A niobium-based complex-derived electrode, its preparation method and application

Abstract

This application relates to the field of flow battery electrode technology, and discloses a niobium-based complex-derived electrode, its preparation method, and its application. The preparation method includes the following steps: slowly adding a solution containing a nitrogen-containing heterocyclic ligand to a mixed solution composed of a first metal source, a second metal source, and a surfactant to obtain a niobium-based bimetallic complex; mixing the niobium-based bimetallic complex, a pore-forming agent, and deionized water, ball milling, and heat treatment to obtain a porous niobium-based bimetallic carbonitride material; dispersing the porous niobium-based bimetallic carbonitride material, a binder, a dispersant, and a conductive carbon material in a reinforced phthalate coupling agent solution to obtain a mixed slurry; immersing a carbon-based electrode in the mixed slurry and allowing it to stand to obtain a mixed slurry-modified carbon-based electrode; and freeze-drying and heat-treating the mixed slurry-modified carbon-based electrode to obtain a niobium-based complex-derived electrode. This method can effectively improve the conductivity of the carbon-based electrode and enhance the energy efficiency of the vanadium redox flow battery.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery electrode technology, and in particular to a niobium-based complex-derived electrode, its preparation method, and its application. Background Technology

[0002] Thanks to its excellent safety, long cycle life, high energy storage capacity, and low cost, flow batteries are considered one of the most promising energy storage technologies currently available. Among them, vanadium redox flow battery technology has matured the most through continuous technological innovation in recent years and has now entered the stage of large-scale commercial operation. However, the cost of flow batteries remains relatively high, and improving battery power density and operating efficiency is one of the effective ways to reduce the cost of flow batteries.

[0003] As a key component of vanadium redox flow batteries, electrodes provide the reaction site and channels for the transport of internal active materials. Electrode materials typically require high surface area, suitable porosity, low electronic resistance, and high electrochemical activity. The performance of electrode materials directly affects the electrochemical reaction rate, battery internal resistance, and electrolyte transport processes. Specifically, the conductivity and catalytic performance of the electrode directly influence the battery's polarization state and current density, thus affecting energy efficiency. The physicochemical stability of the electrode material also directly affects the overall operational stability and actual lifespan of the battery; therefore, electrode materials must possess high chemical inertness and mechanical stability. However, due to the poor electrochemical activity of traditional carbon felt electrodes, flow batteries often experience severe overpotentials during operation, hindering redox reactions. Therefore, developing high-performance flow battery electrodes plays a crucial role in reducing reaction overpotentials and improving battery charge-discharge performance. Summary of the Invention

[0004] The purpose of this invention is to provide a niobium-based complex-derived electrode, its preparation method, and its application, thereby solving the problems of poor activity and low conductivity of existing graphite felt electrodes.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, embodiments of the present invention provide a method for preparing a niobium-based complex-derived electrode, comprising the following steps:

[0007] Step S1: Disperse the first metal source, the second metal source, and the surfactant in a first buffer solution to obtain a first mixed solution; disperse the nitrogen-containing heterocyclic ligand in a second buffer solution to obtain a second mixed solution; slowly add the second mixed solution to the first mixed solution and continuously stir the reaction; then filter, wash, and dry the resulting product to obtain a niobium-based bimetallic complex; wherein, the first metal source is a niobium source.

[0008] Step S2: The niobium-based bimetallic complex, pore-forming agent, and deionized water are transferred to a ball mill for ball milling. The resulting product is then transferred to a tube furnace and heat-treated under a protective gas to obtain a porous niobium-based bimetallic carbonitride material.

[0009] Step S3: Disperse the porous niobium-based bimetallic carbonitride material, binder, dispersant and conductive carbon material in an enhanced phthalate coupling agent solution and stir to obtain a mixed slurry; immerse the carbon-based electrode in the mixed slurry and let it stand to obtain a mixed slurry modified carbon-based electrode.

[0010] Step S4: The carbon-based electrode modified with the mixed slurry is transferred to a vacuum freeze dryer for freeze drying, and then transferred to a tube furnace for heat treatment under active gas to obtain a niobium-based complex-derived electrode.

[0011] Preferably, in step S1:

[0012] The mass ratio of the first metal source, the second metal source, the surfactant, and the first buffer solution is 1:(0.2~3):(0.5~2):(300~500). The amount of niobium source is used as the quantitative measure, and the amount of the second metal source and surfactant needs to be similar. Too much or too little will have a negative impact on the electrode material.

[0013] The mass ratio of the nitrogen-containing heterocyclic ligand to the second buffer solution is 1:(150~300).

[0014] Preferably, the first metal source is selected from at least one of niobium pentanol, niobium oxalate, niobium ethoxy, niobium pentaisopropoxy, and ammonium oxalate hydrate of niobate; molybdenum and tungsten sources readily form complexes with niobium, and their similar electronic structures facilitate electronic structure modulation.

[0015] The second metal source is selected from at least one of molybdenum chloride, molybdenum hexacarbonyl, molybdenum acetylacetonate, tungsten hexachloride, and tungsten hexacarbonyl.

[0016] The surfactant is selected from at least one of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, dodecyl dimethyl benzyl ammonium chloride, and cocamidopropyl betaine. The surfactant can promote the dispersion and stability of the product, prevent agglomeration, and also act as a template / guide to form ordered assemblies, control the nucleation rate, and achieve more uniform product preparation.

