Membrane electrode assemblies, electrochemical cells, stacks, electrolytic systems

Abstract

The embodiment provides a film electrode assembly with excellent durability. [Solution] The membrane electrode assembly of the embodiment comprises 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, wherein the intermediate layer is porous and electrically conductive.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to membrane electrode assemblies, electrochemical cells, stacks, and electrolytic systems. [Background technology]

[0002] In recent years, expectations for renewable energy have been rising. Examples of renewable energy include solar power, hydroelectric power, wind power, and geothermal power. Because the amount of power generated depends on weather and natural conditions, these are power sources whose output fluctuates (variable power sources). Therefore, attempts are being made to regulate power by combining variable power sources with storage batteries.

[0003] Furthermore, as an attempt at decarbonization, carbon dioxide electrolysis technology is attracting attention. This technology electrochemically reduces carbon dioxide (CO2) to chemical substances (chemical energy) such as carbon monoxide (CO), formic acid (HCOOH), methanol (CH3OH), methane (CH4), acetic acid (CH3COOH), ethanol (C2H5OH), ethane (C2H6), and ethylene (C2H4). Connecting a carbon dioxide electrolysis device to a fluctuating or surplus power source using renewable energy has the advantage of simultaneously regulating power and utilizing carbon dioxide as a resource. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Zengcal Liu, et al., Journal of CO2 Utilization, 15, p.50-56 (2016) [Non-Patent Document 2] Sichao Ma, et al., Journal of The Electrochemical Society, 161 (10) F1124-F1131 (2014) [Non-Patent Document 3] Ting et al., Chemistry A Eutropian Journal, 2023 Aug 15;29(46) [Overview of the project] [Problems that the invention aims to solve]

[0005] The embodiment provides a highly durable film electrode assembly. [Means for solving the problem]

[0006] The membrane electrode assembly of the embodiment comprises 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, wherein the intermediate layer is porous and electrically conductive. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram of the film electrode assembly according to the embodiment. [Figure 2] Schematic diagram of an electrochemical cell according to an embodiment. [Figure 3] A schematic diagram of the stack in the embodiment. [Figure 4] A conceptual diagram of the electrolytic device according to the embodiment. [Figure 5] A conceptual diagram of the electrolytic device according to the embodiment. [Figure 6] Flowchart of the refresh operation in the embodiment. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described in detail below with reference to the drawings. In the following explanation, the same reference numerals will be used for identical components, and explanations of components that have already been described will be omitted as appropriate.

[0009] The physical properties in the specification are those obtained at a temperature of 25°C and a pressure of 1 atom. The thickness of each component is the average value over the distance in the lamination direction.

[0010] (First Embodiment) The first embodiment relates to a membrane electrode assembly. FIG. 1 shows a schematic cross-sectional view of the membrane electrode assembly 100 of the embodiment. The membrane electrode assembly 100 includes a first electrode 1 which is an anode electrode, a second electrode 2 which is a cathode electrode, an ion exchange membrane 3, and an intermediate layer 4.

[0011] The membrane electrode assembly 100 of the first embodiment is used, for example, in an electrochemical cell for electrolysis. A specific example of the electrolysis reaction of the membrane electrode assembly 100 is to supply water such as ultrapure water to the anode, decompose water at the anode to generate protons and oxygen, the protons generated by the electrolyte membrane pass through, supply carbon dioxide to the cathode, and have a reaction in which carbon monoxide is generated at the cathode.

[0012] The first electrode 1 is the anode of the membrane electrode assembly 100. The first electrode 1 is an anode that oxidizes water to generate oxygen. The first electrode 1 includes a first base material 1A and a first catalyst layer 1B provided on the first base material 1A. The first electrode 1 is provided adjacent to the ion exchange membrane 3. The first catalyst layer 1B of the first electrode 1 is provided on the side of the ion exchange membrane 3. It is preferable that the first electrode 1 is in direct contact with the ion exchange membrane 3.

[0013] In the first electrode 1, for example, H2O (water) is oxidized to O2 (oxygen), H + (protons) are generated.

[0014] The first base material 1A is a support for the first catalyst layer 1B. The first base material 1A is preferably a conductive member that allows a solution or ions flowing through the first electrode 1 to pass through. The first base material 1A is, for example, a mesh material, a punching material, a porous body of a sintered metal fiber, a porous body of a sintered metal particle, etc. The first base material 1A contains a metal or a carbon material. Examples of the metal used for the first base material 1A include titanium, aluminum, iron, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The first base material 1A may contain a metal element contained in the first catalyst layer 1B. The carbon material is, for example, carbon paper or carbon cloth.

[0015] The first catalyst layer 1B is provided 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 body.

[0016] The first catalyst layer 1B includes, for example, metals such as platinum (Pt), palladium (Pd), 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), lanthanum oxide (La - O), ternary metal oxides such as Ni - Co - O, Ni - Fe - O, La - Co - O, Ni - La - O, Sr - Fe - O, quaternary metal oxides such as Pb - Ru - Ir - O, La - Sr - Co - O, and metal complexes such as Ru complexes and Fe complexes. The material of the first catalyst layer 1B may contain two or more types.

