Carbon dioxide electrolytic reduction system, hydrocarbon production method

Abstract

This invention provides a carbon dioxide electrolytic reduction system capable of producing hydrocarbons by the electrolytic reduction of carbon dioxide, and a method for producing hydrocarbons using the carbon dioxide electrolytic reduction system. [Solution] A carbon dioxide electrolytic reduction system 1 comprises an electrolytic cell 10, a zero-gap cell 20, an acidic anode aqueous solution 30, and a reference electrode 40. The electrolytic cell 10 is divided into a cathode chamber 11 and an anode chamber 12 via the zero-gap cell 20. The zero-gap cell 20 has a working electrode 21 containing a cathode catalyst 22 and a conductive additive, an ion exchange membrane 23, and a counter electrode 24 containing iridium oxide. The working electrode 21, the ion exchange membrane 23, and the counter electrode 24 are stacked in this order. The cathode catalyst 22 is located on the ion exchange membrane 23 side, the working electrode 21 is located on the cathode chamber 11 side, and the counter electrode 24 is located on the anode chamber 12 side. The acidic anode aqueous solution 30 is contained within the anode chamber 12.

Description

[Technical Field]

[0001] This invention relates to a carbon dioxide electrolytic reduction system and a hydrocarbon production method. [Background technology]

[0002] The construction of carbon dioxide reduction systems using electrolysis is being actively researched worldwide as one way to effectively utilize carbon dioxide in the atmosphere. Furthermore, unlike light-driven carbon dioxide reduction systems inspired by photosynthesis, electrolysis is a highly effective reduction method because it is not affected by sunlight hours, weather, or equipment installation location, and does not require special sacrificial reagents.

[0003] Furthermore, zero-gap cells (also known as membrane electrode composite films) have been widely studied for over 30 years, with numerous reported examples (see, for example, Non-Patent Documents 1 and 2, and Patent Documents 1 and 2). Compared to conventional electrolytic cells with a three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode, the advantages of zero-gap cells include the ability to reduce cell resistance caused by foaming of the electrolyte and generated gas, and the ability to perform reactions at high current densities. As a result, zero-gap cells enable electrolytic reactions with higher efficiency. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-191893 [Patent Document 2] International Publication No. 2004 / 048643 [Non-patent literature]

[0005] [Non-Patent Document 1] R. Phillips, CW Dunnill, RSC Adv. 2016, 6, 100643. [Non-Patent Document 2] X. Liu and co-workers, Sci. Rep. 2021, 11, Article Number: 11136.

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Many of the conventional zero-gap cells use an alkaline aqueous solution (e.g., potassium hydroxide aqueous solution, potassium hydrogen carbonate aqueous solution) as the anolyte to facilitate the oxidation of water on the anode side. However, in the case of electrolytic reduction using carbon dioxide as a substrate, due to the nature of the anion exchange membrane used in combination with the alkaline aqueous solution, carbon dioxide on the cathode side, which is the reaction site, becomes a cation such as carbonate ion and permeates through the anion exchange membrane, resulting in the loss of carbon dioxide from the reaction site (see, for example, Non-Patent Document 3). In addition, there was a problem that a salt of a cation derived from the anolyte and carbonate ion precipitated, and the salt inhibited the electrolytic reduction reaction, significantly reducing the reaction efficiency.

[0007] On the other hand, when an acidic aqueous solution (e.g., sulfuric acid aqueous solution) is used as the anolyte, the reaction barrier for the oxidation of water becomes large. Even if the problem of carbon dioxide permeating through the anion exchange membrane can be solved, as a result, the reaction efficiency is significantly reduced.

[0008] By using a cation exchange membrane, the problems of losing carbon dioxide from the reaction site and significantly reducing the reaction efficiency can be solved. However, protons, which are cations, are supplied to the cathode side, and hydrogen generation, which becomes a side reaction when reducing carbon dioxide, becomes dominant, and as a result, it does not lead to the reduction of carbon dioxide.

[0009] To solve these problems, for example, the following two measures can be considered for the electrolytic cell: (1) Use an acidic aqueous solution as the anodic acid, while allowing the oxidation of the acidic aqueous solution to proceed. To prevent salt precipitation, salt is not used as the electrolyte. (2) Prevent carbon dioxide from permeating the anion exchange membrane while limiting the permeation of protons from the anodic acid to the cathode.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a carbon dioxide electrolytic reduction system capable of producing hydrocarbons by the electrolytic reduction of carbon dioxide, and a method for producing hydrocarbons using the carbon dioxide electrolytic reduction system. [Means for solving the problem]

[0011] The present invention has the following aspects. [1] comprising an electrolytic cell, a zero-gap cell, an acidic anodic aqueous solution, and a reference electrode, The electrolytic cell is divided into a cathode chamber and an anode chamber via the zero-gap cell. The zero-gap cell comprises a working electrode containing a cathode catalyst and a conductive additive, an ion exchange membrane, and a counter electrode containing iridium oxide, wherein the working electrode, the ion exchange membrane, and the counter electrode are stacked in this order. The cathode catalyst is positioned on the ion exchange membrane side, The working electrode is positioned on the cathode chamber side, and the counter electrode is positioned on the anode chamber side. The acidic anode aqueous solution is housed in the anode chamber of a carbon dioxide electrolytic reduction system. [2] The carbon dioxide electrolytic reduction system according to [1], wherein the cathode catalyst is at least one selected from tetrabutylammonium tetrathiorenium, tetrabutylammonium tetrathiotungstate, tetrabutylammonium tetrathiomolybdate, and chlorotricarbonyl(2,2'-bipyridine)rhenium(I). [3] The carbon dioxide electrolytic reduction system according to [1] or [2], wherein the conductive additive is a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid. [4] The carbon dioxide electrolytic reduction system according to any one of [1] to [3], wherein the acidic anode aqueous solution is an aqueous phosphoric acid solution, an aqueous nitric acid solution, an aqueous sulfuric acid solution, an aqueous hydrochloric acid solution, an aqueous acetic acid solution, an aqueous boric acid solution, an aqueous perchloric acid solution, or an aqueous diphosphate solution. A method for producing hydrocarbons using a carbon dioxide electrolytic reduction system described in any of [5][1] to [4], The process involves filling the cathode chamber with a gas containing carbon dioxide, and then sealing the cathode chamber. A method for producing hydrocarbons, comprising the steps of applying an electric potential to the working electrode and the counter electrode to electrolytically reduce the carbon dioxide and generate hydrocarbons in the acidic anode aqueous solution. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a carbon dioxide electrolytic reduction system capable of producing hydrocarbons by the electrolytic reduction of carbon dioxide, and a method for producing hydrocarbons using the carbon dioxide electrolytic reduction system. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram showing a carbon dioxide electrolytic reduction system according to a method of fabrication. [Figure 2] This is a schematic perspective view showing a zero-gap cell constituting a carbon dioxide electrolytic reduction system according to one embodiment of the present invention. [Modes for carrying out the invention]

[0014] The carbon dioxide electrolytic reduction system and hydrocarbon production method according to embodiments of the present invention will be described below with reference to the drawings. Note that, for convenience, the drawings used in the following description show enlarged versions of characteristic parts, and the dimensional ratios of each component may differ from those of the actual components. Furthermore, the materials, dimensions, etc., exemplified in the following description are merely examples, and the present invention is not limited to them. They can be modified as appropriate without altering the essence of the invention.