[0017] The nitrogen-containing heterocyclic ligand is selected from at least one of pyridin-2-ylurea, 4,4'-bipyridine, 2,5-thiophene dicarboxylic acid, 1,10-o-phenanthroline and 3-(1H-(1,2,3)triazol-4-yl)-benzonitrile; the nitrogen-containing heterocyclic ligand is mainly used to complex with niobium source and second metal source to form bimetallic complexes.

[0018] The first buffer solution and / or the second buffer solution are selected from at least one of sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution, hexamethylenetetramine-hydrochloric acid buffer solution, and tris(hydroxymethyl)aminomethane hydrochloric acid buffer solution; since alkalinity or acidity has a negative effect on the complexation reaction, a neutral buffer solution is used to stabilize the reaction system, making the bimetallic complex formed more stable.

[0019] The pH of the first buffer solution and / or the second buffer solution is 6.5 to 7.5.

[0020] Preferably, in step S2:

[0021] The mass ratio of the niobium-based bimetallic complex, the pore-forming agent, and the deionized water is (8~12):1:(20~30).

[0022] The pore-forming agent is selected from at least one of ammonium bicarbonate, polymethyl methacrylate, sodium chloride, and polyethylene glycol. Through thermal decomposition and etching, the pore-forming agent induces a hierarchical porous structure in the bimetallic carbon-nitrogen material, thereby increasing the specific surface area of ​​the electrode material and exposing more catalytic active sites.

[0023] Preferably, in step S3:

[0024] The mass ratio of the porous niobium-based bimetallic carbonitride material, the binder, the dispersant, the conductive carbon material, and the reinforced phthalate coupling agent solution is 1:(0.2~1.5):(0.5~3):(4~8):(200~500). By dispersing the bimetallic carbonitride material with the binder, dispersant, and conductive carbon material with the coupling agent and then immersing it in graphite felt, it can achieve better contact and dispersion with the graphite felt electrode, avoiding the shedding and peeling of active materials.

[0025] The mass ratio of the carbon-based electrode to the mixed slurry is 1:(25~50).

[0026] Preferably, in step S3:

[0027] The adhesive is selected from at least one of phenolic resin, acrylic resin, carboxymethyl cellulose, and polyvinyl alcohol.

[0028] The dispersant is selected from at least one of sodium pyrophosphate, sodium hexametaphosphate, sulfonated polystyrene, trimethylstearamide chloride, and polyoxyethylene alkylphenol ether.

[0029] The conductive carbon material is selected from at least one of graphene oxide, carbon nanotubes, graphite powder, and conductive carbon black.

[0030] The volume fraction of the enhanced phthalate coupling agent solution is 2% to 8%.

[0031] The solute in the enhanced phthalate coupling agent solution is selected from at least one of bis(acetylacetonyl)isopropoxyethoxytitanate, neoalkoxytris(dioctylpyrophosphoryloxy)titanate acrylamide chelate, neoalkoxytris(dioctylphosphoryloxy)titanate, and isopropyl dioleate oxy(dioctylphosphoryloxytitanate).

[0032] The solvent in the enhanced phthalate coupling agent solution is selected from at least one of xylene, toluene, N,N-dimethylformamide, and dichloromethane.

[0033] The carbon-based electrode is selected from at least one of graphite felt, carbon paper, carbon cloth, and carbon felt.

[0034] Preferably, the stirring reaction time of the first mixed solution and the second mixed solution in step S1 is 8~12h.

[0035] The protective gas in step S2 is one of nitrogen, argon or ammonia, and the heat treatment temperature is 800~1000℃ for 2~6 hours.

[0036] The settling time in step S3 is 6~12h.

[0037] Preferably, in step S4, the freeze-drying temperature is -50 to -20°C, and the time is 6 to 12 hours; the active gas is either air or oxygen, and the heat treatment temperature is 350 to 500°C, and the time is 1.5 to 4 hours. This freeze-drying followed by heat treatment process effectively fixes the porous structure and the adhesion of the active material to the graphite felt fiber surface, enhances the electrode's corrosion resistance in acidic electrolytes, reduces battery polarization loss, improves the catalytic selectivity for vanadium ion redox reactions, and lowers the activation energy, thereby effectively enhancing the electrochemical activity of the carbon-based electrode in a vanadium redox flow battery.

[0038] Secondly, embodiments of the present invention provide a niobium-based complex-derived electrode, which is prepared using the preparation method of the niobium-based complex-derived electrode described in the above embodiments.

[0039] Thirdly, the present invention provides an application of a niobium-based complex-derived electrode, wherein the niobium-based complex-derived electrode prepared by the preparation method described in the above embodiments or the niobium-based complex-derived electrode described in the above embodiments is applied to a vanadium redox flow battery.

[0040] In summary, the beneficial effects of this invention patent are:

[0041] This invention generates niobium-based bimetallic complexes by reacting a niobium source, a second metal source, and a nitrogen-containing heterocyclic ligand. The addition of a surfactant disperses and stabilizes the metal source, preventing sedimentation. Controlling the reaction rate further generates more stable and uniform niobium-based bimetallic complexes. Using a neutral buffer solution as the reaction system also contributes to system stability, ensuring uniform nucleation and growth of the complexes. This facilitates the uniform dispersion of the generated niobium-based bimetallic complexes, and the niobium-based complex-derived electrodes formed after subsequent processing exhibit a more uniform conductive network, effectively reducing electrode resistance.

