MOF-derived highly porous carbon aerogels and their application in supercapacitors

Abstract

The present invention relates to the technical field of supercapacitors, and particularly to MOF-derived highly porous carbon aerogels and their application to supercapacitors. The MOF-derived highly porous carbon aerogels are obtained by pyrolytic decomposition of the MOF-ZX-5 material, and the MOF-ZX-5 material is [Zn(tppa)2Cl2]. The present invention uses a novel MOF-ZX-5 as a precursor to design and synthesize a novel carbon aerogel material (MOF-derived highly porous carbon aerogel) as an electrode material for supercapacitors. The MOF-ZX-5-derived highly porous carbon aerogels have high porosity, a large specific surface area, and excellent capacitance performance. Their use as supercapacitor electrode materials features high specific capacitance, power density, and energy density, as well as fast charge and discharge rates and excellent cycle stability.

Description

[Technical Field]

[0001] The present invention relates to the technical field of supercapacitors, and in particular to MOF-derived highly porous carbon aerogels and their application in supercapacitors. [Background technology]

[0002] Climate change caused by the combustion of fossil fuels is worsening, increasing the demand for clean energy sources such as solar, tidal, and wind energy. Because these clean energies are subject to significant environmental constraints, a novel energy storage system called supercapacitors has attracted the attention of scientists. Supercapacitors, also known as electrochemical capacitors, are one of the most promising energy storage devices. Compared to conventional capacitors and batteries, supercapacitors offer many advantages, including a long charge-discharge cycle life, high power and energy densities, easy maintenance, small volume, large capacity, environmental friendliness, a wide operating temperature range, high-temperature reliability, and high safety. The underlying mechanism is a reversible process occurring at the electrode-electrolyte interface, which can provide a sustainable life cycle, high power density, and rapid charge-discharge rates. Currently, supercapacitors are widely applied in consumer electronics, memory backup systems, and industrial power supplies and energy management. However, commercially available carbon-based supercapacitors have low energy densities, significantly limiting their practical use.

[0003] Metal-organic frameworks (MOFs) are a new class of materials that utilize inorganic metal ions or ion clusters as cores and organic compounds as ligands to form periodic, multidimensional nanoporous materials. Compared to conventional materials, MOFs can provide abundant and uniformly distributed active centers, and their pore structure favors rapid diffusion of electrolyte ions. Therefore, MOF materials are considered ideal supercapacitor materials. However, the use of MOFs as anodes poses a problem: the pore structure of MOFs irreversibly collapses after hundreds of charge-discharge cycles. This leads to a rapid decrease in the specific surface area of ​​the electrode, reducing the diffusion sites for electrolyte ions and the electrical conductivity. This poses a major challenge to the study of the conduction process of MOF supercapacitors. Summary of the Invention [Problem to be solved by the invention]

[0004] Based on the above, the present invention provides a highly porous carbon aerogel derived from a MOF and its application to supercapacitors. The highly porous carbon aerogel derived from the MOF (MOF-ZX-5) of the present invention has high specific capacitance and cycle stability as a supercapacitor material. [Means for solving the problem]

[0005] In order to achieve the above object, the present invention provides the following scheme.

[0006] One technical scheme of the present invention is a MOF-ZX-5 material, wherein the MOF-ZX-5 material is [Zn(tppa)2Cl2], and the [Zn(tppa)2Cl2] is a single crystal or powder crystal, and the crystal data of the single crystal is monoclinic P2 1 / c and the asymmetric unit contains one Zn II It contains an ion, two ligand tppa molecules, and two chloride ions, and the [Zn(tppa)2Cl2] has an octahedral coordination structure.

[0007] The second technical scheme of the present invention is a method for producing the above-mentioned MOF material, which is Method 1 or Method 2.

[0008] The method 1 is The method includes the steps of dissolving a ligand in a solvent, adding a mixed solution and mixing uniformly, adding an ethanol solution of ZnCl, sealing the mixture and allowing it to stand to obtain a single crystal of [Zn(tppa)2Cl2], where the ligand is tris(4-(pyridin-4-yl)phenyl)amine.

