Carbon dioxide reduction electrode for methane synthesis, manufacturing method of the same, and carbon dioxide electrolysis cell for methane synthesis

Abstract

To provide a carbon dioxide reduction electrode for methane synthesis having high methane selectivity.SOLUTION: Provided are a carbon dioxide reduction electrode for methane synthesis, a method for producing the same, and a carbon dioxide electrolysis cell for methane synthesis. The carbon dioxide reduction electrode for methane synthesis comprises a cathode gas diffusion layer and a cathode catalyst layer in this order. The cathode catalyst layer has a layer containing Cu particles and a layer provided on a part of the layer containing Cu particles and containing at least one kind of metal particles selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles, in this order from the cathode gas diffusion layer side.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a carbon dioxide reduction electrode for methane synthesis, a method for manufacturing the same, and a carbon dioxide electrolysis cell for methane synthesis.

Background Art

[0002] Methane (CH 4 ) can be synthesized by applying electricity to carbon dioxide (CO 2 ) and water (H 2 O) and allowing a reduction reaction of carbon dioxide to proceed on a catalyst. Various reports have been made on the technology of reducing carbon dioxide to synthesize methane.

[0003] For example, Patent Document 1 discloses a technique using a carbon dioxide reduction electrode including a conductive substrate and a catalyst layer provided on the conductive substrate, the catalyst layer including a carbon dioxide reduction catalyst supported on carbon black, and the carbon dioxide reduction catalyst being Cu(II) tetraphenylporphyrin having a specific structure. Patent Document 2 discloses a technique using a semiconductor element having an electrode layer, a first semiconductor layer, and a second semiconductor layer having first and second surfaces facing each other, the electrode layer being provided in contact with the first surface, the first semiconductor layer being provided in contact with the second surface, the lower end potential of the conduction band of the first semiconductor layer being higher than the hydrogen generation potential, the upper end potential of the valence band of the second semiconductor layer being lower than the oxygen generation potential, the band gap of the first semiconductor layer being larger than the band gap of the second semiconductor layer, and a metal being discretely supported as a cocatalyst on the surface of the first semiconductor layer. Patent Document 3 discloses a technique using a reduction catalyst including a current collector having a metal layer containing metal fine particles on the surface and a modified organic molecule bonded to the surface of the metal layer and containing a quaternary nitrogen cation. Patent Document 4 discloses a carbon dioxide absorption and reduction type catalyst used for producing methane from carbon dioxide and hydrogen, which contains magnesium, and includes a powder of a carbon dioxide absorbent that absorbs carbon dioxide and a powder of a methanation catalyst that produces methane from carbon dioxide and hydrogen by a catalytic reaction. A technique using a carbon dioxide absorption and reduction type catalyst in which the powder of the carbon dioxide absorbent and the powder of the methanation catalyst are accommodated in a container in a mixed state is disclosed. Patent Document 5 discloses a microreactor having a microchannel through which a gaseous raw material and a liquid raw material are circulated as reaction raw materials, a gaseous raw material feeding means for feeding the gaseous raw material into the microchannel, a liquid raw material feeding means for feeding the liquid raw material into the microchannel, and a photocatalyst layer provided on the inner surface of the microchannel. The gaseous raw material is carbon dioxide, the liquid raw material is a raw material capable of reacting with carbon dioxide to produce an organic compound, the photocatalyst layer is a layer formed by dispersing and supporting one specific metal as a cocatalyst on titanium dioxide, and the gaseous raw material feeding means and the liquid raw material feeding means are configured to be able to form a pipe flow in which the liquid raw material flows along the inner surface of the microchannel and carbon dioxide flows through the central part. A technique using a carbon dioxide immobilization device is disclosed.

Prior Art Documents

Patent Documents

[0004]

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

[0005] So far, as a method for synthesizing methane, CO is dissolved in an aqueous solution 2 gas, and the dissolved CO 2 is electrolyzed, which has been the mainstream method. However, with this method, the amount of methane that can be synthesized at one time is limited. Therefore, in recent years, a method of reacting CO 2 as a gas to synthesize methane has been adopted. According to this method, although a large amount of methane can be synthesized at one time, by-products other than methane are likely to be generated, and there are still problems in terms of the production efficiency of methane. For this reason, the development of a technology capable of selectively synthesizing methane is desired.

[0006] The problem to be solved by one embodiment of the present disclosure is to provide a carbon dioxide reduction electrode for methane synthesis with high methane selectivity. Another problem to be solved by another embodiment of the present disclosure is to provide a method for manufacturing the carbon dioxide reduction electrode for methane synthesis. Moreover, another problem to be solved by another embodiment of the present disclosure is to provide a carbon dioxide electrolysis cell for methane synthesis including the carbon dioxide reduction electrode for methane synthesis.

