CO2 electrolysis device and method for producing CO2 electrolysis products

Abstract

Provided are: a feature pertaining to a CO2 electrolysis device having an excellent generation efficiency of generating a reduction product (CO, etc.) from CO2; and feature pertaining to a CO2 electrolysis device in which a decrease in CO2 reduction efficiency is minimized and a stable operation is made possible. An embodiment of the present invention is a CO2 electrolysis device having an electrode material. The CO2 electrolysis device includes: a support that includes an electroconductive carrier and a catalyst carried on the electroconductive carrier, the catalyst including metal complex, metal, and / or inorganic compound particles; and a negative ion exchange resin that covers a part or all of the support and that contains an ionomer of formula (1). (In the formula, m and n represent a natural number of 1-200).

Description

[Technical Field]

[0001] The present disclosure relates to a CO2 electrolysis device and a method for producing a CO2 electrolysis product. [Background technology]

[0002] Fossil fuels (oil, coal, and natural gas) support our modern energy-consuming society. Extracting energy from fossil fuels involves the emission of CO2 (carbon dioxide). Rising carbon dioxide concentrations in the atmosphere are said to be one of the causes of global warming, and there is a need to reduce them. CO2 is an extremely stable substance, making it difficult to reuse by decomposition, etc., and new technologies are needed to convert CO2 into other substances and reuse it as a resource.

[0003] As one such technology, research into CO2 reduction using electrical energy is being conducted widely around the world. CO2 reduction devices with polymer electrolyte electrolysis cells have been found to be superior to other devices in that they can sufficiently reduce the resistance to ion migration by using a thin-film polymer electrolyte (Patent Document 1). In general, the cathode for CO2 reduction used in polymer electrolyte electrolysis cells contains catalyst particles and a conductive support.

[0004] In CO2 reduction, the amount of CO2 adsorbed near the CO2 reduction catalyst strongly contributes to the production efficiency of reduction products such as CO (carbon monoxide), and it is desirable to develop an electrode catalyst that can adsorb large amounts of CO2. For example, a method has been devised to increase the adsorption amount of CO2, which is weakly acidic, and improve production efficiency by co-supporting a compound that has the property of interacting with CO2 (such as by adsorbing it) on the electrode (Patent Documents 2 and 3 and Non-Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2019-515142 [Patent Document 2] Japanese Patent Application Publication No. 2019-011492 [Patent Document 3] Republished Publication No. 2019-65258 [Non-patent literature]

[0006] [Non-Patent Document 1] S. Ren, D. Joulie, D. Salvatore, K. Torbensen, M. Wang, M. Robert, CP Berlinguette, Science, 2019, 365, 367-369. Summary of the Invention [Problem to be solved by the invention]

[0007] The invention disclosed in Patent Document 1 proposes the use of various ion-exchange membranes as thin-film polymer electrolytes. Ion-exchange membranes for such applications require high ionic conductivity, high toughness, high chemical and heat resistance, and a moderate water content. However, the ion-exchange membranes proposed in Patent Document 1 may not meet these requirements. For example, low ionic conductivity could reduce the transport efficiency of ions consumed or generated during the CO2 electrolytic reduction reaction, resulting in a slower reaction rate. Furthermore, insufficient toughness, chemical resistance, or heat resistance could prevent the electrodes from withstanding the CO2 reduction reaction conditions. Furthermore, low permselectivity or high water content of the ion-exchange membrane could cause electrolyte permeation from the anode side and overflow to the cathode side. Furthermore, there is a risk of electrolyte salt deposition. These phenomena hinder the supply of CO2 and reduce the CO2 reduction efficiency, thereby hindering the stable operation of CO2 electrolysis devices.

[0008] The inventions disclosed in Patent Documents 2 and 3 have a problem in that under conditions where the partial pressure of supplied CO2 (i.e., CO2 concentration) is low, it is difficult to retain a large amount of low-concentration CO2 near the reduction catalyst, and there is a risk that the production efficiency of reduction products and the CO2 conversion rate of the CO2 electrolysis device will decrease.

[0009] Furthermore, when a carbon dioxide reduction membrane containing a proton-permeable polymer, which is a cation exchange resin, is used on the cathode side electrode, as in the carbon dioxide reduction device disclosed in Patent Document 2, the cation exchange resin is acidic, so a side reaction (a hydrogen generation reaction, which tends to proceed in an acidic environment) is likely to occur. Furthermore, because the cation exchange resin is acidic, it has no CO2 adsorption capacity, and there is a risk that it will be impossible to achieve both ionic conductivity and CO2 adsorption capacity. This is clear from the data presented in Reference Example 5 (paragraph 0061) of Patent Document 2, which shows that the amount of CO2 adsorption decreases when Nafion, a cation exchange resin, is added. Furthermore, since cation exchange resins are permeable to metal ions, precipitation of electrolyte salts is likely to occur, and accumulation of precipitated salts may reduce the efficiency of carbon dioxide electrolysis.

