High-entropy porous tungstate for monoclinic phase supercapacitor electrodes and methods of making

Abstract

The application discloses a high-entropy porous tungstate for a monoclinic phase supercapacitor electrode and a preparation method thereof, and belongs to the technical field of supercapacitor electrode material preparation. The method comprises the following steps: dissolving an organic acid and ethylene glycol in water; adding at least five transition group metal inorganic salts and ammonium metatungstate into the solution according to a:b:...:d:e:1 molar ratio, and stirring uniformly to obtain a precursor solution; gradually heating the precursor solution to a dry gel state, and then heating and calcining; after the calcination is completed and natural cooling is performed, a high-entropy porous tungstate is obtained. The preparation method is suitable for preparing high-entropy porous tungstates with different chemical compositions, and has certain universal applicability. The application has the advantages of simple operation, remarkable effect, single phase of the prepared high-entropy porous tungstate, and good electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of supercapacitor electrode material preparation, and particularly relates to a high-entropy porous tungstate for monoclinic supercapacitor electrodes and a preparation method thereof. Background Art

[0002] Supercapacitors, also known as electric double-layer capacitors, electrochemical capacitors, or farad capacitors, are a new type of energy storage device between traditional capacitors and batteries. As a highly efficient energy storage device, supercapacitors play a vital role in energy storage, electric vehicles, and electronic devices. They possess high power density, long cycle life, and rapid charge and discharge. They can rapidly store and release large amounts of electrical energy, providing instantaneous acceleration for electric vehicles, optimizing the performance of electronic devices, and enabling efficient energy storage and conversion in energy management systems. They are a key force in promoting green energy and sustainable development technologies. Helmholtz discovered the properties of the electric double layer in 1879, and Becker patented the capacitor in 1957, marking the beginning of supercapacitors' true application in energy storage. Electrode materials are a key factor in determining supercapacitor performance. Commonly used supercapacitor electrode materials fall into three main categories: carbon-based materials, metal oxides and hydroxides, and conductive polymers. However, these electrode materials still have some shortcomings or limitations, such as weak conductivity, poor structural stability, high preparation costs, and significant environmental impact. These limitations hinder the performance and widespread application of supercapacitors.

[0003] Currently, tungstate materials have become a research hotspot for supercapacitor electrode materials due to their high energy density, low cost, stable physical and chemical properties, environmental friendliness, and excellent electrochemical performance. Amir et al. summarized the research progress of tungstate supercapacitor materials [Amir Mohammad Sorouri, et al. Metal tungstates nanostructures for supercapacitors: A review. Applied Materials Today, 2023, 32]. In recent years, inspired by high-entropy alloys, a new type of supercapacitor cathode material has emerged: nano-high-entropy porous oxides. Their higher degree of disorder means improved chemical stability. In addition, due to the synergistic and cocktail effects between the multiple metal elements in their structure, high-entropy porous oxides have better ion diffusion characteristics and simpler phase transition processes, resulting in improved specific capacity and electrochemical performance compared to single porous oxides. If high-entropy tungstates can be obtained by applying these ideas, not only can chemical stability be improved, but the performance characteristics of single elements can also be combined to obtain high-energy-density supercapacitor cathode materials. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art and provide a high-entropy porous tungstate for use in monoclinic supercapacitor electrodes and its preparation method. The present invention uses a transition metal inorganic salt, ammonium metatungstate, an organic acid, and ethylene glycol as raw materials and optimizes high-temperature solid-phase calcination parameters to prepare a monoclinic high-entropy porous tungstate material.

[0005] The specific technical solutions adopted in the present invention are as follows:

[0006] In a first aspect, the present invention provides a method for preparing a high-entropy porous tungstate for a monoclinic supercapacitor electrode, as follows:

[0007] S1: dissolving organic acid and ethylene glycol in water;

[0008] S2: adding at least five transition metal inorganic salts and ammonium metatungstate to the solution obtained in S1 in a molar ratio of a:b:…:d:e:1, and stirring uniformly to obtain a precursor solution; wherein a+b+…+d+e=1, and a, b,…, d, and e are the molar numbers of transition metals in the different transition metal inorganic salts;

[0009] S3: gradually heating the precursor solution to a dry gel state, and then heating and calcining;

[0010] S4: After calcination is completed and naturally cooled, a high-entropy porous tungstate is obtained.

