Electrode for electrolysis and electrolysis method using the electrode

Abstract

When a titanium electrode provided with a catalyst layer for increasing the efficiency of electrolysis is used in a strong acid solution containing hydrogen peroxide, the catalyst layer is damaged by the environment in the solution and becomes detached, and the efficiency of electrolysis is reduced. When a protective layer for protecting this catalyst layer is formed from a metal film, the formation process becomes complicated and the cost increases.　However, an electrode comprising a conductive base material, a catalyst layer provided on the conductive base material, and a protective film formed on the catalyst layer and containing silicone protects the catalyst layer from the harsh environment in the treatment solution and can achieve a longer electrode life. Moreover, a protective film formed from an organic material is inexpensive and easy to apply, and therefore can lead to a reduction in the cost of electrodes over the long term.

Description

[Technical field]

[0001] The present invention relates to an electrode used in electrolysis, which is widely used in industrial applications such as plating and recovery of metals present in a solution to be treated. [Background technology]

[0002] Electrolysis is used in a variety of industrial fields. The electrodes used in this process have a current of several A / dm 2 to several hundred A / dm 2 Anodes are used in a wide range of current densities, from 0.1 to 1.0 V. The anode is particularly required to have high oxidation resistance and durability because oxidation reactions such as oxygen and chlorine gas generation occur on its surface. Titanium and its alloys are used as electrode base materials as valve metals for electrodes from the viewpoints of environment and safety. However, although titanium is conductive, its electrical conductivity is not high, and when titanium is used as an electrode, a stable catalyst layer such as a platinum-based metal is provided on its surface.

[0003] In industrial electrolysis, in addition to the above-mentioned cases where high current densities are used, the liquid to be treated may be a strong acid, or may be used in a strong oxidizing environment where hydrogen peroxide is added. In particular, when a catalyst layer is formed on the surface of the electrode material to increase the efficiency of electrolysis, the electrode material may be damaged by the catalyst layer.

[0004] Patent Document 1 discloses an electrode including a valve metal substrate such as titanium, an outer catalyst layer, and a protective layer made of a valve metal oxide interposed between the substrate and the catalyst layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5932028 Summary of the Invention [Problem to be solved by the invention]

[0006] Using metal as a protective layer for the catalyst layer on the electrode is thought to have a high protective ability for the electrode, but it requires complex manufacturing processes, such as heat treatment at high temperatures of nearly 500°C, which increases the cost. There was a demand for a cheaper protective layer that could protect the electrode (especially the catalyst layer) even in harsh environments. [Means for solving the problem]

[0007] The present invention has been conceived in view of the above problems, and provides an electrode for electrolysis having a protective coating made of a resin-based paint that can protect the electrode even in harsh environments.

[0008] Specifically, the electrolysis electrode according to the present invention is A conductive substrate; A catalyst layer provided on the conductive substrate; An alkoxy group-containing organopolysiloxane is formed on the catalyst layer. and , silicone resin and , alkoxysilane having an epoxy group N Contains The thickness is 1μm to 100μm. It is characterized by having a protective coating. Effect of the Invention

[0009] Since the electrolysis electrode of the present invention has a protective coating mainly made of a resin containing silicon, the electrode can be manufactured by simply applying the protective coating and then curing it with a heat treatment of 300°C or less, thereby reducing manufacturing costs. In addition, the protective coating containing silicon can be applied easily and can be reapplied any number of times while the catalyst layer exists. Therefore, the cost of the electrode can be reduced in the long run.

[0010] Furthermore, the shape can be maintained for a long period of time without collapse even in harsh environments such as a strong acid atmosphere and vigorous bubbling of oxygen, etc., and the substrate and the catalyst layer on the substrate can be protected. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram showing an experimental setup for investigating the performance of a composition for an overcoat film. [Diagram 2] FIG. 13 is a graph showing the results of investigating the effect of a protective film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The electrolysis electrode according to the present invention will be described below with reference to the drawings and examples. Note that the following description illustrates one embodiment of the present invention and one example, and the present invention is not limited to the following description. The following description can be modified without departing from the spirit of the present invention. In addition, in the following description, "~" indicating the range of the component composition means more than or equal to or less than. In other words, "A%~B%" means "A% or more, B% or less."

