Method for producing cuprous oxide particle and method for producing catalyst supporting electrode

Abstract

To provide a method for simply producing cuprous oxide particles having controlled crystal planes and diameters in a high yield.SOLUTION: A method for producing cuprous oxide particles comprises reacting a hydrazine compound dissolved in a solvent with a copper carboxylate compound in which a solid phase and a liquid phase of the copper carboxyl compound coexist in the solvent, to produce the cuprous oxide particles.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing cuprous oxide particles and a method for producing a catalyst-supported electrode. [Background technology]

[0002] There is a known technique for producing low carbon number compounds {compounds containing 1 to 3 carbon atoms, such as compounds containing 1 carbon atom (generally referred to as "C1 compounds"), compounds containing 2 carbon atoms (generally referred to as "C2 compounds"), and compounds containing 3 carbon atoms (generally referred to as "C3 compounds")} using carbon dioxide as a raw material and copper as a catalyst. By using such a technique, for example, formic acid (HCOOH), methanol (CH3OH), methane (CH4), acetic acid (CH3COOH), ethanol (C2H5OH), ethane (C2H6), ethylene (C2H4), etc. can be obtained (see, for example, Non-Patent Documents 1 and 2). Non-Patent Documents 1 and 2 report that cuprous oxide exhibits high activity as a catalyst. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Nature Energy, 2019, 4,957 [Non-Patent Document 2] Adv.Sci.2020,7,1902820 Summary of the Invention [Problem to be solved by the invention]

[0004] However, catalytic performance depends on the crystal plane and / or diameter of the copper particles, and Non-Patent Documents 1 and 2 did not disclose a method for easily producing cuprous oxide particles with controlled crystal planes and diameters in high yield.

[0005] Therefore, an object of the present invention is to provide a method for producing cuprous oxide particles and a method for producing a catalyst-supported electrode, which can produce cuprous oxide particles having controlled crystal faces and diameters in a high yield and in a simple manner. [Means for solving the problem]

[0006] One aspect of the present invention is as follows. [1] A method for producing cuprous oxide particles, comprising the steps of: A hydrazine compound dissolved in a solvent is reacted with a copper carboxyl compound in which a solid phase and a liquid phase of the copper carboxyl compound coexist in the solvent to produce cuprous oxide particles. A method for producing cuprous oxide particles. [2] 2. The method for producing cuprous oxide particles according to item 1, wherein the cuprous oxide particles include a (100) plane. [3] 3. The method for producing cuprous oxide particles according to item 1 or 2, wherein the cuprous oxide particles include a (100) plane and a (110) plane. [4] 4. The method for producing cuprous oxide particles according to any one of items 1 to 3, wherein the cuprous oxide particles have an average primary particle diameter of 1 to 100 nm. [5] 5. The method for producing cuprous oxide particles according to any one of items 1 to 4, wherein the solvent is a mixed solvent of water and propylene glycol. [6] 6. The method for producing cuprous oxide particles according to any one of items 1 to 5, wherein a ratio of a molar number of the copper carboxyl compound added to the solvent to a molar number of the hydrazine compound added to the solvent (molar number of the hydrazine compound / molar number of the copper carboxyl compound) is 0.25 to 3.0. [7] 7. The method for producing cuprous oxide particles according to any one of items 1 to 6, wherein the cuprous oxide particles having the hydrazine compound adsorbed thereon are produced. [8] A step of preparing a dispersion containing the cuprous oxide produced by the method according to any one of items 1 to 7; applying the dispersion to an electrode substrate to produce a catalyst-supported electrode; A method for producing a catalyst-supported electrode, comprising the steps of: [9] The catalyst-supported electrode includes a substrate, copper oxide particles, and a reducing agent, and The following formula (1): Item 9. The method for producing a catalyst-supporting electrode according to Item 8, wherein the following condition is satisfied: 0.0001≦(mass of the reducing agent / mass of the copper oxide particles)≦0.10 (1). Effect of the Invention

[0007] According to the present invention, there is provided a method for producing cuprous oxide particles, which can easily produce cuprous oxide particles having controlled crystal faces and diameters in high yield. Furthermore, according to the present invention, there can be provided a method for producing a catalyst-supported electrode using the cuprous oxide particles produced by the above-mentioned production method. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of an electrolysis cell related to this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention is not limited to the present embodiment, and various modifications can be made within the scope of the present invention. In this specification, various measurements are performed based on the methods described in the Examples unless otherwise specified. In this specification, the upper or lower limit of a numerical range described in a stepwise manner may be replaced by the upper or lower limit of a corresponding numerical range described in another stepwise manner, and may also be replaced by the corresponding value described in the Examples. In addition, in this specification, the term "step" includes not only an independent step, but also a step that cannot be clearly distinguished from other steps, as long as the function of the step is achieved. In the contents shown in the drawings, the scale, shape, and length may be exaggerated for further clarity.

[0010] [Embodiment 1] <Method for producing cuprous oxide> One aspect of this embodiment is a method for producing cuprous oxide. In this manufacturing method, Cuprous oxide particles are produced by reacting a hydrazine compound dissolved in a solvent with a copper carboxyl compound in which a solid phase and a liquid phase of the copper carboxyl compound coexist in the solvent. This makes it possible to easily produce cuprous oxide particles having controlled crystal faces and diameters at a high yield.

[0011] The hydrazine compound, the copper carboxyl compound, and the raw materials thereof may be used alone or in combination of two or more, and the solvent may be used alone or in combination of two or more. In the present embodiment, an optional component (an optional additive, etc.) may be used, and in this case, the optional component may be used alone or in combination of two or more.

