JPS6017096A - Production of electrode - Google Patents

Abstract

PURPOSE:To perform smooth and uniform active nickel plating by subjecting an electrode base body made of a metal and an electrolytic cell to plating under specific conditions in a nickel plating bath contg. a soluble sulfurous compd. ammonium ion, etc. CONSTITUTION:A nickel plating bath contg. a soluble sulfurous compd. and/or a sacrificial metal exhibiting the potential baser than nickel and ammonium ion is adjusted to <=6pH and an electrode base body consisting of a metal is attached to an electrolytic cell consisting of a metal and is subjected to active nickel plating under the condition under which the cathodic reaction during plating does not involve generation of gas. Thiocyanate, etc. are used for the soluble sulfurous compd., and zinc, iron, etc. are used for the sacrificial metal. Nickel sulfate, etc. are used for the nickel salt and the concn. thereof is made about 0.3-2.0mol and the plating temp. about 40-80 deg.C. The electrode having substantial durability and high energy efficiency is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an electrode that exhibits low overvoltage, has sufficient durability and corrosion resistance, and is economical. Although it is suitable for various uses as an electrode, such as a generation electrode and an oxygen generation electrode, it is particularly suitable for use (2) as a cathode whose main reaction is a hydrogen generation reaction in an alkaline solution.

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. As a cathode material, iron is inexpensive 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 farming and salt electrolysis technology, further reduction of hydrogen overvoltage is desired from the perspective of energy conservation.
Furthermore, due to the electrolytic conditions of high temperature and high alkali concentration, the corrosion resistance of iron is viewed as a problem.

Therefore, there is a desire for a new cathode that exhibits a lower hydrogen overvoltage than iron cathodes, is economical, and has sufficient durability and corrosion resistance, and various studies are being carried out in various places.

The present inventors have so far proposed several novel low hydrogen overvoltage cathodes. (For example, JP-A-57-19388.
57-47884, 57-47885, 57
-114678, 57-177985, etc.) The present inventors subsequently incorporated various (3) low hydrogen overvoltage electrodes into a large electrolytic cell (at least 1 d or more), and created an extremely narrow anode-cathode distance (5 Electrolysis of saline water has been carried out using an electrolytic cell with a cation exchange membrane sandwiched between them (within order), but it has been found that the following disadvantages often occur.

One is that when the obtained low hydrogen overvoltage cathode is attached to a large electrolytic cell by means such as welding, the electrolytic performance is as expected (i.e., the electrolytic voltage is lower than that when conventional electrodes are used). (decreased). This is, for example,
This is thought to be caused by deterioration of the electrodes due to the thermal effects of welding during electrode removal, or by an increase in electrolytic voltage due to uneven potential and current distribution that occurs in large electrolytic cells. Another problem is that of surface smoothness. For example, electrodes with a low hydrogen overvoltage that have visible surface irregularities may damage and damage the cation exchange membrane if the distance between the electrodes is made too small when assembling the electrolytic cell. Therefore, it is impossible to perform an electrolysis method with an anode/cathode distance close to zero, and the anode/cathode distance needs to be 3 or more, and the resistance of the electrolyte increases. The loss will be 0.1V or more. Furthermore, if the opening of the electrode becomes smaller, if a low hydrogen overvoltage electrode having two protrusions with visible unevenness is attempted to be produced by the electrode coating method, the opening of the electrode may be crushed.

The present inventors continued various studies to overcome the above drawbacks, and as a result, succeeded in overcoming the above drawbacks by using the following method.

According to the studies of the present inventors, it is necessary to attach an electrode base material made of metal to an electrolytic chamber made of metal, and then apply an active coating that exhibits a low hydrogen overvoltage uniformly and smoothly inside the electrode and the electrolytic chamber. The method of choice is to plate a metal that exhibits corrosion resistance. By applying active nickel plating to the inside of the electrode and electrolytic chamber, it is possible to alleviate the increase in electrolytic voltage due to non-uniform potential and current distribution in a large electrolytic cell.

