JP7040220B2 - Electrode material for electrochemical reduction, electrode for electrochemical reduction and electrochemical reduction device - Google Patents

Description

The present invention relates to an electrochemical reduction electrode material, an electrochemical reduction electrode, and an electrochemical reduction device.

As part of measures against global warming, attention is focused on technology that reduces carbon dioxide with a catalyst and converts it into fuels such as carbon monoxide, organic acids, alcohols and hydrocarbons, raw materials for chemical products, or useful substances such as chemical products themselves. For example, a reaction that produces formic acid from carbon dioxide (CO ₂ + H ₂ O → HCOOH + 1 / 2O ₂ ) and a reaction that produces methanol from carbon dioxide (CO ₂ + 2H ₂ O → CH ₃ OH + 3 / 2O). ₂ ) etc. are known.

There are roughly three methods for reducing carbon dioxide with a catalyst: thermodynamic reduction, electrochemical reduction, and photochemical reduction. Of these, the carbon dioxide reduction reaction using electrochemical reduction is plate-shaped. A method of performing electrolytic reduction in an aqueous solution saturated with carbon dioxide (see Non-Patent Document 1), or a method of performing electrolytic reduction using copper nanoparticles supported on carbon as a catalyst. (See Non-Patent Document 2) has been reported. Further, as a carbon dioxide reduction reaction using photochemical reduction, a method of photoreducing carbon dioxide using a catalyst containing a titanium oxide supported by vanadium oxide (see Patent Document 1) and gold on semiconductor particles. , A method of photoreducing carbon dioxide using a noble metal-containing nanoparticles-supporting catalyst on which predetermined noble metal-containing nanoparticles such as silver, copper, and platinum are supported (see Patent Document 2) has been reported.

Japanese Unexamined Patent Publication No. 2016-73963 Japanese Unexamined Patent Publication No. 2017-177094

YOSHIO HORI, 3 outsiders, "ELECTROCATALITIC PROCESS OF CO SELECTIVITY IN ELECTROCHEMICAL REDUCTION OF CO2 AT METAL ELECTRODES IN AQUEOUS MEDIA", Electroc. 11/12, 1994, p1833-1389 Olga A. Baturina, 12 outsiders, "CO2 Electroreducion to Hydrocarbons on Carbon-Supported Cu Nanoparticles", ACS Catalysis, Vol. 4, 2014, p3682-3695.

Among the above three methods, electrochemical reduction is a technique that attracts attention because it has higher reaction efficiency than other methods and can be scaled up. However, in the method described in Non-Patent Document 1, the method described above Since the plate-shaped metal has a very small contact area with carbon dioxide to be reduced, the equipment becomes large and the equipment cost becomes enormous in order to reduce a large amount. In the method described in Non-Patent Document 2, carbon as a carrier may be decomposed during operation, and side reactions such as electrolysis of water occur on the carrier, so that the conversion efficiency to a target product is a metal electrode. Will be inferior to.
As described above, all of the electrode materials (catalysts) used in the conventional methods have room for improvement in terms of performance and cost.

In view of the above situation, the present invention can suppress the decomposition of carriers and the progress of side reactions in the electrochemical reduction reaction of carbon dioxide, and can proceed with the reaction of converting carbon dioxide to a target substance with high efficiency. It is an object of the present invention to provide an electrode material which is advantageous in terms of cost.

The present inventors have studied various electrode materials used for the electrochemical reduction reaction, and have carried a simple substance and / or a compound of a metal element of Group 6 to 16 of the periodic table on a powdered titanium sulfite carrier. By performing an electrochemical reduction reaction of carbon dioxide using as an electrode material, there is no carbon decomposition reaction that occurs when carbon is used as a carrier, and the progress of side reactions is suppressed to be the target compound of carbon dioxide. We have found that the conversion reaction to can be carried out with high efficiency, and that a reaction apparatus can be made more compact than when a plate-shaped metal is used as a catalyst, and the present invention has been completed.

That is, the present invention is an electrode material used for electrochemical reduction, in which a simple substance and / or a compound of a metal element of Group 6 to 16 of the periodic table is supported on a powdered titanium borooxide carrier. It is an electrode material for electrochemical reduction characterized by having a structure.

The electrode material has a structure in which a single metal element of Group 6 to 16 of the periodic table is supported on the powdered titanium sulfite carrier, and is supported on the surface of the powdered titanium hydroxide carrier with respect to the total surface area of the electrode material. It is preferable that the coverage ratio represented by the ratio of the surface area of a single metal element of Group 6 to 16 of the periodic table is 0.5% or more.

The electrode material has a structure in which a compound of a metal element of Group 6 to 16 of the periodic table is supported on a powdered titanium hydroxide carrier, and is supported on the surface of the powdered titanium oxide carrier with respect to the total surface area of the electrode material. It is preferable that the coverage ratio represented by the ratio of the surface area of the compound of the metal element of Group 6 to 16 of the periodic table is 3.0% or more.

