Membrane electrode assembly, electrochemical cell, cell stack, and electrolysis system

Abstract

The invention relates to a membrane electrode assembly, an electrochemical cell, a cell stack, and an electrolysis system. A membrane electrode assembly according to an embodiment includes a first electrode, a second electrode, an ion exchange membrane provided between the first electrode and the second electrode, and an intermediate layer provided between the ion exchange membrane and the second electrode. The intermediate layer has porosity and electrical conductivity.

Description

Citation of relevant applications

[0001] This application is based on Japanese Patent Application 2024-158712 (filed on September 13, 2024) and enjoys priority to the aforementioned application. This application incorporates the entire contents of the aforementioned application. Technical Field

[0002] This invention relates to membrane electrode assemblies (MEAs), electrochemical cells, battery stacks, and electrolysis systems. Background Technology

[0003] In recent years, people's expectations for renewable energy have been rising. Examples of renewable energy sources include solar power, hydropower, wind power, and geothermal power. Because the power generation of these energy sources depends on weather and natural conditions, they are considered power sources with fluctuating output power (fluctuating power sources). Therefore, people are exploring combining fluctuating power sources with batteries to regulate electricity.

[0004] Furthermore, as an attempt at decarbonization, the electrochemical reduction of carbon dioxide (CO2) to convert it into chemical substances (chemical energy) such as carbon compounds (CO), formic acid (HCOOH), methanol (CH3OH), methane (CH4), acetic acid (CH3COOH), ethanol (C2H5OH), ethane (C2H6), and ethylene (C2H4) has attracted considerable attention. By connecting a fluctuating power source utilizing renewable energy and other power sources to the carbon dioxide electrolysis unit, it has the advantage of simultaneously enabling power regulation and the resource recovery of carbon dioxide. Summary of the Invention

[0005] The implementation methods involve membrane electrode assemblies, electrochemical cells, battery stacks, and electrolysis systems.

[0006] The membrane electrode assembly of the embodiment includes: a first electrode, a second electrode, an ion exchange membrane disposed between the first electrode and the second electrode, and an intermediate layer disposed between the ion exchange membrane and the second electrode, the intermediate layer being porous and conductive.

[0007] Based on the above structure, a membrane electrode assembly with less carbonate formation at the cathode can be obtained. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the membrane electrode assembly according to the embodiment. Figure 2 This is a schematic diagram of an electrochemical cell according to an embodiment. Figure 3 This is a schematic diagram of the battery stack in the implementation method. Figure 4 This is a conceptual diagram of the electrolysis apparatus according to the implementation method. Figure 5 This is a conceptual diagram of the electrolysis apparatus according to the implementation method. Figure 6 This is a flowchart of the refreshing operation in the implementation method.

[0009] Explanation of reference numerals in the attached figures 1: First electrode 1A: First substrate 1B: First catalyst layer 2: Second electrode 2A: Second substrate 2B: Second catalyst layer 3: Ion exchange membrane 4: Intermediate layer 5: Electrolyte supply path 6: Electrolyte drain path 7: First partition 8: Second partition 9: Fastening plate 10: Fastening plate 11: Power Supply 12: CO2 gas supply device 13: Product Recycling Department 14: Pure water tank 15: Filter 16: Valves 17: Pump 18: Conductivity meter 19: Ion Concentration Meter 20: Electrolyte tank 21: Pump 22: Valves 23: Ion Concentration Meter 24: Electrolyte replenishment tank 25: Pump 26: Valves 100: Membrane electrode assembly 200: Electrochemical Cell 300: Battery stack 400: Electrolysis apparatus Specific implementation methods

[0010] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that in the following description, the same reference numerals are used for the same parts, and descriptions of parts that have already been described are appropriately omitted.

[0011] The physical property values ​​described in the instruction manual were measured at a temperature of 25°C and a pressure of 1 atom. The thickness of each component is the average of the distances in the stacking direction.

[0012] The thickness and structure of the components described in the specification can be known, for example, from images obtained by observing the cross-section using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM). Furthermore, the boundaries of the components described in the specification can be determined from images obtained by scanning electron microscopy or transmission electron microscopy, measurements obtained by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS) or transmission electron microscopy equipped with energy dispersive X-ray spectroscopy (TEM-EDX), or secondary ion mass spectrometry. Additionally, the composition of the components described in the specification can be determined by secondary ion mass spectrometry, inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, or transmission electron microscopy equipped with energy dispersive X-ray spectroscopy. Furthermore, the crystallinity of the components described in the specification can be evaluated, for example, by images obtained through X-ray diffraction (XRD), electron backscatter diffraction (EBSD), or high-angle annular dark-field scanning transmission electron microscopy, scanning electron microscopy, or transmission electron microscopy. The materials contained in the components described in the specification (such as crystal defects, bonding states, etc.) can be evaluated using high-angle annular dark-field scanning transmission electron microscopy, photoluminescence (PL), or X-ray photoelectron spectroscopy (XPS). These analytical methods are merely illustrative and do not negate the specific analytical methods described in the specification.

[0013] (First Embodiment) The first embodiment relates to a membrane electrode assembly. Figure 1 A cross-sectional schematic diagram of the membrane electrode assembly 100 according to an embodiment is shown. The membrane electrode assembly 100 includes: a first electrode 1 serving as an anode electrode, a second electrode 2 serving as a cathode electrode, an ion exchange membrane 3, and an intermediate layer 4.

