JP2020012125A - Electrode for electrolysis and electric equipment provided with the same - Google Patents

Abstract

To suppress a reduction in ozone generation by peeling a surface layer from an intermediate layer of a noble metal.SOLUTION: A conductive substrate 12 and a reaction layer 13 formed on a surface of the conductive substrate 12 are provided, and the reaction layer 13 contains a conductive noble metal 14 and an oxide 15 of the conductive substrate. Therefore, since the reaction layer 13 contains an oxide of the same component as that of the conductive substrate 12, adhesion to the conductive substrate 12 is improved, peeling is suppressed, and long-term durability is improved. Moreover, since, in the reaction layer 13, the conductive noble metal 14 to be a reaction field for ozone generation is contained within a layer of the oxide of the conductive substrate to be a dielectric, an oxygen overvoltage is improved, ozone can be generated efficiently.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrode for electrolysis that can electrolyze water to generate an active substance such as ozone.

  Conventionally, this type of electrode for electrolysis forms an intermediate layer containing any of a noble metal, an alloy containing a noble metal, and a noble metal oxide on the surface of a conductive substrate, and forms a dielectric layer having an oxidation catalytic action on the surface of the intermediate layer. A layered surface layer including a body is formed, and holes are formed in the surface layer to penetrate the surface layer and reach the intermediate layer (for example, see Patent Document 1).

  FIG. 4 is a schematic cross-sectional enlarged view of a conventional electrolytic electrode described in Patent Document 1 in a thickness direction.

  As shown in FIG. 4, in the electrode for electrolysis 1, an intermediate layer 3 made of a noble metal, an alloy containing a noble metal, or a noble metal oxide is formed on one surface of a conductive substrate 2. A surface layer 4 of a dielectric material made of an oxide obtained by thermally decomposing a mixture of a solvent and an alkoxide compound such as tantalum, aluminum, titanium, tungsten, or niobium is formed.

  In addition, the surface layer 4 is formed by repeating a process of applying a dielectric material on the surface of the intermediate layer 3, drying at room temperature, drying at 220 ° C., and baking at a high temperature of 600 to 700 ° C. more than ten times, to form a layered structure. Formed. Thereby, many cracks are generated in the surface layer 4 in the thickness direction, and holes 5 are formed starting from the cracks and penetrating through the surface layer 4 and reaching the intermediate layer 3.

  When the electrode 1 for electrolysis is used as an anode and water is electrolyzed using a cathode electrode, water reaches the intermediate layer 3 through the holes 5 on the side of the electrode 1 for electrolysis, so that an intermediate layer connected to the holes 5 is formed. An electrode reaction occurs on a small area of the surface portion of the surface layer 3, the current density of the noble metal in the portion of the intermediate layer 3 connected to the hole 5 increases, and oxygen is catalyzed by the dielectric material around the hole 5 of the surface layer 4. Is oxidized to produce ozone.

JP 2006-97122 A

  However, in the above-described conventional configuration, the intermediate layer 3 is formed by applying a coating solution having a high platinum concentration of 50 g / L and performing baking 20 times to form the intermediate layer. Formed by objects. Therefore, the adhesion of the conductive substrate 2 to titanium is low, and when a long-term current is applied, the conductive substrate 2 and the intermediate layer 3 are peeled off, and there is a problem of lack of durability.

  In order to solve the above conventional problems, an electrode for electrolysis of the present invention comprises a conductive substrate and a reaction layer formed on the surface of the conductive substrate, wherein the reaction layer is formed of a conductive noble metal and the conductive substrate. Containing an oxide of

Thereby, since the reaction layer that generates ozone contains an oxide of the same component as the conductive base material, the adhesion to the conductive base material is improved, peeling is suppressed, and long-term durability is improved. be able to. In addition, in the reaction layer, the conductive noble metal serving as a reaction field for ozone generation is contained in the oxide layer of the conductive base material serving as the dielectric, so that the oxygen overvoltage of the reaction layer is increased and the ozone is efficiently increased. Can be generated.

