A kind of vacant site type ZIF-8 pseudocapacitive material and preparation method and application

Abstract

The application discloses a kind of vacancy type ZIF-8 pseudocapacitive materials and preparation method and application, belong to supercapacitor material technical field, the preparation method of the present application is: in alcohol organic solvent, zinc source and imidazole organic ligand are added, and coordination reaction occurs, and zeolite imidazolate framework material-8 is obtained;Zeolite imidazolate framework material-8 is pyrolyzed under air atmosphere, and defect zeolite imidazolate framework material-8 is obtained;Defect zeolite imidazolate framework material-8, acetylene black, binder and solvent are mixed uniformly to prepare slurry, and the slurry is coated on foam nickel, and load electrode sheet is obtained;Using standard three-electrode system, with load foam nickel as working electrode, the working electrode is activated in potassium hydroxide solution by pulse potential, and defect ZIF-8 pseudocapacitive material is obtained.The vacancy type ZIF-8 pseudocapacitive material prepared according to the method of the application has higher specific capacitance, and has excellent energy density and power density.

Description

Technical Field

[0001] This invention relates to the field of supercapacitor materials technology, and more specifically to a vacancy-type ZIF-8 pseudocapacitive material, its preparation method, and its application. Background Technology

[0002] Supercapacitors are a new type of energy storage component in the energy industry, playing a strategic role in the energy revolution. Supercapacitors offer rapid energy regulation; compared to the minute-level dispatch response of lithium batteries, their millisecond-level response has a significantly higher success rate in regulating instantaneous grid fluctuations. Simultaneously, supercapacitors boast an excellent long cycle life, typically reaching 100,000 cycles, saving large-scale IoT devices up to ten years of maintenance costs, resulting in substantial economic benefits. Furthermore, the power-energy dual-track synergy formed by supercapacitors and other energy devices such as lithium batteries is building a more robust and complete energy ecosystem, playing a crucial role in important fields such as smart grids, new energy vehicles, and aerospace.

[0003] Unlike traditional capacitors, supercapacitors have a separate charge layer at the interface between the positive and negative electrodes and the electrolyte. Therefore, supercapacitors are also called double-layer capacitors. Charge is stored and released within this charge layer without involving Faraday reactions. During charging, the positive and negative charges in the double layer attract each other, while electrolyte ions on the electrodes cannot migrate into the electrolyte, thus maintaining a stable potential difference between the positive and negative electrodes and achieving energy storage. During discharging, electrons from the negative electrode are transferred to the positive electrode through the load, breaking the double-layer balance between the positive and negative electrodes. Electrolyte ions return to the electrolyte, completing the charge release. Pseudocapacitive supercapacitors typically utilize transition metal oxides, hydroxides, sulfides, etc., to initiate Faraday reactions, which can enhance charge storage capacity. Zeolite imidazole ester framework material-8, as a metal-organic framework material, has wide applications in supercapacitors due to its high specific surface area and small pore size; its specific surface area can reach up to 1300 m². 2 / g~1600m 2 / g, pore size ≤2nm. Pure zeolite imidazole ester framework material - the specific capacitance of the material is only on the order of tens of F / g, which can be improved after air calcination, but still below 200 F / g. Etching is a commonly used processing method that can enlarge the pore size to expand ion transport channels and expose more active sites to improve the conductivity and energy storage capacity of the material. Common etching methods include acid etching, alkaline etching, template etching, and plasma etching, but they have drawbacks such as complex processes, long reaction times, and high costs, which limit their widespread application. There is a lack of efficient, low-cost, and simple etching methods. Summary of the Invention

[0004] To address the above problems, this invention provides a vacancy-type ZIF-8 pseudocapacitor material, its preparation method, and its applications. The vacancy-type ZIF-8 pseudocapacitor material prepared according to the method of this invention has high specific capacitance and excellent energy density and power density.

[0005] The first objective of this invention is to provide a method for preparing a vacancy-type ZIF-8 pseudocapacitive material, comprising the following steps:

[0006] In an alcoholic organic solvent, a zinc source and an imidazole organic ligand are added to induce a coordination reaction. During the reaction, the nitrogen of the imidazole organic ligand coordinates with the zinc ions in the zinc source to obtain the zeolite imidazole ester framework material-8.

