Non-planar pi-conjugated naphthoquinone derivative with asymmetric structure as well as preparation method and application thereof in aqueous flow battery

Abstract

The invention discloses a non-planar pi-conjugated naphthoquinone derivative with an asymmetric structure, a preparation method of the non-planar pi-conjugated naphthoquinone derivative and application of the non-planar pi-conjugated naphthoquinone derivative in an aqueous flow battery, and relates to the technical field of electrochemical energy storage. Methyl 4-aminobenzoate is added into hydrochloric acid, then the mixture and sodium nitrite are dissolved in water to be mixed to obtain a diazonium salt solution, and 2-hydroxy-1, 2, 4-triazole is added into the diazonium salt solution to be mixed to obtain a diazonium salt solution; 2, 4-naphthoquinone is dissolved in a KOH solution and mixed with a diazonium salt solution, after hydrochloric acid acidification, acetic acid recrystallization purification is conducted, and BANQ is obtained; the capacity fading rate of the modified naphthoquinone derivative BANQ is as low as 0.00018% per circle, the modified naphthoquinone derivative BANQ shows excellent cycling stability and redox reversibility, the BANQ molecule has an asymmetric non-planar pi conjugation characteristic, and the sensitivity of a redox core to nucleophilic / electrophilic attack is greatly reduced, so that the cycling stability is improved, and the service life is prolonged. And a new direction and possibility are provided for constructing green sustainable large-scale organic redox active molecules for energy storage through artificial modification of natural products.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to an asymmetric nonplanar π-conjugated naphthoquinone derivative, its preparation method, and its application in aqueous flow batteries. Background Technology

[0002] The development of large-scale, low-cost, and long-duration energy storage systems is of paramount importance for alleviating the imbalance between power supply and demand, reducing the intermittency of renewable energy sources, and ensuring the stable and reliable operation of the power grid. Among existing large-scale energy storage technologies, aqueous organic redox flow batteries (AORFBs) have emerged as promising candidates due to their abundant raw material sources, tunable electrochemical performance, and environmental friendliness. In these systems, the liquid redox-active electrolyte is decoupled from the stack structure, allowing for flexible control of energy storage capacity and power output by adjusting the electrolyte volume, thus adapting to different energy demands and grid application scenarios. In recent years, quinone compounds, especially anthraquinone derivatives with side-chain functionalization, have attracted considerable attention due to their excellent performance in alkaline AORFBs. In contrast, although naphthoquinone derivatives are widely distributed in nature, their application in AORFBs is relatively limited, mainly because their electrochemical stability is significantly lower than that of anthraquinone derivatives. For example, the natural dye Lawsone (i.e., 2-hydroxy-1,4-naphthoquinone, 2-HNQ) can be extracted in large quantities from henna leaves or water hyacinth, making it environmentally friendly and widely available. However, 2-HNQ itself has limited water solubility and poor electrochemical stability, which seriously hinders its practical application in AORFBs. Furthermore, the C–H bond adjacent to the carbonyl group in 2-HNQ is prone to Michael addition under alkaline conditions, leading to molecular degradation due to nucleophilic attack during cycling. Simultaneously, the reduced-state 2-HNQ molecule undergoes enol-keto tautomerism, resulting in the formation of 4-(3-hydroxy-1,4-dioxo-1,2,3,4-tetrahydronaphth-2-yl)benzoic acid, causing significant capacity decay. Therefore, improving the water solubility and cycling stability of natural naphthoquinone derivatives through rational molecular design is a crucial scientific problem that urgently needs to be solved. Summary of the Invention

[0003] Technical problems solved: This application provides a structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative, its preparation method, and its application in aqueous flow batteries. It addresses the common problems in existing technologies where natural naphthoquinone compounds in aqueous organic flow batteries suffer from low solubility and significantly lower electrochemical stability compared to anthraquinone derivatives. Furthermore, 2-HNQ itself has limited water solubility and poor electrochemical stability, severely hindering its practical application in AORFBs. In 2-HNQ, the C–H bond adjacent to the carbonyl group readily undergoes Michael addition under alkaline conditions, leading to molecular degradation due to nucleophilic attack during cycling. The reduced-state 2-HNQ molecule undergoes enol-ketone tautomerism, resulting in the formation of 4-(3-hydroxy-1,4-dioxo-1,2,3,4-tetrahydronaphth-2-yl)benzoic acid, causing degradation and severe capacity decay.

