JP2021155818A - Electrode and method for producing hydrogen peroxide using this electrode - Google Patents

Abstract

[Problem] Hydrogen peroxide is produced at low cost with a lower applied voltage, higher current efficiency, and higher current density. [Solution] A method for producing hydrogen peroxide uses a specified electrode as a cathode to reduce oxygen in an electrolyte. This electrode is produced through a mixing and grinding process in which conductive carbon particles and a nickel salt are mixed in a liquid, the liquid is removed, and then the mixture is ground to obtain a composite containing the conductive carbon particles and the nickel salt, and a coating process in which a dispersion of the composite is applied to an electrode substrate, and the composite is held on the electrode substrate to obtain an electrode. This electrode has an electrode substrate, conductive carbon particles held on the electrode substrate, and nickel salt supported on the conductive carbon particles. [Selected Figure] Figure 1

Description

The present application relates to an electrode suitable for producing hydrogen peroxide by reducing oxygen in an electrode reaction, a method for producing this electrode, and a method for producing hydrogen peroxide using this electrode.

Hydrogen peroxide is used for disinfection, sterilization, bleaching, washing, oxidation, etc., and is industrially produced by the anthraquinone method utilizing hydrogenation and air oxidation of 2-alkylanthraquinone (non-patent documents). 1). However, since the anthraquinone method uses an anthraquinone derivative and an organic substance such as an organic solvent, it has a large environmental load. Further, the production of hydrogen peroxide by the anthraquinone method requires a separation operation and the like, which is expensive. Therefore, other industrial methods for producing hydrogen peroxide have been studied.

As another method for producing hydrogen peroxide, for example, reduction of oxygen in the cathode electrode (Patent Document 1, Patent Document 2, Patent Document 3, and Non-Patent Document 2), or an electrolytic solution containing a carbonate is used. A method for electrochemically producing hydrogen peroxide by an electrode reaction has been proposed, as in the case of oxidation of water at an anode electrode via an anion carbonate intermediate (Patent Document 4). Further, in principle, if the anode electrode has a positive potential higher than + 1.8V (RHE) and the potential of the cathode electrode has a negative potential higher than +0.68V (RHE), these can be combined and simultaneously overwhelmed at both poles. Hydrogen peroxide can also be produced.

Further, the conductive carbon oxide obtained by subjecting various electrically conductive carbon materials such as activated carbon or carbon black to oxidation treatment such as sulfate oxidation or nitric acid oxidation reduces oxygen to produce hydrogen peroxide. It has been found to be an excellent material for cathode electrodes. It has been reported that by using this conductive carbon oxide as a cathode electrode, not only the current efficiency in an alkaline electrolytic solution is improved, but also hydrogen hydrogen can be produced with high efficiency even in an acidic electrolytic solution having a low current efficiency. (Patent Document 5).

Further, in the oxidation of water at the anode electrode using an electrolytic solution containing a carbonate, light energy such as sunlight can be used by performing an electrode reaction under light irradiation using a light electrode as the anode electrode. Therefore, a method of producing hydrogen peroxide at low cost without applying an external voltage or by applying a low external voltage has also been proposed. (Non-Patent Document 3 and Patent Document 6). Further, by combining a cathode electrode using an oxidation-treated conductive carbon material as an electrode material and an anode electrode using an optical electrode, oxygen reduction in the cathode electrode and an anode electrode using an electrolytic solution containing a carbonate can be used. A method has been proposed in which water is simultaneously oxidized under light irradiation in (Patent Document 7) to efficiently produce hydrogen peroxide at both electrodes with high current efficiency (Patent Document 7).

Japanese Unexamined Patent Publication No. 2005-146344 Japanese Unexamined Patent Publication No. 2007-162033 Japanese Unexamined Patent Publication No. 2005-281507 Japanese Unexamined Patent Publication No. 2017-039981 Japanese Unexamined Patent Publication No. 2010-144203 JP-A-2017-171554 JP-A-2019-157223

Chemistry Handbook Applied Chemistry, 7th Edition, p. 632 I. Yamanaka et al. Chem. Lett., 2006, 35, No.12, 1330 K. Fuku et al. Chem. Commun., 2016, 52, 5406

It is preferred that the electrode reaction produce hydrogen peroxide at low cost with lower applied voltage, higher current efficiency, and higher current density. An object of the present application is to improve the performance of a cathode electrode that reduces oxygen so that hydrogen peroxide can be produced under such more preferable conditions.