[0007] In an air atmosphere, zeolite imidazole ester framework material-8 is pyrolyzed to obtain defective zeolite imidazole ester framework material-8.

[0008] A slurry was prepared by uniformly mixing defective zeolite imidazole ester framework material-8, acetylene black, binder and solvent. The slurry was then coated onto nickel foam to obtain a loaded electrode sheet.

[0009] A standard three-electrode system was used, with a carbon rod as the counter electrode, an Hg / HgO electrode as the reference electrode, and a loaded nickel foam as the working electrode. The working electrode was activated by pulsed potential in a potassium hydroxide solution. During the activation process, Zn... 2+ Ions are etched from the organic ligand on 2-methylimidazole to obtain defective ZIF-8 pseudocapacitive materials. During pulsed potential activation, the pulse intensity needs to be controlled, adjusted according to the pulse intensity that the material can withstand, to ensure that vacancies are generated without damaging the material.

[0010] In a preferred embodiment of the present invention, during the pulse activation process, short pulses of cathode potential and short pulses of anode potential are repeated. The cathode potential is -1.5V to -1.3V and the duration is 1s to 2s; the anode potential is 1.3V to 1.5V and the duration is 1s to 2s. This process is repeated 150 times to form one activation cycle.

[0011] The activation cycle is 3 to 5 times.

[0012] In a preferred embodiment of the present invention, the pyrolysis temperature is 350°C to 400°C.

[0013] In a preferred embodiment of the present invention, the pyrolysis time is 0.5 h and the heating rate is 5 °C / min.

[0014] In a preferred embodiment of the present invention, the mass ratio of ZIF-8 powder to acetylene black is 8:1.

[0015] The mass ratio of ZIF-8 powder to binder is 8:1.

[0016] The ratio of ZIF-8 powder to solvent is 8 mg: 10 µL.

[0017] In a preferred embodiment of the present invention, the loading amount of defective zeolite imidazole ester framework material-8 on the loaded electrode sheet is 1 mg / cm². 2 .

[0018] In a preferred embodiment of the present invention, the concentration of the potassium hydroxide solution is 1 mol / L.

[0019] The second objective of this invention is to provide a vacancy-type ZIF-8 pseudocapacitor material prepared by the above-described preparation method.

[0020] A third objective of this invention is to provide the application of the aforementioned vacancy-type ZIF-8 pseudocapacitive material in pseudocapacitive supercapacitors.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] In preparing the defective ZIF-8 pseudocapacitive material according to this invention, the synthesized ZIF-8 itself has a high specific surface area. Further, air calcination forms N-doped porous carbon, which not only enhances conductivity but also provides the pseudocapacitive activity unique to metal oxides through the generated ZnO. Furthermore, pulse activation etches Zn atoms from their intrinsic hexahedral organic framework, creating defects in the original 3D ordered porous structure without collapsing the hexahedral structure. This defective structure not only provides abundant active sites but also significantly enhances electron transfer efficiency, thereby improving pseudocapacitive performance. Specifically, compared to ZIF-8 material without air calcination and electrochemical etching, the defective ZIF-8 pseudocapacitive material prepared by this invention increases the number of active sites and pseudocapacitive performance, resulting in improved charge transfer efficiency and increased Faraday reactions (redox reactions) during supercapacitor operation, manifesting as a leap in the energy storage capacity of the supercapacitor.

[0023] The defective ZIF-8 material prepared by the method of the present invention has excellent pseudocapacitive properties, exhibits high specific capacitance, excellent energy density and power density, and can maintain good redox performance and energy storage capacity during long-term electrochemical reactions.

[0024] Furthermore, the preparation method of the present invention is simple to operate, requires little equipment, and the operation process is highly controllable, which can further improve the yield of pseudocapacitive materials, making it very suitable for large-scale production and of great value. Attached Figure Description

[0025] Figure 1 This is a ZIF-8 field emission scanning electron microscope image synthesized in step 1 of embodiment 1 of the present invention.

