阅读说明：本技术 一种全钒液流电池电解液及其制备方法与应用 (All-vanadium redox flow battery electrolyte and preparation method and application thereof ) 是由 胡超 刘宏辉 董玉明 张伟 徐红彬 于 2021-10-14 设计创作，主要内容包括：本发明涉及一种全钒液流电池电解液及其制备方法与应用,所述制备方法包括如下步骤：(1)将钒的氧化物与硫酸进行混合,得到混合物；(2)将步骤(1)所得混合物进行活化,得到活化物；(3)将步骤(2)所得活化物进行溶解,得到含五价钒溶液；(4)向步骤(3)所得含五价钒溶液中通入氢气并加入催化剂,进行还原反应,得到所述全钒液流电池电解液。本发明采用水热还原法将五价钒氧化物还原制备低价态钒电解液,通过加热活化、对还原气体及反应条件调控,增加了五价钒溶解度,简化了制备工艺,降低生产成本。所述方法工艺简单,原料便宜,条件温和,环境友好、避免杂质引入、设备要求低等优势,适合用于全钒液流电池电解液的制备。(The invention relates to an all-vanadium redox flow battery electrolyte and a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) mixing vanadium oxide with sulfuric acid to obtain a mixture; (2) activating the mixture obtained in the step (1) to obtain an activated substance; (3) dissolving the activated substance obtained in the step (2) to obtain a solution containing pentavalent vanadium; (4) and (4) introducing hydrogen into the solution containing pentavalent vanadium obtained in the step (3), adding a catalyst, and carrying out reduction reaction to obtain the all-vanadium redox flow battery electrolyte. The method adopts a hydrothermal reduction method to reduce the pentavalent vanadium oxide to prepare the low-valence vanadium electrolyte, and increases the solubility of the pentavalent vanadium through heating and activating, regulating and controlling the reducing gas and reaction conditions, simplifies the preparation process and reduces the production cost. The method has the advantages of simple process, cheap raw materials, mild conditions, environmental friendliness, no impurity introduction, low equipment requirement and the like, and is suitable for preparing the electrolyte of the all-vanadium redox flow battery.)

1. The preparation method of the electrolyte of the all-vanadium flow battery is characterized by comprising the following steps of:

(1) mixing vanadium oxide with sulfuric acid to obtain a mixture;

(2) activating the mixture obtained in the step (1) to obtain an activated substance;

(3) dissolving the activated substance obtained in the step (2) to obtain a solution containing pentavalent vanadium;

(4) and (4) introducing hydrogen into the solution containing pentavalent vanadium obtained in the step (3), adding a catalyst, and carrying out reduction reaction to obtain the all-vanadium redox flow battery electrolyte.

2. The preparation method according to claim 1, wherein the molar ratio of the vanadium oxide to the sulfuric acid in the step (1) is 1 (1-4);

the concentration of the sulfuric acid in the step (1) is 12-18.4 mol/L;

the vanadium oxide of step (1) comprises vanadium pentoxide.

3. The method for preparing the compound of claim 1, wherein the temperature for activating in the step (2) is 50-300 ℃;

the activation time of the step (2) is 1-3 h.

4. The method according to claim 1, wherein the solvent for dissolution in step (3) comprises water or dilute sulfuric acid having a concentration of 2 to 6 mol/L;

the liquid-solid ratio of the solvent to the activator is 5-10 mL/g;

the dissolving temperature is 10-80 ℃;

the dissolving time is 0.5-3 h.

5. The method as claimed in claim 1, wherein the flow rate of the introduced hydrogen in step (4) is 160-1000 mL/min;

the hydrogen partial pressure of the reduction reaction in the step (4) is below 6 MPa.

6. The method of claim 1, wherein the catalyst of step (4) comprises any one of palladium-based, platinum-based, rhodium-based, or anthraquinone catalysts or a combination of at least two of them.

7. The method according to claim 1, wherein the temperature of the reduction reaction in step (4) is 50 to 180 ℃ and the time is 4 to 24 hours.

