Electrode manufacturing method and ozone generator

Abstract

To provide an electrode, a production method of the electrode, and an ozone generator, those of which can be used for generating an electrolytic ozone, continuously realizing the generation of ozone.SOLUTION: An electrode 10 comprises: an electrode substrate 13 in which an oxide film 12 of a first metal 14 is formed on a surface 11a of a metal base 11 made of the first metal 14; and a deposition metal part 16 formed in a state of being deposited onto the metal base 11 within a concave part 15 that is formed so as to reach the metal base 11 while part of the surface 12a of the oxide film 12 of the electrode substrate 13 is removed. The deposition metal part 16 includes an alloy of the first metal and another second metal different from the first metal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode that can be suitably used for electrolysis, etc., a method for manufacturing the electrode, and an ozone generator. [Background technology]

[0002] Patent Document 1 describes an electrode having a main electrode material formed from a first metal and a second metal scattered on the surface of the main electrode material, with an oxide film of the first metal on the surface of the main electrode material, and the second metal being present in a position on the surface of the main electrode material avoiding grooves, and a method for producing ozone using this electrode to electrolyze water and generate ozone. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-160502 Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of the invention described in Patent Document 1, ozone is generated immediately after the scattered precious metal particles are formed, but then the generation of ozone stops, and it was found that it is difficult to generate ozone continuously.

[0005] An object of the present invention is to provide an electrode that can be used to generate electrolytic ozone and that can achieve continuous ozone generation, a method for manufacturing the electrode, and an ozone generator. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides the following aspects. A first aspect of the present invention is an electrode comprising an electrode substrate having a metal base formed from a first metal and an oxide film of the first metal formed on the surface of the metal base, and an attached metal portion formed in a recess formed by removing a portion of the surface of the oxide film of the electrode substrate so as to reach the metal base, and the attached metal portion is attached to the metal base within the recess, and the attached metal portion comprises an alloy of the first metal and a second metal different from the first metal.

[0007] A second aspect of the present invention is the electrode according to the first aspect, wherein the first metal is more easily oxidized than the second metal. A third aspect of the present invention is the electrode according to the first or second aspect, characterized in that the second metal is a noble metal. A fourth aspect of the present invention is the electrode according to the first or second aspect, characterized in that the second metal is at least one selected from platinum, iridium, palladium, and indium. A fifth aspect of the present invention is the electrode according to any one of the first to fourth aspects, wherein the deposited metal portion contains the second metal in an amount of 40 atom % or more. A sixth aspect of the present invention is the electrode according to any one of the first to fifth aspects, characterized in that the first metal is titanium or lead dioxide.

[0008] A seventh aspect of the present invention is a method for manufacturing an electrode, which includes an adhesion metal portion forming step using an anode having a metal base formed from a first metal and an oxide film of the first metal formed on the surface of the metal base, and a cathode formed from a second metal different from the first metal, applying a voltage between the anode and the cathode, and sliding a contact end of the cathode over the surface of the anode while pressing it against the oxide film of the anode, to form a recess in the anode where a portion of the surface of the oxide film is removed and reaches the metal base, and an adhesion metal portion adhered to the metal base within the recess, and which is characterized in that an alloy of the first metal and a second metal different from the first metal is formed in the adhesion metal portion.

[0009] An eighth aspect of the present invention is a method for manufacturing an electrode according to the seventh aspect, characterized in that in the metal attachment portion forming process, the contact end of the cathode is slid against the anode in water while being pressed against the oxide film of the anode. A ninth aspect of the present invention is a method for manufacturing an electrode according to the seventh or eighth aspect, characterized in that in the attachment metal portion forming process, the contact end is formed tapered and slid against the anode in a state of point contact or line contact with the anode.

[0010] A tenth aspect of the present invention is an ozone generator comprising: an anode having a metal base formed from a first metal and an oxide film of the first metal formed on the surface of the metal base; a cathode formed from a second metal different from the first metal; a voltage application device that applies a voltage between the anode and the cathode; a water tank in which the anode and the cathode can be immersed in stored water; and a sliding mechanism that slides a contact end of the cathode over the surface of the anode while pressing the contact end against the oxide film of the anode. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an electrode, an electrode manufacturing method, and an ozone generator that can be used to generate electrolytic ozone and that can realize continuous ozone generation. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view showing an example of an electrode. [Figure 2] FIG. 10 is an explanatory view showing an example of an adhering metal portion forming step. [Figure 3] FIG. 1 is a schematic diagram illustrating an example of an ozone generator. [Figure 4] 1 is a graph showing the amount of ozone generated in Experiment 1. [Figure 5] 1 is a graph showing the amount of ozone generated in Experiment 2. [Figure 6] 10 is a graph of current changes in Experiment 2. [Figure 7] 1 is a micrograph showing an example of a PtTi alloy. [Figure 8]1A to 1C are micrographs showing the structural changes caused by electrolysis in order of (a) to (c). [Figure 9] 1 is a micrograph showing an example of a sponge-like Pt nanoparticle porous body. [Figure 10] 1 is a photomicrograph showing an example of a porous body after electrolysis of an InTi alloy. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described below based on preferred embodiments.

