JPH0633487B2 - Method of manufacturing cathode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a cathode having a low hydrogen overvoltage and excellent durability, and particularly to a method for producing a cathode suitable for diaphragm electrolysis of an aqueous sodium chloride solution. To do.

[Prior Art] Conventionally, the electrolysis of an aqueous solution of an alkali metal, in particular, the development of a technique for obtaining chlorine and sodium hydroxide by the electrolysis of an aqueous solution of sodium chloride by an ion exchange membrane method has progressed, and electrolysis with an increasingly high current efficiency and a low voltage, That is, the power consumption rate is being improved. Among these technological trends, the improvement of current efficiency is mainly due to the improvement of the ion exchange membrane, and regarding the voltage reduction, in parallel with the improvement of the ion exchange membrane, studies are underway to reduce the overvoltage during electrolysis at the electrodes. It is being appreciated. Of these, various excellent proposals have already been made for the anode, and an electrode in which the anode overvoltage is hardly a problem is industrially used.

[Problems to be solved by the invention]

However, as a cathode, that is, an electrode for hydrogen generation, one made of soft iron or nickel is generally used industrially, and since a high hydrogen overvoltage of, for example, about 400 millivolts is allowed, there is a need for improvement. It has been pointed out.

In recent years, various patent applications have been made for the purpose of reducing hydrogen overvoltage. For example, JP-A-55-164491,
JP-A-55-131188, JP-A-56-93885
In the electrode shown in Japanese Patent Laid-Open No. 58-167788, particles of nickel, cobalt, iron or the like or alloy particles of these metals and aluminum or other metals are welded or deposited on the electrode base. An electrode of fine particle fixed type, which is made to be partially exposed in a metal layer for holding silver, zinc, magnesium, tin or the like so as to be exposed, and in some cases, chemically erodes a part of the metal layer for holding to make it porous, Alternatively, as in JP-A-54-60293, there has been proposed a hydrogen generating electrode in which a hydrogen overvoltage is reduced by an electrodeposition method of an active metal in which a plating bath containing a sulfur-containing nickel salt is used to electroplate. ing.

Although it is possible to obtain a cathode having a relatively small hydrogen overvoltage by these proposals, there is a need for various improvements such as a smaller overvoltage, a longer sustainability of the cathode performance, and a lower cost. . For example, in the case of the fine particle fixed type electrode, the fine particle metal itself is expensive, its preparation is not easy, etc., and in addition, the production method is generally complicated and the performance of the obtained electrode is likely to vary. Performance tends to lack. Further, in the latter electroplating with a sulfur-containing nickel bath, it is difficult to sufficiently reduce the hydrogen overvoltage, and in some cases, there are drawbacks such as low durability.

On the other hand, as another method, a method has been proposed in which a substrate made of, for example, nickel, iron, or an alloy thereof is surface-treated by etching, sand plast, or the like. However, since the substrate based on these methods was not originally manufactured for use as a cathode (catalyst), hydrogen overvoltage cannot be sufficiently reduced by the above-mentioned mechanical surface treatment, and the durability is also low. There was also a problem with sex.

Therefore, an object of the present invention is to use a relatively inexpensive raw material, have a high mechanical strength, and have a low hydrogen overvoltage, for example, a hydrogen overvoltage of 20 A / dm ^{2 at} a current density of 20 A / dm ^2.
The present invention provides a method for producing a cathode, which is 0 mV or less, particularly 150 mV or less, and the performance of which can be stably used for a long period of time.

[Means for solving problems]

In order to achieve the above object, the present invention is a cathode in which a porous material is formed on an electrode substrate and then an active material layer made of an alloy of nickel and chromium having a specific chromium content is sinter-coated. That is, according to the present invention, after forming a porous material layer on an electrode substrate, it is composed of at least nickel and chromium in a reducing atmosphere, and chromium is 16 to 65 wt% of nickel and chromium based on the weight of nickel and chromium. The method for producing a cathode is characterized in that an active material made of the alloy of (1) is coated by sintering.

