A method for modifying an electrode of a flow battery by in-situ growing carbon nanotubes on a surface of a laser-induced carbon felt electrode

Abstract

This invention relates to the field of flow battery electrode material modification technology, specifically a method for modifying flow battery electrodes by laser-induced in-situ growth of carbon nanotubes on the surface of a carbon felt electrode. The method uses a carbon felt electrode as a substrate, first performing a pretreatment process by cleaning; then, a catalyst precursor is impregnated or sprayed onto the substrate; subsequently, continuous-wave CO2 laser scanning irradiation is used in a reducing atmosphere to induce carbon nanotube growth; finally, a modified electrode is obtained. This invention utilizes laser irradiation to directly grow carbon nanotubes on the surface of a carbon felt. The carbon nanotube-modified carbon felt electrode possesses extremely high specific surface area, excellent conductivity, and abundant defect sites, significantly enhancing the catalytic activity for redox reactions of active materials in flow batteries, providing an innovative solution for improving the energy efficiency and power density of flow batteries.

Description

Technical Field

[0001] This invention relates to the field of flow battery electrode material modification technology, specifically a flow battery electrode modification method for in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode. Background Technology

[0002] Flow batteries, as a large-scale energy storage technology, have broad application prospects in renewable energy grid integration and grid peak shaving due to their advantages such as high safety, long lifespan, and independent design of power and capacity. Common flow batteries include vanadium redox flow batteries, iron-chromium flow batteries, iron redox flow batteries, and zinc-based flow batteries. However, the overall performance of flow batteries is largely limited by electrode materials. Although the widely used carbon felt electrodes have good conductivity and chemical stability, their specific surface area is limited (usually <1 m² / g), resulting in insufficient catalytic activity for the redox reactions of active materials. Surface modification is required to improve electrochemical performance.

[0003] Carbon nanotubes, as one-dimensional nanomaterials, possess extremely high specific surface area (theoretically up to 1300 m² / g), excellent conductivity, and unique electronic structure, making them ideal electrode modification materials. Studies have shown that introducing carbon nanotubes onto the surface of carbon felt can significantly increase the density of active sites in the electrode, improve electrolyte wettability, and promote electron transport. However, traditional carbon nanotube modification methods mostly employ coating or chemical vapor deposition, which have the following problems: coating methods have weak adhesion, and carbon nanotubes are easily detached; chemical vapor deposition requires high temperatures (600℃~900℃) and long processing times (tens of minutes to several hours), resulting in high energy consumption and potential damage to the carbon felt matrix.

[0004] Laser processing technology, with its high energy density, precise control, and localized heating, exhibits unique advantages in the field of material surface modification. In recent years, lasers have been used for cutting, carbonizing, doping, and patterning carbon materials. For example, CO2 lasers can be used for the surface activation of carbon fibers. However, methods for directly growing carbon nanotubes in situ on the surface of carbon felt using lasers and applying them to the modification of flow battery electrodes have not yet been reported. Summary of the Invention

[0005] To address the limitations of existing carbon felt electrodes, such as limited specific surface area and insufficient catalytic activity, as well as the complexity and weak bonding of traditional carbon nanotube modification methods, this invention provides a laser-induced in-situ growth method for carbon nanotubes on the surface of a carbon felt electrode used in flow batteries. This method involves pre-loading a catalyst precursor and utilizing the instantaneous high energy density of a laser to generate localized high temperatures on the carbon fiber surface. Simultaneously, the catalytic precursor decomposes to form nanocatalyst particles, initiating the catalytic cracking of the gaseous carbon source, thereby growing carbon nanotube structures in situ on the carbon fiber surface.

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

[0007] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode includes the following steps:

[0008] (1) Pretreatment of carbon felt substrate: The carbon felt substrate is cleaned and dried. It is ultrasonically cleaned in acetone, ethanol and deionized water at a power of 100W-500W for 10 minutes-60 minutes respectively. It is then dried in a vacuum drying oven at 60℃-90℃ for 6 hours-24 hours to remove surface impurities and obtain the pretreated carbon felt.

[0009] (2) Catalyst loading: The pretreated carbon felt is immersed in a solution containing the catalyst precursor, so that the catalyst precursor is uniformly loaded on the carbon fiber surface. After removal, it is dried to remove the solvent.

[0010] (3) Laser-induced growth: The carbon felt loaded with catalyst precursor is placed in the reaction chamber and the surface of the carbon felt is scanned and irradiated by a continuous wave CO2 laser in a reducing atmosphere or an inert atmosphere; the laser energy induces the catalyst precursor to decompose and form nano-catalyst particles, and at the same time triggers the gas phase carbon source; the catalytic cracking on the nano-catalyst particles, through the gas-liquid-solid mechanism, grows carbon nanotube structure in situ on the carbon fiber surface, and obtains the laser-treated carbon felt.

