Preparation and application of nickel-vanadium double hydroxide and phosphorus-selenium co-doped vanadium-nickel metal organic framework / foamed nickel

Abstract

The invention relates to a novel nano material synthesis and supercapacitor application technology, and discloses a preparation method and application of a nickel-vanadium double hydroxide-phosphorus-selenium co-doped vanadium-nickel metal organic framework / foamed nickel. The purpose of the invention is to improve the conductivity and cycle performance of the electrode material through anion doping and core-shell structure design. The preparation method mainly comprises the following steps: 1, preparing a nickel-doped vanadium metal organic framework / foamed nickel (VNi-MOF / NF) by a solvothermal method; 2, carrying out annealing treatment to prepare a phosphorus-selenium co-doped vanadium-nickel metal organic framework / foamed nickel (P, Se-doped VNi-MOF / NF); and 3, preparing the nickel-vanadium double hydroxide (at) phosphorus-selenium co-doped vanadium-nickel metal organic framework / foamed nickel (NiV-LDH (at) P, Se-doped VNi-MOF / NF) by a hydrothermal method. The method has the advantages of simple process, low cost, high yield and the like. Due to the high conductivity of the P and Se-doped VNi-MOF / NF (core) and the high capacitance characteristic of the NiV-LDH (shell), the specific capacitance of the NiV-LDH at the P and Se-doped VNi-MOF / NF reaches 2083.7 C g <-1 > when the specific capacitance is 1A g <-1 >, and the capacitance retention rate still reaches 90% after 10,000 times of circulation under 10A g <-1 >.

Description

Technical Field

[0001] The present invention relates to the fields of material preparation, electrochemistry and energy, and particularly relates to the preparation and application of nickel vanadium double hydroxide@phosphorus selenium co-doped vanadium nickel metal organic framework / nickel foam. Background Art

[0002] Supercapacitors (SCs) have become one of the most representative energy storage devices due to their excellent high-power output, fast charge and discharge performance, and long lifespan. Although the energy density of commercial supercapacitors has far exceeded that of traditional capacitors, compared with lithium-ion and sodium-ion batteries, etc., their energy density is still relatively low, which limits their wide application. Therefore, how to improve the energy density of supercapacitors while maintaining high power density and long cycle life has become an urgent problem to be solved. The magnitude of the energy density is closely related to the specific capacitance of the electrode material and the voltage window of the device. Selecting and optimizing the composition and structure of the electrode material and assembling it into a hybrid supercapacitor is considered a very effective strategy to improve the energy density.

[0003] Vanadium metal-organic frameworks (V-MOFs) have a flexible coordination environment, adjustable porous structure, and multiple oxidation states, which enable them to form diverse morphologies and exhibit relatively ideal electrochemical properties. Among them, the V-MOF nanorod array can provide a fast and efficient channel for electron transfer, and at the same time significantly shorten the diffusion path of electrolyte ions, thereby effectively improving the rate performance of the material. However, due to the interaction between metal nodes and organic ligands and the characteristic of being easily soluble in aqueous electrolytes, the conductivity and structural stability of V-MOFs still need to be improved.

[0004] When synthesizing V-MOF on nickel foam, nickel foam inevitably participates in the reaction during the solvothermal process to form VNi-MOF, thereby improving its conductivity to a certain extent. Introducing anions (such as phosphorus, sulfur, selenium, boron, and nitrogen) usually causes local charge imbalance near the metal center of MOFs, which is beneficial to promoting electron migration and enhancing conductivity. Phosphorus has a low electronegativity and exhibits a strong electron donor ability. And selenium can introduce additional charge carriers and change the electronic structure. Therefore, the co-doping of phosphorus and selenium is expected to significantly improve the electron transfer rate, electrochemical reaction kinetics, and conductivity of VNi-MOF through a synergistic effect.

