Water electrolysis device

Abstract

A water electrolysis device according to the present invention comprises a power supply, a water electrolysis electrolyte solution that includes a water-based magnetic fluid, a pair of electrodes that include a positive electrode and a negative electrode, a magnetic field application mechanism that applies a non-uniform magnetic field to at least one of the pair of electrodes, and a container that accommodates the water electrolysis electrolyte solution. The water-based magnetic fluid includes water, an electrolyte, and magnetic nanoparticles. The pair of electrodes comprise a metal porous body that comprises a non-magnetic material and has a porosity of 30%–85%, a specific surface area of at least 1.0×104 m2 / m3, a transmittance of at least 0.6×10-12 m2, a volume resistivity of at least 3.2×10-7 Ωm but no more than 6.3×10-6 Ωm, and an average pore diameter of at least 1 μm but no more than 3000 μm.

Description

water electrolysis device

[0001] The present disclosure relates to a water electrolysis device. This application claims priority to Japanese Patent Application No. 2024-111721, filed on July 11, 2024. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] As products using hydrogen energy, such as fuel cell vehicles, are put into practical use, and as demand for hydrogen energy expands, the efficiency of hydrogen production is becoming increasingly important. ２ Water electrolysis, which produces high-purity hydrogen without emitting CO₂, is attracting attention.

[0003] In a water electrolysis device, the larger the surface area of ​​the electrodes, the lower the resistance of the electrodes and the lower the power required to generate hydrogen. Patent Document 1 proposes a technology that uses spongy porous electrodes made of carbon with a large surface area as electrodes for a water electrolysis device.

[0004] Furthermore, in Patent Document 1, a water-based magnetic fluid is used as an electrolyte for water electrolysis, and the action of magnetic buoyancy is used to promote the removal of bubbles from within the porous electrode.

[0005] Japanese Patent Application Laid-Open No. 2019-194349

[0006] The water electrolysis device of the present disclosure includes a power source, an electrolyte solution for water electrolysis containing a water-based magnetic fluid, a pair of electrodes consisting of an anode and a cathode, a magnetic field application mechanism that applies a non-uniform magnetic field to at least one of the pair of electrodes, and a container for storing the electrolyte solution for water electrolysis, wherein the water-based magnetic fluid contains water, an electrolyte, and magnetic nanoparticles, and the pair of electrodes are made of a porous metal body, the porosity of the porous metal body is 30% or more and 85% or less, and the specific surface area of ​​the porous metal body is 1.0 × 10 ４ m ２ / m ３ The metal porous body has a transmittance of 0.6×10 －１２ m ２ and the volume resistivity of the porous metal body is 3.2 × 10 －７ Ωm or more 6.3 x 10 －６the porous metal body has an average pore size of 1 μm or more and 3000 μm or less, and the porous metal body is made of a non-magnetic material.

[0007] Fig. 1 is a diagram illustrating a typical configuration example of a water electrolysis apparatus according to embodiment 1. Fig. 2 is a diagram illustrating buoyancy and magnetic buoyancy acting on bubbles. Fig. 3 is a diagram illustrating the configuration of a water electrolysis apparatus fabricated in an example.

[0008] In recent years, from the viewpoint of energy conservation, there has been a demand for water electrolysis devices with improved water electrolysis efficiency. Therefore, an object of the present disclosure is to provide a water electrolysis device with improved water electrolysis efficiency.

[0009] According to the present disclosure, it is possible to provide a water electrolysis device with improved water electrolysis efficiency.

[0010] First, embodiments of the present disclosure will be described below. (1) A water electrolysis device according to the present disclosure includes a power source, an electrolyte solution for water electrolysis containing a water-based magnetic fluid, a pair of electrodes consisting of an anode and a cathode, a magnetic field application mechanism for applying a non-uniform magnetic field to at least one of the pair of electrodes, and a container for storing the electrolyte solution for water electrolysis, wherein the water-based magnetic fluid contains water, an electrolyte, and magnetic nanoparticles, and the pair of electrodes are made of a porous metal body, the porosity of the porous metal body is 30% or more and 85% or less, and the specific surface area of ​​the porous metal body is 1.0 × 10 ４ m ２ / m ３ The metal porous body has a transmittance of 0.6×10 －１２ m ２ and the volume resistivity of the porous metal body is 3.2 × 10 －７ Ωm or more 6.3 x 10 －６ the porous metal body has an average pore size of 1 μm or more and 3000 μm or less, and the porous metal body is made of a non-magnetic material.