The metal elements of Groups 6 to 16 of the Periodic Table are Sn, In, Ga, Ge, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ir, Pt, Au, Ru, Rh, Pd, Ag, Mo. , W is preferably at least one element selected from the group.

The powdered titanium oxide carrier is preferably represented by the composition formula TiOn ( _n represents a number of 1.5 or more and 1.9 or less).

The electrode material for electrochemical reduction is preferably used for electrochemical reduction of carbon dioxide.

The present invention is also an electrochemical reduction electrode, characterized in that the electrochemical reduction electrode material of the present invention is used.

The present invention is also an electrochemical reduction apparatus characterized by using the electrochemical reduction electrode of the present invention.

The electrode material for electrochemical reduction of the present invention uses powdered titanium sulfite as a carrier, so that there is no carbon decomposition reaction that occurs when a carbon carrier is used, and carbon dioxide suppresses the progress of side reactions. It is an electrode material that can proceed with the conversion reaction to the target product with high efficiency, and it is advantageous in terms of cost as compared with the case where a plate-shaped metal or the like is used as a catalyst. Therefore, the electrochemical reduction reaction of carbon dioxide Can be suitably used as an electrode of.

It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in Example 1. It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in Example 2. It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in the comparative example 1. FIG. It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in the comparative example 2. It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in the comparative example 3. FIG. It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in the comparative example 4. It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in the comparative example 5. It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in the comparative example 6. It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in the comparative example 7. It is a backscattered electron image by the transmission type electron microscope observation of the electrode material powder obtained in the comparative example 8.

Hereinafter, preferred embodiments of the present invention will be specifically described, but the present invention is not limited to the following description, and can be appropriately modified and applied without changing the gist of the present invention.

1. 1. Electrochemical reduction electrode material The electrochemical reduction electrode material of the present invention is a powdered titanium sulfite carrier containing a single metal element and / or a compound of Group 6 to 16 of the Periodic Table (hereinafter referred to as a single metal element and a compound). It is characterized by having a structure in which / or compounds are collectively referred to as "metal species"). Since the electrode material for electrochemical reduction of the present invention uses powdered titanium dioxide as the carrier, the carbon decomposition reaction, which is a problem when a carbon carrier is used, does not occur. In addition, since the carrier that contributes to the side reaction is uniformly coated with the metal species that contribute to the conversion to the main organism (also called the main product), it is possible to proceed with the conversion reaction to the target substance of carbon dioxide with high efficiency. The desired product can be obtained in a high yield.
Furthermore, the contact area of the substance to be reduced with carbon dioxide is larger than that of a plate-shaped metal as a catalyst or a metal plate plated on another metal plate, so that the device can be made compact. It is possible.

The electrode material for electrochemical reduction of the present invention is not particularly limited as long as it has a structure in which a simple substance and / or a compound of the metal elements of Groups 6 to 16 of the periodic table with respect to the powdered titanium oxide carrier is supported. The coverage ratio expressed by the ratio of the surface area of the single metal element of Group 6 to 16 of the periodic table supported on the surface of the powdered titanium oxide carrier to the total surface area of the electrode material is 0.5% or more. preferable. With such a coverage, the catalytic activity of the electrode material becomes higher, and the conversion selectivity from carbon dioxide to the target product is further improved. The coverage is more preferably 1.0% or more, still more preferably 3.0% or more. The coverage is preferably 60.0% or less.

In particular, when the simple substance and / or compound of the metal element supported on the powdered titanium oxide carrier is only the compound of the metal element of Group 6 to 16 of the periodic table, the coverage may be 3.0% or more. preferable. The coverage is more preferably 6.0% or more, still more preferably 10.0% or more. With such a coverage, the catalytic activity of the electrode material becomes higher, and the conversion selectivity from carbon dioxide to the target product is further improved. The coverage is preferably 60.0% or less.
The coverage can be measured by the method described in Examples described later.

The average primary particle size of the simple substance of the metal element of Group 6 to 16 of the periodic table and / or the simple substance of the compound supported on the powdered titanium oxide carrier is preferably 600 nm or less. With such an average primary particle size, a simple substance of a metal element can exhibit higher activity as a catalyst for electrochemical reduction. The average primary particle size is more preferably 1 to 200 nm.
The average primary particle size of a simple substance and / or a compound of a metal element can be measured by measuring the primary particle size of 40 pieces using a photograph taken by a transmission electron microscope (TEM) and calculating the average.

The electrode material for electrochemical reduction of the present invention comprises a carrier carrying a simple substance and / or a compound of the metal elements of Groups 6 to 16 of the Periodic Table, but as the metal elements of Groups 6 to 16 of the Periodic Table. Is selected from the group consisting of Sn, In, Ga, Ge, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ir, Pt, Au, Ru, Rh, Pd, Ag, Mo, and at least one. Species elements are preferred. More preferably, it is at least one element selected from the group consisting of Sn, In, Ga, Ge, Ni, Cu, and Zn, and even more preferably, it is a group consisting of Sn, In, Ga, Ge, Cu, and Zn. At least one element more selected.
By using a simple substance and / or a compound of at least one element selected from the group consisting of Sn, In, Ga, Ge, Cu, and Zn, a target product can be obtained with a higher selectivity by a reduction reaction of carbon dioxide. Can be done.

