Composite electrode, method for preparing the same, and all-vanadium redox flow battery

Abstract

The present application belongs to the field of liquid flow battery, and particularly relates to a composite electrode, a preparation method thereof and a full vanadium liquid flow battery. The composite electrode comprises an electrode substrate and first core-shell structure particles and second core-shell structure particles 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 covering the first metal particle core; the first metal particle core is a bismuth metal particle; the second core-shell structure shell layer comprises 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 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 can effectively improve the efficiency and stability of the full vanadium liquid flow battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of flow battery, and particularly relates to a composite electrode, a preparation method thereof and a vanadium flow battery. BACKGROUND

[0002] Vanadium redox flow battery (VRFB) is a promising energy storage system due to its long lifetime, safety, environmental friendliness and scalability. In VRFB, the electrode is a core component, and its performance directly determines the overall efficiency of the VRFB. Carbon-based electrode materials (such as graphite felt, carbon felt, carbon cloth, etc.) have the characteristics of developed three-dimensional network structure, good electrical conductivity, excellent chemical stability and high cost performance. However, they also face the problem of incompatibility of solid-liquid interface and lack of active sites.

[0003] In order to overcome the inherent problems of carbon-based electrodes, researchers have been committed to increasing the specific surface area of the material, improving the hydrophilicity and catalytic efficiency of the material by intrinsic treatment or introducing catalysts. Although intrinsic treatment can improve the performance of carbon-based electrodes by increasing the specific surface area and oxygen-containing functional groups, intrinsic treatment has limitations, and the number of active sites and specific surface area cannot be increased significantly, which cannot meet the demand of high-power operation of VRFB. By introducing catalysts, there is a risk of catalyst falling off or being slowly oxidized and corroded during long-term operation, which negatively affects the stability of VRFB.

[0004] Therefore, it is urgent to develop an electrode material that can effectively improve the efficiency and stability of the VRFB. SUMMARY

[0005] To solve the problems existing in the prior art, the present application provides a composite electrode, a preparation method thereof and a vanadium flow battery. The composite electrode material of the present application can significantly improve the initial performance and long-term cycling stability of the VRFB.

[0006] The present application provides a composite electrode, which comprises an electrode substrate and first core-shell structure particles and second core-shell structure particles 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 covering the first metal particle core; the first metal particle core is a bismuth metal particle; the second core-shell structure particles comprise 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 tin metal particle, an antimony metal particle, a copper metal particle, an iron metal particle, a cobalt metal particle or a nickel metal 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 structure particle is 25-65 nm.

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

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

[0011] In one or more embodiments, the particle size of the second metal particle core is 5-15 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, the first carbon quantum dot shell layer surface and the second carbon quantum dot shell layer surface have polar functional groups, and the polar functional groups include sulfonic acid groups.

[0015] In one or more embodiments, the polar functional groups further include one or both of carboxyl groups and amino groups.

[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 and the second metal particle core is (0.8-1):1.

[0018] The present application provides a method for preparing the composite electrode described in the present application, comprising the following steps:

[0019] (1) placing an electrode substrate in a mixed metal solution, using an electrochemical method to deposit metals on the surface of the electrode substrate, and after washing, obtaining an electrode material precursor loaded with a first metal particle core and a second metal particle core; the mixed metal solution includes 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;

[0020] (2) placing the electrode material precursor in a carbon quantum dot precursor solution, and performing a hydrothermal reaction, after the hydrothermal reaction is completed, washing and drying to obtain an electrode material intermediate; the carbon quantum dot precursor solution includes an amine source, a first carbon source, a second carbon source, a surfactant and a solvent, the first carbon source contains sulfur elements, and the second carbon source does not contain sulfur elements;

[0021] (3) annealing the electrode material intermediate to obtain the composite electrode.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] In one or more embodiments, in step (1), the mixed metal solution further comprises sulfuric acid; and the concentration of the sulfuric acid in the mixed metal solution is 3.0-5.0 mol / L.

[0027] In one or more embodiments, in step (1), the solvent in the mixed metal solution is water.