Further, there is no need for complicated operations such as loading and unloading the electrodes into the electrolytic cell, and therefore deterioration of the electrodes caused by these operations can be avoided.

(5) Furthermore, if there is a concern about the corrosion resistance of the electrode chamber base material, according to the present method, an active coating with good corrosion resistance is applied to the electrode chamber as well, thereby suppressing the problem of corrosion.

This method, in which the electrode is placed in the electrolytic chamber and the electrode and the electrolytic chamber are coated with active nickel plating, has already been described in the case of nickel-zinc in JP-A-54-25275, and is a known method. It is a method. However, JP-A-54-
According to the studies of the present inventors, the mixed bath of nickel chloride and zinc chloride as described in No. 25275 has a coating power that is insufficient to provide sufficiently uniform and smooth plating inside the electrode and electrolytic chamber. Moreover, the adhesion to the base material is also poor.

As a result of extensive studies regarding various active nickel plating methods, the present inventors have discovered that a nickel plating method containing a soluble sulfur-containing compound, a metal salt exhibiting a more base potential than nickel, or both, and ammonium ions, and By using a nickel plating bath with a pH of 6 or less and applying active nickel plating under conditions where the cathode reaction during plating does not cause a gas-generating reaction (6), the inside of the electrode and electrolytic chamber can be uniformly and It was discovered that a smooth active coating could be applied, and the present invention was completed.

The invention will be described in further detail below.

The electrodes and substrates in the electrolytic chamber to which active nickel plating is applied in the present invention include iron, nickel, chromium, copper, or alloys thereof.

Furthermore, the shape of the electrode substrate may be any shape such as a flat plate, mesh shape, porous shape, etc., but when used as a hydrogen generating electrode at high current density, expanded metal, punched metal, wire mesh, etc. Preferably, a base shape is used.

In order to provide the electrode of the present invention, it is necessary to attach the electrode base material to the stain removal chamber by any means such as welding, and to apply smooth and uniform active nickel plating inside the electrode and the electrolytic chamber.

The plating bath used in the present invention contains a soluble sulfur-containing compound and/or a metal salt having a more base potential than nickel, and ammonium ions, has a pH (7) of 6 or less, and has a It is necessary to perform activated nickel plating under conditions where the cathode reaction does not involve gas-generating reactions.

Among the above-mentioned various requirements characterizing the present invention, the greatest strength of the present invention is that the cathode reaction during plating does not involve a gas-generating reaction.

The gas generation reaction of the cathode reaction during plating is mainly a hydrogen gas generation reaction, but when the hydrogen gas generation reaction occurs, hydrogen gas adheres to the substrate to be plated, and crystals grow to surround the gas. The surface of the resulting film is rough, has a deposited layer of brittle granular crystals and powdery crystals, and has poor film strength and adhesion to the substrate. If a porous cathode is used, an ion exchange membrane should be installed between the narrow anode/cathode distance to prevent the stain electrode properties from being degraded by crushing the openings in the mesh, or to avoid rough unevenness. If this happens, problems such as damage to the membrane will occur.

Therefore, in the electrode manufacturing method of the present invention, the plating conditions for active nickel plating during plating must first be such that no gas generation reaction occurs.

The conditions necessary to prevent the gas generation reaction are, first of all, that the pH of the plating bath be 6 or less, preferably 3 or more and 6 or less. When the pH exceeds 6, the plating reaction occurs in an alkaline region. In order to prevent nickel from forming a precipitate in an alkaline region, a known complexing agent that turns nickel into a complex ion can be added, and nickel that has turned into a complex ion in this way generally has the activity required for precipitation. The plating overvoltage is high, and in that sense, it is possible to obtain uniform plating, but unfortunately, hydrogen gas generation reaction is the main reaction, and only a rough, brittle coating with poor adhesion can be obtained. .

Furthermore, if the pH is less than 3, there is a high possibility that hydrogen gas will be generated due to the increase in acidity, and if the gas generation reaction is to be suppressed, active plating must be performed with an extremely small electric current. The work efficiency of activated nickel plating decreases, leading to increased costs.

