Oxygen gas supply redox flow battery system

Abstract

The present invention relates to an oxygen supply redox flow battery system, wherein the redox flow battery of the present invention comprises: a positive cell comprising a positive electrode and a positive electrolyte; a negative cell comprising a negative electrode and a negative electrolyte; an ion exchange membrane located between the positive cell and the negative cell; and an oxygen supply unit for supplying oxygen to the positive electrolyte; and may further comprise a water supply unit for supplying water to the positive electrolyte.

Description

Technology Field

[0001] The present invention relates to an oxygen supply redox flow battery system. Background Technology

[0003] To achieve sustainable development without carbon dioxide, the primary culprit of the greenhouse effect, there is growing interest in shifting away from conventional fossil fuel-based electricity production and utilizing abundant and renewable energy sources such as solar, wind, and geothermal energy. However, these energy sources have a significant drawback: while they are renewable, they do not provide a continuous supply throughout the year.

[0004] Accordingly, the importance of Energy Storage Systems (ESS) is increasing in order to resolve issues such as the intermittency of power generation and non-uniformity of power quality. For ESS to operate in conjunction with renewable energy, large capacity and high safety are essential characteristics that must be possessed, and an ESS that possesses both of these characteristics is the Redox Flow Battery (RFB) that operates in water systems.

[0005] RFBs offer the advantage of allowing the desired voltage and capacity to be freely set depending on the type of active material and electrolyte. Additionally, since the electrodes themselves do not react, their lifespan can be extended. The key factors influencing the performance of RFBs are primarily the electrodes, ion exchange membranes, and the electrolyte and the active material dissolved therein. In particular, the active material is a critical element that determines the core characteristics of redox flow batteries, such as voltage, capacity, and electrolyte conditions.

[0006] The most widely known RFB is the all-vanadium redox flow battery (V-RFB), which uses vanadium active material for both the cathode and anode. Although it offers excellent performance, the active material (vanadium) is expensive and has limitations in terms of voltage. For these reasons, various iron-based active materials are being researched to improve the performance and reduce the cost of redox flow batteries.

[0007] Iron-based redox flow batteries (Fe-RFBs) generate a potential difference between the negative and positive electrodes by combining iron ions with various coordination compounds to create a potential difference between the negative and positive electrodes.

[0008] Potassium ferrocyanide is the most widely used anode for Fe-RFB. Potassium ferrocyanide is Fe 3+ and CN - Although it is a coordination compound and is the positive active material with the highest positive potential available for use in water systems to date, there is a limit to improving the battery capacity due to the low self-solubility of potassium ferrocyanide. The problem to be solved

[0010] One objective of the present invention is to increase the capacity of a redox flow battery by using an active material of the positive electrode and a positive electrode electron transfer medium.

[0011] Another objective of the present invention is to increase the capacity of a redox flow battery by additionally supplying oxygen as an active material to provide electrons to an electron transfer medium.

[0012] Another objective of the present invention is to supply humid oxygen to the anode electrolyte to prevent a decrease in redox flow battery capacity caused by the evaporation of the anode electrolyte.

[0013] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0015] A redox flow battery according to one embodiment of the present invention comprises: a positive cell comprising a positive electrode and a positive electrolyte; a negative cell comprising a negative electrode and a negative electrolyte; an ion exchange membrane located between the positive cell and the negative cell; and an oxygen supply unit that supplies oxygen to the positive electrolyte.

[0016] A redox flow battery according to one embodiment of the present invention may further include a water supply unit that supplies water to the anode electrolyte.

[0017] The above oxygen supply unit may supply moist oxygen.

