WO2023101338A1 - Method for preparing vanadium electrolyte solution - Google Patents

Abstract

The present invention relates to a method for preparing a vanadium electrolyte solution. The present invention may prevent crossover of vanadium ions. The present invention may shorten a reaction time. The present invention may lower the production cost of a vanadium electrolyte solution.

Description

Manufacturing method of vanadium electrolyte solution

The present invention relates to a method for preparing a vanadium electrolyte solution.

The present invention relates to a method for preparing a vanadium electrolyte using a reactor of a different type from the conventional one.

Since vanadium can lose at least 2 electrons and up to 5 electrons, it can undergo oxidation and reduction reactions without phase change even in aqueous solutions. A vanadium redox flow battery (VRFB) using this principle can store electricity in an electrolyte, unlike a general secondary battery that stores electricity in an electrode. As a result, VRFB is attracting attention as a high-safety large-capacity energy storage device because it is free to design the output and energy capacity of the battery and there is no risk of fire due to the generation of solids such as dendrites.

A normal VRFB consists of a graphite current collector, a graphite felt electrode, an ion exchange membrane, and an electrolyte solution. Here, the electrolyte has the highest cost ratio. The electrolyte is prepared in a 3.5 form (V(III/IV)) in which trivalent vanadium ions (V(III)) and tetravalent vanadium ions (V(IV)) are mixed in a volume ratio of about 1:1. The 3.5-valent electrolyte is oxidized to pentavalent at the anode and reduced to divalent at the cathode through a pre-charging process in the battery, and has an electromotive force of 1.25 V. Hereinafter, a solution in which a trivalent vanadium compound (V(III)) and a tetravalent vanadium compound (V(IV)) are mixed in a volume ratio of about 1:1 is referred to as a vanadium electrolyte.

As a method for preparing a vanadium electrolyte, vanadium pentoxide (V ₂ O ₅ ) powder having a pentavalent oxidation number during ionization and vanadium trioxide (V ₂ O ₃ ) powder having a trivalent value are mixed in an appropriate ratio and then dissolved in an aqueous sulfuric acid solution to obtain a 3.5 valent electrolyte. There is a method of producing a 4-valent electrolyte solution by reacting vanadium pentoxide (V ₂ O ₅ ) powder with a reducing agent in an aqueous sulfuric acid solution, and then preparing a 3.5-valent electrolyte solution through an additional electrochemical reaction. The former can easily produce a 3.5 valent electrolyte without a separate electrochemical reaction, but the latter is mainly used because of the high cost of raw materials. Vanadium pentoxide (V ₂ O ₅ ) powder is reduced to tetravalent ions by reacting with a reducing agent in aqueous sulfuric acid solution, and reduction to a lower oxidation number does not occur. need this Various techniques are known for obtaining a 3.5 valent vanadium electrolyte solution using an electrochemical reaction.

First, there is a method of preparing 4-valent vanadium ions by reacting vanadium pentoxide powder with an organic reducing agent such as oxalic acid in an aqueous solution of sulfuric acid, and then injecting this into the anode and cathode of an electrochemical reactor to prepare a 3.5-valent electrolyte at the cathode (patent see Literature 1). In this method, since the electrochemical reaction proceeds at a relatively low voltage between 1.4 V and 1.6 V, inexpensive graphite can be used as an electrode. However, when the current density is increased to 100 mA/cm ² or more, the voltage exceeds 1.6 V, so there is a problem in that the graphite electrode is decomposed. In addition, since the method generates pentavalent vanadium ions at the anode of the electrochemical reactor, a reuse process of reducing the anode product to tetravalent vanadium ions by reacting the anode product with a reducing agent is required to reuse vanadium. Therefore, in the case of this method, the production rate of the electrolyte solution is slow, a large amount of reducing agent is required, and the process is complicated. 1 is a P&ID of the prior art for producing a vanadium electrolyte.

