Flowing electrode material with hierarchical structure and preparation method and application thereof

Abstract

The application discloses a flow electrode material with a hierarchical structure and a preparation method and application thereof, and belongs to the technical field of flow electrode capacitive deionization. The material comprises an electrolyte solution, a carbon material and zero-valent Fe loaded on the surface of the carbon material; the carbon material comprises a rod-like carbon material main body and nanosheet graphite generated in situ on the surface of the rod-like carbon material main body. The special hierarchical structure of the electrode material and trace zero-valent Fe can form a continuous conductive network in the flow electrode in cooperation with the electrolyte solution, effectively improving the specific capacitance and conductivity of the electrode material, and when the electrode material is applied to seawater desalination or wastewater treatment, the desalination efficiency of FCDI can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of flow electrode capacitor deionization technology, specifically relating to a flow electrode material with a hierarchical structure, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization, the discharge of high-salt inorganic wastewater, such as electroplating wastewater and metallurgical wastewater, has become increasingly serious. This wastewater contains a large amount of sodium. + Cl - SO4 2- Soluble salt ions, if directly discharged, can lead to water pollution and pose a serious threat to the ecological environment and water resource utilization.

[0003] Capacitive deionization (CDI) technology is widely used in low-salinity water treatment due to its low energy consumption and ease of operation. However, because the adsorption capacity of fixed electrodes is limited, it can only treat wastewater in an intermittent mode, thus presenting a significant bottleneck in the treatment of high-salinity water. Flow electrode capacitive deionization (FCDI), on the other hand, is an electrochemical desalination technology that replaces traditional fixed electrodes with flowable electrodes. It can achieve continuous water desalination, concentration and recovery, and electrode regeneration. Theoretically, it has unlimited adsorption capacity and high ion removal efficiency, making it more suitable for seawater desalination and high-salinity wastewater treatment.

[0004] Currently, flow electrodes are typically composed of activated carbon and electrolyte solution, while the desalination rate of FCDI technology is affected by properties such as the conductivity and capacitance of activated carbon.

[0005] Chinese patent application CN105293487A discloses an electrode material for capacitive deionization technology prepared by modifying activated carbon through ultrasonication, ozone oxidation, and freeze-drying after mixing it with water. This electrode material exhibits excellent hydrophilicity and capacitance, effectively improving desalination capacity and efficiency. However, the conductivity of the activated carbon remains unimproved, requiring a higher activated carbon loading to enhance conductivity. In contrast, Chinese patent application CN110372067A directly utilizes carbon black as an electroadsorption material. Since carbon black has a multilayered graphite structure, mostly amorphous with few or no pores, it avoids the migration of salt ions into and out of the double layer within the electrode pores, thus increasing the desalination rate. However, carbon black typically suffers from relatively low specific capacitance, and its nanoscale structure introduces higher surface energy, increasing the risk of aggregation and clogging in aqueous flow electrodes.

[0006] Therefore, developing a type of activated carbon with strong conductivity and high specific capacitance to improve interparticle contact and connectivity, enhance electron transport efficiency and desalination performance is a key requirement for current FCDI technology. Summary of the Invention

[0007] To address the problems of low specific capacitance, poor conductivity, and difficulty in adapting to high salt concentrations in existing flow electrodes, the first objective of this invention is to provide a flow electrode material with a hierarchical structure. The special hierarchical structure of this electrode material and the trace amounts of zero-valent Fe can work synergistically with the electrolyte solution to form a continuous conductive network in the flow electrode, effectively improving the specific capacitance and conductivity of the electrode material.

[0008] The second objective of this invention is to provide a method for preparing a flow electrode material with a hierarchical structure. This invention obtains an electrode material with a special microstructure by introducing a step of synergistic heat treatment and calcination with iron and alkali reagents. The process is simple and the material is readily available.

[0009] The third objective of this invention is to provide an application of a flow electrode material with a hierarchical structure, which, when used as an electrode material in seawater desalination or wastewater treatment, can significantly improve the desalination efficiency of FCDI.

[0010] To achieve the above-mentioned technical objectives, the present invention provides a flow electrode material with a hierarchical structure, the material comprising an electrolyte solution, a carbon material and zero-valent Fe loaded on its surface; the carbon material comprises a rod-shaped carbon material body and nanosheet graphite generated in situ on its surface.

