JPH0344159B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a cathode, primarily for electrolysis, which exhibits an excellent low hydrogen overpotential in 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 electrochemical catalytic action inherent to the active metal material layer, attempts have also been made to increase the active surface area to further promote the hydrogen overvoltage reduction effect. As one of these cathodes, some of the present inventors have previously proposed a method using so-called dispersion plating, in which the surface of the cathode substrate is electroplated using a plating bath in which carbonaceous fine particles are dispersed. (Unexamined Japanese Patent Publication No. 57-
35689, JP-A-57-89491, JP-A-57-94582, JP-A-57-94583, etc.) The present inventors have developed a low hydrogen overvoltage cathode using a plating bath in which carbonaceous fine particles are dispersed, and have developed a method for using it as an active cathode. As a result of studies aimed at improving robustness and further reducing hydrogen overvoltage, the present invention was completed. That is, in the present invention, the surface of the cathode substrate is electroplated at a plating current density of 7 A/dm ² or more using a plating bath in which carbonaceous fine particles are dispersed and also contains a metal component mainly consisting of nickel as the plating metal, A low hydrogen overvoltage cathode characterized in that a plating layer that is easily separated from the surface is removed, and then the electroplating and the removal of the plating layer that is easily removed from the surface are repeated, or reinforcing plating is applied. This is the manufacturing method. One of the characteristics of the method of the present invention is to perform so-called dispersion plating on the surface of the cathode substrate at a plating current density of 7 A/dm ² or higher as described above. Corrosion-resistant materials are used that are easy to apply and do not cause any particular problems with the adhesion of plating, specifically iron, copper,
Alkali-resistant metal materials such as nickel, alloys containing these, and valve metals are preferably used, and such metal materials may be previously plated with nickel plating or the like. There are no particular restrictions on the shape, but expanded metal, a flat plate with holes pressed from it,
Perforated plate shapes such as punched metal and woven wire mesh are preferably used, and their porosity is 1 to 99.
% range is preferable. Such dispersion plating is performed on the surface of a substrate by electroplating using a plating bath containing fine particles of carbonaceous material dispersed in a range of about 1 to 50 g/l and containing a metal component mainly composed of nickel as the plating metal. It is intended to provide The above-mentioned nickel-based metal component in the plating bath is nickel alone or contains nickel in a predominant amount (50% (weight %; the same shall apply hereinafter) or more), and has no adverse effect on performance, has economic advantage,
It includes one or a combination of two or more other metals in consideration of other factors. Such combined metals include cobalt, iron, silver,
Examples include copper, phosphorus, tungsten, magnesium, titanium, molybdenum, beryllium, chromium, zinc, manga, tin, lead, and bismuth. This nickel-based metal plating bath is used as a bath containing one or more of nickel sulfamate, nickel sulfate, nickel chloride, nickel bromide, etc. as a main component, and is used to obtain suitable plating products other than those mentioned above. Boric acid, citric acid, hydrochloric acid, sulfuric acid, ammonia, ammonium chloride, potassium chloride, etc. are added to the solution as appropriate. Further, an anti-pitting agent, a flattening agent, etc. may be added to this. It is also a simple method to use a generally known nickel plating bath, such as a Watt bath or a nickel sulfate bath, as a dispersion 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 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. When performing electroplating using such a plating bath, the temperature, PH plating time, etc. should be selected to be suitable for the plating bath, but the plating current density is particularly important in the present invention. be. In other words, the current density during plating must be 7A/ ^dm2 or higher, and the plating bath described above
When plating is carried out under conditions of a constant current density of 7 A/pm ² or more, the plating layer is dense and hard and has a low hydrogen overvoltage, and the other is a layer that is relatively flexible and has a low hydrogen overvoltage that can be easily detached from the surface. A layer is formed. In this case, if this is used as it is, for example, as a cathode in an ion exchange membrane electrolytic cell, the flexible layer may detach during operation and contaminate the ion exchange membrane, or it may dissolve and cause a decrease in the activity of the cathode. There is a risk of creating Therefore, in the method of the present invention, such an easily detachable layer is removed in advance to eliminate the above-mentioned problem, and it can be removed relatively easily by light polishing or the like. In this case, the abrasiveness can be removed by jetting pressurized water at about 50 to 200 kg/cm ² , by applying soft buffing, or by scrubbing with a scrubbing brush or by hand. Generally speaking, the plating current density mentioned above
When dispersion plating is performed under conditions of 7A/dm2 or ^higher ,
