US20240410068A1 - Electrolyte Membrane and Manufacturing Method of Electrolyte Membrane - Google Patents

Electrolyte Membrane and Manufacturing Method of Electrolyte Membrane Download PDF

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Publication number
US20240410068A1
US20240410068A1 US18/699,379 US202118699379A US2024410068A1 US 20240410068 A1 US20240410068 A1 US 20240410068A1 US 202118699379 A US202118699379 A US 202118699379A US 2024410068 A1 US2024410068 A1 US 2024410068A1
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electrolyte membrane
water
reduction
repellent
carbon dioxide
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Akihiro Kono
Yuya Uzumaki
Sayumi Sato
Takeshi Komatsu
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NTT Inc USA
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Nippon Telegraph and Telephone Corp
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B13/00—Diaphragms; Spacing elements
    • C25B13/04—Diaphragms; Spacing elements characterised by the material
    • C25B13/08—Diaphragms; Spacing elements characterised by the material based on organic materials
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/23—Carbon monoxide or syngas
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/50—Processes
    • C25B1/55—Photoelectrolysis
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B13/00—Diaphragms; Spacing elements
    • C25B13/02—Diaphragms; Spacing elements characterised by shape or form
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/25—Reduction
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/25—Reduction
    • C25B3/26—Reduction of carbon dioxide
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
    • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/50—Cells or assemblies of cells comprising photoelectrodes; Assemblies of constructional parts thereof

Definitions

  • the present invention relates to an electrolyte membrane and a method for manufacturing an electrolyte membrane.
  • Non Patent Literature 1 discloses a carbon dioxide reduction device using light illumination.
  • an oxidation tank when an oxidation electrode is illuminated with light, electron-hole pairs are generated and separated at the oxidation electrode, and oxygen and protons (H + ) are generated by an oxidation reaction of water in an electrolytic solution.
  • the protons pass through an electrolyte membrane and reach a reduction tank, and electrons flow to the reduction electrode via a conducting wire.
  • a carbon dioxide reduction reaction by protons, electrons, and carbon dioxide dissolved in a solution is caused at the reduction electrode in the solution. This reduction reaction generates carbon monoxide, formic acid, methane, and the like that can be used as energy resources.
  • the reduction electrode is immersed in a solution, and carbon dioxide is dissolved in the solution, and thereby the carbon dioxide is supplied to the reduction electrode.
  • a method of reducing carbon dioxide since the reduction electrode is immersed in the solution, there are limitations on a dissolved carbon dioxide concentration in the solution and a diffusion coefficient of carbon dioxide in the solution, and the amount of carbon dioxide supplied to the reduction electrode is limited.
  • Non Patent Literature 2 by using a reduction tank having a structure in which carbon dioxide in a gas phase is directly supplied to a reduction electrode, a supply amount of carbon dioxide to the reduction electrode is increased, and the carbon dioxide reduction reaction is promoted.
  • the present invention has been made to address the problems described above, and an object of the present invention is to provide a technology capable of improving reduction reaction efficiency of carbon dioxide.
  • An electrolyte membrane according to an aspect of the present invention is disposed between an electrolytic solution in an oxidation tank and a reduction electrode in a reduction tank to be in contact with both the electrolytic solution and the reduction electrode and is used in a carbon dioxide reduction device which performs a carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode, the electrolyte membrane including: a water-repellent film on a part of a surface which is in contact with the electrolytic solution.
  • a method for manufacturing an electrolyte membrane according to an aspect of the present invention is a method for manufacturing the electrolyte membrane described above, the method including: a step of applying a water-soluble polymer to one surface of the electrolyte membrane; a step of removing moisture in the water-soluble polymer; a step of performing a water-repellent treatment on both surfaces of the electrolyte membrane; and a step of removing the water-soluble polymer from the one surface of the electrolyte membrane.
  • a method for manufacturing an electrolyte membrane according to an aspect of the present invention is a method for manufacturing the electrolyte membrane described above, the method including: a step of applying a water-repellent polymer to one surface of the electrolyte membrane; and a step of removing a solvent in the water-repellent polymer.
  • a method for manufacturing an electrolyte membrane according to an aspect of the present invention is a method for manufacturing the electrolyte membrane described above, the method including: a step of applying a water-soluble polymer to one surface of the electrolyte membrane; a step of removing moisture in the water-soluble polymer; a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on both surfaces of the electrolyte membrane; and a step of removing the water-soluble polymer from the one surface of the electrolyte membrane.