Means for Solving the Problems

[0007] Specific means for solving the problems include the following aspects. <1> A carbon dioxide reduction electrode for methane synthesis having a cathode gas diffusion layer and a cathode catalyst layer in this order, wherein the cathode catalyst layer has, in this order from the cathode gas diffusion layer side, a layer containing Cu particles and a layer provided on a part of the layer containing Cu particles and containing at least one kind of metal particles selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles. <2> The carbon dioxide reduction electrode for methane synthesis according to <1>, wherein the layer containing the metal particles is a layer containing at least one kind of metal particles selected from Ag particles and Zn particles. <3>The area ratio in plan view of the layer containing the metal particles occupying on the layer containing the Cu particles is 15% to 80%, which is the carbon dioxide reduction electrode for methane synthesis according to <1> or <2>. <4>The contour length in plan view of the layer containing the metal particles per unit area in plan view of the layer containing the Cu particles is 1.0 μm / μm 2 ~3.0 μm / μm 2 which is the carbon dioxide reduction electrode for methane synthesis according to any one of <1> to <3>. <5> A method for manufacturing a carbon dioxide reduction electrode for methane synthesis according to any one of <1> to <4>, comprising: forming a layer containing the Cu particles by attaching Cu particles to one surface of a cathode gas diffusion layer by an arc plasma method; forming a layer containing the metal particles by attaching at least one kind of metal particles selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles to a part of the surface of the layer containing the Cu particles on the side opposite to the cathode gas diffusion layer side by an electrodeposition method or an ion exchange method; and a method for manufacturing a carbon dioxide reduction electrode for methane synthesis. <6> A carbon dioxide electrolysis cell for methane synthesis comprising the carbon dioxide reduction electrode for methane synthesis according to any one of <1> to <4>, an electrolyte, and an anode electrode.

Advantages of the Invention

[0008] According to one embodiment of the present disclosure, a carbon dioxide reduction electrode for methane synthesis with high methane selectivity is provided. According to another embodiment of the present disclosure, a method for manufacturing the carbon dioxide reduction electrode for methane synthesis is provided. Also, according to another embodiment of the present disclosure, a carbon dioxide electrolysis cell for methane synthesis comprising the carbon dioxide reduction electrode for methane synthesis is provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0010] 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. The ratio of dimensions in the drawings does not necessarily represent the ratio of actual dimensions.

[0011] In the present disclosure, a numerical range represented using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0012] In the numerical ranges described stepwise 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 stepwise 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 stepwise descriptions. In the numerical ranges described stepwise 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, a 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 the case where it cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved.

[0015] [Carbon Dioxide Reduction Electrode for Methane Synthesis] The carbon dioxide reduction electrode for methane synthesis of the present disclosure (hereinafter, also simply referred to as "carbon dioxide reduction electrode") has a cathode gas diffusion layer and a cathode catalyst layer in this order, and the cathode catalyst layer includes a layer containing Cu particles and a layer provided on a part of the layer containing Cu particles and containing at least one kind of metal particles selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles, in this order from the cathode gas diffusion layer side. The carbon dioxide reduction electrode of the present disclosure has the characteristic of high methane selectivity. The present inventors have found that a combination of Cu and a specific metal other than Cu as a metal catalyst in the cathode catalyst layer is effective for selectively synthesizing methane. The carbon dioxide reduction electrode of the present disclosure has a structure in which a layer containing at least one kind of metal particles selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles is laminated on a part of the layer containing Cu particles in the cathode catalyst layer, and by having the layer containing Cu particles on the cathode gas diffusion layer side, for example, compared with the case of using Cu alone, which is a metal known to have high methane selectivity conventionally, methane can be synthesized more selectively.

[0016] On the other hand, none of the layers containing the catalysts described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2021-7919), Patent Document 2 (International Publication No. 2012 / 137240), Patent Document 3 (Japanese Patent Application Laid-Open No. 2015-132012), Patent Document 4 (Japanese Patent Application Laid-Open No. 2020-163248), and Patent Document 5 (Japanese Patent Application Laid-Open No. 2009-29811) has a layer containing at least one kind of metal particles selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles on a part of the layer containing Cu particles. So far, there has been no report focusing on the relationship between the laminated structure of a layer containing Cu particles and a layer containing particles of a specific metal other than Cu in the catalyst layer for reducing carbon dioxide and the selective synthesis of methane.

[0017] In the present disclosure, the "layer containing Cu particles" is also referred to as the "Cu particle layer". In the present disclosure, a "layer containing at least one kind of metal particle selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles" is also referred to as a "specific metal particle layer", a "layer containing Ag particles" is also referred to as an "Ag particle layer", a "layer containing Zn particles" is also referred to as a "Zn particle layer", a "layer containing Sn particles" is also referred to as a "Sn particle layer", and a "layer containing Al particles" is also referred to as an "Al particle layer". In addition, in the present disclosure, "at least one kind of metal particle selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles" may be collectively referred to as "specific metal particles".

[0018] <Cathode gas diffusion layer> The carbon dioxide reduction electrode of the present disclosure has a cathode gas diffusion layer. Members used in a conventionally known carbon dioxide reduction electrode may be applied to the cathode gas diffusion layer. As the cathode gas diffusion layer, a material that enables the flow of fluid within the layer can be used. For example, a porous body, a powder sintered body, and a fiber sintered body formed of a conductive material can be preferably used. As the conductive material, a conductive carbon material is preferable. The cathode gas diffusion layer is preferably a sintered body of carbon fibers, and more preferably a sintered body of graphite fibers. When the cathode gas diffusion layer is a sintered body of carbon fibers (preferably graphite fibers; the same applies hereinafter), the sintered body of carbon fibers preferably has a microporous layer (MPL) formed of a conductive carbon material on its surface. When the cathode gas diffusion layer has an MPL, 2 the contact points between the CO gas, the catalyst of the cathode catalyst layer, and the electrolyte increase, so that the reduction reaction of carbon dioxide can proceed more efficiently. The MPL is preferably formed of a conductive carbon material, and more preferably formed of graphite particles.

