JPH0579737B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an electrode for solution electrolysis made of a surface-activated amorphous alloy, which is suitable as an electrode material for the electrolysis of aqueous sodium chloride solutions of various concentrations, temperatures, and PHs, for example. BACKGROUND 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 used industrially for sodium chloride aqueous solution electrolysis.
In addition, the present inventors have also disclosed patent No. 1153531 using a platinum group amorphous alloy as a material for the same purpose.
No. 1213069 and patent application No. 1213069.
- Filed as No. 171162. Problems to be Solved by the Invention The electrodes currently used industrially, which are corrosion-resistant metals coated with noble metals, have drawbacks such as, for example, being easily peeled off when used as anodes in seawater, and having low corrosion resistance and short lifespan. On the other hand, electrodes in which noble metal oxides are coated on corrosion-resistant metals also have drawbacks such as the oxide peeling off during use and the generation of relatively large amounts of oxygen along with the oxidation of chlorine ions, resulting in low energy efficiency. There is. Furthermore, a common problem with noble metal coated electrodes, noble metal oxide coated electrodes, and amorphous platinum group alloy electrodes is that they are based on expensive noble metals. Means for Solving the Problems The present invention, when used as an anode for the electrolysis of various sodium chloride aqueous solutions, generates a large amount of chlorine gas at a low voltage, has a low amount of mixed oxygen, and can be used as a long-life electrode. It is an object of the present invention to provide an electrode for solution electrolysis that is made of an amorphous alloy with a low concentration of expensive platinum group elements and has excellent performance as an energy-saving and highly corrosion-resistant electrode. The present invention is an electrode for solution electrolysis with a specific composition containing Nb, Ni, and platinum group metals as essential components. Usually, alloys are crystallized in the solid state, but
If we apply a method that does not create long-period regularity in the atomic arrangement during the solidification process, such as by limiting the alloy composition and solidifying it from a molten state by ultra-rapid cooling, we can create an amorphous material that does not have a crystalline structure and resembles a liquid. structure is obtained,
Such alloys are called amorphous alloys. Amorphous alloys have significantly higher strength than conventional practical metals, and exhibit various properties, including unusually high corrosion resistance, depending on their composition. On the other hand, two of the present inventors previously obtained patent No. 1153531.
No. 1 and No. 1213069, he invented and applied for an amorphous alloy electrode material for electrolysis that mainly consists of platinum group metals and semimetals. These patents demonstrate that these materials exhibit extremely high electrocatalytic activity in the production of carbon dioxide, but are inert to the generation of oxygen, a competing interfering reaction, and are highly efficient, energy-saving materials with high corrosion resistance. Disclosed by. Further, the present inventors have invented and applied for a surface-activated amorphous alloy for electrodes in solution electrolysis, the main components of which are platinum group metals and semimetals, in Japanese Patent Application No. 171162/1982. This is fabricated by applying a method for activating the surface of an amorphous alloy, which was previously filed by the two inventors in Japanese Patent Application No. 84413/1983, to the above-mentioned alloy that exhibits excellent electrocatalytic activity. It is. This electrode generates chlorine by electrolyzing a solution that has a concentration similar to seawater and is difficult to generate chlorine, such as unheated dilute NaCl solution, and is an excellent electrode for producing sodium hypochlorite. This provides a material with catalytic activity. Although each of these inventions provides electrode materials with excellent properties, all of them are expensive because their main component is a platinum group metal. The present inventors focused on these excellent properties of amorphous alloys and conducted further research. As a result, the inventors discovered that amorphous alloys have the high corrosion resistance necessary for stable electrode materials and can be treated with surface activation treatment. The inventors have now discovered that a material with sufficiently high electrocatalytic activity can be obtained even with a low concentration of expensive platinum group elements, and the present invention has been achieved. The present invention consists of the first to fourth inventions set forth in Claims 1 to 4, each of which is an electrode for solution electrolysis comprising a predetermined element. The following Table 1 shows the constituent elements and content rates of these first to fourth inventions.

