WO2019206121A1 - Manufacturing method and device of flow battery electrolyte - Google Patents

Abstract

The present invention relates to a manufacturing method and device of a flow battery electrolyte. The manufacturing method of a vanadium electrolyte comprises: employing an electrochemical method to reduce a tetravalent vanadium ion to a divalent vanadium ion; and reacting the divalent vanadium ion with a low cost, low purity higher-valence vanadium oxide to form a tetravalent vanadium ion. The invention provides a closed-loop production process for continuous production, can be operated easily, has low material costs and low energy consumption, does not directly consume power, and generates no additional chemical contaminants.

Description

Preparation method and preparation device for liquid battery electrolyte Technical field

The invention relates to a preparation method and a preparation device for a liquid flow battery electrolyte, and more particularly to a method and a preparation device for preparing a vanadium flow battery electrolyte by an electrochemical-chemical method.

Background technique

The flow battery technology has the natural advantage of large-scale energy storage: the amount of stored electricity is linearly proportional to the volume of the electrolyte, and the charge and discharge power is determined by the size and quantity of the stack, so it can be designed according to the demand, from kW to MW. Charge and discharge power, a flow battery with different energy storage capacity for 1 hour to several days. Based on common inorganic acids, inorganic salts have stable chemical composition, convenient storage, low environmental impact, and low self-discharge coefficient, suitable for long-term electrical energy storage. The reaction temperature of the battery is normal temperature and normal pressure. The electrolyte flow process is a natural water-based circulation heat dissipation system, and the safety performance is extremely high. The accident impact is much lower than other large energy storage solutions. Due to its stable and reliable charge and discharge cycle, there is no upper limit to the theoretical number of charge and discharge cycles.

In flow batteries, electrolytes are an important part of electrical energy storage, and their stability and longevity directly determine the capacity of the entire battery system. At present, most of the liquid battery companies in the world are still in demonstration projects for grid-level energy storage, far from meeting the reliability and stability requirements of commercial products. The battery system that has reached the scale of the demonstration project uses a pure sulfuric acid-based electrolyte containing vanadium ions, and a small amount of a sulfuric acid/hydrochloric acid-based mixed electrolyte containing vanadium ions.

At present, the preparation methods of all vanadium redox flow battery electrolytes are mainly divided into chemical, electrolytic and electrochemical-chemical methods. The chemical method mainly uses VOSO ₄ ·5H ₂ O or V ₂ O ₅ as the initial reactant, usually in a diluted sulfuric acid solution, adding a reducing agent or a low-cost vanadium oxide, so that the high-priced vanadium ions are finally gradually formed. Reduced to an equilibrium electrolyte. For example, Citation 1 discloses a vanadium electrolyte in which a mixture of V(III) and V(IV) is chemically reduced by adding a reducing agent such as oxalic acid or butyraldehyde to a mixed system of V ₂ O ₅ and a sulfuric acid solution. The main problem of this method is that the degree of reduction is not easy to control accurately; the V ₂ O ₅ prepared by the prior process is difficult to achieve high purification, and the electrolyte disposed in this process contains more impurities; the addition of reducing agent introduces new impurities into vanadium. The electrolyte system affects the purity of the electrolyte. Citation 2 discloses a mixed vanadium electrolyte prepared by dissolving VOSO ₄ in a sulfuric acid solution and electrochemically adjusting the valence state to prepare a concentration ratio of V(III) and V(IV) of 1:1. The main problem with this method is that the VOSO ₄ manufacturing process is relatively complicated and expensive, which is not conducive to large-scale popularization in VRB (ie vanadium redox battery); VOSO _{4 is} difficult to achieve high purity, electrolyte configured in this process Containing more impurities; electrochemical treatment is needed to adjust the V(III) and V(IV) concentration ratio to 1:1, so that the average valence state of vanadium ions in the electrolyte is +3.5.

In the electrolysis method, VOSO ₄ ·5H ₂ O or V ₂ O _{5 is} dissolved in a sulfuric acid electrolyte, and after adding a stabilizer, electrolysis is performed to finally obtain an electrolyte solution in an equilibrium state. For example, Citation 3 describes the addition of V ₂ O ₅ to a sulfuric acid solution, and a mixed vanadium electrolyte having a V(III) and V(IV) concentration ratio of 1:1 is prepared by constant current electrolysis. The preparation of vanadium electrolyte by electrolysis is suitable for large-scale electrolyte production, but requires pre-activation treatment, requires additional electrolysis equipment and consumes electric energy; and there are also problems of more electrolyte impurities.

The electrochemical-chemical rule combines the technical characteristics of the above two methods. The high-valence vanadium compound is used as a starting material, and a part of the reducing agent is consumed and a part of the electric energy is consumed to obtain a low-valent vanadium electrolyte. For example, in Citation 4, Citation 5 and Citation 6, a method of preparing a vanadium electrolyte by chemically and electrochemically combining is disclosed.

Citation 4 discloses a method for preparing a high-purity 3.5-valent vanadium solution by using a electrolytic device in a chemically and electrochemically combined manner by consuming a part of electric energy and a reducing agent capable of reducing pentavalent vanadium and using tetravalent vanadium as a raw material. Although this document mentions that re-use of the positive electrode electrolyte can be achieved, it is necessary to continuously add a reducing agent to the positive electrode. At the same time, the electrochemical-chemical method also requires precise control of the positive and negative feed ratios and the electrolysis amount at the initial stage of the reaction. Therefore, the simplicity and environmental friendliness of the preparation process still need to be further improved.

