Multi-electron negative electrode electrolyte for inhibiting hydrogen evolution reaction and neutral aqueous organic flow battery

Abstract

The invention discloses a multi-electron negative electrode electrolyte for inhibiting a hydrogen evolution reaction and a neutral aqueous organic flow battery, and belongs to the technical field of flow batteries. According to the electrolyte, a high-concentration supporting electrolyte is adopted as a main component of a system, and a high-concentration water-in-salt structure is constructed by remarkably improving the concentration of the supporting electrolyte, so that the hydrogen evolution reaction is effectively inhibited. In the system, water molecules as a solvent and cations or anions in the salt form strong coordination, so that the degree of freedom and reaction activity of the water molecules in the system are reduced, and electrochemical decomposition (especially hydrogen evolution reaction) of water is remarkably weakened. According to the electrolyte system, by constructing a high-concentration salt-in-water structure, hydrogen evolution side reaction can be effectively inhibited under a neutral condition, so that attack damage to negative electrode electrolyte organic active molecules is reduced, and a new thought and a technical path are provided for developing a high-voltage, high-energy-density and long-service-life aqueous organic flow battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of large-scale energy storage, and relates to a multi-electron negative electrode electrolyte for inhibiting hydrogen evolution reaction and a neutral aqueous organic liquid flow battery. Background Art

[0002] Clean and renewable energy sources, such as solar and wind power, play a key role in driving the transformation of the global energy structure towards a low-carbon, green direction. However, such renewable energy sources are characterized by strong intermittency and large fluctuations in output power, and direct grid connection may pose a threat to the stability and security of the power grid. Therefore, there is an urgent need for efficient, safe, and long-term energy storage technologies to support their large-scale application. Neutral aqueous organic flow batteries, which use water as a solvent, have the characteristics of high intrinsic safety, independent design and regulation of power and capacity, and show broad prospects in applications such as renewable energy supporting energy storage, peak shaving and valley filling, and emergency power supply. This type of flow battery uses reversible redox-resistant water-soluble organic molecules as the organic active material of the electrolyte. Its molecular structure is diverse, its energy level is adjustable, and its design is flexible. It can be used to build high-voltage and high-capacity energy storage systems, and helps reduce dependence on non-ferrous metal resources. However, current aqueous organic flow batteries still face a series of key challenges, especially the propensity for hydrogen evolution reactions (HERs) in the anode electrolyte during cycling. This not only reduces coulombic efficiency and energy density, but can also cause pH fluctuations in the solution, triggering structural degradation and irreversible degradation of the organic active materials, thereby accelerating capacity decay and shortening battery life. Therefore, there is an urgent need to develop highly stable multi-electron anode electrolytes capable of inhibiting HERs to improve the overall performance and application reliability of aqueous organic flow batteries. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a multi-electron negative electrode electrolyte and a neutral aqueous organic liquid flow battery that inhibit the hydrogen evolution reaction, so as to solve the problems of poor stability of the active molecular structure and capacity loss of the liquid flow battery in the prior art.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A multi-electron negative electrode electrolyte that inhibits hydrogen evolution reaction, wherein the multi-electron negative electrode electrolyte comprises an organic active substance and a supporting electrolyte;

[0006] The organic active material is a multi-electron redox active compound, the supporting electrolyte is a salt solution, the concentration of the salt solution is 3M to saturation concentration, and the saturation concentration is the solubility saturation of the salt in the multi-electron negative electrode electrolyte;

[0007] The organic active substance is selected from viologen compounds, quinone compounds or azine compounds.

[0008] A further improvement of the present invention is:

[0009] Preferably, the viologen compound is 1,1'-bis(2-hydroxy-3-trimethylammoniumpropyl)-[4,4'-bipyridyl]-1,1'-diol, 1-methyl-1'-[3-(trimethylammonium)propyl]-4,4'-bipyridyl-1,1'-diol, 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium, bis(3-sulfonic acid propyl)-2,2',6,6'- Any one or more of tetramethyl-4,4'-bipyridine, 4,4'-(1,4-phenylene)bis[2-methyl-1-(3-(trimethylammonium)propyl)pyridin-1-ium], 4,4'-(thiophene-2,5-diyl)bis[1-(3-(trimethylammonium)propyl)pyridin-1-ium] and 4,4'-(1,4-phenylene)bis[1-(3-(1-methylpyrrolidinium-1-yl)propyl)pyridin-1-ium].

[0010] Preferably, the quinone compounds are naphthoquinone compounds and anthraquinone compounds.

[0011] Preferably, the naphthoquinone compound is any one or more of 2-hydroxy-1,4-naphthoquinone, 5,8-disulfonic acid-1,4-naphthoquinone and 3-[(trimethylammonium)methyl]-2-hydroxy-1,4-naphthoquinone chloride.

