JP2011174164A - Electrolyzing electrode, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyzing electrode capable of generating ozone with high efficiency by electrolysis of water at the low current density. <P>SOLUTION: The electrolyzing electrode 1 includes a base body 2 and a surface layer 4 formed on the base body 2. The surface layer 4 of the electrolyzing electrode 1 is formed of an amorphous dielectric substance, such as niobium oxide. By setting the amount of supported niobium to be ≥2 μmol/cm<SP>2</SP>and ≤16 μmol/cm<SP>2</SP>, ozone is efficiently generated by the electrolysis of electrolyte solution with the low current density with the electrode being used for an anode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrode for electrolysis used in an industrial or consumer electrolysis process, and a method for producing the electrode.

  In general, ozone is a substance having a very strong oxidizing power, and water in which the ozone is dissolved, so-called ozone water is widely used for cleaning and sterilization such as water and sewage, food, etc., and cleaning treatment in semiconductor device manufacturing processes. Expected to be used in processing. As a method of generating ozone water, a method of dissolving ozone generated by ultraviolet irradiation or discharge in water, a method of generating ozone in water by electrolysis of water, and the like are known.

  Patent Document 1 discloses an ozone water generating device that includes ozone generating means for generating ozone gas by an ultraviolet lamp and a tank for storing water, and generates ozone water by supplying the generated ozone gas to water in the tank. Has been. Patent Document 2 discloses an ozone water generator that mixes ozone gas and water generated by a discharge-type ozone gas generator at a predetermined ratio with a mixing pump in order to efficiently dissolve ozone gas in water. Yes.

  However, in the ozone water generation method in which ozone gas is generated by the ultraviolet lamp or the discharge type as described above and this ozone gas is dissolved in water, an operation for dissolving the ozone gas in the water is required because of an ozone gas generation device or an operation for dissolving the ozone gas in water. There is a problem that it is easy to make complicated, and it is difficult to generate ozone water having a desired concentration with high efficiency because the generated ozone gas is dissolved in water.

  Patent Document 3 discloses a method for generating ozone in water by electrolysis of water as a method for solving the above problems. In such a method, an electrode for generating ozone, which is configured to include an electrode substrate formed of a porous body or a net-like body and an electrode catalyst containing an oxide of a platinum group element or the like, is used.

  Patent Document 4 discloses that ozone is generated by electrolytic treatment of simulated tap water as an electrolyte solution with an electrode for electrolysis having a surface layer made of a dielectric such as tantalum oxide.

Japanese Patent Laid-Open No. 11-77060 JP-A-11-333475 JP 2002-80986 A JP 2007-016303 A

However, in the method shown in Patent Document 3 as described above, since diamond is used as the electrode material, there is a problem that the cost of the device itself increases. In the method for generating ozone water, platinum group elements are standard anode materials and are hardly dissolved in an aqueous solution containing no organic matter. However, the ozone generation efficiency is low as an electrode for generating ozone. It is difficult to generate ozone water by an efficient electrolysis method. Furthermore, in the conventional ozone water generation by the electrolytic method using the electrode for generating ozone, electrolysis for generating ozone requires a high current density of 1 A / cm ² or more, and the electrolyte is used at a low temperature. There is a problem that a great deal of energy is consumed. In addition, when lead dioxide is used, there is a problem that it is toxic.

  Further, even when the electrode for electrolysis disclosed in Patent Document 4 as described above is used, ozone is generated, but the ozone depends on the film thickness dependence of the surface layer and the crystallinity of the substance constituting the layer. There was variation in production efficiency. Therefore, improvement in current efficiency in ozone generation has been desired.

  Accordingly, the present invention has been made to solve the conventional technical problems, and provides an electrode for electrolysis that can generate ozone with high efficiency by electrolysis of water with a low current density. To do.

  In order to solve the above problems, the invention of claim 1 is an electrode for electrolysis comprising a substrate and a surface layer formed on the substrate, and the surface layer is an amorphous dielectric. It is characterized by.

According to a second aspect of the invention, in the invention of claim 1, the dielectric is a metal oxide, and, wherein the supported amount of the metal element is 2 [mu] mol / cm ² or more 16μmol / cm ² or less.

  A third aspect of the invention is characterized in that, in the second aspect of the invention, the metal constituting the metal oxide is an element of Group 3, 4, or 5 of the periodic table.

  The invention of claim 4 is characterized in that, in the invention of claim 2 or claim 3, the metal constituting the metal oxide is niobium or tantalum.

  The invention of claim 5 is the invention of claim 4, wherein the metal constituting the metal oxide is tantalum, and the dielectric contains a noble metal, and the ratio of the noble metal to the base metal is greater than 0 and 20%. It is characterized by the following.

  The invention of claim 6 is the invention of claim 5, wherein the noble metal is platinum, gold or iridium.

  The invention of claim 7 is the invention according to any one of claims 1 to 6, wherein the substrate is located on the inner surface of the surface layer and formed on the surface of the substrate, and at least a hardly oxidizable metal, or An intermediate layer including either a metal oxide having conductivity or a metal having conductivity even when oxidized is formed.

  The invention of claim 8 is the invention of claim 7, wherein the intermediate layer is made of platinum, gold, iridium, or iridium oxide.

  The invention of claim 9 comprises a substrate and a surface layer made of a dielectric on the substrate, the surface layer comprising at least a thin region having a small thickness and a thick region having a large thickness. The thickness of the thin region is in the range of 0.2 μm to 2.5 μm, and the thickness of the thick region is 5 μm or more.

  The invention of claim 10 is characterized in that, in the invention of claim 9, the thin region is in the range of 20% to 50% of the entire area of the surface layer.

  The invention of claim 11 is characterized in that, in the invention of claim 9 or claim 10, the thickness region is in the range of 20% to 50% of the total area of the surface layer.

  According to a twelfth aspect of the present invention, in any of the ninth to eleventh aspects, the dielectric is an amorphous niobium oxide or an amorphous tantalum oxide.

  According to a thirteenth aspect of the present invention, an amorphous surface layer is formed by applying a heat treatment after applying a surface layer material to a substrate.

  According to the fourteenth aspect of the present invention, there is provided a first step of forming an intermediate layer on the surface of the substrate by applying an intermediate layer raw material to the surface of the substrate and then performing a heat treatment, and after the first step, the surface of the intermediate layer And a second step of forming an amorphous surface layer by applying a heat treatment after coating the surface layer material.

  The invention of claim 15 is characterized in that, in the invention of claim 13 or claim 14, the surface layer is made of amorphous niobium oxide or amorphous tantalum oxide.

  The invention of claim 16 is the invention of any one of claims 13 to 15, wherein the surface layer is a niobium oxide, and the heat treatment temperature in the heat treatment is 300 ° C. to 500 ° C. And

  The invention according to claim 17 is the invention according to any one of claims 13 to 15, wherein the surface layer is made of tantalum oxide, and the heat treatment temperature in the heat treatment is 450 ° C. to 600 ° C. And

  According to an eighteenth aspect of the invention, in any of the thirteenth to seventeenth aspects of the invention, the surface layer is formed by repeating the heat treatment step 15 to 50 times after the surface layer material is applied to the substrate. Features.

  According to a nineteenth aspect of the present invention, in any one of the thirteenth to eighteenth aspects, the raw material of the surface layer contains an organic metal.

  According to the first aspect of the present invention, in the electrode for electrolysis comprising the substrate and the surface layer formed on the substrate, the surface layer is an amorphous dielectric, so that the electrode is used as an anode. Ozone can be efficiently generated by electrolysis of the electrolyte solution with a low current density.

  In particular, since the temperature of the electrolyte solution is not particularly low as in the prior art and a high current density is not required, it is possible to reduce the power consumption required for ozone generation.

According to the second aspect of the invention, in addition to the above, the dielectric is a metal oxide, and, since the loading amount of the metal element is at 2 [mu] mol / cm ² or more 16μmol / cm ² or less, the ozone at a high efficiency Can be generated.

  According to the invention of claim 3, in addition to the above, the metal constituting the metal oxide is an element of Group 3, 4, or 5 of the periodic table, and particularly niobium as in the invention of claim 4, Or since it is a tantalum, the electrode which implement | achieves high ozone production | generation efficiency can be comprised easily. In addition, by forming the metal oxide with niobium or tantalum, the production cost can be reduced, and since no toxic substances such as lead dioxide are used, the environmental load can be reduced.

  According to the invention of claim 5, in addition to the above, the metal constituting the metal oxide is tantalum, and the dielectric is a noble metal such as platinum, gold, iridium as in the invention of claim 6. In addition, since the ratio of the noble metal to the base metal is greater than 0 and 20% or less, the stability of the material constituting the surface layer can be achieved with the metal oxide without reducing the ozone generation efficiency.

  According to the invention of claim 7, in addition to each of the above inventions, the substrate is located on the inner surface of the surface layer and formed on the surface of the substrate, and is at least a hardly oxidizable metal or a conductive metal. An intermediate layer containing either an oxide or a metal that has conductivity even when oxidized, for example, the intermediate layer is formed of platinum, gold, iridium, and iridium oxide as in the invention of claim 8. Electrons in the electrode reaction can be effectively moved in the surface layer. Therefore, an electrode reaction can occur at a high energy level on the surface of the surface layer. Thereby, ozone can be generated efficiently at a lower current density.

