Carbon dioxide electrolytic cell for methane synthesis

Abstract

This invention provides a carbon dioxide electrolytic cell for methane synthesis with high methane selectivity. [Solution] A carbon dioxide electrolytic cell for methane synthesis that synthesizes methane by the reduction reaction of carbon dioxide, comprising, in this order: an anode separator having a channel through which an electrolyte flows; a frame member having a thickness of 2 mm to 10 mm; an electrolyte; a cathode catalyst layer; a cathode gas diffusion layer; and a cathode separator having a channel for supplying carbon dioxide and a channel for discharging methane, wherein the frame member forms a space between the anode separator and the electrolyte membrane in which the electrolyte can be stored.

Description

Technical Field

[0001] The present disclosure relates to a carbon dioxide electrolysis cell for methane synthesis.

Background Art

[0002] There is a known technique in which electricity is applied to carbon dioxide (CO2) and water (H2O) using a cell including a solid polymer membrane, a gas diffusion layer, and a catalyst, and a C-based product such as methane is synthesized by causing a reduction reaction of carbon dioxide to proceed on the catalyst. For example, various reports have been made on techniques for reducing carbon dioxide to synthesize methane (see, for example, Patent Documents 1 to 5).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the synthesis of methane by the reduction reaction of carbon dioxide using a carbon dioxide electrolysis cell, in addition to methane, components such as hydrogen, carbon monoxide (CO), and ethylene (C2H4) are generated as by-products. When these by-products are generated, extra energy consumption occurs and the energy conversion efficiency to methane decreases. Therefore, the development of a carbon dioxide electrolysis cell with high methane selectivity is desired.

[0005] This disclosure has been made in light of the circumstances described above. One embodiment of this disclosure aims to solve the problem of providing a carbon dioxide electrolytic cell for methane synthesis with high methane selectivity. [Means for solving the problem]

[0006] The following are examples of specific means for solving the problem: <1> A carbon dioxide electrolytic cell for methane synthesis that synthesizes methane by the reduction reaction of carbon dioxide, an anode separator having a channel through which electrolyte flows, Frame members with a thickness of 2mm to 10mm, Electrolyte membrane, Cathode catalyst layer, Cathode gas diffusion layer, A cathode separator having a channel for supplying the above-mentioned carbon dioxide and a channel for discharging the above-mentioned methane, They are provided in this order, A carbon dioxide electrolytic cell for methane synthesis, wherein the above-mentioned frame member forms a space between the anode separator and the electrolyte membrane in which the electrolyte can be stored. <2> The material of the above frame member is an insulating material. <1> A carbon dioxide electrolytic cell for methane synthesis as described above. <3> The above insulating material includes at least one of polyetheretherketone and polytetrafluoroethylene. <2> A carbon dioxide electrolytic cell for methane synthesis as described above. <4> The cathode catalyst layer described above is subjected to a water-repellent treatment. <1> ~ <3> A carbon dioxide electrolytic cell for methane synthesis as described in any one of the following. <5> The above carbon dioxide reduction reaction is carried out in a temperature environment between 0°C and 50°C. <1> ~ <4> A carbon dioxide electrolytic cell for methane synthesis as described in any one of the following. [Effects of the Invention]

[0007] According to one embodiment of the present disclosure, a carbon dioxide electrolytic cell for methane synthesis with high methane selectivity is provided.

Brief Description of the Drawings

[0008] [Figure 1] FIG. 1 is a schematic diagram for explaining the configuration of a carbon dioxide electrolysis cell for methane synthesis according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a graph showing the results of the composition of the generated gas and the Faraday efficiency of each component in the methane generation methods of Example 1-1, Comparative Example 1-1, and Comparative Example 2-1. [Figure 3] FIG. 3 is a graph showing the results of the composition of the generated gas and the Faraday efficiency of each component in the methane generation methods of Example 1-2, Comparative Example 1-2, and Comparative Example 2-2. [Figure 4] FIG. 4 is a graph showing the results of the composition of the generated gas and the Faraday efficiency of each component in the methane generation methods of Example 1-3, Comparative Example 1-3, and Comparative Example 2-3. <000​​​​​​​​​​​​​​​​​​

[0012] In the numerical ranges described step by step in the present disclosure, the upper limit value described in a certain numerical range may be replaced with the upper limit value of the numerical range described in other step-by-step descriptions, and the lower limit value described in a certain numerical range may be replaced with the lower limit value of the numerical range described in other step-by-step descriptions. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[0013] In the present disclosure, the combination of two or more preferred embodiments is a more preferred embodiment.

[0014] In the present disclosure, the term "step" includes not only an independent step but also, even if it cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved.

[0015] In the present disclosure, the "carbon dioxide reduction electrode" refers to a structure formed by a cathode catalyst layer and a cathode gas diffusion layer. In the present disclosure, the "electrode body" refers to a structure formed by a carbon dioxide reduction electrode and an electrolyte membrane.

[0016] In the present disclosure, the "methane selectivity" means the selective productivity of methane.

[0017] [Carbon Dioxide Electrolysis Cell for Methane Synthesis] The carbon dioxide electrolysis cell for methane synthesis of the present disclosure (hereinafter, also simply referred to as "carbon dioxide electrolysis cell") is a carbon dioxide electrolysis cell that synthesizes methane by the reduction reaction of carbon dioxide. The carbon dioxide electrolytic cell of this disclosure comprises, in this order, an anode separator having a channel through which an electrolyte solution flows, a frame member having a thickness of 2 mm to 10 mm, an electrolyte membrane, a cathode catalyst layer, a cathode gas diffusion layer, and a cathode separator having a channel for supplying the carbon dioxide and a channel for discharging the methane, wherein the frame member forms a space (hereinafter also referred to as "anolite cell") capable of storing the electrolyte solution between the anode separator and the electrolyte membrane. The carbon dioxide electrolytic cell described herein exhibits high methane selectivity. The reason why the carbon dioxide electrolytic cell of this disclosure may produce such effects is not clear, but the inventors speculate as follows. However, the following speculation is not intended to be an exclusive interpretation of the carbon dioxide electrolytic cell of this disclosure, but is explained as an example.

