Method for manufacturing an electrode catalyst for carbon dioxide electrolysis and method for manufacturing an electrolytic apparatus

Abstract

The present invention provides a method for producing an electrode catalyst for carbon dioxide electrolysis that can reduce carbon dioxide to produce a product containing at least one of carbon monoxide and hydrocarbons. [Solution] A method for producing an electrode catalyst for carbon dioxide electrolysis includes the steps of: coordinating a ligand containing at least one selected from the group consisting of 4,4'-dinonyl-2,2'-bipyridine, 4,7-dimethyl-1,10-phenanthroline, 4,4'-dimethyl-2,2'-bipyridine, 6,6'-dimethyl-2,2'-bipyridine, 6,6'-diamino-2,2'-bipyridine, 4,4'-di-tert-butyl-2,2'-bipyridine, and 2,2'-bipyridine-6,6'-dicarboxylic acid to a central metal to produce a metal complex; supporting the metal complex on a support to produce a metal complex support; and heating the metal complex support at a temperature of 500K to 1000K.

Description

[Technical Field]

[0001] This disclosure relates to a method for producing an electrode catalyst for carbon dioxide electrolysis and a method for producing an electrolytic apparatus. [Background technology]

[0002] Carbon dioxide is a major concern as a cause of global warming, and efforts to reduce carbon dioxide emissions are gaining momentum worldwide. One known method for reducing carbon dioxide emissions into the atmosphere and effectively utilizing it is to use electricity derived from renewable energy sources to electrolyze carbon dioxide and water into reduction products such as carbon monoxide and oxygen, and then recycle them.

[0003] Patent Document 1 discloses a carbon dioxide reduction apparatus comprising an anode that oxidizes water to produce oxygen and a cathode that reduces carbon dioxide to produce carbon dioxide reduction products. The cathode is disclosed to contain a metal complex catalyst having a diimine ligand to which an electron-withdrawing substituent has been introduced. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-76331 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, it is desirable to further reduce carbon dioxide to produce at least one of carbon monoxide and hydrocarbons.

[0006] The present disclosure aims to provide a method for producing an electrolytic electrode catalyst for carbon dioxide electrolysis and a method for producing an electrolytic apparatus that can reduce carbon dioxide to produce a product containing at least one of carbon monoxide and hydrocarbons. [Means for solving the problem]

[0007] The method for manufacturing an electrode catalyst for carbon dioxide electrolysis according to the present disclosure includes a step of coordinating a ligand containing at least one selected from the group consisting of 4,4'-dinonyl-2,2'-bipyridine, 4,7-dimethyl-1,10-phenanthroline, 4,4'-dimethyl-2,2'-bipyridine, 6,6'-dimethyl-2,2'-bipyridine, 6,6'-diamino-2,2'-bipyridine, 4,4'-di-tert-butyl-2,2'-bipyridine, and 2,2'-bipyridine-6,6'-dicarboxylic acid to a central metal to form a metal complex. The above method includes a step of supporting the metal complex on a carrier to form a metal complex-supported carrier, and a step of heating the metal complex-supported carrier at 500 K or higher and 1000 K or lower.

[0008] The central metal may contain iron, cobalt, nickel, or copper.

[0009] The temperature for heating the metal complex-supported carrier may be 623 K or higher and 673 K or lower.

[0010] The supported amount of the central metal in the electrode catalyst for carbon dioxide electrolysis may be 0.5 wt% or higher and 10 wt% or lower.

[0011] The ligand may contain 4,4'-dinonyl-2,2'-bipyridine.

[0012] The ligand contains 4,4'-dinonyl-2,2'-bipyridine, and the central metal may contain cobalt.

[0013] The ligand contains 4,4'-dinonyl-2,2'-bipyridine, and the central metal may contain iron.

[0014] In the method for manufacturing an electrolysis device according to the present disclosure, the electrolysis device includes a cathode including an electrode catalyst for carbon dioxide electrolysis manufactured by the method for manufacturing an electrode catalyst for carbon dioxide electrolysis and reducing carbon dioxide. The electrolysis device includes an anode that oxidizes water to generate oxygen, and an electrolyte membrane disposed between the cathode and the anode. [Effects of the Invention]

[0015] According to this disclosure, it is possible to provide a method for producing an electrode catalyst for carbon dioxide electrolysis and a method for producing an electrolytic apparatus that can reduce carbon dioxide to produce a product containing at least one of carbon monoxide and hydrocarbons. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram showing an electrolytic apparatus according to one embodiment. [Figure 2] This figure shows a list of ligands used in the experimental examples. [Figure 3] This is a schematic diagram showing the electrolytic apparatus used in the experimental example. [Figure 4] This graph shows the reaction rate r and Faraday efficiency FE when complexes with different ligand types are used as cathode catalysts. [Figure 5] This graph shows the relationship between the heat treatment temperature and electrolytic properties of 1 wt% Co-dnbpy / KB(TK). [Figure 6] This graph shows the relationship between heat treatment temperature, cathode potential, and electrolytic characteristics when using a proton exchange membrane (PEM) with a viscosity of 1 wt% Co-dnbpy / KB(TK). [Figure 7] This graph shows the relationship between the central metal species and the electrolytic properties of 1 wt% M-dnbpy / KB (623K). [Figure 8] This graph shows the relationship between the heat treatment temperature and electrolytic properties of 1 wt% Fe-dnbpy / KB(TK). [Figure 9] This graph shows the relationship between heat treatment temperature, terminal voltage, and electrolytic characteristics for 1 wt% Fe-dnbpy / KB(TK). [Figure 10] This graph shows the relationship between the central metal type, terminal voltage, and electrolytic characteristics of 1wt%M-dnbpy / KB(623K). [Figure 11]This graph shows the relationship between terminal voltage and electrolytic characteristics for 1wt%Fe-dnbpy / KB(673K) and 1wt%Fe-4,4'-dmbpy / KB(673K). [Figure 12] This graph shows the relationship between the amount of iron supported in Xwt%Fe-dnbpy / KB(673K) and its electrolytic properties. [Figure 13] This graph shows the relationship between the electrolyte type, terminal voltage, and electrolytic characteristics for 1 wt% Fe-dnbpy / KB (623K). [Modes for carrying out the invention]

[0017] Several exemplary embodiments will be described below with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0018] [Method for manufacturing electrode catalysts for carbon dioxide electrolysis] The method for producing an electrode catalyst for carbon dioxide electrolysis according to this embodiment includes a metal complex formation step, a metal complex support formation step, and a metal complex support heating step. The electrode catalyst is used for the electrolysis of carbon dioxide.

