Electrolysis system and electrolysis method

Abstract

An electrolysis system (1) is provided with an electrolytic cell (2) and a mediator reduction tank (4). The electrolytic cell (2) is provided with: an anode electrode (10) that electrochemically oxidizes a reduced body MRed of a mediator; and a cathode electrode (8) that performs at least one of the generation of hydrogen gas on the basis of the electrochemical reduction of protons or water and the generation of an organic hydride on the basis of the electrochemical reduction of the hydride. The mediator reduction tank (4) non-photochemically reduces the oxidizer MOx of the mediator generated in the electrolytic cell (2).

Description

Technical Field

[0001] The present invention relates to an electrolysis system and an electrolysis method. Background Art

[0002] In recent years, in order to suppress the amount of carbon dioxide emissions during the generation process of energy, the use of renewable energy obtained from solar, wind, hydro, geothermal power generation, etc. has been expected. As an example, an electrolysis system that generates hydrogen by electrolyzing water using electricity from renewable energy has been proposed (for example, refer to Patent Document 1).

[0003] In addition, as an energy carrier for large-scale transportation and storage of hydrogen from renewable energy, organic hydrides have attracted attention. Regarding the manufacturing technology of organic hydrides, an electrolysis system is known in which protons are generated from water in an anode electrode, and an organic hydride is generated by hydrogenating a hydride using protons in a cathode electrode.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-165392

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2021-098872

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2017-178640

[0009] Patent Document 4: Japanese Patent Application Laid-Open No. 2015-509650 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] The inventors of the present invention have repeatedly conducted in-depth research on the above-mentioned electrolysis system, and as a result, have recognized that there is room for further improving the safety of the conventional electrolysis system.

[0012] The present invention has been completed in view of such a situation, and one of its purposes is to improve the safety of the electrolysis system.

[0013] Means for Solving the Problems

[0014] One aspect of the present invention is an electrolysis system. The electrolysis system includes an electrolytic cell and a mediator reduction tank connected to the electrolytic cell. The electrolytic cell has: an anode electrode that electrochemically oxidizes a reduced form of a mediator; and a cathode electrode that performs at least one of hydrogen generation and organic hydride generation, the hydrogen generation being based on electrochemical reduction of protons or water, and the organic hydride generation being based on electrochemical reduction of a hydride. The mediator reduction tank non-photochemically reduces an oxidized form of the mediator generated in the electrolytic cell.

[0015] Another aspect of the present invention is an electrolysis method using an electrolysis system including an electrolytic cell and a mediator reduction tank connected to the electrolytic cell. The electrolysis method includes: electrochemically oxidizing a reduced form of a mediator to generate an oxidized form of the mediator at an anode electrode of the electrolytic cell, electrochemically reducing a proton or water to generate at least one of hydrogen and electrochemically reducing a hydride to generate an organic hydride at a cathode electrode of the electrolytic cell, and non-photochemically reducing the oxidized form generated in the electrolytic cell to generate a reduced form in the mediator reduction tank.

[0016] In addition, any combination of the above-described components and a mode obtained by transforming the expressions of the present disclosure among methods, apparatuses, systems, etc. are also effective as modes of the present disclosure.

[0017] Effects of the Invention

[0018] According to the present invention, improvement in the safety of the electrolysis system can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the electrolysis system of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings. The embodiments are illustrative and do not limit the technical scope of the present invention. All features described in the embodiments and their combinations are not necessarily essential to the invention. Therefore, within the scope not departing from the inventive concept defined in the claims, various design changes such as changes, additions, and deletions of components can be made. The new embodiments with design changes have the effects of both the combined embodiments and the modifications. In the embodiments, regarding the content that allows such design changes, marks such as "in the present embodiment" and "in this embodiment" are used for emphasis, but even the content without such marks allows design changes. Any combination of the components described in the embodiments is also effective as a mode of the present invention. The same or equivalent components, members, and processes shown in the respective drawings are denoted by the same reference numerals, and repeated explanations are appropriately omitted. In addition, the scales and shapes of the respective parts shown in the drawings are conveniently set for easy explanation and are not subject to restrictive interpretation unless otherwise specified. In addition, when terms such as "first" and "second" are used in this specification or the claims, these terms do not indicate any order or importance but are used to distinguish one component from another. In addition, in each drawing, a part of the members that are not important for explaining the embodiments is omitted.

[0021] Figure 1Schematic diagram of the electrolysis system 1 of the embodiment. As an example, the electrolysis system 1 includes an electrolytic cell 2, a mediator reduction tank 4, and a catholyte tank 6. It should be noted that, in Figure 1 only one electrolytic cell 2 is illustrated, but the electrolysis system 1 may also include a plurality of electrolytic cells 2. In this case, the electrolytic cells 2 are stacked in the same orientation with the same arrangement of the cathode electrode 8 and the anode electrode 10, for example, and are connected in series electrically. It should be noted that the electrolytic cells 2 may also be connected in parallel, or a combination of series connection and parallel connection may be used. In addition, the configuration of the electrolysis system 1 is not limited to the configuration described below, and the configuration of each part may be changed appropriately.

[0022] The electrolytic cell 2 has a cathode electrode 8 (cathode), an anode electrode 10 (anode), and an electrolyte membrane 12. The cathode electrode 8 performs at least one of hydrogen generation and organic hydride generation. The hydrogen generation is based on the electrochemical reduction of protons or water, and the organic hydride generation is based on the electrochemical reduction of hydrides. "Electrochemical" in this embodiment means that a reaction is carried out by applying a voltage or superimposing a current from the outside of the electrolytic cell 2. The cathode electrode 8 has a cathode catalyst 9 for generating at least one of hydrogen and organic hydrides. As an example, a cathode catalyst layer containing the cathode catalyst 9 is provided on the cathode electrode 8.

[0023] In the case of generating hydrogen by the electrochemical reduction of protons or water, the cathode catalyst 9 may use a known catalyst such as platinum (Pt). In the case of generating organic hydrides by the electrochemical reduction of hydrides, the cathode catalyst 9 may use a known catalyst such as platinum and ruthenium (Ru). It should be noted that both hydrogen and organic hydrides may be generated in one electrolytic cell 2. For example, it may be an operation mode in which hydrogen is generated during the day when the demand for hydrogen is high, and organic hydrides are generated at night when the demand for hydrogen is low to store hydrogen. In the cathode catalyst layer, the cathode catalyst 9 may be supported by a porous catalyst carrier. The catalyst carrier is composed of an electronically conductive material such as porous carbon, porous metal, and porous metal oxide, for example. In addition, considering the possibility of the mediator permeating through the electrolyte membrane 12, the cathode catalyst 9 preferably has degradation resistance to the mediator. In addition, it is preferably not easy to adsorb the mediator. In addition, it is preferably not easy to precipitate the mediator.