[0004] The specific technical solution of this invention is as follows: An asymmetric, nonplanar π-conjugated naphthoquinone derivative, wherein the asymmetric, nonplanar π-conjugated naphthoquinone derivative is 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid, has the following structural formula: .

[0005] A method for preparing a structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative includes the following steps: S1. Dissolve 10 mmol of 2-HNQ and 10 mmol of N-iodosuccinimide in 40 mL of dichloromethane (DCM) according to the dosage ratio, and react at 40 °C for 2 hours; then cool the reaction solution and wash it three times with 40 mL of cold water each time. S2. The organic phase was dried with anhydrous Na2SO4 and the solvent was removed under reduced pressure. Then it was dried at 60°C for 24 hours to obtain 2-hydroxy-3-iodonaphthalene-1,4-dione, with a final yield of 92%. S3. 5.0 mmol of 2-hydroxy-3-iodonaphthalene-1,4-dione, 7.5 mmol of methyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzoate, 15 mmol of K₂CO₃, and 0.025 mmol of Pd(OAc)₂ were added to 50 mL of water and mixed. The mixture was heated and stirred at 100 °C under a nitrogen atmosphere at a stirring speed of 20-1000 rpm for 8 hours. After the reaction was complete, the mixture was gradually cooled to room temperature, and 40 mL of 2 M HCl solution was added. The mixture was then filtered to obtain a solid precipitate. S4. The solid precipitate was washed 1-3 times successively with acetic acid, ethanol and aqueous solution. The obtained solid was then added to 40 mL of 15% KOH solution and stirred at 60℃ for 12 hours at a stirring speed of 20-1000 rpm. After cooling to room temperature, the pH was adjusted to 0-4 with 1M HCl solution. After filtration, the filter residue was collected, washed 1-3 times with water and recrystallized with acetic acid. Finally, it was dried at 60℃ for 24 hours to obtain 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid BANQ, with a final yield of 63%.

[0006] Furthermore, in S1, the mass ratio of 2-HNQ to N-iodosuccinimide is 2-HNQ:N-iodosuccinimide = 1.74:2.25.

[0007] Further, in S3, the mass ratio of 2-hydroxy-3-iodonaphthalene-1,4-dione : methyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzoate : K2CO3 : Pd(OAc)2 is 1.50 : 1.97 : 2.07 : 0.056.

[0008] Furthermore, the reaction formula for the structurally asymmetric nonplanar π-conjugated naphthoquinone derivative is as follows: .

[0009] A method for preparing a structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative includes the following steps: Step 1: Add 10 mmol of methyl 4-aminobenzoate to a 6M hydrochloric acid solution at 0°C according to the dosage ratio, and stir in an ice bath for 0.5 hours at a stirring speed of 20-1000 rpm to obtain a methyl 4-aminobenzoate solution; dissolve 10 mmol of sodium nitrite in 40 mL of water, and then add it dropwise to the methyl 4-aminobenzoate solution, and continue stirring for 0.5 hours to generate a diazonium salt solution; dissolve 10 mmol of 2-hydroxy-1,4-naphthoquinone in 30% KOH solution, and then add it dropwise to the diazonium salt solution to obtain the reaction mixture; Step 2: The reaction mixture was heated to 45°C and stirred for 1 hour at a stirring speed of 20-1000 rpm. It was then cooled to room temperature and poured into 300 mL of water. The pH was adjusted to less than 4 by acidification with hydrochloric acid. The resulting solid was collected by filtration, dried under reduced pressure, and purified by recrystallization from acetic acid to obtain 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid BANQ, with a final yield of 65%.

[0010] Furthermore, in the first step, the mass-to-volume ratio of methyl 4-aminobenzoate to hydrochloric acid is methyl 4-aminobenzoate: hydrochloric acid = 1.37 g: 20 mL; the mass-to-volume ratio of sodium nitrite to water is sodium nitrite: water = 0.69 g: 40 mL; and the mass-to-volume ratio of 2-hydroxy-1,4-naphthoquinone (2-HNQ) to KOH is 2-hydroxy-1,4-naphthoquinone: KOH = 1.75 g: 150 mL.