[0018] In the synthesis of methane by the reduction reaction of carbon dioxide using a carbon dioxide electrolytic cell, components other than methane, such as hydrogen, carbon monoxide, and ethylene, tend to be produced as by-products. In the process of developing a carbon dioxide electrolytic cell that can more selectively synthesize methane, the inventors noticed that the effects obtained with a gas diffusion type half-cell were not always obtained with a gas diffusion type full-cell. The inventors found that this was due to insufficient penetration of the electrolyte into the electrolyte membrane, and that insufficient penetration of the electrolyte into the electrolyte membrane tends to reduce the efficiency of methane production in the carbon dioxide electrolytic cell. Based on this finding, they completed the carbon dioxide electrolytic cell of this disclosure.

[0019] The carbon dioxide electrolytic cell of this disclosure includes a frame member between the anode separator and the electrolyte membrane, forming a space enclosed by the anode separator, the electrolyte membrane, and the frame member. This space can store the electrolyte flowing through the anode separator. In the carbon dioxide electrolytic cell of this disclosure, since the thickness of the frame member is above a specific value, the anolite cell can store an amount of electrolyte that can sufficiently penetrate the electrolyte membrane. In the carbon dioxide electrolytic cell of this disclosure, since the electrolyte can sufficiently penetrate the electrolyte membrane, a decrease in methane selectivity due to insufficient penetration is unlikely to occur. Furthermore, in the carbon dioxide electrolytic cell of this disclosure, since the thickness of the frame member is below a specific value, the distance between the anode separator and the electrolyte membrane in the anolite cell is such that ions in the electrolyte can move sufficiently when electrolyte is stored in the anolite cell. In the carbon dioxide electrolytic cell of this disclosure, since ions in the electrolyte can move sufficiently between the anode separator and the electrolyte membrane, the reduction reaction of carbon dioxide proceeds easily, and the efficiency of methane production is increased. Based on the above, it can be inferred that the carbon dioxide electrolysis cell described herein has high methane selectivity.

[0020] On the other hand, while the technologies described in Patent Documents 1 to 5 are all technologies for synthesizing methane by reducing carbon dioxide, they differ from the technologies in this disclosure in that they do not relate to carbon dioxide electrolytic cells equipped with a mechanism for storing electrolyte on the anode side of the electrolyte membrane. Furthermore, the technologies described in Patent Documents 1 to 5 do not focus on the relationship between methane selectivity and the penetration of electrolyte into the electrolyte membrane.

[0021] The outline of the carbon dioxide electrolytic cell of this disclosure will be described below with reference to the drawings. Figure 1 is a schematic diagram illustrating the configuration of the carbon dioxide electrolytic cell according to the embodiment of this disclosure. The carbon dioxide electrolytic cell 1 according to this disclosure comprises, in order from top to bottom in Figure 1, a fastening plate 10, a current collector plate 20, an anode separator 30, a frame member 40, a gasket 50, an electrolyte membrane 60, a carbon dioxide reduction electrode 70, a cathode separator 80, a current collector plate 20, and a fastening plate 10. Between the anode separator 30 and the electrolyte membrane 60, a space (a so-called anolite cell) capable of storing electrolyte is formed by the frame member 40.

[0022] The anode separator 30 has a channel through which the electrolyte flows. The anode separator 30 is a metal plate measuring 8 cm x 8 cm, and has a channel section 32 in which a grid-like channel is provided at a pitch of 1 mm in a 3 cm square area in the center of the surface on the frame member 40 side, and is equipped with a mechanism for circulating the electrolyte introduced into the anode separator 30 via the anolite cell. In the carbon dioxide electrolytic cell 1, the anode separator 30 is formed of a material that functions as an anode catalyst and also serves as the anode catalyst layer.

[0023] The frame member 40 is an insulating plate measuring 8 cm x 8 cm and 2 mm thick, with an opening in the center that is the same shape and area as the flow channel 32 of the anode separator 30. By being positioned between the anode separator 30 and the electrolyte membrane 60, it forms a space (a so-called anolite cell) in which the electrolyte can be stored. The formation of this space makes it possible to supply the electrolyte to the electrolyte membrane 60 efficiently.

[0024] The electrolyte membrane 60 is an anion exchange membrane measuring 4 cm x 4 cm and 50 μm thick. The anion exchange membrane selectively supplies anions to the cathode catalyst layer.

[0025] The carbon dioxide reduction electrode 70 has a cathode catalyst layer (not shown) that has been treated with a water-repellent coating and a cathode gas diffusion layer (not shown), and the cathode catalyst layer is positioned on the electrolyte membrane 60 side. The cathode gas diffusion layer has a conductive fiber layer (not shown) and a microporous layer (not shown) which is a porous body formed of conductive particles, and the conductive fiber layer is positioned on the cathode separator 80 side.

[0026] The cathode separator 80 has a channel for supplying carbon dioxide and a channel for discharging methane, etc. The cathode separator 80 is a metal plate measuring 8 cm x 8 cm, and has a channel section 82 in which a grid-like channel is provided at a pitch of 1 mm in a 3 cm square area in the center of the surface facing the carbon dioxide reduction electrode 70, and is equipped with a mechanism for supplying carbon dioxide introduced into the cathode separator 80 to the carbon dioxide reduction electrode 70 while diffusing it.

[0027] The electrolyte introduced into the anode separator 30 is supplied to the anolite cell during the circulation process. Since the anolite cell constantly stores electrolyte, even as it is replaced, it allows sufficient electrolyte to permeate the electrolyte membrane 60. Carbon dioxide (CO2) introduced into the cathode separator 80 is supplied to the cathode catalyst layer from the cathode gas diffusion layer side of the carbon dioxide reduction electrode 70. The supplied carbon dioxide, along with the electrolyte that has permeated the electrolyte membrane 60, is reduced by the application of electricity, synthesizing methane (CH4) and other substances.