[0017] As the anode solution, for example, water with a pH of 5 or more and 8 or less, preferably 5.5 or more and 7.5 or less, is supplied to the first electrode 1. The electrical resistivity of the anode solution supplied to the first electrode 1 is preferably 0.1 [MΩ·cm] or more and 18.24 [MΩ·cm] or less, and the pH of the anode solution in the first electrode 1 is preferably 1 or more and 7 or less, more preferably 3 or more and 7 or less. The pH of the anode solution in the first electrode 1 is preferably measured at the outlet of the flow path of the anode solution.

[0018] The metal ion concentration (total concentration of metal ions) in the anode solution contained in the first electrode 1 is preferably 0% or more and 10% or less, more preferably 0% or more and 7% or less, and still more preferably 1% or more and 5% or less of the metal ion concentration (total concentration of metal ions) in the electrolyte solution of the intermediate layer 4.

[0019] The carbonate ion concentration (HCO3) in the anode solution contained in the first electrode 1 - and CO3 2- The total concentration of (HCO3) is the carbonate ion concentration (HCO3) in the electrolyte of the intermediate layer 4. - and CO3 2- The total concentration of the substances is preferably 0% or more and 30%, more preferably 1% or more and 20%, and even more preferably 3% or more and 10%.

[0020] The second electrode 2 is the cathode of the membrane electrode assembly 100. The second electrode 2 is a cathode that reduces carbon dioxide to produce carbon compounds. The second electrode 2 has a second substrate 2A and a second catalyst layer 2B provided on the second substrate 2A. The second electrode 2 is provided adjacent to the ion exchange membrane 3. The second catalyst layer 2B of the second electrode 2 is provided on the intermediate layer 4 side. It is preferable that the second electrode 2 is in direct contact with the intermediate layer 4.

[0021] At the second electrode 2, for example, CO2 (carbon dioxide) is reduced to produce CO (carbon monoxide) and O2 (oxygen). In addition to CO, CO2 can also be reduced to produce CH4 (methane), C2H6 (ethane), C2H4 (ethylene), CH3OH (methanol), C2H5OH (ethanol), C2H6O2 (ethylene glycol), etc. At the second electrode 2, the reduction reaction of water can occur simultaneously with the reduction of carbon dioxide to produce H2 (hydrogen).

[0022] A gas containing CO2 is supplied to the second electrode 2. Preferably, 30 vol% to 100 vol% of the gas supplied to the second electrode 2 is CO2. Liquid is supplied to the first electrode 1 and the intermediate layer 4, but gas, not liquid, is supplied to the second electrode 2.

[0023] The second substrate 2A is a support for the second catalyst layer 2B. The second substrate 2A is a so-called gas diffusion layer. The second substrate 2A is preferably a conductive material that allows gas, solution, or ions flowing through the second electrode 2 to pass through. The second substrate 2A is, for example, carbon paper or carbon cloth.

[0024] It is preferable to subject the second substrate 2A to a treatment that imparts appropriate hydrophobicity. Hydrophobicity is the property of having low affinity for water. Examples of hydrophobic materials include fluororesins such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, and perfluoroalkoxy fluororesins. By incorporating such fluororesins into carbon paper or carbon cloth, a second substrate 2A can be obtained that maintains conductivity while imparting appropriate hydrophobicity. Between the carbon paper or carbon cloth and the second catalyst layer 2B, a porous layer in which carbon particles such as carbon black are aggregated may be included in the second substrate 2A. The average primary particle size of the carbon particles is, for example, 10 nm to 300 nm. The carbon particles may also be provided with the above-mentioned fluororesin. The carbon particles are provided between the carbon paper or carbon cloth and the second catalyst layer 2B.

[0025] The second substrate 2A is preferably more hydrophobic than the first electrode 1 and more hydrophobic than the intermediate layer 4. The aqueous solution contained in the intermediate layer 4 is less likely to penetrate to the second substrate 2A side due to the high hydrophobicity of the second substrate 2A.

[0026] The second catalyst layer 2B is provided between the second substrate 2A and the intermediate layer 4. Preferably, the second catalyst layer 2B is in direct contact with the second substrate 2A. Preferably, the second catalyst layer 2B is in direct contact with the intermediate layer 4. Preferably, the second catalyst layer 2B is a porous material.

[0027] The second catalyst layer 2B can be made of 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), as well as alloys and intermetallic compounds containing at least one of these metals, carbon materials such as carbon (C), graphene, CNT (carbon nanotube), fullerene, and Ketjenblack, and metal complexes such as Ru complexes and Re complexes. The above catalyst material is provided on the intermediate layer 4 side of the second substrate 2A.

[0028] The second catalyst layer 2B may contain an ionomer.

[0029] The ion exchange membrane 3 is provided between the first electrode 1 and the intermediate layer 4. Preferably, the ion exchange membrane 3 is in direct contact with the intermediate layer 4. Preferably, the ion exchange membrane 3 is in direct contact with the surface of the intermediate layer 4 facing the first electrode 1.