[0014] The membrane electrode assembly 100 of the first embodiment is used, for example, in an electrochemical cell for electrolysis. Specific examples of the electrolysis reaction of the membrane electrode assembly 100 include the following reaction: water, such as ultrapure water, is supplied to the anode, where water is decomposed to generate protons and oxygen; the generated protons pass through the electrolyte membrane and carbon dioxide is supplied to the cathode, where carbon monoxide is generated.

[0015] The first electrode 1 is the anode of the membrane electrode assembly 100. The first electrode 1 is the anode for oxidizing water to produce oxygen. The first electrode 1 has a first substrate 1A and a first catalyst layer 1B disposed on the first substrate 1A. The first electrode 1 is disposed adjacent to the ion exchange membrane 3. The first catalyst layer 1B of the first electrode 1 is disposed on the ion exchange membrane 3 side. Preferably, the first electrode 1 is in direct contact with the ion exchange membrane 3.

[0016] In electrode 1, for example, H2O (water) is oxidized to produce O2 (oxygen) and H+. + (Proton).

[0017] The first substrate 1A serves as a support for the first catalyst layer 1B. The first substrate 1A is preferably a conductive component that allows the solution and ions flowing through the first electrode 1 to pass through. The first substrate 1A can be, for example, a mesh material, a perforated material, a porous body of sintered metal fibers, or a porous body of sintered metal particles. The first substrate 1A contains metal or carbon materials. Examples of metals used in the first substrate 1A include titanium, aluminum, iron, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The first substrate 1A may contain the same metal elements as those contained in the first catalyst layer 1B. Carbon materials are, for example, carbon paper or carbon cloth.

[0018] The first catalyst layer 1B is disposed between the first substrate 1A and the ion exchange membrane 3. The first catalyst layer 1B is preferably in direct contact with the first substrate 1A. The first catalyst layer 1B is preferably in direct contact with the ion exchange membrane 3. The first catalyst layer 1B is preferably a porous material.

[0019] The materials for the first catalyst layer 1B include, for example, metals such as platinum (Pt), palladium (Pd), and nickel (Ni), alloys containing these metals, intermetallic compounds containing these metals, binary metal oxides such as 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), lithium oxide (Li-O), and lanthanum oxide (La-O), ternary metal oxides such as Ni-Co-O, Ni-Fe-O, La-Co-O, Ni-La-O, and Sr-Fe-O, quaternary metal oxides such as Pb-Ru-Ir-O and La-Sr-Co-O, and metal complexes such as Ru complexes or Fe complexes. The materials for the first catalyst layer 1B may contain two or more types.

[0020] The anolyte supplied to the first electrode 1 is water with a pH value of, for example, 5 or higher and 8 or lower, preferably 5.5 or higher and 7.5 or lower. The resistivity of the anolyte supplied to the first electrode 1 is preferably 0.1 [MΩ·cm] or higher and 18.24 [MΩ·cm] or lower, and the pH value of the anolyte in the first electrode 1 is preferably 1 or higher and 7 or lower, more preferably 3 or higher and 7 or lower. The pH value of the anolyte in the first electrode 1 is preferably measured at the outlet of the anolyte flow path.

[0021] The concentration of metal ions (total concentration of metal ions) in the anolyte contained in the first electrode 1 is preferably 0% to 10% of the concentration of metal ions (total concentration of metal ions) in the electrolyte of the intermediate layer 4, more preferably 0% to 7%, and even more preferably 1% to 5%.

[0022] The concentration of carbonate ions (HCO3-) in the anolyte solution contained in electrode 1 - and CO3 2- The total concentration is preferably the carbonate ion concentration (HCO3-) in the electrolyte of the intermediate layer 4. - and CO3 2- The total concentration is 0% to 30%, more preferably 1% to 20%, and even more preferably 3% to 10%.

[0023] The second electrode 2 is the cathode of the membrane electrode assembly 100. The second electrode 2 is a cathode for reducing carbon dioxide to generate carbon compounds. The second electrode 2 has a second substrate 2A and a second catalyst layer 2B disposed on the second substrate 2A. The second electrode 2 is disposed adjacent to the ion exchange membrane 3. The second catalyst layer 2B of the second electrode 2 is disposed on the side of the intermediate layer 4. Preferably, the second electrode 2 is in direct contact with the intermediate layer 4.

[0024] In electrode 2, for example, CO2 (carbon dioxide) is reduced to produce CO (carbon monoxide) and O2 (oxygen). Besides CO, the reduction of CO2 can also produce carbon compounds such as CH4 (methane), C2H6 (ethane), C2H4 (ethylene), CH3OH (methanol), C2H5OH (ethanol), and C2H6O2 (ethylene glycol). In addition to the reduction of carbon dioxide, water can also be reduced simultaneously in electrode 2 to produce H2 (hydrogen).

[0025] A gas containing CO2 is supplied to the second electrode 2. Preferably, the CO2 content in the gas supplied to the second electrode 2 is 30 vol% or more and 100 vol% or less. Liquid is supplied to the first electrode 1 and the intermediate layer 4, but gas is supplied to the second electrode 2 instead of liquid.

[0026] The second substrate 2A serves as a support for the second catalyst layer 2B. The second substrate 2A is a so-called gas diffusion layer. Preferably, the second substrate 2A is a conductive component that allows gases, solutions, and ions flowing through the second electrode 2 to pass through. The second substrate 2A is, for example, carbon paper or carbon cloth.