[0042] By ball milling and then heat-treating the niobium-based bimetallic complex with a pore-forming agent, the resulting porous niobium-based bimetallic carbonitride material possesses a suitable pore size structure. The pore-forming agent, through thermal decomposition and etching, creates a hierarchical porous structure, thereby increasing the specific surface area of ​​the electrode material and exposing more catalytic active sites. Immersing the porous niobium-based bimetallic carbonitride material, dispersed with a binder, dispersant, and conductive carbon material with a coupling agent, into a carbon-based electrode ensures better contact and dispersion, preventing the active material from detaching or peeling off. The subsequent freeze-drying followed by heat treatment fixes the pore structure and the adhesion of the active material to the carbon-based electrode fiber surface, enhancing the corrosion resistance of the carbon-based electrode in acidic electrolytes, reducing battery polarization loss, improving the catalytic selectivity for vanadium ion redox reactions, and lowering the activation energy, thus effectively enhancing the electrochemical activity of the carbon-based electrode in vanadium redox flow batteries.

[0043] This invention organically complexes a niobium source with a second metal source to form a niobium-based bimetallic complex. The synergistic effect of niobium and the second metal optimizes the electronic structure, lowers the reaction energy barrier, and enhances the catalytic activity of the electrode. The coordination of the nitrogen-containing heterocyclic ligand with the niobium-based bimetal can form a conjugated conductive network, promoting electron transfer, reducing electrochemical reaction impedance, decreasing charge transfer resistance, and improving electrode conductivity. This ensures sufficient and efficient dispersion and flow of current at the electrode surface. Subsequently, by combining with conductive carbon materials and modifying the carbon-based electrode surface, the conductivity of the carbon-based electrode is effectively improved, thereby enhancing the energy efficiency of the vanadium redox flow battery. Attached Figure Description

[0044] Figure 1 This is a schematic flowchart of a method for preparing a niobium-based complex-derived electrode.

[0045] Figure 2 This is a SEM image of the niobium-based complex-derived electrode prepared in Example 1. Detailed Implementation

[0046] like Figure 1 As shown, a method for preparing a niobium-based complex-derived electrode includes the following steps:

[0047] Step S1: Disperse the first metal source, the second metal source, and the surfactant in a first buffer solution to obtain a first mixed solution; disperse the nitrogen-containing heterocyclic ligand in a second buffer solution to obtain a second mixed solution; slowly add the second mixed solution to the first mixed solution and continuously stir the reaction, then filter, wash, and dry the resulting product to obtain a niobium-based bimetallic complex; wherein, the first metal source is a niobium source; the mass ratio of the first metal source, the second metal source, the surfactant, and the first buffer solution is 1:(0.2~3):(0.5~2):(300~500); the mass ratio of the nitrogen-containing heterocyclic ligand and the second buffer solution is 1:(150~300); the first metal source is selected from at least one of niobium pentanol, niobium oxalate, niobium ethoxy, niobium pentaisopropoxy, and ammonium oxalate hydrate of niobate; the second metal source is selected from molybdenum chloride, molybdenum hexacarbonyl, At least one of molybdenum acetylacetonate, tungsten hexachloride, and tungsten hexacarbonyl; the surfactant is selected from at least one of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, dodecyl dimethylbenzylammonium chloride, and cocamidopropyl betaine; the nitrogen-containing heterocyclic ligand is selected from at least one of pyridin-2-ylurea, 4,4'-bipyridine, 2,5-thiophene dicarboxylic acid, 1,10-o-phenanthroline, and 3-(1H-(1,2,3)triazol-4-yl)-benzonitrile; the first buffer solution and / or the second buffer solution are selected from at least one of sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution, hexamethylenetetramine-hydrochloric acid buffer solution, and tris(hydroxymethyl)aminomethane hydrochloric acid buffer solution; the pH of the first buffer solution and / or the second buffer solution is 6.5 to 7.5; the stirring reaction time of the first mixed solution and the second mixed solution is 8 to 12 h.

[0048] Step S2: The niobium-based bimetallic complex, pore-forming agent, and deionized water are transferred to a ball mill for ball milling. The resulting product is then transferred to a tube furnace and heat-treated under a protective gas atmosphere to obtain a porous niobium-based bimetallic carbonitride material. The mass ratio of the niobium-based bimetallic complex, pore-forming agent, and deionized water is (8~12):1:(20~30). The pore-forming agent is selected from at least one of ammonium bicarbonate, polymethyl methacrylate, sodium chloride, and polyethylene glycol.