[0015] [Carbon dioxide electrolysis reduction system] Figure 1 is a schematic diagram showing a carbon dioxide electrolytic reduction system according to one embodiment of the present invention. Figure 2 is a schematic perspective view showing a zero-gap cell constituting the carbon dioxide electrolytic reduction system according to one embodiment of the present invention. As shown in Figure 1, the carbon dioxide electrolytic reduction system 1 of this embodiment comprises an electrolytic cell 10, a zero-gap cell 20, an acidic anodic aqueous solution 30, and a reference electrode 40.

[0016] The electrolytic cell 10 has a cathode chamber 11 and an anode chamber 12. The cathode chamber 11 is for filling with a gas containing carbon dioxide to be electrolytically reduced by the carbon dioxide electrolytic reduction system 1 of this embodiment. The anode chamber 12 is for containing an acidic anode aqueous solution 30. The electrolytic cell 10 is divided into the cathode chamber 11 and the anode chamber 12 via a zero-gap cell 20.

[0017] As shown in Figures 1 and 2, the zero-gap cell 20 has a working electrode 21, an ion exchange membrane 23, and a counter electrode 24. The working electrode 21, the ion exchange membrane 23, and the counter electrode 24 are stacked in this order. The working electrode 21 includes a cathode catalyst 22. The working electrode 21 is located on the cathode chamber 11 side. The cathode catalyst 22 is located on the ion exchange membrane 23 side. The counter electrode 24 is located on the anode chamber 12 side.

[0018] A conductive tape 25 for applying a potential to the working electrode 21 is connected to the working electrode 21. A conductive tape 26 for applying a potential to the counter electrode 24 is connected to the counter electrode 24. Copper tape, aluminum tape, stainless steel tape, etc. can be used as the conductive tapes 25 and 26. Among these, copper tape is preferred due to its excellent conductivity.

[0019] The material of the electrolytic cell 10 is not particularly limited as long as it does not deteriorate due to the acidic anodic aqueous solution 30 or the hydrocarbons produced by the electrolytic reduction of carbon dioxide, but examples include quartz glass.

[0020] The cathode chamber 11 has a flange portion 11A in the portion facing the anode chamber 12 via a zero-gap cell 20. The anode chamber 12 has a flange portion 12A in the portion facing the cathode chamber 11 via a zero-gap cell 20. A silicone rubber packing (not shown) is placed on the surface of flange portion 11A facing flange portion 12A, and on the surface of flange portion 12A facing flange portion 11A. The cathode chamber 11 and the anode chamber 12 are joined together so as to face each other via a zero-gap cell 20, and are fixed in place by fitting fixing jigs onto the outer circumferences of flange portions 11A and 12A and tightening the fixing jigs with screws.

[0021] The cathode chamber 11 has two septum openings 11B. A degassing needle (not shown) is positioned in one of the septum openings 11B.

[0022] The working electrode 21 includes a cathode catalyst 22 and a conductive additive. The cathode catalyst 22 is located on one main surface 21a of the substrate 21A of the working electrode 21. The conductive additive is located on one main surface 21a of the substrate 21A or is absorbed into the substrate 21A.

[0023] The base material 21A is composed of a porous material having conductivity. Examples of base material 21A include carbon paper and metal mesh. Examples of metals that make up the metal mesh include platinum, aluminum, and titanium.

[0024] The thickness of the substrate 21A is preferably 50 μm or more and 500 μm or less, more preferably 80 μm or more and 300 μm or less, and even more preferably 100 μm or more and 200 μm or less. If the thickness of the working electrode 21 is greater than or equal to the lower limit, it becomes less likely to break during electrolytic cell assembly. If the thickness of the working electrode 21 is less than or equal to the upper limit, it becomes superior in terms of gas permeability and retention of catalytic function.

[0025] Examples of the cathode catalyst 22 include tetrabutylammonium tetrathiorenium, tetrabutylammonium tetrathiotungstate ((TBA)2WS4), tetrabutylammonium tetrathiomolybdate ((TBA)2MoS4), and chlorotricarbonyl(2,2'-bipyridine)rhenium(I)(ReCl(CO)3(bpy)). The cathode catalyst 22 may be used individually or in combination of two or more types.

[0026] The thickness of the cathode catalyst 22 placed on one main surface 21a of the substrate 21A is preferably 1 μm or more and 300 μm or less, more preferably 10 μm or more and 200 μm or less, and even more preferably 50 μm or more and 100 μm or less. If the thickness of the cathode catalyst 22 is above the lower limit, the function of the catalyst is fully exhibited. If the thickness of the cathode catalyst 22 is below the upper limit, the function is ensured in proportion to the amount of catalyst supported.

[0027] The area of ​​the cathode catalyst 22 placed on one main surface 21a of the substrate 21A is preferably 10% to 50% of the total area of ​​the one main surface 21a of the substrate 21A, more preferably 15% to 40%, and even more preferably 20% to 30%. If the area of ​​the cathode catalyst 22 is above the lower limit, the function of the catalyst is fully exhibited. If the area of ​​the cathode catalyst 22 is below the upper limit, the function is ensured in proportion to the amount of catalyst supported.

[0028] The mass of the cathode catalyst 22 placed on one main surface 21a of the substrate 21A is 0.01 mg / cm² per unit area of ​​one main surface 21a of the substrate 21A. 2 More than 10mg / cm 2 Preferably, it is 0.1 mg / cm³. 2 More than 5mg / cm 2 It is more preferable that the following is the case: 0.2 mg / cm³ 2 More than 1mg / cm 2 It is even more preferable that the following conditions are met: If the mass of the cathode catalyst 22 is equal to or greater than the lower limit, the function of the catalyst is fully exhibited. If the mass of the cathode catalyst 22 is equal to or less than the upper limit, the function is ensured in proportion to the amount of catalyst supported.