  According to the present invention, stable generation of ozone can be achieved, and long-term durability can be improved.

FIG. 2 is an enlarged schematic cross-sectional view of the electrode for electrolysis in the thickness direction according to Embodiment 1 of the present invention Schematic diagram of an electrolysis device using the same electrode for electrolysis Schematic enlarged cross-sectional view in the thickness direction of the electrode for electrolysis according to Embodiment 2 of the present invention. Schematic cross-sectional enlarged view in the thickness direction of a conventional electrode for electrolysis

  A first invention includes a conductive substrate and a reaction layer formed on the surface of the conductive substrate, wherein the reaction layer contains a conductive noble metal and an oxide of the conductive substrate.

  Thereby, the reaction layer that generates ozone contains an oxide of the same component as the conductive substrate, so that the adhesion to the conductive substrate is improved, peeling is suppressed, and long-term durability is improved. be able to. In addition, in the reaction layer, the conductive noble metal serving as a reaction field for ozone generation is contained in the oxide layer of the conductive base material serving as the dielectric. Ozone can be generated.

  In the second invention, in particular, the conductive substrate of the first invention is Ti, and the oxide of the conductive substrate is titanium oxide (IV).

  Thus, the corrosion resistance of the electrode substrate is ensured, and the titanium (IV) oxide can effectively increase the oxygen overvoltage as a dielectric in the reaction layer and efficiently generate ozone.

  In the third invention, in particular, the conductive noble metal of the first invention or the second invention contains at least one element of Pt, Au, Ir, and Ru.

  Thereby, since it is excellent in conductivity and corrosion resistance, conduction between the conductive noble metals dispersed in the reaction layer can be ensured, and it can function as a reaction field for ozone generation, and can oxidize the surface of the electrode substrate and Pitting corrosion can be suppressed.

  In a fourth aspect, a dielectric is formed on the surface of the reaction layer according to any one of the first to third aspects.

  As a result, a fine electrolyte flow path is formed up to the reaction layer at the stage of forming the dielectric, so that the oxygen overvoltage in the reaction layer can be increased, and active oxygen species such as hydroxy radicals can be further removed together with ozone. Can be generated.

  According to a fifth aspect of the present invention, in particular, the dielectric body according to the fourth aspect of the invention includes at least one element of Ta, Si, Al, and Ti.

  This makes it easy to form a dense and finely divided flow passage as a dielectric on the reaction layer, and can easily adjust the increase in oxygen overvoltage.

  Hereinafter, the present embodiment will be described with reference to the drawings. Note that the present invention is not limited by the present embodiment.

(Embodiment 1)
FIG. 1 is a schematic enlarged cross-sectional view in the thickness direction of an electrode for electrolysis according to Embodiment 1 of the present invention.

  In FIG. 1, a reaction layer 13 is formed on one surface of a Ti base, which is a conductive base 12, in an electrode for electrolysis 11. The reaction layer 13 contains Pt of the conductive noble metal 14 and titanium oxide (IV) 15 which is an oxide of a Ti base, and Pt 14 is dispersed in the titanium oxide (IV) 15 formed in a layer shape in the form of particles. Exist.

  For example, a metal such as titanium, niobium, tantalum, or stainless steel can be used for the conductive base 12. However, it is possible to conduct electricity applied from a power supply to Pt of the conductive noble metal 14 of the reaction layer 13 at a low voltage. Titanium is suitable from the viewpoints of capability, corrosion resistance, mechanical strength, workability, and price.

  As the conductive noble metal 14 of the reaction layer 13, a noble metal such as Au, Ir, or Ru can be used in addition to Pt. However, it is possible to secure conduction between the conductive noble metals 14 and oxidize the surface of the conductive base 12. Pt is suitable in terms of pitting corrosion suppression and the like. Further, a flow passage 16 through which the electrolyte flows is formed in the reaction layer 13, through which the electrolyte flows into the reaction layer 13 from the outside to perform electrolysis.

