An ultra-high stability phenazine-based alkaline aqueous organic flow battery electrolyte and flow battery

Abstract

The present invention discloses an ultra-high stability phenazine alkaline aqueous organic liquid flow battery electrolyte and a liquid flow battery, belonging to the field of electrochemical energy storage technology. The electrolyte contains a cyclic supramolecule with a hydrophobic inner cavity and a hydrophilic outer cavity, a phenazine organic rigid conical cavity structure, and an alkaline aqueous solution. The cyclic supramolecule is cyclodextrin or its derivatives, which can improve the reaction kinetics of phenazine organic matter, improve utilization and stability, have the advantages of easy raw material availability, simple operation and low cost, and can realize an alkaline aqueous organic liquid flow battery with smaller polarization, higher capacity utilization, better rate performance, higher energy efficiency and better stability.

Description

Technical Field

[0001] The invention relates to an ultra-high-stability phenazine alkaline aqueous organic liquid flow battery electrolyte and a liquid flow battery, belonging to the technical field of electrochemical energy storage. Background Art

[0002] With the continuous development of human society and economy, the supply of fossil fuels has gradually decreased, leading to an increasingly urgent energy shortage problem. At the same time, with the improvement of human production capacity and the surge in demand for products, the burning of a large amount of traditional fuels has led to increasingly serious environmental pollution problems. The intermittent and volatile problems of renewable energy itself have further promoted the pursuit of large-scale long-term energy storage technology. Redox flow batteries (RFBs) store a large amount of energy in the electrolyte, have good scalability, variable modular design and reliable safety, and are an ideal solution for large-scale energy storage.

[0003] In the past, researchers have extensively studied aqueous redox flow batteries (ARFBs) using water-soluble transition metal ions as redox active materials. However, these batteries still face long-standing challenges. Among them, although all-vanadium flow batteries have been commercialized due to their high power density and long cycle life, their widespread application is limited by the high cost of vanadium. To address this problem, researchers have been working on developing cheap and stable water-soluble organic compounds for aqueous organic flow batteries (AORFBs), such as quinones, viologens, TEMPO, phenazines, and ferrocenes. Compared with inorganic systems, aqueous organic flow batteries show greater application potential: (1) organic molecules as active materials are abundant, low-cost, environmentally friendly, and can be synthesized in large quantities; (2) organic molecules have diverse structures and their physical, chemical, and electrochemical properties can be controlled.

[0004] Phenazine has three fused aromatic rings and is insoluble in water. Phenazine compounds have attracted attention due to their low potential and the involvement of two-electron and two-proton reactions. Past research has generally focused on improving the performance of phenazine compounds and regulating their redox potential through molecular design and synthesis engineering. Some good progress has been made, but there are still some problems. (1) The actual utilization rate of organic active molecules is not high, especially when charging and discharging at a higher current density. This is mainly because the molecular design in the past often focused on improving the solubility and stability of phenazine active molecules and ignored the improvement of reaction kinetics, resulting in poor rate performance and low utilization. (2) Although a lot of efforts have been made in the past to improve the stability of phenazine active molecules through molecular design and certain results have been achieved, the stability of typical phenazine active molecules designed in the past is still far from practical application. (3) Some molecules have harsh synthesis conditions (high temperature and pressure, hydrogen), high synthesis costs (expensive raw materials, requiring special catalysts), complex reactions (involving multi-step synthesis and separation), and low yields, all of which greatly increase the actual cost. Therefore, these reasons lead to the fact that the actual operation of aqueous organic flow batteries represented by phenazine compounds is still far from large-scale development.

[0005] Among them, benzophenazine (BHPC) was proposed earlier as a phenazine active molecule and has shown excellent performance in alkaline flow batteries, making it representative. In addition, there is limited room for further molecular modification of BHPC, but the reported utilization rate, rate performance, energy efficiency and stability still have a lot of room for improvement. Therefore, BHPC needs further research, and other means can be used to further improve performance to a higher level, laying the foundation for the large-scale development of alkaline aqueous organic flow batteries. Summary of the invention

[0006] The purpose of the present invention is to provide an ultra-high stability phenazine alkaline aqueous organic liquid flow battery electrolyte and liquid flow battery. The polyhydroxy cyclic supramolecular additive in the electrolyte can improve the reaction kinetics of phenazine organic matter, improve the utilization rate and stability, and has the advantages of easy availability of raw materials, simple operation and low cost. It can realize an alkaline aqueous organic liquid flow battery with smaller polarization, higher capacity utilization, better rate performance, higher energy efficiency and better stability.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A phenazine-based alkaline aqueous organic flow battery electrolyte with ultra-high stability comprises polyhydroxy cyclic supramolecules, phenazine-based organic matter and an alkaline aqueous solution.