[0005] Due to its fast reaction kinetics, large active area, and excellent structural stability, the core-shell heterostructure material exhibits great application potential in the field of high-performance electrodes. As an ideal shell material, NiV-LDH nanosheet arrays possess good redox activity, high theoretical specific capacitance, and large surface area. When in-situ grown on the surface of P,Se-doped VNi-MOF nanorods, it can further increase the specific surface area of P,Se-doped VNi-MOF and expose more electrochemically active sites. More critically, the NiV-LDH shell can effectively prevent the core material from directly contacting the electrolyte solution, thereby reducing the dissolution of the electrode material and alleviating the volume change that may occur during the redox process, and then significantly enhancing the overall stability. Therefore, constructing a core-shell heterostructure by coating NiV-LDH on the surface of P,Se-doped VNi-MOF is expected to improve the stability of P,Se-doped VNi-MOF.

[0006] In summary, the present invention successfully synthesized nickel vanadium double hydroxide@phosphorus selenium co-doped vanadium nickel metal-organic framework / nickel foam. Benefiting from the phosphorus selenium co-doping and core-shell heterostructure design, this material exhibits excellent electrochemical performance and has broad application prospects as a supercapacitor electrode material. Summary of the Invention

[0007] The object of the present invention is to develop a vanadium-based metal-organic framework-based material with excellent conductivity and stability to enhance the electrochemical performance of supercapacitors, and to propose a preparation method for a nickel vanadium double hydroxide@phosphorus selenium co-doped vanadium nickel metal-organic framework / nickel foam electrode material.

[0008] The preparation method of the nickel vanadium double hydroxide@phosphorus selenium co-doped vanadium nickel metal-organic framework / nickel foam electrode material of the present invention is carried out according to the following steps: I. Vanadium nickel metal-organic framework / nickel foam doped with nickel (VNi-MOF / NF) Dissolve 0.1~2.0 mmol of vanadyl acetylacetonate, 0.1~2.0 mmol of ammonium metavanadate, and 0.2~4.0 mmol of terephthalic acid in 50~80 ml of N,N-dimethylformamide solution. Immerse the nickel foam in the above solution for 30 s. Then place it on a ceramic boat and anneal it in air at 300~450°C for 1 h with a heating rate of 5°C / min. Finally, transfer the solution and the annealed nickel foam to an autoclave and keep it at 160°C for 12~48 h to obtain VNi-MOF / NF.

[0009] II. Phosphorus selenium co-doped vanadium nickel metal-organic framework / nickel foam (P,Se-doped VNi-MOF / NF) 0.3 - 2.0 g of sodium hypophosphite, 0.1 - 1.0 g of selenium powder and VNi-MOF / NF were respectively placed in the upper, middle and lower reaches of a tube furnace, and the distance between the porcelain boats was 5 cm. Under an Ar atmosphere, annealing treatment was carried out at 300 - 450 °C for 2 h with a heating rate of 2 °C / min to obtain P,Se-doped VNi-MOF / NF.

[0010] III. Nickel vanadium double hydroxide @ phosphorus and selenium co-doped vanadium nickel metal-organic framework / nickel foam (NiV-LDH@P,Se-doped VNi-MOF / NF) 0.1 - 0.5 mmol of sodium chloride hexahydrate, 0.1 - 0.5 mmol of vanadium chloride, 1 - 6 mmol of urea and 1 - 5 mmol of ammonium fluoride were dissolved in 50 - 80 mL of deionized water and stirred at room temperature for 30 min. Subsequently, the mixed solution and P,Se-doped VNi-MOF were transferred to a high-pressure reactor and reacted at 120 °C for 2 - 12 h to obtain NiV-LDH@P,Se-doped VNi-MOF / NF.

[0011] Compared with the existing technologies, the present invention has the following beneficial effects: The present invention uses phosphorus and selenium co-doping to significantly improve the conductivity of VNi-MOF / NF. Using NiV-LDH as the shell material to coat the P,Se-doped VNi-MOF / NF core material significantly improves the stability of the electrode material.

