Application of chloral hydrate as anode electrolyte electroactive material of aqueous organic flow battery

Abstract

The invention belongs to the field of flow batteries, and particularly relates to application of chloral hydrate as an electroactive material of a positive electrode electrolyte of an aqueous organic flow battery. When the chloral hydrate is used as the electroactive material of the positive electrode electrolyte of the aqueous organic flow battery, the chloral hydrate contains a strong electron withdrawing group of trichloromethyl, so that the chloral hydrate is stably oxidized in an acid medium, and has the properties of high water solubility (10.9 mol / L), high positive potential (about 1.17 V vs. Ag / AgCl), high reversibility and the like. Besides, under different current densities, the voltage efficiency (VE), coulombic efficiency (CE) and energy efficiency (EE) of the aqueous flow battery based on chloral hydrate are all kept at a relatively high level, the aqueous flow battery has good cycling stability, and the capacity fading rate is as low as 0.5% per cycle.

Description

Technical Field

[0001] This invention belongs to the field of flow batteries, specifically relating to the application of hydrated chloral as an electroactive material in the positive electrode electrolyte of aqueous organic flow batteries. Background Technology

[0002] Flow batteries have become an important technological direction in the field of large-scale energy storage due to their core advantages such as high energy conversion efficiency, high power density, long cycle life, and flexible design. By storing electroactive materials in an external container, they achieve spatial decoupling between power output and energy output, providing unique application flexibility. Based on the electrolyte solvent type, flow batteries can be divided into two main categories: aqueous and non-aqueous. Aqueous flow batteries, using water as the medium, have significant advantages in terms of high safety, environmental friendliness, and low cost, making them more suitable for the actual needs of large-scale energy storage scenarios. Over the past decade, organic-based redox active materials for aqueous flow batteries have seen rapid development, with various types reported, including quinones, viologens, nitrogen-containing aromatic heterocyclic compounds, ferrocene, TEMPO radicals, and azobenzenes. However, these publicly disclosed organic materials still have room for further optimization in key indicators such as energy density and cycle performance at high current densities.

[0003] The energy density of a flow battery is determined by three core factors: the effective concentration of the active material in the electrolyte system, the number of electrons participating in the redox reaction, and the potential difference between the positive and negative electrode active electrolyte materials. Therefore, to maximize the energy density of flow batteries, it is necessary to simultaneously develop two types of key materials: positive electrode active electrolyte materials with high solubility and high potential, and negative electrode active electrolyte materials with high solubility and low potential. However, due to the inherent characteristics of their molecular structure, most organic materials have low redox potentials and can only be used as negative electrode active electrolyte materials in flow batteries. Currently, only ferrocene and TEMPO derivatives are publicly reported as positive electrode organic active electrolyte materials for neutral flow batteries. Therefore, developing positive electrode organic active electrolyte materials with both high solubility and high electrochemical activity is one of the core challenges that urgently needs to be overcome in the field of organic aqueous flow batteries.

[0004] Existing organic active electrolyte materials for cathodes have significant limitations: First, their applicability to various systems is restricted; ferrocene and TEMPO derivatives are mostly suitable for neutral systems, but their electrochemical stability in acidic media is insufficient. Second, their performance indicators need improvement; the water solubility of some materials is not at a high level (e.g., 10 mol / L and above), and their energy efficiency and cycle stability at high current densities are difficult to meet practical application requirements—for example, the capacity decay rate cannot be reduced to an extremely low level, which restricts the long cycle life of the battery. Therefore, developing novel organic active electrolyte materials for cathodes that are suitable for acidic systems and possess ultra-high water solubility, high redox potential, and excellent cycle stability is of great significance for promoting the industrial application of organic aqueous flow batteries. Summary of the Invention

[0005] Based on this, the present invention discovered that when chloral hydrate is used as an electroactive material for the positive electrode electrolyte of an aqueous organic flow battery, it still exhibits excellent electrochemical activity in an acidic system, and therefore chloral hydrate can be used as an electroactive material for the positive electrode electrolyte of an aqueous organic flow battery.