[0026] Figure 2 This is a ZIF-8 field emission scanning electron microscope image synthesized in step 1 of embodiment 2 of the present invention.

[0027] Figure 3 This is a ZIF-8 field emission scanning electron microscope image synthesized in step 1 of embodiment 3 of the present invention.

[0028] Figure 4 This is a field emission scanning electron microscope image of the defect ZIF-8 after electrochemical etching in Example 1 of the present invention.

[0029] Figure 5 This is the Fourier transform infrared spectrum of ZIF-8 synthesized in Example 1 of the present invention before and after calcination in air at 350°C.

[0030] Figure 6 These are cyclic voltammetry diagrams of the materials prepared in Example 1 and Comparative Examples 1 to 2 of this invention.

[0031] Figure 7 These are X-ray photoelectron spectra of the materials synthesized in Example 1 and Comparative Examples 1-2 of this invention.

[0032] Figure 8 This is a specific surface area adsorption-desorption isotherm curve of ZIF-8 prepared in Comparative Example 1 of this invention.

[0033] Figure 9 This is a specific capacitance diagram of the materials prepared in Embodiment 1 and Comparative Examples 1 to 2 of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Unless otherwise specified, the experimental and detection methods described below are conventional methods; unless otherwise specified, the reagents and raw materials described below are commercially available reagents and raw materials. Additionally, it should be noted that in this invention, 2-methylimidazole is denoted as H-MIM, polyvinylidene fluoride as PVDF, and N-methylpyrrolidone as NMP.

[0036] Example 1

[0037] This embodiment provides a method for preparing a vacancy-type ZIF-8 pseudocapacitive material. The specific preparation steps are as follows:

[0038] Step 1: Weigh 1.0864 g of Zn(NO3)2·6H2O and 17.0253 g of H-MIM into beakers A and B, respectively, according to a molar ratio of Zn(NO3)2·6H2O of 1:56.85. Then, pour 36 ml of methanol into beaker A containing Zn(NO3)2·6H2O and 292.5 ml of methanol into beaker B containing H-MIM. Sonicate both beakers A and B for 10 min to ensure complete dissolution and dispersion. Then, transfer beaker B to a magnetic stirrer at 700 rpm and slowly add the solution from beaker A dropwise to beaker B. Stir for 2 h. Allow the resulting milky white suspension to stand at room temperature for 22 h to obtain a mixed solution, which is the Zn-2-methylimidazolium complex.

[0039] After the reaction time was completed, the mixed solution was centrifuged, and the solid was washed three times with methanol. The temperature of the mixed solution needed to be controlled during this process; specifically, an ice-water bath was used to stabilize the temperature at 5℃~10℃ to facilitate successful product separation. The sediment was then collected and dried overnight in air at 60℃. After drying, the sample was allowed to cool naturally to room temperature before being removed; this dried sample is ZIF-8.

[0040] Step 2: Grind the ZIF-8 obtained in Step 1 into powder in an agate grinding bowl for 15 minutes and place it in a quartz boat. Then place it in a tube furnace and pyrolyze it in an air atmosphere at a temperature of 350℃ and a heating rate of 5℃·min. -1 The powder was kept at 350℃ for 0.5 hours and then allowed to cool naturally to obtain defective ZIF-8 powder, denoted as ZIF-8-350℃.

[0041] Step 3: According to the ratio of ZIF-8-350℃, acetylene black, PVDF, and NMP as 8mg:1mg:1mg:10µL, take 1mg ZIF-8-350℃, 0.125mg acetylene black, 0.125mg PVDF, and 1.25µL NMP into a centrifuge tube. After sonicating for 1 hour to disperse evenly, use a pipette to evenly drop the mixture onto a 1×1cm plate. 2 On the nickel foam mesh, the loading of defective ZIF-8 active material is approximately 1.0 mg·cm³. -2 In this embodiment, the ZIF-8 loading on each electrode sheet is 1 mg, and it is dried overnight at 60°C in a vacuum environment to obtain electrode sheets with ZIF-8 loading defects.

