JPH03240987A - Organic matter electrolyzing electrode and its production - Google Patents

Abstract

PURPOSE:To produce the electrode usable over a long period without abnormal consumption and hindrance by providing an iridium oxide-tantalum oxide layer on a conductive substrate and then a specified oxide layer thereon. CONSTITUTION:A soln. contg. an iridium compd. and a tantalum compd. ia applied on a conductive substrate of titanium, etc., and heat-treated in an oxidizing atmosphere to form a base layer consisting of the iridium oxide and tantalum oxide contg. 50-90atom% iridium and 50-10% tantalum. A soln. contg. at least one kind of compd. selected from the compds. of titanium, tantalum, tin, zirconium, niobium and antimony is applied thereon and heat-treated to form an overcoat layer consisting of at least one kind of oxide among the oxides of titanium, tantalum, tin, zirconium, niobium and antimony, and an org. matter electrolyzing electrode is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a novel electrode for electrolysis of organic substances that can be suitably used in electrolysis of electrolytes containing organic substances, and a method for manufacturing the same. More specifically, the present invention provides an electrode for organic substance electrolysis having excellent durability and low oxygen overvoltage, which is suitably used in a reaction in which an aqueous solution containing a desired organic substance is electrolyzed to generate oxygen at an anode. The present invention relates to a method for manufacturing this easily and efficiently.

2. Description of the Related Art Conventionally, metal electrodes in which titanium metal is used as a conductive substrate and a coating layer of a platinum group metal or its oxide is provided thereon have been used in various fields of electrolysis industry.

For example, an electrode in which a titanium substrate is coated with oxides of ruthenium and titanium or oxides of ruthenium and tin is known as an anode for chlorine generation by salt electrolysis (Japanese Patent Publication No. 46-21884, Publication No. 48-3954, Japanese Patent Publication No. 11330-197).

By the way, in the electrolysis industry, in addition to electrolysis that involves chlorine generation as in the case of the salt electrolysis mentioned above, there is also the recovery of acids, alkalis, or salts, the extraction of metals such as copper and zinc, plating, metal surface treatment, and cathodic protection. Electrolytic processes that involve oxygen generation are also used in many fields, such as electrolysis, waste liquid treatment, and electrolytic synthesis of organic substances.

In such electrolysis involving oxygen generation, lead-based electrodes are most commonly used. Other known biosoluble electrodes include electrodes in which iridium oxide and platinum are coated on a titanium substrate, iridium oxide-based electrodes such as iridium oxide-tin oxide-based electrodes, iridium oxide-tantalum oxide-based electrodes, and platinum-plated titanium electrodes. ing.

However, these known electrodes may cause various problems depending on the purpose of use and are not necessarily suitable. For example, if a soluble zinc anode is used as an anode for zinc plating, the anode will dissolve significantly, so the distance between the electrodes must be adjusted frequently, and if a lead-based insoluble anode is used, it will be mixed into the electrolyte. Plating defects occur due to the influence of lead. Furthermore, platinum-plated titanium electrodes are severely worn out and cannot be used when performing so-called high-speed zinc plating at a high current density of 100 A/d- or higher.

Furthermore, the iridium oxide-tantalum oxide based electrode disclosed in JP-A No. 63-235493 has sufficient durability for practical use as an anode for zinc plating that does not contain any organic additives during plating. When used as a galvanizing anode containing organic additives in the plating bath, durability decreases and practicality is lost.

On the other hand, when synthesizing organic materials through an electrolytic reduction reaction on the cathode, the anode reaction often uses the oxygen generation reaction by electrolysis of pure sulfuric acid as the counter electrode reaction, but in this case, under normal operating conditions, If a platinum-iridium oxide based anode is used as the anode, the anode has sufficient durability for practical use, and a desired organic substance can be synthesized without any problem.

However, if the diaphragm ruptures and organic matter in the cathode chamber mixes with pure sulfuric acid in the anode chamber, the anode becomes extremely worn out and becomes unusable in a short period of time.

