JPH02190491A - Electrolytic electrode - Google Patents

Abstract

PURPOSE:To prolong the service life of the electrode under high-current-density conditions by providing an intermediate layer consisting of dispersed Pt and a metal oxide having a specified composition and an outer layer consisting of a metallic oxide having a specified composition on a base body of a Ti-based metal. CONSTITUTION:The electrolytic electrode is obtained by successively providing the intermediate layer and the outer layer on the base body of Ti or a Ti alloy. The intermediate layer consists of Pt dispersedly coating the base body so that the surface is partially exposed and a multicomponent or mixed metal oxide coating the exposed part and contg. 0-20mol% of >=1 kind among Ir oxide, Mn oxide, Co oxide, Sn oxide, and Sb oxide and 80-100mol% of >=1 king among Nb oxide, Ta oxide, and Zr oxide or a single metal oxide. The outer layer consists of a mixed metal oxide contg. 5-95mol% Ir oxide and 5-95mol% of >=1 king among Nb oxide, Ta oxide, and Zr oxide.

Description

[Detailed Description of the Invention] The invention relates to an electrode for electrolysis, and more specifically, an electrode for electrolysis that has a low oxygen overvoltage, is excellent in durability, is stable even in a base potential environment, has a low membrane resistance in the intermediate layer, and particularly has an electrode that does not allow oxygen generation in the anode. The present invention relates to an electrode for electrolysis useful as an anode in electrolysis of seawater, surface treatment of metals, metal 5 metal foil production, recovery, etc.

BACKGROUND OF THE INVENTION Conventionally, titanium electrodes have been used in many fields of the electrolytic industry, in which a platinum group metal or a platinum group metal oxide is coated on a titanium alloy substrate.

However, in the fields of high-speed metal plating and metal foil production that operate under high current densities, there is a problem that the interface between the catalyst and the base material deteriorates, resulting in poor conductivity and shortened electrode life.

Furthermore, in fields where the cathode itself is a product, such as surface treatment of metals, it becomes necessary to replace the cathode after the treatment, and electrolysis must be stopped each time. At this time, there are many cases where the anode is exposed to a base potential environment due to the formation of a short circuit, and there is a problem in that the electrode coated with an oxide becomes unstable, and the life of the electrode is shortened.

The present inventors have completed the present invention as a result of intensive research to overcome the drawbacks of the conventional electrolytic electrodes as described above.

Thus, according to the present invention, on an electrode base made of titanium or a titanium alloy, (a) platinum dispersed and coated to such an extent that the base surface is partially exposed, and iridium oxide covering at least the exposed portion of the base surface; 0 to 20 mol% of at least one metal oxide selected from manganese oxide, cobalt oxide, tin oxide, and antimony oxide, and 80 to 100 mol% of at least one metal oxide selected from niobium oxide, tantalum oxide, and zirconium oxide. an intermediate layer composed of a composite metal oxide, mixed metal oxide, or single metal oxide; An electrode for electrolysis is provided, characterized in that it is provided with an outer layer composed of a mixed metal oxide comprising 5 to 95 mol % of a seed metal oxide.

Hereinafter, the electrode for electrolysis of the present invention will be explained in more detail.

The material of the electrode substrate used in the present invention includes titanium or a titanium-based alloy. As the titanium-based alloy, a corrosion-resistant and conductive alloy mainly composed of titanium is used. For example, Ti-Ta-Nb1Ti-Pd, Ti
-Zr, Ti-W.

Examples include Ti-based alloys that are composed of a combination of Ti-A (1, etc.) and are commonly used as electrode materials.

These electrode materials can be processed into a desired shape such as a plate shape, a perforated plate shape, a rod shape, a net plate shape, etc., and used as an electrode base material.

For the above-mentioned electrode base, as is usually done,
It is desirable to provide the intermediate layer after pretreatment.

Preferred specific examples of such pretreatment include those described below.

