JPH09324289A - Active cathode its production and its regenerating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active cathode which is low in a manufacturing cost, is capable of maintaining a low hydrogen overvoltage, is simply and easily regeneratable in case of deterioration and degradation in its activity, maintains the initial high activity and is stably usable over long period of time even after the regeneration and is highly industrially practicable. SOLUTION: This active cathode is formed of a metallic base body, a first layer mainly composed of nickel of a high surface area on this material and a second layer mainly composed of rhodium of a high surface area of the cathode operation on this first layer. The metallic base body of this active cathode is preferably a nickel metal or nickel alloy. The cathode base body formed with the first layer mainly composed of the metallic nickel of the high surface area on the metallic base body is subjected to an immersion treatment in a rhodium salt-contg. soln. or is immersed into this rhodium salt-contg. soln. and is subjected to an electrolytic treatment with the cathode base body as cathode in the rhodium salt-contg. soln., by which the second layer mainly composed of the rhodium is formed on the first layer mainly composed of the nickel and the active cathode is thus produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active cathode, a method for producing the same and a method for regenerating the same, and more specifically, electrolysis of an aqueous solution of an alkali metal salt such as an alkali metal halide or an alkali metal hydroxide at a low hydrogen overvoltage for a long period of time. The present invention relates to an active cathode that can be used, a manufacturing method thereof, and a reproducing method thereof.

[0002]

2. Description of the Related Art Conventionally, when an alkali metal halide aqueous solution or an alkali metal hydroxide aqueous solution is electrolyzed by a diaphragm method, an ion exchange membrane method or the like, a material mainly containing soft iron is generally used as a cathode. Met. However, in these electrolysis, hydrogen is generated at the cathode, and the soft iron used as the cathode has a drawback that the hydrogen overvoltage is high. Therefore, various active cathodes have been proposed which exhibit a hydrogen overvoltage lower than that of conventional cathodes mainly composed of soft iron.
For example, Raney nickel alone or a Raney nickel-based active cathode in which Raney nickel and hydrogen storage alloy are composite-plated (Japanese Patent Publication No. 61-12032 and Japanese Patent Publication No. 61-365).
No. 90), a nickel alloy type active cathode electroplated with a nickel alloy (Japanese Patent Publication No. 63-4920, Japanese Patent Laid-Open No. 6-9920)
2-253791, JP-A-62-284094) and the like. These proposed active cathodes are formed on a metal substrate such as soft iron mainly as a coating of a simple substance of nickel, cobalt, a platinum group element, a mixture thereof, or an oxide thereof. As a method, an electroplating method, an electroless plating method, a dispersion electroplating method, a thermal spraying method, a dipping method and the like have been proposed.

[0003]

However, the conventional low hydrogen overvoltage active cathodes proposed above have problems, and are not yet sufficient active cathodes from the viewpoint of industrial implementation. For example, although the Raney nickel-based active cathode has a feature of maintaining a low hydrogen overvoltage, it has the drawbacks that it is easily oxidized and deteriorated when it comes into contact with air, and that it cannot be easily regenerated and the regeneration cost increases. Further, the nickel alloy-based active cathode has a drawback that the hydrogen overvoltage is higher than that of the Raney nickel-based active cathode and, moreover, increases over time. On the other hand, according to Japanese Patent Publication No. 5-27712, when the activity of an active cathode obtained by plating a conventional soft iron substrate with nickel and aluminum is deteriorated, a soluble platinum group compound is added to the cathode chamber for electrolytic treatment. Methods have been proposed to restore activity. However, according to this method, a large amount of expensive platinum group metal is required to restore the surface activity, and the cost is high. Further, although the initial activity is sufficiently restored, the activity is immediately lowered and the regeneration treatment is complicated. However, the platinum group metal film may be peeled off during use while the regeneration treatment is repeated, which is a problem in industrial practicality.

