A method of modifying a carbon-based electrode, a carbon-based electrode, a flow battery

Abstract

This application provides a method for modifying a carbon-based electrode, which is then used in a flow battery. The method includes pretreating the carbon-based electrode; mixing an organic solution of aromatic sulfonyl chloride (0.05-0.20 mol / L) with a tertiary amine organic base-acid absorbent at a molar ratio of 1:1-1:2.5 to obtain an aromatic sulfonyl chloride reaction solution; immersing the pretreated carbon-based electrode in the aromatic sulfonyl chloride reaction solution at 50-75°C under an inert gas atmosphere with continuous stirring for 6-18 hours; and removing the carbon-based electrode from the aromatic sulfonyl chloride reaction solution, washing, and vacuum drying to obtain a sulfonyl-modified carbon-based electrode. The carbon-based electrode modified by this method is suitable for the long-term operating environment of flow batteries, such as vanadium redox flow batteries.

Description

Technical Field

[0001] This application relates to the field of batteries, and more particularly to a method for modifying a carbon-based electrode, a carbon-based electrode, and a flow battery. Background Technology

[0002] Vanadium redox flow batteries (VRBs) have broad application prospects in renewable energy grid integration and grid peak shaving due to their high safety, long lifespan, and suitability for large-scale energy storage. However, hydrogen evolution reaction (HER) is a common side reaction at the negative electrode during VRB operation, especially under high charge state or long-term operation conditions where the negative electrode potential is low and HER is prone to occur at the electrode interface. The occurrence of HER can lead to changes in electrolyte composition, reduce the battery's coulombic efficiency, and may cause gas accumulation, thus affecting the battery's operational stability and safety, becoming one of the important factors restricting the long-term stable operation of VRBs.

[0003] To address the hydrogen evolution problem at the negative electrode, existing technologies mainly focus on electrode material modification and system regulation. For example, heat treatment, acid treatment, or plasma treatment of carbon felt electrodes can alter their surface functional group composition and microstructure, thereby regulating the electrochemical reaction behavior on the electrode surface. Alternatively, doping carbon materials with non-metallic elements such as nitrogen and sulfur can change their surface electronic structure, thus affecting the tendency for side reactions to occur. Furthermore, some studies have attempted to introduce organic or inorganic additives into the negative electrode electrolyte or to mitigate hydrogen evolution by optimizing operating conditions.

[0004] However, the above methods still have certain limitations. Some surface treatment or doping methods have relatively harsh process conditions, making it difficult to control repeatability and consistency; some electrolyte additives lack stability under strong acid environments and long-term operating conditions, which may introduce new side reaction risks; at the same time, existing studies mostly focus on suppressing hydrogen evolution side reactions from the perspective of intrinsic material activity or system conditions, while research on the reaction environment and its regulation at the negative electrode interface remains relatively limited.

[0005] Therefore, there is a need for an improved carbon-based electrode for flow batteries, especially for the negative electrode of flow batteries. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0007] In one aspect, this application provides a method for modifying a carbon-based electrode, the method comprising the following steps: 1) Pretreatment of carbon-based electrodes; 2) Mix an organic solution of aromatic sulfonyl chloride with a concentration of 0.05-0.20 mol / L and a tertiary amine organic base-acid absorbent at a molar ratio of 1:1-1:2.5 to obtain an aromatic sulfonyl chloride reaction solution; 3) In an inert gas atmosphere, at a temperature of 50-75℃, the pretreated carbon-based electrode is immersed in an aromatic sulfonyl chloride reaction solution and stirred continuously for 6-18 hours; and 4) Remove the carbon-based electrode from the aromatic sulfonyl chloride reaction solution, clean it and vacuum dry it to obtain the sulfonyl-modified carbon-based electrode.

[0008] In an exemplary embodiment, in step 1), the pretreatment includes ultrasonically cleaning the carbon-based electrode sequentially with acetone, anhydrous ethanol, and deionized water, with each solvent cleaning time being 20-40 min; then oxidizing the cleaned carbon-based electrode with a 4-8 mol / L nitric acid aqueous solution at a temperature of 70-90°C for 1-3 h; then rinsing the oxidized carbon-based electrode with deionized water; and finally vacuum drying at a temperature of 70-90°C.