[0019] The thickness of the cathode gas diffusion layer is not particularly limited, but for example, it is preferably 100 μm to 300 μm.

[0020] A commercially available carbon paper may be used for the cathode gas diffusion layer. Examples of commercially available carbon papers that can function as the cathode gas diffusion layer include SIGRACET 28BC [trade name, a carbon paper having a microporous layer (MPL) made of graphite particles on a sintered body of graphite fibers which are carbon fibers, thickness: 235 μm, density: 0.45 g / cm 3 , manufactured by SGL CARBON), and Toray Paper TGP-H-060 [trade name, thickness: 190 μm, density: 0.44 g / cm 3 , manufactured by Toray Industries, Inc.].

[0021] <Cathode catalyst layer> The carbon dioxide reduction electrode of the present disclosure has a cathode catalyst layer. The cathode catalyst layer is disposed between the cathode gas diffusion layer and the electrolyte. The cathode catalyst layer has a layer containing Cu particles (i.e., a Cu particle layer) and a layer containing at least one kind of metal particle selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles (i.e., a specific metal particle layer), and the specific metal particle layer is provided on a part of the Cu particle layer. The cathode catalyst layer is disposed with the Cu particle layer on the cathode gas diffusion layer side and the specific metal particle layer on the electrolyte side.

[0022] The Cu particle layer is a layer containing Cu particles, and preferably a layer consisting of Cu particles. The particle diameter of the Cu particles is not particularly limited, but for example, it is preferably 10 nm or less, and more preferably 5 nm to 10 nm. The smaller the particle diameter of the Cu particles, the more the production efficiency of methane tends to improve.

[0023] In the present disclosure, the "particle diameter of Cu particles" means the average particle diameter of Cu particles. The average particle diameter of Cu particles is a value obtained by the following method. Observe the surface of the Cu particle layer using a scanning transmission electron microscope (STEM), and measure the particle diameters of all the Cu particles present in five fields of view with a 200 nm square. Calculate the arithmetic mean value of the measured values, and use the obtained value as the average particle diameter of the Cu particles.

[0024] The thickness of the Cu particle layer is not particularly limited, but for example, it is preferably 300 nm to 400 nm.

[0025] In the present disclosure, the "thickness of the Cu particle layer" means the average thickness of the Cu particle layer. The average thickness of the Cu particle layer is a value obtained by the following method. Observe the cross-section of the Cu particle layer using a scanning transmission electron microscope (STEM). Measure the thicknesses at six randomly selected locations in the thickness direction of the Cu particle layer. Calculate the arithmetic mean value of the measured values, and use the obtained value as the average thickness of the Cu particle layer.

[0026] The Cu particle layer may contain components other than Cu particles as necessary, as long as the effects of the present disclosure are not impaired. Examples of components other than Cu particles include Ag particles, Zn particles, Sn particles, and Al particles.

[0027] The specific metal particle layer is a layer containing at least one kind of metal particle selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles, preferably a layer containing at least one kind of metal particle selected from Ag particles and Zn particles, and more preferably a layer containing Ag particles or Zn particles. Further, the specific metal particle layer may be a layer composed of at least one kind of metal particle selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles. For example, it may be a layer composed of Ag particles and Zn particles, a layer composed of Ag particles, a layer composed of Zn particles, a layer composed of Sn particles, or a layer composed of Al particles.

[0028] The particle diameter of the specific metal particle is not particularly limited, but for example, it is preferably 1 μm or less, and more preferably 5 nm to 20 nm.

[0029] In the present disclosure, the "particle diameter of specific metal particles" means the average particle diameter of specific metal particles. The average particle diameter of specific metal particles is a value obtained by the following method. Observe the surface of the specific metal particle layer using a scanning electron microscope (SEM), and measure the particle diameters of all the specific metal particles present in three fields of view of 1 μm square. Calculate the arithmetic mean value of the measured values, and use the obtained value as the average particle diameter of the specific metal particles.

[0030] The thickness of the specific metal particle layer is not particularly limited, but for example, it is preferably 300 nm to 400 nm.

[0031] In the present disclosure, the "thickness of the specific metal particle layer" means the average thickness of the specific metal particle layer. The average thickness of the specific metal particle layer is a value obtained by the following method. Observe the cross-section of the specific metal particle layer using a scanning transmission electron microscope (STEM). Measure the thicknesses at six randomly selected locations in the thickness direction of the specific metal particle layer. Calculate the arithmetic mean value of the measured values, and use the obtained value as the average thickness of the specific metal particle layer.

[0032] The specific metal particle layer may be provided on a part of the Cu particle layer. The area ratio in plan view of the specific metal particle layer occupying on the Cu particle layer is preferably, for example, 15% to 80%, and more preferably 30% to 65%. When the area ratio in plan view of the specific metal particle layer occupying on the Cu particle layer is within the above range, the methane selectivity tends to be further increased.

[0033] The area ratio of the specific metal particle layer in plan view on the Cu particle layer can be controlled by, for example, electrodeposition conditions when the electrodeposition method is adopted as a method for forming the specific metal particle layer. For example, increasing the amount of electricity for electrodeposition can increase the area ratio of the specific metal particle layer in plan view on the Cu particle layer, and decreasing the amount of electricity for electrodeposition can decrease the area ratio of the specific metal particle layer in plan view on the Cu particle layer.