[0028] In one or more embodiments, in step (1), the electrochemical method is a constant potential method.

[0029] In one or more embodiments, in step (1), the deposition time is 5-30 min.

[0030] In one or more embodiments, in step (1), the stirring speed during the deposition is 200-500 rpm.

[0031] In one or more embodiments, the constant potential method uses 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; and the voltage relative to the saturated calomel electrode is 0 V-0.8 V.

[0032] 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.

[0033] In one or more embodiments, in step (2), the first carbon source is p-phenylsulfonic acid sodium and / or p-aminobenzenesulfonic acid.

[0034] In one or more embodiments, in step (2), the second carbon source is citric acid and / or glucose.

[0035] In one or more embodiments, in step (2), the surfactant is selected from one or more of polyvinylpyrrolidone, polyetherimide and cetyltrimethylammonium bromide.

[0036] 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.

[0037] In one or more embodiments, in step (2), the content of the amine source in the carbon quantum dot precursor solution is 4.0-8.5 wt%.

[0038] In one or more embodiments, in step (2), the content of the surfactant in the carbon quantum dot precursor solution is 0.05-0.2 wt%.

[0039] In one or more embodiments, in step (2), the temperature of the hydrothermal reaction is 160-220℃.

[0040] In one or more embodiments, in step (2), the time of the hydrothermal reaction is 6-12 h.

[0041] In one or more embodiments, in step (2), the number of washing is 3-5 times.

[0042] In one or more embodiments, in step (2), the temperature of the drying is 60-80℃.

[0043] In one or more embodiments, in step (2), the time of the drying is 6-12 h.

[0044] In one or more embodiments, in step (3), the temperature of the annealing treatment is 200-400℃.

[0045] In one or more embodiments, in step (3), the time of the annealing treatment is 1-3 h.

[0046] In one or more embodiments, in step (3), the annealing is performed in a mixed atmosphere of a protective gas and hydrogen.

[0047] The present application provides a full vanadium liquid flow battery comprising the composite electrode as described in the present application.

[0048] The application has the following beneficial effects: the composite electrode material of the application selects two metal particle cores as catalytic active centers, has higher catalytic activity, better reaction selectivity and stronger deactivation resistance than single metal particle cores, can greatly accelerate the efficiency of vanadium ion redox reaction; the carbon quantum dot shell has high specific surface area and rich functional groups, can improve the hydrophilicity of the electrode surface, increase the adsorption of vanadium ions on the electrode and reduce the interface impedance; in addition, the carbon quantum dot shell forms a coordination bond with the metal particle core through the surface functional groups, which can protect the metal particle core from corrosion by strong acidic electrolyte and prevent the metal particle core from falling off in the cycle process by using the steric hindrance effect. The use of the composite electrode material of the application can significantly improve the initial performance and long-time cycle stability of the all-vanadium redox flow battery. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 A schematic diagram of the microstructure of the composite electrode prepared for some embodiments of the application. DETAILED DESCRIPTION

[0050] To enable persons skilled in the art to understand the characteristics and effects of the application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used in the text are of the usual meaning understood by those skilled in the art of the application, and in case of conflict, the definition in the specification shall prevail.

[0051] Theories or mechanisms described and disclosed herein, whether correct or not, should not be considered limiting the scope of the application, i.e., the application can be practiced without any particular theory or mechanism.

[0052] In this text, "comprising", "including", "containing" and similar phrases cover the meaning of "consisting essentially of" and "consisting of", for example, when this text discloses "A comprising B and C", "A consisting essentially of B and C" and "A consisting of B and C" should be considered to have been disclosed herein.

[0053] In this text, all features defined in the form of numerical ranges or percentage ranges such as values, quantities, contents and concentrations are only for the sake of brevity and convenience. Therefore, the description of numerical ranges or percentage ranges should be considered to have covered and specifically disclosed all possible sub-ranges and individual values within the range (including integers and fractions).