[0012] The cuprous oxide particles obtained by the manufacturing method of this embodiment (hereinafter, may be simply referred to as "cuprous oxide particles") preferably contain copper particles with a (100) plane, from the viewpoint of more stably adsorbing an intermediate generated during electrolysis (reduction reaction) of carbon dioxide onto the cuprous oxide (catalyst). From the viewpoint of facilitating the production of copper particles with a (100) plane, it is preferable to use 0.5 to 2.0 moles of the hydrazine compound per mole of the copper carboxyl compound, and more preferably, it is preferable to use an equal amount or more of hydrazine, which has a high adsorption energy to the (100) plane, with respect to the copper carboxyl compound.

[0013] From the viewpoint of efficiency in producing C1 and C2 compounds, the cuprous oxide particles preferably contain copper particles having a (100) plane and a (110) plane. From the viewpoint of ease in producing copper particles having a (100) plane and a (110) plane, it is preferable to use 0.5 to 1.5 moles of the hydrazine compound per mole of the copper carboxyl compound, specifically, to add 0.5 to 1.5 moles of hydrazine.

[0014] By adding an acid component to the solvent, the pH of the solvent can be lowered, which makes it easier to produce copper particles containing (100) and (110) faces. The pH is preferably in the range of 3 to 8, more preferably 4 to 7.

[0015] The cuprous oxide particles preferably have an average primary particle diameter of 100 nm or less, and more preferably 1 nm or more. If the average primary particle diameter is 100 nm or less, it is easy to form a nano-sized structure on the surface of the secondary particles, and this makes it easy to improve the specific surface area. If the average primary particle diameter is 1 nm or more, it is easy to achieve good dispersibility. From the same viewpoint, the average primary particle diameter of the primary particles is more preferably 50 nm or less, even more preferably 20 nm or less, and more preferably 2 nm or more, and even more preferably 5 nm or more. It is preferably 100 nm or less, and more preferably 1 nm or more.

[0016] From the viewpoint of easily preventing oxidation of the surface of the cuprous oxide particles, it is preferable that a hydrazine compound is adsorbed, and more preferable that hydrazine is adsorbed. In other words, in this embodiment, it is preferable to prepare the cuprous oxide particles to which a hydrazine compound is adsorbed. The amount of hydrazine adsorbed is preferably 0.051 to 100 mg, more preferably 0.1 to 20 mg, per 1 g of cuprous oxide.

[0017] Copper carboxyl compounds The copper carboxyl compound is a copper raw material used in this embodiment. The copper carboxyl compound is preferably one that is soluble in water at a rate of 10% by mass or more. As the copper carboxyl compound, for example, copper acetate is preferable. Note that, as the copper carboxyl compound, a commercially available product may be used.

[0018] In addition, the copper carboxyl compound may be a compound obtained by reacting a copper salt with a carboxyl group-containing compound. Examples of the copper salt include copper hydroxide, copper nitrate, and copper carbonate, and examples of the carboxyl group-containing compound include compounds containing a carboxylic acid or a salt thereof in the compound molecule, such as saturated carboxylic acid, unsaturated carboxylic acid, and salts thereof. Specific examples of the carboxyl group-containing compound include formic acid, acetic acid, propionic acid, and butyl acetate.

[0019] The reaction between the copper salt and the carboxyl compound may be carried out in the vessel in which the hydrazine compound is charged, or may be carried out in advance in a separate vessel.

[0020] <Hydrazine compounds> The hydrazine compound is hydrazine and / or a hydrazine derivative. Among these, hydrazine is an inorganic compound represented by the chemical formula N2H4, and as "hydrazine" in the present embodiment, either anhydrous hydrazine or hydrated hydrazine (hydrazine hydrate) can be used. Among hydrazine compounds, hydrazine is preferred from the viewpoint of ease of controlling the crystal plane of the resulting cuprous oxide particles.

[0021] Examples of hydrazine derivatives include alkyl hydrazines such as monomethyl hydrazine, dimethyl hydrazine, and β-hydroxyethyl hydrazine; hydrazine salts such as hydrazine sulfate, neutral hydrazine sulfate, and hydrazine carbonate; etc. These have a nitrogen-nitrogen bond in their structure and have reducing properties, similar to hydrazine.

[0022] When the hydrazine compound is liquid, it may be put into the container as it is, or may be diluted with a predetermined solvent and then put into the container. When the hydrazine compound is solid, it is preferable to dissolve it in a predetermined solvent and then put into the container. When diluting or dissolving the hydrazine compound, the concentration of the hydrazine compound in the solvent is preferably more than 20 mass %, more preferably 60 mass % or more, from the viewpoint of easily controlling the primary particle size of the obtained cuprous oxide particles.

[0023] In order to adjust the reducing power of the hydrazine compound, a basic substance may be mixed into the solvent or the aqueous solution of the hydrazine compound within a range that does not affect the reaction product. This is advantageous in obtaining cuprous oxide having a small particle size, since it is easy to control the particle size of the resulting cuprous oxide particles to be small. As the basic compound, an inorganic basic compound such as sodium hydroxide or potassium hydroxide is preferable.

[0024] In the present invention, the mole number of the hydrazine compound to be added to the solvent is preferably 0.25 to 3.0 moles per mole of the copper carboxyl compound to be added to the solvent from the viewpoint of facilitating an increase in particle size and from the viewpoint of improving yield. In other words, the ratio of the mole number of the copper carboxyl compound to the mole number of the hydrazine compound to be added to the solvent (the mole number of the hydrazine compound / the mole number of the copper carboxyl compound) is preferably 0.25 to 3.0. From the viewpoint of easily controlling the crystal plane of the obtained copper oxide particles, the number of moles of the hydrazine compound added to the solvent is preferably 0.4 to 2.0 moles per mole of the copper carboxyl compound added to the solvent. From the viewpoint of suitably obtaining copper particles having a (110) plane, the number of moles of the hydrazine compound added to the solvent is more preferably 0.25 to 1.5 moles per mole of the copper carboxyl compound added to the solvent. From the viewpoint of suitably obtaining copper oxide particles having a (100) plane, the number of moles of the hydrazine compound added to the solvent is further preferably 0.5 to 2.0 moles per mole of the copper carboxyl compound added to the solvent.

