Electrochemical reactor

Abstract

An electrochemical reactor 10 comprises a cathode 13, an anode 23, and an electrolytic solution. The electrolytic solution: includes a cathode electrolytic solution 16X which has carbon dioxide dissolved therein and which is in contact with the cathode 13, and an anode electrolytic solution 26X which is a halide aqueous solution and which is in contact with the anode 23; or is a bipolar electrolytic solution which is a halide aqueous solution having carbon dioxide dissolved therein and which is in contact with the cathode 13 and the anode 23. The cathode 13 contains a first catalyst that promotes a reaction for reducing carbon dioxide to carbon monoxide, and generates a halogen at the anode 23.

Description

Electrochemical reactor

[0001] The present invention relates to an electrochemical reaction apparatus that reduces carbon dioxide to carbon monoxide at the cathode and generates a halogen at the anode.

[0002] Electrochemical synthesis methods have recently gained attention because they do not require the use of highly toxic substrates or highly explosive oxygen gas mixtures, and because they can directly utilize electricity from renewable energy sources. Furthermore, in recent years, there has been research into reducing carbon dioxide through electrochemical reactions to produce valuable substances, with the aim of mitigating global warming and replacing fossil fuels.

[0003] Carbon dioxide reduction is known to be performed using electrochemical cells, and it is common for carbon dioxide to be reduced on the cathode side. In this case, it is being considered to generate various compounds on the anode side as well, and it is known that halogens such as chlorine are generated by using an alkali metal chloride-containing solution as the electrolyte (see, for example, Patent Document 1). Carbon dioxide reduction is generally carried out by a gas-phase reaction, and in Patent Document 1, the cathode chamber is provided with a gas space separated from the electrolyte space by a gas diffusion electrode, and carbon dioxide reduction is carried out in the gas space.

[0004] Special Publication No. 2022-551135

[0005] However, as shown in Reference 1, when halogenated salts such as chlorides are used as electrolytes in carbon dioxide reduction and the system is operated continuously, the amount of base on the cathode side increases. As a result, carbon dioxide reacts with cations such as sodium ions and hydroxide ions generated by carbon dioxide reduction near the cathode, making it easy to form carbonates such as sodium bicarbonate. In particular, when a gas diffusion electrode is used on the cathode side, the generated carbonates have no choice but to precipitate on the electrode, and the precipitated carbonates cause a loss of activity in the carbon dioxide reduction reaction, leading to a decrease in performance.

[0006] Therefore, the present invention aims to prevent a decrease in reactivity due to the precipitation of carbonate near the cathode in an electrochemical reactor in which carbon dioxide is reduced on the cathode side and a halogen is generated on the anode side using an aqueous halogenated salt solution as the electrolyte.

[0007] The present invention provides the following [1] to

[10] : [1] An electrochemical reactor comprising a cathode, an anode, and an electrolyte, wherein the electrolyte includes a cathode electrolyte in which carbon dioxide is dissolved and in contact with the cathode, and an anode electrolyte which is an aqueous solution of a halogenated salt and in contact with the anode, or an aqueous solution of a halogenated salt in which carbon dioxide is dissolved and in contact with the cathode and the anode, and the cathode contains a first catalyst that promotes the reaction of reducing carbon dioxide to carbon monoxide, and generates a halogen at the anode. [2] The electrochemical reactor according to [1], further comprising a cation exchange membrane present between the cathode and the anode. [3] The electrochemical reactor according to [1] or [2], wherein the cathode electrolyte contains a dissolved halogenated salt and hydrogen halide, and has a pH of 2 or more and 6.5 or less. [4] The electrochemical reactor according to any one of [1] to [3], wherein the halogenated salt is an alkali metal halide. [5] The electrochemical reactor according to any one of [1] to [4] above, wherein the first catalyst is obtained by calcining a mixture containing a metal derivative, a nitrogen-containing compound, and a carbon compound, and the nitrogen-containing compound is at least one selected from the group consisting of pyridine derivatives, imidazole derivatives, pyrazole derivatives, and triazole derivatives. [6] The electrochemical reactor according to [5] above, wherein the pyridine derivative is at least one selected from the group consisting of aminopyridine, which is a compound having one pyridine ring in one molecule; pyridine oligomers having four or more pyridine rings and having a weight-average molecular weight of less than 10,000; and polymers having multiple pyridine rings in one molecule and having a weight-average molecular weight of 10,000 or more. [7] The electrochemical reactor according to [5] or [6] above, wherein the first catalyst contains a pyridine derivative as the nitrogen-containing compound. [8] The electrochemical reactor according to any one of [5] to [7] above, wherein in the first catalyst, the molar ratio of the nitrogen-containing aromatic ring of the nitrogen-containing compound to the metal element of the metal derivative (nitrogen-containing aromatic ring / metal element) is 2 or more and 20 or less. [9] The electrochemical reactor according to any one of [5] to [8] above, wherein the metal content derived from the metal derivative in the mixture is 1% by mass or more and 8% by mass or less.

[10] The electrochemical reactor according to any one of [5] to [9] above, wherein the metal element in the metal derivative is at least one selected from the group consisting of Co, Fe, and Ni.

[0008] According to the present invention, in an electrochemical reactor in which carbon dioxide is reduced on the cathode side and a halogen is generated on the anode side using an aqueous halogenated salt solution as the electrolyte, it is possible to prevent a decrease in reactivity due to the precipitation of carbonate near the cathode.

[0009] This is a schematic diagram showing an electrochemical reactor according to the first embodiment. This is a schematic diagram showing an electrochemical reactor according to the second embodiment. This is a schematic diagram showing an electrochemical reactor according to the third embodiment.

[0010] The electrochemical reaction apparatus of the present invention will be described below with reference to the drawings. In the following description, elements having the same configuration will be denoted by the same reference numerals.

[0011] <First Embodiment> Figure 1 shows an electrochemical reactor 10 according to the first embodiment of the present invention. The electrochemical reactor 10 comprises an electrolytic device composed of an electrolytic cell 11, and the electrolytic cell 11 contains a cathode (first electrode) 13, a diaphragm 19, an anode (second electrode) 23, and an electrolyte. The diaphragm 19 is located between the cathode 13 and the anode 23. The inside of the electrolytic cell 11 is divided by the diaphragm 19 into a cathode chamber (first electrolytic section) 16 in which the cathode 13 is located, and an anode chamber (second electrolytic section) 26 in which the anode 23 is located.

[0012] In this embodiment, the electrolytic cell 11 contains a cathode electrolyte 16X filled inside the cathode chamber 16 and an anode electrolyte 26X filled inside the anode chamber 26 as the electrolyte. The cathode electrolyte 16X and the anode electrolyte 26X are in contact with the cathode 13 and anode 23, respectively. In this embodiment, an electrolyte in which carbon dioxide is dissolved is used as the cathode electrolyte 16X, and an aqueous halogenated salt solution in which a halogenated salt is dissolved is used as the anode electrolyte 26X. Furthermore, it is preferable that a halogenated salt is also dissolved in the cathode electrolyte 16X. The halogenated salt in the cathode electrolyte 16X is preferably the same as that in the anode electrolyte 26X. The halogenated salt added here is preferably used as an electrolyte.

[0013] A power supply 25 is connected to the cathode 13 and anode 23, and an electric current flows from the power supply 25 between the cathode 13 and anode 23, thereby causing electrochemical reactions to occur in the cathode 13 and anode 23, respectively. In this embodiment, the cathode 13 contains a first catalyst that promotes the reaction of reducing carbon dioxide to carbon monoxide. Therefore, carbon monoxide is produced as a reduced product in the cathode 13. Typically, the reaction shown in the following formula (i) takes place in the cathode 13. CO ２ +2H ２ O + 2e － →CO + 2OH － (i)

[0014] As described later, it is preferable that cations such as metal ions constituting the halide salt in the anode electrolyte 26X in the anode chamber 26 move to the cathode chamber 16 via the diaphragm 19 and form hydroxides. Therefore, the reaction shown in formula (i) is preferably the reaction shown in formula (i-1) below. Note that formula (i-1) shows an example where the cation is a sodium ion, but the cation is not limited to a sodium ion. ２ +2H ２ O + 2Na ＋ +2e － →CO+2NaOH (i-1)

[0015] Furthermore, in the anode 23, since the anode electrolyte is an aqueous halide salt solution, a reaction that generates halogen occurs. Typically, the reaction represented by the following formula (ii) takes place at the anode 23. In formula (ii), X represents a halogen atom. 2X － → X ２ + 2e － (ii)

[0016] The cathode chamber 16 may preferably be connected with a first supply line 17 as a supply means and a first discharge line 18 as a discharge means. A cathode electrolyte 16X containing carbon dioxide is supplied to the cathode chamber 16 via the first supply line 17. Then, carbon monoxide produced by reduction at the cathode 13 is discharged to the outside of the cathode chamber 16 via the first discharge line 18 together with the cathode electrolyte 16X. The supply and discharge of the cathode electrolyte 16X may preferably be performed continuously, whereby the cathode electrolyte 16X is allowed to flow with a constant flow inside the cathode chamber 16, and the reduction reaction at the cathode 13 is efficiently performed.

[0017] The anode chamber 26 may preferably be connected with a second supply line 27 as a supply means and a second discharge line 28 as a discharge means. An aqueous halide salt solution as the anode electrolyte 26X is supplied into the anode chamber 26 via the second supply line 27. Furthermore, halogen generated at the anode 23 is discharged to the outside of the anode chamber 26 via the second discharge line 28 together with the anode electrolyte. The supply and discharge of the anode electrolyte 26X may preferably be performed continuously, whereby the anode electrolyte 26X is allowed to flow with a constant flow inside the anode chamber 26, and the oxidation reaction at the anode 23 is efficiently performed.