[0014] As shown in Figure 1, the electrode 10 of this embodiment includes an electrode substrate 13 having a metal base 11 formed of a first metal 14 and an oxide film 12 of the first metal 14 formed on the surface 11a thereof, and an attached metal portion 16 formed in a recess 15 in which a portion of the surface 12a of the oxide film 12 has been removed and the recess 15 has been formed so as to reach the metal base 11. The attached metal portion 16 includes an alloy of the first metal and a second metal. The second metal is a metal different from the first metal 14 that forms the metal base 11.

[0015] The electrode substrate 13 can be formed, for example, by electrochemically anodizing the surface of a metal plate made of the first metal 14. In this case, the metal base 11 is formed from an unoxidized metal plate. The oxide film 12 is formed as a surface layer that has been anodized.

[0016] The electrode substrate 13 is preferably made of a material in which an oxide film 12 of titanium oxide (TiO2) is formed on the surface 11a of a titanium metal base 11. The electrode substrate 13 may also be configured to be entirely made of lead dioxide (PbO2). In this case, the first metal 14 may be lead dioxide or lead (Pb).

[0017] The oxide film 12 of the electrode substrate 13 has a recess 15 formed by removing a portion of the surface 12a. In the illustrated example, the recess 15 reaches the metal base 11. Although not particularly illustrated, the surface of the metal base 11 does not have to be peeled off at the recess 15 where the oxide film 12 has been removed, and a portion of the metal base 11 may be peeled off or removed.

[0018] The width of the recess 15 is not particularly limited, but is preferably about 100 μm or less. When the recess 15 is formed linearly within the plane, the width of the recess 15 is the dimension perpendicular to the length and depth directions of the recess 15. When multiple recesses 15 are formed on the surface 12a of the oxide film 12, the length directions of the recesses 15 may be uniform or may be oriented in various directions. The recess 15 may extend straight along the surface 12a of the oxide film 12, or may extend in a curved or bent linear manner.

[0019] As described above, the second metal is a metal different from the first metal. The second metal is preferably a noble metal or a metal having catalytic activity. Here, the noble metal refers to gold (Au), silver (Ag), platinum group metals, or alloys containing one or more selected from these. Platinum group metals are a collective term for ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). Furthermore, the second metal is preferably at least one selected from platinum (Pt), iridium (Ir), palladium (Pd), and indium (In).

[0020] The distribution and composition ratio of the first metal, the second metal, and other elements in or near the metal deposit portion 16 can be confirmed by observation using, for example, a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), a scanning electron microscope (SEM), electron beam diffraction, or the like. For example, the cross section or surface of the metal deposit portion 16 may be observed. When the first metal and the second metal are present at the same position (same coordinates in the in-plane direction and the depth direction) in nanometer-order observation of the metal deposit portion 16, it can be assumed that the first metal and the second metal form an alloy. Furthermore, elements can be quantified by locally irradiating an energy beam such as an electron beam and analyzing the emitted X-ray intensity. The composition ratio measured in this way can be converted into atomic ratio (atom%), mass ratio (mass%), or the like. It is preferable that the metal deposit portion 16 contains 40 atom% or more of the second metal.

[0021] When the electrode 10 of the embodiment is used as an anode for generating ozone (O) by electrolysis of water (H O), the electrode 10 can ensure ozone generation characteristics. That is, the electrode 10 can be used as an ozone generating electrode.

[0022] Next, an example of a manufacturing method for the electrode 10 will be described. In the manufacturing method of the embodiment, first, an electrode substrate 13 is prepared, in which an oxide film 12 of the first metal is formed on the surface 11a of a metal base 11 formed from a first metal 14. At this stage, the electrode substrate 13 may not have the recesses 15 and the attached metal portions 16 formed thereon.