[0009] In an exemplary embodiment, in step 2), the aromatic sulfonyl chloride compound is selected from one of benzenesulfonyl chloride, p-toluenesulfonyl chloride, p-chlorobenzenesulfonyl chloride, p-nitrobenzenesulfonyl chloride, naphthalenesulfonyl chloride, or biphenylsulfonyl chloride.

[0010] In one exemplary embodiment, the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and acetonitrile.

[0011] In one exemplary embodiment, the organic solvent is anhydrous N,N-dimethylformamide.

[0012] In one exemplary embodiment, the tertiary amine organic base acid absorbent is selected from one or more of triethylamine, N,N-diisopropylethylamine, pyridine, and 4-dimethylaminopyridine.

[0013] In one exemplary embodiment, uniform mixing includes magnetic stirring for 1-30 minutes.

[0014] In an exemplary embodiment, in step 3), the inert gas is selected from nitrogen or argon.

[0015] In one exemplary embodiment, step 4) includes cleaning with DMF, anhydrous ethanol and deionized water in sequence.

[0016] In one exemplary embodiment, vacuum drying includes vacuum drying the cleaned carbon-based electrode at a temperature of 70-90°C for 8-14 hours.

[0017] In one exemplary embodiment, the material used for the carbon-based electrode is glassy carbon, carbon paper, graphite felt, or carbon felt.

[0018] On the other hand, this application provides a carbon-based electrode modified by the above method.

[0019] In another aspect, this application provides a flow battery including the aforementioned carbon-based electrode as a negative electrode.

[0020] In another aspect, this application provides a flow battery including the aforementioned carbon-based electrode as the positive electrode.

[0021] In one exemplary embodiment, the flow battery is a full vanadium current battery.

[0022] The aromatic sulfonyl chloride compounds introduced in this application have the general formula Ar–SO2Cl, and their molecular structures all contain an active sulfonyl chloride functional group (-SO2Cl). This functional group exhibits consistent reactivity in organic chemistry, and can undergo substitution reactions with nucleophilic groups containing hydroxyl, amino, etc., to generate stable sulfonate esters or sulfonamide structures. After pretreatment, the carbon-based electrode material in this application has oxygen-containing functional groups such as hydroxyl and carboxyl groups, as well as defective active sites on its surface. These sites can all serve as reactive centers, undergoing interfacial reactions with the introduced aromatic sulfonyl chloride compounds, thereby covalently fixing the sulfonyl group to the carbon-based electrode surface, thus achieving covalent fixation of the sulfonyl group structure.

[0023] Specifically, in the reaction process of this application, aromatic sulfonyl chloride can react with oxygen-containing functional groups on the surface of carbon-based materials to form a sulfonyl covalent bond structure: C-OH + Ar-SO2Cl → CO-SO2-Ar + HCl; at the same time, in the presence of an acid absorbent such as triethylamine (TEA), the HCl generated during the reaction is neutralized, thereby promoting the reaction.

[0024] For different aromatic sulfonyl chloride compounds, the aromatic ring moiety (Ar) exists only as a substituent and does not participate in the formation of reactive centers. The differences in their electronic effects mainly affect the reaction rate, without changing the basic reaction type of the sulfonyl chloride functional group. Therefore, under the reaction conditions of this application, different aromatic sulfonyl chlorides can all undergo similar reactions with the surface active sites of carbon-based electrode materials to form similar sulfonyl linkage structures.

[0025] Compared with existing technical solutions that rely solely on physical adsorption, surface oxidation, or electrolyte additives, the modified structure formed in this application is less prone to detachment or failure under strong acidic electrolytes and flow conditions, exhibiting high stability and making it suitable for the long-term operating environment of vanadium redox flow batteries.

[0026] This application only modifies the surface of the carbon-based electrode material, without adjusting the electrolyte system composition, introducing metal or inorganic catalysts, or altering the structure of the existing battery system. Compared to existing technologies that require changes to the electrolyte formulation or the introduction of dissimilar materials, the carbon-based electrode obtained in this application can be directly applied to existing flow battery systems such as vanadium redox flow batteries, exhibiting good engineering compatibility.

