Electrolysis device and method for manufacturing electrolysis device

Abstract

An electrolysis device includes: a cathode; an anode; a cathode space on the cathode and through which a gaseous reducible material is supplied; an anode space on the anode and through which a liquid or gaseous oxidizable material is supplied; and a diaphragm between the cathode and the anode. The cathode includes a substrate and a catalyst layer. The catalyst layer has: a metal complex for promoting a chemical reaction of reducing the reducible material to produce a reduction product; alcohol with C2 or less, or an aprotic solvent having a relative dielectric constant of 3.0 or more; a catalyst carrier carrying the metal complex and having conductivity; and a binder binding the substrate and the catalyst carrier.

Description

FIELD

[0001] Arrangements relate to an electrolysis device and a method for manufacturing the electrolysis device.BACKGROUND

[0002] The production amount of ammonia is about 140 million tons (1.4 × 10 11< kg) in the world in a year and continues to rise. About 80% of the production amount is utilized as a raw material for fertilizer and is mainly converted to other nitrogen compounds such as urea, nitric acid, ammonium nitrate, and ammonium sulfate. On the other hand, the remaining 20% thereof is utilized for the manufacture of synthetic resin and fiber. To cope with the global population growth, the shortage of cultivated acreage, and the food shortages due to the sophistication of diet mainly in developing countries, the demand for ammonia is increased. Further, ammonia attracts attention as a use of an energy carrier owing to its ease of handling, high energy density, and a characteristic of containing no carbon and emitting no carbon dioxide when used.

[0003] At present, ammonia is industrially synthesized from a hydrogen gas and a nitrogen gas derived from fossil fuels such as petroleum, coal, or natural gas by the method called Haber-Bosh process invented about 100 years ago. This synthesis reaction requires severe conditions such as high temperature (400 to 650°C) and high pressure (200 to 400 atm), consumes 1.2% of total energy in the world, and therefore emits a large amount of carbon dioxide. To form a sustainable society in the future, the development of an alternative process with low dependence on fossil fuels is expected.

[0004] Regarding the above point, a catalyst for producing ammonia from nitrogen at normal temperature and pressure in an electrolysis method and an electrolysis device for manufacturing ammonia (NH 3 ) by reducing nitrogen (NH 3 ) through electrolysis is under development. For example, it has been reported that a molybdenum iodide complex having a PNP 2,6-bis(di-tert-butylphosphinomethyl)pyridine) ligand as a catalyst, and a solution containing alcohol or water as a proton source, and an organic low-molecule containing a halide (II) of a lanthanoid metal as a reducing agent, for example, samarium (II) iodide as a solvent, are stirred in the presence of a nitrogen gas at normal temperature to thereby produce up to 4350 equivalents of ammonia per catalyst. In addition, a method using the molybdenum iodide complex having the PNP ligand as the catalyst, and using a solution to be used in a cathode storage or both an electrolyte membrane and the solution to be used in the cathode storage, as the proton source has been reported.

[0005] In the above electrolysis device which manufactures ammonia (NH 3 ) by the reduction of nitrogen (N 2 ), when fabricating a cathode which reduces the nitrogen gas to produce ammonia, a method of carrying the catalyst using the organic low-molecular solvent for a gas diffusion electrode being a carrier (also referred to as a catalyst carrying method) is used. On the other hand, the organic low-molecular solvent is relatively high in adsorption selectivity to the carrier, and thus becomes a factor that decreases a carrying amount of the catalyst and increases the hydrophilicity of the carrier to cause a flooding phenomenon. These become factors that decrease the production amount and production efficiency of an electrolysis product such as ammonia on the cathode side. Besides, in the case of using a material that reacts with excessive moisture to become inactive such as a molybdenum complex as the catalyst, the hydrophilicity of the cathode is decreased to enable a catalytic reaction to proceed efficiently. Hence, it is desired to optimize the solvent to be used in a cathode fabrication process and the process and optimize the composition of the cathode so as to realize a cathode with a high catalyst carrying amount and low hydrophilicity and increase the manufacturing efficiency and the recovery efficiency of the electrolysis product such as ammonia. The object is required not only in a nitrogen electrolysis device which manufactures ammonia by reduction of nitrogen but also in electrolysis devices such as an electrolysis device having a cathode fabricated using the catalyst carrying method and producing a reduction product different from ammonia, for example, a water electrolysis device which electrolyzes water (H 2 O) to produce hydrogen (H 2 ) and so on, a carbon dioxide electrolysis device which electrolyzes carbon dioxide (CO 2 ) to produce a carbon compound such as carbon monoxide (CO), formic acid (HCOOH), methanol (CH 3 OH), ethanol (C 2 H 5 OH), or the like, and so on.SUMMARY

[0006] A problem to be solved by the present invention is to provide an electrolysis device capable of manufacturing a reduction product with high efficiency by an electrolytic reaction.

[0007] An electrolysis device in an arrangement includes: a cathode; an anode; a cathode space on the cathode and through which a gaseous reducible material is supplied; an anode space on the anode and through which a liquid or gaseous oxidizable material is supplied; and a diaphragm between the cathode and the anode. The cathode has a substrate and a catalyst layer. The catalyst layer has: a metal complex for promoting a chemical reaction of reducing the reducible material to produce a reduction product; alcohol with C2 or less, or an aprotic solvent having a relative dielectric constant of 3.0 or more; a catalyst carrier carrying the metal complex and having conductivity; and a binder for binding the substrate and the catalyst carrier.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a schematic diagram illustrating a structure example of an electrolysis device. FIG. 2 is a schematic diagram illustrating a first example of an electrochemical reaction unit. FIG. 3 is a schematic diagram illustrating a second example of the electrochemical reaction unit. FIG. 4 is a schematic diagram illustrating a third example of the electrochemical reaction unit. FIG. 5 is a cross-sectional schematic view illustrating a structure example of a cathode. DETAILED DESCRIPTION

[0009] Electrolysis devices in arrangements will be explained below with reference to the drawings. In the arrangements explained below, substantially the same components are denoted by the same reference signs, and the explanation thereof may be partially omitted. The drawings are schematic in which the relationship between the thickness and planar dimensions, a thickness ratio among the components, and so on may be different from actual ones. Nitrogen electrolysis devices which manufacture ammonia (NH 3 ) by the reduction of nitrogen (N 2 ) will be mainly explained here as the electrolysis devices of the arrangements, but the electrolysis devices in the arrangements are not limited to the nitrogen electrolysis device. The electrolysis devices in the arrangements may be, for example, a water electrolysis device which electrolyzes water (H 2 O) to produce hydrogen (H 2 ) and so on, and a carbon dioxide electrolysis device which electrolyzes carbon dioxide (CO 2 ) to produce a carbon compound such as carbon monoxide (CO), formic acid (HCOOH), methanol (CH 3 OH), and so on.

[0010] FIG. 1 is a schematic diagram illustrating a structure example of an electrolysis device in an arrangement. FIG. 1 illustrates a nitrogen electrolysis device 1. The nitrogen electrolysis device 1 is an ammonia manufacturing device, and includes: an electrochemical reaction unit (electrolysis cell) 5 including a first reaction space (reduction reaction electrolytic bath) 2 which is supplied with a gaseous reducible material (for example, nitrogen), a second reaction space (oxidation reaction electrolytic bath) 3 which is supplied with a liquid or gaseous oxidizable material (for example, an electrolytic solution containing water, or water vapor), and a diaphragm 4; a nitrogen supply unit 7 including a nitrogen supply part (supply device) 6 for supplying nitrogen to a cathode space; an ammonia collection part (ammonia collection unit) 9 including a collector (collection device) 8 which can collect ammonia contained in gas exhausted from the cathode space; an oxidizable material supply unit 11 for supplying an electrolytic solution from an electrolytic solution storage 10 containing the electrolytic solution to the second reaction space 3; and an ammonia separation unit 13 including an ammonia separation part (separation device) 12 which separates ammonia contained in the electrolytic solution discharged from the second reaction space 3. Hereinafter, the components will be explained in detail.

[0011] FIG. 2 illustrates a first example of the electrochemical reaction unit 5. The electrochemical reaction unit 5 illustrated in FIG. 2 includes: a first reaction space (reduction reaction electrolytic bath) 2 as the cathode space; a second reaction space (oxidation reaction electrolytic bath) 3 as an anode space; a diaphragm 4 provided between the first reaction space 2 and the second reaction space 3; a cathode 14 arranged in the first reaction space 2 and used for an electrochemical reduction reaction; and an anode 15 arranged in the second reaction space 3 and used for an electrochemical oxidation reaction, which constitute an electrochemical reaction cell (electrolysis cell). The electrochemical reaction unit 5 is separated into the first reaction space 2 and the second reaction space 3 by the diaphragm 4 which can move ions such as hydrogen ion (H +< ) and hydroxide ion (OH -< ). Into the first reaction space 2, gaseous nitrogen (N 2 ) is supplied from the nitrogen supply unit 7 via a pipe. Into the second reaction space 3, an electrolytic solution containing water (H 2 O) or water vapor (H 2 O) generated by evaporation of the electrolytic solution is supplied from the oxidizable material supply unit 11 via a pipe.

[0012] FIG. 3 illustrates a second example of the electrochemical reaction unit 5. The electrochemical reaction unit 5 illustrated in FIG. 3 has a first flow path plate 2a instead of the first reaction space 2 which is supplied with gaseous nitrogen being the reducible material, and a second flow path plate 3a instead of the second reaction space 3 which is supplied with the electrolytic solution or water vapor being the oxidizable material. The first flow path plate 2a has a first flow path (also referred to as a cathode flow path) which is supplied with gaseous nitrogen being the reducible material, as a cathode space facing a cathode 14. The second flow path plate 3a has a second flow path (also referred to as an anode flow path) which is supplied with an electrolytic solution or water vapor being the oxidizable material, as an anode space facing an anode 15. The electrochemical reaction unit 5 illustrated in FIG. 3 has the cathode 14 to be used for the electrochemical reduction reaction adjacent to the first flow path plate 2a, the anode 15 to be used for the electrochemical oxidation reaction adjacent to the second flow path plate 3a, and a diaphragm 4 provided between the cathode 14 and the anode 15, which are sandwiched between the first flow path plate 2a and the second flow path plate 3a, and they constitute an electrochemical reaction cell (electrolysis cell). According to FIG. 3, the distance between the cathode 14 and anode 15 is equivalent to the thickness of the diaphragm 4, thus making it possible to decrease the electric resistance and quickly move hydrogen ion (H +< ) and hydroxide ion (OH -< ) between the electrodes. This can decrease the power consumption of the electrolysis cell and increase the ammonia manufacturing efficiency. Note that for the other explanation of the first flow path plate 2a and the second flow path plate 3a, the explanation of the first reaction space 2 and the second reaction space 3 may be used as appropriate.

[0013] FIG. 4 illustrates a third example of the electrochemical reaction unit 5. The electrochemical reaction unit 5 illustrated in FIG. 4 includes a third reaction space 16 which is provided between a first reaction space 2 supplied with gaseous nitrogen (N 2 ) and a diaphragm 4, and supplied with an electrolytic solution (cathode solution) containing water. The first reaction space 2 and the third reaction space 16 are in contact with each other via a porous cathode 14, which constitute a cathode space. The cathode space having the first reaction space 2 and the third reaction space 16 is in contact with a second reaction space 3 as an anode space via the diaphragm 4 and a porous anode 15. The electrochemical reaction unit 5 illustrated in FIG. 4 can dissolve ammonia (NH 3 ) produced by reducing the gaseous nitrogen (N 2 ) supplied to the first reaction space 2, into the electrolytic solution (cathode solution) supplied to the third reaction space 16 to take it to the outside of the electrochemical reaction cell (electrolysis cell) 5. This can increase the recovery efficiency of ammonia.

[0014] The cathode 14 and the anode 15 are connected to an external electrode. By supplying current or voltage to the cathode 14 and the anode 15 from the external electrode to feed power, a reduction reaction occurs at the cathode 14 and an oxidation reaction occurs at the anode 15. In the anode space, for example, water (H 2 O) in the electrolytic solution is oxidized at the anode 15 to produce oxygen (O 2 ), hydrogen ions (H +< ), and electrons (e -< ). In the cathode space, nitrogen (N 2 ) is reduced by an ammonia production catalyst to produce ammonia (NH 3 ). The nitrogen containing ammonia is led to the outside of the cathode space via a pipe and continuously sent to the ammonia collection unit 9. Further, a part of the ammonia produced in the cathode space moves to the anode space through the diaphragm 4. The electrolytic solution containing water mixed with ammonia in the anode space and oxygen produced at the anode 15 or water vapor is led to the outside of the anode space via a pipe and continuously or intermittently sent to the ammonia separation unit 13.

[0015] The anode space is supplied with the electrolytic solution containing water (H 2 O) or water vapor as explained above. The electrolytic solution may be an aqueous solution containing an electrolyte or the like. It is preferable that the electrolytic solution is high in ion conductivity and the electrolyte itself does not react. Examples of the electrolyte contained in the electrolytic solution include lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), lithium bromide (LiBr), sodium bromide (NaBr), potassium bromide (KBr), lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), lithium nitrate (LiNO 3 ), sodium nitrate (NaNO 3 ), potassium nitrate (KNO 3 ), lithium sulfate (Li 2 SO 4 ), sodium sulfate (Na 2 SO 4 ), potassium sulfate (K 2 SO 4 ), lithium hydrogen sulfate (LiHSO 4 ), sodium hydrogen sulfate (NaHSO 4 ), potassium hydrogen sulfate (KHSO 4 ), lithium peroxodisulfate (Li 2 S 2 O 8 ), sodium peroxodisulfate (Na 2 S 2 O 8 ), potassium peroxodisulfate (K 2 S 2 O 8 ), lithium phosphate (Li 3 PO 4 ), sodium phosphate (Na 3 PO 4 ), potassium phosphate (K 3 PO 4 ), dilithium hydrogen phosphate (Li 2 HPO 4 ), disodium hydrogen phosphate (Na 2 HPO 4 ), dipotassium hydrogen phosphate (K 2 HPO 4 ), lithium dihydrogen phosphate (LiH 2 PO 4 ), sodium dihydrogen phosphate (NaH 2 PO 4 ), potassium dihydrogen phosphate (KH 2 PO 4 ), lithium hydrogen carbonate (LiHCO 3 ), sodium hydrogen carbonate (NaHCO 3 ), potassium hydrogen carbonate (KHCO 3 ), lithium carbonate (Li 2 CO 3 ), sodium carbonate (Na 2 CO 3 ), potassium carbonate (K 2 CO 3 ), lithium tetraborate (Li 2 B 4 O 7 ), sodium tetraborate (Na 2 B 4 O 7 ), potassium tetraborate (K 2 B 4 O 7 ), lithium silicate (Li 2 SiO 3 ), sodium silicate (Na 2 SiO 3 ), potassium silicate (K 2 SiO 3 ), ionic liquid, and so on. It is preferable to use water as a solvent. The electrolyte concentration in the electrolytic solution is preferably, for example, in a range of 0.001 to 1 mol / L.

[0016] As the positive ion of the ionic liquid, an ion such as an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, or a piperidinium ion is used. Examples of the imidazolium ion include 1-ethyl-3-methylimidazolium, 1-methyl-3-propylimidazolium, 1-butyl-3-methylimidazolium, 1-methyl-3-pentylimidazolium, 1-hexyl-3-methylimidazolium, and so on. A 2nd position of the imidazolium ion may be substituted. Examples of the substituted one include 1-ethyl-2,3-dimethylimidazolium, 1,2-dimethyl-3-propylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,2-dimethyl-3-pentylimidazolium, 1-hexyl-2,3-dimethylimidazolium, and so on. Examples of the pyridinium ion include methylpyridinium, ethylpyridinium, propylpyridinium, butylpyridinium, pentylpyridinium, hexylpyridinium, and so on. Examples of the pyrrolidinium ion include ethyl-methylpyrrolidinium, methyl-propylpyrrolidinium, butyl-methylpyrrolidinium, methyl-pentylpyrrolidinium, hexyl-methylpyrrolidinium, and so on. Examples of the piperidinium ion include ethyl-methylpiperidinium, methyl-propylpiperidinium, butyl-methylpiperidinium, methyl-pentylpiperidinium, hexyl-methylpiperidinium, and so on. In all of the imidazolium ion, pyridinium ion, pyrrolidinium ion, and piperidinium ion, the alkyl group may be substituted, and an unsaturated bond may exist. As the positive ion of the ionic liquid, a single cation or a plurality of cations combined are used.

[0017] Examples of the negative ion of the ionic liquid include a fluoride ion, a chloride ion, a bromide ion, an iodide ion, an acetate ion, a nitrate ion, a hydrogen sulfate ion, a phosphate ion, a dicyanamide ion, BF 4 -< , PF 6 -< , CF 3 COO -< , CF 3 SO 3 -< , SCN -< , (CF 3 SO 2 ) 3 C -< , a bis(trifluoromethoxysulfonyl)imide ion, a bis(trifluoromethoxysulfonyl)imide ion, a bis(perfluoroethylsulfonyl)imide ion, and so on. As the negative ion of the ionic liquid, a single anion or a plurality of anions combined are used. Further, a dipolar ion made by connecting the cation and the anion of the ionic liquid by hydrocarbon may be used. One type of the ionic liquid may be used alone or two or more types may be used in combination.

[0018] The anode space has the anode 15 arranged therein, and is supplied with the electrolytic solution. At the anode 15, when the hydrogen ion concentration of the electrolytic solution is 7 or less (pH ≤ 7), H 2 O is oxidized to produce O 2 and H +< . On the other hand, when the hydrogen ion concentration of the electrolytic solution is greater than 7 (pH > 7), OH -< is oxidized to produce O 2 and H 2 O. The anode 15 is constituted of a material which decreases the activation energy for causing an oxidation reaction. In other words, the anode 15 is constituted of a material which decreases the overvoltage when causing a reaction of oxidizing H 2 O or OH -< to pull out electrons. Examples of the constituent material of the anode 15 include binary metal oxides such as platinum (Pt), manganese oxide (Mn-O), iridium oxide (Ir-O), nickel oxide (Ni-O), cobalt oxide (Co-O), iron oxide (Fe-O), tin oxide (Sn-O), indium oxide (In-O), and ruthenium oxide (Ru-O), ternary metal oxides such as Ni-Co-O, La-Co-O, Ni-La-O, and Sr-Fe-O, quaternary metal oxides such as Pb-Ru-Ir-O and La-Sr-Co-O, and metal complexes such as a Ru complex and a Fe complex.