[0024] When an organic hydride is generated at the cathode electrode 8 and the electrolyte membrane 12 has proton conductivity, the cathode catalyst 9 is covered with a cation-exchange type ionomer. For example, the catalyst support in the state of being loaded with the cathode catalyst 9 is covered with the ionomer. Examples of the cation-exchange type ionomer include perfluorosulfonic acid polymers such as Nafion (registered trademark), Flemion (registered trademark), Aquivion (registered trademark), Aciplex (registered trademark), and hydrocarbon-based sulfonic acid polymers. The ionomer preferably partially covers the cathode catalyst 9. Thereby, the three elements (hydride, proton, electron) required for the electrochemical reaction in the cathode electrode 8 can be efficiently supplied to the reaction field.

[0025] When an organic hydride is generated at the cathode electrode 8 and the electrolyte membrane 12 has anion conductivity, the cathode catalyst 9 is covered with an anion-exchange type ionomer. For example, the catalyst support in the state of being loaded with the cathode catalyst 9 is covered with the ionomer. Examples of the anion-exchange type ionomer include polymers such as Fumion (registered trademark). The ionomer preferably partially covers the cathode catalyst 9. Thereby, the three elements (hydride, water, electron) required for the electrochemical reaction in the cathode electrode 8 can be efficiently supplied to the reaction field.

[0026] A cathode diffusion layer may also be provided at the cathode electrode 8. As an example, the cathode catalyst layer is disposed in contact with one main surface of the electrolyte membrane 12. The cathode diffusion layer is disposed in contact with the main surface of the cathode catalyst layer opposite to the electrolyte membrane 12. The cathode diffusion layer is made of a conductive material such as carbon or metal. In addition, the cathode diffusion layer is a porous body such as a sintered body of fibers or particles, or a foam-formed body. Examples of the material constituting the cathode diffusion layer include carbon woven fabric (carbon cloth), carbon non-woven fabric, carbon paper, etc. It should be noted that the cathode diffusion layer may sometimes be omitted.

[0027] The anode electrode 10 electrochemically oxidizes the reduced form M of the mediator. Red The anode electrode 10 has an anode catalyst 11 that oxidizes the reduced form M of the mediator Red to generate the oxidized form M of the mediator Ox and electrons. As an example, an anode catalyst layer containing the anode catalyst 11 is provided in the anode electrode 10. The anode catalyst 11 can use a known porous body having conductivity. As a specific example of the anode catalyst 11, carbon porous bodies such as carbon paper and carbon felt can be used; metal porous bodies such as foamed metal; three-dimensional structures composed of a mixture of conductive particles and a binder, etc. It should be noted that the anode catalyst 11 may also be a structure in which a catalytic substance is loaded on a porous body that does not have catalytic activity or has catalytic activity.

[0028] The anode catalyst 11 only needs to have the activity for the oxidation reaction of the reductant M Red and does not need the activity for the oxygen evolution reaction (OER). Therefore, depending on the mediator used, a cheap electrode such as carbon can be used as the anode catalyst 11. It should be noted that the anode catalyst 11 preferably has durability at the redox potential of the mediator. In addition, the anode catalyst 11 may not undergo a redox reaction in the range of 0 to 2.5 V vs. RHE at the pH of the solution containing the mediator. In addition, the anode catalyst 11 preferably does not undergo a phase change in the range of 0.1 to 2.3 V vs. RHE, and more preferably does not undergo a phase change in the range of 0.2 to 2.0 V vs. RHE.

[0029] The mediator is preferably a liquid or a solid at normal temperature and pressure. "Normal temperature and pressure" in the present embodiment is, for example, 20°C and 1 atmosphere. When the mediator is a solid at normal temperature and pressure, it is preferably used in a state where the mediator is dissolved in a solvent such as the anode liquid LA described later. By using a mediator that is a liquid at normal temperature and pressure or a solution containing a solid mediator, the mediator can be easily supplied to the anode electrode 10. In addition, the mediator can easily react in the anode electrode 10. In addition, compared with a mediator that is a gas at normal temperature and pressure, the variety of mediators that can be selected can be increased.

[0030] In addition, the mediators can be classified into two types: inorganic substances and organic substances. Inorganic substances are mainly ionic salts. As an example, ions react as mediators in a state dissolved in a solvent. Organic substances themselves react as mediators. It should be noted that organic substances include organometallic compounds. Inorganic substances tend to have higher durability than organic substances. In particular, they have high stability in an oxidizing atmosphere. On the other hand, compared with inorganic substances, the structure of organic substances is easier to change, so it is easier to adjust physical properties such as potential and solubility than inorganic substances.

[0031] In addition, considering the possibility of moving through the electrolyte membrane 12 to the cathode electrode 8, it is preferable that the mediator is not easily deposited at the hydrogen generation potential of the cathode electrode 8. In addition, the mediator preferably does not easily penetrate the electrolyte membrane 12. In addition, the mediator preferably does not undergo a phase change in the range of -0.5 to 2.5 V vs. RHE at the pH of the solution containing the mediator, more preferably does not undergo a phase change in the range of -0.4 to 2.3 V vs. RHE, and further preferably does not undergo a phase change in the range of -0.3 to 2.0 V vs. RHE.

[0032] Preferably, the mediator is composed of a redox pair having an electrode potential higher than the electrode potential for generating oxygen at the anode electrode 10 at the operating temperature of the electrolytic cell 2. Examples of such a redox pair include a pair of an oxidized form and a reduced form of at least one substance selected from the group consisting of silver (Ag), manganese (Mn), cerium (Ce), cobalt (Co), chromium (Cr), a halogen, a halogen oxyacid, nickel (Ni), persulfuric acid, thallium (Tl), and selenic acid. In addition, by forming appropriate complexes of these substances, the redox potential of the mediator can be adjusted. The mediator may exist in a state dissolved or dispersed in the anode liquid LA described later. The standard electrode potential for oxygen evolution at the anode electrode 10 at the operating temperature of the electrolytic cell 2 can be calculated based on the Nernst equation.

[0033] In addition, when using an aqueous solution containing a mediator, the electrode potential of the mediator aqueous solution is preferably 1.12 V vs. RHE or higher, more preferably 1.48 V vs. RHE or higher. The theoretical reaction potential in the oxygen evolution reaction is 1.12 V vs. RHE at 150°C. In addition, the thermoneutral potential is 1.48 V vs. RHE. The "thermoneutral potential" means the potential at which there is no heat absorption or heat release during the reaction.