[0018] In this embodiment, the electrochemical reactor 10 may further include an anode-side storage section 32. The anode-side storage section 32 stores an anode electrolyte 26X, which is an aqueous halogenated salt solution. The anode-side storage section 32 is not particularly limited in its configuration as long as it can store the anode electrolyte 26X, but it may be provided with a stirring device as appropriate, and the stored anode electrolyte 26X may be mixed by the stirring device. A second supply line 27 may connect the anode chamber 26 and the anode-side storage section 32, and a second discharge line 28 may connect the anode chamber 26 and the anode-side storage section 32. As a result, the anode electrolyte 26X stored in the anode-side storage section 32 is supplied to the anode chamber 26 via the second supply line 27, and the anode electrolyte from the anode chamber 26 is discharged to the anode-side storage section 32, causing the anode electrolyte 26X to circulate between the anode chamber 26 and the anode-side storage section 32. In other words, the anode electrolyte is discharged to the outside from the anode chamber 26 and then circulates back to the anode chamber 26. In this way, the circulation of the anode electrolyte 26X allows halogens to be generated more efficiently in the anode 23. In this embodiment, the anode-side circulation path consists of the anode chamber 26, the second discharge line 28, the anode-side storage section 32, and the second supply line 27.

[0019] The anode-side storage section 32 preferably has a space at its top (i.e., a gas phase 32G). Halogens produced at the anode 23 generally have low solubility in water. Therefore, the presence of the gas phase 32G makes it easier for halogens that cannot dissolve in the anode electrolyte 26X to be released into the gas phase 32G of the anode-side storage section 32. This allows for a lower halogen content in the anode electrolyte 26X, making it easier for the reaction at the anode 23 to occur. Furthermore, the anode-side gas discharge line 29 is connected to the gas phase 32G of the anode-side storage section 32, and the gas in the gas phase 32G of the anode-side storage section 32 is discharged to the outside through the anode-side gas discharge line 29. This makes it easier to recover the halogens produced at the anode 23.

[0020] Furthermore, the anode-side storage unit 32 may be connected to an anode electrolyte supply line, an anode electrolyte discharge line, etc. (not shown), and the anode electrolyte may be supplied or discharged through these lines. This allows the anode-side storage unit 32 to appropriately replace the anode electrolyte 26X when the reaction on the anode side progresses and the concentration of halogen salts in the anode electrolyte 26X circulating through the above-mentioned circulation path becomes low, thereby enabling continuous operation for a long period of time. However, each component constituting the anode electrolyte 26X (solvent, electrolyte, etc.) may be supplied to the anode-side storage unit 32 separately.

[0021] Furthermore, the cathode electrolyte 16X containing carbon dioxide is not particularly limited, but it is preferable that it be prepared in a cathode-side storage unit (not shown) and supplied to the cathode chamber 16 by a first supply line 17. The cathode-side storage unit is, for example, connected to a carbon dioxide supply line and an electrolyte supply line, and carbon dioxide is supplied to the cathode-side storage unit from a carbon dioxide supply source (not shown) via the carbon dioxide supply line, and cathode electrolyte is supplied from the electrolyte supply line, and in the cathode-side storage unit, the carbon dioxide and cathode electrolyte are mixed to prepare a cathode electrolyte 16X in which carbon dioxide is dissolved. Furthermore, an electrolyte discharge line is connected to the cathode-side storage unit, and the cathode electrolyte is discharged as appropriate. The carbon dioxide supply source is not particularly limited, but may be a gas cylinder or the like. Also, the carbon dioxide may be obtained from exhaust gas emitted from a power plant, steel mill, cement factory, or waste incinerator, and any of these facilities may be used as the carbon dioxide supply source.

[0022] Furthermore, the first discharge line 18 may be connected to the cathode-side storage section. This allows the cathode electrolyte to circulate appropriately between the cathode chamber 16 and the cathode-side storage section, similar to the anode side. In this embodiment, the cathode-side circulation path may consist of the cathode chamber 16, the first discharge line 18, the cathode-side storage section (not shown), and the first supply line 17. The cathode-side storage section may also have a space (i.e., a gas phase) at its top, similar to the anode-side storage section 32. Carbon monoxide generated in the cathode 13 generally has low solubility in solvents such as water. Therefore, the presence of a gas phase makes it easier for carbon monoxide that cannot dissolve in the cathode electrolyte 16X to be released into the gas phase of the cathode-side storage section, lowering the concentration of carbon monoxide in the circulating cathode electrolyte 16X and making it easier for the reaction in the cathode 13 to occur. Furthermore, connecting a gas discharge line to the gas phase makes it easier to recover carbon monoxide.

[0023] The supply and discharge of the cathode electrolyte 16X and the anode electrolyte 26X (or circulation in the circulation path described above) may be performed continuously or intermittently. Furthermore, the cathode electrolyte 16X and the anode electrolyte 26X may be pumped in a specific direction. The pump is not particularly limited, but examples include diaphragm pumps, syringe pumps, and peristaltic pumps. The flow of the cathode electrolyte 16X and the anode electrolyte 26X may also be formed by known means other than pumps, for example, by using gravity.

[0024] On the cathode 13 surface of this embodiment (the surface in contact with the cathode electrolyte 16X), for example, hydroxide ions generated by the cathode reaction as shown in formula (i) above, and cations derived from the halide salt present in the cathode electrolyte 16X (for example, in the reaction shown in formula (i-1), Na ＋), and a carbonate is produced as a by-product from carbon dioxide. However, in the present embodiment, carbon dioxide is dissolved in the cathode electrolyte 16X, and the reaction on the cathode 13 side is carried out in a liquid phase. Therefore, on the cathode 13 side, even if carbonate is generated on the surface of the cathode 13, the carbonate is dissolved in the cathode electrolyte 16X, so precipitation of the carbonate is suppressed. Accordingly, it is possible to prevent a decrease in the reactivity of the reduction reaction at the cathode 13 caused by precipitation of the carbonate on the cathode.

[0025] The cations derived from the halogenated salt described above are metal ions such as those from alkali metal salts and alkaline earth metal salts, ammonium ions, and the like, and are preferably alkali metal ions. Accordingly, examples of the carbonate include ammonium salts of carbonic acid such as ammonium carbonate and ammonium hydrogen carbonate, and metal salts of carbonic acid such as alkali metal carbonates, alkali metal hydrogen carbonates, alkaline earth metal carbonates, and alkaline earth metal hydrogen carbonates. Among these, alkali metal salts of carbonic acid such as alkali metal carbonates and alkali metal hydrogen carbonates are preferred, and among these, alkali metal hydrogen carbonates are more preferred. Note that, as described later, as the alkali metal in the halogenated salt, potassium and sodium are more preferred, and sodium is most preferred. Therefore, as the carbonate, sodium hydrogen carbonate, sodium carbonate, potassium hydrogen carbonate, and potassium carbonate are more preferred; sodium hydrogen carbonate and potassium hydrogen carbonate are further preferred; and sodium hydrogen carbonate is most preferred.

[0026] Furthermore, in the present embodiment, as will be described later, a cation exchange membrane is preferably used as the diaphragm 19. By using a cation exchange membrane, cations constituting the halogenated salt in the anode chamber 26 (for example, Na ＋ +) move to the cathode chamber 16 through the cation exchange membrane. Therefore, on the cathode side (cathode chamber 16), the cations derived from the halogenated salt and hydroxide ions (OH －Hydroxides are generated by this process, and these hydroxides are contained in the cathode electrolyte 16X, and it is preferable that these hydroxides also constitute the electrolyte. The cations derived from the halogenated salt are as described above, but are preferably alkali metal ions, more preferably potassium ions, sodium ions, and even more preferably sodium ions. Therefore, sodium hydroxide (NaOH) is even more preferable as the hydroxide generated on the cathode side.

[0027] The temperature of the electrolytes inside the electrolytic cell 11 (i.e., the cathode chamber 16 and the anode chamber 26, respectively) (i.e., the cathode electrolyte 16X and the anode electrolyte 26X, respectively, in this embodiment) is not particularly limited and may be, for example, around 0 to 95°C. However, it is preferable that the temperature is such that the generated halogen becomes a gas, and therefore, it is preferable that it is above the boiling point of the generated halogen. Furthermore, from the viewpoint of preventing the precipitation of carbonates, it is preferable that the temperature is above a certain level, specifically 60°C or higher. By having a temperature of 60°C or higher, the solubility of carbonates in water, especially sodium bicarbonate in water, is increased, further suppressing the precipitation of carbonates on the cathode 13 side and further preventing a decrease in reactivity. Therefore, it is preferable that the temperature of at least the cathode electrolyte 16X be 60°C or higher.

[0028] Furthermore, the electrolysis cell 11 may be provided with a heater. The heater is not particularly limited, and examples thereof include heating wires. A decrease in reactivity due to carbonate precipitation occurs mainly when carbonates precipitate at the cathode 13. Therefore, from the viewpoint of further preventing a decrease in reactivity, the temperature of the cathode 13 and its surroundings may be set to a certain temperature or higher. Specifically, it is preferable that the temperature of the cathode 13 and the temperature of the cathode electrolyte 16X around the cathode 13 be 60°C or higher. This makes it possible to efficiently prevent a decrease in reactivity caused by carbonate precipitation. Furthermore, from the viewpoint of easily increasing the temperature of the cathode 13 and its surroundings, the heater may be attached to the cathode 13, or may be attached to the periphery of the cathode 13 (for example, the inner surface of the electrolysis cell 11 constituting the cathode chamber 16). Note that when the heater is attached to the cathode 13, the first catalyst may be applied and supported on, for example, one surface of the cathode 13, and in that case, the heater is preferably attached to the surface of the cathode 13 opposite to the side on which the first catalyst is applied.