[0019] The cathode space has the cathode 14 arranged therein, and is supplied with the nitrogen gas. When carrying out the reduction reaction, the cathode 14 is preferably constituted of a material having conductivity so as to transmit the electrons supplied from the external electrode to the catalyst, having gas diffusibility so as to more quickly diffuse the reducible material, and having a porous structure for carrying more catalyst. Further, the cathode 14 is preferably low in hydrophilicity so as to prevent a flooding phenomenon due to the electrolytic solution moving from the anode space through the diaphragm 4. The hydrophilicity of the cathode 14 can be adjusted, for example, by the thickness or the construction material of the cathode 14.

[0020] FIG. 5 is a cross-sectional schematic view illustrating a structure example of the cathode 14. An example of the cathode 14 has a gas diffusion layer 141 being a substrate and a catalyst layer (also referred to as a cathode catalyst layer) 142. Note that the structure of the cathode 14 is not limited to the structure illustrated in FIG. 5.

[0021] The gas diffusion layer 141 is formed using, for example, a material such as carbon paper, carbon cloth, carbon felt, glass cloth, porous polymer membrane, or the like. The gas diffusion layer 141 may include a layer called a multiporous layer (MPL) for improving the gas diffusibility and water repellency.

[0022] The catalyst layer 142 is provided on the surface of the gas diffusion layer 141. FIG. 5 illustrates an example in which the catalyst layer 142 is, but not limited to, stacked on the gas diffusion layer 141. For example, at least a part of the catalyst layer 142 may be formed on the surface of the gas diffusion layer 141 in a pore of the gas diffusion layer 141. The catalyst layer 142 has at least a material being a reduction catalyst, a material responsible for conductivity, a material serving as a catalyst carrier, and a material having a roll of binding them (binder), so that the same material may take a plurality of rolls. Specifically, the catalyst layer 142 may contain an organic-inorganic composite material (composite material of an organic material and an inorganic material) for controlling the hydrophilicity of a second catalyst carrier and the catalyst layer 142 using a carbon material as a conductor and a catalyst carrier as a main component, and an organic polymeric material for binding a porous carbon material and an inorganic oxide fine particle, in addition to the reduction catalyst for reducing nitrogen to produce ammonia. The organic-inorganic composite material and the organic polymeric material may have ion conductivity, and thus can enhance the conductivity and supplyability of ions such as a hydrogen ion (H +< ), a hydroxide ion (OH -< ), and so on to the reduction catalyst to thereby increase the reduction efficiency of nitrogen (N), namely, the production efficiency of ammonia (NH 3 ).

[0023] The reduction catalyst (ammonia production catalyst) used for the cathode 14 promotes the production of ammonia from nitrogen, and, for example, not limited to, a molybdenum complex is used. Examples of the ammonia production catalyst include (A) to (D) molybdenum complexes explained below.

[0024] A first example is (A) a molybdenum complex having, as a PCP ligand, N,N-bis(dialkylphosphinomethyl)dihydrobenzimidazolidene (where two alkyl groups may be the same or different, and at least one hydrogen atom of a benzene ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom).

[0025] A second example is (B) a molybdenum complex having, as a PNP ligand, 2,6-bis(dialkylphosphinomethyl)pyridine (where two alkyl groups may be the same or different, and at least one hydrogen atom of a pyridine ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom).

[0026] A third example is (C) a molybdenum complex having, as a PPP ligand, bis(dialkylphosphinomethyl)arylphosphine (where two alkyl groups may be the same or different).

[0027] A fourth example is (D) a molybdenum complex expressed by trans-Mo(N 2 ) 2 (R1R2R3P) 4 (where R1, R2, R3 are arealkyl groups or aryl groups which may be the same or different, and two R3s may connect with each other to form an alkylene chain).

[0028] In the above molybdenum complexes, the alkyl group may be, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or the like, or may be a straight chain or branched alkyl group of a structural isomer of them, or a cyclic alkyl group such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, or a cyclohexyl group. The carbon number of the alkyl group is preferably 1 to 12, and more preferably 1 to 6. The alkoxy group may be, for example, a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group, a hexyloxy group, or the like, or may be a straight chain or branched alkoxy group of a structural isomer of them, or a cyclic alkoxy group such as a cyclopropoxy group, a cyclobutoxy group, a cyclopentoxy group, or a cyclohexyloxy group. The carbon number of the alkoxy group is preferably 1 to 12, and more preferably 1 to 6. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and so on.

[0029] An example of the (A) molybdenum complex is a molybdenum complex expressed by Formula (A1) below.

[0030] In the formula, R1 and R2 may be the same or different alkyl groups, X is an iodine atom, a bromine atom, or a chlorine atom, and at least one hydrogen atom on the benzene ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom.

[0031] Examples of the alkyl group, alkoxy group, and halogen atom include the same as those already exemplified. R1 and R2 are preferably bulky alkyl groups (for example, tert-butyl groups or isopropyl groups). It is preferable that the hydrogen atom on the benzene ring is not substituted or that hydrogen atoms at position 5 and position 6 are substituted with chain, cyclic, or branched alkyl groups with 1 to 12 carbons.

[0032] An example of the (B) molybdenum complex is a molybdenum complex expressed by Formula (B1), Formula (B2), or Formula (B3) below.

[0033] In the formula, R1 and R2 may be the same or different alkyl groups, X is an iodine atom, a bromine atom, or a chlorine atom, and at least one hydrogen atom on the pyridine ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom.

[0034] Examples of the alkyl group, alkoxy group, and halogen atom include the same as those already exemplified. R1 and R2 are preferably bulky alkyl groups (for example, tert-butyl groups or isopropyl groups). It is preferable that the hydrogen atom on the pyridine ring is not substituted or that a hydrogen atom at position 4 is substituted with a chain, cyclic, or branched alkyl group with 1 to 12 carbons.

[0035] An example of the (C) molybdenum complex is a molybdenum complex expressed by Formula (C1) below.

[0036] In the formula, R1 and R2 may be the same or different alkyl groups, R3 is an aryl group, and X is an iodine atom, a bromine atom, or a chlorine atom.

[0037] Examples of the alkyl group include the same as those already exemplified. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, the one in which at least one of cyclic hydrogen atoms of them is substituted with an alkyl group or a halogen atom, and so on. Examples of the alkyl group and halogen atom include the same as those already exemplified. R1 and R2 are preferably bulky alkyl groups (for example, tert-butyl groups or isopropyl groups). R3 is preferably, for example, a phenyl group.

[0038] An example of the (D) molybdenum complex is a molybdenum complex expressed by Formula (D1) or Formula (D2) below.

[0039] In the formula, R1, R2, and R3 may be the same or different alkyl groups or aryl groups, and n is 2 or 3.

[0040] Examples of the alkyl group and the aryl group include the same as those already exemplified. In Formula (D1), it is preferable that R1 and R2 are aryl groups (for example, phenyl groups) and R3 is an alkyl group with 1 to 4 carbons (for example, a methyl group), or that R1 and R2 are alkyl groups with 1 to 4 carbons (for example, methyl groups) and R3 is an aryl group (for example, a phenyl group). In Formula (D2), it is preferable that R1 and R2 are aryl groups (for example, phenyl groups) and n is 2.

[0041] The ammonia production catalyst (reduction catalyst) which promotes the production of ammonia from nitrogen may be, for example, a metallocene complex expressed by Formula (E1) below.

[0042] In the formula, M is a tetravalent metal ion, and is one of titanium, zirconium, and hafnium. X1 and X2 are the same or different negative ions having a coordination property. The negative ion is preferably Cl -< , Br -< , I -< , CH 3 -< or OH -< , and more preferably Cl -< . Specifically, it is desirably a metallocene complex such as bis(cyclopentadienyl)titanium dichloride or bis(cyclopentadienyl)zirconium dichloride.

[0043] Further, as the ammonia production catalyst (reduction catalyst), a metal catalyst such as molybdenum, bismuth, iron, rhodium, ruthenium, titanium, or zirconium may be used. One of them may be used alone or two or more of them may be used in combination.

[0044] The material responsible for conductivity contained in the catalyst layer 142 is preferably a material which does not cause itself a reduction reaction as a catalyst. More specifically, a material with high overvoltage regarding the reduction reaction of proton, water, electrolyte, which is a side reaction is suitable, and a carbon material is mainly used. Examples of the carbon material (carbon particle) include channel black, furnace black, thermal black, acetylene black, activated carbon, natural graphite, artificial graphite, graphitized carbon, graphene, carbon nanotube (CNT), fullerene, ketjen black, glassy carbon, and so on.

[0045] The catalyst carrier can carry an ammonia production catalyst (reduction catalyst). The reduction catalyst is, for example, a metal complex. The catalyst carrier may be the carbon material or may be an organic-inorganic composite material. Examples of the inorganic material include magnesium oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, vanadium oxide, molybdenum oxide, tungsten oxide, tin oxide, zinc oxide, microporous three-dimensional aluminum silicate such as zeolite, layered silicate minerals such as montmorillonite, beidellite, saponite, steven site, and hectorite, and so on. Examples of the organic-inorganic composite material include metal organic frameworks (MOF), a material in which an organic molecule is inserted between sites or layers of an inorganic crystal structure, and so on. The use of these materials as the catalyst carrier makes it possible to fix the ammonia production catalyst with high density and efficiency. Accordingly, a three-phase interface controlled cathode 14 capable of direct reaction of nitrogen (N 2 ) can be realized. This can significantly increase the production efficiency of ammonia by a gas phase.

[0046] The ammonia production catalyst is adsorbed and held on the surface of the catalyst carrier and thereby can be used as the catalyst carrier for the reduction reaction of nitrogen. For example, when the ammonia production catalyst is a molybdenum complex, the molybdenum complex is dissolved in a solvent to prepare a catalyst solution and the catalyst solution is brought into contact with the catalyst carrier, thereby causing adsorption on the surface of the catalyst carrier. As the characteristic of the catalyst carrier capable of preferably holding the ammonia production catalyst, the specific surface area for increasing the reaction area is preferably 800 m 2< / g or more.

[0047] The characteristic of the catalyst carrier can be evaluated by a gas adsorption method by a specific surface area measurement device. For measuring the specific surface area, an inert gas (adsorbate) which performs reversible adsorption such as nitrogen, argon, or krypton is used. In a measurement operation, a sample is put into a sample tube with a known volume, an adherent of the sample is removed by heated vacuum drying, then a fixed amount of adsorbate is introduced into the sample tube, and the adsorbate is brought into contact with the sample surface. The adsorption amount increases with time, and the increase in adsorption amount stops in due time. The state at the time is called an adsorption equilibrium state, the adsorption amount is called an equilibrium adsorption amount, and the pressure is called an equilibrium pressure. The adsorption amount is determined by measuring a change in pressure until the adsorption equilibrium state is reached. For the specific surface area, an amount of an adsorption first layer is calculated from the amount of adsorbate adsorbed to the sample surface by the BET theory, and a specific surface area value is found using the area occupied by one molecule of the adsorbate.

[0048] Since the production amount of ammonia by a gas phase increases with a larger amount of the molybdenum production catalyst contained in the catalyst layer 142, the catalyst layer 142 is made thicker to increase the amount of the catalyst carrier, thereby making it possible to realize the cathode 14 which produces a larger amount of ammonia. On the other hand, if the catalyst layer 142 is thicker than necessary, gas of a reducible material supplied from the gas diffusion layer 141 is less likely to reach the surface side of the catalyst layer 142, causing hydrogen production by a side reaction to decrease the production efficiency of ammonia. Therefore, the thickness of the catalyst layer 142 is preferably 0.035 mm or more and 0.200 mm or less, and more preferably 0.050 mm or more and 0.150 mm or less. By adjusting the thickness of the catalyst layer 142 to 0.035 mm or more and 0.200 mm or less, the production efficiency of ammonia can be increased.

[0049] The reduction catalyst is preferably a chemical reactant of a metal complex which promotes the chemical reaction of reducing the reducible material to produce the reduction product and alcohol with C2 or less or an aprotic solvent. In the case where the ammonia production catalyst being the reduction catalyst is, for example, a molecular catalyst such as the molybdenum complex, the solubility of the molecular catalyst into the solvent and the affinity of the solvent and a catalyst carrier material influence the difficulty of adsorption. As the solvent for dissolving the molybdenum complex, methanol, ethanol, tetrahydrofuran, acetone, acetonitrile, chloroform, or the like is used. The molybdenum complex dissolves in methanol or ethanol, but does not dissolve in alcohol having a carbon number equal to or more than propanol. Further, the molybdenum complex is likely to dissolve in a polar solvent such as tetrahydrofuran, but does not dissolve in a nonpolar solvent such as hexane. Thus, the solvent is preferably alcohol with C2 or less or an aprotic solvent, and a relative dielectric constant ε of the aprotic solvent is preferably 3.0 or more and more preferably 20.0 or more, for example, at 20°C. The upper limit of the relative dielectric constant ε is not particularly limited, but is, for example, 50.0 or less.

[0050] On the other hand, when considering the interaction between the solvent and the molybdenum complex and between the molybdenum complex and the catalyst carrier material, a solvent lower in solubility with respect to the molybdenum complex is considered to be more likely to be adsorbed to the catalyst carrier. Besides, when a porous carbon material is the catalyst carrier, a solvent preferably has moderate hydrophilicity in order to prevent the solvent from being preferentially adsorbed to the carbon material. From the background, it is preferable to use methanol low in boiling point and having characteristics achieving both the moderate hydrophilicity and the solubility, as the solvent. For example, the temperature at which the molybdenum complex is adsorbed to the porous carbon material is preferably 0 to 90°C and more preferably 5 to 40°C, taking the decomposition temperature of the molybdenum complex and the boiling point of the solvent into consideration. If the time for adsorption of the molybdenum complex to the porous carbon material is short, adsorption may not be completed. On the other hand, if the adsorption time is too long, the ammonia production capacity by the reaction between the molybdenum complex and the solvent and workability will deteriorate. Therefore, the time for adsorption of the molybdenum complex to the porous carbon material is preferably in a range of 0.5 to 48 hours and more preferably 1 to 24 hours.

[0051] Next, a forming method of the cathode 14 in the method for manufacturing the electrolysis device will be explained. In the case where the ammonia production catalyst is a molecular catalyst such as the molybdenum complex, examples of a method of causing the catalyst carrier to adsorb the molecular catalyst include a drop casting method of preparing in advance a molecular catalyst solution in which a molecular catalyst is dissolved in a solvent and dropping the molecular catalyst solution to a catalyst carrier and evaporating the solvent to carry a molecular catalyst, and an immersion method of immersing a catalyst carrier into a molecular catalyst solution to carry a molecular catalyst. The immersion method is preferable for the purpose of uniformly carrying the molecular catalyst in the catalyst carrier, and can fabricate a cathode 14 large in catalyst carrying amount by holding the molecular catalyst solution in which the catalyst carrier is immersed under a reduced pressure or by holding it under an ultrasonic irradiation by an ultrasonic generator.

[0052] The inorganic material or the organic-inorganic composite material can be considered to function as an ion conductor in the catalyst layer 142 and undertake a role of supplying ions required for the reaction of the ammonia production catalyst. When the hydrogen ion concentration in the electrolytic solution is 7 or less (pH ≤ 7), hydrogen ions (H +< ) are supplied to the ammonia production catalyst, whereas when the hydrogen ion concentration in the electrolytic solution is greater than 7 (pH > 7), hydroxide ions (OH -< ) are supplied to the ammonia production catalyst. The catalyst layer 142 contains a material having ion conductivity and thereby can enhance the transmissibility and supplyability of the hydrogen ions (H +< ), hydroxide ions (OH -< ), and so on with respect to the reduction catalyst. Accordingly, the reduction efficiency of nitrogen (N) and the initial reduction efficiency of nitrogen can be increased, and therefore the production efficiency of ammonia (NH 3 ) can be improved.

[0053] The organic polymeric material which binds the material responsible for conductivity, the catalyst carrier carrying the reduction catalyst, and the gas diffusion layer 141 is preferably a water-insoluble polymeric material which can maintain the catalyst layer structure even in a wet environment. As the polymeric material, a fluorine-based resin such as perfluoroalkoxyalkane (PFA), perfluoroethylene propene copolymer (FEP), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), or ethylene-chlorotrifluoroethylene copolymer (ECTFE), polystyrene, polyvinyl butyral, poly(4-vinylpyridine), or the like is used. The polymeric material as the binder may have ion conductivity, and examples of the polymeric material having ion conductivity include Nafion (registered trademark) being a fluorocarbon resin made by sulfonating and polymerizing tetrafluoroethylene of DuPont Inc., Sustainion (registered trademark) of Dioxide Materials Inc., PiperION (registered trademark) of Versogen Inc., and so on.

[0054] The mass ratio of the polymeric material in the catalyst layer 142 is preferably in a range of 0.1 or more and 0.5 or less to the total mass of the material constituting the catalyst layer 142. Further, the ratio of the mass of the material having conductivity is preferably in a range of 0.3 or more and 0.9 or less to the total mass of the material constituting the catalyst layer 142. In these ranges, the production of ammonia can be promoted without causing a decrease in binding property and conductivity of the catalyst layer 142.

[0055] In the case where the polymeric material in the catalyst layer 142 is a material increasing the water repellency such as polytetrafluoroethylene, it is possible to realize a catalyst layer lower in hydrophilicity by increasing the percentage of the polymeric material in the catalyst layer 142. On the other hand, in order to increase the catalyst carrying amount, it is necessary to increase the percentage of the catalyst carrier in the catalyst layer 142. For example, the mass ratio between the catalyst carrier and the water repellent polymeric material is preferably in a range of 8:2 to 4:6 and more preferably in a range of 7:3 to 5:5. By adjusting the ratio between the catalyst carrier and the water repellent polymeric material to the above range, the production efficiency of ammonia by a gas phase can be improved.

[0056] The catalyst layer 142 may contain an ionic liquid. By arranging the ionic liquid on the surface of the catalyst carrier to suppress adhesion of excessive moisture, an effect of decreasing the hydrogen production by reduction of water and promoting the ammonia production reaction can be obtained. For the ionic liquid contained in the reduction catalyst, the same material as the one used in the above electrolytic solution can be used.