[0029] Examples of the conductive auxiliary agent include a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (hereinafter abbreviated as "PEDOT:PSS"), Nafion, Ketjenblack, etc. Among these, from the viewpoint of affinity with the catalyst, PEDOT:PSS is preferred.

[0030] The area of the conductive auxiliary agent disposed on one main surface 21a of the base material 21A is preferably 10% or more and 50% or less, more preferably 15% or more and 40% or less, and even more preferably 20% or more and 30% or less with respect to the total area of one main surface 21a of the base material 21A. When the area of the conductive auxiliary agent is not less than the lower limit value, the function of the conductive auxiliary agent is sufficiently exerted. When the area of the conductive auxiliary agent is not more than the upper limit value, the function is ensured in proportion to the amount of the conductive auxiliary agent carried.

[0031] The mass of the conductive auxiliary agent disposed on one main surface 2 21a of the base material 2 21A is preferably 0.01 mg / cm 2 or more and 10 mg / cm 2 or less, more preferably 0.1 mg / cm 2 or more and 5 mg / cm 2 or less, and even more preferably 0.2 mg / cm 2 or more and 1 mg / cm 2 or less. When the mass of the conductive auxiliary agent is not less than the lower limit value, the function of the conductive auxiliary agent is sufficiently exerted. When the mass of the conductive auxiliary agent is not more than the upper limit value, the function is ensured in proportion to the amount of the conductive auxiliary agent carried.

[0032] As the ion exchange membrane 23, for example, Selemion (registered trademark) DSVN (product name) of AGC Engineering Co., Ltd. can be used. 000019900002000000201The thickness of the ion exchange membrane 23 is 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 100 μm or less. When the thickness of the ion exchange membrane 23 is above the lower limit, the function of the ion exchange membrane is fully exhibited. When the thickness of the ion exchange membrane 23 is below the upper limit, the resistance value of the entire cell can be kept low.

[0034] The counter electrode 24 consists of a conductive porous substrate and iridium oxide (IrO) placed on one main surface of the substrate or absorbed into the substrate. x ) has the same as substrate 21A as the conductive porous substrate. Iridium oxide (IrO x ) preferably x is 1 or more and 6 or less, more preferably 1 or more and 4 or less, and even more preferably 2 or more and 3 or less. When x is equal to or above the lower limit, the function of iridium oxide is fully exhibited. When x is equal to or below the upper limit, the function is ensured in proportion to the amount of iridium oxide supported.

[0035] The thickness of the conductive porous substrate is preferably 50 μm or more and 500 μm or less, more preferably 100 μm or more and 200 μm or less, and even more preferably 100 μm or more and 200 μm or less. If the thickness of the conductive porous substrate is above the lower limit, it becomes less likely to break during electrolytic cell assembly. If the thickness of the conductive porous substrate is below the upper limit, it becomes superior in terms of gas permeability and retention of catalytic function.

[0036] Iridium oxide (IrO) placed on a conductive porous substrate x The area of ​​the film made of iridium oxide (IrO) is preferably 10% to 50% of the total area of ​​the conductive porous substrate, more preferably 20% to 30%, and even more preferably 20% to 30%. xWhen the area of ​​the film made of iridium oxide (IrO) is greater than or equal to the lower limit, the function of iridium oxide is fully exhibited. x If the area of ​​the film consisting of ) is less than or equal to the upper limit, the function is guaranteed in proportion to the amount of iridium oxide supported.

[0037] Iridium oxide (IrO) is placed on one main surface of a porous substrate that has electrical conductivity. x The mass of the film consisting of ) is 0.1 mg / cm² per unit area of ​​the main surface of one of the conductive porous substrates. 2 More than 10mg / cm 2 Preferably, the following is the case: 0.5 mg / cm³ 2 More than 5mg / cm 2 More preferably, the following is true: 1 mg / cm³ 2 More than 3mg / cm 2 It is even more preferable that the following conditions be met: Iridium oxide (IrO x When the mass of the film made of iridium oxide (IrO) is greater than or equal to the lower limit, the function of iridium oxide is fully exhibited. x If the mass of the film consisting of ) is less than or equal to the upper limit, the function is guaranteed in proportion to the amount of iridium oxide supported.

[0038] The acidic anodic aqueous solution 30 is an aqueous solution of phosphoric acid (H2PO4), an aqueous solution of nitric acid (HNO3), an aqueous solution of sulfuric acid (H2SO4), an aqueous solution of hydrochloric acid (HCl), an aqueous solution of acetic acid (CH3COOH), an aqueous solution of boric acid (B(OH)3), an aqueous solution of perchloric acid (HClO4), or an aqueous solution of diphosphate (H4P2O7). These acidic anodic aqueous solutions may be used individually or in combination of two or more.

[0039] The concentration of the acidic anodic aqueous solution 30, that is, the acid content in the acidic anodic aqueous solution 30, is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.2 mol / L or more and 1.5 mol / L or less, and even more preferably 0.5 mol / L or more and 1 mol / L or less. When the concentration of the acidic anodic aqueous solution 30 is above the lower limit, the function of the acidic anodic aqueous solution is fully exhibited. When the concentration of the acidic anodic aqueous solution 30 is below the upper limit, the function is ensured in proportion to the concentration of the acidic anodic aqueous solution.

[0040] The reference electrode 40 is placed inside the anode chamber 12. An example of the reference electrode 40 is a silver / silver chloride electrode (Ag / AgCl).

[0041] According to the carbon dioxide electrolytic reduction system 1 of this embodiment, hydrocarbons can be produced by electrolytically reducing carbon dioxide using a hydrocarbon production method described later.

[0042] [Manufacturing method for carbon dioxide electrolysis reduction system] A method for manufacturing a carbon dioxide electrolytic reduction system according to one embodiment of the present invention comprises the steps of: manufacturing a zero-gap cell (hereinafter referred to as the "manufacturing step"); assembling an electrolytic cell by arranging a cathode chamber and an anode chamber opposite each other via the zero-gap cell (hereinafter referred to as the "assembly step"); containing an acidic anode aqueous solution in the anode chamber (hereinafter referred to as the "containment step"); and placing a reference electrode in the anode chamber (hereinafter referred to as the "placement step").

[0043] The method for manufacturing the carbon dioxide electrolytic reduction system of this embodiment will be described with reference to Figures 1 and 2.

