Electrolytic reduction method for adjusting valence state of vanadium electrolyte
By using a three-dimensional porous carbon-based material with a large specific surface area as the cathode, combined with an H-type electrolytic cell and DC or pulsed current, the problem of low current density in the prior art is solved, achieving efficient vanadium electrolyte valence state adjustment and significantly improving current efficiency.
Patent Information
- Application Number
- CN202511420912.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-30
- Publication Date
- 2025-11-18
AI Technical Summary
In existing methods for adjusting the valence state of vanadium electrolytes, the cathode material has low current density or low current efficiency, making it difficult to efficiently reduce high-valence vanadium to low-valence vanadium.
A hydrophilic three-dimensional porous carbon-based material with a large specific surface area is used as the cathode. Combined with DC or pulsed current, vanadium pentavalent or tetravalent is reduced to trivalent vanadium in an acidic aqueous solution through an H-type electrolytic cell. Graphite felt or lead or bismuth modified graphite felt is used as the cathode material.
The current efficiency was significantly improved at high current densities, with an increase of 12-23%, achieving efficient vanadium electrolyte valence state regulation.
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Abstract
Description
(I) TECHNICAL FIELD
[0001] The present application belongs to the field of electrolytic synthesis, and relates to an electrolytic reduction method for adjusting the valence state of a vanadium electrolyte. (II) BACKGROUND
[0002] A full vanadium redox flow battery is a kind of redox battery with vanadium as an active substance in a circulating flow liquid state, and has the advantages of high safety and long service life, and has important application prospects in large-scale energy storage. The initial electrolyte of the battery is a sulfuric acid aqueous solution containing 3-valent and 4-valent vanadium (the concentrations of 3-valent and 4-valent vanadium are close to each other), or a sulfuric acid 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] The electrolytic reduction method is an important method for adjusting the valence state of a vanadium electrolyte, and has the advantages of high efficiency and accuracy. On the one hand, the electrolytic reduction method can adjust an acidic aqueous solution containing 5-valent vanadium or 4-valent vanadium into an acidic aqueous solution containing 3.5-valent vanadium (the concentrations of 3-valent and 4-valent vanadium are close to each other) or an acidic aqueous solution containing only 3-valent vanadium ions; on the other hand, the electrolytic reduction method can also adjust the valence state of the electrolyte of a full vanadium redox flow battery after long-term use (mainly reducing 5-valent vanadium in the positive electrode chamber of the full vanadium redox flow battery into 4-valent vanadium). The cathode materials used in the electrolytic reduction method for adjusting the valence state of a vanadium electrolyte are mainly graphite and lead plates, and the electrolytic reduction method using these cathode materials has the problems of low current density or low current efficiency. (III) SUMMARY
[0004] The present application aims to provide a high-efficiency electrolytic reduction method for adjusting the valence state of a vanadium electrolyte, which uses a hydrophilic three-dimensional porous carbon-based material with a large specific surface area as a cathode, can reduce high-valence vanadium into low-valence vanadium at a large current density with high current efficiency, and solves the problems of low current density or low current efficiency of existing methods.
[0005] The technical solution adopted by the present application is as follows:
[0006] The present application provides a high-efficiency electrolytic reduction method for adjusting the valence state of a vanadium electrolyte, which uses a diaphragm electrolytic cell, a three-dimensional porous carbon-based material with a moderate specific surface area as a cathode, an acidic aqueous solution containing high-valence vanadium as a catholyte, and an acidic aqueous solution as an anolyte, and reduces 5-valent vanadium or 4-valent vanadium into 3-valent vanadium ions by passing a direct current or a pulse current from the anode to the cathode through the anolyte, the diaphragm and the catholyte in sequence.
[0007] Further, the three-dimensional porous carbon-based material is a graphite felt or carbon felt material, or a graphite felt or carbon felt material modified with lead or bismuth, and has a specific surface area of 5-200 m 2 / g and a water droplet contact angle of 0-90°, and preferably a specific surface area of 10-150 m 2 / g, water droplet contact angle is 0-30°.
[0008] Furthermore, the lead or bismuth content in the lead or bismuth modified graphite felt or carbon felt material is 0.01-10 wt%.
[0009] Furthermore, the cathode solution is an aqueous solution containing 1-5 mol / L sulfuric acid + 0-2 mol / L methanesulfonic acid + 1-3 mol / L vanadium oxysulfate (tetravalent vanadium) or 0.5-1.5 mol / L vanadium pentoxide (pentavalent vanadium).
