Carbon dioxide electrolysis cell for methane synthesis

Abstract

A carbon dioxide electrolysis cell for methane synthesis with high methane selectivity is provided. [Solution] A carbon dioxide electrolysis cell for methane synthesis, which synthesizes methane by a reduction reaction of carbon dioxide, comprises, in this order: an anode separator having a flow path 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 flow path for supplying carbon dioxide and a flow path 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 technology]

[0002] A technology is known in which a cell equipped with a solid polymer membrane, a gas diffusion layer, and a catalyst is used to apply electricity to carbon dioxide (CO2) and water (HO), causing a reduction reaction of carbon dioxide on the catalyst, thereby synthesizing carbon-based products such as methane. For example, various reports have been made so far regarding techniques for synthesizing methane by reducing carbon dioxide (see, for example, Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-7919 [Patent Document 2] International Publication No. 2012 / 137240 [Patent Document 3] Japanese Patent Application Publication No. 2015-132012 [Patent Document 4] Japanese Patent Application Publication No. 2020-163248 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-29811 Summary of the Invention [Problem to be solved by the invention]

[0004] When methane is synthesized by the reduction of carbon dioxide using a carbon dioxide electrolysis cell, other by-products are produced in addition to methane, including hydrogen, carbon monoxide (CO), and ethylene (C2H4). The production of these by-products results in excess energy consumption and reduces the efficiency of energy conversion to methane. Therefore, there is a need to develop a carbon dioxide electrolysis cell with high methane selectivity.

[0005] The present disclosure has been made in consideration of the above circumstances. An object of one embodiment of the present disclosure is to provide a carbon dioxide electrolysis cell for methane synthesis that has high methane selectivity. [Means for solving the problem]

[0006] Specific means for solving the problems include the following aspects. <1> A carbon dioxide electrolysis cell for methane synthesis that synthesizes methane by a reduction reaction of carbon dioxide, comprising: an anode separator having a flow path through which an electrolytic 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; a cathode separator having a flow path for supplying the carbon dioxide and a flow path for discharging the methane; In this order, a space capable of storing the electrolytic solution is formed between the anode separator and the electrolyte membrane by the frame member. <2> The frame member is made of an insulating material. <1> The carbon dioxide electrolysis cell for methane synthesis according to claim 1. <3> The insulating material includes at least one of polyether ether ketone and polytetrafluoroethylene. <2> The carbon dioxide electrolysis cell for methane synthesis according to claim 1. <4> The cathode catalyst layer is subjected to a water-repellent treatment. <1> ~ <3> 10. The carbon dioxide electrolysis cell for methane synthesis according to claim 9, wherein the electrolysis cell is a carbon dioxide electrolysis cell for methane synthesis. <5> The carbon dioxide reduction reaction is carried out in a temperature environment of more than 0°C and less than 50°C. <1> ~ <4> 10. The carbon dioxide electrolysis cell for methane synthesis according to claim 9, wherein the electrolysis cell is a carbon dioxide electrolysis cell for methane synthesis. [Effects of the Invention]

[0007] According to one embodiment of the present disclosure, a carbon dioxide electrolysis cell for methane synthesis is provided that has high methane selectivity. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating 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 composition of the produced gas and the Faraday efficiency of each component in the methane production methods of Example 1-1, Comparative Example 1-1, and Comparative Example 2-1. [Figure 3] FIG. 3 is a graph showing the composition of the produced gas and the Faraday efficiency of each component in the methane production methods of Example 1-2, Comparative Example 1-2, and Comparative Example 2-2. [Figure 4] FIG. 4 is a graph showing the composition of the produced gas and the Faraday efficiency of each component in the methane production methods of Examples 1-3, Comparative Examples 1-3, and 2-3. [Figure 5] FIG. 5 is a graph showing the composition of the produced gas and the Faraday efficiency of each component in the methane production methods of Examples 1-1, 1-2, 1-3, 1-4, 1-5, and 1-6. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail. The present disclosure is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present disclosure.

[0010] When describing embodiments of the present disclosure with reference to the drawings, the configuration of the embodiments is not limited to the configuration shown in the drawings. Components indicated by the same reference numerals in the drawings are the same components. The dimensional ratios in the drawings do not necessarily represent the actual dimensional ratios.

[0011] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0012] In the numerical ranges described in stages in this disclosure, the upper limit value described in one numerical range may be replaced by the upper limit value of another numerical range described in stages, and the lower limit value described in one numerical range may be replaced by the lower limit value of another numerical range described in stages. In the numerical ranges described stepwise in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

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

[0014] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

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

[0016] In this disclosure, "methane selectivity" means the selective production of methane.