[0012] Preferably, the anthraquinone compound is any one or more of 9,10-anthraquinone-2,7-disulfonic acid, 1,8-bis[2-(2-(2-hydroxyethoxy)ethoxy)ethoxy]anthraquinone, 2,6-bis(ethylphosphonate)anthraquinone, 2,7-anthraquinone disulfonic acid and anthraquinone-2,7-disulfonic acid diammonium salt.

[0013] Preferably, the azine compound is any one or more of 1,6-bis(β-alanine)phenazine, tris(4-pyridyl)-1,3,5-triazine hexachloride, and 2,7-disulfonic acid-5,10-dimethylphenazine.

[0014] Preferably, the concentration of the organic active substance in the multi-electron negative electrode electrolyte is 0.05M to 2.0M.

[0015] Preferably, the supporting electrolyte is any one or more of KCl, NaCl, NH4Cl, Na2SO4, K2SO4 or (NH4)2SO4.

[0016] Preferably, the saturation concentration of the supporting electrolyte changes with temperature.

[0017] A neutral organic aqueous flow battery comprises a liquid storage tank containing the aforementioned negative electrode electrolyte, a liquid storage tank containing a positive electrode electrolyte, and a battery stack, wherein the battery stack uses an ion exchange membrane as a separator; the liquid storage tank containing the negative electrode electrolyte is connected to the negative electrode, the liquid storage tank containing the positive electrode electrolyte is connected to the positive electrode, and the separator is disposed between the positive and negative electrodes;

[0018] The supporting electrolyte of the positive electrode electrolyte is the same as the supporting electrolyte of the negative electrode solution.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention discloses a multi-electron negative electrode electrolyte that inhibits the hydrogen evolution reaction, in which the main supporting electrolyte concentration is set to a high-concentration electrolyte, and the hydrogen evolution reaction is inhibited by increasing the concentration of the supporting electrolyte to form a "salt-in-water" structure. The high-concentration "salt-in-water" electrolyte dissolves soluble salts (such as sodium chloride NaCl, ammonium fluoride NH4F, etc.) in water, so that the mass and volume of the solute salt are much higher than the solvent water, thereby forming an ultra-high concentration aqueous solution. As the salt concentration increases, the water activity in the electrolyte decreases, increasing the electrochemical stability window of the electrolyte. At the same time, the equilibrium point of the water decomposition reaction changes. Specifically, the high-concentration salt ions in the electrolyte will compete with the water molecules for coordination, reducing the availability of water molecules, thereby reducing the water decomposition equilibrium potential (equilibrium potential of H2O / H2). This change means that at the same potential, the possibility of water decomposing into hydrogen is reduced, or a lower potential is required for water decomposition to occur, and the conditions for the hydrogen evolution reaction become harsh. In addition, due to the presence of abundant anions (such as Cl - 、SO4 2- ) and cations (such as Na + , K + NH4 + ), the coordinated water molecules in the solvation structure are replaced by a large number of anions, further reducing the activity of water and the likelihood of water molecules participating in the reaction. This not only improves the stability of the electrolyte but also reduces the occurrence of side reactions, especially effectively inhibiting hydrogen evolution. By regulating the solvation structure of the electrolyte, this method effectively inhibits the hydrogen evolution reaction and slows the alkalinization of the multi-electron negative electrode electrolyte, significantly improving the cycling stability and energy density of aqueous organic flow batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a graph showing the cycle number, coulombic efficiency, energy efficiency, and discharge capacity of a battery using 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bispyridinium negative electrode electrolyte in 1M KCl in Example 1 of the present invention.

[0022] Figure 2 This is a graph showing the cycle number, coulombic efficiency, energy efficiency, and discharge capacity of a battery using 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bispyridinium negative electrode electrolyte in 3M KCl in Example 2 of the present invention.

[0023] Figure 3 This is a graph showing the amount of hydrogen released and the pH change during the charge and discharge process of a 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium negative electrode viologen compound electrolyte in a 1M KCl electrolyte in Example 3 of the present invention.

[0024] Figure 4 This is a graph showing the amount of hydrogen released and the pH change during the charge and discharge process of a 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium negative electrode viologen compound electrolyte in a 3M KCl electrolyte in Example 4 of the present invention.

[0025] Figure 5 This is a graph showing the cycle number, coulombic efficiency, energy efficiency, and discharge capacity of the battery in Example 5 of the present invention in a 1 M 1,1′-bis[3-(trimethylammonium)propyl]-4,4′-(1,4-phenylene)bispyridinium / 3 M KCl system.

[0026] Figure 6 This is a graph of cycle number, coulombic efficiency, energy efficiency, and discharge capacity for a battery using 0.05 M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bispyridinium negative electrode electrolyte in a saturated KCl electrolyte in Example 6 of the present invention.

