JPS5867883A - Manufacture of low hydrogen overvoltage cathode - Google Patents

Abstract

PURPOSE:To lower the hydrogen overvoltage of a cathode to be used in a cell for electrolyzing an aqueous solution, by plating a base material for the electrode with Ni in a plating solution containing impalpable carbon particles and then forming Ni or S-contg. Ni plating layer on the surface. CONSTITUTION:To the surface of the base material of an electrode made of Fe, Ni, stainless steel, Cu or these alloy as a cathode to be used for electrolyzing an aqueous alkali solution, a plating layer of Ni or an Ni alloy containing Ni> 20% is formed by using a plating solution dispersing impalpable carbon (graphite, active carbon, carbon black or coke) powder having a particle size below 10mu in it at a rate or 0.1-100g/l. Ni or sulfur-contg. Ni plating layer is then formed thereonto by a conventional electroplating method. The combination of said plating treatments is repeated one time or more, and the plated electrod is baked at 100-500 deg.C to make the electrode having low hydrogen overvoltage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a cathode that is used in electrolysis and exhibits a low hydrogen overvoltage, especially in aqueous solutions of alkali hydroxides, alkali carbonates, and other alkaline solutions. Regarding the cathode shown.

Conventionally, techniques for generating hydrogen gas at the cathode, such as ion exchange de-alkali chloride aqueous electrolysis and water electrolysis using membranes, have been known.In recent years, especially from the perspective of energy conservation, reduction of the electrolysis voltage has been desired in this type of technology. It has been proposed that the hydrogen overvoltage at the cathode can be reduced by using the ring.

Regarding low hydrogen overvoltage cathodes, electrodes made of various materials have been proposed in the past, and the present inventors first electroplated the electrode base material using a plating bath containing nickel in which carbonaceous fine particles were dispersed. We have filed an application for a method for producing a cathode that exhibits excellent low hydrogen overvoltage. (Special application 1986-1
No. 11066, patent application No. 164682, patent application No. 1983
(No. 5-169059, Japanese Patent Application No. 55-169060) In all of the cathodes obtained by these methods, the metal coated on the surface of the electrode base material is mainly nickel, and either a layer of nickel alone or a layer of nickel predominant. Although a layer of an alloy containing a certain amount of nickel is formed in a dispersion plating bath of the carbonaceous fine particles, and a cathode with low hydrogen overvoltage and excellent durability is obtained, the mechanical strength as an 11L electrode, especially It is still not sufficient in terms of corrosion caused by bubbles generated during electrolytic operation.

As a result of continued research into a method for manufacturing a cathode using such a dispersion plating bath of carbonaceous fine particles, the present inventors have successfully completed the invention while maintaining low hydrogen overvoltage characteristics.

That is, the present invention provides a method for forming a nickel plating layer or a 20-layer plating layer on the surface of an electrode base material by electroplating using (a) nickel in which carbonaceous particles are dispersed, or a plating bath containing nickel and other metal components. The process consists of forming an alloy plating layer containing more than a nickel, and then (b) forming a nickel plating layer or a sulfur-containing nickel plating layer on the surface by conventional electroplating. ) is performed at least once.

In the method of the present invention described above, first, in step (a), electroplating is applied to the surface of the substrate using a dispersion plating bath using carbonaceous fine particles, which is substantially the same as in the previous application, and in such plating, the coating is Although the presence of nickel as a metal is essential, the amount thereof does not necessarily require a predominant amount of nickel, and it is sufficient if the layer is coated with a layer containing 20% or more of nickel by weight, and of course, it may be composed of nickel alone. good.

Using a plating bath in which carbonaceous fine particles are dispersed in this manner, a cathode in which nickel is precipitated by 20 weights or more has a large surface area and an excellent activity and low hydrogen overvoltage cathode can be obtained, but the present invention Then, a layer of nickel or sulfur-containing nickel is further formed on the surface by electroplating.