[0009] The method 2 is The method includes the steps of dissolving a ligand in a solvent to obtain a ligand solution, adding the ligand solution dropwise to an ethanol solution of ZnCl, stirring and allowing to stand, and then suction filtering to obtain a precipitate, and drying the precipitate to obtain the [Zn(tppa)Cl] powder crystal, wherein the ligand is tris(4-(pyridin-4-yl)phenyl)amine.

[0010] Furthermore, in Method 1, the solvent is chloroform (chloroform can dissolve the ligand tppa), the molar volume ratio of the ligand to the solvent is 0.01 mmol:1 mL, the mixed solution is a mixture of chloroform and ethanol in a volume ratio of 1:1 (a mixture of chloroform and ethanol has the characteristic of low toxicity), the volume ratio of the solvent to the mixed solution is 3:4 (this ratio provides the best product crystal form), the molar volume ratio of ZnCl2 to ethanol in the ZnCl2 ethanol solution is 0.01 mmol:3 mL, and the volume ratio of the solvent to the ZnCl2 ethanol solution is 1:1.

[0011] In Method 2, the solvent is chloroform, the molar volume ratio of the ligand to the solvent is 0.1 to 0.2 mmol:15 mL, the molar volume ratio of ZnCl2 to ethanol in the ethanol solution of ZnCl2 is 0.01 mmol:3 mL, the volume ratio of the ligand solution to the ethanol solution of ZnCl2 is 1:1, the stirring time is 6 to 10 hours, the standing time is 4 to 12 hours, and the drying temperature is 50 to 100°C.

[0012] In Method 1, the sealed and left standing time is 20 days, and the purpose is to grow a white massive single crystal structure suitable for X-ray structural analysis.

[0013] In Method 2, the purpose of stirring for 6 to 10 hours and leaving for 4 to 12 hours is to synthesize powder crystals, and to meet the demands of rapid industrialization, this synthesis cannot be used for structural analysis.

[0014] The third technical scheme of the present invention is a highly porous carbon aerogel derived from MOFs (highly porous carbon aerogel derived from MOF-ZX-5), which can be obtained by pyrolyzing the above-mentioned MOF-ZX-5 material.

[0015] The fourth technical scheme of the present invention is a method for producing the MOF-derived highly porous carbon aerogel, in which the MOF-ZX-5 material is calcined and pyrolyzed to obtain the MOF-derived highly porous carbon aerogel.

[0016] Furthermore, the calcination pyrolysis is specifically carried out by increasing the temperature to 700 to 1000°C at a rate of 3 to 5°C / min in an inert atmosphere and maintaining the temperature for 2 to 4 hours.

[0017] The fifth technical scheme of the present invention is the application of the highly porous carbon aerogel derived from the above-mentioned MOFs to supercapacitors.

[0018] The sixth technical scheme of the present invention is a supercapacitor electrode material, which comprises the highly porous carbon aerogel derived from the above-mentioned MOFs.

[0019] The seventh technical scheme of the present invention is a supercapacitor, the electrode material of which comprises the MOF-ZX-5-derived highly porous carbon aerogel. [Effects of the Invention]

[0020] The present invention discloses the following technical effects.

[0021] The gel portion in MOF-based aerogels can provide some structural support for MOFs, improving their stability during cycling. This invention uses the novel MOF-ZX-5 ([Zn(tppa)2Cl2]) precursor to design and synthesize a novel carbon aerogel material (MOF-derived highly porous carbon aerogel) for use as a supercapacitor electrode material. The MOF-ZX-5-derived highly porous carbon aerogel possesses high porosity, a large specific surface area, and excellent capacitance performance. Its use as a supercapacitor electrode material offers high specific capacitance, power density, and energy density, as well as fast charge / discharge rates and excellent cycling stability. [Brief explanation of the drawings]