8. The method of claim 1, comprising the steps of:

(1) mixing vanadium pentoxide and 12-18.4mol/L concentrated sulfuric acid according to a molar ratio of 1 (1-4) to obtain a mixture;

(2) activating the mixture obtained in the step (1) for 1-3h at 50-300 ℃ to obtain an activated substance;

(3) dissolving the activator in the step (2) at 10-80 ℃ in 2-6mol/L dilute sulfuric acid with the solvent at 5-10mL/g and the dissolving time of 0.5-3h to obtain a solution containing pentavalent vanadium;

(4) adding a catalyst into the solution containing pentavalent vanadium in the step (3), and introducing hydrogen at the flow rate of 160-1000mL/min for reduction reaction to obtain the electrolyte of the all-vanadium redox flow battery; the temperature of the reduction reaction is 50-180 ℃, the time is 4-24h, and the hydrogen partial pressure of the reduction reaction is below 6 MPa; the catalyst comprises any one of palladium-based, platinum-based, rhodium-based or anthraquinone catalysts or a combination of at least two of the catalysts.

9. The all-vanadium redox flow battery electrolyte obtained by the preparation method according to any one of claims 1 to 8, wherein the average valence of vanadium in the all-vanadium redox flow battery electrolyte is 3 to 4, and the total concentration of vanadium ions in the all-vanadium redox flow battery electrolyte is 1.5 to 2 mol/L.

10. Use of the all-vanadium flow battery electrolyte according to claim 9, wherein the all-vanadium flow battery electrolyte is used in a flow battery.

Technical Field

The invention belongs to the technical field of electrochemistry, relates to a flow battery electrolyte, and particularly relates to an all-vanadium flow battery electrolyte as well as a preparation method and application thereof.

Background

Environmental concerns are driving the development and use of higher quality, higher quantities of renewable energy sources. However, due to the unstable nature of renewable energy sources, the Electrochemical Energy Storage (EES) is urgently needed for practical utilization in grid applications. The redox flow battery has the advantages of large energy capacity, high safety, flexible control of energy-power ratio and the like, and is a system with great prospect in EES application. Notably, all Vanadium Redox Flow Batteries (VRFB) are of great interest because of their high efficiency and long life without concern for cross contamination. However, despite these advantages, commercialization of VRFB is hampered due to expensive battery components. In particular, vanadium electrolytes account for a significant portion of the VRFB cost due to the need for expensive vanadium precursor materials and the high production costs of the electrolytes. For example, for a system of 10kW/120kWh, the vanadium electrolyte costs account for 40% and 41% of the total energy costs, respectively. Furthermore, the fraction of the total VRFB cost of electrolyte increases as the system energy capacity increases. Therefore, cost-effective VRFB electrolyte production must be developed to achieve wider acceptance of VRFB.

The cost of the electrolyte mainly comprises the cost of raw materials and the cost of preparation. At present, from V₂O₅Preparation of V⁴⁺The main methods for electrolytes and electrolytes of lower valence are chemical reduction and electrolysis. The chemical method is that the vanadium-containing compound is heated in sulfuric acid solution and added with reducing agent to generate tetravalent vanadium electrolyte, the method has fast reaction rate and simple method, but is easy to introduce impurities, and tetravalent vanadium ions are difficult to further reduce into low-valence electrolyte; although the electrolytic method can continuously prepare a large amount of high-concentration vanadium electrolyte, is simple to operate and easy for industrial production, the electrolytic method also has the defects of low speed, high equipment requirement, high energy consumption, high cost and the like.

WO 2013/056175a1 discloses a method for preparing an all vanadium redox flow battery electrolyte, wherein vanadium pentoxide is reduced into a tetravalent vanadium solution by a reducing agent, trivalent and pentavalent vanadium solutions are prepared by respectively placing the tetravalent vanadium solution on a positive electrode and a negative electrode and electrolyzing the tetravalent vanadium solution, and the pentavalent vanadium solution is reduced by the reducing agent for recycling. The method has complex process and introduces new impurities, which is not beneficial to preparing the high-purity vanadium electrolyte. CN 103066312A discloses a preparation method of an electrolyte for a vanadium redox flow battery, wherein vanadium pentoxide is activated by concentrated sulfuric acid and then prepared into the electrolyte by an electrolysis method. The invention uses a large amount of sulfuric acid to increase the cost, and a large amount of waste water is generated to increase the treatment cost. CN 104310475A and CN 103626230A both disclose a method for preparing vanadyl sulfate, wherein, vanadium pentoxide is added into dilute sulfuric acid, and a reducing agent is added after stirring, and vanadyl sulfate crystals are obtained after filtration and evaporative crystallization; in the latter, vanadium pentoxide is dissolved in oxalic acid solution, and then sulfuric acid is added to stir and roast, so as to obtain vanadyl sulfate powder. The preparation method has the advantages of complex process, high preparation cost and high reaction impurity.

