KR102510192B1 - Carbonized matrix-particle composite and manufacturing method thereof - Google Patents

Abstract

The present invention includes a plurality of metal or metal oxide nanoparticles dispersed inside a metal-organic composite carbonized matrix, and the metal or metal oxide nanoparticles have a particle size standard deviation of 5 nm or less. - It relates to a method for producing a carbonized matrix-particle composite comprising the step of carbonizing an organic composite by irradiating a laser, and an electrode, catalyst, and adsorbent containing a carbonized matrix-particle.

Description

Carbonized matrix-particle composite and its manufacturing method {CARBONIZED MATRIX-PARTICLE COMPOSITE AND MANUFACTURING METHOD THEREOF}

The present invention relates to a carbonized matrix-particle composite, particularly a carbonized matrix-particle composite applicable to sensors, energy storage electrodes, catalysts, and adsorbents, and a technique for synthesizing MOF by irradiating a laser with a controlled wavelength.

Size is really important in nanoscience in that the properties of nanoparticles (NPs) are size dependent. The pursuit of facile and efficient methodologies for controlling the size of nanoparticles has attracted considerable interest in preparing ultrafine nanoparticles with the same properties for related applications. However, nano-sized particles are thermodynamically unstable. Because of their high surface energy, they are vulnerable to agglomerates and migrate under harsh reaction conditions to form larger particles. Therefore, nanoparticles generally retain their size and shape by attaching capping ligands to the particle surface to prevent uncontrolled growth. In addition, porous matrices are often used to entrap nanoparticles of confined pores.

Metal-organic frameworks (MOFs), porous crystalline materials made by coordination bonding of metal ions and organic linkers, have attracted much attention as pioneers in developing stable nanoparticles for catalysis, gas storage, sensors, and energy-related applications. In a conventional manner, MOFs are thermally decomposed in an inert atmosphere, organic linkers are carbonized into porous carbon, and metal ions are aggregated to form nanoparticles. The diversity of metal ions leads to the production of various metal or metal oxide/carbide nanoparticles. Various methods have been developed to fabricate ultrafine nanoparticles with controlled size and shape, such as template synthesis, encapsulation, and single metal ion trapping. Nonetheless, these methods are often multi-step and are mostly applicable to the synthesis of specific metal or oxide nanoparticles. Therefore, there is an urgent need to develop an easy method for preparing various stable metal/metal oxide nanoparticles and controlling their size.

Laser quenching is recognized in industry as a fast, efficient and environmentally friendly technology for topical surface treatment. This technology provides intense pulses of light energy to quickly heat a limited amount of a surface, which is then cooled at very high rates by the surrounding environment, either the bulk material, the atmosphere or a gas flow. Rapid heating and cooling are key features of laser annealing. This enables the formation of novel microstructures and greatly improves the properties of the laser treated component. Laser reduction of graphene oxide and laser-induced formation of graphene have been extensively studied over the past years for various applications such as supercapacitors, sensors and electrocatalysts. Nonetheless, pioneering work on laser processing of MOFs for the production of metal nanoparticles is still adequately reported.

In addition, the popularization of electric vehicles and portable/wearable electronic devices has greatly increased the demand for next-generation power sources with high energy and power density and long lifespan. Batteries and supercapacitors are energy storage devices that could potentially meet the requirements if their energy and power densities are mutually inclusive. Batteries provide high energy densities because they use the entire electrode material to store large amounts of energy through large amounts of redox reactions. However, the low power density cannot meet the requirements for acceleration and braking of electric vehicles and fast charging of portable/wearable devices. In contrast, conventional supercapacitors store energy through adsorption of surface charge, which provides long lifetime and high power density at low energy densities. The demand for supercapacitors with higher energy densities is driving the adoption of pseudocapacitive materials.

Pseudocapacitance reflects redox processes at or close to the surface with fast kinetics like a supercapacitor while storing more charge like a battery. Intuitively, size control of quasi-capacitive materials on the nanometer scale is a fashionable way to achieve higher surface areas and faster redox rates, which can significantly improve energy and power densities. Various approaches have been reported to synthesize quasi-capacitive nanomaterials and improve their capacitive performance. Therefore, designing electrodes with a uniform distribution of size-controlled nanoparticles in high-surface-area conductive scaffolds may be a promising strategy for fabricating supercapacitors with both higher energy and power densities.

Metal-organic frameworks (MOFs), porous crystalline materials composed of coordination bonds of inorganic metal centers and organic ligands, have been developed for various nanomaterials (i.e., porous carbon, metals, and metal oxides) for catalysis, gas storage, chemical sensors, and energy-related applications. ) has been used as a precursor to produce. Upon thermal decomposition of MOFs at high temperatures, metal ions are reduced to metal nanoparticles or combined with other elements in the framework to produce multi-metal nanoparticles. By distributing the obtained nanoparticles to the ligand-derived porous carbon scaffold, the nanoparticles can be stabilized for a long period of time. However, size control of MOF-derived nanoparticles is quite difficult due to high temperature pyrolysis and temperature variations. In particular, nanometer-scale system size control has so far remained a challenging problem.

The present invention has been made to solve the above problems, and one aspect of the present invention provides an approach to prepare ultrafine stable metal / metal oxide nanoparticles through laser heat treatment of metal organic frameworks (MOFs), carbonization A matrix-particle composite and a method for producing the same are provided.

In addition, in another embodiment of the present invention, in the nanoscale, the metal / metal oxide nanoparticle size is optimized to lower the charge transfer resistance of the surface and improve the quantum diffusivity of the particle to maximize the electrochemical performance. A carbonized matrix-particle composite capable of obtaining a synergistic effect of narrow size distribution and uniform dispersion of nanoparticles and a method for preparing the same are provided.

However, the technical problem to be achieved by the present invention is not limited to the above-mentioned technical problem, and other technical problems not mentioned are clearly understood by those skilled in the art from the description below. It could be.

As a technical means for achieving the above-described technical problem, one aspect of the present invention,

Provided is a carbonized matrix-particle composite comprising a plurality of metal or metal oxide nanoparticles dispersed in a metal-organic composite carbonized matrix, wherein the metal or metal oxide nanoparticles have a particle size standard deviation of 5 nm or less. .

The metal or metal oxide nanoparticles may have an average particle size of 4 nm to 12 nm.

The metal or metal oxide nanoparticles may have an average particle size of 4.6 nm to 9.6 nm.

The metal or metal oxide nanoparticles may be one selected from the group consisting of Ni, Co, Fe, Fe ₂ O ₃ , Fe ₃ O ₄ , ZnO, MnO, and mixtures thereof.

The metal or metal oxide nanoparticles may be Ni, and the metal or metal oxide nanoparticles may have an average particle size of 4.6 nm to 6.1 nm.

The metal or metal oxide nanoparticles may be Fe, and the metal or metal oxide nanoparticles may have an average particle size of 6.4 nm to 9.7 nm.

The metal or metal oxide nanoparticles may be MnO, and the metal or metal oxide nanoparticles may have an average particle size of 5.2 nm to 8.3 nm.

The carbonization may be laser carbonization.

In addition, another aspect of the present invention,

Provided is a method for producing the carbonized matrix-particle composite of claim 1, comprising the step of carbonizing the metal-organic composite by irradiating a laser.

The metal-organic composite may be in the form of a film.

The film may have a thickness of 1 to 50 μm.

The laser may be a CO ₂ laser.

The laser may have a wavelength (λ) of 5 to 15 μm.

The laser may be irradiated up to a maximum temperature of 700 ~ 900 ℃.

The laser may be irradiated for 0.001 to 10 seconds.

The laser may be irradiated under a nitrogen atmosphere.

In addition, another aspect of the present invention,

An electrode comprising the carbonized matrix-particle composite is provided.

In addition, another aspect of the present invention,

A catalyst comprising the carbonized matrix-particle composite is provided.

In addition, another aspect of the present invention,

An adsorbent comprising the carbonized matrix-particle composite is provided.

