JP4290169B2 - Electrode for electrolysis and method for producing persulfate-dissolved water using the electrode - Google Patents

Description

  The present invention relates to an electrode for electrolysis used in an industrial or consumer electrolysis process and a method for producing persulfate-dissolved water using the electrode for electrolysis.

  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 generating method in which ozone gas is generated by the ultraviolet lamp or discharge method 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 generating device and 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 obtaining ozone water by generating ozone in water by electrolysis of water as a method for solving the above problems. In such a method, an ozone generating electrode including an electrode base material formed of a porous body or a net body and an electrode catalyst including an oxide of a platinum group element, and the ozone generating electrode are used. .

  On the other hand, persulfuric acid is known as a substance having a very strong oxidizing power. This persulfuric acid is an oxidant widely used in semiconductor cleaning, polymerization initiators, oxidizing agents, bleaching agents, photographic processing agents, oxidizing agents for reagents such as manganese and chromium, and analytical reagents. In general, sulfuric acid is used for cleaning semiconductors. However, since persulfuric acid has a stronger oxidizing power than sulfuric acid, it is possible to perform cleaning efficiently at a lower concentration and in a smaller amount than sulfuric acid. .

  The persulfuric acid production method is generally based on an electrochemical method. For example, a platinum ribbon is used as an electrode for persulfuric acid production. However, in the electrolytic treatment using the platinum ribbon, the amount of consumption increases depending on the electrolysis conditions, and there are inconveniences such as contamination by impurities and frequent electrode replacement.

Therefore, as shown in Patent Document 4, an electrode using a conductive diamond supported on a substrate has been developed as an electrode for producing persulfuric acid.
Japanese Patent Laid-Open No. 11-77060 JP-A-11-333475 JP 2002-80986 A JP 2001-192874 A

  In the method of generating ozone water by electrolysis of water as described above, the platinum group element is a standard anode material and has a feature that it hardly dissolves in an aqueous solution containing no organic matter. However, as an electrode for generating ozone, Ozone generation efficiency is low, and it is difficult to generate ozone water by a highly efficient electrolysis method. In addition, such conventional ozone water generation by electrolysis using an electrode for ozone generation requires electrolysis at a high current density for ozone generation, and there is a problem in energy consumption and electrode life.

  In addition, in the electrode for producing persulfuric acid using the conductive diamond as described above, there is a problem that the production cost of the electrode itself rises, and development of an electrode material capable of producing persulfuric acid at low cost is desired. It was rare.

  Therefore, the present invention has been made to solve the conventional technical problem, and an electrolysis electrode capable of generating ozone water with high efficiency by electrolysis of water with low current density and A method for producing persulfate-dissolved water using the electrode is provided.

The electrode for electrolysis for generating ozone of the present invention includes a base, a conductive intermediate layer containing platinum formed on the surface of the base, and a surface that is a dielectric formed by sputtering on the surface of the intermediate layer. And the dielectric is any one of tantalum oxide, niobium oxide, zirconium oxide, titanium oxide, or tungsten oxide, and the thickness of the surface layer is 40 nm or more and less than 1000 nm. It is characterized by that.

Method of generating a persulfate dissolved water of a second aspect of the present invention, electrolysis of a generation method of persulfate dissolved water to form an aqueous solution to an electrolytic process to persulfate dissolved water containing sulfate ions, according to claim 1, wherein The electrode for use is used as an anode.

By performing electrolysis with the electrode for electrolysis of the present invention , ozone can be efficiently generated at a low current density.

Moreover , according to the method for producing persulfate-dissolved water of the present invention, there is provided a method for producing persulfate-dissolved water by electrolytically treating an aqueous solution containing sulfate ions to produce persulfate-dissolved water, wherein By using it as an anode, it becomes possible to efficiently produce persulfuric acid-dissolved water .

  Hereinafter, preferred embodiments of the electrode for electrolysis of the present invention will be described with reference to the drawings. FIG. 1 is a plan sectional view of an electrode 1 for electrolysis according to the present invention.

  As shown in FIG. 1, the electrode for electrolysis 1 includes a 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.

