Composite electrode, preparation method thereof and all-vanadium redox flow battery

Abstract

The invention belongs to the field of flow batteries, and particularly relates to a composite electrode, a preparation method thereof and an all-vanadium flow battery. The composite electrode comprises an electrode base material, and first core-shell structure particles and second core-shell structure particles which are positioned on the surface of the electrode base material, each first core-shell structure particle comprises a first metal particle core and a first carbon quantum dot shell layer coating the first metal particle core; the first metal particle core is a metal bismuth particle; the second core-shell structure shell layer comprises a second metal particle core and a second carbon quantum dot shell layer coating the second metal particle core; and the second metal particle core is a metal tin particle, a metal antimony particle, a metal copper particle, a metal iron particle, a metal cobalt particle or a metal nickel particle. The composite electrode provided by the invention can effectively improve the efficiency and stability of the all-vanadium redox flow battery.

Description

Technical Field

[0001] The present invention belongs to the field of liquid flow batteries, and in particular relates to a composite electrode, a preparation method thereof and an all-vanadium liquid flow battery. Background Art

[0002] Vanadium redox flow batteries (VRFBs) have attracted considerable attention as energy storage systems due to their long lifespan, safety, environmental friendliness, and scalability. Electrodes are core components in VRFBs, and their performance directly determines the overall efficiency of the battery. Carbon-based electrode materials (such as graphite felt, carbon felt, and carbon cloth) are characterized by their well-developed three-dimensional network structure, good electrical conductivity, excellent chemical stability, and high cost-effectiveness. However, they also face significant drawbacks, such as solid-liquid interface incompatibility and a limited number of active sites.

[0003] To overcome the inherent problems of carbon-based electrodes, researchers are working to increase the specific surface area of ​​the material through intrinsic treatment or the introduction of catalysts, thereby improving the material's hydrophilicity and catalytic efficiency. While intrinsic treatment can improve the performance of carbon-based electrodes by increasing the specific surface area and oxygen-containing functional groups, it has limitations. The increase in the number of active sites and specific surface area is limited, and it cannot meet the high-power operation requirements of VRFBs. The introduction of catalysts also carries the risk of catalyst shedding or slow oxidation corrosion during long-term operation, negatively impacting the stability of VRFBs.

[0004] Therefore, there is an urgent need to develop an electrode material that can effectively improve the efficiency and stability of all-vanadium redox flow batteries. Summary of the Invention

[0005] To address the problems of the prior art, the present invention provides a composite electrode, a preparation method thereof, and an all-vanadium redox flow battery. The composite electrode material of the present invention can significantly improve the initial performance and long-term cycling stability of an all-vanadium redox flow battery.

[0006] The present invention provides a composite electrode, which includes an electrode substrate and first core-shell structure particles and second core-shell structure particles located on the surface of the electrode substrate; the first core-shell structure particles include a first metal particle core and a first carbon quantum dot shell layer covering the first metal particle core; the first metal particle core is a metal bismuth particle; the second core-shell structure particles include a second metal particle core and a second carbon quantum dot shell layer covering the second metal particle core; the second metal particle core is a metal tin particle, a metal antimony particle, a metal copper particle, a metal iron particle, a metal cobalt particle or a metal nickel particle.

[0007] In one or more embodiments, the electrode substrate is a carbon-based material selected from one or more of carbon felt, graphite felt, carbon cloth, graphite cloth and carbon paper.

[0008] In one or more embodiments, the particle size of the first core-shell structured particles is 25-65 nm.

[0009] In one or more embodiments, the particle size of the second core-shell structured particles is 25-65 nm.

[0010] In one or more embodiments, the particle size of the first metal particle core is 5 to 15 nm.

[0011] In one or more embodiments, the particle size of the second metal particle core is 5 to 15 nm.

[0012] In one or more embodiments, the thickness of the first carbon quantum dot shell layer is 20-50 nm.

[0013] In one or more embodiments, the thickness of the second carbon quantum dot shell layer is 20-50 nm.

[0014] In one or more embodiments, polar functional groups exist on the surface of the first carbon quantum dot shell layer and the surface of the second carbon quantum dot shell layer, and the polar functional groups include sulfonic acid groups.

[0015] In one or more embodiments, the polar functional group further includes one or both of a carboxyl group and an amino group.

[0016] In one or more embodiments, the total loading amount of the first metal particle core and the second metal particle core on the electrode substrate is 0.8-3.0 mg / cm 2 .