In summary, the existing electrolyte preparation methods have the disadvantages of complex process flow, high production cost, environmental pollution, low purity and the like, so that it is necessary to find an electrolyte preparation process which is simple in process, low in production cost, environment-friendly and free of impurity introduction.

Disclosure of Invention

In view of the problems in the prior art, the invention provides the all-vanadium redox flow battery electrolyte and the preparation method and application thereof, the preparation method has the advantages of simple process, low production cost and environmental friendliness, the pentavalent vanadium is subjected to hydrothermal hydrogen reduction to obtain the low-valence vanadium electrolyte, the concentration of vanadium ions is increased by heating and activating, and regulating and controlling reducing gas and reaction conditions, the process flow is shortened, and the preparation process is simplified.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a preparation method of an all-vanadium redox flow battery electrolyte, which comprises the following steps:

(1) mixing vanadium oxide with sulfuric acid to obtain a mixture;

(2) activating the mixture obtained in the step (1) to obtain an activated substance;

(3) dissolving the activated substance obtained in the step (2) to obtain a solution containing pentavalent vanadium;

(4) and (4) introducing hydrogen into the solution containing pentavalent vanadium obtained in the step (3), adding a catalyst, and carrying out reduction reaction to obtain the all-vanadium redox flow battery electrolyte.

According to the preparation method of the all-vanadium redox flow battery electrolyte, provided by the invention, the all-vanadium redox flow battery electrolyte with the average valence state of vanadium being stabilized at 3-4 can be prepared by a hydrothermal hydrogen reduction method and by regulating and controlling the process steps of heating and activating, reducing gas, reaction conditions and the like.

Preferably, the molar ratio of the vanadium oxide to the sulfuric acid in step (1) is 1 (1-4), and may be, for example, 1:1, 1:1.5, 1:2, 1:3 or 1:4, but is not limited to the recited values, and other values not recited in the numerical range are also applicable, and are preferably 1 (2-4).

Preferably, the concentration of the sulfuric acid in the step (1) is 12-18.4mol/L, for example, 12mol/L, 14mol/L, 16mol/L, 18mol/L or 18.4mol/L, but not limited to the listed values, and other values not listed in the range of the values are also applicable.

Preferably, the vanadium oxide of step (1) comprises vanadium pentoxide.

Preferably, the mixing method of step (1) comprises stirring for 0.5h to 3h, for example, 0.5h, 1h, 1.5h, 2h or 3 h; the stirring temperature is 10-30 deg.C, for example 10 deg.C, 15 deg.C, 20 deg.C, 25 deg.C or 30 deg.C, but is not limited to the values listed, and other values not listed in the range of values are also applicable.

Preferably, the activation temperature in step (2) is 50-300 deg.C, such as 50 deg.C, 100 deg.C, 200 deg.C, 250 deg.C or 300 deg.C, but not limited to the values listed, and other values not listed in this range are equally applicable, preferably 100-200 deg.C.

Preferably, the activation time in step (2) is 1-3h, for example 1h, 1.5h, 2h, 2.5h or 3h, but not limited to the recited values, and other values not recited in the range of values are also applicable.

The vanadium oxide and the sulfuric acid react to generate the vanadium oxide in the activation process(VO₂)₂SO₄Activated (VO)₂)₂SO₄The solubility in water is higher, the subsequent reaction is accelerated, if the activation is not carried out, the subsequent reaction is directly dissolved, so that partial vanadium oxide exists in the solution in a solid form, the concentration of vanadium ions in the solution is lower, the hydrothermal hydrogen reduction process is slow, and the reaction is not facilitated.

Preferably, the solvent used in the dissolving process in the step (3) comprises water or dilute sulfuric acid with the concentration of 2-6 mol/L.

The concentration of the dilute sulfuric acid is 2 to 6mol/L, and may be, for example, 2mol/L, 3mol/L, 4mol/L, 5mol/L or 6mol/L, but is not limited to the recited values, and other values not recited in the numerical range are also applicable, and preferably 2 to 4 mol/L.

Preferably, the liquid-solid ratio of the solvent to the activator is 5-10mL/g, such as 5mL/g, 6mL/g, 7mL/g, 8mL/g, 9mL/g, or 10mL/g, but not limited to the recited values, and other values not recited in this range are equally applicable.

Preferably, the temperature of the dissolution in step (3) is 10-80 ℃, for example 10 ℃, 20 ℃, 30 ℃, 35 ℃, 40 ℃, 50 ℃, 55 ℃ or 80 ℃, but is not limited to the recited values, and other values not recited in the range of values are equally applicable, preferably 35-60 ℃.