[0042] Step 4: Using a standard three-electrode system, a carbon rod is used as the counter electrode, an Hg / HgO electrode as the reference electrode, and the electrode sheet prepared above as the working electrode. The defective ZIF-8 working electrode is activated by pulse potential in a 1M potassium hydroxide solution. The cathode potential is -1.5V for 1 second, and the anode potential is +1.5V for 1 second. This is repeated 150 times, with the short cathode potential pulse immediately following the short anode potential pulse. This 150-times cycle constitutes one activation cycle. The total activation cycle time is 300 seconds. In this embodiment, there are 4 activation cycles, and the total holding time for oxidation and reduction activation is 1200 seconds. This process is used to activate Zn... 2+ Ions are etched from the organic ligands on 2-methylimidazole, further creating defects in the organic framework, resulting in vacancy-type ZIF-8 electrode sheets, i.e. vacancy-type ZIF-8 pseudocapacitive materials, denoted as vacancy-type ZIF-8.

[0043] Example 2

[0044] This embodiment provides a method for preparing a vacancy-type ZIF-8 pseudocapacitive material. The specific preparation steps are as follows:

[0045] Step 1: Weigh 1.0864 g of Zn(NO3)2·6H2O and 16.493 g of H-MIM into beakers A and B, respectively, according to a molar ratio of Zn(NO3)2·6H2O of 1:55. Then, pour 35 ml of methanol into beaker A containing Zn(NO3)2·6H2O and 292 ml of methanol into beaker B containing H-MIM. Sonicate both beakers A and B for 10 min to ensure complete dissolution and dispersion. Then, transfer beaker B to a magnetic stirrer at 600 rpm and slowly add the solution from beaker A dropwise to beaker B, stirring for 2 h. Let the resulting milky white suspension stand at room temperature for 23 h to obtain a mixed solution, which is the Zn-2-methylimidazolium complex.

[0046] After the reaction time was completed, the mixed solution was centrifuged, and the solid was washed three times with methanol. The temperature of the mixed solution needed to be controlled during this process; specifically, an ice-water bath was used to stabilize the temperature at 5℃~10℃ to facilitate successful product separation. The sediment was then collected and dried overnight in air at 60℃. After drying, the sample was allowed to cool naturally to room temperature before being removed; this dried sample is ZIF-8.

[0047] Step 2: Grind the ZIF-8 obtained in Step 1 into powder in an agate grinding bowl for 15 minutes and place it in a quartz boat. Then place it in a tube furnace and pyrolyze it in an air atmosphere at a temperature of 400℃ and a heating rate of 5℃·min. -1 The powder was kept at 400℃ for 20 minutes and then allowed to cool naturally to obtain defective ZIF-8 powder.

[0048] Step 3: According to the ratio of defective ZIF-8 powder, acetylene black, PVDF, and NMP of 8 mg: 1 mg: 1 mg: 10 µL, take 1 mg of defective ZIF-8 powder, 0.125 mg of acetylene black, 0.125 mg of PVDF, and 1.25 µL of NMP in a centrifuge tube. After sonicating for 1 hour to disperse evenly, use a pipette to evenly drop the mixture onto a 1×1 cm plate. 2 On the nickel foam mesh, the loading of defective ZIF-8 active material is approximately 1.0 mg·cm³. -2 In this embodiment, the ZIF-8 loading on each electrode sheet is 1 mg, and it is dried overnight at 60°C in a vacuum environment to obtain electrode sheets with ZIF-8 loading defects.

[0049] Step 4: Using a standard three-electrode system, a carbon rod is used as the counter electrode, an Hg / HgO electrode as the reference electrode, and the electrode sheet prepared above as the working electrode. The defective ZIF-8 working electrode is activated by pulse potential in a 1M potassium hydroxide solution. The cathode potential is -1.3V for 2 seconds, and the anode potential is +1.3V for 2 seconds. This is repeated 150 times, with the short cathode potential pulse immediately following the short anode potential pulse. This 150-times cycle constitutes one activation cycle. The total activation cycle time is 600 seconds. In this example, the activation cycle is repeated 3 times, and the total holding time for oxidation and reduction activation is 1800 seconds. This process is used to activate Zn... 2+ Ions are etched from the organic ligands on 2-methylimidazole, further creating defects in the organic framework, resulting in vacancy-type ZIF-8 electrode sheets, i.e. vacancy-type ZIF-8 pseudocapacitive materials.

