Patent Application
20250129496
This application is based on and claims the benefit of priority from Japanese Patent Application No. 2023-182239, filed on 24 Oct. 2023, the content of which is incorporated herein by reference.
The present invention relates to a cathode used in the electrolysis of carbon dioxide and/or carbon monoxide, a method for manufacturing the cathode, and an electrolyzer.
Conventionally, efforts to mitigate or reduce the effects of climate change have been ongoing, and research and development on reducing carbon dioxide emissions has been conducted to achieve this goal.
Patent Document 1 describes a steep interface CO2 electroreduction catalyst for converting CO2 to a multi-carbon compound. The steep interface CO2 electroreduction catalyst includes a porous gas diffusion layer having a gas contacting side configured to be in contact with CO2 gas and to allow CO2 gas to pass to the opposite reaction interface side, and a catalyst layer disposed on the reaction interface side of the porous gas diffusion layer, having an electrolyte contacting side configured to cover the reaction interface side of the porous gas diffusion layer and to be in contact with 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 reaction interface side opposite the catalyst layer, is composed of one or more metals selected to convert CO2 to a multi-carbon compound under determined electrolytic reduction conditions, prevents diffusion restriction of CO2 in the aqueous electrolyte, and is thin enough to enhance the selectivity of multi-carbon compounds.
However, the steep interface CO2 electroreduction catalyst described in Patent Document 1 has a low Faraday efficiency for the main product.
It is an object of the present invention to provide a cathode capable of improving the Faraday efficiency of the main product from the electrolytic reduction reaction of carbon dioxide and/or carbon monoxide.
A first aspect relates to a cathode for use in electrolytic reduction of carbon dioxide and/or carbon monoxide, including: a gas diffusion layer; a first layer containing nanodiamonds; and a second layer containing a catalyst that promotes electrolytic reduction of the carbon dioxide and/or carbon monoxide.
A second aspect relates to the cathode as described in the first aspect, in which the nanodiamonds are hydrogen-terminated.
A third aspect relates to the cathode as described in the first or second aspect, in which a weight of the first layer per unit geometric area of the gas diffusion layer is 0.005 mg/cm2 or more and 10 mg/cm2 or less.
A fourth aspect relates to the cathode as described in any one of the first to third aspects, further including a third layer containing a fluororesin.
A fifth aspect relates to the cathode as described in any one of the first to third aspects, in which the first layer further includes a fluororesin.
A sixth aspect relates to a method for manufacturing a cathode for use in electrolytic reduction of carbon dioxide and/or carbon monoxide, including: applying a dispersion containing nanodiamonds on a gas diffusion layer to form a first layer; and sputtering a catalyst that promotes electrolytic reduction of the carbon dioxide and/or carbon monoxide on the gas diffusion layer to form a second layer.
A seventh aspect relates to a method as described in the sixth aspect, further including applying a dispersion containing a fluororesin on the gas diffusion layer to form a third layer.
An eighth aspect relates to the method as described in the sixth aspect, in which the dispersion further contains a fluororesin.
A ninth aspect relates to an electrolyzer including the cathode as described in any one of the first to fifth aspects.
According to the present invention, it is possible to provide a cathode capable of improving the Faraday efficiency of the main product from the electrolytic reduction reaction of carbon dioxide and/or carbon monoxide.
Embodiments of the present invention will be described below with reference to the drawings.
A cathode 10 is used for electrolytic reduction of carbon dioxide and/or carbon monoxide, and in the cathode 10, a first layer 12 containing nanodiamonds, a second layer 13 containing a catalyst that promotes electrolytic reduction of carbon dioxide and/or carbon monoxide, and a third layer 14 containing a fluororesin are sequentially stacked on a gas diffusion layer 11.
The gas diffusion layer 11 is not particularly limited as long as it is a porous layer capable of permeating raw material gas containing carbon dioxide and/or carbon monoxide, gas produced by the electrolytic reduction of carbon dioxide and/or carbon monoxide, and hydrogen produced by the electrolytic reduction of water.
The gas diffusion layer 11, for example, is a porous layer formed on a porous substrate. In this case, the first layer 12 is formed on the porous layer.
The thickness of the porous substrate is not particularly limited, and for example, it is 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.
The mode pore size of the porous substrate is not particularly limited, and 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 mode pore size of the porous substrate is measured, for example, by the mercury injection method.
Examples of the porous substrate include nonwoven fabrics and woven fabrics.