In view of the above-mentioned conventional active cathode and the current state of its regeneration, the present invention has no fear of deterioration due to oxidation reaction,
Moreover, it can hold a sufficiently low hydrogen overvoltage, and can be easily regenerated when the activity of the active cathode is lowered, and the regenerated active cathode recovers the active cathode performance almost equal to the manufactured new active cathode. It is an object of the present invention to provide an active cathode, which can be stably used for a long period of time, and which is rich in industrial practicality, a method for producing the same, and a method for reproducing the same. The inventors have re-examined the structure of a conventional active cathode for the above purpose, hold a high surface area to reduce the hydrogen overvoltage, and regenerate the active cathode with reduced activity to easily form a high active layer. It was confirmed that satisfying the two requirements that the regenerated active surface is stable is a requirement for an excellent active cathode,
The inventors have made earnest studies to obtain an active cathode having such requirements. As a result, by using a metal substrate, particularly a nickel or nickel alloy substrate, and forming a two-layer cathode working surface of a nickel layer and a rhodium layer on the metal substrate, it is possible to simply coat nickel on a conventionally proposed soft iron substrate. The present invention has been found to be capable of preventing deterioration due to oxidation and maintaining high activity as compared with those coated with a metal-based coating, and further capable of effectively regenerating an active cathode having a reduced activity by predetermined treatment. .

[0005]

According to the present invention, a metal substrate, a high surface area nickel-based first layer on the metal substrate, and a cathode operating high surface area rhodium-based second layer on the first layer.
An active cathode is provided which is formed of a layer. In the active cathode of the present invention, the metal substrate is preferably nickel metal or nickel alloy. Further, it is preferable that the first layer composed mainly of nickel is Raney nickel, and that the second layer contains 0.1 to 5 g of rhodium per 1 m ² of the projected area of the cathode.
Further, the cathode working area is preferably 30 to 3000 times the projected area of the cathode of 1 m ² . In the present invention, the cathode working area means a surface area of a portion which can be substantially operated as a cathode, unlike an apparent area (projected area) of the cathode.

According to the present invention, a cathode substrate comprising a metal substrate and a first layer mainly composed of metal nickel having a high surface area is dipped in a rhodium salt-containing solution or dipped in a rhodium salt-containing solution. There is provided a method of manufacturing an active cathode, which comprises performing a negative polarization treatment to form a second layer mainly composed of rhodium on the first layer. In the method for producing an active cathode of the present invention, it is preferable that the metal substrate is nickel metal or nickel alloy.

Further, in the present invention, in the electrolytic treatment of an alkali metal halide aqueous solution or an alkali metal hydroxide aqueous solution using each of the above-mentioned active cathodes, a rhodium salt is added to the electrolytic cathode chamber when the activity of the active cathode is lowered. Provided is a method of regenerating an active cathode, which comprises continuing the electrolytic treatment to recover the activity of the active cathode. In the method for regenerating an active cathode of the present invention, the addition amount of the rhodium salt is preferably 1 × 10 ^{−3 to} 5 × 10 ⁻² mol per 1 m ^{2 of} projected cathode area.

The present invention is constructed as described above, and has a large surface area formed on a metal substrate, preferably a nickel-based metal substrate of nickel or nickel alloy, which is mainly composed of Raney nickel having a high nickel activity. Layers and
Since a second layer mainly composed of rhodium is further formed thereon by coating, the rhodium surface of the second layer, which is the substantial working surface of the cathode, has a high surface area similar to Raney nickel and becomes highly active. Furthermore, the rhodium metal of the second layer is formed by immersion deposition or electroplating, and thus is composed of fine particles and has a higher surface area. Unlike Raney nickel, the rhodium metal used as the cathode operating surface is unlikely to be oxidized and its activity is less likely to decrease, and it is possible to maintain high activity with low hydrogen overvoltage for a long period of time. The Raney nickel of the first layer has irregularities such as fine pores on the surface thereof, and the rhodium of the second layer is firmly adhered and formed due to the fine irregularities, and can be used stably for a long period of time.

Further, in the active cathode of the present invention, the first layer composed mainly of nickel, which is formed of metallic nickel such as Raney nickel or a nickel compound such as nickel oxide, is formed on a nickel-based metallic substrate and is extremely stable. Since the second layer composed mainly of rhodium coated with fine particles of rhodium metal is formed on the surface of the first layer having a high surface area, the surface area contributing to the cathode operation is increased and the surface activity can be improved. . Furthermore, when the activity decreases due to long-term use, the surface of the rhodium having the same activity as the new active cathode is formed by immersing in a rhodium-containing solution and performing electrolytic plating as in the case of forming the second layer. It can be regenerated, and high activity can be stably maintained after the regeneration. Although the reason for the remarkable recovery of the high activity after the regeneration and the significant improvement of the maintenance of the high activity is not clear, compared with the conventional active cathode based on soft iron, the base is made of nickel metal or nickel-based metal of nickel alloy. Since the first layer is formed of nickel or a nickel compound immediately above it and rhodium metal is selected as the second layer for covering the surface of the first layer, the bondability of each layer is excellent and stable. High activity is obtained. Further, the regeneration of the second layer mainly composed of rhodium due to the lowered activity is easy, and the recovery of the activity and its stability are remarkably excellent.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The material of the metal substrate of the active cathode of the present invention is not particularly limited, but a nickel-based substrate at least the surface of which is formed of nickel-based metal such as nickel metal or nickel alloy is preferable. Therefore, the substrate itself may be formed of nickel metal or nickel alloy, or a nickel metal or nickel alloy coating may be formed on the surface of a conventional metal substrate such as stainless steel, nickel, or cobalt used in conventional active cathodes. What was formed can be used. For example, an active cathode formed by coating a conventional soft iron substrate with a nickel-based metal such as Raney nickel for use in electrolytic treatment and having reduced activity can also be used as the metal substrate of the active cathode of the present invention. The structure of the nickel-based substrate may be flat plate, expanded metal, perforated plate, net, rod or the like, and is not particularly limited.

