JPS6029487A - Manufacture of cathode with low hydrogen overvoltage - Google Patents

Abstract

PURPOSE:To obtain a cathode with low hydrogen overvoltage and superior durability by electroplating the surface of a substrate with Ni contg. dispersed carbonaceous fine particles, and removing a formed flexible upper layer. CONSTITUTION:The surface of a substrate for a cathode is electroplated with Ni-base metal in a bath contg. about 1-50g/l dispersed carbonaceous fine particles. At this time, the current density is regulated to >=7 A/dm<2> to form a dense and hard under layer with low hydrogen overvoltage and an easily removable flexible upper layer with low hydrogen overvoltage. The upper layer is removed by slight polishing or other method. A cathode for electrolysis having a dense layer with low hydrogen overvoltage formed by dispersion plating is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention exhibits excellent low hydrogen overpotential in aqueous solution.
It mainly relates to a method for manufacturing cathodes for electrolysis.

Electrolysis of an aqueous alkali metal salt solution using a diaphragm (including a porous diaphragm such as asbestos and a dense diaphragm such as an ion exchange membrane) has been 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 with reduced hydrogen overpotential properties onto the surface of an alkali-resistant substrate such as iron, copper, dichloride, alloys containing these, or pulp metal. It is obtained by coating by means such as decomposition, immersion in a melt, electroplating, chemical plating, vapor deposition, explosion bonding, etc., and in particular, forms fine irregularities on the surface of the active metal material layer to make it porous. By creating a rough active surface of
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 hydrogen overvoltage reduction effect.

As a method for developing these cathodes, the present inventors previously proposed a method using so-called dispersion plating, in which electroplating is performed using a plating bath in which carbonaceous fine particles are dispersed on the surface of a cathode substrate. (JP-A-57-35689, JP-A-57-89
491, JP-A-57-94582, JP-A-57-945
As a result of studies aimed at improving the robustness and further reducing hydrogen overvoltage (e.g., 83), the present invention was completed.

That is, the present invention applies a plating current density of 7 A/dm to the surface of a cathode substrate 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.
The above is a method for producing a low hydrogen overvoltage cathode characterized by performing electroplating and removing a plating layer that is easily separated from the surface.

One of the characteristics of the method of the present invention is to perform dispersion plating on the surface of the cathode base material at a plating current density of 71 y'dmF or higher as described above. Corrosion-resistant materials are used that are easy to apply and do not cause any particular problems with plating adhesion. Specifically, alkali-resistant materials made of iron, copper, dikel, alloys containing these, and pulp metals are used. Similar metal materials are preferably used, and metal materials that have been previously plated with a nickel plating bath can also be used.

Although there is no special restriction on its shape, expanded metal, perforated flat plates made of pressed metal, punched metal, woven wire mesh, and other perforated plate shapes are preferably used, and their porosity is 1 to 99. It is preferable that it be within the range of

Dispersion plating applied to the surface of such a base material involves dispersing carbonaceous fine particles in a range of y1 to so p/l, and electrolytically using a plating bath containing a metal component mainly consisting of nickel as the plating metal. It is plated.

The above-mentioned nickel-based gold scrap component in the plating bath is one that contains only nickel or nickel in a predominant amount (more than 50% (weight range: the same applies hereinafter)), has no adverse effect on performance, is economically advantageous, It includes one or a combination of two or more other metals in consideration of other factors.

Cobalt, iron, silver, copper, phosphorus, tungsten, magnesium, titanium, molybdenum,
Beryllium, chromium, zinc, manga, tin, lead, bismuth, etc. can be mentioned.

This nickel-based metal plating bath is used as a bath containing one or more of nickel sulfamate, He nickel, nickel chloride, nickel bromide, etc. as a main component. Boric acid, citric acid, hydrochloric acid, sulfuric acid, ammonia, ammonium chloride, potassium chloride, etc. are added as appropriate.

Furthermore, a pit preventive 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 sulfur bath, as a dispersion plating bath.

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

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

When performing electroplating using such a plating bath, the plating conditions such as temperature, pH value, and time should be selected to be suitable for the plating bath, but in the present invention, the plating current density is particularly important. This is important, that is, the current density during plating must be 7 A/dm or higher, and in the above plating bath, the current density must be 77%7d7.
When plating under conditions of a constant current density of ++“ or more,
The plating layer forms a dense and hard layer with a low hydrogen overvoltage, and a layer with a low hydrogen overvoltage that is relatively flexible and can be easily separated from the surface. In this case, if this is used as it is, for example, as a cathode in an ion-exchange membrane electrolyte tank, the flexible layer may detach during operation and contaminate the ion-exchange membrane, or it may dissolve and reduce the activity of the cathode. There is a risk of causing this. Therefore, in the method of the present invention, such a layer that is easily separated is removed in advance to eliminate the above-mentioned problem, and this can be removed relatively easily by light polishing or the like. It can be removed by spraying pressurized water at a pressure of about 50 to 200 -/♂, applying soft buffing, or scrubbing with a scrubbing brush or hand.

