JPH11229170A - Activated cathode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an activated cathode for salt water electrolysis reduced in poisoning caused by mercury in an electrolyte in the case of ion exchange membrane process electrolysis by the replacement of mercury process electrolysis. SOLUTION: The activated cathode for ion exchange membrane process alkali chloride electrolysis is constituted so as to use nickel as a base material, to have an electrodeposition layer of nickel, in which ruthenium oxide is dispersed, thereon and to cover the surface with an electroconductive oxide consisting essentially of a rutile type titanium oxide. In such a case, the rutile type titanium oxide preferably contains 20% (by weight) ruthenium oxide. An alloy layer consisting of a rare earth metal and nickel is preferably provided between the nickel base material and the electrodeposition layer of nickel, in which ruthenium oxide is dispersed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an activated cathode having a low overvoltage used in chloralkali electrolysis by an ion exchange membrane method.

[0002]

2. Description of the Related Art In a salt electrolysis process using an ion exchange membrane method, reduction of energy consumption is the most important problem. The overvoltage of the cathode and the anode as a constituent factor is completely useless, and while other factors are inevitable from the structure and the like, this is a factor that can be reduced by selecting the electrode, and Various reductions have been considered as possible. As for the anode, the so-called D
The overvoltage can be reduced to 50 mV or less by the insoluble metal electrode having the coating of the platinum group metal oxide based on SE, and the overvoltage has reached an almost undesired level. On the other hand, as for the cathode, conventionally used mild steel, nickel or stainless steel is 300 to 400 m.
Activating this surface to have an overvoltage of the order of V has been done and many patents have been filed.

[0003] That is, while a normal cathode is made of mild steel, stainless steel or nickel as it is, in order to enlarge this surface or cover it with an active metal surface, an active metal coating such as Raney nickel is applied by electroplating. Or metal is sprayed by a plasma spraying method so as to have a large surface area. Also, it has been practiced to obtain a large surface area by roughening the surface by suspension plating of metal or activated carbon. By increasing the surface area, the effective surface area can be made several hundred times to tens of thousands times that of the original one, and the overvoltage as a hydrogen generating electrode (cathode) can be reduced by 200 mV or more, and substantially 150 to
The voltage can be reduced to 200 mV, which has been put to practical use. However, the surface of these cathodes
In order to provide a large surface area, the surface is considerably rough, and the state of the surface can be considered to be a file.
This is less problematic in so-called gap cells or narrow gap cells where the ion exchange membrane and the cathode do not directly touch, but in the so-called zero-gap type cell where the ion exchange membrane is directly in contact with or in contact with the cathode, it is made of resin. When the ion-exchange membrane comes into contact with the cathode, it has a problem that a hole is formed.

On the other hand, by selecting the cathode material, the overvoltage is reduced by utilizing the electrode catalysis of the cathode material. In this method, it is not necessary to increase the surface area of the electrode. have. Representatively, an electrode in which ruthenium oxide is contained in nickel by suspending and plating fine particles of ruthenium oxide as a catalyst substance in a nickel plating bath is known. Again, a small overvoltage of about 100 to 250 mV is known. It has gained.
Electrodes formed by electroless plating of platinum or a platinum group metal alloy are also known. Also, a method of plating an alloy of tin and nickel has been used.

In these electrodes, the electrode surface is smooth even in a zero-gap type electrolytic cell, so that the ion exchange membrane is hardly damaged. However, there is no problem when stable electrolysis is performed even in an electrolysis cell using such an electrode.However, when electrolysis stops suddenly due to an accident or power failure, the cathode and anode are usually electrically connected through a rectifier. Therefore, a reverse current due to reverse decomposition of the electrolytic product flows. As a result, the activity as a cathode may be deteriorated, possibly due to a change in the surface state such as partial elution of a metal as a cathode component. Especially in the case of a zero gap electrolytic cell,
When the partially eluted nickel component precipitates in the contacted ion exchange membrane, not only the cathode but also the ion exchange membrane is poisoned.

In order to substantially prevent the elution of nickel even if this reverse current cannot be prevented, and to reduce the damage of the ion exchange membrane even in the case of a zero gap cell, a nickel alloy coating means is known. . For example, the above-described nickel-tin alloy plating is a typical example. As a result, although the tin is selectively eluted, damage to the ion exchange membrane can be prevented to some extent, but there is a problem that the electrode is gradually deteriorated in terms of electrode activity. As an electrode having such characteristics, there is nickel manganese alloy plating and the like. However, the fact that nickel metal is exposed on the surface inevitably deteriorates the ion exchange membrane due to elution of nickel metal in long-term electrolysis.

