Electrochemical preparation method of high-performance graphite felt electrode of sulfur-nitrogen co-doped flow battery

Abstract

The preparation method comprises the following steps: preparing an ammonium sulfate aqueous solution with the concentration of 120-140 mg / mL, and carrying out ultrasonic dispersion for more than 10 minutes to obtain an ammonium sulfate dispersion liquid; dropwise adding sulfuric acid into the ammonium sulfate dispersion liquid to adjust the pH value to 4.5-5.5, and carrying out ultrasonic treatment for more than 5 minutes to obtain a weakly acidic ammonium sulfate solution; cleaning and drying a flake graphite felt, fixing the flake graphite felt between the positive electrode and the negative electrode of a direct-current power supply, applying 4.5-6.0 V / cm voltage to the longest side direction of the flake graphite felt under the action of the direct-current power supply, carrying out electrochemical oxidation for 45-55 seconds, taking out the flake graphite felt, and repeating the operation once after the positive electrode and the negative electrode are exchanged; and alternately washing the treated flake graphite felt with absolute ethyl alcohol and deionized water for 3-5 times in sequence, and then drying the flake graphite felt in a drying oven at 70-90 DEG C for 2-3 hours to obtain the modified graphite felt electrode of the all-vanadium redox flow battery electrode.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery technology, and particularly to a method for preparing an electrode for a vanadium redox flow battery and the electrode itself. Background Technology

[0002] Currently, redox flow battery technology has become one of the most environmentally friendly and sustainable technologies in the energy storage field due to its unique energy and power capacity decoupling capability. Vanadium redox flow battery technology eliminates cross-contamination, improves system durability, and boasts advantages such as long cycle life, high safety, and modular design, making it one of the best candidates for large-scale energy storage. Among the components of a vanadium redox flow battery, the electrodes play a crucial role in determining its overall performance, as they directly affect the kinetics of the redox reaction and charge transfer efficiency. Traditional carbon-based electrodes, such as graphite felt and carbon paper, often exhibit poor electrochemical activity and wettability, leading to high polarization losses and reduced energy efficiency. To overcome these limitations, various methods have been extensively studied for electrode materials, including surface oxidation, heteroatom doping, and the deposition of catalytic nanoparticles. However, these methods often involve complex synthesis processes, high costs, or limited scalability. Electrode sheets fabricated by electrochemical oxidation under neutral conditions can improve electrochemical activity, but their cycle life is short, resulting in low overall energy efficiency. The reason for this is that in a neutral environment, the conditions are relatively mild, allowing only unstable active sites to grow on the surface of the graphite felt. This is detrimental to the long-term use of the electrode and also hinders the improvement of battery energy efficiency. Therefore, developing an electrode modification method that is low-cost, has good electrochemical activity, minimal losses, and high energy efficiency is crucial.

[0003] The information disclosed in the background section is only for enhancing the understanding of the background of this invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] This invention provides a method for preparing an electrode for a vanadium redox flow battery and the electrode itself. The electrode is prepared by electrochemical oxidation under weak acid conditions, allowing it to withstand 200 mA·cm⁻¹. -2 The energy efficiency can reach 90.2% at 500 mA·cm⁻¹. -2 Energy efficiency can reach 75%.

[0005] A method for preparing an all-vanadium redox flow battery electrode includes:

[0006] Prepare an aqueous solution of ammonium sulfate with a concentration of 120–140 mg / mL and ultrasonically disperse it for more than 10 minutes to obtain an ammonium sulfate dispersion.

[0007] The pH of the ammonium sulfate dispersion was adjusted to 4.5–5.5 by adding sulfuric acid dropwise, and then sonicated again for more than 5 minutes to obtain a weakly acidic ammonium sulfate solution.

[0008] After cleaning and drying, the sheet graphite felt is fixed between the positive and negative terminals of a DC power supply. The two electrodes are at the same horizontal height and facing each other, with a distance of 1.5–2.5 cm. The graphite felt is completely immersed in the weakly acidic ammonium sulfate solution.

