Cathode, method of producing cathode, and electrolysis device

Abstract

To provide a cathode capable of improving the Faraday efficiency of a main product of an electrolytic reduction reaction of carbon dioxide and / or carbon monoxide.SOLUTION: A cathode 10 is used in the electrolytic reduction of carbon dioxide and / or carbon monoxide. The cathode 10 comprises a gas diffusion layer 11, a first layer 12 including nanodiamond, and a second layer 13 including a catalyst that promotes the electrolytic reduction of carbon dioxide and / or carbon monoxide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cathode used in the electrolysis of carbon dioxide and / or carbon monoxide, a method for producing the cathode, and an electrolysis apparatus. [Background technology]

[0002] Traditionally, efforts have been made to mitigate or reduce the impact of climate change, and research and development into reducing carbon dioxide emissions has been carried out to achieve this.

[0003] Patent Document 1 describes a steep interface CO2 electroreduction catalyst for converting CO2 to multi-carbon compounds. The steep interface CO2 electroreduction catalyst includes a porous gas diffusion layer having a gas contact side configured to contact CO2 gas and pass CO2 gas to the opposite reaction interface side, and a catalyst layer disposed on the reaction interface side of the porous gas diffusion layer, covering the reaction interface side of the porous gas diffusion layer, and having an electrolyte contact side configured to contact an aqueous electrolyte. The porous gas diffusion layer is composed of a hydrophobic material. The catalyst layer is hydrophilic so that the aqueous electrolyte passes through the catalyst layer to form a gas-liquid interface on the opposite reaction interface side of the catalyst layer, and is composed of one or more metals selected to convert CO2 to multi-carbon compounds under determined electroreduction conditions, and is thin enough to prevent diffusion limitation of CO2 in the aqueous electrolyte and to enhance selectivity of multi-carbon compounds. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 232515 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the steep interface CO2 electroreduction catalyst described in Patent Document 1 has low faradaic efficiency of the main product.

[0006] An object of the present invention is to provide a cathode capable of improving the faradaic efficiency of the main product of the electrolytic reduction reaction of carbon dioxide and / or carbon monoxide. [Means for solving the problem]

[0007] (1) A cathode for use in the electrolytic reduction of carbon dioxide and / or carbon monoxide, the cathode comprising a gas diffusion layer, a first layer comprising nanodiamond, and a second layer comprising a catalyst that promotes the electrolytic reduction of the carbon dioxide and / or carbon monoxide.

[0008] (2) The cathode described in (1), wherein the nanodiamond is terminated with hydrogen.

[0009] (3) The weight of the first layer per unit geometric area of ​​the gas diffusion layer is 0.005 mg / cm 2 More than 10mg / cm 2 A cathode according to (1) or (2), which is:

[0010] (4) The cathode according to any one of (1) to (3), further comprising a third layer containing a fluororesin.

[0011] (5) The cathode according to any one of (1) to (3), wherein the first layer further contains a fluororesin.

[0012] (6) A method for producing a cathode for use in the electrolytic reduction of carbon dioxide and / or carbon monoxide, comprising the steps of applying a dispersion liquid containing nanodiamond onto a gas diffusion layer to form a first layer, and sputtering a catalyst that promotes the electrolytic reduction of carbon dioxide and / or carbon monoxide onto the gas diffusion layer to form a second layer.

[0013] (7) The method for producing a cathode according to (6), further comprising the step of applying a dispersion liquid containing a fluororesin onto the gas diffusion layer to form a third layer.

[0014] (8) The method for producing a cathode according to (6), wherein the dispersion liquid further contains a fluororesin.

[0015] (9) An electrolytic device comprising the cathode according to any one of (1) to (5). Effect of the Invention

[0016] According to the present invention, it is possible to provide a cathode capable of improving the faradaic efficiency of the main product of the electrolytic reduction reaction of carbon dioxide and / or carbon monoxide. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a schematic cross-sectional view showing a cathode according to one embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic cross-sectional view showing a cathode according to another embodiment of the present invention. [Diagram 3] 1 is a schematic cross-sectional view showing an electrolysis device according to one embodiment of the present invention. [Figure 4] 1 is a graph showing the faradaic efficiency of the product of the electrolytic reduction reaction of carbon dioxide when the cathodes of Examples 1 to 5 and Comparative Examples 1 and 2 are used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] FIG. 1 shows a cathode according to one embodiment of the present invention.

[0020] The cathode 10 is used for the electrolytic reduction of carbon dioxide and / or carbon monoxide, and comprises a gas diffusion layer 11 on which a first layer 12 containing nanodiamond, a second layer 13 containing a catalyst that promotes the electrolytic reduction of carbon dioxide and / or carbon monoxide, and a third layer 14 containing a fluororesin are sequentially laminated.