Citation 5 discloses an electrochemical preparation device for low-cost vanadium. The combination of chemical and electrochemical reduction is used to control the ratio of positive and negative feeds and the amount of electrolysis in the electrolytic cell, and the tetravalent vanadium is reduced to 2 in the negative electrode. ～3 valence, and the tetravalent vanadium is oxidized to 5 valence in the positive electrode, then the negative electrode electrolyte is discharged, a new tetravalent vanadium solution is injected, and a reducing agent is added to the positive electrode electrolyte to reduce the valence vanadium to 4 valence. Reuse of the positive electrode electrolyte and continuous production of 2 to 3 vanadium. Similar to the above cited document 4, it requires special control means in the initial stage of preparation, and requires continuous input of a reducing agent.

Citation 6 discloses a method for producing a high-purity and high-concentration vanadium electrolyte using a solid or solution containing a soluble vanadate, particularly a vanadium slag leaching solution after vanadium-titanium magnetite steelmaking, which is characterized by impurity removal, Acid vanadium, multiple alkali leaching vanadium, calcination, reduction step, can obtain sulfuric acid vanadium sulfate electrolyte with sulfuric acid concentration of 1 ~ 6 mole / liter, vanadium concentration of 1 ~ 5 mole / liter, combined with electrochemical method can be made A 3.5-valent or a trivalent vanadium electrolyte is obtained. Similarly, the vanadium electrolyte of the anode can be repeatedly used by chemical reduction after electrolysis, that is, it is still necessary to continuously consume the chemical reducing agent at the anode.

Therefore, from the existing technology, although the current electrochemical-chemical method has certain advantages, the existing electrochemical-chemical method still further improves the simplicity of continuous production, environmental friendliness and economy. Requirements.

List of citations

Citation 1: CN101562256A

Citation 2: US Patent US849094

Citation 3: PCT patent AKU88/000471

Citation 4: CN104638288A

Citation 5: CN104638289A

Citation 6: CN104037439A

Summary of the invention

Problems to be solved by the invention

As mentioned above, in the simple chemical preparation process, there are disadvantages of slow dissolution rate, low yield, and some reducing agents may cause pollution, accompanied by high energy consumption and low safety; and simple electrolysis preparation of all vanadium electrolysis The liquid not only needs to be activated for the initial raw material, but also has the disadvantage that the initial raw material vanadium pentoxide powder has limited solubility in the sulfuric acid solution, the electrolysis reaction rate is slow, the raw materials need to be added in batches, the electrolysis time is long, and the energy consumption is large. The resulting electrolyte also has a problem of more impurities.

At the same time, the above electrochemical-chemical preparation scheme has high requirements on the raw material ratio and the purity of the raw materials, and most of the reactions are carried out in a sulfuric acid environment. In order to increase the overall energy density of the vanadium redox flow battery, theoretically, the effective ion in the electrolyte, that is, the higher the vanadium ion concentration, the better. At room temperature, a mixture of vanadium ion sulfuric acid or sulfuric acid/hydrochloric acid which is above a certain concentration is extremely unstable, and precipitation precipitates after a certain period of time. Stabilizers need to be added, which increases the complexity of electrolyte preparation. If the concentration of vanadium ions in the acid solution is lowered, the overall energy density of the flow battery will be lowered. In addition, the above-mentioned electrochemical-chemical method still relies mainly on direct consumption of electrical energy, and the cost is high.

In addition, the price of vanadium sulfate, one of the main raw materials in the implementation of the electrochemical-chemical method, is relatively high, accounting for a considerable proportion (more than 30%) of the cost of the entire flow battery system, which is a huge reduction in battery cost and competitiveness. Obstruction. The preparation method using high-purity vanadium oxide as the starting material has high requirements on the purity of vanadium oxide, which is bound to have a great influence on the cost of the electrolyte.

In addition, it is still common in electrochemical-chemical methods to add a chemical reducing agent to the anode to reduce high-valent vanadium to low-valent vanadium, which also imposes an environmental burden.

Therefore, the present invention mainly provides a preparation of an all-vanadium redox flow battery electrolyte which can be conveniently subjected to continuous production, simple operation, low raw material cost, low energy consumption, and no direct consumption of electric energy, and does not generate an additional source of chemical pollution. method. The method of the invention reduces the tetravalent vanadium ions to divalent vanadium ions by electrochemical method, and then the divalent vanadium ions and the low-cost low-purity high-valence vanadium oxide form tetravalent vanadium ions, so that the entire production process forms a closed-loop continuous production. Moreover, as the reducing gas, hydrogen produced by solar electrolyzed water can be used, making the whole set of equipment more energy-saving and environmentally friendly.

Solution to solve the problem

In view of the above problems, the present invention proposes to use pure hydrochloric acid as an electrolyte solution, and combines electrochemical and chemical methods, and uses low-cost low-purity V ₂ O ₅ as a starting material without continuous pressure, heating or cooling. A method of producing an all-vanadium electrolyte. The specific plan is as follows:

The invention firstly provides a preparation method of a vanadium electrolyte, which comprises the following steps:

i) flowing a VO ^{2+ -containing} hydrochloric acid solution through the positive electrode to cause a reducing gas to flow through the negative electrode to cause a reduction reaction of VO ²⁺ to form a V ^{2+ -containing} hydrochloric acid solution;

Ii) reacting a V ^{2+ -containing} hydrochloric acid solution with a raw material V ₂ O ₅ to form a VO ^{2+ -containing} hydrochloric acid solution,

Optionally, iii) introducing a VO ^{2+ -containing} hydrochloric acid solution obtained in said ii) back to the positive electrode to continuously produce a V ^{2+ -containing} hydrochloric acid solution;

Iv) mixing a V ^{2+ -containing} hydrochloric acid solution with a VO ^{2+ -containing} hydrochloric acid solution to prepare an electrochemically equilibrated vanadium electrolyte.

According to the preparation method described above, the reducing gas includes hydrogen, and preferably, the hydrogen is derived from hydrogen produced by a solar electrolysis water method.

