Method for manufacturing a composite, method for manufacturing a slurry containing a composite, method for manufacturing an electrode, electrode, ion exchange membrane-electrode assembly, and CO2 electrolysis device

Abstract

Provided are a composite in which at least one of a metal monomer or a metal compound having a small particle size and high dispersibility is supported on a carrier, and a slurry obtained using the composite. A related technology is a method for manufacturing a composite in which at least one of a metal monomer or a metal compound is supported on a carrier, the method for manufacturing a composite including: a depressurization step (S1-1) in which a dispersion liquid containing a solvent and the carrier is exposed to a depressurized environment at a temperature of ordinary temperature and at a pressure of less than 80 kPa (absolute pressure), a raw material mixture preparation step (S1-2) in which a raw material mixture is prepared by mixing, in the dispersion liquid, a metal ion supply agent that is a source of metal ions of the metal monomer or the metal compound, and a supporting step (S1-3) in which a reducing agent is mixed in the raw material mixture, and at least one of the metal monomer or the metal compound is supported on a surface of the carrier.

Description

Technical Field

[0001] This application relates to methods for manufacturing composites, methods for manufacturing slurries containing composites, methods for manufacturing electrodes using them, electrodes, ion exchange membrane-electrode junctions, and CO2 electrolysis apparatus. Background Technology

[0002] Fossil fuels (oil, coal, and natural gas) power modern energy-intensive societies. Extracting energy from fossil fuels involves the emission of CO2 (carbon dioxide). The rising concentration of carbon dioxide in the atmosphere is reportedly one of the causes of global warming, and its reduction is necessary. Because CO2 is an extremely stable substance, it is difficult to reuse through decomposition or other methods; therefore, new technologies are needed to convert CO2 into other substances for resource recovery.

[0003] As one of these technologies, research on the reduction of CO2 using electrical energy is being conducted extensively worldwide. It has been found that CO2 reduction devices with polymeric electrolyte electrolyzers have advantages over other devices in that they can significantly reduce ion movement resistance by using thin-film polymeric electrolytes (Patent Document 1). Generally, the cathode used for CO2 reduction in polymeric electrolyte electrolyzers contains catalyst particles and a conductive support.

[0004] In CO2 reduction, the number of active sites and crystal faces on the surface of the electrode catalyst significantly contribute to the reaction rate. Therefore, it is desirable for the electrode catalyst particles to have small particle size and high dispersion. As a method for dispersing and supporting metal particles of the electrode catalyst on a support, for example, there is a method of directly supporting the support, metal ions, and reducing agent on the support by stirring the support, metal ions, and reducing agent in an organic solvent for a long time (Non-Patent Literature 1).

[0005] Furthermore, in CO2 reduction, the amount of CO2 adsorbed near the CO2 reduction catalyst significantly contributes to the formation efficiency of reduction products such as CO (carbon monoxide), and it is desirable to develop electrode catalysts capable of adsorbing large amounts of CO2. A method has been devised, for example, whereby an ion exchange resin with properties that interact with CO2 adsorption and a catalyst are co-supported on an electrode using high-temperature and high-pressure treatment, thereby increasing the adsorption capacity of weakly acidic CO2 and improving the formation efficiency (Patent Document 3).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Publication No. 2019-515142

[0009] Patent Document 2: International Publication No. 2020 / 130078

[0010] Patent Document 3: Japanese Patent Application Publication No. 2012-43612

[0011] Non-patent literature

[0012] Non-patent literature 1: K. Iizuka, T. Wato, Y. Miseki, K. Saito, A. Kudo, J. Am. Chem. Soc., 2011, 133, 20863. Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] Generally, carbon supports and ceramic supports are used in electrode catalysts. Carbon and ceramic supports are hydrophobic particles, therefore, they easily attract air bubbles in solution. Consequently, when catalysts such as metal particles are supported on the support, there is a possibility that the metal particles may become enlarged, small in size, or insufficiently dispersed. Furthermore, when co-supported with ion exchange resins as described above, there is a possibility that the catalyst and resin may deteriorate due to high-temperature and high-pressure treatment, and that the process cost may increase.

[0015] Therefore, the purpose of this application is to provide a composite formed by supporting at least one of a metal monomer or metal compound with small particle size and high dispersibility on a carrier, and related technologies for slurries obtained using the composite.

[0016] According to one aspect of this application, related technology for manufacturing a composite is provided, which is a method for manufacturing a composite by supporting at least one of a metal monomer or a metal compound on a carrier.

[0017] The manufacturing method of the aforementioned composite includes:

[0018] The decompression step (S1-1) involves exposing the dispersion containing the solvent and the aforementioned carrier to a reduced pressure environment of less than 80 kPa (absolute pressure) at room temperature.

[0019] The raw material mixture preparation step (S1-2) involves mixing a metal ion feeder, which serves as a metal ion source for the aforementioned metal monomer or metal compound, into the aforementioned dispersion to prepare the raw material mixture.

[0020] The loading step (S1-3) involves mixing a reducing agent into the aforementioned raw material mixture to load the aforementioned metal monomer or metal compound onto the surface of the aforementioned carrier.

[0021] Additionally, according to one aspect of this application, related technology for a method of manufacturing a slurry can be provided, which includes a method for manufacturing a slurry comprising a composite material of a metal monomer or metal compound supported on a carrier and a polymer material.

[0022] The aforementioned method for manufacturing the slurry includes:

[0023] The first dispersion containing solvent (A) and the aforementioned complex is subjected to a decompression step (S2-1) at room temperature under a reduced pressure environment of less than 80 kPa (absolute pressure), and

[0024] The slurry preparation step (S2-2) involves mixing the aforementioned polymeric material into the first dispersion to prepare the slurry.

[0025] Invention Effects

[0026] According to this application, there is a technology that provides a composite formed by supporting at least one of a metal monomer or metal compound with small particle size and high dispersibility on a carrier, and a slurry obtained using the composite. Attached Figure Description

[0027] Figure 1 (a): A flowchart illustrating a manufacturing method for producing the composite used in this embodiment. Figure 1 (b): A flowchart illustrating the method for manufacturing the slurry composite used in this embodiment.

[0028] Figure 2 This is a schematic diagram illustrating the polymer covering complex in this application.

[0029] Figure 3 This is an example of a schematic diagram illustrating an ion exchange membrane-electrode junction suitable for use in this application.

[0030] Figure 4 This is an example of a schematic diagram illustrating a suitable CO2 electrolysis apparatus for use in this application. Detailed Implementation

[0031] The following describes in detail the manufacturing methods of the composite and the slurry in this application. It should be noted that the invention described in this application is not limited to the form described below.

[0032] In this manual, "normal temperature" and "normal pressure" are based on the description in JIS Z8703-1983 "Standard conditions of test sites".

[0033] The inventors discovered that in the loading process of a carrier such as metal particles, air bubbles adhere to the carrier when it is dispersed in a solvent. These air bubbles not only hinder the loading of the carrier such as metal particles, but also preferentially generate crystal nuclei due to the unstable local concentration gradient near the gas-liquid interface, resulting in the precipitation of metal particles being concentrated in certain areas. Therefore, it was discovered that by exposing the solvent to a reduced pressure (e.g., an absolute pressure of 80 kPa or less) for a specified time when dispersing the carrier in the solvent, these air bubbles can be expelled from the system. As a result, the local formation of crystal nuclei can be suppressed, solving the aforementioned problem, thus completing the technology of this application.

[0034] 1. Complex

[0035] The composite described in this application is, for example, a composite formed by supporting at least one of a metal monomer or a metal compound as a catalyst on a support.