  • a method for manufacturing an electrolyte membrane according to an aspect of the present invention is a method for manufacturing the electrolyte membrane described above, the method including: a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on one surface of the electrolyte membrane.
  • FIG. 1 is a view illustrating a configuration example of a carbon dioxide reduction device according to a first embodiment.
  • FIG. 2 is a view illustrating a configuration example of a water-repellent film.
  • FIG. 3 is a flowchart illustrating a first method for manufacturing the water-repellent film.
  • FIG. 4 is a flowchart illustrating a second method for manufacturing the water-repellent film.
  • FIG. 5 is a flowchart illustrating a third method for manufacturing the water-repellent film.
  • FIG. 6 is a flowchart illustrating a fourth method for manufacturing the water-repellent film.
  • FIG. 7 is a graph illustrating a measurement result of Faraday efficiency of formic acid according to the first embodiment.
  • FIG. 8 is a view illustrating a configuration example of a carbon dioxide reduction device according to a second embodiment.
  • FIG. 9 is a graph illustrating a measurement result of Faraday efficiency of formic acid according to the second embodiment.
  • FIG. 1 is a view illustrating a configuration example of a carbon dioxide reduction device 100 according to a first embodiment.
  • the carbon dioxide reduction device 100 includes an oxidation electrode 1 , an oxidation tank 2 , an electrolytic solution 3 , a reduction electrode 4 , a reduction tank 5 , an electrolyte membrane 6 , a conducting wire 7 , a light source 8 , and a water-repellent film 9 .
  • the oxidation electrode 1 is immersed in the electrolytic solution 3 in the oxidation tank 2 .
  • the oxidation electrode 1 is formed by forming a semiconductor on a substrate having a predetermined area.
  • the oxidation electrode 1 is formed, for example, by forming a film of a compound exhibiting photoactivity or redox activity, such as a nitride semiconductor, titanium oxide, amorphous silicon, a ruthenium complex, or a rhenium complex, on a surface of a sapphire substrate.
  • the oxidation tank 2 contains an electrolytic solution 3 in which the oxidation electrode 1 is immersed.
  • the electrolytic solution 3 is contained in the oxidation tank 2 .
  • Examples of the electrolytic solution 3 include a potassium hydrogen carbonate aqueous solution, a sodium hydrogen carbonate aqueous solution, a potassium chloride aqueous solution, a sodium chloride aqueous solution, a potassium hydroxide aqueous solution, a rubidium hydroxide aqueous solution, and a cesium hydroxide aqueous solution.
  • the reduction electrode 4 is disposed in the reduction tank 5 .
  • the reduction electrode 4 is formed on a substrate having a predetermined area similarly to the oxidation electrode 1 .
  • the reduction electrode 4 is, for example, a porous body made of copper, platinum, gold, silver, indium, palladium, gallium, nickel, tin, cadmium, or an alloy thereof.
  • the reduction electrode 4 may be made of a compound such as silver oxide, copper oxide, copper (II) oxide, nickel oxide, indium oxide, tin oxide, tungsten oxide, tungsten (VI) oxide, or copper oxide, or a porous metal complex having a metal ion and an anionic ligand.
  • the reduction tank 5 contains the reduction electrode 4 disposed inside and gas phase carbon dioxide supplied from the outside through a pipe.
  • the electrolyte membrane 6 is disposed between the oxidation tank 2 and the reduction tank 5 . To be accurate, the electrolyte membrane 6 is disposed between the electrolytic solution 3 and the reduction electrode 4 to be in contact with both the electrolytic solution and the reduction electrode.
  • the electrolyte membrane 6 is, for example, any one of Nafion (registered trademark), FORBLUE, and Aquivion that are an electrolyte membrane having a carbon-fluorine skeleton, or SELEMION, NEOSEPTA, or the like that is an electrolyte membrane having a carbon-hydrogen skeleton.
  • the conducting wire 7 physically and electrically connects the oxidation electrode 1 and the reduction electrode 4 .
  • the light source 8 is disposed close to the oxidation tank 2 .
  • the light source 8 is, for example, sunlight, a xenon lamp, a pseudo sunlight source, a halogen lamp, a mercury lamp, or a combination thereof.
  • the reduction electrode 4 and the electrolyte membrane 6 may be formed of the same material.