[0049] Step S3: Disperse the porous niobium-based bimetallic carbonitride material, binder, dispersant, and conductive carbon material in a reinforced phthalate coupling agent solution and stir to obtain a mixed slurry; immerse the carbon-based electrode in the mixed slurry and allow it to stand to obtain a carbon-based electrode modified with the mixed slurry; the mass ratio of the porous niobium-based bimetallic carbonitride material, binder, dispersant, conductive carbon material, and reinforced phthalate coupling agent solution is 1:(0.2~1.5):(0.5~3):(4~8):(200~500); the mass ratio of the carbon-based electrode to the mixed slurry is 1:(25~50); the binder is selected from at least one of phenolic resin, acrylic resin, carboxymethyl cellulose, and polyvinyl alcohol; the dispersant is selected from sodium pyrophosphate, sodium hexametaphosphate, sulfonated polystyrene, trimethylstearamide chloride, and polyoxyethylene alkylene. At least one of the following: phenolic ether; conductive carbon material selected from at least one of graphene oxide, carbon nanotubes, graphite powder, and conductive carbon black; the volume fraction of the enhanced phthalate coupling agent solution is 2%~8%; the solute in the enhanced phthalate coupling agent solution is selected from at least one of bis(acetylacetonyl)isopropoxyethoxytitanate, neoalkoxytris(dioctylpyrophosphoryloxy)titanate acrylamide chelate, neoalkoxytris(dioctylphosphoryloxy)titanate, and isopropyl dioleate oxy(dioctylphosphoryloxytitanate); the solvent in the enhanced phthalate coupling agent solution is selected from at least one of xylene, toluene, N,N-dimethylformamide, and dichloromethane; the carbon-based electrode is selected from at least one of graphite felt, carbon paper, carbon cloth, and carbon felt; the standing time in step S3 is 6~12h.

[0050] Step S4: The carbon-based electrode modified with the mixed slurry is transferred to a vacuum freeze dryer for freeze drying, and then transferred to a tube furnace for heat treatment under an active gas to obtain a niobium-based complex-derived electrode; the freeze drying temperature is -50~-20℃, and the time is 6~12h; the active gas is either air or oxygen, and the heat treatment temperature is 350~500℃, and the time is 1.5~4h.

[0051] Example 1: This example includes the following steps.

[0052] Step S1: Ethoxyniobium, molybdenum chloride, and dodecyl dimethyl benzyl ammonium chloride were dispersed in a sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution at pH 6.5 to obtain a first mixture. 4,4'-bipyridine was dispersed in the same buffer solution to obtain a second mixture. The second mixture was slowly added to the first mixture while continuously stirring. The resulting product was then filtered, washed, and dried to obtain a niobium-based bimetallic complex. The mass ratio of niobium source, molybdenum acetate, dodecyl dimethyl benzyl ammonium chloride, and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution was 1:3:0.5:300. The mass ratio of 4,4'-bipyridine to sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution in the second mixture was 1:150. The stirring time was 10 h, and the volume ratio of the first mixture to the second mixture was 1:1.

[0053] Step S2: The niobium-based bimetallic complex, ammonium bicarbonate and deionized water are transferred to a ball mill for ball milling. The mass ratio of the niobium-based bimetallic complex, ammonium bicarbonate and deionized water is 8:1:30. The resulting product is then transferred to a tube furnace and heat-treated under nitrogen protection at a temperature of 1000℃ for 4 hours to obtain porous niobium-based bimetallic carbonitride material.

[0054] Step S3: The porous niobium-based bimetallic carbonitride material, acrylic resin, polyoxyethylene alkylphenol ether, and graphite powder are dispersed in a 3% (v / v) N,N-dimethylformamide solution of neoalkoxytris(dioctylpyrophosphoryloxy)titanate acrylamide chelate to obtain a mixed slurry. The mass ratio of the porous niobium-based bimetallic carbonitride material, acrylic resin, polyoxyethylene alkylphenol ether, graphite powder, and the N,N-dimethylformamide solution of neoalkoxytris(dioctylpyrophosphoryloxy)titanate acrylamide chelate is 1:1.5:0.5:4:200. The graphite felt electrode is immersed in the mixed slurry and allowed to stand to obtain a carbon-based electrode modified with the mixed slurry. The mass ratio of the graphite felt electrode to the mixed slurry is 1:40, and the immersion time is 8 hours.

[0055] Step S4: The carbon-based electrode modified with the mixed slurry is transferred to a vacuum freeze dryer and freeze-dried at -20°C for 12 hours. Then it is transferred to a tube furnace and heat-treated in air at 500°C for 4 hours to obtain a niobium-based complex-derived electrode.

[0056] like Figure 2As shown, the niobium-based complex-derived electrode prepared in Example 1 forms a rich coating structure on the surface of graphite felt fibers. This provides favorable positions for metal active sites, making them easier to contact with electroreaction intermediates. The conjugated conductive network formed by the coordination of nitrogen-containing heterocyclic ligands with niobium-based bimetals promotes electron transfer and reduces electrochemical reaction impedance. Through subsequent heat treatment, the carbon network substrate and metal active sites are organically combined to optimize the conductive network for electroreaction, reducing electronic resistance during the vanadium ion valence state transition, thereby improving electrode conductivity and ensuring sufficient and efficient dispersion and flow of current at the electrode surface. Similarly, thanks to the ball milling and heat treatment processes, the carbon mesh substrate on its surface has a rich porous structure, which can effectively enhance the specific surface area and electrochemical active area of ​​the electrode, thereby improving the catalytic selectivity for vanadium ion redox reactions, reducing the reaction activation energy, and effectively enhancing its electrochemical activity in vanadium redox batteries.

[0057] Example 2: This example includes the following steps.

[0058] Step S1: Niobium oxalate, molybdenum hexacarbonyl, and hexadecyltrimethylammonium bromide were dispersed in a hexamethylenetetramine-hydrochloric acid buffer solution at pH 7.5 to obtain a first mixture. 2,5-thiophene dicarboxylic acid was dispersed in the same buffer solution to obtain a second mixture. The second mixture was slowly added to the first mixture while stirring continuously. The resulting product was then filtered, washed, and dried to obtain a niobium-based bimetallic complex. The mass ratio of niobium oxalate, scandium chloride hexahydrate, hexadecyltrimethylammonium bromide, and hexamethylenetetramine-hydrochloric acid buffer solution was 1:0.2:2:500. The mass ratio of 2,5-thiophene dicarboxylic acid to hexamethylenetetramine-hydrochloric acid buffer solution in the second mixture was 1:200. The stirring time was 12 h, and the volume ratio of the first mixture to the second mixture was 1:0.5.

