Redox-mediated electrolysis cell, redox-mediated secondary battery cell, dynamic regenerative redox-mediated electrolysis cell, redox-mediated electrolysis device, redox-mediated rechargeable metal-air battery, and method for producing hydrogen

Abstract

Provided are: a redox-mediated electrolysis cell which is capable of lowering overvoltage at the anode side; a redox-mediated secondary battery cell; a dynamic regenerative redox-mediated electrolysis cell; a redox-mediated electrolysis device; and a method for producing hydrogen. A redox-mediated electrolysis cell according to the present invention is provided with a first anode, a first cathode, a first anode electrolyte solution, a first cathode electrolyte solution, and a first diaphragm that separates the first anode electrolyte solution and the first cathode electrolyte solution from each other. The first anode electrolyte solution contains a redox-mediated reduced form. At the first anode, the oxidation potential of the redox-mediated reduced form is lower than the oxygen generation potential.

Description

Redox-mediated electrolytic cell, redox-mediated secondary battery cell, dynamically regenerated redox-mediated electrolytic cell, redox-mediated electrolytic device, redox-mediated rechargeable metal-air battery, and hydrogen production method.

[0001] The present invention relates to a redox-mediated electrolytic cell, a redox-mediated secondary battery cell, a dynamically regenerated redox-mediated electrolytic cell, a redox-mediated electrolytic device, a redox-mediated rechargeable metal-air battery, and a method for producing hydrogen. This application claims priority based on Japanese Patent Application No. 2025-053459, filed in Japan on March 27, 2025, the contents of which are incorporated herein by reference.

[0002] In recent years, hydrogen produced using renewable energy has attracted attention as a clean energy source to address issues such as global warming. However, hydrogen production using renewable energy requires costs comparable to those of conventional hydrogen production through fossil fuel reforming. Therefore, hydrogen production using renewable energy requires a high level of energy efficiency and inexpensive equipment that could not be achieved with conventional technologies. One hydrogen production method that can meet these requirements is the electrolysis of water (water electrolysis).

[0003] Electrolytic cell units (water electrolysis cells) used in water electrolysis typically consist of an oxygen electrode (anode), a hydrogen electrode (cathode), and an ion-permeable diaphragm (diaphragm) separating the oxygen and hydrogen electrodes. When an electric current is applied, oxygen is generated at the oxygen electrode and hydrogen is generated at the hydrogen electrode. The main factors contributing to power loss in water electrolysis include overpotential in the oxygen evolution reaction (OER) at the oxygen electrode, overpotential at the hydrogen electrode, ohmic loss in the ion-permeable diaphragm, and ohmic loss due to the structural resistance of the electrolytic cells constituting the electrolytic cell unit. Reducing these power losses makes it possible to lower the power consumption per unit of hydrogen production.

[0004] In typical water electrolysis, power loss due to overvoltage at the oxygen electrode accounts for a significant portion, approximately 60%, of the total power loss. Therefore, methods to reduce the overvoltage at the oxygen electrode are attracting attention as a way to minimize power loss in water electrolysis equipment.

[0005] In water electrolysis for hydrogen production, catalysts using high-cost rare elements such as Ir are used to reduce the influence caused by the overpotential of the oxygen evolution reaction on the oxygen electrode (anode) side (see, for example, Patent Document 1).

[0006] On the other hand, similar to the water electrolysis reaction, reduction of OER overpotential is also important in other electrochemical reactions accompanied by an electrolytic reduction reaction at the cathode. For example, in electrolytic cells utilizing reactions such as electrochemical carbon dioxide reduction and electrochemical nitrogen reduction, it is required to reduce the overpotential of the oxygen electrode in order to reduce power loss.

[0007] Japanese Unexamined Patent Publication No. 10-52641

[0008] When a catalyst using high-cost rare elements such as Ir is used, there has been a problem that the equipment cost for water electrolysis increases. Therefore, there is a demand for a method of reducing the overpotential on the anode side at low cost without resource constraints.

[0009] The present invention has been made in view of the above problems, and aims to provide a redox-mediated electrolytic cell, a redox-mediated secondary battery cell, a dynamically regenerated redox-mediated electrolytic cell, a redox-mediated electrolysis apparatus, a redox-mediated rechargeable metal-air battery, and a method for producing hydrogen that can reduce overpotential by blending a reduced form of redox mediator having an oxidation potential lower than the oxygen evolution potential into an electrolytic solution. Another object of the present invention is to provide a dynamically regenerated redox-mediated electrolytic cell incorporating a mechanism for chemically and electrochemically regenerating oxidized redox species.

[0010] In order to solve the above problems, the present invention provides the following means.

[0011] [1] A redox-mediated electrolytic cell comprising: a first anode; a first cathode; a first anode electrolyte; a first cathode electrolyte; and a first diaphragm separating the first anode electrolyte and the first cathode electrolyte, wherein the first anode electrolyte contains a redox-mediated reduced form, and in the first anode, the oxidation potential of the redox-mediated reduced form is lower than the oxygen evolution potential. [2] The redox-mediated electrolytic cell according to [1], wherein at least the redox-mediated reduced form is a water-soluble organic compound. [3] The redox-mediated electrolytic cell according to [2], wherein the organic compound is a reduced form of a compound having a quinone structure. [4] The redox-mediated electrolytic cell according to [3], wherein the compound having a quinone structure is at least one compound selected from the group consisting of compounds represented by the following formulas (1) to (10). (In formulas (1) to (10), each aromatic ring may have substituents independently. If there is one or more substituents in the same formula, at least one substituent is hydrophilic. If there is two or more substituents in the same formula, the substituents may be the same or different.) [5] The redox-mediated electrolytic cell according to any one of [1] to [4], wherein the open-circuit potential (0A) of the first anode is 0.5 or more and 2.0 or less with respect to a standard hydrogen electrode (SHE). [6] The redox-mediated electrolytic cell according to any one of [1] to [5], further comprising: a first anode chamber containing the first anode electrode and a first anode electrolyte; a flow cell composed of at least one part of a transparent material; a circulation means for circulating the electrolyte between the first anode chamber and the flow cell; and an ultraviolet-visible light source. [7] A redox-mediated secondary battery cell comprising: a second cathode; a second anode; a second cathode electrolyte; a second anode electrolyte; and a second diaphragm separating the second cathode electrolyte and the second anode electrolyte, wherein the second cathode electrolyte contains a redox-mediated oxidizing agent; in a discharge state, the redox-mediated oxidizing agent is reduced in the second cathode to a redox-mediated reduced agent; in a charge state, the redox-mediated reduced agent is oxidized in the second cathode to a redox-mediated oxidizing agent; and in the second cathode, the oxidation potential of the redox-mediated reduced agent (oxidation-reduction agent) is lower than the oxygen evolution potential. [8] A dynamically regenerated redox-mediated electrolytic cell comprising a redox-mediated electrolytic cell according to any one of [1] to [6] and a redox-mediated secondary battery cell according to [7], wherein the first anode of the redox-mediated electrolytic cell and the second cathode of the redox-mediated electrolytic cell are placed in a common electrolyte, the common electrolyte is used as the first anode electrolyte of the redox-mediated electrolytic cell and as the second cathode electrolyte of the redox-mediated secondary battery cell, and the redox-mediated reduced form of the redox-mediated electrolytic cell is the same as the redox-mediated reduced form of the redox-mediated secondary battery cell.[9] A redox-mediated electrolysis apparatus, comprising: the redox-mediated electrolysis cell according to any one of [1] to [6]; and a voltage applicator that applies a voltage between the first cathode and the first anode.

[10] A method for producing hydrogen, characterized by using the redox-mediated electrolysis apparatus according to [9].

[11] A redox-mediated electrolysis apparatus, comprising: the redox-mediated electrolysis cell according to [8]; and a voltage applicator that applies a voltage between the first cathode and the first anode.

[12] A method for producing hydrogen, characterized by using the redox-mediated electrolysis apparatus according to

[11] .

[13] A redox-mediated rechargeable metal-air battery comprising the redox-mediated electrolysis cell according to any one of [1] to [6] and a metal-air battery cell, wherein the metal-air battery cell comprises a positive electrode including an air electrode, a negative electrode including a metal (M), and an electrolyte containing the metal (M) ions, and a first cathode electrolyte of the redox-mediated electrolysis cell contains the metal (M) ions.

[0012] According to the present invention, there can be provided a redox-mediated electrolysis cell, a redox-mediated secondary battery cell, a dynamically regenerated redox-mediated electrolysis cell, a redox-mediated electrolysis apparatus, a redox-mediated rechargeable metal-air battery, and a method for producing hydrogen that are capable of reducing overpotential on the anode side.