On the other hand, a method of manufacturing an electrode is known in which the outer surface is coated with tantalum oxide or titanium oxide. Forming a titanium dioxide layer on the surface of a thin film-forming metal,
A method for producing an electrode for electrolysis by coating the surfaces of several layers with at least one layer of platinum group metal and/or its oxide and a layer of tantalum oxide in any order (Japanese Patent Publication No. 57-38675
A layer of a working electrode material is formed on the surface of a support of a thin film-forming metal, and a coating consisting of a thermally decomposable organic compound of a thin film-forming metal in a liquid vehicle is applied onto the layer. Method for manufacturing electrodes by heating a film (UK Patent No. 12)
06863 specification). However, although the electrodes obtained by these methods have excellent durability when used in mercury method salt electrolysis, the layer of working electrode material other than the tantalum oxide or titanium oxide layer applied to the outer surface is platinum group metal. Consisting of a metal or platinum group metal oxide alone,
It lacks durability and is not practical as an electrode for organic electrolysis.

In this way, there are electrodes that can be used for oxygen generation in electrolytes that do not contain organic substances, but there are electrodes that do not cause abnormal wear and have good durability even when the electrolyte contains organic substances. is desperately needed. The causes of abnormal wear on the oxygen generating electrode when organic matter is mixed into the electrolyte are complex and not clear, but include an increase in the anode potential and a decrease in the effective surface area of the electrode due to the adsorption of organic matter on the electrode surface. It is assumed that this is caused by.

Problems to be Solved by the Invention The present invention provides an electrode for electrolyzing an electrolytic solution containing an organic substance, which can be used for a long period of time without causing abnormal wear.
The purpose of this invention is to provide an electrode that can be used without any problems, has a long life, is excellent in durability, and exhibits a low anodic potential.

Means for Solving the Problems The present inventors have conducted various studies in order to develop an electrode for electrolysis of organic substances having the above-mentioned preferable properties. A tantalum oxide layer is provided, an iridium oxide layer is provided thereon as necessary, and at least one oxide selected from titanium oxide, tantalum oxide, tin oxide, zirconium oxide, niobium oxide, and antimony oxide is provided. By providing a similar layer, it is possible to prevent the organic matter in the electrolyte from being directly adsorbed on the surface of the electrode active material iridium oxide or iridium oxide-tantalum oxide mixture. discovered that abnormal wear was suppressed, durability was increased, and furthermore, the anode potential was low and there was no scale, and based on these findings, the present invention was accomplished.

That is, the present invention provides 50 to 90 atomic % of iridium and 50 to 10 atomic % of tantalum in terms of metal on a conductive substrate.
On the base layer made of iridium oxide and tantalum oxide containing On an electrode for organic electrolysis and a conductive substrate, a layer consisting of iridium oxide and tantalum oxide containing 50 to 90 J]i atomic % of iridium and 50 to 1,000 atomic % of tantalum in terms of metal. , an iridium oxide layer is provided, and an outermost layer made of at least one oxide selected from titanium oxide, tantalum oxide, tin oxide, zirconium oxide, niobium oxide, and antimony oxide is provided thereon. The present invention provides a characteristic electrode for organic electrolysis.

Here, atomic % is the atomic fraction expressed as a percentage (%).

