JPH0726211B2 - Method of activating surface amorphous alloy for solution electrolysis electrodes - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for activating an amorphous alloy which is suitable as an electrode material for electrolysis of an aqueous sodium chloride solution having various concentrations, temperatures and pHs.

[0002]

2. Description of the Related Art Conventionally, electrodes in which a corrosion-resistant metal such as titanium is coated with a noble metal or a noble metal oxide have been industrially used for electrolysis of an aqueous sodium chloride solution. Also,
The present inventors have registered Japanese Patent Nos. 1153531 and 1213069 using a platinum group amorphous alloy as materials for the same purpose, and Japanese Patent Application No. 58-1711.
Filed as No. 62.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Electrodes which are currently used industrially and which are coated with a noble metal on a corrosion-resistant metal are liable to be peeled off when used as an anode in seawater, and have low corrosion resistance and short life. There is. On the other hand, electrodes with a corrosion-resistant metal coated with a noble metal oxide also have drawbacks such as oxide peeling during use, and a relatively large amount of oxygen generated along with the oxidation of chlorine ions, resulting in low energy efficiency. There is. Further, a common problem of the noble metal-coated electrode, the noble metal oxide-coated electrode, and the amorphous platinum group alloy electrode is that an expensive noble metal is used as a main raw material.

[0004]

When the present invention is used as an anode in the electrolysis of various sodium chloride aqueous solutions, for example, it produces a large amount of chlorine gas at a low voltage, contains a small amount of oxygen, and has a long life as an electrode. It is an object of the present invention to provide a surface activation treatment method for an amorphous alloy which has excellent performance as an energy-saving and highly corrosion-resistant electrode and can be used, and which is expensive and has a low platinum group element concentration. Therefore, the present invention
The technical configuration of is as follows: (1) 25-65 atomic% Nb and Ru, Rh, Pd, Ir
And one or more elements selected from the group of Pt
0.01-10 atomic% and the balance is substantially Ni
Amorphous alloy for electrodes in solution electrolysis
Solution that preferentially dissolves fine alloys in Ni and Nb
The platinum group metal responsible for electrode activity is concentrated on the surface by immersing in
Activity of amorphous alloys for electrodes in solution electrolysis characterized by:
Processing method. (2) Three kinds of Ti, Zr and less than 20 atomic% Ta
One or more selected from the group of metals and 10 atom%
Including 25 to 65 atomic% in total with the above Nb, further R
One selected from the group consisting of u, Rh, Pd, Ir and Pt
Or containing 0.01-10 atomic% of two or more elements, and the balance
Amorphous alloy for solution electrolysis electrodes consisting essentially of Ni
Then, the amorphous alloy for electrodes is replaced with Ni, Nb, Ta, Ti.
The electrode is immersed in a corrosive solution that preferentially dissolves Zr and Zr.
It is characterized by concentrating the platinum group metal responsible for activity on the surface
A method for activating an amorphous alloy for a solution electrolysis electrode. (3) 25-65 atomic% of Nb and Ru, Rh, Pd, Ir
And one or more elements selected from the group of Pt
0.01-10 atomic% and 7 atomic% or less P are included, and the balance is actual
Amorphous alloy for solution electrolysis electrodes consisting of Ni qualitatively
And preferentially dissolve Ni and Nb in the amorphous alloy for electrodes.
Platinum group metal that plays a role in electrode activity when immersed in a corrosive solution
For electrode of solution electrolysis characterized by concentrating on the surface
Amorphous alloy activation process and (4) three types of Ti, Zr and less than 20 atomic% Ta
One or more selected from the group of metals and 10 atom%
It comprises 25-65 atomic% in total of the above Nb, further in, R
One selected from the group consisting of u, Rh, Pd, Ir and Pt
Or two or more elements 0.01-10 atomic% and 7 atomic% or less
Solution of P, and the balance consisting essentially of Ni for solution electrolysis.
In the amorphous alloy for electrodes, the amorphous alloy for electrodes is
A sausage that preferentially dissolves i, Nb, Ta, Ti and Zr
Immerse it in an edible solution and concentrate the platinum group metal, which is responsible for electrode
Amorphous alloys for solution electrolysis electrodes characterized by shrinkage
Activation method.