The first layer of the present invention is a layer mainly composed of nickel formed on the above nickel-based substrate, and a layer formed in the same manner as the conventionally proposed active cathode can be used. The first layer mainly composed of nickel is formed of nickel metal, nickel alloy such as nickel-tin and nickel-chromium, nickel compound such as nickel oxide and the like.
In particular, Raney nickel or a Raney nickel system formed from Raney nickel and a hydrogen storage alloy is preferable. It is well known that these have a vast and high surface area conventionally. When a conventional nickel-based active cathode having a reduced activity is used as the metal substrate, it is preferable to newly form the first layer mainly containing nickel on the nickel-based surface. The nickel-based first layer can be formed by a usual electroplating method, electroless plating method, dispersion electroplating method, thermal spraying method or dipping method, and may be appropriately selected according to the type of the main nickel. The thickness of the first layer is 1
The thickness may be 0 to 500 μm, and can be appropriately selected according to usage conditions and the like. Usually, it is 50 to 300 μm.

The second layer of the active cathode of the present invention is formed by coating the surface of the first layer with rhodium. The amount of rhodium forming the second layer of the active cathode of the present invention is determined by the type of the first layer,
It can be appropriately selected depending on a target value of hydrogen overvoltage, a rhodium deposition method, and the like. Usually, it is 0.1 to 5 g, preferably 0.2 to ² g per 1 m ² of the projected area of the cathode. If the amount of rhodium is less than 0.1 g, the effect of lowering the overvoltage cannot be sufficiently exerted. If it is more than 5g,
It is not preferable because hydrogen overvoltage reduction corresponding to the amount of rhodium used cannot be obtained. In the present invention, the amount of rhodium is
Depending on the surface morphology of the first layer, it can be appropriately selected so as to cover at least 1% or more, preferably the entire region, of the nickel-based high surface area first layer.

The rhodium-based second layer of the present invention has a thickness of
About 0.001-0.5 μm, preferably 0.005-
0.1 μm. The amount of rhodium used in the present invention is extremely small as described above, and platinum or ruthenium has been often used as the platinum group metal and has been used in an amount of about 10%.
Equivalent activity can be obtained with a usage amount of 1 / min. This was first discovered by the present inventors. It is presumed that rhodium has a very high reaction activity for hydrogen generation. Further, for those skilled in the art, rhodium has a high unit price, and although it has not been planned to be used at all even though it has been conventionally exemplified as a platinum group metal, the present invention makes it possible to use it in a practically small amount for the first time. . In fact, active cathodes can be manufactured cheaper than platinum and ruthenium.

The second layer of the active cathode of the present invention is formed on the above-mentioned nickel-based first layer and has a large surface area.
It has a high cathode operating area. In the present invention, the term "cathode working surface area" refers to a surface area which operates substantially as a cathode, and is about 30 to 3 per unit apparent surface area of the active cathode, that is, a projected area of the cathode of 1 m ² as the surface area which operates as a cathode.
It is preferable to have a surface area that is 000 times as large. The cathode working surface area of the second layer of the present invention depends largely on the morphology of the first layer. In the active cathode of the present invention, as described above, the surface of the nickel-based substrate is covered with the first layer containing nickel as a main component, and the surface of the first layer is composed of the second layer containing rhodium which is more chemically durable and less likely to be oxidized than nickel. Therefore, even if an electrolytic cell is formed, the ion exchange membrane is not contaminated, and the decrease in activity is suppressed.