Base 2 in the present invention, as a conductive material, e.g., platinum (Pt) or tantalum (Ta), zirconium (Zr), niobium (Nb) metal such or these metals two or more alloys, or silicon ( Si) or the like. In particular, since the substrate 2 used in the present embodiment preferably has a particularly flat surface, silicon whose surface is processed to be flat is used.

  The intermediate layer 3 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, or the like. The metal having conductivity even when oxidized is composed of ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir) or silver (Ag) contained in the platinum group element. 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. In this embodiment, the intermediate layer 3 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, the surface layer 4 is formed in a layered manner on the surface of the substrate 2 by a dielectric together with the intermediate layer 3 so as to cover the intermediate layer 3, and the surface layer 4 has a predetermined thickness, which is 0 in this embodiment. Largely configured to 2000 nm or less. Although the details of the thickness of the surface layer 4 will be described later, it is more preferable that the thickness be 40 nm or more and less than 1000 nm.

  As the dielectric constituting the surface layer 4, tantalum oxide, aluminum oxide, titanium oxide, tungsten oxide, niobium oxide, or the like is used.

The surface layer 4 has different crystal structures such as oxides containing two or more kinds of metal elements such as perovskite oxides such as barium titanate (BaTiO ₃ ), and titanium oxide and tantalum oxide. A mixture of two or more kinds of oxides may be used, and in this case also, those containing the above-mentioned noble metal or noble metal oxide in addition to these oxides can be used.

Here, tantalum oxide means crystalline TaO, Ta ₂ O ₅ , TaO _1-X , Ta ₂ O _5-X in which some oxygen vacancies are generated in such an oxide, and amorphous (amorphous) TaO _X, etc., is intended to indicate a substance in general that tantalum and oxygen and compounds. Aluminum oxide refers to Al ₂ O ₃ , AlO _x, etc., titanium oxide refers to TiO ₂ , Ti ₂ O ₃ , TiOx, etc., and tungsten oxide refers to WO ₃ , WOx, etc. In addition, other dielectrics for forming the surface layer 4 include Na ₂ O, NaOx, MgO, MgOx, SiO ₂ , SiOx, K ₂ O, KOx, CaO, CaOx, Sc ₂ O ₃ , ScOx, V _{2 O 5, VOx, CrO 2} , CrOx, Mn 3 O 4, MnOx, Fe 2 O 3, FeOx, CoO, CoOx, NiO, NiOx, CuO, CuOx, ZnO, ZnOx, GaO, GaOx, GeO 2, GeOx, Rb ₂ O ₃ , RbOx, SrO, SrOx, Y ₂ O ₃ , YOx, ZrO ₂ , ZrOx, Nb ₂ O ₅ , NbOx, MoO ₃ , MoOx, In ₂ O ₃ , InOx, SnO ₂ , SnOx, Sb ₂ O _{5, sbOx, Cs 2 O 5} , CsOx, BaO, BaOx, La 2 O 3, LaOx, CeO 2, CeOx, PrO 2, PrOx, Nd 2 O 3, NdOx, Pm ₂ O ₃ , PmOx, Sm ₂ O ₃ , SmOx, Eu ₂ O ₃ , EuOx, Gd ₂ O ₃ , GdOx, Tb ₂ O ₃ , TbOx, Dy ₂ O ₃ , DyOx, Ho ₂ O ₃ , HoOx, Er ₂ O ₃ , ErOx, Tm ₂ O ₃ , TmOx, Yb ₂ O ₃ , YbOx, Lu ₂ O ₃ , LuOx, HfO ₂ , HfOx, PbO ₂ , PbOx, Bi ₂ O ₃ , BiOx, etc. are applicable.

  Next, the manufacturing method of the electrode for electrolysis of this invention is demonstrated with reference to the flowchart figure of FIG. Silicon is used as the substrate 2. The silicon used has a very flat surface. In this embodiment, silicon is used as the substrate 2, but other than this, a conductive material as described above, preferably one having a flat surface may be used.

