JPH025825B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for activating a cathode, particularly a method for activating a cathode for electrolysis, which exhibits an excellent low hydrogen overvoltage in an aqueous solution. Conventionally, electrolysis of aqueous alkali metal salt solutions using diaphragms (including porous diaphragms such as asbestos and tight diaphragms such as ion exchange membranes) has been known as a technique for generating hydrogen gas at the cathode, and water electrolysis etc. This 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 spraying, pyrolyzing, or depositing a layer of an active metal material with reduced hydrogen overvoltage characteristics on the surface of an alkali-resistant substrate such as iron, copper, nickel, alloys containing these, or valve metal. Obtained by coating by means such as immersion in a melt, electroplating, chemical plating, vapor deposition, explosion bonding, etc., among others:
By forming fine irregularities on the surface of the active metal material layer to create a porous and rough active surface,
In addition to the inherent electrochemical catalytic action of the active metal material layer, efforts have also been made to increase the active surface area to further enhance the effect of reducing the hydrogen overvoltage. As one of these cathodes, some of the present inventors have previously proposed a method in which the surface of a cathode substrate is electroplated using a plating bath in which carbonaceous fine particles are dispersed. (JP-A-57-35689, JP-A-57-86491, JP-A-57-94582, JP-A-57-94583, etc.) The present invention further improves the workability during plating to obtain such an active cathode. At the same time, the purpose is to improve the adhesion between the obtained cathode base material and the plated material and extend the life of the cathode. When activating the cathode by electroplating using a plating bath containing This is a cathode activation method characterized by performing the above-mentioned electroplating (hereinafter referred to as dispersion plating) through a wafer. The cathode substrate used in the method of the present invention is easy to form and does not pose any particular problem in adhesion with regard to the formation of the roughening coating layer present on the surface and the dispersion plating layer applied to the surface. Specifically, alkali-resistant metal materials such as iron, copper, nickel, alloys containing these, and valve metals are preferably used, and such metal materials are preferably plated with nickel plating or the like in advance. You can also use the prepared one. Although there is no particular restriction on the shape, porous shapes such as expanded metal, perforated flat plates made of pressed metal, punched metal, and woven wire mesh are preferably used, and the void ratio thereof is in the range of 1 to 99%. is preferred. In the method of the present invention, a roughened coating layer is formed on the surface of such a substrate. Rather than creating a rough surface, a roughening coating layer is separately placed in close contact with the surface of the cathode base material, thereby firmly bonding the dispersion plating layer to be applied next to the base material. I can do it. In this case, there are two types of cases: cases where a new cathode base material is used and new activity is imparted to it, and cases where activity is imparted by replating a cathode whose performance has deteriorated as a result of its use as a cathode. . 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. Distributed plating is applied to the bottom. There are various methods for forming such a roughened coating layer, but preferred methods include thermal spraying of metal or non-metal particles, and dispersion of specific particulate solids in place of the carbonaceous fine particles used in the above-mentioned dispersion plating. One example is plating using a plating bath whose bath composition is substantially the same as that of the dispersion plating bath, except that the plating bath composition is the same as that of the dispersion plating bath. Thermal spraying in this case can be carried out by ordinary flame spraying or plasma spraying, and the particles used include metal particles such as nickel, cobalt, and silver, and nonmetallic particles such as nickel oxide, zirconium oxide, and ceramic. 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 metals such as nickel. Particles with an average particle size in the range of approximately 0.01 to 100μ are used, and these are electroplated in a plating bath that has a bath composition similar to that of the dispersion plating bath and contains carbonaceous fine particles in place of the above particles. This can be achieved by applying Next, in the latter case mentioned above, that is, when replating the cathode whose performance has deteriorated and imparting activity,