[0034] The higher the temperature, the lower the theoretical reaction potential of the oxygen evolution reaction, that is, the mediator reduction reaction. However, considering the boiling point of water, etc., it is assumed that the oxygen evolution reaction is carried out at 150°C or lower in the mediator reduction tank 4. In this case, if the electrode potential of the mediator aqueous solution is lower than 1.12 V vs. RHE, it is difficult to spontaneously carry out the oxygen evolution reaction in the mediator reduction tank 4. Therefore, the electrode potential of the mediator aqueous solution is preferably 1.12 V vs. RHE or higher. In addition, when the electrode potential of the mediator aqueous solution is 1.48 V vs. RHE or higher, which is the thermoneutral potential, the heat supply to the mediator reduction tank 4 from the outside can be omitted. Thereby, the reaction rate of the oxygen evolution reaction occurring in the mediator reduction tank 4 can be easily increased.

[0035] In addition, the electrode potential of the mediator aqueous solution is preferably 2.5 V vs. RHE or lower, more preferably 2.0 V vs. RHE or lower. In the anode electrode 10, heat generation loss equivalent to (the potential of the mediator - the thermoneutral potential) × current is generated. Therefore, the lower the potential of the mediator, the less the energy loss during the reaction. In fact, from the viewpoint of balancing the calorific value and the cooling cost of the electrolytic cell 2, that is, from the viewpoints of energy efficiency and electrode deterioration, the electrode potential of the mediator aqueous solution is preferably 2.5 V vs. RHE or lower. In addition, when the electrode potential of the mediator aqueous solution is 2.0 V vs. RHE or lower, it is easy to obtain an energy efficiency comparable to that of existing water electrolysis and organic hydride production.

[0036] An anode diffusion layer may also be provided on the anode electrode 10. As an example, the anode catalyst layer is arranged in contact with the other main surface of the electrolyte membrane 12. The anode diffusion layer is arranged in contact with the main surface of the anode catalyst layer on the side opposite to the electrolyte membrane 12. The anode diffusion layer may have the same structure as the cathode diffusion layer.

[0037] The electrolyte membrane 12 is disposed between the cathode electrode 8 and the anode electrode 10. As an example, the electrolyte membrane 12 has proton conductivity. In this case, the electrolyte membrane 12 allows protons to move from the anode electrode 10 to the cathode electrode 8. As an example, the electrolyte membrane 12 is composed of a solid polymer electrolyte membrane (PEM) having proton conductivity. Examples of the PEM include fluorine-based ion exchange membranes having sulfonic acid groups such as Nafion (registered trademark), and hydrocarbon-based ion exchange membranes such as Fumasep. It should be noted that, Figure 1 although the electrolyte membrane 12 having proton conductivity is illustrated, the configuration is not particularly limited thereto, and the electrolyte membrane 12 may also have anion conductivity. In this case, the electrolyte membrane 12 allows hydroxide ions to move from the cathode electrode 8 to the anode electrode 10. As an example, the electrolyte membrane 12 is composed of a solid polymer electrolyte membrane (AEM) having anion conductivity. Examples of the AEM include well-known anion exchange membranes such as Fumasep (registered trademark), Pention, and Sustainion (registered trademark). The electrolyte membrane 12 is preferably an electrolyte membrane through which mediators are less likely to pass.

[0038] As an example, the membrane electrode assembly composed of the cathode electrode 8, the anode electrode 10, and the electrolyte membrane 12 is sandwiched between the plate member 14a and the plate member 14b. The plate members 14a and 14b are made of metals such as stainless steel and titanium, for example. The plate member 14a is laminated on the membrane electrode assembly from the cathode electrode 8 side. The plate member 14b is laminated on the membrane electrode assembly from the anode electrode 10 side. The gap between the plate member 14a and the membrane electrode assembly is sealed by the gasket 16a. The gap between the plate member 14b and the membrane electrode assembly is sealed by the gasket 16b. In the case where the electrolysis system 1 includes only one electrolytic cell 2, the pair of plate members 14a and 14b may correspond to so-called end plates. In the case where the electrolysis system 1 includes a plurality of electrolytic cells 2 and other electrolytic cells 2 are arranged beside the plate member 14a or the plate member 14b, this plate member may correspond to so-called separators.

[0039] The cathode electrode 8 is connected to the cathode flow path 18. The cathode flow path 18 supplies and discharges the cathode liquid LC to and from the cathode electrode 8. It should be noted that a groove may also be provided on the main surface of the plate member 14a on the side facing the cathode electrode 8, and this groove constitutes the cathode flow path 18. When hydrogen is generated at the cathode electrode 8, the cathode liquid LC is, for example, water. When an organic hydride is generated at the cathode electrode 8, the cathode liquid LC contains the substance to be hydrogenated (hydrogenation target substance) as a raw material for the organic hydride. As an example, the cathode liquid LC does not contain an organic hydride before the start of operation of the electrolysis system 1, and an organic hydride generated by electrolysis is mixed in after the start of operation, thereby becoming a mixed liquid of the substance to be hydrogenated and the organic hydride. The substance to be hydrogenated and the organic hydride are preferably liquids at 20 °C and 1 atmosphere.

[0040] The substance to be hydrogenated and the organic hydride are not particularly limited as long as they are organic compounds that can add / remove hydrogen by reversibly undergoing a hydrogenation reaction / dehydrogenation reaction. As the substance to be hydrogenated and the organic hydride used in the present embodiment, an acetone - isopropanol system, a benzoquinone - hydroquinone system, an aromatic hydrocarbon system, etc. can be widely used. Among them, from the viewpoints of transportability during energy transport, etc., an aromatic hydrocarbon system is preferred. Generally, the substance to be hydrogenated and the organic hydride of the aromatic hydrocarbon system are hydrophobic.

[0041] The aromatic hydrocarbon compound used as the substance to be hydrogenated is a compound containing at least 1 aromatic ring. Examples of the aromatic hydrocarbon compound include, for example, benzene, alkylbenzene, naphthalene, alkylnaphthalene, anthracene, diphenylethane, etc. Alkylbenzene includes compounds in which 1 to 4 hydrogen atoms of the aromatic ring are substituted by a linear or branched alkyl group having 1 to 6 carbon atoms. Examples of such compounds include, for example, toluene, xylene, mesitylene, ethylbenzene, diethylbenzene, etc. Alkylnaphthalene includes compounds in which 1 to 4 hydrogen atoms of the aromatic ring are substituted by a linear or branched alkyl group having 1 to 6 carbon atoms. Examples of such compounds include, for example, methylnaphthalene, etc. They can be used alone or in combination.