[0028] The fastening plate 10 is a pair of plate-shaped materials used to tightly secure and fix the materials together after the constituent materials have been laminated. The current collector plate 20 is a plate-shaped material used to apply voltage to a carbon dioxide electrolytic cell and extract the generated current to the outside. The gasket 50 is an insulating board measuring 8 cm x 8 cm and 200 μm thick, with an opening in the center that is the same shape and area as the electrolyte membrane 60. By combining the carbon dioxide reduction electrode 70 and the electrolyte membrane 60, leakage of the electrolyte is prevented.

[0029] The carbon dioxide electrolytic cell of this disclosure synthesizes methane by the reduction reaction of carbon dioxide. In the carbon dioxide electrolytic cell of this disclosure, an electrolyte is supplied to the anode side (i.e., the electrolyte membrane side) of the electrode body, carbon dioxide is supplied to the cathode side (i.e., the cathode gas diffusion layer side) of the electrode body, and when electricity is applied, the carbon dioxide on the cathode side is reduced on the cathode catalyst layer to produce methane, hydrogen, carbon monoxide, ethylene, etc. In the carbon dioxide electrolytic cell of this disclosure, the reduction reaction of carbon dioxide is preferably carried out in a temperature environment that is greater than 0°C and less than or equal to 50°C. In temperatures above 0°C, freezing of the electrolyte is suppressed. Under temperatures below 50°C, the proportion of by-products other than methane (especially hydrogen) tends to decrease, while the proportion of methane production increases. This is presumed to be because the suppression of hydrogen production improves the energy conversion efficiency to methane. The reduction reaction of carbon dioxide is more preferably carried out in a temperature environment above 0°C and below 40°C, and even more preferably in a temperature environment above 0°C and below 30°C.

[0030] The electrolyte is not particularly limited, and any known electrolyte can be used. Specific examples of electrolytes include aqueous solutions of potassium hydroxide (KOH), potassium bicarbonate (KHCO3), and potassium sulfate (K2SO4). The concentration of the electrolyte is not particularly limited, and can range from 0.1 mol / L to 5.0 mol / L.

[0031] The method of supplying carbon dioxide is not particularly limited, but it is preferable to supply it at a flow rate of, for example, 10 ml / min to 100 ml / min.

[0032] The method of applying electricity is not particularly limited, but it is preferable to apply a voltage to the cathode gas diffusion layer side such that the potential between the working electrode and the reference electrode is -0.9V to -3.0V.

[0033] The components of the carbon dioxide electrolytic cell described herein will be explained in detail below.

[0034] [Anode separator] The anode separator has a channel through which the electrolyte flows. The anode separator preferably has a flow channel on the frame member side that allows the electrolyte to flow through the anolite cell. The shape of the channel section is not particularly limited. Examples of channel section shapes include rectangles (e.g., squares and rectangles), polygons (except rectangles), circles, ellipses, and the like. The size of the flow channel is not particularly limited, but it is preferable, for example, to be the same as the size of the opening of the frame member (so-called inner frame), or to be smaller than the size of the opening of the frame member, and more preferably to be the same as the size of the opening of the frame member. The shape of the channel provided in the channel section is not particularly limited, and examples include a grid shape and a mesh shape. When the shape of the channel is grid-like, the pitch of the channel is not particularly limited and can be, for example, 0.5 mm to 2.0 mm.

[0035] The material of the anode separator is not particularly limited, and examples include titanium, stainless steel, and carbon. For example, from the viewpoint of suppressing oxidation by oxygen generated on the anode side, it is preferable that the material of the anode separator contains at least titanium. The anode separator may be coated with a corrosion-resistant conductive material (a so-called coating material) to suppress increased resistance due to oxidation. Examples of coating materials include platinum, gold, silver, titanium nitride, titanium carbide, and titanium carbonitride.

[0036] The anode separator may also function as an anode catalyst layer. By using a material that functions as an anode catalyst for the anode separator, the anode separator can be given the function of an anode catalyst layer.

[0037] [Frame members] The frame members have a thickness of 2 mm to 10 mm from the viewpoint of methane selectivity. If the frame member thickness is 2 mm or more, the anolite cell can store enough electrolyte to sufficiently permeate the electrolyte membrane. This allows for sufficient permeation of the electrolyte membrane, making it less likely for a decrease in methane selectivity to occur due to insufficient permeation. When the frame member thickness is 10 mm or less, the distance between the anode separator and the electrolyte membrane in the anolite cell becomes sufficient for ions in the electrolyte to move when the electrolyte is stored in the anolite cell. As a result, ions in the electrolyte can move sufficiently between the anode separator and the electrolyte membrane, which is thought to facilitate the reduction reaction of carbon dioxide and increase the efficiency of methane production. In one embodiment, the thickness of the frame member may be 2mm to 8mm, 2mm to 6mm, or 2mm to 4mm.

[0038] The thickness of the frame members refers to the average thickness of the frame members. The average thickness of the frame members is determined by the following method. Using a digital caliper, measure the thickness of eight arbitrarily selected locations in the thickness direction of the frame member (for example, if the outer frame of the frame member is rectangular, measure two arbitrarily selected locations on each of the four sides). Calculate the arithmetic mean of the measured values ​​and define the resulting value as the average thickness of the frame member.

[0039] The shape of the opening in the frame member (the so-called inner frame) is not particularly limited. The shape of the opening in the frame member may be the same as, for example, the shape of the electrolyte membrane, or it may be different, but it is preferable that it be the same. Examples of shapes for the opening in the frame member include rectangles (e.g., squares and rectangles), polygons (except rectangles), circles, ovals, etc.

[0040] The area of ​​the opening in the frame member is preferably in the range of 80% to less than 120% of the area of ​​the flow path portion of the separator, and more preferably in the range of 90% to 110%, from the viewpoint of efficient supply of electrolyte. In this disclosure, area refers to the area in a plan view.

