Single-atom catalyst composite electrode for all-vanadium redox flow battery and preparation and application thereof

Abstract

The application relates to a preparation and application of a single-atom catalyst composite electrode for a vanadium redox flow battery, and belongs to the field of energy storage technology batteries. The composite electrode preparation method is as follows: graphite felt is used as a substrate to in-situ carry ZIF-8, then carbonization treatment is carried out, and a liquid phase immersion process is used to adsorb Bi 3+ on the basis of the micropore structure of ZIF-8, high-temperature calcination is carried out again in the later period to anchor Bi atoms by using nitrogen atoms to form Bi-N bonds, and the Bi single atoms are uniformly and stably dispersed on the carbon substrate sintered by ZIF-8, so that the single-atom catalyst composite electrode with high catalytic activity and high stability is prepared. The catalyst preparation method provided by the application is simple and easy to control, has high energy efficiency, electrocatalytic activity and cycle stability, and is expected to realize large-scale commercial production.

Description

Technical Field

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

[0002] Among numerous energy storage technologies, vanadium redox flow batteries (VRBs) are increasingly being used 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 higher energy densities 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 sufficient 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, but anchoring oxygen over a wide voltage window remains a problem; surface structure modulation, which increases the specific surface area of ​​the electrode through etching methods such as KOH and NiO, but this can damage the mechanical properties of the electrode; direct loading of metal catalysts, which significantly increases the cost for noble metals such as Pt and Pd, and reduces the conductivity of the electrode for metal oxides such as WO3 and Mn3O4; and loading carbon-based catalysts with large specific surface areas such as carbon nanotubes and mesoporous carbon, which can reduce activation polarization to a certain extent, but the pore structure is relatively fragile and cannot meet the requirements for long-term stable operation of the battery. Therefore, how to prepare highly active and highly stable catalysts has become an urgent problem to be solved.

[0005] To address the above issues, a single-atom bismuth catalyst with high catalytic activity and high stability was prepared. Bi was adsorbed through its microporous structure via a liquid-phase impregnation process. 3+ In the subsequent high-temperature calcination and carbonization process, nitrogen atoms from the precursor are used to anchor Bi atoms to form Bi-N bonds, allowing Bi atoms to be stably dispersed on the ZIF-8 sintered carbon substrate, thereby preparing a 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 energy efficiency, electrocatalytic activity, and cycle stability, and is expected to achieve large-scale commercial production. Summary of the Invention

[0006] This invention addresses the aforementioned problems by using graphite felt as a substrate to in-situ support ZIF-8, followed by carbonization treatment, and utilizing its microporous structure to adsorb Bi through a liquid-phase impregnation process. 2+ In the subsequent high-temperature calcination and carbonization process, nitrogen atoms in the precursor are used to anchor Bi atoms to form Bi-N bonds, allowing Bi to be uniformly and stably dispersed on the ZIF-8 sintered carbon substrate, thereby preparing a single-atom catalyst with high catalytic activity and high stability. The electrocatalyst preparation method provided by this invention is simple and easy to control, and has high energy efficiency, electrocatalytic activity, and cycle stability.

[0007] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0008] 1) Add 2-7g of zinc nitrate hexahydrate solution A to 50-200ml of methanol and stir;

[0009] Add 4-15g of 2-methylimidazole to 50-200ml of methanol and stir.

[0010] 2) Graphite felt (2mm thick, with a surface area of ​​12cm² on both sides) 2 Soak in solution A for 1-2 hours. Pour solution B into solution A and stir slowly for 24-36 hours.

[0011] 3) The obtained ZIF8-supported graphite felt was washed with methanol, dried, and the dried sample was calcined at high temperature.

[0012] 4) Place the obtained sample into a 0.1-3 mg / ml container. -1 In a bismuth salt solution, let stand for 12-24 hours;

[0013] 5) Take out the sample and dry it, then calcine it again at high temperature to obtain a single-atom catalyst composite electrode;

[0014] The electrode described in step 2) can be graphite felt, carbon cloth, carbon paper, etc.