[0019] (Metal complex formation process) In the process of forming a metal complex, ligands are coordinated to a central metal to create the metal complex. The metal complex contains a central metal and ligands coordinated to the central metal. The central metal may include transition metals. For example, the central metal may include iron, cobalt, nickel, or copper.

[0020] The ligand includes at least one selected from the group consisting of 4,4'-dinonyl-2,2'-bipyridine shown in the following chemical formula (1), 4,7-dimethyl-1,10-phenanthroline shown in the following chemical formula (2), 4,4'-dimethyl-2,2'-bipyridine shown in the following chemical formula (3), 6,6'-dimethyl-2,2'-bipyridine shown in the following chemical formula (4), 6,6'-diamino-2,2'-bipyridine shown in the following chemical formula (5), 4,4'-di-tert-butyl-2,2'-bipyridine shown in the following chemical formula (6), and 2,2'-bipyridine-6,6'-dicarboxylic acid shown in the following chemical formula (7).

[0021] [ka]

[0022] [ka]

[0023] [ka]

[0024] [ka]

[0025] [ka]

[0026] [ka]

[0027] [ka]

[0028] For example, the ligand may contain 4,4'-dinonyl-2,2'-bipyridine. Electrode catalysts for carbon dioxide electrolysis prepared using such ligands exhibit excellent efficiency in the production of carbon monoxide and hydrocarbons.

[0029] Furthermore, the ligand may contain 4,4'-dinonyl-2,2'-bipyridine, and the central metal may contain cobalt. Electrode catalysts for carbon dioxide electrolysis prepared using such ligands and central metals exhibit particularly excellent carbon monoxide production efficiency.

[0030] Furthermore, the ligand may contain 4,4'-dinonyl-2,2'-bipyridine, and the central metal may contain iron. Electrode catalysts for carbon dioxide electrolysis prepared using such ligands exhibit particularly excellent hydrocarbon production efficiency.

[0031] The amount of central metal supported in the electrocatalyst for carbon dioxide electrolysis may be 0.5% by weight or more and 10% by weight or less. By setting the amount of support within the above range, the efficiency of carbon dioxide reduction product generation can be improved. The amount of support may also be 1% by weight or more, 2% by weight or more, 4% by weight or more, or 4.7% by weight or more. Furthermore, the amount of support may be 9% by weight or less, 8% by weight or less, 7% by weight or less, or 6.6% by weight or less. The amount of central metal supported can be calculated according to the following formula (1).

[0032] The amount of central metal supported (weight %) = (weight of central metal) / (weight of central metal) + (weight of ligands) + (weight of carriers) (1)

[0033] The method for preparing the metal complex is not particularly limited, but for example, the metal complex solution may be prepared by dissolving the ligand and the metal salt in a solvent. Alternatively, the metal complex solution may be prepared by mixing a solution of the ligand dissolved in a solvent with a solution of the metal salt dissolved in a solvent. The solvent is not particularly limited, but may contain alcohols such as ethanol. The metal salt is not particularly limited, but may contain nitrates. The ligand and metal salt may be prepared so that the ligand is in an amount of 0.1 equivalent or more, 0.5 equivalent or more, or 0.7 equivalent or more relative to the central metal. Alternatively, the ligand and metal salt may be prepared so that the ligand is in an amount of 10 equivalents or less, 7 equivalents or less, 6 equivalents or less, or 5 equivalents or less relative to the central metal.

[0034] (Metal complex support formation process) In the metal complex support formation process, a metal complex support is produced. In the metal complex support formation process, a metal complex is supported on a carrier to produce a metal complex support. The metal complex support comprises a metal complex and a carrier that supports the metal complex.

[0035] The support may be conductive. The support is not particularly limited, but may include, for example, at least one of carbon and conductive ceramics. The carbon may include at least one selected from the group consisting of Ketjenblack, acetylene black, carbon black, carbon nanotubes, graphene, and fullerene. The conductive ceramic may include at least one selected from the group consisting of titanium oxide and tin oxide. The support may be porous.

[0036] The method for supporting the metal complex on the support is not particularly limited, but for example, the support may be added to the metal complex solution obtained as described above and mixed, and the metal complex may be supported on the support by impregnation. After that, the solvent in the metal complex solution may be removed and dried, for example by evaporation to dryness, to produce a metal complex support in which the metal complex is supported on the support.

[0037] (Metal complex support heating process) In the metal complex support heating step, the metal complex support is heated. In the metal complex support heating step, the metal complex support is heated at a temperature of 500K to 1000K. By heating the metal support at such temperatures, an electrode catalyst for carbon dioxide electrolysis can be produced that can reduce carbon dioxide to produce a product containing at least one of carbon monoxide and hydrocarbons. The electrode catalyst for carbon dioxide electrolysis can be used as a cathode catalyst in an electrolytic device, as described later. The heating temperature for the metal complex support may be 523K or higher, or 573K or higher. The heating temperature for the metal complex support may be 973K or lower, 873K or lower, or 773K or lower. Preferably, the heating temperature for the metal complex support is 623K to 673K. The heating time is not particularly limited and may be, for example, 1 to 10 hours. The number of heating cycles may be one or multiple.