[0011] (4) Post-processing: The carbon felt after laser treatment is cleaned to remove residues and dried to obtain a modified carbon felt electrode with carbon nanotubes grown on the surface.

[0012] Further, in step (1), the carbon felt substrate is one of polyacrylonitrile-based carbon felt, pitch-based carbon felt, and adhesive-based carbon felt.

[0013] Further, in step (2), the catalyst precursor is one or more of the following: nitrates, acetates, chlorides, or acetylacetonates of iron, cobalt, nickel, or copper; the solvent is one or more of water, ethanol, ethylene glycol, or N,N-dimethylformamide; the concentration of the catalyst precursor solution is 0.001 mol / L to 0.1 mol / L; the impregnation time is 10 minutes to 60 minutes; the drying temperature is 40℃ to 80℃; and the drying time is 2 hours to 6 hours.

[0014] Further, in step (3), the reducing atmosphere is hydrogen or a hydrogen / argon mixture, the hydrogen gas fraction is 5%~20%, and the gas flow rate is 10mL / min~100mL / min; the inert atmosphere is argon or nitrogen.

[0015] Further, in step (3), the wavelength of the continuous wave CO2 laser is 10.6 μm, the laser power is 10 W to 100 W, the scanning speed is 1 mm / s to 50 mm / s, the spot diameter is 0.1 mm to 2 mm, and the ratio of laser power to scanning speed is 0.5 J / mm to 50 J / mm.

[0016] Furthermore, in step (3), the diameter of the carbon nanotube is controlled by adjusting the laser power. The higher the laser power, the larger the diameter. The diameter of the carbon nanotube is 10nm~50nm. The length of the carbon nanotube is controlled by adjusting the scanning speed. The slower the scanning speed, the longer the length. The length of the carbon nanotube is 0.5μm~10μm. The growth density of the carbon nanotube is controlled by adjusting the concentration of the catalyst precursor. The higher the concentration, the greater the growth density.

[0017] Furthermore, in step (3), the scanning path of the laser irradiation is a reciprocating parallel scan or a cross scan, the scanning interval is 0.1mm~1mm, and the number of scans is 1~5 times.

[0018] Further, in step (3), the gaseous carbon source comes from hydrocarbon fragments generated by the local vaporization of the carbon felt substrate under laser irradiation, or by introducing an additional carbon-containing gas as a carbon source; the additional carbon-containing gas is one or more of methane, acetylene, ethylene or ethanol vapor, with a flow rate of 10 mL / min to 50 mL / min.

[0019] Further, in step (4), the cleaning is ultrasonic cleaning with deionized water or ethanol at a power of 100W-500W for 5 to 15 minutes; the drying temperature is 60℃ to 100℃ and the time is 6 hours to 12 hours.

[0020] This invention provides a modified carbon felt electrode with surface-grown carbon nanotubes prepared by the above method. The electrode is suitable for use as an electrode in vanadium redox flow batteries, iron-chromium flow batteries, iron redox flow batteries, and zinc-based flow batteries.

[0021] The design concept of this invention is:

[0022] This invention creatively combines catalyst loading with laser irradiation technology for in-situ growth of carbon nanotubes on carbon felt electrodes. Laser irradiation generates instantaneous high temperatures (up to 1000°C or higher) on the carbon fiber surface, which falls precisely within the optimal temperature range for carbon nanotube growth. Under laser irradiation, the catalyst precursor loaded on the carbon fiber surface rapidly decomposes and melts to form nanoscale catalyst droplets. Simultaneously, the high temperature causes partial vaporization of the carbon fiber surface, generating hydrocarbon fragments, or decomposes external carbon source gas, providing a carbon source for carbon nanotube growth. These carbon atoms dissolve in the catalyst droplets, and upon reaching supersaturation, precipitate to form carbon nanotubes, which then grow in situ on the carbon fiber surface via a gas-liquid-solid mechanism.

[0023] This "laser-induced in-situ growth" strategy has the following unique advantages: First, the growth process occurs only in the laser scanning area, enabling selective regional modification and patterned growth; second, the carbon nanotubes and carbon fiber substrate form chemical bonds and physical entanglement through in-situ growth, resulting in extremely strong bonding, far superior to coating methods; third, laser processing is fast (on the order of minutes), consumes little energy, and requires no overall heating, thus avoiding thermal damage to the carbon felt substrate; and fourth, the morphology of carbon nanotubes can be precisely controlled by adjusting laser parameters and catalyst concentration.

[0024] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0025] 1. This invention utilizes laser irradiation to directly grow carbon nanotubes on the surface of carbon felt, eliminating the need for high-temperature furnaces and long processing times required by traditional chemical vapor deposition, thus reducing the growth time from tens of minutes to several minutes.

[0026] 2. This invention can complete the growth of carbon nanotubes with a single laser scan. The equipment is simple, easy to operate, and suitable for continuous production and large-scale application.