Examples of the compound of the metal element of Group 6 to 16 of the periodic table include oxides, nitrides, oxynitrides, hydroxides and the like, and among these, oxides are preferable.

The powdered titanium oxide used as a carrier in the electrode material for electrochemical reduction of the present invention is reduced titanium oxide, and has the following formula (1);
TiOn (1.5 ≦ n ≦ 1.9) (1)
It is preferably represented by.

The powdered titanium dioxide used as a carrier in the electrode material for electrochemical reduction of the present invention is represented by the above composition formula, has a rutile-type crystal structure or a magnetic structure, and a single phase of Ti ₃ O ₅ and Ti ₂ O ₃ . Alternatively, a mixture may be mentioned. By having these crystal structures, the conductivity required as an electrode material can be more sufficiently exhibited.

The powdered titanium dioxide is a titanium dioxide having a shape usually recognized as a powder, having an average primary particle diameter of 1 μm or less measured by the same method as the average primary particle diameter of a simple substance and / or a compound of the above-mentioned metal element. It should be.

The powdered titanium dioxide used as a carrier in the electrode material for electrochemical reduction of the present invention preferably has a BET specific surface area of 10 m ² / g or more. When the BET specific surface area of the powdered titanium suboxide of the carrier is 10 m ² / g or more, simple substances and / or compounds of metal elements necessary for electrolytic reduction of carbon dioxide can be effectively supported. The specific surface area of the powdered titanium oxide carrier is more preferably 13 m ² / g or more.

The powdered titanium dioxide carrier used in the electrode material for electrochemical reduction of the present invention has a powder volume specific resistance value of 1.0 × 10 ^-6 Ω · cm or more and ^1.0 × 100 Ω · cm or less. Is preferable. By using a powdered titanium oxide carrier in which the volume specific resistance value of the powder is in such a range, an electrode catalyst having high electron conductivity can be produced and highly active against the electrochemical reduction of carbon dioxide. Can be obtained. The upper limit of the volume resistivity of the powder of the powdered titanium oxide carrier is more preferably 5.0 × 10 ^-1 Ω · cm or less, and further preferably 1.0 × 10 ^-1 Ω · cm. It is as follows.
The volume resistivity value of the powder of the powdered titanium oxide carrier can be measured by the method described in Examples.

2. 2. Manufacturing method of electrode material for electrochemical reduction
The method for producing the electrode material for electrochemical reduction of the present invention is not particularly limited, but the step (1) for obtaining a powdered titanium oxide carrier whose composition is represented by TiOn (1.5 ≦ n ≦ 1.9). , Can be easily and easily obtained by a production method including the step (2) of supporting a simple metal and / or a compound thereof on the surface of the powdered titanium dioxide carrier obtained in the step (1). If necessary, this production method may further include one or more other steps adopted in ordinary powder production.
Hereinafter, each step will be further described.

1) Process (1)
The step (1) is a step of obtaining a powdered titanium dioxide carrier having a composition represented by TiOn (1.5 ≦ n ≦ 1.9). By subjecting the powdered titanium oxide carrier to the step of supporting a simple substance of a metal and / or a compound thereof (step (2)), it is possible to provide an electrode material having high conductivity and high carbon dioxide reducing activity. can.
The step (1) is not particularly limited as long as it can obtain the powdered titanium oxide carrier, but it is preferably a step of calcining a raw material containing titanium oxide in a reducing atmosphere. The crystal structure of titanium oxide is not particularly limited, and examples thereof include rutile-type titanium oxide and anatase-type titanium oxide. More preferably, titanium oxide having a specific surface area of 20 m ² / g or more is used, whereby a powdered titanium oxide carrier having a large specific surface area and excellent conductivity can be obtained more efficiently. Further, the raw material may contain a reducing aid such as metallic titanium or titanium hydride.
The preferable crystal structure and specific surface area of the powdered titanium oxide carrier are as described above.

The reducing atmosphere is not particularly limited, and examples thereof include a hydrogen (H ₂ ) atmosphere, a carbon monoxide (CO) atmosphere, an ammonia (NH ₃ ) atmosphere, and a mixed gas atmosphere of hydrogen and an inert gas. Further, the firing may be performed once or twice or more, and may be a single atmosphere or a combination of a plurality of atmospheres.

The temperature at which the raw material containing titanium oxide is fired is preferably 500 to 1100 ° C. More preferably, it is 650 to 1000 ° C.
The firing time is preferably 5 minutes to 100 hours in consideration of sufficient reduction to titanium oxide and production efficiency. More preferably, it is 30 minutes to 24 hours.

