Method for manufacturing diamond electrode, diamond electrode, electrolytic treatment apparatus, and ozone generator

Abstract

To provide a method for manufacturing a diamond electrode which efficiently forms a conductive diamond layer on base materials having various shapes and sizes, and can manufacture a diamond electrode, a diamond electrode capable of being manufactured by the manufacturing method, and an electrolytic treatment apparatus and an ozone generator which include the diamond electrode.SOLUTION: A method for manufacturing a diamond electrode includes a step of applying an electric field to suspension liquid containing conductive diamond particles and migrating the conductive diamond particles, and accumulating the conductive diamond particles on a base material arranged in the suspension liquid and forming a conductive diamond layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a diamond electrode, a diamond electrode, an electrolytic treatment device, and an ozone generation device. [Background technology]

[0002] Diamond electrodes have excellent properties such as a wide potential window, high oxygen overvoltage, physical and chemical stability, and low background current, and are therefore increasingly being used in a wide range of fields, including the production of sterilized water, wastewater treatment, and electrochemical sensors.

[0003] A commonly known method for manufacturing diamond electrodes is to form a conductive diamond layer on a substrate by chemical vapor deposition (CVD). Another method has been proposed in which a conductive coating agent containing conductive diamond powder and a coating agent such as polysilazane is applied to a substrate by screening printing or spraying to form a conductive layer containing conductive diamond powder (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-199478 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when forming a conductive diamond layer by the CVD method, there are limitations on the material, shape, and size of the applicable substrate, making it difficult to form a three-dimensional conductive diamond layer. In this regard, the method described in Patent Document 1 makes it possible to form a conductive layer on substrates of various shapes and sizes. However, the method described in Patent Document 1 has the problem that the conductive layer contains a relatively large amount of coating agent, which prevents contact between the conductive diamond powders and reduces conductivity. In addition, the method described in Patent Document 1 forms the conductive layer by screening printing or spraying, which causes a problem of large material loss.

[0006] Therefore, an object of the present invention is to provide a method for manufacturing a diamond electrode that can efficiently form a conductive diamond layer on substrates of various shapes and sizes and manufacture a diamond electrode, a diamond electrode that can be manufactured by this manufacturing method, and an electrolytic treatment device and an ozone generation device that are equipped with this diamond electrode. [Means for solving the problem]

[0007] Specific means for solving the above problems include the following embodiments. <1> A method for manufacturing a diamond electrode, comprising a conductive diamond layer forming step of applying an electric field to a suspension containing conductive diamond particles to cause the conductive diamond particles to migrate, and depositing the conductive diamond particles on a substrate placed in the suspension to form a conductive diamond layer. <2> The method further comprises, before the conductive diamond layer forming step, forming an underlayer on the substrate, the underlayer containing at least one selected from the group consisting of platinum, metal oxides, and semi-metal oxides. <1> A method for manufacturing a diamond electrode according to claim 1. <3> a support layer forming step of forming a support layer containing at least one selected from a metal oxide and a semi-metal oxide between the conductive diamond particles of the conductive diamond layer after the conductive diamond layer forming step; <1> or <2> A method for manufacturing a diamond electrode according to claim 1. <4> The suspension further contains a binder resin. <1> ~ <3> 10. A method for producing a diamond electrode according to claim 9.

[0008] <5> A diamond electrode having a substrate, an underlayer formed on the substrate and containing at least one selected from the group consisting of platinum, metal oxides, and semi-metal oxides, and a conductive diamond layer formed on the underlayer, which is a deposited layer of conductive diamond particles. <6> The conductive diamond layer further comprises a support layer formed between the conductive diamond particles and containing at least one selected from a metal oxide and a semi-metal oxide. <5> The diamond electrode according to claim 1. <7> an electrolytic cell; <5> or <6> An electrolytic treatment apparatus comprising an anode which is the diamond electrode according to claim 1 and a cathode. <8> an electrolytic cell; <5> or <6> An ozone generating device comprising an anode which is the diamond electrode according to claim 1 and a cathode. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for manufacturing a diamond electrode that can efficiently form a conductive diamond layer on substrates of various shapes and sizes and manufacture a diamond electrode, a diamond electrode that can be manufactured by the manufacturing method, and an electrolytic treatment device and an ozone generation device that are equipped with the diamond electrode. [Brief explanation of the drawings]

