Water-soluble viologen derivatives based on vinyl conjugation extension and preparation methods thereof and applications in neutral aqueous organic flow batteries

Abstract

The present invention proposes a water-soluble viologen derivative based on vinyl conjugation extension, a preparation method thereof, and an application in a neutral aqueous organic flow battery. Using DMF as a solvent, 1,2-di(4-pyridyl)ethylene and (3-bromopropyl)-trimethylammonium bromide undergo a quaternary ammonium salt ionization reaction to obtain a viologen derivative bromide salt; the viologen derivative bromide salt is subjected to anion exchange to obtain 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt. The present invention uses a novel vinyl conjugated extended water-soluble viologen derivative as a negative electrode electrolyte of an aqueous organic flow battery, which can effectively improve the electrochemical performance of a viologen-based aqueous organic flow battery. The synthesis method of the present invention is simple, the raw material cost is low, and it is easy to achieve large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of battery materials and energy storage, and in particular to the preparation of a vinyl conjugated extended water-soluble viologen derivative and its application in a neutral aqueous organic liquid flow battery. Background Art

[0002] In recent years, the overexploitation and utilization of fossil energy and the resulting problems of resource shortage, climate change, environmental pollution, etc. have made the development of renewable green energy very urgent. The intermittent and discontinuous nature of renewable energy requires large-scale energy storage technology to achieve energy storage and stable output. Electrochemical energy storage technology is not restricted by the external environment and can directly store and release electrical energy, showing good development potential. All-vanadium redox flow battery is a relatively mature energy storage technology at present. However, as a rare metal, vanadium has problems such as high cost and limited resources. In contrast, aqueous organic flow battery uses a variety of organic molecules as electrochemically active substances, which can not only greatly reduce the cost of redox couples, but also can regulate the electrode potential, solubility and stability of organic active electrolytes through reasonable molecular design. It is an effective way to develop the next generation of high-safety, low-cost, large-capacity new energy storage technology.

[0003] According to the different redox potentials of active organic matter, they can be used in positive and negative electrolytes respectively. Among them, the positive electrolytes mainly include ferrocene, benzoquinone and TEMPO derivatives, and the negative electrolytes mainly include anthraquinone and viologen derivatives. Compared with acidic and alkaline electrolytes, neutral electrolytes are less corrosive, safer, more environmentally friendly and less expensive; in addition, neutral systems have fewer side reactions, which can effectively alleviate the degradation of electrolytes and improve battery stability. Compared with other active organic matter, viologen compounds have better solubility in neutral aqueous solutions and are easy to synthesize, so they have received more and more attention.

[0004] The N-atom terminal on the pyridine ring in viologen compounds is prone to substitution reactions, and its structure and performance can be easily regulated by molecular design. When viologen derivatives undergo electrochemical redox reactions, the second-step reduction reaction will generate neutral viologen molecules, which have very low solubility in aqueous solution, and the reaction is often irreversible. Modification of viologen molecules with hydrophilic groups (such as quaternary ammonium groups, sulfonic acid groups, hydroxyl groups, and phosphate groups, etc.) can achieve the dissolution of two-electron reduction products in aqueous solution. Furthermore, by expanding the π-conjugated structure and the range of electron delocalization, the stability of the intermediate free radical is improved, so that the reversibility of the two-step electron transfer process is enhanced, effectively improving the battery energy density and cycle stability. Summary of the invention

[0005] In order to solve the above-mentioned technical problems, the present invention provides a novel vinyl conjugated extended water-soluble viologen derivative, and applies it to the negative active electrolyte of an aqueous organic liquid flow battery. A vinyl bipyridyl quaternary ammonium salt compound is prepared by a bipyridyl fusion reaction and a quaternary ammonium salt ionization reaction. By introducing a quaternary ammonium salt-soluble group at the end of bipyridyl, the water solubility of the viologen derivative is greatly improved. By connecting the vinyl group between the bipyridyl rings, the π conjugated structure and the electron delocalization range can be expanded, the stability of the intermediate free radical can be improved, and the reversibility of the two-step electron transfer process can be enhanced, thereby improving the energy density and cycle stability of the viologen-based aqueous organic liquid flow battery.