[0013] It is a schematic diagram showing a redox-mediated electrolysis cell according to an embodiment of the present invention (when the first cathode is a hydrogen generation electrode). It is a schematic diagram showing a conventional water electrolysis cell. It is a schematic diagram showing a comparison of electrolytic overpotential between a redox-mediated secondary battery cell of an embodiment of the present invention and a conventional water electrolysis cell. It is a schematic diagram showing a redox-mediated secondary battery cell according to an embodiment of the present invention. It is a schematic diagram showing a dynamically regenerated redox-mediated electrolysis cell according to an embodiment of the present invention (when the first cathode is a hydrogen generation electrode). It is a diagram showing measurement results of current and voltage when the applied voltage between the first cathode and the first anode is swept in a range from 0 V to 4.0 V in Examples 1 to 2 and Comparative Example 1. In Example 3, the applied current between the second cathode and the second anode ranges from 0 mA / cm ２ to 3.0 mA / cm ２This figure shows the measurement results of current and voltage when sweeping within the specified range. This figure shows the measurement results of current and voltage when sweeping between the cathode and anode in the range of 0V to 4.0V with the applied voltage relative to the reversible hydrogen electrode (RHE) in Example 4 and Comparative Example 2. This figure shows the measurement results of current and voltage when sweeping between the cathode and anode in the range of 0V to 4.0V with the applied voltage relative to the reversible hydrogen electrode (RHE) in Example 5 and Comparative Example 3. This figure shows the measurement results of current and voltage when sweeping between the cathode and anode in the range of 0V to 4.0V with the applied voltage relative to the reversible hydrogen electrode (RHE) in Example 6 and Comparative Example 4. This figure shows the measurement results of current density when 1.5V is applied in each measurement when sweeping between the cathode and anode up to 8 times in the range of 0V to 4.0V with the applied voltage relative to the reversible hydrogen electrode (RHE) in Example 7 and Comparative Example 5. This is a schematic diagram showing the redox-mediated rechargeable metal-air battery of this embodiment. This is a schematic diagram showing the charge state of the redox-mediated rechargeable metal-air battery of this embodiment. This is a schematic diagram showing the discharge state of the redox-mediated rechargeable metal-air battery of this embodiment. This is a schematic diagram showing the regenerated redox-mediated electrolytic cell (flow cell) of Example 8. This is a diagram showing the evaluation results of Example 8, Example 9, and Comparative Example 6. This is a diagram showing the conversion of BQ to HQ by photoreduction in an acidic solution. This is a diagram showing the conversion of BQ to HQ by photoreduction in a neutral solution. This is a diagram showing the relationship between the attenuation of BQ by photoreduction and the light irradiation time. This is a schematic diagram showing the electrolytic cells of Example 10, Example 11, and Comparative Example 7. This is a diagram showing the measurement results of current and voltage when the applied voltage between the cathode and anode was swept in the range of 0V to 4.0V with respect to the reversible hydrogen electrode (RHE) in Example 10 and Comparative Example 7. This figure shows the measurement results of current and voltage when the applied voltage between the cathode and anode was swept in the range of 0V to 4.0V relative to the reversible hydrogen electrode (RHE) in Example 11 and Comparative Example 8. This is a schematic diagram showing the apparatus of Example 12 for verifying the effect of a redox-mediated charging type metal-air battery. In Example 12, the applied current was 0mA / cm between the first cathode (zinc negative electrode) and the first anode, and between the air electrode (positive electrode) and the zinc negative electrode. ２ ~20 mA / cm ２This figure shows the measurement results of current and voltage when swept within the range. This is a schematic diagram showing the apparatus of Comparative Example 9, which compares the effects of redox-mediated charging metal-air batteries. In Comparative Example 9, the applied current between the air electrode (positive electrode) and the zinc negative electrode is 0 mA / cm². ２ ~20 mA / cm ２ This figure shows the measurement results of current and voltage when sweeping within the specified range. This figure shows the measurement results of current and voltage when the applied voltage between the cathode and anode was swept within the range of 0.5V to 2.5V with respect to the reversible hydrogen electrode (RHE) in Example 13, Comparative Example 10, and Comparative Example 11.

[0014] The present embodiment will be described in detail below with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience to clearly illustrate the features of the present invention, and the dimensional ratios of each component may differ from those in reality. The materials, dimensions, etc., exemplified in the following description are examples only, and the present invention is not limited to them. It can be implemented with appropriate modifications without altering its essence.

[0015] (Redox-mediated electrolytic cell) A redox-mediated electrolytic cell according to one embodiment of the present invention comprises a first anode, a first cathode, a first anode electrolyte, a first cathode electrolyte, and a first diaphragm separating the first anode electrolyte and the first cathode electrolyte. The first anode electrolyte contains a redox-mediated reducing form. In the first anode, the oxidation potential of the redox-mediated reducing form is lower than the oxygen evolution potential. In the redox-mediated electrolytic cell of this embodiment, since the first anode electrolyte contains a redox-mediated reducing form (Re), on the first anode side, the reduced form (Re) is oxidized by the oxidation reaction (ReOR) of the redox-mediated reducing form (Re), and a redox-mediated oxidized form (Ox) is produced.

[0016] In the redox-mediated electrolytic cell of this embodiment, the electrochemical reaction on the first cathode side is not particularly limited and can include, for example, a hydrogen evolution reaction, a carbon dioxide reduction reaction, a nitrogen reduction reaction, and so on. That is, the redox-mediated electrolytic cell of this embodiment can be used as a redox-mediated water electrolytic cell, a redox-mediated carbon dioxide reduction cell, a redox-mediated nitrogen reduction cell, and so on, depending on the type of electrochemical reaction on the first cathode side.

[0017] The redox-mediated electrolytic cell of this embodiment does not depend on the type of electrochemical reaction on the first cathode side, and since the first anode electrolyte contains redox-mediated reduced form (Re), the reduced form (Re) is oxidized by the redox-mediated oxidation reaction (ReOR) of the reduced form (Re) on the first anode side, producing redox-mediated oxidized form (Ox). Below, as shown in Figure 1, the redox-mediated electrolytic cell 10 will be described when the electrochemical reaction on the first cathode side is, as an example, a hydrogen evolution reaction. The redox-mediated electrolytic cell of the present invention is not limited to a hydrogen evolution reaction for the electrochemical reaction on the first cathode side.

[0018] As shown in Figure 1, the redox-mediated electrolytic cell 10 of this embodiment comprises a first anode 2, a first cathode 4, a first anode electrolyte 2E, a first cathode electrolyte 4E, and a first diaphragm 6 that separates the first anode electrolyte 2E and the first cathode electrolyte 4E. The first anode electrolyte 2E contains a redox-mediated reduced form. The redox-mediated electrolytic cell 10 does not depend on the type of electrochemical reaction of the first cathode 4, and because the first anode electrolyte 2E contains a redox-mediated reduced form (Re), the reduced form (Re) is oxidized in the first anode 2 by an oxidation reaction (ReOR) of the redox-mediated reduced form (Re), and a redox-mediated oxidized form (Ox) is produced.

[0019] In a conventional water electrolysis cell 100, as shown in Figure 2, the first anode electrolyte 102E does not contain redox-mediated reducing agents, and therefore oxygen is produced by an oxygen evolution reaction (OER).

[0020] FIG. 3 is a comparison between the conventional water electrolysis cell 100 shown in FIG. 2 and the redox-mediated electrolysis cell 10 of the present embodiment shown in FIG. 1, illustrating electrolysis overpotential (E １ ) (FIG. 3A) caused by the conventional oxygen evolution reaction (OER) and the electrolysis overpotential (E ２ ) (FIG. 3B) caused by the oxidation reaction of redox-mediated reduced form (Re) (ReOR). In the first anode 2 of the redox-mediated electrolysis cell 10 of the present embodiment, the redox-mediated reduced form has an oxidation potential lower than the oxygen evolution potential, so generation of electrolysis overpotential is reduced.

[0021] The water electrolysis overpotential (E1) shown in FIG. 3A is determined by the potential difference between the hydrogen evolution reaction (HER) at the first cathode 4 and OER at a current density I.

[0022]

[0023] On the other hand, when a redox-mediated reduced form (Re: hydroquinone (HQ) is taken as an example) as shown in FIG. 3B is added to an electrolytic solution, the potential of the oxidation reaction (ReOR) of the reduced form (Re) is sufficiently lower than the OER potential, and the oxidation reaction (ReOR) to the redox-mediated oxidized form (Ox: benzoquinone (BQ) is taken as an example) occurs preferentially. As a result, the electrolysis overpotential (E ２ ) becomes the potential difference between HER and ReOR, and the electrolysis overpotential is reduced regardless of the catalyst type.

[0024] [Redox-mediated reduced form] The redox-mediated reduced form according to the present embodiment is not particularly limited as long as it is a compound whose oxidation reaction potential is lower than the potential of the oxygen evolution reaction (oxygen evolution potential). The redox-mediated reduced form may be inorganic or organic. Examples of inorganic types include vanadium ions and the like. Examples of organic types include water-soluble organic compounds and the like. Further, it is more preferable that both the redox-mediated reduced form and the oxidized form are water-soluble. When both the redox-mediated reduced form and the oxidized form are water-soluble organic compounds, products and the like do not adhere to the electrode, and the electrolytic reaction proceeds stably. It is preferable that the redox mediator according to the present embodiment is a compound having a quinone structure.

[0025] In this invention, the term "quinone structure" includes compounds having one or more conjugated C3-10 carbocyclic fused rings that are substituted by two or more oxo groups (=O) in their oxidized form (Ox), and in which the oxo groups are conjugated to one or more of these conjugated rings.

[0026] Examples of compounds having the quinone structure include at least one compound selected from the group consisting of compounds represented by the following formulas (1) to (10).

[0027] In formulas (1) to (10) above, each aromatic ring may independently have substituents. If a formula has one or more substituents, at least one substituent is hydrophilic. If a formula has two or more substituents, the substituents may be the same or different; the substituents may bond to each other to form a ring structure; or the aromatic rings may bond to each other via substituents to form a polymer. Examples of substituents include halogen atoms, hydroxyl groups, amino groups, carboxyl groups, alkyl groups, alkoxy groups, aryl groups, amide groups, cyano groups, sulfonic acid groups, and phosphate groups.