[0030] The ion exchange membrane 3 is preferably a cation exchange (proton conductive) membrane. The ion exchange membrane 3 is preferably a fluorine-based polymer or an aromatic hydrocarbon polymer having one or more groups selected from the group consisting of sulfonic acid groups, sulfonimide groups, and sulfate groups. The ion exchange membrane 3 is preferably a fluorine-based polymer having sulfonic acid groups. Examples of fluorine-based polymers having sulfonic acid groups include Nafion (trademark, manufactured by DuPont), Flemion (trademark, manufactured by Asahi Kasei Corporation), Celemion (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, CO3 generated on the cathode side... 2- (Carbonate ions) and HCO3 - Since (bicarbonate ions) can easily pass through the ion exchange membrane 3, a cation exchange membrane is preferred for the ion exchange membrane 3.

[0031] The thickness of the ion exchange membrane 3 can be appropriately determined considering the membrane's permeability characteristics and durability. From the viewpoint of strength, solubility, 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].

[0032] The intermediate layer 4 is provided between the ion exchange membrane 3 and the second electrode 2. Preferably, the side of the intermediate layer 4 facing the second electrode 2 is in direct contact with the second catalyst layer 2B of the second electrode 2. Preferably, the side of the intermediate layer 4 opposite to the second electrode 2 is in direct contact with the ion exchange membrane 3.

[0033] The intermediate layer 4 is preferably a porous material. The intermediate layer 4 is preferably an electrically conductive porous material. The intermediate layer 4 is preferably hydrophilic. The intermediate layer 4 is preferably a conductive porous material, and its porous structure is preferably hydrophilic.

[0034] The intermediate layer 4 preferably has cation permeability.

[0035] The intermediate layer 4 preferably contains carbon material and / or metallic material. The intermediate layer 4 preferably contains one or more selected from the group consisting of carbon particles, carbon fibers, metallic fibers, and metallic particles. The intermediate layer 4 preferably consists of one or more selected from the group consisting of carbon particles, carbon fibers, metallic fibers, and metallic particles.

[0036] The porosity of the intermediate layer 4 is preferably 30% to 80%, more preferably 40% to 75%, and even more preferably 50% to 70%.

[0037] The volume resistivity of the intermediate layer 4 is preferably 0.01 [Ω·cm] or more and 100 [Ω·cm] or less, more preferably 0.1 [Ω·cm] or more and 50 [Ω·cm] or less, and even more preferably 0.2 [Ω·cm] or more and 10 [Ω·cm] or less.

[0038] The intermediate layer 4 contains an electrolytic solution containing metal ions. The electrolytic solution containing metal ions is preferably an aqueous solution. The metal ions contained in the electrolytic solution included in the intermediate layer 4 are preferably monovalent metal ions. The metal ions contained in the electrolytic solution included in the intermediate layer 4 are preferably monovalent alkali metal ions. The metal ions contained in the electrolytic solution included in the intermediate layer 4 preferably include one or more selected from the group consisting of potassium ions, sodium ions, lithium ions, platinum ions, manganese ions, and cerium ions, and more preferably include one or more selected from the group consisting of potassium ions, sodium ions, and lithium ions.

[0039] The anion (counter ion of the metal ion) contained in the electrolytic solution of the intermediate layer 4 is HCO3 - (bicarbonate ion) and CO3 2- (carbonate ion), and one or more selected from the group consisting thereof are preferable, and HCO3 - (bicarbonate ion) and / or CO3 2- (carbonate ion) are preferable. Also, phosphate ions, phosphite ions, borate ions, etc. may be included from the viewpoints of improving the conductivity of the electrolytic solution, improving the ion migration performance, pH adjustment, improving the catalytic performance, etc.

[0040] The metal ion concentration contained in the electrolytic solution is preferably 0.01 [mol / L] or more and 1 [mol / L] or less, more preferably 0.03 [mol / L] or more and 0.7 [mol / L] or less, and even more preferably 0.05 [mol / L] or more and 0.5 [mol / L] or less.

[0041] The above-mentioned anion concentration contained in the electrolytic solution is preferably 0.1 [mol / L] or more and 1 [mol / L] or less, more preferably 0.2 [mol / L] or more and 1 [mol / L] or less, and even more preferably 0.3 [mol / L] or more and 0.7 [mol / L] or less.

[0042] The electrolyte of the intermediate layer 4 is preferably an aqueous solution containing one or more selected from the group consisting of KHCO3, NaHCO3, LiHCO3, RbCO3, and CsCO3, more preferably an aqueous solution containing one or more selected from the group consisting of KHCO3, NaHCO3, and LiHCO3, more preferably an aqueous solution containing one selected from the group consisting of KHCO3, NaHCO3, and LiHCO3, and more preferably an aqueous solution containing KHCO3.