In order to prevent the reverse current itself, or to prevent the poisoning by preventing the corrosion of the electrode material, a hydrogen storage alloy dispersed in the electrode has been proposed. As a result, the surface roughness becomes large and a problem arises in some cases for a zero-gap electrolytic cell.However, in the case of power supply stop, the electrode itself is protected because the hydrogen storage metal works to keep the potential near zero. There is a characteristic that. As a manufacturing method of this, for example, by suspending and plating hydrogen storage metal fine powder, it is difficult to set conditions for this,
Apart from supporting the catalyst material for activation, there is an annoyance that a hydrogen storage metal must be formed.
The present inventors have obtained an extremely stable activated cathode by previously performing metal hydride suspension plating on a nickel base material surface and further performing ruthenium oxide suspension plating on the surface thereof. With the problem of overlapping,
There was an annoyance that setting the conditions required relatively complicated electrodeposition.

[0008]

On the other hand, although there is no problem in a new electrolytic plant, ion-exchange membrane electrolysis is the most advanced method and is often replaced by mercury electrolysis. May contain a small amount of mercury in the feed brine. This mercury is known to reach the cathode chamber through the ion exchange membrane and harm the cathode. The conventional activated cathode having a large surface area has relatively little harm, but the catalytic activated cathode has a problem that it is easily poisoned. The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a cathode in which poisoning by mercury in an electrolyte is reduced.

[0009]

According to the present invention, there is provided an electroconductive oxide comprising nickel as a base material, an electrodeposited layer of nickel in which ruthenium oxide is dispersed on the surface thereof, and a conductive oxide mainly comprising rutile type titanium oxide on the surface. An activated cathode for ion-exchange membrane method chlor-alkali electrolysis covered with a substance. Shows a small overvoltage, reduces poisoning by mercury in the electrolyte, and shows particularly excellent characteristics for conversion from mercury electrolysis to ion exchange membrane electrolysis, and excellent durability for stable electrolysis. Activated cathode.

That is, the present invention has solved the above-mentioned problems by the following means. (1) An ion comprising a nickel base material, a surface of which has an electrodeposited layer of nickel in which ruthenium oxide is dispersed, and the surface of which is covered with a conductive oxide mainly composed of rutile-type titanium oxide. Activated cathode for chloralkali electrolysis by exchange membrane method. (2) 20% of rutile type titanium oxide (weight, the same applies hereinafter)
The activated cathode according to the above (1), comprising the following ruthenium oxide. (3) The activated cathode according to (1), wherein an alloy layer made of a rare earth metal and nickel is provided between the nickel base material and the electrodeposited layer of nickel in which ruthenium oxide is dispersed. Hereinafter, the present invention will be described in detail.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, the following facts can be understood or presumed for a cathode used in contact with an ion exchange membrane in chloralkali electrolysis by an ion exchange membrane method. It was done by things. Ruthenium oxide is effective as an electrode material for the activated cathode. Electrodes in which ruthenium oxide is dispersed in nickel exhibit excellent characteristics. However, it is relatively vulnerable to poisoning by mercury. Almost no poisoning by mercury occurs by covering the surface with conductive titanium oxide. The existence state of titanium oxide is that the rutile type is stable. For that purpose, it is optimal to add a small amount of ruthenium oxide to titanium oxide.

[0012] Even if a titanium oxide coating is formed, the characteristics as a cathode hardly change. It seems that poisoning due to elution of nickel to the ion exchange membrane hardly occurs even when used in contact with the ion exchange membrane. Since the alloy of rare earth metal and nickel has a certain hydrogen storage function, it stores hydrogen during normal electrolysis, which seems to prevent reverse current by releasing hydrogen when current is interrupted. Rutile-type titanium oxide, which acts as a cathode to some extent, is stable even in high-concentration caustic soda during anodization, and exhibits a resistance effect as an anode for reverse current to flow when current is interrupted, attenuating the flow of current or Have a function of blocking. As a result of studying to find an electrode and to form an electrode corresponding to the result, the present invention has been achieved.

