Electrolysis cell

Abstract

An object of the present disclosure is to provide a novel direct air electrolysis method, and preferably a direct air electrolysis method that does not require the use of a strongly basic or strongly acidic solution and a noble metal electrode catalyst.SOLUTION: An electrolytic cell comprising: an anode; a cathode facing the anode; a substrate having pores; and a water-absorbing compound, wherein the substrate is disposed between the anode and the cathode, and the water-absorbing compound is present in the pores of the substrate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to electrolysis cells. [Background technology]

[0002] Water electrolysis is a method of electrolyzing water to generate oxygen at the anode and hydrogen at the cathode, and has attracted attention as a technology that can produce hydrogen without emitting carbon dioxide by using electricity derived from renewable energy. Known water electrolysis methods include alkaline and anion exchange membrane types that use strongly basic solutions, and proton exchange types that use strongly acidic solutions.

[0003] In recent years, direct air electrolysis (DAE), which directly electrolyzes moisture in the air, has been proposed. Non-Patent Document 1 describes a method of performing DAE using a cell with a structure in which a water-storing part such as a melamine sponge or sintered glass foam is sandwiched between electrodes, and using sulfuric acid, which is a water-absorbent and strongly acidic material, potassium acetate, which is a weak base, or potassium hydroxide, which is a strong base, as the electrolyte, and further using a noble metal electrode catalyst such as IrO2 or Pt. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Jining Guo et al., "Hydrogen Production from the Air" Nature Communications 2022, 13, 5046. Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure aims to provide a new direct air electrolysis method, preferably a direct air electrolysis method that does not require the use of a strongly basic or strongly acidic solution or a noble metal electrocatalyst. [Means for solving the problem]

[0006] The present disclosure includes the following aspects. [1] an anode, a cathode facing the anode, a porous substrate, and a water-absorbing compound; the substrate is disposed between the anode and the cathode; the water-absorbing compound is present in the pores of the substrate; The water-absorbing compound comprises an anion and a cation. [2] The electrolytic cell according to [1], wherein the anions include one or more anions selected from the group consisting of inorganic anions and organic anions. [3] The electrolytic cell according to [1] or [2], wherein the inorganic anions include one or more anions selected from the group consisting of nitrate anions, hydrogen sulfate anions, and phosphite anions. [4] The electrolytic cell according to any one of [1] to [3], wherein the organic anions include one or more selected from the group consisting of carboxylate anions, lactate anions, and organic phosphate anions. [5] The electrolytic cell according to any one of [1] to [4], wherein the cations include one or more selected from the group consisting of inorganic cations and organic cations. [6] The electrolytic cell according to any one of [1] to [5], wherein the inorganic cations include ammonium cations. [7] The electrolytic cell according to any one of [1] to [6], wherein the organic cation contains a monovalent or divalent or higher organic ammonium ion. [8] The electrolytic cell according to any one of [1] to [7], wherein the water-absorbing compound includes one or more selected from the group consisting of salts and deep eutectic solvents. [9] The electrolysis cell according to any one of [1] to [8], wherein the substrate contains a metal oxide and / or a zeolite.

[10] The electrolytic cell according to any one of [1] to [9], wherein the substrate contains metal oxide particles.

[11] The electrolytic cell according to [9] or

[10] , wherein the metal oxide comprises one or more selected from silica, titania, and alumina.

[12] The electrolysis cell according to any one of [1] to

[11] , wherein the substrate contains zeolite particles.

[13] The electrolytic cell according to any one of [1] to

[12] , wherein the pH of an aqueous solution of the water-absorbing compound with a concentration of 50 mass % is 3 or more and 10 or less.

[14] The electrolytic cell according to any one of [1] to

[13] , wherein the content of the water-absorbing compound is 30 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the total of the base materials.

[15] The electrolysis cell according to any one of [1] to

[14] , which is a direct air electrolysis cell.

[16] A direct air electrolysis method, comprising applying a voltage to the electrolytic cell according to any one of [1] to

[15] in air having a humidity of 50% RH or more to generate oxygen and hydrogen.

[17] A method for producing oxygen and hydrogen, comprising applying a voltage to the electrolytic cell according to any one of [1] to

[15] in air having a humidity of 50% RH or more, to generate oxygen and hydrogen.