According to one aspect of the present invention, laser heat treatment of metal-organic frameworks (MOFs) enables rapid, efficient and environmentally-friendly synthesis of ultrafine stable nanoparticles of various metals and metal oxides.

In addition, according to another aspect of the present invention, in the nanoscale, the size of the metal / metal oxide nanoparticles is optimized to lower the charge transfer resistance of the surface and to improve the quantum diffusivity of the particles to maximize the electrochemical performance, high surface area conductive carbon It is possible to provide a carbonized matrix-particle composite that can obtain a synergistic effect of narrow size distribution and uniform nanoparticle dispersion and a manufacturing method thereof.

The effects of the present invention are not limited to the above effects, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the configuration of the invention described in the claims.

1 is a schematic diagram showing the difference between conventional pyrolysis and laser heat treatment.
Figure 2 shows the crystal structure of MOF-derived materials by pyrolysis and laser heat treatment.
Figure 3 shows the relationship between the standard reduction potential of metal ions in MOF and metal or metal oxide formation by laser heat treatment.
Figure 4 shows an Ellingham diagram showing the thermodynamic reducibility of various metal oxides.
Figure 5 shows the formation mechanism of the proposed MOF-derived nanocrystals by laser heat treatment and pyrolysis.
6 is a schematic diagram showing a sample preparation process through laser heat treatment.
7 is a photograph of a MOF sample before and after laser heat treatment.
8 shows the microstructural properties of MOF-derived materials by pyrolysis and laser heat treatment.
9 to 13 show the morphological changes of MOF-Ni, MOF-Co, MOF-Fe, MOF-Zn, and MOF-Mn by pyrolysis and laser heat treatment, respectively.
14 shows microstructural properties of MOF-derived materials.
Figure 15. Long-term stability of MOF-derived Ni, Co and Fe nanoparticles by laser thermal treatment after storage in air for several months is shown.
16 shows the fabrication of Ni nanoparticles having a different size from MOF-N, and (A) is a schematic diagram showing the fabrication of Ni nanoparticles in a carbon scaffold by laser heat treatment and pyrolysis of MOF-Ni. (B) shows representative time-temperature profiles of laser heat treatment and pyrolysis. The inserted figure is a schematic diagram showing the experimental setup for each method. Pyrolysis was carried out under an inert gas flow in a high-temperature furnace lasting from several hours to a day. In laser heat treatment, the sample is placed in an inert chamber and the laser scan is performed in a very short time from a few seconds to a few minutes. Thermal decomposition produced broad-sized Ni nanoparticles, while laser annealing produced narrow-sized ultrafine nanoparticles. (C) is an XRD spectrum showing the crystallographic changes of the sample before and after synthesis. Ni foam was added as a Ni bulk basis.
17 shows chemical properties of MOF-Ni and its representative derivatives, (A) Raman spectrum and (B) XPS profile of Ni 2p3/2.
18 shows microstructural characteristics of Ni nanoparticles of different sizes, (A) is representative scanning electron microscopy (SEM) images of MOF-Ni and its derivatives at various particle sizes of 4.8, 5.5, 6.1 and 12.5 nm. , (B) is a transmission electron microscope (TEM) image. The fringe spacing of 2.04 Å coincided with the (111) plane of the Ni cubic structure. (C) shows the corresponding size distribution of Ni nanoparticles in (B).
19 shows the elemental characteristics of surface nanoparticles, and (A) is a high-resolution SEM image showing the surface morphology of MOF-Ni crystals after thermal decomposition. The inset is a low-magnification image of the crystal. (B) is the corresponding EDX line profile showing the distribution of all elements in the white line scan of (A). The increase in Ni content along with the decrease in C content at the nanoparticle site confirmed that the nanoparticle was Ni metal.
Figure 20 shows the electrochemical performance according to the size of Ni nanoparticles, (A) is a CV curve measured at a scan rate of 5 mV / s. (B) shows the corresponding specific capacitance as a function of nanoparticle size at 5 mV/s. (C) is the GCD profile of nanoparticles at a loading current of 1 A/g. (D) shows the specific capacitance at various load currents.
21 shows the cyclic stability of Ni-5.5-nm nanoparticles after 10,000 loading cycles.
22 shows factors determining the size-dependent similar capacitance of Ni nanoparticles, and (A) is a Nyquist plot showing the electrochemical impedance of Ni nanoparticles of different sizes. (B) is the charge transfer resistance (Rct) for nanoparticles of different sizes. Rct is related to the Faradaic reaction kinetics at the nanoparticle and electrolyte interface. (C) is the charge storage behavior (b values) of nanoparticles of different sizes. b = 1 represents the capacitive character with a surface-controlled capacitive process and b = 0.5 represents the battery characteristic with a diffusion-limited redox process. (D) is the quantum diffusion coefficient (D) of nanoparticles of different sizes.
23 shows the dependence of peak current on scan rate from Cyclic Voltammetry (CV) scans for Ni-5.5-nm nanoparticles. (A) is the CV profile at different scan rates from 1 to 50 mV/s. (B) is the corresponding plot of Log (Peak current) and Log (Scan rate). The b value is the slope of the linear fit line of the plot, and the b value is the variable that appears in the power law relationship between the peak current (i) and the scan rate (v) in the CV scan (i.e. i = av ^b where a is an adjustable parameter variable). A b value of 0.5 indicates a diffusion-limited redox process occurring in the nanoparticles, while a b value of 1.0 suggests a surface-controlled capacitive process.
24 shows a model depicting the charge storage mechanism of Ni nanoparticles on a porous carbon support. The charge transfer resistance (Rct) of the nanoparticles, the proton (H ⁺ ) diffusion resistance and the electrical resistance of the carbon scaffold are the most likely factors affecting the size-dependent pseudocapacitance of the Ni nanoparticles.
Figure S5. It shows the electrochemical performance of commercial activated carbon (AC). (A) is the cyclic voltammetry (CV) profile at various scan rates. (B) shows the specific capacitance calculated from the CV curve.
26 shows the electrochemical performance of an asymmetric supercapacitor. The device was fabricated with Ni-5.5-nm nanoparticles as the cathode and commercial activated carbon (Ni 5.5//AC) as the anode. (A) is a comparative CV curve of Ni-5.5-nm and AC electrodes at a scan rate of 10 mV/s. (B) is the charge and discharge curves of the device with a voltage window of 1.6 V at different load currents. (C) is the Nyquist plot of the device. (D) is a Ragone plot of the asymmetric supercapacitor, rGO SC, CNT SC, NiO//AC, NiCo ₂ O ₄ , NiO/NiCo2O4//AC and Fe ₃ O ₄ -CNT//Mn3O4-CNT. The performance of other supercapacitors, including (E) shows lighting up a light emitting diode (LED) for ~5 min using a fabricated supercapacitor with a cathode mass of ~1.6 mg.
27 shows the electrochemical performance of the Ni 5.5//AC asymmetric supercapacitor device. (A) is the specific capacitance of the device. (B) shows the cycling stability of the device after 20,000 loading cycles at 200 mV/s.

Hereinafter, the present invention will be described in more detail. However, the present invention can be implemented in many different forms, and the present invention is not limited by the embodiments described herein, and the present invention is only defined by the claims to be described later.

In addition, terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In the entire specification of the present invention, 'including' a certain element means that other elements may be further included, rather than excluding other elements unless otherwise stated.

The first aspect of the present application is,

Provided is a carbonized matrix-particle composite comprising a plurality of metal or metal oxide nanoparticles dispersed in a metal-organic composite carbonized matrix, wherein the metal or metal oxide nanoparticles have a particle size standard deviation of 5 nm or less. .

Hereinafter, the carbonized matrix-particle composite according to the first aspect of the present application will be described in detail.

In one embodiment of the present application, the metal or metal oxide nanoparticles may be characterized in that they have a particle size standard deviation of 5 nm or less, preferably 3 nm or less, more preferably 2 nm or less. This can be attributed to the carbonization of the metal-organic composite by laser.