[0006] To achieve the above object, the present invention is implemented by the following technical scheme: based on vinyl conjugation extended water-soluble viologen derivatives, the vinyl conjugated extended water-soluble viologen derivatives are 1,2-di(4-pyridyl)ethylene diquaternary ammonium salts, having the structural formula shown in (I):

[0007]

[0008] The preparation method of water-soluble viologen derivatives based on vinyl conjugation extension includes the following steps: using DMF as solvent, 1,2-di(4-pyridyl)ethylene and (3-bromopropyl)-trimethylammonium bromide undergo quaternary ammonium salt ionization reaction to obtain viologen derivative bromide salt; the viologen derivative bromide salt is subjected to anion exchange to obtain 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt. The chemical reaction formula is as follows:

[0009]

[0010] Furthermore, in a molar ratio, 1,2-di(4-pyridyl)ethylene:(3-bromopropyl)-trimethylammonium bromide=1:3.

[0011] Furthermore, the quaternary ammonium salt ionization reaction is carried out at 100 to 120° C. under inert gas protection for reflux reaction for 12 to 72 hours.

[0012] Further, the anion exchange is to react the viologen derivative bromide with Anion exchange was performed using an anion resin column in the chloride form.

[0013] The invention provides an application of a vinyl conjugated extended water-soluble viologen derivative in a neutral aqueous organic flow battery.

[0014] Furthermore, a negative electrode electrolyte is prepared by using a vinyl conjugated extended water-soluble viologen derivative as an active electrolyte, a neutral chloride salt as a supporting electrolyte, and water as a solvent.

[0015] Furthermore, a TEMPO derivative or a ferrocene derivative is used as the positive electrode electrolyte, and an ion exchange membrane or a porous membrane is used as the separator.

[0016] The beneficial effects of the present invention are:

[0017] 1. The viologen derivative based on vinyl conjugation expansion proposed in the present invention has low raw material cost, high product purity, high yield in its preparation method, and the synthesized product aqueous solution does not need to be purified and can be directly applied to liquid flow batteries.

[0018] 2. Compared with traditional bipyridine compounds, the viologen derivatives based on vinyl conjugation extension proposed in the present invention introduce vinyl groups between bipyridine rings, expand the molecular conjugation area, and improve the reversibility of electron transfer and structural stability of the viologen molecule.

[0019] 3. The present invention introduces a vinyl group in the middle of the bipyridine ring. Due to the electron-donating effect of the vinyl group, the redox potential of the viologen derivative is negatively shifted, thereby effectively improving the voltage window and energy density of the viologen-based aqueous organic liquid flow battery.

[0020] 4. In order to improve the cycle stability, solubility and electrode potential of viologen derivatives as active electrolytes of aqueous organic flow batteries, the present invention proposes to simply connect vinyl groups between two pyridine rings to increase the conjugation of viologen derivatives; the introduction of vinyl groups improves the delocalization of electrons in viologen molecules, improves the stability of molecular structure, promotes electron transfer, and improves its electrochemical redox reaction kinetics; the larger molecular structure can inhibit the penetration of viologen molecules through the diaphragm to the positive electrode, which is beneficial to improving the cycle stability of the battery; the electron-donating effect of vinyl groups can shift the redox potential of viologen derivatives negatively, which can increase the output voltage of the corresponding flow battery. Further introducing a hydrophilic quaternary ammonium salt functional group at the end of the pyridine ring can effectively improve the water solubility of viologen derivatives and increase the energy density of the battery.

[0021] 5. The present invention uses a novel vinyl conjugated extended water-soluble viologen derivative as the negative electrode electrolyte of an aqueous organic liquid flow battery, which can effectively improve the electrochemical performance of a viologen-based aqueous organic liquid flow battery. The synthesis method is simple, the raw material cost is low, and it is easy to achieve large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the hydrogen nuclear magnetic resonance spectrum of the viologen derivative prepared in Example 1.

[0023] Figure 2 It is the UV-visible absorption spectrum and standard curve diagram of the aqueous solution of the viologen derivative prepared in Example 1 (inset).

