A rhombus nanosheet-shaped copper-doped nickel-cobalt transition metal selenide material, a preparation method and application thereof

Abstract

The application discloses rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide and a preparation method and application thereof. The preparation method of the material is as follows: after a coordination agent, a surfactant, a nickel salt, a cobalt salt and a copper salt are mixed with a solvent, the mixture is placed in a microwave COD digester to perform a microwave-assisted solvothermal reaction, a copper-doped nickel-cobalt MOFs precursor is obtained; the copper-doped nickel-cobalt MOFs precursor and a selenite are respectively placed in the downstream and the upstream of a tube furnace, and a selenization reaction is performed under a protective atmosphere, and the rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide is obtained. The material has an ultrathin rhombic nanosheet-shaped structure, the surface of the material is rough, the particle size distribution of the material is uniform, and the material has excellent electrochemical performance; when the material is used as an electrode material of a supercapacitor, the capacitance performance can be greatly improved. The preparation process is simple, the conditions are mild, the time consumption is short, and the cost is low, and the preparation process meets the industrial production standards.

Description

TECHNICAL FIELD

[0001] The present application relates to an energy storage device material, in particular to a rhombus-shaped nanosheet-like copper-doped nickel-cobalt transition metal selenide material, and also to a preparation method and applications thereof, and belongs to the technical field of electrochemical energy storage device preparation. BACKGROUND

[0002] With the proposal and implementation of the "double carbon" target vision, it is crucial to find and develop new, low-cost and environmentally friendly sustainable green energy storage and conversion devices. Among numerous energy storage devices, supercapacitors stand out due to their excellent capacitive performance. It not only has the advantages of fast charging and discharging speed, wide working temperature range, long cycle life and green pollution-free, but also has higher power density than secondary batteries and higher energy density than traditional static capacitors. As a promising electrochemical energy storage device, the selection of electrode materials for supercapacitors has a key impact on the energy storage characteristics of the device.

[0003] Transition metal compounds can obtain higher theoretical specific capacity from Faraday reactions, and have better energy storage effects than carbon materials and other pseudo-capacitive electrode materials (conductive polymers). In addition, due to the advantages of abundant reserves, low cost, good conductivity and high theoretical specific capacity, transition metal selenides have gradually become good substitutes for other transition metal chalcogenides (transition metal oxides, transition metal sulfides). However, due to the irreversibility of the oxidation-reduction reaction in the material preparation process, the volume expansion effect will further affect the rate performance and cycle stability of the material. Research has found that the introduction of hetero-metallic elements in single-metal selenides can improve the conductivity of electrode materials, provide more active sites, and exhibit more excellent capacitive performance. For example, Sun et al. prepared a heterostructure (MnSe2@NiCo2Se4) composed of nanorod-like MnSe2 and nanosheet-like NiCo2Se4 using a hydrothermal method. Due to the synergistic effect of MnSe2 and NiCo2Se4, the MnSe2@NiCo2Se4 electrode has excellent capacitance (1078 C·g -1 ,1A·g -1 ) and cycle stability (8000 times, 90.7%) (Journal of Energy Storage, 2023, 63). Manchi et al. synthesized CuO / Ni3V2O8 nanosheets using a simple hydrothermal method, and then carried out a selenization reaction to obtain a Cu 6.0 Se 5.22 / Ni 2.0 V 4.0 Se 8.0 electrode material, which also exhibits excellent capacitive performance (94.4mAh·g -1 ,10m A·cm -2The reaction yield was good, with good cycling stability (8000 cycles, 103.8%) (Applied Surface Science, 2023, 622). However, the preparation of transition metal selenides by hydrothermal or solvothermal methods usually involves long reaction times, difficulty in morphology control, and low yields. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the first objective of this invention is to provide a rhombic nanosheet-like copper-doped nickel-cobalt transition metal selenide material. This material possesses an ultrathin rhombic nanosheet structure with a rough surface and uniform particle size distribution, while also exhibiting excellent electrochemical performance.