[0036] The metal content of the metal monomers or metal compounds in the composite is not particularly limited as long as it does not impair the effect of the technology described in this application. For example, when the content of the carrier is set to 100 parts by mass, it is 1 part by mass or more, preferably 10 parts by mass or more, and more preferably 20 parts by mass or more. As an upper limit for the metal content in the composite, it can be set to 100 parts by mass, for example.

[0037] The metal content of the metal monomers or compounds in the composite is determined using the following method. The metal content of the composite is determined using a fluorescence X-ray analysis device. Specifically, a standard curve is prepared using a fluorescence X-ray analysis device to compare the metal content with the detection peak of the specified metal, for powders containing a carrier and a specified metal that are already known. The detection peak of the specified metal in the actual composite is then measured using the fluorescence X-ray analysis device, and the metal content is determined based on the standard curve.

[0038] The average particle size of the composite is not particularly limited as long as it does not impair the effect of the technology described in this application; for example, it can be set to 200 nm or less, preferably 100 nm or less. The lower limit can be set to 1 nm or more. The average particle size of the composite can be determined by calculating the number mean of the particle sizes measured using a scanning electron microscope for 100 randomly selected particles. During the measurement, the length of the longest direction of the composite particles is measured as the major axis, and this major axis is measured as the particle size.

[0039] The carrier is not particularly limited as long as it does not impair the effectiveness of the technology described in this application; it can be any solid substance capable of supporting and fixing metal monomers or their compounds. Examples of carrier materials include carbon carriers, metal carriers, metal nitride carriers, metal carbide carriers, and metal oxide carriers. Furthermore, the carrier can be in particle, fibrous, or sheet form.

[0040] When the composite is used as an electrode material containing a catalyst, the support is a conductive support. Preferably, the conductive support comprises carbon materials, titanium, tantalum, gold, silver, or copper. These can be used individually or in combination. Their selection is based on consideration of corrosion resistance. The conductive support is preferably a material different from the catalyst used.

[0041] Here, the carbon material is not particularly limited as long as it is conductive and does not hinder the effect of the technology of this application. As the carbon material, materials known to be used in electrode materials can be used, such as graphitic carbon, glassy carbon, carbon black, graphene, carbon nanotubes, etc.

[0042] The carrier / conductive carrier is preferably in the form of particles or short fibers. Alternatively, the carrier / conductive carrier can be an aggregate obtained by the aggregation of particles (primary particles) or short fibers. Here, "particle-like" or "short fiber-like" refers to what is judged to be particle-like or short fiber-like based on general technical knowledge. Furthermore, in this application, aggregates obtained by the aggregation of short fibers are also included within secondary particles.

[0043] The average particle size of the primary particles or the average fiber length of the short fibers of the carrier are not particularly limited as long as they do not impair the effect of the technology described in this application. For example, they can be set to 10–100 nm, preferably 20–50 nm. The average particle size and average fiber length of the conductive carrier can be freely selected considering the surface area and the porosity of the conductive carrier. Here, the average particle size refers to the average particle size including both primary particles and short fibers and secondary particles. Here, when the conductive carrier contains short fibers, the average particle size is set to the value obtained by averaging the particle size obtained by considering the fiber length of the short fibers as the primary particle size and the particle size of the secondary particles of the short fibers. In the determination of the average particle size, the carrier particles are measured using a scanning electron microscope for 100 randomly selected particles. The length in the longest direction of the observed particles is measured as the major diameter, and the average value of the obtained major diameters is calculated. The observation method can be selected according to the average particle size. In addition, the average primary particle size of the carrier / conductive carrier is preferably more than twice the average primary particle size of the catalyst.

[0044] The specific surface area of ​​the carrier is not particularly limited as long as it does not impair the effect of the technology described in this application; for example, it can be set to 100–3000 m². 2 / g, preferably 200-1800m 2 / g. When the specific surface area of ​​the support falls within this range, the loading of metal monomers or metal compounds becomes sufficient, and the CO2 diffusion at the surface of the CO2 reduction catalyst becomes excellent when the resulting polymer-coated complex, or the complex described later, is used as a CO2 reduction catalyst.

[0045] The hydrophobicity of the carrier is not particularly limited as long as it does not impair the effectiveness of the technology described in this application. For example, when an ion-exchange water droplet is added to the carrier (a substance obtained by molding carrier powder into a thin film) at 25°C, the contact angle between the tangent of the droplet and the carrier surface is preferably 80 to 140°. When the contact angle falls within this range, a good balance between hydrophilicity and hydrophobicity is achieved.

[0046] That is, if the hydrophobicity is too low (the hydrophilicity is too high), after the slurry described later is dispersed onto the substrate by spraying or the like, the solvent (A) described later is removed by drying or the like, and a polymer-coated composite with a coating layer (supported together with metal monomers or metal compounds) is formed by more uniformly covering part or all of the surface of the composite. The catalytic activity of the composite manufactured by the manufacturing method of the suitable composite described later will be reduced when used as a CO2 reduction catalyst.

[0047] In addition, if the hydrophobicity is too high (the hydrophilicity is too low), the dispersibility of the carrier will decrease, and therefore the particle size of the complex will increase.

[0048] The metal monomers and metal compounds used as catalysts in this application are not particularly limited as long as they do not impair the effectiveness of the technology described in this application. When the composite is used as an electrode material containing the catalyst, the metal monomers and metal compounds preferably include any one of Au, Ag, Cu, Pt, Ir, Pd, Ru, Ni, Co, Mn, Bi, Sn, Zn, and Al. Here, the metal compound is defined as a metal compound containing an alloy. In addition, oxides or metal complexes of Ag, Cu, Ir, Pd, Ru, Ni, Co, Mn, Bi, Sn, Zn, and Al are preferred as metal compounds.

[0049] Examples of metal oxides include ruthenium oxide (RuO2, RuO2). x ), rhenium oxide (ReO2, ReO3, Re2O7, ReO x ), palladium oxide (PdO, PdO) x ), Iridium oxide (IrO2, IrO) x They can be used individually or in combination.

[0050] Examples of metal complexes include phthalocyanine complexes containing Cu, Re, Ru, Ni, Fe, Co, and Mn, porphyrin complexes, pyridine complexes, and metal-supported covalently bonded triazine structures.

[0051] The shape of the metal monomers and metal compounds is not particularly limited as long as it does not impair the effect of the present invention; for example, they can be in the form of particles or films. Furthermore, when using metal monomers and metal compounds as catalysts, the effect of the catalyst increases if the surface area of ​​the catalyst supported on the support increases; therefore, a particle shape is preferred. Here, particles are not limited to primary particles, but can be secondary particles formed by the aggregation of primary particles. Additionally, the particle shape is not limited to shapes judged as particle-shaped according to general technical knowledge, but also includes shapes where the particles are very small and referred to as "monatomic particles," formed by the atomic-level dispersion of coordinated-bonded metals.

[0052] The average particle size of metal monomers and metal compounds in the form of particles is not particularly limited as long as it does not hinder the effect of the present application technology. For example, it can be set to 1-200 nm, preferably 1-100 nm, and more preferably 1-50 nm. When metal monomers and metal compounds are used as catalysts, the larger the particle size, the larger the surface area of ​​the catalyst. Therefore, there is an effect that the catalyst has more active sites (sites) that contribute to the reaction. On the other hand, depending on the particle size of the catalyst, in addition to the aforementioned surface area effect, there is also an effect called size effect, which significantly changes the activity and selectivity. Therefore, the particle size of the catalyst can be selected as long as the activity of the catalyst is confirmed. As for the average particle size of the catalyst involved in the reduction reaction of carbon dioxide, a smaller size effect is effective. In the present application technology, the average particle size of the catalyst is preferably 100 nm or less, and more preferably 50 nm or less. In addition, the catalyst is more effective when it is dispersed without aggregation, that is, when it contains more primary particles. Here, the average particle size of metal monomers and metal compounds (catalysts) refers to the average particle size of the primary particles of metal monomers and metal compounds (catalysts). Regarding the determination of average particle size, an arbitrary rectangle with a length of 4.5 μm and a width of 6.0 μm within the secondary electron image confirmed by a scanning electron microscope under the conditions of an accelerating voltage of 10 kV and a magnification of 20,000 times was set as the measurement range. All particles carried by the complex in the part that did not overflow from the measurement range were observed, and the length of the longest direction of the observed particles was measured as the major axis. The average value of the obtained major axes was set as the average particle size.

