A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology

Abstract

The application discloses a carbon-based electrode modification method of a flow battery based on a flame spray pyrolysis technology and belongs to the technical field of electrode material modification of a flow battery. The method comprises the following steps: pretreating a carbon-based electrode substrate; adjusting the type and molar ratio of metals, controlling precursor composition, and obtaining a uniform precursor solution with a target concentration of total metal ions; adopting a flame spray pyrolysis technology to deposit the precursor solution on the surface of the carbon-based electrode, so that the carbon fiber surface of the carbon-based electrode is uniformly covered with a coating of different metal oxides; heat treatment is performed to control the crystal type transformation of the metal oxides; the surface of the carbon-based electrode is uniformly covered with a composite metal oxide with different crystal structures; and then inorganic strong acid soaking and cleaning are performed, and after drying, a carbon-based modified electrode with a polymorphic cooperative structure is obtained. The application can controllably construct a composite oxide coating composed of specific crystal types on a complex three-dimensional carbon-based substrate, and by utilizing the interface effect and cooperation between crystal types, the catalytic activity and service life of the electrode are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of flow battery electrode material modification technology, specifically relating to a method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology and a carbon-based modified electrode for flow batteries. 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, zinc-based flow batteries, and iron-chromium flow batteries. However, the overall performance of flow batteries is largely limited by electrode materials. Although the widely used carbon felt electrodes possess good conductivity and chemical stability, their catalytic activity for the redox reactions of active materials in flow batteries is insufficient, requiring surface modification to improve electrochemical performance.

[0003] Loading metal oxide catalysts onto electrode surfaces is an effective way to enhance their activity. Recent research in materials science has shown that polymorphic synergy can significantly improve catalyst performance. Different crystal forms of metal oxides have different electronic structures, surface properties, and catalytic activities. When they coexist in the same material, interfacial effects, lattice matching, and charge transfer between crystal forms can produce synergistic catalytic effects, superior to the performance of a single crystal form. For example, composite materials with coexisting spinel and rock salt phases, or crystalline and amorphous phases, often exhibit higher catalytic activity and stability.

[0004] However, applying this "polymorphic synergy" concept to flow battery electrode modification—specifically, the controllable construction of composite oxide coatings with specific crystal structures on complex three-dimensional carbon felt substrates while achieving precise control over grain size and interfacial density—remains a pressing technical challenge. Furthermore, the surface properties of the carbon felt substrate are crucial to coating adhesion, and traditional cleaning methods struggle to introduce sufficient active functional groups onto the carbon fiber surface. Flame spray pyrolysis (FSP), as a continuous and scalable nanomaterial synthesis technology, can transform precursor solutions into functional nanoparticles within milliseconds, offering significant advantages such as simple process flow, high production efficiency, and controllable product crystal structure. Applying FSP technology to flow battery electrode modification holds promise for the efficient and controllable construction of polymorphic composite oxide coatings. Summary of the Invention

[0005] To address the problems of insufficient catalytic activity, difficulty in controllable construction of polymorphic synergistic structures, and weak adhesion between the substrate and coating in existing flow battery electrodes, this invention aims to provide a method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology. The method involves depositing a composite metal oxide coating with a polymorphic structure on the surface of a carbon-based electrode using flame spray pyrolysis technology. This modified electrode utilizes the interface effect, lattice matching, and electronic structure differences between different crystal forms to generate a polymorphic synergistic catalytic effect.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a method for modifying a carbon-based electrode for a flow battery based on flame spray pyrolysis technology, comprising the following steps:

[0008] Pretreatment of carbon-based electrode substrate: The carbon-based electrode substrate is cleaned and impurities are removed, then surface modification is carried out by chemical oxidation, and finally it is rinsed repeatedly with water and dried for later use.

[0009] Precursor solution preparation:

[0010] The metal catalyst precursor is dissolved in a mixed system of organic solvent, organic acid and water and stirred until completely dissolved. The type and molar ratio of the metal are adjusted to control the composition of the precursor and obtain a homogeneous precursor solution with the target concentration of total metal ions. When a single metal catalyst is used, an appropriate amount of amorphous phase inducer is added during the stirring process.

[0011] Flame spray pyrolysis deposition:

[0012] Flame spray pyrolysis technology is used to deposit a precursor solution onto the surface of a carbon-based electrode. By adjusting the deposition process parameters, the carbon fiber surface of the carbon-based electrode is uniformly covered with a coating of different metal oxides. Then, heat treatment is performed. By adjusting the heat treatment process parameters, the metal oxides are controlled to complete the crystal transformation. After heat treatment, the electrode is naturally cooled to room temperature, and the surface of the carbon-based electrode is uniformly covered with composite metal oxides with different crystal structures.

[0013] Post-processing:

[0014] The carbon-based electrode after flame spray pyrolysis deposition was immersed and cleaned in a dilute solution of strong inorganic acid, then repeatedly rinsed with water until neutral, and dried to obtain a carbon-based modified electrode with a polymorphic synergistic structure.

[0015] Furthermore, in the carbon-based electrode substrate pretreatment, the carbon-based electrode substrate is a polyacrylonitrile-based carbon felt or carbon paper;

[0016] The cleaning and impurity removal process involves sequentially ultrasonically cleaning the carbon-based electrode substrate in acetone, ethanol, and deionized water.

[0017] The processing parameters for the electrochemical oxidation method are as follows: using carbon felt as the working electrode, platinum sheet as the counter electrode, and saturated calomel electrode as the reference electrode, a constant potential of 1.0V-2.5V is applied in a 0.5M-2.0M sulfuric acid solution, and the processing time is 1min-10min.

[0018] Furthermore, in the preparation of the precursor solution, the metal catalyst precursor is one or more of the following: nitrates, acetates, and chlorides of cobalt, nickel, manganese, iron, cerium, zirconium, copper, and zinc.

[0019] The organic solvent is selected from one or more of methanol, ethanol, isopropanol, and ethylene glycol, and the organic acid is selected from one or more of citric acid, tartaric acid, oxalic acid, and ethylenediaminetetraacetic acid.