[0005] The second objective of this invention is to provide a method for preparing rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide materials. This method is simple, has mild reaction conditions, is relatively quick, highly reproducible, has high energy conversion efficiency, and is low in cost, which is conducive to large-scale production.

[0006] A third objective of this invention is to provide an application of a rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide material. When used as an electrode material in supercapacitors, it can significantly improve capacitance performance.

[0007] To achieve the above-mentioned technical objectives, this invention provides a method for preparing rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide materials. The method involves mixing a ligand, surfactant, nickel salt, cobalt salt, and copper salt with a solvent, and then placing the mixture in a microwave-assisted solvothermal reaction in a microwave COD digester to obtain a copper-doped nickel-cobalt MOF precursor. The copper-doped nickel-cobalt MOF precursor and selenite are then placed downstream and upstream of a tube furnace, respectively, and subjected to a selenization reaction under a protective atmosphere to obtain the final product.

[0008] This invention employs a microwave-assisted solvothermal reaction to prepare copper-doped nickel-cobalt MOF precursors. During the synthesis process, microwave radiation is used on the reactants; simultaneously, a unique microwave-assisted solvothermal heating method, operating from the inside out, rapidly increases the reaction temperature, thereby influencing the coordination state of the metal central ion and ligands, and further affecting and controlling the morphology and structure of the material. Since the morphology and size of the material significantly influence its electrochemical performance, MOF precursor materials with complete morphology and suitable size can be obtained by controlling the microwave reaction power and reaction time.

[0009] The preparation process of this precursor is as follows:

[0010]

[0011] As a preferred embodiment, the nickel salt, cobalt salt, and copper salt are all metallic nitrates. Examples of nickel salts include hydrated nickel nitrate, cobalt salts include hydrated cobalt nitrate, and copper salts include hydrated copper nitrate.

[0012] As a preferred embodiment, the molar ratio of the nickel salt, cobalt salt, and copper salt is 1:0.5–0.9:0.5–0.1, more preferably 1:0.6–0.8:0.4–0.2. Controlling the amount of the three transition metal salts within a suitable range is beneficial to improving the electrochemical performance of the material. Specifically, too low a Cu doping amount is insufficient to improve the performance of the bimetallic selenide, while too high a doping amount can easily lead to changes in the morphology and structure of the raw material.

[0013] As a preferred embodiment, the ligand comprises terephthalic acid and / or trimesic acid.

[0014] As a preferred embodiment, the surfactant comprises polyvinylpyrrolidone and / or polyethylene glycol.

[0015] As a preferred embodiment, the molar ratio of the ligand to the nickel salt is 2 to 4:1.

[0016] As a preferred embodiment, the mass ratio of the surfactant to the nickel salt is 3 to 7:1.

[0017] As a preferred embodiment, the solvent comprises DMF, ethanol, and water; the volume ratio of DMF, ethanol, and water is 2–4:3–1:1–2, more preferably 1:1:1. This mixed solvent, containing weak coordination bonds and a low-boiling-point solvent, can lower the microwave activation temperature and minimize the impact on the structural integrity of MOFs.

[0018] As a preferred embodiment, during the microwave-assisted solvothermal reaction, the power of the microwave COD digester is controlled at 350–550 W, and the reaction time is 10–30 min. More preferably, the power of the microwave COD digester is 400–500 W, and the reaction time is 10–20 min.

[0019] Controlling microwave heating power and time within a reasonable range is beneficial to improving the overall performance of materials. When the microwave heating power is too low, only low-boiling-point solvents, such as ethanol and water molecules, can be removed, resulting in an inhomogeneous nanosheet structure. Increasing the reaction power can further remove DMF molecules, yielding MOF materials with specific structures. However, excessively high heating power can cause the collapse of the material's framework structure, leading to particle stacking. Furthermore, if the microwave reaction time is too short, it is insufficient to uniformly heat the reactants, affecting the integrity of the MOF material structure; if the reaction time is too long, it can lead to the collapse of the crystal structure.

[0020] As a preferred embodiment, the mass ratio of the selenite to the copper-doped nickel-cobalt MOF precursor is 5 to 10:1, more preferably 5:1.