[0012] The nickel vanadium double hydroxide @ phosphorus and selenium co-doped vanadium nickel metal-organic framework / nickel foam electrode material prepared by the present invention has a core material of P,Se-doped VNi-MOF nanorod arrays with good conductivity, which can serve as a channel for directional electron transfer to improve the charge and discharge rate. Its shell material of NiV-LDH nanosheet arrays has rich redox activity and a large specific surface area, which provides additional charge storage capacity and promotes the rapid transport of ions, thus achieving a high specific capacity. Description of the Drawings

[0013] Figure 1 is the scanning electron microscopy image of the prepared nickel vanadium double hydroxide @ phosphorus and selenium co-doped vanadium nickel metal-organic framework / nickel foam material; Figure 2 is the transmission electron microscopy image of the prepared nickel vanadium double hydroxide @ phosphorus and selenium co-doped vanadium nickel metal-organic framework / nickel foam material; Figure 3 is the crystal structure and chemical composition of the prepared nickel vanadium double hydroxide @ phosphorus and selenium co-doped vanadium nickel metal-organic framework / nickel foam material; Figure 4The electrochemical performance of the prepared nickel-vanadium double hydroxide@phosphorus-selenium co-doped vanadium-nickel metal-organic framework / nickel foam material in a three-electrode system; Figure 5 The electrochemical performance of the hybrid supercapacitor assembled with the prepared nickel-vanadium double hydroxide@phosphorus-selenium co-doped vanadium-nickel metal-organic framework / nickel foam and activated carbon in a two-electrode system; Figure 6 Scanning electron microscope morphology image of the prepared nickel-vanadium double hydroxide@phosphorus-selenium co-doped vanadium-nickel metal-organic framework / nickel foam. Specific implementation plan Specific implementation method 1: Preparation method of nickel-vanadium double hydroxide@phosphorus-selenium co-doped vanadium-nickel metal-organic framework / nickel foam material, which is specifically carried out according to the following steps: I. Nickel-doped vanadium metal-organic framework / nickel foam (VNi-MOF / NF) Dissolve 0.1 - 1.5 mmol of vanadyl acetylacetonate, 0.1 - 2.0 mmol of ammonium metavanadate, and 0.2 - 4.0 mmol of terephthalic acid in 50 - 80 ml of N,N-dimethylformamide solution. Immerse nickel foam into the above solution and keep it for 30 s. Then place it on a ceramic boat and anneal it in air at 300 - 450 °C for 1 h with a heating rate of 5 °C / min. Finally, transfer the solution and the annealed nickel foam to an autoclave and store it at 160 °C for 12 - 48 h to obtain VNi-MOF / NF.

[0015] II. Phosphorus-selenium co-doped vanadium-nickel metal-organic framework / nickel foam (P,Se-doped VNi-MOF / NF) Place 0.3 - 2.0 g of sodium hypophosphite, 0.1 - 1.0 g of selenium powder, and VNi-MOF / NF at the upper, middle, and lower reaches of a tube furnace respectively, with a distance of 5 cm between the ceramic boats. Under an Ar atmosphere, anneal it at 300 - 450 °C for 2 h with a heating rate of 2 °C / min to obtain P,Se-doped VNi-MOF / NF.

[0016] III. Nickel-vanadium double hydroxide@phosphorus-selenium co-doped vanadium-nickel metal-organic framework / nickel foam (NiV-LDH@P,Se-doped VNi-MOF / NF) Dissolve 0.1 - 0.5 mmol of sodium chloride hexahydrate, 0.1 - 0.5 mmol of vanadium chloride, 1 - 6 mmol of urea, and 1 - 5 mmol of ammonium fluoride in 50 - 80 mL of deionized water, and stir at room temperature for 30 min. Subsequently, transfer the homogeneous solution and P,Se-doped VNi-MOF to a high-pressure reaction kettle, and react at 120 °C for 2 - 12 h to obtain NiV-LDH@P,Se-doped VNi-MOF / NF.

[0017] Specific Embodiment 2: Preparation method of nickel vanadium double hydroxide@phosphorus selenium co-doped vanadium nickel metal-organic framework / nickel foam, which is specifically carried out according to the following steps: The difference between this embodiment method and Specific Embodiment 1 is that: in Step 1, the reaction solution contains 0.1 - 0.5 mmol of vanadyl acetylacetonate. Others are the same as Specific Embodiment 1.

[0018] Specific Embodiment 3: Preparation method of nickel vanadium double hydroxide@phosphorus selenium co-doped vanadium nickel metal-organic framework / nickel foam, which is specifically carried out according to the following steps: The difference between this embodiment method and Specific Embodiments 1 and 2 is that: in Step 2, the content of sodium hypophosphite is 0.3 - 1.5 g. Others are the same as Specific Embodiments 1 and 2.