[0006] To achieve the above objectives, the present invention can adopt the following technical solutions: This invention provides the application of hydrated chloral as an electroactive material in the positive electrode electrolyte of aqueous organic flow batteries.

[0007] Preferably, in the above applications, the positive electrode electrolyte also includes a supporting electrolyte.

[0008] More preferably, in the above applications, the supporting electrolyte is selected from hydrochloric acid and / or phosphate.

[0009] More preferably, in the above applications, the pH of the positive electrode electrolyte is 1 to 7.

[0010] More preferably, in the above applications, the concentration of the supporting electrolyte in the positive electrode electrolyte is 0.5 mol / L to 1.5 mol / L; and / or the concentration of chloral hydrate is 4 mmol / L to 6 mmol / L.

[0011] More preferably, in the above applications, the concentration of the supporting electrolyte in the positive electrode electrolyte is 1 mol / L; and / or the concentration of chloral hydrate is 5 mmol / L.

[0012] Preferably, in the above applications, the aqueous organic flow battery further includes a porous carbon electrode, a separator, and a graphite counter electrode.

[0013] More preferably, in the above applications, the diaphragm is selected from Nafion membranes or anion-conducting membranes; and / or the porous carbon electrode is selected from graphite felt, carbon felt, or porous graphene.

[0014] The beneficial effects of this invention include at least the following: When chloral hydrate is used as the electroactive material of the positive electrode electrolyte in an aqueous organic flow battery, it exhibits high water solubility (10.9 mol / L), high positive potential (approximately 1.17 V vs. Ag / AgCl), and high reversibility due to the presence of a strong electron-withdrawing trichloromethyl group in chloral hydrate, which allows for stable oxidation in acidic media. Furthermore, the aqueous flow battery based on chloral hydrate maintains high voltage efficiency (VE), coulombic efficiency (CE), and energy efficiency (EE) at different current densities, and demonstrates good cycle stability with a capacity decay rate as low as 0.5% per cycle (the usable capacity decreases by 0.5% of the initial capacity after each charge-discharge cycle). Attached Figure Description

[0015] Figure 1 The cyclic voltammetric curves of chloral hydrate in HCl solution are shown. Figure 2 The constant current charge-discharge curve of chloral hydrate in HCl solution; Figure 3 The long-term charge-discharge curves of chloral hydrate in HCl solution are shown. Figure 4 The voltage efficiency, coulombic efficiency, and energy efficiency of chloral hydrate in HCl solution over a long cycle are given. Figure 5 10 mA·cm -2 Battery charge / discharge capacity variation curves under current density; Figure 6 The potential-capacity curves of chloral hydrate in HCl solution under different current densities are shown. Figure 7 This represents the relationship between voltage efficiency, coulombic efficiency, and energy efficiency and current density. Detailed Implementation

[0016] The embodiments described are provided to better illustrate the present invention, but are not intended to limit the scope of the invention to the embodiments described. Therefore, non-essential improvements and adjustments made to the embodiments by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0017] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. Singular expressions include plural expressions unless they have a distinct meaning in the context. As used herein, it should be understood that terms such as “comprising,” “having,” “including,” are intended to indicate the presence of features, numbers, operations, components, parts, elements, materials, or combinations thereof. The terminology of the invention is disclosed in the specification and is not intended to exclude the possibility that one or more other features, numbers, operations, components, parts, elements, materials, or combinations thereof may be present or added. As used herein, “ / ” may be interpreted as “and” or “or,” depending on the context.

[0018] This invention provides the application of hydrated chloral as an electroactive material in the positive electrode electrolyte of an aqueous organic flow battery.

