JPS602685A - Activating method of cathode - Google Patents

Abstract

PURPOSE:To obtain an activated cathode which exhibits an excellent low hydrogen overvoltage and has good adhesion by subjecting the surface of a cathode base body to electroplating consisting essentially of Ni and contg. fine carbonaceous particles via a coating layer which is preliminarily provided on said surface and has a roughened surface. CONSTITUTION:Metallic particles of Ni, Co, etc. or nonmetallic particles of nickel oxide, ceramics, etc. are thermally sprayed on the surface of a cathode base material of iron, copper, nickel, etc. by a flame spraying method, etc. to form a roughened coating layer. The surface of said base material is then subjected to electroplating using a plating bath consisting essentially of Ni dispersed with fine carbonaceous particles and contg. other metallic components such as Co, Fe or the like via the above-mentioned roughened coating layer. The dispersed plating layer is intruded between the troughs of the ruggedness existing on the porous surface of the roughened coating layer adhered securely to the surface of the cathode base material by the above-mentioned treatment, by which the cathode for electrolysis having high adhesion and an excellent low hydrogen overvoltage characteristic is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for activating a cathode, particularly a method for activating a cathode mainly for electrolysis, which exhibits an excellent low hydrogen overvoltage in an aqueous solution.

Conventionally, electrolysis of an aqueous alkali metal salt solution using a diaphragm (including a porous furnace diaphragm such as asbestos and a dense diaphragm such as an ion exchange membrane) is known as a technique for generating hydrogen gas at a cathode, and water electrolysis etc. This also applies.

In recent years, from the viewpoint of energy saving, it has been desired to reduce the electrolysis voltage in this type of technology, and various active cathodes have been proposed as a means for reducing the electrolysis voltage.

Such active cathodes are typically made by thermally spraying or heat-spraying a layer of an active metal material that also has reduced hydrogen overvoltage characteristics onto the surface of an alkali-resistant substrate such as iron, copper, nickel, alloys containing these, or valve metals. It is obtained by coating by means such as decomposition, immersion in molten material, electroplating, chemical plating, vapor deposition, explosion bonding, etc., and in particular, forming fine irregularities on the surface of the active metal material layer to make it porous. By creating a rough active surface, in addition to the electrochemical catalytic action inherent to the active metal material layer, the active surface area is increased to further enhance the hydrogen overvoltage reduction effect.

As one of these cathodes, the present inventors previously proposed a method of electroplating using a plating bath in which carbonaceous fine particles were dispersed on the surface of the cathode substrate. (Unexamined Japanese Patent Publication No. 57-
35689, JP-A-57-89491, JP-A-57-9
4582, Japanese Unexamined Patent Publication No. 57-94583, etc.) The present invention further improves the workability during plating with regard to obtaining an active cathode, and also improves the adhesion between the obtained cathode base material and the plated object, thereby improving the effectiveness of the cathode. In order to extend the life of the cathode, the cathode is activated by electroplating the surface of the cathode base material using a plating bath containing a metal component mainly composed of nickel in which carbonaceous fine particles are dispersed. A cathode characterized in that the electroplating described above (hereinafter referred to as dispersion plating) is applied through a coating layer having a roughened surface (hereinafter referred to as a roughened coating layer) that is present on the surface of a base material. This is an activation method.

As for the cathode substrate used in the method of the present invention, the roughening coating layer present on the surface and the dispersion plating layer applied to the surface are easy to form and there is no particular problem in adhesion. Specifically, iron, copper, nickel, alloys containing these, and alkaline earth gold layer materials that are more resistant to abrasion than valve metals are preferably used;
It is also possible to use a metal material that has been plated with nickel or the like in advance.

There are no particular restrictions on its shape, but it can be expanded metal, a perforated flat plate made by pressing it, punched metal,
Perforated plates such as woven wire mesh are preferably used, and the porosity thereof is preferably in the range of 1 to 99 inches.

In the method of the present invention, a roughening coating layer is present on the surface of such a substrate, and this is done by imparting surface roughness to the surface of the cathode substrate itself by sandblasting or etching with a chemical solution. It is not a surface condition, but a roughening coating layer is separately adhered to the surface of the cathode substrate, and the next dispersion plating layer is firmly bonded to the substrate. I can do it.

In this case, there are two types of cases: one is to use a new cathode base material and add new activity to it, and the other is to re-plate a cathode whose performance has deteriorated as a result of being used as a cathode and give it activity. I can do it.

In the former case, it is necessary to form a new roughened coating layer on the surface of the new cathode substrate and apply dispersion plating to that surface. Dispersion plating is applied underneath.

There are various methods for forming such a roughened coating layer, but
A desirable method is thermal spraying of metal or non-metal particles, or a plating bath whose bath composition is approximately the same as that of the dispersion plating bath, except that specific particulate solids are dispersed in place of the carbonaceous fine particles used in the above-mentioned dispersion plating. One example is plating.