[0041] The shape and size of the outer frame of the frame member are not particularly limited and may be set appropriately to match the desired shape and size of the carbon dioxide electrolysis cell.

[0042] The material of the frame member is not particularly limited, but it is preferably an insulating material, for example. Examples of insulating materials include resins, glass, ceramics, and rubber. The insulating material preferably contains either polyetheretherketone (PEEK) or polytetrafluoroethylene (PTFE), more preferably contains polyetheretherketone, and even more preferably contains polyetheretherketone.

[0043] The frame member may also function as a gasket. By using a material that functions as a gasket for the frame members, the frame members can be given the function of a gasket.

[0044] [Electrolyte membrane] The electrolyte membrane can be selected from known ion-exchange membrane type electrolyte membranes used in carbon dioxide electrolytic cells. The ion-exchange membrane type electrolyte membrane may have the property of selectively permeating cations, or it may have the property of selectively permeating anions, but it is preferable that it has the property of selectively permeating anions, that is, that it is an anion exchange membrane. Examples of electrolyte membranes include polymer electrolyte membranes. The electrolyte membrane may be, for example, a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane.

[0045] The thickness of the electrolyte membrane is not particularly limited, but is preferably, for example, 50 μm to 300 μm.

[0046] The electrolyte membrane thickness refers to the average thickness of the electrolyte membrane. The average thickness of the electrolyte membrane is determined by the following method. The cross-section of the electrolyte membrane is observed using a scanning electron microscope (SEM). The thickness is measured at six arbitrarily selected points in the thickness direction of the electrolyte membrane. The arithmetic mean of the measured values ​​is calculated, and the resulting value is taken as the average thickness of the electrolyte membrane.

[0047] A commercially available product can be used as the electrolyte membrane. Examples of commercially available electrolyte membranes include "Nafion" (registered trademark) [manufactured by Chemours K.K.], "Flemion" (registered trademark) [manufactured by AGC Inc.], "Neosepta" (registered trademark) [manufactured by Atoms Co., Ltd.], "Ceremion" (registered trademark) [manufactured by AGC Inc.], and "Sustainion" (registered trademark) [manufactured by Dioxide Materials Inc.].

[0048] [Cathode catalyst layer] The cathode catalyst layer is a layer containing a cathode catalyst. A cathode catalyst accelerates the reduction reaction of carbon dioxide. The type of cathode catalyst is not particularly limited, as long as it can promote the reduction reaction of carbon dioxide. Examples of cathode catalysts include metals or alloys such as Cu, Pt, Ag, Zn, Sn, and Al. The cathode catalyst is preferably in the form of particles of these metals or alloys. The cathode catalyst layer is preferably a layer containing Cu particles, for example, from the viewpoint of methane production efficiency. In this disclosure, the layer containing Cu particles is also referred to as the "Cu particle layer". The Cu particle layer is preferably a layer made up of Cu particles.

[0049] When the cathode catalyst is made of Cu particles, the particle size of the Cu particles is not particularly limited and may be, for example, 1 nm to 100 nm, 5 nm to 50 nm, or 5 nm to 10 nm.

[0050] The particle size of Cu particles refers to the average primary particle size of the Cu particles. The average primary particle diameter of Cu particles is determined by image analysis of the primary particles of Cu particles obtained by observing the surface of the cathode catalyst layer using a scanning transmission electron microscope (STEM).

[0051] From the viewpoint of methane selectivity, it is preferable that the cathode catalyst layer be treated with a water-repellent coating. If excess water is present on the catalyst, hydrogen production is promoted, which can lead to unnecessary energy consumption. However, if the cathode catalyst layer is treated with a water-repellent coating, water is appropriately removed from the catalyst, thereby suppressing hydrogen production. As a result, the energy consumption required for methane synthesis is reduced, and methane tends to be synthesized more selectively. The water-repellent treatment applied to the cathode catalyst layer is not particularly limited. For the water-repellent treatment, known water-repellent treatments can be applied. One example of a water-repellent treatment is the formation of a water-repellent film. Examples of water-repellent films include fluororesin films such as polytetrafluoroethylene (PTFE). The water-repellent treatment applied to the cathode catalyst layer may be applied to the entire cathode catalyst layer or to a part of it, but it is preferable that it be applied to the entire layer.

[0052] The thickness of the cathode catalyst layer is not particularly limited, but is preferably, for example, 200 nm to 350 nm.

[0053] The thickness of the cathode catalyst layer refers to the average thickness of the cathode catalyst layer. The average thickness of the cathode catalyst layer is determined by the following method. The cross-section of the cathode catalyst layer is observed using a scanning electron microscope (SEM). The thickness is measured at six arbitrarily selected locations in the thickness direction of the cathode catalyst layer. The arithmetic mean of the measured values ​​is calculated, and the resulting value is taken as the average thickness of the cathode catalyst layer.

[0054] ~Method for forming a cathode catalyst layer~ The method for forming the cathode catalyst layer is not particularly limited. A suitable method for forming a cathode catalyst layer will be explained using the example of a case where the cathode catalyst layer is a layer containing Cu particles as a cathode catalyst (i.e., a Cu particle layer). The cathode catalyst layer, which is a layer of Cu particles, can be formed, for example, by depositing Cu particles onto one side of the cathode gas diffusion layer (the side with the MPL if the cathode gas diffusion layer has an MPL) using an arc plasma method. By forming a Cu particle layer using the arc plasma method, a cathode catalyst layer capable of more efficiently producing methane tends to be obtained. The arc plasma method is a gas-phase method that generates metal nanoparticles by vaporizing a metal through a high-temperature arc discharge between two electrodes. In the arc plasma method, the metal evaporates and vaporizes due to the plasma generated between the two electrodes, and the resulting metal vapor cools while reacting with the ambient gas, growing into nano-sized particles. Therefore, the arc plasma method can form a Cu particle layer on one side of the cathode gas diffusion layer (the MPL side if the cathode gas diffusion layer has an MPL). The smaller the particle size of the Cu particles forming the Cu particle layer, the larger the contact area with carbon dioxide, and the more effectively they function as a catalyst, so it is thought that methane is produced more efficiently.

