JPH06248484A - Electrode and its production - Google Patents

Abstract

PURPOSE:To provide the electrode for electrolysis industry having a long service life. CONSTITUTION:This electrode is constituted by subjecting the surface of a base material consisting of a metal simple substance or alloy to a nitriding treatment, thereby forming a nitride later of the metal simple substance or alloy in the extreme surface layer part or a nitrogenous layer essentially consisting of a nitrogen diffused layer in the lower part thereof. The nitrogenous layer is then exposed by removing the nitride layer of the extreme surface layer part and thereafter, a catalyst layer consisting of the oxide of platinum group metals is formed on the surface of the nitrogenous layer, by which the electrode is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode, and more specifically, it has excellent durability when used as an anode in the electrolytic industry such as salt solution electrolysis, water electrolysis, plating, electrolytic refining, organic electrolytic synthesis and cathodic protection. The present invention relates to an electrode that exhibits excellent properties.

[0002]

2. Description of the Related Art In the electrolysis industry, saving the amount of electric power used has been pursued as the most important issue. As part of this, the development of an electrode capable of efficiently promoting the reaction on the electrode surface even with the application of the lowest voltage. Is being promoted. For example, in the field of saline electrolysis, as the anode,
An electrode is used in which the surface of a base material of metal Ti or its alloy is covered with a layer containing conductive ruthenium oxide as a main component. Further, as an anode accompanied by generation of oxygen in the electrodeposition of Cu, Zn, etc., for example, an electrode in which the surface of a metal Ti plate is covered with a layer containing conductive iridium oxide as a main component is used.

When the electrode having such a structure is used, the above-mentioned metal oxide layer of ruthenium oxide, iridium oxide or the like functions as a conductive catalyst layer, whereby the anodic reaction is promoted and the overvoltage is lowered. Therefore, the electrode reaction can proceed smoothly and the electric power energy used can be saved. In this case, it is preferable to increase the activity of the electrode whose surface is coated with the catalyst layer and to increase the specific surface area of the electrode surface by making the surface of the catalyst layer relatively porous. Has been done.

Such a catalyst layer is usually made of Ru described above.
A compound of a platinum group element such as Cr and Ir, for example, a solution obtained by dissolving a chloride in a solvent such as butyl alcohol is applied to the surface of the base material, and then thermally decomposed in an oxygen-containing atmosphere to oxide the metal. It is formed by a method of forming a layer.

[0005]

By the way, when a predetermined electrolysis operation is carried out in an aqueous solution using an electrode having a large specific surface area of a catalyst layer, a comparison is made even though the catalyst layer is present on the surface of the base material. The electrolysis voltage may rise rapidly in a very short time. In particular, when the electrolytic solution is acidic or when the electrolytic solution contains an organic electrolyte, the above-mentioned phenomenon remarkably occurs. It is generally determined that the service life of the electrode is exhausted at the time when such a phenomenon occurs.

[0006] The above-mentioned phenomenon is that during operation of the electrode, an oxide such as a strongly acidic electrolytic solution or an organic substance penetrates into the catalyst layer and reaches the surface of the base material to corrode the surface of the base material. By doing so, the adhesion between the catalyst layer and the base material is weakened and the catalyst layer is peeled off, or the catalytic activity of the catalyst layer as a whole is reduced, or the base material surface is oxidized by the invading oxidizing component, It is considered that an oxide film having a high electric resistance is formed on the interface between the catalyst layer and the base material, and eventually the electrolysis voltage increases.

Therefore, even if the electrode had excellent catalytic properties at the initial stage of use, the above phenomenon may occur depending on the electrolysis conditions to be applied, and the life thereof may be shortened. To solve such a problem, it has been proposed to form a thin layer of nitride as an intermediate layer before forming the catalyst layer.

Although this nitride layer has excellent corrosion resistance, it usually has defects consisting of micropores, so that the electrolytic solution penetrates and weakens the adhesion to the surface of the base material. The layer is liable to be peeled off, and the catalyst layer is liable to be peeled off. It is an object of the present invention to provide a novel electrode having a long service life and excellent durability, and a method for producing the same, which solves the above-mentioned problems in the conventional electrode coated with a catalyst layer.