[0023] 2 and 3 , an anode 21 that can be formed from an electrode substrate 13 and a cathode 22 that is formed from a second metal 17 are used, and a voltage is applied between the anode 21 and the cathode 22. The anode 21 and the cathode 22 may be connected to voltage application devices 23 and 24, respectively. The voltage application devices 23 and 24 apply a voltage between the anode 21 and the cathode 22.

[0024] The manufacturing method of the embodiment includes a metal attachment forming step, in which the tip of cathode 22 is brought into contact with the surface of anode 21, and contact end 22a of cathode 22 is slid over the surface of anode 21 while being pressed against oxide film 12 of anode 21. Oxide film 12 has lower electrical conductivity than first metal 14 and second metal 17, so it does not immediately conduct electricity. However, if an electrical short occurs and part of oxide film 12 is destroyed, recess 15 is formed.

[0025] When the recess 15 reaches the metal base 11 after a portion of the surface 12a of the oxide film 12 is removed, the first metal 14 of the electrode substrate 13 and the second metal 17 of the cathode 22 bond to form an adhesion metal portion 16. The adhesion metal portion 16 adheres to the metal base 11 within the recess 15, forming an alloy of the first metal 14 and the second metal 17. FIG. 1 shows the adhesion metal portion 16 in a schematic manner. The adhesion metal portion 16 may be thinner than the oxide film 12, may be approximately the same thickness as the oxide film 12, or may be thicker and protrude than the oxide film 12. The adhesion metal portion 16 may be formed over the entire recess 15 or may be formed only in a portion of the recess 15.

[0026] The first metal 14 is preferably a metal that is more easily oxidized than the second metal 17 in the anode 21. The second metal 17 is preferably a metal that is less easily oxidized than the first metal 14 in the anode 21. This makes it easier for the first metal 14 to dissolve or peel off after forming an alloy between the first metal 14 and the second metal 17, and for the second metal 17 to remain on the anode 21. If the second metal 17 remaining on the anode 21 becomes porous, such as sponge-like, the surface area increases, which increases the reaction activity and catalytic activity, thereby promoting ozone generation. The ease with which metals are oxidized can be compared based on ionization tendency, electrode potential, etc.

[0027] In the process of forming the deposited metal portion 16, it is preferable to slide the contact end 22a of the cathode 22 against the anode 21 while pressing it against the oxide film 12 of the anode 21 in water 26. A water tank 25 can be provided in which the anode 21 and the cathode 22 can be placed in stored water 26. The water 26 may contain an electrolyte to increase conductivity. It is preferable that the electrolyte is non-volatile and does not chemically change during electrolysis. For example, sulfuric acid (H2SO4) of about 0.5 mol / L can be used.

[0028] In the step of forming the deposited metal portion 16, it is preferable to form the contact end 22a of the cathode 22 in a tapered shape, so that the contact end 22a comes into point or line contact with the anode 21 and slides over the anode 21. In this case, a local short circuit is likely to occur at the point where the contact end 22a comes into contact with the anode 21, and the pressure of the contact end 22a is concentrated, which makes it easy for the oxide film 12 to peel off locally.

[0029] In addition to the above-mentioned anode 21, cathode 22, voltage application devices 23 and 24, and water tank 25, ozone generator 20 preferably has a sliding mechanism (not shown) that slides contact end 22a of cathode 22 over the surface of anode 21 while pressing it against oxide film 12 of anode 21. The sliding mechanism may drive at least one of anode 21 or cathode 22. The sliding mechanism may be driven electrically or manually.

[0030] The present invention has been described above based on preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. [Example]

[0031] The present invention will be specifically described below with reference to examples.

[0032] (Experiment 1) A flat titanium plate was used as the first metal. An anode was fabricated by forming a titanium oxide film on the surface of the titanium plate through anodizing. The anode was placed in water, and a platinum wire was used as the cathode. While a voltage was applied between the anode and cathode, the platinum wire was rubbed against the surface of the anode. This method is called the ME (Multiple Electrostrike) method. Electrodes fabricated using the ME method have platinum (Pt) supported on the titanium oxide film on the surface.

[0033] The graph in Figure 4 shows the amount of ozone generated when water was electrolyzed using an electrode fabricated by the ME method as the cathode. For comparison, Figure 4 also shows the amount of ozone generated when a platinum (Pt) electrode or a diamond electrode was placed as the cathode in water with an anode placed in it. When the platinum cathode was not in contact with the anode, no ozone generation was confirmed even when a DC voltage of 7.5 V was applied. When an electrode fabricated by the ME method was used, the cathode was short-circuited by contacting it with the anode in water, and the platinum of the cathode was supported on the surface of the anode, and bubbles containing a high concentration of ozone were generated from the anode.