For the above reasons, the pH is preferably 6 or less, 9) It is desirable to set the value to 3 or more and 6 or less.

The second condition necessary to prevent the gas-evolving reaction from occurring is the addition of ammonium ions to the plating bath.

Addition of ammonium ions not only suppresses gas generation reactions, but also suppresses dendrite-like precipitation, significantly increasing the covering power and uniform electrodeposition of the plating. The current density range that provides uniform, smooth, and glossy activated nickel plating extends to two orders of magnitude, making it possible to avoid variations in plating current density that occur when plating objects with complex shapes, such as electrolytic baths. Even under uniform conditions, it is possible to provide a uniform, smooth and glossy active plating coating from low current density regions to high current density regions.

Furthermore, the addition of ammonium ions significantly increases the adhesion of the plating film to the base material, providing a strong and durable plating film, and the hydrogen overvoltage of the resulting activated nickel plated electrode is extremely low. Become something. The ammonium ion concentration added to the plating bath is preferably at least 0.5 times the molar concentration relative to the amount of (10) sulfur in the soluble sulfur-containing compound and/or the amount of sacrificial metal in the sacrificial metal salt. 0 If the ammonium ion concentration is less than 0.5 times the molar concentration, the above effect of adding ammonium ions will be insufficient.

Furthermore, the plating bath composition and plating conditions are as follows in order to provide smooth and uniform activated nickel plating without causing any hydrogen gas generation reaction during plating.

The nickel salt may be any soluble salt, and usually one or more of any water-soluble nickel salts such as nickel sulfate, nickel chloride, nickel ammonium sulfate, nickel sulfamate, etc. are used.

The concentration of the nickel salt is preferably used in a range of 0.3 mol or more and 2.0 mol or less. The concentration of nickel salt is 0.3
When the concentration is less than molar, gas generation reactions tend to occur, and in order to suppress this reaction, it is necessary to add a large amount of ammonium ions and to lower the plating current density, which is not practical.

(11) Further, if the concentration exceeds 2.0 molar concentration, problems such as solubility and nickel loss due to liquid loss during operation will occur, which is not preferable.

A soluble sulfur-containing compound and/or a sacrificial metal salt having a potential less noble than nickel is added to the plating bath used in the present invention to provide an active nickel plating exhibiting a low hydrogen overpotential. The soluble sulfur-containing compound used in the plating bath is thiocyanate.

Thiourea means an oxoacid salt with a sulfur oxidation number of 5 or less, and the oxoacid salt with a sulfur oxidation number of 5 or less means, for example, salts of sulfite, 9-bisulfite, thiosulfate, dithionite, etc. do.

The concentration of thiocyanate, thiourea, and oxoacid salts with a sulfur oxidation number of 5 or less to be added to the plating bath is within the range of 0.01 molar concentration or more and 1 molar concentration or less based on the amount of sulfur in the compound. This is desirable.

If the concentration of the sulfur compound is less than 0.01 molar concentration, the hydrogen overvoltage of the resulting nickel plated surface will be insufficiently reduced, and if it exceeds 1.0 molar concentration, the adhesion to the plating film will be poor.

JP-A-17096(4) Sacrificial metal salts having a potential less base than nickel used in plating baths are, for example, salts of zinc, iron, chromium, manganese, etc. These sacrificial metals are Although it eutectoids with nickel on the cathode surface, at least a portion of it is selectively removed by using it in an alkaline solution. The concentration of the sacrificial metal salt used is expressed as the sacrificial metal ion concentration.
0.0 compared to the nickel ion concentration in the nickel ring
It is desirable to use it in a range of 1-fold molar concentration or more and 1.0-fold molar concentration. If the sacrificial metal ion concentration is less than 0.01 times the molar concentration, the hydrogen overvoltage of the resulting nickel plated surface will be insufficiently reduced; If the molar concentration exceeds O times, the adhesion between the base material and the plating film becomes poor.