This electrode for organic electrolysis can be made by first applying a solution containing an iridium compound and a tantalum compound onto a conductive substrate, and then heat-treating it in an oxidizing atmosphere to produce 50 to 90 atomic percent of iridium and tantalum in terms of metal. 50-10
A base layer consisting of iridium oxide and tantalum oxide containing atomic percent is formed, and then a titanium compound,
After applying a solution containing at least one compound selected from tantalum compounds, tin compounds, zirconium compounds, niobium compounds, and antimony compounds, heat treatment is performed in an oxidizing atmosphere to form titanium oxide, tantalum oxide, and antimony compounds. A top layer made of at least one oxide selected from tin, zirconium oxide, niobium oxide, and antimony oxide is formed, or on a conductive substrate,
First, a solution containing an iridium compound and a tantalum compound is applied, and then heat treated in an oxidizing atmosphere to produce 50-90% iridium and 50-90% tantalum in metal terms.
A layer consisting of iridium oxide and tantalum oxide containing 10 atomic % is formed, then a solution containing an iridium compound is applied thereon, and an iridium oxide layer is formed by heat treatment in an oxidizing atmosphere. After applying a solution containing at least one compound selected from titanium compounds, tantalum compounds, tin compounds, zirconium compounds, niobium compounds, and antimony compounds on top, heat treatment is performed in an oxidizing atmosphere to form titanium oxide. ,
It can be manufactured by forming an outermost layer made of at least one oxide selected from tantalum oxide, tin oxide, zirconium oxide, niobium oxide, and antimony oxide.

The present invention will be explained in detail below.

Examples of the conductive substrate used in the electrode of the present invention include valve metals such as titanium, tantalum, zirconium, and niobium, or alloys of two or more metals selected from these valve metals.

In the electrode of the present invention, a layer made of iridium oxide and tantalum oxide is provided on these conductive substrates, and the proportion of each component in this layer is 50 to 90 atomic % of iridium in terms of metal, It is necessary that tantalum be in the range of 50 to 10 atomic percent. The iridium is 50 atomic %
If it is less than that, the durability of the electrode will decrease and the
The conductivity of the tantalum oxide layer itself also decreases, and
If it exceeds J19%, the adhesion with the conductive substrate will decrease and the durability of the electrode will decrease.In addition, in order to fully achieve the desired effect, the amount of iridium oxide in the coating layer must be 0% in terms of iridium. It is preferable to apply at a ratio of .2+I+9/cm" or more.

Further, when the coating layer is used as a base layer and an iridium oxide layer is coated thereon, the amount of the coating layer is preferably 5 mg/cm2 or less in terms of iridium. 5+I
If it exceeds 1 g/cm2, the adhesion strength of the electrode film and the adhesion strength between the oxide layer provided as the outermost layer and the coating layer will decrease, the amount of electrode consumption will increase, and the durability will decrease.

Further, a layer made of at least one oxide selected from titanium oxide, tantalum oxide, tin oxide, zirconium oxide, niobium oxide, and antimony oxide is provided on the upper layer or the outermost layer, but it is preferable to provide the desired effect. In order to fully achieve this, the coverage of the land layer or outermost layer should be 0.0 in metal terms
It is preferable to select it within the range of 2 to 3 IIIg/C112.

If the coating amount is less than 0.02+I1g/cm, the effect of preventing organic substances from being adsorbed to the iridium oxide-tantalum oxide layer or the iridium oxide layer of the underlayer is not sufficient, and the iridium oxide-tantalum oxide layer of the underlayer is Because the catalytic effect produced by the combination of the tantalum layer or iridium oxide layer and the land layer or outermost layer is insufficient, the anode potential increases and the durability of the electrode decreases.
If it exceeds this, the anode potential becomes too high and the adhesion strength inevitably decreases.

Next, to explain a preferred embodiment for manufacturing this electrode for organic electrolysis, first, a solution containing an iridium compound and a tantalum compound is applied onto a conductive substrate, and then heat-treated in an oxidizing atmosphere. Then, a base layer made of iridium oxide and tantalum oxide is formed, which contains 50 to 90 atom % of iridium and 50 to 10 atom % of tantalum in terms of metal.