By doing so, it is possible to improve the mechanical strength of the electrode, further improve the low hydrogen overvoltage characteristics of nickel, and maintain high performance over a long period of time. In particular, when the nickel component of the plating formed in the carbonaceous fine particle dispersion plating bath described above is not in a dominant amount, such nickel plating or sulfur-containing nickel plating can compensate for the nickel component and ensure a low hydrogen overvoltage. In this case, plating is performed not by the above-mentioned dispersion plating bath of carbonaceous fine particles, but by ordinary electroplating.

The electrode base materials used in the method of the present invention include iron, nickel, stainless steel, copper, and alloys thereof, iron balls plated with nickel, copper, chromium, etc., and pulp metal plated with specific metals. Many materials such as plated particles can be used. On the other hand, the carbonaceous particles to be dispersed in the plating bath include carbons such as charcoal, coal, and bone charcoal, as well as graphite, activated carbon, carbon black, coke, etc. In particular, activated carbon made from wood, coconut husk, etc. is advantageous both in terms of performance and economics. As mentioned above, the metal component used in the dispersion plating bath for such carbonaceous particles is nickel. It contains cobalt, iron, silver, copper, phosphorus,
Many metals such as tungsten, molybdenum, magnesium, titanium, beryllium, chromium, lead, manganese, tin, zinc, and bismuth are used, and one or more of these may be used in combination.

However, it is necessary that these alloy compositions have sufficient corrosion resistance under the conditions of use, and if the above-mentioned metals other than nickel are included in an excessive amount, the corrosion resistance will deteriorate. Therefore, it is necessary that the electroplated plating layer contains 20% by weight or more of nickel based on the plating metal, and the mixing ratio should be suitably adjusted depending on the combination of metals used.・For example, in the combination of nickel-cobalt and nickel-iron, 20% by weight or more of nickel, preferably 25% by weight or more is appropriate in terms of corrosion resistance, and in the combination of nickel-steel, a= Nickel 3 weight -
The above is good.

In view of corrosion resistance and ease of plating operation, the most preferable plating bath is one containing only nickel.Although the effect of carbonaceous particles in the above-mentioned dispersion plating bath is not clear, during electroplating, It is presumed that this adhesion to the base material surface along with other metals makes the cathode surface rough, increases the catalytic ability, and contributes to a reduction in the hydrogen overvoltage.

The finer the fine particles, the more advantageous they are, but preferably 100 μm or less, particularly 10 μm or less. However, since many commercially available fine particles have a fairly wide particle size distribution,
As long as 5 Ots or more of particles with a size of 0 μ or less are contained, there will be no particular problem in achieving the object of the present invention.

When such fine particles are dispersed in a plating bath, the concentration thereof is 0.1 to 100 g/l, preferably 1 to 20 g/l.
It is.

Even if the concentration of these fine particles exceeds a certain level, it will not affect the hydrogen overvoltage of the cathode much, but if the concentration becomes too high, uniform dispersion becomes difficult. Operation becomes cumbersome. Furthermore, if the concentration is too low, it becomes difficult to obtain the desired low hydrogen overvoltage cathode, so the concentration range described above is desirable. Appropriate stirring is required to disperse carbon and elementary particles in the plating bath, and specific methods include gas blowing, liquid circulation, or using a stirrer. In addition, in the case of a small scale, a stirring method using a magnetic stirrer is also recommended.

If this stirring is insufficient, a uniform plated product cannot be obtained, and on the other hand, if it is too strong, an active plated product cannot be obtained. Furthermore, if the plating operation continues for a long time, the carbonaceous particles will be consumed, and many of the fine particles in particular will be reduced, but in this case, all the particles should be removed using a Brecoat filter, etc., and new particles should be added again. It is recommended to operate the

When performing the above plating, the plating conditions, i.e. plating bath composition, plating temperature, plating current density, plating solution PH%
By appropriately selecting the metal composition of the mating electrode, the desired plated product can be obtained.

In this case, by adding a trace amount of a third metal component that is not included in the plating bath or the mating electrode, a plated product with even lower overvoltage can be obtained.

