MOF-Derived Highly Porous Carbon Aerogel and Its Application to 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 particularly to MOF-derived highly porous carbon aerogels and their applications to supercapacitors.

Background Art

[0002] Climate change caused by the combustion of fossil fuels is worsening, and the demand for clean energy such as solar energy, tidal energy, and wind energy is increasing. Since these clean energies are greatly restricted by the environment, a new energy storage system called a supercapacitor has attracted the attention of scientists. A supercapacitor, also called an electrochemical capacitor, is one of the most promising energy storage devices. Compared with conventional capacitors and batteries, supercapacitors have many excellent advantages, such as a long cycle life of charge and discharge, high power density and energy density, easy maintenance, small volume, large capacity, environmental friendliness, a wide operating temperature range, and high high-temperature reliability and safety. Its potential mechanism is a reversible process occurring at the electrode-electrolyte interface, which can provide a sustainable life cycle, high output density, and rapid charge and discharge rate. Currently, supercapacitors are widely applied to consumer electronics, memory backup systems, industrial power supplies, and energy management. However, commercially available carbon-based supercapacitors have a low energy density, and their practical use is greatly restricted.

[0003] Metal-organic frameworks (MOFs) are a series of novel materials centered around inorganic metal ions or ion clusters, with organic compounds as ligands, forming periodic three-dimensional nanoporous materials. Compared with conventional materials, MOFs can provide rich and uniformly distributed active centers, and their pore structure is beneficial for the rapid diffusion of electrolyte ions. Therefore, MOF materials are considered ideal supercapacitor materials. However, when using MOFs as the anode of electrode materials, there is a problem that after hundreds of charge-discharge cycles, the pore structure of MOFs irreversibly collapses. As a result, the specific surface area of the electrode decreases rapidly, and the diffusion position and conductivity of electrolyte ions decrease. This has brought great challenges to the research on the conduction process of MOF supercapacitors.

Summary of the Invention

Problems to be Solved by the Invention

[0004] From the above, the present invention provides a highly porous carbon aerogel derived from 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 Problems

[0005] To achieve the above object, the present invention provides the following scheme.

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

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

[0008] The above Method 1 includes dissolving the ligand in a solvent, then adding a mixed solution and uniformly mixing them, and then adding an ethanol solution of ZnCl2, and sealing and standing still to obtain [Zn(tppa)2Cl2] single crystals, where the ligand is tris(4-(pyridin-4-yl)phenyl)amine.

[0009] The above Method 2 includes dissolving the ligand in a solvent to obtain a ligand solution, dropwise adding the ligand solution to an ethanol solution of ZnCl2, stirring and standing still, then performing suction filtration to obtain a precipitate, and drying the precipitate to obtain the [Zn(tppa)2Cl2] powder crystals, where 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 with a volume ratio of 1:1 (the mixture of chloroform and ethanol has the characteristic of low toxicity), the volume ratio of the solvent to the mixed solution is 3:4 (at this ratio, the crystal form of the product is the best), the molar volume ratio of ZnCl2 to ethanol in the ethanol solution of ZnCl2 is 0.01 mmol:3 mL, and the volume ratio of the solvent to the ethanol solution of ZnCl2 is 1:1.

[0011] In Method 2, the solvent is chloroform, the molar volume ratio of the ligand to the solvent is 0.1 - 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 - 10 h, the standing time is 4 - 12 h, and the drying temperature is 50 - 100 °C.

[0012] In Method 1, the time for sealed static placement is 20 d, and the aim is to grow a white massive single crystal structure suitable for X-ray structural analysis.

[0013] In Method 2, the aim of stirring for 6 to 10 h and static placement for 4 to 12 h is the synthesis of powder crystals. To meet the requirements of rapid industrialization, this synthesis cannot be used for structural analysis.

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

[0015] The fourth technical scheme of the present invention is a method for manufacturing the above MOF-derived highly porous carbon aerogel, which fires and pyrolyzes the MOF-ZX-5 material to obtain the MOF-derived highly porous carbon aerogel.