[0042] The substance to be hydrogenated is preferably at least one of toluene and benzene. It should be noted that nitrogen - containing heterocyclic aromatic compounds such as quinoline, isoquinoline, N - alkylpyrrole, N - alkylindole, N - alkyldibenzopyrrole, etc. can also be used as the substance to be hydrogenated. The organic hydride is obtained by hydrogenating the above - mentioned substance to be hydrogenated, and examples thereof include cyclohexane, methylcyclohexane, dimethylcyclohexane, decahydroquinoline, etc.

[0043] The anode electrode 10 is connected to the anode flow path 20. The anode flow path 20 supplies and discharges the anode liquid LA to and from the anode electrode 10. It should be noted that a groove may also be provided on the main surface of the plate member 14b on the side facing the anode electrode 10, and this groove constitutes the anode flow path 20. The anode liquid LA supplied to the anode electrode 10 contains the reduced form M of the mediator RedThe anolyte LA discharged from the anode electrode 10 contains the oxidized form M of the mediator. Ox In addition, when the electrolyte membrane 12 is made of PEM, the anolyte LA supplied to the anode electrode 10 also contains protons. Further, when the electrolyte membrane 12 is made of AEM, the anolyte LA discharged from the anode electrode 10 also contains hydroxide ions.

[0044] Electric power is supplied from the power source 22 to the electrolytic cell 2. By supplying the electric power from the power source 22, a prescribed electrolysis voltage is applied between the cathode electrode 8 and the anode electrode 10, and an electrolysis current flows. The power source 22 delivers the electric power supplied from the external power supply device 38 to the electrolytic cell 2. The power supply device 38 may be composed of a power generation device that generates electric power using renewable energy, such as a wind power generation device 40, a solar power generation device 42, etc. In this case, the power source 22 supplies electric power from renewable energy to the electrolytic cell 2. It should be noted that the power supply device 38 is not limited to a renewable energy power generation device, and may also be a system power supply, or a power storage device that stores electric power from a renewable energy power generation device or a system power supply, etc. Further, it may also be a combination of two or more of them.

[0045] The reactions that occur when hydrogen is generated in the electrolytic cell 2 equipped with PEM are as follows. It should be noted that in the following reactions, as an example of the mediator, the redox pair of Mn 2+ / Mn 3+ is shown.

[0046] <Electrode reaction at the anode electrode>

[0047] 2Mn 2+ →2Mn 3+ +2e -

[0048] <Electrode reaction at the cathode electrode>

[0049] 2H + +2e - →H 2

[0050] That is, the electrode reaction at the anode electrode 10 and the electrode reaction at the cathode electrode 8 proceed in parallel. In the anode electrode 10, an oxidation reaction of the reductant M Red contained in the anolyte LA occurs, generating the oxidized form M Ox and electrons. That is, the anode electrode 10 oxidizes the reductant M Red through a reaction that does not involve the generation of gas. "Oxidizing the reductant M Red through a reaction that does not involve the generation of gas" in the present embodiment means that when the reductant M RedNo gas is generated in the main oxidation reaction, which also includes the case where a side reaction accompanied by gas generation occurs during the oxidation of the reductant Red The electrons generated are sent to the cathode electrode 8 by the power source 22. The oxidized substance M Ox is discharged from the anode flow path 20 to the outside of the electrolytic cell 2. In addition, protons in the anolyte LA move from the anode electrode 10 to the cathode electrode 8 through the electrolyte membrane 12. At the cathode electrode 8, hydrogen gas is generated by the reaction of protons moving from the anode electrode 10 side with electrons. The generated hydrogen gas is discharged from the cathode flow path 18 to the outside of the electrolytic cell 2.

[0051] The reactions that occur when generating organic hydrides in the electrolytic cell 2 equipped with a PEM are as follows. It should be noted that in the following reactions, as an example of a mediator, the redox pair of Mn 2+ / Mn 3+ is shown, and as an example of a hydride, toluene (TL) is shown. When toluene is used as the hydride, the resulting organic hydride is methylcyclohexane (MCH).

[0052] <Electrode reaction at the anode electrode>

[0053] 6Mn 2+ →6Mn 3+ +6e -

[0054] <Electrode reaction at the cathode electrode>

[0055] TL + 6H + + 6e - →MCH

[0056] That is, the electrode reaction at the anode electrode 10 and the electrode reaction at the cathode electrode 8 proceed in parallel. At the anode electrode 10, an oxidation reaction of the reductant M Red contained in the anolyte LA occurs, generating the oxidized substance M Ox and electrons. The generated electrons are sent to the cathode electrode 8 by the power source 22. The oxidized substance M Ox is discharged from the anode flow path 20 to the outside of the electrolytic cell 2. In addition, protons in the anolyte LA move from the anode electrode 10 to the cathode electrode 8 through the electrolyte membrane 12. At the cathode electrode 8, toluene is hydrogenated to form methylcyclohexane by the reaction of toluene contained in the catholyte LC with protons moving from the anode electrode 10 side. The generated methylcyclohexane is discharged from the cathode flow path 18 to the outside of the electrolytic cell 2.

[0057] The reactions that occur when generating hydrogen gas in the electrolytic cell 2 equipped with an AEM are as follows. It should be noted that in the following reactions, as an example of a mediator, the redox pair of Mn 2+ / Mn 3+Redox pair.

[0058] <Anodic electrode reaction>

[0059] Mn 2+ →Mn 3+ +e -

[0060] <Cathodic electrode reaction>

[0061] H 2 O+e - →1 / 2H 2 +OH -

[0062] That is, the electrode reaction at the cathodic electrode 8 proceeds in parallel with the electrode reaction at the anodic electrode 10. In the cathodic electrode 8, a reduction reaction of the water contained in the catholyte LC occurs to generate hydrogen and hydroxide ions. The generated hydrogen is discharged from the cathode flow path 18 to the outside of the electrolytic cell 2. The generated hydroxide ions move from the cathodic electrode 8 to the anodic electrode 10 through the electrolyte membrane 12, and then are discharged from the anode flow path 20 to the outside of the electrolytic cell 2. In the anodic electrode 10, through the reaction of the reductant M Red contained in the anolyte LA, the oxidant M Ox and electrons are generated. The generated electrons are sent to the cathodic electrode 8 by the power source 22. The oxidant M Ox is discharged from the anode flow path 20 to the outside of the electrolytic cell 2.

[0063] The reaction that occurs when an organic hydride is generated in the electrolytic cell 2 equipped with AEM is as follows. It should be noted that in the following reactions, as an example of a mediator, the redox pair of Mn 2+ / Mn 3+ is shown, and as an example of a hydride, toluene (TL) is shown.

