A bi-atomic catalyst composite electrode for a vanadium redox flow battery and a preparation method and application thereof

Abstract

This invention relates to the preparation and application of a single-atom catalyst composite electrode for vanadium redox flow batteries, belonging to the field of energy storage technology batteries. The composite electrode preparation method involves in-situ support of sodium citrate precursor on a graphite felt substrate, followed by carbonization treatment, and then using its microporous structure to adsorb phytic acid and Bi through liquid-phase impregnation. 3+ The mixture is then subjected to high-temperature calcination to utilize the P atoms to anchor Bi atoms, forming a Bi-P4 coordination structure. This ensures that Bi atoms are uniformly and stably dispersed on a carbon substrate, thereby preparing a Bi single-atom catalyst composite electrode with high catalytic activity and high stability. The catalyst preparation method provided by this invention is simple and easy to control, and exhibits high energy efficiency, electrocatalytic activity, and cycle stability, making it promising for large-scale commercial production.

Description

Technical Field

[0001] This invention belongs to the field of energy storage technology batteries, and specifically relates to a method for preparing a Bi single-atom catalyst with high catalytic activity and high cycle stability and its application. Background Technology

[0002] The increasing consumption of fossil fuels has led to severe environmental pollution, necessitating the full utilization of renewable energy. However, the intermittency and volatility of renewable energy sources have resulted in over 20% of renewable energy not being stored, severely impacting grid stability. This necessitates large-scale energy storage technologies. Among various energy storage technologies, vanadium redox flow batteries (VRBs) are increasingly being applied in large-scale energy storage due to their flexible design, high safety, high energy efficiency, and low cost potential. However, the cost of the fuel cell stack and vanadium salts limits the commercial use of VRBs. One effective approach is to enable VRBs to operate at higher current densities while maintaining high energy density to reduce stack costs. However, increasing current density leads to increased battery polarization, resulting in decreased battery performance.

[0003] Electrodes, as a key component of vanadium redox flow batteries, are closely related to the battery's activation polarization, ohmic polarization, and concentration polarization. Currently, commonly used electrodes include graphite felt and carbon felt, primarily due to their good conductivity, stability, and low cost. However, at higher current densities, their lack of sufficiently high specific surface area and hydrophilicity leads to significant polarization losses. Therefore, electrode modification is necessary to improve their catalytic activity, hydrophilicity, and stability.

[0004] Currently, electrode modification methods mainly include surface functionalization, which improves the hydrophilicity of the electrode surface through oxidation, nitriding, and other treatments; however, anchoring oxygen over a wide voltage window remains a problem. Surface structure modulation, using etching methods such as KOH and NiO to increase the specific surface area of ​​the electrode, but this damages the mechanical properties of the electrode. Supporting carbon-based catalysts with large specific surface areas, such as carbon nanotubes and mesoporous carbon, can reduce activation polarization to some extent, but the fragile pore structure cannot meet the requirements for long-term stable operation of the battery. Directly supporting metal catalysts, such as Pt, Pd, and Ag, can improve their electrocatalytic activity to some extent, but it produces severe hydrogen evolution side reactions. While supporting Bi, Sn, and Pb can effectively suppress hydrogen evolution, their electrocatalytic activity is insufficient. Furthermore, metal catalysts are limited by particle size, uniformity of distribution, and structural stability, which greatly reduces their electrocatalytic activity and stability. Therefore, how to prepare metal catalysts with high activity, high hydrogen evolution overpotential, and high stability has become an urgent problem to be solved. Summary of the Invention

[0005] To address the problems existing in current technologies, this invention provides a Bi single-atom catalyst composite electrode for vanadium redox flow batteries, its preparation method, and its application. This invention uses graphite felt as a substrate to in-situ support sodium citrate, followed by carbonization. The microporous structure of the graphite felt is utilized through a liquid-phase impregnation process to react with phytic acid and Bi. 3+ In the subsequent high-temperature calcination and carbonization process, the P atoms in the phytic acid precursor are used to anchor Bi atoms to form a Bi-P4 coordination structure, allowing Bi atoms to be stably dispersed on the carbon substrate, thereby preparing a Bi single-atom catalyst with high catalytic activity and high stability. The catalyst preparation method provided by this invention is simple and easy to control, and has high electrocatalytic activity and high cycling stability, making it promising for large-scale commercial production.

