ELECTROLYSIS CELL, ELECTROLYSIS DEVICE, AND METHOD OF MANUFACTURING ELECTROLYSIS CELL

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2024-160163, filed on Sep. 17, 2024; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments relate to an electrolysis cell, an electrolysis device, and a method of manufacturing an electrolysis cell.

BACKGROUND

In recent years, from the perspective of both energy and environmental issues, it has become desirable not only to convert renewable energy such as sunlight into electric energy for use, but also to convert it into a form that can be stored and transported. There has been known, for example, a carbon dioxide electrolysis device including a cathode that reduces carbon dioxide (CO₂) generated from power plants or waste disposal plants and an anode that oxidizes water (H₂O) as a device that produces chemical substances using renewable energy such as sunlight. At the cathode, for example, carbon dioxide is reduced to produce carbon compounds such as carbon monoxide (CO). In this case, gaseous carbon dioxide is supplied directly to a catalyst layer of the cathode, thereby allowing the reduction reaction to proceed quickly.

Further, there has been known a nitrogen electrolysis device including a cathode that reduces nitrogen (N₂) in the air and an anode that oxidizes water, similarly. At the cathode, for example, nitrogen is reduced to produce carbon compounds such as ammonia (NH₃).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a configuration example of an electrolysis device.

DETAILED DESCRIPTION

An electrolysis cell in an embodiment includes: a cathode having a reduction catalyst that promotes a reduction reaction of reducing a reducible material to produce a reduction product, and the reducible material being carbon dioxide or nitrogen; an anode having an oxidation catalyst that promotes an oxidation reaction of oxidizing water to produce oxygen; a diaphragm provided between the cathode and the anode; a cathode flow path facing on the cathode and through which a gas of the reduction material flows; an anode flow path facing on the anode and through which an electrolytic solution containing the water flows; and a chemical species between the anode flow path and the diaphragm, the chemical species being configured to decompose, capture, or inactivate an active oxygen species.

There will be explained embodiments with reference to the drawings below. In each of the following embodiments, substantially the same components are denoted by the same reference numerals and symbols, and explanations thereof may be partly omitted. The drawings are schematic, and a relation between thickness and planar dimension, a thickness ratio among parts, and so on may be different from actual ones.

In this specification, “connection” includes not only direct connection but also indirect connection in some cases, unless otherwise specified.

FIG. 1 is a schematic view illustrating a configuration example of an electrolysis device (electrochemical reaction device). FIG. 1 illustrates an electrolysis device 1. The electrolysis device 1 includes an electrochemical reaction structure 10, a flow path P1, a flow path P2, a flow path P3, and a flow path P4.

The electrochemical reaction structure 10 includes a cathode 11, an anode 12, a diaphragm 13, a flow path plate 14, a flow path plate 15, a current collector 16, a current collector 17, and a chemical species 18.

The cathode 11 is, for example, a reduction electrode required for performing a reduction reaction of at least one reducible material (substance to be reduced). Examples of the reducible material include nitrogen and carbon dioxide. A reduction product can be produced by reducing a reducible material.

The cathode 11 reduces, for example, carbon dioxide supplied as a gas of the reducible material or carbon dioxide contained in a first electrolytic solution (cathode solution) to produce a carbon compound being the reduction product. Examples of the carbon compound include carbon monoxide, formic acid, methanol, methane, ethanol, ethane, ethylene, formaldehyde, ethylene glycol, acetic acid, propanol, and so on. The cathode 11 may cause a side reaction of generating hydrogen through a reduction reaction of water as well as a reduction reaction of carbon dioxide. The cathode 11 may, for example, reduce nitrogen supplied as a gas of the reducible material to produce ammonia being the reduction product.

The cathode 11 has, for example, a reduction catalyst that promotes a reduction reaction that reduces a reducible material to produce a reduction product. The reduction catalyst can be formed using a material that reduces the activation energy for reducing a reducible material, for example. In other words, the reduction catalyst can be formed using a material that lowers the overvoltage when producing a reduction product by the reduction reaction of the reducible material, for example.

The cathode 11 can be formed using a metal material or a carbon material, for example. Examples of the metal material include metals such as gold, aluminum, copper, silver, platinum, palladium, zinc, mercury, indium, nickel, and titanium, alloys containing these metals, and so on. Examples of the carbon material include graphene, carbon nanotube (CNT), fullerene, ketjen black, and so on. The cathode 11 is not limited to these materials, and may be formed using a metal complex such as a Ru complex or a Re complex, or an organic molecule having an imidazole skeleton or a pyridine skeleton, for example. The cathode 11 may be formed using a mixture of a plurality of materials. The cathode 11 may have a structure having the reduction catalyst in a thin film shape, a mesh shape, a particle shape, a wire shape, or the like provided on a conductive substrate, for example. The type of the reduction product produced by the reduction reaction also differs depending on the type of reduction catalyst.

The anode 12 is an oxidation electrode required for performing an oxidation reaction of at least one oxidizable material (substance to be oxidized), for example. Examples of the oxidizable material include water. The anode 12 oxidizes an oxidizable material such as a substance or ion in a second electrolytic solution (anode solution) to produce oxygen, for example.

The anode 12 has an oxidation catalyst that promotes an oxidation reaction that oxidizes water to produce oxygen, for example. The oxidation catalyst can be formed using a material that reduces the activation energy when oxidizing an oxidizable material, in other words, a material that lowers the reaction overpotential, for example. Examples of the oxidation reaction at the anode 12 include reactions of oxidizing water to produce oxygen or hydrogen peroxide water, oxidizing chloride ions (Cl⁻) to produce chlorine, oxidizing carbonate ions or hydrogen carbonate ions to produce carbon dioxide, and so on.

