JPH0633489B2 - Electrode for dilute salt water electrolysis - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrode for dilute salt water electrolysis, and more specifically,
The present invention relates to an electrode excellent in durability and current efficiency, which is suitably used for electrolyzing dilute salt water to generate hypochlorous acid used for sterilization and bleaching.

Utilizing seawater, electrolyzing this to generate hypochlorous acid,
A method for sterilizing water supply or sewer is already known, and the conventional sterilization method using chlorine gas is being gradually replaced by this method. By the way, this electrolysis method using seawater (hereinafter referred to as seawater electrolysis method) can sufficiently perform its function in areas where seawater can be easily obtained, but instead of seawater in areas where it is difficult to use seawater. An electrolysis method using a saline solution (hereinafter referred to as a salt water electrolysis method is performed.

In such electrolysis, chlorine is usually generated at the anode of the diaphragmless electrolysis device, and hypochlorite ion is generated by the reaction between the chlorine and hydroxide ion. The hypochlorous acid thus obtained is used for sterilization as described above, or for bleaching.

2. Description of the Related Art The salt electrolysis method is one of the similar technologies to the dilute salt water electrolysis method, and the RuO ₂ type electrode is known as an electrode in this case. A typical example of this RuO ₂ type electrode is (Ru-Ti)
An O ₂ solid solution coating layer formed on a valve metal substrate (Japanese Patent Publication No. 46-21884) or SnO _{2 of} 50 mol% or more (Ru-S
n) An electrode having a coating layer of O ₂ solid solution (Japanese Examined Patent Publication No. 50-11330) and the like. These electrodes are widely recognized for their excellent durability when used in the salt electrolysis method, and have been put to practical use as typical examples of metal electrodes. However, when these electrodes are used in the dilute salt water electrolysis method,
The efficiency of hypochlorous acid generation is relatively good, but the corrosion resistance is low, and therefore the electrode cannot be practically used for dilute salt water electrolysis.

Further, an anode having a coating layer composed of platinum, ruthenium dioxide, palladium oxide and titanium dioxide (Japanese Patent Publication No. 55-35).
No. 473), an anode having a coating layer composed of platinum and pardium oxide (Japanese Patent Publication No. 558595) is also proposed. However, although these palladium oxide-based anodes show a high value for hypochlorous acid generation efficiency, they have a problem in durability and have a drawback that durability is extremely poor especially at low temperatures.

Furthermore, as an electrode for seawater electrolysis, an electrode in which an alloy of platinum or a platinum group metal is plated on a corrosion resistant substrate is known, but this one has a relatively large degree of wear and has an electrolytic voltage during operation. It is high and the current efficiency is not satisfactory either.

In addition, an electrode for dilute salt water electrolysis having a coating layer made of platinum and iridium oxide (Japanese Patent Publication No. 55-50479), and an electrode for seawater electrolysis having a coating layer made of platinum, iridium oxide and ruthenium oxide (JP-A-59-59). No. 25988), electrodes have been proposed. However, although the former electrode has good corrosion resistance, it tends to deteriorate in performance with use. Further, the latter electrode has a drawback that the corrosion resistance in low temperature seawater electrolysis is not sufficient.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The object of the present invention is to overcome the drawbacks of the conventional electrodes in such a dilute salt water electrolysis method and to show a relatively low anode potential and high current efficiency even in low temperature seawater electrolysis. And to provide an electrode having excellent durability and corrosion resistance.

Means for Solving the Problems As a result of intensive studies by the present inventors, on the conductive substrate,
Based on this finding, it was found that an electrode provided with a coating layer composed of ruthenium oxide, iridium oxide, platinum of specific composition and tin oxide or tin oxide in which tin or tin is partially substituted with antimony can meet the purpose. The present invention has been completed.

That is, the present invention, in an electrode for electrolysis having a coating layer of a platinum group metal oxide catalyst on a conductive substrate, the coating layer, tin oxide 10 to 50 mol%, ruthenium oxide, iridium oxide and platinum. And a dilute salt water electrolysis electrode in which an amount of not more than 10 mol% of tin in the tin oxide is replaced with antimony. To do.

Examples of the conductive base material used for the electrode of the present invention include valve metals such as titanium, tantalum, zirconium, and niobium. Among these, titanium is particularly preferable. Further, its shape and the like can be appropriately changed according to the application.

In the electrode of the present invention, on such a conductive substrate,
A coating layer is provided which consists of ruthenium oxide, iridium oxide, platinum and tin oxide or tin oxide in which tin is partly replaced by antimony.

The content of tin oxide in the coating layer needs to be in the range of 10 to 50 mol%, and tin oxide is usually contained in the form of SnO ₂ . This tin oxide has the effects of facilitating the control of oxygen overvoltage and enhancing the adhesion strength of the coating layer to the conductive substrate. The content of tin oxide is 10
If it is less than mol%, the above effect is not exhibited, and the mechanical strength of the coating layer is lowered. On the other hand, if it exceeds 50 mol%, the anode potential is increased and durability and current efficiency are lowered.