It is preferable that such a trace amount of the third component be present in the precipitated metal in an amount of 1% by weight or less, and effective examples include platinum group metals such as platinum, rhodium, iridium, and palladium, or copper, chromium, and aluminum. , tin, zinc, barium, silver, etc.

When the above-mentioned second component other than nickel is included, it is necessary to appropriately select the third component other than nickel.

In the method of the present invention, after the above-mentioned plating, nickel plating or sulfur-containing nickel plating is performed in step (b), but as described above, the plating in this case does not use a dispersion plating bath using carbonaceous fine particles. Instead, use a normal plating bath, for example, a plating bath mainly containing nickel sulfate, nickel chloride, nickel 7-amino acid, etc.
Alternatively, a bath capable of forming a sulfur-containing nickel plating layer by electroplating, such as a bath in which thiourea, thiocyanate, thiosulfate, thioglycolate, etc. are added to the above-mentioned ordinary plating bath, is used. The steps of dispersion plating using carbonaceous fine particles and normal nickel plating or sulfur-containing nickel plating as described above can also be combined to form a laminated plating by repeating the combination two or more times. Incidentally, the final layer of plating formed by these combinations is a nickel plating layer or a sulfur-containing nickel plating layer, which is advantageous in terms of handling and the like.

The thickness of the plated product obtained by this method is approximately 10 to 150 μ in total when plating with a bath in which carbonaceous fine particles are dispersed, and approximately 5 to 100 μ in total when plating with a nickel or sulfur-containing nickel bath in terms of pure metal. However, the actual plated material is considerably thicker due to the presence of carbonaceous fine particles9, which is estimated to be in the range of 2 to 50 times that of pure metal.

After performing such a combination of steps at least once,
By firing this plated product at a temperature of 100 to 500°C, it has increased corrosion resistance as an electrode and has sufficient resistance to operation at high current density.

For example, a current density of 150 A/13 tr with a cathode made by the method of the present invention without such firing? 50-150 in
If water accumulates for a long time, the plating may peel off in some areas and show a tendency for deterioration.
00A/d! n? No deterioration was observed even after 100 hours of hydrogen generation operation.

The atmosphere for this firing may generally be an inert gas or air atmosphere. Products fired in an air atmosphere initially have a high hydrogen overvoltage, but after hydrogen generation for several hours to several days, they show a low hydrogen overvoltage. become.

The inert gas in this case means a gas that does not react with the plated material, and when the main deposited metal is nickel, it includes argon, helium, neon, nitrogen, carbon dioxide, hydrogen, etc.

Firing is often carried out within a relatively low temperature range of 100 to 5.00°C, and firing at temperatures below 100°C and above 500°C both result in lower cathode resistance than firing within the above temperature range. The lifespan of the product will be shortened.

Products fired within the above temperature range not only extend the life of the cathode, but also
In particular, it has excellent resistance to operation under high current density, and the plating may peel off due to friction during normal handling.

The cathode obtained by the method of the present invention as described above is used as a cathode for hydrogen generation in various electrochemical reaction devices, but it is especially used in ion exchange membrane method, alkaline chloride aqueous solution electrolysis, or furnace diaphragm such as asbestos. It is effective for use in aqueous alkali chloride electrolysis using the so-called diaphragm method, and its utility value is extremely large.

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

Example 1 An electrode base material made of a nickel round rod with a diameter of 3 mmφ was degreased with trichlorethylene, etched by immersing it in hydrochloric acid at 80°C for 30 minutes, washed with water, and then plated with the composition shown in Table 1 below. Electroplating was performed using different baths and plating conditions.

Table 1 (Plating using carbonaceous fine particle dispersion plating bath) [Plating bath composition] Nickel sulfate 84g/nickel chloride 30g/ammonium chloride
4.5g/potassium chloride
6g/l boric acid 30g/
Particulate activated carbon (KV-3, manufactured by Nimura Kagaku ■, 5g/110
[Plating conditions] Plating bath pH 3.5 Counter electrode Electrolytic nickel plate temperature 40℃ Plating current density 2A/(back plating time 2 hours) Next, this plated product was placed in the plating bath shown in Table 2 below. Electroplating was performed under the following plating conditions.