[0038] The electrode catalyst for carbon dioxide electrolysis may be washed with an acidic aqueous solution. Due to the heat treatment described above, metal oxides or metals may be produced as by-products. Therefore, washing the electrode catalyst with an acidic aqueous solution can purify it. The acidic aqueous solution is not particularly limited, but may contain nitric acid, sulfuric acid, or hydrochloric acid.

[0039] A carbon dioxide electrolytic electrode catalyst can reduce carbon dioxide to produce a product containing at least one of carbon monoxide and a hydrocarbon. The hydrocarbon may include at least one selected from the group consisting of methane, ethane, propane, ethylene, and propylene. Furthermore, the carbon dioxide electrolytic electrode catalyst may produce products other than carbon monoxide and hydrocarbons.

[0040] As described above, the method for producing an electrode catalyst for carbon dioxide electrolysis according to this embodiment includes the step of coordinating a ligand, which includes at least one selected from the group consisting of 4,4'-dinonyl-2,2'-bipyridine, 4,7-dimethyl-1,10-phenanthroline, 4,4'-dimethyl-2,2'-bipyridine, 6,6'-dimethyl-2,2'-bipyridine, 6,6'-diamino-2,2'-bipyridine, 4,4'-di-tert-butyl-2,2'-bipyridine, and 2,2'-bipyridine-6,6'-dicarboxylic acid, to a central metal to produce a metal complex. The above production method includes the step of supporting the metal complex on a support to produce a metal complex support, and the step of heating the metal complex support at a temperature of 500K to 1000K.

[0041] The carbon dioxide electrolytic catalyst produced by the method according to this embodiment can reduce carbon dioxide to produce a product containing at least one of carbon monoxide and hydrocarbons.

[0042] [Electrolytic device and method for manufacturing the same] As shown in Figure 1, the electrolytic apparatus 1 according to this embodiment comprises an electrolytic cell 10 and a power supply 20. The electrolytic cell 10 comprises a membrane electrode assembly 11. The membrane electrode assembly 11 comprises a cathode 12, an anode 13, and an electrolyte membrane 14. The power supply 20 is connected to the cathode 12 and the anode 13 and supplies power to the electrolytic cell 10. Although the electrolytic apparatus 1 according to this embodiment comprises a single electrolytic cell 10, it may comprise a plurality of electrolytic cells 10.

[0043] When a proton exchange membrane (PEM) is used as the electrolyte membrane 14, applying a potential to the anode 13 causes the oxidation reaction of water (H2O) to proceed at the anode 13, generating oxygen (O2) and hydrogen ions (H2O), as shown in the following reaction equation (1). + ) and electrons (e - ) is generated. 2H2O → 4H + +O2+4e - (1)

[0044] The hydrogen ions generated on the anode 13 side reach the cathode 12 through the electrolyte membrane 14 that conducts protons. At the cathode 12, a reduction reaction of carbon dioxide (CO2) occurs due to the electrons supplied to the cathode 12 and the hydrogen ions that have moved to the cathode 12. Specifically, as shown in the following reaction formulas (2) to (8), various reduction products and water are generated. By reducing carbon dioxide, reaction formula (2) produces carbon monoxide, reaction formula (3) produces methane, reaction formula (4) produces ethane, reaction formula (5) produces propane, reaction formula (6) produces ethylene, reaction formula (7) produces propylene. Also, as a side reaction, as shown in the following reaction formula (8), a hydrogen generation reaction in which hydrogen ions are directly reduced proceeds. CO2 + 2H + + 2e - → CO + H2O (2) CO2 + 8H + + 8e - → CH4 + 2H2O (3) 2CO2 + 14H + + 14e - → C2H6 + 4H2O (4) 3CO2 + 20H + + 20e - → C3H8 + 6H2O (5) 2CO2 + 12H + + 12e - → C2H4 + 4H2O (6) 3CO2 + 18H + + 18e - → C3H6 + 6H2O (7) 2H + + 2e - → H2 (8)

[0045] When an anion exchange membrane (AEM) is used as the electrolyte membrane 14, the electrons supplied to the cathode 12 and water cause a reduction reaction of carbon dioxide (CO2) at the cathode 12. Specifically, as shown in the following reaction equations (9) to (15), various reduction products and hydroxide ions are produced. The reduction of carbon dioxide produces carbon monoxide (9), methane (10), ethane (11), propane (12), ethylene (13), and propylene (14). In addition, as a side reaction, a hydrogen production reaction proceeds in which water is directly reduced, as shown in the following reaction equation (15). The hydroxide ions produced at the cathode 12 move to the anode 13 side via the electrolyte membrane 14, which conducts anions. CO2 + H2O + 2e - →CO+2OH - (9) CO2 + 6H2O + 8e - →CH4+8OH - (10) 2CO2 + 10H2O + 14e - →C2H6+14OH - (11) 3CO2 + 14H2O + 20e - →C3H8+20OH - (12) 2CO2 + 8H2O + 12e - →C2H4+12OH - (13) 3CO2 + 12H2O + 18e - →C3H6+18OH - (14) 2H2O + 2e - →H2+2OH - (15)

[0046] At anode 13, hydroxide ions (OH) - The oxidation reaction of ) proceeds, and as shown in the following reaction equation (16), oxygen (O2), hydrogen (H2O) and electrons (e - ) is generated. 4OH - →O2+2H2O+4e - (16)

[0047] The cathode 12 is an electrode that reduces carbon dioxide to produce hydrocarbons. Since the cathode 12 is equipped with the cathode catalyst, it can produce a product containing at least one of carbon monoxide and hydrocarbons by reducing carbon dioxide. The cathode 12 may include a gas diffusion layer and a cathode catalyst provided on the gas diffusion layer. The gas diffusion layer is not particularly limited, but may include a carbon porous material. The shape of the cathode 12 is not particularly limited, and may be plate-shaped, mesh-shaped, wire-shaped, particulate, porous, thin-film-shaped, or island-shaped, for example.