[0027] Preferably, the second substrate 2A is treated to impart appropriate hydrophobicity. Hydrophobicity refers to a property of low affinity for water. Examples of materials exhibiting hydrophobicity include fluoropolymers such as polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVC), and perfluoroalkoxy fluoropolymers. By incorporating such fluoropolymers into carbon paper or carbon cloth, a second substrate 2A can be obtained that imparts appropriate hydrophobicity while maintaining conductivity. The second substrate 2A between the carbon paper or carbon cloth and the second catalyst layer 2B may contain a porous layer formed by the aggregation of carbon particles such as carbon black. The average primary particle size of the carbon particles is, for example, 10 nm or more and 300 nm or less. The aforementioned fluoropolymer can be disposed on the carbon particles. The carbon particles are disposed between the carbon paper or carbon cloth and the second catalyst layer 2B.

[0028] The second substrate 2A and the second electrode 2 are preferably more hydrophobic than the first electrode 1, and more preferably more hydrophobic than the intermediate layer 4. Due to the high hydrophobicity of the second substrate 2A, the aqueous solution contained in the intermediate layer 4 is difficult to penetrate into the second substrate 2A.

[0029] The second catalyst layer 2B is disposed between the second substrate 2A and the intermediate layer 4. The second catalyst layer 2B is preferably in direct contact with the second substrate 2A. The second catalyst layer 2B is preferably in direct contact with the intermediate layer 4. The second catalyst layer 2B is preferably a porous structure.

[0030] Examples of catalyst layers 2B include: metals such as gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), nickel (Ni), cobalt (Co), iron (Fe), manganese (Mn), titanium (Ti), cadmium (Cd), zinc (Zn), indium (In), gallium (Ga), lead (Pb), and tin (Sn); alloys or intermetallic compounds containing at least one of these metals; carbon materials such as carbon (C), graphene, CNTs (carbon nanotubes), fullerenes, and Ketjen black; and metal complexes such as Ru complexes or Re complexes. These catalyst materials are disposed on the intermediate layer 4 sides of the second substrate 2A.

[0031] The second catalyst layer 2B may contain ionomers.

[0032] An ion exchange membrane 3 is disposed between the first electrode 1 and the intermediate layer 4. The ion exchange membrane 3 is preferably in direct contact with the intermediate layer 4. Preferably, the ion exchange membrane 3 is in direct contact with the side of the intermediate layer 4 facing the first electrode 1.

[0033] The ion exchange membrane 3 is preferably a cation exchange (proton-conducting) membrane. As the ion exchange membrane 3, it is preferable to have one or more fluorinated polymers or aromatic hydrocarbon polymers selected from sulfonic acid groups, sulfonylimide groups, and sulfate groups. As the ion exchange membrane 3, a fluorinated polymer having sulfonic acid groups is preferred. Examples of fluorinated polymers having sulfonic acid groups include: Nafion (trademark, manufactured by DuPont), Flemion (trademark, manufactured by Asahi Kasei Corporation), Selemion (trademark, manufactured by Asahi Kasei Corporation), Aquivion (trademark, manufactured by Solvay Specialty Polymers), or Aciplex (trademark, manufactured by Asahi Glass Co., Ltd.). If an anion exchange membrane or a porous membrane is used, the CO3 generated on the cathode side... 2- (carbonate ions) or HCO3- - (Bicarbonate ions) can easily pass through ion exchange membrane 3, therefore ion exchange membrane 3 is preferably a cation exchange membrane.

[0034] The thickness of the ion exchange membrane 3 can be appropriately determined considering the membrane's permeation characteristics and durability. From the viewpoints of strength, solubility resistance, and MEA output characteristics, the thickness of the ion exchange membrane 3 is preferably 20 μm to 500 μm, more preferably 30 μm to 300 μm, and even more preferably 50 μm to 200 μm.

[0035] An intermediate layer 4 is disposed between the ion exchange membrane 3 and the second electrode 2. Preferably, the surface of the intermediate layer 4 on the side of the second electrode 2 is in direct contact with the second catalyst layer 2B of the second electrode 2. Preferably, the surface of the intermediate layer 4 on the side opposite to the side of the second electrode 2 is in direct contact with the ion exchange membrane 3.

[0036] The intermediate layer 4 is preferably a porous material. More preferably, the intermediate layer 4 is a conductive porous material. More preferably, the intermediate layer 4 is hydrophilic. More preferably, the intermediate layer 4 is a conductive porous material, and the porous material is hydrophilic.

[0037] The intermediate layer 4 preferably has cation permeability.

[0038] The intermediate layer 4 preferably comprises carbon material and / or metal material. More preferably, the intermediate layer 4 comprises one or more selected from carbon particles, carbon fibers, metal fibers, and metal particles. More preferably, the intermediate layer 4 is composed of one or more selected from carbon particles, carbon fibers, metal fibers, and metal particles.

[0039] The porosity of the intermediate layer 4 is preferably 30 vol% or more and 80 vol% or less, more preferably 40 vol% or more and 75 vol% or less, and even more preferably 50 vol% or more and 70 vol% or less.

[0040] The volume resistivity of the intermediate layer 4 is preferably 0.01 [Ω·cm] to 100 [Ω·cm] or less, more preferably 0.1 [Ω·cm] to 50 [Ω·cm] or less, and even more preferably 0.2 [Ω·cm] to 10 [Ω·cm] or less.

[0041] The intermediate layer 4 contains an electrolyte containing metal ions. The electrolyte containing metal ions is preferably an aqueous solution. The metal ions contained in the electrolyte of the intermediate layer 4 are preferably monovalent metal ions. More preferably, the metal ions contained in the electrolyte of the intermediate layer 4 are monovalent alkali metal ions. More preferably, the metal ions contained in the electrolyte of the intermediate layer 4 include one or more selected from potassium ions, sodium ions, lithium ions, platinum ions, manganese ions, and cerium ions; even more preferably, they include one or more selected from potassium ions, sodium ions, and lithium ions.