[0034] The diamond electrode is made of diamond (BDD) that has been made electrically conductive by doping with boron. When the diamond electrode was used as the cathode, the amount of ozone generated tended to gradually increase over time. When the electrode made by the ME method was used as the cathode, the initial increase in the amount of ozone generated was more significant than with the diamond electrode, but after about 60 minutes, the amount of ozone generated tended to gradually decrease.

[0035] (Experiment 2) When electrolyzing water using an electrode fabricated by the ME method as the cathode, the cathode was repeatedly brought into contact with the anode in water to short-circuit it. Figure 5 shows the amount of ozone generated (ppm), and Figure 6 shows the change in current. In Figure 6, the peak in the current corresponds to the moment the electrode was short-circuited. By repeating the short-circuiting about once every 5 minutes, a high concentration of ozone was generated for 1 hour and 30 minutes. After that, when the cathode was left without contacting the anode for about 20 minutes, a gradual decrease in the amount of ozone generated was observed. After that, when the cathode was again brought into contact with the anode to short-circuit it, the amount of ozone generated increased.

[0036] (Discussion of Experiments 1 and 2) When H2O binds to the Pt deposit on the anode, the H2O releases electrons (e - ) is taken away and oxidized. As a result, the oxidation proceeds stepwise as shown in (a) to (e) below, generating O3 (Reference: Mio Hayashi et al., "Electrolytic Ozone Generation at Pt / Ti Electrode Prepared by Multiple Electrostrike Method," Chemistry Letters, 2019, Vol. 48, No. 6, pp. 574-577).

[0037] <When ozone is generated> (a) Pt adhesion area H2O (b) Pt adhesion area -OH (c) Pt adhesion area - O (d) Pt adhesion part - OOH (e) Pt adhesion part O3

[0038] <When ozone is not generated> (a) Pt adhesion area H2O (b) Pt adhesion area -OH (c) Pt adhesion area - O (d) Pt adhesion part - OOH (f) Pt adhesion part O2

[0039] The reaction pathways (a) to (b) and (b) to (c) above are e - With the removal of H + However, the reaction pathways (c) to (d) and (d) to (e) above proceed with the release of e - Removal of and H + In addition to the release of CO, a supply of H2O is required. If the supply of H2O is insufficient, reaction pathways (d) to (f) will proceed, and oxygen (O2) will be generated.

[0040] In electrodes fabricated using the ME method, when the surface of the Ti plate shorts out due to contact with Pt, the TiO2 film is locally destroyed, and the Pt comes into contact with Ti, forming an alloy of Pt and Ti. In the formed alloy, Ti, which is easily oxidized, dissolves, leaving only Pt, forming a sponge-like nanoparticle porous structure. In the formed sponge-like Pt nanoparticle porous body, an increased supply of H2O increases the probability of reaction pathways (d) to (e), increasing the efficiency of O3 production. However, as electrolysis progresses, if the Pt attachment dissolves or becomes poisoned by ions in the electrolyte, the probability of reaction pathways (d) to (f) increases, which is thought to decrease the efficiency of O3 production.

[0041] (Experiment 3) The surface of the electrode (anode) fabricated using the ME method was observed with an SEM and subjected to elemental analysis. As a result, linear depressions were formed on the surface of the anode where the platinum wire had been rubbed, and it was found that Pt was present in the areas where the oxide film had been removed. It was also found that the outside of the areas where the oxide film had been removed remained covered with a TiO2 film.

[0042] As part of the observation and analysis results, a STEM photograph showing a cross section of the PtTi alloy layer formed on the anode is shown in Figure 7. The elemental compositions of the regions corresponding to Areas 1 to 3 were analyzed using EDS (energy dispersive X-ray spectroscopy), and the results are as follows:

[0043] Area 1: Ti 3.6atom%, Pt 67.7atom% Area 2: Ti 29.1atom%, Pt 45.3atom% Area 3: Ti 60.6atom%, Pt 20.9atom%

[0044] The upper part of the photograph in Figure 7 is the side of the deposited metal portion 16 containing the PtTi alloy that is closer to the surface of the electrode 10. The lower part of the photograph in Figure 7 is the side of the deposited metal portion 16 that is closer to the Ti metal base portion 11. In the upper Area 1, the proportion of Ti was low and the proportion of Pt was high. In Area 2 below Area 1, the proportion of Ti was slightly low and the proportion of Pt was slightly high. In the lower Area 3, the proportion of Ti was high and the proportion of Pt was slightly low.