[0044] "Manufacturing Process" (Fabrication of the working electrode) In the manufacturing process, a catalyst solution is prepared by dissolving a substance that will serve as the cathode catalyst in a solvent. The solvent is not particularly limited as long as it can dissolve the cathode catalyst, but examples include N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0045] The content of the cathode catalyst in the catalyst solution is preferably 0.1 μmol or more and 10 μmol or less, more preferably 0.5 μmol or more and 5 μmol or less, and even more preferably 1 μmol or more and 2 μmol or less. When the content of the cathode catalyst is above the lower limit, the function of the cathode catalyst is fully exhibited. When the content of the cathode catalyst is below the upper limit, the function is ensured in proportion to the content of the cathode catalyst.

[0046] Prepare a conductive additive solution by dissolving the conductive additive in water. Distilled water is used as the water source.

[0047] The content of the conductive additive in the conductive additive solution is preferably 0.01% by mass or more and 1% by mass or less, more preferably 0.05% by mass or more and 0.8% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less. When the content of the conductive additive is above the lower limit, the function of the conductive additive is fully exhibited. When the content of the conductive additive is below the upper limit, the function is ensured in proportion to the content of the conductive additive.

[0048] The catalyst solution and the conductive additive solution are mixed to prepare the electrode solution paste. The mixing ratio of the conductive additive solution to the catalyst solution (conductive additive solution / catalyst solution) is preferably 1 / 20 or more and 20 / 1 or less by volume, more preferably 2 / 1 or more and 10 / 1 or less, and even more preferably 3 / 1 or more and 5 / 1 or less. When the mixing ratio is above the lower limit, the functions of the conductive additive and catalyst are fully exhibited. When the mixing ratio is below the upper limit, the functions are ensured in proportion to the content of the conductive additive and catalyst.

[0049] After dropping electrode liquid paste onto one main surface 21a of the substrate 21A, the electrode liquid paste is spread so that the coating film made of electrode liquid paste covers a predetermined area, thereby forming a coating film made of electrode liquid paste of a predetermined area.

[0050] The amount (mass) of electrode solution paste to be dropped onto one main surface 21a of the base material 21A is 10 mg / cm² per unit area of ​​one main surface 21a of the base material 21A. 2 More than 100mg / cm 2 Preferably, it is 20 mg / cm³ 2 More than 80mg / cm 2 More preferably, the following is 30 mg / cm³ 2 More than 50mg / cm 2 It is even more preferable that the following conditions are met: If the mass of the electrode liquid paste is equal to or greater than the lower limit, the functions of the conductive additive and catalyst are fully exhibited. If the mass of the electrode liquid paste is equal to or less than the upper limit, the functions are ensured in proportion to the content of the conductive additive and catalyst.

[0051] The area of ​​the coating film, which consists of electrode liquid paste, formed on one main surface 21a of the substrate 21A, is preferably 10% to 50%, more preferably 15% to 40%, and even more preferably 20% to 30% of the total area of ​​one main surface 21a of the substrate 21A. When the area of ​​the coating film is above the lower limit, the functions of the conductive additive and catalyst are fully exhibited. When the area of ​​the coating film is below the upper limit, the functions are ensured in proportion to the content of the conductive additive and catalyst.

[0052] A substrate 21A, on which a coating film made of electrode liquid paste has been formed, is vacuum-dried to form a cathode catalyst 22 containing a conductive additive on one main surface 21a of the substrate 21A, thereby obtaining a working electrode 21.

[0053] The working electrode 21 is sandwiched between two conductive tapes 25.

[0054] (Preparation of the opposing pole) Prepare the counter electrode solution by dissolving iridium chloride n hydrate (where n is between 1 and 6) in water. Distilled water is used as the water source.

[0055] The iridium n chloride hydrate content in the counter electrode solution is preferably 10 mmol / L or more and 100 mmol / L or less, more preferably 20 mmol / L or more and 80 mmol / L or less, and even more preferably 30 mmol / L or more and 70 mmol / L or less. When the iridium n chloride hydrate content is above the lower limit, the function of the iridium oxide is fully exhibited. When the iridium n chloride hydrate content is below the upper limit, the function is ensured in proportion to the amount of iridium oxide supported.

[0056] After dropping the counter electrode solution onto one main surface of a porous conductive substrate, the counter electrode solution is spread so that the coating film consisting of the counter electrode solution covers a predetermined area.

[0057] The amount (mass) of counter electrode solution to be dropped onto one main surface of a conductive porous substrate is 1 mg / cm² per unit area of ​​one main surface of the conductive porous substrate. 2 More than 100mg / cm 2 Preferably, it is 10 mg / cm³ 2 More than 80mg / cm 2 More preferably, the following is 20 mg / cm³ 2 More than 50mg / cm 2 The following conditions are even more preferable: If the mass of the counter electrode solution is greater than or equal to the lower limit, the function of the iridium oxide is fully exhibited. If the mass of the counter electrode solution is less than or equal to the upper limit, the function is ensured in proportion to the amount of iridium oxide supported.

[0058] The area of ​​the coating film, which consists of a counter electrode solution formed on one main surface of a conductive porous substrate, is preferably 10% to 50%, more preferably 20% to 30%, and even more preferably 20% to 30% of the total area of ​​one main surface of the conductive porous substrate. When the area of ​​the coating film is above the lower limit, the function of iridium oxide is fully exhibited. When the area of ​​the coating film is below the upper limit, the function is ensured in proportion to the amount of iridium oxide supported.

[0059] A conductive porous substrate on which a coating film made of the counter electrode solution has been formed is fired in an air atmosphere at a temperature of 300°C to 500°C for 4 to 20 hours to obtain the counter electrode 24.

[0060] The counter electrode 24 is sandwiched between two conductive tapes 26.

[0061] (Preparation of ion exchange membranes) The ion exchange membrane 23 is immersed in a 0.1 mol / L potassium hydroxide aqueous solution for at least 8 hours. After that, the ion exchange membrane 23 is rinsed with a 0.5 mol / L anodic aqueous solution. The anodic aqueous solution used is the same as that used for the acidic anodic aqueous solution 30.

[0062] (Creation of zero-gap cells) The working electrode 21, ion exchange membrane 23, and counter electrode 24 obtained as described above are stacked in this order. At this time, the conductive tapes 25 and 26 are stacked concentrically so that they do not come into contact with each other. The working electrode 21 is positioned such that the side of the working electrode 21 on which the cathode catalyst 22 is placed (one of the main surfaces 21a) faces the ion exchange membrane 23.

[0063] "Assembly Process" In the assembly process, the cathode chamber 11 and anode chamber 12 are positioned opposite each other via a zero-gap cell 20 to assemble the electrolytic cell 10. With the cathode chamber 11 and anode chamber 12 joined together so as to face each other via the zero-gap cell 20, fixing jigs are fitted onto the outer circumferences of flange portions 11A and 12A, and the fixing jigs are secured by tightening them with screws.