In the present invention, in order to enhance conductivity and current efficiency, the tin oxide may be optionally substituted with 10 mol% or less, preferably 5 mol% or less, of antimony of tin. Good. In this case, antimony is usually contained in SnO ₂ as a dopant in the form of SbO ₃ replacing tin. If the amount of substitution of antimony exceeds 10 mol%, the effect of antimony substitution is reduced, and rather the corrosion resistance deteriorates.

Components other than tin oxide, that is, ruthenium oxide, iridium oxide, and platinum, are contained in a proportion of 90 to 50 mol% in total. If this total amount is less than 50 mol%, the anode potential will increase and the current efficiency will decrease.
When it is more than mol%, the oxygen overvoltage decreases, the amount of oxygen generated increases, and the adhesiveness of the coating layer to the conductive substrate decreases.

Iridium oxide is usually present in the form of IrO ₂ and is added to improve durability at low temperature and prolong electrode life, but if this amount is too small, its effect will not be exhibited,
Further, if it is too much, the current efficiency is impaired, so the range of 5 to 40 mol% is preferable based on the total amount.

Ruthenium oxide is usually present in the form of RuO ₂ and is added to reduce the anode potential, but if the amount is too small, the effect is not exerted, and if it is too large, the current efficiency and durability deteriorate. As a cause, it is usually 3-40 mol%
It is preferable to use in the range of.

Furthermore, platinum has the effect of lowering the anode potential,
If the amount is too small, the effect is not recognized, and if the amount is too large, the current efficiency is significantly lowered at low temperature. Therefore, it is usually preferable to use it in the range of 3 to 50 mol%.

Incidentally, it is generally considered that ruthenium oxide, iridium oxide and tin oxide form a solid solution in the coating layer.

The thickness of the coating layer in the present invention is usually 0.5 to 10 μm.
It only has to be about.

Next, one example of a preferred method for producing the electrode for dilute salt water electrolysis of the present invention will be described. First, a compound which becomes ruthenium oxide by thermal decomposition, for example, ruthenium chloride (RuCl ₃
3H ₂ O) and the like, and compounds that become iridium oxide by thermal decomposition, such as iridium chloride (H ₂ IrCl ₆ · 6H ₂ O), and compounds that become platinum by thermal decomposition, such as platinum halides Acids, especially chloroplatinic acid (H ₂ PtCl ₆・ 6H ₂ O), and compounds that become tin oxide by thermal decomposition, such as stannous halides such as stannous chloride and carboxylic acids such as octenoic acid. Acid, phosphonic acid, stannous complex salt such as phosphocarboxylic acid, and further, if necessary, a salt that becomes antimony oxide by thermal decomposition, for example, antimony halide such as antimony chloride, in a predetermined ratio. A coating solution is prepared by dissolving in a suitable solvent. Next, this coating solution is applied on a conductive substrate and dried, and then in the presence of oxygen.
The electrode of the present invention is obtained by firing at a temperature of 450 to 650 ° C. In addition, two or more kinds of coating liquids containing one or more of these components may be prepared, and these may be dried and baked after being multilayer-coated on the conductive substrate.

When antimony trichloride is used as a dopant for tin oxide, a large amount of this compound is volatilized and lost during firing, so it is necessary to add several times more than the desired final dope when preparing the coating solution. is there.

Effect of the Invention The electrode of the present invention is effectively used as an anode in the electrolysis of dilute salt water such as the seawater electrolysis method and the saltwater electrolysis method.

That is, when the electrode of the present invention is used for dilute salt water electrolysis such as seawater electrolysis, it is possible to maintain the characteristics that the cell voltage is low and the current efficiency is high, and it is also resistant to mechanical wear and withstands long-term use. . In addition, even when used for electrolysis of low-temperature seawater of 10 ° C. or lower, the decrease in current efficiency due to low temperature is relatively small, and the corrosion resistance to oxygen generation reaction is excellent.

As described above, the electrode of the present invention is sufficiently satisfactory for practical use as an electrode for dilute salt water electrolysis.

EXAMPLES Next, the present invention will be described in more detail with reference to examples.

Example 1 As a raw material for forming a coating layer, RuCl ₃ .3H ₂ O, H
₂ IrCl ₆・ 6H ₂ O, H ₂ PtCl ₆・ 6H ₂ O and C ₁₆ H ₃₀ O ₄ Sn are used,
Dissolve each in butanol and convert to 100g metal
Each raw material liquid of / was prepared. In addition, C ₁₆ H ₃₀ O ₄ Sn and SbCl ₃
Were dissolved in butanol so that Sb was 5 mol% with respect to Sn, to prepare a raw material solution having a metal-concentration of 100 g /.

Each of these raw material liquids was sampled with a mespetet so as to have a predetermined amount ratio, mixed, and then stirred to prepare a coating liquid.