[0010] [Figure 1] 1A and 1B are diagrams illustrating an example of a method for forming a conductive diamond layer on a substrate by electrophoretic deposition. [Figure 2] 10A and 10B are diagrams showing another example of a method for forming a conductive diamond layer on a substrate by electrophoretic deposition. [Figure 3] FIG. 1 is a diagram showing a schematic example of a layer structure of a diamond electrode. [Figure 4] FIG. 1 is a diagram showing an example of a schematic configuration of an ozone generator equipped with a diamond electrode. [Figure 5] FIG. 10 is a diagram showing the relationship between the film thickness of the underlayer and the change in electrolysis voltage during electrolysis. DETAILED DESCRIPTION OF THE INVENTION

[0011] Specific embodiments to which the present invention is applied will be described below. In this specification, unless otherwise specified, the expression "x to y" using numerical values ​​x and y means "greater than or equal to x and less than or equal to y." In such expressions, when a unit is assigned only to the numerical value y, the unit is also applied to the numerical value x.

[0012] <Diamond electrode manufacturing method> The method for manufacturing a diamond electrode according to this embodiment includes a conductive diamond layer forming step of applying an electric field to a suspension containing conductive diamond particles to cause the conductive diamond particles to migrate, and depositing the conductive diamond particles on a substrate placed in the suspension to form a conductive diamond layer. Below, essential or optional steps included in the method for manufacturing a diamond electrode according to this embodiment will be described.

[0013] [Conductive diamond layer formation process] In the conductive diamond layer forming process, an electric field is applied to a suspension containing conductive diamond particles to cause the conductive diamond particles to migrate, and the conductive diamond particles are deposited on a substrate placed in the suspension to form a conductive diamond layer. That is, in the conductive diamond layer forming process, a conductive diamond layer is formed on the substrate by electrophoretic deposition (EPD). According to the electrophoretic deposition method, the conductive diamond particles can be reliably contacted with each other, so that a conductive diamond layer with excellent conductivity can be formed.

[0014] (base material) The substrate is preferably one having excellent corrosion resistance. Examples of the substrate material include metals such as titanium, tantalum, niobium, zirconium, and platinum; semiconductors such as silicon; and ceramics. The substrate may be a composite substrate made up of multiple substrates made of different materials.

[0015] The shape of the substrate is not particularly limited, and may be planar or may have a special three-dimensional shape such as a curved shape, a cylindrical shape, a stepped shape, a spiral shape, etc. The planar substrate may have a flat main surface, or the main surface may have irregularities, grooves, etc. Furthermore, the substrate may be porous, and a plurality of through-holes may be formed in the main surface of the substrate.

[0016] When the diamond electrode is used as the anode of the ozone generator described later, the substrate is preferably a porous planar substrate or a planar substrate having a plurality of through-holes.The porous planar substrate can be, for example, a metal nonwoven fabric obtained by sintering metal fibers.In addition, the planar substrate having a plurality of through-holes can be, for example, a metal substrate such as a metal mesh, expanded metal, rolled lath, punched metal, etc.

[0017] The substrate may be roughened by a known method such as blasting or etching in order to enhance adhesion to a layer formed on the substrate.

[0018] (Conductive diamond particles) As the conductive diamond, diamond that is doped with an element of group 13 or group 15 to give conductivity can be mentioned.The conductivity of conductive diamond particles is, for example, 0.01S / cm or more.As the element of group 13 or group 15, for example, boron, nitrogen, phosphorus etc. can be mentioned.Among conductive diamond particles, boron-doped diamond particles (BDDP) that are doped with boron are preferred because of their low electrical resistance.

[0019] The method for producing BDDP is not particularly limited, and known production methods such as those described in Japanese Patent Application Laid-Open No. 2008-36631 and Japanese Patent Application Laid-Open No. 2018-76216 can be used. A preferred production method is to form a boron-doped diamond layer (BDD layer) on the surface of a particulate substrate. This production method will be described below.

[0020] The particulate substrate is not particularly limited as long as it does not melt or deform during the formation of the BDD layer, and can be appropriately selected according to the purpose.The particulate substrate can be, for example, natural or artificial diamond particles; silicon particles; metal particles such as molybdenum particles; metal oxide particles such as alumina particles; boron nitride particles, quartz particles; etc.Among these, natural or artificial diamond particles are preferred.

[0021] The method for forming the BDD layer is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method for forming the BDD layer include CVD methods such as microwave plasma CVD and hot filament CVD; physical vapor deposition (PVD) methods such as ion beam deposition and ionization deposition; and high-temperature and high-pressure methods. Among these, microwave plasma CVD is preferred.