[0027] The sulfonyl modification in this application mainly occurs on the surface of carbon-based electrodes, such as carbon felt, without damaging the original three-dimensional porous structure and overall conductive network of the carbon felt. Compared with existing modification methods involving partial high-temperature treatment, deep doping, or coating with a dense layer, this application can maintain the basic mass transfer and conductivity characteristics of the carbon-based electrode while achieving anode performance regulation.

[0028] This application employs a combination of solution reaction and conventional heat treatment for electrode modification. The process conditions are mild, and the reaction parameters can be adjusted by solution concentration, reaction temperature, and time. Compared with existing technologies that have narrow process windows or rely on complex equipment, this application is more conducive to achieving stable and reproducible preparation and large-scale application. The preparation process is controllable, with good repeatability and consistency.

[0029] The modification method described in this application is applicable to different types of carbon-based electrode materials. Compared with existing technologies designed for single materials or single conditions, this application offers greater flexibility and scalability, and has a wider range of applications.

[0030] The carbon-based electrode modified using the method of this application, when used as the negative electrode in flow batteries such as vanadium redox flow batteries, helps to reduce the probability of hydrogen evolution side reactions during negative electrode operation, thereby improving the efficiency and operational stability of the battery.

[0031] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the solutions described in the description and the accompanying drawings. Attached Figure Description

[0032] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0033] Figure 1 The graphs show cyclic voltammetry tests of the carbon felt electrode of Example 1 and the conventional carbon felt electrode; Figure 2 The carbon felt electrode of Example 1 and a conventional carbon felt electrode are shown at 160 mA / cm. 2 A graph of voltage efficiency at current density; Figure 3 The graphs show cyclic voltammetry tests of the carbon felt electrode of Example 2 and the conventional carbon felt electrode; Figure 4 The carbon felt electrode of Example 2 and the conventional carbon felt electrode are shown at 160 mA / cm. 2 A graph of voltage efficiency at current density; Figure 5 The graphs show cyclic voltammetry tests of the carbon felt electrode of Example 3 and a conventional carbon felt electrode; and Figure 6 The carbon felt electrode of Example 3 and the conventional carbon felt electrode are shown at 160 mA / cm. 2 A graph showing the voltage efficiency at current density. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application are described in detail below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be arbitrarily combined with each other.

[0035] Example 1 1) Commercially available 4.2mm carbon felt was selected as the material for the carbon-based electrode, and the carbon felt was cut into 10cm×10cm pieces. The cut carbon felt was then ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water in sequence, with a cleaning time of 40min for each solvent. After cleaning, the carbon felt was oxidized in a 6mol / L nitric acid aqueous solution at 80℃ for 2h. After that, the carbon felt was repeatedly washed with deionized water until the washing solution was neutral, and then vacuum dried at 90℃ to obtain the pretreated carbon felt electrode.

[0036] 2) Weigh benzenesulfonyl chloride and add it to DMF (anhydrous N,N-dimethylformamide) to prepare a 0.1 mol / L DMF solution of benzenesulfonyl chloride; add 0.2 mol / L triethylamine (TEA) as an acid absorbent to the DMF solution of benzenesulfonyl chloride, the amount of TEA added is 2.5 times the molar amount of benzenesulfonyl chloride; stir magnetically for 30 min at room temperature to mix it thoroughly and evenly to obtain a benzenesulfonyl chloride reaction solution.

[0037] 3) The pretreated carbon felt electrode was completely immersed in the benzenesulfonyl chloride reaction solution prepared in step 2), and the reaction vessel was placed in a closed reaction environment under nitrogen protection. The reaction temperature was controlled at 75℃ and the reaction time was 18 h. Stirring was carried out continuously during the reaction to ensure that the reaction solution was in full contact with the surface of the substrate material.

[0038] 4) After the reaction is complete, the carbon felt electrode is removed from the reaction solution and washed repeatedly with DMF, anhydrous ethanol, and deionized water to remove unreacted benzenesulfonyl chloride and residual reaction reagents. After cleaning, the substrate material is vacuum dried at 90°C for 14 hours to obtain a carbon felt electrode with a sulfonyl group structure fixed on its surface.

