Cathode electrode for gas diffusion electrolysis flow cell, and gas diffusion electrolysis flow cell

Abstract

To provide a cathode electrode for a gas diffusion type electrolytic flow cell, capable of improving the production amount of a C2+ reduced product by suppressing the hydrogen generation as a side reaction at a low cell potential.SOLUTION: In a cathode electrode 22 for a gas diffusion type electrolytic flow cell which reduces carbon monoxide to produce a carbon monoxide reduction product, the cathode electrode comprises a catalyst layer 26 which contains: a molecule catalyst having copper atoms; an alkali metal salt; and a conductive carbon material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cathode electrode for a gas diffusion electrolysis flow cell and a gas diffusion electrolysis flow cell. [Background technology]

[0002] In recent years, concerns have arisen about the depletion of fossil fuels such as oil and coal, and expectations are growing for sustainable renewable energy sources. From the perspective of such energy issues and environmental issues, progress is being made in the development of technologies that can electrochemically reduce carbon monoxide to create storable chemical energy sources.

[0003] Conventionally, a method for electrochemically reducing carbon monoxide using a copper-based metal catalyst has been known as a method for reducing carbon monoxide (for example, Patent Document 1 and Non-Patent Documents 1-4). Patent Document 1 and Non-Patent Documents 1, 3, and 4 disclose a gas diffusion electrolysis flow cell including an anode electrode, a cathode electrode, and an ion-conductive polymer membrane sandwiched between the electrodes, to electrochemically reduce carbon monoxide and obtain a carbon monoxide reduction product. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2022-0213604 [Non-patent literature]

[0005] [Non-Patent Document 1] Proceedings of the National Academy of Sciences, 2021, 118.2, e2010868118 [Non-patent document 2] ACS Cent. Sci. 2017, 3, 9, 1032-1040 [Non-patent document 3] Chem. Eur. J. 2022, 28, e202200340 [Non-patent document 4] Nature Energy, 2022, 7, 170-176 Summary of the Invention [Problem to be solved by the invention]

[0006] By the way, in the carbon monoxide reduction reaction, C produced from more than one CO molecule 2+ The reduction products (e.g., ethylene, ethanol, propanol, etc.) are useful as energy resources, so it is important to suppress the side reaction of hydrogen production and promote C 2+ It is desirable to improve the yield of reduction products.

[0007] However, in conventional gas diffusion electrolysis flow cells, due to the large reaction overvoltages of the anode and cathode, it is difficult to suppress the hydrogen generation, which is a side reaction, at a low cell potential and achieve C 2+ It is difficult to increase the yield of reduction products.

[0008] Therefore, the object of the present invention is to suppress the hydrogen generation, which is a side reaction, at a low cell potential and to achieve C 2+ An object of the present invention is to provide a cathode electrode for a gas diffusion electrolysis flow cell and a gas diffusion electrolysis flow cell that can improve the amount of reduction product produced. [Means for solving the problem]

[0009] The present invention provides a cathode electrode for a gas diffusion electrolysis flow cell that reduces carbon monoxide gas to produce a carbon monoxide reduction product, the cathode electrode comprising a molecular catalyst having copper atoms and an alkali metal salt. solid and a catalyst layer having a conductive carbon material.

[0010] In the cathode electrode for the gas diffusion electrolysis flow cell, the molecular catalyst having copper atoms is preferably supported on the conductive carbon material.

[0011] The present invention also provides a gas diffusion electrolysis flow cell comprising an anode electrode to which an anode solution is supplied, a cathode electrode to which carbon monoxide gas is supplied, and an ion-conductive polymer membrane sandwiched between the anode electrode and the cathode electrode, wherein the cathode electrode is a cathode electrode for the gas diffusion electrolysis flow cell. [Effects of the Invention]

