Electrolytic cell, electrolytic device, and method for manufacturing an electrolytic cell

Abstract

To extend the lifespan of electrolytic devices. [Solution] The electrolytic cell comprises a cathode having a reduction catalyst that promotes a reduction reaction to reduce a target substance, which is carbon dioxide or nitrogen, and produce a reduction product; an anode having an oxidation catalyst that promotes an oxidation reaction to oxidize water and produce oxygen; a diaphragm provided between the cathode and the anode; a cathode channel facing the cathode through which the gas of the target substance to be reduced flows; an anode channel facing the anode through which an electrolyte solution containing water flows; and a chemical species present between the anode channel and the diaphragm that decomposes, captures, or inactivates reactive oxygen species.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to an electrolytic cell, an electrolytic device, and a method for manufacturing an electrolytic cell. [Background technology]

[0002] In recent years, from the perspectives of both energy and environmental issues, there has been a growing desire not only to convert renewable energy sources such as solar power into electrical energy for use, but also to convert it into a form that can be stored and transported. As a device that generates chemical substances using renewable energy sources such as solar power, a carbon dioxide electrolysis device is known, which has a cathode that reduces carbon dioxide (CO2) generated from power plants or waste treatment plants, and an anode that oxidizes water (H2O). In the cathode, for example, carbon dioxide is reduced to produce carbon compounds such as carbon monoxide (CO). In this case, by directly supplying gaseous carbon dioxide to the catalyst layer of the cathode, it is possible to rapidly advance the reduction reaction.

[0003] Furthermore, a nitrogen electrolysis apparatus is known that similarly comprises a cathode that reduces nitrogen (N2) in the air and an anode that oxidizes water. In the cathode, for example, nitrogen is reduced to produce carbon compounds such as ammonia (NH3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2013 / 183584 [Patent Document 2] International Publication No. 2020 / 158719 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The problem that this embodiment aims to solve is to extend the lifespan of the electrolytic device. [Means for solving the problem]

[0006] The electrolytic cell of the embodiment includes a cathode having a reduction catalyst that promotes a reduction reaction for reducing a reduction target, which is carbon dioxide or nitrogen, to produce a reduction product, an anode having an oxidation catalyst that promotes an oxidation reaction for oxidizing water to produce oxygen, a diaphragm provided between the cathode and the anode, a cathode flow path that faces the cathode and through which the gas of the reduction target flows, an anode flow path that faces the anode and through which an electrolytic solution containing water flows, and a chemical species that exists between the anode flow path and the diaphragm and decomposes, captures, or inactivates reactive oxygen species.

Brief Description of the Drawings

[0007] [Figure 1] It is a schematic diagram showing a configuration example of an electrolytic device.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments will be described with reference to the drawings. In each of the embodiments shown below, substantially the same constituent parts are denoted by the same reference numerals, and the description thereof may be partially omitted. The drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thicknesses of each part, etc. may be different from the actual ones.

[0009] In this specification, "connect" includes not only directly connecting but also indirectly connecting, unless otherwise specified.

[0010] FIG. 1 is a schematic diagram showing a configuration example of an electrolytic device (electrochemical reaction device). FIG. 1 shows an electrolytic device 1. The electrolytic device 1 has an electrochemical reaction structure 10, a flow path P1, a flow path P2, a flow path P3, and a flow path P4.

[0011] The electrochemical reaction structure 10 has 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.

[0012] Cathode 11 is a reduction electrode for carrying out a reduction reaction of at least one substance to be reduced. Examples of substances to be reduced include nitrogen and carbon dioxide. By reducing the substance to be reduced, a reduction product can be produced.

[0013] Cathode 11 reduces, for example, carbon dioxide supplied as the gas to be reduced, or carbon dioxide contained in the first electrolyte (cathode solution), to produce a carbon compound as a reduction product. Examples of carbon compounds include carbon monoxide, formic acid, methanol, methane, ethanol, ethane, ethylene, formaldehyde, ethylene glycol, acetic acid, propanol, etc. Along with the reduction reaction of carbon dioxide, cathode 11 may produce a side reaction in which hydrogen is generated by the reduction reaction of water. Cathode 11 may also reduce, for example, nitrogen supplied as the gas to be reduced, to produce ammonia as a reduction product.

[0014] Cathode 11 has, for example, a reduction catalyst that promotes a reduction reaction to reduce a target substance and produce a reduction product. The reduction catalyst can be formed using, for example, a material that reduces the activation energy required to reduce the target substance. In other words, the reduction catalyst can be formed using, for example, a material that lowers the overpotential when a reduction product is produced by the reduction reaction of the target substance.

[0015] The cathode 11 can be formed using, for example, a metallic material or a carbon material. Examples of metallic materials include metals such as gold, aluminum, copper, silver, platinum, palladium, zinc, mercury, indium, nickel, and titanium, as well as alloys containing such metals. Examples of carbon materials include graphene, carbon nanotubes (CNTs), fullerenes, and Ketjenblack. However, the cathode 11 is not limited to these materials and may be formed using, for example, a metallic complex such as a Ru complex or a Re complex, or an organic molecule having an imidazole skeleton or a pyridine skeleton. The cathode 11 may also be formed using a mixture of multiple materials. The cathode 11 may have a structure in which a reduction catalyst in the shape of, for example, a thin film, a lattice, particulate, or wire is placed on a conductive substrate. The type of reduction product produced by the reduction reaction also differs depending on the type of reduction catalyst.

[0016] Anode 12 is an oxidation electrode for carrying out an oxidation reaction of at least one oxidizing agent (substance to be oxidized). Examples of oxidizing agents include water. Anode 12 oxidizes oxidizing agents such as substances or ions in the second electrolyte (anodic solution) to produce oxygen.

