each layer of the graphene multilayer structure, a denser metal nanoparticle-graphene composite can be obtained, and accordingly, the pathway of plating-inducing factors is blocked, thereby further enhancing the corrosion prevention ability.

[0063] Third embodiment

[0064] In the third embodiment of the present invention, other conditions were the same as in the first embodiment, and highly soluble graphene was used as the graphene.

[0065] Due to its hydrophobic nature, graphene tends to aggregate and settle rather than disperse uniformly. Consequently, when using standard graphene for coating, the aggregated particles disperse and subsequently aggregate on the substrate, resulting in a non-uniform coating. While the concentration of the graphene dispersion can be lowered to address this, it prolongs the time required to form multilayer graphene. Furthermore, adding a dispersant results in the agent being coated onto the material itself, causing issues such as reduced electrical conductivity and a lack of uniformity.

[0066] In this embodiment, to solve these problems, high solubility graphene with added sulfur and oxygen to have high solubility in a spray solution was used, thereby resolving the aggregation phenomenon and forming a more uniform multilayer structure.

[0067] FIG. 10 is an electron microscope image showing the coating surface of (a) a case where ordinary graphene is spray-coated and (b) a case where highly soluble graphene is coated according to an example.

[0068] When general graphene is used, it can be seen that clumping occurs on the surface of the substrate after spray coating due to the attractive forces between the graphene layers. However, when high-solution graphene with added sulfur and oxygen is used, it can be confirmed that there is no clumping and the graphene is well dispersed and coated on the substrate. Therefore, subsequent metal nanoparticles can also be evenly dispersed and plated.

Claims

Claim 1 A method for forming a metal nanoparticle-graphene composite using electroplating, comprising the steps of: preparing a base material made of stainless steel; coating graphene on the base material by spray coating; and depositing metal nanoparticles on the graphene coating by electroplating, wherein the metal nanoparticles adsorb, nucleate, and grow at defect sites where the hexagonal structure of the graphene is destroyed, thereby forming a metal nanoparticle-graphene composite in which metal nanoparticles are dispersed on the graphene, wherein the graphene is formed in multiple layers on the base material, the spray coating is performed using a spray solution in which highly soluble graphene containing sulfur and oxygen is dispersed, the spray amount of the spray solution is 0.5 to 1 ml, the graphene is coated to a thickness of 20 to 50 nm, and the metal forming the metal nanoparticles is gold (Au). Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 delete Claim 10 delete

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