[0011] Further, in the second step, the acetic acid recrystallization purification specifically involves dissolving the solid dried under reduced pressure in 20 mL of acetic acid, heating it to 100°C, and when 5 mL of acetic acid has evaporated, cooling the temperature to room temperature, filtering it again, and rinsing it three times with 40 mL of deionized water to collect the solid.

[0012] Furthermore, the synthetic route for the structurally asymmetric nonplanar π-conjugated naphthoquinone derivative is as follows: .

[0013] This application also discloses the application of any of the above-mentioned structurally asymmetric nonplanar π-conjugated naphthoquinone derivatives in aqueous flow batteries.

[0014] Explanation of the principle: This patent proposes a nonplanar π-conjugation extension strategy, which introduces a polar benzoic acid side group onto the redox core of 2-HNQ, thereby enhancing its π-conjugation degree and molecular polarity. Through directional structural modification of the natural product 2-HNQ, a nonplanar naphthoquinone derivative with an asymmetric structure, namely 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid (BANQ), was successfully synthesized, exhibiting significantly enhanced water solubility and excellent redox reversibility. Theoretical calculations show that B... The redox core and the π-conjugated benzoic acid side group in the ANQ molecule have a specific angle, forming a unique non-planar configuration. This structural feature, combined with the strong deprotonation behavior of BANQ under alkaline conditions, leads to a non-equilibrium charge distribution within the molecule and significantly increases its polarity, thereby greatly improving the water solubility of BANQ under alkaline conditions. Compared with 2-HNQ, which is thermodynamically unstable and prone to enol-keto tautomerism during cycling, the BANQ molecule exhibits good thermodynamic stability and can maintain the integrity of its redox core structure during cycling.

[0015] The beneficial effects of this invention are: This invention addresses the core bottlenecks of low solubility and poor electrochemical stability of natural naphthoquinone compounds in aqueous organic flow batteries. It proposes an innovative structurally asymmetric nonplanar π-conjugated naphthoquinone derivative. By introducing a polar benzoic acid side group onto the redox core of 2-HNQ, a unique nonplanar π-conjugated structure is constructed, which fundamentally regulates the molecular charge distribution and significantly enhances molecular polarization, thereby optimizing the structural performance of natural naphthoquinone. This structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative significantly improves the water solubility and alkaline electrolyte compatibility of BANQ molecules, effectively suppresses unfavorable side reactions such as enol-ketone tautomerism and nucleophilic addition that are prone to occur in natural 2-HNQ during cycling, and enables BANQ molecules to maintain a high degree of structural integrity during long-term electrochemical cycling. The modified naphthoquinone derivative BANQ exhibits a capacity decay rate as low as 0.00018% per cycle (or 0.045% / day), demonstrating excellent cycling stability and redox reversibility. The theoretical calculations and experimental results are in high agreement, clearly demonstrating that the asymmetric non-planar structure plays a key role in improving molecular stability. This invention is based on natural products, has a simple and scalable design route, and uses green and environmentally friendly materials. It provides a brand-new approach and technological breakthrough for constructing high-performance, low-cost, and sustainable large-scale aqueous organic flow battery active molecules, and has significant application potential.

[0016] Calculations using the abbreviated Fukui function (CFF) show that BANQ molecules with asymmetric nonplanar π-conjugation features have significantly reduced sensitivity of their redox core to nucleophilic / electrophilic attacks, thereby improving their cycling stability. This patent demonstrates a technical approach to significantly improve the electrochemical performance of naphthoquinone derivatives through an asymmetric nonplanar π-conjugation extension strategy, providing new directions and possibilities for constructing green and sustainable large-scale energy storage organic redox active molecules by artificially modifying natural products. Attached Figure Description