[0009] Under the action of DC power, apply a voltage of 4.5–6.0 V / cm to the longest side of the sheet graphite felt for electrochemical oxidation for 45–55 seconds, then remove it, reverse the positive and negative electrodes and repeat the operation once;

[0010] The treated sheet graphite felt was washed alternately with anhydrous ethanol and deionized water 3–5 times, and then dried in a drying oven at 70–90℃ for 2–3 hours to obtain the modified graphite felt electrode for the vanadium redox flow battery electrode.

[0011] In the method for preparing an all-vanadium redox flow battery electrode, the concentration of the ammonium sulfate aqueous solution is 130 mg / mL, and the ultrasonic time is 15 minutes.

[0012] In the preparation method of the vanadium redox flow battery electrode, sulfuric acid is added dropwise to the ammonium sulfate dispersion to adjust the pH value to 5, and the solution is sonicated again for more than 5 minutes to obtain a weakly acidic ammonium sulfate solution.

[0013] In the method for preparing an electrode for a vanadium redox flow battery, the sheet graphite felt has dimensions of 2×2×0.6cm (length×width×height) and a distance of 2cm between the positive and negative electrodes.

[0014] In the method for preparing an all-vanadium redox flow battery electrode, the voltage is 5V / cm under the action of a DC power supply, and the single oxidation time is 45 seconds.

[0015] In the preparation method of the vanadium redox flow battery electrode, the treated sheet graphite felt is washed three times alternately with anhydrous ethanol and deionized water, and then dried in a drying oven at 70–℃ for 3 hours to obtain the modified graphite felt electrode of the vanadium redox flow battery electrode.

[0016] In the preparation method of the vanadium redox flow battery electrode, an ammonium sulfate aqueous solution with a concentration of 130 mg / mL is prepared and ultrasonically dispersed for 20 minutes to obtain an ammonium sulfate dispersion; sulfuric acid is added dropwise to the ammonium sulfate dispersion to adjust the pH value to 5, and ultrasonication is performed again for 10 minutes to obtain a weakly acidic ammonium sulfate solution; after cleaning and drying, a sheet graphite felt is fixed between the positive and negative electrodes of a DC power supply, with the two electrodes at the same horizontal height and facing each other, with a distance of 2 cm, and the graphite felt is completely immersed in the weakly acidic ammonium sulfate solution; under the action of the DC power supply, a voltage of 5.3 V / cm is applied to the longest side of the sheet graphite felt for electrochemical oxidation for 50 seconds, and then it is removed, the positive and negative electrodes are reversed, and the operation is repeated once; the treated sheet graphite felt is washed alternately with anhydrous ethanol and deionized water 4 times, and then placed in an 80℃ drying oven for 2.5 hours to obtain a modified graphite felt electrode for the vanadium redox flow battery electrode.

[0017] An all-vanadium redox flow battery electrode, prepared by the method described above.

[0018] In the aforementioned vanadium redox flow battery electrode, it operates at 200 mA·cm⁻¹ in the vanadium redox flow battery. -2 The energy efficiency at current density is no less than 90.2%, at 500 mA·cm⁻¹. -2 The energy efficiency at current density is no less than 75%.

[0019] The vanadium redox flow battery electrode retains a capacity of no less than 95% after 1000 charge-discharge cycles in the vanadium redox flow battery.

[0020] Compared with the prior art, the present invention has the following advantages: the electrode sheet of the present invention has improved electrochemical activity and long cycle life, especially at 200 mA·cm⁻¹. -2 The energy efficiency can reach 90.2% at 500 mA·cm⁻¹. -2 The energy efficiency can reach 75%. The capacity retention rate of the electrodes in the vanadium redox flow battery is no less than 95% after 1000 charge-discharge cycles. Attached Figure Description

[0021] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0022] In the attached diagram:

[0023] Figure 1 This is a process flow diagram of the GF@NS prepared according to the present invention;

[0024] Figure 2 This is a graph showing the energy efficiency of GF@NS prepared in this invention during electrochemical oxidation at different time lengths;

[0025] Figure 3 Here is a SEM image of the GF@NS prepared in this invention;

[0026] Figure 4 This is the XPS energy spectrum of GF@NS prepared in this invention;