Second, there is a method of supplying a slurry obtained by mixing vanadium pentoxide powder and an aqueous sulfuric acid solution to the cathode of an electrochemical reactor, and supplying the aqueous sulfuric acid solution to a noble metal-plated anode to cause a water electrolysis reaction (see Non-Patent Document 1). This method is eco-friendly because water is decomposed at the anode and only oxygen is generated, so the above-mentioned reuse process can be omitted and a reducing agent is not applied. However, since the reaction rate is very slow because vanadium pentoxide in a slurry state is directly injected into the cathode, and the slurry can block the flow path of the electrochemical reactor, a multiple layer stack structure with a narrow cell gap is used. cannot be applied In addition, since this method uses an aqueous solution of sulfuric acid as an anode reactant, loss due to crossover of vanadium may occur at the cathode. 2 is a P&ID of the prior art for preparing a vanadium electrolyte.

Third, there is a technique of using the decomposition reaction of hydrogen peroxide as an anode (see Patent Document 2). This method does not require a step of reusing the pentavalent electrolyte and can use an inexpensive graphite electrode. However, in this method, hydrogen peroxide may cross over to the cathode during the reaction to oxidize vanadium ions. In addition, since this method uses a sulfuric acid aqueous solution-based hydrogen peroxide mixture as an anode reactant, loss due to crossover of vanadium may occur at the cathode. And since this method uses a graphite electrode, the reaction time is long. 3 is a P&ID of the prior art for producing a vanadium electrolyte.

Therefore, it is necessary to study a method for preparing a vanadium electrolyte that can solve the problems listed above.

An object of the present invention is to provide a method for preparing a vanadium electrolyte capable of preventing crossover of vanadium ions.

The present invention is to provide a method for preparing a vanadium electrolyte solution capable of shortening the reaction time.

The present invention is intended to provide a method for preparing a vanadium electrolyte solution capable of producing a vanadium electrolyte solution at low cost.

The method for producing a vanadium electrolyte of the present invention is a method for producing a vanadium electrolyte using a reactor including a membrane electrode assembly having a cathode, an ion exchange membrane, an anode catalyst, and an anode in the above order, and a cathode containing a tetravalent vanadium compound A reactant is supplied to the cathode of the reactor, an anode reactant containing an aqueous solvent is supplied to the anode of the reactor, and then an electric charge is applied to the reactor to form a tetravalent vanadium compound (V(IV)) and a trivalent vanadium compound (V(IV)) at the cathode. obtaining a product comprising a vanadium compound (V(III)) in a volume ratio of 4:6 to 6:4 (V(IV):V(III));

The present invention can prevent crossover of vanadium ions.

The present invention can shorten the reaction time.

The present invention can lower the production cost of the vanadium electrolyte.

1 to 3 are P&IDs of the prior art for preparing a vanadium electrolyte.

4 is a schematic diagram of an apparatus for producing a vanadium electrolyte in the present invention.

Hereinafter, the contents of the present application will be described in more detail.

The present invention relates to a method for preparing a vanadium electrolyte solution. As described above, the “vanadium electrolyte” referred to in the present invention includes a trivalent vanadium compound (V(III)) and a tetravalent vanadium compound (V(IV)), and a trivalent vanadium compound (V(III)) and a tetravalent vanadium compound (V(IV)) in a volume ratio of about 1:1. However, the above mixing ratio may be appropriately extended in consideration of errors and the like. For example, the volume ratio (V(IV):V(III)) of the tetravalent vanadium compound (V(IV)) and the trivalent vanadium compound (V(III)) in the vanadium electrolyte is 4:6 to It can be within the 6:4 range. The ratio (V(III):V(IV)) may be 4:6 to 6:4, 4.5:5.5 to 5.5:4.5, 4.9:5.1 to 5.1:4.9, or about 1:1. Hereinafter, a solution in which a trivalent vanadium compound (V(III)) and a tetravalent vanadium compound (V(IV)) are mixed at a volume ratio (V(III):V(IV)) within the range of 4:6 to 6:4 is called a vanadium electrolyte.