[0057] For the diaphragm 4 provided between the cathode space and the anode space of the electrochemical reaction unit 5, a membrane which can selectively pass anions or cations is used. The membrane constituting the diaphragm 4 is preferably a membrane-like polymeric material having ion conductivity. As the polymeric material having ion conductivity, an ion exchange membrane such as NEOSEPTA (registered trademark) of ASTOM Corporation, Selemion (registered trademark) of Asahi Glass Co., Ltd., Aciplex (registered trademark) of Asahi Kasei Corp., Fumasep (registered trademark) and fumapem (registered trademark) of Fumatech GmbH., Nafion (registered trademark) being a fluorocarbon resin made by sulfonating and polymerizing tetrafluoroethylene of DuPont Inc., lewabrane (registered trademark) of LANXESS Co. Ltd., IONSEP (registered trademark) of IONTECH Inc., Mustang (registered trademark) of PALL Corp., ralex (registered trademark) of mega Corp., Gore-Tex (registered trademark) of Gore-Tex Inc., Sustainion (registered trademark) of Dioxide Materials Inc., PiperION (registered trademark) of Versogen Inc., or the like can be used. The diaphragm 4 may be a composite film composed of a composite containing an organic-inorganic composite material having ion conductivity and a polymeric material for binding the organic-inorganic composite material.

[0058] In the case where the polymeric material in the catalyst layer 142 and the material in the diaphragm 4 are ion exchange membranes, the cathode 14 and the diaphragm 4 may be used while being immersed in an electrolyte solution in order to change counter cations and counter anions contained in the ion exchange membrane. Examples of the electrolyte solution for exchanging the counter cations include solutions containing ions such as lithium ion, sodium ion, potassium ion, cesium ion, ammonium ion, and so on, and examples of the electrolyte solution for exchanging the counter anions include solutions containing ions such as containing fluorine ion, chlorine ion, bromide ion, iodine ion, and so on. Note that the ion contained in the electrolyte solution is not limited to the above ions. By exchanging the counter ions of the ion exchange membrane, it is possible to control the water permeability of the ion exchange membrane to promote the production of ammonia.

[0059] The nitrogen supply unit 7 is a unit which supplies gaseous nitrogen to the first reaction space (reduction reaction electrolytic bath) 2, and includes a nitrogen supply device 6. As the nitrogen to be supplied from the nitrogen supply device 6, for example, but is not limited to, nitrogen in the air is used. Since air contains about 21% of oxygen, it is preferable to separate oxygen in advance from the air to be used and then take out nitrogen. In the case of using nitrogen in the air, an oxygen separation device which separates oxygen in the air and takes out nitrogen is used for the nitrogen supply device 6. As a separation method of oxygen in the air in the oxygen separation device 6, for example, the cryogenic separation method of separating oxygen by utilizing a difference in boiling point, the adsorption separation method utilizing a difference in adsorbing characteristics with respect to gas molecules of a zeolite-based adsorbent, the membrane separation method of separating oxygen by utilizing the fact that the speeds of permeating a membrane differ depending on gas molecules, or the like is used and can be appropriately selected according to the cost and device scale, and the separation method is not particularly limited. The nitrogen supply unit 7 may further include a humidifying device that humidifies nitrogen taken out of the air. It is preferable to supply the humidified nitrogen to the cathode space.

[0060] A nitrogen gas containing ammonia and a hydrogen gas produced by a side reaction are discharged from the cathode space, and part of the electrolytic solution passing through the diaphragm (electrolyte membrane) 4 is discharged from the anode 15. A discharge pipe of the cathode space is connected to the ammonia collection unit 9. The ammonia collection unit 9 is a unit that collects ammonia contained in the substance to be discharged from the cathode space, and includes an ammonia collection device 8. The ammonia collection device 8 is not particularly limited and, for example, a device which selectively collects ammonia by bringing the exhaust gas into contact with an aqueous solution (collection solution) with a pH of 0 to 7 for absorbing ammonia is used. The ammonia collection device 8 can simultaneously separate by-product hydrogen and unreacted nitrogen contained in the exhaust gas.

[0061] The ammonia collected by the ammonia collection device 8 and the part of the electrolytic solution passing through the diaphragm (electrolyte membrane) 4 from the anode 15 are contained in the collection solution and thus sent to an ammonia separation device 19 which separates ammonia from the collection solution. For the ammonia separation device 19, for example, the distillation method or the cryogenic separation method of separating ammonia by utilizing the difference in boiling point, the adsorption separation method utilizing the difference in adsorbing characteristics with respect to gas molecules of the zeolite-based adsorbent, the membrane separation method of separating ammonia by utilizing the fact that the speeds of permeating the membrane differ depending on the gas molecules, or the like is applied. The ammonia separation device 19 can be appropriately selected according to the cost and device scale and is not particularly limited. The ammonia separation device 19 is provided with a pipe for recovering the ammonia separated from the collection solution.

[0062] In the case of separating ammonia from the collection solution by distillation, a distillation column is used as the ammonia separation device 19. The distillation column is configured to separate ammonia having a boiling point lower than water used as at least part of the collection solution. In the distillation column, ammonia is separated by distillation by the conventional method from the supplied collection solution. Concretely, ammonia is discharged from a pipe at a column top part of the distillation column by subjecting the collection solution to reduced-pressure distillation under a reduced pressure of 10 to 120 Torr (1333 to 15999 Pa). The ammonia discharged from the pipe is recovered into a not-illustrated tank or the like.

[0063] For the separation of ammonia, the stripping method of bringing the collection solution into contact with vapor and moving the ammonia in the collection solution to the vapor to recover the ammonia may be used. In this case, the ammonia separation device 19 includes a stripping column whose inside is partitioned by a porous plate and is configured to make the supplied collection solution flow from an upper tier to a lower tier of the stripping column. The vapor flows from the lower tier to the upper tier and rises in the solution dammed by the porous plate. By the contact of the collection solution with the vapor, the ammonia in the collection solution vaporizes and moves into the vapor and is thereby discharged from the pipe at the column top part. Besides, in the case of using a carbonate aqueous solution as the collection solution, the ammonia in the collection solution can be converted to ammonium hydrogen carbonate, which can be thermally decomposed by a thermal decomposition device to separate and recover ammonia and carbon dioxide. The moisture separated in the ammonia separation device 19 and a part of the electrolytic solution passing through the diaphragm (electrolyte membrane) 4 from the anode 15 are sent again to the electrolytic solution storage 10 and utilized again as the electrolytic solution (anode electrolytic solution) to be supplied to the anode space.

[0064] Next, an additional configuration example, modification example, and so on of the nitrogen electrolysis device 1 in the arrangement will be explained. In the anode space, a circulation mechanism such as a pump may be provided. The circulation mechanism can promote the circulation of the electrolytic solution to improve the circulation of ions (H +< and OH -< ) between the anode space and the cathode space for oxidation reaction. Further, the first and second reaction spaces 2 and 3 may be provided with a flow path and may be provided with a plurality of circulation mechanisms. Further, a plurality of (three or more) reaction space flow paths may be provided in order to decrease the diffusion of ions and more efficiently circulate ions. By forming a flow of liquid by the circulation mechanism, it is possible to prevent generated air bubbles from staying on the electrode surfaces or the surfaces of the reaction spaces to thereby promote the reaction.

[0065] The second reaction space 3 is connected to the electrolytic solution circulation unit. The electrolytic solution circulation unit may include at least the electrolytic solution storage 10, the liquid feed pump 20, and a circulation pipe 24. The electrolytic solution circulation unit is a unit that circulates the electrolytic solution inside the circulation pipe 24 so as to take the electrolytic solution containing the produced ammonia out of the second reaction space 3 to the outside and supply the electrolytic solution again to the second reaction space 3. The circulation pipe 24 is provided with a liquid feed pump 20 for circulating the electrolytic solution, and an electrolytic solution storage 10 for storing the electrolytic solution and regulating the electrolyte concentration, pH, and so on. The electrolytic solution circulation unit is configured to circulate the electrolytic solution between the second reaction space 3 and the electrolytic solution storage 10 by the liquid feed pump 20.

[0066] Though the liquid feed pump 20 is provided in the circulation pipe 24 which sends the electrolytic solution from the second reaction space 3 to the electrolytic solution storage 10 in FIG. 1, the liquid feed pump 20 may be provided in the circulation pipe 24 which sends the electrolytic solution from the electrolytic solution storage 10 to the second reaction space 3. The electrolytic solution circulation unit preferably includes an exhaust unit which exhausts excessive nitrogen that has not dissolved in the electrolytic solution and gas that has been produced by the oxidation reaction. As the exhaust unit, for example, a pipe equipped with a valve is used and is provided, for example, in the electrolytic solution storage 10. The electrolytic solution storage 10 functions as a gas-liquid separation space, in which oxygen (O 2 ) produced by the oxidation reaction is separated from the electrolytic solution.

[0067] The ammonia separation unit 13 is a unit which recovers ammonia (NH 3 ) that is a reduced substance of nitrogen, from the electrolytic solution. The ammonia separation unit 13 may include an ammonia separation device 12 which separates ammonia from the electrolytic solution, a three-way valve 22 which takes out at least part of the electrolytic solution circulating inside the circulation pipe 24, a pipe 23 which sends the electrolytic solution taken out of the three-way valve 22 to the ammonia separation device 12, and the circulation pipe 24 which sends the electrolytic solution from which ammonia has been separated in the ammonia separation device 12 to the electrolytic solution storage 10. The three-way valve 22 is provided in the circulation pipe 24, and the ammonia separation unit 13 is connected to the electrolytic solution circulation unit via the three-way valve 22. The taking-out of the electrolytic solution circulating inside the circulation pipe 24 may be implemented not only by using the three-way valve 22 provided in the circulation pipe 24 but also by connecting a pipe having a valve to the electrolytic solution storage 10, and its configuration is not particularly limited. The ammonia separation device 12 uses a similar separation method to that of the ammonia separation device 19, and has a similar configuration.

[0068] Next, an ammonia manufacturing process using the above nitrogen electrolysis device (ammonia manufacturing device) will be explained. First, as an initial stage, a humidified nitrogen gas is supplied to the cathode space. The electrolytic solution is supplied into the anode space. In this state, electric power is supplied from the external electrode to the cathode 14 and the anode 15.

[0069] The anode 15 and the cathode 14 may be connected to an external power supply 17 via external electrodes. The external power supply 17 may be an ordinary commercial power supply, a battery, or the like, or a power supply that converts renewable energy to electric energy and supplies it. Examples of the power supply include a power supply that converts kinetic energy or potential energy such as wind power, water power, geothermal power, or tidal power into electric energy, a power supply such as a solar cell having a photoelectric conversion element that converts light energy into electric energy, a power supply such as a fuel cell or a storage battery that converts chemical energy into electric energy, a device that converts vibrational energy such as sound into electric energy, and so on. The photoelectric conversion element has a function of performing charge separation by energy of radiated light such as sunlight. Examples of the photoelectric conversion element include a pin-junction solar cell, a pn-junction solar cell, an amorphous silicon solar cell, a multijunction solar cell, a single-crystal silicon solar cell, a polycrystalline silicon solar cell, a dye-sensitized solar cell, an organic thin-film solar cell, a perovskite solar cell, and so on.

[0070] By supplying electric power from the external electrodes to the cathode 14 and the anode 15, an oxidation reaction of water (H 2 O) or hydroxide ion (OH -< ) in the electrolytic solution electrochemically occurs at the anode 15. For example, when the hydrogen ion concentration in the electrolytic solution is 7 or less (pH ≤ 7), H 2 O is oxidized to produce O 2 and H +< based on Formula (1) below. When the hydrogen ion concentration in the electrolytic solution is greater than 7 (pH > 7), OH -< is oxidized to produce O 2 and H 2 O based on Formula (2) below.         3H 2 O → 3 / 2O 2 + 6H +< + 6e -< ...     (1)         6OH -< → 3 / 2O 2 + 3H 2 O + 6e -< ...     (2)

[0071] In the cathode space, nitrogen (N 2 ) is reduced by the ammonia production catalyst to produce ammonia (NH 3 ). The ammonia production catalyst is as explained above. N 2 is reduced by conducting ion species in the diaphragm 4 to produce ammonia (NH 3 ) based on Formula (3) or Formula (4) below.         N 2 + 6H 2 O + 6e -< → 2NH 3 + 6OH -< ...     (3)         N 2 + 6H +< + 6e -< → 2NH 3 ...     (4)

[0072] The gas containing NH 3 produced by the N 2 reduction explained above is sent to the ammonia collection device 8, in which the exhaust gas is brought into contact with the aqueous solution (collection solution) with a pH of 0 to 7 to selectively collect ammonia as explained above. At the same time, the byproduct hydrogen and unreacted nitrogen contained in the exhaust gas are separated. The collection solution containing ammonia is sent to the ammonia separation device 12, in which ammonia is separated from the collection solution.

[0073] Part of NH 3 produced by the N 2 reduction is sent via the diaphragm 4 to the anode space and dissolved in the electrolytic solution. The electrolytic solution containing NH 3 is sent via the circulation pipe to the electrolytic solution storage, in which oxygen (O 2 ) is separated, and then sent again to the anode space. By circulating the electrolytic solution inside the circulation pipe 24, an ammonia concentration in the electrolytic solution increases. By sending at least part of the electrolytic solution with increased ammonia concentration to the ammonia separation device 12 via the three-way valve 22, ammonia is separated from the electrolytic solution.

[0074] The supply of the electrolytic solution containing ammonia to the ammonia separation device 12 may be performed continuously from the start of operation of the device but is preferably intermittently performed at the point in time when the concentration of ammonia contained in the electrolytic solution becomes high enough. In other words, when the concentration of ammonia contained in the electrolytic solution is low, the energy to be input to recover ammonia from the electrolytic solution becomes larger than the energy amount stored in ammonia, resulting in an increase in manufacturing cost of ammonia. Regarding this point, the electrolytic solution is circulated by the circulation pipe 24 via the second reaction space 3 and the electrolytic solution storage 10, thereby making it possible to obtain the electrolytic solution containing ammonia at high concentration. It is preferable to send the electrolytic solution containing ammonia at high concentration to the ammonia separation device 12. This makes it possible to recover ammonia being a reduction product of N 2 with high efficiency. To improve the recovery efficiency of ammonia, it is preferable to send the electrolytic solution containing ammonia at a concentration of 0.01 to 50 mass% to the ammonia separation device 12.

[0075] The cathode space and the anode space may be provided with a temperature regulating mechanism which regulates the temperature of the electrolytic solution. By the temperature control using the temperature regulating mechanism, the catalytic performance can be controlled. For example, by making the temperature of the reaction system uniform, the performance of the catalyst can be stabilized. Further, a temperature rise can also be prevented for stabilization of the system. The reaction temperature in the electrochemical reaction unit 5 can be appropriately selected in a range of 5 to 95°C in consideration of the electrolytic solution being an aqueous solution, the reaction efficiency, and the economic efficiency. Preferably, the reaction temperature only needs to be about room temperature (10 to 60°C)

[0076] The electrochemical reaction unit 5 can increase the reaction area by making the electrode porous, to acquire more reaction current. The electrochemical reaction unit 5 may have an electrode structure in which the diaphragm 4 is sandwiched between a porous anode 15 and a porous cathode 14. More specifically, in the electrochemical reaction unit 5 illustrated in FIG. 2, the porous anode 15 and the porous cathode 14 are arranged in contact with both surfaces of the diaphragm 4, respectively. The electrolytic solution is supplied to a surface of the porous anode 15 that is opposite to a surface in contact with the diaphragm 4. The ammonia production catalyst is arranged at a surface of the porous cathode 14 in contact with the diaphragm 4. Nitrogen is supplied to a surface of the porous cathode 14 that is opposite to a surface in contact with the diaphragm 4. The electrochemical reaction unit 5 may have the porous cathode 14 and a nitrogen supply pipe which supplies nitrogen to the ammonia production catalyst via the porous anode 15. In a route through which nitrogen flows, a flow path may be provided. By providing a plurality of (three or more) gas flow paths, nitrogen can be uniformly distributed to the porous cathode 14.