[0016] Furthermore, the firing and pyrolysis specifically involves heating up to 700 to 1000 °C at a rate of 3 to 5 °C / min under an inert atmosphere and maintaining a constant temperature for 2 to 4 h.

[0017] The fifth technical scheme of the present invention is the application of the above MOF-derived highly porous carbon aerogel to a supercapacitor.

[0018] The sixth technical scheme of the present invention is an electrode material for a supercapacitor, which includes the above MOF-derived highly porous carbon aerogel.

[0019] The seventh technical scheme of the present invention is a supercapacitor, and the electrode material of the supercapacitor includes the above MOF-ZX-5-derived highly porous carbon aerogel.

Advantages of the Invention

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

[0021] The gel part in the MOFs-based aerogel can support the structure of MOFs to a certain extent and improve the stability of MOFs during the cycle. The present invention uses a novel MOF-ZX-5 ([Zn(tppa)2Cl2]) as a precursor to design and synthesize a novel carbon aerogel material (MOF-derived highly porous carbon aerogel) as the electrode material of a supercapacitor. The MOF-ZX-5-derived highly porous carbon aerogel has high porosity, a large specific surface area, and excellent capacitance performance. Its use as a supercapacitor electrode material has the characteristics of high specific capacitance, high power density, high energy density, fast charge and discharge rate, and excellent cycle stability.

Brief Description of the Drawings

[0022] Hereinafter, to more clearly explain the embodiments of the present invention or the technical schemes in the prior art, the drawings required 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 also obtain other drawings based on these drawings without creative effort.

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Modes for Carrying Out the Invention

[0023] Here, some exemplary embodiments of the present invention will be described in detail. However, this detailed description should not be considered as limiting the present invention, but rather as a more detailed explanation of some aspects, characteristics, and embodiments of the present invention.

[0024] It should be understood that the terms described in the present invention are for the purpose of explaining particular embodiments and are not intended to limit the present invention. Also, with regard to the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of this range is specifically disclosed. Each small range between any stated value or intermediate value within the stated range, as well as between any other stated value or intermediate value within that range, is also included in the present invention. The upper and lower limits of these small ranges can be included in the range or excluded independently.

[0025] Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field of the present invention. Although the present invention describes preferred methods and materials, methods and materials similar to or equivalent to those described herein can also be used in the practice or testing of the present invention. All documents referred to in this specification are incorporated by reference for the purpose of disclosing and describing the methods and / or materials related to that document. In case of any conflict with any incorporated document, the content of this specification shall prevail.

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

[0027] Terms such as "comprising", "including", "having", "containing", etc. used in this text are all open terms, meaning including but not limited to.

[0028] Unless otherwise specified, "room temperature" referred to in the present invention represents 15 to 30 °C in all cases.

[0029] Unless otherwise specified, the chemicals and reagents used in the examples of the present invention can be obtained from the purchase route.

[0030] The chemicals and reagents used in the examples of the present invention are all 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 using a Shanghai Chenhua Electrochemical Station.

[0033] Manufacture of the working electrode: The prepared carbon aerogel material, acetylene black and polyvinylidene fluoride are mixed at a mass ratio of 8:1:1, put into an agate mortar, and a few drops of ethanol are added and ground until a homogeneous black slurry is obtained. Here, the carbon material is the active material, acetylene black is the conductive agent, and polyvinylidene fluoride is the binder. Then, the mixed black slurry is transferred to a pre-washed nickel foam with an area of 1 cm 2 , thickness 2 mm. Then, this is placed in an oven at 100 °C and dried for 12 hours. Finally, the dried nickel foam is pressed at a certain high pressure (10 MPa) to make a supercapacitor electrode.