Generally speaking, when dispersion plating is performed under the above-mentioned conditions of plating current density of 7 Vdm' or more, the dense hard dispersion plating layer is generally the lower layer (on the cathode base material side) K, and the dispersion plating layer is relatively flexible and easily separated. A 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 and does not cause the lower dense layer to separate, resulting in a low hydrogen overvoltage characteristic formed only by the lower dense dispersed plating layer. A cathode with excellent properties can be obtained.

There is no particular upper limit to the plating current density in dispersion plating, but from the viewpoint of rectifiers for plating and plating efficiency,
00a/d is preferable, especially 15 to 50 A/di
It is practically preferable that the plating current density be within the range of 7A.
/d77f or lower, the above-mentioned dense layer and
Although two layers are formed, a soft layer and a soft layer, the degree of density of the dense layer is different, and with long-term use, the plating will peel off, and the effectiveness of reducing the hydrogen overvoltage will gradually decline.

In the method described above, after removing the easily separated plating layer formed on the surface of the cathode, by repeating the dispersion plating and light polishing, it is possible to obtain a low hydrogen overvoltage cathode with an even longer lifespan. In general, it is possible to extend the life of the culm by repeating this process frequently, but considering the thickness of the plating layer and deterioration due to impurities in the catholyte during use, it is not practical to repeat this process too often, and it is not desirable. It is best to repeat 10 times or less.

Furthermore, after removing the easily separated plating layer after plating, it is also suitable to apply nickel plating, nickel-sulfur plating, or other reinforcing plating thereon in order to extend the life of the cathode. In addition, so-called laminated plating, in which reinforcing plating is performed after the reinforcing plating is performed again by the method of the present invention to remove the layer that easily separates from the surface, can also be carried out suitably, and the number of laminations is also limited from practical considerations. Preferably 10 times or less.

The above-mentioned nickel-sulfur plating refers to electroplating in which thiourea, thiocyanate, thiosulfate, sulfite, thioglycolic acid, etc. are added 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 fixation of the dispersed plating layer to the base layer, it is preferable to add a trace amount of the metal described below.

That is, the trace metal components include copper, aluminum,
Examples include one or more selected from chromium, tin, barium, zinc, silver, platinum, iridium, rhodium, palladium, and the like.

These trace metal components are used in trace amounts, generally less than 1 part, in the dispersion plating bath, and are added in the form of compounds such as chlorides, sulfates, and carbonates.

The desirable concentration range of trace metal components is various ions,
Although it varies depending on the type of plating bath, type of carbonaceous fine particles, plating operation conditions, etc., it is generally as follows depending on each metal component.

Cu+0.5~250+97J, Al″' 50~50
00 layer g/IZn+50~500 k//, A door 50~
5000rtg/ICv' or Cr'''50~20DO
tny/l, Sn"50~5DDDzy//Ba+50
~5000ny/l, Pt 5~3000F! g, /
IRh 5-3001117/jl, Ir person or 1r
414 or (r) Ilikan 10-3000fi/l, Pd"1-300fi!9/J
As mentioned above, the addition of trace amounts of metals to the dispersion plating bath is effective in improving the fixation of plating, but the addition of trace amounts of metals to the dispersion plating bath is effective in improving the fixation of plating. There are metals of the same type that partially overlap with the metal components that are used in combination with nickel in the nickel-based metal components listed above, that is, the metals used in combination.

If the amount of trace metal added during plating increases significantly beyond the above range, it tends to lose its effectiveness as a trace metal, so when using a combination metal and a trace metal, It is desirable to select the metal of the pole and keep the trace metal within the above addition range, but when using the same kind of metal and wanting the effectiveness of the trace metal, the total view of the same kind of metal is within the above addition amount range of the trace metal. 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 six-sided round rods made of Ni (SN-HC7!) were etched at 80°C for 30 minutes. Two of the rods were sealed with shrink tubes, leaving 20% of the tips. Plating was carried out for 10 minutes at a density of 20 A/di under the bath composition and plating conditions shown in Table 1.

Next, the plated surface was rubbed strongly by hand, and then washed with water. One of these was plated in the same bath for an additional 10 minutes, then rubbed by hand in the same manner and washed with water. these things,
20cm KOH, 60℃, 20A/dm”, H&/
The hydrogen generation potential was measured based on 1-1110. As a result, the potential of the one plated once was -1.15 V, and the potential of the two plated one was -1.13 V. On the other hand, a Ni round bar that had only been etched with hydrochloric acid was plated under the same conditions as shown in Table 1. Go1・j [Plating time: 10 minutes Example 2 Six Ni round bars were plated at 80°C using 6N-HC7.
Etching was performed for 60 minutes at ℃. Seal two of them with a shrink tube, leaving 20% of the tips, and apply a current density of 2o.
Plating was carried out at A/dm for 10 minutes under the bath composition and plating conditions shown in Table 2.

