All-vanadium electrolyte, preparation method thereof and all-vanadium redox flow battery

Abstract

The invention discloses an all-vanadium electrolyte, a preparation method thereof and an all-vanadium redox flow battery, and belongs to the technical field of batteries. The method comprises the steps that S1, alkaline leaching treatment is conducted on the vanadium slag through an alkaline leaching agent, an alkaline leaching product is obtained, and a vanadium enrichment is separated out; s2, mixing the vanadium concentrate, a first ammonium salt and a first solvent for reaction II to obtain a vanadium precipitation product, and separating to obtain an ammonium vanadate-containing sediment; carrying out first calcining heat treatment on the mixture to obtain vanadium oxide; mixing the vanadium oxide with a first reducing agent and a second solvent for reaction III to obtain a first tetravalent vanadium-containing solution; and S3, under the action of a hydrogen evolution catalyst, the first tetravalent vanadium is subjected to a reaction IV, and a trivalent vanadium-containing solution is obtained. According to the method, all-vanadium electrolyte with different valence states can be efficiently extracted, vanadium slag solid waste resource utilization is achieved, the production cost is effectively reduced, and the environmental protection risk is reduced; and meanwhile, the vanadium ion reduction rate is increased by means of the hydrogen evolution electrocatalyst, other reducing agents are not introduced, and the operation safety and reliability are improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an all-vanadium electrolyte and a preparation method thereof, and an all-vanadium liquid flow battery. Background Art

[0002] The vanadium electrolyte preparation process of all-vanadium flow battery (VFB) has a significant impact on battery performance and service life. 4+ Restore to V 3+ The reaction kinetics of VFB are relatively slow, which leads to higher energy consumption in the preparation process, thereby increasing the production cost of vanadium electrolyte and limiting the development and commercial application of VFB.

[0003] Vanadium ions, as active substances in electrolytes, store and release electrical energy through changes in ion valence. There are three main methods for preparing vanadium electrolytes: physical, chemical and electrolytic. The raw materials are all high-purity VOSO4 or V2O5, which are expensive. Among them, the physical method is to directly dissolve high-purity VOSO4 in sulfuric acid to prepare vanadium electrolyte. The process is simple, but the price of high-purity VOSO4 is relatively high and the process economy is poor, which limits its large-scale industrial production. The chemical reduction method has the advantage of raw material cost when preparing low-concentration vanadium electrolytes, but the overall process is lengthy, and impurities are easily introduced into the electrolyte during the preparation process, resulting in low electrochemical activity of the prepared electrolyte, which is not conducive to the industrialization process. The electrolytic method uses V2O5 as the main raw material, and uses a diaphragm to divide the electrolytic cell of the battery stack into positive and negative electrode regions. A H2SO4 solution containing V2O5 is added to the negative electrode region and reduced to V 3+ or V 4+ The electrolysis process is simple, but the solubility of vanadium ions in the electrolyte is limited (especially when the temperature is higher than 40°C, V 5+ Easy to precipitate, when the temperature is below 10℃, V 2+ 、V 3+ 、V 4+ (easy to precipitate) and slow reaction rate limit its development. In summary, there are still many technical difficulties to be overcome in the preparation of vanadium electrolytes, such as the preparation, reduction, and electrolysis of high-purity vanadium oxides. The preparation process is lengthy and energy-intensive. In addition, the preparation of vanadium electrolytes using vanadium oxides as raw materials will produce high-salt wastewater, which puts great pressure on the environmental protection and makes large-scale production and application difficult. At present, some researchers have prepared vanadium electrolytes by adding hydrogen evolution platinum (Pt)-based electrocatalysts and have achieved certain results. However, the precious metal Pt is not only rare and has limited reserves, but also when Pt-based catalysts are used for catalytic reduction to prepare vanadium electrolytes, because they need to be immersed in acidic electrolytes, they must not only have a certain degree of corrosion resistance, but also have strong electrocatalytic activity, which limits their large-scale application.

[0004] The prior art proposes to use vanadium slag as raw material to prepare vanadyl sulfate electrolyte through a process combining "impurity removal, extraction-strip extraction, oil removal, and deep desalination by electrosorption". Although this method shortens the traditional process flow, there are some problems. The introduction of organic reagents in the extraction-strip extraction process may bring in additional impurities, thereby increasing the risk of electrolyte contamination. At the same time, the introduction of electrosorption desalination will result in a low recovery rate of vanadium in the vanadyl sulfate solution, which in turn leads to low preparation efficiency and high energy consumption.

[0005] The existing technology proposes to use ammonium vanadate compounds as raw materials, remove impurities by heating (>338°C) with an acidic (HCl+H2SO4) solvent, and dissolve the vanadium-containing compound under hot pressing after introducing a reducing agent, thereby preparing a vanadium-containing electrolyte. In the impurity removal step, this method avoids the addition of impurity removers and improves the purity of the treated material; however, during the high-temperature evaporation process, the heating temperature exceeds 300°C, which places extremely high requirements on the corrosion resistance and airtightness of the equipment; at the same time, high-temperature heating will also lead to high energy consumption.

[0006] The existing technology also proposes to use ammonium polyvanadate as raw material to prepare high-purity vanadium pentoxide through the method of "redissolution-crystallization-water dissolution-ammonium precipitation-calcination", but this method has a low crystallization temperature (2~5°C) and a long crystallization time (20~40h), which requires additional refrigeration equipment to maintain a low temperature environment, increasing equipment costs and energy consumption.

[0007] The prior art also proposes to use sodium vanadate solution as raw material and to prepare calcium vanadate solid by chemical precipitation. Under strong acidic conditions, a reduction reaction occurs with oxalic acid, and pentavalent vanadate ions are reduced to tetravalent oxyvanadium ions to form a tetravalent vanadium solution of oxyvanadium sulfate. At this time, calcium ions and sulfate ions form calcium sulfate precipitation, and a tetravalent vanadium solution is obtained by solid-liquid separation. The tetravalent vanadium solution is electrolyzed to obtain a 3.5-valent vanadium electrolyte. Although this method shortens the preparation process of the vanadium electrolyte to a certain extent, it consumes excessive sulfuric acid during the electrolysis process and produces a large amount of waste acid and acid mist, which not only increases the cost of raw materials, but also poses a risk of environmental pollution.

[0008] The prior art also proposes to reduce high-purity vanadium pentoxide under reducing gas to obtain low-valent vanadium oxide. The low-valent vanadium oxide is then mixed with an activator and heated for activation to obtain a vanadium-containing paste electrolyte. Finally, the vanadium paste electrolyte is dissolved by adding water to obtain a vanadium electrolyte with an average valence of vanadium ranging from positive trivalent to positive tetravalent. This method has certain advantages and is relatively fast and effective, but it still requires vanadium pentoxide as a reactant, is costly, and the method cannot accurately obtain a 3.5-valent vanadium oxysulfate electrolyte, which may be limited in some application scenarios that have strict requirements on the specific valence of the electrolyte.

[0009] In the existing technical method, vanadium oxide is used as the raw material for purification, and vanadium electrolyte is prepared through "activation-dissolution-catalytic reduction". The electrolyte prepared by this method has a high concentration, and compared with the "calcination-chemical reduction-electrochemical reduction" process, the process is short and the cost is low. However, in the catalytic reduction process, hydrogen is inevitably introduced as a reducing gas. On the one hand, storing hydrogen in gaseous form requires high-pressure containers or cryogenic storage tanks, which are accompanied by safety issues and high infrastructure costs; on the other hand, hydrogen is flammable and poses a safety hazard; because hydrogen is odorless and colorless, its flame is almost invisible, which makes leak detection challenging.

[0010] Therefore, a method for preparing a 3.5-valent vanadium electrolyte with a fast reduction rate and economical and efficient performance is an urgent problem to be solved in the all-vanadium liquid flow battery industry. Summary of the invention

[0011] The main purpose of the present application is to provide an all-vanadium electrolyte and a preparation method thereof and an all-vanadium liquid flow battery, so as to solve the problems of high cost, complex process and low reaction rate in the preparation of all-vanadium electrolyte in the prior art.

[0012] In order to achieve the above object, according to one aspect of the present application, a method for preparing an all-vanadium electrolyte is provided, comprising the following steps:

[0013] Step S1: using an alkaline leaching agent to perform an alkali leaching treatment on the vanadium slag to perform reaction I, to obtain an alkali leaching product, and the alkali leaching product is subjected to solid-liquid separation to obtain a vanadium enriched product and a filtrate;

[0014] Step S2: mixing the vanadium-enriched material, the first ammonium salt and the first solvent to carry out reaction II to obtain a vanadium precipitation product, and the vanadium precipitation product is subjected to solid-liquid separation to obtain a sediment containing ammonium vanadate; performing a first calcination heat treatment on the sediment containing ammonium vanadate to obtain vanadium oxide; mixing the vanadium oxide and the first reducing agent in a second solvent to carry out reaction III to obtain a first tetravalent vanadium-containing solution;

[0015] Step S3: subjecting the first tetravalent vanadium-containing solution to reaction IV under electrocatalytic reduction conditions of a hydrogen evolution catalyst to obtain a trivalent vanadium-containing solution.

[0016] Further, the first tetravalent vanadium-containing solution obtained in step S2 is divided into two parts; one part of the first tetravalent vanadium-containing solution is subjected to reaction IV under the condition of electrocatalytic reduction of a hydrogen evolution catalyst to obtain a trivalent vanadium-containing solution; the remaining part of the first tetravalent vanadium-containing solution is subjected to the process of step S4 after step S3;

[0017] The process of step S4 includes: mixing the remaining part of the first tetravalent vanadium-containing solution and the trivalent vanadium-containing solution and dissolving them in a sulfuric acid solution to obtain a trivalent-to-quadrivalent vanadium electrolyte.

[0018] Furthermore, the molar ratio of the sulfuric acid solution to the tetravalent vanadium ions in the remaining part of the first tetravalent vanadium-containing solution is (1.5~6.0):(1.0~2.5), and the molar ratio of the sulfuric acid solution to the trivalent vanadium ions in the trivalent vanadium-containing solution is (1.5~6.0):(1.0~2.5); the molar concentration of the sulfuric acid solution is 2.0~5.0 mol / L.

[0019] Furthermore, the molar concentration of tetravalent vanadium ions in the remaining first tetravalent vanadium-containing solution and the molar concentration of trivalent vanadium ions in the trivalent vanadium-containing solution are adjusted to be 1:1 to obtain a 3.5-valent vanadium electrolyte.

[0020] Further, the vanadium-enriched product obtained in step S1 is divided into two parts; wherein one part of the vanadium-enriched product is mixed with the first ammonium salt and the first solvent to carry out reaction II to obtain a vanadium precipitation product; and the remaining part of the vanadium-enriched product is subjected to roasting treatment;

[0021] The roasting process includes: roasting the remaining vanadium enriched material to obtain roasted slag containing calcium oxide; mixing the roasted slag containing calcium oxide, an alkaline leaching agent and vanadium slag in a mass ratio of (1.0~30):(2.5~80):(1.5~20) to carry out vanadium enrichment treatment to obtain a vanadium enriched product, and the vanadium enriched product is separated to obtain a calcium vanadate enriched material.

[0022] Furthermore, the calcium vanadate enriched material and the vanadium enriched material are mixed, and then mixed with the first ammonium salt and the first solvent to carry out reaction II to obtain a vanadium precipitation product.

[0023] Further, the calcium vanadate concentrate and the second reducing agent are mixed in a third solvent to carry out reaction V to obtain a second tetravalent vanadium-containing solution.

[0024] Furthermore, between step S2 and step S3, step S23-1 is also included: mixing the first tetravalent vanadium-containing solution and the second tetravalent vanadium-containing solution to obtain a mixed solution containing tetravalent vanadium; and subjecting the mixed solution containing tetravalent vanadium to reaction IV under conditions of electrocatalytic reduction of a hydrogen evolution catalyst to obtain a solution containing trivalent vanadium.

[0025] Furthermore, the conditions of reaction V include: reaction temperature of 60-120° C., and constant temperature reaction time of 3.0-5.0 h.

[0026] Furthermore, the mass ratio of the calcium vanadate enrichment to the second reducing agent is (1.0~3.5):(0.5~3.0).

[0027] Furthermore, the second reducing agent is selected from at least one of oxalic acid, sodium oxalate, potassium oxalate, carboxylic acid, citric acid, tartaric acid and NH4HSO3.

[0028] Furthermore, the third solvent is selected from at least one of H2SO4, HNO3, HCl, H2CO3 and H3PO4.

[0029] Furthermore, the concentration of the third solvent is 0.1-5.0 mol / L.

[0030] Furthermore, the pH value of the system of reaction V is 1.0-7.0.

[0031] Further, the mixed solution containing tetravalent vanadium obtained in step S23-1 is divided into two parts; one part of the mixed solution containing tetravalent vanadium is subjected to reaction IV under the condition of electrocatalytic reduction of a hydrogen evolution catalyst to obtain a solution containing trivalent vanadium; and the remaining part of the mixed solution containing tetravalent vanadium is subjected to the process of step S4 after step S3;

[0032] The process of step S4 includes: mixing the remaining part of the mixed solution containing tetravalent vanadium and the solution containing trivalent vanadium and dissolving them in a sulfuric acid solution to obtain a trivalent-tetravalent vanadium electrolyte.

[0033] Furthermore, the molar ratio of the tetravalent vanadium ions in the sulfuric acid solution to the remaining tetravalent vanadium-containing mixed solution is (1.5-6.0):(1.0-2.5), and the molar ratio of the sulfuric acid solution to the trivalent vanadium ions in the trivalent vanadium-containing solution is (1.5-6.0):(1.0-2.5); the molar concentration of the sulfuric acid solution is 2.0-5.0 mol / L.