[0029] Furthermore, the heated electrolyte may be supplied to the electrolysis cell 11 so that the electrolyte inside the electrolysis cell 11 is adjusted to the above temperature. For example, the cathode electrolyte 16X heated to 60°C or higher may be supplied from the first supply line 17. In this case, the cathode electrolyte 16X may be heated by a heater in, for example, a cathode-side storage part, or heated by a heater in the first supply line 17, but there is no particular limitation thereon.

[0030] The following describes in more detail each component of the electrochemical reaction apparatus according to this embodiment. (Anode Electrolyte) As described above, an aqueous solution of a halide salt is used as the anode electrolyte 26X. The anode electrolyte 26X is preferably a solution in which the halide salt is dissolved in water with water as the solvent. Examples of halide salts include alkali metal halides, alkaline earth metal halides, and ammonium halides. Here, examples of alkali metals include lithium, sodium, and potassium, and examples of alkaline earth metals include magnesium and calcium. Among these, alkali metals are preferred, sodium and potassium are more preferred, and sodium is even more preferred.

[0031] As the halogenated salt, a chloride salt is preferred, and therefore, it is preferable that chlorine is generated at anode 23. Chloride salts are known as highly versatile compounds such as sodium chloride, and are industrially advantageous. Furthermore, chlorine has low solubility in water and is easy to separate from the electrolyte. In addition, for example, compounds with high industrial value such as phosgene can be easily produced using carbon monoxide and chlorine generated in this electrochemical reaction apparatus 10 as raw materials.

[0032] Examples of alkali metal halides include lithium halides such as lithium chloride and lithium bromide, sodium halides such as sodium chloride and sodium bromide, and potassium halides such as potassium chloride and potassium bromide. Examples of alkaline earth metal halides include magnesium halides such as magnesium chloride and magnesium bromide, and calcium halides such as calcium chloride and calcium bromide. Examples of ammonium halides include ammonium chloride and ammonium bromide.

[0033] Among these, alkali metal halides are preferred, specifically lithium chloride, lithium bromide, sodium chloride, sodium bromide, potassium chloride, and potassium bromide, with sodium chloride, sodium bromide, potassium chloride, and potassium bromide being more preferred. Alkali metal chlorides are also preferred, therefore sodium chloride and potassium chloride are even more preferred, and sodium chloride is the most preferred.

[0034] In the anode electrolyte 26X, one type of halogenated salt may be used alone, or two or more types may be used in combination. The concentration of the halogenated salt in the anode electrolyte is not particularly limited, but is often, for example, 0.01 to 10 M, preferably 0.02 to 3 M, and more preferably 0.05 to 2 M. The anode electrolyte may also contain components other than water and halogenated salts as appropriate, for example, electrolytes other than halogenated salts may be included. Furthermore, the anode electrolyte may contain by-products such as carbonates and hydroxides.

[0035] (Cathode Electrolyte) The cathode electrolyte 16X is preferably a solvent capable of dissolving carbon dioxide, such as water or an organic solvent. As the organic solvent, it can be appropriately selected from solvents commonly used in electrochemical reactions, such as alcohol-based solvents such as methanol, ethanol, phenol, 1-propanol, ethylene glycol, and propylene glycol; nitrile-based solvents such as acetonitrile; carbonate-based solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactone-based solvents such as γ-butyrolactone; ether-based solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; phosphate ester solvents; phosphoric acid compounds; sulforane-based solvents; pyrrolidone compounds, etc. These organic solvents may be used individually or in combination of two or more. In this specification, the term "alcohol-based" includes aromatic hydroxy compounds, such as phenol, in which a hydroxyl group is directly bonded to an aromatic ring such as a benzene ring. As for the solvent in the cathode electrolyte 16X, at least one of an alcohol-based solvent or water is preferred from the viewpoint of being able to dissolve a certain amount of carbon dioxide and the carbonate produced by the reduction reaction, and at least one of methanol or water is more preferred, with water being even more preferred.

[0036] The cathode electrolyte 16X preferably contains an electrolyte in the solvent. The electrolyte is preferably dissolved in the solvent. By containing an electrolyte, the cathode electrolyte allows the electrochemical reaction to proceed appropriately and enables the proper reduction of carbon dioxide to carbon monoxide. As the electrolyte, a halide salt is preferably used. Specific examples of halide salts, including preferred embodiments, are as described in the section on the anode electrolyte.

[0037] In the cathode electrolyte 16X, one type of halogenated salt may be used alone, or two or more types may be used in combination. The concentration of the halogenated salt in the cathode electrolyte 16X is not particularly limited, but is often, for example, 0.01 to 10 M, preferably 0.02 to 3 M, and more preferably 0.05 to 2 M. The cathode electrolyte may contain components other than the solvent, carbon dioxide, and halogenated salt as appropriate, for example, electrolytes other than halogenated salts may be included. Furthermore, the cathode electrolyte 16X may contain by-products such as carbonates and hydroxides.

[0038] (Cathode) The cathode 13 may have an electrode substrate. The electrode substrate is not particularly limited as long as it is a material conventionally used for the cathode of an electrochemical cell, and examples include carbon substrates, metal substrates, and metal oxide substrates, and it is preferable that it is conductive. The electrode substrate may also be a porous material. The substrate is a substrate that constitutes the electrode, and may be in the form of a sheet, a plate, etc., or it may be a layered material laminated on the wall of the cathode chamber 16.

[0039] Examples of carbon substrates include porous carbon such as carbon nonwoven fabrics. The carbon nonwoven fabric is not particularly limited, and known carbon nonwoven fabrics can be used. For example, commercially available carbon nonwoven fabrics for fuel cells can be used, such as Toray Industries' "Torayca" (registered trademark) carbon paper, Toray060, New Metal & Chemicals' "AvCarb 1071HCB", and SGL's BC series. Examples of metal substrates include metal meshes, and metals that can be used include gold, silver, platinum, nickel, titanium, and chromium. Examples of metal oxides used in metal oxide substrates include indium oxide, tin oxide, tin-doped indium oxide, and fluorine-doped tin oxide (FTO).

[0040] (First Catalyst) The first catalyst is a reduction catalyst capable of reducing carbon dioxide to carbon monoxide. The first catalyst is contained in cathode 13. The reduction catalyst (first catalyst) is not particularly limited as long as it is a catalyst capable of reducing carbon dioxide to carbon monoxide. For example, the reduction catalyst may contain a metal element, and the metal element may be the metal itself or a metal compound. The metal element in the above metal is not particularly limited, but examples include V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, Zn, Os, and Nd. As the above-mentioned metal compounds, inorganic metal compounds and organometallic compounds of these metals can be used. Specifically, examples include metal halides, metal oxides, metal hydroxides, metal nitrates, metal sulfates, metal acetates, metal phosphates, metal carbonyls, and metal acetylacetonates, among which metal oxides are preferred.

[0041] The metal element used in the first catalyst is preferably a metal element from Group 7 to Group 12. Preferred specific examples include Mn, Fe, Ni, Ru, Co, Rh, Cu, Zn, Ag, Au, Pd, Ir, Pt, and Os, among which Co, Fe, Ni, Au, and Ag are more preferred, Co, Fe, and Ni are even more preferred, and Co is particularly preferred. Using these metal elements makes it easier to increase the conversion efficiency from carbon dioxide to carbon monoxide and thus increases catalytic activity. The metal element may be used alone or in combination of two or more.

[0042] The first catalyst may also preferably contain a carbon compound in addition to the above-mentioned metal or metal compound. A conductive carbon compound is preferred as the carbon compound. More specifically, examples of carbon compounds include mesoporous carbon, activated carbon, carbon black such as Ketjenblack and acetylene black, graphite, carbon fiber, graphene, and carbon nanotubes, among which carbon black is preferred, and conductive carbon black is even more preferred. Furthermore, the carbon compound is preferably porous carbon. When the first catalyst contains a carbon compound, the metal or metal compound may be supported on the carbon compound.

[0043] The first catalyst is preferably a catalyst containing a nitrogen element and a metal element (also called a "nitrogen-containing metal catalyst"), and more preferably contains a nitrogen element, a metal element, and a carbon compound. Here, the nitrogen element used in the nitrogen-containing metal catalyst is preferably derived from a nitrogen-containing compound, as described later. Specific examples of metal elements used in the nitrogen-containing metal catalyst are as described above, and the preferred metal elements are also as described above. Using a nitrogen-containing metal catalyst increases the efficiency of carbon monoxide production.

[0044] The first catalyst is preferably a catalyst obtained by calcining a mixture containing a metal derivative and a carbon compound, or a mixture containing a metal derivative and a nitrogen-containing compound (hereinafter referred to as the "first catalyst raw material mixture"). In particular, it is preferable that the catalyst is obtained by calcining a first catalyst raw material mixture containing a metal derivative, a nitrogen-containing compound, and a carbon compound. When a nitrogen-containing metal catalyst is produced by calcining the first catalyst raw material mixture, metal-nitrogen element bonds derived from the metal derivative and the nitrogen-containing compound are formed in the catalyst. The carbon compound functions as a support in the catalyst, and components derived from the metal derivative and the nitrogen-containing compound are supported on the carbon compound. A nitrogen-containing metal catalyst having the above configuration efficiently reduces carbon dioxide to carbon monoxide, resulting in high conversion efficiency.

[0045] The metal elements in the metal derivative are as described above. The metal derivative preferably contains metal ions. Furthermore, the metal derivative may be used, for example, in the form of a metal salt. Examples of metal salts include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates, with metal nitrates being preferred among these. Alternatively, hydrates of metal salts may be used as the metal derivative. The metal salt may be used alone or in combination of two or more types.