[0054] In this text, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0055] In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, independent of any other instances of the term. In describing representative embodiments or examples of the application, specific terminology is used for the sake of clarity. The term "comprising" and its derivatives, as used herein, are intended to be open-ended and include the possibility that there are additional elements other than the listed elements. The term "consisting of" is intended to be closed, i.e., only those elements listed are present in the composition or process. The term "consisting essentially of" is intended to have its ordinary meaning as understood by those of ordinary skill in the art. It is not intended to be limiting, but rather to add that claims which consist essentially of the elements as set forth in this definition are deemed equivalent to those claims which recite the specific elements in complete, unambiguous, and exhaustive detail. Thus, it is intended that the definition of the term consisting essentially of is as broad as the definition of the term consisting of. The term "about" means approximately or nearly as understood by those of ordinary skill in the art. The terms "coupled" and "connected," along with derivatives thereof, are used. It should be understood that these terms are not intended as synonyms for each other. Rather, particular embodiments or examples of the application can include variations of the coupling or connection, as readily understood by those of ordinary skill in the art, and the specific examples are not intended to exclude other embodiments or examples that accomplish substantially the same functionality in substantially the same or different ways. In this document, the terms "first," "second," "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. In this document, the term "step" does not imply or require that the steps be performed in a particular order. Moreover, in the following claims, the terms used should not be construed to limit the application to the specific embodiments or examples disclosed in the specification, but should be given the broadest possible interpretation accessible under the terms of the law.

[0056] In this document, all possible combinations of the various features described in the various embodiments or examples are not described. Therefore, as long as there is no contradiction in the combination of the features, the features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as the scope of the present specification.

[0057] The composite electrode of the present application comprises an electrode substrate and first core-shell structure particles and second core-shell structure particles 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 covering 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 covering the second metal particle core. The composite electrode of the present application selects multiple metal ions as active centers, and improves the catalytic activity, selectivity and stability through electronic synergistic effect and geometric effect. The composite electrode of the present application selects carbon quantum dots as carbon layer protection, and the polar functional groups on the surface thereof can increase the liquid affinity of the electrode, and can also avoid corrosion of the metal particles by the electrolyte, and prevent the metal particles from falling off during the cycle process.

[0058] In the present application, the electrode substrate can be a carbon-based material, which can be one or more selected from carbon felt, graphite felt, carbon cloth, graphite cloth and carbon paper.

[0059] In the present application, the first metal particle core can be a metal bismuth particle. The second metal particle core can be 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 of the present application selects the above metal particles as active centers, and improves the catalytic activity, selectivity and stability through electronic synergistic effect and geometric effect.

[0060] In the present application, the particle size of the first core-shell structure particle 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 application, 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 layer can be 20-50 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm. In the present application, if the thickness of the first carbon quantum dot shell layer 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 layer within the above range is beneficial to ensure that the all-vanadium redox flow battery has excellent initial performance and long-term cycle stability.

[0061] In the present application, the particle size of the second core-shell structure particle 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 application, 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 layer can be 20-50 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm. In the present application, if the thickness of the second carbon quantum dot shell layer 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 layer within the above range is beneficial to ensure that the all-vanadium redox flow battery has excellent initial performance and long-term cycle stability.

[0062] In the present application, the total loading of the first metal particle core and the second metal particle core on the electrode substrate can be 0.8-3.0 mg / cm 2 , for example, 0.8 mg / cm 2 , 1.0 mg / cm 2 , 1.2 mg / cm 2 , 1.4 mg / cm 2 , 1.6 mg / cm 2 , 1.8 mg / cm 2 , 2.0 mg / cm 2 , 2.2 mg / cm 2 , 2.4 mg / cm 2 , 2.6 mg / cm 2 , 2.8 mg / cm 2 , 3.0 mg / cm 2 . In the present application, the mass ratio of the first metal particle core and the second metal particle core can be 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1.

