Grafted electrode, method for its preparation and use

Abstract

This invention belongs to the field of flow batteries, specifically relating to a grafted electrode, its preparation method, and its application. The grafted electrode of this invention includes a carbon skeleton and grafts on the carbon skeleton; the grafts include disulfide linkers and end groups; the disulfide linkers are -(CO-NH)-(Ar)-(R0)-(S-S)-(CH2)a-; wherein, R0 is absent, or includes 1-6 Ars and / or 1-6 -(S-S)-; Ar is a thiadiazole ring; a is any integer from 1 to 6; the end groups are R-CH(NH2)-CO-NH- or NH2-(CH2)c-SO2-NH-, -R is -(CH2)bR1, c is any integer from 1 to 6, b is any integer from 1 to 6, and R1 is an amino, carboxyl, guanidine, or mercapto group; the methylene group of the disulfide linker is connected to the end group. The grafted battery of this invention achieves "same molecule, dual function, and time-controllable" performance. It can enhance interfacial catalytic performance by relying on disulfide bond linkers and release amino acid stabilizers as needed, significantly improving battery efficiency and long-term cycle stability under high temperature conditions.

Description

Technical Field

[0001] This invention belongs to the field of flow batteries, specifically relating to a grafted electrode, its preparation method, and its application. Background Technology

[0002] Vanadium redox flow battery (VRFB) has broad application prospects in the field of large-scale energy storage due to its advantages such as high safety, long cycle life, and independent design of power and capacity. However, VRFB still faces two major bottlenecks in practical applications: (1) Insufficient high-temperature stability: pentavalent vanadium ions (V(V)) in the positive electrode electrolyte are easily hydrolyzed to form V2O5 precipitate when the temperature is higher than 40°C, which leads to flow channel blockage and rapid capacity decay; (2) Insufficient electrode catalytic activity: the catalytic activity of traditional carbon felt electrode for vanadium ion redox reaction is limited, which restricts the improvement of battery energy efficiency and power density.

[0003] The main technical routes to solve the above problems are divided into two categories: (1) Electrolyte additive method: adding stabilizers such as amino acids and phosphates to the electrolyte to inhibit the hydrolysis and precipitation of V(V) through complexation. However, this method has problems such as continuous consumption of additives, need to be replenished regularly, high cost, and difficulty in maintaining the effect for a long time; (2) Electrode surface modification method: introducing oxygen-containing / nitrogen-containing functional groups on the surface of carbon felt through acid oxidation, electric grafting and other methods to improve the catalytic activity of the electrode. However, this method only improves the electrode interface reaction and cannot solve the problem of high temperature stability of the electrolyte liquid phase.

[0004] Current technologies generally treat electrolyte additives and electrode modification as two independent technical routes, lacking a design approach that synergizes their functions. In particular, there is no known "spatiotemporal partitioning" electrode design that pre-grafts functional molecules onto the electrode surface and releases them controllably into the electrolyte under specific operating conditions. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a grafted electrode, its preparation method, and its application. The grafted battery of this invention achieves "one molecule, dual function, and time-controllable operation," enhancing interfacial catalytic performance through disulfide bond linkers and releasing amino acid stabilizers as needed, significantly improving the long-term cycle stability of the battery under high-temperature conditions.

[0006] Specifically, the present invention provides a grafted electrode comprising a carbon skeleton and a graft on the carbon skeleton; the graft comprises a disulfide linker and a terminal group; the disulfide linker is -(CO-NH)-(Ar)-(R0)-(SS)-(CH2)a-; wherein, R0 is absent, or comprises 1-6 Ar and / or 1-6 -(SS)-; Ar is a thiadiazole ring; a is any integer from 1 to 6; the terminal group is R-CH(NH2)-CO-NH- or NH2-(CH2)c-SO2-NH-, -R is -(CH2)bR1, c is any integer from 1 to 6, b is any integer from 1 to 6, R1 is an amino, carboxyl, guanidine, or mercapto group; the methylene group of the disulfide linker is connected to the terminal group.

[0007] In one or more embodiments, the R0 includes one Ar and one -(SS)-.

[0008] In one or more implementations, a is 2.

[0009] In one or more embodiments, R is -CH2COOH, -(CH2)2COOH, -(CH2)4NH2, -(CH2)3NHC=NHNH2 or -CH2SH.

[0010] This invention provides a method for preparing any of the grafted electrodes described herein, the method comprising the following steps: (1) The electrode substrate is placed in an oxidizing acid solution for the first reaction to obtain a carboxylated electrode; (2) A first condensing agent is added to the reaction system containing the carboxylated electrode and the disulfide bond linking reaction solution precursor obtained in step (1) to obtain the disulfide bond linking reaction solution. A second reaction is carried out under a first protective atmosphere to obtain a disulfide bond linker modified electrode. The disulfide bond linking reaction solution contains a disulfide bond precursor compound, which contains a thiadiazole ring and a sulfur-containing group. The sulfur-containing group is a thiol group and / or a disulfide bond. The first condensing agent promotes the formation of amide bonds between the disulfide bond precursor compound and the carboxylated electrode. (3) The disulfide bond linker modified electrode obtained in step (2) is placed in an amine compound solution and subjected to a third reaction under a second protective atmosphere to obtain a disulfide bond linker cystamined electrode; the amine compound solution contains amine compounds; the amine compounds contain amino, methylene and sulfur-containing groups; the sulfur-containing groups are thiol groups and / or disulfide bonds; (4) The disulfide bond linker cystamine electrode obtained in step (3) is placed in an amino acid solution and a fourth reaction is carried out under a third protective atmosphere to obtain the grafted electrode.

[0011] In one or more embodiments, in step (1), the electrode substrate is carbon paper, carbon cloth, carbon felt or graphite felt.

[0012] In one or more embodiments, in step (1), the oxidizing acid solution is a concentrated nitric acid solution and / or a concentrated sulfuric acid solution.

[0013] In one or more embodiments, in step (1), the time for the first reaction is 1-6 hours.

[0014] In one or more embodiments, in step (1), the temperature of the first reaction is 80-160°C.

[0015] In one or more embodiments, in step (2), the disulfide bond linkage reaction liquid precursor includes a disulfide bond precursor compound, a first solution and a first reducing agent; the first solution is a first organic solvent or a first buffer solution; the first buffer solution includes a first inorganic solvent and a first buffer pair.

[0016] In one or more embodiments, in step (2), the disulfide bond linkage reaction solution includes a disulfide bond precursor compound, a first solution, a first reducing agent and a first condensing agent; the first solution is a first organic solvent or a first buffer solution; the first buffer solution includes a first inorganic solvent and a first buffer pair.

[0017] In one or more embodiments, in step (2), the first condensing agent is selected from one or more of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxythiosuccinimide, N,N'-dicyclohexylcarbodiimide and 2-(7-azobenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate.

[0018] In one or more embodiments, in step (2), the concentration of the first condensing agent in the disulfide bond linkage reaction solution is 0.01-0.05 mol / L.

[0019] In one or more embodiments, in step (2), the first protective atmosphere is nitrogen and / or argon.

[0020] In one or more embodiments, in step (2), the second reaction takes 4-12 hours.

[0021] In one or more embodiments, in step (2), the temperature of the second reaction is 0-70°C.

[0022] In one or more embodiments, in step (3), the amine compound solution comprises an amine compound, a second reducing agent, a second buffer pair, and a second solvent.

[0023] In one or more embodiments, in step (3), the pH of the amine compound solution is 7.0-9.0.

[0024] In one or more embodiments, in step (3), the second protective atmosphere is nitrogen and / or argon.

[0025] In one or more embodiments, in step (3), the third reaction takes 4-8 hours.

[0026] In one or more embodiments, in step (3), the temperature of the third reaction is 0-50°C.

[0027] In one or more embodiments, in step (4), the amino acid solution comprises an amino acid, a second condensing agent, a third buffer pair, and a third solvent.

[0028] In one or more embodiments, in step (4), the pH of the amino acid solution is 5.0-8.0.

[0029] In one or more embodiments, in step (4), the third protective atmosphere is nitrogen and / or argon.

[0030] In one or more embodiments, in step (4), the fourth reaction takes 12-24 hours.

[0031] In one or more embodiments, in step (4), the temperature of the fourth reaction is 0-60°C.

