Flow battery capacity monitoring and hydrogen online recovery system

Abstract

The invention provides a flow battery capacity monitoring and hydrogen online recovery system, and belongs to the field of energy storage batteries. The system comprises a flow battery negative electrode hydrogen production unit, a flow battery positive electrode gas production unit, a battery charging and discharging unit, a flow battery capacity monitoring unit, a product circulation unit, a negative electrode hydrogen circulation unit and a positive electrode gas circulation unit. The battery charging and discharging unit directly takes positive and negative electrode gases of the flow battery as reactants to complete a battery charging or discharging process; and the flow battery capacity monitoring unit calculates the capacity fading degree of the flow battery system caused by hydrogen evolution side reaction in real time according to the discharge capacity fed back by the battery charge and discharge unit, and supplements a restorer to the system in time according to the result. According to the invention, online recycling of the by-product hydrogen is realized, the hydrogen treatment cost and risk in the flow battery system are effectively reduced, the attenuation condition of the discharge capacity of the flow battery system is accurately calculated in real time according to the discharge condition of the battery, and continuous and stable operation of the flow battery system is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage batteries and relates to a liquid flow battery capacity monitoring and hydrogen online recovery system. Background Art

[0002] The large-scale use of fossil fuels has led to a series of problems, including environmental pollution and climate change. To achieve a clean and sustainable energy supply, promoting the widespread adoption of renewable energy sources such as wind and solar power is crucial. However, due to the intermittent and fluctuating nature of renewable energy, its integration into the grid often leads to power fluctuations, which has become a major constraint to its large-scale application. Therefore, the development of grid-scale energy storage technology is seen as an important approach to addressing this issue. Among existing large-scale energy storage technologies, flow batteries demonstrate significant application potential and broad development prospects due to their excellent scalability, safety, long lifespan, and low lifecycle costs.

[0003] Existing types of flow batteries include all-vanadium flow batteries, iron-chromium flow batteries, iron-vanadium flow batteries, and zinc-bromine flow batteries. The redox reaction potential of the negative electrode of these flow batteries is generally less than 0 V vs. SHE. During charging, hydrogen evolution will occur at the negative electrode. The occurrence of side reactions such as hydrogen evolution will lead to an imbalance in the ion valence state, which in turn leads to a decrease in battery capacity, performance, and service life. At the same time, a certain amount of hydrogen will accumulate on the top of the negative electrode electrolyte tank. In existing flow battery systems, most of them use a method of regular hydrogen discharge to avoid accumulation. For example, Chinese patent CN217903167U discloses a hydrogen discharge system suitable for flow batteries to achieve timely hydrogen discharge. However, with the continuous development of flow battery systems, the increase in hydrogen volume and the explosion risk caused by hydrogen contact with other gases cannot be ignored. Therefore, it is necessary to process the generated hydrogen in real time.

[0004] There are currently some invention patents to solve the problem of battery capacity decay caused by the production of hydrogen as a byproduct during the charge and discharge process of liquid flow batteries. For example, Chinese patent CN109659587A discloses a liquid flow battery capacity decay control system and method, which uses gas chromatography to measure the concentration of hydrogen in the negative electrode electrolyte storage tank, and periodically calculates the total amount of hydrogen evolution from the hydrogen concentration; calculates the liquid flow battery capacity decay based on the amount of hydrogen evolution, and replenishes the positive electrode electrolyte storage tank with a corresponding amount of capacity recovery agent when the liquid flow battery is discharged. However, the gas chromatography detection scheme has a lag, and the results of hydrogen detection cannot be fed back in time. Real-time monitoring of capacity decay in the liquid flow battery system cannot be achieved, and therefore real-time replenishment of capacity recovery agent cannot be achieved. Summary of the Invention

[0005] To address the aforementioned issues, the present invention designs a liquid flow battery capacity monitoring and online hydrogen recovery system. The system comprises a liquid flow battery anode hydrogen production unit, a liquid flow battery cathode gas production unit, a battery charge and discharge unit, a liquid flow battery capacity monitoring unit, a product circulation unit, a negative electrode hydrogen circulation unit, and a positive electrode gas circulation unit. The battery charge and discharge unit directly uses the liquid flow battery cathode and negative electrode gases as reactants to complete the battery charging or discharging process. The battery charge and discharge unit provides feedback on the discharge volume and calculates the system's hydrogen production in real time based on the discharge volume. Furthermore, the system's capacity decay due to the hydrogen evolution side reaction is calculated in real time, and recovery agents are replenished to the system based on the results.

