A graphite felt electrode loaded with nano-bismuth particles and a preparation method thereof

Abstract

The application relates to the field of preparation of liquid flow battery electrode materials, and discloses a graphite felt electrode loaded with nano bismuth particles and a preparation method thereof. The method comprises the following steps: pretreating a graphite felt electrode to obtain a hydrophilic graphite felt electrode; immersing the hydrophilic graphite felt electrode into a solution containing bismuth ions, taking out and drying to obtain a graphite felt loaded with reduced bismuth precursor crystals; and treating the graphite felt loaded with the reduced bismuth precursor crystals by using plasma to obtain the graphite felt electrode loaded with nano bismuth particles. By using the plasma reduction technology, the bismuth ions adsorbed on the surface of the graphite felt fibers are directly reduced into nano bismuth metal particles. The method can avoid high temperature and a complex process flow in the traditional method, realizes a simple and efficient preparation process, and is suitable for large-scale electrode modification.

Description

A graphite felt electrode loaded with bismuth nanoparticles and its preparation method Technical Field

[0001] This invention relates to the field of flow battery electrode material preparation, and more particularly to a graphite felt electrode loaded with nano-bismuth particles and its preparation method. Background Technology

[0002] Flow batteries, as a novel large-scale energy storage technology, possess unique advantages such as independently adjustable energy and power, high safety, and long cycle life. Among them, iron-chromium (Fe-Cr) flow batteries have become a highly promising energy storage technology due to their abundant active material resources, low cost, and environmental friendliness. However, the development of iron-chromium flow batteries is constrained by some key technological bottlenecks, mainly in the negative electrode chromium ion (Cr3+)... + / Cr3 + The slow kinetics of redox reactions and the tendency for hydrogen evolution side reactions to occur on traditional carbon-based electrode materials result in low battery efficiency and shortened cycle life, making it difficult to meet the requirements of large-scale applications.

[0003] In existing technologies, electrodes typically use untreated raw graphite felt or heat-treated graphite felt. However, due to their low specific surface area and electrocatalytic activity, they exhibit poor electrochemical catalytic performance for the chromium anode in batteries and are prone to strong hydrogen evolution side reactions during charging. Bismuth (Bi) metal, due to its unique electronic structure and catalytic properties, is effective for the electrochemical catalysis of Cr3+. + / Cr3 + The redox couple exhibits excellent catalytic activity. Bismuth's low hydrogen evolution overpotential (relatively high hydrogen evolution overpotential) allows it to effectively suppress hydrogen evolution side reactions during electrochemical reactions, improving the coulombic efficiency and energy efficiency of the battery. Furthermore, bismuth metal can reduce Cr3+. + / Cr3 + The redox overpotential of the redox couple accelerates the reaction kinetics. Therefore, loading bismuth metal particles onto the electrode material has become one of the main ways to improve the performance of iron-chromium flow batteries.

[0004] Traditional bismuth modification methods, such as in-situ electrodeposition and high-temperature reduction, are difficult to meet the needs of large-scale preparation and practical application. The main reasons are as follows: (1) Large particle size and uneven distribution. The bismuth particles prepared by these methods are usually large in size (about a few micrometers) and are unevenly distributed on the electrode surface, which makes them easy to aggregate, resulting in limited active sites and failing to fully exert the catalytic effect of bismuth. (2) Complex process and high energy consumption. The high-temperature reduction method needs to be carried out under high temperature conditions, which consumes a lot of energy and has a complicated process flow. (3) Easy to clog electrode channels. During the in-situ electrodeposition process, bismuth particles are prone to excessive deposition at the electrode inlet, which leads to channel blockage and affects the flow of electrolyte and the stability of battery performance, because bismuth catalysts cannot be loaded in the stack using the in-situ electrodeposition method.

[0005] Therefore, the existing technology still needs further improvement and enhancement. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a graphite felt electrode loaded with nano-bismuth particles and its preparation method. By using plasma reduction technology, bismuth ions adsorbed on the surface of graphite felt fibers are directly reduced to nano-sized bismuth metal particles. This method avoids the high temperatures and complex processes of traditional methods, achieving a simple and efficient preparation process, and is suitable for large-scale electrode modification.

