JPS6152385A - Electrode for electrolyzing diluted aqueous sodium chloride solution - Google Patents

Abstract

PURPOSE:To improve the durability and current efficiency of the titled electrode having a coating layer of a catalyst contg. the oxides of Pt group metals on an electrically conductive substrate by using RuO2, IrO2, Pt and SnO2 mixed in a specified ratio as the constituents of the coating layer. CONSTITUTION:When a dil. aqueous NaCl soln. such as seawater is electrolyzed to manufacture hypochlorous acid for disinfection, bleaching or other use, an electrode having a coating layer of a catalyst is used. The electrode is obtd. by applying a mixture consisting of, by mole, 3-40% RuO2, 5-40% IrO2, 3- 50% Pt and 10-50% SnO2 to the cleaned surface of a substrate of an electrically conductive metal such as Ti, Zr or Nb and by carrying out baking. In the mixture, Sb may be substituted in the form of SbO3 for <=10% of Sn in SnO2. The resulting electrode has superior durability and current efficiency when a dil. aqueous NaCl soln. is electrolyzed to manufacture hypochlorous acid.

Description

[Detailed Description of the Invention] The industrial application field of the invention relates to electrodes for dilute salt water electrolysis, and more specifically,
The present invention relates to an electrode with good durability and current efficiency, which is suitably used to electrolyze dilute salt water to produce hypochlorous acid used for killing, bleaching, etc.

Using seawater, it is electrolyzed to generate hypochlorous acid,
Methods for sterilizing water supplies, sewerage systems, etc. are already known, and conventional sterilization methods using chlorine gas are being gradually replaced by these methods. By the way, this electrolysis method using seawater (hereinafter referred to as seawater electrolysis method) can be fully functional in areas where seawater is easily available, but in areas where it is difficult to use seawater, it is recommended that seawater be used instead of seawater. An electrolysis method using a saline solution (hereinafter referred to as seawater electrolysis method) has been carried out.

In such electrolysis, a non-diaphragm electrolyzer is usually used to generate chlorine at its anode, and hypochlorite ions are generated by the reaction between the chlorine and hydroxide ions. The hypochlorous acid thus obtained is used for sterilization as described above, or for bleaching.

BACKGROUND ART One of the similar technologies to the dilute salt water electrolysis method is the salt electrolysis method, and the electrode used in this method is of the RuO2 type. A typical example of this RuOz type electrode is (R
u-Ti)02 solid solution coating layer formed on a valve metal base material (Japanese Patent Publication No. 46-21884), 5n02
Examples include an electrode having a coating layer of (Ru-Sn) 02 solid solution having a molar ratio of 50 or more (Japanese Patent Publication No. 11330/1983). These electrodes are widely recognized for their excellent durability when used in the salt electrolysis method,9 and are put into practical use as representative examples of metal electrodes. However, when these electrodes are used in dilute salt water electrolysis, although the hypochlorous acid generation efficiency is relatively good, their corrosion resistance is low, so these electrodes cannot be used practically for dilute salt water electrolysis. do not have.

In addition, an anode having a coating layer consisting of platinum, ruthenium dioxide, palladium oxide, and titanium dioxide
35473) and an anode having a coating layer consisting of platinum and palladium oxide (% Publication No. 55-8595) have also been proposed. However, although these palladium oxide-based anodes exhibit a high value for hypochlorous acid generation efficiency, they have a problem in durability, particularly in that their durability at low temperatures is extremely poor.

Furthermore, as electrodes for seawater electrolysis, electrodes in which platinum or platinum group metal alloys are plated on a corrosion-resistant substrate are known, but these have a relatively high wear rate and have a high electrolysis voltage during operation. , the current efficiency is also not satisfactory.

In addition, electrodes for dilute salt water electrolysis having a coating layer consisting of platinum and iridium oxide (Japanese Patent Publication No. 55-50479), electrodes for seawater electrolysis having a coating layer consisting of platinum, iridium oxide, and ruthenium oxide (Japanese Patent Publication No. 59/1986) -2598
No. 8) and other electrodes have been proposed. However, although the former electrode has good corrosion resistance,
Performance tends to deteriorate with use. Bota,
The latter electrode has the disadvantage of insufficient corrosion resistance in low-temperature seawater electrolysis.

Problems to be Solved by the Invention The purpose of the present invention is to overcome the drawbacks of conventional electrodes in dilute salt water electrolysis, and to provide a relatively low anode potential and high current effect even in low-temperature seawater electrolysis. To provide an electrode with excellent durability and corrosion resistance.Means for solving the problemsThe inventors have conducted extensive research and have found that on a conductive base material,
Based on this finding, we have discovered that an electrode provided with a coating layer consisting of ruthenium oxide, iridium oxide, platinum, and tin oxide of a specific composition, or tin oxide in which tin is partially substituted with antimony, is suitable for this purpose. The present invention has now been completed.

