JPH0633484B2 - Method for manufacturing cathode for hydrogen generation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a method for efficiently producing a novel hydrogen generating cathode used as a cathode for electrolysis of salt, electrolysis of water and the like.

[Prior art and its problems]

Conventionally, the development of a technique for obtaining chlorine and sodium hydroxide by electrolysis of an aqueous solution of an alkali metal salt, in particular, an aqueous solution of sodium chloride by an ion exchange membrane method has progressed, and electrolysis by an increasingly high current efficiency and a low voltage, that is, a power consumption Is being improved. Among these technological trends, the improvement of current efficiency is mainly due to the improvement of the ion exchange membrane, and the reduction of voltage is being studied in parallel with the improvement of the ion exchange membrane to reduce the overvoltage during electrolysis at the electrodes. There is. 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.

However, as a cathode, that is, a cathode for hydrogen generation, one made of soft iron or nickel is generally used industrially, and for example, a high hydrogen overvoltage of about 400 millivolts (mv) is allowed, and therefore, improvement thereof is required. The need has been pointed out. In recent years, various patent applications have been made for a cathode intended to reduce hydrogen overvoltage. For example, JP-A-55
In the electrodes described in JP-A-164491, JP-A-55-131188, JP-A-56-93885, JP-A-58-167788 and the like, particles of nickel, cobalt, silver or the like are formed on the electrode substrate. Or welding particles of alloys of these metals with aluminum or other metals or silver,
Particulate-immobilized electrodes, which are made by burying a part of the holding metal layer of zinc, magnesium, tin, etc. so as to be exposed, and in some cases chemically eroding a part of the holding metal layer to make it porous, As in JP-A-54-60293, there has been proposed a hydrogen generating cathode in which the hydrogen overvoltage is lowered by an electrodeposition method of an active metal in which a plating bath containing a sulfur-containing nickel salt is electroplated. .

Although it is possible to obtain a cathode having a relatively low hydrogen overvoltage by these proposals, there is a need for various improvements such as lowering the overvoltage and increasing the sustainability of the cathode performance, or lowering the cost. Industrially desired. For example, in the above-mentioned particulate fixed type cathode, in addition to the particulate metal itself being expensive, its preparation not being easy, etc., the manufacturing method is generally complicated, and the performance of the obtained cathode is not uniform. It tends to lack performance stability such as easy. In the latter case of 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.

Therefore, the object of the present invention is to use raw materials relatively inexpensively and to reduce hydrogen overvoltage, for example, 30A by an extremely easy means.
Hydrogen overvoltage is 200 mV or less at current density of / dm ² ,
Particularly, it is to provide a cathode for hydrogen generation which is 100 mV or less and which is stably maintained for a long period of time.

[Means for solving problems]

As a result of intensive studies in view of the above, the present inventors have found that the target hydrogen generating cathode can be easily obtained by allowing the specified active substance to be present in the conductive electrode substrate by the specified electroplating means. The present invention has led to the proposal of the present invention. That is, the present invention uses a plating bath containing nickel ions and tin ions as main components in a cathode chamber in which the anode is separated by an anion exchange membrane, and the nickel content on the surface of the conductive electrode substrate is 25 to 99% by weight. Is a method for manufacturing a cathode for hydrogen generation, which comprises depositing nickel-tin alloy at a ratio of

The electrode substrate used in the present invention may be any conductive substance,
Generally, a metal that is durable under the environment used as a cathode for hydrogen generation is used. Therefore, it is preferable to use soft iron or nickel as the electrode substrate when it is used for the electrolysis of alkali metal salts, especially alkali metal halides or the electrolysis of water. However, good conductive metals such as copper or copper alloys, and in some cases titanium, may also be used. The shape of the electrode is determined by the shape of the electrode substrate, and the shape is not particularly limited in the present invention, and a shape generally used as a cathode in an electrolytic cell is used. For example, a flat plate shape, a net shape, a punched metal, an expanded metal, a scalloped shape, and the like. Prior to electroplating, the electrode substrate is preferably subjected to degreasing and pretreatment before etching. As the method, a known method used during ordinary plating can be used without particular limitation.