[0022] In the CVD method described above, the carbon and boron sources used as raw materials for the BDD layer are not particularly limited. Examples of carbon sources include aliphatic hydrocarbons such as methane, ethane, propane, butane, pentane, hexane, heptane, and octane; alicyclic hydrocarbons such as cyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; alcohols such as methanol, ethanol, isopropyl alcohol, and butanol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ethers such as diethyl ether, dimethoxyethane, tetrahydrofuran, and dioxane; and esters such as methyl acetate, ethyl acetate, isopropyl acetate, and butyl acetate. Examples of boron sources include boron oxide, boron carbide, boron nitride, boric acid, diborane, triethylborane, trimethoxyborane, triethoxyborane, tripropoxyborane, and tri(1,1-dimethylethoxy)borane.

[0023] In the BDD layer, the number of boron atoms doped into the diamond is preferably 10 to 100,000 ppm, more preferably 100 to 50,000 ppm, and even more preferably 1,000 to 30,000 ppm, relative to the number of carbon atoms constituting the diamond.

[0024] The shape of the conductive diamond particles is not particularly limited, and examples thereof include spherical, polyhedral, needle-like, and spindle-like shapes.

[0025] The average particle size of the conductive diamond particles is preferably 5 to 10,000 nm, more preferably 100 to 1,000 nm, and even more preferably 200 to 500 nm. The average particle size of the conductive diamond particles is the volume average particle size measured by dynamic light scattering (DLS).

[0026] The conductive diamond particles may be surface-treated with a silane coupling agent or a silicone oligomer, as needed, which tends to improve dispersibility in the suspension.

[0027] Examples of silane coupling agents include vinyltriethoxysilane, vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane.

[0028] Examples of silicone oligomers include silicone alkoxy oligomers having at least one alkoxy group selected from a methoxy group and an ethoxy group. The silicone alkoxy oligomer may have at least one organic substituent selected from the group consisting of an epoxy group, a methyl group, a mercapto group, an acryloyl group, a methacryloyl group, a vinyl group, and a phenyl group. Commercially available silicone alkoxy oligomers include KR-516, KR-517, KR-518, KR-519, and X-24-9590 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0029] The surface treatment method using silane coupling agent or silicone oligomer is not particularly limited, and any method can be adopted.One example is a method in which conductive diamond particles and silane coupling agent or silicone oligomer are added to an alcohol-based solvent, and then mixed by ultrasonic homogenizer or the like to perform surface treatment, and then the conductive diamond particles after surface treatment are taken out by centrifugation, decantation or the like.

[0030] Furthermore, the conductive diamond particles may be surface-treated with a binder resin as required. By surface-treating with a binder resin, the conductive diamond particles tend to have improved shape retention when they are electrophoresed and deposited on a substrate.

[0031] Examples of binder resins include vinyl resins such as polyvinyl alcohol, polyvinyl butyral, and polyvinylpyrrolidone; fluorine-based resins such as polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and polytetrafluoroethylene (PTFE); hydrocarbon resins such as polyethylene, polypropylene, styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber (HSBR), butylene rubber, acrylonitrile-butadiene rubber, polybutadiene, and polyisoprene; acrylic resins, styrene resins, amide resins, imide resins, urethane resins, urea resins, polyester resins, polyether resins, phenolic resins, epoxy resins, polycarbonate resins, and silicone resins. Among these, polyvinyl butyral and / or polyvinylpyrrolidone are preferred from the viewpoint of migration properties after surface treatment.

[0032] The mass average molecular weight of the binder resin is 1.0 x 10 3 ~5.0×10 7 Preferably, it is 1.0 × 10 4 ~5.0×10 6 More preferably, it is 1.0 × 10 5 ~1.0×10 6It is more preferable that the weight average molecular weight of the binder resin is: The weight average molecular weight of the binder resin can be measured as a polystyrene-equivalent molecular weight using gel permeation chromatography (GPC).

[0033] The surface treatment method using the binder resin is not particularly limited, and any method can be adopted. One example is a method in which conductive diamond particles and a binder resin are added to an alcohol-based solvent, mixed using an ultrasonic homogenizer or the like to perform surface treatment, and then the surface-treated conductive diamond particles are removed by centrifugation, decantation, or the like.