[0032] In one or more embodiments, the method further includes: in step (1), after the first reaction, a first cleaning and drying is performed to obtain a carboxylated electrode.

[0033] In one or more embodiments, the method further includes: in step (2), after the second reaction, a second cleaning and drying is performed to obtain a disulfide bond linker modified electrode.

[0034] In one or more embodiments, the method further includes: in step (3), after the third reaction, a third washing and drying is performed to obtain a disulfide-linked cystamine electrode.

[0035] In one or more embodiments, the method further includes: in step (4), after the fourth reaction, a fourth cleaning and drying is performed to obtain the grafted electrode.

[0036] In one or more embodiments, in step (1), the concentrated nitric acid solution has a mass fraction of 65wt%-68wt%.

[0037] In one or more embodiments, in step (1), the concentrated sulfuric acid solution has a mass fraction of 95wt%-98wt%.

[0038] In one or more embodiments, in step (2), the disulfide bond linkage reaction precursor contains the first buffer pair, and the pH of the disulfide bond linkage reaction precursor is 5.0-7.0.

[0039] In one or more embodiments, in step (2), the disulfide bond linkage reaction solution contains the first buffer pair, and the pH of the disulfide bond linkage reaction solution is 5.0-7.0.

[0040] In one or more embodiments, in step (2), the method for preparing the reaction system comprising the carboxylated electrode and the disulfide bond-linked reaction liquid precursor obtained in step (1) includes: mixing the disulfide bond precursor compound with a first buffer containing the first buffer pair and the first inorganic solvent, adding the carboxylated electrode obtained in step (1) thereto, and then adding the first reducing agent to obtain the reaction system comprising the carboxylated electrode and the disulfide bond-linked reaction liquid precursor obtained in step (1).

[0041] In one or more embodiments, in step (2), the preparation method of the reaction system comprising the carboxylated electrode and the disulfide bond-linked reaction liquid precursor obtained in step (1) includes: mixing the disulfide bond precursor compound and the first organic solvent, adding a first reducing agent, and then performing a pre-reduction treatment under a fourth protective atmosphere to obtain the disulfide bond-linked reaction liquid precursor; finally, adding the carboxylated electrode obtained in step (1) to the disulfide bond-linked reaction liquid precursor to obtain the reaction system comprising the carboxylated electrode and the disulfide bond-linked reaction liquid precursor obtained in step (1).

[0042] In one or more embodiments, in step (2), the disulfide precursor compound is selected from one or more of 2,5-dimercapto-1,3,4-thiadiazole, bis(1,3,4-thiadiazole-2,5-dimercapto) disulfide and 2-amino-5-mercapto-1,3,4-thiadiazole.

[0043] In one or more embodiments, in step (2), the first reducing agent is selected from one or more of tris(2-carboxyethyl)phosphine, dithiothreitol, and tris(3-hydroxypropyl)phosphine.

[0044] In one or more embodiments, in step (2), the first buffer pair is 2-morpholine ethanesulfonic acid, 3-(N-morpholine)-2-hydroxypropanesulfonic acid, or bis(2-hydroxyethyl)aminotrihydroxymethylmethane.

[0045] In one or more embodiments, in step (2), the first organic solvent is selected from one or more of N,N-dimethylformamide, dichloromethane, and isopropanol.

[0046] In one or more embodiments, in step (2), the first inorganic solvent is water.

[0047] In one or more embodiments, in step (2), the concentration of the disulfide bond precursor compound in the disulfide bond linkage reaction liquid precursor is 0.02-0.10 mol / L.

[0048] In one or more embodiments, in step (2), the concentration of the first buffer pair in the disulfide bond-linking reaction solution precursor is 0.05-0.20 mol / L.

[0049] In one or more embodiments, in step (2), the concentration of the first reducing agent in the disulfide bond linkage reaction precursor is 0.010-0.020 mol / L.

[0050] In one or more embodiments, in step (2), the concentration of the disulfide bond precursor compound in the disulfide bond linkage reaction solution is 0.02-0.10 mol / L.

[0051] In one or more embodiments, in step (2), the concentration of the first buffer pair in the disulfide bond linkage reaction solution is 0.05-0.20 mol / L.

[0052] In one or more embodiments, in step (2), the concentration of the first reducing agent in the disulfide bond linkage reaction solution is 0.010-0.020 mol / L.

[0053] In one or more embodiments, in step (3), the method for preparing the amine compound solution includes: mixing the amine compound with a second buffer containing the second buffer pair and the second solvent to obtain the amine compound solution.

[0054] In one or more embodiments, in step (3), the amine compound is selected from one or more of cystamine dihydrochloride, cystamine hydrochloride, cystamine, and cystamine.

[0055] In one or more embodiments, in step (3), the second reducing agent is selected from one or more of tris(2-carboxyethyl)phosphine, dithiothreitol, and tris(3-hydroxypropyl)phosphine.

[0056] In one or more embodiments, in step (3), the second buffer pair is tris(hydroxymethyl)aminomethane hydrochloric acid, 4-hydroxyethylpiperazine ethanesulfonic acid, or N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid.

[0057] In one or more embodiments, in step (3), the second solvent is water.

[0058] In one or more embodiments, in step (3), the concentration of the amine compound in the amine compound solution is 0.03-0.20 mol / L.

[0059] In one or more embodiments, in step (3), the concentration of the second reducing agent in the amine compound solution is 0.03-0.20 mol / L.

[0060] In one or more embodiments, in step (3), the concentration of the second buffer pair in the amine compound solution is 0.05-0.20 mol / L.

[0061] In one or more embodiments, in step (4), the method for preparing the amino acid solution includes: mixing the amino acid, the second condensing agent and a third buffer containing the third buffer pair and the third solvent, and then performing a pre-activation treatment under a fifth protective atmosphere to obtain the amino acid solution.

[0062] In one or more embodiments, in step (4), the amino acid is R-CH(NH2)-COOH or NH2-(CH2)c-SO2-NH-, -R is -(CH2)bR1, c is any integer from 1 to 6, b is any integer from 1 to 6, and R1 is an amino, carboxyl, guanidine, or thiol group; preferably, the amino acid is selected from one or more of aspartic acid, glutamic acid, lysine, arginine, taurine, and cysteine.

[0063] In one or more embodiments, in step (4), the second condensing agent is selected from one or more of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxythiosuccinimide, N,N'-dicyclohexylcarbodiimide and 2-(7-azobenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate.

[0064] In one or more embodiments, in step (4), the third buffer pair is 2-morpholine ethanesulfonic acid, 3-(N-morpholine)-2-hydroxypropanesulfonic acid, or bis(2-hydroxyethyl)aminotrihydroxymethylmethane.

[0065] In one or more embodiments, in step (4), the third solvent is water.

[0066] In one or more embodiments, in step (4), the concentration of the amino acid in the amino acid solution is 0.01-0.50 mol / L.

[0067] In one or more embodiments, in step (4), the concentration of the second condensing agent in the amino acid solution is 0.01-0.05 mol / L.

[0068] In one or more embodiments, in step (4), the concentration of the third buffer pair in the amino acid solution is 0.05-0.20 mol / L.

[0069] In one or more embodiments, the first cleaning and drying includes: ultrasonic cleaning 3-5 times sequentially with N,N-dimethylformamide, anhydrous ethanol and water.

[0070] In one or more embodiments, the second cleaning and drying includes: ultrasonic cleaning 3-5 times sequentially with N,N-dimethylformamide, anhydrous ethanol and water.

[0071] In one or more embodiments, the third cleaning and drying includes: ultrasonic cleaning 3-5 times sequentially with N,N-dimethylformamide, anhydrous ethanol and water.

[0072] In one or more embodiments, the fourth cleaning and drying process includes ultrasonic cleaning 3-5 times sequentially with N,N-dimethylformamide, anhydrous ethanol, and water.

[0073] In one or more embodiments, in step (2), the temperature of the pre-reduction treatment is 10-70°C.

[0074] In one or more embodiments, in step (2), the pre-reduction process takes 5-60 minutes.

[0075] In one or more embodiments, in step (2), the fourth protective atmosphere is nitrogen and / or argon.

[0076] In one or more embodiments, in step (4), the temperature of the pre-activation treatment is 0-60°C.

[0077] In one or more embodiments, in step (4), the pre-activation treatment time is 10-60 min.

[0078] In one or more embodiments, in step (4), the fifth protective atmosphere is nitrogen and / or argon.

