MnCo2O4 / ZnCo2O4 nanocomposites, their preparation methods, and applications

Abstract

The application belongs to the technical field of electrode materials, and particularly relates to a MnCo2O4 / ZnCo2O4 nanocomposite material, a preparation method and application thereof. The application takes soluble manganese salt and soluble cobalt salt as raw materials, takes foamed nickel as a carrier, and obtains MnCo-LDH / NF through a hydrothermal reaction in an alkaline environment. Then, the MnCo-LDH / NF is immersed in a precursor solution composed of soluble cobalt salt, soluble zinc salt and 2-methyl imidazole, and a coordination reaction is carried out to obtain MnCo-LDH@ZIF-67 / ZIF-8. Finally, heat treatment is carried out to obtain the MnCo2O4 / ZnCo2O4 nanocomposite material. In the MnCo2O4 / ZnCo2O4 nanocomposite material obtained by the method, the nanorod structure of MnCo2O4 and the dodecahedron structure of ZnCo2O4 form a heterojunction, which overcomes the defect of poor conductivity of MnCo2O4.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically MnCo2O4 / ZnCo2O4 nanocomposite materials, their preparation methods, and applications. Background Technology

[0002] Among the metal oxides reported so far, those with the general formula A x B 3-x In the spinel structure of O4, where A and B are independently selected from two different transition metals such as Co, Mn, and Ni, it has been shown to possess excellent electrochemical energy storage performance, attributed to its richer redox reaction activity and higher electronic conductivity compared to binary metal oxides. In particular, the cobalt-manganese composite material MnCo2O4 has attracted considerable interest from researchers. MnCo2O4 has garnered significant attention in energy storage due to its highest theoretical specific capacitance, high rate performance, natural abundance, low cost, and environmental friendliness among cobalt-based spinel structures. This is because cobalt has a higher oxidation potential, while manganese can transport more electrons, resulting in higher capacity. Furthermore, the p-type semiconductor Co3O4 and the n-type semiconductor MnCo2O4 can form a pn heterostructure, which will actively modulate the electronic structure and further enhance catalytic performance.

[0003] However, MnCo2O4 itself has poor conductivity, which limits its use in applications that require good conductivity. The lack of conductivity leads to low electron transport efficiency, affecting the reaction rate and efficiency. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention provides MnCo2O4 / ZnCo2O4 nanocomposites, their preparation methods, and applications. This invention uses soluble manganese and cobalt salts as raw materials and nickel foam as a carrier. A hydrothermal reaction is carried out under alkaline conditions to obtain MnCo-LDH / NF. Then, MnCo-LDH / NF is immersed in a precursor solution composed of soluble cobalt salt, soluble zinc salt, and 2-methylimidazole, and a coordination reaction is performed to obtain MnCo-LDH@ZIF-67 / ZIF-8. Finally, heat treatment is performed to obtain the MnCo2O4 / ZnCo2O4 nanocomposites. In the MnCo2O4 / ZnCo2O4 nanocomposite material obtained by the method of the present invention, the nanorod-shaped MnCo2O4 and the dodecahedral ZnCo2O4 form a heterojunction. The dodecahedral ZnCo2O4 has a large number of nanoparticles and pores, which is conducive to the diffusion of electrolytes and effectively buffers the volume change during the electrochemical reaction, thus overcoming the defect of poor conductivity of MnCo2O4.

[0005] Based on the above technical objectives, the present invention adopts the following technical solution:

[0006] This invention protects a method for preparing MnCo2O4 / ZnCo2O4 nanocomposites, comprising the following steps:

[0007] Soluble manganese salt, soluble cobalt salt, urea and ammonium fluoride are mixed together in water to obtain a mixture. Nickel foam is immersed in the mixture and subjected to a hydrothermal reaction to obtain MnCo-LDH / NF.

[0008] Soluble metal salts and 2-methylimidazole were dispersed separately in a solvent and then mixed evenly to obtain a precursor solution. MnCo-LDH / NF was then immersed in the precursor solution to carry out a coordination reaction, resulting in MnCo-LDH@ZIF-67 / ZIF-8.

[0009] The soluble metal salts consist of soluble cobalt salts and soluble zinc salts.

[0010] MnCo-LDH@ZIF-67 / ZIF-8 was heat-treated to obtain MnCo2O4 / ZnCo2O4 nanocomposite material.

[0011] Preferably, the heat treatment conditions are: heating at 250℃~300℃ for 0.5h.

[0012] Preferably, the heat treatment conditions are: heating at 275°C for 0.5 hours.

[0013] Preferably, the molar ratio of soluble manganese salt, soluble cobalt salt, urea and ammonium fluoride is 0.5:0.8~1.2:6:1.5~3.

[0014] Preferably, the hydrothermal reaction conditions during the preparation of MnCo-LDH / NF are: heating at 100°C to 140°C for 8 to 12 hours.