[0015] Step 3) Drying after washing: Dry at 60-80℃ for 3-6 hours, then calcine the sample at 900-1100℃ for 1 hour, with a heating rate of 5℃ / min. -1 ;

[0016] Step 4) The bismuth salt is one or more of bismuth nitrate and bismuth chloride;

[0017] Step 5) High-temperature calcination: calcination at 700-1000℃ for 1 hour in a nitrogen atmosphere, with a heating rate of 5℃ / min. -1 The loading of the obtained single-atom catalyst composite electrode catalyst was 1-5 mg cm⁻¹.-2 .

[0018] This invention utilizes graphite felt as a substrate to in-situ support ZIF-8, followed by carbonization treatment, and then adsorbs Bi through its microporous structure via a liquid-phase impregnation process. 3+ The catalyst is then subjected to high-temperature calcination again to utilize the nitrogen atoms to anchor Bi atoms and form Bi-N bonds, thereby uniformly and stably dispersing Bi single atoms on the ZIF-8 sintered carbon substrate. This process produces a 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.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) Using ZIF8 sintered carbon with a surface rich in microporous structure as a precursor, Bi can be effectively adsorbed through a liquid phase impregnation process. 3+

[0021] (2) Since the carbon sintered by ZIF-8 has a large number of nitrogen atoms, it can anchor Bi atoms to form Bi-N bonds, so that Bi is uniformly and stably dispersed on the carbon substrate sintered by ZIF-8, thereby preparing a single-atom catalyst with high catalytic activity and high stability.

[0022] (3) This catalyst structure not only has a high specific surface area, but the formed Bi-N bonds can also efficiently and stably catalyze the redox reaction of vanadium, significantly reducing electrode polarization and ensuring the reliability of the catalyst at 200 mA cm⁻¹. -2 During 1500 cycles, the energy efficiency shows almost no decay, which can meet the needs of practical applications;

[0023] (4) The preparation method is simple, the production equipment is conventional, and it is suitable for large-scale production. Attached Figure Description

[0024] Figure 1 SEM image of a single-atom catalyst composite electrode;

[0025] Figure 2 HAADF-STEM image of a catalyst that has been sintered on carbon adsorbed with bismuth salt and then sintered at 800℃. Detailed Implementation

[0026] The present invention will be described in detail below through embodiments, but the present invention is not limited to the embodiments.

[0027] The fabricated electrodes were used as the positive and negative electrodes in a vanadium redox flow battery. Electrochemical tests were then conducted using the assembled battery.

[0028] Example 1

[0029] (1) Add 3.5g of zinc nitrate hexahydrate to 150ml of methanol and stir; add 7g of 2-methylimidazole to 150ml of methanol and stir.

[0030] (2) Graphite felt (2mm thick, with a surface area of ​​12cm² on both sides) 2 Soak in solution A for 2 hours, then pour solution B into solution A and stir slowly for 24 hours.

[0031] (3) The obtained ZIF8-loaded graphite felt was rinsed three times with methanol, then dried at 60℃ for 6 hours. The dried sample was then calcined at 1100℃ with argon gas for 1 hour, with a heating rate of 5℃ / min to reach the calcination temperature. -1 (4) Place the obtained sample into 25 ml of 0.5 mg / ml solution. -1 (5) The sample was dried at 60°C for 6 hours and then calcined at 800°C under nitrogen atmosphere for 1 hour until the calcination temperature reached a heating rate of 5°C / min. -1 A graphite felt electrode supported on a bismuth single-atom catalyst was obtained, with a catalyst loading of 3 mg / cm³. -2 The preparation method provided by this invention is simple and easy to control, the electrode structure is controllable, and it has excellent electrochemical activity and cycle stability.

[0032] 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 The catalyst-supported graphite felt electrodes obtained in a single cell were used as the positive and negative electrodes. The electrode thickness was 2 mm, and the surface area of ​​the two 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.

[0033] from Figure 1 and Figure 2 As can be seen, a single-atom catalyst is supported on the graphite felt, and the size of the bismuth single atom is... It is uniformly dispersed on the carbon substrate formed by ZIF8.

[0034] As can be seen from Table 1, the prepared electrode has a performance of 200 mA / cm². -2 The energy efficiency reaches 83.05%. There is no energy efficiency degradation after 1500 battery cycles.

[0035] Example 2

[0036] The preparation method, process and performance testing process are the same as in Example 1, except that step (5) is calcined again at 700°C in a nitrogen atmosphere for 1 hour.

[0037] Example 3

[0038] The preparation method, process and performance testing process are the same as in Example 1, except that step (5) is calcined again at 850°C in a nitrogen atmosphere for 1 hour.