[0064] <Anodic electrode reaction>

[0065] 6Mn 2+ →6Mn 3+ +6e -

[0066] <Cathodic electrode reaction>

[0067] TL+6H 2 O+6e - →MCH+6OH -

[0068] That is, the electrode reaction at the cathode electrode 8 proceeds in parallel with the electrode reaction at the anode electrode 10. In the cathode electrode 8, a reduction reaction of toluene contained in the catholyte LC occurs, generating methylcyclohexane and hydroxide ions. The water used for the electrode reaction at the cathode electrode 8 is supplied, for example, by water that enters from the anode electrode 10 side through the electrolyte membrane 12. The generated methylcyclohexane is discharged from the cathode flow path 18 to the outside of the electrolytic cell 2. The generated hydroxide ions move from the cathode electrode 8 to the anode electrode 10 through the electrolyte membrane 12 and then are discharged from the anode flow path 20 to the outside of the electrolytic cell 2. In the anode electrode 10, through the reaction of the reductant M Red in the anolyte LA, an oxidant M Ox and electrons are generated. The generated electrons are sent to the cathode electrode 8 by the power supply 22. The oxidant M Ox is discharged from the anode flow path 20 to the outside of the electrolytic cell 2.

[0069] The cathode flow path 18 is connected to the catholyte tank 6 through the first cathode pipe 24 and the second cathode pipe 26. The catholyte LC is stored in the catholyte tank 6. One end of the first cathode pipe 24 is connected to the catholyte tank 6, and the other end of the first cathode pipe 24 is connected to the inlet of the cathode flow path 18. A cathode pump 28 is provided in the middle of the first cathode pipe 24. The cathode pump 28 can be composed of a known pump such as a gear pump or a piston pump. It should be noted that the circulation of the catholyte LC can also be achieved by a liquid delivery device other than a pump. One end of the second cathode pipe 26 is connected to the outlet of the cathode flow path 18, and the other end of the second cathode pipe 26 is connected to the catholyte tank 6.

[0070] The catholyte LC in the catholyte tank 6 flows into the cathode electrode 8 through the first cathode pipe 24 by driving the cathode pump 28. The catholyte LC in the cathode electrode 8 returns to the catholyte tank 6 through the second cathode pipe 26. When hydrogen is generated in the cathode electrode 8, the generated hydrogen flows into the catholyte tank 6 together with the catholyte LC. The catholyte tank 6 also functions as a gas-liquid separator to separate the hydrogen in the catholyte LC from the catholyte LC. The separated hydrogen is taken out of the system for utilization. It should be noted that when an organic hydride is generated in the cathode electrode 8, hydrogen may sometimes be generated due to side reactions. In this case, the hydrogen is also separated from the catholyte LC in the catholyte tank 6 and taken out of the system. It should be noted that a gas-liquid separator can also be provided separately from the catholyte tank 6.

[0071] In this embodiment, the catholyte LC is circulated between the cathode electrode 8 and the catholyte tank 6. However, the configuration is not limited thereto, and the catholyte LC may be configured to be transported out of the system from the cathode electrode 8 without returning to the catholyte tank 6. In addition, when hydrogen is generated at the cathode electrode 8 of the electrolytic cell 2 equipped with a PEM, the supply of the catholyte LC to the cathode electrode 8 can be omitted. Thus, the catholyte tank 6, the first cathode pipe 24, the cathode pump 28, etc. related to the supply of the catholyte LC can also be omitted.

[0072] The anode flow path 20 is connected to the mediator reduction tank 4 via the first anode pipe 30 and the second anode pipe 32. Therefore, the electrolytic cell 2 and the mediator reduction tank 4 are physically separated from each other. "Physically separated" in this embodiment means that the electrolytic cell 2 itself or the housing of the electrolytic cell 2 is separated from the tank wall of the mediator reduction tank 4, that is, they are not in direct contact, and there may be a space between the two, or a certain substance or structure may be interposed therebetween. The anolyte LA is stored in the mediator reduction tank 4. When the electrolyte membrane 12 is composed of a PEM, considering the oxidation reaction of the reductant M Red occurring at the anode electrode 10, it is preferable to place the anode electrode 10 under acidic conditions. Therefore, the anolyte LA is preferably acidic. When the electrolyte membrane 12 is composed of an AEM, the anolyte LA is preferably alkaline. When using the redox pair of Mn 2+ / Mn 3+ as the mediator, as an example, the anolyte LA is an aqueous sulfuric acid solution containing Mn 2+ / Mn 3+ . It should be noted that on the cathode side, instead of the redox reaction of the mediator, hydrogen and organic hydrides, which are the target substances, are directly generated. Therefore, the cathode electrode 8 can also be set under non-acidic conditions.

[0073] One end of the first anode pipe 30 is connected to the mediator reduction tank 4, and the other end of the first anode pipe 30 is connected to the inlet of the anode flow path 20. An anode pump 34 is provided in the middle of the first anode pipe 30. The anode pump 34 can be composed of a known pump such as a gear pump or a cylinder pump, for example. It should be noted that the circulation of the anolyte LA can also be achieved by a liquid delivery device other than a pump. One end of the second anode pipe 32 is connected to the outlet of the anode flow path 20, and the other end of the second anode pipe 32 is connected to the mediator reduction tank 4.

[0074] The anolyte LA in the mediator reduction tank 4 flows into the anode electrode 10 via the first anode pipe 30 by driving the anode pump 34. The anolyte LA in the anode electrode 10 returns to the mediator reduction tank 4 via the second anode pipe 32. The oxidant M generated at the anode electrode 10 OxIt is sent to the mediator reduction tank 4 in a state of being contained in the anolyte LA. When the electrolyte membrane 12 is composed of AEM, the hydroxide ions moving from the cathode electrode 8 to the anode electrode 10 are also sent to the mediator reduction tank 4 in a state of being contained in the anolyte LA.

[0075] The mediator reduction tank 4 non-photochemically reduces the oxidized form M of the mediator generated in the electrolytic cell 2. Ox By using a mediator that reacts non-photochemically, for example, the following operation can be performed: the mediator is oxidized using the electric power obtained by solar power generation during the day, and the OER reaction is performed at night to reduce the mediator. Thus, a system that can effectively utilize solar power generation can be constructed. "Non-photochemically" in the present embodiment means that the reaction proceeds without relying on a photocatalyst. In addition, the "photocatalyst" in the present embodiment refers to a photocatalyst having an effect of promoting the chemical reaction of other substances using light energy as a driving force, that is, a photocatalyst that exhibits a catalytic action through light energy. As an example, the mediator reduction tank 4 has a mediator reduction catalyst 36 that reacts the oxidized form M Ox with water or hydroxide ions to generate a reduced form M Red and oxygen. As a specific example of the mediator reduction catalyst 36, at least one oxide or compound selected from the group consisting of iridium (Ir), ruthenium, platinum (Pt), palladium (Pd), rhodium (Rh), nickel, cobalt, manganese, chromium, iron, etc. can be cited.