[0043] The pH of the electrolyte contained in the intermediate layer 4 is preferably 3 to 9, more preferably 4 to 8.5, and even more preferably 5 to 8.

[0044] The difference between the pH of the electrolyte in the intermediate layer 4 and the pH of the water 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.

[0045] Although the electrolyte is supplied to the intermediate layer 4, the ion exchange membrane 3 uses a cation exchange membrane, so the anions contained in the electrolyte have difficulty moving to the first electrode 1 through the cation exchange membrane.

[0046] 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.

[0047] The thickness of the intermediate layer 4 is preferably 1 to 3 times the thickness of the ion exchange membrane 3, more preferably 1 to 2.5 times, and even more preferably 1 to 2 times.

[0048] When CO2 supplied to the cathode and metal ions contained in the electrolyte supplied to the membrane electrode assembly 100 pass through the ion exchange membrane 3 and reach the cathode, the metal ions and CO2 (ions) react, and carbonates are easily formed. In the membrane electrode assembly 100 of this embodiment, the movement of metal ions to the cathode is suppressed, so the formation of carbonates is effectively suppressed. Even if carbonates are formed on the cathode side, they can be washed away with water.

[0049] Furthermore, by using a cation exchange membrane for the ion exchange membrane 3, the CO2 supplied to the cathode does not easily pass through the ion exchange membrane 3 even if it is ionized, thus the membrane electrode assembly 100 of this embodiment has the advantage of having less loss of CO2 supplied as raw material.

[0050] (Second Embodiment) The second embodiment relates to an electrochemical cell. Figure 2 shows a cross-sectional view of the electrochemical cell 200 of the second embodiment. In the electrochemical cell 200 of the second embodiment, it is preferable that the membrane electrode assembly 100 of the first embodiment is used.

[0051] As shown in Figure 2, 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 sealing materials such as gaskets for sealing the electrodes and current collectors.

[0052] The first electrode 1, second electrode 2, ion exchange membrane 3, and intermediate layer 4 of the second embodiment are the first electrode 1, second electrode 2, ion exchange membrane 3, and 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.

[0053] The electrolyte supply channel 5 is located on one side of the intermediate layer 4 where neither the second electrode 2 nor the ion exchange membrane 3 is provided. The electrolyte supply channel 5 is, for example, a pipe for supplying electrolyte to the intermediate layer 4. The electrolyte contained in the intermediate layer 4 is supplied to the intermediate layer 4 from the electrolyte supply channel 5. The electrolyte is pumped by a liquid transfer pump (not shown) and supplied to the intermediate layer 4 via the electrolyte supply channel 5.

[0054] When the electrolyte supply channel 5 is in contact with the ion exchange membrane 3, it is preferable that the electrolyte supply channel 5 is made of a carbon material and / or a metallic material. It is preferable that the electrolyte supply channel 5 is made of a solid material rather than a porous material.

[0055] The electrolyte discharge channel 6 is located on the side of the intermediate layer 4 where neither the second electrode 2, the ion exchange membrane 3, nor the electrolyte supply channel 5 are provided. The electrolyte contained in the intermediate layer 4 is discharged through the electrolyte discharge channel 6. The electrolyte discharge channel 6 is, for example, a pipe for discharging the electrolyte from the intermediate layer 4.

[0056] The first separator 7 is provided on the first substrate 1A side of the first electrode 1. The first separator 7 is provided with a channel for supplying liquid water, which is the anode solution, to the first electrode 1.

[0057] The second separator 8 is provided on the second substrate 2A side of the second electrode 2. The second separator 8 is provided with a flow path for supplying a gas containing CO2 to the second electrode 2.

[0058] Next, the operation of the electrochemical cell 200 will be described. A power supply 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 aqueous solution), preferably pure water, is supplied to the first separator 7, and water is supplied to the first electrode 1. The water supplied to the first electrode 1 reacts in the first catalyst layer 1B, and H2O is reduced. The water is discharged from the outlet of the first separator 7.

[0059] CO2 gas is supplied to the second separator 8, and CO2 is supplied to the second electrode 2. The CO2 supplied to the second electrode 2 reacts there, reducing the CO2 and producing CO and other products. The products such as CO are recovered from the outlet of the second separator 8.

[0060] The intermediate layer 4 is a channel through which the electrolyte is supplied. The amount of electrolyte supplied to the intermediate layer 4 may be less than the amount of pure water supplied to the first electrode 1. The amount of electrolyte supplied to the intermediate layer 4 is preferably 0.05 to 0.9 times the amount of pure water supplied to the first electrode 1, more preferably 0.1 to 0.2 times, and even more preferably 0.3 to 0.8 times.

[0061] If the ion exchange membrane 3 is a cation exchange membrane, carbon dioxide will have difficulty passing through the ion exchange membrane 3 even after being ionized. Therefore, the carbon dioxide supplied to the second electrode 2 will have difficulty moving towards the first electrode 1, and the loss of carbon dioxide supplied to the second electrode 2 can be reduced.