The coating liquid used at this time is a compound that becomes iridium oxide through thermal decomposition, such as chloroiridic acid (H21rC
I2.・6H20), iridium compounds such as iridium chloride, and compounds that become tantalum oxide through thermal decomposition,
For example, it can be prepared by dissolving a tantalum compound such as a tantalum halide such as tantalum chloride or a tantalum alkoxide such as ethoxytantalum in an appropriate solvent in a predetermined ratio. This heat treatment in an oxidizing atmosphere is performed by coating the coating solution on the conductive substrate, drying it, and then applying the coating solution to a temperature of preferably 400 to 55% in the presence of oxygen.
This is done by firing at a temperature in the range of 0°C. This operation is repeated multiple times until the required amount of loading is achieved.

A coating layer made of iridium oxide and tantalum oxide prepared in this way is placed on a base layer with a desired amount of support.
Furthermore, at least one compound that becomes titanium oxide, tantalum oxide, tin oxide, zirconium oxide, niobium oxide, and antimony oxide by thermal decomposition, such as chloride and alkoxide, is dissolved in a suitable solvent in a predetermined ratio. After applying the coating solution prepared by the above method, a top layer is formed by heat treatment in an oxidizing atmosphere. In this heat treatment in an oxidizing atmosphere, the coating solution is applied onto the base layer, dried, and then heated in the presence of oxygen.
It is preferably carried out by firing at a temperature in the range of 400 to 600°C. This operation is repeated multiple times until the required amount of loading is reached. In this way,
An oxide overlayer having a desired loading amount is applied on the underlayer to obtain the electrode of the present invention.

Further, to explain another preferred embodiment for manufacturing an electrode for organic electrolysis, first, a solution containing an iridium compound and a tantalum compound is applied onto a conductive substrate, and then heat-treated in an oxidizing atmosphere. Then, a base layer made of iridium oxide and tantalum oxide is formed, which contains 50 to 90 atomic % of iridium and 50-10 atomic % of tantalum in terms of metal.

The coating liquid used at this time is a compound that becomes iridium oxide through thermal decomposition, such as chloroiridic acid (HzlrC).
(216HzO), an iridium compound such as iridium chloride and a tantalum compound such as a compound that becomes tantalum oxide by thermal decomposition, such as a tantalum halide such as tantalum chloride or a tantalum alkoxide such as ethoxytantalum, in a predetermined ratio. It can be prepared by dissolving it in a suitable solvent. In this heat treatment in an oxidizing atmosphere, the coating solution is applied onto a conductive substrate, dried, and then heated to a temperature of preferably 400 to 550% in the presence of oxygen.
This is done by firing at a temperature in the range of °C. This operation is repeated multiple times until the required amount of loading is achieved.

By applying a solution containing an iridium compound on the base layer with a desired amount of the coating layer made of iridium oxide and tantalum oxide prepared as described above, and then heat-treating it in an oxidizing atmosphere, Preferably, an iridium oxide layer is applied in an amount corresponding to an amount of iridium of 5 rtrg/cH2 or less in terms of metal. The solution containing the iridium compound used at this time is a compound that becomes iridium oxide through thermal decomposition, such as iridium chloride #(H2
It can be prepared by dissolving an iridium compound such as 1rC1a.6H,O) in a suitable solvent.

The coating layer formed from the base layer formed from iridium oxide and tantalum oxide and the intermediate layer formed from iridium oxide prepared as described above is loaded with a desired amount, and then titanium oxide and tantalum oxide are further applied by thermal decomposition. After applying a coating solution prepared by dissolving at least one compound such as tin oxide, zirconium oxide, niobium oxide, or antimony oxide, such as chloride or alkoxide, in a suitable solvent in a predetermined ratio, The outermost oxide layer is formed by heat treatment in an oxidizing atmosphere. This heat treatment in an oxidizing atmosphere is performed by applying the coating solution onto the coating layer, drying it, and then baking it in the presence of oxygen, preferably at a temperature in the range of 400 to 600°C. . This operation is repeated multiple times until the required amount of loading is reached. In this way, the outermost oxide layer having a desired loading amount is applied on the coating layer, thereby obtaining the electrode of the present invention.