[0027] 3. In this invention, carbon nanotubes form chemical bonds and physical entanglement with carbon fiber substrates through in-situ growth, overcoming the shortcomings of easy detachment and short lifespan of coating methods, and significantly improving the cycle stability of the electrode.

[0028] 4. This invention can control the diameter of carbon nanotubes from 10nm to 50nm by adjusting the laser power (10W~100W); the length of carbon nanotubes from 0.5μm to 10μm by adjusting the scanning speed (1mm / s~50mm / s); and the growth density by adjusting the catalyst concentration.

[0029] 5. In this invention, carbon nanotube modification increases the electrode specific surface area by 50% to 200%, the electrochemical active area by 100% to 300%, and significantly increases the density of reactive active sites.

[0030] 6. The abundant defect sites, edge structures and end openings of carbon nanotubes in this invention have excellent catalytic performance on the active material of flow batteries, reducing charge transfer resistance by 40% to 60% and improving energy efficiency by 6% to 10% compared with unmodified electrodes. Attached Figure Description

[0031] Figure 1 The image shows the electrochemical specific surface area (CV) of the electrode prepared in Example 1.

[0032] Figure 2 The image shows a comparison of the electrochemical specific surface area of ​​the electrode prepared in Example 1. Detailed Implementation

[0033] The technical solution of the present invention will be described in detail below with reference to the embodiments, but the scope of protection claimed by the present invention is not limited to the embodiments described.

[0034] This invention relates to a method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode, comprising the following steps and process:

[0035] In the specific implementation process, the carbon felt substrate is first cleaned and pretreated; then the catalyst precursor is impregnated or sprayed; subsequently, carbon nanotubes are irradiated by continuous wave CO2 laser in a reducing atmosphere to induce their growth; finally, the modified electrode is obtained after cleaning and drying.

[0036] (1) Substrate pretreatment: Cut the carbon felt into 10cm×10cm sizes. The carbon felt substrate is one of polyacrylonitrile-based carbon felt, pitch-based carbon felt, or adhesive-based carbon felt. Clean the carbon felt sequentially in acetone, ethanol, and deionized water with ultrasonic power of 100W-500W for 10 minutes-60 minutes each, and dry it in a vacuum drying oven at 60℃-90℃ for 6 hours-24 hours.

[0037] (2) Catalyst loading: Prepare a solution containing a catalyst precursor, wherein the catalyst precursor is one or more of the following: nitrates, acetates, chlorides or acetylacetonates of iron, cobalt, nickel or copper; the solvent is one of water, ethanol, ethylene glycol or N,N-dimethylformamide; the concentration of the catalyst precursor solution is 0.001 mol / L to 0.1 mol / L; immerse the pretreated carbon felt in the solution containing the catalyst precursor for 10 to 60 minutes, and then dry it in a drying oven at 40℃ to 80℃ for 2 to 6 hours to ensure that the catalyst precursor is uniformly loaded on the carbon fiber surface;

[0038] (3) Laser-induced growth: The carbon felt loaded with the catalyst precursor is placed in a reaction chamber, and a reducing atmosphere or an inert atmosphere is introduced. The reducing atmosphere is hydrogen or a hydrogen / argon mixture, with a hydrogen integral of 5% to 20% and a gas flow rate of 10 mL / min to 100 mL / min. The inert atmosphere is argon or nitrogen. The surface of the carbon felt is scanned and irradiated using a continuous wave CO2 laser. The laser power, scanning speed, spot diameter, and scanning path are set. The wavelength of the continuous wave CO2 laser is 10 nm. The laser irradiation process involves a laser diameter of 0.6 μm, a laser power of 10 W to 100 W, a scanning speed of 1 mm / s to 50 mm / s, a spot diameter of 0.1 mm to 2 mm, a laser power to scanning speed ratio of 0.5 J / mm to 50 J / mm, a laser irradiation scanning path of reciprocating parallel scanning or cross scanning, a scanning interval of 0.1 mm to 1 mm, and 1 to 5 scans. During laser irradiation, the catalyst precursor decomposes to form nanoparticles, simultaneously initiating a gaseous carbon source and catalyzing the carbon source to decompose and grow carbon nanotubes.

[0039] The gaseous carbon source is derived from hydrocarbon fragments generated by the local vaporization of the carbon felt substrate under laser irradiation, or by introducing an additional carbon-containing gas as a carbon source; the additional carbon-containing gas is one or more of methane, acetylene, ethylene or ethanol vapor, with a flow rate of 10 mL / min to 50 mL / min.

[0040] The diameter of carbon nanotubes is controlled by adjusting the laser power; the higher the laser power, the larger the diameter, ranging from 10 nm to 50 nm. The length of carbon nanotubes is controlled by adjusting the scanning speed; the slower the scanning speed, the longer the length, ranging from 0.5 μm to 10 μm. The growth density of carbon nanotubes is controlled by adjusting the concentration of the catalyst precursor; the higher the concentration, the greater the growth density.