[0062] If, for example, an aqueous KHCO3 solution is used as the electrolyte in the electrochemical cell 200, and the second substrate 2A of the second electrode 2 is water-repellent, potassium ions will have difficulty moving to the second electrode 2 and will not react easily with the carbon dioxide supplied to the second electrode 2. The electrochemical cell 200 employs a configuration that makes it difficult for potassium ions to react with carbon dioxide even when ions such as potassium ions are supplied, thus suppressing the formation of reaction products (e.g., KHCO3) between potassium ions and carbon dioxide on the second electrode 2 side. Even if compounds such as KHCO3 are formed on the second electrode 2, the generated KHCO3 can be removed by supplying water to the second separator 8.

[0063] (Third embodiment) The third embodiment relates to a stack. Figure 3 is a schematic cross-sectional view showing a stack 300 of the third embodiment. The stack 300 of the third embodiment shown in Figure 3 consists of multiple membrane electrode assemblies 100 or electrochemical cells 200 connected in series. Clamping plates 9 and 10 are attached to both ends of the membrane electrode assemblies 100 or electrochemical cells 200.

[0064] Since the amount of CO and other substances produced in an electrochemical cell 200 consisting of a single membrane electrode assembly 100 is small, a stack 300 can be constructed by connecting multiple membrane electrode assemblies 100 or multiple electrochemical cells 200 in series, thereby obtaining a large amount of CO and other substances.

[0065] (Fourth Embodiment) The fourth embodiment relates to an electrolytic apparatus. Figure 4 shows a conceptual diagram of the electrolytic apparatus of the fourth embodiment. The electrolytic apparatus 400 uses an electrochemical cell 200 or a stack 300. The electrolytic apparatus 400 in Figure 4 is for CO2 electrolysis, but it can also be used for other electrolysis. The electrolytic apparatus 400 illustrates a part of the configuration of an actual electrolytic apparatus. The electrolytic apparatus 400 is controlled, for example, by a control device (not shown). The arrows in the figure indicate the direction of fluid flow. The fluid flow may be in the opposite direction to that shown.

[0066] A power supply 11 is attached to the electrochemical cell 200, and a voltage is applied between the first electrode 1 and the second electrode 2 (anode and cathode). CO2 gas is supplied from the CO2 gas supply means 12 to the second separator 8 of the second electrode (cathode) 2, and the CO2 gas is used for the reaction at the second electrode 2. The product at the second electrode 2 (e.g., CO gas), which contains some unreacted CO2 gas, is recovered in the product recovery unit 13. It is preferable to separate the CO2 gas and the product in the product recovery unit 13.

[0067] Pure water is pumped from the pure water tank 14 to the first separator 7 on the first electrode 1 side by the pump 17 and used for the reaction at the first electrode (anode) 1. A valve 16 is located between the pump 17 and the first separator 7. The water discharged from the first separator 7 after passing through the first electrode 1 is filtered by a filter 15 such as an ion filter and stored again in the pure water tank 14. The water discharged from the first separator 7 is measured by a conductivity meter 18 and an ion concentration meter 19. The conductivity and ion concentration, which change depending on the contamination of the water discharged from the first separator 7, are measured by the conductivity meter 18 and the ion concentration meter 19. The water filtered by the filter 15 may also be measured after filtration to ensure that the conductivity and ion concentration are below the set values.

[0068] Electrolyte is supplied from the electrolyte tank 20 to the electrolyte supply channel 5 connected to the intermediate layer 4 by a pump 21. A valve 22 is located between the pump 21 and the electrolyte supply channel 5. The electrolyte that has passed through the intermediate layer 4 is discharged from the electrolyte discharge channel 6. The ion concentration of the discharged electrolyte can be measured with an ion concentration meter 23. The electrolyte discharged from the intermediate layer 4 is returned to the electrolyte tank 20 and reused. Additional electrolyte can be supplied from the electrolyte replenishment tank 24. Electrolyte is pumped from the electrolyte replenishment tank 24 by a pump 25, passes through a valve 26, and can merge with the electrolyte flow path.

[0069] (Fifth embodiment) The fifth embodiment relates to an electrolytic system. Figure 5 shows a conceptual diagram of the electrolytic device 500 used in the electrolytic system of the fifth embodiment. The electrolytic device 500 is a modified version of the electrolytic device 400. The explanation of the parts common to the electrolytic device 400 of the fourth embodiment and the electrolytic device 500 of the fifth embodiment will be omitted.

[0070] The electrolytic device 500 further includes an element for performing a refresh operation of the second electrode 2, which is the cathode. The electrolytic device 500 has a valve 27, a rinse agent supply means 28, and a rinse agent discharge means 29. The valve 27 is, for example, one or more multi-position valves. As the multi-position valve, a 2-position 8-port valve or the like can be used. The valve 27 controls the flow of CO2 gas and rinse agent during electrolysis operation and refresh operation. The rinse agent is liquid and / or gaseous water, and pure water is preferred.