In the present invention, an alloy layer composed of a specific proportion of nickel and tin, which are active substances to be coated on the surface of the electrode substrate,
It is not always necessary to cover the entire surface of the electrode substrate, but it is advantageous to cover the entire surface in the sense of increasing the effective area of the electrode. When the electrode substrate is made of, for example, copper and may corrode itself under the environment where the cathode is used, the entire surface of the substrate (the entire surface immersed in the solution) should be naturally covered. is there. Further, in the present invention, the composition of the active layer coated on the surface of the electrode substrate has an extremely important meaning for hydrogen overvoltage, and is an alloy composed of at least nickel and tin. It is also effective to add a third component for increasing the amount of the compound, and it is possible to include other elements or compounds which are inevitably mixed. Ratio of nickel (Ni) and tin (Sn) in this active layer, that is, Should be in the range of 25 to 99 (wt%). When the nickel content deviates from this range, the hydrogen overvoltage increases surprisingly. As described above, the inventors of the present invention do not fully explain why the hydrogen overvoltage is low only for the alloy having a specific ratio of nickel and tin, but the range of the specific ratio of nickel and tin is set by the electroplating means. When co-deposited in it, it takes the form of a special crystal or morphology that is deposited on the substrate. It is speculated that such a state of adhesion causes a low hydrogen overvoltage. The state of the deposit actually observed with a microscope often has a shape like a stack of gravel. Further, in X-ray diffraction, a very broad peak is given, and it is considered that crystal strain or the presence of fine crystals is present.
It is possible that it is related to activity.

The present invention provides an anion exchange membrane to obtain a target hydrogen generating cathode having a low hydrogen overvoltage by coating the surface of an electrode substrate with an active substance composed of nickel and tin in a specified composition ratio by electroplating means. It is extremely important to carry out the electroplating in the cathode chamber where the anode is separated by. That is, according to the production method of the present invention, the adhesion (durability) between the electrode substrate and the plating layer is higher than that in the usual electroplating method without using an anion exchange membrane (without separating the anode). Can be obtained, and not only a hydrogen generating cathode having a low hydrogen overvoltage can be obtained, but also the life of the plating bath is improved, so that a large amount of the desired hydrogen generating cathode can be efficiently obtained. Since the anode is separated by the anion-exchange membrane, the tin ions Sn ²⁺ in the plating bath in the cathode chamber are converted to Sn ⁴⁺ by the oxygen and the anode generated in the anode. It is presumed that this is due to the fact that it is not oxidized and the complexing agent added to the plating bath is not oxidized.

As the anode used in the present invention, generally, an insoluble anode made of, for example, titanium or titanium-palladium alloy is preferably used. As the anion exchange membrane, a known ion exchange membrane having anion selective permeability can be used without particular limitation.

Nickel ions which are the main components of the plating bath used in the present invention are, for example, nickel chloride, nickel sulfate, nickel nitrate, nickel bromide and the like, and tin ions are, for example, tin chloride and stannous pyrophosphate.

Electroplating is performed by supplying a plating bath containing nickel ions and tin ions to the negative and positive electrode chambers of the above electroplating apparatus, and depositing nickel-tin alloy at a nickel content of 25 to 99%. Done.

At this time, in general, nickel ions and tin ions have different reduction potentials from each other, and therefore, when electrodeposition is usually performed on a substrate in the presence of both ions, almost only tin ions are selectively reduced and deposited, and Therefore, the precipitation of nickel will start when the tin ions are exhausted. In this case, almost no alloy is formed and the metal is deposited in two layers. When such a form is used as a cathode, the hydrogen overvoltage becomes extremely high at 400 mv or more.

Therefore, in order to perform the alloy plating of nickel and tin, it is necessary to bring the reduction potentials of the two close to each other. Therefore, using various complexing agents to make the reduction potential of tin ions more base, or to make the reduction potential of nickel ions more noble,
You need to use both of them. For example, "Metal Surface Technology", Vol. 32, No. 1 (1981), page 23, discusses tin-nickel alloy plating from a pyrophosphate bath, and states that addition of various amino acids is effective. . That is, many amino acids, especially α-amino acids such as glycine, shift the deposition potential of nickel ions in the plating bath to a noble direction on the polarization curve.
Further, when a bath mainly containing fluoride as shown in "Journal, of Electrochemicals, Society," Vol. 100, page 107 (1953), etc. is used, the complex formation of fluoride and Sn ²⁺ causes It shifts to the base direction of the Sn ²⁺ deposition potential and brings it closer to the nickel deposition potential. Similar effects can be expected with chlorides and the like. In addition, amines such as pyridine, pyrazole and ethylenediamine, oxycarboxylic acids and salts thereof such as citric acid and tartaric acid, sulfur-containing compounds such as thiourea and zandogensan, oxysulfonic acids such as cresolsulfonic acid and salts thereof and salts thereof, sulfamines Aminosulfonic acids such as acids and salts thereof and salts thereof are effective. Among these complexing agents, glycine, alanine, β-alanine, valine, aspartic acid, glutamic acid, alginic acid, lysine, histidine, proline, serine, threonine and other amino acids and ethylenediamine are particularly effective, followed by sodium fluoride and the like. Soluble fluoride salt and hydrofluoric acid or salt and hydrochloric acid are effective. However, the present invention is not particularly limited as long as it forms a complex with nickel and / or tin and the metal deposition potential from the complex brings the deposition potentials of nickel and tin close to each other. The amount of these complexing agents to be used is also not limited, but generally it is sufficient to be present at 0.1 to 5 times molar equivalents, and preferably 0.5 to 3 times equivalents, relative to the metal ions forming the complex.