The electrode substrate used in the present invention may be a conductive substance, and is generally made of a metal that is durable as a cathode and is used as a cathode. Therefore, when used for the electrolysis of alkali metal salts, especially alkali metal halides or the electrolysis of water, it is preferable to use soft iron or nickel as the electrode substrate. However, a highly conductive metal such as copper or a copper alloy, and titanium in some cases can be used.

The shape of the electrode is determined by the shape of the electrode substrate and is not particularly limited in the present invention, and the shape generally used as the cathode in the electrolytic cell is used. For example, it may be a flat plate, a net, a punched metal, an expanded metal, or a scalloped shape. The electrode substrate is
Prior to forming the porous material layer on the surface, it is preferable to perform pretreatment such as degreasing and etching. As the method, a known method can be used without particular limitation.

In the present invention, as a method for forming the porous substance layer on the surface of the electrode substrate, generally, a method in which a metal plating layer containing conductive particles is present is preferably used. For example, as described in JP-A-56-133484, a method of electroplating using a metal plating bath containing conductive particles can be adopted.

The conductive particles may be particles having conductivity and durability. For example, chromium, molybdenum, tungsten, vanadium, niobium, tantalum, iron, cobalt, nickel,
Fine metal particles such as gold and silver; tungsten carbide, silicon carbide, boron carbide, zirconium carbide, titanium carbide, hafnium carbide, niobium carbide, tantalum carbide, graphite, vanadium carbide and other carbides; iron boride, nickel boride Such as boride; nitride such as vanadium nitride, niobium nitride, titanium nitride, etc., particularly preferably tungsten carbide, having a particle size of 0.05 to
It is preferably 50 μm, and particularly preferably 0.5 to 5 μm.

As the metal plating bath, conventionally known plating baths can be used without any particular limitation. Particularly, a plating bath made of a Group VIII metal of the 4th period of the periodic table such as silver, nickel, iron or cobalt is preferable. A watt bath, a nickel black bath, a nickel complex salt bath or the like is used, and a silver plating bath is a cyan bath or the like.

The plating conditions using the above plating bath may be appropriately selected, but generally 1 to 100 conductive particles are contained in the metal plating bath.
It is preferable to select the plating conditions such that the content of the conductive particles in the obtained plated layer on the electrode substrate is 2 to 30% by volume in the state of being suspended at a concentration of g /. By doing so, a porous material layer having irregularities is formed on the surface of the electrode substrate, and the porous material layer not only increases the surface area of the electrode, but also facilitates the impregnation of a cathode material described later, The effect that the substances are tightly bound,
Further, it also has an effect of suppressing crystal growth of the active substance.

The method of forming the porous substance layer on the electrode substrate is not particularly limited to the above-mentioned plating method, and in addition, the conductive particles may be fixed on the electrode substrate by means such as thermal spraying. At this time, the thickness of the porous material layer is not particularly limited, but in order to obtain a cathode with a lower hydrogen overvoltage, at least it should be thicker than the thickness of the active layer obtained by sintering and coating the active material described below. is necessary.

In the present invention, the alloy layer containing nickel and chromium, which are active substances, present on the surface of the electrode substrate in a specific ratio does not necessarily cover the entire surface of the electrode substrate, but it is necessary to increase the effective area of the electrode. It is advantageous to cover the entire surface. When the electrode substrate is made of, for example, copper and may itself be corroded under the environment where the cathode is used, the entire surface of the substrate (the entire surface immersed in the solution) should be covered. . Further, in the present invention, the composition of the active substance present on the surface of the electrode substrate has a very important meaning for hydrogen overvoltage. That is, the active substance is an alloy of at least nickel and chromium, but it is also effective to add nickel and chromium, and optionally a third component for increasing the surface area. Further, it is possible to include other elements or compounds which are inevitably mixed in. The ratio of nickel (Ni) and chromium (Cr) in the active substance, that is, Should be in the range of 16 to 65% by weight, preferably 20 to 60% by weight. If the chromium content deviates from this range, the hydrogen overvoltage will increase.