[0011] The key to the significantly improved specific capacitance and conductivity of the flow electrode material of this invention lies in the synergistic effect of its unique hierarchical structure and the introduction of trace amounts of zero-valent Fe. Specifically, in this hierarchical structure, the high aspect ratio rod-shaped carbon material can reduce the electropercolation threshold to an extremely low level within the flow electrode slurry through a "line contact" bridging effect, forming a connected electronically conductive framework even with low solid content, fundamentally alleviating the problem of insufficient conductivity of FCDI. Meanwhile, the nanosheet graphite generated in situ on its surface significantly expands the active surface area, forming numerous open interlayer channels and high-roughness surface features, significantly shortening the ion diffusion path, thereby enhancing the rapid response of the electric layer capacitance and improving the utilization rate of active sites. On this basis, trace amounts of zero-valent Fe nanoparticles are uniformly anchored on this hierarchical carbon material, further reducing the electron transport resistance within the material and improving the overall conductivity through their high intrinsic conductivity; at the same time, zero-valent Fe can contribute additional pseudocapacitance during charge and discharge, directly increasing the specific capacitance of the material. More importantly, the high-speed electron transport network and fast ion transport channels provided by the graded carbon material enable the zero-valent Fe dispersed on it to be fully and efficiently utilized, maximizing the pseudocapacitance and conductivity enhancement effects without failing due to agglomeration or poor contact, ultimately achieving a significant synergistic improvement in the specific capacitance and conductivity of the flow electrode material.

[0012] As a preferred embodiment, the aspect ratio of the rod-shaped carbon material body is 5:1 or higher. The high aspect ratio of the carbon material body of this invention makes it easier to form a continuous conductive network in the flow electrode than particles, creating a bridging effect of "line contact," which effectively alleviates the problem of insufficient conductivity in FCDI.

[0013] As a preferred embodiment, the loading of zero-valent Fe on the carbon material is 0.5~3 at.%. This trace loading of zero-valent Fe is beneficial for improving conductivity and increasing the specific capacitance of the material.

[0014] This invention also provides a method for preparing a flow electrode material with a hierarchical structure, comprising the following steps:

[0015] S1 involves crushing cellulose raw materials into powder and then heat-treating them under a protective atmosphere to obtain carbon material precursors.

[0016] S2 The carbon material precursor is mixed with iron reagent and alkali in solution and dried. The resulting powder is then calcined under a protective atmosphere to obtain activated carbon material.

[0017] The activated carbon material described in S3 is mixed with the electrolyte solution to obtain the final product.

[0018] The preparation method of this invention firstly selects cellulose as the raw material for activated carbon, which retains its unique high aspect ratio rod-shaped morphology after carbonization. Simultaneously, a dual etching process using alkali and iron reagents opens the interlayer pores, causing the surface to delaminate into layers. Furthermore, the introduction of iron reagents causes the carbon surrounding the Fe to rearrange, forming a highly graphitized carbon particle structure, significantly enhancing the degree of graphitization. Thus, rod-shaped and sheet-like morphologies coexist, with the sheet-like morphology supported on the surface of the rod-shaped morphology. During high-temperature calcination, the introduced iron reagent undergoes a reduction reaction with the carbon material, generating a small amount of zero-valent Fe as a byproduct.

[0019] As a preferred embodiment, the Fe salt includes at least one of ferric oxide, ferrous oxide, ferric chloride, ferrous chloride, ferric sulfate, and ferric nitrate.

[0020] As a preferred embodiment, the cellulose raw material is crushed and then filtered through a 200-600 mesh sieve.

[0021] As a preferred embodiment, in S1, the heat treatment temperature is 200~600℃, and the holding time is 0.5~4h. This invention mainly controls the stability of the morphology through heat treatment and calcination. Experiments have shown that if cellulose and iron reagents are directly carbonized, iron will be embedded in the carbon structure, resulting in multiple processes such as pore formation, Fe thermal reduction, and graphitization occurring simultaneously, leading to numerous variables and making it impossible to obtain the hierarchical structure of this invention; the original cellulose structure will be destroyed. However, after pre-heat treatment, Fe is used for surface modification, causing surface rearrangement of carbon without changing the original carbon structure. A further preferred holding time is 2~4h.