[0012] According to the present invention, hydrogen generation, which is a side reaction, is suppressed at a low cell potential, and C 2+ It is possible to provide a cathode electrode for a gas diffusion electrolysis flow cell and a gas diffusion electrolysis flow cell that can improve the amount of reduction product produced. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a gas diffusion electrolysis flow cell according to an embodiment of the present invention. [Figure 2] 1 shows the change over time in the faradaic efficiency of the products (C2H4, H2) in carbon monoxide electrolysis in Example 1. [Figure 3] 1 shows the change over time in the faradaic efficiency of the products (C2H4, H2) in carbon monoxide electrolysis in Comparative Example 1. [Figure 4] 1 shows the change over time in current density at the cathode electrode during carbon monoxide electrolysis in Example 1 and Comparative Example 1. [Figure 5] 1 shows the change over time in the faradaic efficiency of the products (C2H4, H2) in carbon monoxide electrolysis in Example 2. [Figure 6] 1 shows the change over time in the faradaic efficiency of the products (C2H4, H2) in carbon monoxide electrolysis in Comparative Example 2. [Figure 7] 1 shows the change over time in current density at the cathode electrode during carbon monoxide electrolysis in Example 2. [Figure 8] 1 shows the change over time in current density at the cathode electrode during carbon monoxide electrolysis in Comparative Example 2. [Figure 9]1 shows the change over time in the faradaic efficiency of the products (C2H4, H2) in carbon monoxide electrolysis in Comparative Examples 3 to 5. [Figure 10] 1 shows the change over time in current density at the cathode electrode during carbon monoxide electrolysis in Comparative Examples 3 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0015] FIG. 1 is a schematic diagram illustrating an example of a gas diffusion electrolysis flow cell according to this embodiment. The gas diffusion electrolysis flow cell 1 shown in FIG. 1 is a device in which carbon monoxide gas is directly supplied to a cathode electrode 22. The carbon monoxide gas is a gas containing carbon monoxide, preferably a gas containing carbon monoxide and water vapor. The gas diffusion electrolysis flow cell 1 shown in FIG. 1 includes an anode unit 10, a cathode unit 12, and an ion-conductive polymer membrane 14. The anode unit 10 includes an anode electrode 16 and an anode solution flow path 18. The anode electrode 16 is disposed between and in contact with the ion-conductive polymer membrane 14 and the anode solution flow path 18. The anode solution flow path 18 supplies the anode electrode 16 with an anode solution and is formed by a pit (groove or recess) formed in an anode current collector plate 20. The cathode unit 12 includes a cathode electrode 22 and a gas flow path 24. The cathode electrode 22 is disposed between the gas flow path 24 and the ion-conductive polymer membrane 14. The cathode electrode 22 includes a catalyst layer 26. The cathode electrode 22 preferably includes a gas diffusion layer 28. The cathode electrode 22 shown in FIG. 1 includes, in this order from the ion-conductive polymer membrane 14 side, the catalyst layer 26 and the gas diffusion layer 28. The gas flow path 24 supplies carbon monoxide gas to the cathode electrode 22 and is formed by a pit (groove or recess) provided in the cathode current collector plate 30. The ion-conductive polymer membrane 14 is sandwiched between the anode electrode 16 and the cathode electrode 22. That is, the anode electrode 16 and the cathode electrode 22 are separated by the ion-conductive polymer membrane 14.

[0016] Anode current collector 20 is connected to, for example, a solution inlet and a solution outlet (neither of which are shown). Anode solution is introduced into anode solution flow path 18 through the solution inlet, passes through anode solution flow path 18 while in contact with anode electrode 16, and is discharged from the anode solution outlet. Anode current collector 20 is preferably made of a material that is highly chemically reactive and highly conductive. Examples of such materials include metal materials such as Ti and SUS, and carbon.

[0017] The cathode current collector 30 is connected to, for example, a gas inlet and a gas outlet (neither of which are shown). Carbon monoxide gas is introduced into the gas flow channel 24 through the gas inlet, passes through the gas flow channel 24 while coming into contact with the catalyst layer 26 via the gas diffusion layer 28, and is then discharged from the gas outlet. As with the anode current collector 20, the cathode current collector 30 is preferably made of a material that has low chemical reactivity and high conductivity. Examples of such materials include metal materials such as Ti and SUS, and carbon.

[0018] 1 denotes a power supply that electrically connects and supplies power between the anode electrode 16 and the cathode electrode 22. The power supply 32 is not particularly limited, and examples thereof include a chemical battery (including a primary battery, a secondary battery, etc.), a constant voltage source, and a solar cell.