The method of sinter-coating the active substance consisting of the above-mentioned specific alloy on the electrode substrate is carried out by nickel or chromium in the form of a compound such as chloride, bromide, iodide or a solvent such as ethanol or butanol in the form of formate or nitrate. Generally, it is dissolved in a concentration of 0.5 to 15% by weight, a solution of the cathode active material is coated on the plated electrode substrate, and then pyrolysis is performed. The method for coating the cathode active substance solution is not particularly limited, and a method such as spraying, coating, dipping or the like is used. The thermal decomposition condition is generally 200 to 8 in an inert gas or reducing atmosphere for the electrode substrate coated with the cathode active material solution.
The particular nickel-chromium alloy is sintered by heating at a temperature of 00 ° C. for 15 minutes to 3 hours. Even after the thermal decomposition, it is preferable to maintain the substrate in an inert gas or reducing atmosphere until the temperature of the substrate becomes 100 ° C. or less. Pyrolysis in an oxidizing atmosphere is not preferable because it causes deterioration in performance.

In the present invention, the thickness of the active layer formed by sintering the cathode active material is 0.01 to 20 μm, preferably 0.1 to 20 μm.
In general, coating and thermal decomposition are repeated to obtain 3μ.

[Action and effect]

The cathode of the present invention has a chromium content of 16 to 65 wt% after a porous material layer is formed on the surface of an electrode substrate made of a conductive material, preferably iron, nickel or an alloy containing one of these metals as a component. % Nickel-chromium gold to form an active layer, resulting in an extremely low hydrogen overvoltage,
For example, it is possible to set the hydrogen overvoltage to 100 mV at a current density of 30 A / dm ² in 90 ° C. and 11 N—NaOH. Although the reason why such an effect is produced is not always clear, by mixing chromium with nickel,
It is estimated that hydrogen overvoltage is reduced when it is used as a cathode because it improves the catalytic ability that causes distortion in crystals and / or the underlying porous material layer increases the dispersity of the above-mentioned catalyst particles. .

〔Example〕

 Examples of the present invention will be shown below.

Example 1 A degreased and etched mild steel expanded metal (SW: 3 mm, LW: 6 mm, plate thickness: 1.5 mm) was subjected to a dispersion plating bath shown in Table 1 according to JP-A-56-133484 to obtain 5 A / It was plated with dm ² for 5 minutes. This thus treated on a substrate, NiCl ₂ · 6H
A butanol solution in which ₂ O and CrCl ₃ .6H ₂ O were dissolved was applied so that the sum of supported amounts of nickel and chromium was 1.7 mg / cm ² in five thermal decompositions in all the examples.
Pyrolysis was performed in a nitrogen gas (N ₂ ) atmosphere at a temperature of 330 ° C. while changing the chromium content in various ways. The hydrogen overvoltage of the thus-obtained electrode was measured at 90 ° C. in 11N-NaOH at a current density of 30 A / dm ² . The results are shown in Table 2.

Example 2 The same as Example 1 except that the firing temperature was 430 ° C. The results are shown in Table 3.

Comparative Example 1 The hydrogen overvoltage was 200 mV when the same as in Example 1 except that the Cr content in the Ni—Cr alloy was 5 wt%.

Comparative Examples 2 to 4 The same procedure as in Example 2 was performed except that the Cr content in the Ni-Cr alloy was 5 wt%, 70 wt%, and 80 wt%. The results are shown in Table 4.

Comparative Examples 5 to 9 Comparative Examples 5 to 9 were performed in the same manner as in Example 2 except that dispersion plating containing tungsten carbide was not performed. The results are shown in Table 5.

Comparative Examples 10 to 12 Comparative Examples 10 to 12 were performed in the same manner as in Example 2 except that firing was performed in air. The results are shown in Table 6.

Example 3 Table 7 shows the results obtained in the same manner as in Example 2 except that the firing was performed in a hydrogen atmosphere.

Claims (2)

[Claims] 1. After forming a porous material layer on an electrode substrate,
Consists of at least nickel and chromium in a reducing atmosphere,
And a method for producing a cathode, characterized in that chromium is sintered and coated with an active material consisting of an alloy of nickel and chromium in an amount of 16 to 65% by weight based on the weight of nickel and chromium. 2. The method for producing a cathode according to claim 1, wherein the porous material layer is a metal plating layer containing conductive particles.