According to the above production method, the positive electrode includes a carbon-based material, preferably a graphite felt; and a separator is present between the positive electrode and the negative electrode.

According to the production method described above, the gas diffusion layer is provided on the negative electrode side of the separator.

According to the production method described above, the gas diffusion layer contains a catalyst.

Prepared according to the method described above, wherein the starting material V ₂ O ₅ is a noble metal impurity content than low-purity raw material cost 10PPM V ₂ O _5.

According to the above-described production method, it further comprises the step (i') before the step (i): reducing the hydrochloric acid solution of the raw material V ₂ O ₅ by using a reducing agent to obtain a VO ^{2+ -containing} hydrochloric acid solution.

The preparation method according to the above, characterized in that the reducing agent comprises an organic reducing agent and an inorganic reducing agent, preferably an organic reducing agent.

In addition, the present invention provides a preparation apparatus of a vanadium electrolyte, the apparatus including a positive electrode, a negative electrode, and a separator existing between the positive electrode and the negative electrode, and having a gas diffusion layer on a negative electrode side of the separator, The hydrochloric acid solution containing VO ²⁺ flows through the positive electrode, and the reducing gas flows through the negative electrode.

According to the apparatus described above, the VO ^{2+ -containing} hydrochloric acid solution has the same or opposite flow direction as the reducing gas.

Effect of the invention

According to the above technical solution of the present invention, the present invention can achieve the following technical effects:

(1) The preparation method of the present invention avoids the main raw material VOSO _{4 having a} limited solubility. On the one hand, it avoids the limited solubility of VOSO ₄ in acidic solution, which is prone to precipitation and precipitation, which causes the reactor to be obsolete; on the other hand, the pure hydrochloric acid solution environment ensures a higher concentration of vanadium ions in the solution, thereby improving the battery system. The overall energy density. In addition, pure hydrochloric acid is selected as the solution substrate. In the actual operation of the liquid flow battery, the acidity decreases due to various reasons, and the HCl gas can be recovered in time without changing the overall volume of the electrolyte and the vanadium ion concentration. The acidity of the electrolyte.

(2) The present invention is directed to the key technology for preparing electrolytes in the field of all-vanadium redox flow batteries, especially in the premise that the price of vanadium products continues to rise in recent years, avoiding the selection of high-purity raw materials of vanadium oxide, and innovative use Low-cost vanadium oxide with low impurity content of up to 1000PPM or higher is used as the starting material, and pure vanadium ion solution is continuously produced by combining electrochemical method with electrochemical method.

(3) The electrochemical reaction of the present invention occurs automatically, and does not need to directly consume electric energy as in the conventional electrolysis method, wherein the catalyst is an atmospheric pressure room temperature catalyst, the hydrogen does not need to be heated and pressurized, and the electrolyte simultaneously functions to cool the stack, so The overall temperature is highly controllable. In addition, the electrochemical-chemical method of the present invention not only avoids the disadvantage that the simple electrolysis method consumes too much electric energy, but also solves the simple chemical method requiring high-purity starting materials and vanadium oxides of different valence states, requiring heating or cooling, And unfavorable factors such as gas generation in the reaction. Further, in the present invention, the battery reaction in which hydrogen reduces the tetravalent vanadium ion VO ²⁺ is similar to the discharge process of the fuel cell, and thus does not consume energy, which further greatly reduces the electric energy consumed in a large amount in the electrolysis method.

(4) In the present invention, the solution of tetravalent vanadium ions can be recycled, and the entire production process forms a closed loop continuous, so that the entire reaction is clean without any discharge. Moreover, the entire reaction process is simple to operate, extremely easy to control, and does not create an environmental burden.

(5) The hydrogen required for the reaction of the present invention can be produced by low-cost solar electrolyzed water, further reducing energy consumption and improving environmental friendliness.

DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a method of preparing a vanadium redox flow battery electrolyte of the present invention.

2 is a schematic view showing an apparatus for preparing a vanadium redox flow battery electrolyte of the present invention.

detailed description

<First embodiment>

In the first embodiment of the present invention, a method for preparing a vanadium redox flow battery electrolyte is mainly provided. Including the following steps:

(i) flowing a VO ^{2+ -containing} hydrochloric acid solution through the positive electrode to cause a reducing gas to flow through the negative electrode to cause a reduction reaction of VO ²⁺ to form a V ^{2+ -containing} hydrochloric acid solution;

(ii) reacting the V ^{2+ -containing} hydrochloric acid solution formed above with the raw material V ₂ O ₅ to form a VO ^{2+ -containing} hydrochloric acid solution,

Optionally, (iii) introducing a VO ^{2+ -containing} hydrochloric acid solution obtained in the above ii) back to the positive electrode to continuously produce a V ^{2+ -containing} hydrochloric acid solution;

(iv) mixing a V ^{2+ -containing} hydrochloric acid solution with a VO ^{2+ -containing} hydrochloric acid solution to prepare a vanadium electrolyte.

Raw material V ₂ O ₅

Conventional impurities such as Na, K, Si, Al, Fe, Cr, etc. can be removed in the preparation process of the existing mainstream vanadium electrolyte. Therefore, the initial raw material preparation method is to carry out a series of processes such as vanadium precipitation/filtration/depuration by conventional addition of pure aluminum salt, sodium salt, calcium salt, etc., to remove relatively high content of Fe, Al, Si, Na, K and other elements, so as to obtain high-purity vanadium pentoxide and other raw materials, the traditional impurity removal process can only remove relatively high levels of common impurities, and as the starting material of vanadium sulphate pentahydrate or vanadium pentoxide, of which The impurities have a very low precious metal ion content and are not easily removed.