The inventors of the present application examined the prior art and proceeded with experiments under various conditions with the aim of further improving the performance of the cathode electrode. As a result, it was found that the performance in the production of hydrogen peroxide is improved by newly adding a nickel salt to the conductive carbon material used as the material of the cathode electrode. Further, it has been found that the performance of the conductive carbon material containing a nickel salt of the present application is improved by immersing it in a liquid containing a carbonate.

An electrode of an aspect of the present application is an electrode for a cathode that reduces oxygen in an electrolytic solution to produce hydrogen hydrogen, and has an electrode base material, conductive carbon particles, and a nickel salt. The electrode of another aspect of the present application has an electrode base material, conductive carbon particles held on the electrode base material, and a nickel salt supported on the conductive carbon particles.

The method for producing an electrode of the present application includes a mixing and pulverizing step of mixing conductive carbon particles and a nickel salt in a liquid, removing the liquid, and then pulverizing the mixture to obtain a composite containing the conductive carbon particles and the nickel salt. It has a coating step of applying a dispersion liquid of a composite to an electrode base material and holding the composite on the electrode base material to obtain an electrode. The method for producing hydrogen peroxide of the present application uses the electrode of the present application or the electrode produced by the method for producing an electrode of the present application as a cathode electrode to reduce oxygen in an electrolytic solution.

According to the present application, hydrogen peroxide can be produced by reducing oxygen with high efficiency by using a cathode electrode containing conductive carbon particles and a nickel salt.

The schematic diagram of the cathode electrode of an embodiment. The schematic diagram of the apparatus used in the method for producing hydrogen peroxide of an embodiment. (A) Electron microscope image of the complex of Example 2, (b) Electron microscope image of the complex of Example 4.

FIG. 1 schematically shows an electrode 16 according to an embodiment of the present application. In the present embodiment, the electrode 16 is a cathode electrode that reduces oxygen in the electrolytic solution to produce hydrogen peroxide. The electrode 16 includes an electrode base material 34, conductive carbon particles 31, a nickel salt 32, and a binder 33. The electrode base material 34 is carbon paper obtained by molding carbon fibers into a sheet shape. The electrode base material 34 is not particularly limited as long as it is a base material made of a conductive material, and may be carbon fiber, conductive glass, a metal plate, or the like in addition to carbon paper.

As shown in FIG. 1, the conductive carbon particles 31 are held by the electrode base material 34. The conductive carbon material constituting the conductive carbon particles 31 is not particularly limited as long as it is a conductive carbon material, and examples thereof include carbon black and activated carbon. Among these, carbon black having excellent conductivity (for example, Ketjen black) is preferable. Further, the conductive carbon particles 31 may be made of a conductive carbon material that has been oxidized with nitric acid or the like.

As shown in FIG. 1, the nickel salt 32 is supported on the conductive carbon particles 31. That is, the nickel salt 32 is attached around the conductive carbon particles 31. The nickel salt 32 is an ionic bonding substance formed by an ionic bond between a nickel ion and a counter ion. Nickel salt 32 includes water-soluble nickel nitrate, nickel sulfate, nickel chloride, and nickel acetate, as well as water-insoluble nickel oxide, nickel hydroxide, nickel carbonate, nickel oxalate, nickel pyrophosphate, nickel arsenide, and the like. And nickel phosphate. Among these, the nickel salt 32 is preferably one or more of nickel nitrate, nickel sulfate, nickel chloride, nickel acetate, nickel oxide, nickel hydroxide, and nickel carbonate. This is because, as shown in the examples, a high-performance electrode 16 can be obtained.

Details will be described later, but in the process of producing the electrode 16 using the water-soluble nickel salt 32, the nickel salt 32 is dissolved in water in which the conductive carbon particles 31 are dispersed and is uniform in the conductive carbon particles 31. It is highly dispersed and easily supported. When the nickel salt 32 is uniformly and highly dispersed on the conductive carbon particles 31, the characteristics of the obtained electrode 16 are improved. Therefore, the nickel salt 32 is preferably water-soluble.