[0028] "Alkyl group" means a linear, branched, or cyclic saturated or unsaturated aliphatic hydrocarbon group having 1 to 6 carbon atoms. Examples of alkyl groups include methyl, ethyl, n- and iso-propyl, n-, sec-, iso- and tert-butyl, neopentyl, and others. The alkyl group may further have substituents such as a cyano group, hydroxyl group, carboxyl group, amino group, amide group, sulfonic acid group, or phosphate group. "Alkoxy group" means a group of the formula -OX, where X is an alkyl group as defined above. Examples of aryl group include benzene, naphthalene, and biphenyl. The aryl group may have substituents such as a cyano group, hydroxyl group, carboxyl group, amino group, amide group, sulfonic acid group, or phosphate group.

[0029] The compounds represented by formulas (1) to (10) are preferably the compounds represented by the following formulas (1A) to (10A).

[0030] In formulas (1A) to (10A) above, R in each formula is independent. The n Rs in the same formula may be the same or different, and each has at least one hydrophilic substituent. Each n is an independent integer of 0 or more.

[0031] Furthermore, the range of n in each of the above formulas (1A) to (10A) is preferably as follows, for example: Formula (1A), Formula (2A): n = 0 to 4; Formula (3A), Formula (4A), Formula (5A), Formula (6A): n = 0 to 6; Formula (7A): n = 0 to 8; Formula (8A), Formula (9A): n = 0 to 10; Formula (10A): n = 0 to 14.

[0032] R can be independently represented by halogen atoms, hydroxyl groups, amino groups, carboxyl groups, alkyl groups, alkoxy groups, amide groups, cyano groups, sulfonic acid groups, phosphate groups, and the like.

[0033] When R is a hydrophilic substituent, examples of the hydrophilic substituent include cyano groups, hydroxyl groups, carboxyl groups, amino groups, amide groups, sulfonic acid groups, phosphate groups, thiol groups, formyl groups, nitro groups, ether groups; or substituents having these groups. Examples of the substituent include alkoxy groups, aralkyloxy groups, aryloxy groups, amide groups, alkyloxycarbonyl groups, aryloxycarbonyl groups, alkyl groups, cycloalkyl groups, aralkyl groups, or aryl groups.

[0034] As used herein, the term "hydrophilic substituent" refers to a group that readily bonds with water, and a hydrophilic group typically includes at least one hydrophilic functional group such as a hydroxyl, amino, carboxyl, sulfonic acid, or phosphate group.

[0035] Specific examples of redox-mediated reduced forms according to this embodiment include, for example, the reduced forms of the compounds shown in formulas (1) to (10) above. Among the compounds shown in formulas (1) to (10) above, benzoquinone (BQ), naphthoquinone (NQ), anthraquinone (AQ), anthraquinone sulfonic acid (AQS), and anthraquinone disulfonic acid (AQDS) are preferred. For example, the reduced form of benzoquinone (BQ), which is the compound shown in formula (1) above, is hydroquinone (HQ). The redox-mediated reduced forms according to this embodiment are preferably hydroquinone (HQ), catechol, hydronaphthoquinone, hydroanthraquinone, hydroanthraquinone sulfonic acid, and hydroanthraquinone disulfonic acid, with hydroquinone (HQ) being more preferred.

[0036] [First Anode] The first anode in this embodiment may be a conventional anode for electrochemical cells and is not particularly limited. The first anode is preferably made of carbon (carbon material) or metal. Examples of the metal include metals such as Fe, Co, Ni, Cu, Zn, Pt, Au, Ag, and alloys containing any two of these metals. The shape of the first anode is not particularly limited and may be plate-shaped, mesh-shaped, rod-shaped, etc.

[0037] [First Cathode] The first cathode in this embodiment may be a conventional cathode for electrochemical cells and is not particularly limited. Preferably, the first cathode is carbon (carbon material) or metal. Examples of the metal include metals such as Fe, Co, Ni, Cu, Zn, Pt, Au, Ag, and alloys containing any two of these metals. The shape of the first cathode is not particularly limited and may be plate-shaped, mesh-shaped, rod-shaped, etc.

[0038] [First Anode Electrolyte] The first anode electrolyte according to this embodiment may be a conventional electrochemical cell electrolyte and is not particularly limited. The first anode electrolyte may be an aqueous electrolyte or a non-aqueous electrolyte. An aqueous electrolyte is preferred. The pH of the aqueous electrolyte is not particularly limited and may be in the acidic range, neutral range, or basic range. Preferably, the pH is 7.6 or less. Examples of electrolytes include salts such as NaCl, acids such as sulfuric acid, and bases such as potassium hydroxide. The concentration of the electrolyte in the electrolyte is, for example, 1 × 10⁻⁶. －６ It is preferable that it be M or higher, 1 x 10 －５ It is more preferable that it be M or greater, 1 × 10 －４ It is more preferable that the concentration be M or higher. It may also be 1 M or less. The first anode electrolyte contains the redox-mediated reducing form according to this embodiment. The concentration of the redox-mediated reducing form in the electrolyte is preferably 0.001 M or higher, more preferably 0.01 M or higher, and more preferably 0.1 M or higher. It may also be 10 M or less. If the concentration of the redox-mediated reducing form in the electrolyte is within the above range, it is possible to reduce the overvoltage on the anode side. The redox-mediated electrolytic cell of this embodiment further has a first anode chamber. The first anode electrolyte is contained in the first anode chamber.

[0039] [First Cathode Electrolyte] The first cathode electrolyte in this embodiment may be a conventional electrolyte for electrochemical cells and is not particularly limited. The first cathode electrolyte may be an aqueous electrolyte or a non-aqueous electrolyte. An aqueous electrolyte is preferred. The pH of the aqueous electrolyte is not particularly limited and may be in the acidic range, neutral range, or basic range. Examples of electrolytes include salts such as NaCl, acids such as sulfuric acid, and bases such as potassium hydroxide. The concentration of the electrolyte in the electrolyte is, for example, 1 × 10⁻⁶. －６ It is preferable that it be M or higher, 1 x 10 －５ It is more preferable that it be M or greater, 1 × 10 －４It is even more preferable that the electrolyte is M or greater. It may also be 1M or less. The redox-mediated electrolytic cell of this embodiment further has a first cathode chamber. The first cathode electrolyte is contained in the first cathode chamber.

[0040] [First Diaphragm] The first diaphragm in this embodiment may be a conventional diaphragm for electrochemical cells and is not particularly limited. Examples of the first diaphragm include a proton-conducting membrane such as Nafion® and an anion-conducting membrane such as Sustainion®.

[0041] The first diaphragm according to this embodiment can be, for example, a conventional diaphragm for alkaline water electrolysis. For example, it may include a sheet-like porous support and a porous membrane containing an organic polymer resin impregnated into the support from one surface of the support. The organic polymer resin may be at least one selected from the group consisting of polysulfone, polyethersulfone, polyphenylsulfone, polyvinylidene fluoride, polycarbonate, polytetrafluoroethylene, polypropylene, polyphenylene sulfide, polyketone, polyetheretherketone, polyimide, and polyetherimide. The porous support may be a nonwoven fabric, woven fabric, or composite fabric of a nonwoven fabric and a woven fabric formed from at least one fiber selected from the group consisting of polyphenylene sulfide, polypropylene, polysulfone, polyethersulfone, polyphenylsulfone, fluorine resin, polyketone, polyimide, and polyetherimide.

[0042] The thickness of the first diaphragm according to this embodiment is preferably 10 μm or more, more preferably 30 μm or more, and even more preferably 50 μm or more. It may also be 1 mm or less.

[0043] Specific examples of the first diaphragm include PEMs such as Nafion® and AEMs such as Sustainion®. For example, Nafion (film thickness: 50 μm) manufactured by Chemours and Sustainion (film thickness: 50 μm) manufactured by Dioxide Materials are examples. When the redox-mediated electrolytic cell of this embodiment includes a first anode chamber and a first cathode chamber, the first diaphragm partitions the first anode chamber and the first cathode chamber.

[0044] [Electrode Reaction] In the redox-mediated secondary battery cell of this embodiment, the electrode reaction of the redox-mediated secondary battery cell of this embodiment will be described as an example where the electrochemical reaction of the first cathode is a hydrogen evolution reaction and the redox-mediated reduced form is hydroquinone (HQ) (a reduced form of benzoquinone (BQ)). In the redox-mediated secondary battery cell shown in Figure 1, when the first anode electrolyte contains hydroquinone (HQ), the electrochemical reactions on the first anode side and the first cathode side are as follows.

[0045] On the first anode side, the potential for the oxidation reaction of hydroquinone (HQ) is lower than the potential for the oxygen evolution reaction, so the oxidation reaction of hydroquinone (HQ) preferentially occurs over the oxygen evolution reaction. Hydroquinone (HQ) is oxidized and converted to benzoquinone (BQ). As a result, as shown in Figure 3, the electrolytic overpotential (E ２ ) is the electrolytic overpotential (E) due to the conventional oxygen evolution reaction. １ It can be lowered from ).

[0046] The open-circuit potential (0A) of the first anode is preferably 0.5 to 2.0, and more preferably 0.5 to 1.5, relative to the standard hydrogen electrode (SHE). When the open-circuit potential (0A) of the first anode is within the above range, the redox-mediated electrolytic cell can reduce the overvoltage on the anode side.