[0009] Preferably, the polyhydroxy cyclic supramolecule is a cyclodextrin or a derivative thereof having a polyhydroxy rigid conical cavity structure with a hydrophobic inner cavity and a hydrophilic outer cavity.

[0010] Preferably, in the electrolyte, the concentration ratio of the phenazine organic matter to the polyhydroxy cyclic supramolecule is 1:(0.1-0.5); the preferred range is 1:(0.1-0.4).

[0011] Preferably, the polyhydroxy cyclic supramolecule is α-cyclodextrin or a derivative thereof, and / or β-cyclodextrin or a derivative thereof, and / or γ-cyclodextrin or a derivative thereof.

[0012] Preferably, in the electrolyte, the concentration of the phenazine organic matter is 0.05-0.3 mol / L; the concentration of the polyhydroxy cyclic supramolecule is 0.01-0.3 mol / L; and the concentration of the alkaline electrolyte in the alkaline aqueous solution is 0.5-2M.

[0013] Preferably, the phenazine organic compound is one or more of benzophenazine (BHPC), hydroxyphenazine (HP), aminophenazine (AHP) and their derivatives.

[0014] A liquid flow battery comprises any of the above-mentioned electrolytes.

[0015] A method for increasing the reaction rate of a phenazine alkaline aqueous organic flow battery comprises using any of the above-mentioned electrolytes and controlling the concentration of the polyhydroxy cyclic supramolecules in the electrolyte to be 0.01-0.03 mol / L.

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

[0017] Cyclodextrin is a class of low-cost, highly stable natural macromolecules with a unique multi-hydroxy rigid conical cavity structure with a hydrophobic inner cavity and a hydrophilic outer cavity. Cyclodextrin has a suitable pKa value, undergoes multiple deprotonations in alkaline solutions, is redox inert under alkaline water conditions, has a good ability to form hydrogen bonds with organic molecules, and has host-guest complexation with suitable cavity sizes. Therefore, cyclodextrin can significantly improve the reaction kinetics and stability of these phenazine organic compounds;

[0018] Compared with the huge cost and limitations of molecular design and synthesis engineering, adding a small amount of cyclodextrin to the phenazine electrolyte of alkaline aqueous organic flow battery has the advantages of easy raw material availability, simple operation and low cost. In addition, the constructed alkaline aqueous organic flow battery can achieve smaller polarization, higher capacity utilization (>95%), better rate performance, and higher energy efficiency (EE>80%@100 mA cm -2 ) and better stability (>80 days, capacity decay rate <0.02% / day), which is very competitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 CV curves of phenazine electrolytes without or with different additives;

[0020] Figure 2 CV curves of phenazine electrolytes with different additive contents;

[0021] Figure 3 The Tafel curves of phenazine electrolytes without or with different additives;

[0022] Figure 4 The Tafel curves of phenazine electrolytes with different additive contents;

[0023] Figure 5 The battery rate performance of phenazine electrolyte without additives, including discharge capacity, coulombic efficiency, voltage efficiency and energy efficiency at different current densities;

[0024] Figure 6 The rate performance of phenazine electrolytes with α-cyclodextrin additives, including discharge capacity, coulombic efficiency, voltage efficiency and energy efficiency at different current densities;

[0025] Figure 7 The rate performance of the battery using phenazine electrolyte with β-cyclodextrin additive, including discharge capacity, coulombic efficiency, voltage efficiency and energy efficiency at different current densities;

[0026] Figure 8 The rate performance of phenazine electrolytes with γ-cyclodextrin additives, including discharge capacity, coulombic efficiency, voltage efficiency and energy efficiency at different current densities;

[0027] Fig. 9 Battery stability test of phenazine electrolyte with α-cyclodextrin additive (@100 mA cm -2 ). Attenuation 0.013% / day, 0.0014‰ / circle;

[0028] Fig.10 Battery stability test of phenazine electrolyte with β-cyclodextrin additive (@100 mA cm -2 ). Attenuation: 0.011% / day, 0.0010‰ / circle;

[0029] Fig.11 The stability test of the battery using phenazine electrolyte with γ-cyclodextrin additive (@100 mA cm -2 ). Attenuation: 0.014% / day, 0.0015‰ / turn. DETAILED DESCRIPTION

[0030] The present invention will be specifically described below in conjunction with the accompanying drawings and embodiments.