[0017] In one or more embodiments, the mass ratio of the first metal particle core to the second metal particle core is (0.8~1):1.

[0018] The present invention provides a method for preparing the composite electrode of the present invention, comprising the following steps: (1) placing an electrode substrate in a mixed metal solution, electrochemically depositing metal on the surface of the electrode substrate, and washing the substrate to obtain an electrode material precursor loaded with a first metal particle core and a second metal particle core; the mixed metal solution comprises a first metal compound and a second metal compound, the first metal is bismuth, and the second metal is tin, antimony, copper, iron, cobalt, or nickel; (2) placing the electrode material precursor in a carbon quantum dot precursor liquid to carry out a hydrothermal reaction, and after the hydrothermal reaction is completed, washing and drying to obtain an electrode material intermediate; the carbon quantum dot precursor liquid comprises an amine source, a first carbon source, a second carbon source, a surfactant and a solvent, wherein the first carbon source contains sulfur and the second carbon source does not contain sulfur; (3) Annealing the electrode material intermediate to obtain the composite electrode.

[0019] In one or more embodiments, in step (1), the concentration of the first metal compound in the mixed metal solution is 0.005-0.020 mol / L.

[0020] In one or more embodiments, in step (1), the concentration of the second metal compound in the mixed metal solution is 0.010-0.020 mol / L.

[0021] In one or more embodiments, in step (1), the first metal compound is selected from one or more of bismuth chloride, bismuth oxide, bismuth nitrate and bismuth sulfate.

[0022] In one or more embodiments, in step (1), the second metal compound is selected from one or more of a chloride, an oxide, a nitrate and a sulfate of the second metal.

[0023] In one or more embodiments, in step (1), the mixed metal solution further comprises sulfuric acid; and the concentration of sulfuric acid in the mixed metal solution is 3.0-5.0 mol / L.

[0024] In one or more embodiments, in step (1), the solvent in the mixed metal solution is water.

[0025] In one or more embodiments, in step (1), the electrochemical method is a constant potential method.

[0026] In one or more embodiments, in step (1), the deposition time is 5 to 30 minutes.

[0027] In one or more embodiments, in step (1), during the deposition process, the stirring speed is 200-500 rpm.

[0028] In one or more embodiments, the constant potential method adopts a three-electrode working system, the working electrode is the electrode substrate, the reference electrode is a saturated calomel electrode, the counter electrode is a graphite electrode, and the voltage relative to the saturated calomel electrode is 0V~-0.8V.

[0029] In one or more embodiments, in step (2), the amine source is selected from one or more of ethylenediamine, p-phenylenediamine, o-phenylenediamine and urea.

[0030] In one or more embodiments, in step (2), the first carbon source is sodium terephthalate and / or p-aminobenzenesulfonic acid.

[0031] In one or more embodiments, in step (2), the second carbon source is citric acid and / or glucose.

[0032] In one or more embodiments, in step (2), the surfactant is selected from one or more of polyvinyl pyrrolidone, polyetherimide, and cetyltrimethylammonium bromide.

[0033] In one or more embodiments, in step (2), the mass ratio of the amine source, the first carbon source, and the second carbon source is (0.1-0.8):(0.1-0.8):1.

[0034] In one or more embodiments, in step (2), the content of the amine source in the carbon quantum dot precursor liquid is 4.0-8.5 wt%.

[0035] In one or more embodiments, in step (2), the content of the surfactant in the carbon quantum dot precursor liquid is 0.05-0.2 wt %.

[0036] In one or more embodiments, in step (2), the temperature of the hydrothermal reaction is 160-220°C.

[0037] In one or more embodiments, in step (2), the hydrothermal reaction time is 6 to 12 hours.

[0038] In one or more embodiments, in step (2), the washing is performed 3 to 5 times.

[0039] In one or more embodiments, in step (2), the drying temperature is 60-80°C.

[0040] In one or more embodiments, in step (2), the drying time is 6 to 12 hours.

[0041] In one or more embodiments, in step (3), the temperature of the annealing treatment is 200-400°C.

[0042] In one or more embodiments, in step (3), the annealing treatment time is 1 to 3 hours.

[0043] In one or more embodiments, in step (3), annealing is performed in a mixed atmosphere of a protective gas and hydrogen.

[0044] The present invention provides an all-vanadium redox flow battery comprising the composite electrode of the present invention.