[0034] Furthermore, the molar concentration of tetravalent vanadium ions in the remaining tetravalent vanadium-containing mixed solution and the molar concentration of trivalent vanadium ions in the trivalent vanadium-containing solution are adjusted to be 1:1 to obtain a 3.5-valent vanadium electrolyte.

[0035] Furthermore, the conditions of reaction I in step S1 include: reaction temperature of 90-180° C., and constant temperature reaction time of 3.0-5.0 h.

[0036] Furthermore, the mass ratio of the alkaline leaching agent to the vanadium slag is (1.5~200):(2.5~50).

[0037] Furthermore, the pH of the mixed system of the alkaline leaching agent and the vanadium slag is 10.5-12.0.

[0038] Furthermore, the concentration of the alkaline leaching agent is 0.01~10.0mol / L.

[0039] Furthermore, the alkaline leaching agent is selected from at least one of NaOH aqueous solution, Na2CO3 aqueous solution, NaHCO3 aqueous solution, KOH aqueous solution, K2CO3 aqueous solution and KHCO3 aqueous solution.

[0040] Furthermore, the vanadium-enriched material, water and organic solvent I in step S2 are first mixed to form a suspension of the vanadium-enriched material, and the suspension of the vanadium-enriched material is then mixed with the first ammonium salt and the first solvent to carry out reaction II to obtain a vanadium precipitation product.

[0041] Furthermore, the volume ratio of water to the organic solvent I is (50~1000):(5~500).

[0042] Further, the organic solvent I is at least one selected from the group consisting of methanol, ethanol, propanol, ethylene glycol, isopropanol, polyacrylic acid, N,N-dimethylformamide, N,N-dimethylacetamide and diethylformamide.

[0043] Furthermore, the conditions of reaction II in step S2 include: reaction temperature of 10-90° C., and constant temperature reaction time of 1.0-5.0 h.

[0044] Furthermore, the mass ratio of the vanadium enriched material to the first ammonium salt is (2.0-30.0): (0.5-50.0).

[0045] Furthermore, the first ammonium salt is selected from at least one of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium bicarbonate, ammonium carbonate, polydopamine, hexamethylenetetramine, melamine, ammonium polyacrylate and dopamine hydrochloride.

[0046] Furthermore, the first ammonium salt and the first solvent are mixed to form a first ammonium salt solution; the concentration of the first ammonium salt solution is 0.01-5.0 mol / L.

[0047] Furthermore, the first solvent is a mixture of water and an inorganic acid.

[0048] Furthermore, the volume ratio of water to the inorganic acid is (50~1000):(5~500); wherein the inorganic acid is selected from at least one of hydrochloric acid, nitric acid, boric acid, sulfuric acid, carbonic acid and phosphoric acid; and the concentration of the inorganic acid is 0.1~5.0 mol / L.

[0049] Furthermore, the electrocatalytic reduction conditions in step S3 include: an electrolysis voltage of 0.5-5.0 V, an electrolysis temperature of 20-60° C., an electrolysis time of 0.5-3.0 h, and a distance between electrode plates of 2.0-10.0 cm.

[0050] Furthermore, the conditions of reaction III in step S2 include: reaction temperature of 60-120° C., and constant temperature reaction time of 3.0-5.0 h.

[0051] Furthermore, the mass ratio of the vanadium oxide to the first reducing agent is (1.0-3.5):(0.5-3.0).

[0052] Further, the first reducing agent is selected from at least one of SO2, NH4HSO3, H2O2, oxalic acid, sodium oxalate, potassium oxalate, ascorbic acid, sodium ascorbate, sodium sulfite, sodium pyrosulfite and carboxylic acid.

[0053] Furthermore, the second solvent is selected from at least one of H2SO4, HCl and phosphoric acid; and the concentration of the second solvent is 0.1-5.0 mol / L.

[0054] Furthermore, the process of the first calcination heat treatment includes in sequence: a first stage heat treatment, a second stage heat treatment, and a third stage heat treatment; wherein, the process of the first stage heat treatment includes: heating from 25°C to 150~200°C at a heating rate of 5~30°C / min, and keeping warm for 1.0~1.5h; the process of the second stage heat treatment includes: continuing to heat to 300~350°C at a heating rate of 5~10°C / min, and keeping warm for 1.0~3.0h; the process of the third stage heat treatment includes: continuing to heat to 450~500°C at a heating rate of 5~10°C / min, and keeping warm for 1.0~3.0h.

[0055] Furthermore, the first calcination heat treatment process is carried out in a first protective atmosphere; the first protective atmosphere is selected from at least one of argon, nitrogen, helium and NH3.

[0056] Furthermore, the gas flow rate of the first protective atmosphere is 1-10 L / min.

[0057] Furthermore, the first calcination heat treatment process is carried out in a tubular vacuum furnace.

[0058] Furthermore, the first calcination heat treatment also includes an annealing treatment, the process of which includes: cooling to 300-400°C at a cooling rate of 5-10°C / min, introducing oxygen; the flow rate of oxygen is 1-10 L / min, and after maintaining the constant temperature for 1.0-3.0 hours, the temperature is naturally cooled to room temperature.

[0059] Furthermore, step S23-2 is further included between step S2 and step S3: dividing the ammonium vanadate-containing sediment obtained in step S2 into two parts; subjecting one part of the ammonium vanadate-containing sediment to the first calcination heat treatment in step S2 to obtain vanadium oxide; and using the remaining part of the ammonium vanadate-containing sediment to prepare a vanadium-based hydrogen evolution electrocatalyst;

[0060] The preparation process of the vanadium-based hydrogen evolution electrocatalyst includes: mixing the remaining part of the ammonium vanadate-containing sediment with the second ammonium salt, the precious metal compound, the chelating agent, the third reducing agent and the fourth solvent to carry out reaction VI to obtain a reaction VI product; and performing a second calcination heat treatment on the reaction VI product and the fourth reducing agent in a second protective atmosphere to obtain a vanadium-based hydrogen evolution electrocatalyst loaded with precious metals.

[0061] Furthermore, the conditions of reaction VI include: reaction temperature of 0-160° C., and constant temperature reaction time of 1.0-5.0 h.

[0062] Furthermore, the mass ratio of the remaining part of the sediment containing ammonium vanadate to the second ammonium salt is (1.0-20.0): (0.001-15.0).

[0063] Furthermore, the mass ratio of the remaining part of the ammonium vanadate-containing sediment to the precious metal compound is (1.0-20.0): (0.1-10.0).

[0064] Furthermore, the mass ratio of the noble metal compound to the chelating agent is (0.1~10.0):(0.001~15.0).

[0065] Furthermore, the molar ratio of the noble metal compound to the third reducing agent is (0.001-0.1): (0.005-0.5).

[0066] Furthermore, the mass ratio of the fourth reducing agent to the product of reaction VI is (0.1~0.5):1.

[0067] Further, the second ammonium salt is selected from at least one of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium bicarbonate, ammonium carbonate, polydopamine, ethylenediaminetetraacetic acid, ethylenediamine, triethylenetetramine, triethanolamine, hexamethylenetetramine, melamine, ammonium polyacrylate and dopamine hydrochloride.

[0068] Further, the noble metal compound is selected from at least one of chloroplatinic acid, chloroplatinate, [Pt(acac)2], diammine dinitrite platinum and [Pt(CH3NH2)4][PtCl4].

[0069] Furthermore, the chelating agent is selected from at least one of thiourea, sulfite, phosphoric acid, oxalic acid, arsenic acid, polyacrylic acid and polyvinyl alcohol.

[0070] Furthermore, the third reducing agent is selected from at least one of elemental sulfur, ascorbic acid, sodium ascorbate, sodium citrate, formaldehyde, acetaldehyde, formic acid, acetic acid, hydrazine hydrate, metal borohydride salt, sulfite and oleylamine.

[0071] Furthermore, the fourth reducing agent is elemental carbon.

[0072] Further, the fourth solvent is selected from water and / or ethylene glycol.

[0073] Furthermore, the protective atmosphere of the second calcination heat treatment is selected from at least one of argon, nitrogen, helium and NH3.

[0074] Furthermore, the process of the second calcination heat treatment includes a first stage heat treatment, a second stage heat treatment, a third stage heat treatment and a fourth stage heat treatment in sequence; wherein the first stage heat treatment includes: heating from 25°C to 300~350°C at a heating rate of 5~30°C / min, and keeping warm for 1.0~1.5h; the second stage heat treatment includes: continuing to heat to 600~650°C at a heating rate of 5~10°C / min, and keeping warm for 1.0~3.0h; the third stage heat treatment includes: continuing to heat to 800~900°C at a heating rate of 5~10°C / min, and keeping warm for 1.0~3.0h; the fourth stage heat treatment includes: continuing to heat to 1100~1200°C at a heating rate of 5~10°C / min, and keeping warm for 1.0~3.0h, and after naturally cooling to room temperature, a vanadium-based hydrogen evolution electrocatalyst loaded with precious metals is obtained.

[0075] Furthermore, a vanadium-based hydrogen evolution electrocatalyst loaded with a noble metal, a Nafion solution and an organic solvent II are mixed to obtain a slurry; the slurry is coated on the surface of a membrane electrode to obtain a catalyst membrane electrode.

[0076] Furthermore, the mixing ratio of the noble metal-loaded vanadium-based hydrogen evolution electrocatalyst, the Nafion solution, and the organic solvent II is (2.5-15.0) mg: (100.0-150.0) μL: (1.0-10.0) mL; the concentration of the Nafion solution is 0.5-10.0 wt%.

[0077] Furthermore, the loading amount of precious metal in the vanadium-based hydrogen evolution electrocatalyst is 20.0~40.0wt%, and the pore volume is 0.01~10.0cm 3 / g, average pore size of 5~50nm, specific surface area of ​​450~600m 2 / g.

[0078] According to a second aspect of the present application, an all-vanadium electrolyte is provided, which is prepared by the above-mentioned method for preparing the all-vanadium electrolyte.

[0079] According to a third aspect of the present application, there is provided an all-vanadium liquid flow battery, comprising an all-vanadium electrolyte, which is the all-vanadium electrolyte described above.

[0080] The technical solution of the present application is applied to provide an all-vanadium electrolyte and a preparation method thereof. The method uses vanadium slag as raw material, adopts a hydrometallurgical process, and according to the different pH interval characteristics of the solution system, promotes the phase transformation of vanadium ion compounds, and then achieves efficient separation from impurity elements, thereby obtaining vanadium enriched products; at the same time, the process can separate valuable elements and achieve vanadium extraction through valence state regulation; the method can not only efficiently extract all-vanadium electrolytes of different valence states, but also make full use of vanadium slag solid waste, realize the clean and high-value comprehensive utilization of vanadium slag resources, and further construct a closed-loop circulation system for green and low-carbon metallurgy of vanadium metal, reducing production and environmental costs and energy consumption. When preparing vanadium electrolyte by electrolysis, the vanadium electrolyte is prepared by electrocatalytic reduction at room temperature and pressure with the help of hydrogen evolution electrocatalyst, so as to achieve the purpose of efficient catalytic reduction; the rate of vanadium ion reduction reaction is improved by the electrocatalytic reduction reaction of hydrogen evolution catalyst. Compared with the traditional electrolysis method, the method has a faster reaction rate and does not introduce other reducing agents, so it has better safety and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0082] Figure 1 A schematic diagram of the process for preparing a vanadium electrolyte according to an embodiment of the present application;

[0083] Figure 2 A schematic diagram of the structure of a device for preparing a vanadium electrolyte according to an embodiment of the present application;

[0084] Figure 3 This is the XRD phase diagram of the chrome-vanadium slag alkali leaching product in Example 1 of the present application;

[0085] Figure 4 This is a transmission electron microscopy image (TEM image) of the Pt / VN catalyst prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0086] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0087] In order to solve the problems of high cost, complex process and low reaction rate in the prior art for preparing all-vanadium electrolyte, according to one aspect of the present application, a method for preparing all-vanadium electrolyte is provided, comprising the following steps:

[0088] Step S1: using an alkaline leaching agent to perform an alkali leaching treatment on the vanadium slag to perform reaction I, to obtain an alkali leaching product, and the alkali leaching product is subjected to solid-liquid separation to obtain a vanadium enriched product and a filtrate;

[0089] Step S2: mixing the vanadium-enriched material, the first ammonium salt and the first solvent to carry out reaction II to obtain a vanadium precipitation product, and the vanadium precipitation product is subjected to solid-liquid separation to obtain a sediment containing ammonium vanadate; performing a first calcination heat treatment on the sediment containing ammonium vanadate to obtain vanadium oxide; mixing the vanadium oxide and the first reducing agent in a second solvent to carry out reaction III to obtain a first tetravalent vanadium-containing solution;

[0090] Step S3: subjecting the first tetravalent vanadium-containing solution to reaction IV under electrocatalytic reduction conditions of a hydrogen evolution catalyst to obtain a trivalent vanadium-containing solution.

[0091] This application adopts the above-mentioned vanadium extraction method, which can not only efficiently extract all-vanadium electrolytes of different valence states, but also make full use of vanadium slag solid waste, realize the clean and high-value comprehensive utilization of vanadium slag resources, and realize the green and low-carbon metallurgical closed-loop circulation of vanadium metal, thereby reducing production costs and energy consumption, and reducing environmental risks; and in the preparation process of vanadium electrolyte, efficient catalytic reduction can be achieved with the help of hydrogen evolution electrocatalysts. The rate of vanadium ion reduction reaction is improved by the electrocatalytic reduction reaction of the catalyst. Compared with the traditional electrolysis method, this method has a faster reaction rate and does not require the introduction of other reducing agents, and has better safety and economy.

