CN114380336A

CN114380336A - Keggin type manganese tungstate with manganese center as well as preparation method and application thereof

Info

Publication number: CN114380336A
Application number: CN202111510985.9A
Authority: CN
Inventors: 傅志勇; 罗鹏; 梁振兴; 胡树枝
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2021-12-10
Filing date: 2021-12-10
Publication date: 2022-04-22
Anticipated expiration: 2041-12-10
Also published as: CN114380336B

Abstract

The invention discloses a Keggin type manganese tungstate with a manganese center and a preparation method and application thereof; the invention synthesizes the vacancy-deficient Keggin-type silicotungstic acid polyanion [ SiW ]₁₁O₃₉]^8‑A solution; adding salt to separate out the Keggin-deficient silicotungstic acid polyanion salt from the solution, filtering to obtain a precipitate, washing and drying in vacuum; reacting the vacancy Keggin-type silicotungstic acid polyanion salt and soluble divalent manganese salt in a solution to synthesize Keggin-type manganese tungstic acid polyanion; adding methanol to separate out Keggin type manganese tungstate polyanion salt from the solution, and filtering to obtain the Keggin type manganese tungstate polyanion saltPrecipitating, washing and vacuum drying. The polyanionic structure can prevent the disproportionation reaction of the trivalent manganese in an oxidation state, thereby ensuring the chemical stability of the oxidation state of active molecules of the positive electrolyte; the electrolyte is applied to the anode electrolyte of the water-based flow battery, and can obtain stable cycle performance.

Description

Keggin type manganese tungstate with manganese center as well as preparation method and application thereof

Technical Field

The invention belongs to the technical field of flow batteries; relates to the technical field of inorganic polyanion synthesis, in particular to Keggin type manganese tungstate with a manganese center and a preparation method and application thereof.

Background

With the increasing pressure and demand for energy worldwide, the traditional energy structures based on fossil fuels have raised a number of serious environmental problems. In recent decades, clean energy represented by solar energy and wind energy has been widely developed and utilized to overcome the problem of environmental pollution. The integration of large-scale intermittent energy sources (such as solar or wind energy) into the grid requires the design of energy storage systems for stable power supply. Among available energy storage solutions, Aqueous Redox Flow Batteries (ARFBs) have received much attention because of their advantages of high energy efficiency, long cycle life, deep charge and discharge, good safety, and the like. The Vanadium Redox Flow Battery (VRFB) is respectively provided with V^Ⅴ/V^ⅣAnd V^Ⅲ/V^ⅡAs an anode and cathode energy storage medium, the ARFBs are one of the most mature ARFBs at present, and a commercial demonstration project of megawatt-level energy storage capacity is realized. However, the problems of the scarce vanadium resource, the high price and the like are still important factors for limiting the popularization of the VRFB. Therefore, researchers are continuously trying to develop more suitable energy storage materials for flow batteries.

Compared with vanadium, manganese is an abundant element on earth 12 th, is abundant in resources, low in price and also has multiple valence states. In all valence states of manganese, the redox couple Mn^Ⅲ/Mn^ⅡHas a redox potential of up to 1.51V (vs. SHE), ratio V^Ⅴ/V^ⅣThe redox potential of the positive electrode is higher than 0.5V, and the positive electrode is an ARFBs positive electrode material with great potential. The main factor limiting the application of manganese in flow batteries is that trivalent manganese is unstable in aqueous solution and is easily disproportionated into divalent manganese ions and manganese dioxide. Manganese dioxide is insoluble in water and is precipitated from solution, and the manganese dioxide is deposited on an electrode to cause the problems of mass transfer obstruction, pressure drop increase, electrode passivation and the like, so that the irreversible attenuation of the capacity and power of the battery is caused. For disproportionation of trivalent manganeseTo respond to the problem, researchers have proposed some solutions. Fang-Qin Xue, Xin-Dong Wang et al reported the electrochemical reaction process of manganese sulfate as an active molecule on carbon felt, graphite felt, and the effect of acid concentration on the disproportionation of trivalent manganese (Investigation on the electrochemical process of the Mn (II)/Mn (III)) on redox flow batteries. Research shows that the increase of the acid concentration can shift the disproportionation reaction equilibrium of the trivalent manganese leftwards, thereby inhibiting the disproportionation reaction to a certain extent, and when the sulfuric acid concentration reaches 5M, the effect of inhibiting the disproportionation reaction is best. However, the high concentration of sulfuric acid greatly increases the viscosity of the electrolyte, increases the pumping work, and further reduces the energy efficiency of the flow battery. Further, the effect of merely increasing the acid concentration on the inhibition of the disproportionation reaction of trivalent manganese is not significant, and this method is not suitable for practical application of a flow battery. Therefore, the problem to be solved by the existing aqueous manganese-based flow battery is to provide a method for effectively inhibiting the disproportionation reaction of trivalent manganese in an aqueous solution.