[0017] [Carbon dioxide electrolysis cell for methane synthesis] The carbon dioxide electrolysis cell for synthesizing methane (hereinafter also simply referred to as a "carbon dioxide electrolysis cell") according to the present disclosure is a carbon dioxide electrolysis cell that synthesizes methane through a reduction reaction of carbon dioxide. The carbon dioxide electrolysis cell of the present disclosure comprises, in this order: an anode separator having a flow path through which an electrolytic 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 the flow path for supplying carbon dioxide and the flow path for discharging methane. The frame member forms a space (hereinafter also referred to as an "anolyte cell") between the anode separator and the electrolyte membrane in which the electrolytic solution can be stored. The carbon dioxide electrolysis cells of the present disclosure are highly selective for methane. The reason why the carbon dioxide electrolysis cell of the present disclosure can achieve such effects is unclear, but the inventors speculate as follows: However, the following speculation is not intended to limit the carbon dioxide electrolysis cell of the present disclosure, but is provided as an example.

[0018] When methane is synthesized by the reduction reaction of carbon dioxide using a carbon dioxide electrolysis 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 electrolysis cell capable of more selectively synthesizing methane, the inventors noticed that the effects obtained with a gas diffusion type half cell may not be obtained with a gas diffusion type full cell. The inventors discovered that this was due to insufficient permeation of the electrolyte solution into the electrolyte membrane, and that insufficient permeation of the electrolyte solution into the electrolyte membrane tends to reduce the efficiency of methane production in a carbon dioxide electrolysis cell, leading to the completion of the carbon dioxide electrolysis cell disclosed herein.

[0019] The carbon dioxide electrolysis cell according to the present disclosure includes a frame member between the anode separator and the electrolyte membrane, and a space is formed surrounded by the anode separator, the electrolyte membrane, and the frame member. This space can store the electrolyte solution that flows through the anode separator. In the carbon dioxide electrolysis cell of the present disclosure, the thickness of the frame member is equal to or greater than a specific value, allowing the anolyte cell to store an electrolyte solution to a degree that allows sufficient permeation into the electrolyte membrane. In the carbon dioxide electrolysis cell of the present disclosure, the electrolyte solution can be sufficiently permeated into the electrolyte membrane, making it less likely that a decrease in methane selectivity due to insufficient permeation will occur. Furthermore, in the carbon dioxide electrolysis cell of the present disclosure, the thickness of the frame member is equal to or less than a specific value, allowing the distance between the anode separator and the electrolyte membrane in the anolyte cell to be a distance that allows sufficient movement of ions in the electrolyte solution when the electrolyte solution is stored in the anolyte cell. In the carbon dioxide electrolysis cell of the present disclosure, the ions in the electrolyte solution can be sufficiently moved between the anode separator and the electrolyte membrane, facilitating the carbon dioxide reduction reaction and increasing the efficiency of methane production. From the above, it is presumed that the carbon dioxide electrolysis cell of the present disclosure has high methane selectivity.

[0020] On the other hand, although the technologies described in Patent Documents 1 to 5 all involve reducing carbon dioxide to synthesize methane, they differ from the technology disclosed herein in that they do not relate to carbon dioxide electrolysis cells equipped with a mechanism for storing an electrolyte solution 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 permeation of the electrolyte solution into the electrolyte membrane.

[0021] An overview of the carbon dioxide electrolysis cell of the present disclosure will now be described with reference to the drawings. Figure 1 is a schematic diagram illustrating the configuration of a carbon dioxide electrolysis cell according to an embodiment of the present disclosure. 1, a carbon dioxide electrolysis cell 1 according to this embodiment of the present disclosure includes, in order from the top, 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, the current collector plate 20, and the fastening plate 10. Between the anode separator 30 and the electrolyte membrane 60, the frame member 40 forms a space (a so-called anolyte cell) in which an electrolyte solution can be stored.

[0022] The anode separator 30 has a flow path through which the electrolyte flows. The anode separator 30 is a metal plate measuring 8 cm × 8 cm, and has a flow path section 32 in which lattice-shaped flow paths are provided at a pitch of 1 mm within a 3 cm square area at the center of the surface facing the frame member 40, and is equipped with a mechanism for circulating the electrolyte introduced into the anode separator 30 via an anolyte cell. In the carbon dioxide electrolysis cell 1, the anode separator 30 is formed from a material that functions as an anode catalyst, and also serves as an anode catalyst layer.

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

[0024] The electrolyte membrane 60 is an anion exchange membrane having a size of 4 cm×4 cm and a thickness of 50 μm. 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 to be water repellent, and a cathode gas diffusion layer (not shown), and is arranged so that the cathode catalyst layer faces the electrolyte membrane 60. The cathode gas diffusion layer has a conductive fiber layer (not shown) and a microporous layer (not shown) that is a porous body formed from conductive particles, and is arranged so that the conductive fiber layer faces the cathode separator 80.