[0027] Figure 7 This is a graph showing the amount of hydrogen released and the pH change during the charge and discharge process of a 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium negative electrode viologen compound electrolyte in a saturated KCl electrolyte in Example 7 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in further detail below with reference to the accompanying drawings:

[0029] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0030] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0031] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0032] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0033] In a first aspect, the present invention discloses a multi-electron anode electrolyte for inhibiting the hydrogen evolution reaction. The anode electrolyte comprises an active material and a supporting electrolyte, wherein the active material is a multi-electron redox-active compound and the supporting electrolyte is a salt electrolyte. The concentration of the supporting electrolyte ranges from 3M to a saturation concentration, where the saturation concentration is the saturation concentration of the salt in the multi-electron anode electrolyte.

[0034] The electrolyte uses a high concentration of supporting electrolyte as the main component of the system, and by significantly increasing the concentration of the supporting electrolyte, a "high concentration salt-in-water" structure is constructed, thereby effectively suppressing the occurrence of hydrogen evolution reaction. The high concentration electrolyte system is an innovative aqueous electrolyte configuration, and its basic principle is to use a high concentration of soluble salt to dissolve in water, so that the mass and volume of the solute (salt) exceed the ratio of the water solvent, and finally form an ultra-high concentration aqueous solution. In this system, water molecules form strong coordination with the cations or anions in the salt as a solvent, thereby significantly reducing the degree of freedom and reactivity of water molecules in the system. By regulating the coordination competition relationship between water molecules and ions, the number of free water molecules is effectively suppressed, and the electrochemical decomposition of water (especially hydrogen evolution reaction) is therefore significantly weakened. Compared with the traditional dilute electrolyte system, the high concentration electrolyte strategy proposed in the present invention not only improves the electrochemical stability window of the electrolyte, but also enhances the structural stability and reduced state storage capacity of organic active molecules, and is particularly suitable for negative electrode electrolyte systems with higher redox potentials in multi-electron transfer processes. In summary, the electrolyte system achieves the goal of effectively inhibiting the hydrogen evolution side reaction by constructing a high-concentration salt-in-water structure while maintaining a neutral water system, thereby reducing the offensive damage to the organic active molecules of the negative electrode electrolyte.

[0035] In some embodiments of the present invention, the multi-electron redox active compound includes viologen compounds, anthraquinone compounds and oxazines.

[0036] In the present invention, the viologen compounds are 1,1'-bis(2-hydroxy-3-trimethylammoniumpropyl)-[4,4'-bipyridyl]-1,1'-diol (Dex-Vi), 1-methyl-1'-[3-(trimethylammonium)propyl]-4,4'-bipyridyl-1,1'-diol ((Me)(NPr)V), 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium (APBPy), bis(3-sulfonic acid propyl)-2,2',6,6'-tetramethyl -4,4'-bipyridine (R-Vi), 4,4'-(1,4-phenylene)bis[2-methyl-1-(3-(trimethylammonium)propyl)pyridin-1-ium] (exDMeBP), 4,4'-(thiophene-2,5-diyl)bis[1-(3-(trimethylammonium)propyl)pyridin-1-ium] ((NPr)2TV), 4,4'-(1,4-phenylene)bis[1-(3-(1-methylpyrrolidinium-1-yl)propyl)pyridin-1-ium] (PyrPV).

[0037] Viologen compounds, such as 4,4'-bipyridinium viologens, possess two redox-active centers within their bipyridyl salt structure, capable of storing two electrons. Their two-electron reduction process typically occurs at more negative potentials. However, when the electrode potential is excessively negative, a high negative charge density accumulates on the electrode surface, which can easily induce proton-coupled electron transfer reactions, leading to water decomposition to produce hydrogen atoms or hydrogen gas. The reduction process in common negative electrolytes typically occurs at more negative potentials. Under these conditions, residual hydroxide ions in the water can trigger a dealkylation reaction through nucleophilic attack, cleaving the C(alkyl)–N bond in the viologen compound and deactivating the active molecular structure. This process can cause irreversible capacity loss and significantly shorten the cycle life in neutral aqueous organic flow batteries. By introducing a high-concentration salt solution, water decomposition can be effectively inhibited, preventing the generation of hydrogen atoms or hydrogen gas. This reduces the accumulation of hydroxide ions and inhibits their nucleophilic attack on the viologen molecules, ultimately extending the stability and service life of the entire electrolyte system.