[0041] (4) Post-treatment: After laser treatment, the laser-treated carbon felt is placed in deionized water or ethanol and ultrasonically cleaned with a power of 100W-500W for 5 to 15 minutes to remove residues. It is then dried in a vacuum drying oven at 60℃ for 6 hours to obtain a modified carbon felt electrode with carbon nanotubes grown on the surface.

[0042] The raw materials and equipment used, such as carbon felt of different specifications and catalyst precursors, are all commercially available.

[0043] The present invention will now be described in further detail through embodiments.

[0044] Example 1

[0045] In this embodiment, a method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode using a nickel nitrate catalyst and a hydrogen atmosphere is as follows:

[0046] (1) Substrate pretreatment: Cut the adhesive carbon felt into 10cm×10cm pieces, and clean them in acetone, ethanol and deionized water by ultrasonic cleaning at 100W power for 15 minutes each. Then dry them in a vacuum drying oven at 60℃ for 12 hours for later use.

[0047] (2) Catalyst loading: Prepare an ethanol solution with a concentration of 0.05 mol / L nickel nitrate, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0048] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min; the carbon felt surface was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path was reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0049] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 100W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-1.

[0050] Modified electrode CF-CNT-1: Scanning electron microscopy shows that carbon nanotubes are uniformly grown on the surface of carbon fibers, with a diameter of about 25 nm and a length of about 3 μm; high-resolution transmission electron microscopy shows that the carbon nanotubes have a multi-walled structure, with catalyst particles located at the ends of the tubes. Figure 1 This is the CV plot of the electrochemical specific surface area of ​​the electrode prepared in this embodiment. Figure 2 This is a comparison chart of the electrochemical specific surface area of ​​the electrodes prepared in this embodiment. As shown in the chart, the specific surface area of ​​the modified carbon felt electrode CF-CNT-1 prepared in this embodiment is increased to 2.6 m² / g, and the electrochemical specific surface area is increased to 58.7 mF / cm². -2 The cells were assembled into a single vanadium redox flow battery and tested at a current density of 200 mA / cm², showing an energy efficiency of 84.3%.

[0051] Example 2

[0052] In this embodiment, a method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is described below, using cobalt nitrate catalyst as a catalyst precursor:

[0053] (1) Substrate pretreatment: Cut the adhesive carbon felt into 10cm×10cm pieces, and clean them in acetone, ethanol and deionized water with ultrasonic power of 200W for 60 minutes each. Then dry them in a vacuum drying oven at 60℃ for 12 hours for later use.

[0054] (2) Catalyst loading: Prepare an ethanol solution of cobalt nitrate with a concentration of 0.05 mol / L, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0055] (3) Laser-induced growth: The carbon felt loaded with cobalt nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min. The surface of the carbon felt was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0056] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 500W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-Co.

[0057] Modified electrode CF-CNT-Co: Scanning electron microscopy revealed uniform growth of carbon nanotubes on the carbon fiber surface, with a diameter of approximately 20 nm and a length of approximately 2.5 μm; high-resolution transmission electron microscopy showed that the carbon nanotubes had a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area increased to 2.3 m² / g, and the electrochemical specific surface area increased to 52.1 mFcm. -2 The cells were assembled into a single vanadium redox flow battery and tested at a current density of 200 mA / cm², showing an energy efficiency of 83.5%.

[0058] Example 3

[0059] In this embodiment, ferric nitrate catalyst is used as the catalyst precursor. A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0060] (1) Substrate pretreatment: Cut the adhesive carbon felt into 10cm×10cm pieces, and clean them in acetone, ethanol and deionized water by ultrasonic cleaning at 500W power for 60 minutes each. Then dry them in a vacuum drying oven at 60℃ for 12 hours for later use.

[0061] (2) Catalyst loading: Prepare an ethanol solution of 0.05 mol / L ferric nitrate, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0062] (3) Laser-induced growth: The carbon felt loaded with ferric nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min. The carbon felt surface was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0063] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 200W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-Fe.

[0064] Modified electrode CF-CNT-Fe: Scanning electron microscopy revealed uniform growth of carbon nanotubes on the carbon fiber surface, with a diameter of approximately 22 nm and a length of approximately 2.8 μm; high-resolution transmission electron microscopy showed that the carbon nanotubes had a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area increased to 2.4 m² / g, and the electrochemical specific surface area increased to 54.3 mF / cm². -2 The cells were assembled into a single vanadium redox flow battery and tested at a current density of 200 mA / cm², showing an energy efficiency of 83.8%.

[0065] Example 4

[0066] The difference from Example 1 is that the solution containing the catalyst precursor in this example is an ethanol solution of nickel nitrate with a concentration of 0.01 mol / L.

[0067] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0068] (1) Substrate pretreatment: Cut the adhesive carbon felt into 10cm×10cm pieces, and clean them in acetone, ethanol and deionized water by ultrasonic cleaning at 500W power for 60 minutes each. Then dry them in a vacuum drying oven at 60℃ for 12 hours for later use.