According to the working principle of the flow battery, during the charging process of the battery, the electric energy is converted into chemical energy via the stack, and the chemical energy is stored in the electrolyte. Due to the electrochemical reaction that occurs during the charging and discharging process of the electrolyte, it is very sensitive to impurities in the solution, especially noble metal ions. Most of the precious metal elements, such as copper, silver, gold, nickel, etc., even at very low concentrations, can catalyze side reactions of the flow battery, generating a large amount of dangerous gases, causing the electrolyte to quickly fail. Therefore, ensuring the purity of the electrolyte and removing precious metal ion impurities other than the effective ions is an important part of the electrolyte preparation process.

The traditional process is not only relatively cumbersome and complicated, but also has no ideal effect on the removal of precious metal ions. This not only greatly increases the production cost of the electrolyte, limits the selection range of the initial raw materials, but also catalyzes the side reaction of the flow battery, generates a large amount of dangerous gas, and causes the electrolyte to quickly fail.

In the present invention, unlike the conventional electrochemical-chemical method, the raw material V ₂ O _{5 is} not particularly limited, that is, a commercially available high-purity raw material can be used, and in particular, a raw material having a low purity can be used. V ₂ O ₅ . In some preferred embodiments of the invention, for example, the starting material V ₂ O ₅ may be allowed to have a certain amount of noble metal ions.

The raw material V ₂ O _{5 of the} present invention allows the presence of noble metal ions such as silver or gold, and the upper limit of the content of these ions is not limited, and in some embodiments of the present invention, it may be 10 ppm or more, or 100 ppm or more, 500 ppm or more, or even More than 1000ppm.

Therefore, in the production method of the present invention, the raw material V ₂ O ₅ may be "low purity raw material V ₂ O ₅ ". Noble metal impurities "low purity starting material V ₂ O _5" may be defined as V ₂ O ₅ starting material in the present invention is about higher than 10PPM of V ₂ O _5. Usually vanadium electrolytes require a precious metal content of 0.1-10 PPM (depending on which precious metal), and the usual method requires that the starting material be lower than the final electrolyte product. Further, the method for producing an electrolytic solution of the present invention can use a low-purity raw material V ₂ O ₅ having a noble metal impurity content of up to 1000 PPM, thereby greatly reducing the cost.

In the present invention, when a VO ^{2+ -containing} solution containing a noble metal ion is passed through the positive electrode, the reducing gas is diffused to the separator in the presence of the catalyst, so that the metal ions in the solution flowing through the positive electrode are reduced. For vanadium ions, as described above, the reduction of VO ²⁺ to V ²⁺ can be achieved, while at the same time, the noble metal ions are at least partially reduced from this process. Therefore, the electrochemical reaction process according to the present invention can not only obtain vanadium ions in a desired valence state, but also function to purify noble metal ions in the raw material V ₂ O ₅ .

In the present invention, the raw material for the initial use of V ₂ O _5, may be V ₂ O ₅ starting material was prepared as VO ²⁺ chemical method, the reaction as starting materials. The acidic solution may be dissolved in V ₂ O ₅ . The acidic solution in the preparation of the starting material of the present invention is not particularly limited, and may be, for example, sulfuric acid or hydrochloric acid. In a preferred embodiment, hydrochloric acid is used to match the subsequent preparation process. In the presence of an acidic material, a reducing agent is added and the amount is adjusted such that the pentavalent vanadium oxide is reduced to tetravalent vanadium.

The reducing agent is not particularly limited, and may be a conventional reducing agent for preparing a liquid flow battery electrolyte by a chemical method in the art, and may be an organic reducing agent or an inorganic reducing agent, preferably an organic reducing agent. The organic reducing agent includes a one-carbon reagent, a two-carbon reagent, a three-carbon reagent, and a reagent of four or more carbons.

The one carbon reagent may include methanol, formaldehyde, formic acid, or the like. The dicarbon reagent may include ethanol, acetaldehyde, acetic acid, ethylene glycol, glycolic acid, oxalic acid, and the like. The three carbon reagent may include 1-propanol, 2-propanol, propylene glycol, glycerin, propionic acid, and the like. The reagent of four or more carbons may include glucose or other sugars and the like.

For example, when a V ₂ O ₅ hydrochloric acid solution is reduced using methanol (when the raw material V ₂ O _{5 is} dissolved in hydrochloric acid, it will be present as VO ₂ ⁺ ions), the following reaction will occur:

CH ₃ OH+6VO ₂ ⁺ +6H ⁺ →6VO ²⁺ +5H ₂ O+CO ₂

For example, when a solution of V ₂ O ₅ in hydrochloric acid is reduced using glycerol, the following reaction occurs:

7V ₂ O ₅ +C ₃ H ₈ O ₃ +28HCl→14VOCl ₂ +3CO ₂ +18H ₂ O

When other organic reducing agents are used, they are similar to the above reaction. From this, it is understood that by-products after the reaction of the organic reducing agent are generally carbon dioxide and water.

Further, the reducing agent may also use a nitrogen-containing compound, and specifically may be an anthracene or an amine. The anthraquinone may be hydrazine, barium sulfate, benzoquinone, phenylhydrazine sulfate, or the like, and the amine may be hydroxylamine sulfate, hydrazine, hydrazine sulfate, or the like.

In addition to the above organic reducing agent, an inorganic reducing agent such as sulfur or the like can also be used. However, the use of an inorganic reducing agent may cause undesired impurity ions to appear in the solution after the end of the reaction. Therefore, it is preferred to use an organic reducing agent.

Electrochemical reaction

In the step (i) of the present invention, a VO ^{2+ -containing} hydrochloric acid solution is passed through the positive electrode, and a reducing gas is passed through the negative electrode to cause a reduction reaction of VO ²⁺ to form a V ^{2+ -containing} hydrochloric acid solution.

The reaction here is similar to the discharge reaction of a fuel cell. Such a reaction needs to be carried out in the presence of a positive electrode, a negative electrode and a separator.