[0006] The technical solution of the present invention is: A flow battery capacity monitoring and hydrogen online recovery system, comprising: A battery charge and discharge unit 1, wherein the battery charge and discharge unit 1 includes a charge and discharge battery, and the charge and discharge battery is mainly a membrane electrode structure battery, including a negative electrode, a membrane and a positive electrode; The liquid flow battery negative electrode hydrogen production unit 2 passes the hydrogen gas released from the liquid flow battery electrolyte negative electrode storage tank into the negative electrode of the battery charge and discharge unit 1; Anode hydrogen circulation unit 3, which circulates the remaining hydrogen after the battery charge and discharge unit 1 battery reaction back to the flow battery cathode hydrogen production unit 2; The liquid flow battery positive electrode gas production unit 6 passes the positive electrode gas precipitated from the liquid flow battery electrolyte positive electrode storage tank into the positive electrode of the battery charging and discharging unit 1; The positive electrode circulation unit 4 circulates the products generated by the battery charge and discharge unit 1 and the remaining positive electrode gas to the product circulation unit 5 and the liquid flow battery positive electrode gas production unit 6 respectively; A product circulation unit 5, which collects products generated by the electrochemical reaction of the positive and negative electrode gases in the battery charging and discharging unit 1; The liquid flow battery capacity monitoring unit 7 calculates the liquid flow battery hydrogen production in real time according to the discharge amount of the battery charge and discharge unit 1, and calculates the liquid flow battery electrolyte valence offset based on the hydrogen production, thereby obtaining the liquid flow battery capacity attenuation in real time.

[0007] Furthermore, the battery charging and discharging unit 1 also includes a charging and discharging potentiometer.

[0008] Furthermore, the negative electrode of the charge-discharge battery is provided with a hydrogen inlet and a hydrogen outlet, which are respectively connected to the liquid flow battery negative electrode hydrogen production unit 2 and the negative electrode hydrogen circulation unit 3. The hydrogen output by the liquid flow battery negative electrode hydrogen production unit 2 is passed into the negative electrode through the hydrogen inlet, and after the battery reaction, it returns to the liquid flow battery negative electrode hydrogen production unit 2 from the hydrogen outlet through the negative electrode hydrogen circulation unit 3; the positive electrode of the charge-discharge battery is provided with a positive electrode gas inlet and a product outlet, which are respectively connected to the liquid flow battery positive electrode gas production unit 6 and the positive electrode circulation unit 4. The positive electrode gas enters the positive electrode through the liquid flow battery positive electrode gas production unit 6. After the battery reaction, the product and unreacted gas are circulated to the product circulation unit 5 and the liquid flow battery positive electrode gas production unit 6 respectively through the positive electrode circulation unit 4.

[0009] Furthermore, the negative electrode includes a negative electrode flow channel plate, a negative electrode gas diffusion layer and a negative electrode catalyst; the positive electrode includes a positive electrode flow channel plate, a positive electrode gas diffusion layer and a positive electrode catalyst; wherein the flow channel plate material includes graphite material, conductive carbon material and metal plate; the flow channel includes parallel flow channels, serpentine flow channels or cross flow channels, etc.; the negative electrode gas diffusion layer and the positive electrode gas diffusion layer include carbon felt, carbon cloth and carbon paper.

[0010] Furthermore, the negative electrode catalyst includes a noble metal carbon-based catalyst, a noble metal alloy catalyst, a noble metal single atom catalyst or a non-noble metal catalyst; the positive electrode selects different positive electrode catalysts according to the reaction gas, including noble metal carbon-based catalysts, noble metal alloy catalysts or metal oxides.

[0011] Furthermore, the precious metal carbon-based catalysts include platinum carbon, iridium carbon, palladium carbon, ruthenium carbon, rhodium carbon, etc.; the precious metal alloy catalysts include platinum ruthenium, platinum palladium, platinum rhodium, platinum cobalt, platinum iron, platinum gold, platinum silver, platinum nickel, ruthenium nickel, etc.; the precious metal single atom catalysts include platinum single atom, iridium single atom, etc.; the non-precious metal catalysts include nickel-molybdenum alloy, nickel-copper alloy, nickel single atom catalyst, nickel-nitrogen co-doped catalyst, tungsten carbide, etc.; the metal oxides include ruthenium oxide, iridium oxide, platinum oxide, palladium oxide, cobalt oxide, nickel oxide, etc.