[0011] Preferably, the organic acid is one of succinic acid, citric acid, oxalic acid, and ascorbic acid, or a mixture of two or more thereof.

[0012] Preferably, in the precursor solution, the molar ratio of the organic acid, ethylene glycol and ammonium metatungstate is (1-4):(2-8):(1-5).

[0013] Preferably, the inorganic salt of transition metal is one of nitrate, carbonate, acetate and chloride.

[0014] Preferably, there are five transition metal inorganic salts.

[0015] Preferably, the gradual heating and temperature raising operation is achieved by a thermostatic mixer; the rotation speed of the thermostatic mixer is 500 rpm, first heating at 80-120°C for 0 to 10 hours, then heating at 200-280°C for 2 to 10 hours, and finally heating at 400°C for 1 hour.

[0016] Preferably, the heating and calcining is carried out in a muffle furnace under air atmosphere, with a heating temperature of 500 to 1200°C and a heating rate of 1-20°C min -1, the insulation time is 1-10 hours.

[0017] In a second aspect, the present invention provides a high-entropy porous tungstate obtained by any preparation method described in the first aspect.

[0018] Preferably, the high entropy porous tungstate has a monoclinic crystal form and does not contain a second phase, has a porous structure, and the material after phase and structure optimization exhibits electrochemical properties.

[0019] In a third aspect, the present invention provides an application of the high-entropy porous tungstate as described in the second aspect in a monoclinic supercapacitor electrode.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The high-entropy porous tungstate material obtained by this invention has a pure monoclinic crystal form and is free of secondary phases. After phase and structural optimization, the material exhibits excellent electrochemical performance. The high-entropy tungstate prepared by this invention exhibits favorable properties such as large specific surface area, controllable structural units, and a multi-level pore structure, making it suitable for use as supercapacitor electrode materials and catalysts. This invention avoids the presence of secondary phases during the composition design phase, and combined with the subsequent optimized high-temperature calcination reaction, it can effectively improve the efficiency of material preparation and research. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the XRD pattern of the single-phase monoclinic high-entropy porous tungstate positive electrode material prepared in Example 1.

[0023] Figure 2 This is a scanning electron microscope photograph of the single-phase monoclinic high-entropy porous tungstate positive electrode material prepared in Example 1.

[0024] Figure 3 This is a transmission electron microscope photograph of the single-phase monoclinic high-entropy porous tungstate positive electrode material prepared in Example 1.

[0025] Figure 4 This is the constant current charge-discharge curve of the single-phase monoclinic high-entropy porous tungstate positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0026] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0027] The present invention provides a method for preparing a high-entropy porous tungstate for a monoclinic supercapacitor electrode. The preparation method is specifically as follows:

[0028] S1: Dissolve the organic acid and ethylene glycol in deionized water in a certain proportion.

[0029] As a preferred embodiment of the present invention, in this step, the organic acid is one of succinic acid, citric acid, oxalic acid, and ascorbic acid, or a mixture of two or more thereof.

[0030] S2: adding at least five transition metal inorganic salts and ammonium metatungstate to the solution obtained in S1 in a molar ratio of a:b:…:d:e:1, and stirring uniformly to obtain a precursor solution; wherein, a+b+…+d+e=1, and a, b,…, d, e are the molar numbers of transition metals in different transition metal inorganic salts.

[0031] In a preferred embodiment of the present invention, the molar ratio of the organic acid, ethylene glycol, and ammonium metatungstate in the precursor solution of this step is (1-4):(2-8):(1-5). The inorganic transition metal salt is preferably one of nitrate, carbonate, acetate, and chloride. In this embodiment, there are five inorganic transition metal salts, but the number of inorganic transition metal salts can be increased as needed.