[0010] Therefore, an object of the present disclosure is to provide a technology related to a CO2 electrolysis device that has excellent efficiency in generating reduction products (such as CO) from CO2, and a technology related to a CO2 electrolysis device that can suppress a decrease in CO2 reduction efficiency and operate stably.

[0011] The inventors of the present invention have found that the above-mentioned problems can be solved by using a support containing a catalyst and a conductive carrier coated with a specific anion exchange resin as an electrode material, since anion exchange resins are basic and therefore the side reactions are unlikely to occur. Furthermore, they have found that the above-mentioned problems can be solved by using an anion exchange membrane made of a similar anion exchange resin as a thin-film polymer electrolyte (solid electrolyte), thereby satisfying the requirements of a thin-film polymer electrolyte, such as high ionic conductivity, high selective permability, high toughness, high chemical resistance and heat resistance, and a moderate water content. These findings led to the completion of the presently disclosed technology. Specifically, the presently disclosed technology is as follows:

[0012] According to one aspect of the present disclosure, a support comprising a conductive support and a catalyst supported on the conductive support, the catalyst comprising one or more particles of a metal complex, a metal, or an inorganic compound; a CO2 electrolysis device having an electrode material comprising: an anion exchange resin that coats part or all of the surface of the support and contains an ionomer represented by the following formula (1): [ka] (In the formula, m and n represent natural numbers from 1 to 200.) [Effects of the Invention]

[0013] The present disclosure makes it possible to provide technologies relating to electrode materials with excellent production efficiency for generating reduction products (such as CO) from CO, as well as membrane-electrode assemblies and CO electrolysis devices that suppress a decrease in CO reduction efficiency and enable stable operation. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing an example of a CO electrolysis device suitably used in the present disclosure. [Figure 2] 1 is a schematic diagram illustrating an electrode material according to the present disclosure. FIG. [Figure 3] 1 is a schematic diagram illustrating an example of a membrane-electrode assembly that can be suitably used in the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] The CO electrolysis device according to the present disclosure will be specifically described below. However, the invention according to the present disclosure is not limited to the embodiments described below.

[0016] The CO electrolysis device of the present disclosure includes an electrode material. The electrode material of the present disclosure, when used as a cathode, can provide a CO electrolysis device with excellent CO reduction efficiency, particularly when the CO concentration is low. The CO electrolysis device can be used, for example, in a method for producing CO electrolysis products such as CO.

[0017] An example of a CO electrolysis device according to the present disclosure will be described with reference to Fig. 1. The CO electrolysis device includes a cathode 101, an anode 102 that forms a pair of electrodes with the cathode 101, a solid electrolyte 103 that is at least partially in contact with the cathode 101 and the anode 102, a current collector 104 that is in contact with the cathode 101 at a surface 101-2 opposite to a contact surface 101-1 with the solid electrolyte 103, a support plate 105 that is in contact with the anode 102 at a surface 102-1 opposite to a contact surface 102-2 with the solid electrolyte 103, and a voltage application unit 106 that applies a voltage between the current collector 104 and the support plate 105 (i.e., between the cathode and the anode). Gas-phase CO and an aqueous electrolyte solution of a supporting electrolyte, such as H2O or KHCO3, are supplied by a supply source and a supply device (not shown). 1 is shown with each component, such as the cathode 101 and the anode 102, separated for ease of explanation, but in reality, the current collector 104, the cathode 101, the solid electrolyte 103, the anode 102, and the support plate 105 are each bonded by a predetermined method to form an integrated structure. A single CO2 electrolysis device 100 can be constructed with each component configured to be detachable.

[0018] Here, the electrode material according to the present disclosure is used for the cathode 101.

[0019] Furthermore, the membrane-electrode assembly according to the present disclosure plays the roles of the current collector 104, the cathode 101, and the solid electrolyte 103 in Fig. 1. That is, the current collector constituting the membrane-electrode assembly serves as the current collector 104, the electrode material according to the present disclosure serves as the cathode 101, and the anion exchange membrane serves as the solid electrolyte 103, thereby forming an integrated cathode. The electrode material according to the present disclosure will be described below.