[0031] (1)Simplified synthesis of phenazine organic compounds.

[0032] Taking benzo[a]hydroxyphenazine-7 / 8-carboxylic acid (BHPC) and its derivatives as an example, BHPC and its derivatives are synthesized by a one-step method. 2-Hydroxynaphthoquinone and its derivatives and 3,4-diaminobenzoic acid and its derivatives are refluxed in an acetic acid solution for 12-24 hours, and then filtered and dried to obtain BHPC and its derivatives without further purification.

[0033] (2) Preparation of phenazine electrolyte containing cyclodextrin additive.

[0034] Phenazine organic matter and cyclodextrin are mixed in a certain proportion and dissolved in a 1M concentration KOH solution. Phenazine organic matter includes but is not limited to BHPC and its derivatives; cyclodextrin includes but is not limited to α-cyclodextrin and its derivatives, β-cyclodextrin and its derivatives, γ-cyclodextrin and its derivatives; the concentration ratio of phenazine organic matter to cyclodextrin is in the range of 1:0.1-1:3.

[0035] (3) Performance test of phenazine electrolyte containing cyclodextrin additive.

[0036] (3.1) Electrochemical performance test.

[0037] Electrochemical performance tests were performed using an electrochemical workstation (CHI660E) and a standard three-electrode device, with a glassy carbon electrode as the working electrode, a platinum electrode as the counter electrode, and a saturated Ag / AgCl electrode as the reference electrode. Cyclic voltammetry analysis was performed on the redox properties of phenazine electrolytes without or with different additives; cyclic voltammetry analysis was performed on the redox properties of phenazine electrolytes with different additive contents.

[0038] (3.2) Tafel kinetic test.

[0039] Tafel kinetics test was carried out using an electrochemical workstation (CHI660E) and a standard three-electrode device, in which a glassy carbon electrode was used as the working electrode, a platinum electrode was used as the counter electrode, and a saturated Ag / AgCl electrode was used as the reference electrode. Tafel tests were performed on the redox kinetics of phenazine electrolytes without or with different types of additives; Tafel tests were performed on the redox kinetics of phenazine electrolytes with different amounts of additives.

[0040] (4) Full cell testing of an alkaline aqueous organic liquid flow battery based on a phenazine electrolyte containing a cyclodextrin additive.

[0041] The battery performance test was carried out using the Xinwei constant current battery test system and a standard flow battery single cell module. A cation exchange membrane (including but not limited to perfluorosulfonic acid membrane and non-fluorinated membrane) was used as the diaphragm. The reaction area was based on the area of ​​the graphite felt electrode (4 cm 2 In all battery tests in this application, the negative electrode electrolyte volume was 10.0 mL and the concentration of phenazine organic matter was 0.1 mol L -1 The concentration of cyclodextrin additive was in the range of 0.01-0.30 mol L -1 ; The volume of the positive electrode electrolyte is 40.0 mL, and the concentration of potassium ferrocyanide is 0.1 mol L -1 The positive and negative electrolytes were pumped through a peristaltic pump (BT100-2J) at a rate of 100 mL min -1 The flow rate circulates between the battery and the tank.

[0042] (4.1) Battery rate performance test.

[0043] The single cell was tested with a 40-120 mA cm -2 Constant current charge and discharge rate test under current density.

[0044] (4.2) Battery constant current charge and discharge stability test.

[0045] The single cell was tested with a 100 mA cm -2 Constant current charge and discharge test at current density.

[0046] Performance testing of phenazine electrolytes containing cyclodextrin additives.

[0047] Electrochemical performance test.