[18] Immersing a substrate having pores in an aqueous solution of a water-absorbing compound to obtain a structure in which the pores are filled with a dilute solution of the water-absorbing compound; and and stacking the structure with an anode and a cathode so that the structure is disposed between the anode and the cathode to obtain an electrolysis cell. [Effects of the Invention]

[0007] The present disclosure may provide a new direct air electrolysis method, preferably one that does not require the use of a strongly basic or strongly acidic solution or a noble metal electrocatalyst. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1(a) is a graph showing the relationship between voltage and current density when direct air electrolysis was performed using the electrolytic cell of the example, and FIG. 1(b) is a graph showing the relationship between time and current density when direct air electrolysis was performed using the electrolytic cell of the example. [Figure 2] FIG. 2 is a schematic diagram illustrating the mechanism of direct air electrolysis in the electrolysis cell of the present disclosure. [Figure 3] FIG. 3(a) is a graph showing the relationship between voltage and current density when direct air electrolysis was performed using the electrolytic cell of the example, and FIG. 3(b) is a graph showing the relationship between time and current density when direct air electrolysis was performed using the electrolytic cell of the example. DETAILED DESCRIPTION OF THE INVENTION

[0009] (First embodiment: electrolysis cell) An electrolysis cell according to one embodiment of the present disclosure will be described below, but the present disclosure is not limited to this embodiment.

[0010] The electrolytic cell in this embodiment includes an anode, a cathode facing the anode, a substrate having pores, and a water-absorbing compound, the substrate being disposed between the anode and the cathode, and the water-absorbing compound being present in the pores, and in a preferred embodiment, the water-absorbing compound may cover at least a portion of the surface of the pores of the substrate. Hereinafter, the anode (positive electrode) and the cathode (negative electrode) may be collectively referred to as electrodes.

[0011] The electrolysis cell of the present disclosure can be used to provide a new direct air electrolysis method, preferably a direct air electrolysis method that does not require the use of a strongly basic or strongly acidic solution or a noble metal electrocatalyst.

[0012] Although the present disclosure should not be interpreted as being limited to any particular theory, the reason why the electrolytic cell of the present disclosure can achieve such effects is believed to be as follows. Specifically, the water-absorbing compound contained in the electrolytic cell of the present disclosure is believed to absorb moisture in the air on the surfaces of the pores of the substrate. The absorbed moisture is believed to remain on the surfaces of the pores of the substrate due to interaction with the water-absorbing compound. Then, when the moisture present on the surfaces of the pores of the substrate forms a conductive path connecting the electrodes, a current begins to flow through the conductive path, and water electrolysis is believed to begin. Therefore, the electrolytic cell of the present disclosure does not require the use of a strongly basic or strongly acidic solution, nor does it require the use of a precious metal electrode catalyst.

[0013] (electrode) The electrolysis cell of the present disclosure has an anode (positive electrode) and a cathode (negative electrode). In the electrolysis cell of the present disclosure, the anode and cathode face each other, and a substrate is disposed between the anode and cathode. In such an electrolysis cell, application of a voltage between the anode and cathode causes a current to flow through water present in the pores of the substrate, and water electrolysis can proceed. At this time, the following electrochemical reactions are thought to proceed at the anode and cathode, respectively. Electrochemical reaction at the anode: H2O → O2+4H + +4e - (Weakly acidic to neutral) 4OH - → O2 + 2H2O + 4e - (Neutral to weakly basic) Electrochemical reaction at the cathode: 2H + +2e - → H2 (weakly acidic to neutral) 2H2O+2e - → H2+2OH - (Neutral to weakly basic)

[0014] The electrode may be a metal electrode containing a metal material or a carbon electrode containing a carbon material. Examples of the metal material include metals such as iron, titanium, nickel, cobalt, palladium, iridium, ruthenium, platinum, and gold; and alloys containing these metals. Examples of the carbon material include graphene, carbon nanotubes, fullerene, and ketjen black. These electrodes may also include a metal electrode or carbon electrode carrying a metal oxide or metal nitride electrocatalyst containing iron, nickel, cobalt, palladium, iridium, ruthenium, platinum, or the like.

[0015] The shape of the electrode is not particularly limited, and may be a plate or mesh.

[0016] The anode and the cathode are preferably in contact with a substrate, which will be described later.

[0017] (base material) The electrolysis cell of the present disclosure includes a substrate having pores. Preferably, the substrate may be a porous layer having a plurality of pores. In the electrolysis cell of the present disclosure, the substrate is disposed between the anode and the cathode. By having pores, the substrate can retain water in the pores and function as a water-retaining layer. The water retained in the pores forms a flow path, and electrolysis of water can proceed by applying a voltage to the flow path. In the present disclosure, the substrate may be referred to as a water-retaining layer. Furthermore, a structure having a water-absorbing compound in the pores of the substrate may be referred to as a composite.