[0077] The electrochemical reaction unit 5 may have an electrolytic solution between the porous cathode 14 and the diaphragm 4. More specifically, the electrochemical reaction unit 5 illustrated in FIG. 4 can supply nitrogen from a surface of the cathode 14 opposite to the ammonia production catalyst. As explained above, the structure of the electrochemical reaction unit 5 can be variously changed.EXAMPLES

[0078] Next, examples and their evaluation results will be explained.[Fabrication of the cathode]

[0079] The cathode was fabricated by spray coating of catalyst ink on carbon paper formed with a carbon particle layer (MPL layer). The catalyst ink used for the cathode was prepared using ketjen black (manufactured by LION SPECIALTY CHEMICALS CO., LTD., EC600JD, BET specific surface area: 1270 m 2< / g) 0.3 g and PTFE 0.2 g as a carrier for the molybdenum complex, and 2-propanol 35 mL and pure water 35 mL as a dispersion medium. The catalyst ink was prepared by mixing ketjen black, PTFE, 2-propanol, and pure water in a glass vial bottle and dispersing them for 20 minutes using an ultrasonic homogenizer. Next, a catalyst layer was formed by spray coating of the catalyst ink on carbon paper (manufactured by Avcarb Co., Ltd., MB-30 (product name)) which was fixed to a metal plate and heated to 90°C. The catalyst layer was coated on the MPL layer side. At this time, amounts of ketjen black and PTFE per 1 cm 2< of the coated surface were 2.2 mg and 1.5 mg, respectively. The electrode was baked at 380°C in an argon atmosphere for one hour and thereby bound, and then the electrode was cut into a square of 20 mm × 20 mm. The thickness of the catalyst layer was found by subtracting the previously measured thickness of the carbon paper from the thickness of the fabricated electrode. The thickness of the catalyst layer produced under these conditions was 0.047 mm. Next, four electrodes each formed with the catalyst layer were immersed in a sample bottle containing a catalyst solution in which a molybdenum triiodide complex (as ligand, 1,3-bis(ditertiarybutylphosphinomethylbenzoimidazole-2-ylidene) being a PCP ligand) was dissolved in methanol (a solution in which about 10 mg of molybdenum complex was dissolved in 10 mL of methanol), at room temperature and in a nitrogen atmosphere, and the sample bottle was irradiated with an ultrasonic wave for one hour. The electrodes were then air-dried under nitrogen flow to form into cathodes (20 mm × 20 mm squares). The amount of the carried molybdenum complex in the catalyst layer was quantified by the fluorescent X-ray analysis and the inductively coupled plasma emission spectroscopy. A mass ratio (KB:PTFE) between ketjen black (KB) and PTFE in the cathode was 5.9:4.1. KB:PTFE was calculated from the mass of KB and the mass of PTFE per 1 cm 2< of the coated surface.[Quantification of the molybdenum complex amount by the fluorescent X-ray analysis and the inductively coupled plasma emission spectroscopy]

[0080] A cathode for acquiring calibration curve data was prepared in advance, a fluorescent X-ray intensity corresponding to the molybdenum atoms contained in the cathode was measured, and the inductively coupled plasma emission spectroscopy was performed on the solution made by pressure acid decomposition of the sample to create the calibration curve of the weight of the molybdenum atoms corresponding to the fluorescent X-ray intensity. From the fluorescent X-ray intensity corresponding to the molybdenum atoms obtained by the fluorescent X-ray analysis of the measurement-target sample, the weight of the molybdenum atoms contained in the cathode was estimated using the calibration curve created in the above. The weight of the molybdenum atoms was divided by the molybdenum element content to calculate the number of molybdenum atoms contained in the cathode. Since one molybdenum atom is contained in one molecule of the molybdenum complex, the molybdenum complex amount was estimated using the number of molybdenum atoms as the number of molecules of the molybdenum complex. The molybdenum complex amount per cathode estimated as above was 2.26 µmol.[Fabrication of the anode]

[0081] The anode was fabricated by making Ti into a mesh structure by an etching method and forming iridium oxide as an oxidation catalyst on a wire mesh (20 mm × 20 mm square) with an increased surface area.[Fabrication of a membrane electrode assembly and a N 2 electrolysis cell]

[0082] An experiment was carried out with the configuration of the electrolysis cell illustrated in FIG. 3. A membrane electrode assembly (catalyst area of 400 mm 2< ) was prepared by sandwiching Nafion (registered trademark) 117 membrane (25 mm × 25 mm square) of Dupont Inc. as the diaphragm between the anode and the cathode to stack them. Nafion 117 membrane was pre-treated by boiling it in 3% hydrogen peroxide, 1 M sulfuric acid, and pure water for one hour each and then immersing it in 1 M KOH solution. Note that the cathode catalyst layer and the diaphragm were arranged in contact with each other. The membrane electrode assembly was sandwiched between titanium flow paths (serpentine, a land width of 0.4 mm, a flow path width of 1.5 mm, a flow path depth of 1 mm) via a Teflon gasket to assemble the N 2 electrolysis cell.[Constant potential electrolysis measurement (ammonia production experiment)]

[0083] A 0.1 M tripotassium phosphate solution was supplied as the electrolytic solution to the anode flow path of the N 2 electrolysis cell at 10 mL / min. The pH of the electrolytic solution was 11. On the other hand, dry N 2 gas (> 99.99%) was supplied to the cathode flow path at a flow rate of 80 mL / min. A power supply device (Biologic VMP-300) was electrically connected to the cathode and the anode from outside the cathode flow path plate and the anode flow path plate, and a constant current of 1.6 A (current density of 400 mA / cm 2< ) was applied for 15 min. A 0.1 M sulfuric acid was connected as trap liquid to the cathode flow path outlet of the N 2 electrolysis cell, and the reduction product produced from the cathode was recovered and analyzed every five minutes.[Ammonia quantification method]

[0084] The quantification of ammonia was performed by an ion chromatography. The liquid containing ammonia gas and ammonia discharged from the cathode flow path outlet is all converted into ammonium ions by the sulfuric acid trap liquid. The ammonium ions in the sulfuric acid trap liquid were quantified using ion chromatography by which the calibration curve was created in advance using a prescribed amount of ammonium ion solution.

[0085] Ammonia production partial current density and Faraday efficiency were calculated based on the current consumed for the cathode reduction reaction and quantitative analysis of reduction products. The partial current density corresponds to the ammonia production speed of the electrolysis cell, and the Faraday efficiency is expressed by a percentage of the quantity of electricity required to produce the reduction products relative to the quantity of electricity input. The Faraday efficiency of each reduction product analyzed was used as selectivity (%) of the product. In the N 2 electrolysis cell prepared by the above method, the partial current density was 13.3 mA / cm 2< and the Faraday efficiency was 3.33%.

[0086] The ammonia production amount was estimated from the ammonia production partial current density, and divided by the amount of the molybdenum complex contained in the cathode to estimate the turn over frequency (TOF) per hour. In the N 2 electrolysis cell created by the above method, the TOF was 294 h -1< . These results are listed in Table 1.(Example 2)

[0087] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of ethanol. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 1.20 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 8.54 mA / cm 2< , the Faraday efficiency was 2.14%, and the TOF was 355 h -1< . These results are listed in Table 1.(Example 3)

[0088] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of tetrahydrofuran. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 2.38 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 13.1 mA / cm 2< , the Faraday efficiency was 3.28%, and the TOF was 274 h -1< . These results are listed in Table 1.(Example 4)

[0089] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of chloroform. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 1.44 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 8.97 mA / cm 2< , the Faraday efficiency was 2.24%, and the TOF was 309 h -1< . These results are listed in Table 1.(Example 5)

[0090] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of acetone. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 1.21 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 10.4 mA / cm 2< , the Faraday efficiency was 2.61%, and the TOF was 428 h -1< . These results are listed in Table 1.(Example 6)

[0091] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of acetonitrile. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 0.59 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 3.65 mA / cm 2< , the Faraday efficiency was 0.91%, and the TOF was 309 h -1< . These results are listed in Table 1.(Comparative example 1)

[0092] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of 2-propanol. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 0.36 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 0.11 mA / cm 2< , the Faraday efficiency was 0.03%, and the TOF was 16 h -1< . These results are listed in Table 1.(Comparative example 2)

[0093] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of hexane. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 0.19 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, no ammonia was detected. These results are listed in Table 1.

[0094] According to Examples 1 to 6 and Comparative examples 1 and 2, the molybdenum complex is likely to dissolve in alcohol with C2 or less such as methanol and ethanol or a polar solvent such as tetrahydrofuran, so that the carrying amount of the cathode catalyst increases and the ammonia production amount also increases. On the other hand, the molybdenum complex does not dissolve in alcohol with C3 or more such as 2-propanol or a nonpolar solvent such as hexane, so that the carrying amount of the cathode catalyst decreases and the ammonia production amount also decreases. Based on the above, a relative dielectric constant ε of the aprotic solvent to be used for the solvent of the catalyst solution is preferably 3.0 or more and more preferably 20.0 or more.(Example 7)

[0095] The cathode catalyst layer ink composition was changed and a cathode containing 3.3 mg of ketjen black and 2.2 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.10 mm. KB:PTFE was 6.0:4.0. The molybdenum complex amount per cathode was 2.61 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 15.7 mA / cm 2< , the Faraday efficiency was 3.94%, and the TOF was 301 h -1< . These results are listed in Table 1.(Example 8)

[0096] The cathode catalyst layer ink composition was changed and a cathode containing 4.4 mg of ketjen black and 3.0 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.149 mm. KB:PTFE was 5.9:4.1. The molybdenum complex amount per cathode was 4.02 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 13.4 mA / cm 2< , the Faraday efficiency was 3.35%, and the TOF was 166 h -1< . These results are listed in Table 1.(Example 9)

[0097] The cathode catalyst layer ink composition was changed and a cathode containing 1.1 mg of ketjen black and 0.7 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.032 mm. KB:PTFE was 6.1:3.9. The molybdenum complex amount per cathode was 1.20 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 9.91 mA / cm 2< , the Faraday efficiency was 2.48%, and the TOF was 410 h -1< . These results are listed in Table 1.(Example 10)

[0098] The cathode catalyst layer ink composition was changed and a cathode containing 6.6 mg of ketjen black and 4.5 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.210 mm. KB:PTFE was 5.9:4.1. The molybdenum complex amount per cathode was 2.24 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 10.4 mA / cm 2< , the Faraday efficiency was 2.60%, and the TOF was 232 h -1< . These results are listed in Table 1.

[0099] According to Examples 1, 7, 8, 9, and 10, a larger thickness of the cathode catalyst layer can carry a larger amount of molybdenum complex, but the carrying amount decreases when the thickness is a certain thickness or more. On the other hand, when the catalyst layer is thicker more than necessary, gas to be reduced supplied from the gas diffusion layer is less likely to reach the surface side of the catalyst layer, causing hydrogen production by a side reaction to decrease the production efficiency of ammonia. Accordingly, the thickness of the catalyst layer is more preferably 0.035 to 0.200 mm.(Example 11)

[0100] The cathode catalyst layer ink composition was changed and a cathode containing 1.5 mg of ketjen black and 2.2 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.046 mm. KB:PTFE was 4.0:6.0. The molybdenum complex amount per cathode was 0.95 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 8.35 mA / cm 2< , the Faraday efficiency was 2.09%, and the TOF was 438 h -1< . These results are listed in Table 1.(Example 12)

[0101] The cathode catalyst layer ink composition was changed and a cathode containing 2.9 mg of ketjen black and 0.8 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.078 mm. KB:PTFE was 7.8:2.2. The molybdenum complex amount per cathode was 1.78 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 6.49 mA / cm 2< , the Faraday efficiency was 1.62%, and the TOF was 182 h -1< . These results are listed in Table 1.(Comparative example 3)

[0102] The cathode catalyst layer ink composition was changed and a cathode containing 3.7 mg of ketjen black and no PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. KB:PTFE was 10:0. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the catalyst layer peeled off the carbon paper in a molybdenum complex immersion process, failing to manufacture ammonia. These results are listed in Table 1.

[0103] According to Examples 1, 11, and 12 and Comparative example 3, in the case where the polymeric material in the catalyst layer is a material increasing the water repellency such as polytetrafluoroethylene, it is possible to realize a catalyst layer lower in hydrophilicity by increasing the percentage of the polymeric material in the catalyst layer. On the other hand, in order to increase the catalyst carrying amount, it is necessary to increase the percentage of the catalyst carrier in the catalyst layer, and the ratio between the catalyst carrier and the water repellent polymeric material is preferably in a range of 7.5:2.5 to 4:6 and more preferably in a range of 7:3 to 5:5 in order to improve the production efficiency of ammonia by a gas phase.

[0104] The TOF indicates the magnitude of the ammonia amount produced by one catalyst, and a larger TOF indicates that the catalyst more efficiently works. Also in the TOF, the same interpretation as in the above paragraph can be made. More specifically, it is possible to increase the TOF by bringing at least one of the type of the catalyst solvent, the thickness of the catalyst layer, and the ratio between the catalyst carrier and the water repellent polymeric material to a preferable material or numerical range. [Table 1]Catalyst solventCatalyst thickness (mm)KB : PTFEMolybdenum complex amount (µmol)Partial current density (mA / cm 2< )Faraday efficiency (%)TOF (h -1< )Example 1Methanol0.0475.9 : 4.12.2613.33.33294Example 2Ethanol0.0475.9 : 4.11.208.542.14355Example 3Tetrahydrofuran0.0475.9 : 4.12.3813.13.28274Example 4Chloroform0.0475.9 : 4.11.448.972.24309Example 5Acetone0.0475.9 : 4.11.2110.42.61428Example 6Acetonitrile0.0475.9 : 4.10.593.650.91309Example 7Methanol0.1006.0 : 4.02.6015.73.94301Example 8Methanol0.1495.9 : 4.14.0213.43.35166Example 9Methanol0.0326.1 : 3.91.209.912.48410Example 10Methanol0.2105.9 : 4.12.2410.42.60232Example 11Methanol0.0464.0 : 6.00.958.352.09438Example 12Methanol0.0787.8 : 2.21.786.491.62182Comparative example 12-propanol0.0475.9 : 4.10.360.110.0316Comparative example 2Hexane0.0475.9 : 4.10.19---Comparative example 3Methanol0.04710 : 0----

[0105] Note that the configurations of the above-described arrangements can be employed in combination or can be partly replaced. While certain arrangements of the present invention have been described herein, these arrangements have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel arrangements described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the arrangements described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

[0106] Clauses of the above arrangements are attached below.(Clause 1)

[0107] An electrolysis device including: a cathode; an anode; a cathode space on the cathode and through which a gaseous reducible material is supplied; an anode space on the anode and through which a liquid or gaseous oxidizable material is supplied; and a diaphragm between the cathode and the anode, wherein the cathode includes a substrate, and a catalyst layer, the catalyst layer having: a metal complex for promoting a chemical reaction of reducing the reducible material to produce a reduction product; alcohol with C2 or less, or an aprotic solvent having a relative dielectric constant of 3.0 or more; a catalyst carrier carrying the metal complex and having conductivity; and a binder binding the substrate and the catalyst carrier. (Clause 2)

[0108] The electrolysis device according to Clause 1, wherein: a thickness of the catalyst layer is 0.035 mm or more and 0.200 mm or less.(Clause 3)

[0109] The electrolysis device according to Clause 1 or Clause 2, wherein a mass ratio (catalyst carrier:binder) between the catalyst carrier and the binder in the catalyst layer is in a range of 4:6 to 7.5:2.5.(Clause 4)

[0110] The electrolysis device according to any one of Clause 1 to Clause 3, wherein the catalyst carrier is a porous carbon material.(Clause 5)

[0111] The electrolysis device according to any one of Clause 1 to Clause 4, wherein the binder is an organic polymeric material.(Clause 6)

[0112] The electrolysis device according to any one of Clause 1 to Clause 5, wherein the catalyst layer contains methanol.(Clause 7)

[0113] The electrolysis device according to any one of Clause 1 to Clause 6, wherein the metal complex is a molybdenum complex which promotes a chemical reaction of reducing nitrogen to produce ammonia.(Clause 8)

[0114] The electrolysis device according to Clause 7, further including: a nitrogen supply unit including a nitrogen supply part configured to introduce gaseous nitrogen into the cathode space; an ammonia collection unit including an ammonia collection part configured to collect ammonia in a substance to be discharged from the cathode space; and an ammonia separation unit including an ammonia separation part configured to separate ammonia from an electrolytic solution to be discharged from the anode space. (Clause 9)

[0115] The electrolysis device according to Clause 8, further including: a circulation pipe through which an electrolytic solution circulates outside the anode space and is supplied to the anode space; and an electrolytic solution circulation unit arranged in the middle of the circulation pipe and including an electrolytic solution storage for storing the electrolytic solution. (Clause 10)

[0116] 10. A method for manufacturing an electrolysis device, the electrolysis device including: a cathode; an anode; a cathode space on the cathode and though which a gaseous reducible material is supplied; an anode space on the anode and through which a liquid or gaseous oxidizable material is supplied; and a diaphragm between the cathode and the anode, and the method comprising forming the cathode by a process including: mixing a metal complex, alcohol with C2 or less or an aprotic solvent having a relative dielectric constant of 3.0 or more, a catalyst carrier, and a binder, to prepare a solution; and forming a catalyst layer on a substrate using the solution.

Examples

examples

[0078]Next, examples and their evaluation results will be explained.

[Fabrication of the cathode]

[0079]The cathode was fabricated by spray coating of catalyst ink on carbon paper formed with a carbon particle layer (MPL layer). The catalyst ink used for the cathode was prepared using ketjen black (manufactured by LION SPECIALTY CHEMICALS CO., LTD., EC600JD, BET specific surface area: 1270 m 2< / g) 0.3 g and PTFE 0.2 g as a carrier for the molybdenum complex, and 2-propanol 35 mL and pure water 35 mL as a dispersion medium. The catalyst ink was prepared by mixing ketjen black, PTFE, 2-propanol, and pure water in a glass vial bottle and dispersing them for 20 minutes using an ultrasonic homogenizer. Next, a catalyst layer was formed by spray coating of the catalyst ink on carbon paper (manufactured by Avcarb Co., Ltd., MB-30 (product name)) which was fixed to a metal plate and heated to 90°C. The catalyst layer was coated on the MPL layer side. At this time, amounts of ketjen black and...

example 2

(Example 2)

[0087]The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of ethanol. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 1.20 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 8.54 mA / cm 2< , the Faraday efficiency was 2.14%, and the TOF was 355 h -1< . These results are listed in Table 1.

example 3

(Example 3)

[0088]The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of tetrahydrofuran. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 2.38 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 13.1 mA / cm 2< , the Faraday efficiency was 3.28%, and the TOF was 274 h -1< . These results are listed in Table 1.

FIELD

[0001] Arrangements relate to an electrolysis device and a method for manufacturing the electrolysis device.BACKGROUND

[0002] The production amount of ammonia is about 140 million tons (1.4 × 10 11< kg) in the world in a year and continues to rise. About 80% of the production amount is utilized as a raw material for fertilizer and is mainly converted to other nitrogen compounds such as urea, nitric acid, ammonium nitrate, and ammonium sulfate. On the other hand, the remaining 20% thereof is utilized for the manufacture of synthetic resin and fiber. To cope with the global population growth, the shortage of cultivated acreage, and the food shortages due to the sophistication of diet mainly in developing countries, the demand for ammonia is increased. Further, ammonia attracts attention as a use of an energy carrier owing to its ease of handling, high energy density, and a characteristic of containing no carbon and emitting no carbon dioxide when used.

[0003] At present, ammonia is industrially synthesized from a hydrogen gas and a nitrogen gas derived from fossil fuels such as petroleum, coal, or natural gas by the method called Haber-Bosh process invented about 100 years ago. This synthesis reaction requires severe conditions such as high temperature (400 to 650°C) and high pressure (200 to 400 atm), consumes 1.2% of total energy in the world, and therefore emits a large amount of carbon dioxide. To form a sustainable society in the future, the development of an alternative process with low dependence on fossil fuels is expected.