[0021] As a preferred embodiment, the selenite includes at least one of sodium selenite, sodium hydrogen selenite, potassium selenite, and zinc selenite.

[0022] As a preferred embodiment, the selenization reaction process is as follows: under a nitrogen atmosphere, the temperature is increased to 300-400℃ at a heating rate of 1-5℃ / min and reacted for 1-2 hours. A further preferred heating rate is 1-2℃ / min, and a further preferred reaction temperature is 300-350℃. Controlling the selenization reaction temperature, reaction time, and heating rate within a suitable range is beneficial for obtaining selenide materials with excellent performance. Too low a reaction temperature is detrimental to the complete selenization of the precursor, while too high a reaction temperature and too rapid a heating rate can lead to material structural collapse.

[0023] The present invention also provides a rhombic nanosheet copper-doped nickel-cobalt transition metal selenide material, which is prepared by the above method.

[0024] This ternary metal selenide retains the specific layered nanosheet structure of its MOF precursor material, exhibiting a high specific surface area and total pore volume, which greatly optimizes the energy storage performance of transition metal selenides. Furthermore, the introduction of low-cost Cu atoms to replace some Co atoms not only promotes synergistic effects among the metal atoms, enabling multiple valence state transitions and facilitating multiple redox reactions, thus producing better electrochemical activity than single-component transition metal selenides, but also significantly reduces production costs.

[0025] As a preferred embodiment, the chemical formula of the copper-doped nickel-cobalt transition metal selenide is NiCo. x Cu x Se, where x = 0.5–0.9, y = 0.5–0.1, and x + y = 1. Further preferred values ​​are x = 0.6–0.8, y = 0.4–0.2, and x + y = 1.

[0026] This invention also provides an application of a rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide material as an electrode material for supercapacitors. Using this selenide material as an electrode material in supercapacitors can significantly improve capacitance performance.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The copper-doped nickel-cobalt transition metal selenide material of the present invention has an overall ultrathin rhombic nanosheet structure, which has the characteristics of high specific surface area and total pore volume. The surface is rough, which can provide more active sites, exhibiting good charge storage characteristics and greatly optimizing the capacitance performance.

[0029] (2) The microwave-assisted solvothermal method is used to replace the traditional hydrothermal and solvothermal methods to prepare the precursor of copper-doped nickel-cobalt transition metal selenide. This method can achieve rapid heating of the reactants, greatly reduce the reaction time and temperature, and avoid the use of complex experimental equipment. At the same time, it can effectively control the morphology of the material, ensure its uniform particle size distribution, and improve the selectivity of the process and the yield of the product.

[0030] (3) In the selenide material of the present invention, copper atoms are used to replace cobalt atoms, which greatly reduces the cost while improving the conductivity of the composite material and promoting the synergistic effect between metal atoms, thereby improving the capacitance performance of the material.

[0031] (4) When the selenide material of the present invention is used as an electrode material in a supercapacitor, it has good capacitance performance and its specific capacitance is significantly improved compared with that of nickel-cobalt bimetallic selenide material. Attached Figure Description

[0032] Figure 1 The nickel-cobalt transition metal selenides with different copper doping levels prepared in Examples 1-5 and Comparative Example 1 of this invention are shown in 1 A·g -1 Constant current charge-discharge curve (GCD).

[0033] Figure 2 The NiCo prepared in Example 3 of this invention 0.7 Cu 0.3 Se and NiCoSe prepared in Comparative Example 1 are in the range of 0.5–10 A·g. -1 Specific capacitance variation curve under current density.

[0034] Figure 3 The NiCo materials prepared under different microwave power conditions in Embodiment 3 and Comparative Example 2 of this invention are shown. 0.7 Cu 0.3 Se materials at 1 A·g -1 The GCD curve below.

[0035] Figure 4 The nickel-cobalt transition metal selenides with different copper doping levels prepared in Examples 1-5 and Comparative Example 1 of this invention were tested at 10 mV·s. -1 Cyclic voltammetry (CV) curves at scan rate.