[0048] The carbon dioxide reduced by cathode 12 may be in the form of a gas such as CO2 gas, or in the form of a solution containing carbon dioxide. If it is in the form of a solution, it is preferable to use a solution with a high carbon dioxide absorption rate. Examples of such solutions include aqueous solutions of LiHCO3, NaHCO3, KHCO3, CsHCO3, Li2CO3, Na2CO3, K2CO3, and Cs2CO3. Alternatively, a solution containing carbon dioxide may be prepared using alcohols such as methanol, ethanol, and acetone as solvents. It is desirable that the solution containing carbon dioxide is a solution that increases the reduction potential of carbon dioxide, has high ionic conductivity, and contains a carbon dioxide absorbent. An example of such a solution is a solution containing a cation such as an imidazolium ion or a pyridinium ion, and BF4 - or PF6 - Examples of ionic liquids or aqueous solutions thereof that are composed of salts with anions such as ethanolamine and remain in a liquid state over a wide temperature range include ionic liquids or aqueous solutions thereof. Other examples of solutions include amine solutions or aqueous solutions thereof such as ethanolamine, imidazole, and pyridine. The amine may be a primary amine, secondary amine, or tertiary amine.

[0049] Anode 13 is an electrode that oxidizes the water contained in the electrolyte to produce oxygen and hydrogen ions. The electrolyte may be water or an aqueous solution containing an electrolyte. The water may be deionized water or pure water. An aqueous solution containing an electrolyte can accelerate the oxidation reaction of water. The aqueous solution containing an electrolyte may be, for example, an aqueous solution of potassium bicarbonate (KHCO3) or an aqueous solution of potassium hydroxide (KOH).

[0050] Anode 13 may include a known anode catalyst capable of oxidizing water to produce oxygen and hydrogen ions. The anode catalyst may include, for example, metals such as iridium, platinum, palladium, and nickel; alloys or intermetallic compounds containing these metals; binary metal oxides such as iridium oxide, manganese oxide, nickel oxide, cobalt oxide, iron oxide, tin oxide, indium oxide, and ruthenium oxide; ternary metal oxides such as Ni-Co-O, Ni-Fe-O, La-Co-O, Ni-La-O, and Sr-Fe-O; quaternary metal oxides such as Pb-Ru-Ir-O and La-Sr-Co-O; and metal complexes such as Ru complexes or Fe complexes. Anode 13 may include a gas diffusion layer and an anode catalyst provided on the gas diffusion layer. The gas diffusion layer is not particularly limited, but may include a carbon porous body. The shape of anode 13 is not particularly limited and may be, for example, plate-shaped, mesh-shaped, wire-shaped, particulate, porous, thin-film-shaped, or island-shaped.

[0051] The electrolyte membrane 14 is positioned between the cathode 12 and the anode 13. In this embodiment, the electrolyte membrane 14 is in contact with the cathode 12, but the electrolyte membrane 14 may be separated from the cathode 12. Also, in this embodiment, the electrolyte membrane 14 is in contact with the anode 13, but the electrolyte membrane 14 may be separated from the anode 13.

[0052] The electrolyte membrane 14 can transfer ions between the cathode 12 and the anode 13. The electrolyte membrane 14 may be an anion exchange membrane (AEM) or a proton exchange membrane (PEM).

[0053] As described above, the electrolytic apparatus 1 is manufactured by a method for producing an electrode catalyst for carbon dioxide electrolysis and includes a cathode 12 containing an electrode catalyst for carbon dioxide electrolysis that reduces carbon dioxide. The electrolytic apparatus 1 also includes an anode 13 that oxidizes water to produce oxygen and an electrolyte membrane 14 disposed between the cathode 12 and the anode 13.

[0054] Since the electrolytic apparatus 1 manufactured by the method according to this embodiment contains the above-mentioned electrode catalyst for carbon dioxide electrolysis, it can reduce carbon dioxide to produce a product containing at least one of carbon monoxide and hydrocarbons. [Examples]

[0055] The embodiment will be described in more detail below with reference to experimental examples, but the embodiment is not limited to these examples.

[0056] [Experimental Example 1] The electrolytic properties of a cathode catalyst using the ligand L shown in Figure 2 were evaluated. 2,2'-bipyridine (2,2'-bpy) 4,4'-bipyridine (4,4'-bpy) 2,2':6',2''-terpyridine (tpy) 2,2'-biquinoline 1,10-Phenanthroline (phen) 4,7-dimethyl-1,10-phenanthroline (Me2phen) 4,4'-dimethyl-2,2'-bipyridine (4,4'-dmbpy) 5,5'-dimethyl-2,2'-bipyridine (5,5'-dmbpy) 6,6'-dimethyl-2,2'-bipyridine (6,6'-bmbpy) 4,4'-diamino-2,2'-bipyridine (4,4'-dabpy) 6,6'-diamino-2,2'-bipyridine (6,6'dabpy) 4,4'-di-tert-butyl-2,2'-bipyridine (d t Bubpy) 4,4'-Dinonyl-2,2'-Bipyridine (dnbpy) 4,4'-Bis(hydroxymethyl)-2,2'-bipyridine (dhmbpy) 2,2'-bipyridine-6,6'-dicarboxylic acid (bpydc) 2,2'-biimidazole (biim)