Examples of the oxidation catalyst include metal materials. Examples of the metal material include ruthenium, iridium, platinum, cobalt, nickel, iron, manganese, tantalum, zirconium, tin, and so on. Further, examples of the metal material include a binary metal oxide, a ternary metal oxide, a quaternary metal oxide, and so on. Examples of the binary metal oxide include manganese oxide (Mn—O), iridium oxide (Ir—O), nickel oxide (Ni—O), cobalt oxide (Co—O), iron oxide (Fe—O), tin oxide (Sn—O), indium oxide (In—O), ruthenium oxide (Ru—O), and so on. Examples of the ternary metal oxide include nickel-iron oxide (Ni—Fe—O), nickel-cobalt oxide (Ni—Co—O), lanthanum-cobalt oxide (La—Co—O), nickel-lanthanum oxide (Ni—La—O), strontium-iron oxide (Sr—Fe—O), and so on. Examples of the quaternary metal oxide include lead-ruthenium-iridium oxide (Pb—Ru—Ir—O), lanthanum-strontium-cobalt oxide (La—Sr—Co—O), and so on. The oxidation catalyst is not limited to these materials, and may be formed using a metal hydroxide containing a metal such as cobalt, nickel, iron, or manganese, or a metal complex such as a ruthenium complex or an iron complex. Further, the oxidation catalyst may be formed by mixing a plurality of materials.

The anode 12 may be formed using a composite material containing both an oxidation catalyst and a conductive material. Examples of the conductive material include carbon materials such as carbon black, activated carbon, fullerene, carbon nanotube, graphene, ketjen black, and diamond, transparent conductive oxides such as indium tin oxide (ITO), zinc oxide (ZnO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), and antimony-doped tin oxide (ATO), metals such as copper, aluminum, titanium, nickel, silver, tungsten, cobalt, and gold, alloys each containing at least one of the metals, and so on. The anode 12 may have a structure having the oxidation catalyst in a thin film shape, a mesh shape, a particle shape, a wire shape, or the like provided on a conductive substrate, for example. The conductive substrate can be formed using a metal material containing titanium, titanium alloy, or stainless steel, for example.

The diaphragm 13 is provided between the cathode 11 and the anode 12. The diaphragm 13 can separate a cathode chamber 140 and an anode chamber 150. The diaphragm 13 can move ions such as hydrogen ions (H⁺), hydroxide ions (OH⁻), hydrogen carbonate ions (HCO₃⁻), and carbonate ions (CO₃²⁻). By the diaphragm 13, an electrolysis cell (electrochemical reaction cell) having a two-chamber structure can be formed. The diaphragm 13 may be provided in contact with the cathode 11 and the anode 12.

The diaphragm 13 can be formed using a membrane capable of selectively allowing anions or cations to pass therethrough, for example. This allows the composition of the second electrolytic solution in contact with the anode 12 to be different from that of the first electrolytic solution in contact with the cathode 11, and furthermore, differences in ionic strength, pH, and so on can promote the reduction reaction or the oxidation reaction. The diaphragm 13 may have a function of permeating part of ions contained in the electrolytic solutions in which the cathode 11 and the anode 12 are immersed therethrough, namely, a function of blocking one or more kinds of ions contained in the electrolytic solutions. This makes it possible to make the pH or the like different between the two electrolytic solutions, for example. Further, in terms of the blocking of ions, a diaphragm that does not completely block part of ions but is effective enough to limit the amount of movement by ion species may be used.

The diaphragm 13 can be formed using an ion exchange membrane such as, for example, NEOSEPTA (registered trademark) of ASTOM Corporation, Selemion (registered trademark), Aciplex (registered trademark) of ASAHI GLASS CO., LTD., Fumasep (registered trademark), fumapem (registered trademark) of Fumatech GmbH, Nafion (registered trademark) being fluorocarbon resin made by sulfonating and polymerizing tetrafluoroethylene of DuPont de Nemours, Inc., lewabrane (registered trademark) of LANXESS AG, IONSEP (registered trademark) of IONTECH Inc., Mustang (registered trademark) of PALL Corporation, ralex (registered trademark) of mega Corporation, Gore-Tex (registered trademark) of Gore-Tex Co., Ltd. Sustainion (registered trademark) of DIOXIDE MATERIALS, or PiperION (registered trademark) of Versogen, Inc. The ion exchange membrane may be formed using a membrane having hydrocarbon as a basic skeleton, for example. An anion exchange membrane may be formed using a membrane having an amine group, for example. In the case where there is a pH difference between the first electrolytic solution and the second electrolytic solution, by forming the diaphragm 13 using a bipolar membrane made by stacking a cation exchange membrane and an anion exchange membrane, the electrolytic solutions can be used while stably keeping the pHs thereof.

The diaphragm 13 may be formed using materials such as porous membranes of a silicone resin, fluorine-and-sulfur-based resins such as perfluoroalkoxyalkane (PFA), perfluoroethylene propene copolymer (FEP), polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polysulfone (PSU), polyethersulfone (PES), and polyphenylsulfone (PPSU) and ceramics, packing filled with glass filter, agar, and so on, insulating porous bodies of zeolite, metal oxide, metal hydroxide, metal nitrate, and metal sulfate, and so on, for example. In particular, a hydrophilic porous membrane is preferable as the material for the diaphragm 13 because it can inhibit clogging due to air bubbles. Further, each of the organic resin materials and each of the inorganic materials cited above may be combined and used as the diaphragm material. In this case, by imparting hydrophilicity to a stable hydrophobic organic material with an inorganic material, a stable hydrophilic porous membrane capable of withstanding long-term operation is obtained, which is preferable. A contact angle with water in the hydrophobic material is, for example, 100 degrees or more and less than 180 degrees. Further, a contact angle with water in the hydrophilic material is, for example, greater than 0 degree and less than 90 degrees.