[0071] The refresh operation, as shown in the flow diagram in Figure 6, involves supplying CO2 gas to the second electrode 2 in the first phase (specifically, flowing CO2 gas through the flow path of the second separator 8), and then, while the supply of CO2 gas to the second electrode 2 in the first phase is maintained, or when the supply of CO2 gas that was supplied in the first phase to the second electrode 2 is stopped, a rinsing agent is flowed to the second electrode 2 in the second phase to clean it (specifically, the rinsing agent is flowed through the flow path of the second separator 8). The direction in which the rinsing liquid is flowed is either opposite to the direction in which the CO2 gas is supplied to the second electrode 2 in the first phase, or in the direction in which the CO2 gas is supplied to the second electrode 2 in the first phase. In the second phase, if the rinsing agent is flowed in the opposite direction to the direction in which CO2 gas was supplied to the second electrode 2 in the first phase, then in the second phase, the supply of CO2 gas to the second electrode 2 is stopped, or CO2 gas is supplied to the second electrode 2 in the opposite direction to the direction in which it was supplied in the first phase.

[0072] Since water is supplied to the first electrode 1 during electrolysis, there is no need to perform a refresh operation on the first electrode 1.

[0073] When no refresh operation is performed, the CO2 gas supplied from the CO2 gas supply means 12 flows through the valve 27, through the second electrode 2, and then back through the valve 27 to the product recovery unit 13 (for example, the ACDB path). The rinse agent is either not supplied from the rinse agent supply means 28, or the valve 27 loops the rinse agent supply means 28 back to the rinse agent discharge means 29 (for example, the EF path through which the rinse agent circulates).

[0074] When performing a refresh operation, the rinse agent supplied from the rinse agent supply means 28 flows through the valve 27, through the second electrode 2, and again through the valve 27 to the rinse agent discharge means 29, and the rinse agent used in the refresh operation is discharged from the rinse agent discharge means 29 (for example, the EGHF path). The rinse agent during the refresh operation may flow in the opposite direction to the direction in which CO2 gas flows during the electrolytic operation (for example, the EGHF path) (for example, the EHGF path).

[0075] It is preferable that the rinse agent flows in the opposite direction to the CO2 gas flow, as this reduces the amount of rinse agent that needs to be introduced. By flowing the rinse agent in the opposite direction to the CO2 gas in this way, the area with the most salt deposition in the upstream part of the flow path of the second electrode 2 can be efficiently dissolved and discharged. On the other hand, when considering salt dissolution, if the rinse agent flows from the upstream to the downstream part in the same direction as the CO2 gas, the salt will dissolve in the upstream part, and a small amount of salt will be dissolved in a liquid with a high salt concentration. When the rinse agent flows in the opposite direction to the CO2 gas, flowing the rinse agent from the downstream side of the flow path allows the relatively large amount of salt in the upstream part to be dissolved in a liquid with a low salt concentration, thus efficiently dissolving and discharging the salt. For this reason, a refreshing effect can be obtained even with a small amount of rinse agent, and it is also preferable from the viewpoint that the output can be maintained by suppressing the amount of moisture in the second substrate 2A and the second catalyst layer 2B.

[0076] Figure 5 shows a configuration where CO2 gas pathways C and D and rinsing agent pathways G and H are separated, but CO2 gas and rinsing agent may also be routed through a common pathway.

[0077] During a refresh operation, it is preferable to either stop the flow of CO2 gas, loop the CO2 gas between the CO2 gas supply means 12 and the valve 27, or control the valve 27 so that the CO2 gas flows in the opposite direction to that of a non-refresh operation (for example, through the ADCB path). By controlling the valve 27 so that the CO2 gas flows in the opposite direction to that of a non-refresh operation, it is possible to perform a refresh operation while maintaining the reaction of the electrolytic operation, and the decrease in the electrolytic reaction due to the refresh operation can be suppressed. When stopping the flow of CO2 gas during a refresh operation, it is preferable to stop the application of voltage by the power supply 11.

[0078] During non-refresh operations, it is preferable to stop the flow of the rinse fluid or to create a loop between the rinse agent supply means 28 and the valve 27.

[0079] During the refresh operation, the supply of the anode solution and / or electrolyte may be stopped as needed.

[0080] Furthermore, the direction in which the CO2 gas flows may be reversed after each refresh operation. Specifically, during the first electrolytic operation (non-refresh operation), CO2 is flowed through the ACDB pathway; during the second electrolytic operation and refresh operation, CO2 is flowed through the ADCB pathway and the rinse solution is flowed through the EHGF pathway; during the third electrolytic operation (non-refresh operation), CO2 is flowed through the ADCB pathway; during the fourth electrolytic operation and refresh operation, CO2 is flowed through the ACDB pathway and the rinse agent is flowed through the EGHF pathway; and during the fifth electrolytic operation (non-refresh operation), CO2 is flowed through the ACDB pathway. By reversing the direction in which the CO2 gas flows during the refresh operation and flowing the rinse agent in the reversed direction, salt precipitation can be prevented from becoming concentrated in one place, which is preferable.

[0081] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples.