[0018] The substrate may be an inorganic substrate containing an inorganic material, or an organic substrate containing an organic material. The substrate is preferably an inorganic substrate. The shape of the inorganic material and the organic material is not particularly limited, and may be particulate, capillary, sponge, or monolithic.

[0019] The inorganic material preferably contains a metal oxide and / or a zeolite. The metal oxide may be one or more selected from silica, titania, and alumina. In a preferred embodiment, the inorganic material may contain metal oxide particles and / or zeolite particles, and more preferably metal oxide particles.

[0020] The substrate is not particularly limited as long as it has pores. Preferably, the substrate may be porous. Preferably, the pores may include through-holes connecting the anode and the cathode. The shape of the substrate may be a shape filled with particles, such as a capillary shape, a sponge shape, a monolith shape, or the like. Preferably, the substrate is a shape filled with particles.

[0021] When the inorganic and organic materials are in particulate form, the average particle size of the particles may be preferably 0.05 μm or more and 10 μm or less, more preferably 0.05 μm or more and 5 μm or less, and even more preferably 0.1 μm or more and 1 μm or less. In the present disclosure, the average particle size may be the volume average particle size (D50), which can be measured by a dynamic light scattering method or by observation with a scanning electron microscope and calculation of the particle size distribution.

[0022] The porosity of the substrate may be preferably 25% by volume or more and 50% by volume or less, more preferably 30% by volume or more and 45% by volume or less, and even more preferably 35% by volume or more and 45% by volume or less. In the present disclosure, the porosity can be measured by a liquid immersion method using water.

[0023] The thickness of the substrate may be preferably 0.5 mm or more and 50 mm or less, more preferably 1 mm or more and 20 mm or less, and even more preferably 1 mm or more and 10 mm or less.

[0024] In one embodiment, the substrate is prepared by filling particles of an inorganic material into a mold and applying a pressure of 100 to 360 kgf / cm 2 The material can be produced by applying a pressure of 1000 kJ / cm 2 to the material and then heating the material to 400 to 800°C.

[0025] (water-absorbing compound) The electrolytic cell of the present disclosure includes a water-absorbing compound. The water-absorbing compound is present in the pores of the substrate, and in a preferred embodiment, is disposed on the surfaces of the pores of the substrate, preferably covering at least a portion of the surfaces of the pores of the substrate. The water-absorbing compound can retain water in the pores of the substrate, preferably on the surface of the substrate, and can contribute to the formation and / or retention of water flow paths in the pores. The water-absorbing compound may be present in the pores of the substrate in a water-absorbed state or as an aqueous solution.

[0026] In the present disclosure, the water-absorbing compound refers to a compound that can exhibit deliquescence, and a compound whose saturated water vapor pressure of a saturated aqueous solution of the compound is lower than the water vapor pressure in the atmosphere.

[0027] The moisture absorption capacity (DC) of the water-absorbing compound is preferably 10% RH / g or more and 100% RH / g or less, more preferably 10% RH / g or more and 80% RH / g or less, and even more preferably 15% RH / g or more and 50% RH / g or less.

[0028] The above moisture absorption capacity is measured at atmospheric pressure, a temperature of 30°C, and a capacity of 1,150 cm 3 When about 1.0 g of a water-absorbing compound is placed in a sealed container and left to stand until there is no change in humidity in the sealed container, the humidity change Δ% RH in the sealed container can be calculated by dividing the humidity change Δ% RH in the sealed container by the mass of the water-absorbing compound.

[0029] The water-absorbing compound contains anions and cations. In the water-absorbing compound, the anions and cations may exist in the form of salts or deep eutectic solvents (see "Deep Eutectic Solvents Formed between Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids", Andrew P. Abbott, David Boothby, Glen Capper, David L. Davies, and Raymond K. Rasheed, J. Am. Chem. Soc. 2004, 126, 9142-9147, and "Deep Eutectic Solvents (DESs) and Their Applications", Emma L. Smith, Andrew P. Abbott, and Karl S. Ryder, Chem. Rev. 2014, 114, 11060-11082). That is, the water-absorbing compound may contain one or more species selected from the group consisting of salts and deep eutectic solvents. The salt may be a solid salt or an ionic liquid (Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis, Thomas Welton, Chem. Rev. 1999, 99, 2071-2083).

