JPH0245719B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Structure of the Invention [Field of Industrial Application] The present invention provides an active cathode with low hydrogen overvoltage characteristics that is suitably used for electrolysis of aqueous alkali chloride solutions or water electrolysis. This relates to a manufacturing method.

[Conventional technology]

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. Applies to.

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, pyrolyzing, or melting a layer of an active metal material with low hydrogen overvoltage characteristics onto the surface of an alkali-resistant substrate such as iron, copper, nickel and their alloys, or valve metal. soaking,
It is obtained by coating by electroplating, chemical plating, vapor deposition explosion deposition, etc., and in particular by forming fine irregularities on the surface of this active metal material layer to create a porous and rough active surface. In addition to the electrochemical catalytic action inherent in the active metal material layer, it has also been promoted by the effect of reducing hydrogen overvoltage by increasing the active surface area.

An active cathode using so-called dispersion plating has also been proposed, in which a plating bath in which solid fine particles are dispersed is used as the active cathode, and the solid fine particles are plated on the surface of the cathode substrate together with the plating metal component therein. (For example, JP-A No. 57-35689, JP-A No. 57-89491,
57-94582, 57-94583, etc.)

[Problem that the invention seeks to solve]

Although the performance of hydrogen generating cathodes obtained in this way has shown remarkable progress, it is still possible to manufacture such cathodes more efficiently, at lower cost, and with excellent long-lasting activity. It is also essential to do so. As a practical matter, keeping electrode manufacturing costs low and efficient is an important issue that cannot be ignored, as it is reflected in the overall cost required for, for example, aqueous alkali chloride electrolysis.

The present invention aims to improve the plating efficiency and reduce the manufacturing cost in the method for manufacturing a cathode using the above-mentioned dispersion plating.

[Means for solving problems]

The present invention aims to significantly reduce costs when producing an active cathode by electroplating using a plating bath in which solid fine particles are dispersed, and to stabilize the plating operation to easily produce an excellent low hydrogen overvoltage cathode. This is a method that can produce.

The plating bath in the present invention is a plating bath containing a plating component in which the main metal component to be plated is nickel, and solid fine particles are dispersed therein. Electroplating is applied to the surface.

As mentioned above, plating using a plating bath in which solid fine particles are dispersed is generally referred to as dispersion plating, but the method of the present invention aims to improve the efficiency of plating mainly by specifying the solid fine particles in such dispersion plating. This is what we do.

As the cathode base material used in the method of the present invention, a corrosion-resistant metal material that does not particularly impede the adhesion of plating is used. Specifically, corrosion-resistant metal materials such as iron, copper, nickel, alloys containing these, and valve metals are used. An alkaline metal material is preferably used, and it is also possible to use such a metal material that has been 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 plates such as punched metal and woven wire mesh are preferably used, and their porosity is 1 to 99.
% range is preferable.

As mentioned above, the plating bath used in the present invention deposits a metal mainly composed of nickel on the cathode substrate, but it also contains cobalt, cobalt, and other components other than nickel.
It can contain molybdenum, iron, tungsten, aluminum, etc. However, from the viewpoint of corrosion resistance, nickel is the main component, and as long as it is not very effective, a simple one is desired from the viewpoint of managing the plating bath.

The main component, nickel, is added in the form of nickel sulfate, nickel chloride, nickel sulfamate, etc. In addition, ammonium or its salt, boric acid or its salt, citric acid or its salt, pyrophosphate, alkali chloride, etc. is added to form the bath. The solid particles to be dispersed include nickel,
Metal powders such as cobalt, silver, and Raney nickel; oxides such as nickel oxide, zirconium oxide, molybdenum oxide, and rhodium oxide; carbides such as tungsten carbide and silicon carbide; sulfides such as nickel sulfide and molybdenum sulfide; and other nitrides. Examples include carbon. Some of these solid fine particles have a low hydrogen overpotential by themselves, and some have a hydrogen sensitive voltage that is lowered by dispersion plating.

In the method of the present invention, the particle size of solid fine particles is
Particles with a size of 0.01 to 100μ are preferable, and particles with a larger particle size can also be used, but on the other hand, particles with a narrow particle size distribution are not good;
Those with a wide distribution of 10 μ or more are used.

If solid fine particles with a particle size distribution width of less than 10μ are used, a plated product can be obtained, but the hydrogen overvoltage may be poor, the plating may be uneven, or too many or too small particles may be attached, so it is difficult to use in the plating bath. It is necessary that the distribution of solid fine particles is 10μ or more.