[0055] The arc plasma conditions are not particularly limited. The applied voltage is preferably 80V to 150V, and more preferably 110V to 120V. For example, a discharge cycle of 50 to 1000 times is preferable. For example, a capacitance of 300μF to 1500μF is preferred. A pulse frequency of, for example, 0.2 Hz to 10 Hz is preferred. A preferred example of arc plasma conditions is an applied voltage of 120V, a discharge cycle of 500 times, a capacitor capacitance of 1080μF, and a pulse frequency of 1Hz. As the arc plasma apparatus, the arc plasma nanoparticle formation apparatus (model: APD-1S-C) manufactured by Advance Engineering Co., Ltd. can be suitably used. However, the arc plasma apparatus is not limited to this.

[0056] [Cathode gas diffusion layer] The cathode gas diffusion layer can be made from materials used as cathode gas diffusion layers in known carbon dioxide electrolytic cells. For example, the cathode gas diffusion layer can be made of a material that is conductive and allows fluids (e.g., gases and liquids; the same applies hereinafter) to flow through it. Examples of such materials include porous bodies, powder sintered bodies, and fiber sintered bodies made of conductive materials. Conductive fibers are preferred as the conductive material. Specific examples of conductive fibers include carbon fibers and titanium fibers. The carbon fibers and titanium fibers may both be sintered bodies. Carbon fibers are preferred as the conductive fibers. Graphite fibers are preferred as the carbon fibers.

[0057] When the cathode gas diffusion layer is a layer formed of conductive fibers (also called the "conductive fiber layer"), the porosity of the conductive fiber layer is not particularly limited, but is preferably, for example, 30% to 80%.

[0058] The density of the conductive fiber layer is not particularly limited, but for example, 0.10 g / cm³ 3 ~1.00g / cm 3 It is preferable that this be the case.

[0059] The density of a conductive fiber layer is a value determined from the mass per unit area and the thickness.

[0060] The thickness of the conductive fiber layer is not particularly limited, but is preferably 100 μm to 300 μm, and more preferably 100 μm to 250 μm.

[0061] The thickness of the conductive fiber layer refers to the average thickness of the conductive fiber layer. The average thickness of the conductive fiber layer is determined by the following method. The cross-section of the conductive fiber layer is observed using a scanning electron microscope (SEM). The thickness is measured at six arbitrarily selected locations in the thickness direction of the conductive fiber layer. The arithmetic mean of the measured values ​​is calculated, and the resulting value is taken as the average thickness of the conductive fiber layer.

[0062] The cathode gas diffusion layer preferably comprises a conductive fiber layer and a microporous layer (MPL) provided on the conductive fiber layer and formed of conductive particles. When the cathode gas diffusion layer has an MPL on the conductive fiber layer, the number of contact points between carbon dioxide, the catalyst of the cathode catalyst layer, and the electrolyte membrane increases, allowing the reduction reaction of carbon dioxide to proceed more efficiently. In the case where the cathode gas diffusion layer has an MPL on a conductive fiber layer, it is preferable that the MPL is provided on the surface facing the cathode catalyst layer. When the MPL is provided on the surface facing the cathode catalyst layer, carbon dioxide can more easily come into contact with the cathode catalyst in the cathode catalyst layer, the reduction reaction of carbon dioxide proceeds efficiently, and methane tends to be produced selectively and efficiently.

[0063] The conductive particles are not particularly limited as long as they contain a conductive material. Examples of conductive particles include carbon particles and conductive metal particles. Examples of conductive metal particles include titanium particles, copper particles, silver particles, and platinum particles. Carbon particles are preferred as the conductive particles. Graphite particles are preferred as the carbon particles.

[0064] The shape of the conductive particles is not particularly limited. The shape of the conductive particles may be, for example, spherical (e.g., perfectly spherical and ellipsoidal), plate-like, or irregular in shape.

[0065] The particle size of the conductive particles is preferably 50 nm or larger, for example, from the viewpoint of forming pores of a size that allows fluid to flow smoothly. In one embodiment, the particle size of the conductive particles may be 50 nm to 500 nm, or 50 nm to 200 nm.

[0066] The particle size of conductive particles refers to the average primary particle size of the conductive particles. The average primary particle diameter of conductive particles is determined by image analysis of the primary particles of conductive particles obtained by observing the surface of the MPL using a scanning electron microscope (SEM).

[0067] The shape of the pores in the porous material MPL is not particularly limited. The shape of the hole may be, for example, circular (e.g., perfectly circular and elliptical), rectangular, or irregular.

[0068] The size of the pores in a porous material like MPL (also called the "pore diameter of MPL") is not particularly limited, as long as fluid flow is possible. The pore size of the MPL is preferably 0.01 μm or larger, and more preferably 0.1 μm or larger. Furthermore, the pore size of the MPL is preferably 3.0 μm or smaller, and more preferably 1.0 μm or smaller. In one embodiment, the pore size of the MPL may be 0.01 μm to 3.0 μm, or 0.1 μm to 1.0 μm.

[0069] The pore size of MPL refers to the average pore size of the MPL. The average pore diameter of MPL is determined by image analysis of the pores in MPL obtained by observing the cross-section in the thickness direction of MPL using a scanning electron microscope (SEM).

[0070] The pore size of the MPL can be controlled, for example, by the size of the conductive particles.

[0071] The thickness of the MPL is not particularly limited, but is preferably 150 μm or less, more preferably 50 μm to 150 μm, and even more preferably 50 μm to 100 μm.

[0072] The thickness of the MPL refers to the average thickness of the MPL. The average thickness of MPL is a value that can be determined by the following method. The cross-section of the MPL is observed using a scanning electron microscope (SEM). The thickness is measured at six arbitrarily selected points in the thickness direction of the MPL. The arithmetic mean of the measured values ​​is calculated, and the resulting value is taken as the average thickness of the MPL.