[0009]

In order to achieve the above object, in the present invention, a substrate having a metal simple substance or alloy and a nitrogen-containing layer of the metal simple substance or alloy formed on the surface thereof, And a catalyst layer made of a platinum group metal oxide formed by coating the nitrogen-containing layer of the base material, and a substrate made of a simple metal or an alloy. By subjecting the surface of the material to a nitriding treatment, a nitride layer of the elemental metal or alloy is formed in the outermost layer portion, and a nitrogen-containing layer mainly composed of the diffusion of nitrogen into the elemental metal or alloy is formed under the layer. After forming a layer, and then removing the nitride layer of the outermost surface layer to expose the nitrogen-containing layer, a catalyst layer made of a platinum group metal oxide is formed on the surface of the nitrogen-containing layer. An electrode manufacturing method characterized by It is.

In the electrode of the present invention, the material used for the base material is, for example, Ti or Z belonging to Group IVa of the periodic table.
r, Hf or an alloy containing them as a main component; V, Nb, Ta belonging to the group Va of the periodic table or an alloy containing them as a main component; Cr, Mo, W belonging to the group VIa of the periodic table or their main components An alloy containing; Mn, Tc, Re belonging to Group VIIa of the periodic table or an alloy containing them as a main component; Fe and C among metals belonging to Group VIII of the periodic table
o, Ni or an alloy containing them as the main component;

Of these, for example, IVa group (Ti group) such as Ti and Zr or Fe such as Fe, Co and Ni
Group simple metals or alloys containing them as a main component are preferable, and Ti, Zr and Cr steels are particularly preferable. The surface of this base material is subjected to a nitriding treatment. First, before performing the nitriding treatment, the surface of the base material is roughened to about 5 to 20 μm. This is because if the surface of the base material is roughened, the adhesion between the base material and the catalyst layer can be enhanced when the catalyst layer is subsequently formed.

In this case, as a method for roughening the surface of the substrate, for example, a concentration of 5 to 40% by weight and a temperature of 50 to 10 are used.
A method of immersing the base material in an oxalic acid solution at 0 ° C. for about 1 to 8 hours, or for example, immersing the base material in a sulfuric acid aqueous solution having a concentration of 5 to 50% and a current density of about 5 to 30 A / dm ² for 1 to 10 minutes It is possible to adopt a method of etching to a certain degree. As the nitriding method, for example, an ion nitriding method, a gas nitriding method, a salt bath nitriding method, or the like can be performed, and an ion nitriding method using gas nitrogen or a gas nitriding method is preferable.

By this nitriding treatment, the reaction between the constituent metal or alloy of the outermost surface layer of the base material and nitrogen proceeds in a substantially stoichiometric manner, so that the outermost surface layer portion of the base material contains the metal or alloy and nitrogen. Convert to nitride. Then, in the lower part of this nitride layer, although a slight nitriding reaction also occurs, the diffusion of nitrogen mainly progresses. Therefore, in the lower part of the outermost layer, which is a layer of nitride, there is a nitrogen-containing layer in which a small amount of nitride produced by the nitriding reaction and diffused nitrogen are mixed, and the composition is a non-stoichiometric composition. is there. Further, the nitrogen diffusion layer has a high nitrogen concentration on the outermost layer side and a lower nitrogen concentration on the center side of the base material.

In the present invention, next, the nitride layer of the outermost surface layer formed by the above nitriding treatment is removed to expose the above nitrogen-containing layer on the surface of the substrate. As a result, the electrolytic solution easily permeates, and as a result, the nitride layer that peels off from the substrate surface is removed in advance, and the dense and corrosion-resistant nitrogen-containing layer becomes the surface layer of the substrate. The peeling of the catalyst layer from the base material can be prevented.

As a method of removing the outermost surface layer, chemical means and mechanical means can be applied. As the chemical means, for example, there is a method of immersing the base material in an inorganic acid such as hot sulfuric acid or electrolyzing to dissolve and remove the nitride layer,
As the mechanical means, for example, sandblasting using SiO ₂ particles or the like can be applied.

The surface of the nitrogen-containing layer thus exposed is then covered with a catalyst layer. As the metal used for forming the catalyst layer, at least a metal that forms an oxide exhibiting catalytic activity corresponding to an intended electrode reaction is appropriately selected. For example, Ru, Rh, P
Platinum group elements such as d, Os, Ir and Pt or alloys thereof can be mentioned.