[0018] The anode electrolyte comprises a positive electrolyte, a positive active material, and a positive electron transfer medium, and the cathode electrolyte comprises a negative electrolyte and a cathode active material, and the anode electron transfer medium comprises BIS-TRIS (2-bis(2-hydroxyethyl)amino-2-(hydroxymethyl)-1,3-propanediol), MES (2-(N-morpholino)ethanesulfonic acid), ADA (N-(2-acetamido)iminodiacetic acid), PIPES (piperazine-N,N'-bis(2-ethanesulfonic acid), ACES (N-(2-acetamido)-2-aminoethanesulfonic acid), BES (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), MOPS (3-(N-morpholino)propanesulfonic acid). The mixture comprises at least one selected from the group consisting of TES (N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid), HEPES (N-2-hydroxyethyl-piperazine-N'-2-ethanesulfonic acid), DIPSO (3-(N,N-bis[2-hydroethyl]amino)-2-hydroxypropanesulfonic acid), TEA (triethanolamine), and TiPA (triisopropanolamine); and a cobalt (Co)-based material; wherein the negative electrode active material is a mixture of BIS-TRIS (2-bis(2-hydroxyethyl)amino-2-(hydroxymethyl)-1,3-propanediol), MES (2-(N-morpholino)ethanesulfonic acid), ADA (N-(2-acetamido)iminodiacetic acid), PIPES (piperazine-N,N'-bis(2-ethanesulfonic acid), It may be a mixture of at least one selected from the group consisting of ACES (N-(2-acetamido)-2-aminoethanesulfonic acid), BES (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), MOPS (3-(N-morpholino)propanesulfonic acid), TES (N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid), HEPES (N-2-hydroxyethyl-piperazine-N'-2-ethanesulfonic acid), DIPSO (3-(N,N-bis[2-hydroethyl]amino)-2-hydroxypropanesulfonic acid), TEA (triethanolamine) and TiPA (triisopropanolamine); and an iron (Fe)-based material.

[0019] A redox flow battery according to one embodiment of the present invention further comprises a measuring unit for the remaining amount of anode electrolyte of the anode cell; and when the remaining amount of anode electrolyte measured by the measuring unit is less than a set amount, water may be supplied to the anode electrolyte or humidified oxygen may be supplied. Effects of the invention

[0021] According to the redox flow battery of the present invention, the capacity of the battery can be increased by using oxygen as a positive electrode active material. Since oxygen as a positive electrode active material can be continuously supplied and used up to the maximum solubility of the negative electrode active material, the capacity of the redox flow battery can be increased. In particular, the decrease in capacity of the redox flow battery caused by the loss of electrolyte due to the evaporation of the electrolyte can be prevented by supplying moisture or humid oxygen. Brief explanation of the drawing

[0023] FIG. 1 is a schematic diagram showing the configuration of a redox flow battery including an oxygen supply unit that supplies oxygen to an anode electrolyte according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of a redox flow battery according to another embodiment of the present invention, comprising an oxygen supply unit that supplies oxygen to the anode electrolyte and a water supply unit that supplies water to the anode electrolyte. FIG. 3 is a schematic diagram showing the configuration of a redox flow battery including an oxygen supply unit that supplies moist oxygen, according to another embodiment of the present invention. FIG. 4 is a schematic diagram showing the configuration of a redox flow battery including a residual amount of anode electrolyte measuring unit for measuring the residual amount of anode electrolyte of an anode cell according to another embodiment of the present invention. FIG. 5 is a graph showing the relative humidity of oxygen injected into a positive electrolyte storage container (tank) according to the state of oxygen supplied during the operation of the redox flow battery of the present invention (dry oxygen / wet oxygen). Specific details for implementing the invention

[0024] Hereinafter, embodiments are described in detail with reference to the attached drawings. However, various modifications may be made to the embodiments, and thus the scope of the patent application is not limited or restricted by these embodiments. It should be understood that all modifications, equivalents, and substitutions to the embodiments are included within the scope of the rights.

[0025] The terms used in the embodiments are for illustrative purposes only and should not be interpreted as intended to be limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0026] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the embodiments pertain. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0027] In addition, when describing with reference to the attached drawings, identical components are assigned the same reference numeral regardless of drawing symbols, and redundant descriptions thereof are omitted. In describing the embodiments, if it is determined that a detailed description of related prior art could unnecessarily obscure the essence of the embodiments, such detailed description is omitted.

[0028] In addition, terms such as first, second, A, B, (a), (b), etc. may be used when describing the components of the embodiments. These terms are used merely to distinguish the components from other components, and the essence, order, or sequence of the components is not limited by the terms.