[0012] Furthermore, the negative electrode catalyst and the positive electrode catalyst are both attached to the membrane or gas diffusion layer by means of a binder; the binder includes any one of perfluorosulfonic acid polyelectrolyte (Nafion), sulfonated polyetheretherketone polyelectrolyte, sulfonated polysulfone polyelectrolyte, phosphated polybenzimidazole, quaternized polysulfone polyelectrolyte, polybenzimidazole polyelectrolyte, polyvinyl alcohol polyelectrolyte, heteropolyacid electrolyte, and polytetrafluoroethylene, or any combination thereof.

[0013] Furthermore, the membrane between the negative electrode and the positive electrode of the charge and discharge battery in the battery charge and discharge unit 1 includes a proton exchange membrane, an anion exchange membrane or a bipolar membrane.

[0014] Furthermore, the proton exchange membrane includes any one of a perfluorosulfonic acid membrane, a fluorinated polyetherketone membrane, a non-fluorinated sulfonic acid membrane, a polybenzimidazole membrane (PBI membrane), a PTFE-reinforced composite membrane, a PVDF-reinforced composite membrane, etc.; the anion exchange membrane includes any one of an amino anion exchange membrane, a quaternary ammonium salt-based anion exchange membrane, an aromatic polymer-based anion exchange membrane, a polyethylene-based anion exchange membrane, a polypropylene-based anion exchange membrane, a quaternary ammonium salt-functionalized anion exchange membrane, etc.

[0015] Furthermore, the thickness of the film between the negative electrode and the positive electrode of the charge-discharge battery is 20-300 μm.

[0016] Furthermore, the gas flow rate of hydrogen entering the negative electrode of the liquid flow battery is 0.5~10 L / min, and the gas temperature is 20~80℃; the gas flow rate of gas entering the positive electrode of the liquid flow battery is 0.5~10 L / min, and the gas temperature is 20~80℃; the operating voltage window range of the charge and discharge battery is -1~1.6V; and the operating temperature is 20~80℃.

[0017] Furthermore, the cathode gas includes one or more combinations of oxygen, air, chlorine, carbon dioxide or carbon monoxide.

[0018] Furthermore, the flow battery includes an all-vanadium flow battery, an iron-vanadium flow battery, an iron-chromium flow battery, a vanadium-chromium flow battery, a zinc-bromine flow battery, a zinc-cerium flow battery, a vanadium-manganese flow battery or an all-iron flow battery.

[0019] Beneficial effects of the present invention: (1) The system realizes the real-time online recycling and utilization of by-product hydrogen, effectively reducing the cost and risk of hydrogen treatment in the liquid flow battery system, and ensuring the safe and stable operation of the liquid flow battery system.

[0020] (2) The system can accurately calculate the amount of hydrogen generated in the system in real time based on the battery discharge situation, and calculate the attenuation of the system discharge capacity due to the hydrogen evolution side reaction of the liquid flow battery system in real time, so as to facilitate the rapid replenishment of the capacity recovery agent, realize the continuous and stable operation of the entire system, reduce the maintenance frequency, and reduce labor costs.

[0021] (3) The system can immediately detect abnormal hydrogen evolution rate in the system and take timely measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a system structure diagram of the battery system of the present invention.

[0023] Figure 2 1 is the discharge curve of the charge-discharge unit in Example 1 at different hydrogen-oxygen flow rates.

[0024] Figure 3 1 is the discharge curve of the charge-discharge unit in Example 1 during the charge-discharge process of the liquid flow battery system.

[0025] Figure 4 1 is the discharge curve of the charge-discharge unit in Example 2 during the charge-discharge process of the liquid flow battery system.

[0026] Figure 5 3 is the discharge curve of the charge and discharge unit in Example 3 during the charge and discharge process of the liquid flow battery system.

[0027] In the figure: 1-battery charge and discharge unit, 2-liquid flow battery negative electrode hydrogen production unit, 3-negative electrode hydrogen circulation unit, 4-positive electrode circulation unit, 5-product circulation unit, 6-liquid flow battery positive electrode gas production unit, 7-liquid flow battery capacity monitoring unit. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is described in detail below in conjunction with the technical solutions and drawings.