[0027] Figure 5 This is the Raman spectrum of GF@NS prepared in this invention;

[0028] Figure 6 This is a cyclic voltammetry curve of GF@NS prepared in this invention;

[0029] Figure 7 This is an impedance curve of the GF@NS prepared according to the present invention;

[0030] Figure 8 This is a charge-discharge curve of the GF@NS prepared in this invention;

[0031] Figure 9 This is a graph showing the energy efficiency of the GF@NS prepared according to this invention;

[0032] Figure 10 This is a polarization curve of the GF@NS prepared in this invention;

[0033] Figure 11 This is a graph showing the 1000-cycle performance of GF@NS prepared in this invention.

[0034] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0035] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0036] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0037] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0038] like Figures 1 to 11 As shown, the preparation method of the electrode for an all-vanadium redox flow battery includes the following steps:

[0039] Prepare an aqueous solution of ammonium sulfate with a concentration of 120–140 mg / mL and ultrasonically disperse it for more than 10 minutes to obtain an ammonium sulfate dispersion.

[0040] The pH of the ammonium sulfate dispersion was adjusted to 4.5–5.5 by adding sulfuric acid dropwise, and then sonicated again for more than 5 minutes to obtain a weakly acidic ammonium sulfate solution.

[0041] After cleaning and drying, the sheet graphite felt is fixed between the positive and negative terminals of a DC power supply. The two electrodes are at the same horizontal height and facing each other, with a distance of 1.5–2.5 cm. The graphite felt is completely immersed in the weakly acidic ammonium sulfate solution.

[0042] Under the action of DC power, apply a voltage of 4.5–6.0 V / cm to the longest side of the sheet graphite felt for electrochemical oxidation for 45–55 seconds, then remove it, reverse the positive and negative electrodes and repeat the operation once;

[0043] The treated sheet graphite felt was washed alternately with anhydrous ethanol and deionized water 3–5 times, and then dried in a drying oven at 70–90℃ for 2–3 hours to obtain the modified graphite felt electrode for the vanadium redox flow battery electrode.

[0044] In a preferred embodiment of the method for preparing an all-vanadium redox flow battery electrode, the concentration of the ammonium sulfate aqueous solution is 130 mg / mL, and the ultrasonic time is 15 minutes.

[0045] In a preferred embodiment of the method for preparing an all-vanadium redox flow battery electrode, sulfuric acid is added dropwise to the ammonium sulfate dispersion to adjust the pH value to 5, and the mixture is sonicated again for more than 5 minutes to obtain a weakly acidic ammonium sulfate solution.

[0046] In a preferred embodiment of the method for preparing an electrode for a vanadium redox flow battery, the sheet graphite felt has dimensions of 2×2×0.6cm (length×width×height) and a distance of 2cm between the positive and negative electrodes.

[0047] In a preferred embodiment of the method for preparing an all-vanadium redox flow battery electrode, the voltage is 5V / cm under the action of a DC power supply, and the single oxidation time is 45 seconds.

[0048] In a preferred embodiment of the method for preparing an all-vanadium redox flow battery electrode, the treated sheet graphite felt is washed three times alternately with anhydrous ethanol and deionized water, and then dried in a 70°C drying oven for 3 hours to obtain the modified graphite felt electrode for the all-vanadium redox flow battery electrode.

[0049] In a preferred embodiment of the preparation method of the vanadium redox flow battery electrode, an ammonium sulfate aqueous solution with a concentration of 130 mg / mL is prepared and ultrasonically dispersed for 20 minutes to obtain an ammonium sulfate dispersion; sulfuric acid is added dropwise to the ammonium sulfate dispersion to adjust the pH value to 5, and ultrasonication is performed again for 10 minutes to obtain a weakly acidic ammonium sulfate solution; after cleaning and drying, the sheet graphite felt is fixed between the positive and negative electrodes of a DC power supply, with the two electrodes at the same horizontal height and facing each other, with a distance of 2 cm, and the graphite felt is completely immersed in the weakly acidic ammonium sulfate solution; under the action of the DC power supply, a voltage of 5.3 V / cm is applied to the longest side of the sheet graphite felt for electrochemical oxidation for 50 seconds, and then it is removed, the positive and negative electrodes are reversed, and the operation is repeated once; the treated sheet graphite felt is washed alternately with anhydrous ethanol and deionized water 4 times, and then placed in an 80°C drying oven for 2.5 hours to obtain the modified graphite felt electrode of the vanadium redox flow battery electrode.