The porous substrate preferably contains a carbon material. Thereby, the electrical conductivity of the gas diffusion layer 11 is improved, and the electrolytic reduction reaction of carbon dioxide and/or carbon monoxide can be carried out efficiently.
The carbon materials are not particularly limited as long as they can improve the electrical conductivity of the gas diffusion layer 11, and examples thereof include carbon materials such as carbon fibers, carbon black, graphite, activated carbon, carbon nanotubes, carbon nanofibers, fullerene, and amorphous carbon, and two or more thereof may be used in combination.
For example, a metal or alloy mesh material, a metal or alloy perforated material, or a metal fiber sintered material may be used as a porous substrate. The metals are not particularly limited, and examples thereof include titanium, nickel, and iron. The alloys are not particularly limited, and examples thereof include stainless steel.
It is preferable that the porous layer has a smaller average pore size and a larger specific surface area than the porous substrate. Thereby, the amount of nanodiamonds supported in the gas diffusion layer 11 can be increased.
The thickness of the porous layer is not particularly limited, and 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.
The mode pore size of the porous layer is not particularly limited, and 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.
The porous layer preferably contains a fluororesin. This suppresses infiltration of the electrolyte. As a result, the Faraday efficiency of the main product from the electrolytic reduction reaction of carbon dioxide and/or carbon monoxide is increased, while the Faraday efficiency of hydrogen, the product from the electrolytic reduction reaction of water, is decreased.
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 from the viewpoint of water repellency of the gas diffusion layer 11.
The porous layer preferably contains a carbon material as well as a porous substrate. Thereby, the electrical conductivity of the gas diffusion layer 11 is improved, and the electrolytic reduction reaction of carbon dioxide and/or carbon monoxide can be carried out efficiently.
The content of carbon material in the porous layer is not particularly limited, and is, for example, 70 mass % or more and 95 mass % or less, preferably 75 mass % or more and 92 mass % or less, and more preferably 80 mass % or more and 90 mass % or less. The content of carbon material in the porous layer is measured, for example, by the combustion method.
A commercial product of the gas diffusion layer 11 includes, for example, Sigracet 39 BB (manufactured by SGL Carbon).
The first layer 12 is formed on the gas diffusion layer 11, and the nanodiamonds in the first layer 12 are supported on at least a part of the surfaces (outer and inner surfaces) of the gas diffusion layer 11.
The particle size of nanodiamonds is not particularly limited, and is, for example, 1 nm or more and 20 nm or less.
Nanodiamonds are produced, for example, by a detonation method, and are doped with elements such as silicon and germanium.
The nanodiamonds may be terminated with either hydrogen or oxygen, preferably with hydrogen. This improves the Faraday efficiency of the main product from the electrolytic reduction reaction of carbon dioxide and/or carbon monoxide.
The weight of the first layer 12 per unit geometric area of the gas diffusion layer 11 is preferably 0.005 mg/cm2 or more and 10 mg/cm2 or less, and more preferably 0.5 mg/cm2 or more and 1.0 mg/cm2 or less. When the weight of the first layer 12 per unit geometric area of the gas diffusion layer 11 is 0.005 mg/cm2 or more and 10 mg/cm2 or less, the Faraday efficiency of the main product from the electrolytic reduction reaction of carbon dioxide and/or carbon monoxide is improved.
The first layer 12 is formed, for example, by applying a dispersion containing nanodiamonds, followed by drying. The method of applying the dispersion containing nanodiamonds is not particularly limited, and examples thereof include the drop-casting method.
The dispersion containing nanodiamonds may further contain a dispersion medium (water, tetrahydrofuran, isopropanol, methyl isobutyl ketone, toluene, etc.) and a surfactant. The content of nanodiamond in the dispersion containing a fluororesin is not particularly limited, and is, for example, 0.1 mass % or more and 15 mass % or less, and preferably 0.5 mass % or more and 10 mass % or less.
Commercial products of dispersions containing nanodiamonds terminated with hydrogen include, for example, DINNOVARE ζ+nanodiamond aqueous dispersion (manufactured by Daicel). Also, commercially available dispersions containing nanodiamonds terminated with oxygen include, for example, DINNOVARE ζ−nanodiamond aqueous dispersion (manufactured by Daicel).