(Table 2 shows plating using Keckel plating bath) [Plating bath composition] Nickel sulfate s 4 g/l Nickel chloride 30 g/l ammonium chloride 4. sg/potassium chloride
6 g/l boric acid
30 g/l [Plating conditions] Plating bath pH 4 Counter electrode Nickel plate temperature 40℃ Plating current density 2-4-Plating time
The hydrogen generation potential of the plated material obtained in this way was compared with 2O-KOH at 20°C and 20A/J-.
When measured using the sc/&0 electrode standard, the voltage was -1.15V.

Example 2 An electrode base material made of a nickel round rod with a diameter of 3rrrnφ was degreased and cleaned with trichlorethylene, and then heated at 80°C in hydrochloric acid.
, etched for 30 minutes, washed with water, electroplated using the plating bath composition and plating conditions shown in Table 3, then electroplated using the plating bath composition and plating conditions shown in Table 4,
Thereafter, plating according to Table 3 and plating according to Table 4 were performed again.

[Plating bath composition]

Nickel sulfate 84 g/nickel chloride 30 g/ammonium chloride
4. sg/L potassium chloride
6 g/l boric acid 30
g/l [Plating conditions] Plating bath pH 3.5 Counter electrode Ni 30. Co709b alloy temperature 40℃ Plating current density 2A/dm' Plating time 1 hour [Plating bath composition] Nickel sulfate 84g/ to nickel chloride aog/ to ammonium chloride
4. sg/potassium chloride
6 g/l boric acid 3Og
/l Thiourea sg/l [Plating conditions] Plating bath pH 4 Mating electrode Nickel temperature
40℃ Plating current density 2A/d? F7'' Plating time: 0.5 hours The hydrogen generation potential of the plated product thus obtained was -1.11V, and when the surface of the plated product shown in Table 3 was peeled off and analyzed for metal components, it was found to be Ni 32 %, Co68%.

Example 3 The same procedure as in Example 2 was carried out except that the conditions in Table 3 below were replaced with those in Table 5 below.

[Plating bath composition]

Nickel sulfate 1oog/l Potassium molybdate 55 g/l Sodium citrate 91 g/l [Plating conditions] Plating bath pH 3,5 Mating electrode Nickel plate temperature 30°C Plating current density 2 Alapr? Plating time: 1 hour The hydrogen generation potential of the plated product thus obtained was -1.11V, and the fifth
When the surface of the plated surface was peeled off and the metal components were analyzed, the results were 70% Ni and 30% Mo.

Example 4 The same procedure as in Example 1 was carried out except that the conditions in Table 1 below were replaced with the conditions in Table 1 in Example 1. [Plating bath composition] Nickel sulfamate 410 g/l Iron sulfamate 115 g / urea
30g/l poric acid 25g/l saccharin
0.3 g/l ammonium hydrogen fluoride 10 g/l [Plating conditions] Plating bath PH3.0 Counter electrode Electrolytic nickel plate temperature 70°C Plating current density 3A/dyd Plating time 1.3 hours When the plated surface was peeled off and the metal components were analyzed, it was found to be 138% N and 62% Fe.

Example 5 A large number of 3 nm diameter nickel round bars were etched in the same manner as in Example 1, plated under the plating conditions shown in Table 7 below, and then plated under the plating conditions shown in Table 4 of Example 2.

Table 7 (Plating using carbonaceous fine particle fractional plating bath) [Plating bath composition] Nickel sulfate 84 g/nickel chloride 30 g/ammonium chloride 4.5 g/potassium chloride
6 g/L boric acid s
ag/L fine granular activated carbon 5 g/
L (KV-: 1 ” manufactured by Nisaku Kagaku ■) Sulfuric acid steel 100 lie/l [Plating conditions] Plating bath pH 3,5 Mating electrode 40% Ni, 60% Co Plate temperature 40℃ Plating current density 2A/dW?Plating time 1 The compositional analysis result of the plated part obtained over time was 42% Ni and 58% Co.