[0057] (Preparation of 1 wt% Co-dnbpy / KB (573K)) A 1 wt% Co-dnbpy / KB (573K) solution was prepared such that the Co load was 1 wt% and the ligand dnbpy was 5 equivalents relative to the Co. Specifically, 50 mL of ethanol and 69.35 mg of dnbpy were placed in a 100 mL beaker and stirred with a stirrer for 20 minutes to completely dissolve the dnbpy in the ethanol. Next, 850 μL of a 40 mM Co(NO3)2 / EtOH solution was added to the dnbpy solution and stirred for 15 minutes to prepare a Co-dnbpy solution. Then, 124.4 mg of the support KB (Ketjenbrak) was added to the Co-dnbpy solution and stirred while heating on a hot stirrer. When the solvent evaporated and the solution became viscous, the stirrer was stopped and the mixture was stirred manually. Once the solution dried and became powdery, the powder was dried overnight on a 70°C hot plate to obtain a 1 wt% Co-dnbpy / KB metal complex support. Subsequently, the metal complex support powder was heated under argon flow at 25 K / min, then heat-treated at 423 K for 1 hour and 573 K for 3 hours. In this way, a cathode catalyst of 1 wt% Co-dnbpy / KB (573 K) was prepared by supporting 1 wt% Co-dnbpy on KB.

[0058] (Preparation of 1 wt% Co-L / KB (573K)) Similar to the 1 wt% Co-dnbpy / KB (573K) cathode catalyst, a 1 wt% Co-L / KB (573K) cathode catalyst was prepared such that the Co loading amount was 1 wt% and the ligand L amounted to 5 equivalents relative to the Co.

[0059] (Acid treatment of the cathode catalyst) 50 mL of HCl or H2SO4 was placed in a 100 mL beaker, and 50 mg of the cathode catalyst prepared as described above was added. The mixture was ultrasonically stirred for 1 minute, and then stirred at room temperature using a stirrer and a stirring bar. This was filtered by suction using a hydrophilic membrane filter with a pore size of 0.1 μm, and the filtrate was washed several times with 20 mL of deionized water until the pH of the filtrate was 6-7. After that, the filtrate was washed three times with 20 mL of 2-propanol. The filtrate was placed in a vial and dried under reduced pressure at 353 K for at least 1 hour to prepare an acid-treated cathode catalyst.

[0060] (Cathode fabrication) A cathode catalyst ink was prepared by stirring an acid-treated cathode catalyst, 1-propanol, and an ionomer (Sustanion® XA-9, manufactured by Dioxide Materials) by ultrasonic irradiation. The ink was then applied to a 2cm layer on the surface of a gas diffusion layer (SIGRACET® GDL36BB, manufactured by sgl carbon). 2 A cathode catalyst ink was applied to the region and dried under reduced pressure. A container containing a 1M KOH aqueous solution was prepared, and the vacuum-dried material was placed in the container so that the side coated with the catalyst ink was in contact with the KOH aqueous solution and treated with KOH.

[0061] (Preparation of anode catalyst) First, an iridium chloride aqueous solution equivalent to 60 mg of iridium was diluted with deionized water to a total volume of 60 mL. Then, 240 mg of Ketjenblack support was added to the iridium chloride aqueous solution and impregnated. The resulting powder was placed on a hot plate and dried in air at 343 K for 16 hours. This powder was then placed in a flat-bottomed quartz reactor and heated in an electric furnace at 25 K / min while flowing hydrogen at 20 mL / min, followed by hydrogen reduction treatment at 423 K for 1 hour, and then at 573 K for 2 hours to prepare the anode catalyst.

[0062] (Anode preparation) The anode catalyst prepared as described above, along with 1-propanol and ionomer (Sustanion® XA-9, manufactured by Dioxide Materials), was stirred by ultrasonic irradiation to prepare an anode catalyst ink. A 2cm layer of the gas diffusion layer (SIGRACET® GDL36BB, manufactured by sgl carbon) was then applied to the surface. 2 The region was coated with an anode catalyst ink and dried under reduced pressure. A container containing a 1M KOH aqueous solution was prepared, and the vacuum-dried material was placed in the container so that the side coated with the catalyst ink was in contact with the KOH aqueous solution, and the added ionomer was replaced.

[0063] A membrane electrode assembly was fabricated by sandwiching an electrolyte membrane of AEM (Sustanion® X-37, manufactured by Dioxide Materials, Inc.) so that the cathode catalyst and anode catalyst were in contact with each other.

[0064] (Creation of evaluation cells) To evaluate the electrolytic properties, an electrolytic apparatus 1 as shown in Figure 3 was fabricated. The electrolytic apparatus 1 comprises an electrolytic cell 10 and a potentiostat which is a power supply 20. The electrolytic apparatus 1 comprises a membrane electrode assembly 11 which includes a cathode 12, an anode 13, and an electrolyte membrane 14. The cathode 12 is housed in a cathode chamber 15, and the anode 13 is housed in an anode chamber 16. CO2 gas was circulated through the cathode chamber 15 at a rate of 10 mL / min. A 0.1 M KHCO3 electrolyte was contained in the anode chamber 16, and argon gas was circulated through the electrolyte at a rate of 20 mL / min. Then, in order to perform the carbon dioxide electrolysis reaction, a constant potential electrolysis experiment was conducted by controlling the potential of the cathode 12 with a potentiostat (Hokuto Denko Co., Ltd., HZ5000) so that the terminal voltage was 2.8 V. The electrolysis temperature was 298 K, and the electrolysis time was 30 minutes.

[0065] (Evaluation of electrolytic properties) The gas produced by reducing CO2 was introduced into a gas chromatograph (GC-8A, manufactured by Shimadzu Corporation) and subjected to quantitative analysis.