[0079] The basic flow battery provided by the present invention includes any of the grafted electrodes described in the present invention or grafted electrodes prepared by any of the methods described in the present invention and a base electrolyte.

[0080] In one or more embodiments, the matrix electrolyte comprises vanadium ions and an acidic matrix.

[0081] This invention provides a method for preparing an amino acid-functionalized flow battery. The method includes controlling the single-cell discharge voltage of any of the basic flow batteries described in this invention to be 0.8-1.0V, and the corresponding continuous discharge time at the voltage to be 30-180s. The terminal group reaction in the grafted electrode generates amino acids which are released into the matrix electrolyte, thereby obtaining an amino acid-functionalized flow battery.

[0082] This invention provides an amino acid-functionalized flow battery prepared using any of the methods described in this invention.

[0083] This invention provides the application of any of the grafted electrodes described in this invention or grafted electrodes prepared by any of the methods described in this invention in improving the stability and / or energy efficiency of flow batteries.

[0084] In one or more embodiments, (a) when the single-cell discharge voltage is greater than 1.0V and less than or equal to 1.7V, the grafted electrode improves the energy efficiency of the flow battery.

[0085] In one or more embodiments, (b) when the single-cell discharge voltage is greater than or equal to 0.8V and less than or equal to 1.0V, the terminal group reaction in the grafted electrode generates amino acids which are released into the electrolyte of the flow battery, thereby improving the stability of the flow battery.

[0086] Compared with the prior art, the present invention has the following beneficial technical effects: (1) After amino acids are grafted onto the electrode surface, the hydrophilicity of the electrode surface can be significantly improved, the electrolyte wetting resistance can be reduced, and highly active electrochemical reaction centers can be formed, effectively reducing the redox overpotential of vanadium ions and improving the battery energy efficiency. (2) The amino acid grafted electrode and controllable release method have outstanding engineering application advantages. The core of this method is that it is easy to implement and the operation process is simplified. For the application of vanadium redox flow batteries in high-temperature engineering scenarios of 40~60℃, the pre-charge and discharge strategy is used for control: when the battery discharges to the total voltage drop to 0.8~1.0 V, the disulfide bond in the disulfide bond linker undergoes reduction and cracking, triggering the rapid release of amino acid molecules into the electrolyte system. This process realizes the functional switch from "interfacial catalysis" to "bulk phase stability", thereby effectively suppressing the problem of the positive electrode V(V) ions hydrolyzing at high temperature to generate vanadium pentoxide precipitate. Attached Figure Description

[0087] Figure 1 This is a process flow diagram for preparing grafted electrodes according to some embodiments of the present invention.

[0088] Figure 2 This is a schematic diagram of the linear structure of the grafted electrode obtained in Embodiment 1 of the present invention.

[0089] Figure 3This is a schematic diagram of the structure of the grafted electrode obtained in Embodiment 1 of the present invention after bond breakage. Detailed Implementation

[0090] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0091] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0092] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0093] In this document, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0094] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0095] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0096] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0097] The grafted electrode provided by this invention may include a carbon skeleton and grafts on the carbon skeleton; the grafts may include disulfide linkers and end groups; the disulfide linkers may be -(CO-NH)-(Ar)-(R0)-(SS)-(CH2)a-; wherein, R0 may be absent, or may include 1-6 Ars and / or 1-6 -(SS)-; Ar is a thiadiazole ring (C2N2S); a may be any integer from 1 to 6; the end group may be R-CH(NH2)-CO-NH- or NH2-(CH2)c-SO2-NH-, -R is -(CH2)bR1, c may be any integer from 1 to 6, b may be any integer from 1 to 6, R1 may be amino, carboxyl, guanidine or mercapto; the methylene group of the disulfide linker may be connected to the end group. In the grafted electrode of this invention, disulfide linkers covalently graft amino acid molecules onto the carbon skeleton surface of the electrode substrate. During the initial operation of the flow battery, the grafted amino acids and disulfide linkers synergistically act as catalytic active sites, efficiently promoting the redox reaction of vanadium ions. When a specific electrochemical reduction potential is reached, the disulfide linkers undergo electrochemical reduction cleavage, and the amino acid molecules are controllably released from the electrode surface into the electrolyte, playing a stabilizing role by inhibiting high-temperature precipitation of V(V). This invention achieves "one molecule, dual function, and time-controllable"—both enhancing interfacial catalytic performance through disulfide linkers and releasing amino acid stabilizers as needed, thereby significantly improving the long-term cycle stability of the battery under high-temperature conditions.

[0098] In this invention, R0 may include one Ar and one -(SS)-. In this invention, a can be 2.

[0099] In this invention, R can be -CH2COOH, -(CH2)2COOH, -(CH2)4NH2, -(CH2)3NHC=NHNH2, or -CH2SH. In this invention, when the terminal group of the grafted electrode is -CH2COOH, -(CH2)2COOH, -(CH2)4NH2, -(CH2)3NHC=NHNH2, or -CH2SH, the grafted electrode can function in both the electrode and the electrolyte, thereby enhancing the catalytic activity of the electrode and the high-temperature stability of the electrolyte.

[0100] This invention provides a method for preparing any of the grafted electrodes of this invention, the method comprising the following steps: (1) placing an electrode substrate in an oxidizing acid solution for a first reaction to obtain a carboxylated electrode; (2) adding a first condensing agent to a reaction system containing the carboxylated electrode obtained in step (1) and a disulfide bond linking reaction solution precursor to obtain a disulfide bond linking reaction solution, and performing a second reaction under a first protective atmosphere to obtain a disulfide bond linker modified electrode; the disulfide bond linking reaction solution contains a disulfide bond precursor compound, which may contain a thiadiazole ring and a sulfur-containing group; the sulfur-containing group may be a thiol group and / or a mercapto group. Or disulfide bond; the first condensing agent promotes the formation of amide bond between the disulfide bond precursor compound and the carboxylated electrode; (3) the disulfide bond linker modified electrode obtained in step (2) is placed in an amine compound solution and a third reaction is carried out under a second protective atmosphere to obtain a disulfide bond linker cystamined electrode; the amine compound solution contains amine compounds; the amine compounds may contain amino, methylene and sulfur-containing groups; the sulfur-containing groups may be thiol and / or disulfide bonds; (4) the disulfide bond linker cystamined electrode obtained in step (3) is placed in an amino acid solution and a fourth reaction is carried out under a third protective atmosphere to obtain a grafted electrode.

[0101] In step (1) of this invention, the electrode substrate is placed in an oxidizing acid solution for a first reaction to obtain a carboxylated electrode. Step (1) is a carboxylation treatment, which can introduce carboxyl functional groups on the surface of the electrode substrate, providing reactive groups for subsequent reactions.

[0102] In step (1) of this invention, the electrode substrate can be carbon paper, carbon cloth, carbon felt, or graphite felt. In step (1) of this invention, the oxidizing acid solution can be concentrated nitric acid solution and / or concentrated sulfuric acid solution. In step (1) of this invention, the mass fraction of the concentrated nitric acid solution can be 65wt%-68wt%, for example, 65wt%, 66wt%, 67wt%, or 68wt%. In step (1) of this invention, the mass fraction of the concentrated sulfuric acid solution can be 95wt%-98wt%, for example, 95wt%, 96wt%, 97wt%, or 98wt%. In step (1) of this invention, when concentrated sulfuric acid solution and concentrated nitric acid solution are used simultaneously, they can be used in any ratio.

[0103] In step (1) of this invention, the time for the first reaction can be 1-6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours. In step (1) of this invention, the temperature for the first reaction can be 80-160°C, for example, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or 160°C. Step (1) of this invention can employ reaction methods commonly used in the art, such as hydrothermal reactions.

[0104] The method for preparing the grafted electrode according to the present invention may further include: in step (1), after the first reaction, a first cleaning and drying is performed to obtain the carboxylated electrode. In the present invention, the first cleaning and drying may include a first cleaning and a first drying. In the present invention, the first cleaning may be performed by ultrasonic cleaning with N,N-dimethylformamide (DMF), anhydrous ethanol, and water sequentially for 3-5 times. In the present invention, the first drying may be performed at 40-80℃ for 4-12 hours. In the present invention, each cleaning session may last for 10-15 minutes. In the present invention, the above cleaning steps can thoroughly remove residual reagents and adsorbates.

