Catalyst, membrane electrode assembly, electrolytic cell, electrolytic device, and method for producing catalyst

Abstract

To provide a catalyst, a membrane electrode assembly, an electrolytic cell, an electrolytic device, and a method for producing the catalyst, for synthesizing hydrocarbons by electrolysis of carbon dioxide.SOLUTION: A catalyst used for electrolysis of carbon dioxide comprises: a carrier; a nitrogen-containing heteroaromatic ring compound containing poly(4-vinylpyridine) or a specific compound, which is supported on the carrier; cobalt ions coordinated with nitrogen atoms on the heteroaromatic ring of the nitrogen-containing heteroaromatic ring compound; and at least one compound supported on the carrier selected from the group consisting of iron phthalocyanine, iron tetraphenylporphyrin chloride, and cobalt phthalocyanine.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a catalyst, a membrane electrode assembly, an electrolysis cell, an electrolysis device, and a method for producing a catalyst. [Background technology]

[0002] Carbon dioxide is considered a problematic cause of global warming, and efforts to curb carbon dioxide emissions are gaining momentum worldwide. As a method for reducing carbon dioxide emissions into the atmosphere and effectively utilizing carbon dioxide, a method is known in which carbon dioxide and water are electrolyzed using electricity derived from renewable energy to produce reduction products such as carbon monoxide and oxygen, and then recycled for reuse.

[0003] Conventionally, electrochemical reduction of carbon dioxide has been carried out using a cathode catalyst such as copper oxide or silver in an alkaline environment. Although there are many options for catalyst materials in an alkaline environment, there is a problem that carbon dioxide dissolves in the alkali and generates carbonates as impurities. Meanwhile, Patent Document 1 proposes a method of electrochemically reducing carbon dioxide using a cobalt complex catalyst and a proton exchange membrane in an acidic environment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-138994 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the catalysts that can be used in an acidic environment are limited, and the selectivity of the reduction products is limited to carbon monoxide and hydrogen. Therefore, it has been an issue to synthesize hydrocarbons that can be used as fuels or chemical raw materials by electrolysis of carbon dioxide.

[0006] The present disclosure aims to provide a catalyst, a membrane electrode assembly, an electrolysis cell, an electrolysis device, and a method for producing the catalyst for synthesizing hydrocarbons by electrolysis of carbon dioxide. [Means for solving the problem]

[0007] The catalyst according to the present disclosure is a catalyst for use in the electrolysis of carbon dioxide, comprising a support and poly(4-vinylpyridine) or a catalyst represented by the general formula (1) supported on the support. [ka] (In the general formula (1), R1 is H or an alkyl group.) the nitrogen-containing heteroaromatic ring compound containing a compound represented by the formula (I), a cobalt ion coordinated with a nitrogen atom on the heteroaromatic ring of the nitrogen-containing heteroaromatic ring compound, and at least one compound selected from the group consisting of iron phthalocyanine, iron tetraphenylporphyrin chloride, and cobalt phthalocyanine, which is supported on a carrier.

[0008] The membrane electrode assembly according to the present disclosure may include an anode that oxidizes water to produce oxygen, a cathode equipped with a catalyst that reduces carbon dioxide to produce a product including a hydrocarbon, and an electrolyte membrane sandwiched between the anode and the cathode.

[0009] The electrolyte membrane may be a proton exchange membrane.

[0010] The hydrocarbon may include at least one selected from the group consisting of methane, ethane, propane, ethylene and propylene.

[0011] The electrolysis cell according to the present disclosure may comprise a membrane electrode assembly.

[0012] The electrolysis device according to the present disclosure may include an electrolysis cell.

[0013] The method for producing a catalyst according to the present disclosure is a method for producing a catalyst used in the electrolysis of carbon dioxide, and includes a step of calcining a poly(4-vinylpyridine)-cobalt complex on a support to support the complex on the support, and then supporting at least one compound selected from the group consisting of iron phthalocyanine, iron tetraphenylporphyrin chloride, and cobalt phthalocyanine on the support. Effect of the Invention