[0063] In the present application, the 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; preferably, the polar functional groups can also include carboxyl groups and / or amino groups. In some preferred embodiments, the polar functional groups existing on the surface of the first carbon quantum dot shell layer and the surface of the second carbon quantum dot shell layer include sulfonic acid groups and carboxyl groups. In some more preferred embodiments, the polar functional groups existing on the surface of the first carbon quantum dot shell layer and the surface of the second carbon quantum dot shell layer include sulfonic acid groups, carboxyl groups and amino groups. When the polar functional groups on the surface of the first carbon quantum dot shell layer and the surface of the second carbon quantum dot shell layer simultaneously include sulfonic acid groups, carboxyl groups and amino groups, the three functional groups synergistically act, so that the all-vanadium redox flow battery has excellent initial performance and long-term cycle stability.

[0064] In some embodiments, in the composite electrode of the present application, the positions on the electrode substrate where the first core-shell structure particles and the second core-shell structure particles do not exist are covered with a third carbon quantum dot layer.

[0065] The present application provides a method for preparing a composite electrode, comprising the following steps:

[0066] (1) placing an electrode substrate in a mixed metal solution, depositing metals on the surface of the electrode substrate by electrochemical method, and after washing, obtaining an electrode material precursor loaded with first metal particle cores and second metal particle cores; the mixed metal solution includes 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;

[0067] (2) placing the electrode material precursor in a carbon quantum dot precursor solution to perform hydrothermal reaction, after the hydrothermal reaction is completed, washing and drying to obtain an electrode material intermediate; the carbon quantum dot precursor solution includes an amine source, a first carbon source, a second carbon source, a surfactant and a solvent, the first carbon source contains sulfur element, and the second carbon source does not contain sulfur element;

[0068] (3) annealing the electrode material intermediate to obtain the composite electrode.

[0069] In step (1), the concentration of the first metal compound in the mixed metal solution can be 0.005-0.020 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 can be 0.010-0.020 mol / L, for example, 0.010 mol / L, 0.015 mol / L, or 0.020 mol / L. In step (1), the first metal compound can be one or more selected from the group consisting of bismuth chloride, bismuth oxide, bismuth nitrate, and bismuth sulfate. In step (1), the second metal compound can be one or more selected from the group consisting of chloride, oxide, nitrate, and sulfate of the second metal, for example, tin chloride, antimony chloride, copper oxide, nickel sulfate, cobalt nitrate, and iron chloride. In step (1), the mixed metal solution can further include sulfuric acid, and the concentration of the sulfuric acid is preferably 3.0-5.0 mol / L, for example, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, or 5.0 mol / L. In step (1), the solvent in the mixed metal solution can be water, preferably deionized water.

[0070] In step (1), the electrochemical method can be a constant potential method. The constant potential method uses 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 application, the voltage relative to the saturated calomel electrode can be 0 V-0.8 V (relative to saturated calomel SCE), for example, -0.8 V, -0.7 V, -0.6 V, -0.5 V, -0.4 V, -0.3 V, -0.2 V, or -0.1 V. In step (1), the deposition time can be 5-30 min, for example, 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min. In step (1), stirring can be added during the deposition process. The stirring can be magnetic stirring, and the stirring speed can be 200-500 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm. The present application increases the stirring during the deposition process, which can make the catalyst solution as uniform as possible during the deposition, reduce the concentration polarization, and prevent the problem of low concentration of reactants near the surface of the electrode and high concentration far from the surface.

[0071] In step (2), the amine source can be one or more selected from ethylenediamine, p-phenylenediamine, o-phenylenediamine and urea. In the present application, the introduction of amino groups by the amine source can enhance the activity and hydrophilicity of the surface of the carbon quantum dots. In step (2), the content of the amine source in the carbon quantum dot precursor solution can be 4-8.5 wt%, for example 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%. In step (2), the first carbon source can be sodium p-toluene sulfonate and / or p-aminobenzenesulfonic acid. In the present application, the first carbon source containing sulfur elements is added to increase the sulfonic acid groups (-SO3H) on the surface of the carbon quantum dots, and the sulfonic acid groups have a positive effect on the electrode activity. Without adding the first carbon source, the sulfonic acid groups will not be generated. In step (2), the second carbon source can be citric acid and / or glucose. In the present application, the addition of the second carbon source can introduce carboxyl groups on the surface of the carbon quantum dots, and 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 polyvinylpyrrolidone, polyetherimide and cetyltrimethylammonium bromide. In the present application, the addition of the above-mentioned surfactant as a stabilizer can effectively prevent the agglomeration of the carbon quantum dots. In step (2), the amount of the surfactant added in the carbon quantum dot precursor solution can be 0.05-0.2 wt%, for example 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%.