[0022] As a preferred embodiment, in S2, the mass ratio of the carbon material precursor to the iron reagent is (1~8):(0.5~2). This invention, by controlling the amount of iron reagent to be slightly excessive, can both promote the graphitization degree of the enhanced carbon material, improve the conductivity of the carbon material, and alleviate the problem of insufficient conductivity of the carbon slurry in FCDI, while simultaneously avoiding the complete removal of residual zero-valent iron byproducts during subsequent acid washing, thereby retaining trace amounts of zero-valent Fe to improve conductivity and increase the specific capacitance of the material. A further preferred mass ratio is (5~6):(1~2).

[0023] As a preferred embodiment, the roasting treatment is followed by acid washing and water washing. Acid washing and water washing can remove residual unreacted iron reagents, but the number of washing cycles should not be excessive, otherwise the byproduct zero-valent iron will be completely washed away. Furthermore, the acid washing uses 1M hydrochloric acid.

[0024] As a preferred embodiment, the mass ratio of the carbon material precursor to the alkali is 1:(0.5~6). In this invention, the etching and pore-forming effect on the material is controlled by adjusting the amount of alkali used. If the amount of alkali is too small, the pore structure in the final material will be reduced, thereby inhibiting the adsorption performance of salt ions; while if the amount of alkali is too large, it will lead to structural damage and a decrease in conductivity. A further preferred ratio is 1:(1~6). As a preferred embodiment, the solid-liquid mass ratio in the solution is 1:(10~20).

[0025] As a preferred embodiment, the calcination treatment is carried out at a temperature of 800~1200℃ for 1~2 hours. In this invention, if the calcination temperature is too low, the catalytic graphitization effect of the iron reagent will be weakened. Within the preferred calcination temperature range of this invention, a flow electrode material with optimal overall performance can be obtained. A further preferred calcination temperature is 800~900℃.

[0026] As a preferred embodiment, the alkali comprises KOH. More preferably, the alkali comprises at least one selected from KOH, potassium carbonate, potassium bicarbonate, sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0027] As a preferred embodiment, the electrolyte in the electrolyte solution includes at least one of sodium sulfate, sodium chloride, sodium nitrate, potassium nitrate, potassium sulfate, potassium chloride, ammonium sulfate, and ammonium chloride; the mass concentration of the electrolyte solution is 0.5~5 g / L.

[0028] As a preferred embodiment, the activated carbon material has a mass fraction of 0.5% to 10% in the flow electrode material. Within this preferred range of activated carbon material dosage, both the conductivity and desalination effect of the slurry can be guaranteed, while also taking into account cost and process implementation difficulty. A further preferred dosage is 4% to 8%.

[0029] Finally, this invention also provides an application of a flow electrode material with a hierarchical structure, which is used as an electrode material in seawater desalination or wastewater treatment.

[0030] The electrode material of this invention has a rod-shaped structure with a higher aspect ratio, which can improve the conductivity of the electrode in the flow state. At the same time, the surface micro-level structure is conducive to the optimization of ion migration. The combination of the two structures forms a hierarchical structure that simultaneously enhances electron and ion transport and has a strong ion adsorption capacity, thereby significantly improving the desalination efficiency of FCDI.

[0031] As a preferred embodiment, the salt ion concentration in the seawater desalination or wastewater treatment is greater than 0 and less than or equal to 20,000 ppm. The electrode material of this invention can be applied to the treatment of high-salinity wastewater, offering significant advantages over existing electrode materials.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] (1) The flow electrode material provided by the present invention has a hierarchical structure, which refers to the rod-shaped carbon material body and the nano-sheet graphite generated in situ on its surface. Through this special hierarchical structure and trace amounts of zero-valent Fe, the electrolyte solution can work together to form a continuous conductive network in the flow electrode, effectively improving the specific capacitance and conductivity of the electrode material.

[0034] (2) The flow electrode provided by this invention solves the problem that ordinary metal materials are difficult to apply in FCDI in the prior art. In the prior art, electrode particles in the slurry need to rely on contact conductivity, but the surface of pure metal particles is easily oxidized and passivated to form an insulating layer, which affects the conductivity of the slurry. The hierarchical structure adopted in this invention has both a conductive structure and sufficient pores to adsorb salt ions. At the same time, its nano / micron scale can be adapted to dispersion in the fluid to meet the flowability requirements, which has significant practical application value.

