JPH0260759B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a cathode having a low hydrogen overvoltage and sufficient durability and corrosion resistance. Conventionally, iron cathodes have been mainly used in water electrolysis or electrolysis of aqueous alkali chloride solutions in which hydrogen generation reaction is the main reaction at the cathode. Iron is inexpensive as a cathode material and exhibits a fairly low hydrogen overvoltage, but in recent years there has been a need to further improve this. In particular, with the development of cation exchange membrane salt electrolysis technology, a further reduction in hydrogen overvoltage is desired from the perspective of energy conservation, and due to the electrolytic conditions of high temperature and high alkali concentration, the corrosion resistance of iron is becoming a problem. . For this reason, there is a desire for a new cathode that exhibits lower hydrogen overvoltage than iron cathodes, is economical, and has sufficient durability and corrosion resistance. Various studies have been conducted in various places, and several methods have been proposed. has been done. Among them, nickel metals that provide a low hydrogen overvoltage that have been proposed in the course of the development of conventional water electrolysis technology, such as nickel metals containing sulfur, (for example, nickel metals containing sulfur, It has been known for a long time, and is attracting attention because it is cheaper than electrodes coated with platinum group metals, etc. The present inventors conducted a detailed study on the plating films obtained by the above method, and found that there are several drawbacks of these plating films, namely, poor adhesion to the base material and poor surface coating. He discovered a method for manufacturing an electrode that overcomes the disadvantages of being brittle and weak, and furthermore, that the reduction in hydrogen overvoltage was still insufficient, and filed a patent application (Japanese Patent Application No. 55-092295, same).
No. 56-000305) As a result of further studies on the electrode made by the above method, the present inventors have discovered a cathode that exhibits even better durability and corrosion resistance, and has a low hydrogen overvoltage. Generally, nickel plating containing sulfur has voids inside, and its adhesion to the base material cannot be said to be sufficient. This problem is particularly serious when iron is used as the base material. In other words, due to the voids that exist in the nickel plating containing sulfur, a part of the base material is in contact with a high-temperature, highly concentrated alkaline solution, which prevents the iron in the base material from dissolving during electrolysis or cutting. It happens. moreover,
These nickel-based plating coatings exhibiting low hydrogen overpotentials often have a more noble electrode potential than the base material in alkaline solutions, and therefore,
It has a tendency to promote dissolution of the base material. in this way,
When the interface between the base material and the coating begins to erode, the gas generated by electrolysis may cause the coating to swell or even peel off.Also, iron ions eluted from the base material may adhere to the electrode, etc. As a result, electrode performance deteriorates. Furthermore, when this electrode is used as a cathode for cation-exchange membrane salt electrolysis, iron ions eluted from the base material may deteriorate the membrane performance of the ion-exchange membrane, and furthermore, there is a risk that the product quality of the resulting caustic soda may deteriorate. There is. In order to improve the adhesion between the base material and the sulfur-containing nickel plating (for example, the Rodan nickel plating layer), for example, Japanese Patent Publication No. 7444/1983 proposes applying copper plating as the base plating for the Rodan nickel layer. ing. However, copper has some problems in corrosion resistance in alkali, and has poor adhesion to nickel plating containing sulfur.
After copper plating as proposed in Publication No. 7444,
The method of performing heat treatment in an inert atmosphere and then performing Rodan nickel plating is not necessarily economical. In order to overcome the above-mentioned drawbacks, the present inventors conducted a detailed study on the base plating of nickel plating containing sulfur, and as a result, the present inventors developed a nickel plating bath containing ammonium ions (but not containing carbonaceous particles). The nickel-plated layer using the sulfur-containing nickel-plated layer exhibits excellent adhesion to the sulfur-containing nickel-metallic layer, and also exhibits sufficient corrosion resistance in high-temperature, high-concentration alkaline aqueous solutions, thereby successfully obtaining a cathode that overcomes the above drawbacks. . Therefore, the present invention performs nickel plating on the surface of a metal substrate using a nickel plating bath containing ammonium ions (but not containing carbonaceous particles) as a base plating, and then applying a low hydrogen overvoltage thereon. show. By applying nickel plating containing sulfur, the cathode is characterized by having excellent corrosion resistance and durability, and which maintains a low hydrogen overvoltage for a long period of time. The base material of the present invention is made of iron, nickel, copper, or an alloy thereof, and as described above, iron or
When an alloy containing iron as a main component is used, the effects of the present invention are remarkable. This means that the present invention is highly economical. Furthermore, regarding the base shape, flat plate, mesh shape, porous shape, etc.