[0004] Regarding the above point, a catalyst for producing ammonia from nitrogen at normal temperature and pressure in an electrolysis method and an electrolysis device for manufacturing ammonia (NH 3 ) by reducing nitrogen (NH 3 ) through electrolysis is under development. For example, it has been reported that a molybdenum iodide complex having a PNP 2,6-bis(di-tert-butylphosphinomethyl)pyridine) ligand as a catalyst, and a solution containing alcohol or water as a proton source, and an organic low-molecule containing a halide (II) of a lanthanoid metal as a reducing agent, for example, samarium (II) iodide as a solvent, are stirred in the presence of a nitrogen gas at normal temperature to thereby produce up to 4350 equivalents of ammonia per catalyst. In addition, a method using the molybdenum iodide complex having the PNP ligand as the catalyst, and using a solution to be used in a cathode storage or both an electrolyte membrane and the solution to be used in the cathode storage, as the proton source has been reported.

[0005] In the above electrolysis device which manufactures ammonia (NH 3 ) by the reduction of nitrogen (N 2 ), when fabricating a cathode which reduces the nitrogen gas to produce ammonia, a method of carrying the catalyst using the organic low-molecular solvent for a gas diffusion electrode being a carrier (also referred to as a catalyst carrying method) is used. On the other hand, the organic low-molecular solvent is relatively high in adsorption selectivity to the carrier, and thus becomes a factor that decreases a carrying amount of the catalyst and increases the hydrophilicity of the carrier to cause a flooding phenomenon. These become factors that decrease the production amount and production efficiency of an electrolysis product such as ammonia on the cathode side. Besides, in the case of using a material that reacts with excessive moisture to become inactive such as a molybdenum complex as the catalyst, the hydrophilicity of the cathode is decreased to enable a catalytic reaction to proceed efficiently. Hence, it is desired to optimize the solvent to be used in a cathode fabrication process and the process and optimize the composition of the cathode so as to realize a cathode with a high catalyst carrying amount and low hydrophilicity and increase the manufacturing efficiency and the recovery efficiency of the electrolysis product such as ammonia. The object is required not only in a nitrogen electrolysis device which manufactures ammonia by reduction of nitrogen but also in electrolysis devices such as an electrolysis device having a cathode fabricated using the catalyst carrying method and producing a reduction product different from ammonia, for example, a water electrolysis device which electrolyzes water (H 2 O) to produce hydrogen (H 2 ) and so on, a carbon dioxide electrolysis device which electrolyzes carbon dioxide (CO 2 ) to produce a carbon compound such as carbon monoxide (CO), formic acid (HCOOH), methanol (CH 3 OH), ethanol (C 2 H 5 OH), or the like, and so on.SUMMARY

[0006] A problem to be solved by the present invention is to provide an electrolysis device capable of manufacturing a reduction product with high efficiency by an electrolytic reaction.

[0007] An electrolysis device in an arrangement includes: a cathode; an anode; a cathode space on the cathode and through which a gaseous reducible material is supplied; an anode space on the anode and through which a liquid or gaseous oxidizable material is supplied; and a diaphragm between the cathode and the anode. The cathode has a substrate and a catalyst layer. The catalyst layer has: a metal complex for promoting a chemical reaction of reducing the reducible material to produce a reduction product; alcohol with C2 or less, or an aprotic solvent having a relative dielectric constant of 3.0 or more; a catalyst carrier carrying the metal complex and having conductivity; and a binder for binding the substrate and the catalyst carrier.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a schematic diagram illustrating a structure example of an electrolysis device. FIG. 2 is a schematic diagram illustrating a first example of an electrochemical reaction unit. FIG. 3 is a schematic diagram illustrating a second example of the electrochemical reaction unit. FIG. 4 is a schematic diagram illustrating a third example of the electrochemical reaction unit. FIG. 5 is a cross-sectional schematic view illustrating a structure example of a cathode. DETAILED DESCRIPTION

[0009] Electrolysis devices in arrangements will be explained below with reference to the drawings. In the arrangements explained below, substantially the same components are denoted by the same reference signs, and the explanation thereof may be partially omitted. The drawings are schematic in which the relationship between the thickness and planar dimensions, a thickness ratio among the components, and so on may be different from actual ones. Nitrogen electrolysis devices which manufacture ammonia (NH 3 ) by the reduction of nitrogen (N 2 ) will be mainly explained here as the electrolysis devices of the arrangements, but the electrolysis devices in the arrangements are not limited to the nitrogen electrolysis device. The electrolysis devices in the arrangements may be, for example, a water electrolysis device which electrolyzes water (H 2 O) to produce hydrogen (H 2 ) and so on, and a carbon dioxide electrolysis device which electrolyzes carbon dioxide (CO 2 ) to produce a carbon compound such as carbon monoxide (CO), formic acid (HCOOH), methanol (CH 3 OH), and so on.

[0010] FIG. 1 is a schematic diagram illustrating a structure example of an electrolysis device in an arrangement. FIG. 1 illustrates a nitrogen electrolysis device 1. The nitrogen electrolysis device 1 is an ammonia manufacturing device, and includes: an electrochemical reaction unit (electrolysis cell) 5 including a first reaction space (reduction reaction electrolytic bath) 2 which is supplied with a gaseous reducible material (for example, nitrogen), a second reaction space (oxidation reaction electrolytic bath) 3 which is supplied with a liquid or gaseous oxidizable material (for example, an electrolytic solution containing water, or water vapor), and a diaphragm 4; a nitrogen supply unit 7 including a nitrogen supply part (supply device) 6 for supplying nitrogen to a cathode space; an ammonia collection part (ammonia collection unit) 9 including a collector (collection device) 8 which can collect ammonia contained in gas exhausted from the cathode space; an oxidizable material supply unit 11 for supplying an electrolytic solution from an electrolytic solution storage 10 containing the electrolytic solution to the second reaction space 3; and an ammonia separation unit 13 including an ammonia separation part (separation device) 12 which separates ammonia contained in the electrolytic solution discharged from the second reaction space 3. Hereinafter, the components will be explained in detail.

[0011] FIG. 2 illustrates a first example of the electrochemical reaction unit 5. The electrochemical reaction unit 5 illustrated in FIG. 2 includes: a first reaction space (reduction reaction electrolytic bath) 2 as the cathode space; a second reaction space (oxidation reaction electrolytic bath) 3 as an anode space; a diaphragm 4 provided between the first reaction space 2 and the second reaction space 3; a cathode 14 arranged in the first reaction space 2 and used for an electrochemical reduction reaction; and an anode 15 arranged in the second reaction space 3 and used for an electrochemical oxidation reaction, which constitute an electrochemical reaction cell (electrolysis cell). The electrochemical reaction unit 5 is separated into the first reaction space 2 and the second reaction space 3 by the diaphragm 4 which can move ions such as hydrogen ion (H +< ) and hydroxide ion (OH -< ). Into the first reaction space 2, gaseous nitrogen (N 2 ) is supplied from the nitrogen supply unit 7 via a pipe. Into the second reaction space 3, an electrolytic solution containing water (H 2 O) or water vapor (H 2 O) generated by evaporation of the electrolytic solution is supplied from the oxidizable material supply unit 11 via a pipe.

[0012] FIG. 3 illustrates a second example of the electrochemical reaction unit 5. The electrochemical reaction unit 5 illustrated in FIG. 3 has a first flow path plate 2a instead of the first reaction space 2 which is supplied with gaseous nitrogen being the reducible material, and a second flow path plate 3a instead of the second reaction space 3 which is supplied with the electrolytic solution or water vapor being the oxidizable material. The first flow path plate 2a has a first flow path (also referred to as a cathode flow path) which is supplied with gaseous nitrogen being the reducible material, as a cathode space facing a cathode 14. The second flow path plate 3a has a second flow path (also referred to as an anode flow path) which is supplied with an electrolytic solution or water vapor being the oxidizable material, as an anode space facing an anode 15. The electrochemical reaction unit 5 illustrated in FIG. 3 has the cathode 14 to be used for the electrochemical reduction reaction adjacent to the first flow path plate 2a, the anode 15 to be used for the electrochemical oxidation reaction adjacent to the second flow path plate 3a, and a diaphragm 4 provided between the cathode 14 and the anode 15, which are sandwiched between the first flow path plate 2a and the second flow path plate 3a, and they constitute an electrochemical reaction cell (electrolysis cell). According to FIG. 3, the distance between the cathode 14 and anode 15 is equivalent to the thickness of the diaphragm 4, thus making it possible to decrease the electric resistance and quickly move hydrogen ion (H +< ) and hydroxide ion (OH -< ) between the electrodes. This can decrease the power consumption of the electrolysis cell and increase the ammonia manufacturing efficiency. Note that for the other explanation of the first flow path plate 2a and the second flow path plate 3a, the explanation of the first reaction space 2 and the second reaction space 3 may be used as appropriate.

[0013] FIG. 4 illustrates a third example of the electrochemical reaction unit 5. The electrochemical reaction unit 5 illustrated in FIG. 4 includes a third reaction space 16 which is provided between a first reaction space 2 supplied with gaseous nitrogen (N 2 ) and a diaphragm 4, and supplied with an electrolytic solution (cathode solution) containing water. The first reaction space 2 and the third reaction space 16 are in contact with each other via a porous cathode 14, which constitute a cathode space. The cathode space having the first reaction space 2 and the third reaction space 16 is in contact with a second reaction space 3 as an anode space via the diaphragm 4 and a porous anode 15. The electrochemical reaction unit 5 illustrated in FIG. 4 can dissolve ammonia (NH 3 ) produced by reducing the gaseous nitrogen (N 2 ) supplied to the first reaction space 2, into the electrolytic solution (cathode solution) supplied to the third reaction space 16 to take it to the outside of the electrochemical reaction cell (electrolysis cell) 5. This can increase the recovery efficiency of ammonia.

[0014] The cathode 14 and the anode 15 are connected to an external electrode. By supplying current or voltage to the cathode 14 and the anode 15 from the external electrode to feed power, a reduction reaction occurs at the cathode 14 and an oxidation reaction occurs at the anode 15. In the anode space, for example, water (H 2 O) in the electrolytic solution is oxidized at the anode 15 to produce oxygen (O 2 ), hydrogen ions (H +< ), and electrons (e -< ). In the cathode space, nitrogen (N 2 ) is reduced by an ammonia production catalyst to produce ammonia (NH 3 ). The nitrogen containing ammonia is led to the outside of the cathode space via a pipe and continuously sent to the ammonia collection unit 9. Further, a part of the ammonia produced in the cathode space moves to the anode space through the diaphragm 4. The electrolytic solution containing water mixed with ammonia in the anode space and oxygen produced at the anode 15 or water vapor is led to the outside of the anode space via a pipe and continuously or intermittently sent to the ammonia separation unit 13.

[0015] The anode space is supplied with the electrolytic solution containing water (H 2 O) or water vapor as explained above. The electrolytic solution may be an aqueous solution containing an electrolyte or the like. It is preferable that the electrolytic solution is high in ion conductivity and the electrolyte itself does not react. Examples of the electrolyte contained in the electrolytic solution include lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), lithium bromide (LiBr), sodium bromide (NaBr), potassium bromide (KBr), lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), lithium nitrate (LiNO 3 ), sodium nitrate (NaNO 3 ), potassium nitrate (KNO 3 ), lithium sulfate (Li 2 SO 4 ), sodium sulfate (Na 2 SO 4 ), potassium sulfate (K 2 SO 4 ), lithium hydrogen sulfate (LiHSO 4 ), sodium hydrogen sulfate (NaHSO 4 ), potassium hydrogen sulfate (KHSO 4 ), lithium peroxodisulfate (Li 2 S 2 O 8 ), sodium peroxodisulfate (Na 2 S 2 O 8 ), potassium peroxodisulfate (K 2 S 2 O 8 ), lithium phosphate (Li 3 PO 4 ), sodium phosphate (Na 3 PO 4 ), potassium phosphate (K 3 PO 4 ), dilithium hydrogen phosphate (Li 2 HPO 4 ), disodium hydrogen phosphate (Na 2 HPO 4 ), dipotassium hydrogen phosphate (K 2 HPO 4 ), lithium dihydrogen phosphate (LiH 2 PO 4 ), sodium dihydrogen phosphate (NaH 2 PO 4 ), potassium dihydrogen phosphate (KH 2 PO 4 ), lithium hydrogen carbonate (LiHCO 3 ), sodium hydrogen carbonate (NaHCO 3 ), potassium hydrogen carbonate (KHCO 3 ), lithium carbonate (Li 2 CO 3 ), sodium carbonate (Na 2 CO 3 ), potassium carbonate (K 2 CO 3 ), lithium tetraborate (Li 2 B 4 O 7 ), sodium tetraborate (Na 2 B 4 O 7 ), potassium tetraborate (K 2 B 4 O 7 ), lithium silicate (Li 2 SiO 3 ), sodium silicate (Na 2 SiO 3 ), potassium silicate (K 2 SiO 3 ), ionic liquid, and so on. It is preferable to use water as a solvent. The electrolyte concentration in the electrolytic solution is preferably, for example, in a range of 0.001 to 1 mol / L.

[0016] As the positive ion of the ionic liquid, an ion such as an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, or a piperidinium ion is used. Examples of the imidazolium ion include 1-ethyl-3-methylimidazolium, 1-methyl-3-propylimidazolium, 1-butyl-3-methylimidazolium, 1-methyl-3-pentylimidazolium, 1-hexyl-3-methylimidazolium, and so on. A 2nd position of the imidazolium ion may be substituted. Examples of the substituted one include 1-ethyl-2,3-dimethylimidazolium, 1,2-dimethyl-3-propylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,2-dimethyl-3-pentylimidazolium, 1-hexyl-2,3-dimethylimidazolium, and so on. Examples of the pyridinium ion include methylpyridinium, ethylpyridinium, propylpyridinium, butylpyridinium, pentylpyridinium, hexylpyridinium, and so on. Examples of the pyrrolidinium ion include ethyl-methylpyrrolidinium, methyl-propylpyrrolidinium, butyl-methylpyrrolidinium, methyl-pentylpyrrolidinium, hexyl-methylpyrrolidinium, and so on. Examples of the piperidinium ion include ethyl-methylpiperidinium, methyl-propylpiperidinium, butyl-methylpiperidinium, methyl-pentylpiperidinium, hexyl-methylpiperidinium, and so on. In all of the imidazolium ion, pyridinium ion, pyrrolidinium ion, and piperidinium ion, the alkyl group may be substituted, and an unsaturated bond may exist. As the positive ion of the ionic liquid, a single cation or a plurality of cations combined are used.

[0017] Examples of the negative ion of the ionic liquid include a fluoride ion, a chloride ion, a bromide ion, an iodide ion, an acetate ion, a nitrate ion, a hydrogen sulfate ion, a phosphate ion, a dicyanamide ion, BF 4 -< , PF 6 -< , CF 3 COO -< , CF 3 SO 3 -< , SCN -< , (CF 3 SO 2 ) 3 C -< , a bis(trifluoromethoxysulfonyl)imide ion, a bis(trifluoromethoxysulfonyl)imide ion, a bis(perfluoroethylsulfonyl)imide ion, and so on. As the negative ion of the ionic liquid, a single anion or a plurality of anions combined are used. Further, a dipolar ion made by connecting the cation and the anion of the ionic liquid by hydrocarbon may be used. One type of the ionic liquid may be used alone or two or more types may be used in combination.

[0018] The anode space has the anode 15 arranged therein, and is supplied with the electrolytic solution. At the anode 15, when the hydrogen ion concentration of the electrolytic solution is 7 or less (pH ≤ 7), H 2 O is oxidized to produce O 2 and H +< . On the other hand, when the hydrogen ion concentration of the electrolytic solution is greater than 7 (pH > 7), OH -< is oxidized to produce O 2 and H 2 O. The anode 15 is constituted of a material which decreases the activation energy for causing an oxidation reaction. In other words, the anode 15 is constituted of a material which decreases the overvoltage when causing a reaction of oxidizing H 2 O or OH -< to pull out electrons. Examples of the constituent material of the anode 15 include binary metal oxides such as platinum (Pt), manganese oxide (Mn-O), iridium oxide (Ir-O), nickel oxide (Ni-O), cobalt oxide (Co-O), iron oxide (Fe-O), tin oxide (Sn-O), indium oxide (In-O), and ruthenium oxide (Ru-O), ternary metal oxides such as Ni-Co-O, La-Co-O, Ni-La-O, and Sr-Fe-O, quaternary metal oxides such as Pb-Ru-Ir-O and La-Sr-Co-O, and metal complexes such as a Ru complex and a Fe complex.

[0019] The cathode space has the cathode 14 arranged therein, and is supplied with the nitrogen gas. When carrying out the reduction reaction, the cathode 14 is preferably constituted of a material having conductivity so as to transmit the electrons supplied from the external electrode to the catalyst, having gas diffusibility so as to more quickly diffuse the reducible material, and having a porous structure for carrying more catalyst. Further, the cathode 14 is preferably low in hydrophilicity so as to prevent a flooding phenomenon due to the electrolytic solution moving from the anode space through the diaphragm 4. The hydrophilicity of the cathode 14 can be adjusted, for example, by the thickness or the construction material of the cathode 14.

[0020] FIG. 5 is a cross-sectional schematic view illustrating a structure example of the cathode 14. An example of the cathode 14 has a gas diffusion layer 141 being a substrate and a catalyst layer (also referred to as a cathode catalyst layer) 142. Note that the structure of the cathode 14 is not limited to the structure illustrated in FIG. 5.

[0021] The gas diffusion layer 141 is formed using, for example, a material such as carbon paper, carbon cloth, carbon felt, glass cloth, porous polymer membrane, or the like. The gas diffusion layer 141 may include a layer called a multiporous layer (MPL) for improving the gas diffusibility and water repellency.

[0022] The catalyst layer 142 is provided on the surface of the gas diffusion layer 141. FIG. 5 illustrates an example in which the catalyst layer 142 is, but not limited to, stacked on the gas diffusion layer 141. For example, at least a part of the catalyst layer 142 may be formed on the surface of the gas diffusion layer 141 in a pore of the gas diffusion layer 141. The catalyst layer 142 has at least a material being a reduction catalyst, a material responsible for conductivity, a material serving as a catalyst carrier, and a material having a roll of binding them (binder), so that the same material may take a plurality of rolls. Specifically, the catalyst layer 142 may contain an organic-inorganic composite material (composite material of an organic material and an inorganic material) for controlling the hydrophilicity of a second catalyst carrier and the catalyst layer 142 using a carbon material as a conductor and a catalyst carrier as a main component, and an organic polymeric material for binding a porous carbon material and an inorganic oxide fine particle, in addition to the reduction catalyst for reducing nitrogen to produce ammonia. The organic-inorganic composite material and the organic polymeric material may have ion conductivity, and thus can enhance the conductivity and supplyability of ions such as a hydrogen ion (H +< ), a hydroxide ion (OH -< ), and so on to the reduction catalyst to thereby increase the reduction efficiency of nitrogen (N), namely, the production efficiency of ammonia (NH 3 ).