That is, in order to achieve these, first, a nickel plating solution in which a powder mainly composed of ruthenium oxide is suspended on the surface of nickel as a base material is used. Electrodeposit on the substrate surface. The shape of the substrate is not particularly specified, and is selected depending on the purpose. A perforated plate, an expanded mesh, a so-called Uven mesh made by knitting a nickel wire, and the like are preferably used. The production conditions of the ruthenium oxide powder are not particularly limited as long as it has sufficient activity as an electrode catalyst, but a hydrochloric acid or alcohol solution of ruthenic chloride is dried at room temperature or at a temperature of 110 ° C. or lower, and then in air or an oxidizing atmosphere. Pyrolysis at 350 ° C. to 600 ° C. for 30 minutes to 10 hours. At this time, by adding 20% or less of titanium chloride or butyl titanate to the solution, ruthenium oxide can be converted to a composite oxide with titanium oxide. As a result, the characteristics of the electrode are almost the same and the electrode can be more stabilized, and the adhesion to the titanium oxide layer formed on the surface can be increased.

The conditions for electrodeposition are not particularly limited, and the electrodeposition may be performed using a so-called Watt bath, which is a mixed aqueous solution of nickel sulfate and nickel chloride as a plating solution and nickel as a base material as a cathode. Besides this, an aqueous solution of nickel chloride can also be used as the electrodeposition liquid. In this case, the deposited nickel surface is slightly roughened, so that an effect of increasing the surface area can be expected. The amount of dispersion of ruthenium oxide is not particularly specified, but is suitably about 0.5 to 5% with respect to the electrolytic solution. This forms a catalyst layer containing 5 to 40% ruthenium oxide in the electrodeposited layer, depending on the degree of stirring of the liquid. Although the thickness of the plating layer is not particularly specified,
The ruthenium oxide content is desirably about 3 to 15 g / m ² , and the nickel basis weight is 5 to 20 μm
A degree is desirable. The plating conditions may be ordinary conditions. For example, when a watt bath is used, the plating bath is stirred at a temperature of about 40 ° C. and a current density of 5 to 20 A while sufficiently stirring the ruthenium oxide particles. Electroplating is performed at about / dm ² . In the case where a solution containing only nickel chloride is used, a nickel chloride bath containing 10 to 50 g / liter of nickel may be used, and the temperature and current density may be substantially the same as those of a watt bath.

In any of the electrolytic baths, an additive which is a bright material used in ordinary plating may be used. In order to improve the surface roughness, it is desirable that the plating surface has fine irregularities, and for that purpose, an additive may not be used. Next, a thermally decomposed oxide layer mainly composed of titanium oxide is formed on the plating surface. By forming a porous, mainly rutile-type titanium oxide stable layer, physical strength can be maintained. By converting ruthenium into a composite oxide for this titanium oxide,
When the current is cut off, the anode has a relatively high overvoltage. The formation conditions are not particularly specified, but they must be porous to some extent.For this purpose, butyl titanate is used as the titanium raw material, and ruthenium chloride or ruthenium chloride is used as the ruthenium raw material. It is desirable to dissolve the coating solution. Titanium chloride can also be used, but also in this case, isopropyl alcohol or butyl alcohol is added as a solvent.

This solution is applied on the surface subjected to dispersion plating by an arbitrary method, and is thermally decomposed. The thermal decomposition conditions are as follows: 350 to 500 ° C. in an oxidizing atmosphere such as air for 10 minutes to 15 minutes.
Minutes. The steps of coating and thermal decomposition are repeated to obtain a titanium oxide layer having a desired thickness. The reason why ruthenium chloride is added is that titanium oxide generated by thermal decomposition thereby becomes a rutile type main body and also works as a stable protective layer. The amount ratio of ruthenium is preferably 5 to 20% as an oxide, particularly preferably 7 to 10%. If it is less than 5%, the main component of titanium oxide will be anatase type, and it will not be stable in a strong alkali as in the present case. Although the thickness of the titanium oxide layer is not particularly limited, it is usually 1 to 5 μm,
Obtained by repeating 5 times. The alcohol is added to the solvent in order to secure porosity by volatilization of the alcohol during the thermal decomposition, whereby an appropriate porosity can be ensured. However, if the number of repetitions of coating and thermal decomposition is too large, the porosity is hindered.