[0039] Performance testing I. Cyclic voltammetry (CV) tests were performed on the sulfonyl-modified carbon felt electrode prepared in Example 1 and a commercially available conventional carbon felt electrode. The results are as follows: Figure 1 As shown, the vanadium electrolyte was diluted 10 times during testing.

[0040] Depend on Figure 1 (CV curve, x-axis: potential / V vs. Ag|AgCl; y-axis: current / A) It can be seen that: (1) Position of reduction peak: The potential shifts towards the "more positive" direction (increases the difficulty of hydrogen evolution); Traditional carbon felt (black curve): The HER reduction peak appears in a more negative potential range (approximately -0.8V vs. Ag|AgCl), indicating that the hydrogen evolution reaction on the surface of the traditional carbon felt is more likely to occur at this potential (thermodynamically "easier" to release hydrogen). Carbon felt obtained in Example 1 (red curve): The HER reduction peak shifts significantly "to the right" (moves towards the more positive potential direction, such as peak potential approximately -0.7V vs. Ag|AgCl). The more positive the potential, the higher the overpotential required to drive the hydrogen evolution reaction—that is, the "thermodynamic threshold" for hydrogen evolution on the surface of the carbon felt in Example 1 is higher, and hydrogen evolution is more difficult to occur.

[0041] (2) Reduction peak current density: The value decreased significantly (hydrogen evolution rate slowed down); Traditional carbon felt: The current density of the HER reduction peak was greater (the peak height corresponds to a higher absolute value of the current), indicating that more electrons were transferred in the hydrogen evolution reaction per unit time, and the hydrogen evolution rate was faster. Carbon felt of Example 1: The current density of the HER reduction peak decreased significantly (the height of the red peak was much lower than that of the black peak), indicating that the amount of electrons transferred in the hydrogen evolution reaction per unit time was reduced, and the hydrogen evolution reaction was significantly inhibited.

[0042] The changes in peak potential shift and peak current density in the CV curves provide a clear indication that the carbon felt of Example 1, within the potential range for hydrogen evolution at the negative electrode, both corrects the "start-up potential" of the hydrogen evolution reaction (making it thermodynamically less likely to occur) and lowers the "reaction rate" (kinetically inhibiting hydrogen evolution). Therefore, the carbon felt of Example 1 effectively improves the hydrogen evolution behavior at the negative electrode, exhibiting superior hydrogen evolution inhibition performance compared to traditional carbon felts.

[0043] In summary, the result of "peak potential shift to the right + peak current reduction" directly reflects its improvement effect on hydrogen evolution at the negative electrode, indicating that the carbon felt electrode of Example 1 can suppress hydrogen evolution when applied to a full vanadium redox flow battery.

[0044] II. Single cells were assembled using both conventional carbon felt and the carbon felt from Example 1, and charge-discharge tests were conducted. The electrolyte used was a 1.7 mol / L vanadium electrolyte. The voltage efficiency was as follows: Figure 2 As shown.

[0045] Depend on Figure 2 (Horizontal axis: number of cycles; Vertical axis: voltage efficiency / %) It can be seen that: Within the same test cycle (approximately 0-40 cycles), the voltage efficiency of the carbon felt obtained in Example 1 was consistently significantly higher than the black curve corresponding to the conventional carbon felt. From Figure 2 As can be seen, the carbon felt of Example 1 has a significantly higher voltage efficiency than that of traditional carbon felt throughout the process, indicating that it performs better in "reducing hydrogen evolution side reactions and allowing more electrical energy to be used for the target reaction". This is one of the most direct macroscopic manifestations of "suppressing hydrogen evolution".

[0046] Hydrogen evolution is often accompanied by problems such as electrode / catalyst aging, poisoning, or interface deterioration, which leads to a continuous decline in battery performance. The carbon felt obtained in Example 1 not only has high initial voltage efficiency but also remains stable after multiple cycles, which also indicates that its suppression of hydrogen evolution side reactions is more "long-lasting." Even after dozens of cycles, there was no significant loss in voltage efficiency due to increased hydrogen evolution or electrode degradation.