[0017] Anode 12 has an oxidation catalyst that promotes oxidation reactions, for example, by oxidizing water to produce oxygen. The oxidation catalyst can be formed using, for example, a material that reduces the activation energy when oxidizing the substance to be oxidized, in other words, a material that lowers the reaction overpotential. Examples of oxidation reactions at anode 12 include the oxidation of water to produce oxygen or hydrogen peroxide, and the oxidation of chloride ions (Cl - This includes reactions that oxidize ) to produce chlorine, and reactions that oxidize carbonate ions or bicarbonate ions to produce carbon dioxide.

[0018] Examples of oxidation catalysts include metallic materials. Examples of metallic materials include ruthenium, iridium, platinum, cobalt, nickel, iron, manganese, tantalum, zirconium, and tin. Furthermore, examples of metallic materials include binary metal oxides, ternary metal oxides, and quaternary metal oxides. Examples of binary metal oxides 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), and ruthenium oxide (Ru-O). Examples of ternary metal oxides 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), and strontium-iron oxide (Sr-Fe-O). Examples of quaternary metal oxides include lead-ruthenium-iridium oxide (Pb-Ru-Ir-O) and lanthanum-strontium-cobalt oxide (La-Sr-Co-O). However, the oxidation catalyst is not limited to these materials; it may also be formed using metal hydroxides containing metals such as cobalt, nickel, iron, and manganese, or metal complexes such as ruthenium complexes and iron complexes. Furthermore, the oxidation catalyst may be formed by mixing multiple materials.

[0019] The anode 12 may be formed using a composite material that includes both an oxidation catalyst and a conductive material. Examples of conductive materials include carbon materials such as carbon black, activated carbon, fullerene, carbon nanotubes, graphene, Ketjenblack, 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; and alloys containing at least one of these metals. The anode 12 may include a structure having an oxidation catalyst on a conductive substrate, for example, in the form of a thin film, lattice, particulate, or wire. The conductive substrate can be formed using a metallic material, for example, titanium, a titanium alloy, or stainless steel.

[0020] The diaphragm 13 is provided between the cathode 11 and the anode 12. The diaphragm 13 can separate the cathode chamber 140 and the anode chamber 150. The diaphragm 13 contains hydrogen ions (H + ) and hydroxide ions (OH - ), bicarbonate ions (HCO3) - ), carbonate ions (CO3 2- It is possible to move ions such as ). The diaphragm 13 allows for the formation of an electrolytic cell (electrochemical reaction cell) having a two-chamber structure. The diaphragm 13 may be provided in contact with the cathode 11 and the anode 12.

[0021] The diaphragm 13 can be formed using, for example, a membrane that allows anions or cations to flow selectively. This makes it possible to make the composition of the second electrolyte in contact with the anode 12 different from the composition of the first electrolyte in contact with the cathode 11, and further, differences in ionic strength, pH, etc., can promote reduction or oxidation reactions. The diaphragm 13 may also have the function of allowing some ions contained in the electrolyte in which the cathode 11 and anode 12 are immersed to pass through, that is, the function of shielding one or more types of ions contained in the electrolyte. This makes it possible to make the pH, etc., different between the two electrolytes. Furthermore, regarding ion shielding, the diaphragm may not completely shield some ions, but rather exert an effect that limits the amount of movement by ion species.

[0022] The diaphragm 13 can be formed using, for example, ion exchange membranes such as Neosepta® from Astom Corporation, Celemion® and Aciplex® from Asahi Glass Co., Ltd., Fumasep® and fumapem® from Fumatech Corporation, Nafion®, a fluororesin produced by sulfonating and polymerizing tetrafluoroethylene from DuPont Corporation, Lewabrane® from LANXESS Corporation, IONSEP® from IONTECH Corporation, Mustang® from PALL Corporation, ralex® from mega Corporation, Gore-Tex® from Gore-Tex Corporation, Sustainion® from DIOXIDEMATERIALS Corporation, and PiperION® from Versogen Corporation. The ion exchange membrane may be formed using, for example, a membrane with a hydrocarbon as its basic skeleton. The anion exchange membrane may be formed using, for example, a membrane having an amine group. If there is a pH difference between the first electrolyte and the second electrolyte, a diaphragm 13 can be formed using a bipolar membrane in which a cation exchange membrane and an anion exchange membrane are stacked, thereby allowing the pH of each electrolyte to be stably maintained during use.

[0023] The diaphragm 13 may be formed using materials such as silicone resin, 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), polyphenylsulfone (PPSU), and other fluorine and sulfur-based resins, porous ceramic membranes, fillers filled with glass filters or agar, and insulating porous materials such as zeolites, metal oxides, metal hydroxides, metal nitrates, and metal sulfates. In particular, hydrophilic porous membranes are preferred as materials for the diaphragm 13 because they can suppress clogging by air bubbles. Alternatively, the organic resin materials and inorganic materials listed above may be combined and used as diaphragm materials. In that case, adding hydrophilicity with an inorganic material to a stable hydrophobic organic material is preferable because it results in a stable hydrophilic porous membrane that can withstand long-term operation. The contact angle with water of the hydrophobic material is, for example, 100 degrees or more and less than 180 degrees. The contact angle with water of the hydrophilic material is, for example, greater than 0 degrees and less than 90 degrees.

[0024] The cathode 11, anode 12, and diaphragm 13 are stacked to form an electrochemical reaction cell. The electrochemical reaction structure 10 may have a cell stack formed by stacking multiple electrochemical reaction cells. By forming a cell stack, the amount of carbon dioxide reacted per unit area increases, thus increasing the amount of reduction product produced. The number of stacked electrochemical reaction cells is preferably, for example, 10 to 150.