[0007] The above-mentioned objective of the present invention is achieved through the following technical solution: a method for preparing a graphite felt electrode loaded with nano-bismuth particles, wherein the method includes the following steps:

[0008] Pretreatment of graphite felt electrodes yields hydrophilic graphite felt electrodes.

[0009] The hydrophilic graphite felt electrode was immersed in a solution containing bismuth ions, then removed and dried to obtain a graphite felt loaded with reduced bismuth precursor crystals.

[0010] The graphite felt loaded with reduced bismuth precursor crystals was treated with plasma to obtain a graphite felt electrode loaded with nano-bismuth particles.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0012] As a preferred technical solution, the method for preparing the graphite felt electrode loaded with nano-bismuth particles includes a pretreatment method, wherein the pretreatment is a heating pretreatment, wherein the heating temperature is 400-500℃ and the holding time is 4-5h.

[0013] As a preferred technical solution, in the method for preparing the graphite felt electrode loaded with nano-bismuth particles, the concentration of bismuth ions in the solution is 0.01–0.04 mol / L.

[0014] As a preferred technical solution, in the method for preparing the graphite felt electrode loaded with nano-bismuth particles, the drying conditions are baking at 80-100°C for 2-3 hours.

[0015] As a preferred technical solution, the method for preparing the graphite felt electrode loaded with nano-bismuth particles includes treating the graphite felt loaded with reduced bismuth precursor crystals using plasma, comprising:

[0016] The graphite felt loaded with reduced bismuth precursor crystals was placed in a plasma cleaning device, and the parameters of the plasma cleaning device were adjusted to reduce bismuth ions, thereby obtaining a graphite felt electrode material loaded with bismuth metal particles and bismuth oxychloride particles.

[0017] The graphite felt electrode material loaded with bismuth metal particles and bismuth oxychloride particles is cleaned and dried to obtain the graphite felt electrode loaded with nano-bismuth particles.

[0018] As a preferred technical solution, the method for preparing the graphite felt electrode loaded with nano-bismuth particles includes the following parameters: air flow rate of 40-60 ml / min, radio frequency power of 100-150 W, vacuum degree of 10-20 Pa, and cleaning time of 10-20 min.

[0019] As a preferred technical solution, in the method for preparing the graphite felt electrode loaded with bismuth nanoparticles, the particle size of the bismuth nanoparticles is 5-10 nm.

[0020] As a preferred technical solution, in the method for preparing the graphite felt electrode loaded with nano-bismuth particles, the solution is a hydrochloric acid solution containing bismuth ions, and the concentration of the hydrochloric acid solution is 1-3 mol / L.

[0021] Secondly, a graphite felt electrode loaded with bismuth nanoparticles is provided, wherein the graphite felt electrode loaded with bismuth nanoparticles is prepared by the preparation method described above.

[0022] Thirdly, an iron-chromium or vanadium redox flow battery, wherein the iron-chromium or vanadium redox flow battery comprises a graphite felt electrode loaded with nano-bismuth particles as described in the second aspect above.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant technical advantages:

[0024] 1) Nanoscale particles and uniform distribution: Bismuth particles prepared by plasma reduction technology are small in size (5-10 nm), uniformly distributed, and have high specific surface area and surface activity, significantly improving the electrode's performance against Cr3+. + / Cr3 + Catalytic performance of the redox couple.

[0025] 2) Simple process and low energy consumption: Plasma reduction technology is carried out at room temperature or low temperature, with low requirements for equipment and environment, low energy consumption, and fast reaction speed (completed in 10-20 minutes), which improves production efficiency.

[0026] 3) Avoid pore blockage: Compared with traditional electrodeposition methods, plasma reduction avoids particle agglomeration and pore blockage, maintains the pore structure and permeability of the electrode, and maintains good electrolyte flowability and electrode reactivity.

[0027] 4) Easy to scale up production: The process is simple, with few operating steps, mild conditions, no need for complex equipment and high-energy-consuming environment, easy to integrate into existing production lines, and can realize automated and continuous production, reducing production costs. Attached Figure Description

[0028] Figure 1: Scanning electron microscope (SEM) image of the graphite felt electrode material loaded with nano-bismuth particles prepared in Example 1, showing the microstructure of the electrode material surface and the distribution characteristics of the nanoparticles.

[0029] Figure 2: X-ray diffraction (XRD) pattern of the electrode material prepared in Example 1, showing the phase composition and crystal structure characteristics of the electrode material.

