JPS6148591B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a hydrogen generating cathode with low hydrogen overvoltage and long life, particularly a cathode suitable for ion exchange membrane electrolysis or diaphragm electrolysis of aqueous sodium chloride solutions. Conventionally, various electrodes have been proposed in which a coating of a cathode active material is formed on an electrode substrate made of mild steel or the like by methods such as sintering, electroplating, and vacuum evaporation. For example, Japanese Patent Publication No. 55-6715 discloses that a cathode with a low hydrogen overvoltage can be obtained by coating an electrode substrate with a nickel thin film containing manganese and sulfur by a method such as electroplating. The present inventors are also considering improving the performance of the cathode by coating a cathode active material on the substrate by plating means, but a composite plating consisting of conductive fine particles and silver or a metal from Group 4 of the periodic table may be used. The present inventors have discovered that by applying a layer, a cathode with a lower hydrogen overvoltage and better performance can be obtained, and the present invention has been provided. Electrodes are known in which conductive fine particles such as nickel, cobalt, and silver are dispersed in a nickel plating bath and then nickel plated or the like is applied to an electrode base to fix the fine particles in the nickel layer. Such an electrode becomes a cathode with a considerably low hydrogen overvoltage, but in order to further reduce the overvoltage, fine particles of nickel, cobalt, or silver are dispersed to form a mixture of each metal and a second metal of aluminum, zinc, magnesium, or tin. An attempt has been made to further reduce the hydrogen overvoltage by using an alloy and dissolving and removing these second metals after electrode formation to increase the surface area. In this case, the hydrogen overvoltage can be further reduced to some extent, but it takes time to melt the second metal. It is also possible to dissolve it using caustic alkali produced as a cathode, but there are problems such as impurities being mixed into the product, it takes time for the electrode to stabilize, and the durability is still insufficient. However, further improvements were desired. Therefore, the present invention provides a cathode that does not require post-treatment such as dissolution and exhibits an extremely low hydrogen overvoltage. That is, the present invention provides silver or silver containing fine particles of at least one of tungsten carbide and silicon carbide (hereinafter referred to as fine particles in this specification) on an electrode base. The object of the present invention is to provide a cathode characterized in that it has a plating of group metals, namely iron, cobalt and/or nickel. The electrode substrate may be a conductive metal such as iron,
It is a metal such as copper, nickel, titanium, etc., and mild steel and alloys thereof are usually preferred. Also,
Although its shape is not particularly limited, perforated plates such as expanded metal, perforated plates, wire mesh, sintered plates, and pressed plates, flat plates, curved plates, and the like are employed. In particular, it is preferable to use an electrode base made of a porous plate,
Generally, in the manufacturing process of these structures,
It has been subjected to operations such as cutting, shearing, bending, tensioning, compression, rolling, etc., and has a partially activated surface on its surface, or has stress strain remaining locally.
When these porous electrode substrates are subjected to etching treatment as a pretreatment for plating, the etching effect does not appear uniformly, and even if the porous electrode substrate is plated, a cathode with excellent corrosion resistance cannot be obtained. The inventors of the present invention have found that if such a porous electrode substrate is heat-treated and then subjected to etching treatment, the etching effect will appear uniformly, and the inventors have previously proposed this. Therefore, also in the present invention, when using a porous electrode substrate, it is preferable to perform heat treatment in advance. Heat treatment is generally at 300-1100℃ for 5 minutes to 20 hours, preferably
This is carried out by heating at 500 to 900°C for 30 minutes to 2 hours, and then slowly cooling. Heat treatment can be performed in either an oxidizing atmosphere or an inert atmosphere, but if you want to maintain the shape and dimensions of the electrode with high precision, use nitrogen,