[0020] 1. Electrode materials The electrode material according to the present disclosure includes a catalyst, a conductive support, and an anion exchange resin. The catalyst is supported on the conductive support to form a support. The anion exchange resin coats part or all of the surface of the support (see FIG. 2).

[0021] 1-1.Conductive carrier The conductive support according to the present disclosure includes a carbon material, titanium, tantalum, gold, silver, or copper. These may be used alone or in combination. These may be selected in consideration of corrosion resistance.

[0022] The carbon material is not particularly limited as long as it is conductive and does not impair the effects of the present disclosure. Carbon materials that are known to be used as electrode materials can be used, such as graphite carbon, glassy carbon, carbon black, graphene, and carbon nanotubes.

[0023] The conductive support is in the form of particles or short fibers. The conductive support may also be an aggregate of particles (primary particles) or short fibers. Here, "particulate" or "short fiber" refers to a particle or short fiber that is determined to be in the form of particles or short fibers based on common technical knowledge. In the present disclosure, the aggregate of short fibers is also included in the secondary particles.

[0024] The average particle size of the particles or the average fiber length of the short fibers of the conductive support are not particularly limited as long as they do not impair the effects of the disclosed technology, and can be, for example, 10 nm to 1000 μm. The average particle size and average fiber length of the conductive support can be freely selected taking into account the surface area and porosity of the conductive support. Here, the average particle size refers to the average particle size including primary particles or short fibers and secondary particles. Here, when the conductive support is in the form of short fibers, the average particle size is the average value including the primary particle diameter, where the fiber length of the short fibers is considered to be the primary particle diameter, and the particle diameter of the secondary particles of the short fibers. The average particle size can be measured by measuring the particle diameter of 50 randomly selected particles using a known observation method such as an optical microscope, a scanning electron microscope, or a transmission electron microscope, and calculating the average value. The observation method can be selected depending on the average particle size.

[0025] 1-2. Catalyst The catalyst according to the present disclosure is supported on a conductive support to form a support.

[0026] The catalyst is a known catalyst capable of reducing carbon dioxide, and includes particles of metals or inorganic compounds such as gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, tin oxide, copper oxide, or carbon nitride; or particles of metal complexes of copper, nickel, iron, cobalt, zinc, manganese, molybdenum, rhenium, tin, indium, lead, ruthenium, or aluminum. These may be used alone or in combination. These may be selected in consideration of corrosion resistance.

[0027] The catalyst is mainly in particulate form. Alternatively, the catalyst may be in the form of secondary particles formed by aggregation of particles (primary particles). Here, particulate form is not limited to those that are determined to be particulate based on common technical knowledge, but also includes catalysts that are very small, called "monoatomic catalysts," in which coordinate-bonded metals are highly dispersed at the atomic level.

[0028] The average particle size of the catalyst particles is not particularly limited as long as it does not impair the effects of the presently disclosed technology. For example, it can be 0.001 to 100 μm, preferably 0.001 to 1 μm, and more preferably 0.001 to 0.1 μm. The catalyst particle size can be freely selected taking into account the catalyst's surface area and size effect. As the catalyst particle size increases, the catalyst's surface area increases, resulting in an increase in the number of active sites (sites) that contribute to the reaction. On the other hand, in addition to the surface area effect, the catalyst particle size also has an effect known as the size effect, which significantly changes the activity and selectivity. Therefore, the catalyst activity can be confirmed depending on the device being used, and the catalyst particle size can be selected accordingly. The smaller the average primary particle size of the catalyst for the carbon dioxide reduction reaction, the more effective it is due to the size effect. In the presently disclosed technology, the average primary particle size of the catalyst is preferably 50 nm or less, and more preferably 20 nm or less. Furthermore, it is preferable for the catalyst to be dispersed rather than aggregated, i.e., to contain a large number of primary particles, as this increases the catalytic effect. Here, the average particle size of the catalyst refers to the average particle size including the primary particles and secondary particles of the catalyst. Furthermore, the average primary particle size refers to the average particle size of only the primary particle size. These average (or primary) particle sizes can be measured by measuring the particle diameters of 50 randomly selected particles (or primary particles) using a known observation means such as an optical microscope, scanning electron microscope, or transmission electron microscope, and calculating the average value. The observation means can be selected depending on the average (or primary) particle size.

[0029] The amount of catalyst supported on the conductive support is not particularly limited as long as it does not impair the effects of the disclosed technology, but for example, when the total amount of the support is taken as 100 mass%, the amount of catalyst in the support can be 10 mass% or more, 20 mass% or more, 30 mass% or more, 40 mass% or more, and can be 70 mass% or less, 60 mass% or less, 50 mass% or less. When the catalyst support amount is within this range, aggregation of the catalyst can be suppressed and high catalytic activity can be maintained.