Tables 1 to 3 show some examples of plating bath compositions suitable for the present invention.

These examples are just a few of the plating baths used to manufacture the cathode,
The desired nickel content is generally achieved by varying the proportion of nickel and tin ions in the plating bath. That is, when the nickel content in the coating to be electrodeposited on the substrate is increased, the nickel ion concentration in the bath needs to be higher than the tin ion concentration. The relationship between the bath composition and the nickel content in the electrodeposition coating is
Although it depends on the complexing agent to be added and other additives, pH in the bath, current density, etc., it is generally nickel% in the plating bath. And the nickel% in the electrodeposit have a substantially proportional relationship, and the relationship can be easily known by conducting a preliminary examination before carrying out.

Further, in general, it is preferable to use phosphoric acid, particularly pyrophosphoric acid and salts thereof together in order to keep tin ions stable in the plating bath.

The conditions of electroplating are essentially the same as in the case of tin-nickel alloy plating, which is usually performed for decoration or corrosion resistance, but for the purpose of obtaining an active coating in the cathode of the present invention, the above-mentioned decoration or corrosion resistance is used. In general, the nickel content needs to be higher than that of the above. Therefore, the molar ratio of tin and nickel ion concentration in the plating bath is Sn /
Ni as 2 or less, generally 10 ^-4 to 2, preferably 0.001
Used in the range of ~ 1.

The pH during plating is generally in the range of 5 to 10, preferably 6 to 9 when the nickel complex is mainly formed, and is generally low when the tin complex is mainly formed, for example, 1 to 6, preferably 1 to 4, particularly around pH 3. These pH adjustments are carried out depending on the type and amount of complexing agent and other additives used, or if necessary, acids such as hydrochloric acid, phosphoric acid, hydrofluoric acid, etc. or alkalis such as sodium carbonate, sodium hydride, aqueous ammonia, etc. And adjust. Of course, it may be preferable to use it as a buffer solution.

Next, the current density in the electroplating of the present invention is generally 0.
Since it is carried out in the range of 1 to 30 A / dm ² and varies depending on the liquid composition, it cannot be said unconditionally, but it is preferable to use a higher current density than in the case of decoration and corrosion resistance. In general, when the molar ratio (Sn / Ni) of nickel ions and tin ions in the bath is small, the current density is made small, and when the molar ratio is large, the current density is made large to carry out.

The thickness of the coating formed on the electrode substrate by electrodeposition is not particularly limited, but if it is too thin, the effect naturally decreases. In addition, if the coating is too thick, it tends to fall off, so the thickness is usually in the range of 10 to 150 μ, preferably about 15 to 100 μ.

By the above-mentioned method, a cathode having a surprisingly low hydrogen overvoltage can be obtained with a Ni content of 25 to 99 wt%, preferably 35 to 95 wt%, and especially a nickel content of 45 to 80 wt%.

(Operation and Effect) According to the present invention, a substance having conductivity, preferably iron,
A nickel content of 25 to 99 is formed on the surface of an electrode substrate made of a metal such as nickel or an alloy containing one of these metals as a component.
% Of the nickel-tin alloy, the resulting cathode has a very low hydrogen overvoltage, for example 30%.
The hydrogen overvoltage at a current density of A / dm ² can be set to 90 mv or less and the durability is excellent. Although the reason why such an effect is produced is not always clear, as described above, the use of an anion exchange membrane prevents tin ions Sn ²⁺ and complexing agents from being oxidized during plating, and tin is mixed into nickel. As a result, the nickel crystal may be distorted or fine crystals may be generated, and when this is used as a cathode, it is presumed that the hydrogen peroxide has a surprisingly low effect.

Further, according to the present invention, the oxygen generated in the anode and the accumulation of Sn ⁴⁺ due to the oxidation of Sn ²⁺ by the anode and the oxidation of the complexing agent are prevented, so that the life of the plating bath is long, By compensating for the shortage of Sn ²⁺ and Ni ²⁺ , the cathode can be efficiently manufactured without lowering the adhesion strength of the electrodeposit.