[0015] Preferably, the amount of soluble cobalt salt in the precursor solution is 0.6 mmol to 0.8 mmol, and the amount of soluble zinc salt is 0.2 mmol to 0.4 mmol.

[0016] Preferably, the conditions for the coordination reaction are: standing at room temperature for 20-30 hours.

[0017] This invention also protects a MnCo2O4 / ZnCo2O4 nanocomposite material, which is prepared by the above-described method.

[0018] This invention also protects the application of MnCo2O4 / ZnCo2O4 nanocomposite materials in the preparation of positive electrode materials for pseudocapacitive supercapacitors.

[0019] In this invention, LDH represents layered bimetallic hydroxide, AC represents activated carbon, PVA represents polyvinyl alcohol, CV represents cyclic voltammetry, GCD represents constant current fast charge-discharge, EIS represents electrochemical impedance spectroscopy, SEM represents scanning electron microscopy, TEM represents transmission electron microscopy, XRD represents X-ray diffraction, XPS represents X-ray photoelectron spectroscopy, HRTEM represents high-resolution transmission electron microscopy, EDS represents energy-dispersive X-ray spectroscopy, and C... dl This indicates a double-layer capacitor, and ECSA represents the active surface area.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This invention successfully synthesized MnCo₂O₄ / ZnCo₂O₄ nanocomposite materials derived from LDH and ZIF as sacrificial templates on nickel foam using hydrothermal and heat treatment methods. First, soluble manganese salt, soluble cobalt salt, urea, ammonium fluoride, and nickel foam were used as raw materials. Urea and ammonium fluoride jointly provided an alkaline environment. After hydrothermal reaction, a layered MnCo bimetallic hydroxide, MnCo-LDH, was obtained and stably bonded to the nickel foam, yielding MnCo-LDH / NF. A precursor solution was prepared using soluble cobalt salt, soluble zinc salt, and 2-methylimidazole as raw materials. MnCo-LDH / NF was then immersed in the precursor solution. Cobalt ions and cobalt ions undergo coordination reactions with 2-methylimidazole, at which point ZIF-67 and ZIF-8 are embedded together and attached to the surface of MnCo layered bimetallic hydroxide, resulting in MnCo-LDH@ZIF-67 / ZIF-8. MnCo-LDH@ZIF-67 / ZIF-8 is then subjected to heat treatment, which oxidizes ZIF-67 and ZIF-8, yielding MnCo2O4 / ZnCo2O4 nanocomposite material.

[0022] 2. This invention uses soluble manganese salt and soluble cobalt salt as raw materials and nickel foam as a carrier. A hydrothermal reaction is first carried out in an alkaline environment to prepare MnCo-LDH / NF. MnCo-LDH nanoneedles are then grown on the nickel foam to form a nanowire array structure. Next, MnCo-LDH / NF is immersed in a precursor solution composed of soluble cobalt salt, soluble zinc salt, and 2-methylimidazole, and a coordination reaction is carried out to obtain MnCo-LDH@ZIF-67 / ZIF-8. This allows for the composite formation of MnCo-LDH with ZIF-67 and ZIF-8. F-8 nanoneedles are densely grown around MnCo-LDH nanoneedles. Finally, MnCo-LDH@ZIF-67 / ZIF-8 is heat-treated to obtain MnCo2O4 / ZnCo2O4 nanocomposite material. In the MnCo2O4 / ZnCo2O4 nanocomposite material, MnCo2O4 and ZnCo2O4 form a heterojunction, and the polyhedral structure of ZnCo2O4 has a large number of nanoparticles and pores, which are attributed to the release of gas during the heat treatment process. This structure can accommodate large-sized ions and effectively buffers the volume changes during electrochemical reactions, which is conducive to the diffusion of electrolytes.

[0023] 3. In the MnCo2O4 / ZnCo2O4 nanocomposite material of the present invention, MnCo2O4 and ZnCo2O4 are two spinel oxides. That is, the present invention discloses a composite of two spinel oxides. Spinel oxides have excellent chemical stability and are resistant to acid and alkali corrosion; they have abundant active sites, large specific surface area, high redox activity and porous structure, which improves the efficiency of catalytic reaction; they have excellent electrochemical stability and can withstand multiple charge-discharge cycles without easily causing structural collapse or performance degradation, thereby improving cycle life.

[0024] In the double-spindle structure of this invention, ZnCo2O4 exhibits excellent electrical conductivity, which can improve electron transport efficiency and thus compensate for the insufficient conductivity of MnCo2O4. In addition, the synergistic effect of Mn ions and Zn ions promotes electron transfer and reaction, and the heterojunction at the interface of the double-spindle structure further enhances the electrochemical performance of the MnCo2O4 / ZnCo2O4 nanocomposite material.