Disclosure of Invention

Aiming at the defects in the prior art, the technical problem to be solved by the invention is how to inhibit the disproportionation reaction of trivalent manganese in water so as to obtain the reversible conversion of divalent and trivalent manganese on the flow battery. The invention aims to provide a preparation method of Keggin type manganese tungstate taking manganese as a center and application of the Keggin type manganese tungstate in a flow battery. Compared with the prior art, the Keggin type manganese tungstate provided by the invention can obtain stable solution state trivalent manganese, effectively inhibits disproportionation reaction of the trivalent manganese in an aqueous solution, and realizes application of manganese in a flow battery anode.

The method for preparing the Keggin-type manganese tungstate has the advantages of simple synthesis steps, high reaction yield and high purity of the prepared Keggin-type manganese tungstate. Experimental results show that the yield of the preparation method provided by the invention is about 93%, and the purity of the prepared Keggin type manganese tungstate is close to 100%.

The Keggin type manganese tungstate prepared by the invention comprises ammonium manganese tungstate and potassium manganese tungstate.

The purpose of the invention is realized by the following technical scheme:

a preparation method of Keggin type manganese tungstate with a manganese center comprises the following steps:

(1) synthesizing vacancy Keggin type silicotungstic acid polyanion [ SiW ]₁₁O₃₉]^8-A solution;

(2) introducing the vacancy Keggin type silicotungstic acid polyanion [ SiW ] in the step (1)₁₁O₃₉]^8-Adding excessive salt into the solution to enable the Keggin-deficient silicotungstic acid polyanion [ SiW ]₁₁O₃₉]^8-Separating out salt from the solution, filtering to obtain white precipitate, washing, and vacuum drying;

(3) the vacancy Keggin type silicotungstic acid polyanion [ SiW ] in the step (2)₁₁O₃₉]^8-The salt and soluble bivalent manganese salt react in solution to synthesize Keggin type manganese tungstate polyanion [ MnW ]₁₂O₄₀]^6-；

(4) Adding methanol into the solution obtained in the step (3) to prepare Keggin type manganese tungstic acid polyanion [ MnW ]₁₂O₄₀]^6-Separating out salt from the solution, filtering to obtain orange yellow precipitate, washing, and drying in vacuum to obtain the Keggin type manganese tungstate with a manganese center.

Preferably, the synthesis of the site-deficient Keggin-type silicotungstic acid polyanion [ SiW ] in the step (1)₁₁O₃₉]^8-The solution comprises the following steps:

(a) mixing Na₂SiO₃Dissolving in deionized water to obtain solution A;

(b) mixing Na₂WO₄·2H₂Dissolving O in boiling water to obtain a solution B; dropwise adding hydrochloric acid into the solution B, and stirring to obtain a solution C;

(c) adding the solution A into the solution C, then adding hydrochloric acid, and adjusting the pH value of the solution to 5-6; the mixed solution was boiled, then cooled to room temperature and filtered to obtain a clear solution.

Further preferably, Na is contained in the solution A in the step (a)₂SiO₃The concentration of (A) is 0.8-1 mol/L;

further preferably, Na is contained in the solution B in the step (B)₂WO₄·2H₂The concentration of O is 1.7-1.9 mol/L; the saltThe concentration of the acid is 0.4-0.5mol/L, and the dosage is 0.4-0.6 time of that of the solution B;

further preferably, the boiling time of step (c) is 1-2 h;

further preferably, the Na₂SiO₃And Na₂WO₄·2H₂The molar ratio of O is 1:6-1: 6.2.