In a preferred embodiment of the present invention, the positive electrode material may be selected from a carbon-based material, which may have a porous structure, and a communication structure between the holes to accommodate or allow the electrolyte to flow may be formed. The porous structure may be formed by a foaming method or formed by a woven or non-woven method. The nonwoven method can be constituted, for example, by superposition and compression of carbon fiber filaments, or by processing a fiber filament formed by an electrospinning process to obtain a porous fiber aggregate having a certain shape. Typically, the positive electrode material in the present invention may be selected from, for example, carbon felt, carbon paper, carbon fiber, graphite felt, etc., preferably graphite felt.

The negative electrode of the present invention includes a catalyst layer that catalyzes a reduction of the positive electrode metal ions by the reducing gas. The present invention is not particularly limited as long as it is a catalyst capable of achieving catalytic reduction for the catalyst in the catalyst layer. In addition to the above catalyst layer, the negative electrode has a gas diffusion layer which contributes to the diffusion of the reducing gas to the surface of the catalyst. In the present invention, for a reducing gas, hydrogen is included in some preferred embodiments of the invention. Hydrogen diffuses through the gas diffusion layer to the surface of the catalyst to form hydrogen ions and electrons, and the following reactions occur:

Negative electrode reaction: negative electrode reaction: H ₂ → 2H ⁺ + 2e ^-

Further, hydrogen ions migrate to the positive electrode through the electrolyte and the separator, and react with the VO ^{2+ -containing} hydrochloric acid solution flowing through the positive electrode under the action of electrons as follows:

Positive electrode reaction: VO ²⁺ +2H ⁺ +2e ^- →V ²⁺ +H ₂ O

The above total response can be expressed as:

Total reaction: VO ²⁺ +H ₂ →V ²⁺ +H ₂ O

Through the above reaction, the tetravalent vanadium ions in the VO ^{2+ -containing} hydrochloric acid solution flowing through the positive electrode are reduced to divalent vanadium ions.

The electrochemical reactions carried out described above can occur automatically, so that the entire process does not require direct consumption of electrical energy as in conventional electrolysis. Wherein, the catalyst layer in the negative electrode is an atmospheric pressure room temperature catalyst, and hydrogen does not need to be heated and pressurized throughout the reaction process, and the electrolyte simultaneously serves to cool the reaction system, so generally, the electrochemical reaction temperature is highly high. Controlled.

Further, along with the above electrochemical reaction, the noble metal ions present in the electrolytic solution may be reduced by contact with a reducing gas. Therefore, such a process can actually serve the purpose of purifying the precious metal ions in the vanadium electrolyte to a certain extent.

The V ^{2+ -containing} hydrochloric acid solution prepared by the above electrochemical reaction process at least partially undergoes the following chemical reaction.

chemical reaction

The chemical reaction portion of the present invention partially reacts a V ^{2+ -containing} hydrochloric acid solution with a raw material V ₂ O ₅ to form a VO ^{2+ -containing} hydrochloric acid solution.

The raw material V ₂ O _{5 is} dissolved in hydrochloric acid and mixed with a V ²⁺ hydrochloric acid solution to produce a chemical reaction as follows:

V ²⁺ +V ₂ O ₅ +4H ⁺ →3VO ²⁺ +H ₂ O

Thus, a hydrochloric acid solution containing VO ²⁺ ions was obtained.

The above V ^{2+ -containing} hydrochloric acid solution which reacts with the raw material V ₂ O ₅ is at least partially derived from the V ^{2+ -containing} hydrochloric acid solution formed by the above electrochemical reaction. In a preferred embodiment of the invention, the above V ^{2+ -containing} hydrochloric acid solution which reacts with the starting material V ₂ O ₅ is at least partially derived from the V ^{2+ -containing} hydrochloric acid solution formed by the above electrochemical reaction.

Continuous reaction

As described above, in the electrochemical-chemical method of the present invention for preparing a vanadium redox flow battery electrolyte, the initial VO ²⁺ can be obtained under acidic conditions by means of a reducing agent. The initial VO ²⁺ acidic solution undergoes the above electrochemical reaction stage to generate a V ²⁺ acidic solution, and the V ²⁺ acidic solution is further reacted with a new raw material V ₂ O ₅ to form a VO ²⁺ acidic solution, thereby circulating an electrochemical-chemical reaction. In the process, the raw material V ₂ O _{5 is} consumed, and an acidic solution containing VO ^{2+ and} an acidic solution containing V ²⁺ are obtained.

Therefore, the preparation process of the electrolytic solution of the present invention can be carried out continuously without any discharge.

Preparation of electrolyte

The V ²⁺ -containing hydrochloric acid solution is mixed with a VO ^{2+ -containing} hydrochloric acid solution to prepare an electrochemical equilibrium vanadium electrolyte, and the ratio of V ³⁺ and VO ²⁺ in the electrochemical equilibrium vanadium electrolyte is 1:1.

The manner of preparation is not particularly limited. For example, a hydrochloric acid solution of V ²⁺ having the same or close concentration may be mixed with a hydrochloric acid solution containing VO ²⁺ in a volume ratio of 1:3.

<Second Embodiment>

In a second embodiment of the invention, an apparatus for carrying out the first embodiment described above is provided.

The device includes an electrochemical reaction portion, a chemical reaction portion.

The electrochemical reaction portion includes a positive electrode, a negative electrode, and a separator, and the inside of the portion is at least divided into two reaction chambers via a separator, and a positive electrode reaction chamber for performing a positive electrode reaction and a negative electrode reaction chamber for performing a negative electrode reaction, respectively.

The positive electrode reaction chamber includes a positive electrode, and the material as the positive electrode includes at least those positive electrode materials disclosed in the above <First Embodiment>. The negative electrode reaction chamber includes at least a negative electrode including at least a negative electrode as disclosed in the first embodiment.