[0035] (3) The preparation method of the present invention can control the stability of the morphology by introducing iron reagent and alkali reagent for synergistic heat treatment and calcination treatment, and obtain electrode materials with special microstructure. The process is simple and the materials are readily available.

[0036] (4) The flow electrode material provided by the present invention can be adapted to a variety of electrolyte solutions to meet the needs of different scenarios, and is particularly suitable for seawater desalination or wastewater treatment, which can significantly improve the desalination efficiency of FCDI. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0038] Figure 1 SEM images of the activated carbon materials prepared in Example 1 and Comparative Example 1 are shown. Among them, (a) is the SEM image of Example 1 and (b) is the SEM image of Comparative Example 1.

[0039] Figure 2 The Raman spectra of the activated carbon materials prepared in Example 1 and Comparative Example 1 are shown.

[0040] Figure 3 The CV curves are for the activated carbon materials prepared in Example 1 and Comparative Example 1.

[0041] Figure 4 The graph shows a comparison of the desalination effects of the activated carbon materials prepared in Example 1 and Comparative Example 1, and commercial activated carbon (Comparative Example 2) in the same FCDI system.

[0042] Figure 5 This is a diagram of the FCDI operating mode used in this invention.

[0043] Figure 6 The diagram shows the charge-discharge cycle process for Example 1. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] The technical solutions of the various embodiments of the present invention can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0046] Example 1

[0047] A flow electrode material with a hierarchical structure is prepared by the following steps:

[0048] S1 crushes the cellulose raw material into powder, filters it through a 200-600 mesh sieve, places it under a nitrogen atmosphere, and heat-treats it at 550℃ for 2 hours to obtain a carbon material precursor.

[0049] S2 mixed carbon precursor with nano-Fe2O3 material and KOH at a mass ratio of 6:1:6 in 30g of deionized water (solid-liquid ratio 1:10), stirred, dried, and calcined at 900℃ for 2h under a nitrogen atmosphere at a heating rate of 5℃ / min. The mixture was then sequentially washed with 1M hydrochloric acid, washed with deionized water, dried, and ground to obtain activated carbon material. The activated carbon material possesses both a rod-shaped carbon matrix and a nano-sheet graphite microstructure formed in situ on its surface. The aspect ratio of the rod-shaped carbon matrix is ​​5:1, and the loading of zero-valent Fe on the carbon material is 1.0 at.%. In a three-electrode electrolytic cell, under a 1M sodium chloride system and a current density of 0.5A / g, the specific capacitance of the activated carbon material is 76.1 F / g.

[0050] S3. Take 5g of activated carbon material and put it into 100ml of sodium chloride solution with a concentration of 1g / L. Stir magnetically for 4h to obtain a well-mixed black flowing electrode slurry.

[0051] S4 introduces the uniformly mixed flow electrode slurry into the positive and negative electrodes of the FCDI desalination unit, respectively. When flowing out, the slurry is mixed and neutralized, and the process is repeated. The circulation flow rate of the flow electrode is set to 20 ml / min, the concentration of the intermediate brine is 2 g / L sodium chloride, and the flow rate of the intermediate brine is 15 ml / min, and the process is repeated.

[0052] The FCDI device applies a constant electric field of 1.2V, and uses a conductivity meter to measure the conductivity of the intermediate brine in real time to determine the salt concentration.

[0053] Using 30 minutes as the treatment time point, the desalination rate was calculated to be 2.15 μmol / (cm). 2 min).

[0054] Example 2

[0055] A flow electrode material with a hierarchical structure is prepared by the following steps:

[0056] S1 crushes the cellulose raw material into powder, filters it through a 200-600 mesh sieve, places it under a nitrogen atmosphere, and heat-treats it at 550℃ for 2 hours to obtain a carbon material precursor.

[0057] S2 mixed carbon precursor with nano-Fe2O3 material and KOH in a mass ratio of 6:0.5:6 in 30g of deionized water (solid-liquid ratio 1:10), stirred, dried, and calcined at 900℃ for 2h under a nitrogen atmosphere at a heating rate of 5℃ / min. The mixture was then sequentially acid-washed with 1M hydrochloric acid, washed with deionized water, dried, and ground to obtain activated carbon material. In a three-electrode electrolytic cell, under a 1M sodium chloride system and a current density of 0.5A / g, the specific capacitance was 52.5F / g.