  • the present invention can be realized by using a gas diffusion electrode (GDE (registered trademark)) composed of a porous material and a catalyst. Since the gas diffusion electrode can separate liquid and gas and enables cations to move in the electrode, the gas diffusion electrode has actions equivalent to actions of both the reduction electrode 4 and the electrolyte membrane 6 .
  • GDE registered trademark
  • the reduction electrode 4 and the electrolyte membrane 6 are illustrated to have a large width in a horizontal direction of the paper surface, but the width in the horizontal direction of the paper surface may be reduced to have a thin plate shape with a flat surface in a depth direction of the paper surface.
  • an oxidation reaction of water in the electrolytic solution 3 is performed by illumination light (light energy) from the light source 8 by using the electrolytic solution 3 and the semiconductor oxidation electrode 1 immersed in the electrolytic solution 3 .
  • a carbon dioxide reduction reaction is performed using the reduction electrode 4 connected to the oxidation electrode 1 via the conducting wire 7 and carbon dioxide brought into direct contact with the reduction electrode 4 .
  • the light source 8 emits light from the bottom of the oxidation tank 2
  • generation and separation of electron-hole pairs occur in the oxidation electrode 1 in the oxidation tank 2 that has received the illumination light, and oxygen and protons are generated by the oxidation reaction of water in the electrolytic solution 3 .
  • the protons pass through the electrolyte membrane 6 and reach the reduction electrode 4 in the reduction tank 5 from the electrolytic solution 3 in the oxidation tank 2 .
  • the electrons flow from the oxidation electrode 1 in the oxidation tank 2 to the reduction electrode 4 in the reduction tank 5 via the conducting wire 7 .
  • a carbon dioxide reduction reaction is caused by the protons, the electrons, and carbon dioxide in a gas phase brought in direct contact with the reduction electrode 4 in the reduction electrode 4 .
  • This redox reaction generates carbon monoxide, formic acid, methane, and the like that can be used as energy resources.
  • a strong alkaline aqueous solution for example, a 1.0 mol/L sodium hydroxide aqueous solution is used as the electrolytic solution 3 in the oxidation tank 2
  • the electrolyte membrane 6 swells, and the electrolytic solution 3 passes through pores of the electrolyte membrane 6 and is exuded to a surface of the reduction electrode 4 in the reduction tank 5 .
  • a surface of the electrolyte membrane 6 on the side of the oxidation tank 2 may be subjected to a water-repellent treatment, the surface being in contact with the electrolytic solution 3 .
  • the reduction reaction since it is necessary to move protons as a raw material of the reduction reaction using water in the electrolyte membrane 6 as a medium, the reduction reaction may not proceed on the side of the reduction tank 5 when the surface of the electrolyte membrane 6 is completely covered.
  • the water-repellent film 9 is provided on a part of the surface of the electrolyte membrane 6 which is in contact with the electrolytic solution 3 so as not to cover the entire surface of the electrolyte membrane 6 .
  • a plurality of water-repellent films 9 are formed on the surface at predetermined intervals.
  • the water repellency thereof causes the electrolytic solution 3 in the oxidation tank 2 to be suppressed from infiltrating into the electrolyte membrane 6 and causes liquid leakage of the electrolytic solution 3 to the reduction electrode 4 to be suppressed, and the reaction site of the reduction electrode 4 is not covered with the electrolytic solution 3 .
  • the water-repellent film 9 is formed not on the entire surface but on a part of the surface of the electrolyte membrane 6 , a state in which protons can pass through the electrolyte membrane 6 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in reduction reaction efficiency can be suppressed.
  • Examples of the water-repellent treatment for manufacturing the water-repellent film 9 include a liquid phase method and a gas phase method.
  • the liquid phase method is a method in which an object is immersed in a fluorine-based solvent obtained by dissolving a fluorine-based polymer as a water repellent agent, by a dip coating method or the like, and then the fluorine-based polymer is deposited by performing heating or the like on the object and removing the solvent.
  • Another method of the liquid phase method is a method in which a film of the fluorine-based solvent is formed on a surface of an object by a cast coating method, a spin coating method, or the like, and then the fluorine-based polymer is deposited by performing heating or the like on the object and removing the solvent.
  • the gas phase method is a method in which an object and a fluorine-based low molecular substance (silane coupling agent) which is a water repellent agent are put in the same sealed space, the fluorine-based low molecular substance is heated to be evaporated, and then the fluorine-based low molecular substance is deposited on the surface of the object.