[0064] "Containment process" In the containment process, the cathode chamber 11 and the anode chamber 12 are fixed in place, and then the acidic anode aqueous solution 30 is placed inside the anode chamber 12.

[0065] "Placement process" In the placement process, after the acidic anode aqueous solution 30 is placed inside, the anode chamber 12 is covered and secured with screws, and then the reference electrode 40 is placed inside the anode chamber 12.

[0066] Through the above steps, the carbon dioxide electrolytic reduction system 1 of the above embodiment is obtained.

[0067] [Methods for producing hydrocarbons] A hydrocarbon production method according to one embodiment of the present invention is a hydrocarbon production method using a carbon dioxide electrolytic reduction system according to one embodiment of the present invention, comprising the steps of: filling the cathode chamber with a gas containing carbon dioxide and then sealing the cathode chamber (hereinafter referred to as the "first step"); and applying an electric potential to the working electrode and the counter electrode to electrolytically reduce the carbon dioxide and produce hydrocarbons in the acidic anode aqueous solution (hereinafter referred to as the "second step").

[0068] The hydrocarbon production method of this embodiment will be described with reference to Figure 1.

[0069] "First step" In the first step, the cathode chamber 11 of the electrolytic cell 10 is filled with a gas containing carbon dioxide, and then the cathode chamber 11 is sealed. Examples of gases containing carbon dioxide include carbon dioxide alone, air, and exhaust fumes from automobiles and factories.

[0070] When filling the cathode chamber 11 with a gas containing carbon dioxide, the pressure of the gas inside the cathode chamber 11 is set to atmospheric pressure (1013 hPa) or positive pressure. When the gas pressure in the cathode chamber 11 is positive, the gas pressure is preferably between 1000 hPa and 2000 hPa, more preferably between 1000 hPa and 1500 hPa, and even more preferably between 1000 hPa and 1200 hPa. When the gas pressure is above the lower limit, the cell functions adequately. When the gas pressure is below the upper limit, damage to each substrate constituting the cell can be avoided.

[0071] "The second step" In the second step, an electric potential is applied to the working electrode 21 and the counter electrode 24 to electrolytically reduce the carbon dioxide in the cathode chamber 11 and generate hydrocarbons in the acidic anode aqueous solution 30. A predetermined amount of the acidic anode aqueous solution 30 is pre-filled in the anode chamber 12.

[0072] The potential applied to the working electrode 21 and the counter electrode 24, i.e., the electrolysis potential when electrolytically reducing carbon dioxide, is preferably -3.5V or more and -1.5V or less, more preferably -3.0V or more and -2.0V or less, and even more preferably -2.8V or more and -2.2V or less. When the electrolysis potential is above the lower limit, the cell functions sufficiently. When the electrolysis potential is below the upper limit, the progress of carbon dioxide reduction can be accelerated.

[0073] The amount of hydrocarbons produced in the second step (production amount) can be measured using gas chromatography.

[0074] According to the hydrocarbon production method of this embodiment, since the carbon dioxide electrolytic reduction system 1 of the above-described embodiment is used, hydrocarbons can be produced by the electrolytic reduction of carbon dioxide. [Examples]

[0075] The present invention will be described in more detail below with reference to experimental examples, but the present invention is not limited to the following experimental examples.

[0076] [Experimental Example 1] (Fabrication of the working electrode) A catalyst solution was prepared by dissolving 5.6 mg (0.010 mmol) of tetrabutylammonium tetrathiorenate (TBAReS4) (manufactured by Strem Chemical) in 100 μL of N,N-dimethylformamide. A conductive additive solution was prepared by dissolving 30 mg of PEDOT:PSS (manufactured by Sigma-Aldrich) in 10 mL of distilled water. An electrode solution paste was prepared by mixing 10 μL of catalyst solution with 50 μL of conductive additive solution. The electrode solution paste was entirely dropped onto the center of a Toray carbon paper (TGP-H-030, 100 μm thick, no water-repellent coating) that had been cut into a circular shape using a packing punch set (3H-P17) with a size of 25 mm, and then spread into a 7.0 mm x 7.0 mm square. After that, the carbon paper with the electrode solution paste was vacuum-dried for 15 hours to obtain the working electrode (TBAReS4 / PEDOT:PSS / TGP-H-030). This working electrode was sandwiched between two pieces of copper tape (manufactured by Teraoka Seisakusho, 19mm x 5mm).

[0077] (Preparation of the opposing pole) A counter electrode solution was prepared by dissolving 50 mg of iridium chloride n hydrate (manufactured by Furuya Metals Co., Ltd.) in 2.5 mL of distilled water. 50 μL of the counter electrode solution was dropped into the center of a circular piece of Toray carbon paper (TGP-H-060, 200 μm thick) cut to a size of 25 mm using a packing punch set (3H-P17). Subsequently, the carbon paper with the counter electrode solution was fired in an air atmosphere at a temperature between 300°C and 500°C for 15 hours to form the counter electrode (IrO). x -300 / TGP-H-060) was obtained. IrO x -300 refers to an iridium catalyst that has been fired at 300 degrees Celsius. These opposing poles were sandwiched between two pieces of copper tape (manufactured by Teraoka Seisakusho, 19mm x 5mm).

[0078] (Preparation of ion exchange membranes) As an ion exchange membrane, DSVN (model name), an anion exchange membrane from Celemion (registered trademark, manufactured by AGC Engineering Co., Ltd.), was cut into a circular shape with a size of 32 mm using a packing punch set (3H-P17), and this was immersed in a 0.1 M (mol / L) potassium hydroxide aqueous solution for more than 16 hours. The DSVN that had been immersed in the potassium hydroxide aqueous solution was rinsed with a 0.5 M (mol / L) anodic aqueous solution.

[0079] (Creation of zero-gap cells) The working electrode, ion exchange membrane, and counter electrode obtained as described above were stacked in this order. In this stacking, the conductive tapes of the working electrode and the counter electrode were overlapped concentrically so that they did not come into contact. The working electrode was positioned so that the side of the working electrode with the cathode catalyst was facing the ion exchange membrane.