[0066] For quantitative analysis of CO, 1.0 mL of the outlet gas from the cathode chamber was collected using a gas-tight syringe and injected into a gas chromatograph for analysis. The analytical conditions for the gas chromatograph were as follows. Detector: TCD (Thermal Conductivity Detector) Column: MS-5A Gas inlet / detector temperature: 210℃ Analysis temperature: 90℃~110℃ Carrier gas: Helium (40 sccm)

[0067] The CO reaction rate r(CO)[μmol / h / cm²] is calculated from the CO concentration obtained by gas chromatography, taking into account the CO2 gas supply rate and electrode area. 2 The following formula (2) was used to calculate the CO generation current density I based on the CO reaction rate r(CO). CO The following was calculated. As can be seen from reaction equation (2) (or reaction equation (9) if AEM is used, as described later), the reduction from CO2 to CO is a two-electron reaction, so the number of reaction electrons in equation (2) below was set to 2.

[0068] I CO [mA / cm 2 ]=r(CO)[μmol / h / cm 2 ] × 96485 [C / mol] × (number of reaction electrons) × 1 / 3600 [s / h] (2)

[0069] The Faraday efficiency FE(CO) of CO production is given by the CO production current density I CO and total current density I d [mA / cm 2 The following formula (3) was used to calculate the Faraday efficiency. The Faraday efficiency is the ratio of the partial current that contributed to the generation of each substance to the total current.

[0070] FE(CO)[%]=I CO / I d ×100 (3)

[0071] For the quantitative analysis of H2, 0.40 mL of the outlet gas from the cathode chamber was collected using a gas-tight syringe and injected into a gas chromatograph for analysis. The analytical conditions for the gas chromatograph were as follows. Detector: TCD (Thermal Conductivity Detector) Column: Active carbon (φ2.0mm × 2.5m) Gas inlet / detector temperature: 150℃ Analysis temperature: 100℃ Carrier gas: Argon (45 sccm)

[0072] Then, from the H2 concentration obtained by gas chromatography analysis, the H2 reaction rate r(H2) [μmol / h / cm²] can be calculated, similar to the case of CO. 2 The Faraday efficiency FE(H2) was calculated.

[0073] Figure 4 is a graph showing the reaction rate r and Faraday efficiency FE when complexes with different ligand types are used as cathode catalysts. As shown in Figure 4, it was found that dnbpy, Me2phen, 4,4'-dmbpy, 6,6'-dmbpy, 6,6'dabpy, dtBubpy, and bpydc exhibited superior carbon monoxide production activity compared to other ligands. In particular, among these, dnbpy showed the highest carbon monoxide production activity compared to the other ligands.

[0074] [Experimental Example 2] Next, to investigate the relationship between heat treatment temperature and electrolytic properties, several cathode catalysts of 1wt%Co-dnbpy / KB(TK) (where T represents the heat treatment temperature) with different heat treatment temperatures were prepared. Specifically, 1wt%Co-dnbpy / KB(TK) cathode catalysts were prepared in the same manner as in Experimental Example 1, except that the heat treatment temperature of 573K was changed to a predetermined heat treatment temperature, and the electrolytic properties were evaluated.

[0075] Figure 5 is a graph showing the relationship between the heat treatment temperature and electrolytic properties of 1 wt% Co-dnbpy / KB(TK). As shown in Figure 5, catalysts with a heat treatment temperature of 500 K or higher had a higher carbon monoxide generation efficiency compared to catalysts with a heat treatment temperature of less than 500 K. Furthermore, cathode catalysts with a heat treatment temperature of 623 K to 673 K showed particularly high carbon monoxide generation activity. These results indicate that it is possible to improve the carbon monoxide generation activity of cathode catalysts by heating the metal complex support at 500 K or higher.

[0076] [Experimental Example 3] Next, the relationship between the electrolyte membrane and the electrolytic properties was investigated. Specifically, a PEM (DuPont, Nafion 117) was used as the electrolyte membrane instead of an AEM. The membrane electrode assembly was fabricated by sandwiching the electrolyte membrane so that the cathode catalyst and anode catalyst were in contact with each other, and hot-pressing it at 413K and 30MPa for 10 minutes. After that, the membrane electrode assembly was immersed in the electrolyte solution for 5 minutes to allow sufficient electrolyte solution to be absorbed by the electrolyte membrane. Pure water was used as the electrolyte solution. The heat treatment temperatures were set to 623K, 673K, and 723K. An Ag / AgCl electrode (Toa DKK Co., Ltd., +0.199V vs. SHE) was used as the reference electrode. The electrolyte membrane 14 and the reference electrode were immersed in 0.5M sulfuric acid. A saturated KCl solution was used for the liquid junction of the reference electrode. Furthermore, the electrolytic reaction was carried out by changing the cathode potential from -0.4V to -0.8V. Except for the above, the electrolytic properties were evaluated in the same manner as in Experimental Example 1.

[0077] Figure 6 is a graph showing the relationship between heat treatment temperature, cathode potential, and electrolytic characteristics for 1 wt% Co-dnbpy / KB(TK) when PEM is used as the electrolyte membrane. As shown in Figure 6, it was confirmed that CO can be generated by electrolysis when PEM is used as the electrolyte membrane, similar to AEM.

[0078] [Experimental Example 4] Next, the formation of hydrocarbons when electrolysis was carried out using a cathode catalyst was investigated. Specifically, the heat treatment temperature was changed to 623K, the central metal was changed to Fe, Ni, and Cu in addition to Co, and the terminal voltage was set to 2.4V. Except for the above, a cathode catalyst of 1 wt% M-dnbpy / KB (623K) (where M represents the central metal) was prepared in the same manner as in Experimental Example 1, and its electrolytic properties were evaluated. For reference, the preparation method for 1 wt% Fe-dnbpy / KB (623K) is shown below. For Ni and Cu, 1 wt% M-dnbpy / KB (623K) was prepared so that the amount of central metal supported was 1 wt% and the ligand dnbpy was 5 equivalents relative to Ni or Cu.