[0059] Step S2: The niobium-based bimetallic complex, ammonium bicarbonate and deionized water are transferred to a ball mill for ball milling. The mass ratio of the niobium-based bimetallic complex, ammonium bicarbonate and deionized water is 10:1:25. The resulting product is then transferred to a tube furnace and heat-treated under argon protection at a temperature of 900℃ for 6 hours to obtain porous niobium-based bimetallic carbonitride material.

[0060] Step S3: The porous niobium-based bimetallic carbonitride material, carboxymethyl cellulose, trimethyl stearamide chloride, and carbon nanotubes are dispersed in a 3% (v / v) toluene solution of bis(acetylacetonyl)isopropoxyethoxytitanate titanate to obtain a mixed slurry. The mass ratio of the porous niobium-based bimetallic carbonitride material, carboxymethyl cellulose, trimethyl stearamide chloride, carbon nanotubes, and the toluene solution of bis(acetylacetonyl)isopropoxyethoxytitanate is 1:0.2:3:8:500. The carbon paper electrode is immersed in the mixed slurry and allowed to stand to obtain a carbon-based electrode modified with the mixed slurry. The mass ratio of the carbon paper graphite felt electrode to the mixed slurry is 1:25, and the immersion time is 12 h.

[0061] Step S4: The carbon-based electrode modified with the mixed slurry is transferred to a vacuum freeze dryer and freeze-dried at -50°C for 12 hours. Then it is transferred to a tube furnace and heat-treated in oxygen at 400°C for 3 hours to obtain a niobium-based complex-derived electrode.

[0062] Example 3: This example includes the following steps.

[0063] Step S1: A first mixture was obtained by dispersing niobium pentaisopropoxy, molybdenum acetylacetonate, and sodium dodecylbenzenesulfonate in a sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution at pH=7. A second mixture was obtained by dispersing pyridine-2-ylurea in the same buffer solution. The second mixture was slowly added to the first mixture while continuously stirring. The resulting product was then filtered, washed, and dried to obtain a niobium-based bimetallic complex. The mass ratio of niobium pentaisopropoxy, manganese nitrate, sodium dodecylbenzenesulfonate, and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution was 1:1:1:400. The mass ratio of pyridine-2-ylurea to sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution in the second mixture was 1:250. The stirring time was 12 h, and the volume ratio of the first mixture to the second mixture was 1:2.

[0064] Step S2: The niobium-based bimetallic complex, polyethylene glycol, and deionized water are transferred to a ball mill for ball milling. The mass ratio of the niobium-based bimetallic complex, polyethylene glycol, and deionized water is 12:1:20. The resulting product is then transferred to a tube furnace and heat-treated under ammonia protection at 800°C for 5 hours to obtain a porous niobium-based bimetallic carbonitride material.

[0065] Step S3: The porous niobium-based bimetallic carbonitride material, phenolic resin, sodium pyrophosphate, and conductive carbon black are dispersed in a 3% (v / v) dichloromethane solution of neoalkoxytris(dioctylphosphoyloxy)titanate to obtain a mixed slurry. The mass ratio of the porous niobium-based bimetallic carbonitride material, phenolic resin, sodium pyrophosphate, conductive carbon black, and neoalkoxytris(dioctylphosphoyloxy)titanate dichloromethane solution is 1:1:2:6:300. The graphite felt electrode is immersed in the mixed slurry and allowed to stand to obtain a carbon-based electrode modified with the mixed slurry. The mass ratio of the graphite felt electrode to the mixed slurry is 1:50, and the immersion time is 6 hours.

[0066] Step S4: The carbon-based electrode modified with the mixed slurry is transferred to a vacuum freeze dryer and freeze-dried at -40°C for 6 hours. Then it is transferred to a tube furnace and heat-treated in air at 350°C for 1.5 hours to obtain a niobium-based complex-derived electrode.

[0067] Example 4: This example includes the following steps.

[0068] Step S1: Niobium pentanol, tungsten hexachloride, and cocamidopropyl betaine were dispersed in a tris(hydroxymethyl)aminomethane hydrochloric acid buffer solution at pH 6.5 to obtain a first mixture. 3-(1H-(1,2,3)triazol-4-yl)-benzonitrile was dispersed in the same buffer solution to obtain a second mixture. The second mixture was slowly added to the first mixture while stirring continuously. The resulting product was then filtered, washed, and dried to obtain a niobium-based bimetallic complex. The mass ratio of niobium pentanol, zinc lactate, cocamidopropyl betaine, and tris(hydroxymethyl)aminomethane hydrochloric acid buffer solution was 1:2:0.5:350. The mass ratio of 3-(1H-(1,2,3)triazol-4-yl)-benzonitrile to tris(hydroxymethyl)aminomethane hydrochloric acid buffer solution in the second mixture was 1:300. The stirring time was 9 h, and the volume ratio of the first mixture to the second mixture was 1:3.