[0025] 4. The MnCo2O4 / ZnCo2O4 nanocomposite material of this invention exhibits excellent electrochemical performance in energy storage. In a 2 mol / L KOH electrolyte, the current density is 2 mA / cm². 2 At that time, the specific capacitance of the MnCo2O4 / ZnCo2O4 nanocomposite reached 2040 mF / cm. 2Furthermore, this invention also assembled a MnCo2O4 / ZnCo2O4 / / AC supercapacitor with an operating voltage range of 0V~1.6V, demonstrating the typical voltage expansion capability of a series circuit and the typical capacitance increase capability of a parallel circuit. This invention demonstrates the broad practical application prospects of MnCo2O4 / ZnCo2O4 nanocomposite materials in energy storage.

[0026] 5. This invention uses LDH and ZIF composites as precursors to prepare MnCo2O4 / ZnCo2O4 nanocomposites on nickel foam. ZIF-8 and ZIF-67 were composited with MnCo-LDH to obtain MnCo-LDH@ZIF-67 / ZIF-8. Four MnCo2O4 / ZnCo2O4 nanocomposites were prepared by heat treatment at different temperatures and times: S-275-0.5, S-275-1, S-275-2, and S-350-0.5. The heat treatment conditions with the best electrochemical performance were 275℃ for 0.5 h, i.e., S-275-0.5. In a 2 mol / L KOH electrolyte, the current density of S-275-0.5 in a three-electrode system was 1 mA / cm². 2 The specific capacitance reaches 2040 mF / cm at current density. 2 Furthermore, an asymmetric solid-state supercapacitor was assembled using MnCo2O4 / ZnCo2O4 nanocomposite material as the positive electrode, activated carbon as the negative electrode, and PVA / KOH as the solid electrolyte, achieving a current of 2 mA / cm². 2 At the current density, the specific capacitance is 1140 mF / cm. 2 The excellent energy storage performance of this invention is due to the synergistic effect of two pseudocapacitive active materials, MnCo2O4 and ZnCo2O4. Attached Figure Description

[0027] Figure 1 Figure 1 shows the XRD and XPS spectra; Figure 2a shows the XRD spectra of the MnCo2O4 / ZnCo2O4 nanocomposites of Example 1 and Comparative Examples 1 to 3; Figure 3b shows the XPS spectra of Mn 2p of S-275-0.5 in Example 1; Figure 3c shows the XPS spectra of Co 2p of S-275-0.5 in Example 1; Figure 4d shows the XPS spectra of Zn 2p of S-275-0.5 in Example 1.

[0028] Figure 2Figures are electron microscope images; where, Figure a is the SEM image of MnCo-LDH in Example 1; Figures b and c are SEM images of MnCo-LDH@ZIF-67 / ZIF-8 in Example 1 at different magnifications, respectively; Figures d and e are SEM images of S-275-0.5 in Example 1 at different magnifications, respectively; Figure f is the EDS image of S-275-0.5 in Example 1; Figure g is the TEM image of S-275-0.5 in Example 1; Figure h is the HRTEM image of S-275-0.5 in Example 1.

[0029] Figure 3 Figure 1 shows electron microscope (EM) images; where Figure a is the SEM image of S-275-1 in Comparative Example 1; Figure b is the SEM image of S-275-2 in Comparative Example 2; and Figure c is the SEM image of S-350-0.5 in Comparative Example 3.

[0030] Figure 4 Figures show the electrochemical performance. Figure a is the CV curve of the AC electrode and S-275-0.5 from Example 1. Figures b to f are the electrochemical performance of the MnCo2O4 / ZnCo2O4 / / AC supercapacitor assembled using S-275-0.5 from Example 1. Figure b is the CV curve under different potential windows, figure c is the GCD curve under different potential windows, figure d is the CV curve under different scan rates, figure e is the GCD curve under different current densities, and figure f is the specific capacitance graph.

[0031] Figure 5 The figures show the electrochemical performance of the asymmetric solid-state supercapacitor assembled using the S-275-0.5 of Example 1; where a is the CV curve under different potential windows, b is the GCD curve under different potential windows, c is the CV curve under different scan rates, d is the GCD curve under different current densities, and e is the EIS curve.

[0032] Figure 6 Figures a through e show the electrochemical performance of two asymmetric solid-state supercapacitors connected in series. Figure a shows the CV curves under different potential windows, figure b shows the GCD curves under different potential windows, figure c shows the CV curves under different scan rates, figure d shows the GCD curves under different current densities, and figure e is an EIS diagram. Figures f through j show the electrochemical performance of two asymmetric solid-state supercapacitors connected in parallel. Figure f shows the CV curves under different potential windows, figure g shows the GCD curves under different potential windows, figure h shows the CV curves under different scan rates, figure i shows the GCD curves under different current densities, and figure j is an EIS diagram.