[0105] In step (2) of this invention, a first condensing agent is added to the reaction system containing the carboxylated electrode and the disulfide bond-linking reaction solution precursor obtained in step (1) to obtain the disulfide bond-linking reaction solution. A second reaction is carried out under a first protective atmosphere to obtain a disulfide bond-linked electrode. The disulfide bond-linking reaction solution may contain a disulfide bond precursor compound, which may contain a thiadiazole ring and a sulfur-containing group. The sulfur-containing group may be a thiol group and / or a disulfide bond. The first condensing agent can promote the formation of amide bonds between the disulfide bond precursor compound and the carboxylated electrode. Step (2) of this invention is disulfide bond-linking grafting, which allows the disulfide bond-linking linker to be connected to the carboxyl group on the surface of the carboxylated electrode through an amide bond to obtain a disulfide bond-linked electrode, which provides reactive groups for subsequent reactions.

[0106] In step (2) of the present invention, the disulfide bond linkage reaction liquid precursor may include a disulfide bond precursor compound, a first solution and a first reducing agent; the first solution may be a first organic solvent or a first buffer solution; the first buffer solution may include a first inorganic solvent and a first buffer pair.

[0107] In step (2) of this invention, the disulfide precursor compound can be one or more selected from 2,5-dimercapto-1,3,4-thiadiazole (DMcT), bis(1,3,4-thiadiazole-2,5-dimercapto) disulfide (BTDD), and 2-amino-5-mercapto-1,3,4-thiadiazole (AMTD). In the preparation of the grafted electrode, the use of the above-mentioned disulfide precursor compound facilitates the formation of stable amide bonds with the carboxyl groups on the electrode substrate surface, improving grafting efficiency and stability. Consequently, the resulting grafted electrode can function in both the electrode and the electrolyte, enhancing the catalytic activity of the electrode and the high-temperature stability of the electrolyte. In step (2) of this invention, the first reducing agent can be one or more selected from tris(2-carboxyethyl)phosphine (TCEP, a thiol compound), dithiothreitol (DTT), and tris(3-hydroxypropyl)phosphine (THPP). In this invention, the use of the above-mentioned first reducing agent helps prevent thiol oxidation. In step (2) of this invention, the first organic solvent can be one or more selected from N,N-dimethylformamide, dichloromethane, and isopropanol. In the process of preparing the grafted electrode, the use of the aforementioned first reducing agent helps to prevent the thiol groups in the disulfide bond precursor compound from being oxidized to form disulfide bonds and undergoing self-polymerization. This improves the grafting efficiency and stability of the disulfide bond precursor compound on the electrode substrate, allowing the resulting grafted electrode to function in both the electrode and the electrolyte, thereby enhancing the catalytic activity of the electrode and the high-temperature stability of the electrolyte. In step (2) of this invention, the first buffer pair can be 2-morpholinoethanesulfonic acid (MES), 3-(N-morpholino)-2-hydroxypropanesulfonic acid (MOPSO), or bis(2-hydroxyethyl)amino(tris-hydroxymethyl)methane (Bis-Tris). In step (2) of this invention, the first inorganic solvent can be water.

[0108] In step (2) of this invention, the concentration of the disulfide bond precursor compound in the disulfide bond linkage reaction solution precursor can be 0.02-0.10 mol / L, for example 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, or 0.10 mol / L. In step (2) of this invention, the concentration of the first reducing agent in the disulfide bond linkage reaction solution precursor can be 0.010-0.020 mol / L, for example 0.010 mol / L, 0.012 mol / L, 0.014 mol / L, 0.016 mol / L, 0.018 mol / L, or 0.020 mol / L. In step (2) of the present invention, the concentration of the first buffer pair in the disulfide bond-linked reaction solution precursor can be 0.05-0.20 mol / L, for example 0.05 mol / L, 0.10 mol / L, 0.15 mol / L, or 0.20 mol / L.

[0109] In step (2) of the present invention, the disulfide bond linkage reaction liquid precursor contains a first buffer pair, and the pH of the disulfide bond linkage reaction liquid precursor can be 5.0-7.0, for example 5.0, 5.5, 6.0, 6.5, 7.0.

[0110] The preparation method of the reaction system containing the carboxylated electrode and disulfide bond-linked reaction liquid precursor obtained in step (1) in step (2) of the present invention may include: mixing the disulfide bond precursor compound and a first buffer containing a first buffer pair and a first inorganic solvent, adding the carboxylated electrode obtained in step (1) to the mixture, and then adding a first reducing agent to obtain a reaction system containing the carboxylated electrode and disulfide bond-linked reaction liquid precursor obtained in step (1).

[0111] The preparation method of the reaction system comprising the carboxylated electrode and disulfide bond-linked reaction liquid precursor obtained in step (1) of the present invention may include: mixing the disulfide bond precursor compound and the first organic solvent, adding the first reducing agent, and then performing a pre-reduction treatment under a fourth protective atmosphere to obtain the disulfide bond-linked reaction liquid precursor; finally, adding the carboxylated electrode obtained in step (1) to the disulfide bond-linked reaction liquid precursor to obtain a reaction system comprising the carboxylated electrode and disulfide bond-linked reaction liquid precursor obtained in step (1). In step (2) of the present invention, the temperature of the pre-reduction treatment can be 10-70℃, for example, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, or 70℃. In step (2) of the present invention, the time of the pre-reduction treatment can be 5-60 min. In step (2) of the present invention, the fourth protective atmosphere can be nitrogen and / or argon.

[0112] In this invention, DMCT itself is in the form of free thiol (-SH) and can directly enter the reaction process, while the initial form of BTDD is disulfide (-SS-). Pre-reduction of BTDD is a necessary and critical operation, which can convert the inactive disulfide (-SS-) into free thiol (-SH) in situ, thereby driving the subsequent reaction.

[0113] In this invention, adding a first reducing agent before adding a first condensing agent helps to prevent the thiol group in the disulfide bond precursor compound from being oxidized to form a disulfide bond and undergoing self-polymerization. This can improve the grafting efficiency and grafting stability of the disulfide bond precursor compound on the electrode substrate, so that the resulting grafted electrode can play a role in both the electrode and the electrolyte, thereby improving the catalytic activity of the electrode and the high-temperature stability of the electrolyte.

[0114] In step (2) of the present invention, the disulfide bond linkage reaction solution may include a disulfide bond precursor compound, a first solution, a first reducing agent and a first condensing agent; the first solution may be a first organic solvent or a first buffer solution; the first buffer solution may include a first inorganic solvent and a first buffer pair.

[0115] In step (2) of this invention, the first condensing agent can be one or more selected from 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), N-hydroxythiosuccinimide (Sulfo-NHS), N,N'-dicyclohexylcarbodiimide (DCC), and 2-(7-azobenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate (HATU). In the process of preparing the grafted electrode, the use of the above-mentioned first condensing agent can activate and stabilize the carboxyl groups and reaction intermediates on the surface of the carboxylated electrode, which is beneficial for the disulfide bond precursor compound to form stable amide bonds with the carboxyl groups on the surface of the electrode substrate, thereby improving the grafting efficiency and grafting stability. The resulting grafted electrode can then function in both the electrode and the electrolyte, improving the catalytic activity of the electrode and the high-temperature stability of the electrolyte. In some embodiments, the present invention uses a combination of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxythiosuccinimide (Sulfo-NHS), preferably, the molar ratio of EDC to Sulfo-NHS can be 1:(1-3). In step (2) of the present invention, the concentration of the first condensing agent in the disulfide bond linkage reaction solution can be 0.01-0.05 mol / L, for example 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, or 0.05 mol / L. In step (2) of this invention, the concentration of the disulfide bond precursor compound in the disulfide bond linkage reaction solution can be 0.02-0.10 mol / L, for example, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, or 0.10 mol / L. In step (2) of this invention, the concentration of the first reducing agent in the disulfide bond linkage reaction solution can be 0.010-0.020 mol / L, for example, 0.010 mol / L, 0.012 mol / L, 0.014 mol / L, 0.016 mol / L, 0.018 mol / L, or 0.020 mol / L. In step (2) of the present invention, the concentration of the first buffer pair in the disulfide bond linkage reaction solution can be 0.05-0.20 mol / L, for example 0.05 mol / L, 0.10 mol / L, 0.15 mol / L, or 0.20 mol / L.