The binder 33 has a function of holding the conductive carbon particles 31 on the electrode base material 34 while ensuring the conduction between the electrode base material 34 and the conductive carbon particles 31. The binder 33 may be omitted as long as the conductive carbon particles 31 can be held on the electrode base material 34. In the present embodiment, as shown in FIG. 1, the binder 33 is provided so as to surround the contact portion between the electrode base material 34 and the conductive carbon particles 31. Examples of the binder 33 include a fluorine-based polymer (for example, Nafion), a conductive adhesive, and an organic polymer.

From the viewpoint of the performance of the electrode 16, particularly the current efficiency and current density when the electrode 16 is used as the cathode electrode to reduce oxygen in the electrolytic solution to produce hydrogen peroxide, nickel with respect to the mass of the conductive carbon particles 31. The ratio of the mass of the salt 32, that is, the content of the nickel salt 32 (mass of the nickel salt 32 / mass of the conductive carbon particles 31 × 100) is preferably 5% or more and 100% or less, and 5% or more and 50%. It is more preferably 5% or more and 10% or less. If the content of the nickel salt 32 is too large, the nickel salt 32 may aggregate and be supported on the electrode base material 34, and the performance of the electrode 16 may be slightly deteriorated.

The electrode manufacturing method of the embodiment of the present application includes a mixing and pulverizing step and a coating step. In the mixing and pulverizing step, the conductive carbon particles and the nickel salt are mixed in a liquid, the liquid is removed, and then the mixture is pulverized to obtain a composite containing the conductive carbon particles and the nickel salt. Specifically, conductive carbon particles and a nickel salt are added to a liquid, for example, water, and the mixture is mixed and dispersed by stirring, and ultrasonically treated as necessary. When this is filtered, dried, and pulverized, a composite containing conductive carbon particles and a nickel salt supported on the conductive carbon particles is obtained.

At this time, if a nickel salt that dissolves in a liquid, for example, water is used, the nickel salt is uniformly and highly dispersed on the conductive carbon particles. Electrodes obtained from a composite containing conductive carbon particles in which nickel salts are uniformly and highly dispersed are high performance. The mass of the nickel salt carried on the conductive carbon particles is roughly proportional to the mass of the nickel salt charged in the mixing and pulverizing step, and is about 80% to 90% of the mass of the charged nickel salt.

In the coating step, the dispersion liquid of the complex is applied to the electrode base material, and the composite is held on the electrode base material to obtain an electrode. Specifically, the complex and, if necessary, a binder are dispersed in a dispersion medium, for example, ethanol, and the dispersion is dropped onto the electrode substrate little by little to hold the complex on the electrode substrate. In this embodiment, a binder is used. The ratio of the mass of the binder to the mass of the complex is preferably 5% or more and 15% or less. The amount of the complex retained on the electrode substrate ^{is preferably 1.3 mg / cm 2} or more and 1.7 mg / cm ² or less, and more preferably about 1.5 mg / cm ² .

Further, the electrode manufacturing method of the present application may further include a dipping step. In this case, in the mixing and pulverizing step, a water-soluble nickel salt is used, and the conductive carbon particles and the nickel salt are mixed in water. Then, in the dipping step, after the mixing and pulverizing step, the complex is immersed in an aqueous solution of carbonate. The carbonate is not particularly limited as long as it is soluble in water, and examples thereof include carbonates such as alkali metals and alkaline earth metals. Specifically, lithium hydrogen carbonate, potassium hydrogen carbonate and the like can be exemplified. Among these, potassium hydrogencarbonate is preferable from the viewpoint of solubility and metal residue.

By the dipping step, at least a part of the nickel salt in the composite reacts with carbonate ions, and the water-soluble nickel salt becomes nickel carbonate unnecessary for water and is supported on the conductive carbon particles. Nickel, which is supported as a water-soluble salt on the conductive carbon particles constituting the electrode, tends to elute when it comes into contact with the electrolytic solution during the electrode reaction of hydrogen peroxide production. Therefore, by being supported on the conductive carbon particles as nickel carbonate insoluble in water by the dipping step, it is possible to suppress the elution of nickel from the electrode to the electrolytic solution during the electrode reaction of hydrogen generation.