[0029] Example 1 See Figure 1 , is a working principle diagram of a liquid flow battery capacity monitoring and hydrogen online recovery system provided by an embodiment of the present invention. The system includes a battery charging and discharging unit 1, a liquid flow battery anode hydrogen production unit 2, a cathode hydrogen circulation unit 3, a cathode circulation unit 4, a product circulation unit 5, a liquid flow battery anode gas production unit 6, and a liquid flow battery capacity monitoring unit 7. The steps for setting up the battery system in this embodiment 1 are as follows: (1) Construct a membrane electrode structure battery. The battery includes a negative electrode, a membrane, and a positive electrode. The negative electrode is composed of a graphite flow channel plate with a serpentine flow channel, a carbon felt gas diffusion layer, and a Pt-C catalyst layer. The positive electrode is composed of a graphite flow channel plate with a serpentine flow channel, a carbon felt gas diffusion layer, and a Pt-C catalyst. The membrane is a perfluorosulfonic acid membrane (Nafion membrane). The battery operating temperature is 80°C. The positive and negative electrode gas temperature is 80°C.

[0030] (2) The membrane electrode structure battery and the charge and discharge instrument together constitute the battery charge and discharge unit 1.

[0031] (3) The hydrogen production unit 2 at the negative electrode of the liquid flow battery delivers hydrogen into the negative electrode of the battery in the battery charge and discharge unit 1 at a rate of 2 L / min, and the gas temperature is 80°C.

[0032] (4) The negative electrode hydrogen circulation unit 3 enables hydrogen to circulate between the negative electrode hydrogen production unit 2 of the liquid flow battery and the negative electrode of the battery at a rate of 2 L / min.

[0033] (5) The positive electrode gas production unit 6 of the liquid flow battery system delivers the positive electrode gas (oxygen) of the liquid flow battery system into the positive electrode of the battery in the battery charge and discharge unit 1 at a rate of 2 L / min, and the gas temperature is 80°C.

[0034] (6) The positive electrode circulation unit 4 realizes the circulation of positive electrode gas (oxygen) between the positive electrode gas production unit 6 and the positive electrode of the liquid flow battery at a rate of 2 L / min, and sends the product water generated during the operation of the battery to the product circulation unit 5. Among them, the positive electrode of the battery generates O2+4H + +4e - →2H2O reaction, the negative electrode of the battery produces 2H2→4H + +4e - reaction.

[0035] The discharge capacity of the battery is controlled by the charge and discharge instrument of the battery charge and discharge unit 1, and the battery can achieve long-term discharge under constant current, and the battery operating temperature is 80°C. Figure 2 As shown in the figure, the battery's discharge voltage at a constant current varies with changes in the flow rates of hydrogen at the negative electrode and oxygen at the positive electrode. As the hydrogen and oxygen supply increases, the discharge voltage at a constant discharge current (2A) gradually increases. Clearly, for the battery's charge and discharge units, increasing the gas supply significantly improves the battery's discharge capacity. Figure 3 The figure shows that the battery charge and discharge unit 1 maintains a constant current discharge during a charge and discharge cycle of the liquid flow battery system. Hydrogen begins to appear in the liquid flow battery system at the end of charging. The battery charge and discharge unit 1 quickly identifies the hydrogen and begins to discharge. As the amount of hydrogen in the liquid flow battery system accumulates, the battery charge and discharge unit 1 maintains a long period of hydrogen consumption. The liquid flow battery capacity monitoring unit 7 calculates the total consumption of pure hydrogen based on the discharge amount per unit time (30Ah) to be 12.58 L. Based on the 2H + +2V 2+ =2V 3+ +H2↑ determines that the valence state offset of the vanadium electrolyte in the flow battery system is 1.125 mol. An appropriate amount of recovery agent can then be added based on the degree of valence state offset.

[0036] Example 2 The liquid flow battery capacity monitoring and hydrogen online recovery system provided in Example 2 of the present invention is basically the same as the battery system in Example 1, except that the positive electrode gas is converted to chlorine for different liquid flow battery systems. + +2e - →2HCl reaction, the negative electrode of the battery produces H2→2H + +2e - reaction.

[0037] The membrane electrode structure used in the battery features an Ir-C catalyst for the positive electrode and a Pt-C catalyst for the negative electrode. The membrane is a polybenzimidazole (PBI) membrane. The battery operates at a temperature of 60°C, with the positive and negative electrode gas temperatures at 60°C.