[0025] The flow channel plate 14 forms a cathode chamber 140. The cathode chamber 140 is provided on the surface of the flow channel plate 14 facing the cathode 11, and can form a cathode flow channel. The cathode chamber 140 has an inlet for supplying fluid to the cathode chamber 140 and an outlet for discharging fluid from the cathode chamber 140. The surface shape of the cathode flow channel is not particularly limited, but for example, it is serpentine. The flow channel plate 14 can be formed using a conductive material such as a metal material or a carbon material.

[0026] The flow channel plate 15 forms an anode chamber 150. The anode chamber 150 is provided on the surface of the flow channel plate 15 facing the anode 12, and can form an anode flow channel. The anode chamber 150 has an inlet for supplying fluid to the anode chamber 150 and an outlet for discharging fluid from the anode chamber 150. The surface shape of the anode flow channel is not particularly limited, but for example, it is serpentine. The flow channel plate 15 can be formed using a conductive material such as a metal material or a carbon material.

[0027] The current collector 16 is electrically connected to the cathode 11. The current collector 16 may be provided, for example, on the opposite side of the flow channel plate 14 from the cathode 11 and electrically connected to the cathode 11 via the flow channel plate 14. The current collector 17 is electrically connected to the anode 12. The current collector 17 may be provided, for example, on the opposite side of the flow channel plate 15 from the anode 12 and electrically connected to the anode 12 via the flow channel plate 15. The current collectors 16 and 17 can be formed using a conductive material containing a metallic element such as titanium.

[0028] Current collectors 16 and 17 may be connected to a power supply 20. The power supply 20 can, for example, supply power to the electrochemical reaction structure 10. The power supply 20 can supply voltage and current to the electrochemical reaction structure 10 to cause electrolytic reactions such as oxidation and reduction reactions, and is electrically connected to the cathode 11 and anode 12. Using the electrical energy supplied from the power supply 20, the reduction reaction at the cathode 11 and the oxidation reaction at the anode 12 are carried out. The power supply 20 and the current collector 16, and the power supply 20 and the current collector 17 are connected, for example, by wiring. Electrical equipment such as inverters, converters, and batteries may be installed between the electrochemical reaction structure 10 and the power supply 20 as needed. The driving method for the electrochemical reaction structure 10 may be a constant voltage method or a constant current method.

[0029] The power source 20 may be a normal commercial power source or a battery, or it may be a power source that converts renewable energy into electrical energy and supplies it. Examples of such power sources include power sources that convert kinetic energy or potential energy such as wind power, hydropower, geothermal energy, and tidal power into electrical energy; power sources such as solar cells that have a photoelectric conversion element that converts light energy into electrical energy; power sources such as fuel cells and storage batteries that convert chemical energy into electrical energy; and power sources such as devices that convert vibration energy such as sound into electrical energy. The photoelectric conversion element has the function of separating charges using the energy of light such as irradiated sunlight. Examples of photoelectric conversion elements include pin junction solar cells, pn junction solar cells, amorphous silicon solar cells, multi-junction solar cells, monocrystalline silicon solar cells, polycrystalline silicon solar cells, dye-sensitized solar cells, and organic thin-film solar cells. Furthermore, the photoelectric conversion element may be stacked with at least one of the cathode 11 and anode 12 inside the electrochemical reaction structure 10.

[0030] The power supply 20 can adjust, for example, the current or voltage supplied to the electrochemical reaction structure 10. The power supply 20 may have, for example, a power controller that adjusts the current or voltage supplied to the electrochemical reaction structure 10. 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 supplied to the electrochemical reaction structure 10. The power supply 20 may be provided outside the electrolyzer 1.

[0031] The electrolysis reaction such as the oxidation reaction and reduction reaction by the electrochemical reaction structure 10 is preferably carried out at a temperature of room temperature (for example, 25 ° C) or higher and 100 ° C or lower, at which the electrolytic solution does not vaporize. The above temperature is preferably 60 ° C or higher and 95 ° C or lower, and more preferably 60 ° C or higher and 80 ° C or lower. To set the temperature below room temperature, a cooling device such as a chiller is required, and there is a risk that the energy efficiency of the overall system will decrease. In the case of a temperature exceeding 100 ° C, the water in the electrolytic solution becomes steam and the resistance increases, and there is a risk that the electrolysis efficiency will decrease.

[0032] The current density of the cathode 11 is not particularly limited, but in order to increase the production amount of the reduction product per unit area, a higher current density is preferable. The current density is preferably 100 mA / cm 2 or more and 1.5 A / cm 2 or less, and more preferably 300 mA / cm 2 or more and 700 mA / cm 2 or less. If it is less than 100 mA / cm 2 , the production amount of the reduction product per unit area is low and a large area is required. If it exceeds 1.5 A / cm 2 , the side reaction of hydrogen generation increases and the concentration of the reduction product decreases.

[0033] When the Joule heat also increases by increasing the current density and rises above an appropriate temperature, 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, if the temperature is 100 ° C or lower, it may be left at that temperature.

[0034] The flow path P1 is connected to the inlet of the cathode chamber 140. The cathode supply fluid supplied to the cathode chamber 140 can flow through the flow path P1. The cathode supply fluid contains a substance to be reduced, such as carbon dioxide. The cathode supply fluid may be a gas containing a gaseous substance to be reduced or a first electrolyte containing a substance to be reduced.

[0035] The flow path P1 may be connected to a source of reducible materials. The source of reducible materials may have a reducible material separation and recovery device, or may be connected to a reducible material separation and recovery device. The 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 temporarily stored. Examples of sources of reducible materials include, for example, thermal power plants, facilities with various incinerators and combustion furnaces such as waste incinerators, steel mills, facilities with blast furnaces, etc. The source of reducible materials is not limited to these facilities, but may also be other factories that generate reducible materials.