First, the surface of the electrode substrate (hereinafter sometimes referred to as titanium substrate) made of titanium or titanium alloy described above is washed with trichloroethylene, trichloroethane, etc. in accordance with a conventional method, or degreased by electrolysis in an alkaline solution, and then
The oxide film on the surface of the titanium substrate is removed by treatment with hydrofluoric acid or a mixed acid of hydrofluoric acid and other acids such as nitric acid and sulfuric acid with a hydrogen fluoride concentration of about 1 to about 20% by weight. Roughening the titanium grain boundary unit. The acid treatment is performed at room temperature to about 40°C depending on the surface condition of the titanium substrate.
It can be carried out for several minutes to several minutes at a temperature of . Incidentally, in order to sufficiently roughen the surface, a blast treatment may be used in combination.

The surface of the titanium substrate thus acid-treated is brought into contact with concentrated sulfuric acid to roughen the inner surface of the titanium grain boundaries into protrusions and form a thin layer of titanium hydride on the surface of the titanium substrate. This fine roughening of the surface in the form of protrusions is an important process for later forming a dispersion coating of platinum.

The concentrated sulfuric acid used generally has a particle size of 40 to 80% by weight, preferably 50 to 60% by weight, and if necessary, a small amount of sodium sulfate or other substances may be added to this concentrated sulfuric acid for the purpose of stabilizing the process. sulfate etc. may be added.

The contact with the concentrated sulfuric acid can usually be carried out by immersing the titanium substrate in a bath of concentrated sulfuric acid, and the bath temperature at that time is generally in the range of about 100 to about 150°C, preferably about 110 to about 130°C. The temperature can be within 100 mL, and a soaking time of 0.5 to about 10 minutes, preferably about 1 to about 3 minutes, is sufficient. This sulfuric acid treatment makes it possible to roughen the inner surface of the titanium crystal grain boundaries into fine protrusions and form a very thin titanium hydride film on the surface of the titanium substrate.

The titanium substrate treated with sulfuric acid is removed from the sulfuric acid bath and rapidly cooled, preferably in an inert gas atmosphere such as nitrogen or argon, to reduce the surface temperature of the titanium substrate to about 60° C. or less. It is appropriate to use a large amount of cold water for this rapid cooling, which also serves as washing.

The titanium substrate on which a very thin titanium hydride film has been formed in this way is coated with dilute hydrofluoric acid or dilute fluoride aqueous solution (
For example, the titanium hydride film is grown by immersion treatment in sodium fluoride, potassium fluoride, etc., and the film is made uniform and stable.

The concentration of hydrogen fluoride in the dilute hydrofluoric acid or fluoride aqueous solution that can be used here can generally be in the range of 0.05 to 3% by weight, preferably 0.3 to 1% by weight, and , the temperature during immersion treatment with these solutions is generally 1
It is in the range of 0 to 40°C, preferably 20 to 30°C. The treatment can be carried out until a uniform coating of titanium hydride is formed on the surface of the titanium substrate, usually with a thickness of 0.5 to 10 microns, preferably 1 to 3 microns. This titanium hydride (Tidy, where y is a number from 1.5 to 2) exhibits a grayish-brown to blackish-brown color depending on the degree of hydrogenation.
The production of a titanium hydride film having a thickness within the above range can be controlled empirically by comparing the change in color tone of the substrate surface with a standard color source.

The titanium substrate whose surface has been roughened in this way and a titanium hydride film has been formed thereon is subjected to appropriate treatments such as washing with water, and then platinum is partially exposed on the surface of the titanium substrate. Disperse and cover to a certain degree.