The cathode 11, the anode 12, and the diaphragm 13 are stacked to form an electrochemical reaction cell. The electrochemical reaction structure 10 may include a cell stack formed by stacking a plurality of electrochemical reaction cells. By forming a cell stack, the amount of carbon dioxide reacted per unit area increases, thus making it possible to increase the amount of reduction products produced. The number of stacked electrochemical reaction cells is preferably 10 or more and 150 or less, for example.

The flow path plate 14 forms the cathode chamber 140. The cathode chamber 140 is provided on the surface of the flow path plate 14 facing the cathode 11 and can form a cathode flow path. The cathode chamber 140 has an inlet for supplying fluid to the cathode chamber 140 and an outlet for discharging the fluid from the cathode chamber 140. The surface shape of the cathode flow path is not limited in particular, but is serpentine, for example. The flow path plate 14 can be formed using a conductive material such as a metal material or a carbon material.

The flow path plate 15 forms the anode chamber 150. The anode chamber 150 is provided on the surface of the flow path plate 15 facing the anode 12, and can form an anode flow path. The anode chamber 150 has an inlet for supplying fluid to the anode chamber 150 and an outlet for discharging the fluid from the anode chamber 150. The surface shape of the anode flow path is not limited in particular, but is serpentine, for example. The flow path plate 15 can be formed using a conductive material such as a metal material or a carbon material.

The current collector 16 is electrically connected to the cathode 11. The current collector 16 may be provided on the side of the flow path plate 14 opposite the cathode 11, and may be electrically connected to the cathode 11 via the flow path plate 14, for example. The current collector 17 is electrically connected to the anode 12. The current collector 17 may be provided on the side of the flow path plate 15 opposite the anode 12, and may be electrically connected to the anode 12 via the flow path plate 15, for example. The current collectors 16 and 17 can be formed using a conductive material containing a metallic element such as titanium.

The current collectors 16 and 17 may be connected to a power supply 20. The power supply 20 can supply power to the electrochemical reaction structure 10, for example. The power supply 20 can apply voltage or current to the electrochemical reaction structure 10 to cause an electrolytic reaction such as an oxidation reaction or a reduction reaction, and is electrically connected to the cathode 11 and the anode 12. The electric energy supplied by the power supply 20 is used to cause a reduction reaction at the cathode 11 and an oxidation reaction at the anode 12. The power supply 20 and the current collector 16 are connected by wiring and the power supply 20 and the current collector 17 are connected by wiring, for example. Between the electrochemical reaction structure 10 and the power supply 20, electric devices such as inverters, converters, and batteries may be installed as necessary. The electrochemical reaction structure 10 may be driven by a constant-voltage system or a constant-current system.

The power supply 20 may be an ordinary commercial power supply, a battery, or the like, or may be a power supply that converts renewable energy to electric energy and supplies it. Examples of such a power supply include a power supply that converts kinetic energy or potential energy such as wind power, water power, geothermal power, or tidal power to electric energy, a power supply such as a solar cell including a photoelectric conversion element that converts light energy to electric energy, a power supply such as a fuel cell or a storage battery that converts chemical energy to electric energy, and a power supply such as an apparatus that converts vibrational energy such as sound to electric energy. The photoelectric conversion element has a function of performing charge separation by emitted light energy of sunlight or the like. Examples of the photoelectric conversion element include a pin-junction solar cell, a pn-junction solar cell, an amorphous silicon solar cell, a multijunction solar cell, a single crystal silicon solar cell, a polycrystalline silicon solar cell, a dye-sensitized solar cell, an organic thin-film solar cell, and so on. Further, the photoelectric conversion element may be stacked on at least one of the cathode 11 and the anode 12 inside the electrochemical reaction structure 10.

The power supply 20 can adjust the current or voltage to be supplied to the electrochemical reaction structure 10, for example. The power supply 20 may include a power controller that adjusts the current or voltage to be supplied to the electrochemical reaction structure 10, for example. The power supply 20 may have a function of adjusting the pressure in the cathode chamber 140 or the pressure in the anode chamber 150 by adjusting the current or voltage to be supplied to the electrochemical reaction structure 10. The power supply 20 may be provided outside the electrolysis device 1.

Electrolytic reactions such as an oxidation reaction and a reduction reaction caused by the electrochemical reaction structure 10 are preferably performed at a temperature of room temperature (for example, 25° C.) or more and 100° C. or less, at which the electrolytic solution does not vaporize. The above-described temperature is preferably 60° C. or more and 95° C. or less, and more preferably 60° C. or more and 80° C. or less. In order to set the temperature to less than room temperature, a cooling device such as a chiller is required, which may reduce the energy efficiency of an overall system. When the temperature exceeds 100° C., the water in the electrolytic solution turns into vapor and resistance increases, which may reduce the electrolysis efficiency.

The current density of the cathode 11 is not limited in particular, but a higher current density is preferred in order to increase the amount of reduction products produced per unit area. The current density is preferably 100 mA/cm² or more and 1.5 A/cm² or less, and further preferably 300 mA/cm² or more 700 mA/cm² or less. When the current density is less than 100 mA/cm², the amount of reduction products produced per unit area is small, which requires a large area. When the current density exceeds 1.5 A/cm², a side reaction of hydrogen generation increases, leading to a decrease in the concentration of reduction products.