[0019] Specific Embodiment 4: Preparation method of nickel vanadium double hydroxide@phosphorus selenium co-doped vanadium nickel metal-organic framework / nickel foam, which is specifically carried out according to the following steps: The difference between this embodiment method and Specific Embodiments 1 to 3 is that: in Step 2, the content of selenium powder is 0.1 - 0.5 g. Others are the same as Specific Embodiments 1 to 3.

[0020] Specific Embodiment 5: Preparation method of nickel vanadium double hydroxide@phosphorus selenium co-doped vanadium nickel metal-organic framework / nickel foam, which is specifically carried out according to the following steps: The difference between this embodiment method and Specific Embodiments 1 to 4 is that: in Step 3, the content of sodium chloride hexahydrate is 0.1 - 0.3 mmol. Others are the same as Specific Embodiments 1 to 4.

[0021] The following experiment is used to verify the effect of the present invention: The preparation method of nickel vanadium double hydroxide@phosphorus selenium co-doped vanadium nickel metal-organic framework / nickel foam in this experiment is carried out according to the following steps: I. Nickel-doped vanadium metal-organic framework / nickel foam (VNi-MOF / NF) Dissolve 0.5 mmol of vanadyl acetylacetonate, 0.5 mmol of ammonium metavanadate, and 1.0 mmol of terephthalic acid in 70 ml of N,N-dimethylformamide solution. Immerse nickel foam into the above solution and keep it for 30 s. Subsequently, place it on a ceramic boat and anneal it in air at 350 °C for 1 h with a heating rate of 5 °C / min. Finally, transfer the solution and the annealed nickel foam to an autoclave and store it at 160 °C for 48 h to obtain VNi-MOF / NF.

[0022] II. Phosphorus and selenium co-doped vanadium nickel metal-organic framework / nickel foam (P,Se-doped VNi-MOF / NF) Place 1.5 g of sodium hypophosphite, 0.2 g of selenium powder, and VNi-MOF / NF at the upper, middle, and lower reaches of a tube furnace respectively, with a distance of 5 cm between the ceramic boats. Anneal it at 350 °C for 2 h in an Ar atmosphere with a heating rate of 2 °C / min to obtain P,Se-doped VNi-MOF / NF.

[0023] III. Nickel vanadium double hydroxide@phosphorus and selenium co-doped vanadium nickel metal-organic framework / nickel foam (NiV-LDH@P,Se-doped VNi-MOF / NF) Dissolve 0.3 mmol of sodium chloride hexahydrate, 0.1 mmol of vanadium chloride, 5 mmol of urea, and 4 mmol of ammonium fluoride in 60 mL of deionized water and stir at room temperature for 30 min. Subsequently, transfer the homogeneous solution and P,Se-doped VNi-MOF to a high-pressure reaction kettle and react at 120 °C for 12 h to obtain NiV-LDH@P,Se-doped VNi-MOF / NF.

[0024] The present invention uses a three-electrode test system to study the electrochemical performance of the material. The synthesized NiV-LDH@P,Se-doped VNi-MOF / NF is used as the working electrode, Hg / HgO is used as the reference electrode, Pt is used as the counter electrode, and 6 M potassium hydroxide solution is used as the electrolyte to test its electrochemical performance. In a two-electrode system, NiV-LDH@P,Se-doped VNi-MOF / NF is used as the positive electrode, activated carbon / nickel foam (AC / nickel foam) is used as the negative electrode, and 6 M potassium hydroxide solution is used as the electrolyte to test its electrochemical performance.

[0025] Figure 1 It is the electron microscope scanning image of NiV-LDH@P,Se-doped VNi-MOF / NF. In Figure 1In a-c, VNi-MOF nanorod arrays with a well-oriented structure can be observed to grow uniformly and densely on the surface of the nickel foam skeleton. The surface of the nanorods is smooth, with a diameter of about 1 μm and a length of about 10 μm. After doping, the P,Se-doped VNi MOF still maintains the morphology and size of VNi-MOF, as shown in Figure 1 d-f. After hydrothermal treatment, the surface of the P,Se-doped VNi-MOF becomes rough, and the diameter of the nanorods increases to ~1.5 μm, as shown in Figure 1 g-i. At the same time, a large number of ultrathin NiV-LDH nanosheets are uniformly covered on the surface of the nanorods, indicating that the NiV-LDH@P,Se-doped VNi-MOF / NF heterostructure has been successfully synthesized.