  Next, the production method of the electrode for electrolysis of the present embodiment, particularly, the sol-gel method will be described.

  First, the titanium plate of the conductive substrate 12 is immersed in an aqueous acid solution such as oxalic acid, and is heated to 70 to 90 ° C. to perform an etching process. The etching process is performed so that the surface roughness after the etching process is Ra = 2.0 to 3.0 μm. After the etching process, the substrate is subjected to ultrasonic cleaning with pure water and dried.

  Next, the reaction layer 13 is formed on the conductive substrate 12. A raw material for the conductive noble metal 14 of the reaction layer 13 is hexachloroplatinic acid hexahydrate, and a predetermined amount is mixed and dissolved in an organic solvent such as propanol to prepare a coating solution. Here, the Pt concentration of the coating solution is adjusted to 1 to 20 g / L. Desirably, 5 to 10 g / L is a suitable concentration.

  The prepared coating solution is applied to the conductive substrate 12. The coating operation is desirably performed in a glove box in order to stably form a layer. The application to the conductive substrate 12 is performed by a spatula, a brush, a roller, a spray coating, or a dip. Alternatively, a method of applying using a spin coater or a roll coater using mechanical equipment may be used.

  After applying the coating liquid to the conductive substrate 12, the coating liquid is dried at 150 to 250C and baked at 450 to 550C. The drying time and the baking time are each desirably 10 minutes or more. After the first application and firing, the second to fourth application and firing are performed. In the second to fourth times, the coating and baking are performed under the same conditions as in the first time. Here, the coating and baking were performed four times, but the number of times of the coating and baking is appropriately 1 to 10 times, and 4 times is particularly desirable from the viewpoints of corrosion suppression and ozone generation.

The reaction layer 13 of the electrode for electrolysis 11 is manufactured by the above-described manufacturing method. In the reaction layer 13 of the electrode 11 for electrolysis, the surface of the conductive substrate 12 is oxidized and grown by firing, so that titanium (IV) oxide 15 is formed in a layered manner. Then, Pt 14 is present in the form of particles dispersed in the titanium oxide (IV) 15 formed in a layer. By setting the Pt concentration of the coating liquid to 5 to 20 g / L and the number of times of coating and baking to four, a layer mainly composed of Pt is not formed as in the prior art, and the oxidative growth of the conductive substrate 12 is achieved by baking. This promotes the formation of a layer mainly composed of titanium oxide (IV) 15, and forms a structure in which Pt 14 is dispersed in the form of particles inside titanium oxide (IV) 15.

  FIG. 2 is a schematic diagram illustrating an example of a flow-type electrolysis apparatus using the electrolysis electrode 11 of the present embodiment. In FIG. 2, an electrolysis device 17 includes a housing 20 provided with an inlet 18 for water and an outlet 19 for electrolyzed water, an electrode 11 for electrolysis as an anode mounted inside the housing 20, A counter electrode 21 and a DC power supply 22 for supplying electricity to the electrolysis electrode 11 and the counter electrode 21 are provided.

  Electrolysis electrode 11 of the present embodiment is arranged such that the surface on which reaction layer 13 is formed is opposed to counter electrode 21 and is provided with a flow path so that water flows between electrode 11 for electrolysis and counter electrode 20. are doing.

  Next, the operation of the electrolysis device 17 shown in FIG. 2 and ozone generation will be described.

  Water is supplied to the electrolysis device 17 at a predetermined flow rate from an inlet 18 provided at one end, and the supplied water is formed between the two electrodes while contacting the electrolysis electrode 11 and the counter electrode 21. It flows through the flow path and is discharged from the outlet 19. When the space between the electrolysis electrode 11 and the counter electrode 21 in the electrolysis device 17 is filled with water, a voltage or current is applied from the DC power supply 22 using the electrolysis electrode 11 as an anode electrode and the counter electrode 21 as a cathode electrode, and water is applied. Electrolyze.