[0045] The present invention achieves the following beneficial effects: The composite electrode material of the present invention selects two metal particle cores as catalytic active centers. Compared with a single metal particle core, it has higher catalytic activity, better reaction selectivity, and stronger resistance to deactivation, which can greatly accelerate the efficiency of the redox reaction of vanadium ions. The carbon quantum dot shell has a high specific surface area and rich functional groups, which can improve the hydrophilicity of the electrode surface, increase the adsorption of vanadium ions on the electrode, and reduce interfacial impedance. In addition, the carbon quantum dot shell forms coordination bonds with the metal particle core through surface functional groups, which can not only protect the metal particle core from corrosion in strong acidic electrolytes, but also prevent the metal particle core from falling off during the cycle by utilizing steric hindrance effects. Using the composite electrode material of the present invention can significantly improve the initial performance and long-term cycling stability of all-vanadium redox flow batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the microstructure of composite electrodes prepared according to some embodiments of the present invention. DETAILED DESCRIPTION

[0047] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0048] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0049] Herein, “comprising,” “including,” “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of,” for example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to have been disclosed herein.

[0050] Throughout this document, all features, such as values, amounts, contents, and concentrations, specified in numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values ​​within those ranges (including integers and fractions).

[0051] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0052] Herein, when describing embodiments or examples, it should be understood that they are not intended to limit the present invention to these embodiments or examples. On the contrary, all alternatives, modifications and equivalents of the methods and materials described herein are encompassed within the scope defined by the claims.

[0053] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0054] The composite electrode of the present invention comprises an electrode substrate and first core-shell structure particles and second core-shell structure particles located on the surface of the electrode substrate; the first core-shell structure particles comprise a first metal particle core and a first carbon quantum dot shell layer coating the first metal particle core; the second core-shell structure particles comprise a second metal particle core and a second carbon quantum dot shell layer coating the second metal particle core. The composite electrode of the present invention uses a variety of metal ions as active centers to enhance catalytic activity, selectivity, and stability through electronic synergy and geometric effects. The composite electrode of the present invention uses carbon quantum dots as carbon layer protection, and the polar functional groups on its surface can increase the lyophilicity of the electrode, prevent the metal particles from being corroded by the electrolyte, and prevent the metal particles from falling off during the cycle.

[0055] In the present invention, the electrode substrate may be a carbon-based material, and the carbon-based material may be one or more selected from carbon felt, graphite felt, carbon cloth, graphite cloth and carbon paper.

[0056] In the present invention, the first metal core particle can be a bismuth metal particle. The second metal core particle can be a tin metal particle, an antimony metal particle, a copper metal particle, an iron metal particle, a cobalt metal particle, or a nickel metal particle. The composite electrode of the present invention utilizes these metal particles as active centers to enhance catalytic activity, selectivity, and stability through electronic synergy and geometric effects.

[0057] In the present invention, the particle size of the first core-shell structure particles can be 25-65 nm, for example, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm. In the present invention, the particle size of the first metal particle core can be 5-15 nm, for example, 5 nm, 7 nm, 11 nm, 13 nm, 15 nm. The thickness of the first carbon quantum dot shell can be 20-50 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm. In the present invention, if the thickness of the first carbon quantum dot shell is too thick, it will block the active sites, and if it is too thin, it will lead to insufficient protection. Controlling the thickness of the first carbon quantum dot shell within the above range is conducive to ensuring that the all-vanadium redox flow battery has excellent initial performance and long-term cycle stability.

[0058] In the present invention, the particle size of the second core-shell structure particles can be 25-65 nm, for example, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm. In the present invention, the particle size of the second metal particle core can be 5-15 nm, for example, 5 nm, 7 nm, 11 nm, 13 nm, 15 nm. The thickness of the second carbon quantum dot shell can be 20-50 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm. In the present invention, if the thickness of the second carbon quantum dot shell is too thick, it will block the active sites, and if it is too thin, it will lead to insufficient protection. Controlling the thickness of the second carbon quantum dot shell within the above range is conducive to ensuring that the all-vanadium redox flow battery has excellent initial performance and long-term cycle stability.