[0080] (Assembly of electrolytic cells) An electrolytic cell was assembled by arranging the cathode chamber and anode chamber opposite each other via a zero-gap cell. With the cathode chamber and anode chamber joined together so that they face each other via the zero-gap cell, fixing jigs were fitted onto the outer circumference of the flange portions of the cathode chamber and anode chamber, and the fixing jigs were secured by tightening them with screws. After fixing the cathode and anode chambers, 25 mL of 0.5 M (mol / L) phosphoric acid aqueous solution and a stirring bar were placed in the anode chamber. After filling the anode chamber with a phosphoric acid aqueous solution, the anode chamber was covered and secured with screws. Then, an Ag / AgCl (PEEK resin coated type, RE-T16, manufactured by EC Frontier Co., Ltd.) was inserted into the anode chamber as a reference electrode. This was then used as an electrolytic cell. The electrolytic cell was secured with clamps and placed on top of the magnetic stirrer. The reference electrode and the copper tape exposed from the zero-gap cell were connected to the electrochemical measuring device with alligator clips, and the setup was complete. For electrochemical measurements, we used an electrochemical analyzer manufactured by BAS (ALS / [H]CH Instruments Electrochemical Analyzer Model 650E).

[0081] (Electrolytic reduction of carbon dioxide) A degassing needle was inserted into one of the two septum ports of the cathode chamber of the electrolytic cell, and nitrogen gas was introduced into the cathode chamber for 10 minutes to replace the atmosphere with nitrogen gas. Subsequently, carbon dioxide gas was introduced into the cathode chamber for 10 minutes to replace the atmosphere with carbon dioxide gas. After that, the degassing needle was removed from the septum port, the chamber was sealed, and the electrolysis operation of carbon dioxide was started. The parameters for the electrolysis of carbon dioxide are as follows: Electrolysis potential: -2.5V Final current ratio: 0 Measurement time: 3600 seconds (1 hour) Data storage interval: 1 second Pre-electrolysis potential: -2.0V Pre-electrolysis time: 60 seconds

[0082] At the stage when the electrolysis of carbon dioxide was initiated using the above parameters, a magnetic stirrer was used to rotate the stirring bar. 3600 seconds after the completion of the carbon dioxide electrolysis, 100 μL of the generated gas in the anode chamber was collected using a gas-tight syringe (Hamilton, 250 μL). The collected generated gas was analyzed by gas chromatography. The gas chromatograph (Shimadzu GC-2014) was modified to pass through the TCD detector before entering the FID detector, taking into account the properties of the gases with respect to the detectors. The measurement parameters and column are as follows. Evaporation chamber temperature: 150℃ Carrier gas: N2 Column flow rate: 30.0 mL / min Column temperature: 40℃ Detector temperature: 250℃ Detector current: 60mA Measurement time: 45 minutes Column: HayeSep D 100 / 120 Packed Column JK, 4.0m, 3.00mm ID (2 linked)

[0083] After sampling the generated gas using gas chromatography, carbon dioxide gas was again introduced into the cathode chamber for 10 minutes to replace the atmosphere inside the cathode chamber. Then, the electrolytic operation described above was performed. This process of replacing the atmosphere inside the cathode chamber with carbon dioxide gas and the electrolytic operation was repeated twice. The generated gases in the anode chamber were quantified using a calibration curve created based on standard gases. Due to the sensitivity of the detectors, hydrogen and carbon monoxide were quantified based on the peak area detected by the TCD detector, while methane and ethylene were quantified based on the peak area detected by the FID detector. Faraday efficiency (sometimes abbreviated as "FE") is calculated by determining the efficiency of the amount of electrons required to produce the detected hydrogen, carbon monoxide, methane, and ethylene in relation to the electrolytic current (coulombs), and then calculating the average value over three electrolytic operations. The results are shown in Table 1.

[0084] [Experimental Example 2] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that 7.96 mg (0.010 mmol) of (TBA)2WS4 was used as the cathode catalyst. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0085] [Experimental Example 3] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that 7.10 mg (0.010 mmol) of (TBA)2MoS4 was used as the cathode catalyst. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0086] [Experimental Example 4] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that 4.62 mg (0.010 mmol) of ReCl(CO)3(bpy) was used as the cathode catalyst. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0087] [Experimental Example 5] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that 2.49 mg (0.010 mmol) of methyltrioxorhenium(VII) was used as the cathode catalyst. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0088] [Experimental Example 6] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that 2.51 mg (0.010 mmol) of perrhenic acid was used as the cathode catalyst. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0089] [Experimental Example 7] An electrolytic cell was fabricated in the same manner as in Experimental Example 1, except that a cathode catalyst was not used. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0090] [Experimental Example 8] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that a nitric acid solution was used instead of a phosphoric acid solution. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0091] [Experimental Example 9] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that a sulfuric acid solution was used instead of a phosphoric acid solution. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0092] [Experimental Example 10] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that hydrochloric acid solution was used instead of phosphoric acid solution. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0093] [Experimental Example 11] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that an aqueous acetic acid solution was used instead of an aqueous phosphoric acid solution. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0094] [Experimental Example 12] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that a boric acid solution was used instead of a phosphoric acid solution. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0095] [Experimental Example 13] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that a perchloric acid solution was used instead of a phosphoric acid solution. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0096] [Experimental Example 14] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that a diphosphate aqueous solution was used instead of a phosphoric acid aqueous solution. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0097] [Experimental Example 15] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that a lithium dihydrogen phosphate (LiH2PO4) aqueous solution was used instead of a phosphoric acid aqueous solution. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0098] [Experimental Example 16] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that the concentration of the phosphoric acid aqueous solution was set to 0.1 M. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0099] [Experimental Example 17] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that the concentration of the phosphoric acid aqueous solution was set to 0.25 M. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0100] [Experimental Example 18] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that the concentration of the phosphoric acid aqueous solution was set to 1.0 M. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0101] [Experimental Example 19] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that the concentration of the phosphoric acid aqueous solution was set to 1.5 M. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0102] [Experimental Example 20] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that EC600JD (manufactured by Lion Specialty Chemicals Co., Ltd.) was used as the conductive additive for the working electrode. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0103] [Experimental Example 21] An electrolytic cell was prepared in the same manner as in Experimental Example 1, except that EC300J (manufactured by Lion Specialty Chemicals Co., Ltd.) was used as the conductive additive for the working electrode. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0104] [Experimental Example 22] An electrolytic cell was fabricated in the same manner as in Experimental Example 1, except that Nafion (registered trademark, manufactured by Sigma-Aldrich) was used as a conductive additive for the working electrode. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0105] [Experimental Example 23] An electrolytic cell was fabricated in the same manner as in Experimental Example 1, except that a conductive additive was not used in the working electrode. Using the obtained electrolytic cell, electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0106] [Experimental Example 24] In the electrolytic reduction of carbon dioxide, the procedure was the same as in Experimental Example 1, except that the electrolysis potential was set to -1.5V. The amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0107] [Experimental Example 25] In the electrolytic reduction of carbon dioxide, the procedure was the same as in Experimental Example 1, except that the electrolysis potential was set to -2.0V. The amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0108] [Experimental Example 26] In the electrolytic reduction of carbon dioxide, the procedure was the same as in Experimental Example 1, except that the electrolysis potential was set to -3.0V. The amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0109] [Experimental Example 27] In the electrolytic reduction of carbon dioxide, the procedure was the same as in Experimental Example 1, except that the electrolysis potential was set to -3.5V. The amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0110] [Experimental Example 28] Opposite pole (IrO x Instead of -300 / TGP-H-060), the counter electrode (IrO x Except for using -400 / TGP-H-060), the electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the quantification of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. x -400 refers to an iridium catalyst that has been fired at 400 degrees Celsius. The results are shown in Table 3.