  In particular, according to the invention, since the intermediate layer is formed of a hardly oxidizable metal on the surface of the substrate, the problem that the surface of the substrate is oxidized and made non-conductive when electrolysis is performed using the electrode is avoided. can do. Thereby, durability of an electrode can be improved. Further, the production cost can be reduced as compared with the case where the entire substrate is made of the material constituting the intermediate layer, and in such a case, ozone can be generated efficiently in the same manner. .

  According to the ninth aspect of the present invention, in the electrode for electrolysis comprising a base and a surface layer made of a dielectric on the base, the surface layer has at least a thin region having a small thickness and a thick thickness. Since the thickness region is provided, the thickness of the thin region is in the range of 0.2 μm to 2.5 μm, and the thickness of the thick region is 5 μm or more, the electrode is an anode. By performing electrolysis of the electrolyte solution used as the ozone, ozone can be efficiently generated at a low current density.

  In particular, the surface layer has a thin region with a thickness in the range of 0.2 μm to 2.5 μm, so that it is possible to cause electron transfer at a higher energy level, and high efficiency at a low current density. Ozone generation can be realized.

  In addition to the thin region, the surface layer has a thick region with a maximum thickness of 5 μm or more. The durability of the electrode can be improved.

  According to the invention of claim 10, in addition to the above, the thin region is in the range of 20% to 50% of the entire area of the surface layer. Further, according to the invention of claim 11, the thick region is By setting the surface layer to a range of 20% to 50% of the entire area of the surface layer, it is possible to achieve highly efficient ozone generation with a low current density while ensuring the durability of the surface layer.

  According to the invention of claim 12, in addition to the above inventions, since the dielectric is an amorphous niobium oxide or an amorphous tantalum oxide, an electrode that realizes high ozone generation efficiency can be easily formed. Can be configured. In addition, the surface layer is made of niobium oxide or tantalum oxide, so that the production cost can be reduced, and no toxic substances such as lead dioxide are used, thereby reducing the environmental burden. it can.

  In addition, since the dielectric constituting the surface layer is amorphous niobium oxide or tantalum oxide, the current of the electrolyte solution is not particularly low as in the prior art, and a high current density is required. And not. Therefore, it is possible to reduce the power consumption required for ozone generation.

  According to the method for manufacturing an electrode for electrolysis of the invention of claim 13, after the surface layer material is applied to the substrate, an amorphous surface layer is formed by heat treatment, so that the manufactured electrode is used as an anode. Ozone can be efficiently generated by electrolysis of the electrolyte solution with the low current density used.

  In particular, since the temperature of the electrolyte solution is not particularly low as in the prior art and a high current density is not required, it is possible to reduce the power consumption required for ozone generation.

  According to the fourteenth aspect of the present invention, the first step of forming the intermediate layer on the surface of the substrate by applying a heat treatment to the surface of the substrate and then heat-treating the intermediate layer is performed after the first step. A second step of forming an amorphous surface layer by applying a heat treatment after applying the surface layer raw material to the surface of the electrode, and thereby providing an electrolyte solution with a low current density using the manufactured electrode as an anode. Ozone can be generated efficiently by electrolysis.

  In particular, since the temperature of the electrolyte solution is not particularly low as in the prior art and a high current density is not required, it is possible to reduce the power consumption required for ozone generation.

  In addition, an intermediate layer can be formed on the surface of the substrate with an appropriate thickness and an appropriate amount, and an intermediate layer with high adhesion can be formed. Moreover, since the thickness of the intermediate layer suitable for the durability required for the electrode can be easily obtained, the amount of the raw material used for the intermediate layer can be made appropriate, and wasteful use can be reduced.

  Furthermore, a surface layer can be formed on the surface of the intermediate layer with an appropriate thickness and an appropriate amount, and a surface layer with high adhesion can be formed.

  According to the invention of claim 15, in each of the above inventions, the surface layer is made of amorphous niobium oxide or amorphous tantalum oxide, so that an electrode realizing high ozone generation efficiency can be easily obtained. Can be manufactured. In addition, because the surface layer is composed of amorphous niobium oxide or amorphous tantalum oxide, the production cost can be reduced and no toxic substances such as lead dioxide are used. , Environmental load can be reduced.

  According to the invention of claim 16, in each of the above inventions, when the surface layer is a niobium oxide, the heat treatment temperature in the heat treatment is set to 300 ° C. to 500 ° C. It becomes possible to form the surface layer with an oxide. According to the invention of claim 17, when the surface layer is made of tantalum oxide, the heat treatment temperature in the heat treatment is set to 450 ° C. to 600 ° C. Thus, the surface layer can be configured.

  According to the invention of claim 18, in each of the above-described inventions, the surface layer is formed by repeating the heat treatment step 15 to 50 times after applying the surface layer raw material to the substrate. A surface layer can be formed. This makes it possible to realize highly efficient ozone generation with a low current density.

  According to the invention of claim 19, in each of the above-mentioned inventions, the surface layer material can easily form the surface layer on the substrate by containing an organic metal.

It is a plane sectional view of the electrode for electrolysis as an example to which the present invention is applied. It is a flowchart which shows the manufacturing method of the electrode for electrolysis. It is a figure which shows the X-ray-diffraction pattern of the surface layer of the electrode for electrolysis produced by each conditions. It is a schematic explanatory drawing of the electrolysis apparatus to which the electrode for electrolysis is applied. It is a figure which shows the ozone production amount with respect to each baking temperature. It is a figure which shows the current efficiency with respect to each baking temperature. It is a figure which shows the ozone production | generation density | concentration with respect to each niobium carrying amount. It is a figure which shows the ozone generation density with respect to the frequency | count of application | coating of the raw material of a surface layer. It is a cross-sectional SEM photograph of the electrode for electrolysis. It is a figure which shows the X-ray-diffraction pattern of the electrode for electrolysis in which the surface layer was formed with the amorphous tantalum oxide. It is a figure which shows the ozone production amount with respect to each baking temperature. It is a figure which shows the ozone production | generation density | concentration with respect to the composition ratio of Ta with respect to each Pt. It is a figure which shows the ozone production | generation density | concentration with respect to the composition ratio of Nb with respect to each noble metal. It is a cross-sectional SEM photograph of the electrode for electrolysis.

  Examples 1 and 2 will be described below with reference to the drawings as preferred embodiments of the electrode for electrolysis of the present invention.

  FIG. 1 is a plan sectional view of an electrode 1 for electrolysis according to the present invention. As shown in FIG. 1, an electrode for electrolysis 1 includes a base (conductive base) 2, an intermediate layer 3 formed on the surface of the base 2, and a surface layer 4 formed on the surface of the intermediate layer 3. Composed.

  In the present invention, the substrate 2 is a conductive material such as platinum (Pt), valve metal such as titanium (Ti), tantalum (Ta), zirconium (Zr), niobium (Nb), or two or more of these valve metals. It is comprised by the alloy of this. In consideration of cost, workability, corrosion resistance, and the like, titanium is preferable. In this embodiment, a titanium plate is used as the substrate 2.

  The intermediate layer 3 is formed inside the surface layer 4 and is a metal that is difficult to oxidize, such as platinum, gold (Au), or a conductive metal oxide such as iridium oxide, Palladium oxide, ruthenium oxide, oxide superconductor, etc., or as a metal having conductivity even when oxidized, ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium contained in platinum group elements (Ir) or silver (Ag). In addition, about a metal oxide, it is not limited to the thing by which the intermediate | middle layer 3 was comprised previously as an oxide, It shall also include what was oxidized by electrolysis and was made into the metal oxide.

  However, when the intermediate layer 3 is made of a conductive metal oxide, such as iridium oxide, the oxygen atoms constituting the metal oxide adversely affect the conductor. It is desirable to use a hardly oxidizable metal. In this embodiment, the intermediate layer 4 is made of platinum.

  When the base 2 is made of platinum, the surface of the base 2 is naturally made of platinum, so that the intermediate layer 3 need not be specially formed. However, when the base 2 is made of platinum, the cost increases. Therefore, industrially, the base 2 is made of an inexpensive material, and the surface of the base 2 is made of a noble metal or the like. It is preferable to form the intermediate layer 3 to be formed.

  Further, if the base 2 is made of a non-conductive substance, for example, a glass plate, and the base 2 is at least a contact surface with the surface layer 4 described later is coated with a conductive material. For example, it is not limited to the said structure. This also makes it possible to suppress an increase in cost required for the material used for the structure of the base 2.

  The surface layer 4 covers the intermediate layer 3 and is an amorphous dielectric material. The dielectric is a substance that does not exhibit metallic conductivity. In this embodiment, the dielectric is an oxide of a metal corresponding to an element of Group 3, 4, or 5 of the periodic table, preferably niobium (Nb). ), Tantalum (Ta), titanium (Ti), and zirconium (Zr) oxides (metal oxides) are formed in layers on the surface of the substrate 2 on which the intermediate layer 3 is formed (the surface of the intermediate layer 3). . The details of the thickness of the surface layer 4 will be described later.

  In this embodiment, amorphous niobium oxide (NbOx) or tantalum oxide (TaOx) is used as an amorphous single metal oxide as a dielectric, but the present invention is not limited to this. Instead, it may be an amorphous composite metal oxide that is a dielectric.