[0092] In some embodiments, the first tetravalent vanadium-containing solution obtained in step S2 is divided into two parts; wherein, one part of the first tetravalent vanadium-containing solution is subjected to reaction IV under conditions of electrocatalytic reduction of a hydrogen evolution catalyst to generate a trivalent vanadium-containing solution; the remaining part of the first tetravalent vanadium-containing solution is subjected to the process of step S4 after step S3; wherein step S4 specifically comprises: mixing the remaining part of the first tetravalent vanadium-containing solution and the trivalent vanadium-containing solution and dissolving them in a sulfuric acid solution to prepare a 3~4-valent vanadium electrolyte.

[0093] In some embodiments, the molar ratio of the sulfuric acid solution to the tetravalent vanadium ions in the remaining portion of the first tetravalent vanadium-containing solution is (1.5-6.0): (1.0-2.5), for example (2.0-5.0): (1.0-2.0); the molar ratio of the sulfuric acid solution to the trivalent vanadium ions in the trivalent vanadium-containing solution is (1.5-6.0): (1.0-2.5), for example (2.0-5.0): (1.0-2.0); the concentration of the sulfuric acid solution is 2.0-5.0 mol / L, for example 2.0-4.0 mol / L. The molar ratio of the sulfuric acid solution and the vanadium ions of each valence can be adjusted according to actual needs.

[0094] In some embodiments, the molar concentration of tetravalent vanadium ions in the remaining portion of the first tetravalent vanadium-containing solution and the molar concentration of trivalent vanadium ions in the trivalent vanadium-containing solution are adjusted to be 1:1 to obtain a 3.5-valent vanadium electrolyte.

[0095] The present application divides the obtained tetravalent vanadium solution into two parts, one part is directly used as a tetravalent vanadium solution to provide tetravalent vanadium; the other part reduces the tetravalent vanadium to trivalent vanadium under electrocatalytic conditions, thereby obtaining a solution containing trivalent vanadium. By adjusting the molar concentration ratio of vanadium ions in the two solutions, a vanadium electrolyte in a valence state of 3 to 4 can be obtained; therefore, through the above method of the present application, at least trivalent vanadium, 3.5-valent vanadium and tetravalent vanadium ion solutions can be obtained.

[0096] In some embodiments, the vanadium enriched material obtained in step S1 is divided into two parts; wherein, a part of the vanadium enriched material is mixed with the first ammonium salt and the first solvent to react II to obtain a vanadium precipitation product; the remaining part of the vanadium enriched material is roasted; wherein the roasting process includes: roasting the remaining part of the vanadium enriched material to obtain a roasted slag containing calcium oxide; mixing the roasted slag containing calcium oxide, the alkaline leaching agent and the vanadium slag in a mass ratio of (1.0~30): (2.5~80): (1.5~20) to carry out vanadium enrichment treatment to obtain a vanadium enriched product, and the vanadium enriched product is separated to obtain a calcium vanadate enriched material. The present application can realize a new method for enriching vanadium through the above-mentioned roasting treatment, and realize the recycling of the intermediate product of the vanadium enriched material.

[0097] In addition, in step S1 of the present application, some calcium vanadate substances are converted into vanadate ions by alkali solution and enter the solution, which may cause the loss of some vanadium ions. In this regard, the filtrate obtained by solid-liquid separation can be returned to the vanadium slag for alkali leaching again; in order to solve the problem of possible loss of vanadium ions, the present application takes a certain amount (depending on actual needs) of vanadium enriched material for roasting to obtain calcium oxide (calcium oxide can also be obtained from the outside), so that it reacts with vanadate ions to generate calcium vanadate substances. After solid-liquid separation, the calcium vanadate substances are enriched to form calcium vanadate enriched materials; when calcium oxide is mixed with vanadium slag and alkali solution, a small amount of vanadium enriched material prepared in step S1 can also be taken to further enhance the reaction activity of calcium oxide and improve the enrichment degree of vanadium; after obtaining the calcium vanadate enriched material, it can be mixed with the vanadium enriched material to carry out the subsequent process of the vanadium enriched material, and the pentavalent vanadium in the calcium vanadate enriched material can also be reduced to tetravalent vanadium alone.

[0098] In some embodiments, a calcium vanadate enriched material and a vanadium enriched material are mixed, and then a first ammonium salt and a first solvent are added to carry out reaction II to obtain a vanadium precipitation product; alternatively, a calcium vanadate enriched material and a second reducing agent are placed in a third solvent and mixed, and reaction V is carried out to obtain a second tetravalent vanadium-containing solution.

[0099] This application provides a new method for preparing a second tetravalent vanadium solution through the above-mentioned treatment. In this way, the reaction path and treatment method of the all-vanadium electrolyte preparation process are enriched, the way to obtain different products is broadened, and the entire preparation system is made more flexible and diversified, which helps to better meet the various needs in actual preparation and further improve the preparation efficiency and quality of the all-vanadium electrolyte.

[0100] In some embodiments, the conditions of reaction V include: reaction temperature of 60-120°C, for example, 90-100°C; constant temperature reaction time of 3.0-5.0h. The present application can make calcium vanadate release vanadium ions and convert them into tetravalent vanadium solution as much as possible under the above reaction temperature and reaction time conditions.

[0101] In some embodiments, the mass ratio of the calcium vanadate enrichment and the second reducing agent is (1.0~3.5):(0.5~3.0); further is (1.0~2.0):(1.5~3.0); the second reducing agent is selected from at least one of oxalic acid, sodium oxalate, potassium oxalate, carboxylic acid, citric acid, tartaric acid and NH4HSO3; further, the concentration of the second reducing agent solution is 0.001~0.5mol / L, for example 0.01~0.5mol / L; the third solvent is selected from at least one of H2SO4, HNO3, HCl, H2CO3 and H3PO4; the concentration of the third solvent is 0.1~5.0mol / L, and the pH value of the reaction V system is regulated to be 1.0~7.0, further to 1.0~6.0, and further to 1.0~4.0.

[0102] The present application provides suitable reaction conditions by selecting the above-mentioned suitable reducing agent in an acid or mixed acid solvent reaction system, and limiting the acid concentration and the pH of the reaction system, which can promote the efficient reduction of pentavalent vanadium in calcium vanadate to tetravalent vanadium, for example, to generate vanadium oxysulfate.

[0103] In some embodiments, step S23-1 is further included between step S2 and step S3: mixing the first tetravalent vanadium-containing solution and the second tetravalent vanadium-containing solution to obtain a mixed solution containing tetravalent vanadium; and subjecting the mixed solution containing tetravalent vanadium to reaction IV under conditions of electrocatalytic reduction of a hydrogen evolution catalyst to obtain a solution containing trivalent vanadium.

[0104] The above method of the present application realizes a channel for obtaining a tetravalent vanadium solution in another new way, which not only makes full use of the intermediate product of vanadium enrichment, but also adds a new method for extracting vanadium. The present application mixes the tetravalent vanadium obtained by reaction V and the tetravalent vanadium obtained by reaction III, and can directly use them to perform step S3, and reduce all the tetravalent vanadium to trivalent vanadium through electrocatalysis. These tetravalent vanadium solutions can also be divided into two parts (the specific proportion can be determined according to actual needs), one part is used as tetravalent vanadium for standby, and the other part of the tetravalent vanadium is electrocatalytically reduced to trivalent vanadium. When the tetravalent vanadium and trivalent vanadium are mixed, a 3-4 valence vanadium solution can be obtained. Such operation can further expand the deployment and utilization methods of vanadium solutions of different valence states in the preparation of all-vanadium electrolyte, can better meet the diverse preparation needs, and further optimize the overall preparation effect of all-vanadium electrolyte.

[0105] In some embodiments, the mixed solution containing tetravalent vanadium obtained in step S23-1 is divided into two parts; one part of the mixed solution containing tetravalent vanadium is subjected to reaction IV under conditions of electrocatalytic reduction of a hydrogen evolution catalyst to obtain a solution containing trivalent vanadium; the remaining part of the mixed solution containing tetravalent vanadium is subjected to the process of step S4 after step S3; wherein the process of step S4 includes: mixing the remaining part of the mixed solution containing tetravalent vanadium and the solution containing trivalent vanadium and dissolving them in a sulfuric acid solution to obtain a 3~4-valent vanadium electrolyte.

[0106] In some embodiments, the molar ratio of the tetravalent vanadium ions in the sulfuric acid solution to the remaining tetravalent vanadium-containing mixed solution is (1.5-6.0): (1.0-2.5), for example (2.0-5.0): (1.0-2.0); the molar ratio of the sulfuric acid solution to the trivalent vanadium ions in the trivalent vanadium-containing solution is (1.5-6.0): (1.0-2.5), for example (2.0-5.0): (1.0-2.0); the concentration of the sulfuric acid solution is 2.0-5.0 mol / L, further 2.0-4.0 mol / L. The present application adopts the above sulfuric acid concentration and ratio to obtain a vanadium electrolyte that meets the use requirements.

[0107] In some embodiments, the molar concentration of tetravalent vanadium ions in the remaining portion of the mixed solution containing tetravalent vanadium and the molar concentration of trivalent vanadium ions in the solution containing trivalent vanadium are adjusted to be 1:1 to obtain a 3.5-valent vanadium electrolyte.

[0108] The main principles of the application for alkaline leaching, vanadium enrichment, vanadium precipitation and reduction of vanadium slag (or chrome vanadium slag) are as follows:

[0109] The vanadium slag involved in this application is specifically chrome-vanadium slag, which is a hazardous waste and urgently needs to be recycled. The main components of the slag are CaCrO4, Na2Cr2O7·2H2O, CaSO4·2H2O, Ca 1.5Na 3.5 (OH) 0.55 (SO4)3(H2O) 0.44 and calcium vanadate (CaV2O6 (calcium metavanadate), Ca2V2O7 (calcium pyrovanadate), Ca3V2O8 (calcium orthovanadate)); Cr(VI) in alkaline system is CrO4 2- Ions exist, V(V) is VO4 3- 、V2O7 4- , VO3 - It exists in the form of plasma. Therefore, chromium and vanadium can be effectively leached and separated by alkaline leaching, taking advantage of the difference in the properties of vanadium and chromium in the solution, that is, the difference in solubility at different alkali concentrations and temperatures. By adjusting the pH value of the vanadium-chromium solution, when the pH>11.0, that is, at a high pH value, the hexavalent chromium in it is converted into chromate (CrO4 2- ) exists in the solution, i.e. CaCrO4+ HCO3 - +OH - =CrO4 2- + CaCO3↓+H2O. When the solution pH>12.0, vanadate is mainly in the form of VO4 3- The vanadium is present in the form of vanadium, that is, vanadium is separated and enriched in the solution; after concentration, the vanadate in the leaching solution can be precipitated and crystallized to obtain a vanadium-enriched product (i.e., Ca3(VO4)2); thus, vanadium and chromium are effectively separated. Therefore, in the alkaline leaching solution system, vanadium slag can selectively separate the valuable elements through the difference in the solubility product of different ion valence states of the valuable metal elements.

[0110] In order to clearly describe the mechanism, in step S1, the reaction equation involved in adding alkaline leaching solution NaHCO3 and additive calcium oxide to vanadium slag is:

[0111] Ca2V2O7 +2HCO3 - +2OH - =V2O7 4- + 2CaCO3↓+2H2O;

[0112] Ca3V2O8+ 3HCO3 - +3OH - = 2VO4 3- + 3CaCO3↓+3H2O;

[0113] V2O7 4- +2CaO+2H2O = Ca2V2O7↓+ 4OH - ;

[0114] 2VO3 - +CaO+H2O=Ca(VO3)2↓+2OH- ;

[0115] 2VO4 3- +3CaO+3H2O=Ca3(VO4)2↓+6OH - .

[0116] At the same time, the vanadium enriched material contains calcium carbonate. By roasting at 1000℃ for 3.0h, CaCO3 can be thermally decomposed to produce CaO, which has good reaction activity. This shows that the lime obtained from the leaching residue and roasting heat treatment can be used as a vanadium precipitation aid in vanadium slag and vanadate solution system.

[0117] The calcium salt and CaO in the process flow are used to enrich vanadium in the vanadate leaching solution system to obtain a calcium vanadate intermediate product, which undergoes a phase transformation of vanadate ions (i.e., reaction V) under acidic and / or reducing agent conditions (the acidic environment is provided by sulfuric acid, hydrochloric acid, carbonic acid, etc., and the reducing agent is provided by oxalic acid, citric acid, tartaric acid, etc.), thereby recovering and purifying the vanadium element in the low-concentration vanadium slag, and preparing V 4+ Ionic solution, the specific reaction equation is as follows:

[0118] Ca(VO3)2+CO3 2- = 2VO3 - +CaCO3↓;

[0119] Ca3(VO4)2+3CO3 2- = 3CaCO3↓+2VO4 3- ;

[0120] VO4 3- +H2O = VO3 - +2OH - ;

[0121] 2VO3 - +2HCl+3H2SO4= 2VOSO4+Cl2+4H2O+SO4 2- .

[0122] At the same time, in step S2, the vanadate in the vanadium-enriched material reacts with the first ammonium salt to obtain ammonium metavanadate (NH4VO3) (i.e., reaction II), and at the same time, the excess vanadate that does not participate in the precipitation reaction is hydrated to obtain [VO2(H2O)3] + , after deprotonation, VO(OH)3 is generated, and a vanadium precipitation product containing NH4VO3 and a small amount of VO(OH)3 is obtained; the following reactions occur in this process:

[0123] VO3 - +NH4Cl+H2O→HVO3+Cl - +NH4OH;

[0124] Since the solubility of NH4VO3 in water is very low, the following double decomposition reaction occurs:

[0125] HVO3+NH4OH→NH4VO3↓+H2O;

[0126] VO3 - +NH4Cl→NH4VO3↓+Cl - .