[0076] The OER catalyst used in the mediator reduction tank 4, that is, the mediator reduction catalyst 36, is different from the OER catalyst used in the anode electrode where the oxygen evolution reaction occurs, that is, the conventional anode catalyst, and does not require conductivity. Most of the OER catalysts used in the anode electrode use highly active oxides such as metal oxides. However, oxides tend to have low conductivity. Therefore, ensuring the conductivity of the anode electrode has become a problem. In contrast, the OER catalyst used in the mediator reduction tank 4 does not require conductivity, so the above-mentioned compromise can be avoided. The mediator reduction catalyst 36 is preferably stable in the atmosphere of the anolyte LA. In addition, it is preferably durable at the redox potential of the mediator. It should be noted that depending on the type of mediator, there are cases where the reduced form M can be converted into the oxidized form M Red by heating without using the mediator reduction catalyst 36. Ox

[0077] In the mediator reduction tank 4, as shown in the following formula, the oxidized form M Ox reacts with water or hydroxide ions (non-electrochemical reaction and non-photochemical reaction).

[0078] <Reaction 1 in the mediator reduction tank>

[0079] nH 2 O + M Ox ​→ n / 2 O 2 + nH + + M Red (n is an integer of 1 or more)

[0080] <Reaction 2 in the mediator reduction tank>

[0081] nOH - + M Ox → n / 4 O 2 + n / 2 H 2 O + M Red (n is an integer of 1 or more)

[0082] <Reaction 3 in the mediator reduction tank>

[0083] H 2 O + M Ox → 1 / 2 O 2 + M Red

[0084] Reaction 1 is a reaction for generating an acid-based mediator with n-valent redox. The "acid-based mediator" in this embodiment is a mediator composed of the above-mentioned inorganic substances that become ions under acidic conditions with a pH less than 7, and is mainly used when the electrolyte membrane 12 is composed of PEM. In Reaction 1, oxygen, protons, and electrons are generated from water in the anolyte LA. The mediator reduction tank 4 also functions as a gas-liquid separator to separate the generated oxygen from the anolyte LA. The separated oxygen is taken out of the system. It should be noted that a gas-liquid separator can also be provided separately from the mediator reduction tank 4. The electrons generated from water are supplied to the oxidant M in the anolyte LA Ox . Thus, the oxidant M Ox is reduced to generate the reductant M Red .

[0085] Reaction 2 is a reaction for generating a base-based mediator with n-valent redox. The "base-based mediator" in this embodiment is a mediator composed of the above-mentioned inorganic substances that become ions under alkaline conditions with a pH exceeding 7, and is mainly used when the electrolyte membrane 12 is composed of AEM. In Reaction 2, oxygen, water, and electrons are generated from the hydroxide ions in the anolyte LA. Oxygen is separated from the anolyte LA in the mediator reduction tank 4. The electrons are supplied to the oxidant M Ox , generating the reductant M Red .

[0086] Reaction 3 is a reaction of an organic-based mediator. The "organic-based mediator" in this embodiment is a mediator composed of the above-mentioned organic substances, and is mainly used when the electrolyte membrane 12 is composed of PEM. Here, as an example, the mediator and 2 H +Reactions during combination. In Reaction 3, oxygen, protons, and electrons are generated from water in the anolyte LA. Oxygen is separated from the anolyte LA. The electrons and protons are supplied to the oxidant M in the anolyte LA Ox , generating the reductant M Red .

[0087] The reductant M generated in the mediator reduction tank 4 Red is sent to the anode electrode 10 in a state of being contained in the anolyte LA. The reductant M sent to the anode electrode 10 Red is again supplied to the production reaction (electrochemical reaction) of hydrogen or organic hydride. Additionally, in the cases of Reaction 1 and Reaction 3, the protons generated in the mediator reduction tank 4 are also sent to the anode electrode 10 in a state of being contained in the anolyte LA. The protons sent to the anode electrode 10 move to the cathode electrode 8 through the electrolyte membrane 12 composed of PEM

[0088] It should be noted that protons are in an ionized state in the anolyte LA in Reaction 1, but are in a state of being combined with the reductant M Red in Reaction 3. As an example of the state of protons being combined with the reductant M Red , a state can be cited where two keto groups of an anthraquinone derivative constituting an organic mediator are each combined with a proton to form an anthrahydroquinone derivative. In the case of protons being combined with the reductant M Red , the reductant M Red is oxidized while the protons are released and move to the cathode electrode 8 through the electrolyte membrane 12

[0089] Preferably, the operating temperature of the mediator reduction tank 4 is adjusted to a temperature higher than the operating temperature of the electrolytic cell 2. For example, the electrolysis system 1 includes a known heater 44 for heating the mediator reduction tank 4. It should be noted that a heater for heating the electrolytic cell 2 can also be provided. The inside of the mediator reduction tank 4 becomes a temperature higher than that of the membrane electrode assembly of the electrolytic cell 2 by being heated by the heater 44. The oxygen evolution reaction occurring in the mediator reduction tank 4 easily proceeds at a high temperature. Therefore, the mediator reduction tank 4 is preferably adjusted to a temperature of 80 °C or higher, for example. On the other hand, considering the heat resistance of the electrolyte membrane 12 and the like, it is preferable to adjust the electrolytic cell 2 to a temperature lower than the preferable temperature in the mediator reduction tank 4

[0090] In contrast, in the electrolysis system 1 of the present embodiment, the electrolytic cell 2 is separated from the mediator reduction tank 4. Therefore, the temperatures of the electrolytic cell 2 and the mediator reduction tank 4 can be adjusted independently of each other. Thereby, the temperature of the mediator reduction tank 4 can be made higher than that of the electrolytic cell 2, facilitating the oxygen evolution reaction in the mediator reduction tank 4. The heater 44 can also heat the mediator reduction tank 4 using waste heat from facilities such as petroleum refining equipment. It should be noted that the mediator reduction tank 4 may not be heated. Thereby, the heater 44 can be omitted. In addition, the energy required for heating the mediator reduction tank 4 can be reduced.