2) Process (2)
The step (2) preferably includes a step of mixing the powdered titanium oxide carrier obtained in the step (1) with a simple substance of a metal of Groups 6 to 16 of the Periodic Table and / or a water-soluble compound thereof. Specifically, a solvent is added to the product obtained in the above step (1) to form a slurry, and a solution or dispersion of the slurry and a simple substance of a metal of Group 6 to 16 of the Periodic Table and / or a water-soluble compound thereof. It is preferable to include a step of preparing a mixed solution by mixing with and. By including such a step in the step (2), it is possible to obtain an electrode material in which a metal or a compound thereof is highly dispersed and supported on powdered titanium dioxide as a carrier. It should be noted that each component can be used alone or in combination of two or more.

The solvent used when adding a solvent to the product obtained in the above step (1) to form a slurry is not particularly limited as long as the slurry can be prepared, but water is preferable from the viewpoint of ease of handling.
Further, the slurry may contain additives such as an acid, an alkali, a chelate compound, an organic dispersant, and a polymer dispersant in order to improve dispersibility.

The method for obtaining the above-mentioned mixed solution, that is, the method for preparing the above-mentioned mixed solution is not particularly limited. Examples thereof include a method of adding a solution or dispersion of a simple substance of a group metal and / or a water-soluble compound thereof, and stirring and mixing. The mixing may be performed by a stirrer using a stirrer, or a stirrer equipped with a propeller type or paddle type stirring blade may be used.

The solution or dispersion of the single metal of Group 6 to 16 of the periodic table and / or its water-soluble compound is a solution or dispersion containing the single metal of Group 6 to 16 of the periodic table and / or its water-soluble compound. However, the present invention is not particularly limited, but for example, inorganic salts such as metal sulfates, nitrates, chlorides and phosphates; hydroxides; organic acid salts such as metal acetates and oxalates, etc. Or a dispersion solution of a metal of Group 6 to 16 of the periodic table and / or an oxide thereof. Above all, a solution such as a chloride solution or a hydroxide solution is preferable. The metals of Groups 6 to 16 of the Periodic Table are as described above, and it is particularly preferable that the metal is at least one element selected from the group consisting of Sn, In, Ga, Ge, Cu and Zn.

The amount of the simple substance of the metal of Group 6 to 16 of the periodic table and / or the solution or dispersion of the water-soluble compound thereof is not particularly limited, but for example, the total solid content of the product obtained in the step (1) is 100 mass. It is preferable that the amount is 1 part by mass or more in terms of the element of the metal. As a result, the surface of the carrier that contributes to the side reaction is uniformly coated with elemental substances and / or compounds of the metal element, and the conversion selectivity of the main product in the electrolytic reduction of carbon dioxide is improved. It is more preferably 5 parts by mass or more, still more preferably 10 to 30 parts by mass.

When a solvent is added to the product obtained in the above step (1) to form a slurry, and the slurry is mixed with a simple substance of a metal of Group 6 to 16 of the Periodic Table and / or a solution or dispersion of a water-soluble compound thereof. The temperature of the above is not particularly limited, but is preferably 10 to 50 ° C.

In the above step (2), a solvent is added to the product obtained in the above step (1) to form a slurry, and the slurry and a simple substance of a metal of Group 6 to 16 of the periodic table and / or a solution of a water-soluble compound thereof or a solution thereof or When the step of preparing a mixed solution by mixing with the dispersion is included, in step (2), the metal species of Groups 6 to 16 of the periodic table are further supported on the powdered titanium oxide carrier from the mixed solution. Includes the step of obtaining the electrode material.
The method for obtaining an electrode material from the above mixed solution in which the metal species of Groups 6 to 16 of the periodic table are supported on the powdered titanium oxide carrier is not particularly limited, and the mixed solution is heated to evaporate the water content as described later. A method of drying to dryness, a method of precipitating metal species of Groups 6 to 16 of the Periodic Table on the surface of the carrier by neutralization treatment, and the like can be used. When the neutralization treatment is performed, it is preferable to add a basic solution or an acidic solution to the mixed solution.

The basic solution is not particularly limited, and examples thereof include a NaOH aqueous solution, an _NH3 aqueous solution, and a sodium carbonate aqueous solution, and a NaOH aqueous solution is preferable.

The acidic solution is not particularly limited, and examples thereof include an HCl aqueous solution, an H ₂ SO ₄ aqueous solution, an HNO ₃ aqueous solution, and a CH ₃ COOH aqueous solution.

The step (2) is a step of removing water and by-products (also referred to as by-products) from the mixed solution (which may be neutralized as necessary as described above). It is preferable to include it. The removing means at that time is not particularly limited, but for example, a method of removing water and by-products by filtration, washing with water, drying, evaporation under heating, or the like can be used.