[0058] S3. Take 5g of activated carbon material and put it into 100ml of sodium chloride solution with a concentration of 1g / L. Stir magnetically for 4h to obtain a well-mixed black flowing electrode slurry.

[0059] S4 introduces the uniformly mixed flow electrode slurry into the positive and negative electrodes of the FCDI desalination unit, respectively. When flowing out, the slurry is mixed and neutralized, and the process is repeated. The circulation flow rate of the flow electrode is set to 20 ml / min, the concentration of the intermediate brine is 2 g / L sodium chloride, and the flow rate of the intermediate brine is 15 ml / min, and the process is repeated.

[0060] The FCDI device applies a constant electric field of 1.2V, and uses a conductivity meter to measure the conductivity of the intermediate brine in real time to determine the salt concentration.

[0061] Using 30 minutes as the treatment time point, the desalination rate was calculated to be 1.95 μmol / (cm). 2 min).

[0062] Example 3

[0063] The only difference between this embodiment and Embodiment 1 is that the amount of activated carbon material in S3 is changed to 3g; all other steps and conditions are the same.

[0064] Using 30 minutes as the treatment time point, the desalination rate was calculated to be 1.07 μmol / (cm). 2 min).

[0065] Example 4

[0066] The only difference between this embodiment and Embodiment 1 is that the amount of activated carbon material in S3 is changed to 10g; all other steps and conditions are the same.

[0067] Using 30 minutes as the treatment time point, the desalination rate was calculated to be 2.10 μmol / (cm).2 min).

[0068] Comparative Example 1

[0069] The only difference between this comparative example and Example 1 is that nano-Fe2O3 material is not added in S2; all other steps and conditions are the same. In a three-electrode electrolytic cell, with a 1M sodium chloride system and a current density of 0.5 A / g, the specific capacitance is 10.4 F / g.

[0070] Using 30 minutes as the treatment time point, the desalination rate was calculated to be 0.5 μmol / (cm). 2 min).

[0071] Comparative Example 2

[0072] Typical activated carbon for supercapacitors was selected, with Japanese Cortex YP50-F as the carbon material.

[0073] 5g of carbon material was added to 100ml of 1g / L sodium chloride solution and magnetically stirred for 4h to obtain a uniform black flowing electrode slurry. The uniformly mixed slurry was then passed into the positive and negative electrodes of the FCDI desalination device, and mixed and neutralized as it flowed out, and the process was repeated. The circulation flow rate of the flowing electrode was set to 20ml / min, the concentration of the intermediate brine was 2g / L sodium chloride, and the flow rate of the intermediate water was 15ml / min, and the process was repeated.

[0074] The FCDI device applies a constant electric field of 1.2V, and uses a conductivity meter to measure the conductivity of the intermediate brine in real time to determine the salt concentration.

[0075] Using 30 minutes as the treatment time point, the desalination rate was calculated to be 1.4 μmol / (cm). 2 min).

[0076] Comparative Example 3

[0077] The only difference between this comparative example and Example 1 is that S1 is omitted. Instead, cellulose is crushed into powder, filtered through a 200-600 mesh sieve, and then mixed with nano Fe2O3 material and KOH in a mass ratio of 6:1:6 in 30g of deionized water (solid-liquid ratio of 1:10). The mixture is stirred, dried, and then calcined at 900°C for 2 hours under a nitrogen atmosphere at a heating rate of 5°C / min. After being washed with 1M hydrochloric acid, washed with deionized water, dried, and ground, activated carbon material is obtained. All other steps and conditions are the same. The obtained activated carbon material does not have a hierarchical structure.

[0078] Using 30 minutes as the treatment time point, the desalination rate was calculated to be 1.45 μmol / (cm). 2 min).

[0079] Figure 1 The images show SEM images of the activated carbon materials prepared in Example 1 and Comparative Example 1 of this invention. As can be seen from the images, when an iron reagent is introduced during the calcination process, a morphology with a higher degree of graphitization and a more obvious hierarchical structure can be obtained. At the same time, there are also trace amounts of zero-valent Fe residues on the surface of the activated carbon materials.