[0047] Furthermore, the comparison curves showing the change in voltage efficiency with the number of cycles show that the carbon felt obtained in Example 1 is significantly better than the traditional carbon felt in terms of both "initial voltage efficiency" and "cycle stability". This indicates that the carbon felt obtained in Example 1 has a strong ability to suppress the hydrogen evolution side reaction.

[0048] Example 2 1) Commercially available 4.2 mm carbon felt was selected as the material for the carbon-based electrode, and the carbon felt was cut into 10 cm × 10 cm pieces. The cut carbon felt was ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water in sequence, with a cleaning time of 40 min for each solvent. After cleaning, the carbon felt was oxidized in an 80℃, 6 mol / L nitric acid aqueous solution for 2 h. After that, the carbon felt was repeatedly washed with deionized water until the washing solution was neutral, and then vacuum dried at 90℃ to obtain pretreated carbon felt.

[0049] 2) Weigh p-toluenesulfonyl chloride and add it to N,N-dimethylacetamide (DMAc) to prepare a 0.1 mol / L DMAc solution of p-toluenesulfonyl chloride; add 0.15 mol / L N,N-diisopropylethylamine (DIPEA) as an acid absorbent to the solution, the amount of DIPEA added being 2.0 times the molar amount of p-toluenesulfonyl chloride; stir magnetically for 30 min at room temperature to ensure thorough mixing and obtain a p-toluenesulfonyl chloride reaction solution.

[0050] 3) The pretreated carbon felt electrode was completely immersed in the p-toluenesulfonyl chloride reaction solution prepared in step 2), and the reaction vessel was placed in a closed reaction environment under nitrogen protection. The reaction temperature was controlled at 70℃ and the reaction time was 16 h. Stirring was carried out continuously during the reaction to ensure that the reaction solution was in full contact with the surface of the substrate material.

[0051] 4) After the reaction is complete, the carbon felt electrode is removed from the reaction solution and washed repeatedly with DMAc, anhydrous ethanol, and deionized water to remove unreacted p-toluenesulfonyl chloride and residual reaction reagents. After cleaning, the substrate material is vacuum dried at 90°C for 12 hours to obtain a carbon felt electrode with a sulfonyl group structure fixed on its surface.

[0052] Performance testing I. Cyclic voltammetry (CV) tests were performed on the sulfonyl-modified carbon felt electrode prepared in Example 2 and a commercially available conventional carbon felt electrode. The test electrolyte was vanadium electrolyte (diluted 10 times). The results are as follows: Figure 3 As shown.

[0053] Depend on Figure 3 (CV curve, x-axis: potential / V vs. Ag|AgCl; y-axis: current / A) It can be seen that: (1) Position of reduction peak: The potential shifts towards the "more positive" direction (increased difficulty of hydrogen evolution); Traditional carbon felt (black curve): The hydrogen evolution reduction peak (HER) appears in a more negative potential range (around -0.85 V vs. Ag|AgCl), indicating that the hydrogen evolution reaction on the surface of the traditional carbon felt is more likely to occur at this potential (thermodynamically "easier" to release hydrogen). Carbon felt obtained in Example 2 (red curve): The HER reduction peak shifts significantly "to the right" (moves towards the more positive potential direction, such as around -0.75 V vs. Ag|AgCl). The more positive the potential, the higher the overpotential required to drive the hydrogen evolution reaction—that is, hydrogen evolution is more difficult to occur on the surface of the carbon felt in Example 2.

[0054] (2) Reduction peak current density: The value decreased significantly (hydrogen evolution rate slowed down); Traditional carbon felt: The current density of the HER reduction peak was greater (the peak height corresponds to a higher absolute current value), indicating that more electrons were transferred in the hydrogen evolution reaction per unit time, and the hydrogen evolution rate was faster. Carbon felt obtained in Example 2: The current density of the HER reduction peak was significantly reduced (the height of the red peak was much lower than that of the black peak), indicating that the amount of electrons transferred in the hydrogen evolution reaction per unit time was reduced, and the hydrogen evolution reaction was significantly inhibited.