[0034] All electrochemical performance tests were carried out in a three-electrode system with the above-prepared electrode as the working electrode, a platinum wire electrode as the counter electrode, and one Hg / HgO electrode as the reference electrode. An aqueous KOH solution with a concentration of 6 mol / L was used as the electrolyte. Cyclic voltammetry (CV) was carried out within the corresponding potential range (-1 to 0 V) and tested at different sweep rates of 5, 10, 20, 50, and 100 mV s -1 . As a result, a current-potential change curve graph with a similar shape was obtained.

[0035] The constant current charge-discharge test (GCD) was carried out at different current densities of 0.5, 1.0, 2.0, 5.0 and 10 Ag in the corresponding potential range (-1~0V) in the CV test based on the mass of the active material on the working electrode. -1 The constant current charge-discharge curve test was carried out at different current densities. The cycle life of the carbon material was tested using the constant current charge-discharge at a current density of 1.0 Ag. -1

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, and 0.2 mmol of ZnCl2 was dissolved in ethanol (60 mL) to obtain a ZnCl2 ethanol solution. The ZnCl2 ethanol solution was placed in a round-bottom flask, and the tppa chloroform solution was slowly added dropwise to the ZnCl2 ethanol solution through a constant-pressure dropping funnel. After stirring at room temperature for 6 hours and standing for 12 hours, suction filtration was carried out to collect the white precipitate, which was 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 with a yield of 65%.

[0039] Step 2, Preparation of MOF-ZX-5-derived highly porous carbon aerogel (abbreviation: carbon aerogel)

[0040] The MOF-ZX-5 prepared in Step 1 was placed in a tube furnace, and the temperature was raised to 800 °C at a rate of 5 °C / min under a nitrogen atmosphere. After holding at a constant temperature for 3 hours, it was naturally cooled to room temperature to obtain a carbon aerogel product.

[0041] The carbon aerogel prepared in this example had a specific surface area of 996 m 2 g -1 and a pore diameter of 2.17 nm. As an electrode material for supercapacitors, its specific capacitance at a current density of 0.5 Ag -1 was 136 Fg -1reached, and the specific capacitance remained 133 F / g even after 2000 cycles. -1 It remained like this.

[0042] Example 2

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

[0044] Dissolve 0.6 mmol of tppa in chloroform (60 mL) to obtain a tppa chloroform solution, dissolve 0.2 mmol of ZnCl2 in ethanol (60 mL) to obtain a ZnCl2 ethanol solution, put the ZnCl2 ethanol solution into a three-necked flask, slowly dropwise add the tppa chloroform solution to the ethanol solution through a constant-pressure dropping funnel, stir at room temperature for 8 hours, let it stand for 10 hours, then perform suction filtration, collect the white precipitate, and wash it three times with 10 mL of ethanol. Finally, dry the white powder at 80 °C to obtain a white powder MOF-ZX-5 crystal sample, and the yield was 60%.

[0045] Step 2, Manufacture of MOF-ZX-5-derived highly porous carbon aerogel (abbreviation: carbon aerogel)

[0046] Put the MOF-ZX-5 manufactured in Step 1 into a tube furnace, heat it to 700 °C at a rate of 3 °C / min under a nitrogen atmosphere, let it cool naturally to room temperature after holding at a constant temperature for 4 hours to obtain a carbon aerogel product.

[0047] The carbon aerogel manufactured in this example had a specific surface area of 1267 m 2 g -1 , a pore diameter of 2.51 nm. As an electrode material for a supercapacitor, its specific capacitance at a current density of 0.5 A / g -1 reached 138 F / g, and the specific capacitance remained 135 F / g even after 2000 cycles. -1 It remained like this. -1

[0048] Figure 2 is the XRD spectrum of the carbon aerogel prepared in Example 2. 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 has a thin layer structure, is smooth and flat, and has a translucent silk-like appearance, and there are many disordered pore structures in the carbon aerogel.