Thermal spraying in this case can be carried out by the usual flame spraying method or plasma spraying method, and the particles used are metal particles such as dichloromethane, cobalt, silver, etc., and non-metallic particles such as nickel oxide, zirconium oxide, and ceramics. Metal particles can be used.

On the other hand, the formation of a roughening coating using a bath in which particulate solids are dispersed is preferably carried out using carbides such as tungsten carbide and silicon carbide, oxides such as nickel oxide and zirconium oxide, or metal scraps such as nickel oxide and zirconium oxide. Approximately 0.
Using particles with an average particle size in the range of 01 to 100μ,
This can be achieved by electroplating using a plating bath that has substantially the same bath composition as the dispersion plating bath and contains carbonaceous fine particles in place of the above-mentioned particles.

Next, in the latter case described above, that is, when re-plating a cathode whose performance has deteriorated to give it activity, after removing all the surface plating layer and base layer to expose the base material,
In the same manner as described above, the old plating layer on the surface is scraped off with a roughening buff or the like to expose the roughening coating layer that is in close contact with the base material, and then washing with water and dispersion plating may be performed.

In the present invention, the roughened coating layer obtained by the above-mentioned various means is different from the unevenness caused by sandblasting or etching, and the coating layer is firmly bonded to the base material, and moreover, the roughened coating layer is formed in the valleys of the porous unevenness. A cavity-like gap of moderate size is formed, and the plated material of the dispersion plating that will be applied next enters into this state and is bonded, resulting in a strong adhesion. .

The average opening diameter of the recesses formed on the surface of such a roughened coating layer is preferably in the range of 10 to 5000μ,
Also, the average thickness is preferably in the range of 10 to 5000μ.

Next, dispersion plating is applied to the surface of the roughened coating layer. Electroplating is performed using a plating bath mainly composed of, and metal acids in the plating bath do not interfere.

Cobalt, iron, silver, copper, phosphorus, tungsten, magnesium, titanium, molybdenum,
Beryllium, chromium, zinc, manganese, tin, lead, bismuth, etc. can be mentioned, and even trace amounts of metal ions such as copper, aluminum, chromium, tin, One or more selected from barium, zinc, silver, platinum, iridium, rhodium, etc. may also be added.

The use of trace metals improves the adhesion of dispersion plating,
Although it further promotes the effect of reducing the hydrogen overvoltage of the cathode, there is no point in using this trace metal if it is the same type of metal as the metal used in combination, and a different type of metal should be selected and used. The amount of the trace metal added is appropriately determined depending on the type of plating bath, the concentration of carbonaceous fine particles, the type thereof, etc., but it is usually desirable to add 5000 μ/2 or less to the plating bath.

On the other hand, fine particles made of carbonaceous material include charcoal, coal, bone charcoal, graphite, activated carbon, carbon plastic, coke, etc. The particle size preferably has an average particle size of 100μ or less, and 10μ or less. Particularly preferred are those.

The plating conditions were a current density of 0.1 to 15 A/dm2, p
It is desirable to carry out in the range of H2-6.

The dispersion of the fine particles is preferably carried out by blowing gas into the liquid, pump circulation, mechanical stirring using a stirrer, or the like.

As described above, in the cathode coated with two layers, the roughened coating layer is firmly bonded to the surface of the cathode base material as a porous layer with a large surface area, and the roughened coating layer is firmly bonded to the surface of the cathode substrate as a porous layer with a large surface area. The dispersion plating layer penetrates into the coating to provide a coating with strong adhesion.

The cathode obtained in this way has strong adhesion and excellent low hydrogen overvoltage characteristics, and it can also be used as described above when operating the cathode obtained by this method and re-plating and regenerating the cathode whose activity has decreased. As described above, according to the present invention, it is possible to extremely easily re-plat the old plating layer by scraping off the old plating layer leaving behind the base and performing dispersion plating, and the obtained re-plating and plating can be used for operation with excellent performance. .

Activation by such regeneration has the advantage that no particularly complicated pretreatment is required.

The mechanical strength of the plated product can be further improved.

The present invention will be explained below with reference to Examples and Comparative Examples.

Example 1 Expanded metal made of SUS510S (12
LWx6SWx1.5Wx1.5T, unit: mm; LW is the length of the mesh in the longitudinal direction, SW is the length of the mesh in the short direction,
W represents the cutting width and T represents the thickness. (same below) 1dm”
After treatment with hydrochloric acid and quenching, an activation treatment was performed, and nickel plating was performed using the plating bath and plating conditions shown in Table 1 below.

Table 1 Next, dispersion plating using tungsten carbide as dispersed particles was carried out on the surface using the bath and conditions shown in Table 2 below to form a roughened coating layer.

Table 2 Dispersion plating using dispersed particles of activated carbon was applied to this coating layer using the bath and conditions shown in Table 3.

1 Table 3 Furthermore, the surface of the dispersion plated electrode was washed with water and nickel-sulfur plated in a bath containing thiourea as shown in Table 4.