[0039] Example 4

[0040] The preparation method, process, and performance testing process are the same as in Example 1, except that in step (1), the amount of zinc nitrate hexahydrate added is 2g, the amount of 2-methylimidazole added is 4g, and the loading of the prepared composite electrode catalyst is 1mg / cm³. -2 ;

[0041] Example 5

[0042] The preparation method, process, and performance testing process are the same as in Example 1, except that in step (1), the amount of zinc nitrate hexahydrate added is 7g, the amount of 2-methylimidazole added is 15g, and the loading of the prepared composite electrode catalyst is 5mg / cm³. -2

[0043] Comparative Example 1

[0044] The preparation method, process and performance testing process are the same as in Example 1, except that step (5) is calcined again at 900°C in a nitrogen atmosphere for 1 hour.

[0045] Comparative Example 2

[0046] 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 1 hour.

[0047] Comparative Example 3

[0048] The preparation method, process, and performance testing process are the same as in Example 1, except that in step (1), the amount of zinc nitrate hexahydrate added is 1g, the amount of 2-methylimidazole added is 2g, and the loading of the prepared composite electrode catalyst is 0.5mg / cm³. -2

[0049] Comparative Example 4

[0050] The preparation method, process, and performance testing process are the same as in Example 1, except that in step (1), the amount of zinc nitrate hexahydrate added is 8g, the amount of 2-methylimidazole added is 16g, and the loading of the prepared composite electrode catalyst is 6mg / cm³. -2

[0051] Comparative Example 5

[0052] (1) 1. Add 3.5g of zinc nitrate hexahydrate to 150ml of methanol and stir; 2. Add 7g of 2-methylimidazole to 150ml of methanol and stir.

[0053] (2) Soak the graphite felt in solution A for 2 hours, pour solution B into solution A, and stir slowly for 24 hours;

[0054] (3) The obtained ZIF8-loaded graphite felt was rinsed with methanol three times or more, then dried at 60℃ for 6 hours. The dried sample was then calcined at 1100℃ with argon gas for 1 hour, with a heating rate of 5℃ / min to reach the calcination temperature. -1 ;

[0055] (4) Place the obtained sample into a 0.5 mg / ml container. -1 The sample was placed in a bismuth chloride solution and allowed to stand for 12 hours; then it was removed and dried at 60°C for 6 hours. This yielded a graphite felt electrode supported on bismuth nanoparticles (5-10 nm in size).

[0056] 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 78.66%.

[0057] Comparative Example 6

[0058] (1) 1. Add 3.5g of zinc nitrate hexahydrate to 150ml of methanol and stir; 2. Add 7g of 2-methylimidazole to 150ml of methanol and stir.

[0059] (2) Soak the graphite felt in solution A for 2 hours, pour solution B into solution A, and stir slowly for 24 hours;

[0060] (3) The obtained graphite felt loaded with ZIF8 was washed with methanol three times or more, then dried at 60℃ for 6 hours. The dried sample was then calcined at 1100℃ with argon gas for 1 hour at a heating rate of 5℃ / min. -1 A composite electrode supported on carbon material derived from ZIF-8 was obtained.

[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 7

[0063] (1) Clean and dry the sheet graphite felt electrode; the specific cleaning procedure is as follows: place a 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.

[0064] (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.

[0065] (3) Using dried graphite felt electrodes as the positive and negative electrodes, the assembled vanadium redox flow battery consists of three parts: positive and negative electrode electrolyte storage tanks, a pump, and a single cell. The positive and negative electrode electrolytes are both 0.8 MV. 3+ +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 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.

[0066] As can be seen from Table 1, the prepared electrode can only be turned up to 120 mA cm⁻¹. -2 .

[0067] Comparative Example 8

[0068] (1) Clean and dry the sheet carbon felt electrode; the specific cleaning procedure is as follows: place a 12cm sheet carbon felt electrode into a dry place. 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.

[0069] (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.

[0070] (3) Using dried carbon felt electrodes as the positive and negative electrodes, the assembled vanadium redox flow battery consists of three parts: positive and negative electrode electrolyte storage tanks, a pump, and a single cell. The positive and negative electrode electrolytes are both 0.8 MV. 3+ +0.8MV 4+ +3MH2SO4, the volume of electrolyte is 3.5 ml / cm³. -2The 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 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.