In the case where Joule heat also increases by increasing the current density, the temperature increases above an appropriate temperature, so that a cooling mechanism may be provided in or near the electrochemical reaction structure 10. The cooling mechanism may be water cooling or air cooling. Even when the temperature of the electrochemical reaction structure 10 is higher than room temperature, the temperature may remain unchanged as long as it is equal to or less than 100° C.

The flow path P1 is connected to the inlet of the cathode chamber 140. A cathode supply fluid to be supplied to the cathode chamber 140 can flow through the flow path P1. The cathode supply fluid contains a reducible material such as carbon dioxide. The cathode supply fluid may be a gas containing a gaseous reducible material or the first electrolytic solution containing a reducible material.

The flow path P1 may be connected to a reducible material supply source. The reducible material supply source may include a reducible material separation and recovery device, and may be connected to the reducible material separation and recovery device. A reducible material gas from the reducible material separation and recovery device can be supplied to the flow path P1, for example, directly or after being stored once. Examples of the reducible material supply source include facilities having various incinerators or combustion furnaces such as a thermal power plant and a garbage incinerator, facilities having a steel plant and a blast furnace, and so on. The reducible material supply source is not limited to these facilities, but may be other factories that generate reducible materials.

The flow path P2 is connected to the inlet of the anode chamber 150. An anode supply fluid to be supplied to the anode chamber 150 can flow through the flow path P2. The anode supply fluid contains water or the second electrolytic solution. The flow path P2 may be connected to an anode solution supply source. The anode solution supply source can supply the second electrolytic solution, which is used for the anode supply fluid, for example.

The flow path P3 is connected to the outlet of the cathode chamber 140. A cathode discharge fluid to be discharged from the cathode chamber 140 can flow through the flow path P3. The cathode discharge fluid contains a carbon compound and hydrogen, which are an example of reduction products produced by the reduction reaction at the cathode 11, and a part of the reducible material gas or a part of the first electrolytic solution contained in the cathode supply fluid.

The flow path P4 is connected to the outlet of the anode chamber 150. An anode discharge fluid to be discharged from the anode chamber 150 can flow through the flow path P4. The anode discharge fluid contains, for example, gaseous oxygen produced by the oxidation reaction at the anode 12, a reducible material moving from the cathode chamber 140 or the electrolytic solution, and water or a part of the second electrolytic solution contained in the anode supply fluid.

The flow path P3 may be connected to a valuable material production device. Examples of the valuable material production device include a chemical synthesis device that produces valuable materials through chemical synthesis using raw materials such as carbon monoxide, and so on. Examples of the valuable material include methanol produced by a methanol production device, hydrocarbons produced by a Fischer-Tropsch reactor, synthetic gasoline, light oil, jet fuel, olefin compounds produced by an olefin production device, and so on. By providing the valuable material production device after the electrochemical reaction structure 10, valuable materials having a high added value can be produced from the product of the electrochemical reaction structure 10.

The type of the chemical synthesis device is not particularly limited as long as it is capable of causing a reaction to synthesize another substance from the reduction product produced at the cathode 11. Examples of the reaction using the reduction product by the chemical synthesis device include a chemical reaction, an electrochemical reaction, biological conversion reactions using products such as algae, enzyme, yeast, and bacteria, and so on.

The flow path P3 may be connected to a product separator instead of to the valuable material production device. The product separator can separate a carbon compound such as carbon monoxide, which is a product, by separating excess carbon dioxide from the cathode discharge fluid or removing water from the cathode discharge fluid. For example, when the carbon monoxide gas is produced in the electrochemical reaction structure 10 by the above-described expression (2), by using, as a raw material, a mixed gas containing the produced carbon monoxide gas and a hydrogen gas as a byproduct of the reduction reaction, methanol can be produced through methanol synthesis, or jet fuel, light oil, or the like can be produced through Fischer-Tropsch synthesis. The present invention is not limited to this, and the flow path P3 may be connected to a tank that stores gas containing carbon compounds such as carbon monoxide instead of to the valuable material production device.

The first electrolytic solution is preferred to be a solution with a high absorptance of reducible material. The existing form of reducible material in the first electrolytic solution is not always limited to a state of being dissolved therein, but the reducible material in an air bubble state may exist to be mixed in the first electrolytic solution. Examples of the electrolytic solution containing reducible material include aqueous solutions containing hydrogencarbonates and carbonates such as lithium hydrogen carbonate (LiHCO₃), sodium hydrogen carbonate (NaHCO₃), potassium hydrogen carbonate (KHCO₃), cesium hydrogen carbonate (CsHCO₃), sodium carbonate (Na₂CO₃), and potassium carbonate (K₂CO₃), phosphoric acid, boric acid, and so on. The electrolytic solution containing reducible material may contain alcohols such as methanol or ethanol, or ketones such as acetone, or may be an alcohol solution or ketone solution. The first electrolytic solution may be an electrolytic solution containing a reducible material absorbent that lowers the reduction potential for reducible material, has a high ion conductivity, and absorbs reducible material.

As the electrolytic solutions such as the first electrolytic solution and the second electrolytic solution, a solution containing water, which is, for example, an aqueous solution containing any electrolyte, can be used. The solution is preferred to be an aqueous solution that promotes the oxidation reaction of water. Examples of the aqueous solution containing the electrolyte include aqueous solutions containing phosphate ion (PO₄²⁻), borate ion (BO₃³⁻), sodium ion (Na⁺), potassium ion (K⁺), calcium ion (Ca²⁺), lithium ion (Li⁺), cesium ion (Cs⁺), magnesium ion (Mg²⁺), chloride ion (Cl⁻), hydrogen carbonate ion (HCO₃⁻), carbonate ion (CO₃⁻), hydroxide ion (OH⁻), and so on.