[0072] In the present application, the carbon quantum dots form coordination bonds with the metal during the hydrothermal process, and the coordination bonds attract the combination of the carbon quantum dots and the metal, increase the wrapping of the carbon quantum dots on the metal, directly grow on the surface of the bimetal, realize uniform wrapping, and generate a catalyst with core-shell structure. In step (3), the temperature of the hydrothermal reaction can be 160-220℃, for example 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃. 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 washing can be 3-5 times. In step (3), the temperature of drying can be 60-80℃, for example 60℃, 65℃, 70℃, 75℃, 80℃. In step (3), the time of drying can be 6-12h, for example 6h, 7h, 8h, 9h, 10h, 11h, 12h.

[0073] In the present application, the purpose of annealing treatment is to carbonize the residual polymer and enhance the binding force between carbon quantum dots and metal particle core. In step (4), the temperature of annealing treatment can be 200-400℃, for example, 200℃, 250℃, 300℃, 350℃, 400℃. In step (4), the time of annealing treatment can be 1-3h, for example, 1h, 1.5h, 2h, 2.5h, 3h. In step (4), the annealing is carried out in a mixed atmosphere of protective gas and hydrogen, and the protective gas can be nitrogen, argon, and the volume ratio of nitrogen and H2 can be 5:95.

[0074] The present application provides a vanadium redox flow battery comprising the composite electrode of the present application.

[0075] Compared with the prior art, the present application has the following beneficial technical effects:

[0076] (1) The composite electrode material of the present application selects a bimetallic particle core as a catalytically active center, which has higher catalytic activity, better reaction selectivity and stronger deactivation resistance than a single metal particle core, and can greatly accelerate the efficiency of the vanadium ion redox reaction;

[0077] (2) The carbon quantum dots have a high specific surface area and abundant functional groups, which can improve the hydrophilicity of the electrode surface, increase the adsorption of vanadium ions on the electrode, and reduce the interfacial impedance;

[0078] (3) The carbon quantum dot shell forms a coordination bond with the metal particle core through surface functional groups, which can protect the metal particle core from corrosion by strong acidic electrolyte and prevent the metal particle core from falling off during the cycle process by using steric hindrance effect.

[0079] The present application will be described below in the form of specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present application. The methods, reagents and materials used in the examples are conventional in the art unless otherwise specified. The raw material compounds in the examples can be purchased through commercial channels.

[0080] The carbon felt used in the examples and comparative examples of the present application has a thickness of 2.5mm and is produced by Liaoyang Jingu.

[0081] Example 1

[0082] This example prepares Figure 1 The composite electrode shown in the structure, the specific steps are as follows:

[0083] 1. Dissolve 1.575 g of bismuth chloride and 2.605 g of tin chloride into 4.0 mol / L sulfuric acid to obtain a 200 mL bimetallic compound solution; immerse a 6 cm x 8 cm carbon felt into the bimetallic compound solution; use an electrochemical workstation to deposit bimetallic particle cores on the surface of the carbon felt, wherein a graphite rod is used as a counter electrode, saturated calomel is used as a reference electrode, a graphite rod conductive clamp is used to fix the carbon felt as a working electrode, a three-electrode system is built, a constant potential method is selected, the potential is set to -0.20 V to -0.30 V (vs. SCE), the working electrode is taken out after 10 min of deposition and washed with deionized water, and an electrode material precursor loaded with BiSn bimetallic particle cores is obtained.

[0084] 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, and the concentration of polyvinylpyrrolidone in the carbon quantum dot precursor solution is 0.05 wt%.

[0085] 3. Immerse the electrode material precursor into the carbon quantum dot precursor solution, and transfer both into a high-pressure reaction kettle for hydrothermal reaction at 200℃ for 6 h. After the high-pressure kettle is cooled to room temperature, the carbon felt is taken out, washed with deionized water for 5 times, and then placed in a 60℃ drying oven for 12 h to obtain an electrode material intermediate.