Normally, alloys are crystallized in the solid state, but a method that does not form long-periodic regularity in the atomic arrangement in the process of solid formation, such as limiting the alloy composition and supercooling and solidifying from the molten state, is applied. Then, an amorphous structure similar to a liquid is obtained without a crystal structure, and such an alloy is called an amorphous alloy. Amorphous alloys have remarkably high strength as compared with conventional practical metals, and exhibit various properties such as abnormally high corrosion resistance depending on the composition.

On the other hand, two of the inventors of the present invention have previously described the patent No. 11
No. 5,353,1 and No. 1213069, the inventors have invented and applied for an amorphous alloy electrode material for electrolysis containing a platinum group metal and a semimetal as main components, and when these materials were used as an anode for electrolysis of a high temperature concentrated aqueous solution, chlorine It has an extremely high electrocatalytic activity for gas production, but is inactive for the generation of oxygen, which is a competing interfering reaction, and is a highly efficient energy-saving material and has high corrosion resistance. Disclosed by patent.

Furthermore, the inventors of the present invention have disclosed in Japanese Patent Application No. 58-171.
No. 162 has invented and filed a surface activated amorphous alloy for electrodes for solution electrolysis, which is mainly composed of a platinum group metal and a semimetal. This is produced by applying the method for activating the surface of an amorphous metal, which was previously filed by Japanese Patent Application No. 56-84413 by the two inventors of the present invention, to the above-mentioned alloy exhibiting excellent electrocatalytic activity. Is. This is an electrode with excellent electrocatalytic activity as a positive electrode for producing sodium hypochlorite, which generates chlorine by electrolysis of a solution that is difficult to generate chlorine, such as dilute NaCl solution that is not heated and has a concentration of seawater. It is a material provided with. These inventions respectively provide electrode materials having excellent characteristics,
All of them were expensive because their main components were platinum group metals.

Therefore, as a result of further research, the inventors of the present invention set the platinum group metal to 10 atomic% or less, and the balance consisting of one or more valve metals and Ni, and in some cases, a small amount of P. By immersing the contained amorphous alloy in hydrofluoric acid, it was found that a material having a sufficiently high electrocatalytic activity can be obtained even if the expensive platinum group element concentration is low, and the present invention was achieved.

[0009]

In order to further enhance the catalytic activity as the electrode for electrolysis, it is necessary to increase the electrochemically effective surface area and collect the platinum group metal acting as the active point of the electrode reaction on the surface. However, Cu-Ti, Cu-Zr, Fe-Zr
Amorphous alloys such as Ti or Zr by hydrofluoric acid
Is selectively dissolved, but it is known that Ni-Ta, Ni-Nb, and the like are not selectively dissolved.

On the other hand, the present inventors have found that when a platinum group metal is added to a Ni-valve metal alloy, one or more valve metals and one or two platinum group metals are used.
It has been found that nickel and valve metal are selectively dissolved by immersing an amorphous alloy containing at least one kind and substantially consisting of nickel in hydrofluoric acid. The concentration and temperature of the hydrofluoric acid can be appropriately selected according to the composition of the target amorphous alloy, and commercially available concentrated hydrofluoric acid can be used as it is. When an amorphous alloy of Ni-valve metal-platinum group metal is immersed in hydrofluoric acid, some of Ni and Nb, Ta, Ti and Zr constituting the alloy are preferentially dissolved uniformly from the alloy surface, Since the alloy surface becomes finer, it becomes black and the platinum group metal that plays a role of electrode activity is concentrated on the surface. Therefore, the surface activation treatment may be terminated when the surface becomes black. Even if the surface activation treatment is applied to a crystalline alloy having the same average composition as the amorphous alloy of the present invention, since the crystalline alloy has a multiphase structure and contains a compound phase, Ni and Nb, Ta, T
The surface activation treatment is not effective because it is difficult to uniformly dissolve i, Zr and the like. On the other hand, in the amorphous alloy of the present invention, since the constituent elements are uniformly distributed, Ni and Nb, Ta, Ti, Zr, etc. are uniformly dissolved in the hydrofluoric acid, and the effective surface area is remarkably increased. The platinum group metal responsible for the electrode activity is concentrated on the surface, and the entire alloy surface can be sufficiently activated.