[0036] The channel P2 is connected to the inlet of the anode chamber 150. The anode supply fluid supplied to the anode chamber 150 can flow through channel P2. The anode supply fluid includes water or a second electrolyte. Channel P2 may be connected to an anode solution supply source. The anode solution supply source can supply, for example, a second electrolyte used in the anode supply fluid.

[0037] The flow path P3 is connected to the outlet of the cathode chamber 140. The flow path P3 can carry the cathode discharge fluid discharged from the cathode chamber 140. The cathode discharge fluid includes carbon compounds and hydrogen, which are examples of reduction products produced by the reduction reaction in the cathode 11, and a portion of the reduced substance gas contained in the cathode supply fluid or a portion of the first electrolyte.

[0038] The flow path P4 is connected to the outlet of the anode chamber 150. The flow path P4 can carry the anode discharge fluid discharged from the anode chamber 150. The anode discharge fluid includes, for example, gaseous oxygen produced by the oxidation reaction at the anode 12, a substance to be reduced that moves from the cathode chamber 140 or the electrolyte, and water or a portion of the second electrolyte contained in the anode supply fluid.

[0039] The flow path P3 may be connected to a valuable substance production apparatus. Examples of valuable substance production apparatus include chemical synthesis apparatuses that produce valuable substances through chemical synthesis using raw materials such as carbon monoxide. Examples of valuable substances include methanol produced by a methanol production apparatus, hydrocarbons produced by a Fischer-Tropsch reactor, synthetic gasoline, diesel fuel, jet fuel, and olefin compounds produced by an olefin production apparatus. By providing a valuable substance production apparatus downstream of the electrochemical reaction structure 10, valuable substances with high added value can be produced from the products of the electrochemical reaction structure 10.

[0040] The type of chemical synthesis apparatus is not particularly limited, as long as it can react and synthesize other substances from the reduction products generated in cathode 11. Examples of reactions using reduction products from a chemical synthesis apparatus include chemical reactions, electrochemical reactions, and biological transformation reactions using organisms such as algae, enzymes, yeast, and bacteria.

[0041] The flow path P3 may be connected to a product separator instead of a valuable materials production device. The product separator can separate carbon compounds such as carbon monoxide, which are products, by separating excess carbon dioxide from the cathode discharge fluid or by removing water from the cathode discharge fluid. For example, when carbon monoxide gas is produced in the electrochemical reaction structure 10 by formula (2) above, methanol can be produced by methanol synthesis, or jet fuel or diesel fuel can be produced by Fischer-Tropsch synthesis, by using a mixed gas containing the produced carbon monoxide gas and hydrogen gas as a byproduct of the reduction reaction as a raw material. However, the flow path P3 may be connected to a tank that stores gas containing carbon compounds such as carbon monoxide instead of a valuable materials production device.

[0042] The first electrolyte is preferably a solution with a high absorption rate of the substance to be reduced. The form in which the substance to be reduced exists in the first electrolyte is not necessarily limited to a dissolved state; the substance to be reduced may be present as bubbles mixed in the first electrolyte. Examples of electrolytes containing the substance to be reduced include aqueous solutions containing bicarbonates and carbonates such as lithium bicarbonate (LiHCO3), sodium bicarbonate (NaHCO3), potassium bicarbonate (KHCO3), cesium bicarbonate (CsHCO3), sodium carbonate (Na2CO3), and potassium carbonate (K2CO3), as well as phosphoric acid and boric acid. The electrolyte containing the substance to be reduced may also contain alcohols such as methanol and ethanol, or ketones such as acetone, or it may be an alcohol solution or a ketone solution. The first electrolyte may also contain a substance absorbent that lowers the reduction potential of the substance to be reduced, has high ionic conductivity, and absorbs the substance to be reduced.

[0043] The electrolytes, such as the first and second electrolytes, can be solutions containing water, for example, aqueous solutions containing any electrolyte. Preferably, this solution is an aqueous solution that promotes the oxidation reaction of water. Examples of aqueous solutions containing electrolytes include phosphate ions (PO4). 2- ), borate ions (BO3 3- ), sodium ions (Na + ), potassium ions (K + ), calcium ions (Ca 2+ ), lithium ion (Li + ), cesium ions (Cs + ), magnesium ions (Mg 2+ ), chloride ions (Cl - ), bicarbonate ions (HCO3) - ), carbonate ions (CO3 - ), hydroxide ion (OH - Examples include aqueous solutions containing ) and the like.

[0044] The electrolytes mentioned above include, for example, cations such as imidazolium ions and pyridinium ions, and BF4 - PF6 -Ionic liquids or aqueous solutions thereof, which consist of salts with anions such as ethanolamine, and remain in a liquid state over a wide temperature range, can be used. Furthermore, other electrolytes include amine solutions or aqueous solutions thereof, such as ethanolamine, imidazole, and pyridine. Examples of amines include primary amines, secondary amines, and tertiary amines. These electrolytes may have high ionic conductivity, the property of absorbing the substance to be reduced, and the characteristic of lowering the reduction energy.

[0045] Examples of primary amines include methylamine, ethylamine, propylamine, butylamine, pentylamine, and hexylamine. The hydrocarbons of the amines may be substituted with alcohols, halogens, etc. Examples of substituted amine hydrocarbons include methanolamine, ethanolamine, and chloromethylamine. Unsaturated bonds may also be present. The same applies to secondary and tertiary amines.

[0046] Examples of secondary amines include dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dimethanolamine, diethanolamine, and dipropanolamine. The substituted hydrocarbons may be different. This is also true for tertiary amines. For example, examples of amines with different hydrocarbons include methylethylamine and methylpropylamine.

[0047] Examples of tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trimethanolamine, triethanolamine, trippropanolamine, tributanolamine, trihexanolamine, methyldiethylamine, and methyldipropylamine.

[0048] Examples of cations in ionic liquids include 1-ethyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1-butyl-3-methylimidazole ion, 1-methyl-3-pentylimidazolium ion, and 1-hexyl-3-methylimidazolium ion.