When the mixed solution is neutralized in the above step (2), the metal species of Groups 6 to 16 of the periodic table are deposited on the surface of the carrier and then filtered, and by-products such as salts are washed with water. It is preferable to remove it with. If by-products remain in the electrode material, they elute into the system during the operation of electrolytic reduction of carbon dioxide, causing a decrease in the conversion selectivity of the main organism in the electrolytic reduction of carbon dioxide and damage to the electrolytic reduction system. There is a risk.
The method of washing with water is not particularly limited as long as it can remove the water-soluble substance not supported on the powdered titanium dioxide to the outside of the system, and examples thereof include filtered water washing and decantation. At this time, it is preferable to remove by-products by washing with water until the electric conductivity of the water is washed with water to 10 μS / cm or less. More preferably, it is washed with water until the electric conductivity becomes 3 μS / cm or less.

In step (2), it is more preferable to bake the powder after removing water and by-products from the mixed solution. This makes it possible to bring the electrochemical reduction electrode material into a state suitable for developing carbon dioxide reducing activity. When firing the powder, it is preferable to fire it in a reducing atmosphere. The reducing atmosphere is as described above, and a nitrogen atmosphere, a hydrogen atmosphere, or a mixed atmosphere of nitrogen and hydrogen is particularly preferable.
The firing temperature is not particularly limited, but is preferably 200 to 1100 ° C. More preferably, it is 200 to 1000 ° C.
The firing time is not particularly limited, but is preferably 5 minutes to 100 hours. More preferably, it is 30 minutes to 24 hours.

As described above, the electrochemical reduction electrode material of the present invention is preferably used for the electrochemical reduction of carbon dioxide because it exhibits high catalytic activity in the electrochemical reduction reaction of carbon dioxide. Such an electrochemical reduction electrode using the electrochemical reduction electrode material of the present invention and an electrochemical reduction device using the electrochemical reduction electrode are also one of the present inventions.

Specific examples are given below to explain the present invention in detail, but the present invention is not limited to these examples. Unless otherwise specified, "%" and "wt%" mean "% by weight (% by mass)". The method for measuring each physical property is as follows.

1. X-ray diffraction pattern The powder X-ray diffraction pattern was measured using an X-ray diffractometer (manufactured by Rigaku Co., Ltd., trade name "RINT-TTR3") under the following conditions.
X-ray source: Cu-Kα ray Measurement range: 2θ = 10 to 70 °
Scan speed: 5 ° / min
Voltage: 50kV
Current: 300mA

2. 2. Volume resistance (also referred to as volume intrinsic resistance) measurement of titanium borooxide For the measurement of volume resistance, a powder resistance measurement system MCP-PD51 manufactured by Mitsubishi Chemical Analytec Co., Ltd. was used.
The powder resistance measurement system consists of a hydraulic powder press unit, a four-probe probe, and a high resistance measurement device (Lorester GX MCP-T700 manufactured by the same company).
The value of volume resistance (Ω · cm) was determined according to the following procedure.
1) Put the sample powder into a press jig (diameter 20 mm) equipped with a four-probe probe on the bottom and set it in the pressure section of the powder resistance measurement system. Connect the probe and the high resistance measuring device with a cable.
2) Pressurize to 20 kN using a hand press. The powder thickness is measured with a digital caliper, and the resistance value is measured with a high resistance measuring device.
3) From the bottom area, thickness, and resistance value of the powder, the volume resistivity (Ω · cm) is obtained based on the following mathematical formula (1).

3. 3. Coverage measurement In the present specification, "coverage" is expressed as the ratio of the surface area of a simple substance and / or a compound of a metal element supported on the surface of a powdered titanium borooxide carrier to the total surface area of an electrode material. When the carried metal element alone and / or the compound is a particle, the specific surface area is calculated by using the supported amount of the metal element alone and / or the compound, the average primary particle size, and the supported particle density. However, it can be calculated by the product of the surface area of the sphere and the number of particles. At this time, elemental mapping may be performed as necessary to specify the composition of the particles.
That is, it was calculated by the following mathematical formula (2) by setting the average primary particle diameter to P (nm), the supported amount to S (% by weight), and the density of the supported particles to D (g / cm ³ ). The average primary particle diameter, the amount of the carried amount, and the density of the supported particles of the simple substance and / or the compound of the metal element were measured as follows.
Specific surface area of simple substance and / or compound of supported metal element = 6S / PD × 10 (2)
[Average primary particle size]
It was obtained by measuring the diameters of 40 primary particles and calculating the average using photographs taken with a transmission electron microscope (TEM).
[Carrying amount]
Quantification was performed by the method described in (A) or (B) below.
(A) When the carrier is titanium sulfite 50 mg of the sample is added to 20 ml of 95 wt% ammonium sulfate in which 2.5 g of ammonium sulfate is dissolved, and then the sample is dissolved by stirring and heating at 300 ° C. and cooled to room temperature to induce the obtained solution. It was subjected to an inductively coupled plasma emission spectroscope (ICP) and quantified by the calibration curve method.
(B) When the carrier is carbon black 50 mg of the sample is added to a mixture of 20 ml of 95 wt% sulfuric acid and 60 ml of 60 wt% nitrate, the sample is dissolved by stirring and heating at 300 ° C., and the solution obtained by cooling to room temperature is obtained. It was subjected to an inductively coupled plasma emission spectroscope (ICP) and quantified by the calibration curve method.
[Density of supported particles]
Revised 4th Edition Chemistry Handbook Basic Edition Maruzen Co., Ltd. (1993) and 4th Edition Iwanami Rikagaku Jiten Co., Ltd. Iwanami Shoten Co., Ltd. (1987) quoted the values of applicable metal elements or compounds.