  Next, with reference to the flowchart of FIG. 2, the manufacturing method of the electrode 1 for electrolysis as Example 1 of this invention is demonstrated. First, a titanium plate having a thickness of 1 mm, a length of 80 mm, and a width of 20 mm is used as the substrate 2, and the surface of the substrate 2 (surface having a length of 80 mm and a width of 20 mm) is polished with water-resistant abrasive paper (step S 1). . The intermediate layer 3 and the surface layer 4 may be covered only on one side of the surface of the substrate 2, and the surface layer 4 may be used as an electrolysis reaction surface facing the counter electrode. When employed in the apparatus, the intermediate layer 3 and the surface layer 4 may be formed on both surfaces of the surface of the substrate 2 or on the entire surface of the substrate 2. In this case, the manufacturing process such as polishing of the surface of the substrate 2 and etching and heat treatment described below is performed on the surface of the substrate 2 or the entire surface.

  Further, the polishing of the surface of the substrate 2 may be performed as long as the oxide film formed on the surface of the substrate 2 can be deleted. Not only a method using water-resistant abrasive paper, but also a method capable of obtaining similar effects such as sandblasting. For example, other methods may be used.

  Next, the substrate 2 whose surface has been polished is degreased with an organic solvent, in this embodiment, acetone (step S2), and then the surface of the substrate 2 is made to have a predetermined surface roughness with a hot oxalic acid aqueous solution having a concentration of 200 g / L. Then, chemical etching for 3 hours is executed (step S3). In place of the hot oxalic acid aqueous solution, for example, hot sulfuric acid or hydrofluoric acid may be used.

  First, the intermediate layer 3 is formed on the substrate 2 whose surface is roughened by chemical etching. In the present example, since the intermediate layer 3 is formed of platinum, the solvent is adjusted so that the mixing ratio of isopropyl alcohol and 2-ethoxyethanol is 4: 1. Chloroplatinic acid is dissolved and used as the raw material for the intermediate layer 3.

  And the raw material of the said intermediate | middle layer 3 is uniformly apply | coated to the surface of the said base | substrate 2 using a spatula (step S4). In addition to the method of applying the raw material of the intermediate layer 3 with the spatula as described above, the method of applying the raw material of the intermediate layer 3 onto the substrate 2 by spraying, or the intermediate layer 3 The material 2 is housed in a container, and the substrate 2 is immersed in the container, and further, the substrate 2 is rotated and the material for the intermediate layer 3 is applied by centrifugal force (spin coating method). May be.

  The substrate 2 with the intermediate layer 3 material adhered to the surface is then dried at room temperature for 10 minutes (step S5), and then dried at a temperature range of 150 ° C. to 250 ° C., preferably at 200 ° C. for 10 minutes. (Step S6). Further, heat treatment (firing) is performed at a temperature range of 400 ° C. to 550 ° C., preferably 500 ° C. for 10 minutes (step S7). As a result, the solvent component and the like are evaporated, and an intermediate layer 3 made of platinum is formed on the surface of the substrate 2.

  And the base | substrate 2 with which the said intermediate | middle layer 3 was formed is cooled for 10 minutes at room temperature (step S8), Then, as shown in FIG. 2, application | coating of the raw material of the intermediate | middle layer 3 again (step S4), and room temperature drying ( Steps S5), heat treatment at 200 ° C. (Step S6), heat treatment at 500 ° C. (Step S7), and room temperature cooling (Step S8) are repeated until the thickness of the intermediate layer 3 reaches a predetermined thickness (Step S5). S9). In this embodiment, the above process is repeated 10 times. These processes are defined as a first step for producing the intermediate layer 3.

  In this way, by repeating the production process of the intermediate layer 3 a plurality of times, an appropriate thickness on the substrate 2 and an appropriate thickness can be obtained as compared with the case where a large amount of the raw material of the intermediate layer 3 is formed on the surface of the substrate 2 at a time. It becomes possible to coat platinum with an appropriate amount. In addition, the intermediate layer 3 having high adhesion can be formed, and the durability of the electrode itself can be improved. In addition, since the thickness of the intermediate layer 3 matching the durability required for the electrode can be easily obtained, the amount of noble metal or noble metal oxide used can be made appropriate, and wasteful noble metals and noble metal oxides can be used. Use can be reduced.

  Thereafter, a surface layer 4 made of a dielectric is formed on the surface of the intermediate layer 3 formed on the surface of the substrate 2. In this embodiment, since the surface layer 4 is formed of niobium oxide, which is a dielectric, the niobium concentration is 0. 0 in a solvent adjusted so that the mixing ratio of isopropyl alcohol and 2-ethoxyethanol is 4: 1. Niobium pentaethoxide in an amount of 73 mol / L is dissolved to obtain a raw material for the surface layer 4.

  Here, a reagent having a purity of 99% is used for niobium pentaethoxide. Moreover, according to the analysis by the high frequency inductively coupled emission spectrometer (ICP emission spectrometer), as impurities, barium, calcium, zirconium, aluminum, cadmium, cobalt, chromium, copper, iron, magnesium, manganese, nickel, strontium, Titanium, vanadium, zinc, lead, antimony, tin are included. Therefore, niobium pentaethoxide used in this embodiment is one containing about 1% or less of impurities. Moreover, since these impurities do not scatter in the air after firing, the niobium oxide of the surface layer 4 contains about 1% of the impurities. However, these impurities do not affect the characteristics of the surface layer 4 in this embodiment.

  In this embodiment, niobium alkoxide is used as a raw material for the surface layer 4, but the present invention is not limited to this, and an organic metal containing a carboxyl group may be used. Thereby, the formation of the surface layer 4 on the substrate 2 can be facilitated by adopting a material containing an organic metal as a material for the surface layer.

  Then, the raw material of the surface layer 4 is uniformly applied to the surface of the intermediate layer 3 formed on the surface of the substrate 2 using a spatula in the same manner as the raw material application method of the intermediate layer 3 for forming the intermediate layer 3 described above. (Step S10). In addition, in the application of the raw material of the surface layer 4, as in the case of the application of the raw material of the intermediate layer 3, in addition to the method of applying with the spatula, The raw material of the layer 4 is accommodated in a container, and the substrate 2 on which the intermediate layer 3 is formed is immersed in the container. Further, the raw material of the surface layer 4 is applied by rotating the substrate 2 and centrifugal force. A method (spin coating method) or the like may be performed.

  As described above, the surface layer 4 is formed on the substrate 2 having the surface layer 4 raw material attached to the surface of the intermediate layer 3 by a manufacturing process substantially similar to the manufacturing process for forming the intermediate layer 3 described above. .

  That is, the substrate 2 having the surface layer 4 coated on the surface of the intermediate layer 3 is dried at room temperature for 10 minutes (step S11), and then at a temperature range of 150 ° C. to 250 ° C., preferably 200 ° C. Drying for 10 minutes is performed (step S12). And in preparation of this surface layer 4, heat processing (baking) for 10 minutes is performed in the temperature range of 300 to 500 degreeC (step S13). Thereby, a surface layer 4 made of niobium oxide is formed on the surface of the intermediate layer 3 formed on the surface of the substrate 2. In addition, the detail about the temperature in the said heat processing (baking) is mentioned later.

Then, the substrate 2 on which the surface layer 4 is formed is cooled at room temperature for 10 minutes (step S14), and then, as shown in FIG. 2, the material for the surface layer 4 is applied again (step S10) and dried at room temperature (step S11). ), 200 ° C. drying (step S12), heat treatment (firing. Step S13), and room temperature cooling (step S14) are repeated until the thickness of the surface layer 4 reaches a predetermined thickness (step S15). Thereby, the electrode 1 for electrolysis in a present Example is obtained. In this embodiment, the above process is repeated 10 to 50 times. In addition, the detail about the process frequency of the said surface layer 4 is mentioned later. These steps are defined as a second step for producing the surface layer 4.

(1) X-ray diffraction analysis of electrode for electrolysis Next, X-ray diffraction analysis of the surface layer 4 of the electrode 1 for electrolysis obtained as described above is performed, and the crystal structure of the surface layer 4 is analyzed. FIG. 3 shows that the firing temperature of the heat treatment (step 13) when forming the surface layer 4 is 300 ° C., 350 ° C., 400 ° C., 450 ° C., 475 ° C., 500 ° C., 550 ° C., 600 ° C. The X-ray diffraction pattern of each surface layer 4 when the electrode 1 is configured is shown. The number of steps of the surface layer 4 of the electrode 1 for electrolysis produced under each condition is the same as 25 times.

  In general, X-ray diffraction (XRD) is used for the analysis of the crystal structure, whereby the crystal structure of the niobium oxide forming the surface layer 4 can be analyzed. In this example, observation was performed using an X-ray diffractometer (D8 Discover manufactured by Bruker AXS).

According to this, each diffraction peak (2θ) shown in the X-ray diffraction pattern of the surface layer 4 of the electrode 1 for electrolysis obtained at a firing temperature of 500 ° C. or higher (500 ° C., 550 ° C., 600 ° C.) Even in the electrode 1 constituted by the firing temperature, they were about 22.6 °, about 28.5 °, about 36.7 °, about 50.8 °, and about 55.1 ° (see the black circles in FIG. 3). Peak to be displayed). These coincide with the diffraction peak (2θ) peculiar to niobium oxide (Nb ₂ O ₅ ), and the X-ray diffraction pattern of the surface layer 4 of the electrode 1 for electrolysis obtained at a firing temperature of 500 ° C. or higher is Although present, the X-ray diffraction pattern of the surface layer 4 of the electrode 1 for electrolysis obtained at a firing temperature of less than 500 ° C. (in this case, 475 ° C., 450 ° C., 400 ° C., 350 ° C., 300 ° C.) Does not exist.