[0023] The reduction catalyst (ammonia production catalyst) used for the cathode 14 promotes the production of ammonia from nitrogen, and, for example, not limited to, a molybdenum complex is used. Examples of the ammonia production catalyst include (A) to (D) molybdenum complexes explained below.

[0024] A first example is (A) a molybdenum complex having, as a PCP ligand, N,N-bis(dialkylphosphinomethyl)dihydrobenzimidazolidene (where two alkyl groups may be the same or different, and at least one hydrogen atom of a benzene ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom).

[0025] A second example is (B) a molybdenum complex having, as a PNP ligand, 2,6-bis(dialkylphosphinomethyl)pyridine (where two alkyl groups may be the same or different, and at least one hydrogen atom of a pyridine ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom).

[0026] A third example is (C) a molybdenum complex having, as a PPP ligand, bis(dialkylphosphinomethyl)arylphosphine (where two alkyl groups may be the same or different).

[0027] A fourth example is (D) a molybdenum complex expressed by trans-Mo(N 2 ) 2 (R1R2R3P) 4 (where R1, R2, R3 are arealkyl groups or aryl groups which may be the same or different, and two R3s may connect with each other to form an alkylene chain).

[0028] In the above molybdenum complexes, the alkyl group may be, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or the like, or may be a straight chain or branched alkyl group of a structural isomer of them, or a cyclic alkyl group such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, or a cyclohexyl group. The carbon number of the alkyl group is preferably 1 to 12, and more preferably 1 to 6. The alkoxy group may be, for example, a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group, a hexyloxy group, or the like, or may be a straight chain or branched alkoxy group of a structural isomer of them, or a cyclic alkoxy group such as a cyclopropoxy group, a cyclobutoxy group, a cyclopentoxy group, or a cyclohexyloxy group. The carbon number of the alkoxy group is preferably 1 to 12, and more preferably 1 to 6. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and so on.

[0029] An example of the (A) molybdenum complex is a molybdenum complex expressed by Formula (A1) below.

[0030] In the formula, R1 and R2 may be the same or different alkyl groups, X is an iodine atom, a bromine atom, or a chlorine atom, and at least one hydrogen atom on the benzene ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom.

[0031] Examples of the alkyl group, alkoxy group, and halogen atom include the same as those already exemplified. R1 and R2 are preferably bulky alkyl groups (for example, tert-butyl groups or isopropyl groups). It is preferable that the hydrogen atom on the benzene ring is not substituted or that hydrogen atoms at position 5 and position 6 are substituted with chain, cyclic, or branched alkyl groups with 1 to 12 carbons.

[0032] An example of the (B) molybdenum complex is a molybdenum complex expressed by Formula (B1), Formula (B2), or Formula (B3) below.

[0033] In the formula, R1 and R2 may be the same or different alkyl groups, X is an iodine atom, a bromine atom, or a chlorine atom, and at least one hydrogen atom on the pyridine ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom.

[0034] Examples of the alkyl group, alkoxy group, and halogen atom include the same as those already exemplified. R1 and R2 are preferably bulky alkyl groups (for example, tert-butyl groups or isopropyl groups). It is preferable that the hydrogen atom on the pyridine ring is not substituted or that a hydrogen atom at position 4 is substituted with a chain, cyclic, or branched alkyl group with 1 to 12 carbons.

[0035] An example of the (C) molybdenum complex is a molybdenum complex expressed by Formula (C1) below.

[0036] In the formula, R1 and R2 may be the same or different alkyl groups, R3 is an aryl group, and X is an iodine atom, a bromine atom, or a chlorine atom.

[0037] Examples of the alkyl group include the same as those already exemplified. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, the one in which at least one of cyclic hydrogen atoms of them is substituted with an alkyl group or a halogen atom, and so on. Examples of the alkyl group and halogen atom include the same as those already exemplified. R1 and R2 are preferably bulky alkyl groups (for example, tert-butyl groups or isopropyl groups). R3 is preferably, for example, a phenyl group.

[0038] An example of the (D) molybdenum complex is a molybdenum complex expressed by Formula (D1) or Formula (D2) below.

[0039] In the formula, R1, R2, and R3 may be the same or different alkyl groups or aryl groups, and n is 2 or 3.

[0040] Examples of the alkyl group and the aryl group include the same as those already exemplified. In Formula (D1), it is preferable that R1 and R2 are aryl groups (for example, phenyl groups) and R3 is an alkyl group with 1 to 4 carbons (for example, a methyl group), or that R1 and R2 are alkyl groups with 1 to 4 carbons (for example, methyl groups) and R3 is an aryl group (for example, a phenyl group). In Formula (D2), it is preferable that R1 and R2 are aryl groups (for example, phenyl groups) and n is 2.

[0041] The ammonia production catalyst (reduction catalyst) which promotes the production of ammonia from nitrogen may be, for example, a metallocene complex expressed by Formula (E1) below.

[0042] In the formula, M is a tetravalent metal ion, and is one of titanium, zirconium, and hafnium. X1 and X2 are the same or different negative ions having a coordination property. The negative ion is preferably Cl -< , Br -< , I -< , CH 3 -< or OH -< , and more preferably Cl -< . Specifically, it is desirably a metallocene complex such as bis(cyclopentadienyl)titanium dichloride or bis(cyclopentadienyl)zirconium dichloride.

[0043] Further, as the ammonia production catalyst (reduction catalyst), a metal catalyst such as molybdenum, bismuth, iron, rhodium, ruthenium, titanium, or zirconium may be used. One of them may be used alone or two or more of them may be used in combination.

[0044] The material responsible for conductivity contained in the catalyst layer 142 is preferably a material which does not cause itself a reduction reaction as a catalyst. More specifically, a material with high overvoltage regarding the reduction reaction of proton, water, electrolyte, which is a side reaction is suitable, and a carbon material is mainly used. Examples of the carbon material (carbon particle) include channel black, furnace black, thermal black, acetylene black, activated carbon, natural graphite, artificial graphite, graphitized carbon, graphene, carbon nanotube (CNT), fullerene, ketjen black, glassy carbon, and so on.

[0045] The catalyst carrier can carry an ammonia production catalyst (reduction catalyst). The reduction catalyst is, for example, a metal complex. The catalyst carrier may be the carbon material or may be an organic-inorganic composite material. Examples of the inorganic material include magnesium oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, vanadium oxide, molybdenum oxide, tungsten oxide, tin oxide, zinc oxide, microporous three-dimensional aluminum silicate such as zeolite, layered silicate minerals such as montmorillonite, beidellite, saponite, steven site, and hectorite, and so on. Examples of the organic-inorganic composite material include metal organic frameworks (MOF), a material in which an organic molecule is inserted between sites or layers of an inorganic crystal structure, and so on. The use of these materials as the catalyst carrier makes it possible to fix the ammonia production catalyst with high density and efficiency. Accordingly, a three-phase interface controlled cathode 14 capable of direct reaction of nitrogen (N 2 ) can be realized. This can significantly increase the production efficiency of ammonia by a gas phase.

[0046] The ammonia production catalyst is adsorbed and held on the surface of the catalyst carrier and thereby can be used as the catalyst carrier for the reduction reaction of nitrogen. For example, when the ammonia production catalyst is a molybdenum complex, the molybdenum complex is dissolved in a solvent to prepare a catalyst solution and the catalyst solution is brought into contact with the catalyst carrier, thereby causing adsorption on the surface of the catalyst carrier. As the characteristic of the catalyst carrier capable of preferably holding the ammonia production catalyst, the specific surface area for increasing the reaction area is preferably 800 m 2< / g or more.

[0047] The characteristic of the catalyst carrier can be evaluated by a gas adsorption method by a specific surface area measurement device. For measuring the specific surface area, an inert gas (adsorbate) which performs reversible adsorption such as nitrogen, argon, or krypton is used. In a measurement operation, a sample is put into a sample tube with a known volume, an adherent of the sample is removed by heated vacuum drying, then a fixed amount of adsorbate is introduced into the sample tube, and the adsorbate is brought into contact with the sample surface. The adsorption amount increases with time, and the increase in adsorption amount stops in due time. The state at the time is called an adsorption equilibrium state, the adsorption amount is called an equilibrium adsorption amount, and the pressure is called an equilibrium pressure. The adsorption amount is determined by measuring a change in pressure until the adsorption equilibrium state is reached. For the specific surface area, an amount of an adsorption first layer is calculated from the amount of adsorbate adsorbed to the sample surface by the BET theory, and a specific surface area value is found using the area occupied by one molecule of the adsorbate.

[0048] Since the production amount of ammonia by a gas phase increases with a larger amount of the molybdenum production catalyst contained in the catalyst layer 142, the catalyst layer 142 is made thicker to increase the amount of the catalyst carrier, thereby making it possible to realize the cathode 14 which produces a larger amount of ammonia. On the other hand, if the catalyst layer 142 is thicker than necessary, gas of a reducible material supplied from the gas diffusion layer 141 is less likely to reach the surface side of the catalyst layer 142, causing hydrogen production by a side reaction to decrease the production efficiency of ammonia. Therefore, the thickness of the catalyst layer 142 is preferably 0.035 mm or more and 0.200 mm or less, and more preferably 0.050 mm or more and 0.150 mm or less. By adjusting the thickness of the catalyst layer 142 to 0.035 mm or more and 0.200 mm or less, the production efficiency of ammonia can be increased.

[0049] The reduction catalyst is preferably a chemical reactant of a metal complex which promotes the chemical reaction of reducing the reducible material to produce the reduction product and alcohol with C2 or less or an aprotic solvent. In the case where the ammonia production catalyst being the reduction catalyst is, for example, a molecular catalyst such as the molybdenum complex, the solubility of the molecular catalyst into the solvent and the affinity of the solvent and a catalyst carrier material influence the difficulty of adsorption. As the solvent for dissolving the molybdenum complex, methanol, ethanol, tetrahydrofuran, acetone, acetonitrile, chloroform, or the like is used. The molybdenum complex dissolves in methanol or ethanol, but does not dissolve in alcohol having a carbon number equal to or more than propanol. Further, the molybdenum complex is likely to dissolve in a polar solvent such as tetrahydrofuran, but does not dissolve in a nonpolar solvent such as hexane. Thus, the solvent is preferably alcohol with C2 or less or an aprotic solvent, and a relative dielectric constant ε of the aprotic solvent is preferably 3.0 or more and more preferably 20.0 or more, for example, at 20°C. The upper limit of the relative dielectric constant ε is not particularly limited, but is, for example, 50.0 or less.

[0050] On the other hand, when considering the interaction between the solvent and the molybdenum complex and between the molybdenum complex and the catalyst carrier material, a solvent lower in solubility with respect to the molybdenum complex is considered to be more likely to be adsorbed to the catalyst carrier. Besides, when a porous carbon material is the catalyst carrier, a solvent preferably has moderate hydrophilicity in order to prevent the solvent from being preferentially adsorbed to the carbon material. From the background, it is preferable to use methanol low in boiling point and having characteristics achieving both the moderate hydrophilicity and the solubility, as the solvent. For example, the temperature at which the molybdenum complex is adsorbed to the porous carbon material is preferably 0 to 90°C and more preferably 5 to 40°C, taking the decomposition temperature of the molybdenum complex and the boiling point of the solvent into consideration. If the time for adsorption of the molybdenum complex to the porous carbon material is short, adsorption may not be completed. On the other hand, if the adsorption time is too long, the ammonia production capacity by the reaction between the molybdenum complex and the solvent and workability will deteriorate. Therefore, the time for adsorption of the molybdenum complex to the porous carbon material is preferably in a range of 0.5 to 48 hours and more preferably 1 to 24 hours.

[0051] Next, a forming method of the cathode 14 in the method for manufacturing the electrolysis device will be explained. In the case where the ammonia production catalyst is a molecular catalyst such as the molybdenum complex, examples of a method of causing the catalyst carrier to adsorb the molecular catalyst include a drop casting method of preparing in advance a molecular catalyst solution in which a molecular catalyst is dissolved in a solvent and dropping the molecular catalyst solution to a catalyst carrier and evaporating the solvent to carry a molecular catalyst, and an immersion method of immersing a catalyst carrier into a molecular catalyst solution to carry a molecular catalyst. The immersion method is preferable for the purpose of uniformly carrying the molecular catalyst in the catalyst carrier, and can fabricate a cathode 14 large in catalyst carrying amount by holding the molecular catalyst solution in which the catalyst carrier is immersed under a reduced pressure or by holding it under an ultrasonic irradiation by an ultrasonic generator.

[0052] The inorganic material or the organic-inorganic composite material can be considered to function as an ion conductor in the catalyst layer 142 and undertake a role of supplying ions required for the reaction of the ammonia production catalyst. When the hydrogen ion concentration in the electrolytic solution is 7 or less (pH ≤ 7), hydrogen ions (H +< ) are supplied to the ammonia production catalyst, whereas when the hydrogen ion concentration in the electrolytic solution is greater than 7 (pH > 7), hydroxide ions (OH -< ) are supplied to the ammonia production catalyst. The catalyst layer 142 contains a material having ion conductivity and thereby can enhance the transmissibility and supplyability of the hydrogen ions (H +< ), hydroxide ions (OH -< ), and so on with respect to the reduction catalyst. Accordingly, the reduction efficiency of nitrogen (N) and the initial reduction efficiency of nitrogen can be increased, and therefore the production efficiency of ammonia (NH 3 ) can be improved.

[0053] The organic polymeric material which binds the material responsible for conductivity, the catalyst carrier carrying the reduction catalyst, and the gas diffusion layer 141 is preferably a water-insoluble polymeric material which can maintain the catalyst layer structure even in a wet environment. As the polymeric material, a fluorine-based resin such as perfluoroalkoxyalkane (PFA), perfluoroethylene propene copolymer (FEP), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), or ethylene-chlorotrifluoroethylene copolymer (ECTFE), polystyrene, polyvinyl butyral, poly(4-vinylpyridine), or the like is used. The polymeric material as the binder may have ion conductivity, and examples of the polymeric material having ion conductivity include Nafion (registered trademark) being a fluorocarbon resin made by sulfonating and polymerizing tetrafluoroethylene of DuPont Inc., Sustainion (registered trademark) of Dioxide Materials Inc., PiperION (registered trademark) of Versogen Inc., and so on.

[0054] The mass ratio of the polymeric material in the catalyst layer 142 is preferably in a range of 0.1 or more and 0.5 or less to the total mass of the material constituting the catalyst layer 142. Further, the ratio of the mass of the material having conductivity is preferably in a range of 0.3 or more and 0.9 or less to the total mass of the material constituting the catalyst layer 142. In these ranges, the production of ammonia can be promoted without causing a decrease in binding property and conductivity of the catalyst layer 142.

[0055] In the case where the polymeric material in the catalyst layer 142 is a material increasing the water repellency such as polytetrafluoroethylene, it is possible to realize a catalyst layer lower in hydrophilicity by increasing the percentage of the polymeric material in the catalyst layer 142. On the other hand, in order to increase the catalyst carrying amount, it is necessary to increase the percentage of the catalyst carrier in the catalyst layer 142. For example, the mass ratio between the catalyst carrier and the water repellent polymeric material is preferably in a range of 8:2 to 4:6 and more preferably in a range of 7:3 to 5:5. By adjusting the ratio between the catalyst carrier and the water repellent polymeric material to the above range, the production efficiency of ammonia by a gas phase can be improved.

[0056] The catalyst layer 142 may contain an ionic liquid. By arranging the ionic liquid on the surface of the catalyst carrier to suppress adhesion of excessive moisture, an effect of decreasing the hydrogen production by reduction of water and promoting the ammonia production reaction can be obtained. For the ionic liquid contained in the reduction catalyst, the same material as the one used in the above electrolytic solution can be used.

[0057] For the diaphragm 4 provided between the cathode space and the anode space of the electrochemical reaction unit 5, a membrane which can selectively pass anions or cations is used. The membrane constituting the diaphragm 4 is preferably a membrane-like polymeric material having ion conductivity. As the polymeric material having ion conductivity, an ion exchange membrane such as NEOSEPTA (registered trademark) of ASTOM Corporation, Selemion (registered trademark) of Asahi Glass Co., Ltd., Aciplex (registered trademark) of Asahi Kasei Corp., Fumasep (registered trademark) and fumapem (registered trademark) of Fumatech GmbH., Nafion (registered trademark) being a fluorocarbon resin made by sulfonating and polymerizing tetrafluoroethylene of DuPont Inc., lewabrane (registered trademark) of LANXESS Co. Ltd., IONSEP (registered trademark) of IONTECH Inc., Mustang (registered trademark) of PALL Corp., ralex (registered trademark) of mega Corp., Gore-Tex (registered trademark) of Gore-Tex Inc., Sustainion (registered trademark) of Dioxide Materials Inc., PiperION (registered trademark) of Versogen Inc., or the like can be used. The diaphragm 4 may be a composite film composed of a composite containing an organic-inorganic composite material having ion conductivity and a polymeric material for binding the organic-inorganic composite material.

[0058] In the case where the polymeric material in the catalyst layer 142 and the material in the diaphragm 4 are ion exchange membranes, the cathode 14 and the diaphragm 4 may be used while being immersed in an electrolyte solution in order to change counter cations and counter anions contained in the ion exchange membrane. Examples of the electrolyte solution for exchanging the counter cations include solutions containing ions such as lithium ion, sodium ion, potassium ion, cesium ion, ammonium ion, and so on, and examples of the electrolyte solution for exchanging the counter anions include solutions containing ions such as containing fluorine ion, chlorine ion, bromide ion, iodine ion, and so on. Note that the ion contained in the electrolyte solution is not limited to the above ions. By exchanging the counter ions of the ion exchange membrane, it is possible to control the water permeability of the ion exchange membrane to promote the production of ammonia.