[0045] In electrodes made by the ME method, rubbing a Pt wire against the surface removes the soft TiO2 film, but not the hard Ti plate, resulting in the formation of a PtTi alloy on the surface of the Ti plate. In the PtTi alloy formed where the oxide film was removed, Ti was dispersed in the Pt at a relatively low ratio of about 4%, and the ratio of Ti was higher at the bottom of the area where the oxide film was removed.

[0046] (Experiment 4) Figure 8 shows STEM images of the cross section of the PtTi alloy layer formed on the anode, showing the structural changes due to the progression of electrolysis in order from (a) to (c). Figure 8(a) shows the state after 0.5 minutes, Figure 8(b) shows the state after 2 minutes, and Figure 8(c) shows the state after 5 minutes. These images do not necessarily represent the same position, but it is clear that a sponge-like porous material grows and then shrinks above the PtTi alloy, which appears as a bright area in the image. In Figure 8(a), the porous structure is not obvious, but in Figure 8(b), the porous material has significantly expanded. In Figure 8(c), the porous material has thinned, which is thought to be the result of the progression of peeling.

[0047] The mechanism by which ozone generation stops when short circuits are not repeated can be speculated as follows: When Ti in the PtTi alloy is oxidized and eluted at the anode, a sponge-like porous structure of Pt nanoparticles is formed. It was then observed that the Pt gradually peeled off over time. It is thought that ozone generation stops when the sponge-like Pt nanoparticles peel off and disappear, or when a TiO2 layer formed by the oxidation of Ti covers the surface of the Pt porous body.

[0048] (Experiment 5) An anode with a titanium oxide film on the surface was placed in water, and various metal pieces other than Pt were used as cathodes and brought into contact with the anode. Ozone generation was confirmed by measurement with an electrochemical dissolved ozone concentration meter and a color test using potassium iodide starch paper. When linear (0.5 mm diameter) iridium (Ir), linear (1.0 mm diameter) palladium (Pd), and spherical (1.0 mm diameter) indium (In) were used, ozone generation was found to be similar to that when platinum (Pt) was used. Furthermore, observation with an electron microscope revealed that they formed a sponge-like porous structure of nanoparticles, similar to platinum.

[0049] Figure 9 is a STEM photograph showing an enlarged cross section of a sponge-like Pt nanoparticle porous body formed after electrolysis of a PtTi alloy. Figure 10 is a SEM photograph showing the surface of a porous body formed after electrolysis of an InTi alloy. In both cases, it can be seen that a porous body was formed on the surface of the anode. Furthermore, as shown in Figure 10, when the surface of the porous body is observed over a wider area, irregular surface undulations are evident. [Explanation of symbols]

[0050] 10...electrode, 11...metal base, 11a...surface of metal base, 12...oxide film, 12a...surface of oxide film, 13...electrode substrate, 14...first metal, 15...recess, 16...adhered metal portion, 17...second metal, 20...ozone generator, 21...anode, 22...cathode, 23, 24...voltage application device, 25...water tank, 26...water.

Claims

1. an adhesion metal portion forming step of using an anode having an oxide film of a first metal formed on the surface of a metal base formed from the first metal and a cathode formed from a second metal different from the first metal, applying a voltage between the anode and the cathode, and sliding a contact end of the cathode on the surface of the anode while pressing it against the oxide film of the anode, thereby forming a recess in the anode where a part of the surface of the oxide film is removed and reaches the metal base, and an adhesion metal portion adhered to the metal base within the recess, The method for manufacturing an electrode, wherein an alloy of the first metal and a second metal different from the first metal is formed in the attached metal portion.

2. 2. The method for manufacturing an electrode according to claim 1, wherein in the metal deposition step, the contact end of the cathode is slid over the anode while being pressed against the oxide film of the anode in water.

3. 3. The method for manufacturing an electrode according to claim 1, wherein in the forming of the attached metal portion, the contact end is formed in a tapered shape and is slid over the anode in a state of point contact or line contact with the anode.

4. an anode having a metal base made of a first metal and an oxide film of the first metal formed on the surface of the metal base; a cathode formed of a second metal different from the first metal; a voltage application device that applies a voltage between the anode and the cathode; a water tank in which the anode and the cathode can be inserted; a sliding mechanism that slides a contact end of the cathode on the surface of the anode while pressing the contact end against the oxide film of the anode; An ozone generator comprising:

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