[0127] In some embodiments, the alkaline leaching process of step S1 specifically includes: mixing vanadium slag with an alkaline leaching agent to obtain a mixed system, and then adjusting the pH value of the mixed system to 10.5-12.0 with an alkaline solution, for example, the pH is 10.5, 11.0, 11.5, 12.0; for another example, the pH is 10.5-11.5. Subsequently, vanadium is extracted from the vanadium slag suspension solution to obtain a vanadium enrichment. Based on the difference in solubility products of impurity elements, the present application controls the pH value of the mixed system within the above range, which is conducive to the purification and impurity removal of the vanadium-containing leachate (especially the removal of chromium ions), improves the purity of vanadates, and finally obtains an enrichment containing vanadates.

[0128] In some embodiments, the alkaline leachant (alkaline solution or immersion liquid) is selected from at least one of NaOH aqueous solution, Na2CO3 aqueous solution, NaHCO3 aqueous solution, KOH aqueous solution, K2CO3 aqueous solution and KHCO3 aqueous solution; further, the concentration of the alkaline leachant is 0.01~10.0 mol / L, further 1.0~10.0 mol / L; further 1.0~5.0 mol / L; for example, any value of 1.0 mol / L, 2.0 mol / L, 3.0 mol / L, 4.0 mol / L, 5.0 mol / L, 6.0 mol / L, 7.0 mol / L, 8.0 mol / L, 9.0 mol / L, 10.0 mol / L or any range value between two of them.

[0129] In some embodiments, the conditions of reaction I in step S1 include: a reaction temperature of 90-180°C, a constant temperature reaction time of 3.0-5.0h; a mass ratio of alkaline leaching agent to vanadium slag of (1.5-200):(2.5-50), further (1.5-20):(2.5-50), and further (1.0-15):(1.0-3.0); for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1; the above reaction temperature is further 90-150°C, and further 90-120°C, and the reaction time is 3.0h, 4.0h, 5.0h. In order to further improve the solubility and dispersibility of the vanadium slag raw material in the mixed system, the vanadium slag and the alkaline solution are stirred during the mixing process, and the stirring speed is 300~500rpm; the use of the above mixing temperature and mixing ratio is beneficial to improving the solubility and dispersibility of the raw material vanadium slag containing vanadate in the mixed system, thereby facilitating subsequent processing.

[0130] The present application selects the above-mentioned alkali solution as the leaching agent and limits the concentration of the alkali solution to provide a suitable acid-base reaction environment for alkali leaching treatment. Under this reaction environment, the vanadium ions in the vanadium slag are fully extracted and enriched, and are efficiently separated from the chromium ions. The separated enriched products mainly include vanadium-containing enriched materials and part of calcium carbonate. The calcium carbonate can be used for subsequent operations; the extracted vanadium-containing enriched materials include calcium vanadate, calcium pyrovanadate and calcium metavanadate, etc.

[0131] In some embodiments, the conditions of reaction II in step S2 include: reaction temperature of 10-90°C, constant temperature reaction time of 1.0-5.0h; for example, reaction temperature of 20-60°C, reaction time of 1.0-3.0h. The present application limits it within the above range to improve the yield of NH4VO3, facilitate subsequent utilization, or facilitate the preparation of vanadium oxide, or facilitate the preparation of catalyst precursor.

[0132] In some embodiments, the mass ratio of the vanadium enriched material to the first ammonium salt is (2.0-30.0): (0.5-50.0); further (2.0-20.0): (0.5-40.0); further (2.0-10.0): (0.5-30.0), for example (2.0-10.0): (0.5-10.0) or (2.0-10.0): (0.5-5.0), for example (2.0-10.0): (0.5-3.0); by limiting the above ratios, the present application is beneficial to improving the utilization rate of raw materials, increasing the production rate of ammonium metavanadate, and facilitating subsequent processes.

[0133] The present application selects the above-mentioned ammonium salt and vanadium-containing enriched material to undergo a double decomposition reaction of vanadate at the above-mentioned limited temperature, and obtains an ammonium metavanadate (NH4VO3) precipitate by solid-liquid separation; the present application divides the obtained ammonium metavanadate into two parts, one part is used as a precursor of a hydrogen evolution electrocatalyst carrier for subsequent processes, and the other part is used to reduce pentavalent vanadium to tetravalent vanadium through pyrolysis and reduction.

[0134] In some embodiments, in order to facilitate the reaction rate, the vanadium enriched material may be first prepared into a suspension thereof before participating in the reaction; for example, the vanadium enriched material, water and organic solvent I in step S2 are first mixed to form a suspension of the vanadium enriched material, and the suspension of the vanadium enriched material is then mixed with the first ammonium salt and the first solvent to carry out reaction II to obtain a vanadium precipitation product. The distribution ratio of each group of the above suspension is not limited and can be adjusted according to actual needs. For example, the volume ratio of water to the organic solvent I can be (50~1000):(5~500); for another example, the mixing ratio of the vanadium enriched material, water and the organic solvent I is (1.0~10.0) g:(10.0~100.0) mL:(10.0~100.0) mL; wherein the organic solvent I can be selected from at least one of the group consisting of methanol, ethanol, propanol, ethylene glycol, isopropanol, polyacrylic acid, N,N-dimethylformamide, N,N-dimethylacetamide and diethylformamide; further, the weight ratio of the suspension solution containing the vanadium enriched material, the first ammonium salt and the first solvent is (50.0~1500.0):(0.5~50.0):(100.0~1500.0).

[0135] In some embodiments, the first ammonium salt is selected from at least one of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium bicarbonate, ammonium carbonate, polydopamine, hexamethylenetetramine, melamine, ammonium polyacrylate, and dopamine hydrochloride. The above ammonium salts are selected in the present application to fully react with the vanadium-containing enriched material to obtain ammonium vanadate deposits, and the product can be calcined and pyrolyzed to form vanadium oxides.

[0136] In some embodiments, the first ammonium salt and the first solvent are mixed to form a first ammonium salt solution; the concentration of the first ammonium salt solution is 0.01~5.0 mol / L; further 0.1~1.0 mol / L; for example, any value in 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L or a range value between any two of them; wherein the first solvent is a mixture of water and an inorganic acid; the volume ratio of water to the inorganic acid is (50~1000):(5~500), for example (1~10):1; the inorganic acid is selected from at least one of hydrochloric acid, nitric acid, boric acid, sulfuric acid, carbonic acid and phosphoric acid, and the concentration of the inorganic acid is 0.1~5.0 mol / L, further 2.0~5.0 mol / L. The inorganic acid selected in the present application is beneficial to improving the dispersibility of vanadate and ammonium salt, and facilitates the double decomposition reaction of vanadate between the two.

[0137] The control of the concentration of ammonium salt in the present application is beneficial to the utilization rate of the raw materials of ammonium salt, while improving the reaction efficiency of the double decomposition reaction and the yield of the reaction product (containing NH4VO3 and a small amount of VO(OH)3). Mixing the vanadium-containing enriched material obtained after purification and impurity removal with the ammonium salt solution and performing a double decomposition reaction is beneficial to improving the quality of the vanadium electrolyte and the purity of the subsequent preparation of the catalyst carrier precursor. The vanadium-containing enriched material is mixed with the ammonium salt solution and subjected to a double decomposition reaction to obtain an ammonium vanadate product. Moreover, the above method adsorbs free water molecules on the surface of the carrier precursor obtained subsequently, which is beneficial to improving its wettability, facilitating subsequent treatment and facilitating the impregnation adsorption loading of precious metals on the carrier surface, thereby omitting the carrier pretreatment process, making the process simpler and more efficient, with lower energy consumption and more significant cost advantages.

[0138] In order to better control the double decomposition reaction rate, the ammonium salt solution is dripped into the suspension solution containing the vanadium enrichment. In order to further control the reaction rate and make the formed NH4VO3 structure more stable, the dripping rate is controlled to be 1-30 mL / min, for example, 5-15 mL / min.

[0139] In some embodiments, step S2 further includes: sequentially performing solid-liquid separation and drying on the vanadium precipitation product to obtain a precipitate of ammonium vanadate, which is more conducive to the first calcination heat treatment and the preparation of a catalyst carrier precursor.

[0140] The present application facilitates separation of the ammonium vanadate sediment and the first solvent by performing solid-liquid separation on the vanadium precipitation product system to obtain a solid phase product. Drying the solid phase product facilitates removal of the residual solvent entrained in the solid phase product, which is convenient for subsequent processing. In order to improve the separation efficiency of the ammonium vanadate sediment and the solvent, the solid-liquid separation includes but is not limited to centrifugal separation. In order to increase the removal rate of the residual solvent entrained in the solid phase product, the drying temperature is 50~90°C and the time is 6.0~24.0h.

[0141] In some embodiments, the electrolysis conditions in step S3 include: an electrolysis voltage of 0.5 to 5.0 V, such as 1.0 to 3.0 V, an electrolysis temperature of 20 to 60° C., such as 20 to 40° C., an electrolysis time of 0.5 to 3.0 h, such as 0.5 to 1.5 h; and a distance between the electrode plates of 2.0 to 10.0 cm. The present application sets the above electrolysis conditions to utilize vanadium-based catalysts for efficient electrocatalytic reduction and improve the kinetic reaction rate of reducing tetravalent vanadium to trivalent vanadium.

[0142] In some embodiments, the conditions of reaction III in step S2 include: reaction temperature of 60-120°C, further 80-100°C, constant temperature reaction time of 3.0-5.0h; mass ratio of vanadium oxide to first reducing agent of (1.0-3.5):(0.5-3.0), for example (1.0-3.5):1. The present application adopts the above reaction ratio, reaction temperature, etc., which can fully reduce pentavalent vanadium oxide to tetravalent vanadium.

[0143] In some embodiments, the first reducing agent is selected from at least one of SO2, NH4HSO3, H2O2, oxalic acid, sodium oxalate, potassium oxalate, ascorbic acid, sodium ascorbate, sodium sulfite, sodium metabisulfite and carboxylic acid; further, the concentration of the first reducing agent solution is 0.001~5.0 mol / L, further 0.5~5.0 mol / L, and further 1.0~5.0 mol / L; the second solvent is selected from at least one of H2SO4, HCl and phosphoric acid; the concentration of the second solvent is 0.1~5.0 mol / L, further 1.0~5.0 mol / L.

[0144] The present application can fully reduce pentavalent vanadium to tetravalent vanadium (i.e., reaction III) by setting appropriate reaction temperature, reaction time, and reaction ratio of vanadium pentoxide and reducing agent, acid or mixed acid. For example, in a sulfuric acid solution, pentavalent vanadium can be reduced to tetravalent vanadium sulfate under the action of reducing agent H2O2. V2O5 has a low solubility at room temperature in a water / acid system. Under the action of a reducing agent, V2O5 is reduced to soluble VOSO4, which promotes the dissolution of V2O5. In a strong acid system with a pH of ≤1, V 5+ Mainly based on VO2 +The relevant reaction formula is as follows:

[0145] V2O5+H2O →2HVO3;

[0146] HVO3+H + → VO2 + +H2O;

[0147] 2VO2 + +H2O2+2H + →2 VO 2+ +2H2O+O2;

[0148] V2O5+H2O2+2H2SO4→2VOSO4+3H2O+ O2.

[0149] In some embodiments, the process of the first calcination heat treatment includes: first stage heat treatment, second stage heat treatment, and third stage heat treatment in sequence; wherein, the process of the first stage heat treatment includes: heating from 25°C to 150~200°C at a heating rate of 5~30°C / min, and keeping warm for 1.0~1.5h; the process of the second stage heat treatment includes: continuing to heat up to 300~350°C at a heating rate of 5~10°C / min, and keeping warm for 1.0~3.0h; the process of the third stage heat treatment includes: continuing to heat up to 450~500°C at a heating rate of 5~10°C / min, and keeping warm for 1.0~3.0h. The present application can fully calcine and pyrolyze the ammonium vanadate-containing sediment through the above-mentioned multiple stages of pyrolysis process to generate pentavalent vanadium oxide.

[0150] In some embodiments, the first calcination heat treatment process is carried out in a first protective atmosphere; the first protective atmosphere is selected from at least one of argon, nitrogen, helium and NH3; the gas flow rate of the first protective atmosphere is 1-10 L / min; the first calcination heat treatment process is carried out in a tubular vacuum furnace. The above calcination heat treatment conditions selected in the present application are more conducive to the pyrolysis process.

[0151] In some embodiments, the first calcination heat treatment also includes an annealing treatment, the process of which includes: cooling to 300-400°C at a cooling rate of 5-10°C / min, introducing oxygen; the flow rate of oxygen is 1-10 L / min, and after maintaining the constant temperature for 1.0-3.0 hours, the temperature is naturally cooled to room temperature.

[0152] By setting the above-mentioned gradual heating, heat preservation and pyrolysis process, the present application can fully pyrolyze ammonium metavanadate (NH4VO3) into pentavalent vanadium oxides (such as vanadium pentoxide and ammonia), thereby improving the extraction efficiency.