[0029] Components included in any one embodiment and components having common functions shall be described using the same names in other embodiments. Unless otherwise stated, the description in any one embodiment may also apply to other embodiments, and specific descriptions shall be omitted to the extent of overlap.

[0031] Hereinafter, the redox flow battery of the present invention will be described in detail with reference to the embodiments and drawings. However, the present invention is not limited to these embodiments and drawings.

[0033] A redox flow battery according to one embodiment of the present invention comprises: a positive cell comprising a positive electrode and a positive electrolyte; a negative cell comprising a negative electrode and a negative electrolyte; an ion exchange membrane located between the positive cell and the negative cell; and an oxygen supply unit that supplies oxygen to the positive electrolyte.

[0034] In the redox flow battery of the present invention, when charging the redox flow battery, an oxygen evolution reaction occurs at the positive electrode and a reduction reaction of the active material occurs at the negative electrode; when discharging the redox flow battery, a reduction reaction of the positive electron transport medium occurs at the positive electrode and an oxidation reaction of the active material occurs at the negative electrode; and when oxygen is supplied to the positive electrode, the reduced positive electron transport medium reacts with oxygen in the electrolyte storage tank to return to a charged state.

[0035] FIG. 1 is a schematic diagram showing the configuration of a redox flow battery including an oxygen supply unit that supplies oxygen to an anode electrolyte according to one embodiment of the present invention.

[0036] Referring to FIG. 1, a redox flow battery according to one embodiment of the present invention comprises a positive cell including a positive electrode and a positive electrolyte, a negative cell including a negative electrode and a negative electrolyte, and an ion exchange membrane located between the positive cell and the negative cell.

[0037] In addition, the redox flow battery of the present invention includes an oxygen supply unit that supplies oxygen to the anode electrolyte.

[0038] In one embodiment, the anode electrolyte may comprise a positive electrolyte, a positive active material, and a positive electron transfer medium, and the positive active material may comprise oxygen.

[0039] In one embodiment, the oxygen may be supplied from air or may be supplied as pre-prepared oxygen. The air is not limited to atmospheric air and may include a combination of gases containing oxygen or pure oxygen gas.

[0040] When oxygen is used as the above-mentioned positive electrode active material, it has a significant advantage in terms of potential because the maximum positive potential available in an aqueous system can be utilized. However, the voltage actually obtained from the electrochemical reaction of oxygen falls far short of the theoretical value. In the present invention, by using a positive electrode electron transfer medium, the potential of oxygen can be sacrificed to eliminate overvoltage.

[0041] The redox flow battery of the present invention can increase battery capacity by using oxygen as the positive electrode active material. Compared to potassium ferrocyanide, which has low solubility, oxygen can be continuously supplied and utilized up to its maximum solubility, thereby increasing battery capacity. Furthermore, it is possible to design an Fe-RFB capable of operating at high capacity, which can increase the utilization of Fe-RFB.

[0042] As an example, the redox flow battery of the present invention may have a positive electrode and a negative electrode formed on a current collector. As the positive and negative current collectors, a porous material such as a network or mesh shape may be used to rapidly facilitate the diffusion of oxygen, and porous metal plates such as stainless steel, nickel, or aluminum, or porous carbon paper may be used, but are not limited thereto. The current collector may be coated with an oxidation-resistant metal or alloy film to prevent oxidation.

[0044] A redox flow battery according to one embodiment of the present invention may further include a water supply unit that supplies water to the anode electrolyte.

[0045] The redox flow battery of the present invention is a system of an iron-oxygen redox flow battery among electrochemical energy storage devices, and may utilize a cobalt-based electron transfer medium to utilize oxygen as an active material, and may supply continuous moist oxygen to maintain stable performance.

[0046] FIG. 2 is a schematic diagram showing the configuration of a redox flow battery according to another embodiment of the present invention, comprising an oxygen supply unit that supplies oxygen to the anode electrolyte and a water supply unit that supplies water to the anode electrolyte.

[0047] Referring to FIG. 2, as one method of supplying moisture to the anode electrolyte, moisture may be supplied separately from the oxygen supplied to the anode electrolyte. Through this, the moisture content in the electrolyte can be maintained to minimize the degradation of battery performance.