[0046] The metal content derived from the metal derivative in the first catalyst raw material mixture is preferably, for example, 0.1% by mass or more and 50% by mass or less, but is more preferably 0.5% by mass or more and 10% by mass or less. By keeping it within this range, the metal is contained in the catalyst without aggregation, and an appropriate amount of catalytic active sites are formed. This makes it easier to increase the conversion efficiency to carbon monoxide. From the viewpoint of conversion efficiency, the metal content derived from the metal derivative in the first catalyst raw material mixture is more preferably 1% by mass or more, even more preferably 2% by mass or more, even more preferably 10% by mass or less, and even more preferably 8% by mass or less. The total amount of the first catalyst raw material mixture means the total amount of solids in the first catalyst raw material mixture, and if volatile components that volatilize during the manufacturing process (for example, water molecules of solvents or hydrates) are blended into the first catalyst raw material mixture, it is the amount excluding those volatile components.

[0047] (Nitrogen-containing compounds) Nitrogen-containing compounds are compounds that contain nitrogen, and components derived from nitrogen-containing compounds preferably form bonds such as coordination bonds with metal elements derived from metal derivatives in nitrogen-containing metal catalysts. Specifically, nitrogen-containing compounds include compounds containing nitrogen-containing aromatic rings that have nitrogen as a constituent element of the aromatic ring. Specific examples of nitrogen-containing compounds include pyridine derivatives, imidazole derivatives, pyrazole derivatives, and triazole derivatives. These compounds may be used individually or in combination of two or more. Among these, from the viewpoint of conversion efficiency, it is preferable to select one from pyridine derivatives, imidazole derivatives, and triazole derivatives, and particularly preferable to use pyridine derivatives. That is, it is particularly preferable that the nitrogen-containing metal catalyst is a catalyst obtained by calcining a mixture containing a metal derivative, a pyridine derivative, and a carbon compound.

[0048] (Pyridine Derivatives) Pyridine derivatives are compounds having a pyridine ring. A pyridine derivative may be a compound having one pyridine ring in one molecule, two pyridine rings, three pyridine rings, or four or more pyridine rings. A compound having one pyridine ring in one molecule (pyridine monomer) is, for example, a compound with an amino group (-NH) on the pyridine ring. ２ Examples of pyridine monomers include compounds having at least one functional group such as an alkyl group or an alkoxy group. Examples of alkyl groups include alkyl groups having about 1 to 5 carbon atoms, such as methyl, ethyl, butyl, and pentyl (amyl) groups. Examples of alkoxy groups include alkoxy groups having about 1 to 4 carbon atoms, such as methoxy and butoxy groups. Specific examples of pyridine monomers include alkylpyridines such as methylpyridine, ethylpyridine, butylpyridine, and pentylpyridine (amylpyridine), alkoxypyridines such as methoxypyridine and butoxypyridine, and aminopyridines such as 4-aminopyridine.

[0049] Compounds having two pyridine rings in one molecule include compounds having a bipyridine skeleton in which the two pyridine rings are directly bonded by carbon-carbon single bonds (bipyridine derivatives). From the viewpoint of the above-mentioned conversion efficiency when used in a carbon dioxide reduction electrode, bipyridine is preferred as a bipyridine derivative, and 2,2'-bipyridine is more preferred among them. Bipyridine derivatives having an amino group are also preferred, specifically diaminobipyridine, and 4,4'-diamino-2,2'-bipyridine is more preferred among them. Compounds having three pyridine rings in one molecule include compounds having a terpyridine skeleton in which the three pyridine rings are directly bonded by carbon-carbon single bonds (terpyridine derivatives). Examples of terpyridine derivatives include terpyridine.

[0050] Compounds having four or more pyridine rings in one molecule include pyridine oligomers having four or more pyridine rings and a weight-average molecular weight of less than 10,000. Among pyridine oligomers, examples include compounds having a polypyridine skeleton in which pyridine rings are directly bonded to each other by carbon-carbon single bonds. A preferred specific example is polypyridine. Examples of polypyridine include poly(2,5-pyridine) and poly(3,5-pyridine), and among these, poly(2,5-pyridine) is more preferred from the viewpoint of the above-mentioned conversion efficiency when used in a carbon dioxide reduction electrode. The molecular weight of polypyridine such as poly(2,5-pyridine) is not particularly limited, but is preferably 500 to 8,000, preferably 1,000 to 6,000, and more preferably 1,500 to 5,000 in weight-average molecular weight.

[0051] Furthermore, as pyridine derivatives, polymers having multiple pyridine rings in one molecule and a weight-average molecular weight of 10,000 or more are also mentioned. In this case, it is preferable that the pyridine derivative has four or more pyridine rings in one molecule. As specific compounds, polyvinylpyridine, which is a polymer of vinylpyridine, is also preferred, and among these, poly(4-vinylpyridine) is more preferred. Using poly(4-vinylpyridine) makes it easier to increase the conversion efficiency from carbon dioxide to carbon monoxide. From the viewpoint of conversion efficiency, polyvinylpyridine such as poly(4-vinylpyridine) is preferably above a certain molecular weight, for example, 1,000 or more, 10,000 or more, preferably 30,000 or more, and even more preferably 50,000 or more in weight-average molecular weight, and from the viewpoint of its availability, for example, 200,000 or less, preferably 100,000 or less. The weight-average molecular weight is a value measured by gel permeation chromatography (GPC), and polystyrene is preferably used as the standard substance.

[0052] Among the pyridine derivatives mentioned above, aminopyridine, which is a compound having one pyridine ring in its molecule, the pyridine oligomers mentioned above, and polymers with a weight-average molecular weight of 10,000 or more are more preferred from the viewpoint of easily increasing the efficiency of carbon dioxide conversion to carbon monoxide.

[0053] (Imidazole Derivatives) The imidazole derivatives used in active particle-containing catalysts are compounds having an imidazole ring. The imidazole derivative may be a compound having one imidazole ring in one molecule (imidazole monomer), a compound having two, or a compound having three or more. Examples of imidazole monomers include imidazole with an amino group (-NH). ２ Examples include compounds having at least one functional group such as an alkyl group, alkoxy group, halogen group, aryl group, or aralkyl group, and may also have a heterocyclic structure including an imidazole ring.

[0054] Compounds having two imidazole rings in one molecule include compounds having an imidazole skeleton in which the two imidazole rings are directly bonded by carbon-carbon single bonds (biimidazole derivatives). Examples of imidazole derivatives include biimidazole. Furthermore, as compounds having multiple imidazole rings in one molecule, polyvinylimidazole, which is a polymer of vinylimidazole, is preferred, with poly(4-vinylimidazole) and poly(N-vinylimidazole) being more preferred, and poly(4-vinylimidazole) being even more preferred. Polyvinylimidazoles such as poly(4-vinylimidazole) preferably have a molecular weight above a certain level, for example, 1,000 to 200,000, preferably 10,000 to 100,000 in weight-average molecular weight.

[0055] (Pyrazole derivatives) Pyrazole derivatives are compounds having a pyrazole ring. A pyrazole derivative may be a compound having one pyrazole ring in one molecule (pyrazole monomer), a compound having two pyrazole rings, or a compound having three or more pyrazole rings. Examples of pyrazole monomers include compounds with an amino group (-NH) on the pyrazole ring. ２ Examples include compounds having at least one functional group such as an alkyl group, alkoxy group, aryl group, or aralkyl group.

[0056] (Triazole Derivatives) Triazole derivatives are compounds having a triazole ring. A triazole derivative may be a compound having one triazole ring in one molecule (triazole monomer), a compound having two triazole rings, or a compound having three or more triazole rings. Examples of triazole monomers include compounds with an amino group (-NH₂) on the triazole ring. ２Examples include compounds having at least one functional group such as an alkyl group or an alkoxy group. Examples of compounds having two triazole rings in one molecule include compounds having a vitriazole skeleton in which two triazole rings are directly bonded by a carbon-carbon single bond (vitriazole derivatives). Examples of vitriazole derivatives include vitriazole. Furthermore, as compounds having multiple triazole rings in one molecule, polyvinyltriazole, which is a polymer of vinyltriazole, is preferred, and poly(1-vinyl-1,2,4-triazole) is more preferred. The weight-average molecular weight of polyvinyltriazoles such as poly(1-vinyl-1,2,4-triazole) is 1,000 to 200,000, preferably 10,000 to 100,000. In the first catalyst raw material mixture, the nitrogen-containing compound may be used alone or two or more may be used in combination.

[0057] The amount of nitrogen-containing compound in the first catalyst raw material mixture (i.e., the first catalyst) is preferably adjusted so that the molar ratio of nitrogen-containing aromatic rings in the nitrogen-containing compound to the metal elements of the metal derivative (nitrogen-containing aromatic rings / metal elements) is between 2 and 20. Within this range, the occurrence of side reactions is suppressed, a catalyst containing an appropriate amount of metal-nitrogen element bonds can be produced, and the conversion efficiency described above can be easily increased. From the viewpoint of conversion efficiency, the molar ratio is more preferably 2 or more, even more preferably 4 or more, even more preferably 18 or less, and even more preferably 15 or less. The molar ratio represents the ratio of the number of nitrogen-containing aromatic rings in the nitrogen-containing compound to the number of moles of metal elements in the metal derivative.

[0058] The carbon compound used in the nitrogen-containing metal catalyst is not particularly limited as long as it can support heat-treated products (e.g., calcined products) of metal derivatives and nitrogen-containing compounds such as pyridine derivatives, but conductive carbon compounds are preferred. Using a conductive carbon compound increases the electrical conductivity at the cathode, making it easier to increase the conversion efficiency to carbon monoxide. Specific examples of carbon compounds are as described above. The content of the carbon compound in the first catalyst raw material mixture is not particularly limited relative to the total amount of the first catalyst raw material mixture, but is, for example, 10% by mass or more and 90% by mass or less, preferably 15% by mass or more and 80% by mass or less, and more preferably 20% by mass or more and 70% by mass or less. By keeping the carbon compound content within the above range, the metal derivative and heat-treated products of nitrogen-containing compounds can be appropriately supported while maintaining good catalytic activity.