[0033] Figure 7In the figures, figures a through d are CV curves at different scan rates within the non-Radida potential range. Figure a shows S-275-1 of Comparative Example 1, figure b shows S-275-2 of Comparative Example 2, figure c shows S-350-0.5 of Comparative Example 3, figure d shows S-275-0.5 of Example 1, and figure e shows the CV curves of S-275-0.5 of Example 1, S-275-1 of Comparative Example 1, S-275-2 of Comparative Example 2, and S-350-0.5 of Comparative Example 3. dl value. Detailed Implementation

[0034] The technical solution of the present invention will be described more clearly and completely below with reference to specific embodiments. The described embodiments are only some embodiments of the present invention, and not all of them. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0035] Example 1

[0036] The preparation method of MnCo2O4 / ZnCo2O4 nanocomposite materials includes the following steps:

[0037] Preparation of MnCo-LDH: Weigh 125 mg manganese nitrate tetrahydrate, 291 mg cobalt nitrate hexahydrate, 360 mg urea and 92.5 mg ammonium fluoride respectively, and then dissolve them together in a beaker containing 35 mL of distilled water. Stir magnetically for 15 min to form a homogeneous mixture. Immerse a piece of treated 1 cm × 2 cm nickel foam into the mixture, then transfer it to a 50 mL autoclave and heat it in an oven at 100°C for 9 h. After cooling to room temperature, remove it to obtain MnCo-LDH / NF. Wash it 4 times with deionized water and dry it at 70°C for later use.

[0038] Preparation of MnCo-LDH@ZIF-67 / ZIF-8: Weigh 203 mg of cobalt nitrate hexahydrate and 89 mg of zinc nitrate hexahydrate, and dissolve them together in 25 mL of methanol to obtain a salt solution; dissolve 656 mg of 2-methylimidazole in 25 mL of methanol to form a clear solution to obtain a ligand solution; pour the ligand solution into the salt solution to form a precursor solution; immerse a piece of MnCo-LDH / NF in the precursor solution and let it stand at room temperature for 24 h to obtain MnCo-LDH@ZIF-67 / ZIF-8 / NF; wash the obtained MnCo-LDH@ZIF-67 / NF with methanol and dry it at 70°C for 12 h for later use.

[0039] Preparation of MnCo2O4 / ZnCo2O4 nanocomposite material: MnCo-LDH@ZIF-67 / ZIF-8 was placed in a muffle furnace and heat-treated at 275°C for 0.5 h to obtain MnCo2O4 / ZnCo2O4 nanocomposite material, denoted as S-275-0.5.

[0040] Example 2

[0041] The preparation method of MnCo2O4 / ZnCo2O4 nanocomposite materials includes the following steps:

[0042] Preparation of MnCo-LDH: Weigh 125 mg manganese nitrate tetrahydrate, 233 mg cobalt nitrate hexahydrate, 360 mg urea and 55.5 mg ammonium fluoride respectively, and then dissolve them together in a beaker containing 35 mL of distilled water. Stir magnetically for 15 min to form a homogeneous mixture. Immerse a piece of treated 1 cm × 2 cm nickel foam into the mixture, then transfer it to a 50 mL autoclave and heat it in an oven at 100°C for 12 h. After cooling to room temperature, remove it to obtain MnCo-LDH / NF. Wash it 4 times with deionized water and dry it at 70°C for later use.

[0043] Preparation of MnCo-LDH@ZIF-67 / ZIF-8: Weigh 174 mg of cobalt nitrate hexahydrate and 59 mg of zinc nitrate hexahydrate, and dissolve them together in 25 mL of methanol to obtain a salt solution; dissolve 656 mg of 2-methylimidazole in 25 mL of methanol to form a clear solution to obtain a ligand solution; pour the ligand solution into the salt solution to form a precursor solution; immerse a piece of MnCo-LDH / NF in the precursor solution and let it stand at room temperature for 20 h to obtain MnCo-LDH@ZIF-67 / ZIF-8 / NF; wash the obtained MnCo-LDH@ZIF-67 / NF with methanol and dry it at 70°C for 12 h for later use.

[0044] Preparation of MnCo2O4 / ZnCo2O4 nanocomposite material: MnCo-LDH@ZIF-67 / ZIF-8 was placed in a muffle furnace and heat-treated at 250°C for 0.5 h to obtain MnCo2O4 / ZnCo2O4 nanocomposite material.

[0045] Example 3

[0046] The preparation method of MnCo2O4 / ZnCo2O4 nanocomposite materials includes the following steps:

[0047] Preparation of MnCo-LDH: Weigh 125 mg manganese nitrate tetrahydrate, 349 mg cobalt nitrate hexahydrate, 360 mg urea and 111 mg ammonium fluoride respectively, and then dissolve them together in a beaker containing 35 mL of distilled water. Stir magnetically for 15 min to form a homogeneous mixture. Immerse a piece of treated 1 cm × 2 cm nickel foam into the mixture, then transfer it to a 50 mL autoclave and heat it in an oven at 140°C for 8 h. After cooling to room temperature, remove it to obtain MnCo-LDH / NF. Wash it 4 times with deionized water and dry it at 70°C for later use.