[0059] In the present invention, the total loading amount of the first metal core particles and the second metal core particles on the electrode substrate can be 0.8-3.0 mg / cm 2 , for example 0.8 mg / cm 2 , 1.0mg / cm 2 , 1.2mg / cm 2 , 1.4mg / cm 2 , 1.6mg / cm 2 , 1.8mg / cm 2 , 2.0mg / cm 2 , 2.2mg / cm 2 , 2.4mg / cm 2 , 2.6mg / cm 2 , 2.8mg / cm 2 、3.0mg / cm 2 In the present invention, the mass ratio of the first metal particle core to the second metal particle core can be 0.8:1, 0.85:1, 0.9:1, 0.95:1, or 1:1.

[0060] In the present invention, polar functional groups exist on the surface of the first carbon quantum dot shell and the surface of the second carbon quantum dot shell, and the polar functional groups include sulfonic acid groups; preferably, the polar functional groups may also include carboxyl groups and / or amino groups. In some preferred embodiments, the polar functional groups present on the surface of the first carbon quantum dot shell and the surface of the second carbon quantum dot shell include sulfonic acid groups and carboxyl groups. In some more preferred embodiments, the polar functional groups present on the surface of the first carbon quantum dot shell and the surface of the second carbon quantum dot shell include sulfonic acid groups, carboxyl groups and amino groups. When the polar functional groups on the surface of the first carbon quantum dot shell and the surface of the second carbon quantum dot shell simultaneously include sulfonic acid groups, carboxyl groups and amino groups, the composite synergistic effect of the three functional groups enables the all-vanadium liquid flow battery to have excellent initial performance and long-term cycle stability.

[0061] In some embodiments, in the composite electrode of the present invention, locations on the electrode substrate where the first core-shell structure particles and the second core-shell structure particles are not present are covered with a third carbon quantum dot layer.

[0062] The present invention provides a method for preparing a composite electrode comprising the following steps: (1) placing an electrode substrate in a mixed metal solution, electrochemically depositing metal on the surface of the electrode substrate, and washing the substrate to obtain an electrode material precursor loaded with a first metal particle core and a second metal particle core; the mixed metal solution comprises a first metal compound and a second metal compound, the first metal is bismuth, and the second metal is tin, antimony, copper, iron, cobalt, or nickel; (2) placing the electrode material precursor in a carbon quantum dot precursor liquid to carry out a hydrothermal reaction, and after the hydrothermal reaction is completed, washing and drying to obtain an electrode material intermediate; the carbon quantum dot precursor liquid comprises an amine source, a first carbon source, a second carbon source, a surfactant and a solvent, wherein the first carbon source contains sulfur and the second carbon source does not contain sulfur; (3) Annealing the electrode material intermediate to obtain the composite electrode.

[0063] In step (1), the concentration of the first metal compound in the mixed metal solution may be 0.005 to 0.020 mol / L, for example, 0.005 mol / L, 0.010 mol / L, 0.015 mol / L, or 0.020 mol / L. In step (1), the concentration of the second metal compound in the mixed metal solution may be 0.010 to 0.020 mol / L, for example, 0.010 mol / L, 0.015 mol / L, or 0.020 mol / L. In step (1), the first metal compound may be one or more selected from bismuth chloride, bismuth oxide, bismuth nitrate, and bismuth sulfate. In step (1), the second metal compound may be one or more selected from chlorides, oxides, nitrates, and sulfates of the second metal, for example, tin chloride, antimony chloride, copper oxide, nickel sulfate, cobalt nitrate, or ferric chloride. In step (1), the mixed metal solution may further include sulfuric acid, and the concentration of sulfuric acid is preferably 3.0 to 5.0 mol / L, for example, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, 5.0 mol / L; in step (1), the solvent in the mixed metal solution may be water, preferably deionized water.

[0064] In step (1), the electrochemical method can be a constant potential method; the constant potential method adopts a three-electrode working system, the working electrode is the electrode substrate, the reference electrode is a saturated calomel electrode, and the counter electrode is a graphite electrode. In the constant potential method of the present invention, the voltage relative to the saturated calomel electrode can be 0V~-0.8V (relative to saturated calomel SCE), for example, -0.8V, -0.7V, -0.6V, -0.5V, -0.4V, -0.3V, -0.2V, -0.1V. In step (1), the deposition time can be 5~30min, for example, 5min, 10min, 15min, 20min, 25min, 30min. In step (1), stirring can be added during the deposition process, and the stirring can be magnetic stirring. The stirring speed can be 200~500rpm, for example, 200rpm, 250rpm, 300rpm, 350rpm, 400rpm, 450rpm, 500rpm. The present invention adds stirring during the deposition process to make the catalyst solution as uniform as possible during deposition, reduce concentration polarization, and prevent the problem of low reactant concentration near the electrode surface and high concentration far from the electrode surface.