  Therefore, in the method of the present embodiment as described above, in the electrode 1 for electrolysis that forms the surface layer 4 in a temperature range of 300 ° C. or more and less than 500 ° C., the niobium oxide that forms the surface layer 4 is crystalline. It can be seen that it is amorphous having no structure, that is, indefinite, so-called amorphous.

  In this embodiment, the surface layer 4 is uniformly coated on the surface layer 4 containing niobium pentaethoxide using a spatula (in this embodiment, the surface of the intermediate layer 3) and fired at a predetermined temperature. Although the amorphous niobium oxide is formed, the method of forming the surface layer 4 with the amorphous niobium oxide is not limited to this.

  As another method, there is a method of forming the surface layer 4 by a thermal CVD method. In this thermal CVD method, the intermediate layer 3 is formed on the surface of the substrate 2 in the same manner as in the above embodiment, and then an organic solvent containing niobium as a raw material for the surface layer is vaporized, and a reaction tube is used using an appropriate carrier gas. For example, a chemical reaction is performed on the surface of the substrate 2 heated to 300 ° C. to 500 ° C., for example.

  As a result, a substance excluding niobium, which is an organic solvent containing niobium as a raw material for the surface layer, is removed on the surface of the substrate 2 heated to a high temperature, and only niobium reacts with oxygen in the atmosphere, thereby oxidizing niobium. As a product, it is formed on the surface of the substrate 2 (actually the intermediate layer 3). The niobium oxide formed on the surface of the substrate 2 (the surface of the intermediate layer 3) constitutes an amorphous thin film (niobium oxide film).

In addition, as a method for forming the surface layer 4 from amorphous niobium oxide, for example, there is a dipping method.

(2) Calcination Temperature Dependence of Current Efficiency of Ozone Generation Next, the dependency of the calcination temperature on the generation of ozone by electrolysis using the electrode 1 for electrolysis manufactured as described above will be described with reference to FIGS. explain. FIG. 4 is a schematic explanatory diagram of the electrolysis apparatus 10 to which the electrode 1 for electrolysis is applied, FIG. 5 is a diagram showing the amount of ozone generated at each firing temperature, and FIG. 6 is a diagram showing current efficiency at each firing temperature.

  The electrolysis apparatus 10 includes a treatment tank 11, an electrode 1 for electrolysis as an anode as described above, an electrode 12 as a cathode, and a power source 15 that applies a direct current to the electrodes 1 and 12. Then, a cation exchange membrane (diaphragm: Nafion manufactured by DuPont, which is located between the electrodes 1 and 12 and partitioned into one region where the electrode 1 exists in the treatment tank 11 and the other region where the electrode 12 exists) Name)) 14 is provided. Further, a stirring device 16 is provided in a region where the electrode 1 for electrolysis as an anode is immersed.

In the treatment tank 11, simulated tap water 13 as an electrolyte solution is stored. In the experiment in this example, simulated tap water is used as the electrolyte solution. However, by providing a cation exchange membrane, substantially the same effect can be obtained even when other aqueous electrolytes are treated. It is done. The electrolyte solution used in the experiment is an aqueous solution that simulates tap water. The component composition of the simulated tap water 23 is 5.75 ppm for Na ⁺ , 10.02 ppm for Ca ²⁺ , and 6 for Mg ^2+. 0.08 ppm, K ⁺ is 0.98 ppm, Cl ⁻ is 17.75 ppm, SO ₄ ²⁻ is 24.5 ppm, and CO ₃ ²⁻ is 16.5 ppm.

In the electrode 1 for electrolysis, the firing temperature of the heat treatment (step 13) when forming the surface layer 4 is 250 ° C, 300 ° C, 350 ° C, 400 ° C, 450 ° C, 475 ° C, 500 ° C, 550 ° C, 600 ° C. The electrode of each condition was used. In this case, 2 × 4 cm ² is employed as the surface area of each electrode 1 for electrolysis and the electrode 12 serving as a counter electrode.

  With the above configuration, 150 ml of simulated tap water 13 is stored in each region in the treatment tank 11, and the electrode 1 for electrolysis and the electrode 12 are immersed in the simulated tap water, respectively. The distance between each electrode is 10 mm. Then, a constant current of 160 mA is applied to the electrolysis electrode 1 and the electrode 12 by the power source 15. Moreover, the temperature of the simulated tap water 13 shall be +20 degreeC.

  In this example, the amount of ozone generated by each electrode for electrolysis was determined by measuring the amount of ozone generated in simulated tap water 13 after electrolysis for 1 minute under the above conditions by the indigo method (DR4000 manufactured by HACH). FIG. 6 shows the concentration of the ozone generation amount. FIG. 6 shows the ratio of the electric charge that contributed to the ozone generation with respect to the total electric charge amount, that is, the ozone generation current efficiency, from which the electrodes for electrolysis are evaluated.

  As shown in FIG. 5, in this experiment, an electrode for electrolysis in which the firing temperature of the surface layer 4 was 250 ° C. (hereinafter referred to as a firing temperature of 250 ° C., hereinafter, the same applies to each electrode). In this case, the amount of ozone generated is 0.19 mg / L, 0.24 mg / L when the baking temperature is 300 ° C., 0.41 mg / L when the baking temperature is 350 ° C., and 0.54 mg / L when the baking temperature is 400 ° C. L, 0.50 mg / L for a firing temperature of 450 ° C., 0.47 mg / L for a firing temperature of 475 ° C., 0.24 mg / L for a firing temperature of 500 ° C., and 0.2 for a firing temperature of 550 ° C. In the case of 11 mg / L and a firing temperature of 600 ° C., it was 0.11 mg / L.

  In addition, as shown in FIG. 6, when expressed in terms of ozone generation current efficiency, when the firing temperature is 250 ° C., 3.5%, when the firing temperature is 300 ° C., 4.5%, when the firing temperature is 350 ° C., In the case of 7.7%, the firing temperature of 400 ° C., 10.2%, the firing temperature of 450 ° C., 9.3%, the firing temperature of 475 ° C., 8.8%, and the firing temperature of 500 ° C. When the firing temperature was 4%, the firing temperature was 550 ° C., 2.1%, and when the firing temperature was 600 ° C., it was 2.1%.

Comparing these results with the results of the X-ray diffraction analysis, the surface layer 4 is a crystallized niobium oxide (Nb ₂ O ₅ ) at calcination temperatures of 550 ° C. and 600 ° C., and the surface layer 4 When the firing temperature is 350 ° C., 400 ° C., 450 ° C., and 475 ° C., which is an amorphous material having no crystal structure, the ozone generation current efficiency is higher when the surface layer 4 is an amorphous niobium oxide. Is 3.6 times or more high.

  As a result, the surface layer 4 of the electrode 1 for electrolysis is made of niobium oxide as an example of an amorphous dielectric, whereby an electrolyte solution with a low current density (160 mA as an example) using the electrode 1 as an anode. It is possible to efficiently generate ozone by electrolysis of.

  In particular, since the temperature of the electrolyte solution is not particularly low as in the prior art and a high current density is not required, it is possible to reduce the power consumption required for ozone generation.

  On the other hand, when the surface layer 4 is formed at a firing temperature of 500 ° C., the ozone generation current efficiency is more than twice that of the case where the surface layer 4 is formed at a firing temperature of 550 ° C. or 600 ° C. This is a transition temperature at which both crystallized niobium oxide and amorphous niobium oxide are formed at the firing temperature.

  Therefore, even when the firing temperature is 500 ° C., an amorphous niobium oxide is formed. Even at the firing temperature, the effect of the surface layer 4 of the amorphous niobium oxide is obtained. It is done.

  From the experimental results, when the firing temperature is 250 ° C. or 300 ° C., since the surface layer 4 is formed of amorphous niobium oxide, the surface layer 4 is formed by crystallized niobium oxide. The ozone generation current efficiency is higher than that when the firing temperatures are 550 ° C and 600 ° C.

However, when the current efficiency of ozone generation by the electrode for electrolysis is required to be 4% or more, the firing temperature condition for forming the surface layer 4 is desirably 300 ° C. or more and 500 ° C. or less. By setting the firing temperature condition for forming the surface layer 4 to 350 ° C. or higher and lower than 500 ° C., it is possible to achieve a current efficiency of ozone generation of 7.5% or higher (400 ° C. is the maximum value of the current efficiency). Become. Therefore, when the surface layer 4 is composed of an amorphous niobium oxide, the firing temperature condition is desirably set to 350 ° C. or higher and lower than 500 ° C.

(3) Nb loading amount dependency of ozone generation amount Next, the niobium (Nb) loading amount dependency of ozone generation amount by electrolysis using the electrode 1 for electrolysis manufactured as described above will be described with reference to FIGS. The description will be given with reference. FIG. 7 is a diagram showing the ozone generation concentration with respect to each amount of niobium supported, and FIG. 8 is a diagram showing the ozone generation concentration with respect to the number of times of applying the raw material of the surface layer 4.