In this way, an activated cathode having a surface substantially covered with a stable oxide and having a coating mainly composed of ruthenium oxide as an electrode material is produced. It has been confirmed that even when this product is immersed in mercury, no amalgam is formed on the surface and the characteristics as an electrode do not change.
This alone can sufficiently achieve the purpose of mercury resistance, but it is used as a cathode and in a high-concentration caustic alkali, and a reverse current flows due to current interruption.In other words, this electrode operates as an anode, and nickel In order to minimize corrosion of the alloy, an alloy layer having a hydrogen absorbing ability can be provided at the interface between the coating and the nickel substrate. The conditions are not particularly limited, but as a simple method, a coating solution containing a rare earth metal and nickel is applied in advance to the surface of a nickel base material, and thermally decomposed to form a nickel-rare earth alloy layer, that is, a hydrogen storage alloy. By providing a layer, this phenomenon can be considerably mitigated.

This alloy layer is formed by applying a solution obtained by dissolving organic nickel and a rare earth metal salt in an organic solvent which is a reducing solvent as a coating liquid to a previously activated nickel metal substrate surface, It can be obtained by pyrolysis at 600 ° C. The activation treatment of the nickel base material may be performed by a conventional method, for example, sand blasting with alumina sand and / or 40 to 60 ° C., 10 to 2
By pickling with 0% hydrochloric acid. The atmosphere for the thermal decomposition is preferably a reducing or inert atmosphere such as in a hydrogen gas stream or in nitrogen or argon.If it is difficult to obtain such an atmosphere, generation of oxides is slightly observed, but in an air atmosphere. Thermal decomposition may be used. The solvent is not particularly limited, but a ketone such as amyl alcohol, butyl alcohol, diethyl ketone or the like, a higher alcohol solution of resin acid, or the like is preferably used in order to enhance the reducibility. The formation amount of this alloy layer is not particularly specified,
The target amount can be obtained by changing the number of times of application and thermal decomposition.

When the thickness of the alloy layer is increased, the durability against reverse current is improved by an amount corresponding to the increase in the amount of hydrogen occlusion. However, since the physical strength is reduced and the chemical corrosion resistance is not necessarily good, the It is appropriate to carry out the thermal decomposition about 1 to 3 times to make the thickness about 1 μm or less.
However, the number of times may be selected according to conditions. Before forming this alloy layer, the surface of the nickel base may be oxidized in an oxidizing atmosphere to form a thin layer of nickel oxide. Although this condition is not particularly specified, for example, it can be obtained by heating in air at 300 to 600 ° C. The time is suitably from 10 to 200 minutes.

[0020]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 A smooth nickel expanded mesh having a thickness of 1 mm was used as a nickel base material, and the surface thereof was blasted with alumina sand having an average particle diameter of 50 μm. Pickling was performed in hydrochloric acid for 15 minutes to remove alumina sand penetrating the surface and activate the surface. On this surface, a nickel plating layer in which ruthenium oxide was dispersed was formed. As ruthenium oxide, sodium hydroxide was dropped into an aqueous solution of ruthenic chloride to neutralize it, the precipitated ruthenium hydroxide was separated by filtration, washed with pure water, and kept in a muffle furnace at a temperature of 400 ° C. for 1 hour. The oxide was pulverized to 100 mesh or less. Next, a nickel concentration of 50 g / nickel was prepared by mixing nickel chloride and nickel sulfate at a ratio of 1: 3.
1 liter of nickel plating solution
Ruthenium oxide powder prepared at 5 g / liter was added to form a plating solution, and plating was performed using a nickel plate as an anode and a nickel mesh as a test material as a cathode.

No bright material was added to the plating solution. Plating was performed at a temperature of 40 ° C. and a current density of 15 A / dm ² for 4 minutes. As a result, a nickel plating layer having an apparent thickness of 10 μm and ruthenium oxide dispersed therein was formed.
According to the analysis by the fluorescent X-ray method, it was confirmed that about 5 g / m ² of ruthenium was carried on this plating layer. On the surface of the coating layer thus formed, a solution was prepared by dissolving butyl titanate and ruthenic chloride in butyl alcohol at a metal molar ratio of 85:15,
It was applied and thermally decomposed under the same conditions as those for forming ruthenium oxide. This operation was repeated three times to obtain 2 g / m 2 of titanium.
A coating layer of No. ² was formed. X-ray diffraction showed that the anatase phase was slightly formed, but most consisted of the rutile phase.