[0011] According to the present disclosure, it is possible to provide a water electrolysis device with improved water electrolysis efficiency. The reason for this is presumed to be as follows.

[0012] When electrodes made of porous metal are used, the large surface area of ​​the electrodes reduces the resistance of the electrodes and the power required for hydrogen generation. On the other hand, when electrodes made of porous metal are used, hydrogen and oxygen bubbles generated during water electrolysis are confined within the porous electrode and adhere to the electrode surface, preventing the electrolyte from contacting the electrode surface, impeding the progress of electrolysis and potentially reducing the amount of electrolysis. The water electrolysis device disclosed herein includes an electrolyte for water electrolysis containing a water-based magnetic fluid, a pair of electrodes made of porous metal, and a magnetic field application mechanism that applies a non-uniform magnetic field to at least one of the pair of electrodes. Therefore, in the water electrolysis device disclosed herein, as shown in FIG. 2 , magnetic buoyancy B2, together with buoyancy B1, acts on bubbles of hydrogen gas or oxygen gas generated at the electrodes made of porous metal, promoting the detachment of the bubbles from the porous metal. Promoting the detachment of bubbles reduces the likelihood of the electrolyte being unable to reach the electrode surface, promoting oxidation-reduction reactions and improving water electrolysis efficiency.

[0013] The water electrolysis device of the present disclosure uses a pair of electrodes made of a porous metal body. In the water electrolysis device of the present disclosure, the porous metal body has a porosity of 30% or more and 85% or less. When the porous metal body has a porosity of 30% or more, the detachment of gas bubbles is promoted, making it less likely that the electrolyte will be unable to reach the electrode surface, promoting the oxidation-reduction reaction and making it easier to improve the efficiency of water electrolysis. When the porous metal body has a porosity of 85% or less, it is possible to avoid an excessive increase in the electrical resistance of the electrode due to an excessively small amount of metal in the electrode.

[0014] In the water electrolysis apparatus of the present disclosure, the specific surface area of ​​the metal porous body is 1.0 × 10 ４ m ２ / m ３ This makes it possible to sufficiently increase the area of ​​the contact interface between the electrode and the electrolyte, thereby reducing the electrolysis voltage, reducing the power required for hydrogen generation, and improving the efficiency of water electrolysis.

[0015] In the water electrolysis apparatus of the present disclosure, the permeability of the porous metal body is 0.6×10 －１２ m ２As a result, the flow resistance of the hydrogen gas, oxygen gas, and electrolyte solution for water electrolysis passing through the metal porous body is reduced. The reduced flow resistance reduces the likelihood of problems such as gas retention and poor penetration of the electrolyte solution, promotes the oxidation-reduction reaction, and tends to improve the efficiency of water electrolysis.

[0016] In the water electrolysis apparatus of the present disclosure, the volume resistivity of the metal porous body is 3.2 × 10 －７ Ωm or more 6.3 x 10 －６ The volume resistivity of the porous metal body is 3.2 × 10 －７ If the volume resistivity of the porous metal body is less than 6.3×10 Ωm, the porous metal body can be realized only in a state where the porosity is substantially low, and it is difficult to obtain the effect of increasing the area of ​​the contact interface between the electrolyte and the electrode. －６ If the resistance exceeds Ωm, the effect of increasing the area is not as great as the adverse effect of increasing the electrical resistance of the electrode, and therefore the oxidation-reduction reaction is promoted, and the efficiency of water electrolysis is likely to improve.

[0017] In addition, in conventional porous metal bodies, when the specific surface area of ​​the porous metal body increases, the skeleton constituting the porous metal body becomes thinner, and therefore the volume resistivity of the porous metal body also increases. ４ m ２ / m ３ In the above cases, the volume resistivity of the porous metal body is 6.3 × 10 －６ As a result of extensive investigation, the inventors of the present invention have found that the specific surface area is 1.0 × 10 ４ m ２ / m ３ or more, and the volume resistivity is 3.2 × 10 －７ Ωm or more 6.3 x 10 －６ The present inventors have discovered a method for producing a porous metal body having a resistivity of Ωm or less. The method for producing a porous metal body will be described in detail below.