[0006] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a Bi single-atom catalyst composite electrode for an all-vanadium redox flow battery, comprising the following steps:

[0008] 1) Soak the carbon substrate in an aqueous solution of sodium citrate for 2-6 hours to obtain a carbon substrate supported by sodium citrate;

[0009] 2) Dry the sodium citrate-supported carbon substrate obtained in step 1), take the dried sample and calcine it at high temperature, and then wash it with acid.

[0010] 3) Immerse the obtained sample in 0.005-3 mol / L solution. -1 Bi salt and 1-6 mol / ml -1 In a phytic acid-ethanol mixture, let stand for 12-24 hours;

[0011] 4) Take out the sample and dry it, then calcine it at high temperature again to obtain the Bi single-atom catalyst composite electrode.

[0012] Further, the sodium citrate aqueous solution is prepared with a ratio of sodium citrate to water of 2-7 (g): 50-300 (mL).

[0013] Furthermore, the carbon substrate has a thickness of 1–5 mm and a surface area of ​​5–20 cm² on both sides. 2 .

[0014] Furthermore, calcination is carried out at 600-1000℃ for 0.5-3 hours in a nitrogen atmosphere.

[0015] Furthermore, the carbon substrate includes one or more of graphite felt, carbon felt, carbon cloth, and carbon paper.

[0016] Further, the drying in step 2) is as follows: drying at 60-80℃ for 3-6 hours, and then calcining the sample at a high temperature of 600-1000℃, preferably 700-800℃, for 0.5-3 hours, in a calcination atmosphere of one or more inert gases such as nitrogen and argon.

[0017] Further, the Bi salt in step 3) is one or more of bismuth nitrate and bismuth chloride.

[0018] Furthermore, in step 4), the high-temperature calcination conditions are: calcination at 600-1000℃ for 0.5-3 hours in a calcination atmosphere; the calcination atmosphere is one or more of nitrogen and inert gases.

[0019] In the Bi single-atom catalyst composite electrode, the loading of Bi atoms is 1-6 mg / cm³. -2 .

[0020] Secondly, the present invention provides a Bi single-atom catalyst composite electrode prepared by the preparation method described above.

[0021] Thirdly, the present invention provides an application of the electrode, which can be used as the positive or negative electrode of a vanadium redox flow battery.

[0022] Furthermore, the electrodes are used with a high current density of 80-280 mA / cm². -2 .

[0023] This invention utilizes a graphite felt substrate to support sodium citrate in situ, followed by carbonization treatment, and then employs its microporous structure to adsorb phytic acid and Bi through a liquid-phase impregnation process. 3+ A mixed solution is then subjected to high-temperature calcination to utilize the P atoms to anchor Bi atoms, forming a Bi-P4 coordination structure. This allows Bi atoms to be stably dispersed on a carbon substrate, thereby preparing a Bi single-atom catalyst with high catalytic activity and high stability. The catalyst preparation method provided by this invention is simple and easy to control, and exhibits high electrocatalytic activity and high cycling stability.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) By fully utilizing the introduction of P atoms in the later stage of the original carbon substrate, the uniformity of the distribution of P atoms on its surface can be guaranteed, and Bi atoms can be anchored more uniformly, thereby controlling the loading of Bi atoms.

[0026] (2) In the carbon substrate sintered with sodium citrate, P atoms are introduced in the later stage to anchor Bi atoms to form a Bi-P4 coordination structure, so that Bi atoms are stably dispersed on the carbon substrate, thereby preparing a single-atom catalyst with high catalytic activity and high stability.

[0027] (3) This single-atom catalyst with a Bi-P4 coordination structure not only possesses excellent electrocatalytic activity and reduces the three major polarizations of the vanadium redox flow battery, but also ensures electrode stability and promotes the efficient and stable conduct of the vanadium ion redox reaction at 200 mA cm⁻¹. -2 The energy efficiency can reach 80.2%, and there is almost no energy efficiency decay during 1500 cycles, which can meet the needs of practical applications;

[0028] (4) The preparation method is simple, the production equipment is conventional, and it is suitable for large-scale production. Attached Figure Description

[0029] Figure 1 HAADF-STEM image of a Bi single-atom catalyst;

[0030] Figure 2 EDS image of a Bi single-atom catalyst. Detailed Implementation

[0031] The present invention will be described in detail below through embodiments, but the present invention is not limited to the embodiments.

[0032] The fabricated electrode was used as the negative electrode for a vanadium redox flow battery, and the battery was assembled for performance testing.

