A preparation method and application of Co3O4 nanocage

Abstract

The invention discloses a Co 3 O 4 Preparation method and application of nanocages with cobalt (II) acetylacetonate and K 3 [Co(CN) 6 ] as raw material, Br-butyl-3-methyl-imidazole as surfactant, a pink precipitate was obtained by coprecipitation reaction, centrifuged, and the product was washed several times with ethanol and ultrapure water respectively, and vacuum dried to obtain Co 3 [Co(CN) 6 ] 2 Precursor. 3 [Co(CN) 6 ] 2 The precursor was calcined at 350℃ for 1h to obtain Co 3 O 4 Nanocage supercapacitor electrode material. The obvious benefit of the present invention is to reduce the precursor formation speed by utilizing the poor water solubility of organic metals, thus opening up a new way for the development of supercapacitor electrode materials.

Description

Technical Field

[0001] The invention relates to a preparation method of Co3O4 nano cage and its application as electrode material in the field of super capacitor Background Art

[0002] With the continuous development of social industrial level, human society's demand for energy is increasing. Until the beginning of this century, social energy still mainly relied on fossil energy such as coal, natural gas and oil. On the one hand, the excessive use of these energy sources will produce a large amount of greenhouse gases and pollute the environment where humans live. At the same time, these energy sources are non-renewable resources, and human predatory exploitation has gradually caused these energy sources to become exhausted. Therefore, the development of new environmentally friendly clean energy through scientific and technological means has gradually become a major research topic in the field of science and technology. As we all know, electric energy is one of the most widely used clean energy sources, and the widespread use of electric energy has directly promoted the rapid development of energy storage equipment and devices.

[0003] At present, the commonly used electrochemical energy storage technologies include lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, supercapacitors, fuel cells, and solar cells. Among them, supercapacitor technology has gradually become a research hotspot in the field of energy storage equipment and device development due to its remarkable characteristics such as fast charging and discharging speed, long cycle life, and high power density.

[0004] As a typical semiconductor metal oxide, Co3O4 has become a very popular supercapacitor electrode material because of its abundant reserves, low cost, easy availability, green environmental protection and large theoretical specific capacity (3560F / g). At present, the main methods for preparing Co3O4 include sol-gel method, hydrothermal method, solvothermal method, electrochemical deposition method, chemical precipitation method, template method, etc. Among them, the template method is an effective method for preparing Co3O4 nanomaterials with hollow structure. The hollow structure of Co3O4 nanomaterials not only has a large specific surface area, but also provides a convenient path for electron conduction, so it has excellent performance. In recent years, the template materials used to prepare hollow Co3O4 nanomaterials are mainly Co(OH)2, ZIF-67 and Co3[Co(CN)6]2. In comparison, Co3[Co(CN)6]2, as a typical Prussian blue analogue, has a higher metal content and a shorter ligand chain length, so it is more suitable as a template for preparing hollow Co3O4 nanomaterials. However, due to the low solubility of Co3[Co(CN)6]2 in water, the 2+ and [Co(CN)6] 3-The controllability of preparing Co3[Co(CN)6]2 by coprecipitation reaction is poor. Although the nucleation rate of Co3[Co(CN)6]2 can be slowed down by injecting cobalt acetate solution into K3[Co(CN)6] solution in small amounts and multiple times with a syringe, this method is obviously time-consuming and labor-intensive. Therefore, in order to obtain hollow Co3O4 nanomaterials with excellent performance, the synthesis strategy of Co3[Co(CN)6]2 template needs to be improved. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing Co3O4 nanocages and the application of the nanocage material in the field of supercapacitors. The electrode material and supercapacitor prepared by the method have high capacitance retention and high cycle stability.

[0006] The Co3O4 nano cage of the present invention is made by the following method:

[0007] 1. Using Br-butyl-3-methyl-imidazole as a surfactant, K3[Co(CN)6] and cobalt(II) acetylacetonate as reaction raw materials, a pink suspension was obtained by coprecipitation reaction, and then aged for 8 to 12 hours to obtain a Co3[Co(CN)6]2 precursor.

[0008] 2. The above precursors were washed several times with anhydrous ethanol and ultrapure water, respectively, vacuum dried for 8 hours, and then heat-treated in an air atmosphere for 1 hour to obtain Co3O4 nanocages.