This dispersion coating of platinum can usually be carried out by electroplating. The composition of the plating bath that can be used in this electroplating method includes, for example, H3PtCI 1 NH, PtC
l K, PtC1,, Pt(NHs)z 1ot)
A platinum compound such as a is dissolved in a sulfuric acid solution (pH 1 to 3) or an ammonia aqueous solution to a concentration of about 2 to about 201/Q in terms of platinum, and if necessary, sodium sulfate is added to stabilize the bath. (for acidic baths), acidic or alkaline plating baths to which a small amount of sodium sulfite, sodium sulfate (for alkaline baths), etc. are added. Platinum electroplating using a plating bath with such a composition is preferably carried out at a relatively low temperature in the range of about 30 to about 60°C in order to suppress as much as possible the decomposition of the titanium hydride film formed on the surface of the titanium substrate. .

This electroplating makes it possible to form a dispersed coating of platinum on the titanium hydride coating of the titanium substrate. The dispersion state of platinum at this time can be controlled, for example, by empirically adjusting the bath composition of the platinum plating bath and/or the plating conditions (current density, current waveform, etc.).

In this way, a dispersed coating of platinum is deposited on the titanium substrate to such an extent that the surface of the substrate is partially exposed. When observing the state of the dispersion coating using an electron microscope with a magnification of 5,000 times, it can be seen that platinum is dispersed on the surface of the titanium substrate in the form of dots, lines, and networks. The amount of platinum deposited is generally 0.1 to 201/m", preferably 0.2 to 52/m".
If the amount of platinum precipitated is too small, the resulting electrode will have poor durability, while if it is too large, the resulting electrode will become unstable in a base potential environment.

Thus, it is appropriate that the degree of dispersion coating of platinum is generally in the range of 10 to 80%, preferably 30 to 50%, expressed as coverage. In this specification, the "coverage rate" of platinum refers to the surface of a titanium substrate coated with platinum dispersedly coated with 40%,
It is a value calculated by taking an electron micrograph at a magnification of 1,000 times, measuring the area covered by platinum per 1 μm2 of the titanium substrate surface from the photograph, and using the following formula.

The titanium substrate coated with platinum in a dispersed manner is then fired in the atmosphere to thermally decompose the titanium hydride film layer and remove substantially most of the titanium hydride in the layer from the titanium metal. and further converts the titanium into titanium oxide, which has a lower oxidation state. This firing is generally done at a temperature of about 300 to about 600℃.
, preferably at a temperature of about 300 to about 400°C for 10 minutes to
This can be done by heating for about 4 hours.

As a result, a very thin conductive titanium oxide layer is formed on the surface of the titanium substrate. The thickness of this titanium oxide layer is generally 1
00-1. o, 00 people, preferably in the range of 200 to 600 people, and the composition of titanium oxide is TiOx, where X is generally l≦x<2, especially 1,
It is desirable that the range is 9 < x < 2.

Alternatively, the titanium substrate coated with platinum dispersion may be subjected to a direct process without the firing treatment as described above. In this case, during the thermal decomposition treatment in the next step, the titanium hydride film layer on the surface of the titanium substrate is converted into titanium metal and titanium oxide in a low oxidation state.

As described above, the surface of the titanium substrate coated with platinum dispersedly has at least the portion of the substrate surface not coated with platinum covered with (a) oxidation of at least one metal selected from iridium oxide, manganese oxide, cobalt oxide, tin oxide, and antimony oxide. 0 to 20 mol%, preferably 5 to 15 mol%, and (b)
A metal oxide or mixed metal oxide (hereinafter sometimes referred to as an intermediate oxide) consisting of 80 to 100 mol%, preferably 85 to 95 mol%, of at least one oxide selected from niobium oxide, tantalum oxide, and zirconium oxide. ).

This intermediate oxide is useful for filling the gaps in the dispersion-coated platinum and improving the corrosion resistance of the resulting electrode. The dispersed platinum also helps maintain good conductivity of the interlayer. The intermediate oxide not only fills (covers) the gaps of partially deposited platinum (exposed parts of the titanium substrate), but also covers the platinum without any problem. If it becomes too thick, the electrical resistance of the intermediate layer increases, so the coating amount of the intermediate oxide is generally 0.5 to 102/m", preferably 1 to 59
It can be within a range of 7m''.