[0049] The 2-position of the imidazolium ion may be substituted. Examples of cations in which the 2-position of the imidazolium ion 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, and 1-hexyl-2,3-dimethylimidazolium ion.

[0050] Examples of pyridinium ions include methylpyridinium, ethylpyridinium, propylpyridinium, butylpyridinium, pentylpyridinium, and hexylpyridinium. Both the imidazolium ion and the pyridinium ion may be substituted with alkyl groups and may have unsaturated bonds.

[0051] As an anion, fluoride ions (F - ), chloride ions (Cl - ), bromide ions (Br - ), iodide ion (I - ), BF4 - PF6 - CF3COO - CF3SO3 - NO3 - SCN - (CF3SO2)3C - Examples include bis(trifluoromethoxysulfonyl)imide, bis(trifluoromethoxysulfonyl)imide, and bis(perfluoroethylsulfonyl)imide. Twin ions, in which the cation and anion of an ionic liquid are linked by a hydrocarbon, may also be used. A buffer solution such as potassium phosphate solution may be supplied to the anode chamber 150.

[0052] The second electrolyte contains water as the oxidizing agent. By changing the amount of water and electrolyte components in the first and second electrolytes, the reactivity can be altered, thereby changing the selectivity of the reducing agent and the proportion of the generated substances. The first and second electrolytes may contain redox pairs as needed. Examples of redox pairs include Fe. 3+ / Fe 2+ ya IO 3- / I - These are some examples.

[0053] Next, an example of the operation method of the electrolytic device 1 will be described. Here, we will describe the case in which carbon dioxide is reduced to mainly carbon monoxide and water is oxidized to produce oxygen. When a cathode supply fluid containing carbon dioxide is supplied to the cathode chamber 140, and an anode supply fluid containing a second electrolyte is supplied to the anode chamber 150, and a voltage greater than the electrolysis voltage is applied between the cathode 11 and anode 12 by power supply from the power supply 20, an oxidation reaction of water occurs near the anode 12 in contact with the second electrolyte. As shown in equation (1) below, an oxidation reaction of water contained in the second electrolyte occurs, electrons are lost, and oxygen and hydrogen ions are produced. Some of the generated hydrogen ions move to the cathode chamber 140 via the diaphragm 13. 2H2O → 4H + +O2+4e - …(1)

[0054] Hydrogen ions (H) generated on the anode 12 side + As the electrons reach the vicinity of cathode 11, electrons (e) are sent from the power supply 20 to cathode 11. - When ) is supplied, a reduction reaction of carbon dioxide occurs. As shown in equation (2) below, hydrogen ions (H) move to the vicinity of cathode 11. + ) and electrons (e) supplied from power supply 20 - ) reduces carbon dioxide, producing carbon monoxide. 2CO2 + 4H + +4e - → 2CO + 2H2O …(2)

[0055] The gaseous component contained in the anode discharge fluid from the anode chamber 150 is mainly oxygen gas, as shown in equation (1) above. In the reactions at cathode 11 and anode 12, most of the carbon dioxide contained in the cathode supply fluid supplied to cathode chamber 140 is reduced at cathode 11, but some is reduced as carbon dioxide or carbonate ions (CO3 2- ) and bicarbonate ions (HCO3) - These ions flow into the anode 12 side. When the pH of the anode solution (second electrolyte) becomes, for example, 6 or less, the carbonate ions and bicarbonate ions that have moved to the anode 12 side come into existence as carbon dioxide through a chemical equilibrium reaction, and some of them remain dissolved in the anode solution. The carbon dioxide gas that cannot be dissolved in the anode solution is included along with oxygen gas in the anode discharge fluid discharged from the anode chamber 150. Under typical operating conditions of the electrochemical reaction structure 10, the ratio of carbon dioxide gas to oxygen gas in the anode discharge fluid may rise to, for example, 2:1.

[0056] The reduction product may contain carbon dioxide, carbon monoxide, and hydrogen produced by the electrolysis of water. The hydrogen concentration can be adjusted as needed depending on the application. When using hydrogen in a chemical synthesis apparatus, carbon dioxide may be separated from the cathode discharge fluid to use a mixture of carbon monoxide and hydrogen. If hydrogen is not used, only carbon monoxide is separated from the cathode discharge fluid. When producing methanol, the hydrogen produced in cathode 11 can be used as a valuable material by adjusting the number of moles of hydrogen to approximately twice the number of moles of carbon monoxide. On the other hand, by suppressing hydrogen side reactions in cathode 11 depending on the reaction conditions, the concentration of hydrogen in the reduction product can be adjusted to a range of 0.1% to 5% by volume. This allows the electrolytic apparatus to be used as a carbon monoxide production apparatus to produce high-concentration carbon monoxide.

[0057] In an electrolytic 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 to prevent gases (e.g., O2) generated in the anode chamber 150 from moving to the cathode chamber 140, or gases (e.g., CO) generated in the cathode chamber 140 from moving to the anode chamber 150. Furthermore, since ions are the medium that carries electricity (electrons) in an electrolytic device, the diaphragm 13 is required to have high ion permeability in order to allow the reaction to proceed efficiently.

[0058] In polymer electrolyte fuel cells (PEFCs) and polymer electrolyte water electrolysis (PEWEs), ion exchange membranes that achieve both high gas barrier properties and ion permeability are used. In particular, cation exchange membranes such as Nafion (trade name, manufactured by DuPont) and Flemion (trade name, manufactured by AGC) have been used for a long time, but when these are used in carbon dioxide electrolysis devices or nitrogen electrolysis devices, the generation of hydrogen, a side reaction, becomes dominant, and the electrolysis efficiency decreases. On the other hand, when anion exchange membranes such as Sustenion (trade name, manufactured by Dioxide Materials) are used, hydrogen generation is suppressed, but at present these membranes have poor thermal and mechanical stability and are problematic in terms of durability.