[0034] The contour length of the specific metal particle layer in plan view per unit area of the Cu particle layer in plan view is, for example, 1.0 μm / μm 2 ~3.0 μm / μm 2 is preferably, and 2.5 μm / μm 2 ~3.0 μm / μm 2 is more preferably. When the contour length of the metal particle layer in plan view per unit area of the Cu particle layer in plan view is within the above range, the methane selectivity tends to be further increased.

[0035] The contour length of the specific metal particle layer in plan view per unit area of the Cu particle layer in plan view can be controlled by, for example, electrodeposition conditions when the electrodeposition method is adopted as a method for forming the specific metal particle layer. For example, optimizing the electrodeposition time can increase the contour length of the specific metal particle layer in plan view per unit area of the Cu particle layer in plan view, and shortening or lengthening the electrodeposition time can decrease the contour length of the specific metal particle layer in plan view per unit area of the Cu particle layer in plan view.

[0036] In the present disclosure, the area ratio of the specific metal particle layer in plan view on the Cu particle layer and the contour length of the specific metal particle layer in plan view per unit area of the Cu particle layer in plan view are measured by the following method. Using a scanning electron microscope equipped with an energy-dispersive X-ray analyzer (SEM-EDS), enlarged elemental mapping images at magnifications of 3000 to 10000 are obtained. Next, the obtained enlarged elemental mapping images are used with image analysis / editing software [product name: Adobe Photoshop, manufactured by Adobe Inc.] to extract the region where the specific metal particle layer exists, and the contour length within the enlarged region area is measured using the functions of the software. As the SEM-EDS, for example, the new Schottky field emission type scanning electron microscope JSM-F100 (product name) manufactured by JEOL Ltd. can be preferably used. However, the SEM-EDS is not limited thereto.

[0037] The specific metal particle layer may contain components other than the specific metal particles, if necessary, as long as the effects of the present disclosure are not impaired. Examples of the components other than the specific metal particles include metal particles other than the specific metal particles (excluding Cu particles).

[0038] [Method for manufacturing a carbon dioxide reduction electrode for methane synthesis] The method for manufacturing the carbon dioxide reduction electrode of the present disclosure is not particularly limited. The carbon dioxide reduction electrode of the present disclosure can be manufactured by a known method. As the method for manufacturing the carbon dioxide reduction electrode of the present disclosure, for example, from the viewpoint of manufacturing suitability, a step of forming a layer containing the above Cu particles by attaching Cu particles by an arc plasma method on one surface of the cathode gas diffusion layer, and a part of the surface of the layer containing the above Cu particles on the side opposite to the cathode gas diffusion layer side, at least one metal particle selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles is attached by an electrodeposition method or an ion exchange method to form a layer containing the above metal particles (hereinafter, also referred to as "manufacturing method X") is preferable.

[0039] Hereinafter, manufacturing method X will be described, but descriptions of matters common to those described in the section on the carbon dioxide reduction electrode of the present disclosure will be omitted.

[0040] <Manufacturing method X> Manufacturing method X includes a step of forming a Cu particle layer by attaching Cu particles to one surface of the cathode gas diffusion layer by an arc plasma method (hereinafter, also referred to as the "Cu particle layer forming step"), and a part of the surface of the layer containing the Cu particles on the side opposite to the cathode gas diffusion layer side, by an electrodeposition method or an ion exchange method, a step of forming a layer containing the metal particles by attaching at least one kind of metal particle selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles (hereinafter, also referred to as the "specific metal particle layer forming step"). Manufacturing method X may include steps other than the Cu particle layer forming step and the specific metal particle layer forming step (so-called, other steps). Examples of other steps include a step of preparing a cathode gas diffusion layer and a step of washing the electrode with distilled water.

[0041] - Cu particle layer forming step - The Cu particle layer forming step is a step of forming a Cu particle layer by attaching Cu particles to one surface of the cathode gas diffusion layer by an arc plasma method.

[0042] In the Cu particle layer forming step, a Cu particle layer is formed on one surface of the cathode gas diffusion layer. When the cathode gas diffusion layer has a microporous layer (MPL), it is preferable to form a Cu particle layer on the MPL side surface of the cathode gas diffusion layer. When a Cu particle layer is formed on the MPL side surface of the cathode gas diffusion layer, since the Cu particles and carbon dioxide are likely to come into contact, there is a tendency to be able to manufacture a carbon dioxide reduction electrode capable of more efficiently synthesizing methane.

[0043] In the Cu particle layer forming step, a Cu particle layer is formed by an arc plasma method. By forming a Cu particle layer by an arc plasma method, there is a tendency to be able to manufacture a carbon dioxide reduction electrode capable of more efficiently synthesizing methane. The arc plasma method is a vapor phase method for generating metal nanoparticles by vaporizing a metal by generating a high-temperature arc discharge between two electrodes. In the arc plasma method, the metal is evaporated and vaporized by the plasma generated between the two electrodes, and the generated metal vapor is cooled while reacting with the ambient gas, thereby growing into nanoparticles. Therefore, according to the arc plasma method, a Cu particle layer with nanosized Cu particles attached can be formed on one surface of the cathode gas diffusion layer. The Cu particles forming the Cu particle layer have a larger contact area with carbon dioxide as the particle diameter is smaller, and are considered to more efficiently synthesize methane because they effectively exhibit the function as a catalyst.

