Electrolysis electrode, and electrolysis method using said 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

Electrode for electrolysis and electrolysis method using the electrode

[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.

[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 They are used over a wide range of current densities, from 0.1 to over 0.25. Among these, anodes in particular require high oxidation resistance because oxidation reactions, such as the generation of oxygen and chlorine gas, occur on their surfaces, and they also require electrode durability. Furthermore, titanium and its alloys are used as electrode substrates as valve metals for electrodes from environmental and safety perspectives. However, although titanium is electrically conductive, its conductivity is not particularly high. Therefore, 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 use at high current densities as described above, there are also cases where the liquid to be treated is a strong acid, or where it is used in a strong oxidizing environment with the addition of hydrogen peroxide. In particular, if a catalyst layer is formed on the surface of the electrode material to increase the efficiency of electrolysis, the catalyst layer will be damaged.

[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.

[0005] Patent No. 5932028

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

[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 characterized by having a conductive substrate, a catalytic layer provided on the conductive substrate, and a protective coating containing silicon formed on the catalytic layer.

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

[0010] Furthermore, the shape can be maintained for a long period of time without collapse even in a harsh environment such as a strong acid atmosphere where oxygen and the like are bubbling violently, and the substrate and the catalyst layer on the substrate can be protected.

[0011] 1 is a diagram showing an experimental setup for an example in which the performance of a composition for an overcoat film is examined. 2 is a diagram showing a graph showing the results of examining the effect of the overcoat film.

[0012] The electrolysis electrode according to the present invention will be described below with reference to drawings and examples. Note that the following description exemplifies 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. Furthermore, in the following description, "to" indicating the range of component composition means "at least or equal to" or "at most." In other words, "A% to B%" means "at least A% and at most B%."

[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 can be made of a conductive metal that is resistant to a strongly acidic or strongly reducing atmosphere, such as titanium or stainless steel, with titanium being particularly suitable. The titanium may be pure titanium or a titanium alloy. Alternatively, the conductive substrate may have a laminated structure of titanium and another metal. A plate-like conductive substrate is preferred for ease of use, but it may have a shape other than a plate.

[0014] The catalyst layer is provided on a conductive substrate. The catalyst layer only needs to 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. Suitable catalysts include platinum group metals such as platinum (Pt), rhodium (Rh), iridium (Ir), ruthenium (Ru), palladium (Pd), and osmium (Os). 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 the conductive substrate, and then baking it at 400 to 500°C for 20 minutes to 1 hour. To increase the film thickness, repeat this process as many times as necessary. The catalyst layer is formed to a thickness of approximately 0.1 to 20 μm.

[0016] The protective coating is sufficient as long as it is formed at least on the catalyst layer. If 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 surface of the conductive substrate.

[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 with epoxy groups are suitable. Furthermore, conductive particles may be included. Note that hereinafter, 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 with a weight-average molecular weight of 1,000 to 10,000. 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 and X-41-1059A (each having an epoxy group, a methoxy group, or an ethoxy group), X-41-1056 (having an epoxy group and a methoxy group), X-41-1805 (having a mercapto group, a methoxy group, or 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 (having an acryloyl group or a methoxy group), 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 (all of which have a methoxy group), as well as X-40-9238 (having an ethoxy group), 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 No. 2530-83-8) can be preferably 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 atoms in the siloxane skeleton bonded to methyl groups or phenyl groups are preferably used.

[0022] Specifically, suitable methylphenyl silicone resins include KR255, KR311, KR300, and KR510 manufactured by Shin-Etsu Chemical Co., Ltd. Methyl silicone resins include KR251, KR400, KR220L, KR242A, KR240, KR500, and KC89 manufactured by Shin-Etsu Chemical Co., Ltd. SR2400 and Trefil R910 manufactured by Dow Corning Toray Co., Ltd. Silicone resins containing 60 mol% or more of trifunctional T units may also be used. Among these, silicone resins in which 50 mol% or more of the functional groups on Si are methyl groups are particularly suitable. The proportion of trifunctional T units can be measured by NMR.

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

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

[0025] The amount of epoxy is more than 10% but less than 200% of the total solids weight of the silicone oligomer and silicone resin, more preferably 20% to 180%, and most preferably 30% to 150%. Note that the total solids weight of epoxy does not include the weight of the epoxy curing catalyst, as the amount of curing catalyst used is small.

[0026] The protective film layer is formed by mixing a silicone oligomer, a silicone resin, an epoxy, and conductive particles, and applying the mixture to the conductive substrate so that the resulting film has a thickness of 1 μm to 100 μm after drying. 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, but it can also be used as a cathode.

[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 described below. A schematic diagram of the experimental apparatus for the example is shown in Figure 1. Referring to Figure 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 therebetween.

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

[0030] A protective film coating material prepared according to the blending ratio in Table 1 was sprayed onto this catalyst-coated substrate to form a protective film. The thickness of the protective film after drying was 10 μm. After drying, it was cured at 200°C for 1 hour. The catalyst-coated substrate on which the protective film was formed is referred to as a "catalyst substrate with protective film."

[0031]

[0032] In Table 1, "◆Formulation (g)" and "◆Formulation (relative expression)" are shown. "◆Formulation (g)" indicates the actual weighed weight. The solid content of each material is shown in "%". "◆Formulation (relative expression)" is calculated by taking the total weight of the solid content of the oligomer as 100 (the weight of the oligomer ＊ ), resin ＊ represents the weight ratio (%) of the oligomer to the total solid content. ＊ indicates the weight ratio (%) of the total weight of the solid content of the oligomer and resin. ＊ The calculation does not include the curing catalyst. In addition, the comparative example does not contain oligomers or 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 melamine resin. In addition, in this example, 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 its 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.), the solvent was ethyl acetate, and 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] A test simulated liquid to be treated was prepared 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 to be treated 12, and they 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 ２ The voltage was set to be constant and constant current control was performed.

[0038] Durability was evaluated 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. 2.

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

[0040] When only the electrode and the protective film were acrylic coated, 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 start of energization. However, after 40 minutes had passed since the start of energization, the voltage between the terminals rose sharply, exceeding 30 V between 50 and 60 minutes later.

[0041] On the other hand, the electrode according to the present invention, in which a silicone-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 electrolysis electrode according to the present invention was able to extend the electrode life twice as long as an electrode alone or an electrode with a non-silicone-based coating as a protective film. Furthermore, since the initial voltage was not higher than that of an electrode alone, it can be said that the effect of electrolysis was not reduced.

[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.

[0043] REFERENCE SIGNS LIST 10 container 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 having a protective coating formed on the catalyst layer, the protective coating including at least one of a silicone oligomer, a silicone resin, and an alkoxysilane having an epoxy group.

2. An electrode as described in claim 1, wherein the silicone oligomer is an organopolysiloxane.

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

4. 3. The electrode according to claim 2, wherein said organopolysiloxane contains 50% by weight or more of T units.

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

6. 6. The electrolysis method according to claim 5, wherein the liquid to be treated further contains hydrogen peroxide.

7. 7. The electrolysis method according to claim 6, wherein the liquid to be treated further contains an organic acid.