[0086] 4. Place the electrode material intermediate in a tube furnace, introduce nitrogen-hydrogen mixed gas (the volume ratio of nitrogen to hydrogen is 5:95), and anneal at 300℃ for 2 h to obtain a composite electrode with a BiSn bimetal@carbon quantum dot core-shell structure. The surface of the core-shell structure particles on the composite electrode has sulfonic acid groups, carboxyl groups, and amino groups.

[0087] Example 2

[0088] The other conditions of this example are the same as those of Example 1, except that step (2) of this example is as follows: dissolve 10 g of citric acid in 200 mL of deionized water, then add 5.0 g of urea, 3.0 g of p-aminobenzenesulfonic acid, and polyvinylpyrrolidone to obtain a carbon quantum dot precursor solution, and the concentration of polyvinylpyrrolidone in the carbon quantum dot precursor solution is 0.05 wt%. The surface of the core-shell structure particles on the composite electrode has sulfonic acid groups, carboxyl groups, and amino groups.

[0089] Example 3

[0090] The other conditions of the present example are the same as those of Example 1, and the only difference is that step (2) of the present example is as follows: 2.5 g of citric acid is dissolved in 200 mL of deionized water, and then 1.25 g of urea, 0.75 g of p-aminobenzenesulfonic acid and polyvinylpyrrolidone are added to obtain a carbon quantum dot precursor solution, and the concentration of polyvinylpyrrolidone in the carbon quantum dot precursor solution is 0.05 wt%. The surface of the core-shell structure particles on the composite electrode contains sulfonic acid groups, carboxyl groups and amino groups.

[0091] Example 4

[0092] The other conditions of the present example are the same as those of Example 1, and the only difference is that step (1) of the present 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 a 200 mL bimetallic compound solution; a 6 cm x 8 cm carbon felt is immersed in the bimetallic compound solution; a double-metal particle core is deposited on the surface of the carbon felt by 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 to build a three-electrode system; a constant potential method is selected, and the potential is set to -0.10 V to -0.20 V (vs. SCE); the working electrode is taken out after 10 min of deposition and washed with deionized water to obtain an electrode material precursor loaded with a BiSb double-metal particle core. The composite electrode obtained in the present example contains sulfonic acid groups, carboxyl groups and amino groups on the surface of the core-shell structure particles.

[0093] Comparative Example 1

[0094] A carbon felt with a thickness of 2.5 mm produced by Liaoyang Jingu is used as an electrode.

[0095] Comparative Example 2

[0096] The only difference between the present 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.

[0097] Test Example 1

[0098] In the present application, the particle size of the first metal particle core and the particle size of the second metal particle core of the electrode material precursor in the examples and comparative examples are tested by a scanning electron microscope; and the particle size of the first core-shell structure particles and the particle size of the second core-shell structure particles of the electrodes in the examples and comparative examples are tested by a scanning electron microscope. The structure characterization results of the electrodes of the examples and comparative examples are shown in Table 1.

[0099] In the present application, the thicknesses of the first carbon quantum dot shell and the second carbon quantum dot shell of the composite electrode of the examples are characterized by a transmission electron microscope.

[0100] In the present application, the loading amount of the metal particle core is calculated by the concentration difference method, that is, the first metal ion concentration (C A-initial , C A-final ) and the second metal ion concentration (C B-initial , C B-final ) in the mixed metal solution before and after electrochemical deposition are tested by an inductively coupled plasma atomic emission spectrometer (ICP-OES), C A-initial -C A-final , C B-initial -C B-final are calculated, and then multiplied 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.

[0101] Table 1: Structural characterization results of the electrodes of the examples and the comparative examples

[0102]

[0103] Test Example 2

[0104] Preparation of a full vanadium redox flow battery: the active substances in the positive and negative electrolytes are 1.70 mol / L V 4+ / V 5+ and 1.70 mol / L V 2+ / V 3+ , respectively, 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 Kelun, the negative electrode uses the composite electrode of the examples and the comparative examples, respectively, and the positive electrode uses a carbon felt with a thickness of 2.5 mm produced by Liaoyang Jingu, the effective area of the carbon felt is 48 cm 2 , and the compression ratio is 20-25%.