[0050] Example 3

[0051] This embodiment provides a method for preparing a vacancy-type ZIF-8 pseudocapacitive material. The specific preparation steps are as follows:

[0052] Step 1: Weigh 1.0864 g of Zn(NO3)2·6H2O and 17.0927 g of H-MIM into beakers A and B, respectively, according to a molar ratio of Zn(NO3)2·6H2O of 1:57. Then, pour 37 ml of methanol into beaker A containing Zn(NO3)2·6H2O and 293 ml of methanol into beaker B containing H-MIM. Sonicate both beakers A and B for 10 min to ensure complete dissolution and dispersion. Next, transfer beaker B to a magnetic stirrer at 700 rpm and slowly add the solution from beaker A dropwise to beaker B. Stir for 2 h. Allow the resulting milky white suspension to stand at room temperature for 24 h to obtain a mixed solution, which is the Zn-2-methylimidazolium complex.

[0053] After the reaction time was completed, the mixed solution was centrifuged, and the solid was washed three times with methanol. The temperature of the mixed solution needed to be controlled during this process; specifically, an ice-water bath was used to stabilize the temperature at 5℃~10℃ to facilitate successful product separation. The sediment was then collected and dried overnight in air at 60℃. After drying, the sample was allowed to cool naturally to room temperature before being removed; this dried sample is ZIF-8.

[0054] Step 2: Grind the ZIF-8 obtained in Step 1 into powder in an agate grinding bowl for 15 minutes and place it in a quartz boat. Then place it in a tube furnace and pyrolyze it in an air atmosphere at a temperature of 360℃ and a heating rate of 5℃·min. -1 The powder was kept at a constant temperature of 360℃ for 25 minutes and then allowed to cool naturally to obtain defective ZIF-8 powder.

[0055] Step 3: According to the ratio of defective ZIF-8 powder, acetylene black, PVDF, and NMP of 8 mg: 1 mg: 1 mg: 10 µL, take 1 mg of defective ZIF-8 powder, 0.125 mg of acetylene black, 0.125 mg of PVDF, and 1.25 µL of NMP in a centrifuge tube. After sonicating for 1 hour to disperse evenly, use a pipette to evenly drop the mixture onto a 1×1 cm plate. 2 On the nickel foam mesh, the loading of defective ZIF-8 active material is approximately 1.0 mg·cm³. -2 In this embodiment, the ZIF-8 loading on each electrode sheet is 1 mg, and it is dried overnight at 60°C in a vacuum environment to obtain electrode sheets with ZIF-8 loading defects.

[0056] Step 4: Using a standard three-electrode system, a carbon rod is used as the counter electrode, an Hg / HgO electrode as the reference electrode, and the electrode sheet prepared above as the working electrode. The defective ZIF-8 working electrode is activated by pulse potential in a 1M potassium hydroxide solution. The cathode potential is -1.5V for 1 second, and the anode potential is +1.5V for 1 second. This is repeated 150 times, with the short cathode potential pulse immediately following the short anode potential pulse. This 150-times cycle constitutes one activation period. The total activation period is 300 seconds. In this example, there are 5 activation cycles, and the total holding time for oxidation and reduction activation is 1500 seconds. This process is used to activate Zn... 2+ Ions are etched from the organic ligands on 2-methylimidazole, further creating defects in the organic framework, resulting in vacancy-type ZIF-8 electrode sheets, i.e. vacancy-type ZIF-8 pseudocapacitive materials.

