Membrane electrode assembly, electrolytic cell, and electrolytic device

Abstract

The present invention provides a membrane electrode assembly, an electrolytic cell, and an electrolytic device that enable the suppression of membrane degradation. [Solution] The membrane electrode assembly comprises a cathode positioned in contact with the material to be reduced supplied as a raw material gas for reducing the material to be reduced, an anode positioned in contact with the electrolytic solution containing the oxide for oxidizing the oxide, and a diaphragm separating the cathode and the anode. The anode has a porous body having a first surface on the diaphragm side and a second surface opposite the first surface, and an oxidation catalyst in contact with the porous body. The average surface roughness of the first surface is 0.1 μm or more and 17.0 μm or less.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a membrane electrode assembly, an electrolytic cell, and an electrolytic device. [Background technology]

[0002] In recent years, from the perspectives of both energy and environmental issues, there has been a growing desire not only to convert renewable energy sources such as solar power into electrical energy for use, but also to convert it into a form that can be stored and transported. In response to this demand, research and development of power-to-chemical technologies that use sunlight to produce chemical substances, similar to photosynthesis in plants, is progressing. It is expected that such technologies will enable the storage of renewable energy as storable fuels and create value by generating chemical substances that can be used as industrial raw materials.

[0003] As a device that generates chemical substances using renewable energy such as sunlight, a carbon dioxide electrolysis device that reduces carbon dioxide (CO2) generated from power plants and waste incinerators is known. A CO2 electrolysis device consists of a cathode (reducing electrode) that reduces CO2 to produce carbon compounds such as carbon monoxide (CO), and a cathode (reducing electrode) that uses water (H2O) or hydroxide ions (OH). - The device comprises an anode (oxidizing electrode) that oxidizes CO2. In such a carbon dioxide electrolysis apparatus, it is effective to use a cell structure (electrolytic cell) in which the cathode and anode are stacked with a diaphragm such as an ion exchange membrane or a porous membrane in between, and by supplying CO2 directly to the cathode catalyst layer of the electrolytic cell, the reduction reaction of CO2 can be rapidly carried out. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 7524118 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The problem to be solved by the present invention is to provide a membrane electrode assembly, an electrolytic cell, and an electrolytic device that enable suppression of deterioration of a diaphragm.

Means for Solving the Problem

[0006] The membrane electrode assembly of an embodiment is disposed so as to contact a substance to be reduced supplied as a raw material gas, and includes a cathode for reducing the substance to be reduced, an anode disposed so as to contact an electrolytic solution containing an oxidized substance and for oxidizing the oxidized substance, and a diaphragm for separating the cathode and the anode. The anode has a porous body having a first surface on the diaphragm side and a second surface on the opposite side of the first surface, and an oxidation catalyst contacting the porous body. The average surface roughness of the first surface is 0.1 μm or more and 17.0 μm or less.

Brief Description of the Drawings

[0007] [Figure 1] It is a diagram showing an example of an electrolytic device of an embodiment. [Figure 2] It is a diagram showing another example of the electrolytic device of the embodiment.

Modes for Carrying Out the Invention

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

[0009] In the following, an example in which the electrolytic cell and electrolysis apparatus of the embodiment are applied to an electrolytic cell and electrolysis apparatus for carbon dioxide will be mainly described. However, the electrolytic cell and electrolysis apparatus of the embodiment are not limited thereto. The electrolytic cell and electrolysis apparatus of the embodiment may be applied to, for example, an electrolytic cell and electrolysis apparatus that electrolyze nitrogen (N2) to generate ammonia (NH3). Further, it can also be applied to a water electrolysis apparatus, a fuel cell, and the like.

[0010] FIG. 1 is a cross-sectional view showing a carbon dioxide (CO2) electrolysis apparatus 10 of an embodiment. The CO2 electrolysis apparatus 10 shown in FIG. 1 includes an electrolytic cell 20. The electrolytic cell 20 includes a cathode portion 30, an anode portion 40, and a diaphragm 50 disposed so as to separate these.

[0011] The cathode portion 30 includes a cathode (reduction electrode) 31 having a metal catalyst layer, a cathode flow path 32, and a cathode current collector plate 33. The cathode flow path 32 is a flow path for supplying a reducible substance (reduction target) to the cathode 31, and is constituted by pits (grooves) provided in a cathode flow path plate 34. Examples of the reducible substance include CO2 gas. The cathode 31 is disposed so as to contact the CO2 flowing through the cathode flow path 32. The anode portion 40 includes an anode (oxidation electrode) 41, an anode flow path 42, and an anode current collector plate 43. The anode flow path 42 is an electrolytic solution flow path for supplying an electrolytic solution as an anode solution to the anode 41, and is constituted by pits (grooves) provided in an anode flow path plate 44. The electrolytic solution contains water (H2O) or hydroxide ions (OH - ) as an oxidizable substance (oxidation target). The anode 41 is disposed so as to contact the anode solution flowing through the anode flow path 42.

[0012] The CO2 electrolysis apparatus 10 comprises a gas supply unit 60 that supplies CO2, the material to be reduced, as a raw material gas to the electrolytic cell 20, and an electrolytic solution supply unit (supply system) 70 that supplies an anode solution to the electrolytic cell 20. The gas supply unit 60 includes a CO2 storage unit 61, such as a CO2 gas cylinder, and a CO2 adjustment unit 62 that adjusts the flow rate of CO2 gas, and supplies CO2 gas from the CO2 storage unit 61 to the cathode channel 32 via a gas pipe 63. The gas supply unit 60 may also include a humidification unit for humidifying the CO2 gas. The CO2 gas supplied to the cathode channel 32 is not limited to a single gas of CO2, but may be a gas with CO2 as its main component (for example, a gas containing 90% or more by volume of CO2). In the cathode 31 of the electrolytic cell 20 shown in Figure 1, ions are supplied via a diaphragm 50, and CO2 gas is supplied from the cathode channel 32. The CO2 reduction products are mainly discharged from the cathode channel 32.

[0013] The electrolytic solution supply unit 70 comprises an anode solution tank 71 and a pump 72, and supplies the anode solution from the anode solution tank 71 to the anode channel 42 via the pump 72 and electrolytic solution piping 73. The electrolytic solution supply unit 70 may also have an anode solution concentration measuring unit. The anode solution circulates through the anode channel 42 and the electrolytic solution piping 73. The cathode current collector plate 33 and the anode current collector plate 43 in the CO2 electrolytic device 10 are connected to a power supply 80. It is preferable to use a material with low chemical reactivity and high conductivity for the anode channel plate 44 constituting the anode channel 42 and the cathode channel plate 34 constituting the cathode channel 32. Examples of such materials include metallic materials such as Ti and SUS, and carbon.