[0153] In some embodiments, step S23-2 is further included between step S2 and step S3: dividing the ammonium vanadate-containing sediment obtained in step S2 into two parts, subjecting one part of the ammonium vanadate-containing sediment to the first calcination heat treatment in step S2 to obtain vanadium oxide; and using the remaining part of the ammonium vanadate-containing sediment to prepare a vanadium-based hydrogen evolution electrocatalyst;

[0154] The preparation process of the vanadium-based hydrogen evolution electrocatalyst includes: mixing the remaining part of the ammonium vanadate-containing sediment (as a carrier precursor) with a second ammonium salt, a noble metal compound, a chelating agent, a third reducing agent and a fourth solvent to carry out reaction VI to obtain a reaction VI product; and performing a second calcination heat treatment on the reaction VI product and the fourth reducing agent in a second protective atmosphere to obtain a vanadium-based hydrogen evolution electrocatalyst loaded with a noble metal.

[0155] The hydrogen evolution electrocatalyst of the present application can be selected from the prior art or can be homemade. In the above-mentioned homemade process, the ammonium vanadate sediment is fully utilized and used as a precursor of the catalyst carrier, and a suitable noble metal compound and other additives are selected. After the reaction, a catalyst precursor is obtained, and the precursor is reduced and subjected to a second calcination annealing treatment to obtain a supported catalyst, such as vanadium nitride-supported noble metal. The noble metal has good dispersibility on the carrier, good durability and good activity. The raw material for preparing the above-mentioned hydrogen evolution electrocatalyst of the present application directly uses the intermediate product in the vanadium extraction process, and its electrocatalytic reaction activity effect is better, which can increase the reaction rate of reducing tetravalent vanadium to trivalent vanadium.

[0156] The main principles of preparing the above-mentioned vanadium-based electrocatalyst loaded with precious metals in this application are as follows:

[0157] For example, when the second ammonium salt is ammonium chloride and the noble metal-containing compound is chloroplatinic acid:

[0158] H2PtCl6+NH4Cl→(NH4)2PtCl6↓+HCl;

[0159] The present application introduces a chelating agent into the catalyst preparation method so that the noble metal and the chelating agent form a noble metal chelate, thereby making the noble metal more evenly dispersed in the fourth solvent under the action of the steric hindrance of the chelating agent, that is, through the noble metal cation chelate effect, the noble metal ion concentration can be regulated, so that the growth rate of the nanocrystalline nucleus is slowed down, so that the nano Pt grains are deposited in situ with a smaller volume, thereby making the reaction in the system more stable and improving the distribution uniformity of the noble metal in the carrier precursor.

[0160] When the chelating agent is oxalic acid, the phase transformation of platinum salt (NH4)2PtCl6 occurs to generate ammonium chloroplatinite (NH4)2PtCl4 (ammonium chloroplatinite is easily soluble in water), that is, the following reaction occurs:

[0161] (NH4)2PtCl6+H2C2O4→(NH4)2PtCl4+HCl+CO2↑;

[0162] And under the action of reducing agent hydrogen peroxide and / or hydrazine hydrate, the following reaction is carried out:

[0163] (NH4)2PtCl4+HCl+H2O2→(NH4)2PtCl6↓+H2O;

[0164] (NH4)2PtCl6+NH2NH2→(NH4)2PtCl4+N2↑+H2↑+HCl.

[0165] In the present application, V and N atoms from NH4VO3 are converted into VN small particles in situ under a protective atmosphere, and the carbon in the precious metal chelate framework and the added fourth reducing agent (elemental carbon) are consumed to promote the reduction of elemental Pt. Since the atoms in the polymer act as dispersants and protective agents, it is ensured that the particles do not agglomerate and grow while phase separation occurs. At the same time, ammonium metavanadate undergoes thermal decomposition in step S23-2 to obtain vanadium pentoxide (V2O5) and ammonia (NH3), that is, the following reactions occur: NH4VO3→V2O5+NH3↑+H2O, V2O5+NH3→VN+N2+H2O, V2O5+C+N2→VN+CO2+CO; at the same time, VO(OH)3 is dehydrated to form V2O5, and V2O5 is reduced by the fourth reducing agent to form vanadium nitride (VN), thereby forming a supported catalyst with vanadium nitride as a carrier to support precious metals (i.e., reaction VI).

[0166] The following reactions occur during this process:

[0167] (NH4)2PtCl6→Pt+HCl+NH4Cl+N2↑;

[0168] (NH4)2PtCl6→Pt+NH4Cl+Cl2↑.

[0169] When the solution pH is between 2 and 14, the hydrogen evolution potential is lower than V 4+ Restore to V 3+ The potential of the solution can be thermodynamically 4+ Restored to low-priced V 3+ However, experiments have shown that it is difficult to occur in terms of reaction kinetics and the reaction rate is slow. This means that a high activation energy is required for the reduction reaction to occur in a solution system. In addition, the reduction process involving vanadium ions is controlled by the interface reaction rate. Therefore, by introducing a hydrogen evolution electrocatalyst (such as a Pt / C catalyst), the reaction rate can be accelerated, making it easier to convert V 4+ At room temperature and pressure, it is reduced to V 3+ That is, V in the electrolytic cell 4+Ions gain electrons on the membrane electrode surface and a reduction reaction occurs: V 4+ +e − →V 3+ ; Hydrogen evolution electrocatalysts (such as Pt / C catalysts) are used to accelerate the rate of this reduction reaction by providing a lower energy activation energy path.

[0170] In step S3, the vanadium-based catalyst (Pt / VN) produced in step S23-2 is used as an electrocatalyst to prepare a membrane electrode, and the VOSO4 prepared in step S2 is dissolved in sulfuric acid to adjust the vanadium ion concentration to 1.0-2.5 mol / L, and SO4 2- The solution with a concentration of 2.0~5.0mol / L can convert V 4+ Electrocatalytic reduction to V 3+ , which can improve the rate of vanadium ion reduction reaction. Compared with the traditional electrolysis method, no other reducing agents are introduced, which has better safety and economy.

[0171] The vanadium ion solution prepared in steps S2 and S3 is fully mixed with concentrated sulfuric acid and pure water, heated to dissolve, and filtered to obtain a vanadium electrolyte after the reaction is completed. The reaction equation involved is:

[0172] V2O3+3H2SO4=V2(SO4)3+3H2O;

[0173] V2O5+2V 3+ +4H2SO4=4VOSO4+H2O+6H + ;

[0174] V2O5+H2SO4=(VO)2SO4+H2O;

[0175] V2O5+ V2O3+4H2SO4=4VOSO4+4H2O.

[0176] Compared with the traditional deposition reduction method of first preparing a vanadium nitride (VN) carrier and then immersing it in a platinum salt compound solution to load elemental platinum, the present application can deposit the precious metal in situ on the surface of the carrier precursor during the reduction of the precious metal compound. This not only improves the utilization rate of the active component (i.e., the precious metal Pt) in the supported catalyst, but also improves the uniformity of the distribution of the precious metal on the surface of the carrier. Moreover, the precious metal in the prepared supported catalyst is not easy to migrate and aggregate, and the interaction between the precious metal and the carrier can be regulated, and the force between the two can be enhanced, thereby effectively anchoring the precious metal and improving the durability of the supported catalyst. At the same time, the preparation method of the present application requires less precious metal and has a higher atomic utilization rate. In addition, compared with the traditional impregnation deposition reduction method, the preparation method of the present application can better retain its morphology while changing the composition structure of the supported catalyst, so that it exposes more active sites.

[0177] When the catalyst precursor is calcined and annealed, the release of NH3 gas helps to form a porous structure, achieve pore expansion and increase the specific surface area of ​​the carrier, so that the supported catalyst exposes more catalytic active sites. When it is used in an all-vanadium liquid flow battery, it can significantly accelerate the transfer rate of reactants and products during the reduction reaction and enhance the mass transfer effect. On the other hand, under the influence of the osmotic pressure of the local micro-jet flow in the capillary pores of the carrier interface, the interaction between the precious metal particles can be weakened, thereby effectively inhibiting the aggregation and migration of the precious metal particles.

[0178] In addition, the supported catalysts prepared by the phase separation method assisted by precious metal chelates have the following advantages: (1) Due to the good interaction between Pt and VN, the electronic structure at the coupling interface can be regulated; (2) Reducing the particle size can provide more active sites; (3) The unique porous network of the VN carrier can not only improve the structural integrity and electrochemical durability, but also provide ultrafast electron / ion transfer pore channels.

[0179] In some embodiments, the conditions of reaction VI include: reaction temperature of 0-160° C., such as 10-150° C. or 10-100° C. or 10-60° C.; constant temperature reaction time of 1.0-5.0 h.

[0180] In some embodiments, the mass ratio of the remaining portion of the ammonium vanadate-containing sediment to the second ammonium salt is (1.0-20.0): (0.001-15.0); further (1.0-20.0): (0.1-10.0), further (1.0-20.0): (0.5-1.0), and for example (10.0-20.0): 1. The present application adopts this reaction ratio to improve the effect of the platinum salt in phase transformation and the formation of precious metal chelates.

[0181] In some embodiments, the mass ratio of the remaining ammonium vanadate-containing sediment to the precious metal compound is (1.0-20.0): (0.1-10.0), further (1.0-20.0): (1-10.0), and for example (10.0-20.0): 1. The present application limits it to the above range, which is beneficial to improve the utilization rate of precious metals and reduce the amount of precious metals used.

[0182] In some embodiments, the mass ratio of the noble metal compound to the chelating agent is (0.1~10.0):(0.001~15.0), further (0.1~10.0):(0.01~10.0), for example (1.0~10.0):1, and another example is (1.0~5.0):1; further, the concentration of the noble metal compound solution is 0.1~10.0mol / L or 1.0~10.0mol / L, and another example is 1.0~3.0mol / L; the concentration of the chelating agent solution is 0.001~15.0mol / L, for example 0.1~3.0mol / L. In the present application, the weight ratio of the noble metal compound to the chelating agent includes but is not limited to the above range, but limiting it within the above range is conducive to improving the dispersibility of the noble metal compound, and then improving the uniformity of the distribution of the noble metal in the catalyst precursor on the surface of the carrier precursor, which is convenient for the subsequent inhibition of the migration and agglomeration of the noble metal in the supported catalyst.

[0183] In some embodiments, in order to improve the reaction efficiency, the molar ratio of the precious metal compound and the third reducing agent is (0.001~0.1):(0.005~0.5); for example, (0.01~0.1):(0.05~0.5), and another example is (0.05~0.1):0.5; when used, the concentration of the precious metal compound solution is 0.001~0.1 mol / L or 0.01~0.1 mol / L; the concentration of the third reducing agent solution is 0.005~0.5 mol / L, further 0.005~0.1 mol / L, and another example is 0.01~0.1 mol / L.

[0184] In some embodiments, in order to improve the reduction efficiency in the second calcination heat treatment and thus improve the yield of the VN carrier, the weight ratio of the fourth reducing agent to the product of reaction VI is (0.1-0.5):1.

[0185] In order to make the amount of precious metal in the subsequently prepared supported catalyst more appropriate and improve the catalytic activity of the supported catalyst, the weight ratio of the support precursor, the precious metal-containing compound and the fourth solvent can be (1-20): (0.1-10): (100-5000).

[0186] In some embodiments, in order to improve the effect of phase conversion of platinum salt and generate noble metal chelate, the second ammonium salt is selected from at least one of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium bicarbonate, ammonium carbonate, polydopamine, ethylenediaminetetraacetic acid, ethylenediamine, triethylenetetramine, triethanolamine, hexamethylenetetramine, melamine, ammonium polyacrylate and dopamine hydrochloride. The first ammonium salt and the second ammonium salt of the present application may be the same or different.

[0187] In some embodiments, the noble metal compound is selected from at least one of chloroplatinic acid, chloroplatinate, [Pt(acac)2], diamine dinitrite platinum, and [Pt(CH3NH2)4][PtCl4].

[0188] In some embodiments, the chelating agent is selected from at least one of thiourea, sulfite, phosphoric acid, oxalic acid, arsonic acid, polyacrylic acid, and polyvinyl alcohol.

[0189] In some embodiments, the third reducing agent is selected from at least one of elemental sulfur, ascorbic acid, sodium ascorbate, sodium citrate, formaldehyde, acetaldehyde, formic acid, acetic acid, hydrazine hydrate, metal borohydride salts, sulfites and oleylamine; compared with other types, the use of the above types of reducing agents is beneficial to improving the reaction efficiency.

[0190] In some embodiments, the fourth reducing agent is elemental carbon, which can reduce V2O5 to VN, thereby obtaining a VN carrier. In order to better exert the reducing effect of the fourth reducing agent and thereby increase the yield of the VN carrier, the average particle size of the fourth reducing agent is 50-1000 nm.

[0191] In some embodiments, in order to improve the dispersion degree of each raw material in the fourth solvent, the fourth solvent includes but is not limited to water and / or ethylene glycol. When the fourth solvent includes the above-mentioned type of organic solvent, the functional group of the organic solvent replaces the non-bridging hydroxyl group on the surface of the carrier precursor, and plays a certain steric hindrance effect to inhibit the agglomeration of the carrier precursor, and is conducive to controlling the nucleation rate of the noble metal and the size of the noble metal particles; in addition, the organic solvent has a lower surface tension than water, which is conducive to the subsequent calcination annealing treatment.

[0192] In some embodiments, in order to more specifically dissolve each raw material in a suitable solvent to improve the solubility of the raw material in step S23-2, different raw materials can be dissolved in different solvents; for example, step S23-2-1: the carrier precursor (deposits containing ammonium vanadate), the second ammonium salt, the noble metal compound, and the chelating agent can be dissolved in solvent A to form a first mixed solution; step S23-2-2: the third reducing agent, the dispersant and the solvent B are mixed to form a second mixed solution; step S23-2-3: the first mixed solution and the second mixed solution are then mixed and reacted to obtain a reaction VI product system. Wherein, solvent A is water and / or ethylene glycol, and solvent B includes at least one of water, methanol, ethanol, propanol, ethylene glycol, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide and diethylformamide.