This is preferably carried out under an inert atmosphere such as argon. As mentioned above, in the case of a porous electrode substrate, it is preferable to heat-treat the substrate, and in the case of a flat electrode substrate, it is preferable to leave it as is and perform etching treatment after performing rust removal, degreasing, pickling, etc. as necessary. Etching treatment is not particularly limited, but is generally carried out by immersing the electrode substrate in an etching solution of an appropriate concentration such as hydrochloric acid, perchloric acid, or sulfuric acid. Among these, it is particularly preferable to use a perchloric acid solution because it has a large etching effect. When a perchloric acid solution is used, it may be used as an aqueous solution with a concentration of 20 to 50% by weight, and the electrode substrate may be immersed at room temperature or above, particularly 30 to 80°C, for 5 minutes or more than several hours. In order to form a plating layer of silver containing tungsten carbide or (and) silicon carbide or a metal from the fourth period of the periodic table on the electrode substrate by etching, silver, nickel, etc. in which the fine particles are suspended, Electroplating can be done using an iron or cobalt plating bath. At this time, it is necessary to select plating conditions such that the content of the fine particles in the plating layer is 2 to 30% by volume. If the content of the fine particles in the plating layer is less than 2% by volume, a microporous layer cannot be obtained and the electrode performance deteriorates. Further, if the amount exceeds 30% by volume, the adhesion between the fine particles and the plating metal decreases, which is not preferable. In particular, it is preferable that the content of the fine particles be 15 to 25% by volume because this improves electrode performance and provides an electrode with good corrosion resistance. The fine particles are particularly preferably tungsten carbide, and the particle size is preferably 0.05 to 50μ, preferably 0.5 to 50μ.
It is 5μ. In producing the cathode of the present invention, plating is carried out in a state in which the above-mentioned fine particles are suspended in a plating bath of silver, nickel, iron, or kovat, generally at a concentration of 1 to 100 g/g. In this way, the fine particles are uniformly dispersed in the plating layer to form a microporous layer having minute irregularities on the surface, thereby obtaining the cathode of the present invention. As the plating bath, conventionally known plating baths can be used without any restrictions; for example, as a plating bath for nickel, a Watt bath, a nickel black bath, a nickel complex salt bath, etc.; as a plating bath for silver, a cyan bath, etc.; A sulfate chloride bath or the like is used as the iron plating bath. In addition, these metal baths contain sulfur, tungsten, manganese, tin, copper,
Alloy plating may be performed by adding a metal such as molybdenum. Incidentally, an appropriate amount of a surfactant may be added to the plating bath. In the cathode of the present invention, the fine particles are uniformly dispersed in the plating layer, and the fine particles form a microporous layer on the surface of the plating layer. Therefore, the effective area of the electrode surface becomes 10 to 20 times larger than that in the case where no fine particles are present, and the hydrogen overvoltage is significantly reduced due to the interaction between the two. For example, compared to a cathode made of a simple expanded metal made of mild steel, the cathode of the present invention generally exhibits a hydrogen voltage 0.1 to 0.2 V lower. Furthermore, this condition continues for a long time and the corrosion resistance is excellent. Examples will be described below, but the present invention is not limited thereto. Example 1 A mild steel expanded metal (50 mm x 100 mm x 1.6 mm) made from a cold rolled plate was rust-proofed, placed in an electric furnace, and nitrogen gas flowed 50 times the internal volume of the electric furnace.
The air in the furnace was replaced with nitrogen. Next, the temperature was raised to 900°C while flowing nitrogen at a rate of 1/min, held for 2 hours, and then slowly cooled to 100°C and taken out of the furnace. Next, it was immersed in a 40% by weight perchloric acid solution at 60° C. for 1 hour to perform an etching treatment. The pieces were then pickled, washed with water, and plated under the conditions shown in Table 1 using a nickel plating bath to which tungsten carbide with an average particle size of 0.75 μm was added.