4. Carbon dioxide conversion selectivity (1) Preparation of working electrode For the sample to be measured, 5 wt% perfluorosulfonic acid resin solution (manufactured by Sigma Aldrich Japan Co., Ltd.), isopropyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd.) and ultrapure water Was added and dispersed by ultrasonic waves to prepare a paste. The paste was applied to carbon paper (trade name "EC-TP1-090T" manufactured by Electrochem, Inc.), which is a plate-shaped conductive substance, and dried sufficiently. The dried sample was used as the working electrode.
(2) Electrolytic reduction of carbon dioxide (2-1) The working electrode, counter electrode, and reference electrode were connected to the Automatic Polarization System (manufactured by Hokuto Denko Co., Ltd., trade name "HZ-5000"). The electrode with the measurement sample obtained above was used as the working electrode, and a platinum electrode and a reversible hydrogen electrode (RHE) electrode were used as the counter electrode and the reference electrode, respectively.
(2-2) At 25 ° C., carbon dioxide gas was bubbled in an electrolytic solution (0.1 mol / l potassium hydrogencarbonate aqueous solution) for 30 minutes. The flow rate of carbon dioxide gas was 100 ml / min.
(2-3) Continuing to flow carbon dioxide gas, in the electrolytic solution saturated with carbon dioxide gas at 25 ° C. (0.1 mol / l potassium hydrogen carbonate aqueous solution), the cathode with respect to the electrode potential of the anode. A voltage was applied between the anode electrode and the cathode electrode using a potentiostat so that the electrode potential of was negative, causing an electrolytic reaction. The voltage value applied to the cathode electrode was −1.0 V with respect to the reference electrode. Electrolysis was continuously performed for 180 minutes.
(2-4) The electrolytic product produced in the electrolytic cell was identified by liquid chromatography and quantified by the calibration curve method.
The conversion selectivity of the electrolytic product of carbon dioxide was calculated by Faraday efficiency. Faraday efficiency means the ratio of the amount of charge used to produce the desired electrolytic product to the total amount of reaction charge. Specifically, it was calculated based on the following mathematical formula (3).
Faraday efficiency (%) of the target electrolytic product = (reaction charge amount (C) used for producing the target electrolytic product) / (total reaction charge amount (C)) × 100 (3)

Example 1
Ruchil-type titanium oxide (manufactured by Sakai Chemical Industry Co., Ltd., trade name "STR-100N", specific surface area 100 m2 / g) 3.5 g and metallic titanium (manufactured by Wako Pure Chemical Industries, Ltd., trade name "titanium, powder") 0 After dry mixing 525 g, put it in an alumina boat, raise the temperature to 730 ° C at a temperature rise rate of 300 ° C / hr while flowing 100 vol% hydrogen at 400 ml / min in an atmosphere firing furnace, and hold it at 730 ° C for 6 hours. did. After that, the flow of hydrogen was stopped, and the temperature was lowered to 500 ° C. at a temperature lowering rate of 200 ° C./hr while circulating 100 vol% ammonia at 400 ml / min. Then, the circulation of ammonia was stopped, and the mixture was naturally cooled from 500 ° C. to room temperature under a 100 vol% nitrogen atmosphere to obtain titanium oxide powder. The obtained titanium dioxide powder was in the form of a powder having an average primary particle diameter of 100 nm or less, and had a volume resistance of 1.0 × 10 ^-1 Ω · cm.
2.25 g of the obtained titanium dioxide powder and 100 g of ion-exchanged water were weighed in a beaker and mixed by stirring to obtain a titanium dioxide slurry.
In another beaker, _0.753 g of SnCl 4.5H ₂ O (manufactured by Wako Pure Chemical Industries, Ltd.) was added to a mixed solution of 20.0 g of ion-exchanged water and 23.8 g of hydrochloric acid (37%), and the mixture was stirred and mixed. (This is called a "mixed aqueous solution").
While stirring the titanium oxide slurry, the entire amount of the above mixed aqueous solution prepared in another beaker was added, and then the mixture was stirred and mixed for 30 minutes while maintaining the liquid temperature at 30 ° C. Further, a 1 mol / l sodium hydroxide aqueous solution was added until the pH of the solution reached 10, and then the solution was filtered, washed with water and dried to evaporate all the water to obtain a powder (p1).
0.5 g of powder (p1) is placed in an alumina boat, hydrogen is circulated in an atmospheric firing furnace at 400 ml / min, the temperature is raised to 400 ° C. at 600 ° C./hr, the temperature is maintained at 400 ° C. for 1 hour, and then room temperature is reached. The powder was naturally cooled to obtain Example 1 powder.