Although any shape may be used, when used as a hydrogen generating electrode at high current density, it is particularly preferable to use a base shape such as expanded metal, punched metal, or wire mesh shape. In order to provide the electrode of the present invention, it is necessary to perform base plating on the above substrate using a nickel plating bath containing ammonium ions (but not containing carbonaceous particles). Nickel plating baths commonly used as base plating include Watt baths (nickel sulfate, nickel chloride,
Coatings that are nickel-plated using a nickel-plating bath that does not contain ammonium ions, such as a bath containing boric acid, do not exhibit sufficient adhesion to nickel-plated coatings that contain sulfur. However, if a small amount of ammonium ions are added to the plating bath, the resulting nickel plating film will exhibit sufficient adhesion to the sulfur-containing nickel plating film. The nickel plating bath that provides the base plating layer of the present invention contains nickel salt and ammonium ions as essential components. Ammonium ions are added to the plating bath by soluble ammonium salts such as chloride, sulfate, or ammonium hydroxide or other ammonium salts. The adhesion between the base plating film obtained by adding ammonium ions and the sulfur-containing nickel plating film is significantly improved, and the base plating film becomes a dense and strong nickel plating film, resulting in good durability and corrosion resistance. Can provide a cathode. The ammonium ion concentration added to the plating bath is 0.05 molar or more, and the upper limit is not particularly limited, and a saturation concentration is allowed. If the ammonium ion concentration is below the above concentration, the adhesion between the resulting nickel plating film and the sulfur-containing nickel plating film will be insufficient. The nickel salt used in the nickel plating bath applied to the base plating layer may be any soluble salt, such as nickel chloride, nickel sulfate,
Nickel acetate, nickel sulfamate, etc. are used, and the concentration is not particularly limited, but usually
It is desirable to use the concentration in the range of 0.05 molar to 2.0 molar. In addition to the above-mentioned components, other soluble salts may be added to the plating bath used for forming the base plating layer, as long as they do not cause any inconvenience to the resulting surface coating. For example, the use of a buffer such as boric acid, which is often used in nickel plating baths, may improve the properties of the nickel plating film used in the present invention, and may be added as a suitable component to the nickel plating bath used in the present invention. . Furthermore, the operating conditions for plating to form the base plating layer are not subject to any particular strict limitations, but are preferably in the temperature range of about 70°C from room temperature, and in the range of 0.1 to 70°C.
It is desirable to perform plating under stirring at a current density range of about 10 A/dm ² . Furthermore, in order to further improve the corrosion resistance and durability of the cathode of the present invention, for example, copper plating or electroless nickel plating is performed on the iron, base material, etc. in advance, and then the above-mentioned base plating is applied thereon. This can also be an effective means. In particular, when applying nickel plating to the entire surface of the cathode chamber electrode after attaching an electrode with a complicated shape to the cathode chamber, the coverage of the base plating may be insufficient, so use electroless nickel plating with good coverage in advance. application yields favorable results. On top of this electroless nickel plating, a nickel plating bath containing ammonium ions used in the present invention (but not containing carbonaceous particles)
However, providing a coating with good adhesion is one of the additional features of the present invention. As is well known, it is generally difficult to apply nickel plating with good adhesion on top of electroless nickel plating.
Nickel plating is performed using a hydrochloric acid acidic nickel plating bath called strike nickel (a bath consisting of nickel chloride and hydrochloric acid), and then nickel plating, such as the above-mentioned Watt bath, is performed. but,
On such a strike nickel plating, the sulfur-containing nickel plating of the present invention, which exhibits a low hydrogen overvoltage, does not have sufficient adhesion. On the other hand, the coating obtained from the nickel plating bath containing ammonium ions (but not containing carbonaceous particles) used in the present invention has good adhesion to the electroless nickel plating surface, and is also compatible with the nickel plating bath containing sulfur. It shows excellent adhesion. In order to provide the cathode for electrolysis of the present invention, it is necessary to perform nickel plating containing sulfur on the base nickel plating layer to form a coating layer exhibiting a low hydrogen overvoltage. The nickel plating containing sulfur is provided by a nickel plating bath containing a bathable nickel salt and an appropriate amount of a bathable sulfur-containing compound, and more preferably, it is desirable to add an appropriate amount of ammonium ions to the nickel plating bath. Nickel salt can be any bathable salt, usually
It is desirable to use the concentration in the range of 0.1 molar to 2.0 molar. The bathable sulfur-containing compound used in the plating bath means a thiocyanate, a thiourea, or an oxo acid salt having a sulfur oxidation number of 5 or less, and has the effect of providing a plating film exhibiting a low hydrogen overvoltage. The oxoacid salt having a sulfur oxidation number of 5 or less means, for example, salts of sulfite, bisulfite, thiosulfite, dithionite, and the like. The concentration of thiocyanates, thioureas, and oxoacid salts with a sulfur oxidation number of 5 or less added to the bath is 0.01 molar concentration or more than 1.0 in terms of the amount of sulfur in the compound.