[0019] Next, an example of the operation of the gas diffusion electrolytic flow cell 1 shown in FIG. 1 will be described.

[0020] When a current is supplied between the anode electrode 16 and the cathode electrode 22 from the power supply 32, an oxidation reaction of, for example, water (HO) occurs at the anode electrode 16 in contact with the anolyte. Specifically, as shown in the following formula (1), the HO contained in the anolyte is oxidized to oxygen (O) and hydrogen ions (H + ) is generated. 2H2O → 4H + +O2+4e - ···(1)

[0021] On the other hand, on the cathode electrode 22 side, carbon monoxide gas supplied from the gas flow path 24 to the catalyst layer 26 through the gas diffusion layer 28 is converted into electrons (e - ) and H that has migrated from the anode electrode 16 to the cathode electrode 22 side through the ion-conductive polymer membrane 14. + This results in reduction to produce C2H4 as shown in the following formula (2). In addition, as a side reaction, the hydrogen ions receive electrons as shown in the following formula (3), producing hydrogen. 2CO+8H+ +8e - → C2H4+2H2O (2) 2H + +2e - → H2···(3) In addition to the above-mentioned ethylene (C2H4), carbon monoxide reduction products include, for example, methane (CH4), ethane (C2H6), ethylene (C2H4), ethanol (C2H5OH), and propanol (C3H7OH).

[0022] The configurations of the anode electrode 16, the cathode electrode 22, and the ion-conductive polymer membrane 14 will be described in detail below.

[0023] The anode electrode 16 preferably has a substrate made of at least one material selected from the group consisting of Ni, Ti, Fe, and C, as this can reduce the overvoltage of the oxidation reaction. The metal material of Ni, Ti, or Fe also includes an alloy containing at least one of the metals Ni, Ti, and Fe. The substrate preferably has a structure that allows the anode solution and ions to move between the ion-conductive polymer membrane 14 and the anode solution flow path 18, and is preferably, for example, a porous body, a mesh, or a sintered fiber body.

[0024] The anode electrode 16 preferably includes an anode catalyst. Examples of the anode catalyst include a metal containing at least one element selected from the group consisting of Ni, Fe, Co, Mn, Ru, and Ir, an oxide containing the metal, a hydroxide containing the metal, and an oxyhydroxide containing the metal, which can reduce the overvoltage of the oxidation reaction. These may be used alone or in combination of two or more. When an anode catalyst is used, it is preferable that the anode catalyst be supported on the aforementioned substrate.

[0025] For example, in terms of enhancing the oxidation reaction, the anode solution preferably contains at least one ion selected from the group consisting of hydroxide ions, hydrogen carbonate ions, carbonate ions, chloride ions, bromide ions, iodide ions, nitrate ions, sulfate ions, phosphate ions, borate ions, tetraborate ions, hydrogen ions, lithium ions, sodium ions, potassium ions, rubidium ions, and cesium ions.

[0026] The gas diffusion layer 28 constituting the cathode electrode 22 is not particularly limited as long as it ensures electrical conduction between the catalyst layer 26 and the power source 32 and efficiently supplies carbon monoxide gas to the catalyst layer 26. However, it is preferable that the gas diffusion layer 28 be a hydrophobic porous carbon substrate, since it can reduce the amount of water that has migrated from the cathode electrode 22 side.

[0027] As described above, the catalyst layer 26 constituting the cathode electrode 22 promotes the reduction reaction of carbon monoxide in carbon monoxide gas to produce carbon monoxide reduction products and the like. The catalyst layer 26 contains a molecular catalyst having copper atoms, a conductive carbon material, and an alkali metal salt. The catalyst layer 26 also preferably contains a polymer that serves as an ion conductor and a binder. The catalyst layer 26 preferably has a porous structure in order to improve the diffusibility of carbon monoxide gas. The thickness of the catalyst layer 26 is, for example, 5 to 200 μm.