[0030] 1-3. Anion exchange resin The anion exchange resin according to the present disclosure coats a part or the whole of the surface of a support comprising a catalyst and a conductive carrier.

[0031] The anion exchange resin according to the present disclosure is an ionomer represented by the following formula (1):

[0032] [ka] (In the formula, m and n represent natural numbers from 1 to 200.)

[0033] The ion exchange capacity of the anion exchange resin (ionomer) is 0.5 mmol / g or more and 3.5 mmol / g or less, preferably 1.0 mmol / g or more and less than 2.5 mmol / g. When the ion exchange capacity of the anion exchange resin is within this range, an electrode material with excellent CO2 reduction efficiency can be obtained.

[0034] When the catalyst is supported on a conductive support and is not coated with an anion exchange resin, or when the anion exchange resin has a low ion exchange capacity even if the support is coated with an anion exchange resin, the amount and mobility of ions to be produced or consumed in the CO2 reduction reaction decrease, resulting in a slower reduction reaction rate. Furthermore, because the CO2 supplied to the electrode material is gaseous, the CO2 can move freely, limiting its opportunities for adsorption on the active sites of the catalyst and limiting the CO2 reduction efficiency.

[0035] On the other hand, when the support is coated with the anion exchange resin of formula (1), and preferably when the ion exchange capacity of the anion exchange resin of formula 1 is high to a certain level (when the ion exchange capacity is 1.0 mmol / g or more), the amount of ions available to be produced or consumed by the CO2 reduction reaction and the conductivity are improved, thereby improving the reduction reaction rate. In addition, CO2, which is a weak acid incorporated into the coating, is neutralized by the basic sites of the anion exchange resin and is converted mainly into bicarbonate ions (HCO3 -), or carbamic acid ester (carbamate), which can remain in the anion exchange resin. As a result, bicarbonate ions are abundantly stored near the catalyst supported on the support, and these bicarbonate ions turn into CO2 through an equilibrium reaction, 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 when the supplied CO2 concentration is high, but is more effective when the supplied CO2 concentration is low.

[0036] Furthermore, if the ion exchange capacity exceeds 3.5 mmol / g, the material will become highly hydrophilic, which will cause swelling due to the water (H2O) generated during the neutralization reaction described above. This may inhibit the supply of CO2, leading to the progression of the side reaction of H2 generation, or may reduce the mechanical properties of the material as an electrode material for CO2.

[0037] The ion exchange capacity of an anion exchange resin can be adjusted by the ratio of hydrophobic structures to hydrophilic structures in the molecular structure of the ionomer. Here, the hydrophobic structure is the portion of formula (1) represented by the following formula (2):

[0038] [ka]

[0039] The hydrophilic structure is the portion of formula (1) represented by the following formula (3):

[0040] [ka]

[0041] Furthermore, the ratio of hydrophobic to hydrophilic structures in the molecular structure of an ionomer can be expressed as n / m, using m and n in Equation 1. By adjusting this ratio, the ion exchange capacity of the ionomer can be adjusted. In each of the above formulas, the repeating structural portions of the hydrophobic structure and the hydrophilic structure are expressed in parentheses. However, this is not limited to a structure in which the repeating structures are polymerized in blocks (block polymer), and may be a structure in which the repeating structures are bonded to each other in a regular manner, such as randomly or alternately.

[0042] Therefore, the ion exchange capacity of an anion exchange resin can be adjusted by copolymerizing a monomer having a hydrophobic structure or a polymer obtained by pre-polymerizing a monomer with a hydrophilic structure or a polymer obtained by pre-polymerizing a monomer, while adjusting the blending ratio (m / n) of each.

[0043] The ion exchange capacity of an anion exchange resin is obtained from the integral value of the signals of quaternary ammonium groups and other functional groups that serve as basic sites by 1H-NMR measurement.

[0044] The anion exchange resin covers part or all of the surface of the support, and the coverage rate, which is the ratio of the coverage area to the surface area of ​​the support (coverage area / support surface area × 100), can be 70% or more, 80% or more, 90% or more, 95% or more, or 100%. From the perspective of the effect of accumulating a large amount of CO2 near the catalyst, a higher coverage rate is preferable. Here, the coverage rate is the average coverage rate calculated using the above formula by observing the surfaces of 50 randomly selected electrode material particles with a transmission electron microscope.