[Table] According to electron micrograph observation (magnification: 500x) of the surface of the plated material obtained, a microporous layer is formed with many irregularities, and the content of tungsten carbide is about 15% by volume of the plated layer. It was hot.
This plating was applied to the cathode A at a current density of 30 A/dm ² at 85°C in a 30% by weight aqueous sodium hydroxide solution.
It was used as 1. Further, an electrode was similarly plated using a plating bath with the plating bath composition shown in Table 1 except for tungsten carbide, and this electrode was similarly used as cathode B-1. Table 2 shows the changes in hydrogen overvoltage in a 30% by weight aqueous sodium hydroxide solution for depolarized A-1 and cathode B-1.

[Table] From the results in Table 2, it can be seen that the cathode A-1 exhibits a hydrogen overvoltage that is 0.17 V lower at the initial stage and 0.20 V lower after 300 days than the cathode B-1. Comparative Example 1 The electrode substrate used in Example 1 was subjected to the same heat treatment and perchloric acid solution etching as in Example 1, followed by pickling and water washing, and then plating was performed under the conditions shown in Table 14.

[Table] The Raney nickel used in Table 14 is Raney nickel powder (Ni 50wt% Al 50wt% average particle diameter 30 μm) manufactured by Kawaken Fine Chemical Co., Ltd. before development. This plated product was used as cathode C-1 under the same conditions as in Example 1. Cathode A-1 and Cathode C-1
Table 15 shows the changes in hydrogen overvoltage.

[Table] From Table 15, cathode A-1 is initially 0.04V higher than cathode C-1, but after 100 days it is 0.07V, and after 200 days it is 0.12V: after 300 days it is 0.20V lower. Indicated overvoltage. Example 2 The electrode substrate used in Example 1 was subjected to the same heat treatment and perchloric acid solution etching as in Example 1, and after acid washing and water washing, the tungsten carbide (average particle size Plating was carried out under the conditions shown in Table 3 using an alloy plating bath to which 5μ) was added.

[Table] According to electron micrograph observation (magnification: 500x) of the surface of the plated material obtained, a microporous layer is formed due to somewhat large irregularities, and the tungsten carbide content is approximately 20% by volume of the nickel plated layer. It was hot. This plated material was used as cathode A-2 under the same conditions as in Example 1. Further, an electrode was similarly plated using a plating bath with the plating bath composition shown in Table 3 except for tungsten carbide, and this electrode was similarly used as cathode B-2. Table 4 shows the changes in hydrogen overvoltage of cathode A-2 and cathode B-2.

[Table] From the results in Table 4, it can be seen that the cathode A-2 exhibits a hydrogen overvoltage that is 0.1 V lower at the initial stage and 0.12 V lower after 300 days than the cathode B-2. Example 3 The electrode substrate used in Example 1 was subjected to the same heat treatment and perchloric acid solution etching as in Example 1, followed by pickling and water washing, and then silicon carbide (average particle size 1 μm) shown in Table 5 was prepared. Plating was carried out under the conditions shown in Table 5 using a nickel plating bath to which .

[Table] According to electron micrograph observation (magnification: 500x) on the surface of the plated material obtained, a microporous layer is formed by many small irregularities, and the content of silicon carbide in the nickel plated layer is about 15
It was in volume %. This plated material was used as cathode A-3 under the same conditions as in Example 1. In addition, we produced electrodes plated in the same manner using a plating bath with silicon carbide excluded from the plating bath compositions shown in Table 5.
This was similarly used as cathode B-3. Table 6 shows the changes in hydrogen overvoltage of cathode A-3 and cathode B-3.

[Table] From the results in Table 6, it can be seen that the cathode A-3 exhibits a hydrogen overvoltage that is 0.15 V lower at the initial stage and 0.18 V lower after 300 days than the cathode B-3. Comparative Example 2 The electrode substrate used in Example 1 was subjected to the same heat treatment and perchloric acid solution etching as in Example 1, followed by pickling and water washing, and then plating was performed under the conditions shown in Table 16.

[Table] Raney cobalt used in Table 16 is Co50wt%,
The average particle size of 50wt% Al is 30μm. This plated product was used as cathode C-2 under the same conditions as in Example 1. Table 17 shows the changes in hydrogen overvoltage of cathode A-3 and cathode C-2.

[Table] From Table 17, cathode A-3 is 0.02V higher than cathode C-2 at the beginning, but after 100 days, it is 0.08V higher than cathode C-2.
The hydrogen voltage was 0.15V lower after 200 days and 0.18V lower after 300 days. Example 4 The electrode substrate used in Example 1 was subjected to the same heat treatment and perchloric acid etching as in Example 1, followed by pickling and water washing. ) Plating was carried out under the conditions shown in Table 7 using a silver plating bath containing .