[0009] The method for making a supercapacitor using the above electrode material is as follows:

[0010] The nickel foam was cut into rectangular nickel sheets of 1.0 cm × 2.0 cm, and then soaked in acetone, anhydrous ethanol and deionized water for ultrasonic cleaning for 30 min to remove oxides and stains on its surface. The cleaned nickel foam was placed in an oven and dried at 60 ° C for 10 h. The prepared Co3O4 nanocage, acetylene black and polytetrafluoroethylene (PTFE) were mixed in a mass ratio of 8:1:1, and then 4 mL of anhydrous ethanol was added and ultrasonically dispersed for 40 min. The obtained mixed solution was placed in an oven at 60 ° C for 12 h. The obtained slurry was evenly coated on the clean nickel foam, and it was compacted under a pressure of 10 MPa to obtain an electrode sheet for electrochemical performance testing.

[0011] The beneficial effect of the present invention is that the organic metal salt acetylacetonate cobalt (II) is used as Co 2+ Source, taking advantage of its low solubility in water, effectively reduced the Co 2+ and [Co(CN)6] 3-The nucleation speed of forming Co3[Co(CN)6]2 solves the problem of too fast precipitation speed in the existing method for synthesizing Co3[Co(CN)6]2, and provides a new template synthesis strategy for synthesizing hollow structure Co3O4 nanomaterials. The hollow Co3O4 nanocage of the present invention has a stable structure and uniform morphology. When it is used as an electrode material to construct a supercapacitor, the capacitance retention rate of the material after 5000 cycles at a current density of 10A / g is as high as 92.02%. The product synthesis and post-processing methods of the present invention are simple, the material purity is high, the Co3O4 nanocage with a hollow structure has good dispersibility, and the product is easy to separate and purify, and easy to mass produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0013] Figure 1 This is a scanning electron microscope image of the Co3[Co(CN)6]2 precursor of the present invention.

[0014] Figure 2 This is a transmission electron microscopy image of Co3O4 nanocages.

[0015] Figure 3 This is the XRD pattern of Co3[Co(CN)6]2 precursor.

[0016] Figure 4 This is the XRD pattern of Co3O4 nanocages.

[0017] Figure 5 This is the cyclic voltammetry curve of Co3O4 nanocages at the same scan rate.

[0018] Figure 6 The constant current charge and discharge diagram of Co3O4 nanocages at different current densities.

[0019] Figure 7 This is the cyclic stability curve of Co3O4 nanocages.

[0020] Figure 8 This is the EIS spectrum of Co3O4 nanocages. DETAILED DESCRIPTION

[0021] Dissolve 0.02-0.04 g of Br-butyl-3-methyl-imidazole in 25-40 mL of water and stir magnetically until completely dissolved. Then add 0.07-0.10 g of K3[Co(CN)6] and stir magnetically until completely dissolved. Add 0.07-0.12 g of cobalt (II) acetylacetonate to the mixed solution and stir magnetically for 30-60 min to obtain a pink suspension. Let stand and age for 8-12 h to obtain a precursor.

[0022] The precursor was washed with ultrapure water and ethanol several times and then dried in vacuum at 60-80℃ for 6-8h. The SEM image of the powder is shown in Figure 1 As shown in the figure, it can be seen that the precursor is a monodispersed nanocube with a diameter of about 200nm, and the surface is a rough multi-level structure formed by the self-assembly of nanoparticles with a particle size of 5 to 10nm.

[0023] The above precursors are washed several times with anhydrous ethanol and ultrapure water respectively, vacuum dried at 60-80°C for 6-8h, and then heat treated at 350-400°C in air atmosphere for 0.5-1h to obtain Co3O4 nanocages. Figure 2 This is a transmission electron microscope image of the prepared Co3O4 nanocage. It can be seen from the image that the Co3O4 product has a hollow structure and an obvious porous shell, which is a typical nanocage structure.

[0024] The XRD pattern of the precursor (see Figure 3 ) It can be seen that all diffraction peaks in the XRD spectrum of the precursor are consistent with the spectrum of Co3[Co(CN)6]2 (JCPDS No.77-1161) on the standard XRD card, indicating that the product is pure phase Co3[Co(CN)6]2.

[0025] The precursor was heat treated at 350℃ for 1h to obtain Co3O4 nanocages, and its XRD spectrum is shown in Figure 4 All the derivative peaks of the XRD spectrum are consistent with the peak positions of Co3O4 (JCPDS No.42-1467) on the standard XRD card, indicating that the product is pure phase Co3O4.

[0026] In order to study the electrochemical properties of the obtained Co3O4 nanocages, the material was prepared into a supercapacitor for testing.