[0032] S3: gradually heating the precursor solution obtained in S2 to a dry gel state, and then heating and calcining.

[0033] As a preferred embodiment of the present invention, in this step, the gradual heating and temperature raising operation is achieved by a thermostatic mixer. Specifically, the speed of the thermostatic mixer is 500 rpm. The mixture is first heated at 80-120°C for 0 to 10 hours, then heated at 200-280°C for 2 to 10 hours, and finally heated at 400°C for 1 hour. The heating and calcining operation is carried out in a muffle furnace under air atmosphere, with a heating temperature of 500 to 1200°C and a heating rate of 1-20°C min -1 , the insulation time is 1-10 hours.

[0034] S4: After calcination is completed and naturally cooled, a high-entropy porous tungstate is obtained. In order to facilitate subsequent operations, the obtained material can be crushed.

[0035] Taking five transition metal inorganic salts as an example, the high entropy porous tungstate obtained by the above preparation method of the present invention has the general structural formula A a B b C c D d E e WO4, where A, B, C, D, and E are transition metal elements, a, b, c, d, and e are relative molar ratios, and a+b+c+d+e=1; the crystal form is monoclinic and does not contain a secondary phase, with a loose porous structure, and the nanoparticle diameter is between 20-200nm. After phase and structure optimization, the material exhibits electrochemical properties.

[0036] The preparation method and effects of the material of the present invention will be specifically described below through examples.

[0037] Example 1

[0038] 1) Take 0.4 mol of citric acid (C6H8O7) and 0.8 mol of ethylene glycol (C2H6O2) as reaction raw materials, add them to 100 mL of deionized water and mix well;

[0039] 2) Weigh 0.02 mol Fe(NO3)3, 0.02 mol Co(NO3)2, 0.02 mol Ni(NO3)2, 0.02 mol Cu(NO3)2, 0.02 mol Zn(NO3)2, and 0.1 mol ammonium metatungstate and add them to the solution obtained in step 1);

[0040] 3) gradually heating the solution obtained in step 2) and mixing it uniformly using a thermostatic mixer at a magnetic speed of 500 rpm, the temperature set to 80° C. and 280° C., the heating time being 10 and 3 hours, respectively, and finally heating at 400° C. for 1 hour to obtain a xerogel;

[0041] 4) The obtained dry gel was calcined in a muffle furnace at a heating rate of 5 °C min -1 The temperature is 500℃, the holding time is 3 hours, and after the calcination is completed and the product is naturally cooled, a wall breaking machine is used to break the product into powder to obtain high entropy porous tungstate.

[0042] 5) The prepared high-entropy porous tungstate material, polyvinylidene fluoride (PVDF) polymer binder, and conductive material Ketjenblack were mixed in a mass ratio of 1:1:8 and a small amount of solvent N-methylpyrrolidone (NMP) was added to make the concentration not less than 0.5 mol / L to form a uniform slurry. The slurry was then coated on an area of ​​1 cm × 1 cm of nickel foam and then dried at 80°C for 12 hours to form a working electrode.

[0043] The single-phase monoclinic high entropy porous tungstate cathode material prepared by this process has XRD patterns, scanning electron microscopy images, transmission electron microscopy and constant current charge-discharge curves at different magnifications as shown in the figure. Figures 1-4 As shown in the figure, the chemical composition of the material is Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2WO4, with a configurational entropy of 1.61R. The XRD pattern of the material shows that the crystal structure of the material is monoclinic, and no diffraction peaks of other phases are observed; scanning electron microscopy and transmission electron microscopy photos show that the material is composed of regular blocky particles with a particle size of about 20nm. The material is in the voltage range of 0-0.5V (vs.Hg / HgO), 0.5A g -1 The specific capacity at the current density is 385.2F g -1 When the current density increases to 20A g -1 , whose capacity is greater than 250F g -1 , showing good electrochemical performance.