  First, in step S1, the silicon substrate 2 is pretreated with 5% hydrofluoric acid, and the natural oxide film formed on the surface of the silicon substrate 2 is removed. Thereby, the surface of the base 2 is made flatter. Thereafter, the surface of the substrate 2 is rinsed with pure water in step S2, and thereafter introduced into the chamber of the existing sputtering apparatus in steps S3 and S4 to form a film.

  In the present embodiment, the formation of the intermediate layer 3 and the surface layer 4 on the substrate 2 is performed by the rf sputtering method. In this embodiment, since the intermediate layer 3 is made of platinum, an intermediate layer constituting material Pt (80 mmφ) is used as the first target, the rf power is 100 W, the Ar gas pressure is 0.9 Pa, the base 2 and the target. The distance between and is set to 60 mm, and film formation is performed at room temperature for 20 minutes (step S3). Thereby, the intermediate layer 3 having a thickness of about 100 nm is formed on the surface of the base 2.

  Next, the surface layer 4 is formed on 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, the target is changed to Ta which is a surface layer constituent material, and the same conditions as described above, that is, rf power is 100 W, Ar gas pressure is 0.9 Pa, The distance between the substrate 2 and the target is set to 60 mm, and film formation is performed at room temperature for 5 to 180 minutes (step S4). Thereby, a surface layer 4 having a thickness of about 7 nm to 1000 nm is formed on the surface of the intermediate layer 3 of the substrate 2. The film thicknesses of the intermediate layer 3 and the surface layer 4 are obtained by obtaining the supported amounts of Pt and Ta by evaluation with fluorescent X-rays and converting the thicknesses based on the obtained amounts.

  This makes it possible to form the intermediate layer 3 and the surface layer 4 with an appropriate thickness and an appropriate amount with high in-plane uniformity, and to form the intermediate layer 3 and the surface layer 4 with high adhesion. become able to. Therefore, the durability of the electrode 1 for electrolysis can be improved.

Thereafter, the substrate 2 on which the intermediate layer 3 and the surface layer 4 are formed is thermally baked (annealed) in a muffle furnace at 600 ° C. in an air atmosphere for 30 minutes in step S5, so that the electrode 1 for electrolysis is obtained. It is done. Thereby, the metal tantalum constituting the surface layer 4 formed on the surface of the intermediate layer 3 is uniformly oxidized. In addition, since metal tantalum is oxidized and becomes tantalum oxide by the said heat baking, the thickness of the surface layer 4 will be about 14 nm-2000 nm. Further, in this example, after the intermediate layer 3 and the surface layer 4 are formed by the sputtering method, the thermal baking is performed, and the surface of the electrode 1 is oxidized. When the electrode 1 is used for electrolysis, Since the electrode surface is oxidized, it is not necessary to perform the thermal baking.

  In the electrode 1 for electrolysis obtained as described above, the surface layer 4 is all oxidized. Further, the intermediate layer 3 forms silicon of the base 2 and platinum silicide. Further, silicon stops at the intermediate layer 3 and is not diffused into the surface layer 4. Similarly, the platinum constituting the intermediate layer 3 does not reach the inside of the surface layer 4. Furthermore, the surface layer 4 is very uniformly distributed on the surface of the intermediate layer 3, and the layer is uniformly formed on the entire surface of the intermediate layer 3. Thereby, since the surface of the electrode 1 for electrolysis is uniformly covered with the surface layer 4, the base | substrate 2 and the intermediate | middle layer 3 are not exposed. Therefore, since no gaps or cracks are formed in the surface layer 4, the electrolyte to be subjected to electrolytic treatment does not directly reach the internal intermediate layer 3 or the substrate 2. Therefore, the inconvenience that the base body 2 is eroded during electrolysis can be avoided.

  In the present embodiment, since the surface layer 4 is made of only a dielectric, the use of noble metal or noble metal oxide for the surface layer 4 can be reduced, and the cost can be reduced. .