[0017] Figure 1 Example 1 of this invention yielded 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid BANQ. 1 H nuclear magnetic resonance spectrum; Figure 2 This is a verification image of the high-resolution mass spectrometry (HRMS) of 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid BANQ obtained in Example 1 of the present invention. Figure 3This is a solubility test chart of BANQ of the present invention, where a is the UV-Vis curve of BANQ solution of different concentrations at pH 14, and b is the fitting chart of absorbance and concentration of BANQ solution at λ288. Figure 4 This is a graph showing the electrochemical performance of the BANQ according to the present invention; Figure 5 The electrochemical performance diagram of 0.1 M BANQ||K4[Fe(CN)6] AORFB of the present invention is shown, where a is the polarization curve and power density curve under different SOCs, and b is the coulombic efficiency, energy efficiency and specific capacity under different current densities under constant current charge and discharge test. Figure 6 This is a performance test graph of the BANQ-based flow battery of the present invention, where a represents the current density at 100 mA·cm⁻¹. −2 Under constant current cycling conditions, b shows the constant current cycling performance of 0.1 M BANQ||K4[Fe(CN)6] AORFB using SPEEK membrane; c shows the charge-discharge curves of 0.1 M BANQ||K4[Fe(CN)6] AORFB at 10, 750, and 1500 cycles; d shows the cycling performance of 0.1 M BANQ||K4[Fe(CN)6] AORFB under constant current-constant voltage conditions; and d shows the charge-discharge curves of 0.1 M BANQ||K4[Fe(CN)6] AORFB at 10, 500, and 1000 cycles. Figure 7 This is a cycling performance diagram of the 0.5 M BANQ||K4Fe(CN)6 AORFB using a SPEEK membrane according to the present invention, where a is the open-circuit voltage (OCV) diagram at different SOCs; b is the polarization curve and power density curve collected under 20%, 50%, and 100% SOC conditions; c is the 0.5 M BANQ||K4Fe(CN)6 AORFB at constant current densities of 20, 40, 80, 100, and 150 mA·cm⁻¹. −2 Discharge capacity, coulombic efficiency, and energy efficiency at 50 mA·cm⁻¹; d represents the discharge capacity, coulombic efficiency, and energy efficiency of 0.5 M BANQ||K₄Fe(CN)₆ AORFB using a SPEEK membrane at 50 mA·cm⁻¹. −2 The constant current cycling performance at current density is shown in the graph; e represents the charge-discharge curves of 0.5 M BANQ||K4Fe(CN)6 AORFB at the 10th and 400th cycles; f represents the cycling performance of 0.5 M BANQ||K4Fe(CN)6 AORFB under constant current-constant voltage conditions; g represents the charge-discharge curves of 0.5 M BANQ||K4Fe(CN)6AORFB at the 10th, 100th, and 600th cycles. Detailed Implementation

[0018] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0019] Example 1: A method for preparing a structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative, which synthesizes asymmetric, nonplanar π-conjugated BANQ molecules via a Suzuki–Miyaura cross-coupling reaction, comprising the following steps: S1. Dissolve 10 mmol of 2-HNQ and 10 mmol of N-iodosuccinimide in 40 mL of dichloromethane (DCM) according to the dosage ratio, and react at 40 °C for 2 hours; then cool the reaction solution and wash it three times with 40 mL of cold water each time. S2. The organic phase was dried with anhydrous Na2SO4 and the solvent was removed under reduced pressure. Then it was dried at 60°C for 24 hours to obtain 2-hydroxy-3-iodonaphthalene-1,4-dione, with a final yield of 92%. S3. Add 5.0 mmol of 2-hydroxy-3-iodonaphthalene-1,4-dione, 7.5 mmol of methyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzoate, 15 mmol of K2CO3 and 0.025 mmol of Pd(OAc)2 to 50 mL of water according to the specified ratio. Heat and stir at 100 °C under a nitrogen atmosphere at a stirring speed of 20-1000 rpm for 8 hours. After the reaction is complete, gradually cool the mixture to room temperature, add 40 mL of 2M HCl solution, and filter to obtain a solid precipitate. S4. The solid precipitate was washed 1-3 times successively with acetic acid, ethanol and aqueous solution. The obtained solid was then added to 40 mL of 15% KOH solution and stirred at 60 °C for 12 hours at a stirring speed of 20-1000 rpm. After cooling to room temperature, the pH was adjusted to 0-4 with 1M HCl solution. After filtration, the filter residue was collected, washed with water and recrystallized with acetic acid. Finally, it was dried at 60 °C for 24 hours to obtain 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid BANQ, with a final yield of 63%.

[0020] The reaction formula is: .

[0021] like Figure 1 As shown, BANQ's 1 ¹H NMR spectrum, 400 MHz, DMSO-d6.

[0022] like Figure 2As shown, the validation plot of BANQ's high-resolution mass spectrometry (HRMS), [C 17 H 10 O5−H] − The calculated HRMS (ESI) value is 293.04500, and the measured value is 293.04556.