[0028] Examples of molecular catalysts containing copper atoms include copper complex catalysts having copper as a central metal and a ligand. Examples of the ligand include bidentate ligands having a structure such as 2,2'-bipyridine, 2-phenylpyridine, or 1,10-phenanthroline; tridentate ligands having a structure such as 2,2':6',2"-terpyridine; tetradentate ligands having a structure such as porphyrin, phthalocyanine, corrole, chlorine, or 2,2':6',2":6",2"'-quaterpyridine; and pentadentate or higher ligands having a basic skeleton of such a tetradentate or lower ligand and organically linked to a coordinating substituent such as pyridine. Specific examples of copper complex catalysts include copper complex catalysts having a phthalocyanine analogue structure (e.g., copper-tetrapyridino-porphyrazine, copper phthalocyanine).

[0029] The copper complex catalyst may be, for example, a catalyst represented by the general formula: CuMX2(Y)2L2. In the general formula, M is preferably Cu, Ag, or Ni, and more preferably Cu, in terms of high catalytic activity, etc. In the general formula, X is not particularly limited as long as it is a halogen atom, but is preferably selected from Br, Cl, and I, and particularly preferably Br, in terms of the stability of the crystal structure, etc.

[0030] In the general formula, Y is not particularly limited as long as it is a ligand having a phosphorus atom, and examples thereof include trimethylphosphine, triethylphosphine, tri-n-propylphosphine, triisopropylphosphine, tri-n-butylphosphine, tri-tert-butylphosphine, tri-n-pentylphosphine, tricyclopentylphosphine, tri-n-hexylphosphine, tricyclohexylphosphine, tri-n-heptylphosphine, tri-n-octylphosphine, triphenylphosphine, tris(2-methoxyphenyl)phosphine, tris(4-methoxyphenyl)phosphine, tris(2,6-dimethoxyphenyl)phosphine, tris(2-furyl)phosphine, tris(4-dimethylaminophenyl)phosphine, tri-p-tolylphosphine, tris-(4-fluorophenyl)phosphine, tris[3,5-bis(trifluoromethyl)phenyl]phosphine, and tris(pentafluorophenyl)phosphine. Of these, triphenylphosphine (PPh3) is preferred.

[0031] In the general formula, L is not particularly limited as long as it is a ligand having a nitrogen atom, but it is preferably a ligand having a lowest unoccupied molecular orbital (LUMO) that accepts electrons from the electrode, such as a pyridine derivative. Examples of pyridine derivatives include 4,4'-di(4-pyridyl)biphenyl, 4,4'-dipyridyl, 1,2-di(4-pyridyl)ethane, 1,2-di(4-pyridyl)ethylene, N,N'-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide, 4-(4-piperidyl)pyridine, 2-methylpyridine, 2-ethylpyridine, 4-propylpyridine, 2-vinylpyridine, N,N-dimethyl-4-aminopyridine, 4-phenylpyridine, 2-hydroxypyridine, 1,5-naphthyridine, 2,2'-bipyridyl, 1,3-di(4-pyridyl)propane, 4-pyridyl-4'-methylpyridylbiphenyl, 4-methylpyridine, and 3-benzylpyridine. Among these, 4-phenylpyridyl (4PP) is preferred.

[0032] Examples of the conductive carbon material contained in the catalyst layer 26 include carbon black such as Ketjenblack or VULCAN (registered trademark) XC-72, activated carbon, carbon nanotubes, etc. The conductive carbon material is preferably used as a carrier for supporting the molecular catalyst having copper atoms, since it enhances the reduction reactivity of carbon monoxide.

[0033] The alkali metal salt contained in the catalyst layer 26 may be an inorganic alkali metal salt, an organic alkali metal salt, or a combination of these.

[0034] As the inorganic alkali metal salt, various inorganic salts of alkali metals such as lithium, sodium, potassium, rubidium, cesium, etc. can be used, such as chlorides, nitrates, carbonates, sulfates, phosphates, hydroxides, etc. Layered compounds such as clay containing alkali metals can also be used.

