JPS58185788A - Manufacture of electrode - Google Patents

Abstract

PURPOSE:To obtain an electrode having high performance and durability by immersing an electrode substrate having an Ni or Ni alloy surface in an aqueous soln. of a salt of a bivalent or higher-valent metal which is nobler than the oxidation-reduction potential of a soln. in which the high valence state becomes a low valence state. CONSTITUTION:An electrode substrate having an Ni or Ni alloy surface is immersed in an aqueous soln. of a salt of a bivalent or higher valent metal which is nobler than the oxidation-reduction potential of a soln. in which the high valence state becomes a low valence state. Cupric chloride, ferric chloride, ferric nitrate or the like is used as the metallic salt. The concn. of the metallic salt is adjusted to 20-50g/l, and the pH of the aqueous soln. is adjusted to <=4, especially <=2. The substrate is then covered with an active substance for an electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a novel method for manufacturing electrodes. In particular, this is a method for producing an electrode that exhibits a low hydrogen overvoltage when used as a cathode for electrolysis of aqueous alkali metal halide solutions, water electrolysis, and the like.

Conventionally, many comprehensive electrolysis techniques have been known, and among them, reactions that generate hydrogen by electrolysis of aqueous solutions of alkali metal halides, particularly sodium chloride and potassium chloride, and water electrolysis are widely used in industry. . Therefore, the object of the present invention is to obtain an electrode with low hydrogen overvoltage in such a hydrogen generation reaction.

Conventionally, the above-mentioned electrodes have been made of mild steel, the surface of which has been roughened by pickling, electrolytic etching, plasting, etc., and then coated with an electrode active material. However, when electrolysis is carried out using an electrode that has been subjected to the above electrode activation treatment on mild steel, the better the electrode activity is, the easier the elution of iron, which is the electrode base, is accompanied by a decrease in catalyst activity. In order to prevent this, it is necessary to coat a dense catalyst layer with good adhesion and to use a substrate with corrosion resistance or a substrate with a corrosion-resistant film. Nickel and its alloys are generally known as corrosion-resistant materials in this environment. Therefore, it is conceivable to manufacture a substrate using the above-mentioned material and manufacture an electrode by coating the surface of the substrate with an electrode active substance. However,
When nickel and its alloys are used as electrode substrates, the corrosion resistance of the substrate itself makes it difficult to perform pretreatment such as surface roughening for the purpose of improving adhesion for coating the electrode with active materials, and the adhesion of the active materials may deteriorate. Difficult to secure.

Therefore, the present invention provides an electrode that has a surface made of nickel or an alloy containing nickel as a main component and coats the surface with an active substance, which improves the adhesion of the active substance and further improves the electrode. The present invention provides a method for manufacturing an electrode with good performance and durability.

That is, the present invention provides an electrode substrate having a surface made of nickel or an alloy containing nickel as a main component, which has a valence of 2 or more, and whose solution redox potential from a high valence state to a low valence state is the same. This method of manufacturing an electrode is characterized by immersing the substrate in an aqueous salt solution of a metal that is more negative than the electrode potential of nickel metal in the solution, and then coating the substrate with an electrode active material.

The greatest feature of the present invention is that the electrode substrate is treated with an aqueous solution of the above-mentioned specific metal salt. Thereby, for the subsequent coating of the active substance, any known coating means such as electroplating, coating, or baking can be used without restriction. Among these, a sulfur-containing nickel coating, which will be described later, is a preferred active material.

Conventionally, chemical processing of nickel materials, such as plating ■Culm pretreatment and shiteha example, tG, f i) NHO, -H,5o-
H, PO, +HC.

H3O2, ii) Fe Cffjll, iii>
HN O,+ HC12+ ) 1.01 is known. Although the treatment of the present invention includes treatment with a ferric chloride solution, it is said that conventional electrodes in which a substrate subjected to such treatment is coated with an active substance have extremely low hydrogen overvoltage and long-lasting performance. I have no knowledge at all.

The electrode base having a surface made of nickel or an alloy mainly composed of nickel used in the present invention is not only one in which the base is made of nickel or an alloy mainly composed of nickel, but also other metals such as iron such as plated. It is a general term for materials that have a coating layer of nickel or an alloy mainly composed of nickel on the surface.

What is particularly important in the present invention is that the substrate is immersed in an aqueous solution of a specific metal salt. The metal salts include cupric chloride, ferric chloride, ferric nitrate, ferric sulfate,
The redox potential of chromic chloride, tin chloride, chromic nitrate, etc., which has a valence of 2 or more in an aqueous solution and goes from a high valence state to a low valence state, is the same as that of nickel metal in the solution. Any known material can be used without particular restriction as long as it is higher than the electrode potential.

In order to further enhance the effects of the present invention, it is necessary to control the PH1 temperature 1, metal salt concentration, etc. of the aqueous solution.

Taking COCQ2 as an example of the treatment mechanism of the present invention, copper is CLI/COC(l) in a CC coexistence solution.
form a redox system of a'-'' (n: number of electrons),
Since its reduction potential is nobler than Nl/Nl, it oxidizes and dissolves nickel.

That is, in the present invention, it is sufficient that the redox potential of the metal salt water is more negative than the redox potential of the metal salt aqueous solution and the oxidation potential of nickel in the solution. At this time, the nickel is partially dissolved while maintaining the non-uniform layer of metal crystals on the nickel surface, resulting in an excellent surface roughening suitable for electrodes.

The treatment method of the present invention is generally achieved by immersing the electrode substrate in the metal salt aqueous solution shown above. The pH and temperature of the solution at this time vary depending on the type and concentration of the metal salt used, but generally the metal salt concentration is 5 to 100 (]/
(1, preferably 5 - Sou/(l) using a metal salt aqueous solution with a pH of 4 or less, preferably 2 or less, at room temperature or above, especially 3
The substrate may be immersed at 0 to 60''C for several minutes to several tens of minutes.

The roughness of the surface of the nickel substrate obtained by the above method is about 8 to 15 μ-, but this is different from the rough surface formed simply by mechanical means. It is thought that the effect of the present invention is due to some effect other than simply the effect of surface roughness. Note that the present invention does not preclude the use of conventionally known pretreatment means for metal coating such as plating, such as pickling or metal cleaning treatment, and in some cases, etching treatment such as sandblasting or shotblasting. For example, it is preferable to activate the surface of the substrate in advance with hydrochloric acid.

In the present invention, the means for coating the electrode active material on the substrate treated by the above method is not particularly limited, and any conventionally known means can be applied. For example, JP-A-54-1282
A method of plating a Rodan nickel aqueous solution directly or on an intermediate plating layer such as a copper plating layer, as shown in @ publication, a Ni6-Kel plating bath containing conductive fine particles, as shown in JP-A-56-133484, For example, nickel sulfate - nickel chloride - boric acid - tungsten carbide or nickel sulfate - soda tungstate citric acid - nickel chloride - ammonia water -
A method of electroplating in tungsten carbide, as shown in Japanese Patent Application Laid-Open No. 142883/1983, after plating with a nickel plating bath containing the above-mentioned conductive particles to form a metal plating layer, the cathode active material is dissolved in a solvent. This is coated on a plated electrode substrate, and then a plating layer is formed using a method of thermal decomposition, for example, a sulfuric acid-nickel-nickel chloride-boric acid-tungsten carbide bath, and then coated with chloroplatinic acid on the substrate. A method in which a butanol solution is applied, dried and then heated at a temperature of 50 to 350°C, or a plating bath using a complexing agent (e.g. citric acid) and a sulfur-containing ammonium ion as described in JP-A-55-24970. There is a method of applying nickel plating using a bath, or a method of applying nickel plating using a nickel bath containing ammonium ions added to thiocyanic acid as shown in Japanese Patent Application Laid-open No. 57'-19388@. Among these, cathodes treated using a plating bath containing at least one sulfur-containing compound other than sulfuric acid radicals, such as a Rodan nickel bath, are
When used as a cathode in water electrolysis or alkali metal halide aqueous solution electrolysis, it is preferable because the hydrogen overvoltage is low.

Therefore, it is suitable as a cathode for use in industrial-scale electrolysis of aqueous solutions of alkali metal halides, such as sodium chloride and potassium chloride. In particular, in so-called ion-exchange membrane electrolysis using an ion-exchange membrane as wAl, the cathode has a long life and is preferably used.

The present invention will be described below based on specific examples, but the present invention is not limited to the following examples.

Example 1 A nickel micro-expanded metal (breadth axis 1.5+u+, long axis 3.0I) was placed in a solution having the composition shown in Table 1.
R110,5dm2) was immersed. The surface roughness meter (Tokyo Seimitsu Kichi Surfcom 2
The surface roughness was measured at 00A). The results are shown in Table 1.

The weight reduction rate was determined by the following formula, and in this example, the larger the value, the faster the pretreatment effect and the faster the roughening.

Weight reduction rate (%/Hr) = mold opening reduction amount after immersion for 1 hour When this was electrolyzed (30 A/dmil) at 85° C. in a 28 wt % caustic soda solution using a platinum plate as a cathode and a counter electrode, the results shown in Table 3 were obtained.

Table 2 Example 2 The short axis is 1.5I and the long axis is 3. The 0.56N cathode base material made of Ogi theory's nickel microlas I was used as No. 1 in Table 1.
After surface roughening treatment was performed by the method shown in 6 to 6, nickel-tungsten carbide composite plating was performed using a bath having the composition shown in Table 4. Next, a solution consisting of 1 g of chloroplatinic acid, 111 mQ of salt and 10 m12 of butanol was applied onto the plated electrode substrate, and after drying, it was baked at 350° C. for 1 hour in a nitrogen gas atmosphere. This was repeated 5 times.

This was used as a cathode, and a perfluorinated cation exchange membrane of NeAcepta FC-2000 (manufactured by Tatsu Yamaso, trade name) was used, and 3.5N-purified saline was supplied as an anolyte, and the current density was 30A. /dml and 85° C. to obtain a 28% caustic soda aqueous solution from the cathode chamber. The electrolysis results at this time are shown in Table 5.

Table 4 13 - Table 5 Example 3 After removing rust from a 0.5 dmffi cathode substrate made of expanded metal made of iron (SPCC) with a minor axis of 3 Illll and a major axis of 6 II 1 m, a perchloric acid solution of 40 W [%, 60 ° C. 20 inside
It was immersed for a minute and then etched. Next, nickel plating was performed using a bath having the composition shown in Table 6. Thereafter, after treatment with solutions shown in Nos. 1 to 6 in Table 1 of Example 1, nickel-tungsten carbide composite plating was applied under the same conditions as shown in Table 4 of Example 2, and then plating A solution consisting of 1 g of chloroplatinic acid, 1-0 concentrated hydrochloric acid, and 40 m of butanol was applied onto the prepared electrode base 14, and after drying, it was baked in a nitrogen gas atmosphere for 1 hour, and this process was repeated 5 times. Using this as a cathode, electrolysis was performed under the same conditions as in Example 2 to obtain the results shown in Table 7.

Table 6 4

Claims (1)

[Claims] 1) An electrode substrate having a surface made of nickel or an alloy mainly composed of nickel has a valence of 2 or more, and the redox potential of the solution from the high valence state to the low valence state is the nickel in the solution. 1. A method for producing an electrode, which comprises immersing a substrate in an aqueous salt solution of a metal whose potential is lower than the electrode potential of the metal, and then coating the substrate with an electrode active material.