Preferably, the salt in the step (2) is potassium chloride or ammonium chloride; the amount of salt is at least added to the extent that precipitates are formed and at most to the saturation concentration of the salt.

Preferably, the washing in the step (2) is carried out by using cold water washing at 4-6 ℃; the vacuum drying time is 12-24h, and the vacuum drying temperature is 50-60 ℃.

Preferably, the vacancy Keggin type silicotungstic acid polyanion [ SiW ] in the step (3)₁₁O₃₉]^8-The molar ratio of the salt to the soluble divalent manganese salt is 1:1-1.2: 1;

preferably, Keggin-deficient silicotungstic acid polyanion [ SiW ] in the solution in the step (3)₁₁O₃₉]^8-The molar concentration of the salt is 0.17-0.19 mol/L;

preferably, the solvent of the solution in the step (3) is water;

preferably, the soluble divalent manganese salt in the step (3) is manganese chloride or manganese nitrate;

preferably, the reaction in step (3) is boiling for 30-60 min.

Preferably, the adding amount of the methanol in the step (4) is 1.5-2 times of the volume of the solution; the washing uses a methanol-water mixed solution with the volume ratio of 2:1-1.5: 1; the vacuum drying operation time is 12-24 h;

preferably, the manganese-centered Keggin-type manganese tungstate salt of step (4) is further purified by recrystallization in water.

The molecular structure of the Keggin type manganese tungstate with the manganese center prepared by the preparation method comprises one central { MnO [ ({ MnO₄Tetrahedron and peripheral four corner-sharing connected W₃O₁₃Triple Metal Cluster of three of them { WO }₆And the octahedrons are connected in a common edge mode.

The Keggin type manganese tungstate with the manganese center is applied to preparation of positive electrolyte for a flow battery.

Dissolving Keggin type manganese tungstate (ammonium manganese tungstate or potassium manganese tungstate) and supporting electrolyte in deionized water, and fully stirring to prepare uniform solution serving as the positive electrolyte of the flow battery.

Preferably, the supporting electrolyte used in the positive electrode electrolyte is potassium chloride, sodium chloride or ammonium chloride, and the concentration is 1.0-2.0M.

Preferably, the Keggin-type manganese tungstate concentration at the manganese center in the positive electrolyte is 0.01-0.75M.

A flow battery is characterized in that the positive electrolyte of the flow battery is the aqueous solution of Keggin type manganese tungstate at the manganese center, the negative electrolyte is the aqueous solution of sulfonic acid viologen, potassium chloride, sodium chloride or ammonium chloride is used as supporting electrolyte, positive and negative electrodes are carbon felts, a current collector is a titanium sheet, and a diaphragm is a Nafion 212 membrane.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a method for effectively inhibiting disproportionation reaction of trivalent manganese in an aqueous solution. The Keggin type manganese tungstate with manganese as the center is synthesized for the first time, and the regular tetrahedron coordination environment provided by the rigid framework of the Keggin type manganese tungstate reduces the reactivity of trivalent manganese ions, so that the disproportionation reaction of trivalent manganese is effectively inhibited, stable solution state trivalent manganese is obtained, and the reversible redox reaction of divalent manganese and trivalent manganese on an electrode is realized. The invention solves the problems of mass transfer resistance, pressure drop increase, electrode passivation and the like caused by manganese dioxide deposition in the aqueous manganese-based flow battery, and provides a new idea for constructing the aqueous manganese-based flow battery with high stability and high performance.

Drawings

FIG. 1 shows Keggin-type ammonium manganese tungstate (NH) prepared in example 1 of the present invention₄)₆[MnW₁₂O₄₀]X-ray powder diffractogram of (a);

fig. 2 is a schematic structural diagram of the negative electrolyte active molecule sulfonic acid viologen employed in the examples of the present invention;

FIG. 3 shows an embodiment of the present inventionThe positive electrode electrolyte active molecule Keggin type ammonium manganese tungstate (NH) used in the examples₄)₆[MnW₁₂O₄₀]And a cyclic voltammogram of the active molecule sulfonic acid viologen of the negative electrolyte;

fig. 4 is a charging and discharging curve diagram of the flow battery in example 6 of the present invention with different turns;

fig. 5 is a graph of the charge-discharge cycle performance of the flow battery in example 6 of the invention.