[0036] Figure 5 The NiCo prepared in Example 3 of this invention 0.7 Cu 0.3X-ray diffraction (XRD) patterns of Se and NiCoSe prepared in Comparative Example 1.

[0037] Figure 6 This is a scanning electron microscope (SEM) image of the NiCoSe material prepared in Comparative Example 1 of this invention.

[0038] Figure 7 The NiCo prepared in Example 3 of this invention 0.7 Cu 0.3 Scanning electron microscope (SEM) image of Se material.

[0039] Figure 8 The NiCo prepared in Example 3 of this invention 0.7 Cu 0.3 X-ray energy dispersive spectroscopy (EDS) of Se materials. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to examples and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0041] Test method for the capacitance performance of ultrathin rhombic nanosheet copper-doped nickel-cobalt transition metal selenide: Polyvinylidene fluoride (PVDF), acetylene black, and active material were dissolved sequentially in N-methyl-2-pyrrolidone (NMP) solvent at a certain mass ratio (1:1:8). The mixture was then stirred at 200 rpm for 4 hours on a magnetic stirrer to form a homogeneous slurry. The slurry was then evenly coated onto a 1 cm × 1 cm square nickel foam substrate (three-electrode system) or a 1 cm... 2 The electrodes were placed on a circular nickel foam substrate (two-electrode system) and dried in a vacuum drying oven at 70°C for 12 hours. Then, the cooled electrode sheets were pressed at 16 MPa for 1 minute using a tablet press to obtain the electrode plates.

[0042] In the following specific embodiments, cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests were performed using a Shanghai Chenhua CHI660E electrochemical workstation. The three-electrode system employed a nickel foam substrate loaded with active material, a mercury / mercury oxide electrode (Hg / HgO), and a platinum sheet electrode (Pt) as the working electrode, reference electrode, and counter electrode, respectively, with 6M KOH solution as the electrolyte. The morphology, structure, and elemental composition of the materials were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS).

[0043] Example 1

[0044] The preparation of a copper-doped nickel-cobalt transition metal selenide includes the following steps:

[0045] (1) First, 2 mmol PTA (terephthalic acid), 2 g PVP (polyvinylpyrrolidone), 1 mmol Ni(NO3)2·6H2O, 0.9 mmol Co(NO3)2·6H2O, and 0.1 mmol Cu(NO3)2·3H2O were weighed and dissolved in 30 mL of a mixed solvent (volume ratio DMF:C2H5OH:H2O = 1:1:1). The solution was sonicated for 30 min and then magnetically stirred for 2 h to obtain a light pink solution. This solution was then transferred to a 100 mL digestion vessel and placed in a microwave COD digester. The mixture was reacted at 450 W for 10 min. After cooling to room temperature, the supernatant was discarded, the solution was centrifuged, washed three times with anhydrous ethanol, and dried in a 70 °C vacuum drying oven for 12 h. The resulting precursor material was named NiCo. 0.9 Cu 0.1 -MOFs.

[0046] (2) Weigh out 0.5g Na2SeO3 and 0.1g NiCo respectively. 0.9 Cu 0.1 - MOFs were placed in two separate corundum boats, one upstream and one downstream of a tube furnace. The furnace was ventilated under a nitrogen atmosphere for 30 min, and the temperature was increased to 350 °C at a rate of 1 °C / min, held for 2 h, and then cooled to room temperature. The resulting copper-doped nickel-cobalt transition metal selenide was then passed through a 200-mesh sieve and named NiCo. 0.9 Cu 0.1 Se.