[0034] (suspension) The solvent of the suspension can be any solvent used in electrophoretic deposition without any particular limitation.One example is acetone with iodine added.When conductive diamond particles are dispersed in acetone with iodine added, the protons generated by the iodine addition reaction to acetone are adsorbed on the surface of the conductive diamond particles, and as a result, the conductive diamond particles are positively charged.

[0035] There are no particular restrictions on the content of conductive diamond particles in the suspension, and the content of conductive diamond particles may be, for example, 0.01 to 100 mg / mL, or 0.1 to 10 mg / mL.

[0036] Instead of treating the surface of the conductive diamond particles with a binder resin, a binder resin may be added to the suspension.

[0037] (Method for forming a conductive diamond layer) As described above, by applying an electric field to a suspension containing conductive diamond particles to cause the conductive diamond particles to migrate, the conductive diamond particles can be deposited on a substrate placed in the suspension to form a conductive diamond layer.

[0038] For example, as shown in Fig. 1, a suspension 50 is placed in a cell 40, and an anode 20 and a substrate 10 serving as a cathode are immersed in the suspension 50. When a DC voltage is applied between the anode 20 and the substrate 10, the positively charged conductive diamond particles migrate toward the substrate 10 and are deposited on the surface of the substrate 10. As a result, a conductive diamond layer 12 can be formed on one main surface of the substrate 10.

[0039] 1 shows an example in which a conductive diamond layer is formed only on one main surface of the substrate, but the present invention is not limited to this example. By appropriately selecting the shapes of the substrate and electrodes, the arrangement of the electrodes, etc., it is also possible to form a conductive diamond layer on the entire surface of the substrate.

[0040] For example, as shown in Fig. 2, a suspension 50 is placed in a cell 40, and anodes 20, 30 and a substrate 10 serving as a cathode are immersed in the suspension 50. When a DC voltage is applied between the anodes 20, 30 and the substrate 10, the positively charged conductive diamond particles migrate toward the substrate 10 and are deposited on the surface of the substrate 10. As a result, a conductive diamond layer 12 can be formed on both main surfaces of the substrate 10.

[0041] The voltage applied when forming the conductive diamond layer is preferably, for example, 10 to 200 V. The voltage application time can be set appropriately depending on the applied voltage, etc., and is preferably, for example, 0.6 to 60 minutes.

[0042] The deposition amount of the conductive diamond layer is 0.1 to 100 mg / cm 2 is preferably 0.1 to 10 mg / cm 2 It is more preferable that:

[0043] [Underlying layer formation process] The manufacturing method of the diamond electrode according to this embodiment may further comprise a base layer forming step, which comprises at least one selected from the group consisting of platinum, metal oxide and semi-metal oxide, on the substrate before the conductive diamond layer forming step.By forming such a base layer, the oxidation of the substrate is suppressed, and the durability (withstand current density) of the diamond electrode tends to be improved.In addition, when the manufacturing method of the diamond electrode according to this embodiment comprises a base layer forming step, the substrate on which the base layer is formed is used in the above-mentioned conductive diamond layer forming step.

[0044] Examples of metal oxides and metalloid oxides contained in the underlayer include oxides of Group 4 elements (Ti, Zr, Hf) of the periodic table, oxides of Group 5 elements (V, Nb, Ta), oxides of Group 6 elements (Mo), oxides of Group 7 elements (Mn), oxides of Group 13 elements (Al), oxides of Group 14 elements (Si, Ge, Sn, Pb), and oxides of Group 15 elements (As, Sb, Bi). Among these, oxides of Group 4 elements, Group 5 elements, Group 13 elements, and Group 14 elements are preferred from the viewpoint of electrical conductivity.

[0045] The underlayer can be formed by applying a composition for forming an underlayer, which contains at least one compound selected from the group consisting of a platinum compound, a metal oxide precursor, and a semi-metal oxide precursor, and a solvent, to a substrate, and then baking the composition. The composition for forming an underlayer may further contain other components such as an acid and a surfactant.

[0046] The platinum compound is not particularly limited as long as it can produce platinum after calcination, and examples thereof include platinum chloride, platinum complexes, etc. The metal oxide precursor and the semi-metal oxide precursor are not particularly limited as long as it can produce a metal oxide or semi-metal oxide after calcination, and examples thereof include metal or semi-metal chlorides, etc.