Preferably, the dissolution time in step (3) is 0.5 to 3 hours, for example 0.5, 1, 1.2, 1.4, 1.6, 1.8 or 3 hours, but not limited to the recited values, and other values not recited in this range are equally applicable, preferably 1 to 2 hours.

Preferably, the flow rate of the introduced hydrogen in step (4) is 160-1000mL/min, such as 160mL/min, 300mL/min, 500mL/min, 800mL/min or 1000mL/min, but not limited to the listed values, and other non-listed values in the range are also applicable, preferably 300-600 mL/min.

Preferably, the partial pressure of hydrogen in the reduction reaction in step (4) is 6MPa or less, for example, 1MPa, 2MPa, 4MPa, 5MPa or 6MPa, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the catalyst of step (4) comprises any one or a combination of at least two of palladium-based, platinum-based, rhodium-based or anthraquinone catalysts, typical but non-limiting combinations include a combination of palladium-based catalyst and platinum-based catalyst, a combination of palladium-based catalyst and rhodium-based catalyst, a combination of palladium-based catalyst and anthraquinone catalyst, a combination of platinum-based catalyst and rhodium-based catalyst, a combination of platinum-based catalyst and anthraquinone catalyst, or a combination of rhodium-based catalyst and anthraquinone catalyst, preferably a palladium-based catalyst.

The catalyst provided by the invention has strong hydrogen adsorption capacity, for example, 1 volume of palladium-based catalyst can adsorb 700 volumes of hydrogen and dissociate the adsorbed hydrogen into activated hydrogen atoms. Meanwhile, the catalyst reduces the activation energy of the reaction, so that the reaction is carried out at a lower temperature.

Preferably, the temperature of the reduction reaction in step (4) is 50 to 180 ℃, for example 50 ℃, 80 ℃, 100 ℃, 150 ℃ or 180 ℃, but not limited to the recited values, and other values not recited in the range of values are equally applicable, preferably 60 to 120 ℃.

Preferably, the reduction reaction time in step (4) is 4-24h, such as 4h, 10h, 15h, 20h or 24h, but not limited to the recited values, and other values not recited in the range of values are also applicable, preferably 6-12 h.

In the invention, hydrogen is used as a reducing agent to reduce pentavalent vanadium ions in the solution to a low valence state. Passing V-H in the standard state₂The potential-pH diagram of the O system can show that the standard electrode potential of the hydrogen electrode is lower than that of the pentavalent vanadium reduced into tetravalent vanadium, and simultaneously lower than that of the tetravalent vanadium reduced into trivalent vanadium. Thermodynamically, the hydrogen gas can reduce pentavalent vanadium in solution to tetravalent vanadium, and subsequently to trivalent vanadium. In addition, compared with other organic reducing agents, the hydrogen gas is selected as the reducing agent, and the method has the advantages of cleanness and environmental protection.

As a preferable technical solution provided by the preparation method of the first aspect of the present invention, the preparation method comprises the steps of:

(1) mixing vanadium pentoxide and 12-18.4mol/L concentrated sulfuric acid according to a molar ratio of 1 (1-4) to obtain a mixture;

(2) activating the mixture obtained in the step (1) for 1-3h at 50-300 ℃ to obtain an activated substance;

(3) dissolving the activator in the step (2) at 10-80 ℃ in 2-6mol/L dilute sulfuric acid with the solvent at 5-10mL/g and the dissolving time of 0.5-3h to obtain a solution containing pentavalent vanadium;

(4) adding a catalyst into the solution containing pentavalent vanadium in the step (3), and introducing hydrogen at the flow rate of 160-1000mL/min for reduction reaction to obtain the electrolyte of the all-vanadium redox flow battery; the temperature of the reduction reaction is 50-180 ℃, the time is 4-24h, and the hydrogen partial pressure of the reduction reaction is below 6 MPa; the catalyst comprises any one of palladium-based, platinum-based, rhodium-based or anthraquinone catalysts or a combination of at least two of the catalysts.

In a second aspect, the invention provides the all-vanadium redox flow battery electrolyte obtained by the preparation method in the first aspect, wherein the average valence of vanadium in the all-vanadium redox flow battery electrolyte is 3-4, and the total concentration of vanadium ions in the all-vanadium redox flow battery electrolyte is 1.5-2 mol/L.

The average valence of vanadium in the all-vanadium flow battery electrolyte is 3-4, such as 3, 3.2, 3.4, 3.5, 3.8 or 4, but not limited to the listed values, and other values in the numerical range are also applicable, preferably 3.2-3.8.

