JP3554630B2 - Electrolytic electrode with durability - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a durable and durable electrolysis electrode which can be used for electrolysis stably for a long period of time, and more particularly, to a high current density in a strong acid bath such as high-speed zinc plating or electrolytic copper foil production. The present invention relates to a durable electrolysis electrode which can be used under a long period of time, has a long service life, and can hardly contain impurities on a plating layer or a copper foil to be produced.
[0002]
[Prior art and its problems]
In high-speed galvanization represented by EGL (Electro Galvanizing Line), production of electrolytic copper foil, and the like, a lead anode has been conventionally used. The reason is that the electrolytic bath used in the electrolytic operation is an extremely corrosive bath mainly containing sulfuric acid, and there is almost no substance other than lead that can maintain stability and conductivity in this bath. The electrolytic current density is extremely high, and lead is relatively inexpensive. Further, it is also mentioned that lead easily forms an alloy with another metal and is excellent in workability. However, even if the lead has such advantages, and even if it is a lead alloy having high wear resistance, the amount of consumption during electrolysis is several mg / AH, and the plating layer which is likely to cause environmental pollution and is a product And it remains in the electrolytic foil and adversely affects it.
[0003]
As a result of various investigations to solve this problem, a so-called dimensionally stable electrode having a valve metal surface such as titanium coated with a platinum group metal or its oxide has been used for the plating and the like. I have. This dimensionally stable electrode was initially used successfully in chlor-alkali electrolysis to produce caustic soda, but when used in the above-mentioned plating bath, etc., oxygen penetrated into the coating layer of the platinum group metal oxide. There is a problem in that passivation occurs by inducing surface oxidation of titanium as a substrate, and the passivation cannot be avoided even if the type of the platinum group metal oxide is changed.
The present inventors have been studying measures for avoiding this passivation. That is, there is no problem as long as the base itself can maintain the conductivity even if a part of the base is passivated.Therefore, the base metal surface is given oxide close to semiconductivity as an oxide containing another metal in advance, or penetrated. This is a method in which a non-stoichiometric oxide is formed in advance so that conductivity is not lost even if oxygen is excessively contained. In addition, since titanium does not always have absolute stability in sulfuric acid, which is an electrolytic bath used in the above-mentioned applications, its surface is coated with tantalum, and the tantalum surface is coated with an electrode material, or glass. Methods have also been implemented, such as coating the material to completely cover the titanium.
[0004]
These methods have advantages and disadvantages and are not always satisfactory methods. In other words, the present inventors have found that since a semiconductive oxide coating cannot completely form a coating as in the case of manufacturing an electronic device, it reaches a certain point in time and is passivated while leaving a coating substance. Experience and said coatings are not always sufficiently resistant to corrosion. These drawbacks also occur with electrodes in which a conductive material such as platinum is embedded to maintain conductivity.
In the electrode coated with tantalum, the tantalum itself shows sufficient corrosion resistance, but when coating the electrode material on the tantalum surface, depending on the type of the electrode material, volume expansion occurs due to the oxidation operation for the coating, As a result, there is a disadvantage that the conditions for forming the electrode material are extremely limited since the substrate is peeled from titanium as a base, and a sufficient effect cannot be expected. Furthermore, glassy coatings have the disadvantage that their conductivity is not sufficient and that they have poor adhesion to the electrode material. That is, the normal electrode substance and the base are integrated by a strong chemical bond. However, when glass is used as the intermediate layer, the chemical bond cannot be formed and the electrode substance cannot be held strongly, so that high corrosion resistance cannot be expected.
[0005]
In addition to these methods, techniques for forming a corrosion-resistant electrode material on the surface of a base by thermal spraying have been proposed. The thermal sprayed layer formed thereby has sufficient corrosion resistance, but its thickness is at most about 100 microns, so it is difficult to completely prevent the formation of through holes. Corrosive electrolytic solution penetrates between the sprayed layer and the substrate through these minute through-holes, and even during electrolysis, the substrate may be polarized and the interface may be corroded. I can't say that.