[0042] The anions (counter ions of metal ions) contained in the electrolyte of intermediate layer 4 are preferably selected from HCO3. - (bicarbonate ions) and CO3 2- One or more of the following (carbonate ions), more preferably HCO3- - (bicarbonate ions) and / or CO3 2- (Carbate ions). In addition, considering factors such as improving the conductivity of the electrolyte, enhancing ion migration performance, pH adjustment, and improving catalytic performance, phosphate ions, phosphite ions, borate ions, etc., may also be included.

[0043] The concentration of metal ions in the electrolyte is preferably 0.01 mol / L to 1 mol / L, more preferably 0.03 mol / L to 0.7 mol / L, and even more preferably 0.05 mol / L to 0.5 mol / L.

[0044] The concentration of the anions contained in the electrolyte is preferably 0.1 mol / L or more but less than 1 mol / L, more preferably 0.2 mol / L or more but less than 1 mol / L, and even more preferably 0.3 mol / L or more but less than 0.7 mol / L.

[0045] The electrolyte of the intermediate layer 4 is preferably an aqueous solution containing one or more of KHCO3, NaHCO3, LiHCO3, RbCO3 and CsCO3, more preferably an aqueous solution containing one or more of KHCO3, NaHCO3 and LiHCO3, even more preferably an aqueous solution containing one of KHCO3, NaHCO3 and LiHCO3, and even more preferably an aqueous solution containing KHCO3.

[0046] The pH value of the electrolyte contained in the intermediate layer 4 is preferably 3 or higher and 9 or lower, more preferably 4 or higher and 8.5 or lower, and even more preferably 5 or higher and 8 or lower.

[0047] The pH difference between the electrolyte contained in the intermediate layer 4 and the pH difference between the water contained in the first electrode 1 is preferably 0.1 or more and 7 or less, more preferably 1 or more and 6 or less, and even more preferably 1 or more and 4 or less.

[0048] Electrolyte is supplied to the intermediate layer 4, but because the ion exchange membrane 3 uses a cation exchange membrane, the anions contained in the electrolyte have difficulty moving to the first electrode 1 through the cation exchange membrane, thus forming this structure.

[0049] The thickness of the intermediate layer 4 is preferably 10 μm or more and 500 μm or less, more preferably 20 μm or more and 400 μm or less, and even more preferably 30 μm or more and 300 μm or less.

[0050] The thickness of the intermediate layer 4 is preferably more than 1 to 3 times the thickness of the ion exchange membrane 3, more preferably more than 1 to 2.5 times, and even more preferably more than 1 to 2 times.

[0051] When CO2 supplied to the cathode and metal ions contained in the electrolyte supplied to the membrane electrode assembly 100 reach the cathode through the ion exchange membrane 3, the metal ions react with CO2 (ions) to easily form carbonates. In the membrane electrode assembly 100 of this embodiment, since the movement of metal ions towards the cathode is suppressed, the formation of carbonates is effectively suppressed. Even if (a small amount) of carbonates are formed on the cathode side, they can be washed away with water.

[0052] Furthermore, by using a cation exchange membrane in the ion exchange membrane 3, even if the CO2 supplied to the cathode is ionized, it is difficult to pass through the ion exchange membrane 3. Therefore, the membrane electrode assembly 100 of the embodiment has the advantage of less loss of CO2 supplied as raw material.

[0053] (Second Implementation) The second embodiment relates to an electrochemical battery. Figure 2 A cross-sectional view of the electrochemical cell 200 according to the second embodiment is shown. In the electrochemical cell 200 of the second embodiment, the membrane electrode assembly 100 of the first embodiment is preferably used.

[0054] like Figure 2 As shown, the electrochemical cell 200 of the second embodiment includes a first electrode 1, a second electrode 2, an ion exchange membrane 3, an intermediate layer 4, an electrolyte supply passage 5, an electrolyte discharge passage 6, a first separator 7, and a second separator 8. The electrochemical cell 200 may also include other sealing materials such as gaskets for sealing the electrodes and current collectors.

[0055] The first electrode 1, the second electrode 2, the ion exchange membrane 3, and the intermediate layer 4 of the second embodiment are the same as those of the first electrode 1, the second electrode 2, the ion exchange membrane 3, and the intermediate layer 4 of the membrane electrode assembly 100 of the first embodiment. The first electrode 1 is the anode of the electrochemical cell 200, and the second electrode 2 is the cathode of the electrochemical cell 200.

[0056] The electrolyte supply passage 5 is located on the side of the intermediate layer 4 that neither the second electrode 2 nor the ion exchange membrane 3 is disposed. The electrolyte supply passage 5 is, for example, a conduit for supplying electrolyte to the intermediate layer 4. The electrolyte contained in the intermediate layer 4 is supplied to the intermediate layer 4 via the electrolyte supply passage 5. The electrolyte is transported by a pump (not shown) and supplied to the intermediate layer 4 via the electrolyte supply passage 5.

[0057] When the electrolyte supply passage 5 comes into contact with the ion exchange membrane 3, the electrolyte supply passage 5 is preferably made of carbon material and / or metal material. The electrolyte supply passage 5 is preferably made of non-porous solid material (pipe).

[0058] The electrolyte discharge passage 6 is located on the surface of the intermediate layer 4 where neither the second electrode 2, nor the ion exchange membrane 3, nor the electrolyte supply passage 5 is located. The electrolyte contained in the intermediate layer 4 is discharged through the electrolyte discharge passage 6. The electrolyte discharge passage 6 is, for example, a pipe for discharging electrolyte from the intermediate layer 4.