[0050] 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, -1 The D peak is related to the disordered carbon structure, and the larger the disorder defect, the stronger the intensity, and the peak at 1580 cm -1 The G peak in is caused by the vibration of graphitized carbon atoms. The degree of graphitization of a carbon material is usually measured 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 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 destroyed ordered structure of the carbon material, with the carbon atoms randomly distributed, resulting in the least graphitized and most bulky product.

[0051] Figure 5 shows the CV curve graphs 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. -1When tested at different sweep speeds, current potential change curve graphs with similar shapes were obtained. The CV curve shows an area like a large rectangle, and the area of the rectangle increases as the sweep speed increases. As the scan rate and current density increase, the diffusion of electrolyte ions is restricted, so the deformation of the curve becomes more serious. For the CV curve, the specific capacitance can be calculated from Equation (1).

[0052] C = ∫IdV / 2vΔVm (1)

[0053] Here, C (Fg -1 )、I (A)、V (V)、v (mVs -1 )、m (g) represent specific capacitance, instantaneous current, voltage range, sweep speed, and mass of the active material, respectively. As the sweep speed increases from 5 mVs -1 to 100 mVs -1 , the specific capacitance of the electrode decreases from 145 Fg -1 to 94 Fg -1 . This is because when the sweep speed is fast, there is not enough time for the electrolyte to reach the microporous surface, resulting in less electrostatic charge being accumulated.

[0054] Figure 6 shows GCD curves at different current densities in a three-electrode system. At different current densities of 0.5 - 10 Ag -1 , the present invention measured the constant current charge-discharge curves of the working electrode (Figure 6). The specific capacitance can be obtained from Equation (2) according to the discharge curve.

[0055] C = IΔt / ΔVm (2)

[0056] Here, t (s) is the discharge time, and the other variables are the same as in Equation (1). According to the charge-discharge test, the specific capacitances when the current density of the electrode is 0.5, 1, 2, 5, and 10 Ag -1 are 130, 120, 116, 106, and 100 Fg -1That is, it should be noted that as the current density gradually increases, the capacitance value gradually decreases. This is because as the current density increases, the specific surface area that ions can reach by contact decreases.

[0057] Example 3

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

[0059] Dissolve 0.8 mmol of tppa in chloroform (60 mL) to obtain a tppa chloroform solution, dissolve 0.2 mmol of ZnCl2 in ethanol (60 mL) to obtain a ZnCl2 ethanol solution, put the ZnCl2 ethanol solution into a round-bottom flask, slowly dropwise add the tppa chloroform solution to the ethanol solution through a constant-pressure dropping funnel, stir at room temperature for 10 hours, let it stand for 8 hours, then perform suction filtration, collect the white precipitate, and wash it 3 times with 10 mL of ethanol. Finally, dry the white powder at 100 °C to obtain a white powder MOF-ZX-5 crystal sample, and the yield was 62%.

[0060] Step 2, Manufacture of highly porous carbon aerogel derived from MOF-ZX-5 (abbreviation: carbon aerogel)

[0061] Put the MOF-ZX-5 manufactured in Step 1 into a tube furnace, heat it up to 1000 °C at a rate of 3 °C / min under a nitrogen atmosphere, naturally cool it to room temperature after holding at a constant temperature for 2 hours to obtain a carbon aerogel product.

[0062] The carbon aerogel manufactured in this example has a specific surface area of 1293 m 2 g -1 , a pore diameter of 4.24 nm. As an electrode material for a supercapacitor, its specific capacitance at a current density of 0.5 Ag -1 reached 142 Fg -1 , and even after 2000 cycles, the specific capacitance remained at 137 Fg -1 .

[0063] Figure 1 shows Zn in the MOF-ZX-5 of the present invention IIIt is an ion coordination structure diagram. Figure 1 shows the analysis of the single crystal structure of MOF-ZX-5. The space group of MOF-ZX-5 belongs to the monoclinic system P2 1 / c and the asymmetric unit contains one Zn II ion, two ligand tppa molecules and two chlorine ions. As shown in Figure 1, each Zn II ion coordinates with four nitrogen atoms from different tppa molecules and two chlorine ions to form an octahedral coordination structure. The Zn-N coordination bond lengths in its equatorial plane are between 2.167 and 2.186 Å, and the axial Zn-Cl coordination bond length reaches 2.486 Å. Therefore, there is clearly a Jahn-Teller effect in the Zn II ion.