[0018] In the water electrolysis device of the present disclosure, the average pore diameter of the metal porous body is 1 μm or more and 3000 μm or less. When the average pore diameter of the metal porous body is 1 μm or more, the flow resistance of the hydrogen gas and oxygen gas and the electrolyte solution for water electrolysis passing through the metal porous body is reduced. This promotes the oxidation-reduction reaction, and the efficiency of water electrolysis is likely to be improved. When the average pore diameter of the metal porous body is 3000 μm or less, the specific surface area can be reduced to 1.0 × 10４ m ２ / m ３ The oxidation-reduction reaction is accelerated, and the efficiency of water electrolysis is likely to improve.

[0019] (2) In the above (1), the non-magnetic material may be at least one selected from the group consisting of platinum, palladium, iridium, gold, a non-magnetic stainless steel alloy, and a non-magnetic nickel alloy. Alternatively, a porous body may be formed from a non-magnetic metal that can be used as a general electrode, such as copper, silver, zinc, aluminum, tungsten, or molybdenum, and then coated with the above-mentioned components by plating or other methods to provide corrosion resistance. This promotes the removal of gas bubbles, making it less likely that the electrolyte will be unable to reach the electrode surface, promoting the oxidation-reduction reaction and further improving the efficiency of water electrolysis.

[0020] (3) In the above (1) or (2), the magnetic field application mechanism may be a magnet or an electromagnetic coil. Using a magnet eliminates the need for energy to generate a magnetic field, which is advantageous in terms of energy efficiency of the entire device. Using an electromagnetic coil allows the magnitude of the non-uniform magnetic field to be controlled by adjusting the current flowing through it, making it possible to adjust the electric field to any desired level.

[0021] [Details of Embodiments of the Present Disclosure] Specific examples of water electrolysis devices according to the present disclosure will be described below with reference to the drawings. In the drawings, the same reference symbols represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0022] In this specification, the notation in the form of "A to B" means A or more and B or less, and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0023] In the present specification, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is understood to include any conventionally known atomic ratio, and is not necessarily limited to only those within the stoichiometric range.

[0024] In this specification, when one or more numerical values ​​are listed as the lower limit and the upper limit of a numerical range, the combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit is also considered to be disclosed.

[0025] In this specification, "comprises," "includes," "has," and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even a configuration expressed in closed terms may include additional elements that are normally incidental impurities or unrelated to the technology in question.

[0026] [Embodiment 1: Water Electrolysis Apparatus] A water electrolysis apparatus according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") will be described with reference to Fig. 1. As shown in Fig. 1, the water electrolysis apparatus 1 includes a power source 2, an electrolyte solution 3 for water electrolysis containing a water-based magnetic fluid, a pair of electrodes 4 consisting of an anode and a cathode, a magnetic field application mechanism 5 that applies a non-uniform magnetic field to at least one of the pair of electrodes 4, and a container 6 that stores the electrolyte solution 3 for water electrolysis.

[0027] <Water-Based Magnetic Fluid> In the water electrolysis device of embodiment 1, the water-based magnetic fluid contains water, an electrolyte, and magnetic nanoparticles. The water-based magnetic fluid may contain conventionally known components in addition to water, an electrolyte, and magnetic nanoparticles, as long as the effects of the present disclosure are not impaired. For example, the water-based magnetic fluid may contain a surfactant to improve the dispersibility of the magnetic nanoparticles in the water-based magnetic fluid. When the water-based magnetic fluid contains a surfactant, the surfactant is adsorbed to the magnetic nanoparticles. For example, at least one surfactant selected from the group consisting of oleic acid and alkali oleate salts may be used.

[0028] As the electrolyte, a neutral salt or an alkaline salt may be used from the viewpoint of high electrical conductivity and easy disposal. These do not pose a risk of destroying the bond between the magnetic nanoparticles and the surfactant. As the neutral salt, one or both of sodium sulfate and potassium nitrate may be used. As the alkaline salt, potassium hydroxide or sodium hydroxide can be used.

[0029] The magnetic nanoparticles may be at least one selected from the group consisting of metallic iron particles, iron oxide particles, iron carbide, iron nitride, iron sulfide, and iron boride particles. They may contain 50 atomic % or more of iron, with the remaining elements substituted with cobalt, nickel, manganese, zinc, or the like. The saturation magnetic flux density may be 0.2 T or more.

[0030] The average particle size of the magnetic nanoparticles may be 5 nm or more and 50 nm or less, 5 nm or more and 25 nm or less, or 5 nm or more and 15 nm or less.