[0057] Comparative Example 1

[0058] This comparative example provides a method for preparing ZIF-8 pseudocapacitive material, and the specific preparation steps are as follows:

[0059] According to the molar ratio of Zn(NO3)2·6H2O and H-MIM of 1:56.85, 1.0864 g of Zn(NO3)2·6H2O and 17.0253 g of H-MIM were weighed into beaker A and beaker B, respectively. Then, 36 ml of methanol was added to beaker A containing Zn(NO3)2·6H2O, and 292.5 ml of methanol was added to beaker B containing H-MIM. Both beakers A and B were sonicated for 10 min each to ensure complete dissolution and dispersion. Then, beaker B was transferred to a magnetic stirrer at 700 rpm, and the solution from beaker A was slowly added dropwise to beaker B, with stirring for 2 h. The resulting milky white suspension was allowed to stand at room temperature for 22 h to obtain a mixed solution, namely the Zn-2-methylimidazolium complex.

[0060] After the reaction time was completed, the mixed solution was centrifuged, and the solid was washed three times with methanol. The temperature of the mixed solution needed to be controlled during this process; specifically, an ice-water bath was used to stabilize the temperature at 5℃~10℃ to facilitate successful product separation. The sediment was then collected and dried overnight in air at 60℃. After drying, the sample was allowed to cool naturally to room temperature before being removed; this dried sample is ZIF-8.

[0061] Comparative Example 2

[0062] This comparative example provides a method for preparing a defective ZIF-8 pseudocapacitive material. The specific preparation steps are as follows:

[0063] Step 1: Weigh 1.0864 g of Zn(NO3)2·6H2O and 17.0253 g of H-MIM into beakers A and B, respectively, according to a molar ratio of Zn(NO3)2·6H2O of 1:56.85. Then, pour 36 ml of methanol into beaker A containing Zn(NO3)2·6H2O and 292.5 ml of methanol into beaker B containing H-MIM. Sonicate both beakers A and B for 10 min to ensure complete dissolution and dispersion. Then, transfer beaker B to a magnetic stirrer at 700 rpm and slowly add the solution from beaker A dropwise to beaker B. Stir for 2 h. Allow the resulting milky white suspension to stand at room temperature for 22 h to obtain a mixed solution, which is the Zn-2-methylimidazolium complex.

[0064] After the reaction time was completed, the mixed solution was centrifuged, and the solid was washed three times with methanol. The temperature of the mixed solution needed to be controlled during this process; specifically, an ice-water bath was used to stabilize the temperature at 5℃~10℃ to facilitate successful product separation. The sediment was then collected and dried overnight in air at 60℃. After drying, the sample was allowed to cool naturally to room temperature before being removed; this dried sample is ZIF-8.

[0065] Step 2: Grind the ZIF-8 obtained in Step 1 into powder in an agate grinding bowl for 15 minutes, place it in a quartz boat, and then place it in a tube furnace to complete the pyrolysis in an air atmosphere. The pyrolysis temperature is 350℃, and the heating rate is 5℃·min. -1 The powder was kept at 350℃ for 0.5 hours and then allowed to cool naturally to obtain defective ZIF-8 powder, denoted as ZIF-8-350℃.

[0066] Step 3: According to the ratio of ZIF-8-350℃, acetylene black, PVDF, and NMP as 8mg:1mg:1mg:10µL, take 1mg ZIF-8 powder, 0.125mg acetylene black, 0.125mg PVDF, and 1.25µL NMP in a centrifuge tube. After sonicating for 1 hour to disperse evenly, use a pipette to evenly drop the mixture onto a 1×1cm plate. 2 On the nickel foam mesh, the loading of defective ZIF active material is approximately 1.0 mg·cm³. -2 The electrode sheet was dried overnight at 60°C under vacuum to obtain the load defect type ZIF-8.

[0067] To characterize the vacancy-type ZIF-8 pseudocapacitor material prepared in this invention, a standard three-electrode system was used. A carbon rod was used as the counter electrode, an Hg / HgO electrode as the reference electrode, and the electrode sheets prepared in Example 1 and Comparative Example 2 were used as the working electrodes. The performance of the supercapacitor was tested in a 3M potassium hydroxide solution. Cyclic voltammetry was employed, with the scan potential relative to the standard hydrogen electrode between 1.1V and 1.5V to cover the entire redox active potential range of the material, ensuring that all Faraday reactions were fully recorded and represented by complete redox peaks in the cyclic voltammogram. Scan rates of 5mV / s, 10mV / s, 15mV / s, and 20mV / s were used to fully evaluate the material's performance at different scan rates.