  Usually, oxygen is generated by electrolysis of water at the electrode for electrolysis 11 as an anode, and hydrogen is generated at the counter electrode 20 as a cathode. In the present embodiment, a reaction layer 13 is formed on the outermost layer of the electrode for electrolysis 11 that comes into contact with water.

  As shown in FIG. 1, in the reaction layer 13, Pt 14 is dispersed in titanium oxide (IV) 15. The electrolytic solution flows into the reaction layer 13 through the flow passage 16, and the flowing electrolytic solution reaches Pt 14 dispersed in the titanium oxide (IV) 15, and electrolysis of water occurs.

  When Pt is used as the conductive noble metal 14, Pt has an oxygen overpotential, so that the potential at which oxygen is generated is relatively higher than other metals. Further, since titanium oxide (IV) 15 is formed around Pt 14, the titanium oxide (IV) 15 acts as a dielectric, further increases the oxygen overvoltage, and becomes higher than the ozone generation potential. Ozone is generated.

  In addition, the reaction layer 13 is mainly formed of a layer of titanium (IV) oxide 15 on the surface of the conductive substrate 12. Since the reaction layer 13 is formed of the same element as the conductive substrate 12 of the electrode, the adhesion between the conductive substrate 12 and the reaction layer 13 can be ensured. Further, since Pt 14 in contact with the surface of the conductive substrate 12 is a material having excellent corrosion resistance, oxidation and pitting of the conductive substrate 12 can be suppressed.

  As described above, in the present embodiment, the electrode for electrolysis includes the conductive substrate and the reaction layer formed on the surface of the conductive substrate, and the reaction layer is formed of a conductive noble metal and an oxide of the conductive substrate. It contained.

Thereby, since the reaction layer that generates ozone contains an oxide of the same component as the conductive base material, the adhesion to the base material is improved, peeling is suppressed, and long-term durability is improved. Can be. In addition, in the reaction layer, the conductive noble metal serving as a reaction field for ozone generation is contained in the oxide layer of the conductive base material serving as the dielectric. Ozone can be generated.

  The reaction layer 13 is formed by repeatedly applying and baking the surface of the conductive substrate 12 using a platinum acid solution of Pt14 as a coating solution, and using a mixed solution of a mixture of alkoxide of Ti and platinic acid as a coating solution. The reaction layer 13 may be formed by repeatedly applying and firing the surface of the base 12. When the reaction layer 13 is formed by this method, the thickness of the titanium (IV) oxide 15 of the reaction layer 13 can be more easily controlled, so that an electrode for electrolysis with more stable ozone generation can be manufactured. The reaction layer 13 can further employ a method of screen printing, sputtering, or CVD.

(Embodiment 2)
FIG. 3 is an enlarged schematic cross-sectional view in the thickness direction of the electrode for electrolysis according to Embodiment 2 of the present invention.

  In FIG. 3, the electrode 23 for electrolysis has a dielectric 23 formed on the surface of the reaction layer 13. The conductive substrate 12 and the reaction layer 13 are the same as in the first embodiment.

  The method of manufacturing the electrode for electrolysis according to the present embodiment will be described below.

  The pretreatment of the conductive substrate 12 and the formation of the reaction layer 13 are performed by the same method as in the first embodiment. After the formation of the reaction layer 13, the dielectric 23 is formed on the surface of the reaction layer 13.

  A case where tantalum oxide is formed as the dielectric 23 will be described.

  First, a coating liquid of the tantalum oxide 23 is prepared. As a raw material, tantalum pentaethoxide is mixed and dissolved in an organic solvent such as propanol, and a coating solution having a concentration of 0.15 mol / L as Ta is prepared. Here, the concentration of the coating solution is a concentration range in which 0.05 to 2.0 mol / L can be applied. For uniform application to the electrode surface, 0.1 to 0.2 mol / L is desirable. Further, tantalum pentaethoxide is used as the coating liquid, but platinum oxide may be mixed to form the coating liquid. When the dielectric material 23 is formed by mixing platinic acid, the layer of the dielectric material 23 has a dense structure, and the overvoltage is easily increased, and stable ozone generation can be secured.