[0053] 2. Manufacturing method of the composite

[0054] The method for manufacturing the composite of this application will be described. According to the method for manufacturing the composite of this application, a composite can be obtained by supporting at least one of a metal monomer or metal compound with smaller particle size and higher dispersibility on a carrier. It should be noted that the composite produced by the method of manufacturing the composite of this application is more suitable as a composite in the method for manufacturing the slurry described later in this application.

[0055] Here, when the composite produced by the composite manufacturing method of this application is used in the slurry manufacturing method of this application, "solvent" can be replaced with "solvent (B)" and "dispersion" can be replaced with "second dispersion".

[0056] The method for manufacturing the composite in this application includes:

[0057] The decompression step (S1-1) involves exposing a dispersion containing solvent and carrier to a reduced pressure environment of less than 80 kPa (absolute pressure) at room temperature.

[0058] The raw material mixture preparation step (S1-2) involves supplying metal ions to a dispersion using a metal ion feeder, wherein the metal ions become raw materials for metal monomers or metal compounds; and

[0059] The loading step (S1-3) involves adding a reducing agent to the raw material mixture to support metal monomers or metal compounds on the surface of a carrier.

[0060] The composite produced in this way is removed from the solvent and removed by drying or otherwise, thereby making it possible to produce a suitable composite for use in the slurry manufacturing method described later.

[0061] Using the composite manufacturing method of this application, the catalyst formed by supporting at least one of the metal monomers or metal compounds as catalysts on a support, as described above, has a smaller particle size on the surface of the support. Therefore, as a support (e.g., used as an electrode catalyst), the small particle size is also excellent, and it has high dispersibility, which makes it even more superior.

[0062] 2-1. Decompression Procedure (S1-1)

[0063] In the decompression step (S1-1), the dispersion containing solvent and carrier is exposed to a decompression environment of less than 80 kPa (absolute pressure) at room temperature.

[0064] In the decompression step (S1-1), bubbles are removed from the dispersion, thus reducing the particle size of the composite (or support). This is because the removal of bubbles that act as crystal nuclei in the dispersion inhibits the precipitation (formation) of localized metal monomers or compounds, improving the uniformity of the metal monomer or compound particles and reducing their size. For these reasons, using this composite (or support) as an electrode in an electrode catalyst, an ion exchange membrane-electrode junction, or a CO2 electrolysis device can result in excellent efficiency in the formation of reduction products.

[0065] The solvent is, for example, water or an alcohol compound, specifically an alcohol compound that is in the liquid phase at atmospheric pressure and within the temperature range of the preparation and reduction processes. A solvent capable of dissolving both the metal ion donor and the reducing agent is preferred. This allows for a significant increase in catalyst loading. Further preferred is a solvent with a lower vapor pressure compared to the pressure exposed during the vacuum process. This suppresses solvent evaporation during the vacuum process. Examples of such compounds include water, methanol, ethanol, 1-propanol, 1-butanol, isopropanol, ethylene glycol, propylene glycol, diethylene glycol, and glycerol.

[0066] In the decompression step (S1-1), the dispersion obtained by mixing the solvent and the carrier is placed in a vacuum container or a container located within a vacuum chamber. Using a known decompression method, the vacuum container or the container located within the vacuum chamber is decompressed to less than 80 kPa (absolute pressure) at room temperature, exposing the dispersion to the decompression environment. By exposing the dispersion to the decompression environment, air bubbles within the dispersion can be removed. Here, the exposure time can be set to 1–60 minutes.

[0067] Alternatively, as a method of reducing pressure, known pressure-reducing devices such as rotary evaporators and vacuum pumps can be used. Additionally, substances prepared by exposing at least one of the solvent or carrier to a reduced pressure environment of less than 80 kPa (absolute pressure) at room temperature before mixing can be used.

[0068] The pressure during decompression is less than 80 kPa (absolute pressure). The lower the pressure, the better the bubble removal, which is preferred. If the pressure is too low, the solvent may boil. Therefore, 0.1 to 50 kPa (absolute pressure) is preferred, and more preferably 5 to 10 kPa (absolute pressure). When the pressure falls within this range, the particle size of the composite (or support) can be reduced.

[0069] The mixing ratio of solvent and carrier is not particularly limited as long as it does not impair the effect of the technology of this application. For example, it can be set to 100:0.01 to 100:1 by mass.

[0070] The dispersion may contain components other than solvent and carrier.

[0071] 2-2. Preparation steps of raw material mixture (S1-2)

[0072] In the raw material mixture preparation step (S1-2), a metal ion feeder for supplying metal ions is mixed in the dispersion to prepare the raw material mixture, wherein the metal ions are raw materials for metal monomers or metal compounds. The raw material mixture preparation step (S1-2) is not limited to a reduced pressure environment and can be carried out under normal pressure. Furthermore, the raw material mixture preparation step (S1-2) can be performed after the reduced pressure step (S1-1), or simultaneously with the reduced pressure step (S1-1). That is, before exposing the dispersion to a reduced pressure environment, the raw material mixture can be prepared by mixing the metal ion feeder for supplying metal ions as raw materials for metal monomers or metal compounds, and then the raw material mixture can be exposed at room temperature to a reduced pressure environment of less than 80 kPa (absolute pressure).

[0073] A metal ion supplier is mixed into a dispersion to form a raw material mixture. The metal ion supplier supplies metal ions to the raw material mixture. In the raw material mixture, the metal ions are supported (precipitated) onto the surface of a support by adding a reducing agent in the subsequent loading steps (S1-3), thereby forming a complex. That is, the metal ion supplier is the metal ion source for the metal monomers or metal compounds supported on the complex, thus becoming its raw material.

[0074] In this application, the metal ion supplier is not limited to a metal compound containing the desired metal, but also includes the desired metal monomer. Metal monomers can be used as metal ion suppliers; sulfates, nitrates, carbonates, acetates, oxides, hydroxides, fluorides, chlorides, bromides, sulfides, complex salts, etc. More specifically, gold chloride (I), gold chloride (III), tetrachloroauric acid (III), gold bromide (III), potassium gold cyanide (I), silver nitrate (I), silver cyanide (I), copper sulfate (II), copper nitrate (II), copper carbonate (II), copper acetate (I), copper acetate (II), copper citrate (II), copper fluoride (II), copper chloride (I), copper chloride (II), copper bromide (I), copper bromide (II), platinum chloride (II), platinum chloride (IV), chloroplatinic acid (II), chloroplatinic acid (IV), platinum bromide (II), platinum bromide (IV), etc. These can be used alone or in combination.