[0116] In step (2) of the present invention, the disulfide bond linkage reaction solution contains a first buffer pair, and the pH of the disulfide bond linkage reaction solution can be 5.0-7.0, for example 5.0, 5.5, 6.0, 6.5, 7.0.

[0117] In step (2) of this invention, the first protective atmosphere can be nitrogen (N2) and / or argon (Ar). In step (2) of this invention, the second reaction time can be 4-12 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. In step (2) of this invention, the temperature of the second reaction can be 0-70°C, for example, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, or 70°C.

[0118] The method for preparing the grafted electrode according to the present invention may further include: in step (2), after the second reaction, a second cleaning and drying is performed to obtain the disulfide bond linker modified electrode. In the present invention, the second cleaning and drying may include a second cleaning and a second drying. In the present invention, the second cleaning may be performed by ultrasonic cleaning with N,N-dimethylformamide, anhydrous ethanol, and water sequentially for 3-5 times. In the present invention, the second drying may be performed at 40-80℃ for 4-12 hours. In the present invention, each cleaning session may last for 10-15 minutes. In the present invention, the above cleaning steps can thoroughly remove residual reagents and adsorbates.

[0119] In step (3) of this invention, the disulfide-linked linker-modified electrode obtained in step (2) is placed in an amine compound solution and subjected to a third reaction under a second protective atmosphere to obtain a disulfide-linked linker cystamined electrode. The amine compound solution may contain amine compounds; the amine compounds may contain amino groups, methylene groups, and sulfur-containing groups; the sulfur-containing groups may be thiol groups and / or disulfide bonds. Step (3) of this invention involves cystamine treatment, which introduces amino functional groups onto the disulfide-linked linkers of the disulfide-linked linker-modified electrode to obtain a disulfide-linked linker cystamined electrode. In the process of preparing the grafted electrode, step (3) of this invention provides amino reaction sites for subsequent amino acid grafting, which improves grafting efficiency and grafting stability. The resulting grafted electrode can then function in both the electrode and the electrolyte, improving the catalytic activity of the electrode and the high-temperature stability of the electrolyte.

[0120] In step (3) of this invention, the amine compound solution may include an amine compound, a second reducing agent, a second buffer pair, and a second solvent. In step (3) of this invention, the amine compound may be one or more selected from cystamine dihydrochloride, cystamine hydrochloride, cystamine, and cysteamine. In the preparation of the grafted electrode, the use of the above-mentioned amine compounds facilitates the introduction of a large number of stable and highly reactive amino groups onto the surface of the disulfide bond linker-modified electrode, thereby providing the necessary chemical reaction sites for the covalent grafting of amino acids, improving the grafting efficiency and stability of amino acids, and thus the resulting grafted electrode can function in both the electrode and the electrolyte, improving the catalytic activity of the electrode and the high-temperature stability of the electrolyte. In step (3) of this invention, the second reducing agent may be one or more selected from tris(2-carboxyethyl)phosphine, dithiothreitol, and tris(3-hydroxypropyl)phosphine. In step (3) of this invention, the second buffer pair can be tris(hydroxymethyl)aminomethane hydrochloric acid (Tris-HCl), 4-hydroxyethylpiperazine ethanesulfonic acid (HEPES), or N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (TAPS). In step (3) of this invention, the second solvent can be water.

[0121] In step (3) of this invention, the concentration of the amine compound in the amine compound solution can be 0.03-0.20 mol / L, for example, 0.05 mol / L, 0.10 mol / L, 0.15 mol / L, or 0.20 mol / L. In step (3) of this invention, the concentration of the second reducing agent in the amine compound solution can be 0.03-0.20 mol / L, for example, 0.05 mol / L, 0.10 mol / L, 0.15 mol / L, or 0.20 mol / L. In step (3) of this invention, the concentration of the second buffer pair in the amine compound solution can be 0.05-0.20 mol / L, for example, 0.05 mol / L, 0.10 mol / L, 0.15 mol / L, or 0.20 mol / L.

[0122] In step (3) of the present invention, the pH of the amine compound solution can be 7.0-9.0, for example 7.0, 7.5, 8.0, 8.5, 9.0.

[0123] In step (3) of the present invention, the method for preparing the amine compound solution may include: mixing the amine compound with a second buffer containing a second buffer pair and a second solvent to obtain the amine compound solution.

[0124] In step (3) of this invention, the second protective atmosphere can be nitrogen and / or argon. In step (3) of this invention, the time for the third reaction can be 4-8 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours. In step (3) of this invention, the temperature for the third reaction can be 0-50°C, for example, 10°C, 20°C, 30°C, 40°C, or 50°C.

[0125] The method for preparing the grafted electrode according to the present invention may further include: in step (3), after the third reaction, a third cleaning and drying is performed to obtain the disulfide bond-linked cystamined electrode. In the present invention, the third cleaning and drying may include a third cleaning and a third drying. In the present invention, the third cleaning may be performed by ultrasonic cleaning with N,N-dimethylformamide, anhydrous ethanol, and water sequentially for 3-5 times. In the present invention, the third drying may be performed at 40-80℃ for 4-12 hours. In the present invention, each cleaning session may last for 10-15 minutes. In the present invention, the above cleaning steps can thoroughly remove residual reagents and adsorbates.

[0126] In step (4) of this invention, the disulfide linker cystamine electrode obtained in step (3) is placed in an amino acid solution, and a fourth reaction is carried out under a third protective atmosphere to obtain a grafted electrode. In step (4) of this invention, amino acid grafting is performed, which allows the amino acid to be connected to the amino functional group of the disulfide linker through an amide bond, thereby obtaining an amino acid grafted electrode.

[0127] In step (4) of this invention, the amino acid solution may include an amino acid, a second condensing agent, a third buffer pair, and a third solvent. In step (4) of this invention, the amino acid may be R-CH(NH2)-COOH or NH2-(CH2)c-SO2-NH-, -R is -(CH2)bR1, c is any integer from 1 to 6, b is any integer from 1 to 6, and R1 is an amino, carboxyl, guanidinyl, or thiol group; preferably, the amino acid may be one or more selected from aspartic acid, glutamic acid, lysine, arginine, taurine, and cysteine. In step (4) of this invention, the second condensing agent may be one or more selected from 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxythiosuccinimide, N,N'-dicyclohexylcarbodiimide, and 2-(7-azobenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate. In the preparation of the grafted electrode, the use of the aforementioned second condensing agent in this invention facilitates the activation and stabilization of carboxyl groups and reaction intermediates in amino acid molecules, enabling them to form amide bonds more efficiently. This improves the grafting efficiency and stability of the amino acids, allowing the resulting grafted electrode to function in both the electrode and the electrolyte, thereby enhancing the catalytic activity of the electrode and the high-temperature stability of the electrolyte. In some embodiments, this invention uses 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. and The combination of N-hydroxythiosuccinimide, preferably, has a molar ratio of EDC to Sulfo-NHS of 1:(1-3). In step (4) of the present invention, the third buffer pair can be 2-morpholine ethanesulfonic acid, 3-(N-morpholine)-2-hydroxypropanesulfonic acid, or bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane. In step (4) of the present invention, the third solvent can be water.

[0128] In step (4) of this invention, the concentration of amino acids in the amino acid solution can be 0.01-0.50 mol / L, for example, 0.05 mol / L, 0.10 mol / L, 0.15 mol / L, 0.20 mol / L, 0.25 mol / L, 0.30 mol / L, 0.35 mol / L, 0.40 mol / L, 0.45 mol / L, or 0.50 mol / L. In step (4) of this invention, the concentration of the second condensing agent in the amino acid solution can be 0.01-0.05 mol / L, for example, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, or 0.05 mol / L. In step (4) of this invention, the concentration of the third buffer pair in the amino acid solution can be 0.05-0.20 mol / L, for example, 0.05 mol / L, 0.10 mol / L, 0.15 mol / L, or 0.20 mol / L.

[0129] In step (4) of the present invention, the pH of the amino acid solution can be 5.0-8.0, for example 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0.