It is also possible to disperse nickel carbonate and conductive carbon particles in water from the beginning to support nickel carbonate on the conductive carbon particles. However, since nickel carbonate is insoluble in water, it is not easy to uniformly and highly disperse nickel carbonate on the conductive carbon particles in the mixing and pulverizing step. Therefore, by substituting a part or more of the water-soluble nickel salt uniformly and highly dispersedly supported on the conductive carbon particles with nickel carbonate by the dipping step, the nickel salt insoluble in water is uniformly and highly dispersed. A composite supported on conductive carbon particles is obtained.

The dipping step may be performed after the mixing and crushing step and before the coating step, or after the mixing and crushing step and the coating step. Further, a method in which a nickel organic metal complex other than a nickel salt is dispersed and supported on conductive carbon particles and then calcined to remove the organic complex to obtain a composite is also conceivable. However, since the performance of the conductive carbon particles is deteriorated by firing, the method for producing an electrode of the present application is superior.

FIG. 2 schematically shows a hydrogen peroxide producing apparatus 10 used in the method for producing hydrogen peroxide according to the embodiment of the present application. The hydrogen peroxide production apparatus 10 includes an electrolytic tank 12, an anode electrode 14, a cathode electrode 16, an anode electrolytic solution 18, a cathode electrolytic solution 20, a diaphragm 22, an anode chamber 24, and a cathode chamber 26. There is. As the cathode electrode 16, the electrode of the present application or the electrode manufactured by the method for producing the electrode of the present application is used. As the electrolytic cell 12, the anode electrode 14, the anode electrolyte 18, the cathode electrolyte 20, the diaphragm 22, the anode chamber 24, and the cathode chamber 26, the same equipment as the conventional hydrogen peroxide production apparatus by reducing oxygen can be used.

In the method for producing hydrogen peroxide of the present embodiment, the electrode of the present application or the electrode produced by the method of producing the electrode of the present application is used as the cathode electrode 16, and the oxygen of the cathode electrolytic solution 20 which is an electrolytic solution is reduced to obtain hydrogen peroxide. To manufacture. According to the method for producing hydrogen peroxide of the present embodiment, hydrogen peroxide can be produced by reducing oxygen with a current efficiency of 60% or more. It is preferable to supply the reduced oxygen by bubbling the cathode electrolytic solution 20 with an oxygen-containing gas.

When the electrode containing the water-soluble nickel salt is the cathode electrode 16, the cathode electrolyte 20 preferably contains carbonate ions. This is because the electrode reaction of the cathode electrode 16 changes the water-soluble nickel salt into nickel carbonate which is unnecessary for water, and hydrogen peroxide can be produced while suppressing the deterioration of the performance of the cathode electrode 16. In this case, for example, an aqueous potassium hydrogen carbonate solution can be used as the cathode electrolytic solution 20.

That is, an electrode containing a water-soluble nickel salt is used as the cathode electrode 16, and oxygen in the cathode electrolytic solution 20 containing carbonate ions is reduced to produce hydrogen hydrogen. Further, the anode electrolytic solution 18 containing a carbonate can be used to oxidize water on the anode chamber 24 side to produce hydrogen peroxide at the same time as the cathode chamber 26. In this case, by using the optical electrode as the anode electrode 14, hydrogen hydrogen can be produced by using light energy without applying an external voltage or at a low external voltage.

(Example 1)
100 mg of a conductive carbon material (Lion Specialty Chemicals Co., Ltd., Ketjen Black EC600JD) and 5 mg of water-soluble nickel nitrate were mixed and dispersed in 20 mL of water, stirred for 1 hour, and then ultrasonically treated for 1 hour. After filtering this, it was dried at 100 ° C. for 20 hours and pulverized for 10 minutes to prepare a composite of a conductive carbon material and a nickel salt. The ratio of the mass of the nickel nitrate salt to the mass of the conductive carbon particles in the composite, that is, the content of nickel nitrate in the composite was 5% by mass. 3 mg of this complex and 6 mg of a fluorine-based polymer dispersion (Sigma-Aldrich, 5% by mass Nafion dispersion) were dispersed in 200 μL of ethanol to obtain a complex dispersion.

50 μL of this complex dispersion is placed on a carbon paper (Toray Industries, Inc., TGP-H-90 (Teflon water repellent treated)) substrate so that the amount of the complex retained is approximately 1.5 mg / cm ^2. The mixture was dropped once to obtain a cathode electrode. A voltage of + 0.5 V was applied to this cathode electrode to reduce oxygen in the electrolytic solution to produce hydrogen peroxide. A 2.0 M potassium hydrogen carbonate aqueous solution was used as the anode electrolytic solution and the cathode electrolytic solution, Ag / AgCl was used as the reference electrode, and platinum was used as the counter electrode. Table 1 shows the current efficiency and current density when hydrogen peroxide is generated.