[0021] The gas diffusion layer 11 is not particularly limited as long as it is a porous layer that can permeate a raw material gas containing carbon dioxide and / or carbon monoxide, a gas produced by the electrolytic reduction of carbon dioxide and / or carbon monoxide, and hydrogen produced by the electrolytic reduction of water.

[0022] The gas diffusion layer 11 is, for example, a porous layer formed on a porous substrate. In this case, the first layer 12 is formed on the porous layer.

[0023] The thickness of the porous substrate is not particularly limited, but is, for example, from 10 μm to 1000 μm, preferably from 100 μm to 500 μm, and more preferably from 150 μm to 350 μm.

[0024] The most frequent pore size of the porous substrate is not particularly limited, but is, for example, 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 250 μm or less, and even more preferably 25 μm or more and 200 μm or less. The most frequent pore size of the porous substrate is measured, for example, by mercury intrusion porosimetry.

[0025] Examples of the porous substrate include nonwoven fabric and woven fabric.

[0026] The porous substrate preferably contains a carbon material, which improves the electrical conductivity of the gas diffusion layer 11 and allows the electrolytic reduction reaction of carbon dioxide and / or carbon monoxide to be carried out efficiently.

[0027] The carbon material is not particularly limited as long as it is capable of improving the electrical conductivity of the gas diffusion layer 11. Examples of the carbon material include carbon fibers, carbon black, graphite, activated carbon, carbon nanotubes, carbon nanofibers, fullerenes, and amorphous carbon, and two or more of them may be used in combination.

[0028] The porous substrate may be, for example, a mesh material made of a metal or an alloy, a punching material made of a metal or an alloy, or a sintered metal fiber. The metal may be, but is not limited to, titanium, nickel, or iron. The alloy may be, but is not limited to, stainless steel.

[0029] The porous layer preferably has a smaller average pore size and a larger specific surface area than the porous substrate, which allows the amount of nanodiamond supported by the gas diffusion layer 11 to be increased.

[0030] The thickness of the porous layer is not particularly limited, but is, for example, from 1 μm to 500 μm, preferably from 20 μm to 300 μm, more preferably from 50 μm to 200 μm, and even more preferably from 70 μm to 150 μm.

[0031] The most frequent pore size of the porous layer is not particularly limited, but is, for example, 5 nm or more and 500 nm or less, preferably 10 nm or more and 300 nm or less, more preferably 15 nm or more and 100 nm or less, and even more preferably 15 nm or more and 70 nm or less.

[0032] The porous layer preferably contains a fluororesin, which inhibits the infiltration of the electrolyte, thereby improving the faradaic efficiency of the main product of the electrolytic reduction reaction of carbon dioxide and / or carbon monoxide, and decreasing the faradaic efficiency of hydrogen, which is the product of the electrolytic reduction reaction of water.

[0033] The fluororesin is not particularly limited as long as it can improve the water repellency of the gas diffusion layer 11, and examples thereof include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer. Among these, polytetrafluoroethylene is preferred in terms of the water repellency of the gas diffusion layer 11.

[0034] Like the porous substrate, the porous layer preferably contains a carbon material, which improves the electrical conductivity of the gas diffusion layer 11 and allows the electrolytic reduction reaction of carbon dioxide and / or carbon monoxide to be carried out efficiently.

[0035] The content of the carbon material in the porous layer is not particularly limited, but is, for example, 70% by mass to 95% by mass, preferably 75% by mass to 92% by mass, and more preferably 80% by mass to 90% by mass. The content of the carbon material in the porous layer is measured, for example, by a combustion method.

[0036] An example of a commercially available gas diffusion layer 11 is Sigracet 39 BB (manufactured by SGL Carbon).

[0037] The first layer 12 is formed on the gas diffusion layer 11, and the nanodiamonds contained in the first layer 12 are supported on at least a portion of the surface (outer surface and inner surface) of the gas diffusion layer 11.

[0038] The particle size of the nanodiamond is not particularly limited, but is, for example, 1 nm or more and 20 nm or less.

[0039] Nanodiamonds are produced, for example, by the detonation method and are doped with elements such as silicon and germanium.

[0040] Nanodiamonds may be terminated with either hydrogen or oxygen, but are preferably terminated with hydrogen, which improves the faradaic efficiency of the main products of the electrochemical reduction of carbon dioxide and / or carbon monoxide.