After all the surface plating layers and underlayers are removed to expose the base material, a roughening coating layer and a dispersion plating layer may be sequentially formed in the same manner as described above.
The old plating layer on the surface, which is usually formed by dispersion plating and nickel sulfur plating, is scraped away using a wire buff, etc., to leave the base of the old plating layer, and the roughened coating layer that is in close contact with the base material is exposed. After drying, wash with water and apply dispersion plating. 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 has no porous unevenness. A cavity-like gap of moderate size is formed in the valley, and the plating material of the dispersion plating that will be applied next enters into this state and is bonded, creating a strong adhesion. This results in the following. 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 5,000 microns, and the average thickness is also preferably in the range of 10 to 5,000 microns. Next, dispersion plating is applied to the surface of the roughened coating layer. Electroplating is performed using a bath, and the metal component in the plating bath is nickel in a predominant amount (50% by weight or more), but one or more other metals may be used in combination. Such combined metals include 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 metals compared to the above-mentioned nickel or nickel and other combined metals can be mentioned. ions, e.g. copper,
aluminum, chromium, tin, varilim, zinc,
One or more selected from silver, platinum, iridium, rhodium, etc. may also be added. The use of such trace metals improves the adhesion of dispersed plating and further promotes the effect of reducing the hydrogen overvoltage of the cathode. However, if this trace metal is the same type of metal as the above-mentioned combined metal, the meaning of its use may be limited. Therefore, dissimilar metals should be selected and used. The amount of such 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 preferably 5000 mg or less per plating bath. On the other hand, fine particles made of carbonaceous material include charcoal, coal, bone charcoal, graphite, activated carbon, carbon black, coke, etc., and the particle size is 100 μm.
Those having an average particle size of the following are preferable, and those having an average particle size of 10 μ or less are particularly preferable. The plating conditions are current density 0.1-15A/ ^dm2 , PH
It is desirable to carry out in the range of 2-6. The dispersion of the fine particles is carried out by blowing gas into the liquid,
It is preferable to use pump circulation, mechanical stirring using a stirrer, or the like. As described above, in the cathode formed with the two-layer coating, the roughened coating layer is firmly bonded to the surface of the cathode substrate 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 dispersed plating layer penetrates until the end of the coating, resulting in a coating with strong adhesion. The cathode obtained in this way has strong adhesion and excellent low hydrogen overvoltage characteristics, and is also easy to use when operating the cathode obtained by this method and replating and regenerating the cathode whose activity has decreased. As mentioned above, according to the present invention, by scraping off the old plating layer while leaving the underlying layer and performing dispersion plating, re-plating can be performed extremely easily, and the obtained re-plated product can be used for operation with excellent performance. . Activation by such regeneration has the advantage that no particularly complicated pretreatment is required. In addition, the mechanical strength of the cathode obtained by the method of the present invention can be further improved by further performing nickel plating or nickel-sulfur plating on the upper layer of the carbonaceous fine particle dispersed plating. The present invention will be explained below with reference to Examples and Comparative Examples. Example 1 Expanded metal made of SUS310S (12LW
×6SW×1.5W×1.5T, 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) 1d
After etching m ² pieces with hydrochloric acid, an activation treatment was performed, and nickel plating was performed using the plating bath and plating conditions shown in Table 1 below.