[0030] In this disclosure, a salt refers to a compound in which an anion and a cation are bound by an ionic bond and neutralized. An ionic liquid refers to a salt that has a melting point of 100°C or less at normal pressure, and a solid salt refers to a salt other than an ionic liquid. The cations and anions that constitute a salt (i.e., a solid salt or an ionic liquid) may be either inorganic or organic ions. A deep eutectic solvent refers to a compound that becomes liquid at room temperature and normal pressure when a hydrogen bond-accepting salt is mixed with a hydrogen bond-donor molecule in a certain ratio.

[0031] The anions preferably include one or more anions selected from the group consisting of inorganic anions and organic anions.

[0032] The organic anion may be monovalent or divalent or higher, preferably monovalent. Examples of the organic anion include organic phosphate anions such as dimethylphosphate anion (DMPO4) and diethylphosphate anion (DEPO4); organic sulfate anions such as methylsulfate anion (MeSO4) and ethylsulfate anion (EtSO4); organic carboxylate anions such as acetate anion (OAc); lactate ion (Lac); and bistrifluoromethylimide anion (NTf2). The organic anion preferably includes an organic phosphate anion.

[0033] The inorganic anion may be monovalent or divalent or more, preferably monovalent or divalent. Examples of the inorganic anion include nitrate anion (NO3 - ), hydrogen sulfate anion (SO3H - ), and phosphite anion (HPO3 2- The inorganic anion preferably includes a hydrogen sulfate anion or a phosphite anion.

[0034] The cations preferably include one or more selected from the group consisting of inorganic cations and organic cations.

[0035] The inorganic cation is an ammonium cation (NH + ) is preferably included.

[0036] The organic cation may be monovalent or divalent or more, preferably monovalent or divalent. Examples of the organic cation include methyldiethylammonium ion (N 0122 ), methyltriethylammonium ion (N 2221 ), methyldiethyl(2-methoxyethyl)ammonium ion (N 221ME ), methyltributylammonium ion (P 4441), trimethyl(2-hydroxyethyl)ammonium ion (Ch), dimethyldi(2-hydroxyethyl)ammonium ion (BHEDMA), methyltri(2-hydroxyethyl)ammonium ion (THEMA), hexamethylethylenediammonium ion (HMEDA), tetramethyldiethylpropylenediammonium cation (DETMC3), N-methyl-N-ethylpyrrolidine cation (PP 12 ), N,N-dimethylpiperidine cation (DMpip), N-methyl-N-ethylpiperidine cation (EMpip), N,N-dimethylmorpholine cation (DMmor), N-methyl-N-ethylmorpholine cation (EMmor), N-methyl-N-(2-hydroxyethyl)morpholine cation (2HHEMmor), N-ethyl-N-(2-hydroxyethyl)morpholine cation (2HEEmor), N,N'-dimethylbis(2-morpholinoethyl)ether cation (DMbismorC2OC2)); N-methyl-N'-alkylimidazole cation (C n Examples of the organic cation include imidazole ions such as N-methyl-N'-(2-hydroxyethyl)imidazole cation (COHmi), N-ethyl-N'-methyl-2-methylimidazole cation (Cdmim), and pyridine ions such as N-ethyl-2-methylpyridine cation (CmPy). The organic cation preferably contains an organic ammonium ion, and more preferably contains a chain organic ammonium ion.

[0037] The water-absorbing compound preferably contains the above organic anion and the above organic cation, more preferably contains an organic phosphate ion and an ammonium ion, and even more preferably contains an organic phosphate ion and a chain organic ammonium ion.

[0038] The decomposition temperature of the water-absorbing compound may be preferably 100°C or higher, more preferably 150°C or higher and 250°C or lower, and even more preferably 200°C or higher and 250°C or lower.

[0039] The water-absorbing compound is preferably one that gives an aqueous solution that is nearly neutral (weakly acidic to weakly basic). Specifically, the pH of an aqueous solution containing the water-absorbing compound at a concentration of 50% by mass is preferably 3 or more and 10 or less, more preferably 5 or more and 10 or less.

[0040] The content of the water-absorbing compound is preferably 10 parts by mass or more and 70 parts by mass or less, more preferably 20 parts by mass or more and 70 parts by mass or less, and even more preferably 30 parts by mass or more and 60 parts by mass or less, relative to 100 parts by mass of the base material. When the content of the water-absorbing compound is within this range, it becomes easy to carry out direct air decomposition with high efficiency.