[0014] According to the present disclosure, it is possible to provide a catalyst, a membrane electrode assembly, an electrolysis cell, an electrolysis device, and a method for producing a catalyst for synthesizing hydrocarbons by electrolysis of carbon dioxide. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing the principle of electrochemical reduction of carbon dioxide. [Diagram 2] FIG. 1 is a schematic diagram of an experimental device for evaluating electrolysis characteristics, showing an example of an electrolysis cell. [Diagram 3] 1 is a schematic diagram showing a procedure for producing an electrode. [Figure 4] FIG. 2 is a schematic diagram showing a membrane electrode assembly. [Diagram 5] FIG. 1 is a schematic diagram showing the configuration of an electrolysis cell. [Figure 6] FIG. 1 is a schematic diagram showing components of an electrolysis cell. [Figure 7] FIG. 2 is a schematic diagram showing a method for fixing a membrane electrode assembly to an electrolysis cell. [Figure 8] 1 is a graph showing the electrolysis characteristics of carbon dioxide using a composite catalyst using iron phthalocyanine or iron tetraphenylporphyrin chloride. [Figure 9] 1 is a graph showing the electrolysis characteristics of carbon dioxide using a composite catalyst using iron phthalocyanine or cobalt phthalocyanine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, some exemplary embodiments will be described with reference to the drawings. Note that the dimensional ratios of the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios.

[0017] (catalyst) The catalyst according to this embodiment is a catalyst used in the electrolysis of carbon dioxide. The catalyst includes a support, a nitrogen-containing heteroaromatic ring compound, which is supported on the support and includes poly(4-vinylpyridine) or a compound represented by the above general formula (1), and a cobalt ion coordinated with a nitrogen atom on the heteroaromatic ring of the nitrogen-containing heteroaromatic ring compound. The catalyst further includes at least one compound selected from the group consisting of iron phthalocyanine, iron tetraphenylporphyrin chloride, and cobalt phthalocyanine, which is supported on the support. The catalyst is used as a cathode catalyst in the electrolysis of carbon dioxide, and is different from the anode catalyst described below.

[0018] The catalyst includes a carrier. The carrier included in the catalyst is not particularly limited as long as it is conductive and porous and can support the nitrogen-containing heteroaromatic ring compound, and examples thereof include carbon and conductive ceramics. Examples of carbon include ketjen black, acetylene black, carbon black, carbon nanotubes, graphene, and fullerene. Examples of conductive ceramics include titanium oxide and tin oxide.

[0019] The catalyst includes a nitrogen-containing heteroaromatic ring compound, which includes poly(4-vinylpyridine) (hereinafter, P4VPy) or a compound represented by the above general formula (1), supported on a carrier, and a cobalt ion coordinated with a nitrogen atom on the heteroaromatic ring of the nitrogen-containing heteroaromatic ring compound. P4VPy is a polymer having a repeating unit in which R1 in the above general formula (1) is -CH-CH2-. On the other hand, the compound represented by the above general formula (1) is produced by thermal decomposition of a part of P4VPy.

[0020] P4VPy forms a complex with cobalt ions to form a poly(4-vinylpyridine)-cobalt complex (hereinafter, Co-P4VPy). It is then calcined on the support to be supported on the support. When calcined on the support, a part of P4VPy is thermally decomposed to generate the compound represented by the above general formula (1). Therefore, it is considered that the nitrogen atoms in Co-P4VPy after being supported on the support include nitrogen atoms derived from P4VPy and nitrogen atoms derived from the compound represented by the above general formula (1), each of which is coordinated to a cobalt ion.

[0021] The catalyst further comprises at least one compound selected from the group consisting of iron phthalocyanine (hereinafter, FePc), iron tetraphenylporphyrin chloride (hereinafter, FeTPPCl), and cobalt phthalocyanine (hereinafter, CoPc) supported on a support. After Co-P4VPy is supported on a support, at least one compound selected from the group consisting of FePc, FeTPPCl, and CoPc is supported on the support to prepare a composite catalyst. By using this composite catalyst as a cathode catalyst in the electrolysis of carbon dioxide, Co-P4VPy and FePc, FeTPPCl, or CoPc acting as a cocatalyst work in concert to synthesize a product containing a hydrocarbon by reducing carbon dioxide.

[0022] The reaction scheme is as follows. Co-P4VPy is formed by forming a complex between P4VPy and cobalt ions, and the complex has a Co-N4C bond. The complex acts as an active site of the reduction reaction, reducing carbon dioxide to generate a reaction intermediate. The reaction intermediate then moves to FePc, FeTPPCl, or CoPc acting as a cocatalyst, whereby a multi-electron reduction reaction proceeds, promoting the production of hydrocarbons. The hydrocarbons produced by reducing carbon dioxide may include at least one selected from the group consisting of methane, ethane, propane, ethylene, and propylene, as shown in reaction formulas (4) to (8) described later. In addition, when CoPc is used, not only is the production of hydrocarbons promoted, but the electrolysis performance is also improved.

[0023] In the catalyst, the distance between the coordinated nitrogen atom and the cobalt ion is preferably 2.0 Å to 3.0 Å, more preferably 2.0 Å to 2.5 Å, and even more preferably 2.0 Å to 2.2 Å. When the nitrogen-containing heteroaromatic ring compound coordinated to the cobalt ion at such a distance is fixed on the support, the reduction activity of cobalt can be further increased.