In the present invention, a vanadium electrolyte is prepared by using an electrochemical reactor having a specific structure and selecting an appropriate raw material for the reactor. In addition, the main reaction performed in the present invention is a reaction of partially reducing a tetravalent vanadium compound to produce a vanadium electrolyte solution that is a mixture of a tetravalent vanadium compound and a trivalent vanadium compound in an appropriate ratio. Therefore, in the present invention, it proceeds through a process of preparing a specific reactor and a reactant of a specific composition, and reacting the reactant in the reactor to obtain a product of the reaction. The present invention can prevent the crossover of vanadium ions, shorten the reaction time for generating a vanadium electrolyte, and operate at low cost by using a method described later.

In the method of the present invention, a vanadium electrolyte is prepared using a reactor including a membrane electrode assembly (see FIG. 4). The membrane electrode assembly (MEA) includes a cathode, an ion exchange membrane, an anode catalyst, and an anode in the above order. That is, the membrane electrode assembly includes a cathode, an ion exchange membrane on the cathode, an anode catalyst on the ion exchange membrane, and an anode on the anode catalyst. The membrane electrode assembly has a structure in which elements constituting a battery having a very thin thickness, such as a membrane, are laminated or compressed.

As will be described later, the membrane electrode assembly applied in the present invention does not include a cathode catalyst. In the present invention, since the anode catalyst is not applied, the generation of hydrogen gas due to the reduction reaction occurring at the cathode can be prevented.

In the membrane electrode assembly, the negative electrode is an electrode in which a reduction reaction occurs when a battery composed of the membrane electrode assembly is charged. In the membrane electrode assembly, the anode is an electrode where an oxidation reaction occurs when a battery composed of the membrane electrode assembly is charged. The ion exchange membrane is a membrane that serves to pass only ions (cations or anions). The catalyst of the positive electrode serves to promote the reaction at the positive electrode where an oxidation reaction occurs when the battery composed of the membrane electrode assembly is charged.

In one embodiment, each of the cathode and anode applied to the membrane electrode assembly may be a porous electrode. Specifically, each of the cathode and anode applied to the membrane electrode assembly may be a titanium-based porous electrode. Since the meaning of a porous electrode or a titanium-based porous electrode itself is known, a description thereof will be omitted. Titanium-based porous electrodes have strong durability and excellent acid resistance under high voltage or high current conditions. Therefore, using it, the reaction voltage can be increased up to 3 V, and strong acid solutions can be applied.

The type of the ion exchange membrane is not particularly limited as long as it has a function of exchanging cations or anions. In one embodiment, the ion exchange membrane may include a sulfonated tetrafluoroethylene-based copolymer. The copolymer may be a product known in the market as Nafion. The copolymer has excellent thermal stability, excellent chemical resistance, and cationic conductivity.

The thickness of the ion exchange membrane may also be appropriately adjusted. If the ion exchange membrane is too thin, the concentration of the final electrolyte may decrease due to crossover of the anode reactants to the cathode. In addition, if the ion exchange membrane is too thick, the reaction voltage becomes high, so the current density required for driving the reactor cannot be improved. In one embodiment, the thickness of the ion exchange membrane may be in the range of 100 μm to 200 μm. It is possible to drive the reactor at a sufficiently high current density within the above range, and at the same time, it is possible to prevent crossover of the anode reactant.

Components used as the anode catalyst are not particularly limited. This is because the oxidation reaction occurring at the anode is not related to the reduction reaction at the cathode of vanadium, which is the object of the present invention. Therefore, various types of anode catalysts can be used. In particular, as will be described later, since an aqueous solvent is used as a reactant of the anode catalyst in the present invention, known anode catalysts used for electrolysis of water may be used without limitation.

In one embodiment, the anode catalyst may include platinum, iridium, palladium, gold, an oxide thereof, or a mixture of two or more thereof. The anode catalyst may be attached to the anode or ion exchange membrane by means such as a polymer binder. Since the anode catalyst appropriately reduces the reaction voltage and prevents decomposition of the electrode, it must be used in the present invention.

As mentioned above, in the present invention, a membrane electrode assembly including a cathode catalyst is not used. That is, in one embodiment, the cathode and the ion exchange membrane in the membrane electrode assembly may be in direct contact. Direct contact between the cathode and the ion exchange membrane means that no other member exists between the cathode and the ion exchange membrane. When a cathode catalyst is used, hydrogen generation by a reduction reaction occurring at the cathode can be promoted.

