Cathode, cathode manufacturing method 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 to achieve this, research and development into reducing carbon dioxide emissions has been carried out.

[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 allow CO2 gas to pass through to the opposite reaction interface side. A catalyst layer is disposed on the reaction interface side of the porous gas diffusion layer, covers the reaction interface side of the porous gas diffusion layer, and has an electrolyte contact side configured to contact an aqueous electrolyte. The porous gas diffusion layer is made 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. The catalyst layer is made of one or more metals selected to convert CO2 to multi-carbon compounds under determined electroreduction conditions, and is thin enough to prevent diffusion limitations of CO2 in the aqueous electrolyte and increase selectivity for 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 sharp 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 according to (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 The 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 manufacturing a cathode for use in the electrolytic reduction of carbon dioxide and / or carbon monoxide, comprising the steps of: applying a dispersion containing nanodiamonds 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 electrolysis device comprising the cathode according to any one of (1) to (5). [Effects 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 explanation of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view showing a cathode according to one embodiment of the present invention. [Figure 2] FIG. 4 is a schematic cross-sectional view showing a cathode according to another embodiment of the present invention. [Figure 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 INVENTION

[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 is formed by sequentially laminating on a gas diffusion layer 11 a first layer 12 containing nanodiamonds, 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.

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

[0022] The gas diffusion layer 11 is, for example, a porous layer formed on a porous substrate, and 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, 10 μm or more and 1000 μm or less, preferably 100 μm or more and 500 μm or less, and more preferably 150 μm or more and 350 μm or less.

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

[0025] Examples of porous substrates include nonwoven fabrics and woven fabrics.

[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 proceed efficiently.

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

[0028] The porous substrate may be, for example, a metal or alloy mesh material, a metal or alloy punching material, or a metal fiber sintered body. Metals include, but are not limited to, titanium, nickel, and iron. Alloys include, but are 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 nanodiamonds carried by the gas diffusion layer 11 to be increased.

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

[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. 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.

[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 proceed 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] The nanodiamonds may be terminated with either hydrogen or oxygen, but hydrogen termination is preferred, as this improves the faradaic efficiency of the main products of the electrolytic 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 Preferably, it 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 When the temperature is equal to or lower than this, 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 containing nanodiamonds and then drying it. The method for applying the dispersion containing nanodiamonds is not particularly limited, but examples thereof include a drop casting method.

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

[0044] Examples of commercially available dispersions containing hydrogen-terminated nanodiamonds include Dinobear ζ+ Nanodiamond Water Dispersion (manufactured by Daicel). Examples of commercially available dispersions containing oxygen-terminated nanodiamonds include Dinobear ζ- Nanodiamond Water Dispersion (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 also 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, and 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 Feret diameter 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% of 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, sputtering 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] Third layer 14 is formed on second layer 13, and the fluororesin contained in third layer 14 covers at least a portion of the surface of the catalyst contained in 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 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 0.05 mg / cm 2 More than 2.0mg / cm 2 Preferably, it is 0.1 mg / cm or less. 2 More than 1.0mg / cm 2 More preferably, it is:

[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 include drop casting, bar coating, blade coating, screen printing, spray coating, curtain coating, and roll coating. Among these, drop casting and spray coating 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 coats.

[0058] The dispersion containing the fluororesin may further contain a dispersion medium (such as water) and a surfactant (such as a nonionic surfactant). The content of the fluororesin in the dispersion containing the fluororesin is not particularly limited, but is, for example, from 1% by mass to 70% by mass, and preferably from 3% by mass to 60% by mass. An example of a commercially available aqueous dispersion containing a fluororesin is Polyflon PTFE D-210C (manufactured by Daikin), which is used after dilution 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 also 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 atmosphere (nitrogen gas, argon gas, etc.). The firing temperature is not particularly limited, but 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 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 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, 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 comprises 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 and through which a cathode-side electrolyte flows, and a liquid flow path 29a provided between the anode 22 and the anion exchange membrane 23 and through which an anode-side electrolyte flows. The electrolysis device 2 also comprises 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 comprises 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 comprises 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 stacked 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 channel structure 24, and the portion of the groove surrounded by the gas flow channel structure 24 and the cathode 10 forms a gas flow channel 24a. A groove is formed on the anode 22 side of the gas flow channel structure 25, and the portion of the groove surrounded by the gas flow channel structure 25 and the anode 22 forms a gas flow channel 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 channel structure 24 and the gas flow channel structure 25 are each an electrical conductor, and a voltage is applied between the cathode 10 and the anode 22 by power supplied from the power source.

[0069] At the cathode 10, carbon dioxide and / or carbon monoxide are reduced to produce carbon compounds, and water is reduced to produce hydrogen. Here, the cathode 10 has the gas diffusion layer 11 disposed on the gas flow path 24a side, and the third layer 14 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 gas diffusion layer on which a catalyst layer containing an anode catalyst that promotes the electrolytic oxidation of hydroxide ions is formed. Here, the anode 22 has the gas diffusion layer disposed on the gas flow path 25a side, and the catalyst layer 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. Porous materials such as mesh materials, punched materials, and sintered metal fibers may also be used as the gas diffusion layer. Materials constituting the porous material are 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 forming the liquid flow path structures 28, 29 is not particularly limited, but examples thereof include fluororesins such as polytetrafluoroethylene. The material forming the gas flow path structures 24, 25 is not particularly limited, but examples thereof include metals such as titanium, alloys such as stainless steel, and carbon.