[Table] Effects In the present invention, various methods for producing an amorphous alloy can be used, such as melting an alloy having the above-mentioned composition and solidifying it by ultra-rapid cooling, or performing sputter deposition using a mixture having the above-mentioned average composition as a target. The resulting amorphous alloy is a single-phase alloy in which the above elements are uniformly dissolved in solid solution. Originally, in order to provide a metal electrode with selective electrocatalytic activity for a specific electrochemical reaction and high corrosion resistance that can withstand the reaction conditions, it is necessary to create an alloy containing a necessary amount of effective elements. However, in the case of crystalline metals, adding a large amount of various alloying elements often results in a multiphase structure with different chemical properties, and for this reason, it is often difficult to obtain mechanical strength. In contrast, the amorphous alloy of the present invention has a solid phase with an amorphous structure that does not allow the constituent elements to be localized, so it is always a uniform single-phase solid solution and has excellent mechanical properties and corrosion resistance. have Next, the reason for limiting the composition of each component in the present invention will be described. Ni is the basic element of the present invention, and Nb,
It is an element that forms an amorphous structure in coexistence with Ti, Zr, and Ta, and also in the third and fourth inventions of the present invention.
It is necessary to add 20 atomic percent or more. Nb is an element that forms a stable passive film even in a highly corrosive environment where it is exposed to the intense oxidizing power that generates chlorine and chlorine during its generation, and as mentioned above, it coexists with nickel and forms an amorphous layer. An element that forms a structure,
In the second and fourth aspects of the present invention, in order to ensure sufficient corrosion resistance, it is necessary to add 10 atomic % or more. Ru, Rh, Pd, Ir, and Pt are all elements that directly play a role in electrode catalytic activity, and it is necessary to contain one or more of these at 0.01 atomic % or more. However, adding a large amount is not necessarily effective for corrosion resistance, and since surface activation treatment described later is performed, there is no need to add a large amount, and it is sufficient to add 10 atomic % or less. Ti, Zr, and Ta are all elements that coexist with Ni to form an amorphous structure in place of Nb. Among these, alloys containing a large amount of Ta will be filed separately as similar patents containing Ni-Ta-platinum group elements as main components, so the content will be less than 20 atomic % here. Also, Ti, Zr
is exposed to nascent chlorine with high oxidizing power,
It is an element that has the ability to form a passive film.
However, since Ti and Zr have less effect on corrosion resistance than Nb, it is not possible to completely replace Nb with these elements in order to guarantee corrosion resistance.
However, if Nb is contained at 10 atomic % or more, Ti, Zr,
It is sufficient that the total amount of one or more Ta and Nb is 25 atomic % or more. In addition, in order to facilitate amorphous formation, it is necessary to add sufficient Ni, so the total amount of Nb alone or of Nb and one or more of Ti, Zr, and Ta is 65 atomic % or less. P is an element that has strong oxidizing power and has the effect of promoting the formation of stable passive films such as Nb, Ta, Ti, and Zr in an environment where nascent chlorine is generated, and also facilitates the formation of an amorphous structure. be. However, since adding a large amount makes it difficult to form an amorphous structure, it is necessary to limit the amount to 7 at % or less. It should be noted that the amorphous alloy of the present invention contains V of 3 atomic % or less.
The object of the present invention is not hindered even if Mo, 20 atomic % or less of Hf, Cr, and 10 atomic % or less of Fe, Co are contained as impurities. Metalloids such as B, Si, and C are
It is originally known as an element effective in forming an amorphous structure. However, in a highly oxidizing environment, adding a large amount of these metalloids reduces the stability of the passive film. Therefore, it is difficult to designate these elements as particularly effective elements. However, even if up to about 7 atomic % of these elements are contained as impurities, there is no problem because they are not harmful to corrosion resistance and help form an amorphous structure. On the other hand, in order to further enhance the catalytic activity as an electrode for electrolysis, it is necessary to increase the electrochemically effective surface layer and collect platinum group metals that act as active sites for electrode reactions on the surface. For this purpose, the amorphous alloy of the present invention is immersed in hydrofluoric acid. The concentration and temperature of hydrofluoric acid can be appropriately selected depending on the composition of the target amorphous alloy, and commercially available concentrated hydrofluoric acid can be used as is. When the amorphous alloy of the present invention is immersed in hydrofluoric acid, the Ni constituting the alloy
In addition, some of Nb, Ta, Ti, and Zr are preferentially and uniformly dissolved from the alloy surface, and the alloy surface becomes finer, giving it a black tinge, and the platinum group metals responsible for electrode activity are concentrated on the surface. Therefore, the surface activation treatment may be completed when the surface becomes blackish. Note that even if the surface activation treatment is applied to an electrode made of an amorphous alloy having the same average composition as the electrode made of an amorphous alloy of the present invention, the electrode made of a crystalline alloy has a multiphase structure and contains a compound phase. , Ni, Nb, Ta, Ti, Zr, etc. are difficult to uniformly dissolve, so surface activation treatment is not effective. In contrast, in the electrode made of the amorphous alloy of the present invention, the constituent elements are uniformly distributed, so Ni, Nb, Ta, Ti, Zr, etc. are uniformly dissolved in hydrofluoric acid, and the effective surface layer is significantly increased. At the same time, the platinum group metal responsible for electrode activity is concentrated on the surface, and the entire electrode surface can be sufficiently activated. This is the reason why the surface-activated electrode of the present invention has excellent properties as an electrode material for aqueous electrolysis. The electrode made of the amorphous alloy of the present invention can be produced by various methods that are already widely used, namely, various methods in which a liquid alloy is ultra-rapidly solidified, and various methods in which an amorphous alloy is formed through a gas phase. Any method for producing an amorphous alloy may be used, such as a method in which the long-period structure of the solid surface is destroyed by ion implantation, etc., and necessary elements are alloyed. Example 1 Using homemade nickel phosphide and commercially available metals as raw materials, the raw metals were mixed to have the compositions shown in Table 2, and melted by high frequency induction heating in an argon atmosphere to produce raw material alloys. By remelting these alloys in an argon atmosphere and ultra-rapidly solidifying them using a single roll method, thicknesses of 0.01~
An amorphous alloy thin plate of 0.05 mm, width 1-5 mm, and length 3-20 m was obtained. The formation of an amorphous structure was confirmed by X-ray analysis. The surfaces of these alloy samples were polished to No. 1000 silicon carbide paper in cyclohexane. To confirm that the corrosion resistance of these alloys is sufficiently high, the anodic polarization curves of all these alloys were measured in 0.5 M NaCl solution at 30 °C.
As shown in Figure 1, the polarization curves of these alloys are common to Ni-Nb amorphous alloys.
They are so similar that they are almost indistinguishable. All of these alloys are self-passivating, and when polarized anodically, they exhibit a 2×
Shows a low passivity current of less than 10 ^-2 A m ^-2 .
As the potential increases further, from around 1.2V (SCE),
An increase in current due to the evolution of chlorine and oxygen is observed.