[0048] Cyclodextrins are redox inert under alkaline aqueous conditions. Figure 1 The CV curves of phenazine electrolytes without / with different additives (the concentration is set to BHPC: cyclodextrin = 1:0.2), and the CV curve of phenazine electrolytes without cyclodextrin additives is used as the blank group. It can be found that after adding cyclodextrin, the polarization of the CV curve becomes significantly smaller, and the reduction peak intensity increases significantly, among which β-cyclodextrin is the most significant as an additive. It shows that the addition of cyclodextrin helps to increase the current intensity of phenazine electrolytes and reduce polarization. This is mainly because cyclodextrin has a good ability to form hydrogen bonds with organic molecules, so it can effectively inhibit the hydrogen evolution side reaction of the water solvent, thereby improving the redox reaction ability of the organic molecules themselves.

[0049] Figure 2 is the CV curve of phenazine electrolyte with different additive contents. Figure 2It can be found that as the proportion of β-cyclodextrin continues to increase, the polarization of the CV curve shows a trend of first decreasing and then increasing, and the reduction peak intensity shows a trend of first increasing and then weakening. This shows that the optimal concentration ratio of the electrolyte is phenazine organic matter: cyclodextrin = 1:0.2. This is mainly due to the good ability of cyclodextrin to form hydrogen bonds with organic molecules. Therefore, an appropriate concentration of cyclodextrin can effectively inhibit the hydrogen evolution side reaction of the water solvent, thereby improving the redox reaction ability of the organic molecule itself. However, when the concentration of cyclodextrin is further increased, the side effects of increased electrolyte viscosity and decreased conductivity cause the electrolyte polarization to increase and the redox current to decrease.

[0050] Tafel kinetics test.

[0051] Figure 3 The following are the Tafel curves of phenazine electrolytes without / with different additives, and the Tafel curve of phenazine electrolytes without cyclodextrin additives is the blank group. It can be found that after adding cyclodextrin (the concentration is set to BHPC: cyclodextrin = 1:0.2), the exchange current density of the Tafel curve is significantly enhanced, among which β-cyclodextrin is the most significant as an additive. This shows that the addition of cyclodextrin helps to improve the reaction kinetics of phenazine electrolytes. This is mainly because cyclodextrin has a suitable pKa value and undergoes multiple deprotonation in alkaline solutions. The proton regulation strategy helps to accelerate the electrochemical redox process of organic molecules.

[0052] Figure 4 is the Tafel curve of phenazine electrolyte with different additive contents, Figure 4 It can be seen that as the proportion of β-cyclodextrin continues to increase, the exchange current density of the Tafel curve first increases and then decreases, but it is still greater than the exchange current density of the phenazine electrolyte without cyclodextrin. This once again shows that cyclodextrin helps to improve the reaction kinetics of phenazine electrolytes. Among them, the optimal concentration ratio of the electrolyte is phenazine organic matter: cyclodextrin = 1:0.2. This is mainly because the appropriate concentration of cyclodextrin can effectively improve the reaction kinetics of organic molecules. However, when the concentration of cyclodextrin is further increased, the side effects of increased electrolyte viscosity and decreased conductivity weaken the improvement of the reaction kinetics of organic molecules to a certain extent.

[0053] Full cell testing of alkaline aqueous organic flow batteries based on phenazine electrolytes containing cyclodextrin additives.

[0054] Battery rate performance test.

[0055] Figure 5 , 6, 7, and 8 are the battery rate performance diagrams of phenazine electrolytes without / with different additives at different current densities; Table 1 is the comparison results of capacity utilization of different phenazine electrolytes at different current densities and the comparison results of capacity utilization of phenazine electrolytes without / with different additives at different current densities. By comparing the capacity utilization of various phenazine organic liquid flow batteries at different current densities, it is not difficult to find that BHPC has a higher capacity utilization and better rate performance, so it was selected as a representative of phenazine alkaline organic liquid flow batteries for further study. Through the variable current test of phenazine organic liquid flow batteries without / with different additives, it is not difficult to find that the introduction of cyclodextrin helps to improve the capacity utilization and energy efficiency of the battery (>80%@100 mA cm -2 ). This is because the introduction of cyclodextrin additives accelerates the redox reaction kinetics of organic active molecules and reduces polarization, thereby increasing the capacity utilization of organic active molecules and the energy efficiency of the battery.