[0031] In the present disclosure, the average particle size of magnetic nanoparticles refers to the D50 equivalent area diameter of the primary particles of magnetic nanoparticles measured by laser diffraction. The D50 equivalent area diameter of the primary particles of magnetic nanoparticles refers to the D50 equivalent area diameter at which the cumulative number-based frequency of 100 or more magnetic nanoparticles is 50%. The laser diffraction method is performed in accordance with ISO 13320:2020 (JIS Z 8825:2022). The equivalent area diameter is measured in accordance with JIS Z 8827-1:2018. The specific method for measuring the equivalent area diameter of the primary particles of each magnetic nanoparticle is as follows.

[0032] An electrolyte solution for water electrolysis containing a water-based magnetic fluid containing magnetic nanoparticles to be measured is dropped onto a measurement grid and dried to obtain a measurement sample. The measurement sample is observed with a low-voltage transmission electron microscope (LOW-TEM), and an image of the magnetic nanoparticles is acquired. The acceleration voltage during image acquisition is set to 100 kV. The image is captured using a CCD (Charge Coupled Device) camera. The magnification is set to 30,000 to 100,000 times. The LOW-TEM may be an "HT-7500" manufactured by Hitachi, Ltd. The image analysis software used is "ImageJ" (Version 1.54p, February 17, 2025). The length of one side of one pixel in the particle image is set to 1 nm or less.

[0033] In the captured image, areas where magnetic nanoparticles do not overlap are cropped (Image>>Crop, Image>>Duplicate), converted to an 8-bit image (Image>>Type>>8-bit), binarized (Image>>Adjust>>Threshold), and then converted to a binary image (Process>>Binary>>Make Binary). If overlapping areas of magnetic nanoparticles must be used, particle separation and filling are performed as appropriate (Process>>Binary>>Watershed or Fill Holes, etc.). The area of ​​each magnetic nanoparticle is then measured (Analyze>>Analyze particles, measurement target: Area), and the area value is obtained. Based on the area value, the area-equivalent diameter of the primary particle of each magnetic nanoparticle is calculated.

[0034] The area-equivalent diameter of the primary particle diameter of 100 or more magnetic nanoparticles is measured. Based on this result, the area-equivalent diameter D50 at which the cumulative number-based frequency of magnetic nanoparticles reaches 50% is obtained.

[0035] <Electrodes> In the water electrolysis apparatus of embodiment 1, the pair of electrodes is made of a porous metal body. <Structure of porous metal body> The porous metal body has a skeleton made of metal. The skeleton defines a plurality of pores inside the porous metal body. That is, the porous metal body has a plurality of pores.

[0036] <Porosity of Porous Metal Body> The porosity of the porous metal body is 30% or more and 85% or less, and may be 40% or more and 70% or less, or may be 50% or more and 60% or less.

[0037] The porosity of a porous metal body is defined by the following formula 1: Porosity = {1 - [mass of porous metal body [g] / (volume of porous metal body [cm ３ ]×Material density [g / cm ３ ]) )]} × 100 [%] Formula 1 In the above formula 1, the volume [cm ３ ] means the volume including the skeleton and pores.

[0038] <Specific surface area of ​​porous metal body> The specific surface area of ​​the porous metal body is 1.0 × 10 ４ m ２ / m ３ or more, 1.0 × 10 ４ m ２ / m ３ Even if it is more than 1.0 × 10 ４ m ２ / m ３ Above 1.0 x 10 ７ m ２ / m ３ It may be less than 1.0 × 10 ４ m ２ / m ３ Above 1.0 x 10 ５ m ２ / m ３ The following is also acceptable.

[0039] The specific surface area of ​​the porous metal body is measured by a gas adsorption method (JIS Z 8830:2013), using nitrogen gas as the adsorption gas.

[0040] <Transmittance of porous metal body> The transmittance of the porous metal body is 0.6 × 10 －１２ m ２ The upper limit of the transmittance of the porous metal body is 1.0 × 10 －１０ m２ The transmittance of the porous metal body may be 0.6×10 or less. －１２ m ２ Above 1.0 x 10 －１０ m ２ It may be less than 1.0 × 10 －１２ m ２ Above 2.0 x 10 －１１ m ２ or less, or 4.0 × 10 －１２ m ２ Above 1.0 x 10 －１１ m ２ The following is also acceptable.