In the present invention, plating is performed using a material with such a distribution of solid fine particles, but at a certain bath amount, the plating area increases, for example, when plating a rod-shaped base material, the number of sheets to be plated increases. As the number increases, the relationship between the matsuki becomes worse. Therefore, the remaining solid particles are removed from the plating bath midway through, and new solid particles are added.
This requires labor and processing of the removed solid particles. A significant reduction in cost is expected by significantly reducing the frequency of these updates.

For this purpose, solid fine particles are added as plating progresses, but if particles with a similar particle size distribution as the bath are added, the particle size distribution of the bath will gradually differ, and many cathodes will have the same size. You will no longer be able to pamper yourself in the bath. Surprisingly, this problem was resolved by adding to the bath solid particles whose particle size distribution was biased towards finer particles than the particle size distribution of the solid particles used at the beginning of the plating bath and proceeding with electroplating. I found out that it can be done.

There is no particular limit to the degree of deviation of the particle size distribution in this case, but it is undesirable for the particle size distribution to be completely separated without overlapping. It is preferable that the solid particles are deviated by about 1/2 to 1/10.

In this case, it is preferable to add particles having a finer particle size distribution than that of the solid fine particles measured by peeling off the plating of the plated material. By employing this method, the consumption of solid fine particles is reduced by approximately 1/10 to 1/1000. It is preferable that the amount of these additions is about 1.5 to 6 times the amount of plating material deposited. This is because some substances are deposited on the surface.

[Effect]

In the method of the present invention, proper dispersion can be achieved by using solid fine particles with a particle size distribution width of 10μ or more, and by using solid fine particles whose particle size distribution deviates to a finer particle size side than the solid fine particles as plating progresses. It is not clear why Metsuki could do this.

However, the finish of dispersion plating is clearly different between when solid particles are added and when they are not. In the former case, a plating layer with a dense surface is obtained, while in the latter case, the surface is This seems to be due to the electrophoretic action of solid fine particles, since a rough and relatively easy-to-peel plated product is obtained.

〔Example〕

This will be explained below using Examples and Comparative Examples.

Example 1 SUS310S lath net (6SW×12LW×1.5T×
1.8W, unit: mm; SW is the length of the mesh in the short direction,
LW represents the length in the longitudinal direction of the mesh, T represents the thickness, and W represents the width of the cut. Plating was performed using the following process using 20 substrates (1 dm ² (100 mm x 100 mm)) whose both sides were flattened by pressing (the same applies hereinafter).

Trichlorethylene cleaning → electrolytic etching → water washing → strike plating → water washing → dispersion plating → water washing → dispersion plating → water washing The chemicals used and operating conditions for the main parts in this process are as follows.

(1) Electrolytic etching (process) [Etching solution] Sulfuric acid 300g/Surfactant 1-2g/Liquid amount 5 [Conditions] Temperature 5-20℃ Current density 3A/dm ^2Cathode used P _b plate ( ^1dm2 ) Time 6 minutes (2) Strike plating (process) [Plating liquid] Nickel chloride 100g/Hydrochloric acid 100g/Liquid amount 5 [Conditions] Temperature 5-20℃ Current density 3A/dm ² anodes Ni plate Time 3 minutes (3) Dispersion plating (process and) [Plating liquid] Nickel sulfate 84g/Nickel chloride 30 Ammonium chloride 4.5 Potassium chloride 6 Boric acid 30 Copper sulfate 0.4 Activated carbon (initial charge) 15 Liquid amount 5 [Conditions] Temperature: 30 to 60℃ Current density: 20A/dm ² hours 10 minutes Anode Ni plate (liquid is stirred by pump) [Operation] After plating one sheet of lath using the above plating bath, additional activated carbon (initial addition) Replenish 12g of the same activated carbon (pulverized in a ball mill for 48 hours),
Also, the copper sulfate in the bath was analyzed and the deficiency was replenished, and 20 lath nets were plated in this way.
In this case, the particle size distribution of the initially charged activated carbon is
As shown in the figure, the particle size distribution of the additional activated carbon was as shown in FIG.

20 obtained through the above two-time dispersion plating process.
There was no difference in the appearance of the plated products, and potential measurements (20% KOH, room temperature, Hg/ ^dm2 at 20A/dm2)
Measurements were made using HgO as a reference electrode and a Luggin tube brought into direct contact with the back surface of the lath mesh), and the potential was within the range of -1.01 to -1.04V, with no abnormal potentials.

Comparative Example 1 A plated product was obtained in the same manner as in Example 1 except for adding activated carbon.