As the above-described electrolytic solutions, for example, an ionic liquid that is made of salts of cations such as imidazolium ions or pyridinium ions and anions such as BF₄⁻ or PF₆⁻ and is in a liquid state in a wide temperature range, or an aqueous solution thereof can be used. Further, examples of other electrolytic solutions include amine solutions such as ethanolamine, imidazole, and pyridine, and aqueous solutions thereof. Examples of amine include primary amine, secondary amine, tertiary amine, and so on. The electrolytic solutions may be high in ion conductivity and have properties of absorbing reducible material and characteristics of reducing the reduction energy.

Examples of the primary amine include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, and so on. Hydrocarbons of the amine may be substituted by alcohol, halogen, and the like. Examples of amine whose hydrocarbons are substituted include methanolamine, ethanolamine, chloromethylamine, and so on. Further, an unsaturated bond may exist. These hydrocarbons are also the same in the secondary amine and the tertiary amine.

Examples of the secondary amine include dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dimethanolamine, diethanolamine, dipropanolamine, and so on. The substituted hydrocarbons may be different. This also applies to the tertiary amine. Examples with different hydrocarbons include methylethylamine, methylpropylamine, and so on.

Examples of the tertiary amine include trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trimethanolamine, triethanolamine, tripropanolamine, tributanolamine, trihexanolamine, methyldiethylamine, methyldipropylamine, and so on.

Examples of the cation of the ionic liquid include 1-ethyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1-butyl-3-methylimidazole ion, 1-methyl-3-pentylimidazolium ion, 1-hexyl-3-methylimidazolium ion, and so on.

A second place of the imidazolium ion may be substituted. Examples of the cation of the imidazolium ion whose second place is substituted include 1-ethyl-2,3-dimethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl-2,3-dimethylimidazolium ion, 1,2-dimethyl-3-pentylimidazolium ion, 1-hexyl-2,3-dimethylimidazolium ion, and so on.

Examples of the pyridinium ion include methylpyridinium, ethylpyridinium, propylpyridinium, butylpyridinium, pentylpyridinium, hexylpyridinium, and so on. In both of the imidazolium ion and the pyridinium ion, an alkyl group may be substituted, or an unsaturated bond may exist.

Examples of the anion include fluoride ion (F⁻), chloride ion (Cl⁻), bromide ion (Br⁻), iodide ion (I⁻), BF₄⁻, PF₆⁻, CF₃COO⁻, CF₃SO₃⁻, NO³⁻, SCN⁻, (CF₃SO₂)₃C⁻, bis(trifluoromethoxysulfonyl)imide, bis(perfluoroethylsulfonyl)imide, and so on. Dipolar ions in which the cations and the anions of the ionic liquid are coupled by hydrocarbons may be used. A buffer solution such as a potassium phosphate solution may be supplied to the anode chamber 150.

The second electrolytic solution contains water as the oxidizable material. It is possible to change the amount of water or the electrolytic solution components contained in the first and second electrolytic solutions to change the reactivity and then change the selectivity of a reduced substance or the ratio of produced substances. The first and second electrolytic solutions may contain redox couples as necessary. Examples of the redox couple include Fe³⁺/Fe²⁺, IO³⁻/I⁻, and so on.

Next, there is explained an example of an operating method of the electrolysis device 1. Here, there is explained the case where carbon dioxide is reduced to produce carbon monoxide mainly and water is oxidized to produce oxygen. When the cathode supply fluid containing carbon dioxide is supplied to the cathode chamber 140, the anode supply fluid containing the second electrolytic solution is supplied to the anode chamber 150, and a voltage that is equal to or more than the electrolysis voltage is applied between the cathode 11 and the anode 12 by supplying power by the power supply 20, the oxidation reaction of water occurs near the anode 12 in contact with the second electrolytic solution. As expressed in the following expression (1), an oxidation reaction of water contained in the second electrolytic solution occurs, electrons are lost, and oxygen and hydrogen ions are produced. Some of the produced hydrogen ions move to the cathode chamber 140 through the diaphragm 13.

When the hydrogen ions (H⁺) produced on the anode 12 side reach the vicinity of the cathode 11 and at the same time, electrons (e⁻) are supplied to the cathode 11 from the power supply 20, the reduction reaction of carbon dioxide occurs. As expressed in the following expression (2), carbon dioxide is reduced by the hydrogen ions (H⁺) that have moved to the vicinity of the cathode 11 and the electrons (e⁻) supplied from the power supply 20 to produce carbon monoxide.

The gas component contained in the anode discharge fluid from the anode chamber 150 is mainly an oxygen gas, as expressed in the above-described expression (1). In the reactions at the cathode 11 and the anode 12, most of the carbon dioxide contained in the cathode supply fluid supplied to the cathode chamber 140 is reduced at the cathode 11, but some flows to the anode 12 side as carbon dioxide or as ions such as carbonate ions (CO₃²⁻) or hydrogen carbonate ions (HCO₃⁻). The carbonate ions or the hydrogen carbonate ions that have moved to the anode 12 side become present as carbon dioxide by a chemical equilibrium reaction when the pH of the anode solution (second electrolytic solution) becomes, for example, six or less, and some of the carbon dioxide is dissolved in the anode solution. Such a carbon dioxide gas, which is not fully dissolved in the anode solution, is contained with the oxygen gas in the anode discharge fluid discharged from the anode chamber 150. Under general operating conditions of the electrochemical reaction structure 10, the abundance ratio of the carbon dioxide gas to the oxygen gas in the anode discharge fluid increases up to, for example, 2:1 in some cases.