【table】

[Table] Add these alloys to 46% HF at room temperature for a few minutes.
The surface was immersed for 10 minutes until the surface turned black to perform surface activation treatment. After surface activation treatment, 30℃, 0.5N
The anodic polarization curve measured twice in NaCl solution is shown in FIG. The polarization curves of the amorphous alloys of the present invention after the activation treatment are all similar to those shown in FIG. 2, and when they are superimposed on one figure, it is difficult to distinguish which alloy the polarization curves are for. The first polarization curve after activation treatment shows a range of about 0.4 to 0.8V (SCE).
A current density of about 10゜A・m ^-2 is observed. This corresponds to the dissolution of surface components that were not completely dissolved into HF during the activation process. However, when the polarization curve was measured a second time after the activation treatment after polarizing to a higher potential and returning the potential, 0.4~
Current densities around 0.8V (SCE) are no longer observed. Therefore, once polarized to a high potential that generates chlorine and all the components that dissolve from the surface are dissolved, the alloy will not dissolve from the second time onwards. The potential higher than around 1.0V (SCE) is the first and second
The same current for chlorine generation is observed each time.
For example, when comparing the current density before and after activation treatment around 1.2V (SCE), activation treatment actually improves the chlorine generation current by more than four orders of magnitude. To check corrosion resistance during electrolysis, first 1.25V (SCE)
After constant current electrolysis for 12 hours, the sample was washed with distilled water and acetone, and dried in a desiccator for 12 hours. After weighing this sample with a microbalance, it was electrolyzed at 1.25V (SCE) for 24 hours, washed, dried, and weighed in the same manner as described above, and the corrosion loss during constant electrolysis for 24 hours was quantified. When such measurements were carried out on samples Nos. 3, 13, 18, 21, 24, 32, and 36, which were subjected to activation treatment and are typical of the alloys of the present invention, changes in sample weight before and after 24 hours of constant potential electrolysis were observed. could not be detected. Therefore, it was found that these electrodes were not corroded at all even when used in a 0.5N NaCl solution as an electrode for chlorine generation. Furthermore, using some representative alloys of the present invention, constant current electrolysis was performed at various current densities, and chlorine generated during electrolysis at 1000 clones was measured by iodometry. The results are shown in Table 3. It is the most active as a practical electrode for electrolysis under these conditions.
Most of the amorphous alloy electrodes of the present invention are more active than Pt-Ir/Ti electrodes. Furthermore, both alloys are inexpensive due to their low content of platinum group metals.