[0059] The first catalyst is preferably in powder or particulate form. Being in powder or particulate form makes it easier to support on the electrode substrate described later. Furthermore, it increases the contact area with carbon dioxide, making it easier to improve the conversion efficiency to carbon monoxide. The surface area of ​​the first catalyst is, for example, 100 m². 2 / g or more 4000m 2 It is less than or equal to / g, preferably 200m 2 / g or more 3000m 2 The particle size is less than or equal to / g. The average particle size of the first catalyst is, for example, 1 nm to 1000 nm, preferably 5 nm to 500 nm. The surface area of ​​the catalyst can be measured, for example, by gas adsorption analysis. The average particle size of the catalyst can be measured, for example, by dynamic light scattering analysis or electron microscopy observation.

[0060] As described above, the nitrogen-containing metal catalyst obtained by heat treatment (i.e., calcination) contains a metal element and a nitrogen element. However, the metal element may be included in the nitrogen-containing metal catalyst as a metal oxide from the viewpoint of selectivity, ease of manufacture, etc. As described above, cobalt is particularly preferred as the metal element, and therefore, the nitrogen-containing metal catalyst may contain cobalt oxide. Furthermore, it is particularly preferred that the cobalt oxide contains CoO.

[0061] Furthermore, as described above, nitrogen-containing metal catalysts preferably contain components derived from nitrogen-containing compounds after heat treatment. In particular, components derived from pyridine derivatives are preferred. Therefore, nitrogen-containing metal catalysts also preferably contain components derived from cobalt and pyridine derivatives. In addition, nitrogen-containing metal catalysts also preferably contain components derived from cobalt metal and pyridine derivatives, as described later. The nitrogen atoms derived from the nitrogen-containing compound are preferably coordinated to metal elements such as cobalt. The components derived from the nitrogen-containing compound preferably contain nitrogen-containing aromatic ring structures, specifically pyridine ring structures, imidazole ring structures, pyrazole ring structures, and triazole ring structures. Among these, pyridine ring structures, imidazole ring structures, and triazole ring structures are preferred, with pyridine ring structures being particularly preferred. It is estimated that the activation energy of the reaction intermediate is lowered when metal elements such as cobalt coordinate to the nitrogen in the pyridine ring structure, thereby increasing the conversion efficiency. As described above, nitrogen-containing metal catalysts are produced by heat treatment of a mixture containing nitrogen-containing compounds, but the treatment temperature is low. Therefore, nitrogen-containing aromatic rings contained in nitrogen-containing compounds can be retained in nitrogen-containing metal catalysts.

[0062] Furthermore, the nitrogen-containing metal catalyst may contain various metallic elements. Therefore, if the metallic element is cobalt, it may contain cobalt metal. The cobalt metal may, for example, be crystalline. When the nitrogen-containing metal catalyst contains cobalt metal, it is preferable that it has a core-shell structure in which cobalt metal forms the core and cobalt oxide is arranged around the core to coat the cobalt metal. It is presumed that having a core-shell structure in the nitrogen-containing metal catalyst improves the conductivity of the catalyst and makes it easier to improve the reduction rate of carbon dioxide. The core-shell structure may be in particulate form and supported on the carbon compound.

[0063] 《Method for Producing the First Catalyst》 The first catalyst can be produced by heating a mixture of first catalyst raw materials containing a metal derivative and a nitrogen-containing compound such as a pyridine derivative, a metal derivative and a carbon compound, or a metal derivative, a nitrogen-containing compound and a carbon compound. In this case, it is preferable that the mixture of first catalyst raw materials be heat-treated (i.e., calcined) by heating it to a temperature of 150°C to 550°C. By keeping the heating temperature within the above range, the generation of unwanted by-products can be suppressed, and for example, metal-nitrogen element bonds derived from the metal derivative and nitrogen-containing compound can be appropriately generated, thereby imparting appropriate catalytic activity to the nitrogen-containing metal catalyst. Furthermore, keeping the temperature below the above upper limit makes it easier to commercialize industrially. From the viewpoint of improving catalytic activity and increasing conversion efficiency, and from the viewpoint of practical application, the heating temperature is preferably 180°C to 500°C, more preferably 200°C to 470°C, and even more preferably 250°C to 450°C. Furthermore, it is preferable that the above heat treatment be carried out under an inert gas atmosphere such as argon or nitrogen gas. The first catalyst raw material mixture can be heat-treated at the above-mentioned heating temperature to form metal-nitrogen element bonds, and a metal derivative, or a component derived from a metal derivative and a nitrogen-containing compound, can be supported on the carbon compound. The heating time at the above-mentioned heating temperature is not particularly limited, but is, for example, 0.5 hours or more and 10 hours or less, preferably 1 hour or more and 8 hours or less, and more preferably 2 hours or more and 5 hours or less. The first catalyst raw material mixture to be heat-treated is preferably in powder or particulate form. Being in powder or particulate form allows for obtaining a powder or particulate catalyst by heat treatment.

[0064] The first catalyst raw material mixture may be obtained, for example, by preparing a diluted solution of the first catalyst raw material mixture by diluting a metal derivative and a nitrogen-containing compound, a metal derivative and a carbon compound, or a metal derivative, a nitrogen-containing compound, and a carbon compound with a diluent solvent, and then drying the diluted solution. The first catalyst raw material mixture may be obtained, for example, in powder or particulate form. Furthermore, in the diluted solution of the first catalyst raw material mixture, it is preferable that each component (metal derivative, nitrogen-containing compound, and carbon compound) is dispersed or dissolved in the diluent solvent. By dispersing or dissolving each component in the diluent solvent, a first catalyst raw material mixture in which each component is homogeneously mixed can be obtained. Water and organic solvents can be used as the diluent solvent for diluting the first catalyst raw material mixture, but organic solvents are preferred. Alternatively, a mixed solvent of organic solvent and water may be used as the diluent solvent. The concentration of the diluted solution of the first catalyst raw material mixture is not particularly limited, but for example, it is 0.01 to 50 g / L, preferably 1 to 10 g / L.

[0065] The first catalyst may also be a carbon compound containing at least one heteroatom such as nitrogen, or a metal or a metal compound. Examples of such carbon compounds include nitrogen-containing graphite, nitrogen-containing carbon nanotubes, nitrogen-containing graphene, Ni and nitrogen-containing graphite, Ni and nitrogen-containing carbon nanotubes, Ni and nitrogen-containing graphene, Cu and nitrogen-containing graphite, Cu and nitrogen-containing carbon nanotubes, Cu and nitrogen-containing graphene, Co and nitrogen-containing graphite, Co and nitrogen-containing carbon nanotubes, and Co and nitrogen-containing graphene. In cathode 13, the first catalyst may be used alone or in combination of two or more types.

[0066] The first catalyst may be incorporated into the cathode 13 by supporting it on the electrode substrate constituting the cathode 13. The method of supporting the first catalyst on the electrode substrate is not particularly limited, and the first catalyst may be attached to the electrode substrate by known methods. Here, attachment refers to a state in which the catalyst is physically fixed to the electrode substrate, and the atoms constituting the electrode substrate do not necessarily have to be chemically bonded to the atoms constituting the first catalyst.

[0067] Furthermore, the first catalyst may be supported on the cathode 13 together with the catalyst additive. The catalyst additive also functions as a binder when supporting the catalyst on the electrode substrate. In addition, it also functions as an ion conductor, improving the electrochemical reaction efficiency. Examples of catalyst additives include cationic conductive compounds, anionic conductive compounds, and fluorine compounds other than cationic conductive compounds and anionic conductive compounds.

[0068] Cationic conductive compounds used as catalyst additives include, for example, functional groups having Brønsted acids or salts thereof, and compounds having functional groups that become anionic when hydrogen ions are released. Examples of cationic conductive compounds include compounds having at least one functional group such as a sulfonyl group, a phosphate group, a hydroxyl group, and a silicate group. Specifically, a commercially available product is "Nafion" (a trademark of DuPont). Examples of anionic conductive compounds include, for example, compounds having functional groups having Brønsted bases or salts thereof, and compounds having functional groups that become cationized when protons are added. Anionic conductive compounds have excellent conductivity for anions such as hydroxide ions. Specific examples of anionic conductive compounds include compounds having functional groups such as a pyridinium group, an imidazolium group, an amino group, and an ammonium group. As anionic conductive compounds, commercially available products such as FuMA-Tech GmbH's "Fumion FAA-3-SOLUT-10" and Resintech's "PowerMax NXS125 OH" can also be used. Examples of fluorine compounds include polytetrafluoroethylene (PTFE), tetrafluoroethylene oligomer (TFEO), graphite fluoride ((CF)n), and fluorinated pitch (FP).

[0069] The catalyst additive may, for example, be in the form of a powder or particulate matter. When using a catalyst additive, the first catalyst may be mixed with the catalyst additive and supported on the electrode substrate in the form of a mixture (catalyst composition). When the catalyst is supported on the electrode substrate together with the catalyst additive, the content of the catalyst additive relative to the total amount of the catalyst additive and catalyst is preferably 10% to 50% by mass, more preferably 15% to 45% by mass, and even more preferably 20% to 40% by mass, from the viewpoint of improving the conversion efficiency of the catalyst.