[0013] The electrolysis electrode according to the present invention is composed of a conductive substrate, a catalyst layer, and a protective coating. The conductive substrate may be made of a conductive metal such as titanium or stainless steel that is resistant to a strong acidic or strongly reducing atmosphere, with titanium being particularly suitable. The titanium may be pure titanium or a titanium alloy. Alternatively, the conductive substrate may have a structure in which titanium and another metal are laminated. The conductive substrate is preferably in the form of a plate for ease of use, but may have a shape other than a plate.

[0014] The catalyst layer is provided on a conductive substrate. The catalyst layer may be provided on at least one surface of the conductive substrate (the portion facing the opposing electrode). It may also be provided on the entire electrode. As the catalyst, platinum group metals such as platinum (Pt), rhodium (Rh), iridium (Ir), ruthenium (Ru), palladium (Pd), and osmium (Os) can be suitably used. Tantalum (Ta) may also be included.

[0015] The catalyst layer is formed by dissolving the metal salts that make up the catalyst layer in a solvent such as alcohol, applying the solution to a conductive substrate, and then baking it at 400°C to 500°C for 20 minutes to 1 hour. To increase the film thickness, this process is repeated the required number of times. The catalyst layer is formed to a thickness of about 0.1μ to 20μm.

[0016] The protective coating is required to be formed at least on the catalyst layer. When there is a portion of the conductive substrate surface on which the catalyst layer is not formed, the protective coating may be formed directly on the conductive substrate surface.

[0017] The protective coating contains silicon. More specifically, a composition using silicon as the main skeleton is used. For example, silicone oligomer, silicone resin, and alkoxysilane having an epoxy group can be suitably used. Furthermore, conductive particles may be included. In the following, silicone oligomer will be simply referred to as "oligomer" and silicone resin will be simply referred to as "resin".

[0018] Silicone oligomers are also called alkoxy-containing organopolysiloxanes in which organic groups are bonded to a main skeleton formed by siloxane bonds, and refer to those having a weight average molecular weight of 1000 or more and 10000 or less. In the present invention, the organic groups preferably used are those to which methyl groups, phenyl groups, ethoxy groups, methoxy groups, epoxy groups, mercapto groups, amino groups, methacryloyl groups, acryloyl groups, etc. are bonded.

[0019] Specifically, X-41-1053, X-41-1059A (each having an epoxy group, a methoxy group, and an ethoxy group), X-41-1056 (having an epoxy group and a methoxy group), X-41-1805 (having a mercapto group, a methoxy group, and an ethoxy group), X-41-1818 (having a mercapto group and an ethoxy group), X-41-1810 (having a mercapto group and a methoxy group), X-41-2651 (having an amino group and a methoxy group), and X-40-2655 manufactured by Shin-Etsu Chemical Co., Ltd. Alkoxy oligomers such as KR-513 (containing acryloyl and methoxy groups), KC-89S, KR-500, X-40-9225, X-40-9246, X-40-9250, KR-401N, X-40-9227, X-40-9247, KR-510, KR-9218, KR-213, and X-40-2308 (containing methoxy groups), as well as X-40-9238 (containing ethoxy groups), can be suitably used.

[0020] The alkoxysilane having an epoxy group (hereinafter simply referred to as "epoxy") can be one having an alkoxysilane group and an epoxy group. Specifically, a silane coupling agent (3-glycidoxypropyltrimethoxysilane: CAS number 2530-83-8) can be suitably used.

[0021] The protective film layer may also contain a silicone resin. Silicone resin has a siloxane skeleton and a weight-average molecular weight of tens of thousands to millions. Silicon elements in the siloxane skeleton that are preferably bonded to a methyl group or a phenyl group are preferably used.