[0020] Furthermore, in the preparation of the precursor solution, the volume ratio of organic solvent to water is (1-9):(1-9), and the concentration of organic acid is 0.01M-0.2M;

[0021] The molar ratio between different metal precursors is (1-10):(1-10), and the target concentration of total metal ions in the precursor solution is 0.05M-0.5M;

[0022] The amorphous phase inducer is polyvinylpyrrolidone.

[0023] Furthermore, in flame spray pyrolysis deposition, adjusting the deposition process parameters includes adjusting the precursor feed rate to control the coating load, adjusting the dispersed oxygen flow rate to control the spray atomization effect, adjusting the flame temperature to control the crystal composition, and adjusting the deposition time to control the grain size.

[0024] Furthermore, the deposition parameters were adjusted to control the coating loading at 0.1 mg / cm³. 2 -2.0mg / cm 2 The precursor feed rate was 2 mL / min-10 mL / min, and the dispersed oxygen flow rate was 5 L / min-15 L / min. The flame temperature was controlled by adjusting the fuel gas flow rate, which was 3 L / min-8 L / min. The deposition time was 2 min-15 min, and the grain size was 5 nm-50 nm. The interfacial density between the grains and the substrate was 10 μm. -1 -100μm -1 .

[0025] Furthermore, in flame spray pyrolysis deposition, the heat treatment process parameters are: temperature 300℃-800℃, time 0.5h-3h, and atmosphere argon, nitrogen, or air.

[0026] Furthermore, in the post-treatment, the concentration of the dilute inorganic strong acid solution is 0.1M-1.0M, the inorganic strong acid is hydrochloric acid or sulfuric acid, and the soaking time is 10min-60min.

[0027] Furthermore, in post-processing, the polymorphic synergistic structure includes the coexistence of spinel phase and rock salt phase, the coexistence of spinel phase and fluorite phase, or the coexistence of crystalline phase and amorphous phase.

[0028] Secondly, the present invention provides a carbon-based modified electrode for flow batteries, which is modified by the above-mentioned carbon-based electrode modification method for flow batteries based on flame spray pyrolysis technology, and is used as a positive electrode and / or a negative electrode in flow batteries.

[0029] Advantages and effects of the present invention:

[0030] 1. This invention controllably constructs composite oxide coatings composed of specific crystal forms on complex three-dimensional carbon-based substrates, such as spinel-rock salt, spinel-fluorite, crystal-amorphous polymorphic composite structures, and significantly enhances electrode catalytic activity by utilizing the interfacial effect and synergistic effect between crystal forms.

[0031] 2. This invention can controllably adjust the relative content of different crystal form metal oxides in the coating, providing customized solutions for different catalytic needs.

[0032] 3. This invention achieves multi-dimensional and precise control over the electrode microstructure, controlling the grain size to 5nm-50nm and the interface density to 10μm. -1 -100μm -1 .

[0033] 4. This invention introduces abundant oxygen-containing functional groups and increases surface roughness on the carbon fiber surface, effectively improving the adhesion between the coating and the substrate and significantly extending the electrode cycle life.

[0034] 5. This invention effectively removes trace impurity phases, allowing for more complete exposure of active sites and significantly increasing the electrochemical active area. Attached Figure Description

[0035] Figure 1 This is a high-resolution transmission electron microscope image of the modified carbon-based electrode prepared by the flow battery carbon-based electrode modification method based on flame spray pyrolysis technology in Example 1. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0037] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0038] Carbon-based electrode substrate pretreatment: Polyacrylonitrile-based carbon felt or carbon paper is ultrasonically cleaned sequentially in acetone, ethanol and deionized water to remove surface impurities. Then, surface modification is performed by chemical oxidation. Using carbon felt as the working electrode, platinum sheet as the counter electrode and saturated calomel electrode as the reference electrode, a constant potential of 1.0V-2.5V is applied in 0.5M-2.0M sulfuric acid solution for 1min-10min. Finally, it is repeatedly rinsed with deionized water and dried under vacuum heating for later use.

[0039] Precursor solution preparation:

[0040] A metal catalyst precursor was dissolved in a mixture of organic solvent, organic acid, and water and stirred until completely dissolved. The metal catalyst precursor was one or more of the following: nitrates, acetates, and chlorides of cobalt, nickel, manganese, iron, cerium, zirconium, copper, and zinc. The organic solvent was selected from one or more of methanol, ethanol, isopropanol, and ethylene glycol, and the organic acid was selected from one or more of citric acid, tartaric acid, oxalic acid, and ethylenediaminetetraacetic acid. The volume ratio of organic solvent to water was (1-9):(1-9). The atomization and combustion characteristics were optimized by adjusting the organic solvent ratio. The organic acid concentration was 0.01M-0.2M. The organic acid complexation prevented the hydrolysis of metal ions and improved the solution stability. The reducing atmosphere generated by the decomposition of organic acid could regulate the valence state and crystal form of the metal oxide. The molar ratio between different metal precursors was adjusted to (1-10):(1-10) to obtain a homogeneous precursor solution with a total metal ion concentration of 0.05M-0.5M. The interface density between the grains and the substrate could be controlled to 10 μm by adjusting the precursor composition. -1 -100μm -1 .

[0041] Flame spray pyrolysis deposition:

[0042] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were adjusted as follows: precursor feed rate was 2 mL / min–10 mL / min to control the coating loading; oxygen flow rate was 5 L / min–15 L / min to control the spray atomization effect; flame temperature was adjusted by fuel gas flow rate, with higher flow rates resulting in higher flame temperatures, which is beneficial for the formation of thermodynamically stable crystalline phases; fuel gas flow rate was 3 L / min–8 L / min to control the crystal composition; deposition time was 2 min–15 min, with longer deposition times resulting in larger grain sizes; the grain size was controlled to be 5 nm–50 nm. The carbon fiber surface of the carbon-based electrode was uniformly coated with a coating of different metal oxides. The preferred composite metal oxides were Co3O4-NiO, Co3O4-Mn3O4, NiCo2O4-CeO2, or Co3O4-ZrO2, with a coating loading of 0.1 mg / cm³. 2 -2.0mg / cm 2Then, heat treatment is performed to control the metal oxide to complete the crystal transformation. The heat treatment process parameters are adjusted as follows: temperature is 300℃-800℃, time is 0.5h-3h, and atmosphere is argon, nitrogen or air. After heat treatment, the metal oxide is naturally cooled to room temperature, and the carbon-based electrode surface is uniformly covered with a composite metal oxide coating with different crystal structures.