  Next, ozone generation by electrolysis using the electrode 1 for electrolysis manufactured in the above embodiment will be described with reference to FIG. FIG. 3 is a schematic explanatory diagram of an ozone water generator 20 to which the electrode 1 for electrolysis of the present embodiment is applied. The ozone water generator 20 includes a treatment tank 21, an electrode 1 for electrolysis as an anode as described above, an electrode 22 as a cathode, a cation exchange membrane 24, and a power supply 25 that applies a direct current to the electrodes 1 and 22. It consists of. In the treatment tank 21, simulated tap water 23 as an electrolyte solution is stored.

  The electrode 1 for electrolysis is produced by the manufacturing method as described above. The electrolysis electrode 1 used in the ozone water generating apparatus 20 uses a total of five types in which the thickness of the surface layer 4 is about 14 nm, about 56 nm, about 170 nm, about 730 nm, and about 1800 nm. Thus, each electrolysis electrode 1 is evaluated by measuring the amount of ozone generated when each electrolysis electrode 1 is used as an anode.

  On the other hand, platinum is used for the electrode 22 as a cathode. In addition to this, an insoluble electrode obtained by firing platinum on the surface of the silicon substrate 2, a platinum-iridium-based electrode for electrolysis, a carbon electrode, or the like may be used.

  The cation exchange membrane 24 is composed of a fluororesin membrane having durability against an oxidizing agent such as hydrogen peroxide. As a typical cation exchange membrane, there are perfluorosulfonic acid membranes such as Nafion 115, 117, 315, and 350 manufactured by DuPont. Nafion is also used as the cation exchange membrane 24 in this embodiment. Shall.

The electrolyte solution to be electrolytically treated in this example 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 Ca ²⁺ , Mg ^{2. +} Is 6.08 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.

With the above configuration, the simulated tap water 23 having a water temperature of 15 ° C. is stored in the treatment tank 21 in an amount of 150 ml on each of the anode side and the cathode side partitioned by the cation exchange membrane 24, for a total of 300 ml. Electrolysis electrode 1 and electrode 22 are immersed in simulated tap water on the anode side and simulated tap water on the cathode side, with cation exchange membrane 24 interposed therebetween. In addition, the area of the electrode 1 for electrolysis and the electrode 22 in a present Example shall be 40 mm x 20 mm (immersion part 35 mm x 15 mm), and the distance between electrodes shall be 10 mm. Then, a constant current of about 100 mA and a current density of about 20 mA / cm ² is applied to the electrode 1 for electrolysis and the electrode 22 by the power source 25.

  In this embodiment, the amount of ozone generated by the electrolysis electrode 1 is measured by using a colorimetric method for the ozone concentration in the simulated tap water 23 after electrolysis for 1 minute under the above conditions.

  Next, the ozone generation amount with respect to the thickness of the surface layer 4 in the electrode 1 for electrolysis of the present embodiment will be described with reference to FIG. FIG. 4 shows the amount of ozone generated in each of the electrolysis electrodes 1 under the same conditions of the above five types of electrolysis electrodes in this example. In FIG. 4, the vertical axis represents the amount of ozone generated (mg / l), and the horizontal axis represents the thickness (nm) of the surface layer 4 of the electrode 1 for electrolysis.

  According to the experimental results of FIG. 4, when the thickness of the surface layer 4 of the electrode 1 for electrolysis is about 1800 nm, the amount of ozone generated is 0.05 mg / l, and when the thickness is about 14 nm, ozone generation is generated. The amount was as small as 0.12, but the ozone generation amount increased rapidly when the amount was 40 nm or more and less than 1000 nm. The experimental results show that the surface layer 4 has an ozone generation amount of 0.275 mg / l at about 56 nm, 0.28 mg / l at about 170 nm, and 0.25 mg / l at about 730 nm.

  On the other hand, FIG. 5 illustrates experimental results when the material constituting the surface layer 4 of the electrolysis electrode 1 is not only tantalum oxide but also niobium oxide, zirconium oxide, titanium oxide and tungsten oxide. FIG. 5 shows the experimental results showing the current efficiency for ozone with respect to the temperature in the thermal firing (step S5) for each of the above five types of substances.

