Method for synthesizing vanadium electrolyte through direct electrolytic reduction of vanadium pentoxide

Abstract

The invention discloses a method for synthesizing vanadium electrolyte by direct electrolytic reduction of vanadium pentoxide, which adopts a diaphragm electrolytic cell, takes a granular conductive material as a cathode material, takes an acidic aqueous solution containing vanadium pentoxide powder as a catholyte and takes an acidic aqueous solution as an anolyte. Direct current or pulse current sequentially passes through the anolyte, the diaphragm and the catholyte from the anode to the cathode, and pentavalent vanadium is reduced into tetravalent or trivalent vanadium ions. And under the current density of 20-30 A / dm < 2 >, the current efficiency can be improved by 18-22%.

Description

(I) TECHNICAL FIELD

[0001] The present application belongs to the field of electrolytic synthesis, and relates to a method for directly electrolytically reducing vanadium pentoxide to synthesize vanadium electrolyte. (II) BACKGROUND

[0002] All-vanadium redox flow battery is a new type of ideal green secondary battery, which has the characteristics of good safety, no pollution, long service life, easy operation and maintenance, and has broad application prospects in the field of large-scale energy storage. The initial electrolyte of all-vanadium redox flow battery is an acidic aqueous solution containing 3-valent and 4-valent vanadium (3-valent and 4-valent vanadium concentration is close), or an acidic aqueous solution containing 3-valent and 4-valent vanadium as the initial electrolyte of the negative electrode chamber and the positive electrode chamber, respectively.

[0003] Electrolytic reduction is an important method for synthesizing the above initial vanadium electrolyte and 3-valent vanadium-containing acidic aqueous solution (usually from 5-valent vanadium or 4-valent vanadium to 3-valent vanadium), which has the advantages of high efficiency and accuracy. Among them, directly electrolytically reducing vanadium pentoxide to synthesize vanadium electrolyte has the advantages of fewer steps and high purity of electrolyte. The biggest problem limiting the large-scale application of this method is low electrolysis efficiency (low current density or low current efficiency). (III) SUMMARY

[0004] The present application aims to provide a method for directly electrolytically reducing vanadium pentoxide to synthesize vanadium electrolyte, which uses granular conductive material as cathode material, acidic aqueous solution containing vanadium pentoxide powder as cathode liquid, and acidic aqueous solution as anode liquid. The direct current or pulse current passes through the anode liquid, the diaphragm and the cathode liquid in turn from the anode to the cathode, and the 5-valent vanadium is reduced to 4-valent or 3-valent vanadium ions. This method can significantly improve the efficiency of direct electrolytic reduction of vanadium pentoxide.

[0005] The technical solution adopted by the present application is:

[0006] The present application provides a method for directly electrolytically reducing vanadium pentoxide to synthesize vanadium electrolyte with high efficiency, which uses a diaphragm electrolytic cell, granular conductive material as cathode material, acidic aqueous solution containing vanadium pentoxide powder as cathode liquid, and acidic aqueous solution as anode liquid. The direct current or pulse current passes through the anode liquid, the diaphragm and the cathode liquid in turn from the anode to the cathode, and the 5-valent vanadium is reduced to 4-valent or 3-valent vanadium ions.

[0007] Further, the average particle size of the granular conductive material is 1-1000 microns, preferably 100-500 microns.

[0008] Further, the granular conductive material is a carbon material, such as activated carbon, coke and graphite, etc.

[0009] Further, the flow rate of the catholyte is in the range of 1-20 cm / s, preferably 5-10 cm / s.

[0010] Further, the total concentration of vanadium pentoxide in the catholyte is in the range of 0.1-2.5 mol / L. The vanadium pentoxide in the catholyte can also be added in batches to ensure the flowability of the catholyte.

[0011] Further, the acidic aqueous solution in the catholyte is sulfuric acid aqueous solution or sulfuric acid / hydrochloric acid mixed acid aqueous solution; preferably the concentration of sulfuric acid in the catholyte is in the range of 1-5 mol / L (preferably 3-4 mol / L) and / or the concentration of hydrochloric acid is in the range of 1-5 mol / L (preferably 2-3 mol / L).

[0012] Further, the composition of the catholyte is one of the following: (1) 3-4 mol / L sulfuric acid + 1.0-2.5 mol / L vanadium pentoxide; (2) 4 mol / L sulfuric acid + 1.5-2.5 mol / L vanadium pentoxide + 2-3 mol / L hydrochloric acid.

[0013] Further, the acidic aqueous solution in the anolyte is sulfuric acid aqueous solution, preferably the concentration of sulfuric acid is in the range of 1-5 mol / L (preferably 2 mol / L).

[0014] Further, the temperature of the catholyte is in the range of 0-80°C, preferably 30-50°C.

[0015] Further, in the process of synthesizing vanadium electrolyte by direct electrolysis of vanadium pentoxide, the current density is in the range of 5-40 A / dm 2 , preferably 10-30 A / dm 2 .