Among the intermediate oxides, iridium oxide is particularly suitable as the oxide (a).

The intermediate oxide is made by, for example, containing a metal compound that can be converted into the metal oxides of (a) and (b) above by firing in an oxygen-containing gas, usually air, in the above ratio in terms of metal oxide. Dissolve in a suitable low boiling point solvent, apply the resulting solution to the platinum dispersion coated surface of the platinum dispersion coated titanium substrate, dry and remove the solvent, and then sinter in an oxygen-containing gas atmosphere. It can be formed by

Hereinafter, the case of forming an intermediate oxide in which the metal oxide in (a) above is iridium oxide and the metal oxide in (b) above is tantalum oxide will be described in more detail.

On the titanium substrate surface coated with platinum dispersed as described above,
The tantalum compound of the iridium compound is deposited by applying a solvent solution containing an iridium compound and a tantalum compound, preferably a lower alcohol solution, and drying the coating. The iridium compound and tantalum compound that can be used here include compounds soluble in lower alcohol solvents that can be thermally decomposed under the firing conditions described below and converted into iridium oxide and tantalum oxide, respectively.

Examples of such iridium compounds include chloroiridic acid, iridium chloride, iridium potassium chloride, etc.
Further, examples of the tantalum compound include tantalum chloride. On the other hand, examples of lower alcohols that can dissolve these iridium compounds and tantalum compounds include methanol, ethanol, glopanol, isopropanol, butanol, or mixtures thereof.

The lower alcohol solution can be applied to the titanium substrate dispersedly coated with platinum by, for example, brush coating, spray dipping, or the like.

The substrate to which the lower alcohol solution of the iridium compound and the tantalum compound was applied in this way has a yield of about 20 to about 1
After drying at a relatively low temperature in the range of 50°C, it is fired in air. The above-described treatment can be repeated until the amount of intermediate oxide coated falls within the desired range. The firing is generally carried out at about 400 to about 700° C. in a suitable heating furnace such as an electric furnace, a gas furnace, an infrared furnace, etc.
Preferably, this can be carried out by heating to a temperature within the range of about 450 to about 600°C. The heating time at this time can be approximately 5 minutes to 2 hours depending on the size of the substrate to be fired.

By this firing, the iridium compound and the tantalum compound are changed into iridium oxide and tantalum oxide, respectively, to form an intermediate oxide.

Other composite metal oxides, mixed metal oxides, or single metal oxides described above can be formed in the same manner.

On the intermediate layer composed of platinum and intermediate oxide dispersed and coated as described above, there is further added: (i) 5 to 95 mol%, preferably 20 to 80 mol% of iridium oxide; ) An outer layer composed of 5 to 95 mol %, preferably 20 to 80 mol % of at least one metal oxide selected from niobium oxide, tantalum oxide and zirconium oxide is provided. In this outer layer, (
When the proportion of iridium oxide in i) is less than 5 mol%,
There is a tendency for the oxygen overvoltage of the resulting electrode to become high, and on the other hand, if it exceeds 95 mol %, the electrode tends to suffer from large wear.

In addition, when using a mixed metal oxide consisting of iridium oxide and at least one metal oxide selected from niobium oxide, tantalum oxide, and zirconium oxide as the intermediate oxide, the content of iridium oxide in the outer layer (X)
is the content of iridium oxide in the intermediate oxide (Y)
It is desirable that the content of the former is greater than (X mol%)
The difference (X − Y) between the content (Y mol%) of the latter and the latter content (Y mol%) is usually
It is conveniently within the range 5-95, preferably 20-95.

The outer layer consisting of the above components and composition can be formed in the same manner as the method for forming the intermediate oxide. The coverage of the outer layer is generally 1 to 1007/m", preferably 5 to 50jJ/m"
It is appropriate to keep it within the range of .