As described above, various techniques have been proposed to improve the durability of the electrodes, but none of them has sufficiently solved the conventional problems.
[0006]
In recent years, diamond with conductivity has been developed. Diamond has excellent heat conductivity, optical transparency, high temperature and durability against oxidation, and can control electric conductivity by doping. Therefore, diamond is promising as a semiconductor device and an energy conversion element. However, there is almost no report as an electrode for electrolysis. Swain et al. Reported the stability of diamond in acidic electrolyte [Journal of Electrochemical Soc. , Vol. 141, 3382-(1994)], suggesting that the carbon material is far superior to other carbon materials. Fujishima et al. Also reported their application to electrodes for reduction reactions, paying attention to the band gap as large as 5.5 eV [Journal of Electroanalytical Chem. , Vol. 396, 233- (1995), and Electrochemistry, Vol. 60, No. 7, 659- (1992)]. There is also a report of a humidity sensor utilizing the fact that the surface resistance of diamond changes with humidity [Electrical Engineering, Vol. 114, No. 5, 413-1994].
However, there is no report on industrial use in a high potential region where oxygen generation or chlorine generation can occur at a high current density.
[0007]
[Object of the invention]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an electrode for electrolysis that does not elute an electrode substance into an electrolytic solution and has excellent durability.
[0008]
[Means for solving the problem]
Electrolytic electrode of the present invention, includes electrode substrate, an electrode material having a intermediate layer and the platinum group metals and / or oxides thereof was coated intermediate layer surface comprises a conductive Diamon de coated on the electrode substrate surface It is an electrode for electrolysis characterized by comprising.
[0009]
Hereinafter, the present invention will be described in detail. The electrode for electrolysis according to the present invention can be widely used for various kinds of electrolysis, extremely high-speed galvanizing using a corrosive electrolytic bath, producing an electrolytic copper foil, and extremely mixing impurities generated in an electrolytic solution or a generated gas. It can be suitably used for producing acidic water or alkaline water for cleaning semiconductor devices and liquid crystal panels which are not suitable for use, and various kinds of electrolysis such as chlor-alkali electrodes. Conductive Diamon de despite having sufficient conductivity, normal electrode material, for example, since in an oxygen overvoltage of 400 to 500 mV which electrode material of iridium oxide system has not involved in electrolysis, when both coexist In addition, the electrolysis is mainly performed by an iridium oxide-based electrode material. The nature of this conductive Diamon de is particularly important as the nature of the substrate and the intermediate layer of the electrode (base), the electrode material becomes impossible to continue the peeling to electrolysis when electrolysis at the base takes place.
[0010]
Further diamond is the most chemically stable material, according to the study by the present inventors the conductive Diamon de anodic potential as an anode material on a substrate metal such as titanium be performed electrolysis in the above high potential 2V No signs of passivation appeared, presumably because they almost completely prevented the transfer of oxygen, which normally occurs as an anode.
The present invention uses a conductive Diamon de having such properties as the main component of the intermediate layer. Is a conductive Diamon de, boron, and phosphorus, Diamon de, etc. that conductive by doping impurities such as graphite. It is not necessary to add graphite alone, for example, when diamond is obtained by the CVD method described below, a slight amount may be added by adjusting the amount of hydrogen as an atmosphere gas or by slightly changing the temperature. Can coexist in diamond.
[0011]
This substance is coated on the electrode substrate as in the prior art to form an intermediate layer. The substance is desirably fine particles having a particle size of 0.01 to 1 μm, and the coating thickness on the substrate is preferably about 0.1 to 10 μm for the purpose of preventing infiltration of the electrolyte into the substrate. It is particularly preferred that the thickness be 1 to 10 μm. When diamond is used as the intermediate layer material, it is possible to use crushed natural diamond, but since it is very expensive, it is desirable to use synthetic diamond obtained by reducing an organic compound.