[0014] The electrolytic cell 20 is generally sandwiched between a pair of support plates (not shown) and further secured with bolts or the like. The power supply 80 connected to the cathode current collector plate 33 and the anode current collector plate 43 is not limited to ordinary commercial power or batteries, but may also be a power supply that converts renewable energy into electrical energy. Examples of such power supplies include power supplies that convert kinetic or potential energy such as wind, hydro, geothermal, and tidal power into electrical energy; power supplies such as solar cells that convert light energy into electrical energy; power supplies such as fuel cells and storage batteries that convert chemical energy into electrical energy; and power supplies such as devices that convert vibrational energy such as sound into electrical energy. Using renewable energy is environmentally friendly, as it also allows for the efficient use of carbon dioxide.

[0015] The cathode 31 is an electrode (reduction electrode) that causes a reduction reaction of carbon dioxide (CO2) as the gas to be reduced, producing carbon compounds such as carbon monoxide (CO), methane (CH4), ethane (C2H6), ethylene (C2H4), methanol (CH3OH), ethanol (C2H5OH), and ethylene glycol (C2H6O2). In the cathode 31, a side reaction may occur simultaneously with the reduction reaction of carbon dioxide (CO2), generating hydrogen (H2) through the reduction reaction of water (H2O). The cathode 31 has a first surface that is in contact with the diaphragm 50 and a second surface that is in contact with the cathode channel 32. The first surface of the cathode 31 is in contact with one surface of the diaphragm 50.

[0016] The cathode channel 32, which is a channel for CO2-containing gas (hereinafter also referred to as CO2 gas), is composed of pits (grooves / recesses) provided in the cathode channel plate 34. The cathode channel plate 34 is provided with a gas inlet and outlet, which are not shown in the figure. CO2 gas is introduced from the gas supply unit 60 through the gas inlet or gas outlet. Furthermore, reaction product gases containing CO, H2, etc. are discharged through the gas inlet or gas outlet, and the discharged gas is sent to a valuable product manufacturing unit (not shown) or recovered in a product recovery unit. The cathode channel plate 34 and the cathode channel 32 provided thereon are arranged to be in contact with a second surface opposite to the first surface that is in contact with the diaphragm 50 of the cathode 31.

[0017] The cathode 31 has a porous structure that allows ions and water to move between the diaphragm 50 and the cathode channel 32, such as a mesh material, a punching material, a porous body, or a metal fiber sintered body. Preferably, the cathode 31 comprises a porous substrate containing carbon fibers, and a gas diffusion layer and a catalyst layer arranged sequentially on the porous substrate. The catalyst material constituting the catalyst layer of the cathode 31 may have nanoparticles, nanostructures, nanowires, etc., to enhance the reduction reaction. A nanostructure is a structure having nanoscale irregularities on the surface of a catalyst material, etc. The porous substrate is arranged on the cathode channel 32 side, and the cathode catalyst layer is arranged on the diaphragm 50 side. The cathode catalyst layer may be embedded in the gas diffusion layer. Thus, the cathode 31 has a porous structure. At least one of the porous substrate, the gas diffusion layer, and the catalyst layer may have water repellency by forming a surface covered with a fluororesin such as Teflon (registered trademark) as a water repellent. This is because the movement of humidifying water or electrolyte can cause water to accumulate in the porous material (flooding), which may degrade the performance of the electrolytic cell 20.

[0018] The cathode catalyst layer preferably has catalyst nanoparticles or catalyst nanostructures. The porous substrate is preferably made of, for example, carbon paper or carbon cloth and is treated with a water-repellent coating. Ions are supplied to the cathode catalyst layer from the anode 41 via a diaphragm 50. CO2 gas is supplied to the porous substrate from the cathode channel 32, and the products of the CO2 gas reduction reaction are discharged. The CO2 reduction reaction occurs at the three-phase interface of the cathode catalyst layer, and the gaseous products are discharged from the cathode channel 32.

[0019] The cathode catalyst layer of cathode 31 is preferably composed of a catalyst material (cathode catalyst material) capable of reducing CO2 to produce carbon compounds and reducing the overpotential of such reactions. Examples of cathode catalyst materials 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 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. Various shapes such as plate-like, mesh-like, wire-like, particulate, porous, thin-film-like, and island-like can be applied to the cathode catalyst layer.

[0020] Anode 41 undergoes an oxidation reaction of water (H2O) in the anode solution, producing oxygen (O2) and hydrogen ions (H2O). + ) generates hydroxide ions (OH) generated in the cathode section 30. -This electrode causes an oxidation reaction between the diaphragm 50 and the anode channel 42, producing oxygen and water. The anode 41 is positioned between the diaphragm 50 and the anode channel 42, in contact with them. That is, the anode 41 has a first surface facing the diaphragm 50 and a second surface facing the anode channel 42. The first surface of the anode 41 may be in close contact with the diaphragm 50. The anode channel plate 44 is connected to a solution inlet and a solution outlet (neither shown), and the anode solution is introduced and discharged by the pump 72 through these solution inlet and outlet. The anode solution flows through the anode channel 42 in contact with the anode 41. The anode current collector plate 43 is electrically in contact with the surface of the anode channel plate 44 that constitutes the anode channel 42, on the side opposite to the anode 41.

[0021] When an aqueous solution of an electrolyte is used as the anode solution, the anode 41 oxidizes water (H2O) to produce oxygen or hydrogen ions, or hydroxide ions (OH) - Preferably, the catalyst material (anode catalyst material) is mainly composed of a catalyst material (anode catalyst material) that can oxidize ) to produce water and oxygen and reduce the overpotential of such a reaction. Examples of such catalyst materials include metals such as platinum (Pt), palladium (Pd), and nickel (Ni), alloys and 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 and Fe complexes.

[0022] The anode 41 is provided with a porous substrate (porous substrate) as the anode substrate, which has a structure that allows the anode solution and ions to move between the diaphragm 50 and the anode channel 42, for example, a mesh material, a punching material, or a porous sintered body. The porous substrate may be, for example, an aggregate of particles or a sintered body, or an aggregate of fibers or a sintered body. When such a porous substrate is used as the anode substrate, the structure will have large surface irregularities.