[0024] Figure 3It is the UV-visible absorption spectrum and standard curve diagram (inset) of the viologen derivative prepared in Example 1 dissolved in 1M sodium chloride aqueous solution.

[0025] Figure 4 The cyclic voltammetry curves of the viologen derivative negative electrode electrolyte in Example 2 at different scan rates (the scan rates are 0.05, 0.07, 0.1, 0.15, 0.2, 0.25, and 0.3 V / s, respectively).

[0026] Figure 5 is the peak current ip of the viologen derivative in Example 2 and the square root of the scan rate v 1 / 2 Linear relationship diagram.

[0027] Figure 6 is the viologen derivative negative electrode electrolyte in Example 2, N Me -Cyclic voltammetry curves of TEMPO cathode electrolyte.

[0028] Figure 7 The viologen derivative is used as the negative electrode electrolyte, N Me -Schematic diagram of the working principle of a neutral aqueous organic redox flow battery with TEMPO as the positive electrode electrolyte. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to examples.

[0030] Example 1

[0031] (I) Based on vinyl conjugation, the water-soluble viologen derivative is prepared as follows:

[0032] 1,2-di(4-pyridyl)ethylene (0.400 g, 1.389 mmol, 1 equiv) and (3-bromopropyl)-trimethylammonium bromide (1.087 g, 4.167 mmol, ~3 equiv) were dissolved in 50 mL of DMF, refluxed at 110 ° C under inert gas protection for 72 h, cooled to room temperature, and then added with 40 mL of DMF. After vacuum filtration, the mixture was repeatedly washed with DMF and acetone, and then vacuum dried to obtain the bromide salt of the viologen derivative.

[0033] The Br in the bromide salt of the obtained viologen derivative - Through The chloride form anion exchange resin is used to exchange anions for chloride to obtain the target product, a water-soluble viologen derivative based on vinyl conjugation extension, namely 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt. Yield: 83.5%.

[0034] (II) Characterization

[0035] 1H NMR (300MHz, D 2 O)δ=8.85(d,4H),8.25(d,4H),7.87(s,2H),4.66(t,4H),3.48(s,4H),3.11(s,18H),2.55(s,4H); 1H NMR spectrum is shown in Figure 1 As shown. Figure 1 It can be seen that the synthesized water-soluble viologen derivative based on vinyl conjugation extension has high purity, and the obtained viologen derivative contains 7 different hydrogens with an area ratio of 1:2:2:2:2:2:9, which matches the molecular structure of 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt.

[0036] (III) Solubility

[0037] The solubility of 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt in deionized water and 1M NaCl solution was determined by UV-visible spectroscopy. The saturated solutions of 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt in deionized water and 1M NaCl solution were diluted to different concentrations, and the corresponding UV-visible spectral tests were performed to obtain the concentration standard curve of 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt. According to the pre-calibrated absorbance concentration curve of known concentration, the concentration of 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt can be determined. The UV-visible absorption spectrum titration diagram and standard curve diagram of the vinyl viologen derivative (1,2-di(4-pyridyl)ethylene diquaternary ammonium salt) in aqueous solution and sodium chloride solution are shown in the figure. Figure 2 and Figure 3 shown.

[0038] The results show that the vinyl viologen derivative prepared by the present invention exhibits high solubility in deionized water and 1M NaCl solution, which are 1.95 M and 1.63 M, respectively. This is because the hydrophilic groups (quaternary ammonium groups) are introduced at the ends of the two pyridine rings, which greatly increases the solubility of the pyridine groups. Compared with other conjugated viologen derivatives, the solubility of the vinyl viologen derivative is greatly improved.

[0039] Example 2

[0040] Application of water-soluble viologen derivatives based on vinyl conjugation in neutral aqueous organic flow batteries

[0041] The vinyl viologen derivative (1,2-di(4-pyridyl)ethylene diquaternary ammonium salt) prepared in Example 1 was dissolved in 10 mL of a 1 mol / L supporting electrolyte sodium chloride aqueous solution to form a uniform electrolyte solution with a concentration of 0.25 mmol / L. After nitrogen was passed through the electrolyte to deoxygenate, a cyclic voltammetry test was performed using a three-electrode system.