The drying temperature is not particularly limited, and is, for example, 20° C. or more and 120° C. or less, and preferably 50° C. or more and 100° C. or less. The drying time is not particularly limited, and is, for example, 0.5 hours or more and 24 hours or less, and preferably 1 hour or more and 12 hours or less.
The second layer 13 is formed on the first layer 12, and the catalyst in the second layer 13 is supported on at least a part of the surfaces of the nanodiamonds in the first layer 12.
The catalysts are not particularly limited as long as they 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 thereof may be used in combination. Among these, copper is preferred since the main product is ethylene.
When silver, gold, or zinc is used as a catalyst, the main product is carbon monoxide. When lead, indium, tin, or cadmium is used as a catalyst, the main product is formic acid.
The average particle size of the catalyst is not particularly limited, and is, for example, 1 nm or more and 100 nm or less, preferably 3 nm or more and 50 nm or less, and more preferably 5 nm or more and 30 nm or less. The average particle size of the catalyst is determined, for example, as the average value of Feret diameters of 100 particles arbitrarily selected from a scanning electron microscope (SEM) image.
The average thickness of the second layer 13 is not particularly limited, and is, for example, 5 nm or more and 1000 nm or less, preferably 10 nm or more and 500 nm or less, and more preferably 20 nm or more and 200 nm or less. 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.
The method for forming the second layer 13 is not particularly limited, and examples thereof include sputtering, vapor deposition methods such as arc plasma deposition, electron beam deposition, thermal deposition, pulsed laser deposition, and plating methods such as electrolytic plating, electroless plating, and substitution plating. Among these, the sputtering method is preferred from the viewpoint of uniformity of the thickness of the second layer 13.
The content of the second layer 13 in the cathode 10 is not particularly limited, and 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.
The third layer 14 is formed on the second layer 13, and the fluororesin in the third layer 14 covers at least a part of the surface of the catalyst in the second layer 13. Because of this, infiltration of the electrolyte is suppressed. As a result, the Faraday efficiency of the main product from the electrolytic reduction reaction of carbon dioxide and/or carbon monoxide is increased, while the Faraday efficiency of hydrogen, the product from the electrolytic reduction reaction of water, is decreased.
The thickness of the third layer 14 is not particularly limited, and 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.
The fluororesin is not particularly limited, and examples thereof include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer. Among these, polytetrafluoroethylene is preferred from the viewpoint of water repellency of the third layer 14.
The weight of the third layer 14 per unit geometric area of the gas diffusion layer 11 is not particularly limited, and is, for example, 0.02 mg/cm2 or more and 4.0 mg/cm2 or less, preferably 0.05 mg/cm2 or more and 2.0 mg/cm2 or less, and more preferably 0.1 mg/cm2 or more and 1.0 mg/cm2 or less.
The third layer 14 is formed, for example, by applying a dispersion containing a fluororesin, followed by drying. The method of applying the dispersion containing a fluororesin is not particularly limited, and examples thereof 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. The dispersion containing a fluororesin may be applied in layers.
The dispersion containing a 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 a fluororesin is not particularly limited, and is, for example, 1 mass % or more and 70 mass % or less, and preferably 3 mass % or more and 60 mass % or less. A commercially available aqueous dispersion containing a fluororesin includes, for example, POLYFLON PTFE D-210C (manufactured by Daikin), which is diluted with water before use if necessary.
The drying temperature is not particularly limited, and is, for example, 20° C. or more and 120° C. or less, and preferably 50° C. or more and 100° C. or less. The drying time is not particularly limited, and is, for example, 0.5 hours or more and 24 hours or less, and preferably 1 hour or more and 12 hours or less.
After forming the third layer, it may be fired under an inert gas (nitrogen gas, argon gas, etc.) atmosphere. The firing temperature is not particularly limited, and is, for example, 150° C. or more and 450° C. or less, preferably 170° C. or more and 350° C. or less, and more preferably 200° C. or more and 300° C. or less. The firing time is not particularly limited, and is, for example, 10 minutes or more and 240 minutes or less, preferably 20 minutes or more and 180 minutes or less, and more preferably 30 minutes or more and 150 minutes or less. The rate of temperature increase during firing is not particularly limited, and is, for example, 1° C./min or more and 30° C./min or less, preferably 3° C./min or more and 20° C./min or less, and more preferably 5° C./min or more and 15° C./min or less.
A cathode 20 has the same configuration as the cathode 10, except that instead of forming the first layer 12 containing nanodiamonds and the third layer 14 containing a fluororesin, a third layer 21 containing nanodiamonds and a fluororesin is formed.