That is, the present invention provides an electrode for electrolysis having a coating layer of a platinum group metal oxide catalyst on a conductive substrate, in which the coating layer contains 3 to 40 mol% of ruthenium oxide and 5 to 40 mol% of iridium oxide. , 3-50 mol% platinum and 10-50 mol%
In an electrode for dilute salt water electrolysis, which is characterized in that it consists of 0 to 50 mol%, and a coating layer having the above composition,
The present invention provides an electrode for dilute salt water electrolysis, characterized in that the tin oxide is substituted with antimony at a mole ratio of 10 or less relative to tin.

Examples of the conductive base material used in the electrode of the present invention include valve metals such as titanium, tantalum, zirconium, and niobium, and among these, titanium is particularly preferred. Moreover, its shape etc. can be changed as appropriate depending on the purpose.

In the uninvented electrode, on such a conductive base material,
A coating layer consisting of ruthenium oxide, iridium oxide, platinum and tin oxide or tin oxide partially substituted with antemones is provided.

The content of ruthenium oxide in this coating layer must be in the range of 3 to 40 mol%, and ruthenium oxide is usually contained in the form of RuO2.

When the content of ruthenium oxide is less than 3 mol%, the anode potential increases and the current efficiency decreases, while when it exceeds 40 mol%, the oxygen overvoltage decreases, the amount of oxygen generated increases, and the current efficiency deteriorates. , and the durability also deteriorates.

Further, the content of iridium oxide in the coating layer is 5 to 40
It is necessary that the molar coefficient be within the range of molar ratio, and iridium oxide is usually contained in the form of hydrogen oxide. If the iridium oxide content is less than 5 mol%, the durability at low temperatures will be extremely poor and the current efficiency will also decrease, while if it exceeds 40 mol%, the oxygen overvoltage will decrease and the amount of oxygen generated will increase. Current efficiency decreases.

In the present invention, the platinum content in the coating layer is 3 to 5.
It is necessary to fall within the range of 0 molar coefficient.

When this amount is less than 3 mol%, the anode potential increases and the current efficiency decreases, while when it exceeds 50 mol%, the current efficiency decreases greatly in the low-temperature electrode w4.

Further, the content of tin oxide in the coating layer must be in the range of 10 to 50 molar ratios, and tin oxide is usually contained in the form of 5n02.

This tin oxide has the effect of facilitating the control of oxygen overvoltage and increasing the adhesion strength of the coating layer to the conductive substrate. If the content of tin oxide is less than 10 mol%, the above effect will not be exhibited. In addition, the mechanical strength of the coating layer decreases, and on the other hand, if it exceeds 50 mol %, the anode potential increases and the durability and current efficiency decrease.

In the present invention, in order to increase conductivity and improve current efficiency, the tin oxide may be added to a portion of tin, if necessary.
It may be substituted with up to 0 mole percent, preferably 5 mole percent, or less than 11 of antimony. In this case, antimony is used as a dopant in the form of 5n0, usually replacing tin.
Contained in 2. If the amount of antimony substitution exceeds 10 mol %, the effect of antimony substitution will be conversely reduced, rather resulting in deterioration of corrosion resistance.

It is generally believed 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 should be around m.

Next, an example of a preferred manufacturing method for the electrode for dilute salt water electrolysis of the present invention (to explain C), first, thermal decomposition (thus, a 16-metal material that becomes ruthenium oxide, such as salt 1 ruthenium (RuCl3 3H20)) , compounds that become iridium oxide by thermal decomposition, such as chloroiridic acid (j
(2-step rc16 6H20), etc., and compounds that become platinum by thermal decomposition, such as chloroplatinic acid, especially chloroplatinic acid (H2Pt ct6-6H20), and compounds that become tin oxide by thermal decomposition. , for example, a halogen such as 1 part stannous salt, a carboxylic acid such as octenoic acid, a stannous complex salt such as phosphonic acid, phosphocarboxylic acid, etc., and if necessary, thermal decomposition. A coating solution is prepared by dissolving a salt that becomes antimony oxide, such as antimony halide such as antimony chloride, in a predetermined ratio in an appropriate solvent.Then, this coating solution is applied onto a conductive substrate. The electrode of the present invention can be obtained by coating, drying, and baking at a temperature of 450 to 650°C in the presence of oxygen.Also, a coating containing one or more of these components [f: Two or more types may be prepared, and after coating these on a conductive substrate in a multi-N coating, drying and baking may be performed.

When using antimony trisalt as a dopant for tin oxide, a large amount of antimony is lost by volatilization during firing, so when preparing the coating solution, add several times more than the amount desired for the final tope. There is a need.

Effects of the Invention The inventive electrode is effectively used as an anode in dilute salt water electrolysis such as seawater electrolysis and salt water electrolysis. As a result, it is possible to maintain the characteristics of low sliding voltage and high current efficiency, and it is also resistant to mechanical wear and tear.
Great for long-term use. Furthermore, even when used for electrolysis of low-temperature seawater below io° C., the current efficiency decreases due to low temperatures is relatively small, and it also has excellent corrosion resistance against oxygen evolution reactions.