[0035] Examples of organic alkali metal salts include alkali metal salts of aliphatic organic acids such as alkali metal salts of aliphatic sulfonic acids, alkali metal salts of aromatic organic acids such as alkali metal salts of aromatic sulfonic acids, and alkali metal salts of fluoroalkanesulfonic acids in which hydrogen atoms in alkanes are fluorinated. Examples of alkali metal salts of aliphatic sulfonic acids include alkali metal alkanesulfonic acids. Preferred examples of alkanesulfonic acids used in alkali metal alkanesulfonic acid salts include methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, methylbutanesulfonic acid, hexanesulfonic acid, heptanesulfonic acid, and octanesulfonic acid, and these can be used alone or in combination of two or more. Furthermore, alkali metal salts in which some or all of the alkyl groups are substituted with fluorine atoms may also be used. Examples of aromatic sulfonic acids used in the alkali metal aromatic sulfonate include sulfonic acids of monomeric or polymeric aromatic sulfides, sulfonic acids of aromatic carboxylic acids and esters, and sulfonic acids of monomeric or polymeric aromatic ethers, and these can be used alone or in combination of two or more. Organic alkali metal salts that are easily soluble in alcohol are preferred as alkali metal salts. By using an alcohol solvent in which the organic alkali metal salt is dissolved, the organic alkali metal salt can be highly dispersed in the catalyst layer 26.

[0036] The content of the alkali metal salt is preferably in the range of, for example, 2% by mass to 75% by mass with respect to the total amount of the conductive carbon material used in the catalyst layer 26. Furthermore, without being particularly concerned with the weight, the conductive carbon material may simply be immersed in a solution in which the alkali metal salt is dissolved and then dried.

[0037] Examples of the polymers that serve as the ion conductor and binder contained in the catalyst layer 26 include cation exchange resins such as Nafion (registered trademark) (manufactured by DuPont) and Flemion (manufactured by Asahi Glass Co., Ltd.), and anion exchange resins such as Neocepta, Selemion, and Sustenion.

[0038] The catalyst layer 26 may contain phenol or a salt thereof, which can enhance catalytic activity, and the anode electrode 16 may contain iron oxyhydroxide or nickel oxyhydroxide, which can promote water oxidation at a low potential.

[0039] As the ion-conductive polymer membrane 14, for example, a cation exchange membrane such as Nafion or Flemion, or an anion exchange membrane such as Neosepta, Selemion or Sustenion can be used.

[0040] By using a molecular catalyst containing copper atoms, as in the cathode electrode 22 of this embodiment, hydrogen generation, which is a side reaction, can be suppressed and C can be produced more efficiently than when a copper metal catalyst is used. 2+ It is believed that the amount of reduction product produced can be improved. Furthermore, the coexistence of an alkali metal salt and a conductive carbon material, as in the cathode electrode 22 of this embodiment, improves the conductivity of the cathode electrode 22, thereby reducing the electrical energy required for carbon monoxide reduction. Furthermore, the coexistence of an alkali metal salt and a molecular catalyst containing copper atoms, as in the cathode electrode 22 of this embodiment, improves the durability of the molecular catalyst containing copper atoms, thereby maintaining high catalytic activity and enabling carbon monoxide reduction. Furthermore, when the molecular catalyst containing copper atoms reacts with CO, the alkali metal salt (or alkali metal ion) specifically adsorbs to the oxygen side of CO, lowering the activation energy and thus reducing the overvoltage due to the CO reduction reaction. Therefore, by using the cathode electrode 22 of this embodiment, hydrogen generation, a side reaction, can be suppressed at a low cell potential, and C can be reduced. 2+ The amount of reduction product produced can be improved.

[0041] Furthermore, in the gas diffusion electrolysis flow cell 1 of this embodiment, CO is supplied to the cathode electrode 22 as a gas, and therefore the reduction reaction proceeds in the gas phase, where the diffusion rate is high. This allows the current density limit in the CO reduction reaction to be increased and the by-production of H2 to be suppressed, compared to a gas diffusion electrolysis flow cell in which an electrolyte solution in which CO is dissolved is supplied to the cathode electrode 22. Furthermore, the gas diffusion electrolysis flow cell 1 of this embodiment allows the resistance of the entire cell to be reduced, compared to a gas diffusion electrolysis flow cell in which an electrolyte solution is supplied to both electrodes. Therefore, the gas diffusion electrolysis flow cell 1 equipped with the cathode electrode 22 of this embodiment allows the hydrogen production, which is a side reaction, to be suppressed at a low cell potential, and allows C 2+ The amount of reduction product produced can be improved.