[0023] The porous material that serves as the anode substrate has a surface 41a on the diaphragm 50 side and a surface 41b on the anode channel 42 side, which is opposite to surface 41a. The porous material is preferably an aggregate of conductive particles. Here, the particles include not only nearly spherical particles (spherical particles or substantially spherical particles), but also rugby ball-shaped, fibrous, needle-shaped particles, etc., and there are no restrictions on their shape. In this case, not only can the surface roughness of the anode 41 be reduced, but protrusions are less likely to form in the porous material, further reducing the unevenness described later. The conductive particles preferably contain at least one metallic element selected from the group consisting of carbon (C), indium (In), tin (Sn), zinc (Zn), aluminum (Al), copper (Cu), titanium (Ti), nickel (Ni), silver (Ag), tungsten (W), cobalt (Co), and gold (Au).

[0024] The average diameter of the particles or fibers is preferably between 10 nm and 200 μm. It is more preferably between 50 nm and 150 μm, and even more preferably between 100 nm and 100 μm. If the average diameter is too large, the voids inside the anode 41 become large, causing bubbles of generated gases such as oxygen to get stuck and have difficulty escaping, which is undesirable because it increases the electrolytic voltage (cell voltage). If it is too small, it becomes a dense porous body, which is undesirable because it reduces the penetration of the electrolyte and increases the electrolytic voltage.

[0025] The porous material is preferably composed of a conductive material. In addition, it is preferable, but not limited to, a Ti-based material such as Ti or Ti alloys, which have low reactivity. For example, carbon materials such as carbon black, activated carbon, fullerene, carbon nanotubes, graphene, Ketjenblack, and diamond; transparent conductive oxides such as indium tin oxide (ITO), zinc oxide (ZnO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), and antimony-doped tin oxide (ATO); metals such as copper, aluminum, titanium, nickel, silver, tungsten, cobalt, and gold; and alloys containing at least one of these metals are preferred because they have high conductivity. In terms of elements, it is preferable that it is composed of at least one of C, In, Sn, Zn, Al, Cu, Ti, Ni, Ag, W, Co, and Au. Among these, it is more preferable that it is composed of Ti, which has low reactivity and is stable.

[0026] Examples of oxidation catalysts used in porous materials include metals and metal oxides such as ruthenium (Ru), iridium (Ir), platinum (Pt), cobalt (Co), nickel (Ni), iron (Fe), manganese (Mn), lanthanum (La), lithium (Li), indium (In), tantalum (Ta), zirconium (Zr), tin (Sn), and titanium (Ti), as well as binary metal oxides, ternary metal oxides, and quaternary metal oxides. Examples include manganese oxide (Mn-O), iridium oxide (Ir-O), nickel oxide (Ni-O), cobalt oxide (Co-O), iron oxide (Fe-O), tin oxide (Sn-O), indium oxide (In-O), ruthenium oxide (Ru-O), nickel-iron oxide (Ni-Fe-O), nickel-cobalt oxide (Ni-Co-O), lanthanum-cobalt oxide (La-Co-O), nickel-lanthanum oxide (Ni-La-O), strontium-iron oxide (Sr-Fe-O), lead-ruthenium-iridium oxide (Pb-Ru-Ir-O), and lanthanum-strontium-cobalt oxide (La-Sr-Co-O). However, the oxidation catalyst is not limited to these materials and may be formed using metal hydroxides containing metals such as cobalt, nickel, iron, and manganese, or metal complexes such as ruthenium complexes and iron complexes. Furthermore, the oxidation catalyst may be formed by mixing multiple materials. It is preferable that the catalyst contains at least one of the following elements: Ir, Ru, Ni, Fe, Co, Mn, La, Li, In, Sn, and Ti, as this results in a highly active catalyst.

[0027] The porous material constituting the anode 41 and the oxidation catalyst only need to be in contact with at least a portion of each other, and their form is not particularly limited. On the other hand, it is more preferable if the oxidation catalyst is coated over the entire surface of the anode substrate. In this case, a wider surface area of ​​the anode substrate can be used, and the adhesion between the oxidation catalyst and the anode substrate improves, resulting in a highly active anode 41 that can reduce the electrolysis voltage, which is preferable. Furthermore, if the oxidation catalyst is pre-coated and in close contact with the anode substrate, when the diaphragm 50 is a porous membrane, the oxidation catalyst is less likely to peel off from the anode substrate and will not fill the pores of the diaphragm 50, which is also preferable. The oxidation catalyst may also be coated on the surface 41a. The material of the oxidation catalyst preferably has the shape of nanoparticles, nanostructures, nanowires, etc., in order to enhance the oxidation reaction. A nanostructure is a structure that has nanoscale irregularities on the surface of the catalyst material.

[0028] The porosity of the anode 41 is preferably between 10% and 60%. If the porosity is too small, it becomes a dense porous body, which is undesirable because it hinders the penetration of the electrolyte and increases the electrolysis voltage. If the porosity is too large, the conductivity decreases and the electrolysis voltage increases. In that case, the amount of electrolyte moving across the anode 41 from the anode channel 42 increases, causing the cathode 31 to be excessively covered with electrolyte, and the reaction in which hydrogen is secondarily produced (side reaction) becomes dominant over the reduction reaction of the target raw material gas, which is undesirable. The porosity is preferably between 10% and 55%, and more preferably between 10% and 50%. The porosity is specifically determined using X-ray CT and associated software. For example, the volume is calculated from the thickness and area of ​​the anode 41, and the porosity is calculated from the weight and specific gravity of the constituent material of the anode 41. The maximum peak in the pore size distribution of the anode 41 is preferably between 0.1 μm and 100 μm.

[0029] The thickness of the anode 41 is preferably 40 μm or more and 500 μm or less. If the anode 41 is too thin, the mechanical strength of the anode 41 will decrease, which is not preferable. If the anode 41 is too thick, the bubbles of the generated gas such as oxygen will not easily escape, and the electrolysis voltage will increase, which is not preferable. The thickness of the anode 41 is more preferably 40 μm or more and 400 μm or less, and even more preferably 40 μm or more and 300 μm or less. For example, the thickness can be measured specifically by using a micrometer, measuring the thicknesses at the four corners and the central part of the anode 41 to be used, and calculating the average value.

[0030] As the anode solution, an electrolytic solution such as an aqueous solution containing an arbitrary electrolyte can be used. As the aqueous solution containing an electrolyte, for example, an aqueous solution containing phosphate ions (PO4 2- ), borate ions (BO3 3- ), sodium ions (Na + ), potassium ions (K + ), calcium ions (Ca 2+ ), lithium ions (Li + ), cesium ions (Cs + ), magnesium ions (Mg 2+ ), chloride ions (Cl - ), hydrogen carbonate ions (HCO3 - ), carbonate ions (CO3 2- ) etc. can be used. The pH of the anode solution is not particularly limited, but considering the use environment, it is preferably 6 or more and 10 or less. Further, the anode solution is more preferably an alkaline aqueous solution containing HCO3 - , CO3 2- , LiHCO3, NaHCO3, KHCO3 etc.