[0026] Figure 2 Figure Figure 2 Figure 2 2 Se 4 and VP 2 of the (-112) and (-112) crystal planes, indicating the successful introduction of P and Se into the VNi-MOF lattice. Figure 2 d-e shows that the nanorods with a diameter of about 1 μm are uniformly coated with NiV-LDH nanosheets, forming a typical core-shell structure. The boundary between the nanorods and the nanosheets can be observed, and the length of the NiV-LDH nanosheets is about 200 nm. In addition, the HRTEM image shows that the lattice spacings at positions 3 and 4 are 0.193 and 0.155 nm, respectively, corresponding to the (0012) and (110) crystal planes of NiV-LDH ( Figure 2 f). The EDS elemental mapping results ( Figure 2 g) show that Ni, V, C, O, P, and Se elements are uniformly distributed in NiV-LDH@P, Se-doped VNi-MOF.

[0027] Figure 3 is the structural, chemical composition, and valence state analysis of NiV-LDH@P,Se-doped VNi-MOF. In the XRD pattern ( Figure 3a), The characteristic peaks of VNi-MOF are at 14.4°, 16.6°, 17.4°, 18.2°, 19°, 21.9°, 24.5°, 25.5°, 31.2°, 32.6° and 36.8°. These peaks correspond to the (101), (022), (121), (112), (040), (132), (033), (222), (015) and (204) crystal planes of V-MOF (CCDC#166785) respectively. The diffraction peaks of P,Se-doped VNi-MOF match those of VNi MOF, indicating that phosphorus and selenium doping does not change the crystal structure. The characteristic peaks of NiV-LDH are located at 11.6°, 24.3°, 28.8°, 34.7°, 42.8° and 46.9°, which are attributed to the (011), (200), (02-1), (1-3-2) and (134) crystal planes of NiV-LDH (PDF#56-1627) respectively. The characteristic peaks of both P,Se-doped VNi-MOF and NiV-LDH are present in NiV-LDH@P,Se-doped VNi-MOF, confirming the successful synthesis of the heterostructure. In the FTIR spectrum ( Figure 3 b), The absorption bands of VNi-MOF at 3507.7 and 3419 cm -1 are related to the stretching vibration of O-H. The absorption band at 1654 cm -1 corresponds to the bending vibration of water molecules. The two strong peaks at 1538.9 and 1405 cm -1 correspond to the stretching vibration of carboxyl groups. The two absorption bands near 891 and 744 cm -1 are due to the out-of-plane bending vibration of the C=C-H bond within the PTA benzene ring. The absorption peak at 580.5 cm -1 belongs to the stretching vibration of M-O. P,Se-doped VNi-MOF has similar characteristic peaks to VNi MOF, indicating that the introduction of P atoms and Se atoms does not change the crystal structure of VNi-MOF, which is consistent with the XRD analysis results. In addition to the stretching vibration of O-H and the bending vibration of water molecules, NiV-LDH shows three new peaks at 1386.5, 663.4 and 445 cm -1 , corresponding to the asymmetric stretching vibration of the C-O bond in CO 3 2- ions, the stretching vibration of intercalated carbonate, and the lattice vibration of M-O respectively. In the NiV-LDH@P,Se-doped VNi-MOF heterostructure, the characteristic peaks of the above two materials are present, indicating the successful preparation of the composite material. In the XPS survey spectrum ( Figure 3c), The characteristic peaks of Ni 2p, O 1s, V 2p, C 1s, P 2p and Se 3d are present in P,Se-doped VNi-MOF. However, the intensity of the characteristic peak of Ni 2p is significantly lower than that of V 