As mentioned above, in the present invention, a membrane electrode assembly is used, and the membrane electrode assembly is integrally composed of an electrode, an electrode catalyst, and an ion exchange membrane. For example, after preparing a laminate having the above-described sequence, specifically, a cathode, an ion exchange membrane present on the cathode, an anode catalyst present on the ion exchange membrane, and an anode present on the anode catalyst, a high temperature and A membrane electrode assembly can be obtained by pressing under high-pressure conditions. In the present invention, since the electrochemical reactor including the membrane electrode assembly is applied, the reaction voltage can be lowered and the maximum current density that can be driven can be increased.

Since the reactor used in the present invention is one battery, it may further include other elements constituting the battery in addition to the membrane electrode assembly.

In one embodiment, the reactor may further include a current collector. As the term implies, the current collector is an element capable of delivering electrons to the battery. The current collector may be located on both outermost surfaces of the membrane electrode assembly, for example.

In one embodiment, the reactor may further include a separator plate (or bipolar plate). The separator is an element capable of supplying a reactant such as an electrolyte solution to the membrane electrode assembly. The separator may be positioned on both outermost surfaces of the membrane electrode assembly to which the current collector is added.

In one embodiment, the reactor may further include a metal mesh. A metal mesh may be positioned between the membrane electrode assembly inside the reactor and the aforementioned current collector. By applying the metal mesh, a sufficient space through which the electrolyte can flow can be secured, and as a result, resistance within the cell (reactor) can be minimized. If the mesh is not applied, a limitation may occur in increasing the current density due to high internal resistance of the battery.

In one embodiment, the material of the metal mesh may be a material of the same series as the anode and cathode. Therefore, when the anode and the cathode are porous titanium-based electrodes, the metal mesh may be a titanium mesh. This is because it cannot be decomposed even at high voltage and cannot be dissolved in an acidic solution if a mesh of the same type as the electrode is used.

In one embodiment, the material of the separator and the current collector may be the same material as that of the positive electrode and the negative electrode. Accordingly, when the positive electrode and the negative electrode are porous titanium-based electrodes, each material of the separator and the current collector may be a titanium-based material. In this way, oxidation of the cell (reactor) due to the flow of the electrolyte solution can be prevented.

In the method of the present invention, a cathode reactant containing a tetravalent vanadium compound is supplied to the cathode of the reactor, and an anode reactant containing an aqueous solvent is supplied to the anode of the reactor, and then charges are applied to the reactor. When a charge is applied to the reactor, a reaction occurs at the electrode. Specifically, an oxidation reaction of an anode reactant occurs in the anode. At the cathode, a reduction reaction of the cathode reactant occurs. As a result, in the negative electrode, a tetravalent vanadium compound (V(IV)) and a trivalent vanadium compound (V(III)) are mixed at a volume ratio of 4:6 to 6:4 (V(IV):V(III)) to obtain a product containing The desired product of the present invention is the product of the above cathode.

That is, in the present invention, a vanadium electrolyte is prepared using a water decomposition reaction.

In the present invention, an aqueous solvent means a solvent containing water as a main component. Here, including water as a main component may mean that the content of water (H ₂ O) is mostly, for example, 95% by weight or more, 99% by weight or more, or about 100% by weight. In one embodiment, the aqueous solvent may be distilled water. In the conventional method, an aqueous solution of a strong acid such as an aqueous solution of sulfuric acid was applied to the anode, but in this case, there was a problem in that crossover of vanadium ions from the cathode to the anode was promoted. The vanadium crossover is the cause of the decrease in the vanadium reduction efficiency of the anode. In addition, if cationic materials other than water are present at the anode, the activity of the anode catalyst may be reduced due to side reactions. Crossover of vanadium from cathode to anode can be prevented if the anode reactant includes an aqueous solvent.

In one embodiment, as described below, a reduction reaction of a tetravalent vanadium compound (V(IV)) occurs at the cathode of the reactor of the present invention. The reduction reaction of the tetravalent vanadium compound can proceed in the presence of an acidic substance.