[0027] The electrochemical test was carried out on an electrochemical workstation (CHI660E, Shanghai Chenhua Instrument Co., Ltd.). The test used a three-electrode system, with nickel foam as the working electrode, platinum foil electrode as the counter electrode, mercuric oxide electrode as the reference electrode, and the electrolyte solution was 6 mol.L -1 The KOH solution was used for cyclic voltammetry test at a scan rate of 10-100mV / s within the voltage range of 0-0.6V. The constant current charge and discharge test was carried out within the voltage range of 0-0.5V. The current density of 1-10A / g was used for the test respectively; the current impedance test was carried out at a frequency of 100000-1Hz with an AC voltage of 5mV amplitude; the cycle number test was carried out 5000 times under the condition of a current density of 10A / g. The potential-time curve was obtained from this, and the specific capacitance value of the electrode material can be calculated according to the discharge time and potential: C=IΔt / mΔV.

[0028] Where: I is the discharge current, Δt is the discharge time, m is the mass of the electrode active material, and ΔV is the charge and discharge potential difference.

[0029] Figure 5 This is the cyclic voltammetry curve of Co3O4 nanocages at the same scan rate.

[0030] like Figure 6 As shown in the figure, when the current density increases from 1A / g to 10A / g, the specific capacitance only decays from 1230.8F / g to 540F / g, and the capacitance retention rate is 44%, which has good rate performance. The cycle number test experiment was cycled 5000 times under the condition of current density of 10A / g, and the specific capacitance value and capacitance retention rate were calculated as follows Figure 7 As shown in the figure, after 5000 cycles, the specific capacitance dropped from 540F / g to 393.12F / g, with a residual of up to 72.8%, and the specific capacitance value tended to be stable after 2000 cycles. The experimental results of the cycle number test show that the electrode has good cycle stability and has good potential as a supercapacitor electrode material.

[0031] like Figure 8 is the EIS spectrum of the material, where R s is the solution resistance, R ct is the charge transfer resistance. In the high frequency band, the smaller the semicircle radius is, the lower the charge transfer resistance is. It can be seen from the figure that R s 0.478Ω, R ct The smaller resistance value is 1.6Ω, indicating that the material has good charge transfer and electrolyte ion diffusion functions in electrochemical tests.

Claims

1. A method for preparing Co3O4 nanocages, characterized in that The preparation method of the Co3O4 nanocage is carried out according to the following steps:

1. Dissolve Br-butyl-3-methyl-imidazole in water and stir until completely dissolved. Then add K3[Co(CN)6] and stir until completely dissolved. Add cobalt (II) acetylacetonate to the mixed solution and stir magnetically for 30-60 minutes to obtain a pink suspension. Let stand for 8-12 hours to obtain a precursor.

2. Wash the above precursors with anhydrous ethanol and ultrapure water for several times, vacuum dry at 70°C for 6-8h, and then heat treat the precursors at 350-400°C for 1h in air atmosphere to obtain Co3O4 nanocages; The method for preparing supercapacitors using Co3O4 nanocages is as follows: The nickel foam was cut into rectangular nickel sheets of 1.0 cm × 2.0 cm, and they were soaked in acetone, anhydrous ethanol and deionized water for ultrasonic cleaning for 30 min respectively to remove oxides and stains on the surface; the cleaned nickel foam was placed in an oven and dried at 60°C for 10 h; the prepared Co3O4 nanocages, acetylene black and polytetrafluoroethylene were mixed in a mass ratio of 8:1:1, and then 4 mL of anhydrous ethanol was added and ultrasonically dispersed for 40 min, and the obtained mixed solution was placed in an oven and dried at 60°C for 12 h; the obtained slurry was evenly coated on the clean nickel foam, and it was compacted under a pressure of 10 MPa to obtain an electrode sheet for electrochemical performance testing.

2. The method for preparing the Co3O4 nanocage according to claim 1, characterized in that In step 1, 0.02-0.04 g of Br-butyl-3-methyl-imidazole was dissolved in 25-40 mL of water.

3. The method for preparing the Co3O4 nanocage according to claim 1, characterized in that Dissolve 0.07~0.10g K3[Co(CN)6] in step 1 in 25~40mL water.

4. The method for preparing the Co3O4 nanocage according to claim 1, characterized in that Dissolve 0.07-0.12 g of cobalt (II) acetylacetonate in 25-40 mL of water.

5. The method for preparing the Co3O4 nanocage according to claim 1, characterized in that The precursor in step 2 is heat treated at 350-400° C. for 1 h in an air atmosphere.

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