[0047] Example 2

[0048] The preparation of a copper-doped nickel-cobalt transition metal selenide includes the following steps:

[0049] (1) First, 2 mmol PTA, 2 g PVP, 1 mmol Ni(NO3)2·6H2O, 0.8 mmol Co(NO3)2·6H2O, and 0.2 mmol Cu(NO3)2·3H2O were weighed and dissolved in 30 mL of a mixed solvent (DMF:C2H5OH:H2O = 1:1:1). The solution was sonicated for 30 min and then magnetically stirred for 2 h to obtain a light pink solution. This solution was then transferred to a 100 mL digestion vessel and placed in a microwave COD digester. The mixture was reacted at 450 W for 10 min. After cooling to room temperature, the supernatant was discarded, and the solution was centrifuged and washed three times with anhydrous ethanol. It was then dried in a 70 °C vacuum drying oven for 12 h. The resulting precursor material was named NiCo. 0.8 Cu 0.2 -MOFs.

[0050] (2) Weigh out 0.5g Na2SeO3 and 0.1g NiCo respectively. 0.8 Cu0.2 - MOFs were placed in two separate corundum boats, one upstream and one downstream of a tube furnace. The furnace was ventilated under a nitrogen atmosphere for 30 min, and the temperature was increased to 350 °C at a rate of 1 °C / min, held for 2 h, and then cooled to room temperature. The resulting copper-doped nickel-cobalt transition metal selenide was then passed through a 200-mesh sieve and named NiCo. 0.8 Cu 0.2 Se.

[0051] Example 3

[0052] The preparation of a copper-doped nickel-cobalt transition metal selenide includes the following steps:

[0053] (1) First, 2 mmol PTA, 2 g PVP, 1 mmol Ni(NO3)2·6H2O, 0.7 mmol Co(NO3)2·6H2O, and 0.3 mmol Cu(NO3)2·3H2O were weighed and dissolved in 30 mL of a mixed solvent (DMF:C2H5OH:H2O = 1:1:1). The solution was sonicated for 30 min and then magnetically stirred for 2 h to obtain a light pink solution. This solution was then transferred to a 100 mL digestion vessel and placed in a microwave COD digester. The mixture was reacted at 450 W for 10 min. After cooling to room temperature, the supernatant was discarded, and the solution was centrifuged and washed three times with anhydrous ethanol. It was then dried in a 70 °C vacuum drying oven for 12 h. The resulting precursor material was named NiCo. 0.7 Cu 0.3 -MOFs.

[0054] (2) Weigh out 0.5g Na2SeO3 and 0.1g NiCo respectively. 0.7 Cu 0.3 - MOFs were placed in two separate corundum boats, one upstream and one downstream of a tube furnace. The furnace was ventilated under a nitrogen atmosphere for 30 min, and the temperature was increased to 350 °C at a rate of 1 °C / min, held for 2 h, and then cooled to room temperature. The resulting copper-doped nickel-cobalt transition metal selenide was then passed through a 200-mesh sieve and named NiCo. 0.7 Cu 0.3 Se.

[0055] Example 4

[0056] The preparation of a copper-doped nickel-cobalt transition metal selenide includes the following steps:

[0057] (1) First, 2 mmol PTA, 2 g PVP, 1 mmol Ni(NO3)2·6H2O, 0.6 mmol Co(NO3)2·6H2O, and 0.4 mmol Cu(NO3)2·3H2O were weighed and dissolved in 30 mL of a mixed solvent (DMF:C2H5OH:H2O = 1:1:1). The solution was sonicated for 30 min and then magnetically stirred for 2 h to obtain a light pink solution. This solution was then transferred to a 100 mL digestion vessel and placed in a microwave COD digester. The mixture was reacted at 450 W for 10 min. After cooling to room temperature, the supernatant was discarded. The solution was centrifuged and washed three times with anhydrous ethanol. It was then dried in a 70 °C vacuum drying oven for 12 h. The resulting precursor material was named NiCo. 0.6 Cu 0.4 -MOFs.

[0058] (2) Weigh out 0.5g Na2SeO3 and 0.1g NiCo respectively. 0.6 Cu 0.4 - MOFs were placed in two separate corundum boats, one upstream and one downstream of a tube furnace. The furnace was ventilated under a nitrogen atmosphere for 30 min, and the temperature was increased to 350 °C at a rate of 1 °C / min, held for 2 h, and then cooled to room temperature. The resulting copper-doped nickel-cobalt transition metal selenide was then passed through a 200-mesh sieve and named NiCo. 0.6 Cu 0.4 Se.