[0010] Furthermore, the anolyte is an aqueous solution containing 1-5 mol / L sulfuric acid.
[0011] Furthermore, the temperature range of the electrolytic reduction method is 20-80℃, and the cathode current density is 10-40 A / dm³. 2 .
[0012] Furthermore, the electrolytic cell is an H-type electrolytic cell, with a diaphragm between the anode chamber and the cathode chamber, using a titanium-plated iridium-tantalum sheet as the anode and a Nafion-324 membrane as the diaphragm.
[0013] The anode material is not a key factor in this invention. According to the reaction conditions of this invention, various materials that can match the cathode current density and will not corrode can be selected as anode materials, such as platinum sheets or platinum wires as anodes for catalysts, iridium-tantalum anodes, etc.
[0014] The membrane material is not a key factor in this invention. Various membrane materials that can match the cathode current density and will not corrode in the reaction system of this invention can be selected, such as cation membranes, anion membranes, or microporous membranes.
[0015] The electrolytic synthesis of trivalent vanadium can be achieved through various electrolytic reduction pathways. It can be that pentavalent or tetravalent vanadium is directly reduced to trivalent vanadium; or tetravalent vanadium is directly reduced to divalent vanadium, and then divalent vanadium undergoes a disproportionation reaction with tetravalent or pentavalent vanadium to generate trivalent vanadium.
[0016] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following: the present invention has a specific surface area of 10-150m². 2 A three-dimensional porous carbon-based material with a water contact angle of 0-30° is used as the cathode, an acidic aqueous solution as the anolyte, and an acidic aqueous solution containing high-valence vanadium as the catholyte. Electrolysis reduces pentavalent or tetravalent vanadium in the catholyte to trivalent vanadium. At the same current density (10⁻³⁰ A / dm³), [the following parameters are used]. 2 The current efficiency can be improved by 12-23%. (iv) Description of the attached drawings
[0017] Figure 1 This is a schematic diagram of an H-type electrolysis unit, with the diaphragm placed in the center. (V) Detailed Implementation
[0018] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:
[0019] Unless otherwise specified, all aqueous solutions used in the experiments were prepared with deionized water. The H-type electrolytic cell, titanium-plated iridium-tantalum sheet, graphite felt, carbon felt, and lead- or bismuth-modified graphite felt and carbon felt used were purchased from Hangzhou Sai'ao Electrochemical Instrument Co., Ltd.
[0020] The electrolytic reduction current efficiency (CE, %) is defined as follows:
[0021]
[0022] Where V is the volume of the 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).
[0023] Example 1: Synthesis of electrolyte containing trivalent and tetravalent vanadium—using tetravalent vanadium electrolyte as raw material
[0024] use Figure 1 The H-shaped electrolytic cell shown has a diaphragm between the anode and cathode chambers, with a diaphragm area of 7.1 cm². 2 The cathode chamber contains a thermometer and a stirrer, while an external temperature control panel is installed. A titanium-plated iridium-tantalum sheet is used as the anode (electrode area: 2 × 2.5 cm²). 2 Bismuth-modified graphite felt was used as the cathode (electrode area: 2 × 2.5 cm). 2 Thickness 0.3cm, specific surface area 51m² 2 / g, bismuth mass content 0.01%, water droplet contact angle 0°), using a Nafion-324 membrane as the diaphragm. An aqueous solution containing 2 mol / L H₂SO₄ was used as the anolyte (100 mL), and an aqueous solution containing 2 mol / L H₂SO₄ + 2 mol / L VOSO₄ (tetravalent vanadium) was used as the catholyte (100 mL); electrolysis was performed with a current of 1500 mA (both anolyte and catholyte current densities were 30 A / dm²). 2 During electrolysis, the temperatures of the catholyte and anolyte were controlled at 30℃. Electrolysis was stopped after 110 minutes, with a catholyte volume of 103 mL, a trivalent vanadium concentration of 0.98 mol / L, and a current efficiency of 98.4%.