[0026] The cathode separator 80 has a flow path for supplying carbon dioxide and a flow path for discharging methane, etc. The cathode separator 80 is a metal plate measuring 8 cm x 8 cm, and has a flow path section 82 in which lattice-shaped flow paths are provided at a pitch of 1 mm within a 3 cm square area at 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 anolyte cell during the circulation process. The electrolyte is constantly stored in the anolyte cell while being replaced, allowing the electrolyte to sufficiently 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 is reduced together with the electrolyte that has permeated the electrolyte membrane 60 by the addition of electricity, and methane (CH4) and other gases are synthesized.

[0028] The fastening plates 10 are a pair of plate-like members that are used to bond and fix the constituent materials together after they have been stacked. The current collector plate 20 is a plate-shaped member for applying a voltage to the carbon dioxide electrolysis cell and extracting the generated current to the outside. The gasket 50 is an insulating plate measuring 8 cm x 8 cm and 200 μm thick, and has an opening in the center thereof that has 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 solution is prevented.

[0029] The carbon dioxide electrolysis cell of the present disclosure synthesizes methane through a reduction reaction of carbon dioxide. In the carbon dioxide electrolysis cell of the present disclosure, an electrolyte is supplied to the anode side (i.e., the electrolyte membrane side) of the electrode assembly, carbon dioxide is supplied to the cathode side (i.e., the cathode gas diffusion layer side) of the electrode assembly, 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 electrolysis cell of the present disclosure, the reduction reaction of carbon dioxide is preferably carried out in a temperature environment of, for example, more than 0°C and 50°C or less. In a temperature environment above 0°C, the electrolyte is prevented from freezing. In a temperature environment below 50°C, the production rate of by-products other than methane (especially hydrogen) tends to decrease, while the production rate of methane tends to increase. The reason for this is thought to be that the suppression of hydrogen production improves the efficiency of energy conversion to methane. The reduction reaction of carbon dioxide is more preferably carried out in a temperature environment of more than 0°C and not more than 40°C, and even more preferably in a temperature environment of more than 0°C and not more than 30°C.

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

[0031] The method for 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 for applying electricity is not particularly limited, but it is preferable to apply a voltage to the cathode gas diffusion layer side so that the potential between the working electrode and the reference electrode is −0.9V to −3.0V, for example.

[0033] Each component of the carbon dioxide electrolysis cell of the present disclosure will be described in detail below.

[0034] [Anode separator] The anode separator has a flow path through which the electrolyte flows. The anode separator preferably has a flow path on the surface facing the frame member, which allows the electrolyte to flow through the anolyte cell. The shape of the flow path portion is not particularly limited, and examples of the shape of the flow path portion include a rectangle (for example, a square or a rectangle), a polygon (excluding a rectangle), a circle, and an ellipse. The size of the flow path portion is not particularly limited, but for example, it is preferably the same as the size of the opening of the frame member (the so-called inner frame) or smaller than the size of the opening of the frame member, and more preferably the same as the size of the opening of the frame member. The shape of the flow channels provided in the flow channel section is not particularly limited, and examples thereof include a lattice shape and a mesh shape. When the flow channels have a lattice shape, the pitch of the flow channels 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 may be, for example, titanium, stainless steel, or carbon. For example, from the viewpoint of suppressing oxidation due to oxygen generated on the anode side, the material of the anode separator is preferably a material containing at least titanium. The anode separator may be coated with a corrosion-resistant conductive material (so-called coating material) to prevent the anode separator from increasing in resistance due to oxidation. Examples of the coating material 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 member] From the viewpoint of methane selectivity, the frame member has a thickness of 2 mm to 10 mm. When the thickness of the frame member is 2 mm or more, the anolyte cell can store an amount of electrolyte that allows it to fully permeate the electrolyte membrane, which is thought to prevent a decrease in methane selectivity due to insufficient permeation. When the thickness of the frame member is 10 mm or less, the distance between the anode separator and the electrolyte membrane in the anolyte cell is large enough to allow sufficient movement of ions in the electrolyte when the electrolyte is stored in the anolyte cell. This allows sufficient movement of ions in the electrolyte between the anode separator and the electrolyte membrane, which is thought to facilitate the progress of the carbon dioxide reduction reaction and increase the efficiency of methane production. In one embodiment, the thickness of the frame member may be 2 mm to 8 mm, 2 mm to 6 mm, or 2 mm to 4 mm.

[0038] The thickness of the frame member means the average thickness of the frame member. The average thickness of the frame member is a value determined by the following method. The thickness of the frame member is measured using a digital caliper at eight randomly selected locations in the thickness direction (for example, if the outer frame of the frame member is rectangular, two randomly selected locations on each of the four sides). The arithmetic mean of the measured values ​​is calculated, and this value is taken as the average thickness of the frame member.

[0039] The shape of the opening of the frame member (so-called inner frame) is not particularly limited. The shape of the opening of the frame member may be the same as or different from the shape of the electrolyte membrane, but is preferably the same. Examples of the shape of the opening of the frame member include a rectangle (e.g., a square or a rectangle), a polygon (excluding a rectangle), a circle, an ellipse, etc.