[0024] (Catalyst manufacturing method) The method for producing a catalyst according to this embodiment is a method for producing a catalyst used for electrolysis of carbon dioxide. The method for producing a catalyst includes a step of calcining Co-P4VPy on a support to support it on the support, and then supporting at least one compound selected from the group consisting of FePc, FeTPPCl, and CoPc on the support. Here, the nitrogen-containing heteroaromatic ring compound and the support are the same as those in the above-mentioned embodiment of the catalyst.

[0025] The method for preparing Co-P4VPy is not particularly limited, and can be, for example, by dispersing P4VPy and a cobalt salt in a solvent. Alternatively, a Co-P4VPy solution may be prepared by dispersing each of P4VPy and a cobalt salt in a solvent and mixing the two dispersions.

[0026] The method for supporting Co-P4VPy on the carrier is not particularly limited, but for example, the carrier can be added to the Co-P4VPy solution obtained as described above, mixed, and impregnated. After that, the solvent can be removed, for example, by evaporation to dryness, and the carrier can be dried to obtain a carrier supported with Co-P4VPy.

[0027] In the method for producing the catalyst according to the present embodiment, Co-P4VPy is calcined on the support to be supported on the support. The calcination temperature is preferably 600K to 873K, more preferably 600K to 800K. By setting the calcination temperature within the above range, the reduction activity of cobalt can be further increased. Calcination may be performed once, but from the viewpoint of more appropriately fixing the cobalt complex to the support, it may be performed two or more times by changing the temperature. The calcination time is not particularly limited, and can be appropriately set, for example, between 1 hour and 10 hours.

[0028] The catalyst formed by calcination is preferably washed with an acidic aqueous solution since cobalt oxide or metallic cobalt may be generated on the support as a by-product during the formation of the catalyst. The acidic aqueous solution is not particularly limited as long as it can remove cobalt oxide or metallic cobalt without affecting the activity of the catalyst, and examples of the acidic aqueous solution include nitric acid, sulfuric acid, and hydrochloric acid. Washing with nitric acid is preferred.

[0029] The method for producing the catalyst according to the present embodiment includes a step of supporting at least one compound selected from the group consisting of FePc, FeTPPCl and CoPc on the support after calcining Co-P4VPy on the support to support it on the support. The method for supporting FePc, FeTPPCl or CoPc acting as a cocatalyst on the support is not particularly limited, but for example, Co-P4VPy supported on the support can be added to a solution of FePc, FeTPPCl or CoPc to be impregnated and supported. Then, the obtained powder can be dried to prepare a composite catalyst. This composite catalyst can be used as a cathode catalyst in the electrolysis of carbon dioxide.

[0030] In addition, composite catalysts using different cocatalysts may be mixed and used. For example, a composite catalyst using FePc and a composite catalyst using FeTPPCl may be prepared and then mixed and used as a cathode catalyst. Also, multiple cocatalysts may be added during catalyst preparation. For example, when a cocatalyst is supported on a carrier by the above method, Co-P4VPy supported on a carrier may be added to a solution containing FePc and FeTPPCl to prepare a composite catalyst, which may be used as a cathode catalyst.

[0031] (Carbon Dioxide Reduction System) 1 is a schematic diagram showing the principle of electrochemical reduction of carbon dioxide. The carbon dioxide reduction system has an anode chamber 10 that oxidizes water to produce oxygen, a cathode chamber 20 that reduces carbon dioxide to produce products containing hydrocarbons, and an electrolyte membrane 30 sandwiched between the anode chamber 10 and the cathode chamber 20.

[0032] FIG. 2 shows an example of the electrolysis cell 1 according to the present embodiment, and shows an experimental apparatus for evaluating electrolysis characteristics as described below. The electrolysis cell 1 may include a membrane electrode assembly according to the present embodiment. The electrolysis cell 1 includes an anode chamber 10 including an anode 11 and performing a water oxidation reaction, a cathode chamber 20 including a cathode 21 and performing a carbon dioxide reduction reaction, and an electrolyte membrane 30 (31) sandwiched between the anode chamber 10 and the cathode chamber 20. The electrolysis cell 1 includes a membrane electrode assembly 2 in which the electrolyte membrane 31 is sandwiched between the anode 11 and the cathode 21 so as to be in contact with each other, as shown in FIG. 4. That is, the membrane electrode assembly 2 may include an anode 11 that oxidizes water to generate oxygen, a cathode 21 that reduces carbon dioxide to generate a product containing hydrocarbons and includes the above-mentioned cathode catalyst, and an electrolyte membrane 31 that is sandwiched between the anode 11 and the cathode 21.