[0045] The average coating thickness of the anion exchange resin is not particularly limited as long as it does not impair the effects of the disclosed technology, but it can be, for example, 0.01 to 100 μm. When the average coating thickness of the anion exchange resin is 0.01 μm or more, ion conduction channels are sufficiently formed, and hydroxide ions (OH - ) can be transported to the ion exchange membrane more efficiently, and since the number of basic sites is sufficient, the retention of carbonate species such as CO2 and bicarbonate ions is sufficient. Furthermore, if the average coating thickness of the anion exchange resin is 100 μm or less, the distance that ions must travel is appropriate, so the resistance to ion movement is moderate, and voltage increase (efficiency decrease) can be suppressed. Furthermore, the distance that CO2 must diffuse to reach the catalyst is not too long, so CO2 can move easily, and voltage increase (efficiency decrease) can be suppressed. As described above, when the average coating thickness of the anion exchange resin is within this range, an electrode material can be obtained that has excellent efficiency in generating reduction products (CO, etc.) from CO, and that has even more excellent efficiency in generating reduction products, particularly when the supply concentration of CO is low.

[0046] 2. Manufacturing method of electrode materials 2-1. Method for synthesizing anion exchange resin (ionomer) A preferred example of a synthesis method for an anion exchange resin (ionomer) according to the present disclosure will be described below, but the present disclosure is not limited to the synthesis method described below.

[0047] 2-1-1. Synthesis of Monomer 1 A round-bottomed, three-necked flask equipped with a nitrogen inlet and a condenser is charged with 1,6-diiodoperfluorohexane (e.g., 10.0 mmol), 3-chloroiodobenzene (e.g., 50 mmol), and N,N-dimethyl sulfoxide (e.g., 60 mL). After stirring the mixture to form a homogeneous solution, copper powder (e.g., 150 mmol) is added and the reaction is carried out at 120°C for 48 hours. The reaction solution is then dropped into a 0.1 M aqueous nitric acid solution to terminate the reaction. The precipitate is collected by filtration from the mixture, washed with methanol, and the filtrate is recovered. After repeating the same procedure, pure water is added to the combined filtrate to precipitate a white solid, which is then filtered and collected. The solid is washed with a mixture of pure water and methanol (pure water / methanol = 1 / 1) and dried overnight under vacuum at 60°C to synthesize Monomer 1 (white solid) represented by the following formula (4).

[0048] [ka]

[0049] 2-1-2. Synthesis of Monomer 2 Fluorene (e.g., 0.50 mol), N-chlorosuccinimide (e.g., 1.25 mol), and acetonitrile (e.g., 166 mL) are added to a round-bottom, three-necked flask. After stirring to form a homogeneous solution, 12 M hydrochloric acid (e.g., 16.6 mL) is added and the reaction is carried out at room temperature for 24 hours. The precipitate is collected by filtration from the reaction solution, washed with methanol and purified water, and then vacuum-dried overnight at 60°C to obtain Monomer 2 (white solid) represented by the following formula (5).

[0050] [ka]

[0051] 2-1-3. Synthesis of Monomer 3 Monomer 2 (e.g., 35.0 mmol) and 1,6-dibromohexane (e.g., 53 mL) are added to a round-bottom, three-necked flask. After stirring to form a homogeneous solution, a mixed solution of tetrabutylammonium (e.g., 7.00 mmol), potassium hydroxide (e.g., 35.0 g), and purified water (e.g., 35 mL) is added and the reaction is carried out at 80°C for 1 hour. Purified water is added to the reaction solution to quench the reaction. The target product is extracted from the aqueous layer with dichloromethane. The combined organic layer is washed with purified water and brine, and the water, dichloromethane, and 1,6-dibromohexane are distilled off. The crude product is purified by silica gel column chromatography (developing solvent: dichloromethane / hexane = 1 / 4) and then vacuum-dried overnight at 60°C to obtain Monomer 3 (a pale yellow solid) represented by the following formula (6):

[0052] [ka]

[0053] 2-1-4. Synthesis of Monomer 4 Monomer 3 (e.g., 23.4 mol) and tetrahydrofuran (e.g., 117 mL) are added to a round-bottom, three-necked flask. After stirring the mixture to form a homogeneous solution, 40 wt% aqueous dimethylamine solution (e.g., 58.6 mL) is added and the reaction is carried out at room temperature for 24 hours. A saturated aqueous solution of sodium bicarbonate is added to the reaction solution to terminate the reaction. After removing the tetrahydrofuran, hexane is added to extract the target component. The organic layer is washed with brine, and the water and hexane are distilled off. Monomer 4 (pale yellow solid) represented by the following formula (7) can be obtained by drying the mixture in a vacuum at 40°C overnight.