[0040] From the viewpoint of efficient supply of the electrolyte, the area of ​​the opening of the frame member is preferably in the range of 80% to less than 120%, and more preferably in the range of 90% to 110%, of the area of ​​the flow path portion of the separator. In the present disclosure, the 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 appropriately determined according to the shape and size of the desired carbon dioxide electrolysis cell.

[0042] The material of the frame member is not particularly limited, but is preferably, for example, an insulating material. Examples of insulating materials include resin, glass, ceramic, and rubber. The insulating material preferably includes one of polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE), more preferably includes polyetheretherketone, and even more preferably is polyetheretherketone.

[0043] The frame member may also function as a gasket. By using a material that functions as a gasket for the frame member, it is possible to impart the frame member with 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 electrolysis cells. The ion exchange membrane type electrolyte membrane may have the property of selectively permeating cations or the property of selectively permeating anions, but it is preferable that it has the property of selectively permeating anions, i.e., it is an anion exchange membrane. The electrolyte membrane may be, for example, a polymer electrolyte membrane. 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 thickness of the electrolyte membrane means the average thickness of the electrolyte membrane. The average thickness of the electrolyte membrane is a value determined by the following method. The cross section of the electrolyte membrane is observed using a scanning electron microscope (SEM). The thickness of the electrolyte membrane is measured at six randomly selected locations in the thickness direction. The arithmetic mean of the measured values ​​is calculated, and this value is used as the average thickness of the electrolyte membrane.

[0047] As the electrolyte membrane, a commercially available product can be used. Examples of commercially available electrolyte membranes include "Nafion" (registered trademark) (manufactured by Chemours Corporation), "Flemion" (registered trademark) (manufactured by AGC Corporation), "Neosepta" (registered trademark) (manufactured by Atoms Corporation), "Selemion" (registered trademark) (manufactured by AGC Corporation), and "Sustainion" (registered trademark) (manufactured by Dioxide Materials Corporation).

[0048] [Cathode catalyst layer] The cathode catalyst layer is a layer containing a cathode catalyst. The cathode catalyst promotes 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 the cathode catalyst include metals such as Cu, Pt, Ag, Zn, Sn, and Al, or alloys thereof. The cathode catalyst is preferably 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 the present disclosure, a layer containing Cu particles is also referred to as a "Cu particle layer." The Cu particle layer is preferably a layer made of Cu particles.

[0049] When the cathode catalyst is 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 the Cu particles means the average primary particle size of the Cu particles. The average primary particle size of Cu particles is a value 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 to be water-repellent. The presence of excess water on the catalyst promotes hydrogen production, which can result in excessive energy consumption. However, if the cathode catalyst layer is treated to be water-repellent, water is appropriately removed from the catalyst, suppressing hydrogen production. This reduces the energy consumption required for methane synthesis and tends to result in more selective methane synthesis. The water-repellent treatment applied to the cathode catalyst layer is not particularly limited. The water-repellent treatment can be a known water-repellent treatment. An example of the water-repellent treatment is the formation of a water-repellent film. The water-repellent film may be, for example, a film made of a fluororesin 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 the cathode catalyst layer, but is preferably applied to the entire cathode catalyst 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 means the average thickness of the cathode catalyst layer. The average thickness of the cathode catalyst layer is a value determined by the following method. The cross section of the cathode catalyst layer is observed using a scanning electron microscope (SEM). The thickness of the cathode catalyst layer is measured at six randomly selected locations in the thickness direction. The arithmetic mean of the measured values ​​is calculated, and this value is used 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 the cathode catalyst layer will be described by taking as an example a case where the cathode catalyst layer is a layer containing Cu particles as the cathode catalyst (that is, a Cu particle layer). The cathode catalyst layer, which is a Cu particle layer, can be formed, for example, by attaching Cu particles to one surface of the cathode gas diffusion layer (if the cathode gas diffusion layer has an MPL, the surface on the MPL side) using an arc plasma method. Forming a Cu particle layer using the arc plasma method tends to produce a cathode catalyst layer that can produce methane more efficiently. The arc plasma method is a gas-phase method that generates metal nanoparticles by vaporizing metals through a high-temperature arc discharge between two electrodes. In the arc plasma method, the metal is evaporated by the plasma generated between the two electrodes. The generated metal vapor then cools while reacting with the ambient gas, growing into nano-sized particles. Therefore, the arc plasma method can form a Cu particle layer with nano-sized Cu particles attached to one side of the cathode gas diffusion layer (the MPL-side surface, if the cathode gas diffusion layer has an MPL). The smaller the particle diameter of the Cu particles that make up the Cu particle layer, the greater the contact area with carbon dioxide, which effectively functions as a catalyst, leading to more efficient methane production.