[0059] The first partition 7 is disposed on the first substrate 1A side of the first electrode 1. The first partition 7 is provided with a flow path for supplying liquid water, which serves as an anode solution, to the first electrode 1.

[0060] The second partition 8 is disposed on the second substrate 2A side of the second electrode 2. The second partition 8 is provided with a flow path for supplying CO2-containing gas to the second electrode 2.

[0061] Next, the operation of the electrochemical cell 200 will be described. A power source is connected between the first electrode 1 and the second electrode 2, and a voltage is applied to the first electrode 1 and the second electrode 2. Liquid water (including an aqueous solution), preferably pure water, is supplied to the first separator 7, and water is also supplied to the first electrode 1. The water supplied to the first electrode 1 reacts in the first catalyst layer 1B, where H2O is reduced. The water is discharged from the outlet of the first separator 7.

[0062] CO2 gas is supplied to the second partition 8 and the second electrode 2. The CO2 supplied to the second electrode 2 reacts in the second electrode 2, and the CO2 is reduced to produce CO and other products. The CO and other products are recovered from the outlet of the second partition 8.

[0063] Intermediate layer 4 is the flow path for supplying electrolyte. Electrolyte is supplied to intermediate layer 4. The amount of electrolyte supplied to intermediate layer 4 may be less than the amount of pure water supplied to the first electrode 1. The amount (volume) of electrolyte supplied to intermediate layer 4 is preferably 0.05 times to 0.9 times the amount of pure water supplied to the first electrode 1, more preferably 0.1 times to 0.2 times, and even more preferably 0.3 times to 0.8 times.

[0064] When the ion exchange membrane 3 is a cation exchange membrane, carbon dioxide is difficult to pass through the ion exchange membrane 3 even if it is ionized. Therefore, the carbon dioxide supplied to the second electrode 2 is difficult to move towards the first electrode 1, thereby reducing the loss of carbon dioxide supplied to the second electrode 2.

[0065] In the electrochemical cell 200, for example, when an aqueous solution of KHCO3 is used as the electrolyte, if the second substrate 2A of the second electrode 2 is hydrophobic, potassium ions are difficult to move to the second electrode 2 side and do not readily react with carbon dioxide supplied to the second electrode 2. Since the electrochemical cell 200 employs a structure in which potassium ions are difficult to react with carbon dioxide even when ions like potassium ions are supplied, the formation of reaction products (e.g., KHCO3) between potassium ions and carbon dioxide can be suppressed on the second electrode 2 side. Even if a compound like KHCO3 is formed in the second electrode 2, the generated KHCO3 can be removed by supplying water to the second separator 8.

[0066] (Third Implementation) The third embodiment involves a battery stack. Figure 3 This is a cross-sectional schematic diagram showing the battery stack 300 of the third embodiment. Figure 3The battery stack 300 shown in the third embodiment is composed of multiple membrane electrode assemblies 100 or electrochemical cells 200 connected in series. Fastening plates 9 and 10 are respectively installed at both ends of the membrane electrode assemblies 100 and the electrochemical cells 200.

[0067] Since the amount of CO and other substances generated by an electrochemical cell 200 consisting of a single membrane electrode assembly 100 is relatively small, a large amount of CO and other substances can be obtained by connecting multiple membrane electrode assemblies 100 or multiple electrochemical cells 200 in series to form a battery stack 300.

[0068] (Fourth implementation) The fourth embodiment relates to an electrolysis apparatus. Figure 4 A conceptual diagram of the electrolysis apparatus according to the fourth embodiment is shown. The electrolysis apparatus 400 uses an electrochemical cell 200 or a cell stack 300. Figure 4 The electrolysis device 400 in the figure is used for CO2 electrolysis, but it can also be used for other types of electrolysis. The figure shows a portion of the actual structure of the electrolysis device 400. The electrolysis device 400 is controlled, for example, by a control device not shown in the figure. The arrows in the figure indicate the direction of fluid flow. The direction of fluid flow can also be opposite to the direction shown in the figure.

[0069] A power source 11 is connected to an electrochemical cell 200, applying a voltage between the first electrode 1 and the second electrode 2 (anode and cathode). CO2 gas is supplied from a CO2 gas supply device 12 to the second separator 8 of the second electrode (cathode) 2, and the reaction at the second electrode 2 is carried out using this CO2 gas. The product (e.g., CO gas) at the second electrode 2, containing some unreacted CO2 gas, is recovered by a product recovery unit 13. In the product recovery unit 13, it is preferable to separate the CO2 gas from the product.

[0070] Pure water is pumped from the pure water tank 14 into the first partition 7 on the side of the first electrode 1 via pump 17 and used in the reaction of the first electrode (anode) 1. A valve 16 is provided between pump 17 and the first partition 7. Water flowing through the first electrode 1 and discharged from the first partition 7 is filtered by a filter 15, such as an ion filter, and then returned to the pure water tank 14 for storage. The water discharged from the first partition 7 is measured using a conductivity meter 18 and an ion concentration meter 19. The conductivity and ion concentration of the water discharged from the first partition 7, which change due to impurities, are measured by the conductivity meter 18 and the ion concentration meter 19. It is also possible to measure whether the water filtered by the filter 15 reaches a set conductivity and a set ion concentration below the set values ​​after filtration.