[0048] Since the performance of iron-oxygen redox flow batteries containing cobalt-based electron transfer media varies significantly depending on the presence or absence of oxygen, a continuous and effective supply of oxygen is critical. Furthermore, particularly, anode electrolytes using iron-based compounds are vulnerable to contact with oxygen, and if external oxygen is supplied directly to the anode electrolyte, which requires oxygen, electrolyte imbalance may occur due to the evaporation of moisture from the anode electrolyte. To manage this, moisture may be supplied as a method to prevent electrolyte imbalance caused by evaporation and to continuously supply oxygen.

[0050] The above oxygen supply unit may supply moist oxygen. In a system using an anode electrolyte containing a cobalt-based electron transfer medium in an iron-oxygen redox flow battery, oxygen may be continuously supplied to the anode electrolyte during operation to sustain the oxygen reduction reaction, and in supplying moisture for this purpose, moist oxygen may be introduced into the anode electrolyte. Through this, the moisture content of the anode electrolyte can be maintained to improve the operating efficiency of the redox flow battery.

[0051] FIG. 3 is a schematic diagram showing the configuration of a redox flow battery including an oxygen supply unit that supplies moist oxygen, according to another embodiment of the present invention.

[0052] By supplying moist oxygen, oxygen and moisture may be supplied simultaneously to the anode electrolyte, and the device can be simplified as separate oxygen and moisture supply devices are not required. In addition, the oxygen and moisture content in the moist oxygen may be controlled as needed.

[0053] The anode electrolyte comprises a positive electrolyte, a positive active material, and a positive electron transfer medium, and the cathode electrolyte comprises a negative electrolyte and a cathode active material, and the anode electron transfer medium comprises BIS-TRIS (2-bis(2-hydroxyethyl)amino-2-(hydroxymethyl)-1,3-propanediol), MES (2-(N-morpholino)ethanesulfonic acid), ADA (N-(2-acetamido)iminodiacetic acid), PIPES (piperazine-N,N'-bis(2-ethanesulfonic acid), ACES (N-(2-acetamido)-2-aminoethanesulfonic acid), BES (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), MOPS (3-(N-morpholino)propanesulfonic acid). The mixture comprises at least one selected from the group consisting of TES (N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid), HEPES (N-2-hydroxyethyl-piperazine-N'-2-ethanesulfonic acid), DIPSO (3-(N,N-bis[2-hydroethyl]amino)-2-hydroxypropanesulfonic acid), TEA (triethanolamine), and TiPA (triisopropanolamine); and a cobalt (Co)-based material; wherein the negative electrode active material is a mixture of BIS-TRIS (2-bis(2-hydroxyethyl)amino-2-(hydroxymethyl)-1,3-propanediol), MES (2-(N-morpholino)ethanesulfonic acid), ADA (N-(2-acetamido)iminodiacetic acid), PIPES (piperazine-N,N'-bis(2-ethanesulfonic acid), It may be a mixture of at least one selected from the group consisting of ACES (N-(2-acetamido)-2-aminoethanesulfonic acid), BES (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), MOPS (3-(N-morpholino)propanesulfonic acid), TES (N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid), HEPES (N-2-hydroxyethyl-piperazine-N'-2-ethanesulfonic acid), DIPSO (3-(N,N-bis[2-hydroethyl]amino)-2-hydroxypropanesulfonic acid), TEA (triethanolamine) and TiPA (triisopropanolamine); and an iron (Fe)-based material.

[0054] As an example, the ion exchange membrane may comprise at least one selected from the group consisting of Nafion-based materials, porous organic-inorganic materials, polyolefins, polytetrafluoroethylene, polyetheretherketones, polysulfones, polyimides, and polyamideimides.

[0055] As an example, when charging the above redox flow battery, an oxygen evolution reaction may occur at the positive electrode and a reduction reaction of the active material may occur at the negative electrode.

[0056] As an example, during the discharge of the redox flow battery, a reduction reaction of the positive electron transport medium occurs at the positive electrode and an oxidation reaction of the active material occurs at the negative electrode, and when oxygen is supplied to the positive electrode, the reduced positive electron transport medium may react with oxygen in the electrolyte storage tank to return to a charged state.