The synthesized diamond can be synthesized by thermal CVD (chemical vapor deposition) in which organic compounds such as methyl alcohol, ethyl alcohol, and acetone, which are carbon sources, are thermally decomposed in a reducing atmosphere such as hydrogen gas. Other methods such as physical vapor deposition (PVD) Alternatively, it may be synthesized by plasma CVD or the like, but it is desirable to use CVD in which the film formation speed is extremely high. The heating is usually performed by bringing the vapor of the organic compound into contact with the heated filament, and the temperature of the filament is preferably 1800 to 2400 ° C., depending on the capacity and processing speed of the apparatus. The substrate temperature reaches 750-950 ° C. It is desirable that the concentration of the organic compound gas relative to hydrogen is 0.1 to 10% by volume, the total gas flow rate is 10 to 1000 ml / min, and the pressure is atmospheric pressure.
[0012]
Since synthetic diamond as an intermediate layer material is used after being coated on a substrate, it is desirable that the synthetic diamond produced by the reduction operation be directly attached to the surface of the electrode substrate without isolation. Since diamond alone has no conductivity, impurities are usually mixed into the organic compound, which is a raw material, and adhered to the substrate together with the organic compound, thereby obtaining a diamond having good conductivity. As the impurity, a simple substance composed of an element having a different valence from carbon or a compound containing the same, for example, powdered boric acid (boron oxide), diphosphorus pentoxide, or the like can be used. In addition, diborane (B ₂ H ₆ ) and phosphine (PH ₃ ) can also be used as the impurities, but the powder boric acid and diphosphorus pentoxide are preferably used because of high toxicity. The content of the impurities is preferably 1 to 10000 ppm, more preferably 100 to 1000 ppm. The resistivity can be controlled in the range of 100 to 0.1 Ωcm.
[0014]
The substrate may also serve as a current collector, and the material may be titanium, niobium, tantalum, silicon, carbon, nickel tungsten carbide, or the like, and these may be processed into a wire mesh, powder sintered body, metal fiber sintered body, or the like. To use. When electrolysis of an electrolytic solution containing a corrosive component is performed, unlike the electrolysis of pure water, elution of an electrode substance occurs slightly little by little when viewed microscopically. In consideration of the stability of the substrate in this case, in the case of electrolysis of a corrosive component, it is desirable to use niobium or tantalum having high corrosion resistance as the substrate.
Covering the direct conductive Diamon de to the substrate surface but, in order to reduce the and real current density for improving the adhesion between the conductive Diamon de and the base of the intermediate layer performs the roughening of the substrate surface Preferably, the surface is roughened largely using an alumina grid of about # 20 when used under high current density conditions, and # 60 to # 60 when used under relatively low current density under corrosive conditions. It is desirable to roughen the surface with alumina sand as fine as about 120 to improve the adhesion of the coating.
[0015]
The surface of the intermediate layer is coated with an electrode material to manufacture a durable electrolytic electrode according to the present invention. The electrode material may be selected depending on the application of the electrolysis electrode, because even durability somewhat inferior infiltration of the electrolytic solution and oxygen is suppressed by the intermediate layer having the conductive Diamon de, length The electrolysis operation can be continued for a stable period.
However, it is naturally desirable to use a durable electrolytic material, and electrode materials mainly containing platinum group metals such as platinum, palladium, iridium, ruthenium, osmium and rhodium and oxides thereof, for example, iridium oxide and tantalum oxide It is preferable to use a composite oxide of This electrode material may be coated on the surface of the intermediate layer by a commonly used thermal decomposition method.For example, a solution of a mixture of iridium chloride and butyl tantalate is applied as a coating solution on the surface of the intermediate layer, dried, and then thermally decomposed. Then, if necessary, these operations are repeated to coat a desired amount of the electrode substance. The preferred number of repetitions is 10 to 30 times.
[0016]
The electrode manufactured in this manner hardly corrodes the substrate due to the durability of the intermediate layer, has a high electrode potential and excellent durability even in a strongly acidic solution, and is used as either an anode or a cathode. Although it is possible to do so, it is particularly effective for electrolysis under conditions where oxygen transfer under high current density or high temperature becomes severe.