[0047] The total content of the platinum compound, metal oxide precursor, and semi-metal oxide precursor in the undercoat layer-forming composition is preferably 0.01 to 1 mol / L, and more preferably 0.1 to 0.7 mol / L.

[0048] Examples of the solvent include alcoholic solvents such as methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, polyethylene glycol, glycerin, 1,4-butanediol, 1,6-hexanediol, cyclohexanediol, sorbitol, and xylitol; water; and the like.

[0049] The method for applying the undercoat layer-forming composition is not particularly limited and may be appropriately selected depending on the shape of the substrate. Examples of the application method include dip coating and spray coating.

[0050] After the base layer-forming composition is applied, the substrate is dried and fired. The firing temperature is preferably 400 to 800° C. The firing time is preferably 1 to 10 hours.

[0051] The application and baking of the undercoat layer-forming composition may be repeated multiple times until an undercoat layer having a desired thickness is obtained. The thickness of the undercoat layer is preferably 0.01 to 10 μm, and more preferably 0.1 to 1 μm.

[0052] [Holding layer formation process] The method for manufacturing a diamond electrode according to this embodiment may further comprise, after the conductive diamond layer forming step, a retaining layer forming step, which comprises at least one selected from metal oxide and semi-metal oxide between the conductive diamond particles of the conductive diamond layer.By forming such a retaining layer, the durability (withstand current density) of the diamond electrode tends to be improved.In addition, when the diamond electrode is used as the anode of the ozone generating device described later, by forming a retaining layer, water is prevented from penetrating deep into the conductive diamond layer, so that gas is generated inside the conductive diamond layer during electrolysis, which can prevent the conductive diamond layer from being destroyed.

[0053] Examples of the metal oxides and semi-metal oxides contained in the retention layer include oxides of Group 4 elements (Ti, Zr, Hf) of the periodic table, oxides of Group 5 elements (V, Nb, Ta), oxides of Group 13 elements (Al), etc. Among these, metal oxides with lower conductivity than the conductive diamond particles are preferred, and oxides of titanium, tantalum, etc. are more preferred.

[0054] The retention layer can be formed by impregnating the conductive diamond layer with a retention layer-forming composition containing at least one selected from a metal oxide precursor and a semi-metal oxide precursor, and a solvent, and then firing the composition. The retention layer-forming composition may further contain other components such as an acid and a surfactant.

[0055] The metal oxide precursor and the semi-metal oxide precursor are not particularly limited as long as they can produce a metal oxide or semi-metal oxide after firing, and examples thereof include chlorides of metals or semi-metals.

[0056] The total content of the metal oxide precursor and the semi-metal oxide precursor in the composition for forming a support layer is preferably 0.01 to 1 mol / L, and more preferably 0.1 to 0.7 mol / L.

[0057] Examples of the solvent include alcoholic solvents such as methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, polyethylene glycol, glycerin, 1,4-butanediol, 1,6-hexanediol, cyclohexanediol, sorbitol, and xylitol; water; and the like.

[0058] The method of impregnation with the retention layer-forming composition is not particularly limited. For example, the substrate on which the conductive diamond layer has been formed is immersed in the retention layer-forming composition, degassed by reducing the pressure, and then pressurized, thereby allowing the retention layer-forming composition to be impregnated into the conductive diamond layer. The pressure for the pressurization treatment is preferably 0.1 to 300 MPa. The pressurization treatment time is preferably 0.5 to 24 hours.

[0059] After being impregnated with the support layer-forming composition, the material is dried and fired. The firing temperature is preferably 300 to 500° C. The firing time is preferably 0.5 to 10 hours.

[0060] After the impregnation with the retention layer-forming composition and before firing, a pressure treatment using a hot press or the like may be carried out, if necessary. Such a pressure treatment tends to reduce the electrical resistance of the conductive diamond layer.

[0061] <Diamond electrode> The diamond electrode of this embodiment has a substrate and a conductive diamond layer, which is the deposited layer of conductive diamond particles, formed on the substrate, and can be manufactured by the above-mentioned manufacturing method.The diamond electrode of this embodiment can further have a base layer between the substrate and the conductive diamond layer, which comprises at least one selected from platinum and metal oxide.In addition, the diamond electrode of this embodiment can further have a support layer, which comprises metal oxide, formed between the conductive diamond particles of the conductive diamond layer.