[0059] Example 5

[0060] The preparation of a copper-doped nickel-cobalt transition metal selenide includes the following steps:

[0061] (1) First, 2 mmol PTA, 2 g PVP, 1 mmol Ni(NO3)2·6H2O, 0.5 mmol Co(NO3)2·6H2O, and 0.5 mmol Cu(NO3)2·3H2O were weighed and dissolved in 30 mL of a mixed solvent (DMF:C2H5OH:H2O = 1:1:1). The solution was sonicated for 30 min and then magnetically stirred for 2 h to obtain a light pink solution. This solution was then transferred to a 100 mL digestion vessel and placed in a microwave COD digester. The mixture was reacted at 450 W for 10 min. After cooling to room temperature, the supernatant was discarded. The solution was centrifuged and washed three times with anhydrous ethanol. It was then dried in a 70 °C vacuum drying oven for 12 h. The resulting precursor material was named NiCo. 0.5 Cu 0.5 -MOFs.

[0062] (2) Weigh out 0.5g Na2SeO3 and 0.1g NiCo respectively. 0.5 Cu 0.5- MOFs were placed in two separate corundum boats, one upstream and one downstream of a tube furnace. The furnace was ventilated under a nitrogen atmosphere for 30 min, and the temperature was increased to 350 °C at a rate of 1 °C / min, held for 2 h, and then cooled to room temperature. The resulting copper-doped nickel-cobalt transition metal selenide was then passed through a 200-mesh sieve and named NiCo. 0.5 Cu 0.5 Se.

[0063] Comparative Example 1

[0064] As a comparison, the preparation of a nickel-cobalt transition metal selenide without copper doping includes the following steps:

[0065] (1) First, 2 mmol PTA, 2 g PVP, 1 mmol Ni(NO3)2·6H2O, and 1 mmol Co(NO3)2·6H2O were weighed and dissolved in 30 mL of mixed solvent (DMF:C2H5OH:H2O = 1:1:1). The solution was sonicated for 30 min and then magnetically stirred for 2 h to obtain a light pink solution. Then, the solution was transferred to a 100 mL digestion vessel and placed in a microwave COD digester. The reaction was carried out at 450 W for 10 min. After cooling to room temperature, the supernatant was discarded, the solution was centrifuged and washed three times with anhydrous ethanol. The solution was then dried in a vacuum drying oven at 70 °C for 12 h. The resulting precursor material was named NiCo-MOFs.

[0066] (2) Weigh 0.5g Na2SeO3 and 0.1g NiCo-MOFs respectively and place them in two separate corundum boats. Place them upstream and downstream of the tube furnace. Purge under N2 protective atmosphere for 30min. Set the heating rate to 1℃ / min to 350℃ and hold for 2h. After cooling to room temperature, take them out and pass them through a 200-mesh sieve. The resulting undoped nickel-cobalt transition metal selenide is named NiCoSe.

[0067] The different copper-doped nickel-cobalt transition metal selenides prepared in Examples 1-5 and the NiCoSe selenide prepared in Comparative Example 1 were compared at 1 A·g. -1 Perform charge-discharge tests under constant current, such as Figure 1 As shown in the figure, pseudocapacitive plateaus appear in all materials within the 0–0.55V voltage window, indicating the presence of the Faraday reaction process. Furthermore, compared to undoped NiCoSe, NiCo with different copper doping ratios… x Cu x The specific capacitance of Se was improved in all cases, especially in NiCo. 0.7 Cu 0.3 Se has the longest discharge time, indicating that it has the best capacitance performance.

[0068] Figure 2The NiCo prepared in Example 3 of this invention 0.7 Cu 0.3 Se and NiCoSe prepared in Comparative Example 1, in the range of 0.5–10 A·g -1 The specific capacitance variation curve under current density shows that, compared to undoped NiCoSe, NiCo... 0.7 Cu 0.3 Se exhibits superior specific capacitance at all current densities compared to the former, and its specific capacitance at 1 A·g -1 It even showed 1317 F·g at the current density. -1 High specific capacitance. Furthermore, NiCo... 0.7 Cu 0.3 Se still maintains a high specific capacitance (1151 F·g) even at high current densities. -1 This demonstrates excellent rate performance.