[0041] The weight of the first layer 12 per unit geometric area of ​​the gas diffusion layer 11 is 0.005 mg / cm 2 More than 10mg / cm 2 It is preferable that the concentration is 0.5 mg / cm or less. 2 More than 1.0mg / cm 2It is more preferable that the weight of the first layer 12 per unit geometric area of ​​the gas diffusion layer 11 is 0.005 mg / cm or less. 2 More than 10mg / cm 2 or less, the faradaic efficiency of the main product of the electrolytic reduction reaction of carbon dioxide and / or carbon monoxide is improved.

[0042] The first layer 12 is formed, for example, by applying a dispersion liquid containing nanodiamonds and then drying it. The method for applying the dispersion liquid containing nanodiamonds is not particularly limited, but for example, a drop casting method can be used.

[0043] The dispersion liquid containing nanodiamond may further contain a dispersion medium (water, tetrahydrofuran, isopropanol, methyl isobutyl ketone, toluene, etc.) and a surfactant. The content of nanodiamond in the dispersion liquid containing fluororesin is not particularly limited, but is, for example, 0.1% by mass to 15% by mass, and preferably 0.5% by mass to 10% by mass.

[0044] A commercially available dispersion liquid containing hydrogen-terminated nanodiamonds is, for example, Dinovea ζ+ nanodiamond water dispersion liquid (manufactured by Daicel). Also, a commercially available dispersion liquid containing oxygen-terminated nanodiamonds is, for example, Dinovea ζ- nanodiamond water dispersion liquid (manufactured by Daicel).

[0045] The drying temperature is not particularly limited, but is, for example, from 20° C. to 120° C., and preferably from 50° C. to 100° C. The drying time is not particularly limited, but is, for example, from 0.5 hours to 24 hours, and preferably from 1 hour to 12 hours.

[0046] The second layer 13 is formed on the first layer 12 , and the catalyst contained in the second layer 13 is supported on at least a portion of the surface of the nanodiamonds contained in the first layer 12 .

[0047] The catalyst is not particularly limited as long as it can promote the electrolytic reduction of carbon dioxide and / or carbon monoxide, but examples thereof include copper, silver, gold, zinc, lead, indium, tin, and cadmium, and two or more of these may be used in combination. Among these, copper is preferred because the main product is ethylene.

[0048] When silver, gold, or zinc is used as the catalyst, the main product is carbon monoxide, and when lead, indium, tin, or cadmium is used as the catalyst, the main product is formic acid.

[0049] The average particle size of the catalyst is not particularly limited, but is, for example, 1 nm to 100 nm, preferably 3 nm to 50 nm, and more preferably 5 nm to 30 nm. The average particle size of the catalyst is determined, for example, as the average value of the Feret diameters of 100 particles arbitrarily selected from a scanning electron microscope (SEM) image.

[0050] The average thickness of the second layer 13 is not particularly limited, but is, for example, 5 nm to 1000 nm, preferably 10 nm to 500 nm, and more preferably 20 nm to 200 nm. The average thickness of the second layer 13 is the average value of 50 arbitrarily selected thicknesses. The thickness of the second layer 13 is preferably within a range of ±10% based on the average thickness of the second layer 13.

[0051] The method for forming the second layer 13 is not particularly limited, and examples thereof include vapor deposition methods such as sputtering, arc plasma vapor deposition, electron beam vapor deposition, thermal vapor deposition, and pulsed laser vapor deposition, and plating methods such as electrolytic plating, electroless plating, and displacement plating. Among these, the sputtering method is preferred from the viewpoint of uniformity in the thickness of the second layer 13.

[0052] The content of the second layer 13 in the cathode 10 is not particularly limited, but is, for example, 0.10 mass % or more and 2.0 mass % or less, preferably 0.15 mass % or more and 1.5 mass % or less, and more preferably 0.20 mass % or more and 1.0 mass % or less.

[0053] The third layer 14 is formed on the second layer 13, and the fluororesin contained in the third layer 14 covers at least a part of the surface of the catalyst contained in the second layer 13. This prevents the electrolyte from penetrating. As a result, the faradaic efficiency of the main product of the electrolytic reduction reaction of carbon dioxide and / or carbon monoxide is improved, while the faradaic efficiency of hydrogen, which is a product of the electrolytic reduction reaction of water, is reduced.

[0054] The thickness of the third layer 14 is not particularly limited, but is, for example, 0.10 μm or more and 100 μm or less, preferably 0.15 μm or more and 50 μm or less, and more preferably 0.25 μm or more and 10 μm or less.

[0055] The fluororesin is not particularly limited, but examples thereof include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer. Among these, polytetrafluoroethylene is preferred in terms of the water repellency of the third layer 14.