[0041] The electrolytic cell is preferably a direct air electrolytic cell. The electrolytic cell may be used alone or in combination of two or more cells arranged in series and / or parallel.

[0042] In one aspect, the electrolytic cell can be produced by a production method including: immersing the substrate in an aqueous solution of the water-absorbing compound to obtain a structure in which the pores are filled with the aqueous solution of the water-absorbing compound; and stacking the structure, an anode, and a cathode so that the structure is disposed between the anode and the cathode to obtain a laminate (electrolytic cell) in which the water-absorbing compound is present in the pores of the substrate and is disposed between the anode and the cathode. Furthermore, the production method may include removing water from the laminate to obtain a composite in which the water-absorbing compound is adhered to the pores of the substrate and is disposed between the anode and the cathode and is disposed between the anode and the cathode.

[0043] According to this production method, it is possible to uniformly arrange the water-absorbing compound on the surface of the substrate, and it is possible to produce an electrolytic cell capable of more efficiently electrolyzing water.

[0044] The concentration of the aqueous solution of the water-absorbing compound may be preferably 50% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 80% by mass or less, and even more preferably 50% by mass or more and 70% by mass or less.

[0045] The temperature when the substrate is immersed in the aqueous solution of the water-absorbing compound may be preferably 10° C. or higher and 50° C. or lower, more preferably 20° C. or higher and 40° C. or lower. The immersion of the substrate in the aqueous solution of the water-absorbing compound may be carried out, for example, under atmospheric pressure.

[0046] When the aqueous solution of the water-absorbing compound is filled into the pores of the substrate, ultrasonic treatment, decompression treatment, etc. may be carried out.

[0047] The method for laminating the composite with the anode and cathode is not particularly limited.

[0048] The method for removing water from the laminate is not particularly limited, and can be carried out by leaving the laminate to stand, etc. The temperature during the dehydration can be preferably 20°C or higher and 300°C or lower, more preferably 25°C or higher and 200°C or lower, and even more preferably 30°C or higher and 100°C or lower. The pressure during the dehydration can be preferably 1 hPa or higher and 1000 hPa or lower, more preferably 1 hPa or higher and 200 hPa or lower, and even more preferably 1 hPa or higher and 100 hPa or lower.

[0049] (Second embodiment: direct air electrolysis method) The direct air electrolysis method of the present disclosure involves applying a voltage to the electrolysis cell in air with a humidity of 50% RH or higher to generate oxygen and hydrogen.

[0050] The direct air electrolysis method of the present disclosure uses the electrolysis cell described above, and can provide a new direct air electrolysis method. Preferably, the direct air electrolysis method of the present disclosure can perform direct air electrolysis without using a strongly basic or strongly acidic solution or a noble metal electrode catalyst.

[0051] The humidity of the air used in the direct air electrolysis method of the present disclosure is 50% RH or higher, preferably 60% RH or higher and 100% RH or lower, more preferably 70% RH or higher and 100% RH or lower, and even more preferably 80% RH or higher and 100% RH or lower. Because the direct air electrolysis method of the present disclosure uses the electrolytic cell described above, direct air electrolysis can be performed even when the humidity is low. The direct air electrolysis method of the present disclosure uses the electrolytic cell, and in theory, direct air electrolysis is possible in air having a relative humidity equal to or higher than the relative humidity corresponding to the vapor pressure of a saturated aqueous solution of the water-absorbing compound.

[0052] The direct air electrolysis method of the present disclosure can be carried out in a high-temperature environment. For example, the temperature when carrying out the direct air electrolysis method of the present disclosure can be preferably 25°C or higher and 100°C or lower, more preferably 30°C or higher and 80°C or lower, and even more preferably 30°C or higher and 70°C or lower.

[0053] The direct air electrolysis method of the present disclosure can be typically, but not limited to, carried out under atmospheric pressure. The pressure when carrying out the direct air electrolysis method of the present disclosure can be preferably 900 hPa or more and 1,300 hPa or less, more preferably 950 hPa or more and 1,200 hPa or less, and even more preferably 1,000 hPa or more and 1,100 hPa or less.

[0054] According to the direct air electrolysis method of the present disclosure, oxygen and hydrogen can be generated, and a method for producing oxygen and hydrogen, which includes applying a voltage to the electrolytic cell in air having a humidity of 50% RH or more, to generate oxygen and hydrogen, is also included in the technical scope of the present disclosure.