Example 2
0.5 g of the powder (p1) obtained in Example 1 was placed in an alumina boat, and hydrogen was circulated in an atmospheric firing furnace at 400 ml / min, heated to 300 ° C. at 600 ° C./hr, and at 300 ° C. After holding for 1 hour, it was naturally cooled to room temperature to obtain Example 2 powder.

Comparative Example 1
Instead of powdered titanium oxide, carbon black (EC-300J, manufactured by Lion Specialty Chemicals Co., Ltd.) 2.25 g and nonionic surfactant (Neugen EA-157, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) 0 Comparative Example 1 powder was obtained in the same manner as in Example 1 except that .45 g was used.

Comparative Example 2
Instead of powdered titanium oxide, carbon black (EC-300J, manufactured by Lion Specialty Chemicals Co., Ltd.) 2.25 g and nonionic surfactant (Neugen EA-157, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) 0 Comparative Example 2 powder was obtained in the same manner as in Example 2 except that .45 g was used.

Comparative Example 3
2.25 g of carbon black (EC-300J, manufactured by Lion Specialty Chemicals Co., Ltd.), 0.45 g of nonionic surfactant (Neugen EA-157, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 100 g of ion-exchanged water. Weighed in a beaker and stirred and mixed to obtain a carbon black slurry.
In another beaker, 0.691 g of CuCl _{2.2H 2 O} (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 40.0 g of ion-exchanged water, and a mixture was prepared by stirring (this is called a "mixed aqueous solution"). ).
While stirring the carbon black slurry, the entire amount of the above mixed aqueous solution prepared in another beaker was added, and then the mixture was stirred and mixed for 30 minutes while maintaining the liquid temperature at 30 ° C. Further, a 1 mol / l sodium hydroxide aqueous solution was added until the pH of the solution reached 10, and then the solution was filtered, washed with water and dried to evaporate all the water to obtain a powder (p2).
0.5 g of powder (p2) is placed in an alumina boat, and the temperature is raised to 600 ° C. at 600 ° C./hr while hydrogen is distributed at 200 ml / min and nitrogen is distributed at 200 ml / min in an atmosphere firing furnace, and 1 at 600 ° C. After holding for a long time, it was naturally cooled to room temperature to obtain Comparative Example 3 powder.

Comparative Example 4
2.25 g of carbon black (EC-300J, manufactured by Lion Specialty Chemicals Co., Ltd.), 0.45 g of nonionic surfactant (Neugen EA-157, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 100 g of ion-exchanged water. Weighed in a beaker and stirred and mixed to obtain a carbon black slurry.
In another beaker, 1.92 g of Cr (NO ₃ ) _{3.9H 2} O (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 40.0 g of ion-exchanged water, and a mixture was prepared by stirring (this was "mixed"). "Aqueous solution").
While stirring the slurry, all the water was evaporated while maintaining the liquid temperature at 65 to 75 ° C. to obtain a powder (p3).
0.5 g of powder (p3) is placed in an alumina boat, and the temperature is raised to 600 ° C. at 600 ° C./hr while hydrogen is distributed at 200 ml / min and nitrogen is distributed at 200 ml / min in an atmosphere firing furnace, and 1 at 600 ° C. After holding for a long time, it was naturally cooled to room temperature to obtain Comparative Example 4 powder.

Comparative Example 5
Use 1.81 g of Fe (NO ₃ ) _{3.9H 2} O (manufactured by Wako Pure Chemical Industries, Ltd.) instead of Cr (NO ₃ ) _{3.9H 2} O, and 200 ml of hydrogen in an atmosphere firing furnace. Comparative Example 5 powder was obtained in the same manner as in Comparative Example 4 except that 400 ml / min of nitrogen was circulated instead of 200 ml / min of nitrogen.

Comparative Example 6
Use 1.26 g of Co (NO ₃ ) 2.6H ₂ O (manufactured by Wako Pure Chemical Industries, Ltd.) instead of Cr (NO ₃ ) _{3.9H 2} O, and ₂₀₀ ml of hydrogen in an atmosphere firing furnace. Comparative Example 6 powder was obtained in the same manner as in Comparative Example 4 except that 400 ml / min of nitrogen was circulated instead of 200 ml / min of nitrogen.

Comparative Example 7
Use 1.24 g of Ni (NO ₃ ) _{2.6H 2 O} (manufactured by Wako Pure Chemical Industries, Ltd.) instead of Cr (NO ₃ ) _{3.9H 2} O, and 200 ml of hydrogen in an atmosphere firing furnace. Comparative Example 7 powder was obtained in the same manner as in Comparative Example 4 except that 400 ml / min of nitrogen was circulated instead of 200 ml / min of nitrogen.