[0025] "solvent" The solvent used in the step of reacting the copper carboxyl compound with the hydrazine compound is preferably water alone, or a mixed aqueous solution containing 90% by weight or less of an organic compound other than water. The amount of water in the mixed aqueous solution is preferably 20% by weight or more and less than 80% by weight. By using a mixed aqueous solution containing an organic compound other than water as the solvent, it is easy to control the average primary particle size of the obtained cuprous oxide particles to be smaller.

[0026] The organic compound used in the mixed aqueous solution is preferably one that can be mixed uniformly in water and does not react with the hydrazine compound. Examples of such organic compounds include alcohol-based compounds, ether-based compounds, ester-based compounds, and amide-based compounds. From the viewpoint of ease of handling, the organic compound is preferably one that is in a liquid state at room temperature (e.g., 25°C), and among them, an alcohol-based compound is preferable.

[0027] Specific examples of alcohol compounds include methanol, ethanol, propanol, butanol, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, polyethylene glycol, glycerin, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, pentanediol, hexanediol, and octanediol.

[0028] The solvent used in the step of reacting the copper carboxyl compound with the hydrazine compound is preferably a combination of water and an alcohol-based compound, and more preferably a mixed solvent of water and propylene glycol.

[0029] The preferred concentration of the copper carboxyl compound in the solvent is preferably 0.01 to 50% by mass, more preferably 3.0 to 20% by mass, based on the total mass of the solvent and the copper carboxyl compound. The solvent may be capable of dissolving the copper carboxyl compound. In the solvent, it is preferable that the copper carboxyl compound in a state dissolved in the solvent (liquid phase) and the copper carboxyl compound in a solid state (solid phase) coexist. In this embodiment, by reacting the hydrazine compound dissolved in the solvent with the copper carboxyl compound in the solid phase and the liquid phase coexisting in the solvent, the copper carboxyl compound dissolved in the solvent is kept at a constant concentration, and as a result, it is possible to control the particle size with high uniformity.

[0030] In the above reaction, the optimum reaction temperature is appropriately selected depending on the type and combination of the copper carboxyl compound and / or the hydrazine compound, the type of the solvent, and the like, and is preferably, for example, −20° C. or higher and lower than 60° C.

[0031] The cuprous oxide particles obtained in this embodiment are in weak contact with each other to form soft aggregates. After the reaction is completed, aggregates of the cuprous oxide particles are likely to be obtained as sediment at the bottom of the reaction vessel.

[0032] <<Dispersion of cuprous oxide particles (cuprous oxide particle dispersion)>> A further aspect of this embodiment is a dispersion of cuprous oxide particles obtained by the above manufacturing method. Such a dispersion is obtained by dispersing the cuprous oxide particles obtained by the above manufacturing method in a dispersion medium. The cuprous oxide particles obtained by the above manufacturing method are easily redispersible in a dispersion medium, and therefore a highly uniform dispersion having a reduced average secondary particle size can be easily produced, and a highly uniform dispersion can be easily produced. Note that the "average secondary particle size" refers to the average particle size of aggregates (secondary particles) formed by a plurality of primary particles gathering together.

[0033] The cuprous oxide particle dispersion may be, for example, A first step of obtaining, in a first solvent, a soft agglomerate of cuprous oxide particles having an average primary particle size of 100 nm or less and an average secondary particle size of 0.2 μm or more; A second step of separating the soft agglomerates obtained in the first step from the first solvent; A third step of redispersing the soft aggregate separated in the second step in a second solvent (dispersion medium) to obtain a dispersion; It is preferably produced by a method comprising: The cuprous oxide particle dispersion obtained by this production method has an extremely small particle size, and therefore the dispersion can be produced easily and efficiently.

[0034] (1st step) In this step, soft agglomerates of cuprous oxide particles having an average primary particle diameter of 100 nm or less and an average secondary particle diameter of 0.2 μm or more are obtained in a first solvent. In this step, cuprous oxide particles having an average primary particle diameter of 100 nm or less are synthesized, and a precipitate of secondary particles in which the cuprous oxide particles are weakly agglomerated to each other is obtained. This step is, for example, a step of obtaining a precipitate (agglomerates of cuprous oxide particles) through a reaction between a copper carboxyl compound and a hydrazine compound in the "method for producing cuprous oxide particles" of this embodiment.

[0035] (2nd process) In this step, the soft agglomerates obtained in the first step are separated from the first solvent. The soft aggregate obtained in the first step has a secondary particle diameter large enough to cause precipitation, and therefore, in this step, such precipitates are separated from the first solvent. Examples of the separation method include a method of removing the supernatant by decantation and a method of suction filtration. The separated precipitate may have impurities such as reaction by-products attached to its surface, so it is preferable to wash it with a clean solvent.

[0036] (3rd step) In this step, the soft aggregates separated in the second step are redispersed in a second solvent to obtain a dispersion. In this step, the second solvent, the soft aggregates separated in the second step, and other additives as necessary are added to an appropriate container, and then a redispersion treatment is performed. The redispersion treatment may be performed by a physical method of applying physical energy, such as ultrasonic treatment and a high-speed jet mill, or a chemical method, such as adjusting the pH of the second solvent with an acid and / or a base, or by a combination of a plurality of these dispersion means. Here, the "state in which the soft aggregates of the cuprous oxide particles are redispersed" includes any of the concepts of a state in which the cuprous oxide particles are homogeneously distributed in a dispersion medium, a state in which the cuprous oxide particles are suspended in a colloidal state, and a state in which the cuprous oxide particles and the second solvent, etc. are gelled by interaction with each other.