[0044] The arc plasma conditions are not particularly limited. As the applied voltage, for example, 80V to 150V is preferable, and 110V to 120V is more preferable. As the number of discharges, for example, 50 times to 1000 times is preferable. As the capacitor capacitance, for example, 300 μF to 1500 μF is preferable. As the pulse frequency, for example, 0.2 Hz to 10 Hz is preferable. As a preferable example of the arc plasma conditions, there is a condition where the applied voltage is 120V, the number of discharges is 500 times, the capacitor capacitance is 1080 μF, and the pulse frequency is 1Hz. As the arc plasma device, an arc plasma method nanoparticle forming device (model: APD-1S-C) manufactured by Advance Institute of Technology Co., Ltd. can be preferably used. However, the arc plasma device in the present disclosure is not limited thereto.

[0045] - Specific metal particle layer formation step - The specific metal particle layer formation step is a step of forming a specific metal particle layer by attaching at least one kind of metal particle (i.e., specific metal particle) selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles to a part of the surface of the Cu particle layer on the side opposite to the cathode gas diffusion layer by an electrolysis method or an ion exchange method.

[0046] In the specific metal particle layer formation step, a specific metal particle layer is formed on a part of the surface of the Cu particle layer on the side opposite to the cathode gas diffusion layer side. In the specific metal particle layer formation step, it is preferable to form the specific metal particle layer such that the area ratio of the specific metal particle layer in plan view occupying the Cu particle layer is 15% to 80%, and more preferably 30% to 65%. When the specific metal particle layer is formed such that the area ratio of the specific metal particle layer in plan view occupying the Cu particle layer is within the above range, there is a tendency to be able to manufacture a carbon dioxide reduction electrode with higher methane selectivity. The area ratio of the specific metal particle layer in plan view occupying the Cu particle layer can be controlled, for example, by the electrodeposition conditions (in the case of the electrodeposition method) or the immersion time (in the case of the immersion ion exchange method) when forming the specific metal particle layer.

[0047] In the specific metal particle layer formation step, the specific metal particle layer is formed such that the contour length of the specific metal particle layer in plan view per unit area of the Cu particle layer in plan view is 1.0 μm / μm 2 ~3.0 μm / μm 2 and preferably 2.5 μm / μm 2 ~3.0 μm / μm 2 and more preferably formed to be. When the specific metal particle layer is formed such that the contour length of the specific metal particle layer in plan view per unit area of the Cu particle layer in plan view is within the above range, there is a tendency to be able to manufacture a carbon dioxide reduction electrode with higher methane selectivity. The contour length of the specific metal particle layer in plan view per unit area of the Cu particle layer in plan view can be controlled, for example, by the electrodeposition conditions (in the case of the electrodeposition method) or the immersion time (in the case of the immersion ion exchange method) when forming the specific metal particle layer.

[0048] In the specific metal particle layer formation step, the specific metal particle layer is formed by an electrodeposition method or an ion exchange method. According to the electrodeposition method or the ion exchange method, the specific metal particle layer can be easily formed.

[0049] The electrolysis method may be a constant voltage method (so-called chronoamperometry) or a constant current method (so-called chronopotentiometry), but a constant voltage method is preferred. The electrolysis conditions are not particularly limited as long as they are conditions under which a specific metal particle layer can be formed on a part of the surface of the Cu particle layer on the side opposite to the cathode gas diffusion layer side.

[0050] The electrolysis cell used in the electrolysis method is not particularly limited and is appropriately selected according to, for example, the type of specific metal particles. When the specific metal particles are Ag particles, examples of the reference electrode include an Ag wire and an Ag / AgCl electrode, and examples of the counter electrode include an Ag wire and an Ag mesh. When the specific metal particles are Zn particles, examples of the reference electrode include an Ag / AgCl electrode, and examples of the counter electrode include a Zn wire and a Zn mesh. When the specific metal particles are Sn particles, examples of the reference electrode include an Ag / AgCl electrode, and examples of the counter electrode include a Sn wire and a Sn mesh. When the specific metal particles are Al particles, examples of the reference electrode include an Ag / AgCl electrode, and examples of the counter electrode include an Al wire and an Al mesh.

[0051] The electrolytic solution used in the electrolysis method is not particularly limited and is appropriately selected according to, for example, the type of specific metal particles. When the specific metal particles are Ag particles, examples of the electrolytic solution include AgNO 3 aqueous solution, Ag 2 SO 4 aqueous solution, and AgCl aqueous solution. When the specific metal particles are Zn particles, examples of the electrolytic solution include ZnCl 2 aqueous solution and Zn(CH 3 COO) 2 aqueous solution. When the specific metal particles are Sn particles, examples of the electrolytic solution include Sn(NO 3 ) 2 aqueous solution, SnSO 4 aqueous solution, and SnCl2 Examples include aqueous solutions. When the specific metal particles are Al particles, examples of the electrolytic solution include, for example, Al(NO 3 ) 3 aqueous solution, Al 2 (SO 4 ) 3 aqueous solution and AlCl 3 aqueous solution.