[0025] Example 2 Synthesis of trivalent vanadium electrolyte—using pentavalent vanadium electrolyte as raw material
[0026] use Figure 1The H-shaped electrolytic cell shown has a diaphragm between the anode and cathode chambers, with a diaphragm area of 7.1 cm². 2 A titanium-plated iridium-tantalum sheet was used as the anode (electrode area: 2 × 2.5 cm). 2 Lead-modified carbon felt serves as the cathode (electrode area: 2 × 2.5 cm). 2 Thickness 0.3cm, specific surface area 63m² 2 / g, lead content 0.01%, water droplet contact angle 0°), using a Nafion-324 membrane as the diaphragm. An aqueous solution containing 2 mol / L H₂SO₄ was used as the anolyte (100 mL), and an aqueous solution containing 2 mol / L H₂SO₄ + 0.5 mol / L V₂O₅ (pentavalent vanadium) was used as the catholyte (100 mL); electrolysis was performed with a current of 500 mA (both anolyte and catholyte current densities were 10 A / dm²). 2 During electrolysis, the temperatures of the catholyte and anolyte were controlled at 30℃. Electrolysis was stopped after 650 minutes, with a catholyte volume of 100 mL, a trivalent vanadium concentration of 0.99 mol / L, and a current efficiency of 98.0%.
[0027] Examples 3-7 Synthesis of electrolytes containing trivalent and tetravalent vanadium—using tetravalent vanadium electrolyte as raw material—the effect of different reaction conditions
[0028] Unless otherwise specified, the reaction conditions were the same as in Example 1. The experimental results are shown in Table 1. Combined with Example 1, it can be seen that the specific surface area is 11-149 m². 2 The cathode material is graphite felt or bismuth-modified graphite felt with a water droplet contact angle of 0-30° (bismuth content 0.01-9.5 wt%). The catholyte is an aqueous solution containing 1-5 mol / L sulfuric acid + 0-2 mol / L methanesulfonic acid + 1-3 mol / L vanadium oxysulfate (tetravalent vanadium). The anolyte is an aqueous solution containing 1-5 mol / L sulfuric acid. The temperature range is 20-80℃, and the cathode current density is 10-40 A / dm³. 2 Both can achieve excellent electrolysis results.
[0029] Table 1 Effect of different reaction conditions a
[0030]
[0031] Remark: a Electrolysis is stopped after passing in one times the theoretical charge. The theoretical charge is calculated using the following formula: Q = C × V × n × 96500, where Q is the theoretical charge, C is the vanadium ion concentration in the cathode solution, V is the volume of the cathode solution, and n = 0.5 is the number of reaction electrons.
[0032] Examples 8-12 Synthesis of trivalent vanadium electrolyte—using pentavalent vanadium electrolyte as raw material—Effect of different reaction conditions
[0033] Unless otherwise specified, the reaction conditions were the same as in Example 2. The experimental results are shown in Table 2. Combined with Example 2, it can be seen that the specific surface area is 12-148 m². 2 The cathode material is a carbon felt or lead-modified carbon felt with a water droplet contact angle of 0-29° (lead content is 0.01-9.5wt%), and the catholyte contains 2-5 mol / L sulfuric acid + 0-2 mol / L methanesulfonic acid +
[0034] The anode solution consists of a 0.5-1.5 mol / L vanadium pentoxide (pentavalent vanadium) aqueous solution, a 1-5 mol / L sulfuric acid aqueous solution, a temperature range of 20-80℃, and a cathode current density of 10-40 A / dm³. 2 Both can achieve excellent electrolysis results.
[0035] Table 2 Effect of different reaction conditions a
[0036]
[0037]
[0038] Remark: a Electrolysis is stopped after passing in one times the theoretical charge. The theoretical charge is calculated using the following formula: Q = C × V × n × 96500, where Q is the theoretical charge, C is the vanadium atom concentration in the cathode solution, V is the volume of the cathode solution, and n = 2 is the number of reaction electrons.
[0039] Comparative Example 1: Synthesis of electrolytes containing trivalent and tetravalent vanadium—using tetravalent vanadium electrolyte as raw material
[0040] An H-type electrolytic cell is used, with a diaphragm between the anode and cathode chambers. The diaphragm area is 7.1 cm². 2 A titanium-plated iridium-tantalum sheet was used as the anode (electrode area: 2 × 2.5 cm). 2 ), with graphite felt as the cathode (electrode area: 2×2.5cm). 2 Thickness 0.3cm, specific surface area 55m² 2 / g, water droplet contact angle 135°), with Nafion-324 membrane as diaphragm. An aqueous solution containing 2 mol / L H₂SO₄ was used as the anolyte (100 mL), and an aqueous solution containing 2 mol / L H₂SO₄ + 2 mol / L VOSO₄ (tetravalent vanadium) was used as the catholyte (100 mL); electrolysis was performed with a current of 1500 mA (both anolyte and catholyte current densities were 30 A / dm²). 2During electrolysis, the temperatures of the catholyte and anolyte were controlled at 30°C. Electrolysis was stopped after 110 minutes, with a catholyte volume of 102 mL, a trivalent vanadium concentration of 0.76 mol / L, and a current efficiency of 75.5%. Compared to Example 1, changing only the specific surface area of the cathode material and the water contact angle resulted in a 22.9% decrease in current efficiency.