  • FIG. 3 is a flowchart illustrating a first method for manufacturing the water-repellent film 9 .
  • the first method is a method for manufacturing the water-repellent film 9 by a liquid phase method.
  • Nafion was used for the electrolyte membrane 6 .
  • OPTOOL DSX was used as a water repellent agent.
  • first step S 101 a water-soluble polymer is dissolved in pure water to prepare a polyvinyl alcohol aqueous solution with a concentration of 1%.
  • second step S 102 the polyvinyl alcohol aqueous solution is dropped onto one surface of the Nafion membrane by a spin coating method, and a polyvinyl alcohol film is formed on the one surface.
  • the Nafion membrane is left in an oven at 60° C. for one hour to evaporate moisture in polyvinyl alcohol (third step S 103 ).
  • a polymer film (water-soluble polymer) is formed on the one surface of the Nafion membrane.
  • dip coating is performed by immersing the Nafion membrane in an OPTOOL DSX solution (water-repellent polymer) for one minute and pulling up the Nafion membrane (fourth step S 104 ). Through this step, water-repellent films are formed on both surfaces of the Nafion membrane.
  • the Nafion membrane is washed with pure water (fifth step S 105 ).
  • polyvinyl alcohol (water-soluble polymer) coated with the water-repellent film can be removed. That is, the polymer film (water-soluble polymer) is removed from one surface of the Nafion membrane, and the water-repellent film on the polymer film is also removed.
  • a water-repellent film can be formed only on one surface of the Nafion membrane.
  • a relatively thick water-repellent film on the order of micrometers can be formed.
  • FIG. 4 is a flowchart illustrating a second method for manufacturing the water-repellent film 9 .
  • the second method is a method for manufacturing the water-repellent film 9 by another liquid phase method.
  • Nafion was used for the electrolyte membrane 6 .
  • OPTOOL DSX was used as a water repellent agent.
  • the OPTOOL DSX water-repellent polymer
  • first step S 201 the Nafion membrane
  • second step S 202 the solvent in OPTOOL DSX is evaporated.
  • a polymer film water-repellent film
  • the water-repellent film can be formed only on one side of the Nafion membrane.
  • a centrifugal force is used, a thin water-repellent film of sub-micrometer order can be formed in principle.
  • FIG. 5 is a flowchart illustrating a third method for manufacturing the water-repellent film 9 .
  • the third method is a method for manufacturing the water-repellent film 9 by the gas phase method.
  • Nafion was used for the electrolyte membrane 6 .
  • a fluorine-based silane coupling agent for example, heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane was used.
  • a water-soluble polymer is dissolved in pure water to prepare a polyvinyl alcohol aqueous solution with a concentration of 1% (first step S 301 ).
  • the polyvinyl alcohol aqueous solution is dropped onto one surface of the Nafion membrane by a spin coating method, and a polyvinyl alcohol film is formed on the one surface (second step S 302 ).
  • the Nafion membrane is left in an oven at 60° C. for one hour to evaporate moisture in polyvinyl alcohol (third step S 303 ).
  • a polymer film (water-soluble polymer) is formed on the one surface of the Nafion membrane.
  • the Nafion membrane and a fluorine-based silane coupling agent (water-repellent low molecular substance) are put in a Teflon container and sealed (fourth step S 304 ).
  • the Teflon container is put in an oven and heated at 150° C. (fifth step S 305 ).
  • the fluorine-based silane coupling agent is evaporated, and water-repellent films are formed on both surfaces of the Nafion membrane.
  • the Nafion membrane is washed with pure water (sixth step S 306 ).
  • polyvinyl alcohol (water-soluble polymer) coated with the water-repellent film can be removed. That is, the polymer film (water-soluble polymer) is removed from one surface of the Nafion membrane, and the water-repellent film on the polymer film is also removed.
  • the water-repellent film can be formed only on one side of the Nafion membrane.
  • a monomolecular film is formed on the surface of Nafion, a very thin water-repellent film on the order of nanometers can be formed.
  • FIG. 6 is a flowchart illustrating a fourth method for manufacturing the water-repellent film 9 .
  • the fourth method is a method for manufacturing the water-repellent film 9 by another gas phase method.
  • Nafion was used for the electrolyte membrane 6 .
  • a fluorine-based silane coupling agent for example, heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane was used.
  • the Nafion membrane is left in close contact with a bottom of the Teflon container, and a fluorine-based silane coupling agent (water-repellent low molecular substance) is put thereon and sealed (first step S 401 ).