2p, indicating that only a small amount of Ni is introduced into the lattice of V-MOF during the solvothermal process. After NiV-LDH coating, it can be clearly found that the peak intensity of Ni 2p in NiV-LDH@P,Se-doped VNi-MOF increases significantly. In the high-resolution spectrum of Ni 2p ( Figure 3 d), The peaks of P,Se-doped VNi-MOF at 856.8 and 974.2 eV correspond to Ni 2+ in Ni 2p 3 / 2 and Ni 2p 1 / 2 orbits. The other two peaks are the satellite peaks (sat.) of Ni 2p 3 / 2 (862.9 eV) and Ni 2p 1 / 2 (881.3 eV). Compared with P,Se-doped VNi-MOF, the peaks of Ni2p 3 / 2 (855.78 eV) and Ni 2p 1 / 2 (873.38 eV) in NiV-LDH@P,Se-doped VNi-MOF show an obvious negative shift. After further peak fitting, it can be confirmed that both Ni 2+ and Ni 3+ cations are present in the sample, and the increase in oxidation state helps to improve the electrochemical activity. In the high-resolution spectrum of V 2p ( Figure 3 e), P,Se-doped VNi-MOF shows the spin-orbit peaks of V 2p 3 / 2 and V 2p 1 / 2 at 516.78 and 524.18 eV respectively. The peaks at 516.8, 516.88 and 517.78 eV correspond to V 3+ , V 4+ and V 5+ in three different oxidation states, which confirms the existence of vanadium with different valence states in the sample, which helps to increase the number of carriers and thus significantly improve the electrochemical performance. In NiV-LDH@P,Se-doped VNi-MOF, the peak positions of V 2p 3 / 2 and V 2p 1 / 2 show an obvious positive shift, and this change may be due to the interfacial electron redistribution between the core material and the shell material. In the high-resolution spectrum of O 1s ( Figure 3f), in P,Se-doped VNi-MOF, the peaks located at 530.38 eV, 531.48 eV, and 532.58 eV can be found to represent metal-oxygen bonds, metal-OH bonds, and O-C=O bonds, respectively. However, in NiV-LDH@P,Se-doped VNi-MOF, all three peaks shift towards lower binding energies. This change may be due to the interaction between NiV-LDH and P,Se-doped VNi-MOF, resulting in a change in the coordination environment of oxygen atoms. In the high-resolution spectrum of C 1s ( Figure 3 g), after fitting, we observed three peaks at 284.8, 286.6, and 288.6 eV, which are mainly caused by carbon atoms in the lattice and on the surface. Among them, the prominent peak at 284.8 eV represents C-C bonds, which are usually related to carbon atoms in the graphitized lattice. The peaks at 286.6 eV and 288.6 eV mainly correspond to C-O-C and O-C=O functional groups. These results indicate that amorphous carbon atoms can adsorb moisture or form chemical bonds with oxygen atoms in P,Se-doped VNi-MOF and NiV-LDH. In the high-resolution spectrum of P 2p ( Figure 3 h), P, Se-doped VNi-MOF shows two characteristic peaks located at 133.38 and 134.38 eV, corresponding to P 2p 3 / 2 and P 2p 1 / 2 , respectively, indicating that phosphorus mainly exists in the form of metal-phosphorus bonds. After the coating treatment, these two peaks shift towards lower binding energies. In addition, a new peak appears at 137.58 eV, corresponding to P-O bonds. In the high-resolution spectrum of Se 3d ( Figure 3 i), selenium mainly exists in the form of selenium-oxygen bonds in both materials. The peak at 54.88 eV can be deconvoluted into two peaks of Se 3d 5 / 2 (54.58 eV) and Se 3d 3 / 2 (55.38 eV).