[0079] (Preparation of 1 wt% Fe-dnbpy / KB (623K)) First, 50 mL of ethanol and 73.17 mg of dnbpy were placed in a 100 mL beaker and stirred with a stirrer for at least 20 minutes to completely dissolve the dnbpy in the ethanol. Next, Fe(NO3)3 / EtOH with an Fe content equivalent to 2 mg was added to the dnbpy solution and heated and stirred on a hot plate for at least 2 hours to prepare Fe-dnbpy. During this time, a watch glass was placed over the opening of the beaker to prevent the solvent from evaporating. After that, 124.8 mg of KB (Ketjenbrak: carbon ECP, manufactured by Lion Specialty Chemicals Co., Ltd.), which is the support material, was added to the Fe-dnbpy solution and stirred while heating on a hot stirrer. When the solvent evaporated and the solution became viscous, the stirrer was stopped and the mixture was stirred manually. Once the solution dried and became powdery, the powder was dried overnight on a 70°C hot plate to obtain a 1 wt% Fe-dnbpy / KB metal complex support. Subsequently, the metal complex support powder was heated under argon flow at 25 K / min, then heat-treated at 423 K for 1 hour and 623 K for 3 hours. In this way, 1 wt% Fe-dnbpy / KB (623 K) was prepared.

[0080] For quantitative analysis of hydrocarbons, 2.0 mL of the outlet gas from the cathode chamber was collected using a gas-tight syringe and injected into a gas chromatograph for analysis. The analytical conditions for the gas chromatograph were as follows.

[0081] Detector: FID (Flame Ionization Detector) Columns: PorapakQ and PoraPLOT Q Gas inlet / detector temperature: 180℃~210℃ Carrier gas: Nitrogen (40 sccm)

[0082] The reaction rates and Faraday efficiency of hydrocarbons were calculated using the values ​​shown in reaction equations (3) to (7) above (or reaction equations (10) to (14) when AEM is used, as described later) as the number of reaction electrons, and according to equations (2) and (3) above.

[0083] Figure 7 is a graph showing the relationship between the central metal species and the electrolytic characteristics of 1wt%M-dnbpy / KB(623K). As shown in Figure 7, when using a 1wt%Fe-dnbpy / KB(623K) cathode catalyst, hydrocarbons were confirmed to be generated even at a low terminal voltage of 2.4V.

[0084] [Experimental Example 5] Next, the relationship between the heat treatment temperature and electrolytic properties of 1wt%Fe-dnbpy / KB was investigated. Specifically, a cathode catalyst of 1wt%Fe-dnbpy / KB(TK) was prepared in the same manner as in Experimental Example 4, except that the heat treatment temperature of 623K was changed to a predetermined temperature and the terminal voltage was changed to 2.8V, and the electrolytic properties were evaluated.

[0085] Figure 8 is a graph showing the relationship between the heat treatment temperature and the electrolytic properties of 1 wt% Fe-dnbpy / KB(TK). As shown in Figure 8, it was found that the hydrocarbon production efficiency is high when a cathode catalyst with a heat treatment temperature of 623K to 873K is used.

[0086] [Experimental Example 6] Next, the relationship between the heat treatment temperature, terminal voltage, and electrolytic properties of 1wt%Fe-dnbpy / KB was investigated. Specifically, cathode catalysts of 1wt%Fe-dnbpy / KB(TK) were prepared in the same manner as in Experimental Example 5, except that the heat treatment temperatures of 1wt%Fe-dnbpy / KB(TK) were set to 298K, 623K, and 673K, and the electrolytic properties were evaluated.

[0087] Figure 9 is a graph showing the relationship between heat treatment temperature, terminal voltage, and electrolytic characteristics for 1 wt% Fe-dnbpy / KB(TK). As shown in Figure 9, it was found that the hydrocarbon production efficiency is high when a cathode catalyst with a heat treatment temperature of 623K to 673K ​​is used.

[0088] [Experimental Example 7] Next, the relationship between the terminal voltage and electrolytic characteristics of 1 wt% M-dnbpy / KB (623K) was investigated. Specifically, as in Experimental Example 5, cathode catalysts with Fe, Co, Ni, and Cu as the central metal were prepared and their electrolytic characteristics were evaluated.

[0089] Figure 10 is a graph showing the relationship between the central metal species, terminal voltage, and electrolytic characteristics of 1wt%M-dnbpy / KB(623K). As shown in Figure 10, when 1wt%Co-dnbpy / KB(623K) was used as the cathode catalyst, carbon monoxide was confirmed to be produced. Furthermore, when 1wt%Fe-dnbpy / KB(623K), 1wt%Ni-dnbpy / KB(623K), and 1wt%Cu-dnbpy / KB(623K) were used as cathode catalysts, hydrocarbons were confirmed to be produced.

[0090] [Experimental Example 8] Next, the electrolytic properties of 1wt%Fe-dnbpy / KB(673K) and 1wt%Fe-4,4'-dmbpy / KB(673K) were evaluated. Specifically, a cathode catalyst of 1wt%Fe-dnbpy / KB(673K) was prepared and its electrolytic properties were evaluated, similar to Experimental Example 5. In addition, a cathode catalyst of 1wt%Fe-4,4'-dmbpy / KB(673K) was prepared and its electrolytic properties were evaluated, similar to Experimental Example 5, except that the ligand was changed from dnbpy to 4,4'-dmbpy.

[0091] Figure 11 is a graph showing the relationship between terminal voltage and electrolytic characteristics for 1wt%Fe-dnbpy / KB(673K) and 1wt%Fe-4,4'-dmbpy / KB(673K). As shown in Figure 11, it was confirmed that hydrocarbons are generated by electrolysis not only when 1wt%Fe-dnbpy / KB(673K) is used, but also when 1wt%Fe-4,4'-dmbpy / KB(673K) is used as the cathode catalyst.