[0056] Table 1 Comparison of the capacity utilization of different phenazine electrolytes at different current densities and the capacity utilization of phenazine electrolytes without / with different additives at different current densities

[0057]

[0058] Battery constant current charge and discharge stability test.

[0059] Fig. 9 , 10 1 and 11 are the battery rate performance diagrams of phenazine electrolytes with different additives at different current densities; Table 2 shows the performance of different phenazine alkaline organic liquid flow batteries at 100 mA cm -2 Comparison of energy efficiency and capacity retention under current density and performance of phenazine-based alkaline organic flow batteries without and with different additives at 100 mA cm -2 Comparison of energy efficiency and capacity retention under current density. It is not difficult to find that BHPC has a high current density at 100 mA cm -2 It showed the best energy density and capacity retention rate under the current density, so it was selected as a representative of phenazine alkaline organic liquid flow batteries for further research. The test results further showed that the energy density and stability of phenazine alkaline organic liquid flow batteries were significantly improved after adding cyclodextrin. This is mainly due to the formation of a dense hydrogen bond network and host-guest complexation between cyclodextrin and organic active molecules, which can effectively stabilize the oxidized and reduced organic active molecules, thereby significantly improving the stability of the battery.

[0060] Table 2 Performance of different phenazine alkaline organic flow batteries at 100 mA cm -2Comparison of energy efficiency and capacity retention under current density and performance of phenazine-based alkaline organic flow batteries without and with different additives at 100 mA cm -2 Comparison of energy efficiency and capacity retention under current density

[0061]

[0062] References:

[0063] [1] Park, J., Lee, Y., Yun, D. et al. A benzo[a]phenazine-based redoxspecies with highly reversible two-electron reaction for aqueous organicredox flow batteries. Electrochim. Acta, 2023,439,141644;

[0064] [2]Liu,Y., Zhang P., Wu Z. et al. Screening Ultra-Stable(Phenazine)dioxyalkanocic Acids with Varied Water-Solubilizing Chain Lengths for High-Capacity Aqueous Redox Flow Batteries. J. Am. Chem. Soc., 2024,146, 3293−3302;

[0065] [3] Pang, S., Wang,

[0066] [4] Hollas, A., Wei, X., Murugesan, V. et al. A biomimetic high-capacity phenazine-based anolyte for aqueous organic redox flow batteries. Nat Energy, 2018, 3, 508-514.

[0067] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the patent principle of this application. These improvements and modifications should also be regarded as the scope of protection of this application.

Claims

1. A high-reaction kinetic phenazine alkaline aqueous organic flow battery electrolyte, characterized in that: Including polyhydroxy cyclic supramolecules, as well as phenazine organic compounds and alkaline aqueous solutions; The polyhydroxy cyclic supramolecule is cyclodextrin or a derivative thereof; In the electrolyte, the concentration of phenazine organic matter is 0.05-0.3 mol / L; the concentration of polyhydroxy cyclic supramolecule is 0.01-0.1 mol / L; and the concentration ratio of phenazine organic matter to polyhydroxy cyclic supramolecule is 1:(0.1-0.5).

2. The high-reaction-kinetic phenazine-based alkaline aqueous organic liquid flow battery electrolyte according to claim 1, characterized in that: The concentration ratio of phenazine organic matter to polyhydroxy cyclic supramolecules is 1:(0.1-0.4).

3. The high-reaction-kinetic phenazine alkaline aqueous organic flow battery electrolyte according to claim 1, characterized in that: The polyhydroxy cyclic supramolecule is α-cyclodextrin or its derivatives, and / or β-cyclodextrin or its derivatives, and / or γ-cyclodextrin or its derivatives.

4. The high-reaction-kinetic phenazine alkaline aqueous organic flow battery electrolyte according to claim 1, characterized in that: The phenazine organic compound is one or more of benzophenazine, hydroxyphenazine, aminophenazine and their derivatives.

5. A liquid flow battery, characterized in that: The invention comprises the electrolyte described in any one of claims 1 to 4.

6. A method for improving the reaction kinetics of a phenazine alkaline aqueous organic flow battery, characterized in that: The electrolyte according to any one of claims 1 to 4 is used, and the concentration of the polyhydroxy cyclic supramolecule in the electrolyte is controlled at 0.01-0.03 mol / L; the reaction kinetics is measured by the exchange current density of the Tafel curve.

Images