[0033] A potentiostat is connected between the anode 11 and the cathode 21. The cathode 21 is an electrode that reduces carbon dioxide to produce hydrocarbons. The anode 11 is an electrode that oxidizes water to produce oxygen and hydrogen ions. To cause a reduction reaction at the cathode 21, the cathode 21 is connected to a negative terminal of the potentiostat. To cause an oxidation reaction at the anode 11, the anode 11 is connected to a positive terminal of the potentiostat.

[0034] When a potential is applied to the anode 11 from the potentiostat, an oxidation reaction of water (HO) occurs at the anode 11, and oxygen (O) is generated and hydrogen ions (H + ) and electrons (e - ) is generated. 2H2O→4H + +O2+4e - (2)

[0035] The hydrogen ions generated on the anode 11 side reach the cathode 21 through the electrolyte membrane 31, which conducts protons. A reduction reaction of carbon dioxide (CO2) occurs at the cathode 21 by the electrons supplied from the potentiostat to the cathode 21 and the hydrogen ions that have moved to the cathode 21. Specifically, various reduction products and water are generated as shown in the following reaction formulas (3) to (9). By the reduction of carbon dioxide, reaction formula (3) shows that carbon monoxide is generated, reaction formula (4) shows that methane is generated, reaction formula (5) shows that ethane is generated, reaction formula (6) shows that propane is generated, reaction formula (7) shows that ethylene is generated, reaction formula (8) shows that propylene is generated, and reaction formula (9) shows that acetaldehyde is generated. In addition, as a side reaction, a hydrogen generation reaction in which hydrogen ions are directly reduced proceeds as shown in the following reaction formula (10). CO2+2H + +2e - →CO+H2O (3) CO2+8H + +8e - →CH4+2H2O (4) 2CO2+14H + +14e -→C2H6+4H2O (5) 3CO2+20H + +20e - →C3H8+6H2O (6) 2CO2+12H + +12e - →C2H4+4H2O (7) 3CO2+18H + +18e - →C3H6+6H2O (8) 2CO2+10H + +10e - →CH3CHO+3H2O (9) 2H + +2e - →H2(10)

[0036] (Cathode) Since the cathode 21 is provided with the above-mentioned catalyst, a product containing a hydrocarbon is synthesized by the reduction of carbon dioxide.

[0037] The shape of the cathode 21 is not particularly limited, and may be, for example, a plate, a mesh, a wire, a particle, a porous, a thin film, an island, or other various shapes. For example, the cathode 21 may be formed by disposing a catalyst on the surface of a substrate. An example of the substrate on which the catalyst is disposed is carbon paper. Also, for example, the cathode may be formed by molding the catalyst itself.

[0038] The cathode chamber 20 is supplied with carbon dioxide to be reduced by the cathode 21. The carbon dioxide to be reduced may be in the form of a gas such as CO2 gas, or in the form of a solution containing carbon dioxide. When 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, Cs2CO3, etc. Also, a solution containing carbon dioxide may be prepared by using an alcohol solvent such as methanol, ethanol, or acetone. The solution containing carbon dioxide is preferably a solution containing a carbon dioxide absorbent that increases the reduction potential of carbon dioxide, has high ionic conductivity, and absorbs carbon dioxide. Examples of such solutions include a solution containing a cation such as an imidazolium ion or a pyridinium ion and BF4 - or PF6 - Examples of the solution include an ionic liquid or an aqueous solution thereof, which is composed of a salt with an anion such as ethanolamine, imidazole, pyridine, etc., and is in a liquid state over a wide temperature range. Other examples of the solution include a solution of an amine such as ethanolamine, imidazole, pyridine, etc., or an aqueous solution thereof. The amine may be any of a primary amine, a secondary amine, and a tertiary amine.

[0039] (anode) Water to be oxidized by the anode 11 is supplied to the anode chamber 10. Ion-exchanged water or pure water can be used as the water to be oxidized. Instead of ion-exchanged water or pure water, an aqueous solution containing any electrolyte may be used, and it is preferable to use an aqueous solution that promotes the oxidation reaction of water. Examples of such aqueous solutions include sulfuric acid, nitric acid, perchloric acid, and hydrochloric acid.

[0040] The anode 11 is not particularly limited as long as it is a material capable of oxidizing water to generate oxygen and hydrogen ions, and can be made of known materials. Examples of such materials include 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 and Fe complexes. The anode 11 can be applied in various shapes such as a plate, mesh, wire, particle, porous, thin film, and island shape. The anode 11 may be a composite electrode in which these materials are laminated on a substrate.