[0022] Specifically, as the methylphenyl silicone resin, KR255, KR311, KR300, KR510, etc. manufactured by Shin-Etsu Chemical Co., Ltd. can be suitably used. As the methyl silicone resin, KR251, KR400, KR220L, KR242A, KR240, KR500, KC89, etc. manufactured by Shin-Etsu Chemical Co., Ltd. can be suitably used. In addition, SR2400, Trefil R910, etc. manufactured by Toray Dow Corning Co., Ltd. can also be suitably used. In addition, a silicone resin having 60 mol% or more of trifunctional T units may be used. Among them, a silicone resin having 50 mol% or more of the functional groups on Si as methyl groups can be suitably used. The proportion of trifunctional T units can be measured by NMR.

[0023] The protective film layer may also contain conductive particles. As the conductive particles, conductive carbon-based particles such as conductive carbon black and carbon nanotubes can be suitably used. However, a protective film layer formed only from the above silicone material does not reduce the efficiency of electrolysis of the electrode on which the catalyst layer is formed. Therefore, the protective film layer according to the present invention can be suitably used even without conductive particles.

[0024] In addition, the silicone oligomer, silicone resin, epoxy, and conductive particles can be used in the following ranges: With the total solid weight of the silicone oligomer taken as 100, the silicone resin is more than 10% and less than 300%, more preferably 50% to 250%, and most preferably 70% to 170%.

[0025] The epoxy is more than 10% and less than 200% based on the total weight of the solid content of the silicone oligomer and silicone resin. More preferably, it is 20% to 180%, and most preferably, it is 30% to 150%. The total weight of the epoxy solid content does not include the weight of the epoxy curing catalyst. This is because the amount of the curing catalyst used is small.

[0026] The protective film layer is made by mixing silicone oligomer, silicone resin, epoxy and conductive particles, and applying the mixture to the conductive substrate so that the thickness of the film after drying is 1 μm to 100 μm. After drying, the conductive substrate with the protective film layer is cured at 100° C. to 250° C. for 30 minutes to 3 hours to obtain the electrode of the present invention.

[0027] The electrode according to the present invention can be suitably used as an anode in an electrolysis process, although it may also be used as a cathode. EXAMPLES

[0028] An example in which a protective film was formed on a conductive substrate using the protective film composition used in the present invention is shown below. Also, Fig. 1 shows a schematic diagram of an experimental apparatus for the example. Referring to Fig. 1, a liquid to be treated 12 was placed in a container 10, and an anode 14 and a cathode 16 were fixed in a state in which they were partially immersed in the liquid to be treated 12. A constant current source 18 was placed between the anode 14 and the cathode 16, and an ammeter 20 and a voltmeter 22 were also placed.

[0029] A plate material (20 mm x 100 mm x 2 mm) of pure titanium (equivalent to JIS H4600-2) was used as the conductive substrate 30 on which the anode 14 was formed. An alcohol solution in which platinum salt was dissolved was sprayed onto both sides of the conductive substrate 30, and the catalyst layer 32 was formed by baking at 200°C. The catalyst layer 32, which was made of platinum, was formed to a thickness of 2 μm. The conductive substrate on which the catalyst layer 32 was formed is hereinafter referred to as the "substrate with catalyst."

[0030] A protective film was formed by spraying the protective film paint prepared according to the compounding ratio in Table 1 onto this catalyst-coated substrate. The thickness of the protective film was 10 μm after drying. After drying, it was cured at 200°C for 1 hour. The catalyst-coated substrate on which the protective film was formed is called the "catalyst substrate with protective film."

[0031] [Table 1]

[0032] In Table 1, "◆Formulation (g)" and "◆Formulation (relative display)" are shown. "◆Formulation (g)" indicates the actual weighed weight. The solid content of each material is shown as "%". "◆Formulation (relative display)" is calculated by taking the total weight of the solid content of the oligomer as 100 (oligomer * ), resin * indicates the weight ratio (%) of the oligomer to the total solid content. Epoxy * indicates the weight ratio (%) of the oligomer and resin to the total solids. * The calculation does not include the curing catalyst. In addition, the comparative example does not include oligomers and resins, so the relative values ​​of epoxy (25 ** ) is the weight ratio (%) of epoxy to the total weight of the solid content of the acrylic resin and the melamine resin. In this embodiment, conductive particles are not included.