[0052] The pH of the electrolytic solution is not particularly limited, but is preferably, for example, 1 to 6. Electrodeposition is preferably carried out in an environment at room temperature (25 °C). As the set potential, it is preferably, for example, -0.1 V to -1.5 V. Voltage application is preferably terminated, for example, when the charge amount reaches 0.02 C / cm 2 ~0.20 C / cm 2 , and more preferably terminated when the charge amount reaches 0.10 C / cm 2 ~0.15 C / cm 2 . In the electrodeposition method, the deposition amount of the specific metal can be controlled by the charge amount. As an example of the electrodeposition conditions by the constant potential method when the specific metal particles are Ag particles, an electrodeposition cell composed of using an Ag wire as the reference electrode, an Ag mesh as the counter electrode, and 0.01 M AgNO 3 aqueous solution (pH = 2.2) is used, the set potential is -0.5 V (vs. RHE (Reversible Hydrogen Electrode)), and voltage application is terminated when the charge amount reaches 0.14 C / cm 2 . Also, as an example of the electrodeposition conditions by the constant potential method when the specific metal particles are Zn particles, an electrodeposition cell composed of using an Ag / AgCl electrode as the reference electrode, a Zn wire as the counter electrode, and 0.1 M ZnCl 2 aqueous solution (pH = 3.0) is used, the set potential is -0.5 V (vs. RHE (Reversible Hydrogen Electrode)), and voltage application is terminated when the charge amount reaches 0.02 C / cm 2 .

[0053] The ion exchange method is not particularly limited. For example, from the perspective of more easily forming a specific metal particle layer, the immersion ion exchange method is preferred.

[0054] The ion exchange solution used in the ion exchange method is not particularly limited and is appropriately selected according to, for example, the type of specific metal particles. When the specific metal particles are Ag particles, examples of the ion exchange solution include, for example, AgNO 3 aqueous solution, Ag 2 SO 4 aqueous solution, and AgCl aqueous solution. When the specific metal particles are Zn particles, examples of the ion exchange solution include, for example, ZnCl 2 aqueous solution and Zn(CH 3 COO) 2 aqueous solution. When the specific metal particles are Sn particles, examples of the ion exchange solution include, for example, Sn(NO 3 ) 2 aqueous solution, SnSO 4 aqueous solution, and SnCl 2 aqueous solution. When the specific metal particles are Al particles, examples of the ion exchange solution include, for example, Al(NO 3 ) 3 aqueous solution, Al 2 (SO 4 ) 3 aqueous solution, and AlCl 3 aqueous solution. The pH of the ion exchange solution is not particularly limited, but is preferably, for example, 2 to 3.

[0055] In the immersion ion exchange method, the immersion is preferably carried out in an environment at room temperature (25 °C). The immersion is preferably terminated, for example, when the immersion time reaches 5 seconds to 500 seconds, and more preferably terminated when the immersion time reaches 30 seconds to 50 seconds. In the immersion ion exchange method, the deposition amount of the specific metal can be controlled by the immersion time.

[0056] [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") includes the carbon dioxide reduction electrode (so-called cathode electrode) of the present disclosure, an electrolyte, and an anode electrode. Since the carbon dioxide reduction electrode of the present disclosure is as described above, the description thereof is omitted here.

[0057] <Electrolyte> The carbon dioxide electrolysis cell of the present disclosure has an electrolyte. The electrolyte can be selected from known ion exchange membrane type electrolytes used in carbon dioxide electrolysis cells. The ion exchange membrane type electrolyte may have a property of selectively permeating cations or may have a property of selectively permeating anions. Examples of the electrolyte include, for example, a polymer electrolyte membrane (PEM). The electrolyte may be, for example, a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane.

[0058] Commercially available products can be used as the electrolyte. Examples of commercially available products of the electrolyte include "Nafion" (registered trademark) [manufactured by Chemours Co., Ltd.], "Flemion" (registered trademark) [manufactured by AGC Inc.], "Neosepta" (registered trademark) [manufactured by Asahi Kasei Corporation], "Selemembrane" (registered trademark) [manufactured by AGC Inc.], and "Sustainion" (registered trademark) [manufactured by Dioxide Materials].

[0059] <Anode Electrode> The carbon dioxide electrolysis cell of the present disclosure has an anode electrode. The anode electrode is not particularly limited as long as it is a material capable of oxidizing water to generate oxygen and hydrogen ions, and can be selected from known anode electrodes used in carbon dioxide electrolysis cells, for example.

[0060] Examples of the material for the anode electrode include metals such as iridium, platinum, palladium, and nickel, alloys containing these metals, intermetallic compounds containing these metals, binary metal oxides such as iridium oxide, manganese oxide, nickel oxide, cobalt oxide, iron oxide, tin oxide, indium oxide, and ruthenium oxide, ternary metal oxides such as Ni-Co-O, Ni-Fe-O, La-Co-O, Ni-La-O, and Sr-Fe-O, quaternary metal oxides such as Pb-Ru-Ir-O and La-Sr-Co-O, and metal complexes such as Ru complexes and Fe complexes. The anode electrode may be, for example, a composite electrode in which these materials are laminated on a substrate. Various shapes such as mesh, wire, particle, porous, thin film, and island can be applied to the anode electrode.

Example

[0061] Hereinafter, the present disclosure will be described in detail by way of 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.