In one embodiment of the present application, the metal or metal oxide nanoparticles may have an average particle size of 4 nm to 12 nm. Preferably, the metal or metal oxide nanoparticles may have an average particle size of 4.6 nm to 9.6 nm. When the above range is satisfied, electrochemical performance may be excellent.

In one embodiment of the present application, the metal or metal oxide nanoparticles may be one selected from the group consisting of Ni, Co, Fe, Fe ₂ O ₃ , Fe ₃ O ₄ , ZnO, MnO, and mixtures thereof. The above metal or metal oxide is only an example, and may be selected from metals or oxides thereof without limitation.

In one embodiment of the present application, the metal or metal oxide nanoparticles may be Ni, and the metal or metal oxide nanoparticles may have an average particle size of 4.6 nm to 6.1 nm. By satisfying the above range, high electrochemical performance can be achieved.

Ni-based materials are known to exhibit redox reactions on the surface and inside of electrode materials. In a concentrated alkaline electrode, it is employed that the surface of Ni nanoparticles is converted to Ni(OH) ₂ to exhibit similar capacities (i.e., Ni + 2OH ^- → Ni(OH) ₂ + 2e ^- and Ni(OH) ₂ + OH - ↔ NiOOH + H ₂ O + e ^- ). Ni(OH) 2 offers a high theoretical specific capacitance of ~2082 F/g and good stability in alkaline electrolytes widely used as electrode materials in batteries and supercapacitors. For this reason, we first investigated the electrochemical performance of Ni nanoparticles of different sizes by cyclic voltammetry (CV) in a three-electrode setup using 6M KOH electrolyte.

In one embodiment of the present application, the metal or metal oxide nanoparticles may be Fe, and the metal or metal oxide nanoparticles may have an average particle size of 6.4 nm to 9.7 nm. By satisfying the above range, high electrochemical performance can be achieved,

In one embodiment of the present application, the metal or metal oxide nanoparticles may be MnO, and the metal or metal oxide nanoparticles may have an average particle size of 5.2 nm to 8.3 nm. By satisfying the above range, high electrochemical performance can be achieved,

In one embodiment of the present application, the carbonization may be laser carbonization.

Hereinafter, the laiter carbonization will be described in detail.

1 is a schematic diagram showing the difference between conventional pyrolysis and laser heat treatment.

In the case of conventional pyrolysis, the MOF is heated to a high temperature and pyrolyzed for a specific time (i.e., 1 hour or more) in an inert atmosphere (T-MOF). The resulting MOF-derived materials typically consist of coarse metal or oxide/carbide nanoparticles incorporated in a porous carbon matrix. In laser pretreatment, instantaneous heating and cooling (i.e., less than 1 second) of the laser can produce ultrafine nanoparticles of various metals and metal oxides encapsulated in a carbon matrix (L-MOF).

The onset reduction potential for metal ions to form metal or metal oxide nanoparticles in MOF is different from thermal decomposition. In addition, the instantaneous heating and cooling characteristics of the laser can inhibit crystal growth through Ostwald ripening, typical of conventional thermal decomposition, resulting in the formation of ultrafine nanoparticles with uniform size and dispersion.

Figure 2 shows the crystal structure of MOF-derived materials by pyrolysis and laser heat treatment.

To investigate the difference between pyrolysis and laser heat treatment, various techniques for MOF by pyrolysis (T-MOF) and MOF by laser heat treatment (L-MOF) can be used. As shown in FIG. 2, XRD analysis can be performed to study the phase change of MOFs and their derived materials.

In FIG. 2, XRD (X- ray diffraction pattern. Calculated domains of nanoparticles as a function of laser/heating device power for MOF-Ni (B), MOF-Co (D), MOF-Fe (F), MOF-Zn (H) and MOF-Mn (J) indicates size. The domain size of the nanoparticle is calculated from the XRD data using the Scherer equation. It can be seen that the laser annealed MOFs (L-MOF-M, M = metal) appear to have much finer domain sizes than the thermally decomposed MOFs (T-MOF-M).

Figure 3 shows the relationship between the standard reduction potential of metal ions in MOF and metal or metal oxide formation by laser heat treatment.

When correlating the crystalline phase of MOF-derived nanoparticles with the standard reduction potential of metal ions, the thermal decomposition of MOF in N ₂ is 16. Das R., Pachfule P., Banerjee R., Poddar P. Metal and metal oxide nanoparticle synthesis from Metal organic frameworks (MOFs): finding the border of metal and metal oxides. It is in good agreement with the rules reported in Nanoscale 2012, 4, 591-599. Metal ions with reduction potentials above -0.27 V, such as Co ²⁺ (-0.27 V) and Ni ²⁺ (-0.25 V) always form pure metal nanoparticles, whereas reduction such as Fe ²⁺ (-0.44 V) Metal ions Zn ²⁺ (-0.76 V) and Mn ²⁺ (-1.19 V) with low potential tend to combine with oxygen or carbon in organic linkers to form metal oxide/carbide nanoparticles (FIG. 3).

However, unlike conventional approaches, laser annealing of MOFs in N ₂ showed a lower onset reduction potential of −0.44 V to form metal or metal oxide phases. It indicates that the thermodynamics of laser heat treatment may be different from that of conventional thermal decomposition.

The onset reduction potential for the formation of metal or metal oxide/carbide nanoparticles was found to shift from −0.27 V for conventional pyrolysis to −0.44 V for laser thermal treatment with a CO ₂ laser.

Figure 4 shows an Ellingham diagram showing the thermodynamic reducibility of various metal oxides.

The thermodynamic driving force acting on a reaction is quantified by the Gibbs free energy (ΔG) of the reaction. A negative ΔG indicates that the reaction can occur spontaneously without any external input, while a positive value means that the reaction does not occur. The higher the position of the metal in the diagram, the less stable the oxide. The intersection of the two lines represents the redox equilibrium. Carboothermic reduction reactions of metal oxides (C + MO → M + CO↑, where M = metal) are possible at a temperature above the intersection point lower than the line of metal oxides in which the carbon of the ΔG line is reduced.

T_NiO

500 ℃, T_FeO

710 ℃, T_ZnO 950 ℃ 및 T_MnO

1410 ℃). 따라서, 800 ℃에서 열분해된 MOF에서 금속(즉, Co, Ni 및 Fe) 및 산화물 상(즉, ZnO 및 MnO)의 형성이 예상될 수 있다. 그러나, Fe₃C 상이 금속 Fe 대신 T-MOF-Fe에서 발견된다는 것은 본 발명자들의 예측과는 반하는 것이었다. 긴 열분해 공정은 금속 상으로 탄소 원자의 삽입을 촉진하여 Fe₃C를 형성하는, 가장 가능성이 있는 이유이다. 대조적으로, 레이저의 즉각적인 가열 및 냉각은 아마도 탄소가 금속 상으로 확산되기에 불충분한 에너지를 제공했을 것으로 추정되므로, L-MOF-Fe에서 Fe 나노 입자가 얻어진다. ZnO의 탄화 환원이 개시 환원 온도 미만에서 일어날 수 없다는 것을 고려하면, L-MOF-Zn에서 ZnO의 존재는 N₂에서 CO₂ 레이저 조사 시 온도가 ZnO의 개시 환원 온도보다 낮음을 나타낸다. 따라서 온도는 공기 중 MOF의 펄스 레이저 야금(metallurgy) 온도보다 훨씬 낮고, 여기서 금속 Zn은 1000 ℃ 이상에서 국소 환원성 분위기의 형성으로 인해 얻어진다.The thermodynamic driving force required to make the reaction work under given conditions (ie, temperature) is introduced by the Ellingham diagram in FIG. Carbon formed in the heat treatment process serves as a reducing agent, and the reduction of metal oxide is carried out by carbonization reduction (C + MO → M + CO↑, M = metal). Metal oxides (e.g., CoO, NiO, FeO, ZnO, and MnO) can be converted to metals, and the onset reduction temperature by carbon is dependent on the oxide (e.g., T _CoO

T _NiO

500 °C, T _FeO

710 °C, T _ZnO 950 °C and T _MnO

1410 °C). Thus, the formation of metal (i.e. Co, Ni and Fe) and oxide phases (i.e. ZnO and MnO) can be expected in MOFs pyrolyzed at 800 °C. However, the fact that the Fe ₃ C phase is found in T-MOF-Fe instead of metallic Fe was contrary to the inventors' prediction. The long pyrolysis process is the most likely reason for promoting the insertion of carbon atoms into the metal phase to form Fe ₃ C. In contrast, the immediate heating and cooling of the laser presumably provided insufficient energy for carbon to diffuse into the metal phase, thus resulting in Fe nanoparticles in L-MOF-Fe. Considering that carbonization reduction of ZnO cannot occur below the initiation reduction temperature, the presence of ZnO in L-MOF-Zn indicates that the temperature during CO ₂ laser irradiation in N ₂ is lower than the initiation reduction temperature of ZnO. The temperature is therefore much lower than the pulse laser metallurgy temperature of MOF in air, where the metal Zn is obtained due to the formation of a local reducing atmosphere above 1000 °C.