[0041] The permeability of a porous metal body is obtained by measuring the water permeability of the porous metal body in accordance with JIS R 1671:2006 "Test method for water permeability and hydraulic equivalent diameter of porous fine ceramic bodies." In the present disclosure, the water permeability of a porous metal body corresponds to the permeability of a porous metal body. Specifically, an evaluation sample made of a porous metal body having a diameter of 25 mm and a thickness of 3 mm is prepared, and the water permeability of the evaluation sample is measured based on the above JIS standard. If the porous metal body to be evaluated is smaller than the size of the evaluation sample, the evaluation sample may be prepared by combining multiple porous metal bodies to obtain a diameter of 25 mm and a thickness of 3 mm.

[0042] <Volume resistivity> The volume resistivity of the metal porous body is 3.2 × 10 －７ Ωm or more 6.3 x 10 －６ Ωm or less, and is 1.9 × 10 －６ Ωm or more 3.8 x 10 －６ It may be Ωm or less.

[0043] The volume resistivity of the porous metal body is measured in accordance with JIS H 0505-1975. The porous metal body is processed into a rod shape of 3 mm x 3 mm x 35 mm, and 10 pieces are connected with a 3 mm x 3 mm surface to make a length of 350 mm. Then, pure aluminum foil with a thickness of 0.1 mm is applied to both end surfaces, and a pressure of 1 kg / cm is applied. ２ Voltage measurement terminals and current measurement terminals are connected to both end faces, and then the volume resistivity is calculated using the aluminum foil on both ends as electrodes.

[0044] <Average pore diameter of porous metal body> The average pore diameter of the porous metal body is 5 μm or more and 3000 μm or less, or may be 10 μm or more and 1000 μm or less, or may be 100 μm or more and 300 μm or less. The average pore diameter of the porous metal body is measured by mercury intrusion porosimetry.

[0045] <Material of the Porous Metal Body> The porous metal body is made of a non-magnetic material. The non-magnetic material may be at least one selected from the group consisting of platinum, palladium, iridium, gold, a non-magnetic stainless steel alloy, and a non-magnetic nickel alloy.

[0046] <Method for manufacturing porous metal body> The following describes an example of a method for manufacturing the porous metal body used in the water electrolysis apparatus of embodiment 1. The method for manufacturing the porous metal body of embodiment 1 can include a preparation step, a mixing step, a sintering step, and a cleaning step.

[0047] <Preparation Step> In the preparation step, a raw material powder of the porous metal body and sodium chloride powder (NaCl powder) are prepared.

[0048] The raw material powder may be at least one powder selected from the group consisting of platinum, palladium, iridium, gold, non-magnetic stainless steel alloys, and non-magnetic nickel alloys.

[0049] The particle diameter D10 of the raw material powder may be 6 to 45 μm, the D50 may be 13 to 75 μm, and the D90 may be 27 to 106 μm. The particle diameter D10 of the raw material powder is the particle diameter at which the cumulative volume fraction from the small diameter side is 10% in a histogram where the horizontal axis represents particle diameter and the vertical axis represents volume fraction. The particle diameter D50 of the raw material powder is the particle diameter at which the cumulative volume fraction from the small diameter side is 50% in the histogram. The particle diameter D90 of the raw material powder is the particle diameter at which the cumulative volume fraction from the small diameter side is 90% in the histogram. The D10, D50, and D90 are measured by a laser diffraction / scattering method.

[0050] The particle diameter D50 of the NaCl powder may be 45 to 5000 μm. Here, the particle diameter D50 of the NaCl powder is the particle diameter at which the cumulative volume fraction from the smallest diameter side is 50% in a histogram in which the horizontal axis represents particle diameter and the vertical axis represents volume fraction. The histogram is created based on the results of sieving a sample using a sieve specified in JIS Z 8801-1:2019 "Test sieves - Part 1: Metal mesh sieves" and measuring the mass of the sample remaining on each sieve.

[0051] <Mixing Step> Next, in the mixing step, the raw material powder and NaCl powder are mixed to obtain a mixed powder. The mixing ratio of the raw material powder and NaCl powder can be appropriately adjusted depending on the porosity of the metal porous body to be produced. For example, the percentage of NaCl powder in the mixed powder may be 10% by mass or more and 50% by mass or less.

[0052] The mixed powder is placed in a cylindrical glass container with a diameter of 100 mm and a wall thickness of 1 mm, and mixed for 10 to 30 minutes by rotating it in a rotary mill with the axial direction of the glass container as the rotation axis. A W-type mixer, V-type mixer, or drum mixer may also be used if the raw material powders and NaCl powder can be mixed uniformly. If there is a risk of dust explosion from the mixed powder, the atmosphere inside the glass container may be replaced with a low-oxygen atmosphere or an inert atmosphere.