[0059] One possible solution to the problems that arise when using ion exchange membranes as described above is to use a porous membrane that does not have ion passability selectivity as the diaphragm 13. In this method, ions pass through the diaphragm 13 by the direct movement of the electrolyte. This is a method that has been considered in electrolytic devices such as alkaline water electrolyzers, and methods for supplying a stable diaphragm have been proposed.

[0060] However, when the above porous membrane is used as the diaphragm 13, the amount of crossover of the generated gas to the counter electrode is greater compared to an ion exchange membrane. In electrolytic devices such as carbon dioxide electrolytic devices and nitrogen electrolytic devices, hydrogen is generated as a reaction byproduct on the cathode 11 side, and when this reacts with oxygen generated on the anode 12 side, reactive oxygen species such as hydrogen peroxide are generated. These are caused by oxidation reactions of the polymer constituting the porous membrane. As a result, the composition and shape of the membrane may change, which may lead to a decrease in the diaphragm function.

[0061] In contrast, in this embodiment, the deterioration of the diaphragm 13 is suppressed by using chemical species 18. Chemical species 18 consists of chemical species (also called quenchers or inhibitors) that decompose, capture (retain), or inactivate reactive oxygen species generated by the electrochemical reaction structure 10. Reactive oxygen species are highly reactive oxygen species such as hydrogen peroxide, superoxide anion radical, hydroxyl radical, and singlet oxygen. It is thought that reactive oxygen species are generated by the reaction of hydrogen generated at the cathode 11 and oxygen generated at the anode 12. Since hydrogen is more diffusive than oxygen, it is thought that the most reactive oxygen species are concentrated between the diaphragm 13 and the anode 12. Therefore, it is preferable that chemical species 18 be present between the anode 12 and the diaphragm 13.

[0062] The chemical species are metals, metal oxides, or metal hydroxides containing at least one metallic element from the following: cerium (Ce), manganese (Mn), cobalt (Co), platinum (Pt), ruthenium (Ru), tungsten (W), and tin (Sn). Preferred examples of metals are Ce, Mn, Co, Pt, Ru, W, or Sn, with particularly preferred examples being Ce, Mn, Pt, or Co. Examples of metal oxides include MnO, Mn3O4, MnO2, MnO3, Mn2O7, CoO, Co2O3, Co3O4, and CeO2. Examples of metal hydroxides include Mn(OH)2, MnO(OH), MnO(OH)2, and Ce(OH)4. The chemical species may, for example, be attached to the surface of the material constituting the diaphragm 13.

[0063] The decomposition of reactive oxygen species occurs, for example, by converting them into water or oxygen through radical reactions.

[0064] Reactive oxygen species are captured by reacting with them, for example, stable radical compounds, and converting them into inert reactants.

[0065] Inactivation of reactive oxygen species is achieved, for example, by suppressing the radicals generated from reactive oxygen species.

[0066] The chemical species 18 may be supported on the diaphragm 13 or the anode 12. In the manufacturing method of the electrolytic device 1, for example, the above-mentioned metal, metal oxide, or metal hydroxide may be mixed with a binder and applied to the diaphragm 13 or the anode 12. Alternatively, the metal precursor may be impregnated into a porous material or other component used for the anode 12, and then fired (sintered) to support the metal oxide. Alternatively, the above-mentioned metal, metal oxide, or metal hydroxide may be inserted as an independent component between the diaphragm 13 and the anode 12. In this case, the chemical species 18 may consist only of the metal, metal oxide, or metal hydroxide mentioned above, or it may consist of a material containing these.

[0067] The chemical species 18 may be supported on the anode 12 or the diaphragm 13 so as to face the cathode channel via the diaphragm 13 from the inlet to the outlet of the cathode channel. The amount of chemical species 18 may also increase from the channel P1 side (inlet side of the cathode channel) of the cathode chamber 140 to the channel P2 side (outlet side of the cathode channel). On the channel P1 side of the cathode chamber 140, the concentration of the substance to be reduced is high, and hydrogen is unlikely to be generated. On the other hand, on the channel P2 side of the cathode chamber 140, the concentration of the substance to be reduced is lower than on the channel P1 side, so hydrogen is easily generated, and this diffuses into the anode channel and reacts with the oxygen generated by the anode 12, easily generating reactive oxygen species. In other words, since the diaphragm 13 on the channel P2 side is likely to deteriorate, it is preferable that the amount of chemical species 18 facing the channel P2 side is greater than the amount of chemical species 18 facing the channel P1 side. The amount of chemical species 18 per unit area of ​​the anode 12 or diaphragm 13 on the channel P2 side is preferably 1.05 times or more, and more preferably 1.1 times or more, than the amount of chemical species 18 per unit area on the channel P1 side. There is no particular upper limit, but for example, the amount of chemical species 18 per unit area on the channel P2 side may be 20 times or less than the amount of chemical species 18 per unit area on the channel P1 side. The amount of chemical species 18 can be evaluated, for example, by cutting out a laminate of the anode 12, chemical species 18 and diaphragm 13, performing appropriate dissolution pretreatment with acid, etc., and then quantitatively analyzing it using a high-frequency inductively coupled plasma (ICP) emission spectrometer. Furthermore, the difference in the amount of chemical species 18 between the channel P1 side and the channel P2 side can be created, for example, by impregnating the anode 12 with a precursor of chemical species 18, then firing (sintering) to support the chemical species 18 on the anode 12. This can be achieved by first supporting the chemical species 18 on the entire anode 12, then impregnating only a portion of the anode 12 on the channel P2 side with the precursor and firing, or by repeating this process any number of times. When measuring the amount of chemical species 18, the cathode channel can be divided into two parts: the first half from channel P1 to the midpoint, and the second half from the midpoint to channel P2, with the midpoint as the reference point. The first half can be considered the channel P1 side, and the second half the channel P2 side.