[0031] The diaphragm 50 is provided between the cathode 31 and the anode 41 and is stacked with the cathode 31 and the anode 41 to form a membrane electrode assembly (MEA). The diaphragm 50 is made of a material that can move ions between the anode 41 and the cathode 31 and separate the anode portion 40 and the cathode portion 30, specifically an ion exchange membrane such as an anion exchange membrane or a cation exchange membrane, or a porous membrane made of an organic polymer material. Examples of ion exchange membranes used in the diaphragm 50 include cation exchange membranes such as Nafion® and Flemion®, and anion exchange membranes such as Neosepta®, Celemion®, Sustenio®, and PiperION®. The organic polymer material constituting the porous membrane is not particularly limited, but examples include fluororesins such as Teflon® and polyvinylidene fluoride, hydrocarbon polymers such as polyethers, polysulfones, polyethylene, polypropylene, and polyethersulfone, and cellulose.

[0032] When the above porous membrane is used as the diaphragm 50, the amount of crossover of the generated gas to the counter electrode is greater compared to an ion exchange membrane. Here, crossover refers to the phenomenon in which substances such as the reduced substance, the oxide, the reduction product, and the oxidation product unnecessarily move across the diaphragm 50 between the anode 40 and the cathode 30, and the resulting reaction between gases.

[0033] Electrolytic devices that supply raw materials and perform electrolysis to produce desired products, such as carbon dioxide or nitrogen electrolytic devices, generate hydrogen as a reaction byproduct on the cathode 31 side. The generated hydrogen reacts with oxygen generated on the anode 41 side to produce reactive oxygen species, primarily hydrogen peroxide. Reactive oxygen species are caused by the oxidation reaction of polymers that make up the porous membrane. As a result, the composition and shape of the diaphragm 50 change, leading to a decrease in the function of the diaphragm 50, and in the worst case, a short circuit between electrodes may occur, potentially damaging the electrolytic cell.

[0034] Hydrogen peroxide is easily generated, for example, by using acidic and neutral electrolytes. When hydrogen peroxide does not self-decompose easily, this becomes a particular problem, for example, in carbon dioxide electrolytic devices and nitrogen electrolytic devices, and when a porous membrane is used for the diaphragm 50.

[0035] As a result of diligent research, the inventors have concluded that the structure of the anode substrate of the anode 41 is a crucial factor that greatly influences the degree of deterioration of the diaphragm 50, which is initiated by the aforementioned hydrogen generation. In this embodiment, the roughness of the surface of the anode substrate that is in contact with the diaphragm 50 is controlled to create a smooth surface, thereby suppressing the deterioration of the diaphragm 50 in contact with it.

[0036] When assembling an electrolytic cell 20 using an anode 41 made of a material with large surface irregularities, such as fibrous Ti, if it is strongly pressed against a diaphragm 50 made of organic material, unevenness occurs at the contact surface between the anode 41 and the diaphragm 50 due to the irregularities on the surface 41a of the anode 41. This unevenness includes, for example, in-plane unevenness between the contacted and non-contacting parts of the anode 41 and the diaphragm 50, thickness-direction unevenness caused by the diaphragm 50 being pressed and deformed in the contacted parts, and unevenness in voltage and current density resulting from these. Such unevenness promotes partial degradation of the diaphragm 50 by reactive oxygen species, leading to a decrease in its function.

[0037] The surface roughness of the anode 41 can be defined by the average surface roughness Ra. In order to suppress the deterioration of the diaphragm 50 caused by the aforementioned unevenness, it is preferable that the average surface roughness Ra of surface 41a is 17.0 μm or less. It is more preferable that the average surface roughness Ra of surface 41a be 6 μm or less, and even more preferable that it be 3 μm or less. In this case, the aforementioned unevenness is suppressed, the deterioration of the diaphragm 50 is suppressed, and the electrolytic cell 20 can withstand long-term operation. Also, if this average surface roughness Ra is too small, it becomes a dense porous body, which is undesirable because the penetration of the electrolyte becomes poor and the electrolytic voltage increases. For this reason, it is preferable that the average surface roughness Ra of surface 41a be 0.1 μm or more, more preferable that it be 0.2 μm or more, and even more preferable that it be 0.3 μm or more. For example, it is preferable that the average surface roughness Ra of surface 41a be 0.1 μm or more and 17.0 μm or less. The average surface roughness Ra is calculated using equipment capable of observing cross-sectional images, such as X-ray CT (Computed Tomography) devices, scanning electron microscopes (SEMs), microscopes, and laser microscopes, as well as image analysis software. For example, a cross-sectional image of anode 41 is obtained using an X-ray CT device (Zeiss, Xradia620Versa), and the surface roughness curve is obtained using ImageJ (open-source image processing software). A portion of this roughness curve is extracted, and the absolute values ​​of the deviations from the average line of the extracted portion to the roughness curve are summed and averaged to obtain Ra. The size of the roughness curve extracted is, for example, a range of 350 μm along the direction perpendicular to the thickness direction of anode 41.

[0038] While the shape and material of the diaphragm 50 are not particularly limited, porous membranes tend to experience greater crossover of the generated gas to the counter electrode compared to ion exchange membranes, leading to faster degradation of the diaphragm 50, which is often caused by hydrogen. Therefore, porous membranes are more effective in suppressing the degradation of the diaphragm 50 by reducing surface roughness.

[0039] Reactive oxygen species such as hydrogen peroxide, which are one of the factors that degrade the diaphragm 50, readily attack ether groups or sulfonyl groups, thus easily degrading the diaphragm 50. Therefore, if the diaphragm 50 contains a polymer compound crosslinked with at least one of the functional groups, an ether group and a sulfonyl group, there is a significant advantage in suppressing the degradation of the diaphragm 50 by reducing the average surface roughness of the anode 41.

[0040] In electrolytic devices that supply raw materials containing the substance to be reduced and perform reduction, such as carbon dioxide electrolytic devices and nitrogen electrolytic devices, the electrolytic voltage tends to become high. In such cases, a large amount of reactive oxygen species, such as hydrogen peroxide, is generated, and the deterioration of the diaphragm 50 progresses easily. Therefore, in these electrolytic devices, it is very effective to suppress the acceleration of the reaction of reactive oxygen species, which are a factor in deterioration, by using an anode 41 with a smooth surface.