Next, the plated surface was rubbed strongly by hand, and then washed with water. One of these was plated again in the same bath for 10 minutes,
Similarly, rub it by hand and wash it with water. 20% of these things
KOH60℃20A/1hrt l-1,97Hfl
As a result of measuring the hydrogen generation potential based on O standard, the one plated once was -0.97V, and the one plated twice -0.97V.
It showed V. On the other hand, the N1 round bar that was only subjected to hydrochloric acid enoting was
It showed -1.35V under the same conditions.

Table 2 1) Copper sulfate 04.1. 1 Temperature 40°C; Opponent @ Ni & 1 me/ki 1 bath 100 m1 □l 1 m Stirring Magnetic stirrer: Plating current density 20 A/d774 1: Plating time 10 minutes Example 6 Same as Example 2 After etching a Nip round bar (3ヰφ) and performing dispersion plating using the bath composition and plating conditions shown in Table 6 below, it was strongly rubbed by hand and then washed with water to obtain a plated product. The potential of this material was -0.99V.

Table 3 1 1PH approx.

1 plating condition Bath 100 d 1 1 m Stirring - Magnetic cooler: Example 4 Same as Example 2, of the bath composition in Table 2, graphite powder (AT-40 manufactured by Toyo Carbon Co., Ltd.) was used instead of activated carbon at 251/11.
m, and the copper sulfate concentration is 0.51/II, 50A/
The results of measuring the potentials of one plate that was plated with di'' for 7 minutes and the flexible layer removed, and another plate that was further plated for 7 minutes and the flexible layer removed (i.e. one plated and two plated) - 1,00 µ and -1,01 V were obtained.

Example 5 (Same as Example 2) Plating was carried out under the same conditions except that the same bath composition as in Table 2 was used, except that instead of activated carbon, 20 E/l of crushed coke and sieve through a 350 sieve was used. I did it. The i potential of the one-time plating was -0.99V, and the two-time plating was 10.98V.

Example 6 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 the pieces was plated at 5A/1 using the bath shown in Table 4 below. dmjX 15 minute nickel rate was applied.

The other one was subjected to nickel-sulfur plating using the bath shown in Table 5 under conditions of 3 A/dm x 20 minutes.

The potential of the former is -0,99V, and the potential of the latter is 10,97■
showed that.

Table 4 -2 doors 3°7 Table 5 Example 7 Expanded metal made of sUs31oS (12LWx
6 SWx 1.5Wx 1.5 T, unit π+a;L
W 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 1' represents the thickness. (same below) 1di
(100mX 100m) with 6 N-HCl
After pretreatment for activation by etching with hydrochloric acid for 60 minutes, Table 4
Underlying nickel plating was performed using the following bath composition and plating conditions (the bath had a 511 plating current density of 2 A/dmj, and the plating time was 2 hours).

Next, the bath composition and plating conditions shown in Table 2 (however, the bath was 51.
For stirring, the liquid was circulated using a 1@/Ir pump, and the plating current density was 30 A/di. ), then used a scrubbing brush to remove the soft surface layer, and finished by washing with water.

Add this to 20% KOH, room temperature, 20A/di1-1g
When the hydrogen generation potential was measured using the /l1go standard, hydrogen was generated for 60 days with 66-chi NaOH, 11! When the transfer was taken out and the potential was determined to be -1.02 V, it was found to be -1.02 V. 3. Example 8 Using the same Xund metal as in Example \, base nickel plating and dispersion plating as shown in Table 1 were applied in the same manner to 100 kp.
/d high pressure water was used to wash the product, and the potential was -1.01V, which was the same as the one shown below (a multilayer plated product was obtained in which nickel-sulfur plating was performed and reinforced with nickel-sulfur plating).

After 30 days of hydrogen generation operation, it was taken out and the potential was measured and found to be -1.01V.

Comparative Example 1 In Example 7, the plating current density was 5 A/dyf as the dispersion plating conditions after applying the underlying nickel plating.
Plating was carried out under the same conditions as in Example 7 except that the plating time was 20 minutes. If the plated product obtained by this plating was subjected to strong polishing, the plating would peel off, so it was washed only with water, 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,
01■ was shown. This was assembled into an electrolytic cell in the same manner as in Example 7, and after 30 days of hydrogen generation operation, it was taken out and the potential was measured, and it was found to be -1°06■, indicating some deterioration.

Patent applicant name Toagosei Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. Electroplating is applied to the surface of the cathode substrate at a plating current density of 7 A/di' or more using a plating bath in which carbonaceous fine particles are dispersed and contains a metal component mainly consisting of nickel as the plating metal, to eliminate the easy detachment that occurs on the surface. A method for producing a low hydrogen overvoltage cathode, which is characterized by removing the plating layer.