[0055] The peak potential shift (rightward shift) and decrease in peak current density of the CV curves clearly indicate that the carbon felt of Example 2, within the potential range for hydrogen evolution at the negative electrode, both corrects the "start-up potential" of the hydrogen evolution reaction (making it thermodynamically less likely to occur) and lowers the "reaction rate" (kinetically inhibiting hydrogen evolution). Therefore, the carbon felt of Example 2 can effectively improve the hydrogen evolution behavior at the negative electrode, exhibiting superior hydrogen evolution inhibition performance compared to traditional carbon felts.

[0056] In summary, the result of "peak potential shift to the right + peak current reduction" directly reflects its improvement effect on hydrogen evolution at the negative electrode, indicating that the carbon felt electrode of Example 2 can suppress hydrogen evolution when applied to a full vanadium redox flow battery.

[0057] II. Single-cell charge-discharge test (voltage efficiency) of carbon felt in Example 2 and traditional carbon felt. Figure 4 ) Single cells were assembled using both conventional carbon felt and the carbon felt from Example 2, and charge-discharge tests were conducted. The electrolyte was a 1.7 mol / L vanadium electrolyte. The voltage efficiency as a function of cycle number is shown below. Figure 4 As shown.

[0058] Depend on Figure 4 (Horizontal axis: number of cycles; Vertical axis: voltage efficiency / %) It can be seen that: Within the same test cycle (approximately 0-40 cycles), the voltage efficiency of the carbon felt obtained in Example 2 was consistently significantly higher than the black curve corresponding to the conventional carbon felt. As can be seen from Figure 4, the overall voltage efficiency of the carbon felt in Example 2 (approximately 83%) was significantly higher than that of the conventional carbon felt (approximately 78%), indicating that it performed better in "reducing hydrogen evolution side reactions and allowing more electrical energy to be used for the target reaction"—one of the most direct macroscopic manifestations of "suppressing hydrogen evolution".

[0059] Hydrogen evolution is often accompanied by problems such as electrode / catalyst aging, poisoning, or interface deterioration, which leads to a continuous decline in battery performance. The carbon felt obtained in Example 2 not only has high initial voltage efficiency, but also remains stable after multiple cycles (the red curve shows almost no fluctuation), which also indicates that its suppression of hydrogen evolution side reactions is more "long-lasting". Even after dozens of cycles, there is no significant loss in voltage efficiency due to increased hydrogen evolution or electrode degradation.

[0060] Furthermore, the comparison curves showing the change in voltage efficiency with the number of cycles show that the carbon felt obtained in Example 2 is significantly better than the traditional carbon felt in both "initial voltage efficiency" and "cycle stability"; this indicates that the carbon felt obtained in Example 2 has a strong ability to suppress the hydrogen evolution side reaction.

[0061] Example 3 1) Commercially available 4.2 mm carbon felt was selected as the material for the carbon-based electrode, and the carbon felt was cut into 10 cm × 10 cm pieces. The cut carbon felt was ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water in sequence, with a cleaning time of 40 min for each solvent. After cleaning, the carbon felt was oxidized in an 80℃, 6 mol / L nitric acid aqueous solution for 2 h. After that, the carbon felt was repeatedly washed with deionized water until the washing solution was neutral, and then vacuum dried at 90℃ to obtain pretreated carbon felt.

[0062] 2) Weigh p-chlorobenzenesulfonyl chloride and add it to dimethyl sulfoxide (DMSO) to prepare a 0.08 mol / L DMSO solution of p-chlorobenzenesulfonyl chloride; add 0.12 mol / L pyridine as an acid absorbent to the solution, the amount of pyridine added is 1.5 times the molar amount of p-chlorobenzenesulfonyl chloride; stir magnetically for 30 min at room temperature to mix it thoroughly and evenly to obtain a p-chlorobenzenesulfonyl chloride reaction solution.

