A manganese vanadate nanomaterial, its preparation method and light-assisted capacity-enhancing application

Abstract

The invention discloses a manganese vanadate nanomaterial, a preparation method thereof, and a light-assisted capacity-enhancing application, belonging to the technical fields of electrochemistry, inorganic semiconductor materials, and solar energy utilization. The nanomaterial is prepared by a one-step low-temperature wet chemical method, and the prepared manganese vanadate has a layered stacked crystal structure, a grain size of less than 100nm, and can efficiently store photogenerated charges under illumination conditions and has a capacity-enhancing phenomenon. The technology of the invention solves the defect that the capacitance of traditional electrode materials cannot be increased once they are prepared, and can better utilize clean solar energy, and has broad application prospects in the field of new capacitors and optoelectronic devices.

Description

Technical Field

[0001] The invention relates to the technical fields of optics, inorganic semiconductor materials and electrochemical technology, and in particular to a manganese vanadate nanomaterial, a preparation method thereof and a light-assisted capacity-enhancing application thereof. Background Art

[0002] With the continuous consumption of fossil fuels and the intensification of environmental pollution, improving the electrochemical energy conversion and storage capacity is an important means to deal with the energy crisis. Supercapacitors, also known as electrochemical capacitors, are rapidly developing high-performance energy storage devices with advantages such as high power density, fast charge and discharge rate, and long cycle life. They have shown broad application prospects in the fields of digital communications, new energy vehicles, and microelectronic devices, and have become a hot spot of concern and research for more and more scientific researchers.

[0003] According to the principle of energy storage, supercapacitors can be divided into double-layer capacitors and pseudocapacitors. Among them, the electrode materials of double-layer capacitors are not electrochemically active, that is, the double layer is always formed and destroyed during the charging and discharging process, and there is only physical charge accumulation; while the electrode materials of pseudocapacitors are electrochemically active. This type of material uses reversible redox reactions on the electrode surface and near the surface to store energy. Recent studies have found that many semiconductor materials, such as WO3, Cu2O and V2O5, can be used as pseudocapacitor materials or as light absorption materials in photoelectrochemical systems, providing a good idea for the design of new electrode materials under multiple fields. In these electrode material systems, when the light absorption material is excited by light, photogenerated electrons and holes will be generated. If the photogenerated electrons and holes can be effectively utilized, it will be possible to adjust the behavior of the capacitor electrode to a certain extent and regulate its energy storage capacity.

[0004] At present, the systems that have been studied more for pseudocapacitive electrode materials are mainly metal hydroxides or oxides. These material systems can produce higher capacitance through reversible charge transfer reactions. However, these pseudocapacitive materials usually have insufficient absorption performance for visible light and cannot effectively capture solar energy. Therefore, it is necessary to develop a material with light absorption characteristics that better match the sunlight spectrum as an electrode material to promote the development of this field. Summary of the invention

[0005] The purpose of the present invention is to provide a manganese vanadate nanomaterial, a preparation method thereof and a light-assisted capacity-enhancing application. The nanomaterial is prepared by a one-step low-temperature wet chemical method. The prepared manganese vanadate has a layered stacked crystal structure with a grain size of less than 100 nm. It can efficiently store photogenerated charges under light conditions and has a capacity-enhancing phenomenon. The present invention solves the defect that the capacitance of traditional electrode materials cannot be increased once they are prepared, and can better utilize clean solar energy, and has broad application prospects in the field of new capacitors and optoelectronic devices.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A manganese vanadate nanomaterial. The manganese vanadate nanomaterial (Mn(VO3)2) is a pure phase material, a layered crystal structure material, a grain size of less than 100nm, preferably 30-90nm, which can better conduct and separate charges.

[0008] The bandgap width of the manganese vanadate nanomaterial is less than 3eV and can absorb sunlight in the ultraviolet and visible bands.

[0009] Under light conditions, the capacitance of the electrode assembled from manganese vanadate nanomaterials increases, and the capacity increase ratio is 10-400% (preferably 300-400%); specifically, under no light conditions, the capacitance of the manganese vanadate nanomaterial is between 40-50F / g; under light conditions, the capacitance of the manganese vanadate nanomaterial is between 160-180F / g.

[0010] After the electrode assembled by the manganese vanadate nanomaterial is irradiated with light for a period of time, the capacity increase can still be retained when the light is turned off, and the retention time is greater than 1 hour.

[0011] The manganese vanadate nanomaterial is synthesized in one step by a low-temperature wet chemical method, and the specific preparation includes the following steps:

[0012] (1) slowly adding an ammonium metavanadate (NH4VO3) solution into a manganese salt solution and mixing them evenly to obtain a precursor solution; the ammonium metavanadate solution is formed by dissolving ammonium metavanadate (NH4VO3) in water, and the concentration of the ammonium metavanadate solution is 0.05-0.5 mol / L; the manganese salt solution is formed by dissolving a manganese salt in water, and the concentration of the manganese salt solution is 0.05-0.5 mol / L; the manganese salt is one or more of manganese chloride, manganese sulfate, manganese carbonate, manganese nitrate and manganese acetate; in the precursor solution, the molar ratio of V element to Mn element is 1:1.