[0111] [Experimental Example 29] Opposite pole (IrO x Instead of -300 / TGP-H-060), the counter electrode (IrO x Except for using -500 / TGP-H-060), the electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the quantification of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. x -500 refers to an iridium catalyst that has been calcined at 500 degrees Celsius. The results are shown in Table 3.

[0112] [Experimental Example 30] IrO x Except for not using -300, the electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the quantification of the generated gas and the calculation of the Faraday efficiency were also performed in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0113] [Experimental Example 31] The electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, except that the AAVN (model name), an anion exchange membrane from Celemion (registered trademark, manufactured by AGC Engineering Co., Ltd.), was used as the ion exchange membrane. The product gas was quantified and the Faraday efficiency was calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0114] [Experimental Example 32] The electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, except that the AMVN (model name), an anion exchange membrane from Celemion (registered trademark, manufactured by AGC Engineering Co., Ltd.), was used as the ion exchange membrane. The product gas was quantified and the Faraday efficiency was calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0115] [Experimental Example 33] The electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, except that the ASVN (model name), an anion exchange membrane from Celemion (registered trademark, manufactured by AGC Engineering Co., Ltd.), was used as the ion exchange membrane. The quantification of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0116] [Experimental Example 34] The electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, except that the AHO (model name), an anion exchange membrane from Celemion (registered trademark, manufactured by AGC Engineering Co., Ltd.), was used as the ion exchange membrane. The quantification of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0117] [Experimental Example 35] The electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, except that CMVN (model name), a cation exchange membrane from Celemion (registered trademark, manufactured by AGC Engineering Co., Ltd.), was used as the ion exchange membrane. The product gas was quantified and the Faraday efficiency was calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0118] [Experimental Example 36] Except for using Toray's carbon paper (TGP-H-060, 200 μm thick) as the carbon paper constituting the working electrode, the electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0119] [Experimental Example 37] Except for using Toray's carbon paper (TGP-H-090, 300 μm thick) as the carbon paper constituting the working electrode, the electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0120] [Experimental Example 38] Except for using Toray's carbon paper (TGP-H-120, 400 μm thick) as the carbon paper constituting the working electrode, the electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, and the amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0121] [Experimental Example 39] The electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, except that aluminum tape was used instead of copper tape to connect the working electrode, counter electrode, and electrochemical measuring device. The amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0122] [Experimental Example 40] The electrolytic reduction of carbon dioxide was performed in the same manner as in Experimental Example 1, except that the counter electrode was sandwiched between the sample bonding portion (SUS316 nickel-plated base) of a plate electrode (EC Frontier, RE-2-100) and an electrolytic cell that did not have a zero-gap structure was used. The amount of the generated gas and the Faraday efficiency were calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0123] [Table 1]

[0124] [Table 2]

[0125] [Table 3]

[0126] [Table 4]

[0127] The results from Experimental Examples 1-4 shown in Table 1 indicate that when tetrabutylammonium tetrathiorenium, (TBA)2WS4, (TBA)2MoS4, or ReCl(CO)3(bpy) are used as cathode catalysts, the amount of methane produced is high. Furthermore, high Faraday efficiency was observed. From the results of Experimental Example 5 shown in Table 1, it was found that when methyltrioxorhenium(VII) was used as the cathode catalyst, the amount of methane produced was small. From the results of Experimental Example 6 shown in Table 1, it was found that when perrhenic acid was used as the cathode catalyst, the amount of methane produced was small and the Faraday efficiency was low. The results of Experimental Example 7, shown in Table 1, indicate that when a cathode catalyst is not used, methane is produced in large quantities, but carbon monoxide is produced in small quantities.

[0128] The results of Experiment Example 8 shown in Table 1 indicate that when nitric acid solution is used as the acidic anode solution, while the amount of methane produced is high, the Faraday efficiency is low. The results of Experiment Example 9 shown in Table 1 indicate that when sulfuric acid solution is used as the acidic anode solution, the amount of methane produced is small and the Faraday efficiency is low. The results of Experimental Example 10 shown in Table 1 indicate that when hydrochloric acid solution is used as the acidic anode solution, the amount of methane produced is small and the Faraday efficiency is low. The results of Experiment Example 11, shown in Table 2, indicate that when an aqueous acetic acid solution is used as the acidic anode solution, the amount of methane produced is small and the Faraday efficiency is low. The results of Experimental Example 12, shown in Table 2, indicate that when boric acid solution is used as the acidic anodic aqueous solution, the amount of methane produced is low and the Faraday efficiency is low. The results of Experimental Example 13, shown in Table 2, indicate that when perchloric acid solution is used as the acidic anodic aqueous solution, the amount of methane produced is small and the Faraday efficiency is low. The results of Experimental Example 14, shown in Table 2, indicate that when diphosphate aqueous solution is used as the acidic anode aqueous solution, the amount of methane produced is small, but the Faraday efficiency is high. The results of Experimental Example 15, shown in Table 2, indicate that when lithium dihydrogen phosphate aqueous solution is used as the acidic anode aqueous solution, the amount of methane produced is small and the Faraday efficiency is low.

[0129] From the results of Experimental Example 16 shown in Table 2, it was found that when the concentration of the phosphoric acid aqueous solution was 0.1 M, the amount of methane produced was small and the Faraday efficiency was low. From the results of Experiment Example 17 shown in Table 2, it was found that when the concentration of the phosphoric acid aqueous solution was 0.25 M, the amount of methane produced was small, but the Faraday efficiency was high. From the results of Experiment Example 18 shown in Table 2, it was found that when the concentration of the phosphoric acid aqueous solution was 1.0 M, the amount of methane produced was large and the Faraday efficiency was high. From the results of Experiment Example 19 shown in Table 2, it was found that when the concentration of the phosphoric acid aqueous solution was 1.5 M, the amount of methane produced was large and the Faraday efficiency was high.