A dense and hard dispersed plating layer is generally formed on the lower layer (on the cathode base material side), and a relatively flexible and easily separated dispersed plating layer is formed on the upper layer (on the cathode surface side), and the boundary between these two layers is not clear. The above-mentioned light polishing allows only the upper soft layer to be easily removed, without causing the lower dense layer to separate, and thus the low hydrogen overvoltage characteristic formed only by the lower dense dispersed plating layer is achieved. A cathode with excellent properties can be obtained. There is no particular upper limit to the plating current density in distributed plating, but from the viewpoint of the rectifier for plating and the plating efficiency, it is preferably up to 100 A/ ^dm2 , especially 15
A range of ˜50 A/dm ² is practically preferable. When this plating current density is lower than 7A/ ^dm2 , two layers, the dense layer and the flexible layer described above, are formed, but the degree of density of the dense layer is different, and in long-term use, the plating becomes difficult. Peeling occurs, and the effectiveness of hydrogen overvoltage reduction gradually declines. In the method described above, the present invention involves removing the easily separated plating layer formed on the surface of the cathode, and then repeating the dispersion plating and light polishing, or
Alternatively, one of its features is that after removing the easily separated plating layer, a reinforcing plating such as nickel plating, nickel-sulfur plating, etc. It is something that can be obtained. Furthermore, so-called laminated plating, in which the above-mentioned dispersion plating is performed again after the above-mentioned reinforcing plating is performed to remove a layer on the surface that is easily separated, and then reinforcing plating is performed can also be suitably carried out. Generally speaking, the more times you repeat dispersion plating and light polishing, the longer the life will be.
Considering the thickness of the plating layer and deterioration due to impurities in the catholyte during use, it is not practical to repeat the process too many times, and it is preferable to repeat the process 10 times or less. Also, from a practical point of view, the number of layers for laminated plating is 10.
The above-mentioned nickel-sulfur plating refers to a plating obtained by electroplating by adding thiourea, thiocyanate, thiosulfate, sulfite, thioglycolic acid, etc. to a nickel plating bath. As mentioned above, the dispersion plating bath used in the method of the present invention is one in which carbonaceous fine particles are dispersed, and the plating metal component is nickel or nickel and other combined metals as the plating metal. In order to further promote the low hydrogen overvoltage characteristics as a cathode and to further improve the fixing properties of the dispersed plating layer to the substrate, it is preferable to add a trace amount of the metal described below to this bath. That is, such trace metal components include one or more selected from copper, aluminum, chromium, tin, barium, zinc, silver, platinum, iridium, rhodium, palladium, and the like. These trace metal components are used in trace amounts of approximately 1% or less in the dispersion plating bath, and contain chlorides, sulfates,
It is added in the form of compounds such as carbonates. The desirable concentration range of such trace metal components depends on various ions, the type of plating bath, the type of carbonaceous particles,
Although it varies depending on the plating operation conditions etc., it is generally as follows depending on each metal component. Cu ⁺⁺ 0.5~250mg/l, Al ⁺⁺⁺ 50~5000mg/l
Zn ⁺⁺ 50~5000mg/l, Ag ⁺ 50~5000mg/l
Cv ⁺⁺ or Cr ⁺⁺⁺ 50-2000mg/l, Sn ⁺⁺ 50-5000
mg/l Ba ⁺⁺ 50~5000mg/l, Pt ⁺⁺ 5~3000
mg/l Rh ⁺⁺⁺ 5 to 300 mg/l, Ir ⁺⁺ , or Ir ⁺⁺⁺ or Ir ⁺⁺⁺⁺ 10 to 3000 mg/l, Pd ⁺⁺ 1 to 300 mg/l, above, trace metal dispersion plating bath Addition to the inside is
A small amount of it is effective in improving the low hydrogen overvoltage characteristics of the cathode and improving the plating fixing properties.
Among these trace metals, there are metals of the same type that partially overlap with the metal components used in combination with nickel in the nickel-based metal component listed above, that is, the metals used in combination. If the amount of trace metals added during plating increases significantly beyond the above range, they tend to lose their effectiveness as trace metals, so when using combination metals and trace metals, it is important to It is desirable to select metals and keep trace metals within the above addition range. However, when using similar metals to achieve the effectiveness of trace metals, the total amount of the same metals should exceed the above addition range of trace metals. It is desirable to use it to the extent that it does not exceed. The present invention will be explained below with reference to Examples and Comparative Examples. Example 1 Three 3mmφ round rods made of Ni were prepared using 6N-HCl.
Etching was performed at 80°C for 30 minutes. Two of the tubes were sealed with a shrink tube, leaving a 20 m/m section at the tip, and plated for 10 minutes at a current density of 20 A/dm ² under the bath composition and plating conditions shown in Table 1. Next, the plated surface was rubbed vigorously by hand, and then washed with water. One of these pieces was plated in the same bath for an additional 10 minutes, then rubbed by hand in the same manner and washed with water. 20% KOH, 60℃, 20A/
dm ² , hydrogen generation potential was measured on a Hg/HgO basis. As a result, the potential of the one-time plating is -
1.15V, twice plated showed -1.13V.
On the other hand, a Ni round bar only etched with hydrochloric acid showed -1.35V under the same conditions.