Effects of the Invention When the electrode of the present invention is used as an anode in organic electrolysis such as electrolysis of an electrolytic solution containing organic substances, the anode potential can be lowered, it can withstand long-term use with a low sliding voltage, and is durable. Not only does it have excellent properties, but it also has excellent durability and can be used for a long period of time even when electrolyzed at a high current density of 100 A/d+m'' or more.

Thus, the electrode of the present invention is suitable as an electrode for electrolysis of organic substances.

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way.

Examples 1 to 7, Comparative Examples 1 to 8 Chloroiridic acid (H2
1rC (Is j 5+ (2o)) and tantalum butoxide (Ta(OC*Hs)J) were dissolved in butanol to prepare a base coating solution with a metal equivalent concentration of 80 g/Q with varying iridium/tantalum composition ratios. .

In addition, at least one compound selected from titanium butoxide, tantalum butoxide, tin butoxide, zirconium butoxide, niobium butoxide, and antimony butoxide in a predetermined proportion corresponding to the composition of the oxide of the upper layer shown in Table 1. The compound was dissolved in butanol to prepare a top coating solution with a metal equivalent concentration of 50 g/Q.

Separately, the base coating solution was applied with a brush onto a titanium substrate etched with hot oxalic acid, dried, and then placed in an electric furnace and baked at 500°C while blowing air.

These coating, drying, and baking operations were repeated an appropriate number of times until a predetermined amount of support was achieved, thereby preparing each intermediate sample in which the base layer of iridium oxide and tantalum oxide was coated on the substrate.

Further, the above-mentioned top coating liquid was applied with a brush onto the base layer of each intermediate sample, and after drying, the coated layer was placed in an electric furnace and baked at 500°C while blowing air.

By repeating the coating, drying, and baking operations, an electrode sample in which the oxide upper layer is coated on the base layer is prepared.

Further, for comparison, electrode samples provided with the coating layers shown in Table 1 were prepared.

Next, the anode potential of these created electrodes was measured. The measurement method was by potential scanning method.
/(l Current density 20 in phenol sulfonic acid aqueous solution
The value at A/dm2 was determined. The result is the first
Shown in the table. Also, regarding this electrode, 50°C, 709/1
A life test was conducted in an aqueous solution of 2-phenolsulfonic acid.

This electrode is used as an anode and platinum is used as a cathode, with a current density of 1
Electrolysis was carried out at 00 A/di". The results are also shown in Table 1.

As is clear from these results, the electrode of the present invention exhibits a low anodic potential and has a significantly longer lifetime.

The life of the electrode is ○: 1000 hours or more, △: 5
00 to 1000 hours, x: 500 hours or less, indicating the electrolyzable time.

Examples 8 to 12, Comparative Examples 9 to 14 In the same manner as in the preparation of the base layer in the above examples, a coating layer of iridium oxide and tantalum oxide was formed in a composition ratio of 7ON of iridium, 30% of tantalum and 30% of tantalum in terms of metal. A coating solution prepared by dissolving chloroiridic acid in butanol was applied with a brush to a metal equivalent concentration of 8 h/12 on the base layer, and after drying, it was placed in an electric furnace. Baking was performed at 500°C while blowing air. The coating, drying, and baking operations were repeated to coat the base layer with an iridium oxide layer.

Next, on top of this, at least one compound selected from titanium butoxide, tantalum butoxide, tin butoxide, zirconium butoxide, niobium butoxide, and antimony chloride is dissolved in butanol so that the metal equivalent concentration is 50 g/Q. The prepared coating solution was applied with a brush, dried, and then placed in an electric furnace and baked at 500° C. while blowing air. These coating, drying, and baking operations were repeated to produce an electrode sample in which the iridium oxide layer was covered with the outermost oxide layer.

Further, for comparison, electrode samples provided with the coating layers shown in Table 2 were prepared.