[0038] Quinone compounds such as naphthoquinones and anthraquinones. Naphthoquinone compounds include any one or more of 2-hydroxy-1,4-naphthoquinone (2-HNQ), 5,8-disulfonic acid-1,4-naphthoquinone (5,8-DSNQ), and 3-[(trimethylammonium)methyl]-2-hydroxy-1,4-naphthoquinone chloride (3-TMANQ-Cl). Anthraquinone compounds include any one or more of 9,10-anthraquinone-2,7-disulfonic acid (2,7-AQDS), 1,8-bis[2-(2-hydroxyethoxy)ethoxy)ethoxy]anthraquinone (AQ-1,8-3E-OH), 2,6-bis(ethylphosphonate)anthraquinone (2,6-DPPEAQ), 2,7-anthraquinone disulfonic acid (2,7-AQDS), and anthraquinone-2,7-disulfonic acid diammonium salt (AQDS-(NH4)2).

[0039] Quinone compounds, due to their unique multi-electron transfer properties, are often used as negative electrode active materials in aqueous batteries in the form of quinone (Q) and hydroquinone (QH2). However, during two-electron reduction at relatively low potentials, they compete with the hydrogen evolution reaction (HER), resulting in the reduction of hydrogen ions in water to hydrogen gas. This not only consumes electrons and reduces energy efficiency, but can also cause bubble accumulation on the electrode surface, affecting the stability of the reaction interface and, consequently, impairing the battery's cycling performance. Furthermore, during the multi-electron reduction process, quinone molecules may undergo structural changes, breaking some chemical bonds (such as C–H, C–C, or C=O), leading to irreversible degradation. These molecules are particularly susceptible to inactivation under alkaline conditions or hydrolysis reactions. To inhibit the HER side reaction and enhance the stability of quinone compounds, the introduction of high-concentration electrolytes is an effective strategy. High-salt systems can significantly reduce water activity, raising the potential threshold for the HER, thereby reducing competition with the quinone reduction reaction and improving the battery's energy efficiency and cycle life.

[0040] The oxazine compound is any one or more of 1,6-bis(β-alanine)phenazine (1,6-BAPZ), tris(4-pyridyl)-1,3,5-triazine hexachloride (TPyTz), and 2,7-disulfonic acid-5,10-dimethylphenazine (2,7-DS-5,10-DMPZ).

[0041] Due to their electron-rich pyrazine conjugated structure, azine compounds typically possess multi-electron transfer capabilities, capable of storing two or more electrons during the reduction process at the battery's negative electrode. However, at relatively negative electrode potentials, their reduction process often faces competition with the hydrogen evolution reaction, affecting energy conversion efficiency. Furthermore, azine molecules may undergo structural rearrangement or breakage during the reduction process. In particular, the critical N–N or N–C bonds are susceptible to nucleophilic attack by water molecules or hydroxide ions, leading to molecular degradation and reduced activity, which in turn causes battery capacity decay and cycling performance degradation. To alleviate this problem, using a high-concentration salt solution as the electrolyte can effectively increase the system's ionic strength, reduce water activity and the probability of the hydrogen evolution reaction, and inhibit the generation of OH-, thereby enhancing the structural stability of the azine compound and improving the long-term operational reliability of the battery.

[0042] In some embodiments of the present invention, the concentration of the multi-electron redox active compound in the electrolyte is 0.05M to 2M.

[0043] In some embodiments of the present invention, the salt solution is any one or more of KCl, NaCl, NH4Cl, Na2SO4, K2SO4 or (NH4)2SO4. The saturation concentration of the salt solution changes with temperature.

[0044] Furthermore, at 20°C, the saturation concentration of KCl solution is close to 4.0M.

[0045] At 20°C, the saturated concentration of NaCl solution is 5.07M.

[0046] At 25°C, the saturated concentration of sodium sulfate solution is 1.95M.

[0047] At 20°C, the concentration of saturated sodium sulfate is 1.35M.

[0048] At 25°C, the solubility of NaBF4 in water is approximately 4.73M.

[0049] At 20°C, the solubility of sodium acetate is 5.71M.

[0050] It should be understood that the saturation concentrations given above are the saturation of each salt electrolyte at the corresponding temperature. The saturation concentrations of some salt electrolytes are also related to the pH value. As the hydrogen evolution reaction proceeds, the pH value of the system may tend to be alkaline, which will affect the solubility of some salt electrolytes. The hydrogen evolution reaction itself is a reduction reaction:

[0051] 2H2O+2e - →H2+2OH -

[0052] This reaction consumes hydrogen ions (H + ), and hydroxide ions (OH-), causing the pH value of the solution to gradually increase (i.e., alkaline). This will affect the solubility of some salts and the chemical reaction balance of ions, especially the acidic salts in the solution (such as ammonium chloride, bipyridyl quaternary ammonium chloride) will solubilize, which may affect the stability of the system. If the pH value is too high (such as greater than 12), certain ions may be excessively dissolved or form unstable compounds (such as NH4OH, etc.), which not only changes the ion composition of the electrolyte, but also may cause battery performance to decline. Therefore, in actual application, the preparation concentration of salt electrolytes needs to be adjusted according to the use environment. Furthermore, since the final negative electrode electrolyte solution also contains multi-electron redox active compounds, the addition of multi-electron redox active compounds changes the ion competition, the solution pH value and conductivity, and the redox reaction occurs to change the ionic environment of the electrolyte, thereby affecting the saturation concentration of the salt electrolyte.