[0041] Comparative Example 2: Synthesis of a trivalent vanadium electrolyte—using a pentavalent vanadium electrolyte as raw material
[0042] An H-type electrolytic cell is used, with a diaphragm between the anode and cathode chambers. The diaphragm area is 7.1 cm². 2 A titanium-plated iridium-tantalum sheet was used as the anode (electrode area: 2 × 2.5 cm). 2 The carbon felt is used as the cathode (electrode area: 2×2.5cm). 2 Thickness 0.3cm, specific surface area 2m² 2 / g, water droplet contact angle of 0°), with Nafion-324 membrane as diaphragm. An aqueous solution containing 2 mol / L H₂SO₄ was used as the anolyte (100 mL), and an aqueous solution containing 2 mol / L H₂SO₄ + 0.5 mol / L V₂O₅ (pentavalent vanadium) was used as the catholyte (100 mL); electrolysis was performed with a current of 500 mA (both anolyte and catholyte current densities were 10 A / dm²). 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 101 mL, a trivalent vanadium concentration of 0.99 mol / L, and a current efficiency of 85.8%. In Comparative Example 2, changing only the specific surface area of the cathode material and the water contact angle resulted in a 12.2% decrease in current efficiency.
[0043] Comparative Example 3: Synthesis of a trivalent vanadium electrolyte—using a pentavalent vanadium electrolyte as raw material
[0044] An H-type electrolytic cell is used, with a diaphragm between the anode and cathode chambers. The diaphragm area is 7.1 cm². 2 A titanium-plated iridium-tantalum sheet was used as the anode (electrode area: 2 × 2.5 cm). 2 The carbon felt is used as the cathode (electrode area: 2×2.5cm). 2 Specific surface area is 258m² 2 / g, water droplet contact angle of 0°), with Nafion-324 membrane as diaphragm. An aqueous solution containing 2 mol / L H₂SO₄ was used as the anolyte (100 mL), and an aqueous solution containing 2 mol / L H₂SO₄ + 0.5 mol / L V₂O₅ (pentavalent vanadium) was used as the catholyte (100 mL); electrolysis was performed with a current of 500 mA (both anolyte and catholyte current densities were 10 A / dm²). 2During electrolysis, the temperatures of the catholyte and anolyte were controlled at 30°C. Electrolysis was stopped after 800 minutes, with a catholyte volume of 101 mL, a trivalent vanadium concentration of 0.99 mol / L, and a current efficiency of 80.4%. In Comparative Example 2, changing only the specific surface area of the cathode material and the water contact angle resulted in a 17.6% decrease in current efficiency.
Claims
1. A highly efficient electrolytic reduction method for adjusting the valence state of vanadium electrolyte, characterized in that, The method employs a diaphragm electrolytic cell, using a hydrophilic, three-dimensional porous carbon-based material with a suitable specific surface area as the cathode, an acidic aqueous solution containing high-valent vanadium 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 pentavalent or tetravalent vanadium to trivalent vanadium ions.
2. The method as described in claim 1, characterized in that, The three-dimensional porous carbon-based material is graphite felt or carbon felt material, or graphite felt or carbon felt material modified with lead or bismuth.
3. The method as described in claim 1 or 2, characterized in that, The specific surface area of the three-dimensional porous carbon-based material is 5-200 m². 2 / g, water droplet contact angle is 0-90°.
4. The method as described in claim 3, characterized in that, The specific surface area of the three-dimensional porous carbon-based material is 10-150 m². 2 / g, water droplet contact angle is 0-30°.
5. The method as described in claim 2, characterized in that, The lead or bismuth content in the lead or bismuth modified graphite felt or carbon felt material is 0.01-10 wt%.
6. The method as described in claim 1, characterized in that, The cathode solution is an aqueous solution containing 1-5 mol / L sulfuric acid + 0-2 mol / L methanesulfonic acid + 1-3 mol / L vanadium oxysulfate or 0.5-1.5 mol / L vanadium pentoxide.
7. The method as described in claim 1, characterized in that, The anolyte is an aqueous solution containing 1-5 mol / L sulfuric acid.
8. The method as described in claim 1, characterized in that, The electrolytic reduction method has a temperature range of 20-80℃ and a cathode current density of 10-40 A / dm³. 2 .