[0082] (Example 1) An electrochemical cell 200, whose configuration is shown in Figure 2, was fabricated. For the first electrode (anode) 1, an electrode coated with IrO2 nanoparticles on a Ti mesh was used. For the second electrode (cathode) 2, carbon particles supported with gold nanoparticles were coated on carbon paper spray-coated with PTFE were used. Nafion, a cation exchange membrane, was used as the ion exchange membrane 3, and hydrophilic treated PTFE with a thickness of 100 [μm] was used as the intermediate layer 4. 0.1 [mol / L] KHCO3 was supplied to the intermediate layer 4 at a flow rate of 4 [mL / min]. Pure water was supplied to the first electrode 1, and CO2 gas was supplied to the second electrode 2. A power supply 11 was connected between the first electrode 1 and the second electrode 2, and electrolysis was performed, and the amount of carbonate precipitated on the second electrode 2 side was evaluated.

[0083] (Comparative Example 1) Unlike Example 1, the intermediate layer 4 was absent, and an anion exchange membrane was used for the ion exchange membrane 3 to fabricate the electrochemical cell. 0.1 [mol / L] of KHCO3 was supplied to the first electrode 1, and electrolysis was performed in the same manner as in Example 1. The amount of carbonate precipitated on the second electrode 2 side was then evaluated.

[0084] In both Example 1 and Comparative Example 1, it was confirmed that CO was generated from CO2. The amount of carbonate precipitated was less in Example 1 compared to Comparative Example 1. Due to the reduced carbonate precipitate, the electrochemical cell 200 of Example 1 is useful from the viewpoint of continuous operation time, etc. Furthermore, in the electrochemical cell of Example 1, the pressure loss of the CO2 gas at the second electrode 2 increased after operation for a predetermined time, and the Faraday efficiency decreased to below 50%, but the Faraday efficiency could be restored by performing a refresh operation.

[0085] The following is a technical proposal for an embodiment. Technical proposal 1 First electrode and, The second electrode and, An ion exchange membrane is provided between the first electrode and the second electrode, The ion exchange membrane and the second electrode are provided with an intermediate layer, The aforementioned intermediate layer is a porous, electrically conductive film electrode assembly. Technical proposal 2 The first electrode is an anode that converts water into oxygen to produce oxygen. The aforementioned second electrode is a cathode that reduces carbon dioxide to produce carbon compounds. The aforementioned intermediate layer is a membrane electrode assembly according to Technical Proposal 1, through which an electrolyte is supplied. Technical proposal 3 The earlier second electrode is hydrophobic, The membrane electrode assembly according to technical proposal 1 or 2, wherein the intermediate layer is hydrophilic. Technical proposal 4 The ion exchange membrane is a cation exchange membrane, as described in any one of the three technical proposals 1 to 3. Technical proposal 5 The aforementioned intermediate layer is a film electrode assembly according to any one of Technical Proposals 1 to 4, comprising a carbon material and / or a metallic material. Technical proposal 6 The membrane electrode assembly according to any one of the technical proposals 1 to 5, wherein the intermediate layer is in direct contact with the ion exchange membrane. Technical proposal 7 The second electrode comprises a substrate and a catalyst layer provided on the substrate. The aforementioned intermediate layer is in direct contact with the catalyst layer, as described in any one of the technical proposals 1 to 6. Technical proposal 8 The film electrode assembly according to any one of Technical Proposals 1 to 7, wherein the volume resistivity of the intermediate layer is 0.01 [Ω·cm] or more and 1 [Ω·cm] or less. Technical proposal 9 The thickness of the intermediate layer is 10 [μm] or more and 1000 [μm] or less. The membrane electrode assembly according to any one of the technical proposals 1 to 8, wherein the thickness of the intermediate layer is 1 to 3 times the thickness of the ion exchange membrane. Technical proposal 10 The water in the first electrode is pure water. The membrane electrode assembly according to Technical Proposal 2, wherein the electrical resistivity of the pure water is 0.1 [MΩ·cm] or more and 18.24 [MΩ·cm] or less. Technical proposal 11 The water in the first electrode is pure water. The membrane electrode assembly according to Technical Proposal 2 or 10, wherein the pH of the pure water is 5 or more and 8 or less. Technical proposal 12 The electrolyte is a membrane electrode assembly according to Technical Proposal 2, 10, or 11, containing metal ions. Technical proposal 13 The membrane electrode assembly according to Technical Proposal 2, 10, 11, or 12, wherein the pH of the electrolyte is 1 or more and 7 or less. The membrane electrode assembly described above. Technical proposal 14 The electrolyte is HCO3 - and / or CO3 2- A membrane electrode assembly as described in Technical Proposal 2, 10, 11, 12, or 13, including the above. Technical proposal 15 The aforementioned electrolyte comprises one or more selected from the group consisting of potassium ions, sodium ions, and lithium ions, as described in Technical Proposal 2, 10, 11, 12, 13, or 14. Technical proposal 16 An electrochemical cell having a membrane electrode assembly as described in any one of Technical Proposals 1 to 15. Technical proposal 17 The intermediate layer is provided with an electrolyte supply channel and an electrolyte discharge channel. Pure water is supplied to the first electrode. Carbon dioxide gas is supplied to the second electrode. An electrolyte is supplied to the intermediate layer. The electrochemical cell according to Technical Proposal 16, wherein the amount of electrolyte supplied to the intermediate layer is 0.05 times or more and 0.9 times or less the amount of pure water supplied to the first electrode. Technical proposal 18 A stack having an electrochemical cell as described in Technical Proposal 16 or 17. Technical proposal 19 Having the electrochemical cell described in claim 16, In the first phase, CO2 gas is supplied to the second electrode. When the supply of CO2 gas to the second electrode in the first phase is maintained, or when the supply of CO2 gas that was supplied in the first phase to the second electrode is stopped, a rinse agent is flowed through the second electrode in the second phase to clean the second electrode. The rinse agent is an electrolytic system of liquid and / or gaseous pure water. Technical proposal 20 The electrolysis system according to technical proposal 19, wherein in the second phase, the rinsing agent is flowed in the opposite direction to the direction in which CO2 gas is supplied to the second electrode in the first phase.