[0071] As can be seen from Table 1, the prepared electrode has a performance of 200 mA / cm². -2 The energy efficiency reaches 77.50%.

[0072] Table 1 shows a current density of 200 mA / cm². -2 Battery performance comparison, where electrolyte utilization rate = (discharge capacity / theoretical capacity * 100%).

[0073]

[0074] Conclusions and comments: In Example 1, the carbon sintered from ZIF8 with adsorbed bismuth salt was sintered at 800°C for 1 hour under a nitrogen atmosphere. Bismuth atoms formed Bi-N bonds with nitrogen atoms, which could be uniformly and stably dispersed on the carbon substrate, exhibiting high catalytic activity and stability. In Comparative Examples 1 and 2, excessively high carbonization temperatures caused a decrease in the N content of the carbon substrate, resulting in some Bi atoms not being anchored on the carbon substrate, thus reducing the number of catalytic active sites. In Comparative Examples 3 and 4, insufficient catalyst loading could not provide enough active sites, while excessive loading would affect the flow of the electrolyte, causing increased concentration polarization. In Comparative Example 5, compared to bismuth monophosphate, the sintered carbon substrate exhibited high catalytic activity and stability. Bismuth nanoparticles, as atomic catalysts, cannot provide enough reactive sites, which increases battery polarization losses. In Comparative Example 6, the carbon-based catalyst alone also cannot provide enough reactive sites, resulting in a decrease in battery performance. In Comparative Example 7, the graphite felt electrode without catalyst support has low electrochemical activity and poor performance. In Comparative Example 8, the carbon felt electrode has poor performance at high current densities and cannot meet the requirements for practical commercial applications. Therefore, it is determined that the bismuth single-atom catalyst composite electrode can significantly improve the electrochemical activity of vanadium active materials, improve the power density of the battery, and further promote the commercialization of all-vanadium redox flow batteries.

Claims

1. A method for preparing a single-atom catalyst composite electrode for a vanadium redox flow battery, characterized in that: 1) A solution: 2-7 g of zinc nitrate hexahydrate is added to 50-200 ml of methanol and mixed uniformly; B solution: 4-15 g of 2-methylimidazole is added to 50-200 ml of methanol and mixed uniformly; 2) The carbon substrate is soaked in the A solution for 1-2 h, and then the B solution is poured into the A solution and stirred for 12-36 h; 3) The obtained ZIF8 supported carbon substrate is washed with ethanol, dried, and the dried sample is subjected to high-temperature calcination; 4) A bismuth salt is added to the sample, and the mixture is stirred for 1-2 h; 5) The sample is taken out and dried, and high-temperature calcination is performed again to obtain a single-atom catalyst composite electrode; and 6) The high-temperature calcination is performed at 700-850 °C for 0.5-3 h in a nitrogen atmosphere. Step 2) The carbon substrate is one or more of graphite felt, carbon felt, carbon cloth, and carbon paper. Step 3) After washing and drying, the sample is dried at 60-80 °C for 3-6 h, and then subjected to high-temperature calcination at 900-1100 °C for 0.5-3 h in one or more of a nitrogen atmosphere and an inert gas atmosphere. Step 4) The bismuth salt is one or more of bismuth nitrate and bismuth chloride. 4) Immersing the resulting sample in a solution of 0.1-3 mg ml -1 of bismuth salt for 12-24 h; 7. A single-atom catalyst composite electrode obtained by the method of any one of claims 1-6. The electrode serves as a positive electrode and / or a negative electrode of a vanadium redox flow battery.

2. The method of claim 1, wherein: ​ 3. The production method according to claim 1 or 2, characterized by: Step 2) the carbon substrate has a thickness of 1-5 mm and a surface area of 5-20 cm 2 .

4. The method of claim 1, wherein: ​ 5. The method of claim 1, wherein: ​ 6. The method of claim 1, wherein: Step 5) the high temperature calcination: one or more than two of nitrogen gas, inert gas, and the obtained single-atom catalyst composite electrode catalyst has a loading of 1-5 mg cm -2 . ​ 8. Use of the electrode according to claim 7, characterized in that: ​ 9. Use according to claim 8, characterized in that: The high current density applied to the electrode is 80-280 mAcm -2 .

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