2 Table 4 Next, this plated product was subjected to dispersion plating using the bath composition and plating conditions shown in Table 6, and further nickel-sulfur plating was performed using the bath composition and conditions shown in Table 4 (however, the plating time was 60 minutes).

The cathode thus obtained was heated in NaOH at a temperature of 80°C using a nickel plate as a counter electrode, and a current density of 300A/dm2.
．． The adhesion of the coating was tested under conditions of 50 hr of hydrogen generation. As a result, no abnormality was found in the plated material20
Potential in A/dm2 (20% KOH120~40°
C) Measured by bringing the Luggin tube into contact with the back surface of the cathode on an Ig/HgO basis) showed -1,00V.

Example 2 The same expanded metal cathode base material as in Example 1 was nickel-plated in the same manner as in Table 1 of Example 1, and approximately 25 μm of nickel particles with an average particle size of 50 to 80 μm were applied to the upper surface by plasma spraying. It was sprayed to a thickness of .

Since this sprayed product has oxides on its surface, it was immersed in 6N-H (J) at 80°C for 30 minutes to remove it.
Dispersion plating using an activated carbon dispersed nickel plating bath was performed according to Table 3 of Example 1, and then nickel-sulfur plating was performed according to Table 4.

This plated product was heated at 300 A/dm2X as in Example 1.
Although hydrogen was generated for 50 hours, no abnormality was observed, and the potential measurement result also showed -0.99V.

Example 3 Using the same expanded metal cathode base material as in Example 1,
After immersing this in a 6N-HC swamp at 60°C for 30 minutes, it was immersed for 6 minutes in a 0.5 swamp solution containing palladium chloride at a ratio of 0.21743, and after washing with water, nickel chloride 240 g/
Plating bath 1-e consisting of e3 and hydrochloric acid 10011/, e
Electroplating was carried out in a chamber at a temperature of 60° C. and a current density of 3 A/d m for 2.6 minutes. Immediately thereafter, dispersion plating with activated carbon and nickel-sulfur plating were performed under the same conditions as in Tables 6 and 4 of Example 1.

This activated cathode was used as an ion exchange membrane using Nafion9.
01 (manufactured by DuPont), was incorporated into the cathode chamber of a 1 dm'' electrolytic cell having a cathode chamber made of 5US310S, and 31% NaOH was produced by electrolysis at a temperature of 90° C. for 300 days.

The potential of the cathode after 300 days of operation was -1.03 V, and some deterioration was observed.

This cathode was removed, and dispersion plating and nickel 5 sulfur plating were performed using a wire brush in accordance with the Melo table and Table 4. The plated product obtained in this way is 300A
As a result of hydrogen generation under the conditions of /dm2 x 50 hr, no abnormality was observed and the potential was -1,00V.

Example 4 The active cathode obtained in Example 1 (the cathode plated according to Tables 1 to 4) was assembled into a 1 dm" electrolytic cell, and the electrolytic cell was heated to approximately 450 mL under the same configuration and operating conditions as described in Example B. I drove for days.

After the operating period, the potential showed -1.05V, and some deterioration was observed.

Therefore, in order to regenerate this cathode, the old plating layer was removed in the same manner as in Example 3, and after washing with water, dispersion plating and nickel-sulfur plating were performed as described in Tables 3 and 4 of Example 1.

This re-plated cathode is heated to 500 A/dm2X 50
When hydrogen generation was performed for hr, no abnormality was observed and the potential was -1,00V.

Comparative Example 1 Five cathodes whose base materials were coated with nickel 6 lume according to Table 1 in Example 1 were prepared, and the cathodes were heated at 300A.
As a result of hydrogen generation for /dm2 x 50 hours, one piece showed extensive peeling of the nickel plating, two pieces showed partial peeling, and no abnormalities were found on the remaining two pieces. As described above, due to variations in the adhesion of plating, some cases of poor adhesion occurred.

Comparative Example 2 Five identical substrates were prepared and nickel plated under the conditions of 2 A/dm 2 × 4 hr according to Table 1 in Example 1. These surfaces were then roughened by sandblasting using #150 alundum at an air pressure of 5 to 9/mG. These were then incubated at 60°C with 6N-H (1 in J).
After immersion for 0 minutes, dispersion plating and nickel-sulfur plating were performed according to Tables 3 and 4 of Example 1.

These plated items are rated at 300 A/dm2X501-
1 As a result of hydrogen generation, no extensive peeling was observed, but there were two pieces with partial peeling.

Even if sandblasting is performed to create planar irregularities on the surface, poor adhesion will still occur.

Patent applicant name Toagosei Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. When activating the cathode by electroplating the surface of the cathode substrate using a plating bath containing a metal component mainly composed of nickel in which carbonaceous fine particles are dispersed, A method for activating a cathode, characterized in that the electroplating described above is applied through a coating layer having a roughened surface.