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

[Table] Dispersion plating using dispersed particles of activated carbon was performed on this coating layer using the bath and conditions shown in Table 3.

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

[Table] This plated product was then dispersion plated using the bath composition and plating conditions shown in Table 3, and then nickel monosulfur plating was applied using the bath composition and conditions shown in Table 4 (however, the plating time was 60 minutes). The cathode thus obtained was heated at a temperature of 80°C in 30% NaOH using a nickel plate as the other electrode, and at a current density of 300A/
The adhesion of the coating was tested by generating hydrogen under conditions of dm ² and 50 hours. As a result, no abnormality was observed in the plated material, and a potential of 20A/ ^dm2 (20% KOH, 20 to 40℃H) was applied.
g/HgO (measured with a Luggin tube in contact with the back surface of the cathode) 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 nickel particles with an average particle size of 50 to 80 μm were coated on the upper surface with a particle size of about 25 μm by plasma spraying. Sprayed in thickness. Since this sprayed product had oxides on its surface, it was immersed in 6N-HCl at 80°C for 30 minutes to remove this, and then dispersion plating was performed using an activated carbon dispersed nickel plating bath according to Table 3 of Example 1. Next, nickel-sulfur plating was applied according to Table 4. As in Example 1, this plated material was heated at 300A/dm ² ×
Hydrogen was generated for 50 hours, but 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, it was immersed in 6N-HCl at 60°C for 30 minutes, and then immersed in a solution 0.5 containing palladium chloride at a ratio of 0.2 g/min for 3 minutes. After washing with water, plating bath 1 consisting of nickel chloride 240g and hydrochloric acid 100g
inside at a temperature of 30°C and a current density of 3A/dm ² for 3 minutes.
I had it electrified. Immediately thereafter, dispersion plating with activated carbon and nickel sulfur plating were applied under the same conditions as in Tables 3 and 4 of Example 1. This activated cathode can be used as an ion exchange membrane.
Using Nafion901 (manufactured by Dupont), SUS310S
The product was installed in the cathode chamber of a 1 dm ² electrolytic cell with a cathode chamber made of aluminum, and the production of 31% NaOH was carried out by electrolysis at a temperature of 90 °C for 300 days. The potential of the cathode after 300 days of operation shows -1.03V,
Some deterioration was observed. This cathode was removed, and the old plating layer was removed using a wire brush so that the plating layer remained at a thickness of 0.05 to 0.2 mm, exposing the roughened coating layer consisting of the old layer of dispersed plating and nickel sulfur. This was washed with water, and dispersion plating and nickel sulfur plating were performed according to Tables 3 and 4 of Example 1. Hydrogen generation was performed on the plated material obtained in this way under conditions of 300 A/dm ² × 50 hr, and no abnormality was observed and the potential was -
It was 1.00V. Example 4 The active cathode obtained in Example 1 (cathode plated according to Tables 1 to 4) was assembled into a 1 dm ² electrolytic cell under the same configuration and operating conditions as described in Example 3. Driven for 450 days. After the operating period, the potential showed -1.03V, 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 applied as described in Tables 3 and 4 of Example 1. This replated cathode is used at 300A/dm ² ×50hr.
When hydrogen was generated, no abnormality was observed and the potential was -1.00V. Comparative Example 1 Five cathodes with nickel plating on the base material were prepared according to Table 1 in Example 1, and
As a result of hydrogen generation at 300A/dm ² ×50hr, extensive peeling of the nickel plating was observed 1
2 pieces with partial peeling, remaining 2 pieces
No abnormality was observed in the sample. As described above, due to variations in plating adhesion, some cases of poor adhesion occurred. Comparative Example 2 Five identical base materials were prepared and the first one in Example 1 was prepared.
Nickel plating was applied under the conditions of 2 A/dm ² ×4 hr according to the table. These surfaces were then roughened by sandblasting using #150 alundum at an air pressure of 5 kg/cm ² G. Then heat these to 60℃,
Table 3 of Example 1 after immersion in 6N-HCl for 10 minutes,
Dispersion plating and nickel-sulfur plating were applied according to Table 4. When these plated products were subjected to hydrogen generation at 300 A/dm ² ×50 H, no extensive peeling was observed, but two pieces had partial peeling. Even if the sandplast treatment is performed to create planar irregularities on the surface, poor adhesion will still occur. Comparative Example 3 The activated cathode obtained by the method shown in Example 3 was prepared using Nafion 901 (manufactured by Dupont) as an ion exchange membrane and a 1d cathode chamber made of SUS301S.
It was installed in the cathode chamber of a ^m2 electrolytic cell, 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 shows -1.03V,
Some deterioration was observed. This cathode was removed and wet blasting was performed under the following conditions. Pressure 4Kg/cm ² Blasting abrasive glass beads #80 Distance 10cm Time 5 seconds The surface after blasting is uneven, 26% of the total area
was completely peeled off and the base material was exposed. This was washed with water, and dispersion plating and nickel-sulfur plating were performed according to Tables 3 and 4 of Example 1. After plating, the plated material on the exposed part of the base material fell off when it was rinsed with water.

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, the roughness present on the surface of the cathode substrate is activated. A method for activating a cathode, characterized in that the electroplating described above is performed through a coating layer having a planarized surface.