[0041] The thickness of the diaphragm 50 is preferably 3 to 1000 times the average surface roughness Ra of the surface 41a. It is more preferably 4 to 900 times, and even more preferably 5 to 800 times. If the thickness is less than 3 times, when the electrolytic cell is assembled, there will be places where the distance between the cathode 31 and the anode 41 is short as the surface 41a of the anode 41 bites into the diaphragm 50. In this case, the crossover of hydrogen generated at the cathode 31 to the anode 41, which causes deterioration of the diaphragm 50, is more likely to occur, which is undesirable. Also, if the thickness is greater than 1000 times, the solution resistance of the electrolytic cell will increase, and the voltage of the electrolytic cell 20 will increase, which is undesirable.

[0042] To suppress the above-mentioned unevenness, as shown in Figure 2, in addition to the configuration shown in Figure 1, it is effective to provide a layer (also called a surface roughness-reducing layer or intermediate layer) 51 on the surface of the diaphragm 50. The layer 51 can reduce the surface roughness of the surface 41a by being provided, for example, on the surface of the diaphragm 50 facing the surface 41a. The thickness of the layer 51 is preferably 1 / 3 or more of the average surface roughness Ra of the surface 41a, and more preferably 1 / 2 or more, so as to reduce the surface roughness of the surface 41a of the anode 41. The thickness of the layer 51 can be confirmed by a cross-sectional SEM image.

[0043] The maximum peak of the pore diameter in layer 51 is preferably between 10 nm and 50 μm. More preferably between 20 nm and 10 μm. If the pore diameter is too large, the electrolyte present in the anode 41 will penetrate into layer 51 more than necessary, crossing over to the cathode 31 through the diaphragm 50 and causing flooding. If the pore diameter is too small, the electrolyte will not penetrate the diaphragm 50 sufficiently, leading to insufficient drying of the diaphragm 50 or, in the case of a porous membrane, insufficient liquid film formation, which can cause an increase in the electrolysis voltage.

[0044] When a porous membrane is used as the diaphragm 50, the average pore diameter of the diaphragm 50 is preferably 10 nm or more and 0.3 μm or less. More preferably, it is preferably 20 nm or more and 0.2 μm or less. If the pore diameter is too small, the balance between the amount of electrolyte supplied from the anode 41 and the amount of water consumed in the electrolyte within the diaphragm 50 will be disrupted, causing the diaphragm 50 to dry out, leading to crossover if it is a porous membrane, or an increase in electrolysis voltage if it is an ion exchange membrane. The relationship between the average pore diameters of the anode 41, the diaphragm 50, and the layer 51 is preferably such that the average pore diameter of the layer 51 is smaller than that of the anode 41, and the average pore diameter of the diaphragm 50 is smaller than that of the layer 51. For example, by making the average pore diameter of the diaphragm 50 the smallest, the supply of electrolyte from the anode 41 to the layer 51 and the diaphragm 50 can be carried out smoothly and without oversupply. The average pore diameter of the anode 41 can be measured, for example, by the mercury intrusion method.

[0045] The thickness of layer 51 is preferably 90 μm or less. If it exceeds 90 μm, durability is maintained, but the electrolytic voltage increases, which degrades the characteristics of the cell. The lower limit of the thickness of layer 51 is not particularly limited, but for example, it is 1 μm or more. The thickness of layer 51 can be confirmed by a cross-sectional SEM image.

[0046] As the main component of layer 51, an inorganic material with high environmental resistance is preferred. Since the electrolyte and gas need to penetrate for the reaction, layer 51 is porous. To form layer 51, the inorganic material can be selected as particulate matter, fibrous aggregates, or a porous inorganic film. Examples of inorganic materials include oxides, nitrides, and carbon, which are stable in the oxidizing and alkaline states that fluctuate during electrolysis and have high resistance to hydrogen peroxide and radicals that may be produced as byproducts. The chemical species may be common oxides such as aluminum oxide, zirconium oxide, and silicon oxide, or they may be cerium oxide, titanium oxide, or manganese oxide.

[0047] The inorganic substance may be a chemical species (also called a quencher or inhibitor) that decomposes, captures (retains), or inactivates the reactive oxygen species generated by the electrolytic device 10, or it may contain the above-mentioned chemical species. The above-mentioned chemical species can suppress the deterioration of the diaphragm 50. The reactive oxygen species are highly reactive oxygen species such as hydrogen peroxide, superoxide anion radical, hydroxyl radical, and singlet oxygen.

[0048] The chemical species may be metals, metal oxides, or metal hydroxides containing at least one of the following elements: cerium (Ce), manganese (Mn), cobalt (Co), platinum (Pt), ruthenium (Ru), tungsten (W), and tin (Sn), iridium (Ir), cesium (Cs), silver (Ag), iron (Fe), aluminum (Al), and titanium (Ti). Preferred examples of metals are Ce, Mn, Co, Pt, Ru, W, or Sn, with particularly preferred examples being Ce, Mn, or Co. Examples of metal oxides include MnO, Mn3O4, MnO2, MnO3, Mn2O7, CoO, Co2O3, Co3O4, and CeO2. Examples of metal hydroxides include Mn(OH)2, MnO(OH), MnO(OH)2, and Ce(OH)4.

[0049] The decomposition of reactive oxygen species occurs, for example, by converting reactive oxygen species into water or oxygen through radical reactions.

[0050] Reactive oxygen species are captured by reacting with them, for example, stable radical compounds, and converting them into inert reactants.

[0051] Inactivation of reactive oxygen species is achieved, for example, by suppressing the radicals generated from reactive oxygen species.

[0052] In order to mitigate surface irregularities of the anode 41 and to facilitate the diffusion of the electrolytic solution and gas, it is preferable that the average pore diameter of layer 51 be smaller than the surface irregularities and average pore diameter of the anode 41a. For example, it is preferable that the average pore diameter of layer 51 be smaller than the average pore diameter of the anode 41. When the average pore diameter of layer 51 is smaller than the average pore diameter of the anode 41, the electrolytic solution present in the anode 41 does not penetrate the membrane 50 more than necessary, suppressing flooding caused by the movement of water to the cathode 31, and ensuring proper formation of the three-phase interface at the cathode catalyst, thereby obtaining high reaction selectivity and durability. The average pore diameter of layer 51 can be measured by methods such as mercury intrusion or gas adsorption. It is preferable to measure the pore diameter distribution by mercury intrusion, which is less affected by the surface condition. If it is difficult to separate the diaphragm 50 from the layer 51, the average pore diameter of the layer 51 can be determined from the difference between the average pore diameter of the entire diaphragm 50 in which the layer 51 is located and the average pore diameter of the diaphragm 50 alone.