[0069] (2) Catalyst loading: Prepare an ethanol solution of nickel nitrate with a concentration of 0.01 mol / L, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0070] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min; the carbon felt surface was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path was reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0071] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 150W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-lowconc.

[0072] Modified electrode CF-CNT-lowconc: Scanning electron microscopy shows that the carbon nanotubes on the carbon fiber surface are sparsely grown, with a diameter of approximately 20 nm and a length of approximately 2 μm; high-resolution transmission electron microscopy shows that the carbon nanotubes have a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area is increased to 1.6 m² / g, and the electrochemical specific surface area is increased to 41.2 mFcm. -2 The cells were assembled into a single vanadium redox flow battery and tested at a current density of 200 mA / cm², showing an energy efficiency of 81.2%.

[0073] Example 5

[0074] The difference from Example 1 is that the solution containing the catalyst precursor in this example is an ethanol solution of nickel nitrate with a concentration of 0.1 mol / L.

[0075] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0076] (1) Substrate pretreatment: Cut the adhesive carbon felt into 10cm×10cm pieces, and clean them in acetone, ethanol and deionized water by ultrasonic cleaning at 200W power for 10 minutes each. Then dry them in a vacuum drying oven at 80℃ for 12 hours for later use.

[0077] (2) Catalyst loading: Prepare an ethanol solution of nickel nitrate with a concentration of 0.1 mol / L, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0078] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min; the carbon felt surface was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path was reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0079] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 300W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-highconc.

[0080] Modified electrode CF-CNT-highconc: Scanning electron microscopy revealed dense growth of carbon nanotubes on the carbon fiber surface, with a diameter of approximately 30 nm and a length of approximately 4 μm, and localized agglomeration; high-resolution transmission electron microscopy showed that the carbon nanotubes had a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area increased to 2.8 m² / g, and the electrochemical specific surface area increased to 61.5 mFcm. -2 The cells were assembled into a single all-ferric flow battery and tested at a current density of 50 mA / cm², showing an energy efficiency of 84.5%.

[0081] Example 6

[0082] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0083] (1) Substrate pretreatment: The polyacrylonitrile carbon felt is cut into 10cm×10cm pieces, and ultrasonically cleaned in acetone, ethanol and deionized water at 100W power for 60 minutes each. It is then dried in a vacuum drying oven at 80℃ for 12 hours for later use.

[0084] (2) Catalyst loading: Prepare an ethanol solution of nickel nitrate with a concentration of 0.05 mol / L, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours.

[0085] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min. The surface of the carbon felt was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 30 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0086] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 500W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-30W.

[0087] Modified electrode CF-CNT-30W: Scanning electron microscopy revealed uniform growth of carbon nanotubes on the carbon fiber surface, with a diameter of approximately 15 nm and a length of approximately 2 μm; high-resolution transmission electron microscopy showed that the carbon nanotubes had a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area was increased to 2.0 m² / g, and the electrochemical specific surface area was increased to 48.3 mFcm⁻². Assembled into a single all-iron flow battery, the energy efficiency was 82.5% at a current density of 60 mA / cm².

[0088] Example 7

[0089] The difference between this embodiment and embodiment 6 is that the laser power of the continuous wave CO2 in this embodiment is 80W.

[0090] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0091] (1) Substrate pretreatment: The polyacrylonitrile carbon felt is cut into 10cm×10cm pieces, and ultrasonically cleaned in acetone, ethanol and deionized water at 100W power for 60 minutes each. It is then dried in a vacuum drying oven at 80℃ for 24 hours for later use.

[0092] (2) Catalyst loading: Prepare an ethanol solution of nickel nitrate with a concentration of 0.05 mol / L, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours.

[0093] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min. The carbon felt surface was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 80 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0094] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 500W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-80W.

[0095] Modified electrode CF-CNT-80W: Scanning electron microscopy revealed uniform growth of carbon nanotubes on the carbon fiber surface, with a diameter of approximately 40 nm and a length of approximately 5 μm; high-resolution transmission electron microscopy showed that the carbon nanotubes had a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area was increased to 2.7 m² / g, and the electrochemical specific surface area was increased to 60.1 mFcm⁻². Assembled into a single zinc-bromine flow battery, the energy efficiency was 84.0% when tested at a current density of 60 mA / cm².

[0096] Example 8

[0097] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0098] (1) Substrate pretreatment: cut polyacrylonitrile carbon felt into 10cm×10cm size, and ultrasonically clean it in acetone, ethanol and deionized water at 500W power for 60 minutes each, and dry it in a vacuum drying oven at 80℃ for 24 hours for later use.

[0099] (2) Catalyst loading: Prepare an ethanol solution with a concentration of 0.05 mol / L nickel nitrate, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0100] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min; the carbon felt surface was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 10 mm / s, spot diameter 1 mm, scanning path was reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0101] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 500W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-slow.