The reduction product may contain hydrogen obtained by electrolysis of carbon dioxide, carbon monoxide, and water. The concentration of hydrogen can be arbitrarily adjusted depending on use. In the case where hydrogen is used in the chemical synthesis device, carbon dioxide may be separated from the cathode discharge fluid to be used, in order to use the mixture of carbon monoxide and hydrogen. In the case where hydrogen is not used, carbon monoxide is only separated from the cathode discharge fluid. In the case where methanol is produced, by adjusting the number of moles of hydrogen to about twice the number of moles of carbon monoxide, the hydrogen produced at the cathode 11 can be used as a valuable material. In the meantime, at the cathode 11, the side reaction of hydrogen can be inhibited depending on the reaction conditions to adjust the concentration of hydrogen in the reduction product to a range of 0.1% or more and 5% or less in volume percent. This makes it possible to use the electrolysis device as a carbon monoxide production device that produces high-concentration carbon monoxide.

In the electrolysis cell, the selection of the diaphragm 13 that separates the cathode 11 and the anode 12 is important. The diaphragm 13 is required to have high gas barrier properties so as to prevent gas (for example, O₂) produced in the anode chamber 150 from moving to the cathode chamber 140, or gas (for example, CO) produced in the cathode chamber 140 from moving to the anode chamber 150. Further, in the electrolysis device, the medium that carries electricity (electrons) is ions, and thus the diaphragm 13 is required to have high ion permeability in order for the reaction to proceed efficiently.

In polymer electrolyte fuel cells (PEFCs) and polymer electrolyte water electrolysis (PEWE), ion exchange membranes that achieve both high gas barrier properties and high ion permeability have been used. In particular, cation exchange membranes such as Nafion (product name, manufactured by DuPont de Nemours, Inc.) and Flemion (product name, manufactured by AGC Inc.) have been used for a long time. However, when these are used in a carbon dioxide electrolysis device or a nitrogen electrolysis device, the production of hydrogen, which is a side reaction, becomes dominant, resulting in lower electrolysis efficiency. On the other hand, when anion exchange membranes such as Sustainion (product name, manufactured by Dioxide Materials, Inc.) are used, the production of hydrogen can be inhibited. At present, however, these membranes have poor thermal and mechanical stability and have difficulty in terms of durability.

As one of the methods of solving the problems that arise when using such ion exchange membranes as described above, a method of using a porous membrane that does not have ion passage selectivity as the diaphragm 13 is considered. In this method, the electrolytic solution moves directly, causing ions to pass through the diaphragm 13. This is a method that has been examined also in the electrolysis devices such as an alkaline water electrolysis device, and a method for providing a stable diaphragm has been proposed.

However, when the above-described porous membrane is used for the diaphragm 13, the amount of crossover of a produced gas to a counter electrode is larger as compared to the ion exchange membrane. In the electrolysis devices such as a carbon dioxide electrolysis device and a nitrogen electrolysis device, hydrogen is produced as a reaction by-product on the cathode 11 side and the produced hydrogen reacts with oxygen produced on the anode 12 side, and thereby an active oxygen species such as hydrogen peroxide is produced. This causes an oxidation reaction of polymers that form the porous membrane. As a result, the composition or shape of the membrane changes, which may cause a decrease in diaphragm function.

In contrast to this, in this embodiment, the chemical species 18 is used, thereby inhibiting deterioration of the diaphragm 13. The chemical species 18 is composed of a chemical species (also called a quencher or inhibitor) that decomposes, captures (retains), or inactivates an active oxygen species produced by the electrochemical reaction structure 10. The active oxygen species is highly reactive oxygen species such as hydrogen peroxide, superoxide anion radicals, hydroxyl radicals, and singlet oxygen. The active oxygen species is considered to be produced by the reaction of hydrogen produced at the cathode 11 with oxygen produced at the anode 12. Hydrogen has a higher diffusibility than oxygen, and thus it is considered that where the active oxygen species is most concentrated is between the diaphragm 13 and the anode 12. Therefore, it is preferable that the chemical species 18 should be present between the anode 12 and the diaphragm 13.

The chemical species is a metal, metal oxide, or metal hydroxide that contains at least one of the metallic elements of cerium (Ce), manganese (Mn), cobalt (Co), platinum (Pt), ruthenium (Ru), tungsten (W), and tin (Sn). A preferred example of the metal is Ce, Mn, Co, Pt, Ru, W, or Sn, and a particularly preferred example is Ce, Mn, Pt, or Co. Examples of the metal oxide include MnO, Mn₃O₄, MnO₂, MnO₃, Mn₂O₇, CoO, Co₂O₃, Co₃O₄, and CeO₂. Examples of the metal hydroxide include Mn(OH)₂, MnO(OH), MnO(OH)₂, and Ce(OH)₄. The chemical species may be attached to the surface of the material that forms the diaphragm 13, for example.

The decomposition of the active oxygen species is performed by converting the active oxygen species into water or oxygen through a radical reaction, for example.

The capture of the active oxygen species is performed by a stable radical compound or the like reacting with the produced active oxygen species and converting the resultant into an inactive reactant, for example.

The inactivation of the active oxygen species is performed by inhibiting radicals generated from the active oxygen species, for example.

The chemical species 18 may be supported on the diaphragm 13 or the anode 12. In the method of manufacturing the electrolysis device 1, for example, the above-described metal, metal oxide, or metal hydroxide may be mixed with a binder to be applied to the diaphragm 13 or the anode 12. Further, a member such as a porous material to be used for the anode 12 may be impregnated with a precursor of the above-described metal, and then fired (sintered) to support the metal oxide. Further, the above-described metal, metal oxide, or metal hydroxide may also be inserted between the diaphragm 13 and the anode 12 as an independent member. In this case, the chemical species 18 may be composed only of the metal, metal oxide, or metal hydroxide cited previously, or may be composed of a material containing these.