[0056] The basis weight of the third layer 14 per unit geometric area of ​​the gas diffusion layer 11 is not particularly limited, but is, for example, 0.02 mg / cm 2 More than 4.0mg / cm 2 Less than or equal to 0.05 mg / cm 2 More than 2.0mg / cm 2 It is preferable that the concentration is 0.1 mg / cm or less. 2 More than 1.0mg / cm 2 It is more preferable that:

[0057] The third layer 14 is formed, for example, by applying a dispersion liquid containing a fluororesin and then drying it. The method for applying the dispersion liquid containing a fluororesin is not particularly limited, but examples thereof include a drop casting method, a bar coating method, a blade coating method, a screen printing method, a spray coating method, a curtain coating method, and a roll coating method. Among these, the drop casting method and the spray coating method are preferred from the viewpoint of uniformity of the third layer 14. At this time, the dispersion liquid containing a fluororesin may be applied in multiple layers.

[0058] The dispersion liquid containing fluororesin may further contain a dispersion medium (water, etc.) and a surfactant (nonionic surfactant, etc.). The content of fluororesin in the dispersion liquid containing fluororesin is not particularly limited, but is, for example, 1% by mass or more and 70% by mass or less, and preferably 3% by mass or more and 60% by mass or less. An example of a commercially available aqueous dispersion liquid containing fluororesin is Polyflon PTFE D-210C (manufactured by Daikin), which is used by diluting with water as necessary.

[0059] The drying temperature is not particularly limited, but is, for example, from 20° C. to 120° C., and preferably from 50° C. to 100° C. The drying time is not particularly limited, but is, for example, from 0.5 hours to 24 hours, and preferably from 1 hour to 12 hours.

[0060] After the third layer is formed, it may be fired under an inert gas (nitrogen gas, argon gas, etc.) atmosphere. The firing temperature is not particularly limited, but is, for example, 150°C to 450°C, preferably 170°C to 350°C, and more preferably 200°C to 300°C. The firing time is not particularly limited, but is, for example, 10 minutes to 240 minutes, preferably 20 minutes to 180 minutes, and more preferably 30 minutes to 150 minutes. The temperature rise rate during firing is not particularly limited, but is, for example, 1°C / min to 30°C / min, preferably 3°C / min to 20°C / min, and more preferably 5°C / min to 15°C / min.

[0061] FIG. 2 shows a cathode according to another embodiment of the present invention.

[0062] Cathode 20 has the same configuration as cathode 10, except that instead of forming first layer 12 containing nanodiamond and third layer 14 containing fluororesin, a third layer 21 containing nanodiamond and fluororesin is formed.

[0063] FIG. 3 shows an electrolysis device according to one embodiment of the present invention.

[0064] The electrolysis device 2 includes a cathode 10, an anode 22, an anion exchange membrane 23 provided between the cathode 10 and the anode 22, a liquid flow path 28a provided between the cathode 10 and the anion exchange membrane 23 through which a cathode-side electrolyte flows, and a liquid flow path 29a provided between the anode 22 and the anion exchange membrane 23 through which an anode-side electrolyte flows. The electrolysis device 2 also includes a liquid flow path structure 28 for forming the liquid flow path 28a, and a liquid flow path structure 29 for forming the liquid flow path 29a. The electrolysis device 2 also includes a gas flow path structure 24 in which a gas flow path 24a is formed, and a gas flow path structure 25 in which a gas flow path 25a is formed. The electrolysis device 2 also includes a power feeder 26 and a power feeder 27. At this time, the power supply 26, the gas flow path structure 24, the cathode 10, the liquid flow path structure 28, the anion exchange membrane 23, the liquid flow path structure 29, the anode 22, the gas flow path structure 25 and the power supply 27 are laminated in this order.

[0065] A slit is formed in the liquid flow path structure 28, and a region in the slit surrounded by the cathode 10, the anion exchange membrane 23, and the liquid flow path structure 28 forms a liquid flow path 28a. A slit is formed in the liquid flow path structure 29, and a region in the slit surrounded by the anode 22, the anion exchange membrane 23, and the liquid flow path structure 29 forms a liquid flow path 29a.

[0066] A groove is formed on the cathode 10 side of the gas flow path structure 24, and the portion of the groove surrounded by the gas flow path structure 24 and the cathode 10 forms a gas flow path 24a. A groove is formed on the anode 22 side of the gas flow path structure 25, and the portion of the groove surrounded by the gas flow path structure 25 and the anode 22 forms a gas flow path 25a.

[0067] In the electrolysis device 2, a liquid flow path 28a is formed between the cathode 10 and the anion exchange membrane 23, a liquid flow path 29a is formed between the anode 22 and the anion exchange membrane 23, a gas flow path 24a is formed between the cathode 10 and the power supply 26, and a gas flow path 25a is formed between the anode 22 and the power supply 27.