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

Example Next, the present invention will be explained in further detail with reference to Example V.

Example 1 As a raw material for forming the entire coating layer, Ru Cl 3
3H20, H2 engineering rCt66H20, H2ptcz6・
6H20 and Cl6H! Using 1o04sn, each was dissolved in butanol to give a metal equivalent concentration of 100f//,
Each raw material solution was prepared. Furthermore, using C16H5o04Sn and 5bcz, -4, these were dissolved in butanol so that sb was 5 molar relative to SnK, and the metal equivalent m degree was 100? /l of raw material solution was prepared.

Each of these raw material solutions was sampled with a measuring pipette at a predetermined ratio Vc, mixed, and stirred to prepare a coating solution.

Separately, a titanium plate was washed with a hot oxalic acid aqueous solution, the coating liquid was applied to the surface using a spatula, and after drying, the plate was placed in an electric furnace and fired at 500°C for 10 minutes.

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

Next, all seawater electrolysis tests were performed using these electrodes, and the anode potential at a current density of 15 A/dm' was shown on the waistcoat with reference to the hydrogen electrode.

Example 2 Using the electrode prepared in Example 1, the chlorine generation efficiency was measured.

That is, in order to approximate the conditions of seawater electrolysis, 3wt%
NaCt water soluble i'ff1150ml. i electrolyte, 5
Using a US304 disk (diameter 30 mm) as the cathode, the current density was 20 A/dn in a sealed electrolytic cell. After electrolysis under the condition of 100 coulombs of electricity, the electrolytic solution was taken out into an Erlenmeyer flask with a lid, and the concentration of hypochlorite was titrated with iodine over the entire area of sodium thiosulfate, and from this result, the chlorine generation efficiency was calculated. I did all the calculations.

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

The results are shown in all attached drawings.

In the figure, curve a is the sample prepared in Example 1/I61
, the uninvented electrode of A3, the curve S is A6, the curve C is 8,
The curve d is the /I67 electrode and the curve e is the 5 electrode.

Example 3 Among the electrodes produced in Example 1, sample flat 1, flat 3, and A5
Using the samples of ~&8, a 1M H2SO4 aqueous solution was electrolyzed in a batch manner at 60° C. at a current density of 100 A/cl-, and the usage time until the electrode became unusable (expressed as electrode life) was determined. The results are shown in the attached table. Note that the sliding voltage increased due to electrolysis, and when it reached 8 V, it was determined that the electrode could no longer be used.

Example 4 Electrode of the invention with a coating layer consisting of 20 mol of Ru02.20 mol of Ru02.15 mol of Pt and 45 mol of 5n02, and for comparison 20 mol of Ftu02.20. Mol-related work r02 and 60 mole-related P
An electrode having a coating layer made of T was fabricated.

The polarization characteristics of these two types of electrodes were measured by a potential scanning method. For measuring chlorine overvoltage, the temperature is 30°C.
The value at a current density of 20 A/d- was determined in a 30 wt% Na Cl aqueous solution (adjusted to pH 1) maintained at . In addition, regarding oxygen overvoltage, 30°C, I M H2
In SO4 aqueous solution, current density 2A/dn? The value of was calculated.

As a result, the non-inventive electrode containing 45 molti of 5n02' had an oxygen overpotential of 450 mV, whereas the latter had an oxygen overvoltage of 350 mV. Further, the chlorine overvoltage was 40 mV in both cases.

Next, the chlorine generation efficiency was determined by dissolving the 1.5 wt% NaO4 aqueous solution at 20°C. As a result, the former is 8
The latter was 84%, while the latter was 84%.

From these results, the effects of the present invention are clear. In other words, the electrode of the present invention has excellent characteristics such as anode potential and current efficiency, and also has excellent corrosion resistance against oxygen evolution reactions, so it can be used continuously for a long period of time even when used as an electrode for low-temperature seawater electrolysis. Usable.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the aqueous solution/?;!i, temperature, and current efficiency in the electrolysis of a 3-weight salt solution using various electrodes.

Claims (1)

[Scope of Claims] 1. An electrode for electrolysis having a coating layer of a platinum group metal oxide catalyst on a conductive base material, in which the coating layer has a content of 3 to 40 mol%.
of ruthenium oxide, 5 to 40 mol% iridium oxide,
An electrode for dilute salt water electrolysis characterized by comprising 3 to 50 mol% of platinum and 10 to 50 mol% of tin oxide. 2. An electrode for electrolysis having a coating layer of a platinum group metal oxide catalyst on a conductive base material, in which the coating layer has a content of 3 to 40 mol%.
of ruthenium oxide, 5 to 40 mol% iridium oxide,
It consists of 3 to 50 mol% of platinum and 10 to 50 mol% of tin oxide, and the tin oxide is 10 mol% of tin.
An electrode for dilute salt water electrolysis characterized by being substituted with the following antimony.