[0047] [Modifications of the Redox-Mediated Electrolytic Cell of This Embodiment] A problem with the redox-mediated electrolytic cell of this embodiment is that the reduced form (Re) of the redox-mediated solution, such as HQ, is oxidized and consumed. Therefore, it is necessary to either constantly supply the reduced form (Re) of the redox-mediated solution or reduce the oxidized form (Ox) back to its original reduced form (Re) state. As a method for returning to the reduced form (Re) state, for example, one method is to photoreduce the oxidized form (Ox) back to the reduced form (Re) by irradiating the oxidized form (Ox) with light of its absorption wavelength. That is, the redox-mediated electrolytic cell of this embodiment may further include a means for irradiating the electrolyte of the first anode with light. As the light, for example, one example is light having a wavelength within the range of the absorption wavelength of the redox-mediated oxidized form (Ox). Furthermore, it is preferable that the light is outside the range of the absorption wavelength of the redox-mediated reduced form (Re). In other words, it is preferable to photoreduce the redox-mediated oxidized form (Ox) by irradiation with light to produce the reduced form (Re).

[0048] As a means of irradiating the electrolyte of the first anode with light, for example, at least one part of the container for the electrolyte of the first anode may be made of a light-transmitting material (for example, glass or quartz glass). The container may or may not contain the first anode. For example, in the electrolytic cell shown in Figure 1, in the container on the first anode side where the electrolyte of the first anode is located, a part of any one of the top, bottom, or side surfaces may be made of a light-transmitting material (for example, glass or quartz glass). Alternatively, the electrolyte of the first anode may be supplied to another container, and a part of that container may be made of a light-transmitting material (for example, glass or quartz glass).

[0049] The redox-mediated electrolytic cell of this embodiment preferably further comprises a first anode chamber containing the first anode electrode and the first anode electrolyte, a flow cell made of at least one part of a transparent material, a circulation means such as a pump for circulating the electrolyte between the first anode chamber and the flow cell, and an ultraviolet-visible light source. Examples of the transparent material include glass and quartz glass. The flow cell may also be a transparent cell made of a transparent material. The first anode electrolyte in the first anode chamber is circulated to the flow cell by a pump, and ultraviolet-visible light is irradiated onto the first anode electrolyte that has flowed into the flow cell. By irradiating the redox-mediated oxidized form (Ox) of the first anode electrolyte that has flowed into the flow cell with light of its absorption wavelength, the oxidized form (Ox) can be reduced by light. As a result, the oxidized form (Ox) can be reduced back to its original reduced form (Re). The reduced form (Re) recovered in the flow cell is returned to the first anode chamber.

[0050] (Redox-mediated secondary battery cell) A redox-mediated secondary battery cell 20 of one embodiment of the present invention, as shown in Figure 4, comprises a second anode 22, a second cathode 24, a second anode electrolyte 22E, a second cathode electrolyte 24E, and a second diaphragm 26 separating the second cathode electrolyte and the second anode electrolyte. The second cathode electrolyte contains a redox-mediated oxidizing agent (Ox). In the discharge state, the redox-mediated oxidizing agent (Ox) is reduced in the second cathode and converted to a redox-mediated reduced agent (Re). In the charge state, the redox-mediated reduced agent (Re) is oxidized in the second cathode and changed back to a redox-mediated oxidizing agent (Ox). In the second cathode, the oxidation potential of the redox-mediated reduced agent (oxidation-reduction agent) is lower than the oxygen evolution potential.

[0051] The redox-mediated secondary battery cell 20 of this embodiment can continuously discharge even without charging by, for example, supplying hydrogen as fuel to the second anode 22, supplying the metal (M) of the second anode 22 as fuel, or supplying the redox-mediated oxidized form (Ox) as fuel. In that case, it may be called a "redox-mediated fuel cell cell" rather than a redox-mediated secondary battery cell. For example, the "dynamically regenerative redox-mediated electrolytic cell 30" (Figure 5), which will be described later, uses the configuration of the redox-mediated secondary battery cell 20 of this embodiment, but is used in substance as a "redox-mediated fuel cell cell".

[0052] [Redox-mediated oxidized form] The redox-mediated oxidized form (Ox) in this embodiment is not particularly limited as long as the oxidation potential of its reduced form is lower than that of the compound. An example of the redox-mediated oxidized form (Ox) in this embodiment is the oxidized form (Ox) of the redox-mediated reduced form (Re) in the redox-mediated electrolytic cell of this embodiment. An example of the redox-mediated oxidized form (Ox) in this embodiment is at least one compound selected from the group consisting of the compounds shown in formulas (1) to (10) above. Furthermore, it is preferable that the redox-mediated oxidized form (Ox) in this embodiment is at least one compound selected from the group consisting of the compounds shown in formulas (1A) to (10A) above. The substituents that may be present on the aromatic rings of the compounds shown in formulas (1) to (10) and formulas (1A) to (10A) above are the same substituents as those described for the redox-mediated electrolytic cell of this embodiment. In this embodiment, the redox-mediated oxidized form is preferably benzoquinone (BQ), naphthoquinone (NQ), or anthraquinone (AQ).

[0053] [Second Anode] The second anode according to this embodiment is preferably a metal (M) having a large ionization tendency with a standard electrode potential of -8V to 0V. Examples of the metal (M) of the second anode include zinc (Zn), aluminum (Al), magnesium (Mg), iron (Fe), etc. Zinc (Zn) is preferred. The shape of the second anode is not particularly limited and examples include plate-shaped, mesh-shaped, rod-shaped, etc.

[0054] [Second Cathode] The second cathode in this embodiment may be a conventional cathode for electrochemical cells and is not particularly limited. It is preferable that the second cathode is a conductor. Examples of the conductor include stainless steel, nickel, copper, carbon, etc.

[0055] [Second Anode Electrolyte] The second anode electrolyte according to this embodiment may be a conventional electrochemical cell electrolyte and is not particularly limited. The second anode electrolyte may be an aqueous electrolyte or a non-aqueous electrolyte. An aqueous electrolyte is preferred. The pH of the aqueous electrolyte is not particularly limited and may be in the acidic range, neutral range, or basic range. Preferably, the pH is 7.6 or less. Examples of electrolytes include salts such as NaCl, acids such as sulfuric acid, and bases such as potassium hydroxide. The concentration of the electrolyte in the electrolyte is, for example, 1 × 10⁻⁶. －６ It is preferable that it be M or higher, 1 x 10 －５ It is more preferable that it be M or greater, 1 × 10 －４ It is even more preferable that it be M or greater. However, it may also be 1M or less.

[0056] [Second Cathode Electrolyte] The second anode electrolyte according to this embodiment may be a conventional electrolyte for electrochemical cells and is not particularly limited. Preferably, the second cathode electrolyte is the same as the first anode electrolyte of the redox-mediated electrolytic cell of this embodiment. The second cathode electrolyte contains a redox-mediated oxidized type.

[0057] [Second Diaphragm] The second diaphragm in this embodiment may be a conventional diaphragm for electrochemical cells and is not particularly limited. Examples of the second diaphragm include a proton-conducting membrane such as Nafion® and an anion-conducting membrane such as Sustainion®. The second diaphragm may be the same as the first diaphragm of the redox-mediated electrolytic cell of the embodiment.

[0058] [Electrode Reaction] In this embodiment, the electrode reaction of the redox-mediated secondary battery cell will be explained as an example where the second anode is a zinc (Zn) electrode and the redox-mediated oxidized form contained in the second cathode electrolyte is benzoquinone (BQ) (oxidized form of hydroquinone (HQ)). In the redox-mediated secondary battery cell shown in Figure 4, when the second cathode electrolyte contains benzoquinone (BQ), the electrochemical reactions on the second cathode side and the second anode side are as follows.

[0059] On the second cathode side, benzoquinone (BQ) is converted to hydroquinone (HQ) through a reduction reaction. Also, on the second anode side, the Zn electrode is oxidized.

[0060] (Dynamic Regeneration Redox-Mediated Electrolytic Cell) A dynamic regeneration redox-mediated electrolytic cell according to one embodiment of the present invention comprises the redox-mediated electrolytic cell of the above embodiment and the redox-mediated secondary battery cell of the above embodiment. The first anode of the redox-mediated electrolytic cell and the second cathode of the redox-mediated electrolytic cell are placed in a common electrolyte. The common electrolyte is used as the first anode electrolyte of the redox-mediated electrolytic cell and as the second cathode electrolyte of the redox-mediated secondary battery cell. The redox-mediated reduction type of the redox-mediated electrolytic cell is the same as the redox-mediated reduction type of the redox-mediated secondary battery cell.

[0061] In the dynamically regenerating redox-mediated electrolytic cell of this embodiment, the electrochemical reaction on the first cathode side is not particularly limited and can include, for example, an oxygen evolution reaction, a carbon dioxide reduction reaction, a nitrogen reduction reaction, etc. That is, the redox-mediated electrolytic cell of this embodiment can be used as a redox-mediated water electrolytic cell, a redox-mediated carbon dioxide reduction cell, a redox-mediated nitrogen reduction cell, etc., depending on the type of electrochemical reaction on the first cathode side. In the dynamically regenerating redox-mediated electrolytic cell of this embodiment, the first anode electrolyte contains a redox-mediated reduced form (Re), regardless of the type of electrochemical reaction on the first cathode side. Therefore, on the first anode side, the reduced form (Re) is oxidized by a redox-mediated oxidation reaction (ReOR) of the reduced form (Re), generating a redox-mediated oxidized form (Ox). Hereinafter, as shown in Figure 5, the dynamically regenerating redox-mediated electrolytic cell of this embodiment will be described when the electrochemical reaction on the first cathode side is, for example, a hydrogen evolution reaction. The dynamic regenerative redox-mediated electrolytic cell of the present invention is not limited to a hydrogen generation reaction on the first cathode side.