[0062] An example of the layer structure of the diamond electrode according to this embodiment is shown schematically in Figure 3. The diamond electrode 1 shown in Figure 3 has a substrate 10, a foundation layer 11, a conductive diamond layer 12, and a retaining layer 13. In the diamond electrode 1, excellent conductivity is achieved by ensuring contact between the conductive diamond particles in the conductive diamond layer 12. Furthermore, the retaining layer 13 fills the gaps between the particles in the conductive diamond layer 12 to firmly hold the conductive diamond particles, thereby achieving excellent durability (withstand current density).

[0063] Although Figure 3 shows an example in which the base layer, conductive diamond layer, and retention layer are present only on one main surface of the substrate, the present invention is not limited to this example, and the base layer, conductive diamond layer, and retention layer may be present over the entire surface of the substrate.

[0064] The diamond electrode according to this embodiment can be used for various purposes without any particular limitation. For example, the diamond electrode according to this embodiment can be suitably used in electrolytic processing equipment, electrochemical sensors, etc.

[0065] <Electrolytic treatment equipment and ozone generation equipment> The electrolytic treatment device according to this embodiment includes an electrolytic cell, an anode which is the diamond electrode according to this embodiment, and a cathode. The electrolytic treatment device according to this embodiment can be, for example, an ozone generator that generates ozone (ozone water) by electrolysis of water. The ozone generator is preferably a so-called zero-gap cell in which the anode and the cathode are closely attached to a solid polymer electrolyte membrane.

[0066] FIG. 4 shows an example of the schematic configuration of an ozone generator equipped with a diamond electrode according to this embodiment. The ozone generator 100 shown in FIG. 4 includes an anode 110, a cathode 120, a solid polymer electrolyte membrane 130, and an electrolytic cell 140. The anode 110 is in close contact with one surface of the solid polymer electrolyte membrane 130, and the cathode 120 is in close contact with the other surface of the solid polymer electrolyte membrane 130. The electrolytic cell 140 is separated by the solid polymer electrolyte membrane 130 into an anode chamber 140a and a cathode chamber 140b. The anode chamber 140a has a supply port 141a and an outlet 142a. The cathode chamber 140b has a supply port 141b and an outlet 142b.

[0067] The anode 110 may be, for example, a porous planar metal substrate or a planar metal substrate having a plurality of through-holes on which a conductive diamond layer is formed, such as the diamond electrode according to this embodiment. The cathode 120 may be, for example, a porous planar metal substrate or a planar metal substrate having a plurality of through-holes. The solid polymer electrolyte membrane 130 may be, for example, a perfluorosulfonic acid cation exchange membrane.

[0068] In the ozone generator 100, when pure water is supplied from the supply ports 141a and 141b while a DC voltage is applied between the anode 110 and the cathode 120, ozone water is discharged from the outlet 142a of the anode chamber 140a, and hydrogen water is discharged from the outlet 142b of the cathode chamber 140b. [Example]

[0069] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0070] <Experimental Example 1: Production of conductive diamond particles (BDDP)> Diamond particles with a particle diameter of 50 to 500 nm were used as the particulate substrate. First, impurities contained in the diamond particles (Co, Fe, various sp 2To remove impurities (e.g., carbon), the diamond particles were cleaned according to a previously reported method. Specifically, the diamond particles were immersed in aqua regia (a 3:1 volume mixture of hydrochloric acid and nitric acid) and heated at 60°C for 30 minutes, followed by immersion in 30% hydrogen peroxide and heating at 60°C for 30 minutes. The particles were then washed sequentially with ultrapure water, 2-propanol, and acetone, and dried in a heating furnace. Approximately 0.8 g of the cleaned diamond particles were then weighed and subjected to microwave plasma CVD to form a BDD layer on the diamond particle surface, yielding conductive diamond particles (BDDP). The deposition conditions were microwave power: 1300 W, stage temperature: 800°C, chamber pressure: 50 Torr, deposition time: 8 hours, and boron concentration: 20,000 ppm.

[0071] <Experimental Example 2: Examination of the effect of the base layer> After degreasing a Ti plate (1 cm × 5 cm) as the substrate, it was immersed in a first etching solution (DAIN TIA, manufactured by Daiwa Chemical Industries, Ltd.) at 25°C for 1 minute, and then in a fine etching solution (DAIN TIB-SL, manufactured by Daiwa Chemical Industries, Ltd.) at 25°C for 10 minutes, thereby performing a surface roughening treatment.