[0075] The amount of metal ion supply agent is not particularly limited as long as it does not impair the effect of the present application. In the raw material mixture preparation step (S1-2), by reducing the amount of carrier and / or increasing the amount of metal ion supply agent, the loading of metal monomers or metal compounds in the carrier can be increased. For example, when the amount of carrier is set to 100 parts by mass, the amount of metal ion supply agent, calculated as metal monomers or metal compounds, is preferably 65 parts by mass or more and 150 parts by mass or less, more preferably 75 parts by mass or more and 135 parts by mass or less. Furthermore, it is more preferably 75 parts by mass or more and 120 parts by mass or less. By setting the amount of metal ion supply agent to 150 parts by mass or less, the contact probability between metal ions or generated metal particles and the carrier can be greatly increased. In addition, by setting the amount to 65 parts by mass or more, the amount of carrier becomes appropriate relative to the generated metal particles, and a sufficient amount of metal carrier or metal compound can be loaded.

[0076] Furthermore, the concentration of metal ions supplied by the metal ion supply agent in the solvent is not particularly limited as long as it does not impair the effect of the technology of this application; for example, it can be set to 0.1 to 2.0 g / L.

[0077] 2-3. Loading Steps (S1-3)

[0078] In the loading step (S1-3), a reducing agent is added to the raw material mixture prepared in the raw material mixture preparation step (S1-2). The metal ions in the raw material mixture are reduced and precipitated (loaded) onto the carrier surface in the form of metal monomers or metal compounds, forming a complex. The metal compound precipitates as a metal oxide or similar substance bonded to dissolved oxygen in the raw material mixture. The precipitation ratio of metal monomers to metal compounds can be controlled by adjusting the dissolved oxygen concentration in the liquid mixture.

[0079] In the loading steps (S1-3), firstly, the oxygen concentration dissolved in the liquid mixture can be adjusted according to the ratio of the desired metal monomer to the metal compound loaded onto the carrier. The dissolved oxygen concentration can be controlled by introducing a specified gas. For example, to reduce the oxygen partial pressure, an oxygen-free gas such as N2 is introduced. Conversely, to increase the oxygen partial pressure, an oxygen-containing gas such as O2 or air is introduced.

[0080] After adjusting the dissolved oxygen concentration as needed, the liquid mixture is heated to a target temperature corresponding to the specified metal using a heating device (not shown). The raw material mixture is then stirred at a specified time and speed to carry out the reduction reaction. The target temperature can be appropriately changed depending on the metal cation to be reduced.

[0081] When the metal cation to be reduced is copper ion, the target temperature can be set above 40°C, 50°C, or 60°C. When the metal cation to be reduced is other metal ions (such as platinum ions, gold ions, or silver ions), the target temperature can be set above 5°C, 15°C, or 20°C.

[0082] On the other hand, the target temperature is preferably below 100°C, below 90°C, below 80°C, below 70°C, or below 65°C. Excessive heating is disadvantageous from an energy input perspective. According to the method of the present invention, the reduction reaction can be sufficiently carried out even at temperatures below 100°C. Furthermore, when sufficient reduction and precipitation occur at low temperatures according to the present invention, excessive heating can lead to excessive reduction reaction, causing particle aggregation and making it difficult to control particle size.

[0083] The time required for the restoration step depends on various conditions, typically ranging from 0.1 to 24 hours or from 0.5 to 4 hours.

[0084] The reducing agent is not particularly limited as long as it does not impair the effect of the technology described in this application; examples include salts of hypophosphonic acid. Examples of hypophosphonic acid salts include lithium hypophosphonate, sodium hypophosphonate, potassium hypophosphonate, and ammonium hypophosphonate. These can be used alone or in combination.

[0085] The amount of reducing agent mixed in is not particularly limited as long as it does not impair the effect of the present invention. For example, the mixing ratio (Ec / Er) of the reducing metal ion equivalent (Er) of the reducing agent to the metal ion equivalent (Ec) of the metal ion feeder can be set to 0.5 or more, preferably 1.0 or more, more preferably 1.2 or more, and even more preferably 1.5 or more. The upper limit of the above mixing ratio is not particularly limited; for example, from the viewpoint of manufacturing cost, Ec / Er can be set to 5.0 or less. Furthermore, the amount of reducing agent mixed in relative to the raw material mixture can be, for example, set to 1 to 10 g / L.

[0086] 3. Method for preparing the slurry

[0087] The method for manufacturing the slurry of this application is a method for manufacturing a slurry comprising a composite material and a polymer material formed by loading at least one of a metal monomer or a metal compound onto a carrier.

[0088] The method for manufacturing the slurry includes: a decompression step (S2-1) in which a first dispersion containing solvent (A) and the aforementioned composite is exposed at room temperature to a reduced pressure environment of less than 80 kPa (absolute pressure); and a slurry preparation step (S2-2) in which a polymer material is mixed in the first dispersion to prepare the slurry. According to this manufacturing method, the slurry can be prepared without harsh treatments such as high temperature and high pressure (e.g., treatments at 200°C or higher and 20 atmospheres or higher). Therefore, when the ion exchange resin described later is coated on the composite, deterioration of the catalyst (metal monomer or metal compound) and the resin can be prevented. Furthermore, it has the advantage of being manufactured at a low cost because a high temperature and high pressure process is not performed.

[0089] 3-1. Decompression Procedure (S2-1)

[0090] In the decompression step (S2-1), the first dispersion obtained by mixing the solvent (A) and the composite is placed into a vacuum container or a container placed inside a vacuum chamber. Using a known decompression method, the vacuum container or the container placed inside the vacuum chamber is decompressed to less than 80 kPa (absolute pressure) at room temperature, exposing the first dispersion to the decompression environment. This removes air bubbles from the first dispersion. Therefore, when the slurry is dispersed onto the substrate by spraying or the like, and the solvent (A) is removed by drying or the like, the polymer material can more uniformly cover part or all of the composite surface to form a capping layer (co-supported with metal monomers or metal compounds). That is, as a result of removing air bubbles from the first dispersion (or raw material mixture), air bubble residue at the composite-polymer material interface is suppressed, the uniformity of the polymer material capping layer is improved, and a stable capping layer is formed. For the above reasons, a composite having a capping layer with such a polymer material as an ion exchange resin (see reference) is used. Figure 2 (Hereinafter sometimes referred to as polymer-coated complex or polymer-coated composite) Electrodes used as electrode catalysts, ion exchange membrane-electrode junctions, and CO2 electrolysis devices can exhibit excellent efficiency in the formation of reduction products. Here, the exposure time can be set to 1–60 minutes.

[0091] Alternatively, as a method for reducing pressure, known pressure-reducing devices such as rotary evaporators and vacuum pumps can be used. Additionally, a substance prepared by exposing at least one of the solvent (A) or the carrier before mixing to a reduced pressure environment of less than 80 kPa (absolute pressure) at room temperature can be used.

[0092] The pressure during decompression is less than 80 kPa (absolute pressure). The lower the pressure, the better the bubble removal, which is preferred. If the pressure is too low, the solvent (A) may boil. Therefore, 0.1 to 50 kPa (absolute pressure) is preferred, and 5 to 40 kPa (absolute pressure) is more preferred. When the pressure falls within this range, the coating layer of the polymer coating composite can be made uniform.

[0093] The mixing ratio (mass ratio) of solvent (A) to complex is not particularly limited as long as it does not impair the effect of the technology of this application. For example, it can be set to 10000:1 to 1:1.

[0094] The first dispersion may contain components other than the solvent (A) and the carrier.

[0095] 3-1-1. Composites used in the preparation method of slurry

[0096] The method for manufacturing the composite used in the slurry manufacturing method of this application is not particularly limited as long as it does not impair the effect of the technology of this application. As a method for manufacturing the composite used in the slurry manufacturing method, a carrier is mixed with a metal monomer or metal compound using a known mixer to produce a carrier (hereinafter sometimes referred to as a carrier) supporting the metal monomer or metal compound. The mixing time can be set to 3 to 60 minutes.