  Using the same electrolysis apparatus 10 as described above, the evaluation on ozone generation of each electrolysis electrode 1 in which the condition of the amount of niobium constituting the surface layer 4 was changed was performed. In this case, in the electrode 1 for electrolysis, the raw material of the surface layer 4 is a solvent in which the mixing ratio of isopropyl alcohol and 2-ethoxyethanol is adjusted to 4: 1, and the niobium concentration is 0.37 mol / L, 0. Adjustment was made by dissolving niobium pentaethoxide in amounts of .73 mol / L and 1.45 mol / L. The calcining temperature in the heat treatment (firing) (step S13) in FIG. 2 can form amorphous niobium oxide as described above, and can obtain the maximum value of the current efficiency of ozone generation under the same conditions. ℃. Moreover, the application | coating frequency in step S15 of FIG. 2 is repeatedly performed 5 to 50 times, and the evaluation regarding ozone production | generation is performed with the obtained electrode for electrolysis, respectively. The electrolysis conditions are the same as the electrolysis conditions and the method for measuring the amount of ozone generated in (2) above, and thus the description thereof is omitted.

As shown in FIG. 7, in this experiment, the amount of niobium supported on the surface layer 4 is changed by changing the number of times the raw material is applied to the surface layer 4. In the case of an electrode for electrolysis (in the case of Nb concentration of 0.37 mol / L, the same applies to each electrode hereinafter) in which the surface layer 4 is formed from a raw material adjusted to a niobium concentration of 0.37 mol / L. When the supported amount of niobium (Nb) is 2.10 μmol / cm ² , the generated ozone concentration is 0.083 mg / L, when the supported amount of Nb is 3.94 μmol / cm ² , 0.43 mg / L, and the supported amount of Nb is in ^{5.50μmol / cm 2 0.48mg / L,} Nb support amount 6.56μmol / cm ² at 0.54 mg / L, was 0.43 mg / L in Nb supported amount 7.97μmol / cm ^2.

Also, when the Nb concentration 0.73 mol / L, concentration of ozone Nb supporting amount generated by 2.14μmol / cm ² is 0.16 mg / L, Nb support amount in 3.97μmol / cm ² 0.26mg / L, Nb supported amount of 0.48 mg / L at 5.88 μmol / cm ² , Nb supported amount of 0.49 mg / L at 8.08 μmol / cm ² , Nb supported amount of 0.54 mg at 8.90 μmol / cm ² / L, Nb support amount 10.10μmol / cm ² at 0.49 mg / L, Nb support amount in ^{10.86μmol / cm 2 0.30mg / L,} Nb support amount in 11.99μmol / cm ² 0. The amount of Nb supported was 0.03 mg / L at 15.30 μmol / cm ² and the amount of Nb supported was 0.003 mg / L at 15.75 μmol / cm ² .

Also, when the Nb concentration 1.45 mol / L, concentration of ozone Nb supporting amount generated by 4.127μmol / cm ² is 0.035 mg / L, Nb support amount in 7.46μmol / cm ² 0.07mg / L, Nb loading is 0.18 mg / L at 10.24 μmol / cm ² , Nb loading is 0.35 mg / L at 12.82 μmol / cm ² , and Nb loading is 0.26 mg at 15.29 μmol / cm ² . / L.

As shown in FIG. 7, when the amount of Nb supported on the surface layer 4 of the electrode 1 for electrolysis is 2 μmol / cm ^{2 to} 16 μmol / cm ² , the ozone concentration generated in the electrolyte solution is 0.1 mg / L or more. And ozone can be generated with high efficiency. The ozone concentration is such that 99% of pathogenic enterobacteria (for example, O157) can be killed in about 5 seconds, and the amount of Nb supported on the surface layer 4 is ² to 16 μmol / cm ^2. desirable.

Furthermore, the supported amount of Nb in the surface layer 4 of the electrode 1 for electrolysis is ^{4μmol / cm 2 ~13μmol / cm 2} , it is possible ozone concentration generated in the electrolyte solution is to 0.3 mg / L or more. The ozone concentration is such that 99% of the virus can be killed within 5 minutes. When the amount of Nb supported on the surface layer 4 is 4 to 13 μmol / cm ² , higher sterilization and virus inactivation effects can be obtained. realizable.

Furthermore, when the amount of Nb supported on the surface layer 4 of the electrode 1 for electrolysis is 5 μmol / cm ^{2 to} 10 μmol / cm ² , the ozone concentration generated in the electrolyte solution can be 0.5 mg / L or more. The ozone concentration is such that pathogenic spore bacteria (for example, tetanus) can be killed by 99% within 5 minutes, and the amount of Nb supported on the surface layer 4 is 5 to 10 μmol / cm ^2. Can achieve higher sterilization and virus inactivation effect.

In this way, by adjusting the amount of Nb supported on the surface layer 4, it becomes possible to more effectively generate ozone at a concentration corresponding to the purpose of use at a low current.

(4) Dependence of ozone generation amount on surface layer raw material application frequency On the other hand, with reference to FIG. 8, focusing on the number of surface layer raw material application times, the ozone generation concentration with respect to the application frequency is examined. As shown in FIG. 8, in this experiment, when the Nb concentration is 0.37 mol / L, the ozone concentration generated by 10 times of application is 0.083 mg / L, 20 times of application is 0.43 mg / L, and 30 times of application. 0.48 mg / L, 0.54 mg / L after 40 applications, and 0.43 mg / L after 50 applications. In addition, when the Nb concentration is 0.73 mg / L, the ozone concentration generated by 5 times application is 0.003 mg / L, 10 times application is 0.032 mg / L, 15 times application is 0.153 mg / L, 20 times. 0.30 mg / L for application, 0.49 mg / L for 25 application, 0.54 mg / L for 30 application, 0.49 mg / L for 35 application, 0.40 mg / L for 40 application, 45 application It was 0.26 mg / L by application and 0.16 mg / L by 50 applications. In addition, when the Nb concentration is 1.45 mol / L, the ozone concentration generated by 5 times application is 0.035 mg / L, 10 times application is 0.07 mg / L, 15 times application is 0.18 mg / L, 20 times. It was 0.35 mg / L by coating and 0.26 mg / L by 25 coatings.

  Thus, even if it is a case where the raw material of the surface layer 4 adjusted by any Nb density | concentration is used, the relationship with the ozone generation amount with respect to the frequency | count of application | coating takes a maximum value with a certain value. That is, when the Nb concentration is 0.37 mol / L, the ozone concentration generated by the 40 times application is 0.54 mg / L, and when the Nb concentration is 0.73 mol / L, the ozone generated by the 30 times application. When the concentration is 0.54 mg / L and the Nb concentration is 1.45 mol / L, the ozone concentration generated by 20 coatings is 0.35 mg / L.

  This is because the surface layer 4 made of amorphous niobium oxide having a sufficient thickness is not formed when the number of times of applying the raw material of the surface layer 4 is small, and the intermediate layer 3 can be seen electrically. For this reason, it is considered that the reaction field for the exchange of electrons that should be performed in the surface layer 4 cannot be secured sufficiently, and the generation efficiency of ozone is lowered.

  On the other hand, when the number of times of applying the raw material of the surface layer 4 is too large, the surface layer 4 to be formed becomes too thick, and the voltage drop greatly affects. And since the Joule heat generated by the reaction becomes high, the generated ozone is immediately decomposed, and it is considered that the generation efficiency of ozone is lowered.

  Therefore, when the number of times of applying the raw material of the surface layer 4 is 15 to 50 times, the ozone concentration generated in the electrolyte solution can be 0.1 mg / L or more, and ozone can be generated with high efficiency. . The ozone concentration can kill 99% of pathogenic intestinal bacteria (for example, O157) in about 5 seconds, and the number of times of application of the raw material for constituting the surface layer 4 is 15 to 50 times. It is desirable to do.

  Moreover, when the frequency | count of application | coating of the raw material of the surface layer 4 is 20 times-40 times, the ozone concentration produced | generated in electrolyte solution can be 0.3 mg / L or more. The ozone concentration can kill 99% of the virus within 5 minutes, and the sterilization and virus inactivation are higher by applying the raw material for forming the surface layer 4 to 20 to 40 times. The effect can be realized.

  Furthermore, when the number of times of applying the raw material of the surface layer 4 is 25 to 35, the ozone concentration generated in the electrolyte solution can be about 0.5 mg / L or more. The ozone concentration can kill 99% of pathogenic spore bacteria (for example, tetanus) within 5 minutes, and the number of times of applying the raw material of the surface layer 4 is 25 to 35 times. Higher sterilization and virus inactivation effects can be realized.

As described above, by adjusting the number of times of applying the raw material of the surface layer 4 constituting the surface layer 4, it becomes possible to more effectively generate ozone having a concentration corresponding to the purpose of use at a low current.
(5) Surface Layer Thickness Analysis Next, the thickness of the surface layer 4 composed of a dielectric will be examined. FIG. 9 shows a cross-sectional SEM photograph of the electrode 1 for electrolysis produced in Example 1. The electrode 1 for electrolysis comprises the surface layer 4 of amorphous niobium oxide, the firing temperature is 400 ° C., and the number of coatings is 25 times.

  The cross-sectional SEM photograph of FIG. 9 was acquired with a scanning electron microscope (SEM, Hitachi S-3400NX). The layer shown on the upper side from the uneven thin white layer is the surface layer 4 in the present invention, and the layer shown in white (in addition to the surface layer 4 formed in contact with the lower side of the surface layer 4) The intermediate layer 3 is a thinner layer. The layer shown in gray formed in contact with the lower side of the intermediate layer 3 is the base 2.