[0038] Figure 4 The figure shows that the battery charge and discharge unit 1 maintains a constant current discharge during the two charge and discharge cycles of the liquid flow battery system. The liquid flow battery capacity monitoring unit 7 calculates the total consumption of pure hydrogen as 47.9L based on the total discharge volume (115Ah) in 4 cycles, and determines that the pure hydrogen consumption in a single cycle is 23.95L. + +2V 2+ =2V 3+ +H2↑ can clearly show that the valence state shift of the vanadium electrolyte in each cycle in the system is 1.07 mol. Therefore, an appropriate amount of recovery agent can be added according to the degree of valence state shift.

[0039] Example 3 The liquid flow battery capacity monitoring and hydrogen online recovery system provided in Example 3 of the present invention is basically the same as the battery system in Example 1, except that the positive electrode gas is converted to CO2 for different liquid flow battery systems. + +8e − →CH4+2H2O reaction, the negative electrode of the battery produces H2→2H + +2e - The battery used had an IrO2 catalyst at the positive electrode, a Pt-C catalyst at the negative electrode, and a polybenzimidazole (PBI) membrane. The battery operated at 80°C, with the positive and negative gas temperatures at 80°C.

[0040] Figure 5 The battery charge and discharge unit 1 maintains a constant current discharge during the two charge and discharge cycles of the liquid flow battery system. The liquid flow battery capacity monitoring unit 7 calculates the total consumption of pure hydrogen to be 12.58 L based on the total discharge volume (30 Ah) in the two cycles, and clarifies that the pure hydrogen consumption in a single cycle is 6.29 L. + +2V 2+ =2V 3+ +H2↑ can clearly show that the valence state shift of the vanadium electrolyte in each cycle in the system is 0.562 mol. Therefore, an appropriate amount of recovery agent can be added according to the degree of valence state shift.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A flow battery capacity monitoring and hydrogen online recovery system, characterized in that: include: A battery charge and discharge unit, wherein the battery charge and discharge unit comprises a charge and discharge battery, and the charge and discharge battery is a membrane electrode structure battery, comprising a negative electrode, a membrane and a positive electrode; A liquid flow battery negative electrode hydrogen production unit, which passes hydrogen gas released from the liquid flow battery electrolyte negative electrode storage tank into the negative electrode of the battery charge and discharge unit; A negative electrode hydrogen circulation unit, which circulates the remaining hydrogen after the battery charge and discharge unit battery reaction back to the negative electrode hydrogen production unit of the liquid flow battery; A liquid flow battery positive electrode gas production unit, which passes the positive electrode gas precipitated from the liquid flow battery electrolyte positive electrode storage tank into the positive electrode of the battery charge and discharge unit; A positive electrode circulation unit, which circulates the products generated by the battery charge and discharge unit battery reaction and the remaining positive electrode gas to the product circulation unit and the liquid flow battery positive electrode gas production unit respectively; A product circulation unit, which collects products generated by electrochemical reactions between positive and negative electrode gases in the battery charge and discharge unit; A liquid flow battery capacity monitoring unit calculates the liquid flow battery hydrogen production in real time according to the discharge amount of the battery charge and discharge unit, and infers the liquid flow battery electrolyte valence offset based on the hydrogen production, thereby obtaining the liquid flow battery capacity attenuation in real time.

2. A flow battery capacity monitoring and hydrogen online recovery system according to claim 1, characterized in that: The negative electrode of the charge-discharge battery is provided with a hydrogen inlet and a hydrogen outlet respectively connected to the negative electrode hydrogen production unit and the negative electrode hydrogen circulation unit of the liquid flow battery. The hydrogen output by the negative electrode hydrogen production unit of the liquid flow battery is introduced into the negative electrode through the hydrogen inlet, and after the battery reaction, it returns to the negative electrode hydrogen production unit of the liquid flow battery from the hydrogen outlet through the negative electrode hydrogen circulation unit; the positive electrode of the charge-discharge battery is provided with a positive electrode gas inlet and a product outlet respectively connected to the positive electrode gas production unit and the positive electrode circulation unit of the liquid flow battery. The positive electrode gas enters the positive electrode through the positive electrode gas production unit of the liquid flow battery. After the battery reaction, the product and unreacted gas are circulated to the product circulation unit and the positive electrode gas production unit of the liquid flow battery respectively through the positive electrode circulation unit.

