JPS62253791A - Production of cathode for generating hydrogen - Google Patents

Abstract

PURPOSE:To efficiently produce a novel cathode for generating hydrogen by depositing an Ni-Sn alloy contg. a specified amount of Ni on the surface of an electrically conductive substrate for an electrode with a plating bath contg. Ni and Si ions as the principal components. CONSTITUTION:An Ni-Sn alloy contg. 25-99wt% Ni is deposited on the surface of an electrically conductive substrate for an electrode with a plating bath contg. Ni and Sn ions as the principal components in a cathode chamber separated from an anode chamber with an anion exchange membrane to obtain a cathode for generating hydrogen. It is preferable that the electrically conductive substrate is made of soft iron or Ni and pretreated by etching prior to electroplating.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an efficient method for producing a novel hydrogen generating cathode used as a cathode for salt electrolysis, water electrolysis, etc.

[Prior art and its problems]

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 in parallel with improvements in ion-exchange membranes to reduce overvoltage during electrolysis at electrodes. There is. Among these, various excellent proposals have already been made regarding anodes, and electrodes in which anode overvoltage is not a problem are almost always used industrially.

However, as for the cathode, i.e., the cathode for hydrogen generation, those made of soft iron or nickel are generally used industrially and can tolerate a high hydrogen overvoltage of, for example, 400 millivolts (IIv). The necessity has been pointed out. In recent years, various patent applications have been filed regarding cathodes aimed at reducing hydrogen overvoltage. For example, JP-A-5
5-164491, JP-A-55-131188, JP-A-56-93885, JP-A-58-167788, etc., the electrodes contain nickel, cobalt, silver, etc. on the electrode base. Welding particles or particles of alloys of these metals with aluminum or other metals or silver,
Microparticle-fixed electrodes are partially exposed and buried in a holding metal layer such as zinc, magnesium, tin, etc., and in some cases, part of the holding metal layer is chemically eroded to make it porous. A cathode for hydrogen generation in which the hydrogen overvoltage is lowered by an active metal electrodeposition method in which electroplating is carried out on an electrode substrate using a plating bath containing a sulfur-containing nickel salt has been proposed, as in 1982-60293. .

Although it is possible to obtain a cathode with a relatively low hydrogen overvoltage through these proposals, there is a need for various improvements such as lower overvoltage, greater sustainability of cathode performance, and lower cost. Desired industrially. For example, in the case of the above-mentioned fine particle fixed cathode, the fine particle metal itself is expensive, it is not easy to prepare, and the manufacturing method is generally complicated, resulting in variations in the performance of the resulting cathode. They tend to lack performance stability, such as being easy to use. Furthermore, in the latter electroplating using a sulfur-containing nickel bath, it is difficult to sufficiently lower the hydrogen overvoltage, and in some cases there are drawbacks such as low durability.

Therefore, the object of the present invention is to use relatively inexpensive raw materials and to achieve a low hydrogen overvoltage of, for example, 30A/
dm" hydrogen overvoltage is 20011IV
The object of the present invention is to provide a cathode for hydrogen generation that has an IQOa+V or lower and is stable for a long period of time.

゛ [Means for solving the problem] In view of the above, the present inventors have conducted intensive research and have discovered that the desired hydrogen can be produced by making a specified active substance exist in a conductive electrode substrate by a specified electroplating means. The inventors have discovered that a generation cathode can be easily obtained, and have come to propose 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, so that the surface of the conductive electrode substrate has a nickel content of 25 to 99% by weight. This is a method for producing a hydrogen generating cathode characterized by electrodepositing a nickel-tin alloy in a proportion of .

The electrode substrate used in the present invention may be any aIXN material, and generally a metal that is durable under the environment in which it is used as a hydrogen generating cathode is used. Therefore, when used for the electrolysis of alkali metal salts, especially alkali metal halides 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. Further, the shape of the electrode is determined by the shape of the electrode base, 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, the shape is a flat plate, a net, a punched metal, an expanded metal, a sag, etc. It is preferable that the electrode substrate is subjected to pretreatment such as resin treatment and etching prior to electroplating, and any known method used in ordinary plating may be used without particular limitation.