[0070] The method for supporting the first catalyst on the electrode substrate is not particularly limited, but examples include a method in which the first catalyst and non-catalyst components such as catalyst additives added as needed are diluted with a dilution solvent, and the diluted solution is applied to the electrode substrate using various coating devices or by spray coating and then dried, or a method in which the electrode substrate is immersed in the above-mentioned diluted solution and dried.

[0071] (Anode) In this embodiment, the anode 23 may be made of an electrode substrate. Details of the electrode substrate are as described in the section on the cathode and will be omitted here. The material used for the electrode substrate of the anode 23 may be the same material as the electrode substrate of the cathode, or a different material may be used. The anode 23 may contain a catalyst (oxidation catalyst) or may not contain a catalyst.

[0072] (Diaphragm) In this embodiment, the diaphragm 19 is preferably an ion exchange membrane. The cathode 13 and anode 23 may be arranged on both sides of the diaphragm 19 and joined together to form a membrane-electrode assembly, but it is preferable that the cathode 13 and anode 23 are not joined to the diaphragm 19 and are positioned away from the ion exchange membrane, as shown in Figure 1. As the ion exchange membrane, a solid membrane is used, and examples include a cation exchange membrane that can permeate cations such as protons and an anion exchange membrane that can permeate anions such as hydroxide ions, but in this embodiment, it is preferable that a cation exchange membrane is used as described above.

[0073] Examples of cation exchange membranes include those having at least one of the following functional groups: sulfonyl group, carboxyl group, phosphate group, and silicate group. Examples of cation exchange membranes having a sulfonyl group as a functional group include hydrocarbon resin-based polysulfonic acids such as polyethylene sulfonic acid and fullerene crosslinked polysulfonic acid, and fluororesin-based sulfonic acids such as perfluoroethylene sulfonic acid. Examples of perfluoroethylene sulfonic acid include copolymers of tetrafluoroethylene and perfluoro[2-(fluorosulfonylethoxy)propyl vinyl ether], and a commercially available product is "Nafion" (a trademark of DuPont). Examples of membranes having a carboxyl group as a functional group include polycarboxylic acids such as polyacrylic acid. Examples of membranes having a phosphate group or silicate group as a functional group include heteropoly acids such as tetratungstic acid and phosphotungstic acid. Furthermore, as a cation exchange membrane, SiO ２ -P ２ O ５ Ceramics such as phosphated glass and perovskite oxides can also be used.

[0074] Furthermore, examples of anion exchange membranes include resins and polyethers containing quaternary ammonium salts such as poly(styrylmethyltrimethylammonium chloride), and polymers containing imidazolium groups. Examples of resins containing ammonium salts include "FAA-3-50" from FuMA-Tech GmbH and "TM1 Durion Grade" from Orion. Examples of polymers containing imidazolium groups include styrene-based polymers containing imidazolium groups, specifically copolymers of styrene and 1-(p-vinylbenzyl)-3-methylimidazolium (PSMIM), copolymers of styrene and 1-(p-vinylbenzyl)-tetramethylimidazolium (PSTMIM), and copolymers of styrene and 1-(p-vinylbenzyl)-2,3-dimethylimidazolium (PSDMIM).

[0075] In one embodiment of the first embodiment, it is preferable to appropriately predict or detect the carbonate concentration produced as a by-product in the cathode electrolyte 16X to control the process so that carbonate does not precipitate in the cathode chamber 16, or so that the amount of carbonate precipitated in the cathode chamber 16 is reduced. Carbonates generally precipitate easily in alkaline electrolytes with a high pH. Therefore, in one embodiment of the first embodiment, it is preferable to appropriately predict the carbonate concentration in the cathode electrolyte 16X by measuring the pH of the cathode electrolyte 16X. Alternatively, the carbonate concentration may be predicted by means other than pH measurement; specifically, the carbonate concentration may be predicted by measuring the carbon monoxide concentration in the cathode electrolyte 16X. The carbon monoxide concentration in the cathode electrolyte 16X increases as the reduction reaction progresses. As shown in equation (i), there is a correlation between the amount of carbon monoxide generated and the amount of hydroxide ions generated, so the higher the carbon monoxide concentration, the more alkaline the solution becomes. In other words, the higher the carbon monoxide concentration, the higher the carbonate concentration, so the carbonate concentration can also be predicted by measuring the carbon monoxide concentration. While pH and carbon monoxide concentration may be measured by measuring the cathode electrolyte 16X in the cathode chamber 16, it is preferable to measure the pH and carbon monoxide concentration of the cathode electrolyte 16X discharged from the first discharge line 18, from the viewpoint of ease of measurement and measurement stability.

[0076] The carbonate concentration of the cathode electrolyte 16X can be controlled, for example, by controlling the current flowing between the cathode 13 and the anode 23. Specifically, when the pH or carbon monoxide concentration, as measured above, becomes high, the current value should be lowered. Lowering the current value suppresses the generation of carbon monoxide, and consequently, the generation of carbonate in the cathode electrolyte 16X is also suppressed, thereby lowering the carbonate concentration. Alternatively, the current value can be increased when the pH or carbon monoxide concentration becomes low. Increasing the current value increases the amount of carbon monoxide generated, and consequently, more carbonate is generated in the cathode electrolyte 16X, resulting in a higher carbonate concentration. By controlling the carbonate concentration in this way, the pH of the cathode electrolyte 16X should be controlled to be below a certain value. Specifically, the pH of the cathode electrolyte 16X should be controlled to be, for example, 8 or less, preferably 7.5 or less, and more preferably 7 or less. The cathode electrolyte 16X is not particularly limited, but from the viewpoint of maintaining good carbon monoxide production efficiency regardless of the type of first catalyst, it is preferable that its pH be controlled to preferably be 5 or higher, more preferably 6 or higher, and even more preferably 6.5 or higher.

[0077] Furthermore, the carbonate concentration of the cathode electrolyte 16X in the cathode chamber 16 may be controlled by means other than the current value. For example, if the pH or carbon monoxide concentration, as measured above, becomes high, an acidic component may be added to the cathode electrolyte 16X in the cathode chamber 16 to lower the pH. The acidic component is as described later.

[0078] In another embodiment of the first embodiment, an acidic component may be added to the cathode electrolyte 16X. The acidic component may be either an inorganic acid or an organic acid, but an inorganic acid is preferred. Specifically, examples include hydrogen halides such as hydrogen chloride and hydrogen bromide, sulfuric acid, nitric acid, phosphoric acid, selenic acid, and boric acid. Among these, hydrogen halides are preferred, and hydrogen chloride (hydrochloric acid) is more preferred.

[0079] The cathode electrolyte 16X is preferably acidic (i.e., pH less than 7) when the above-mentioned acidic component is added, and from the viewpoint of further preventing the precipitation of carbonate in the cathode electrolyte 16X, a pH of 6.5 or less is more preferable, 6 or less is even more preferable, and 5 or less is even more preferable. On the other hand, it is preferable that the cathode electrolyte 16X has a pH of 2 or higher when it contains the above-mentioned acidic component. A pH of 2 or higher can suppress a decrease in the Faraday efficiency of carbon monoxide production. From the viewpoint of Faraday efficiency, a pH of 3 or higher is preferable. The pH may be measured, for example, by a pH meter.

[0080] Furthermore, while the carbon dioxide reduction catalyst (first catalyst) generally exhibits a lower Faraday efficiency for carbon monoxide production under acidic conditions, in another aspect of this embodiment, it is preferable to use the nitrogen-containing metal catalyst described above as the first catalyst. Surprisingly, the nitrogen-containing metal catalyst can suppress the decrease in Faraday efficiency for carbon monoxide production under acidic conditions. Details of the nitrogen-containing metal catalyst are as described above, as are preferred specific examples thereof. Therefore, the metal elements used in the nitrogen-containing metal catalyst are more preferably Co, Fe, Ni, Au, and Ag, even more preferably Co, Fe, and Ni, and particularly preferably Co. The nitrogen-containing compound, carbon compound, and method of producing the nitrogen-containing metal catalyst are also as described above. The reaction at cathode 13 when the cathode electrolyte 16X is acidic is typically shown by the following formula (i-2). CO ２ +2H ＋ +2e － →CO+H ２ O (i-2)

[0081] <Second Embodiment> Next, the differences between the second embodiment and the first embodiment will be explained with reference to Figure 2. In the first embodiment, the electrolytic cell was divided into an anode chamber and a cathode chamber, making it a two-chamber type. However, in the electrochemical reactor 10A according to the second embodiment, there is no diaphragm, and the electrolytic cell 11 (electrolytic device) is not divided into a cathode chamber and an anode chamber, but is a one-chamber type consisting of a single electrolytic chamber 36. The electrolyte (bipolar electrolyte) 36X is filled into the electrolytic chamber 36, and as a result, it comes into contact with both the cathode 13 and the anode 23 located inside the electrolytic chamber 36.

[0082] In this embodiment, the bipolar electrolyte 36X is an aqueous solution of a halogenated salt in which carbon dioxide is dissolved. That is, the bipolar electrolyte 36X is preferably a solution in which a halogenated salt is dissolved in water with water as the solvent, and carbon dioxide is also dissolved in it. Details of the halogenated salt are as described above. In the bipolar electrolyte 36X, one type of halogenated salt may be used alone, or two or more types may be used in combination. The concentration of the halogenated salt in the bipolar electrolyte is not particularly limited, but is preferably 0.01 to 10 M, more preferably 0.02 to 3 M, and more preferably 0.05 to 2 M. In addition, the bipolar electrolyte 36X may contain components other than water and halogenated salt as appropriate, for example, an electrolyte other than a halogenated salt may be contained. Furthermore, the bipolar electrolyte 36X may contain by-products such as carbonates and hydroxides. In this embodiment as well, an electrochemical reaction takes place in the cathode 13 and the anode 23. In this embodiment, the cathode 13 contains a first catalyst that promotes the reaction of reducing carbon dioxide to carbon monoxide. Therefore, carbon monoxide is produced as a reduced product at cathode 13. Also, a halogen is produced at anode 23. In the second embodiment as well, the reaction shown in formula (i) typically takes place at cathode 13, and the reaction shown in formula (ii) takes place at anode 23.