[0069] Comparative Example 2

[0070] As a comparison, NiCo under different microwave power conditions... 0.7 Cu 0.3 The preparation of Se includes the following steps:

[0071] (1) First, 2 mmol PTA, 2 g PVP, 1 mmol Ni(NO3)2·6H2O, 0.7 mmol Co(NO3)2·6H2O, and 0.3 mmol Cu(NO3)2·3H2O were weighed and dissolved in 30 mL of a mixed solvent (DMF:C2H5OH:H2O = 1:1:1). The solution was sonicated for 30 min and then magnetically stirred for 2 h to obtain a light pink solution. This solution was then transferred to a 100 mL digestion vessel and placed in a microwave COD digester. The mixture was reacted for 10 min at 250 W and 650 W power, respectively. After cooling to room temperature, the supernatant was discarded, the solution was centrifuged, washed three times with anhydrous ethanol, and dried in a 70 °C vacuum drying oven for 12 h. The resulting precursor materials were named NiCo. 0.7 Cu 0.3 -MOFs-250W and NiCo 0.7 Cu 0.3 -MOFs-650W.

[0072] (2) Weigh out 0.5g Na2SeO3 and 0.1g NiCo respectively. 0.7 Cu 0.3 - MOFs were placed in two separate corundum boats, one upstream and one downstream of a tube furnace. The furnace was ventilated under a nitrogen atmosphere for 30 min, and then heated to 350 °C at a rate of 1 °C / min. The temperature was held for 2 h, and after cooling to room temperature, the MOFs were removed and passed through a 200-mesh sieve. The resulting copper-doped nickel-cobalt transition metal selenides were named NiCo.0.7 Cu 0.3 Se-250W and NiCo 0.7 Cu 0.3 Se-650W.

[0073] Figure 3 The NiCo materials prepared in Example 3 and Comparative Example 2 of this invention under different microwave power conditions (250W, 450W, and 650W) are shown. 0.7 Cu 0.3 Se in 1A·g -1 The GCD curves below show that the properties of the materials prepared at microwave power of 250W or 650W are significantly lower than those prepared at microwave power of 450W for NiCo. 0.7 Cu 0.3 Se materials.

[0074] Figure 4 The different copper-doped nickel-cobalt transition metal selenides prepared in Examples 1-5 of this invention and the NiCoSe prepared in Comparative Example 1, at 10 mV·s -1 The cyclic voltammetry (CV) curves at the scan rate show that all materials exhibit a pair of distinct redox peaks, indicating they are pseudocapacitive materials. NiCo, in particular... 0.7 Cu 0.3 The area under the curve for Se is the largest, indicating the highest specific capacitance. The area under the curve for NiCoSe is smaller than that for copper-doped nickel-cobalt trimetallic selenide, suggesting that the synergistic effect between copper ions and other metal ions promotes improved capacitance performance, demonstrating superior specific capacitance compared to NiCoSe bimetallic selenide materials. This is consistent with the results obtained from the GCD curve.

[0075] Figure 5 The NiCo prepared in Example 3 of this invention 0.7 Cu 0.3 The X-ray diffraction (XRD) patterns of Se and NiCoSe prepared in Comparative Example 1 show that the XRD curves of the nickel-cobalt transition metal selenide before and after copper doping are similar. The diffraction peaks at 14.22°, 15.94°, 17.96°, 27.85°, and 35.66° correspond to the (101), (102), (110), (100), and (120) crystal planes of NiSe (JCPDS No. 02-0892) and CoSe2 (JCPDS No. 53-0449), respectively, confirming the successful synthesis of NiCoSe material. The diffraction peak at 43.69° can be attributed to the (220) crystal plane of Cu2Se (JCPDS No. 04-0839). Furthermore, based on NiCoSe material, NiCo... 0.7 Cu0.3 The slight enhancement of the peak intensity of each Se diffraction peak indicates that the doping of copper ions did not cause any change in the crystal structure and phase composition of the nickel-cobalt bimetallic selenide.