During the electrochemical reaction, the VO ^{2+ -containing} acidic solution flows through the positive electrode in a controlled manner. The interconnected porous channels in the positive electrode material provide a flow space for the above flow, and the porous arrangement provides a larger reaction surface area, allowing the above acidic solution to have as much a reaction surface as possible with the positive electrode material.

While the VO ²⁺ acidic solution flows through the positive electrode in a controlled manner, a reducing gas is introduced into the negative reaction chamber, and the reducing gas is contacted with the negative electrode catalyst by the gas diffusion layer. The gas diffusion layer may be carbon paper or the like and may have a thickness of 0.05 to 1 mm. The catalyst includes platinum or the like. The catalyst is typically diluted with graphite powder, carbon black, and other solvents, wherein the catalyst content can range from 5 to 80%.

The positive electrode and the negative electrode are separated by a separator. Suitable membrane materials for the membrane include polymeric membranes or composite membranes comprising polymers and inorganics. In some embodiments, the membrane may comprise a sheet of woven or nonwoven plastic having a reactive ion exchange material such as a resin or functionality embedded in a heterogeneous manner (eg, coextrusion) or a homogeneous manner (eg, radiation grafting). . In some embodiments, the separator can have a high current efficiency Ev and a high coulombic efficiency E _I and can be designed to limit the mass transfer through the membrane to a minimum porous membrane while still promoting ion transport. In some embodiments, the membrane can be made of a polyolefin material or a fluorinated polymer and can have a specified thickness and pore size. In some embodiments, the membrane can be a proton exchange membrane. For example, a NAFION-117 film available from DuPont, USA can be used. One manufacturer having the ability to make these films and other films consistent with the disclosed embodiments is Daramic Microporous Products, LP, N. Community House Rd., Suite 35, Charlotte, NC 28277. In certain embodiments, the membrane can be a non-selective microporous plastic separator, which is also manufactured by Daramic Microporous Products LP.

In actual production, as described above, the catalyst is generally diluted with graphite powder, carbon black and other solvents, and a small amount of a binder, such as Nafion dissolved in ethanol, is added to prepare a fluid, which is then laid on the separator to form a thin film. One layer, and a gas diffusion layer is superimposed, and the gas diffusion layer, the catalyst layer and the separator are pressed into one body.

In some embodiments of the invention, a multilayer electrochemical reaction device can be formed via a multilayer electrode and a multilayer separator. In such a device, a plurality of separators are arranged in a continuous manner, each of which has a positive electrode and a negative electrode as described above on both sides, and has a corresponding space to provide a flow containing the VO ²⁺ acidic solution and the reducing gas. Multilayer electrochemical reactors can greatly increase the efficiency of electrochemical reactions.

In the negative electrode reaction chamber containing the negative electrode, a reducing gas is introduced, and the flow direction of the gas may be set to be the same as or opposite to the flow direction of the VO ²⁺ acidic solution contained in the positive electrode, and is not particularly limited.

The chemical reaction portion includes at least a reaction tank that can provide a chemical reaction, and a transfer pump. In the reaction tank, V ²⁺ is chemically reacted with the raw material V ₂ O ₅ in the presence of an acidic substance. There is no special requirement for the material of the can, as long as it does not cause corrosion due to chemical reaction. After the completion of the above chemical reaction, the obtained VO ^{2+ -containing} acidic solution enters the positive electrode of the electrochemical reaction portion via a line. The flow rate of the VO ²⁺ acidic solution into the positive electrode is controllable and can be controlled by a transfer pump.

The V ²⁺ acidic solution flowing out of the above positive electrode flows at least partially into the reaction tank via a line to provide V ²⁺ required for the above reaction. At the same time, optionally, additional lines may be provided to deliver the V ²⁺ acidic solution from the positive electrode to another reservoir for use. Further, in some embodiments, the V ²⁺ acidic solution flowing out of the positive electrode is controlled by an additional transfer pump through the process of flowing into the above reaction tank.

The reducing gas of the present invention is preferably hydrogen. In the present invention, solar water can be used to prepare hydrogen gas. Therefore, in some preferred embodiments of the present invention, the inlet of the reducing gas of the negative electrode in the electrochemical reaction may be connected through a line to a gas storage tank of hydrogen prepared by solar electrolysis water. The apparatus for solar electrolyzed water is not particularly limited, and includes, but is not limited to, the following methods: solar direct thermal decomposition water hydrogen production method, solar photoelectrochemical decomposition method, photocatalytic hydrogen production method, and the like.

Therefore, in the most preferred embodiment of the present invention, the electrolytic preparation apparatus of the vanadium flow battery includes an electrochemical reaction portion, a chemical reaction portion, a solar water electrolysis device portion, a communication line, and a transfer pump.

Further, a mixing tank may be provided to accommodate a mixed solution of a V ^{2+ -containing} hydrochloric acid solution and a VO ^{2+ -containing} hydrochloric acid solution.

The present invention is not particularly limited as to the specific layout of the respective parts or devices as long as the design of the present invention can be realized.

Hereinafter, a method and apparatus for preparing a vanadium redox flow battery electrolyte of the present invention will be described in more detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the process of a method for preparing a vanadium redox flow battery electrolyte of the present invention. Figure 2 shows a schematic of a device for preparing a vanadium electrolyte (a solar electrolysis water hydrogen plant is not shown).

In the apparatus shown in Fig. 2, the left side is a positive electrode and the right side is a negative electrode. There is a separator between the positive electrode and the negative electrode. A gas diffusion layer is provided on the negative electrode side of the separator, and a catalyst (layer) is contained in the gas diffusion layer.