[0102] Modified electrode CF-CNT-slow: Scanning electron microscopy revealed uniform growth of carbon nanotubes on the carbon fiber surface, with a diameter of approximately 25 nm and a length of approximately 6 μm; high-resolution transmission electron microscopy showed that the carbon nanotubes had a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area increased to 2.9 m² / g, and the electrochemical specific surface area increased to 62.3 mFcm⁻². Assembled into a single zinc-bromine flow battery, the energy efficiency was 77.8% when tested at a current density of 75 mA / cm².

[0103] Example 9

[0104] The difference between this embodiment and embodiment 8 is that the scanning speed in step (3) is 40 mm / s.

[0105] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0106] (1) Substrate pretreatment: cut polyacrylonitrile carbon felt into 10cm×10cm size, and ultrasonically clean it in acetone, ethanol and deionized water at 500W power for 60 minutes each, and dry it in a vacuum drying oven at 80℃ for 24 hours for later use.

[0107] (2) Catalyst loading: Prepare an ethanol solution with a concentration of 0.05 mol / L nickel nitrate, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0108] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min; the carbon felt surface was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 40 mm / s, spot diameter 1 mm, scanning path was reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0109] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 500W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-fast.

[0110] Modified electrode CF-CNT-fast: Scanning electron microscopy revealed uniform growth of carbon nanotubes on the carbon fiber surface, with a diameter of approximately 20 nm and a length of approximately 1.5 μm; high-resolution transmission electron microscopy showed that the carbon nanotubes had a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area was increased to 1.8 m² / g, and the electrochemical specific surface area was increased to 34.6 mFcm⁻². Assembled into a single vanadium redox flow battery, the energy efficiency was 81.8% when tested at a current density of 150 mA / cm².

[0111] Example 10

[0112] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0113] (1) Substrate pretreatment: Cut polyacrylonitrile carbon paper into 10cm×10cm size, and clean it in acetone, ethanol and deionized water by ultrasonic cleaning at 100W power for 10 minutes each. Dry it in a vacuum drying oven at 80℃ for 24 hours for later use.

[0114] (2) Catalyst loading: Prepare an ethanol solution with a concentration of 0.05 mol / L nickel nitrate, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0115] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber. While a hydrogen / argon mixture was introduced, acetylene gas was introduced as a carbon source. The acetylene flow rate was 5 mL / min, and the hydrogen / argon mixture flow rate was 50 mL / min (hydrogen gas integral 10%). The carbon felt surface was scanned and irradiated with a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path was reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0116] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 500W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-C2H2.

[0117] Modified electrode CF-CNT-C2H2: Scanning electron microscopy shows that carbon nanotubes grow more densely on the carbon fiber surface, with a diameter of approximately 25 nm and a length of approximately 5 μm; high-resolution transmission electron microscopy shows that the carbon nanotubes have a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area is increased to 3.2 m² / g, and the electrochemical specific surface area is increased to 65.8 mFcm. -2 The zinc-bromine flow battery was assembled into a single cell and tested at a current density of 50 mA / cm², showing an energy efficiency of 85.2%.

[0118] Example 11

[0119] The difference between this embodiment and Embodiment 10 is that in this embodiment, the external carbon source is methane gas, and the methane flow rate is 10 mL / min.

[0120] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0121] (1) Substrate pretreatment: Cut polyacrylonitrile carbon paper into 10cm×10cm size, and ultrasonically clean it in acetone, ethanol and deionized water at 100W power for 20 minutes each, and dry it in a vacuum drying oven at 80℃ for 24 hours for later use.

[0122] (2) Catalyst loading: Prepare an ethanol solution with a concentration of 0.05 mol / L nickel nitrate, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0123] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber. While a hydrogen / argon mixture was introduced, methane gas was introduced as a carbon source. The methane flow rate was 10 mL / min, and the hydrogen / argon mixture flow rate was 50 mL / min (hydrogen gas integral 10%). The carbon felt surface was scanned and irradiated with a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path was reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0124] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 500W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-CH4.

[0125] Modified electrode CF-CNT-CH4: Scanning electron microscopy showed dense growth of carbon nanotubes on the carbon fiber surface, with a diameter of approximately 22 nm and a length of approximately 4 μm; high-resolution transmission electron microscopy showed that the carbon nanotubes had a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area increased to 2.8 m² / g, and the electrochemical specific surface area increased to 61.9 mFcm⁻². Assembled into a single vanadium redox flow battery, the energy efficiency was 84.5% when tested at a current density of 200 mA / cm².

[0126] Example 12

[0127] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0128] (1) Substrate pretreatment: Cut the asphalt-based carbon felt into 10cm×10cm pieces, and clean them in acetone, ethanol and deionized water by ultrasonic cleaning at 200W power for 30 minutes each. Then dry them in a vacuum drying oven at 80℃ for 24 hours for later use.