[0030] Figure 3: Transmission electron microscope (TEM) morphology images of the electrode material prepared in Example 1 and the corresponding lattice stripe images of the particles, where (a) and (b) are high-resolution TEM images of metallic bismuth nanoparticles and their lattice stripes, and (c) and (d) are the morphology and lattice structure of bismuth oxychloride particles.

[0031] Figure 4: Cyclic voltammetry (CV) curves of the electrode material prepared in Example 1 and the blank control group graphite felt electrode (GF is the original graphite felt, TGF is the graphite felt after thermal pretreatment), comparing the electrochemical performance of different electrode materials.

[0032] Figure 5: Electrode material prepared in Example 1 and graphite felt electrode (blank control group) at a current density of 200 mA / cm². 2 The charge-discharge curves below reflect the battery's polarization characteristics and capacity performance.

[0033] Figure 6: Charge-discharge curves of the electrode material prepared in Example 1 at different current densities (100-300 mA / cm2), demonstrating the rate performance and electrochemical stability of the battery.

[0034] Figure 7: Rate cycling efficiency of the electrode materials prepared in Examples 1, 2, and 3 and the blank control group graphite felt electrode, comparing the energy efficiency and coulombic efficiency of the electrode materials prepared under different process conditions.

[0035] Figure 8: Rate cycling efficiency of the electrode material prepared in Example 1 and the blank control group graphite felt electrode, further evaluating the electrochemical performance of the electrode material at different current densities.

[0036] Figure 9: Efficiency curves of the electrode material prepared in Example 1 and the TGF electrode after 200 cycles at a current density of 200 mA / cm2, reflecting the long-cycle stability of the battery.

[0037] Figure 10: Charge-discharge capacity curves of the electrode material prepared in Example 1 and the TGF electrode after 200 cycles at a current density of 200 mA / cm2, demonstrating the battery capacity retention capability. Detailed Implementation

[0038] This invention provides a graphite felt electrode loaded with bismuth nanoparticles and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0039] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. Simultaneously, the steps or actions in the method description can be rearranged or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various orders in the specification and drawings are merely for the clear description of a particular embodiment and do not imply a mandatory order, unless otherwise stated that a particular order must be followed. The component designations used herein, such as "first," "second," etc., are merely for distinguishing the described objects and do not have any sequential or technical meaning.

[0040] Example 1

[0041] (1) Heat pretreatment of graphite felt

[0042] Commercial graphite felt material was cut into 3cm × 3cm samples and placed in a muffle furnace for heat pretreatment. Specific conditions were: temperature increased to 500℃ in air atmosphere at a heating rate of 10℃ / min, and holding time of 5 hours. This heat treatment process aimed to remove organic impurities from the graphite felt surface, increase surface oxygen-containing functional groups (such as hydroxyl and carboxyl groups), and improve the hydrophilicity and adsorption capacity of the graphite felt for metal ions.

[0043] (2) Preparation and impregnation of bismuth ion solution

[0044] Weigh 0.126 g (approximately 0.4 mmol) of high-purity BiCl3 and dissolve it in 20 mL of 2 mol / L hydrochloric acid. Stir thoroughly until completely dissolved to form a homogeneous and transparent bismuth ion solution. Immerse the heat-pretreated graphite felt sample in this solution and allow it to stand at room temperature (approximately 25°C) for 8 hours to ensure that bismuth ions are fully adsorbed onto the surface of the graphite felt fibers. This process utilizes the hydrophilicity of the graphite felt surface and the complexation effect of oxygen-containing functional groups on metal ions.

[0045] (3) Drying treatment

[0046] After impregnation, the graphite felt sample is taken out, excess solution is gently shaken off the surface, and it is placed in a vacuum drying oven and dried at 80°C for 2 hours to remove adsorbed moisture and unreacted free bismuth ions, thus obtaining graphite felt loaded with bismuth ion precursor.

[0047] (4) Plasma reduction treatment

[0048] The dried graphite felt samples were placed in a plasma cleaner for plasma reduction treatment. Specific parameters were set as follows: air atmosphere, gas flow rate 40 mL / min, RF power 150 W, vacuum 10 Pa, and treatment time 10 minutes. In the plasma environment, high-energy active particles (such as electrons, ions, and free radicals) react with bismuth ions adsorbed on the surface of the graphite felt fibers, reducing them to metallic bismuth nanoparticles. Simultaneously, some bismuth ions may react with oxygen to form bismuth oxychloride (BiOCl) particles.