[0055] According to the present disclosure, a new direct air electrolysis method can be provided, preferably a direct air electrolysis method that does not require the use of a strongly basic or strongly acidic solution or a precious metal electrode catalyst. Since the present disclosure enables hydrogen and oxygen to be produced in air with a relative humidity of 50% RH or higher, it is expected that a means for producing hydrogen and oxygen by direct air electrolysis can be provided even in regions with scarce water resources. [Example]

[0056] The present invention will be explained in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0057] (Manufacturing Example 1: Preparation of Al2O3 water-retaining layer) 0.2 g of alumina particles with a volume average particle size (D50) of 0.1 μm were packed into a cylindrical container with a diameter of 15 mm, and deionized water was added dropwise to the packed alumina particles. 2 After that, the alumina particles were turned upside down and a pressure of 180 to 300 kgf / cm was applied from above. 2 A pressure of 1000 kJ / cm2 was applied for 2 minutes to obtain alumina pellets. The obtained alumina pellets were fired at 600 °C for 180 minutes to prepare a disk-shaped Al2O3 water-retaining layer with a thickness of 1 mm and a diameter of 15 mm.

[0058] (Example 1: [N 1111 ][DMPO4]) [ka] As a water-absorbing compound, freeze-dried [N 1111 1.7889 g of [DMPO4] was placed in a vial, 1.7981 g of deionized water was added, and the mixture was stirred to obtain a 50% by mass solution of [N 1111 The Al2O3 water-retaining layer having a thickness of 1 mm obtained in Production Example 1 was immersed in this solution for 90 seconds, and then a cell was assembled.

[0059] Example 2: [N 2221 About DMPO4 [ka] As a water-absorbing compound, freeze-dried [N 2221 2.9097 g of [DMPO4] was placed in a vial, 2.9941 g of deionized water was added, and the mixture was stirred to obtain a 50% by mass solution of [N 2221The Al2O3 water-retaining layer having a thickness of 1 mm obtained in Production Example 1 was immersed in this solution for 90 seconds, and then a cell was assembled.

[0060] (Example 3: Regarding [DMpip] [DMPO4]) [ka] 1.9364 g of solid [DMpip][DMPO4] was placed in a vial as a water-absorbing compound, and 1.9581 g of deionized water was added and stirred to prepare a 50 mass % aqueous solution of [DMpip][DMPO4]2. The 1 mm-thick Al2O3 water-retaining layer obtained in Production Example 1 was immersed in this solution for 90 seconds, after which a cell was assembled.

[0061] (Example 4: Regarding [Ch][DMPO4]) [ka] 1.6893 g of freeze-dried [Ch][DMPO4] was placed in a vial, and 1.7136 g of deionized water was added and stirred to prepare a 50 mass% aqueous solution of [Ch][DMPO4]. The 1 mm-thick Al2O3 water-retaining layer obtained in Production Example 1 was immersed in this solution for 90 seconds, and then the cell was assembled.

[0062] (Example 5: [BHEDMA][DMPO4]) [ka] 6.4595 g of freeze-dried [BHEDMA][DMPO4] was placed in a vial, and 6.4791 g of deionized water was added and stirred to prepare a 50 mass% aqueous solution of [BHEDMA][DMPO4]. The 1 mm-thick Al2O3 water-retaining layer obtained in Production Example 1 was immersed in this solution for 90 seconds, and then the cell was assembled.

[0063] (Example 6: Regarding [THEMA][DMPO4]) [ka] 11.75 g of freeze-dried [THEMA][DMPO4] was placed in a vial, and 11.77 g of deionized water was added and stirred to prepare a 50 mass% aqueous solution of [THEMA][DMPO4]. The 1 mm-thick Al2O3 water-retaining layer obtained in Production Example 1 was immersed in this solution for 90 seconds, after which a cell was assembled.

[0064] Example 7: [HMEDA][DMPO] [ka] 25.0762 g of powdered [HMEDA][DMPO4] was placed in a vial as a water-absorbing compound, and 5.0105 g of deionized water was added and stirred to prepare a 50 mass% aqueous solution of [HMEDA][DMPO4]2. The 1 mm-thick Al2O3 water-retaining layer obtained in Production Example 1 was immersed in this solution for 90 seconds, after which a cell was assembled.

