JPS61217591A - Production of cathode - Google Patents

Abstract

PURPOSE:To lower the hydrogen overvoltage of the resulting cathode and to improve the durability by forming a porous metallic layer on a substrate for an electrode and coating the layer with an active substance made of a prescribed Ni-Cr alloy by sintering. CONSTITUTION:A porous metallic layer contg. electrically conductive particles is formed on a substrate for an electrode by plating. A soln. prepd. by dissolving NiCl2.6H2O and CrCl3.6H2O in butanol is applied to the layer and the compounds are thermally decomposed to coat the layer with an active substance made of an Ni-Cr alloy contg. 16-65wt% Cr.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a cathode with low hydrogen overvoltage and excellent durability, and particularly provides a method for producing a cathode suitable for diaphragm electrolysis of an aqueous sodium chloride solution. It is something to do.

[Conventional technology]

Conventionally, the development of technologies for obtaining chlorine and sodium hydroxide through the electrolysis of aqueous alkali metal salt solutions, especially the electrolysis of sodium chloride aqueous solutions using ion-exchange membrane methods, has progressed, and electrolysis with higher current efficiency and lower voltage, that is, electric power consumption, has progressed. Improvements are being made. Among these technological trends, the improvement of current efficiency is mainly due to improvements in ion-exchange membranes, and the reduction in voltage is being studied to reduce overvoltage during electrolysis at electrodes in parallel with improvements to ion-exchange membranes. It is being said. Among these, various excellent proposals have already been made for anodes, and electrodes in which -1 anode overvoltage is not a problem are used industrially.

[Problem that the invention seeks to solve]

However, as for the cathode, that is, the electrode for hydrogen generation, those made of soft iron or nickel are generally used industrially and have failed, allowing a high hydrogen overvoltage of, for example, 400 mIJ volts, so there is no need to improve this. The necessity has been pointed out.

In recent years, various patent applications have been filed for the purpose of reducing hydrogen overvoltage. For example, JP-A-55-164491,
JP-A-55-131188, JP-A-56-95885
In the case of the electrode shown in Japanese Patent Laid-Open No. 58-167788, nickel and cobalt are used on the electrode base.

Particles such as silver or particles of alloys of these metals and aluminum or other metals are welded or buried in a holding metal layer such as silver, zinc, magnesium, tin, etc. so that a portion is exposed, and in some cases, they are held. Electrodes with fixed fine particles in which a part of the metal layer is chemically eroded to make them porous, or a plating bath containing a sulfur-containing nickel salt as in Japanese Patent Application Laid-open No. 54-60293, are used to form electrically conductive electrodes on the electrode substrate. A hydrogen-generating electrode has been proposed in which the hydrogen overvoltage is reduced by the active metal electrodeposition method used for plating.

Although it is possible to obtain a cathode with a relatively small hydrogen overvoltage through these proposals, there is a need for various improvements such as lower overvoltage, greater sustainability of cathode performance, or lower cost. . For example, in the case of the above-mentioned fine particle fixed electrode, the fine particle metal itself is expensive, it is not easy to prepare, and the manufacturing method is generally complicated, and the performance of the resulting electrode product may vary. They tend to lack performance stability. Furthermore, in the latter electroplating using 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, other methods such as nickel.

Methods have been proposed in which a substrate made of iron or an alloy thereof is surface-treated by etching, sandblasting, or the like. However, since the substrates based on these methods were not originally manufactured for use as cathodes (catalysts), the mechanical surface treatments described above cannot sufficiently reduce the hydrogen overvoltage, and the durability is limited. There were also problems with sexuality.

Therefore, the object of the present invention is to use relatively inexpensive raw materials, have high mechanical strength, and further have a low hydrogen overvoltage, for example, at a current density of 30A/a-, the hydrogen overvoltage is 20
The object of the present invention is to provide a method for producing a cathode which has a voltage of 0 mV or less, particularly 150 mV or less, and which can be stably used for a long period of time.