[0053] To form small pores, the inorganic particles that make up the layer are preferably fine, with an average particle diameter of 5 nm to 5 μm, and more preferably 7 nm to 1 μm. Here, particles include not only nearly spherical particles (spherical particles or approximately spherical particles), but also rugby ball-shaped, fibrous, needle-shaped, etc., and there are no restrictions on shape. When the average particle diameter is small, the specific surface area of ​​the inorganic material also increases, which is effective in decomposing, capturing, or inactivating the generated reactive oxygen species. Furthermore, the particulate inorganic material may be fibrous, or may be mixed with inorganic material of different shapes such as fibers, or may be mixed with multiple particles of different diameters or multiple particles of different compositions, or organic materials such as binders may be mixed to bind the inorganic materials together. When mixing organic materials such as binders, a mixing ratio of less than 70 weight percent in layer 51 is preferred. In other words, the proportion of inorganic material in layer 51 is preferably, for example, 30 weight percent or more. If the mixture contains 70% or more by weight of organic or non-inorganic materials, the function of promoting the decomposition, capture, or inactivation of reactive oxygen species may be insufficient. In this case, it is preferable that the surface of the inorganic material is exposed as much as possible. When using non-fibrous or non-spherical particles as the inorganic material, the above average particle diameter value represents the fiber diameter or the smaller of the two.

[0054] The diaphragm 50 may be formed using an ion exchange membrane or a porous membrane, but a porous membrane offers a higher introduction effect for layer 51. When using a porous membrane, the gases generated at both electrodes are more likely to cross over than in an ion exchange membrane, which is thought to facilitate the generation of reactive oxygen species, including hydrogen peroxide and radicals. Since the generation of reactive oxygen species accelerates the degradation of the diaphragm 50, it is effective to provide layer 51 on the surface of the diaphragm 50 not only to physically protect the diaphragm 50, but also to protect the diaphragm 50 from reactive oxygen species by using inorganic materials capable of decomposing, capturing, or inactivating them. In this case, materials supporting metal or oxide particles such as Pt or Co, which are capable of decomposing, capturing, or inactivating reactive oxygen species, may be used as the inorganic material. When using a porous membrane, there is a possibility that inorganic materials may penetrate the pores of the diaphragm 50, but this is acceptable as long as the pores are not filled and the through-holes are not eliminated.

[0055] The material used as the diaphragm 50 can be either an ion exchange membrane or a porous membrane, but in the case of a porous membrane, it has through-holes. When the electrolytic cell 20 is in use, a liquid such as an anode solution is filled into the through-holes of the porous membrane, and the filled anode solution allows for the movement of ions. In other words, a porous membrane with through-holes functions as a diaphragm 50 that can move ions between the anode 41 and the cathode 31. Furthermore, by filling the inside of the through-holes of the porous membrane with an anode solution when the electrolytic cell 20 is in use, a wet seal is created between the anode 41 and the cathode 31, that is, the movement of gases and liquids between the anode portion 40 and the cathode portion 30 and the resulting gas-to-gas reactions (crossover) can be suppressed.

[0056] A porous membrane made of organic polymer material used in the diaphragm 50 as described above can be manufactured, for example, as follows. There are various manufacturing methods for organic polymer porous membranes, such as phase separation, melt-quenching, extraction, chemical treatment, stretching, irradiation etching, melting, foaming, compounding, and hollow fiber formation, and the manufacturing method is not particularly limited. Among these, a method called non-solvent organic phase separation (NIPS) can be used, in which a homogeneous film-forming stock solution, in which an organic polymer is dissolved in a solvent, is brought into contact with a solidification solution containing a non-solvent, thereby creating a concentration gradient between the solvent in the film-forming stock solution and the non-solvent in the solidification bath, and this acts as a driving force to cause the non-solvent to replace the solvent in the film-forming stock solution and promote the phase separation phenomenon. Alternatively, a manufacturing method utilizing the thermally induced phase separation phenomenon, in which a polymer solution dissolved at high temperature is cooled to induce phase separation and create porosity, can be employed. In the case of materials that are easily formed into fibers, such as fluororesins, a method of applying shear force to create fine pores in the membrane can be selected. Furthermore, by combining the above methods, a predetermined porous structure can be obtained, inorganic materials may be compounded into the film, or a coating may be applied to the surface to control hydrophilicity. Multiple films may also be layered.

[0057] The CO2 gas supplied to the cathode channel 32 may be supplied in a dry state, but it is more preferable that it be humidified. When a porous membrane of organic polymer material is applied to the diaphragm 50, using humidified CO2 gas makes it easier to form a wet seal on the porous membrane of the organic polymer material. As described above, the wet seal prevents crossover between the anode section 40 and the cathode section 30. To humidify the CO2 gas, the gas supply section 60 may be equipped with a humidification section that humidifies the CO2 gas flowing through the gas piping 63. The humidification section (humidification device) may be equipped with, for example, a humidification water tank and configured to humidify the CO2 gas by vaporizing the humidification water using an ultrasonic oscillator or the like. Alternatively, humidification may be performed by bubbling the CO2 gas through the humidification water tank.

[0058] Next, the operation of the carbon dioxide electrolysis apparatus 10 shown in Figures 1 and 2 will be explained. Here, the case in which carbon monoxide (CO) is produced as the carbon compound will be mainly explained. However, the carbon compound as the reduction product of carbon dioxide is not limited to carbon monoxide, but may also be methane (CH4), ethane (C2H6), ethylene (C2H4), methanol (CH3OH), ethanol (C2H5OH), ethylene glycol (C2H6O2), etc. Furthermore, the carbon monoxide, which is the reduction product, may be further reduced to produce the organic compounds mentioned above.