[0022] In the following, in order to more clearly explain the embodiments of the present invention or the technical scheme in the prior art, the drawings necessary for the embodiments will be briefly described. However, the drawings in the following description are only some embodiments of the present invention, and it is obvious that those skilled in the art can obtain other drawings based on these drawings without exerting creative efforts. [Figure 1] FIG. 1 is a diagram of the ZnII ion coordination structure in MOF-ZX-5 of the present invention. [Figure 2] FIG. 1 is an XRD spectrum diagram of the carbon aerogel produced in Example 2. [Figure 3] 1 is a TEM image of the carbon aerogel produced in Example 2. [Figure 4] FIG. 1 is a Raman spectrum of the carbon aerogel produced in Example 2. [Figure 5] 1 is a graph showing CV curves at different scan rates. [Figure 6] GCD curves at different current densities in a three-electrode system. [Figure 7] FIG. 1 is a diagram of the "diamond" (4,4) network structure of MOF-ZX-5 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] While several exemplary embodiments of the present invention will now be described in detail, this detailed description should not be construed as limiting the present invention, but should be understood as providing a more detailed description of some aspects, features and embodiments of the present invention.

[0024] It should be understood that the terms used in the present invention are for the purpose of describing particular embodiments and are not intended to limit the present invention. Numerical ranges in the present invention should also be understood to specifically disclose every intermediate value between the upper and lower limits of the range. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within that range, are also encompassed by the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded within the range.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although the present invention describes only preferred methods and materials, methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. All publications mentioned herein are incorporated by reference to disclose and describe the methods and / or materials related thereto. In the event of a conflict with any incorporated publication, the present specification controls.

[0026] It will be apparent to those skilled in the art that many modifications and variations can be made to the specific embodiments of the present specification without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art upon learning the present specification. The present specification and examples are merely illustrative.

[0027] As used herein, the terms "including," "comprising," "having," "containing," and the like are all open-ended terms, meaning including but not limited to.

[0028] In the present invention, "room temperature" refers to 15 to 30°C unless otherwise specified.

[0029] Chemicals and reagents used in the examples of the present invention are commercially available unless otherwise specified.

[0030] All chemicals and reagents used in the examples of the present invention are commercially available analytical reagents.

[0031] The electrochemical performance test method in the examples of the present invention is as follows.

[0032] The electrochemical performance test of the material sample (carbon aerogel) was measured using a three-electrode system under room temperature conditions at the Shanghai Chenhua Electrochemical Station.

[0033] Fabrication of working electrode: The prepared carbon aerogel material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, placed in an agate mortar, and a few drops of ethanol were added and ground until a homogeneous black slurry was obtained. Here, the carbon material is the active material, the acetylene black is the conductive agent, and the polyvinylidene fluoride is the binder. Then, the mixed black slurry was poured into a 1 cm2 sample. 2 The resulting mixture is then transferred to a 2 mm thick pre-washed nickel foam. This is then placed in an oven at 100°C and dried for 12 hours. Finally, the dried nickel foam is pressed under a constant high pressure (10 MPa) to form a supercapacitor electrode.

[0034] All electrochemical performance tests were performed in a three-electrode system, with the fabricated electrode as the working electrode, a platinum wire electrode as the counter electrode, and one Hg / HgO electrode as the reference electrode. A 6 mol / L KOH aqueous solution was used as the electrolyte. Cyclic voltammetry (CV) was performed within the corresponding potential range (-1 to 0 V) ​​at 5, 10, 20, 50, and 100 mVs. -1 When different sweep rates were tested, similar curves of the change in current with potential were obtained.