[0019] It should be noted that the hydrated chloral in this invention is well known in the art, and its structural formula is as follows: Chloral hydrate is a carbonyl-containing hydrate. Due to the electron-withdrawing effect of the trichloromethyl group, chloral hydrate retains high electrochemical activity while achieving efficient proton-coupled electron transfer, exhibiting a high redox potential and rapid electrochemical reaction kinetics. However, its application in aqueous flow batteries has not been fully explored. This invention discovers and verifies that chloral hydrate can be used as a highly efficient electroactive material for the positive electrode electrolyte of aqueous organic flow batteries. When chloral hydrate is used as the electroactive material for the positive electrode electrolyte of aqueous organic flow batteries, due to the strong electron-withdrawing trichloromethyl group, it is stably oxidized in acidic media, exhibiting properties such as high water solubility (10.9 mol / L), high positive potential (approximately 1.17 V vs. Ag / AgCl), and high reversibility. Furthermore, the aqueous flow battery based on chloral hydrate maintains high voltage efficiency (VE), coulombic efficiency (CE), and energy efficiency (EE) at different current densities, and has good cycle stability with a capacity decay rate as low as 0.5% per cycle (the usable capacity of the battery decreases by 0.5% of the initial capacity for each charge-discharge cycle).

[0020] It should also be noted that chloral hydrate, when used as an electroactive material in the positive electrode electrolyte of aqueous organic flow batteries, has the following advantages: Firstly, it has high solubility, which can reduce the volume of electrolyte and lower the cost of storage tanks; Secondly, due to its low decay rate (0.5% per cycle) and expected lifespan >1000 cycles, its comparison with existing organic materials is as follows: (1) Compared with TEMPO materials, chloral hydrate (10.9 mol / L) has higher solubility and lower decay than TEMPO materials (3.2 mol / L) (chloral hydrate decays at 0.5% per cycle, while TEMPO materials decay at 0.27% per cycle). -1 (2) Compared with quinones, quinones are unstable in acidic conditions, while chloral hydrate is stable in acidic environments; Third, chloral hydrate has moderate toxicity, is safe to dilute in aqueous solution, poses no flammability risk, and is environmentally friendly; Fourth, chloral hydrate is simple to prepare, can be synthesized in one step, or can be purchased directly, and is widely available; Fifth, the half-cell design based on chloral hydrate as the positive electrode electrolyte is flexible and suitable for integration into a full cell.

[0021] In some specific examples of the above applications, the positive electrolyte also includes a supporting electrolyte.

[0022] It should be noted that the positive electrode electrolyte in this invention also includes a supporting electrolyte, which is known in the art.

[0023] In some specific examples, the supporting electrolyte in the above applications is selected from hydrochloric acid and / or phosphate.

[0024] It should be noted that the supporting electrolyte in this invention can preferably be hydrochloric acid and / or phosphate, with hydrochloric acid and phosphate being more suitable for the positive electrode electrolyte in this invention.

[0025] In some specific examples, the pH of the positive electrode electrolyte in the above applications is 1 to 7.

[0026] In some specific examples, in the above applications, the concentration of the supporting electrolyte in the positive electrode electrolyte is 0.5 mol / L to 1.5 mol / L; and / or the concentration of chloral hydrate is 4 mmol / L to 6 mmol / L.

[0027] It should be noted that the concentration of the supporting electrolyte in the positive electrode electrolyte in this invention is 0.5 mol / L to 1.5 mol / L, such as 0.7 mol / L, 1 mol / L or 1.3 mol / L, etc.; and the concentration of chloral hydrate in the positive electrode electrolyte is 4 mmol / L to 6 mmol / L, such as 4.5 mmol / L, 5 mmol / L or 5.5 mmol / L, etc.

[0028] In some specific examples, in the above applications, the concentration of the supporting electrolyte in the positive electrode electrolyte is 1 mol / L; and / or the concentration of chloral hydrate is 5 mmol / L.

[0029] It should be noted that the concentration of the supporting electrolyte in the positive electrode electrolyte in this invention can be further preferably 1 mol / L, and the concentration of chloral hydrate in the positive electrode electrolyte is 5 mmol / L. The positive electrode electrolyte at this concentration has better electrochemical activity.

[0030] In some specific examples of the above applications, the aqueous organic flow battery also includes a porous carbon electrode, a separator, and a graphite counter electrode.

[0031] It should be noted that the positive electrolyte in this invention can also be combined with a porous carbon electrode, a separator, and a graphite counter electrode to prepare an aqueous flow half-cell.

[0032] In some specific examples, in the above applications, the diaphragm is selected from Nafion membranes or anion-conducting membranes; and / or the porous carbon electrode is selected from graphite felt, carbon felt, or porous graphene.