In the present invention, the alloy bath consisting of a specific proportion of nickel and tin, which are active substances coated on the surface of the electrode substrate, is
Although it is not necessary to cover the entire surface of the electrode substrate, it is advantageous to cover the entire surface from the viewpoint of increasing the effective area of the electrode. In addition, 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, the entire surface of the substrate (the entire surface of the part immersed in the solution) should of course be coated. be. In addition, in the present invention, the composition of the active layer coated on the surface of the electrode substrate has an extremely important meaning against hydrogen overvoltage, and is an alloy consisting of at least nickel and tin, and in particular, nickel and tin, and in some cases, an alloy with a surface area of It is also effective to add a third component to increase the temperature, and it is also possible to include other elements or compounds that are unavoidably mixed. The ratio of nickel (Ni) to tin (Sn) in this active layer needs to be within the range of Ni. When the nickel content is out of this range, the hydrogen overvoltage increases surprisingly. Although the present inventors do not fully explain why the hydrogen overvoltage is so low only in alloys with a specific ratio of nickel and tin, When co-deposited within the substrate, it forms a special crystal or form and adheres to the substrate. It is surmised that this state of adhesion causes a low hydrogen overvoltage. When actually observed under a microscope, the deposits often have a shape that resembles a pile of gravel.

In addition, it gives a very broad peak in X-ray diffraction, which may be due to distortion of the crystal or the presence of microcrystals, which may be related to the activity.

The present invention uses an anion exchange membrane to coat the surface of an electrode substrate with an active substance consisting of nickel and tin in a specified composition ratio by electroplating, in order to obtain the intended cathode for hydrogen generation with a low hydrogen overvoltage. It is extremely important to carry out the electroplating in a cathode chamber with separate anodes. That is, according to the manufacturing method of the present invention, the adhesion (durability) between the electrode substrate and the plating layer is improved compared to the normal electroplating method that does not use an anion exchange membrane (without separating the anode). Not only can a hydrogen generating cathode with good hydrogen overvoltage and low hydrogen overvoltage be obtained, but also the life of the plating bath can be improved, making it possible to efficiently obtain a large amount of the desired hydrogen generating cathode.

The effect exhibited by the present invention is that since the anode is separated by an anion exchange membrane, the tin ions Sn'' in the plating bath in the cathode chamber are not oxidized to Sn' by the oxygen generated at the anode and the anode. This is thought to be due to the fact that the complexing agent added to the plating bath is not oxidized.

As the anode used in the present invention, an insoluble anode made of titanium, titanium-palladium alloy, or the like is generally preferably used. Also, as an anion exchange membrane (
Well-known ion exchange membranes having anion permselectivity can be used without particular limitation.

Examples of nickel ions, which are the main components of the plating bath used in the present invention, include nickel chloride, nickel sulfate, nickel nitrate, and nickel bromide. Examples of tin ions include tin chloride and stannous birophosphate.

Electroplating involves supplying a plating bath containing nickel ions and tin ions to the negative and anode chambers of the electroplating device described above, and electrodepositing a nickel-tin alloy with a nickel content of 25 to 99%. This is done by

At this time, there is generally a difference in reduction potential between nickel ions and tin ions, so if electrodeposition is performed on the substrate in the presence of both ions, almost only the tin ions are selectively reduced and deposited, and the metal ions are deposited in the plating bath. The precipitation of nickel begins when the tin ions are gone. In this case, almost no alloy is formed, and the metal is deposited in two layers. When such a structure is used as a cathode, the hydrogen overvoltage becomes extremely high at 400 mV or more.