[0050] An all-vanadium redox flow battery electrode, prepared by the method described above.

[0051] In a preferred embodiment of the vanadium redox flow battery electrode, it operates at 200 mA·cm⁻¹ in the vanadium redox flow battery. -2 The energy efficiency at current density is no less than 90.2%, at 500 mA·cm⁻¹. -2 The energy efficiency at current density is no less than 75%.

[0052] In a preferred embodiment of the vanadium redox flow battery electrode, the capacity retention rate of the vanadium redox flow battery electrode is not less than 95% after 1000 charge-discharge cycles in the vanadium redox flow battery.

[0053] In one embodiment, the method comprises the following steps:

[0054] Step 1: Prepare an aqueous solution of ammonium sulfate ((NH4)2SO4) of 120-140 mg / ml in a beaker using deionized water. Place the solution in an ultrasonicator and sonicate for more than 10 minutes to completely disperse it, thus obtaining a uniform ammonium sulfate dispersion.

[0055] Step 2: Slowly add 75% sulfuric acid dropwise to the ammonium sulfate solution obtained in Step 1 until the pH value is 4.5-5.5, and then place it in an ultrasonic device for sonication for more than 5 minutes to obtain a uniform weakly acidic ammonium sulfate solution.

[0056] Step 3: Rinse the sheet graphite felt (GF) with deionized water under slow flow and dry it. Then fix it to the positive and negative terminals of the DC power supply, with the two at the same horizontal level and facing each other, with a distance of 1.5-2.5cm between them.

[0057] Step 4: Place the graphite felt electrode sheet fixed in Step 3 into the solution prepared in Step 2, so that it is completely submerged and fully wetted.

[0058] Step 5: Perform electrochemical oxidation using a DC power supply, then apply a voltage of 4.5-6.0V / cm to its longest side for electrochemical oxidation. After oxidation for 45-55 seconds, remove the electrode, reverse the positive and negative electrodes, and immerse it in the solution again for the same operation for 45-55 seconds before removing the graphite felt electrode.

[0059] Step 6: Wash the graphite felt electrode with anhydrous ethanol and deionized water alternately and slowly 3-5 times, then dry it in a drying oven at 70-90℃ for 2-3 hours to finally obtain qualified graphite felt@nitrogen-sulfur (GF@NS) samples.

[0060] Example 1

[0061] like Figure 1 As shown, the method for electrochemically oxidizing graphite felt electrodes in a weakly acidic environment comprises the following steps:

[0062] Step 1: Prepare a 130 mg / ml ammonium sulfate ((NH4)2SO4) aqueous solution in a beaker using deionized water, and sonicate it in an ultrasonicator for 15 minutes to completely disperse it, thus obtaining a uniform ammonium sulfate dispersion.

[0063] Step 2: Slowly add 75% sulfuric acid dropwise to the ammonium sulfate solution obtained in Step 1 until the pH value is 5, and then place it in an ultrasonic device for sonication for 5 minutes to obtain a uniform weakly acidic ammonium sulfate solution.

[0064] Step 3: Rinse the 2*2*0.6cm (length, width, height) sheet graphite felt (GF) with deionized water under slow flow, dry it, and then fix it to the positive and negative terminals of a DC power supply. The two should be at the same horizontal level and facing each other, with a distance of 2cm between them.

[0065] Step 4: Place the graphite felt electrode sheet fixed in Step 3 into the solution prepared in Step 2, so that it is completely submerged and fully wetted.