The average valence state of vanadium provided by the invention is 3-4, and the all-vanadium redox flow battery electrolyte prepared by the method can be used for positive and negative electrodes or positive and negative electrode electrolytes.

The total concentration of vanadium ions in the electrolyte of the all-vanadium redox flow battery is 1.5-2mol/L, and can be, for example, 1.5mol/L, 1.6mol/L, 1.7mol/L, 1.8mol/L, 1.9mol/L or 2mol/L, but is not limited to the listed values, and other values not listed in the numerical range are also applicable.

In a third aspect, the invention provides a use of the all-vanadium flow battery electrolyte according to the second aspect, and the all-vanadium flow battery electrolyte is used for a flow battery.

Due to the adoption of the scheme, the invention has the following beneficial effects:

(1) the method greatly increases the concentration of pentavalent vanadium in the solution through the activation process of concentrated sulfuric acid, and is beneficial to shortening the reaction time;

(2) the method has the advantages that the hydrogen is directly introduced into the activated vanadium solution to be reduced to prepare the low-valence vanadium electrolyte, the process is simple, the hydrogen is used as a reducing agent, the process is clean, the introduction of new impurities is avoided, the use amount of sulfuric acid is reduced, the production cost is reduced, no waste liquid is generated in the process, and the method is environment-friendly;

(3) the reaction conditions involved in the invention are mild, and the requirement on equipment is low, so that the production cost is reduced;

(4) the reaction process of the preparation method is easy to control, and the vanadium electrolyte with the average valence of 3-4 can be prepared by controlling the reduction temperature, the hydrogen partial pressure and the reduction time. .

Drawings

Fig. 1 is a graph of the ultraviolet-visible absorption of the electrolyte of the all-vanadium flow battery provided in example 1.

Fig. 2 is a graph of the uv-vis absorption of the electrolyte of the all-vanadium flow battery provided in example 2.

Fig. 3 is a graph of the uv-vis absorption of the electrolyte of the all-vanadium flow battery provided in example 3.

Fig. 4 is a graph of the uv-vis absorption of the electrolyte of the all-vanadium flow battery provided in example 4.

Fig. 5 is a graph of the uv-vis absorption of the electrolyte of the all-vanadium flow battery provided in example 5.

Fig. 6 is a graph of the uv-vis absorption of the all vanadium flow battery electrolyte provided in example 6.

Fig. 7 is a graph of the uv-vis absorption of the all vanadium flow battery electrolyte provided in example 7.

Fig. 8 is a graph of the uv-vis absorption of the electrolyte of the all-vanadium flow battery provided in comparative example 2.

Fig. 9 is a graph of the uv-vis absorption of the electrolyte of the all-vanadium flow battery provided in comparative example 3.

Fig. 10 is a graph of the uv-vis absorption of the electrolyte of the all-vanadium flow battery provided in comparative example 4.

Detailed Description

The present invention will be described in further detail below with reference to the accompanying drawings by way of specific embodiments. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.

Example 1

The embodiment provides a preparation method of an all-vanadium redox flow battery electrolyte, which comprises the following steps:

(1) mixing vanadium pentoxide and concentrated sulfuric acid according to a molar ratio of 1:2.25, wherein the concentration of the concentrated sulfuric acid is 18.4mol/L, the stirring temperature is 25 ℃, and the stirring time is 0.5h to obtain a mixture;

(2) activating the mixture in the step (1) at the activation temperature of 150 ℃ for 2h to obtain an activated substance (VO)₂)₂SO₄Cooling to room temperature;

(3) activating the activated substance (VO) in the step (2)₂)₂SO₄Stirring and dissolving at 40 deg.C with 3mol/L solvent of dilute sulfuric acid, dilute sulfuric acid and activating substance (VO)₂)₂SO₄The liquid-solid ratio is 6mL/g, and the dissolving and stirring time is 1h to obtain a solution;

(4) adding a Pd/C catalyst (SZ 111-PDC, Siwa technologies Co., Ltd. in Beijing) into the solution obtained in the step (3), introducing hydrogen at a flow rate of 450mL/min, and carrying out a reduction reaction to obtain the all-vanadium redox flow battery electrolyte (see an ultraviolet visible absorption diagram in FIG. 1); the hydrogen partial pressure of the reduction reaction is 0.1MPa, the temperature of the reduction reaction is 120 ℃, and the reduction reaction time is 6 h.