[0130] In step (4) of this invention, the preparation method of the amino acid solution may include: mixing amino acids, a second condensing agent, and a third buffer containing a third buffer pair and a third solvent, and then performing a pre-activation treatment under a fifth protective atmosphere to obtain an amino acid solution. In step (4) of this invention, the temperature of the pre-activation treatment can be 0-60℃, for example, 10℃, 20℃, 30℃, 40℃, 50℃, or 60℃. In this invention, the role of pre-activation is to pre-activate the amino acid molecules in the solution, converting their carboxyl groups into highly active intermediates, preparing for the subsequent formation of efficient, rapid, and stable amide bonds. In step (4) of this invention, the pre-activation treatment time can be 10-60 min, for example, 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min. In step (4) of this invention, the fifth protective atmosphere can be nitrogen and / or argon.

[0131] In step (4) of this invention, the third protective atmosphere can be nitrogen and / or argon. In step (4) of this invention, the time for the fourth reaction can be 12-24 hours, for example, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours. In step (4) of this invention, the temperature for the fourth reaction can be 0-60°C, for example, 10°C, 20°C, 30°C, 40°C, 50°C, or 60°C.

[0132] The method for preparing the grafted electrode according to the present invention may further include: in step (4), after the fourth reaction, a fourth cleaning and drying is performed to obtain the grafted electrode. In the present invention, the fourth cleaning and drying may include a fourth cleaning and a fourth drying. In the present invention, the fourth cleaning may be performed by ultrasonic cleaning with N,N-dimethylformamide, anhydrous ethanol, and water sequentially for 3-5 times. In the present invention, the fourth drying may be performed at 40-80℃ for 4-12 hours. In the present invention, each cleaning session may last 10-15 minutes. In the present invention, the above cleaning steps can thoroughly remove residual reagents and adsorbates.

[0133] The basic flow battery provided by this invention includes any grafted electrode of this invention or a grafted electrode prepared by any method of this invention and a base electrolyte. In this invention, the base electrolyte may include vanadium ions and an acidic matrix. In this invention, the acidic matrix may be sulfuric acid.

[0134] The method for preparing an amino acid-functionalized flow battery according to the present invention includes controlling the single-cell discharge voltage of any basic flow battery of the present invention to be 0.8-1.0V, and the corresponding continuous discharge time at the voltage to be 30-180s. The terminal group reaction in the grafted electrode generates amino acids which are released into the matrix electrolyte, thus obtaining the amino acid-functionalized flow battery. The present invention provides an amino acid-functionalized flow battery prepared using any method of the present invention.

[0135] This invention provides the application of any grafted electrode of this invention or a grafted electrode prepared by any method of this invention in improving the stability and / or energy efficiency of a flow battery. In this invention, when the single-cell discharge voltage is greater than 1.0V and less than or equal to 1.7V, the grafted electrode improves the energy efficiency of the flow battery. In this invention, when the single-cell discharge voltage is greater than or equal to 0.8V and less than or equal to 1.0V, the terminal group reaction in the grafted electrode generates amino acids that are released into the electrolyte of the flow battery, thereby improving the stability of the flow battery.

[0136] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art, unless otherwise stated. The raw material compounds in the embodiments are all commercially available.

[0137] The commercial carbon felt used in the embodiments, comparative examples, and test examples of this invention was produced by Sichuan Jiangyou Runsheng Graphite Felt Co., Ltd. The commercial carbon felt has a thickness of 2.5 mm and a volume of 10 cm × 10 cm.

[0138] The concentrated sulfuric acid in the embodiments and comparative examples of this invention has a mass fraction of 95 wt%. The concentrated nitric acid in the embodiments and comparative examples of this invention has a mass fraction of 65 wt%.

[0139] Example 1

[0140] This embodiment prepares the grafted electrode according to the following steps: 1. A commercial carbon felt was placed in a mixed solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 3:1 and subjected to hydrothermal reaction at 100°C for 3 hours. The mixture was then washed and dried to obtain a carboxylated electrode. 2. 2,5-Dimercapto-1,3,4-thiadiazole (DMcT, molecular weight: 150.2 g / mol) was dissolved in MES buffer (solvent: water). The carboxylated electrode was immersed in the buffer, and then TCEP was added to obtain the disulfide bond linkage reaction precursor (DMcT concentration: 0.06 mol / L, MES buffer concentration: 0.1 mol / L, TCEP concentration: 0.015 mol / L, pH: 6.0-6.5). Finally, Sulfo-NHS and EDC were added sequentially to obtain the disulfide bond linkage reaction solution (Sulfo-NHS concentration: 0.02 mol / L, EDC concentration: 0.02 mol / L). The reaction was carried out at 25°C for 6 hours under N2 protection, and then washed and dried to obtain the disulfide bond linker modified electrode. 3. Cystamine dihydrochloride, TCEP, and Tris-HCl buffer (solvent: water) were mixed to obtain an amino compound solution (wherein, the concentration of cystamine dihydrochloride was 0.10 mol / L, the concentration of TCEP was 0.015 mol / L, the concentration of Tris-HCl buffer was 0.1 mol / L, and the pH was 8.0-8.5); the disulfide linker modified electrode was immersed in the amino acid compound solution and reacted at 25°C for 6 hours under N2 protection, washed, and dried to obtain the disulfide linker cystamined electrode; 4. Cysteine, Sulfo-NHS, EDC, and MES buffer (solvent: water) were mixed and pre-activated at 25°C under N2 protection for 30 minutes to obtain an amino acid solution (wherein, the concentration of cysteine ​​was 0.15 mol / L, the concentration of Sulfo-NHS was 0.02 mol / L, the concentration of EDC was 0.02 mol / L, the concentration of MES buffer was 0.1 mol / L, and the pH was 5.5-6.0); then, the disulfide-linked cystamine electrode was immersed in the amino acid solution and reacted at 25°C under N2 protection for 18 hours. After washing and drying, the grafted electrode was obtained. The washing and drying process in steps 1-4 includes rinsing with deionized water, followed by ultrasonic cleaning with DMF, anhydrous ethanol, and deionized water for 15 minutes each, repeated 3 times, and vacuum drying at 60°C for 6 hours.

[0141] Example 2

[0142] The other conditions in this embodiment are the same as in embodiment 1. The only difference is that in step (4) of this embodiment, 0.20 mol / L taurine is used instead of 0.15 mol / L cysteine, and the reaction time is changed from 18h to 20h.

[0143] Example 3

[0144] The other conditions in this embodiment are the same as in embodiment 1, except that in step (3) of this embodiment, 0.15 mol / L cysteamine hydrochloride is used instead of 0.10 mol / L cysteamine dihydrochloride.

[0145] Example 4

[0146] The other conditions in this embodiment are the same as in Example 1, except that step (2) is as follows: bis(1,3,4-thiadiazole-2,5-diacyl) disulfide (BTDD, molecular weight: 298.44 g / mol) is dissolved in DMF, and then TCEP is added. The mixture is pre-reduced for 10 minutes at 25°C under N2 protection to obtain a disulfide bond linkage reaction solution precursor (BTDD concentration: 0.04 mol / L, TCEP concentration: 0.01 mol / L). The carboxylated electrode is immersed in the disulfide bond linkage reaction solution precursor, and Sulfo-NHS and EDC are added sequentially to obtain a disulfide bond linkage reaction solution (Sulfo-NHS concentration: 0.02 mol / L, EDC concentration: 0.02 mol / L). The reaction is carried out at 25°C for 8 hours under N2 protection. The electrode is then washed and dried to obtain a disulfide bond linker modified electrode.

[0147] Comparative Example 1

[0148] The comparative example prepared the electrode according to the following steps: a commercial carbon felt was placed in deionized water and hydrothermally reacted at 100°C for 3 hours, then washed and dried to obtain a carboxylated electrode; the washing and drying included rinsing with deionized water, followed by ultrasonic cleaning with DMF, anhydrous ethanol and deionized water for 15 minutes each, repeated 3 times, and vacuum drying at 60°C for 6 hours.

[0149] Comparative Example 2

[0150] The other conditions of this comparative example are the same as those of Example 1, except that TCEP is not added in step (2) of this comparative example.

[0151] Comparative Example 3

[0152] The other conditions of this comparative example are the same as those of Example 1, except that this comparative example does not include step (3).

[0153] Comparative Example 4

[0154] The other conditions of this comparative example are the same as those of Example 1, except that EDC and sulfo-NHS were not added in step (2) of this comparative example.