[0059] First, it oxidizes mainly water (H2O) to produce hydrogen ions (H + The reaction process for generating ( ) is described below. When current is supplied from the power supply 80 between the anode 41 and the cathode 31, an oxidation reaction of water (H2O) occurs at the anode 41 in contact with the anode solution. Specifically, as shown in equation (1) below, the H2O contained in the anode solution is oxidized to oxygen (O2) and hydrogen ions (H + ) and are generated. 2H2O → 4H + +O2+4e - …(1)

[0060] H generated at anode 41 + These electrons move through the electrolyte solution and membrane 50 present in the anode 41 and reach the vicinity of the cathode 31. Electrons (e) are generated based on the current supplied from the power supply 80 to the cathode 31. - ) and H moved near cathode 31 + This leads to a reduction reaction of carbon dioxide (CO2). Specifically, as shown in equation (2) below, CO2 supplied from cathode channel 32 to cathode 31 is reduced to produce CO. Also, as shown in equation (3) below, hydrogen ions (H + Hydrogen is produced when ) accepts an electron. At this time, hydrogen may be produced simultaneously with carbon monoxide. 2CO2 + 4H + +4e - → 2CO + 2H2O …(2) 2H + +2e -→ H2…(3)

[0061] Next, mainly carbon dioxide (CO2) is reduced to hydroxide ions (OH) - The reaction process for producing ) is described below. When current is supplied from the power supply 80 between the anode 41 and the cathode 31, water (H2O) and carbon dioxide (CO2) are reduced near the cathode 31 as shown in equation (4) below, resulting in carbon monoxide (CO) and hydroxide ions (OH - ) and are produced. Also, as shown in equation (5) below, hydrogen is produced when water accepts electrons. At this time, hydrogen may be produced at the same time as carbon monoxide. The hydroxide ions (OH) produced by these reactions - ) diffuses near anode 41, and as shown in equation (6) below, hydroxide ions (OH - ) is oxidized to produce oxygen (O2). 2CO2 + 2H2O + 4e - → 2CO + 4OH - …(4) 2H2O + 2e - → H2 + 2OH - …(5) 4OH - → 2H2O + O2 + 4e - …(6)

[0062] The carbon dioxide electrolyzer 10 in this embodiment is not solely dedicated to the reduction of carbon dioxide, but can produce carbon dioxide reduction products and hydrogen in any ratio, such as generating carbon monoxide and hydrogen in a 1:2 ratio and then producing methanol in a subsequent chemical reaction. Since hydrogen is an inexpensive and readily available raw material from water electrolysis or fossil fuels, a high proportion of hydrogen is not necessary. From these viewpoints, it is preferable, from an economic and environmental standpoint, that the ratio of carbon monoxide to hydrogen be at least 1, preferably 1.5 or higher.

[0063] As described above, according to the carbon dioxide electrolysis apparatus 10 of the embodiment, by providing a layer 51 on the surface of the membrane used as the diaphragm 50, unevenness in the pressure applied to the surface of the diaphragm 50 due to surface irregularities of the anode 41 can be mitigated. This makes it possible to make the contact between the anode 41 and the diaphragm 50 uniform, and to suppress deterioration of the diaphragm 50 during the operation of the electrolytic cell 20. Therefore, it becomes possible to operate the carbon dioxide electrolysis apparatus 10 stably for a long period of time.

[0064] It is believed that reactive oxygen species derived from by-product gases cause damage to the diaphragm 50 not only in the carbon dioxide electrolysis apparatus described above, but also in electrolysis apparatuses that synthesize ammonia from nitrogen, perform water electrolysis, and fuel cells. In this case, the rough surface derived from the anode substrate with large irregularities is pressed against the diaphragm 50, accelerating its deterioration. In particular, in carbon dioxide electrolysis and nitrogen electrolysis, the overpotential becomes high at the anode 41 and cathode 31, making it easy for reactive oxygen species such as hydrogen peroxide and radicals to be generated by the generation of hydrogen and oxygen through side reactions, so the introduction of layer 51 is effective. [Examples]

[0065] Next, we will describe the examples and their evaluation results.

[0066] (Example 1, Example 2, Comparative Example 1) Electrolytic devices for Example 1, Example 2, and Comparative Example 1 were prepared. To evaluate degradation due to reactive oxygen species during hydrogen by-production, an inert gas containing nitrogen was supplied to the cathode channel humidified with pure water, and an electrolytic solution containing potassium bicarbonate at a concentration of 0.1 mol / L was supplied to the anode channel as the electrolyte at 700 mA / cm². 2 Each electrolytic device was operated under the following conditions with the following current density: By controlling the voltage with the power supply, a current density of 700 mA / cm² was achieved between the cathode and anode. 2An electric current was passed through the cathode to reduce water and produce hydrogen, and the anode to oxidize water and produce oxygen. Furthermore, the fluid discharged from the cathode channel was collected and analyzed to calculate the hydrogen production Faraday efficiency. The following components were prepared for the electrolytic cell. The cathode was prepared by coating carbon paper with a diffusion layer having a microporous layer with catalyst particles, on which Au nanoparticles (metal catalyst) with an average diameter of 2 nm were supported, with a mixture of this catalyst particle and Nafion solution (trade name, manufactured by DuPont) as an ion-conducting material (ion exchange resin). A porous membrane made of polyethersulfone with a thickness of 100 μm was used as the diaphragm. The anode and cathode were 4 cm × 4 cm (electrode area 16 cm²). 2 It was cut out and used.

[0067] In Example 1, a porous titanium material coated with iridium oxide was used as the anode as an oxidation catalyst. The average surface roughness Ra of the surface in contact with the diaphragm, calculated from the X-ray CT image of this anode, was 1.2 μm. The porosity was 34%. An electrolytic apparatus shown in Figure 1 was fabricated using this anode. When the electrolytic apparatus of Example 1 was operated under the conditions described above, the initial electrolysis voltage was 2.8 V. Furthermore, even after 160 hours of continuous operation, the hydrogen Faraday efficiency did not decrease, and no deterioration of the diaphragm was observed.

[0068] In Example 2, a different porous titanium material was used as the anode, compared to Example 1, which was coated with iridium oxide as an oxidation catalyst. The average surface roughness Ra of the surface in contact with the diaphragm of this anode was 10.3 μm. The porosity was 48%. An electrolytic apparatus shown in Figure 1 was fabricated using this anode. When the electrolytic apparatus of Example 1 was operated under the conditions described above, the initial electrolysis voltage was 2.9 V. Furthermore, even after 40 hours of continuous operation, the hydrogen Faraday efficiency did not decrease, and no deterioration of the diaphragm was observed.

[0069] In Comparative Example 1, a different porous titanium material coated with the same amount of iridium oxide as in Example 1 was used as the anode. The average surface roughness Ra of the surface in contact with the diaphragm, calculated from the X-ray CT image of this anode, was 17.4 μm. The porosity was 56%. An electrolytic apparatus shown in Figure 1 was fabricated using this anode. When the electrolytic apparatus of Comparative Example 1 was operated under the conditions described above, the initial electrolysis voltage was 3.1 V. Furthermore, a decrease in hydrogen Faraday efficiency was observed after 25 hours of continuous operation, and crossover of the generated gas due to diaphragm deterioration was confirmed.

[0070] As described above, it was found that using an anode with a low average surface roughness Ra suppressed the deterioration of the diaphragm and improved durability, thus extending the lifespan of the electrolytic device.