[0076] Figure 6 The image shows a scanning electron microscope (SEM) image of the NiCoSe material prepared in Comparative Example 1 of this invention. As can be seen from the image, the undoped NiCoSe material exhibits a rhombic nanosheet structure with a rough surface and a nanosheet thickness of approximately 0.38 micrometers.

[0077] Figure 7 The NiCo prepared in Example 3 of this invention 0.7 Cu 0.3 Scanning electron microscope (SEM) images of NiCoSe materials show that, compared to undoped NiCoSe, the copper-doped NiCoSe material exhibits significantly higher yields. 0.7 Cu 0.3 The Se sample exhibits an ultrathin rhombic nanosheet structure with stacked layers. The doping of copper ions reduces the thickness of the original nanosheet structure to about 0.05 micrometers, promotes the increase of the specific surface area of ​​the material, and increases the number of active sites, thus showing better capacitance performance.

[0078] Figure 8 The NiCo prepared in Example 3 of this invention 0.7 Cu 0.3 The X-ray energy dispersive spectroscopy (EDS) of Se material shows that Ni, Co, Cu, and Se are uniformly distributed, indicating that NiCo... 0.7 Cu 0.3 Successful preparation of Se nanosheet materials.

[0079] It should be understood that the above description of the preferred embodiments of the present invention is quite detailed and should not be construed as limiting the scope of protection of the present invention.

Claims

1. A method for preparing a rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide material, characterized in that: The ligand, surfactant, nickel salt, cobalt salt, and copper salt are mixed with solvent and placed in a microwave COD digester for microwave-assisted solvothermal reaction to obtain a copper-doped nickel-cobalt MOF precursor. The copper-doped nickel-cobalt MOF precursor and selenite are placed downstream and upstream of a tube furnace, respectively, and selenization reaction is carried out under a protective atmosphere to obtain the final product. The molar ratio of the nickel salt, cobalt salt, and copper salt is 1:0.5~0.9:0.5~0.1; During the microwave-assisted solvothermal reaction, the power of the microwave COD digester is controlled at 350~550W and the reaction time is 10~30min. The selenization reaction process is as follows: the temperature is increased to 300-400℃ at a heating rate of 1-5℃ / min and reacted for 1-2 hours.

2. The method for preparing a rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide material according to claim 1, characterized in that: The ligands include terephthalic acid and / or trimesic acid; The surfactant includes polyvinylpyrrolidone and / or polyethylene glycol; The molar ratio of the ligand to the nickel salt is 2~4:1; The mass ratio of the surfactant to the nickel salt is 3~7:

1.

3. The method for preparing a rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide material according to claim 1, characterized in that: The solvent includes DMF, ethanol and water; the volume ratio of DMF, ethanol and water is 2~4:3~1:1~2.

4. The method for preparing a rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide material according to claim 1, characterized in that: The mass ratio of the selenite to the copper-doped nickel-cobalt MOF precursor is 5~10:1; The selenite includes at least one of sodium selenite, sodium hydrogen selenite, potassium selenite, and zinc selenite.

5. The method for preparing a rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide material according to claim 1 or 4, characterized in that: The protective atmosphere is a nitrogen atmosphere.

6. A rhombic nanosheet-shaped copper-doped nickel-cobalt transition metal selenide material, characterized in that: Prepared by the method described in any one of claims 1 to 5.

7. The rhombic nanosheet copper-doped nickel-cobalt transition metal selenide material according to claim 6, characterized in that: The chemical formula for the copper-doped nickel-cobalt transition metal selenide is NiCo. x Cu x Se, where x = 0.5~0.9, y = 0.5~0.1, and x+y=1.

8. The application of the rhombic nanosheet copper-doped nickel-cobalt transition metal selenide material as described in claim 6 or 7, characterized in that: As an electrode material for supercapacitors.

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