Example 2

The embodiment provides a preparation method of an all-vanadium redox flow battery electrolyte, which comprises the following steps:

(1) mixing vanadium pentoxide and concentrated sulfuric acid according to a molar ratio of 1:2, wherein the concentration of the concentrated sulfuric acid is 12mol/L, the stirring temperature is 15 ℃, and the stirring time is 2.5 hours, so as to obtain a mixture;

(2) activating the mixture in the step (1) at the activation temperature of 100 ℃ for 2.5h to obtain an activated substance (VO)₂)₂SO₄Cooling to room temperature;

(3) activating the activated substance (VO) in the step (2)₂)₂SO₄Stirring and dissolving with the solvent of 2.5mol/L dilute sulfuric acid at 35 deg.C, dilute sulfuric acid and active substance (VO)₂)₂SO₄The liquid-solid ratio of (2) is 8mL/g, and the dissolving and stirring time is 2h to obtain a solution;

(4) adding a Pt/C catalyst (P816263-5 g, 10% Michelin) into the solution obtained in the step (3), and introducing hydrogen at a flow rate of 300mL/min to perform a reduction reaction to obtain the all-vanadium redox flow battery electrolyte (see an ultraviolet visible absorption diagram in FIG. 2); the hydrogen partial pressure of the reduction reaction is 0.05MPa, the temperature of the reduction reaction is 60 ℃, and the time of the reduction reaction is 12 h.

Example 3

The embodiment provides a preparation method of an all-vanadium redox flow battery electrolyte, which comprises the following steps:

(1) mixing vanadium pentoxide and concentrated sulfuric acid according to a molar ratio of 1:3, wherein the concentration of the concentrated sulfuric acid is 18.4mol/L, the stirring temperature is 20 ℃, and the stirring time is 1.5 hours, so as to obtain a mixture;

(2) activating the mixture in the step (1) at 200 ℃ for 1.5h to obtain an activated substance (VO)₂)₂SO₄Cooling to room temperature;

(3) activating the activated substance (VO) in the step (2)₂)₂SO₄Stirring and dissolving at 60 deg.C with 4mol/L solvent of dilute sulfuric acid, dilute sulfuric acid and activating substance (VO)₂)₂SO₄The liquid-solid ratio of (1) is 10mL/g, and the dissolving and stirring time is 1h to obtain a solution;

(4) adding an Rh/C catalyst (206164, Sigma-Aldrich) into the solution obtained in the step (3), and introducing hydrogen at the flow rate of 600mL/min to perform a reduction reaction to obtain the electrolyte of the all-vanadium redox flow battery (see the ultraviolet visible absorption chart in FIG. 3); the hydrogen partial pressure of the reduction reaction is 4MPa, the temperature of the reduction reaction is 120 ℃, and the reduction reaction time is 6 h.

Example 4

The embodiment provides a preparation method of an all-vanadium redox flow battery electrolyte, which comprises the following steps:

(1) mixing vanadium pentoxide and concentrated sulfuric acid according to a molar ratio of 1:1, wherein the concentration of the concentrated sulfuric acid is 18.4mol/L, the stirring temperature is 10 ℃, and the stirring time is 3 hours to obtain a mixture;

(2) activating the mixture in the step (1) at the activation temperature of 50 ℃ for 3h to obtain an activated substance (VO)₂)₂SO₄Cooling to room temperature;

(3) activating the activated substance (VO) in the step (2)₂)₂SO₄Stirring and dissolving at 10 deg.C with 2mol/L dilute sulfuric acid, dilute sulfuric acid and activating substance (VO)₂)₂SO₄The liquid-solid ratio of (1) is 5mL/g, and the dissolving and stirring time is 3h to obtain a solution;

(4) adding a Pd/C catalyst (SZ 111-PDC, Siwa Dasytech Co., Ltd. in Beijing) into the solution in the step (3), introducing hydrogen at a flow rate of 160mL/min, and carrying out reduction reaction to obtain the all-vanadium redox flow battery electrolyte (see an ultraviolet visible absorption diagram in fig. 4); the hydrogen partial pressure of the reduction reaction is 0.01MPa, the temperature of the reduction reaction is 50 ℃, and the time of the reduction reaction is 24 h.