[0062] In the first anode of the dynamic regenerative redox-mediated electrolytic cell of this embodiment, similar to the redox-mediated electrolytic cell of this embodiment, the redox-mediated reducing oxidation potential is lower than the oxygen evolution potential, thus reducing the generation of electrolytic overvoltage.

[0063] The dynamically regenerating redox-mediated electrolytic cell of this embodiment is the same as the redox-mediated electrolytic cell of this embodiment, except that it is further coupled with the redox-mediated secondary battery cell of this embodiment on the first anode side. The problem with the redox-mediated electrolytic cell of this embodiment is that the reduced form (Re) of the redox-mediated element, such as HQ, is oxidized and consumed. Therefore, it is necessary to either constantly supply the reduced form (Re) of the redox-mediated element or reduce the oxidized form (Ox) back to the original reduced form (Re). By combining it with the redox-mediated secondary battery cell of this embodiment, a mechanism for regenerating the consumed reduced form (Re) of the redox-mediated element can be added, solving the above problem. For example, as shown in Figure 5, a second anode 22 (e.g., Zn) similar to the anode of a conventional fuel cell such as a metal-air battery is used, and a second cathode 24 and a second cathode electrolyte 24E are used instead of the cathode of a conventional fuel cell such as a metal-air battery. In the second cathode 24 of the dynamic regenerative redox-mediated electrolytic cell 30 of this embodiment shown in Figure 5, since the second cathode electrolyte 24E contains redox-mediated oxidized form (Ox), the redox-mediated reduction reaction (OxRR) of the oxidized form (Ox) takes precedence over the oxygen reduction reaction (ORR), and the redox-mediated reduced form (Re) is returned from the redox-mediated oxidized form (Ox).

[0064] In this embodiment, the second cathode 24 and the first anode 2 of the dynamically regenerated redox-mediated electrolytic cell 30 are placed in the same electrolytic cell. By performing a reduction reaction (OxRR) at the second cathode on the oxidized form (Ox) of redox-mediated reduced form (Re) such as HQ, which is oxidized from HQ, the oxidized form (Re) is obtained by an electrochemical reaction on the first anode side. This reduces the oxidized form (Ox) to the reduced form (Re), causing the reduced form (Re) to rotate as a redox medium. In other words, the redox-mediated secondary battery cell 20 of this embodiment shown in Figure 4 can be used as a redox-mediated metal fuel cell (for example, a benzoquinone (BQ)-based zinc (Zn) fuel cell). Discharge occurs at the second anode 22 of the dynamically regenerated redox-mediated electrolytic cell 30 of this embodiment due to the oxidation reaction of metal M (for example, Zn). In the second cathode 24, a redox-mediated reduction reaction (OxRR) occurs, converting the oxidized form (Ox) (e.g., BQ) back to the reduced form (Re) (e.g., HQ).

[0065] By providing fuel for the second anode 22 (for example, Zn), it becomes possible to regenerate the reduced form (Re) via redox while extracting energy. The method of introducing the fuel is not particularly limited, but examples include inserting a plate-shaped anode electrode into the electrolyte to directly form electrode contacts, or placing powder or fragments of the anode electrode material into a cage-shaped current collector.

[0066] The first anode, first cathode, first diaphragm, first anode electrolyte, first cathode electrolyte, redox-mediated reduced form, etc. of the dynamically regenerated redox-mediated electrolytic cell of this embodiment are the same as the first anode, first cathode, first diaphragm, first anode electrolyte, first cathode electrolyte, redox-mediated reduced form of the redox-mediated electrolytic cell of this embodiment. The second anode, second cathode, second diaphragm, second anode electrolyte, second cathode electrolyte, redox-mediated oxidized form, etc. of the dynamically regenerated redox-mediated electrolytic cell of this embodiment are the same as the second anode, second cathode, second diaphragm, second anode electrolyte, second cathode electrolyte, redox-mediated oxidized form of the redox-mediated secondary battery cell of this embodiment.

[0067] (Redox-mediated electrolytic apparatus) A redox-mediated electrolytic apparatus according to one embodiment of the present invention comprises a redox-mediated electrolytic cell according to the present embodiment or a dynamically regenerating redox-mediated electrolytic cell according to the present embodiment, and a voltage injector that applies a voltage between the first cathode and the first anode.

[0068] (Method for producing hydrogen) A method for producing hydrogen according to one embodiment of the present invention is characterized by using the redox-mediated electrolytic apparatus of the above embodiment. In the redox-mediated electrolytic apparatus, a hydrogen generation reaction occurs on the first cathode side of the redox-mediated electrolytic cell or the dynamically regenerated redox-mediated electrolytic cell.

[0069] Although the present invention has been described in detail above with reference to several embodiments, the present invention is not limited to the above embodiments and modifications, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims.

[0070] (Redox-mediated rechargeable metal-air battery) A redox-mediated rechargeable metal-air battery according to one embodiment of the present invention includes the redox-mediated electrolytic cell of the above embodiment and a metal-air battery cell. The metal-air battery cell includes a positive electrode containing an air electrode, a negative electrode containing metal (M), and an electrolyte containing metal (M) ions. It is preferable that the first cathode of the redox-mediated electrolytic cell and the negative electrode of the metal-air battery cell are common electrodes. Figure 12 is a diagram showing an example of the redox-mediated rechargeable metal-air battery 50 of this embodiment. Figure 13 is a diagram showing the charged state 50A of the redox-mediated rechargeable metal-air battery of Figure 12. Figure 14 is a diagram showing the discharged state 50B of the redox-mediated rechargeable metal-air battery of Figure 12. The redox-mediated rechargeable metal-air battery 50 shown in Figure 12 includes a redox-mediated electrolytic cell and a metal-air battery cell. The redox-mediated electrolytic cell comprises a first anode 52, a first cathode 54, a first anode electrolyte 52E, a first cathode electrolyte 54E, and a first diaphragm 56 separating the first anode electrolyte 52E and the first cathode electrolyte 54E. The first anode electrolyte 52E contains a redox-mediated reducing form. The redox-mediated rechargeable metal-air battery 50 does not depend on the type of electrochemical reaction of the first cathode 54, and because the first anode electrolyte 52E contains a redox-mediated reducing form (Re), the reduced form (Re) is oxidized in the first anode 52 by a redox-mediated oxidation reaction (ReOR) of the reduced form (Re), and a redox-mediated oxidized form (Ox) is produced. A metal-air battery cell includes a positive electrode containing an air electrode 58, a negative electrode 54 containing a metal (M), and an electrolyte 54E containing ions of the metal (M). In the embodiment shown in Figure 12, the first cathode 54 of the redox-mediated electrolytic cell and the negative electrode 54 of the metal-air battery cell are common electrodes, and the first cathode electrolyte 54E of the redox-mediated electrolytic cell contains ions of the metal (M). In the redox-mediated rechargeable metal-air battery of this embodiment, since the rechargeable electrolyte contains redox-mediated reduced form (Re), at the rechargeable anode side, the reduced form (Re) is oxidized by a redox-mediated oxidation reaction (ReOR) of the reduced form (Re) to produce redox-mediated oxidized form (Ox).

[0071] [First Cathode / Negative Electrode of Metal-Air Battery Cell] The first cathode in this embodiment is an electrode common to the negative electrode of the metal-air battery cell and contains a metal (M). The first cathode preferably has a large ionization tendency, for example, with a standard electrode potential of -8V to 0V. Examples of the metal (M) of the first cathode include zinc (Zn), aluminum (Al), magnesium (Mg), iron (Fe), etc. Zinc (Zn) is preferred. Examples of the material of the first cathode include zinc (Zn), zinc (Zn) alloy, porous material containing zinc (Zn), composite material containing zinc (Zn) particles, etc. The shape of the first cathode is not particularly limited and examples include particulate, mesh, plate-shaped, etc. A current collector may be provided in contact with the first cathode.

[0072] [Air Electrode] The air electrode is a known air electrode used in metal-air batteries such as zinc-air batteries and is not particularly limited. Typically, the air electrode comprises an electronically conductive material and, optionally, a hydroxide ion conductive material. Preferred examples of electronically conductive materials include carbon blacks such as Ketjenblack, acetylene black, channel black, furnace black, lamp black, and thermal black; graphites such as natural graphite like flake graphite, artificial graphite, and expanded graphite; conductive fibers such as carbon fibers and metal fibers; metal powders such as copper, silver, nickel, and aluminum; organic electronically conductive materials such as polyphenylene derivatives; and any mixture thereof. The shape of the electronically conductive material may be particle-like or other shapes, but it is preferable to use it in a form that provides a continuous phase (i.e., an electronically conductive phase) in the thickness direction in the air electrode. For example, the electronically conductive material may be a porous material. The electronically conductive material may also be in the form of a mixture or composite with the air electrode catalyst (e.g., platinum-supported carbon). The content of the electronically conductive material in the air electrode is not particularly limited, but is preferably 10 to 80 volume%, more preferably 15 to 80 volume%, and even more preferably 20 to 80 volume%, relative to the total volume of the air electrode. A current collector may be provided in contact with the air electrode.