In the method of manufacturing an active cathode according to the present invention, as described above, the formation of the rhodium-based second layer on the nickel-based first layer formed on the nickel-based substrate is performed in the first A method of immersing the cathode substrate on which the layer is formed in a rhodium salt-containing solution or immersing the cathode substrate in a negative polarization treatment is adopted. That is, by dipping and holding the cathode substrate having the first layer formed in a soluble rhodium salt-containing aqueous solution, or after the dipping, a negative polarization treatment is performed, that is, electrolysis is performed by electrolysis using the cathode substrate having the first layer forming as a cathode. As a result, rhodium ions are reduced and a rhodium film is formed on the first layer. The negative polarization treatment is effective when a large amount of rhodium is deposited. Further, the electrolysis treatment of the alkali metal salt using the active cathode of the present invention, when the active cathode is deteriorated during the treatment, by adding a soluble rhodium salt-containing solution to the cathode chamber of the electrolysis treatment, The activity can be recovered and regenerated for use. The metal rhodium of the second layer which covers the surface of the first layer by dipping precipitation or electroplating of negative polarization is generally 0.001 to 0.01 μm.
Since the fine particles are m, it is possible to increase the surface area of the first layer to obtain a higher surface area.

The rhodium salt used in the present invention is not particularly limited, and rhodium trichloride trihydrate, rhodium tribromide dihydrate, rhodium sulfate tetrahydrate, rhodium sulfite hexahydrate, rhodium nitrate. Dihydrate, rhodium formate, rhodium acetate, rhodium trifluoride nonahydrate, hexachlororhodic acid, hexachlororhodate, etc. can be used. A rhodium salt is dissolved in a suitable solvent such as water, acid or alkali to prepare a rhodium salt-containing solution. The concentration of the rhodium salt-containing solution depends on the nickel morphology of the first layer, the amount of rhodium to be deposited,
The precipitation coating method can be appropriately selected depending on whether an ionization tendency difference is used or electroplating is performed. Usually, 10 ^{-7 to} 0.1 mol / liter, preferably 10 ^-6
It is about 10 ^-2 mol / liter. Rhodium salt concentration is 10
If it is less than ^-7 mol / liter, there are problems that it takes too much time to coat the first layer with rhodium, and a large amount of solution must be used. When the concentration is more than 0.1 mol / liter, the rhodium treatment of the first layer is too fast, and it is difficult to obtain a rhodium layer having a predetermined thickness, which is not preferable. The active cathode of the present invention comprises a nickel-based substrate and a nickel-based first layer and a rhodium-based second layer, which are sequentially formed on a nickel-based substrate as described above. The first layer surface of the main body is coated with rhodium,
The cathode working surface is substituted with highly active and stable rhodium.

[0017]

EXAMPLES The present invention will now be described in more detail based on examples. However, the present invention is not limited to the following examples. Examples 1 to 4 and Comparative Example 1 (Production of First Layer on Metal Substrate: Production of Cathode Substrate) Nickel expanded metal (20 mm × 20 mm) was degreased with a caustic soda solution, washed with water, and further hydrochloric acid (1 + 1). It was etched in. After washing with water, an active cathode mainly containing Raney nickel was formed on the nickel substrate by the dispersion plating method under the conditions shown in Table 1. The dispersion-plated nickel substrate was washed with water, immersed in a 20% caustic soda solution at 70 to 80 ° C. for 2 hours to remove the aluminum content, and a Raney nickel first layer was formed on the nickel substrate. The above operation 1
0 batches were carried out to prepare a total of 10 cathode substrate samples having the first layer made of Raney nickel. When the surface roughness of each cathode substrate sample was measured by the double layer capacitance method, the average was 1350 m ² / m ² .

[0018]

[Table 1]

(Formation of Rhodium Second Layer) Five cathode substrate samples obtained as described above were washed with water and then exposed to 1 in air.
It was left for 2 hours to reduce the activity. A rhodium layer was formed by electroplating on the first layer with reduced activity. That is, using each cathode substrate sample as a cathode and a nickel plate as an anode,
Immerse in 0% caustic soda, temperature 20 ~ 25 ℃, current density 3
0 A / dm ² , treatment time of 20 minutes, rhodium layers of 0.2, 0.
Electroplated to form 5, 1 and 2 g / m ² . The amount of the rhodium layer deposited was adjusted by changing the amount of hexachlororhodic acid added to the 20% caustic soda solution.