[0057] For example, when Fe(BIS-TRIS) is used as the negative electrode active material, oxygen is used as the positive electrode active material, and Co(TiPA) is used as the positive electrode electron transfer medium, the charge / discharge mechanism may be as follows.

[0058] Charging: (Cathode) Fe(III)(BIS-TRIS) + e - → Fe(II)(BIS-TRIS); (Anode) 4OH - → O2 + 2H2O + 4e -

[0059] Discharge : (Cathode) Fe(II)(BIS-TRIS) → Fe(III)(BIS-TRIS) + e - ; (Anode) Co(Ⅲ)(TiPA) + e- → Co(Ⅱ)(TiPA)Co(Ⅱ)(TiPA) + O2+ 2H2O → Co(Ⅲ)(TiPA) + 4OH -

[0060] When charging, the reduction reaction of the active material (Fe 3+ → Fe 2+) may occur and an oxygen evolution reaction may take place at the anode, and during discharge, an oxidation reaction of the active material occurs at the cathode (Fe 2+ → Fe 3+ ) may be occurring. At the anode, the reduction reaction of the anode electron transport mediator (Co 3+ → Co 2+ ) may be occurring. In this case, if oxygen is supplied to the anode, the reduced anode electron transport medium (Co 2+ ) reacts with oxygen in the electrolyte storage tank to return to a charged state (Co 2+ + O2→ Co 3+ It could be that it returns to ).

[0062] A redox flow battery according to one embodiment of the present invention further comprises a measuring unit for the remaining amount of anode electrolyte of the anode cell; and when the remaining amount of anode electrolyte measured by the measuring unit is less than a set amount, water may be supplied to the anode electrolyte or humidified oxygen may be supplied.

[0063] FIG. 4 is a schematic diagram showing the configuration of a redox flow battery including a residual amount of anode electrolyte measuring unit for measuring the residual amount of anode electrolyte of an anode cell according to another embodiment of the present invention.

[0064] Referring to FIG. 4, the tank in which the anode electrolyte is stored may include a remaining amount measuring unit capable of measuring the remaining amount of the anode electrolyte on the side thereof, provided that FIG. 4 is merely an example and the installation location of the remaining amount measuring unit may be varied.

[0065] In addition, the above-mentioned anode electrolyte remaining amount measuring unit may be a simple level sensor, or it may measure the position by reacting with the remaining anode electrolyte.

[0066] Water may be supplied when the remaining anode electrolyte is less than the amount set according to the remaining amount of anode electrolyte measured by the above-mentioned anode electrolyte remaining amount measuring unit. The water supply unit may be automatically controlled in conjunction with the above-mentioned anode electrolyte remaining amount measuring unit.

[0067] Furthermore, since battery performance may be degraded if a difference occurs between the cathode electrolyte and the anode electrolyte, the present invention further includes a cathode electrolyte remaining amount measuring unit for measuring the remaining amount in the cathode electrolyte storage tank, and if the value measured by the anode electrolyte remaining amount measuring unit differs from the value measured by the cathode electrolyte remaining amount measuring unit by more than a certain level, it may be that water is being supplied.

[0069] As an example, a cathode using oxygen as the cathode active material may include a conductive material, and said conductive material may be porous. For example, it may be a porous carbon-based material. The carbon-based material may be carbon black, graphite, graphene, carbon nanotubes, activated carbon, carbon fiber, etc. Additionally, the conductive material may include metallic conductive materials such as metal fibers or metal mesh; metallic powders such as copper, silver, nickel, or aluminum; or organic conductive materials such as polyphenylene derivatives. The said conductive materials may be used alone or in combination.

[0071] The present invention will be described in detail below with reference to the following examples and comparative examples. However, the technical scope of the present invention is not limited or restricted by them.

[0073] Examples

[0074] A redox flow battery was constructed using 0.2 M Fe(BIS-TRIS) as the negative active material, oxygen as the positive active material, and Co(TiPA) as the positive electron transfer medium.

[0075] 30 mL of a solution containing 2.2 M KOH was used as the anode electrolyte, and 40 mL of a solution containing 1.0 M KOH was used as the cathode electrolyte.