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

[0056] [Cathode gas diffusion layer] For the cathode gas diffusion layer, a member used as a cathode gas diffusion layer in a known carbon dioxide electrolysis cell can be applied. For example, the cathode gas diffusion layer may be made of a material that is electrically conductive and allows fluids (e.g., gases and liquids; the same applies hereinafter) to pass through the layer. Examples of such materials include porous bodies, sintered powder bodies, and sintered fiber bodies made of electrically conductive materials. The conductive material is preferably a conductive fiber. Specific examples of conductive fibers include carbon fibers and titanium fibers. The carbon fiber and titanium fiber may both be sintered. The conductive fiber is preferably a carbon fiber. As the carbon fiber, graphite fiber is preferred.

[0057] When the cathode gas diffusion layer is a layer formed of conductive fibers (also referred to as a "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 is, for example, 0.10 g / cm 3 ~1.00g / cm 3 It is preferable that:

[0059] The density of the 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, for example.

[0061] The thickness of the conductive fiber layer means the average thickness of the conductive fiber layer. The average thickness of the conductive fiber layer is a value determined by the following method. The cross section of the conductive fiber layer is observed using a scanning electron microscope (SEM). The thickness of the conductive fiber layer is measured at six randomly selected locations in the thickness direction. The arithmetic mean of the measured values ​​is calculated, and the obtained value is 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) formed on the conductive fiber layer and composed of conductive particles. When the cathode gas diffusion layer comprises an MPL on the conductive fiber layer, the number of contact points between carbon dioxide, the catalyst in the cathode catalyst layer, and the electrolyte membrane increases, so that the carbon dioxide reduction reaction can proceed more efficiently. In an embodiment in which the cathode gas diffusion layer has an MPL on the conductive fiber layer, the MPL is preferably provided on the surface facing the cathode catalyst layer. When the MPL is provided on the surface facing the cathode catalyst layer, carbon dioxide tends to 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 selectively and efficiently produced.

[0063] The conductive particles are not particularly limited as long as they contain a material having conductivity. 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. The conductive particles are preferably carbon particles. As the carbon particles, graphite particles are preferred.

[0064] The shape of the conductive particles is not particularly limited. The shape of the conductive particles may be, for example, spherical (eg, perfect sphere or oval sphere), plate-like, or irregular.

[0065] The particle diameter of the conductive particles is preferably 50 nm or more, for example, from the viewpoint of forming pores large enough to allow good fluid flow. In one embodiment, the particle diameter of the conductive particles may be 50 nm to 500 nm, or may be 50 nm to 200 nm.

[0066] The particle size of the conductive particles means the average primary particle size of the conductive particles. The average primary particle diameter of the conductive particles is a value determined by image analysis of the primary particles of the 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 MPL is not particularly limited. The shape of the holes may be, for example, circular (for example, perfect circle or ellipse), rectangular, or irregular.

[0068] The size of the pores in the porous MPL (also referred to as the "pore diameter of the MPL") is not particularly limited as long as it allows fluid to pass through. The pore size of the MPL is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, and, for example, preferably 3.0 μm or less, more preferably 1.0 μm or less. In one embodiment, the pore size of the MPL may be 0.01 μm to 3.0 μm, or may be 0.1 μm to 1.0 μm.

[0069] The pore size of the MPL refers to the average pore size of the MPL. The average pore size of the MPL is a value determined by image analysis of the pores in the MPL obtained by observing a cross section of the MPL in the thickness direction 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 the MPL is a value determined by the following method. The cross section of the MPL is observed using a scanning electron microscope (SEM). The thickness of the MPL is measured at six randomly selected locations in the thickness direction. The arithmetic mean of the measured values ​​is calculated, and this value is taken as the average thickness of the MPL.

[0073] The cathode gas diffusion layer may be made of commercially available carbon paper. 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 fiber, which is carbon fiber; thickness: 235 μm; density: 0.45 g / cm). 3 , manufactured by SGL CARBON Co., Ltd.], and Toray Paper TGP-H-060 [trade name, thickness: 190 μm, density: 0.44 g / cm 3 , manufactured by Toray Industries, Inc.

[0074] [Cathode separator] The cathode separator has a flow channel for supplying carbon dioxide and a flow channel for discharging methane. The cathode separator preferably has a flow path on the surface facing the cathode gas diffusion layer, which allows carbon dioxide to be supplied to the cathode catalyst layer. The shape of the flow path portion is not particularly limited, and examples of the shape of the flow path portion include a rectangle (for example, a square or a rectangle), a polygon (excluding a rectangle), a circle, and an ellipse. The size of the flow path portion is not particularly limited, but is preferably the same as 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 flow path provided in the flow path section is not particularly limited, and examples thereof include a lattice shape and a mesh shape. The flow path is preferably lattice-shaped. When the flow path is lattice-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 efficiently proceed the reduction reaction of carbon dioxide and enable methane to be selectively and efficiently produced. When the flow paths are in the form of a lattice, the pitch of the flow paths 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 thereof include titanium, stainless steel, and carbon. The material of the cathode separator is preferably a material containing at least titanium. The cathode separator may be coated with a conductive material (so-called coating material), such as platinum, gold, silver, titanium nitride, titanium carbide, and titanium carbonitride.