Example 5

The embodiment provides a preparation method of an all-vanadium redox flow battery electrolyte, which comprises the following steps:

(1) mixing vanadium pentoxide and concentrated sulfuric acid according to a molar ratio of 1:4, wherein the concentration of the concentrated sulfuric acid is 18.4mol/L, the stirring temperature is 30 ℃, and the stirring time is 0.5h, so as to obtain a mixture;

(2) activating the mixture obtained in the step (1) at the activation temperature of 300 ℃ for 1h to obtain an activated substance (VO)₂)₂SO₄Cooling to room temperature;

(3) activating the activated substance (VO) in the step (2)₂)₂SO₄Stirring and dissolving at 80 deg.C with 6mol/L dilute sulfuric acid, dilute sulfuric acid and activating substance (VO)₂)₂SO₄The liquid-solid ratio of (1) is 10mL/g, and the dissolving and stirring time is 0.5h to obtain a solution;

(4) adding a Pd/C catalyst (SZ 111-PDC, Siwa Dasytech Co., Ltd. in Beijing) into the solution in the step (3), introducing hydrogen at the flow rate of 1000mL/min, and carrying out reduction reaction to obtain the all-vanadium redox flow battery electrolyte (see an ultraviolet visible absorption diagram in figure 5); the hydrogen partial pressure of the reduction reaction is 6MPa, the temperature of the reduction reaction is 180 ℃, and the reduction reaction time is 4 hours.

Example 6

This example provides a method for preparing an electrolyte for an all-vanadium redox flow battery, which is the same as example 1 except that in step (4), the hydrogen flow rate is reduced to 140mL/min, and the partial pressure of hydrogen in the reduction reaction is 0.008 MPa.

The ultraviolet-visible absorption chart of the electrolyte of the all-vanadium redox flow battery obtained in the embodiment is shown in fig. 6.

Example 7

This example provides a method for preparing an electrolyte for an all-vanadium redox flow battery, which is the same as example 1 except that in step (4), the hydrogen flow rate is increased to 1020mL/min, and the hydrogen partial pressure of the reduction reaction is 6.2 MPa.

The ultraviolet-visible absorption chart of the electrolyte of the all-vanadium redox flow battery obtained in the embodiment is shown in fig. 7.

Comparative example 1

The comparative example provides a preparation method of an all-vanadium redox flow battery electrolyte, and the preparation method comprises the following steps:

(1) mixing vanadium pentoxide and concentrated sulfuric acid according to a molar ratio of 1:2.25, wherein the concentration of the concentrated sulfuric acid is 18.4mol/L, the stirring temperature is 25 ℃, and the stirring time is 0.5h to obtain a mixture;

(2) stirring and mixing the mixture obtained in the step (1) and 3mol/L dilute sulfuric acid at 40 ℃, wherein the liquid-solid ratio of the dilute sulfuric acid to the mixture is 6mL/g, and the stirring time is 1h, so as to obtain a solution;

(3) adding a Pd/C catalyst (CAS: 7440-85-3) into the solution obtained in the step (2), and introducing hydrogen at the flow rate of 450mL/min to perform reduction reaction to obtain the electrolyte of the all-vanadium redox flow battery; the hydrogen partial pressure of the reduction reaction is 0.1MPa, the temperature of the reduction reaction is 120 ℃, and the reduction reaction time is 6 h.

Comparative example 2

The comparative example provides a preparation method of an all-vanadium redox flow battery electrolyte, and the method is the same as the method in the example 1 except that hydrogen sulfide is introduced at the flow rate of 450mL/min in the step (4), and the partial pressure of the hydrogen sulfide is 0.1MPa in the reduction reaction.

The ultraviolet-visible absorption chart of the electrolyte of the all-vanadium redox flow battery obtained in the comparative example is shown in FIG. 8.

Comparative example 3

The comparative example provides a preparation method of an all-vanadium redox flow battery electrolyte, and the method is the same as the method in the example 1 except that in the step (4), hydrogen is replaced by formic acid, the addition amount is 1.1 times of the theoretical amount of the required reducing agent, and the addition mode is one-time addition.

The ultraviolet-visible absorption chart of the electrolyte of the all-vanadium redox flow battery obtained in the comparative example is shown in FIG. 9.

Comparative example 4

The comparative example provides a preparation method of an all-vanadium redox flow battery electrolyte, and the method is the same as the method in the example 1 except that the hydrogen is replaced by the acetic acid in the step (4), the addition amount is 1.1 times of the theoretical amount of the required reducing agent, and the addition mode is one-time addition.

The ultraviolet-visible absorption chart of the electrolyte of the all-vanadium redox flow battery obtained in the comparative example is shown in FIG. 10.