[0053] <<Forming Step>> Next, in the forming step, the mixed powder is loaded into a mold made of graphite or alloy tool steel for hot working, and pressurized and heated to obtain a compact. The conditions may be 20 to 800°C, a pressure of 10 to 2000 MPa, and a holding time of 1 second to 30 minutes. Before pressurizing and heating, the mixed powder may be preformed to form a powder compact.

[0054] <<Washing Step>> Next, in the washing step, the compact is immersed in water to dissolve NaCl into the water, thereby obtaining a porous metal body. Specifically, approximately 1 L of pure water is prepared for 10 g of the compact. The pure water is placed in a beaker, and the compact is immersed in the pure water and stirred. By immersing for a total of approximately 50 hours, with the pure water being replaced every 5 hours, NaCl is sufficiently dissolved outside the compact.

[0055] <Heat Treatment Step> When the metal porous body has a high porosity or when a metal with a melting point of 1200°C or higher is used as the raw material powder, the metal porous body is further subjected to a heat treatment step. In the heat treatment step, the metal porous body is heat-treated at a temperature of 750°C or higher and lower than the melting point of the raw material powder. This improves the strength of the skeleton of the metal porous body. It also reduces the electrical resistance of the metal porous body.

[0056] The method for producing the porous metal body described above is characterized in that the raw material powder does not form a skeleton by simple sintering and densification, but the raw material powder is pressed into the spaces formed by the NaCl powder by plastic deformation, so that the metal skeleton forms a strong continuum as a whole even if the porosity is high. As a result, it is possible to obtain a porous metal body having a porosity of 30% or more and 85% or less and a specific surface area of ​​1.0 × 10 ４ m ２ / m ３ or more, and the transmittance is 0.6×10 －１２ m ２ or more, and the volume resistivity is 3.2 × 10 －７ Ωm or more 6.3 x 10 －６ This manufacturing method has been discovered by the present inventors and allows the production of a porous metal body having a pore size of 1 μm or more and an average pore size of 3,000 μm or less.

[0057] <Magnetic Field Application Mechanism> In this specification, "magnetic flux density" is referred to as "magnetic field" for simplicity. The water electrolysis apparatus of embodiment 1 includes a magnetic field application mechanism 5 that applies a non-uniform magnetic field to at least one of a pair of electrodes. For example, a magnet or an electromagnetic coil can be used as the magnetic field application mechanism 5. From the viewpoint of feasibility, the magnitude of the non-uniform magnetic field may be 4 T or less. Furthermore, from the viewpoint of economical and efficient application, the magnitude may be 50 mT or more and 350 mT or less.

[0058] The magnetic field application mechanism 5 is disposed at a location where a magnetic field gradient due to a non-uniform magnetic field can be efficiently applied to at least one of the pair of electrodes 4. The magnetic field application mechanism 5 may be disposed at a location where the magnetic field gradient is as large as possible. The magnetic field application mechanism 5 may cause a magnetic field gradient with an absolute value of 0.1 T / m to 100 T / m to exist in at least a portion of the electrode. Here, "at least a portion of the electrode" refers to a region of 10% or more by volume of the electrode, where the total volume of the electrode is 100% by volume. A smaller magnetic field gradient present in the electrode makes it easier to apply a magnetic field gradient over a wider area, which facilitates the release of bubbles from the metal porous body. From this perspective, the magnetic field application mechanism 5 may cause a magnetic field gradient with an absolute value of 0.1 T / m to 30 T / m or a magnetic field gradient with an absolute value of 0.1 T / m to 10 T / m to exist in at least a portion of the electrode.

[0059] The magnetic field application mechanism 5 may be disposed at a position where a magnetic field is applied perpendicular to the surface of the electrode acting on the electrolysis. If the magnetic field application mechanism 5 is corroded by components of the electrolyte, the magnetic field application mechanism 5 may be disposed at a position where it does not come into contact with the electrolyte.

[0060] As shown in FIG. 1, the magnetic field applying mechanism 5 may include a first magnetic field applying mechanism that applies a non-uniform magnetic field to the anode, and a second magnetic field applying mechanism that applies a non-uniform magnetic field to the cathode.