[0023] Example 2, a method for preparing a structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative, comprising the following steps: Step 1: Add 10 mmol of methyl 4-aminobenzoate to 20 mL of 6 M hydrochloric acid solution at 0 °C according to the dosage ratio, and stir in an ice bath for 0.5 hours at a stirring speed of 20-1000 rpm to obtain a methyl 4-aminobenzoate solution; dissolve 10 mmol of sodium nitrite in 40 mL of water, and then add it dropwise to the methyl 4-aminobenzoate solution, and continue stirring for 0.5 hours to generate a diazonium salt solution; dissolve 10 mmol of 2-hydroxy-1,4-naphthoquinone in 150 mL of 30% KOH solution, and then add the diazonium salt solution dropwise to obtain the reaction mixture; Step 2: The reaction mixture was heated to 45 °C and stirred for 1 hour at a stirring speed of 20-1000 rpm. It was then cooled to room temperature and poured into 300 mL of water. The pH was adjusted to less than 4 by acidification with hydrochloric acid. The resulting solid was collected by filtration, dried under reduced pressure, and purified by recrystallization from acetic acid to obtain 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid (BANQ) with a final yield of 65%. Specifically, the acetic acid recrystallization purification involved dissolving the solid after reduced pressure drying in 20 mL of acetic acid, heating to 100 °C, and cooling to room temperature until 5 mL of acetic acid remained. The mixture was then filtered again and washed three times with 40 mL of deionized water, and the solid was collected.

[0024] The synthetic route is as follows: .

[0025] A lower-cost, scalable, Pd-free diazotization-substitution route offers a novel synthetic path to avoid the use of expensive palladium catalysts.

[0026] Example 3: Solubility test of the structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative BANQ: Standard concentration BANQ solutions dissolved in 1.0 M KOH solution were prepared using a 10 mL graduated cylinder. The absorbance of these solutions was measured at 0.2 nm intervals within the wavelength range of 200 to 700 nm using a UV-Vis spectrophotometer. Concentration curves of the standard solutions were plotted based on the absorbance at their highest absorption peaks. The saturated solution was prepared by gradually adding BANQ molecules and the corresponding molar amount of alkali to 2.0 mL of 1.0 M KOH solution and sonicating until a small amount of precipitate appeared. After centrifugation, 100 μL of the saturated solution supernatant was pipetted and diluted 20,000 times with 1.0 M KOH solution. The maximum solubility of the solution was determined by plotting UV-Vis absorbance versus concentration.

[0027] The solubility of BANQ under alkaline conditions (pH=14) was tested using UV-Vis absorption spectroscopy. The solubility of BANQ at pH=14 was 1.30 M. Figure 3 As shown, a is the UV-Vis curve of BANQ solution at different concentrations at pH 14, where "20 k" indicates that the solution was diluted 20,000 times from the saturated concentration. b is the fitting graph of absorbance and concentration of BANQ solution at λ288.

[0028] Example 4: Electrochemical performance testing of the structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative BANQ: Electrochemical parameters were determined using an electrochemical workstation. A three-electrode configuration was used for CV testing. The working electrode was a pretreated glassy carbon electrode (GC 130, 3 mm in diameter, polished with alumina powder of approximately 50 nm particle size), the counter electrode was a platinum electrode, and the reference electrode was an Ag / AgCl electrode filled with saturated KCl solution. When not in use, the electrode was stored in saturated KCl solution, and its potential relative to the standard hydrogen electrode (SHE) was +0.199 V. The test solution was 5 mM BANQ solution.

[0029] The electrochemical properties of BANQ in aqueous solution at pH 14 were tested by CV. The oxygen reduction potential of BANQ (…) vs. The Ag / AgCl electrode has a voltage of −0.74 V. For example... Figure 4 The figure shows the cyclic voltammetry curves of 2.0 mM BANQ dissolved in 1.0 M KOH solution.

[0030] Example 5: Flow battery performance testing of the structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative BANQ: 1. By using different charging states at 80 mA·cm −2The battery was charged at a specific current density and allowed to stand for 30 seconds before the OCV was recorded, and the SOC curve was measured. When the battery voltage reached 1.5 V, it was charged to 100% SOC.

[0031] 2. To measure the power density of the battery, linear sweep cyclic voltammetry (LSV) was used at 50 mV·s. −1 The scan rate was used to record the current-voltage curves of BANQ flow batteries with concentrations of 0.1 and 0.5 M at 20%, 50%, and 100% SOC.