The amorphous alloy used in the activation treatment method of the present invention can be produced by various methods which have been widely used,
That is, various methods of rapidly quenching and solidifying a liquid alloy, various methods of forming an amorphous alloy through a gas phase, methods of destroying a long-period structure of a solid surface by ion implantation and alloying necessary elements, etc. Any method for producing an amorphous alloy may be used.

Example 1 Using homemade nickel phosphide and a commercially available metal as starting materials, the starting materials were mixed so as to have the composition shown in Table 1 and melted by high frequency induction heating in an argon atmosphere to prepare a starting alloy. By remelting these alloys in an argon atmosphere and solidifying rapidly by using the single roll method,
Thickness 0.01-0.05mm, width 1-5mm, length 3-
A 20 m amorphous alloy thin plate was obtained. The formation of amorphous structure was confirmed by X-ray diffraction. The surfaces of these alloy samples were polished in cyclohexane up to silicon carbide paper No. 1000. To confirm that the corrosion resistance of these alloys is sufficiently high, the anodic polarization curves of all these alloys were measured in 0.5M NaCl solution at 30 ° C. Figure 1
The polarization curves of these alloys are, for example, Ni--Nb.
It is common to amorphous alloys and is almost indistinguishable from each other. All of these alloys are self-passivated, and when anodic polarized, 1.0-1.1V
Up to (SCE), it shows a low passive state holding current of 2 × 10 ^-2 Am- ² or less. When the potential further rises, it is almost 1.2V (SC
E) From the vicinity, an increase in current due to generation of chlorine and oxygen is observed.

[0013]

[Table 1]

[0014]

These alloys were immersed in 46% hydrofluoric acid at room temperature for a few minutes to a few tens of minutes until the surface turned black, and the surface was subjected to a surface activation treatment.
The anodic polarization curve measured twice in a NaCl solution is shown in FIG. The polarization curves of the amorphous alloys of the present invention after the activation treatment are the same as in FIG. 2, and it is difficult to distinguish which alloy's polarization curve is overlaid on one figure.
0.4 to 0.8 V in the first polarization curve after activation treatment
A current density of about 10 ° A · m ⁻² is observed near (SCE). This corresponds to the dissolution of surface components that were not completely dissolved in hydrofluoric acid during the activation treatment. However, when the potential is returned to a higher potential, the potential is returned, and the polarization curve is measured a second time after the activation treatment, the current density around 0.4 to 0.8 V (SCE) is no longer observed. Therefore, it shows that the alloy does not dissolve after the second time if all components that are dissolved from the surface by once being polarized to a high chlorine generation potential are dissolved. 1.0
At a potential higher than near V (SCE), there is no difference between the first and second times, and a chlorine generation current is observed. For example, 1.2V
Comparing the current densities before and after the activation treatment near (SCE), the activation treatment actually improves the chlorine generation current by four digits or more.

In order to examine the corrosion resistance during electrolysis, first 1.25
After conducting constant current electrolysis with V (SCE) for 12 hours, it was washed with distilled water and acetone, and dried in a desiccator for 12 hours. After weighing this sample with a microbalance, 2
Electrolysis was carried out for 4 hours at 1.25 V (SCE), washing, drying and weighing were carried out in the same manner as described above, and the amount of corrosion loss when carrying out constant electrolysis for 24 hours was quantified. Such measurement was carried out on sample No. 3, 13, 1 which has been subjected to activation treatment which is typical of the alloy of the present invention.
No changes in sample weight before and after the constant potential electrolysis for 24 hours could not be detected. Therefore, it was revealed that these electrodes were not corroded at all even when used in 0.5N NaCl solution as electrodes for chlorine generation. Using some of the representative alloys of the present invention, constant current electrolysis was carried out at various current densities, and chlorine generated during electrolysis of 1000 coulomb / l was measured by iodometry. The results are shown in Table 2. Pt- which is the most active as a practical electrode for electrolysis under these conditions
The amorphous alloy electrodes of the present invention are mostly more active than the Ir / Ti electrodes. Further, all the alloys are inexpensive because they have a low platinum group metal content.