[0193] In the present application, a mixed solution of solvent A water and / or ethylene glycol is used in the first mixed solution in the above steps, which is conducive to improving the wettability of the carrier precursor, thereby improving the loading effect of the precious metal particles. In addition, the above process is used to prepare the reaction VI product system, which is conducive to improving the dispersibility of each reaction raw material in the solvent, and is conducive to improving the utilization rate of each reaction raw material. At the same time, it is also conducive to the reaction to proceed more smoothly, thereby improving the yield of the catalyst precursor, and enhancing the distribution uniformity of the precious metal in the catalyst precursor; when the solvent B includes the above-mentioned type of organic solvent, the functional group of the organic solvent replaces the non-bridging hydroxyl group on the surface of the carrier precursor, and plays a certain steric hindrance to inhibit the carrier precursor from agglomerating, and is conducive to controlling the precious metal nucleation rate and the precious metal particle size; and, the organic solvent has a lower surface tension than water, which is convenient for subsequent annealing treatment.

[0194] In some embodiments, in step S23-2-1, the mixing temperature is 0-160°C and the mixing time is 1.0-5.0 hours. The mixing temperature and time include but are not limited to the above ranges, and limiting them within the above ranges is conducive to improving the dispersibility of the carrier precursor, the noble metal-containing compound and the chelating agent in the fourth solvent, which is convenient for subsequent reactions.

[0195] In some embodiments, in step S23-2-2, the molar concentration of the third reducing agent in the second mixed solution is 0.005-0.5 mol / L, for example, 0.01-0.5 mol / L, and another example is 0.01-0.1 mol / L. The molar concentration of the third reducing agent includes but is not limited to the above range, and limiting it within the above range is conducive to improving the reaction efficiency, thereby facilitating the improvement of the yield of the zero-valent noble metal, and improving the catalytic activity of the supported catalyst.

[0196] In some embodiments, in step S23-2-3, the first mixed solution is dripped into the second mixed solution at a rate of 1-10 mL / min. Mixing the first mixed solution with the second mixed solution in the above manner is beneficial to improving the reaction efficiency and thus the yield of the zero-valent noble metal.

[0197] In order to further improve the reaction efficiency and the yield of zero-valent noble metals, the mixing in step S23-2-3 is carried out under stirring conditions with a stirring speed of 300-500 rpm; the reaction time is 10-60 min.

[0198] In order to further improve the dispersibility and compatibility of each raw material during the reaction process, in the second mixed solution, the mass concentration of the dispersant is 1.0~5.0g / L; the dispersant includes but is not limited to one or more of the group consisting of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, methyl cellulose, polyacrylic acid, sodium sulfosuccinate, sodium lauryl sulfate, sodium citrate and quaternary ammonium salts.

[0199] In some embodiments, the preparation method provided by the present application further comprises: sequentially performing solid-liquid separation and freeze-drying treatment on the reaction VI product system to obtain a catalyst precursor. Performing solid-liquid separation on the reaction VI product system can separate the catalyst precursor from the solvent to obtain a solid phase product; freeze-drying the solid phase product can remove the residual solvent in the solid phase product, and compared with other drying treatments, freeze-drying treatment helps to inhibit particle agglomeration caused by capillary adsorption effect.

[0200] In order to improve the separation efficiency of the catalyst precursor from water and solvent, solid-liquid separation includes but is not limited to centrifugal separation. In order to further improve the removal efficiency of residual water and the fourth solvent in the solid phase product and further inhibit the agglomeration of particles, the freeze-drying treatment temperature is -10~-60℃ and the time is 6.0~24.0h.

[0201] In some embodiments, the second protective atmosphere is selected from at least one of argon, nitrogen, helium and NH 3 .

[0202] In some embodiments, the second calcination heat treatment process includes a first stage heat treatment, a second stage heat treatment, a third stage heat treatment and a fourth stage heat treatment in sequence. Compared with a single temperature condition heat treatment, the staged temperature increase treatment is beneficial to improving the annealing effect, improving the yield of VN, and providing more active sites.

[0203] In some embodiments, the first stage heat treatment includes: heating from 25°C to 300~350°C at a heating rate of 5~30°C / min, and keeping warm for 1.0~1.5h; the second stage heat treatment includes: continuing to heat up to 600~650°C at a heating rate of 5~10°C / min, and keeping warm for 1.0~3.0h; the third stage heat treatment includes: continuing to heat up to 800~900°C at a heating rate of 5~10°C / min, and keeping warm for 1.0~3.0h; the fourth stage heat treatment includes: continuing to heat up to 1100~1200°C at a heating rate of 5~10°C / min, keeping warm for 1.0~3.0h, and after naturally cooling to room temperature, a vanadium-based hydrogen evolution electrocatalyst loaded with precious metals is obtained.

[0204] In the first stage heat treatment process of the present application, free water is volatilized by heating, and at the same time, the carrier precursor begins to thermally decompose; in the second stage heat treatment process, V2O5 undergoes a pre-reaction, during which the ammonium salt is fully thermally decomposed, and the released NH3 can act as a reducing agent at high temperature, and under the erosion and release of the gas, it is beneficial to increase the specific surface area and porosity of the carrier; in the third stage heat treatment process, the thermally decomposed platinum salt decomposes into elemental Pt; in the fourth stage heat treatment process, the electronic structure between Pt and VN is adjusted, and the elemental Pt is transformed from a disordered state to an ordered structure, thereby improving the electrocatalytic activity and stability of the supported catalyst.

[0205] In some embodiments, the second calcination heat treatment is performed in a tubular vacuum furnace, and the volume flow rate of the protective gas is 1-10 L / min. The introduction rate of the protective gas includes but is not limited to the above range, and limiting it within the above range is conducive to improving the calcination annealing treatment effect, thereby helping to improve the catalytic activity and stability of the supported catalyst.

[0206] In some embodiments, the preparation method provided in the present application further comprises: after the second calcination heat treatment, grinding the thermal reduction product to obtain a supported catalyst. Compared with not grinding, the supported catalyst obtained after grinding has a more uniform particle size and is conducive to the application in all-vanadium redox flow batteries.

[0207] In some embodiments, in order to improve the catalytic activity of the supported catalyst, the loading amount of the noble metal in the supported catalyst is 20.0-40.0 wt %.

[0208] The supported catalyst provided in the present application has a large specific surface area and can load more precious metals. For example, the pore volume of the supported catalyst is 0.01-10.0 cm 3 / g, average pore size of 5~50nm, specific surface area of ​​450~600m 2 / g.

[0209] In some embodiments, a vanadium-based catalyst loaded with precious metals, a Nafion solution and an organic solvent II are mixed to obtain a slurry; the slurry is attached to the surface of a membrane electrode to obtain a catalyst membrane electrode; wherein the organic solvent II is ethanol and / or acetone.

[0210] In some embodiments, the mixing ratio of the noble metal-loaded vanadium-based catalyst, the Nafion solution, and the organic solvent II is (2.5-15.0) mg: (100.0-150.0) μL: (1.0-10.0) mL; wherein the mass concentration of the Nafion solution is 0.5-10.0 wt %.

[0211] In some embodiments, the process of electrocatalytic reduction of the hydrogen evolution electrocatalyst in step S3 is that the catalyst membrane electrode performs reaction IV under direct current conditions to obtain a solution containing trivalent vanadium.

[0212] Specifically, 12.0 mg of the catalyst prepared in S23-2 was weighed, mixed with 5.0 mL of ethanol and 120.0 μL of Nafion solution (5.0 wt%), and ultrasonically dispersed for 15-45 min. The membrane electrode was prepared by the catalyst coating membrane method with an effective area of ​​2 × 2 cm 2 The electrolysis conditions are: electrolysis voltage 0.5~5.0V, electrolysis temperature 20~60℃, electrolysis time 0.5~3.0h, and the distance between the electrode plates is 2.0~10.0cm; vanadium ion modulation, the vanadium ion-containing acid solution in step S2 (the first tetravalent vanadium-containing solution) and the electrolytic vanadium ion solution (trivalent vanadium-containing solution) in step S3 are fully mixed, and the vanadium ion molar concentration ratio is 1:1 to obtain an electrolyte for an all-vanadium liquid flow battery.

[0213] According to a second aspect of the present application, an all-vanadium electrolyte is provided, which is prepared by the above-mentioned method for preparing the all-vanadium electrolyte.

[0214] According to a third aspect of the present application, there is provided an all-vanadium liquid flow battery, comprising an all-vanadium electrolyte, which is the all-vanadium electrolyte described above.

[0215] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0216] Example 1

[0217] Step S1: Weigh 10.0g of vanadium slag, grind it, add it to a 1.0mol / L NaHCO3 solution (liquid-to-solid mass ratio of 4:1), and stir it thoroughly to make it evenly dispersed; then, use a 1.5mol / L NaOH aqueous solution to adjust the pH value of the reaction system to 11.5±0.5. Place the system in a magnetic stirring environment at 90°C and 500rpm for a constant temperature reaction (reaction I) for 3.0h. After reaction I is completed, cool it naturally to room temperature, filter and wash it in turn, collect the filtrate and vanadium enriched product respectively, and the XRD of the vanadium enriched product is as follows: Figure 3 shown.

[0218] Step S2: At the same time, 0.0175 mol of ammonium carbonate is dissolved in a mixed solvent consisting of 50 mL of water and 10 mL of 5.0 mol / L carbonic acid, and stirred at 300 rpm for 60 min to obtain a first ammonium salt solution with a concentration of 0.292 mol / L; the vanadium enriched material obtained in step S1 is prepared into a 40 mL vanadium enriched material suspension according to a ratio of 5.0 g of vanadium enriched material, 20 mL of water and 20 mL of ethanol; the above 60 mL of ammonium salt solution is added dropwise to the 40 mL vanadium enriched material suspension at a rate of 10 mL / min, and reaction II is carried out at 25° C., and the reaction is carried out at a constant temperature for 60 min; after the reaction is completed, the products are centrifuged in turn, washed three times with anhydrous ethanol, and dried at 60° C. for 12.0 h to obtain ammonium metavanadate.

[0219] After the ammonium metavanadate sample is ground, it is placed in a tube furnace and heated at a rate of 15°C / min. It is first heated to 150°C and kept warm for 1.0h; then heated to 350°C at 10°C / min and kept warm for 1.0h; then heated to 500°C at 5°C / min and kept warm for 1.0h. When the temperature is cooled to 350°C with the furnace, oxygen (gas flow rate 1L / min) is introduced and the temperature is kept constant for 3.0h, and then the temperature is cooled to room temperature with the furnace to obtain vanadium oxide. The obtained vanadium oxide is mixed with the first reducing agent oxalic acid at a mass ratio of 1.75:1, and added to the acid reaction system with a sulfuric acid concentration of 0.1mol / L to carry out reaction III, the reaction temperature is 90°C, and the reaction is kept at a constant temperature for 3.0h; after the reaction system is cooled to room temperature, it is filtered to obtain the first tetravalent vanadium solution (VOSO4) as the electrolyte to be reduced.

[0220] Step S3: Add a H2SO4 solution with a molar concentration of 4.5 mol / L to the positive electrode reaction cell of the electrolytic cell, and prepare a H2SO4 mixed solution containing 1.5 mol / L VOSO4 (tetravalent vanadium ion solution prepared in step S2) and a molar concentration of 3.0 mol / L in the negative electrode electrolytic cell; the hydrogen evolution electrocatalyst uses a commercial Pt / C catalyst (McLean P822267, platinum carbon catalyst), and the Pt loading in the catalyst is 20.0wt%; the Pt / C catalyst is prepared on the two electrodes of the electrolytic cell by the CCM method. The preparation process is as follows: weigh 12.0 mg of Pt / C catalyst, mix it with 5 ml of ethanol and 120 μL of Nafion solution (5.0wt%, a solution of perfluorosulfonic acid resin polymer dissolved in a solvent) to make a slurry, and ultrasonically disperse it for 30 minutes. Then spray the slurry on the front and back sides of the Nafion 115 membrane, with an effective area of ​​2×2cm 2 The electrolytic cell was divided, and constant voltage electrolysis was adopted. The plate spacing was adjusted to 3.0 cm, the cell pressure was controlled to 1.8 V, the electrolysis temperature was set to 30 ° C, and the reaction time was 0.5 h. The vanadium ion solution in the negative electrode electrolytic cell was completely discharged. During this process, the vanadium ion solution obtained electrons on the surface of the negative electrode membrane electrode and an electrocatalytic reduction reaction occurred. That is, the V in the solution was 4+ Reduction occurs and converts to V 3+ (V 4+ +e - →V 3+ During the reaction, the valence state of vanadium ions was determined by redox titration. 4+ Completely converted to V 3+ When the V prepared in step S2 is 4+ Ionic solution, according to n (V3+) : n (V4+) The molar ratio is 1:1, and the mixture is mixed and stirred thoroughly; after being mixed thoroughly, the mixture is filtered to obtain a 3.5-valent vanadium electrolyte for an all-vanadium liquid flow battery; Figure 1 and Figure 2 shown.

[0221] Example 2

[0222] The difference between Example 2 and Example 1 is that a certain amount of 5.0 g of the vanadium enriched material obtained in step S1 (including calcium carbonate) is roasted at a temperature of 1000° C. for 3.0 h to obtain a roasted slag containing calcium oxide (whose components contain calcium oxide), so as to utilize calcium oxide to enrich the vanadium ions in the vanadium slag alkali solution.