It is desirable to use it in a molar concentration or less, preferably in a range of 0.05 molar or more and 1 molar or less. If the concentration of the sulfur compound is less than 0.01 molar concentration, the reduction in hydrogen overvoltage on the resulting nickel plating surface will be insufficient, and if it exceeds 1.0 molar concentration, the adhesion between the base plating and the plating film will be poor. Furthermore, by adding an appropriate amount of ammonium ions to the nickel plating bath that provides the nickel plating containing sulfur, the adhesion of the resulting plating film is improved, the covering power of the plating is also increased, and a film surface with even stronger properties can be obtained. Can be done. The concentration of ammonium ions added to the plating bath should be at least 0.5 times the molar concentration relative to the amount of sulfur in sulfur compounds such as thiocyanates, thioureas, and oxoacids with a sulfur oxidation number of 5 or less. Preferably, the upper limit is not particularly limited and is allowed up to saturation concentration. The pH of the plating bath is preferably 6 or less; if the pH exceeds 6, the resulting plating surface tends to become brittle and prone to electrodeposition, and tends to peel off easily. In addition to the above-mentioned components, other soluble salts may be added to the plating bath used for forming the sulfur-containing nickel plating layer, as long as they do not make the resulting surface coating undesirable. For example, the use of a buffer such as boric acid, which is often used in nickel plating baths, may improve the properties of the nickel plating film used in the present invention.
It may be added as a suitable component to the plating bath used in the present invention. In addition, the plating operating conditions for forming the sulfur-containing nickel plating layer are not subject to any particular strict limitations, but preferably include a temperature range of about 70°C from room temperature, and a current density range of about 0.1 to ¹⁰ A/dm2. It is desirable to perform plating under stirring. Furthermore, after forming the sulfur-containing nickel plating layer, by performing appropriate heat treatment as necessary, the final cathode may exhibit even better durability. Appropriate heat treatment means a non-oxidizing atmosphere, e.g.
This means carrying out in an inert gas atmosphere such as argon, nitrogen, or helium, or a reducing gas atmosphere such as hydrogen, or in a temperature range of 50°C to 500°C under conditions such as vacuum. There is no particular strict limit to the time for this heat treatment, but it is usually desirable to perform it for 30 minutes or more and within 24 hours. As described above, dense nickel plating is performed on a metal substrate using a nickel plating bath containing ammonium ions (but not containing carbonaceous particles) as a base plating for nickel plating containing sulfur, and then By applying sulfur-containing nickel plating that exhibits low hydrogen overvoltage on top of this, it is possible to provide a cathode that has excellent corrosion resistance and durability, maintains low hydrogen overvoltage over a long period of time, and has extremely high energy efficiency. . Examples will be described below, but the present invention is not limited thereto. Example 1, Comparative Example 1 Half-inch expanded metal (breadth diameter) made of mild steel and measuring 5 cm x 10 cm x 0.3 cm as a base material
7.0 mm, major axis 12.7 mm), the following samples were created. That is, in Example 1, after degreasing and pickling the base material, base nickel plating was performed using the nickel plating bath shown in Table 1 under the conditions shown in Table 2. Table 1 Nickel plating solution composition Nickel chloride 0.5M / Ammonium chloride 1.0M / Table 2 Nickel plating conditions Bath temperature 60℃ Current density 1A/dm ² (Substrate peripheral area) Plating time 1 hour Then, using the nickel plating bath shown in Table 3 Nickel plating showing low hydrogen overvoltage was performed under the conditions shown in Table 4. Table 3 Nickel plating bath composition Nickel chloride 0.5M / Thiourea 0.3M / Ammonium chloride 1.0M / Table 4 Nickel plating conditions Temperature 60℃ Current density 1A/dm ^2Plating time 2 hours On the other hand, in Comparative Example 1, the base material was degreased. After pickling, nickel plating with low hydrogen overvoltage was performed directly using the nickel plating bath shown in Table 3 and under the conditions shown in Table 4 without performing base plating. These two samples were used as platinum anodes in a 30 wt% NaON solution for 100 days under electrolytic conditions of 30 A/dm ² at a temperature of 80° C. and the change in cathode potential was measured. The cathode potential was measured by the Luggin capillary method using a mercury oxide electrode. The results are shown in Figure 1. As is clear from FIG. 1, Example 1 maintains an extremely low hydrogen overvoltage for a long period of time. On the other hand, it can be seen that in Comparative Example 1, the electrode potential changed in the base direction, and the electrode performance deteriorated. After 100 days, the electrode of Comparative Example 1 had peeled off in a considerable part, but the electrode of Example 1 of the present invention