[0063] 3) The pretreated carbon felt electrode was completely immersed in the p-chlorobenzenesulfonyl chloride reaction solution prepared in step 2), and the reaction vessel was placed in a closed reaction environment under nitrogen protection. The reaction temperature was controlled at 65℃ and the reaction time was 14 h. Stirring was carried out continuously during the reaction to ensure that the reaction solution was in full contact with the surface of the substrate material.

[0064] 4) After the reaction is complete, the carbon felt electrode is removed from the reaction solution and washed repeatedly with DMSO, anhydrous ethanol, and deionized water to remove unreacted p-chlorobenzenesulfonyl chloride and residual reaction reagents. After cleaning, the substrate material is vacuum dried at 90°C for 12 hours to obtain a carbon felt electrode with a sulfonyl group structure fixed on its surface.

[0065] Performance testing I. Cyclic voltammetry (CV) tests were performed on the sulfonyl-modified carbon felt electrode prepared in Example 3 and a commercially available conventional carbon felt electrode. The test electrolyte was vanadium electrolyte (diluted 10 times). The results are as follows: Figure 5 As shown.

[0066] Depend on Figure 5 (CV curve, x-axis: potential / V vs. Ag|AgCl; y-axis: current / A) It can be seen that: (1) Position of reduction peak: The potential shifts towards the "more positive" direction (increased difficulty of hydrogen evolution); Traditional carbon felt (black curve): The hydrogen evolution reduction peak (HER) appears in a more negative potential range (around -0.85 V vs. Ag|AgCl), indicating that the hydrogen evolution reaction on the surface of the traditional carbon felt is more likely to occur at this potential (thermodynamically "easier" to release hydrogen). Carbon felt obtained in Example 3 (red curve): The HER reduction peak shifts significantly "to the right" (moves towards the more positive potential direction, such as around -0.75 V vs. Ag|AgCl). The more positive the potential, the higher the overpotential required to drive the hydrogen evolution reaction—that is, the "thermodynamic threshold" for hydrogen evolution on the surface of the carbon felt in Example 3 is higher, and hydrogen evolution is more difficult to occur.

[0067] (2) Reduction peak current density: The value decreased significantly (hydrogen evolution rate slowed down); Traditional carbon felt: The current density of the HER reduction peak was greater (the peak height corresponds to a higher absolute current value), indicating that more electrons were transferred per unit time in the hydrogen evolution reaction, and the hydrogen evolution rate was faster. Carbon felt of Example 3: The current density of the HER reduction peak was significantly reduced (the height of the red peak was much lower than that of the black peak), indicating that the amount of electrons transferred per unit time in the hydrogen evolution reaction was reduced, and the hydrogen evolution reaction was significantly inhibited.

[0068] The peak potential shift (rightward shift) and peak current density reduction in the CV curves provide a clear indication that the carbon felt of Example 3, within the potential range for hydrogen evolution at the negative electrode, both corrects the "start-up potential" of the hydrogen evolution reaction (making it thermodynamically less likely to occur) and lowers the "reaction rate" (kinetically inhibiting hydrogen evolution). Therefore, the carbon felt of Example 3 effectively improves the hydrogen evolution behavior at the negative electrode, exhibiting superior hydrogen evolution inhibition performance compared to traditional carbon felts.

[0069] In summary, the result of "peak potential shift to the right + peak current reduction" directly reflects its effect on improving hydrogen evolution at the negative electrode, indicating that the carbon felt electrode of Example 3 can suppress hydrogen evolution when applied to a full vanadium redox flow battery.

[0070] II. Single-cell charge-discharge test of carbon felt in Example 3 and conventional carbon felt Single cells were assembled using both conventional carbon felt and the carbon felt from Example 3, and charge-discharge tests were conducted. The electrolyte was a 1.7 mol / L vanadium electrolyte. The voltage efficiency as a function of cycle number (voltage efficiency) is as follows: Figure 6 As shown.

[0071] Depend on Figure 6 (Horizontal axis: number of cycles; Vertical axis: voltage efficiency / %) It can be seen that: Within the same test cycle (approximately 0-40 cycles), the voltage efficiency of the carbon felt obtained in Example 3 was consistently significantly higher than the black curve corresponding to the conventional carbon felt. As can be seen from the figure, the voltage efficiency of the carbon felt in Example 3 was significantly higher than that of the conventional carbon felt throughout the entire process, indicating that it performs better in "reducing hydrogen evolution side reactions and allowing more electrical energy to be used for the target reaction," which is one of the most direct macroscopic manifestations of "suppressing hydrogen evolution."