[0059] The nitrogen supply unit 7 is a unit which supplies gaseous nitrogen to the first reaction space (reduction reaction electrolytic bath) 2, and includes a nitrogen supply device 6. As the nitrogen to be supplied from the nitrogen supply device 6, for example, but is not limited to, nitrogen in the air is used. Since air contains about 21% of oxygen, it is preferable to separate oxygen in advance from the air to be used and then take out nitrogen. In the case of using nitrogen in the air, an oxygen separation device which separates oxygen in the air and takes out nitrogen is used for the nitrogen supply device 6. As a separation method of oxygen in the air in the oxygen separation device 6, for example, the cryogenic separation method of separating oxygen by utilizing a difference in boiling point, the adsorption separation method utilizing a difference in adsorbing characteristics with respect to gas molecules of a zeolite-based adsorbent, the membrane separation method of separating oxygen by utilizing the fact that the speeds of permeating a membrane differ depending on gas molecules, or the like is used and can be appropriately selected according to the cost and device scale, and the separation method is not particularly limited. The nitrogen supply unit 7 may further include a humidifying device that humidifies nitrogen taken out of the air. It is preferable to supply the humidified nitrogen to the cathode space.

[0060] A nitrogen gas containing ammonia and a hydrogen gas produced by a side reaction are discharged from the cathode space, and part of the electrolytic solution passing through the diaphragm (electrolyte membrane) 4 is discharged from the anode 15. A discharge pipe of the cathode space is connected to the ammonia collection unit 9. The ammonia collection unit 9 is a unit that collects ammonia contained in the substance to be discharged from the cathode space, and includes an ammonia collection device 8. The ammonia collection device 8 is not particularly limited and, for example, a device which selectively collects ammonia by bringing the exhaust gas into contact with an aqueous solution (collection solution) with a pH of 0 to 7 for absorbing ammonia is used. The ammonia collection device 8 can simultaneously separate by-product hydrogen and unreacted nitrogen contained in the exhaust gas.

[0061] The ammonia collected by the ammonia collection device 8 and the part of the electrolytic solution passing through the diaphragm (electrolyte membrane) 4 from the anode 15 are contained in the collection solution and thus sent to an ammonia separation device 19 which separates ammonia from the collection solution. For the ammonia separation device 19, for example, the distillation method or the cryogenic separation method of separating ammonia by utilizing the difference in boiling point, the adsorption separation method utilizing the difference in adsorbing characteristics with respect to gas molecules of the zeolite-based adsorbent, the membrane separation method of separating ammonia by utilizing the fact that the speeds of permeating the membrane differ depending on the gas molecules, or the like is applied. The ammonia separation device 19 can be appropriately selected according to the cost and device scale and is not particularly limited. The ammonia separation device 19 is provided with a pipe for recovering the ammonia separated from the collection solution.

[0062] In the case of separating ammonia from the collection solution by distillation, a distillation column is used as the ammonia separation device 19. The distillation column is configured to separate ammonia having a boiling point lower than water used as at least part of the collection solution. In the distillation column, ammonia is separated by distillation by the conventional method from the supplied collection solution. Concretely, ammonia is discharged from a pipe at a column top part of the distillation column by subjecting the collection solution to reduced-pressure distillation under a reduced pressure of 10 to 120 Torr (1333 to 15999 Pa). The ammonia discharged from the pipe is recovered into a not-illustrated tank or the like.

[0063] For the separation of ammonia, the stripping method of bringing the collection solution into contact with vapor and moving the ammonia in the collection solution to the vapor to recover the ammonia may be used. In this case, the ammonia separation device 19 includes a stripping column whose inside is partitioned by a porous plate and is configured to make the supplied collection solution flow from an upper tier to a lower tier of the stripping column. The vapor flows from the lower tier to the upper tier and rises in the solution dammed by the porous plate. By the contact of the collection solution with the vapor, the ammonia in the collection solution vaporizes and moves into the vapor and is thereby discharged from the pipe at the column top part. Besides, in the case of using a carbonate aqueous solution as the collection solution, the ammonia in the collection solution can be converted to ammonium hydrogen carbonate, which can be thermally decomposed by a thermal decomposition device to separate and recover ammonia and carbon dioxide. The moisture separated in the ammonia separation device 19 and a part of the electrolytic solution passing through the diaphragm (electrolyte membrane) 4 from the anode 15 are sent again to the electrolytic solution storage 10 and utilized again as the electrolytic solution (anode electrolytic solution) to be supplied to the anode space.

[0064] Next, an additional configuration example, modification example, and so on of the nitrogen electrolysis device 1 in the arrangement will be explained. In the anode space, a circulation mechanism such as a pump may be provided. The circulation mechanism can promote the circulation of the electrolytic solution to improve the circulation of ions (H +< and OH -< ) between the anode space and the cathode space for oxidation reaction. Further, the first and second reaction spaces 2 and 3 may be provided with a flow path and may be provided with a plurality of circulation mechanisms. Further, a plurality of (three or more) reaction space flow paths may be provided in order to decrease the diffusion of ions and more efficiently circulate ions. By forming a flow of liquid by the circulation mechanism, it is possible to prevent generated air bubbles from staying on the electrode surfaces or the surfaces of the reaction spaces to thereby promote the reaction.

[0065] The second reaction space 3 is connected to the electrolytic solution circulation unit. The electrolytic solution circulation unit may include at least the electrolytic solution storage 10, the liquid feed pump 20, and a circulation pipe 24. The electrolytic solution circulation unit is a unit that circulates the electrolytic solution inside the circulation pipe 24 so as to take the electrolytic solution containing the produced ammonia out of the second reaction space 3 to the outside and supply the electrolytic solution again to the second reaction space 3. The circulation pipe 24 is provided with a liquid feed pump 20 for circulating the electrolytic solution, and an electrolytic solution storage 10 for storing the electrolytic solution and regulating the electrolyte concentration, pH, and so on. The electrolytic solution circulation unit is configured to circulate the electrolytic solution between the second reaction space 3 and the electrolytic solution storage 10 by the liquid feed pump 20.

[0066] Though the liquid feed pump 20 is provided in the circulation pipe 24 which sends the electrolytic solution from the second reaction space 3 to the electrolytic solution storage 10 in FIG. 1, the liquid feed pump 20 may be provided in the circulation pipe 24 which sends the electrolytic solution from the electrolytic solution storage 10 to the second reaction space 3. The electrolytic solution circulation unit preferably includes an exhaust unit which exhausts excessive nitrogen that has not dissolved in the electrolytic solution and gas that has been produced by the oxidation reaction. As the exhaust unit, for example, a pipe equipped with a valve is used and is provided, for example, in the electrolytic solution storage 10. The electrolytic solution storage 10 functions as a gas-liquid separation space, in which oxygen (O 2 ) produced by the oxidation reaction is separated from the electrolytic solution.

[0067] The ammonia separation unit 13 is a unit which recovers ammonia (NH 3 ) that is a reduced substance of nitrogen, from the electrolytic solution. The ammonia separation unit 13 may include an ammonia separation device 12 which separates ammonia from the electrolytic solution, a three-way valve 22 which takes out at least part of the electrolytic solution circulating inside the circulation pipe 24, a pipe 23 which sends the electrolytic solution taken out of the three-way valve 22 to the ammonia separation device 12, and the circulation pipe 24 which sends the electrolytic solution from which ammonia has been separated in the ammonia separation device 12 to the electrolytic solution storage 10. The three-way valve 22 is provided in the circulation pipe 24, and the ammonia separation unit 13 is connected to the electrolytic solution circulation unit via the three-way valve 22. The taking-out of the electrolytic solution circulating inside the circulation pipe 24 may be implemented not only by using the three-way valve 22 provided in the circulation pipe 24 but also by connecting a pipe having a valve to the electrolytic solution storage 10, and its configuration is not particularly limited. The ammonia separation device 12 uses a similar separation method to that of the ammonia separation device 19, and has a similar configuration.

[0068] Next, an ammonia manufacturing process using the above nitrogen electrolysis device (ammonia manufacturing device) will be explained. First, as an initial stage, a humidified nitrogen gas is supplied to the cathode space. The electrolytic solution is supplied into the anode space. In this state, electric power is supplied from the external electrode to the cathode 14 and the anode 15.

[0069] The anode 15 and the cathode 14 may be connected to an external power supply 17 via external electrodes. The external power supply 17 may be an ordinary commercial power supply, a battery, or the like, or a power supply that converts renewable energy to electric energy and supplies it. Examples of the power supply include a power supply that converts kinetic energy or potential energy such as wind power, water power, geothermal power, or tidal power into electric energy, a power supply such as a solar cell having a photoelectric conversion element that converts light energy into electric energy, a power supply such as a fuel cell or a storage battery that converts chemical energy into electric energy, a device that converts vibrational energy such as sound into electric energy, and so on. The photoelectric conversion element has a function of performing charge separation by energy of radiated light such as sunlight. Examples of the photoelectric conversion element include a pin-junction solar cell, a pn-junction solar cell, an amorphous silicon solar cell, a multijunction solar cell, a single-crystal silicon solar cell, a polycrystalline silicon solar cell, a dye-sensitized solar cell, an organic thin-film solar cell, a perovskite solar cell, and so on.

[0070] By supplying electric power from the external electrodes to the cathode 14 and the anode 15, an oxidation reaction of water (H 2 O) or hydroxide ion (OH -< ) in the electrolytic solution electrochemically occurs at the anode 15. For example, when the hydrogen ion concentration in the electrolytic solution is 7 or less (pH ≤ 7), H 2 O is oxidized to produce O 2 and H +< based on Formula (1) below. When the hydrogen ion concentration in the electrolytic solution is greater than 7 (pH > 7), OH -< is oxidized to produce O 2 and H 2 O based on Formula (2) below.         3H 2 O → 3 / 2O 2 + 6H +< + 6e -< ...     (1)         6OH -< → 3 / 2O 2 + 3H 2 O + 6e -< ...     (2)

[0071] In the cathode space, nitrogen (N 2 ) is reduced by the ammonia production catalyst to produce ammonia (NH 3 ). The ammonia production catalyst is as explained above. N 2 is reduced by conducting ion species in the diaphragm 4 to produce ammonia (NH 3 ) based on Formula (3) or Formula (4) below.         N 2 + 6H 2 O + 6e -< → 2NH 3 + 6OH -< ...     (3)         N 2 + 6H +< + 6e -< → 2NH 3 ...     (4)

[0072] The gas containing NH 3 produced by the N 2 reduction explained above is sent to the ammonia collection device 8, in which the exhaust gas is brought into contact with the aqueous solution (collection solution) with a pH of 0 to 7 to selectively collect ammonia as explained above. At the same time, the byproduct hydrogen and unreacted nitrogen contained in the exhaust gas are separated. The collection solution containing ammonia is sent to the ammonia separation device 12, in which ammonia is separated from the collection solution.

[0073] Part of NH 3 produced by the N 2 reduction is sent via the diaphragm 4 to the anode space and dissolved in the electrolytic solution. The electrolytic solution containing NH 3 is sent via the circulation pipe to the electrolytic solution storage, in which oxygen (O 2 ) is separated, and then sent again to the anode space. By circulating the electrolytic solution inside the circulation pipe 24, an ammonia concentration in the electrolytic solution increases. By sending at least part of the electrolytic solution with increased ammonia concentration to the ammonia separation device 12 via the three-way valve 22, ammonia is separated from the electrolytic solution.

[0074] The supply of the electrolytic solution containing ammonia to the ammonia separation device 12 may be performed continuously from the start of operation of the device but is preferably intermittently performed at the point in time when the concentration of ammonia contained in the electrolytic solution becomes high enough. In other words, when the concentration of ammonia contained in the electrolytic solution is low, the energy to be input to recover ammonia from the electrolytic solution becomes larger than the energy amount stored in ammonia, resulting in an increase in manufacturing cost of ammonia. Regarding this point, the electrolytic solution is circulated by the circulation pipe 24 via the second reaction space 3 and the electrolytic solution storage 10, thereby making it possible to obtain the electrolytic solution containing ammonia at high concentration. It is preferable to send the electrolytic solution containing ammonia at high concentration to the ammonia separation device 12. This makes it possible to recover ammonia being a reduction product of N 2 with high efficiency. To improve the recovery efficiency of ammonia, it is preferable to send the electrolytic solution containing ammonia at a concentration of 0.01 to 50 mass% to the ammonia separation device 12.

[0075] The cathode space and the anode space may be provided with a temperature regulating mechanism which regulates the temperature of the electrolytic solution. By the temperature control using the temperature regulating mechanism, the catalytic performance can be controlled. For example, by making the temperature of the reaction system uniform, the performance of the catalyst can be stabilized. Further, a temperature rise can also be prevented for stabilization of the system. The reaction temperature in the electrochemical reaction unit 5 can be appropriately selected in a range of 5 to 95°C in consideration of the electrolytic solution being an aqueous solution, the reaction efficiency, and the economic efficiency. Preferably, the reaction temperature only needs to be about room temperature (10 to 60°C)

[0076] The electrochemical reaction unit 5 can increase the reaction area by making the electrode porous, to acquire more reaction current. The electrochemical reaction unit 5 may have an electrode structure in which the diaphragm 4 is sandwiched between a porous anode 15 and a porous cathode 14. More specifically, in the electrochemical reaction unit 5 illustrated in FIG. 2, the porous anode 15 and the porous cathode 14 are arranged in contact with both surfaces of the diaphragm 4, respectively. The electrolytic solution is supplied to a surface of the porous anode 15 that is opposite to a surface in contact with the diaphragm 4. The ammonia production catalyst is arranged at a surface of the porous cathode 14 in contact with the diaphragm 4. Nitrogen is supplied to a surface of the porous cathode 14 that is opposite to a surface in contact with the diaphragm 4. The electrochemical reaction unit 5 may have the porous cathode 14 and a nitrogen supply pipe which supplies nitrogen to the ammonia production catalyst via the porous anode 15. In a route through which nitrogen flows, a flow path may be provided. By providing a plurality of (three or more) gas flow paths, nitrogen can be uniformly distributed to the porous cathode 14.

[0077] The electrochemical reaction unit 5 may have an electrolytic solution between the porous cathode 14 and the diaphragm 4. More specifically, the electrochemical reaction unit 5 illustrated in FIG. 4 can supply nitrogen from a surface of the cathode 14 opposite to the ammonia production catalyst. As explained above, the structure of the electrochemical reaction unit 5 can be variously changed.EXAMPLES

[0078] Next, examples and their evaluation results will be explained.[Fabrication of the cathode]

[0079] The cathode was fabricated by spray coating of catalyst ink on carbon paper formed with a carbon particle layer (MPL layer). The catalyst ink used for the cathode was prepared using ketjen black (manufactured by LION SPECIALTY CHEMICALS CO., LTD., EC600JD, BET specific surface area: 1270 m 2< / g) 0.3 g and PTFE 0.2 g as a carrier for the molybdenum complex, and 2-propanol 35 mL and pure water 35 mL as a dispersion medium. The catalyst ink was prepared by mixing ketjen black, PTFE, 2-propanol, and pure water in a glass vial bottle and dispersing them for 20 minutes using an ultrasonic homogenizer. Next, a catalyst layer was formed by spray coating of the catalyst ink on carbon paper (manufactured by Avcarb Co., Ltd., MB-30 (product name)) which was fixed to a metal plate and heated to 90°C. The catalyst layer was coated on the MPL layer side. At this time, amounts of ketjen black and PTFE per 1 cm 2< of the coated surface were 2.2 mg and 1.5 mg, respectively. The electrode was baked at 380°C in an argon atmosphere for one hour and thereby bound, and then the electrode was cut into a square of 20 mm × 20 mm. The thickness of the catalyst layer was found by subtracting the previously measured thickness of the carbon paper from the thickness of the fabricated electrode. The thickness of the catalyst layer produced under these conditions was 0.047 mm. Next, four electrodes each formed with the catalyst layer were immersed in a sample bottle containing a catalyst solution in which a molybdenum triiodide complex (as ligand, 1,3-bis(ditertiarybutylphosphinomethylbenzoimidazole-2-ylidene) being a PCP ligand) was dissolved in methanol (a solution in which about 10 mg of molybdenum complex was dissolved in 10 mL of methanol), at room temperature and in a nitrogen atmosphere, and the sample bottle was irradiated with an ultrasonic wave for one hour. The electrodes were then air-dried under nitrogen flow to form into cathodes (20 mm × 20 mm squares). The amount of the carried molybdenum complex in the catalyst layer was quantified by the fluorescent X-ray analysis and the inductively coupled plasma emission spectroscopy. A mass ratio (KB:PTFE) between ketjen black (KB) and PTFE in the cathode was 5.9:4.1. KB:PTFE was calculated from the mass of KB and the mass of PTFE per 1 cm 2< of the coated surface.[Quantification of the molybdenum complex amount by the fluorescent X-ray analysis and the inductively coupled plasma emission spectroscopy]

[0080] A cathode for acquiring calibration curve data was prepared in advance, a fluorescent X-ray intensity corresponding to the molybdenum atoms contained in the cathode was measured, and the inductively coupled plasma emission spectroscopy was performed on the solution made by pressure acid decomposition of the sample to create the calibration curve of the weight of the molybdenum atoms corresponding to the fluorescent X-ray intensity. From the fluorescent X-ray intensity corresponding to the molybdenum atoms obtained by the fluorescent X-ray analysis of the measurement-target sample, the weight of the molybdenum atoms contained in the cathode was estimated using the calibration curve created in the above. The weight of the molybdenum atoms was divided by the molybdenum element content to calculate the number of molybdenum atoms contained in the cathode. Since one molybdenum atom is contained in one molecule of the molybdenum complex, the molybdenum complex amount was estimated using the number of molybdenum atoms as the number of molecules of the molybdenum complex. The molybdenum complex amount per cathode estimated as above was 2.26 µmol.[Fabrication of the anode]

[0081] The anode was fabricated by making Ti into a mesh structure by an etching method and forming iridium oxide as an oxidation catalyst on a wire mesh (20 mm × 20 mm square) with an increased surface area.[Fabrication of a membrane electrode assembly and a N 2 electrolysis cell]

[0082] An experiment was carried out with the configuration of the electrolysis cell illustrated in FIG. 3. A membrane electrode assembly (catalyst area of 400 mm 2< ) was prepared by sandwiching Nafion (registered trademark) 117 membrane (25 mm × 25 mm square) of Dupont Inc. as the diaphragm between the anode and the cathode to stack them. Nafion 117 membrane was pre-treated by boiling it in 3% hydrogen peroxide, 1 M sulfuric acid, and pure water for one hour each and then immersing it in 1 M KOH solution. Note that the cathode catalyst layer and the diaphragm were arranged in contact with each other. The membrane electrode assembly was sandwiched between titanium flow paths (serpentine, a land width of 0.4 mm, a flow path width of 1.5 mm, a flow path depth of 1 mm) via a Teflon gasket to assemble the N 2 electrolysis cell.[Constant potential electrolysis measurement (ammonia production experiment)]

[0083] A 0.1 M tripotassium phosphate solution was supplied as the electrolytic solution to the anode flow path of the N 2 electrolysis cell at 10 mL / min. The pH of the electrolytic solution was 11. On the other hand, dry N 2 gas (> 99.99%) was supplied to the cathode flow path at a flow rate of 80 mL / min. A power supply device (Biologic VMP-300) was electrically connected to the cathode and the anode from outside the cathode flow path plate and the anode flow path plate, and a constant current of 1.6 A (current density of 400 mA / cm 2< ) was applied for 15 min. A 0.1 M sulfuric acid was connected as trap liquid to the cathode flow path outlet of the N 2 electrolysis cell, and the reduction product produced from the cathode was recovered and analyzed every five minutes.[Ammonia quantification method]

[0084] The quantification of ammonia was performed by an ion chromatography. The liquid containing ammonia gas and ammonia discharged from the cathode flow path outlet is all converted into ammonium ions by the sulfuric acid trap liquid. The ammonium ions in the sulfuric acid trap liquid were quantified using ion chromatography by which the calibration curve was created in advance using a prescribed amount of ammonium ion solution.