Accordingly, in one embodiment, the anode reactant may further include a strong acid material. Specifically, the cathode reactant may further include an aqueous solution of sulfuric acid.

As will be described later, the reaction time of the electrochemical reaction occurring in the method of the present invention can be determined by the current density of the applied current and the composition of the reactants. That is, the composition of the components constituting the anode reactant may be appropriately adjusted in consideration of the reaction rate. Specifically, the number of moles of the tetravalent vanadium compound in the anode reactant may be appropriately adjusted. In one embodiment, the negative electrode reactant may include the tetravalent vanadium compound in a mole number in the range of 1.5 M to 2.0 M. In another embodiment, the concentration of the tetravalent vanadium compound may be in the range of 1.75 M to 1.85 M. In this case, partial reduction of the tetravalent vanadium compound (V(IV)) to the trivalent vanadium compound (V(III)), which is the desired reaction, can be rapidly performed under current density conditions described later.

In the present invention, the production of the product can proceed within a short time. To this end, when the amount of supplied charge is constant, the current is higher than the conventional current density, for example, 100 mA / cm ² to 1,000 mA / cm ² It is necessary to be able to apply charges of a current density within the range, the method of the present invention The reactor applied in can receive such a high current density charge. In one embodiment, the current density of the charge applied to the reactor may be in the range of 100 mA/cm ² to 1,000 mA/cm ² . The range of the current density, in another example, may be 150 mA / cm ² or more, 200 mA / cm ² or more, 250 mA / cm ² or more, or 300 mA / cm 2 or more, 950 mA / cm ^{2 or} less, 800 mA /cm ² or less, 850 mA/cm ² or less, 800 mA/cm ² or less, 750 mA/cm ² or less, or 700 mA/cm ^{2 or} less.

When the vanadium electrolyte is prepared as described above, crossover of vanadium ions can be prevented, reaction time can be shortened, and operation can be performed at low cost.

In addition, in addition to the above, other processes known to be necessary for obtaining a vanadium electrolyte may be additionally performed in the present invention.

Hereinafter, the present invention will be described in more detail with examples. However, the present invention is not limited to the following examples.

[Production Example] - Tetravalent Vanadium Electrolyte

A glass reactor having an agitator and capable of temperature control was prepared. A 4.1 M aqueous solution of sulfuric acid was introduced into the reactor. Then, vanadium pentoxide powder was added in an amount such that the vanadium atom concentration was 1.78 M in the sulfuric acid aqueous solution. While maintaining the rotational speed of the stirrer at 300 rpm, 0.5 times the number of moles of oxalic acid was added to the number of moles of vanadium atoms. Then, the temperature of the reactor was increased to 80 °C and reacted for 3 hours. When the reaction was completed, the temperature of the reactor was lowered to room temperature, and unreacted vanadium pentoxide was removed by filtering with a filter having a pore size of 5 μm to 10 μm. A tetravalent vanadium electrolyte containing 1.78 M of a tetravalent vanadium compound and 4.1 M of sulfate ions was obtained.

[Comparative Example 1] - 3.5 valent vanadium electrolyte

Both the cathode and anode are composed of a graphite plate current collector and a graphite felt electrode (thickness: 2 T), a Nafion membrane (Chemours) is used as an ion exchange membrane, and an electrochemical reactor having an electrode area of 5 cm * 5 cm is manufactured. did.

50 mL each of the vanadium electrolyte prepared in Preparation Example was put into each of two 100 mL beakers. Using a master flex pump, the electrolyte solution in the two beakers was injected into the cathode and anode of the electrochemical reactor at the same speed (85 rpm). After maintaining the circulation for about 1 minute, a charge of 1.19 Ah was applied by setting the current density of the electrochemical reactor to 20 mA/cm ² .

[Comparative Example 2] - 3.5 valent vanadium electrolyte

Both the cathode and anode are composed of a graphite plate current collector and a graphite felt electrode (thickness: 2 T), a Nafion membrane (Chemours) is used as an ion exchange membrane, and an electrochemical reactor having an electrode area of 5 cm * 5 cm is manufactured. did.