An electrolyzer 2 comprises the cathode 10, an anode 22, an anion exchange membrane 23 between the cathode 10 and the anode 22, a liquid flow path 28a between the cathode 10 and the anion exchange membrane 23 through which the cathode-side electrolyte flows, and a liquid flow path 29a between the anode 22 and the anion exchange membrane 23, through which the anode-side electrolyte flows. The electrolyzer 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. Furthermore, the electrolyzer 2 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 electrolyzer 2 also comprises a power feeder 26 and a power feeder 27. The power feeder 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 feeder 27 are sequentially stacked.
A slit is formed in the liquid flow path structure 28, and the area surrounded by the cathode 10, the anion exchange membrane 23, and the liquid flow path structure 28 in the slit is the liquid flow path 28a. A slit is also formed in the liquid flow path structure 29, and the area surrounded by the anode 22, the anion exchange membrane 23, and the liquid flow path structure 29 in the slit is the liquid flow path 29a.
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 is the 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 is the gas flow path 25a.
In the electrolyzer 2, the liquid flow path 28a is formed between the cathode 10 and the anion exchange membrane 23, the liquid flow path 29a is formed between the anode 22 and the anion exchange membrane 23, the gas flow path 24a is formed between the cathode 10 and the power feeder 26, and the gas flow path 25a is formed between the anode 22 and the power feeder 27.
The power feeder 26 and the power feeder 27 are each electrically connected to a power source that supplies power to the electrolyzer 2. Here, the gas flow path structure 24 and the gas flow path structure 25 are conductors, respectively, and voltage is applied between the cathode 10 and the anode 22 by the power supplied from the power source.
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, gas diffusion layer 11 is disposed on the side of the gas flow path 24a and the third layer 14 is disposed on the side of the liquid flow path 28a.
In the anode 22, hydroxide ions are oxidized to produce oxygen. In the anode 22, for example, a catalyst layer including an anode catalyst that promotes electrolytic oxidation of hydroxide ions is formed on the gas diffusion layer. Here, in the anode 22, the gas diffusion layer is disposed on the side of the gas flow path 25a and the catalyst layer is disposed on the side of the liquid flow path 29a.
The gas diffusion layer is not particularly limited, and examples thereof include carbon paper and carbon cloth. Porous materials such as a mesh material, a perforated material, and sintered metal fibers may be used as the gas diffusion layer. The materials that make up the porous material are not particularly limited, and examples thereof include metals such as titanium, nickel, and iron, and alloys such as stainless steel.
The anode catalysts are not particularly limited, and examples thereof include metals such as platinum, palladium, and nickel, their alloys or intermetallic compounds, 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 thereof may be used in combination.
The materials that make up the liquid flow path structures 28 and 29 are not particularly limited, and examples thereof include a fluororesin such as polytetrafluoroethylene. The materials that make up the gas flow path structures 24 and 25 are not particularly limited, and examples thereof include metals such as titanium, alloys such as stainless steel, and carbon.
The materials that make up the power feeders 26 and 27 are not particularly limited, and examples thereof include metals such as copper, gold, and titanium, alloys such as stainless steel, and carbon. A copper substrate with a plating treatment such as gold plating on the surface may be used as the power feeders 26 and 27.
As the anion exchange membrane 23, any known anion exchange membrane can be used.
The electrolyzer 2 comprises a pump that supplies cathode-side electrolyte A from a liquid flow path 64 to the liquid flow path 28a, a pump that supplies anode-side electrolyte B from a liquid flow path 65 to the liquid flow path 29a, and a pump that supplies raw material gas G containing carbon dioxide and/or carbon monoxide from a gas flow path 76 to the gas flow path 24a.
Alkaline aqueous solutions can be used as cathode-side electrolyte A and anode-side electrolyte B, respectively. The alkaline aqueous solution is not particularly limited, and examples thereof include potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, potassium carbonate aqueous solution, and sodium carbonate aqueous solution. Among these, potassium hydroxide aqueous solution is preferred from the viewpoint that the Faraday efficiency of hydrogen, the product from the electrolytic reduction reaction of water, is decreased.
The pH of cathode-side electrolyte A and anode-side electrolyte B can be adjusted accordingly, and the pH of anode-side electrolyte B is preferably lower than that of cathode-side electrolyte A. The pH of cathode-side electrolyte A is, for example, greater than 14, and the pH of anode-side electrolyte B is, for example, 8 or more and 14 or less.