[0068] The power supply 26 and the power supply 27 are each electrically connected to a power source that supplies power to the electrolysis device 2. Here, the gas flow path structure 24 and the gas flow path structure 25 are each an electrical conductor, and a voltage is applied between the cathode 10 and the anode 22 by the power supplied from the power source.

[0069] In the cathode 10, carbon dioxide and / or carbon monoxide are reduced to produce carbon compounds, and water is reduced to produce hydrogen. Here, in the cathode 10, the gas diffusion layer 11 is disposed on the gas flow path 24a side, and the third layer 14 is disposed on the liquid flow path 28a side.

[0070] In the anode 22, hydroxide ions are oxidized to generate oxygen. The anode 22 has, for example, a catalyst layer including an anode catalyst that promotes the electrolytic oxidation of hydroxide ions formed on a gas diffusion layer. Here, the gas diffusion layer of the anode 22 is disposed on the gas flow path 25a side, and the catalyst layer is disposed on the liquid flow path 29a side.

[0071] The gas diffusion layer is not particularly limited, but examples thereof include carbon paper and carbon cloth. The gas diffusion layer may be a porous body such as a mesh material, a punching material, or a sintered metal fiber body. The material constituting the porous body is not particularly limited, but examples thereof include metals such as titanium, nickel, and iron, and alloys such as stainless steel.

[0072] The anode catalyst is not particularly limited, and examples thereof include metals such as platinum, palladium, and nickel, alloys or intermetallic compounds thereof, metal oxides such as manganese oxide, iridium oxide, nickel oxide, cobalt oxide, iron oxide, tin oxide, indium oxide, ruthenium oxide, lithium oxide, and lanthanum oxide, and metal complexes such as ruthenium complexes and rhenium complexes, and two or more of these may be used in combination.

[0073] The material constituting the liquid flow path structures 28 and 29 is not particularly limited, but may be, for example, a fluororesin such as polytetrafluoroethylene. The material constituting the gas flow path structures 24 and 25 is not particularly limited, but may be, for example, a metal such as titanium, an alloy such as stainless steel, or carbon.

[0074] The material constituting the power feeders 26 and 27 is not particularly limited, but may be, for example, a metal such as copper, gold, or titanium, an alloy such as stainless steel, or carbon. The power feeders 26 and 27 may be made of a copper base material having a surface plated with gold or other plating.

[0075] As the anion exchange membrane 23, a known anion exchange membrane can be used.

[0076] The electrolysis device 2 includes a pump that supplies the cathode-side electrolytic solution A from the liquid flow path 64 to the liquid flow path 28a, a pump that supplies the anode-side electrolytic solution B from the liquid flow path 65 to the liquid flow path 29a, and a pump that supplies a raw material gas G containing carbon dioxide and / or carbon monoxide from the gas flow path 76 to the gas flow path 24a.

[0077] An alkaline aqueous solution can be used as the cathode-side electrolyte A and the anode-side electrolyte B. The alkaline aqueous solution is not particularly limited, but examples thereof include an aqueous potassium hydroxide solution, an aqueous sodium hydroxide solution, an aqueous potassium carbonate solution, and an aqueous sodium carbonate solution. Among these, an aqueous potassium hydroxide solution is preferred from the viewpoint of reducing the faradaic efficiency of hydrogen, which is a product of the electrolytic reduction reaction of water.

[0078] The pH of the cathode-side electrolyte A and the anode-side electrolyte B can be appropriately adjusted, but the pH of the anode-side electrolyte B is preferably lower than the pH of the cathode-side electrolyte A. The pH of the cathode-side electrolyte A is, for example, greater than 14, and the pH of the anode-side electrolyte B is, for example, 8 or more and 14 or less.

[0079] The alkali concentration of the cathode side electrolyte A is not particularly limited, but is, for example, 4 mol / L to 12 mol / L, preferably 5 mol / L to 11 mol / L, and more preferably 6 mol / L to 10 mol / L. The temperature of the cathode side electrolyte A is not particularly limited, but is, for example, 10° C. to 60° C. The flow rate of the cathode side electrolyte A is not particularly limited, but is, for example, 0.5 mL / min to 5 mL / min.

[0080] The alkali concentration of the anode-side electrolyte B is not particularly limited, but is, for example, 0.1 mol / L to 3 mol / L, preferably 0.2 mol / L to 2.5 mol / L, and more preferably 0.5 mol / L to 2 mol / L. The temperature of the anode-side electrolyte B is not particularly limited, but is, for example, 10° C. to 60° C. The flow rate of the anode-side electrolyte B is not particularly limited, but is, for example, 0.5 mL / min to 5 mL / min.