[0042] Ag / AgCl was used as the reference electrode, platinum electrode as the counter electrode, and glassy carbon electrode as the working electrode. The scan rate was increased from 50mV / s to 300mV / s. The cyclic voltammetry scan results are shown in Figure 2. Figure 4 At different scan rates, the positions of the oxidation peak and reduction peak in the CV curve remain unchanged, indicating its high redox reversibility.

[0043] The corresponding peak currents Ipa and Ipc during the redox process of vinyl viologen derivatives are linearly related to the square root of the scan rate, which confirms that the redox reaction of vinyl viologen derivatives is controlled by the diffusion process, such as Figure 5 shown.

[0044] The redox properties of vinyl viologen derivatives were studied by cyclic voltammetry (CV). Figure 6 The data show that in 1M NaCl, the vinyl viologen derivative has two pairs of obvious redox peaks in the range of -0.9V to -0.5V, located at -0.475V vs.SHE and -0.565V vs.SHE, corresponding to two single-electron redox reactions, which is about 75mV lower than the redox potential of BTMAP-Vi (-0.4V vs.SHE), and exhibits a more negative redox potential as a negative electrode electrolyte. In addition, the potential difference between the two pairs of oxidation peaks and reduction peaks is small, reflecting its excellent electrochemical reaction kinetics. Compared with N Me -TEMPO positive electrode active electrolyte pairing, can show a theoretical voltage of 1.486V.

[0045] The above results show that by inserting a vinyl group between two pyridine rings (forming an extended viologen compound), the reversibility of the electrochemical reaction of the viologen molecule is effectively improved, and its redox potential as an anode active electrolyte is reduced. The two-electron storage mechanism, excellent electrochemical reaction kinetics and relatively negative redox potential are conducive to achieving higher battery energy density and power density.

[0046] Schematic diagram of the working principle of neutral aqueous organic redox flow battery Figure 7 As shown. The positive electrode active electrolyte is 0.1M N Me -TEMPO, the negative electrode active electrolyte was 0.1 M of the vinyl viologen derivative prepared in Example 1, the supporting electrolyte was 1 M sodium chloride, and the electrolyte flow rate was controlled at 20 mL min by a peristaltic pump. -1 , the electrode is graphite felt, and the diaphragm is DSV anion exchange membrane.

Claims

1. A water-soluble viologen derivative based on vinyl conjugation extension, characterized in that: The water-soluble viologen derivative based on vinyl conjugation extension is 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt, having the structural formula shown in (I):

2. The method for preparing a water-soluble viologen derivative based on vinyl conjugation extension according to claim 1, characterized in that: The method comprises the following steps: using DMF as a solvent, subjecting 1,2-di(4-pyridyl)ethylene and (3-bromopropyl)-trimethylammonium bromide to a quaternary ammonium salt ionization reaction to obtain a viologen derivative bromide salt; and subjecting the viologen derivative bromide salt to anion exchange to obtain a 1,2-di(4-pyridyl)ethylene diquaternary ammonium salt.

3. The preparation method according to claim 2, characterized in that: In terms of molar ratio, 1,2-di(4-pyridyl)ethylene:(3-bromopropyl)-trimethylammonium bromide=1:

3.

4. The preparation method according to claim 2, characterized in that: The quaternary ammonium salt ionization reaction is carried out at 100-120° C. under the protection of an inert gas and reflux for 12-72 hours.

5. The preparation method according to claim 2, characterized in that: The anion exchange is to react the viologen derivative bromide with Anion exchange was performed using an anion resin column of IRA-900 in chloride form.

6. Use of the vinyl conjugated extended water-soluble viologen derivative according to claim 1 in neutral aqueous organic flow batteries.

7. The use according to claim 6, characterized in that: The negative electrode electrolyte is prepared by using a vinyl conjugated extended water-soluble viologen derivative as an active electrolyte, a neutral chloride salt as a supporting electrolyte, and water as a solvent.

8. The use according to claim 7, characterized in that: A TEMPO derivative or a ferrocene derivative is used as a positive electrode electrolyte, and an ion exchange membrane or a porous membrane is used as a separator.

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