When such an electrode is incorporated into an electrolytic cell, the electrolytic cell is divided into two chambers of an anode chamber and a cathode chamber or three chambers of an anode chamber, an intermediate chamber and a cathode chamber using an ion exchange membrane. It is installed in at least one of the anode compartment and the cathode compartment. The ion exchange membrane may be made of either a fluororesin or a hydrocarbon resin, but the former is preferred from the viewpoint of corrosion resistance. The ion exchange membrane has a function to prevent each ion generated at the anode and the cathode from being consumed at the counter electrode, and to promptly advance the electrolysis when the conductivity of the liquid is low.
[0017]
When the electrode is used as a gas electrode in a two-chamber electrolytic cell, a cathode chamber may be provided between the ion exchange membrane and the cathode, and an anode chamber may be provided between the anode and the ion exchange membrane. When the liquid conductivity is low, the cell voltage rises, the tank structure becomes complicated, and gas-liquid separation is required at each electrode.Therefore, it is most preferable to adopt a structure in which electrodes are bonded to an ion exchange membrane. desirable. In this case, the anode chamber is substantially a gas chamber, while the cathode chamber is in a gas-liquid mixed state. The material of the electrolytic cell varies depending on the electrolytic solution to be used, the gas to be generated, and the like, but from the viewpoint of durability and stability, use of a glass lining material, carbon, an intermediate layer having high corrosion resistance, stainless steel and PTFE resin, etc. desirable.
If it is desired to make the electrode and the ion exchange membrane adhere to each other, they may be mechanically combined in advance, or a pressure may be applied during electrolysis. The pressure at this time is preferably 0.1 to 30 kgf / cm ² .
The electrolysis conditions vary depending on the electrolytic solution to be used, but it is preferable that the temperature is 5 to 40 ° C. and the current density is 0.01 to 10 A / dm ² .
[0018]
【Example】
Next, examples of the electrode for electrolysis according to the present invention will be described, but the examples do not limit the present invention.
[0019]
Embodiment 1
A commercially available pure titanium plate having a thickness of 1.5 mm was used as a base metal, and its surface was blasted at a pressure of 4 kg / cm ² using # 60 alumina sand. After the blast sand remaining on the surface was removed with a wire brush, it was pickled in boiling 20% hydrochloric acid for 15 minutes. The surface roughness of the base metal was JISRa = 6 μm.
A thin film of a diamond layer having a thickness of 1 μm was formed on this substrate using ethyl alcohol as a raw material and a conductive diamond structure manufacturing apparatus 1 shown in FIG. 1 by a thermal CVD method. That is, while keeping the pressure in the chamber constant, the vapor of ethyl alcohol, which is a reaction raw material gas in which a trace amount (1000 ppm) of boric acid (boron oxide) as an impurity for imparting conductivity is dissolved, and the atmosphere are reduced. Hydrogen gas was introduced at a pressure of 1 atm from the reactant gas raw material inlet 2 and the hydrogen gas inlet 3 to maintain the properties and selectively form only diamond by the following process. The introduced steam is decomposed by the heated tungsten filament 4 and a diamond, which is a decomposition product of ethyl alcohol, is formed on a substrate 7 disposed on a molybdenum cover 6 on a substrate holder 5 immediately below the filament 4 (interval 3 cm). Was deposited. The substrate was heated at 1300 ° C. so that the temperature of the substrate was maintained at 750 to 800 ° C. by the thermocouple 8.
[0020]
This surface was coated with a solution of butyl alcohol and hydrochloric acid in which iridium chloride and butyl tantalate were mixed at a metal molar ratio of 2: 1 and used as a coating solution, dried, and then heated at 530 ° C. for 10 minutes in flowing air. Decomposition was performed, and this was repeated 12 times to coat 0.05 mol / m ² of electrode material in terms of iridium.