[0073] [Electrolyte of Metal-Air Battery Cell / First Cathode Electrolyte] The electrolyte of the metal-air battery cell according to this embodiment may be an aqueous electrolyte or a non-aqueous electrolyte. An aqueous electrolyte is preferred. The pH of the aqueous electrolyte is not particularly limited and may be in the acidic range, neutral range, or basic range. Preferably, the pH is 14.7. The electrolyte includes, for example, ions of the metal (M) contained in the negative electrode of the metal-air battery cell. Other electrolytes include salts such as NaCl, acids such as sulfuric acid, and bases such as potassium hydroxide. The concentration of the metal (M) ions in the electrolyte is, for example, 1 × 10⁻⁶. －６ It is preferable that it be M or higher, 1 x 10 －５ It is more preferable that it be M or greater, 1 × 10 －４ It is even more preferable that the concentration be M or higher. It may also be 10 M or lower. The concentration of other electrolytes in the electrolyte solution may be, for example, 1 × 10⁻⁶. －６ It is preferable that it be M or higher, 1 x 10 －５ It is more preferable that it be M or greater, 1 × 10 －４ It is even more preferable that it be M or higher. It may also be 10M or lower.

[0074] [First Anode Electrolyte] The first anode electrolyte according to this embodiment may be an aqueous electrolyte or a non-aqueous electrolyte. An aqueous electrolyte is preferred. The pH of the aqueous electrolyte is not particularly limited and may be in the acidic range, neutral range, or basic range. Preferably, the pH is 4. The first anode electrolyte contains the redox-mediated reducing form according to this embodiment. The concentration of the redox-mediated reducing form in the electrolyte is preferably 0.001 M or higher, more preferably 0.01 M or higher, and even more preferably 0.1 M or higher. It may also be 10 M or lower. If the concentration of the redox-mediated reducing form in the electrolyte is within the above range, it is possible to reduce the overvoltage on the charging anode side. Examples of electrolytes include salts such as NaCl, acids such as sulfuric acid, and bases such as potassium hydroxide. The concentration of the electrolyte in the electrolyte is, for example, 1 × 10⁻⁶ －６ It is preferable that it be M or higher, 1 x 10 －５It is more preferable that it be M or greater, 1 × 10 －４ It is even more preferable that the value is M or greater. It may also be 10M or less. Furthermore, it may contain ions of the metal (M) contained in the first cathode.

[0075] [Electrode Reaction of Redox-Mediated Rechargeable Metal-Air Battery] In the redox-mediated rechargeable metal-air battery of this embodiment, charging and discharging are performed in a redox-mediated electrolytic cell including a first anode and a first cathode, and in a metal-air battery cell including an air electrode and a metal (M) electrode, respectively.

[0076] <Electrode Reaction (Charging) of Redox-Mediated Electrolytic Cell> The electrode reaction of the redox-mediated electrolytic cell according to this embodiment will be explained. Figure 13 shows a redox-mediated rechargeable metal-air battery 50A during charging. The electrode reaction of the redox-mediated electrolytic cell of this embodiment will be explained as an example where the electrochemical reaction of the first cathode 54 is a reduction reaction of metal ions, and the redox-mediated reduced form is hydroquinone (HQ) (a reduced form of benzoquinone (BQ)). In the redox-mediated electrolytic cell during charging shown in Figure 13, when the first anode electrolyte 52E contains hydroquinone (HQ), the electrochemical reactions on the first anode 52 side and the first cathode 54 side are as follows (example where metal M is divalent). At the first cathode 54, the metal (M) ions are converted to metal (M) through a reduction reaction. At the first anode 52, since the potential of the oxidation reaction of hydroquinone (HQ) is lower than the potential of the oxygen evolution reaction, the oxidation reaction of hydroquinone (HQ) preferentially occurs over the oxygen evolution reaction. Hydroquinone (HQ) is oxidized and converted to benzoquinone (BQ). As a result, as shown in Figure 3, the electrolytic overpotential (E ２ ) is the electrolytic overpotential (E) due to the conventional oxygen evolution reaction. １ It can be lowered from ).

[0077] The open-circuit potential (0A) of the first anode 52 is preferably 0.5 to 2.0, and more preferably 0.5 to 1.5, relative to the standard hydrogen electrode (SHE). When the open-circuit potential (0A) of the first anode 52 is within the above range, the redox-mediated electrolytic cell can reduce the overvoltage on the anode side.

[0078] <Electrode Reaction (Discharge) of Metal-Air Battery Cell> The electrode reaction of the metal-air battery cell according to this embodiment will be explained. Figure 14 shows a redox-mediated charging type metal-air battery 50B during discharge. The reactions of the positive electrode (air electrode) 58 and negative electrode 54 (metal (M)-containing electrode) during discharge of the metal-air battery are as follows. Note that it is assumed that the metal (M) is a divalent metal. Positive electrode: O ２ +2H ２ O + 4e- → 4OH － Negative electrode: 2M+4OH － → 2MO + 2H ２ O+4e － At the positive electrode 58, oxygen in the air undergoes a reduction reaction, resulting in OH － This is converted to a metal oxide. Furthermore, at the negative electrode 54, the metal (M) electrode is changed to a metal oxide through an oxidation reaction.

[0079] [Modified Examples of the Redox-Mediated Metal-Air Battery of This Embodiment] In the redox-mediated metal-air battery 50 of this embodiment shown in Figure 12, the negative electrode 54 of the metal-air battery cell and the first cathode 54 of the redox-mediated electrolytic cell use electrodes containing the same metal (M). A modified example of the redox-mediated metal-air battery of this embodiment is a flow-type battery in which the negative electrode of the metal-air battery cell and the first cathode electrode of the redox-mediated electrolytic cell are installed separately, and conductive materials other than metal (M) are used to circulate metal (M) particles such as zinc. In this case, the negative electrode side of the metal-air battery cell and the first cathode side of the redox-mediated electrolytic cell may contain a common electrolyte. The electrolyte may contain, for example, metal (M) particles such as zinc and metal (M) ions such as zinc ions, and may optionally contain metal (M) oxide particles such as zinc oxide (slurry-like fluid). Metal (M) particles such as zinc are regenerated on the first cathode side of the redox-mediated electrolytic cell and supplied to the metal-air battery cell. A storage section may also be included between the metal-air battery cell and the redox-mediated electrolytic cell. The storage section may use the same electrolyte as the electrolyte on the negative electrode side of the metal-air battery cell and the electrolyte on the first cathode side of the redox-mediated electrolytic cell. During charging, metal (M) particles such as zinc are regenerated on the first cathode side of the redox-mediated electrolytic cell and supplied to the storage section. During discharging, the electrolyte containing the regenerated metal (M) particles such as zinc is supplied from the storage section to the metal-air battery cell.

[0080] (Evaluation Method) Using a potentiometer / galvanostat (AMETEK Co., Ltd.: VersaSTAT4), linear sweep voltammetry (LSV) measurements were performed to measure the voltage and current when a voltage was swept between the cathode and anode, and current-voltage characteristic measurements (IV characteristics) were performed to measure the current and voltage when a load current was swept from the cathode to the anode.

[0081] (Example 1) In the redox-mediated electrolytic cell shown in Figure 1, the electrodes and electrolyte were as follows: First cathode: SUS mesh: thickness 0.20 mm, size 10 mm x 50 mm, wire diameter 0.15 mm, 30 mesh First anode: SUS mesh: thickness 0.20 mm, size 10 mm x 50 mm, wire diameter 0.15 mm, 30 mesh First cathode electrolyte: sulfuric acid aqueous solution (concentration: 0.05 M H) ２ SO ４ ), pH = 1 First anode electrolyte: Acidic aqueous solution (0.5 M H) ２ SO ４ (A 1 M KOH aqueous solution is mixed to achieve a pH of 4.) First diaphragm: Nafion®, proton exchange membrane (PEM), manufactured by Chemours, film thickness: 183 μm Redox-mediated reduced form: Hydroquinone (HQ) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), concentration in the first anode electrolyte: 0.2 M

[0082] The applied voltage between the first cathode and the first anode was swept in the range of 0V to 4.0V, and the current and voltage were measured. The results are shown in Figure 6.

[0083] (Example 2) The same measurements as in Example 1 were performed, except that the concentration of hydroquinone (HQ) in the first anode electrolyte was set to 0.4 M. The results are shown in Figure 6.

[0084] (Comparative Example 1) The same measurements as in Example 1 were performed, except that the concentration of hydroquinone (HQ) in the first anode electrolyte was 0 M (HQ-free). The results are shown in Figure 6.

[0085] (Discussion) From the results in Figure 6, in Examples 1 and 2, because the first anode electrolyte contained hydroquinone (HQ), an oxidation reaction of hydroquinone (HQOR) occurred on the first anode side instead of an oxygen evolution reaction (OER), resulting in a lower overpotential than in Comparative Example 1.

[0086] (Example 3) In the redox-mediated secondary battery cell shown in Figure 4, the electrodes and electrolyte were as follows: Second cathode: SUS mesh: thickness 0.20 mm, size 10 mm x 50 mm, wire diameter 0.15 mm, 30 mesh Second anode: Zn plate, thickness 0.20 mm, size 10 mm x 50 mm Second cathode electrolyte: acidic aqueous solution (0.5 M H) ２ SO ４ (A 1 M KOH aqueous solution is mixed to achieve a pH of 4) Second anode electrolyte: Basic aqueous solution (0.1 M KOH aqueous solution), pH = 13 Second diaphragm: Sustainion®, anion exchange membrane (AEM), manufactured by Dioxide Materials, film thickness: 50 μm Redox-mediated oxidized form: Benzoquinone (BQ) converted by the oxidation reaction of hydroquinone (HQOR) produced in Example 1 (concentration 0.2 M)

[0087] The applied current between the second cathode and the second anode is 0 mA / cm. ２ ~3.0 mA / cm ２ The current and voltage were measured when sweeping within the specified range. The results are shown in Figure 7.