[0033] Example 1

[0034] (1) Add 3g of sodium citrate to 100ml of ultrapure water and stir to obtain sodium citrate aqueous solution;

[0035] (2) Graphite felt (2mm thick, with a surface area of ​​12cm² on both sides) 2 Soak in sodium citrate solution for 6 hours;

[0036] (3) The obtained graphite felt loaded with sodium citrate was dried at 60℃ for 6 hours. The dried sample was then calcined at 800℃ under nitrogen for 1 hour at a heating rate of 5℃ / min. -1 After 3 mol L -1 The hydrochloric acid was used for pickling.

[0037] (4) Place the obtained sample into a solution with a concentration of 0.01 mol / mL. -1 Bi salt and 3mol ml -1 Add phytic acid to 100 ml of ethanol solution and let stand for 12 hours;

[0038] (5) The sample was dried at 60℃ for 6 hours and then calcined again at 800℃ under nitrogen atmosphere for 1 hour to obtain a graphite felt electrode supported on a Bi single-atom catalyst with a catalyst loading of 2 mg / cm³. -2The preparation method provided by this invention is simple and easy to control, the electrode structure is controllable, and it has excellent electrochemical activity and high cycling stability.

[0039] Performance Testing: The assembled vanadium redox flow battery consists of three parts: positive and negative electrolyte storage tanks, a pump, and individual cells. Both the positive and negative electrolytes are 0.8 MV. 3+ +0.8MV 4+ +3M H2SO4, the volume of electrolyte is 3.5 ml cm -2 In a single cell, a catalyst-supported graphite felt electrode was used as the negative electrode, and the graphite felt itself was used as the positive electrode. The electrode thickness was 2 mm, and the surface area of ​​both sides of the electrode was 12 cm². 2 Nafion 212 membrane is an intermediate septum membrane, operating at 80-280 mA / cm². -2 Under constant current charging and discharging at a certain current density, the battery charging and discharging cutoff voltage is 1.55V, and the discharging cutoff voltage is 1.0V.

[0040] from Figure 1 It can be seen that Bi single-atom catalysts are supported on the graphite felt, and the size of the Bi single atom is within... Uniformly dispersed on a carbon substrate. From Figure 2 It can be seen that the overall dispersed structure contains Bi, P, and C elements. Table 1 shows that the prepared electrode exhibits performance at 200 mA / cm². -2 The energy efficiency reaches 80.2%.

[0041] Example 2

[0042] The preparation method, process and performance testing process are the same as in Example 1, except that step (5) is calcined again at 800°C in a nitrogen atmosphere for 2 hours.

[0043] Example 3

[0044] The preparation method, process and performance testing process are the same as in Example 1, except that step (5) is calcined again at 1000°C in a nitrogen atmosphere for 2 hours.

[0045] Example 4

[0046] The preparation method, process, and performance testing process are the same as in Example 1, except that the concentration of Bi salt added in step (4) is 0.05 mol / mL. -1

[0047] Example 5

[0048] The preparation method, process, and performance testing process are the same as in Example 1, except that the concentration of Bi salt added in step (4) is 0.02 mol / mL.-1

[0049] Example 6

[0050] The preparation method, process, and performance testing process are the same as in Example 1, except that the concentration of phytic acid added in step (4) is 2 mol / mL. -1

[0051] Example 7

[0052] The preparation method, process, and performance testing process are the same as in Example 1, except that the concentration of phytic acid added in step (4) is 4 mol / mL. -1

[0053] Example 8

[0054] The preparation method, process and performance testing process are the same as in Example 1, except that step (5) is calcined again at 800°C in a nitrogen atmosphere for 30 minutes.

[0055] Example 9

[0056] The preparation method, process and performance testing process are the same as in Example 1, except that step (5) is calcined again at 800°C in a nitrogen atmosphere for 3 hours.

[0057] Comparative Example 1

[0058] (1) Add 3g of sodium citrate to 100ml of ultrapure water and stir to obtain sodium citrate aqueous solution; (2) Soak the graphite felt in sodium citrate aqueous solution for 2 hours;

[0059] (3) The obtained graphite felt loaded with sodium citrate was dried at 60℃ for 6 hours. The dried sample was then calcined at 800℃ under nitrogen for 1 hour at a heating rate of 5℃ / min. -1 After 3

[0060] mol L -1 Hydrochloric acid washing treatment yielded a carbon nanomaterial-supported composite electrode with a catalyst loading of 1.5 mg / cm³. -2 .