[0043] Post-processing:

[0044] The carbon-based electrode after flame spray pyrolysis deposition is immersed and cleaned in 0.1M-1.0M dilute hydrochloric acid or dilute sulfuric acid solution for 10min-60min, then repeatedly rinsed with deionized water until neutral, and dried under vacuum to obtain a carbon-based modified electrode with a polymorphic synergistic structure. The polymorphic synergistic structure includes the coexistence of spinel phase and rock salt phase, the coexistence of spinel phase and fluorite phase, or the coexistence of crystalline phase and amorphous phase.

[0045] A carbon-based modified electrode for flow batteries is obtained by modifying the carbon-based electrode of flow batteries using the above-mentioned flame spray pyrolysis technology. It can be used as a positive electrode and / or negative electrode in various flow batteries such as vanadium redox flow batteries, zinc-based flow batteries, and iron-chromium flow batteries.

[0046] This invention creatively combines the concept of polymorphic synergy with flame spray pyrolysis technology for the modification of flow battery electrodes. Studies have shown that different crystalline metal oxides possess different electronic structures and surface properties: spinel phases (such as Co3O4 and NiCo2O4) exhibit good electronic conductivity and abundant redox sites; rock salt phases (such as NiO and CoO) have high ion diffusion coefficients; fluorite phases (such as CeO2 and ZrO2) are rich in oxygen vacancies, promoting oxygen migration and activation; and amorphous phases possess numerous unsaturated coordination sites and defect sites. When these oxides of different crystalline forms coexist in the same coating, electron redistribution and lattice mismatch strain occur at the interfaces between the crystal forms, resulting in electronic structures different from those of a single crystal form. This optimizes the adsorption energy for active material intermediates in the flow battery, enhancing catalytic activity.

[0047] Simultaneously, this invention employs an electrochemical oxidation method to pretreat the carbon felt substrate, introducing abundant oxygen-containing functional groups (such as carboxyl, hydroxyl, and carbonyl groups) onto the carbon fiber surface and increasing surface roughness, significantly enhancing the adhesion between the subsequent coating and the substrate, and improving the long-term stability of the electrode. An acidic organic-water mixture is used to prepare the precursor solution. The complexation effect of the organic acid prevents the hydrolysis of metal ions, improving solution stability. By adjusting the ratio of organic solvent to water, the surface tension, viscosity, and combustion characteristics of the solution can be optimized, providing a precise control method for the flame spray pyrolysis process. The organic acid decomposes during flame spray pyrolysis to generate a reducing atmosphere, which can further regulate the valence state and crystal form of the metal oxide. Flame spray pyrolysis technology can complete the rapid heating and quenching of the precursor within milliseconds, providing unique kinetic conditions for the formation of polymorphic structures. By precisely controlling the precursor composition, flame temperature, and deposition time, precise control over the crystal type, relative content, grain size, and interface density can be achieved. Finally, dilute acid-assisted cleaning removes trace impurity phases, further purifying the active sites, providing a complete technical platform for the design of "polymorphic synergistic" electrodes.

[0048] Example 1

[0049] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0050] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.8V was applied in 1.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0051] Precursor solution preparation:

[0052] Cobalt nitrate and nickel nitrate were weighed according to a Co:Ni molar ratio of 2:1 and dissolved in a mixed system consisting of ethanol, water and citric acid, with a volume ratio of ethanol to water of 1:1 and a citric acid concentration of 0.05 M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.2 M.

[0053] Flame spray pyrolysis deposition:

[0054] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate of 5 mL / min, dispersed oxygen flow rate of 8 L / min, methane fuel gas flow rate of 4 L / min, and deposition time of 8 min. A Co3O4-NiO coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 1.2 mg / cm³. 2 The grain size was 15 nm. The deposited electrode was then heat-treated in a tube furnace under an argon atmosphere, heated to 400 °C at a rate of 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly coated with a Co3O4-NiO coating consisting of both spinel and rock salt phases. The interfacial density between the grains and the substrate was 50 μm. -1 .

[0055] Post-processing:

[0056] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.5M dilute hydrochloric acid solution for 30 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of two crystal forms: spinel phase Co3O4 and rock salt phase NiO.

[0057] This embodiment 1 presents a modified carbon-based electrode obtained using a flow battery carbon-based electrode modification method based on flame spray pyrolysis technology. The electrode surface coating contains two crystal forms: spinel phase Co3O4 and rock salt phase NiO, with a mass ratio of approximately 70:30 and a lattice mismatch of approximately 3.2%. TEM testing showed... Figure 1 As shown, a clear crystal interface is visible.

[0058] The modified carbon-based electrode from Example 1 was used to assemble a single vanadium redox flow battery cell, with an effective cell area of ​​25 cm². 2 The Nafion 212 membrane was used, and the electrolyte was 50 mL of 1.5 mol / L electrolyte at both the positive and negative electrodes. 4+ / V 3+ + 3mol / L H2SO4, test temperature 25±1℃, electrolyte flow rate 40mL / min, charge cutoff voltage 1.65V, discharge cutoff voltage 0.8V, after 3 small current activations, at 200mA / cm 2 The energy efficiency was 82.3% when tested at current density.

[0059] Example 2

[0060] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0061] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.0V was applied in 2.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0062] Precursor solution preparation:

[0063] Cobalt nitrate and nickel nitrate were weighed according to a Co:Ni molar ratio of 1:1 and dissolved in a mixed system consisting of ethanol, water and citric acid, with a volume ratio of ethanol to water of 1:1 and a citric acid concentration of 0.05 M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.2 M.

[0064] Flame spray pyrolysis deposition:

[0065] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 5 mL / min, dispersed oxygen flow rate 8 L / min, methane fuel gas flow rate 4 L / min, and deposition time 8 min. A Co3O4-NiO coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 1.5 mg / cm³. 2 The grain size was 20 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 400 °C at a rate of 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a Co3O4-NiO coating in which spinel and rock salt phases coexist. The interfacial density between the grains and the substrate was 50 μm. -1 .

[0066] Post-processing:

[0067] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.5M dilute hydrochloric acid solution for 30 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of two crystal forms: spinel phase Co3O4 and rock salt phase NiO.

[0068] In Example 2, a modified carbon-based electrode was obtained using a flow battery carbon-based electrode modification method based on flame spray pyrolysis technology. The electrode surface coating contains two crystal forms: spinel phase Co3O4 and rock salt phase NiO, with a mass ratio of approximately 50:50 and a lattice mismatch of approximately 2.8%. TEM observation revealed a clear crystal interface.

[0069] The modified carbon-based electrode of Example 2 was used to assemble a single vanadium redox flow battery (same as Example 1 except for the modified electrode), at 200 mA / cm². 2 The energy efficiency was 83.1% when tested at current density.

[0070] Example 3

[0071] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0072] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.0V was applied in 0.5M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0073] Precursor solution preparation:

[0074] Cobalt nitrate and nickel nitrate were weighed according to a Co:Ni molar ratio of 1:2 and dissolved in a mixed system consisting of ethanol, water and citric acid, with a volume ratio of ethanol to water of 1:1 and a citric acid concentration of 0.05 M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.2 M.

[0075] Flame spray pyrolysis deposition:

[0076] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 5 mL / min, dispersed oxygen flow rate 8 L / min, methane fuel gas flow rate 4 L / min, and deposition time 8 min. A Co3O4-NiO coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 0.4 mg / cm³. 2 The grain size was 20 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 400 °C at a rate of 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a Co3O4-NiO coating in which spinel and rock salt phases coexist. The interfacial density between the grains and the substrate was 20 μm. -1 .

[0077] Post-processing:

[0078] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.5M dilute hydrochloric acid solution for 30 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of two crystal forms: spinel phase Co3O4 and rock salt phase NiO.

[0079] In Example 3, a modified carbon-based electrode was obtained using a flow battery carbon-based electrode modification method based on flame spray pyrolysis technology. The electrode surface coating contains two crystal forms: spinel phase Co3O4 and rock salt phase NiO, with a mass ratio of approximately 30:70 and a lattice mismatch of approximately 2.5%. TEM observation revealed a clear crystal interface.

[0080] The modified carbon-based electrode from Example 3 was used to assemble a single cell of an all-iron flow battery, with an effective cell area of ​​25 cm². 2 The Nafion 212 membrane was used, and the positive electrode electrolyte was 50 mL of 1 mol / L Fe. 3+ / Fe 2+ + 2 mol / L H2SO4, negative electrode electrolyte is 50 mL 1.0 mol / L Fe 2+ + 2mol / L H2SO4, test temperature 25±1℃, electrolyte flow rate 40mL / min, charge cutoff voltage 1.2V, discharge cutoff voltage 0.5V, after 3 small current activations, at 90mA / cm 2 The energy efficiency was 74.8% when tested at current density.

[0081] Example 4

[0082] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0083] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.8V was applied in 1.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0084] Precursor solution preparation:

[0085] Cobalt nitrate and cerium nitrate were weighed according to a Co:Ce molar ratio of 4:1 and dissolved in a mixed system consisting of ethanol, water and citric acid, with a volume ratio of ethanol to water of 1:1 and a citric acid concentration of 0.08 M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.2 M.

[0086] Flame spray pyrolysis deposition:

[0087] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 6 mL / min, dispersed oxygen flow rate 9 L / min, methane fuel gas flow rate 5 L / min, and deposition time 7 min. A Co3O4-CeO2 coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 0.1 mg / cm³. 2 The grain size was 5 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 450 °C at 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a Co3O4-CeO2 coating in which spinel and fluorite phases coexist. The interfacial density between the grains and the substrate was 20 μm. -1 .

[0088] Post-processing:

[0089] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.5M dilute hydrochloric acid solution for 30 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of two crystal forms: spinel phase Co3O4 and fluorite phase CeO2.

[0090] In Example 4, a modified carbon-based electrode for a flow battery was obtained using a flame spray pyrolysis technique. The electrode surface coating contains two crystal phases: spinel Co3O4 and fluorite CeO2, with a mass ratio of approximately 70:30 and a lattice mismatch of approximately 3.5%. TEM observation revealed a clear crystal interface.

[0091] The modified carbon-based electrode of Example 4 was used to assemble a single cell of an all-iron flow battery (same as Example 3 except for the modified electrode), at 200 mA / cm. 2 The energy efficiency was 84.2% when tested at current density.

[0092] Example 5

[0093] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0094] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.8V was applied in 1.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0095] Precursor solution preparation:

[0096] Nickel nitrate, cobalt nitrate, and cerium nitrate were weighed according to a Ni:Co:Ce molar ratio of 2:4:1 and dissolved in a mixed system of ethanol, water, and citric acid, with a volume ratio of ethanol to water of 1:1 and a citric acid concentration of 0.08 M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.25 M.

[0097] Flame spray pyrolysis deposition:

[0098] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 5 mL / min, dispersed oxygen flow rate 8 L / min, methane fuel gas flow rate 4 L / min, and deposition time 9 min. A NiCo₂O₄-CeO₂ coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 0.7 mg / cm³. 2 The grain size was 5 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 350 °C at 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a NiCo2O4-CeO2 coating in which spinel and fluorite phases coexist. The interfacial density between the grains and the substrate was 10 μm. -1 .

[0099] Post-processing:

[0100] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.5M dilute hydrochloric acid solution for 30 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of spinel phase NiCo2O4 and fluorite phase CeO2.

[0101] Example 5 presents a modified carbon-based electrode obtained using a flow battery carbon-based electrode modification method based on flame spray pyrolysis technology. The electrode surface coating contains two crystal forms: spinel phase NiCo2O4 and fluorite phase CeO2, with a mass ratio of approximately 70:30 and a lattice mismatch of approximately 2.8%. TEM observation reveals a clear crystal interface.

[0102] The modified carbon-based electrode from Example 5 was used to assemble a single zinc-bromine flow battery, with an effective cell area of ​​252 cm². 2 The Nafion 212 membrane was used, and the positive electrode electrolyte was 50 mL of 0.8 mol / L Br₂. - + 2mol / L ZnBr2, the negative electrode electrolyte is 50mL 0.8mol / L Zn 2+ + 2mol / L ZnBr2, test temperature 25±1℃, electrolyte flow rate 40mL / min, charge cutoff voltage 2.0V, discharge cutoff voltage 1.0V, after 3 small current activations, at 50mA / cm 2 The energy efficiency was 84.8% when tested at current density.

[0103] Example 6

[0104] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0105] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.8V was applied in 1.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0106] Precursor solution preparation:

[0107] Manganese nitrate, cobalt nitrate, and zirconium nitrate were weighed according to a Mn:Co:Zr molar ratio of 4:8:1.2 and dissolved in a mixed system of ethanol, water, and citric acid, with a volume ratio of ethanol to water of 1:1 and a citric acid concentration of 0.06 M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.2 M.

[0108] Flame spray pyrolysis deposition:

[0109] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 4 mL / min, dispersed oxygen flow rate 7 L / min, methane fuel gas flow rate 4 L / min, and deposition time 10 min. A uniform MnCo₂O₄-ZrO₂ coating was formed on the carbon fiber surface of the carbon-based electrode, with a coating loading of 0.4 mg / cm³. 2The grain size was 20 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 500 °C at a rate of 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a MnCo2O4-ZrO2 coating in which spinel and fluorite phases coexist. The interfacial density between the grains and the substrate was 10 μm. -1 .

[0110] Post-processing:

[0111] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.5M dilute hydrochloric acid solution for 30 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of spinel phase MnCo2O4 and fluorite phase ZrO2.

[0112] In Example 6, a modified carbon-based electrode for a flow battery was obtained using a flame spray pyrolysis technique. The electrode surface coating contains two crystal forms: spinel phase MnCo2O4 and fluorite phase ZrO2, with a mass ratio of approximately 70:30 and a lattice mismatch of approximately 3%. TEM observation revealed a clear crystal interface.

[0113] The modified carbon-based electrode of Example 6 was used to assemble a single vanadium redox flow battery (same as Example 1 except for the modified electrode), at 250 mA / cm². 2 The energy efficiency was 83.7% when tested at current density.

[0114] Example 7

[0115] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0116] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.8V was applied in 1.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0117] Precursor solution preparation:

[0118] Weigh out cobalt nitrate and dissolve it in a mixture of ethanol, water and citric acid, with a volume ratio of ethanol to water of 1:1 and a citric acid concentration of 0.05 M. Add a small amount of polyvinylpyrrolidone (PVP) as an amorphous phase inducer and stir magnetically for 2 hours until completely dissolved to obtain a homogeneous precursor solution with a total metal ion concentration of 0.15 M.

[0119] Flame spray pyrolysis deposition:

[0120] Flame spray pyrolysis technology was used to deposit the precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate of 3 mL / min, dispersed oxygen flow rate of 6 L / min, methane fuel gas flow rate of 3 L / min, and deposition time of 6 min. Co3O was uniformly coated on the carbon fiber surface of the carbon-based electrode. 4- CoO x The coating has a coating loading of 1.7 mg / cm³. 2 The grain size was 50 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 300 °C at a rate of 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a spinel phase and a coexisting amorphous Co3O. 4- CoO x Coating; interfacial density between grains and substrate is 100 μm -1 .

[0121] Post-processing:

[0122] The carbon-based electrode, after flame spray pyrolysis deposition, was immersed in 0.5M dilute hydrochloric acid solution for 30 min, then repeatedly rinsed with deionized water until neutral, and finally dried in a vacuum drying oven at 60℃ for 12 h to obtain a spinel phase Co3O4 and amorphous CoO. x A carbon-based modified electrode with a synergistic structure of two crystal forms.

[0123] In Example 7, the modified carbon-based electrode obtained by the flow battery carbon-based electrode modification method based on flame spray pyrolysis technology has a coating on the electrode surface containing spinel phase Co3O4 and amorphous CoO. x Two crystal forms were observed, with a two-phase mass ratio of approximately 65:35 and a lattice mismatch of approximately 2.7%. TEM observation revealed clear crystal interfaces.

[0124] The modified carbon-based electrode of Example 7 was used to assemble a single vanadium redox flow battery (same as Example 1 except for the modified electrode), at 200 mA / cm². 2 The energy efficiency was 82.9% when tested at current density.

[0125] Example 8

[0126] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0127] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.8V was applied in 1.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0128] Precursor solution preparation:

[0129] Cobalt nitrate and nickel nitrate were weighed according to a Co:Ni molar ratio of 2:1 and dissolved in a mixed system consisting of ethanol, water and citric acid, with a volume ratio of ethanol to water of 1:1 and a citric acid concentration of 0.05 M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.2 M.

[0130] Flame spray pyrolysis deposition:

[0131] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 2 mL / min, dispersed oxygen flow rate 8 L / min, methane fuel gas flow rate 4 L / min, and deposition time 2 min. A Co3O4-NiO coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 0.6 g / cm³. 2 The grain size was 25 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 400 °C at a rate of 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a Co3O4-NiO coating in which spinel and rock salt phases coexist. The interfacial density between the grains and the substrate was 100 μm. -1 .

[0132] Post-processing:

[0133] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.3M dilute hydrochloric acid solution for 30 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of two crystal forms: spinel phase Co3O4 and rock salt phase NiO.

[0134] This embodiment 8 presents a modified carbon-based electrode obtained by a flow battery carbon-based electrode modification method based on flame spray pyrolysis technology. The electrode surface coating contains two crystal forms: spinel phase Co3O4 and rock salt phase NiO, with a mass ratio of approximately 65:35 and a lattice mismatch of approximately 2.5%. TEM observation reveals a clear crystal interface.

[0135] The modified carbon-based electrode of Example 8 was used to assemble a single cell of an all-iron flow battery (same as Example 3 except for the modified electrode), at 60 mA / cm 2 The energy efficiency was 84.1% when tested at current density.

[0136] Example 9

[0137] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0138] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.8V was applied in 1.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0139] Precursor solution preparation:

[0140] Cobalt nitrate and nickel nitrate were weighed according to a Co:Ni molar ratio of 2:1 and dissolved in a mixed system consisting of ethanol, water and citric acid, with a volume ratio of ethanol to water of 4:9 and a citric acid concentration of 0.05M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.2M.

[0141] Flame spray pyrolysis deposition:

[0142] Flame spray pyrolysis technology was used to deposit the precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate of 10 mL / min, dispersed oxygen flow rate of 8 L / min, methane fuel gas flow rate of 4 L / min, and deposition time of 2 min. A Co3O4-NiO coating was uniformly coated on the carbon fiber surface of the carbon-based electrode, with a coating loading of 2 g / cm³. 2 The grain size was 25 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 400 °C at a rate of 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a Co3O4-NiO coating in which spinel and rock salt phases coexist. The interfacial density between the grains and the substrate was 100 μm. -1 .

[0143] Post-processing:

[0144] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.5M dilute hydrochloric acid solution for 15 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of two crystal forms: spinel phase Co3O4 and rock salt phase NiO.

[0145] In Example 9, a modified carbon-based electrode was obtained using a flow battery carbon-based electrode modification method based on flame spray pyrolysis technology. The electrode surface coating contains two crystal forms: spinel phase Co3O4 and rock salt phase NiO, with a mass ratio of approximately 50:50 and a lattice mismatch of approximately 3%. TEM observation revealed a clear crystal interface.

[0146] The modified carbon-based electrode of Example 9 was used to assemble a single cell of an all-iron flow battery (same as Example 3 except for the modified electrode), at 200 mA / cm 2 The energy efficiency was 76.1% when tested at current density.

[0147] Example 10

[0148] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0149] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.8V was applied in 1.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0150] Precursor solution preparation:

[0151] Cobalt nitrate and nickel nitrate were weighed according to a Co:Ni molar ratio of 3:2 and dissolved in a mixed system consisting of ethanol, water and citric acid, with a volume ratio of ethanol to water of 1:1 and a citric acid concentration of 0.05 M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.22 M.

[0152] Flame spray pyrolysis deposition:

[0153] Flame spray pyrolysis technology was used to deposit the precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate of 5 mL / min, dispersed oxygen flow rate of 8 L / min, methane fuel gas flow rate of 4 L / min, and deposition time of 8 min. A NiCo2O4-NiO coating was uniformly coated on the carbon fiber surface of the carbon-based electrode, with a coating loading of 2 g / cm³. 2The grain size was 45 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 400 °C at 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a NiCo2O4-NiO coating in which spinel and rock salt phases coexist. The interfacial density between the grains and the substrate was 100 μm. -1 .

[0154] Post-processing:

[0155] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.5M dilute hydrochloric acid solution for 30 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of spinel phase NiCo2O4 and rock salt phase NiO.

[0156] In Example 10, a modified carbon-based electrode for a flow battery was obtained using a flame spray pyrolysis technique. The electrode surface coating contains two crystal forms: spinel phase Co3O4 and rock salt phase NiO, with a mass ratio of approximately 50:50 and a lattice mismatch of approximately 2.8%. TEM observation revealed a clear crystal interface.

[0157] The modified carbon-based electrode of Example 10 was used to assemble a single cell of an all-iron flow battery (same as Example 3 except for the modified electrode), at 200 mA / cm 2 The energy efficiency was 83.2% when tested at current density.

[0158] Example 11

[0159] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0160] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon felt was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. The carbon felt was used as the working electrode, the platinum sheet as the counter electrode and the saturated calomel electrode as the reference electrode. A constant potential of 1.8V was applied in 1.0M sulfuric acid solution for 5min. Finally, it was rinsed repeatedly with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0161] Precursor solution preparation:

[0162] Cobalt nitrate and nickel nitrate were weighed according to a Co:Ni molar ratio of 2:1 and dissolved in a mixed system consisting of ethanol, water and citric acid, with a volume ratio of ethanol to water of 1:9 and a citric acid concentration of 0.05M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.2M.

[0163] Flame spray pyrolysis deposition:

[0164] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 5 mL / min, dispersed oxygen flow rate 8 L / min, methane fuel gas flow rate 4 L / min, and deposition time 10 min. A Co3O4-NiO coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 0.9 g / cm³. 2 The grain size was 35 nm. The deposited electrode was then placed in a tube furnace for heat treatment. Under an argon atmosphere, the temperature was increased to 400 °C at a rate of 5 °C / min, held for 1 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a Co3O4-NiO coating in which spinel and rock salt phases coexist. The interfacial density between the grains and the substrate was 150 μm. -1 .

[0165] Post-processing:

[0166] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.3M dilute hydrochloric acid solution for 20 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of two crystal forms: spinel phase Co3O4 and rock salt phase NiO.

[0167] In Example 11, a modified carbon-based electrode for a flow battery was obtained using a flame spray pyrolysis technique. The electrode surface coating contains two crystal forms: spinel phase Co3O4 and rock salt phase NiO, with a mass ratio of approximately 50:50 and a lattice mismatch of approximately 3%. TEM observation revealed a clear crystal interface.

[0168] The modified carbon-based electrode of Example 11 was used to assemble a single cell of an all-iron flow battery (same as Example 3 except for the modified electrode), at 200 mA / cm 2 The energy efficiency was 82.2% when tested at current density.

[0169] Example 12

[0170] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0171] Carbon-based electrode substrate pretreatment: Polyacrylonitrile-based carbon paper was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then, surface modification was carried out by chemical oxidation. Using carbon felt as the working electrode, platinum sheet as the counter electrode and saturated calomel electrode as the reference electrode, a constant potential of 2.5V was applied in 1.0M sulfuric acid solution for 1min, and finally, it was repeatedly rinsed with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0172] Precursor solution preparation:

[0173] Ferric nitrate and copper nitrate were weighed according to a Fe:Cu molar ratio of 10:1 and dissolved in a mixed system consisting of methanol, water, and tartaric acid. The volume ratio of methanol to water was 9:1, and the concentration of tartaric acid was 0.05M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.05M.

[0174] Flame spray pyrolysis deposition:

[0175] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 2 mL / min, dispersed oxygen flow rate 15 L / min, methane fuel gas flow rate 3 L / min, and deposition time 2 min. A Fe3O4-CuO coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 0.4 mg / cm³. 2 The grain size was 20 nm. The deposited electrode was then heat-treated in a tube furnace under air atmosphere, heated to 300 °C at a rate of 5 °C / min, held for 0.5 h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly coated with a Fe3O4-CuO coating consisting of both spinel and rock salt phases. The interfacial density between the grains and the substrate was 50 μm. -1 .

[0176] Post-processing:

[0177] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.1M dilute sulfuric acid solution for 10 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of two crystal forms: spinel phase Fe3O4 and rock salt phase CuO.

[0178] In Example 12, a modified carbon-based electrode for a flow battery was obtained using a flame spray pyrolysis technique. The electrode surface coating contains two crystal forms: spinel phase Fe3O4 and rock salt phase CuO, with a mass ratio of approximately 70:30 and a lattice mismatch of approximately 3.1%. TEM observation revealed a clear crystal interface.

[0179] The modified carbon-based electrode of Example 12 was used to assemble a single vanadium redox flow battery (same as Example 1 except for the modified electrode), at 200 mA / cm². 2 The energy efficiency was 76.2% when tested at current density.

[0180] Example 13

[0181] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0182] Pretreatment of carbon-based electrode substrate: Polyacrylonitrile-based carbon paper was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then the surface was modified by chemical oxidation. Using carbon felt as working electrode, platinum sheet as counter electrode and saturated calomel electrode as reference electrode, a constant potential of 2.5V was applied in 1.0M sulfuric acid solution for 10min. Finally, it was repeatedly rinsed with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0183] Precursor solution preparation:

[0184] Ferric nitrate and zinc nitrate were weighed according to a Fe:Zn molar ratio of 1:10 and dissolved in a mixed system consisting of ethylene glycol, water, tartaric acid, and oxalic acid. The volume ratio of ethylene glycol to water was 9:5, and the concentrations of tartaric acid and oxalic acid were 0.05M and 0.01M, respectively. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.05M.

[0185] Flame spray pyrolysis deposition:

[0186] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 2 mL / min, dispersed oxygen flow rate 5 L / min, methane fuel gas flow rate 8 L / min, deposition time 15 min, and grain size 45 nm. A Fe3O4-ZnO coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 0.3 mg / cm³. 2 The deposited electrode was then placed in a tube furnace for heat treatment. Under a nitrogen atmosphere, the temperature was increased to 800℃ at a rate of 5℃ / min, held for 3 hours, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a Fe3O4-ZnO coating in which spinel and rock salt phases coexisted. The interfacial density between the grains and the substrate was 10 μm. -1 .

[0187] Post-processing:

[0188] The carbon-based electrode after flame spray pyrolysis deposition was immersed in a 1.0M dilute sulfuric acid solution for 60 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of spinel phase Fe3O4 and rock salt phase ZnO.

[0189] In Example 13, a modified carbon-based electrode was obtained using a flow battery carbon-based electrode modification method based on flame spray pyrolysis technology. The electrode surface coating contains two crystal forms: spinel phase Fe3O4 and rock salt phase ZnO, with a mass ratio of approximately 50:50 and a lattice mismatch of approximately 3.4%. TEM observation revealed a clear crystal interface.

[0190] The modified carbon-based electrode of Example 13 was used to assemble a single vanadium redox flow battery (same as Example 1 except for the modified electrode), at 180 mA / cm 2 The energy efficiency was 83.5% when tested at current density.

[0191] Example 14

[0192] A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology includes the following steps:

[0193] Carbon-based electrode substrate pretreatment: Polyacrylonitrile-based carbon paper was cut into 10cm×10cm pieces and ultrasonically cleaned in acetone, ethanol and deionized water for 30min in sequence; then, surface modification was carried out by chemical oxidation. Using carbon felt as the working electrode, platinum sheet as the counter electrode and saturated calomel electrode as the reference electrode, a constant potential of 2.5V was applied in 1.0M sulfuric acid solution for 1min, and finally, it was repeatedly rinsed with deionized water and dried in a vacuum drying oven at 80°C for 12h for later use.

[0194] Precursor solution preparation:

[0195] Ferric nitrate and copper nitrate were weighed according to a Fe:Cu molar ratio of 10:1 and dissolved in a mixed system consisting of isopropanol, water, and ethylenediaminetetraacetic acid (EDTA). The volume ratio of isopropanol to water was 1:5, and the concentration of EDTA was 0.2 M. The mixture was magnetically stirred for 2 hours until completely dissolved, resulting in a homogeneous precursor solution with a total metal ion concentration of 0.5 M.

[0196] Flame spray pyrolysis deposition:

[0197] Flame spray pyrolysis technology was used to deposit a precursor solution onto the surface of a carbon-based electrode. The deposition process parameters were set as follows: precursor feed rate 10 mL / min, dispersed oxygen flow rate 5 L / min, methane fuel gas flow rate 8 L / min, deposition time 15 min, and grain size 50 nm. A Fe3O4-CuO coating was uniformly applied to the carbon fiber surface of the carbon-based electrode, with a coating loading of 1.8 mg / cm³. 2 The deposited electrode was then placed in a tube furnace for heat treatment. Under a nitrogen atmosphere, the temperature was increased to 800℃ at a rate of 5℃ / min, held for 0.5h, and then naturally cooled to room temperature. The carbon-based electrode surface was uniformly covered with a Fe3O4-CuO coating in which spinel and rock salt phases coexisted; the interfacial density between the grains and the substrate was 100μm. -1 .

[0198] Post-processing:

[0199] The carbon-based electrode after flame spray pyrolysis deposition was immersed in 0.5M dilute hydrochloric acid solution for 30 min, then rinsed repeatedly with deionized water until neutral, and then dried in a vacuum drying oven at 60℃ for 12 h to obtain a carbon-based modified electrode containing a synergistic structure of two crystal forms: spinel phase Fe3O4 and rock salt phase CuO.

[0200] In Example 14, a modified carbon-based electrode for a flow battery was obtained using a flame spray pyrolysis technique. The electrode surface coating contains two crystal forms: spinel phase Fe3O4 and rock salt phase CuO, with a mass ratio of approximately 70:30 and a lattice mismatch of approximately 2.8%. TEM observation revealed a clear crystal interface.

[0201] The modified carbon-based electrode of Example 14 was used to assemble a single vanadium redox flow battery (same as Example 1 except for the modified electrode), at 200 mA / cm². 2 The energy efficiency was 80.7% when tested at current density.

[0202] As demonstrated by the above embodiments, the flame spray pyrolysis technology of this invention, combined with electrochemical oxidation pretreatment and an acidic organic-water mixed system precursor solution, enables the successful construction of a composite oxide with a polymorphic synergistic structure on the surface of a carbon-based electrode through a simple and controllable deposition process. By adjusting the precursor molar ratio, the relative content of different crystal forms can be precisely controlled. The introduction of the acidic organic-water mixed system utilizes organic acid complexation to prevent metal ion hydrolysis and regulate the valence state of the metal oxide. Dilute acid-assisted cleaning effectively removes trace impurities and purifies active sites, achieving multi-dimensional precise control of the electrode's microstructure. The prepared modified electrode exhibits polymorphic interface effects and synergistic effects that optimize the electronic structure of the catalyst, significantly enhancing the catalytic activity for the redox reactions of active materials in flow batteries. Through its inherent polymorphic synergistic engineering design, this electrode effectively coordinates the multiple requirements of flow battery electrodes for high catalytic activity, rapid electron conduction, and stable cycle life, providing a key electrode material solution for developing next-generation high-performance, high-stability flow batteries.

Claims

1. A method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology, characterized in that, The steps include the following: Pretreatment of carbon-based electrode substrate: The carbon-based electrode substrate is cleaned and impurities are removed, then surface modification is carried out by chemical oxidation, and finally it is rinsed repeatedly with water and dried for later use. Precursor solution preparation: The metal catalyst precursor was dissolved in a mixed system of organic solvent, organic acid and water and stirred until completely dissolved. The types and molar ratios of the metals were adjusted to control the composition of the precursor and obtain a homogeneous precursor solution with the target total metal ion concentration. When using a single metal catalyst, an appropriate amount of amorphous phase inducer is added during the stirring process; Flame spray pyrolysis deposition: Flame spray pyrolysis technology is used to deposit a precursor solution onto the surface of a carbon-based electrode. By adjusting the deposition process parameters, the carbon fiber surface of the carbon-based electrode is uniformly covered with a coating of different metal oxides. Then, heat treatment is performed. By adjusting the heat treatment process parameters, the metal oxides are controlled to complete the crystal transformation. After heat treatment, the electrode is naturally cooled to room temperature, and the surface of the carbon-based electrode is uniformly covered with composite metal oxides with different crystal structures. Post-processing: The carbon-based electrode after flame spray pyrolysis deposition was immersed and cleaned in a dilute solution of strong inorganic acid, then repeatedly rinsed with water until neutral, and dried to obtain a carbon-based modified electrode with a polymorphic synergistic structure.

2. The method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology as described in claim 1, characterized in that, In the pretreatment of carbon-based electrode substrates, the carbon-based electrode substrate is a polyacrylonitrile-based carbon felt or carbon paper; The cleaning and impurity removal process involves sequentially ultrasonically cleaning the carbon-based electrode substrate in acetone, ethanol, and deionized water. The processing parameters for the electrochemical oxidation method are as follows: using carbon felt as the working electrode, platinum sheet as the counter electrode, and saturated calomel electrode as the reference electrode, a constant potential of 1.0V-2.5V is applied in a 0.5M-2.0M sulfuric acid solution, and the processing time is 1min-10min.

3. The method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology as described in claim 1, characterized in that, In the preparation of the precursor solution, the metal catalyst precursor is one or more of the following: nitrates, acetates, and chlorides of cobalt, nickel, manganese, iron, cerium, zirconium, copper, and zinc. The organic solvent is selected from one or more of methanol, ethanol, isopropanol, and ethylene glycol, and the organic acid is selected from one or more of citric acid, tartaric acid, oxalic acid, and ethylenediaminetetraacetic acid.

4. The method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology as described in claim 1, characterized in that, In the preparation of the precursor solution, the volume ratio of organic solvent to water is (1-9):(1-9), and the concentration of organic acid is 0.01M-0.2M; The molar ratio between different metal precursors is (1-10):(1-10), and the target concentration of total metal ions in the precursor solution is 0.05M-0.5M; The amorphous phase inducer is polyvinylpyrrolidone.

5. The method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology as described in claim 1, characterized in that, In flame spray pyrolysis deposition, adjusting deposition process parameters includes adjusting the precursor feed rate to control the coating load, adjusting the dispersed oxygen flow rate to control the spray atomization effect, adjusting the flame temperature to control the crystal composition, and adjusting the deposition time to control the grain size.

6. The method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology as described in claim 5, characterized in that, The deposition parameters were adjusted to control the coating loading at 0.1 mg / cm³. 2 -2.0mg / cm 2 The precursor feed rate was 2 mL / min-10 mL / min, and the dispersed oxygen flow rate was 5 L / min-15 L / min. The flame temperature was controlled by adjusting the fuel gas flow rate, which was 3 L / min-8 L / min. The deposition time was 2 min-15 min, and the grain size was 5 nm-50 nm. The interfacial density between the grains and the substrate was 10 μm. -1 -100μm -1 .

7. The method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology as described in claim 1, characterized in that, In flame spray pyrolysis deposition, the heat treatment process parameters are: temperature 300℃-800℃, time 0.5h-3h, and atmosphere argon, nitrogen, or air.

8. The method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology as described in claim 1, characterized in that, In the post-treatment, the concentration of the dilute inorganic strong acid solution is 0.1M-1.0M, the inorganic strong acid is hydrochloric acid or sulfuric acid, and the soaking time is 10min-60min.

9. The method for modifying carbon-based electrodes for flow batteries based on flame spray pyrolysis technology as described in claim 1, characterized in that, In the process, the polymorphic synergistic structure includes the coexistence of spinel phase and rock salt phase, the coexistence of spinel phase and fluorite phase, or the coexistence of crystalline phase and amorphous phase.

10. A carbon-based modified electrode for a flow battery, characterized in that, The carbon-based electrode of the flow battery is modified using the flame spray pyrolysis technology described in any one of claims 1-9, and is used as a positive electrode and / or negative electrode in the flow battery.

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