Figure 5 shows the formation mechanism of the proposed MOF-derived nanocrystals by laser heat treatment and pyrolysis.

The present inventors proposed a model to explain the phenomenon to explain these size differences in the thermal decomposition and laser heat treatment of MOFs. The MOF consists of well-ordered metal ion nodes in a crystalline framework (Fig. 5A). Under laser or thermal heating, the metal ions gain sufficient energy and become able to migrate in the framework (FIG. 5B). At the same time, the organic linker decomposes or decomposes to produce porous carbon. Depending on the reduction potential of the metal ion, it is carbonized by carbon to form a metal atom or combined with oxygen/carbon from a decomposed organic linker to form a metal oxide/carbide molecule. Surrounding atoms/molecules are agglomerated to reduce surface energy to form small nanoparticles of uniform size. At this stage, if the sample is cooled very quickly (i.e., less than 1 second), a microstructure similar to that of a laser-cooled MOF can be obtained (Fig. 5C). Further annealing of the sample for a longer period of time (preferably, 1 hour or more) in pyrolysis leads to the formation of larger nanoparticles by Ostwald ripening in which small nanoparticles dissolve and redeposit onto larger ones ( Fig. 5D). Ostwald ripening is known as a size defocusing process during nanocrystal synthesis, and parameters must be precisely controlled to avoid Ostwald ripening to obtain ultrafine nanocrystals with a narrow size distribution.

The second aspect of the present application is,

Provided is a method for producing the carbonized matrix-particle composite of claim 1, comprising the step of carbonizing the metal-organic composite by irradiating a laser.

Although detailed descriptions of portions overlapping with those of the first aspect of the present application have been omitted, the contents described for the first aspect of the present application can be equally applied even if the description is omitted from the second aspect.

Hereinafter, a method for producing a carbonized matrix-particle composite according to the second aspect of the present application will be described in detail.

6 is a schematic diagram showing a sample preparation process through laser heat treatment.

In one embodiment of the present application, the metal-organic composite may be in the form of a film. Preferably, it is in the form of a free-standing MOF, such as a film or a pellet, to prevent laser scattering and non-uniform processing.

For laser heat treatment according to one embodiment of the present application, MOF crystals may be mixed with a solvent to form a homogeneous slurry, and then attached to a Cu foil, as a non-limiting example, to prepare a MOF film. Cu foil can facilitate laser carbonization due to its high thermal conductivity and stability.

In one embodiment of the present application, the film may have a thickness of 1 to 50 μm. Preferably, the thickness of the film may be 5 to 30 μm, more preferably 10 to 25 μm, and more preferably 15 μm.

In one embodiment of the present application, the laser may be a CO ₂ laser. The CO ₂ laser is a continuous mid-infrared laser with strong characteristic absorption for many natural and synthetic materials. The laser energy is converted to heat where it is absorbed, which rapidly rises in temperature and is immediately cooled by the surrounding environment.

In one embodiment of the present application, the laser may have a wavelength (λ) of 5 to 15 μm. Preferably, the wavelength of the laser may be 6 to 11 um.

As a non-limiting example, the above-mentioned laser has been developed in various wavelength regions ranging from visible light, infrared light, ultraviolet light, and X-ray, and any laser that can be used in various media such as gas, liquid, and solid may be used without limitation.

In one embodiment of the present application, the laser may be irradiated up to a maximum temperature of 700 ~ 900 ℃. Preferably, the laser may be irradiated up to a maximum temperature of 750 ~ 850 ℃.

In one embodiment of the present application, the laser may be irradiated for 0.001 to 10 seconds. Preferably, the laser may be irradiated for 0.1 to 8 seconds, more preferably for 0.5 to 5 seconds.

In one embodiment of the present application, the laser may be irradiated under a nitrogen atmosphere. However, this is a non-limiting example, and it is okay to use a gas other than nitrogen as long as it is irradiated under an inert atmosphere.

The third aspect of the present application is,

An electrode comprising the carbonized matrix-particle composite is provided.

Detailed descriptions of portions overlapping with the first and second aspects of the present application have been omitted, but the contents described for the first and second aspects of the present application can be equally applied even if the description is omitted in the third aspect. .

Hereinafter, an electrode including the carbonized matrix-particle composite according to the third aspect of the present application will be described in detail.

In one embodiment of the present application, the electrode may be used in a secondary battery or a supercapacitor, and the carbonized matrix-particle composite is nanoparticles distributed in a uniform size inside porous carbon, and various deformation situations of the devices It can be driven stably in (bending) and at the same time have high energy storage characteristics.

In one embodiment of the present application, the carbonized matrix-particle composite is used as an electrode active material, which may be formed on an electrode current collector. In this case, the type of the electrode current collector may not be significantly limited as long as it has conductivity without causing chemical change of the device. For example, the electrode current collector may include stainless steel, aluminum, nickel, titanium, calcined carbon, or a material in which carbon, nickel, titanium, silver, or the like is surface-treated on the surface of aluminum or stainless steel. Meanwhile, the electrode current collector may have a thickness of about 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase adhesion of the electrode active material. That is, it may be usable in various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

In one embodiment of the present application, the electrode active material may further include a conductive material and a binder in addition to the active material. In this case, the conductive material is used to impart conductivity to the electrode, and may be any material that has electrical conductivity without causing a chemical change in the device. For example, the conductive material is graphite such as natural graphite or artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, carbon-based materials such as carbon fiber, copper, nickel, aluminum , metal powder or metal fibers such as silver, conductive whiskey such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide or conductive polymers such as polyphenylene derivatives, and combinations thereof. it may be Meanwhile, the conductive material may be used in an amount of 1 to 30 parts by weight based on 100 parts by weight of the electrode active material.

In addition, the binder may serve to improve adhesion between particles of the electrode active material and adhesion between the electrode active material and the current collector. Specifically, the binder may be, for example, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, Carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), alcohol It may include a material selected from the group consisting of phonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof and combinations thereof. Meanwhile, the binder may be typically used in an amount of 1 to 30 parts by weight based on 100 parts by weight of the electrode active material.

In addition, the supercapacitor may preferably be a hybrid supercapacitor, and the hybrid supercapacitor may specifically include: an anode; cathode; It may include a separator and an electrolyte interposed between the positive electrode and the negative electrode. In this case, the electrode active material may be preferably used as an active material of the negative electrode, and activated carbon may be used as a positive electrode active material of the positive electrode.