[0061] The performance testing process was the same as in Example 1. As can be seen from Table 1, the prepared electrode performed well at 200 mA / cm². -2 The energy efficiency reached 74.83%.

[0062] Comparative Example 2

[0063] (1) Add 3g of sodium citrate to 100ml of ultrapure water and stir to obtain sodium citrate aqueous solution; (2) Soak the graphite felt in sodium citrate aqueous solution for 2 hours;

[0064] (3) The obtained graphite felt loaded with sodium citrate was dried at 60℃ for 6 hours. The dried sample was then calcined at 800℃ under nitrogen for 1 hour at a heating rate of 5℃ / min. -1 After 3

[0065] mol L -1 Hydrochloric acid pickling treatment;

[0066] (4) Place the obtained sample into a 0.01 mol / mL solution. -1 Add the Bi salt to 100 ml of ethanol solution and let stand for 12 h;

[0067] (5) The sample was dried at 60℃ for 6 hours and then calcined again at 800℃ under nitrogen atmosphere for 1 hour to obtain a graphite felt electrode supported on a Bi single-atom catalyst with a catalyst loading of 2 mg / cm³. -2 .

[0068] The performance testing process was the same as in Example 1. As can be seen from Table 1, the prepared electrode performed well at 200 mA / cm². -2 The energy efficiency reaches 76.73%.

[0069] Comparative Example 3

[0070] (1) Clean and dry the graphite felt electrode; the specific cleaning procedure is as follows: 12cm 2 The sheet graphite felt (electrode thickness of 2 mm) was rinsed three times with deionized water, then cleaned three times with anhydrous ethanol, and then ultrasonically cleaned for 40 min in an ethanol-water solution with a volume ratio of 1:1.

[0071] (2) The specific operation of the drying process is as follows: the cleaned graphite felt is placed in a vacuum drying oven and dried at 80°C for 4 hours; the dried graphite felt electrode is obtained.

[0072] (3) Using dried graphite felt electrodes as the negative electrode, the assembled vanadium redox flow battery consists of three parts: positive and negative electrode electrolyte storage tanks, a pump, and a single cell. Both the positive and negative electrode electrolytes are 0.8 MV. 3+ +

[0073] 0.8MV 4+ +3MH2SO4, the volume of electrolyte is 3.5 ml / cm³. -2 The graphite felt electrodes obtained in the single cell serve as the positive and negative electrodes, with a thickness of 2 mm and a surface area of ​​12 cm² on both sides. 2 ;

[0074] Nafion 212 membrane is used as an intermediate septum membrane, with a range of 80-280 mA / cm². -2Under constant current charging and discharging at a certain current density, the battery charging and discharging cutoff voltage is 1.55V, and the discharging cutoff voltage is 1.0V.

[0075] As can be seen from Table 1, the prepared electrode can only be turned up to 120 mA cm⁻¹. -2 .

[0076] Comparative Example 4

[0077] (1) Clean and dry the carbon felt electrode; the specific cleaning procedure is as follows: 12cm 2 The sheet-like carbon felt (electrode thickness of 2 mm) was rinsed three times with deionized water, then cleaned three times with anhydrous ethanol, and then ultrasonically cleaned for 40 min in an ethanol-water solution with a volume ratio of 1:1.

[0078] (2) The specific operation of the drying process is as follows: the cleaned carbon felt is placed in a vacuum drying oven and dried at 80°C for 4 hours; the dried carbon felt electrode is obtained.

[0079] (3) Using dried carbon felt electrodes as the negative electrode, the assembled vanadium redox flow battery consists of three parts: positive and negative electrode electrolyte storage tanks, a pump, and a single cell. Both the positive and negative electrode electrolytes are 0.8 MV. 3+ +

[0080] 0.8MV 4+ +3MH2SO4, the volume of electrolyte is 3.5 ml / cm³. -2 The graphite felt electrodes obtained in the single cell serve as the positive and negative electrodes, with a thickness of 2 mm and a surface area of ​​12 cm² on both sides. 2 ;

[0081] Nafion 212 membrane is used as an intermediate septum membrane, with a range of 80-280 mA / cm². -2 Under constant current charging and discharging at a certain current density, the battery charging and discharging cutoff voltage is 1.55V, and the discharging cutoff voltage is 1.0V.