  • a fluorine-based silane coupling agent water-repellent low molecular substance
  • the Teflon container is put in an oven and heated at 150° C. (second step S 402 ).
  • the fluorine-based silane coupling agent is evaporated, and a water-repellent film is formed on one surface of the Nafion membrane.
  • the water-repellent film can be formed only on one side of the Nafion membrane.
  • a monomolecular film is formed on the surface of Nafion, a very thin water-repellent film on the order of nanometers can be formed.
  • a nickel oxide (NiO) co-catalyst thin film was formed by epitaxially growing a thin film of gallium nitride (GaN) which is an n-type semiconductor and aluminum gallium nitride (AlGaN) in this order on a sapphire substrate, vacuum-depositing nickel (Ni) thereon, and performing heat treatment. Accordingly, the co-catalyst thin film was used as the oxidation electrode 1 , and the oxidation electrode 1 was immersed in the electrolytic solution 3 of a 1.0 mol/L potassium hydroxide aqueous solution in the oxidation tank 2 .
  • GaN gallium nitride
  • AlGaN aluminum gallium nitride
  • the reduction electrode 4 was formed using a copper porous body, the reduction electrode 4 was connected to the oxidation electrode 1 by the conducting wire 7 , and the reduction electrode 4 was installed in the reduction tank 5 .
  • Nafion was used for the electrolyte membrane 6 which physically separates the oxidation tank 2 and the reduction tank 5 from each other.
  • the electrolyte membrane 6 which physically separates the oxidation tank 2 and the reduction tank 5 from each other.
  • one surface on which the water-repellent film 9 was formed was disposed to be in contact with the electrolytic solution 3 in the oxidation tank 2
  • the other surface was disposed to be in contact with the reduction electrode 4 in the reduction tank 5 .
  • the light source 8 a 300 W xenon lamp was used. A wavelength of 450 nm or more was cut with a filter, and the illuminance was set to 6.6 mW/cm2. An illumination area of the oxidation electrode 1 was set to 2.5 cm2.
  • nitrogen and carbon dioxide were supplied to the oxidation tank 2 and the reduction tank 5 , respectively, at a flow rate of 5 ml/min and a pressure of 0.5 MPa.
  • the bubbling of nitrogen into the oxidation tank 2 was performed for the purpose of analyzing reaction products.
  • the insides of the oxidation tank 2 and the reduction tank 5 were sufficiently replaced with nitrogen and carbon dioxide, respectively, and were illuminated with light from the light source 8 . Thereafter, the carbon dioxide reduction reaction proceeded on the surface of the copper porous body which is the reduction electrode 4 .
  • the current that flows between the oxidation electrode 1 and the reduction electrode 4 by the illumination light was measured by an electrochemical measurement device (potentiogalvanostat Model 1287 manufactured by Solartron Analytical).
  • an electrochemical measurement device potentiogalvanostat Model 1287 manufactured by Solartron Analytical.
  • gases and liquids generated in the oxidation tank 2 and the reduction tank 5 were collected, and the reaction products were analyzed using a gas chromatograph, a liquid chromatograph, and a gas chromatograph mass spectrometer.
  • Example 1 the water-repellent film 9 manufactured by Manufacturing Method 1 using Nafion as the electrolyte membrane 6 , OPTOOL DSX as the water-repellent agent, and a polyvinyl alcohol aqueous solution with a concentration of 1% dissolved in pure water as the water-soluble polymer was used.
  • Example 2 the water-repellent film 9 manufactured by Manufacturing Method 2 using Nafion as the electrolyte membrane 6 and using OPTOOL DSX as the water-repellent agent was used.
  • Example 3 the water-repellent film 9 manufactured by Manufacturing Method 3 using Nafion as the electrolyte membrane 6 , heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane as the water-repellent agent, and a polyvinyl alcohol aqueous solution with a concentration of 1% dissolved in pure water as the water-soluble polymer was used.
  • Example 4 the water-repellent film 9 manufactured by Manufacturing Method 4 using Nafion as the electrolyte membrane 6 and heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane as the water-repellent agent was used.
  • Nafion on which the water-repellent film 9 was not formed was directly used as the electrolyte membrane 6 .
  • FIG. 7 is a graph illustrating a measurement result of Faraday efficiency of formic acid according to the first embodiment.
  • the Faraday efficiency decreased after six hours.