In one embodiment of the present application, the electrolyte used in the hybrid supercapacitor may be a mixture of a salt and an additive in an organic solvent. At this time, the organic solvent is ACN (Acetonitrile), EC (Ethylene carbonate), PC (Propylene carbonate), DMC (Dimethyl carbonate), DEC (Diethyl carbonate), EMC (Ethylmethyl carbonate), DME (1,2-dimethoxyethane), It may include a material selected from the group consisting of γ-butrolactone (GBL), methyl formate (MF), methyl propionate (MP), and combinations thereof. In addition, the salt is used in an amount of 0.8 to 2 M, and may be a mixture of a lithium (Li) salt and a non-lithium salt. The lithium (Li) salt accompanies an intercalation/desorption reaction into the structure of the anode active material, that is, the metal-organic framework, and its types include LiBF ₄ , LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ , lithium bis(oxalato)borate (LiBOB), and combinations thereof. In addition, the non-lithium salt accompanies an adsorption/desorption reaction on the surface area of the carbon material additive, and may be used by mixing 0 to 0.5 M with the lithium salt. In this case, the non-lithium salt includes a material selected from the group consisting of TEABF ₄ (Tetraethylammonium tetrafluoroborate), TEMABF ₄ (Triethylmethylammonium tetrafluoroborate), SBPBF ₄ (spiro-(1,1′)-bipyrrolidium tetrafluoroborate), and combinations thereof it may be In addition, the carbon material additive may include a material selected from the group consisting of vinyl carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), and combinations thereof.

In one embodiment of the present application, the separator is positioned between the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from being in physical contact with each other and electrically shorted, and a porous material may be used. For example, the separator may include a material selected from the group consisting of polypropylene, polyethylene, polyolefin, and combinations thereof.

In one embodiment of the present application, the hybrid supercapacitor having the above configuration can achieve high energy density and power density with excellent cycling stability because a carbonized matrix-particle composite is used as an electrode active material. That is, since the carbonized matrix-particle composite has a particle size standard deviation of 5 nm or less by metal or metal oxide nanoparticles by laser carbonization, a hybrid supercapacitor including the carbonized matrix may exhibit excellent specific capacitance and output characteristics. .

The fourth aspect of the present application is,

A catalyst comprising the carbonized matrix-particle composite according to the first aspect of the present application is provided.

In addition, the fifth aspect of the present application,

An adsorbent comprising the carbonized matrix-particle composite according to the first aspect of the present application is provided.

Detailed descriptions of parts overlapping with the first to third aspects of the present application have been omitted, but the description of the first to third aspects of the present application is the same even if the description is omitted in the fourth and fifth aspects. can be applied

In one embodiment of the present application, the carbonized matrix-particle composite may be used as a catalyst for water purification, an anticancer drug, a treatment for immunodeficiency virus, a treatment for fungal and bacterial infection, a treatment for malaria, various drug delivery materials, and a photocatalyst, in addition to a supercapacitor or an electrode active material for a secondary battery. , sensors, aerospace materials, etc. Applicable in various fields, it can be used as a commercially very useful material.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Example 1.1 [M ₂ (DOBDC)(EG) ₂ ] (M = Ni, Co, Fe, Zn, Mn) Preparation of MOF

M(NO ₃ ) ₂ 6H ₂ O (0.600 g) (M = Ni, Co, Fe, Zn and Mn) was dissolved in 2.0 mL of N,N-diethylformamide as H ₄ DOBDC (0.116 g, 0.590 mmol). After dissolution by sonicating with 10 mL of ethylene glycol ((CH ₂ OH) ₂ ) was added to the solution, melamine (0.100 g, 0.793 mmol) was added to the solution and dissolved by shaking. The clean solution was transferred to a Teflon-lined bomb reactor and reacted at 130 °C for 16 hours. After cooling to room temperature, it was filtered to obtain MOF crystals. The crystals were first washed with dimethylformamide (DEF) to remove unreacted ligands, and then exchanged with methanol for DEF. Finally, the crystals were collected and dried under vacuum.

Example 1.2 Preparation of MOF Film

The prepared MOF and poly(vinylidinedifluoride) (PVDF) (mass ratio 10:1) were mixed with N-methyl-2-pyrrolidinone (NMP) solvent for 30 min in an agate mortar to obtain a homogeneous mixture. A slurry was formed. A MOF film was prepared by pasting the slurry onto cleaned Cu foil (17 μm thick) using a polymer squeegee. The film was then dried on a hot plate at 70° C. for 2 hours and allowed to dry naturally overnight before further processing. The thickness of the prepared film is ~15 μm.

Example 1.3 Laser Quenching of MOF Film

Laser annealed MOFs were fabricated using a commercial laser system equipped with a 10.6 μm wavelength CO ₂ laser (C40 60W, Coryart, Korea). This equipment can perform laser scanning at a speed of 20-500mm/s while maintaining the laser line spacing at 0.5 mm. The laser power at the sample location was measured by scanning an area of 3 x 14 mm using a laser power meter (Gentec-EO Pronto-250). A 2×1 cm ² MOF film was loaded into an inert chamber equipped with a CO ₂ laser-transparent ZnSe window. Since laser treatment in air results in strong oxidation of the MOF, the experiment was performed in a vacuum chamber with a CO ₂ laser-transparent window under a N ₂ atmosphere. After the chamber was evacuated to 600 mmHg vac by a vacuum pump, while maintaining the chamber pressure at 500 mmHg vac, it was purged at a constant N ₂ flow rate. The laser was set to scan mode with controlled laser power (W) and scan speed (mm/s). The laser spot size on the sample was 0.5 mm.

7 is a photograph of a MOF sample before and after laser heat treatment. When irradiated under N ₂ conditions, the color of the MOF turned black within a few seconds, confirming the carbonization of the MOF. The change of the colored MOF film to a black film indicates carbonization of the MOF sample. It is also noteworthy that the Cu substrate was not damaged before and after laser annealing.

Example 1.4 Thermolysis of MOF

After loading the MOF crystal into an alumina boat, it was inserted into a quartz tube. The tube was evacuated to -0.1 Torr by a vacuum pump and heated to 800 °C at a heating rate of 5 °C/min by a furnace (4000 W, Daepoong Industry Co., Ltd.). The sample was annealed for 1 hour under an Ar flow rate of 150 sccm before naturally cooling to room temperature.

Example 1.5 Material properties and results

The structure and surface morphology of the samples were analyzed using FE-SEM (JSM-700F, JEOL). TEM (Tecnai F30, FEI) was used to characterize the samples at 300 kV. X-ray powder diffraction (XRD) (Empyrean, PANalytical) was used to study the crystallinity of the samples. The domain size (L) of crystalline nanoparticles was estimated by the Scherer equation: L = 0.9λ/(δcosθ), where δ is the full width at half maximum (FWHM) of the diffraction peak and θ is the diffraction angle (in radians) )am.

Figure 2 shows the crystal structure of MOF-derived materials by pyrolysis and laser heat treatment. For all MOFs, the disappearance of the strong characteristic diffraction peak at ~ ^12o and the formation of a new diffraction peak indicates complete decomposition of the MOF into metal or oxide/carbide nanoparticles. Depending on the pyrolysis or laser treatment, the crystal structure of the product and the corresponding domain size depend on the MOF. Upon pyrolysis, metal nanoparticles (i.e. Ni and Co, Fig. 2A-D) and metal carbides/oxides (i.e. Fe ₃ C, ZnO and MnO, Fig. 2EJ) were found in the T-MOF. Based on the full width at half maximum of the diffraction peak, the domain size of the nanoparticles was calculated to range from 8 to 35 nm. In particular, in laser heat treatment, more metal (ie, Ni, Co and Fe) nanoparticles were obtained. In addition, the domain size (4 to 14 nm) of the laser annealed nanoparticles was found to be much finer than that of the thermally decomposed nanoparticles.

8 shows the microstructural properties of MOF-derived materials by pyrolysis and laser heat treatment. A, C, and E show representative transmission electron microscopy (TEM) images and crystal size distributions of Ni, Fe ₃ C and MnO nanoparticles through pyrolysis, respectively. B, D, and F show representative TEM images and size distributions of Ni, Fe and MnO nanoparticles through laser annealing, respectively.

9 to 13 show the morphological changes of MOF-Ni, MOF-Co, MOF-Fe, MOF-Zn, and MOF-Mn by pyrolysis and laser heat treatment, respectively.