[0048] Preparation of MnCo-LDH@ZIF-67 / ZIF-8: Weigh 232 mg of cobalt nitrate hexahydrate and 118.7 mg of zinc nitrate hexahydrate, and dissolve them together in 25 mL of methanol to obtain a salt solution; dissolve 656 mg of 2-methylimidazole in 25 mL of methanol to form a clear solution to obtain a ligand solution; pour the ligand solution into the salt solution to form a precursor solution; immerse a piece of MnCo-LDH / NF in the precursor solution and let it stand at room temperature for 30 h to obtain MnCo-LDH@ZIF-67 / ZIF-8 / NF; wash the obtained MnCo-LDH@ZIF-67 / NF with methanol and dry it at 70°C for 12 h for later use.

[0049] Preparation of MnCo2O4 / ZnCo2O4 nanocomposite material: MnCo-LDH@ZIF-67 / ZIF-8 was placed in a muffle furnace and heat-treated at 300°C for 0.5 h to obtain MnCo2O4 / ZnCo2O4 nanocomposite material.

[0050] Comparative Example 1

[0051] The preparation method of MnCo2O4 / ZnCo2O4 nanocomposite material is the same as that in Example 1, except that the heat treatment time in step S3 is replaced by 1 hour instead of 0.5 h, denoted as S-275-1.

[0052] Comparative Example 2

[0053] The preparation method of MnCo2O4 / ZnCo2O4 nanocomposite material is the same as that in Example 1, except that the heat treatment time in step S3 is replaced by 2 hours instead of 0.5 hours, denoted as S-275-2.

[0054] Comparative Example 3

[0055] The preparation method of MnCo2O4 / ZnCo2O4 nanocomposite material is the same as that in Example 1, except that the heat treatment temperature in step S3 is replaced by 350°C instead of 275°C, denoted as S-350-0.5.

[0056] Examples 1 to 3 of this invention all yielded MnCo2O4 / ZnCo2O4 nanocomposites with excellent electrochemical properties. The following research uses the MnCo2O4 / ZnCo2O4 nanocomposites from Example 1 and Comparative Examples 1 to 3 as examples. Specific research methods and results are shown below:

[0057] I. Phase, chemical element, and morphological analysis of MnCo2O4 / ZnCo2O4 nanocomposites:

[0058] The chemical composition of the MnCo2O4 / ZnCo2O4 nanocomposites of Example 1 and Comparative Examples 1 to 3 was studied by XRD. Figure 1 The peaks shown in Figure a correspond well to the PDF cards for MnCo2O4 and ZnCo2O4, with no other extraneous peaks, indicating that MnCo-LDH@ZIF-67 / ZIF-8 has been completely oxidized. Among them, MnCo2O4 corresponds to the JCPDS No. 23-1237 card, and the diffraction peaks near 36° and 64° belong to MnCo2O4, corresponding to the (311) and (440) crystal planes, respectively; ZnCo2O4 corresponds to the JCPDS No. 23-1390 card, and the diffraction peaks near 19°, 30.5°, and 58.7° belong to ZnCo2O4, corresponding to the (111), (220), and (511) crystal planes, respectively; the remaining strong diffraction peaks at 44.5° and 51.8° belong to the (006) and (220) crystal planes of Ni, which corresponds to the JCPDS No. 04-0850 card. This demonstrates that MnCo2O4 / ZnCo2O4 nanocomposites were successfully prepared under different heat treatment conditions.

[0059] XPS was used to further analyze the chemical elemental composition and valence states of the MnCo2O4 / ZnCo2O4 nanocomposite material. The XPS spectrum of Mn 2p is shown below. Figure 1 As shown in Figure b, the fitting peaks at 642.3 eV and 653.8 eV, respectively, belong to Mn 2p. 3 / 2 and Mn 2p 1 / 2 The two main peaks, Mn 2p 3 / 2 and Mn 2p 1 / 2 The band gap is approximately 11.5 eV, indicating that most of the Mn ions are in the Mn valence state. 3+ and Mn 4+Between; among them, the diffraction peak at 642.3 eV belongs to Mn 3+ The diffraction peak at 653.8 eV is attributed to Mn. 4+ The XPS spectrum of Co2p is as follows: Figure 1 As shown in Figure c, the high-resolution XPS spectrum of Co 2p was separated into two satellite peaks and two characteristic peaks located at 786.4 eV and 803.7 eV, respectively, using Gaussian fitting. These peaks are attributed to Co. 2+ Co 2p 3 / 2 and Co 2p 1 / 2 Orbital. And based on the fact that MnCo2O4 and NiCo2O4 have similar structures, in the existing technology "Marco JF, Gancedo JR, Gracia M, et al. Characterization of the nickel cobaltite, NiCo2O4, prepared by several methods: an XRD, XANES, EXAFS, and XPS study [J]. Journal of SolidState Chemistry, 2000, 153(1): 74-81", Marco reported Ni 3+ and Ni 4+ Located in an octahedral position, it is speculated that Mn in this invention... 3+ Mn 4+ It may occupy an octahedral position. The XPS spectrum of Zn 2p is shown below. Figure 1 As shown in d-plot, the diffraction peaks containing two main peaks, with binding energies of 1020.9 eV and 1043.9 eV, are attributed to Zn 2p, respectively. 3 / 2 and Zn 2p 1 / 2 .