[0086] In the specification, some elements are represented only by their element symbols.

[0087] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments described above 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, as well as in the claims and their equivalents. [Explanation of symbols]

[0088] 1 :1st electrode 1A: 1st base material 1B: 1st catalyst layer 2 :Second electrode 2A: 2nd base material 2B: 2nd catalyst layer 3: Ion exchange membrane 4: Middle class 5: Electrolyte supply path 6: Electrolyte drain path 7: First separator 8: Second separator 9: Clamping plate 10: Clamping plate 11: Power supply 12: CO2 gas supply means 13: Product Recovery Section 14: Pure water tank 15: Filter 16: Valve 17: Pump 18: Conductivity meter 19: Ion concentration meter 20: Electrolyte tank 21: Pump 22: Valve 23: Ion concentration meter 24: Electrolyte replenishment tank 25: Pump 26: Valve 100: Membrane electrode assembly 200: Electrochemical cell 300: Stack 400: Electrolysis unit

Claims

1. First electrode and, The second electrode and An ion exchange membrane is provided between the first electrode and the second electrode, The ion exchange membrane and the second electrode are provided with an intermediate layer, The aforementioned intermediate layer is a porous, electrically conductive film electrode assembly.

2. The first electrode is an anode that converts water into oxygen to produce oxygen. The aforementioned second electrode is a cathode that reduces carbon dioxide to produce carbon compounds. The membrane electrode assembly according to claim 1, wherein the intermediate layer is a channel through which an electrolyte is supplied.

3. The aforementioned second electrode is hydrophobic, The membrane electrode assembly according to claim 1, wherein 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 film electrode assembly according to claim 1, wherein the intermediate layer comprises a carbon material and / or a metallic material.

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

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

8. The film electrode assembly according to claim 1, wherein the volume resistivity of the intermediate layer is 0.01 [Ω·cm] or more and 1 [Ω·cm] or less.

9. The thickness of the intermediate layer is 10 [μm] or more and 1000 [μm] or less. The membrane electrode assembly according to claim 1, wherein the thickness of the intermediate layer is one to three times the thickness of the ion exchange membrane.

10. The water in the first electrode is pure water. The membrane electrode assembly according to claim 2, wherein the electrical resistivity of the pure water is 0.1 [MΩ・cm] or more and 18.24 [MΩ・cm] or less.

11. The water in the first electrode is pure water. The membrane electrode assembly according to claim 2, wherein the pH of the pure water is 5 or more and 8 or less.

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 pH of the electrolyte is 1 or more and 7 or less.

14. The aforementioned electrolyte is HCO ３ － and / or CO ３ ２－ The membrane electrode assembly according to claim 2, comprising:

15. The membrane electrode assembly according to claim 2, wherein the electrolyte comprises one or more selected from the group consisting of 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 intermediate layer is provided with an electrolyte supply channel and an electrolyte discharge channel. Pure water is supplied to the first electrode. Carbon dioxide gas is supplied to the second electrode. An electrolyte is supplied to the intermediate layer. The electrochemical cell according to claim 16, wherein the amount of the electrolyte supplied to the intermediate layer is 0.05 times or more and 0.9 times or less the amount of the pure water supplied to the first electrode.

18. A stack having the electrochemical cell according to claim 16.

19. Having the electrochemical cell described in claim 16, CO ２ The gas is supplied to the second electrode, CO in the first phase ２ When the supply of gas to the second electrode is maintained, or when the CO supplied in the first period is ２ When the supply of gas to the second electrode is stopped, in the second phase, a rinsing agent is flowed through the second electrode to clean it. The rinse agent is an electrolytic system in which liquid and / or gaseous pure water.

20. In the second period, CO ２ The electrolytic system according to claim 19, wherein the rinsing agent is flowed in the opposite direction to the direction in which the gas is supplied to the second electrode.

Images