[0035] The constant current charge-discharge (GCD) tests were performed at 0.5, 1.0, 2.0, 5.0, and 10 Ag over the corresponding potential range (-1 to 0 V) ​​in the CV test, based on the mass of the active material on the working electrode. -1 Constant current charge / discharge curve tests were performed at different current densities. -1 The cycle life of the carbon material was tested using constant current charging and discharging at 1000kJ / s. [Example]

[0036] Example 1

[0037] Step 1: Synthesis of [Zn(tppa)2Cl2], i.e., MOF-ZX-5

[0038] 0.4 mmol of TPPA was dissolved in chloroform (60 mL) to obtain a TPPA chloroform solution. 0.2 mmol of ZnCl2 was dissolved in ethanol (60 mL) to obtain a ZnCl2 ethanol solution. The ZnCl2 ethanol solution was placed in an Erlenmeyer flask, and the TPPA chloroform solution was slowly added dropwise to the ZnCl2 ethanol solution through a constant pressure dropping funnel. The mixture was stirred at room temperature for 6 hours, and after 12 hours of standing, the white precipitate was collected by suction filtration and washed three times with 8 mL of ethanol. Finally, the white powder was dried at 50 °C to obtain a white powder MOF-ZX-5 crystal sample. The yield was 65%.

[0039] Step 2: Production of highly porous carbon aerogel derived from MOF-ZX-5 (abbreviated as carbon aerogel)

[0040] The MOF-ZX-5 produced in step 1 was placed in a tube furnace and heated to 800°C at a rate of 5°C / min under a nitrogen atmosphere. After 3 hours of constant temperature, the furnace was allowed to cool naturally to room temperature to obtain a carbon aerogel product.

[0041] The carbon aerogel produced in this example has a specific surface area of ​​996 m 2 g -1 The pore size is 2.17 nm, and the current density is 0.5Ag as an electrode material for supercapacitors. -1 The specific capacitance at -1After 2000 cycles, the specific capacitance remains at 133 Fg -1 It remained as it was.

[0042] Example 2

[0043] Step 1: Synthesis of [Zn(tppa)2Cl2], i.e., MOF-ZX-5

[0044] 0.6 mmol of TPPA was dissolved in chloroform (60 mL) to obtain a TPPA chloroform solution. 0.2 mmol of ZnCl2 was dissolved in ethanol (60 mL) to obtain a ZnCl2 ethanol solution. The ZnCl2 ethanol solution was placed in an Erlenmeyer flask, and the TPPA chloroform solution was slowly added dropwise to the ethanol solution through a constant pressure dropping funnel. The mixture was stirred at room temperature for 8 hours, and after 10 hours of standing, the white precipitate was collected by suction filtration and washed three times with 10 mL of ethanol. Finally, the white powder was dried at 80 °C to obtain a white powder MOF-ZX-5 crystal sample. The yield was 60%.

[0045] Step 2: Production of highly porous carbon aerogel derived from MOF-ZX-5 (abbreviated as carbon aerogel)

[0046] The MOF-ZX-5 produced in step 1 was placed in a tube furnace and heated to 700°C at a rate of 3°C / min under a nitrogen atmosphere. After 4 hours of constant temperature, the material was allowed to cool naturally to room temperature to obtain a carbon aerogel product.

[0047] The carbon aerogel produced in this example has a specific surface area of ​​1267 m 2 g -1 The pore size is 2.51 nm, and the current density is 0.5Ag as an electrode material for supercapacitors. -1 The specific capacitance at -1 The specific capacitance remains at 135 Fg even after 2000 cycles. -1 It remained as it was.

[0048] Figure 2 shows the XRD spectrum of the carbon aerogel prepared in Example 2. As can be seen from Figure 2, the carbon aerogel has two obvious weak broad peaks at around 25° and 44°, which correspond to the (002) and (101) crystal planes of carbon, respectively, indicating that the carbon aerogel has a low degree of graphitization.

[0049] Figure 3 is a TEM image of the carbon aerogel prepared in Example 2. Figure 2 shows the morphology and pore structure of the carbon aerogel. As can be seen from Figure 3, the carbon aerogel exhibits a thin layer structure, is smooth, flat, and translucent, like silk, and contains numerous disordered pore structures.