[0076] [Other configurations] The carbon dioxide electrolysis cell of the present disclosure may further include other features. Other configurations may be selected from known carbon dioxide electrolysis 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 may be members used in known carbon dioxide electrolysis cells. [Example]

[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 appropriately changed without departing from the spirit of the present disclosure.

[0078] [Preparation of carbon dioxide electrolysis cell] [Production Example 1] (1) Preparation of carbon dioxide reduction electrode Carbon paper (CP) [product name: SIGRACET (registered trademark) 28BC, density: 0.45 g / cm 3 A 5 cm square piece of CP (235 μm thick, manufactured by SGL CARBON) was cut out and used as a cathode gas diffusion layer. The CP consisted of a conductive fiber layer made of sintered carbon fiber and a microporous layer (MPL) made of graphite particles on top of it. Next, Cu particles were deposited on the MPL side of the cut CP by arc plasma deposition using an arc plasma device (product name: Arc Plasma Nanoparticle Formation Device, model: APD-1S-C, manufactured by Advance Riko Co., Ltd.). Specifically, the cut CP was placed in the arc plasma device using imide tape so that the MPL side was exposed. Cu was then evaporated in a vacuum to generate Cu particles, which were then attached to the MPL side of the CP. The arc plasma conditions were set to a voltage of 120 V, a capacitor capacitance of 1080 μF, and 500 discharge cycles. As described above, first, a laminate having a layer structure of cathode gas diffusion layer (conductive fiber layer / MPL) / cathode catalyst layer (Cu particle layer) was produced. The laminate was then cut into 4.0 cm square pieces. Polytetrafluoroethylene (PTFE) [product name: Fusso Placoat, product number: FC-115, manufactured by Fine Chemical Japan Co., Ltd.] was then sprayed onto both sides of the cut laminate using a spray coating method, and the laminate was then dried at room temperature (25°C) for 15 minutes. In this way, a carbon dioxide reduction electrode was fabricated. The fabricated carbon dioxide reduction electrode had a layer structure of a cathode gas diffusion layer (conductive fiber layer / MPL) / cathode catalyst layer (Cu particle layer), and both sides of the cathode catalyst layer were treated with PTFE to make them water-repellent.

[0079] (2) Preparation of the electrode body An electrode assembly was fabricated using the carbon dioxide reduction electrode fabricated above and an electrolyte. First, the electrolyte was subjected to the following pretreatment. An electrolyte (trade name: Sustainion (registered trademark) X37-50 Grade 60 Membrane, an anion exchange membrane, thickness: 50 μm, manufactured by Dioxide Materials) was immersed in an electrolyte solution (trade 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 the surface of the electrolyte was washed with pure water. Next, the pretreated electrolyte and the carbon dioxide reduction electrode were overlapped so that the electrolyte and the surface of the cathode catalyst layer of the carbon dioxide reduction electrode on the Cu particle layer side were in contact with each other, and then press-molded at room temperature (25°C) using a press (product name: small heat press, model: H300-05, manufactured by AS ONE Corporation; the same applies hereinafter). In this manner, an electrode assembly was fabricated. The pressing conditions were a pressure of 5 MPa and a pressing time of 5 minutes. To keep the electrolyte moist, Kimwipes (registered trademark) moistened with pure water were placed in contact with the surface of the electrolyte that was not overlapped with the carbon dioxide reduction electrode during press-molding. The fabricated electrode assembly had a layer structure of a carbon dioxide reduction electrode [cathode gas diffusion layer (conductive fiber layer / MPL) / water-repellent-treated cathode catalyst layer] / electrolyte.

[0080] (3) Preparation of carbon dioxide electrolysis cell The electrode assembly prepared above was incorporated into a gas diffusion-type full cell to produce a carbon dioxide electrolysis cell. Specifically, a separator, a current collector, and a fastening plate were laminated in this order on both sides of the electrode assembly, and a frame member was sandwiched between the anode-side separator (the so-called anode separator) and the electrolyte provided in the electrode assembly via a gasket, thereby producing the carbon dioxide electrolysis cell of Production Example 1. As shown in FIG. 1 , the carbon dioxide electrolysis cell of Production Example 1 has a configuration of fastening plate / current collector / cathode separator / electrode assembly [carbon dioxide reduction electrode [cathode gas diffusion layer (conductive fiber layer / MPL) / cathode catalyst layer with water-repellent treatment] / electrolyte] / gasket / frame member / anode separator / current collector / fastening plate. Both the cathode separator and the anode separator have a flow path section with a lattice-like flow path arranged at a pitch of 1 mm within a 3 cm square area at the center of the metal plate, and each is equipped with a mechanism for supplying gas and liquid while diffusing them. The frame member has an opening in the center of a 2 mm thick insulating plate with the same area as the flow path section of the anode separator, and by placing it between the anode separator and the electrolyte, it forms an anolyte cell, which is a space where the electrolyte is stored. The electrolyte stored in the anolyte cell is constantly replaced by supply from and discharge to the outside. The details of each component of the carbon dioxide electrolysis cell of Production Example 1 are shown below.