[0041] (electrolyte membrane) The electrolyte membrane 31 may be made of any material that can move ions between the cathode 21 and the anode 11, and the type of material is not particularly limited. The electrolyte membrane 31 may be a proton exchange membrane. Examples of the electrolyte membrane 31 include Nafion (registered trademark, manufactured by Du Pont), Flemion (registered trademark, manufactured by AGC Corporation), and Aciplex (registered trademark, manufactured by Asahi Kasei Corporation).

[0042] The configuration of the electrolysis cell shown in Fig. 2 is merely one example, and various modifications are possible as long as the system is capable of performing a carbon dioxide reduction reaction using a cathode equipped with the catalyst according to the above embodiment. For example, the electrolysis cell shown in Fig. 2 is arranged between the anode 11 and the cathode 21 such that the electrolyte membrane 31 is in contact with the anode 11 and the cathode 21, but the anode 11 and the cathode 21 may be separated from the electrolyte membrane 31. In addition, for example, an electrolyte flow path for circulating the electrolyte may be provided so that the anode 11 and the cathode 21 are in contact with the electrolyte. Various other modifications are possible.

[0043] (electrolyzer) The electrolysis device according to this embodiment may include the electrolysis cell 1. By including the electrolysis cell 1, the electrolysis device can be applied to a carbon dioxide reduction system that electrolyzes carbon dioxide into hydrocarbons in order to reduce carbon dioxide emissions and effectively utilize the carbon dioxide. The electrolysis device also includes a device in which the electrolysis cell 1 is scaled up, such as a stack in which a plurality of electrolysis cells are stacked.

[0044] The catalyst, membrane electrode assembly, electrolytic cell, electrolytic device, and catalyst manufacturing method according to the present embodiment will be described in more detail below with reference to examples, but the present invention is not limited to these examples. EXAMPLES

[0045] (Preparation of Co-P4VPy) To prepare the cathode catalyst, first, Co-P4VPy was prepared. 80 mg of P4VPy (weight average molecular weight 60000, manufactured by Sigma-Aldrich) was added to ethanol (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and dissolved thoroughly. On the other hand, cobalt nitrate hexahydrate (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in ethanol (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to prepare a cobalt solution with a concentration of 40 mM. 1.70 mL of cobalt solution was added to the solution of P4VPy dissolved in ethanol prepared as described above, and ethanol was further added to make the total volume 50 mL, and the mixture was stirred for 15 minutes to form a complex.

[0046] (Supporting Co-P4VPy on a carrier) 107.6 mg of Ketjen Black support (Carbon ECP, Lion Specialty Chemicals Co., Ltd.) was mixed into the solution after the preparation of Co-P4VPy to perform impregnation. After that, the mixture was heated to 343K while stirring on a hot plate, and evaporated to dryness. The obtained powder was placed on a hot plate and dried in air at 343K for 16 hours. Then, this powder was placed in a flat-bottom quartz reactor, and while flowing argon at 20mL / min in an electric furnace, the temperature was increased at a rate of 25K / min, and the catalyst was pyrolyzed at 423K for 1 hour and then at 673K ​​or 773K for 3 hours to prepare the catalyst. Hereinafter, this catalyst is referred to as Co-P4VPy / KB(TK). Here, T represents the temperature during pyrolysis, which is 673 or 773.

[0047] (Refining the cathode catalyst) Co-P4VPy / KB(TK) was added to 0.1M nitric acid, covered with a watch glass and stirred for 1 hour. This suspension was filtered under reduced pressure using a membrane filter with a pore size of 0.1 μm. The filtrate was washed with ion-exchanged water until it became neutral, and then washed three times with 20 mL of 2-propanol. The filtered powder was dried under reduced pressure at 353 K for 1 hour to obtain a catalyst powder.

[0048] (Preparation of cathode catalyst) After supporting Co-P4VPy on a support, at least one compound selected from the group consisting of FePc, FeTPPCl, and CoPc was supported on the support to prepare a composite catalyst. The prepared composite catalyst was used as a cathode catalyst to evaluate the electrolytic properties.

[0049] The preparation method of the composite catalyst with FePc added as a cocatalyst is explained below. First, FePc was weighed out so that it was equivalent to 2 wt% Fe, and 60 mL of dichloromethane was added to it, and it was thoroughly dissolved by stirring on a hot stirrer for 30 minutes. Co-P4VPy / KB(TK) was added to the obtained solution and impregnated. The obtained powder was then placed on a hot plate and dried at 343K for 16 hours. The dried powder was then mixed uniformly in an agate mortar to prepare a composite electrode catalyst. The prepared composite electrode catalyst is referred to as FePc / (Co-P4VPy / KB(TK)).