  Next, the coating solution adjusted as described above is applied to the surface of the reaction layer 13. The coating operation is preferably performed in a humidity-adjusted space, for example, in a glove box, in order to stably form a layer of highly reactive alkoxide such as tantalum pentaethoxide. The application to the reaction layer 13 is performed by a spatula, a brush, a roller, a spray coating, or a dip, similarly to the reaction layer 13. Alternatively, a method of applying using a spin coater or a roll coater using mechanical equipment may be used.

  After applying the coating solution to the reaction layer 13, the coating is dried at 150 to 250 ° C. and baked at 550 to 650 ° C. The drying time and the baking time are each desirably 10 minutes or more.

  After the first application and firing, the second to 25th application and firing are performed. From the second time to the 25th time, the coating and baking are performed under the same conditions as the first time. Here, the number of times of application and firing is 25 times, but 20 to 30 times is an appropriate number of times of application and firing, and 25 times is particularly desirable in terms of ozone generation and manufacturing process cost.

  Next, the action of ozone generation for the electrode for electrolysis 11 shown in FIG. 3 will be described.

  As shown in FIG. 3, the electrolyte flowing through the tantalum oxide 23 and the flow passage 16 formed in the reaction layer 13 reaches Pt 14 dispersed in the titanium (IV) oxide 15, and electrolysis of water occurs. . A titanium oxide (IV) 15 is formed around Pt 14 of the reaction layer 13, and a tantalum oxide 23 is formed on the titanium oxide (IV) 15. Thereby, due to the dielectric action of tantalum oxide 23, the oxygen overvoltage can be further increased as compared with the first embodiment, and active oxygen species such as hydroxy radicals can be generated together with ozone.

  As described above, in the present embodiment, by forming the tantalum oxide 23 on the surface of the reaction layer 13, the oxygen overvoltage can be further increased by the dielectric action of the tantalum oxide, and the hydroxy Active oxygen species such as radicals can be generated.

  Further, in the present embodiment, the dielectric 23 is made of tantalum oxide, but an oxide of Al, Si, or Ti may be formed. When the oxide of Si is used, the electrode durability in an alkaline environment is improved. When a Ti oxide is used, the adhesion of the reaction layer 13 to the titanium (IV) oxide 15 can be ensured, and the electrode durability is improved.

  Although the sol-gel method has been described in the present embodiment as a method for forming the dielectric 23, a method using screen printing, sputtering, or CVD may be employed.

  As described above, the electrode for electrolysis according to the present invention improves the production and durability of stable ozone, and is excellent in productivity. The present invention can be applied to an electric device having an electrolytic device having functions such as deodorization, bath water purification, and prevention of bathtub contamination.

DESCRIPTION OF SYMBOLS 11 Electrolysis electrode 12 Conductive base 13 Reaction layer 14 Conductive noble metal 15 Oxide of conductive base 23 Dielectric

Claims (5)

An electrolysis electrode comprising: a conductive substrate; and a reaction layer formed on the surface of the conductive substrate, wherein the reaction layer contains an oxide of the conductive substrate and a conductive noble metal. The electrode for electrolysis according to claim 1, wherein the conductive substrate is Ti, and the oxide of the conductive substrate is titanium oxide (IV) TiO2. The electrode for electrolysis according to claim 1 or 2, wherein the conductive noble metal is at least one of Pt, Au, Ir, and Ru. The electrode for electrolysis according to any one of claims 1 to 3, wherein a dielectric is formed on a surface of the reaction layer. The electrode according to claim 4, wherein the dielectric includes at least one of oxides of Ta, Al, Si, and Ti.

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