[0088] (Example 4) The effect of the redox-mediated electrolytic cell of this embodiment was confirmed using a beaker half-cell. In this example 4, a reference electrode was placed in the beaker half-cell. Cathode: SUS mesh: thickness 0.20 mm, size 10 mm x 50 mm, wire diameter 0.15 mm, 30 mesh Anode: Pt wire electrode Reference electrode: Hg / HgO (1 M NaOH aqueous solution) Electrolyte: 1 M KOH aqueous solution pH = 14; 0.2 M hydroquinone (HQ)

[0089] The current and voltage were measured when the applied voltage between the cathode and anode was swept in the range of 0V to 4.0V with respect to a reversible hydrogen electrode (RHE). The results are shown in Figure 8.

[0090] (Comparative Example 2) Current and voltage were measured in the same manner as in Example 4, except that the electrolyte did not contain hydroquinone (HQ). The results are shown in Figure 8.

[0091] (Example 5) The current and voltage were measured in the same manner as in Example 4, except that a 1 M NaCl aqueous solution (pH = 7.0) was used as the electrolyte instead of a 1 M KOH aqueous solution, and Ag / AgCl (saturated KCl aqueous solution) was used as the reference electrode. The results are shown in Figure 9.

[0092] (Comparative Example 3) Current and voltage were measured in the same manner as in Example 5, except that the electrolyte did not contain hydroquinone (HQ). The results are shown in Figure 9.

[0093] (Example 6) Instead of a 1 M KOH aqueous solution, the electrolyte was an acidic aqueous solution (0.5 M H ２ SO ４ The current and voltage were measured in the same manner as in Example 4, except that a mixture of 1 M KOH aqueous solution and a 1 M KOH aqueous solution (to a pH of 5) was used, and Ag / AgCl (saturated KCl aqueous solution) was used as the reference electrode. The results are shown in Figure 10.

[0094] (Comparative Example 4) Current and voltage were measured in the same manner as in Example 6, except that the electrolyte did not contain hydroquinone (HQ). The results are shown in Figure 10.

[0095] (Example 7) The photoreduction effect was confirmed in the redox-mediated electrolytic cell of this embodiment using a glass cell (quartz glass cell for UV-Vis spectrophotometer, made of fused silica glass, 10 mm optical path length). Cathode / anode: Pt wire electrode: wire diameter 0.5 mm, length 50 mm Electrolyte: 0.5 M H ２ SO ４ + 1 M KOH aqueous solution; pH = 5.8; 0.2 M hydroquinone (HQ)

[0096] The glass cell was placed in a darkroom environment, and the voltage applied between the cathode and anode was swept from 0V to 4.0V relative to the reversible hydrogen electrode (RHE), and the current and voltage were measured. This was repeated, and after the seventh current measurement, the entire quartz glass cell was exposed to room light for two hours, and then the eighth current density was measured again in the same manner. The measurement results of the current density when 1.5V was applied in each measurement are shown in Figure 11.

[0097] (Comparative Example 5) Current and voltage were measured in the same manner as in Example 7, except that the electrolyte did not contain hydroquinone (HQ). The measurement results of the current density when 1.5V was applied are shown in Figure 11.

[0098] (Discussion) From the results of Examples 4-6 and Comparative Examples 2-4 above, when the pH of the cathode electrolyte is 5, 7, and 14, the overpotential of the examples is lower than that of the comparative examples. This is because the potential of the HQ oxidation reaction is lower than the potential of the oxygen evolution reaction, so at the anode, the oxidation reaction of hydroquinone (HQOR) occurred instead of the oxygen evolution reaction (OER), thus lowering the overpotential.

[0099] From the results of Example 7 and Comparative Example 5 described above, almost no current flowed in Comparative Example 5. On the other hand, in Example 7, where HQ was added, a high current density value was observed. Furthermore, in Example 7, the current density decreased during repeated measurements. This indicates that HQ was oxidized and converted to BQ, causing a decrease in HQ concentration. However, after light irradiation, the current value recovered. This indicates that BQ, which has light absorption in the ultraviolet-visible region, was photoreduced by indoor light, and the HQ concentration recovered. From these results, it was demonstrated that photoreduction of BQ is possible.

[0100] (Example 8) The redox-mediated electrolytic cell shown in Figure 15 of this embodiment is equipped with a quartz glass flow cell 77 capable of supplying electrolyte 73E, an ultraviolet / visible light source, and a pump (not shown) as a circulation means on the anode 72 side. A UV lamp is provided in the flow cell 77 to irradiate it with UV light as an ultraviolet / visible light source. Anode 72: Pt wire electrode, wire diameter 0.5 mm, immersion length 23 cm, electrode area 3.61 cm² ２ Cathode 74: Pt wire electrode, wire diameter 0.5 mm, immersion length 23 cm, electrode area 3.61 cm² ２ Electrolyte 73E: Acidic aqueous solution (0.5M H ２ SO ４(A 1M KOH aqueous solution is mixed to achieve a pH of 4) Redox-mediated reduced form: Hydroquinone (HQ) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), concentration in anode electrolyte: 0.2M Flow cell: Photo Flow System T-1 (manufactured by Asahi Lab Trading Co., Ltd.) UV lamp: Low-pressure mercury lamp, wavelength peak: 254 nm Circulation pump: Quantitative liquid delivery pump MP-2100 (Tokyo Rikakiki Co., Ltd.)

[0101] While irradiating the flow cell with a UV lamp, apply a current of 10 mA / cm between the cathode and anode. ２ The voltage was applied and measured for 30 minutes (1800 seconds). The results are shown in Figure 16.

[0102] (Example 9) Except that the flow cell was not irradiated with a UV lamp, the current applied between the cathode and anode was 10 mA / cm², similar to Example 8. ２ The voltage was applied and measured for 30 minutes. The results are shown in Figure 16.

[0103] (Comparative Example 6) Except for not containing hydroquinone (HQ) and not irradiating the flow cell with a UV lamp, the current applied between the cathode and anode was 10 mA / cm², similar to Example 8. ２ The voltage was applied and measured for 30 minutes. The results are shown in Figure 16.

[0104] (Reference Example 1) An acidic (pH 4) aqueous solution containing 0.2 mM BQ was placed in a quartz cell with a path length of 10 mm, and the absorption spectrum was measured using a UV-Vis-Near-Infrared spectrophotometer manufactured by JASCO Corporation. The results are shown in Figure 17. An acidic (pH 4) aqueous solution containing 0.2 mM BQ was placed in a flow cell, a UV lamp (irradiation peak wavelength: 254 nm) was installed, and irradiation was performed for 15 minutes. After irradiation, the absorption spectrum was measured in the same manner as above. Similarly, the absorption spectra of BQ aqueous solutions irradiated for a total of 30 minutes, 60 minutes, and 120 minutes were measured. The results are shown in Figure 17. Similarly, the absorption spectrum of an aqueous solution of 0.2 mM HQ was measured. The results are shown in Figure 17. Figure 19 shows the attenuation of absorbance for light at a wavelength of 246 nm for the BQ aqueous solutions after irradiation for each total irradiation time, with respect to the irradiation time.

[0105] (Reference Example 2) Except for using a neutral (pH 7) BQ aqueous solution, the absorption spectra for each irradiation time were measured in the same manner as in Reference Example 1. The results are shown in Figures A18 and 19.

[0106] (Example 10) The effect of the redox-mediated electrolytic cell of this embodiment was confirmed using the beaker half-cell 80 shown in Figure 20. In this embodiment, a reference electrode 88 was placed in the beaker half-cell. Anode 82: Pt wire electrode, wire diameter 0.5 mm, immersion length 23 cm, electrode area 3.61 cm² ２ Cathode 84: Pt wire electrode, wire diameter 0.5 mm, immersion length 23 cm, electrode area 3.61 cm² ２ Reference electrode 88: Ag / AgCl (saturated KCl aqueous solution) Electrolyte 83E: acidic aqueous solution (0.5M H ２ SO ４ (Mix with a 1M KOH aqueous solution to achieve a pH of 4) Mediator: 0.1M hydroquinone (HQ)

[0107] The current and voltage were measured when the applied voltage between the cathode and anode was swept within the range of 0.3V to 3.8V, relative to the reversible hydrogen electrode (RHE). The results are shown in Figure 21.

[0108] (Comparative Example 7) Current and voltage were measured in the same manner as in Example 10, except that the electrolyte did not contain hydroquinone (HQ). The results are shown in Figure 21.

[0109] (Example 11) Catechol (CC) Current and voltage were measured in the same manner as in Example 10, except that 0.1 M catechol (CC) was used instead of 0.1 M hydroquinone (HQ) as the mediator. The results are shown in Figure 22.

[0110] (Comparative Example 8) Current and voltage were measured in the same manner as in Example 11, except that the electrolyte did not contain catechol (CC). The results are shown in Figure 22.