The electrolyte of the all-vanadium redox flow battery obtained in the examples 1-7 and the comparative examples 1-4 and the battery prepared from the electrolyte of the all-vanadium redox flow battery according to GB/T37204 and 2018 are tested, the valence state and the concentration of vanadium ions in the electrolyte are measured by an ultraviolet visible spectrophotometer, the vanadium ion valence state and the concentration are shown in the attached figure, a blue electric test system is used for carrying out charge and discharge test on the battery, the charging platform is 1.7V, and the discharging platform is flatThe table is 0.8V at 50mA/cm²The current efficiency, voltage efficiency, and energy efficiency of the battery were tested, and the results are shown in table 1.

TABLE 1

Test number	Average valence state of vanadium ions in electrolyte	Current efficiency	Efficiency of voltage	Energy efficiency
					Example 1	3.5 valent	93.8%	88.3%	82%
Example 2	3.5 valent	94.6%	86.3%	83.5%
					Example 3	3.5 valent	94.2%	87.7%	83.4%
Example 4	Valence of 3.9	92.6%	85.6%	81.8%
					Example 5	Valence of 3.1	91.3%	84.6%	81.1%
Example 6	4.0 valence	86.5%	75.7%	73.4%
					Example 7	Valence of 3.0	86.2%	76.4%	72.5%
Comparative example 1	4.5 valent	—	—	—
					Comparative example 2	4.0 valence	85.2%	72.3%	71.5%
Comparative example 3	3.5 valent	82.1%	73.2%	70.5%
					Comparative example 4	3.5 valent	83.4%	74.6%	71.1%

From the above results, it can be seen that:

(1) from examples 1 to 5, it can be known that the method for preparing the all-vanadium redox flow battery electrolyte provided by the invention prepares the all-vanadium redox flow battery electrolyte with high vanadium ion solubility and excellent electrochemical performance by heating and activating, and regulating and controlling reducing gas and reaction conditions.

(2) As can be seen from the comparison between examples 6 and 7 and example 1, when the flow rate of the introduced hydrogen gas exceeds the preferable range of the present invention, the electrochemical performance of the electrolyte of the all-vanadium redox flow battery prepared in the same time is deteriorated, which indicates that the flow rate of the introduced hydrogen gas provided by the present invention is an important step in the preparation method, and the control of the flow rate of the hydrogen gas is helpful for preparing the electrolyte of the all-vanadium redox flow battery with high vanadium ion solubility and excellent electrochemical performance, and improves the reaction efficiency.

(3) As can be seen from comparison between comparative example 1 and example 1, when the activation step is not performed, the average valence of vanadium obtained by reduction is 4.5, and vanadium with valence of 4.5 cannot be used as an electrolyte of an all-vanadium redox flow battery, which illustrates that the activation step provided by the invention is an important step in the preparation method, and the activation step is an important step in the preparation method, so that the activation of the mixture is beneficial to preparing the electrolyte of the all-vanadium redox flow battery with high vanadium ion solubility and excellent electrochemical performance, and the reaction efficiency is improved.

(4) As can be seen from comparison of comparative example 2 with example 1, when replacing with other inorganic reducing gas such as hydrogen sulfide, which has the same reducibility as hydrogen, the electrochemical performance of the electrolyte of the all-vanadium redox flow battery is deteriorated and is easy to cause pollution, which indicates that the hydrogen provided by the invention is an important step in the preparation method as the reducing gas, which is helpful for preparing the electrolyte of the all-vanadium redox flow battery with high vanadium ion solubility and excellent electrochemical performance, and reduces environmental pollution.

(5) As can be seen from comparison of comparative examples 3 and 4 with example 1, when an organic reducing agent, such as formic acid or acetic acid, is replaced, the electrochemical performance of the electrolyte of the all-vanadium redox flow battery is deteriorated and is easily polluted, which indicates that the hydrogen provided by the invention is an important step in the preparation method as a reducing gas, which facilitates preparation of the electrolyte of the all-vanadium redox flow battery with high vanadium ion solubility and excellent electrochemical performance, and reduces environmental pollution.

Comprehensively, the method for preparing the vanadium electrolyte by adopting the hydrothermal hydrogen reduction method has simple process, avoids the introduction of new impurities, does not generate waste liquid in the process, has good environment friendliness, can conveniently and conveniently regulate and control the ratio of the valence state in the vanadium solution through subsequent reaction time, simplifies the preparation process and reduces the reaction conditions. The method has the advantages of simple process, cheap raw materials, mild conditions, environmental friendliness, no impurity introduction, low equipment requirement and the like, and is suitable for preparing the electrolyte of the all-vanadium redox flow battery.

The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.