[0062] [Fabrication of Carbon Dioxide Reduction Electrode] <Example 1> Cathode gas diffusion layer [trade name: Toray Paper TGP-H-060, water repellency: 50%, carbon paper (CP) made of graphite fiber which is carbon fiber, thickness: 190 μm, density: 0.44 g / cm 3, a 2 cm square piece was cut out from Toray Industries, Inc. Next, using an arc plasma device [trade name: Arc Plasma Method Nanoparticle Formation Device, model: APD-1S-C, manufactured by Advance Riko Co., Ltd.], Cu particles were deposited on one side of the cut cathode gas diffusion layer by the arc plasma method. Specifically, after placing the cut cathode gas diffusion layer in the arc plasma device using imide tape, Cu was evaporated and vaporized in a vacuum to generate Cu particles, and the generated Cu particles were adhered to one side of the cathode gas diffusion layer. The arc plasma conditions were set with a voltage of 120 V, a capacitor capacitance of 1080 μF, and the number of discharges of 500 times. In this way, first, a laminate having a layer structure of a cathode gas diffusion layer (carbon fiber sintered body) / Cu particle layer was fabricated. Next, the laminate was cut out into a circle with a diameter of 2 cm. Then, using an electrolytic cell, Ag particles were adhered to the surface of the cut laminate on the Cu particle layer side by the electrolysis method. The electrolytic cell was composed of an Ag wire as a reference electrode, an Ag mesh as a counter electrode, and a 0.01 M AgNO 3 aqueous solution (pH = 2.2). The electrolysis was carried out by chronoamperometry (so-called constant voltage method) in an environment at room temperature (25 °C), and the set potential was -0.5 V (vs. RHE (Reversible Hydrogen Electrode)). The deposition amount of Ag was defined by the amount of electricity, and the application of voltage was set to end when the amount of electricity reached 0.14 C / cm 2 . In this way, the carbon dioxide reduction electrode of Example 1 having a layer structure of a cathode gas diffusion layer (carbon fiber sintered body) / cathode catalyst layer (Cu particle layer / Ag particle layer) was fabricated.

[0063] When the surface of the Ag particle layer side of the cathode catalyst layer provided in the carbon dioxide reduction electrode of Example 1 was observed using a scanning electron microscope equipped with an energy dispersive X-ray analyzer (SEM-EDS) [trade name: New Schottky Field Emission Type Scanning Electron Microscope JSM-F100, manufactured by JEOL Ltd.], it was confirmed that Ag particles were adhered to a part of the Cu particle layer to form a layer. A partial SEM image (magnification: 6000 times) of the surface on the Ag particle layer side of the cathode catalyst layer included in the carbon dioxide reduction electrode of Example 1 is shown in FIG. 1.

[0064] Also, based on the obtained SEM-EDS images, the area ratio in plan view of the Ag particle layer occupying on the Cu particle layer and the contour length in plan view of the Ag particle layer per unit area in plan view of the Cu particle layer were measured using image analysis / editing software [product name: Adobe Photoshop, manufactured by Adobe]. As a result, they were 61.8% and 2.8 μm / μm, respectively. 2 respectively.

[0065] <Example 2> The same operations as in Example 1 were performed to fabricate a laminate. Next, the laminate was cut out into a circle with a diameter of 2 cm. Then, using an electrolysis cell, Zn particles were deposited on the surface on the Cu particle layer side of the cut-out laminate by electrolysis. The electrolysis cell was composed of an Ag / AgCl electrode as a reference electrode, a Zn wire as a counter electrode, and a 0.1 M ZnCl 2 aqueous solution (pH = 3.0). The electrolysis was carried out by chronoamperometry (so-called constant voltage method) in an environment at room temperature (25°C), and the set potential was -0.5 V (vs. RHE (Reversible Hydrogen Electrode)). The deposition amount of Zn was defined by the amount of electricity, and the voltage application was set to end when the amount of electricity reached 0.02 C / cm 2 Thus, a carbon dioxide reduction electrode of Example 2 having a layer structure of a cathode gas diffusion layer (carbon fiber sintered body) / cathode catalyst layer (Cu particle layer / Zn particle layer) was fabricated.

[0066] When the surface on the Zn particle layer side of the cathode catalyst layer included in the carbon dioxide reduction electrode of Example 2 was observed using a scanning electron microscope equipped with an energy dispersive X-ray analyzer (SEM-EDS) [product name: New Schottky field emission type scanning electron microscope JSM-F100, manufactured by JEOL Ltd.], it was confirmed that Zn particles were attached to a part of the Cu particle layer to form a layer.

[0067] <Example 3> The same operations as in Example 1 were performed to fabricate a laminate. Next, the laminate was cut out into a circle with a diameter of 2 cm. Then, Ag particles were attached to the surface of the cut-out laminate on the side of the Cu particle layer by the immersion ion exchange method. As the ion exchange solution, 0.01 M AgNO 3 aqueous solution (pH = 2.2) was used. The deposition amount of Ag was defined by the immersion time. The immersion was carried out for 50 seconds in an environment at room temperature (25°C). In this way, a carbon dioxide reduction electrode of Example 3 having a layer structure of a cathode gas diffusion layer (carbon fiber sintered body) / cathode catalyst layer (Cu particle layer / Ag particle layer) was fabricated.

[0068] When the surface of the Ag particle layer side of the cathode catalyst layer included in the carbon dioxide reduction electrode of Example 3 was observed using a scanning electron microscope equipped with an energy dispersive X-ray analyzer (SEM-EDS) [trade name: New Schottky field emission type scanning electron microscope JSM-F100, manufactured by JEOL Ltd.], it was confirmed that Ag particles were attached to a part of the Cu particle layer to form a layer.

[0069] <Comparative Example 1> The same operations as in Example 1 were performed to fabricate a laminate. The fabricated laminate was used as the carbon dioxide reduction electrode of Comparative Example 1.