[0013] (2) Low temperature crystallization: the precursor solution is kept at 150-350°C for 1-10 hours (preferably 2-3 hours), and then naturally cooled to room temperature to obtain a suspension;

[0014] (3) Washing and drying: The suspension obtained in step (2) is centrifuged, and the separated powder is washed alternately with deionized water and anhydrous ethanol for 5-8 times, and then the washed powder is dried at 60° C. for 1-2 days to obtain the manganese vanadate nanomaterial (Mn(VO3)2).

[0015] The manganese vanadate nanomaterial is used in new supercapacitors under light fields and efficient utilization of solar energy.

[0016] The design mechanism of the present invention is as follows:

[0017] The present invention will design and synthesize a semiconductor material whose light absorption characteristics are more compatible with the solar spectrum. The material also has a variable valence element, which can better separate and store charges. In particular, the crystal growth is controlled so that the material has a layered stacked crystal structure, and the grain size is controlled at the nanometer level, so that it itself has the ability to efficiently separate photogenerated electrons and holes. When it is used as an electrode material, under illumination, the photogenerated carriers are separated and act on the electrochemical redox reaction of charging and discharging. The above characteristics deepen the degree of redox to a certain extent, thereby improving energy conversion and charge storage efficiency, and achieving the effect of light-assisted energy storage. Finally, the stored charge can also slowly release the charge under the condition of illumination and electric field withdrawal, so that its capacity increase effect can be maintained for a long time.

[0018] The advantages of the present invention are:

[0019] 1. The present invention adopts a simple low-temperature wet chemical method to synthesize high-purity small-particle nanomaterials at a lower temperature and in a shorter time using safer raw materials.

[0020] 2. The manganese vanadate material obtained by the present invention has the characteristics of both semiconductor material and electrode material, and can better utilize light energy and electrical energy.

[0021] 3. The adoption of the technical means of the present invention achieves a significant increase in the specific capacitance of the electrode material under light conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the X-ray diffraction pattern of the pure phase manganese vanadate nanomaterial prepared in step (2) of Example 1.

[0023] Figure 2 This is the UV-visible absorption spectrum of the pure phase manganese vanadate nanomaterial in Example 1.

[0024] Figure 3 1 is a cyclic voltammetry curve of the pure phase manganese vanadate nanomaterial in Example 1 under dark and light conditions.

[0025] Figure 4 This is a cyclic voltammetry curve of the pure phase manganese vanadate nanomaterial in Example 1 after 30-240 minutes of illumination.

[0026] Figure 5 This is the impedance diagram of the pure phase manganese vanadate nanomaterial in Example 1 under dark and light conditions. DETAILED DESCRIPTION

[0027] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0028] The present invention adopts a wet chemical synthesis method to synthesize a small-grain-size pure-phase manganese vanadate nanomaterial in one step. The nano semiconductor material has a certain absorption in the range of ultraviolet to visible light. After being made into an electrode, the capacitance of the electrode sheet under light conditions can be significantly increased compared with that without light.

[0029] In the following examples, the performance test of the prepared working electrode is carried out in a three-electrode system, where a full-spectrum light source is used to irradiate the electrode material to test the electrochemical performance of the material.

[0030] Example 1

[0031] In this embodiment, manganese vanadate nanomaterials were prepared and used as working electrodes. The specific process is as follows:

[0032] (1) Preparation of precursor solution: 0.01 mol of MnCl2 was dissolved in 50 mL of deionized water and stirred to dissolve to form a manganese chloride solution. 0.01 mol of NH4VO3 was dissolved in 50 mL of deionized water to form an ammonium metavanadate solution. The NH4VO3 solution was then slowly added dropwise to the MnCl2 solution while stirring to form a precursor solution.

[0033] (2) Solvothermal synthesis: 100 mL of the precursor solution was evenly divided into two portions, and each portion was transferred into a polytetrafluoroethylene hydrothermal autoclave of the same volume. The autoclave was placed in a forced air drying oven at 200 °C for 2.5 h to obtain a mixed suspension.

[0034] (3) Washing and drying: The mixed suspension is taken out and placed in a centrifuge tube, and centrifuged at a rate of 10,000 r / min for 5 minutes. After centrifugation, the supernatant is taken out, deionized water or anhydrous ethanol is added, and the residual reactants are removed by ultrasonic washing. The mixture is washed with deionized water for 3 to 5 times and with anhydrous ethanol for 2 to 3 times, and finally dried at 60° C. for 12 hours to obtain the manganese vanadate nanomaterial.

[0035] (4) Electrode preparation: The titanium foil was cleaned with acetone, 10 vol.% nitric acid, deionized water and anhydrous ethanol in sequence to remove surface oxides, oil stains and other impurities, and then dried in a vacuum drying oven at 60°C for 1-2 days; manganese vanadate nanomaterials were ground and mixed with acetylene black and PVDF in a weight ratio of 8:1:1, and then N-methylpyrrolidone was added and the mixture was stirred for 15 hours to prepare an electrode slurry; the electrode slurry was applied to the titanium foil electrode substrate by spin coating, and dried in a forced air drying oven at 60°C for 12 hours to prepare a working electrode.