As an anode reactant, 50 mL of a 1 M hydrogen peroxide aqueous solution dissolved in a 4.1 M sulfuric acid aqueous solution was prepared. 50 mL of the vanadium electrolyte prepared in Preparation Example and 50 mL of the anode reactant were put into each of two 100 mL beakers. The vanadium electrolyte was supplied to the cathode of the electrochemical reactor using a master flex pump, and the anode reactant was supplied to the anode, and each supply speed was the same at 85 rpm. After maintaining the circulation for about 1 minute, a charge of 1.19 Ah was applied by setting the current density of the electrochemical reactor to 20 mA/cm ² .

[Comparative Example 3] - 3.5 valent vanadium electrolyte

Merck's Iridium black powder was dispersed in Chemours' Nafion solution to prepare a slurry having a Nafion content of 10% by weight. The slurry was applied to a porous titanium fiber felt (thickness: 0.35 T) having a size of 5 cm*5 cm by spraying, and coated with 2 mg/cm ² of iridium.

An iridium-coated titanium fiber felt was used as an anode and an uncoated titanium fiber felt was used as a cathode, and Chemours Nafion 117 cation exchange membrane was placed between the two electrodes. The thus-arranged structure was placed in a hot press and treated at 130 DEG C and 100 atm for about 2 minutes to obtain a membrane electrode assembly. The membrane electrode assembly was fastened to an electrochemical reactor composed of a titanium mesh and a titanium precursor (see FIG. 4).

Two 100 mL beakers were prepared, and 50 mL of the vanadium electrolyte of Preparation Example was placed in one beaker as a cathode reactant, and 50 mL of 4.1 M sulfuric acid aqueous solution was placed in the other beaker as a cathode reactant.

The vanadium electrolyte was supplied to the cathode of the electrochemical reactor using a master flex pump, and the anode reactant was supplied to the anode, and each supply speed was the same at 85 rpm. After maintaining the circulation for about 1 minute, a charge of 1.19 Ah was applied by setting the current density of the electrochemical reactor to 20 mA/cm ² .

[Example 1] - 3.5 valent vanadium electrolyte

The same process as in Comparative Example 3 was performed except that 50 mL of distilled water as an anode reactant was put in a 100 mL beaker, and the current density of the electrochemical reactor was set to 300 mA/cm ² to apply an electric charge of 1.19 Ah.

[Example 2] - 3.5 valent vanadium electrolyte

The same process as in Comparative Example 3 was performed, except that 50 mL of distilled water as an anode reactant was put in a 100 mL beaker, and the current density of the electrochemical reactor was set to 700 mA/cm ² to apply an electric charge of 1.19 Ah.

[Experimental Example 1] - Charge calculation

The amount of charge required for the reduction reaction of the tetravalent vanadium electrolyte was calculated according to Equation 1 below:

[Equation 1]

[Experimental Example 2] - Reaction Time

The time required for the reduction reaction of the tetravalent vanadium electrolyte was calculated as follows according to the applied charge and current density:

[Equation 2]

[Experimental Example 3] - Anode vanadium crossover measurement

After the electrochemical reaction, the vanadium concentration at the anode was measured using an inductively coupled plasma emission spectrometer from PerkinElmer.

[Experimental Example 4] - Measurement of negative vanadium concentration

After the electrochemical reaction, the concentration of the 3.5-valent vanadium electrolyte was measured using a Titrando automatic potentiometer from Metrohm. Specifically, by oxidizing 1 mL of vanadium electrolyte with 0.2 M KMnO ₄ solution, the potential of the reference electrode changes rapidly, and the amount of KMnO ₄ solution injected at the point where the second derivative of the potential and the amount of KMnO ₄ becomes zero is the concentration of vanadium ions. was measured with Here, the vanadium concentration in the initial vanadium electrolyte and the input amount of KMnO ₄ have a relationship as shown in Equation 4 below:

[Equation 4]

In addition, the concentrations of trivalent and tetravalent vanadium (positive ions) in the 3.5 valent vanadium electrolyte have the following relationships as shown in Equations 5 and 6:

[Equation 5]

[Equation 6]

The reaction conditions and results in the above Examples and Comparative Examples are shown in Table 1 below.

division		comparative example One	comparative example 2	comparative example 3	Example One	Example 2
condition	electrode material	graphite	graphite	Ti-based	Ti-based	Ti-based
	Cell method	Non-MEA	Non-MEA	MEA	MEA	MEA
	cathode reactant	1.78M V4++ 4.1MH 2 SO 4	1.78M V4+ + 4.1MH 2 SO 4	1.78M V4+ + 4.1MH 2 SO 4	1.78M V4+ + 4.1MH 2 SO 4	1.78M V4+ + 4.1MH 2 SO 4
	anode reactant	1.78M V4+ + 4.1MH 2 SO 4	1 M H 2 O 2 + 4.1MH 2 SO 4	4.1MH 2 SO 4	H 2 O	H 2 O
	current density (mA/cm 2 )	20	20	20	300	700
	Charge amount supplied (Ah)	1.19	1.19	1.19	1.19	1.19
result	average voltage (V)	1.45	1.41	1.85	2.21	2.57
	reaction time (minute)	142	142	142	9.5	4
	Cathode V concentration (M)	1.74	1.71	1.73	1.69	1.71
	Anode V concentration (ppm)	-	120	92	0	0
	Cathode V 3+ ratio (%)	51.0	38.1	50.1	50.2	50.1
	Cathode V 4+ ratio (%)	49.0	61.9	49.9	49.8	49.9
	anode product	V5+	Oxygen	Oxygen	Oxygen	Oxygen
	Re-use process	necessary	Unnecessary	Unnecessary	Unnecessary	Unnecessary

[Evaluation and Conclusion]

Comparative Example 1 uses a tetravalent vanadium electrolyte as an anode reactant. In this case, vanadium crossover occurred between cathode and anode, and it was difficult to control the oxidation number. Also, since a 5-valent vanadium electrolyte was generated at the anode, a separate reuse process was required. In addition, since graphite was used as the electrode, the maximum operating voltage was limited to 1.6 V, so the current density could not be increased.

Comparative Example 2 did not require a reuse process because hydrogen peroxide was used as an anode reactant. However, in Comparative Example 2, a portion of hydrogen peroxide was crossover to the anode through the ion exchange membrane to oxidize vanadium ions in the anode, so the ratio of trivalent vanadium ions was relatively low.

Comparative Example 3 used an aqueous solution of sulfuric acid as a cathode reactant, and as a result of crossover of vanadium ions from the cathode to the anode, loss of vanadium ions occurred.

In Example 1, the reaction time was greatly reduced, and the ratio of the trivalent vanadium compound to the tetravalent vanadium compound in the negative electrode product was close to 1:1.

In Example 2, the reaction time was shortened by about 35 times compared to the comparative example, and the ratio of trivalent vanadium cations to tetravalent vanadium cations in the anode product was closer to 1:1.

Claims (4)

1. A method for producing a vanadium electrolyte using a reactor comprising a membrane electrode assembly having a cathode, an ion exchange membrane, an anode catalyst, and an anode in the above order,

   A cathode reactant containing a tetravalent vanadium compound is supplied to the cathode of the reactor, and a cathode reactant containing an aqueous solvent is supplied to the anode of the reactor, and then electric charge is applied to the reactor to generate a tetravalent vanadium compound ( obtaining a product comprising V(IV)) and a trivalent vanadium compound (V(III)) in a volume ratio of 4:6 to 6:4 (V(IV):V(III));

   A method for preparing a vanadium electrolyte.
2. According to claim 1,

   In the membrane electrode assembly, the cathode and the ion exchange membrane are in direct contact,

   A method for preparing a vanadium electrolyte.
3. According to claim 1,

   The aqueous solvent is distilled water,

   A method for preparing a vanadium electrolyte.
4. According to claim 1,

   The current density of the charge applied to the reactor is in the range of 100 mA/cm ² to 1,000 mA/cm ² ,

   A method for preparing a vanadium electrolyte.

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