[0073] Commercially available carbon paper may be used for the cathode gas diffusion layer. An example of a commercially available carbon paper that can function as a cathode gas diffusion layer is SIGRACET 28BC (trade name, carbon paper with a microporous layer (MPL) made of graphite particles on a sintered body of graphite fibers, thickness: 235 μm, density: 0.45 g / cm³). 3 [Manufactured by SGL CARBON], and Toray Paper TGP-H-060 [product name, thickness: 190 μm, density: 0.44 g / cm³]. 3 Examples include products manufactured by Toray Industries, Inc.

[0074] [Cathode separator] The cathode separator has a channel for supplying carbon dioxide and a channel for discharging methane. The cathode separator preferably has a flow channel on the side facing the cathode gas diffusion layer that allows carbon dioxide to be supplied to the cathode catalyst layer. The shape of the channel section is not particularly limited. Examples of channel section shapes include rectangles (e.g., squares and rectangles), polygons (except rectangles), circles, ellipses, and the like. The size of the flow channel is not particularly limited, but it is preferably the same as the size of the cathode catalyst layer, or smaller than the size of the cathode catalyst layer, and more preferably smaller than the size of the cathode catalyst layer. The shape of the channel in the channel section is not particularly limited, and examples include a grid shape and a mesh shape. A grid shape is preferred for the channel. When the channel is grid-shaped, carbon dioxide can be diffused, making it easier for carbon dioxide to come into contact with the cathode catalyst in the cathode catalyst layer, which tends to allow the reduction reaction of carbon dioxide to proceed efficiently and for methane to be produced selectively and efficiently. When the shape of the flow channel is grid-like, the pitch of the flow channel is not particularly limited and can be, for example, 0.5 mm to 2.0 mm.

[0075] The material of the cathode separator is not particularly limited, and examples include titanium, stainless steel, and carbon. Preferably, the material of the cathode separator is one that contains at least titanium. The cathode separator may be coated with a conductive material (a so-called coating material). Examples of coating materials include platinum, gold, silver, titanium nitride, titanium carbide, and titanium carbonitride.

[0076] [Other configurations] The carbon dioxide electrolytic cell of this disclosure may further include other components. Other components may be selected from known carbon dioxide electrolytic cell components. Other components include, for example, an anode catalyst layer, an anode gas diffusion layer, a gasket, a current collector plate, and a fastening plate. The anode catalyst layer, anode gas diffusion layer, gasket, current collector plate, and fastening plate can be made from materials known to be used in carbon dioxide electrolytic cells. [Examples]

[0077] The present disclosure will be described in detail below with reference to examples. However, the present disclosure is not limited to the following examples. The matters shown in the following examples may be modified as appropriate without departing from the spirit of the present disclosure.

[0078] [Fabrication of carbon dioxide electrolysis cells] [Manufacturing Example 1] (1) Fabrication of carbon dioxide reduction electrode Carbon paper (CP) [Product name: SIGRACET® 28BC, Density: 0.45 g / cm³] 3 A CP (carbon fiber composite) with a thickness of 235 μm, manufactured by SGL CARBON, was cut into 5 cm squares and used as a cathode gas diffusion layer. The CP has a structure in which a microporous layer (MPL), which is a porous body formed of graphite particles, is provided on a conductive fiber layer made of a sintered carbon fiber body. Next, Cu particles were deposited on the MPL side surface of the cut-out CP using an arc plasma device (product name: Arc Plasma Nanoparticle Forming Device, model: APD-1S-C, manufactured by Advance Riko Co., Ltd.) by the arc plasma method. Specifically, the cut-out CP was placed in the arc plasma device using imide tape so that the MPL side surface was exposed, and then Cu particles were generated by evaporating and vaporizing Cu in a vacuum, and the generated Cu particles were deposited on the MPL side surface of the CP. The arc plasma conditions were set to a voltage of 120 V, a capacitor capacity of 1080 μF, and a discharge cycle of 500 times. As described above, a laminate having a layer structure of a cathode gas diffusion layer (conductive fiber layer / MPL) and a cathode catalyst layer (Cu particle layer) was first fabricated. Next, the laminate was cut into 4.0 cm squares. Then, polytetrafluoroethylene (PTFE) [product name: Fluoro-Placoat, product number: FC-115, manufactured by Fine Chemical Japan Co., Ltd.] was spray-coated onto both sides of the cut laminate, and then dried at room temperature (25°C) for 15 minutes. In this manner, a carbon dioxide reduction electrode was fabricated. The fabricated carbon dioxide reduction electrode has a layer structure consisting of a cathode gas diffusion layer (conductive fiber layer / MPL) and a cathode catalyst layer (Cu particle layer), and both sides of the cathode catalyst layer are treated with a water-repellent coating using PTFE.

[0079] (2) Fabrication of electrode bodies An electrode body was fabricated using the carbon dioxide reduction electrode and electrolyte prepared as described above. First, the following pretreatment was performed on the electrolytes. An electrolyte (product name: Sustainion® X37-50 Grade 60 Membrane, anion exchange membrane, thickness: 50 μm, manufactured by Dioxide Materials Inc.) was immersed in an electrolyte solution (product name: 1 mol / L KOH solution, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) for 24 hours. The electrolyte was removed from the electrolyte solution and its surface was washed with pure water. Next, the pre-treated electrolyte and the carbon dioxide reduction electrode were stacked so that the electrolyte and the Cu particle layer side of the cathode catalyst layer of the carbon dioxide reduction electrode were in contact. Then, the electrode was press-molded at room temperature (25°C) using a press machine [product name: small hot press machine, model: H300-05, manufactured by AS ONE Corporation; hereinafter the same]. The electrode body was manufactured in the manner described above. The pressing conditions were a pressing pressure of 5 MPa and a pressing time of 5 minutes. In addition, to keep the electrolyte moist, Kimwipes (registered trademark) moistened with pure water were placed in contact with the side of the electrolyte that was not stacked with the carbon dioxide reduction electrode during press molding. The manufactured electrode body has a layer structure of carbon dioxide reduction electrode [cathode gas diffusion layer (conductive fiber layer / MPL) / water-repellent treated cathode catalyst layer] / electrolyte.