[0036] Figure 1 The XRD pattern of the pure phase manganese vanadate nanomaterial prepared in step (3) of this embodiment is shown in Figure 1. According to analysis, the grain size of the prepared manganese vanadate nanomaterial is about 30-90 nm.

[0037] Figure 2 The ultraviolet-visible absorption spectrum of the pure phase manganese vanadate nanomaterial obtained in step (3) of this embodiment is shown in FIG. Figure 2 It can be seen that the light absorption range of the prepared pure phase manganese vanadate nanomaterial is 400-800nm, and it has strong absorption in the visible light range.

[0038] Figure 3 The cyclic voltammetry curves of the working electrode made of the pure phase manganese vanadate nanomaterial prepared in step (4) of this embodiment tested in a 0.5 mol / L KOH electrolyte solution under dark and light conditions are shown in FIG. Figure 3 It can be seen that the capacitance of the working electrode made of manganese vanadate nanomaterials increases significantly under light irradiation. After calculation, the capacitance enhancement rate is 263.8%.

[0039] Figure 4 The cyclic voltammetry curve of the working electrode made of pure phase manganese vanadate nanomaterial prepared in step (4) of this embodiment is tested in a 0.5 mol / L KOH electrolyte solution 30-240 minutes after light exposure. Figure 4 It can be seen that after illumination, manganese vanadate still slowly releases charge 4 hours after the light and electric field are removed, so that the capacity increase effect can be maintained for a long time. After 4 hours of stopping the illumination, compared with the specific capacitance when there is no illumination, there is still an enhancement rate of 54.85%.

[0040] Figure 5 The impedance diagram of the working electrode made of the pure phase manganese vanadate nanomaterial prepared in step (4) of this embodiment tested in a 0.5 mol / L KOH electrolyte solution under dark and light conditions shows that the charge transfer resistance of the manganese vanadate electrode is significantly reduced under light, which is beneficial to the charge transfer reaction.

[0041] The above embodiments are for reference only. Electrode materials with light-assisted energy storage behavior that are similar to this patent or extended from the concept of this patent and their preparation methods and applications are all within the scope of protection of this patent.

Claims

1. A manganese vanadate nanomaterial, characterized in that: The manganese vanadate nanomaterial is a layered crystal structure material with a grain size of 30-90nm; The bandgap width of the manganese vanadate nanomaterial is less than 3eV, and it can absorb sunlight in the ultraviolet and visible bands; Under light conditions, the capacitance of electrodes assembled from manganese vanadate nanomaterials increases, with the capacity increase ratio ranging from 10-400%.

2. The manganese vanadate nanomaterial according to claim 1, characterized in that: Under no-light conditions, the capacitance of the manganese vanadate nanomaterial is between 40-50 F / g; under light conditions, the capacitance of the manganese vanadate nanomaterial is between 160-180 F / g.

3. The manganese vanadate nanomaterial according to claim 1, characterized in that: After the electrode assembled from the manganese vanadate nanomaterial is irradiated with light for a period of time, the capacity increase can still be retained when the light is turned off, and the retention time is greater than 1 hour.

4. The method for preparing the manganese vanadate nanomaterial according to any one of claims 1 to 3, characterized in that: The manganese vanadate nanomaterial is synthesized in one step by a low-temperature wet chemical method.

5. The method for preparing the manganese vanadate nanomaterial according to claim 4, characterized in that: The method comprises the following steps: (1) slowly adding ammonium metavanadate (NH4VO3) solution into manganese salt solution and mixing well to obtain a precursor solution; (2) Low temperature crystallization: The precursor solution is placed at 150-350°C for 1-10 hours and then naturally cooled to room temperature to obtain a suspension; (3) Washing and drying: The suspension obtained in step (2) is centrifuged, and the separated powder is washed alternately with deionized water and anhydrous ethanol for 5-8 times, and then the washed powder is dried at 60° C. for 1-2 days to obtain the manganese vanadate nanomaterial (Mn(VO3)2).

6. The method for preparing the manganese vanadate nanomaterial according to claim 5, characterized in that: The ammonium metavanadate solution is formed by dissolving ammonium metavanadate (NH4VO3) in water, and the concentration of the ammonium metavanadate solution is 0.05-0.5 mol / L; the manganese salt solution is formed by dissolving a manganese salt in water, and the concentration of the manganese salt solution is 0.05-0.5 mol / L; the manganese salt is one or more of manganese chloride, manganese sulfate, manganese carbonate, manganese nitrate and manganese acetate.

7. The method for preparing the manganese vanadate nanomaterial according to claim 5, characterized in that: In the precursor solution, the molar ratio of V element to Mn element is 1:

1.

8. The light-assisted capacity-enhancing application of manganese vanadate nanomaterials according to claim 1, characterized in that: The manganese vanadate nanomaterial is used in new supercapacitors under light fields and efficient utilization of solar energy.

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