[0050] FIG. 4 is a Raman spectrum of the carbon aerogel prepared in Example 2. The degree of graphitization of the carbon aerogel material was analyzed by Raman spectroscopy. As shown in FIG. 4, the graphitization of the carbon aerogel material was observed at 1360 cm -1 The D peak is related to the disordered carbon structure, and the larger the disorder defects, the stronger the intensity, and the peak at 1580 cm -1 The G peak in the graphitized carbon material is generated by the vibration of graphitized carbon atoms. The degree of graphitization of a carbon material is usually determined by the relative ratio of the integrated areas of the D peak and the G peak (I D / I G ) is measured. As a result of calculation, the I of the carbon aerogel produced in Example 2 D / I G The value is 4.01, which suggests that the carbon aerogel produced under the conditions of the method of the present invention has a disrupted ordered structure of the carbon material, with the carbon atoms randomly distributed, resulting in the least degree of graphitization and the most bulky product.

[0051] Figure 5 shows the CV curves at different scan rates. Cyclic voltammetry (CV) was performed within the corresponding potential range (-1 to 0 V) ​​at 5, 10, 20, 50, and 100 mVs. -1Tests at different sweep rates yielded similar-shaped curves of current versus potential. The CV curves exhibited large rectangular areas, and the area of ​​the rectangles increased with increasing sweep rate. As the scan rate and current density increased, the curves became increasingly distorted due to limited diffusion of electrolyte ions. For the CV curves, the specific capacitance could be calculated using equation (1).

[0052] C=∫IdV / 2vΔVm (1)

[0053] Here, C(Fg -1 ), I(A), V(V), v(mVs -1 ), m(g) represent the specific capacity, instantaneous current, voltage range, sweep rate, and mass of the active material, respectively. -1 to 100mVs -1 As the capacitance increases, the specific capacitance of the electrode increases to 145 Fg -1 to 94Fg -1 This is because at high sweep speeds, the electrolyte does not have enough time to reach the microporous surface, resulting in less electrostatic charge being accumulated.

[0054] Figure 6 shows the GCD curves at different current densities in a three-electrode system. -1 The present invention measured the constant current charge / discharge curves of the working electrode at different current densities (Figure 6). The specific capacity can be obtained from the discharge curve using equation (2).

[0055] C=IΔt / ΔVm (2)

[0056] where t (s) is the discharge time, and the other variables are the same as in equation (1). Charge-discharge tests showed that the current density of the electrode was 0.5, 1, 2, 5, and 10Ag -1 The specific capacitances at these times are 130, 120, 116, 106, and 100 Fg, respectively. -1It is noteworthy that as the current density gradually increases, the capacitance value gradually decreases because the specific surface area available for ions to reach the contact decreases with increasing current density.

[0057] Example 3

[0058] Step 1: Synthesis of [Zn(tppa)2Cl2], i.e., MOF-ZX-5

[0059] 0.8 mmol of TPPA was dissolved in chloroform (60 mL) to obtain a TPPA chloroform solution. 0.2 mmol of ZnCl2 was dissolved in ethanol (60 mL) to obtain a ZnCl2 ethanol solution. The ZnCl2 ethanol solution was placed in an Erlenmeyer flask, and the TPPA chloroform solution was slowly added dropwise to the ethanol solution through a constant pressure dropping funnel. The mixture was stirred at room temperature for 10 hours, and after allowing to stand for 8 hours, the white precipitate was collected by suction filtration and washed three times with 10 mL of ethanol. Finally, the white powder was dried at 100 °C to obtain a white powder MOF-ZX-5 crystal sample. The yield was 62%.

[0060] Step 2: Production of highly porous carbon aerogel derived from MOF-ZX-5 (abbreviated as carbon aerogel)

[0061] The MOF-ZX-5 produced in step 1 was placed in a tube furnace and heated to 1000°C at a rate of 3°C / min under a nitrogen atmosphere. After 2 hours of constant temperature, the product was allowed to cool naturally to room temperature to obtain a carbon aerogel product.

[0062] The carbon aerogel produced in this example has a specific surface area of ​​1293 m 2 g -1 The pore size is 4.24 nm, and the current density is 0.5Ag as an electrode material for supercapacitors. -1 The specific capacitance at -1 The specific capacitance remains at 137 Fg even after 2000 cycles. -1 It remained as it was.