[0042] A preferred embodiment of reducing the cell potential in a gas diffusion electrolysis flow cell is to reduce the overvoltage on the anode electrode side in addition to reducing the overvoltage on the cathode electrode side. To reduce the overvoltage on the anode electrode side, as described above, it is preferable to use a substrate made of at least one material selected from the group consisting of Ni, Ti, Fe, and C for the anode electrode 16, or to use, as the anode catalyst, a metal containing at least one element selected from the group consisting of Ni, Fe, Co, Mn, Ru, and Ir, an oxide containing the metal, a hydroxide containing the metal, or an oxyhydroxide containing the metal.

[0043] The alkaline anode solution is preferably an aqueous solution with a pH of 12 or higher, for example, in view of a decrease in cell voltage. The ion-conductive polymer membrane 14 is preferably an anion-conductive polymer membrane, for example, in view of a tendency for a hydrogen ion concentration difference to be formed, which in turn leads to a decrease in cell voltage. [Example]

[0044] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0045] Example 1 [Cathode electrode] 60 mg of carbon black (VULCAN® XC-72R) was added to 40 mL of dimethylformamide solution and sonicated for 30 minutes. Then, 1 mg of copper phthalocyanine complex catalyst (Cupper-tetrapyridino-porphyrazine, hereafter referred to as CuPyPc) was added and sonicated for another 30 minutes. The solution was stirred at room temperature for 24 hours, filtered, and washed to obtain a catalyst material in which CuPyPc was supported on carbon black (hereafter referred to as CuPyPc / C). 10 mg of CuPyPc / C, 1 mg of potassium triflate (hereafter referred to as KOtf), an alkali metal salt, and 0.1 mL of Nafion solution were added to 0.9 mL of ethanol solution. The resulting mixture was sonicated for 5 minutes and then stirred using a vortex mixer. This solution was applied to carbon paper (Avcarb, GDS3250) used as a gas diffusion layer and dried at 60°C. In this way, a cathode electrode having a catalyst layer formed on carbon paper was obtained.

[0046] [Anode electrode] A Ni-doped β-FeOOH colloidal solution was prepared by mixing a 0.1 M aqueous solution of iron chloride, a 0.05 M aqueous solution of nickel nitrate, and an aqueous solution of ethylenediamine hydrochloride, and adjusting the pH to 2.3. 10 mL of this Ni-doped β-FeOOH colloidal solution was mixed with 10 mL of an aqueous solution containing 0.063 M nickel chloride and 0.055 mM iron chloride. 1.13 cm 2 After immersing nickel foam (EQ-BCNF-16m, manufactured by MTI) in the above solution, it was dried at 150°C for 8 hours to support Ni-doped β-FeOOH on the nickel foam. This was used as the anode electrode.

[0047] [Gas diffusion electrolysis flow cell] An anion conductive resin (Sustainion (registered trademark) X37-50 Grade) was sandwiched between the anode electrode and the cathode electrode. The cathode electrode was positioned so that the catalyst layer was in contact with the anion conductive resin. This membrane / electrode assembly was placed in a reaction cell (Complete 5 cm 2 The reaction cell was placed in a CO2 Electrolyzer (manufactured by Dioxide Materials). The reaction cell was equipped with a cathode gas current collector plate with a gas flow channel formed therein and an anode current collector plate with an anode solution flow channel formed therein. The membrane / electrode assembly was placed so as to be in contact with the gas flow channel of the cathode current collector plate and the anode solution flow channel of the anode current collector plate. This was used as a gas diffusion electrolysis flow cell.

[0048] [Carbon monoxide electrolysis] Carbon monoxide electrolysis was performed using the gas diffusion electrolysis flow cell. Specifically, carbon monoxide gas (CO, 99.995%) was supplied to the gas flow path at 10 sccm, and a 1 M potassium hydroxide aqueous solution was supplied to the anode solution flow path. An electrochemical measurement system (Bio-Logic Science Instruments, SP-150) was then connected to the anode and cathode sides in a two-electrode configuration, and a voltage of -2.2 V was applied to both electrodes to perform carbon monoxide electrolysis. An online gas chromatograph (SRI Instruments, Multiple Gas Analyzer #5) was used to identify and quantify the products produced by carbon monoxide electrolysis. A Molecular Sieve SA and a Hayesep-D column were used, and a thermal conductivity detector (TCD) and a flame ionization detector (FID) were used as detectors.