[0049] (5) Cleaning and final drying

[0050] After reduction treatment, the graphite felt sample was removed and gently washed three times with deionized water to remove unreacted residues and byproducts. Then, it was placed in a vacuum drying oven and dried at 80°C for 2 hours to obtain the final graphite felt electrode material loaded with nano-bismuth particles.

[0051] Characterization of the prepared graphite felt electrode material loaded with bismuth nanoparticles

[0052] (1) SEM analysis (Figure 1)

[0053] The surface morphology of the electrode material was observed using scanning electron microscopy (SEM). As shown in Figure 1, the graphite felt surface was uniformly loaded with sheet-like bismuth oxychloride (BiOCl) particles, with a particle size of approximately 50–100 nm. These sheet-like particles are beneficial for increasing the specific surface area and active sites of the electrode.

[0054] (2) XRD analysis (Figure 2)

[0055] The phase composition of the electrode material was analyzed using X-ray diffraction (XRD). As shown in Figure 2, characteristic diffraction peaks of metallic bismuth (Bi) and bismuth oxychloride (BiOCl) were observed, proving that bismuth ions were successfully converted into metallic bismuth and BiOCl during plasma reduction. The presence of these two substances helps to improve the electrochemical catalytic activity of the electrode.

[0056] (3) TEM analysis (Figure 3)

[0057] Transmission electron microscopy (TEM) was used to observe the electrode material at a higher resolution. As shown in Figures 3(a) and (b), metallic bismuth nanoparticles with a diameter of approximately 5 nm and their clear lattice fringes were observed, further confirming the successful preparation of nanoscale bismuth particles. Figures 3(c) and (d) show the morphology and lattice structure of the BiOCl particles. The presence of these nanoparticles provides more active sites for electrochemical reactions.

[0058] Electrochemical performance testing of the prepared graphite felt electrode material loaded with bismuth nanoparticles.

[0059] (1) Cyclic voltammetry (CV) test (Figure 4)

[0060] The electrochemical performance of the electrode materials was evaluated using a traditional three-electrode system. The working electrode was a graphite felt electrode loaded with nano-bismuth particles, while the control groups were the original graphite felt (GF) and the heat-pretreated graphite felt (TGF). The reference electrode was a saturated calomel electrode, and the auxiliary electrode was a platinum sheet. The electrolyte was a 3 mol / L hydrochloric acid solution, the active material concentration was 0.1 mol / L CrCl3, and the scan rate was 20 mV / s. As shown in Figure 4, compared with the control group, the electrode material loaded with nano-bismuth particles exhibited significantly enhanced electrochemical catalytic activity. The redox peak current increased, the peak potential difference (ΔE) decreased, and the redox peak current ratio was close to 1, indicating that the electrode has good reversibility and rapid charge transfer capability for the Cr3+ / Cr2+ redox couple. Due to its hydrophobic surface, GF could not effectively adsorb chromium ions, and almost no obvious redox peaks were observed; although TGF showed improved hydrophilicity, it lacked catalytically active components, resulting in only a weak oxidation peak.

[0061] (2) Constant current charge and discharge test (Figures 5 and 6)

[0062] In the flow cell device, the Neware battery testing system was used to perform constant current charge-discharge tests on the battery. The negative electrode was a graphite felt loaded with nano-bismuth particles, the positive electrode was a heat-pretreated graphite felt (TGF), the separator was Nafion 212, and the effective area of ​​the whole cell was 2 cm × 2 cm. The electrolytes were: negative electrode: 1 mol / L CrCl3, 3 mol / L HCl; positive electrode: 1 mol / L FeCl2, 3 mol / L HCl. The electrolyte volume was 25 mL, and the flow rate was 30 mL / min. The test voltage range was 0.7 V to 1.3 V. As shown in Figure 5, at a current density of 200 mA / cm², the battery with the nano-bismuth particle-loaded electrode exhibited a lower polarization voltage and a higher discharge capacity, showing a significant performance improvement compared to the blank control group. Figure 6 shows the charge-discharge curves at different current densities (100–300 mA / cm²). With the increase of current density, the discharge capacity of the battery decreased, but it still maintained good rate performance.