[0081] ·Electrolytes Size: 4cm x 4cm Thickness: 50 μm Carbon dioxide reduction electrode Size: 4cm x 4cm Cathode gas diffusion layer thickness: 235 μm Anolite Cells Material: Polyetheretherketone (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 Flow path area: 3cm x 3cm Flow path pitch: 1 mm Flow path shape: Slit-shaped Current collector plate Material: Gold (Au) plated copper (Cu) Fastening plate Material: Stainless steel

[0082] [Comparative Production Example 1] A carbon dioxide electrolysis cell of Comparative Production Example 1 was prepared in the same manner as Production Example 1, except that an anolyte cell was not used.

[0083] [Comparative Production Example 2] A carbon dioxide electrolysis cell of Comparative Production Example 2 was produced in the same manner as Production Example 1, except that the thickness of the anolyte cell was changed from "2 mm" to "15 mm."

[0084] [Evaluation of methane selectivity (1)] <Example 1-1> A carbon dioxide electrolysis cell was prepared as shown in Production Example 1, and the following evaluations were carried out. The electrolyte used was a 1 mol / L KHCO3 aqueous solution. The KHCO3 aqueous solution was first bubbled with CO2 gas (purity: 99.99%) and then adjusted to a pH of 7.7 before use. A Cu electrode was used as the working electrode (WE), an Ag / AgCl electrode was used as the reference electrode (RE), and a Pt-plated Ti electrode was used as the counter electrode (CE).

[0085] The electrolyte was filled into a tank connected to the anode line. CO2 gas (purity: 99.99%) was constantly bubbled into the electrolyte in the tank to maintain a constant pH. CO2 gas (purity: 99.99%) was flowed at a flow rate of 5 ml / min to the cathode gas diffusion layer side of the carbon dioxide reduction electrode at a temperature of 25°C, and the gas in the carbon dioxide electrolysis cell was replaced with CO2 gas. At the same time, the electrolyte in the tank was flowed at a flow rate of 6 ml / min and circulated to the anode line. After sufficient gas replacement in the carbon dioxide electrolysis cell, a voltage was applied so that the potential difference between the working electrode and the reference electrode was -1.4 V. After starting the application of voltage and confirming that current was flowing, the product gas was collected for 1 minute in a sample bag installed after the cathode outlet of the carbon dioxide electrolysis cell. The line was then switched to the exhaust line, and the flow rate (unit: ml / min) of the product gas was measured three times using a flow meter (trade name: Defender (registered trademark) 530+, manufactured by Mesa Labs). The arithmetic mean value of the measured values ​​was calculated, and the obtained value was used as the measurement result of the product gas flow rate. Next, the sample bag containing the collected product gas was connected to a gas chromatograph (trade name: Nexis (registered trademark) GC-2030, manufactured by Shimadzu Corporation). The product gas was passed through the flow path of the gas chromatograph and introduced into a column (trade name: Micropacked-ST, manufactured by Shinwa Chemical Industry Co., Ltd.), and the composition of the product gas was analyzed.

[0086] From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, the amounts of hydrogen (H), carbon monoxide (CO), methane (CH), and ethylene (CH) produced were calculated and converted into electric charge. The production efficiency of hydrogen, carbon monoxide, methane, and ethylene (so-called Faraday efficiency) was calculated from the ratio of the converted electric charge to the actual current value. The composition of the produced gas and the Faraday efficiency of each component are shown in Table 1 and FIG.

[0087] The faradaic efficiency indicates the proportion of the current used in the reaction to the product, and the higher the faradaic efficiency (unit: %) for methane, the higher the methane selectivity of the carbon dioxide electrolysis cell can be evaluated.

[0088] <Comparative Example 1-1> A carbon dioxide electrolytic cell was prepared as shown in Comparative Production Example 1, and the flow rate of the produced gas and the composition of the produced gas were analyzed in the same manner as in Example 1-1, except that this prepared carbon dioxide electrolytic cell was used. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 1 and FIG.

[0089] <Comparative Example 2-1> A carbon dioxide electrolytic cell was prepared as shown in Comparative Production Example 2, and the flow rate of the produced gas and the composition of the produced gas were analyzed in the same manner as in Example 1-1, except that this prepared carbon dioxide electrolytic cell was used. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 1 and FIG.

[0090] <Example 1-2> A carbon dioxide electrolysis cell was prepared as shown in Production Example 1. The flow rate of the produced gas was measured and the composition of the produced gas was analyzed in the same manner as in Example 1-1, except that a voltage was applied so that the potential difference between the working electrode and the reference electrode was −2.0 V. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 2 and FIG.