[0016] Further, the diaphragm electrolytic cell is selected to be a plate-frame structure electrolytic cell, with Nafion-324 membrane as the diaphragm, and titanium plated iridium tantalum plate as the anode.

[0017] The anode material is not a key factor of the present application. According to the reaction conditions of the present application, various materials that can match the cathode current density and will not be corroded can be selected as the anode material, such as platinum sheet or platinum wire as the catalytic material of the anode, iridium tantalum as the catalytic material of the anode, etc.

[0018] The diaphragm material is also not a key factor of the present application. Various diaphragm materials that can match the cathode current density and will not be corroded in the reaction system of the present application can be selected, such as cationic membrane, anionic membrane, or microporous membrane, etc.

[0019] Compared with the prior art, the present application has the following beneficial effects: the present application uses granular conductive material as cathode material, uses acidic aqueous solution containing vanadium pentoxide powder as catholyte, uses acidic aqueous solution as anolyte, and reduces 5-valence vanadium into 4-valence or 3-valence vanadium ion by making direct current or pulse current pass through anolyte, diaphragm and catholyte in turn from anode to cathode. At 20-30 A / dm 2 Current efficiency can be increased by 18-22% at 20-30 A / dm (Four) Brief Description of Drawings

[0020] Figure 1 It is a schematic diagram of plate-and-frame electrolytic cell. (Five) Specific Embodiment

[0021] The present application will be further described in conjunction with specific examples, but the protection scope of the present application is not limited to the following:

[0022] Unless otherwise specified, all aqueous solutions used in the experiments are prepared with deionized water. The electrolytic cell, ion exchange membrane, titanium-plated iridium-tantalum sheet, graphite felt and respective carbon materials used are purchased from Hangzhou Saiyao Electrochemical Instrument Co., Ltd.

[0023] The electrolytic reduction current efficiency (CE, %) is defined as:

[0024]

[0025] Wherein, V is the volume of catholyte at the end of electrolysis (L), C is the concentration of newly generated low-valence vanadium in the catholyte at the end of electrolysis (mol / L), n is the number of electrons required to generate each new low-valence vanadium, I is the electrolysis current (A), and t is the electrolysis time (min).

[0026] The flow rate (r) of the catholyte is defined as:

[0027]

[0028] Wherein, q is the flow rate into the electrolytic cell (cm 3 / s), and S is the cross-sectional area of the cathode chamber filled with granular conductive material in the electrolytic cell (cm 2 ).

[0029] The projected area (S1) is defined as:

[0030] S1 = L x D

[0031] Wherein, L is the length of the electrode in the plane parallel to the diaphragm (cm), and D is the width of the electrode in the plane parallel to the diaphragm (cm).

[0032] Example 1: Synthesis of electrolyte containing 3-valence vanadium and 4-valence vanadium

[0033] A plate-and-frame electrolytic cell as shown in Figure 1 is used, with a diaphragm between the anode and cathode compartments, the diaphragm having an area of 7.1 cm 2 . Titanium coated with iridium and tantalum is used as the anode (projected area: 5 cm 2 ), and graphite particles (average particle size 255 microns) are used as the cathode (thickness 10 mm, projected area: 5 cm 2 ). A Nafion-324 membrane is used as the diaphragm. A plastic grid is provided in the anode compartment to position the diaphragm, and a graphite plate is provided in the cathode compartment to collect the current from the particle electrode. An aqueous solution containing 2 mol / L H2SO4 is used as the anolyte (200 mL), and an aqueous solution containing 4 mol / L H2SO4 + 1 mol / L V2O5 (pentavalent vanadium) is used as the catholyte (200 mL), with a flow rate of 7 cm / s. A current of 1000 mA is applied (anode and cathode current density: 20 A / dm 2 ). During electrolysis, the temperature of the catholyte and anolyte is controlled at 30°C. After 1000 minutes of electrolysis (1 times the theoretical amount of electricity), the electrolysis is stopped, the volume of the catholyte is 202 mL, the concentrations of the tetravalent and trivalent vanadium in the catholyte are 0.98 mol / L and 1.01 mol / L, respectively, and the current efficiency is 97.4%.

[0034] Example 2-8. Synthesis of an electrolyte containing trivalent and tetravalent vanadium - effect of different reaction conditions

[0035] The reaction conditions are the same as in Example 1, except as otherwise specified. The results are shown in Table 1. It can be seen that, with the cathode material being active carbon particles, coke particles and graphite particles, and the average particle size being 1-1000 microns, and the catholyte being an aqueous solution of sulfuric acid containing a suspension of vanadium pentoxide or an aqueous solution of sulfuric acid / hydrochloric acid mixed acid, and the flow rate being 1-20 cm / s, excellent electrolysis results can be obtained.