[0105] Initial performance test: the initial performance of the full vanadium redox flow battery assembled from the electrodes of the examples and the comparative examples is tested by constant current, the settings are as follows: the current densities are 110, 200, and 250 mA / cm 2 , respectively, the upper limit of charging is 1.55 V, the lower limit of discharging is 1.00 V, each current density is cycled for 5 times, and the data of the 4th cycle are taken as the initial performance, and the test results of the initial performance of the full vanadium redox flow battery assembled from the electrodes of the examples and the comparative examples are shown in Table 2.

[0106] Cycle performance test: the cycle performance of the full vanadium redox flow battery assembled from the electrodes of the examples and the comparative examples is tested by constant current, the settings are as follows: the current density is 250 mA / cm 2 , the upper limit of charging is 1.55 V, the lower limit of discharging is 1.00 V, and the cycle is 1000 times, and the test results of the cycle performance of the full vanadium redox flow battery assembled from the electrodes of the examples and the comparative examples are shown in Table 3.

[0107] Table 2: Initial performance of the vanadium redox flow batteries assembled from the electrodes of the examples and comparative examples

[0108]

[0109] Table 3: Cycling performance of the vanadium redox flow batteries assembled from the electrodes of the examples and comparative examples

[0110]

Claims

1. A composite electrode, characterized by, The composite electrode comprises an electrode substrate and first core-shell structure particles and second core-shell structure particles 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 bismuth metal particle; The second core-shell structure particle comprises 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 tin metal particle, an antimony metal particle, a copper metal particle, an iron metal particle, a cobalt metal particle or a nickel metal particle; 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 comprise sulfonic acid groups.

2. The composite electrode of claim 1, wherein The composite electrode has one or more of the following characteristics: 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; The particle size of the first core-shell structure particle is 25-65 nm; The particle size of the second core-shell structure particle is 25-65 nm; The particle size of the first metal particle core is 5-15 nm; The particle size of the second metal particle core is 5-15 nm; The thickness of the first carbon quantum dot shell layer is 20-50 nm; The thickness of the second carbon quantum dot shell layer is 20-50 nm; The polar functional groups further comprise one or both of carboxyl groups and amino groups; The total loading of the first metal particle core and the second metal particle core on the electrode substrate is 0.8 to 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 of preparing the composite electrode of claim 1 or 2, characterized in that, The method comprises the following steps: (1) placing an electrode substrate in a mixed metal solution, depositing metals on the surface of the electrode substrate by an electrochemical method, and washing to obtain an electrode material precursor loaded with first metal particle cores and second metal particle cores; 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 solution, performing a hydrothermal reaction, and after the hydrothermal reaction is completed, washing and drying to obtain an electrode material intermediate; the carbon quantum dot precursor solution comprises an amine source, a first carbon source, a second carbon source, a surfactant and a solvent, the first carbon source contains sulfur elements, and the second carbon source does not contain sulfur elements; (3) annealing the electrode material intermediate to obtain the composite electrode.

4. The method of 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 of 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 5-30 min. In step (1), the stirring speed during deposition is 200-500 rpm.

6. The method of claim 5, wherein, The constant potential method uses 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. The voltage relative to the saturated calomel electrode is 0V-0.8V.

7. The method of 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 p-toluene sulfonate 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 polyvinylpyrrolidone, 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 solution is 4.0-8.5wt%; In step (2), the content of the surfactant in the carbon quantum dot precursor solution is 0.05-0.2wt%.

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

9. The method of claim 3, wherein, The method has one or more of the following characteristics: In step (3), the annealing temperature is 200-400℃; In step (3), the annealing time is 1-3h; In step (3), the annealing is carried out in a mixed atmosphere of protective gas and hydrogen.

10. A full vanadium flow battery comprising the composite electrode of claim 1 or 2.

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