[0091] As described above, in the electrolysis system 1 of the present embodiment, oxygen is not generated in the electrolytic cell 2, but is generated in the mediator reduction tank 4 provided separately from the electrolytic cell 2. Therefore, even when the electrolyte membrane 12 is broken, oxygen can be prevented from mixing into the hydrogen generated at the cathode electrode 8. Thereby, the safety of the electrolysis system 1 can be improved. In addition, it can be used for the oxidation reaction of the reductant M Red The catalyst for the oxidation reaction has a higher degree of freedom of selection compared to the anode catalysts in conventional water electrolysis and organic hydride production. Therefore, the cost reduction of the electrolysis system 1 can be achieved.

[0092] In addition, the reaction occurring at the anode electrode 10 does not generate a gas with a large volume increase. Therefore, the diameters of the manifold of the electrolytic cell 2 and the piping located downstream of the electrolytic cell 2 can be reduced. Thereby, a significant cost reduction of the electrolysis system 1 can be achieved. In addition, there is no need to take measures against pressure fluctuations caused by gas generation in the electrolytic cell 2, or the strength required for the electrolytic cell 2 as such a measure can be reduced. Therefore, the structure of the electrolytic cell 2 can be simplified. Thereby, the volume of the electrolytic cell 2 can be reduced, and cost reduction can be achieved. In addition, when an organic hydride is generated at the cathode electrode 8, substantially no gas is generated at the cathode electrode 8 either. Thereby, the structure of the electrolytic cell 2 can be further simplified. In addition, when the power supply 22 supplies power from a renewable energy source with large output fluctuations to the electrolytic cell 2, the load applied to the electrolytic cell 2 is also likely to change greatly. In contrast, by not generating gas at least at the anode electrode 10, the electrolytic cell 2 can easily withstand load fluctuations. Therefore, a leveling device such as a storage battery provided to stabilize the supplied power can be omitted.

[0093] In addition, by at least not substantially generating gas at the anode electrode 10, the possibility of physical damage to the electrolyte membrane 12 can be reduced. Further, when oxygen is generated at the anode electrode, sometimes the oxygen permeates through the electrolyte membrane and moves to the cathode electrode. The oxygen that has moved to the cathode electrode is reduced at the cathode electrode to form oxygen radical species. These oxygen radical species can decompose the electrolyte membrane. Therefore, chemical deterioration of the electrolyte membrane may occur. In contrast, according to the electrolysis system 1 of the present embodiment, chemical deterioration of the electrolyte membrane 12 can also be suppressed. Thereby, long life of the electrolyte membrane 12 and thus the electrolytic cell 2 can be achieved. In addition, in conventional electrolytic cells, in order to suppress chemical deterioration of the electrolyte membrane, an expensive perfluorosulfonic acid-based electrolyte membrane with high durability against oxygen radical species has been used. In addition, the thickness of the electrolyte membrane has been increased. In contrast, according to the electrolysis system 1 of the present embodiment, a cheap electrolyte membrane with low durability against oxygen radical species, such as a hydrocarbon membrane, can be used. In addition, thinning of the electrolyte membrane can also be achieved. Thereby, significant cost reduction of the electrolytic cell 2 can be achieved.

[0094] In addition, since the mediator reduction catalyst 36 is isolated from the electrolytic cell 2, it is easy to replace the mediator reduction catalyst 36. Thereby, improvement in the maintainability of the electrolysis system 1 can be achieved. In addition, in conventional electrolytic cells, deterioration of the OER catalyst (anode catalyst) is dominant for the life of the electrolytic cell. In contrast, in the present embodiment, since the OER catalyst (mediator reduction catalyst 36) is isolated from the electrolytic cell 2, long life of the electrolytic cell 2 can be achieved.

[0095] In addition, since the mediator reduction catalyst 36 is isolated from the electrolytic cell 2, the durability required for the mediator reduction catalyst 36 can be reduced. Thereby, an OER catalyst with low durability but low cost can be used. In addition, since it is released from the restriction of the filling volume due to the size of the electrolytic cell 2, a large amount of OER catalyst can be filled in the mediator reduction tank 4. Thereby, an OER catalyst with a slow reaction rate can also be used. That is, the degree of freedom in selecting the mediator reduction catalyst 36 is increased, and cost reduction of the electrolysis system 1 can be achieved.

[0096] In addition, since no oxygen evolution reaction occurs at the anode electrode 10, the anode electrode 10 is not restricted by the polarization resistance of the oxygen evolution reaction, the heat generation caused by the polarization resistance, the mass transfer resistance caused by the generation of oxygen, the pressure change, etc. Thereby, operation of the electrolysis system 1 at a higher current density can be achieved.

[0097] In addition, in the anode electrode 10, the mediator is oxidized electrochemically rather than photochemically. In the case of causing the mediator to undergo a photochemical reaction, it is necessary to supply three substances, namely light, a catalyst, and the mediator, to the anode electrode 10. Therefore, it is necessary for the anode chamber and the current collector to have light-transmitting properties. In addition, depending on the structure of the anode electrode 10, the anolyte LA containing the mediator also needs to have light-transmitting properties. In addition, the coating amount of the catalyst may also be restricted. In addition, the stacking of the electrolytic cells 2 becomes difficult, which may also lead to the complication of the structure of the electrolytic cells 2 and an increase in cost. In contrast, by electrochemically oxidizing the mediator, the above-mentioned restrictions can be avoided. Thereby, the structures of the anode electrode 10 and the electrolytic cells 2 can be simplified.

[0098] In addition, in the cathode electrode 8, no redox reaction of the mediator occurs, but a direct formation reaction of hydrogen and organic hydrides occurs. The overvoltage of the hydrogen generation reaction in the cathode electrode 8 is extremely small. In addition, a highly durable catalyst such as Pt can also be used for the cathode electrode 8. In addition, the possibility of hydrogen and oxygen mixing when the electrolyte membrane 12 breaks can be suppressed by using a mediator in the reaction at the anode electrode 10. Therefore, there is no reason to even use a mediator in the reaction at the cathode electrode 8. In addition, when an organic hydride is generated on the cathode side, it is extremely difficult to mix the catholyte LC with the aqueous mediator solution and bring it into contact with the cathode catalyst 9. Or, in order to mix the catholyte LC with the aqueous mediator solution and bring it into contact with the cathode catalyst 9, it may be necessary to assemble a complex structure in the electrolysis system 1. For these reasons, the direct formation of the target substance in the cathode electrode 8 is adopted in the present embodiment. Thereby, the simplification of the structure of the electrolysis system 1 and the improvement of the production efficiency of the target substance can be achieved.