For example, in the case of an electrode used for a reaction in which chlorine is generated, such as saline electrolysis, the catalyst layer is Ru.
Is preferable, and in the case of an electrode used for a reaction in which oxygen generation occurs such as plating or metal refining, Ir oxide is preferable. As the metal oxide of the catalyst layer, each of the above-mentioned metal oxides may be used alone, or may be a mixture thereof or with another metal oxide. When used in a mixture,
The mixing ratio of ruthenium oxide or iridium oxide is 50
It is preferable that the content is at least wt%.

To form the catalyst layer, for example, a solution prepared by dissolving a predetermined metal salt in a suitable solvent or a solution prepared by dissolving an organic compound of the predetermined metal in a suitable solvent is used for the nitrogen-containing layer. A method of repeatedly applying the composition to the surface and then heating it in an oxygen-containing atmosphere to thermally decompose the metal salt or organic compound and convert it into an oxide to obtain a desired thickness; PVD method for targeting objects, CVD
For example, a method of directly forming a catalyst layer on the surface of the nitrogen-containing layer by a method is applied.

[0019]

Examples of the invention

Example 1 A type II Ti plate having a length of 200 mm, a width of 20 mm and a thickness of 2 mm was degreased and washed with acetone and then dried. Then, this Ti plate was immersed in an oxalic acid solution having a concentration of 10% by weight (solution temperature 90 ° C.) for 5 hours for roughening treatment, washed with water and dried.

This Ti plate was set in an ion nitriding apparatus as a cathode, the inside of the apparatus was evacuated to 1 × 10 ^-3 Torr, and high-purity N ₂ gas was introduced so as to have a gas pressure of 3 Torr. A DC voltage was applied to cause glow discharge, and the Ti plate was held at a temperature of 800 to 850 ° C. for 1.5 hours for ion nitriding treatment. The surface of the Ti plate became golden indicating the presence of a nitride layer consisting primarily of titanium nitride.

Next, this Ti plate was immersed in 2 liters of a sulfuric acid solution having a liquid temperature of 100 ° C. and a concentration of 1 mol / liter for 5 hours. As a result, the outermost titanium nitride layer was removed and the nitrogen-containing layer was exposed. The surface of the Ti plate changed from gold to silver gray. A solution for the catalyst layer was prepared by dissolving 12.2 g of iridium chloride and 8.7 g of tantalum penta-n-butoxide in 100 ml of n-butanol.

This solution was brushed on the surface of the Ti plate and then dried at a temperature of 120 ° C. for 3 minutes.
The electrode of the present invention was obtained by repeating the operation of brushing, drying and heating the solution 4 times by heating in an atmosphere of 50 ° C. for 10 minutes. The final heating time was 1 hour. The obtained electrode was used as Example electrode 1. For comparison, an electrode was produced by directly forming a catalyst layer on the gold nitride layer of the Ti plate shown in FIG. 1 under the same conditions as above without dipping in hot sulfuric acid as described above, This was designated as Comparative Example Electrode 1.

These two electrodes were each immersed in a sulfuric acid solution (solution temperature 100 ° C.) having a concentration of 1 mol / liter as an anode, and a Pt plate was used as a cathode to apply a DC voltage between both electrodes to obtain 100 A / dm. Energized at a current density of ² . The terminal voltage is 3V when the anode is operating normally. However, when the anode deteriorates, the anode potential sharply rises and the terminal voltage also sharply rises to 10 V or more.

When the time from the start of energization until the terminal voltage exceeds 10 V was measured, it was 910 hours for Example electrode 1 and 560 hours for Comparative electrode 1. Example 2 A type II Ti plate having a length of 200 mm, a width of 20 mm and a thickness of 2 mm was degreased and washed with acetone and then dried. Then, this Ti plate was immersed in an oxalic acid solution having a concentration of 10% by weight (solution temperature 30 ° C.), and the Ti plate was used as an anode, and the Pt plate was used as a cathode for electrolytic etching at a current density of 10 A / dm ² for 30 minutes to roughen the surface. After liquefying, it was washed with water and dried.

This Ti plate was set in a gas nitriding apparatus.
That is, a Ti plate was set in a quartz glass tube with a rubber stopper, and N ₂ gas having a purity of 99.999% was introduced into the quartz glass tube to replace the air in the tube. Incidentally. 1 x 1 in the pipe
After reducing the pressure to 0 ^-4 Torr, N ₂ gas was introduced into the tube until the pressure became 1 × 10 ^-1 Torr again. This operation was repeated 10 times to completely remove the air in the tube and fill the tube with N ₂ gas.