Therefore, in order to perform alloy plating of nickel and tin, it is necessary to bring the reduction potentials of both materials close to each other. For this reason, it is necessary to use various complexing agents to make the reduction potential of tin ions more base, or to make the reduction potential of nickel ions more noble.
It is necessary to use both of them. For example, "Metal Surface Technology" Vol. 32, Nal (1981), p. 23 discusses tin-nickel alloy plating from a birophosphoric acid bath and states that the 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 in a direction above the polarization curve. In addition, when using a bath mainly containing fluoride, as shown in "Journal of Electrochemical, Subsidiary Society", Vol. 100, p. 107 (1953),
The formation of a complex between the fluoride and Sn'' causes the deposition potential of Sn'' to shift to a less noble direction, bringing it closer to the deposition potential of nickel. Similar effects can be expected from chlorides and the like. In addition, amines such as pyridine, pyrazole, and ethylenediamine, oxycarboxylic acids and their salts such as citric acid and tartaric acid, sulfur-containing compounds such as thiourea and xandogensan,
Oxysulfonic acids and their salts such as cresolsulfonic acid and its salts, aminosulfonic acids and its salts such as smafamic acid and its salts, etc. are effective. Among these complexing agents, amino acids such as glycine, alanine, β-alanine, valine, aspartic acid, glutamic acid, alginic acid, lysine, histidine, proline, serine, and threonine, and ethylenediamine are particularly effective, followed by sodium fluoride, etc. Soluble fluoride salts and hydrochloric acid, or common salt and hydrochloric acid are effective. However, in the present invention, there is no particular limitation as long as a complex is formed 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 it is sufficient if they are present in an amount of 0.1 to 5 times the molar equivalent, preferably 0.5 to 3 times, relative to the metal ion forming the complex with -a. It would be equivalent.

Some examples of plating bath compositions suitable for the present invention are shown in Tables 1-3.

Table 1 Table 2 These are some examples of plating baths used in cathode production.
A desired nickel content is generally achieved by varying the ratio of nickel ions to tin ions in the plating bath. That is, when increasing the nickel content in the coating to be electrodeposited onto the substrate, it is necessary to increase the nickel ion concentration in the bath relative to the tin ion concentration.

The relationship between the bath composition and the nickel content in the electrodeposited coating is approximately proportional to the complexing agent and other additives added, and the pH1 current in the bath. You can easily know the relationship between them.

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

The conditions for electroplating are essentially the same as those for 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 conditions for electroplating are as follows: It is generally necessary to have a higher nickel content than in the case of Therefore, the molar ratio of both tin and nickel ion concentrations in the plating bath is S
n/Ni is used in a range of 2 or less, generally 10-4 to 2, preferably 0.0 Oi to 1.

The pH during plating is generally in the range of 5 to 10, preferably 6'-9, if a nickel complex is to be mainly formed, and is generally lower, for example 1, if a tin complex is to be mainly formed. -6, preferably 1-4, especially p
It is best to set it around H3.

These pFI adjustments depend on the type and amount of complexing agents and other additives used, or as necessary, acids such as hydrochloric acid, phosphoric acid, hydrofluoric acid, etc. or alkalis such as sodium carbonate, sodium hydride, aqueous ammonia, etc. Add and adjust. Of course, it may also be preferable to use it as a buffer solution.

Next, the current density in electroplating of the present invention is generally 0.
．． It is carried out in the range of 1 to 3 OA/d+w", and although it cannot be generalized because it varies depending on the liquid composition, it is preferable to use a higher current density than for decorative or corrosion-resistant applications. In general, the current density is higher than that for decorative or corrosion-resistant applications. Molar ratio of tin ions (Sn/
Good results are obtained by reducing the current density when Ni) is small, and by increasing the current density when the molar ratio is large.

The thickness of the coating formed by electrodeposition on the electrode substrate is not particularly limited, but if it is too thin, the effect will naturally decrease. Furthermore, if the coating is too thick, it tends to fall off easily, so the thickness is usually in the range of 10 to 150 microns, preferably about 15 to 100 microns. “The method described above allows cathodes with surprisingly low hydrogen overpotentials to be obtained at Ni contents of 25 to 99 wt%, preferably 35 to 95 wt%, especially 45 to 80 wt%.

(Operations and Effects) According to the present invention, a conductive substance, preferably iron,
The surface of the electrode base made of metal such as nickel or an alloy containing these metals as one component has a nickel content of 25 to 99%.
% of the active material consisting of a nickel-tin alloy, the resulting cathode has an extremely low hydrogen overpotential, e.g.
A/dse” hydrogen overvoltage at a current density of 90a+
It is possible to make it less than v and has excellent durability. Although the reason for producing such effects is not necessarily clear,
As mentioned above, by using an anion exchange membrane, tin ions and complexing agents are prevented from being oxidized during plating, and tin mixed into nickel may cause distortion in the nickel crystals or cause fine particles to form. It is presumed that this leads to the formation of crystals, which, when used as a cathode, produces the effect of a surprising reduction in hydrogen current flow.