  According to this, when 10 or more SEM photographs (photographs of electrode cross section at a magnification of 2000 times) obtained as described above are obtained and the film thickness of the surface layer 4 is observed from the data, the surface layer 4 is at least as thick as possible. This is a non-uniform thickness structure having a thin thin area and a thick thick area. The thickness of the thin region is in the range of 0.2 μm to 2.5 μm, preferably 0.2 μm to 1.5 μm, and / or an average of 0.5 μm. The thickness of the thick region is 5 μm or more, preferably 11 μm or more, and is 20 μm or less in consideration of electrode production costs and ozone generation efficiency.

  Further, when the ratio of film thickness variation is statistically processed and analyzed from the above data, the thin region having a thickness of 0.2 μm to 2.5 μm or less is the entire area of the surface layer 4 of the electrode 1 for electrolysis. Of 20% to 50%. The thickness region having a thickness of 5 μm or more was in the range of 20% to 50% of the entire area of the surface layer 4 of the electrode 1 for electrolysis. And the surface layer 4 of the electrode 1 for electrolysis of these thin areas and parts other than a thick area is an area | region made into thickness larger than 2.5 micrometers and less than 5 micrometers.

  In the present embodiment, the thin region and the thick region of the surface layer 4 are formed by etching the base 2 of the electrode 1 for electrolysis so as to have a predetermined surface roughness in step S3 in FIG. The intermediate layer 3 is formed by applying the raw material of the intermediate layer 3 in a plurality of times on the surface having the predetermined surface roughness, and further, the raw material of the surface layer 4 is applied on the surface in a plurality of times. Is made by

  Thus, in the present embodiment, the surface layer 4 made of niobium oxide as an amorphous dielectric has a thin region with a predetermined thickness range and a thick region with a predetermined thickness range. Since it is configured to be formed, as described above, it is possible to efficiently generate ozone at a low current density by electrolyzing the electrolyte solution using the electrode 1 for electrolysis as an anode. .

  In particular, the surface layer 4 has a thin region with a thickness in the range of 0.2 μm to 2.5 μm, so that it is possible to cause the movement of electrons at a higher energy level, and a high current at a low current density. Efficient ozone generation can be realized.

  In addition to the thin region, the surface layer 4 has a thickness region of 5 μm or more, preferably 11 μm or more and 20 μm or less, so that the thin region is effectively peeled off by the thick region. Therefore, the durability of the electrode for electrolysis can be improved.

  Further, the thin region is in a range of 20% to 50% of the entire area of the surface layer 4, and further, the thick region is in a range of 20% to 50% of the entire area of the surface layer 4. While ensuring the durability of the surface layer 4, it is possible to realize highly efficient ozone generation with a low current density.

  Next, the electrode for electrolysis of Example 2 of the present invention will be described. The method for manufacturing the electrode for electrolysis obtained by the example is the same as the flowchart of FIG. 2 in Example 1, and the schematic configuration diagram is also substantially the same as FIG. Omitted.

  That is, in the electrode for electrolysis in this example, the intermediate layer 3 is made of platinum on the surface of the titanium plate constituting the substrate 2 as in the above examples. The details of the substrate 2 and the intermediate layer 3 are the same as those in the first embodiment.

  Next, the surface layer 4 is formed on the surface of the intermediate layer 3. In this embodiment, the surface layer 4 is composed of an oxide of tantalum as an amorphous dielectric. In this case, an organic tantalum compound solution as a raw material for the surface layer 4 is applied to the surface of the substrate 2 on which the intermediate layer 3 is formed. In this embodiment, since the surface layer 4 is made of tantalum oxide, tantalum pentaethoxide is used in this embodiment.

  In this embodiment, tantalum pentaethoxide uses a reagent having a purity of 99%. Moreover, according to the analysis by the high frequency inductively coupled emission spectrometer (ICP emission spectrometer), the same impurities as niobium pentaethoxide as described above were contained. For this reason, the tantalum pentaethoxide in the present embodiment employs an impurity containing about 1% or less of impurities. Moreover, since these impurities do not scatter in the air after firing, the tantalum oxide of the surface layer 4 contains about 1% or less of the impurities. However, these impurities do not affect the characteristics of the surface layer 4 in this embodiment.

In this embodiment, a solvent in which isopropyl alcohol and 2-ethoxyethanol are mixed at a ratio of 4: 1 is used as a tantalum pentaethoxide solvent. In this embodiment, tantalum pentaethoxide is used as a raw material for the surface layer 4, but the tantalum pentaethoxide is not limited to this, and is a compound containing tantalum, which removes substances other than tantalum by firing, and oxidizes. Any substance that can be deposited with tantalum is acceptable. In this embodiment, a solvent in which isopropyl alcohol and 2-ethoxyethanol are mixed at a ratio of 4: 1 is used as a solvent. However, the present invention is not limited to this, and other solvents such as alcohols may be used. Good. In addition, considering the solution stability, a noble metal organic solvent is added to the raw material of the surface layer 4 as will be described in detail later.

  And the raw material of the said surface layer 4 is apply | coated uniformly on the surface of the base | substrate 2 with which the intermediate | middle layer 3 was formed. In addition, in the application of the raw material of the surface layer 4, as in the case of the application of the raw material of the intermediate layer 3, in addition to the method of applying with the spatula, The raw material of the layer 4 is accommodated in a container, and the substrate 2 on which the intermediate layer 3 is formed is immersed in the container. Further, the raw material of the surface layer 4 is applied by rotating the substrate 2 and centrifugal force. A method (spin coating method) or the like may be performed.

The substrate 2 having the surface layer 4 coated on the surface of the intermediate layer 3 is dried at room temperature for 10 minutes, and then dried at a temperature range of 150 ° C. to 250 ° C., preferably 200 ° C. for 10 minutes. . And in preparation of this surface layer 4, heat processing (baking) for 10 minutes is performed in the temperature range of 400 to 625 degreeC. Thereby, a surface layer 4 made of tantalum oxide is formed on the surface of the intermediate layer 3 formed on the surface of the substrate 2.

(1) X-ray diffraction analysis of electrode for electrolysis Next, X-ray diffraction analysis of the surface layer 4 of the electrode 1 for electrolysis obtained as described above is performed, and the crystal structure of the surface layer 4 is analyzed. FIG. 10 shows a case where the electrode 1 for electrolysis is configured with the firing temperature of the heat treatment (step 13) when forming the surface layer 4 being 400 ° C., 450 ° C., 500 ° C., 550 ° C., 600 ° C., and 625 ° C. The X-ray diffraction pattern of each surface layer 4 is shown. The number of steps of the surface layer 4 of the electrode 1 for electrolysis produced under each condition is the same as 25 times.

  In general, X-ray diffraction (XRD) is used for the analysis of the crystal structure, whereby the crystal structure of the tantalum oxide forming the surface layer 4 can be analyzed. In this example, observation was performed using an X-ray diffractometer (D8 Discover manufactured by Bruker AXS).

According to this, each diffraction peak (2θ) shown in the X-ray diffraction pattern of the surface layer 4 of the electrode 1 for electrolysis obtained at a firing temperature higher than 600 ° C. (625 ° C.) is constituted by any firing temperature. Even in the case of the electrode 1, about 22.9 °, about 25.8 °, about 28.5 °, about 33.4 °, about 36.8 °, about 50.7 °, and about 56.0 °. (Peak indicated by a black triangle in FIG. 10). These coincide with the diffraction peak (2θ) peculiar to tantalum oxide (Ta ₂ O ₅ ), and the X-ray diffraction pattern of the surface layer 4 of the electrode 1 for electrolysis obtained at a firing temperature higher than 600 ° C. In the X-ray diffraction pattern of the surface layer 4 of the electrode 1 for electrolysis obtained at a firing temperature of 600 ° C. or lower (in this case, 600 ° C., 550 ° C., 500 ° C., 450 ° C., 400 ° C.) Does not exist.

  Therefore, in the method of the present embodiment as described above, in the electrode 1 for electrolysis that forms the surface layer 4 in a temperature range of 400 ° C. to 600 ° C., the tantalum oxide that forms the surface layer 4 is crystalline. It can be seen that it is amorphous having no structure, that is, indefinite, so-called amorphous.

  In this embodiment, the surface layer 4 is uniformly applied to the surface layer raw material containing tantalum pentaethoxide using a spatula (in this embodiment, the surface of the intermediate layer 3) and fired at a predetermined temperature. Although the amorphous tantalum oxide is formed, the method of forming the surface layer 4 with the amorphous tantalum oxide is not limited to this.

  As another method, there is a method of forming the surface layer 4 by a thermal CVD method. In this thermal CVD method, the intermediate layer 3 is formed on the surface of the substrate 2 in the same manner as in the above embodiment, and then an organic solvent containing tantalum as a raw material for the surface layer is vaporized, and a reaction tube is used using an appropriate carrier gas. For example, a chemical reaction is performed on the surface of the substrate 2 heated to 400 ° C. to 600 ° C., for example.

  As a result, a substance excluding tantalum, which is an organic solvent containing tantalum as a raw material for the surface layer, for example, an organic substance is removed on the surface of the substrate 2 heated to a high temperature, and only tantalum reacts with oxygen in the atmosphere to tantalum oxidation. As a product, it is formed on the surface of the substrate 2 (actually the intermediate layer 3). The tantalum oxide formed on the surface of the substrate 2 (the surface of the intermediate layer 3) constitutes an amorphous thin film (tantalum oxide film).

In addition, as a method for forming the surface layer 4 from amorphous tantalum oxide, for example, there is a dip method.