[0053] In some embodiments of the present invention, the method for preparing the multi-electron anode electrolyte that inhibits the hydrogen evolution reaction comprises the following steps: weighing the multi-electron redox-active compound required as the active material, a salt as the supporting electrolyte, and aqueous solvent, mixing them, and sonicating them to fully dissolve the active material and the supporting electrolyte. This preparation method, which requires no chemical modification, is simple and easy to operate, ultimately improving the cycle life of flow batteries and reducing capacity fade.

[0054] The present invention also discloses a neutral aqueous organic flow battery, which comprises a positive electrolyte, a positive flow field plate, a positive electrode, an ion separator, a negative electrode, a negative flow field plate, and a negative electrolyte. The negative electrode uses the aforementioned multi-electron negative electrolyte. The positive electrode active material is a mixture of one or more of potassium ferrocyanide, cyclic nitroxide free radical derivatives, ferrocene derivatives, iodine and its salts (sodium iodide, potassium iodide, ammonium iodide), and bromine and its salts (potassium bromide, sodium bromide, ammonium bromide). The electrolyte is a mixture of one or more neutral aqueous salt solutions.

[0055] Preferably, the aqueous organic liquid flow battery uses a copper plate as a current collector, a graphite plate as a flow field plate, a carbon felt as a reaction electrode, and an ion exchange membrane between the positive electrode and the negative electrode.

[0056] Specifically, the aqueous organic liquid flow battery uses a copper plate as a current collector, a graphite plate as a flow field plate, and a carbon felt as a reaction electrode. The positive electrode and the negative electrode are separated by an ion exchange membrane, and the positive electrode electrolyte uses a 2,2,6,6-tetramethylpiperidine-nitrogen-oxide (TEMPO) derivative.

[0057] In one embodiment disclosed in the present invention, the negative electrode electrolyte uses the viologen compound 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium as the active substance at a concentration of 0.05M, and the supporting electrolyte is 3M KCl. The positive electrode electrolyte consists of 4-hydroxy-TEMPO and KCl, wherein the concentration of 4-hydroxy-TEMPO is 0.05M and the concentration of KCl is also 3M. The assembly order of the battery is: copper current collector, graphite plate flow channel, carbon paper / graphite felt electrode, ion exchange membrane, carbon paper / graphite felt electrode, graphite plate flow channel and copper current collector.

[0058] The following is a further analysis in conjunction with specific embodiments.

[0059] Example 1 (Comparative Example)

[0060] Prepare the negative electrode electrolyte, including 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium viologen and 1M KCl supporting electrolyte; prepare the positive electrode electrolyte, including 0.1M 4-hydroxy-TEMPO and 1M KCl supporting electrolyte. In the battery assembly, 8mL of negative electrode electrolyte and 12mL of positive electrode electrolyte were taken; the diaphragm used was the anion exchange membrane AMVN, and carbon felt was used as the electrode material for the positive and negative electrodes respectively, copper plate was used as the current collector, and graphite plate was used as the flow field plate. The assembled aqueous liquid flow battery was subjected to full battery performance testing, such as Figure 1 Test results show a low first-cycle coulombic efficiency of only 90%. The initial energy efficiency was 80%, dropping to 75% after 30 cycles. Capacity retention was also poor, remaining at only 66% after 30 cycles. The primary reason for this performance degradation is that the high activity of free water molecules in the low-concentration 1M supporting electrolyte easily leads to hydrogen evolution reactions, generating large amounts of OH-. This, in turn, triggers nucleophilic attacks, leading to dealkylation of the viologen molecules and a reduction in the active material content, ultimately causing capacity fading and shortening the cycle life.

[0061] Example 2

[0062] The negative electrode electrolyte was prepared, including 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium viologen and 3M KCl supporting electrolyte; the positive electrode electrolyte was prepared, including 0.1M 4-hydroxy-TEMPO and 3M KCl supporting electrolyte. During the battery assembly process, 8mL of negative electrode electrolyte and 12mL of positive electrode electrolyte were taken respectively; AMVN anion exchange membrane was used as the separator, carbon felt was used for both positive and negative electrodes, copper plate was used as the current collector, and graphite plate was used as the flow field plate. Full battery performance test was carried out in 3M KCl high concentration electrolyte system to evaluate the effect of ion concentration on battery performance. The results are as follows Figure 2 As shown. The test results show that: the first cycle coulombic efficiency is increased to 96%, and is stably maintained at 99% in subsequent cycles; the initial energy efficiency is increased to 90%, and the capacity retention rate reaches 80% after 30 cycles. This is mainly attributed to the fact that the 3M high-concentration electrolyte effectively reduces the activity of water, making the potential of the hydrogen evolution reaction higher than the viologen reduction reaction window, thereby inhibiting the occurrence of the hydrogen evolution reaction and avoiding the dealkylation degradation reaction of the viologen molecules induced by the generation of OH-. Therefore, compared with the 1M KCl electrolyte system, the 3M high-concentration system shows significant improvements in coulombic efficiency, energy efficiency and capacity retention. It is worth noting that in 60 charge and discharge cycles, the 3M KCl electrolyte system exhibits excellent cycle stability and high coulombic efficiency, further verifying its application potential in aqueous liquid flow batteries.