[0063] FIG. 1 shows the Zn in MOF-ZX-5 of the present invention. IIFigure 1 shows the ion coordination structure. The analysis of the MOF-ZX-5 single crystal structure is shown. The space group of MOF-ZX-5 is monoclinic P2 1 / c The asymmetric unit contains one Zn II ions, two ligand tppa molecules, and two chloride ions. As shown in Figure 1, each Zn II The Zn-N coordination bond length in the equatorial plane is between 2.167 and 2.186 Å, while the Zn-Cl coordination bond length in the axial plane reaches 2.486 Å. Therefore, Zn II The Jahn-Teller effect clearly exists for ions.

[0064] Figure 7 shows the "diamond" (4,4) network structure of MOF-ZX-5 of the present invention. Although the tppa molecule has three nitrogen atoms, only two nitrogen atoms are involved in the coordination during the assembly process. That is, each tppa ligand is connected to two Zn II The ions are bridged to obtain a two-dimensional "diamond" (4,4) network with a lattice size of 12.2 × 12.2 Å. 2 (Figure 7) The pore size reaches the nanometer order.

[0065] Carbon-based electrode materials used in supercapacitors have excellent reversibility, fast charging capability, long cycle life, and environmental friendliness, but their relatively low specific capacitance and low energy density limit their comprehensive applications. MOFs, as a typical porous compound, possess favorable structural characteristics, such as long-range order and a large specific surface area. This invention uses the novel macroporous MOF-ZX-5 as a precursor to synthesize a new carbon aerogel electrode material, improving the specific capacitance and energy density of the supercapacitor electrode material.

[0066] The above-described embodiments merely describe preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical scope of the present invention without departing from the design spirit of the present invention should be included in the scope of protection defined by the claims of the present invention.

Claims

1. An electrode material for a supercapacitor, comprising: MOF-ZX-5 material, wherein the MOF-ZX-5 material is [Zn(tppa) ２ Cl ２ ], and the [Zn(tppa) ２ Cl ２ ] is a single crystal or powder crystal, and the crystal data of the single crystal is monoclinic P2 １／ｃ and the asymmetric unit contains one Zn ＩＩ ion, two ligand tppa molecules and two chloride ions, ２ Cl ２ ] is an octahedral coordination structure, and a highly porous carbon aerogel derived from MOFs is obtained by pyrolyzing the MOF-ZX-5 material.

2. 2. A method for producing the MOF-ZX-5 material of claim 1, comprising: The ligand is dissolved in a solvent to obtain a ligand solution, and the ligand solution is dissolved in ZnCl ２ The mixture is added dropwise to an ethanol solution of the above, stirred, allowed to stand, and then subjected to suction filtration to obtain a precipitate. The precipitate is dried to obtain the above [Zn(tppa) ２ Cl ２ wherein the ligand is tris(4-(pyridin-4-yl)phenyl)amine.

3. The solvent is chloroform, the molar volume ratio of the ligand to the solvent is 0.1 to 0.2 mmol:15 mL, and the ZnCl ２ ZnCl in an ethanol solution of ２ The molar volume ratio of the ligand solution to the ZnCl solution was 0.01 mmol:3 mL. ２ The method according to claim 2, wherein the volume ratio of the ethanol solution to the ethanol solution is 1:1, the stirring time is 6 to 10 hours, the standing time is 4 to 12 hours, and the drying temperature is 50 to 100°C.

4. The method for producing an electrode material for a supercapacitor according to claim 1, characterized in that the MOF-ZX-5 material is subjected to pyrolysis by calcination to obtain the MOF-derived highly porous carbon aerogel.

5. The method for producing an electrode material for a supercapacitor according to claim 4, characterized in that the calcination pyrolysis is carried out by heating the material to 700-1000°C at a rate of 3-5°C / min in an inert atmosphere and maintaining the temperature for 2-4 hours.

6. A supercapacitor characterized by comprising the electrode material of the supercapacitor described in claim 1.

Images