The diamond layer was evaluated by electron microscope and Raman spectroscopy. Although the surface of the diamond layer was polycrystalline, no morphological change due to the addition of impurities was observed. The lattice spacing calculated by electron beam diffraction almost coincided with the diamond value reported by ASTM. In Raman spectroscopy, a sharp diamond peak was observed around 1332 cm ^-1 and an amorphous diamond was found near 1550 cm ^-1 , but the latter peak intensity was extremely small. From the above analysis, it was confirmed that the formed thin film had polycrystalline diamond.
[0021]
On one side of the cation exchange membrane Nafion 117 (manufactured by DuPont), the electrode thus prepared was used as an anode, a zirconium plate was used as a counter electrode, and both electrodes were immersed in 20% sulfuric acid (80 ° C.) to obtain a current density of 300 A. / Dm ² was electrolyzed. Electrolysis could be continued after 2,000 hours.
[0022]
[Comparative Example 1]
An electrode was formed under the same conditions as in Example 1 except that the titanium substrate surface was oxidized at 600 ° C. for 2 hours without forming an intermediate layer to form a corrosion-resistant oxide on the substrate surface, and the surface was directly coated with an electrode material. When the electrode was used as an anode and subjected to an electrolytic test in the same manner as in Example 1, the coating was considered to be corroded after 600 hours, and the coating was considered to be desorbed, so that electrolysis could not be continued.
[0026]
【The invention's effect】
The present invention is an electrode substrate, in that it comprises an electrode material having a intermediate layer and the platinum group metals and / or oxides thereof was coated intermediate layer surface comprises a conductive Diamon de coated on the electrode substrate surface Characteristic electrode for electrolysis.
When forming the intermediate layer having conductivity Diamon de between the substrates and the electrode material, the existent electrode of the intermediate layer, the electrode material surface to peeled off the electrode material corrodes ingress to said substrate on said substrate Oxygen gas or electrolytic solution generated in the intermediate layer is prevented from penetrating in the direction of the substrate due to the presence of the intermediate layer, and the substrate does not come into contact with the electrolytic solution or generated gas. In addition, it shows sufficient corrosion resistance and enables stable electrolysis operation for a long period of time.
[0027]
Furthermore, when electrolysis is performed under a high current density, the generation rate of generated gas increases. In this case, however, the intermediate layer almost completely prevents intrusion of oxygen and the like, thereby protecting the base metal and removing the electrode material. Block.
The material constituting the intermediate layer of the present invention are conductive Diamon de, there is a diamond As typical. However, since diamond is not usually conductive, boron, phosphorus, graphite, etc., which are impurities for imparting conductivity, are added before or after attaching diamond to a substrate. It is not necessary to add the graphite alone, and when obtaining diamond by the CVD method, a small amount of graphite coexists in the diamond by adjusting the amount of hydrogen, which is an atmosphere gas, or by slightly changing the temperature. Ru can be.
[0028]
May be selected electrodes materials depending on the application but, platinum group metals and their oxides, it is desirable in particular to use an electrode material mainly composed of iridium oxide. The material of the electrode base is not particularly limited, and valve metals such as carbon, titanium, niobium, and tantalum can be used. In particular, in the case of electrolysis of an electrolytic solution having a corrosive component, it is more expensive than inexpensive titanium. However, it is desirable to use niobium, tantalum, or the like having excellent corrosion resistance.

[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus for manufacturing a conductive diamond structure used in an example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Production apparatus of conductive diamond structure 2 ... Reaction material gas raw material inlet 3 ... Hydrogen gas inlet 4 ... Filament 5 ... Base holder 6 ... Cover 7 ... Base 8 ... thermocouple

Claims (3)

Electrode substrate, electrolyte, characterized in that it comprises an electrode material having a intermediate layer and the intermediate layer surface to a platinum group metal coated and / or an oxide thereof comprising the coated conductive Diamon de to the electrode substrate surface Electrodes. The electrode for electrolysis according to claim 1, wherein the electrode substance is mainly composed of iridium oxide. Electrode substrate, carbon or titanium electrode for electrolysis according to 請 Motomeko 1 Ru valve metal der selected from tantalum and niobium.

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