[0065] (Example 8: Regarding [DETMC3][DEPO4]2) [ka] As a water-absorbing compound, 2.1951 g of freeze-dried [DETMC3][DEPO4]2 was placed in a vial, and 2.2026 g of deionized water was added and stirred to prepare a 50 mass % aqueous solution of [DETMC3][DEPO4]2. The 1 mm-thick Al2O3 water-retaining layer obtained in Production Example 1 was immersed in this solution for 90 seconds, and then the cell was assembled.

[0066] (Example 9: Regarding [DETMC2OC2][DEPO4]2) [ka] 2.4299 g of freeze-dried [DETMC2OC2][DEPO4]2 was placed in a vial as a water-absorbing compound, and 2.4424 g of deionized water was added and stirred to prepare a 50 mass % aqueous solution of [DETMC2OC2][DEPO4]2. The 1 mm-thick Al2O3 water-retaining layer obtained in Production Example 1 was immersed in this solution for 90 seconds, after which a cell was assembled.

[0067] Example 10: [DMbismorC2OC2][DMPO4]2 [ka] As a water-absorbing compound, 1.9202 g of freeze-dried [DMbismorC2OC2][DMPO4]2 was placed in a vial, and 1.9331 g of deionized water was added and stirred to prepare a 50 mass% aqueous solution of [DMbismorC2OC2][DMPO4]2. The 1 mm-thick Al2O3 water-retaining layer obtained in Production Example 1 was immersed in this solution for 90 seconds, and then the cell was assembled.

[0068] (Measurement of water absorption rate) Atmospheric pressure, temperature 30°C, volume 1,150cm 3 Approximately 1.0 g of a water-absorbing compound was placed in a sealed container, and the sealed container was left standing until the humidity in the sealed container stopped changing. The %RH at which the humidity in the sealed container became constant was measured. The amount of water absorption (gH2O) was calculated from the obtained final humidity (%RH) and the saturated water vapor pressure at 30°C. The amount of water absorption (gH2O) was divided by the time (1 / 2T) required to absorb half of the maximum amount of water (gIL) and the amount of water-absorbing compound used to calculate the water absorption rate. (Water absorption rate) = (amount of water absorbed) / (time required to absorb half of the maximum amount of water) / (mass of water-absorbing compound used)

[0069] (Measurement of water vapor pressure and relative humidity) The water vapor pressure was determined by reference to the values ​​described in Reference 2 (Toshiyuki Itoh et al., "Design of quaternary ammonium type-ionic liquids as desiccants for an air-conditioning system" Green Chemical Engineering, 2020, 1, 5046.) and Reference 3 (Toshiyuki Itoh et al., "Dicationic-Type Quaternary Ammonium Salts as Candidates of Desiccants for an Air-Conditioning System" ACS Sustainable Chem. Eng., 2021, 9, 14502-14514.). Since the water vapor pressure at 50% by mass for Examples 1, 3, 8, and 10 was not reported, the water vapor pressure at different mass% (80%, 60%, and 40% by mass) was interpolated and calculated. Furthermore, from the obtained water vapor pressure, the following formula: (Relative humidity) = {(Water vapor pressure) / (Saturated water vapor pressure at 25°C 31.7 hPa)} x 100 The relative humidity was calculated based on the above.

[0070] The measured water absorption rate, water vapor pressure, and relative humidity are shown in Table 1. Note that blank spaces in Table 1 indicate that no measured values ​​were found.

[0071] [Table 1]

[0072] (direct air electrolysis) The electrolytic cell obtained in the examples was placed in a desiccator and dried at 0.01 MPa for 3 hours. A humidity control device and a bubbler were connected to the desiccator, and the cell was filled with air at a relative humidity of 50% RH or approximately 90% RH and left to stand. After a predetermined time had elapsed since the start of air introduction, direct air electrolysis was performed by applying and sweeping a voltage between the anode and cathode.

[0073] Figure 1(a) shows the relationship between voltage and current density after 20 hours of standing in air at a relative humidity of approximately 90%RH. The current density increases as the voltage increases, indicating that current is flowing through the electrolysis cell. Furthermore, since no other noticeable redox peaks are observed, it is believed that there is little decomposition of water-absorbing compounds, etc., and that water electrolysis is primarily proceeding.

[0074] Figure 1(b) shows the relationship between voltage and current density at various times when the electrolytic cell was placed in air with a relative humidity of approximately 90% RH. It was confirmed that current began to flow through the electrolytic cell and gradually increased over time. As shown in Figure 2, immediately after the electrolytic cell was placed, the water-absorbing compound is thought to be absorbing moisture from the air and retaining water on the pore surface of the water-retaining layer. The water, which is thought to be scattered in the initial stage, is thought to become continuous as more moisture from the air is absorbed by the water-absorbing compound. Furthermore, when a water conduction path is formed between the anode and cathode, current begins to flow. As more water is retained on the pore surface of the water-retaining layer, the number of conduction paths increases, and the current density increases.