[0065] In step (2), the amine source can be one or more selected from ethylenediamine, p-phenylenediamine, o-phenylenediamine and urea. In the present invention, the introduction of amino groups by the amine source can enhance the activity and hydrophilicity of the carbon quantum dot surface. In step (2), the content of the amine source in the carbon quantum dot precursor liquid can be 4~8.5wt%, for example, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%. In step (2), the first carbon source can be sodium p-phenylenedisulfonate and / or p-aminobenzenesulfonic acid. In the present invention, the addition of the first carbon source containing sulfur elements is to increase the sulfonic acid group (-SO3H) on the surface of the carbon quantum dot. The sulfonic acid group has a positive effect on the electrode activity. If the above-mentioned first carbon source is not added, the generation of sulfonic acid groups will be lacking. In step (2), the second carbon source can be citric acid and / or glucose. In the present invention, the addition of the second carbon source can introduce carboxyl groups on the surface of the carbon quantum dot. The carboxyl groups have a positive effect on the electrode performance. In step (2), the mass ratio of the amine source, the first carbon source, and the second carbon source can be (0.1-0.8):(0.1-0.8):1. In step (2), the surfactant can be one or more selected from polyvinyl pyrrolidone, polyetherimide, and hexadecyltrimethylammonium bromide. The addition of the above-mentioned surfactant as a stabilizer in the present invention can effectively prevent the agglomeration of carbon quantum dots. In step (2), the amount of the surfactant added to the carbon quantum dot precursor liquid can be 0.05-0.2wt%, for example, 0.05wt%, 0.1wt%, 0.15wt%, and 0.2wt%.

[0066] In the present invention, during the hydrothermal process, the carbon quantum dots form a coordination bond with the metal, and the coordination bond attracts the carbon quantum dots to combine with the metal, thereby increasing the carbon quantum's wrapping of the metal, growing directly on the bimetallic surface, achieving uniform wrapping, and generating a core-shell structure catalyst. In step (3), the temperature of the hydrothermal reaction can be 160-220°C, for example, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C. In step (3), the time of the hydrothermal reaction can be 6-12h, for example, 6h, 7h, 8h, 9h, 10h, 11h, 12h. In step (3), the number of washings can be 3-5 times. In step (3), the drying temperature can be 60-80°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C. In step (3), the drying time can be 6 to 12 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, and 12 hours.

[0067] In the present invention, the purpose of the annealing treatment is to carbonize the residual polymer and enhance the bonding force between the carbon quantum dots and the metal particle core. In step (4), the temperature of the annealing treatment can be 200-400°C, for example, 200°C, 250°C, 300°C, 350°C, or 400°C. In step (4), the annealing treatment time can be 1-3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2. hours, or 3 hours. In step (4), the annealing is performed in a mixed atmosphere of a protective gas and hydrogen. The protective gas can be nitrogen or argon, and the volume ratio of nitrogen to H2 can be 5:95.

[0068] The present invention provides an all-vanadium redox flow battery comprising the composite electrode of the present invention.

[0069] Compared with the prior art, the present invention has the following beneficial technical effects: (1) The composite electrode material of the present invention selects a bimetallic particle core as the catalytic active center. Compared with a single metal particle core, it has higher catalytic activity, better reaction selectivity, and stronger resistance to deactivation, which can greatly accelerate the redox reaction efficiency of vanadium ions; (2) The carbon quantum dots of the present invention have a high specific surface area and rich functional groups, which can improve the hydrophilicity of the electrode surface, increase the adsorption of vanadium ions on the electrode, and reduce the interface impedance; (3) The carbon quantum dot shell of the present invention forms a coordination bond with the metal particle core through the surface functional groups, which can not only protect the metal particle core from corrosion by the strong acid electrolyte, but also prevent the metal particle core from falling off during the cycle by utilizing the steric hindrance effect.

[0070] The present invention will be described below by way of specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present invention. The methods, reagents, and materials used in the examples are, unless otherwise stated, conventional methods, reagents, and materials in the art. The starting compounds in the examples can all be purchased from commercial sources.