[0099] In addition, in the mediator reduction tank 4, the mediator is reduced non-photochemically. In the case of causing the mediator to undergo a photochemical reaction, it is necessary to supply three substances, namely light, a catalyst, and the mediator, into the mediator reduction tank 4. Therefore, it is necessary for the mediator reduction tank 4 and the anolyte LA to have light-transmitting properties. In contrast, by reducing the mediator non-photochemically, the above-mentioned restrictions can be avoided. Thereby, the structure of the mediator reduction tank 4 can be simplified.

[0100] In addition, in the case of an acid-based mediator or an organic-based mediator, in the mediator reduction tank 4, a reaction occurs in which the oxidized form M Ox of the mediator and water generate the reduced form M Red and oxygen. In addition, in the case of a base-based mediator, a reaction occurs in which hydroxide ions from water and the oxidized form M Ox generate the reduced form M Red and oxygen. That is, it is possible to directly or indirectly use inexpensive and easily available water to reduce the mediator. In addition, the by-product generated by the reduction reaction of the mediator is oxygen that can be directly discharged into the air. Thereby, from the viewpoints of the supply and treatment of materials, an inexpensive system can be constructed.

[0101] The embodiments can also be specified by the items described below.

[0102] [First item]

[0103] An electrolysis system (1) comprising an electrolytic cell (2) and a mediator reduction tank (4) connected to the electrolytic cell (2),

[0104] The electrolytic cell (2) has: an anode electrode (10) that electrochemically oxidizes a reduced form of a mediator (M Red ); and a cathode electrode (8) that performs at least one of hydrogen generation and organic hydride generation, the hydrogen generation being based on the electrochemical reduction of protons or water, and the organic hydride generation being based on the electrochemical reduction of a hydride.

[0105] The mediator reduction tank (4) non-photochemically reduces the oxidized form of the mediator (M Ox ) generated in the electrolytic cell (2).

[0106] [Second item]

[0107] The electrolysis system (1) according to the first item, wherein the mediator reduction tank (4) reacts the oxidized form (M Ox ) with water or hydroxide ions to generate a reduced form (M Red ) and oxygen.

[0108] [Third item]

[0109] The electrolysis system (1) according to the first item or the second item, wherein the mediator consists of a redox pair having an electrode potential higher than the electrode potential for generating oxygen at the anode electrode (10) at the operating temperature of the electrolytic cell (2).

[0110] [Fourth item]

[0111] The electrolysis system (1) according to any one of the first item to the third item, wherein the operating temperature of the mediator reduction tank (4) is adjusted to a temperature higher than the operating temperature of the electrolytic cell (2).

[0112] [Fifth item]

[0113] The electrolysis system (1) according to any one of the first item to the fourth item, wherein the anode electrode (10) oxidizes the reduced form (M Red ) by a reaction not accompanied by gas generation.

[0114] [Sixth item]

[0115] The electrolysis system (1) according to any one of Items 1 to 5, wherein the electrolytic cell (2) and the mediator reduction tank (4) are physically separated from each other.

[0116] [Item 7]

[0117] The electrolysis system (1) according to any one of Items 1 to 6, wherein the cathode electrode (8) generates an organic hydride.

[0118] [Item 8]

[0119] The electrolysis system (1) according to any one of Items 1 to 7, further comprising a power source (22) that supplies power from a renewable energy source to the electrolytic cell (2).

[0120] [Item 9]

[0121] An electrolysis method using the electrolysis system (1), the electrolysis system (1) comprising an electrolytic cell (2) and a mediator reduction tank (4) connected to the electrolytic cell (2),

[0122] The electrolysis method includes: in the anode electrode (10) of the electrolytic cell (2), electrochemically oxidizing a reduced form (M Red ) of a mediator to generate an oxidized form (M Ox ) of the mediator,

[0123] in the cathode electrode (8), electrochemically reducing at least one of protons or water to generate hydrogen and electrochemically reducing a hydride to generate an organic hydride,

[0124] in the mediator reduction tank (4), non-photochemically reducing the oxidized form (M Ox ) generated in the electrolytic cell (2) to generate a reduced form (M Red ) of the mediator.

[0125] Industrial applicability

[0126] The present invention can be used for an electrolysis system and an electrolysis method.

[0127] Explanation of reference numerals

[0128] 1 Electrolysis system, 2 Electrolytic cell, 4 Mediator reduction tank, 8 Cathode electrode, 9 Cathode catalyst, 10 Anode electrode, 11 Anode catalyst, 12 Electrolyte membrane, 36 Mediator reduction catalyst.

Claims

1. An electrolysis system comprising an electrolytic cell and a mediator reduction tank connected to the electrolytic cell, The electrolytic cell has: an anode electrode that electrochemically oxidizes a reduced form of a mediator; and a cathode electrode that performs at least one of hydrogen generation and organic hydride generation, the hydrogen generation being based on the electrochemical reduction of protons or water, and the organic hydride generation being based on the electrochemical reduction of a hydride. The mediator reduction tank non-photochemically reduces the oxidized form of the mediator generated in the electrolytic cell.

2. The electrolysis system according to claim 1, wherein, The mediator reduction tank causes the oxidized form to react with water or hydroxide ions to generate the reduced form and oxygen.

3. The electrolysis system according to claim 1 or 2, wherein, The mediator is composed of a redox pair having an electrode potential higher than the electrode potential for generating oxygen at the anode electrode at the operating temperature of the electrolytic cell.

4. The electrolysis system according to claim 1 or 2, wherein, The operating temperature of the mediator reduction tank is adjusted to a temperature higher than the operating temperature of the electrolytic cell.

5. The electrolysis system according to claim 1 or 2, wherein, The anode electrode oxidizes the reduced form through a reaction that does not involve gas generation.

6. The electrolysis system according to claim 1 or 2, wherein, The electrolytic cell and the mediator reduction tank are physically separated from each other.

7. The electrolysis system according to claim 1 or 2, wherein, The cathode electrode generates the organic hydride.

8. The electrolysis system according to claim 1 or 2, further comprising a power source that supplies power from a renewable energy source to the electrolytic cell.

9. An electrolysis method, which is an electrolysis method using an electrolysis system comprising an electrolytic cell and a mediator reduction tank connected to the electrolytic cell, This electrolysis method includes: In the anode electrode of the electrolytic cell, electrochemically oxidizing the reduced form of the mediator to generate the oxidized form of the mediator, In the cathode electrode of the electrolytic cell, performing at least one of electrochemically reducing protons or water to generate hydrogen and electrochemically reducing a hydride to generate an organic hydride, In the mediator reduction tank, non-photochemically reducing the oxidized form generated in the electrolytic cell to generate the reduced form.

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