[0081] When the raw material gas G contains carbon dioxide, the concentration of carbon dioxide in the raw material gas G is not particularly limited, but is, for example, 1 volume % or more and 100 volume % or less. When the raw material gas G contains carbon monoxide, the concentration of carbon monoxide in the raw material gas G is not particularly limited, but is, for example, 1 volume % or more and 100 volume % or less. The temperature of the raw material gas G is not particularly limited, but is, for example, 10°C or more and 60°C or less. The flow rate of the raw material gas G is not particularly limited, but is, for example, 5 mL / min or more and 50 mL / min or less.

[0082] In the electrolysis device 2, the cathode-side electrolytic solution A containing the liquid (carbon compounds) generated at the cathode 10 is discharged from the liquid flow path 63, and the product gas E containing the gas (carbon compounds and hydrogen) generated at the cathode 10 is discharged from the gas flow path 67. In addition, in the electrolysis device 2, the anode-side electrolytic solution B is discharged from the liquid flow path 66, and oxygen (O2) generated at the anode 22 is discharged via the gas flow path 25a. Note that, in the case where the product gas E contains ethylene, the product gas E discharged from the electrolysis device 2 may be sent to a reactor and brought into gas-phase contact with an olefin polymerization catalyst to polymerize ethylene.

[0083] Examples of carbon compounds generated by the electrolytic reduction of carbon dioxide at the cathode 10 include C1 compounds such as carbon monoxide, formic acid, formaldehyde, methanol, and methane, and C2 compounds such as acetic acid, acetaldehyde, ethanol, and ethylene. Among these, ethylene is preferred because it is useful in the chemical industry.

[0084] Examples of carbon compounds produced by electrolytic reduction of carbon monoxide at the cathode 10 include C1 compounds such as formaldehyde, methanol, and methane, and C2 compounds such as acetic acid, acetaldehyde, ethanol, and ethylene.

[0085] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and the above embodiment may be modified as appropriate within the scope of the spirit of the present invention. EXAMPLES

[0086] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0087] [Example 1] (Gas diffusion layer) Using a press cutter (Thomson cutter) MB type (manufactured by Aichi Technical), Sigracet 39 BB (manufactured by SGL Carbon) was cut into a square with each side measuring 30 mm to obtain a gas diffusion layer. Here, Sigracet 39 BB has a microporous layer treated with 5% by mass of PTFE formed on one side of a carbon fiber nonwoven fabric (carbon paper).

[0088] (Formation of the first layer) On a hot plate heated to 60°C, 0.5 mL of DINOBAER 1 mass% Nanodia IPA dispersion (manufactured by Daicel) was applied by drop casting onto the microporous layer of the gas diffusion layer, and then dried for 1 hour in a dryer at 80°C to form a first layer. At this time, the weight of the first layer per unit geometric area of ​​the gas diffusion layer was 0.50 mg / cm. 2 Here, the nanodiamonds contained in the DINOBEA 1 mass % Nanodiamond IPA dispersion (manufactured by Daicel) are terminated with hydrogen.

[0089] (Formation of the second layer) A second layer having a thickness of 25 nm was formed on the first layer by sputtering Cu under the following conditions. Sputtering method: DC magnetron sputtering Exhaust system: Rotary pump + cryopump Target material: Cu Target diameter: 8 inches Sputtering rate: 0.8 nm / sec Pre-sputtering: 5 minutes Sputtering time: 33 seconds Gas diffusion layer temperature: 25℃

[0090] (Formation of the third layer) Polyflon PTFE D-210C (manufactured by Daikin) was diluted 10 times with distilled water to obtain a coating solution. Next, two layers of the coating solution were applied onto the second layer by a drop cast method on a hot plate heated to 60°C, and then dried in a dryer at 80°C for one hour to form a third layer. At this time, the basis weight of the third layer per unit geometric area of ​​the gas diffusion layer was 2.8 mg / cm. 2 It was.

[0091] (Firing) Using a tubular furnace, the gas diffusion layer having the first layer, second layer and third layer laminated in that order was fired under conditions of a nitrogen gas atmosphere, a heating rate of 10°C / min, a holding temperature of 200°C and a holding time of 2 hours, to obtain a cathode.

[0092] [Example 2] A cathode was obtained in the same manner as in Example 1, except that a 1% by mass DINOBAER nanodiamond toluene dispersion (manufactured by Daicel) was used instead of a 1% by mass DINOBAER nanodiamond IPA dispersion (manufactured by Daicel). At this time, the weight of the first layer per unit geometric area of ​​the gas diffusion layer was 0.500 mg / cm. 2 The mass of the third layer per unit geometric area of ​​the gas diffusion layer is 2.9 mg / cm 2 Here, the nanodiamonds contained in DINOBEA 1% by mass nanodiamond toluene dispersion (manufactured by Daicel) are terminated with hydrogen.