Using this as a sample, an electrolytic test was conducted under salt electrolysis conditions.
Was done. For comparison, the main surface is made of titanium oxide.
Was made in the same manner as in Example except that no coating layer was formed.
A sample was prepared. The electrolysis test was performed using du as an ion exchange membrane.
Using the brand name Nafion 961 manufactured by Pont,
The ion exchange is performed in a two-chamber ion exchange membrane electrolytic cell as a diaphragm.
Press the anode and cathode in close contact with the membrane
Mercury chloride so that the Hg concentration becomes 100 ppm as a liquid
200 g / l of saline solution, and catholyte
And a 32 wt% aqueous solution of caustic soda
° C, current density 40A / dm ^TwoI went in. The anode
Ruthenium oxide on the titanium expanded mesh surface
Composite oxide consisting of aluminum, iridium oxide and titanium oxide
An insoluble metal anode with a cover was used.

Continuous 100 hours, current density 40 A / dm ²
When the electrolysis was performed, the cathode voltage of the electrode of the present example hardly changed, and the overvoltage was 150 to 170 mV. In contrast, although the comparative example showed a low overvoltage of about 140 mV at first, it gradually deteriorated. 100 hours after the start, the overvoltage became 300 mV or more. After the electrolysis, the electrolytic cell was disassembled, the electrodes were taken out, and after washing with dilute hydrochloric acid, the surface deposits were analyzed by X-ray fluorescence. Adhesion was observed. It is considered that amalgam with surface nickel was formed.

Example 2 A smooth nickel expanded mesh having a thickness of 1 mm was used as a nickel base material.
After plasting with 0 μm alumina sand, the aluminum sand was washed with hydrochloric acid at a temperature of 60 ° C. and a concentration of 20% for 15 minutes to remove and activate the alumina sand eroded on the surface. On the surface of this nickel base material, a solution obtained by dissolving cerium chloride corresponding to the same number of moles of misch metal in nickel butoxide in a mixed solvent of diethyl ether and butyl alcohol as a coating solution is applied by a brush, and after air-drying, Pyrolysis was performed at 450 ° C. for 20 minutes in a muffle furnace with nitrogen flow. This operation was repeated three times to form a nickel-mish metal alloy layer having a thickness of 1 μm on the surface. However, before forming the alloy, the nickel substrate is
Heated at 50 ° C. for 1 hour to form a nickel oxide layer on the surface. A nickel plating layer in which ruthenium oxide was dispersed was formed on the surface of the alloy layer thus prepared under the same conditions as in Example 1, and a surface layer was further formed.

Here, the ruthenium oxide powder was obtained by placing an aqueous ruthenium chloride solution in a crucible, drying at 110 ° C., and thermally decomposing at 450 ° C. for 3 hours while flowing air. It was found that about 1% of chlorine was present in ruthenium oxide with respect to the amount of ruthenium. This electrode was subjected to an electrolytic test under the same conditions as in Example 1. After 100 hours of continuous electrolysis, the current value was reduced to half the current value for 1 hour / 10 minutes, that is, a current density of 20 A /
A reverse current was passed as dm ² . 20 reverse current conduction tests
Repeated times. The cathode overvoltage, which was initially 140 mV,
There was no change after this test. No mercury deposition was observed on the electrode surface after the electrolytic test.

[0027]

According to the present invention, the following effects can be obtained. (1) By forming a cathode in which the entire electrode surface is covered with a conductive oxide made of rutile-type titanium oxide, a stable activated cathode having sufficient resistance to mercury in the electrolytic solution could be obtained. . (2) By having a nickel electrodeposition layer containing ruthenium oxide as an electrode material, the cathode overvoltage could be reduced. (3) When used in contact with the ion exchange membrane, the influence on the ion exchange membrane was minimized. (4) It was found that the electrode hardly deteriorated even when the current was interrupted. (5) It was found that the electrode was not deteriorated even if a reverse current was applied if the amount was small. (6) Nickel is used for the cathode base material, but the elution of nickel is minimal at the time of electrolysis and current interruption, and no attack of nickel on the ion exchange membrane is observed, so that stable electrolysis can be continued. all right. For this reason, it turned out that this invention is especially effective as a cathode used in contact with an ion exchange membrane.

Claims (3)

[Claims] The present invention is characterized in that a nickel base material, a nickel electrodeposited layer in which ruthenium oxide is dispersed is provided on the surface, and the surface is covered with a conductive oxide mainly composed of rutile type titanium oxide. Activated cathode for chloralkali electrolysis using ion exchange membrane method. 2. The activated cathode according to claim 1, wherein the rutile type titanium oxide contains 20% (by weight) or less of ruthenium oxide. 3. The activated cathode according to claim 1, wherein an alloy layer composed of a rare earth metal and nickel is provided between the nickel base material and the nickel electrodeposited layer in which ruthenium oxide is dispersed.