[0071] The carbon felt used in the examples and comparative examples of the present invention has a thickness of 2.5 mm and is produced in Jingu, Liaoyang.

[0072] Example 1 Preparation of this example Figure 1 The composite electrode shown in the structure, the specific steps are as follows: 1. Dissolve 1.575g of bismuth chloride and 2.605g of tin chloride in 4.0mol / L sulfuric acid to obtain 200mL of a bimetallic compound solution. Immerse a 6cm×8cm piece of carbon felt in the bimetallic compound solution. Deposit bimetallic particle cores on the carbon felt using an electrochemical workstation. A graphite rod serves as the counter electrode, saturated calomel serves as the reference electrode, and a graphite rod conductive clip secures the carbon felt as the working electrode. A three-electrode system was constructed using a potentiostatic method with a potential set between -0.20V and -0.30V (vs. SCE). After 10min of deposition, remove the working electrode and rinse with deionized water to obtain an electrode material precursor loaded with BiSn bimetallic particle cores.

[0073] 2. Dissolve 5.0 g of citric acid in 200 mL of deionized water, then add 2.5 g of urea, 1.5 g of p-aminobenzenesulfonic acid, and polyvinylpyrrolidone to obtain a carbon quantum dot precursor solution. The concentration of polyvinylpyrrolidone in the carbon quantum dot precursor solution is 0.05 wt%.

[0074] 3. Immerse the electrode material precursor in the carbon quantum dot precursor solution and transfer both to an autoclave for a hydrothermal reaction at 200°C for 6 hours. After the autoclave cools to room temperature, remove the carbon felt, wash it five times with deionized water, and dry it at 60°C for 12 hours to obtain the electrode material intermediate.

[0075] 4. The electrode material intermediate was placed in a tube furnace and introduced with a nitrogen-hydrogen mixture (nitrogen-to-hydrogen ratio of 5:95 by volume). Annealing was then performed at 300°C for 2 hours to produce a BiSn bimetallic@carbon quantum dot core-shell composite electrode. The core-shell structured particles in the composite electrode exhibited sulfonic acid, carboxyl, and amino groups on their surfaces.

[0076] Example 2 The other conditions of this example were the same as those of Example 1, with the only difference being that step (2) of this example was to dissolve 10 g of citric acid in 200 mL of deionized water, and then add 5.0 g of urea, 3.0 g of p-aminobenzenesulfonic acid, and polyvinylpyrrolidone to obtain a carbon quantum dot precursor solution. The concentration of polyvinylpyrrolidone in the carbon quantum dot precursor solution was 0.05 wt %. Sulfonic acid groups, carboxyl groups, and amino groups existed on the surface of the core-shell structured particles on the composite electrode.

[0077] Example 3 The other conditions of this example were the same as those of Example 1, with the only difference being that step (2) of this example was to dissolve 2.5 g of citric acid in 200 mL of deionized water, and then add 1.25 g of urea, 0.75 g of p-aminobenzenesulfonic acid, and polyvinylpyrrolidone to obtain a carbon quantum dot precursor solution. The concentration of polyvinylpyrrolidone in the carbon quantum dot precursor solution was 0.05 wt %. Sulfonic acid groups, carboxyl groups, and amino groups existed on the surface of the core-shell structured particles on the composite electrode.

[0078] Example 4 The other conditions of this example are the same as those of Example 1, except that step (1) of this example is as follows: 1.575 g of bismuth chloride and 2.281 g of antimony chloride are dissolved in 4.0 mol / L sulfuric acid to obtain 200 mL of a bimetallic compound solution; a 6 cm × 8 cm carbon felt is immersed in the bimetallic compound solution; and bimetallic particle cores are deposited on the surface of the carbon felt using an electrochemical workstation, wherein a graphite rod is used as a counter electrode, saturated calomel is used as a reference electrode, and a graphite rod conductive clamp is used to fix the carbon felt as a working electrode. A three-electrode system is constructed, and a constant potential method is used. The potential is set at -0.10 V to -0.20 V (vs. SCE). After 10 minutes of deposition, the working electrode is removed and rinsed with deionized water to obtain an electrode material precursor loaded with BiSb bimetallic particle cores. The core-shell structure particles on the composite electrode finally prepared in this example have sulfonic acid groups, carboxyl groups, and amino groups on their surfaces.

[0079] Comparative Example 1 Carbon felt with a thickness of 2.5 mm produced in Liaoyang Jingu was used as the electrode.