Detailed Description

The present invention is specifically described below with reference to the drawings and examples, but the mode of carrying out the invention and the scope of protection are not limited to the following examples.

In the embodiment of the invention, sulfonic acid viologen serving as an active molecule of the cathode of the flow battery is matched with Keggin type manganese tungstate, and the molecular structure of the sulfonic acid viologen is shown in figure 2. Sulfonic acid viologen and (NH) were tested using cyclic voltammetry₄)₆[MnW₁₂O₄₀]Electrochemical behavior in neutral aqueous solution Using 1M KCl as supporting electrolyte, active molecule concentration 5mM, sweep rate 100mV s^-1. As shown in FIG. 3, (NH)₄)₆[MnW₁₂O₄₀]There is a reversible redox process at 0.75V (vs. she), corresponding to the transition between divalent and trivalent manganese; the sulfonic viologen has a reversible redox process at-0.39V (vs. she).

And respectively taking Keggin type manganese tungstate and sulfonic acid viologen as positive and negative active molecules to assemble the flow battery.

Example 1

Precursor vacancy Keggin type ammonium silicotungstate (NH)₄)₈[SiW₁₁O₃₉]The preparation of (1):

(1) 3.2964g (27mmol) Na were weighed in a beaker₂SiO₃30mL of deionized water was added and magnetically stirred until all dissolved to obtain solution A.

(2) 54.4252g (165mmol) Na were weighed in a beaker₂WO₄·2H₂And O, adding the mixture into 90mL of near-boiling deionized water, and magnetically stirring until the mixture is completely dissolved to obtain a solution B.

(3) 49.5mL of 4M hydrochloric acid was added dropwise to solution B, and vigorously stirred to dissolve the resulting white precipitate, giving solution C.

(4) Solution A was added to solution C, followed by the rapid addition of 15mL of 4M hydrochloric acid to adjust the pH of the solution to 5-6.

(5) The mixed solution was boiled for 1h, then cooled to room temperature and filtered to obtain a clear solution.

(6) To the resulting clear solution was added 55g NH₄And Cl, and stirring. To NH₄After the Cl solid is dissolved, white precipitate is slowly separated out of the solution, the solution is continuously stirred for 20min, filtered to obtain the white precipitate, the white precipitate is washed by 5mL of cold water with the temperature of about 6 ℃, and the white precipitate is dried for 12h in vacuum at the temperature of 45 ℃.

Keggin type ammonium manganese tungstate (NH)₄)₆[MnW₁₂O₄₀]The preparation of (1):

(1) 12.6825g (4.5mmol) (NH) were weighed in a beaker₄)₈[SiW₁₁O₃₉]25mL of deionized water was added and heated with stirring until completely dissolved.

(2) 0.7996g (4mmol) of MnCl were added to the solution₂·4H₂O, the solution quickly turned orange. The solution was boiled for 30min to ensure the reaction was complete.

(3) After cooling to room temperature, it was filtered to remove a small amount of insoluble impurities.

(4) Adding 50mL of methanol into the solution to separate out a reaction product from the solution, continuously stirring for 20min, filtering to obtain an orange yellow precipitate, washing with 10mL of methanol-water mixed solution with the volume ratio of 2:1, and vacuum drying for 12h to obtain a final product. Further purification can be achieved by recrystallization from water.

Using an X-ray diffractometer to measure Keggin type ammonium manganese tungstate (NH)₄)₆[MnW₁₂O₄₀]Powder X-ray diffraction (PXRD) tests were performed as shown in figure 1. Simulated PXRD patterns were calculated based on 200K X-ray single crystal diffraction data using MDI Jade 6.0 software. The results show that the test data and the simulation result are well matched, and the synthesized compound is proved to have higher phase purity.