[0080] (3) Fabrication of a carbon dioxide electrolysis cell The electrode body prepared as described above was incorporated into a gas diffusion type full cell to produce a carbon dioxide electrolytic cell. Specifically, a separator, a current collector plate, and a fastening plate were stacked on both sides of the electrode body in this order, and a frame member was sandwiched between the anode-side separator (so-called anode separator) and the electrolyte provided by the electrode body via a gasket, thereby obtaining the carbon dioxide electrolytic cell of Production Example 1. As shown in Figure 1, the carbon dioxide electrolytic cell of Production Example 1 has the following configuration: fastening plate / current collector plate / cathode separator / electrode body [carbon dioxide reduction electrode [cathode gas diffusion layer (conductive fiber layer / MPL) / water-repellent treated cathode catalyst layer] / electrolyte] / gasket / frame member / anode separator / current collector plate / fastening plate. Both the cathode separator and the anode separator have a flow channel section with a grid-like network of channels spaced 1 mm apart within a 3 cm square area in the center of a metal plate, and are equipped with a mechanism for supplying gas and liquid while diffusing them, respectively. The frame member has an opening in the center of a 2 mm thick insulating plate with the same area as the flow channel section of the anode separator, and by being placed between the anode separator and the electrolyte, it forms an anolite cell, which is a space in which the electrolyte is stored. The electrolyte stored in the anolite cell is constantly being replaced by external supply and discharge, keeping it in a state of continuous storage. The details of each component of the carbon dioxide electrolysis cell in manufacturing example 1 are shown below.

[0081] ·Electrolytes Size: 4cm x 4cm Thickness: 50 μm • Carbon dioxide reduction electrode Size: 4cm x 4cm Thickness of the cathode gas diffusion layer: 235 μm • Anolite Cell Material: Polyether ether ketone (PEEK) Size: 8cm x 8cm Opening area: 3cm x 3cm Thickness: 2mm ·gasket Material: Polytetrafluoroethylene (PTFE) Size: 8cm x 8cm Opening area: 4cm x 4cm Thickness: 200 μm • Separator Material: Platinum (Pt) plated titanium (Ti) Size: 8cm x 8cm Area of ​​the channel: 3cm x 3cm Flow channel pitch: 1mm Flow channel shape: Slit-shaped • Current collector plate Material: Gold (Au) plated copper (Cu) • Fastening plate Material: Stainless steel

[0082] [Comparative Manufacturing Example 1] The carbon dioxide electrolytic cell for comparative manufacturing example 1 was fabricated in the same manner as in manufacturing example 1, except that an anolite cell was not used.

[0083] [Comparative Manufacturing Example 2] The carbon dioxide electrolytic cell for comparative manufacturing example 2 was fabricated in the same manner as in manufacturing example 1, except that the thickness of the anolite cell was changed from "2 mm" to "15 mm".

[0084] [Evaluation of methane selectivity (1)] <Example 1-1> As shown in Manufacturing Example 1, a carbon dioxide electrolytic cell was fabricated and the following evaluations were performed. A 1 mol / L KHCO3 aqueous solution was used as the electrolyte. The KHCO3 aqueous solution was pre-treated by thoroughly bubbling it with CO2 gas (purity: 99.99%), and then adjusting the pH to 7.7 before use as the electrolyte. A Cu electrode was used as the working electrode (WE), an Ag / AgCl electrode as the reference electrode (RE), and a Pt-plated Ti electrode as the counter electrode (CE).

[0085] The electrolyte was filled into a tank connected to the anode line. CO2 gas (purity: 99.99%) was continuously bubbled into the electrolyte in the tank to maintain a constant pH. At a temperature of 25°C, CO2 gas (purity: 99.99%) was flowed at a flow rate of 5 ml / min through the cathode gas diffusion layer side of the carbon dioxide reduction electrode to replace the gas inside the carbon dioxide electrolytic cell with CO2 gas. Simultaneously, the electrolyte from the tank was flowed at a flow rate of 6 ml / min and circulated to the anode line. After sufficient gas replacement inside the carbon dioxide electrolytic cell, a voltage was applied so that the potential difference between the working electrode and the reference electrode was -1.4V. After applying voltage and confirming that current was flowing, the generated gas was collected for 1 minute in a sample bag placed downstream of the cathode outlet of the carbon dioxide electrolysis cell. Then, the system was switched to the exhaust line, and the flow rate of the generated gas (in ml / min) was measured three times using a flow meter (product name: Defender® 530+, manufactured by Mesa Labs). The arithmetic mean of the measured values ​​was calculated, and the resulting value was used as the measured flow rate of the generated gas. Next, the sample bag containing the collected product gas was connected to a gas chromatograph (product name: Nexis® GC-2030, manufactured by Shimadzu Corporation). The product gas was circulated through the gas chromatograph's flow path and introduced into a column (product name: MICROPACKED-ST, manufactured by Shinwa Chemical Co., Ltd.) to analyze the composition of the product gas.

[0086] Based on the measured flow rate of the generated gases and the analysis of their composition, the amounts of hydrogen (H2), carbon monoxide (CO), methane (CH4), and ethylene (C2H4) produced were calculated and converted into electric charge. The production efficiency (so-called Faraday efficiency) of hydrogen, carbon monoxide, methane, and ethylene was determined from the ratio of the converted electric charge to the actual current flow. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 1 and Figure 2.

[0087] Faraday efficiency indicates the proportion of the total current used for the reaction of a particular product. A higher Faraday efficiency value for methane (in %) indicates a carbon dioxide electrolytic cell with high methane selectivity.

[0088] <Comparative Example 1-1> As shown in Comparative Manufacturing Example 1, a carbon dioxide electrolytic cell was prepared, and the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Example 1-1, except that this prepared carbon dioxide electrolytic cell was used. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 1 and Figure 2.