The electrode of the present invention described above can have a long life even under high current density, and has various advantages such as resource saving and easy maintenance of the device.

In addition, the electrode of the present invention can stabilize the electrode even in a base potential environment, almost eliminates deterioration of the electrode when energization is stopped, and extends the life of the electrode even in electrolysis that requires many switching operations.

Furthermore, the electrode of the present invention can also be used in AC electrolysis and pulsed electrolysis, which are useful for surface treatment of metals.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 JIS Class 2 titanium plate material (LO, 5X'l OX"
After degreasing and cleaning the 10mm) with trichlorethylene, 2
treated with 8 wt% aqueous HF at 0 °C for 2 min, then 1
601 at 20° C. was treated in a solution containing % H, SO for 3 minutes. The titanium substrate was then removed from the sulfuric acid solution and quenched by spraying with cold water in a nitrogen atmosphere. Furthermore, 0.
It was immersed in a 3% by weight aqueous HF solution for 2 minutes and then washed with water.

After washing with water, dinitrodiaminoplatinum was dissolved in a sulfuric acid solution and pt
Pt was dispersed and precipitated by plating at 15 mA/cm'' for about 50 seconds in a platinum plating bath with a content of 5 I/12 and a pH adjusted to 2.50°C.The dispersed coating amount was 197 m2. The platinum coverage on the titanium substrate at this time was about 40%.

In this way, the dispersion-coated platinum was applied to the titanium substrate for 40 minutes.
Heat treatment was performed in the atmosphere at 0°C for 1 hour.

Next, a butanol solution of chloroiridic acid and an ethanol solution of tantalum chloride were mixed to prepare a coating solution containing ■r5.9:j/Q and Ta50jl/Q (metal equivalent), and then a 1 cm" 2.7μQ per
After weighing and applying it to the above substrate, it was vacuum dried at room temperature for 30 minutes, and further baked in air at 500° C. for 10 minutes. This process was repeated twice.

Then, to obtain the outer layer, a butanol solution of chloroiridic acid and an ethanol solution of tantalum chloride were mixed, and Ir5
After preparing a coating solution containing Oj/Q and Ta201/I2 (metal equivalent), the same steps as above were repeated eight times using this coating solution to create Example Electrode-1.

Next, Example electrodes 2 to 9 with different oxide compositions were prepared in the same manner as Example electrode 1.

Furthermore, a comparative example was prepared in which a titanium substrate was treated in the same manner as in the above example, then heat treated in the atmosphere at 400°C for 1 hour, and further coated with an oxide in the same process as in the production of Example Electrode-1. Comparative Example Electrode-2 was prepared by coating only Electrode-1 and outer layer oxide. Furthermore, comparative electrodes 3 and 4 having the oxide compositions shown in Table 1 were also produced. Table 1 shows the electrode life when each electrode thus obtained was electrolyzed under the following conditions.

<Electrolytic conditions> Electrolyte: IMH2Son-IMNazsOt Current density' 4 A / (mz Counter electrode 2 Pt Distance between electrodes: 10 mm Table 1 Note) The electrodes No. 2 to 9.12 in the above table are platinum 1. ? / m
! It is a dispersion coated electrode.

Note 2) An intermediate layer obtained by applying a coating solution containing chloroplatinic acid and tantalum chloride and thermally decomposing it.

Example 2 Platinum was dispersed and precipitated at 12/m' on a titanium plate in the same manner as described in Example 1, and then heat-treated in the atmosphere at 400°C for 1 hour.

Next, a butanol solution of chloroiridic acid and an ethanol solution of tantalum chloride were mixed, and Ir13/α and T
a After preparing a coating solution containing 50 fl/Q (metal equivalent), apply 2.7 fl/Q per 1 cm with a micropipette.
μα was weighed, applied to the substrate, vacuum dried at room temperature for 30 minutes, and further baked in air at 500° C. for 10 minutes. This process was repeated twice.