A method of preparing a vanadium electrolyte using the apparatus shown in Fig. 2 and the process shown in Fig. 1 will be described in detail below.

Step (i)

Before carrying out step (i), step (i') may be carried out to reduce the hydrochloric acid solution of the raw material V ₂ O ₅ by a reducing agent to obtain a VO ^{2+ -containing} hydrochloric acid solution required in the step (i). Specifically, first, as shown in the state 101 of Fig. 1, a small amount of a hydrochloric acid solution of a low-purity raw material V ₂ O ₅ is prepared. Then, an appropriate amount of a reducing agent is added to reduce V ₂ O ₅ to VO ²⁺ to obtain a VO ^{2+ -containing} hydrochloric acid solution of the state of 102 in Fig. 1 .

The reducing agent used in the above step (i') may be an organic reducing agent or an inorganic reducing agent as described above, preferably an organic reducing agent.

Next, step (i) is carried out, that is, a hydrochloric acid solution containing VO ²⁺ is introduced into the positive electrode and a reducing gas such as H _{2 is} introduced into the negative electrode (see FIG. 2), whereby an electrochemical reaction occurs, and the state of 103 shown in FIG. 1 is obtained. A solution of hydrochloric acid containing V ²⁺ .

When a reducing gas such as hydrogen in the negative electrode flows through the catalyst-containing gas diffusion layer, a pair of electrons is lost, and an oxidation reaction occurs to generate hydrogen ions H ⁺ ; when the tetravalent vanadium ion VO ²⁺ in the hydrochloric acid solution flows through the positive electrode , a pair of electrons will be obtained, and a reduction reaction will occur to form a divalent vanadium ion V ²⁺ . The hydrogen ion H ⁺ generated by the negative electrode migrates to the positive electrode through the catalyst-containing proton exchange membrane, thereby ensuring the integrity of the entire circuit.

In the reaction, the flow rate of the hydrogen gas is controlled to be 1-1000 liters/min, preferably 50-200 liters/min. The flow rate of the hydrochloric acid solution containing the tetravalent vanadium ion VO ²⁺ is controlled to be 1-200 liters/min, preferably 10-100 liters. /minute.

In the present invention, the battery reaction in which hydrogen reduces the tetravalent vanadium ion VO ²⁺ is similar to the discharge process of the fuel cell, and thus does not consume energy. Moreover, the hydrogen in the reaction of the present invention does not require heating and pressurization. Therefore, the preparation method of the present invention can save cost and energy, and the reaction system is clean and environmentally friendly.

Step (ii)

The hydrochloric acid solution containing divalent vanadium ion V ²⁺ (ie, state 103 in FIG. 1 ) formed by the above electrochemical reaction is spontaneously reacted with the raw material V ₂ O ₅ to form a hydrochloric acid solution containing tetravalent vanadium ion VO ²⁺ ( That is, state 102 in Fig. 1).

Step (iii)

As shown in FIG. 2, a hydrochloric acid solution containing a tetravalent vanadium ion VO ^{2+ formed} by reacting a solution of a divalent vanadium ion V ²⁺ with a raw material V ₂ O ₅ can be pumped back to the positive electrode of the battery to generate an electrochemical reaction. The reaction (i.e., step (i)) allows continuous formation of a hydrochloric acid solution containing divalent vanadium ions V ²⁺ . Of course, this step (iii) is optional, that is, step (i) can also be performed only once.

Step (iv)

In step (iv), an appropriate ratio of a V ^{2+ -containing} hydrochloric acid solution (state 103 in FIG. 1 ) and a VO ^{2+ -containing} hydrochloric acid solution (state 102 in FIG. 1 ) are mixed to obtain an equilibrium state. Pure hydrochloric acid based all vanadium electrolyte (state 104 in Figure 1).

Containing divalent vanadium ions V ²⁺ hydrochloric acid solution when the volume containing tetravalent vanadium ion, VO ²⁺ mixed solution of hydrochloric acid according to the concentration ratio of the two different different. The concentration of the V ²⁺ -containing hydrochloric acid solution and the VO ²⁺ -containing hydrochloric acid solution may be the same or different, and is usually 0.1 to 6 M, preferably 0.3 to 3 M, more preferably 1 to 2.5 M. When the concentration of the hydrochloric acid solution containing the divalent vanadium ion V ^{2+ and} the hydrochloric acid solution containing the tetravalent vanadium ion VO ²⁺ are equal, the pure hydrochloric acid-based all-vanadium electrolysis can be obtained by mixing at a volume ratio of 1:3. liquid.

It can be seen from the above description that in the present invention, pure hydrochloric acid is selected as the solution substrate, so that in the actual operation of the flow battery, when the acidity is lowered due to various reasons, the entire volume of the electrolyte and the vanadium ion concentration can be passed without changing the electrolyte volume. Fill with HCl gas to restore the acidity of the electrolyte in time.

Further, an embodiment of the present invention is also directed to a vanadium redox flow battery comprising a vanadium electrolyte prepared according to the production method of the present invention as described above.

It can be seen from the description of the preparation method described above that the method for preparing a vanadium electrolyte of the present invention can be continuously produced by using a low-cost low-purity vanadium oxide as a starting material and a pure hydrochloric acid as a base by electrochemical and chemical combination methods. Vanadium electrolyte. Moreover, the preparation device of the invention is simple in operation, extremely easy to control, and low in cost. Moreover, the hydrogen required for the reaction can be produced by low-cost solar electrolyzed water, and the entire reaction is clean and non-emission.

Example

2.3 L of concentrated hydrochloric acid was added to the reaction vessel, and stirring was carried out using a Teflon stirrer while slowly adding 1.32 kg of low purity V ₂ O ₅ and 5.5 ml of high purity glycerin. According to the following reaction formula:

7V ₂ O ₅ +C ₃ H ₈ O ₃ +28HCl→14VOCl ₂ +3CO ₂ +18H ₂ O (i)

In the obtained VOCl ₂ solution, the total content of VOCl ₂ was 13.5 mol by UV-Vis test.