[0091] <Comparative Example 1-2> A carbon dioxide electrolytic cell was prepared as shown in Comparative Production Example 1, and the flow rate of the produced gas and the composition of the produced gas were analyzed in the same manner as in Example 1-2, except that this prepared carbon dioxide electrolytic cell was used. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 2 and FIG.

[0092] <Comparative Example 2-2> A carbon dioxide electrolytic cell was prepared as shown in Comparative Production Example 2, and the flow rate of the produced gas and the composition of the produced gas were measured and analyzed in the same manner as in Example 1-2, except that this prepared carbon dioxide electrolytic cell was used. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 2 and FIG.

[0093] <Examples 1-3> A carbon dioxide electrolysis cell was prepared as shown in Production Example 1. The flow rate of the produced gas was measured and the composition of the produced gas was analyzed in the same manner as in Example 1-1, except that a voltage was applied so that the potential difference between the working electrode and the reference electrode was −2.5 V. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 3 and FIG.

[0094] <Comparative Example 1-3> A carbon dioxide electrolytic cell was prepared as shown in Comparative Production Example 1, and the flow rate of the produced gas and the composition of the produced gas were measured and analyzed in the same manner as in Example 1-3, except that this prepared carbon dioxide electrolytic cell was used. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 3 and FIG.

[0095] <Comparative Example 2-3> A carbon dioxide electrolytic cell was prepared as shown in Comparative Production Example 2, and the flow rate of the produced gas and the composition of the produced gas were measured and analyzed in the same manner as in Example 1-3, except that this prepared carbon dioxide electrolytic cell was used. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 3 and FIG.

[0096] [Table 1]

[0097] [Table 2]

[0098] [Table 3]

[0099] 2 to 4, the carbon dioxide electrolytic cells of the Examples (Production Examples 1 and 2) exhibited higher faradaic efficiencies for methane than the carbon dioxide electrolytic cells of the Comparative Examples (Comparative Production Examples 1 and 2) at all potential differences. From the above, it is clear that the carbon dioxide electrolytic cells of the present disclosure have high methane selectivity.

[0100] [Evaluation of methane selectivity (2)] <Examples 1-4> A carbon dioxide electrolysis cell was prepared as shown in Production Example 1. The flow rate of the produced gas was measured and the composition of the produced gas was analyzed in the same manner as in Example 1-1, except that CO gas (purity: 99.99%) was flowed into the cathode gas diffusion layer side of the carbon dioxide reduction electrode in a temperature environment of 5°C. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 4 and FIG.

[0101] <Examples 1-5> A carbon dioxide electrolysis cell was prepared as shown in Production Example 1. The flow rate of the produced gas was measured and the composition of the produced gas was analyzed in the same manner as in Example 1-2, except that CO gas (purity: 99.99%) was flowed into the cathode gas diffusion layer side of the carbon dioxide reduction electrode in a temperature environment of 5°C. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 4 and FIG.

[0102] <Examples 1-6> A carbon dioxide electrolysis cell was prepared as shown in Production Example 1. The flow rate of the produced gas was measured and the composition of the produced gas was analyzed in the same manner as in Example 1-3, except that CO gas (purity: 99.99%) was flowed into the cathode gas diffusion layer side of the carbon dioxide reduction electrode in a temperature environment of 5°C. From the measurement results of the flow rate of the produced gas and the analysis results of the composition of the produced gas, 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 produced gas and the Faraday efficiency of each component are shown in Table 4 and FIG.

[0103] [Table 4]

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

[0105] The results shown in Table 4 and FIG. 5 reveal that in the carbon dioxide electrolysis cell of the present disclosure, methane can be synthesized more selectively when the carbon dioxide reduction reaction is performed in a temperature environment of 5°C than when it is performed in a temperature environment of 25°C. [Explanation of symbols]

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

Claims

1. A carbon dioxide electrolysis cell for methane synthesis that synthesizes methane by a reduction reaction of carbon dioxide, comprising: an anode separator having a flow path through which an electrolytic 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; a cathode separator having a flow path for supplying the carbon dioxide and a flow path for discharging the methane; In this order, a space capable of storing the electrolytic solution is formed between the anode separator and the electrolyte membrane by the frame member; the anode separator is a metal plate containing at least titanium, and has a flow path portion on a surface facing the frame member that allows the electrolyte solution to flow therethrough, and is equipped with a mechanism for circulating the electrolyte solution introduced into the anode separator through a space capable of storing the electrolyte solution, the cathode separator is a metal plate containing at least titanium, the metal plate having a flow path portion on the surface facing the cathode gas diffusion layer, the flow path portion enabling the supply of carbon dioxide to at least the cathode catalyst layer.

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

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

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

5. 3. The carbon dioxide electrolysis cell for methane synthesis according to claim 1, wherein the carbon dioxide reduction reaction is carried out in a temperature environment of more than 0°C and not more than 50°C.

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