Example 2

Front body defect Keggin type potassium silicotungstate K₈[SiW₁₁O₃₉]The preparation of (1):

(6) To the resulting clear solution was added 50g of KCl, and stirred. After the KCl solid is dissolved, slowly separating out white precipitate from the solution, continuously stirring for 20min, filtering to obtain white precipitate, washing with 5mL of cold water at about 6 ℃, and vacuum drying at 45 ℃ for 12 h.

Keggin type potassium manganese tungstate K₆[MnW₁₂O₄₀]The preparation of (1):

(1) 13.4381g (4.5mmol) K were weighed in a beaker₈[SiW₁₁O₃₉]25mL of deionized water was added and heated with stirring until completely dissolved.

(2) 0.7996g (4mmol) of MnCl were added to the solution₂·4H₂O, the solution quickly turned orange-red. The solution was boiled for 30min to ensure the reaction was complete.

Example 3

Limited by K₆[MnW₁₂O₄₀]Solubility in water, low concentration batteries were assembled to verify [ MnW₁₂O₄₀]^6-Availability as positive active molecules for flow batteries.

Pretreating a Nafion-212 membrane: the Nafion-212 membrane is soaked in 1M KOH aqueous solution, heated at 80 ℃ for 12h and then soaked in deionized water for standby.

K with a concentration of 0.01M₆[MnW₁₂O₄₀]The aqueous solution is used as the positive electrolyte of the flow battery, the sulfonic acid viologen aqueous solution with the concentration of 0.01M is prepared as the negative electrolyte of the flow battery, 1M KCl is used as the supporting electrolyte of the positive electrolyte and the negative electrolyte, and the area is 3 multiplied by 3cm²The carbon felt is used as the positive electrode and the negative electrode of the flow battery, the metal titanium plate is used as the current collector of the flow battery, the Nafion-212 ion exchange membrane is used as a battery diaphragm, the stainless steel end plate, the current collector, the electrode frame and the carbon felt electrode are assembled into a single cell stack according to a specific sequence, and electrolyte is conveyed by a peristaltic pump to circulate between an external liquid storage tank and the stack along a pipeline. [ Mn ] in positive electrode electrolyte during charging^ⅡW₁₂O₄₀]^6-Is oxidized to [ Mn^ⅢW₁₂O₄₀]^5-Reducing the sulfonic acid viologen in the negative electrolyte; [ Mn ] in the positive electrode electrolyte during discharge^ⅢW₁₂O₄₀]^5-Is reduced to [ Mn^ⅡW₁₂O₄₀]^6-And the purple essence of sulfonic acid in the electrolyte of the negative electrode is oxidized.

As shown in Table 1, at 10mA cm^-2A constant-current charge-discharge cycle test is carried out under the current density, the coulombic efficiency is 96.01%, the energy efficiency is 84.75%, and the cycle retention rate is 99.99%/turn.

Example 4

When the counter ion is ammonium ion, the solubility can be greatly improved. Flow cells of saturated concentration were assembled to examine at high concentration conditions [ MnW₁₂O₄₀]^6-Stability of (2).

Prepared to have a concentration of 0.75M (NH)₄)₆[MnW₁₂O₄₀]The aqueous solution is used as the positive electrolyte of the flow battery, and the sulfonic acid viologen aqueous solution with the concentration of 0.75M is prepared as the negative electrolyte of the flow battery. Since the positive electrode side has a sufficiently high concentration of NH₄ ⁺And no supporting electrolyte is additionally added into the electrolyte. To balance the osmotic pressure of the positive and negative electrolytes and to provide sufficient conductivity, 4.5M (NH)₄) Cl serves as a supporting electrolyte for the negative electrolyte. The adopted area is 3 multiplied by 3cm²The carbon felt is used as the positive electrode and the negative electrode of the flow battery, the metal titanium plate is used as the current collector of the flow battery, the Nafion-212 ion exchange membrane is used as a battery diaphragm, the stainless steel end plate, the current collector, the electrode frame and the carbon felt electrode are assembled into a single cell stack according to a specific sequence, and electrolyte is conveyed by a peristaltic pump to circulate between an external liquid storage tank and the stack along a pipeline. [ Mn ] in positive electrode electrolyte during charging^ⅡW₁₂O₄₀]^6-Is oxidized to [ Mn^ⅢW₁₂O₄₀]^5-Reducing the sulfonic acid viologen in the negative electrolyte; [ Mn ] in the positive electrode electrolyte during discharge^ⅢW₁₂O₄₀]^5-Is reduced to [ Mn^ⅡW₁₂O₄₀]^6-And the purple essence of sulfonic acid in the electrolyte of the negative electrode is oxidized.