[0069] Step S2: The niobium-based bimetallic complex, sodium chloride, and deionized water are transferred to a ball mill for ball milling. The mass ratio of the niobium-based bimetallic complex, sodium chloride, and deionized water is 9:1:25. The resulting product is then transferred to a tube furnace and heat-treated under nitrogen protection at a temperature of 850°C for 2 hours to obtain a porous niobium-based bimetallic carbonitride material.

[0070] Step S3: The porous niobium-based bimetallic carbonitride material, polyvinyl alcohol, sulfonated polystyrene, and graphene oxide are dispersed in a xylene solution of 3% (v / v) isopropyl dioleate oxy(dioctylphosphoyloxy)titanate and stirred to obtain a mixed slurry. The mass ratio of the porous niobium-based bimetallic carbonitride material, phenolic resin, sodium pyrophosphate, conductive carbon black, and neoalkoxytris(dioctylphosphoyloxy)titanate in dichloromethane solution is 1:0.8:1:5:400. The carbon felt electrode is immersed in the mixed slurry and allowed to stand to obtain a carbon-based electrode modified with the mixed slurry. The mass ratio of the carbon felt electrode to the mixed slurry is 1:35, and the immersion time is 10 h.

[0071] Step S4: The carbon-based electrode modified with the mixed slurry is transferred to a vacuum freeze dryer and freeze-dried at -30°C for 8 hours. Then it is transferred to a tube furnace and heat-treated in oxygen at 450°C for 2 hours to obtain a niobium-based complex-derived electrode.

[0072] Example 5: This example includes the following steps.

[0073] Step S1: Ammonium niobate oxalate hydrate, tungsten hexacarbonyl, and dodecyl dimethyl benzyl ammonium chloride were dispersed in a tris(hydroxymethyl)aminomethane hydrochloric acid buffer solution at pH=7 to obtain a first mixture. 1,10-o-phenanthroline was dispersed in the same buffer solution to obtain a second mixture. The second mixture was slowly added to the first mixture while stirring continuously. The resulting product was then filtered, washed, and dried to obtain a niobium-based bimetallic complex. The mass ratio of ammonium niobate oxalate hydrate, cobalt acetate, dodecyl dimethyl benzyl ammonium chloride, and tris(hydroxymethyl)aminomethane hydrochloric acid buffer solution was 1:1.5:0.5:450. The mass ratio of 1,10-o-phenanthroline to tris(hydroxymethyl)aminomethane hydrochloric acid buffer solution in the second mixture was 1:200. The stirring time was 11 h, and the volume ratio of the first mixture to the second mixture was 1:1.5.

[0074] Step S2: The niobium-based bimetallic complex, polymethyl methacrylate, and deionized water were transferred to a ball mill for ball milling. The mass ratio of the niobium-based bimetallic complex, sodium chloride, and deionized water was 11:1:30. The resulting product was then transferred to a tube furnace and heat-treated under argon protection at a temperature of 950°C for 3 hours to obtain a porous niobium-based bimetallic carbonitride material.

[0075] Step S3: The porous niobium-based bimetallic carbonitride material, phenolic resin, sodium hexametaphosphate, and graphene oxide are dispersed in a 3% (v / v) dichloromethane solution of bis(acetylacetone)isopropoxyethoxytitanate titanate to obtain a mixed slurry. The mass ratio of the porous niobium-based bimetallic carbonitride material, phenolic resin, sodium pyrophosphate, conductive carbon black, and neoalkoxytris(dioctylphosphoyloxy)titanate titanate in dichloromethane solution is 1:0.6:1.5:7:400. The carbon cloth electrode is immersed in the mixed slurry and allowed to stand to obtain a carbon-based electrode modified with the mixed slurry. The mass ratio of carbon cloth electrode to mixed slurry is 1:45, and the immersion time is 9 hours.

[0076] Step S4: The carbon-based electrode modified with the mixed slurry is transferred to a vacuum freeze dryer and freeze-dried at -50°C for 9 hours. Then it is transferred to a tube furnace and heat-treated in oxygen at 500°C for 2.5 hours to obtain a niobium-based complex-derived electrode.

[0077] Comparative Example 1 includes the following steps:

[0078] Step S1: Ethoxyniobium was dispersed in a sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution at pH=7 to obtain a first mixture. 4,4'-bipyridine was dispersed in the same buffer solution to obtain a second mixture. The second mixture was slowly added to the first mixture while continuously stirring. The resulting product was then filtered, washed, and dried to obtain a niobium-based bimetallic complex. The mass ratio of the niobium source to the sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution was 1:300, the mass ratio of 4,4'-bipyridine to the sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution in the second mixture was 1:150, the stirring time was 10 h, and the volume ratio of the first mixture to the second mixture was 1:1.

[0079] Step S2: The niobium-based bimetallic complex, ammonium bicarbonate and deionized water are transferred to a ball mill for ball milling. The mass ratio of the niobium-based bimetallic complex, ammonium bicarbonate and deionized water is 8:1:30. The resulting product is then transferred to a tube furnace and heat-treated under ammonia protection at a temperature of 800℃ for 4 hours to obtain porous niobium-based bimetallic carbonitride material.

