JPS6092496A - Manufacture of cathode having low hydrogen overvoltage - Google Patents

Abstract

PURPOSE:To manufacture a cathode for electrolysis having low hydrogen overvoltage and usable for a long term by coating a cathode used in the electrolysis of alkali chloride or water with an Ni-S layer having superior adhesive strength by plating in a plating bath having a specified composition. CONSTITUTION:A cathode used in a cell for electrolyzing an aqueous NaCl soln. or water is coated with an Ni-S film contg. S bonded to Ni as the base by plating in a plating bath. This plating bath contains 0.05-0.4mol/l (expressed in terms of Ni) water soluble Ni compound such as nickel chloride, 0.001-0.05mol/ lthioglycolic acid, its Na salt, K salt or ester as S source and 0.2-1.2mol/l pyrophosphoric acid, its Na salt or K salt. The Ni-S film formed by plating has superior adhesive strength and is not stripped, and a cathode having low hydrogen overvoltage is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a low hydrogen overvoltage cathode suitable for use in electrolysis of aqueous alkali chloride solutions or water electrolysis.

Traditionally, the technology used to generate hydrogen gas at the cathode was [, diaphragm (
Electrolysis of an aqueous solution of prucari metal salts using a porous 8:F diaphragm such as asbestos and a dense diaphragm of an ion exchange membrane is known, and water electrolysis is also effective.

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 of reducing the electrolysis voltage.

Such active cathodes are typically made by thermally spraying, pyrolyzing, or melting a layer of an active metal material with reduced hydrogen overvoltage characteristics onto the surface of an alkali-resistant substrate such as iron, copper, nickel, alloys containing these, or pulp metal. It can be obtained by coating by means such as dipping, electroplating, chemical plating, vapor deposition, explosion bonding, etc.

Nickel is the main metal contained in the base material of such an active cathode, and so-called nickel-sulfur plating, in which sulfur is bonded to this metal, is known. It is relatively frequently used in electrolysis, etc.

However, such cathodes with nickel-sulfur plating have problems with the adhesion of the plating, and the drawbacks are that the surface peels off due to hydrogen generation over a relatively long period of time, and the plating components elute into the liquid. ing.

The present inventors have developed a new nickel-sulfur plated cathode! The invention was completed as a result of experimental research on the surface of a base material, and when producing a low hydrogen overvoltage cathode by electroplating the surface of a base material, it is possible to use plated gold, its ester, and pyrophosphoric acid or its salt. This is a method for producing a low hydrogen overvoltage cathode that specifically relies on the use of a plating bath containing.

As the cathode substrate used in the method of the present invention, the known materials mentioned above can be used, and the shape thereof is not particularly limited.

Conventionally, additives that precipitate sulfur during plating include thiourea, thiocyanate, thiosulfate, thioglycolic acid or its salts, and sodium sulfite, but in the present invention, The plating metal consists mainly of nickel, which causes the plating to form.
At that time, it is essential that thioglycolic acid, its salt, or its ester as the above-mentioned sulfur-containing compound be present in the plating bath, and also pyrophosphoric acid or its salt be blended.

Although it is unclear how a bath containing a heating component exerts its effects, the use of such a bath does not impair the excellent low hydrogen overvoltage properties of nickel-sulfur plating. (It is possible to significantly improve plating adhesion and obtain a long-life cathode.

A more specific explanation of the plating bath in the present invention is as follows.

First, the main metal component to be deposited on the cathode base material is nickel, and its concentration is 0.05 to Q, 4 mol/l.
A small amount of metal other than nickel may be added to a desired degree.

The amount is 1 to 40% by weight based on nickel, but depending on the type of precipitated metal, even this range may exceed the amount of Ni precipitated, so the corrosion resistance of Ni becomes significantly worse. In the case of the present invention, as the sulfur-precipitating compound other than Ni, it is essential to use thioglycolic acid or a salt or ester as described above.As the salt or ester of 6° thioglycolic acid, sodium thioglycolate is used. , potassium, and ammonium, methyl thioglycolate, ethyl, and the like.

The preferred range of these concentrations is 0.001 to 0.05 m
o l/l, and if the concentration is low, the hydrogen overvoltage will not decrease, and if the concentration is high, the corrosion resistance will deteriorate, so this range is desirable.

On the other hand, as a salt of pyrophosphate, sodium pyrophosphate,
(N a4 ”t Oy ) Potassium birophosphate (K4
PtOt), disodium dihydrogen pyrroliate (Na, H
.

Pt0y> Dipotassium dihydrogen pyrophosphate (Kt Ht
Pt0J trisodium pyrophosphate-hydrogen (N a s
HP! 0? ), tripotassium hydrogen pyrophosphate (K
s HPt Or ) Nickel pyrophosphate (NiyPt
Oy), etc.

The concentration of pyrophosphoric acid and its salts is 0.2-1.2 mol
/l is desirable in order to obtain a plated product with good adhesion.

The pH of the plating bath is preferably in the range of 8 to 11, and the pH is preferably adjusted using sodium chloride or hydrochloric acid.

Although there is no particular restriction on the plating temperature, a temperature of 20 to 60° C. is practical, as temperatures exceeding 80° C. cause rapid deterioration of the bath, and temperatures lower than 90° C. require time and effort to adjust the bath. - The plating current density is in the range of 0.1 to 10 A/dtrt, and if the current density is too high, the adhesion tends to deteriorate.

Particularly good plated products can be obtained by performing nickel-sulfur plating using a birophosphoric acid bath within the range described above.

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

Example 1 Expanded metal (12LW) made of stainless steel (8US310S) was used as the cathode substrate.
X68WX1.5TX2W; Unit: LW is the length of the mesh in the longitudinal direction, SW is the length of the mesh in the lateral direction, T is the thickness, and W is the width of the cut. The current density is 2A/d on the surface of
2 hours of nickel plating was used.

2 under the conditions of Example 10 in Table 11C on this cathode base material.
Plating was performed for A/dm"
Hydrogen generation (referred to as high temperature hydrogen generation) was performed at 0° C. at 20 A/dm'×20 hr.

After that, as a result of analyzing the eluted nickel content in the solution, it was found that 18
It was ppm.

In addition, the same cathode as above was installed in a 1 di" electrolytic cell under the conditions shown in Table 2 and operated for 20 days. The average saving voltage (voltage difference from the reference cell) for the last 5 days was 0. 16V
Met. (The reference cell is 80S504 for both the cathode and cathode chamber.
It was used. ) Example 2 Plating was performed on the same substrate for 3 Al'm'' x 40 minutes under the conditions of Example 20 in Table 1.The amount of Ni eluted after high-temperature hydrogen generation conducted in the same manner as in Example 1 was 2. When I did a 5 ppm conversion and checked the average saving voltage for the last 5 days, it was 0.
．． It was 15V.

Example 3 Plating was carried out at 2^/dm" x 60 minutes under the conditions of Example 30 in Table 1. The amount of H1 eluted after high-temperature hydrogen generation. As a result of operation in the same manner as in Example 1, the saving voltage was 0. 16
It was V.

Patent applicant name Toagosei Chemical Industry Co., Ltd.

Claims (1)

[Claims] t When manufacturing a low hydrogen overvoltage cathode by electroplating the surface of a base material, the plating metal component contains a metal mainly composed of nickel, and the bath contains thioglycolic acid or its salt or its ester, and pyrophosphoric acid. or a salt thereof.