[0050] The composite catalyst with FeTPPCl added as a cocatalyst was prepared in the same manner as above, except that FeTPPCl was used instead of FePc. The composite electrode catalyst thus prepared is denoted as FeTPPCl / (Co-P4VPy / KB(TK)).

[0051] Furthermore, a composite catalyst containing CoPc as a cocatalyst was prepared in the same manner as above, except that CoPc was used instead of FePc and was weighed out to be equivalent to 2% by weight based on Co. The prepared composite catalyst is denoted as CoPc / (Co-P4VPy / KB(TK)).

[0052] (Preparation of anode catalyst) First, an aqueous solution of iridium chloride equivalent to 60 mg of iridium was diluted with ion-exchanged water to a total volume of 60 mL. Then, 240 mg of Ketjen Black carrier was added to the aqueous solution of iridium chloride and impregnated. The obtained powder was placed on a hot plate and dried in air at 343 K for 16 hours. Then, this powder was placed in a flat-bottomed quartz reactor, and while flowing hydrogen at 20 mL / min in an electric furnace, it was subjected to hydrogen reduction treatment at 423 K for 1 hour with a heating rate of 25 K / min and then at 573 K for 2 hours to prepare a catalyst.

[0053] (Preparation of electrodes) Electrodes were prepared using the cathode catalyst and anode catalyst prepared as described above. Specifically, the cathode 21 and anode 11 were prepared by coating the catalyst ink on the gas diffusion electrode. As shown in FIG. 3, the cathode catalyst or anode catalyst, 10 wt% Nafion solution (Sigma-Aldrich) and acetone were weighed in a sample bottle with the composition ratio shown in Table 1. This was stirred by ultrasonic irradiation to prepare the catalyst ink. Furthermore, this catalyst ink was uniformly applied to the water-repellent layer side surface of carbon paper 100 (SGL Carbon) with a diameter of 16 mm. The applied electrode was dried under reduced pressure for 10 minutes to thoroughly remove the acetone solvent, and the cathode 21 and anode 11 were prepared.

[0054] [Table 1]

[0055] (Pretreatment of electrolyte membrane) Nafion117 (manufactured by Du Pont) was used for the electrolyte membrane 31. 27 sheets of the electrolyte membrane cut into appropriate shapes were boiled in 3% hydrogen peroxide for 1 hour to remove oil and organic matter from the membrane. Next, the membrane was boiled in ion-exchanged water for 1 hour and in 2N sulfuric acid for 1 hour to replace the metal ions in the membrane with hydrogen ions. The electrolyte membrane 31 was further boiled in ion-exchanged water for 1 hour and then stored in the ion-exchanged water.

[0056] (Fabrication of membrane electrode assembly) 4 , the electrolyte membrane 31 was sandwiched between the cathode 21 and the anode 11 so as to be in contact with each other, and hot pressed at 413 K and 30 MPa for 10 minutes to produce a membrane electrode assembly. Thereafter, the electrolysis unit was immersed in ion-exchanged water for 5 minutes to allow the electrolyte membrane 31 to absorb a sufficient amount of water.

[0057] (Preparation of evaluation cell) The cell for evaluating electrolytic properties was assembled from the cell parts shown in FIG. 5. Electrical conduction was ensured by physically contacting the electrodes of the electrolytic unit with the current collector. The current collector 41 was prepared by wrapping a circular Teflon (registered trademark) plate 50 (diameter 16 mm, thickness 1 mm) with a hole of 3 mm in diameter with a gold mesh 42 (Kureba Co., Ltd., 200 mesh) as shown in FIG. 6(c)-(e). On the other hand, in order to fix the current collector 41 and connect it to an external circuit, a Teflon plate 52 shown in FIG. 6(b) was used. The Teflon plate 52 with a diameter of 56 mm had a hole in the center, leaving a cross shape with a width of 2 mm, and a gold lead wire was wound around the cross to fix the current collector and connect it to the circuit. In order to further maintain airtightness, the Teflon plate 51 shown in FIG. 6(a) and a 5 mm thick silicon sheet (not shown) were attached in the order shown in FIG. 5, and fixed by tightening bolts and nuts using a flange.

[0058] A reference electrode was connected to measure and control the potential. To connect the reference electrode, a Teflon plate 51 on the anode 11 side and an electrolyte membrane 31 were cut out as shown in FIG. 7. The leg part of the electrolyte membrane 31 extended downward was 5 mm wide and 57 mm long. The electrode and the reference electrode were connected by immersing the leg part of the electrolyte membrane 31 extended downward and the reference electrode through a liquid junction in 0.5 M sulfuric acid. An Ag / AgCl electrode (manufactured by DKK-TOA Corporation, +0.199 V vs. SHE) was used as the reference electrode, and a saturated KCl solution was used as the liquid junction. The leg part of the electrolyte membrane 31 extended downward was fixed with a Teflon plate 53 as shown in FIG. 7.