[0071] The configurations of each embodiment can be applied in combination and partially substituted. While several embodiments of the present invention have been described here, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as described in the claims.

[0072] The above embodiments can be summarized in the following technical proposal. (Technical proposal 1) A cathode is positioned in contact with the material to be reduced, which is supplied as a raw material gas, for reducing the material to be reduced. An anode is positioned in contact with an electrolytic solution containing the oxide, and is used to oxidize the oxide. A diaphragm separating the cathode and the anode, It is equipped with, The aforementioned anode is A porous body having a first surface on the diaphragm side and a second surface on the opposite side of the first surface, An oxidation catalyst in contact with the porous body, It has, The average surface roughness of the first surface is 0.1 μm or more and 17.0 μm or less. Membrane electrode assembly. (Technical proposal 2) The aforementioned porous material is an aggregate of conductive particles. A membrane electrode assembly as described in Technical Proposal 1. (Technical proposal 3) The average diameter of the conductive particles is between 10 nm and 200 μm. A membrane electrode assembly as described in Technical Proposal 2. (Technical proposal 4) The conductive particles include at least one selected from the group consisting of carbon, indium, tin, zinc, aluminum, copper, titanium, nickel, silver, tungsten, cobalt, and gold. A membrane electrode assembly as described in Technical Proposal 2 or Technical Proposal 3. (Technical proposal 5) The porosity of the anode is between 10% and 60%. A membrane electrode assembly according to any one of Technical Proposals 1 to 4. (Technical proposal 6) The thickness of the anode is 40 μm or more and 500 μm or less. A membrane electrode assembly according to any one of Technical Proposal 1 to Technical Proposal 5. (Technical proposal 7) The oxidation catalyst comprises at least one selected from the group consisting of iridium, ruthenium, nickel, iron, cobalt, manganese, lanthanum, lithium, indium, tin, and titanium. A membrane electrode assembly according to any one of Technical Proposals 1 to 6. (Technical proposal 8) The oxidation catalyst is coated on the first surface, A membrane electrode assembly as described in any one of Technical Proposal 1 to Technical Proposal 7. (Technical proposal 9) The aforementioned diaphragm is a porous membrane. A membrane electrode assembly as described in any one of Technical Proposal 1 to Technical Proposal 8. (Technical proposal 10) The thickness of the diaphragm is 3 times or more and 1000 times or less the average surface roughness of the first surface. A membrane electrode assembly according to any one of Technical Proposals 1 to 9. (Technical proposal 11) The diaphragm comprises a polymer compound crosslinked with at least one functional group selected from the group consisting of ether groups and sulfonyl groups. A membrane electrode assembly as described in any one of Technical Proposal 1 to Technical Proposal 10. (Technical proposal 12) The substance to be reduced is a gas. A membrane electrode assembly as described in any one of Technical Proposal 1 to Technical Proposal 11. (Technical proposal 13) The reduced substance is carbon dioxide or nitrogen. A membrane electrode assembly as described in Technical Proposal 12. (Technical proposal 14) The film electrode assembly described in any one of Technical Proposal 1 to Technical Proposal 13, A cathode section having a cathode channel for supplying the raw material gas to the cathode, An anode section having an anode channel for supplying the electrolytic solution to the anode, An electrolytic cell equipped with the following. (Technical proposal 15) The electrolytic cell described in Technical Proposal 14, A gas supply unit that supplies the raw material gas to the cathode flow path, An electrolytic solution supply unit that supplies the electrolytic solution to the anode channel, An electrolytic device equipped with the following. [Explanation of Symbols]

[0073] 10... Electrolytic device, 20... Electrolytic cell, 30... Cathode section, 31... Cathode, 32... Cathode channel, 40... Anode section, 41... Anode, 41a... Surface, 41b... Surface, 42... Anode channel, 50... Diaphragm, 51... Layer, 60... Gas supply section, 61... CO2 containment section, 62... CO2 adjustment section, 63... Gas piping, 70... Electrolytic solution supply section, 71... Anode solution tank, 72... Pump, 73... Electrolytic solution piping, 80... Power supply.

Claims

1. A cathode is positioned in contact with the material to be reduced, which is supplied as a raw material gas, for reducing the material to be reduced. An anode is positioned in contact with an electrolytic solution containing the oxide, and is used to oxidize the oxide. A diaphragm separating the cathode and the anode, It is equipped with, The aforementioned anode is A porous body having a first surface on the diaphragm side and a second surface on the opposite side of the first surface, An oxidation catalyst in contact with the porous body, It has, The average surface roughness of the first surface is 0.1 μm or more and 17.0 μm or less. Membrane electrode assembly.

2. The aforementioned porous material is an aggregate of conductive particles. The membrane electrode assembly according to claim 1.

3. The average diameter of the conductive particles is 10 nm or more and 200 μm or less. The membrane electrode assembly according to claim 2.

4. The conductive particles include at least one selected from the group consisting of carbon, indium, tin, zinc, aluminum, copper, titanium, nickel, silver, tungsten, cobalt, and gold. The membrane electrode assembly according to claim 2.

5. The porosity of the anode is 10% or more and 60% or less. The membrane electrode assembly according to claim 1.

6. The thickness of the anode is 40 μm or more and 500 μm or less. The membrane electrode assembly according to claim 1.

7. The oxidation catalyst comprises at least one selected from the group consisting of iridium, ruthenium, nickel, iron, cobalt, manganese, lanthanum, lithium, indium, tin, and titanium. The membrane electrode assembly according to claim 1.

8. The oxidation catalyst is coated on the first surface, The membrane electrode assembly according to claim 1.

9. The aforementioned diaphragm is a porous membrane. The membrane electrode assembly according to claim 1.

10. The thickness of the diaphragm is 3 times or more and 1000 times or less the average surface roughness of the first surface. The membrane electrode assembly according to claim 1.

11. The diaphragm comprises a polymer compound crosslinked with at least one functional group selected from the group consisting of ether groups and sulfonyl groups. The membrane electrode assembly according to claim 1.

12. The substance to be reduced is a gas. The membrane electrode assembly according to claim 1.

13. The reduced substance is carbon dioxide or nitrogen. The membrane electrode assembly according to claim 12.

14. The film electrode assembly according to any one of claims 1 to 13, A cathode section having a cathode channel for supplying the raw material gas to the cathode, An anode section having an anode channel for supplying the electrolytic solution to the anode, An electrolytic cell equipped with the following.

15. The electrolytic cell according to claim 14, A gas supply unit that supplies the raw material gas to the cathode flow path, An electrolytic solution supply unit that supplies the electrolytic solution to the anode channel, An electrolytic device equipped with the following.

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