[0082] As can be seen from Table 1, the prepared electrode has a performance of 200 mA / cm². -2 The energy efficiency reaches 77.50%.

[0083] Table 1 shows a current density of 200 mA / cm². -2 Battery performance comparison, where electrolyte utilization rate = (discharge capacity / theoretical capacity * 100%).

[0084]

[0085] Conclusions and Comments: In Example 1, the carbon nanomaterials formed from the sodium citrate precursor adsorbing a mixture of bismuth salt and phytic acid were sintered at 800°C for 1 hour under a nitrogen atmosphere. Bi atoms and phosphorus atoms formed a Bi-P4 coordination structure, which could be uniformly and stably dispersed on the carbon substrate, exhibiting high catalytic activity and high stability. In Examples 8 and 9, excessively long carbonization times led to a decrease in the phosphorus content of the carbon substrate, causing some Bi atoms to fail to anchor on the carbon substrate, thus reducing the number of catalytic active sites. Insufficiently short carbonization temperatures resulted in not all Bi nanoparticles being converted into atomic-level catalysts, further reducing the number of active sites. In Comparative Example 1, relying solely on carbon nanomaterials… The results showed that the addition of Bi salt alone could not provide sufficiently high electrocatalytic activity. In Comparative Example 2, the lack of P atoms provided by phytic acid prevented the formation of a single-atom catalyst, resulting in the formation of Bi nanoparticles and a decrease in electrochemical activity. In Comparative Example 3, the graphite felt electrode without a catalyst support exhibited low electrochemical activity and poor performance. In Comparative Example 4, the carbon felt electrode performed poorly at high current densities, failing to meet the requirements for practical commercial applications. Therefore, it was determined that the obtained single-atom bismuth composite electrode with a Bi-P4 coordination structure could significantly improve the electrochemical activity of vanadium active materials, increase the power density of the battery, and further promote the commercialization of all-vanadium redox flow batteries.

Claims

1. A method for preparing a Bi single-atom catalyst composite electrode for an all-vanadium redox flow battery, characterized in that: Includes the following steps: 1) Soak the carbon substrate in an aqueous solution of sodium citrate for 2–6 hours to obtain a carbon substrate supported by sodium citrate; 2) Dry the sodium citrate-supported carbon substrate obtained in step 1), take the dried sample and calcine it at high temperature, and then wash it with acid. 3) Immerse the obtained sample in 0.005-3 mol / ml water. -1 Bi salt and 1-6 mol / ml -1 In a phytic acid-ethanol mixture, let stand for 12-24 hours; 4) Take out the sample and dry it, then calcine it at high temperature again to obtain the Bi single-atom catalyst composite electrode.

2. The preparation method according to claim 1, characterized in that: Prepare the sodium citrate aqueous solution with a ratio of sodium citrate to water of 2-7 (g): 50-300 (mL).

3. The preparation method according to claim 1, characterized in that: The carbon substrate has a thickness of 1–5 mm and a surface area of ​​5–20 cm² on both sides. 2 .

4. The preparation method according to claim 1, characterized in that: The carbon substrate includes one or more of graphite felt, carbon felt, carbon cloth, and carbon paper.

5. The preparation method according to claim 1, characterized in that: The drying process described in step 2) is as follows: Dry at 60-80℃ for 3-6 hours. After drying, calcine the sample at a high temperature of 600-1000℃, preferably 700-800℃, for 0.5-3 hours. The calcination atmosphere should be one or more of nitrogen, argon, or other inert gases.

6. The preparation method according to claim 1, characterized in that: Step 3) The Bi salt is one or more of bismuth nitrate and bismuth chloride.

7. The preparation method according to claim 1, characterized in that: In step 4), the high-temperature calcination conditions are: calcination at 600-1000℃ for 0.5-3 hours in a calcination atmosphere; the calcination atmosphere is one or more of nitrogen and inert gases. In the Bi single-atom catalyst composite electrode, the loading of Bi atoms is 1-6 mg / cm³. -2 .

8. A Bi single-atom catalyst composite electrode prepared by any one of the preparation methods of claims 1-7.

9. An application of the electrode according to claim 8, characterized in that: The electrode can be used as the positive or negative electrode of a vanadium redox flow battery.

10. The application of the electrode according to claim 9, characterized in that: The electrodes used have a high current density of 80-280 mA / cm². -2 .

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