[0060] The morphology and structure of MnCo-LDH, MnCo-LDH@ZIF-67 / ZIF-8, and the MnCo2O4 / ZnCo2O4 nanocomposite material of Example 1 were characterized by SEM and TEM. The results are as follows: Figure 2 As shown. Figure 2 As shown in Figure a, MnCo-LDH nanoneedles grow uniformly and densely on a nickel foam substrate. Figure 2As shown in Figures b to c, after combining MnCo-LDH with ZIF-67 and ZIF-8, the resulting MnCo-LDH@ZIF-67 / ZIF-8 still largely retains the original nanowire array structure. ZIF-67 and ZIF-8 exhibit smooth, polyhedral shapes and densely grow around the MnCo-LDH nanoneedles. SEM images of the MnCo2O4 / ZnCo2O4 nanocomposite material are shown in [images missing]. Figure 2 In the d~e diagram, after heat treatment, the MnCo-LDH@ZIF-67 / ZIF-8 derived MnCo2O4 and ZnCo2O4 retain similar nanorod and dodecahedral shapes, respectively. To determine the chemical composition of the MnCo2O4 / ZnCo2O4 nanocomposite material, EDS analysis was performed. Figure 2 The f-image shows a relatively uniform distribution of Mn, Co, Zn, and O elements, further confirming the synthesis of the MnCo2O4 / ZnCo2O4 nanocomposite. Typical TEM images of the MnCo2O4 / ZnCo2O4 nanocomposite are shown below. Figure 2 As shown in Figure g, the structure of nanorods and polyhedra is presented more clearly. The polyhedral structure of ZnCo₂O₄ exhibits a large number of nanoparticles and pores, attributed to the release of gases during heat treatment. This structure accommodates large-sized ions and effectively buffers volume changes during electrochemical reactions, facilitating electrolyte diffusion. Figure 2 As shown in the h figure, the interface between the two substances can be clearly seen, and the lattice spacing of 0.34 nm corresponds to the (440) crystal plane of MnCo2O4, while the lattice spacing of 0.32 nm belongs to the (511) crystal plane of ZnCo2O4. This is consistent with the previous XRD results, further verifying the synthesis of MnCo2O4 / ZnCo2O4 nanocomposite material and the formation of heterojunction.

[0061] Figure 3 Figures a to c in the figure are SEM images of the MnCo2O4 / ZnCo2O4 nanocomposites of Comparative Examples 1 to 3. Compared with S-275-0.5 in Example 1, some nanosheet structures were found, while the morphology and structure of the composites were not much different from those of S-275-0.5.

[0062] II. Electrochemical performance analysis of MnCo2O4 / ZnCo2O4 nanocomposites:

[0063] The three-electrode system is set up as follows: a saturated calomel electrode is used as the reference electrode, a Pt sheet is used as the counter electrode, and the working electrode is used to form a three-electrode system. The working electrode is prepared by mixing the catalyst material, conductive agent, binder and solvent and loading them onto the current collector. The catalyst material is the material synthesized in this invention. The mass ratio of the catalyst material, conductive agent and binder is 8:1:1.