[0085] Ammonia production partial current density and Faraday efficiency were calculated based on the current consumed for the cathode reduction reaction and quantitative analysis of reduction products. The partial current density corresponds to the ammonia production speed of the electrolysis cell, and the Faraday efficiency is expressed by a percentage of the quantity of electricity required to produce the reduction products relative to the quantity of electricity input. The Faraday efficiency of each reduction product analyzed was used as selectivity (%) of the product. In the N 2 electrolysis cell prepared by the above method, the partial current density was 13.3 mA / cm 2< and the Faraday efficiency was 3.33%.

[0086] The ammonia production amount was estimated from the ammonia production partial current density, and divided by the amount of the molybdenum complex contained in the cathode to estimate the turn over frequency (TOF) per hour. In the N 2 electrolysis cell created by the above method, the TOF was 294 h -1< . These results are listed in Table 1.(Example 2)

[0087] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of ethanol. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 1.20 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 8.54 mA / cm 2< , the Faraday efficiency was 2.14%, and the TOF was 355 h -1< . These results are listed in Table 1.(Example 3)

[0088] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of tetrahydrofuran. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 2.38 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 13.1 mA / cm 2< , the Faraday efficiency was 3.28%, and the TOF was 274 h -1< . These results are listed in Table 1.(Example 4)

[0089] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of chloroform. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 1.44 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 8.97 mA / cm 2< , the Faraday efficiency was 2.24%, and the TOF was 309 h -1< . These results are listed in Table 1.(Example 5)

[0090] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of acetone. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 1.21 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 10.4 mA / cm 2< , the Faraday efficiency was 2.61%, and the TOF was 428 h -1< . These results are listed in Table 1.(Example 6)

[0091] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of acetonitrile. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 0.59 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 3.65 mA / cm 2< , the Faraday efficiency was 0.91%, and the TOF was 309 h -1< . These results are listed in Table 1.(Comparative example 1)

[0092] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of 2-propanol. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 0.36 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 0.11 mA / cm 2< , the Faraday efficiency was 0.03%, and the TOF was 16 h -1< . These results are listed in Table 1.(Comparative example 2)

[0093] The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of hexane. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 0.19 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, no ammonia was detected. These results are listed in Table 1.

[0094] According to Examples 1 to 6 and Comparative examples 1 and 2, the molybdenum complex is likely to dissolve in alcohol with C2 or less such as methanol and ethanol or a polar solvent such as tetrahydrofuran, so that the carrying amount of the cathode catalyst increases and the ammonia production amount also increases. On the other hand, the molybdenum complex does not dissolve in alcohol with C3 or more such as 2-propanol or a nonpolar solvent such as hexane, so that the carrying amount of the cathode catalyst decreases and the ammonia production amount also decreases. Based on the above, a relative dielectric constant ε of the aprotic solvent to be used for the solvent of the catalyst solution is preferably 3.0 or more and more preferably 20.0 or more.(Example 7)

[0095] The cathode catalyst layer ink composition was changed and a cathode containing 3.3 mg of ketjen black and 2.2 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.10 mm. KB:PTFE was 6.0:4.0. The molybdenum complex amount per cathode was 2.61 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 15.7 mA / cm 2< , the Faraday efficiency was 3.94%, and the TOF was 301 h -1< . These results are listed in Table 1.(Example 8)

[0096] The cathode catalyst layer ink composition was changed and a cathode containing 4.4 mg of ketjen black and 3.0 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.149 mm. KB:PTFE was 5.9:4.1. The molybdenum complex amount per cathode was 4.02 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 13.4 mA / cm 2< , the Faraday efficiency was 3.35%, and the TOF was 166 h -1< . These results are listed in Table 1.(Example 9)

[0097] The cathode catalyst layer ink composition was changed and a cathode containing 1.1 mg of ketjen black and 0.7 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.032 mm. KB:PTFE was 6.1:3.9. The molybdenum complex amount per cathode was 1.20 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 9.91 mA / cm 2< , the Faraday efficiency was 2.48%, and the TOF was 410 h -1< . These results are listed in Table 1.(Example 10)

[0098] The cathode catalyst layer ink composition was changed and a cathode containing 6.6 mg of ketjen black and 4.5 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.210 mm. KB:PTFE was 5.9:4.1. The molybdenum complex amount per cathode was 2.24 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 10.4 mA / cm 2< , the Faraday efficiency was 2.60%, and the TOF was 232 h -1< . These results are listed in Table 1.

[0099] According to Examples 1, 7, 8, 9, and 10, a larger thickness of the cathode catalyst layer can carry a larger amount of molybdenum complex, but the carrying amount decreases when the thickness is a certain thickness or more. On the other hand, when the catalyst layer is thicker more than necessary, gas to be reduced supplied from the gas diffusion layer is less likely to reach the surface side of the catalyst layer, causing hydrogen production by a side reaction to decrease the production efficiency of ammonia. Accordingly, the thickness of the catalyst layer is more preferably 0.035 to 0.200 mm.(Example 11)

[0100] The cathode catalyst layer ink composition was changed and a cathode containing 1.5 mg of ketjen black and 2.2 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.046 mm. KB:PTFE was 4.0:6.0. The molybdenum complex amount per cathode was 0.95 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 8.35 mA / cm 2< , the Faraday efficiency was 2.09%, and the TOF was 438 h -1< . These results are listed in Table 1.(Example 12)

[0101] The cathode catalyst layer ink composition was changed and a cathode containing 2.9 mg of ketjen black and 0.8 mg of PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. The thickness of the catalyst layer of the cathode was 0.078 mm. KB:PTFE was 7.8:2.2. The molybdenum complex amount per cathode was 1.78 µmol. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 6.49 mA / cm 2< , the Faraday efficiency was 1.62%, and the TOF was 182 h -1< . These results are listed in Table 1.(Comparative example 3)

[0102] The cathode catalyst layer ink composition was changed and a cathode containing 3.7 mg of ketjen black and no PTFE per 1 cm 2< of the coated surface was fabricated. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the cathode was changed. KB:PTFE was 10:0. Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the catalyst layer peeled off the carbon paper in a molybdenum complex immersion process, failing to manufacture ammonia. These results are listed in Table 1.

[0103] According to Examples 1, 11, and 12 and Comparative example 3, in the case where the polymeric material in the catalyst layer is a material increasing the water repellency such as polytetrafluoroethylene, it is possible to realize a catalyst layer lower in hydrophilicity by increasing the percentage of the polymeric material in the catalyst layer. On the other hand, in order to increase the catalyst carrying amount, it is necessary to increase the percentage of the catalyst carrier in the catalyst layer, and the ratio between the catalyst carrier and the water repellent polymeric material is preferably in a range of 7.5:2.5 to 4:6 and more preferably in a range of 7:3 to 5:5 in order to improve the production efficiency of ammonia by a gas phase.

[0104] The TOF indicates the magnitude of the ammonia amount produced by one catalyst, and a larger TOF indicates that the catalyst more efficiently works. Also in the TOF, the same interpretation as in the above paragraph can be made. More specifically, it is possible to increase the TOF by bringing at least one of the type of the catalyst solvent, the thickness of the catalyst layer, and the ratio between the catalyst carrier and the water repellent polymeric material to a preferable material or numerical range. [Table 1]Catalyst solventCatalyst thickness (mm)KB : PTFEMolybdenum complex amount (µmol)Partial current density (mA / cm 2< )Faraday efficiency (%)TOF (h -1< )Example 1Methanol0.0475.9 : 4.12.2613.33.33294Example 2Ethanol0.0475.9 : 4.11.208.542.14355Example 3Tetrahydrofuran0.0475.9 : 4.12.3813.13.28274Example 4Chloroform0.0475.9 : 4.11.448.972.24309Example 5Acetone0.0475.9 : 4.11.2110.42.61428Example 6Acetonitrile0.0475.9 : 4.10.593.650.91309Example 7Methanol0.1006.0 : 4.02.6015.73.94301Example 8Methanol0.1495.9 : 4.14.0213.43.35166Example 9Methanol0.0326.1 : 3.91.209.912.48410Example 10Methanol0.2105.9 : 4.12.2410.42.60232Example 11Methanol0.0464.0 : 6.00.958.352.09438Example 12Methanol0.0787.8 : 2.21.786.491.62182Comparative example 12-propanol0.0475.9 : 4.10.360.110.0316Comparative example 2Hexane0.0475.9 : 4.10.19---Comparative example 3Methanol0.04710 : 0----

[0105] Note that the configurations of the above-described arrangements can be employed in combination or can be partly replaced. While certain arrangements of the present invention have been described herein, these arrangements have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel arrangements described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the arrangements described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

[0106] Clauses of the above arrangements are attached below.(Clause 1)

[0107] An electrolysis device including: a cathode; an anode; a cathode space on the cathode and through which a gaseous reducible material is supplied; an anode space on the anode and through which a liquid or gaseous oxidizable material is supplied; and a diaphragm between the cathode and the anode, wherein the cathode includes a substrate, and a catalyst layer, the catalyst layer having: a metal complex for promoting a chemical reaction of reducing the reducible material to produce a reduction product; alcohol with C2 or less, or an aprotic solvent having a relative dielectric constant of 3.0 or more; a catalyst carrier carrying the metal complex and having conductivity; and a binder binding the substrate and the catalyst carrier. (Clause 2)

[0108] The electrolysis device according to Clause 1, wherein: a thickness of the catalyst layer is 0.035 mm or more and 0.200 mm or less.(Clause 3)

[0109] The electrolysis device according to Clause 1 or Clause 2, wherein a mass ratio (catalyst carrier:binder) between the catalyst carrier and the binder in the catalyst layer is in a range of 4:6 to 7.5:2.5.(Clause 4)

[0110] The electrolysis device according to any one of Clause 1 to Clause 3, wherein the catalyst carrier is a porous carbon material.(Clause 5)

[0111] The electrolysis device according to any one of Clause 1 to Clause 4, wherein the binder is an organic polymeric material.(Clause 6)

[0112] The electrolysis device according to any one of Clause 1 to Clause 5, wherein the catalyst layer contains methanol.(Clause 7)

[0113] The electrolysis device according to any one of Clause 1 to Clause 6, wherein the metal complex is a molybdenum complex which promotes a chemical reaction of reducing nitrogen to produce ammonia.(Clause 8)

[0114] The electrolysis device according to Clause 7, further including: a nitrogen supply unit including a nitrogen supply part configured to introduce gaseous nitrogen into the cathode space; an ammonia collection unit including an ammonia collection part configured to collect ammonia in a substance to be discharged from the cathode space; and an ammonia separation unit including an ammonia separation part configured to separate ammonia from an electrolytic solution to be discharged from the anode space. (Clause 9)

[0115] The electrolysis device according to Clause 8, further including: a circulation pipe through which an electrolytic solution circulates outside the anode space and is supplied to the anode space; and an electrolytic solution circulation unit arranged in the middle of the circulation pipe and including an electrolytic solution storage for storing the electrolytic solution. (Clause 10)

[0116] 10. A method for manufacturing an electrolysis device, the electrolysis device including: a cathode; an anode; a cathode space on the cathode and though which a gaseous reducible material is supplied; an anode space on the anode and through which a liquid or gaseous oxidizable material is supplied; and a diaphragm between the cathode and the anode, and the method comprising forming the cathode by a process including: mixing a metal complex, alcohol with C2 or less or an aprotic solvent having a relative dielectric constant of 3.0 or more, a catalyst carrier, and a binder, to prepare a solution; and forming a catalyst layer on a substrate using the solution.

Examples

examples

[0078]Next, examples and their evaluation results will be explained.

[Fabrication of the cathode]

[0079]The cathode was fabricated by spray coating of catalyst ink on carbon paper formed with a carbon particle layer (MPL layer). The catalyst ink used for the cathode was prepared using ketjen black (manufactured by LION SPECIALTY CHEMICALS CO., LTD., EC600JD, BET specific surface area: 1270 m 2< / g) 0.3 g and PTFE 0.2 g as a carrier for the molybdenum complex, and 2-propanol 35 mL and pure water 35 mL as a dispersion medium. The catalyst ink was prepared by mixing ketjen black, PTFE, 2-propanol, and pure water in a glass vial bottle and dispersing them for 20 minutes using an ultrasonic homogenizer. Next, a catalyst layer was formed by spray coating of the catalyst ink on carbon paper (manufactured by Avcarb Co., Ltd., MB-30 (product name)) which was fixed to a metal plate and heated to 90°C. The catalyst layer was coated on the MPL layer side. At this time, amounts of ketjen black and...

example 2

(Example 2)

[0087]The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of ethanol. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 1.20 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 8.54 mA / cm 2< , the Faraday efficiency was 2.14%, and the TOF was 355 h -1< . These results are listed in Table 1.

example 3

(Example 3)

[0088]The solvent in the catalyst solution was changed from 10 mL of methanol to the same amount of tetrahydrofuran. An N 2 electrolysis cell was fabricated in the same manner as in Example 1 except that the solvent in the catalyst solution was changed. The molybdenum complex amount per cathode was 2.38 µmol.Manufacture of ammonia was tried in the same manner as in Example 1 using the N 2 electrolysis cell. As a result, the partial current density was 13.1 mA / cm 2< , the Faraday efficiency was 3.28%, and the TOF was 274 h -1< . These results are listed in Table 1.

Claims

1. An electrolysis device comprising: a cathode; an anode; a cathode space on the cathode and through which a gaseous reducible material is supplied; an anode space on the anode and through which a liquid or gaseous oxidizable material is supplied; and a diaphragm between the cathode and the anode, wherein the cathode comprises a substrate, and a catalyst layer, the catalyst layer having: a metal complex for promoting a chemical reaction of reducing the reducible material to produce a reduction product; alcohol with C2 or less, or an aprotic solvent having a relative dielectric constant of 3.0 or more; a catalyst carrier carrying the metal complex and having conductivity; and a binder binding the substrate and the catalyst carrier.

2. The electrolysis device according to claim 1, wherein a thickness of the catalyst layer is 0.035 mm or more and 0.200 mm or less.

3. The electrolysis device according to claim 1 or claim 2, wherein a mass ratio (catalyst carrier:binder) between the catalyst carrier and the binder in the catalyst layer is in a range of 4:6 to 7.5:2.5.

4. The electrolysis device according to any one of claim 1 to claim 3, wherein the catalyst carrier is a porous carbon material.

5. The electrolysis device according to any one of claim 1 to claim 4, wherein the binder is an organic polymeric material.

6. The electrolysis device according to any one of claim 1 to claim 5, wherein the catalyst layer contains methanol.

7. The electrolysis device according to any one of claim 1 to claim 6, wherein the metal complex is a molybdenum complex which promotes a chemical reaction of reducing nitrogen to produce ammonia.

8. The electrolysis device according to claim 7, further comprising: a nitrogen supply unit including a nitrogen supply part configured to introduce gaseous nitrogen to the cathode space; an ammonia collection unit including an ammonia collection part configured to collect ammonia in a substance to be discharged from the cathode space; and an ammonia separation unit including an ammonia separation part configured to separate ammonia from an electrolytic solution to be discharged from the anode space.

9. The electrolysis device according to claim 8, further comprising: a circulation pipe through which an electrolytic solution circulates outside the anode space and is supplied to the anode space; and an electrolytic solution circulation unit arranged in the middle of the circulation pipe and including an electrolytic solution storage for storing the electrolytic solution.

10. A method for manufacturing an electrolysis device, the electrolysis device comprising: a cathode; an anode; a cathode space on the cathode and through which a gaseous reducible material is supplied; an anode space on the anode and through which a liquid or gaseous oxidizable material is supplied; and a diaphragm between the cathode and the anode, and the method comprising forming the cathode by a process including: mixing a metal complex, alcohol with C2 or less or an aprotic solvent having a relative dielectric constant of 3.0 or more, a catalyst carrier, and a binder, to prepare a solution; and forming a catalyst layer on a substrate using the solution.

11. The method according to claim 10, wherein a thickness of the catalyst layer is 0.035 mm or more and 0.200 mm or less.

12. The method according to claim 10 or claim 11, wherein a mass ratio (catalyst carrier:binder) between the catalyst carrier and the binder in the catalyst layer is in a range of 4:6 to 7.5:2.5.

13. The method according to any one of claim 10 to claim 12, wherein the catalyst carrier is a porous carbon material.

14. The method e according to any one of claim 10 to claim 13, wherein the binder is an organic polymeric material.

15. The method according to any one of claim 10 to claim 14, wherein the catalyst layer contains methanol.

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