[0083] The electrolytic chamber 36 is preferably connected to a supply line 37 as a supply means and a discharge line 38 as a discharge means. An aqueous halogenated salt solution containing carbon dioxide (i.e., bipolar electrolyte 36X) is supplied to the electrolytic chamber 36 by the supply line 37. The carbon monoxide produced by reduction at the cathode 13 and the halogen produced at the anode 23 are discharged to the outside of the electrolytic chamber 36 along with the bipolar electrolyte 36X by the discharge line 38. In addition, as the reaction shown in formula (i) above takes place, hydroxides such as NaOH are typically produced in the electrolytic chamber 36, and these hydroxides are also preferably discharged to the outside along with the bipolar electrolyte 36X. The supply and discharge of the bipolar electrolyte 36X is preferably carried out continuously, so that the electrolyte 36X flows with a constant flow inside the electrolytic chamber 36, and the reduction and oxidation reactions at the cathode 13 and anode 23 are carried out efficiently. The supply and discharge of the electrolyte 36X described above may be carried out continuously or intermittently. The supply and discharge of the bipolar electrolyte 36X (or circulation in the circulation path described later) may be carried out by a pump, as in the first embodiment, or by known means other than a pump.

[0084] In this embodiment, the electrochemical reactor 10A may further include a storage section 42 and a reactor 43. The storage section 42 stores the bipolar electrolyte 36X. The storage section 42 is not particularly limited in its configuration as long as it can store the bipolar electrolyte 36X, but it may be provided with a stirring device as appropriate, and the stored anode electrolyte may be mixed by the stirring device. The discharge line 38 is preferably connected to the storage section 42. As a result, the bipolar electrolyte 36X containing carbon monoxide and halogens is supplied to the storage section 42 via the discharge line 38 and stored in the storage section 42. In addition, as described above, the bipolar electrolyte 36X typically also contains hydroxides, and therefore, it is preferable that the storage section 42 stores the bipolar electrolyte 36X containing hydroxides.

[0085] In the storage section 42, it is preferable to have a space at the top (i.e., a gas phase 42G). Carbon monoxide produced in the cathode 13 and halogens produced in the anode 23 generally have low solubility in water. Therefore, the presence of the gas phase 42G makes it easier for halogens and carbon monoxide that cannot dissolve in the anode electrolyte 26X to be released into the gas phase 42G of the storage section 42. Furthermore, it is preferable that a gas discharge line 39 is connected to the gas phase 42G of the storage section 42, and that the gas in the gas phase 42G of the anode-side storage section 42 is discharged to the outside from the gas discharge line 39. In this embodiment, the gas discharge line 39 is connected to the synthesizer 43, and halogens and carbon monoxide are supplied to the synthesizer 43 via the gas discharge line 39.

[0086] In this embodiment, the synthesizer 43 is configured to produce reaction products such as carbonyl halides from a halogen and carbon monoxide. Preferably, the halogen is chlorine, and it is preferable that phosgene is synthesized in the synthesizer 43. In other words, in this embodiment, the electrochemical reactor 10A can also be called a phosgene synthesizer. The synthesizer 43 may contain a catalyst as appropriate so that the reaction products are produced. For example, when phosgene is produced, the synthesizer 43 may be one in which activated carbon is packed inside as a catalyst. Alternatively, phosgene may be produced by reacting chlorine and carbon monoxide in the presence of activated carbon at a temperature of about 50 to 150°C, at normal pressure or under pressure.

[0087] In this embodiment as well, similar to the first embodiment, the supply line 37 may be connected to the storage unit 42, and the bipolar electrolyte 36X may circulate between the storage unit 42 and the electrolytic chamber 36. In this case, the circulation path may be formed by the electrolytic chamber 36, the discharge line 38, the storage unit 42, and the supply line 37.

[0088] In this embodiment as well, the internal temperature of the electrolytic cell 11 (i.e., the temperature of the electrolyte 36X) is the same as in the first embodiment, and the electrolytic cell 11 may be appropriately equipped with a heater, and the cathode 13 and the like may be appropriately heated, as in the first embodiment. Furthermore, in the second embodiment as well, as one aspect, the carbonate concentration generated in the bipolar electrolyte 36X may be appropriately predicted or detected and controlled so that carbonate does not precipitate in the electrolytic chamber 36, or the amount of carbonate precipitated in the electrolytic chamber 36 is reduced. Specifically, as in the first embodiment, the carbonate concentration of the electrolyte 36X may be predicted by measuring the pH of the bipolar electrolyte 36X, or the carbonate concentration may be predicted by measuring the carbon monoxide concentration. In this case, the pH and carbon monoxide concentration may be measured by measuring the electrolyte 36X in the electrolytic chamber 36, but from the viewpoint of ease of measurement and stability of measurement, it is preferable to measure the pH and carbon monoxide concentration of the electrolyte 36X discharged from the discharge line 38. The carbonate concentration of the electrolyte 36X can be controlled, for example, by controlling the current flowing between the cathode 13 and the anode 23, and the details thereof may be the same as in the first embodiment described above. Alternatively, the carbonate concentration of the electrolyte 36X may be controlled by adding acidic or alkaline components to the electrolyte 36X as appropriate.

[0089] In the second embodiment described above, carbon dioxide is dissolved in the bipolar electrolyte 36X, and the reaction on the cathode 13 side takes place in the liquid phase. Therefore, even if carbonate is generated on the cathode 13 side by the generated hydroxide ions, cations derived from the halide salt, and carbon dioxide, the carbonate is dissolved in the electrolyte 36X, and the precipitation of carbonate is suppressed. Thus, it is possible to prevent a decrease in the reactivity of the reduction reaction at cathode 13 due to the generation of carbonate. In addition, since the products at each electrode are all gases, the products are less likely to come into contact with the electrodes (cathode and anode), so the generation of by-products can be suppressed. Furthermore, in this embodiment, the diaphragm 19 is omitted, so the configuration of the electrolytic device can be simplified. Moreover, by synthesizing other reaction products such as phosgene from the generated halogen and carbon monoxide, there is no need for gas separation, and the overall configuration of the electrochemical reactor 10A can be simplified.

[0090] <Third Embodiment> Next, a third embodiment will be described with reference to Figure 3. The electrochemical reactor 10B according to the third embodiment differs from the second embodiment in that there is a space above the electrolytic chamber 36 filled with bipolar electrolytes 36X, where a gas phase 36G is formed. In addition, the electrolytic cell 11 is connected to a gas discharge line 48 connected to the gas phase 36G and an electrolyte discharge line 49 connected to the electrolyte 36X filling the electrolytic chamber 36, so that the gas of the gas phase and the electrolyte are discharged separately. The differences between the third embodiment and the second embodiment will be described below.

[0091] In this embodiment as well, the bipolar electrolyte 36X is an aqueous solution of a halogenated salt in which carbon dioxide is dissolved. That is, the bipolar electrolyte 36X is a solution in which a halogenated salt is dissolved in water with water as the solvent, and carbon dioxide is also dissolved in it. In this embodiment as well, electrochemical reactions occur in the cathode 13 and anode 23, with carbon monoxide being produced as a reduced product in the cathode 13 and a halogen being produced in the anode 23.

[0092] A supply line 47 is connected to the electrolytic chamber 36 as a supply means, and as described above, a gas discharge line 48 and an electrolyte discharge line 49 are also connected as discharge means. An aqueous halogenated salt solution containing carbon dioxide (i.e., bipolar electrolyte 36X) is supplied to the electrolytic chamber 36 by the supply line 47. The carbon monoxide produced by reduction at the cathode 13 and the halogen produced at the anode 23 are released into the gas phase 36G and discharged to the outside of the electrolytic chamber 36 by the gas discharge line 48. The bipolar electrolyte 36X is also discharged to the outside of the electrolytic chamber 36 from the electrolyte discharge line 49. The bipolar electrolyte 36X discharged from the electrolyte discharge line 49 may appropriately contain hydroxides such as NaOH, as described in the second embodiment. The supply and discharge of the bipolar electrolyte 36X is preferably carried out continuously, so that in this embodiment as well, the electrolyte 36X flows within the electrolytic chamber 36 in a constant flow, and the reduction and oxidation reactions in the cathode 13 and anode 23 are carried out efficiently.

[0093] In this embodiment, as in the second embodiment, the electrochemical reactor 10B may include a storage unit 42 and a reactor 43. The storage unit 42 may be connected to a carbon dioxide supply line 46, and carbon dioxide may be supplied from a carbon dioxide supply source (not shown) via the carbon dioxide supply line 46. In the storage unit 42, carbon dioxide is mixed with the halogenated salt aqueous solution, thereby obtaining an electrolyte 36X containing carbon dioxide. The storage unit 42 may be connected to a liquid supply line, a liquid discharge line, etc. (not shown), and the halogenated salt aqueous solution (electrolyte 36X) may be supplied to the storage unit 42 via the liquid supply line, and the halogenated salt aqueous solution (electrolyte 36X) may be discharged to the outside via the liquid discharge line.

[0094] In this embodiment, the supply line 47 connects the electrolytic chamber 36 and the storage unit 42, and the electrolyte discharge line 49 also connects the electrolytic chamber 36 and the storage unit 42. As a result, the electrolyte 36X stored in the storage unit 42 is supplied to the electrolytic chamber 36 via the supply line 47, and the electrolyte 36X from the electrolytic chamber 36 is discharged to the storage unit 42, causing the electrolyte 36X to circulate between the electrolytic chamber 36 and the storage unit 42. In this way, the circulation of the electrolyte 36X allows for more efficient generation of carbon monoxide and halogens in the cathode 13 and anode 23.