[0093] [Example 3] A cathode was obtained in the same manner as in Example 1, except that the first layer was not formed and the third layer was formed as follows.

[0094] (Formation of the third layer) Polyflon PTFE D-210C (manufactured by Daikin) 40μL as an aqueous dispersion of polytetrafluoroethylene (PTFE) and DINOBEA 1 mass% ζ+nanodiamond aqueous dispersion (manufactured by Daicel) 40μL were mixed, and then 40μL of distilled water was added and mixed to obtain a coating solution. Here, the nanodiamond contained in DINOBEA 1 mass% ζ+nanodiamond aqueous dispersion (manufactured by Daicel) is terminated with hydrogen. Next, the coating solution was applied onto the second layer by the drop casting method on a hot plate heated to 60°C, and then dried in a dryer at 80°C for 1 hour to form a third layer. At this time, the basis weight of the third layer per unit geometric area of ​​the gas diffusion layer was 2.4mg / cm 2 It was.

[0095] [Example 4] A cathode was obtained in the same manner as in Example 1, except that the first layer was not formed and the third layer was formed as follows.

[0096] (Formation of the third layer) 40μL of Polyflon PTFE D-210C (manufactured by Daikin) as an aqueous dispersion of polytetrafluoroethylene (PTFE) and 80μL of Dinobear 1% by mass ζ+nanodiamond aqueous dispersion (manufactured by Daicel) were mixed to obtain a coating solution. Here, the nanodiamonds contained in Dinobear 1% by mass ζ+nanodiamond aqueous dispersion (manufactured by Daicel) are terminated with hydrogen. Next, the coating solution was applied onto the second layer by the drop casting method on a hot plate heated to 60°C, and then dried in a dryer at 80°C for 1 hour to form a third layer. At this time, the basis weight of the third layer per unit geometric area of ​​the gas diffusion layer was 2.7mg / cm 2 It was.

[0097] [Example 5] A cathode was obtained in the same manner as in Example 1, except that the first layer was formed as follows.

[0098] (Formation of the first layer) 1.0 mL of 2-propanol (IPA) was added to 6.0 mg of the nanodiamond powder used in Dinobear 1% by mass ζ+ nanodiamond water dispersion (manufactured by Daicel), and then the mixture was dispersed for 5 minutes using an ultrasonic cleaner ASU-3M (manufactured by As One) to obtain an IPA dispersion of nanodiamond. Here, the nanodiamonds contained in the nanodiamond powder are terminated with hydrogen.

[0099] On a hot plate heated to 60°C, 0.5 mL of nanodiamond IPA dispersion was applied by drop casting onto the microporous layer of the gas diffusion layer, and then dried for 1 hour in a dryer at 80°C to form the first layer. At this time, the weight of the first layer per unit geometric area of ​​the gas diffusion layer was 0.75 mg / cm. 2 It was.

[0100] [Comparative Example 1] A cathode was obtained in the same manner as in Example 1, except that the first and third layers were not formed.

[0101] [Comparative Example 2] A cathode was obtained in the same manner as in Example 1, except that the first layer was not formed.

[0102] [Faraday efficiency] Carbon dioxide was electrolyzed under the following conditions using the electrolysis device 2 (see FIG. 2). Pretreatment conditions: Cyclic voltammetry Atmosphere: Nitrogen gas atmosphere Sweep range: -0.85V~-0.10V Sweep count: 10 cycles Electrolysis conditions: constant potential electrolysis Voltage: -2.5V Electrolysis time: 30 minutes

[0103] Here, as the cathode side electrolyte A supplied through the liquid flow path 64, a 7 mol / L potassium hydroxide (KOH) aqueous solution was used, and the flow rate of the cathode side electrolyte A was set to 1 mL / min. As the anode side electrolyte B supplied through the liquid flow path 65, a 1 mol / L potassium hydroxide (KOH) aqueous solution was used, and the flow rate of the anode side electrolyte B was set to 1 mL / min. As the cathode 10, the cathodes of Examples 1 to 5 and Comparative Examples 1 and 2 were used. As the anode 22, nickel foam EQ-bcnf-03 (manufactured by MTI) was used. As the anion exchange membrane 23, Fumasep FAB-PK-130 (manufactured by FuMA-Tech) was used. As the raw material gas G supplied through the gas flow path 76, carbon dioxide was used, and the flow rate of the raw material gas G was set to 20 mL / min.