  In addition, each heat-firing temperature in the said experiment is 300 degreeC, 400 degreeC, 500 degreeC, 600 degreeC, and the thickness of the surface layer 4 is all around 50 nm. Four types are used for each substance, whereby each electrolysis electrode 1 is evaluated by measuring current efficiency for ozone when each electrolysis electrode 1 is used as an anode.

  Further, platinum is used for the electrode 22 as the cathode as in the experiment in FIG. 4, and Nafion is used for the cation exchange membrane 24. The simulated tap water 23 similar to the above aqueous solution is also used for the electrolytic solution to be subjected to electrolytic treatment.

With the above configuration, a simulated tap water 23 having a water temperature of + 15 ° C. is stored in the treatment tank 21 in an amount of 150 ml on each of the anode side and the cathode side partitioned by the cation exchange membrane 24, for a total of 300 ml. Electrolysis electrode 1 and electrode 22 are immersed in simulated tap water on the anode side and simulated tap water on the cathode side, with cation exchange membrane 24 interposed therebetween. In this embodiment, the area of the electrode 1 for electrolysis and the electrode 22 is 2.25 cm ² and the distance between the electrodes is 10 mm. Then, a constant current of about 50 mA and a current density of about 22.2 mA / cm ² is applied to the electrode 1 for electrolysis and the electrode 22 by the power source 25. Perform electrolysis for 1 minute under the above conditions.

  According to the experimental results in FIG. 5, when the surface layer 4 of the electrode 1 for electrolysis is made of tantalum oxide, the current efficiency for ozone when the firing temperature is 300 ° C. is 8.4%, 400 The current efficiency at ℃ was 9.6%, the current efficiency at 500 ° C was 9.6%, and the current efficiency at 600 ° C was 10.8%. When the surface layer 4 of the electrode 1 for electrolysis is made of niobium oxide, the current efficiency for ozone when the firing temperature is 300 ° C. is 6.0%, and the current efficiency when the temperature is 500 ° C. is 6. The current efficiency at 0% and 600 ° C. was 7.2%. When the surface layer 4 of the electrode 1 for electrolysis is made of zirconium oxide, the current efficiency for ozone when the firing temperature is 300 ° C. is 7.8%, and the current efficiency when the firing temperature is 400 ° C. is 5. The current efficiency at 4% and 500 ° C. was 6.6%, and the current efficiency at 600 ° C. was 7.2%. When the surface layer 4 of the electrode 1 for electrolysis is made of titanium oxide, the current efficiency for ozone when the baking temperature is 300 ° C. is 6.0%, and the current efficiency when the temperature is 400 ° C. is 3. The current efficiency at 6% and 500 ° C. was 6.0%, and the current efficiency at 600 ° C. was 8.4%. When the surface layer 4 of the electrode 1 for electrolysis is made of tungsten oxide, the current efficiency for ozone when the firing temperature is 300 ° C. is 7.2%, and the current efficiency when the temperature is 400 ° C. is 10. The current efficiency at 2% and 500 ° C. was 9.6%, and the current efficiency at 600 ° C. was 0.6%.

  From the above experimental results, even when the surface layer 4 constituting the surface of the electrolysis electrode 1 is made of tantalum oxide, niobium oxide, zirconium oxide, titanium oxide, tungsten oxide, or the like which is not a metal, as described above. It can be seen that electrolysis of the electrolyte solution is possible. This is because the thickness of the surface layer 4 made of tantalum oxide, niobium oxide, zirconium oxide, titanium oxide, tungsten oxide, or the like is relatively thin, for example, about 40 nm as described above. This is presumably because electrons moved to the intermediate layer 3 made of a conductive material through the impurity level or by the Fowler-Nordheim tunnel.

  In the experiment shown in FIG. 4 as described above, the voltage between the electrodes at the time of electrolysis was about 90 V (using an electrode having a thickness of the surface layer 4 of 56 nm). This is because the electrode voltage during electrolysis in the case where the electrode 1 for electrolysis is composed only of platinum silicide is about 75 V, but does not reach a remarkably large value. Further, the ozone generation efficiency when the electrode 1 for electrolysis of the present invention is used is higher than that when an electrode composed of platinum silicide is used.