As a result, a change in appearance was observed from the 5th layer of the lath mesh, and by the 10th layer, the surface was unevenly plated with particles of large size partially attached to the surface. The potential was -1.02 to -1.04V for the 1st and 2nd sheets, and -1.06 to -1.08V for the 9th and 10th sheets. The 1st and 10th samples were stored in 30% NaOH at 90°C and 50A/dM ² at 48
When hydrogen was generated for an hour and the potential was measured again,
The first one showed -1.01V, and the tenth one showed -1.11V, indicating a significant difference in performance.

Example 2 Same material and shape as Example 1, area 80dM ²
Plating was carried out using a lath net (700 x 1140 mm) using the following steps. The composition of the plating bath is the same as in Example 1 in the same process.

Trichlorethylene cleaning → Electrolytic etching → Water washing → Strike plating → Water washing → Dispersion plating → Water washing → Nickel sulfur plating → Water washing → Dispersion plating → Water washing → Nickel sulfur plating → Water washing → Dispersion plating → Water washing → Nickel sulfur plating → Water washing In the above process Degreasing was performed by washing with trichlorethylene, electrolytic etching was performed in a 0.3M ² plating bath, and after washing with water, strike plating was performed in a 0.3M ² plating bath.

After washing with water, perform dispersion plating at 5A/dM ² × 20 minutes, and after washing with water, perform dispersion plating at 5A/dM.
dM ² x 20 minutes.

Dispersion plating was performed three times as described above, and the final nickel sulfur plating was performed at 5A/dM ² ×40 minutes.

The activated carbon used here was the same as in Example 1, and after plating one sheet, copper sulfate was analyzed and the missing amount was added. Also, 100% fine activated carbon
Added each g.

Thirty-six lath nets were plated in this way, and no abnormalities were observed in their appearance. Next, 1 dM ² was cut out ^from the 2nd and 35th sheets and the amount of plating deposited was analyzed.
The 35th sheet is 9.7 to 10.1 g/dM ² , and the analysis result of the carbon content in this plated material is 3.8 to 4.2%, 35
The rate for the second sheet was 3.9-4.3%. The potential is -1.02 on the first sheet
~-1.04V The 35th photo was between -1.02 and -1.05V, with no change observed. In addition, the results of measuring the particle size distribution of the 2nd and 35th adhered sheets are shown in Figures 3 and 4.
Looking at this, almost no change in particle size distribution is observed.

Example 3 In the same process as in Example 1, 30 g of solid fine Raney nickel was added to the dispersion plating bath (Ni55% Al45).
%) Dispersion plating was performed without copper sulfate.

The initial particle size of Raneynickel is 6-
8μ, the smaller particle size was 1μ, and the larger particle size was 24μ. The particle size of the additional Raney nickel was 3-4μ on average, with the smaller particle size being 1μ or less and the larger particle size being 12μ. This additional Raney nickel was added at 1 dM ² and 55 g per sheet, and 5 sheets were plated. The potential of the first sheet was -1.07V, and the potential of the fifth sheet was -1.08V, and no difference was observed in appearance.

〔Effect of the invention〕

According to the present invention, an excellent and simple method of performing dispersion plating by simply using additional solid particles whose particle size distribution is shifted to a finer particle size side than the particle size distribution of the initially charged solid particles can be achieved. A high-quality active cathode can be obtained, and this makes it possible to mass-produce active cathodes while saving on solid particles.

Furthermore, this method has the advantage that active cathodes of constant quality can be manufactured at low cost, and the present invention has great utility in these respects.

[Brief explanation of the drawing]

Figures 1 and 2 are histograms showing the particle size distribution of solid fine particles used in Example 1. Figure 1 shows the case of solid fine particles for initial charging, and Figure 2 shows the case of solid fine particles for additional charging. This shows the case. Figures 3 and 4 are histograms showing the particle size distribution of solid fine particles in the plating formed on the dispersed plating active cathode obtained in Example 2, and Fig. 3 is the second one in the cathode manufacturing order. Figure 4 also shows the 35th picture.

Claims (1)

[Claims] 1 Electroplating is performed on the cathode substrate using a plating bath containing a plating component in which the main metal component to be plated is nickel and in which fine solid particles are dispersed, and the width of the particle size distribution is An active cathode characterized in that electroplating is performed using the above-mentioned solid fine particles of 10μ or more, and adding solid fine particles whose particle size distribution is biased toward a finer particle size side than the particle size distribution of the solid fine particles as plating progresses. manufacturing method.