[0080] Comparative Example 2 The difference between this comparative example and Example 1 is that steps (2) and (3) of Example 1 are omitted, and the electrode material precursor obtained in step (1) is directly annealed to obtain a composite electrode without a carbon quantum dot shell layer.

[0081] Test Example 1 In the present invention, the electrode material precursors in the Examples and Comparative Examples were measured using scanning electron microscopy to determine the particle size of the first metal core particle and the particle size of the second metal core particle. The electrodes in the Examples and Comparative Examples were also measured using scanning electron microscopy to determine the particle size of the first core-shell structure particles and the particle size of the second core-shell structure particles. The structural characterization results of the electrodes in the Examples and Comparative Examples are shown in Table 1.

[0082] In the present invention, the thicknesses of the first carbon quantum dot shell layer and the second carbon quantum dot shell layer of the composite electrode of the embodiment are characterized by transmission electron microscopy.

[0083] In the present invention, the loading amount of the metal particle core is calculated by the concentration difference method, that is, the concentration of the first metal ion (C A-initial 、C A-final ) and the second metal ion concentration (C B-initial 、C B-final ), by calculating C A-initial -C A-final 、C B-initial -C B-final, and then multiply it by the relative molecular mass of each metal to obtain the loading amount of the first metal particle core and the loading amount of the second metal particle core.

[0084] Table 1: Structural characterization results of electrodes of Examples and Comparative Examples

[0085] Test Example 2 Preparation of all-vanadium redox flow battery: the active substances in the positive and negative electrolytes are 1.70 mol / LV respectively 4+ / V 5+ and 1.70 mol / L 2+ / V 3+ The supporting electrolyte is 4.3 mol / L sulfuric acid. The volume of the positive and negative electrolytes is 70 mL. The perfluorosulfonic acid proton membrane is produced by Suzhou Kerun. The negative electrode uses the composite electrode of the embodiment and the comparative example respectively. The positive electrode uses the carbon felt with a thickness of 2.5 mm produced by Liaoyang Jingu. The effective area of ​​the carbon felt is 48 cm 2 , the compression ratio is 20~25%.

[0086] Initial performance test: The initial performance of the all-vanadium redox flow battery assembled with the electrodes of the embodiment and the comparative example was tested using a constant current, with the current density set to 110, 200, and 250 mA / cm 2 The upper limit of charge is 1.55V, the lower limit of discharge is 1.00V, and the battery is cycled 5 times at each current density. The data of the 4th cycle are uniformly taken as the initial performance. The test results of the initial performance of the all-vanadium liquid flow battery assembled by the electrodes of the embodiment and the comparative example are shown in Table 2.

[0087] Cycling performance test: The cycling performance of the all-vanadium redox flow battery assembled with the electrodes of the embodiment and the comparative example was tested using a constant current, with the setting of a current density of 250 mA / cm 2 The upper limit of charge is 1.55V, the lower limit of discharge is 1.00V, and the cycle is 1000 times. The test results of the cycle performance of the all-vanadium liquid flow battery assembled by the electrodes of the embodiment and the comparative example are shown in Table 3.

[0088] Table 2: Initial performance of all-vanadium redox flow batteries assembled from electrodes of Examples and Comparative Examples

[0089] Table 3: Cycling performance of all-vanadium redox flow batteries assembled from electrodes of Examples and Comparative Examples

Claims

1. A composite electrode, characterized in that: The composite electrode comprises an electrode substrate and first core-shell structure particles and second core-shell structure particles located on the surface of the electrode substrate; The first core-shell structure particle comprises a first metal particle core and a first carbon quantum dot shell layer covering the first metal particle core; the first metal particle core is a metal bismuth particle; The second core-shell structure particles include a second metal particle core and a second carbon quantum dot shell layer covering the second metal particle core; the second metal particle core is a metal tin particle, a metal antimony particle, a metal copper particle, a metal iron particle, a metal cobalt particle or a metal nickel particle.