[0063] Example 3 (Comparative Example)

[0064] A test system integrating in-situ pH monitoring and gas chromatography was used to monitor the pH changes of a flow battery assembled using 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium viologen solution as the negative electrolyte and 0.1M 4-hydroxy-TEMPO solution as the positive electrolyte in a 1M KCl electrolyte during the charge and discharge process. The results are shown in Figure 2. Figure 3 As shown in the figure, the amount of hydrogen released after the first cycle is 0.25μmol, and it reaches 0.35μmol in the sixth cycle; the pH changes from 7 to 11 after the first cycle, and reaches 12 after the sixth cycle. This is because the free water molecules in the 1M low concentration electrolyte are highly active and prone to hydrogen evolution reaction. For every 1μmol H2 generated, 2μmol OH is generated. - , so the pH suddenly rises and becomes alkaline.

[0065] Example 4

[0066] A test system integrating in-situ pH monitoring and gas chromatography was used to monitor in real time the pH changes during charge and discharge of a flow battery assembled using 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium viologen solution as the negative electrolyte and 0.1M 4-hydroxy-TEMPO solution as the positive electrolyte in a 3M KCl electrolyte. The results are shown in Figure 2. Figure 4 As shown in the figure, it can be seen that the amount of hydrogen released is stable at 0.01 μmol. After the first cycle, the pH changes from 7 to 10, and after the sixth cycle, the pH reaches 11. This is because the 3M high-concentration electrolyte reduces water activity and significantly reduces free water molecules, resulting in a decrease in the concentration of reactants in the hydrogen evolution reaction, which directly inhibits the reaction rate, making the hydrogen content almost zero and the pH lower than the 1M KCl low-concentration electrolyte in Example 3. The hydrogen generation in the electrolyte was analyzed by gas chromatography, and the amount of hydrogen generated at high concentrations was significantly reduced, indicating that the hydrogen evolution reaction was suppressed.

[0067] Example 5

[0068] The negative electrode electrolyte was prepared, including 1M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bispyridinium (violet essence) and 3M KCl supporting electrolyte; the positive electrode electrolyte was prepared, including 2M 4-hydroxy-TEMPO and 3M KCl supporting electrolyte. During the battery assembly process, 8mL of negative electrode electrolyte and 12mL of positive electrode electrolyte were taken respectively; the diaphragm used AMVN anion exchange membrane, the positive and negative electrodes were both carbon felt electrodes, the copper plate was used as the current collector, and the graphite plate was used as the flow field plate. The full battery performance test was carried out under this system, and the results are as follows Figure 5 As shown. It can be seen that the battery coulombic efficiency is always stable at 99%; after 100 cycles, the energy efficiency is still maintained at 85%, and the capacity retention rate is still high, still maintained at 90%. Compared with Example 2, under the same 3M KCl high concentration supporting electrolyte conditions, the performance of this example is better. The main reason is that the higher concentration of viologen active material (1M) significantly increases the viscosity of the electrolyte, thereby effectively reducing the diffusion rate of OH-, slowing down the C-N bond cleavage process caused by nucleophilic attack, reducing the degradation and loss of active materials, and significantly extending the cycle life.

[0069] Example 6

[0070] Prepare the negative electrode electrolyte, including 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium violet and nearly saturated (4M) KCl electrolyte solution; prepare the positive electrode electrolyte, including 0.1M 4-hydroxy-TEMPO and 4M KCl electrolyte solution; take 8mL of the negative electrode and 12mL of the positive electrode for the assembly of the aqueous liquid flow battery. The battery separator uses an anion exchange membrane AMVN, and the positive and negative electrodes use carbon felt respectively. The current collector is a copper plate and the graphite plate is a flow field plate. Carry out full battery testing, the performance boundary conditions of 4M KCl electrolyte solution in aqueous liquid flow batteries, evaluate the effect of high concentration electrolyte on battery stability and efficiency, combined with Figure 6 As can be seen, the coulombic efficiency approaches over 99% at the beginning of the cycle and remains stable with increasing cycle number, showing no significant attenuation. The energy efficiency remains stable at 92%, and the capacity retention rate improves, remaining at 83% after 30 cycles. Therefore, the 4M KCl electrolyte demonstrates excellent cycling stability and coulombic efficiency over 60 charge-discharge cycles. The high concentration of 4M KCl in the electrolyte reduces water activity, significantly reducing the number of free water molecules, resulting in a lower concentration of reactants in the hydrogen evolution reaction, which directly inhibits the reaction rate.