[0080] Step S3: The porous niobium-based bimetallic carbonitride material, acrylic resin, and polyoxyethylene alkylphenol ether are dispersed in a 3% (v / v) N,N-dimethylformamide solution of neoalkoxytris(dioctylpyrophosphoryloxy)titanate acrylamide chelate to obtain a mixed slurry. The mass ratio of the porous niobium-based bimetallic carbonitride material, acrylic resin, polyoxyethylene alkylphenol ether, graphite powder, and the N,N-dimethylformamide solution of neoalkoxytris(dioctylpyrophosphoryloxy)titanate acrylamide chelate is 1:1.5:0.5:4:200. The graphite felt electrode is immersed in the mixed slurry and allowed to stand to obtain a carbon-based electrode modified with the mixed slurry. The mass ratio of the graphite felt electrode to the mixed slurry is 1:40, and the immersion time is 8 hours.

[0081] Step S4: The carbon-based electrode modified with the mixed slurry is transferred to a vacuum freeze dryer and freeze-dried at -20°C for 12 hours. Then it is transferred to a tube furnace and heat-treated in air at 500°C for 4 hours to obtain a niobium-based complex-derived electrode.

[0082] Comparative Example 2 includes the following steps

[0083] Step S1: Ethoxyniobium, hexacarbonylmolybdenum, and dodecyl dimethyl benzyl ammonium chloride were dispersed in a sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution at pH=7 to obtain a first mixture. 4,4'-bipyridine was dispersed in the same buffer solution to obtain a second mixture. The second mixture was slowly added to the first mixture while continuously stirring. The resulting product was then filtered, washed, and dried to obtain a niobium-based bimetallic complex. The mass ratio of niobium source, molybdenum acetate, dodecyl dimethyl benzyl ammonium chloride, and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution was 1:3:0.5:300. The mass ratio of 4,4'-bipyridine to sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution in the second mixture was 1:150. The stirring time was 10 h, and the volume ratio of the first mixture to the second mixture was 1:1.

[0084] Step S2: The niobium-based bimetallic complex and deionized water are transferred to a ball mill for ball milling. The mass ratio of the niobium-based bimetallic complex to deionized water is 8:30. The resulting product is then transferred to a tube furnace and heat-treated under ammonia protection at a temperature of 900°C for 4 hours to obtain porous niobium-based bimetallic carbonitride material.

[0085] Step S3: The porous niobium-based bimetallic carbonitride material, acrylic resin, polyoxyethylene alkylphenol ether, and graphite powder are dispersed in a 3% (v / v) N,N-dimethylformamide solution of neoalkoxytris(dioctylpyrophosphoryloxy)titanate acrylamide chelate to obtain a mixed slurry. The mass ratio of the porous niobium-based bimetallic carbonitride material, acrylic resin, polyoxyethylene alkylphenol ether, graphite powder, and the N,N-dimethylformamide solution of neoalkoxytris(dioctylpyrophosphoryloxy)titanate acrylamide chelate is 1:1.5:0.5:4:200. The graphite felt electrode is immersed in the mixed slurry and allowed to stand to obtain a carbon-based electrode modified with the mixed slurry. The mass ratio of the graphite felt electrode to the mixed slurry is 1:40, and the immersion time is 8 hours.

[0086] Step S4: The carbon-based electrode modified with the mixed slurry is naturally dried, and then transferred to a tube furnace for heat treatment in air at a temperature of 500°C for 4 hours to obtain a niobium-based complex-derived electrode.

[0087] Comparative Example 3: The electrodes were made of untreated blank graphite felt.

[0088] Resistivity testing method: A digital four-probe tester was used for testing. The electrodes were cut to a size of 8cm×4cm, and resistivity was tested at 5 fixed positions (four corners and the middle position). The average value was taken to obtain the resistivity.

[0089] Electrode specific surface area determination: Four 0.5cm×0.5cm electrodes were randomly selected and tested using a Beijing Bestech BSD-660S fully automatic physical adsorption instrument. The specific surface area was measured under nitrogen atmosphere and recorded.

[0090] Battery testing method: The electrodes obtained from Examples 1-5 and Comparative Examples 1-3 were assembled into a battery stack, and the battery charge and discharge performance was tested under the same operating conditions. The coulombic efficiency, voltage efficiency and energy efficiency were recorded.

[0091] The results of the above tests are shown in Table 1:

[0092] Table 1. Electrode and Battery Performance Test Results

[0093]

[0094] As shown in Table 1, compared with Comparative Example 1, Examples 1-5 exhibited lower resistivity and higher energy efficiency. This is because the niobium source can form a good organic complex with the second metal source and the nitrogen-containing heterocyclic ligand, and is transformed into a good bimetallic-nitrogen-carbon material through subsequent heat treatment. The formed conductive network can effectively promote electron transfer and reduce impedance, thereby effectively improving the conductivity of the electrode and increasing the energy efficiency of the electrode in the vanadium redox flow battery. Compared with Comparative Example 2, Examples 1-5 exhibited lower resistivity, larger specific surface area and energy efficiency. This may be because the niobium-based complex was generated by a hierarchical porous structure through etching effect after ball milling with a pore-forming agent and then heat treatment. The pore structure was fixed by the subsequent freezing and then heat treatment process, which provided the electrode with a larger specific surface area and electron transport channels, effectively exposing more active sites and enhancing the electrode conductivity, thereby effectively improving the energy efficiency and voltage efficiency of the electrode in the vanadium redox flow battery.