Separately, a titanium plate was washed with a hot oxalic acid aqueous solution, the surface of the titanium plate was coated with a coating solution, dried, and then placed in an electric furnace and baked at 500 ° C. for 10 minutes.

This operation was repeated 10 times to produce an electrode in which a coating layer as shown in another table was formed on a titanium plate. The composition in the table was measured by fluorescent X-ray analysis.

Then, a seawater electrolysis test was conducted using these electrodes, and the anodic potential at a current density of 15 A / dm ² is shown in the table on the basis of the hydrogen electrode.

Example 2 The chlorine generation efficiency was measured using the electrode prepared in Example 1.

That is, in order to approximate the conditions for seawater electrolysis, 3 wt% Na
SUS304 disc (diameter 30m)
m) as the cathode and current density of 20
After electrolysis under conditions of A / dm ² and 100 coulombs of electricity, the electrolytic solution was taken out to an Erlenmeyer flask with a lid, and the hypochlorous acid concentration was iodometrically titrated with sodium thiosulfate. (%) Was calculated.

At this time, the temperature of the 3 wt% NaCl aqueous solution was changed, and the relationship between the temperature of the aqueous solution and the chlorine generation efficiency was determined.

The results are shown in the attached drawings.

In the figure, the curve a is sample No. 1 or N produced in Example 1.
No. 6 of the present invention, curve b is No. 6, curve c is No. 8,
The curve d is the No. 7 electrode and the curve e is the No. 5 electrode.

Example 3 Using the electrode samples No. 1 to No. 9 produced in Example 1, 6
A 1 MH ₂ SO ₄ aqueous solution at 0 ° C. was electrolyzed by a batch method at a current density of 100 A / dm ² to determine a use time (expressed as electrode life) until the electrode became unusable. The results are shown in the attached table. The electrode was judged to be unusable when the cell voltage increased by electrolysis and reached 8 V.

As is clear from this table, No. 5, which lacks any one of iridium oxide, ruthenium oxide, and platinum,
Samples 6 and 9 have the drawbacks of high anode potential and short electrode life. In addition, the sample No. 7 lacking tin oxide and ruthenium oxide has a significantly higher anodic potential than other samples.

On the other hand, the sample of No. 8 containing all the components of tin oxide, iridium oxide, ruthenium oxide and platinum but having a tin oxide content of more than 50 mol% has a high anodic potential and a short electrode life. .

On the other hand, all the samples of Nos. 1 to 4 having the constitutional requirements of the present invention have a low anode potential and a long electrode life.

Example 4 An electrode according to the invention having a coating layer consisting of 20 mol% RuO ₂ , 20 mol% IrO ₂ , 15 mol% Pt and 45 mol% SnO ₂ , and for comparison 20 mol% RuO ₂ , 20 mol%
An electrode having a coating layer consisting of IrO ₂ and 60 mol% Pt was prepared.

The polarization characteristics of these two types of electrodes were measured by the potential scanning method. For measuring chlorine overvoltage, 30 ℃
The value at a current density of 20 A / dm ² was determined in a 30 wt% NaCl aqueous solution (adjusted to pH 1) maintained at. Regarding the oxygen overvoltage, the value at a current density of 2 A / dm ² was obtained in a 1 MH ₂ SO ₄ aqueous solution at 30 ° C.

As a result, the electrode of the present invention containing 45 mol% SnO ₂ had an oxygen overvoltage of 450 mV, while the latter had 350 mV. The chlorine overvoltages were both 40 mV.

Next, at 20 ° C., a 1.5 wt% NaCl aqueous solution is used as an electrolytic solution,
The chlorine generation efficiency was calculated. As a result, the former was 88%, while the latter was 84%.

From these results, the effect of the present invention is clear. That is, the electrode of the present invention is excellent in characteristics such as anode potential and current efficiency, and also has excellent corrosion resistance to the oxygen generation reaction, and thus even when used as an electrode for low-temperature seawater electrolysis, long-term continuous use is possible. It can be used.

[Brief description of drawings]

The figure is a graph showing the relationship between aqueous solution temperature and current efficiency in electrolysis of a 3 wt% sodium chloride aqueous solution using various electrodes.

Claims (2)

[Claims] 1. An electrode for electrolysis having a coating layer of a platinum group metal oxide catalyst on a conductive substrate, wherein the coating layer comprises 10 to 50 mol% of tin oxide, ruthenium oxide, iridium oxide and platinum. An electrode for dilute salt water electrolysis, which comprises 90 to 50 mol% in total. 2. An electrode for electrolysis having a coating layer of a platinum group metal oxide catalyst on a conductive substrate, wherein the coating layer comprises 10 to 50 mol% of a mixed oxide of tin and antimony, ruthenium oxide, An electrode for dilute salt water electrolysis, which comprises 90 to 50 mol% of iridium oxide and platinum in total, and the amount of antimony in the mixed oxide of tin and antimony does not exceed 10 mol% with respect to tin.