[0072] Hydrogen evolution is often accompanied by problems such as electrode / catalyst aging, poisoning, or interface deterioration, which leads to a continuous decline in battery performance. The carbon felt obtained in Example 3 not only has high initial voltage efficiency but also remains stable after multiple cycles, which also indicates that its suppression of hydrogen evolution side reactions is more "long-lasting." Even after dozens of cycles, there was no significant loss in voltage efficiency due to increased hydrogen evolution or electrode degradation.

[0073] Furthermore, the comparison curves showing the change in voltage efficiency with the number of cycles show that the carbon felt obtained in Example 3 is significantly better than the traditional carbon felt in terms of both "initial voltage efficiency" and "cycle stability". This indicates that the carbon felt obtained in Example 3 has a strong ability to suppress the hydrogen evolution side reaction.

[0074] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for modifying a carbon-based electrode, characterized in that, The method includes the following steps: 1) Pretreatment of carbon-based electrodes; 2) Mix an organic solution of aromatic sulfonyl chloride with a concentration of 0.05-0.20 mol / L and a tertiary amine organic base-acid absorbent at a molar ratio of 1:1-1:2.5 to obtain an aromatic sulfonyl chloride reaction solution; 3) In an inert gas atmosphere, at a temperature of 50-75℃, the pretreated carbon-based electrode is immersed in an aromatic sulfonyl chloride reaction solution and stirred continuously for 6-18 hours; and 4) Remove the carbon-based electrode from the aromatic sulfonyl chloride reaction solution, clean it and vacuum dry it to obtain the sulfonyl-modified carbon-based electrode.

2. The method according to claim 1, characterized in that, In step 1), the pretreatment includes ultrasonically cleaning the carbon-based electrode sequentially with acetone, anhydrous ethanol, and deionized water, with each solvent cleaning time being 20-40 min; then oxidizing the cleaned carbon-based electrode with a 4-8 mol / L nitric acid aqueous solution at a temperature of 70-90℃ for 1-3 h; then rinsing the oxidized carbon-based electrode with deionized water; and finally vacuum drying at a temperature of 70-90℃.

3. The method according to claim 1, characterized in that, In step 2), the aromatic sulfonyl chloride compound is selected from one of benzenesulfonyl chloride, p-toluenesulfonyl chloride, p-chlorobenzenesulfonyl chloride, p-nitrobenzenesulfonyl chloride, naphthalenesulfonyl chloride, or biphenylsulfonyl chloride; and / or, The organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and acetonitrile; and / or, Tertiary amine organic base-acid absorbents are selected from one or more of triethylamine, N,N-diisopropylethylamine, pyridine, and 4-dimethylaminopyridine; and / or, Mix thoroughly by magnetic stirring for 1-30 minutes.

4. The method according to claim 1, characterized in that, In step 2), the organic solvent is anhydrous N,N-dimethylformamide.

5. The method according to claim 1, characterized in that, In step 3), the inert gas is selected from nitrogen and argon.

6. The method according to claim 1, characterized in that, In step 4), the cleaning process includes sequentially using DMF, anhydrous ethanol, and deionized water; and / or, Vacuum drying involves vacuum drying the cleaned carbon-based electrode at a temperature of 70℃-90℃ for 8-14 hours.

7. The method according to any one of claims 1-6, characterized in that, Materials used for carbon-based electrodes include glassy carbon, carbon paper, graphite felt, or carbon felt.

8. A carbon-based electrode, characterized in that, The carbon-based electrode is modified by the method described in any one of claims 1-7.

9. A flow battery, characterized in that, Including the carbon-based electrode as described in claim 8 as the negative electrode.

10. The flow battery according to claim 9, characterized in that, The flow battery is selected from vanadium redox flow batteries, zinc-bromine flow batteries, and iron-chromium flow batteries.

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