JPH09194972A - Low-hydrogen overvoltage cathode and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode with a sufficiently low-hydrogen overvoltage and a manufacturing method thereof when used in the electrolysis of water or electrolysis of an aqueous solution of alkali metal chloride such as salt. SOLUTION: This product is a low-hydrogen overvoltage cathode coated with an alloy layer contgn. nickel and manganese on a conductive substrate. The low-hydrogen overoltage cathode is constituted of the alloy layer incorporating 50 to 95wt.% nickel, 5 to 50wt.% manganese and having a main peak between the diffraction angle 2θ=42 to 45 degrees and half value width of 0.4 to 7 degrees.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low hydrogen overvoltage cathode used for electrolysis of water or an aqueous solution of an alkali metal chloride such as sodium chloride, and a method for producing the same.

[0002]

2. Description of the Related Art The water or alkali metal chloride aqueous solution electrolysis industry is a multi-power-consuming industry, and various technologies for energy saving are being developed. The means of energy saving is to substantially reduce the electrolytic voltage consisting of the theoretical decomposition voltage, solution resistance, diaphragm resistance, anode overvoltage, cathode overvoltage, etc. Because of its morphology, it has attracted many researchers and has been developed. In the ion exchange membrane method of salt electrolysis, attention has been focused on reducing anode overvoltage, and as a result of vigorous research and development, an electrode with excellent durability and almost no anode overvoltage problem has been completed. It has been widely used industrially.

On the other hand, many proposals have been made on a low hydrogen overvoltage electrode for reducing a cathode overvoltage, that is, an active cathode. An electrode capable of reducing the voltage by 200 to 250 mV with respect to an iron cathode having a hydrogen overvoltage of 400 mV, for example, as shown in JP-A-59-25940 or JP-A-6-146046, hydrogen is absorbed on the surface of the electrode substrate. An alloy or a platinum group oxide is attached, as shown in Japanese Patent Publication No. 40-9130, a transition metal such as iron, cobalt, nickel and tungsten,
One coated with an alloy layer with molybdenum is disclosed. However, the former electrode with a hydrogen storage alloy or platinum group oxide attached has a high production cost because the material is relatively expensive, and the alloy coating according to the latter patent has a low production cost but reduces hydrogen overvoltage. Both sides have problems such as insufficient effect.

[0004] As described above, many active cathodes disclosed hitherto consist of an electrode substrate and a catalyst material layer having a specific composition exhibiting a low hydrogen overvoltage coated thereon. There are various methods. For example, a wet plating method of electrodepositing a catalyst substance from a bath in which an active substance is dispersed or a bath in which a metal salt is dissolved, as in the example of the above patent,
For example, as shown in JP-A-61-41786, a method of directly spraying a molten catalyst substance metal onto a substrate, or, as disclosed in JP-A-61-295386, a metal salt solution-based solution is used. There is a method in which the catalyst substance layer is obtained by applying it on a material, drying it, and reducing it. However, in the former wet plating method, the alloy composition that can be coated is limited due to a difference in electrodeposition potential or the like. Further, there are problems that the composition of the active substance and the metal component in the plating bath tends to change with the plating time, and that sufficient bath control is required to always stably obtain a homogeneous alloy layer. On the other hand, in the latter two methods,
Since high-temperature heat treatment is performed at the time of coating, it is difficult to alloy the elements with large differences in vapor pressure. Further, since crystallization is promoted by heat treatment at a high temperature, there is a problem that it is difficult to obtain an amorphous or microcrystalline structure having excellent performance.
Among these, as a method for avoiding crystallization, for example, Japanese Patent Laid-Open No. 7-
Although the sputtering method and the like described in No. 268676 have been tried, they still have problems such as a low film forming rate.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cathode having a sufficiently low hydrogen overvoltage when used for electrolysis of water or an aqueous solution of an alkali metal chloride such as salt, and a method for producing the same. It is in.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, an arc discharge type in which target constituent atoms are vaporized and ionized by arc discharge and a base material is coated with a catalytic substance. It has been found that the cathode prepared by the ion plating method has excellent low hydrogen overvoltage. In addition, the wet plating method controls the bath composition in a specific region without adding an additive to the conventional plating bath and complicating the system, thereby providing a composition and structure excellent in low hydrogen overvoltage performance at low cost. It was also found that an electrode coated with the above film can be produced.

That is, according to the present invention, an electrode in which an alloy layer of nickel and manganese is coated on the surface of a conductive substrate by an arc discharge type ion plating method or a wet plating method in which the bath composition is controlled in a specific region And the content of nickel in the alloy layer is 50 to 95% by weight, the content of manganese is 5 to 50% by weight, and in the X-ray diffraction by CuKα ray, the diffraction angle is between 2θ = 42 to 45 degrees. A low hydrogen overvoltage cathode comprising an alloy layer having a main peak and a half width of 0.4 to 7 degrees, and a method for producing the same.