[0061] The magnetic field application mechanism 5 may include a plurality of magnetic field application mechanisms, including at least one first magnetic field application mechanism that applies a non-uniform magnetic field to the anode and at least one second magnetic field application mechanism that applies a non-uniform magnetic field to the cathode. In this case, the magnitude of the non-uniform magnetic field applied by the first magnetic field application mechanism to the anode and the magnitude of the non-uniform magnetic field applied by the first magnetic field application mechanism to the cathode may be the same or different. If the magnitudes are different, water electrolysis can be promoted by making the surface area of ​​the electrode with the smaller non-uniform magnetic field larger than the surface area of ​​the electrode with the larger non-uniform magnetic field.

[0062] The magnetic field application mechanism 5 may include at least one first magnetic field application mechanism that applies a non-uniform magnetic field to the anode, or at least one second magnetic field application mechanism that applies a non-uniform magnetic field to the cathode. That is, the magnetic field application mechanism 5 may apply a non-uniform magnetic field to either the anode or the cathode. In this case, water electrolysis can be promoted by making the surface area of ​​the electrode not subjected to the non-uniform magnetic field larger than the surface area of ​​the electrode subjected to the non-uniform magnetic field.

[0063] <Power Supply> In the water electrolysis apparatus of the first embodiment, a conventionally known power supply can be used as the power supply.

[0064] <Container> In the water electrolysis apparatus of Embodiment 1, the container is not particularly limited as long as it can store the electrolyte solution for water electrolysis, and any conventionally known container can be used.

[0065] <Other Configurations> As shown in FIG. 2 , the water electrolysis apparatus of embodiment 1 may include a power supply element 8 provided in contact with the electrodes and supplying electric power from a power source to the electrodes, and a diaphragm 7 separating the anode and the cathode.

[0066] The material of the power supply body is not particularly limited as long as it is a non-magnetic, alkali-resistant, conductive material. For example, non-magnetic SUS, non-magnetic nickel alloy, copper, or aluminum alloy coated with a conductive, alkali-resistant coating (such as nickel-phosphorus plating) can be used. The power supply body may have a through-hole through which the electrolyte for water electrolysis passes.

[0067] The material of the diaphragm is not particularly limited, and may be any material as long as it has wettability, ion permeability, alkali resistance, non-conductivity, non-air permeability, thermal stability, non-magnetic properties, etc. Examples of such diaphragm materials include acrylic resin, fluororesin impregnated with potassium titanate, polyantimonic acid, polysulfone, hydrophilized polyphenylene sulfide, polyvinylidene fluoride, polytetrafluoroethylene, and Zirfon Perl UTP 500 manufactured by AGFA.

[0068] The water electrolysis apparatus of the first embodiment may include a pump for circulating the electrolyte for water electrolysis, a device for gas-liquid separation of hydrogen gas and oxygen gas in the electrolyte, and the like.

[0069] <Applications> The water electrolysis apparatus of embodiment 1 can be applied to any of alkaline water electrolysis apparatuses, proton exchange membrane water electrolysis apparatuses, and anion exchange membrane water electrolysis apparatuses.

[0070] The water electrolysis device of embodiment 1 can have excellent water electrolysis efficiency, and therefore can be made smaller than conventional water electrolysis devices.

[0071] In the water electrolysis apparatus of the first embodiment, the action of magnetic buoyancy that occurs independently of gravity, as well as the buoyancy caused by gravity, promotes the separation of bubbles from the porous metal body, and therefore the water electrolysis apparatus of the first embodiment can also be applied to water electrolysis apparatuses used in microgravity environments such as outer space.

[0072] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0073] <Production of porous metal body> <Preparation step> A raw material powder and NaCl powder were prepared. The composition, D10, D50, and D90 of the raw material powder are as shown in the "Raw material powder" column of Table 1. The average particle size of the NaCl powder is as shown in the "NaCl powder" column of Table 1.

[0074]

[0075] <Mixing Step> A mixed powder was obtained by mixing the raw material powder and NaCl powder in a ratio such that the amount of each powder in the mixed powder was the mass % shown in the "Mixed Powder" column of Table 2. A rotary mill without media was used for mixing. The mixing conditions (rotation speed, time) were as shown in the "Mixing" column of Table 2.

[0076] The mixed powder was sealed in a graphite mold and heated under pressure to obtain a compact. The conditions for heating and pressurizing (pressure, temperature, and time) were as shown in the "Molding" column in Table 2.

[0077] <<Washing Step>> Next, the molded body was immersed in water to dissolve NaCl into the water, thereby obtaining a porous metal body for each sample.