[0072] In addition, an ethanol solution (2.00 mL) containing 1 M SnCl4·2H2O, an ethanol solution (0.408 mL) containing 0.1 M SbCl3, diethylene glycol (5.0 mL), 35% hydrochloric acid (1.3 mL), and purified water (1.3 mL) were mixed to prepare a composition for forming an undercoat layer.

[0073] The substrate after the surface roughening treatment was immersed in the composition for forming an undercoat layer and withdrawn at a rate of 1 cm / min to coat the composition for forming an undercoat layer on the substrate. After drying at room temperature for 60 minutes, the substrate was baked at 100°C for 3 hours, then at 250°C for 3 hours, and then at 600°C for 3 hours. The application and baking of the composition for forming an undercoat layer was repeated 5, 10, or 15 times to obtain a substrate on which an undercoat layer was formed. The thickness of the undercoat layer was measured by X-ray fluorescence analysis. The thickness was 0.05 μm after 5 coatings, 0.10 μm after 10 coatings, and 0.14 μm after 15 coatings, indicating that the thickness of the undercoat layer increased with the number of coatings.

[0074] The substrate with the underlayer formed thereon was used as the anode, and the platinum-plated Ti flat plate was used as the cathode. Both electrodes were placed inside a 12 mL glass cell (Azlabo Glass Cell G-106, manufactured by AS ONE Corporation) to prepare an electrolytic cell (distance between electrodes: 3 cm). Then, using the prepared electrolytic cell, electrolysis was carried out under the following conditions. Electrolyte: 0.1M Na2SO4 aqueous solution Electrolytic current: 30mA (Max DC48V) Electrolysis area: 2cm 2 (1cm x 2cm) Current density: 0.015A / cm 2 Electrolysis time: 180min

[0075] The change in electrolysis voltage during electrolysis is shown in Figure 5. As shown in Figure 5, when the thickness of the underlayer was 0.10 μm or more, the increase in electrolysis voltage due to electrolysis was small, and oxidation of the substrate due to electrolysis was suppressed. From this result, it is thought that the thickness of the underlayer should preferably be 0.1 μm or more.

[0076] <Experimental Example 3: Manufacturing of diamond electrodes> (Formation of base layer) After degreasing a Ti plate (1 cm × 5 cm) as the substrate, it was immersed in a first etching solution (DAIN TIA, manufactured by Daiwa Chemical Industries, Ltd.) at 25°C for 1 minute, and then in a fine etching solution (DAIN TIB-SL, manufactured by Daiwa Chemical Industries, Ltd.) at 25°C for 10 minutes, thereby performing a surface roughening treatment.

[0077] In addition, an ethanol solution (2.00 mL) containing 1 M SnCl4·2H2O, an ethanol solution (0.408 mL) containing 0.1 M SbCl3, diethylene glycol (5.0 mL), 35% hydrochloric acid (1.3 mL), and purified water (1.3 mL) were mixed to prepare a composition for forming an undercoat layer.

[0078] The substrate after the surface roughening treatment was immersed in the composition for forming an undercoat layer and pulled up at a rate of 1 cm / min to apply the composition for forming an undercoat layer to the substrate. After drying at room temperature for 60 minutes, the substrate was baked at 100°C for 3 hours, then at 250°C for 3 hours, and then at 600°C for 3 hours. The application of the composition for forming an undercoat layer and the baking were repeated a total of five times to obtain a substrate on which an undercoat layer was formed.

[0079] (Formation of a conductive diamond layer) The conductive diamond particles produced in Experimental Example 1 were pretreated as follows. The conductive diamond particles (3 mg) produced in Experimental Example 1 were placed in a container, and silicone oligomer (KR-516, manufactured by Shin-Etsu Chemical Co., Ltd.) (0.2 mL) was added. Isoflurane was then added to adjust the total volume to 3 mL. The mixture was then stirred using an ultrasonic homogenizer, centrifuged, and decanted to obtain conductive diamond particles surface-treated with silicone oligomer. Next, an isopropanol solution (3 mL) containing 0.5% polyvinylpyrrolidone (mass average molecular weight: approximately 40,000) and 0.5% polyvinyl butyral (mass average molecular weight: approximately 50,000) was added to the container. The mixture was then stirred using an ultrasonic homogenizer and centrifuged to obtain conductive diamond particles surface-treated with binder resin.