[0008] The conductive substrate covering the alloy layer is, for example,
Nickel, iron, copper, titanium and stainless steel alloys can be used as long as they have excellent corrosion resistance to caustic alkali. The shape of the conductive substrate is not particularly limited, and is generally a shape adapted to the cathode of the electrolytic cell, such as a flat plate, a curved plate, an expanded metal, a punched metal, a mesh, a perforated plate, and the like. Is used.

Prior to coating the surface of such a conductive substrate with the alloy layer, it is preferable to perform general pretreatments such as degreasing, vacuum heating, and ion bombardment in advance. Also,
Appropriate nickel alloy plating on conductive base material, or adhesion of conductive fine particles such as carbon or platinum group metal, etc., increase the degree of unevenness of the base material surface and strengthen the adhesion between base material and alloy layer. Is also effective. If the alloy layer is too thin, it will be affected by the base material, and if it is too thick, it will easily peel off.

The method for obtaining the alloy layer having the composition and structure of the present invention will be specifically described below in the order of arc discharge type ion plating method (AIP method) and then wet plating method.

First, the AIP method will be described. The target used for the AIP method is generally manufactured by the same method as the target used for the ion plating method.
That is, the target constituent elements are physically mixed by a ball mill or the like and then pressure-molded by CIP (cold isostatic pressing), HIP (hot isostatic pressing) or the like, but the method is not particularly limited. The target constituent elements are uniformly mixed and used as a dense material. Further, at the time of manufacturing the target, it is not always necessary to alloy.

In the AIP method, the composition of the film alloy is basically the same as the composition of the target. Therefore, by controlling the composition of the target, a film of any composition can be easily obtained. The film thickness can be easily controlled by the film formation time. In the case of nickel-manganese alloy, the film formation speed is several μ
Although it is about m / 10 minutes, it is possible to increase the film forming speed by simultaneously using a plurality of targets, and it is easy to increase the film thickness, which is difficult by other ion plating methods or sputtering methods.

In order to obtain the alloy layer having the composition and structure of the present invention by the AIP method, the target composition and film forming conditions may be controlled. That is, 50 to 95% by weight of nickel,
Using a target containing 5 to 50% by weight of manganese, a potential of -100 to 50 V is applied to the base material to form a film. Further, a film containing at least one of hydrogen, carbon, nitrogen, and oxygen is introduced as a reaction gas to perform film formation. The hydrogen-containing gas is a gas containing a hydrogen atom in a gas component, such as H ₂ and H ₂ O, for example. Examples of the carbon-containing gas include CH ₄ , C ₂ H _{6 and the} like, examples of the nitrogen-containing gas include N ₂ and NH ₃ , and examples of the oxygen-containing gas include O ₂ and CO. Is not limited to the gas exemplified here. By performing arc discharge type ion plating under the above conditions, the nickel content in the alloy layer is 50 to 95% by weight, the manganese content is 5 to 50% by weight, and the X-ray diffraction by CuKα ray A low hydrogen overvoltage cathode comprising an alloy layer having a main peak at a bending angle 2θ of 42 to 45 degrees and a half-value width of 0.4 to 7 degrees can be obtained.

The electric potential of the base material is more preferably -60 to 30V. In the ion plating method, target constituent atoms are ionized to cover the base material. However, if the potential of the base material deviates from the claimed range, the kinetic energy of the coated ions becomes excessive, and the collision with the base material causes The temperature of the base material rises remarkably, and it is not possible to obtain the film having the crystal structure described in the claims. In addition, when the absolute value of the potential of the base material increases, the difference between the coating composition and the target composition increases, and an alloy layer having a desired composition cannot be obtained.

Next, the wet plating method will be described. In the wet plating method, the type of counter electrode used for plating is not particularly limited, but a soluble electrode such as a nickel plate or an insoluble electrode such as a platinum plate or a platinum-coated titanium plate can be used.

In order to produce the alloy layer having the composition and structure of the present invention, the composition of the plating bath used in the wet plating must be controlled in a specific concentration range. That is, a plating bath containing nickel ions, manganese ions and a complexing agent in a plating bath having a molar ratio of nickel ions to manganese ions of Mn / (Ni + Mn) = 10 to 70 mol% is used. Is to use. The nickel source and the manganese source are not particularly limited, but the former may be generally used nickel sulfate such as nickel sulfate and nickel chloride, or may be used by mixing them, and the latter may be manganese sulfate such as manganese sulfate and manganese chloride. After all, it may be used alone or as a mixture. The complexing agent added to the plating bath is not particularly limited except for the sulfur-containing complexing agent,
For example, citrate, tartrate, pyrophosphate, etc. are used. According to our study, for example, when plating is performed in a plating bath containing a sulfur-containing complexing agent such as thiourea, sulfur is incorporated into the alloy layer, and the manganese content is less than 1% and almost all manganese is contained. There is no alloy layer. The nickel-sulfur-manganese alloy layer also exhibits excellent low hydrogen overvoltage performance, but it also exhibits a phenomenon in which sulfur is eluted during electrolysis in an alkaline solution and the hydrogen overvoltage is significantly increased. Although the amount of the complexing agent used is not particularly limited, it is generally about 0.5 to 2 times the molar amount of the total concentration of nickel ions and manganese ions in the plating bath.