[0223] The specific steps are as follows: weigh 5.0 g of the vanadium enriched product obtained in step S1, add 62.5 mL of 1.5 mol / L NaHCO3 alkaline leaching solution, adjust the vanadium slag concentration to 80.0g / L (in terms of V2O5, the vanadium enrichment is added to promote the reaction between calcium oxide and vanadium ions), then add 1.5g of roasted slag (containing CaO), adjust the pH value of the solution system to 11.5±0.5 with 1.5mol / L NaOH solution, and carry out vanadium enrichment operation; react at 95℃ for 180min, and after the reaction is completed, obtain a vanadium-enriched product, filter and wash the product to obtain a solid powder containing calcium vanadate, then add 200mL of deionized water, and at the same time add 100mL of a mixed acid of 98% sulfuric acid and 20% hydrochloric acid by mass fraction, adjust the pH value of the system to 1.5, ultrasonically disperse for 15min, and after uniform dispersion, add the second reducing agent sodium oxalate according to the mass ratio of m (calcium vanadate): m (second reducing agent) = 1:1, and stir at 95℃ for 3.0h to react V. After the reaction is completed, filtering is performed to obtain a white precipitate (mainly calcium carbonate) and a blue tetravalent vanadium oxysulfate (VOSO4) solution, i.e., a second tetravalent vanadium-containing solution; the first tetravalent vanadium-containing solution prepared in step S2 is mixed with the second tetravalent vanadium-containing solution to form a tetravalent vanadium mixed solution, which is used as an electrolyte to be reduced (VOSO4), and then step S3 is continued; Figure 1 and Figure 2 shown.

[0224] Example 3

[0225] The difference between Example 3 and Example 1 is that step S3 uses a homemade hydrogen evolution catalyst, and the specific steps are as follows: the ammonium metavanadate prepared in step S2 is divided into two parts, one part is used for pyrolysis into vanadium oxide and then reduced to tetravalent vanadium, and this process is the same as in Example 1; the other part is used to prepare the hydrogen evolution catalyst.

[0226] The preparation process of the hydrogen evolution catalyst is as follows: take an appropriate amount of ammonium metavanadate in step S2 as a carrier precursor, that is, mix 5.75g of the carrier precursor, 0.3g of ammonium chloride, 0.42g of chloroplatinic acid, 0.02g of oxalic acid, 150mL of water and 50mL of ethylene glycol at 10°C for 60min to form a first mixed solution; mix 1.76g of the third reducing agent ascorbic acid with 0.2g of polyacrylic acid and 100mL of water to prepare 100mL, 0.1mol / L ascorbic acid solution (i.e., the second mixed solution); under stirring at 300rpm, add 200mL of the first mixed solution to 100mL of the second mixed solution at a drip rate of 10mL / min to carry out a Pt salt phase transformation double decomposition reaction VI, react at 30°C for 60min, and obtain a VI product system containing a catalyst precursor, which is centrifuged and washed with anhydrous ethanol three times in sequence, and freeze-dried at -50°C for 12.0h to obtain a catalyst precursor.

[0227] The above-prepared catalyst precursor and carbon powder with an average particle size of 100 nm were transferred together into a tubular vacuum furnace for calcination and annealing treatment; nitrogen was introduced with a flow rate controlled at 1L / min. First, the temperature was increased from 25°C to 350°C at a heating rate of 15°C / min and kept warm for 1.0h, then the temperature was continued to be increased to 650°C at a rate of 10°C / min and kept warm for 1.0h, then the temperature was continued to be increased to 900°C at a rate of 5°C / min and kept warm for 1.0h, and then the temperature was increased to 1200°C at a heating rate of 5°C / min and kept warm for 3.0h. After naturally cooling to room temperature, a loaded catalyst was obtained. The catalyst uses VN as a carrier and precious metal Pt as an active component, wherein the loading amount of the precious metal is 20.0wt%. The characterization of the prepared catalyst is as follows Figure 4 shown.

[0228] The Pt / VN catalyst obtained above was used to prepare membrane electrodes on the two electrodes of the electrolytic cell using the CCM method; the preparation steps of the membrane electrode are as follows: 12.0 mg of catalyst, 5.0 ml of ethanol and 120.0 μL of 5 wt% Nafion solution (a solution of perfluorosulfonic acid resin polymer dissolved in a solvent) were weighed and mixed to make a slurry, and then ultrasonically dispersed for 30 minutes. The slurry was sprayed on the front and back sides of the Nafion 115 membrane with an effective area of ​​2×2 cm 2 The specification split electrolytic cell adopts constant voltage electrolysis mode, controls the cell pressure at 1.8V, completely discharges the vanadium ion solution in the negative electrode electrolytic cell, and an electrocatalytic reduction reaction occurs on the surface of the negative electrode membrane electrode, that is, the V in the solution 4+ Restored to V 3+ During the reaction, the valence state of vanadium ions was determined by redox titration. 3+ When the V prepared in step S2 is 4+ Ionic solution by n(V3+) : n (V4+) The mixture is mixed in a ratio of 1:1, stirred sufficiently, and filtered after being sufficiently mixed to obtain a 3.5-valent vanadium electrolyte for an all-vanadium liquid flow battery; Figure 1 and Figure 2 shown.

[0229] Example 4

[0230] The difference between Example 4 and Example 1 is that the alkaline leaching agent is KHCO3 aqueous solution, the temperature of alkaline leaching reaction I is 180°C, and the time of reaction I is 3.0h.

[0231] Example 5

[0232] The difference between Example 5 and Example 1 is that the first ammonium salt is ammonium sulfate, the temperature of vanadium precipitation reaction II is 90° C., and the reaction time is 2.0 h.

[0233] Example 6

[0234] The difference between Example 6 and Example 1 is that in the reduction reaction III, the first reducing agent is potassium oxalate, the solution concentration of which is 5.0 mol / L, the temperature of the reaction III is 120° C., and the reaction time is 3.0 h.

[0235] Example 7

[0236] The difference between Example 7 and Example 3 is that in step S2, the first ammonium salt is ammonium bisulfate, and the solution concentration thereof is 5.0 mol / L.

[0237] Example 8

[0238] The difference between Example 8 and Example 3 is that the third reducing agent is acetic acid; and the molar ratio of chloroplatinic acid to the third reducing agent acetic acid is 0.001:0.005.

[0239] Example 9

[0240] The difference between Example 9 and Example 3 is that 0.85 g of sodium chloroplatinate is used instead of chloroplatinic acid to obtain the first mixed solution.

[0241] Example 10

[0242] The difference between Example 10 and Example 3 is that 0.4 g [Pt(acac)2] is used instead of chloroplatinic acid to obtain the first mixed solution.

[0243] Embodiment 11

[0244] The difference between Example 11 and Example 3 is that 0.65 g of diammine dinitrite platinum is used instead of chloroplatinic acid to obtain the first mixed solution.

[0245] Comparative Example 1

[0246] Comparative Example 1 provides a method for preparing an all-vanadium liquid flow battery electrolyte, comprising:

[0247] (1) mixing vanadium pentoxide and concentrated sulfuric acid at a molar ratio of 1:2.25, the concentration of the concentrated sulfuric acid being 18.4 mol / L, with magnetic stirring at 500 rpm, the temperature being 25° C., and the stirring time being 0.5 h to obtain a mixture;

[0248] (2) Activating the mixture of step (1) at an activation temperature of 150° C. for an activation time of 2.0 h to obtain an activated product (VO2)2SO4, which was then cooled to room temperature;

[0249] (3) Stir and dissolve the activated product (VO2)2SO4 in step (2) at a temperature of 40°C, using 3.0 mol / L dilute sulfuric acid as the solvent, a liquid-to-solid ratio of dilute sulfuric acid to the activated product (VO2)2SO4 of 6 mL / g, and a dissolution stirring time of 1.0 h to obtain a solution;

[0250] (4) Pd / C catalyst was added to the solution of step (3), and hydrogen was introduced at a flow rate of 450 mL / min to carry out a reduction reaction to obtain an all-vanadium liquid flow battery electrolyte. The hydrogen partial pressure of the reduction reaction was 0.1 MPa, the temperature of the reduction reaction was 120° C., and the reduction reaction time was 6.0 h.

[0251] The vanadium ion valence state of the all-vanadium electrolyte prepared by Examples 1 to 11 and Comparative Example 1 was tested and analyzed according to GB / T 37204-2018, and an all-vanadium flow battery was assembled to test the constant current charge and discharge performance of the vanadium electrolyte. Constant current charge and discharge test conditions: 100, 80, 60, 40 mA / cm 2 Current density; Cycle stability test conditions: 100 mA / cm 2 The charge and discharge cut-off voltages are 1.65 V and 0.8 V respectively. The coulombic efficiency (%), voltage efficiency (%) and energy efficiency (%) of the test battery are shown in Table 1.

[0252] Table 1

[0253]

[0254] The test data in Table 1 show that the all-vanadium electrolytes prepared in Examples 1 to 11 of the present application have good charge and discharge performances.

[0255] In Example 1 of the present application, the initial raw material for preparing the vanadium electrolyte is solid waste vanadium slag. First, it is subjected to alkaline leaching and ammonium salt vanadium precipitation treatment to obtain pure tetravalent vanadium; then, the tetravalent vanadium is reduced to trivalent vanadium by electrocatalysis; finally, the ratio of trivalent vanadium to tetravalent vanadium is adjusted and mixed to finally obtain a 3.5-valent vanadium electrolyte.

[0256] Example 2 of the present application further utilizes the filter residue produced by preparing the vanadium electrolyte: first, active calcium oxide is obtained by roasting; then, pentavalent calcium vanadate is obtained by vanadium enrichment treatment; then, a reducing agent is used to reduce in an acid / mixed acid system to obtain a tetravalent vanadium solution; finally, trivalent vanadium is prepared by electrocatalytic reduction. In this method, not only the waste calcium carbonate roasting residue is fully utilized, but also the purity of the vanadium enrichment is improved, and a new way to prepare tetravalent vanadium is realized, further improving the efficiency of vanadium extraction.

[0257] Example 3 of the present application uses the intermediate product ammonium vanadate deposit produced when preparing vanadium electrolyte to prepare a new type of electrocatalyst. Specifically, by selecting a suitable noble metal (such as Pt) as the active metal, and selecting a suitable reducing agent, solvent, ammonium salt, etc., the noble metal Pt is in situ deposited on the surface of the carrier, and after heat treatment and in situ reduction, a new type of vanadium-based catalyst loaded with platinum metal is obtained; then, the catalyst is applied to the membrane electrode of the liquid flow battery to catalyze the electrolytic reduction reaction to improve the efficiency of reducing the tetravalent vanadium electrolyte to the trivalent vanadium electrolyte.

[0258] Comparative Example 1 uses vanadium pentoxide as a raw material, and after reduction and high-temperature activation treatment, pentavalent vanadium is reduced to a valence state between 3 and 5 under the action of an electrocatalyst. The electrochemical performance of the electrolyte in Comparative Example 1 is lower than that of the electrolyte prepared in the embodiment of the present application, and the process of Comparative Example 1 can only obtain an electrolyte of one valence state, and it is impossible to achieve the goal of preparing a full vanadium electrolyte of more than three valence states using a single process. In addition, the raw material of Comparative Example 1 is vanadium oxide, while the present application uses solid waste vanadium slag as a raw material, which realizes the full utilization of waste resources and greatly reduces costs.

[0259] The method for preparing all-vanadium electrolyte provided in the embodiment of the present application can make full use of solid waste vanadium slag. From the initial raw materials to the intermediate products, the method is to prepare high value-added materials, and such materials can also be used in the preparation process of vanadium electrolyte. This method can not only obtain vanadium electrolytes of different valence states, but also realize the clean and high-value comprehensive utilization of vanadium slag resources, while realizing the closed-loop circulation of green and low-carbon metallurgy of vanadium metal, greatly reducing production costs, and reducing the production risks brought by traditional hydrogen reduction processes. The vanadium-based hydrogen evolution electrocatalyst prepared by it has high-efficiency reduction activity and effectively improves the reduction rate of vanadium ions; compared with the traditional electrolyte preparation method, this method has a faster reaction rate, lower risk, and does not introduce other reducing agents, and has better safety and economy.

[0260] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0261] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing an all-vanadium electrolyte, characterized in that: The preparation method comprises the following steps: Step S1: using an alkaline leaching agent to perform an alkali leaching treatment on the vanadium slag to perform reaction I, to obtain an alkali leaching product, and the alkali leaching product is subjected to solid-liquid separation to obtain a vanadium enriched product and a filtrate; Step S2: mixing the vanadium-enriched material, the first ammonium salt and the first solvent to carry out reaction II to obtain a vanadium precipitation product, and the vanadium precipitation product is subjected to solid-liquid separation to obtain a sediment containing ammonium vanadate; performing a first calcination heat treatment on the sediment containing ammonium vanadate to obtain vanadium oxide; mixing the vanadium oxide and the first reducing agent in a second solvent to carry out reaction III to obtain a first tetravalent vanadium-containing solution; Step S3: subjecting the first tetravalent vanadium-containing solution to reaction IV under electrocatalytic reduction conditions of a hydrogen evolution catalyst to obtain a trivalent vanadium-containing solution.

2. The method for preparing the all-vanadium electrolyte according to claim 1, characterized in that: The first tetravalent vanadium-containing solution obtained in step S2 is divided into two parts; a part of the first tetravalent vanadium-containing solution is subjected to reaction IV under the condition of electrocatalytic reduction of the hydrogen evolution catalyst to obtain the trivalent vanadium-containing solution; The remaining portion of the first tetravalent vanadium-containing solution is subjected to the process of step S4 after step S3; The process of step S4 includes: mixing the remaining portion of the first tetravalent vanadium-containing solution and the trivalent vanadium-containing solution and dissolving them in a sulfuric acid solution to obtain a trivalent-to-quadrivalent vanadium electrolyte.