[0066] Step 5: Perform electrochemical oxidation using a DC power supply, then apply a 5V / cm voltage to its longest side for further electrochemical oxidation. (Based on...) Figure 2 Energy efficiency graphs for different electrochemical oxidation times: After oxidizing for 45 seconds, the electrode was removed, the positive and negative electrodes were reversed, and the same operation was performed again after immersing it in the solution for 45 seconds. The graphite felt electrode was then removed.

[0067] Step 6: Wash the graphite felt electrode three times with alternating slow flow of anhydrous ethanol and deionized water, then dry it in a 70℃ drying oven for 3 hours to finally obtain a qualified sample GF@NS.

[0068] The GF@NS samples prepared in the above steps were characterized as follows:

[0069] Figure 3 This is a SEM image of GF@NS. The large number of particulate deposits and wrinkles on the interface indicate that more active sites and pores were generated during the electrochemical oxidation process. Figure 4 The XPS spectra of GF@NS show that the contents of C, O, N and S in each sample are significantly different. Figure 5 The image shows the Raman spectrum of GF@NS, indicating that GF@NS has a more ordered structure and provides more active sites. Figure 6 The cyclic voltammetry curve of GF@NS shows that GF@NS has better activation performance; Figure 7 The electrochemical impedance spectroscopy of GF@NS shows that GF@NS has the lowest charge transport resistance due to its abundant active sites and pores. Figure 8 The charge-discharge curves show the excellent charge-discharge performance of GF@NS at different current densities. Figure 9 The graph shows the energy efficiency of GF@NS, indicating that it has high energy efficiency under different current densities. Figure 10 The polarization curve of GF@NS shows that a higher power density was obtained by increasing the electron transfer rate and the adsorption of active substances. Figure 11 The graph shows the long-cycle performance of GF@NS, demonstrating its excellent lifespan in actual use. This embodiment exhibits the best overall performance, with high energy efficiency, long cycle life, and superior characterization data compared to other embodiments, making it the recommended best implementation scheme of this invention.

[0070] Example 2

[0071] Parameter settings

[0072] Ammonium sulfate concentration: 140 mg / ml

[0073] pH adjustment: 5.5

[0074] Graphite felt dimensions: 2×2×0.6cm

[0075] Electrode spacing: 2.5cm

[0076] Voltage gradient: 6.0V / cm

[0077] Oxidation time: 45s × 2 times

[0078] Drying temperature: 90℃

[0079] Drying time: 2 hours

[0080] Implementation steps

[0081] Except for the following adjustments, the remaining steps are the same as in Example 1:

[0082] Use a 140 mg / ml ammonium sulfate solution;

[0083] Adjust the pH to 5.5;

[0084] The distance between the positive and negative electrodes is set to 2.5cm;

[0085] The voltage gradient is set to 6.0V / cm;

[0086] The drying temperature is raised to 90℃ and the drying time is 2 hours.

[0087] Characterization results and performance testing

[0088]

[0089] Although a higher voltage and concentration were used, the surface modification was not sufficient due to the lack of extended oxidation time; at the same time, high-temperature drying may cause some functional groups to desorb, resulting in overall performance that was slightly inferior to that of Example 1.

[0090] Example 3

[0091] Parameter settings

[0092] Ammonium sulfate concentration: 120 mg / ml

[0093] pH adjustment: 4.5

[0094] Graphite felt dimensions: 2×2×0.6cm

[0095] Electrode spacing: 1.5cm

[0096] Voltage gradient: 4.5V / cm

[0097] Oxidation time: 55s × 2 times

[0098] Drying temperature: 70℃

[0099] Drying time: 3 hours

[0100] Implementation steps

[0101] Except for the following adjustments, the remaining steps are the same as in Example 1:

[0102] Use a 120 mg / ml ammonium sulfate solution;

[0103] Adjust the pH to 4.5;

[0104] The distance between the positive and negative electrodes is set to 1.5cm;

[0105] The voltage gradient is set to 4.5V / cm;

[0106] The oxidation time for a single oxidation cycle has been extended to 55 seconds.

[0107] Characterization results and performance testing

[0108]

[0109] Although the oxidation time was extended, the oxidation intensity was insufficient due to the low voltage, the active sites formed on the surface were unstable, and the low pH environment failed to effectively promote stable doping. Therefore, the overall performance was not as good as that of Example 1.

