JPS5832234B2 - Manufacturing method of cathode electrode for electrolysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a cathode electrode for electrolysis, and more particularly to a method for manufacturing a cathode electrode for generating hydrogen in water electrolysis or salt electrolysis.

Metal materials selected from low carbon steel, iron, titanium, nickel, chromium, and alloys of these metals have long been available as cathode materials for electrolysis of aqueous alkaline solutions.

In the past, the metal materials mentioned above in the form of perforated plates or meshes were used as cathodes, but in recent years more and more severe conditions have been required to increase electrolytic efficiency, resulting in high current densities and high temperatures, which has caused the surface of these electrode materials to deteriorate. There is a tendency to use cathodes coated with various metals or alloys thereof, or surface enlarged cathodes with a large working surface area.

For example, by coating with a noble metal catalyst such as platinum,
It has the advantage that the cathode potential can be lowered compared to conventionally used cathode electrodes.

However, noble metal catalysts are expensive and have unavoidable economic disadvantages.

The use of cobalt and molybdenum double oxides as electrode catalysts has also been proposed.

At the beginning of electrolysis, this electrode was placed at a temperature of 70°C and a current density of 1.00 A7'di, at a temperature of 1182 m with respect to the reversible hydrogen electrode.
It has a low cathode potential of V.

However, if the electrode is left immersed in an alkaline solution without electricity flowing into the electrolytic cell for a long period of time, there is a drawback that the activity of the electrode is substantially reduced.

In view of the current situation, the present inventors have been conducting research on cathode electrodes for electrolysis that have a low cathode potential and can maintain their activity over a long period of time.

In this study it was found that nickel-molybdenum alloy has a low cathodic potential.

Based on this discovery, the present invention was finally completed as a result of searching for a method for strongly coating nickel electrodes (including surface enlarged nickel electrodes) with nickel-molybdenum alloy. The electrode is heated in an oxidizing atmosphere to generate nickel oxide on the surface, then treated with a molybdenum salt solution or a mixed solution of molybdenum salt and nickel salt, and then heated in a reducing atmosphere. The present invention relates to a method of manufacturing a cathode electrode for electrolysis.

According to the research of the present inventor, nickel is deposited on the nickel electrode.
When coating molybdenum, if nickel is replaced with an oxide and then coated with molybdenum salt or molybdenum salt and nickel salt and then reduced, the nickel-molybdenum alloy can be firmly coated on the nickel electrode. It became clear.

More specifically, even if a molybdenum salt is applied directly onto a nickel electrode and heated in a reducing atmosphere, the base nickel and molybdenum will not be uniformly wetted, and the molybdenum that flows and precipitates during evaporation will be unevenly distributed.

However, the inventor's research has revealed that if the nickel electrode is heated in an oxidizing atmosphere beforehand to form an oxide, it has a greater affinity with molybdenum and a nickel-molybdenum alloy is precipitated uniformly and thinly. be.

In the present invention, the nickel-based electrode is fired at 900° C. or higher in an atmosphere containing oxygen to once form an oxide film.

This oxide film is porous, and the molybdenum salt solution or molybdenum salt/nickel salt solution is uniformly wetted and impregnated to the inside.

Next, metallic molybdenum is precipitated on the nickel surface by reduction treatment at 300 to 600° C. in a hydrogen stream, and simultaneously reacts with nickel to form a strong nickel-molybdenum alloy layer.

Therefore, a stronger bonding layer is formed than when deposited directly on the nickel electrode.

The nickel electrode of the base used in the present invention is as follows:
Surface-enlarged nickel electrodes are preferred, although perforated plates or nets can also be used.

As the surface enlarged nickel electrode, any of the conventionally known ones can be effectively used, and examples include those manufactured by sintering, elution, thermal spray coating, etc.

More specifically, there is a method in which foamed nickel is used as a base and finely powdered nickel is sprinkled on the base and sintered, a method in which a nickel alloy is coated by plating or the like and other components are removed by an elution method,
Another example is one manufactured by coating a nickel-aluminum alloy by plasma spraying or the like and then developing it with an alkali to obtain an active layer.

These base nickel electrodes are heated at a temperature of 900°C or higher and lower than the melting temperature, preferably 900°C or higher, in air or a mixed gas containing oxygen.
When heated at 1100° C., a Ni0 layer is formed on the surface.

At temperatures below 900° C., it is difficult to form oxides.

In the present invention, the material is then treated with a molybdenum salt solution or a mixed solution of a molybdenum salt and a nickel salt.

As the molybdenum salt, water-soluble salts such as chlorides, sulfates, and ammonium salts can be used, and ammonium molybdate is particularly preferred.

Further, as the nickel salt, water-soluble salts such as chloride, sulfate, and nitrate can be used.

These salts are usually used as an aqueous solution or a solution separately dissolved in aqueous ammonia.

The amount of molybdenum salt to be contained in such a solution is not particularly limited and can be appropriately selected within a wide range, but the molybdenum salt is usually mixed so that the concentration is about 0.02 to 0.1 molar. It is better to do so.

The amount of nickel salt to be contained in the solution is not particularly limited and can be appropriately selected within a wide range, but usually the nickel-molybdenum alloy formed on the nickel electrode by the treatment described below is : It is preferable to mix nickel salt into the above solution so that the alloy composition becomes 1.

For example, it is preferable to mix the nickel salt so that the concentration is about 0.01 to 0.4 molar.

In the present invention, it is preferable to treat with a molybdenum salt solution from the viewpoint of workability and the like.

Treatment with a molybdenum salt solution or a mixed solution of molybdenum salt and nickel salt is usually carried out by coating or spraying at around room temperature, but in order to increase the impregnation concentration on the electrode surface, the electrode is heated and then sprayed. A method of spraying is also used.

Next, it is heated and reduced in hydrogen or a mixed gas of hydrogen and an inert gas.

Reduction temperature is 300-600℃, preferably 400-50℃
It is 0°C.

At temperatures above 600°C, sintering progresses and the enlarged surface tends to shrink.

The reduction treatment is usually carried out for 1 to 3 hours. In this reduction process, molybdenum salts, nickel salts, and nickel oxides are completely reduced to metals, and a nickel-molybdenum alloy coated electrode with a large surface area is obtained.

In the electrode of the present invention, nickel is made into an oxide, and then impregnated with a molybdenum salt solution or a mixed solution of molybdenum salt and nickel salt, and heated in a reducing atmosphere. Molybdenum and the like are uniformly precipitated on the nickel surface and simultaneously react with the nickel to form a nickel-molybdenum alloy to form a strong film.

For this reason, it has the property of being able to withstand use for an extremely long period of time.

The present invention will be specifically explained below with reference to several examples.

Example 1 A nickel-aluminum alloy (weight ratio Ni/M! = 4/1) was applied to the surface of a foamed nickel (manufactured by Sumitomo Electric Industries, Ltd., "Serumets T-/1621") of 80 mm diameter and 5 rrunt.
) was coated uniformly to a thickness of 10 to 100 μm using a plasma spraying method, and aluminum was eluted with a 30% KOH aqueous solution at room temperature to 400 G to create a surface enlarged electrode.

This electrode was fired at 1000° C. for 1 hour in an air atmosphere to generate NiO on the surface.

Next, aqueous ammonia (28φ
) The above baked product was sufficiently immersed in a solution to which 5 ml of 5 ml of the above-mentioned material had been added to impregnate it, and then transferred to a hydrogen atmosphere furnace and subjected to a reduction treatment at 400° C. for 1 hour.

Performance evaluation of the electrode thus obtained was performed using the following electrolysis device.

That is, a nickel flange (150 mmφ x 15 mm
C) Using two sheets, a test electrode (cathode and anode) and a diaphragm were sandwiched between Aflas (manufactured by Asahi Glass Co., Ltd., fluororubber) backing to assemble a cell.

The electrolytic solution was configured to flow from the bottom of the cell between the electrodes or between the electrodes and the diaphragm and be discharged from the top.

As the diaphragm, a composite material membrane (effective resistance 0.28 Ω-1, 25° C.) consisting of perforated Teflon filled with potassium titanate was used.

And 21 which doubles as a nickel gas-liquid separator and bath liquid storage tank.
A heater was attached to the container containing the contents, allowing the temperature to be adjusted from room temperature to 110°C.

The electrolytic solution was a 30% KOH aqueous solution, which was circulated through the electrolytic cell at a rate of 0.5 to 11 min.

For electrolysis, a current was passed through the nickel terminal plate, and after a break-in operation at 20 A/di for about 5 hours, the relationship between current density and sliding voltage at a constant temperature was determined.

The results are shown in FIG.

Figure 1 shows a flat nickel electrode, B shows an enlarged surface electrode, and C shows a flat nickel electrode.
represents the electrode of the present invention.

Example 2 Carbonyl decomposed nickel (approximately 5μ) was made into a paste with carboxymethyl cellulose to the same foamed nickel as in Example 1, and the mixture was mixed with 0.02 to 0.0% per gram of nickel.
Apply it evenly to a total weight of 2g, and apply it at 1000 g in a hydrogen stream.
℃ for 30 minutes to create a base electrode.

This electrode was fired in air at 1000'C for 1 hour to form an oxide layer on the surface, and then treated in the same manner as in Example 1 to deposit a nickel-molybdenum alloy layer.

Comparative Example 1 In Example 2 above, the base electrode was immersed in a molybdenum salt solution without any oxidation treatment, and the same treatment was carried out thereafter.

The results of comparing the performance using the same apparatus as in Example 1 are shown in FIG.

An electrode made of sintered carbonyl-decomposed nickel (D in the figure) and an electrode made by impregnating it with molybdenum and reducing it (E in the figure)
Almost the same values were obtained, indicating that the nickel-molybdenum alloy layer was not uniformly coated.

On the other hand, the electrode according to the present invention (F in the figure) is the above two types of electrodes (
It showed a lower cathode potential than D and E).

Example 3 20 ml of ammonia water (28%) was added to a mixed solution of 501 rL of an aqueous solution in which ammonium molybdate was dissolved at a 1/30 molar concentration and 50 ml of an aqueous solution in which nickel nitrate was dissolved at a 0.2 molar concentration, and the above solution was added. The base electrode subjected to the oxidation treatment in Example 2 was immersed, and thereafter treated in the same manner as in Example 1.

The performance of the electrode thus obtained was comparable to that of the electrode obtained in Example 2.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between sliding voltage and current density when water is electrolyzed using three types of electrodes, and Figure 2 is a graph showing the relationship between sliding voltage and current density when water is electrolyzed using three types of electrodes. It is a graph which shows the relationship between and current density.

Claims (1)

[Claims] 1. A nickel electrode is heated in an oxidizing atmosphere to generate nickel oxide on the surface, then treated with a molybdenum salt solution or a mixed solution of molybdenum salt and nickel salt, and then heated in a reducing atmosphere. 1. A method for producing a cathode electrode for electrolysis, the method comprising heating the cathode electrode by heating the cathode electrode. 2. The method according to claim 1, wherein the nickel electrode is a surface enlarged nickel electrode.