[0074] The material for the current collectors 26 and 27 is not particularly limited, but examples thereof include metals such as copper, gold, and titanium, alloys such as stainless steel, and carbon. The current collectors 26 and 27 may be made of a copper base material whose surface is 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 the 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 each of 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 solution A and the anode-side electrolyte solution B can be adjusted as appropriate, but the pH of the anode-side electrolyte solution B is preferably lower than the pH of the cathode-side electrolyte solution A. The pH of the cathode-side electrolyte solution A is, for example, greater than 14, and the pH of the anode-side electrolyte solution 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% by volume or more and 100% by 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% by volume or more and 100% by 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) produced 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, when 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 produced 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 of its industrial utility 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 embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the above-described embodiments may be modified as appropriate within the scope of the spirit of the present invention. [Example]

[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 sides of 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 DINOBEA 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 in a dryer at 80°C for 1 hour to form the first layer. At this time, the basis 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 Dinobear 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. Two layers of the coating solution were then applied onto the second layer by drop casting on a hot plate heated to 60°C, followed by drying in a dryer at 80°C for 1 hour to form a third layer. The 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, in which the first, second and third layers were sequentially stacked, was fired under a nitrogen gas atmosphere at 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 DINOBEA nanodia toluene dispersion (manufactured by Daicel) was used instead of a 1% by mass DINOBEA nanodia IPA dispersion (manufactured by Daicel). At this time, the basis weight of the first layer per unit geometric area of ​​the gas diffusion layer was 0.500 mg / cm. 2 The weight 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 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) 40 μL of Polyflon PTFE D-210C (manufactured by Daikin) as an aqueous dispersion of polytetrafluoroethylene (PTFE) and 40 μL of Dinobear 1 mass% ζ + nanodiamond aqueous dispersion (manufactured by Daicel) were mixed, and then 40 μL of distilled water was added and mixed to obtain a coating solution. Here, the nanodiamonds contained in the Dinobear 1 mass% ζ + nanodiamond aqueous dispersion (manufactured by Daicel) are terminated with hydrogen. Next, the coating solution was applied to the second layer by drop casting on a hot plate heated to 60 ° C, and then dried in an oven 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 2.4 mg / 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) A coating solution was obtained by mixing 40 μL of Polyflon PTFE D-210C (manufactured by Daikin) as an aqueous dispersion of polytetrafluoroethylene (PTFE) with 80 μL of Dinobear 1 mass% ζ + nanodiamond aqueous dispersion (manufactured by Daicel). Here, the nanodiamonds contained in the Dinobear 1 mass% ζ + nanodiamond aqueous dispersion (manufactured by Daicel) are terminated with hydrogen. Next, the coating solution was applied onto the second layer by drop casting 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 2.7 mg / 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) 6.0 mg of nanodiamond powder used in Dinobear 1% by mass ζ+ Nanodiamond Water Dispersion (Daicel) was added to 1.0 mL of 2-propanol (IPA), and then dispersed for 5 minutes using an ultrasonic cleaner ASU-3M (As One) to obtain an IPA dispersion of nanodiamonds. Here, the nanodiamonds contained in the nanodiamond powder were 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 in a dryer at 80°C for 1 hour 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 using the electrolysis device 2 (see FIG. 2) under the following conditions. Pretreatment conditions: cyclic voltammetry Atmosphere: Nitrogen gas atmosphere Sweep range: -0.85V to -0.10V Number of sweeps: 10 cycles Electrolysis conditions: constant potential electrolysis Voltage: -2.5V Electrolysis time: 30 minutes

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

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

[0105] Meanwhile, when the electrolysis time reached 30 minutes, the cathode-side electrolyte A containing the produced liquid (formic acid (HCOOH), acetic acid (CHCOOH), and ethanol (CHCHOH)) was collected from the liquid flow path 63 and neutralized with concentrated hydrochloric acid. The concentration of the produced liquid was then measured under the following conditions using a high-performance liquid chromatograph, Prominence (manufactured by Shimadzu Corporation). The concentration of the produced liquid was converted to determine the amount of substance [mol] of the produced 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 substance of each product [mol] × n / Number of electrons consumed at 30 minutes of electrolysis [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 [mol] required to produce 1 mol of each product. - 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] 4 shows 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 because no layer containing nanodiamonds is 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 second layer formed on the gas diffusion layer and including a catalyst that promotes the electrolytic reduction of carbon dioxide and / or carbon monoxide; a third layer formed on the second layer, the third layer comprising nanodiamonds and a fluororesin.

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

3. The weight per unit geometric area of ​​the first gas diffusion layer is 0.5 mg / cm ２ 1.0mg / cm or more ２ 3. The cathode of claim 1, wherein:

4. 1. A method for producing a cathode for use in the electrolytic reduction of carbon dioxide and / or carbon monoxide, comprising: 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; and applying a dispersion containing nanodiamonds and a fluororesin onto the second layer to form a third layer.

5. An electrolytic device comprising the cathode according to claim 1 or 2.

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