[0070] [Evaluation: Methane selectivity] Using the carbon dioxide reduction electrodes of Example 1, Example 2, Example 3 and Comparative Example 1, the methane selectivity of the cathode diffusion layer was evaluated. The evaluation of methane selectivity was based on the Faraday efficiency. The Faraday efficiency indicates the ratio of the current used for the reaction of the product to the total current that has reacted. First, the carbon dioxide reduction electrode was incorporated into a gas diffusion type half cell (see Figure 2). As shown in Figure 2, the half cell stores the electrolyte on the surface opposite to the cathode gas diffusion layer of the carbon dioxide reduction electrode, and CO is on the surface side of the cathode gas diffusion layer of the carbon dioxide reduction electrode. 2It has a structure capable of supplying gas. For the working electrode (WE), a Cu electrode was used; for the reference electrode (RE), an Ag / AgCl electrode was used; and for the counter electrode (CE), a carbon rod was used. Also, as the electrolyte, 1M KHCO 3 aqueous solution was used. Note that the KHCO 3 aqueous solution was bubbled with CO 2 gas (purity: 99.99%) and then used after adjusting the pH to 7.9. Next, in an environment at room temperature (25°C), CO 2 gas (purity: 99.99%) was flowed at a flow rate of 5 cc / min to the cathode gas diffusion layer side of the carbon dioxide reduction electrode, and the CO 2 gas in the line was replaced. Then, with the Ag / AgCl electrode, which is the reference electrode, as a reference, a voltage was applied so that the potential between the working electrode and the reference electrode became -1.4 V (vs. RHE) on the cathode gas diffusion layer side of the carbon dioxide reduction electrode. After starting the application of the voltage and confirming that a current was flowing, for 1.5 to 2 minutes, the flow rate of the generated gas was measured using a flow meter [trade name: Defender (registered trademark) 530+, manufactured by Mesa Labs] connected to the exhaust line of a gas chromatograph [trade name: Nexis (registered trademark) GC-2030, manufactured by Shimadzu Corporation]. After measuring the flow rate of the generated gas, the composition of the generated gas was analyzed using the gas chromatograph in the flow path. The generated gas was constantly circulated through the flow path of the gas chromatograph, and by performing a switching operation of the flow path at regular time intervals, the generated gas was introduced into a column [trade name: MICROPACKED-ST, manufactured by Shinwa Chemical Industries Co., Ltd.] for analysis. From the measurement results of the flow rate of the generated gas and the analysis results of the composition of the generated gas, the production amount of methane (CH 4 ) was calculated and converted into the amount of charge. From the ratio of the amount of charge obtained by the conversion to the actual current value that flowed, the production efficiency of methane (so-called Faraday efficiency) was determined, and the methane selectivity was evaluated. The composition of the generated gas and the Faraday efficiency of each component are shown in Table 1. The higher the value of the Faraday efficiency (unit: %), the more it can be evaluated that the carbon dioxide reduction electrode has high methane selectivity.

[0071]

Table 1

[0072] From the results shown in Table 1, the carbon dioxide reduction electrode has a cathode gas diffusion layer and a cathode catalyst layer in this order, the cathode catalyst layer is a laminate of a Cu particle layer and a specific metal particle layer provided on a part of the Cu particle layer, and by having the Cu particle layer and the specific metal particle layer in this order from the cathode gas diffusion layer side, it was confirmed that the cathode catalyst layer has a very high methane selectivity compared to the case where the cathode catalyst layer is only the Cu particle layer.

Claims

1. A cathode gas diffusion layer and a cathode catalyst layer are provided in this order, wherein the cathode catalyst layer has, in this order from the cathode gas diffusion layer side, a layer containing Cu particles and a layer provided on a part of the layer containing the Cu particles and containing at least one kind of metal particles selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles, a carbon dioxide reduction electrode for methane synthesis.

2. The carbon dioxide reduction electrode for methane synthesis according to Claim 1, wherein the layer containing the metal particles is a layer containing at least one kind of metal particles selected from Ag particles and Zn particles.

3. The carbon dioxide reduction electrode for methane synthesis according to Claim 1, wherein the area ratio in a plan view of the layer containing the metal particles occupying on the layer containing the Cu particles is 15% to 80%.

4. The contour length per unit area in plan view of the layer containing the metal particles per unit area in plan view of the layer containing the Cu particles is 1.0 μm / μm ２ to 3.0 μm / μm ２ The carbon dioxide reduction electrode for methane synthesis according to claim 1, wherein the carbon dioxide reduction electrode is as described above.

5. A method for manufacturing a carbon dioxide reduction electrode for methane synthesis according to any one of Claims 1 to 4, a step of forming the layer containing the Cu particles by adhering Cu particles to one surface of the cathode gas diffusion layer by an arc plasma method; a step of forming the layer containing the metal particles by adhering at least one kind of metal particles selected from the group consisting of Ag particles, Zn particles, Sn particles, and Al particles to a part of the surface of the layer containing the Cu particles on the side opposite to the cathode gas diffusion layer side by an electrodeposition method or an ion exchange method; A method for manufacturing a carbon dioxide reduction electrode for methane synthesis, including the above steps.

6. A carbon dioxide electrolysis cell for methane synthesis, comprising the carbon dioxide reduction electrode for methane synthesis according to any one of Claims 1 to 4, an electrolyte, and an anode electrode.

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