[0049] <Example 2> A gas diffusion electrolysis flow cell was prepared in the same manner as in Example 1, except that CuBr(PPh)(4PP) was used to prepare the cathode electrode instead of CuPyPc. Carbon monoxide electrolysis was performed in the same manner as in Example 1. CuBr(PPh)(4PP) was prepared as follows. First, an acetonitrile solution containing copper bromide (CuBr) was added to an acetone solution containing 84 mg of 4-phenylpyridine (4PP) and 130 mg of triphenylphosphine (PPh), and the mixture was stirred overnight at room temperature. The mixture was then distilled under reduced pressure, washed with acetone and ethanol, and purified with silica gel in the following order: 100% CHCl, 99% CHCl, and 1% CHCN. Finally, the mixture was vacuum-dried to synthesize CuBr(PPh)(4PP).

[0050] <Comparative Example 1> A gas diffusion electrolysis flow cell was prepared in the same manner as in Example 1, except that the cathode electrode was prepared without using KOtf, and carbon monoxide electrolysis was carried out in the same manner as in Example 1.

[0051] <Comparative Example 2> On the carbon paper used as a gas diffusion layer, 0.2 mg of potassium trifluoromethanesulfonate (hereinafter referred to as KOtf), an alkali metal salt dissolved in ethanol, was applied, and then 1 mg of CuBr(PPh)(4PP) was applied. A gas diffusion electrolysis flow cell was fabricated in the same manner as in Example 1, except that this was used as the cathode electrode, and carbon monoxide electrolysis was performed in the same manner as in Example 1.

[0052] <Comparative Example 3> On the carbon paper used as the gas diffusion layer, 0.2 mg of potassium trifluoromethanesulfonate (hereinafter referred to as KOtf), an alkali metal salt dissolved in ethanol, was applied, and then 1 mg of Cu was applied. A gas diffusion electrolysis flow cell was fabricated in the same manner as in Example 1, except that this was used as the cathode electrode, and carbon monoxide electrolysis was performed in the same manner as in Example 1.

[0053] <Comparative Example 4> On the carbon paper used as the gas diffusion layer, 0.2 mg of potassium trifluoromethanesulfonate (hereinafter referred to as KOtf), an alkali metal salt dissolved in ethanol, was applied, and then 1 mg of CuO was applied. A gas diffusion electrolysis flow cell was fabricated in the same manner as in Example 1, except that this was used as the cathode electrode, and carbon monoxide electrolysis was performed in the same manner as in Example 1.

[0054] <Comparative Example 5> On the carbon paper used as the gas diffusion layer, 0.2 mg of potassium trifluoromethanesulfonate (hereinafter referred to as KOtf), an alkali metal salt dissolved in ethanol, was applied, and then 1 mg of CuO was applied. A gas diffusion electrolysis flow cell was fabricated in the same manner as in Example 1, except that this was used as the cathode electrode, and carbon monoxide electrolysis was performed in the same manner as in Example 1.

[0055] FIG. 2 shows the change over time in the faradaic efficiency of the products (C2H4, H2) in the carbon monoxide electrolysis in Example 1, FIG. 3 shows the change over time in the faradaic efficiency of the products (C2H4, H2) in the carbon monoxide electrolysis in Comparative Example 1, and FIG. 4 shows the change over time in the current density of the cathode electrode during carbon monoxide electrolysis in Example 1 and Comparative Example 1. In Example 1, after 2 hours had elapsed, the faradaic efficiency of C2H4 was 56%, the faradaic efficiency of H2 was 20%, and the faradaic efficiency of ethylene (C 2+ On the other hand, in Comparative Example 1, after 2 hours, the faradaic efficiency of C2H4 was 28% and the faradaic efficiency of H2 was 50%, indicating high production of hydrogen (by-product). Furthermore, the current density in Example 1 was -100 mA / cm after 2 hours. 2 In contrast, the current density in Comparative Example 1 was −50 mA / cm after 2 hours. 2 These results suggest that the presence of alkali metal salts in the catalytic layer of the cathode electrode suppresses the side reaction of hydrogen generation and promotes C 2+ It can be said that the amount of reduction product produced can be improved.