The electrode showed excellent adhesion without any problem of peeling. Example 2, Comparative Example 2 3 As Example 2, the base material used in Example 1 was subjected to pretreatment such as degreasing and pickling, and then the nickel plating bath shown in Table 5 was used to prepare the base material shown in Table 2 as in Example 1. The base nickel plating was performed under the conditions shown in . Table 5 Nickel plating bath composition Nickel sulfate 0.91M / Nickel chloride 0.19M / Boric acid 0.49M / Ammonium chloride 1.0M / Thereafter, using the nickel plating bath shown in Table 6, under the conditions shown in Table 4 as in Example 1. , a nickel-metal test showing a low hydrogen overpotential was performed. Table 6 Nickel plating bath composition Nickel chloride 0.5M / Sodium thiocyanate 0.2M / Ammonium chloride 0.5M / Boric acid 0.3M / On the other hand, in Comparative Example 2, after the base material was degreased and pickled, it was directly coated without undercoat plating. Using the nickel plating bath shown in Table 6, nickel plating showing low hydrogen overvoltage was performed under similar conditions. In Comparative Example 3, after the base material was degreased and pickled, a nickel plating solution with the same nickel plating bath composition as shown in Table 5 except for ammonium chloride was used as the base plating bath, and the other components were the same under the same conditions. I did the base nitskelmettsuki. (In addition,
The plating bath in which ammonium chloride is removed from the nickel plating bath composition in Table 5 is a general nickel plating bath and is called a Watt bath. ) Thereafter, in the same manner as in Example 2, nickel plating showing low hydrogen overvoltage was performed. These three samples, namely Example 2 and Comparative Example 2,
3 as a cathode and platinum as an anode in a 30wt% NaOH solution at a temperature of 80℃ and 50A/d for the outer circumferential area of the sample.
It was used as a cathode for 200 days at a current density of m ² . Figure 2 shows the cathode potential (V vs. Hg/HgO) of each sample.
indicates the value of As described above, Example 2 of the present invention maintains an extremely low hydrogen overvoltage for 200 days, exhibits good adhesion without the problem of peeling of the plating layer, and has excellent corrosion resistance and durability. I understand. On the other hand, in Comparative Example 2, it can be seen that the electrode potential changes in the base direction and the electrode performance deteriorates. After 200 days had passed, the electrode of Comparative Example 2 had peeled off in a considerable portion, and iron deposits were also observed on the surface. Also, in Comparative Example 3, the adhesion between the base plating and the plating film exhibiting low hydrogen overvoltage was insufficient, and the plating film exhibiting low hydrogen overvoltage was considerably peeled off, resulting in a considerable deterioration in electrode performance. I know what you're doing. Example 3 After pretreatment such as degreasing and pickling, the base material used in Example 1 was subjected to base nickel plating using the base nickel plating bath composition shown in Table 7 and the conditions shown in Table 8. Thereafter, using the nickel plating bath shown in Table 9, nickel plating was performed under the conditions shown in Table 10, showing a low hydrogen overvoltage. Table 7 Nickel plating bath composition Nickel chloride 0.3M / Ammonium chloride 0.3M / Table 8 Nickel plating conditions Bath temperature 40℃ Current density 0.5A/dm ² Plating time 1 hour Table 9 Nickel plating bath composition Nickel sulfate 0.9M / Nickel chloride 0.1M / Thio Urea 0.2M/Boric acid 0.3M/Table 10 Nickel plating conditions Bath temperature 40°C Current density 0.5A/dm ² Plating time 4 hours This sample was used as a cathode for 100 days under the same conditions as in Example 2. As a result, the cathode potential is −1.10~
-1.12V vs. Hg/HgO showed a nearly constant value, there was no peeling problem, and the adhesion was good. As described above, it can be seen that Example 3 of the present invention maintains an extremely low hydrogen overvoltage for a long period of time and exhibits excellent durability and corrosion resistance. Example 4 The base material was made of nickel and was 14 cm x 14 cm x 0.3 cm.