[0037] The time required to obtain a dispersion depends on the dispersion method, etc., but for example, when ultrasonic treatment is used as the method of redispersion treatment, it is about 5 minutes. Since cuprous oxide particles may be oxidized by oxygen, it is preferable to carry out the dispersion treatment in an inert atmosphere such as a nitrogen atmosphere.

[0038] The soft aggregates separated in the second step have an extremely small primary particle size, and the secondary particle size can be easily reduced by the subsequent redispersion treatment in the present step. Therefore, this step makes it easy to produce a colloidal dispersion in which the cuprous oxide particles are suspended in a colloidal state in the dispersion medium. In order to obtain a stable colloidal dispersion in which the cuprous oxide particles do not settle, it is preferable that the average secondary particle size of the cuprous oxide particles in the colloidal dispersion is less than 10 μm. It is more preferable that it is less than 7 μm, and even more preferable that it is less than 5 μm.

[0039] The second solvent used in the third step may be the same as or different from the first solvent. The solid content of the cuprous oxide particles in the entire dispersion can be adjusted as desired depending on the application, for example, to 0.1 to 80 mass%. The proportion of the cuprous oxide particles in the entire dispersion is preferably 1 mass% or more, more preferably 10 mass% or more.

[0040] In the redispersion treatment in the third step, it is preferable to reduce the particle size to such an extent that all precipitates can be dispersed and suspended in the second solvent. On the other hand, if precipitation is observed even after the redispersion treatment, such precipitates can be separated and removed by decantation or centrifugation. When reducing the average particle size of the cuprous oxide particles in the second solvent, it is preferable to separate and remove large particles by sedimentation using a technique such as centrifugation.

[0041] In the third step, a dispersion aid for stably dispersing the cuprous oxide particles in the second solvent may be mixed into the second solvent. Examples of such an aid include polymers and oligomers, and also compounds having polar groups such as hydroxyl groups, amino groups, and carboxyl groups.

[0042] Examples of the compound having a polar group include alcohol compounds, amine compounds, amide compounds, ammonium compounds, and phosphorus compounds. Examples of the compound having a polar group include commercially available surfactants. Examples of the surfactant include cationic surfactants, anionic surfactants, and non-polar surfactants. Examples of the compound having a polar group include polyvinylpyrrolidone, polyvinyl alcohol, and polymethyl vinyl ether.

[0043] As the auxiliary, inorganic or organic particles having a polar group on the surface may be used. Examples of such auxiliary include silica particles and latex particles. Metal element particles or metal compound particles may be supported and dispersed on the surface of these particles.

[0044] A liquid dispersion aid may be used as the second solvent. As such a dispersion aid, a polyhydric alcohol is preferable. A polyhydric alcohol is an organic compound having two or more hydroxyl groups in a molecule, and among them, a polyhydric alcohol having 10 or less carbon atoms is preferable as a dispersion aid. Such compounds include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, pentanediol, hexanediol, octanediol, and glycerol.

[0045] A phosphorus-containing organic substance may be used as a dispersion aid. The phosphorus-containing organic substance may be adsorbed onto copper oxide, in which case aggregation is easily suppressed due to the steric hindrance effect. The phosphorus-containing organic substance may be a single molecule or a mixture of multiple types of molecules.

[0046] The number average molecular weight (Mn) of the dispersion auxiliary is preferably, for example, 300 to 30,000. If the number average molecular weight is 300 or more, the storage stability of the resulting copper oxide ink is likely to be increased, and if the number average molecular weight is 30,000 or less, the catalytic performance is likely to be excellent. The structure of the dispersion auxiliary is preferably a phosphate ester of a high molecular weight copolymer having a group that has affinity for copper oxide. For example, a structure represented by chemical formula (1): [ka] is preferred because it is easily adsorbed by copper oxide, particularly cuprous oxide, and has excellent adhesion to the substrate.

[0047] Dispersing aids that are phosphorus-containing organics are preferred because they increase the storage stability of the copper oxide. The decomposition temperature of the phosphorus-containing organic substance is preferably 600° C. or lower, more preferably 400° C. or lower, and even more preferably 200° C. or lower. The boiling point of the phosphorus-containing organic substance is preferably 300° C. or lower, more preferably 200° C. or lower, and preferably 150° C. or lower.

[0048] Examples of the dispersion aid include polymers having basic groups, and specific examples thereof include salts of long-chain polyaminoamides and polar acid esters, unsaturated polycarboxylic acid polyaminoamides, polycarboxylates of polyaminoamides, and salts of long-chain polyaminoamides and acid polymers. Examples of the dispersion aid include alkylammonium salts, amine salts, and amidoamine salts of polymers such as acrylic polymers, acrylic copolymers, modified polyester acids, polyether ester acids, polyether carboxylic acids, and polycarboxylic acids. Further, examples of the dispersion aid include ion exchange resins.