3. The method for preparing the all-vanadium electrolyte according to claim 2, characterized in that: The molar ratio of the tetravalent vanadium ions in the sulfuric acid solution to the remaining tetravalent vanadium ions in the first tetravalent vanadium-containing solution is (1.5-6.0): (1.0-2.5), and the molar ratio of the sulfuric acid solution to the trivalent vanadium ions in the trivalent vanadium-containing solution is (1.5-6.0): (1.0-2.5); the concentration of the sulfuric acid solution is 2.0-5.0 mol / L; And / or, the molar concentration of tetravalent vanadium ions in the first tetravalent vanadium-containing solution of the remaining part and the molar concentration of trivalent vanadium ions in the trivalent vanadium-containing solution are adjusted to be 1:1 to obtain a 3.5-valent vanadium electrolyte.

4. The method for preparing the all-vanadium electrolyte according to claim 1, characterized in that: The vanadium-enriched material obtained in step S1 is divided into two parts; wherein a part of the vanadium-enriched material is mixed with the first ammonium salt and the first solvent to carry out the reaction II to obtain the vanadium precipitation product; and the remaining part of the vanadium-enriched material is subjected to roasting treatment; The roasting process comprises: roasting the remaining part of the vanadium enriched material to obtain a roasted slag containing calcium oxide; mixing the roasted slag containing calcium oxide, the alkaline leaching agent and the vanadium slag in a mass ratio of (1.0-30): (2.5-80): (1.5-20) to perform vanadium enrichment treatment to obtain a vanadium enriched product, and separating the vanadium enriched product to obtain a calcium vanadate enriched material; The calcium vanadate enriched material and the vanadium enriched material are mixed, and then mixed with the first ammonium salt and the first solvent to carry out the reaction II to obtain the vanadium precipitation product; Alternatively, the calcium vanadate concentrate and the second reducing agent are mixed in a third solvent to carry out reaction V to obtain a second tetravalent vanadium-containing solution; The step S23-1 is further included between step S2 and step S3: mixing the first tetravalent vanadium-containing solution and the second tetravalent vanadium-containing solution to obtain a mixed solution containing tetravalent vanadium; and subjecting the mixed solution containing tetravalent vanadium to reaction IV under the conditions of electrocatalytic reduction of the hydrogen evolution catalyst to obtain the solution containing trivalent vanadium.

5. The method for preparing the all-vanadium electrolyte according to claim 4, characterized in that: The conditions of the reaction V include: a reaction temperature of 60 to 120° C. and a constant temperature reaction time of 3.0 to 5.0 h; And / or, the mass ratio of the calcium vanadate enrichment to the second reducing agent is (1.0-3.5): (0.5-3.0); and / or, the second reducing agent is selected from at least one of oxalic acid, sodium oxalate, potassium oxalate, carboxylic acid, citric acid, tartaric acid and NH4HSO3; And / or, the third solvent is selected from at least one of H2SO4, HNO3, HCl, H2CO3 and H3PO4; the concentration of the third solvent is 0.1-5.0 mol / L; And / or, the pH value of the system of reaction V is 1.0-7.0; And / or, the mixed solution containing tetravalent vanadium obtained in step S23-1 is divided into two parts; a part of the mixed solution containing tetravalent vanadium is subjected to reaction IV under the conditions of electrocatalytic reduction of the hydrogen evolution catalyst to obtain the solution containing trivalent vanadium; and the remaining part of the mixed solution containing tetravalent vanadium is subjected to the process of step S4 after step S3; The process of step S4 includes: mixing the remaining part of the mixed solution containing tetravalent vanadium and the solution containing trivalent vanadium and dissolving them in a sulfuric acid solution to obtain a trivalent to tetravalent vanadium electrolyte; The molar ratio of the tetravalent vanadium ions in the sulfuric acid solution to the remaining tetravalent vanadium-containing mixed solution is (1.5-6.0): (1.0-2.5), and the molar ratio of the trivalent vanadium ions in the sulfuric acid solution to the trivalent vanadium-containing solution is (1.5-6.0): (1.0-2.5); the concentration of the sulfuric acid solution is 2.0-5.0 mol / L; The molar concentration of tetravalent vanadium ions in the remaining part of the mixed solution containing tetravalent vanadium and the molar concentration of trivalent vanadium ions in the trivalent vanadium-containing solution are adjusted to be 1:1 to obtain a 3.5-valent vanadium electrolyte.

6. The method for preparing the all-vanadium electrolyte according to any one of claims 1 to 5, characterized in that: The conditions of the reaction I in step S1 include: a reaction temperature of 90 to 180° C. and a constant temperature reaction time of 3.0 to 5.0 h; And / or, the mass ratio of the alkaline leaching agent to the vanadium slag is (1.5-200): (2.5-50); and / or, the pH of the mixed system of the alkaline leaching agent and the vanadium slag is 10.5-12.0; And / or, the concentration of the alkaline leaching agent is 0.01-10.0 mol / L; and / or, the alkaline leaching agent is selected from at least one of a NaOH aqueous solution, a Na2CO3 aqueous solution, a NaHCO3 aqueous solution, a KOH aqueous solution, a K2CO3 aqueous solution and a KHCO3 aqueous solution; And / or, the vanadium enriched material, water and organic solvent I in step S2 are first mixed to form a suspension of the vanadium enriched material, and the suspension of the vanadium enriched material is then mixed with the first ammonium salt and the first solvent to carry out the reaction II to obtain the vanadium precipitation product; wherein the volume ratio of the water to the organic solvent I is (50-1000): (5-500); the organic solvent I is at least one selected from the group consisting of methanol, ethanol, propanol, ethylene glycol, isopropanol, polyacrylic acid, N,N-dimethylformamide, N,N-dimethylacetamide and diethylformamide; And / or, the conditions of the reaction II in the step S2 include: the reaction temperature is 10-90° C., and the constant temperature reaction time is 1.0-5.0 h; And / or, the mass ratio of the vanadium enriched material to the first ammonium salt is (2.0-30.0): (0.5-50.0); and / or, the first ammonium salt is selected from at least one of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium bicarbonate, ammonium carbonate, polydopamine, hexamethylenetetramine, melamine, ammonium polyacrylate and dopamine hydrochloride; and / or, the first ammonium salt and the first solvent are mixed to form a first ammonium salt solution; the concentration of the first ammonium salt solution is 0.01-5.0 mol / L; And / or, the first solvent is a mixture of water and an inorganic acid; the volume ratio of the water to the inorganic acid is (50-1000): (5-500); wherein the inorganic acid is selected from at least one of hydrochloric acid, nitric acid, boric acid, sulfuric acid, carbonic acid and phosphoric acid; the concentration of the inorganic acid is 0.1-5.0 mol / L; And / or, the electrocatalytic reduction conditions in step S3 include: electrolysis voltage of 0.5-5.0 V, electrolysis temperature of 20-60° C., electrolysis time of 0.5-3.0 h, and a distance between electrode plates of 2.0-10.0 cm.

7. The method for preparing the all-vanadium electrolyte according to any one of claims 1 to 5, characterized in that: The conditions of the reaction III in step S2 include: a reaction temperature of 60-120° C. and a constant temperature reaction time of 3.0-5.0 h; And / or, the mass ratio of the vanadium oxide to the first reducing agent is (1.0-3.5): (0.5-3.0); and / or, the first reducing agent is selected from at least one of SO2, NH4HSO3, H2O2, oxalic acid, sodium oxalate, potassium oxalate, ascorbic acid, sodium ascorbate, sodium sulfite, sodium pyrosulfite and carboxylic acid; and / or, the second solvent is selected from at least one of H2SO4, HCl and phosphoric acid; the concentration of the second solvent is 0.1-5.0 mol / L; And / or, the process of the first calcination heat treatment includes: a first stage heat treatment, a second stage heat treatment, and a third stage heat treatment in sequence; wherein the process of the first stage heat treatment includes: heating from 25°C to 150-200°C at a heating rate of 5-30°C / min, and keeping the temperature for 1.0-1.5h; the process of the second stage heat treatment includes: continuing to heat to 300-350°C at a heating rate of 5-10°C / min, and keeping the temperature for 1.0-3.0h; the process of the third stage heat treatment includes: continuing to heat to 450-500°C at a heating rate of 5-10°C / min, and keeping the temperature for 1.0-3.0h; And / or, the first calcination heat treatment process is carried out in a first protective atmosphere; the first protective atmosphere is selected from at least one of argon, nitrogen, helium and NH3; the gas flow rate of the first protective atmosphere is 1-10 L / min; the first calcination heat treatment process is carried out in a tubular vacuum furnace; And / or, the first calcination heat treatment further includes an annealing treatment, the process of which includes: cooling to 300-400°C at a cooling rate of 5-10°C / min, introducing oxygen; the flow rate of the oxygen is 1-10 L / min, the temperature is kept constant for 1.0-3.0 hours, and then the temperature is naturally cooled to room temperature; And / or, step S23-2 is further included between step S2 and step S3: dividing the ammonium vanadate-containing sediment obtained in step S2 into two parts; subjecting one part of the ammonium vanadate-containing sediment to the first calcination heat treatment in step S2 to obtain the vanadium oxide; and using the remaining part of the ammonium vanadate-containing sediment to prepare a vanadium-based hydrogen evolution electrocatalyst; The preparation process of the vanadium-based hydrogen evolution electrocatalyst comprises: mixing the remaining portion of the ammonium vanadate-containing sediment, the second ammonium salt, the noble metal compound, the chelating agent, the third reducing agent and the fourth solvent to carry out reaction VI to obtain a reaction VI product; and performing a second calcination heat treatment on the reaction VI product and the fourth reducing agent in a second protective atmosphere to obtain a vanadium-based hydrogen evolution electrocatalyst loaded with noble metals.

8. The method for preparing the all-vanadium electrolyte according to claim 7, characterized in that: The conditions of reaction VI include: reaction temperature of 0-160° C., constant temperature reaction time of 1.0-5.0 h; And / or, the mass ratio of the remaining part of the ammonium vanadate-containing sediment to the second ammonium salt is (1.0-20.0): (0.001-15.0); And / or, the mass ratio of the remaining part of the ammonium vanadate-containing sediment to the precious metal compound is (1.0-20.0): (0.1-10.0); And / or, the mass ratio of the noble metal compound to the chelating agent is (0.1-10.0): (0.001-15.0); and / or, the molar ratio of the noble metal compound to the third reducing agent is (0.001-0.1):(0.005-0.5); and / or, the mass ratio of the fourth reducing agent to the product of reaction VI is (0.1-0.5):1; and / or, the second ammonium salt is selected from at least one of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium bicarbonate, ammonium carbonate, polydopamine, ethylenediaminetetraacetic acid, ethylenediamine, triethylenetetramine, triethanolamine, hexamethylenetetramine, melamine, ammonium polyacrylate and dopamine hydrochloride; and / or, the noble metal compound is selected from at least one of chloroplatinic acid, chloroplatinate, [Pt(acac)2], diammine dinitrite platinum and [Pt(CH3NH2)4][PtCl4]; And / or, the chelating agent is selected from at least one of thiourea, sulfite, phosphoric acid, oxalic acid, arsenic acid, polyacrylic acid and polyvinyl alcohol; and / or, the third reducing agent is selected from at least one of elemental sulfur, ascorbic acid, sodium ascorbate, sodium citrate, formaldehyde, acetaldehyde, formic acid, acetic acid, hydrazine hydrate, metal borohydride salt, sulfite and oleylamine; And / or, the fourth reducing agent is elemental carbon; and / or, the fourth solvent is selected from water and / or ethylene glycol; And / or, the second protective atmosphere is selected from at least one of argon, nitrogen, helium and NH3; And / or, the process of the second calcination heat treatment includes a first stage heat treatment, a second stage heat treatment, a third stage heat treatment and a fourth stage heat treatment in sequence; wherein, the first stage heat treatment includes: heating from 25°C to 300-350°C at a heating rate of 5-30°C / min, and keeping warm for 1.0-1.5h; the second stage heat treatment includes: continuing to heat to 600-650°C at a heating rate of 5-10°C / min, and keeping warm for 1.0-3.0h; the third stage heat treatment includes: continuing to heat to 800-900°C at a heating rate of 5-10°C / min, and keeping warm for 1.0-3.0h; the fourth stage heat treatment includes: continuing to heat to 1100-1200°C at a heating rate of 5-10°C / min, and keeping warm for 1.0-3.0h, and naturally cooling to room temperature to obtain the vanadium-based hydrogen evolution electrocatalyst loaded with precious metals; And / or, the noble metal-loaded vanadium-based hydrogen evolution electrocatalyst, Nafion solution and organic solvent II are mixed to obtain slurry; the slurry is coated on the surface of a membrane electrode to obtain a catalyst membrane electrode; Wherein, the mixing ratio of the noble metal-loaded vanadium-based hydrogen evolution electrocatalyst, the Nafion solution and the organic solvent II is (2.5-15.0) mg: (100.0-150.0) μL: (1.0-10.0) mL; the concentration of the Nafion solution is 0.5-10.0 wt%; And / or, the loading amount of the noble metal in the vanadium-based hydrogen evolution electrocatalyst is 20.0-40.0 wt % and the pore volume is 0.01-10.0 cm 3 / g, average pore size of 5~50nm, specific surface area of ​​450~600m 2 / g.

9. An all-vanadium electrolyte, characterized in that: The all-vanadium electrolyte is prepared by the method for preparing the all-vanadium electrolyte according to any one of claims 1 to 8.

10. An all-vanadium liquid flow battery, comprising an all-vanadium electrolyte; characterized in that: The all-vanadium electrolyte is the all-vanadium electrolyte according to claim 9.

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