  Usually, when a metal electrode is used as an electrode for electrolysis, an electrode reaction at the anode occurs when an empty level just above the Fermi level receives electrons from the electrolyte. On the other hand, when the electrode 1 for electrolysis formed with the surface layer 4 composed of a dielectric according to the present invention is used, an empty space near the bottom of the conductor at an energy level about half the band gap higher than the Fermi level. A level is generated by receiving electrons from the electrolyte.

  Therefore, when the electrode 1 for electrolysis according to the present invention is used, compared with the case where a platinum silicide electrode is used, the transfer of electrons at a higher energy level occurs and the electrode reaction occurs, so that the ozone generation efficiency is higher. It is thought to rise.

  Thereby, by forming the surface layer 4 composed of the dielectric of the electrode for electrolysis 1 to be larger than 0 and 2000 nm or less, ozone can be generated with high efficiency even at a low current density. An electrode can be obtained. In particular, by forming the surface layer 4 with a thickness of 40 nm or more and less than 1000 nm, ozone can be generated with high efficiency even at a significantly lower current density.

  In this embodiment, the substrate 2 on which the intermediate layer 3 and the surface layer 4 are formed is made of a material having a flat surface, so that the intermediate layer 3 and the surface layer 4 are uniformly formed on the surface of the substrate 2. be able to. Therefore, the thickness of each layer 3 or 4 is formed uniformly with respect to the electrode surface, whereby uniform electrical conduction can be realized over the entire surface of the electrode 1 for electrolysis. Thereby, the variation in the electric conduction in the whole electrode surface can be suppressed, and the ozone generation efficiency can be improved.

  In the present embodiment, since the intermediate layer 3 and the surface layer 4 are formed on the surface of the substrate 2 by sputtering, the layers can be more uniformly formed on the surface of the substrate 2. This also makes it possible to form the intermediate layer 3 and the surface layer 4 having a uniform thickness over the entire surface of the substrate 2, so that electric conduction can be performed uniformly over the entire electrode surface. As a result, the ozone generation efficiency can be improved. In such a case, even if the treatment for flattening the surface of the substrate 2 is somewhat insufficient, the sputtering method forms the layer with a uniform thickness over the entire surface on which the layer is to be formed. This also makes it possible to conduct electricity uniformly over the entire electrode surface.

  The method for forming the intermediate layer 3 and the surface layer 4 is not limited to the sputtering method as in this embodiment, and may be, for example, a CVD method, a vapor deposition method, an ion plating method, a plating method, or the like. Shall.

  The material of the surface layer 4 used in the experiment is tantalum oxide, niobium oxide, zirconium oxide, titanium oxide, tungsten oxide or the like. Remarkably high ozone generation efficiency is seen.

  Further, as described above, in this embodiment, the substrate 2 made of silicon is made of at least a hardly oxidizable metal, a metal oxide having conductivity, or a metal having conductivity even when oxidized. The electrode 2 for electrolysis is formed by forming the intermediate layer 3 including the above and further forming the surface layer 4 as described above on the surface of the intermediate layer 3, but the substrate 2 is made of the same material as the intermediate layer 3. That is, when it is made of a material containing at least a hardly oxidizable metal, a conductive metal oxide, or a metal that is conductive even when oxidized, the intermediate layer 3 Similarly, an electrode capable of efficiently generating ozone can be configured without forming the electrode. However, by covering the base 2 with the intermediate layer 3 made of the above material as in the present invention, the electrode 1 that can similarly generate ozone can be realized at a low production cost. Is possible.

Next, the production of persulfuric acid (peroxodisulfuric acid: H ₂ S ₂ O ₈ ) by electrolysis using the electrode 1 for electrolysis produced in the above embodiment will be described with reference to FIG. FIG. 6 is a schematic explanatory diagram of a persulfuric acid-dissolved water generating apparatus 30 to which the electrolysis electrode 1 of this embodiment is applied. The persulfuric acid-dissolved water generating device 30 applies a direct current to the treatment tank 31, the electrode 1 for electrolysis as an anode, the electrode 32 as a cathode, the cation exchange membrane 34, and the electrodes 1 and 32 as described above. And a power source 35. In the treatment tank 31, 0.1 M sulfuric acid (electrolyte solution 33) is stored as an electrolyte solution containing sulfate ions on the anode side with the cation exchange membrane 34 interposed therebetween.