  • the Faraday efficiency did not decrease even after six hours. This is because, as a result of introducing the water-repellent film 9 to the Nafion membrane, liquid leakage of the electrolytic solution 3 to the reduction electrode 4 was suppressed, and the reaction site of the reduction electrode 4 was not covered with the electrolytic solution 3 .
  • a coverage rate of the water-repellent film 9 to the Nafion membrane was estimated using the Cassie-Baxter equation.
  • a contact angle of the Nafion membrane coated with the water-repellent film 9 is denoted by ⁇
  • a contact angle of the surface of the Nafion membrane is denoted by ⁇ 1
  • a proportion of the surface of the Nafion membrane is denoted by f1
  • a contact angle of a surface of the water-repellent film 9 is denoted by ⁇ 2
  • a proportion of the surface of the water-repellent film 9 is denoted by f2
  • the contact angles ⁇ of the Nafion membrane coated with the water-repellent film 9 were 100°, 95°, 75°, and 70°, respectively.
  • the coverage rates of the water-repellent film 9 to the Nafion membrane were estimated to be 84%, 79%, 64%, and 60%, respectively. This suggests that the water-repellent film 9 not covering the entire surface of the electrolyte membrane 6 could be formed.
  • the Faraday efficiency of carbon dioxide indicates a ratio of the number of electrons used in the carbon dioxide reduction reaction to the number of electrons moved between the oxidation electrode 1 and the reduction electrode 4 by light illumination or current/voltage application, and can be calculated by Equation (2).
  • Faraday ⁇ efficiency ⁇ number ⁇ of ⁇ electrons ⁇ in ⁇ reduction ⁇ reaction ⁇ ⁇ / ⁇ number ⁇ of ⁇ electrons ⁇ moved ⁇ between ⁇ electrodes ⁇ ( 2 )
  • the “number of electrons in the reduction reaction” in Equation (2) is obtained by converting the measured value of the integrated amount of the generated carbon dioxide reduction products into the number of electrons required for the production reaction.
  • the “number of electrons in the reduction reaction” in a case where the reduction product is a gas can be calculated by Equation (3).
  • A denotes a concentration (ppm) of the reduction reaction product.
  • B denotes a flow rate (L/sec) of carrier gas.
  • Z denotes the number of electrons required for the reduction reaction.
  • F denotes the Faraday constant (C/mol).
  • T denotes a light illumination time or a current/voltage application time (sec).
  • V g denotes a molar volume of gas (L/mol).
  • the “number of electrons in the reduction reaction” in a case where the reduction product is a liquid can be calculated by Equation (4).
  • C denotes a concentration (mol/L) of the reduction reaction product.
  • V 1 denotes a volume (L) of a liquid sample.
  • Z denotes the number of electrons required for the reduction reaction.
  • F denotes the Faraday constant (C/mol).
  • a first embodiment of the present invention will be described. According to the carbon dioxide reduction device 100 of the first embodiment, it is possible to provide the carbon dioxide reduction device 100 that enables the carbon dioxide reduction reaction to proceed without reducing the Faraday efficiency.
  • the carbon dioxide reduction device 100 includes the oxidation tank 2 that performs the oxidation reaction of water by the illumination light from the light source 8 by using the electrolytic solution 3 and the semiconductor oxidation electrode 1 immersed in the electrolytic solution 3 , the reduction tank 5 that performs the carbon dioxide reduction reaction by using the reduction electrode 4 connected to the oxidation electrode 1 via the conducting wire 7 and carbon dioxide brought into direct contact with the reduction electrode 4 , and the electrolyte membrane 6 disposed between the electrolytic solution 3 in the oxidation tank 2 and the reduction electrode 4 in the reduction tank 5 to be in contact with both the electrolytic solution and the reduction electrode, in which the electrolyte membrane 6 includes the water-repellent film 9 on a part of the surface which is in contact with the electrolytic solution 3 .
  • the water repellency of the water-repellent films 9 provided on a surface of the electrolytic solution 3 causes the electrolytic solution 3 in the oxidation tank 2 to be suppressed from infiltrating into the electrolyte membrane 6 and causes liquid leakage of the electrolytic solution 3 to the reduction electrode 4 to be suppressed, and thus the reaction site of the reduction electrode 4 is not covered with the electrolytic solution 3 .
  • the water-repellent film 9 is provided on a part of the surface of the electrolyte membrane 6 , a state in which protons can pass through the electrolyte membrane 6 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in reduction reaction efficiency can be suppressed.