[0129] (2) Catalyst loading: Prepare an ethanol solution with a concentration of 0.05 mol / L nickel nitrate, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in a drying oven at 60℃ for 4 hours;

[0130] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min. The surface of the carbon felt was scanned and irradiated with a continuous wave CO2 laser. After the first scan was performed according to the parameters in Example 1, the second scan with the same parameters was performed after an interval of 30 seconds. The process parameters were set as follows: laser power 50 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path is reciprocating parallel scanning, and scanning interval 0.5 mm.

[0131] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 100W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-2scan.

[0132] Modified electrode CF-CNT-2scan: Scanning electron microscopy shows that carbon nanotubes grow more densely on the carbon fiber surface, with a diameter of approximately 28 nm and a length of approximately 5 μm; high-resolution transmission electron microscopy shows that the carbon nanotubes have a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area is increased to 3.0 m² / g, and the electrochemical specific surface area is increased to 63.7 mFcm. -2 The cells were assembled into a single vanadium redox flow battery and tested at a current density of 200 mA / cm², showing an energy efficiency of 85.0%.

[0133] Example 13

[0134] A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode is as follows:

[0135] (1) Substrate pretreatment: Cut the asphalt-based carbon felt into 10cm×10cm pieces, and clean them in acetone, ethanol and deionized water with ultrasonic power of 100W for 20 minutes each. Then dry them in a vacuum drying oven at 80℃ for 24 hours for later use.

[0136] (2) Catalyst loading: Prepare an ethylene glycol solution with a concentration of 0.05 mol / L nickel nitrate, immerse the pretreated carbon felt in the solution for 30 minutes, and then dry it in an 80℃ drying oven for 4 hours;

[0137] (3) Laser-induced growth: The carbon felt loaded with nickel nitrate was placed in the reaction chamber and a hydrogen / argon mixture (hydrogen gas fraction 10%) was introduced at a flow rate of 50 mL / min; the carbon felt surface was scanned and irradiated using a continuous wave CO2 laser. The process parameters were set as follows: laser power 50 W, scanning speed 20 mm / s, spot diameter 1 mm, scanning path was reciprocating parallel scanning, scanning interval 0.5 mm, and scanning times 1.

[0138] (4) Post-processing: After laser treatment, the carbon felt is placed in ethanol and ultrasonically cleaned with 100W power for 10 minutes, and then dried in a vacuum drying oven at 60℃ for 6 hours to obtain the modified carbon felt electrode CF-CNT-EG.

[0139] Modified electrode CF-CNT-EG: Scanning electron microscopy shows dense growth of carbon nanotubes on the carbon fiber surface, with a diameter of approximately 25 nm and a length of approximately 4.5 μm; high-resolution transmission electron microscopy shows that the carbon nanotubes have a multi-walled structure, with catalyst particles located at the ends of the tubes; the specific surface area is increased to 2.9 m² / g, and the electrochemical specific surface area is increased to 62.8 mFcm. -2 The cells were assembled into a single all-ferric flow battery and tested at a current density of 70 mA / cm², showing an energy efficiency of 84.9%.

[0140] The results of the embodiments show that the laser-induced in-situ growth method of the present invention can successfully construct carbon nanotube structures on the surface of carbon felt electrodes through a simple and controllable process. The growth quality and morphology of carbon nanotubes can be controlled by adjusting the catalyst type (Ni, Co, Fe); the growth density of carbon nanotubes can be controlled by adjusting the catalyst concentration (0.001 mol / L~0.1 mol / L); the diameter of carbon nanotubes (10 nm~50 nm) can be precisely controlled by adjusting the laser power (10 W~100 W); the length of carbon nanotubes (0.5 μm~10 μm) can be controlled by adjusting the scanning speed (1 mm / s~50 mm / s); and the length of carbon nanotubes can be further increased by adding an external carbon source (acetylene, methane) or selecting a carbon-containing solvent. The prepared carbon nanotube-modified electrode exhibits a significantly enhanced catalytic activity for the redox reaction of active materials in flow batteries due to its extremely high specific surface area (50%~200% higher than untreated), excellent conductivity, and abundant defect sites. The charge transfer resistance is reduced by 40%~60%, and the electrochemical active area is increased to 40 mF / cm². -2 ~65mFcm -2 This electrode, through its surface carbon nanotube structure design, effectively coordinates the multiple requirements of flow battery electrodes for high specific surface area, high catalytic activity, and rapid electron conduction, providing a key electrode material solution for the development of next-generation high-performance, high-power-density flow batteries.