  The electrode 1 for electrolysis is produced by the manufacturing method as described above. In the electrode 1 for electrolysis used in the persulfuric acid-dissolved water generating apparatus 30, tantalum oxide is used as an oxide as a dielectric contained in the surface layer 4, and the thickness of the surface layer 4 is from 0. The thickness is set to 2000 nm or less, preferably 40 nm or more and less than 1000 nm. In this embodiment, the one with about 56 nm is used.

  On the other hand, platinum is used for the electrode 32 as a cathode. In addition to this, an insoluble electrode obtained by firing platinum on the surface of the silicon substrate 2, a platinum-iridium-based electrode for electrolysis, a carbon electrode, or the like may be used.

  The cation exchange membrane 34 is composed of a fluororesin-based membrane having durability against a predetermined oxidant. As a typical cation exchange membrane, there are perfluorosulfonic acid type membranes such as Nafion 115, 117, 315, and 350 manufactured by DuPont. Nafion is also used as the cation exchange membrane 34 in this embodiment. Shall.

  With the above configuration, 0.1 M sulfuric acid (electrolyte solution 33) is stored in the treatment tank 31 on each of the anode side and the cathode side partitioned by the cation exchange membrane 34, and the electrode 1 for electrolysis and the electrode 32 are respectively stored. The anode side electrolyte solution 33 and the cathode side electrolyte solution 33 are immersed in a cation exchange membrane 34. Thereafter, a direct current is applied to the electrodes 1 and 32 by the power source 35 to electrolyze the electrolyte solution 33.

Normally, when water is electrolyzed using an electrode for electrolysis, oxygen gas is generated on the anode side (reaction A). In addition to oxygen, ozone and hydrogen peroxide are generated by selecting a material for the electrode for electrolysis (reaction B and reaction C). Hereinafter, reactions A to C are shown.
Reaction A 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻
Reaction B 3H ₂ O → O ₃ + 6H ⁺ + 6e ⁻
Reaction C 2 H ₂ O → H ₂ O ₂ + 2H ⁺ + 2e ⁻

When the electrolytic solution 33 containing sulfate ions is electrolyzed using the electrode 1 for electrolysis according to the present invention as an anode, persulfuric acid is generated on the anode side (reaction D). It should be noted that persulfate ions are similarly generated when the electrolyte solution 33 contains sulfite ions (reaction E). Hereinafter, reactions D and E are shown.
Reaction D 2SO ₄ ²⁻ → S ₂ O ₈ ²⁻ + 2e ⁻
Reaction E 2HSO ₄ ⁻ → S ₂ O ₈ ²⁻ + 2H ⁺ + 2e ⁻

  This is because a normal electrolysis electrode has a narrow potential window, and therefore, a reaction on the anode side having a low theoretical electrolysis voltage, particularly an oxygen generation reaction occurs preferentially. On the other hand, the electrode 1 for electrolysis in this example has an extremely wide potential window and an extremely high active overvoltage for the oxygen generation reaction. Therefore, the target oxidation reaction, i.e., in this example, takes precedence over the oxygen generation reaction. The oxidation reaction of sulfate ions contained in the electrolyte solution 33 proceeds. Thus, persulfuric acid-dissolved water can be obtained by electrolytic treatment of an aqueous solution containing sulfate ions.

  On the other hand, FIG. 7 shows a case where the electrolytic solution 33 is electrolyzed by the electrolysis electrode 1 by changing the potential of the electrolysis electrode 1 constituting the anode with time using a constant potential electrolysis device (potentiostat). Is a current-potential curve (cyclic voltammogram). FIG. 8 is a current-potential curve when an electrolytic solution containing perhydrochloric acid shown for comparison with FIG. 7 is electrolyzed.