3. A flow battery capacity monitoring and hydrogen online recovery system according to claim 1 or 2, characterized in that: The negative electrode includes a negative electrode flow channel plate, a negative electrode gas diffusion layer and a negative electrode catalyst; the positive electrode includes a positive electrode flow channel plate, a positive electrode gas diffusion layer and a positive electrode catalyst; wherein the flow channel plate material includes graphite material, conductive carbon material and metal plate; the flow channel includes parallel flow channels, serpentine flow channels or cross flow channels; the negative electrode gas diffusion layer and the positive electrode gas diffusion layer include carbon felt, carbon cloth and carbon paper.

4. A flow battery capacity monitoring and hydrogen online recovery system according to claim 3, characterized in that: The negative electrode catalyst includes a noble metal carbon-based catalyst, a noble metal alloy catalyst, a noble metal single atom catalyst or a non-noble metal catalyst; the positive electrode catalyst includes a noble metal carbon-based catalyst, a noble metal alloy catalyst or a metal oxide.

5. A flow battery capacity monitoring and hydrogen online recovery system according to claim 4, characterized in that: The noble metal carbon-based catalyst includes platinum carbon, iridium carbon, palladium carbon, ruthenium carbon or rhodium carbon; the noble metal alloy catalyst includes platinum ruthenium, platinum palladium, platinum rhodium, platinum cobalt, platinum iron, platinum gold, platinum silver, platinum nickel or ruthenium nickel; the noble metal single atom catalyst includes platinum single atom or iridium single atom; the non-noble metal catalyst includes nickel-molybdenum alloy, nickel-copper alloy, nickel single atom catalyst, nickel-nitrogen co-doped catalyst or tungsten carbide; the metal oxide includes ruthenium oxide, iridium oxide, platinum oxide, palladium oxide, cobalt oxide or nickel oxide.

6. A flow battery capacity monitoring and hydrogen online recovery system according to claim 3, characterized in that: The negative electrode catalyst and the positive electrode catalyst are both attached to the membrane or the gas diffusion layer by means of a binder; Preferably, the binder comprises at least one of perfluorosulfonic acid polyelectrolyte, sulfonated polyetheretherketone polyelectrolyte, sulfonated polysulfone polyelectrolyte, phosphated polybenzimidazole, quaternized polysulfone polyelectrolyte, polybenzimidazole polyelectrolyte, polyvinyl alcohol polyelectrolyte, heteropolyacid electrolyte or polytetrafluoroethylene.

7. A flow battery capacity monitoring and hydrogen online recovery system according to claim 1, characterized in that: The membrane between the negative electrode and the positive electrode of the charge-discharge battery includes a proton exchange membrane, an anion exchange membrane or a bipolar membrane; Preferably, the proton exchange membrane comprises a perfluorosulfonic acid membrane, a fluorinated polyetherketone membrane, a non-fluorinated sulfonic acid membrane, a polybenzimidazole membrane, a PTFE-reinforced composite membrane or a PVDF-reinforced composite membrane; the anion exchange membrane comprises an amino anion exchange membrane, a quaternary ammonium salt-based anion exchange membrane, an aromatic polymer-based anion exchange membrane, a polyethylene-based anion exchange membrane, a polypropylene-based anion exchange membrane or a quaternary ammonium salt-functionalized anion exchange membrane; Preferably, the thickness of the film between the negative electrode and the positive electrode of the charge-discharge battery is 20-300 μm.

8. The liquid flow battery capacity monitoring and hydrogen online recovery system according to claim 1, characterized in that: The gas flow rate of hydrogen entering the negative electrode of the liquid flow battery is 0.5~10 L / min, and the gas temperature is 20~80℃; the gas flow rate of gas entering the positive electrode of the liquid flow battery is 0.5~10 L / min, and the gas temperature is 20~80℃; the operating voltage window range of the charge and discharge battery is -1~1.6V; the operating temperature is 20~80℃.

9. A flow battery capacity monitoring and hydrogen online recovery system according to claim 1, characterized in that: The cathode gas includes at least one of oxygen, air, chlorine, carbon dioxide or carbon monoxide.

10. A flow battery capacity monitoring and hydrogen online recovery system according to claim 1, characterized in that: The flow battery includes an all-vanadium flow battery, an iron-vanadium flow battery, an iron-chromium flow battery, a vanadium-chromium flow battery, a zinc-bromine flow battery, a zinc-cerium flow battery, a vanadium-manganese flow battery or an all-iron flow battery.

Images