[0068] Figure 1 This is a field emission scanning electron microscope image of the ZIF-8 synthesized in step 1 of Example 1 of the present invention. It can be seen that the product has a regular hexahedral morphology, and its average particle size is 30 nm.

[0069] Figure 2 This is a field emission scanning electron microscope image of the ZIF-8 synthesized in step 1 of Example 2 of the present invention. By increasing the reaction time from 24h to 25h, its average particle size increased to 39nm.

[0070] Figure 3 This is a field emission scanning electron microscope image of the ZIF-8 synthesized in step 1 of Example 3 of the present invention. By increasing the reaction time from 24h to 26h, its average particle size increased to 52nm.

[0071] Figure 4 This is a field emission scanning electron microscope image of the defect ZIF-8 after electrochemical etching in Example 1 of the present invention. It can be seen that the framework of ZIF-8 is well preserved after electrochemical etching.

[0072] Figure 5 These are the Fourier transform infrared spectra of ZIF-8 synthesized in Example 1 of this invention before and after calcination in air at 350°C. It can be seen that air calcination causes certain defects in ZIF-8, leading to changes in the intensity of functional groups, such as at 450 cm⁻¹. -1 ~1500cm -1 The weakening of the C=C aromatic ring vibration between wavenumbers indicates partial decomposition of the imidazole ring, 1700 cm⁻¹ -1 ~1750cm -1 The enhancement of the shoulder peak between wavenumbers is attributed to the formation of C=O bonds, indicating partial oxidation of the ligands, which is beneficial to the hydrophilicity of the material and facilitates performance control. Meanwhile, at 500 cm⁻¹... -1 ~600cm -1 The appearance of weak peaks between wavenumbers is attributed to the Zn-O vibration, indicating the formation of ZnO on the surface, which leads to the exposure of Zn²⁺, forming unsaturated coordination sites and enhancing pseudocapacitive activity.

[0073] After the ZIF-8 prepared in Comparative Example 1 and the defective ZIF-8 in Comparative Example 2 were respectively made into electrode sheets, the supercapacitor performance of Example 1, Comparative Example 1 and Comparative Example 2 were tested.

[0074] Figure 6 These are cyclic voltammetry diagrams of ZIF-8 prepared in Example 1 and Comparative Example 1 and Comparative Example 2, respectively, for supercapacitor performance testing. It can be seen that after etching, the redox peak of ZIF-8 as a pseudocapacitive material is shifted to a certain extent, and the capacitance is significantly improved.

[0075] Figure 7 These are X-ray photoelectron spectra of the products prepared in Example 1 and Comparative Examples 1-2 of this invention. It can be seen that Zn in ZIF-8... 2+ After electrochemical etching, the surface was successfully etched and the defective ZIF-8 was successfully transformed into the vacancy-type ZIF-8.

[0076] Figure 8 This is the specific surface area adsorption-desorption isotherm curve of ZIF-8 prepared in Comparative Example 1 of this invention. It can be seen that the ZIF-8 prepared in this invention has an adsorption hysteresis loop, belongs to mesoporous materials, and has a large specific surface area, which can provide more charge adsorption sites, accelerate ion transport, and is beneficial to subsequent etching.

[0077] Figure 9The cyclic voltammetry tests of the vacancy-type ZIF-8 prepared in Example 1, the ZIF-8 prepared in Comparative Example 1, and the defect-type ZIF-8 prepared in Comparative Example 2 at different scan rates show that after introducing defects through air calcination and creating vacancies through electrochemical etching, the specific capacitance of ZIF-8 gradually increases from tens of farads to 300-400 farads and then to 1500-2000 farads. This demonstrates that the method proposed in this invention has a good performance improvement effect on pseudocapacitive materials.