Next, a nickel plating layer was formed on this under the conditions according to Table 2 of Example 1, and further plating was performed using a carbonaceous fine particle dispersed nickel plating bath according to Table 7, and finally a nickel plating layer was formed under the conditions according to Table 2. was formed. The hydrogen generation potential of the obtained plated product was -i, osv.

Example 6 The same procedure as in Example 5 was carried out except that the third component shown in Table 8 below was used in place of the copper sulfate used as the third component in the plating bath composition shown in Table 7 in Example 5. Table 8 shows the hydrogen generation potential of each plated product obtained as a result.

Table 8 Example 7 The same procedure as in Example 5 was carried out except that a plate of 80% Ni and 20% Co was used as the mating electrode under the plating conditions shown in Table 7.

In this case, the first dispersion plating using carbonaceous particles (
The precipitated metal composition of the plating obtained in the first plating according to Table 7 was 81% Ni and 19% Co.

Next, make a large number of plated items by the same operation as above,
These were heated to 100 to 600℃ in air and argon gas.
Baked for 30 minutes at a predetermined temperature in the range of
0 A/dtr? in 3O−1 NaOH at 80°C, 10
After hydrogen was generated for an hour, the potential was measured by the method of Example 1, and the life of the electrode was determined when the potential was below -1.15 V twice, and its performance (corrosion resistance) was examined.

This test was conducted on three samples for each temperature.

The results are shown in FIG. 1 (firing in an argon atmosphere) and FIG. 2 (firing in an air atmosphere). Note that A in the figure shows the performance of an electrode that is not fired.

Example 8 and Comparative Example 1 Using the same six baths as in Example 5, plated products were obtained by the same operations. However, the electrode base material used was made of nickel and had a diamond-shaped opening shape, and had a thickness of IX and a width of 1.
．． 5X, the length of the mesh in the transverse direction was 6.5%, and the length in the longitudinal direction was 12.7%.

This plated product was fired at a temperature of 300° C. in argon gas, and was incorporated into a cation exchange membrane electrolytic cell as a cathode to carry out salt electrolysis. (Example 8) At this time, salt electrolysis was also carried out using an electrolytic cell incorporating a nickel lath mesh without plating as a cathode. (Comparative Example 1) Both of these electrolytic cells have an electrode area of 1 dm", and the Na
C1 decomposition rate 45%, bath temperature 90°C, catholyte (NaOH)
The concentration was 30%, the ion exchange membrane was a sulfonic acid membrane with one side modified to a carboxylic acid type, and the operation was carried out for 6 months.

Table 9 shows the measured values of the sliding voltage and current efficiency at the third and sixth months in this case.

Table 9

[Brief explanation of drawings]

Both drawings show the time required for the cathode obtained by the method of the present invention to deteriorate at each firing temperature. Figure 1 shows the case when fired in an argon gas atmosphere, and Figure 2 shows the time taken for the cathode to deteriorate in an air atmosphere. Indicates the case where Patent applicant Toagosei Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. Forming on the surface of the electrode base material (a) a plating layer of nickel in which carbonaceous particles are dispersed, or an alloy plating layer containing nickel and other metals, and then (b) the surface thereof. It consists of forming a sulfur-containing nickel plating layer or a sulfur-containing nickel plating layer by conventional electroplating, and these (a), (
A method for producing a low hydrogen overvoltage cathode, characterized by carrying out the combination of (b) at least once. 2. A nickel plating layer is formed on the surface of the electrode base material by electroplating using (a) nickel in which carbonaceous fine particles are dispersed, or a plating bath containing other metal components.
It consists of forming an alloy plating layer containing 0 weight or more of nickel, and then (b) forming a nickel plating layer or a sulfur-containing nickel plating layer on the surface by conventional electroplating, and these (a), ( A method for producing a low hydrogen overvoltage cathode, which comprises performing the combination (b) at least once and then firing at a temperature of 100 to 500°C.