[Table] According to an electron micrograph (magnification: 500x) of the surface of the obtained plated product, a microporous layer is formed by many small irregularities, and the content of tungsten carbide in the silver plated layer is approximately 15 volume%
It was hot. This electrode was used as cathode A-4 under the same conditions as in Example 1.
used as. In addition, an electrode was similarly plated in a plating bath with the plating bath composition shown in Table 7 except for tungsten carbide, and this electrode was similarly used as cathode B-4. Table 8 shows the changes in hydrogen overvoltage for these cathodes.

[Table] From the results in Table 8, it can be seen that the A-4 cathode exhibits a hydrogen overvoltage that is 0.11 V lower at the initial stage and 0.11 V lower after 300 days than the B-4 cathode. Example 5 The electrode substrate used in Example 1 was subjected to the same heat treatment and perchloric acid etching as in Example 1, and after acid washing and water washing, the tungsten carbide shown in Table 9 (average particle size 10μ) was formed. Plating was carried out under the conditions shown in Table 9 using a plating bath to which .

[Table] According to an electron micrograph (magnification: 500x) on the surface of the plated material obtained, a microporous layer is formed by numerous irregularities, and the content of tungsten carbide in the plated layer is 15% by volume. It was hot. This electrode was used as cathode A-5 under the same conditions as in Example 1.
used as. Further, an electrode was produced by plating in the same manner as in the plating bath composition shown in Table 9 excluding tungsten carbide, and this was similarly used as cathode B-5. Table 10 shows the changes in hydrogen overpotential for these cathodes.

[Table] From the results in Table 10, it can be seen that the A-5 cathode exhibits a hydrogen overvoltage that is 0.11 V lower at the initial stage and 0.12 V lower after 300 days than the B-5 cathode. Example 6 Six sheets of expanded metal made of mild steel (800 mm W x 1200 mm L x 1.6 mm T) made of cold-rolled plates were prepared, three of which were set as set C, and the remaining three were set as set D. The three sheets of Set C were placed in a large electric furnace and heated to 900°C while flowing nitrogen gas, held for 2 hours, slowly cooled to 100°C, and then taken out of the furnace. Next, regarding this set C, 40Wt%80
Etching treatment was performed in a perchloric acid solution at ℃ for 10 minutes. After treatment, wash with 15wt% HCl aqueous solution for 3 minutes,
Plating was carried out using a nickel plating bath containing tungsten carbide as shown in Table 11.

[Table] Plating-treated set C and untreated set D were used in the ion-exchange membrane method saline electrolyzer TSE- manufactured by Tokuyama Soda Co., Ltd.
270 by spot welding and subjected to industrial salt thermal decomposition under the electrolytic conditions shown in Table 12. Table 13 shows the changes in battery voltage over the 300 days.

【table】

[Table] From Table 13, cell-C is earlier than cell-D and approximately
It can be seen that the cell voltage is 0.17V, and after 300 days the cell voltage is 0.20V lower. This is understood to be because the hydrogen overvoltage of set C is lower than the hydrogen overvoltage of set D.

Claims (1)

[Scope of Claims] 1. Silver containing 2 to 30 volume % of fine particles of at least one of tungsten carbide and silicon carbide on an electrode base, or silver containing 2 to 30 volume % of fine particles of at least one of tungsten carbide and silicon carbide.
A cathode comprising a plating layer of a periodic group metal. 2. The cathode according to claim 1, wherein the electrode substrate is a perforated plate made of mild steel such as an expanded metal, a perforated plate, or a wire mesh. 3. The cathode according to claim 2, wherein the porous plate electrode substrate is heat-treated in advance. 4. The cathode according to claim 1, wherein the electrode substrate is etched with a perchloric acid solution. 5. The cathode according to claim 1, having a metal plating layer containing 2 to 30 volume % of fine particles of at least one of tungsten carbide and silicon carbide having a particle size of 0.05 to 5.0 μm. 6. The cathode according to claim 1, wherein the metal of the fourth period group of the periodic table is nickel.