[0111] (Example 12) <Verification experiment of redox-mediated rechargeable metal-air battery> Figure 23 shows a rechargeable metal-air battery 150 used to verify the effectiveness of the redox-mediated rechargeable metal-air battery of the present invention. The following electrodes and electrolytes were used. Charging unit anode 152: SUS mesh: thickness 0.20 mm, size 10 mm x 50 mm, wire diameter 0.15 mm, 30 mesh Charging unit cathode (discharge unit negative electrode) 154: Zn plate, thickness 0.2 mm, size (aperture diameter) φ20 mm Discharge unit positive electrode (air electrode) 158: SUS mesh 158-1: thickness 0.20 mm, size 10 mm x 50 mm, wire diameter 0.15 mm, 30 mesh; gas diffusion layer 158-2: carbon electrode TGP-H-120 (manufactured by Toray Industries, Inc., thickness 0.37 mm, size (aperture diameter) φ11.4 mm); catalyst layer 158-3: iron azaphthalocyanine supported carbon (manufactured by AZUL Energy, Inc., product name AZ-FTCB02CA) Charging unit electrolyte 153E: alkaline aqueous solution (6M KOH aqueous solution); redox-mediated reduced form: hydroquinone (HQ) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), concentration in the charging unit electrolyte: 0.1 M; Zn (CH ３ COO) ２ (Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): Concentration in the electrolyte of the charging unit: 0.2 M. Electrolyte of the discharge unit 158E: Alkaline aqueous solution (aqueous solution of 6 M KOH); Zn(CH ３ COO) ２ (Manufactured by Fujifilm Wako Pure Chemical Industries): Concentration in the electrolyte of the charging unit: 0.2 M

[0112] During charging: Apply a current of 0 mA / cm between the cathode 154 and anode 152 of the charging unit. ２ ~20.0mA / cm ２ Current and voltage were measured when sweeping within the specified range. The results are shown in Figure 24.

[0113] During discharge: The applied current is 0 mA / cm between the discharge unit positive electrode (air electrode) 158 and the discharge unit negative electrode 154. ２ ~20.0mA / cm ２ Current and voltage were measured when sweeping within the specified range. The results are shown in Figure 24.

[0114] (Comparative Example 9) Comparative Example 9 is a zinc-air secondary battery 160 shown in Figure 25, and had the same configuration as the hydroquinone rechargeable zinc-air battery 150 of Example 12, except that the electrolyte 152 of the charging unit of Example 12 did not contain hydroquinone (HQ). During discharge, measurements were taken in the same manner as in Example 12. The results are shown in Figure 26. During charging, the air electrode was used as the anode and the Zn plate as the cathode. The applied current between the air electrode and the Zn plate was 0 mA / cm². ２ ~20.0mA / cm ２ The current and voltage were measured when sweeping within the specified range. The results are shown in Figure 26.

[0115] (Discussion) Comparing Example 12 with Comparative Example 9, the potential of the hydroquinone oxidation reaction (HQOR) occurring at the cathode of the charging unit was lower than the potential of the oxygen evolution reaction (OER) occurring at the air electrode, so the charging voltage was reduced.

[0116] (Example 13) The effect of a redox-mediated seawater electrolysis cell was confirmed using a beaker half-cell. The beaker half-cell in Example 13 was equipped with a reference electrode. Cathode: Pt wire electrode Anode: Pt wire electrode Reference electrode: Ag / AgCl (saturated KCl aqueous solution) Electrolyte: Artificial seawater (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 0.6 M NaCl aqueous solution, pH = 6); 0.2 M hydroquinone (HQ)

[0117] The current and voltage were measured when the applied voltage between the cathode and anode was swept within the range of 0.5V to 2.5V, relative to the reversible hydrogen electrode (RHE). The results are shown in Figure 27.

[0118] (Comparative Example 10) "Chlorine Evolution Reaction (CER)" The current and voltage were measured in the same manner as in Example 13, except that the electrolyte did not contain hydroquinone (HQ). The results are shown in Figure 27.

[0119] (Comparative Example 11) "Oxygen Evolution Reaction (OER)" 0.5 M H in electrolyte ２ SO ４ A neutralized solution was prepared by mixing the aqueous solution with a 1 M KOH aqueous solution to a pH of 6. The current and voltage were measured in the same manner as in Example 13, except that it did not contain hydroquinone (HQ). The results are shown in Figure 27.

[0120] (Discussion) Comparing Example 13 with Comparative Examples 10 and 11, in an aqueous solution with a pH of 6, if hydroquinone (HQ) is not present, the potential of the chlorine generation reaction (CER) is lower than the potential of the oxygen generation reaction (OER). Therefore, in aqueous solutions containing chlorine, such as seawater, chlorine is generated from the cathode side. If hydroquinone (HQ) is present, the potential of the hydroquinone oxidation reaction (HQOR) occurring at the cathode is lower than the potential of chlorine generation, so neither oxygen nor chlorine is generated.

[0121] 2, 52, 72, 102...First anode 2E, 52E, 102E...First anode electrolyte 4, 54, 74, 104...First cathode 4E, 54E, 104E...First cathode electrolyte 6, 56, 76, 106...First diaphragm 10, 70...Redox-mediated electrolytic cell 20...Redox-mediated secondary battery cell 22...Second anode 22E...Second anode electrolyte 24...Second cathode 24E...Second cathode electrolyte 26...Second diaphragm 30...Dynamic regenerative redox-mediated electrolytic cell 50, 50A, 50B...Redox-mediated rechargeable metal-air battery 54...Negative electrode 58...Air electrode 73E, 83E...Electrolyte 77...Quartz glass flow cell 80...Beaker half cell 82... Cathode (Pt Wire) 84... Anode 88... Reference electrode 100... Water electrolytic cell (conventional technology) 150... Redox-mediated charging metal-air battery 152, 162... Anode current collector (SUS mesh) 153E, 163E... Electrolyte 154... Cathode (negative electrode, Zn plate) 155, 165... Gasket 158... Air electrode (positive electrode of discharge unit) 158-1... Air electrode current collector as positive electrode (SUS mesh) 158-2... Gas diffusion layer 158-3... Catalyst layer 158E... Electrolyte 160... Zinc-air battery

Claims

1. A redox-mediated electrolytic cell comprising: a first anode; a first cathode; a first anode electrolyte; a first cathode electrolyte; and a first diaphragm separating the first anode electrolyte and the first cathode electrolyte, wherein the first anode electrolyte contains a redox-mediated reducing form, and in the first anode, the oxidation potential of the redox-mediated reducing form is lower than the oxygen evolution potential.

2. The redox-mediated electrolytic cell according to claim 1, wherein at least the reduced form of the redox-mediated form is a water-soluble organic compound.

3. The redox-mediated electrolytic cell according to claim 2, wherein the organic compound is a reduced form of a compound having a quinone structure.

4. The redox-mediated electrolytic cell according to claim 3, wherein the compound having the quinone structure is at least one compound selected from the group consisting of compounds represented by the following formulas (1) to (10). (In formulas (1) to (10), each aromatic ring may independently have substituents. If a formula has one or more substituents, at least one substituent must be hydrophilic. If a formula has two or more substituents, the substituents may be the same or different.) 5. The redox-mediated electrolytic cell according to claim 1, wherein the open-circuit potential (0A) of the first anode is 0.5 or more and 2.0 or less relative to a standard hydrogen electrode (SHE).

6. The redox-mediated electrolytic cell according to claim 1, further comprising: a first anode chamber containing the first anode and the first anode electrolyte; a flow cell whose at least part is made of a transparent material; a circulation means for circulating the electrolyte between the first anode chamber and the flow cell; and an ultraviolet-visible light source.

7. A redox-mediated secondary battery cell comprising: a second cathode; a second anode; a second cathode electrolyte; a second anode electrolyte; and a second diaphragm separating the second cathode electrolyte and the second anode electrolyte, wherein the second cathode electrolyte contains a redox-mediated oxidizing agent; in a discharge state, the redox-mediated oxidizing agent is reduced in the second cathode to a redox-mediated reduced agent; in a charge state, the redox-mediated reduced agent is oxidized in the second cathode to a redox-mediated oxidizing agent; and in the second cathode, the oxidation potential of the redox-mediated reduced agent (oxidation-reduction agent) is lower than the oxygen evolution potential.

8. A dynamically regenerated redox-mediated electrolytic cell comprising a redox-mediated electrolytic cell according to any one of claims 1 to 6 and a redox-mediated secondary battery cell according to claim 7, wherein the first anode of the redox-mediated electrolytic cell and the second cathode of the redox-mediated electrolytic cell are placed in a common electrolyte, the common electrolyte is used as the first anode electrolyte of the redox-mediated electrolytic cell and as the second cathode electrolyte of the redox-mediated secondary battery cell, and the redox-mediated reduced form of the redox-mediated electrolytic cell is the same as the redox-mediated reduced form of the redox-mediated secondary battery cell.

9. A redox-mediated electrolytic apparatus comprising a redox-mediated electrolytic cell according to any one of claims 1 to 6, and a voltage injector for applying a voltage between the first cathode and the first anode.

10. A method for producing hydrogen, characterized by using the redox-mediated electrolysis apparatus described in claim 9.

11. A redox-mediated electrolytic apparatus comprising: a redox-mediated electrolytic cell according to claim 8; and a voltage injector for applying a voltage between the first cathode and the first anode.

12. A method for producing hydrogen, characterized by using the redox-mediated electrolysis apparatus described in claim 11.

13. A redox-mediated rechargeable metal-air battery comprising a redox-mediated electrolytic cell according to any one of claims 1 to 6 and a metal-air battery cell, wherein the metal-air battery cell comprises a positive electrode including an air electrode, a negative electrode including a metal (M), and an electrolyte containing ions of the metal (M), and the first cathode electrolyte of the redox-mediated electrolytic cell contains ions of the metal (M).

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