[0032] 3. For the 0.1 M BANQ battery cycle test, the negative electrode electrolyte was 5 mL of 0.1 M BANQ solution (pH 14), and the positive electrode electrolyte was 40 mL of 0.1 M K₄[Fe(CN)₆] solution (pH 14). Cycling was performed at 100 mA·cm⁻¹ between 1.5 V and 0.5 V. −2 The constant current was used to conduct cyclic testing of the flow battery.

[0033] 4. For the constant current-constant voltage charge-discharge test of 0.1 M BANQ in 1 M KOH solution, initially at 100 mA·cm⁻¹ −2 The current density is charged to 1.5 V, and then maintained at that voltage until the current density drops to 6 mA·cm⁻¹. −2 It is then discharged to 0.5 V and maintained at that voltage until the current density drops to 6 mA·cm⁻¹. −2 .

[0034] 5. For the constant current cycling test of 0.5 M BANQ, the negative electrode electrolyte was 5 mL of 0.5 M BANQ solution (pH 14), and the positive electrode electrolyte was 40 mL of 0.4 M K₄[Fe(CN)₆] solution (pH 14). The constant current cycling was performed at 50 mA·cm⁻¹ between 1.5 V and 0.5 V. −2 The constant current was used to perform cycle tests on the flow battery.

[0035] 6. For the constant current-constant voltage charge-discharge test of 0.5 M BANQ in 1 M KOH solution, initially at 100 mA·cm⁻¹ −2 The current density is charged to 1.5 V, and then maintained at that voltage until the current density drops to 6 mA·cm⁻¹. −2 It is then discharged to 0.5 V and maintained at that voltage until the current density drops to 6 mA·cm⁻¹. −2 .

[0036] 7. For the constant current cycling test of 1.0 M BANQ, the negative electrode electrolyte was 5 mL of 1.0 M BANQ solution (pH 14), and the positive electrode electrolyte was 40 mL of 0.6 M Na₄[Fe(CN)₆] solution (pH 14). The constant current cycling was performed at 100 mA·cm⁻¹ between 1.5 V and 0.5 V. −2 The constant current was used to perform cycle tests on the flow battery.

[0037] Performance testing of BANQ-based flow batteries was conducted, investigating the AORFB power density performance of low-concentration 2-HNQ negative electrode electrolyte, K4[Fe(CN)6] positive electrode electrolyte, and SPEEK film. Figure 5 As shown in Figure a, the negative electrode electrolyte is 5 mL of 0.1 M BANQ in 1.0 M KOH, and the positive electrode electrolyte is 40 mL of 0.1 M K₄[Fe(CN)₆] in 1.0 M KOH. At 100% SOC, the power density of 0.1 M BANQ||K₄[Fe(CN)₆] AORFB is 122 mW·cm⁻¹. −2 .

[0038] Between 20 and 150 mA·cm −2 Rate performance tests were conducted within the current density range, such as... Figure 5 As shown in Figure b, for the 0.1 M BANQ||K4[Fe(CN)6] system, its performance at 20 and 150 mA·cm −2 The discharge capacities at the following values ​​are 4.76 and 3.95 Ah·L, respectively. −1 The corresponding theoretical capacity utilization rates are 88.8% and 73.7%, respectively.

[0039] 1550 cycles were performed using a constant current charge-discharge process at a current density of 100 mA·cm⁻¹. −2 Under these conditions, long-cycle cyclic testing was performed on 0.1 M BANQ||K4[Fe(CN)6] AORFBs, such as... Figure 6 a and Figure 6 As shown in Figure b, for the 0.1 M BANQ||K4[Fe(CN)6] system, its initial discharge capacity is 4.54 Ah·L. −1 After 1550 cycles (5.83 days), it remained at 4.53 Ah·L. −1 The capacity retention rate exceeds 99.98%. Its capacity decay rate is only 0.00018% per revolution, or 0.045% per day. In addition, the coulombic efficiency of the system remains close to 100%, with an average energy efficiency of 79%.