Next, the oxygen overvoltage of these electrodes was measured. The measurement method was the potential scanning method at 30°C and 220°C.
g/QfILwjL sodium + 20 g/Q sodium acetate + sulfuric acid (pH-1) current density 20 A/d in aqueous solution
The value at I112 was determined. The results are shown in Table 2.

Regarding this electrode, 50℃, 220g/4 sodium sulfate + 20e/Q sodium acetate + sulfuric acid (pH-1)
A life test was conducted in an aqueous solution. Using this electrode as an anode and platinum as a cathode, electrolysis was carried out at a current density of 150 A/da''. The results are shown in Table 2.

As is clear from these results, the electrode of the present invention exhibits a low oxygen overpotential and has a significantly longer lifetime.

The life of the electrode is ○: 1000 hours or more, Δ: 5
0θ to 1000 hours, X: 500 hours or less, indicating the electrolyzable time.

Example 13 The electrodes obtained in Example 3 and the electrodes obtained in Comparative Examples 3 and 4 were subjected to a life test in a 5% by weight ammonium adipate aqueous solution at 50'C.

That is, using these electrodes as anodes and titanium as cathodes, electrolysis was performed at a current density of 2OA/d1.

As a result, the electrodes of Comparative Examples 3 and 4 both became incapable of electrolysis within 1000 hours, but the electrode of Example 3
Electrolysis was possible for more than an hour.

From the above results, it is clear that the electrode of the present invention has excellent durability in electrolysis of an electrolytic solution containing an organic substance.

Claims (1)

[Claims] 1 Iridium 50 to 90 in terms of metal on a conductive substrate
At least one selected from titanium oxide, tantalum oxide, tin oxide, zirconium oxide, niobium oxide, and antimony oxide on a base layer made of iridium oxide and tantalum oxide containing 50 to 10 atom % of tantalum. An electrode for electrolysis of organic matter, characterized in that an upper layer made of an oxide of a species is provided. 2. On a conductive substrate, an iridium oxide layer is provided on a layer consisting of iridium oxide and tantalum oxide containing 50 to 90 atomic % of iridium and 50 to 10 atomic % of tantalum in terms of metal, and a titanium oxide layer is further provided on the layer of iridium oxide and tantalum oxide. 1. An electrode for organic electrolysis, comprising an outermost layer made of at least one oxide selected from tantalum oxide, tin oxide, zirconium oxide, niobium oxide, and antimony oxide. 3. First, a solution containing an iridium compound and a tantalum compound is applied onto a conductive substrate, and then heat treated in an oxidizing atmosphere to form a solution containing 50 to 90 at% of iridium and 50 to 10 at% of tantalum in terms of metal. a base layer made of iridium oxide and tantalum oxide, and then containing at least one compound selected from a titanium compound, a tantalum compound, a tin compound, a zirconium compound, a niobium compound, and an antimony compound. After applying the solution, heat treatment is performed in an oxidizing atmosphere.
A method for manufacturing an electrode for organic electrolysis, comprising forming an upper layer made of at least one oxide selected from titanium oxide, tantalum oxide, tin oxide, zirconium oxide, niobium oxide, and antimony oxide. 4. First, a solution containing an iridium compound and a tantalum compound is applied onto a conductive substrate, and then heat treated in an oxidizing atmosphere to form a solution containing 50 to 90 at% of iridium and 50 to 10 at% of tantalum in terms of metal. A layer consisting of iridium oxide and tantalum oxide is formed, and then a solution containing an iridium compound is applied on this layer, and then a heat treatment is performed in an oxidizing atmosphere to form iridium oxide, and a titanium compound, tantalum compounds, tin compounds,
After applying a solution containing at least one compound selected from zirconium compounds, niobium compounds, and antimony compounds, heat treatment is performed in an oxidizing atmosphere to form titanium oxide, tantalum oxide, tin oxide, zirconium oxide, and titanium oxide. A method for producing an electrode for organic electrolysis, comprising forming an outermost layer made of at least one oxide selected from niobium and antimony oxide.