14 shows microstructural properties of MOF-derived materials. A, and B show TEM images of Co and ZnO nanoparticles through pyrolysis. C,D show TEM images of Co and ZnO nanoparticles through laser annealing.

Figure 15. Long-term stability of MOF-derived Ni, Co and Fe nanoparticles by laser thermal treatment after storage in air for several months is shown.

Although the MOF-derived materials showed similar morphologies to the original MOFs (FIGS. 9 to 13), studies on the microstructural properties of MOF-derived materials by pyrolysis and laser heat treatment revealed significant differences. Representative transmission electron microscopy images confirm the presence of Ni, Co, Fe, Fe ₃ C, ZnO and MnO nanoparticles encapsulated in the ligand-derived carbon matrix ( FIGS. 8 and 14 ). The nanoparticles prepared by pyrolysis show a large size with high dispersion (i.e., Ni: 13.7 ± 12.3 nm, Fe3C: 23.5 ± 8.5 nm, and MnO: 51.8 ± 23.1 nm) (A, C, E in Fig. 8). , laser annealing showed a uniform size with narrow dispersion (i.e., Ni: 5.3 ± 0.7 nm, Fe: 8.0 ± 1.6 nm, and MnO: 6.7 ± 1.5 nm) (Fig. 8B, D, F). The crystallite size of the laser annealed nanoparticles was found to deviate less from the domain size calculated from the XRD data, indicating the uniform shape and narrow size distribution of the nanoparticles. In addition, the MOF-derived carbon matrix served as a barrier to protect the nanoparticles from the oxidizing atmosphere and enable stable preservation for several months in air (FIG. 15).

In conclusion, laser annealing was demonstrated to be a fast, feasible and environmentally friendly technique for preparing ultrafine stable nanoparticles of metals and metal oxides from MOFs. Ultrafine nanocrystals of various metals (Ni, Co, Fe) and metal oxides (ZnO and MnO) are uniformly distributed in the porous carbon matrix. In particular, Fe nanoparticles, which are difficult to manufacture by a long pyrolysis process due to the formation of Fe ₃ C, can be easily prepared by laser heat treatment. The present inventors found that the onset reduction potential of metal ions in the MOF for the formation of metal or metal oxide nanoparticles shifted from -0.27 V in the case of conventional pyrolysis to -0.44 V in the case of laser thermal decomposition. Moreover, thanks to the instantaneous heating and cooling of the laser, ultrafine nanoparticles with sizes of 4 to 14 nm were easily fabricated without the need for complicated controlled synthesis to suppress the typical crystal growth by Ostwald ripening in conventional pyrolysis. This method has great potential to serve as a general platform for preparing ultrafine stable metal/metal oxide nanoparticles with controlled size and dispersion for a variety of applications.

Example 2.1 Preparation of MOF-74 (Ni)

Ni(NO ₃ ) ₂ 6H ₂ O (0.600 g, 2.063 mmol) and 2.0 mL of N,N-diethylformamide were dissolved by sonication with H ₄ DOBDC (0.116 g, 0.590 mmol), and then 10 mL of Ethylene glycol ((CH ₂ OH) ₂ ) was added to the solution to synthesize MOF-74(Ni). Melamine (0.100 g, 0.793 mmol) was added to this solution and dissolved by shaking. The clear solution was transferred to a Teflon-lined bomb reactor and reacted at 130 °C for 16 hours. After cooling to room temperature, MOF-74(Ni) crystals were obtained by filtration. The crystals were washed with methanol and then dried under vacuum.

Example 2.2 Preparation of MOF-74 (Ni) Film

Prepared MOF-74 (Ni) and poly(vinylidinedifluoride) (PVDF) (mass ratio 10:1) were mixed with N-methyl-2-pyrrolidinone (NMP) solvent in an agate mortar for 30 min. while mixing to form a homogeneous slurry. A MOF-74(Ni) film was prepared by pasting the slurry onto cleaned Cu foil (17 μm thick) using a polymer squeegee. The film was then dried on a hot plate at 70° C. and allowed to dry naturally overnight before further processing. The thickness of the prepared film is ~15 μm.

Example 2.3 Pyrolysis of MOF-74 (Ni)

After loading the prepared MOF-74 (Ni) sample into an alumina boat, it was inserted into a quartz tube. The tube was evacuated to -0.1 Torr by a vacuum pump and heated at a heating rate of 5 °C/min to defined temperatures (e.g., 400 and 800 °C). The sample was annealed for 1 hour under an Ar flow rate of 150 sccm before naturally cooling to room temperature.

In the case of conventional pyrolysis, the samples were annealed in a high temperature furnace with an inert atmosphere. Unlike laser synthesis, pyrolysis could produce larger-sized Ni nanoparticles with a longer processing time (i.e., several hours).

Example 2.4 Laser Quenching of MOF-74 (Ni) Film

Ni nanoparticles were prepared from MOF-74(Ni) film using a commercial laser system equipped with a 10.6 μm wavelength CO ₂ laser (C40 60W, Coryart, Korea). This equipment can perform laser scanning at a speed of 20-500mm/s while maintaining the laser line spacing at 0.5 mm. The laser power at the sample location was measured using a laser power meter (Gentec-EO Pronto-250). A 2×2 cm ² piece of MOF film was loaded into an inert chamber equipped with a CO ₂ laser-transparent ZnSe window. Since laser treatment in air results in strong oxidation of the MOF, the experiment was performed in a vacuum chamber with a CO ₂ laser-transparent window under a N ₂ atmosphere. After the chamber was evacuated to 600 mmHg by a vacuum pump, while maintaining the chamber pressure at 500 mmHg, it was purged at a constant N ₂ flow rate. The laser was set to scan mode with controlled laser power (W) and scan speed (mm/s). The laser spot size on the sample was -0.5 mm.

Example 2.5 Temperature measurement during laser heat treatment

A high-performance infrared temperature sensor (Optris CTlaser 3MH3) with a measurable temperature range of 250–1800 °C and an ultrafast response time of 1 ms was used to track the temperature change of the sample during laser synthesis. The sensor's short spectral wavelength of 2.3 μm reduces temperature reading errors on surfaces with low or unknown emissivity and also avoids the effects of the 10.6 μm CO ₂ laser wavelength. The sensor was placed ~45 cm away from the sample to obtain the smallest measuring spot of ~1.5 mm on the sample. To obtain a more accurate temperature value, the emissivity (ε) of the MOF-74 (Ni) film was measured as 0.94 and used to set the emissivity in the management software (CompactConnect). During laser synthesis, the emissivity is assumed to be constant.

Under laser scanning, the temperature of the absorbed site increased rapidly and then was rapidly cooled by the surroundings (i.e. gas flow and substrate). The time-temperature profile of the sample during laser synthesis was recorded using a high performance pyrometer. It took less than 2 seconds to heat and cool the sample from 250 to 830 °C and vice versa. During this process, organic ligands in the framework were transformed into porous carbon and Ni ions were thermally decomposed into Ni metal, which appeared in the form of nanoparticles.

Example 2.6 Electrochemical properties

Electrochemical measurements were performed using an electrochemical workstation (VSP, Bio-Logic Science Instruments ) was performed by The working electrode was prepared by mixing 85 wt% active material, 10 wt% carbon black, and 5 wt% PVDF, followed by grinding in an agate mortar with NMP solvent for 30 minutes. The obtained slurry was then pressed with a piece of nickel foam at a mass loading of 1.6 to 2.2 mg/cm ² . The electrode was prepared by drying the sample on a hot plate at 80 °C for 3 hours and then in a vacuum oven at 100 °C for 2 hours. The typical electrode area considered was 1 cm ² for all samples. Cyclic voltammetry (CV) was measured in a potential window of 0-0.5V under different scan rates ranging from 1 to 100 mV/s. Galvanostatic charge-discharge (GCD) was studied in a potential window of 0 to 0.4 V under various current densities ranging from 0.3 to 10 A/g. Electrochemical impedance spectroscopy (EIS) was performed in the frequency range from 100 kHz to 0.1 Hz at an open circuit potential with an AC voltage amplitude of 10 mV.