[0080] Figure 2 The images show the Raman spectra of the activated carbon materials prepared in Example 1 and Comparative Example 1 of this invention.

[0081] Figure 3 The figures show the CV curves of the activated carbon materials prepared in Example 1 and Comparative Example 1 of this invention. As can be seen from the figures, both activated carbon materials exhibit a typical double-layer adsorption mechanism. The larger the rectangular area encompassed, the greater the specific capacitance of the material; Example 1 shows a larger capacitance. Furthermore, the regular rectangular structure indicates good reversibility.

[0082] Figure 4 This is a comparison graph showing the desalination effects of the activated carbon materials prepared in Example 1 and Comparative Example 1, and commercial activated carbon (Comparative Example 2), in the same FCDI system. The vertical axis represents the conductivity of the simulated wastewater. As treatment progresses, the lower the conductivity of the wastewater, the fewer salt ions are present, and the cleaner the water quality becomes. The wastewater conductivity in Example 1 decreased faster, indicating a faster desalination rate and better treatment effect.

[0083] Figure 6 The diagram shows the charge-discharge cycle process of Example 1, which demonstrates that the system maintains good stability even after multiple cycles.

Claims

1. A flow electrode material with a hierarchical structure, characterized in that: This includes electrolyte solutions, carbon materials, and zero-valent Fe loaded on their surfaces; The carbon material includes a rod-shaped carbon material body and nanosheet graphite generated in situ on its surface.

2. The flow electrode material with a hierarchical structure according to claim 1, characterized in that: The aspect ratio of the rod-shaped carbon material body is 5:1 or higher.

3. A flow electrode material with a hierarchical structure according to claim 1 or 2, characterized in that: The loading of zero-valent Fe on the carbon material is 0.5~3 at.%.

4. The method for preparing a flow electrode material with a hierarchical structure as described in any one of claims 1 to 3, characterized in that: Includes the following steps: S1 involves crushing cellulose raw materials into powder and then heat-treating them under a protective atmosphere to obtain carbon material precursors. S2 The carbon material precursor is mixed with iron reagent and alkali in solution and dried. The resulting powder is then calcined under a protective atmosphere to obtain activated carbon material. The activated carbon material described in S3 is mixed with the electrolyte solution to obtain the final product.

5. The method for preparing a flow electrode material with a hierarchical structure according to claim 4, characterized in that: The cellulose raw material is crushed and then filtered through a 200-600 mesh sieve; The heat treatment temperature is 200~600℃, and the holding time is 0.5h~4h.

6. The method for preparing a flow electrode material with a hierarchical structure according to claim 5, characterized in that: In S2, The mass ratio of the carbon material precursor to the iron reagent is (1~8):(0.5~2). The mass ratio of the carbon material precursor to the alkali is 1:(0.5~6); The solid-liquid mass ratio in the solution is 1:(10~20); The calcination treatment is carried out at a temperature of 800~1200℃ for 1~2 hours. The iron reagent includes at least one of ferric oxide, ferrous oxide, ferric chloride, ferrous chloride, ferric sulfate, and ferric nitrate. Preferably, the alkali includes at least one selected from KOH, potassium carbonate, potassium bicarbonate, sodium hydroxide, sodium carbonate, and sodium bicarbonate.

7. The method for preparing a flow electrode material with a hierarchical structure according to claim 6, characterized in that: The electrolyte solution contains at least one of sodium sulfate, sodium chloride, sodium nitrate, potassium nitrate, potassium sulfate, potassium chloride, ammonium sulfate, and ammonium chloride; the mass concentration of the electrolyte solution is 0.5~5 g / L.

8. The method for preparing a flow electrode material with a hierarchical structure according to claim 4 or 7, characterized in that: The activated carbon material has a mass fraction of 0.5-10% in the flow electrode material.

9. The application of a flow electrode material with a hierarchical structure as described in any one of claims 1 to 3, or a flow electrode material obtained by the preparation method as described in any one of claims 4 to 8, characterized in that: It can be used as an electrode material for seawater desalination or wastewater treatment.

10. The application according to claim 9, characterized in that: The salt ion concentration in the seawater desalination or wastewater treatment is greater than 0 and less than or equal to 20,000 ppm.

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