[0092] [Experimental Example 9] Next, the relationship between the amount of iron loaded and the electrolytic properties was investigated. Specifically, the amount of iron loaded was changed to 0.6 wt%, 1.2 wt%, 2.4 wt%, 4.7 wt%, 6.6 wt%, and 9.0 wt%. In addition, PEM (DuPont, Nafion 117) was used as the electrolyte membrane instead of AEM. The membrane electrode assembly was fabricated by sandwiching the electrolyte membrane so that the cathode catalyst and anode catalyst were in contact with each other, and hot-pressing at 413K and 30MPa for 10 minutes. After that, the membrane electrode assembly was immersed in the electrolyte solution for 5 minutes to allow sufficient electrolyte solution to be absorbed by the electrolyte membrane. Pure water was used as the electrolyte solution. An Ag / AgCl electrode (Toa DKK Co., Ltd., +0.199V vs. SHE) was used as the reference electrode. The electrolyte membrane 14 and the reference electrode were immersed in 0.5M sulfuric acid. A saturated KCl solution was used for the liquid junction of the reference electrode. Except as described above, a cathode catalyst of Xwt%Fe-dnbpy / KB(673K) (where X represents the amount of iron supported) was prepared in the same manner as in Experimental Example 5. The cathode catalyst was prepared using the formulations shown in Table 1. Furthermore, the electrolytic reaction was carried out with the cathode potential changed to -0.7V, and the electrolytic characteristics were evaluated.

[0093] [Table 1]

[0094] Figure 12 is a graph showing the relationship between the amount of iron supported in Xwt%Fe-dnbpy / KB(673K) and its electrolytic properties. As shown in Figure 12, it was confirmed that hydrocarbon production activity was excellent when the amount of iron supported was between 0.5% and 10% by weight. Furthermore, it was confirmed that cathode catalysts with an iron support of 4.7% to 6.6% by weight exhibited particularly high hydrocarbon production activity.

[0095] [Experimental Example 10] Next, the electrolytic properties were evaluated when 0.1 M KHCO3 (pH 9-10) and 1 M KOH (pH 14) were used as electrolytes. Specifically, a cathode catalyst of 1 wt% Fe-dnbpy / KB (623 K) was prepared in the same manner as in Experimental Example 4. Then, an electrolytic apparatus with 0.1 M KHCO3 as the electrolyte was prepared in the same manner as in Experimental Example 4. In addition, an electrolytic apparatus was prepared in which 0.1 M KHCO3 was replaced with 1 M KOH. The electrolytic properties of these electrolytic apparatuses were then evaluated.

[0096] Figure 13 is a graph showing the relationship between the electrolyte type, terminal voltage, and electrolytic characteristics for 1 wt% Fe-dnbpy / KB (623K). As shown in Figure 13, it was confirmed that carbon monoxide can be generated regardless of whether 0.1 M KHCO3 or 1 M KOH is used as the electrolyte.

[0097] Although several embodiments have been described, it is possible to modify or transform the embodiments based on the above disclosure. All components of the above embodiments, and all features described in the claims, may be taken individually and combined, provided that they do not conflict with each other.

[0098] This disclosure can contribute, for example, to United Nations Sustainable Development Goal (SDG) 13, "Take urgent action to combat climate change and its impacts." [Explanation of symbols]

[0099] 1 Electrolyzer 12 Cathode 13 Anodes 14 Electrolyte membrane

Claims

1. A step of producing a metal complex by coordinating a ligand containing at least one selected from the group consisting of 4,4'-dinonyl-2,2'-bipyridine, 4,7-dimethyl-1,10-phenanthroline, 4,4'-dimethyl-2,2'-bipyridine, 6,6'-dimethyl-2,2'-bipyridine, 6,6'-diamino-2,2'-bipyridine, 4,4'-di-tert-butyl-2,2'-bipyridine, and 2,2'-bipyridine-6,6'-dicarboxylic acid to a central metal, A step of supporting the metal complex on a carrier to produce a metal complex carrier, A step of heating the metal complex support at a temperature of 500K to 1000K, A method for producing an electrode catalyst for carbon dioxide electrolysis, including the above.

2. The method for producing an electrode catalyst for carbon dioxide electrolysis according to claim 1, wherein the central metal includes iron, cobalt, nickel, or copper.

3. The method for producing an electrode catalyst for carbon dioxide electrolysis according to claim 1 or 2, wherein the temperature at which the metal complex support is heated is 623K or higher and 673K ​​or lower.

4. A method for producing a carbon dioxide electrolytic electrode catalyst according to claim 1 or 2, wherein the amount of the central metal supported in the carbon dioxide electrolytic electrode catalyst is 0.5% by weight or more and 10% by weight or less.

5. The method for producing an electrode catalyst for carbon dioxide electrolysis according to claim 1 or 2, wherein the ligand comprises 4,4'-dinonyl-2,2'-bipyridine.

6. The method for producing an electrode catalyst for carbon dioxide electrolysis according to claim 1 or 2, wherein the ligand comprises 4,4'-dinonyl-2,2'-bipyridine and the central metal comprises cobalt.

7. A method for producing an electrode catalyst for carbon dioxide electrolysis according to claim 1 or 2, wherein the ligand comprises 4,4'-dinonyl-2,2'-bipyridine and the central metal comprises iron.

8. A method for manufacturing an electrolytic device, The electrolytic device is A cathode comprising a carbon dioxide electrolytic electrode catalyst that reduces carbon dioxide, manufactured by the method for producing a carbon dioxide electrolytic electrode catalyst according to claim 1 or 2, The anode oxidizes water to produce oxygen, An electrolyte membrane disposed between the cathode and the anode, A method for manufacturing an electrolytic device, comprising the following:

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