[0033] Silicone oligomer KR500 has a weight average molecular weight of about 3,000 to 10,000 and has a methoxy group in the skeleton. Silicone resin KR251 has a weight average molecular weight of 3,000,000 to 4,000,000.

[0034] The epoxy used was KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), and ethyl acetate was used as the solvent. D20 (manufactured by Shin-Etsu Chemical Co., Ltd.) was added as a silicone curing catalyst.

[0035] As comparative resins, an acrylic resin (52-668BA: manufactured by DIC Corporation) and a melamine resin (L-145-60: manufactured by DIC Corporation) were prepared.

[0036] The liquid to be treated was prepared as a test sample containing 10% sulfuric acid, 4% hydrogen peroxide, 0.5% formic acid, and 0.5% lactic acid (each based on a weight ratio relative to the total weight of the liquid to be treated).

[0037] A catalyst substrate with a protective film was immersed as the anode 14 and a titanium plate material was immersed as the cathode 16 in the test simulated liquid 12, and the electrodes were fixed with a distance L between the opposing surfaces of 30 mm. Each electrode was connected to a constant current power source 18, and a current density of 200 A / dm 2The current was set to be constant and constant current control was performed.

[0038] The durability evaluation was performed by monitoring the voltage between the electrodes in FIG. 1 with a voltmeter 22 and measuring the time it took for the voltage between the electrodes to reach 30 V. The results are shown in FIG.

[0039] Referring to Fig. 2, the horizontal axis is the electrolysis time (minutes) and the vertical axis is the terminal voltage (V). The solid line and triangles indicate the results for the electrode without a protective film (only a catalyst layer is formed on a conductive substrate). The dashed and dotted line and squares indicate the electrode according to the present invention in which a silicone-based coating is applied as a protective film. The dashed line and circles indicate the electrode of the comparative example in which an acrylic-based coating is applied as a protective film.

[0040] When only the electrode was used and the protective film was an acrylic coating, the initial voltage was about 10 and 15 V, respectively, and remained constant at 11 to 12 V from 30 to 40 minutes after the current was applied. However, after 40 minutes had passed, the voltage between the terminals rose sharply, exceeding 30 V at 50 to 60 minutes.

[0041] On the other hand, the electrode according to the present invention, in which a silicon-based coating was applied as a protective film on the catalyst layer, had an initial terminal voltage of about 15 V, and it took 120 minutes for the terminal voltage to rise to 30 V. In other words, the electrode for electrolysis according to the present invention was able to extend the electrode life twice as long as the electrode alone or the electrode with a non-silicon-based coating as a protective film. In addition, since the initial voltage was not high compared to the electrode alone, it can be said that the effect of electrolysis is not reduced. [Industrial Applicability]

[0042] The electrolysis electrode according to the present invention can be suitably used as an electrode when electrolyzing a liquid to be treated in which a strong acid, hydrogen peroxide, and an organic acid are present. [Explanation of symbols]

[0043] 10 containers 12 Liquid to be treated 14 Anode 16 Cathode 18 Constant current power supply 20 ammeter 22 Voltmeter 30 Conductive substrate 32 Catalyst layer 34 Protective film

Claims

1. A conductive substrate; A catalyst layer provided on the conductive substrate; An electrode for electrolysis having a protective coating formed on the catalyst layer, the protective coating containing an alkoxy group-containing organopolysiloxane, a silicone resin, and an alkoxysilane having an epoxy group and having a thickness of 1 μm to 100 μm.

2. 2. The electrolysis electrode according to claim 1, wherein the catalyst layer comprises at least one of iridium (Ir) and platinum (Pt).

3. The electrolysis electrode according to claim 1 or 2 is used as an anode, An electrolysis method comprising a step of electrolyzing a liquid to be treated that contains sulfuric acid.

4. 4. The electrolysis method according to claim 3, wherein the liquid to be treated further contains hydrogen peroxide.

5. 5. The electrolysis method according to claim 4, wherein the liquid to be treated further contains an organic acid.

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