[0028] Figure 4 Figure for the electrochemical performance test of NiV-LDH@P,Se-doped VNi-MOF / NF. Figure 4a shows the CV curves of NiV-LDH@P,Se-doped VNi-MOF / NF at different scanning rates, with a pair of obvious redox peaks. Combining the above XPS analysis results, it can be seen that this includes the Faraday redox reaction with nickel ions as the active center. In addition, as the scanning rate increases, the integral area of the closed curve gradually increases. However, obvious shifts occur in the peak potentials at both the cathode and anode, resulting in an increase in the peak separation. This indicates the redox reversibility of the NiV-LDH@P,Se-doped VNi-MOF / NF electrode material, and its Faraday response is quasi-reversible. Figure 4 b shows the GCD curves of NiV-LDH@P,Se-doped VNi-MOF / NF at different current densities. An obvious plateau region can be observed, which is different from the electric double layer capacitance, indicating its battery-type capacitance storage characteristics. Moreover, the GCD curves at different current densities have good symmetry, proving that NiV-LDH@P,Se-doped VNi-MOF / NF has excellent rate performance and high Coulomb efficiency. The electrochemistry reaction kinetics and energy storage mechanism of the active material NiV-LDH@P,Se-doped VNi-MOF / NF were further analyzed through the CV curves. The b values corresponding to the cathodic peak and anodic peak of NiV-LDH@P,Se-doped VNi-MOF / NF are 0.49 and 0.50 respectively, indicating that the diffusion control process has a greater contribution during the redox reaction process ( Figure 4 c). Therefore, diffusion control dominates during the energy storage process of NiV-LDH@P,Se-doped VNi-MOF / NF, indicating that the electrode material exhibits battery-type behavior during the electrochemical process. The specific contribution ratios of the two control processes can be calculated by the formula. When the scanning rate is 10 mV s -1 , the proportion of diffusion control is 76% and the surface control is 24%, as shown in Figure 4 d. As the scanning rate increases (10 - 100 mV s -1 ), the proportion of diffusion control decreases from 76% to 33%, and the proportion of surface control increases from 24% to 67%. This is mainly because at high scanning rates, the redox reaction of the material is insufficient, resulting in a decrease in the proportion of diffusion. At a current density of 10 A g -1The NiV-LDH@P,Se-doped VNi-MOF / NF was subjected to 10,000 repeated charge-discharge tests under certain conditions to analyze the cycling stability of the sample. After 10,000 cycles, the NiV-LDH@P,Se-doped VNi-MOF / NF sample retained 90% of its initial capacitance, with only a 10% capacity loss and a Coulombic efficiency of 99.5%, which demonstrated the excellent cycling stability of NiV-LDH@P,Se-doped VNi-MOF / NF.

[0029] Figure 5 The electrochemical performance of the hybrid supercapacitor assembled with the prepared NiV-LDH@P,Se-doped VNi-MOF / NF and AC / NF in a two-electrode system. Using the NiV-LDH@P,Se-doped VNi-MOF / NF material as the positive electrode and AC / NF as the negative electrode, a two-electrode system test was carried out in a 6 M KOH electrolyte solution, and the schematic diagram is as Figure 5 shown in Fig. a. First, in a three-electrode system, at a scanning rate of 10 mV s -1 , the electrochemical performance of NiV-LDH@P,Se-doped VNi-MOF / NF and AC / NF was investigated ( Figure 5 Fig. b). The AC / NF showed a quasi-rectangle in the voltage window of -1.0 - 0.0 V, while obvious redox peaks appeared in the NiV-LDH voltage window of VNi-MOF / NF at -0.8 V. To further determine the actual working voltage window of the device, in a two-electrode system, the CV behavior of the device at different voltage windows at a scanning rate of 20 mV s -1 was investigated ( Figure 5 Fig. c). When the voltage window was higher than 1.7 V, obvious polarization occurred in the CV curve of the device. Therefore, 0 - 1.7 V was selected as the voltage window for the stable operation of the device. Figure 5 Fig. d shows the CV curves of the device at different scanning rates. It can be seen that no obvious spikes appeared at the beginning and end of the voltage, indicating that the selected voltage window was appropriate. At different scanning rates, the shape of the CV curve did not change significantly, indicating that the assembled device had good stability. As the scanning rate increased, the enclosed curve area became larger and the shape of the curve did not change, indicating the good reversibility of the device. Figure 5 Fig. e shows the GCD curves at different current densities. By calculation, the specific capacitance of the device was 452.2 C g -1 at 1 A g -1 , and 280 C g -1 at 10 A g -1 . As shown in Fig. 5f. It can be observed that the device had a power density of 866.8 W Kg-1 At a power density of, an energy density of 110.6 Wh / kg can be achieved -1 with a high energy density. Even when the power density is as high as 9.44 kW / kg -1 , the energy density can still reach 73.4 Wh / kg -1 . Utilizing the superior electrochemical performance of NiV-LDH@P,Se-doped VNi-MOF / NF / / AC / NF, this device is further applied to practical electronic applications, such as Figure 5 shown in g. After two devices are connected in series and connected to the LED circuit board marked with a heart shape, the LED board can work normally for more than 30 minutes for a long time. These results favorably illustrate the possibility of the NiV-LDH@P,Se-doped VNi-MOF / NF / / AC / NF device as a power supply system. As Figure 5 shown in h, the cycling stability of the device was investigated by cycling 10,000 times at a current density of 10 A / g -1 . It was found that the capacity retention rate and Coulomb efficiency of the device were 91.5% and 99.7% respectively, showing good cycling stability and reversibility. The built-in figure shows the charge-discharge curves of the device in the first 10 cycles and the last 10 cycles before cycling. It can be seen from the figure that after repeated charge-discharge, the curve did not change significantly, further confirming its excellent cycling stability. Figure 5 Figure i shows the EIS test of the device before and after cycling. It can be found that the Rs and Rct of the device before the test were 1.215 Ω and 0.105 Ω respectively. After cycling, the Rs and Rct were 1.187 Ω and 0.453 Ω respectively. The results show that the impedance change is small before and after cycling, indicating that the device has good charge transfer kinetics.