[Means for solving problems]

To achieve the above object, the present invention provides a cathode in which a porous material layer is formed on a nickel and electrode substrate, and then an active layer made of a nickel and chromium alloy with a specific chromium content is sintered and coated. That is, in the present invention, after forming a porous material layer on an electrode substrate, the chromium content is reduced to at least 16 to 16% in a reducing atmosphere.
A method for producing a cathode, characterized in that an active material consisting of an alloy of 65% by weight of nickel and chromium is sintered and coated.

The electrode substrate used in the present invention may be made of any conductive material and is generally made of a metal that is durable under the environment in which it is used as a cathode. Therefore, when used for the electrolysis of alkali metal salts, especially halogenated alkali metals, or water, it is preferable to use soft iron or nickel as the electrode substrate. In some cases, titanium or the like may also be used.

The shape of the electrode is determined by the shape of the electrode base, and is not particularly limited in the present invention, and a shape generally used as a cathode in an electrolytic cell is used.

For example, it has a flat plate shape, a net shape, a punched metal shape, an expanded metal shape, a sag shape, etc. The electrode substrate is preferably subjected to pretreatment such as degreasing and etching prior to forming a porous material layer on the surface. Any known method can be used without particular limitation.

In the present invention, as a method for forming a porous material layer on the surface of an electrode substrate, a method in which metal plating containing conductive particles is generally used 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 corrosion resistance. 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.

Carbides such as vanadium carbide; borides such as iron diboride and nickel boride; vanadium nitride.

Niobium nitride, titanium nitride, and other nitrides, particularly tungsten carbide, with a particle size of 0.05 to 50
μ is preferred, and 0.5 to 5 μ is particularly preferred.

As the metal plating bath, conventionally known plating baths can be used without particular restriction, but plating baths made of metals from group Ⅰ of the fourth period of the periodic table, such as silver, nickel, iron, and cobalt, are particularly preferred; for example, nickel plating baths and 1, a Watt bath, a nickel black bath, a nickel complex bath, etc. are used, and a cyan bath, etc. is used as a silver plating bath.

The plating conditions using the above plating bath may be selected as appropriate, but in general, 1 to 100 conductive particles are added to the metal plating bath.
'? /L, the content of conductive particles in the plated layer on the electrode substrate obtained is 2 to 0.
It is preferable to select plating conditions so that the volume % is achieved. By applying K in this manner, 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 impregnation of the cathode active material described below. It has the effect of strongly binding the substance and also has the effect of suppressing the growth of crystals of the active substance.

The method for forming the porous material layer on the electrode substrate is not particularly limited to the above-mentioned plating method, and 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, it should be made thicker than the active layer obtained by sintering and coating the active material described below. is necessary.

In the present invention, the alloy layer of a specific ratio of nickel and chromium, which are active substances, to be present on the surface of the electrode substrate does not necessarily have to cover the entire surface of the electrode substrate, but from the point of view of increasing the effective area of the electrode. It is advantageous to cover the entire surface. Furthermore, if the electrode substrate is made of copper, for example, and there is a risk of corrosion in the environment in which the cathode is used, it is natural that the entire surface of the substrate (the entire surface of the part immersed in the solution) should be coated. . Furthermore, in the present invention, the composition of the active substance present on the surface of the electrode substrate has an extremely important meaning with respect to hydrogen overvoltage. That is, the active material is an alloy consisting of at least nickel and chromium;
In particular, it is effective to add a third component to increase the surface area in addition to nickel and chromium. Furthermore, it is also possible to contain other elements or compounds that are unavoidably mixed. The amount of nickel (N1) and chromium (Cr) in the active substance must be in the range of 65% by weight, preferably 20-60% by weight. When the chromium content deviates from this range, hydrogen overvoltage increases.

A method of sintering and coating an electrode substrate with an active material made of the above-mentioned specific alloy is to sinter nickel or chromium in the form of a compound such as chloride, bromide, iodide, or formate, nitrate, etc. in ethanol.