[0063] Battery performance analysis

[0064] (1) Rate cycling efficiency (Figures 7 and 8)

[0065] The electrode materials prepared in Examples 1, 2, and 3 were subjected to rate cycling tests to measure the coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) of the batteries. As shown in Figures 7 and 8, the electrode materials loaded with bismuth nanoparticles maintained high efficiency even at high current densities. Specifically, the average CE was greater than 95%, and the current density could be increased to 250 mA / cm² when the EE reached 80%, demonstrating excellent rate performance.

[0066] (2) Long-term cycling stability (Figures 9 and 10)

[0067] The battery was subjected to 200 charge-discharge cycles at a current density of 200 mA / cm². As shown in Figure 9, the battery's charge-discharge (CE) and discharge-exchange (EE) remained stable throughout the cycle, with EE maintaining between 76% and 80%. Figure 10 shows the change in charge-discharge capacity, demonstrating high capacity retention and a capacity decay rate of only 0.3% per cycle, proving the excellent cycle stability and durability of the electrode material.

[0068] Results Analysis: Based on the above tests and characterization, the following conclusions can be drawn: the introduction of nano-bismuth particles significantly improves the electrochemical catalytic activity of the electrode. This is attributed to the high specific surface area and abundant active sites of the nanoparticles, which accelerate the electrochemical catalytic activity of Cr3+. + / Cr3 +The redox reaction kinetics of the redox couple were studied. The electrode material exhibited excellent rate performance and cycle stability. Even at high current densities, the battery maintained high energy efficiency, meeting the demands of rapid charge-discharge in practical applications. The electrode material prepared by plasma reduction has the advantages of simple processing and low cost. This method avoids high temperatures and complex processes, making it easy to scale up production.

[0069] Example 2

[0070] Based on Example 1, the plasma reduction treatment time was changed to 20 minutes, while the remaining steps and conditions remained unchanged.

[0071] Performance testing and results analysis

[0072] As shown in Figure 7, the voltage efficiency of the battery decreased slightly (by less than 2%) with increasing reduction time, but the overall performance remained excellent. This is likely due to the aggregation of some bismuth nanoparticles caused by excessively long reduction time, resulting in a reduction of active sites. Therefore, proper control of the reduction time is crucial for obtaining optimal electrode performance.

[0073] Example 3

[0074] Based on Example 1, the amount of BiCl3 was reduced by half, i.e., 0.063g of BiCl3 was weighed out. 3， Reduce the concentration of bismuth ions, while keeping the rest of the steps and conditions unchanged.

[0075] Performance testing and results analysis

[0076] As shown in Figure 7, reducing the bismuth ion concentration slightly decreases the battery's voltage efficiency (by approximately 3%), but it still maintains a high performance level. This indicates that although the bismuth loading has some impact on electrode performance, the electrode material can still meet the requirements for high-efficiency energy conversion over a wide concentration range.

[0077] In summary, this invention provides a graphite felt electrode loaded with nano-bismuth particles and its preparation method. Through plasma reduction technology, bismuth ions adsorbed on the surface of graphite felt fibers are directly reduced to nano-sized bismuth metal particles. During plasma reduction, high-energy active particles (such as electrons, ions, and free radicals) undergo a rapid and efficient reduction reaction with the bismuth ions adsorbed on the graphite felt fiber surface. Due to the high density, high energy, and low temperature characteristics of plasma, bismuth ions can be reduced to metallic bismuth atoms in a very short time. These atoms rapidly nucleate on the graphite felt surface, and, limited by surface diffusion and growth mechanisms, form nano-sized bismuth particles with a particle size of 5–10 nanometers. The formation process of nanoparticles is controlled by the kinetics of plasma reduction, avoiding excessive particle growth and agglomeration. Compared with micron-sized bismuth particles prepared by traditional high-temperature reduction methods, nano-sized bismuth particles have a larger specific surface area and higher surface activity, providing more electrochemical reaction active sites and significantly improving the electrode's performance against Cr3+. + / Cr3 + The catalytic performance of the redox couple. Furthermore, the uniform distribution of nanoparticles ensures the uniformity of catalytic activity on the electrode surface, which is beneficial for improving the overall performance of the battery.