[0044] Example 2

[0045] 1) Take 0.2 mol ascorbic acid (C6H8O6), 0.1 mol succinic acid (C4H6O4), and 0.5 mol ethylene glycol (C2H6O2) as the reaction raw materials, add them to 100 mL of deionized water and mix well;

[0046] 2) Weigh 0.01 mol Mn(NO3)2, 0.03 mol Fe(NO3)2, 0.02 mol Ni(NO3)2, 0.03 mol Cu(NO3)2, 0.01 mol AgNO3, and 0.1 mol ammonium metatungstate and add them to the solution obtained in step 1);

[0047] 3) gradually heating the solution obtained in step 2) and mixing it uniformly using a thermostatic mixer at a speed of 500 rpm and the temperature set to 100° C. and 250° C. for 3 hours respectively, and finally heating at 400° C. for 1 hour to obtain a xerogel;

[0048] 4) The obtained dry gel was calcined in a muffle furnace at a heating rate of 5 °C min -1 The temperature is 500℃ and the holding time is 6 hours. After the calcination is completed and the product is cooled naturally, a wall breaking machine is used to break the product into powder to obtain high entropy porous tungstate. The material composition is Mn 0.1 Fe 0.3 Ni 0.2 Cu 0.3 Ag 0.1 WO4, configuration entropy is 1.51R.

[0049] Example 3

[0050] 1) Take 0.4 mol of succinic acid (C4H6O4) and 0.7 mol of ethylene glycol (C2H6O2) as reaction raw materials, add them to 100 mL of deionized water and mix well;

[0051] 2) Weigh 0.01 mol Fe(OH)(CH3COO)2, 0.03 mol Co(CH3COO)2, 0.015 mol Ni(CH3COO)2, 0.025 mol Cu(CH3COO)2, 0.02 mol Zn(CH3COO)2, 0.1 mol ammonium metatungstate into the solution obtained in step 1);

[0052] 3) The solution obtained in step 2) is gradually heated and uniformly mixed using a constant temperature stirrer, the rotating speed is 500 rpm, the temperature is set to 80℃ and 240℃ respectively, and heated for 5 hours and 3 hours respectively, and finally heated at 400℃ for 1 hour to obtain a dry gel;

[0053] 4) The obtained dry gel is calcined in a muffle furnace, the heating rate is 10℃ / min -1 , the temperature is 800℃, and the holding time is 5 hours. After the calcination is completed and the product is naturally cooled, the product is broken into powder using a cell disruptor to obtain a high-entropy porous tungstate, the composition of the material is Fe 0.1 Co 0.3 Ni 0.15 Cu 0.25 Zn 0.2 WO4, and the configurational entropy is 1.54R.

[0054] Example 4

[0055] 1) Take 0.1 mol oxalic acid (H2C2O4), 0.2 mol ascorbic acid (C6H8O6), 0.3 mol citric acid (C6H8O7), and 0.8 mol ethylene glycol (C2H6O2) as reaction raw materials, and add them to 100 mL of deionized water and mix uniformly;

[0056] 2) Weigh 0.015 mol FeCl3, 0.015 mol CoCl2, 0.02 mol MnCl2, 0.015 mol CuCl2, 0.035 mol ZnCl2, and 0.1 mol ammonium metatungstate into the solution obtained in step 1);

[0057] 3) The solution obtained in step 2) is gradually heated and uniformly mixed using a constant temperature stirrer, the rotating speed is 500 rpm, the temperature is set to 200℃, and heated for 8 hours, and finally heated at 400℃ for 1 hour to obtain a dry gel;

[0058] 4) The obtained dry gel is calcined in a muffle furnace, the heating rate is 15℃ / min -1 , the temperature is 1000℃, and the holding time is 10 hours. After the calcination is completed and the product is naturally cooled, the product is broken into powder using a cell disruptor to obtain a high-entropy porous tungstate, the chemical composition of the material is Fe 0.15 Co0.15 Mn 0.2 Cu 0.15 Zn 0.35 WO4, configuration entropy is 1.54R.