[0040] The AORFB was subjected to 1100 cycles using a constant current-constant potential charge-discharge process. During charging, the potential was maintained at 1.5 V until the current density dropped to 6 mA·cm⁻¹. −2 Similarly, during discharge, the potential is maintained at 0.5 V until the current density drops to 6 mA·cm⁻¹. −2 These conditions can induce near-100% redox activity in active molecules, thus aiding in the study of their electrochemical stability during complete charge-discharge processes. For example... Figure 6 c and Figure 6 As shown in Figure d, 0.1 M BANQ||K4[Fe(CN)6]AORFB exhibits excellent stability under constant current-constant voltage cycling conditions. After 1250 cycles (5.63 days), its discharge capacity only decreased by 4.77 Ah·L. −1 Decreased to 4.73 Ah·L −1 The corresponding capacity decay rate is only 0.00067% per cycle, or 0.15% per day. This result fully demonstrates the good electrochemical stability of 0.1 M BANQ||K4[Fe(CN)6] AORFB under 100% SOC conditions.

[0041] Performance testing: Considering practical applications, this patent also investigated the electrochemical performance of 0.5 M BANQ||K4[Fe(CN)6] AORFB, such as... Figure 7 As shown. Figure 7 As shown in Figure a, the open-circuit voltage (OCV) values ​​of high-concentration BANQ||K4[Fe(CN)6]AORFB from 10% to 100% SOC were recorded. At 50% SOC, the open-circuit voltage was 1.02 V. Polarization curves at 20%, 50%, and 100% SOC were obtained using a linear sweep voltammetry method, and the power density was calculated, as shown in Figure a. Figure 7 As shown in Figure b. Notably, at 100% SOC, the observed peak power density is 263 mW·cm⁻¹. −2 This value is highly competitive among existing quinone-based AORFBs. The increased power density at high concentrations is attributed to improved ionic conductivity, which reduces ohmic polarization and enhances the usability of the active material.

[0042] At 20, 40, 80, 100 and 150 mA·cm −2 The rate performance of high-concentration BANQ||K4[Fe(CN)6]AORFB was measured at a current density, such as... Figure 7 As shown in c. With the current density increasing from 20 mA·cm⁻¹... −2 (22.9 Ah·L) −1 The rise reached 150 mA·cm−2 (18.5 Ah·L) −1 The discharge capacity remained at 69%. This observation highlights the excellent rate performance of BANQ||K4[Fe(CN)6]AORFB and validates its great application potential in high-power energy storage scenarios.

[0043] At 50 mA·cm −2 The galvanostatic cycling stability of high-concentration BANQ||K4[Fe(CN)6] AORFB was evaluated at a current density (using a SPEEK membrane), as shown in the figure. Figure 7 d and Figure 7 As shown in Figure e. During 400 cycles (350 hours), the capacity increased from 22.2 Ah·L. −1 Decreased to 22.0 Ah·L −1 The corresponding capacity decay rate is 0.002% per cycle or 0.062% per day.

[0044] Constant current-constant voltage charge-discharge tests were performed on 0.5 M BANQ||K4[Fe(CN)6] AORFB, as shown below. Figure 7 f and Figure 7 As shown in g. At 100 mA·cm −2 After rigorous testing for 600 cycles (equivalent to 320 hours), the capacity increased from the initial value of 25.63 Ah·L. −1 Reduced to 24.97 Ah·L −1 The capacity decay rate is 0.0043% per cycle or 0.19% per day. The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures and preparation methods not specifically described or explained in this invention, unless otherwise specified or limited, shall be implemented using conventional methods in the art.

Claims

1. A structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative, characterized in that, The structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative is 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid, with the following structural formula: .