Then, to obtain the outer layer, a butanol solution of chloroiridic acid and an ethanol solution of tantalum chloride were mixed, and Ir5
After preparing a coating solution containing 0j'/ff and Ta2O&/R (metal equivalent), the same steps as above were repeated 12 times using this coating solution to produce Example Electrode-1O.

For comparison, a titanium substrate was treated in the same manner as in Example 1O above, and then electroplated with 32 I/m'' of platinum (platinum coverage at this time was over 99%), and this platinum-coated titanium plate was coated with 400 A comparative example electrode 5.6 was prepared by heat-treating in the atmosphere at °C for 1 hour, and then repeating the same steps as for Example electrode-10 to obtain an outer layer.

The time course of the consumption of the catalyst thus obtained was shown in the attached FIG. 1 when each electrode was electrolyzed under the following conditions.

Electrolyte: I MH! S 04-IMN azs
O + current waveform: After electrolysis for 80 seconds at +lA/cm'', electrolysis was repeated for 20 seconds at 0 and lA/cm''. Counter electrode: Pt From FIG. It can be seen that the electrode is stable even when

Example 3 Example electrodes-11 to 13 shown in Table-2 were prepared in the same manner as described in Example 1, but only the oxide composition of the outer layer was changed.
and comparative example electrode-8 and 322/m” Pt on the titanium plate.
Comparative Example Electrode-9 was prepared by plating.

The potential-current characteristics of these electrodes in a lμ/a sulfuric acid aqueous solution at a liquid temperature of 60°C are shown in the attached FIG. 2.

From FIG. 2, it can be seen that the electrode of the example has a low oxygen overvoltage.

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes over time in catalyst consumption of the electrode prepared in Example 2, and FIG. 2 is a graph showing potential-current characteristics of the electrode prepared in Example 3 in an aqueous sulfuric acid solution. Figure 1 Time (hours) Example electrode-10nia 0 mol%Ir0z-30 mol%T
ag, /Pt-(20 mol% IrOx 80 mol% T
a0x)/Ti[x/Ti Comparative Example ti-5 Near 0 mol% Ir0z 30 mol% Ta
OX/ P t /TLOX/TL Comparative Example Electrode-6 Near 0 mol% Ir0h30 mol% TaO
*/20 mol% Ir0z-80 mol% Ta0X/pt
/TiOx/Ti

Claims (1)

[Claims] 1. On an electrode base made of titanium or a titanium alloy, (a) platinum dispersed and coated to such an extent that the base surface is partially exposed, and iridium oxide covering at least the exposed portion of the base surface; , 0 to 20 mol % of at least one metal oxide selected from manganese oxide, cobalt oxide, tin oxide, and antimony oxide, and 80 to 100 mol % of at least one metal oxide selected from niobium oxide, tantalum oxide, and zirconium oxide. (b) 5 to 95 mol% of iridium oxide, niobium oxide,
1. An electrolytic electrode comprising an outer layer made of a mixed metal oxide containing 5 to 95 mol% of at least one metal oxide selected from tantalum oxide and zirconium oxide. 2. The electrode for electrolysis according to claim 1, wherein the platinum coverage in the intermediate layer is 10 to 80%. 3. The intermediate layer includes platinum dispersed and coated to such an extent that the substrate surface is partially exposed, 5 to 15 mol% of iridium oxide, and at least one metal oxide selected from niobium oxide, tantalum oxide, and zirconium oxide 85 The electrode for electrolysis according to claim 1 or 2, comprising a mixed metal oxide comprising 95 mol%. 4. The electrode for electrolysis according to claim 3, wherein the content of isridium oxide in the mixed metal oxide of the intermediate layer is lower than the content of iridium oxide in the mixed metal oxide of the outer layer.