[0059] (Carbon dioxide electrolysis reaction) Using the evaluation cell obtained as described above, a carbon dioxide electrolysis reaction was performed in the following manner to evaluate the electrolysis characteristics. Specifically, a constant-potential electrolysis experiment was performed by controlling the cathode potential using a potentiostat (HZ5000, manufactured by Hokuto Denko Corporation). As shown in FIG. 2, ion-exchanged water was injected into the anode chamber 10, argon gas was passed through the ion-exchanged water, and the gas was discharged (Vent). Meanwhile, CO2 gas was passed through the cathode chamber 20, and the gas generated by reducing the CO2 gas was introduced into a gas chromatograph (hereinafter, GC) and quantitatively analyzed. Before starting the electrolysis reaction, argon gas was passed through the anode chamber 10 at 20 mL / min, and CO2 gas was passed through the cathode chamber 20 at 10 mL / min for 15 minutes or more. The experimental conditions are as shown in Table 2.

[0060] [Table 2]

[0061] (Method of analysis of generated substances) The reaction was carried out for 30 minutes at each potential, and the outlet gas 30 minutes after the start of the reaction at each potential was introduced into a GC (GC-8A, Shimadzu Corporation) for quantitative analysis.

[0062] The quantitative analysis of CO was carried out by taking 1.0 mL of the outlet gas from the cathode chamber 20 during the reaction using a gas-tight syringe and injecting it into a GC for analysis. The GC analysis conditions were as shown in Table 3.

[0063] [Table 3]

[0064] By taking into account the CO2 gas supply rate and the electrode area, the CO production rate r(CO) [μmol / h / cm 2 From reaction formula (3), considering that the reduction of CO2 to CO is a two-electron reaction, the CO generation rate r(CO) was calculated according to the following calculation formula (11) as the CO generation current density I CO was converted to. I CO [mA / cm 2 ]=r(CO)[μmol / h / cm 2 ]×96485[C / mol]×2×1 / 3600[s / h] (11)

[0065] The faradaic efficiency of CO formation, FE(CO), is the current density of CO formation, I CO and the total current density I d [mA / cm 2 The Faraday efficiency was calculated using the following formula (12): Faraday efficiency indicates the ratio of the partial current that contributed to the production of each substance to the total current. FE(CO)[%]=I CO / I d ×100 (12)

[0066] Quantitative analysis of hydrocarbons was performed by taking 2.0 mL of the outlet gas from the cathode chamber 20 during the reaction using a gas-tight syringe and injecting it into GC for analysis. The GC analysis conditions were as shown in Table 3.

[0067] The production rate and Faraday efficiency for each hydrocarbon were calculated in the same manner as in the case of CO using equations (11) and (12). However, the number of reaction electrons was determined to be the values ​​shown in equations (4) to (9), and the value of 2 in equation (11) was changed to the corresponding number of reaction electrons.

[0068] FIG. 8 is a graph showing the electrolytic characteristics of carbon dioxide using a composite catalyst with FePc or FeTPPCl added as a cocatalyst. As examples, FePc / (Co-P4VPy / KB(673K)), FePc / (Co-P4VPy / KB(773K)), FeTPPCl / (Co-P4VPy / KB(673K)) and FeTPPCl / (Co-P4VPy / KB(773K)) were used. On the other hand, as comparative examples, Co-P4VPy / KB(673K) and Co-P4VPy / KB(773K) without using a cocatalyst were used. In FIG. 8, the graph on the far left shows the total current density I d [mA / cm 2 ] is shown, and the other graphs show the production rate and Faraday efficiency for each product. For FePc / (Co-P4VPy / KB(673K)), the production rate and Faraday efficiency of methane, ethane, and propane tended to increase. For FePc / (Co-P4VPy / KB(773K)), the production rate and Faraday efficiency of methane tended to increase. For the composite catalyst using FeTPPCl, the production rate and Faraday efficiency of ethane and propane tended to increase. On the other hand, for Co-P4VPy without FePc and FeTPPCl, the production rate and Faraday efficiency of carbon monoxide were high, but it was found that it did not contribute much to the production of hydrocarbons. Therefore, it was found that when the composite catalyst was used, the production of carbon monoxide was suppressed and the production of hydrocarbons was promoted.