As shown in Table 1, at 60mA cm^-2Constant current charging and discharging are carried out under the current density, and experimental results show that the coulombic efficiency of the flow battery is 99.98%, the energy efficiency is 71.29%, and the cycle retention rate is 99.28%/turn.

Example 5

Study (NH)₄)₆[MnW₁₂O₄₀]Rate performance of sulfonic acid viologen flow batteries.

Prepared to have a concentration of 0.5M (NH)₄)₆[MnW₁₂O₄₀]The aqueous solution is used as the positive electrolyte of the flow battery, the sulfonic acid viologen aqueous solution with the concentration of 0.5M is prepared as the negative electrolyte of the flow battery, and 1M KCl is used as the positive and negative electrodesThe supporting electrolyte of the electrolyte solution has an area of 3 × 3cm²The carbon felt is used as the positive electrode and the negative electrode of the flow battery, the metal titanium plate is used as the current collector of the flow battery, the Nafion-212 ion exchange membrane is used as a battery diaphragm, the stainless steel end plate, the current collector, the electrode frame and the carbon felt electrode are assembled into a single cell stack according to a specific sequence, and electrolyte is conveyed by a peristaltic pump to circulate between an external liquid storage tank and the stack along a pipeline. [ Mn ] in positive electrode electrolyte during charging^ⅡW₁₂O₄₀]^6-Is oxidized to [ Mn^ⅢW₁₂O₄₀]^5-Reducing the sulfonic acid viologen in the negative electrolyte; [ Mn ] in the positive electrode electrolyte during discharge^ⅢW₁₂O₄₀]^5-Is reduced to [ Mn^ⅡW₁₂O₄₀]^6-And the purple essence of sulfonic acid in the electrolyte of the negative electrode is oxidized.

The assembled flow battery is arranged at 10, 20, 30 and 40mA cm^-2And carrying out a multiplying power test under the current density. As shown in Table 1, when the current density was 30mA cm^-2The coulombic efficiency was 99.39% and the energy efficiency was 61.14%.

Example 6

Study (NH)₄)₆[MnW₁₂O₄₀]Cycling stability of the sulfonic acid viologen flow battery at high current density.

Prepared to have a concentration of 0.5M (NH)₄)₆[MnW₁₂O₄₀]The aqueous solution is used as the positive electrolyte of the flow battery, the sulfonic acid viologen aqueous solution with the concentration of 0.5M is prepared as the negative electrolyte of the flow battery, 2M NaCl is used as the supporting electrolyte of the positive electrolyte and the negative electrolyte, and the area is 3 multiplied by 3cm²The carbon felt is used as the positive electrode and the negative electrode of the flow battery, the metal titanium plate is used as the current collector of the flow battery, the Nafion-212 ion exchange membrane is used as a battery diaphragm, the stainless steel end plate, the current collector, the electrode frame and the carbon felt electrode are assembled into a single cell stack according to a specific sequence, and electrolyte is conveyed by a peristaltic pump to circulate between an external liquid storage tank and the stack along a pipeline. [ Mn ] in positive electrode electrolyte during charging^ⅡW₁₂O₄₀]^6-Is oxidized to [ Mn^ⅢW₁₂O₄₀]^5-Reducing the sulfonic acid viologen in the negative electrolyte; [ Mn ] in the positive electrode electrolyte during discharge^ⅢW₁₂O₄₀]^5-Is reduced to [ Mn^ⅡW₁₂O₄₀]^6-And the purple essence of sulfonic acid in the electrolyte of the negative electrode is oxidized.

As shown in Table 1 and FIGS. 4 and 5, the current density was 60mA cm^-2Performing constant current charge-discharge circulation for 400 circles under the current density; experiment results show that the coulombic efficiency of the flow battery is 99.98%, the energy efficiency is 67.50%, and the cycle retention rate is 99.29%/turn.