[0017]

[Table 2]

Example 2 The amorphous alloy of the present invention prepared in the same manner as in Example 1 and subjected to the surface activation treatment is used in chlorine production in the soda electrolysis industry for chlorine production in a 4M NaCl solution at pH 4 and 80 ° C. The generation characteristics were investigated. FIG. 3 is an example of a polarization curve and shows that an inexpensive material like the present invention has a sufficiently high electrocatalytic activity.

[0019]

Industrial Applicability As described above in detail, even though the amount of expensive platinum group element is extremely low, it has an extremely high electrocatalytic ability as an electrode for electrolysis of an aqueous sodium chloride solution, and corrodes microscopically under electrolytic conditions. It is a long-life, energy-saving and stable electrode material with high stability that cannot be detected even in balance.

[Brief description of drawings]

FIG. 1 is a polarization curve of an as-quenched and solidified amorphous alloy measured in a 0.5N NaCl solution at 30 ° C. (Sample No. 1).
6, No. 17),

2 is a polarization curve of a surface-activated amorphous alloy measured in a 0.5 N NaCl solution at 30 ° C. (Sample N
o. 26),

FIG. 3 is a polarization curve (Sample No. 16) of a surface-activated amorphous alloy measured in a 4M NaCl solution at 80 ° C. and pH 4.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C25B 1/14 11/08 A 11/10 B

Claims (4)

[Claims] 1. Nb of 25-65 atomic% and Ru, Rh,
One or two selected from the group of Pd, Ir and Pt
It contains 0.01-10 atomic% of the above elements, and the balance is substantially
In an amorphous alloy for a solution electrolysis electrode made of Ni,
Ni and Nb are preferentially dissolved in the amorphous alloy for electrodes
The platinum group metal that plays a role of electrode
Amorphous for electrode of solution electrolysis characterized by being concentrated to
Alloy activation treatment method. 2. Ti, Zr and Ta less than 20 atomic%.
And one or more selected from the group of three metals
25-65 atomic% in total with 10 atomic% or more of Nb
Further selected from the group of Ru, Rh, Pd, Ir and Pt.
It contains 0.01-10 atomic% of one or more selected elements.
The rest is amorphous for electrode of solution electrolysis consisting essentially of Ni
Quality alloy, the amorphous alloy for the electrode is replaced with Ni, Nb,
Immerse in a corrosive solution that preferentially dissolves Ta, Ti and Zr
Soak it to condense on the surface the platinum group metal that is responsible for the electrode activity.
Treatment of amorphous alloys for electrode in solution electrolysis characterized by
Reasoning method. 3. Nb of 25-65 atomic% and Ru, Rh,
One or two selected from the group of Pd, Ir and Pt
The above elements 0.01-10 atomic% and 7 atomic% or less P are included.
The rest is amorphous for electrode of solution electrolysis consisting essentially of Ni
Quality alloy, the amorphous alloy for the electrode is replaced with Ni and Nb.
Is immersed in a corrosive solution that preferentially dissolves
Solution characterized by concentrating platinum group metal on the surface
A method for activating an amorphous alloy for electrolytic electrodes. 4. Ti, Zr and Ta less than 20 atomic%.
And one or more selected from the group of three metals
25-65 atomic% in total with 10 atomic% or more of Nb
From the group of Ru, Rh, Pd, Ir and Pt.
0.01-10 atom% of one or more selected elements
Contains P of 7 atomic% or less, and the balance is substantially Ni.
Amorphous alloys for electrodes in solution electrolysis
The alloy preferentially dissolves Ni, Nb, Ta, Ti and Zr.
Platinum group metal that plays a role in electrode activity when immersed in a corrosive solution
For electrode of solution electrolysis characterized by concentrating on the surface
Method for activating amorphous alloy.