Furthermore, according to the present invention, the life of the plating bath is extended because it prevents the accumulation of Sn'' caused by the oxidation of Sn'' by the oxygen generated at the anode and the anode, and the oxidation of the complexing agent. By making up for the deficiencies in Sn'' and N12'', a cathode can be efficiently produced without reducing the adhesion strength of the electrodeposit.

When an anion exchange membrane is not used, the amount of divalent tin ions (<Sn'') decreases not only by the amount deposited, but also by the amount oxidized to Sn 4 + by the anode and oxygen generated at the anode. Therefore, if an anion exchange membrane is not used, as the number of plates plated increases, Sn'' will accumulate, 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 also be unstable. It's easy to become.

Furthermore, since complexing agents such as glycine and birophosphoric acid are oxidized and accumulated, the adhesion strength of the deposits decreases. Therefore, even if the ratio of Ni to Sn in the deposits is 25 to 99-t%, as the number of plates is increased, the adhesion strength of the deposits decreases, the hydrogen overvoltage increases, and the durability deteriorates. descend.

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

Example 1゜The plating bath shown in Table 4 was adjusted to IIt, and the anion exchanger tA
II! was introduced into the cathode chamber and the cathode chamber of the electroplating apparatus, which has an anode chamber and a cathode chamber.

The anion exchange membrane was an anion exchange membrane manufactured by Tokuyama Soda Co., Ltd., NEO3EPTA AC3, and the anode was Ti.
- Using a Pt electrode, a soft steel expanded metal with a size of 0.5 dm (S W 3 mm, L W 6 m
Ni-Sn composite plating was applied to +s plate thickness 1.5 mm). The current density was IOA/dm2 and the amount of electricity was 7200Q. In this case, the number of plated wires and Nt”, Sn in the cathode chamber
Figure 1 shows the relationship between the concentration changes of ``'', 5 n 4 '' 1, and the number of plated plates, the synthetic composition (Ni content), the amount of electrodeposition, and the hydrogen overvoltage of the obtained electrode (90°C, 11 NNaOH
, 30A/dm'') are shown in Table 5.Furthermore, the relationship between the 1st grain and 5 mouth electrodes obtained in this manner under the above environment (90°C, 11 NNa0 H, 30A/dgm'') is shown in Table 5. ) The results of the durability test are shown in Figure 3.

Table 4 Table 5 Comparative Example 1 The same procedure as Example 1 was carried out except that an anion exchange membrane was not used.

Figure 2 shows the relationship between the number of plated pieces and the Ni'', Sn'', and Sn'' in the plating bath, and the relationship between the number of plated pieces, the synthetic composition, the amount of electrodeposition, and the hydrogen overvoltage of the obtained cathode (90''C111NNa0H
30A/dm'') is shown in Table 6.Furthermore, the electrodes for the first and second grains thus obtained were subjected to a durability test in the same manner as in Example 1.The results are shown in Table 6. This is shown in Figure 3. ``If an anion exchange membrane is not used, the amount of Sn'' decreases not only by the amount deposited but also by the amount replaced by Sn'''-, so the ratio of Ni to Sn in the electrodeposit decreases. Also, as 3 n 4 + increases, the amount of electrodeposition decreases even if the same amount of electricity is applied, and in addition, complexing agents such as glycine and potassium birophosphate etc. is oxidized at the anode, and the adhesion strength of the deposits also decreases.Therefore, even if the ratio of N1 and Sn in the deposits is almost the same, the hydrogen overvoltage values are different because the amount of deposits and the adhesion strength are different. It is presumed that this is because of this.

hydrogen overvoltage

[Brief explanation of drawings]

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

Claims (1)

[Claims] (1) In a cathode chamber where the anode is separated by an anion exchange membrane, a plating bath containing nickel ions and tin ions as main components is used to coat the surface of the conductive electrode substrate with nickel containing 25 to 99% by weight of nickel. - A method for producing a cathode for hydrogen generation characterized by electrodepositing a tin alloy