[Table] Example 2 Three 3mmφ round rods made of Ni were treated using 6N-HCl.
Etching was performed at 80°C for 30 minutes. Two of the tubes were sealed with a shrink tube, leaving a 20 m/m section at the tip, and plated for 10 minutes at a current density of 20 A/dm ² under the bath composition and plating conditions shown in Table 2. Next, the plated surface was rubbed vigorously by hand, and then washed with water. One of these pieces was plated again in the same bath for 10 minutes, and then rubbed by hand and washed with water. Add these to 20% KOH60℃20A/dm ² Hg/HgO
As a result of measuring the hydrogen generation potential using the standard, the one plated once - 0.97V, and the one plated twice -
It showed 0.97V. On the other hand, Ni etched only with hydrochloric acid
The round bar showed -1.35V under the same conditions.

[Table] Example 3 Same as Example 2, graphite powder (AT-40 manufactured by Toyo Carbon Co., Ltd.) was used instead of activated carbon in the bath composition in Table 2.
Adding 25g/l, and setting the copper sulfate concentration to 0.5g/l,
The potentials were measured for one plated at 30 A/dm ² for 7 minutes and the flexible layer removed, and another plated for 7 minutes and the flexible layer removed (i.e., plated once and plated twice). Result −1.00V and −
I got 1.01V. Example 4 Plating was carried out under the same conditions as in Example 2, except that in the bath composition shown in Table 2, instead of activated carbon, pulverized coke and sieved through a 350 mesh sieve were used at 20 g/l. The potential after plating once was -0.99V, and the potential after plating twice was -0.98V. Example 5 Two pieces plated once using the same bath composition and plating conditions as Example 2 were washed with water to remove the soft layer, and one of these pieces was plated at 3A/d using the bath shown in Table 3 below.
Nickel plating was applied for m ² ×15 minutes. The other one is 3A/dm ² ×20 using the bath shown in Table 4.
Nickel-sulfur plating was carried out under the following conditions: The former potential is -0.99V, the latter potential is -0.97V
showed that.

【table】

[Table] Comparative 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 lateral direction, W is the width of the cut, and T is the thickness. 1dm ² (100
mm x 100 mm) was etched with hydrochloric acid in 6N-HCl x 30 minutes, and after pretreatment for activation, the bath composition and plating conditions shown in Table 3 (however, the bath was 5 liters, and the plating current density was
The base plate was plated with nickel at a rate of 2 A/dm ² and the plating time was 2 hours. Next, dispersion plating was performed using the bath composition and plating conditions shown in Table 2 (the bath was 5 liters, the liquid was circulated with a pump of 1 m ³ /hr for stirring, and the plating current density was 30 A/dm ² ), and then a scrubber was used. The soft surface layer was removed and washed with water. 20% KOH, room temperature, 20A/dm ²
When the hydrogen generation potential was measured on a Hg/HgO basis, -1.01V was obtained. In addition, this was incorporated into an ion-exchange membrane method electrolytic cell with a cathode chamber made of SUS310S, and the temperature was 90℃ and 33%.
After 30 days of hydrogen generation operation with NaOH, it was taken out and the potential was measured, and it was -1.02V. Example 6 Using the same expanded metal as in Comparative Example 1, base nickel plating and dispersion plating as shown in Table 1 were applied in the same manner, followed by washing using high pressure water of 100 kg/ ^cm2 , and then bath composition and plating conditions as shown in Table 3. (However, plating is done in a bath of 5 liters, plating current density of 5 A/ ^dm , and plating time of 20 minutes. After washing with water, use a bath containing activated carbon in Table 1 again at 30 A/dm.
After plating for dm ² ×10 minutes and washing with high-pressure water, nickel-sulfuric acid plating was performed as shown in Table 4 to obtain a laminated plated product reinforced with nickel-sulfur plating. The potential of this material was -1.01V. This was installed as a cathode in an ion-exchange membrane method electrolytic cell with a cathode chamber made of Ni.
After one day of hydrogen generation operation, I took it out and measured the potential, which was -1.01V. Comparative Example 2 In Comparative Example 1, the plating current density was set as the dispersion plating condition after applying nickel plating to the base.
Plating was carried out under the same conditions as in Example 7 except that the plating time was 5 A/dm ² and the plating time was 20 minutes. The plated product obtained by this plating was washed only with water because strong polishing would cause the plating to peel off, and then dispersion plating was applied again under the same dispersion plating conditions as above. The potential of the plated material obtained in this way is -1.01V
showed that. This was assembled into an electrolytic cell in the same manner as in Comparative Example 1, and after 30 days of hydrogen generation operation, it was taken out and the potential was measured, and it was -1.06V, indicating some deterioration.

Claims (1)

[Claims] 1 Electroplating is applied to the surface of the cathode substrate at a plating current density of 7 A/dm ² or more using a plating bath in which carbonaceous fine particles are dispersed and also contains a metal component mainly consisting of nickel as the plating metal, to remove easily detachable particles that occur on the surface. A method for producing a low hydrogen overvoltage cathode, which comprises removing the plating layer, and then repeating the electroplating and removing the easily detachable plating layer formed on the surface, or applying reinforcing plating.