The alkali concentration of cathode-side electrolyte A is not particularly limited, and is, for example, 4 mol/L or more and 12 mol/L or less, preferably 5 mol/L or more and 11 mol/L or less, and more preferably 6 mol/L or more and 10 mol/L or less. The temperature of cathode-side electrolyte A is not particularly limited, and is, for example, 10° C. or more and 60° C. or less. The flow rate of cathode-side electrolyte A is not particularly limited, and is, for example, 0.5 mL/min or more and 5 mL/min or less.
The alkali concentration of anode-side electrolyte B is not particularly limited, and is, for example, 0.1 mol/L or more and 3 mol/L or less, preferably 0.2 mol/L or more and 2.5 mol/L or less, and more preferably 0.5 mol/L or more and 2 mol/L or less. The temperature of anode-side electrolyte B is not particularly limited, and is, for example, 10° C. or more and 60° C. or less. The flow rate of anode-side electrolyte B is not particularly limited, and is, for example, 0.5 mL/min or more and 5 mL/min or less.
When the raw material gas G contains carbon dioxide, the concentration of carbon dioxide in the raw material gas G is not particularly limited, and 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, and is, for example, 1 volume % or more and 100 volume % or less. The temperature of the raw material gas G is not particularly limited, and 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, and is, for example, 5 mL/min or more and 50 mL/min or less.
In the electrolyzer 2, the cathode-side electrolyte A containing liquid (carbon compound) generated at the cathode 10 is discharged from a liquid flow path 63, and the produced gas E containing gas (carbon compound and hydrogen) generated at the cathode 10 is discharged from the gas flow path 67. In the electrolyzer 2, the anode-side electrolyte B is discharged from a liquid flow path 66, and the oxygen (O2) generated at the anode 22 is discharged via the gas flow path 25a. If the produced gas E contains ethylene, the produced gas E discharged from the electrolyzer 2 may be sent to a reactor and brought into gas phase contact with an olefin polymerization catalyst to polymerize ethylene.
Carbon compounds produced by the electrolytic reduction of carbon dioxide at the cathode 10 include, for example, 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 usefulness in the chemical industry.
Carbon compounds produced by the electrolytic reduction of carbon monoxide at the cathode 10 include, for example, C1 compounds such as formaldehyde, methanol, and methane, and C2 compounds such as acetic acid, acetaldehyde, ethanol, and ethylene.
Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and the above embodiments may be modified as appropriate within the scope of the spirit of the present invention.
Examples of the present invention are described below, but the present invention is not limited to the examples.
Using a press cutter (Thomson cutter) Model MB (manufactured by Aichi Technical), Sigracet 39 BB (manufactured by SGL Carbon) was cut into a square of 30 mm on each side to obtain a gas diffusion layer. Here, Sigracet 39 BB has a microporous layer on one side of the carbon fiber nonwoven fabric (carbon paper), which is treated with 5 mass % PTFE.
On a hot plate heated to 60° C., 0.5 mL of DINNOVARE 1 mass % nanodiamond IPA dispersion (manufactured by Daicel) was applied on the microporous layer of the gas diffusion layer by drop-casting method, and then dried in a dryer at 80° C. for 1 hour to form a first layer. The weight of the first layer per unit geometric area of the gas diffusion layer was 0.50 mg/cm2. Here, the nanodiamonds in DINNOVARE 1 mass % nanodiamond IPA dispersion (manufactured by Daicel) are hydrogen-terminated.
On the first layer, Cu was sputtered under the following conditions to form a second layer with a thickness of 25 nm.
POLYFLON PTFE D-210C (manufactured by Daikin) as an aqueous dispersion of polytetrafluoroethylene (PTFE) was diluted 10 times with distilled water to obtain a coating solution. Next, two layers of the coating solution were applied on the second layer on a hot plate heated to 60° C. by drop-casting method, and then dried 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/cm2.
Using a tube furnace, the gas diffusion layer, in which the first, second, and third layers were sequentially stacked, was fired under conditions of a temperature increase rate of 10° C./min, a holding temperature of 200° C., and a holding time of 2 hours under a nitrogen gas atmosphere to obtain a cathode.