[0078] The synthesis method of this invention can stably synthesize ZIF-8 with smaller particle size and higher specific surface area, with a particle size of less than 40 nm and a specific surface area of ​​>1600 m². 2 / g, with optimal capacitance performance.

[0079] In their article "The calcined zeolitic imidazolate framework-8 (ZIF-8) under different conditions as electrode for supercapacitor applications" published in the Journal of Solid State Electrochemistry, Volume 18, Issue 11, 2014, GAO Y et al. found that the specific capacitances of the original ZIF-8 and the air-calcined ZIF-8 were 96 F / g and 156 F / g, respectively, which are lower than the specific capacitance of 300 F / g of the air-calcined ZIF-8 prepared in this invention.

[0080] Compared with existing technologies, this invention improves the etching method for defective ZIF-8 pseudocapacitive materials. Unlike traditional methods that involve adding chemicals, this invention employs an electrochemical etching method, which is simpler, increases production, and saves energy. This method can effectively control the degree of defect etching in ZIF-8 materials, providing abundant active sites, thus facilitating electron transfer and improving the energy storage performance of ZIF-8 as a pseudocapacitive material. Furthermore, the material synthesis and etching methods are simple to operate, convenient to implement, and suitable for large-scale production, exhibiting significant green and economic benefits, and can be widely applied in the field of supercapacitors.

[0081] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0082] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a vacancy-type ZIF-8 pseudocapacitive material, characterized in that, Includes the following steps: In an alcoholic organic solvent, a zinc source and an imidazole organic ligand are added to induce a coordination reaction. During the reaction, the nitrogen of the imidazole organic ligand coordinates with the zinc ions in the zinc source to obtain the zeolite imidazole ester framework material-8. In an air atmosphere, zeolite imidazole ester framework material-8 is pyrolyzed to obtain defective zeolite imidazole ester framework material-8. A slurry was prepared by uniformly mixing defective zeolite imidazole ester framework material-8, acetylene black, binder and solvent. The slurry was then coated on nickel foam to obtain a loaded electrode sheet. A standard three-electrode system was used, with a carbon rod as the counter electrode, an Hg / HgO electrode as the reference electrode, and a loaded nickel foam as the working electrode. The working electrode was activated by pulsed potential in a potassium hydroxide solution. During the activation process, Zn... 2+ Ions were etched from the organic ligand on 2-methylimidazole to obtain defective ZIF-8 pseudocapacitive material.

2. The method for preparing a vacancy-type ZIF-8 pseudocapacitor material according to claim 1, characterized in that, During the pulse activation process, short pulses at the cathode potential and the anode potential are repeated. The cathode potential is -1.5V to -1.3V, and the duration is 1s to 2s. The anode potential is 1.3V to 1.5V, and the duration is 1s to 2s. This process is repeated 150 times to complete one activation cycle. The activation cycle is 3 to 5 times.

3. The method for preparing a vacancy-type ZIF-8 pseudocapacitor material according to claim 1, characterized in that, The pyrolysis temperature is 350℃~400℃.

4. The method for preparing a vacancy-type ZIF-8 pseudocapacitor material according to claim 1, characterized in that, The pyrolysis time was 0.5 h, and the heating rate was 5 °C / min.

5. The method for preparing a vacancy-type ZIF-8 pseudocapacitor material according to claim 1, characterized in that, The mass ratio of ZIF-8 powder to acetylene black is 8:1; The mass ratio of ZIF-8 powder to binder is 8:1; The ratio of ZIF-8 powder to solvent is 8 mg: 10 µL.

6. The method for preparing a vacancy-type ZIF-8 pseudocapacitor material according to claim 1, characterized in that, On the loaded electrode sheet, the loading of defective zeolite imidazole ester framework material-8 was 1 mg / cm³. 2 .

7. The method for preparing a vacancy-type ZIF-8 pseudocapacitive material according to claim 1, characterized in that, The concentration of the potassium hydroxide solution is 1 mol / L.

8. A vacancy-type ZIF-8 pseudocapacitor material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the vacancy-type ZIF-8 pseudocapacitive material as described in claim 8 in a pseudocapacitive supercapacitor.

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