[0155] Test case

[0156] 1. Preparation of a single cell: A single cell is assembled by combining positive and negative electrolytes, a positive electrode, a negative electrode, and a separator; wherein the positive and negative electrolytes contain active materials and supporting electrolytes, and the active materials are 1.7 mol / L V. 4+ / V 5+ and 1.7 mol / LV 2+ / V 3+ The electrolyte used was 4 mol / L sulfuric acid, with 70 mL volumes for both the positive and negative electrodes. The membrane was a perfluorosulfonic acid proton exchange membrane (produced by Suzhou Kerun). The positive electrode used the electrodes prepared in Examples 1-4 and Comparative Examples 1-4, and the negative electrode used commercial carbon felt. The effective area of ​​the electrodes was 48 cm². 2 The compression ratio is 25%.

[0157] 2. Three efficiency tests: The coulombic efficiency, voltage efficiency, and energy efficiency of a single cell are tested using a constant current method, with current density values ​​of 150 and 250 mA / cm². 2 The upper limit of charging is 1.60 V, the lower limit of discharging is 1.10 V, and the circuit is cycled 5 times under each voltage level. The test results are shown in Table 1.

[0158] Table 1

[0159] 3. Controlled release assay of amino acid molecules: Experiment a: (1) Charging stage: constant current charging at a current density of 80 mA / cm² until the single cell voltage reaches 1.60V, completing the charging; (2) Discharge triggering stage: constant current discharge at 5 A, when the single cell voltage drops to 0.8 V, switch to constant voltage mode, and maintain the voltage at 0.8 V for 60 s; (3) The triggering process ends, and the test program is terminated. The amino acid content in the electrolyte of the flow battery containing the electrodes of Examples 1-4 and Comparative Examples 1-4 was tested by high performance liquid chromatography (HPLC), and the test results are shown in Table 2.

[0160] Experiment b: (1) Charging stage: constant current charging at a current density of 80 mA / cm² until the single cell voltage reaches 1.60V, completing the charging; (2) Discharge triggering stage: constant current discharge at 5 A, when the single cell voltage drops to 1.0 V, switch to constant voltage mode, and maintain the voltage at 1.0 V for 60 s; (3) The triggering process ends, and the test program is terminated. The amino acid content in the electrolyte of the flow battery containing the electrodes of Examples 1-4 and Comparative Examples 1-4 was tested by high performance liquid chromatography (HPLC), and the test results are shown in Table 2.

[0161] Table 2: Amino acid content in the electrolyte of flow battery containing electrodes from Examples 1-4 and Comparative Examples 1-4

[0162] 4. Pentavalent vanadium precipitation time test: The positive electrode electrolyte in the flow battery that underwent the controlled release test of amino acid molecules (test a) was subjected to deep oxidation using the constant voltage overcharge method to fully convert vanadium ions in the positive electrode electrolyte into pentavalent vanadium. The pentavalent vanadium electrolyte with a molar fraction of 95% was obtained by potentiometric titration. The pentavalent vanadium electrolyte was then allowed to stand in a water bath at 45°C to precipitate, and the inhibitory effect of the amino acid stabilizer on the hydrolysis of pentavalent vanadium was tested. The test results are shown in Table 3.

[0163] Table 3: Pentavalent Vanadium Precipitation Time in Examples 1-4 and Comparative Examples 1-4

[0164] As shown in Comparative Example 2, without the addition of TCEP, the thiol groups of DMcT are oxidized during the reaction to form disulfide bonds and undergo self-polymerization, which prevents DMcT from being effectively grafted onto the carbon felt surface, and significantly reduces the efficiency of subsequent cystamineization and amino acid grafting.

[0165] As can be seen from Comparative Example 3, since the DMCT molecule itself does not contain free amino groups (-NH2), after omitting the cystamine step, the carbon felt surface lacks sites for reacting with the carboxyl groups of amino acids, and cysteine ​​cannot be grafted onto the carbon felt surface through amide bonds.

[0166] As shown in Comparative Example 4, without the activation of the carboxyl groups by the first condensing agent, DMcT cannot form stable amide bonds with the carboxyl groups on the carbon felt surface, resulting in extremely low grafting efficiency.

Claims

1. A grafted electrode, characterized in that, The grafted electrode includes a carbon skeleton and grafts on the carbon skeleton; the grafts include disulfide linkers and end groups. The disulfide linker is -(CO-NH)-(Ar)-(R0)-(SS)-(CH2)a-; wherein R0 is absent, or includes 1-6 Ars and / or 1-6 -(SS)-; Ar is a thiadiazole ring; a is any integer from 1 to 6; The terminal group is R-CH(NH2)-CO-NH- or NH2-(CH2)c-SO2-NH-, -R is -(CH2)bR1, c is any integer from 1 to 6, b is any integer from 1 to 6, and R1 is an amino, carboxyl, guanidine, or mercapto group; The methylene group of the disulfide linker is connected to the terminal group.

2. The grafted electrode as described in claim 1, characterized in that, The grafted electrode has one or more of the following characteristics: The R0 includes one Ar and one -(SS)-; a is 2; The R is -CH2COOH, -(CH2)2COOH, -(CH2)4NH2, -(CH2)3NHC=NHNH2 or -CH2SH.

3. A method for preparing the grafted electrode according to claim 1 or 2, characterized in that, The method includes the following steps: (1) The electrode substrate is placed in an oxidizing acid solution for the first reaction to obtain a carboxylated electrode; (2) A first condensing agent is added to a reaction system containing the carboxylated electrode and the disulfide bond linking reaction solution precursor obtained in step (1) to obtain a disulfide bond linking reaction solution. A second reaction is carried out under a first protective atmosphere to obtain a disulfide bond linker modified electrode. The disulfide bond linking reaction solution contains a disulfide bond precursor compound, which contains a thiadiazole ring and a sulfur-containing group. The sulfur-containing group is a thiol group and / or a disulfide bond. The first condensing agent is used to form an amide group between the disulfide bond precursor compound and the carboxylated electrode. (3) The disulfide bond linker modified electrode obtained in step (2) is placed in an amine compound solution and subjected to a third reaction under a second protective atmosphere to obtain a disulfide bond linker cystamined electrode; the amine compound solution contains amine compounds; the amine compounds contain amino, methylene and sulfur-containing groups; the sulfur-containing groups are thiol groups and / or disulfide bonds; (4) The disulfide bond linker cystamine electrode obtained in step (3) is placed in an amino acid solution and a fourth reaction is carried out under a third protective atmosphere to obtain the grafted electrode.

4. The method as described in claim 3, characterized in that, The method has one or more of the following characteristics: In step (1), the electrode substrate is carbon paper, carbon cloth, carbon felt or graphite felt; In step (1), the oxidizing acid solution is a concentrated nitric acid solution and / or a concentrated sulfuric acid solution; In step (1), the first reaction takes 1-6 hours; In step (1), the temperature of the first reaction is 80-160℃; In step (2), the disulfide bond linkage reaction liquid precursor includes a disulfide bond precursor compound, a first solution, and a first reducing agent; the first solution is a first organic solvent or a first buffer solution; the first buffer solution includes a first inorganic solvent and a first buffer pair; In step (2), the disulfide bond linkage reaction solution includes a disulfide bond precursor compound, a first solution, a first reducing agent, and a first condensing agent; the first solution is a first organic solvent or a first buffer solution; the first buffer solution includes a first inorganic solvent and a first buffer pair; In step (2), the first condensing agent is selected from one or more of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxythiosuccinimide, N,N'-dicyclohexylcarbodiimide and 2-(7-azobenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate; In step (2), the concentration of the first condensing agent in the disulfide bond linkage reaction solution is 0.01-0.05 mol / L; In step (2), the first protective atmosphere is nitrogen and / or argon; In step (2), the second reaction takes 4-12 hours; In step (2), the temperature of the second reaction is 0-70℃; In step (3), the amine compound solution includes an amine compound, a second reducing agent, a second buffer pair, and a second solvent; In step (3), the pH of the amine compound solution is 7.0-9.0; In step (3), the second protective atmosphere is nitrogen and / or argon; In step (3), the third reaction takes 4-8 hours; In step (3), the temperature of the third reaction is 0-50℃; In step (4), the amino acid solution comprises an amino acid, a second condensing agent, a third buffer pair, and a third solvent; In step (4), the pH of the amino acid solution is 5.0-8.0; In step (4), the third protective atmosphere is nitrogen and / or argon; In step (4), the fourth reaction takes 12-24 hours; In step (4), the temperature of the fourth reaction is 0-60℃; The method further includes: in step (1), after the first reaction, a first cleaning and drying is performed to obtain a carboxylated electrode; The method further includes: in step (2), after the second reaction, a second cleaning and drying is performed to obtain a disulfide bond linker modified electrode; The method further includes: in step (3), after the third reaction, a third washing and drying is performed to obtain a disulfide bond-linked cystamine electrode; The method further includes: in step (4), after the fourth reaction, a fourth cleaning and drying is performed to obtain the grafted electrode.