[0110]

[0111] Example 1 represents the optimal implementation of the present invention; the selected parameters (such as 130 mg / ml ammonium sulfate, pH=5, 5 V / cm voltage, 45 s × 2 oxidation cycles, etc.) enable the most effective electrochemical oxidation modification under weakly acidic conditions; this method significantly improves the electrochemical activity, wettability, and charge transport capability of the graphite felt electrode, thereby achieving high energy efficiency (90.2% @ 200 mA·cm) in a vanadium redox flow battery. -2 It also exhibits excellent cycling stability (>1000 cycles with no decay).

[0112] This invention uses a weakly acidic environment (pH = 4.5–5.5) where 75% sulfuric acid is slowly added dropwise to an ammonium sulfate solution to adjust the pH to 4.5–5.5. This provides a suitable oxidizing environment to promote the controlled oxidation of the carbon structure on the graphite felt surface; it avoids severe corrosion under strong acid conditions and prevents excessive damage to the carbon skeleton structure; under this weakly acidic condition, the NH4+ in (NH4)2SO4... +Easier release, providing a precursor for subsequent nitrogen doping; facilitates the introduction and stable presence of sulfur in the carbon structure, forming N / S co-doped active sites; compared to neutral conditions, it induces the formation of more stable functional groups, enhancing long-term stability. In Example 3, using pH=4.5 prolonged the oxidation time, but the low acidity led to instability of the active sites; while in Example 2, at pH=5.5, some N / S may not have been fully doped due to alkalinity shift. Therefore, pH=5 is the optimal equilibrium point. Ammonium sulfate concentration (120–140 mg / ml) provides sufficient NH4+. + and SO4 2- Ions serve as nitrogen and sulfur sources. At concentrations that are too low (e.g., 120 mg / ml), insufficient dopant elements are provided, resulting in fewer active sites. At concentrations that are too high (e.g., 140 mg / ml), localized high concentrations may occur, leading to uneven doping or even agglomeration. Appropriate concentrations ensure the uniformity and stability of N / S co-doping. In Example 1, using a concentration of 130 mg / ml, XPS results showed the optimal N / S ratio, and SEM images showed uniform pore distribution, indicating the best performance. However, in Example 2, a slight agglomeration occurred at 140 mg / ml, affecting conductivity. Voltage gradient control (4.5–6.0 V / cm) was applied along the longest side of the graphite felt for electrochemical oxidation. Sufficient voltage drives electron migration, inducing oxidation reactions on the surface of carbon materials. Too low a voltage (e.g., 4.5 V / cm) leads to incomplete oxidation and a limited number of active sites; too high a voltage (e.g., 6.0 V / cm) triggers severe oxidation, damaging the carbon framework and reducing mechanical strength. A moderate voltage (e.g., 5 V / cm) achieves a mild yet effective oxidation reaction. Example 1 achieved optimal energy efficiency and cycle life at 5 V / cm, while Example 2 exhibited slightly higher impedance and slightly lower energy efficiency at 6.0 V / cm, indicating that excessively high voltage is detrimental to long-term stability.

[0113] Bidirectional oxidation treatment (positive and negative electrode swapping) technique: After one oxidation cycle, the electrodes are removed, and the positive and negative electrodes are swapped for the same oxidation time. This ensures that both sides of the graphite felt are effectively oxidized, avoiding the asymmetric modification caused by unidirectional oxidation. Bidirectional treatment can improve the overall wettability and reaction uniformity of the electrode, enhance charge transport capacity, and improve the symmetry performance of the battery. All examples used bidirectional oxidation, and the results were consistently better than the unidirectional oxidation control group (not listed), demonstrating its significant contribution to performance improvement. Oxidation time control (45–55 seconds × 2 times): The oxidation time was controlled at 45–55 seconds for each oxidation cycle, totaling 90–110 seconds for both cycles. Too short an oxidation time (<45s) cannot form enough active sites; too long a time (>55s) can easily cause over-oxidation and structural damage; the intermediate value (45s × 2 times) can introduce functional groups and micropores to the maximum extent without destroying the structure. In Example 1, the 45s × 2 times treatment yielded the best SEM structure, Raman order, and energy efficiency, indicating that this time is the optimal choice. Drying temperature and time (70–90℃, 2–3h): After electrode oxidation, wash with alternating ethanol / water and dry at the specified temperature for 2–3 hours. Too high a drying temperature (>90℃) may cause functional group desorption or structural collapse; too low a temperature (<70℃) will not effectively remove residual solvent and moisture. Appropriate drying helps to fix the N / S doped structure while maintaining good wettability; too short a drying time (<2h) will cause residual solvent to affect electrode stability.