Claims

1. Preparation and application of nickel-vanadium double hydroxide@phosphorus-selenium co-doped vanadium-nickel metal organic framework / nickel foam, characterized in that The preparation method of nickel-vanadium double hydroxide@phosphorus-selenium co-doped vanadium-nickel metal organic framework / nickel foam as supercapacitor material is carried out according to the following steps:

1. Nickel-doped vanadium metal organic framework / nickel foam (VNi-MOF / NF) 0.1~2.0 mmol of acetylacetonatovanadium, 0.1~2.0 mmol of ammonium metavanadate and 0.2~4.0 mmol of terephthalic acid were dissolved in 50~80 ml of N,N-dimethylformamide solution. The nickel foam was immersed in the above solution and kept for 30 s. It was then placed on a ceramic boat and annealed at 300~450℃ in air for 1 h at a heating rate of 5℃ / min. Finally, the solution and the annealed nickel foam were transferred to an autoclave and stored at 160℃ for 12~48 h to obtain VNi-MOF / NF. 2.

2. Phosphorus-Selenium co-doped Vanadium-Nickel Metal Organic Framework / Nickel Foam (P,Se-doped VNi-MOF / NF) 0.3-2.0 g of sodium hypophosphite, 0.1-1.0 g of selenium powder and VNi-MOF / NF were placed in the upper, middle and downstream of the tube furnace, respectively, with the distance between the porcelain boats being 5 cm. P,Se-doped VNi-MOF / NF was obtained by annealing at 300-450℃ for 2 h in an Ar atmosphere at a heating rate of 2℃ / min.

3. Nickel-vanadium double hydroxide @ phosphorus-selenium co-doped vanadium-nickel metal organic framework / nickel foam (NiV-LDH@P,Se-dopedVNi-MOF / NF) 0.1~0.5 mmol of sodium chloride hexahydrate, 0.1~0.5 mmol of vanadium chloride, 1~6 mmol of urea and 1~5 mmol of ammonium fluoride were dissolved in 50~80 mL of deionized water and stirred at room temperature for 30 min. The mixed solution and P,Se-doped VNi-MOF were then transferred to a high-pressure reactor and reacted at 120°C for 2~12 h to obtain NiV-LDH@P,Se-doped VNi-MOF / NF.

4. The preparation method according to claim 1, characterized in that: The content of vanadyl acetylacetonate described in step 1 is 0.1-1.0 mmol.

5. The preparation method according to claim 1, characterized in that: The solvent thermal time described in step 1 is 24 to 48 hours.

6. The preparation method according to claim 1, characterized in that: The content of sodium hypophosphite described in step 2 is 0.5-1.5 g, and the content of selenium powder is 0.1-0.5 g.

7. The preparation method according to claim 1, characterized in that: The annealing temperature described in step 2 is 300-350°C.

8. The preparation method according to claim 1, characterized in that: The content of sodium chloride hexahydrate described in step 2 is 0.1-0.3 mmol, and the content of vanadium chloride is 0.1-0.3 mmol.

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