Claims

1. A method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode, characterized in that, Includes the following steps: (1) Pretreatment of carbon felt substrate: The carbon felt substrate is cleaned and dried. It is ultrasonically cleaned in acetone, ethanol and deionized water at a power of 100W-500W for 10 minutes-60 minutes respectively. It is then dried in a vacuum drying oven at 60℃-90℃ for 6 hours-24 hours to remove surface impurities and obtain the pretreated carbon felt. (2) Catalyst loading: The pretreated carbon felt is immersed in a solution containing the catalyst precursor, so that the catalyst precursor is uniformly loaded on the carbon fiber surface. After removal, it is dried to remove the solvent. (3) Laser-induced growth: The carbon felt loaded with catalyst precursor is placed in the reaction chamber and the surface of the carbon felt is scanned and irradiated by a continuous wave CO2 laser in a reducing atmosphere or an inert atmosphere; the laser energy induces the catalyst precursor to decompose and form nano-catalyst particles, and at the same time triggers the gas phase carbon source; the catalytic cracking on the nano-catalyst particles, through the gas-liquid-solid mechanism, grows carbon nanotube structure in situ on the carbon fiber surface, and obtains the laser-treated carbon felt. (4) Post-processing: The carbon felt after laser treatment is cleaned to remove residues and dried to obtain a modified carbon felt electrode with carbon nanotubes grown on the surface.

2. The method of claim 1, wherein the laser-induced carbon felt electrode surface in-situ grown carbon nanotube flow battery electrode modification method is characterized by, In step (1), the carbon felt substrate is one of polyacrylonitrile-based carbon felt, pitch-based carbon felt, or adhesive-based carbon felt.

3. The method of claim 1, wherein the laser-induced carbon felt electrode surface in-situ grown carbon nanotube flow battery electrode modification method is characterized by, In step (2), the catalyst precursor is one or more of the following: nitrates, acetates, chlorides, or acetylacetonates of iron, cobalt, nickel, or copper; the solvent is one or more of the following: water, ethanol, ethylene glycol, or N,N-dimethylformamide; the concentration of the catalyst precursor solution is 0.001 mol / L to 0.1 mol / L; the impregnation time is 10 minutes to 60 minutes; the drying temperature is 40℃ to 80℃; and the drying time is 2 hours to 6 hours.

4. The method of claim 1, wherein the laser-induced carbon felt electrode surface in-situ grown carbon nanotube flow battery electrode modification method is characterized by, In step (3), the reducing atmosphere is hydrogen or a hydrogen / argon mixture, the hydrogen gas fraction is 5%~20%, and the gas flow rate is 10mL / min~100mL / min; the inert atmosphere is argon or nitrogen.

5. The method of claim 1, wherein the laser-induced carbon felt electrode surface in-situ grown carbon nanotube flow battery electrode modification method is characterized by, In step (3), the wavelength of the continuous wave CO2 laser is 10.6 μm, the laser power is 10 W to 100 W, the scanning speed is 1 mm / s to 50 mm / s, the spot diameter is 0.1 mm to 2 mm, and the ratio of laser power to scanning speed is 0.5 J / mm to 50 J / mm.

6. The method of claim 1, wherein the laser-induced carbon felt electrode surface in-situ grown carbon nanotube flow battery electrode modification method is characterized by, In step (3), the diameter of the carbon nanotube is controlled by adjusting the laser power. The higher the laser power, the larger the diameter. The diameter of the carbon nanotube is 10nm~50nm. The length of the carbon nanotube is controlled by adjusting the scanning speed. The slower the scanning speed, the longer the length. The length of the carbon nanotube is 0.5μm~10μm. The growth density of the carbon nanotube is controlled by adjusting the concentration of the catalyst precursor. The higher the concentration, the greater the growth density.

7. The method of claim 1, wherein the laser-induced carbon felt electrode surface in-situ grown carbon nanotube flow battery electrode modification method is characterized by, In step (3), the scanning path of laser irradiation is reciprocating parallel scanning or cross scanning, the scanning interval is 0.1mm~1mm, and the number of scans is 1 to 5.

8. The method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode according to claim 1, characterized in that, In step (3), the gaseous carbon source comes from hydrocarbon fragments generated by the local vaporization of the carbon felt substrate under laser irradiation, or from the additional introduction of carbon-containing gas as a carbon source; the additional carbon-containing gas is one or more of methane, acetylene, ethylene or ethanol vapor, and the flow rate is 10 mL / min to 50 mL / min.

9. The method for modifying a flow battery electrode by in-situ growth of carbon nanotubes on the surface of a laser-induced carbon felt electrode according to claim 1, characterized in that, In step (4), the cleaning is performed by ultrasonic cleaning with deionized water or ethanol at a power of 100W-500W for 5 to 15 minutes; the drying temperature is 60℃ to 100℃ and the time is 6 hours to 12 hours.

10. A modified carbon felt electrode with surface-grown carbon nanotubes prepared by the method of any one of claims 1-9, characterized in that, The electrode is suitable for use as an electrode in vanadium redox flow batteries, iron-chromium redox flow batteries, iron redox flow batteries, and zinc-based redox flow batteries.

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