[0049] As the dispersion aid, commercially available products may be used. Commercially available products include, for example, DISPERBYK®-101, DISPERBYK-102, DISPERBYK-110, DISPERBYK-111, DISPERBYK-112, DISPERBYK-118, DISPERBYK-130, DISPERBYK-140, DISPERBYK-142, DISPERBYK-145, DISPERBYK-160, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163, DISPERBYK-2155, DISPERBYK-2163, DISPERBYK-2164, DISPERBYK-180, DISPERBYK-2000, DISPERBYK-202 ...5, DISPERBYK-2166, DISPERBYK-2167, DISPERBYK-2168, DISPERBYK-2169, DISPERBYK-2170, DISPERBYK-2171, DISPERBYK-2172, DISPERBYK-2173, DISPERBYK-2174, DISPERBYK-2175, DISPERBYK-2176, DISPERBYK-2177, DISPERBYK-2178, DISPERBYK-2179, DISPERBYK-2180, DISPERBYK-2182, DISPERBYK-2184, DISPERBYK-2185, DISPERBYK-2186, DISPERBYK-218 BYK-2164, BYK-9076, BYK-9077, TERRA-204, TERRA-U (all manufactured by BYK-Chemie), FLORON DOPA-15B, FLORON DOPA-15BHFS, FLORON DOPA-22, FLORON DOPA-33, FLORON DOPA-44, FLORON DOPA-17HF, FLORON TG-662C, FLORON KTG-2400 (all manufactured by Kyoeisha Chemical Co., Ltd.), ED-117, ED-118, ED-212, ED-213, ED-214, ED-216, ED-350, ED-360 (all manufactured by Kusumoto Chemical Co., Ltd.), Plysurf (registered trademark) M208F, Plysurf DBS (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Nafion (manufactured by Dupond), Sustainion (Dioxide Examples of suitable ion exchange polymers include EPDM (manufactured by EPDM Materials), and PiperION (manufactured by Versogen).

[0050] The amount of the dispersion auxiliary is often proportional to the amount of copper oxide, and may be adjusted in consideration of the required dispersion stability. In this embodiment, the mass ratio of the dispersion auxiliary contained in the cuprous oxide particle dispersion (mass of dispersion auxiliary / mass of copper oxide) is 0.0050 to 0.30, preferably 0.050 to 0.25, and more preferably 0.10 to 0.23. The amount of the dispersion auxiliary may affect the dispersion stability. If the amount of the dispersion auxiliary is small, the cuprous oxide particles are likely to aggregate, and if the amount of the dispersion auxiliary is large, the dispersion stability of the cuprous oxide particles is likely to improve.

[0051] In order to reduce impurities in the dispersion obtained in the third step, the cuprous oxide particles in the dispersion may be aggregated and precipitated again through the first and second steps, and the precipitate may be separated from the second solvent, and then dispersed again in a clean second solvent, etc. Such a washing step may be repeated multiple times.

[0052] In the third step, additives such as a viscosity modifier and a reducing agent may be added to the second solvent, and a part of the second solvent may be removed by concentration or the like to adjust the viscosity. Adding a reducing agent to the dispersion tends to suppress oxidation of the cuprous oxide particles. The content of the reducing agent is preferably 0.01 to 50 mass %, more preferably 0.01 to 30 mass %, based on the total mass of the dispersion. Examples of the reducing agent include aldehydes, sugar alcohols, sugars, hydrazine and its derivative diimides, and oxalic acid. Hydrazine and its derivatives as reducing agents may be further used in the third step, apart from the hydrazine compound used in the reaction with the copper carboxyl compound in the first step. The molar number of hydrazine and its derivatives further used in the third step is not included in the calculation formula for the molar ratio (molar number of hydrazine compound added to solvent / molar number of copper carboxyl compound added to solvent) during the reaction in the first step.

[0053] Examples of aldehydes include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobitylaldehyde, valeraldehyde, isovaleraldehyde, pivalaldehyde, capronaldehyde, heptaldehyde, caprylaldehyde, pelagonaldehyde, undecylaldehyde, lauric aldehyde, tridecylaldehyde, myristic aldehyde, pentadecyl aldehyde, palmitic aldehyde, margaric aldehyde, and stearic acid. aliphatic saturated aldehydes such as aldehyde; aliphatic dialdehydes such as glyoxal and succindialdehyde; aliphatic unsaturated aldehydes such as acrolein, crotonaldehyde, and propioaldehyde; aromatic aldehydes such as benzaldehyde, o-tolualdehyde, m-tolualdehyde, p-tolualdehyde, salicylaldehyde, cinnamaldehyde, α-naphthaldehyde, and β-naphthaldehyde; heterocyclic aldehydes such as furfural; and the like.

[0054] Examples of sugar alcohols include glycerol, erythritol, pentaerythritol, pentitol, pentose, hexitol, hexose, and heptose. Examples of sugars include sorbitol, mannitol, xylitol, threitol, maltitol, arabitol, lactitol, adonitol, cellobitol, glucose, fructose, sucrose, lactose, mannose, galactose, erythrose, xylulose, allulose, ribose, sorbose, xylose, arabinose, isomaltose, dextrose, and glucoheptose.

[0055] Diimides can be obtained by thermal decomposition of azodicarboxylate, hydroxylamine-O-sulfonic acid, N-arenesulfonylhydrazide, and N-acylsulfonylhydrazide. Among these, N-arenesulfonylhydrazide and N-acylsulfonylhydrazide include p-toluenesulfonylhydrazide, benzenesulfonylhydrazide, 2,4,6-trisisopropylbenzenesulfonylhydrazide, chloroacetylhydrazide, o-nitrobenzenesulfonylhydrazide, m-nitrobenzenesulfonylhydrazide, and p-nitrobenzenesulfonylhydrazide.

[0056] <Production method of C1 compound and C2 compound> A further aspect of the present embodiment is a method for producing a low carbon number compound, in particular a method for producing a C1 compound and a C2 compound, which utilize the above-mentioned cuprous oxide particles. Examples of C1 compounds include methane, methanol, carbon monoxide, and formic acid. C1 compounds can be produced, for example, by the reduction reaction of one molecule of carbon dioxide. C2 compounds include ethane, ethylene, ethanol, acetic acid, etc. C1 compounds can be produced, for example, by the reaction of two molecules of carbon dioxide.

[0057] Here, as the method for producing a C1 compound and a C2 compound, a method for producing ethylene and methanol will be described. In addition, by synthesizing a target low carbon number compound, other low carbon number compounds may be produced as a by-product together with the low carbon number compound. Here, too, by synthesizing ethylene and methanol, other C1 compounds and other C2 compounds may be produced as a by-product.

[0058] Ethylene can be produced by a technique using a cuprous oxide catalyst as an electrocatalyst. Such a method may, for example, include the following steps: A step of isolating the center of the H-shaped cell with an ion exchange membrane or the like, thereby dividing the cell into an anode chamber and a cathode chamber; A step of attaching an oxidation electrode made of a metal material or a carbon material such as carbon paper to the positive electrode chamber; A step of mounting an electrode carrying cuprous oxide (catalyst-supported electrode) in a negative electrode chamber; filling both the positive and negative electrode compartments with an electrolyte acting as an ion conductor, the electrolyte filling the negative electrode compartment having been saturated with carbon dioxide in advance and being stirred while blowing in carbon dioxide; connecting a power source to the oxidation electrode and the catalyst-supporting electrode and passing a current; This allows a gas containing ethylene to be generated from the catalyst-supported electrode.

[0059] Methanol can be produced by a technique that uses a cuprous oxide catalyst as a photocatalyst. Such a method may, for example, include the following steps: A step of mixing the cuprous oxide particle dispersion with water previously saturated with carbon dioxide to obtain a mixed solution; A step of placing the mixture in a highly transparent container (e.g., a glass container) that allows visible light to pass through; a step of stirring the mixture while blowing carbon dioxide into it, and irradiating the mixture with visible light from an external source such as a xenon lamp; Carbon dioxide can be reduced and methanol produced by this.

[0060] <Method for producing catalyst-supported electrode> A further aspect of the present embodiment is a method for producing a catalyst-supported electrode. The manufacturing method includes: forming a dispersion comprising the cuprous oxide; applying the dispersion to an electrode substrate to produce a catalyst-supported electrode; has.

[0061] Catalyst-supported electrode A catalyst-supported electrode can be produced by applying a cuprous oxide dispersion to an electrode substrate (e.g., a carbon electrode substrate). The cuprous oxide dispersion may be applied to the electrode substrate and then dried. The catalyst-supported electrode may be provided in the form of a layer, for example, and in this case, the catalyst-supported electrode layer may be a single layer or multiple layers. A layer other than the catalyst-supported electrode (for example, a conductive material layer, a resin layer, etc.) may be laminated on the catalyst-supported electrode.

[0062] The catalyst-supported electrode includes a substrate, copper oxide particles, and a reducing agent, and The following formula (1): 0.0001≦(mass of reducing agent / mass of copper oxide particles)≦0.10 (1) It is preferable that the following is satisfied. This makes it easy to suitably manufacture a catalyst-supporting electrode having various excellent properties.

[0063] (base material) The substrate may be a substrate with a gas diffusion layer, a metal substrate, a carbon substrate such as carbon paper, or other various substrates. Among them, a porous substrate with excellent gas permeability is preferable as the substrate. As the substrate, a commercially available product, for example, a substrate with a gas diffusion layer made of a composite material of carbon fiber and carbon, may be used. Examples of commercially available products include Pyrofil (manufactured by Mitsubishi Chemical Corporation), SIGRACET (manufactured by SGL Carbon Co., Ltd.), and Torayca Carbon Paper (manufactured by Toray Industries, Inc.).

[0064] (reducing agent) Examples of the reducing agent include hydrazine compounds, sodium, carbon, potassium iodide, oxalic acid, iron(II) sulfide, sodium thiosulfate, ascorbic acid, tin(II) chloride, diisobutylaluminum hydride, formic acid, sodium borohydride, and sulfites. Among these, from the viewpoint of easily improving the dispersion stability of copper oxide in the coating film, hydrazine compounds are preferred as the reducing agent, and hydrazine is more preferred.

[0065] (Copper oxide particles) The average secondary particle diameter of the copper oxide particles in the coating film is preferably less than 10 μm, and more preferably 5 nm or more. If the average secondary particle diameter is less than 10 μm, the specific surface area of ​​the copper oxide particles is likely to be large, and if the average secondary particle diameter is 5 nm or more, the long-term storage stability of the dispersion is likely to be improved. From the same viewpoint, the average secondary particle diameter of the fine particles is more preferably less than 7 μm, even more preferably less than 5 μm, and more preferably 10 nm or more, even more preferably 15 nm or more.

[0066] The average primary particle diameter of the primary particles constituting the secondary particles is preferably 100 nm or less, and more preferably 1 nm or more. If the average primary particle diameter is 100 nm or less, it is easy to form a nano-sized structure on the surface of the secondary particles, and this makes it easy to improve the specific surface area. If the average primary particle diameter is 1 nm or more, it is easy to achieve good dispersibility. From the same viewpoint, the average primary particle diameter of the primary particles is more preferably 50 nm or less, even more preferably 20 nm or less, and more preferably 2 nm or more, and even more preferably 5 nm or more.

[0067] (Dispersion aid) The catalyst-supported electrode may further contain a dispersion assistant. This makes it easy to suitably form a coating film containing cuprous oxide. The mass ratio of the dispersion assistant contained in the coating film (mass of dispersion assistant / mass of copper oxide) is preferably 0.0050 to 0.30, more preferably 0.050 to 0.25, and more preferably 0.10 to 0.23. This makes it easy to suitably prevent aggregation of the cuprous oxide particles and to improve the dispersion stability.

[0068] <Electrolytic cell> A further aspect of the present embodiment is a method for manufacturing an electrolysis cell. The manufacturing method includes: preparing an electrolysis chamber including an anode chamber including an anode, a cathode chamber including a cathode, and a diaphragm separating the anode chamber and the cathode chamber, thereby preparing an electrolysis cell; Here, the above-mentioned catalyst-supporting electrode is used as the negative electrode.

[0069] FIG. 1 is a schematic diagram showing an example of the configuration of an electrolysis cell related to this embodiment. As shown in the figure, the electrolysis cell 10 has an electrolysis cell 6 including an anode chamber 3A containing a cathode (catalyst-supported electrode 1), a cathode chamber 4A containing a cathode 2, and a diaphragm 5 that separates the anode chamber 3A and the cathode chamber 4A. The electrolytic cell 10 has a structure in which porous current collecting electrodes (a current collecting electrode for a negative electrode and a current collecting electrode for a positive electrode) are arranged on both sides of a diaphragm 5, thereby dividing the space separated by the diaphragm 5 into a negative electrode chamber 3A on one side and a positive electrode chamber 4A on the other side, and the thickness of both chambers is ensured by a spacer.

[0070] The anode chamber 3A contains an anode electrolyte 3, and the cathode chamber 4A contains a cathode electrolyte 4. An anode electrolyte pump 7 is connected to the anode chamber 3A, and a cathode electrolyte pump 8 is connected to the cathode chamber 4A. The anode electrolyte pump 7 supplies the anode electrolyte 3 from an anode electrolyte tank (not shown) to the anode chamber 3A. The cathode electrolyte pump 8 supplies the cathode electrolyte 4 from a cathode electrolyte tank (not shown) to the cathode chamber 4A. The anode (catalyst-supported electrode 1) and the cathode 2 of the electrolysis cell 10 are each connected to a power supply device 9. The power supply device 9 is controlled by a control unit (not shown). In the electrolytic cell 10, the positive electrode 2, the diaphragm 5, the electrolyte solution, and the like may have known configurations. EXAMPLES

[0071] The present embodiment will be described in more detail by giving examples and comparative examples. However, the present embodiment is not limited to only the following examples. Regarding the examples and comparative examples, various production, quantification, measurement, evaluation, etc. were performed by the following methods.

[0072] [Quantitative determination of hydrazine] Hydrazine in cuprous oxide dispersion (copper nanoink) was quantified using the internal standard method.

[0073] 50 μL of sample (copper nano ink) was mixed with 33 μg of hydrazine and a surrogate substance (hydrazine15 33 μg of N2H4 and 1 ml of a 1% by mass solution of benzaldehyde in acetonitrile were added. Finally, 20 μL of phosphoric acid was added, and after 4 hours, measurements were performed using a gas chromatograph mass spectrometer (GC / MS).

[0074] Similarly, 50 μL of sample (copper nano ink) was mixed with 66 μg of hydrazine and a surrogate substance (hydrazine 15 33 μg of N2H4 and 1 ml of a 1% by mass solution of benzaldehyde in acetonitrile were added. Finally, 20 μL of phosphoric acid was added, and after 4 hours, measurements were performed by GC / MS.

[0075] Similarly, 50 μL of sample (copper nano ink) was mixed with 133 μg of hydrazine and a surrogate substance (hydrazine 15 33 μg of N2H4 and 1 ml of a 1% by mass solution of benzaldehyde in acetonitrile were added. Finally, 20 μL of phosphoric acid was added, and after 4 hours, measurements were performed by GC / MS.

[0076] Finally, 50 μL of the sample (copper nanoink) was diluted with hydrazine and the surrogate substance (hydrazine 15 33 μg of N2H4) and 1 ml of a 1% by mass solution of benzaldehyde in acetonitrile were added, and finally, 20 μL of phosphoric acid was added. After 4 hours, measurement was performed by GC / MS.

[0077] From the above four measurement results, the peak area value of hydrazine was obtained from the chromatogram of m / z=207. Next, the peak area value of the surrogate was obtained from the mass chromatogram of m / z=209. A calibration curve was obtained by plotting "mass of added hydrazine / mass of added surrogate substance" on the x-axis and "peak area value of hydrazine / peak area value of surrogate substance" on the y-axis.

[0078] The Y-intercept value obtained from the calibration curve was divided by "mass of added hydrazine / mass of added surrogate substance", thereby obtaining the mass of hydrazine.

[0079] [Measurement of average primary particle size] The average primary particle size of copper oxide particles in the cuprous oxide dispersion was measured using a JEM-F200 transmission electron microscope (TEM) manufactured by JEOL Ltd. Ten or more copper particles were randomly selected, and the arithmetic mean value of the particle diameter was calculated using the equivalent circle diameter by image analysis, and this was taken as the average particle size (nm).

[0080] [Measurement of average secondary particle size] The average secondary particle size of the copper oxide particles (copper oxide catalyst) in the cuprous oxide dispersion was measured by the cumulant method using FPAR-1000 manufactured by Otsuka Electronics Co., Ltd.

[0081] [Analysis of facet crystal planes] The Miller indices of the facet crystal planes of the copper oxide catalyst were analyzed using a JEM-F200 transmission electron microscope (TEM) manufactured by JEOL Ltd. The particle orientation was identified by FFT pattern analysis of the lattice image of the copper particles, and the Miller indices of the planes visible in the particle image were determined.

[0082] [Example 1] In a nitrogen atmosphere, 202 g of copper (II) acetate monohydrate (Kanto Chemical) was added in powder form to a mixed solvent of 1890 g of distilled water (Kyoei Pharmaceutical) and 874 g of 1,2-propylene glycol (Kanto Chemical), and the liquid temperature was controlled to -5°C by an external temperature controller. 59 g of hydrazine monohydrate (Tokyo Chemical Industry) was added to the solution in which the solid remained over a period of 20 minutes, and the mixture was stirred for 30 minutes under a nitrogen atmosphere. After that, the liquid temperature was controlled to 25°C by an external temperature controller, and the mixture was stirred for 90 minutes. After stirring, the resulting dispersion was centrifuged to separate the supernatant and the precipitate. 240 g of diethylene glycol (Merck) was added to 98 g of the resulting precipitate, and the mixture was dispersed using a homogenizer under a nitrogen atmosphere. As a result, 338 g of a cuprous oxide dispersion (copper nano ink) containing copper oxide particles (copper oxide catalyst) was obtained.