[0097] Other methods for preparing the catalyst support include methods that precipitate metal monomers or metal compounds onto the support via a reduction reaction. More specifically, by mixing the support, a metal ion feeder supplying metal ions that are the raw materials for the aforementioned metal monomers or metal compounds, and a reducing agent to reduce the metal cations, the catalyst metal can be supported on a conductive support. The mixing time in this method can be set to 1 to 48 hours. According to this manufacturing method, metal monomers or metal compounds with smaller particle sizes can be supported on the support, and are therefore preferred.

[0098] The method for manufacturing the composite used in the preferred method for manufacturing the slurry is the method for manufacturing the composite described in this application, which includes: a decompression step (S1-1) in which a second dispersion containing a solvent (B) and a carrier is exposed at room temperature to a decompression environment of less than 80 kPa (absolute pressure); a raw material mixture preparation step (S1-2) in which a metal ion supplying agent for supplying metal ions is mixed in the dispersion to prepare a raw material mixture, wherein the metal ions are raw materials for metal monomers or metal compounds; and a loading step (S1-3) in which a reducing agent is added to the raw material mixture to load the metal monomers or metal compounds onto the surface of the carrier.

[0099] According to this method, it is possible to obtain a composite material in which at least one of a metal monomer or metal compound with smaller particle size and higher dispersibility is supported on a carrier.

[0100] 3-1-2. Solvent (A)

[0101] Solvent (A) is a water or alcohol compound that is in the liquid phase at atmospheric pressure and within the temperature range of the vacuum reduction process. Ideally, the solvent should have a low vapor pressure compared to the pressure exposed during the vacuum reduction process. This suppresses solvent evaporation during the vacuum reduction process. Examples of such compounds include water, methanol, ethanol, 1-propanol, 1-butanol, isopropanol, ethylene glycol, propylene glycol, diethylene glycol, and glycerol.

[0102] The mixing ratio (mass ratio) of solvent (A) to carrier is not particularly limited as long as it does not impair the effect of the technology of this application. For example, it can be set to 10000:1 to 1:1.

[0103] 3-2. Slurry preparation steps (S2-2)

[0104] In the slurry preparation step (S2-2), a slurry is prepared by mixing polymers in the first dispersion. The slurry preparation step (S2-2) is not limited to a reduced pressure environment and can be carried out under normal pressure. Furthermore, the slurry preparation step (S2-2) can be performed after or simultaneously with the reduced pressure step (S2-1). That is, the slurry can be prepared by mixing polymers before exposing the first dispersion to a reduced pressure environment, and then the slurry can be exposed to a reduced pressure environment of less than 80 kPa (absolute pressure) at room temperature.

[0105] There is no particular limitation on the amount of polymer to be mixed, as long as it does not impair the effect of the technology of this application. For example, when the amount of the composite to be mixed is set to 100 parts by mass, it can be set to 1 to 100 parts by mass.

[0106] When the slurry prepared by the manufacturing method of the slurry of this application is dispersed onto a substrate by spraying or the like, and the solvent (A) is removed by drying or the like, the polymer described in this application can form a coating layer covering part or all of the surface of the composite (supported together with metal monomers or metal compounds).

[0107] There are no particular limitations on the polymer material as long as it does not impair the effectiveness of the technology described in this application. When using a polymer-coated support as an electrode catalyst, ion exchange resins are preferred, especially anion exchange resins, as these can produce an electrode catalyst that adsorbs a large amount of CO2 and, in CO2 reduction, can achieve excellent efficiency in the formation of reduction products such as CO (carbon monoxide).

[0108] The anion exchange resin described in this application is preferably an ionomer containing amino or quaternary ammonium groups. That is, the anion exchange resin preferably has a structure in which an amino or quaternary ammonium group is added to the base resin of the ionomer. Here, amino groups include primary amino, secondary amino, and tertiary amino groups.

[0109] The density of basic sites on the anion exchange resin (ionomer) is 2.0 mmol / cm³. 3 Above and 5.0 mmol / cm 3 The preferred value is 2.5 mmol / cm. 3 Above and below 4.5 mmol / cm 3 More preferably 2.9 mmol / cm 3 Above and below 4.5 mmol / cm 3 When the density of the base sites of the anion exchange resin falls within this range, an electrode catalyst with excellent CO2 reduction efficiency can be obtained even when the CO2 concentration at the periphery of the electrode catalyst is low.

[0110] Even when the support is not covered by anion exchange resin, or when the support is covered by anion exchange resin, if the density of the base sites of the anion exchange resin is low, the CO2 supplied to the electrode catalyst is gaseous, so CO2 can move freely. The chance of CO2 adsorbing onto the active sites of the catalyst is limited, and the CO2 reduction efficiency is also limited.

[0111] On the other hand, when the support is covered by anion exchange resin and the base site density of the anion exchange resin is high enough (base site density is 2.0 mmol / cm³), 3 Under the above conditions, CO2, which is a weak acid, entering the cover is neutralized by the basic sites of the anion exchange resin, and can mainly react as bicarbonate ions (HCO3-). - The bicarbonate ions remain in the anion exchange resin in the form of urethane or carbamate. As a result, a large amount of bicarbonate ions are stored near the catalyst supported on the support, and these bicarbonate ions form CO2 through an equilibrium reaction, thereby allowing CO2 to be efficiently adsorbed onto the active sites of the catalyst. This improves the CO2 reduction efficiency of the electrode material. This effect is effective even with high CO2 concentrations and even more effective with low CO2 concentrations.

[0112] Additionally, the base site density exceeds 5.0 mmol / cm². 3 In this case, due to the increased hydrophilicity, the swelling caused by the water (H2O) produced during the above neutralization reaction intensifies, and there is a risk of a decrease in the mechanical properties of the electrode catalyst.

[0113] The base site density of anion exchange resin can be adjusted by the ratio of hydrophobic to hydrophilic structures within the molecular structure of the ionomer. Therefore, as a method to adjust the base site density of anion exchange resin, it can be adjusted by copolymerizing monomers with hydrophobic structures and polymers obtained by prepolymerizing the monomers, and monomers with hydrophilic structures and polymers obtained by prepolymerizing the monomers.

[0114] The density of base sites of anion exchange resins is determined by... 1 H-NMR determination is obtained by integrating the signals of amino, quaternary ammonium, and other functional groups that form base sites.

[0115] The base resin for the ionomer is not particularly limited as long as it does not impair the effect of the technology described in this application. For example, it can be a copolymer obtained by copolymerizing ethylene monomers, styrene monomers, urethane monomers, halogen monomers, and polymers prepolymerized from these monomers. As copolymers, any of random copolymers, block copolymers, graft copolymers, alternating copolymers, etc., can also be used. Furthermore, they can be used alone or in combination.

[0116] The ionomers described in this application have amino or quaternary ammonium groups, but since these are hydrophilic groups, it is preferable to pre-add them to the monomers or polymers to adjust the base site density. Furthermore, as the hydrophobic monomers or polymers added to adjust the base site density, halogenated monomers, aromatic monomers, monomers containing ether bonds, or polymers thereof can be used, depending on the degree of hydrophobicity; fluorinated monomers are particularly preferred.

[0117] An anion exchange resin (the same applies to polymers) covers part or all of the surface of the support. The ratio of the coverage area to the surface area, i.e., the coverage ratio θ, can be set to 70% or more, 80% or more, 90% or more, 95% or more, or 100%. From the viewpoint of accumulating a large amount of CO2 near the catalyst, a higher coverage ratio θ is preferred. Here, the coverage ratio θ refers to the electrochemical double-layer capacitance C of the electrode in a dry state, calculated by electrochemical impedance spectroscopy under an inactive gas atmosphere. dl / i The electrostatic capacitance C of the double layer in a wet state dl / W It is represented by the following formula 1.