[0064] To investigate the potential of MnCo2O4 / ZnCo2O4 nanocomposite materials in practical applications of solid-state capacitors, this invention assembles a MnCo2O4 / ZnCo2O4 / / AC supercapacitor, abbreviated as ASC device, in a 2 mol / L KOH electrolyte solution, wherein the MnCo2O4 / ZnCo2O4 nanocomposite material is the positive electrode and the AC electrode is the negative electrode. Figure 4 Figure a shows the CV curves of the MnCo2O4 / ZnCo2O4 nanocomposite material and the AC electrode measured in a three-electrode system. The CV curve of the AC electrode indicates that it is a typical double-layer electrode material. From this figure, it can be roughly inferred that the optimal operating potential of the MnCo2O4 / ZnCo2O4 / / AC supercapacitor is between 0V and 1.6V. Figure 4 As shown in Figures b-c, cyclic voltammetry and constant current charge-discharge tests were performed on the ASC device under different potential windows. The CV curve and GCD curve maintained similar shapes. The CV curve showed significant polarization in the 0V-1.8V range, indicating that the normal operating potential of the ASC device is below 1.8V, within the 0V-1.6V range, consistent with the above... Figure 4 The CV curves in Figure a show a relatively consistent pattern, and the GCD curves from 0V to 1.6V indicate that the ASC device has the longest discharge time within this voltage range, further demonstrating that the ASC device exhibits optimal capacitance performance in the 0V to 1.6V range. Furthermore, the CV curves of the ASC device were tested at different scan rates within the 0V to 1.6V potential window, as shown below. Figure 4 As shown in Figure d, when the scan rate increases from 5 mV / s to 100 mV / s, it maintains a roughly similar shape, exhibiting only slight changes with increasing scan rate, indicating that the ASC device has fast charge-discharge characteristics. Furthermore, all CV curve shapes show a combination of double-layer capacitance and pseudocapacitance generated by the Faraday redox reaction, confirming its excellent rate performance. Figure 4 The e~f plot shows the GCD curves and specific capacitance at different current densities within a potential window of 0V to 1.6V. The GCD curves exhibit good symmetry, indicating that the ASC device has good coulombic efficiency. At a current density of 2mA / cm²... 2 5mA / cm 2 10mA / cm 2 15mA / cm 2and 20mA / cm 2 The specific capacitance is 1.2 mF / cm. 2 980mF / cm 2 880mF / cm 2 830mF / cm 2 and 730mF / cm 2 20mA / cm 2 The specific capacitance at that time is 2mA / cm 2 The rate of 61.4% indicates that the assembled ASC device has good rate performance.

[0065] To explore the application of MnCo2O4 / ZnCo2O4 nanocomposite materials in solid-state supercapacitors, an activated carbon negative electrode was prepared by coating activated carbon slurry onto nickel foam. This activated carbon negative electrode was designated AC / NF. The preparation of the activated carbon negative electrode followed these steps: activated carbon, polyvinylidene fluoride (PVDF), and conductive carbon black were weighed in a mass ratio of 8:1:1 and added to a beaker containing N-methylpyrrolidone. The mixture was magnetically stirred for 12 hours to obtain a black activated carbon slurry. This slurry was then uniformly coated onto the treated nickel foam and dried in a vacuum drying oven for 12 hours. An asymmetric solid-state supercapacitor was assembled using the MnCo2O4 / ZnCo2O4 nanocomposite material as the positive electrode, AC / NF as the negative electrode, and PVA / KOH as the solid gel electrolyte. The specific operation is as follows: Weigh 5g of PVA particles and add them to 35mL of deionized water. Heat the solution in a water bath at 90°C and stir for 50min to completely dissolve the PVA. Then weigh 5.6g of KOH and add it to 15mL of deionized water. Stir the solution evenly with a magnetic stirrer to obtain a KOH solution. Add the KOH solution to the PVA solution dropwise with a dropper and stir at a constant temperature for 20min to obtain a PVA / KOH gel solid electrolyte. Immerse both the positive and negative electrodes in the PVA / KOH gel solid electrolyte to coat the outer layers of both electrodes. After standing at room temperature for 24h to evaporate the moisture, the asymmetric solid supercapacitor is successfully prepared.

[0066] Figure 5 Figure a shows the CV curves measured at a scan rate of 10 mV / s under different potential windows. Within the voltage range of 0V~0.8V to 0V~1.8V, the shape of the CV curves remains basically consistent. The GCD curves are as follows... Figure 5 As shown in Figure b, at a current density of 5 mA / cm² 2 At that time, the charge and discharge curves in each voltage range showed a good charge and discharge process. Figure 5Figure c shows the CV curves at different scan rates in the voltage range of 0V to 1.4V. It can be seen that the shape of the CV curve remains basically unchanged at all scan rates. Figure 5 The d-plot in the figure shows the GCD curves under different current densities. Based on the discharge time, it was calculated that when the current density is 2 mA / cm²... 2 4mA / cm 2 5mA / cm 2 8mA / cm 2 and 10mA / cm 2 The specific capacitance at that time was 990mF / cm 2 880mF / cm 2 803mF / cm 2 731mF / cm 2 614mF / cm 2 . Figure 5 Figure e in the figure shows the impedance diagram of an asymmetric solid-state supercapacitor, where the resistance in the high-frequency region is approximately 7.4 Ω.