Comparative Example 8
Use 1.14 g of Zn (NO ₃ ) _{2.3H 2 O} (manufactured by Wako Pure Chemical Industries, Ltd.) instead of Cr (NO ₃ ) _{3.9H 2} O, and 200 ml of hydrogen in an atmosphere firing furnace. Comparative Example 8 powder was obtained in the same manner as in Comparative Example 4 except that 400 ml / min of nitrogen was circulated instead of 200 ml / min of nitrogen.

Comparative Example 9
The titanium hydroxide powder obtained in the same manner as in Example 1 was used without supporting the metal species and without raising the temperature by the atmosphere furnace.

Comparative Example 10
Carbon black (EC-300J, manufactured by Lion Specialty Chemicals Co., Ltd.) was used without supporting metal species and without raising the temperature by an atmosphere furnace.

The above-mentioned analysis and evaluation were performed on each of the powders (samples) obtained in Examples 1 and 2 and Comparative Examples 1 to 10 described above. The results are shown in Table 1. Further, the reflected electron images of the powders obtained in Examples 1 and 2 and Comparative Examples 1 to 8 are shown in FIGS. 1 to 10.

From the results of Examples and Comparative Examples, the following were confirmed as shown in Table 1.
The powder obtained in Example 1 is an electrode material in which tin is supported on the surface of powdered titanium oxide as a metal and the coverage is 0.5% or more. On the other hand, the powder obtained in Comparative Example 1 is different from the electrode material of the present invention in that the coverage is less than 0.5%. Under such a difference, when the Faraday efficiency, which is an index of conversion selectivity in carbon dioxide electrolytic reduction, is compared, the powder obtained in Example 1 has a significantly higher Faraday efficiency than the powder obtained in Comparative Example 1. You can see that.
Further, the powder obtained in Example 2 is an electrode material in which tin is supported on the surface of powdered titanium oxide as an oxide and the coverage is 3.0% or more. On the other hand, the powder obtained in Comparative Example 2 is different from the electrode material of the present invention in that the coverage is less than 3.0%. Under such a difference, when the Faraday efficiency, which is an index of conversion selectivity in carbon dioxide electrolytic reduction, is compared, the powder obtained in Example 2 has a significantly higher Faraday efficiency than the powder obtained in Comparative Example 2. You can see that.
Therefore, it was found that the electrode material of the present invention has high Faraday efficiency in addition to high coverage, and is excellent in selectivity of the main organism in carbon dioxide electrolytic reduction.

The powders obtained in Comparative Examples 3 to 8 had copper, zinc, chromium, iron, cobalt, and nickel supported on carbon, respectively, and it was found that these also produced formic acid, but the carrier was a powdery sub. The Faraday efficiency was lower than that of titanium oxide.

Claims (7)

An electrode material used for the electrochemical reduction of carbon dioxide .
The electrode material is an electrode material for electrochemical reduction of carbon dioxide, which has a structure in which a simple substance and / or a compound of a metal element of Group 6 to 16 of the periodic table is supported on a powdered titanium oxide carrier. .. The electrode material has a structure in which a single metal element of Group 6 to 16 of the periodic table is supported on the powdered titanium sulfite carrier, and is supported on the surface of the powdered titanium hydroxide carrier with respect to the total surface area of the electrode material. The electrode for electrochemical reduction of carbon dioxide according to claim 1, wherein the coverage ratio represented by the ratio of the surface area of a single metal element of Group 6 to 16 of the periodic table is 0.5% or more. material. The electrode material has a structure in which a compound of a metal element of Group 6 to 16 of the periodic table is supported on a powdered titanium hydroxide carrier, and is supported on the surface of the powdered titanium oxide carrier with respect to the total surface area of the electrode material. The electrode for electrochemical reduction of carbon dioxide according to claim 1, wherein the coverage ratio represented by the ratio of the surface area of the compound of the metal element of Group 6 to 16 of the periodic table is 3.0% or more. material. The metal elements of Group 6 to 16 of the periodic table are Sn, In, Ga, Ge, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ir, Pt, Au, Ru, Rh, Pd, Ag and Mo. The electrode material for electrochemical reduction of carbon dioxide according to any one of claims 1 to 3, wherein the element is at least one element selected from the group consisting of W and W. The powdered titanium oxide carrier according to any one of claims 1 to 4, wherein the powdered titanium oxide carrier is represented by the composition formula TiO _n (n represents a number of 1.5 or more and 1.9 or less). Electrode material for electrochemical reduction of carbon dioxide . An electrode for electrochemical reduction of carbon dioxide according to any one of claims 1 to 5 , wherein the electrode material for electrochemical reduction of carbon dioxide is used. An electrochemical reduction device for carbon dioxide according to claim 6 , wherein the electrode for electrochemical reduction of carbon dioxide is used.

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