[0130] The results of Experimental Example 20, shown in Table 2, indicate that when EC600JD is used as a conductive additive for the working electrode, a large amount of methane is produced and the Faraday efficiency is high. From the results of Experimental Example 21 shown in Table 3, it was found that when EC300J was used as a conductive additive for the working electrode, the amount of methane produced was small, but the Faraday efficiency was high. The results of Experimental Example 22, shown in Table 3, indicate that using Nafion® as a conductive additive for the working electrode resulted in increased methane production and high Faraday efficiency. The results of Experimental Example 23, shown in Table 3, indicate that when no conductive additive is used at the working electrode, the amount of methane produced is high and the Faraday efficiency is high.

[0131] From the results of Experimental Example 24 shown in Table 3, it was found that when the electrolysis potential was set to -1.5V, the amount of methane produced was small and the Faraday efficiency was low. From the results of Experimental Example 25 shown in Table 3, it was found that when the electrolysis potential was set to -2.0V, the amount of methane produced was small, but the Faraday efficiency was high. From the results of Experimental Example 26 shown in Table 3, it was found that when the electrolysis potential was set to -3.0V, the amount of methane produced was large and the Faraday efficiency was high. From the results of Experimental Example 27 shown in Table 3, it was found that when the electrolysis potential was set to -3.5V, the amount of methane produced was large, but the Faraday efficiency was low.

[0132] From the results of experimental example 28 shown in Table 3, the counter electrode (IrO x Instead of -300 / TGP-H-060), the counter electrode (IrO x When using -400 / TGP-H-060, it was found that methane production was high and the Faraday efficiency was high. From the results of experimental example 29 shown in Table 3, the counter electrode (IrO x Instead of -300 / TGP-H-060), the counter electrode (IrO x When using -500 / TGP-H-060, it was found that the amount of methane produced was large and the Faraday efficiency was high. From the results of experimental example 30 shown in Table 3, IrO x It was found that when -300 was not used, the amount of methane produced was low and the Faraday efficiency was low.

[0133] The results of Experimental Example 31, shown in Table 4, indicate that when AAVN is used as the ion exchange membrane, the amount of methane produced is low and the Faraday efficiency is low. The results of Experimental Example 32, shown in Table 4, indicate that when AMVN is used as the ion exchange membrane, the amount of methane produced is low and the Faraday efficiency is low. The results of Experimental Example 33, shown in Table 4, indicate that when ASVN is used as the ion exchange membrane, the amount of methane produced is low and the Faraday efficiency is low. The results of Experimental Example 34, shown in Table 4, indicate that when AHO is used as the ion exchange membrane, the amount of methane produced is low and the Faraday efficiency is low. The results of Experimental Example 35, shown in Table 4, indicate that when CMVN is used as the ion exchange membrane, the amount of methane produced is low and the Faraday efficiency is low.

[0134] From the results of Experimental Example 36 shown in Table 4, it was found that when carbon paper (TGP-H-060) was used as the carbon paper constituting the working electrode, the amount of methane produced was large and the Faraday efficiency was high. From the results of Experimental Example 37 shown in Table 4, it was found that when carbon paper (TGP-H-090) was used as the carbon paper constituting the working electrode, the amount of methane produced was small and the Faraday efficiency was low. From the results of Experimental Example 38 shown in Table 4, it was found that when carbon paper (TGP-H-120) was used as the carbon paper constituting the working electrode, the amount of methane produced was small and the Faraday efficiency was low.

[0135] The results of Experimental Example 39, shown in Table 4, indicate that when aluminum tape was used instead of copper tape to connect the working electrode, counter electrode, and electrochemical measuring device, the amount of methane produced was low, but the Faraday efficiency was high.

[0136] From the results of Experimental Example 40 shown in Table 4, it was found that when an electrolytic cell was used that did not have a zero-gap structure, with the counter electrode sandwiched between the sample junction (SUS316 nickel-plated base) of a plate electrode (EC Frontier, RE-2-100), the amount of methane produced was small and the Faraday efficiency was low. [Explanation of Symbols]

[0137] 1. Carbon dioxide electrolysis reduction system 10 electrolytic cells 11 Cathode chamber 11A Flange section 12 Anode chamber 12A Flange section 20 zero-gap cells 21 Working electrode 21A Base material 22 Cathode catalyst 23 Ion exchange membrane 24 Opposite Poles 25,26 Conductive tape 30 Acidic anode solution 40 Reference electrode

Claims

1. It comprises an electrolytic cell, a zero-gap cell, an acidic anodic aqueous solution, and a reference electrode. The electrolytic cell is divided into a cathode chamber and an anode chamber via the zero-gap cell. The zero-gap cell comprises a working electrode containing a cathode catalyst and a conductive additive, an ion exchange membrane, and a counter electrode containing iridium oxide, wherein the working electrode, the ion exchange membrane, and the counter electrode are stacked in this order. The cathode catalyst is positioned on the ion exchange membrane side, The working electrode is positioned on the cathode chamber side, and the counter electrode is positioned on the anode chamber side. The acidic anode aqueous solution is housed in the anode chamber of a carbon dioxide electrolytic reduction system.

2. The carbon dioxide electrolytic reduction system according to claim 1, wherein the cathode catalyst is at least one selected from tetrabutylammonium tetrathiorenium, tetrabutylammonium tetrathiotungstate, tetrabutylammonium tetrathiomolybdate, and chlorotricarbonyl(2,2'-bipyridine)rhenium(I).

3. The carbon dioxide electrolytic reduction system according to claim 1, wherein the conductive additive is a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid.

4. The carbon dioxide electrolytic reduction system according to claim 1, wherein the acidic anodic aqueous solution is an aqueous phosphoric acid solution, an aqueous nitric acid solution, an aqueous sulfuric acid solution, an aqueous hydrochloric acid solution, an aqueous acetic acid solution, an aqueous boric acid solution, an aqueous perchloric acid solution, or an aqueous diphosphate solution.

5. A method for producing hydrocarbons using a carbon dioxide electrolytic reduction system according to any one of claims 1 to 4, The process involves filling the cathode chamber with a gas containing carbon dioxide, and then sealing the cathode chamber. A method for producing hydrocarbons, comprising the steps of applying an electric potential to the working electrode and the counter electrode to electrolytically reduce the carbon dioxide and generate hydrocarbons in the acidic anode aqueous solution.

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