(Measurement of Hydrogen Overvoltage) The hydrogen overvoltage of the active cathode having the Raney nickel first layer and the rhodium second layer on the nickel metal substrate produced as described above was measured by the current interrupter method. The measurement conditions are: temperature 80 ° C., NaOH 32%, current density 30 A / d
m ² and the reference electrode were Hg / HgO (32% NaOH). Further, the hydrogen overvoltage was similarly measured for one cathode substrate sample having a Raney nickel first layer on a nickel metal substrate which was not electroplated (Comparative Example 1). The results are shown in Table 2.

[0021]

[Table 2]

From the above examples and comparative examples, the active cathode of the present invention, in which the second layer of rhodium is electroplated on the surface of the conventional Raney nickel active cathode which has been oxidized and deteriorated,
It can be seen that the hydrogen overvoltage is lower than that of the deteriorated Raney nickel active cathode. Further, it can be seen that as the amount of rhodium coated on the surface increases at 0.2 to 2.0 g / m ² , it gradually decreases.

Examples 5 to 8 and Comparative Example 2 Of the five active cathode samples having the first layer of Raney nickel prepared by the same treatment as in Examples 1 to 4, four were rhodium deposited due to the difference in ionization tendency. Processed. That is, 2
About 0.002% by weight aqueous solution of rhodium mixed with 0% caustic soda and 0.1% by weight hexachlororhodic acid solution,
Each active cathode sample was dipped to deposit rhodium on the surface. The amount of precipitated rhodium was determined from the difference in rhodium concentration before and after immersion. The rhodium deposition amount was changed by changing the dipping time to obtain the same deposition amount as in Examples 1 to 4. The hydrogen overvoltage of each active cathode sample coated with rhodium in the amounts shown in Table 3 was similarly measured. In addition, the hydrogen overvoltage of the active cathode sample that was not treated with rhodium was measured in the same manner (Comparative Example 2). Table 3 shows the results.

[0024]

[Table 3]

From the above Examples and Comparative Examples, the active cathode of the present invention in which the second layer of rhodium is deposited on the surface of the conventional Raney nickel active cathode by the tendency of ionization has a lower hydrogen overvoltage than the Raney nickel active cathode before deterioration. I see. The amount of rhodium coated on the surface is 0.2
It can be seen that it gradually decreases with an increase of ~ 2.0 g / m ² .

Examples 9 to 11 and Comparative Example 3 Nickel expanded metal (100 mm × 10
0 mm) is welded to a nickel cathode chamber frame body, the outer surface of the frame body is covered with a synthetic resin tape, and Pt / Ti is used as an anode.
An electrolytic cell was formed using a plate (1 dm ² ), and a nickel expanded metal portion as a cathode was electroplated under the conditions shown in Table 4. This produced an active cathode with four nickel-tin surfaces.

[0027]

[Table 4]

Then, the four active cathodes thus obtained were put into an electrolytic cell using a cation exchange membrane (Nafion 962 manufactured by DuPont) and an insoluble anode for salt electrolysis (manufactured by Permelek) with an electrode distance of 2 mm. Assembly, temperature 85 ℃,
With a current density of 30 A / dm ² , a 32 wt% aqueous sodium hydroxide solution as the catholyte, and a concentration of fresh salt water flowing out of the anode chamber of 200 g / liter, saline was electrolyzed continuously for 45 days. Stops driving on the 46th day,
A short circuit test in which the anode and the cathode were conductively connected with a copper wire was carried out 10 times every hour. After the short circuit test, hexachlororhodic acid solution (Rh of 1.1 g /
(Containing liter) 0.6 (Example 9) and 1.5, respectively.
(Example 10), 3.0 (Example 11) ml was added. Operate the same amount of hexachlororhodic acid solution for 4 days
It was also added on days 7 and 48. Table 5 shows the relationship between the amount of rhodium deposited and the electrolysis voltage. In addition, the electrolytic voltage when rhodium was not added is also shown in Table 5 (Comparative Example 3).

[0029]

[Table 5]

It can be seen that by adding a rhodium salt-containing aqueous solution to the cathode chamber of the electrolytic cell for electrolysis, the active cathode on the surface of the nickel-tin which has deteriorated due to the increase in the electrolysis voltage is regenerated and the electrolysis voltage decreases. Further, it can be seen that the activity increases as the amount of Rh deposited on the surface increases.