The chemical species 18 may be supported on the anode 12 or the diaphragm 13 so as to face the cathode flow path through the diaphragm 13 from an inlet to an outlet of the cathode flow path. Further, the amount of the chemical species 18 may increase from the flow path P1 side of the cathode chamber 140 (an inlet region of the cathode flow path) to the flow path P2 side of the cathode chamber 140 (an outlet region of the cathode flow path). The concentration of the reducible material is high on the flow path P1 side of the cathode chamber 140, and it is considered that hydrogen is less likely to be produced. On the other hand, on the flow path P2 side of the cathode chamber 140, the concentration of the reducible material is lower than that on the flow path P1 side, and thus hydrogen is more likely to be produced. The produced hydrogen diffuses into the anode flow path and reacts with oxygen produced by the anode 12, and the active oxygen species is likely to be produced. That is, the diaphragm 13 on the flow path P2 side is considered to easily deteriorate, and thus the amount of the chemical species 18 facing the flow path P2 side is preferably larger than that of the chemical species 18 facing the flow path P1. The amount of the chemical species 18 per unit area of the anode 12 or the diaphragm 13 on the flow path P2 side is preferably equal to or more than 1.05 times, and more preferably equal to or more than 1.1 times the amount of the chemical species 18 per unit area on the flow path P1 side. The upper limit is not particularly limited, but for example, the amount of the chemical species 18 per unit area on the flow path P2 side may be equal to or less than 20 times the amount of the chemical species 18 per unit area on the flow path P1 side. The amount of the chemical species 18 can be evaluated, for example, by cutting out a laminate of the anode 12, the chemical species 18, and the diaphragm 13, performing, on the cut-out laminate, an appropriate dissolution pretreatment with acid or the like, and then quantitatively analyzing the cut-out laminate using a high-frequency inductively coupled plasma (ICP) emission spectrometer. Further, the difference in the amount of the chemical species 18 between the flow path P1 side and the flow path P2 side can be formed as follows, for example, when the anode 12 is impregnated with a precursor of the chemical species 18 and then fired (sintered) to support the chemical species 18 on the anode 12, the chemical species 18 is once supported on the entire anode 12 and then the precursor is impregnated with only a portion of the anode 12 on the flow path P2 side and fired, or this is performed repeatedly any number of times. In the case of measuring the amount of the chemical species 18, the cathode flow path is divided into a first half from the flow path P1 to the midpoint and a second half from the midpoint to the flow path P2 with the midpoint of the cathode flow path set as a reference, and the first half can be set as the flow path P1 side and the second half can be set as the flow path P2 side.

By using the chemical species 18, the deterioration of the diaphragm 13 can be inhibited, resulting in that it is possible to inhibit deterioration of the electrolysis device and improve its durability. The above-described active oxygen species is likely to attack an ether group or a sulfonyl group and deteriorate the diaphragm 13. Therefore, when the diaphragm 13 contains a high molecular compound cross-linked with at least one functional group of an ether group and a sulfonyl group, with the introduction of the chemical species 18, the advantage in inhibiting deterioration of the diaphragm 13 is very significant.

EXAMPLES

Electrolysis devices in Examples 1, 2, 3, and 4 and an electrolysis device in Comparative example 1 were each fabricated. In order to evaluate the deterioration caused by the active oxygen species during hydrogen by-production and the effect of inhibiting deterioration obtained by introducing the chemical species 18, a cathode supply fluid containing nitrogen, which is an inert gas, was humidified with pure water and supplied to a cathode flow path, and an anode supply fluid containing potassium hydrogen carbonate at a concentration of 0.1 mol/L as an electrolytic solution was supplied to an anode flow path, and each of the electrolysis devices was operated under the following conditions at a current density of 700 mA/cm². By controlling the voltage with the power supply 20, a current was passed between the cathode 11 and the anode 12 at a current density of 700 mA/cm², water was reduced at the cathode 11 to produce hydrogen, and water was oxidized at the anode 12 to produce oxygen. Further, a cathode discharge fluid discharged from the cathode flow path was collected and analyzed to calculate the Faradaic efficiency of hydrogen production.

Each of the electrolysis devices was evaluated according to the change in the Faradaic efficiency of hydrogen production as follows. The electrolysis device in which the time from the start of operation until the Faradaic efficiency of hydrogen production decreased by 10% was less than 50 hours was evaluated as × (durability: Bad), the electrolysis device in which the above-described time was 50 hours or more and less than 100 hours was evaluated as ∘ (durability: Good), and the electrolysis device in which the above-described time was 100 hours or more was evaluated as ⊚ (durability: Very Good).

Example 1

A 0.5 mol/L manganese chloride solution was prepared using a solution of ethanol and water mixed in a ratio of 9:1. An iridium-coated titanium porous material to be used as the anode 12 was immersed in this solution, taken out, and dried. Then, the above-described porous material was dried in a dryer at 60° C. for 5 hours. Then, the above-described porous material was sintered in an electric furnace at 600° C. for 2 hours to fabricate the anode 12 supporting manganese species as the chemical species 18. This anode 12 was used to fabricate the electrolysis device illustrated in FIG. 1. The evaluation result of the electrolysis device in Example 1 was ⊚ (durability: Very Good). The results are illustrated in Table 1.

Example 2

A 0.5 mol/L cobalt chloride hexahydrate solution was prepared using a solution of ethanol and water mixed in a ratio of 9:1. An iridium-coated titanium porous material to be used as the anode 12 was immersed in this solution, taken out, and dried. Then, the above-described porous material was dried in a dryer at 60° C. for 5 hours. Then, the above-described porous material was sintered in an electric furnace at 450° C. for 1 hour to fabricate the anode 12 supporting cobalt species as the chemical species 18. This anode 12 was used to fabricate the electrolysis device illustrated in FIG. 1. The evaluation result of the electrolysis device in Example 2 was ⊚ (durability: Very Good). The results are illustrated in Table 1.