[0078] Plasma reduction technology can be implemented at room temperature or low temperature, with lower requirements for equipment and environmental conditions. Compared to high-temperature reduction methods that require temperatures of several hundred degrees or even higher, plasma reduction avoids the challenges posed by high-temperature environments to equipment materials and energy consumption, significantly reducing energy consumption. Furthermore, the plasma reduction process has a fast reaction rate, typically completing reduction in just 10–20 minutes, greatly improving production efficiency. The entire process is simple to operate; precise control can be achieved by adjusting the parameters of the plasma cleaner (such as gas flow rate, RF power, vacuum level, and processing time). Reduction conditions are easy to optimize and repeat, resulting in strong process controllability.

[0079] Compared to traditional in-situ electrodeposition methods, which require the direct addition of bismuth ions to the electrolyte, where bismuth ions are electrochemically reduced to metallic bismuth on the electrode surface, plasma reduction methods address this issue. Bismuth ions tend to over-deposit at the electrode inlet due to electrolyte fluidity, forming large particles that clog the electrode's pore structure, affecting electrolyte flow and mass transfer, and ultimately degrading battery performance. In contrast, plasma reduction first adsorbs bismuth ions onto the surface of graphite felt fibers and then reduces them to nanoscale bismuth particles in a plasma environment. Because the reduction reaction occurs on a solid surface, it avoids the particle agglomeration and pore blockage problems caused by direct deposition in the electrolyte. The uniform distribution and suitable size of the nanoscale bismuth particles ensure that the pore structure and permeability of the graphite felt electrode remain unaffected, maintaining good electrolyte fluidity and electrode reactivity.

[0080] Furthermore, the plasma reduction process is simple, involving mainly pretreatment, impregnation, drying, plasma reduction, and cleaning and drying. It involves few steps, mild process conditions, and requires no complex equipment or high-energy-consuming environment. Plasma equipment is small, highly operable, and easily integrated into existing production lines. In addition, the plasma reduction process is easily automated and can be scaled up continuously; production scale can be adjusted by controlling equipment parameters to meet the needs of industrial production. Compared to high-temperature reduction methods, plasma reduction reduces production costs.

[0081] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a graphite felt electrode loaded with nano-bismuth particles, characterized in that, The method includes the following steps: pretreating the graphite felt electrode to obtain a hydrophilic graphite felt electrode; immersing the hydrophilic graphite felt electrode in a solution containing bismuth ions, removing it and drying it to obtain a graphite felt loaded with reduced bismuth precursor crystals; and treating the graphite felt loaded with reduced bismuth precursor crystals using plasma to obtain a graphite felt electrode loaded with nano-bismuth particles. The graphite felt loaded with reduced bismuth precursor crystals is treated with plasma, comprising: placing the graphite felt loaded with reduced bismuth precursor crystals in a plasma cleaning device, adjusting the parameters of the plasma cleaning device to reduce bismuth ions, and obtaining a graphite felt electrode material loaded with bismuth metal particles and bismuth oxychloride particles; cleaning and drying the graphite felt electrode material loaded with bismuth metal particles and bismuth oxychloride particles to obtain a graphite felt electrode loaded with nano-bismuth particles; the parameters include: air flow rate of 40~60ml / min, radio frequency power of 100~150W, vacuum degree of 10~20pa, cleaning time of 10~20min; the particle size of the nano-bismuth particles is 5~10nm; the solution is a hydrochloric acid solution containing bismuth ions, and the concentration of the hydrochloric acid solution is 1-3mol / L.

2. The method for preparing a graphite felt electrode loaded with nano-bismuth particles according to claim 1, characterized in that, The pretreatment is a heating pretreatment, wherein the heating temperature is 400~500℃ and the holding time is 4~5h.

3. The method for preparing a graphite felt electrode loaded with nano-bismuth particles according to claim 1, characterized in that, The concentration of bismuth ions in the solution is 0.01~0.04 mol / L.

4. The method for preparing a graphite felt electrode loaded with nano-bismuth particles according to claim 1, characterized in that, The drying conditions are baking at 80~100℃ for 2~3 hours.

5. A graphite felt electrode loaded with nano-bismuth particles, characterized in that, The graphite felt electrode loaded with bismuth nanoparticles is prepared using any one of the preparation methods described in claims 1-4.

6. A type of iron-chromium or vanadium redox flow battery, characterized in that, The iron-chromium or vanadium redox flow battery comprises the graphite felt electrode loaded with nano-bismuth particles as described in claim 5.

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