[0054] [ka]

[0055] 2-1-5. Polymerization reaction Monomer 1 (e.g., 2.91 mmol), monomer 4 (e.g., 1.67 mmol), 2,2'-bipyridine (e.g., 10.9 mmol), and N,N-dimethylacetamide (e.g., 11 mL) were added to a round-bottom, three-neck flask equipped with a nitrogen inlet and a condenser. After stirring to form a homogeneous solution, bis(1,5-cyclooctadiene)nickel(0) (e.g., 10.9 mmol) was added and the mixture was allowed to react at 80°C for 3 hours. The reaction mixture was then added dropwise to a mixture of methanol and 12 M hydrochloric acid (methanol / 12 M hydrochloric acid = 1 / 1) to quench the reaction. The precipitate was collected by filtration and washed with 12 M hydrochloric acid, 0.2 M potassium carbonate aqueous solution, and purified water. It was then dried overnight under vacuum at 60°C to obtain the anion exchange resin precursor polymer (yellow solid) represented by the following formula (8).

[0056] [ka]

[0057] 2-1-6. Quaternization reaction A round-bottom, three-necked flask is charged with an anion exchange resin precursor polymer (e.g., 1.70 g) and N,N-dimethylacetamide (e.g., 9.6 mL). After stirring to form a homogeneous solution, methyl iodide (e.g., 7.22 mmol) is added and the reaction is allowed to proceed at room temperature for 48 hours. The reaction solution containing N,N-dimethylacetamide (e.g., 10 mL) is filtered. The filtrate is poured onto a silicone-rimmed glass plate and dried on a leveled hot plate (50 °C). The resulting membrane is washed with pure water (e.g., 2 L) and then vacuum-dried overnight at 60 °C to obtain a pale brown, transparent membrane. The counterion of the ion exchange group (quaternary ammonium group) can be converted from iodide to hydroxide by immersing the membrane in a 1 M potassium hydroxide solution for 48 hours and then washing with degassed pure water. This allows for the production of an anion exchange resin (ionomer) represented by the following formula (1) (for example, when m / n=1 / 0.60, the ion exchange capacity is 1.47 mmol / g). The resulting anion exchange resin can be formed into a membrane, which can be made into an anion exchange membrane. The membrane can be produced by a known method, such as a casting method using an applicator.

[0058] [ka]

[0059] 2-2. Manufacturing method of electrode material A predetermined amount of conductive support and catalyst are mixed using a known mixer to prepare a support. The mixing time can be 3 to 60 minutes. Another method for preparing a support can be a method in which the catalyst is precipitated on the conductive support by a reduction reaction. More specifically, a predetermined amount of conductive support, catalytic metal, and reducing agent are mixed, and the catalytic metal can be supported on the conductive support by reducing the cations. The mixing time in this method can be 1 to 48 hours. An organic solvent is placed in a container, and an anion exchange resin (ionomer) is added and dissolved to prepare an ionomer solution. The ionomer concentration in the ionomer solution is 0.1 to 50 mass% based on the total amount of the ionomer solution, and the coating thickness and coverage rate can be adjusted by adjusting the ionomer concentration in the ionomer solution. The organic solvent used in the ionomer solution is not particularly limited as long as it can dissolve the ionomer, and can be freely selected taking the solubility of the ionomer into consideration. The obtained support is placed in the prepared ionomer solution and mixed with a mixer etc. to prepare a support dispersion solution. The mixing time can be 5 to 60 minutes. The obtained support dispersion solution is sprayed onto an electrode support such as carbon paper using a known spraying device such as a sprayer, and dried to prepare an electrode material adhered to the carbon paper, etc. Drying can be carried out naturally or, if necessary, using a drying oven or the like.

[0060] 3. Uses of electrode materials The electrode material of the present disclosure can be used in a CO2 electrolysis device by forming it into an electrode or a membrane-electrode assembly.

[0061] 3-1. Membrane-electrode assembly When a membrane-electrode assembly is formed using the electrode material of the present disclosure, a membrane-electrode assembly with high CO2 reduction efficiency can be obtained.

[0062] The membrane-electrode assembly of the present disclosure includes the electrode material of the present disclosure, a solid electrolyte, and a current collector, and the electrode material of the present disclosure is used by being disposed between the solid electrolyte and the current collector. The electrode material can be formed into an electrode of a desired shape by molding the electrode material or by attaching it to a substrate. The solid electrolyte is an anion exchange membrane.