[0118] (Equation 1)

[0119] θ=(C dl / i / C dl / w )×100

[0120] Here, the equivalent circuit is set as a circuit consisting of a capacitor and a resistor (A) in parallel, and a resistor (B) connected in series with them. The capacitance of the capacitor when its electrodes are in a dry state is considered as C. dl / i Furthermore, the capacitance of the capacitor when its electrodes are wet is considered as C. dl / w Here, "dry" means the measurement is performed in an environment with a relative humidity of less than 10% or when the moisture content of the supplied raw gas is less than 0.5% by volume (with the total volume of the raw gas set at 100%). "Wet" means the measurement is performed in an environment with a relative humidity of 100%. It should be noted that other details related to the determination of coverage are based on the methods described in the Journal of Electroanalytical Chemistry, Volume 693, 15 March 2013, Pages 34-41.

[0121] Here, coverage θ can be further improved by exposing the anion exchange resin (or polymer) to a higher depressurization environment (lower pressure) during or after mixing with the support.

[0122] The average coating thickness of the anion exchange resin is not particularly limited as long as it does not impair the effect of the technology of this application; for example, it can be set to 0.01 to 100 μm.

[0123] If the average coating thickness of the anion exchange resin is greater than 0.01 μm, sufficient ion conduction channels are formed, enabling the exchange of hydroxide ions (OH-) generated through the reaction. - This allows for more efficient delivery to the ion exchange membrane, and consequently, due to the sufficient amount of alkaline sites, the retention of carbonate species such as CO2 and bicarbonate ions is adequate.

[0124] Furthermore, if the average coating thickness of the anion exchange resin is less than 100 μm, the distance that ions must travel is appropriate. Therefore, the resistance to ion movement becomes moderate, and the increase in voltage (reduction in inhibition efficiency) can be suppressed. Consequently, the distance that CO2 must diffuse to reach the catalyst is not too great, so CO2 moves easily, and the increase in voltage (reduction in inhibition efficiency) can be suppressed.

[0125] For the reasons mentioned above, when the average coverage thickness of the anion exchange resin falls within this range, the generation efficiency of reduction products (such as CO) from CO2 is excellent. In particular, when the CO2 supply concentration is low, electrode materials with even better generation efficiency of reduction products can be obtained.

[0126] 4. Uses of the slurry

[0127] The slurry obtained by the manufacturing method of this application is dispersed by spraying or the like, and the solvent (A) is removed by drying or the like, thereby forming a polymer-coated composite obtained by coating the surface of a composite in which at least one of a metal monomer or a metal compound is supported on a carrier with a polymer. As described above, by using a catalyst as a metal monomer or a metal compound, using a conductive support as a support, and using an anion exchange resin as a polymer, an electrode catalyst can be formed. The electrode catalyst obtained in this way is superior from the viewpoint of excellent small particle size and high dispersibility. Therefore, the electrode obtained therefrom can be made into an electrode with excellent efficiency in generating reduction products. In addition, by bonding this electrode to an ion exchange membrane, an ion exchange membrane-electrode conjugate can be formed, and it can also be used in CO2 electrolysis devices.

[0128] 4-1. Ion exchange membrane-electrode junction

[0129] If the electrode material of this application is used to form a membrane-electrode junction, a membrane-electrode junction with high CO2 reduction efficiency can be obtained.

[0130] The ion exchange membrane-electrode assembly of this application mainly comprises the electrode catalyst, ion exchange membrane, and current collector (also referred to as a current collector plate when used in a plate shape) described in this application. Furthermore, the electrode catalyst of this application is disposed between the ion exchange membrane and the current collector. The electrode catalyst can be attached to a substrate or formed into an electrode of a desired shape.

[0131] 4-1-1. Ion exchange membrane

[0132] The ion exchange membrane described in this application is not particularly limited as long as it does not impair the effectiveness of the technology described herein. Examples include cation exchange membranes such as Nafion (registered trademark) and Aquivion (registered trademark); and anion exchange membranes such as Sustainion (registered trademark) and Fumasep (registered trademark). Anion exchange membranes are preferred. Furthermore, in the ion exchange membrane-electrode junction of this application, anion exchange membranes containing primary amino, secondary amino, tertiary amino, quaternary ammonium groups, or a mixture of these ion exchange groups are particularly preferred. Specific examples include NEOSEPTA (registered trademark), ASE, AHA, AMX, ACS, AFN, AFX (manufactured by Tokuyama Corporation); Selemion (registered trademark), AMV, AMT, DSV, AAV, ASV, AHO, AHT, APS4 (manufactured by Asahi Glass Co., Ltd.).

[0133] The anion exchange membrane can be made of the same polymer as the ion exchange resin covering the electrode catalyst of this application, or it can be made of a different material. When the anion exchange membrane is made of the same material as the anion exchange resin covering the electrode catalyst of this application, it is possible to avoid deterioration of the interface between the anion exchange resin and the anion exchange membrane. In addition, by preventing phase separation at the interface between the anion exchange resin and the anion exchange membrane, ion movement (conduction) can proceed smoothly, which is therefore preferred.

[0134] 4-1-2. Current collector

[0135] Examples of suitable current collectors for this application include metals such as copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass. From the viewpoint of ease of processing and cost, copper is preferred. When the current collector is a metallic material, the shape of the negative current collector can be, for example, metal foil, metal plate, metal film, expanded metal, perforated metal, or foamed metal.

[0136] Here, the current collector is provided with vents for supplying and recovering gases (raw material gas and product gas) to the electrode (or electrode catalyst). Through these vents, raw material gas can be uniformly and efficiently introduced into the electrode (or electrode catalyst) and product gas (including unreacted raw material gas) can be discharged. It should be noted that the number, location, and size of the vents are not limited and can be appropriately set. Furthermore, if the current collector is ventilable, vents are not required. Figure 3 The diagram shows an illustration of an ion exchange membrane-electrode junction, but... Figure 3 The current collector in the text refers to a current collector made of a porous, breathable material.

[0137] 4-2. CO2 Electrolysis Unit

[0138] By using the electrode catalyst and ion exchange membrane-electrode junction described in this application as the cathode, a CO2 electrolysis apparatus with excellent CO2 reduction efficiency, especially more efficient when the supplied CO2 concentration is low, can be obtained. The CO2 electrolysis apparatus can be used in methods for producing CO2 electrolysis products such as CO.

[0139] For the example of the CO2 electrolysis device of this application, using Figure 4The CO2 electrolysis apparatus includes: a cathode 101; an anode 102 forming a pair of electrodes with the cathode 101; a solid electrolyte 103 existing between the cathode 101 and the anode 102 in at least partial contact; a current collector 104 in contact with a surface 101-2 on the opposite side of the contact surface 101-1 of the cathode 101 and the solid electrolyte 103; a support plate 105 in contact with a surface 102-1 on the opposite side of the contact surface 102-2 of the anode 102 and the solid electrolyte 103; and a voltage application unit 106 for applying a voltage between the current collector 104 and the support plate 105 (i.e., between the cathode and the anode). Furthermore, CO2 in a gaseous state and an aqueous solution of an electrolyte such as H2O or KHCO3, which serves as the supporting electrolyte, are supplied via a supply source and supply device (not shown). It should be noted that, for ease of explanation, Figure 4 The CO2 electrolysis device 100 described herein is illustrated with the cathode 101, anode 102, and other components separated. However, in reality, the current collector 104, cathode 101, solid electrolyte 103, anode 102, and support plate 105 are bonded together in a single unit using a prescribed method. The components can also be configured to be detachable and assembled, thus forming a single CO2 electrolysis device 100.