【table】

[Table] Example 2 Regarding the amorphous alloy of the present invention produced in the same manner as in Example 1 and subjected to surface activation treatment, 4M at PH4 and 80°C used for chlorine production in the soda electrolysis industry
The chlorine generation characteristics in NaCl solution were investigated. FIG. 3 is an example of a polarization curve, showing that an inexpensive material like the one of the present invention has sufficiently high electrocatalytic activity. Effects of the Invention As detailed above, the surface-activated amorphous alloy for electrodes in solution electrolysis of the present invention has an extremely low concentration of expensive platinum group elements, but the surface-activated amorphous alloy for electrodes in solution electrolysis can be used in electrodes for electrolysis of aqueous sodium chloride solutions. It is a long-life, energy-saving, and stable electrode material that has an extremely high electrocatalytic ability and is highly stable under electrolytic conditions so that corrosion cannot be detected even with microbalance. Furthermore, since any of the already widely used techniques for producing amorphous alloys can be applied to the production of the alloy of the present invention, no special equipment is required, and the present invention is highly practical.

[Brief explanation of the drawing]

Figures 1, 2 and 3 are representative examples of polarization curves measured for alloys of the present invention. Figure 1 shows the polarization curves of the amorphous alloy as rapidly solidified as measured in 0.5N NaCl solution at 30°C (Sample No. 16, No.
17), Figure 2 shows the polarization curve of the surface-activated amorphous alloy (sample No. 26) measured in 0.5N NaCl solution at 30°C, and Figure 3 shows the polarization curve of the amorphous alloy (sample No. 26) measured in 0.5N NaCl solution at 30°C. NaCl
This is a polarization curve of an amorphous alloy subjected to surface activation treatment (sample No. 16) measured in a solution.

Claims (1)

[Scope of Claims] 1. The substrate contains 25-65 atomic % of Nb and Ru, Rh, Pd,
It is an amorphous alloy containing 0.01-10 atom% of one or more elements selected from the group of Ir and Pt, and the balance is Ni, and the surface layer is a platinum group metal. Electrode for solution electrolysis. 2. The substrate contains a total of 25 to 65 atomic % of one or more selected from the group of three metals, Ti, Zr, and less than 20 atomic % of Ta, and 10 atomic % or more of Nb, and further An amorphous alloy containing 0.01 to 10 at% of one or more elements selected from the group of Ru, Rh, Pd, Ir and Pt, with the balance being Ni,
An electrode for solution electrolysis, characterized in that the surface layer is a platinum group metal. 3 The substrate contains 25-65 at% of Nb and Ru, Rh, Pd,
An amorphous alloy containing 0.01-10 at.% of one or more elements selected from the group of Ir and Pt and 7 at.% or less of P, with the balance consisting of 20 at.% or more of Ni, An electrode for solution electrolysis, characterized in that the surface layer is a platinum group metal. 4. The substrate contains a total of 25 to 65 atomic % of one or more selected from the group of three metals, Ti, Zr, and less than 20 atomic % of Ta, and 10 atomic % or more of Nb, and further , 0.01-10 atomic% of one or more elements selected from the group of Ru, Rh, Pd, Ir and Pt
An electrode for solution electrolysis, characterized in that it is an amorphous alloy consisting of 7 at % or less of P, and the balance is 20 at % or more of Ni, and the surface layer is a platinum group metal.