[0063] 3-1-1.Solid electrolyte The solid electrolyte of the present disclosure is not particularly limited as long as it does not impair the effects of the present disclosure. 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 membrane-electrode assembly of the present disclosure, it is particularly preferred to use anion exchange membranes containing primary amino groups, secondary amino groups, tertiary amino groups, quaternary ammonium groups, or a mixture of these ion exchange groups. Specific examples include Neosepta (registered trademark), ASE, AHA, AMX, ACS, AFN, and AFX (manufactured by Tokuyama Corporation), Selemion (registered trademark), AMV, AMT, DSV, AAV, ASV, AHO, AHT, and APS4 (manufactured by Asahi Glass Co., Ltd.). Furthermore, ion exchange membranes formed from an ionomer of the following formula (1) can be used.

[0064] [ka]

[0065] The material of the anion exchange membrane may be the same as or different from the material of the anion exchange resin that coats the electrode material of the present disclosure. When the material of the anion exchange membrane is the same as the material of the anion exchange resin that coats the electrode material of the present disclosure, it is possible to provide a membrane-electrode assembly and a CO electrolysis device that are capable of suppressing a decrease in CO reduction efficiency and enabling stable operation. Furthermore, when an anion exchange resin and an anion exchange membrane are combined, it is possible to prevent deterioration of the interface between the anion exchange resin and the anion exchange membrane, and it is also possible to achieve the effect of smoothing ion migration (conduction) by preventing phase separation at the interface between the anion exchange resin and the anion exchange membrane.

[0066] The ion exchange capacity of the anion exchange membrane is from 0.3 mmol / g to 3.5 mmol / g, preferably from 0.5 mmol / g to 2.5 mmol / g. When the ion exchange capacity of the anion exchange membrane is within this range, it is possible to provide a membrane-electrode assembly and a CO electrolysis device that can suppress a decrease in CO reduction efficiency and operate at a lower voltage and in a more stable manner.

[0067] 3-1-2. Current collector Examples of current collectors according to the present disclosure include metal materials such as copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass, with copper being preferred from the standpoints of ease of processing and cost. When the negative electrode current collector is made of a metal material, its shape may be, for example, a metal foil, a metal plate, a metal thin film, an expanded metal, a punched metal, or a foamed metal.

[0068] Here, the current collector is provided with vent holes for supplying and recovering gas (raw material gas and generated gas) to the electrode (or electrode material). These vent holes make it possible to uniformly and efficiently deliver raw material gas to the electrode (or electrode material) and discharge generated gas (including unreacted raw material gas). The number, location, and size of the vent holes are not limited and may be set appropriately. In addition, if the current collector is breathable, vent holes are not necessary. Figure 3 shows an explanatory diagram of a membrane-electrode assembly, and the current collector in Figure 3 is made of a porous, breathable material. [Example]

[0069] Next, the disclosed technology will be described in detail using examples and comparative examples, but the disclosed technology is not limited to these in any way.

[0070] <<Preparation of electrode materials>> <Synthesis of anion exchange resin (ionomer)> Ionomers of the above formula (1) with different ion exchange capacities were synthesized by the method described above, and used as the ionomers of Examples 1 and 2.

[0071] <Fabrication of Electrodes> As a catalyst, 2 mg of Ag nanoparticles (particle diameter 1 - 100 nm) and 10 mg of conductive carbon black (average particle diameter 30 nm) were deposited on Ag + The powder obtained by precipitation through reduction of ions was mixed using a mixer (equipment name and processing conditions) to fabricate a support. In a container, the support was dispersed in an ionomer solution prepared by dissolving 6 mg of ionomers with different ion exchange capacities in an organic solvent as described below, and then coated onto carbon paper (area 2.25 cm 2 ) using a spray to obtain the electrodes of Examples 1 - 2. Also, for the ionomers of Comparative Examples 1 - 2, electrodes were fabricated in the same manner to obtain the electrodes of Comparative Examples 1 - 2, respectively. The coverage rate of the electrode materials for each example and comparative example was 100%. (Raw Materials) [[ID=IO]]Ionomer of Example 1: The ionomer of formula (1), ion exchange capacity 2.1 mmol / g Ionomer of Example 2: The ionomer of formula (1), ion exchange capacity 1.5 mmol / g Ionomer of Comparative Example 1: Ion exchange capacity 2.0 mmol / g, FAA - 3 - 50 manufactured by FUMATECH BWT GmbH Ionomer of Comparative Example 2: Ion exchange capacity 1.1 mmol / g, XA - 9 manufactured by Dioxide Materials