[0033] It should be noted that the diaphragm and porous carbon electrode in this invention are known in the art, including but not limited to the diaphragm and porous carbon electrode listed above.

[0034] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0035] In the following examples, chloral hydrate (CCl3CH(OH)2, purity ≥98%, supplied by MREDA) was used directly for electrolyte preparation without further purification.

[0036] In the following example, the positive electrode electrolyte solution was prepared as follows: chloral hydrate was dissolved in deionized water (resistivity 18 MΩ·cm) to prepare a chloral hydrate solution; then, HCl solution (supporting electrolyte) was added to the solution and stirred until completely dissolved to form a positive electrode electrolyte solution; this positive electrode electrolyte solution is stable at 25°C, and the water solubility of chloral hydrate is as high as 10.9 mol / L, ensuring potential applications with high energy density.

[0037] Example 1 This invention provides a cyclic voltammetry (CV) test and a test method for a battery constructed based on a positive electrode electrolyte solution prepared with chloral hydrate, in order to evaluate its electrochemical performance.

[0038] The specific experimental setup used in this embodiment of the invention is a three-electrode system, as detailed below: The working electrode is a glassy carbon disk electrode (3 mm in diameter, polished with 0.05 μm alumina paste and rinsed with deionized water); the counter electrode is a platinum wire (99.9% purity); and the reference electrode is Ag / AgCl (3 M KCl). The testing instrument was a BioLogic SP-150 potentiostat; Under a nitrogen atmosphere (nitrogen purity ≥99.9%, used for deoxygenation to avoid oxygen interference), 5 mmol / L chloral hydrate solution was dissolved in 50 mL of 1 mol / L HCl solution (supporting electrolyte), the temperature was controlled at 25℃, and the scanning potential range was (-0.5 V to +1.5 V) vs. Ag / AgCl, with a scan rate of 10 mV·s. -1 50 mV·s -1 100 mV·s -1 and 200mV·s -1 The built-in IR compensation function of the instrument is used to correct the solution resistance.

[0039] Test CV curve as follows Figure 1 As shown, the CV curve exhibits clear redox peaks, confirming the high electrochemical activity of chloral hydrate. Specifically, in acidic medium, the redox potential of chloral hydrate is approximately 1.17 V vs. Ag / AgCl, and the peak current ratio is... i pa / i pc The value ≈1.0 indicates quasi-reversible behavior. This behavior is attributed to the strong electron-withdrawing effect of the trichloromethyl group, which promotes proton-coupled electron transfer at the oxygen center, forming a carbonyl-like intermediate. These test results provide fundamental data for future flow battery applications.

[0040] Example 2 This embodiment provides a flow test scenario and method for a half-cell constructed based on a positive electrode electrolyte solution prepared with chloral hydrate, in order to evaluate its performance in a real flow battery environment.

[0041] The specific device in this embodiment of the invention is a custom single-channel flow battery: The positive electrode is graphite felt (GF, size 2cm×2cm, supplier: Liaoning Jingu Carbon Materials Co., Ltd.); the separator is a pretreated Nafion 117 membrane (the pretreatment of the Nafion 117 membrane is as follows: the cut Nafion 117 membrane is placed in a mixed solution of 25 mL of 30% (volume fraction) hydrogen peroxide and 125 mL of deionized water, and incubated at 80 ℃ for 1 h; after the water bath, the membrane is removed, rinsed, and then placed in deionized water at 80 ℃ for 1 h; after the water bath, the membrane is removed and placed in a mixed solution of 7 mL of 98% (mass fraction) sulfuric acid and 153 mL of deionized water, and incubated at 80 ℃ for 1 h; after the water bath, the membrane is removed, rinsed, and then placed in deionized water at 80 ℃ for 1 h; then it is soaked in ultrapure water for storage); the counter electrode is a graphite electrode. The positive electrode electrolyte is 50 mL of 0.1 mol / L chloral hydrate solution dissolved in 1 mol / L HCl solution, dispensed using a peristaltic pump at a rate of 10 mL / min. -1 The flow rate is circulated; the negative electrode electrolyte is 50 mL of 1 mol / L HCl solution; The testing instrument was a Donghua DH7600B potentiostat, and the temperature was controlled at 25 ℃. Constant current charge-discharge mode was used, with current densities of 5 mA·cm⁻¹. -2 10 mA·cm -2 15 mA·cm -2 20 mA·cm -2 and 25 mA·cm -2 The upper limit voltage was 1.1 V vs. Ag / AgCl, and 50 cycles were performed, with each test repeated three times and the average value taken to ensure repeatability.