[0059] Example 5

[0060] 1) Take 0.1 mol oxalic acid (H2C2O4), 0.2 mol ascorbic acid (C6H8O6), and 0.6 mol ethylene glycol (C2H6O2) as reaction raw materials, add them to 100 mL deionized water and mix well;

[0061] 2) Weigh 0.01 mol FeCl3, 0.02 mol CoCl2, 0.02 mol MnCl2, 0.015 mol CuCl2, 0.035 mol ZnCl2, and 0.1 mol ammonium metatungstate and add them to the solution obtained in step 1);

[0062] 3) gradually heating the solution obtained in step 2) and mixing it uniformly using a thermostatic mixer at a speed of 500 rpm and the temperature set to 90° C. and 280° C. for 3 hours respectively, and finally heating it at 400° C. for 1 hour to obtain a xerogel;

[0063] 4) The obtained dry gel was calcined in a muffle furnace at a heating rate of 10 °C min -1 The temperature is 1200℃, the holding time is 8 hours, and after the calcination is completed and the product is cooled naturally, the product is broken into powder using a wall breaking machine to obtain high entropy porous tungstate. The material composition is Fe 0.1 Co 0.2 Mn 0.2 Cu 0.15 Zn 0.35 WO4, configuration entropy is 1.53R.

[0064] The preparation method of the present invention is applicable to the preparation of high-entropy porous tungstates with different chemical compositions and has certain universal applicability. The advantages of the present invention are simple operation, significant results, and the prepared high-entropy porous tungstate is a single phase and has good electrochemical properties.

[0065] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A method for preparing a high entropy porous tungstate for a monoclinic supercapacitor electrode, characterized in that: The details are as follows: S1: dissolving organic acid and ethylene glycol in water; S2: adding at least five transition metal inorganic salts and ammonium metatungstate to the solution obtained in S1 in a molar ratio of a: b: ...: d: e: 1, and stirring uniformly to obtain a precursor solution; wherein a + b + ... + d + e = 1, and a, b, ..., d, and e are the molar numbers of transition metals in the different transition metal inorganic salts; S3: gradually heating the precursor solution to a dry gel state, and then heating and calcining; S4: After calcination is completed and naturally cooled, high entropy porous tungstate is obtained; The stepwise heating operation is achieved by a thermostatic mixer; the rotation speed of the thermostatic mixer is 500 rpm, first heating at 80-120°C for 0 to 10 hours but the heating time is not 0, then heating at 200-280°C for 2 to 10 hours, and finally heating at 400°C for 1 hour; The heating and calcining is carried out in a muffle furnace under air atmosphere, with a heating temperature of 500 to 1200 °C and a heating rate of 1-20 °C min -1 , the insulation time is 1-10 hours.

2. The method for preparing a high entropy porous tungstate for a monoclinic supercapacitor electrode according to claim 1, wherein: The organic acid is one of succinic acid, citric acid, oxalic acid and ascorbic acid, or a mixture of two or more thereof.

3. The method for preparing a high entropy porous tungstate for a monoclinic supercapacitor electrode according to claim 1, wherein: In the precursor solution, the molar ratio of the organic acid, ethylene glycol and ammonium metatungstate is (1-4): (2-8): (1-5).

4. The method for preparing a high entropy porous tungstate for a monoclinic supercapacitor electrode according to claim 1, wherein: The inorganic salt of transition metal is one of nitrate, carbonate, acetate and chloride.

5. The method for preparing a high entropy porous tungstate for a monoclinic supercapacitor electrode according to claim 1, wherein: There are five kinds of transition metal inorganic salts.

6. A high entropy porous tungstate obtained by the preparation method according to any one of claims 1 to 5.

7. The high entropy porous tungstate according to claim 6, characterized in that The crystal form is monoclinic and does not contain a second phase. It has a porous structure. The material after phase and structure optimization exhibits electrochemical properties.

8. Use of the high entropy porous tungstate according to claim 6 in a monoclinic supercapacitor electrode.

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