[0072] <CO₂ Electrolyzer> The electrodes of each obtained example and comparative example were used as the cathode, and a titanium mesh supporting iridium oxide was used as the anode. Also, an anion exchange membrane with an ion exchange capacity of 1.5 mmol / g and a membrane thickness of 30 - 35 μm was used as the solid electrolyte. An electrolytic solution tank (0.5 M aqueous KHCO₃ solution) was used as the solution on the anode side, respectively. They were arranged in the order of cathode, solid electrolyte, anode, and electrolytic solution tank, with a structure where the cathode and the electrolytic solution tank sandwich the ion exchange membrane and the anode. The evaluation was carried out by supplying a gas mixed at a volume ratio of CO₂:N₂ = 3:1 to the cathode, and setting the applied potential of the cathode to - 1.8 V with respect to a silver / silver chloride reference electrode.

[0073] <<Evaluation>> <Evaluation of Electrolysis Performance> Using a CO2 electrolysis device incorporating the electrodes of each example and each comparative example, the CO generation current density J when electrolyzing CO2 to CO CO [mA / cm 2 ] was measured.

[0074] [Table 1]

[0075] <Stability evaluation> The solid electrolyte of the CO2 electrolysis device incorporating the electrodes of Example 1 was changed to the ion exchange membrane shown below, and the CO2 electrolysis devices of Examples A to D were evaluated for stability. The stability evaluation was carried out under the same conditions as in the electrolysis performance evaluation above, by operating the device continuously for 20 hours and measuring the CO generation current density J when CO2 was electrolyzed to CO. CO [mA / cm 2 The stability was evaluated according to the following criteria. The results are shown in Table 2. (solid electrolyte) Example A: Ionomer of formula (1), ion exchange capacity 1.0 mmol / g Example B: Ionomer of formula (1), ion exchange capacity 1.5 mmol / g Example C: Ionomer of formula (1), ion exchange capacity 2.1 mmol / g Example D: FAS-30 manufactured by FUMATECH BWT GmbH with an ion exchange capacity of 1.8 mmol / g (Evaluation criteria) ◎: J 20 hours after the start of electrolysis CO is 50mA / cm 2 Furthermore, the CO selectivity is 90% or more 20 hours after the start of electrolysis. ○: J 20 hours after the start of electrolysis CO is 50mA / cm 2 or more, and the CO selectivity 20 hours after the start of electrolysis is less than 90%. △: J 20 hours after the start of electrolysis CO is 50mA / cm 2 is less than.

[0076] [Table 2] [Explanation of symbols]

[0077] 1 Electrode materials 10 Conductive support 11 Catalyst (active site) 12 Ion exchange resin 100 CO2 electrolyzer 101 Cathode 101-1 Cathode surface in contact with solid electrolyte 101-2 Surface of cathode in contact with current collector 102 Anode 102-1 Surface of anode in contact with support plate 102-2 Anode surface in contact with solid electrolyte 103 Solid electrolyte 104 Current collector 104-1 Gas supply hole on current collector 104-2 Gas collection hole in current collector 105 Support plate 105-1 Gas flow path of support plate 106 Voltage application section

Claims

1. a support comprising a conductive support and a catalyst supported on the conductive support, the catalyst comprising one or more particles of a metal complex, a metal, or an inorganic compound; an anion exchange resin that coats a part or all of the surface of the support and contains an ionomer represented by the following formula (1): The electrode material is used for a cathode, The anion exchange capacity of the anion exchange resin is 0.5 mmol / g or more and less than 3.5 mmol / g. ２ Electrolyzer. 【Chemistry 1】 (where m and n represent natural numbers from 1 to 200)

2. a membrane-electrode assembly including the electrode material, a solid electrolyte, and a current collector; 2. The CO 2 battery according to claim 1, wherein the electrode material is provided between the solid electrolyte and the current collector. ２ Electrolyzer.

3. 3. The CO2 gas separator according to claim 2, wherein the solid electrolyte is an anion exchange membrane. ２ Electrolyzer.

4. 4. The CO 2 membrane according to claim 3, wherein the anion exchange membrane comprises an ionomer represented by the following formula (1): ２ Electrolyzer. 【Chemistry 2】 (where m and n represent natural numbers from 1 to 200)

5. 5. The CO2 separator according to claim 3, wherein the anion exchange capacity of the anion exchange membrane is 0.3 mmol / g or more and less than 3.5 mmol / g. ２ Electrolyzer.

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