[0071] Electrolyte is supplied from electrolyte tank 20 to electrolyte supply passage 5, which is connected to intermediate layer 4, via pump 21. A valve 22 is provided between pump 21 and electrolyte supply passage 5. Electrolyte passing through intermediate layer 4 is discharged through electrolyte discharge passage 6. The ion concentration of the discharged electrolyte can be measured using ion concentration meter 23. Electrolyte discharged from intermediate layer 4 is returned to electrolyte tank 20 for reuse. Electrolyte can be additionally supplied from electrolyte replenishment tank 24. Electrolyte is pumped from electrolyte replenishment tank 24 via electrolyte replenishment tank 24 and can be merged with the electrolyte flow path via valve 26.

[0072] (Fifth Embodiment) The fifth embodiment relates to an electrolysis system. Figure 5 A conceptual diagram of the electrolysis apparatus 500 used in the electrolysis system of the fifth embodiment is shown. The electrolysis apparatus 500 is a variation of the electrolysis apparatus 400. Descriptions of contents identical to those in the electrolysis apparatus 400 of the fourth embodiment and the electrolysis apparatus 500 of the fifth embodiment are omitted.

[0073] The electrolysis apparatus 500 also includes components for refreshing the second electrode 2, which serves as the cathode. The electrolysis apparatus 500 has a valve 27, a cleaning agent supply device 28, and a cleaning agent discharge device 29. The valve 27 can be, for example, one or more multi-position valves. A two-position eight-way valve, etc., can be used as a multi-position valve. The flow of CO2 gas and cleaning agent during electrolysis and the cleaning operation is controlled by the valve 27. The cleaning agent is liquid and / or gaseous water, preferably pure water.

[0074] like Figure 6 As shown in the flowchart, the cleaning operation is performed as follows: In the first stage, CO2 gas is supplied to the second electrode 2 (specifically, CO2 gas flows through the flow path of the second partition 8). While maintaining the supply of CO2 gas to the second electrode 2 in the first stage, or when the supply of CO2 gas to the second electrode 2 in the first stage is stopped, the second stage begins: a cleaning agent flows through the second electrode 2 to clean the second electrode 2 (specifically, the cleaning agent flows through the flow path of the second partition 8). The flow direction of the cleaning liquid is opposite to, or the same as, the direction of the supply of CO2 gas to the second electrode 2 in the first stage. In the second stage, when the flow direction of the cleaning agent is opposite to the direction of the supply of CO2 gas to the second electrode 2 in the first stage, the supply of CO2 gas to the second electrode 2 is stopped in the second stage, or CO2 gas is supplied to the second electrode 2 in the opposite direction to the direction of the supply of CO2 gas to the second electrode 2 in the first stage.

[0075] Since water is supplied to the first electrode 1 during electrolysis, there is no need to clean the first electrode 1.

[0076] When no cleaning operation is performed, the CO2 gas supplied from the CO2 gas supply device 12 passes through valve 27, through the second electrode 2, and then flows back into the product recovery section 13 via valve 27 (e.g., the path of ACDB). When no cleaning operation is performed, the cleaning agent is either not supplied from the cleaning agent supply device 28, or the cleaning agent is circulated between the cleaning agent supply device 28 and the cleaning agent discharge device 29 via valve 27 (e.g., EF is the path of the cleaning agent circulation).

[0077] During the cleaning operation, the cleaning agent supplied from the cleaning agent supply device 28 passes through valve 27, through the second electrode 2, and again through valve 27 into the cleaning agent discharge device 29. The cleaning agent used for the cleaning operation is discharged from the cleaning agent discharge device 29 (e.g., the path of EGHF). The cleaning agent during the cleaning operation may also flow in the opposite direction to the CO2 gas flow direction during the electrolysis operation (e.g., the path of EGHF) (e.g., the path of EHGF).

[0078] Preferably, the direction of the cleaning agent flow is opposite to the direction of the CO2 gas flow, as this reduces the amount of cleaning agent introduced. By making the cleaning agent flow counter-currently to the CO2 gas, salt precipitates can be effectively dissolved and removed, especially in the upstream section of the flow path of the second electrode 2 where salt precipitation occurs most frequently. On the other hand, considering salt dissolution, if the cleaning agent flows from the upstream to the downstream section in the same direction as the CO2 gas, the salt dissolves in the upstream section, resulting in a small amount of salt being dissolved in a liquid with a high salt concentration. If the cleaning agent flows counter-currently to the CO2 gas, entering from the downstream side of the flow path, a larger amount of salt in the upstream section can be dissolved in a liquid with a low salt concentration, thereby effectively dissolving and removing the salt. Therefore, a cleaning effect can be achieved even with a small amount of cleaning agent. Furthermore, from the viewpoint of maintaining production output, it is preferable to suppress the moisture content of the second substrate 2A and the second catalyst layer 2B, etc.

[0079] Figure 5 The diagram shows a structure where the paths C and D for CO2 gas are separate from the paths G and H for the cleaning agent, but CO2 gas and cleaning agent can also flow through a common path.

[0080] During the cleaning operation, it is preferable to control valve 27 to stop the flow of CO2 gas, or to circulate the CO2 gas between the CO2 gas supply device 12 and valve 27, or to allow the CO2 gas to flow in the opposite direction to the non-cleaning operation (e.g., the path of ADCB). By controlling valve 27 to allow the CO2 gas to flow in the opposite direction to the non-cleaning operation, the cleaning operation can be performed while maintaining the electrolytic reaction and the reduction in electrolytic reaction caused by the cleaning operation can be suppressed. When stopping the flow of CO2 gas during the cleaning operation, it is preferable to stop the voltage applied from the power supply 11.