(Examples 2 to 4)
The cathode electrodes of Examples 2 to 4 were prepared in the same manner as in Example 1 except that the content was changed to the nickel nitrate content shown in Table 1. The amount of nickel retained on the carbon paper substrate was estimated from XRF. As a result, Example 2, 2.6μg / cm ^2, was Example 4, 24.5μg / cm ^2. The nickel salt was retained on the carbon paper substrate in approximately proportion to the nickel nitrate content. Further, in the same manner as in Example 1, hydrogen peroxide was produced using the cathode electrodes of Examples 2 to 4. Table 1 shows the current efficiency and current density when hydrogen peroxide is generated.

(Comparative Example 1)
The cathode electrode of Comparative Example 1 was produced in the same manner as in Example 1 except that it did not contain nickel nitrate. Further, in the same manner as in Example 1, hydrogen peroxide was produced using the cathode electrode of Comparative Example 1. Table 1 shows the current efficiency and current density when hydrogen peroxide is generated.

In Comparative Example 1, the current efficiency was 59%, whereas in Examples 1 to 4, a high current efficiency of 65% or more was obtained. Further, even if the applied voltage was the same, the current densities of Examples 1 to 4 were 5.0 mA / cm ² or more, which was larger than the current density of 4.0 mA / cm ^{2 of Comparative Example 1.} In Examples 1 and 2 in which the nickel nitrate content was 5% by mass and 10% by mass, the current efficiency was 80% or more, which was particularly high.

3 (a) and 3 (b) show electron micrographs of the complexes of Example 2 and Example 4, respectively. In the complex of Example 2, the particle size of nickel nitrate was 10 to 40 nm, and in the complex of Example 4, the particle size of nickel nitrate was 1 μm or more. As described above, as the content of nickel nitrate increased, the dispersibility of nickel nitrate decreased and the particle size of nickel nitrate increased. The nickel nitrate contained in the complex of Example 2 was excellent in dispersibility. As described above, in the production of hydrogen peroxide using the cathode electrode in which the nickel salt is well dispersed, the current efficiency is high and the current density is high.

(Examples 5 to 10)
The cathode electrodes of Examples 5 to 11 were prepared in the same manner as in Example 2 except that the nickel salt shown in Table 2 was used. Further, in the same manner as in Example 1, hydrogen peroxide was produced using the cathode electrodes of Examples 5 to 11. Table 2 shows the current efficiency and current density when hydrogen peroxide is generated.

(Example 11)
The complex obtained in Example 2 was immersed in a 2.0 M aqueous potassium hydrogen carbonate solution and washed with water. Then, in the same manner as in Example 2, a cathode electrode was prepared using this complex. Further, hydrogen peroxide was produced using this cathode electrode in the same manner as in Example 1. Table 2 shows the current efficiency and current density when hydrogen peroxide is generated.

(Example 12)
A cathode electrode was produced in the same manner as in Example 2 except that the conductive carbon material subjected to the nitrate oxidation treatment disclosed in Patent Document 7 was used. Further, hydrogen peroxide was produced using this cathode electrode in the same manner as in Example 1. Table 2 shows the current efficiency and current density when hydrogen peroxide is generated.

(Example 13)
The complex obtained in Example 2 was washed with water. Then, in the same manner as in Example 1, a cathode electrode was prepared using this complex. Further, hydrogen peroxide was produced using this cathode electrode in the same manner as in Example 1. Table 2 shows the current efficiency and current density when hydrogen peroxide is generated.

As shown in Examples 5 to 7 of Table 2, when hydrogen peroxide is generated using a cathode electrode containing a water-soluble nickel salt other than nickel nitrate, a high current efficiency of 80% or more can be obtained. , The current density has also increased. Further, as shown in Examples 8 to 10 of Table 2, even if hydrogen peroxide is generated using a cathode electrode containing a nickel salt insoluble in water, a current of 70% or more higher than that of Comparative Example 1 is generated. Efficiency was obtained and the current density was high.