[0140] Here, the electrode catalyst described in this application is used as cathode 101.

[0141] Furthermore, the ion exchange membrane-electrode junction of this application exhibits… Figure 4 The functions of the current collector 104, cathode 101, and solid electrolyte 103 are as follows: The current collector constituting the ion exchange membrane-electrode junction is the current collector 104, the electrode catalyst of this application is the cathode 101, and the anion exchange membrane constitutes the solid electrolyte 103, thereby enabling the formation of an integrated cathode.

[0142] Example

[0143] Next, the technology of this application will be described in detail through examples and comparative examples, but the technology of this application is not limited to them at all.

[0144] <<The Creation of Complexes>>

[0145] <Example 1>

[0146] In a beaker, 0.3 g of carbon black (support) was mixed with 100 mL of ethanol (solvent (B)) and subjected to ultrasonic treatment for 10 minutes. Then, the mixture was exposed to vacuum at 10 kPa (absolute pressure) for 10 minutes. Subsequently, 11.7 mL of 0.1 mol / L silver nitrate solution (metal ion donor) and 1 mL of 2.3 mol / L sodium phosphonate solution (reducing agent) were mixed and stirred at room temperature for 8 hours to reduce silver nitrate. After the reaction, the resulting slurry was washed with distilled water, recovered using a centrifuge, and vacuum dried at 60 °C for 12 hours to obtain silver catalyst powder (composite).

[0147] <Example 2>

[0148] The amount of carbon black mixed into the ethanol was set to 0.15 g, and the silver catalyst powder was prepared in the same manner as in Example 1.

[0149] <Example 3>

[0150] The amount of carbon black mixed into the ethanol was set to 0.1 g, and the silver catalyst powder was prepared in the same manner as in Example 1.

[0151] <Example 4>

[0152] The amount of carbon black mixed into the ethanol was set to 0.075 g. Otherwise, the process was the same as in Example 1 to prepare silver catalyst powder.

[0153] <Comparative Example 1>

[0154] The amount of carbon black mixed into ethanol was set to 0.6 g, and no exposure to a reduced pressure environment was performed. Otherwise, the process was the same as in Example 1 to prepare silver catalyst powder.

[0155] <Comparative Example 2>

[0156] No exposure to a reduced pressure environment was performed; otherwise, the process was the same as in Example 1 to prepare silver catalyst powder.

[0157] <<Determination of the loading and average particle size of metal monomers or metal compounds in composites>>

[0158] <Determination of the loading of metal monomers or metal compounds>

[0159] For the composites obtained in each of the embodiments and comparative examples, fluorescence X-ray analysis was performed on multiple composites. The mass content of silver in the composites was determined using a standard curve prepared by performing the same determination on powders with known contents of the carrier and metal.

[0160] <Determination of the average particle size of metal monomers or metal compounds>

[0161] For the composites of the obtained embodiments and comparative examples, a scanning electron microscope (JSM-7001F, manufactured by Nippon Electron Co., Ltd.) was used. A rectangle measuring 4.5 μm x 6.0 μm was defined within the secondary electron image obtained under conditions of 10 kV acceleration and 20,000x magnification. The silver particles carried by the entire composite in the portion not overflowing from the measurement range were observed, and the length of the longest direction of the observed silver particles was measured as the major axis. The obtained major axis values ​​were averaged, and significant figures were summarized to two digits according to JIS Z8401:2019. The results of the average particle size of the silver particles are shown in Table 1. Furthermore, it can be inferred that the average particle size of the metal monomers or metal compounds in each embodiment could be reduced because there were no bubbles and therefore no local crystallization nuclei formed (high dispersibility).

[0162] [Table 1]

[0163]

[0164] <<Preparation of the Complex>>

[0165] <Example 5>

[0166] In a beaker, 0.6 g of carbon black (support) was mixed with 100 mL of ethanol (solvent (B)) and subjected to ultrasonic treatment for 10 minutes. Then, the mixture was exposed to vacuum at 10 kPa (absolute pressure) for 10 minutes. Subsequently, 11.7 mL of 0.1 mol / L silver nitrate solution (metal ion donor) and 1 mL of 2.3 mol / L sodium phosphonate solution (reducing agent) were mixed and stirred at room temperature for 16 hours to reduce silver nitrate. After the reaction, the resulting slurry was washed with distilled water, recovered using a centrifuge, and vacuum dried at 60 °C for 12 hours to obtain silver catalyst powder (composite).

[0167] <Example 6>

[0168] The composite was not exposed to a reduced pressure environment during synthesis, except that the silver catalyst powder (composite) was obtained by following the same steps as in Example 5.

[0169] <Example 7>

[0170] The pressure of the reduced pressure environment during the synthesis of the composite was set to 30 kPa (absolute pressure). Otherwise, the same steps as in Example 5 were followed to obtain silver catalyst powder (composite).

[0171] <Example 8>

[0172] Except that the pressure of the reduced pressure environment in the composite synthesis was set to 60 kPa (absolute pressure), a silver catalyst powder (composite) was obtained by following the same procedure as in Example 5.

[0173] <Comparative Example 3>

[0174] Except that no exposure under reduced pressure environment was performed in the composite synthesis, treatment was carried out in the same manner as in Example 5 to obtain the silver catalyst powder (composite) of Comparative Example 3.

[0175] <<Preparation of Slurry and Fabrication of Electrode>>

[0176] <Examples 5 to 8>

[0177] Using the obtained composites of Examples 5 to 8, the slurries of Examples 5 to 8 were prepared according to the following procedure, and then the electrodes of Examples 5 to 8 were further fabricated.

[0178] In a beaker, 15 mL of ethanol (solvent (A)) was mixed with 0.02 g of the obtained composite, and 0.01 g of powder of a polymer ionomer (an anion exchange resin which has a base site density of 2.9 mmol / cm 3 , serves as a base material, is a resin with aromatic groups located in the main chain, and has quaternary ammonium groups (alkyl quaternary amine groups) as side chains bonded to the main chain) was further mixed, and the mixture was exposed to a vacuum chamber with a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes to prepare a slurry. Thereafter, the obtained slurry was coated onto carbon paper under atmospheric pressure and dried to fabricate an electrode.

[0179] <Comparative Example 3>

[0180] Except that no exposure under reduced pressure environment was performed when mixing the ionomer, treatment was carried out in the same manner as in Examples 5 to 8 to obtain the slurry and electrode of Comparative Example 3.

[0181] <<Evaluation>>

[0182] <Structure of CO2 Electrolysis Device>

[0183] The obtained electrodes of each Example and Comparative Example were used as cathodes, and an iridium oxide-supported titanium mesh was used as an anode. In addition, an anion exchange membrane having an ion exchange capacity of 1.5 mmol / g and a film thickness of 30 to 35 μm was used as the solid electrolyte. An electrolyte tank (0.5 M KHCO3 aqueous solution) was used as the solution on the anode side. Arrangement was performed in the order of cathode, solid electrolyte, anode, and electrolyte tank, to form a structure in which the cathode and the electrolyte tank sandwich the ion exchange membrane and the anode.

[0184] <Measurement of Ionomer Coverage>

[0185] CO₂ is supplied to the cathode using the device, the applied potential of the cathode is set to -0.2 V relative to a silver / silver chloride reference electrode, and the ionomer-based coverage θ is calculated by electrochemical impedance measurement. For the calculation, the electric double layer capacitance C of the cathode in a dry state measured under N₂ supply dl / i and the electric double layer capacitance C of the cathode in a wet state measured under supply of CO₂ bubbled into ion-exchanged water dl / W , the calculation is performed according to the following formula 1.