To provide the electrode of the invention, the current density is 5A/blood2
It is preferable to use the following ranges. If the plating current density exceeds 5 A/ebR2, there is a possibility that a gas generation reaction will occur. In addition, if plating is performed at too low a current density, the plating time required for active nickel plating will increase.
A/dX2 or less is used.

Furthermore, regarding the plating temperature, as the temperature increases, the gas generation reaction tends to be suppressed.
A temperature condition of 80° C. or lower is desirable.

Furthermore, proper stirring during plating is one of the desirable measures to avoid concentration polarization of nickel.

In addition, in order to provide the cathode for electrolysis of the present invention, the substrate may be pretreated by conventional pretreatment methods such as degreasing, pickling, electrolytic cleaning, etching treatment, gelatin treatment, chemical or electrical polishing, etc. , by selecting any pretreatment method. Furthermore,
Providing an appropriate intermediate plating, such as copper plating or nickel plating, between the base material and the nickel plating film of the present invention improves the adhesion of the plating, and as a result, In some cases, the durability and corrosion resistance of the electrode may be further improved, and within the range of not losing the smooth, uniform, and extremely low hydrogen overvoltage characteristics of the nickel-plated surface coating of the present invention (14), These intermediate platings may also be applied.

As described above, in the method of attaching an electrode substrate made of metal to an electrolytic bath made of metal and applying active nickel plating inside the electrode and the electrolytic chamber, the nickel plating bath contains soluble sulfur-containing compounds and/or nickel. Activated nickel plating must be performed under conditions that include a sacrificial metal salt that exhibits a very base potential and ammonium ions, that has a pH of 6 or less, and that the cathode reaction during plating does not involve a gas-generating reaction. This makes it possible to provide an electrode with sufficient durability and extremely high energy efficiency.

Examples will be described below, but the present invention is not limited thereto.

Example 1. Comparative Examples 1 to 3 As in Example 1, a nickel expanded metal (1 m x 1 m size, opening width: 3 mm short axis, long axis s mrtt) was attached to the cathode chamber 2 whose inner surface was made of nickel, and the inside of the cathode chamber, the cathode After normal pretreatment such as degreasing and pickling, the surface was nickel plated (15) using the nickel plating bath shown in Table 1 under the conditions shown in Table 2.

Table 1. Nickel plating bath composition Nickel chloride 1. Omob Power Ammonium Chloride 1.0 Sodium Thiocyanate 0.2 pH4 Table 2. Nickel plating condition bath Temperature: 60°C Current density: 1A/Blood 2 Plating time: 1 hour The resulting nickel plating layer has a uniform, smooth surface with a silvery luster, and the cathode reaction during plating causes gas generation. There were no reactions.

The thus obtained cathode and the cathode chamber were separated into an anode coated with lupium oxide on a titanium lath through a cation exchange membrane,
In combination with an anode chamber and an anode chamber, an electrolytic cell was constructed, and saline solution was electrolyzed under the electrolytic conditions shown in Table 3.

Table 3. Electrolysis conditions; anode chamber NaC4! Concentration 210±5 g#Cathode chamber NaO
H concentration 32-33 wt% Electrolysis temperature 90°C Current density 30 A/blood 2 Distance between positive and negative electrodes Approx. 41 (The cation exchange membrane was pressed against the anode side and fixed in position.) On the other hand, as Comparative Example 1, activated nickel Electrolysis was performed under the same conditions using the electrolytic cell shown in Example 1 without plating.

Further, as Comparative Example 2, only the cathode was subjected to active nickel plating under the conditions shown in Table 19 and Table 2, and then attached to the cathode chamber by welding, and electrolysis of saline water was performed in the same manner as in Example 1.

Furthermore, as Comparative Example 3, ammonium hydroxide was added to the nickel plating bath in Table 1 to adjust the pH to 7, and the same method as in Example 1 was used to apply active nickel plating and electrolysis of saline solution. . At this time, the plating reaction was accompanied by a gas-generating reaction (17).The plating surface was rough, dull, and dull, and some of the openings of the mesh were crushed by the electrodeposit. There were some places.