[0104] When the electrolysis time reached 30 minutes, the generated gas (hydrogen (H2), carbon monoxide (CO), methane (CH4) and ethylene (C2H4)) was collected from the gas flow path 67 using a Smart Bag PA (manufactured by GL Sciences), and the concentration of the generated gas was measured using a gas chromatograph CP-4900 Micro GC (manufactured by Varian). At this time, H2, CO and CH4 were quantified using argon gas as the carrier gas and a Molsieve 5A column (manufactured by GL Sciences). C2H4 was quantified using helium gas as the carrier gas and a PoraPLOT Q column (manufactured by GL Sciences). The concentration of the generated gas was converted to obtain the amount of substance [mol] of the generated gas.

[0105] On the other hand, when the electrolysis time reached 30 minutes, the cathode side electrolyte A containing the generated liquid (formic acid (HCOOH), acetic acid (CH3COOH) and ethanol (CH3CH2OH)) was collected from the liquid flow path 63 and neutralized with concentrated hydrochloric acid, and the concentration of the generated liquid was measured under the following conditions using a high performance liquid chromatograph Prominence (manufactured by Shimadzu Corporation). The concentration of the generated liquid was converted to obtain the amount of substance [mol] of the generated liquid. Eluent: 0.010mol / L sulfuric acid aqueous solution Column: Shodex SUGAR SC1821, Shodex Rspak DE 13L (manufactured by Resonac) Column temperature: 50℃

[0106] The faradaic efficiency [%] of each product was calculated based on the following formula: Amount of each product [mol] × n / Number of electrons consumed when electrolysis time reached 30 minutes [mol] × 100

[0107] Here, n is the number of electrons [mol] required to produce 1 mol of each product. Specifically, n is the number of electrons in the reaction equation in which each product is produced. - The reaction formula for each product is as follows: 2H + +2e - →H2 CO2+2H + +2e - →CO+H2O CO2+2H + +2e - →HCOOH CO2+8H + +8e - →CH4+2H2O 2CO2+8H + +8e - →CH3COOH+2H2O 2CO2+12H + +12e - →CH3CH2OH+3H2O 2CO2+12H + +12e - →C2H4+4H2O

[0108] FIG. 4 shows the faradaic efficiency of the product of the electrolytic reduction reaction of carbon dioxide when the cathodes of Examples 1 to 5 and Comparative Examples 1 and 2 were used.

[0109] From Fig. 4, it can be seen that the faradaic efficiency of ethylene (main product) is high when the cathodes of Examples 1 to 5 are used. In contrast, the faradaic efficiency of ethylene (main product) is low in the cathodes of Comparative Examples 1 and 2, since a layer containing nanodiamond is not formed. [Explanation of symbols]

[0110] 10, 20 cathode 11 Gas diffusion layer 12 First layer 13 Second layer 14, 21 Third layer 2 Electrolyzer 22 Anode 23 Anion exchange membrane 24 Gas flow path structure 24a Gas flow path 25 Gas flow path structure 25a Gas flow path 26 Power feeder 27 Power feeder 28 Liquid flow path structure 28a Liquid flow path 29 Liquid flow path structure 29a Liquid flow path 63, 64, 65, 66 Liquid flow path 67, 76 Gas flow path A Cathode side electrolyte B Anode side electrolyte E Produced gas G Raw material gas

Claims

1. A cathode for use in the electrolytic reduction of carbon dioxide and / or carbon monoxide, comprising: A gas diffusion layer; a first layer comprising nanodiamonds; and a second layer comprising a catalyst promoting the electrolytic reduction of carbon dioxide and / or carbon monoxide.

2. 10. The cathode of claim 1, wherein the nanodiamond is hydrogen terminated.

3. The weight of the first layer per unit geometric area of ​​the gas diffusion layer is 0.005 mg / cm ２ 10mg / cm or more ２ 3. The cathode of claim 1 or 2, wherein:

4. 3. The cathode of claim 1 or 2, further comprising a third layer comprising a fluororesin.

5. The cathode of claim 1 or 2, wherein the first layer further comprises a fluororesin.

6. 1. A method for producing a cathode for use in the electrolytic reduction of carbon dioxide and / or carbon monoxide, comprising the steps of: A step of applying a dispersion liquid containing nanodiamonds onto a gas diffusion layer to form a first layer; and forming a second layer on the gas diffusion layer by sputtering a catalyst that promotes the electrolytic reduction of carbon dioxide and / or carbon monoxide.

7. The method for producing a cathode according to claim 6 , further comprising the step of forming a third layer by applying a dispersion liquid containing a fluororesin onto the gas diffusion layer.

8. The method for producing a cathode according to claim 6 , wherein the dispersion further contains a fluororesin.

9. Electrolysis device comprising the cathode according to claim 1 or 2.

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