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

[0065] Carbon-based electrode materials are used in supercapacitors and have good reversibility, rapid charging ability, long cycle life, good environmental affinity, etc. However, due to their relatively low specific capacitance and low energy density, their comprehensive application is limited. As one of the typical porous compounds, MOFs have good structural characteristics such as long-range ordered structure and large specific surface area. The present invention uses a new 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 illustrate preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made by those skilled in the art to the technical scope of the present invention should be included in the protection scope defined by the claims of the present invention.

Claims

1. The 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 a powder crystal, and the crystal data of the single crystal is monoclinic system P2 １／ｃ . The asymmetric unit contains one Zn ＩＩ ion, two ligand tppa molecules and two chlorine ions, and the [Zn(tppa) ２ Cl ２ has an octahedral coordination structure. The MOF-ZX-5 material is characterized by the above.

2. A method for manufacturing the MOF-ZX-5 material according to Claim 1, which is Method 1 or Method 2, wherein Method 1 is Dissolve the ligand in a solvent, then add the mixed solution and mix uniformly. After that, add an ethanol solution of ZnCl ２ seal and let stand to obtain the [[Zn(tppa)]] ２ Cl ２ . The process includes the step of obtaining, and the ligand is tris(4-(pyridin-4-yl)phenyl)amine, wherein Method 2 is Dissolve the ligand in a solvent to obtain a ligand solution, and dropwise add the ligand solution to an ethanol solution of ZnCl ２ . After stirring and standing, perform suction filtration to obtain a precipitate, and dry the precipitate to obtain the ２ Cl ２ . The method comprises a step of obtaining [Zn(tppa)Cl]. The ligand is tris(4-(pyridin-4-yl)phenyl)amine.

3. In Method 1, the solvent is chloroform, 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 with a volume ratio of 1:1, the volume ratio of the solvent to the mixed solution is 3:4, and the ethanol solution of ZnCl ２ in the ethanol solution of ZnCl ２ and ethanol has a molar volume ratio of 0.01 mmol: 3 mL, and the volume ratio of the solvent to the ethanol solution of ZnCl ２ is 1:

1. 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, and the ZnCl ２ in the ethanol solution of ２ and ethanol is 0.01 mmol: 3 mL. The volume ratio of the ligand solution to the ethanol solution of ２ is 1:

1. The stirring time is 6 to 10 h, the standing time is 4 to 12 h, and the drying temperature is 50 to 100 °C. The manufacturing method according to claim 2, characterized by the above.

4. A highly porous carbon aerogel derived from MOFs, characterized in that it is obtained by subjecting the MOF-ZX-5 material according to Claim 1 to pyrolysis by firing.

5. A method for manufacturing a highly porous carbon aerogel derived from MOFs according to Claim 4, characterized in that the MOF-ZX-5 material is pyrolyzed by firing to obtain the highly porous carbon aerogel derived from MOFs.

6. Specifically, the pyrolysis by firing is characterized in that the temperature is raised to 700 to 1000 °C at a rate of 3 to 5 °C / min and kept at a constant temperature for 2 to 4 h under an inert atmosphere. A method for manufacturing a highly porous carbon aerogel derived from MOFs according to Claim 5.

7. A method for using the highly porous carbon aerogel derived from MOFs according to Claim 4 in a supercapacitor.

8. An electrode material for a supercapacitor, characterized in that it contains the highly porous carbon aerogel derived from MOFs according to Claim 4.

9. A supercapacitor, characterized in that the electrode material of the supercapacitor contains the highly porous carbon aerogel derived from MOFs according to Claim 4.

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