[0042] Test (test current density is 10 mA·cm) -2 The constant current charge-discharge curves are shown in the figure. Figure 2 As shown, a stable charge-discharge plateau with a high plateau voltage (~1.2 V) is demonstrated, indicating good potential for energy density.

[0043] Test (test current density is 10 mA·cm) -2 The long-term charge-discharge curves are shown in the following figures. Figure 3 As shown in the figure, the results demonstrate that the half-cell constructed based on chloral hydrate exhibits excellent durability.

[0044] Test (test current density is 10 mA·cm) -2 The relationships between voltage efficiency (VE), coulombic efficiency (CE), and energy efficiency (EE) over long cycles and the number of cycles are shown in the following figures. Figure 4As shown, the results indicate that the voltage efficiency (VE), coulombic efficiency (CE), and energy efficiency (EE) do not change significantly with the increase of the number of cycles, indicating excellent cycle stability.

[0045] Tested at a current density of 10 mA·cm -2 The capacity changes after 20 charge and discharge cycles were analyzed to assess capacity decay and rate performance. The results are as follows: Figure 5 As shown, the results indicate that the charging and discharging capacities gradually increase with the number of cycles, remaining stable overall, indicating that chloral hydrate has good cycle stability. Furthermore, the calculated capacity decay rate of the constructed half-cell is approximately 0.5% per cycle (based on...). Figure 3 (Average decay rate calculated from long-cycle cyclic data).

[0046] Testing different current densities (5 mA·cm) -2 ~25 mA·cm -2 The changes in potential and capacitance under these conditions are shown in the following figures. Figure 6 As shown, the results indicate that polarization increases with increasing current density, but the curve still shows a clear plateau, proving the feasibility of chloral hydrate at high rates.

[0047] The relationship between voltage efficiency, coulombic efficiency, and energy efficiency and current density was tested, and the results are as follows: Figure 7 As shown, the results indicate that the voltage efficiency (VE) remains at a high level, while the coulombic efficiency (CE) and energy efficiency (EE) decrease slightly with increasing current density, but the overall performance is excellent.

[0048] The results above show that when chloral hydrate is used as the positive electrode active material of organic flow batteries, its voltage efficiency (VE) is >50%, coulombic efficiency (CE) is >60%, energy efficiency (EE) is >50%, and it remains stable at high current densities.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. Application of chloral hydrate as an electroactive material in the positive electrode electrolyte of aqueous organic flow batteries.

2. The application according to claim 1, characterized in that, The positive electrode electrolyte also includes a supporting electrolyte.

3. The application according to claim 2, characterized in that, The supporting electrolyte is selected from hydrochloric acid and / or phosphate.

4. The application according to claim 3, characterized in that, The pH of the positive electrode electrolyte is 1~7.

5. The application according to any one of claims 2 to 4, characterized in that, In the positive electrode electrolyte, Supported electrolyte concentrations are 0.5 mol / L to 1.5 mol / L; and / or The concentration of chloral hydrate is 4 mmol / L to 6 mmol / L.

6. The application according to claim 5, characterized in that, In the positive electrode electrolyte, Support electrolyte concentration of 1 mol / L; and / or The concentration of chloral hydrate was 5 mmol / L.

7. The application according to claim 1, 2, 3, 4 or 6, characterized in that, Aqueous organic flow batteries also include porous carbon electrodes, separators, and graphite counter electrodes.

8. The application according to claim 7, characterized in that, The diaphragm is selected from Nafion membranes or anion-conducting membranes; and / or The porous carbon electrode is selected from graphite felt, carbon felt or porous graphene.

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