Although the pH of the plating bath varies depending on the complexing agent used, it is usually necessary to select a region in which the complexing with metal ions is sufficient and the complexing agent can exist stably.
For example, in the case of using potassium pyrophosphate as the complexing agent, the plating bath may be selected from pH 8 to 10 at which nickel and pyrophosphate ions form a stable complex and no decomposition occurs. There are no particular restrictions on the chemicals used to adjust the pH, but inorganic acids such as sulfuric acid and hydrochloric acid, sodium hydroxide and aqueous ammonia may be used.

The composition and structure of the alloy layer in the present invention are also influenced by the temperature of the plating bath and the plating current density, and these are described in, for example, JP-B-40-9130 and JP-A-55-65376. It can be maintained by selecting a general range of conditions as shown in. That is, the temperature of the plating bath may be selected in the range of 20 ° C. to 70 ° C. At lower temperatures, the plating efficiency is low, so that it is difficult to be economical. At higher temperatures, the coating of the alloy layer becomes brittle. Problem arises. Further, the plating current density may be selected in the range of ^{2 to} 20 A / dm ² , and at the plating current density lower than this, the manganese content of the alloy layer becomes lower than the range of the present invention, and thus the cathode overvoltage is high. Only electrodes can be obtained, and at higher current densities, the plating efficiency is low and the economy is poor.

In the wet plating method, the performance of the alloy layer is not affected by the third component added for the purpose of increasing the surface area or other impurities existing in the plating bath and taken into the alloy layer. Be maintained by adhering to.

The coating composition is more preferably 60 to 95% by weight of nickel and 5 to 40% by weight of manganese, further preferably 65 to 92% by weight of nickel and 8 to 3 of manganese.
5% by weight. If the content of nickel or manganese deviates from the scope of the claims, the region of nickel or manganese metal alone occupies most of the film, and an alloy layer of nickel and manganese cannot be obtained, resulting in a marked increase in overvoltage. Also,
Even if the nickel and manganese contents are within the above ranges, if the peak position or the half width is outside the scope of the claims, the crystal structure is different from the crystal structure exhibiting a low hydrogen overvoltage, and the overvoltage is high.

[0021]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

Examples 1 to 5 Arc discharge type ion plating was carried out using a target prepared with a composition of 80 wt% Ni-20 wt% Mn to obtain samples of Examples 1 to 5. The base material is a nickel plate (40 x 50 mm ² ) whose surface has been cleaned by degreasing, etc.
Was used. Arc discharge type ion plating
It was performed using Showa Vacuum SIA-400T. 1 × 10
^-3 Torr vacuum, arc current 100A, film formation for 50 minutes, Ni-Mn alloy layer on the substrate about 20 ~ 30μ
An m-thick coated electrode was prepared. Table 1 shows the film forming conditions of each film, and Table 2 shows the properties of the obtained films.

[0023]

[Table 1]

[0024]

[Table 2]

The alloy composition of the film is analyzed by an X-ray microanalyzer, and the converted value is expressed as Ni concentration + Mn concentration = 100. The position of the main peak and the half width were CuKα
It was determined from the X-ray diffraction pattern by X-ray. The hydrogen overvoltage was 40 A / d in 90 ° C., 32.5% caustic soda solution.
It was measured by the current interrupter method at a current density of m ² . The X-ray diffraction pattern of the film obtained in Example 1 is shown in FIG.

Comparative Examples 1 and 2 Film formation was carried out under the same conditions as in Example 1 except that the potential of the base material was set to -300V. Tables 1 and 2 show the conditions of film formation and the performance of the obtained film, respectively. Since the full width at half maximum of the obtained coating is outside the scope of claims, the overvoltage is 30
It shows a high value around 0 mV.

Examples 6 to 8 Targets having three types of compositions, with the balance of Mn being 5 to 50 wt% and the balance being Ni, were used, under a vacuum of 1 × 10 ⁻³ Torr and an arc current of 100 A for 50 minutes. Film formation was performed under the conditions shown in Table 3. The performance of the obtained coating is shown in Table 4.