[0095] On the other hand, the carbon monoxide and halogens generated in the cathode 13 and anode 23 are released as gas into the gas phase 36G and subsequently supplied to the reactor 43 via a gas discharge line 48 connected to the reactor 43. Then, in the reactor 43, reaction products such as phosgene are generated from the carbon monoxide and halogens, similar to the second embodiment.

[0096] In the third embodiment described above, since the reaction on the cathode 13 side is carried out in the liquid phase, even if carbonate is generated, the carbonate is dissolved in the electrolyte 36X, and the precipitation of carbonate is suppressed, thus preventing a decrease in the reactivity of the reduction reaction at cathode 13 due to the generation of carbonate. Furthermore, by making the products at each electrode into gases, the products are less likely to come into contact with the electrodes (cathode and anode), thus suppressing the generation of by-products. In addition, the configuration of the electrolytic apparatus can be simplified by omitting the diaphragm 19, and by synthesizing other reaction products such as phosgene from the generated halogen and carbon monoxide, there is no need for gas separation, and the overall configuration of the electrochemical reactor 10B can also be simplified.

[0097] <Other Embodiments> The embodiments described above are merely examples of the present invention, and various modifications or improvements are possible as long as the gist of the invention is not altered. For example, although the above embodiments were described on the premise that the process is carried out in a continuous manner, it is not necessary to carry it out in a continuous manner, and it may be carried out in a batch manner, in which case the supply and discharge of the electrolyte does not need to be carried out continuously. Also, in the above embodiments, the anode-side storage section 32 and the storage section 42 may be omitted as appropriate, in which case the anode electrolyte or bipolar electrolyte may be circulated without a storage section, but the electrolyte does not need to be circulated.

[0098] Furthermore, in the second and third embodiments, the generated halogen and carbon monoxide were supplied to the reactor, but it is not necessary to supply them to the reactor; they may be supplied elsewhere. Also, reaction products other than halogenated carbonyls may be synthesized in the reactor. For example, a reaction substrate such as an alcohol compound may be contained in the reactor, and carbon monoxide and the alcohol compound may be reacted in the presence of a halogen to synthesize a carbonyl compound such as an organic carbonate. In addition, the carbon monoxide and halogen generated in the first embodiment may also be supplied to the reactor, and reaction products may be synthesized in the reactor.

[0099] The present invention will be described in more detail by reference to examples, but the present invention is not limited in any way by these examples.

[0100] [Catalyst preparation method] (Co-C) 100 mg (0.345 mmol) of Co(NO) ３ ) ２ 6H ２ O (Aldrich), 200 mg (1.91 mmol, pyridine ring equivalent) of poly(4-vinylpyridine) (Aldrich) and 100 mg of Ketjenbrak (product name "EC-300J" (Lion Chemicals), BET specific surface area 800 m² ２ The 1 / g of the catalyst was dispersed in 200 mL of ethanol, dried in an evaporator, and heated at 350°C for 2 hours to obtain a powdered catalyst.

[0101] (Ag-C) 100 mg of Ag(NO) ３ ) ２ (Aldrich) and 100 mg of Ketjenblack (product name "EC-300J" (Lion Chemicals), BET specific surface area 800 m²) ２ The 1 / g of the catalyst was dispersed in 200 mL of ethanol, dried in an evaporator, and heated at 350°C for 2 hours to obtain a powdered catalyst.

[0102] (Au-C) 100mg AuCl ３ (Aldrich) and 100 mg of Ketjenblack (product name "EC-300J" (Lion Chemicals), BET specific surface area 800 m²) ２ The 1 / g of the catalyst was dispersed in 200 mL of ethanol, dried in an evaporator, and heated at 350°C for 2 hours to obtain a powdered catalyst.

[0103] [Cathode Preparation Method] Dispersions were prepared by dissolving 10 mg and 25 mg of each catalyst shown in Table 1 in a 20 wt% Nafion solution (manufactured by Wako) in 10 mL of ethanol and performing ultrasonic testing for 30 minutes. The prepared dispersion was sprayed onto carbon paper (product name "H23", manufactured by Freudenberg), and after the ethanol was evaporated under atmospheric pressure, the paper was dried in an oven at 120°C for several hours to obtain a cathode supported with the catalyst.

[0104] (Examples 1-3) A batch-type electrochemical reactor 10, as shown in Figure 1, was prepared. However, a version without an anode reservoir 32 was prepared. 100 mL of a 0.2 M NaCl aqueous solution was prepared as the cathode electrolyte and filled into the cathode chamber 16. Also, 100 mL of a 0.2 M NaCl aqueous solution was prepared as the anode electrolyte and filled into the anode chamber 26. A cathode supported with the catalyst shown in Table 1 was used as the cathode 13. A platinum electrode was used as the anode 23. The electrode area of ​​each electrode was 1 cm². ２ The following steps were taken. Here, the pH of the cathode electrolyte was adjusted as shown in Table 1 by adding hydrogen chloride (HCl), and each batch No. was carried out. The pH was measured using a pH meter (LAQUA F-73, manufactured by Horiba, Ltd.). However, the example with pH = 7 was a batch in which hydrogen chloride (HCl) was not added. Carbon dioxide gas was blown into the cathode electrolyte at a flow rate of 50 sccm for 20 minutes to dissolve the carbon dioxide in the cathode electrolyte. For each batch, a voltage was applied between the cathode 13 and the anode 23, and the electrolytic reaction was carried out with a constant current (50 mA). Ten minutes after the start of electrolysis, the gas accumulated in the electrolytic cell on the cathode side was taken out, and the carbon monoxide gas concentration was measured by gas chromatography (GC). Based on the measured results, the Faraday efficiency (FE(CO)) of carbon monoxide production was calculated. Faraday efficiency was evaluated as follows: 'A' if FE(CO) exceeded 80%, 'B' if FE(CO) was between 50% and 80%, and 'C' if FE(CO) was less than 50%. The results are shown in Table 1.

[0105]

[0106] As shown in Examples 1 to 3 above, by dissolving carbon dioxide in the cathode electrolyte and carrying out the reduction reaction in the liquid phase, the precipitation of carbonates could be prevented. In particular, in each example, no sodium bicarbonate precipitation was observed in any batch No. when the pH was adjusted to 7 or below. Furthermore, as shown in Examples 2 and 3, when a catalyst in which a metal element is supported on a carbon compound was used as the first catalyst, carbon monoxide could be produced with high reduction efficiency at high pH, ​​but it could not be produced with high reduction efficiency at low pH. In contrast, as shown in Example 1, when a nitrogen-containing metal catalyst was used as the first catalyst, surprisingly, carbon monoxide could be produced with high reduction efficiency not only at high pH but also at low pH.

[0107] 10, 10A, 10B Electrochemical Reactor 13 Cathode 16 Cathode Chamber 16X Cathode Electrolyte 19 Diaphragm 23 Anode 25 Power Supply 26 Anode Chamber 26X Anode Electrolyte 32 Anode-side Storage Section 32G, 36G, 42G Gas Phase 36 Electrolytic Chamber 36X Bipolar Electrolyte 42 Storage Section 43 Reactor

Claims

1. An electrochemical reactor comprising a cathode, an anode, and an electrolyte, wherein the electrolyte includes a cathode electrolyte in which carbon dioxide is dissolved and in contact with the cathode, and an anode electrolyte which is an aqueous halogenated salt solution and in contact with the anode, or an aqueous halogenated salt solution in which carbon dioxide is dissolved and in contact with both the cathode and the anode, and the cathode contains a first catalyst that promotes the reaction of reducing carbon dioxide to carbon monoxide, and generates a halogen at the anode.

2. The electrochemical reaction apparatus according to claim 1, further comprising a cation exchange membrane located between the cathode and the anode.

3. The electrochemical reaction apparatus according to claim 1, wherein the cathode electrolyte contains a dissolved halogen salt and hydrogen halide, and has a pH of 2 or more and 6.5 or less.

4. The electrochemical reaction apparatus according to any one of claims 1 to 3, wherein the halide salt is an alkali metal halide.

5. The electrochemical reactor according to any one of claims 1 to 3, wherein the first catalyst is obtained by calcining a mixture containing a metal derivative, a nitrogen-containing compound, and a carbon compound, and the nitrogen-containing compound is at least one selected from the group consisting of pyridine derivatives, imidazole derivatives, pyrazole derivatives, and triazole derivatives.

6. The electrochemical reactor according to claim 5, wherein the pyridine derivative is at least one selected from the group consisting of aminopyridine, which is a compound having one pyridine ring in one molecule; pyridine oligomers having four or more pyridine rings and having a weight-average molecular weight of less than 10,000; and polymers having multiple pyridine rings in one molecule and having a weight-average molecular weight of 10,000 or more.

7. The electrochemical reaction apparatus according to claim 5, wherein the first catalyst contains a pyridine derivative as the nitrogen-containing compound.

8. The electrochemical reaction apparatus according to claim 5, wherein in the first catalyst, the molar ratio of the nitrogen-containing aromatic ring of the nitrogen-containing compound to the metal element of the metal derivative (nitrogen-containing aromatic ring / metal element) is 2 or more and 20 or less.

9. The electrochemical reaction apparatus according to claim 5, wherein the metal content derived from the metal derivative in the mixture is 1% by mass or more and 8% by mass or less.

10. The electrochemical reaction apparatus according to claim 5, wherein the metal element in the metal derivative is at least one selected from the group consisting of Co, Fe, and Ni.

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