[0089] <Comparative Example 2-1> As shown in Comparative Manufacturing Example 2, a carbon dioxide electrolytic cell was prepared, and the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Example 1-1, except that this prepared carbon dioxide electrolytic cell was used. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 1 and Figure 2.

[0090] <Examples 1-2> A carbon dioxide electrolytic cell was fabricated as shown in Manufacturing Example 1. Except for applying a voltage such that the potential difference between the working electrode and the reference electrode was -2.0V, the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Example 1-1. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 2 and Figure 3.

[0091] <Comparative Example 1-2> As shown in Comparative Manufacturing Example 1, a carbon dioxide electrolytic cell was prepared, and the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Example 1-2, except that this prepared carbon dioxide electrolytic cell was used. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 2 and Figure 3.

[0092] <Comparative Example 2-2> As shown in Comparative Manufacturing Example 2, a carbon dioxide electrolytic cell was prepared, and the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Example 1-2, except that this prepared carbon dioxide electrolytic cell was used. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 2 and Figure 3.

[0093] <Examples 1-3> A carbon dioxide electrolytic cell was fabricated as shown in Manufacturing Example 1. Except for applying a voltage such that the potential difference between the working electrode and the reference electrode was -2.5V, the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Example 1-1. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 3 and Figure 4.

[0094] <Comparative Example 1-3> As shown in Comparative Manufacturing Example 1, a carbon dioxide electrolytic cell was prepared, and the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Examples 1-3, except that this prepared carbon dioxide electrolytic cell was used. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 3 and Figure 4.

[0095] <Comparative Example 2-3> As shown in Comparative Manufacturing Example 2, a carbon dioxide electrolytic cell was prepared, and the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Examples 1-3, except that this prepared carbon dioxide electrolytic cell was used. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 3 and Figure 4.

[0096] [Table 1]

[0097] [Table 2]

[0098] [Table 3]

[0099] As shown in Tables 1-3 and Figures 2-4, the carbon dioxide electrolytic cells of the examples (Production Example 1 and Production Example 2) showed higher methane Faraday efficiency values ​​at all potential differences compared to the carbon dioxide electrolytic cells of the comparative examples (Comparative Production Example 1 and Comparative Production Example 2). From the above, it is clear that the carbon dioxide electrolytic cells of this disclosure have high methane selectivity.

[0100] [Evaluation of methane selectivity (2)] <Examples 1-4> A carbon dioxide electrolytic cell was fabricated as shown in Manufacturing Example 1. In a temperature environment of 5°C, the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Example 1-1, except that CO2 gas (purity: 99.99%) was flowed through the cathode gas diffusion layer side of the carbon dioxide reduction electrode. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 4 and Figure 5.

[0101] <Examples 1-5> A carbon dioxide electrolytic cell was fabricated as shown in Manufacturing Example 1. In a temperature environment of 5°C, the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Example 1-2, except that CO2 gas (purity: 99.99%) was flowed through the cathode gas diffusion layer side of the carbon dioxide reduction electrode. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 4 and Figure 5.

[0102] <Examples 1-6> A carbon dioxide electrolytic cell was fabricated as shown in Manufacturing Example 1. In a temperature environment of 5°C, the flow rate of the generated gas and the composition of the generated gas were measured and analyzed in the same manner as in Examples 1-3, except that CO2 gas (purity: 99.99%) was flowed through the cathode gas diffusion layer side of the carbon dioxide reduction electrode. Based on the measurement results of the flow rate of the generated gases and the analysis results of the composition of the generated gases, the Faraday efficiencies of hydrogen, carbon monoxide, methane, and ethylene were determined in the same manner as in Example 1-1. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 4 and Figure 5.

[0103] [Table 4]

[0104] Examples 1-1, 1-2, and 1-3 described in Table 4 and Figure 5 are all included for comparison with the other examples described in Table 4 and Figure 5, and are the same examples as Example 1-1 described in Table 1 and Figure 2, Example 1-2 described in Table 2 and Figure 3, and Example 1-3 described in Table 3 and Figure 4, respectively.

[0105] The results shown in Table 4 and Figure 5 reveal that, in the carbon dioxide electrolytic cell of this disclosure, methane can be synthesized more selectively when the reduction reaction of carbon dioxide is carried out at a temperature of 5°C than when carried out at a temperature of 25°C. [Explanation of symbols]

[0106] 1: Carbon dioxide electrolysis cell 10: Fastening plate 20: Current collector plate 30: Anode separator 32: Flow channel 40: Frame member 50: Gasket 60: Electrolyte membrane 70: Carbon dioxide reduction electrode 80: Cathode separator 82: Flow channel

Claims

1. A carbon dioxide electrolytic cell for methane synthesis that synthesizes methane by the reduction reaction of carbon dioxide, an anode separator having a channel through which electrolyte flows, Frame members with a thickness of 2 mm to 10 mm, Electrolyte membrane, Cathode catalyst layer, Cathode gas diffusion layer, A cathode separator having a channel for supplying carbon dioxide and a channel for discharging methane, They are provided in this order, A carbon dioxide electrolytic cell for methane synthesis, wherein the frame member forms a space between the anode separator and the electrolyte membrane in which the electrolyte can be stored.

2. The carbon dioxide electrolytic cell for methane synthesis according to claim 1, wherein the material of the frame member is an insulating material.

3. The carbon dioxide electrolytic cell for methane synthesis according to claim 2, wherein the insulating material comprises at least one of polyetheretherketone and polytetrafluoroethylene.

4. The carbon dioxide electrolytic cell for methane synthesis according to claim 1 or claim 2, wherein the cathode catalyst layer is subjected to a water-repellent treatment.

5. The carbon dioxide electrolytic cell for methane synthesis according to claim 1 or claim 2, wherein the carbon dioxide reduction reaction is carried out in a temperature environment greater than 0°C and less than or equal to 50°C.

Images