[0081] During non-cleaning operations, it is preferable to stop the flow of the cleaning fluid or to allow the cleaning agent to circulate between the cleaning agent supply device 28 and the valve 27.

[0082] During the cleaning operation, the delivery of the anolyte and / or electrolyte may be stopped as needed.

[0083] Furthermore, the flow direction of CO2 gas can be changed during each cleaning operation. Specifically, in the first stage of electrolysis (non-cleaning operation), CO2 flows through the ACDB path; in the second stage of electrolysis combined with cleaning operation, CO2 flows through the ADCB path, and the cleaning solution flows through the EHGF path; in the third stage of electrolysis (non-cleaning operation), CO2 flows through the ADCB path; in the fourth stage of electrolysis combined with cleaning operation, CO2 flows through the ACDB path, and the cleaning solution flows through the EGHF path; in the fifth stage of electrolysis (non-cleaning operation), CO2 flows through the ACDB path. By reversing the flow direction of CO2 gas during the cleaning operation and ensuring the cleaning agent flows in the reverse direction, the salt precipitation is not concentrated in one location, which is therefore preferred. Example

[0084] The present invention will now be described in more detail based on the embodiments, but the present invention is not limited to the following embodiments.

[0085] (Example 1) Made Figure 2 The electrochemical cell 200 shown is constructed as follows: The first electrode (anode) 1 is an electrode coated with IrO2 nanoparticles on a Ti mesh. The second electrode (cathode) 2 is a material coated with carbon particles loaded with gold nanoparticles on carbon paper sprayed with PTFE. A cation exchange membrane Nafion is used as the ion exchange membrane 3; a 100 μm thick hydrophilically treated PTFE layer is used as the intermediate layer 4. 0.1 mol / L KHCO3 is supplied to the intermediate layer 4 at a flow rate of 4 ml / min. Pure water is supplied to the first electrode 1, and CO2 gas is supplied to the second electrode 2. A power supply 11 is connected between the first electrode 1 and the second electrode 2 for electrolysis operation, and the amount of carbonate precipitation on the second electrode 2 side is evaluated.

[0086] (Comparative Example 1) Unlike Example 1, there is no intermediate layer 4; instead, an anion exchange membrane is used as the ion exchange membrane 3 to fabricate the electrochemical cell. 0.1 mol / L KHCO3 was supplied to the first electrode 1, and electrolysis was performed in the same manner as in Example 1, evaluating the amount of carbonate precipitation on the second electrode 2 side.

[0087] In both Example 1 and Comparative Example 1, CO was confirmed to be generated from CO2. Compared with Comparative Example 1, the amount of carbonate precipitation in Example 1 was less. Due to the less carbonate precipitation, the electrochemical cell 200 of Example 1 is useful from the viewpoint of continuous operating time, etc. Furthermore, for the electrochemical cell of Example 1, after a predetermined operating time, the pressure loss of CO2 gas at the second electrode 2 increased, and the Faraday efficiency decreased to below 50%. However, the Faraday efficiency could be restored by performing a cleaning operation.

[0088] The technical solutions for the implementation methods are described below. Technical Solution 1 A membrane electrode assembly having: Electrode 1, Second electrode, An ion exchange membrane is disposed between the first electrode and the second electrode, and An intermediate layer disposed between the ion exchange membrane and the second electrode The intermediate layer is porous and conductive. Technical Solution 2 According to the membrane electrode assembly described in technical solution 1, wherein... The first electrode is the anode that oxidizes water to produce oxygen. The second electrode is a cathode for reducing carbon dioxide to produce carbon compounds. The intermediate layer is the flow path for supplying the electrolyte. Technical Solution 3 According to the membrane electrode assembly described in technical solution 1 or 2, wherein, The second electrode is hydrophobic. The intermediate layer is hydrophilic. Technical Solution 4 According to any one of technical solutions 1 to 3, the membrane electrode assembly wherein the ion exchange membrane is a cation exchange membrane. Technical Solution 5 According to any one of technical solutions 1 to 4, the membrane electrode assembly wherein the intermediate layer comprises carbon material and / or metal material. Technical Solution 6 According to any one of technical solutions 1 to 5, the membrane electrode assembly wherein the intermediate layer is in direct contact with the ion exchange membrane. Technical Solution 7 According to any one of technical solutions 1 to 6, the membrane electrode assembly wherein... The second electrode has a substrate and a catalyst layer disposed on the substrate. The intermediate layer is in direct contact with the catalyst layer. Technical Solution 8 According to the membrane electrode assembly described in any one of technical solutions 1 to 7, wherein... The volume resistivity of the intermediate layer is between 0.01 [Ω·cm] and 100 [Ω·cm]. Technical Solution 9 According to the membrane electrode assembly described in any one of technical solutions 1 to 8, wherein... The thickness of the intermediate layer is between 10 μm and 500 μm. The thickness of the intermediate layer is more than 1 and less than 3 times the thickness of the ion exchange membrane. Technical Solution 10 According to the membrane electrode assembly described in technical solution 2, wherein... The water in the first electrode is pure water. The resistivity of the pure water is 0.1 MΩ·cm or more and 18.24 MΩ·cm or less. Technical Solution 11 According to the membrane electrode assembly described in technical solution 2 or 10, wherein, The water in the first electrode is pure water. The pH value of the pure water is above 5 and below 8. Technical Solution 12 According to the membrane electrode assembly described in technical solutions 2, 10, or 11, wherein, The electrolyte contains metal ions. Technical Solution 13 According to the membrane electrode assembly described in technical solutions 2, 10, 11 or 12, the pH value of the electrolyte is above 1 and below 7. Technical Solution 14 According to the membrane electrode assembly described in technical solutions 2, 10, 11, 12 or 13, the electrolyte contains HCO3. - and / or CO3 2- . Technical Solution 15 According to the membrane electrode assembly described in technical solutions 2, 10, 11, 12, 13 or 14, the electrolyte contains one or more selected from potassium ions, sodium ions and lithium ions. Technical Solution 16 An electrochemical battery having a membrane electrode assembly according to any one of technical solutions 1 to 15. Technical Solution 17 According to the electrochemical battery described in technical solution 16, wherein, The intermediate layer is provided with an electrolyte supply passage and an electrolyte discharge passage. Pure water is supplied to the first electrode. Carbon dioxide gas is supplied to the second electrode. Electrolyte is supplied to the intermediate layer. The amount of electrolyte supplied to the intermediate layer is more than 0.05 times and less than 0.9 times the amount of pure water supplied to the first electrode. Technical Solution 18 A battery stack having an electrochemical cell according to technical solution 16 or 17. Technical Solution 19 An electrolysis system having an electrochemical cell according to claim 16, In the first stage, CO2 gas is supplied to the second electrode. While maintaining the supply of CO2 gas to the second electrode in the first stage, or when stopping the supply of CO2 gas to the second electrode in the first stage, the second stage begins: the cleaning agent is allowed to flow through the second electrode to clean it. The cleaning agent is pure water in liquid and / or gaseous form. Technical Solution 20 According to the electrolysis system of technical solution 19, in the second stage, the cleaning agent flows in the opposite direction to the direction of supplying CO2 gas to the second electrode in the first stage.