[0069] FIG. 9 is a graph showing the electrolytic characteristics of carbon dioxide using a composite catalyst to which FePc or CoPc was added as a cocatalyst. As examples, the graphs labeled FePc and CoPc show FePc / (Co-P4VPy / KB(673K)) and CoPc / (Co-P4VPy / KB(673K)), respectively. On the other hand, as a comparative example, none(Co-P4VPy / KB) was used, which did not use a cocatalyst. As a further comparative example, a composite catalyst was used that was prepared in the same manner as above, except that MnPc (manganese phthalocyanine), NiPc (nickel phthalocyanine), CuPc (copper phthalocyanine) or ZnPc (zinc phthalocyanine) was used instead of FePc in the above preparation method. In FIG. 9, the graph on the upper left shows the total current density I d [mA / cm 2 ] is shown, and the other graphs show the production rate and Faraday efficiency for each product. For the composite catalyst using FePc, the production rate or Faraday efficiency of methane, ethane, propane, ethylene and propylene tended to increase. For the composite catalyst using CoPc, the production rate or Faraday efficiency of methane, ethane, propane, acetaldehyde, ethylene and propylene tended to increase. On the other hand, for the Co-P4VPy / KB without a cocatalyst, it was found that the carbon monoxide production rate and Faraday efficiency were high, but it did not contribute much to the production of hydrocarbons. For the composite catalysts with cocatalysts other than FePc and CoPc added in other comparative examples, no hydrocarbons with particularly high production rates and Faraday efficiencies were detected, and it was found that they did not contribute much to the production of hydrocarbons.

[0070] In Figure 9, the total current density was the highest for the composite catalyst using CoPc. The total current density of the composite catalyst with other than CoPc added as a cocatalyst was 100 mA / cm 2 The total current density of Co-P4VPy / KB without cocatalyst is about 130mA / cm 2 In contrast, the total current density of CoPc / (Co-P4VPy / KB(673K)) was about 200mA / cm 2This shows that the composite catalyst using CoPc not only promotes the production of hydrocarbons, but also improves the electrolysis performance.

[0071] In this way, by using a composite catalyst in which FePc, FeTPPCl or CoPc was added as a cocatalyst to Co-P4VPy as a cathode catalyst, it was possible to synthesize hydrocarbons by electrolysis of carbon dioxide. In addition, the electrolysis performance was improved when using a composite catalyst with CoPc.

[0072] Although several embodiments have been described, the embodiments can be modified or modified based on the above disclosure. All components of the above embodiments and all features described in the claims may be individually extracted and combined as long as they are not mutually inconsistent.

[0073] This disclosure can contribute, for example, to Goal 7 of the United Nations-led Sustainable Development Goals (SDGs), "Ensure access to affordable, reliable, sustainable and modern energy for all" and Goal 13, "Take urgent action to combat climate change and its impacts." [Explanation of symbols]

[0074] 1 Electrolysis cell 2 Membrane electrode assembly 11 Anode 21 Cathode 31 Electrolyte membrane

Claims

1. A catalyst for use in the electrolysis of carbon dioxide, comprising: A carrier; Poly(4-vinylpyridine) or a compound represented by the general formula (1) supported on the carrier 【Chemistry 1】 (In general formula (1), R １ is H or an alkyl group. A nitrogen-containing heteroaromatic ring compound including a compound represented by the formula: a cobalt ion coordinated to a nitrogen atom on a heteroaromatic ring of the nitrogen-containing heteroaromatic ring compound; at least one compound selected from the group consisting of iron phthalocyanine, iron tetraphenylporphyrin chloride, and cobalt phthalocyanine, supported on the support; A catalyst comprising:

2. an anode that oxidizes water to produce oxygen; A cathode comprising the catalyst of claim 1 for reducing carbon dioxide to produce products comprising hydrocarbons; an electrolyte membrane sandwiched between the anode and the cathode; A membrane electrode assembly comprising:

3. 3. The membrane electrode assembly of claim 2, wherein the electrolyte membrane is a proton exchange membrane.

4. 4. The membrane electrode assembly according to claim 2, wherein the hydrocarbon comprises at least one selected from the group consisting of methane, ethane, propane, ethylene and propylene.

5. An electrolysis cell comprising the membrane electrode assembly according to claim 2 or 3.

6. An electrolysis apparatus comprising the electrolysis cell according to claim 5.

7. A method for producing a catalyst for use in the electrolysis of carbon dioxide, comprising the steps of: A method for producing a catalyst, comprising the steps of: calcining a poly(4-vinylpyridine)-cobalt complex on a carrier to cause the complex to be supported on the carrier; and then causing at least one compound selected from the group consisting of iron phthalocyanine, iron tetraphenylporphyrin chloride, and cobalt phthalocyanine to be supported on the carrier.

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