Then, the surface of the Ti plate was heated to about 1100 ° C. and kept at that temperature for 1 hour for nitriding treatment. After cooling, the surface of the Ti plate taken out from the quartz glass tube had a gold color peculiar to titanium nitride. The surface of this Ti plate was sandblasted for about 30 seconds using SiO ₂ having a diameter of 10 μm. As a result, the nitrogen-containing layer was exposed, the surface became silver gray, and it was confirmed that the titanium nitride layer was almost completely removed.

A solution for a catalyst layer was prepared by dissolving 12.2 g of iridium chloride and 8.7 g of tantalum penta-n-butoxide in 100 ml of n-butanol. After this solution is brushed on the surface of the Ti plate, the temperature is 120 ° C.
The electrode of the present invention was obtained by drying over a period of 10 minutes, further heating in an atmosphere of 450 ° C. for 10 minutes, and repeating the steps of brush coating, drying and heating of the solution four times. The final heating time was 1 hour. The obtained electrode was used as Example electrode 2.

For comparison, an electrode in which a catalyst layer was directly formed on a gold-colored TiN layer under the same conditions as described above without carrying out the above sandblasting treatment was prepared, and was used as a comparative electrode 2. The time from the start of energization to the terminal voltage exceeding 10 V was measured for these two electrodes under the same conditions as in Example 1. In the case of the example electrode 2, it was 870 hours, and in the case of the comparative electrode 2, it was 450 hours.

[0029]

As is apparent from the above description, the electrode of the present invention has very excellent durability and long service life, and is useful as an electrode in the electrolytic industry. this is,
It is formed in the outermost layer when the surface of the base material is nitrided and has many micropores, which allows the electrolyte solution to permeate, resulting in
Dense nitrogen-containing material in which nitrogen is diffused into the constituent metals and alloys of the base material by removing only the nitride layer consisting mainly of titanium nitride, because adhesion to the base material becomes weak and peeling from the base material is likely to occur. Expose the layer (nitrogen diffusion layer). By forming the catalyst layer on this, as a result, it is possible to prevent the catalyst layer from falling off as a result of peeling between the nitrogen-containing layer coated with the catalyst layer and the base material.

Claims (8)

[Claims] 1. A base material having a metal simple substance or alloy and a nitrogen-containing layer mainly formed by nitrogen diffusion formed on the surface of the metal simple substance or alloy, and by coating the nitrogen-containing layer of the base material. An electrode comprising the formed catalyst layer made of an oxide of a platinum group metal. 2. The electrode according to claim 1, wherein the base material is made of at least one selected from the group consisting of Ti, Zr, and Hf or an alloy containing them as a main component. 3. The electrode according to claim 1, wherein the nitrogen-containing layer comprises a nitrogen diffusion layer for Ti or a nitrogen diffusion layer for Zr. 4. The catalyst layer comprises Ru, Rh, Pd, O.
The electrode according to claim 1, which is made of any one selected from the group consisting of s, Ir, and Pt or an oxide of a metal alloy containing them as a main component. 5. The electrode according to claim 4, wherein the oxide of the platinum group metal or the mixture thereof contains at least 50% by weight of ruthenium oxide or iridium oxide. 6. A nitriding treatment is applied to the surface of a base material composed of a simple metal or an alloy to form a nitride layer of the simple metal or an alloy on the outermost surface portion, and a nitride layer of the simple metal or an alloy is formed below the nitride layer. To form a nitrogen-containing layer mainly diffusion of nitrogen into the, then, the nitride layer of the outermost surface layer is removed to expose the nitrogen-containing layer, the surface of the nitrogen-containing layer, platinum. A method for producing an electrode, which comprises forming a catalyst layer made of an oxide of a group metal. 7. The method for manufacturing an electrode according to claim 6, wherein the nitriding treatment is performed by ion nitriding treatment or gas nitriding treatment. 8. The method for producing an electrode according to claim 6, wherein the removal of the nitride layer of the outermost layer portion is performed by crushing or electrolytic treatment using an inorganic acid aqueous solution or sandblasting.