(2) Calcination Temperature Dependence of Current Efficiency of Ozone Generation Next, with reference to FIG. 4 and FIG. 11, the dependency of the calcination temperature on the generation of ozone by electrolysis using the electrode 1 for electrolysis manufactured as described above will be described. explain. FIG. 4 is a schematic explanatory diagram of the electrolysis apparatus 10 to which the electrolysis electrode 1 is applied, and FIG. 11 is a diagram showing the amount of ozone generated with respect to each firing temperature.

  The electrolysis apparatus 10 includes a treatment tank 11, an electrode 1 for electrolysis as an anode as described above, an electrode 12 as a cathode, and a power source 15 that applies a direct current to the electrodes 1 and 12. Then, a cation exchange membrane (diaphragm: Nafion manufactured by DuPont, which is located between the electrodes 1 and 12 and partitioned into one region where the electrode 1 exists in the treatment tank 11 and the other region where the electrode 12 exists) Name)) 14 is provided. Further, a stirring device 16 is provided in a region where the electrode 1 for electrolysis as an anode is immersed.

  In the treatment tank 11, simulated tap water 13 as an electrolyte solution is stored. In the experiment in this example, simulated tap water is used as the electrolyte solution. However, by providing a cation exchange membrane, substantially the same effect can be obtained even when other aqueous electrolytes are treated. It is done. The electrolyte solution used in the experiment is an aqueous solution simulating tap water. The component composition of the simulated tap water 23 is 5.75 ppm for Na +, 10.02 ppm for Ca2 +, 6.08 ppm for Mg2 +, K + Is 0.98 ppm, Cl- is 17.75 ppm, SO42- is 24.5 ppm, and CO32- is 16.5 ppm.

As the electrode 1 for electrolysis, electrodes having various conditions are used in which the firing temperature of the heat treatment (step 13) when forming the surface layer 4 is 400 ° C., 450 ° C., 500 ° C., 550 ° C., 600 ° C., and 625 ° C. In this case, 2 × 4 cm ² is employed as the surface area of each electrode 1 for electrolysis and the electrode 12 serving as a counter electrode.

  With the above configuration, 150 ml of simulated tap water 13 is stored in each region in the treatment tank 11, and the electrode 1 for electrolysis and the electrode 12 are immersed in the simulated tap water, respectively. The distance between each electrode is 10 mm. Then, a constant current of 160 mA is applied to the electrolysis electrode 1 and the electrode 12 by the power source 15. Moreover, the temperature of the simulated tap water 13 shall be +20 degreeC.

  In this example, the amount of ozone generated by each electrolysis electrode was measured by the indigo method (DR4000 manufactured by HACH) by measuring the amount of ozone generated in the simulated tap water 13 after electrolysis for 1 minute under the above conditions. The concentration of the amount of ozone generated is shown, and the electrodes for electrolysis are evaluated from this.

  As shown in FIG. 11, in this experiment, the electrode for electrolysis in which the firing temperature of the surface layer 4 was 400 ° C. (hereinafter referred to as a firing temperature of 400 ° C., hereinafter, the same applies to each electrode). In this case, the ozone generation amount is 0.01 mg / L, 0.19 mg / L when the baking temperature is 500 ° C., 0.26 mg / L when the baking temperature is 550 ° C., and 0.43 mg / L when the baking temperature is 600 ° C. In the case of L and the firing temperature of 625 ° C., it was 0.08 mg / L.

Comparing these results with the result of the X-ray diffraction analysis, the surface layer 4 is a crystallized tantalum oxide (Ta ₂ O ₅ ) with a firing temperature of 625 ° C. and the surface layer 4 has a crystal structure. In the case where the baking temperature is 450 ° C., 500 ° C., 550 ° C., and 600 ° C., which is amorphous, and the surface layer 4 is made of amorphous tantalum oxide, the ozone generation current efficiency is 1. It is 5 to 5.4 times higher.

  Thus, the surface layer 4 of the electrode for electrolysis 1 is made of tantalum oxide as an example of an amorphous dielectric, so that the electrolyte solution with a low current density (160 mA as an example) using the electrode 1 as an anode is used. It is possible to efficiently generate ozone by electrolysis of.

In particular, since the temperature of the electrolyte solution is not particularly low as in the prior art and a high current density is not required, it is possible to reduce the power consumption required for ozone generation.

(3) Dependence of surface layer material due to noble metal content Here, tantalum pentaethoxide as a surface layer material used for forming the surface layer 4 has poor solution stability. Therefore, in order to improve the solution stability, the raw material of the surface layer 4 is an example of Ta and a noble metal in a solvent adjusted so that the mixing ratio of isopropyl alcohol and 2-ethoxyethanol is 4: 1. An organic solvent in an amount such that the total concentration of Pt is 1.45 mol / L is dissolved to obtain a raw material for the surface layer 4. In the tantalum pentaethoxide solution, hexachloroplatinic acid as a raw material for Pt is adjusted by changing the Pt ratio to Ta in the range of 0 to 100%. The firing temperature when forming the surface layer 4 of each electrode for electrolysis in this experiment is 600 ° C., and the number of coatings is 25 times.

  When Pt is added, when hexachloroplatinic acid / hexahydrate is used as a raw material for Pt, chlorine in the hexachloroplatinic acid / hexahydrate is not scattered by firing, Although the layer 4 also contains chlorine, this does not affect the characteristics of the surface layer 4 in this embodiment.

  Using the same electrolysis apparatus 10 as described above, the evaluation on ozone generation of each electrolysis electrode 1 in which the composition ratio of Ta and noble metal Pt constituting the surface layer 4 was changed was performed. Since the electrolysis conditions are the same as the electrolysis conditions and the method for measuring the amount of ozone generated in (2) of Example 2 above, description thereof is omitted. The experimental results are shown in the graph in FIG. 12 showing the ozone generation concentration with respect to the composition ratio of Ta to each Pt.

  In this experiment, when the composition ratio of Ta to Pt constituting the surface layer 4 (hereinafter simply referred to as Ta) is 0%, the generated ozone concentration is 0, and when Ta is 10%, 0.02 mg / L. When Ta is 20%, 30%, 40% and 50%, 0 is all, when Ta is 60%, 0.01 mg / L, when Ta is 70%, when 0.06 mg / L and Ta is 75% 0.15 mg / L, when Ta is 80%, 0.38 mg / L, when Ta is 85%, 0.26 mg / L, when Ta is 90%, 0.27 mg / L, when Ta is 95%. It was 0.32 mg / L when 19 mg / L and Ta was 100%.

  Thus, when the composition ratio of Ta to Pt is 80%, that is, the ratio of the noble metal (in this case, Pt) to the base metal (in this case, Ta) included in the dielectric constituting the surface layer 4 is 20% or less. In this case, the ozone concentration generated in the electrolyte solution can be 0.1 mg / L or more, and ozone can be generated with high efficiency.

  Moreover, the solution stability can be ensured by adding Pt to the raw material of the surface layer 4 composed of Ta. Therefore, when the ratio of the noble metal to the base metal is greater than 0 and 20% or less, the stability of the raw material constituting the surface layer 4 can be achieved with the metal oxide without lowering the ozone generation efficiency.

  In this embodiment, when the surface layer 4 is composed of amorphous tantalum oxide, platinum is included as a noble metal. However, the noble metal is not limited to this, Or iridium.

  FIG. 13 shows the dependency of the amount of ozone generated when noble metal is added to the raw material of the surface layer 4 employed in the first embodiment. In this case, the raw material of the surface layer 4 is a solvent adjusted so that the mixing ratio of isopropyl alcohol and 2-ethoxyethanol is 4: 1, respectively, and the total concentration of Nb and noble metal (M) is 0.73 mol / An amount of an organic solvent that is L is dissolved to obtain a raw material for the surface layer 4. Platinum (Pt), gold (Au), and iridium (Ir) are used as noble metals, niobium pentaethoxide as an Nb raw material, hexachloroplatinic acid as a Pt material, hexachloroauric acid as an Au material, Ir The iridium chloride as the material is adjusted by changing the Pt ratio, Au ratio, and Ir ratio with respect to Nb in the range of 0 to 50%. The firing temperature when forming the surface layer 4 of each electrode for electrolysis in this experiment is 400 ° C., and the number of coatings is 25 times.

  In this case as well, the electrolysis apparatus 10 was used to evaluate the ozone generation of each electrolysis electrode 1 in which the composition ratio of Nb constituting each surface layer 4 and each noble metal Pt, Au, Ir was changed. . Since the electrolysis conditions are the same as the electrolysis conditions and the method for measuring the amount of ozone generated in (2) of Example 2 above, description thereof is omitted.

  In this experiment, when the composition ratio of Nb to Pt constituting the surface layer 4 (hereinafter simply referred to as Nb) is 50.5%, the generated ozone concentration is 0.005 mg / L, and Nb is 62.6. % Is 0.015 mg / L, Nb is 63.1%, 0.02 mg / L, Nb is 64.6%, 0.017 mg / L, and Nb is 85.6%, 0.27 mg / L. When Nb was 93.3%, it was 0.36 mg / L, and when Nb was 100%, it was 0.54 mg / L.

  When the composition ratio of Nb to Au constituting the surface layer 4 (hereinafter simply referred to as Nb) is 50.5%, the generated ozone concentration is 0.03 mg / L, and 0 when Nb is 80.0%. It was 0.245 mg / L when Nb was 88.0%, 0.38 mg / L when Nb was 95.5%, and 0.54 mg / L when Nb was 100%.