As shown in Example 11 of Table 2, by immersing the composite containing the conductive carbon material and the water-soluble nickel nitrate in a solution containing carbonate ions, the nickel component can be removed even if it is subsequently washed with water. It was not removed much from the composite, and the current efficiency was 82% and the current density was 4.0 mA / cm ² , and favorable results were obtained as in Example 2. Further, in Example 12, in addition to a high current efficiency of 83%, a large current density of ^{12.0 mA / cm 2 was obtained.}

For the carbon electrodes of Examples 2 and 11, the amount of nickel supported on the carbon paper substrate was estimated from XRF. A second embodiment in 2.6μg / cm ^2, it was 2.3μg / cm ² in Example 11. From this result, most of the water-soluble nickel salt supported on the surface of the conductive carbon material remained even after the subsequent washing with water of the composite by immersing the composite in a solution containing carbonate ions. I found out that I would do it. This is because when the complex containing the water-soluble nickel salt is immersed in a solution containing carbonate ions, the water-soluble nickel salt is changed to nickel carbonate which is insoluble in water, and is not removed so much in the subsequent washing with water.

In the cathode electrode of Example 13 prepared after washing the composite containing water-soluble nickel nitrate with water without immersing it in an aqueous potassium hydrogen carbonate solution, the current efficiency was 62% and the current density was 4.0 mA /. It was cm ^2. The cathode electrode of Example 13 had higher current efficiency than the cathode electrode of Comparative Example 1. As described above, if the composite containing water-soluble nickel nitrate is not immersed in a solution containing carbonate ions, the nickel is reduced in the subsequent washing of the composite with water, and the performance of the cathode electrode is deteriorated. However, since not all of the nickel components are removed by washing the complex with water, the cathode electrode of Example 13 was superior to the cathode electrode of Comparative Example 1.

10 Hydrogen peroxide production equipment 12 Electrolytic cell 14 Anode electrode 16 Electrode (cathode electrode)
18 Anode electrolyte 20 Cathode electrolyte 22 Cathode 24 Anode chamber 26 Cathode chamber 31 Conductive carbon particles 32 Nickel salt 33 Binder 34 Electrode base material

Claims (12)

An electrode for the cathode that reduces oxygen in the electrolyte to produce hydrogen peroxide.
An electrode having an electrode base material, conductive carbon particles, and a nickel salt. An electrode having an electrode base material, conductive carbon particles held on the electrode base material, and a nickel salt supported on the conductive carbon particles. In claim 1 or 2,
An electrode in which the ratio of the mass of the nickel salt to the mass of the conductive carbon particles is 5% or more and 100% or less. In claim 3,
An electrode in which the ratio of the mass of the nickel salt to the mass of the conductive carbon particles is 5% or more and 50% or less. In claim 4,
An electrode in which the ratio of the mass of the nickel salt to the mass of the conductive carbon particles is 5% or more and 10% or less. In any of claims 1 to 5,
An electrode in which the nickel salt is water-soluble. In any of claims 1 to 5,
An electrode in which the nickel salt is one or more of nickel nitrate, nickel sulfate, nickel chloride, nickel acetate, nickel oxide, nickel hydroxide, and nickel carbonate. A mixing and pulverizing step of mixing conductive carbon particles and a nickel salt in a liquid, removing the liquid, and then pulverizing the mixture to obtain a composite containing the conductive carbon particles and the nickel salt.
A coating step of applying the dispersion liquid of the complex to the electrode base material and holding the complex on the electrode base material to obtain an electrode.
A method for manufacturing an electrode having. In claim 8.
A method for producing an electrode in which the nickel salt in the complex is supported on the conductive carbon particles. In claim 8 or 9,
The nickel salt is water-soluble and
In the mixing and pulverizing step, the conductive carbon particles and the nickel salt are mixed in water, and the mixture is mixed.
A method for producing an electrode, further comprising a dipping step of immersing the composite in an aqueous solution of the carbonate after the mixing and pulverizing step. A method for producing hydrogen hydrogen, which reduces oxygen in an electrolytic solution, using the electrode according to any one of claims 1 to 8 or the electrode produced by the production method according to claim 9 or 10 as a cathode electrode. A method for producing hydrogen hydrogen, which reduces oxygen in an electrolytic solution containing carbonate ions, using the electrode of claim 6 or the electrode produced by the production method of claim 10 as a cathode electrode.

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