[0068] By using chemical species 18, the degradation of the diaphragm 13 can be suppressed, thereby suppressing the degradation of the electrolytic device and improving its durability. The above-mentioned reactive oxygen species readily attack ether groups or sulfonyl groups, and thus easily degrade the diaphragm 13. Therefore, when the diaphragm 18 contains a polymer compound crosslinked with at least one of the functional groups of an ether group and a sulfonyl group, the introduction of chemical species 18 offers a significant advantage in suppressing the degradation of the diaphragm 13. [Examples]

[0069] Electrolytic devices for Examples 1, 2, 3, and 4, and Comparative Example 1 were fabricated. To evaluate the degradation caused by reactive oxygen species during hydrogen by-production and the degradation suppression effect of introducing chemical species 18, a cathode supply fluid containing nitrogen, an inert gas, was supplied to the cathode channel humidified with pure water, and an anode supply fluid containing potassium bicarbonate at a concentration of 0.1 mol / L was supplied to the anode channel as the electrolyte at 700 mA / cm². 2 Each electrolytic device was operated under the following conditions with the following current density: By controlling the voltage with power supply 20, the current density between cathode 11 and anode 12 was set to 700 mA / cm². 2 An electric current was passed through the cathode 11 to reduce water and produce hydrogen, and the anode 12 to oxidize water and produce oxygen. Furthermore, the cathode discharge fluid discharged from the cathode channel was collected and analyzed to calculate the hydrogen production Faraday efficiency.

[0070] Each electrolytic device was evaluated as follows according to the change in hydrogen production Faraday efficiency: Electrolytic devices in which the time until the hydrogen production Faraday efficiency decreased by 10% from the start of operation was less than 50 hours were evaluated as × (Durability: Bad), electrolytic devices in which the above time was 50 hours or more but less than 100 hours were evaluated as ○ (Durability: Good), and electrolytic devices in which the above time was 100 hours or more were evaluated as ◎ (Durability: Very Good).

[0071] (Example 1) A 0.5 mol / L manganese chloride solution was prepared by mixing ethanol and water in a 9:1 ratio. An iridium-coated titanium porous body, to be used as anode 12, was immersed in this solution, removed, and dried. It was then dried in a 60°C oven for 5 hours. Subsequently, the porous body was sintered in an electric furnace at 600°C for 2 hours to produce anode 12 supporting manganese as chemical species 18. An electrolytic apparatus, as shown in Figure 1, was fabricated using this anode 12. The evaluation result for the electrolytic apparatus of Example 1 was ◎ (Durability: Very Good). The results are shown in Table 1.

[0072] (Example 2) A 0.5 mol / L cobalt chloride hexahydrate solution was prepared by mixing ethanol and water in a 9:1 ratio. An iridium-coated titanium porous body, to be used as anode 12, was immersed in this solution, removed, and dried. It was then dried in a 60°C oven for 5 hours. Subsequently, the porous body was sintered in an electric furnace at 450°C for 1 hour to produce anode 12 with cobalt species supported as chemical species 18. An electrolytic apparatus, as shown in Figure 1, was fabricated using this anode 12. The evaluation result for the electrolytic apparatus of Example 1 was ◎ (Durability: Very Good). The results are shown in Table 1.

[0073] (Example 3) A 0.5 mol / L cerium nitrate hexahydrate solution was prepared using pure water. An iridium-coated titanium porous body, to be used as anode 12, was immersed in this solution, removed, and dried. It was then dried in a 60°C oven for 5 hours. Subsequently, the porous body was sintered in an electric furnace at 450°C for 1 hour to produce anode 12 supporting a cerium species as chemical species 18. An electrolytic apparatus, as shown in Figure 1, was fabricated using this anode 12. The evaluation result for the electrolytic apparatus of Example 1 was ○ (Durability: Good). The results are shown in Table 1.

[0074] (Example 4) A 0.05 mol / L bis(acetylacetonate)platinum solution was prepared using acetone. An iridium-coated titanium porous body, to be used as anode 12, was immersed in this solution, removed, and dried. It was then dried in a 60°C oven for 5 hours. Subsequently, the porous body was sintered in an electric furnace at 450°C for 1 hour to produce anode 12 supporting a platinum species as chemical species 18. An electrolytic apparatus, as shown in Figure 1, was fabricated using this anode 12. The evaluation result for the electrolytic apparatus of Example 1 was ○ (Durability: Good). The results are shown in Table 1.

[0075] (Comparative Example 1) Without introducing chemical species 18, the iridium-coated titanium porous material was used directly as the anode 12 to fabricate the electrolytic apparatus shown in Figure 1. The evaluation result of the electrolytic apparatus in Example 1 was × (Durability: Bad). The results are shown in Table 1.

[0076] [Table 1]

[0077] As shown in Table 1, introducing cerium or platinum as chemical species 18 improves durability, and introducing cobalt or manganese further improves durability, thus extending the lifespan of the electrolytic device.

[0078] The configurations of each embodiment described above can be applied in combination, and can also be partially replaced. Although several embodiments of the present invention have been described here, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as described in the claims.