The specific capacitance was calculated on the CV curve using the formula: C = Q/(2mνΔV), where Q is the integrated charge over the entire potential range or area of the CV curve, m is the active mass of the electrode material, v is the potential scan rate and ΔV is the potential window. Alternatively, the specific capacitance was also calculated from the GCD curve: C = IΔt/(mΔV), where I is the discharge current and Δt is the discharge time.

An asymmetric supercapacitor was fabricated with Ni-5.5-nm nanoparticles as the cathode and activated carbon as the anode and measured in a two-electrode setup. The fabrication of the cathode is as described above. To make the anode, activated carbon was extracted from a commercial supercapacitor (Samwha Capacitor) and then mixed with carbon black and PVDF (mass ratio 18:2:1) in NMP for 30 minutes to form a uniform slurry before being pasted onto a piece of nickel foam. and dried in a vacuum oven at 100 °C for 2 h. For the full cell assembly, the electrode mass was determined by the charge between the two electrodes (i.e., C+m+V+ = C_m_V_, where C+, m+, V+ and C_, m_, V_ are the ratios of the cathode and anode materials, respectively). capacitance, active mass, and potential window). To assemble the whole cell, the cathode and anode were placed between cellulose membranes inside the test cell. Electrodes and separators were wetted for 3 hours before electrochemical measurements using 6M KOH electrolyte.

The specific capacitance (C _d , F/g), energy density (E, Wh/kg) and power density (P, W/kg) of the supercapacitor device were calculated from the GCD curves of the assembled asymmetric supercapacitor as : C _d = IΔt/(m ₀ ΔV), E = C _d .(ΔV) ² /7.2 and P = 3600E/Δt, where I is the discharge current (mA) and m ₀ is the total mass of active material in the cathode and anode (mg), Δt is the discharge time, and ΔV is the voltage window (V).

Example 2.7 Material properties and results

The structure and surface morphology of the samples were analyzed using a field emission scanning electron microscope (FE-SEM, JSM-700F, JEOL). The FE-SEM was equipped with electron dispersive X-ray spectroscopy (EDX) to study the elemental composition at 10 kV. Samples were characterized at 300 kV using a transmission electron microscope (TEM, Tecnai F30, FEI). X-ray powder diffraction (XRD) (Empyrean, PANalytical) was used to study the crystallinity of the samples. X-ray photoelectron spectroscopy (XPS) was performed using an Al Kα X-ray source (Multilab 2000, Thermo Scientific) with a spot size of 0.5 μm ² . Porosity was measured by the Brunauer-Emmett-Teller N ₂ sorption test (BET, BELSORP-max, BEL Japan Inc.). Sample weights were determined using an analytical balance (CPA225D, Sartorius) with a minimum resolution of 0.01 mg.

As can be seen from the X-ray diffraction (XRD) profile (Fig. 16C), the crystallographic changes of the samples were analyzed. The disappearance of the MOF-74(Ni) peak at 2θ = ^11.7o suggested decomposition of the organic framework. The formation of new diffraction peaks at 44.5, 51.8 and 76.4o corresponded to the (111), (002) and (022) planes of the Ni cubic structure (reference code: 98-005-2265, PANalytical HighScore Plus). The sharpening of the Ni diffraction peak indicates the size of the crystalline domain, which is inversely proportional to the full width at half maximum (FWHM). The average domain sizes of the samples were 3.0, 4.8, 5.5, 6.1 and 12.5 nm (Table 1).

Energy dispersive X-ray spectroscopy (EDX) data confirmed that MOF-74(Ni) and its derivatives were composed only of Ni, C and O. In particular, the Ni content gradually increased as the size of the Ni nanoparticles increased. High temperatures and long treatment times were considered which resulted in more effective removal of carbon and oxygen during synthesis. It also means that the lower oxygen content of the sample with larger particles improves the electrical conductivity of the carbon scaffold. The chemical properties of the samples were further studied by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) (FIG. 17). The Raman spectrum showed the disappearance of the MOF-74(Ni) peaks (eg, 1282, 1419, 1497, 1560 and 1631 cm ^-1 ) with the formation of two carbon peaks at ~ 1350 and ~ 1595 cm ^-1 , confirmed complete conversion of the organic framework to graphitic-like carbon. The XPS spectrum of Ni 2p _3/2 shifted from 857.2 to 852.5 eV with the lower binding energy of the spin-orbit core, confirming the reduction of Ni ²⁺ to Ni ⁰ in metal nanoparticles in MOF-74(Ni).

The phase, chemical and compositional changes indicate significant morphological and microstructural changes of MOF-74(Ni) before and after synthesis. Originally, MOF-74 (Ni) has a rod-like shape with a relatively smooth surface and an ultrafine structure (FIG. 18A). After synthesis, the surface was roughened with nanoparticles that grew larger with increasing temperature or treatment time. The nanoparticles appeared to be Ni metal as confirmed by EDX line scan (FIG. 19). Further microstructural studies showed that MOF-74(Ni) was transformed into a composite of crystalline nanoparticles homogeneously dispersed in a carbon matrix (Fig. 18B). Observations on individual particles showed a fringe spacing of 2.04 Å, corresponding to the (111) plane of the Ni cubic structure. The calculated nanoparticle sizes (i.e., 4.8 ± 0.6, 5.4 ± 1.5, 6.1 ± 2.0 and 13.5 ± 11.3 nm) were in good agreement with the average domain sizes of Ni 4.8, 5.5, 6.1 and 12.5 from XRD (Fig. 18C). . It was found that the size distribution of the nanoparticles became wider as the nanoparticles became larger. The large disparity of the nanoparticles probably originates from the growth of the nanoparticles under high temperature treatment and long treatment times. The microstructural transformation also implied large changes in the porosity properties of the samples (Table 2).

The original MOF-74 (Ni) has a high porosity with a specific surface area (SA) of 617 m ² /g and a total pore volume (V _total ) of 0.302 cm ³ /g. When almost half of the specific surface area decreased and the V _total of the MOF derivatives increased by more than 1.5 times, the organic framework was shown to be transformed into porous carbon. The further decrease in specific surface area and V _total as the nanoparticles become larger appears to be due to the decrease in carbon content, as shown in Table 1. In general, a uniform dispersion of ultrafine Ni nanoparticles in highly porous carbon was thought to provide high electrochemical performance, as presented below.

20A shows the CV curves of all samples at a scan rate of 5 mV/s. For each sample, a pair of redox peaks were observed in the CV profile representing the capacitive response of the paradigm response. The anodic peak at ~0.30V corresponds to the formation of Ni ³⁺ and the cathodic peak at ~0.14V represents the reduction to Ni ²⁺ . The dependence of specific capacitance on particle size is presented in FIG. 20B. From conventional intuition, one would think that smaller particles exhibit better electrochemical performance. Thereby, the smallest Ni nanoparticle of 3.0 nm will exhibit the highest specific capacitance. Indeed, the specific capacitance increased from 0.75 to 856 F/g as the grain size decreased to 5.5 nm in the Ni bulk, and decreased rapidly upon further reduction of the grain size to 3.0 nm. This suggests that the Ni-5.5-nm nanoparticles are the optimal size for the best electrochemical performance. The galvanostatic charge/discharge (GCD) curve of the sample at a current density of 1 A/g is presented in FIG. 20C. The inflection of the discharge curves suggested similar capacitance effects consistent with the results of the CV curves. The specific capacitance as a function of the current density is shown in D of FIG. 20 . The Ni-5.5-nm nanoparticles exhibited the highest specific capacitance among these samples, again confirming the optimal size for the best electrochemical performance. The nanoparticles also exhibited high cycling stability with 93% capacity retention after 10,000 loading cycles at a scan rate of 100 mV/s (FIG. 21).