[0071] Example 7

[0072] Using a test system integrating in-situ pH monitoring and gas chromatography, the pH changes of the flow battery assembled using 0.05M 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium violet solution as the negative electrolyte and 0.1M 4-hydroxy-TEMPO solution as the positive electrolyte in a 4M KCl saturated electrolyte during charge and discharge were monitored in real time, and the hydrogen generation in the electrolyte was analyzed by gas chromatography. It can be seen that the amount of hydrogen released is stable at 0.01μmol, the pH changes from 7 to 10 after the first cycle, and the pH reaches 11 after the sixth cycle. The amount of hydrogen generated at the limiting concentration is further reduced, indicating that the effect of suppressing the hydrogen evolution reaction is obvious. 4M KCl is close to saturation, but has no obvious advantage over the 3M system in Example 4. This shows that when the KCl concentration is ≥3M, the hydrogen evolution reaction rate has dropped below the detection limit (<0.01μmol / cycle), and the effect of suppressing the hydrogen evolution reaction is close to saturation.

[0073] Example 8

[0074] A negative electrolyte solution was prepared, consisting of 0.05M 2-hydroxy-1,4-naphthoquinone and 1M NaCl electrolyte solution; a positive electrolyte solution was prepared, consisting of 0.1M potassium ferrocyanide and 1M NaCl electrolyte solution. 8mL of the negative electrolyte and 12mL of the positive electrolyte were used to assemble the aqueous flow battery. The battery separator used a cation exchange membrane, Nafion, while the positive and negative electrodes were carbon felt. The current collectors were copper plates and the flow field plates were graphite plates. Full-cell testing was conducted, and comparative experiments were conducted to analyze the differences in the inhibitory effects of different multi-electron redox-active compounds and supporting electrolytes on the hydrogen evolution reaction in the battery, further optimizing the battery's reaction mechanism and operational stability.

[0075] Example 9

[0076] Prepare the negative electrolyte, consisting of 0.05M 9,10-anthraquinone-2,7-disulfonic acid and 3M NaCl, and the positive electrolyte, consisting of 0.1M potassium ferrocyanide and 3M NaCl. 8mL of the negative electrolyte and 12mL of the positive electrolyte were used to assemble the aqueous flow battery. The battery separator used a cation exchange membrane, Nafion, while the positive and negative electrodes each used carbon felt. The current collectors were copper plates, and the flow field plates were graphite plates.

[0077] Example 10

[0078] Prepare the negative electrolyte, consisting of 0.05M 1,6-bis(β-alanine)phenazine and 3M NaCl solution; prepare the positive electrolyte, consisting of 0.1M potassium ferrocyanide and 3M NaCl solution. 8mL of the negative electrolyte and 12mL of the positive electrolyte were used to assemble the aqueous flow battery. The battery separator used a cation exchange membrane, Nafion; the positive and negative electrodes used carbon felt, respectively. The current collectors were copper plates, and the flow field plates were graphite plates.

[0079] Example 11

[0080] A negative electrolyte solution was prepared, consisting of 0.08M 4,4'-(1,4-phenylene)bis[2-methyl-1-(3-(trimethylammonium)propyl)pyridin-1-ium] and 1M Na2SO4 electrolyte solution. A positive electrolyte solution was prepared, consisting of 0.16M 4-hydroxy-TEMPO and 1M Na2SO4 electrolyte solution. 8mL of the negative electrolyte and 12mL of the positive electrolyte were used to assemble the aqueous flow battery. The battery separator used an anion exchange membrane, AMVN. The positive and negative electrodes used carbon felt, respectively. The current collector was a copper plate, and the flow field plate was a graphite plate.

[0081] Example 12

[0082] A negative electrolyte solution was prepared, consisting of 0.05M 4,4'-(1,4-phenylene)bis[2-methyl-1-(3-(trimethylammonium)propyl)pyridin-1-ium] and 4M NaBF4 electrolyte solution. A positive electrolyte solution was prepared, consisting of 0.1M 4-hydroxy-TEMPO and 4M NaBF4 electrolyte solution. 8mL of the negative electrolyte and 12mL of the positive electrolyte were used to assemble the aqueous flow battery. The battery separator used an anion exchange membrane, AMVN, and the positive and negative electrodes used carbon felt, respectively. The current collector was a copper plate, and the flow field plate was a graphite plate.