[0036] Table 1. Effect of different reaction conditionsa

[0037]

[0038] Notes: a The electrolysis is stopped after the passage of 1 times the theoretical amount of electricity. The theoretical amount of electricity is calculated by the formula: Q = C x V x n x 96500, where Q is the theoretical amount of electricity, C is the concentration of vanadium atoms in the catholyte, V is the volume of the catholyte, and n = 1.5 is the number of reaction electrons.bThe vanadium pentoxide powder in the catholyte is added in batches.

[0039] Comparative Example 1. Synthesis of an electrolyte containing trivalent and tetravalent vanadium

[0040] A plate-and-frame electrolytic cell as shown in Figure 1 is used, with a diaphragm between the anode and cathode compartments, the diaphragm having an area of 7.1 cm2 Using a titanium-plated iridium-tantalum plate as the anode (projected area: 5cm²) 2 ), graphite felt as cathode (thickness 10mm, projected area: 5cm²). 2 The membrane was Nafion-324. An aqueous solution containing 2 mol / L H₂SO₄ was used as the anolyte (200 mL), and an aqueous solution containing 4 mol / L H₂SO₄ + 1 mol / L V₂O₅ (vanadium pentavalent) was used as the catholyte (200 mL). The catholyte flow rate was 7 cm / s. Electrolysis was performed with a current of 1000 mA (both anolyte and catholyte current densities were 20 A / dm³). 2 During electrolysis, the temperatures of the catholyte and anolyte were controlled at 30°C. Electrolysis was stopped after 1000 minutes, with a catholyte volume of 203 mL and tetravalent and trivalent vanadium concentrations of 1.56 mol / L and 0.43 mol / L, respectively. The current efficiency was 79.0%. Compared to Example 1, only the cathode material was changed, resulting in an 18% decrease in current efficiency.

[0041] Comparative Example 2: Synthesis of electrolytes containing trivalent and tetravalent vanadium

[0042] Adopting such Figure 1 The plate-and-frame electrolytic cell shown has a diaphragm between the anode and cathode chambers, with a diaphragm area of ​​7.1 cm². 2 Using a titanium-plated iridium-tantalum plate as the anode (projected area: 5cm²) 2 ), graphite felt as cathode (thickness 10mm, projected area: 5cm²). 2 The membrane was Nafion-324. An aqueous solution containing 2 mol / L H₂SO₄ was used as the anolyte (200 mL), and an aqueous solution containing 4 mol / L H₂SO₄ + 1 mol / L V₂O₅ (vanadium pentavalent) was used as the catholyte (200 mL). The catholyte flow rate was 7 cm / s. Electrolysis was performed with a current of 1500 mA (both anolyte and catholyte current densities were 30 A / dm³). 2 During electrolysis, the temperatures of the catholyte and anolyte were controlled at 30°C. Electrolysis was stopped after 750 minutes, with a catholyte volume of 202 mL and tetravalent and trivalent vanadium concentrations of 1.51 mol / L and 0.48 mol / L, respectively. The current efficiency was 71.3%. Compared to Example 8, only the cathode material was changed, resulting in a 22.1% decrease in current efficiency.

Claims

1. A highly efficient method for the direct electrolytic reduction of vanadium pentoxide to synthesize vanadium electrolyte, characterized in that, The method employs a diaphragm electrolytic cell, using granular conductive material as the cathode material, an acidic aqueous solution containing vanadium pentoxide powder as the catholyte, and an acidic aqueous solution as the anolyte. A direct current or pulsed current is passed sequentially from the anode to the cathode through the anolyte, the diaphragm, and the catholyte to reduce vanadium pentavalent to vanadium tetravalent or trivalent ions.

2. The method as described in claim 1, characterized in that, The average particle size of the particulate conductive material is 1-1000 micrometers.

3. The method as described in claim 1, characterized in that, The granular conductive material is a carbon material.

4. The method as described in claim 3, characterized in that, The carbon material includes one of activated carbon, coke, and graphite.

5. The method as described in claim 1, characterized in that, In the process of direct electrolytic reduction of vanadium pentoxide to synthesize vanadium electrolyte, the flow rate of the cathode liquid ranges from 1 to 20 cm / s.

6. The method as described in claim 1, characterized in that, The total concentration of vanadium pentoxide in the catholyte is 0.1-2.5 mol / L.

7. The method as described in claim 1, characterized in that, The acidic aqueous solution in the catholy solution is an aqueous solution of sulfuric acid or a mixed aqueous solution of sulfuric acid and hydrochloric acid; the acidic aqueous solution in the anolyse solution is an aqueous solution of sulfuric acid.

8. The method as described in claim 1, characterized in that, The concentration of sulfuric acid in the catholyte is 1-5 mol / L and / or the concentration of hydrochloric acid is 1-5 mol / L; the concentration of sulfuric acid in the anolyte is 1-5 mol / L.

9. The method as described in claim 1, characterized in that, The temperature range of the catholyte is 0-80℃.

10. The method as described in claim 1, characterized in that, In the process of direct electrolytic reduction of vanadium pentoxide to synthesize vanadium electrolyte, the current density ranges from 5 to 40 A / dm³. 2 .

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