  • light is generated by a xenon lamp in order to quantitatively manage an illumination amount of light with respect to the oxidation electrode 1 , but it is also possible to cause an oxidation reaction by using sunlight or the like.
  • the case where the light source 8 and the oxidation electrode 1 made of a semiconductor are used has been described.
  • an oxidation/reduction reaction is caused to proceed using an external power supply and an oxidation electrode 1 composed of a metal.
  • FIG. 8 is a view illustrating a configuration example of a carbon dioxide reduction device 100 according to the second embodiment.
  • the oxidation electrode 1 is made of platinum.
  • the oxidation electrode 1 may be made of, for example, gold or silver.
  • the external power supply 10 is an electrochemical measurement device and is connected in series to the conducting wire 7 connecting the oxidation electrode 1 with the reduction electrode 4 .
  • the power supply 10 may be another power supply device.
  • the other configurational elements are similar to those of the first embodiment.
  • the oxidation reaction of water in the electrolytic solution 3 is performed by current and voltage (electrical energy) from the power supply 10 by using the electrolytic solution 3 and the platinum (metal) oxidation electrode 1 immersed in the electrolytic solution 3 .
  • a carbon dioxide reduction reaction is performed using the reduction electrode 4 connected to the power supply 10 (source of electrical energy) and carbon dioxide brought into direct contact with the reduction electrode 4 .
  • the water-repellent film 9 is provided on a part of the surface of the electrolyte membrane 6 which is in contact with the electrolytic solution 3 so as not to cover the entire surface of the electrolyte membrane 6 .
  • a plurality of water-repellent films 9 are formed on the surface at predetermined intervals.
  • the water-repellent film 9 is manufactured by the first to fourth manufacturing methods, similarly to the first embodiment.
  • FIG. 9 is a graph illustrating a measurement result of the Faraday efficiency of formic acid according to the second embodiment.
  • Examples using the same electrolyte membrane 6 as in Examples 1 to 4 described in the first embodiment are referred to as Examples 5 to 8, respectively.
  • a comparative example using Nafion on which the water-repellent film 9 is not formed as the electrolyte membrane 6 is also described.
  • the second embodiment is described. According to the carbon dioxide reduction device 100 of the second embodiment, it is possible to provide the carbon dioxide reduction device 100 that enables the carbon dioxide reduction reaction to proceed without reducing the Faraday efficiency.
  • the carbon dioxide reduction device 100 includes the oxidation tank 2 that performs the oxidation reaction of water by the current and voltage from the power supply 10 by using the electrolytic solution 3 and the platinum (metal) oxidation electrode 1 immersed in the electrolytic solution 3 , the reduction tank 5 that performs the carbon dioxide reduction reaction by using the reduction electrode 4 connected to the power supply 10 and carbon dioxide brought into direct contact with the reduction electrode 4 , and the electrolyte membrane 6 disposed between the electrolytic solution 3 in the oxidation tank 2 and the reduction electrode 4 in the reduction tank 5 to be in contact with both the electrolytic solution and the reduction electrode, in which the electrolyte membrane 6 includes the water-repellent film 9 on a part of the surface which is in contact with the electrolytic solution 3 .
  • the water repellency of the water-repellent films 9 provided on a surface of the electrolytic solution 3 causes the electrolytic solution 3 in the oxidation tank 2 to be suppressed from infiltrating into the electrolyte membrane 6 and causes liquid leakage of the electrolytic solution 3 to the reduction electrode 4 to be suppressed, and thus the reaction site of the reduction electrode 4 is not covered with the electrolytic solution 3 .
  • the water-repellent film 9 is provided on a part of the surface of the electrolyte membrane 6 , a state in which protons can pass through the electrolyte membrane 6 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in reduction reaction efficiency can be suppressed.
  • the present invention can be widely used in the field related to the recycling of carbon dioxide.
  • the light energy is used in the first embodiment, and the electrical energy is used in the second embodiment; however, other renewable energy may be used.
  • the first embodiment and the second embodiment can be combined.
  • the present invention can also be applied to any electrolyte membrane as long as the electrolyte membrane 6 is disposed between the electrolytic solution 3 in the oxidation tank 2 and the reduction electrode 4 in the reduction tank 5 to be in contact with both the electrolytic solution and the reduction electrode and is used in the carbon dioxide reduction device 100 which performs the carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode 4 .

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