[0083] Example 13

[0084] Prepare the negative electrolyte, consisting of 2M 1,8-bis[2-(2-(2-hydroxyethoxy)ethoxy)ethoxy]anthraquinone and 3M KCl electrolyte solution; prepare the positive electrolyte, consisting of 0.5M potassium ferrocyanide and 3M KCl electrolyte solution. 8mL of the negative electrolyte and 12mL of the positive electrolyte were used to assemble the aqueous flow battery. The battery separator used a cation exchange membrane, Nafion, and the positive and negative electrodes used carbon felt, respectively. The current collector was a copper plate, and the flow field plate was a graphite plate.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-electron negative electrode electrolyte for inhibiting hydrogen evolution reaction, characterized in that: The multi-electron negative electrode electrolyte includes an organic active substance and a supporting electrolyte; The organic active material is a multi-electron redox active compound, the supporting electrolyte is a salt solution, the concentration of the salt solution is 3M to saturation concentration, and the saturation concentration is the solubility saturation of the salt in the multi-electron negative electrode electrolyte; The organic active substance is selected from viologen compounds, quinone compounds or azine compounds.

2. The multi-electron negative electrode electrolyte for suppressing hydrogen evolution reaction according to claim 1, characterized in that The viologen compounds are 1,1'-bis(2-hydroxy-3-trimethylammoniumpropyl)-[4,4'-bipyridyl]-1,1'-diol, 1-methyl-1'-[3-(trimethylammonium)propyl]-4,4'-bipyridyl-1,1'-diol, 1,1'-bis[3-(trimethylammonium)propyl]-4,4'-(1,4-phenylene)bipyridinium, bis(3-sulfonic acid propyl)-2,2',6,6'-tetramethyl any one or more of 4,4'-(1,4-phenylene)bis[2-methyl-1-(3-(trimethylammonium)propyl)pyridin-1-ium], 4,4'-(thiophene-2,5-diyl)bis[1-(3-(trimethylammonium)propyl)pyridin-1-ium] and 4,4'-(1,4-phenylene)bis[1-(3-(1-methylpyrrolidinium-1-yl)propyl)pyridin-1-ium].

3. The multi-electron negative electrode electrolyte for suppressing hydrogen evolution reaction according to claim 1, characterized in that The quinone compounds are naphthoquinone compounds and anthraquinone compounds.

4. The multi-electron negative electrode electrolyte for suppressing hydrogen evolution reaction according to claim 3, characterized in that The naphthoquinone compound is any one or more of 2-hydroxy-1,4-naphthoquinone, 5,8-disulfonic acid-1,4-naphthoquinone and 3-[(trimethylammonium)methyl]-2-hydroxy-1,4-naphthoquinone chloride.

5. The multi-electron negative electrode electrolyte for suppressing hydrogen evolution reaction according to claim 3, characterized in that The anthraquinone compound is any one or more of 9,10-anthraquinone-2,7-disulfonic acid, 1,8-bis[2-(2-(2-hydroxyethoxy)ethoxy)ethoxy]anthraquinone, 2,6-bis(ethylphosphonate)anthraquinone, 2,7-anthraquinone disulfonic acid and anthraquinone-2,7-disulfonic acid diammonium salt.

6. The multi-electron negative electrode electrolyte for suppressing hydrogen evolution reaction according to claim 1, characterized in that The azine compound is any one or more of 1,6-bis(β-alanine)phenazine, tris(4-pyridyl)-1,3,5-triazine hexachloride, and 2,7-disulfonic acid-5,10-dimethylphenazine.

7. The multi-electron negative electrode electrolyte for suppressing hydrogen evolution reaction according to claim 1, characterized in that The concentration of the organic active substance in the multi-electron negative electrode electrolyte is 0.05M to 2.0M.

8. The multi-electron negative electrode electrolyte for suppressing hydrogen evolution reaction according to claim 1, characterized in that The supporting electrolyte is any one or more of KCl, NaCl, NH4Cl, Na2SO4, K2SO4 or (NH4)2SO4.

9. The multi-electron negative electrode electrolyte for suppressing hydrogen evolution reaction according to claim 1, characterized in that The saturation concentration of the supporting electrolyte changes with temperature.

10. A neutral organic aqueous flow battery, characterized in that: The invention comprises a liquid storage tank containing the negative electrode electrolyte according to claim 1, a liquid storage tank containing the positive electrode electrolyte and a battery stack, wherein the battery stack uses an ion exchange membrane as a diaphragm; the liquid storage tank containing the negative electrode electrolyte is connected to the negative electrode, the liquid storage tank containing the positive electrode electrolyte is connected to the positive electrode, and the diaphragm is arranged between the positive electrode and the negative electrode; The supporting electrolyte of the positive electrode electrolyte is the same as the supporting electrolyte of the negative electrode solution.

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