The following samples were made using half-inch expanded metal. First, after degreasing and pickling the base material, base nickel plating was performed using the nickel plating bath shown in Table 11 under the conditions shown in Table 12. Table 11 Nickel plating bath composition Nickel chloride 0.5M / Ammonium chloride 0.3M / Boric acid 0.3M / Table 12 Nickel plating conditions Bath temperature 50℃ Current density 2A/dm ² plating time 15 minutes Then, using the nickel plating bath shown in Table 13, , Nickel plating showing low hydrogen overvoltage was performed under the conditions shown in Table 14. Table 13 Nickel plating bath composition Nickel chloride 0.5M / Sodium thiocyanate 0.3M / Ammonium chloride 1.0M / Boric acid 0.3M / Table 14 Nickel plating conditions Bath temperature 50℃ Current density 0.5A/dm ² Plating time 5 hours This sample was used as a cathode A saline solution was electrolyzed under the following conditions using a cation exchange membrane and a DSA type expanded metal having a RuO ₂ film on Ti as an anode. For comparison, electrolysis was performed under the same conditions using expanded metal made of mild steel as a cathode. Electrolysis conditions: Temperature 90℃ Current density 30A/dm ² cathode chamber NaOH concentration 32-33wt% Table 15 shows the cathode potential value at the initial stage of energization and after one year for the case of the nickel cathode used as the base material and the cathode of the present invention. The cathode potential value and the bath voltage value are shown in the same table.

[Table] As described above, Example 4 of the present invention exhibited excellent durability and corrosion resistance, maintained an extremely low hydrogen overvoltage for a long period of time, and was able to maintain a 250 m
It shows a hydrogen overvoltage as low as 300 mV, and also a bath voltage, indicating that it is an excellent electrolytic cathode with high energy efficiency. Example 5 An expanded metal made of mild steel with a size of 14 cm x 14 cm x 0.1 m and 1/4 inch (length: 6 mm, breadth: 3 mm) was used as an electrode base material, and this was attached to a mild steel cathode chamber. Next, after pretreatment such as degreasing and pickling, electroless plating was performed at 90° C. for 30 minutes using Kanigen's Blue Schumer electroless nickel plating solution. Thereafter, by the method shown in Example 1, the entire surface of the cathode and cathode chamber was nickel plated to provide a base nickel plating and a low hydrogen overvoltage. Using this sample as a cathode, saline solution was electrolyzed under the same conditions as in Example 4. Table 16 shows the cathode potential value at the initial stage of energization, the cathode potential value after one year, and the bath voltage value for the cathode of the present invention in the case of an iron cathode.

[Table] As described above, Example 5 of the present invention exhibits excellent durability and corrosion resistance, maintains an extremely low hydrogen overvoltage for a long period of time, and has a hydrogen overvoltage approximately 250 mV lower than that of conventional iron cathodes. It can be seen that it is an excellent electrolytic cathode with high energy efficiency.

[Brief explanation of drawings]

FIGS. 1 and 2 show changes in cathode potential over time in Examples of the present invention and Comparative Examples.

Claims (1)

[Scope of Claims] 1. Underlayer nickel plating is performed on the surface of a metal substrate using a nickel plating bath that contains ammonium ions and does not contain carbonaceous particles, and further, a nickel plating bath that contains a dissolved sulfur-containing compound thereon. A method for producing a cathode, characterized by performing nickel plating using. 2. The method for producing a cathode according to claim 1, which uses a nickel plating bath for the base nickel plating, in which the ammonium ion concentration is 0.05 molar or more. 3 The sulfur-containing compound is thiourea, thiocyanate,
3. The method for producing a cathode according to claim 1, wherein the cathode is at least one kind of oxoacid salt having a sulfur oxidation number of 5 or less. 4. The method for producing a cathode according to any one of claims 1 to 3, wherein the metal substrate is previously plated with copper or electroless nickel.