[0083] In the dispersion, the copper oxide particles were well dispersed. The proportion of cuprous oxide in the dispersion was 20 mass %, and the proportion of hydrazine was 1500 mass ppm. The average primary particle diameter of the copper oxide particles in the dispersion was 10 nm, and the average secondary particle diameter was 19 nm. It was also confirmed that the copper oxide particles had a (100) plane and a (110) plane.

[0084] In order to measure the amount of hydrazine adsorbed to the cuprous oxide particles, the obtained dispersion was repeatedly concentrated in a UF membrane module under a nitrogen atmosphere and diluted with ethanol (dehydrated) (Kanto Chemical Co., Ltd.), and the hydrazine liberated in the dispersion was taken out in the filtrate. From the results of measuring the amount of hydrazine remaining in the cuprous oxide dispersion, the amount of hydrazine adsorbed to the cuprous oxide was calculated to be 7 mg per 1 g of cuprous oxide.

[0085] The resulting dispersion was impregnated into a gas diffusion layer substrate MFK (manufactured by Mitsubishi Chemical Corporation) under a nitrogen atmosphere and then dried on a hot plate at 150°C for 1 hour to produce an electrode carrying a cuprous oxide catalyst (catalyst-supported electrode). The amount of cuprous oxide supported in the resulting catalyst-supported electrode was 4 mg / cm. 2 It was.

[0086] The obtained catalyst-supported electrode was used to construct an electrolytic cell as shown in FIG. As the positive electrode, a titanium platinum electrode (manufactured by AS ONE Corporation); As the negative electrode, the catalyst-supported electrode obtained by the above method was used; As a diaphragm, Nafion 212 (manufactured by Dupont); As the positive electrode electrolyte, 10 mL of a 1 M potassium bicarbonate aqueous solution prepared by dissolving potassium bicarbonate (Kanto Chemical Co., Ltd.) in ultrapure water was used; As the negative electrode electrolyte, 15 mL of 1 M potassium bicarbonate aqueous solution that had been saturated with carbon dioxide by bubbling carbon dioxide into it for at least 1 hour; Each was used.

[0087] The electrolysis cell was connected to a power supply PFX2011 (manufactured by Kikusui Electronics Co., Ltd.), and electrolysis was carried out for 1 hour at a low voltage of 3.5 V using a control unit PFX2121 (manufactured by Kikusui Electronics Co., Ltd.) During this time, carbon dioxide was continuously blown into the electrolyte in the negative electrode chamber.

[0088] After the electrolysis was completed, the electrolyte in the negative electrode chamber was collected and analyzed by ion chromatography IC-2001 (Tosoh Corporation). Formic acid and acetic acid were detected at 100 μg / mL and 34 μg / mL, respectively.

[0089] [Comparative Example] Comparative examples include, for example: Non-patent document: Nature Energy, 2019, 4,957 Non-patent document: Adv.Sci.2020,7,1902820 2. The method for producing cuprous oxide particles according to claim 1, However, in this production method, the reaction between the copper carboxyl compound and the specific reducing agent is not a special reaction in which a solid phase and a liquid phase coexist, and in this case, it is difficult to easily produce cuprous oxide particles having a particle size of 100 nm or less and a controlled crystal face at a high yield, as compared with the examples. [Industrial Applicability]

[0090] The cuprous oxide catalyst produced by the production method of the present invention is suitably used for the production of methanol, ethanol, methane, ethane, ethylene, formic acid, acetic acid, and the like. [Explanation of symbols]

[0091] 1 Catalyst-supported electrode (negative electrode) 2 Positive electrode 3 Negative electrolyte 3A negative electrode chamber 4 Positive Electrolyte 4A positive electrode chamber 5 Diaphragm 6 Electrolysis chamber 7. Anode electrolyte pump 8 Positive Electrolyte Pump 9 Power supply 10 Electrolysis Cell

Claims

1. A method for producing cuprous oxide particles, comprising the steps of: A hydrazine compound dissolved in a solvent is reacted with a copper carboxyl compound in which a solid phase and a liquid phase of the copper carboxyl compound coexist in the solvent to produce cuprous oxide particles. A method for producing cuprous oxide particles.

2. 2. The method for producing cuprous oxide particles according to claim 1, wherein the cuprous oxide particles include a (100) face.

3. 2. The method for producing cuprous oxide particles according to claim 1, wherein the cuprous oxide particles include a (100) plane and a (110) plane.

4. 2. The method for producing cuprous oxide particles according to claim 1, wherein the cuprous oxide particles have an average primary particle size of 1 to 100 nm.

5. The method for producing cuprous oxide particles according to claim 1 , wherein the solvent is a mixed solvent of water and propylene glycol.

6. 2. The method for producing cuprous oxide particles according to claim 1, wherein a ratio of a molar number of the copper carboxyl compound added to the solvent to a molar number of the hydrazine compound added to the solvent (molar number of the hydrazine compound / molar number of the copper carboxyl compound) is 0.25 to 3.

0.

7. The method for producing cuprous oxide particles according to claim 1 , wherein the cuprous oxide particles have a hydrazine compound adsorbed thereon.

8. forming a dispersion comprising the cuprous oxide produced by the method of any one of claims 1 to 7; applying the dispersion to an electrode substrate to produce a catalyst-supported electrode; A method for producing a catalyst-supported electrode, comprising the steps of:

9. The catalyst-supported electrode includes a substrate, copper oxide particles, and a reducing agent, and The following formula (1): The method for producing a catalyst-supporting electrode according to claim 8 , wherein the following condition is satisfied: 0.0001≦(mass of the reducing agent / mass of the copper oxide particles)≦0.10 (1).

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