This VOCl ₂ solution, all used as a positive electrode electrolyte, was slowly flowed through the positive electrode graphite felt by a pump; at the same time, the negative electrode was filled with hydrogen gas, and the total amount was about 400 L.

The gas diffusion layer is carbon paper, the catalyst is platinum dispersed in carbon black, and the membrane is a proton exchange membrane.

According to the following reaction formula

VO ²⁺ +H ₂ →V ²⁺ +H ₂ O (ii)

After the two were completely reacted, the total V ²⁺ content was 13.2 mol in the V ²⁺ solution formed by UV-Vis test. Pour all of the V ²⁺ solution into the reaction vessel and slowly add 4.6 L of concentrated hydrochloric acid. Stirring was carried out using a stir bar, and then 2.56 kg of low purity V ₂ O ₅ was slowly added. According to the following reaction formula

V ²⁺ +V ₂ O ₅ +4H ⁺ →3VO ²⁺ +2H ₂ O (iii)

In the obtained VO ²⁺ solution, the total content of VO ²⁺ was 39 mol by UV-Vis test.

Take one-third of the solution containing 13 mol of VO ²⁺ as the initial reactant of the positive electrode of reaction (ii), and slowly flow through the positive graphite felt by a pump; while the negative electrode is filled with hydrogen, the total amount is about 400L.

Obtaining V ³⁺ solution:

According to the reaction formula (ii), after the two were completely reacted, the V ²⁺ content in the resulting V ²⁺ solution was 12.7 mol. Sample of the reaction (iii), the remaining half of VO ²⁺ solution, i.e. a third of the reaction (iii) the total VO ²⁺ solution, i.e. a solution containing 13molVO ^2+, and the step of generating the content of V 12.7mol ^{The 2+} solution is mixed to obtain a V ³⁺ solution having a content of 25.5 mol.

Acquisition of V ³⁺ and VO ²⁺ equilibrium electrolytes:

The test results of UV-Vis, and the concentration of the solution of VO ²⁺ V ²⁺ solution close to 1 volume ratio of the solution according to the calculated V ^2+, and VO ²⁺ solution: 3 mixture, obtained V ³⁺ and VO The equilibrium electrolyte with a ²⁺ ratio of 1:1 and a total concentration of V ³⁺ and VO ²⁺ of 2.5 mol/L. The final equilibrium vanadium electrolyte can be prepared by adding deionized water to the final desired electrolyte concentration. If a final solution of 1.25 mol/L is required, the V ³⁺ and VO ²⁺ equilibrium electrolytes may be mixed with deionized water in a volume ratio of 1:1.

Industrial applicability

The method and apparatus provided by the present invention can be used industrially for the preparation of flow battery electrolysis.

The above-disclosed embodiments of the present invention are merely illustrative and are intended to teach those skilled in the art to practice the general methods of the invention. Changes may be made in the elements, materials, and the like described herein without departing from the spirit and scope of the invention. Therefore, further modifications of the embodiments of the invention will be apparent to those skilled in the art in view of this disclosure.

Claims (10)

1. A method for preparing a vanadium electrolyte, characterized in that it comprises the following steps:

   (i) flowing a VO ^{2+ -containing} hydrochloric acid solution through the positive electrode to cause a reducing gas to flow through the negative electrode to cause a reduction reaction of VO ²⁺ to form a V ^{2+ -containing} hydrochloric acid solution;

   (ii) reacting the V ^{2+ -containing} hydrochloric acid solution formed above with the raw material V ₂ O ₅ to form a VO ^{2+ -containing} hydrochloric acid solution,

   Optionally, (iii) introducing a VO ^{2+ -containing} hydrochloric acid solution obtained in the above ii) back to the positive electrode to continuously produce a V ^{2+ -containing} hydrochloric acid solution;

   (iv) mixing a V ^{2+ -containing} hydrochloric acid solution with a VO ^{2+ -containing} hydrochloric acid solution to prepare an electrochemically equilibrated vanadium electrolyte.
2. The production method according to claim 1, wherein the reducing gas comprises hydrogen, and preferably, the hydrogen is derived from hydrogen produced by a solar electrolysis water method.
3. The production method according to claim 1 or 2, wherein the positive electrode comprises a carbon-based material, preferably a graphite felt; and a separator is present between the positive electrode and the negative electrode.
4. The production method according to claim 3, wherein a gas diffusion layer is provided on a negative electrode side of the separator.
5. The production method according to claim 4, wherein the gas diffusion layer contains a catalyst.
6. Preparation method according to any one of claims 1 to 5, wherein said V ₂ O ₅ starting material is a noble metal impurity content of less than 10PPM V ₂ O ₅ starting material.
7. The preparation method according to any one of claims 1 to 6, characterized in that it further comprises the step (i') before the step (i): reducing the hydrochloric acid solution of the raw material V ₂ O ₅ by using a reducing agent, Thus, a hydrochloric acid solution containing VO ²⁺ was obtained.
8. The production method according to claim 7, wherein the reducing agent comprises an organic reducing agent and an inorganic reducing agent, preferably an organic reducing agent.
9. A device for preparing a vanadium electrolyte, comprising: a positive electrode, a negative electrode, and a separator present between the positive electrode and the negative electrode, and having a gas diffusion layer on the negative electrode side of the separator, wherein the VO is contained therein ^{The 2+} hydrochloric acid solution flows through the positive electrode, and the reducing gas flows through the negative electrode.
10. The preparation apparatus according to claim 9, wherein the VO ^{2+ -containing} hydrochloric acid solution has the same or opposite flow direction as the reducing gas.

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