[0079] The above embodiments can be summarized in the following technical proposal. (Technical proposal 1) A cathode having a reduction catalyst that promotes a reduction reaction to reduce a target substance, which is carbon dioxide or nitrogen, and produce a reduction product, An anode having an oxidation catalyst that promotes an oxidation reaction that oxidizes water to produce oxygen, A diaphragm is provided between the cathode and the anode, A cathode channel facing the cathode and through which the gas of the substance to be reduced flows, An anode channel facing the anode and through which the electrolyte containing water flows, A chemical species present between the anode channel and the diaphragm that decomposes, captures, or inactivates reactive oxygen species, An electrolytic cell equipped with the following features. (Technical proposal 2) The aforementioned 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. The electrolytic cell described in Technical Proposal 1. (Technical proposal 3) The chemical species is supported on the anode or the diaphragm so as to face the cathode channel via the diaphragm from the inlet to the outlet of the cathode channel, The amount of the chemical species per unit area of ​​the anode or diaphragm facing the outlet side is 1.05 times or more the amount of the chemical species per unit area of ​​the anode or diaphragm facing the inlet side. An electrolytic cell as described in Technical Proposal 1 or Technical Proposal 2. (Technical proposal 4) The aforementioned diaphragm is a porous membrane that does not have ion passability selectivity. An electrolytic cell as described in any one of Technical Proposal 1 to Technical Proposal 3. (Technical proposal 5) The diaphragm comprises a molecular compound crosslinked with at least one functional group selected from the group consisting of ether groups and sulfonyl groups. An electrolytic cell as described in any one of Technical Proposal 1 to Technical Proposal 4. (Technical proposal 6) The reactive oxygen species is hydrogen peroxide, superoxide anion radical, hydroxyl radical, or singlet oxygen. An electrolytic cell as described in any one of Technical Proposal 1 to Technical Proposal 5. (Technical proposal 7) An electrolytic cell described in any one of Technical Proposal 1 to Technical Proposal 6, A power supply that conducts current between the anode and the cathode, It is equipped with, The substance to be reduced is carbon dioxide. Electrolyzer. (Technical proposal 8) An electrolytic cell described in any one of Technical Proposal 1 to Technical Proposal 6, A power supply that conducts current between the anode and the cathode, It is equipped with, The substance to be reduced is nitrogen. Electrolyzer. (Technical proposal 9) A method for manufacturing an electrolytic cell, The aforementioned electrolytic cell is A cathode having a reduction catalyst that promotes a reduction reaction to reduce a target substance, which is carbon dioxide or nitrogen, and produce a reduction product, An anode having an oxidation catalyst that promotes an oxidation reaction that oxidizes water to produce oxygen, A diaphragm is provided between the cathode and the anode, A cathode channel facing the cathode and through which the gas of the substance to be reduced flows, An anode channel facing the anode and through which the electrolyte containing water flows, It is equipped with, The aforementioned manufacturing method is A porous body containing the oxidation catalyst is immersed in a solution containing a precursor of a chemical species that decomposes, captures, or inactivates reactive oxygen species. The porous body is sintered to form the anode. A method for manufacturing electrolytic cells. [Explanation of Symbols]

[0080] 1...Electrolytic device, 10...Electrochemical reaction structure, 11...Cathode, 12...Anode, 13...Diaphragm, 13a...Surface, 13b...Surface, 14...Flow channel plate, 15...Flow channel plate, 16...Current collector, 17...Current collector, 18...Chemical species, 20...Power supply, 140...Cathode chamber, 150...Anode chamber, P1...Flow channel, P2...Flow channel, P3...Flow channel, P4...Flow channel.

Claims

1. A cathode having a reduction catalyst that promotes a reduction reaction to reduce a target substance, which is carbon dioxide or nitrogen, and produce a reduction product, An anode having an oxidation catalyst that promotes an oxidation reaction that oxidizes water to produce oxygen, A diaphragm is provided between the cathode and the anode, A cathode channel facing the cathode and through which the gas of the substance to be reduced flows, An anode channel facing the anode and through which the electrolyte containing water flows, A chemical species present between the anode channel and the diaphragm that decomposes, captures, or inactivates reactive oxygen species, An electrolytic cell equipped with the following features.

2. The aforementioned 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. The electrolytic cell according to claim 1.

3. The chemical species is supported on the anode or the diaphragm so as to face the cathode channel via the diaphragm from the inlet to the outlet of the cathode channel, The amount of the chemical species per unit area of ​​the anode or diaphragm facing the outlet side is 1.05 times or more the amount of the chemical species per unit area of ​​the anode or diaphragm facing the inlet side. The electrolytic cell according to claim 1.

4. The aforementioned diaphragm is a porous membrane that does not have ion passability selectivity. The electrolytic cell according to claim 1.

5. The diaphragm comprises a molecular compound crosslinked with at least one functional group selected from the group consisting of ether groups and sulfonyl groups. The electrolytic cell according to claim 1.

6. The reactive oxygen species is hydrogen peroxide, superoxide anion radical, hydroxyl radical, or singlet oxygen. The electrolytic cell according to claim 1.

7. An electrolytic cell according to any one of claims 1 to 6, A power supply that conducts current between the anode and the cathode, It is equipped with, The substance to be reduced is carbon dioxide. Electrolyzer.

8. An electrolytic cell according to any one of claims 1 to 6, A power supply that conducts current between the anode and the cathode, It is equipped with, The substance to be reduced is nitrogen. Electrolyzer.

9. A method for manufacturing an electrolytic cell, The aforementioned electrolytic cell is A cathode having a reduction catalyst that promotes a reduction reaction to reduce a target substance, which is carbon dioxide or nitrogen, and produce a reduction product, An anode having an oxidation catalyst that promotes an oxidation reaction that oxidizes water to produce oxygen, A diaphragm is provided between the cathode and the anode, A cathode channel facing the cathode and through which the gas of the substance to be reduced flows, An anode channel facing the anode and through which the electrolyte containing water flows, It is equipped with, The aforementioned manufacturing method is A porous body containing the oxidation catalyst is immersed in a solution containing a precursor of a chemical species that decomposes, captures, or inactivates reactive oxygen species. The porous body is sintered to form the anode. A method for manufacturing electrolytic cells.

Images