This is carried out by dissolving VC in a solvent such as butanol to a concentration of generally 0.5 to 15% by weight, coating this cathode active material solution on a plated electrode substrate, and then thermally decomposing it. The method of coating this cathode active material solution is not particularly limited, and may be spraying or coating.

Methods such as immersion are used. The thermal decomposition conditions are generally such that the electrode substrate coated with the cathode active material solution is heated to 200 to 800 ml under an inert gas or reducing atmosphere.
Certain nickel-chromium alloys are sintered by heating at temperatures of 0.degree. C. for 15 minutes to 3 hours. Note that even after thermal decomposition, it is preferable to maintain the substrate under an inert gas or reducing atmosphere until the temperature of the substrate becomes 100° C. or lower. It is not preferable to carry out thermal decomposition in an oxidizing atmosphere because this will result in a decrease in performance.

In the present invention, the active layer formed by sintering and coating the cathode active material has a thickness of 0.01 to 20 μm, preferably 0.01 μm to 20 μm.
．． It is common to repeat coating and thermal decomposition so that the particle size is 1 to 3μ.

[Action and effect]

The cathode of the present invention is made of a conductive material, preferably iron.

After forming a porous material layer on the surface of an electrode substrate made of nickel or an alloy containing these metals as one component, an active layer made of a nickel-chromium alloy with a chromium content of 16 to 65% by weight is formed. By forming extremely low hydrogen overpotentials, e.g. at 90°C, 11N-Na0E(
In the hydrogen overvoltage 100 at a current density of 30 A/d-
It is also possible to set it to mV. The reason for this effect is not necessarily clear, but the mixing of chromium into nickel causes distortion in the crystals and improves the catalytic ability, and the underlying porous material layer increases the degree of dispersion of the catalyst particles mentioned above. Therefore, it is presumed that this causes a decrease in hydrogen overvoltage when used as a cathode.

〔Example〕

Examples of the present invention will be shown below.

Example 1 Degreased and ebbed mild steel extracted band metal (
8W: 5wttr * LW: 6wm
Plating was carried out at 5 A/d- for 5 minutes using the dispersion plating bath shown in Table 1 according to JP-A-56-133484 (Plate thickness = 1.5 days). On the substrate treated in this way, NiC22・6H20, 8nCt2・2H2
A butanol solution in which nickel and chromium were dissolved was applied, and the sum of supported amounts of nickel and chromium decreased to 1 after 5 thermal decompositions in all examples.
．． It was set to 7W/e11N. Thermal decomposition was carried out at a temperature of 330°C in a nitrogen gas (N2) atmosphere while varying the chromium content.

The thus obtained electrode was heated to 90°C with 11N-NaO
The hydrogen overpotential was measured in H at a current density of 3 OA/d. The results are shown in Table 2.

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

Table 3 Comparative Example 1 When the same procedure as Example 1 was carried out except that the Cr content in the Nj, -Cr alloy was 5 wt%, the hydrogen overvoltage was 200%.
It was mV.

Comparative examples 2 to 4 The Cr content in the Ni-Cr alloy is 5 wt%.

The same procedure as in Example 2 was carried out except that the concentrations were 70 wt% and 80 wt%. The results are shown in the t84 table.

Table 4 Comparative Examples 5 to 9 The same procedure as Example 2 was carried out except that dispersion plating containing tungsten carbide was not performed. ts5 result
Shown in the table.

Table 5 Comparative Examples 10 to 12 The same procedure as in Example 2 was carried out except that the firing was carried out in air. The results are shown in Table 6.

Table 6

Claims (1)

[Claims] 1) After forming a porous material layer on an electrode substrate, sintering and coating an active material made of an alloy of nickel and chromium with a chromium content of at least 16 to 65% by weight in a reducing atmosphere. 2) A method for producing a cathode according to claim 1, wherein the porous material layer is a metal plating layer containing conductive particles.