Comparison 4-7 Stainless steel expanded metal (100 mm × 100
mm) is welded to a stainless steel frame and the outer surface of the frame is covered with a synthetic resin tape, followed by electrolytic etching → washing with water →
Strike plating → Washing → Dispersion plating → Washing →
An active cathode having a nickel-dispersed plating layer containing activated carbon and sulfur was produced by the operations of dispersion plating and washing with water. Using this active cathode, a cation exchange membrane (Flemion 893 made by Asahi Glass), an insoluble anode for salt electrolysis (made by Permelek)
Was used to form an electrolytic cell having three electrolytic chambers with an interelectrode distance of 2 mm. In the formed electrolytic cell, the temperature was 85 ° C., the current density was 30 A / dm ² , the aqueous solution of 32 wt% sodium hydroxide was used as the catholyte, the concentration of fresh salt water flowing out from the anode chamber was 200 g / liter, and the electrolysis of saline solution was performed to 2
It was carried out continuously for 00 days. On the 201st day of operation, hexachlororhodic acid (1.1 g / liter aqueous solution containing Rh) was added to each of the three cathode chambers of the electrolytic cell at 0.6 (Comparative Example 4), 1.5 (Comparative Example 5), and 3 respectively. 0 (Comparative Example 6) and 0 (Comparative Example 7) milliliters were added. The same amount of hexachlororhodic acid solution was also added to the operation days 202 and 203. The hexachlororhodic acid solution was added to the cathode chamber of the electrolytic cell by adding a predetermined amount of the hexachlororhodic acid solution at once to the pure water pouring line fed into the cathode chamber. Table 6 shows the relationship between the amount of rhodium deposited and the electrolysis voltage.

[0032]

[Table 6]

From the above comparative example, electrolytic treatment of sodium chloride was performed using an active cathode having a nickel-dispersed plating layer containing activated carbon and sulfur on the surface of an ordinary metal substrate which is not a nickel-based substrate, and the electrolytic voltage was increased to raise the active cathode. In the case of deterioration, by adding a rhodium salt-containing aqueous solution to the cathode chamber of the active cathode and electrolyzing, the deteriorated active cathode is regenerated and the electrolysis voltage decreases, but the voltage is lower than in Examples 9 to 11 above. It can be seen that the active cathode using a nickel-based substrate is highly excellent in activity after regeneration of the rhodium coating.

[0034]

In the active cathode of the present invention, an active cathode having a nickel-based cathode working surface formed on a nickel-based substrate is used as a cathode substrate, and further, the nickel-based surface is used as a first layer and a chemical layer is formed thereon. Is coated with a relatively stable and highly active rhodium as a second layer and is formed to have a particularly large cathode working area. Therefore, the active cathode of the present invention has a reduced hydrogen overvoltage and can stably maintain the activity. In addition, a small amount of rhodium may be used, and it can be manufactured inexpensively and easily. Furthermore, the activity of a conventionally known active cathode whose activity has decreased can be regenerated by a simple operation.

Claims (9)

[Claims] 1. A metal substrate, a high surface area nickel-based first layer on the metal substrate, and a cathode operating high surface area rhodium-based second layer on the first layer. Active cathode. 2. The active cathode according to claim 1, wherein the metal substrate is nickel metal or nickel alloy. 3. The active cathode according to claim 1, wherein the nickel-based first layer is Raney nickel. 4. The active cathode according to claim 1, 2 or 3, wherein the second layer has 0.1 to 5 g of rhodium per 1 m ² of projected area of the cathode. 5. The cathode working area is the projected area 1 of the cathode.
The active cathode according to any one of claims 1 to 4, which has a ratio of 30 to 3000 times m ² . 6. A cathode substrate comprising a metal substrate and a first layer mainly composed of a metal nickel having a high surface area formed on the metal substrate is dipped in a solution containing rhodium salt or dipped in a solution containing rhodium salt and subjected to negative polarization treatment. A rhodium-based second layer on the first layer.
A method for manufacturing an active cathode, which comprises forming a layer. 7. The active cathode according to claim 6, wherein the metal substrate is nickel metal or nickel alloy. 8. In the electrolytic treatment of an alkali metal halide aqueous solution or an alkali metal hydroxide aqueous solution using the active cathode according to claim 1, rhodium is contained in the electrolytic cathode chamber when the activity of the active cathode decreases. Add salt,
A method for regenerating an active cathode, which comprises continuing the electrolytic treatment to recover the activity of the active cathode. 9. The method for regenerating an active cathode according to claim 8, wherein the addition amount of the rhodium salt is 1 × 10 ^{−3 to} 5 × 10 ⁻² mol per 1 m ^{2 of the} projected area of the cathode.