  According to the current-potential curve in the case where the electrolyte solution 33 containing sulfate ions shown in FIG. 7 is electrolyzed, an oxygen generation peak is shown in the vicinity of the potential of 3.5 V. A chemical reaction peak is shown around 2.5V. Since the electrolyte solution 33 does not contain substances other than sulfuric acid and water, it can be seen that there was an oxidation reaction of sulfate ions. The current-potential curve shown in FIG. 8 is obtained by electrolyzing an electrolyte solution containing perhydrochloric acid. In the current-potential curve, no chemical reaction peak is shown in addition to the oxygen generation peak. By comparing these FIG. 7 and FIG. 8, it is clear that a chemical reaction peak is shown in FIG. 7 in addition to the oxygen production peak.

  Therefore, by fixing the potential of the electrode 1 for electrolysis constituting the anode to around 2.5 V where the chemical reaction peak is shown, a solution containing sulfate ions, that is, the electrolytic solution 33 is subjected to electrolytic treatment, so that a high current is obtained. Persulfuric acid can be produced efficiently.

  In this way, persulfuric acid having a very strong oxidizing power can be efficiently produced by electrolytic treatment of an aqueous solution containing sulfate ions at the site of use. The danger due to can be avoided. Therefore, it is easy to use persulfuric acid, which has a stronger oxidizing power than sulfuric acid, as a cleaning agent for semiconductors, a polymerization initiator, an oxidizing agent, a bleaching agent, a photographic processing agent, an oxidizing agent for reagents such as manganese and chromium, and an analytical reagent. Become. In particular, when using the persulfuric acid-dissolved water in semiconductor cleaning, it is possible to achieve the purpose with a lower concentration and a smaller amount than before, so the amount of solution required for cleaning is reduced. This makes it possible to simplify waste water treatment.

  Further, the electrolysis electrode 1 capable of realizing the production of persulfuric acid in the present embodiment is composed of silicon constituting the substrate 2, platinum constituting the intermediate layer 3, and tantalum oxide constituting the surface layer 4. Therefore, it can be manufactured at a lower cost than an electrode using a conventional conductive diamond, and the production cost can be reduced.

It is a schematic sectional drawing of the electrode for electrolysis of this invention. It is a flowchart figure of the manufacturing method of the electrode for electrolysis of this invention. It is a schematic explanatory drawing of the ozone water generating apparatus of this invention. It is a figure which shows the ozone production amount with respect to the thickness of the surface layer of the electrode of this invention in the ozone water production | generation apparatus of FIG. It is a figure which shows the current efficiency which made ozone object with respect to the calcination temperature of each electrode for electrolysis. It is a schematic explanatory drawing of a persulfuric acid dissolved water production | generation apparatus. It is an electric current-potential curve at the time of electrolyzing the electrolyte solution containing a sulfate ion. It is an electric current-potential curve at the time of electrolyzing the electrolyte solution containing perhydrochloric acid.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode for electrolysis 2 Base | substrate 3 Intermediate | middle layer 4 Surface layer 20 Ozone water production | generation apparatus 21, 31 Treatment tank 22, 32 Electrode 23 Simulated tap water 24, 34 Cation-exchange membrane 25, 35 Power supply 30 Persulfate dissolved water production | generation apparatus 33 Electrolyte solution

Claims (2)

A substrate, a conductive intermediate layer containing platinum formed on the surface of the substrate, and an intermediate layer
A surface layer, which is a dielectric formed by sputtering on the surface of the layer, and is formed in layers,
The dielectric is tantalum oxide, niobium oxide, zirconium oxide, titanium oxide,
Or tungsten oxide,
The surface layer has a thickness of 40 nm or more and less than 1000 nm.
Electrode for electrolysis for generating ozone. Persulfate-dissolved water that produces persulfate-dissolved water by electrolytic treatment of aqueous solutions containing sulfate ions
A generation method of
The electrolysis electrode for ozone generation according to claim 1 is used as an anode.
A method for producing persulfate-dissolved water.

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