[0056] FIG. 5 shows the change over time in the faradaic efficiency of the products (C2H4, H2) during carbon monoxide electrolysis in Example 2, FIG. 6 shows the change over time in the faradaic efficiency of the products (C2H4, H2) during carbon monoxide electrolysis in Comparative Example 2, FIG. 7 shows the change over time in the current density at the cathode electrode during carbon monoxide electrolysis in Example 2, and FIG. 8 shows the change over time in the current density at the cathode electrode during carbon monoxide electrolysis in Comparative Example 2. In both Example 2 and Comparative Example 2, after 2 hours had elapsed, the faradaic efficiency of C2H4 was approximately 40%, the faradaic efficiency of H2 was approximately 25%, and the faradaic efficiency of ethylene (C 2+ The current density in Example 2 was -50 mA / cm on average. 2 In contrast, the current density in Comparative Example 2 was -10 mA / cm on average. 2 These results suggest that the presence of conductive carbon material in the catalytic layer of the cathode electrode suppresses the side reaction of hydrogen generation and promotes C 2+ It can be said that the amount of reduction product produced can be improved.

[0057] Furthermore, Examples 1 and 2 are driven at a cell potential 0.3 V lower than the cell potential (2.5 V) of a conventional gas diffusion electrolysis flow cell using metal electrodes (Non-Patent Document 4). Therefore, according to Examples 1 and 2, hydrogen generation, a side reaction, is suppressed at a cell potential lower than that of the conventional one, and C 2+ It is possible to increase the amount of reduction product produced.

[0058] Figure 9 shows the change over time in the faradaic efficiency of the products (C2H4, H2) during carbon monoxide electrolysis in Comparative Examples 3 to 5, and Figure 10 shows the change over time in the current density at the cathode electrode during carbon monoxide electrolysis in Comparative Examples 3 to 5. In Comparative Example 3, the faradaic efficiency of C2H4 was 40% and that of H2 was 30%; in Comparative Example 4, the faradaic efficiency of C2H4 was 30% and that of H2 was 40%; and in Comparative Example 5, the faradaic efficiency of C2H4 was 20% and that of H2 was 70%. The current density in Comparative Example 3 was -30 mA / cm 2 The current density in Comparative Example 4 was −20 mA / cm 2The current density in Comparative Example 5 was −50 mA / cm 2 In all of Comparative Examples 3 to 5, the faradaic efficiency of C2H4 was low and the current density was also small compared to Examples 1 and 2. [Explanation of symbols]

[0059] 1 Gas diffusion electrolysis flow cell 10 anode part, 12 cathode part, 14 ion conductive polymer membrane, 16 anode electrode, 18 anode solution flow path, 20 anode current collector, 22 cathode electrode, 24 gas flow path, 26 catalyst layer, 28 gas diffusion layer, 30 cathode current collector, 32 power supply.

Claims

1. 1. A cathode electrode for a gas diffusion electrolysis flow cell that reduces carbon monoxide gas to produce a carbon monoxide reduction product, comprising: A cathode electrode for a gas diffusion electrolysis flow cell, comprising a catalyst layer having a molecular catalyst having copper atoms, a solid alkali metal salt, and a conductive carbon material.

2. 2. The cathode electrode for a gas diffusion electrolysis flow cell according to claim 1, wherein the molecular catalyst having copper atoms is supported on the conductive carbon material.

3. A gas diffusion electrolysis flow cell comprising: an anode electrode to which an anode solution is supplied; a cathode electrode to which carbon monoxide gas is supplied; and an ion-conductive polymer membrane sandwiched between the anode electrode and the cathode electrode, 3. A gas diffusion electrolysis flow cell, wherein the cathode electrode is a cathode electrode for a gas diffusion electrolysis flow cell according to claim 1 or 2.

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