Table 4 shows the results of the electrolytic voltage of the saline solutions of Example 1 and Comparative Examples 1 to 3.

From the above, it can be seen that Example 1 of the present invention provides a significantly lower electrolytic voltage and has excellent durability compared to Comparative Examples 1 to 3.

Example 2 The cathode and cathode chamber were constructed in the same manner as in Example 1 (18), except that nickel plating was performed using the nickel plating bath shown in Table 5 and under the plating conditions shown in Table 6. , assembled an electrolytic cell.

Table 5. Nickel plating bath composition Nickel chloride 1 mol/g Zinc chloride 0.03 Thiourea 0.1 Ammonium chloride 1 Boric acid 0.5 pH 5 Table 6. Nickel plating conditions Temperature: 60°C Current density: 0.5 A/blood 2 Plating time: 2 hours The resulting nickel-plated cathode was uniform, smooth, and
The cathode reaction during plating was not accompanied by a gas-generating reaction since the surface had a dark luster.

When this electrolytic cell was used to electrolyze saline water under the same conditions as in Table 3, except that the distance between the positive and negative electrodes was changed to two, the value remained almost constant for one month at an electrolytic voltage of 3.08 V. (19) was maintained.

Example 3 5US304 was used in the cathode chamber whose inner surface was made of SUS304.
An expanded metal (size: 1.5 m x 2.4 m, openings are 3 in the short axis and 6 in the long axis) was attached, and the inside of the cathode chamber and the cathode surface were subjected to active nickel plating using the method shown below. .

First, usual pretreatments such as degreasing and pickling are performed. Next, the first base nickel plating was performed using the nickel plating bath shown in Table 7 under the conditions shown in Table 8, and then the first base nickel plating was performed using the nickel plating bath shown in Table 9 under the conditions shown in Table 10. The second base was plated with nickel.

Table 7. Nickel plating bath composition Nickel chloride 1 mol/1 Hydrochloric acid 80 mol/1 Table 8. Nickel plating conditions Temperature Room temperature current density 3 A/&2 Time 5 minutes JP-A-17096 (6) Table 9 Nickel plating bath composition Nickel chloride l, Q movl Ammonium chloride 2.0 moIv1 Table 10. Nickel plating conditions Temperature: 60°C Current density: 2A/djn2 Time: 30 minutes After applying the base nickel plating in this way, using the nickel plating bath shown in Table 11, under the conditions shown in Table 12,
Active nickel plating was performed.

Table 11. Nickel plating bath composition Nickel chloride 1.0 mol/l Ammonium chloride 2.0 Thiourea 0.5 pH 4,5 (21) Table 12. Nickel plating conditions Temperature: 60°C Current density: 2A/djn2 Time: 1 hour The resulting nickel plating coated cathode was uniform and smooth.
The surface had a golden luster, and the cathodic reaction during plating was not accompanied by a gas-generating reaction.

The cathode and cathode chamber obtained in this way were passed through a cation exchange membrane to form an anode made of titanium lath coated with rutinium oxide,
In combination with the anode chamber and an anode chamber, an electrolytic cell was constructed, and saline solution was electrolyzed under the same electrolytic conditions as in Example 2.

As a result, the current efficiency was over 95%, and the electrolytic voltage was 3.0%.
5 V for 100 days indicates a constant value,
It can be seen that the cathode of the present invention has excellent electrolytic properties and durability.

Patent applicant: Toyo Soda Kogyo Co., Ltd.

Claims (1)

[Claims] In this method, an electrode substrate made of metal is attached to an electrolytic bath made of metal, and active nickel plating is applied to the inside of the electrode and electrolytic chamber, in which the nickel plating bath contains soluble sulfur-containing compounds and/or
Or, activated nickel plating is performed under conditions that contain a sacrificial metal salt that exhibits a more base potential than nickel, and ammonium ions, and have a pH of 6 or less, and that the cathode reaction during plating does not involve a gas-generating reaction. A method for manufacturing an electrode characterized by: