JPH0553877B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an electrode for electrolysis, and in particular, uses lead or a lead alloy as a base material, precipitates a noble metal by a chemical substitution method, and then deposits manganese and a lead alloy as a base material. /
Alternatively, the present invention relates to a method for manufacturing an electrolytic electrode coated with a cobalt oxide.

The electrode of the present invention is applicable as an electrode in various electrochemical devices, but is particularly suitable for use as an electrode for industrial electrolysis, for example, as an anode for oxygen generation in a sulfuric acid solution, and has a low This shows oxygen overvoltage characteristics.

[Conventional technology]

As an anode for a sulfuric acid acid electrolysis system, for example, an industrial electrowinning system for zinc, copper, manganese, chromium, cadmium, etc., or a sulfuric acid bath plating system for chromium, etc., lead or a lead-based alloy is used as an oxygen generating anode. It is used.

However, this lead-based anode has poor durability, and its oxygen overvoltage shows an extremely high value of around 1V under normal electrolysis conditions.In particular, with the recent rise in electricity prices, the oxygen overvoltage of lead-based anodes has been There is a strong desire for a reduction in In order to improve this lead-based anode, many proposals have been made to use so-called noble metal sintered coated electrodes, for example, titanium coated with iridium oxide or ruthenium oxide. (For example, JP-A No. 59-200781, etc.) However, these electrodes using titanium as a base material have the problem of passivation of the titanium base material and a considerable amount of precious metal, so the effects obtained are not comparable. Therefore, the cost required for electrode production is high, and there are few examples of practical use in industrial electrolytic systems such as sulfuric acid bath electrowinning systems.

[Problems to be solved by the present invention]

The purpose of the present invention is to create a new low oxygen overvoltage electrode that aims to reduce the high oxygen overvoltage of around 1V exhibited by current lead-based anodes by an economical method without using large amounts of expensive materials such as precious metals. It is about providing.

[Means for solving problems]

As a result of various studies regarding an economical manufacturing method of an electrode that exhibits a low oxygen overvoltage, the present inventors used lead or a lead alloy as a base material to precipitate noble metals by a chemical substitution method, and then deposited precious metals on lead or lead alloys, and then deposited manganese and/or It was discovered that by coating with a cobalt oxide, an electrode that is economical and exhibits a low oxygen overvoltage can be obtained, and the present invention was completed.

The details will be explained below.

As the metal substrate used in the present invention, lead or lead alloy, those used as anodes in conventional industrial electrowinning systems can be used.

The lead alloy means a lead alloy containing, for example, 0.1% to several% of one or more of silver, calcium, tellurium, antimony, thallium, tin, and the like.

These lead or lead alloys are economical materials for oxygen-generating anodes, and like valve metals such as titanium, tantalum, and niobium, they form a strong passive film during continued electrolysis. There is no inconvenience.

In the method of manufacturing the electrode of the present invention, it is necessary to precipitate a noble metal on the lead or lead alloy base material by a chemical substitution method, and then coat it with manganese and/or cobalt oxide.

The chemical substitution method is a method in which lead or a lead alloy is immersed in a solution containing noble metal ions to oxidize and dissolve a portion of the lead on the surface of the base material, and at the same time reduce and precipitate the noble metal. The condition that a solution containing noble metal ions must meet in order to establish the chemical substitution method is that the redox potential of the noble metal ions in the solution must be higher than the redox potential of lead. are platinum, iridium, ruthenium, palladium, silver, gold, etc. ions, and the solution types are nitric acid,
A solution of hydrofluoric acid, boric acid, silicic acid, etc. is preferable. It is sufficient that the concentration of the solution containing noble metal ions is 1 mg/min or more, and the time for chemical substitution is not particularly limited, but it is usually 10 minutes to 24 minutes.
takes place over a period of time.

For example, in a particularly preferred embodiment, a nitric acid solution containing iridium ions as a noble metal ion is desirable, and when lead is immersed for about 30 minutes in a nitric acid solution containing a trace amount of iridium (about 5 mg), a trace amount of iridium is deposited on the surface. do. The obtained sample showed that the number of particles under normal electrolytic conditions was
Although it exhibits an oxygen overpotential that is 100 mV lower, the film obtained by chemical substitution is extremely thin, and therefore, as electrolysis continues for a long time, the film collapses and falls off.
The durability of the electrode is poor.

In the method for manufacturing the electrode of the present invention, it is necessary to deposit a noble metal on lead or a lead alloy by the chemical substitution method described above, and then further coat the lead or lead alloy with an oxide of manganese and/or cobalt. By coating with manganese and/or cobalt oxide, the resulting electrode has excellent durability.

Methods for coating manganese and/or cobalt oxides include wet electrolytic deposition, thermal spraying, pyrolysis coating, CVD, etc., but as an economical and preferred embodiment, wet electrolytic deposition, i.e., Anodic deposition and pyrolytic coating methods are chosen.

The anodic deposition method uses a solution of manganese and/or cobalt salts such as sulfates and nitrates, and a film in which precious metals are deposited by a chemical substitution method is placed on a lead or lead alloy base material as an anode. This is a method in which manganese and/or cobalt oxides are precipitated on the surface by electrolysis.

Regarding the composition of the solution, an aqueous solution containing 0.1 mol/~1 mol/manganese and/or cobalt ions can be used, but the composition should be below neutral, usually PH3.
It can be used within the following range. The current density is
It is preferable to carry out the electrolysis in the range of 0.1 A/dm ² to 10 A/dm ² , and the electrolysis temperature can be carried out in the range of room temperature to 95°C.

As described above, manganese and/or cobalt oxides can be coated on a film in which precious metals are deposited by chemical substitution on a lead or lead alloy base material, but the coating usually contains moisture. Since it is in the state of a lower oxide, it may lack electronic conductivity, and therefore it is desirable to perform heat treatment after anodic deposition. By applying heat treatment, the resulting electrode has good electronic conductivity and excellent durability.

The heat treatment temperature is carried out in the range of 100℃ to 300℃, but if the heat treatment temperature exceeds 300℃, the lead or lead alloy of the base material will melt, and if the temperature is lower than 100℃,
The effect of heat treatment is not visible. The heat treatment time is not particularly limited, but is usually carried out in a range of 30 minutes to 24 hours.

In the method for producing an electrode of the present invention, another preferred embodiment of the method for coating manganese and/or cobalt oxide is a pyrolysis coating method.

The pyrolysis coating method involves depositing precious metals on a lead or lead alloy base material by a chemical substitution method, and further,
On top of this, a solution of salts that can be thermally decomposed at relatively low temperatures, such as manganese and/or cobalt nitrates, is applied.
This is a method of coating manganese and/or cobalt oxides by depositing them by means such as dipping and thermally decomposing them at a temperature of 100°C to 300°C.

The composition of the solution is 0.5mol/~5mol/
An aqueous solution containing manganese ions and/or cobalt ions, such as a nitrate solution, can be used, but an organic solvent such as butanol or isopropanol can also be added thereto. These solutions are deposited on a film in which precious metals are precipitated on lead or lead alloy by chemical displacement method, and then thermally decomposed at a temperature of 100℃ to 300℃, to form a coating on lead or lead alloy substrate. Manganese and/or cobalt oxides can be formed on a film in which a noble metal is deposited by a chemical substitution method. The temperature of thermal decomposition is carried out in the range of 100℃ to 300℃, but if the heat treatment temperature exceeds 300℃, the base material lead or lead alloy will melt, and if the temperature is lower than 100℃, the effect of heat treatment will not be visible. It won't happen. The heat treatment time is not particularly limited, but is usually performed for 30 minutes to 24 hours.

The electrode obtained by the method described above exhibits an oxygen overvoltage several 100 mV lower than that of conventional lead-based anodes under normal industrial electrolysis conditions, and has excellent durability.

[Effects of the present invention]

As described above, in the method of manufacturing the electrode of the present invention, an inexpensive lead or an alloy mainly composed of lead is used as a base material, and a small amount of precious metal is deposited on the base material by a chemical substitution method. Then, by an economical method of coating with manganese and/or cobalt oxides, it is possible to reduce the oxygen overvoltage by several hundred mV, and the industrial value of the present invention is extremely large.

〔Example〕

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

Example 1, Comparative Example 1 A lead base material with an area of 1 cm x 1 cm was used as an electrode base material, and its periphery was covered with a resin. This base material
After performing pretreatment such as degreasing and pickling, it was immersed in a nitric acid solution containing iridium ions shown in Table 1 for 1 hour, and iridium was deposited on the surface by a chemical substitution method. Table 1 Substitution liquid composition IrC ₄ 1 mg 2% HNO ₃ 100 ml Thereafter, manganese dioxide was anodically deposited using the manganese sulfate aqueous solution shown in Table 2.

Table 2 Electrolyte composition and electrolysis conditions Electrolyte composition Electrolysis conditions MnSO ₄ 25g / Current density 1A/dm ² H ₂ SO ₄ 25g / Electrolysis temperature 80℃ Electrolysis time 60 minutes This sample was further heat treated at a temperature of 150℃ for 2 hours. and created an electrode.

In order to measure the oxygen overvoltage characteristics of the obtained electrode, a current-potential curve regarding oxygen evolution in 1MH ₂ SO ₄ was measured. The results are shown in Figure 1. Incidentally, as Comparative Example 1, a graph of a conventional lead anode is also shown in FIG. 1 at the same time.

As is clear from FIG. 1, the electrode obtained according to the present invention exhibits an oxygen overpotential that is 400 to 500 mV lower than that of a conventional lead anode.

Example 2 An electrode was created under the same conditions as in Example 1 using lead with an area of 5 cm x 5 cm as an electrode base material.

To measure the durability of the obtained electrode, 1MH ₂
Water electrolysis was carried out for 7 days at a current density of 10 A/dm ² in SO ₄ and the consumption rate was measured by the weight loss method. The results are shown in Table 3.

For comparison, the consumption rate of conventional lead anodes is also shown in Table 3.
Shown below.

Table 3 Durability of electrode Sample Wearing rate (mg/AH) Invented electrode 0.1 Conventional lead anode 10.5 As is clear from Table 3, the obtained electrode is more than 100 times more durable than the conventional lead anode. ing.

Example 3 A lead alloy (99% lead, 1% silver) with an area of 1 cm x 1 cm was used as an electrode base material, and its periphery was covered with resin.

After performing pretreatment such as degreasing and pickling, this base material was immersed for 30 minutes in a chemical substitution solution of silver nitrate shown in Table 4 to deposit silver on the surface.

Table 4 Substitution liquid composition AgNO ₃ 5 mg 2% HNO ₃ 100 ml Thereafter, an aqueous solution containing cobalt shown in Table 5 was applied and heat treated at a temperature of 200° C. for 1 hour. This coating-heat treatment process was repeated five times to create an electrode.

Table 5 Coating solution composition Cobalt nitrate 50g Isopropanol 50mg Water 50mg The obtained electrode was used as an anode at a current density of 10A/ _{dm2 in 1MH2SO4 ,} and the oxygen evolution potential was measured, and it was 1.6V vs SCE, which was the same as that of the conventional one ^. The oxygen overvoltage was more than 300mV lower than that of lead-based anodes.

[Brief explanation of drawings]

FIG. 1 shows current-potential curves obtained in Example 1 of the present invention and Comparative Example 1. In FIG. 1, (1) represents the curve of the example product of the present invention, and (2) represents the curve of the comparative example product.

Claims (1)

[Scope of Claims] 1. Using lead or a lead-based alloy as a base material, depositing a precious metal on the base material by a chemical substitution method,
A method for manufacturing an electrode for electrolysis, which is then coated with an oxide of manganese and/or cobalt. 2 Using lead or an alloy mainly composed of lead as a base material, depositing a precious metal on the base material by a chemical substitution method, and then depositing manganese and/or cobalt on the film from an aqueous solution containing manganese ions and/or cobalt ions. 1. A method for producing an electrode for electrolysis, which comprises coating an oxide by an anodic deposition method, and then heat-treating at a temperature of 100°C to 300°C. 3 Using lead or an alloy mainly composed of lead as a base material, depositing a precious metal on the base material by a chemical substitution method, and then depositing a solution containing manganese ions and/or cobalt ions on the surface of the film at 100°C.
A method for producing an electrode for electrolysis, characterized in that it is coated with manganese and/or cobalt oxide by thermal decomposition at a temperature of ~300°C.