2. The composite electrode according to claim 1, wherein The composite electrode has one or more of the following features: The electrode substrate is a carbon-based material, and the carbon-based material is selected from one or more of carbon felt, graphite felt, carbon cloth, graphite cloth and carbon paper; The particle size of the first core-shell structure particles is 25-65 nm; The particle size of the second core-shell structure particles is 25-65 nm; The particle size of the first metal particle core is 5 to 15 nm; The particle size of the second metal particle core is 5 to 15 nm; The thickness of the first carbon quantum dot shell is 20-50 nm; The thickness of the second carbon quantum dot shell is 20-50 nm; Polar functional groups exist on the surface of the first carbon quantum dot shell layer and the surface of the second carbon quantum dot shell layer; the polar functional groups include sulfonic acid groups, and optionally also include one or both of carboxyl groups and amino groups; The total loading amount of the first metal particle core and the second metal particle core on the electrode substrate is 0.8-3.0 mg / cm 2 ; The mass ratio of the first metal particle core to the second metal particle core is (0.8~1):

1.

3. A method for preparing the composite electrode according to claim 1 or 2, characterized in that: The method comprises the following steps: (1) placing an electrode substrate in a mixed metal solution, electrochemically depositing metal on the surface of the electrode substrate, and washing the substrate to obtain an electrode material precursor loaded with a first metal particle core and a second metal particle core; the mixed metal solution comprises a first metal compound and a second metal compound, the first metal is bismuth, and the second metal is tin, antimony, copper, iron, cobalt, or nickel; (2) placing the electrode material precursor in a carbon quantum dot precursor liquid to carry out a hydrothermal reaction, and after the hydrothermal reaction is completed, washing and drying to obtain an electrode material intermediate; the carbon quantum dot precursor liquid comprises an amine source, a first carbon source, a second carbon source, a surfactant and a solvent, wherein the first carbon source contains sulfur and the second carbon source does not contain sulfur; (3) Annealing the electrode material intermediate to obtain the composite electrode.

4. The method according to claim 3, wherein The method has one or more of the following characteristics: In step (1), the concentration of the first metal compound in the mixed metal solution is 0.005-0.020 mol / L; In step (1), the concentration of the second metal compound in the mixed metal solution is 0.010-0.020 mol / L; In step (1), the first metal compound is selected from one or more of bismuth chloride, bismuth oxide, bismuth nitrate and bismuth sulfate; In step (1), the second metal compound is selected from one or more of a chloride, an oxide, a nitrate and a sulfate of the second metal; In step (1), the mixed metal solution further comprises sulfuric acid; the concentration of sulfuric acid in the mixed metal solution is 3.0-5.0 mol / L; In step (1), the solvent in the mixed metal solution is water.

5. The method according to claim 3, wherein The method has one or more of the following characteristics: In step (1), the electrochemical method is a constant potential method; In step (1), the deposition time is 5 to 30 minutes; In step (1), during the deposition process, the stirring speed is 200~500rpm.

6. The method according to claim 5, wherein The constant potential method adopts a three-electrode working system, wherein the working electrode is the electrode substrate, the reference electrode is a saturated calomel electrode, the counter electrode is a graphite electrode, and the voltage relative to the saturated calomel electrode is 0V~-0.8V.

7. The method according to claim 3, wherein The method has one or more of the following characteristics: In step (2), the amine source is selected from one or more of ethylenediamine, p-phenylenediamine, o-phenylenediamine and urea; In step (2), the first carbon source is sodium terephthalate and / or p-aminobenzenesulfonic acid; In step (2), the second carbon source is citric acid and / or glucose; In step (2), the surfactant is selected from one or more of polyvinyl pyrrolidone, polyetherimide and cetyltrimethylammonium bromide; In step (2), the mass ratio of the amine source, the first carbon source, and the second carbon source is (0.1-0.8):(0.1-0.8):1; In step (2), the content of the amine source in the carbon quantum dot precursor liquid is 4.0-8.5 wt%; In step (2), the content of the surfactant in the carbon quantum dot precursor liquid is 0.05-0.2 wt%.

8. The method according to claim 3, wherein The method has one or more of the following characteristics: In step (2), the temperature of the hydrothermal reaction is 160-220°C; In step (2), the hydrothermal reaction time is 6 to 12 hours; In step (2), the washing is performed 3 to 5 times; In step (2), the drying temperature is 60-80°C; In step (2), the drying time is 6 to 12 hours.

9. The method according to claim 3, wherein The method has one or more of the following characteristics: In step (3), the annealing temperature is 200-400°C; In step (3), the annealing treatment time is 1 to 3 hours; In step (3), annealing is performed in a mixed atmosphere of protective gas and hydrogen.

10. An all-vanadium redox flow battery comprising the composite electrode according to claim 1 or 2.

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