A cathode was obtained in the same manner as in Example 1, except that DINNOVARE 1 mass % nanodiamond toluene dispersion (manufactured by Daicel) was used instead of DINNOVARE 1 mass % nanodiamond IPA dispersion (manufactured by Daicel). The weight of the first layer per unit geometric area of the gas diffusion layer was 0.500 mg/cm2, and the weight of the third layer per unit geometric area of the gas diffusion layer was 2.9 mg/cm2. Here, the nanodiamonds in DINNOVARE 1 mass % nanodiamond toluene dispersion (manufactured by Daicel) are hydrogen-terminated.
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.
40 μL of POLYFLON PTFE D-210C (manufactured by Daikin) as an aqueous dispersion of polytetrafluoroethylene (PTFE) and 40 μL of DINNOVARE 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 in DINNOVARE 1 mass % (+nanodiamond aqueous dispersion (manufactured by Daicel) are hydrogen-terminated. Next, the coating solution was applied on the second layer on a hot plate heated to 60° C. by drop-casting method, and then dried 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 2.4 mg/cm2.
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.
40 μL of POLYFLON PTFE D-210C (manufactured by Daikin) as an aqueous dispersion of polytetrafluoroethylene (PTFE) and 80 μL of DINNOVARE 1 mass % ζ+nanodiamond aqueous dispersion (manufactured by Daicel) were mixed to obtain a coating solution. Here, the nanodiamonds in DINNOVARE 1 mass % ζ+nanodiamond aqueous dispersion (manufactured by Daicel) are hydrogen-terminated. Next, the coating solution was applied on the second layer on a hot plate heated to 60° C. by drop-casting method, and then dried 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 2.7 mg/cm2.
A cathode was obtained in the same manner as in Example 1, except that the first layer was formed as follows.
The IPA dispersion of nanodiamond was obtained by adding 1.0 mL of 2-propanol (IPA) to 6.0 mg of nanodiamond powder used in DINNOVARE 1 mass % ζ+nanodiamond aqueous dispersion (manufactured by Daicel), then dispersing it for 5 minutes using an ultrasonic cleaner ASU-3M (manufactured by AS ONE). Here, the nanodiamonds in the nanodiamond powder are hydrogen-terminated.
On a hot plate heated to 60° C., 0.5 mL of IPA dispersion of nanodiamond was applied on the microporous layer of the gas diffusion layer by drop-casting method, and then dried in a dryer at 80° C. for 1 hour to form a first layer. The weight of the first layer per unit geometric area of the gas diffusion layer was 0.75 mg/cm2.
The cathode was obtained in the same manner as in Example 1, except that the first and third layers were not formed.
The cathode was obtained in the same way as in Example 1, except that the first layer was not formed.
Carbon dioxide was electrolyzed using electrolyzer 2 (see
Here, 7 mol/L potassium hydroxide (KOH) 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 1 mL/min. As anode-side electrolyte B supplied through the liquid flow path 65, 1 mol/L potassium hydroxide (KOH) solution was used, and the flow rate of anode-side electrolyte B was 1 mL/min. As the cathode 10, cathodes from 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. 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 20 mL/min.
When the electrolysis time reached 30 minutes, the gases produced (hydrogen (H2), carbon monoxide (CO), methane (CH4), and ethylene (C2H4)) were collected from the gas flow path 67 using a Smart Bag PA (manufactured by GL Sciences) and the concentration of the gases produced was measured using a gas chromatograph CP-4900 Micro GC (manufactured by Varian). H2, CO, and CH4 were quantified using argon gas as a carrier gas and a Molsieve 5A column (manufactured by GL Sciences). C2H4 was quantified using helium gas as a carrier gas and a PoraPLOT Q column (manufactured by GL Sciences). The concentration of the gas produced was converted to obtain the amount of substance [mol] of the gas produced.
When the electrolysis time reached 30 minutes, cathode-side electrolyte A containing the liquids produced (formic acid (HCOOH), acetic acid (CH3COOH), and ethanol (CH3CH2OH)) was collected from the liquid flow path 63, neutralized with concentrated hydrochloric acid, and then the concentration of the liquids produced was measured using a high-performance liquid chromatograph Prominence (manufactured by Shimadzu Corporation) under the following conditions. The concentration of the liquid produced was converted to obtain the amount of substance [mol] of the liquid produced.
The Faraday efficiency [%] of each product was determined based on the following equation.
Amount of substance in each product [mol]×n/Number of electrons consumed when electrolysis time reaches 30 minutes
[mol]×100
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
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-182239 | Oct 2023 | JP | national |