[0067] Figure 6 Figures a through e in the diagram show the electrochemical performance of two asymmetric solid-state supercapacitors connected in series. Figure 6 Figure f~j shows the electrochemical performance of two parallel asymmetric solid-state supercapacitors. Figure 6 Figure a shows the CV curves obtained from two asymmetric solid-state supercapacitors connected in series under different voltage ranges, from 0V to 1.6V and from 0V to 2.8V. The CV curves exhibit a generally consistent shape and show no obvious polarization. The GCD curves within the same voltage range are shown below. Figure 6 As shown in Figure b, at a current density of 5 mA / cm² 2 At this time, the two asymmetric solid-state supercapacitors connected in series exhibited good charge-discharge behavior in every potential window. The CV curves at different scan rates within the 0V~2.8V voltage range are shown below. Figure 6 As shown in Figure c, the CV curves at various scan rates are basically similar in shape. Within the voltage range of 0V to 2.8V, the GCD curves of two asymmetric solid-state supercapacitors connected in series at different current densities were tested, as shown in Figure c. Figure 6 As shown in Figure d, the results show that the charging and discharging time increases with the increase of current density, while the charging time is longer and the discharging time is shorter, indicating that the coulombic efficiency of two asymmetric solid-state supercapacitors connected in series is not high. Figure 6 The figure above shows the EIS curves of two asymmetric solid-state supercapacitors connected in series, with an internal resistance of approximately 12Ω, roughly conforming to the characteristics of a series circuit. The CV curves of two asymmetric solid-state supercapacitors connected in parallel under different voltage ranges are shown below. Figure 6As shown in Figure f, the voltage range is from 0V to 1.0V to 0V to 1.4V, and the shape of the CV curve does not change significantly at each voltage. The GCD curves for each voltage range are shown below. Figure 6 As shown in Figure g, different voltage ranges exhibit typical charge and discharge behavior. Figure 6 The h-plot in the image shows the CV curves at different scan rates; the CV curves at each scan rate are basically similar in shape. The GCD curves at different current densities are shown below. Figure 6 As shown in Figure i, the GCD curve does not have good symmetry, indicating that the coulombic efficiency of two parallel asymmetric solid-state supercapacitors is not high. Figure 6 Figure j shows the EIS curves of two asymmetric solid-state supercapacitors connected in parallel, with an internal resistance of approximately 4Ω, which roughly conforms to the resistance pattern of parallel circuits.

[0068] To investigate the active surface area of ​​MnCo2O4 / ZnCo2O4 nanocomposites, this invention uses cyclic voltammetry to obtain CV curves. The CV values ​​of the MnCo2O4 / ZnCo2O4 nanocomposites of Example 1 and Comparative Examples 1-3 are measured at different scan rates in the non-Radar potential region. dl To evaluate ECSA, the non-Radar potential region is 0V~0.1V, and the results are as follows: Figure 7 As shown in figures a~d, the CV curves all exhibit typical double-layer capacitance behavior. Figure 7 As shown in Figure e, compared with the MnCo2O4 / ZnCo2O4 nanocomposites of Comparative Examples 1 to 3, the C of S-275-0.5 is significantly higher. dl The value is greater than S-275-1, S-275-2, and S-350-0.5, and the C of S-275-0.5 is... dl The value is 13mF / cm 2 S-275-1's C dl The value is 8.6 mF / cm 2 S-275-2's C dl The value is 10.7 mF / cm 2 S-350-0.5 of C dl The value is 12.8 mF / cm 2 This demonstrates that S-275-0.5 has a larger active surface area than other samples.

[0069] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for preparing MnCo2O4 / ZnCo2O4 nanocomposite materials, characterized in that, Includes the following steps: Soluble manganese salt, soluble cobalt salt, urea and ammonium fluoride are mixed together in water to obtain a mixture. Nickel foam is immersed in the mixture and subjected to a hydrothermal reaction to obtain MnCo-LDH / NF. Soluble metal salts and 2-methylimidazole were dispersed in solvents and then mixed evenly to obtain a precursor solution. MnCo-LDH / NF was then immersed in the precursor solution to carry out a coordination reaction to obtain MnCo-LDH@ZIF-67 / ZIF-8. The soluble metal salts consist of soluble cobalt salts and soluble zinc salts. MnCo-LDH@ZIF-67 / ZIF-8 was heat-treated to obtain MnCo2O4 / ZnCo2O4 nanocomposite material; The heat treatment conditions are as follows: heating at 250℃~300℃ for 0.5h; The molar ratio of soluble manganese salt, soluble cobalt salt, urea and ammonium fluoride is 0.5:0.8~1.2:6:1.5~3; The conditions for the coordination reaction are: standing at room temperature for 20-30 hours.

2. The method for preparing the MnCo2O4 / ZnCo2O4 nanocomposite material according to claim 1, characterized in that, The heat treatment conditions are: heating at 275℃ for 0.5h.

3. The method for preparing the MnCo2O4 / ZnCo2O4 nanocomposite material according to claim 1, characterized in that, During the preparation of MnCo-LDH / NF, the hydrothermal reaction conditions are: heating at 100°C~140°C for 8h~12h.

4. The method for preparing the MnCo2O4 / ZnCo2O4 nanocomposite material according to claim 1, characterized in that, The precursor solution contains 0.6 mmol to 0.8 mmol of soluble cobalt salt and 0.2 mmol to 0.4 mmol of soluble zinc salt.

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