[0114] Excessive drying time (>3 hours) may lead to thermal degradation. In Example 1, drying at 70°C for 3 hours yielded the best results, while in Example 2, drying at 90°C for 2 hours resulted in the loss of some functional groups and a decrease in performance.

[0115] This invention achieves surface structure manipulation (introducing numerous pores and wrinkles); N / S co-doping (enhancing electrochemical activity and conductivity); improved structural order (reducing charge transfer resistance); improved surface wettability (increasing electrolyte contact area); and enhanced cycle stability (no significant degradation after 1000 cycles). Ultimately, this enables the all-vanadium redox flow battery to maintain excellent energy efficiency (200 mA·cm⁻¹) even at high current densities. -2 Reaching 90.2%, 500mA·cm -2 It reaches 75% and has good durability in practical applications.

[0116] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A method for preparing an electrode for an all-vanadium redox flow battery, characterized in that, Includes the following steps: Prepare an aqueous solution of ammonium sulfate with a concentration of 120–140 mg / mL and ultrasonically disperse it for more than 10 minutes to obtain an ammonium sulfate dispersion. The pH of the ammonium sulfate dispersion was adjusted to 4.5–5.5 by adding sulfuric acid dropwise, and then sonicated again for more than 5 minutes to obtain a weakly acidic ammonium sulfate solution. After cleaning and drying, the sheet graphite felt is fixed between the positive and negative terminals of a DC power supply. The two electrodes are at the same horizontal height and facing each other, with a distance of 1.5–2.5 cm. The graphite felt is completely immersed in the weakly acidic ammonium sulfate solution. Under the action of DC power, apply a voltage of 4.5–6.0 V / cm to the longest side of the sheet graphite felt for electrochemical oxidation for 45–55 seconds, then remove it, reverse the positive and negative electrodes and repeat the operation once; The treated sheet graphite felt was washed alternately with anhydrous ethanol and deionized water 3–5 times, and then dried in a drying oven at 70–90℃ for 2–3 hours to obtain the modified graphite felt electrode for the vanadium redox flow battery electrode.

2. The method for preparing an all-vanadium redox flow battery electrode according to claim 1, characterized in that, Preferably, the concentration of the ammonium sulfate aqueous solution is 130 mg / mL, and the ultrasonic time is 15 minutes.

3. The method for preparing an all-vanadium redox flow battery electrode according to claim 2, characterized in that, The pH of the ammonium sulfate dispersion was adjusted to 5 by adding sulfuric acid dropwise, and then sonicated again for more than 5 minutes to obtain a weakly acidic ammonium sulfate solution.

4. The method for preparing an all-vanadium redox flow battery electrode according to claim 1, characterized in that, The sheet-like graphite felt has dimensions of 2×2×0.6cm (length×width×height) and a positive-to-negative electrode spacing of 2cm.

5. The method for preparing an all-vanadium redox flow battery electrode according to claim 1, characterized in that, Under the action of a DC power supply, the voltage is 5V / cm, and the single oxidation time is 45 seconds.

6. The method for preparing an all-vanadium redox flow battery electrode according to claim 1, characterized in that, The treated sheet graphite felt was washed three times alternately with anhydrous ethanol and deionized water, and then dried in a 70–℃ drying oven for 3 hours to obtain the modified graphite felt electrode for the vanadium redox flow battery electrode.

7. An electrode for an all-vanadium redox flow battery, characterized in that, It is prepared by the method described in any one of claims 1-6.

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