The flow battery performance data for the above examples are shown below (table 1):

TABLE 1

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of Keggin type manganese tungstate with a manganese center is characterized by comprising the following steps:

(2) introducing the vacancy Keggin type silicotungstic acid polyanion [ SiW ] in the step (1)₁₁O₃₉]^8-Polyanion [ SiW ] of Keggin-deficient silicotungstic acid by adding salt into solution₁₁O₃₉]^8-The salt is separated out of the solution and filtered to obtain a precipitatePrecipitating, washing and vacuum drying;

(4) Adding methanol into the solution obtained in the step (3) to prepare Keggin type manganese tungstic acid polyanion [ MnW ]₁₂O₄₀]^6-Separating out salt from the solution, filtering to obtain precipitate, washing, and drying in vacuum to obtain the Keggin type manganese tungstate with a manganese center.

2. The method for preparing Keggin-type manganese tungstate with manganese center as claimed in claim 1, wherein the synthesis of the Keggin-deficient silicotungstic acid polyanion [ SiW ] in step (1)₁₁O₃₉]^8-The solution comprises the following steps:

(a) mixing Na₂SiO₃Dissolving in deionized water to obtain solution A;

3. The method of claim 2, wherein the solution A in step (a) contains Na₂SiO₃The concentration of (A) is 0.8-1 mol/L;

na in the solution B in the step (B)₂WO₄·2H₂The concentration of O is 1.7-1.9 mol/L; the concentration of the hydrochloric acid is 0.4-0.5mol/L, and the dosage of the hydrochloric acid is 0.4-0.6 time of the volume of the solution B;

the boiling time of the step (c) is 1-2 h;

the Na is₂SiO₃And Na₂WO₄·2H₂The molar ratio of O is 1:6-1:6.2。

4. The preparation method of manganese-centered Keggin-type manganese tungstate according to claim 1, wherein the salt in the step (2) is potassium chloride or ammonium chloride;

the washing is carried out by using cold water at 4-6 ℃; the vacuum drying time is 12-24h, and the vacuum drying temperature is 50-60 ℃.

5. The preparation method of Keggin-type manganese tungstate with manganese center as claimed in claim 1, wherein the Keggin-deficient silicotungstic acid polyanion [ SiW ] in step (3)₁₁O₃₉]^8-The molar ratio of the salt to the soluble divalent manganese salt is 1:1-1.2: 1;

keggin-deficient silicotungstic acid polyanion [ SiW ] in the solution₁₁O₃₉]^8-The molar concentration of the salt is 0.17-0.19 mol/L;

the solvent of the solution is water;

the soluble divalent manganese salt is manganese chloride or manganese nitrate;

the reaction is boiling for 30-60 min.

6. The preparation method of manganese-centered Keggin-type manganese tungstate according to claim 1, wherein the methanol in the step (4) is added in an amount of 1.5-2 times of the volume of the solution; the washing uses a methanol-water mixed solution with the volume ratio of 2:1-1.5: 1; the vacuum drying operation time is 12-24 h;

the Keggin-type manganese tungstate with the manganese center is further purified by recrystallization in water.

7. The manganese-centered Keggin-type manganese tungstate prepared by the preparation method of any one of claims 1 to 6, wherein the molecular structure contains one centered { MnO₄Tetrahedron and peripheral four corner-sharing connected W₃O₁₃Triple Metal Cluster of three of them { WO }₆And the octahedrons are connected in a common edge mode.

8. The use of the manganese-centered Keggin-type manganese tungstate of claim 7 in the preparation of a positive electrolyte for a flow battery.

9. The use according to claim 8, wherein the Keggin-type manganese tungstate concentration at the manganese center in the anolyte is 0.01-0.75M.

10. A flow battery, characterized in that, the positive electrolyte of the flow battery is the aqueous solution of Keggin type manganese tungstate of manganese center of claim 7, the negative electrolyte is the aqueous solution of sulfonic acid viologen, potassium chloride, sodium chloride or ammonium chloride is used as supporting electrolyte, the positive and negative electrodes are carbon felts, the current collector is titanium sheet, and the diaphragm is Nafion 212 membrane.