When an anion exchange membrane is not used, the amount of tin divalent ions (Sn ²⁺ ) is reduced in addition to the amount deposited, and the amount oxidized to Sn ⁴⁺ by the oxygen generated at the anode and anode. To do. Therefore, if an anion exchange membrane is not used, Sn ⁴⁺ will accumulate as the number of plating layers increases, and the amount of electrodeposition will decrease even if the same amount of electricity is applied, and the ratio of Ni to Sn in the electrodeposit will be unstable. It is easy to become.

In addition, the complexing agent glycine, pyrophosphoric acid, etc. are also oxidized and accumulated, so that the adhesion strength of the deposit is reduced. Therefore, even if the ratio of Ni to Sn in the electrodeposit is 25 to 99 wt%, as the number of plating layers increases, the adhesion strength of the electrodeposit decreases, resulting in an increase in hydrogen overvoltage and a decrease in durability. .

Examples of the present invention will be shown below, but the present invention is not limited to these examples.

Example 1. One of the plating baths shown in Table 4 was adjusted and placed in a cathode chamber and an anode chamber of an electroplating apparatus having an anode chamber and a cathode chamber through an anion exchange membrane.

Anion exchange membrane manufactured by Tokuyama Soda Co., Ltd.
Membrane, NEOSEPTA ACS, Ti-Pt electrode for anode
Using 0.5 dm²Size of mild steel expanded metal
(SW3mm, LW6mm plate thickness 1.5mm) Ni-Sn alloy plating
Was applied. Current density is 10A / dm²And the amount of electricity is 7200
Q was set. In this case, the number of plating and the Ni in the cathode chamber²⁺, Sn
²⁺, Sn⁴⁺Fig. 1 shows the relationship of the concentration change of
Alloy composition (Ni content), amount of electrodeposition and water of the obtained electrode
Overvoltage (90 ℃, 11N NaOH, 30A / dm²of time
The relationship is shown in Table 5. Furthermore, 1 obtained in this way
Under the above environment of the first and fifth electrodes (90 ° C, 11N NaO
H, 30A / dm²3) shows the results of the durability test
It was shown to.

Comparative Example 1. The procedure of Example 1 was repeated except that the anion exchange membrane was not used.

The relationship between the number of plating and the Ni ²⁺ , Sn ²⁺ , Sn ^{4+ in} the plating bath is also shown in Fig. 2. Also, the number of plating and the alloy composition, the amount of electrodeposition and the hydrogen overvoltage of the obtained cathode (90 ° C, 11N NaOH 30A / Dm
The relationship of ² o'clock) is shown in Table 6. Further, the first and second electrodes thus obtained were subjected to a durability test in the same manner as in Example 1. The results are shown in FIG.

If an anion exchange membrane is not used, the amount of Sn ²⁺ will decrease in addition to the amount deposited, and the amount replaced by Sn ⁴⁺ will decrease.
The ratio of Ni to Sn is also different from the case of using an anion exchange membrane, and if Sn ⁴⁺ increases, the amount of electrodeposition will decrease even if the same amount of electricity is applied. It can be seen that potassium pyrophosphate and the like are oxidized at the anode, and the adhesion strength of the electrodeposit is also reduced. Therefore, it is presumed that the hydrogen overvoltage values are different even if the ratio of Ni and Sn in the deposit is almost the same because the deposit amount and the adhesion strength are different.

Comparative Example 2 The same expanded metal of 0.5 dm ₂ as that used in the example was used, and this was plated with copper in an ordinary manner by an alkaline bath, and after thorough washing, platinum was added in a solution containing 120 g / rhodan nickel. Rhodan nickel was plated as an anode to obtain a cathode (this is referred to as B).

On the other hand, Nafion was used as a diaphragm in an electrolytic cell using the same type of expanded metal as ruthenium oxide coated with ruthenium oxide and the first electrode of Example 1 (this is referred to as cathode A) and cathode B, respectively. (Product name of DuPont), and supply 5N saline to the anode chamber,
75 while supplying water to the cathode chamber so that it becomes 6N caustic soda
Electrolysis was performed at -80 ° C and a current density of 30 A / dm ³ , and the overvoltage of each cathode was measured. The results are shown in Table 7.

[Brief description of drawings]

FIG. 1, FIG. 2 and FIG. 3 are diagrams showing the electrode performance obtained by the methods of Examples and Comparative Examples.

Claims (1)

[Claims] 1. A cathode chamber in which an anode is separated by an anion exchange membrane, a plating bath containing nickel ions and tin ions as main components is used, and the nickel content on the surface of a conductive electrode substrate is 25 to 99% by weight. For producing a cathode for hydrogen generation, characterized in that the above nickel-tin alloy is electrofolded