To elucidate the origin of the size-dependent quasi-capacitance of the Ni nanoparticles, we measured electrochemical impedance spectroscopy (EIS) of the samples. In the Nyquist plot, all MOF-Ni derivatives showed well-defined semicircles in the high to mid-frequency region and diagonal lines in the low-frequency region (Fig. 22A). The Nyquist plot was fitted to the equivalent circuit model [R _s (R _ct CPE ₁ ) CPE ₂ ] (inset of FIG. 22A ). The starting point of the semicircle on the real axis of the plot is the equivalent series resistance (R _s ) related to the electrolyte and contact resistances. The semicircle that follows is dominated by redox charge transfer processes that occur primarily at the interface between the nanoparticles and the electrolyte. It consists of a parallel combination of interface resistance (R _ct ) and constant phase element (Constant Phase Element, CPE). R _ct is related to the electrical resistance of the carbon scaffold as well as the kinetics of the Faraday reaction at the interface. In CPE, imperfect specific capacitances generated at interfaces are created by semi-circular and non-ideal capacitive behavior. The diagonal line is dominated by diffusion-limited charge transfer in nanoparticles. The analysis of the Nyquist plot is summarized in Figure 22B and Table 3.

The lowest R _ct in the Ni-5.5-nm nanoparticles exhibits the highest redox kinetics at the nanoparticle and electrolyte interface. The R _ct of higher nanoparticles below 5.5 nm explains the greater resistivity of the carbon scaffold, whereas nanoparticles above 5.5 nm have less active surface area. In addition, it is known that the total pseudocapacitance of Ni-based electrode materials occurs not only in surface-controlled capacitive processes but also in proton diffusion-limited redox processes. Thus, the total current (i) is measured under scan. In CV measurements, the rate (v) can be interpreted as the sum of the capacitive current (ic) required to initiate the surface redox reaction and the diffusion-limited current (id) of protons in Ni nanoparticles (i.e., i = i _c + i _d = a _vb or log(i) = log(a) + b log(v), where a and b are adjustable parameters). The b value provides kinetic information for the electrochemical reaction determined from the slope of the linear plot of log(i) and log(v) (Fig. 23). A b value of 0.5 indicates a diffusion limited redox process. While the value of b is 1.0, what occurs in the nanoparticles suggests a surface-controlled capacitive process (inset of Fig. 22C). The gradual decrease of the value of b from 0.89 to 0.75 during the cathodic scan indicated that the charge storage behavior shifted from a capacitive to a capacitive and diffusion limited process as the nanoparticles decreased from 12.5 to 3 nm (Fig. 22). c). This suggests that the contribution of the proton diffusion-limited current becomes larger as the size of the nanoparticles becomes smaller. The relationship between peak current (ip), proton diffusion coefficient (D) and scan rate (ν) in CV measurement is formulated as follows in the Randles-Sevcik equation. ip = 0.4463 nFAC(nFνD/RT)1/2, where n is the number of electron transfers in the redox reaction, A is the electrode area, F is the Faraday constant, C is the initial concentration of the reactant, R is the gas constant, and T is the temperature am. D in FIG. 22 shows the change in D value according to the size of the Ni nanoparticles. The D value was found to be the highest for the Ni-5.5-nm nanoparticles, indicating the fastest diffusion controlled process for the highest electrochemical performance.

In general, the excellent electrochemical performance of Ni-5.5-nm with high capacity retention can be attributed to the synergistic effect of the narrow size distribution and homogeneous dispersion of Ni nanoparticles in the conductive porous carbon scaffold. First, the narrow size distribution of nanoparticles will reduce the variation in electrochemical performance due to the influence of size-dependent properties. Second, the porous carbon scaffold will mitigate stress-induced structural changes due to redox reactions during long-term electrochemical reactions. Third, the homogeneous dispersion of nanoparticles in the conductive carbon scaffold resulted in low charge transfer resistance, which was verified by EIS analysis. Finally, we presented a model describing the charge storage mechanism of Ni nanoparticles in the porous carbon scaffold of FIG. 24 . The charge transfer resistance, proton diffusion resistance and electrical resistance (ρc) of the carbon scaffold are the most probable factors determining its size. Ni nanoparticle-dependent pseudocapacitance. Small Rct, high D, and low ρc maximize the use of active materials, providing excellent electrochemical performance.

To demonstrate the practical applicability of MOF-derived Ni nanoparticles, we fabricated an asymmetric supercapacitor device with Ni-5.5-nm nanoparticles as the cathode and commercially available activated carbon (AC) as the cathode (Ni 5.5//AC). did First, the electrochemical performance of AC was investigated by CV measurement (FIG. 25). The anode material showed typical electric double layer capacitance with a specific capacitance of 10 4 F/g at 10 mV/s. Using the comparative CV curves of the two electrode materials, it is possible to establish a stable operating potential window of the supercapacitor (Fig. 26A) and determine the mass of the active material of each electrode. For example, m _anode = 3.46 m _cathode ). At different load currents in the voltage window of 0–1.6 V, the typical GCD curves of the device exhibited inverted discharge curves exhibiting quasi-capacitance characteristics (Fig. 26B). This device exhibited a specific capacitance of 54 F/g at 0.5 A/g with reasonable cycle stability after 20,000 loading cycles (FIG. 27). It is believed that the specific capacitance of the device is greatly improved when anode materials with higher electrochemical performance are used. The Nyquist plot of this device showed a quasi-vertical profile, indicating good capacitive behavior. The overall performance of the supercapacitor is summarized in the Ragone plot (Fig. 26D) compared to other energy storage devices. Maximum energy densities of ~ 20 Wh/kg and power densities of 8,000 W/kg have been recorded. Finally, a coin cell asymmetric supercapacitor was fabricated from the material, and a light emitting diode (LED) was illuminated using the coin cell asymmetric supercapacitor (FIG. 26E). Two fully charged supercapacitors connected in series with a cathode mass of ~1.6 mg were able to light the LED device for more than 5 min.

In summary, we demonstrated size-dependent pseudocapacitance of Ni nanoparticles for high-performance supercapacitors. Ni nanoparticles with controlled sizes ranging from 3 to 12.5 nm uniformly dispersed in porous carbon were easily prepared from MOF-74 (Ni) through laser synthesis and pyrolysis. Contrary to conventional intuition, it was found that the highest electrochemical performance was achieved at a particle size of 5.5 nm. This maximizes the electrochemical performance by lowering the charge transfer resistance of the particle surface and the proton diffusion resistance of the particle due to the synergistic effect of the narrow size distribution and homogeneous dispersion of Ni nanoparticles in the porous and conductive carbon support. In addition, the supercapacitor made of Ni 5.5 nm//commercial activated carbon achieves a high energy density of 20 Wh/kg and a power density of 8,000 W/kg with excellent cycling stability.

Claims (19)

mixing the metal-organic complex with a solvent to form a slurry; preparing the metal-organic composite film by pasting the slurry on a Cu foil; and irradiating the metal-organic composite film with a CO ₂ laser having a wavelength (λ) of 5 to 15 μm in a nitrogen atmosphere for 0.5 to 5 seconds; It is prepared according to a manufacturing method comprising
The laser is irradiated up to a maximum temperature of 700 ~ 900 ℃,
Porous carbon and a plurality of metal or metal oxide nanoparticles having a particle size standard deviation of 5 nm or less dispersed in the porous carbon,
The metal or metal oxide nanoparticles are Ni having an average particle size of 4.6 nm to 6.1 nm, Fe having an average particle size of 6.4 nm to 9.7 nm, or MnO having an average particle size of 5.2 nm to 8.3 nm. A method for producing a carbonized matrix-particle composite.
delete delete delete delete delete delete delete delete delete According to claim 1,
Method for producing a carbonized matrix particle composite in which the film has a thickness of 1 to 50 μm.
delete delete delete delete delete An electrode comprising a carbonized matrix-particle composite according to any one of claims 1 or 11.
A catalyst comprising a carbonized matrix-particle composite according to any one of claims 1 or 11.
An adsorbent comprising a carbonized matrix-particle composite according to any one of claims 1 or 11.

Images