[0186] (Formula 1)

[0187] θ=(C dl / i / C dl / w )×100

[0188] The equivalent circuit is a circuit composed of a capacitor and a resistor (A) connected in parallel, and a resistor (B) connected in series therewith. The capacitance when the electrode of the capacitor is in a dry state is regarded as C dl / i , and the capacitance when the electrode of the capacitor is in a wet state is regarded as C dl / w . The results are shown in Table 3. The coverage of Example 6 is the same as that of Example 5.

[0189] <Measurement of CO Partial Current Density for Generation>

[0190] Using the device, a gas mixed at a volume ratio of CO₂:N₂ = 3:1 is supplied to the cathode, the applied potential of the cathode is set to -1.8 V relative to a silver / silver chloride reference electrode, CO₂ is electrolyzed, and the CO partial current density for generation [mA / cm 2 upon CO generation is measured. The results are shown in Table 2 and Table 3. From these results, it can be inferred that when depressurization treatment is performed during mixing of the ionomer, air bubbles in the slurry are removed, so no air bubbles exist at the interface between the ionomer covering the surface of the composite and the carrier (including silver particles), and a more uniform covering layer can be formed. As a result, an effect of excellent reduction efficiency (CO partial current density for generation) can be obtained. Furthermore, the lower the pressure during the depressurization treatment, the more significantly this effect appears.

[0191] [Table 2]

[0192]

[0193] [Table 3]

[0194]

[0195] <<Preparation of Composite Loaded with Nickel Single-Atom Particles>>

[0196] In a beaker, 0.4 g of carbon black (support), 1.1 mmol of pentaethylenehexamine and 0.7 mmol of nickel(II) chloride hexahydrate are mixed into 15 mL of ethanol, and the obtained ethanol dispersion is irradiated with ultrasonic waves for 10 minutes. Thereafter, the ethanol dispersion is heated and dried to evaporate ethanol, and the obtained mixture is heated and calcined at 900°C in an inert gas for 30 seconds or more using an electric furnace. Thereafter, the product is washed with an aqueous sulfuric acid solution, and the solid is recovered by a suction filter and vacuum-dried at 60°C for 12 hours, to obtain a catalyst powder (composite) loaded with a Ni complex. This catalyst powder is used as the catalyst powder of Example 9 and Comparative Example 4.

[0197] In the obtained catalyst powder, the mass of the loaded Ni is 1 part by mass relative to 100 parts by mass of carbon black serving as the support.

[0198] <<Preparation of Slurry and Fabrication of Electrode>>

[0199] <Example 9>

[0200] In a beaker, 15 mL of ethanol is mixed with 0.02 g of the obtained composite, and a polymer ionomer ("Nafion (registered trademark)", a cation exchange resin, manufactured by Sigma Aldrich) is further mixed, and the mixture is exposed to a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes, to prepare the slurry of Example 9. Thereafter, the obtained slurry is coated onto carbon paper at atmospheric pressure and dried, to fabricate the electrode of Example 9.

[0201] <Comparative Example 4>

[0202] Except that exposure under a reduced pressure environment was not performed when mixing the ionomer, the same treatment as in Example 9 was carried out to obtain the electrode of Comparative Example 4.

[0203] <<Evaluation>>

[0204] <Configuration of CO2 Electrolysis Apparatus>

[0205] The obtained electrode of Example 9 or Comparative Example 4 is used as a cathode, and an iridium oxide-loaded titanium mesh is used as an anode. Additionally, an anion exchange membrane having an ion exchange capacity of 1.5 mmol / g and a membrane thickness of 30 to 35 μm is used as the solid electrolyte. An electrolyte tank (0.5 M KHCO3 aqueous solution) is used as the solution on the anode side in each case. The cathode, solid electrolyte, anode, and electrolyte tank are arranged in this order, forming a structure in which the ion exchange membrane and the anode are clamped between the cathode and the electrolyte tank.

[0206] <Measurement of Partial Current Density of CO Generation>

[0207] Using this device, CO2 is supplied to the cathode, with the applied potential at the cathode set to -1.4V relative to the silver / silver chloride reference electrode. CO2 is electrolyzed, and the CO generation current density [mA / cm²] is measured during CO formation. 2 The results are shown in Table 4. Based on these results, it can be inferred that, similarly to the case of using a silver catalyst, excellent reduction efficiency (CO generation current density) can be obtained when performing reduced pressure treatment on mixed ionomers.

[0208] [Table 4]

[0209]

[0210] Explanation of reference numerals in the attached figures

[0211] 1. Composite (or carrier)

[0212] 10 carriers

[0213] 11. Particles of metallic monomers or metallic compounds

[0214] 12 Polymers

[0215] 100CO2 electrolysis unit

[0216] 101 Cathode

[0217] 101-1 The surface of the cathode in contact with the solid electrolyte (ion exchange resin)

[0218] 101-2 The surface of the cathode in contact with the current collector

[0219] 102 Anode

[0220] 102-1 The surface of the anode in contact with the support plate

[0221] 102-2 The surface of the anode in contact with the solid electrolyte (ion exchange resin)

[0222] 103 Solid Electrolyte (Ion Exchange Resin)

[0223] 104 collectors

[0224] 104-1 Current Collector Gas Supply Port

[0225] 104-2 Gas recovery port of current collector

[0226] 105 Support Plate

[0227] 105-1 Gas flow path of support plate

[0228] 106 Voltage application section

Claims

1. A method for manufacturing a slurry, comprising a method for manufacturing a slurry of a composite material and a polymer material formed by supporting at least one of a metal monomer or a metal compound on a carrier, wherein the slurry is for use in a CO2 electrolytic reduction electrode, and the metal monomer or the metal compound comprises any one of Au, Ag, Cu, Pt, Ir, Pd, Ru, Ni, Co, Mn, Bi, Sn, Zn, and Al, and the carrier is a conductive carrier. The method for manufacturing the slurry includes: Decompression step S2-1: A decompression step in which the first dispersion containing solvent A and the composite is exposed at room temperature to a decompression environment with an absolute pressure of less than 80 kPa. Slurry preparation step S2-2: A slurry preparation step in which the polymer material is mixed in the first dispersion to prepare the slurry. The polymer material includes an ion exchange resin. The ion exchange resin includes anion exchange resin.

2. The method for manufacturing the slurry according to claim 1, wherein, The composite is manufactured by a manufacturing method including the following steps: Decompression step S1-1: A decompression step in which the second dispersion containing solvent B and the carrier is exposed at room temperature to a decompression environment with an absolute pressure of less than 80 kPa. Raw material mixture preparation step S1-2: A raw material mixture preparation step in which a metal ion feeder, serving as a metal ion source for the metal monomer or the metal compound, is mixed in the second dispersion to prepare the raw material mixture. Loading step S1-3: A loading step in which a reducing agent is mixed in the raw material mixture to load the metal monomer or the metal compound onto the surface of the carrier.

3. The method for manufacturing the slurry according to claim 1 or 2, wherein, The metal monomer or the metal compound comprises metal monomers or metal compounds in the form of particles. The average particle size of the particulate metal monomer or metal compound is less than 100 nm.

4. A method for manufacturing an electrode, comprising coating an electrode onto a substrate with a slurry manufactured by the method described in claim 1 or 2. The carrier is a conductive carrier.

5. An electrode manufactured by the manufacturing method described in claim 4.

6. An ion exchange membrane-electrode assembly comprising the electrode of claim 5.

7. A CO2 electrolysis apparatus comprising the ion exchange membrane-electrode assembly as described in claim 6.

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