2. A method for preparing the structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative according to claim 1, characterized in that, Includes the following steps: S1. Dissolve 10 mmol of 2-HNQ and 10 mmol of N-iodosuccinimide in 40 mL of dichloromethane (DCM) according to the dosage ratio, and react at 40 °C for 2 hours; then cool the reaction solution and wash it three times with 40 mL of cold water each time. S2. The organic phase was dried with anhydrous Na2SO4 and the solvent was removed under reduced pressure. Then it was dried at 60°C for 24 hours to obtain 2-hydroxy-3-iodonaphthalene-1,4-dione, with a final yield of 92%. S3. 5.0 mmol of 2-hydroxy-3-iodonaphthalene-1,4-dione, 7.5 mmol of methyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzoate, 15 mmol of K₂CO₃, and 0.025 mmol of Pd(OAc)₂ were added to 50 mL of water and mixed. The mixture was heated and stirred at 100 °C under a nitrogen atmosphere at a stirring speed of 20-1000 rpm for 8 hours. After the reaction was complete, the mixture was gradually cooled to room temperature, and 40 mL of 2 M HCl solution was added. The mixture was then filtered to obtain a solid precipitate. S4. The solid precipitate was washed 1-3 times successively with acetic acid, ethanol and aqueous solution. The obtained solid was then added to 40 mL of 15% KOH solution and stirred at 60℃ for 12 hours at a stirring speed of 20-1000 rpm. After cooling to room temperature, the pH was adjusted to 0-4 with 1M HCl solution. After filtration, the filter residue was collected, washed 1-3 times with water and recrystallized with acetic acid. Finally, it was dried at 60℃ for 24 hours to obtain 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid BANQ, with a final yield of 63%.

3. The method for preparing the structurally asymmetric nonplanar π-conjugated naphthoquinone derivative according to claim 2, characterized in that, The mass ratio of 2-HNQ to N-iodosuccinimide in S1 is 2-HNQ:N-iodosuccinimide = 1.74:2.

25.

4. The method for preparing the structurally asymmetric nonplanar π-conjugated naphthoquinone derivative according to claim 2, characterized in that, In the S3, the mass ratio of 2-hydroxy-3-iodonaphthalene-1,4-dione: methyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzoate: K2CO3: Pd(OAc)2 is 1.50: 1.97: 2.07: 0.

056.

5. The method for preparing the structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative according to claim 2, characterized in that, The reaction formula for the structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative is as follows: .

6. A method for preparing the structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative according to claim 1, characterized in that, Includes the following steps: Step 1: Add 10 mmol of methyl 4-aminobenzoate to a 6M hydrochloric acid solution at 0°C according to the dosage ratio, and stir in an ice bath for 0.5 hours at a stirring speed of 20-1000 rpm to obtain a methyl 4-aminobenzoate solution; dissolve 10 mmol of sodium nitrite in 40 mL of water, and then add it dropwise to the methyl 4-aminobenzoate solution, and continue stirring for 0.5 hours to generate a diazonium salt solution; dissolve 10 mmol of 2-hydroxy-1,4-naphthoquinone in 30% KOH solution, and then add it dropwise to the diazonium salt solution to obtain the reaction mixture; Step 2: The reaction mixture was heated to 45°C and stirred for 1 hour at a stirring speed of 20-1000 rpm. It was then cooled to room temperature and poured into 300 mL of water. The pH was adjusted to less than 4 by acidification with hydrochloric acid. The resulting solid was collected by filtration, dried under reduced pressure, and purified by recrystallization from acetic acid to obtain 4-(3-hydroxy-1,4-dioxo-1,4-dihydronaphth-2-yl)benzoic acid BANQ, with a final yield of 65%.

7. The method for preparing the structurally asymmetric nonplanar π-conjugated naphthoquinone derivative according to claim 6, characterized in that: In the first step, the mass-to-volume ratio of methyl 4-aminobenzoate to hydrochloric acid is methyl 4-aminobenzoate: hydrochloric acid = 1.37 g: 20 mL; the mass-to-volume ratio of sodium nitrite to water is sodium nitrite: water = 0.69 g: 40 mL; and the mass-to-volume ratio of 2-hydroxy-1,4-naphthoquinone (2-HNQ) to KOH is 2-hydroxy-1,4-naphthoquinone: KOH = 1.75 g: 150 mL.

8. The method for preparing the structurally asymmetric nonplanar π-conjugated naphthoquinone derivative according to claim 6, characterized in that, The second step of acetic acid recrystallization purification specifically involves dissolving the solid dried under reduced pressure in 20 mL of acetic acid, heating it to 100°C, and cooling it to room temperature when 5 mL of acetic acid has evaporated. The solid is then filtered again and washed three times with 40 mL of deionized water before being collected.

9. The method for preparing the structurally asymmetric nonplanar π-conjugated naphthoquinone derivative according to claim 6, characterized in that, The synthetic route for the structurally asymmetric, nonplanar π-conjugated naphthoquinone derivative is as follows: 。 10. The application of the structurally asymmetric nonplanar π-conjugated naphthoquinone derivative of claim 1 in an aqueous flow battery.

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