[0075] 3(a) shows the relationship between voltage and current density after 20 hours when the electrolytic cell of Example 4 was left standing in air at a relative humidity of 50% RH. The current density increased with increasing voltage, which suggests that current was flowing through the electrolytic cell and that water electrolysis was progressing.

[0076] 3(b) shows the current density at 4 V at each time point when the electrolytic cell of Example 4 was placed in air at a relative humidity of 50% RH and the relationship between voltage and current density was examined over time. It was confirmed that current began to flow and the current density increased over time.

[0077] 3(a) and (b) confirm that direct air decomposition is possible even in air at a relative humidity of 50% RH by using the electrolytic cell of the present disclosure. [Industrial Applicability]

[0078] According to the present disclosure, a new direct air electrolysis method can be provided, preferably a direct air electrolysis method that does not require the use of a strongly basic or strongly acidic solution or a precious metal electrode catalyst. Since the present disclosure enables hydrogen and oxygen to be produced in air with a relative humidity of 50% RH or higher, it is expected that a means for producing hydrogen and oxygen by direct air electrolysis can be provided even in regions with scarce water resources.

[0079] This disclosure was supported by the 2023-2024 JKA Subsidized Project, "Development of high-performance catalysts and electrolytes enabling water electrolysis from low-humidity air."

Claims

1. an anode, a cathode facing the anode, a porous substrate, and a water-absorbing compound; the substrate is disposed between the anode and the cathode; the water-absorbing compound is present in the pores of the substrate; The water-absorbing compound comprises an anion and a cation.

2. 2. The electrolytic cell according to claim 1, wherein the anions include one or more anions selected from the group consisting of inorganic anions and organic anions.

3. 2. The electrolytic cell according to claim 1, wherein the inorganic anions include one or more selected from the group consisting of nitrate anions, hydrogen sulfate anions, and phosphite anions.

4. 2. The electrolytic cell according to claim 1, wherein the organic anion comprises one or more anions selected from the group consisting of a carboxylate anion, a lactate anion, and an organic phosphate anion.

5. 2. The electrolytic cell according to claim 1, wherein the cations include one or more selected from the group consisting of inorganic cations and organic cations.

6. 10. The electrolytic cell of claim 1, wherein the inorganic cation comprises an ammonium cation.

7. 2. The electrolytic cell of claim 1, wherein the organic cation comprises a monovalent, divalent or higher valent organic ammonium ion.

8. The electrolytic cell according to claim 1 , wherein the water-absorbing compound comprises one or more selected from the group consisting of salts and deep eutectic solvents.

9. 10. The electrolysis cell of claim 1, wherein the substrate comprises a metal oxide and / or a zeolite.

10. The electrolysis cell of claim 1 , wherein the substrate comprises metal oxide particles.

11. 10. The electrolytic cell according to claim 9, wherein the metal oxide comprises one or more selected from the group consisting of silica, titania, and alumina.

12. 10. The electrolysis cell of claim 1, wherein the substrate comprises particles of zeolite.

13. 2. The electrolysis cell according to claim 1, wherein the pH of an aqueous solution of the water-absorbing compound having a concentration of 50% by mass is 3 or more and 10 or less.

14. 2. The electrolysis cell according to claim 1, wherein the content of the water-absorbing compound is 30 parts by mass or more and 70 parts by mass or less relative to 100 parts by mass of the total of the base materials.

15. 10. The electrolysis cell of claim 1, which is a direct air electrolysis cell.

16. A direct air electrolysis method comprising applying a voltage to the electrolytic cell according to any one of claims 1 to 15 in air having a humidity of 50% RH or more to generate oxygen and hydrogen.

17. A method for producing oxygen and hydrogen, comprising applying a voltage to the electrolytic cell according to any one of claims 1 to 15 in air having a humidity of 50% RH or more to generate oxygen and hydrogen.

18. Immersing a substrate having pores in an aqueous solution of a water-absorbing compound to obtain a structure in which the pores are filled with a dilute solution of the water-absorbing compound; and and stacking the structure with an anode and a cathode so that the structure is disposed between the anode and the cathode to obtain an electrolysis cell.

Images