  When the composition ratio of Nb to Ir composing the surface layer 4 (hereinafter simply referred to as Nb) is 85.5%, the generated ozone concentration is 0, and when Nb is 92.3%, 0.173 mg / L When Nb was 100%, it was 0.54 mg / L.

As described above, even when the surface layer 4 is composed of niobium oxide, when the composition ratio of Nb to the noble metal is 80%, that is, the base metal contained in the dielectric constituting the surface layer 4 (in this case) When the ratio of noble metals to Nb) (in this case, in particular, Pt and Au) is 20% or less, the ozone concentration generated in the electrolyte solution can be 0.1 mg / L or more, and high efficiency Can produce ozone.

(2) Surface Layer Thickness Analysis Next, the thickness of the surface layer 4 composed of a dielectric will be examined. FIG. 14 shows a cross-sectional SEM photograph of the electrode 1 for electrolysis produced in Example 2. The electrode 1 for electrolysis comprises the surface layer 4 made of amorphous tantalum oxide, the firing temperature is 600 ° C., the number of coating is 25 times, the solution stability of the raw material of the surface layer 4 and the generation of ozone. In consideration of efficiency, a Pt material is added to the raw material of the surface layer 4, and the composition ratio of Ta to Pt constituting the surface layer 4 is 90%.

  The cross-sectional SEM photograph of FIG. 14 was acquired with a scanning electron microscope (SEM, Hitachi S-3400NX). The layer shown in white is the surface layer 4 in the present invention, and the layer shown in dark gray (thin layer compared to the others) formed in contact with the lower side of the surface layer 4 is This is the intermediate layer 3. The layer shown in gray formed in contact with the lower side of the intermediate layer 3 is the base 2.

  According to this, when 10 or more SEM photographs (photographs of electrode cross section at a magnification of 2000 times) obtained as described above are obtained and the film thickness of the surface layer 4 is observed from the data, the surface layer 4 is at least as thick as possible. This is a non-uniform thickness structure having a thin thin area and a thick thick area. The thickness of the thin region is in the range of 0.2 μm to 2.5 μm, preferably 0.2 μm to 1.5 μm, and / or an average of 0.5 μm. The thickness of the thick region is 5 μm or more, preferably 11 μm or more, and is 20 μm or less in consideration of electrode production costs and ozone generation efficiency.

  Further, when the ratio of film thickness variation is statistically processed and analyzed from the above data, the thin region having a thickness of 0.2 μm to 2.5 μm or less is the entire area of the surface layer 4 of the electrode 1 for electrolysis. Of 20% to 50%. The thickness region having a thickness of 5 μm or more was in the range of 20% to 40% of the entire area of the surface layer 4 of the electrode 1 for electrolysis. And the surface layer 4 of the electrode 1 for electrolysis of these thin areas and parts other than a thick area is an area | region made into thickness larger than 2.5 micrometers and less than 5 micrometers.

  In the present embodiment, the thin region and the thick region of the surface layer 4 are formed by etching the base 2 of the electrode 1 for electrolysis so as to have a predetermined surface roughness in step S3 in FIG. The intermediate layer 3 is formed by applying the raw material of the intermediate layer 3 in a plurality of times on the surface having the predetermined surface roughness, and further, the raw material of the surface layer 4 is applied on the surface in a plurality of times. Is made by

  Thus, in this embodiment, the surface layer 4 made of tantalum oxide as an amorphous dielectric has a thin region with a predetermined thickness range and a thick region with a predetermined thickness range. Since it is configured to be formed, as described above, it is possible to efficiently generate ozone at a low current density by electrolyzing the electrolyte solution using the electrode 1 for electrolysis as an anode. .

  In particular, the surface layer 4 has a thin region with a thickness in the range of 0.2 μm to 2.5 μm, so that it is possible to cause the movement of electrons at a higher energy level, and a high current at a low current density. Efficient ozone generation can be realized.

  In addition to the thin region, the surface layer 4 has a thickness region of 5 μm or more, preferably 11 μm or more and 20 μm or less, so that the thin region is effectively peeled off by the thick region. Therefore, the durability of the electrode for electrolysis can be improved.

  Further, the thin region is in the range of 20% to 50% of the entire area of the surface layer 4, and the thick region is in the range of 20% to 40% of the entire area of the surface layer 4. While ensuring the durability of the surface layer 4, it is possible to realize highly efficient ozone generation with a low current density.

  As described above, the amorphous metal oxide as the dielectric constituting the surface layer 4 of the electrode 1 for electrolysis in each embodiment is preferably an element of Group 3, 4, or 5 of the periodic table, and more preferably By using niobium or tantalum, the electrode 1 realizing high ozone generation efficiency can be easily configured. In addition, by forming the metal oxide with niobium or tantalum, the production cost can be reduced, and since no toxic substances such as lead dioxide are used, the environmental load can be reduced.

  In addition, the electrode 1 for electrolysis in each embodiment is formed on the surface of the base 2 on the base 2 and on the surface of the base 2, and is at least a hardly oxidizable metal or a conductive metal oxide. Or the intermediate layer 3 containing any of the metals that are conductive even if oxidized, for example, as described above, the intermediate layer is formed of platinum, gold, iridium, iridium oxide, so that the electrode at the anode Electrons in the reaction can effectively move in the surface layer 4. Therefore, an electrode reaction can occur at a high energy level on the surface of the surface layer 4. Thereby, ozone can be generated efficiently at a lower current density.

  In particular, since the intermediate layer 3 is formed of a hardly oxidizable metal on the surface of the base body 2, when electrolysis is performed by the electrode 1, the problem that the surface of the base body 2 is oxidized and becomes non-conductive is avoided. Can do. Thereby, durability of the electrode 1 can be improved. Further, the production cost can be reduced as compared with the case where the entire base 2 is made of the material constituting the intermediate layer, and in such a case, ozone can be generated efficiently in the same manner. it can.

1 Electrode for Electrolysis 2 Substrate (Conductive Substrate)
3 Intermediate Layer 4 Surface Layer 10 Electrolyzer 11 Treatment Tank 12 Electrode (Cathode)
13 Electrolyte solution (simulated tap water)
14 Cation exchange membrane 15 Power supply 16 Stirrer

Claims (19)

An electrode for electrolysis comprising a substrate and a surface layer formed on the substrate,
The electrode for electrolysis, wherein the surface layer is an amorphous dielectric. ^{2. The} electrode for electrolysis according to claim 1, wherein the dielectric is a metal oxide, and a loading amount of the metal element is 2 μmol / cm ² or more and 16 μmol / cm ² or less.   3. The electrode for electrolysis according to claim 2, wherein the metal constituting the metal oxide is an element of Group 3, 4, or 5 of the periodic table.   The electrode for electrolysis according to claim 2 or 3, wherein the metal constituting the metal oxide is niobium or tantalum.   5. The metal constituting the metal oxide is tantalum, and the dielectric contains a noble metal, and a ratio of the noble metal to a base metal is greater than 0 and 20% or less. The electrode for electrolysis of description.   The electrode for electrolysis according to claim 5, wherein the noble metal is platinum, gold, or iridium.   The base is formed inside the surface layer and is formed on the surface of the base, and is at least a hardly oxidizable metal, a conductive metal oxide, or conductive even when oxidized. The electrode for electrolysis according to any one of claims 1 to 6, wherein an intermediate layer containing any one of metals is formed.   The electrode for electrolysis according to claim 7, wherein the intermediate layer is composed of platinum, gold, iridium, or iridium oxide. An electrode for electrolysis comprising a substrate and a surface layer composed of a dielectric on the substrate,
The surface layer includes at least a thin region having a small thickness and a thick region having a large thickness,
An electrode for electrolysis having an uneven thickness structure in which a thickness of the thin region is in a range of 0.2 μm to 2.5 μm and a thickness of the thick region is 5 μm or more.   The electrode for electrolysis according to claim 9, wherein the thin region is in a range of 20% to 50% of the entire area of the surface layer.   11. The electrode for electrolysis according to claim 9, wherein the thick region is in a range of 20% to 50% of the entire area of the surface layer.   12. The electrode for electrolysis according to claim 9, wherein the dielectric is amorphous niobium oxide or amorphous tantalum oxide.   A method for producing an electrode for electrolysis, wherein an amorphous surface layer is formed by applying a heat treatment after applying a surface layer material to a substrate. A first step of forming the intermediate layer on the surface of the substrate by applying a heat treatment after applying the raw material of the intermediate layer on the surface of the substrate;
An electrode for electrolysis comprising a second step of forming an amorphous surface layer by applying a heat treatment after applying a raw material of the surface layer to the surface of the intermediate layer after the first step. Production method.   The method for producing an electrode for electrolysis according to claim 13 or 14, wherein the surface layer is made of amorphous niobium oxide or amorphous tantalum oxide.   The electrode for electrolysis according to any one of claims 13 to 15, wherein the surface layer is niobium oxide, and a heat treatment temperature in the heat treatment is set to 300 ° C to 500 ° C. Production method.   The electrode for electrolysis according to any one of claims 13 to 15, wherein the surface layer is made of tantalum oxide, and a heat treatment temperature in the heat treatment is set to 450 ° C to 600 ° C. Production method.   The electrode for electrolysis according to any one of claims 13 to 17, wherein the surface layer is formed by repeating a heat treatment step 15 to 50 times after coating a raw material of the surface layer on the substrate. Manufacturing method.   The method for producing an electrode for electrolysis according to any one of claims 13 to 18, wherein the raw material of the surface layer contains an organic metal.