[0080] A 12 mL glass cell (Azlabo Glass Cell G-106, AS ONE Corporation) was charged with 3 mg of pretreated conductive diamond particles, 30 μL of 0.1 M nitric acid solution, and 200 μL of acetone containing 1% iodine. The total volume was adjusted to 10 mL with acetone, and the mixture was stirred with an ultrasonic homogenizer to prepare a suspension. The substrate with the underlayer formed on it served as the cathode, and the IrO2 / Ti was used as the anode. The substrate was immersed in the suspension (electrode distance: 3 cm). A voltage of 200 V was applied for 20 minutes, causing the conductive diamond particles to migrate toward the cathode, forming a conductive diamond layer on the underlayer.

[0081] (Formation of retention layer) An ethanol solution (6 mL) containing 0.73 M TiCl4, 35% hydrochloric acid (2 mL), and diethylene glycol (2 mL) were mixed to prepare a composition for forming a retention layer.

[0082] The substrate on which the conductive diamond layer was formed was immersed in the composition for forming a retaining layer and pressurized at 0.55 MPa for approximately 12 hours, thereby impregnating the conductive diamond layer with the composition for forming a retaining layer. After drying at 100°C for 3 hours, it was fired at 400°C for 4 hours to obtain a diamond electrode on which a retaining layer was formed.

[0083] <Experimental Example 4: Ozone generation using an electrolytic cell equipped with diamond electrodes> The diamond electrode prepared in Experimental Example 3 was used as the anode, and the Ti lath plate was used as the cathode. A solid polymer electrolyte membrane (Nafion N-117, manufactured by DuPont) was sandwiched between the anode and cathode and placed inside a lidded water tank (W 70 mm × D 35 mm × H 45 mm) with a supply port and a discharge port formed therein to prepare an electrolysis cell. To apply electricity to the electrode, a terminal was exposed from a hole formed in the water tank, and the gap between the terminal and the hole was sealed with an O-ring. Then, using the prepared electrolysis cell, electrolysis was carried out under the following conditions. The amount of ozone generated by the electrolysis and the current efficiency are shown in Table 1 below. Electrolyte: Purified water Electrolytic current: 30mA (Max DC48V) Electrolysis area: 2cm 2 (1cm x 2cm) Current density: 0.15A / cm 2 Electrolysis time: 60min x 3 times (total 180min)

[0084] [Table 1]

[0085] As shown in Table 1, the electrolytic cell equipped with diamond electrodes formed by electrophoretic deposition was able to generate ozone stably for 180 minutes. [Explanation of symbols]

[0086] 1 diamond electrode, 10 substrate, 11 underlayer, 12 conductive diamond layer, 13 support layer, 20, 30 anode, 40 cell, 50 suspension, 100 ozone generator, 110 anode, 120 cathode, 130 solid polymer electrolyte membrane, 140 electrolytic cell, 140a anode chamber, 140b cathode chamber, 141a, 141b supply port, 142a, 142b outlet

Claims

1. A method for manufacturing a diamond electrode, comprising a conductive diamond layer forming step of applying an electric field to a suspension containing conductive diamond particles to cause the conductive diamond particles to migrate, and depositing the conductive diamond particles on a substrate placed in the suspension to form a conductive diamond layer.

2. 2. The method for producing a diamond electrode according to claim 1, further comprising a base layer forming step of forming a base layer containing at least one selected from the group consisting of platinum, metal oxides, and semi-metal oxides on the substrate before the conductive diamond layer forming step.

3. 3. The method for manufacturing a diamond electrode according to claim 1 or 2, further comprising, after the conductive diamond layer forming step, a retaining layer forming step of forming a retaining layer containing at least one selected from metal oxides and semi-metal oxides between the conductive diamond particles of the conductive diamond layer.

4. The method for producing a diamond electrode according to claim 1 or 2, wherein the suspension further contains a binder resin.

5. A diamond electrode having a substrate, an underlayer formed on the substrate and containing at least one selected from the group consisting of platinum, metal oxides, and semi-metal oxides, and a conductive diamond layer formed on the underlayer, which is a deposited layer of conductive diamond particles.

6. 6. The diamond electrode according to claim 5, further comprising a support layer formed between the conductive diamond grains of the conductive diamond layer and containing at least one selected from metal oxides and semi-metal oxides.

7. 7. An electrolytic treatment apparatus comprising an electrolytic cell, an anode which is the diamond electrode according to claim 5 or 6, and a cathode.

8. An ozone generating device comprising an electrolytic cell, an anode which is the diamond electrode according to claim 5 or 6, and a cathode.

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