[0089] The embodiments of the present invention have been described above, but the present invention is not limited to the interpretations described above. During implementation, the constituent elements can be modified and specified without departing from the spirit of the present invention. Furthermore, various inventions can be formed by appropriately combining the various constituent elements disclosed in the above embodiments. For example, constituent elements of different embodiments can be appropriately combined as in the modified examples.

Claims

1. A membrane electrode assembly, comprising: Electrode 1, Second electrode, An ion exchange membrane is disposed between the first electrode and the second electrode, and An intermediate layer disposed between the ion exchange membrane and the second electrode; The intermediate layer is porous and conductive.

2. The membrane electrode assembly according to claim 1, wherein, The first electrode is the anode that oxidizes water to produce oxygen. The second electrode is a cathode for reducing carbon dioxide to produce carbon compounds. The intermediate layer is the flow path for supplying the electrolyte.

3. The membrane electrode assembly according to claim 1, wherein, The second electrode is hydrophobic. The intermediate layer is hydrophilic.

4. The membrane electrode assembly according to claim 1, wherein, The ion exchange membrane is a cation exchange membrane.

5. The membrane electrode assembly according to claim 1, wherein, The intermediate layer comprises carbon materials and / or metallic materials.

6. The membrane electrode assembly according to claim 1, wherein, The intermediate layer is in direct contact with the ion exchange membrane.

7. The membrane electrode assembly according to claim 1, wherein, The second electrode has a substrate and a catalyst layer disposed on the substrate. The intermediate layer is in direct contact with the catalyst layer.

8. The membrane electrode assembly according to claim 1, wherein, The volume resistivity of the intermediate layer is above 0.01 Ω·cm and below 100 Ω·cm.

9. The membrane electrode assembly according to claim 1, wherein, The thickness of the intermediate layer is greater than 10 μm and less than 500 μm. The thickness of the intermediate layer is more than one time and less than three times the thickness of the ion exchange membrane.

10. The membrane electrode assembly according to claim 2, wherein, The water in the first electrode is pure water. The resistivity of the pure water is above 0.1 MΩ·cm and below 18.24 MΩ·cm.

11. The membrane electrode assembly according to claim 2, wherein, The water in the first electrode is pure water. The pH value of the pure water is above 5 and below 8.

12. The membrane electrode assembly according to claim 2, wherein, The electrolyte contains metal ions.

13. The membrane electrode assembly according to claim 2, wherein, The electrolyte has a pH value of 1 or higher and 7 or lower.

14. The membrane electrode assembly according to claim 2, wherein, The electrolyte contains HCO3. - and / or CO3 2- .

15. The membrane electrode assembly according to claim 2, wherein, The electrolyte contains one or more ions selected from potassium ions, sodium ions, and lithium ions.

16. An electrochemical cell having a membrane electrode assembly according to any one of claims 1 to 15.

17. The electrochemical cell according to claim 16, wherein, The intermediate layer is provided with an electrolyte supply passage and an electrolyte discharge passage. Pure water is supplied to the first electrode. Carbon dioxide gas is supplied to the second electrode. Electrolyte is supplied to the intermediate layer. The amount of electrolyte supplied to the intermediate layer is more than 0.05 times and less than 0.9 times the amount of pure water supplied to the first electrode.

18. A battery stack having an electrochemical cell according to claim 16.

19. An electrolysis system having the electrochemical cell according to claim 16, In the first stage, CO2 gas is supplied to the second electrode. While maintaining the supply of CO2 gas to the second electrode in the first stage, or when stopping the supply of CO2 gas to the second electrode in the first stage, the second stage begins: the cleaning agent is allowed to flow through the second electrode to clean it. The cleaning agent is pure water in liquid and / or gaseous form.

20. The electrolysis system according to claim 19, wherein, In the second stage, the cleaning agent flows in the opposite direction to the direction in which CO2 gas is supplied to the second electrode in the first stage.

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