[0076] Graphite felt was used as the cathode and anode electrodes, Nafion 115 was used as the separator, and the electrode area was 2 cm². It was made to × 2 cm.

[0077] Carbon was used as the cathode and anode pair plates. Gold-coated copper plates were used as the cathode and anode current collectors.

[0078] The supply flow rate of dry oxygen was 100 cc / min to 300 cc / min, and the humidity of dry oxygen was RH 0% to 5%.

[0079] Dry oxygen was supplied through a humidification system, and the humidity of the humid oxygen was RH 70% to 100%.

[0081] The humidity of the oxygen supplied in the above example is shown in FIG. 5. FIG. 5 is a graph showing the relative humidity of oxygen injected into the anode electrolyte storage container (tank) according to the state of oxygen supplied (dry oxygen / wet oxygen) during the operation of the redox flow battery of the present invention. It was confirmed that wet oxygen with a relative humidity of 80% or higher is supplied immediately upon supply of wet oxygen.

[0083] Although the embodiments have been described above with reference to the limited drawings, those skilled in the art can apply various technical modifications and variations based on the above. For example, suitable results may be achieved even if the described techniques are performed in a different order than described, and / or if the components of the described system, structure, device, circuit, etc. are combined or assembled in a form different from described, or replaced or substituted by other components or equivalents.

[0084] Therefore, other implementations, other embodiments, and equivalents to the claims also fall within the scope of the claims set forth below.

Claims

Claim 1 A redox flow battery comprising: an anode cell including an anode and an anode electrolyte; a cathode cell including a cathode and a cathode electrolyte; an ion exchange membrane located between the anode cell and the cathode cell; and an oxygen supply unit supplying oxygen to the anode electrolyte. Claim 2 A redox flow battery comprising, in claim 1, a water supply unit for supplying water to the anode electrolyte. Claim 3 A redox flow battery according to claim 1, wherein the oxygen supply unit supplies humid oxygen. Claim 4 In claim 1, the anode electrolyte comprises a positive electrolyte, a positive active material, and a positive electron transfer medium, and the cathode electrolyte comprises a negative electrolyte and a cathode active material, and the anode electron transfer medium comprises BIS-TRIS (2-bis(2-hydroxyethyl)amino-2-(hydroxymethyl)-1,3-propanediol), MES (2-(N-morpholino)ethanesulfonic acid), ADA (N-(2-acetamido)iminodiacetic acid), PIPES (piperazine-N,N'-bis(2-ethanesulfonic acid), ACES (N-(2-acetamido)-2-aminoethanesulfonic acid), BES (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), MOPS (3-(N-morpholino)propanesulfonic acid). The mixture comprises at least one selected from the group consisting of TES (N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid), HEPES (N-2-hydroxyethyl-piperazine-N'-2-ethanesulfonic acid), DIPSO (3-(N,N-bis[2-hydroethyl]amino)-2-hydroxypropanesulfonic acid), TEA (triethanolamine), and TiPA (triisopropanolamine); and a cobalt (Co)-based material; wherein the negative electrode active material is a mixture of BIS-TRIS (2-bis(2-hydroxyethyl)amino-2-(hydroxymethyl)-1,3-propanediol), MES (2-(N-morpholino)ethanesulfonic acid), ADA (N-(2-acetamido)iminodiacetic acid), PIPES (piperazine-N,N'-bis(2-ethanesulfonic acid), A redox flow cell comprising at least one selected from the group consisting of ACES (N-(2-acetamido)-2-aminoethanesulfonic acid), BES (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid), MOPS (3-(N-morpholino)propanesulfonic acid), TES (N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid), HEPES (N-2-hydroxyethyl-piperazine-N'-2-ethanesulfonic acid), DIPSO (3-(N,N-bis[2-hydroethyl]amino)-2-hydroxypropanesulfonic acid), TEA (triethanolamine) and TiPA (triisopropanolamine); and a mixture of an iron (Fe)-based material. Claim 5 A redox flow battery according to claim 1, further comprising a remaining amount measuring unit of the anode electrolyte of the anode cell; wherein, when the remaining amount of the anode electrolyte measured by the remaining amount measuring unit is less than a set amount, moisture is supplied to the anode electrolyte or humidified oxygen is supplied.

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