[0078] <Heat Treatment Step> Next, heat treatment was performed. The heat treatment conditions are as shown in the "Heat Treatment" column of Table 2. The heat treatment was performed in a reduced pressure nitrogen gas atmosphere to prevent the composition of the base material from changing. In all samples, the metal porous body had a plate-like shape. The size of the metal porous body was 30 mm x 30 mm x 10 mm.

[0079]

[0080] <Evaluation of Metal Porous Body> The composition, porosity, specific surface area, transmittance, volume resistivity, and average pore diameter of each sample of metal porous body were measured. The measurement methods for each item were as described in embodiment 1. The results are shown in Table 3. In all samples, the metal porous body was made of a non-magnetic stainless steel alloy (SUS316L).

[0081]

[0082] <Evaluation of Water Electrolysis Device> The porous metal body of each sample was processed to obtain two 10 mm x 10 mm x 10 mm cubes. These were used as a pair of electrodes to fabricate a water electrolysis device, and the water electrolysis efficiency was evaluated. The configuration of the water electrolysis device is as shown in FIG. 1 . The water electrolysis device 1 includes a power source 2, an electrolyte solution 3 for water electrolysis containing a water-based magnetic fluid, a pair of electrodes 4, a magnetic field application mechanism 5, a container 6, a diaphragm 7, and a power supply 8. In Sample 1-1, the carbon spongy electrode (Soft Felt GF-20-10F manufactured by Nippon Carbon Co., Ltd.) used in Example 15 of Patent Document 1 was used as the electrode 4. Sample 1-1 corresponds to a conventional example.

[0083] The current feeder 8 was made of SUS304 plate material. The container 6 was made of acrylic resin, combining 5 mm thick sheets of acrylic resin. The container had outer dimensions of 50 mm x 50 mm x 80 mm and inner dimensions of 40 mm x 40 mm, with only the top part open. The diaphragm 7 was made of acrylic resin, and the fastening screws and nuts were made of polycarbonate resin. The magnetic field application mechanism 5 used an anisotropic neodymium sintered magnet (40 mm x 40 mm x 15 mm, magnetized perpendicular to the plate surface, surface magnetic flux 300 mT).

[0084] Each sample was placed on both the anode and cathode, and the water electrolysis device was operated at an applied voltage of 2.0 V. The current value per unit area (unit: mA / cm ２ The average values ​​for 120 seconds after the start of operation of the electrolytic cell are shown in Table 3. A larger current value per unit area indicates a more efficient water electrolysis.

[0085] <Discussion> The water electrolysis devices of Samples 1 to 5 correspond to Examples. The water electrolysis devices of Samples 1-1 to 1-5 correspond to Comparative Examples. It was confirmed that the water electrolysis devices of Samples 1 to 5 had a larger current value per unit area than the water electrolysis devices of Samples 1-1 to 1-5, and thus had improved water electrolysis efficiency.

[0086] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0087] 1 Water electrolysis device, 2 Power supply, 3 Electrolyte for water electrolysis, 4 Electrode, 5 Magnetic field application mechanism, 6 Container, 7 Diaphragm, 8 Power supply, B1 Buoyancy, B2 Magnetic buoyancy.

Claims

1. A water electrolysis device comprising: a power source; an electrolyte solution for water electrolysis containing a water-based magnetic fluid; a pair of electrodes consisting of an anode and a cathode; a magnetic field application mechanism that applies a non-uniform magnetic field to at least one of the pair of electrodes; and a container for storing the electrolyte solution for water electrolysis, wherein the water-based magnetic fluid contains water, an electrolyte, and magnetic nanoparticles; the pair of electrodes are made of a porous metal body; the porosity of the porous metal body is 30% or more and 85% or less; and the specific surface area of ​​the porous metal body is 1.0 x 10 ４ m ２ / m ３ or more, and the transmittance of the porous metal body is 0.6×10 －１２ m ２ or more, and the volume resistivity of the porous metal body is 3.2×10 －７ Ωm or more 6.3 x 10 －６ a water electrolysis device, wherein the porous metal body has a pore size of 1 μm or more and 3000 μm or less, and the porous metal body is made of a non-magnetic material.

2. The water electrolysis apparatus according to claim 1, wherein the non-magnetic material is at least one selected from the group consisting of platinum, palladium, iridium, gold, non-magnetic stainless steel alloys, and non-magnetic nickel alloys.

3. The water electrolysis device according to claim 1 or 2, wherein the magnetic field application mechanism is a magnet or an electromagnetic coil.

Images