Example 3

A 0.5 mol/L cerium nitrate hexahydrate solution was prepared using pure water. An iridium-coated titanium porous material to be used as the anode 12 was immersed in this solution, taken out, and dried. Then, the above-described porous material was dried in a dryer at 60° C. for 5 hours. Then, the above-described porous material was sintered in an electric furnace at 450° C. for 1 hour to fabricate the anode 12 supporting cerium species as the chemical species 18. This anode 12 was used to fabricate the electrolysis device illustrated in FIG. 1. The evaluation result of the electrolysis device in Example 3 was o (durability: Good). The results are illustrated in Table 1.

Example 4

A 0.05 mol/L bis(acetylacetonato)platinum solution was prepared using acetone. An iridium-coated titanium porous material to be used as the anode 12 was immersed in this solution, taken out, and dried. Then, the above-described porous material was dried in a dryer at 60° C. for 5 hours. Then, the above-described porous material was sintered in an electric furnace at 450° C. for 1 hour to fabricate the anode 12 supporting platinum species as the chemical species 18. This anode 12 was used to fabricate the electrolysis device illustrated in FIG. 1. The evaluation result of the electrolysis device in Example 4 was o (durability: Good). The results are illustrated in Table 1.

Comparative Example 1

The electrolysis device illustrated in FIG. 1 was fabricated using an iridium-coated titanium porous material as it is as the anode 12 without introducing the chemical species 18. The evaluation result of the electrolysis device in Comparative example 1 was × (durability: Bad). The results are illustrated in Table 1.

	TABLE 1
	Chemical species	Durability

	Example 1	Manganese species	⊚
	Example 2	Cobalt species	⊚
	Example 3	Cesium species	◯
	Example 4	Platinum species	◯
	Comparative	None	X
	example 1

As illustrated in Table 1, by introducing cerium or platinum as the chemical species 18, the durability improves, and introducing cobalt or manganese makes it possible to further improve durability, and thus it is possible to extend the life of the electrolysis device.

Note that the above-described configurations in the embodiments are applicable in combination, and parts thereof are also replaceable. While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

The above-described embodiment can be summarized into the following Clauses.

Clause 1

An electrolysis cell comprising:

• • a cathode having a reduction catalyst that promotes a reduction reaction of reducing a reducible material to produce a reduction product, and the reducible material being carbon dioxide or nitrogen;
  • an anode having an oxidation catalyst that promotes an oxidation reaction of oxidizing water to produce oxygen;
  • a diaphragm provided between the cathode and the anode;
  • a cathode flow path facing on the cathode and through which a gas of the reduction material flows;
  • an anode flow path facing on the anode and through which an electrolytic solution containing the water flows; and
  • a chemical species between the anode flow path and the diaphragm, the chemical species being configured to decompose, capture, or inactivate an active oxygen species.

Clause 2

The electrolysis cell according to the clause 1, wherein

• • the chemical species is a metal, metal oxide, or metal hydroxide containing at least one metallic element selected from the group consisting of cerium, manganese, cobalt, platinum, ruthenium, tungsten, and tin.

Clause 3

The electrolysis cell according to the clause 1 or the clause 2, wherein

• • the chemical species is supported on the anode or the diaphragm so as to face the cathode flow path through the diaphragm from an inlet to an outlet of the cathode flow path, and
  • the amount of the chemical species per unit area of the anode or the diaphragm, the chemical species facing on an outlet region of the cathode path, is equal to or more than 1.05 times the amount of the chemical species per unit area of the anode or the diaphragm, the chemical species facing on an inlet region of the cathode path.

Clause 4

The electrolysis cell according to any one of the clause 1 to the clause 3, wherein

• • the diaphragm is a porous membrane that does not have ion passage selectivity.

Clause 5

The electrolysis cell according to any one of the clause 1 to the clause 4, wherein

• • the diaphragm contains a molecular compound cross-linked with at least one functional group selected from the group consisting of an ether group and a sulfonyl group.

Clause 6

The electrolysis cell according to any one of the clause 1 to the clause 5, wherein

• • the active oxygen species is hydrogen peroxide, superoxide anion radicals, hydroxyl radicals, or singlet oxygen.

Clause 7

An electrolysis device, comprising:

• • the electrolysis cell according to any one of clause 1 to clause 6; and
  • a power supply that supplies current between the anode and the cathode, wherein
  • the reducible material is carbon dioxide.

Clause 8

An electrolysis device, comprising:

• • the electrolysis cell according to any one of clause 1 to clause 6; and
  • a power supply that supplies current between the anode and the cathode, wherein
  • the reducible material is nitrogen.

Clause 9

A method of manufacturing an electrolysis cell, wherein

• • the electrolysis cell comprising:
  • a cathode having a reduction catalyst that promotes a reduction reaction of
  • reducing a reducible material to produce a reduction product, the reducible material being carbon dioxide or nitrogen;
  • an anode having an oxidation catalyst that promotes an oxidation reaction of oxidizing water to produce oxygen;
  • a diaphragm provided between the cathode and the anode;
  • a cathode flow path facing on the cathode and through which a gas of the reduction material flows; and
  • an anode flow path facing on the anode and through which an electrolytic solution containing the water flows,
  • the method comprising:
  • immersing a porous material containing the oxidation catalyst in a solution containing a precursor of a chemical species configured to decompose, capture, or inactivate an active oxygen species; and
  • sintering the porous material and forming the anode.