5. The method as described in claim 4, characterized in that, The method has one or more of the following characteristics: In step (1), the concentrated nitric acid solution has a mass fraction of 65wt%-68wt%. In step (1), the concentrated sulfuric acid solution has a mass fraction of 95wt%-98wt%. In step (2), the disulfide bond linkage reaction solution precursor contains the first buffer pair, and the pH of the disulfide bond linkage reaction solution precursor is 5.0-7.0; In step (2), the disulfide bond linkage reaction solution contains the first buffer pair, and the pH of the disulfide bond linkage reaction solution is 5.0-7.0; In step (2), the preparation method of the reaction system containing the carboxylated electrode and the disulfide bond-linked reaction liquid precursor obtained in step (1) includes: mixing the disulfide bond precursor compound with a first buffer containing the first buffer pair and the first inorganic solvent, adding the carboxylated electrode obtained in step (1) to the mixture, and then adding the first reducing agent to obtain the reaction system containing the carboxylated electrode and the disulfide bond-linked reaction liquid precursor obtained in step (1); In step (2), the preparation method of the reaction system containing the carboxylated electrode and the disulfide bond-linked reaction liquid precursor obtained in step (1) includes: mixing the disulfide bond precursor compound and the first organic solvent, adding the first reducing agent, and then performing a pre-reduction treatment under a fourth protective atmosphere to obtain the disulfide bond-linked reaction liquid precursor. Finally, the carboxylated electrode obtained in step (1) is added to the disulfide bond-linked reaction liquid precursor to obtain the reaction system containing the carboxylated electrode and the disulfide bond-linked reaction liquid precursor obtained in step (1). In step (2), the disulfide precursor compound is selected from one or more of 2,5-dimercapto-1,3,4-thiadiazole, bis(1,3,4-thiadiazole-2,5-dimercapto) disulfide and 2-amino-5-mercapto-1,3,4-thiadiazole; In step (2), the first reducing agent is selected from one or more of tris(2-carboxyethyl)phosphine, dithiothreitol, and tris(3-hydroxypropyl)phosphine; In step (2), the first buffer pair is 2-morpholine ethanesulfonic acid, 3-(N-morpholine)-2-hydroxypropanesulfonic acid, or bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane; In step (2), the first organic solvent is selected from one or more of N,N-dimethylformamide, dichloromethane, and isopropanol; In step (2), the first inorganic solvent is water; In step (2), the concentration of the disulfide bond precursor compound in the disulfide bond linkage reaction solution precursor is 0.02-0.10 mol / L; In step (2), the concentration of the first buffer pair in the disulfide bond-linking reaction solution precursor is 0.05-0.20 mol / L; In step (2), the concentration of the first reducing agent in the disulfide bond linkage reaction liquid precursor is 0.010-0.020 mol / L; In step (2), the concentration of the disulfide bond precursor compound in the disulfide bond linkage reaction solution is 0.02-0.10 mol / L; In step (2), the concentration of the first buffer pair in the disulfide bond linkage reaction solution is 0.05-0.20 mol / L; In step (2), the concentration of the first reducing agent in the disulfide bond linkage reaction solution is 0.010-0.020 mol / L; In step (3), the method for preparing the amine compound solution includes: mixing the amine compound with a second buffer containing the second buffer pair and the second solvent to obtain the amine compound solution; In step (3), the amine compound is selected from one or more of cystamine dihydrochloride, cystamine hydrochloride, cystamine, and cystamine; In step (3), the second reducing agent is selected from one or more of tris(2-carboxyethyl)phosphine, dithiothreitol, and tris(3-hydroxypropyl)phosphine; In step (3), the second buffer pair is tris(hydroxymethyl)aminomethane-hydrochloric acid, 4-hydroxyethylpiperazine ethanesulfonic acid, or N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid; In step (3), the second solvent is water; In step (3), the concentration of the amine compound in the amine compound solution is 0.03-0.20 mol / L; In step (3), the concentration of the second reducing agent in the amine compound solution is 0.03-0.20 mol / L; In step (3), the concentration of the second buffer pair in the amine compound solution is 0.05-0.20 mol / L; In step (4), the method for preparing the amino acid solution includes: mixing the amino acid, the second condensing agent, and a third buffer containing the third buffer pair and the third solvent, and then performing a pre-activation treatment under a fifth protective atmosphere to obtain the amino acid solution; In step (4), the amino acid is R-CH(NH2)-COOH or NH2-(CH2)c-SO2-NH-, -R is -(CH2)bR1, c is any integer from 1 to 6, b is any integer from 1 to 6, and R1 is an amino group, carboxyl group, guanidinyl group, or thiol group; preferably, the amino acid is selected from one or more of aspartic acid, glutamic acid, lysine, arginine, taurine, and cysteine; In step (4), the second condensing agent is selected from one or more of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxythiosuccinimide, N,N'-dicyclohexylcarbodiimide and 2-(7-azobenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate; In step (4), the third buffer pair is 2-morpholine ethanesulfonic acid, 3-(N-morpholine)-2-hydroxypropanesulfonic acid, or bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane; In step (4), the third solvent is water; In step (4), the concentration of the amino acid in the amino acid solution is 0.01-0.50 mol / L; In step (4), the concentration of the second condensing agent in the amino acid solution is 0.01-0.05 mol / L; In step (4), the concentration of the third buffer pair in the amino acid solution is 0.05-0.20 mol / L; The first cleaning and drying process includes: ultrasonic cleaning with N,N-dimethylformamide, anhydrous ethanol and water in sequence for 3-5 times; The second cleaning and drying process includes ultrasonic cleaning 3-5 times sequentially with N,N-dimethylformamide, anhydrous ethanol and water. The third cleaning and drying process includes: ultrasonic cleaning with N,N-dimethylformamide, anhydrous ethanol and water in sequence for 3-5 times; The fourth cleaning and drying process includes ultrasonic cleaning 3-5 times sequentially with N,N-dimethylformamide, anhydrous ethanol, and water.

6. The method as described in claim 5, characterized in that, The method has one or more of the following characteristics: In step (2), the temperature of the pre-reduction treatment is 10-70℃; In step (2), the pre-reduction treatment takes 5-60 minutes; In step (2), the fourth protective atmosphere is nitrogen and / or argon; In step (4), the temperature of the pre-activation treatment is 0-60℃; In step (4), the pre-activation treatment time is 10-60 min; In step (4), the fifth protective atmosphere is nitrogen and / or argon.

7. A basic flow battery, characterized in that, The basic flow battery includes the grafted electrode as described in claim 1 or 2, or the grafted electrode prepared by the method described in any one of claims 3-6, and a matrix electrolyte.

8. The basic flow battery as described in claim 7, characterized in that, The matrix electrolyte comprises vanadium ions and an acidic matrix.

9. A method for preparing amino acid-functionalized flow batteries, characterized in that, The method includes controlling the single-cell discharge voltage of the basic flow battery according to claim 7 or 8 to be 0.8-1.0V, and the corresponding continuous discharge time at the voltage to be 30-180s, wherein the terminal group reaction in the grafted electrode generates amino acids which are released into the matrix electrolyte, thereby obtaining an amino acid functionalized flow battery.

10. An amino acid-functionalized flow battery prepared by the method of claim 9.

11. The use of a grafted electrode as described in claim 1 or 2, or a grafted electrode prepared by any one of claims 3-6, in improving the stability and / or energy efficiency of a flow battery.

12. The application as described in claim 11, characterized in that, The applications include: (a) When the single-cell discharge voltage is greater than 1.0V and less than or equal to 1.7V, the grafted electrode improves the energy efficiency of the flow battery; or (b) When the single-cell discharge voltage is greater than or equal to 0.8V and less than or equal to 1.0V, the terminal group reaction in the grafted electrode generates amino acids which are released into the electrolyte of the flow battery, thereby improving the stability of the flow battery.

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