Claims

1. A method for preparing a niobium-based complex-derived electrode, characterized in that, Includes the following steps: Step S1: Disperse the first metal source, the second metal source, and the surfactant in a first buffer solution to obtain a first mixed solution; A nitrogen-containing heterocyclic ligand is dispersed in a second buffer solution to obtain a second mixed solution; the second mixed solution is slowly added to the first mixed solution while the reaction is continuously stirred, and then the resulting product is filtered, washed and dried to obtain a niobium-based bimetallic complex; wherein, the first metal source is a niobium source; and the second metal source is selected from at least one of molybdenum chloride, molybdenum hexacarbonyl, molybdenum acetylacetonate, and tungsten hexachloride and tungsten hexacarbonyl. Step S2: The niobium-based bimetallic complex, pore-forming agent and deionized water are transferred to a ball mill for ball milling. The resulting product is then transferred to a tube furnace and heat-treated under a protective gas to obtain a porous niobium-based bimetallic carbonitride material. Step S3: Disperse the porous niobium-based bimetallic carbonitride material, binder, dispersant and conductive carbon material in a reinforced phthalate coupling agent solution and stir to obtain a mixed slurry; immerse the carbon-based electrode in the mixed slurry and let it stand to obtain a mixed slurry modified carbon-based electrode; Step S4: The carbon-based electrode modified with the mixed slurry is transferred to a vacuum freeze dryer for freeze drying, and then transferred to a tube furnace for heat treatment under active gas to obtain a niobium-based complex-derived electrode.

2. The preparation method according to claim 1, characterized in that, In step S1: The mass ratio of the first metal source, the second metal source, the surfactant, and the first buffer solution is 1:(0.2~3):(0.5~2):(300~500). The mass ratio of the nitrogen-containing heterocyclic ligand to the second buffer solution is 1:(150~300).

3. The preparation method according to claim 1 or 2, characterized in that, The first metal source is selected from at least one of niobium pentanol, niobium oxalate, niobium ethoxy, niobium pentaisopropoxy, and ammonium oxalate hydrate of niobate; The surfactant is selected from at least one of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, dodecyl dimethyl benzyl ammonium chloride, and cocamidopropyl betaine; The nitrogen-containing heterocyclic ligand is selected from at least one of pyridin-2-ylurea, 4,4'-bipyridine, 2,5-thiophene dicarboxylic acid, 1,10-o-phenanthroline and 3-(1H-(1,2,3)triazol-4-yl)-benzonitrile; The first buffer solution and / or the second buffer solution are selected from at least one of sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution, hexamethylenetetramine-hydrochloric acid buffer solution and tris(hydroxymethyl)aminomethane hydrochloric acid buffer solution; The pH of the first buffer solution and / or the second buffer solution is 6.5 to 7.

5.

4. The preparation method according to claim 1, characterized in that, In step S2: The mass ratio of the niobium-based bimetallic complex, the pore-forming agent, and the deionized water is (8~12):1:(20~30). The pore-forming agent is selected from at least one of ammonium bicarbonate, polymethyl methacrylate, sodium chloride, and polyethylene glycol.

5. The preparation method according to claim 1, characterized in that, In step S3: The mass ratio of the porous niobium-based bimetallic carbonitride material, the binder, the dispersant, the conductive carbon material, and the reinforced phthalate coupling agent solution is 1:(0.2~1.5):(0.5~3):(4~8):(200~500). The mass ratio of the carbon-based electrode to the mixed slurry is 1:(25~50).

6. The preparation method according to claim 1 or 5, characterized in that, In step S3: The adhesive is selected from at least one of phenolic resin, acrylic resin, carboxymethyl cellulose, and polyvinyl alcohol; The dispersant is selected from at least one of sodium pyrophosphate, sodium hexametaphosphate, sulfonated polystyrene, trimethylstearamide chloride, and polyoxyethylene alkylphenol ether; The conductive carbon material is selected from at least one of graphene oxide, carbon nanotubes, graphite powder, and conductive carbon black. The volume fraction of the enhanced phthalate coupling agent solution is 2%~8%; The solute in the enhanced phthalate coupling agent solution is selected from at least one of bis(acetylacetonyl)isopropoxyethoxytitanate, neoalkoxytris(dioctylpyrophosphoryloxy)titanate acrylamide chelate, neoalkoxytris(dioctylphosphoryloxy)titanate and isopropyl dioleate oxy(dioctylphosphoryloxytitanate). The solvent in the enhanced phthalate coupling agent solution is selected from at least one of xylene, toluene, N,N-dimethylformamide and dichloromethane; The carbon-based electrode is selected from at least one of graphite felt, carbon paper, carbon cloth, and carbon felt.

7. The preparation method according to claim 1, characterized in that, The stirring reaction time of the first mixed solution and the second mixed solution in step S1 is 8~12h; The protective gas in step S2 is one of nitrogen, argon or ammonia, and the heat treatment temperature is 800~1000℃ for 2~6 h. The settling time in step S3 is 6~12h.

8. The preparation method according to claim 1, characterized in that, In step S4, the freeze-drying temperature is -50 to -20°C and the time is 6 to 12 hours; the active gas is either air or oxygen, and the heat treatment temperature is 350 to 500°C and the time is 1.5 to 4 hours.

9. A niobium-based complex-derived electrode, characterized in that, The niobium-based complex-derived electrode is prepared using the method described in any one of claims 1-8.

10. An application of a niobium-based complex-derived electrode, characterized in that, The niobium-based complex-derived electrode prepared by the preparation method according to any one of claims 1-8 or the niobium-based complex-derived electrode according to claim 9 is applied to an all-vanadium redox flow battery.

Images