[0028]

[Table 3]

[0029]

[Table 4]

Comparative Examples 3 to 4 Comparative Examples 3 and 4 each have a composition ratio of 98 wt%.
Ni-2wt% Mn and 40wt% Ni-60wt%
Film formation was performed under the same conditions as in Example 6, using a Mn target. The film forming conditions and the characteristics of the obtained film are shown in Table 3 and Table 4, respectively. In Comparative Example 3, the Ni and Mn contents were high, and in Comparative Example 4, the Ni and Mn contents and the peak positions were outside the scope of the claims, so the overvoltage was high. FIG. 2 shows the X-ray diffraction pattern of the film obtained in Comparative Example 4.

Examples 9 to 13 Nickel sulfate (hexahydrate) 0.228 mol / liter,
Trisodium citrate (dihydrate) 0.344 mol / l
Dissolve the bottle and add manganese sulfate (pentahydrate) to the plating bath
Mn / (Ni + Mn) molar ratio of 12, 30, 50,
Dissolve so as to be 60, 68 mol% and each plating bath
Was prepared. Alcohol degreasing, nitric acid as electrode base material
Etched nickel disc plate (electrode area 7
8.5 mm ^Two) Is used, and a nickel plate is used as the counter electrode material.
Was.

While controlling each plating bath at 40 ° C., plating was performed at a current density of 8 A / dm ² for 25 minutes,
An electrode was prepared by depositing a nickel-manganese alloy layer on the electrode base material. The alloy composition was analyzed by an X-ray microanalyzer, and the position of the main peak and the full width at half maximum were determined by X-ray diffraction measurement using CuKα rays.

Also, using this electrode, the
Current density 40 A / dm ^{2 in} 2.5% caustic soda solution
The hydrogen overvoltage was measured at. Table 5 shows the results.

[0034]

[Table 5]

Comparative Examples 5 to 6 The amount of manganese sulfate (pentahydrate) added was Mn / (Ni + M).
n) Plating was performed in the same manner as in Example 9 except that the molar ratio was 8 mol% and 80 mol%. Table 5 shows the results. In Comparative Example 5, the Ni and Mn contents and the full width at half maximum are
However, since the Ni and Mn contents were out of the claimed range, the overvoltage became high.

[0036]

The active cathode obtained by the production method of the present invention is treated at 90 ° C. in a 32.5% caustic soda solution at 40 A.
/ Dm ² , the hydrogen overvoltage is 120
As low as ~ 160 mV, it was revealed that the cathode obtained by the present invention has very excellent cathode performance. The cathode performance is an electrode in which an alloy layer made of at least nickel and manganese is coated on the surface of a conductive base material, the manganese content of the alloy layer is in the range of 5 to 50% by weight, and the CuKα of the alloy layer is X-ray diffraction measurement by X-ray has a main peak between diffraction angles 2θ = 42 to 45 degrees, and is obtained by controlling so that only a diffraction peak having a half width of 0.4 to 7 degrees is shown. Is.

When this cathode is applied to the alkali metal chloride aqueous solution electrolysis, it becomes possible to save power consumption, which greatly contributes to energy saving in the chloralkali industry.

[Brief description of the drawings]

1 shows an X-ray diffraction pattern of the alloy layer obtained in Example 1. FIG.

FIG. 2 shows an X-ray diffraction pattern of the alloy layer obtained in Comparative Example 4.

Claims (4)

[Claims] 1. A low hydrogen overvoltage cathode comprising a conductive base material coated with an alloy layer containing nickel and manganese, wherein the nickel content is 50 to 95% by weight and the manganese content is 5 to 5.
0% by weight, and in X-ray diffraction by CuKα ray, there is a main peak between diffraction angles 2θ = 42 to 45 degrees,
A low hydrogen overvoltage cathode comprising an alloy layer having a full width at half maximum of its main peak of 0.4 to 7 degrees. 2. Nickel 50 to 95% by weight, manganese 5 to 5.
A target containing 50% by weight is used, and the electric potential of the conductive substrate is set to −100 to 50 V, and hydrogen is used as a reaction gas.
2. The method for producing a low hydrogen overvoltage cathode according to claim 1, wherein a gas containing at least one of carbon, nitrogen and oxygen is introduced, and the gas is produced by an arc discharge ion plating method. 3. A plating bath containing nickel ions, manganese ions and a complexing agent, wherein the molar ratio of nickel ions to manganese ions in the plating bath is Mn / (Ni + Mn) = 10.
The method for producing a low hydrogen overvoltage cathode according to claim 1, wherein at least nickel and manganese are co-electrodeposited by using a 70 mol% plating bath. 4. Nickel 50 to 95% by weight, manganese 5 to 5.
A target containing 50% by weight is used, and the electric potential of the conductive substrate is set to −100 to 50 V, and hydrogen is used as a reaction gas.
The low hydrogen overvoltage cathode according to claim 1, which is obtained by introducing a gas containing at least one of carbon, nitrogen and oxygen and manufacturing it by an arc discharge type ion plating method.